Surfacing and Additive Technologies in Welded Fabrication: International Welding Engineers Textbook Series Under the Editorship of Borys Paton 3031343891, 9783031343896

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Igor Ryabtsev · Serhii Fomichov · Valerii Kuznetsov · Yevgenia Chvertko · Anna Banin

Surfacing and Additive Technologies in Welded Fabrication

Surfacing and Additive Technologies in Welded Fabrication

Igor Ryabtsev · Serhii Fomichov · Valerii Kuznetsov · Yevgenia Chvertko · Anna Banin

Surfacing and Additive Technologies in Welded Fabrication Recommended by the Academic Council of the National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute” as textbook for students and post-graduate students majoring in “Materials Science” and “Mechanics”

Igor Ryabtsev Department of Surfacing E. O. Paton Electric Welding Institute Kyiv, Ukraine Valerii Kuznetsov Institute of Materials Science and Welding; IIW/EWF Approved Training Body National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute” Kyiv, Ukraine Anna Banin Centauri Business Group Inc. Bellevue, WA, USA

Serhii Fomichov Institute of Materials Science and Welding; IIW/EWF Approved Training Body National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute” Kyiv, Ukraine Yevgenia Chvertko Institute of Materials Science and Welding; IIW/EWF Approved Training Body National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute” Kyiv, Ukraine

ISBN 978-3-031-34389-6 ISBN 978-3-031-34390-2 (eBook) https://doi.org/10.1007/978-3-031-34390-2 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Foreword

Dear fellow welders! The welding family unites millions of specialists working in all areas of modern manufacturing on land, underwater, and in outer space. Today, welding belongs to the category of the most popular manufacturing specialties in Europe, North America, Asia, Latin America, Australia, and Africa. Welding and the related processes are part of the most complex manufacturing technologies based on the fundamentals of mechanics, electrical engineering, physical chemistry, materials science, applied mathematics, computer science, and robotics. This requires a high level of competence from all categories of those associated with welding: manual workers, engineers, and scientists. Scientific and educational literature on welding is constantly being updated. This textbook series for international welding engineers aims to help in the study of physics fundamentals and welding technologies in accordance with the requirements of international standards and the educational requirements of the International Institute of Welding (IIW). The authors illustrated the text throughout the textbook and tried to make it useful to a wide range of specialists, primarily engineers. We hope that the introductory parts of the textbook sections will also help onsite welders to understand the basics of welding and the related processes. I wish you, dear fellow welders, creative successes, and business achievements in mastering the complex, modern, and very exciting science of welding and the related processes.

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Foreword

Borys Paton Director of the E.O. Paton Electric Welding Institute Kyiv, Ukraine

Introduction

The textbook “Surfacing and Additive Manufacturing in Welding Fabrication” is part of a series of textbooks for international welding engineers. The content of the textbook corresponds to the “IIW Guideline for International Welding Engineers, Technologists, Specialists and Practitioners. Minimum Requirements for Education, Examination and Qualification”. The purpose of the series of textbooks is to present modern knowledge in the field of welding science, technology, and equipment. The work was initiated, spearheaded, and edited by Academician Borys Paton. The textbook provides physical basics and detailed technologies of a wide range of surfacing methods. Features of formation of structure and properties of the deposited metal, reasons of formation of imperfection and directions of their prevention, certification of surfacing procedures are described in the book. All sections contain information according to international standards. Textbook material is accessible and illustrative. This was an important task that the authors set when writing. The textbook is based on many years of experience of leading experts of the E. O. Paton Electric Welding Institute and of the National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute” in the development and implementation of welding processes and technologies, as well as in training of M.Sc., doctorate students and international welding engineers. The textbook is also designed for: . M.Sc. and doctorate students who specialize in welding and technology, as well as non-destructive testing based on bachelor’s in mechanics, materials science, or electrical engineering. . University professors specializing in welding and related processes. . Specialists in the welding industry and related processes. In the reference tables, the brands of surfacing materials are given in the manufacturer’s designations to provide identification. Analogues from other manufacturers should be determined by the chemical composition of the components.

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Contents

1

Definition and Classification of Surfacing Processes . . . . . . . . . . . . . .

1

2

Electric Arc Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Physical Principles of Electric Arc Surfacing . . . . . . . . . . . . . . . . 2.2 Manual Metal Arc Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Automated Submerged Arc Surfacing . . . . . . . . . . . . . . . . . . . . . . 2.3.1 Automated Submerged Arc Surfacing with Solid Wire or Strip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2 Automated Submerged Arc Surfacing with Solid or Flux-Cored Strip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Automated and Mechanized Gas Shielded Surfacing . . . . . . . . . 2.5 Vibro-Arc Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6 CMT Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7 Features of Physical and Metallurgical Processes in Electric Arc Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.7.1 Methods of Alloying of Deposited Metal . . . . . . . . . . . . . 2.7.2 Effect of Electric Arc Surfacing Parameters on Chemical Composition of the Deposited Metal . . . . . 2.8 Materials for Electric Arc Surfacing . . . . . . . . . . . . . . . . . . . . . . . 2.8.1 Coated Electrodes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.8.2 Solid Wires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.8.3 Flux-Cored Wires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.8.4 Cold-Rolled, Flux-Cored and Sintered Strips . . . . . . . . . . 2.8.5 Fluxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.8.6 Protective Gases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.9 Electric Arc Surfacing Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 2.9.1 Parameters of Electric Arc Surfacing . . . . . . . . . . . . . . . . 2.9.2 Electric Arc Surfacing of Rotating Bodies . . . . . . . . . . . . 2.9.3 Electric Arc Surfacing of Flat Parts . . . . . . . . . . . . . . . . . . 2.9.4 Electric Arc Surfacing of Complex-Shaped Parts . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

7 8 13 15 16 17 22 24 27 28 28 30 32 32 34 34 38 42 45 46 47 49 54 55 58

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Contents

Plasma Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Physical Phenomena of Plasma Surfacing Process . . . . . . . . . . . . 3.2 Methods of Plasma Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1 Plasma Jet Surfacing with Current-Carrying Filler Wire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2 Plasma Arc Surfacing with Electrically Neutral Filler Wire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3 Plasma Arc Surfacing with Current-Carrying Filler Wire . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.4 Plasma Arc Surfacing with Two Current-Carrying Filler Wires Fed into the Arc . . . . . . . . . . . . . . . . . . . . . . . 3.2.5 Plasma Arc Surfacing with Two Current-Carrying Filler Wires Fed to the Surfacing Pool . . . . . . . . . . . . . . . 3.2.6 Plasma Surfacing with Consumable Electrode . . . . . . . . . 3.2.7 Plasma-Powder Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.8 Plasma Surfacing on a Fixed Additive . . . . . . . . . . . . . . . 3.3 Materials for Plasma Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Procedures of Plasma Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

59 59 61

Electroslag Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Physical Phenomena of Electroslag Surfacing . . . . . . . . . . . . . . . 4.2 Methods of Electroslag Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 Classification of Methods of Electroslag Surfacing . . . . 4.2.2 Electroslag Surfacing with Electrode Wires . . . . . . . . . . . 4.2.3 Electroslag Surfacing with Electrodes of Large Cross-Section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.4 Electroslag Surfacing with Discrete Filler Metal . . . . . . . 4.2.5 Electroslag Surfacing with Liquid Filler Metal . . . . . . . . 4.2.6 Electroslag Surfacing with Strips with Free Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Features of Physic-Chemical Processes During Electroslag Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Materials for Electroslag Surfacing . . . . . . . . . . . . . . . . . . . . . . . . 4.4.1 Fluxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.2 Electrode Wires and Strips . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.3 Electrodes with Large Cross-Section . . . . . . . . . . . . . . . . . 4.4.4 Discrete Filler Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.5 Liquid Filler Materials . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

83 83 86 86 88

99 100 100 105 106 106 106 107

Gas Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Physical Phenomena of Gas Surfacing . . . . . . . . . . . . . . . . . . . . . . 5.2 Materials for Gas Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Gas Surfacing Procedures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

109 109 113 119 121

62 63 64 65 66 67 68 69 70 77 81

91 92 94 95

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Induction Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 Physical Phenomena of Induction Surfacing . . . . . . . . . . . . . . . . . 6.2 Methods of Induction Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 Materials for Induction Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . Reference . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

123 123 125 130 131

7

Laser Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1 Physical Phenomena of Laser Surfacing . . . . . . . . . . . . . . . . . . . . 7.2 Methods of Laser Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 Materials for Laser Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.1 Filler Powders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.2 Filler Wires . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4 Procedures of Laser Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

133 133 137 140 140 143 143 147

8

Other Methods of Coating Production . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1 Rolling and Extrusion Cladding . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 Explosion Cladding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3 Electric Resistance Weld Cladding . . . . . . . . . . . . . . . . . . . . . . . . . 8.4 Furnace Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5 Electron-Beam Surfacing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.6 Friction Stir Surface Cladding . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

149 149 151 154 155 155 157

9

Additive Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.1 Terminology and Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2 Laser and Electron Beam Melting . . . . . . . . . . . . . . . . . . . . . . . . . 9.3 Wire Arc Additive Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . 9.4 Calculation of Stress–Strain State . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

161 161 164 167 167 172

10 Structure and Properties of Surfaced Metal of Different Alloying Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.1 General Classification of Surfacing Metals of Different Alloying Systems and Typical Applications According to EN 14700:2014 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.2 Unalloyed and Low-Alloyed Steels with Carbon Content up to 0.4% (Fe1 Group) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.3 Surfaced Unalloyed and Low-Alloyed Steels with Carbon Content Above 0.4% (Fe2 Group) . . . . . . . . . . . . . . . . . . . . . . . . . 10.4 Surfaced Chrome-Tungsten, Chrome-Molybdenum, and Other Heat-Resistant Tool Steels (Fe3 Group) . . . . . . . . . . . 10.5 Surfaced High-Speed Steels (Fe4 Group) . . . . . . . . . . . . . . . . . . . 10.6 Surfaced Low-Carbon Chromium Steels (Fe7 Group) . . . . . . . . . 10.7 Surfaced Chromium Steels with Increased Carbon Content (Fe8 Group) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.8 Surfaced High-Manganese Austenitic Steels (Fe9 Group) . . . . .

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173 186 187 189 191 193 195 197

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10.9

Surfaced Chromium-Nickel, Chromium-Nickel-Manganese Stainless Austenitic Steels (Fe10, Fe11, Fe12 Groups) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.10 Surfaced High-Chromium High-Alloyed Cast Irons (Fe14, Fe15, Fe16 Groups) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.11 Surfaced Nickel-Based Alloys Alloyed with Chromium, Boron, and Silicon (Ni1, Ni3 Groups) . . . . . . . . . . . . . . . . . . . . . . 10.12 Surfaced Nickel-Based Alloys Alloyed with Molybdenum and Chromium (Ni2 Group) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.13 Surfaced Carbide-Based Alloys (Fe20, Ni20 Groups) . . . . . . . . . 10.14 Surfaced Cobalt Alloys Alloyed with Chromium and Tungsten (Co1, Co2, Co3 Groups) . . . . . . . . . . . . . . . . . . . . . 10.15 Surfaced Copper-Based Alloys (Cu1 Group) . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Surfacing and Additive Manufacturing Imperfections . . . . . . . . . . . . 11.1 General Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Cracks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3 Gas Pores . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.4 Lack of Fusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.5 Imperfect Bead Shape . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.6 Less Common Surfacing and Additive Manufacturing Imperfections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 Procedures’ Qualification for Surfacing and Additive Manufacturing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.1 Definitions of Procedure Qualification . . . . . . . . . . . . . . . . . . . . . . 12.2 Control Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12.3 Program of Control Samples’ Testing . . . . . . . . . . . . . . . . . . . . . . 12.4 Welding Procedure Qualification Record (WPQR) . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

198 201 202 204 205 206 208 209 211 211 213 215 216 217 218 220 221 221 222 223 225 226

About the Authors

Igor Ryabtsev works in the E. O. Paton Electric Welding Institute since 1972 as a researcher and since 1997 as the head of the surfacing department. The main areas of scientific activity are related to the study of physical and metallurgical processes of the most common surfacing methods (arc, electroslag, plasma powder, etc.), the development of new types of surfacing materials and technologies for surfacing parts operating under conditions of various types of wear, including parts metallurgical equipment: rolling rolls of various types, rollers of continuous casting machines, roller table rollers, etc. He investigates the features of inheritance and structure formation in the system surfacing material-weld pool-deposited metal with various surfacing methods. Based on these studies, the principles of controlling the structure and properties of the deposited metal for various purposes have been developed. Serhii Fomichov is a professor at the Institute of Materials Science and Welding at the National Technical University of Ukraine ‘Igor Sikorsky Kyiv Polytechnic Institute’; the director of IIW/EWF Approved Training Body; the chairman of the Safeguarding Impartiality Committee of Bureau Veritas Ukraine; a board member of Ukrainian Association for Quality. He has long experience working on nondestructive testing and monitoring of technical conditions of main gas pipelines, oil pipelines and ammonia pipelines, tanks, pressure vessels, ship trans-shippers, and wheels of hydroturbines. He was involved in the development of equipment and techniques of magnetic and acoustic control NDT methods. Most of all he loves his daughters Alina and Julia. Sergey is an instructor in alpine skiing and mountaineering. Valerii Kuznetsov is a professor of the Institute of Materials Science and Welding of the National Technical University of Ukraine ‘Igor Sikorsky Kyiv Polytechnic Institute’. The main field of scientific interests is welding, surfacing, and coatings, improving and implementing welding and weld surfacing processes at aircraft manufacturing, shipbuilding, and chemical and power engineering enterprises.

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About the Authors

Yevgenia Chvertko received her B.S., M.S. and Ph.D. in welding and related technologies from the National Technical University of Ukraine “Igor Sikorsky Kyiv Polytechnic Institute” (Igor Sikorsky KPI), Ukraine, in 1999, 2001 and 2012, respectively. She worked as an assistant at the Welding Faculty of Igor Sikorsky KPI from 2001 to 2012, and as an associate professor from 2012 to 2020. From 2020 to present, she works as associate professor of the E. O. Paton Institute of Materials Science and Welding and is engaged at activities of the International Institute of Welding and European Federation for Welding, Joining and Cutting in Ukraine. Currently, Dr. Chvertko is a member of the Board of Directors of the International Institute of Welding. Anna Banin Master of Science has over 15 years (since 2008) of experience in quality assurance, quality control and quality management systems development and support. Anna is the founder and owner of Centauri Business Group Inc.—a US based corporation that provides support to management system professionals—where she oversees: the development of online training courses on standard management systems: ISO 9001, ISO 14001, ISO 45001, ISO 50001, ISO 9001 and ISO 26000; the development of documented information for Quality Management Systems in accordance with ISO 9001.

Chapter 1

Definition and Classification of Surfacing Processes

Abstract Definitions of the methods of applying surface layers to products are given: surfacing, cladding, spraying. The indicators of penetration and geometry of the deposited beads were analyzed. The basic classification of surfacing and cladding processes is given according to the purpose and physics of the energy sources used to apply the layers.

Most metal products operate in harsh conditions under the influence of four main factors: . . . .

loads, including fatigue, friction and abrasive particles, aggressive environment, including weathering, high temperatures, including cyclic ones.

All operational factors act, first of all, on the product surface. Surface resistance to the action of operational factors determines the service life of the product. In this regard, it is economically feasible to use low-cost metals for products, and to apply layers of expensive materials on their surface. Metals, resistant to the effects of relevant operational factors, are primarily used for this purpose. In addition, the application of surface layers is necessary during repairs to restore the geometric dimensions of the product after wear or corrosion. Methods of applying surface layers to products include: . surfacing, in which the surface layer is created by melting the filler metal and the base metal, a pool of molten metal forms in the process, . cladding, in which the surface layer is created due to the mutual deformation of the applied metal layer and the base metal when heated, or due to the mutual significant deformation of the layers in the cold state, . spraying, in which the surface layer is created by high-speed deformation of particles in the form of powder or drops of molten metal when heated without melting the base metal. This textbook discusses the methods of surfacing and cladding.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 I. Ryabtsev et al., Surfacing and Additive Technologies in Welded Fabrication, https://doi.org/10.1007/978-3-031-34390-2_1

1

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1 Definition and Classification of Surfacing Processes

Fig. 1.1 Characteristics of penetration and weld bead geometry

Fc Fb

c

h

b

Surfacing is the application of a layer of metal to the surface of the product by melting the applied metal and the base metal. A common surfacing pool is formed in which the molten metal is mixed with the molten surface layer of the parent metal. After crystallization of the surfacing pool on the surface of the product, the weld bead is formed. Adjacent beads cover the surface forming a deposited layer. The chemical composition, structure and, therefore, the mechanical properties of the weld bead depend on the penetration and cooling rate. Penetration—a characteristic of the interaction of the weld metal with the parent metal. Penetration is determined by two indicators: (1) Depth of penetration—the distance h (Fig. 1.1), which forms a single surfacing pool of the surfacing metal and the base metal. (2) The proportion of base metal in the deposited γ—the ratio of the penetration area Fb (Fig. 1.1) to the total cross-sectional area of the deposited bead: γ =

Fb F b +F c

(1.1)

Penetration determines: . the number of layers that need to be deposited to obtain a given chemical composition, structure, and properties of the deposited layer, . efficiency of the chosen method of surfacing. Therefore, when surfacing, one of the main tasks is to minimize the depth of penetration and the quota of base metal in the surfacing. Penetration depends on: . method and technology of surfacing, . differences in the melting temperatures of the weld metal and the base metal, . the difference between the thermal conductivity of the weld metal and the base metal, . differences in heat capacity and other physical characteristics of the weld metal and the base metal.

1 Definition and Classification of Surfacing Processes

3

The surfacing technology must provide the specified geometrical characteristics of the weld bead: . width b, . height c, . form factor χ . x=

b c

(1.2)

In the case of arc surfacing processes, geometrical characteristics depend on surfacing heat input q which determines energy spent per length unit of surfaced bead: q = UI

σt v

(1.3)

where . . . .

I—current, U—arc voltage, σt —thermal efficiency of heating, v—speed of surfacing.

The economic indicator of the process is the surfacing productivity G—the amount of metal that is deposited per unit of time. Surfacing and cladding processes are classified by . . . .

purpose (basic classification), physics of energy sources used for layering (basic classification), degree of mechanization (auxiliary classification), technological features (auxiliary classification).

According to purpose, there are three areas (1) Manufacturing—surfacing, designed to obtain new bimetallic (multilayer) products. Such products consist of a base (base metal), which provides the required structural strength, and a welded working layer (surfacing metal) with special properties (wear resistance, corrosion resistance, heat resistance, etc.). (2) Restoration—local surfacing, designed to restore the original size of worn or damaged parts. In this case, the weld metal in composition and properties may be either close to the base metal (restorative dimensional surfacing), or better than the base metal (restorative wear-resistant surfacing). (3) Additive (3D)—multilayer three-dimensional surfacing, designed to create a new product of the desired shape and size. Additive surfacing is aimed at minimizing material costs (usually expensive), minimizing labor costs, ensuring the possibility of manufacturing products of any complex shape (impossible to be obtained by casting and subsequent machining).

4

1 Definition and Classification of Surfacing Processes Methods of surfacing and cladding

MECHANICAL

Friction stir surface cladding

Electric Arc

Plazma

THERMAL

Roller cladding

Explosion cladding

Electroslag

Electronbeam

Laser

THERMOMECHANICAL

Electric resistance weld cladding

Inductive

Oxy-gas

Extrusion cladding

Furnace

Fig. 1.2 Classification of surfacing processes by physics of energy sources used

According to the physics of energy sources used for the application of layers, there are thirteen methods of surfacing and cladding, which are combined into three groups (Fig. 1.2): . thermal—using only thermal energy (electric arc, plasma, electroslag, electron beam, laser, induction, gas, furnace surfacing)—is the most common group, . thermomechanical—using a combination of thermal energy and pressure (rolling cladding, resistance surfacing, extrusion cladding), . mechanical—using only mechanical energy and pressure (explosion cladding, friction cladding). NOTE According to the degree of mechanization the processes can be classified as (refers primarily to electric arc and plasma surfacing): . Manual—all process operations are performed manually: striking of the arc, manipulation of the electrode and its movement, finishing of the surfacing process. In this case coated electrodes are used for surfacing. . Mechanized—wire supply to the arc zone is performed automatically, striking of the arc, of the torch movement and finishing of the surfacing process are performed manually. In this case wires—solid and flux-cored—are used for surfacing. . Automated—all process operations are performed automatically according to the specified program. Wires—solid or flux-cored, strips—solid, flux-cored or sintered—are used in this case. Classification by technological features includes: . The method of metal protection in the area of the surfacing pool (refers to electric arc surfacing): under flux, in protective gases, open arc self-protective flux-cored wire or self-protective flux-cored stripe.

1 Definition and Classification of Surfacing Processes

5

. Type of current: alternating current, direct current of the reverse polarity (electrode positive), direct current of direct polarity (electrode negative). . The nature of the electrode: non-consumable electrode, consumable electrode. . The number of electrodes: single-electrode, double-electrode, multielectrode.

Chapter 2

Electric Arc Surfacing

Abstract The physical phenomena and structure of an electric arc are described. The characteristics of the cathode zone, the arc column and the anode zone, as well as the characteristics of the electric arc of direct and reverse polarity are given. The energy balance of the electric arc is analyzed. The principles and schemes of manual metal arc surfacing are considered. The advantages and disadvantages of the method are given. The peculiarities of automated submerged arc surfacing are analyzed. The general scheme of the process of automated submerged arc surfacing with an electrode wire is described. Recommendations for use are given, advantages and disadvantages of the method are presented. The general scheme of the process of automated submerged arc surfacing with one and two electrode strips is described. The purpose is determined and the main options for profiling electrode strips are considered. Peculiarities of metal transfer and alloying during surfacing with powder strips are presented. The principles and schemes of arc welding in shielding gases with consumable (MIGMAG) and non-consumable (TIG) electrodes are considered. Recommendations are provided regarding the parameters of the surfacing process, the advantages and disadvantages of the method are given. The features and cycle of the vibrating arc surfacing process are considered. Recommendations are provided regarding the parameters of the surfacing process, the advantages and disadvantages of the method are given. Features and stages of the Cold Metal Transfer (CMT) surfacing process are considered. The advantages and disadvantages of the method are given. The features of alloying of deposited metal by various methods are analyzed: through filler metal, through flux, through the gas phase, and by using four combinations of alloying sources. The influence of the parameters of the electric arc on the chemical composition of the deposited metal when using different alloying methods is considered. Materials for electric arc surfacing are described in detail with chemical composition tables: coated electrodes; solid wires; powder wires; cold-rolled, powder and sintered strips; fused and ceramic fluxes; protective gases. The production experience of developing electric arc surfacing procedures is presented, including tables of parameters, the most common types of products: external and internal surfaces of cylindrical and conical bodies of rotation; flat surfaces; parts of complex shape.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 I. Ryabtsev et al., Surfacing and Additive Technologies in Welded Fabrication, https://doi.org/10.1007/978-3-031-34390-2_2

7

8

2 Electric Arc Surfacing

2.1 Physical Principles of Electric Arc Surfacing In electric arc surfacing, the source of energy for heating and melting of the electrode (filler) metal and the base metal is an electric arc. Electric arc—a type of discharge in gases, characterized by a decrease in voltage between the electrodes (up to tens of volts) because of increasing the degree of ionization (ion and electron density) and current (up to a thousand amperes) and, consequently, reaching high temperature (from 4000 to 20,000 °C). The electric arc (Fig. 2.1) consists of a cathode zone, an arc column, and an anode zone. 1. The cathode zone is a layer about 0.1 μm thick, consisting of free electrons and positive ions. Free electrons of the cathode zone come from the cathode as a result of thermoelectron emission, in which the work of the electron output occurs due to the heating energy of the cathode. Thermoelectron emission at the cathode is one of the two main sources of charged particles in an electric arc. The intensity of thermoelectron emission increases with increasing cathode heating temperature. Note: Free electrons of the cathode zone are formed to a lesser extent as a result of: • secondary emission, in which the work of the electron output occurs due to the kinetic energy transmitted by positive ions during slowing down on the cathode surface, • photoelectron emission, in which the work of electron output occurs due to the absorption by the cathode of light quanta from the arc regions. Positive ions of the cathode zone come from the arc column at high speed. They are neutralized by free electrons and are inhibited on the cathode surface

Z

1 8 7 6 5

9

+

Uc

2

Up Ua

3 4

Uea

U

Fig. 2.1 Electric arc diagram: 1—electrode, 2—cathode spot, 3—arc column, 4—anode spot, 5— surfacing pool, 6—base metal, 7—heated non-conductive gas halo, 8—molten metal droplet, 9— power source

2.1 Physical Principles of Electric Arc Surfacing

9

with the release of a large amount of heat. As a result, the cathode is heated and melted, and thermoelectron emission from the cathode surface takes place. The surface of the cathode adjacent to the cathode zone is called cathode spot 2 (Fig. 2.1). The temperature in the area of the cathode spot during fusion welding reaches 2500–3000 °C. The voltage drop in the cathode region Uc (Fig. 2.1) is 10–20 V. 2. Arc column 3 (Fig. 2.1) is formed from positive ions moving in the direction of the cathode, free electrons and negative ions moving in the direction of the anode, as well as neutral atoms and molecules. The arc column begins where the free electron from the cathode zone collides with the first neutral gas atom (the free path of the electron ends). An arc discharge becomes possible if the kinetic energy of a free electron is sufficient to ionize a neutral atom—the process of separating electrons from a neutral atom and removing them at a distance at which the electron extends beyond the force field of the positive ion formed. As the degree of ionization increases, the temperature of the arc column increases. Further ionization, in addition to the collision with free electrons, proceeds by the following mechanisms: • Thermal ionization—increasing of speed of chaotic thermal motion of neutral atoms result in increasing of number of collisions and increasing of energy of each collision, • Photoionization—due to the absorption of light quanta (photons) from the arc regions by neutral atoms. The ionization of neutral atoms in an arc column is the second major source of charged particles in an electric arc. The intensity of ionization depends on the composition of the gas. Note: Gases with low ionization work (energy required for the ionization process) and, as a consequence, low ionization potential are called plasma-forming gases. These include argon, as well as mixtures of argon with helium, nitrogen, or hydrogen. Simultaneously with the ionization process in the arc column, the reverse process of recombination takes place—the reduction of the neutral atom as a result of the linking of positive ions and free electrons. When the intensity of recombination equals the intensity of ionization, a steady state occurs. The arc column is thus a weakly ionized gas (the degree of ionization is about 3– 5%) and, in general, is electrically neutral—in each section there are equal amounts of positively and negatively charged particles. The temperature of the arc column is about 6000–18000 °C.

10

2 Electric Arc Surfacing

The voltage drop, Up, (Fig. 2.1) is proportional to the length of the arc column, Lp: U p = E pL p

(2.1)

where Ep ~ 2,5 V/mm for surfacing of steels. 3. The anode zone is a layer about 1 μm thick, consisting of a stream of free electrons coming out of the arc column, inhibited, and neutralized on the surface of the anode with the release of thermal energy. This leads to strong heating and melting of the anode metal. The surface of the anode adjacent to the anode zone is called the anode spot 4 (Fig. 2.1). The temperature in the area of the anode spot during fusion welding reaches 2500–4000 °C, which is on average higher than the temperature of the cathode spot. The voltage drop in the anode zone Ua (Fig. 2.1) is 3–6 V. In general, in the electric arc, the positive electrode emits 43% of the total amount of heat of the welding arc, the negative—36% and the arc column—21%. In the anode spot, the heating depth of the metal is greater than that on the cathode spot due to the release of more heat and high electron permeability. In this regard, in direct current welding and surfacing the following schemes are used: (1) Electric arc of direct polarity—negative pole of the power supply is connected to the electrode, positive one—to the workpiece. The electric arc of direct polarity is widely used in welding as it provides an increase in depth of penetration of the welded parts. (2) Electric arc of reverse polarity—positive pole of a power supply is connected to the electrode, negative one—to the workpiece. An electric arc of reverse polarity is widely used in surfacing because it provides: • reduction of base metal penetration, therefore reducing the quota of base metal in the weld, • increase in the heating volume of the electrode wire or strip, thus increasing the productivity of the electrode melting. Primary ionization of the gaseous medium between the electrodes is required to ignite the electric arc. The process begins with a short circuit of the electrodes. Due to the contact resistance, the cathode is heated. With a further increase in the distance between the electrodes a spark discharge occurs. The number of charged particles increases and the arc processes are initiated. The voltage drop in the electric arc Uea (Fig. 2.1) equals: U ea = U a + U p + U a

(2.2)

The cathode and anode spots on the electrodes of most metals are heated to temperatures close to the temperature of their evaporation. Therefore, the existence

2.1 Physical Principles of Electric Arc Surfacing

11

of any contaminant films in active spots is unlikely. The surfaces of the metals in these spots are clean and ready for the formation of metal bonds. An electric arc converts electrical energy into heat. This provides a concentrated introduction of heat into the welded product. When surfacing on direct current, the power released in the anode and cathode zones, respectively, equals: q a = U a I ea

(2.3)

q c = U c I ea

(2.4)

where U a and U c Voltage drop, respectively, in the anode and cathode zones, V, I ea Electric current arc, A. Part of the power of the arc column is transmitted to the heating spot by radiation. When surfacing with an open arc (in shielding gases and with a coated electrode), part of this power is lost to the environment. As the arc deepens into the metal, the proportion of these losses decreases. When surfacing with a consumable electrode, a large number of molten droplets fall into the area of the heating spot and transfer their energy to it. Some of these drops are spattered, carrying their energy from the deposition zone. When surfacing under a layer of flux, energy is not lost due to radiation, there are almost no losses and spattering. However, when surfacing under a layer of flux, part of the energy is spent on heating and melting the flux. The energy balance of the open arc and the submerged arc is shown in Fig. 2.2 [1]. Effective arc power qe ratio to the total arc power qg gives heating efficiency ηe : • ηe = 50–60%—when surfacing with non-consumable electrode with shielding gas, • ηe = 60–75%—when surfacing with open arc consumable electrode, • ηe = 80–95%—when under flux surfacing [1]. Approximately half of the total arc power is spent to melt the base metal (Fig. 2.2). The power spent to melt the base metal qm ratio to the total arc power qg gives thermal efficiency of melting ηt = qm /qg . Total thermal efficiency of electric arc ηg = ηt ηe : • ηg = 0.25—when surfacing with open arc consumable electrode, • ηg = 0,35—when under flux surfacing. Productivity of arc surfacing is usually evaluated by deposition rate Km : Km =

m I ea t

(2.5)

12

2 Electric Arc Surfacing

a

4

1

5 6

3

7

2 4

b

3 1 2

5 6

Fig. 2.2 Electric arc energy balance: a—open arc 1—total arc power qg (100%), 2—heat absorption by the base metal (≈ 50%), 3—heat absorption by the electrode (≈ 30%), 4—heat scattering into environment (≈ 20%), 5—losses of heat due to spattering (≈ 5%), 6—heat transfer with molten metal droplets (≈ 25%), 7—heat transferred from arc to metal—effective arc power qe (≈ 75%), b—under flux arc: 1—total arc power qg (100%), 2—heat absorption by the base metal (≈ 54%), 3—heat transfer with molten metal droplets (≈ 28%), 4—heat losses on flux melting (≈ 18%), 5—losses of heat due to spattering (≈ 1%), 6—heat transferred from arc to metal—effective arc power qe (≈ 81%) [1]

where m Mass of molten metal, Iea Surfacing current, t Time of electrode melting. During the formation of the weld bead, the metal of the consumable electrode is transferred to the pool in the form of droplets of different sizes. The time of droplet formation, the time and trajectory of droplet motion and the nature of the metallurgical interaction of the droplets with the liquid and gaseous phases of the surfacing zone affect the quality parameters of the weld metal. There are two forms of metal transfer during electric arc surfacing with a consumable electrode: • transfer with short circuits of an arc interval, • transfer with free flying droplets. The short circuit metal transfer occurs at low surfacing parameters—low current and low arc voltage. The short circuit metal transfer is a characteristic of surfacing in a carbon dioxide environment.

2.2 Manual Metal Arc Surfacing

13

Free-flight metal transfer occurs at high surfacing parameters. The average diameter of the droplets decreases with increasing of arc current. When the arc current exceeds a certain critical value, the droplets become very small and form a stream of liquid metal. According to the classification of the International Institute of Welding, there are five types of free-flight droplet transfer [2]: • • • • •

globular, globular with deviation of droplets, globular with small-sized droplets, spray, rotating-spray.

When transferred from the consumable electrode, part of the metal falls outside the pool—in this way spattering occurs. Spattering depends on the dynamic characteristics of the power source (especially in case of short-circuit transfer), the composition of the shielding gas (the use of gas mixtures reduces spraying), arc current (with increasing of arc current spattering increases). Methods of surfacing differ in technological capabilities, including productivity, the proportion of the base metal in the surfacing and the thickness of the layer of surfacing metal (Table 2.1).

2.2 Manual Metal Arc Surfacing Manual metal arc (MMA) surfacing with a coated electrode is a universal method and is suitable for parts of different configurations in all welding positions. The formation of the shape of the weld bead is influenced by such a phenomenon as mechanical arc blowing—the action of excess pressure created by the formation of an arc discharge. By analogy with the action of the fan, if you blow on the surfacing pool, as in the ‘back angle’ diagram (Fig. 2.3a), the liquid metal moves from the bottom to the rear. A high weld bead with deep penetration is created. If you blow on the surfacing pool, as in the ‘forward angle’ diagram (Fig. 2.3b), the action of the arc will be aimed at melting the base metal in front of the pool. In this case, a liquid layer remains in the crater (at the bottom) of the pool, which reduces the heat transfer from the arc to the base metal and, accordingly, the depth of penetration. Liquid metal is in a much calmer state. A low weld bead with low penetration is created. MMA surfacing is usually carried out at a ‘forward angle’. Reducing the angle of inclination and using ‘forward angle’ technique reduces the thermal impact on the surface of the part and the depth of penetration, allows to get wider and smoother beads with less reinforcement. The nature of the movement of the electrode across the surfacing bead is determined by the width of this bead. Narrow beads, up to 1.5 electrode diameter, are obtained by rectilinear movement of the electrode along the direction of surfacing, without oscillating movements. It should be borne in mind that the pool of molten

14

2 Electric Arc Surfacing

Table 2.1 Comparison of general methods of arc surfacing [3] Method of surfacing

Deposition rate, kg/h

The proportion of base metal in the deposited %

The thickness of the metal layer, deposited in one pass, mm

Manual metal arc

1–5

10–40

1.0–5.0

• Single electrode wire

2–10

30–50

2.0–5.0

• Two electrodes

5–30

15–30

3.0–8.0

• Electrode strip

5–30

5–20

2.5–5,0

Automated submerged arc

Automated self-protective flux-cored wire • Single electrode wire

2–9

25–50

1.5–5.0

• Two electrodes

5–20

25–50

2.5–7.0

Mechanized self-protective flux-cored wire

2–7

25–50

1.5–5.0

Automated self-protective flux-cored strip • Single electrode wire

10–20

15–40

2.5–5.0

• Two electrodes

20–40

10–40

6.0–8.0

Automated and mechanized solid wire in shielding gas

1.5–8

30–50

2.0–5.0

Automated and mechanized flux-cored wire in shielding gas

2–10

30–50

1.5–5.0

Tungsten inert gas with filler

0.5–2

5–15

1.5–4.0

metal in case of narrow bead is small. The metal cools quickly and gases may remain in it because of lack of time to be released, resulting in the formation of pores. Wider beads are obtained by transverse oscillating movement of the electrode tip. The best quality of surfacing occurs when the width of the bead is 2.5 diameter of the electrode. At such movement of an electrode the flatter bead is obtained. Such beads are favorable for restoration of parts with small wear on thickness. Advantages: • universal for all sizes and welding positions • simple and easily available equipment and technologies • ability of alloying of deposited metal in wide range

Disadvantages: • low productivity • difficult working conditions • unstable quality of deposited layer • high penetration into the base metal

2.3 Automated Submerged Arc Surfacing

15

a

Vc

b

Vc

Fig. 2.3 MMA surfacing diagrams: a—‘back angle’, b—‘forward angle’

2.3 Automated Submerged Arc Surfacing Automated submerged arc (SAW) surfacing is the most common method. Features of automated SAW surfacing: • continuity of the process, which is achieved by using an electrode wire or strip in the form of large skeins, • supply of current to the electrode at a minimum distance from the arc column, which provides less resistance and allows the use of high currents without overheating the electrode, • combining the function of the alloying component and the protective medium when using a flux,

16

2 Electric Arc Surfacing

• the use of special devices for feeding the electrode material into the arc and mechanisms for moving the arc or the workpiece.

2.3.1 Automated Submerged Arc Surfacing with Solid Wire or Strip At automated SAW surfacing (Fig. 2.4) the electrode wire moves into the zone of arc burning (5) by means of the feeding mechanism (4). The flux on the surface of the workpiece comes from the flux feeder (3). The relative movement of the workpiece and the electrode is provided by the mechanism of the surfacing installation. Both the installation relative to the fixed part and the part relative to the fixed installation can move. The arc burns between the electrode and the workpiece (1), to which current is supplied from the power source (2). A pool of molten metal (8) is formed on the surface of the workpiece. The welded area is covered with a thick layer of loose flux (7). The arc partially melts the flux and burns inside the cavity, which is surrounded by an elastic shell of molten flux (6). The molten flux reliably isolates liquid metal from air gases, prevents spattering of electrode metal and promotes preservation of heat of the arc. After cooling, the molten flux forms a slag crust (10). As a result of crystallization of the pool metal, a weld bead (9) is formed. The bead is covered with slag and a non-melted flux. 4

Vw

Vel

3

5

8

6

7

9

10

2 1

Fig. 2.4 Diagram of automated SAW surfacing with solid wire: 1—workpiece, 2—power source, 3—flux feeder, 4—wire feeding mechanism, 5—electric arc, 6—molten flux, 7—layer of flux, 8—molten metal pool, 9—weld bead, 10—slag

2.3 Automated Submerged Arc Surfacing

17

The slag is separated after cooling the bead. The non-molten flux is collected for subsequent use. When SAW surfacing with a solid wire, the electrode stick-out (the distance from the tip of the electrode, where the arc burns, to the contact tip) is small and the heating of the electrode metal due to electrical resistance is minimal. This allows to increase the surfacing current without the risk of overheating the electrode. For example, for a wire with a diameter of 5 mm, one can use a current of up to 1000 A. It is most effective to use automatic SAW surfacing in cases when it is necessary to surface a layer of metal thicker than 3 mm. Such parts include, for example, rolling mills for various purposes, hot or cold metal feed rollers, crane wheels and other parts of machines and mechanisms of the mining and metallurgical complex, parts of the chassis of tractors and other construction and agricultural machines—rollers, pins, axles etc. As mentioned above, the penetration depth is affected by the angle of the electrode relative to the part. When surfacing, the ‘forward angle’ diagram is used, in which the depth of penetration is less than when surfacing according to the ‘back angle’ diagram. When SAW surfacing ‘forward angle’ flat parts are installed at an angle and surfacing is carried out ‘on the descent’. Curved mouthpieces are also used. The penetration depth also decreases with the increase of electrode stick-out. For automated SAW surfacing with a solid wire, installation of both hanging and tractor types are used. Hanged type installations are more common. Rectifiers of various types, including inverters, are used as power sources. Advantages of SAW surfacing Disadvantages of SAW surfacing • productivity is 5–20 times higher than that of • limited use on site, for short curved beads, MMA surfacing for surfacing in different positions • good protection of surfacing pool due to the flux layer which reduces imperfection formation • high current density and a possibility to add stabilizing elements to flux ensures arc stability both on AC and DC • ability to alloy the deposited metal through flux

2.3.2 Automated Submerged Arc Surfacing with Solid or Flux-Cored Strip Automated SAW surfacing with an electrode strip provides a small penetration depth and slight mixing of the weld metal with the base metal. This allows us to obtain a given chemical composition of the weld metal by single- or double-layer surfacing. When SAW surfacing with an electrode wire, this is possible only in the third or fourth layer.

18

2 Electric Arc Surfacing

α

Vc

Fig. 2.5 Diagram of automated SAW with electrode strip—the strip is oriented relatively to travel direction transversely (α = 0°)

The width of the deposited layer in one pass is adjusted, as a rule, by changing the width of the strip. In the absence of such a possibility, the width of the layer can be adjusted by rotating the strip around to its vertical axis at an angle α. The position of the strip perpendicular to the direction of surfacing is taken as the zero position (α = 0º) (Fig. 2.5). When welding with an electrode strip, the electric arc moves along the strip edge at high speed. As the current increases, the speed of movement of the electric arc increases and, accordingly, the melting speed of the strip increases with a simultaneous decrease in size of the droplets. When surfacing with strip, it is possible to show the effect of magnetic blowing— the deflection of the arc, as a flexible conductor of current, in external electromagnetic fields. This leads to a deterioration in the formation of weld beads. The magnetic blow is manifested, for example, by a large displacement of the place of attachment of the reverse current supply wire relative to the center of the width of the electrode strip. The magnetic blow of the arc has a significant negative effect on the formation of the weld bead when the width of the electrode strip is more than 80 mm. To eliminate the magnetic blow and increase the stability of the formation of the weld bead using magnetic control of the displaced arc along the electrode strip, a transverse alternating magnetic field is applied, which provides reciprocating movements of the electric arc along the edge of the electrode strip. The arc does not wander, but moves in the direction, melting the electrode strip across its width.

2.3 Automated Submerged Arc Surfacing

19

Surfacing current increase

Arc movement speed

Strip melting speed increase

Droplet size decrease

Less effect on the molten metal pool Surfaced layer of good quality

However, for each strip thickness there is a certain critical value of current, after which the process becomes uncontrollable. The use of a grooved strip (Fig. 2.6b) reduces the formation of defects. Surfacing can be carried out by bending the strip forward or backward. To increase the burning time of the arc along the edges of the weld bead (hence the duration of the pool existence on the edges of the bead in places of accumulation of

a

b

c

Fig. 2.6 Shapes of electrode strip for automated SAW surfacing: a—flat, b—grooved, c—with flanged edges

20

2 Electric Arc Surfacing

slag) and increase the weld metal on the edges of the bead strips with flanged edges are used (Fig. 2.6c). This prevents the formation o 2-IIW-Surf-En-link f defects such as slag inclusion and undercuts and creates a weld bead with the same cross-sectional thickness. The easiest way to profile electrode strips with a thickness of 0.3–0.4 mm from low-carbon non-alloy or low-alloy—plastic steels are used. Profiled strips (grooved and with flanged edges) provide: • good formation of the edges of the weld bead, • high stability of the arc process, • increased rigidity (which prevents bending of the strip when passing it through the layer of flux), • increased range of surfacing speed. With a rigid characteristic of the source and a constant feed rate of the strip, the process of self-regulation improves, and the arc burns more stably. To a large extent, the uniform feed of the strip depends on the design of the rollers feeding the strip (Fig. 2.7). To increase the productivity of surfacing, two parallel electrode strips are used, which with a small gap are simultaneously fed into the arc zone (Fig. 2.8). The flux between the strips melts and the electroslag process begins in the area between the

a

b

c Fig. 2.7 Structural shapes of strip feeding rollers: a—flat, b—grooved, c—with flanged edges

2.3 Automated Submerged Arc Surfacing

21

strips. The electroslag process, in comparison with the arc process, provides minimal penetration of the base metal and increases the productivity of surfacing. To expand the possibilities of the weld metal alloying, automated SAW surfacing with a strip on granular powder, which is poured on the base metal in front of the strip, is sometimes used (Fig. 2.9). When surfacing, a layer of granular alloying powder consists of relatively inexpensive materials, but this method is not very suitable if you aim to high stability of the chemical composition and performance properties of the weld metal. To ensure the alloying of the weld metal in a wide range and increase of the process productivity the flux-cored strips are used. The flux-cored strip consists of a metal shell and a filler powder.

Vc

Fig. 2.8 Diagram of automated SAW surfacing with twin strips 5 4

2

Vc

3

6

1

Fig. 2.9 Automated SAW surfacing with strip on granular powder: 1—workpiece, 2—electrode strip, 3—deposited metal layer, 4—granulated powder feeder, 5—flux feeder, 6—slag

22

2 Electric Arc Surfacing

When surfacing with flux-cored strip, the electric arc, depending on the composition and the degree of compaction of the charge, mainly burns on the metal shell of the strip due to the high resistance of the filler powder. The electric arc moves rapidly along the electrode and for a long time (longer than when using solid strip) burns on the side walls of the shell. The high resistance of the filler powder also leads to greater heating of the electrode tip and intensifies the melting process of the strip. When surfacing, 75–80% of the metal passes into the surfacing pool in the form of droplets, and the rest enters the surfacing pool in the form of powder, bypassing the stage of melting. This reduces the pool temperature and penetration depth. With increasing current and voltage, the stability of arc burning increases. It is better on the direct polarity than on the reverse. Increasing the current, in addition to increasing productivity, enhances convection mixing in the pool, thus reducing the heterogeneity of the chemical composition of the weld metal. Solid high-alloy wires and strips give more homogeneous metal when deposited than flux-cored wires and strips. However, high-alloy solid wires and strips are much more expensive.

2.4 Automated and Mechanized Gas Shielded Surfacing The process of gas shielded arc surfacing differs from surfacing under a layer of flux in the following: the dropping in this case is possible only with the help of electrode or filler metal (solid wire, strip, flux-cored wire). Gas shielded arc surfacing can be carried out with a consumable—MIG-MAG (Fig. 2.10a) and non-consumable—TIG (Fig. 2.10b) electrode. In TIG surfacing, the arc burns between the workpiece and the non-consumable tungsten electrode. The filler metal in the form of a rod or wire of small diameter is fed into the arc area separately at almost a right angle to the electrode. TIG surfacing provides a small depth of penetration of the base metal, and it is possible to weld thin layers—from 0.5 mm. Gas is supplied to the arc zone under low pressure, which displaces air and protects the molten metal from the effects of oxygen and nitrogen in the air. Carbon dioxide, argon (for surfacing of all metals), helium (for surfacing of highalloy steels and non-ferrous metals), nitrogen (for surfacing of copper and its alloys) are used as shielding gases. Carbon dioxide provides large droplet transfer and relatively high spatter. Mixtures of Ar + CO2 or Ar + CO2 + He gases are used to reduce spattering and ensure small-sized droplet (or spray) transfer. When nitrogen or hydrogen enters the pool, the weld metal becomes porous. In this case it is necessary to add 5–10% of oxygen or 10–20% of carbon dioxide into argon. This increases the stability of the arc and prevents the formation of pores. The wire in this case must have an increased number of alloying elements, considering their burnout in the presence of oxygen.

2.4 Automated and Mechanized Gas Shielded Surfacing

23

Vc 1

2

4

3

5

a) with consumable electrode

Vc 1 7 6 3

4 5

b) with non-consumable electrode Fig. 2.10 Diagrams of gas shielded arc welding or surfacing: 1—nozzle, 2—electrode, 3—electric arc, 4—shielding gas, 5—workpiece, 6—filler wire, 7—non-consumable electrode

24

2 Electric Arc Surfacing

When surfacing with a non-consumable electrode, a mixture of argon and carbon dioxide is used. This reduces argon consumption by 5…6 times. The most common is surfacing in the environment of carbon dioxide. DC power sources with flat characteristics are used in this case. When surfacing worn parts of small diameter, the voltage is in the range of 17– 22 V with a wire diameter of 0.5–1.2 mm, and within 28–32 V with a wire diameter of 2.0–2.5 mm. Current density 150–200 A per 1 mm2 of electrode cross section. As the cross section of the part increases, a larger diameter of the electrode wire and a larger electrode stick-out (from 10 to 30 mm) are used. The displacement of the electrode from the zenith during the surfacing of cylindrical parts (distance “a” in Fig. 2.3) is 3–8 mm. Surfacing speed is up to 80–00 m/h, wire feed speed depends on its diameter. For example, for a wire 0.8–1.0 mm, the feed speed will be 160–200 m/ h. The set of gas equipment includes gas cylinder, reducer with flow meter, dehumidifier—gas heater, rubber hoses for gas supply. When surfacing with carbon dioxide as a shielding gas wire with high content of manganese and silicon, which are deoxidizers, are used. Arc surfacing with self-protective flux-cored wires and strips ensures arc stability, alloying and protection of molten metal by means of electrode material core components. In all cases of electric arc surfacing, it is possible to achieve the desired composition of deposited metal only in the third—fourth layer due to higher base metal penetration. Advantages: • universality • high productivity • possibility to obtain deposited metal of any alloying system

Disadvantages: • high base metal penetration

2.5 Vibro-Arc Surfacing Vibro-arc surfacing is a type of electric arc surfacing with a consumable electrode, which is carried out with forced transfer of drops. Features of vibro-arc surfacing are: (1) Vibration of the electrode, which provides alternation of short circuits, shortterm arc and open circuit. (2) Continuous cooling of the surface with liquid. The coolant is fed to the combustion zone of the arc and protects the liquid metal from the effects of oxygen and nitrogen in the air.

2.5 Vibro-Arc Surfacing

25

Features of vibro-arc surfacing provide minimal thermal impact on the product (compared to other arc methods) and, therefore, are minimal: • • • •

heat affected zone, penetration, structural heterogeneity, shrinkage force and deformation.

In addition, the hardness of the deposited layer is increased due to hardening. In the process of vibro-arc surfacing (Fig. 2.11) electrode wire (2) and coolant (3) are fed into the vibrating contact tip (1). 3–4% aqueous solution of baking soda or 10–20% aqueous solution of glycerin are often used as coolants. The presence of ionizing elements improves the arcing conditions. Vibrator (4) provides vibration of the contact tip. The oscillations are carried out by an electromagnet and are regulated by a spring or a change in voltage in the coil of the electromagnet of the vibrator in the range from 20 to 36 V. The cycle of the vibro-arc surfacing process consists of three stages: (1) short circuits (Fig. 2.11a)—a drop of molten metal passes from the tip of the electrode wire to the surface of the product,

2

a

4 5

b

3 1

c

Fig. 2.11 Diagram of vibro-arc surfacing: 1—vibrating contact tip 2—electrode wire, 3—coolant, 4—vibrator, 5—base part (a—short circuit, b—short-term arc, c—open circuit)

26

2 Electric Arc Surfacing

(2) short-term arc (Fig. 2.11b)—a droplet of molten metal is formed on the electrode tip, (3) open circuit (Fig. 2.11c)—rupture of the electrical circuit with increase of the distance between the electrode tip and the product. About 10% of heat of the total heat balance is released at the stage of short circuit and 90%—at the stage of short-term arc. Transfer of metal in small drops ensures the formation of equal dense layers of weld metal with minimal mixing with the base metal. The vibro-arc surfacing mode is characterized by the strength and type of current, voltage, electrode wire feed rate, surfacing speed, amplitude, and oscillation frequency of the vibrating contact tip. A reverse polarity DC is used (electrode positive). The current is determined by the diameter of the electrode wire. The current density is 60–75 A/mm2 for the electrode wire up to 2 mm diameter and 50–70 A/mm2 for the electrode wire with a diameter of more than 2 mm. The arc voltage during surfacing with a layer up to 1 mm thick is 12–15 V, with a thickness of more than 1 mm—17–20 V. The feed rate of the electrode wire should not exceed 1.65 m/min. The surfacing speed is set within 0.5–0.65 m/min. The oscillation amplitude of the vibrating contact tip is set within 0.5–3.5 mm (usually 1.8–3.2 mm), the oscillation frequency is 110 Hz. The surfacing step is 2.3–2.8 mm per turn, the wire angle is 15–30°. The minimum diameter of the surfaced part can be 8–10 mm, and the thickness of the welded layer in one pass, depending on the conditions and mode of surfacing— 0.5–3 mm. With a greater layer thickness, surfacing is performed in several passes. The coefficient of surfacing in vibro-arc surfacing is from 2.5 to 7 g / (A • h). Vibro-arc surfacing is used to restore the outer and inner surfaces of cylindrical parts, outer surfaces of conical parts, surfaces of flat parts, shaft slots, etc. Vibro-arc surfacing is less productive in comparison to SAW. Thus vibro-arc is used when application of SAW is problematic. Advantages • insignificant heating of the base surface • small deformation and shrinking force • minimal HAZ and structural hheterogeneity • surface hardening without heat-treatment

Disadvantages • small gas pores are formed as a result of pulsating nature of the process and effect of coolant • low productivity • reduction of fatigue strength of parts up to 40%

2.6 CMT Surfacing

27

2.6 CMT Surfacing CMT (Cold Metal Transfer) is a type of electric arc surfacing with a consumable electrode with gas shielding, which is carried out with forced transfer of droplets in a cycle of three stages (Fig. 2.12): (1) electric arc process with the formation of a droplet during the direct movement of the electrode wire in the direction to the welded part, (2) short circuit with transfer of a droplet, stop of the electrode wire feeding, (3) reverse of the electrode wire with arc burning. Note: (1) The developer of CMT processes and equipment for welding and surfacing is Fronius. (2) The term “cold transfer” in the name of the process is conditional because the process of formation of the deposited layer (or the joint) occurs by crystallization of the metal from the liquid phase. Minimization of time of thermal influence of an electric arc on a droplet and on a pool of molten metal at CMT surfacing provides the minimum thermal influence on a product and the minimum stirring of metal and, as a result, the minimum: • heat affected zone, • penetration,

Vc

a

b

c

Fig. 2.12 Diagram of CMT surfacing: a—electric arc process with formation of the droplet during electrode wire movement in the direction to the part to be surfaced, b—short circuit with droplet transfer, stop of electrode wire feeding, c—reverse of electrode wire with arc burning

28

2 Electric Arc Surfacing

• structural heterogeneity, • shrinkage force and deformation. In the first stage of CMT surfacing (Fig. 2.12a), the electrode wire is fed in the direction of the welded part at an increased speed which provides a shortening of the arc up to a short circuit. During the arc process, the droplet of molten metal on the electrode wire tip grows. The second stage of CMT surfacing is a short circuit (Fig. 2.12b). The electrode wire feeding is stopped. A droplet of molten metal from the electrode tip transfers to the surface of the welded product. There is a gap between the electrode wire and the surface of the product, and the electric arc ignites. At the third stage of CMT surfacing (Fig. 2.12c) the electrode wire is fed in the reverse direction. The length of the electric arc at the end of the electrode reverse can be adjusted and are among the parameters of the CMT surfacing mode. The cycle repeats. Disadvantages Advantages • minimal stirring of deposited • low productivity (in comparison to automated SAW with solid or flux-cored strip, solid or flux-cored wire) meta • insignificant heating of the base surface • minimal heating of the part to be surfaced • small deformation and shrinking force • minimal HAZ and structural heterogeneity

2.7 Features of Physical and Metallurgical Processes in Electric Arc Surfacing 2.7.1 Methods of Alloying of Deposited Metal In contrast to welding, in which the weld metal is chemically close to the base metal, when surfacing the metal of the deposited layer in chemical composition and properties in many cases differs significantly from the base one. For the case of arc surfacing there are three possible methods of alloying the deposited metal [1]: (1) by introducing alloying components into the surfacing materials—consumable electrodes or filler wires (the main method), (2) exchange reactions between the metal and oxides that are contained in fluxes, (3) through the gas phase (limited use).

2.7 Features of Physical and Metallurgical Processes in Electric Arc Surfacing

29

When choosing the alloying method, the following should be considered: • requirements for obtaining a given chemical composition and structure of the deposited metal, which depend on the purpose and operating conditions of the surfaced parts (when surfacing corrosion-resistant layers, the requirements for stability and homogeneity of the metal composition are higher than when surfacing layers resistant to abrasive wear), • the possibility of fluctuations in the chemical composition of the deposited metal during fluctuations in the surfacing parameters, • the possibility of heterogeneity of chemical composition across the cross section of the deposited layer, • cost-effectiveness and ease of application of the alloying method for specific conditions. Alloying through introduction of alloying components to the surfacing materials is the most widely used method. When surfacing with coated electrodes, the alloying components can be introduced through the rod and/or through the electrode coating. If the alloying components are introduced through the electrode coating, their concentration in the deposited layer is proportional to the thickness of the coating. Alloying processes occur at the stage of droplet formation and in the surfacing pool. With a large coating thickness, its outer layers melt and flow directly into the surfacing pool, bypassing the droplet. Alloying components get into the tail part of the pool and do not have time to completely dissolve and be evenly distributed in the molten metal. As a result, chemical inhomogeneity increases and the performance properties of the deposited metal decreases. When surfacing with coated electrodes, the coefficient of transition to the deposited metal of titanium and carbon does not exceed 0.5 for vanadium and 0.6 for manganese and silicon. Higher results are achieved if the alloying components are introduced not through the electrode coating, but through the wire. In automated submerged arc surfacing, four methods of alloying the deposited metal are used [4]: I. Alloyed solid electrode wire or strip in combination with fused flux, II. Flux-cored electrode wire or strip with alloying components in the core and in the shell in combination with a fused flux, III. Unalloyed solid electrode wire or strip in combination with alloying flux, IV. Unalloyed solid electrode wire or strip in combination with alloying additives in the form of wire, strip, rod, paste, powder, stacked or applied to the surfacing surface. All these methods can be considered combined, as none of them occurs in its pure form. Thus, the liquid electrode material always interacts with the liquid flux and part of the alloying elements passes into the weld metal from the flux (except for getting through the metal of the electrode). An example of alloying due to exchange reactions between the metal and oxides contained in the fluxes are manganese- and silicon-reduction processes during

30

2 Electric Arc Surfacing

deposition under a layer of highly active fluxes with a high content of SiO2 and MnO: (SiO2 ) + 2[Me] = [Si] + 2(MeO)

(2.6)

(MnO) + 2[Me] = [Mn] + 2(MeO)

(2.7)

According to the degree of reduction of oxygen affinity, the elements introduced into the electrode coatings or cored of flux-cored wires and strips can be arranged in the following row: Ca > Al > Ti > Si > Mn > Fe

(2.8)

Based on the affinity of oxygen, each previous element of this series will reduce the oxides of subsequent elements. Alloying through the gas phase is used for steels containing chromium, titanium, vanadium, and some other nitride-forming elements. Solid and strong nitrides that form increase the wear resistance of steels. An example of alloying is electric arc surfacing in nitrogen. Alloying by reducing metals from flux oxides or through the gas phase does not provide the required set, the level of the content of alloying elements and the accuracy of a given chemical composition of the deposited metal. Therefore, their use is limited.

2.7.2 Effect of Electric Arc Surfacing Parameters on Chemical Composition of the Deposited Metal The parameters of the surfacing affect the chemical composition of the deposited metal due to two factors: • changes in the proportion of base metal in the weld, • changes in the nature of chemical reactions in molten metal. In multilayer surfacing, when the proportion of the base metal in the weld metal becomes negligibly small, the character of chemical reactions in the molten metal has the decisive influence on the chemical composition of the deposited metal. If the alloying element is not oxidized and is not reduced during the surfacing process and enters the surfacing pool only from the electrode, its content in the i-th layer can be calculated by the formula: Rc = Re −

Re γ i

(2.9)

2.7 Features of Physical and Metallurgical Processes in Electric Arc Surfacing

31

Where: Rc Content of the alloying element in the deposited metal, Re Content of alloying element in the electrode metal, γ Ratio of base metal in the deposited one. If in the first layer the content of the base metal in the weld is 30%, in the third layer it is close to 0%. The content of each alloying element in the weld metal is almost no different from the content in the metal of the electrode. In the case of automated SAW surfacing the influence of the process parameters (current, voltage, surfacing speed, electrode diameter and stick-out) on the composition of the deposited metal is the most significant. In this case, changing the parameters of the surfacing mode changes the relative mass of the liquid flux—the amount of liquid flux per unit mass of the molten electrode. The kinetic conditions of interaction between metal and liquid flux also change. The impact of these changes on the alloying process depends on what is the main source of alloying elements—electrode or flux. The influence of parameters on alloying through solid or flux-cored wire by methods I or II (Sect. 2.7.1) depends on the type of flux (chemically active, neutral, or alloying). (a) When surfacing under chemically active fluxes containing SiO2 and MnO, the increase in the relative mass of the liquid flux leads to the oxidation of the alloying elements and the transition of silicon and manganese to the surfacing pool. Silicon and manganese are reduced from oxides by reactions (2.6) and (2.7). A change in the deposition parameters is also accompanied by a change in the kinetics of the interaction of the phases at the stage of the droplet formation: the lifetime of the droplet and the time of interaction with the slag increases. As a result, the chemical composition of the deposited metal changes. (b) When depositing under a layer of neutral flux, the degree of influence of the relative mass of the liquid flux on the oxidation and alloying processes decreases. This is due to the lower oxidizing ability of the flux and due to the fact that not all the mass of the liquid flux interacts with the metal. Thus, when alloyed through the electrode wire, the effect of the parameters on the chemical composition of the weld metal decreases with decrease of the oxidizing ability of the flux. (c) When surfacing under a layer of alloying flux, a significant (level of alloying is achieved already at the stage of droplet formation. With the increase of relative mass of the liquid flux (in case of voltage increase or current decrease), the content of alloying elements in the droplet remains constant. The overall level of alloying of the weld metal increases. The slight effect of the surfacing parameters on the composition of the droplet is due to the fact that it interacts with a relatively small and constant proportion of liquid flux. In conditions of high temperatures and intensive mixing of the interacting phases, the process of infusion of the

32

2 Electric Arc Surfacing

droplet with alloying elements has time to pass quite fully, regardless of the parameters. Thus, when surfacing under a layer of alloying flux, the surfacing parameters affect the composition of the deposited metal through the processes occurring at the stage of the surfacing pool [4]. When surfacing with a consumable electrode upon fixed alloying additive (method IV of alloying during SAW—Sect. 2.7.1) the amount of additive is chosen so that it is all remelted by the electric arc. Surfacing is carried out with unalloyed solid wire or strip combined with fused fluxes. The alloying components are distributed along the cross section and length of the deposited bead quite evenly due to intensive mixing in the surfacing pool. In this method the oxidation of alloying elements occurs to a small extent by limiting reactions with oxides of liquid flux. After melting the additive, the alloying components are immediately transferred into the metal pool. Liquid flux has less of an effect on alloying components than when alloying through wire. When surfacing with a consumable electrode upon alloying fixed additive, the chemical composition of the deposited metal largely depends on the feed rate of the electrode (current) and the rate of surfacing, as the proportion of unalloyed electrode metal changes significantly. For this reason, a given chemical composition of the weld metal can be obtained in a limited range of surfacing parameters.

2.8 Materials for Electric Arc Surfacing Each type of deposited metal can be obtained through a number of surfacing materials’ combinations. All types of surfacing materials (coated electrodes for manual surfacing, solid and flux-cored wires, cold rolled (solid), flux-cored and sintered strips, powders and rods) are included in the European standard EN 14,700 “Welding consumables—Welding consumables for hard facing” [5].

2.8.1 Coated Electrodes A wide range of coated electrodes for manual electric arc surfacing provides a wide application of the method primarily for restorative surfacing of worn machine parts in any position, despite the low productivity. The chemical composition, hardness of the weld metal and areas of application are given in Table 2.2.

≤ 0.3

≤ 0.4

10.0–12.0 22.0–28.5

0.8–1.2 ≤ 0.3 ≤ 0.8

0.4–1.0

0.05–0.12

0.08–0.18

-08X17H8C6G

-13X16H8M5C5G4B

3.0–5.0

1.0–2.0

≤ 0.7

11.0–14.0

0.50–0.80

0.50–0.80

-65X11H3

-65X25G13H3 3.8–5.2

4.8–6.4 14.0–19.0

15.0–18.4

2.3–3.2

8.0–11.0

0.50–0.90

1.4–2.8

-70X3CMT

0.4–1.0

0.20–0.40

0.25–0.50

2.0–3.5

–

≤ 0.6

5.5–6.5

-30B8X3

0.25–0.45

-35G6

0.5–1.0

≤ 0.15 0.9–1.3

–

≤ 0.15 0.8–1.3

1.2–2.0

1.5–2.0

4.1–5.2

– –

≤ 0.15 ≤ 0.15

Cr

Si

-37X9C2

0.22–0.38

0.12–0.20

-30G2XM

-16G2XM

0.12–0.18

-15G5

3.6–4.5

2.0–3.3

0.08–0.12

0.09–0.14

-12G4

Mn

C

Mass fraction of elements, %

-10G2

Types of electrodes

Table 2.2 Coated electrodes for electric arc surfacing

6.5–10.5

7.0–9.0

2.0–3.5

2.5–3.5

–

–

–

–

–

–

–

–

–

Ni

3.5–7.0 Mo 0.5–1.2 Nb

–

–

–

0.3–0.7 Mo

–

7.0–9.0 W

–

0.7–0.9 Mo

0.3–0.7 Mo

–

–

–

Others

38–50

28–37

25–35

25–33

52–60

52–58

40–50

50–57

35–39

31–41

40–44

35–40

20–28

HRC

Sealing surfaces of oil fittings, boilers and pipelines

Ball mills, crushers, excavator buckets

Cold stamping stamps

Hot stamping stamps

Parts operated in the conditions of impact loadings (axes, shafts, rails)

Surfacing objects

2.8 Materials for Electric Arc Surfacing 33

34

2 Electric Arc Surfacing

Table 2.3 Steel surfacing solid wires Wire brand

Mass fraction of elements, % C

Mn

Si

Hardness

Surfacing objects

Cr

Ni

≤ 0.3 160–220 HB Axles, ≤ 0.3 170–230 HB spindles, shafts

Hp-30

0.27–0.35 0.5–0.8 0.2–0.4

≤ 0.25

Hp-45

0.42–0.50 0.5–0.8 0.2–0.4

≤ 0.25

Hp-50

0.45–0.55 0.5–0.8 0.2–0.4

≤ 0.25

≤ 0.3 180–240 HB Tension wheels, rollers, slopes

Hp-65

0.60–0.70 0.5–0.8 0.2–0.4

≤ 0.25

≤ 0.3 220–300 HB Support rollers, axles

Hp-80

0.75–0.85 0.5–0.8 0.2–0.4

≤ 0.25

≤ 0.3 220–300 HB Crankshafts, crosspieces of cardans

Hp-40G

0.35–0.45 0.7–1.0 0.2–0.4

≤ 0.3

≤ 0.3 180–240 HB Axles, spindles, shafts

Hp-65G

0.6–0.7

≤ 0.3

≤ 0.3 230–310 HB Crane wheels, axles, shafts

0.7–1.0 0.2–0.4

Hp-30XGCA 0.27–0.35 0.8–1.1 0.9–1.2 0.8–1.1 Hp-30X5

0.27–0.35 0.4–0.7 0.2–0.5 4.0–6.0

≤ 0.4 220–300 HB Crane wheels, rolling mills ≤ 0.4 37–42 HRC

Rolling mills

2.8.2 Solid Wires Mainly the two groups of electrode wires are used in production: • for submerged arc surfacing—2.0 to 4.0 mm diameter, • for surfacing with gas shielding—1.2 to 1.6 mm diameter. Regulatory documentation supports the production of a wider range of sections— 0.3 to 6.0 mm diameter. The chemical composition, hardness of the weld metal and the purpose of surfacing solid wires are given in Tables 2.3 and 2.4. In addition, for restorative surfacing, as well as surfacing of intermediate layers (sublayers) solid wires given in Table 2.5 are used.

2.8.3 Flux-Cored Wires Flux-cored wire (Fig. 2.13) consists of: • shells of soft tape (steel, nickel, etc.),

1.8–2.3

0.8–1.2

1.3–1.8

≤ 0.7

0.35–0.43

0.45–0.55

0.55–1.1

0.16–0.25

0.25–0.35

0.25–0.35

0.4–0.5

0.55–0.65

≤ 0.12

Hp-40X2G2M

Hp-50X6FMC

Hp-105X

Hp-20X14

Hp-30X13

Hp-30X10G10T

Hp-45X4B3F

Hp-65X3B10F

Hp-X20H80T

10–12

≤ 03.5

≤ 0.8

0.4–0.7

0.7–1.0

≤ 0.8

≤ 0.8

10–12

12–14

≤ 0.8

19–23

2.6–3.6

3.6–4.6

13–15

0,2–0.4

1.3–1.6

1.8–2.3

1.8–2.3

Cr

≤ 0.8

0.8–1.2

0.4–0.7

Si

0.15–0.4

0.3–0.6

Mn

Mass fraction of elements, %

C

Wire brand

Table 2.4 Steel surfacing solid wires

0.3–0.55 V 1.2–1.6 Mo –

≤ 0.4 ≤ 0.4

9.0–10.5 W 0.3–0.5 V

≤ 0.4

0.15–0.40 Ti

0.1–0.2 W 0.3–0.5 V

Base

0.15–0.30 Ti

≤ 0.6

–

≤ 0.6

–

–

0.8–1.2 Mo

≤ 0.4

≤ 0.6

Others

Ni

180–220 HB

42–50 HRC

38–45 HRC

200–220 HB

38–45 HRC

34–39.5 HRC

32–38 HRC

42–48 HRC

54–56 HRC

Hardness

Engine valves

Stamps for hot stamping, rolling mills

Knives for cutting hot metal, press tools

Blades, screws, shafts

Hydraulic press plungers

Latches

Cold stamping stamps, shafts

Stamps of hot stamping, rolling mills

Crankshafts, rotary fists

Surfacing objects

2.8 Materials for Electric Arc Surfacing 35

≤ 0.8

1–2

≤ 0.12

≤ 0.03

Cv-10X17T

Cv-01X19H9

0.5–1.0

≤ 0.7

≤ 0.3

≤ 0.3

0.16–0.24

0.7–0.95 0.9–1.2

Cv-20X13

1.8–2.1

0.6–0.9

0.6–0.85

≤ 0.03

≤ 0.03

Si

0.8–1.1

0.05–0.11

0.15–0.22

Cv-08G2C

0.8–1.1

≤ 0.14

Cv-12GC

Cv-18XGC

1.5–1.9

1.4–1.7

≤ 0.12

≤ 0.1

0.35–0.60

≤ 0.1

Cv-10G2

Mn

C

Mass fraction of elements, %

Cv-08GC

Cv-08

Wire brand

Table 2.5 Steel surfacing solid wires

18–20

16–18

12–14 8–10

≤ 0.6

–

0.2–0.5Ti

–

– –

≤ 0.3 ≤ 0.3

≤ 0.2 0.8–1.1

–

–

–

–

Others

≤ 0.3

≤ 0.3

≤ 0.3

≤ 0.3

Ni

≤ 0.2

≤ 0.2

≤ 0.2

≤ 0.15

Cr

228–247 HB

30–38 HRC

42–48 HRC

240–300 HB

180–210 HB

190–220 HB

180–200 HB

180–210 HB

120–160 HB

Hardness

Latches for steam and water

General industrial fittings

Rollers

Axles, shafts, rollers

Axes, shafts, sublayer

Surfacing objects

36 2 Electric Arc Surfacing

2.8 Materials for Electric Arc Surfacing

37

a

b

c

d

e

f

Fig. 2.13 Flux-cored wires: a—tubular, b—butt, c—with edge overlap, d—with one bent edge, e—with both edges bended, f—double-layered

• cores of powders of alloying components (ferroalloys, pure metals, carbides, borides, etc.). Compared to solid wires, flux-cored wires provide much greater opportunities for alloying the weld metal. The industry uses three types of flux cored wires: • for SAW surfacing, • for surfacing with gas shielding, • self-protective. When using self-protective flux-cored wires, surfacing can be carried out with an open electric arc without flux and protective gases. In the core of the selfprotective flux-cored wire, in addition to alloying components, gas- and slag-forming substances, deoxidizers and elements having a high chemical affinity for nitrogen are also introduced. When surfacing with self-protective flux-cored wire, the protection of the pool is provided by the formation of a layer of liquid flux, which is formed due to the slag-forming substances. The most common are butt flux cored wires (Fig. 2.13b) and ones with overlapping edges (Fig. 2.13c). In special cases, flux-cored wires with bent edges (Fig. 2.13d and e) or double-layered flux-cored wires (Fig. 2.13f) are used.

38

2 Electric Arc Surfacing

The characteristic of flux-cored wires is the filling factor—the ratio of the mass of the filler powder to the total mass of the wire, expressed as a percentage. For surfacing flux-cored wires, the filling factor usually does not exceed 45%. Diameters of the most used flux-cored wires for surfacing: • 1.6–2.8 mm—with gas shielding and self-protective, • 3.6 mm—under a layer of flux, products of medium sizes, • 5.0–6.0 mm—under the flux layer, large products. Flux-cored wires are made of tape on special mills. The tape is rolled into a tube in the profile-bending device, which is equipped with a charge dispenser in the form of a powder of a given chemical and particle size distribution. Then the tube with the powder is dragged in successively arranged cages on the flux-cored wire of the required diameter. Table 2.6 shows the chemical composition of the weld metal and the purpose of the most common flux-cored wires [3].

2.8.4 Cold-Rolled, Flux-Cored and Sintered Strips Electrode strips are usually used for SAW surfacing. Some brands of flux-cored strips are used as self-protective. Advantages of electrode strip surfacing in Disadvantages of electrode strip surfacing in comparison to electrode wire surfacing comparison to electrode wire surfacing • high process productivity • the process cannot be applied to small parts and parts with a complex surface shape • small depth of penetration of the base metal (low current density leads to a relatively small arc pressure on the surface of the pool) • large width of the surfaced bead

Cold-rolled steel strips are made of structural, tool, spring, stainless and corrosion-resistant steels, as well as nickel alloys (Table 2.7). The thickness of the most common surfacing cold-rolled electrode strips is 0.2– 1.0 mm, width—20 to 90 mm. Strips with a width of 100, 120, 150, 180 and 210 mm are used for special purposes. Cold-rolled strips can only be made of fairly malleable alloys with low carbon content. This limits their use. Flux-cored strips (Fig. 2.14) consist of a metal shell (1) and a powder-filler (2). The components of the powder-filler are: • metal powder—provides alloying and filling of the surfaced bead, • ceramic powder—provides wear resistance of the deposited layer (for example, tungsten carbide W2 C + WC), • flux (for self-protective strip)—provides protection of a surfacing pool.

0.5

1.4

1.5

0.15

0.18

0.30

PP-AH198

PP-Hp-30X2H2G

Mn

PP-Hp-18X1G1M

1.1

0.6

0.8

0.6

0.8

0.9

13.0

0.4

0.15

0.15

0.12

0.25

0.30

0.35

0.8

1.5

PP-Hp-15X4GCMF

PP-Hp-15X13

PP-AH174

PP-Hp-25X5FMC

PP-Hp-30X2M2FH

PP-Hp-35B9X3CF

PP-AH105

PP-AH192

PP-Hp-14GCT

0.5

C

0.4

0.4

0.8

1.0

1.0

0.6

0.8

0.9

0.6

0.8

0.5

0.6

Si

5.0

–

3.0

2.5

5.0

13.0

13.0

3.7

1.8

1.4

0.4

–

Cr

Mass fraction of elements, %

0.14

Wire brand

Table 2.6 Most common surfacing flux-cored wires Mo

–

–

–

2.4

1.1

0.8

–

1.1

–

0.4

–

–

V

–

–

0.3

0.5

0.4

0.2

–

0.4

–

–

–

–

Others

3.5 Ti

3.0 Ni

9.0 W

1.0 Ni

-

1.6 Ni

–

–

1.4 Ni

–

0.3 Al 0.3 Ti

0.4 Ti

50–56 HRC

160–240 HB

48–52 HRC

42–48 HRC

48–52 HRC

38–48 HRC

38–48 HRC

42–48 HRC

42–48 HRC

320–380 HB

220–310 HB

240–260 HB

Hard-ness

Agricultural machinery

Crossroads

Shafts, rollers, knives and stamps for hot stamping

Rollers

Axles, shafts, rollers

Axles, shafts, cranks

Axles, shafts, crane wheels

Axles, shafts

Surfacing objects

2.8 Materials for Electric Arc Surfacing 39

0.06

0.03

0.07

NiCr22Mo9Nb

0.16–0.25

Cv-2X13

Cv-04X19H11M3

0.2–0.3

25X5FMC

Cv-03X22H11B

0.46–0.54

50XFA

0.40

1.5–2.0

1.0–2.8

0.8

0.5–1.0

0.8–1.0

0.9–1.2

0.7–1.0

0.45–0.56

0.6–0.7

50G

Mn

C

0.10

0.2–0.4

0.06

0.8

0.6–1.2

0.17–0.37

0.17–0.37

0.17–0.37

Si

Mass fraction of elements, %

65G

Strip brand

Table 2.7 Steel cold-rolled strips for SAW surfacing

21.5

21.7–23.5

18–20

12–14

4.8–5.7

0.95–1.20

0.3

0.3

Cr

rest

10.3–11.3

10–12

–

–

0.4

0.3

0.3

Ni

9.0 Mo 3.8 Nb + Ta 1.5 Fe; 0.03 N

0.95–1.2 Nb

2–3 Mo

–

0.2–0.6 V

0.15–0.25 V

–

–

Others

Nuclear energy engineering

Reactor buildings of petrochemical equipment

Hydraulic press plungers

Rolling mills, roller conveyor rollers

Cold stamping stamps

Crane wheels, rollers

Rollers, axles, shafts

Surfacing objects

40 2 Electric Arc Surfacing

2.8 Materials for Electric Arc Surfacing

41

2 1

a 2 1

b Fig. 2.14 Flux-cored strip (1—metal shell, 2—filler powder): a—two-lock, b—one-lock

By design, there are two-lock (Fig. 2.14a) and one-lock (Fig. 2.14b) flux-cored strips. Flux-cored strips are made on special mills, which include rollers for forming a tape-shell, a dosing device for filling with powder-filler, a device for rolling and sealing. The thickness of flux-cored strips for surfacing is 3–4 mm, width—10 to 30 mm. The filling factor of the flux-cored strips reaches 70%, which allows us to obtain a deposited metal with a higher degree of alloying than when surfacing with flux-cored wire. Table 2.8 shows chemical composition and purpose of the most common fluxcored strops for surfacing. Sintered iron-based strips are made by powder metallurgy by cold rolling and subsequent sintering in a protective atmosphere at a temperature of 1200–1300 °C. The powder for the manufacture of sintered strips consists of a mixture of fractions with a size of 70–200 μm, which includes: • metal powders, • ferroalloys, • graphite and other materials. The thickness of sintered strips is 0.8–1.2 mm, width—25 to 100 mm. Table 2.9 shows chemical composition and purpose of the most common sintered strips for surfacing.

42

2 Electric Arc Surfacing

Table 2.8 Surfacing flux-cored strips Mass fraction of elements, %

Strip brand

C

Mn Si

Cr

Ti

HRC Others

PL-Hp-10G2CT

0.1

2.0

1.0

–

PL-Hp-20X2G2CT

0.2

2.0

1.0

2.0 0.7 0.4 Mo 38–45

PL-Hp-300X25C3H2G2

3.0

2.0

3.0 25.0 –

PL-Hp-400X38G3PCT

3.0

3.0

1.0 38.0 0.3 0.2 Al 0.9 B

PL-Hp-120X22P3G2C

1.2

2.0

1.0 22.0 1.0 3.0 B

PL-Hp-450X20B7M6B2

4.5

–

2.0 20.0 –

2.0 W 55–62 7.0 Nb 6.0 Mo

PL-Hp-500X40H40C2P

5.0

1.0

2.0 40.0 –

40 Ni 0.2 B

PL-Hp-550X44H34GCP

5.5

0.8

0.8 44.0 –

34 Ni 0.3 B

PL-Hp-12X16H8M6C5G4B 0.12 4.0

5.0 16.0 –

8.0 Ni 38–50 Energy, petrochemical 6.0 Mo fittings 1.0 Nb

0.12 2.0

PL-Hp-12X18H9C5G2T

0.2 –

Surfacing objects

20–26 Axles, shafts

2.0 Ni

50–56 Teeth bucket 50–54 excavators, bimetallic sheets 54–60

50–56 Cones and bowls of blast 54–62 furnaces

5.0 18.0 0.2 9.0 Ni

27–34

Table 2.9 Sintered strips for surfacing Strip brand

Mass fraction of elements, % C

Mn

Si

LC-70X3MH

1.0

0.4

0.7

LC-25X5FMC

0.4

0.4

0.7

Cr

HRC

Surfacing objects

1 Ni

54–60

Parts of the automobile chassis

0.8 V

38–44

Rolling mills

Mo

Others

4.5

0.9

6.2

1.5

LC-50X4B3FC

0.7

0.4

0.5

5.0

1.5

0.7 V; 4.0 W

42–46

LC-15X13

0.2

0.5

0.5

16.5

–

–

38–42

LC-12X14H3

0.2

1.1

0.5

16.0

–

3.5 Ni

38–42

LC-02X20H11G

0.02

2.0

0.4

20.0

–

11 Ni

–

Rollers Petrochemical equipment

2.8.5 Fluxes One of the main characteristics of the flux is the chemical activity, which is determined by its total oxidizing ability Af : ] [ SiO2 + 0.5TiO2 + 0.4(Al2 O3 + ZrO2 ) + 0.42B2 (MnO) Af = 100B

(2.10)

2.8 Materials for Electric Arc Surfacing

43

where: (SiO2 ), (TiO2 ) etc.—flux component content, %, Another flux characteristic is the basicity coefficient B. [ B=

] 0.018CaO + 0.015MgO + 0.006CaF2 + 0.014(Na2 O + K2 O) + 0.007(MnO + FeO) [0.017SiO2 + 0.005(Al2 O3 + TiO2 + ZrO2 )]

(2.11)

By oxidizing ability Af fluxes are divided into four groups. • • • •

highly active Af > 0.6, active 0.3 ≤ Af ≤ 0.6, low-active 0.1 ≤ Af < 0.3, neutral Af < 0.1.

Basicity index also determines activity of reactions between the molten flux and molten metal (Bonishevskyi formula): ] [ CaO + MgO + BaO + K2 O + Na2 O + 0.5(CaF2 + MnO + FeO) (2.12) B= [SiO2 + 0.5(TiO2 + ZrO2 + Al2 O3 )] By basicity index B fluxes are divided into three groups: • acidic, with 0.5 ≤ B < 1, • neutral, with B = 1 / 1.5, • basic, with 1.5 < B ≤ 3.5. By factor of the transition of alloying elements from the flux to the weld metal, which is defined as the difference between the chemical composition of the weld metal and the chemical composition of the electrode metal, fluxes are classified according to ISO 14174 “Welding consumables—Fluxes for submerged arc welding and electroslag welding. Classification”. By the composition and manufacturing technology of fluxes are divided into two groups: • fused fluxes, • ceramic fluxes. Fused fluxes are made by fusing the constituent components. The manufacturing process includes: • grinding to the required size of raw materials (manganese ore, quartz sand, chalk, etc.), • mixing components in certain proportions, melting in gas-flame or electric furnaces, • granulation in order to obtain certain grain size of the flux particles. The composition of fused fluxes includes slag-forming components that provide good protection, the formation of the surfaced bead, the separation of the slag crust.

44

2 Electric Arc Surfacing

The chemical composition of the most common fused fluxes for surfacing are given in Table 2.10. Fused fluxes are used for surfacing of low-carbon low-alloy steels, or for surfacing of alloy and high-alloy steels in combination with alloyed electrode wires (strips). Highly active fluxes AH-348A, AH-60 and TA.St.6 with a high content of SiO2 and MnO are used for surfacing of low-carbon and low-alloyed steels. These fluxes provide good formation of the deposited bead, low tendency to the formation of pores and good separation of the slag crust. Active manganese-free flux AH-26 is used for surfacing of alloyed and highalloyed steels, in particular, austenitic chromium-nickel steels. The advantage of this flux is the excellent formation of the deposited bead and a very low tendency to form pores. Low-silica flux AH-20 is used for surfacing of low- and medium-alloyed steels. It provides a satisfactory formation of the surfaced bead and easy separation of the slag crust from the surface of both cold and heated to 250–300 °C metal. Low-silica flux AH-70 has smaller grains and is more refractory than AH-20, it provides the possibility of surfacing of cylindrical surfaces of small diameters. Neutral manganese fluxes AH-15, AH-28 and 48-OF-10 have a pumice-like structure of particles and are used for surfacing of medium- and high-alloy steels and alloys. These fluxes have low oxidizing ability to the metal of the surfacing pool and provide good formation of the weld bead. The disadvantage of these fluxes is Table 2.10 Chemical composition of fused fluxed for surfacing Flux brand

AH-348A

Mass fraction of components, % SiO2

MnO

CaO

MgO

42.0

36.0

≤ 6.5 6.0

Al2 O3 CaF2

FeO

≤ 4.5

≤ 2.0 –

4.5

K2 O Others + Na2 O –

AH-60

42.0

38.0

6.0

2.0

≤ 5.0

6.0

≤ 1.5 –

–

AH-26

30.0

3.0

6.0

17.0

21.0

22.0

≤ 1.5 –

–

AH-20

20.0

≤ 0.5 7.0

11.0

30.0

29.0

≤ 1.0 2.5

–

AH-15 M

8.0

≤ 2.0 30.0

≤ 1.0 35.0

18.0

≤ 1.0 –

4 NaF

AH-28

8.0

≤ 1.0 38.0

≤ 2.0 38.0

10.0

≤ 2.0 1.5

–

AH-70

7.0

–

30.0

–

30.0

1.0 2.0

–

30.0

AH-72

8.0

1.0

48-OF-6

≤ 4.0

≤ 0.3 20.0

48-OF-10

11.0

–

–

20.0

30.0

≤ 2.0 –

3.0

25.0

52.0

1.5 –

–

30.0

40.0

≤ 1.0 –

–

≤ 8.0 12.0

10 ZrO2

2–4

≤ 1.5 –

–

19–23 16–19 14–17

4–6

≤ 1.0 3.0

–

≤ 8.0 15–20 26–32

17–23

≤ 1.0 8.0

2–6 ZrO2

TA.St.6

40–45 36–40 5–8

TNA.St.1

29–33 8–11

TNA.St.11CrNi 20–26 –

30.0

–

5–7

2.8 Materials for Electric Arc Surfacing

45

the poor separation of the slag crust from the surface of the beads containing vanadium and niobium. They also have high hygroscopicity, which requires mandatory high-temperature calcination (900–970 °C for 3–5 h) before use. Fluoride fluxes AH-72 and AH-90 are used for electric arc and, mainly, electroslag surfacing of alloyed and high-alloyed steels and alloys with electrode strips. The advantages of these fluxes include excellent separation of the slag crust, good formation of the deposited bead and refining properties (removal of impurities from the surfacing pool). Neutral flux TNA.St.1 (B = 1.25) is used for wear-resistant surfacing of alloyed steels, for example, 30XGCA and 40X13. Flux TA.St.11CrNi (B = 0.15) is used for surfacing of high-alloyed corrosionresistant steels. The presence of zirconium dioxide, alumina, magnesium oxide, silicon dioxide and calcium fluoride promote the formation of a slag, which is easily separated from the surface of the weld bead and provides a good formation when surfacing with wire and strip. Zirconium dioxide helps to reduce the chemical activity of the flux and to improve the formation of the deposited bead. The increased number of oxides of potassium and sodium stabilizes the electric arc. Ceramic fluxes are made from mixtures of powder materials bonded with adhesives, mainly liquid glass. The composition of ceramic fluxes for surfacing includes magnesium-aluminate base and alloying components—chromium, carbon, and others. Ceramic fluxes are used to obtain a weld metal of high hardness and wear resistance. Advantages of ceramic alloying fluxes: • possibility of their use in combination with low-carbon electrode wire or strip

Disadvantages of ceramic alloying fluxes: • low mechanical strength of the grains (tendency to crushing) • increased sensitivity to moisture compared to fused fluxes

When using ceramic alloying fluxes, it is necessary to strictly adhere to the optimal range of surfacing parameters, otherwise the composition of the deposited metal could significantly deviate from the specification [3].

2.8.6 Protective Gases Active shielding gases are used for electric arc surfacing with a consumable electrode of low-alloy steels: carbon dioxide, gas mixtures: CO2 + Ar, or CO2 + Ar + O2 , less often: CO2 + O2 . Active gases protect the surfacing area from air. However, they themselves participate in chemical reactions with the weld metal and can also dissolve in it. The oxidizing effect of the gas mixture on the liquid metal increases. This improves the formation of the weld bead, increases the mechanical properties of the weld metal.

46

2 Electric Arc Surfacing

Inert gases: argon, helium or their mixtures are used for electric arc surfacing with a consumable electrode of high-alloyed steels, nickel, copper, aluminum, and their alloys. Inert gases are practically insoluble in the weld metal and do not chemically react with it. Inert gases provide higher quality weld metal compared to active gases. High costs limit the widespread use of inert gases, especially helium. Electric arc in helium, compared with argon: • • • •

has a greater penetration ability, is less concentrated, creates a better shape of penetration, provides a smoother transition between the weld bead and the base metal due to the lower surface tension of liquid chromium-nickel steels.

Mixtures of inert gases (by volume) are used when surfacing alloy steels with a consumable electrode: 70% Ar + 30% He, or 35–40% Ar + 65–60% He, etc. To improve the shape of the weld bead and reduce spattering, up to 5% CO2 or O2 is added to argon. When surfacing copper and its alloys with a consumable electrode, argon, or mixtures of 50–30% Ar + 50–% He are used. The purity of these gases must be at least 99.99%. Nitrogen does not dissolve in copper and does not interact with it, but it is not used due to the unstable transfer of metal in the arc, strong spraying, and uneven surface of the bead. Sometimes a mixture of 80–70% Ar + 20–30% N2 is used, which improves the transfer of the electrode metal, the formation of the bead and provides deeper penetration. When surfacing austenitic steels, nickel, copper, aluminum and their alloys with a non-consumable electrode, argon is used. For surfacing of austenitic steels, nickel, and its alloys, one can also use a mixture of 90% Ar + 10% H2 , which increases the temperature and power of the electric arc, reduces surface tension, improves the formation of the weld bead.

2.9 Electric Arc Surfacing Procedures The surfacing procedure includes: • • • •

surfacing method, surfacing parameters, diagram of imposition of the deposited beads and sequence of operations.

Note: Issues related to quality assurance, including the development of documented procedures and quality control, are set out in [6].

2.9 Electric Arc Surfacing Procedures

47

2.9.1 Parameters of Electric Arc Surfacing The surfacing process must provide quality indicators: • • • •

good formation of each bead, maximum surfacing productivity, minimal (but reliable) penetration of the base metal, or previously deposited layer, minimum allowance for machining. The parameters of electric arc surfacing include:

• • • • • • • •

current, arc voltage, surfacing speed, number of electrodes, electrode stick-out, surfacing step, inclination angle of the electrode, displacement from the zenith—when surfacing the bodies of rotation.

The current determines the productivity of surfacing. The higher the current, the higher the performance. As the current increases, the length of the surfacing pool increases. When depositing rotating bodies, this can lead to metal runoff. The current also determines the cross-sectional shape of the surfaced bead—an increase in current leads to a sharp increase in the depth of penetration and the formation of high and narrow beads. The arc voltage at a given current largely determines the cross-sectional shape of the bead. At too low voltage a narrow and high surfaced bead is formed. Increasing the voltage increases the width and reduces the height of the bead. When the voltage is too high, a very wide bead is obtained, which can lead to the formation of longitudinal cracks in the center of the bead. In SAW surfacing the increase of voltage leads to an increase in the mass of the molten flux. This can affect the composition of the deposited metal. In addition, in this case, when surfacing the bodies of rotation may drain the liquid flux. The arc voltage must match the current. Figure 2.15 shows the optimal dependence of the arc voltage from the current (blue zone) during surfacing under the flux layer. The dotted line shows the allowable range of arc voltage change. The speed of surfacing (the speed of movement of the arc relative to the product), in contrast to the speed of welding, does not directly determine the productivity of the process, but affects the cross-sectional shape of the deposited bead (Fig. 2.16). At low deposition speed (10–20 m/h), a decrease in speed leads to a decrease in the penetration depth. When performing the surfacing process with low-speed indigestion and violation of the formation of the deposited bead are possible. In the middle range (20–40 m/h) the penetration depth is almost independent of the deposition rate.

48

2 Electric Arc Surfacing

U, V 40

30

20 0

200

400

600

I, A

Fig. 2.15 Dependence of arc voltage from current for SAW surfacing

a

c

b

d

e

Fig. 2.16 Effect of surfacing speed V on deposited bead shape: a—V = 10 m/h, b—V = 20 m/h, c—V = 40 m/h, d—V = 60 m/h, e—V = 100 m/h

As the deposition rate increases, the width of the bead decreases. At speeds of 40–60 m/h, an increase in the deposition rate causes a simultaneous decrease in the penetration depth and the width of the deposited bead. At high speeds of surfacing the appearance of undercuts is possible. The number of electrodes affects the surfacing performance and the shape of the surfacing pool. When surfacing with one or two electrodes, the optimal formation is obtained with the opposite polarity. When surfacing with three or four electrodes, one can use a direct polarity, which increases the melting rate of the wire by 30–40%. Multi-electrode surfacing and electrode strips are used for surfacing of rotating bodies more than 300 mm diameter. The optimal electrode stick-out (the distance between the edge of the contact tip and the electrode tip) depends on the physical properties and diameter (or thickness) of the wire (or strip). The electrode is heated at the length of the stick-out by welding current due to electrical resistance. The greater the electrical resistance and

2.9 Electric Arc Surfacing Procedures

49

m

a

b

m

b

b Fig. 2.17 Effect of surfacing step m on rate of base metal in the deposited one Ƴ: a—surfaced layer when m ≈ b, Ƴ = 0.65, b—surfaced layer when m = 0.46 b, Ƴ = 0.45

the smaller the diameter of the electrode wire, the shorter should be the stick-out. Overheating of the electrode wire at the length of the stick-out leads to bending of the wire and the formation of twisted beads. This also worsens the formation of the deposited bead. The stick-out length for SAW deposition is 8–15 de , where de is the diameter of the electrode. The deposition step (transverse movement of the electrode during the transition to the deposition of the next bead) determines the smoothness of the coating surface and the proportion of base metal in the weld. Big surfacing step can cause irregularities and excessive dilution of the weld metal by the base metal. Small step can cause imperfections in the form of overlaps and lack of fusion. To obtain a high-quality welded layer, the surfacing step should be 0.4 to 0.75 of the width of the deposited bead (Fig. 2.17).

2.9.2 Electric Arc Surfacing of Rotating Bodies Electric arc surfacing of rotating bodies is usually done using: • automated SAW process, • automated surfacing with gas protection. The diagram of automated SAW surfacing is given in Fig. 2.18. The electrode wire (1) is fed to the arc zone. Flux (2) on the surface of the product (3) comes from the bunker. The rotation of the product is provided by the mechanisms of the surfacing equipment.

50 Fig. 2.18 Diagram of SAW surfacing of cylindrical parts (a—electrode displacement from zenith): 1—electrode, 2—flux layer, 3–part, 4—direction of part’s rotation

2 Electric Arc Surfacing

a 1

2 3 4

During SAW surfacing a fairly large pool of weld metal is formed. To prevent runoff of liquid metal and liquid flux, as well as to prevent the formation of imperfections, the surfacing area should be located horizontally or at a small angle. For this purpose, the electrode is set with some displacement from the upper point of the part—the zenith (Fig. 2.18). Surfacing is carried out with spiral or circular beads with periodic offset by a step (Fig. 2.19). When surfacing with spiral beads (Fig. 2.19a), the part rotates, and the electrode moves slowly parallel to the axis of rotation. When surfacing with circular beads (Fig. 2.19b), the electrode at the end of each full turn of the part moves by the size of the surfacing step. Advantages of surfacing with spiral or circular beads • continuity of the process provides high productivity • good formation of the deposited layer allows to minimize the allowance for processing • symmetry of residual stresses in relation to the longitudinal axis eliminates the curvature of the longitudinal axis of the product

Difficulties of surfacing with spiral or circular beads • difficult retention of liquid metal in the arc area (especially difficult on parts less than 80 mm diameter) • difficulties in removing slag crust from the surfaced bead due to the complex spatial geometry

2.9 Electric Arc Surfacing Procedures

a

51

b

c Fig. 2.19 Technique of surfacing of solids of revolution: a—spiral beads, b—circular beads, c— wide beads

To increase productivity and reduce the depth of penetration of the base metal surfacing with wide beads is used (Fig. 2.19c), which are obtained by: • transverse oscillations of the electrode wire—for products with diameter of 150– 300 mm, • several electrode wires or electrode strip—for products with diameter of more than 300 mm. When there is a danger of overheating another technique is used: surfacing along the generating line. To reduce deformation, the deposited beads must be symmetrical on the longitudinal axis of the product. For this purpose, the technique of "crossshaped" compensation is used—the product is rotated by 180° after surfacing of the previous bead. This increases the time to install the part in position, which reduces the productivity of the process. The parameters of surfacing of rotating bodies, in addition to ensuring quality indicators (Sect. 2.9.1), must exclude the runoff of liquid metal and liquid flux (Fig. 2.18). The optimal ranges of current depending on the diameter of the welded product, when surfacing with different numbers of electrodes, are given in Fig. 2.20. The optimal range of surfacing speed (linear rotation speed of the product surface) with one electrode depending on the diameter of the surfacing product is shown in Fig. 2.21. At multi-electrode surfacing and surfacing with an electrode strip lower surfacing speeds (in the range of 10–14 m/h) are applied.

52 Fig. 2.20 Optimal current for surfacing with spiral bead depending on product diameter: 1—one electrode Ø 3.0–3.5 mm, 2—one electrode Ø 4.0–5.0 mm, 3—three electrodes Ø 3.0–3.5 mm

2 Electric Arc Surfacing

I, A

800

3

700

2

600 500

1

400 300 200 100

Fig. 2.21 Optimal range of linear surfacing speed values depending on product diameter

200

400

600

800 Ø, mm

V, m/h 50 40 30 20

10

200

400

600

800

Ø, mm

The surfacing step when surfacing with one electrode is chosen within 3–10 mm depending on the diameter of the electrode, the thickness of the deposited layer, the depth of penetration, so as to ensure the overlap of the previous bead at 40– 60%. When multi-electrode surfacing and surfacing with an electrode strop, the step increases accordingly. The displacement of the electrode from the zenith (Fig. 2.18) should be close to the length of the surfacing pool, which depends on the current, arc voltage, product temperature.

2.9 Electric Arc Surfacing Procedures

53

If the electrode is excessively displaced forward against rotation, the level of liquid metal in the crater increases. The molten metal is displaced by the arc. The penetration depth decreases. A wide surfaced bead is formed. It is possible to drain the molten flux and liquid metal forward. If the electrode is excessively displaced backwards in the direction of rotation, the level of liquid metal in the crater decreases. The penetration depth increases. A narrow bead is formed. Imperfections may form and the molten flux and liquid metal may be drained back in the direction of the part rotation. The displacement of the electrode from zenith should increase with increase of diameter of the product and with increase of the current. When surfacing parts with a diameter from 250 to 800 mm, the displacement of the electrode from zenith is set in the range from 20 to 60 mm. The angle of inclination of the electrode (deviation of the axis of the electrode from the vertical) should be from 5 to 15°. Tables 2.11, 2.12 and 2.13 give optimal modes of automated SAW surfacing with gas protection of solids of revolution. Table 2.11 Parameters of automated SAW surfacing with solid wire (DC EP) Part diameter mm

Wire diameter, mm

Current, A

Voltage, V

Rotation speed, 1/ min

Surfacing step, mm

The angle of the electrode, deg

Displacement from the zenith, mm

200

2.5

220

25

1.1

4.2

5–10

10

250

2.5

280

28

1.3

6.3

5–10

13

300

3.25

300

26

0.5

5.4

5–10

14

400

3.25

400

30

0.4

6.0

10–15

21

400

4.0

360

25

0.32

5.6

10–15

18

500

4.0

440

28

0.32

6.1

10–15

21

600

4.0

500

31

0.27

7.0

10–15

26

600

5.0

500

29

0.27

6.6

10–15

26

700

5.0

580

34

0.23

8.3

10–15

35

800

5.0

640

36

0.20

9.0

10–15

38

Table 2.12 Parameters of automated SAW surfacing with cold-rolled electrode strip (DC EP) Part diameter, mm

Strip cross section, mm

Current A

Voltage V

Rotation speed, 1/min

Surfacing step, mm

Deposited layer height, mm

300

0.3 × 40

620

31

0.25

37

2.4

400

0.5 × 40

630

28

0.19

39

2.1

600

0.5 × 40

740

30

0.16

39

2.1

600

0.5 × 60

840

32

0.13

58

2.3

54

2 Electric Arc Surfacing

Table 2.13 Parameters of surfacing with gas shielding (Ar + 18% CO2) with solid wire 1.2 mm diameter (DC EP) Part diameter, mm

Current A

Voltage V

Rotation speed, 1/min

Longitudinal feed mm/min

Surfacing step, mm

30

120

20

6.0

24.0

4.0

80

140

21

2.6

11.7

4.5

100

160

23

1.9

9.5

5.0

150

180

25

1.2

7.2

6.0

200

210

26

1.0

8.0

8.0

Surfacing of conical surfaces is carried out similarly to cylindrical ones if the forming cone is inclined no more than 20º to the horizontal axis of rotation. Special equipment is used for surfacing conical surfaces with bigger angles. The cone is installed so that its generating line is in the horizontal position or close to it. Surfacing of internal cylindrical surfaces is usually carried out in one layer at an inclined axis of rotation. This facilitates the supply of flux, provides unauthorized removal of slag crust and excess flux. A layer 2–4 mm thick is deposited in one pass. The electrode wire is fed through a curved contact tip. Surfacing begins at the lowest point of the surface. The electrode slowly moves parallel to the axis of rotation of the product, and the deposited bead is spiral.

2.9.3 Electric Arc Surfacing of Flat Parts The following processes are commonly used for electric arc surfacing of flat surfaces: • automated SAW surfacing with solid or flux-cored wires or strips, • automated surfacing with self-protective flux-cored wires or strips. If SAW surfacing is used, the beads can be deposited sequentially, after removing slag from the previous bead. This surfacing technique reduces the productivity of the process. One can also apply the beads at such a distance from each other that there is no need to remove the slag crust separately from each bead. The slag crust is removed from all beads at once. Then the beads are welded in gaps. This results in a fairly deep penetration of the base metal. Broad-layer surfacing provides the best results. The electrode performs transverse oscillations. In each extreme position, the electrode or product is moved by the surfacing step. The electrode is returned to the edge of the surfaced bead until the hardening of the slag crust occurs. Depending on the deposition mode and the viscosity of the flux used, it is possible to deposit a bead up to 400 mm wide without removing the slag crust. The depth of penetration may be less than the deposition of individual beads. In addition, the time spent on removing the slag crust is reduced.

2.9 Electric Arc Surfacing Procedures

55

Automated surfacing with self-protective flux-cored wires or strips is used for wear-resistant surfacing of large flat surfaces. Surfacing with self-protective fluxcored wires is carried out with transverse oscillations. Since in this case there is no slag crust of large thickness, the range of oscillations of the electrode is almost unlimited. When surfacing flat surfaces, in addition to providing a large area with a minimum depth of penetration of the base metal, it is necessary to ensure minimal distortion of the product.

2.9.4 Electric Arc Surfacing of Complex-Shaped Parts For electric arc surfacing of complex-shaped parts the following processes are usually used: • • • •

manual electric arc surfacing with a coated electrode, mechanized surfacing in inert gas with a tungsten electrode (TIG), automated SAW surfacing, mechanized surfacing in shielding gases (MIG-MAG) with flux-cored or solid wire.

Manual electric arc surfacing with a coated electrode in different positions is used for small surfaces of complex shape (Fig. 2.22). The main parameters of the manual arc surfacing mode are: polarity (in the case of direct current) and current, electrode diameter, arc voltage and surfacing speed. In the case of flat surfaces of large parts, coated electrodes of large diameter are used. This allows one to perform the process at high current and, thus, increases the productivity of surfacing. Mechanized surfacing in inert gas with a tungsten electrode (TIG) is used in combination with a solid or flux-cored filler material for a single restoration of complex shape parts that require application of small amount of metal (Fig. 2.23). Automated SAW surfacing is used to restore and harden large parts, and sometimes complex surfaces. When surfacing bodies of complex shape, it is important to prevent non-fusion and jamming of the slag crust. When processing surfaces bounded by a vertical wall (Fig. 2.24), the process should begin so as to avoid a narrow gap between the vertical wall and the deposited bead. Mechanized MIG-MAG surfacing with flux-cored or solid wire is used mainly for coating stainless chromium-nickel steels and high-alloyed tool steels.

56

2 Electric Arc Surfacing

Fig. 2.22 Examples of complex shape parts, for which manual electric arc surfacing with a coated electrode is used: a—mining combine knife, b—gear wheel, c—stem of the thermal power plant shut-off valve (the sequence of rollers is shown by numbers) Fig. 2.23 Cams of camshafts of the car engine surfaced with TIG

2.9 Electric Arc Surfacing Procedures

57

a

1

2

3

14 13 12 11 10 9 8

1

2

3

4

5

7

6

b

1

2

3

12 11 10 9 8

1

2

3

4

7

5

6

Fig. 2.24 Diagram of surfacing of complex-shaped parts: a—beads are in the right way, b—beads are located wrongly (jamming of the slag crust on top of bead number 12)

58

2 Electric Arc Surfacing

References 1. Maxinoctpoenie (2006) nciklopedi . Texnologi cvapki, pa ki i pezki. T.III-4. Pod pedakcie B.E.Patona. – M.: Maxinoctpenie, 768 c 2. Classification of metal transfer on arc electric welding processes. (IIW Doc. XII-535–77). Welding in the World 1977, nr 5/6. 3. P bcev IA, Cenqenkov IK, Typyk B (2015) Haplavka. Matepialy, texnologii, matematiqeckoe modelipovanie. - g.Glivice (Gliwice), Pol xa: Izd-vo Cilezckogo ´ askiej), 590 c politexniqeckogo inctityta (Wydawnictwo Politechniki Sl˛ 4. Fpymin II (1961) Avtomatiqecka lektpodygova naplavka. – Xap kov: Metallypgizdat, 421 c 5. EN 14700:2014 Welding consumables—Welding consumables for hard-facing. https://www. iso.org/standards.html 6. Fomichov S, Skachkov I, Chvertko E, Minakov S, Banin A (2021) Quality Management in Welded Fabrication. In: Part of International welding engineers textbook series under the editorship of Borys Paton, vol 1, Kyiv, Polytechnica, p 222

Chapter 3

Plasma Surfacing

Abstract The physical phenomena of plasma are determined. The scheme and principle of operation of the plasmatron are described. Schemes are provided and features for the main methods of plasma surfacing are analyzed: plasma jet with a currentconducting filler wire; plasma arc with an electrically neutral filler wire; plasma arc with a current-conducting filler wire; plasma arc with two current-conducting filler wires fed into the arc; plasma arc with two current-conducting filler wires fed into the surfacing pool; consumable electrode; plasma-powder surfacing and plasma surfacing with a fixed additive. The physical-technological properties are analyzed and tables of the chemical composition of surfacing powders based on nickel, cobalt, iron and copper are given. The characteristics of solid wires and flux-cored wires are provided—analogs of wires for electric arc welding in shielding gas. Recommendations are given on the procedures of the main methods of plasma surfacing, including the surfacing parameters.

3.1 Physical Phenomena of Plasma Surfacing Process In plasma surfacing, the heat source is the plasma arc. Filler and electrode materials are solid wires, flux cored wires, powders, fixed additive in the form of cast or sintered rings, rods, paste, etc. [1]. Plasma arc is an electric arc in which due to compression (reduction of diameter) there is a higher degree of ionization and a higher temperature, compared to a freeburning arc, at the same current and voltage. Compression of the electric arc column is created in the plasmatron by plasma-forming gas and a water-cooled nozzle. Plasma is a fully or partially ionized gas formed from charged particles (ions and electrons) and neutral atoms (or molecules). A distinctive feature of plasma is its electrical neutrality—in any volume of plasma the sum of the charges of positive and negative particles is the same. Plasma is called the fourth physical state of matter (after solid, liquid, and gaseous). According to the degree of ionization and temperature plasma is classified as: • low-temperature plasma with a temperature of about 10,000–30,000 °C (used in welding and surfacing processes [1]), © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 I. Ryabtsev et al., Surfacing and Additive Technologies in Welded Fabrication, https://doi.org/10.1007/978-3-031-34390-2_3

59

60

3 Plasma Surfacing

• high-temperature plasma with a temperature above 1,000,000 °C. During plasma surfacing, the plasma temperature is 15,000–20,000 °C. During surfacing, a directed flow of plasma moving at high speed is created, using a special device—plasmatron. The plasmatron (Fig. 3.1) consists of a nozzle (1) with a channel for coolant (water) (5), a protective nozzle (3) and an electrode (6). The electrode is usually a non-consumable cathode and is made of tungsten or copper with refractory inserts. Plasma-forming gas (4) is supplied through the nozzle of the plasmatron (1), and protective gas (3) is supplied through the protective nozzle (2). Argon, less often helium or air, is usually used as the plasma-forming ones. The diameter of the nozzle of the plasmatron is chosen depending on the current so that it is smaller than the diameter of the freely expanding electric arc and provides compression of the arc column with increasing ionization and plasma temperature. In addition to the geometric factor, the increase in the degree of ionization and plasma temperature occurs as a result of heating and ionization of the plasma-forming gas. As a result of heating, the volume of plasma-forming gas increases by several orders of magnitude, which leads to a significant increase in the rate of plasma flow from the nozzle. The plasma jet creates a dynamic pressure on the surfacing pool and causes an increase in its depth. The efficiency of heating the product with plasma using argon as a plasma-forming gas and protective gases is in the range of 55–80%. Replacement of argon as a plasma-forming gas with helium leads to a decrease in efficiency to the range of 46–74% due to the higher thermal conductivity of helium [1]. Fig. 3.1 Structure of a plasmatron: 1—nozzle, 2—protective nozzle, 3—protective gas, 4—plasma-making gas, 5—cooling water, 6—electrode, 7—plasma, 8—part to be surfaced, 9—power source

5

4

6

- 9 +

3

2 1

7 8

3.2 Methods of Plasma Surfacing

61

In surfacing and welding, electric arcs (and, accordingly, plasma arc) can be of direct and indirect action. In an electric arc of direct action, one of the electrodes is the product, the other one—the electrode itself. An indirect electric arc burns between two electrodes (non-consumable, consumable, or a combination of both) or between a non-consumable electrode and a currentcarrying nozzle. The arc column (plasma) is blown by plasma-forming gas on the product. Therefore, surfacing by electric arc of indirect action is also called plasma jet surfacing. The product is excluded from the electrical circuit. The surface of the base metal is heated by a jet of plasma and drops of filler metal, which significantly reduces the penetration of the base metal. In plasma jet surfacing, there is no clear relationship between the effective thermal power of the arc spent on heating and melting the parent metal on the one hand, and the amount of filler metal entering the surfacing pool on the other hand. In this regard, the methods of plasma jet surfacing have ample opportunities to control the penetration of the base metal, the shape and size of the surfaced beads, the chemical composition and structure of the deposited metal. For most methods of plasma surfacing, the proportion of the base metal in the deposited, Ƴ0 , Ƴ ≤ 10%. In the first layer, the content of the alloying element in the bead metal is almost no different from its content in the electrode (filler) metal. This is the main advantage of these plasma surfacing methods.

3.2 Methods of Plasma Surfacing According to the type of filler or electrode material used, the methods of plasma surfacing can be divided into: (1) Surfacing with wire [1, 2]: • • • • • •

plasma jet with current-carrying filler wire, plasma arc with electrically neutral filler wire, plasma arc with current-carrying filler wire, plasma arc with two current-carrying filler wires fed into the arc, plasma arc with two current-carrying filler wires fed into the surfacing pool, consumable electrode.

(2) Plasma-powder surfacing. (3) Surfacing on a fixed additive. For wire surfacing, the most effective is the combined inclusion of a plasmatron, in which the system “plasmatron-wire-product” simultaneously burns two arcs—of direct and indirect action. The arc of direct action provides melting of the base metal, the arc of indirect action—melting of the filler wire.

62

3 Plasma Surfacing

3.2.1 Plasma Jet Surfacing with Current-Carrying Filler Wire Plasma jet surfacing with a current-carrying filler wire (Fig. 3.2) is performed on a direct current of direct polarity. The plasma arc burns between the tungsten electrode of the plasmatron—the cathode—and the filler wire. The filler wire is fed from the side at right angles to the axis of the plasmatron. Between the electrode of the plasmatron (cathode) and the current-carrying nozzle of the plasmatron additionally constantly burns a low-current (15–25 A) arc (not shown on the figure), which provides reliable excitation and stable combustion of the working arc due to ionization of the electrode of the plasmatron—filler wire. Due to the magnetic blast, the plasma jet generated by the arc of the electrode of the plasmatron—the filler wire, deviates from the axis of the plasmatron during the wire feed. To compensate for this deviation, the plasmatron is installed at an angle of 50–60° to the surface of the product so that the plasma jet is directed to the surfacing pool at approximately right angle to the surface. In this case, it not only supports the metal of the surfacing pool in the liquid state, but also promotes its spreading on the surface of the base metal. The method provides a small penetration of the base metal. For example, when surfacing copper and its alloys on steel, the share of the base metal in the surfaced in the first layer is only 0.3–1.5%, and when surfacing chromium-nickel austenitic steels on pearlitic steel—5 to 10%. Fig. 3.2 Plasma jet surfacing scheme with current-carrying filler wire: 1—tungsten electrode—cathode, 2—neutral welded part, 3—current-carrying filler wire—anode, 4—power supply

1

- 4 + 3

2

3.2 Methods of Plasma Surfacing

63

The plasma jet generated by the arc of the plasmatron electrode—the filler wire, is an independent source of heat. Advantages of plasma jet surfacing with current-carrying filler wire: • low penetration of the base metal, • the ability to separately regulate the heating and melting of the base metal and filler metal

3.2.2 Plasma Arc Surfacing with Electrically Neutral Filler Wire When surfacing with a plasma arc of direct or reverse polarity with an electrically neutral filler wire (Fig. 3.3), it should be borne in mind that the plasma arc is a more local and more efficient source of heating of the base metal than the plasma jet. When surfacing with a plasma arc, the heating efficiency of the base metal is 50–75%, and when surfacing with a plasma jet—20 to 45%. With the help of a plasma arc, it is possible both to weld massive products, and to carry out precision surfacing of very small parts. In addition, the plasma arc of reverse polarity has the effect of cathodic purification. This allows the surfacing of aluminum alloys and alloys containing titanium and other elements that form difficult to recover refractory oxides.

Fig. 3.3 Diagram of plasma arc surfacing with electrically neutral filler wire: 1—tungsten electrode of the plasmatron (cathode or anode), 2—welded part (anode or cathode), 3—neutral filler wire, 4—power source

1

-(+) 4 +(-) 3

2

64

3 Plasma Surfacing

Advantages of plasma arc surfacing with electrically neutral filler wire:

Disadvantages of plasma arc surfacing with electrically neutral filler wire:

• minimal overheating of the droplets, • reduction of spraying when surfacing with flux-cored wire, • prevention of dissolution of carbide grains during surfacing of composite alloys, • reduction of burnout of easily evaporating alloying elements, • the ability to perform not only mechanized but also manual processes

• the reduction of the melting intensity of the filler wire

3.2.3 Plasma Arc Surfacing with Current-Carrying Filler Wire When surfacing with a plasma arc of direct or reverse polarity with a current-carrying filler wire (Fig. 3.4) two plasma arcs are burning simultaneously and are powered by two autonomous sources: • between the electrode of the plasmatron and the welded part, • between the electrode of the plasmatron and the filler wire.

Fig. 3.4 Diagram of plasma arc surfacing with current-carrying filler wire: 1—tungsten electrode of the plasmatron (cathode or anode), 2—welded part (anode or cathode), 3—filler wire (anode or cathode), 4—power supply of the plasma arc “plasmatron electrode—surfacing part”, 5—power supply of the plasma arc “plasmatron electrode—filler wire”

1

-(+) 5

+(-) -(+) 4

3

+(-) 2

3.2 Methods of Plasma Surfacing

65

Melting of filler material occurs due to: • plasma arc column of the arc burning between plasmatron electrode and product, • heat in the active spot of the plasma arc burning between plasmatron electrode and a filler wire. The intensity of melting depends on the current of both arcs, polarity, diameter of the filler wire. Advantages of plasma arc surfacing with current-carrying filler wire are: • in comparison with surfacing by a plasma arc with a neutral filler wire—higher productivity and smaller penetration of the base metal, • in comparison with surfacing by a plasma jet with a current-carrying filler wire—greater versatility and reliability

3.2.4 Plasma Arc Surfacing with Two Current-Carrying Filler Wires Fed into the Arc The zone of the plasma arc surfacing with two current-carrying filler wires fed into the direct-acting arc towards each other (Fig. 3.5) is protected from air by means of a nozzle of rather large dimensions—about 230 mm × 120 mm (not shown on the figure). The shielding gas is argon or a mixture of argon and hydrogen. Plasmaforming gas is argon or a mixture of argon and helium. The surfacing process can be observed through a special window in the nozzle and through the holes for wire contact tips.

Fig. 3.5 Diagram of plasma arc surfacing with two current-carrying filler wires fed into the arc: 1—tungsten electrode of the plasmatron—cathode, 2—welded part—anode, 3—filler wires—anodes, 4—power source of the plasma arc “plasmatron electrode—surfacing part”, 5—power source of the plasma arc “plasmatron electrode—filler wire”

1

5

+

3

-4 +

3

2

66

3 Plasma Surfacing

Advantages of plasma arc surfacing with two current-carrying filler wires fed into the arc: • compensation of magnetic blast due to the mutual influence of arcs is provided, • surfacing productivity increases to 30 kg/h and more

3.2.5 Plasma Arc Surfacing with Two Current-Carrying Filler Wires Fed to the Surfacing Pool Plasma arc surfacing with two current-carrying (“hot”) filler wires fed into the surfacing pool provides additional heating of the wires due to Joule heat (Fig. 3.6). The surfacing pool is created by a powerful plasma arc of direct action between the electrode of the plasmatron—cathode (1) and the surfacing part—the anode (2). The two current-carrying filler wires (3) are arranged V-shaped at an angle of 30° to each other. The wires are connected in series through the surfacing pool in the circuit of the AC source (5). The AC source has a flat external characteristic (Unl = 40 V, I = 600 A). The wires melt in a surfacing pool without forming an arc between them. The current flowing through the filler wires creates an electromagnetic field that tends to deflect the plasma arc “the electrode of the plasmatron—a surfacing part” (the effect of magnetic blowing). When filler wires are connected in series and Vshaped, their magnetic fields mainly compensate for each other. This eliminates the effect of magnetic blow on the electric arc. The magnitude of the alternating current of the source (5), the feed rate of the filler wires and the distance from the current-carrying nozzles to the surface of the Fig. 3.6 Diagram of plasma arc surfacing with two current-carrying filler wires fed to the surfacing pool (“hot” wires): 1—tungsten electrode of the plasmatron—cathode, 2—welded part—anode, 3—current-carrying filler wires, 4—power source of the plasma arc “plasmatron electrode—surfacing part”, 5—alternating current source for heating wires due to Joule heat

1

5 3 3

4 + 2

3.2 Methods of Plasma Surfacing

67

surfacing pool, i.e., the length of the heated wires are chosen so that the wires are heated almost to melting point. Advantages of plasma arc surfacing with “hot” wires are: • • • •

increased productivity, small heat investment in the base metal, a small proportion of the base metal in the deposited layer, minimum size of heat affected zone

3.2.6 Plasma Surfacing with Consumable Electrode Plasma surfacing with a consumable electrode (Fig. 3.7) differs from electric arc surfacing with a consumable electrode. The electric arc (5) “consumable electrode— product” is additionally surrounded by a plasma flow created by a plasma arc of indirect action (6) “current-carrying nozzle of the plasmatron—product”.

1

8

2

+ -

+ 3

7

5 6 4

Fig. 3.7 Diagram of plasma surfacing with a consumable electrode: 1—consumable electrode— anode, 2—contact tip, 3—current-carrying nozzle of the plasmatron—anode, 4—welded part— cathode, 5—electric arc of direct action “consumable electrode—surfacing part”, 6—plasma arc of indirect action “current-carrying nozzle of the plasmatron—surfacing part”, 7—power source of the electric arc “consumable electrode—surfacing part”, 8—power source of the plasma arc of indirect action “current-carrying nozzle of the plasmatron—surfacing part”

68

3 Plasma Surfacing

Advantages of plasma surfacing with a consumable electrode: • the melting rate of the electrode wire increases, • arc stability increases, • the nature of the electrode metal transfer and the formation of surfaced beads are improved

3.2.7 Plasma-Powder Surfacing Plasma-powder surfacing is the most common method of plasma surfacing. Powder is used as a filler material. When plasma-powder surfacing, in contrast to plasma-powder spraying: • a surfacing pool is created, • complete melting of the particles of filler powder in the plasma arc and in the surfacing pool takes place, • after crystallization of the surfacing pool, a bead is formed, which forms a deposited layer. The supply of filler powder to the surfacing zone is carried out by the transport gas, usually through the longitudinal channels in the wall of the plasmatron nozzle (Fig. 3.8). A direct-acting plasma arc is used. Argon is used as a transporting and plasma-forming gas. The filler powder is fed either to the front part of the plasma arc while surfacing—“angle back”, or to the rear—surfacing “angle forward”. Advantages of plasma-powder surfacing: • use of powders as filler material, which makes it possible to process wear-resistant, heat-resistant and other high-alloyed materials, from which it is difficult or impossible to make an electrode wire, • small penetration of the base metal, which allows to get the required composition of the deposited metal in the first layer, regardless of its thickness, and to abandon multilayer surfacing, • reduction of costs of surfacing materials and duration of surfacing, • excellent formation and high stability of the beads, • reduction of costs for machining of surfaced parts, small allowances for machining, lower consumption of surfacing materials, • the ability to change parameters in a wide range, flexibility and versatility of the process, which allows to surface small parts that need to apply only a few grams of alloy, and large structures on which the mass of deposited metal can be tens of kilograms, • ease of automation of the surfacing process

3.2 Methods of Plasma Surfacing

8

-

1

2

4

69

5

-8 +

3

+

6

7

Vc

a

Vc

b

Fig. 3.8 Diagrams of plasma-powder surfacing with the supply of filler powder through the longitudinal channels in the wall of the nozzle of the plasmatron (a—“back angle”, b—“forward angle”): 1—tungsten electrode of plasmatron—cathode, 2—introduction of plasma-forming gas, 3—introduction of protective gas, 4—introduction of cooling water, 5—introduction of filler powder by the transport gas, 6—longitudinal channel in the wall of the nozzle of the plasmatron, 7—surfaced part—anode, 8—power source of the plasma arc “plasmatron electrode—surfacing part” [1]

3.2.8 Plasma Surfacing on a Fixed Additive Plasma surfacing on a fixed additive is used in rare cases. Rings, plates, powders, pastes, etc. can serve as a fixed additive. The fixed additive is placed on the part in the place of surfacing and melted by a plasma arc. An example is the plasma surfacing of the exhaust valves of internal combustion engines (Fig. 3.9). Valve (1) is mounted vertically on the heat-dissipating copper substrate (4) to prevent burning of the valve edge. Filler ring (2) is placed in the zone of surfacing. Plasmatron (3) is located at an angle of 45° to the axis of the valve. When the filler ring melts, a deposited layer of heat-resistant corrosion-resistant alloy is formed. Centrifugal plasma-powder surfacing is the melting by a direct-action plasma arc of the powder held on the walls of a rotating cylindrical part due to centrifugal forces. The diagram of centrifugal plasma-powder surfacing is presented in Fig. 3.10. Before surfacing in the cavity of the horizontally located part (1), filler powder (4) is applied. The part rotates around the longitudinal axis at high speed. Under the action of centrifugal forces, the filler powder is evenly distributed on the inner surface of the part. Plasmatron (2) is inserted into the part. A direct-acting plasma arc is ignited between the electrode of the plasmatron—the cathode and the part—the anode. Due

70

3 Plasma Surfacing

2

1 3

4

5 Fig. 3.9 Diagram of plasma surfacing on a fixed additive: 1—surfacing part (valve of the internal combustion engine), 2—filler ring, 3—plasmatron, 4—heat-dissipating copper substrate, 5—cooling water

to the high-speed rotation of the part, the surfacing pool (3) takes the shape of a ring. The plasmatron is moved along the axis of rotation of the part. Deposited layer (5) is formed. Centrifugal plasma-powder surfacing is used to form thin layers (from 0.5 to 4 mm) of material with special properties on the inner surfaces of cylindrical parts— bushings, sleeves, etc.

3.3 Materials for Plasma Surfacing Two main types of filler and electrode materials are used for plasma surfacing [1, 3, 4]: (1) Wires—similar to wires for automated and mechanized surfacing in shielding gases: • solid wires (Sect. 2.8.2, Tables 2.3 and 2.4), • flux-cored wires (Sect. 2.8.3 and Table 2.5). (2) Powders of alloys based on nickel, cobalt, iron, and copper.

3.3 Materials for Plasma Surfacing

+

71

1

3

2

6

Vc

5

4

Fig. 3.10 Diagram of centrifugal plasma-powder surfacing: 1—surfacing part, 2—plasmatron, 3—ring surfacing bath, 4—filler powder, 5—deposited layer, 6—device rotating the part

Powders are a universal filler material, as they can be obtained from any surfacing alloys with a wide range of characteristics (chemical composition, strength, hardness, etc.). Powders developed and recommended for gas-powder surfacing and plasma spraying are also successfully used for plasma surfacing. Requirements for surfacing powders [1, 3, 4] are aimed at: • obtaining high-quality deposited metal, which is determined primarily by the chemical composition and physical and technological properties of the powder, • ensuring long-term and stable operation of equipment (powder dispensers and plasmatrons), which is determined primarily by the fluidity and particle size distribution of the powder. Physical and technological properties of surfacing powders: • • • • •

fluidity, bulk mass, pycnometric density, particle size distribution, particle shape, specific surface area and its state.

Powder fluidity is a characteristic of the ability of a powder to pour out through openings at a greater or lesser rate. The fluidity depends on the density, size, and shape of the powder particles. The fluidity of the powder is determined by the time (in seconds) of pouring a standard portion (50 g) of metal powder through a calibrated funnel hole of standardized dimensions (Hall device), according to EN ISO 4490. The fluidity of the powder must be sufficient for uniform and uninterrupted operation of dosing devices and plasmatrons. In plasmatrons, the powder must pass

72

3 Plasma Surfacing

through a system of small cross-section channels before entering the plasma arc. At low fluidity it is possible to clog the transport tube and channels with powder, and at high fluidity—involuntary pouring of powder due to vibration of the equipment. Optimal for surfacing powders fluidity is within 4–10 s. Powders should not clump and agglomerate during storage. The humidity of surfacing powders should be minimal. After long-term storage, the powder must be dried before surfacing. The bulk density of the powder is the mass per unit volume of the loose powder. The bulk mass characterizes the density of the particles of the powder and the degree of porosity of the particles. The greater the bulk mass, the smaller the powder particles and the more correct spherical shape they have. Pycnometric density is the metal density of powder particles. The greater the pycnometric density, the lower the porosity of the powder. The particle size distribution is the range of particle sizes of the powder. The particle size distribution is determined by the size of the sieve cells, through which the powder is poured during sieving. Powders of granulometric composition of 0.06– 0.315 mm are used for plasma surfacing (increase of the maximum particle diameter to 0.4 mm is allowed). The optimal particle size distribution of the powder for plasma surfacing is determined mainly by the design of the plasmatron and, to a lesser extent, depends on the material properties of the powder particles. The presence in the powder of particles smaller than 0.06 mm leads to adhesion to the walls of the plasmatron nozzle in the area of introduction of the powder into the arc. On the other hand, too large particles do not have time to melt in the plasma arc and in the surfacing pool, which leads to imperfections in the weld metal. The shape of the powder particles affects the fluidity and bulk density and is an important physical and technological property to ensure the quality of the weld metal. The spherical shape of the particles is preferred. The chemical composition of surfacing powders is determined by the content of alloying elements and gases and is the main characteristic when choosing a surfacing powder. Powders of nickel and cobalt alloys are most widely used for plasma surfacing. Powders of iron-based alloys as well as copper alloys are used in smaller quantities. Powders of self-fluxing Ni–Cr–Si–B–C alloys are the most common nickel-based materials for plasma surfacing (Table 3.1). They are used for surfacing of: • • • •

disks, wedges, spools and seats of shut-off valves, shafts, protective bushings, sealing rings and support disks of centrifugal pumps, camshafts, valves and seats of internal combustion engines, parts of metallurgical equipment, etc.

Powders of alloys #14 and #15 (Table 3.1) are used mainly for restoration of cast iron parts. Powders of cobalt-based alloys (Table 3.2) are intended for surfacing of details of armature, valves and saddles of internal combustion engines, the tool for hot deformation of metal, knives for cellulose cutting, plugs of pumps, etc. Alloy powder

3.3 Materials for Plasma Surfacing

73

Table 3.1 Chemical composition of powders from Nickel-based alloys and hardness of surfaced metal [1] #

Powder brand

Mass fraction of elements, % C

Cr

Si

HRC Fe

Ni

B

Others

1

PG-CP2

0.2–0.5

12–15 2.0–3.0

≤ 5.0 Base 1.5–2.1 –

35–45

2

PG-CP3

0.4–0.7

13–16 2.5–3.5

≤ 5.0

2.0–2.8 –

45–50

3

PG-CP4

0.6–1.0

15–18 3.0–4.5

≤ 5.0

2.8–3.8 –

55–60

4

PG-10H-01

0.6–1.0

14–20 4.0–4.5 3–7

2.8–4.2 0.8–1.2 56–63 Al

5

PG-12H-01

0.3–0.6

8–14

1.7–2.8 0.8 Al

36–46

6

PG-12H-02

0.4–0.8

10–16 3–5

3–6

2–4

46–55

7

PG-HQ3

≤ 0.2

–

0.5–0.9

≤ 0.3

0.6–1.0 38–42 Cu

–

8

PP-HX13CP

0.2–0.4

12–14 2.0–2.8

≤ 5.0

1.2–1.8 –

25–35

9

PP-HX15CP2

1.2–3.2 2–5

–

0.35–0.6 14–16 2.8–3.5

≤ 5.0

1.8–2.3 –

37–47

10 PP-HX16CP3

0.6–0.9

15–17 2.7–3.7

≤ 5.0

2.3–3.0 –

47–57

11 PP-HX17CP4

0.8–1.2

16–18 3.8–4.5

≤ 5.0

3.1–4.0 –

≥ 55

12 PP-HX18C5P4

0.9–1.5

16–19 4–5

≤ 5.0

3.8–4.7

13 PP-HX25C5P

0.4–0.6

24–26 4.6–5.2 8–12

0.7–1.1 –

45–48

14 PP-HD42CP

0.1–0.3

–

0.6–1.2

≤ 3.0

0.7–1.3 40–45 Cu

HB170

6–10

1.5–3.0

≤ 5.0

2.3–3.5 3–9 Cu –

15 PP-HX8D6CPP 0.5–1.2

≤ 1.0 Mn

≥ 60

PP-KX30H6BCP (PH-AH34) (Table 3.2, alloy #17) contains boron and a large amount of nickel, due to which it has a reduced tendency to crack. Table 3.3 shows the chemical composition of surfacing powders of iron-based alloys. Powders PG-C1 (Table 3.3, alloy #1) and PG-AH1 (Table 3.3, alloy #4) are high-carbon and high-chromium alloys with carbide or carbide-boride hardening. These alloys are stable under conditions of intense abrasive wear but are prone to cracking during surfacing. They are intended for surfacing of working bodies of tillage machines and earthmoving equipment, disks, and saddles of armature for pulp pipelines, parts of the metallurgical equipment, etc. The metal deposited with PH-AH2 powder (Table 3.3, alloy # 5) is not inferior in wear resistance to the metal deposited with PG-C1 powder, but it is more ductile and not prone to cracking. This is due to the austenitic-martensitic structure with a carbide eutectic located along the grain boundaries and with small, evenly distributed primary carbides. Its corrosion resistance is higher than that of chromium steels 20X13 (X20Cr13) type. PH-AH2 powder is used for surfacing screws of extruders and thermoplastics, fittings for bulk materials transportation systems, working bodies of tillage machines, etc.

PG-10K-01

PG-10K-02

PG-10K-03

PG-10K-04

19

21

22

PP-KX30H2BC (PH-AH35)

18

20

PP-K60X30BC (B3K)

PP-KX30H6BCP (PH-AH34)

16

17

Powder brand

#

21–25

2.6–3.0

0.8–1.2 27–30

28–32

28–32

1.3–1.7

1.0–1.3

28–32

28–32

28–32

Cr

1.3–1.7

0.7–1.0

0.9–1.3

C

0.4–1.0

0.8–1.2

2.0–2.7

0.8–1.3

1.5–2.5

1.5–2.5

2.0–2.7

Si

Mass fraction of elements, %

–

0.5–0.9

≤ 3.0 –

28–32 0.5–2.0

≤ 2.0

1–3

≤ 3.0 ≤ 2.0

0.5–2.0 4–8

≤ 2.0 ≤ 3.0

Ni

Fe Base

Co

–

0.07–0.1

≤ 0.5

1.2–1.8

–

0.5–0.9

–

B

Table 3.2 Chemical composition of powders from Nickel-based alloys and hardness of surfaced metal [1]

12–14W; 0.5–0.9 Mn

7–9 W; 0.2–0.5 Mn

4–5 W

3.5–4.5 W

4–5 W

4–5 W

4–5 W

Others

55–60

45–52

≥ 40

45–50

43–48

44–48

38–42

HRC

74 3 Plasma Surfacing

3.3 Materials for Plasma Surfacing

75

Table 3.3 Chemical composition of powders from iron-based alloys and hardness of surfaced metal [1] #

Powder brand

Mass fraction of elements, % C

Cr

Si

HRC Mn

Ni

Fe

Others

1

PG-C1

2.5–3.3

27–31

2.8–4.2 4.0–4.5 3.0–5.0 Base

2

PG-UC25

4.4–5.4

35–41

1.6–2.6

3

PG-C27

3.3–4.5

25–28

1.0–2.0 0.8–1.5 –

0.2–0.4 W; 53–55 0.08–0.15 Mo

4

PG-AH1

2.0–2.8

26–32

1.5–2.5 0.5–1.5 –

1.2–1.8 B

54–58

5

PP-X18FHM

2.1–2.4

17–19

0.5–0.8 0.6–1.0 2.0–3.0

7–8 V; 2.0–2.6 Mo

44–50

6

PP-X18H9

≤ 0.12

16–20

≤ 0.8

≤ 1.0

8–11

≤ 0.02 S, P

–

7

PP-X20H80

≤ 0.1

19–22

0.5

≤ 0.1

Base

≤ 1,0

≤ 0.04 S

–

8

PP-10P6M5

0.96–1.05 3.8–4.4

≤ 0.5

≤ 0.5

–

Base

6.0–7.0 W; 58–60 1.7–2.1 V 5.0–5.5 Mo

9

PP-170X5 B3MF5C

1.6–1.8

5.2–5.4 2.0–2.4 0.2–0.4 –

4.9–5.1 V; 2.8–3.1 W 0.3–0.6 Mo

10 PP-220X6 BMF8C

0.9–2.1

5.2–5.9 1.0–1.4 0.6–0.8 –

0.8–1.1 W; 54–58 7.5–7.8 V 0.2–0.5 Mo

4–6

1.8–2.5W; 42–48 0.35–0.6 V 0.9–1.3 Mo

11 PP-25X5FMC 0.2–0.3

≤ 2.5

1.0–1.8

0.9–1.1 0.6–0.9 –

–

51–54

–

55–57

55–60

Powders #6 and #7 (Table 3.3) are designed for corrosion-resistant coatings and can also be used as a sublayer. Powders #8–11 (Table 3.3) are intended for surfacing of cutting tools blanks, dies, and technological equipment. Tool blanks are annealed before machining, and then hardened and released. The hardness of the weld metal increases from HRC 56–59 to HRC 62–64. The powder PP-10P6M5 (Table 3.3, alloy #8) provides a high-speed steel type deposited layer and is used for surfacing cutters, reamers, large taps, disc knives for cutting sheet metal, knives for cutting wood, paper, etc. PP220X6BMF8C powder (Table 3.3, alloy #10) is used to surface stamping tools for hot and cold deformation, and PP-25X5FMC powder (Table 3.3, alloy #11) is used for hot rolling, dies, and knives for cutting hot metal.

76

3 Plasma Surfacing

Powders of copper-based alloys (Table 3.4) are used for surfacing parts of friction pairs and parts of ship fittings made of non-ferrous alloys. Powder surfacing of copper alloys is performed on the reverse polarity. This is especially important in the presence of aluminum in the powder. Gases can be contained in the surfacing powders in dissolved form, in the form of internal pores and in the form of oxides on the surface of the particles. The total gas content of the powder should be as small as possible. The high content of gases can cause splashing of metal during surfacing and the appearance of pores and nonmetallic inclusions in the deposited layer. The high oxygen content also leads to the formation of slag on the surface of the beads, which complicates multilayer surfacing. Production of surfacing powders is carried out: • By the method of spraying and granulation of droplets in a stream of gas or water—for alloys with a melting point not exceeding 1650 °C. The jet of liquid metal is broken into small drops by a high-speed flow of inert gas or water. The droplets are cooled and crystallized in an inert gas or water. The method provides good flowability of powders and low oxygen content (0.02–0.10%). • Centrifugal spraying of melts—for refractory alloys. The refractory alloy rod rotates around the longitudinal axis at a high speed in a vertical position. The upper end of the rod is heated by an arc or plasma. The molten metal under the action of centrifugal force forms small droplets and is sprayed. Hardened droplets of liquid metal are collected in a chamber filled with inert gas. This method allows us to obtain spherical particles of 0.03–0.5 mm dia. The cost of production of powders by this method is significantly higher than when spraying with gas. However, in the case of sputtering of refractory materials (tungsten carbide) or high-alloy alloys, this method can provide significant advantages. Table 3.4 Chemical composition of powders from copper-based alloys [1] Powder brand

Mass fraction of elements, % Si

Mn

Fe

Ni

Al

Sn

Others

PP-BpA HMn 8,5-4-5-1,5

≤ 0.2

1.0–1.8

3.7–4.3

4.3–5.3

8.2–9.0

–

≤ 0.01 B; ≤ 0.01 V

PP-OCC 5-5-5

≤ 0.05

–

≤ 0.4

≤ 1.0

≤ 0.06

4.0–6.0

4.0–6.0 Zn; 4.0–6.0 Pb

PP-AMn9-2

≤ 0.2

1.5–2.5

≤ 0.5

–

8–10

≤ 0.1

≤ 1.0 Zn; ≤ 0.1 Pb

PP-KMn3-1

2.5–3.5

0.8–1.8

≤ 0.5

–

–

≤ 0.03

≤ 0.5 Zn; ≤ 0.03 Pb

PP-OH 8,5-3

0.5–1.5

–

≤ 0.5

2.5–3.5

≤ 0.05

7.5–9.5

≤ 0.3 Zn; ≤ 0.3 Pb

PP-MH 40

≤ 0.05

–

≤ 0.2

35–40

≤ 0.05

–

≤ 0.1 Pb; ≤ 0.5 Zn

3.4 Procedures of Plasma Surfacing

77

3.4 Procedures of Plasma Surfacing Mechanized plasma surfacing is used most often. Automated surfacing is used for rotating parts and flat parts of large areas. In rare cases, plasma surfacing is performed manually using rods or powders as an additive. Plasma surfacing is performed on a direct current of direct polarity (rarely— reverse polarity). Alternating current is used only in the method of surfacing with heating of two filler wires. The plasma arc is fed by direct current of direct polarity, which provides greater stability of the process. The parameters of the surfacing affect the change in the chemical composition of the surfaced metal because: • they determine the proportion of the base metal in the deposited layer, • they affect the completeness of redox reactions between the molten metal and the environment. In the case where the proportion of the base metal in the deposited metal was small, redox reactions have a decisive influence on the chemical composition of the deposited metal. Plasma jet surfacing with a current-carrying filler wire (Sect. 3.2.1) is essentially a filling of the product surface with liquid filler metal. Therefore, the quality of surfacing is significantly affected by the preparation of the surface of the product and filler wire for surfacing. Before surfacing, the wire is subjected to chemical cleaning, and the surface of the product is machined to Rz 80 µm–Rz 40 µm and degreased. This preparation ensures reliable wetting of the solid metal with liquid and spreading of the metal of the surfacing pool on the surface of the product. In terms of productivity (4–10 kg of deposited metal per hour), plasma jet surfacing with a conductive wire is comparable to submerged arc surfacing with an electrode wire. The surfacing coefficient is 25–30 g/A·h. The recommended parameters of plasma jet surfacing with a current-carrying wire are given in Table 3.5. For all modes, the optimal distance from the tip of the plasmatron to the filler wire is 5–8 mm, the distance from the filler wire to the product—8 to 17 mm. The deposition rate is chosen equal to the rate of spreading of the deposited metal. Depending on the size of the product, the width of the beads, mode parameters and thermophysical properties of the base and filler metals, the surfacing speed is 3–12 m/h. Surfacing is recommended to be carried out with transverse oscillations of the plasmatron and filler wire. The amplitude of oscillations does not exceed 50–60 mm. The oscillation frequency is 20–50 min−1 [1]. Plasma jet surfacing with current-carrying filler wire is used in shipbuilding for production of antifriction and corrosion-resistant coatings. Surfacing of shafts, rods, pistons of armature and other parts is carried out with copper alloys with use of solid or flux-cored wires Bp KMc 3-1, Bp AMc 9-2, Bp A HMc 8,5-4-5-1,5, MH KT 5-1-0,2-0,2, Bp OH8-3, etc. [1]. When surfacing copper and its alloys on steel, the minimum iron content in the weld metal is less than 1%. The risk of imperfections is associated with the penetration

78

3 Plasma Surfacing

Table 3.5 Recommended parameters of plasma jet surfacing with current-carrying wire [1] Dimensions of parts, mm

Surfacing parameters

Thickness, mm

Current, A

Diameter mm

Gas consumption, l/min Plasma-forming

Protective

The amplitude of oscillations, mm

Frequency of oscillations 1/min

5–8

140–170

2.5–2.6

16–18

10–40

30–50

10–20

160–180

2.6–2.7

16–18

10–40

30–50

22–40

190–210

2.6–3.0

18–20

10–40

30–40

30–40

140–150

2.5–2.6

16–18

10–30

40–50

50–70

160–190

2.5–2.6

18–20

10–30

35–50

80–100

190–210

2.6–2.7

18–20

10–40

30–50

of copper into steel. Liquid copper can penetrate solid steel at the grain boundaries. The boundaries of steel grains filled with copper become stress concentrators. In the process of cooling in the deposited layer, residual tensile stresses are formed, and cracks may form at the sites of penetration. The width and depth of penetration of copper into steel increases with increasing heating temperature of the steel surface and the duration of contact of solid and liquid phases. To prevent penetration of copper into steel, it is recommended to [1]: • ensure minimal heating of the base metal and limit the contact time of the liquid and solid phases, • use copper alloys with a minimum diffusion rate in steel, • weld a sublayer of metal that prevents the diffusion of copper into iron, such as nickel, • apply methods to reduce residual tensile stresses in the deposited layer, such as preheating. Plasma arc surfacing with electrically neutral filler wire (Sect. 3.2.2) in comparison with plasma jet surfacing with conductive filler wire provides: • much less penetration of the base metal at the reverse polarity (plus a power supply is connected to the electrode), • However, higher penetration of the parent metal (about 15%) at direct polarity. On the reverse polarity, the heat flux in the product is more evenly distributed, the arc pressure is less, and favorable conditions are created for wetting the surface of the base metal with the metal of the surfacing pool. Direct polarity is used less often—in cases where high penetration of the base metal is not crucial: when restoring the size of worn parts, when locally repairing previously welded by the plasma method parts, etc. Plasma arcs with electrically neutral filler wire is used to surface valves and valve seats of internal combustion engines, parts of pipeline fittings for water, steam and

3.4 Procedures of Plasma Surfacing

79

gas, knives for cutting metal, rolling rolls, dies, screws, locks, and couplings of drill pipes [1]. For the repair of small precision cutting dies, which are widely used in the instrument making and electrical industries, use manual micro-plasma surfacing with filler flux-cored wire type PP-AH148 1.6–2.0 mm dia. Surfacing is carried out on a direct current of reverse polarity 25–30 A at an arc voltage up to 40 V. Low thermal effect of micro-plasma arc on the base metal ensures the hardness of the restored dies, no need for further high-temperature heat treatment, minimal machining costs after surfacing [1]. Plasma arc surfacing with two current-carrying filler wires fed into the arc (Sect. 3.2.4) provides high productivity—up to 30 kg/h. The disadvantage is the increase in the penetration of the base metal and, therefore, the increase in the proportion of base metal in the deposited layer as a result of deposition by direct plasma arc at low feed rates. Surfacing is carried out with transverse oscillations of the plasmatron (oscillation amplitude up to 70 mm). The thickness of the deposited layer can be adjusted within 3–8 mm. Plasma arc surfacing with two current-carrying filler wires fed into the arc is used in nuclear and chemical engineering [1]. For example, tube boards of heat exchangers with a diameter of 1000–2000 mm, 120–380 mm thick are surfaced with wires 1.6 mm diameter from chromium-nickel steels of the X21H11 type or from nickel alloys with productivity of 16 kg/h. Plasma surfacing with a consumable electrode (Sect. 3.2.6) is carried out with transverse oscillations of the plasmatron in modes that provide jet transfer of metal. In this case, the penetration of the base metal is minimal. The surfacing metal is evenly distributed on the surface of the product, wide (up to 40 mm) flat beads are obtained. Argon is usually used as a plasma-forming gas. As a shielding gas, depending on the composition of the electrode wire and the base metal, argon and its mixtures with oxygen, carbon dioxide, helium, nitrogen, or hydrogen, as well as carbon dioxide are used. Surfacing productivity increases with increasing current. At a current of 500 A and an electrode stick-out of 65 mm, the productivity is 34 kg/h, the melting coefficient is 56 g/A·h. For arc surfacing, the melting coefficient does not exceed 28 g/A·h. Plasma-powder surfacing (Sect. 3.2.7) is characterized by the following parameters: • • • • • • •

arc current I, voltage U, surfacing speed vn , amplitude of oscillations of the plasmatron a, oscillation frequency of the plasmatron f, particle size distribution of powder d, mass feed rate of powder Gn ,

80

3 Plasma Surfacing

• type of plasma-forming, transporting and protective gases and their costs q, the distance from the plasmatron to the product h, • diameter of the inner di and outer de nozzles of the plasmatron, • heating temperature of the welded part, Th . The microstructure during plasma-powder surfacing is characterized by a small width of the transition zone from the base metal to the bead and typical for the weld metal directed columnar structure. However, by changing the effective thermal power of the plasma arc and the particle size distribution of the powder one can suppress the directional growth of columnar crystallites. Plasma-powder surfacing is used in the mass production of a wide range of products [1]: • sealing surfaces of fittings for thermal and nuclear power plants, petrochemical enterprises, and ship installations, • extruder screws for plastics processing, • ship equipment parts, • locks and couplings of drill pipes, • parts of metallurgical equipment, • punches, • metal cutting tools, • valves of internal combustion engines, • bushings of circulating pumps of nuclear reactors, etc. Centrifugal plasma-powder surfacing (Sect. 3.2.8) is performed in argon or other shielding gas. Powders of alloys Ni–Cr–Si–B, Co–Cr–W–C, Fe–Cr–C–B and others with a particle size distribution of 100–250 microns are used as additives. A prerequisite is the high quality of surface treatment before surfacing. The method allows minimal allowances for machining after surfacing. Surfacing productivity reaches 12 kg/h. Examples of parameters of centrifugal plasma-powder surfacing of cylindrical parts are given in Table 3.6. The thickness of the deposited layer of all parts is 1.5 mm. Table 3.6 Examples of centrifugal plasma-powder surfacing parameters of cylindrical parts [1] The inner diameter of the workpiece, mm

Surfacing parameters Current A Rotation speed, rev/min

Plasmatron movement speed, mm/rev

Number of plasmatrons

66

300

1250

0.033

1

93

450

1000

0.042

1

163

450

630

0.079

2

References

81

References 1. Gladki P.B., Pepepletqikov E.F., P bcev I.A. Plazmenna naplavka. – Kiev: kotexnologi , 2007. – 292 c 2. P bcev I.A., Cenqenkov I.K., Typyk .B. Haplavka. Matepialy, texnologii, matematiqeckoe modelipovanie. - g.Glivice (Gliwice), Pol xa: Izd-vo Cilezckogo ´ askiej), 2015. – 590 c politexniqeckogo inctityta (Wydawnictwo Politechniki Sl˛ 3. EN 14700:2014 Welding consumables—welding consumables for hard-facing. https://www.iso. org/standards.html 4. Quality management in welded fabrication. Part of international welding engineers textbook series under the editorship of Borys Paton/ S. Fomichov, I. Skachkov, E. Chvertko, S. Minakov, A. Banin.- vol. 1, Kyiv, Polytechnica, 2021/ - 222 P

Chapter 4

Electroslag Surfacing

Abstract The physical phenomena are defined and a general diagram of the electroslag process is provided. The heat balance of the process and stability factors of the electroslag process are analyzed. The classification of methods of electroslag surfacing is presented. Schemes are provided and features of electroslag surfacing with electrode wires are analyzed; electroslag surfacing with electrodes of large cross-section; electroslag surfacing with discrete filler metal; electroslag surfacing with liquid filler metal; electroslag surfacing with strips with free formation. Recommendations on the choice of surfacing parameters are provided. The peculiarities of alloying of the deposited metal through the electrode (filler) metal are considered. The requirements for physical–chemical properties are analyzed and tables of the chemical composition of fluxes for electroslag surfacing of iron-based and copperbased alloys are provided. Varieties and requirements for the chemical composition of electrode wires and strips, electrodes of large cross-section, discrete filler materials, liquid filler metals are given.

4.1 Physical Phenomena of Electroslag Surfacing In electroslag surfacing (ESS), the source of energy for heating and melting the electrode (filler) metal and the base metal is a slag pool. The slag pool is a molten flux. The molten flux becomes electrically conductive due to the thermal dissociation of chemical compounds that are part of the flux, and the formation of single- and double-charged ions [1]. In the slag pool, Joule heat is released as a result of the passage of electric current through the electrical circuit: the electrode—slag pool—a part to be surfaced. The slag pool has the greatest resistance and, consequently, the greatest voltage drop in the circuit. The heat of the slag pool is spent on melting of the electrode tip. ESS includes two stages: dilution of the slag pool with “solid” or “liquid” start (Sect. 4.2.1) and support of the electroslag process. In the electroslag process (Fig. 4.1), the current passing between the electrode (1) and the surfaced part (2) heats the slag pool (3). The slag pool, in turn, melts the electrode immersed in it and melts the surface of the surfaced part. The molten metal © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 I. Ryabtsev et al., Surfacing and Additive Technologies in Welded Fabrication, https://doi.org/10.1007/978-3-031-34390-2_4

83

84

4 Electroslag Surfacing

in the form of drops flows from the electrode tip and falls to the bottom of the slag pool, because it has a much higher density compared to molten slag. As a result, a metal pool (4) is formed at the bottom of the slag pool. The slag pool is in the upper part and protects the metal pool from atmospheric air. The metal pool crystallizes in the deposited layer (5). The large volume of slag and metal pools in most ESS methods necessitates the use of devices for forced formation of the deposited layer— sliders or molds (7), which can be of any size and shape. Between the wall of the slider-crystallizer and the deposited layer often a crust of solidified slag (6) (garnish) is formed. The electrical conductivity of the slag pool depends on the composition of the slag and the temperature of the slag melt. The amount of heat released in the slag pool varies depending on its temperature. The amount of heat given off by the slag pool depends on the geometric dimensions and shape of the melting space, the surface area and depth of the slag pool, heat transfer coefficients, the design of the molds and other factors [1]. Figure 4.2 shows the heat balance of the ESS process with a solid electrode. Most of the heat goes to the mold. The effective efficiency of metal heating at ESS is ηes = 0.75–0.95. Fig. 4.1 ESS process diagram: 1—electrode, 2—surfaced part, 3—slag pool, 4—metal pool, 5—surfaced layer, 6—crust of solidified slag (garnish), 7—slider or crystallizer, 8—water cooling, 9—contact tip

9 2

1

7

8

3 4 5 6

85

ELECTRODE

SURFACED PART

Fig. 4.2 Heat balance of solid electrode ESS process [1]

CRYSTALLIZER

4.1 Physical Phenomena of Electroslag Surfacing

3% Incoming heat 100%

19% 41%

29% 8% METAL POOL SURFACED LAYER

The stability of the electroslag process and the quality of the deposited layer are ensured by: (a) Stabilization of the slag pool temperature. The amount of heat released in the slag pool should be equal to the amount of heat given off by the slag pool. Violation of the balance of supply and heat consumption can lead either to supercooling of the slag pool and the termination of the electroslag process, or to overheating of the slag pool and its boiling. Boiling of the slag pool dramatically reduces the amount of heat that goes to the melting of the electrode and base metals. (b) Excluding the formation of an arc discharge. The arc occurs at the bottom of the slag pool, or between the electrode and the slag surface. In the first case, the process is accompanied by splashes of slag, in the second—the temperature of the slag pool decreases sharply. (c) Sufficient depth of the slag pool. At a small depth of the slag pool transition of the process into an arc becomes possible, at a great depth—energy consumption to support the electroslag process increases.

86

4 Electroslag Surfacing

4.2 Methods of Electroslag Surfacing 4.2.1 Classification of Methods of Electroslag Surfacing According to technical and technological characteristics, there are the following ESS processes: with forced or free formation, with DC or AC power supply, with movable or stationary electrodes, with horizontal, inclined, or vertical arrangement of the surfacing surface, single- or multi-electrode, with connection of electrodes on single-phase, bifilar, or three-phase schemes, with liquid or solid start (Fig. 4.3b) [1]. For the forced formation of the deposited layer, mobile or stationary forming devices are used—sliders or crystallizers. The sliders have a simple geometric shape, usually in the form of rectangular plates cooled by water. The crystallizers have a developed shape, usually of closed cross-section. The crystallizers can be electrically neutral or current-supplied. When using current-supplied crystallizers, measures are required to protect them from electroerosion. ESS methods with forced formation of the deposited layer are the most common because they have the following advantages: • high productivity (tens and hundreds of kilograms of weld metal per hour), • high stability of the process on direct and alternating current, ELECTROSLAG SURFACING Technical and technological features

Forming of deposited metal

Forced

Type of current

Alternating

Free

Nonconsumable

Direct Mobile

Electrodes’ movement

Tungsten Surfacing materials

Combined

ELECTRODE

Immobile

Wire Consumable

Combined Position of surface

Large crosssection

Vertical

Shavings

Many

Multiple phase

Bifiliar ESS process start method

Discreet

One

Single-phase Electrodes’ connection

Strip

Horizontal

Inclined Number of electrodes

Copper Graphite

Wet start Solid start

Fig. 4.3 Classification of ESS processes

Fractions Granules

FILLER

Wire Solid

Strip Large crosssection Liquid metal

4.2 Methods of Electroslag Surfacing

87

• wide range of current density (0.2–300 A/mm2 ), • the possibility of using electrodes of a wide range of cross-sections, including electrode wires with a diameter of 2.0 mm and more, electrodes of large crosssection (up to 35,000 mm2 ), • the possibility of using a wide range of filler materials—wires, strips, tubes, rods, fractions, shavings, as well as liquid filler metal, • the ability to process steels and alloys with a high cracking susceptibility, • lower in comparison to arc surfacing, relative consumption of electricity and flux (per unit mass of surfaced metal), • the ability to control and regulate the surfacing process, • a wide range of thicknesses of the deposited layer, • the possibility of surfacing layers of large thickness in one pass, • the ability to form the specified geometric dimensions of the deposited layer in the surfacing process, which reduces the allowances for machining, or allows to completely abandon it. The disadvantages of ESS with forced formation of the deposited layer include: • • • • • •

overheating of the weld metal and the heat-affected zone, coarse-grained structure of the deposited layer, complexity and large dimensions of equipment, high energy consumption of the surfacing process, high consumption of cooling water, limited possibility of alloying (for most ESS methods alloying is possible only through electrode or filler materials, not through flux), • difficult start of the surfacing process, • impossibility of surfacing layers less than 10 mm thick. When using fixed electrodes, their melting occurs due to the constant rise of slag and metal pools. If the electrodes are movable, they are continuously fed into the slag pool as it melts. A combination of these methods is also possible. The electrodes can be connected in single-phase, bifilar or three-phase circuits. In some cases, more complex electrical wiring diagrams are used. Electroslag processes can be started with “solid” or “liquid” starts. In case of “solid” start the electrode is closed on a product through special mixes of fluxes which are electrically conductive in a solid state, or through flux-metal mixes. When using a “solid” start, it is necessary to use special technological pockets, in which the flux melts, the formation of a slag pool and the stabilization of the electroslag process. In case of “liquid” start, the process begins with melting the slag in a separate container and pouring it between the part and the mold (slider). The method allows immediately after pouring the slag to conduct a stable electroslag process and obtain a high-quality connection of the base and weld metals without the use of technological pockets. ESS can be classified by type of surfacing materials—electrode or filler (Fig. 4.3).

88

4 Electroslag Surfacing

Voltage is supplied to the electrode materials from the power source. Consumable electrodes are fed into the slag pool and melt in it. Consumable electrodes are made in the form of solid or flux-cored wires, solid or flux-cored strips, plates, rods, tubes. Non-consumable electrodes do not melt and serve to support the electroslag process. Non-consumable electrodes are made of copper, graphite, tungsten, or use various combined designs. Voltage is not applied to the filler materials, and they serve only to form a deposited layer. Solid filler materials have the same shape as electrode materials. Discrete filler materials include chips formed during machining, fractions for different purposes, as well as granules of different shapes and sizes. In addition, liquid metals are used as filler materials.

4.2.2 Electroslag Surfacing with Electrode Wires ESS electrode wires can be used for surfacing of: • flat surfaces—vertical or horizontal, • cylindrical surfaces—external or internal. ESS with electrode wires of a flat surface in the vertical position (Fig. 4.4) is performed in the gap formed by the surface of the part (5) and the movable slider (1) of the three folded plates. In the process of surfacing, the slider is pressed by a special device to the workpiece and moves up as the gap is filled. Electrode wires (2) during surfacing can make reciprocating movements along the gap. The speed of transverse oscillations of the electrode wires should be such that the slag does not have time to solidify until the return of the electrode wires to their original position. The process begins on a substrate or in a special mold. Modes of surfacing (number of electrodes, current, voltage, speed of longitudinal movement of the slider, speed of transverse movement of electrodes, etc.) are set depending on the size of the deposited layer (4). The surfacing process ends at the output plate or mold surfacing. In case of ESS with electrode wires of a flat surface in horizontal position for formation of the deposited layer and the maintenance of a slag pool copper sliders without cooling or water-cooled copper crystallizers are used (Fig. 4.5). Surfacing is performed by one or more electrodes with transverse oscillations of the electrodes or without oscillations. To ensure a sustainable electroslag process, without the transition to the arc, the depth of the slag pool should be at least 30 mm. The use of several electrode wires provides rapid stabilization of the electroslag process and high quality of the deposited layer and the fusion zone. The advantages of the method include the small depth of penetration of the parent metal. ESS with electrode wires of the external cylindrical surface of relatively short length (up to 300 mm) with the vertical location of the axis is performed in stationary crystallizers. The process begins on graphite or steel substrates. After dilution of the slag pool synchronous rotation of the weld part and the crystallizer is performed.

4.2 Methods of Electroslag Surfacing

89

Fig. 4.4 Diagram of ESS of flat surface in vertical position: 1—slider, 2—electrode wires, 3—slag pool, 4—surfaced layer, 5—part

5 2 3 1

Vc

4

Contact tips through which the wire is fed in the process of surfacing, move only upwards. The number of electrodes and surfacing modes are chosen depending on the diameter of the workpiece and the size of the gap [1]. In the case of ESS of external cylindrical surfaces of big length (more than 300 mm) (Fig. 4.6) the crystallizer (1) is moving upwards. The surfaced part (5) is stationary. Contact tips (2) perform oscillating movements around the surfaced part. The diagram of ESS with electrode wires of the internal cylindrical surface is shown in Fig. 4.7. In the process of surfacing, the rod-crystallizer (1) and the surfacing part (6) rotate synchronously around the vertical axis. Contact tips feeding the electrode wire (2) rise up as the layer (5) forms [1].

90

4 Electroslag Surfacing

Fig. 4.5 Diagram of ESS of flat surface in horizontal position: 1—electrode, 2—part, 3—slag pool, 4—metal pool, 5—surfaced layer, 6—crystallizer

4

6

3

1

5 2

Fig. 4.6 Diagram of ESS with electrode wires of the external cylindrical surface of big length: 1—slider-crystallizer, 2—contact tips for wire feeding, 3—slag and metal pools, 4—surfaced layer, 5—surfaced part, 6—starting backing

5

2

2

Vc

1 4

3

6

4.2 Methods of Electroslag Surfacing

2

91

1

2

7

3 6

4 5

5

Fig. 4.7 Diagram of ESS of internal cylindrical surface: 1—rod—crystallizer, 2—electrode wire, 3—slag pool, 4—metal pool, 5—surfaced layer, 6—surfaced part, 7—run-off tab

4.2.3 Electroslag Surfacing with Electrodes of Large Cross-Section ESS with electrodes of large cross-section in the form of tubes (round, square, rectangular), rods, etc. provides the possibility of surfacing with high productivity of a layer of considerable thickness. ESS with electrode-tube (Fig. 4.8) [1] provides a relatively uniform temperature field in the annular gap between the surface of the surfaced cylindrical part and, accordingly, the same melting conditions of the electrode around its perimeter and the formation of the fusion zone. In the case of ESS with tube electrodes no defects in the form of cracks, gas pores and non-metallic inclusions are observed in the deposited layer. The absence of cracks during the surfacing of non-plastic metals (e.g., cast iron) is associated with significant heating of the outer layers of the surfaced part during the surfacing stage. At the cooling stage, the outer heated layers of the part undergo thermal compression. As a result, compression stresses occur in the adjacent deposited layer. Compression stresses partially compensate (reduce) tensile stresses that occur in the deposited layer because of shrinkage. NOTE. An example of electroslag surfacing with electrodes of large cross section of steel (steel 45) and cast-iron rolling rolls for hot rolling. Tube electrodes 370 mm diameter, wall thickness 15–20 mm of alloyed cast iron. Preheating with an inductor up to 200–250 °C. Surfacing parameters: current—5000

92

4 Electroslag Surfacing

Fig. 4.8 Diagram of ESS with tube electrode: 1—crystallizer, 2—tube electrode, 3—contact tip, 4—starting ring, 5—surfaced part, 6—surfaced layer, 7—metal pool, 8—slag pool

3

5

2 1

8 7 6 4

A, voltage—40–43 V, surfacing speed—4.3–5.7 mm/min, thickness of the deposited layer—35–40 mm, surfacing productivity—120 kg/h. ESS electrodes of large cross section are used for manufacturing of: • • • •

blanks for rolling sheet bimetals, teeth of excavator buckets, cones for drilling, parts of agricultural machinery.

4.2.4 Electroslag Surfacing with Discrete Filler Metal The use of discrete filler metal in ESS provides: • increase in the amount of deposited metal and productivity of ESS, • expanding the possibilities of alloying the deposited layer, • exclusion of costs for the manufacture of electrodes.

4.2 Methods of Electroslag Surfacing

93

Discrete filler metal can be used in any ESS method, only the appropriate equipment is required for its supply. Tungsten or graphite are most often used as nonconsumable electrodes. Copper water-cooling electrodes are rarely used due to intense electroerosion in aggressive slag medium. The scheme of ESS of stamps with discrete filler metal with non-consumable electrodes is shown in Fig. 4.9. The surfaced part (worn stamp) (6) is installed in the crystallizer (1), which is located on the steel tray (4). Molten slag (8) from the bucket (5) is poured on the surface of the part. A slag pool (8) is formed (Fig. 4.9a). Non-consumable (graphite) electrodes (2) are immersed into the slag pool. The electroslag process in the slag pool begins (Fig. 4.9b). Due to the heat released in the slag pool, the surface of the stamp melts. The bunker (9) feeds filler metal (chip steel) (10) into the slag pool. Molten droplets fall to the bottom of the slag pool and form a layer of molten metal (7). The surfacing process begins (Fig. 4.9c). The wear-resistance of surfaced stamps is 1.5–4.0 times higher than that of forged ones.

8

5 1 6 4

9 10

3

a

8 7 6

2 8

4

c b Fig. 4.9 Diagram of ESS with discrete filler material and non-consumable electrode (a—stage of pouring of molten slag on the surface to be surfaced, b—electroslag process of heating of the surface to the molten state with non-consumable electrodes in a slag pool, c—electroslag surfacing process): 1—crystallizer, 2—non-consumable (graphite) electrodes, 3—contact tip, 4—steel tray, 5—bucket for molten slag, 6—surfaced part, 7—metal pool, 8—slag pool, 9—bunker, 10—filler material for surfacing

94

4 Electroslag Surfacing

ESS with discrete filler metal is used: • • • •

in the manufacture of blanks for rolling bimetallic sheets, in mechanical engineering for surfacing of stamps, in metallurgical production for surfacing of roller rolls, in the mining industry to restore the teeth of excavator buckets, teeth of large gears.

4.2.5 Electroslag Surfacing with Liquid Filler Metal The use of liquid filler metal in ESS provides: • the possibility of surfacing metal of almost any chemical composition, • the possibility of multilayer surfacing of metals of different chemical composition without interrupting the process, • elimination of the need to manufacture consumable electrodes, • a significant increase in the productivity of the surfacing process due to the lack of a stage of melting in the slag pool of solid filler material. ESS with liquid filler metal can be performed according to three technologies using: • non-consumable graphite electrodes, • crystallizer that supplies current, • consumable electrodes. Figure 4.10 shows the diagram of ESS with liquid filler metal using nonconsumable graphite electrodes [1]. The surfaced part (7) is installed in the crystallizer (1), which is located on the steel tray (4). The molten slag (9) from the bucket with liquid slag (5) is poured on the surface of the surfaced part (Fig. 4.10a). Non-consumable (graphite) electrodes (2) are immersed into the formed slag pool. The electroslag process begins (Fig. 4.10b). After heating the surface of the workpiece to molten state the molten metal (8) from the bucket for liquid filler metal (6) is poured (Fig. 4.10c). The molten metal sinks to the bottom of the slag pool and forms a metal pool. The non-consumable electrodes are re-immersed into the slag pool (Fig. 4.10d). The electroslag process is used to control the temperature and crystallization rate of the molten metal. As a result, a two-layer part is obtained. ESS technology with liquid filler metal allows to process the outer surfaces of cylindrical workpieces 40 to 1000 mm diameter and more with a thickness of the deposited layer of 10–150 mm with high productivity—up to 800 kg of deposited metal per hour [1]. ESS with liquid filler metal is used in the manufacture of rolling rolls with a working layer of high-speed steel.

4.2 Methods of Electroslag Surfacing

95

9

3

2

9 5 1

7 4

a

b

8

9 8

6

7

c

d

Fig. 4.10 Diagram of ESS with liquid filler metal using non-consumable graphite electrodes (a stage of pouring of liquid slag on the surface of the surfaced part, b electroslag process of heating the surface of the part before melting by non-consumable electrodes in the slag pool, c stage of pouring of liquid metal into the slag pool, d electroslag process of surfacing with non-consumable electrodes in a slag pool with liquid metal): 1—crystallizer, 2—non-consumable (graphite) electrodes, 3—contact tip, 4—steel tray, 5—bucket for liquid slag, 6—bucket for liquid filler metal, 7—surfaced part, 8—metal pool, 9—slag pool

4.2.6 Electroslag Surfacing with Strips with Free Formation ESS with one or two electrode strips in the horizontal position of the surfacing surface is carried out with the free formation of a layer of deposited metal without crystallizers. The process begins with a short circuit of the electrode strip on the product and striking of the electric arc. After melting the tip of the electrode strip and after the length increasing the electric arc goes out. The process turns into electroslag.

96

4 Electroslag Surfacing

1 2 3

Vc 8

7

6

5

4

Fig. 4.11 Diagram of ESS with one electrode strip: 1—electrode strip, 2—flux feeder, 3—flux, 4—metal pool, 5—slag pool, 6—surfaced part, 7—deposited layer, 8—slag crust

In case of ESS one electrode strip (Fig. 4.11) flux (3) from the flux feeder (2) is fed only from one side—in front of the electrode strip (1) in the direction of surfacing. The thickness of the flux layer is about 30 mm. Slag pool (5) with metal pool (4) in the lower part is formed by the electrode strip. In the tail of the metal pool a deposited layer (7) is formed under the layer of slag crust (8). NOTE. An example of surfacing parameters for the most often used cold-rolled strip 60 × 0.5 mm. Current 1050–1080 A, voltage 24–25 V, surfacing speed 20–22 cm/min. The obtained thickness of the deposited layer is 3 mm. Increasing the width and thickness of the strip allows to increase the current and productivity of surfacing. However, this increases the depth of penetration and the proportion of base metal in the surfaced metal. The penetration depth of the base metal decreases with increasing surfacing speed. During ESS with electrode strip with a width of more than 80 mm the harmful effects of magnetic blowing start to show up, which affects the quality of the fusion zone and the formation of the surfaced metal. In case of ESS with two electrode tapes (1) (Fig. 4.12) flux (3) moves from two sides. A feature of the process is the large volume of the slag pool (5). Compared to the arc process, the heat input to the base metal is more dispersed. A small depth of penetration and a small proportion of the base metal in the surfaced layer is achieved. In addition, the heating efficiency of the electrode strips and the productivity of the process increase. To sustain the electroslag process, the electrode strips are fed into the slag pool with a gap. Liquid slag under the action of the pinch effect rises in the gap between the electrode strips by 20–30 mm. The size of the gap affects the electroslag process.

4.2 Methods of Electroslag Surfacing

97

1 9

+

2 10

2

Vc

8

7

5

4

3

6

Fig. 4.12 Diagram of ESS with two electrode strips: 1—electrode strips, 2—flux feeders, 3—flux, 4—metal pool, 5—slag pool, 6—surfaced part, 7—surfaced layer, 8—slag crust, 9—rollers for strip feeding, 10—copper contact tip

In case of a small gap between the electrode strips, the slag pool overheats and boils. The surfacing process transfers from electroslag to arc. In case of a large gap the surface area of the slag pool increases, its temperature drops, the electrical resistance increases. The surfacing process transfers from electroslag to arc. The gap between the electrode strips is a parameter of the ESS. It increases with increasing power. During ESS two tapes with increasing current at constant voltage (32 V) and the rate of deposition (17 m/h) the height and width of the deposited bead increases at a constant value of the proportion of base metal in the deposited layer (Fig. 4.13a). With increasing voltage at constant current (1250 A) and the rate of deposition (17 m/h) the height and width of the deposited bead also increases at a constant value of the proportion of base metal in the deposited layer (Fig. 4.13b). Increasing the rate of surfacing at constant current (1250 A) and voltage (32 V) leads to a decrease in the size of the bead and to a slight decrease in the proportion of base metal in the surfaced layer (Fig. 4.13c). Cold-rolled and sintered electrode strips 0.4–1.2 mm thick and 30–120 mm wide made of stainless steels, nickel- and cobalt-based alloys are used for ESS. The use of flux-cored strips is limited due to their unstable melting in the slag pool. The

98

4 Electroslag Surfacing

γ, %

a

b

γ, %

15

15

10

10

5

5

h, mm 6,0

h, mm

4,0

4,0

2,0

2,0

S, mm

S, mm

80 70 60

70 60

800 1000 1200 1400 1600 1800 I, A

γ, %

20

25

30

35

U, B

c

15

10 5

h, mm 4,0 2,0

S, mm 70 60 10

18

26

34

V, m/h

Fig. 4.13 Influence of current I (a), voltage U (b) and deposition rate V (c) on the width of the bead S, the height of the bead h and the proportion of base metal in the deposited metal γ during ESS with two strips made of 07Cr23Ni12Mn, cross section 60 × 0.8 mm with a gap of 16 mm [1]

electrode strip melts in a slag pool with a depth of 4–6 mm at a temperature of 2100– 2300 °C. A surfaced layer 3–6 mm thick is formed. The width of the deposited layer depends on the size of the strip and the surfacing parameters. When the carbon content in the electrode strip is up to 0.1%, the electroslag process remains stable. With increasing carbon content in the electrode strip with a constant content of deoxidizers (manganese and silicon) in the surfacing pool, it undergoes intense oxidation of carbon with the release of large amounts of CO. This causes intense boiling of the pool and the alternation of the electroslag process with the arc one.

4.3 Features of Physic-Chemical Processes During Electroslag Surfacing

99

For ESS with electrode tapes, it is necessary to use fluxes of the CaF2 –Al2 O3 – SiO2 system with increased electrical conductivity in the molten state. The required electrical conductivity of the slag is provided by fluorides CaF2 and NaF, which eliminates the appearance of an electric arc in the slag pool of shallow depth. Electroslag process is most stable when using fluxes with relatively low CaF2 content and high SiO2 content. The melts of these fluxes have increased electrical resistance, which leads to an increase in heat release and an increase in the temperature of the slag pool. The above provides rapid heating of the electrode strips and increases the productivity of the process in comparison with arc surfacing. The penetration of the base metal decreases. The main advantage of ESS with electrode strips is a significant reduction in the proportion of base metal in the surfaced layer compared to other methods of surfacing. The share of base metal in the first layer is 6–8%. This is because there is no direct effect of electric arc on the base metal. A small proportion of the base metal in the surfaced metal provided by ESS with electrode strips can reduce the number of surfacing layers, which reduces deformation, the cracking susceptibility of the surfaced metal and the complexity of the process. ESS with electrode strips is used in nuclear, energy and chemical engineering. To ensure high corrosion resistance, the internal surface of the equipment made of lowalloy pearlitic steels is surfaced with a layer of chromium-nickel austenitic steels. When ESS is used, one layer deposited with two tapes is enough (when electric arc anticorrosive surfacing is used, it is necessary to produce two or three layers). High quality of the deposited layer and twofold increase in surfacing productivity is provided [1].

4.3 Features of Physic-Chemical Processes During Electroslag Surfacing Physic-chemical processes take place at all stages of the interaction between the surfacing metal and slag. When electrode or filler metal are used in the solid state, the stages of interaction are: • • • •

melting of the electrode (filler), formation of a droplet of liquid metal, transfer of a droplet through a slag pool, contact of surfaces of slag and metal pools.

When liquid filler metal is used, the stage of interaction of liquid metal and slag melt when pouring from a bucket replaces melting of the electrode and the formation of the droplet. The direction and speed of reactions at these stages depend on the ratio of the chemical compositions of the surfaced metal and slag, temperature, type of

100

4 Electroslag Surfacing

Table 4.1 Chemical composition of flux and slag during electroslag welding Flux/slag

Mass fraction of components, % SiO2

Al2 O3

CaO

MgO

MnO

FeO

CaF2

P

Flux AH-8

32.62

9.4

7.6

7.02

25.3

1.6

15.9

0.038

Slag pool

29.0

7.0

7.8

5.5

30.6

7.7

12.5

0.0074

current and polarity. The final result is determined by the direction of reactions (thermodynamic factor) and their speed (kinetic factor). In submerged arc surfacing the melting electrode interacts with a fresh portion of the flux at any time, and the chemical composition of the surfaced metal on the entire surface is within specified limits. In contrast to SAW process, during ESS with forced formation fresh portions of the flux do not fall into the surfacing zone. As a result of the interaction of the electrode (filler) metal with the slag melt, the composition of the slag may change. If a dosed addition of fresh portions of flux in the slag pool is not performed, the composition of the deposited metal may change. The Table 4.1 shows the composition of the flux and slag after equilibration in electroslag welding on alternating current with Sv-10G2 wire. Thus, in ESS, alloying is possible only through the electrode (filler) metal. Alloying through flux with the specified chemical composition of the surfaced metal is complicated. On the other hand, in contrast to SAW surfacing, in ESS, liquid metal droplets are in contact with the slag melt for a longer time. Redox and refining processes are more complete. As a result, it is possible to obtain a surfaced metal of higher quality.

4.4 Materials for Electroslag Surfacing 4.4.1 Fluxes In ESS, fluxes influence the following: • stability of the electroslag process, • surfacing productivity, • quality of surfaced metal. Flux requirements for ESS: • ensuring rapid dilution of the slag pool and the stability of the surfacing process in a wide range of process parameters, • ability to form a bead with easy separation of the slag crust, • prevention of the formation of pores, cracks, non-metallic inclusions and other imperfections in the deposited metal,

4.4 Materials for Electroslag Surfacing

101

• ensuring a guaranteed minimum but complete penetration of the base metal over the entire surfacing surface, • optimal fluid flow to prevent leakage of the slag pool into the gaps between the mold (slider) and the product, • lack of easily reducing oxides, expensive components and a large number of alloying elements, • ensuring the necessary sanitary and hygienic working conditions during the manufacturing process, • manufacturability. Fluxes for ESS of iron-based alloys can be divided by chemical composition into the following groups (Table 4.2) [1]: • low-silica manganese (AH-8, AH-8 M, AH-22, TU-St-B, etc.), • oxide-fluoride (AH-25, AHF-6, AHF-7, 48-OF-10, etc.), • fluoride (AHF-1, AHF-5, etc.). Their technological properties, such as the formation of the deposited layer and its fusion with the base metal depend on the chemical composition of the fluxes. Fluxes with lower melting point are used for ESS of non-ferrous metals, because of the low melting point. For the surfacing of copper on steel, fluxes based on sodium fluoride (melting point 995 °C) are used (Table 4.3). The stability and effectiveness of the electroslag process depend on the following properties of the slag: • • • • • •

electrical conductivity, viscosity, melting point, wetting, moisture-fluidity, stability of chemical composition during surfacing.

The electrical conductivity of the slag should be within certain limits. At high electrical conductivity of slag, an electric arc between the electrode and the slag surface is possible. At low electrical conductivity of slag disturbance of stability or the termination of electroslag process is possible. The amount of heat released in the slag pool and, therefore, the energy intensity of the process and the depth of penetration of the base metal also depend on the electrical conductivity of the slag. At low electrical conductivity of slag, it is necessary to use higher voltage. Viscosity (internal friction) is the property of liquid slag to resist the movement of one part relative to another. The viscosity of slag determines the intensity of physical and chemical processes. According to the nature of the change in viscosity depending on the heating temperature slags are classified as (Fig. 4.14):

SiO2

A12 O3

11–15

33–36

TU-St-B

–

–

AHF-1

AHF-5

Fluoride fluxes

–

–

–

–

–

–

–

28–34

–

9–12

–

–

21–26

7–9

30

AHF-7

–

AHF-6

–

48-OF-10

6–9

AH-25

Oxide-fluoride fluxes

19–23

18–21

≤ 5.5

AH-22

21–25

28–32

11–15

33–36

35–38

AH-8

AH-8M

MnO

Mass fraction of components, %

Low silicon manganese fluxes

Flux brand

Table 4.2 Fluxes for ESS of iron-based alloys

–

5 –

–

– 11–14

≤ 8.0

–

2–4

5–7

11–15

≤ 1.0

5–7.5

MgO

20

–

12–15

4–7

12–15

4–8

4–7

CaO

80

95

35–45

80

70

34–40

13–19

20–24

12–16

13–19

CaF2

–

≤ 1.5

–

–

≤ 1.0

–

–

20 NaF

–

–

–

–

30–40 TiO2

1–2 Na2 O + K2 O

≤ 1.0

–

3–4 Na2 O + K2 O

–

Others

≤ 1.5

1.5–3.5

FeO

1160–1180

1390–1410

1380–1420

1200–1220

1320–1340

950–1050

1100–1150

950–1050

950–1050

Melting temperature °C

102 4 Electroslag Surfacing

50–70

50–60

50–60

AH-M11

AH-M21

NaF

–

–

10–20

LiF

5–15

5

–

Na3 AlFe6

Mass fraction of components,%

AH-M10

Flux brand

5–15

10–20

–

B2 O3

–

15–20

–

K2 CO3

Table 4.3 Fluoride-oxide fluxes for ESS of copper and copper alloys Na2 CO3

–

15–20

–

CaF2

–

–

10–20

Others

–

10–20 Na2 B4 O7

5–10 SiO2 ≤ 3 CaO

750–800

700–750

800–850

Melting temperature °C

4.4 Materials for Electroslag Surfacing 103

104

4 Electroslag Surfacing

μ,Pa·sec

μ,Pa·sec

0, 16

2

4

3

4

0, 14 3

0,12

1

0,10 0,08

2

0,06 0,04

1

0,02 1000 1100 1200 1300 1400

T, 0C

1100 1200 1300 1400 1500

T, 0C

Fig. 4.14 Change of slag viscosity ‘μ’ depending on heating temperature ‘T’ [1]: “long” slags—1 (AH-8) and 4 (48-OF-10), “short” slags—2 (AH-22) and 3 (AHF-5)

• “long” slag—characterized by a small change in viscosity with a significant increase in temperature, • “short” slag—characterized by a significant change in viscosity with a slight increase in temperature. The use of “long” slags allows to change the thermal mode of surfacing in a wider range. The “shorter” the slag, the greater the thickness of the garnish and the worse the quality of the deposited surface, other things being equal. The use of very viscous slag can lead to squeezing of the mold (slider) from the metal surface and change the shape of the deposited layer or leakage of the surfacing pool. Melting point. Fluxes change from solid to liquid and vice versa in a certain temperature range. Therefore, when we talk about the melting point of fluxes, melting means the transition from a viscous state to a liquid-flowing state. The melting point of the flux is determined by the inflection point on the curve “viscosity-temperature”. The melting point of fluxes for ESS is usually lower than the liquidus temperature of the metal (in some cases the temperatures may be equal). The use of such fluxes provides the most economically effective energy consumption. Wetting characterizes the interaction of liquid slag molecules with surface molecules of the base metal. If the adhesion of liquid slag molecules (cohesion) is weaker than the adhesion of liquid slag molecules to the molecules of the base metal surface (adhesion), the liquid slag spreads well on the surface—there is a strong wetting. If the adhesion of liquid slag molecules to each other (cohesion) is stronger than the adhesion of liquid slag molecules to the molecules of the base metal surface (adhesion), the spreading of liquid slag on the surface is difficult—there is weak wetting.

4.4 Materials for Electroslag Surfacing

105

The oxide film on the surface of the base metal prevents the formation of metal bonds. The condition for the interaction of the active components of the slag with the surface of the base metal and the purification of the surface from oxides is good wetting of the molten slag. With increasing temperature of the electroslag process, the cohesion and surface tension of the slag decreases, which improves wetting. However, with good wetting, the slag should not have high adhesion to the base metal, as this leads to the appearance of slag inclusions in the fusion area. Moisture flow is a measure of the mobility of liquid slag, which is characterized by the ability to accurately and completely fill the reference mold. High moisture fluidity can lead to leakage of slag when moving the crystallizer. However, when ESS is performed in current-supplying crystallizer with a liquid start, with increasing moisture content the rate of slag spread around the perimeter of the mold increases (for several seconds). If this does not happen, it complicates the beginning of the electroslag process, increases the time of the slag pool and reduces the durability of the crystallizer. The stability of the chemical composition of the slag during the surfacing is especially important for ESS in vertical or inclined positions using crystallizers (sliders). The consumption of flux in these methods of ESS is small—4–5% by weight of the deposited metal. The slag pool is not renewed for a long time, or this renewal is insignificant. The chemical composition of the slag changes (depletes). As a result, the chemical composition and performance properties of the deposited metal change. When changing the chemical composition of the slag can also disrupt the stability of the electroslag process.

4.4.2 Electrode Wires and Strips Varieties of electrode wires and strips for ESS are: • Solid electrode wires (Table 2.3 and 2.4) and flux-cored wires (Table 2.5) (same electrode wires are used in electric arc surfacing). The diameter of the wires for ESS is 3.0–5.0 mm. • Cold-rolled (Table 2.6) and sintered (Table 2.8) electrode strips (same electrode strips are used in electric arc surfacing). Flux-cored strips (Table 2.7) for ESS are practically not used. This is because it is easier to make electrodes of large cross-section of the required chemical composition by casting or rolling than to make flux-cored strip on special mills.

106

4 Electroslag Surfacing

4.4.3 Electrodes with Large Cross-Section Varieties of electrodes with large cross section (over 100 mm2 ) [1]: • rods of round, square or rectangular cross section, • tubes, • melting contact tips—current supplying tubes or plates with holes through which electrode wires are fed into the slag pool. Both electrode wires and tubes (or plates) melt in the process of ESS. The composition of the electrodes of large cross section: • • • •

low-alloy carbon steels (34XHM, 65G, 75GHD, 9X), tool steels (3B8X2, X12), high-manganese steels (110G13L), chromium and chromium-nickel cast irons, etc.

4.4.4 Discrete Filler Materials Discrete filler materials cannot independently support the electroslag process, so they are always used in conjunction with consumable or non-consumable electrodes [1]. Varieties of discrete filler materials are: • • • • •

powders obtained by spraying, powders obtained by mechanical crushing of cast blanks or ferroalloys, shavings obtained as a result of machining of alloyed steels and alloys, fractions, small pieces of wire.

The composition of discrete filler materials: • • • •

carbon structural steels (5XHM, 9X), tool steels (P6M5, P3M3F2), chromium and low-alloy cast irons, tungsten carbide with various additives, etc.

4.4.5 Liquid Filler Materials Liquid filler metal, like discrete filler materials, cannot independently support the electroslag process, so it is used with a sectional current-supplying crystallizer [1] or with consumable electrodes. Liquid filler material is obtained by smelting in induction or arc furnaces (basic technology), or by electroslag remelting of the electrode material.

Reference

107

The composition of liquid filler metals: • • • • • •

carbon non-alloyed steels (steel 60), tool steels (5XHM, 30X4HMBF, 45XHM TP), high-carbon high-speed steels (up to 2.5% C), high-carbon steels (110X11HMC, 250X2H3MFA, 185X5H2B4M4F4), stainless steels (X18H10T), cast iron, etc.

Reference 1. Kyckov .M., P bcev I.A., Kyz menko O.G., Lent gov I.P. lektpoxlakovye texnologii naplavki i peciklinga metalliqeckix i metallocodep awix otxodov. - Kiev: Intepcepvic, 2020. – 288 c

Chapter 5

Gas Surfacing

Abstract Definitions of the methods of applying surface layers to products are given: surfacing, cladding, spraying. The indicators of penetration and geometry of the deposited beads were analyzed. The basic classification of surfacing and cladding processes is given according to the purpose and physics of the energy sources used to apply the layers.

5.1 Physical Phenomena of Gas Surfacing In gas surfacing, the source of energy for heating and melting of the filler metal and the base metal is a gas flame formed by the combustion of fuel gases (Table 5.1) in a mixture with oxygen in a gas torch. Acetylene is usually used as a fuel gas because it has one of the highest specific heat of combustion and, accordingly, provides the highest temperature of the gas flame. Gas flame (Fig. 5.1) consists of: • core (1), which contains a mixture of fuel gas with oxygen in the stage of thermal and chemical preparation for combustion, • recovery zone (2)—the main working area where the combustion of the gas mixture takes place, • outer envelope (3), where the gas mixture burns. During welding and surfacing, the amount of oxygen supplied to the gas mixture is less than that required for complete combustion. Full combustion of gases is due to oxygen in the air, as a result of which the flame in different parts of the outer envelope is heterogeneous in thermophysical characteristics. The flame structure of all fuel hydrocarbon gases in a mixture with oxygen is fundamentally the same and is determined mainly by the ratio of oxygen and fuel gas in the mixture: β0 =

O2 Cx H y

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 I. Ryabtsev et al., Surfacing and Additive Technologies in Welded Fabrication, https://doi.org/10.1007/978-3-031-34390-2_5

(5.1) 109

110

5 Gas Surfacing

Table 5.1 Thermal characteristics of fuel gases used for gas surfacing Fuel gas (Chemical formula)

Specific heat of combustion Q, J/m3

Maximum flame temperature, T, °C

The optimal oxygen to fuel gas ratio, β 0

Acetylene (C2 H2 )

52.5

3150

2.0

Hydrogen (H2 )

10

2182

0.5

Methane (CH4 )

35.4

1850

2.0

Propane-butane (mixture C3 H8 and C4 H10 )

85.8

2043

5.0

Natural gas (mixture CH4 , C2 H6 , C3 H8 etc.)

35

1850

2.0

1

L

2 3

Fig. 5.1 Structure of gas flame: 1—core, 2—recovery zone, 3—outer envelope

According to the ratio of gases (composition of the combustible mixture) gas flame could be (Fig. 5.2): • Neutral, • Oxidizing, • Carburizing or reducing. In neutral flame (see Fig. 5.2a) ratio of gases βo = 1. The neutral flame has a pronounced core—a smoothly outlined cone. The core consists of fuel, gas, and oxygen. When the core touches the part, the metal is intensively oxidized. The reducing (working) zone consists of CO and H2 , which reduce metal oxides. At a distance of 2–3 mm from the core, the temperature of the recovery zone reaches

5.1 Physical Phenomena of Gas Surfacing

111

2

1

a

1

b

2

3

3

1

3

c Fig. 5.2 Types of gas flame: a—neutral, b—oxidizing, c—carburizing (1—core, 2—recovery zone, 3—outer envelope)

a maximum (Fig. 5.3). For acetylene flame, the maximum temperature is 3150 °C, for other fuel gases—slightly lower. The gas flame outer envelope is a mixture of gases such as CO2 , H2 O, N2 and others. The outer envelope has an oxidizing nature and a relatively low temperature. Oxidizing flame (Fig. 5.2b) is formed when excess oxygen (β > 1,2) is supplied to the gas torch. With this ratio of gases, the middle zone of the flame is oxidizing, because it contains free O2 and CO2 . The dimensions of the cone and the outer envelope are reduced. The outer envelope turns purple. T, 0C 3150 3050 2850 2650

300 03 4 11

25

X, mm

Fig. 5.3 Distribution of temperature T by distance X from the core in acetylene flame

112

5 Gas Surfacing

Carburizing flame (Fig. 5.2c) is formed when excess fuel gas (β < 1.0) is fed into the gas torch. The core has the same properties as one of a neutral flame, but due to lack of oxygen the oxidation reaction in the core is slowed down. Decomposition of fuel gas into carbon and hydrogen is manifested. The core is stretched, its boundary is blurred. An orange veil is formed. Free carbon also appears in the outer envelope with a significant excess of fuel gas. The envelope lengthens and turns red. When using fuel gases—acetylene substitutes, the maximum flame temperature is reduced. The amount of heat released in the recovery zone decreases. The decrease in the calorific value of acetylene substitutes is offset by an increase in their consumption. The diameter of the nozzle of gas torches, the diameter of the jet of the gas mixture and the size of the gas flame increases. The heating area of the metal increases by 2.5–4.0 times. The length and width of the surfacing pool increases by 1.5–2.0 times. The power of the gas torch is determined by the formula: q=WQ

(5.2)

where W Gas consumption, Q Unit heat of gas combustion (Table 5.1). Gas consumption is in direct ratio with its outflow rate v and area of torch nozzle cross-section S: W = vS

(5.3)

The gas consumption is set so that when igniting and burning the flame could not penetrate into the torch channel (flow rate is too low) or break away from the nozzle (flow rate is too high). The efficiency of heating and melting of the metal during gas surfacing is η = 0.30–0.80. Gas flame is the least intense source of heat, so its use causes a larger, compared to other methods of surfacing, heat affected zone. When using a gas flame, the metal does not evaporate. A feature of gas surfacing is a small penetration of the base metal (up to 2–3 mm) and a small proportion of the base metal in the deposited layer (5–15%). This is due to the lack of significant pressure of the gas jet on the surface of the surfacing pool. Gas flow pressure P is calculated by the formula, which allows you to easily control the process of gas surfacing: P=

W 2ρ L

(5.4)

5.2 Materials for Gas Surfacing

113

where W Gas consumption, ρ Gas density, L Distance from nozzle tip to the surfacing pool. Advantages of gas surfacing are: • The possibility of surfacing thin layers, as well as parts of complex shape in different positions, • Low probability of cracking, as the surfacing process is combined with preheating, • low cost of surfacing equipment

Disadvantages of gas surfacing are: • Low productivity of the process (up to 0.8 kg/h), • Instability of the quality of the deposited layer, depending on the qualification of the surfacer, • High probability of undesirable structural changes in the base metal as a result of intense heating of the part, • Limited range of filler materials

5.2 Materials for Gas Surfacing The following filler materials are used for gas surfacing: • • • •

rods, wires, strips, granular powders.

In the case of using granular powders, the coating layer is formed due to mechanical adhesion of powder particles to the substrate, as well as the diffusion of individual elements from the coating into the substrate, as in spraying. At the same time the applied layer melts without melting of the base metal and without the formation of a surfacing pool. However, the term gas-powder “surfacing” is usually used to describe such a process, rather than “spraying”. Gas surfacing of steel parts is performed using surfacing wires (Table 2.3), welding wires (Table 2.4) and rods for gas welding of non-alloyed and heat-resistant steels according to EN 12536:2000 [1]. Same fluxes as those for gas welding of high-alloyed and medium-alloyed steels are used. Surfacing of carbon steels can be performed without flux. Flame with an excess of acetylene is preferable (Fig. 5.2c), in which the main components of carbon, carbon monoxide and hydrogen reduce the oxides of iron and other metals.

114

5 Gas Surfacing

Gas surfacing of cast iron parts is performed with cast rods (Table 5.2): • • • •

for gas welding grade A—for surfacing of massive parts with local heating, for gas welding grade B—for surfacing of small parts with heating, for surfacing of FeC1, FeC4 , FeC5 grades (according to EN ISO 1071:2003 [2]), for wear-resistant surfacing of BQ, XQ grades.

The hardness of the surface of the deposited metal should be: HRC 44 to 66—for BQ grade rods, HRC 48 to 52—for XQ grade rods, HB up to 230—for A and B grade rods. Cast iron rods are cast with a diameter of 4, 6, 8, 10, 12 mm and a length of 400–700 mm. The surface of rods must be clean. Slag inclusions are not allowed in fractures of rods. To remove oxides of iron, manganese, and silicon, which are formed during the process, from the surfacing pool and to reduce the porosity of the deposited layer the following fluxes are used: • borax (Na2 B4 O7 · 10H2 O), • a mixture of 56% borax, 22% sodium carbonate (Na2 CO3 ) and 22% potassium carbonate (K2 CO3 ). Gas surfacing with high-chromium and high-carbon iron-based alloys is used for parts that operate in conditions of abrasive wear with impact load. For conditions of intensive abrasive wear with moderate shock loads (working bodies of road, construction, and agricultural machines) rods PP-C1 and PP-C2 are used (Table 5.3). For similar conditions, but at high operating temperatures—up to 500 °C (parts of filling devices of blast furnaces, parts of centrifugal pumps, fittings for petroleum products), PP-C27 alloy rods are used. Diameters of cast bars from these alloys are 4, 5, 6 and 8 mm, length is 300– 500 mm. Gas surfacing with copper is used to apply an electrically conductive layer on parts or to restore the size of copper parts. Table 5.2 Chemical composition of cast rods for gas surfacing of parts made of cast iron Brand of rod

Mass fraction of elements, % C

Si

Mn

P

S

Others

A

3.0–3.5

3.0–3.4

0.5–0.8

0.2–0.4

≤ 0.08

≤ 0.05 Cr; ≤ 0.3 Ni

B

3.0–3.5

3.5–4.0

0.5–0.8

0.3–0.5

≤ 0.08

≤ 0.05 Cr; ≤ 0.3 Ni

FeC1

3.0–3.6

2.0–3.5

≤ 0.8

≤ 0.5

≤ 0.1

3.0 Al

FeC4

3.2–3.5

2.7–3.0

0.6–0.75

0.5–0.75

≤ 0.1

–

FeC5

3.2–3.5

2.0–2.5

0.5–0.7

0.2–0.4

≤ 0.1

1.2–1.6 Ni; 0.25–0.45 Mo

BQ

2.5–3.0

1.0–1.5

0.2–0.6

≤ 0.1

≤ 0.05

–

XQ

2.5–3.0

1.2–1.5

0.5–0.8

≤ 0.1

≤ 0.05

1.2–2.0 Cr

5.2 Materials for Gas Surfacing

115

Table 5.3 Chemical composition of cast rods for gas surfacing with high-chromium and highcarbon iron-based alloys and hardness of deposited metal Brand of rod

Mass fraction of elements, % Fe

Cr

Ni

C

HRC Si

Pp-C1/ PPH-U30X28H4C3

Base 27–31 3–5

Pp-C2/ PPH-U20X17H2

Base 13–17 1.5–2.5 1.5–2

Mn

W

2.5–3.3 2.8–3.5 0.4–1.5 –

50–54

1.5–2.2 0.4–1.1 –

40–45

Pp-C27/ Base 25–28 1.5–2.0 3.3–4.5 1.0–2.0 1.0–1.5 0.2–0.4 PPH-U45X28H2CBM

≥ 53

PStelNi-50

50

Base 30

5

3

–

0.6

–

Difficulties in surfacing with copper: • The tendency of copper to dissolve hydrogen, which causes embrittlement. • High thermal conductivity of copper necessitates the introduction of large amounts of heat in the case of preheating of the surfaced part. Overheating of the part leads to coarse-grained structure and reduced strength. • Penetration of copper into iron, which can lead to cracks. For gas surfacing with copper, as a rule, a neutral acetylene-oxygen gas flame is used. A reducing flame can also be used to reduce the oxidation of copper. Deoxidation of copper and removal of slag of copper oxide Cu2 O, formed during surfacing, is carried out using the same fluxes as those for gas welding of copper: • borax (Na2 B4 O7 · 10H2 O), • a mixture of 50% borax and 50% boric acid (H3 BO3 ). Low-alloy copper bars S Cu 1897 (CuAg1) in accordance with EN ISO 24373: 2009 [3] are used as filler metal. Gas surfacing with bronze is used to restore tin bronze bearing inserts or to repair bronze casting defects. Wires or rods similar in chemical composition to the base metal are used as filler metals (Table 5.4). Table 5.4 Chemical composition of rods for gas surfacing with bronze according to EN ISO 24373:2009 [3] Brand of rod

Mass fraction of elements, % Cu

Al

Fe

Mn

Sn

P

Ni + Co

BpOF7-02/CuSn8

Base

–

–

–

7–8

0.1–0.25

–

BpA7

Base

6–8

–

–

–

–

–

CuAl8

Base

6.0–9.5

0.5

0.5

–

–

0.8

CuNi10

Base

–

0.5–2

0.5–1.5

–

–

9–11

116

5 Gas Surfacing

Same fluxes as those used for gas welding of copper and brass are used for surfacing with bronze. Fluxes containing fluoride and chloride compounds of sodium, potassium, barium, and lithium are used in the gas surfacing of aluminum bronzes to remove refractory aluminum oxide from the surface. Gas surfacing of brass is carried out using filler materials, which, in addition to copper (about 60%) and zinc, contain small additives of silicon, tin, silver, manganese, nickel and iron. Silicon limits the evaporation of zinc during surfacing. The chemical composition of brass rods for gas surfacing on carbon steel is given in Table 5.5. Siliceous brass should not be used for surfacing the first layer, because in this case a brittle layer is formed at the boundary of fusion with steel or cast iron. Silicon-free rods, such as CuZn40Sn, should be used to produce the first layer on carbon steel and cast iron. Surfacing with brass is carried out using fluxes which are designed for welding brass. For example, BM-1 gaseous flux supplied to the torch flame is used for gas surfacing of brass. The flux consists of 55–70% methyl borate (B(OCH3 )3 ) and methyl alcohol (CH3 OH). Vapors of this flux are poisonous, so when using it one must follow safety measures. Gas surfacing with aluminum and its alloys is carried out using wires or rods of the same chemical composition as the base metal. Aluminum bars S Al 1200 (Al99,0), as well as alloys S Al 4043 (AlSi5) and S Al 4047 (AlSi12) in accordance with EN ISO 18273: 2004 are used for surfacing. Surfacing is complicated because of the presence of a surface film of refractory aluminum oxides (melting point 2053–2072 °C). The oxide film complicates the formation of compounds of the filler metal and the base metal, as well as preventing the release of gases from the molten metal. To remove aluminum oxides fluxes containing chloride or fluoride salts are used. Gas surfacing with cobalt-based alloys (stellites) is used to strengthen and restore parts operated in conditions of corrosion, abrasive and erosion wear, shock loads and friction of metal with metal (turbine blades, valves of internal combustion engines, Table 5.5 Chemical composition of rods for gas surfacing with brass according to EN ISO 24373:2009 [3] Brand of rod

Mass fraction of elements,% Cu

Sn

Si

Mn

Zn

B

LK62-05

60.05–63.5

–

0.3–0.7

–

Rest

–

LKBO62-0,2-0,04-0,5

60.05–63.5

0.3–0.7

0.1–0.3

–

Rest

0.03–0.10

LOK59-1–0,3

58.0–60.0

0.7–1.1

0.2–0.4

–

Rest

–

CuZn40SnSi

58–62

1.0

0.1–0.5

0.3

Rest

–

CuZn40Sn

57–61

0.25–1.0

–

–

Rest

–

5.2 Materials for Gas Surfacing

117

knives for hot and cold cutting, stamping tools). Stellites (Table 5.6) retain their performance properties at high temperatures (up to 800 °C). Stellite rods are made with a diameter of 2.5–7.0 mm and a length of 200–450 mm. Surface is mechanically processed before surfacing to remove sharp edges (see Fig. 5.4) [4]. Before surfacing, the parts are preheated to 400–650 °C to prevent the formation of cracks in the deposited layer. When surfacing large parts, this temperature is maintained throughout the surfacing process. For low weight parts, pre- and inprocess heating is not required, as heating is provided by the heat of the flame during surfacing. After surfacing, slow cooling of the part should be ensured. It is recommended to perform tempering heat-treatment immediately after surfacing to remove residual stress. Heat treatment parameters: heating temperature 620–640 °C, holding time depending on the weight of the part 1.5–5.0 h, slow cooling with the furnace at a speed of 30–50 °C/h. Gas surfacing with composite alloys based on tungsten carbide powder WC-W2C (relit) is used to strengthen and restore parts operated in intensive abrasive conditions with moderate shock loads (drill bits, drill pipe locks and couplings, mining equipment). Chemical composition of cast tungsten carbides: 95.8–96.4% W, 3.6–4.0% C, ≤ 0.15% Fe. The microhardness is 2800–3100 HB. Low-carbon steel tubes filled with tungsten carbide powder or flux-cored strips are used for surfacing. A flux-cored strip is a shell in the form of a flat tube filled with filler. Table 5.6 Chemical composition of stellites and hardness of deposit metal Brand of wire/rod

Mass fraction of elements, % Co

Cr

W

C

Mo

Si

Fe

–

1.0–2.0

≤ 2.0 46–48

1.0–1.3 0.5–2.0

–

2.0–2.7

≤ 2.0 42–43

1.6–2.0 0.1–2.0

–

1.2–1.5

≤ 2.0

Pp-B2K

Base 27–33 13–17 1.8–2.5

Pp-BZK / PpH-U10XK63B5

Base 28–32 4–5

Pp-BZK-P / Base 28–32 7–11 PpH-U20XK57B10

HRC Ni < 2.0

≥ 46

Stellite 1

Base 30

13

2.5

< 2.0

< 1.0

< 2.0

< 2.0 51–60

Stellite 6

Base 28.5

4.6

1.2

< 2.0

< 1.0

< 2.0

< 2.0 40–46

Stellite 12

Base 30

8.5

1.45

< 2.0

< 1.0

< 2.0

< 2.0 43–53

Stellite 20

Base 32.5

17.5

2.55

< 2.0

< 1.0

< 1.0

< 2.0 52–62

Stellite 25

Base 20

15

0.1

10

< 1.0

< 1.0

Pstel CoWB-40

Base 26

5

0.5

–

–

1.2

< 3.0 40

Pstel CoWB-50

Base 26

7

0.8

–

–

1.6

< 3.0 48

Pstel CoWB-55

Base 26

13

1.6

–

–

3.5

< 3.0 54

2.0 45

118

5 Gas Surfacing

a

b

Fig. 5.4 Preparation of parts for surfacing: a—wrong, b—right

The filler contains a mixture of tungsten carbide powder (not less than 65%) as well as deoxidizing, alloying, flux-forming components. The shell is made of alloys based on iron, nickel, or copper, alloyed with chromium, manganese, molybdenum. The content of tungsten carbide powder in the deposited metal is 50…65%.

5.3 Gas Surfacing Procedures

119

5.3 Gas Surfacing Procedures During gas surfacing, a flame is directed on the cleaned surface to heat it above the melting temperature of the filler material, but the base metal is not brought to melting. Then the filler metal is melted and it spreads on the heated surface. The parameters of the gas surfacing depend on the thermophysical properties of the metal, shape and size of the product and include: • • • • • • •

method of surfacing, type and diameter of the filler rod (wire), flux type, composition and consumption of fuel gas, torch angle, the angle of the rod (wire) feeding, the procedure for applying deposited beads.

There are leftward and rightward techniques of gas surfacing (Fig. 5.5). When the leftward technique is used (Fig. 5.5 a), the gas flame is directed to the still unsurfaced area of base metal. The filler rod is moved in front of the flame. The bead is formed from right to left. The rod is moved in a zigzag pattern for more uniform heating and mixing of the surfacing pool. The torch is moved without transverse oscillations. In the leftward technique the bead is formed better because of preheating of the surface. When the rightward technique is used (Fig. 5.5c) the gas flame is directed to the deposited bead. The filler rod is moved behind the flame in a spiral. The bead forms from left to right. The rightward technique of surfacing increases the productivity of the process and reduces the specific consumption of gases due to the use of flame heat mainly to melt the filler metal. When choosing the technique of gas surfacing one should take into consideration the spatial position of the surface. For a horizontal position the surfacing process can be conducted in both leftward and rightward ways. When surfacing on vertical or inclined surfaces, the convenience of surfacing and better formation of the bead provided by the leftward technique is decisive. The angle β of inclination of the torch to the surface depends on the thickness and thermophysical properties of the surfaced part. As the thickness, melting point and thermal conductivity of the metal increase, the angle β should increase. For the leftward technique: β = 60–70° (α = 30–45°), for the rightward technique: β = 40–50° (α = 30–45°). Fuel gas consumption also depends on thermophysical properties of the filler metal and surfacing rate. The higher its melting temperature and thermal conductivity, the greater the consumption of fuel gas. The nature of the reactions occurring in the surfacing pool is determined mainly by the composition of the middle zone of the flame, which depends on the ratio of fuel gas and oxygen—β0 .

120 Fig. 5.5 Techniques of gas surfacing: a—leftward, b—rightward (α—rod feeding angle, β—torch angle, Vc—direction of surfacing)

5 Gas Surfacing

2

1

Vc

3

a Vc

b Gas surfacing of low-carbon steels and iron-based alloys is performed using a neutral gas flame. The middle zone of the gas flame consists of carbon monoxide and hydrogen. Carbon monoxide and hydrogen reduce metal oxides well. Thus, by regulating the composition of the flame, it is possible to prevent the formation of iron oxides as well as those of most alloying elements. When surfacing steel, the allowable ratio of oxygen and fuel gas in the gas flame, which does not oxidize the surfacing pool, should be: β0 < 1,3. Gas surfacing of high-carbon steels and cast irons can be carried out using reducing flame (with increased amount of fuel gas). A thin layer with an increase in carbon of up to 1.5% is formed on the surface of the deposited metal. This layer has a reduced melting point and is easier to melt with a gas flame. Gas surfacing of copper and its alloys is carried out using a neutral flame (β0 = 1.05–1.1) to avoid oxidation.

References

121

Exceptions are brasses, gas surfacing of which is usually carried out using oxidizing flame (β0 = 1,4). At the same time, a film of zinc oxide is formed on the surface of molten brass, which protects the surfacing pool from evaporation and oxidation of zinc. Gas surfacing of nickel and cobalt alloys is carried out using a neutral flame. Gas surfacing of tungsten carbides (relit) is carried out by a reducing flame.

References 1. EN 12536:2000 Welding consumables—Rods for gas welding of non-alloy and creep-resisting steels—Classification. General information. https://www.iso.org/standards.html 2. ISO 1071: 2003 Welding consumables—Covered electrodes, wires, rods and tubular cored electrodes for fusion welding of cast iron—Classification. https://www.iso.org/standards.html 3. ISO 24373:2009 Welding consumables—Solid wires and rods for fusion welding of copper and copper alloys—Classification. https://www.iso.org/standards.html 4. P bcev IA, Cenqenkov IK, Typyk B (2015) Haplavka. Matepialy, texnologii, matematiqeckoe modelipovanie. - g.Glivice (Gliwice), Pol xa: Izd-vo Cilezckogo ´ askiej), 2015. – 590 c politexniqeckogo inctityta (Wydawnictwo Politechniki Sl˛

Chapter 6

Induction Surfacing

Abstract Sources of thermal energy and the scheme of induction heating are considered. The principles, advantages and disadvantages of induction surfacing are given. Technological schemes are considered and recommendations are given regarding the application of the main methods of induction surfacing: reinforcement of molten surface layer of the base metal with refractory and sparingly soluble additive; pouring liquid filler metal on the heated base metal; melting of briquetted or solid filler material on the base metal; immersion of the heated part in a crucible with melt; centrifugal surfacing of cylindrical parts; melting of powder additive on the surface of the part; furnace surfacing of composite powders. Examples of widely used materials for induction surfacing are given.

6.1 Physical Phenomena of Induction Surfacing During induction surfacing the heating and melting of the electrode (filler) metal and the heating of the base metal is carried out due to electromagnetic induction, which is created by the high frequency current Ii of the inductor (2) (Fig. 6.1). In part 1 there are two sources of thermal energy: (1) Eddy currents Ie , arising in a closed conduction circuit of a metal part due to changing of the magnetic flux ϕe . (2) Friction between magnetic domains when the metal is being rapidly remagnetized by an alternating magnetic flux ϕe . This effect occurs exclusively in ferromagnetic metals. Eddy currents Ie occur on the metal surface. The magnetic flux density ϕe is also much higher on the metal surface. Therefore, during induction surfacing the surface layer of the metal is heated. The higher the frequency of the current in the inductor Ii , the thinner layer in metal is heated. After the metal is heated above the Curie point (768 °C), the depth of penetration of induced currents will increase by 10–20 times (depending on the frequency). The temperature distribution in the metal is uniform.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 I. Ryabtsev et al., Surfacing and Additive Technologies in Welded Fabrication, https://doi.org/10.1007/978-3-031-34390-2_6

123

124 Fig. 6.1 Schematic diagram of heating during induction surfacing: 1—core being heated, 2—inductor, 3—current supply

6 Induction Surfacing

1

2

Φi

Ie

Ii

3

Parts or solid additives are heated to the melting point of the metal and joined. Fluxes are used to prevent oxidation and to improve the fusion of base and filler metals [1]. In the main methods of induction surfacing powder mixtures containing metal powders and flux additives reused as a filler material. The metal granules are isolated from each other by flux particles, as a result of which the electrical conductivity of filler mixture and the release of thermal energy in it are small. Heating and melting of the additive happen due to heat transfer from the metal of the heated part. In this case, the melting point of the additive must be lower than that of the base metal.

6.2 Methods of Induction Surfacing

Advantages of induction surfacing: • High productivity (up to 15 kg/h), • Easy mechanization and automation, • Possibility of surfacing of thin layers (0.4–2.5 mm), • No melting of the base metal, • Wide range of surface shapes (flat, cylindrical, conical)

125

Disadvantages of induction surfacing: • Low process efficiency, • Overheating of the base metal, • The need to use only those filler materials that have a melting point below that of the base metal (for most methods of induction surfacing), • Deformations that occur during heating and cooling of the surfaced part, in case of surfacing of critical parts operated under dynamic loads, normalization of parts after surfacing is required to eliminate residual deformations and stresses

6.2 Methods of Induction Surfacing The main methods of induction surfacing [1] are: (1) Reinforcement of molten surface layer of the base metal with refractory and sparingly soluble additive, (2) Pouring liquid filler metal on the heated base metal, (3) Melting of briquetted or solid filler material on the base metal, (4) Immersion of the heated part in a crucible with melt, (5) Centrifugal surfacing of cylindrical parts, (6) Melting of powder additive on the surface of the part, (7) Furnace surfacing of composite powders. Reinforcement of the molten surface layer of the base metal with refractory and sparingly soluble additive is performed by granular relit (tungsten carbide) or crushed metal-ceramic alloys. Relit together with flux (boric acid) is applied to the surface of the part. The part is placed in the inductor. The surface layer of the part is heated to the melting point and melted. The grains of the filler material do not melt and are immersed in the molten surface layer of the part. Fixation of relit grains in the matrix is due to their wetting with the melt and partial dissolution. The reinforced surface layer is a cast steel matrix with fused grains of the refractory component. Refractory particles do not change their structure and hardness. The method is easy to perform and provides high performance properties of surfaced parts. The method is used to strengthen the cones of drill bits.

126 Fig. 6.2 Diagram of induction surfacing by pouring liquid filler metal on the heated base metal: 1—surfaced part, 2—inductor, 3—refractory layer, 4—copper water cooling ring, 5—molten metal, 6—bucket

6 Induction Surfacing

5

1

3

6 2 4

Pouring liquid filler metal on the heated base metal is shown in Fig. 6.2. The part surface (1) is covered with a layer of flux and placed in the inductor (2). The surface of the inductor is protected by a refractory layer (3). After heating the part, the inductor is turned off. The bottom of the inductor is in contact with copper water-cooled ring (4). In the space between the part and the inductor molten metal (5) is poured from the bucket (6). The method of surfacing with liquid filler material is used for surfacing of parts operated in abrasive wear conditions: • • • • •

support rollers of tractors, details of coal-grinding mills, fingers of bucket excavators, bimetallic bushings, pushers of valves of automobile engines, etc.

In the case of surfacing of cast iron on the working surfaces of renewable parts, one can get a layer of white cast iron with high wear resistance [1]. The melting of briquetted or solid filler material on the base metal is illustrated by an example of surfacing of valves of internal combustion engines (Fig. 6.3). The filler material is a cast ring 3 of heat-resistant alloy Nickel-based (wt.%, %: C—1.2, Si—3.0, Mn—0.4, Cr—17.0, Ti—0.2, Al—0.6, Fe—3.0, B—1.5, Cu— 0.25, Ni—base). The ring is placed in the recess on the support surface of valve (1). Heating and surfacing take place in the annular inductor (2). Shielding gas (argon) is fed through inductor (5). The heating temperature is 50–100 °C higher than the melting temperature of the alloy. At the end of the process, the surface of the valve opposite to the surfaced one is wetted with water from the sprayer (4). This

6.2 Methods of Induction Surfacing

5

127

1

6

2

3

4 Fig. 6.3 Diagram of induction surfacing of valves of internal combustion engines by melting briquetted or solid filler material on the base metal: 1—surfaced valve, 2—ring inductor, 3—a ring made of heat-resistant alloy, 4—sprayer for water cooling, 5—protective gas, 6—clamp

provides directional crystallization of the alloy and ensures its increased performance properties. Immersion of the heated part in the crucible with molten metal is performed as follows (Fig. 6.4). Part (2) heated in the inductor (1) is immersed in a ceramic mold (3) with molten metal (4). The ceramic mold repeats the contours of the processed surface. The melting of the filler material is carried out by inductor (5). To deoxidize the melt, prevent burnout of alloying elements and improve the alloying with the base metal in the crucible flux (6) is added. In this method of surfacing the ratio of melting temperatures of the base and filler metals doesn’t matter. To increase cooling rate and ensure directional crystallization of the surfaced metal, forced cooling of the crucible with water can be performed (not shown in Fig. 6.4). The method is used in the restoration of the surfaces of the working bodies of parts operated in abrasive wear conditions (soil-cutting equipment, teeth of excavator buckets, etc.). Centrifugal surfacing of cylindrical parts can be performed in two ways with different states of the filler metal during the process [1]: (1) Filler metal in the solid state (Fig. 6.5a) in the form of metal powders, shavings, etc. The melting of the filler metal happens due to heat transfer from the base metal, which is heated by the inductor. (2) Filler metal in the molten state (Fig. 6.5b). Melting of filler metal takes place in a separate container. Liquid metal is poured into the rotating cylinder to be surfaced.

128

6 Induction Surfacing

2 1 6 3

5

4

Fig. 6.4 Diagram of induction surfacing by immersing a heated part in a crucible mold with molten metal: 1—heating inductor, 2—surfaced part, 3—ceramic crucible, 4—molten filler metal, 5— inductor for melting, 6—liquid flux

Features of the formation of the deposited layer under the action of centrifugal forces: • uniform distribution of the melt on the surface of the base metal, • removal of harmful impurities, • increase of liquation. Features of the formation of the deposited layer under the action of centrifugal forces are considered when determining the parameters of the surfacing mode: the amount of metal to be poured, temperature and duration of heating, rotation speed of the centrifugal machine, cooling rate of the deposited layer. Centrifugal induction surfacing is most common in the manufacture of bimetallic bushings: liners for automobile engines, liners for hydraulic cylinders and worm machines, plain bearings. Example: surfacing of lead bronze CuPb30 on plain bearings. The filler metal in form of bronze chips is mixed with flux (borax) in a ratio of 100:1 and poured into the sleeve, which is surfaced. The sleeve is rotated at a linear speed of 200- - 250 m/min. Current with frequency of 8000 Hz is supplied to inductor. Heating temperature is 1120- - 1150 C. Duration of surfacing- - - 28- - 30 s. The thickness of

6.2 Methods of Induction Surfacing

129

2 1

3

5 6 4

a 8

9 7

b Fig. 6.5 Diagrams of centrifugal induction surfacing using solid (a) and molten (b) filler material: 1 - spindle of the centrifugal machine, 2—surfaced part, 3—inductor, 4—gasket, 5—cover, 6— powder, 7—ceramic gutter, 8—molten metal, 9—bucket

the deposited bronze layer is 3.5- - 4.0 mm. After crystallization of the melt, forced cooling is carried out using a sprayer at a rate of 150 °C/sec. Melting of the powder additive on the part surface is carried out by induction heating of the base metal. Subsequent melting of the powder occurs due to heat transfer. When surfacing (Fig. 6.6) powder additive (1) (mixture of powder with flux, such as borax, boric anhydride, or calcium fluoride) is applied to the part surface (2). The part is inserted into inductor (3). The design of the inductor depends on the surface configuration of the part. The power source is usually a high-frequency generator with a frequency of about 70 kHz. The electromagnetic field of the inductor induces eddy currents in the surface layers of the part, which leads to rapid heating. The layer of powder additive practically does not react to the influence of an alternating electromagnetic field. The powder is heated mainly by heat transfer from the base metal. For this reason, the melting point of the additive must be lower than that of the parent metal. The flux contained in the powder additive provides dissolution of oxides, wetting of the surface and spreading of the melt on it. The method does not require special surface preparation of the product. It is possible to process both mechanically treated surfaces and those having a layer of oxides after rolling.

130

6 Induction Surfacing

3

1 2

Fig. 6.6 Diagram of induction surfacing by melting powder additive on the part surface: 1—powder additive, 2—surfaced part, 3—inductor

Melting of the powder additive on the part surface is the most common method of induction surfacing. It is used in mass production of plowshares, cultivator legs, cutter knives, parts of coal conveyors and other parts. Surfacing productivity reaches 10 kg/h. It is possible to obtain deposited layers with a thickness of 0.4 mm or more.

6.3 Materials for Induction Surfacing In furnace surfacing of composite powders, as a rule, relit is used - a eutectic mixture of tungsten carbides WC and W2 C with a granulation of 0.4–2.5 mm. The relit is intended for wear-resistant surfacing of parts operated under intensive abrasive wear with moderate impact loadings. Crushed cobalt titanium alloy powder can also be used. For induction surfacing of valves of internal combustion engines cast rings made of nickel-based alloys are used (mass ratio, %): (a)

P-616 (HX16C2P2): 1.2 C, 3.0 Si, 0.4 Mn, 17.0 Cr, 3.0 Fe, 0.2 Ti, 0.6 Al, 1.5 B, 0.25 Cu, 73 Ni, (b) P–869 (XH75TB ): ≤ 0.1 C, ≤ 0.8 Si, ≤ 0.3 Mn, 15.0–18.0 Cr, 19.1–27.4 Fe, ≤ 0.03 Se, 2.6–3.5 Al, ≤ 0.1 Ba, 55–58 Ni. Powders of iron-based alloys are used for induction surfacing of working bodies of agricultural, road and construction machines (Table 6.1).

Reference

131

Table 6.1 Chemical composition of metal powders for induction surfacing and deposited metal hardness Powder brand

Mass fraction of elements, %

HRC

C

Mn

Si

Cr

Ni

Other

PP-U30X28H4C4 (PG-C1)

3.0

1.2

3.5

29.0

4.0

–

49–52

PP-U40X27H2C2BM (PG-C27)

3.8

1.2

1.5

26.5

1.8

0.3 W; 0.1 Mo

51–54

PP-U50X38H2C2G2 (PG-UC25)

5.0

2.5

2.0

38.0

1.5

–

53–56

PP-U45X35G3P2C (PG-FBX6-2)

4.5

3.0

1.8

35.0

–

1.6 B

55–60

Powders of iron-based alloys

Iron-based surfacing mixtures 800X24G7C (C2M)

8.0

7.5

2.0

25.0

–

–

50–55

450X45PC (KBX)

5.0

0.5

1.3

47.0

–

–

56–60

50X40P7C (BX)

0.7

0.5

1.0

40.0

–

8.0 B

60–65

400X30G4P2C2 (FBX6-2)

4.5

4.0

2.0

32.0

–

1.7 B

50–55

Powder additive for induction surfacing is a mixture of metal powders (82–85%) with flux (the rest). The most widely used fluxes are a mixture of borax and boric anhydride (boric acid). The best spreading of the flux melt is provided when the mixture contains 40% of borax (Na2B4O7 × 10H2O) and 60% of boric anhydride (B2O3). To improve deoxidation, up to 10% of silicocalcium (ferroalloy containing 10–30% Ca, 6–25% Fe, 1–2% Al, < 0.5% C, Si—the rest) is introduced into the flux.

Reference 1. P bcev IA, Cenqenkov IK, Typyk B (2015) Haplavka. Matepialy, texnologii, matematiqeckoe modelipovanie. g.Glivice (Gliwice), Pol xa: Izd-vo Cilezckogo ´ askiej), 2015. – 590 c politexniqeckogo inctityta (Wydawnictwo Politechniki Sl˛

Chapter 7

Laser Surfacing

Abstract The physical phenomena and properties of the laser beam, the scheme of forced radiation, the design and functional scheme of the laser are considered. The methods of one-stage and two-stage surfacing, features of laser surfacing with filler wire and filler powder are analyzed. Directions for use and properties of nickel-based alloy powders, cobalt-based alloy powders, iron-based alloy powders, titanium-based alloy powders, and composite powders are given. Tables of brands and characteristics of the main types of filler wires and rods are provided. The parameters of laser surfacing are listed and examples are given.

7.1 Physical Phenomena of Laser Surfacing A laser (or optical quantum generator) is a device that converts pumping energy (light, electrical, thermal, chemical, etc.) into the energy of electromagnetic waves (laser beam), which have the following obligatory properties (Fig. 7.1): (1) coherence (Fig. 7.1a)—(coincidence in time) a constant phase difference in the time of the laser beam waves, which gives when compiling a wave of the same frequency of the total amplitude, (2) monochromaticity (Fig. 7.1b)—the same wavelength of the laser beam, (3) polarization (Fig. 7.1c)—fixed orientation of the vectors of electric and magnetic fields in space relative to the direction of propagation of the laser beam, (4) collimation (Fig. 7.1d)—small angle of divergence of the laser beam. Wavelength in the range of 0.33–10.6 μm (mainly visible light range with partial overlap of ultraviolet and infrared ranges) is used in lasers. Properties of the laser beam cause an extraordinary density of energy that is spent to heat and melt the filler and base metals during surfacing. Laser beam generation is based on forced radiation (Fig. 7.2)—the formation of a new photon γg during the transition of the atom from higher E1 to lower E0 energy level under the influence of the inducing photon γi . The energy of the inducing photon is equal to the energy difference (E1–E0) of the energy levels of the atom. The photon © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 I. Ryabtsev et al., Surfacing and Additive Technologies in Welded Fabrication, https://doi.org/10.1007/978-3-031-34390-2_7

133

134

7 Laser Surfacing

I

1

2

a

λ

b

E

d

c

α 0 H x

Fig. 7.1 Properties of the laser beam: a coherence, b monochromaticity, c polarization, d collimation (I–light intensity, λ–wavelength, E–electric field strength, H–magnetic field strength, α–angle of divergence of the laser beam, 1—wavelength range of the laser beam, 2—wavelength range of sunlight)

formed has the same wavelength, phase, polarization, and direction of propagation as the inducing photon. The inducing photon is not absorbed. Both photons are coherent (the resulting photon is an “exact copy” of the inducing photon).

+ γi

E0

γg

E1

γi

Fig. 7.2 Diagram of forced radiation: E0—lower energy level (normal state of the atom), E1— higher energy level (excited state of the atom), γi —inducing photon, γg —photon formed

7.1 Physical Phenomena of Laser Surfacing

4

2

135

5

1

6

7

3

Fig. 7.3 Functional diagram of the laser: 1—active medium, 2—photons, 3—pumping system, 4— reflective mirror of the optical resonator, 5—translucent mirror of the optical resonator, 6—focusing lens, 7—laser beam

This distinguishes the laser beam from spontaneous radiation, in which emitted photons have random directions of propagation, polarization and phase. The laser beam can be continuous, with constant power or pulsed, reaching extremely high peak power. The structure of lasers includes three main components (Fig. 7.3): (1) Active (working) medium (1)—a substance in which due to the forced radiation photons are formed, propagated and amplified (2). According to the physical state of the active medium, lasers are divided into solid-state, gas, liquid, and semiconductor, by the time of laser beam generation—continuous and pulsed. The active medium in solid-state lasers is optical glass with impurities of neodymium and other rare earth elements, in gas lasers—carbon dioxide or a mixture of helium and neon. (2) Pumping system (3)—an external source of energy for the excitation of the active medium, transition of atoms to a higher energy state and creation of conditions for forced radiation. The following devices can be used as an external source of energy: • • • •

gas discharge lamp (optical pumping)—in solid-state lasers, another low-power laser—in solid-state lasers, electric discharge—in gas and liquid lasers, current through the “p-n” junction—in semiconductor lasers.

(3) Optical resonator—a device containing several elements that repeatedly reflect the initial electromagnetic waves in the active medium and amplify the light flux due to: • lengthening the path during which new electromagnetic waves are formed by forced radiation,

136

7 Laser Surfacing 7

3

6

4

1

4

2

5

Fig. 7.4 Diagram of a powerful CO2 laser with accelerated longitudinal pumping: 1—tube with a mirror inner surface for the working medium (CO2 ), 2, 3—system of pumping the working medium, 4—electrodes of the high-frequency generator, 5—reflective mirror, 6—translucent mirror, 7—laser beam

• formation of resonant standing optical waves. A simple optical resonator consists of two mirrors—coaxial, parallel, and facing each other. One mirror is regular (4). The second mirror is translucent (5)—part of the light flux is reflected as from a mirror, and the other part of the light flux passes as through a lens and forms a laser beam (7). Widely used lasers for surfacing are: CO2 lasers (Fig. 7.4), solid-state lasers with diode pumping (Yb: YAG disk lasers, Nd: YAG lasers), high power fiber lasers (HPFL), high power diode lasers HPDL. Low-power lasers, including pulsed lasers, are used to apply layers of small thickness or for surfacing of small parts. The amount of thermal energy released on the surface of the material depends on: the wavelength and spatial distribution of the power density of the laser beam, the type of material, the state and temperature of the surface, the nature of the protective medium. The power density of the laser beam during surfacing is determined by the ratio of the power of the laser beam to the area of the heating spot and varies in range of 104–105 W/cm2 . The power of lasers used for surfacing is from 200 W to 10 kW. The efficiency of laser surfacing is ηe = 0.02–0.20. Areas of use of lasers: • • • •

cutting, welding, brazing and soldering, surface engineering—laser surfacing, vacuum-laser spraying, laser doping, 3D printing.

7.2 Methods of Laser Surfacing

137

Advantages of the laser beam: • high temperature, which allows to weld materials that cannot be welded in other ways (for example, metal and ceramics), • shallow penetration depth, which allows to obtain the desired composition and properties of the weld metal in the first layer • high concentration of energy, which minimizes the size of heat affected zone on the base metal, minimizes the level of residual stresses and strains, • the ability to focus on a point with a diameter of a micron, which fits microelectronic applications, • the ability to transmit energy over long distances in a non-contact manner, • possibility of use in the air, • high possibilities of automation of technological process

7.2 Methods of Laser Surfacing Laser surfacing is performed in one or two stages: (1) During one-stage surfacing (Fig. 7.5a) the filler material is fed directly into the surfacing zone in the form of powders, solid or flux-cored wires, rods.

Vc

Vc

1

1

4

3

2

a

5

3

2

b

Fig. 7.5 Methods of laser surfacing (a one-stage, b two-stage): 1—laser beam, 2—protective gas, 3—deposited layer, 4—filler wire, 5—applied filler material

138

7 Laser Surfacing

(2) During two-stage surfacing (Fig. 7.5b) at the first stage before surfacing the filler material is placed on a product surface using one of three methods: • spraying—allows to get thick deposited layers, • powder pastes, • powder with a binder component (glue). At the second stage, the applied filler material is melted by the laser beam by sequential scanning of the entire processed surface. It is recommended to focus the beam at some distance above the surface of the filler material—use a defocused laser beam—during the two-stage surfacing. In multilayer surfacing a layer of new filler material is applied after each pass. The main disadvantages of two-stage laser surfacing are low productivity due to the high complexity of the first stage of the process and the unevenness of the coating caused by the surface tension forces of the liquid metal. Laser melting of coatings with a thickness of more than 0.5 mm shows a tendency to form shrinkage cracks due to the large temperature difference. Due to the disadvantages of two-stage laser surfacing is used much less often than single-stage. Laser surfacing with filler wire (Fig. 7.5a) can be performed: • with cold wire, • with heated wire. The use of heated wire can increase the productivity of surfacing. The wire is heated before entering the area of the laser beam to a temperature close to the melting point with the current flowing through the wire. Laser surfacing with filler powder can be performed: • With lateral supply of powder and transporting gas by one nozzle (Fig. 7.6a)— widely used. The nozzle can be located either on the side relative to the beam or in front of the beam. • With lateral supply of powder and transporting gas by two nozzles (Fig. 7.6b)—less used. The nozzles are located radially symmetrically. • With coaxial supply of powder and transporting gas (Fig. 7.7). The conical nozzle of the plasmatron has channels for filler powder with transporting gas and channels for shielding gas. The powder stream directly enters the focus area of the laser beam. The method provides symmetrical supply of powder relative to the laser beam, uniform formation of beads, high productivity at low loss of powder, and high efficiency of surfacing of complex surfaces. The disadvantage of the method of coaxial supply of powder is its complexity. Methods of hybrid laser surfacing [1]: • Laser + MIG/MAG, • Laser + microplasma, • Laser + associated high-frequency heating.

7.2 Methods of Laser Surfacing

139

Vc

Vc

2

1

2

4

2

3

1

3

4

b

a

Fig. 7.6 Diagram of laser-powder surfacing with lateral supply of filler powder and transporting gas (a one nozzle, b two nozzles): 1—laser beam, 2—powder and transport gas supply nozzle, 3—deposited layer, 4—surfacing pool

1

2

5

6

7

3

4

Fig. 7.7 Diagram of laser surfacing with coaxial supply of filler powder: 1—laser beam, 2— focusing lens, 3—surfacing pool, 4—deposited layer, 5—supply of filler powder and transporting gas, 6—supply of shielding gas, 7—cooling system channel

140

7 Laser Surfacing

7.3 Materials for Laser Surfacing 7.3.1 Filler Powders Filler materials for laser surfacing are: • powders developed for plasma surfacing (Tables 3.1, 3.2 and 3.3), • special powders for laser surfacing based on Ni, Co, Fe, Ti. When choosing a powder for laser surfacing, the recommendations of the EN 14700 standard are used [2]. The particle size distribution of the powder determines the shape of the deposited bead, process performance and quality of the deposited metal. Powders of granulometric composition of 45–100 microns are usually used. The smaller powder forms a suspension in the air, the larger ones may not have enough time to melt. The possibility of using the powder of this particle size distribution is determined mainly by the design of the mixer and nozzle. Nickel-based powders for laser surfacing and their typical applications are given in Tables 7.1 and 7.2. Cobalt-based powders for laser surfacing are made of heat-resistant alloys of the Co–Cr–W alloying system (up to 65% Co, up to 35% Cr, up to 30% W and up to 3.5% C) (Table 7.3). They were developed for surfacing of parts operated at elevated temperatures in conditions of corrosion, abrasive and erosion wear, impact loads and friction of metal on metal (Table 7.4). If the resistance to wearing of stellite powder is insufficient, powders with high hardness, such as carbides WC, W2 C, borides and nitrides are additionally used. Corrosion-resistant and heat-resistant stellite powders of the 700 series in which tungsten is replaced by molybdenum are also used for laser surfacing (stellite 706, 712). Table 7.1 Chemical composition of nickel-based powders for laser surfacing [1] Alloy brand

Mass fraction of elements, % Ni

Co

Cr W

C

HRC Mo Fe

Si

Others

Deloro 22

BASE –

–

–

< 0.05 –

< 1.0 2.5 1.4 B

20–22

Deloro 30

–

9

–

0.2

–

2.3

3.2 1.2 B

27–31

Deloro 45

–

9

–

0.35

–

2.5

3.7 1.9 B

44–47

Deloro 50

–

11 –

0.45

–

3.3

3.9 2.3 B

48–52

Deloro 55

–

12 –

0.6

–

4.0

4.0 2.7 B

52–57

Deloro 60

–

15 –

0.7

–

4.0

4.4 3.1 B

57–62

0.08

Tribaloy T-700

< 1.5 16 –

32

< 1.5 3.4

< 1.0 B

45–52

EuTroLoy 16800

15

–

4.5 0.1

16

5

–

22–24

EuTroLoy 16221

–

4

–

–

≤ 2.0 2.5 1.0 B; 1.0 Al 27–30

0.2

–

7.3 Materials for Laser Surfacing

141

Table 7.2 Typical applications and characteristics of nickel-based powders for laser surfacing [1] Alloy brand

Alloy composition

Typical applications

Characteristics

PL 6416SH

Ni–Cr–B–Si–Fe + 60% WC

Screws of conveyors, High resistance to abrasive wear details of mixers, drilling and woodworking tools

PL 6421

Ni–Cr–B–Si–Al

Forms for pressing of glass, drawing matrices, intermediate layers on cast iron parts

High resistance to thermal shocks and high temperatures. High adhesion with gray and spheroidal cast iron

PL 6425

Ni–Cr–Mo–Nb–Fe

Details of ship systems, power plants, equipment of offshore drilling platforms, cryogenic equipment, tools for underwater works

High plastic properties. High corrosion resistance in seawater. High wear resistance at low temperatures

PL 6480

Ni–Mo–Cr–W

Details of mixers, systems for paper industry, knives of hot cutting, stamps of hot stamping, extruders, saddles of valves, parts of pumps of the chemical industry

High resistance against intergranular corrosion, against corrosion in oxidizing environment, in nitric and sulfuric acid. High corrosion resistance in acetic, lactic, citric and fatty acids, caustic soda and chloride-containing media

Table 7.3 Chemical composition of cobalt-based powders for laser surfacing [1] Alloy brand

Mass fraction of elements, % Co

Cr

W

HRC

C

Ni

Mo

Fe

Si

Others

Stellite 6

BASE 28.5 4.6

1.2

< 2.0 < 1.0

< 2.0

< 2.0

< 1.0

40–46

Stellite 12

30

1.45

< 2.0 < 1.0

< 2.0

< 2.0

< 1.0

43–53

Stellite 20

32.5 17.5 2.55

< 2.0 < 1.0

< 1.0

52–62

Stellite 25

20

15

0.1

10

Stellite 706

29

–

1.25

Stellite 712

29

–

EuTroLoy 16008

26

–

EuTroLoy 16012

30

EuTroLoy PG 5218

29

8.5

< 2.0

< 1.0

< 1.0

2.0

< 1.0

< 2.0

4.5

< 2.0

< 1.0

< 1.0

39–44

2.0

< 2.0

8.5

< 2.0

< 1.0

< 1.0

46–53

0.3

3

5.5

–

–

< 1.0

27–30

9

1.6

2

< 1.0

1.7

1.2

< 1.0

~ 46

5.3

1.3

2.1

< 1.0

1.9

1.2

< 1.0

46–50

1.9 Mn 20–45

142

7 Laser Surfacing

Table 7.4 Typical applications and characteristics of cobalt-based powders for laser surfacing [1] Alloy brand

Alloy composition Typical applications

Characteristics

PL 6406

Co–Cr–W–Ni–Fe

Valve seats, safety couplings, shaft sealing surfaces, wood and plastic processing tools, faucet parts, extruder screws

High resistance to abrasive wear under pressure and impact load. Heat resistance and corrosion resistance. Low coefficient of friction. Insensitivity to adhesion. High operating temperature—up to 700 °C

PL 6408

Co–Cr–Mo

Tools for hot processing, valve seats, couplings, shaft sealing surfaces, pump and turbine parts

Resistance to corrosion, temperature, cavitation, heat shock and creep. Strengthening under slander. Low coefficient of friction. Ease of machining, good polishing

Iron-based powders for laser surfacing (Tables 7.5 and 7.6) are made of supereutectic alloys of the Fe–Cr–C alloying system with a content of up to 35% Cr and 2–5% C. The addition of 1.5–2.0% of boron provides spherical shape of powder particles. There are no pores in the deposited layer. Titanium-based powders for laser surfacing are presented in Table 7.7. Composite powders (carbides, nitrides, or oxides) cladded with metal (Ni, Co, Al, Cu, Fe, Cr) are also used for laser surfacing. Composite powders provide functional characteristics, such as wear resistance, in the deposited layer. Metal is a binder. Table 7.5 Chemical composition of iron-based powders for laser surfacing [1] Alloy brand Delcrome 90

Mass fraction of elements, % Fe

Co

BASE –

Cr

W

27

–

HRC C 2.8

Ni

Mo Si

Others

–

–

1.0 Mn

1.0

60

Delcrome 92

< 0.5 < 1.0 ≤ 3.8 3.7

< 1.0 10

< 1.0 < 1.0 Mn 55–63

Tristelle TS-3

12

35

–

10

4.8

0.3 Mn

47–51

Delcrome 316

< 0.5 17

–

0.05 11

2.6

1.8

0.4 Mn

< 180 HV

Delcrome 317

< 0.5 18

–

< 0.03 13

2.6

1.8

0.7 Mn

< 180 HV

EuTroLoy 16316

–

17.5

–

≤ 0.03 13

2.7

–

–

140–170 HV

EuTroLoy 16604

15

15.0

–

≤ 0.2

–

–

–

2.5 Mo

43–46

EuTroLoy 16606

–

4.5

5.5

1.2

–

–

–

4V

43–46

3.1

7.4 Procedures of Laser Surfacing

143

Table 7.6 Typical applications and characteristics of iron-based powders for laser surfacing [1] Alloy brand

Alloy composition

Typical applications

Characteristics

PL 6316 Fe–Cr–Ni–Mo

Parts of the equipment of the chemical and food industry, sublayer when surfacing of a hard-alloy coating

High resistance to pitting and intergranular corrosion up to 400 °C. Heat resistance up to 800 °C. Good polishing

PL 6461N

Fan blades, crusher hammers, pump rotors

High resistance to abrasive wear at elevated temperatures and against erosion with moderate impacts

Tools for cold processing, knives for cutting thin sheets, cams, screws of extruders for plastics, equipment for cutting vegetables

High resistance to abrasive wear and wear caused by friction on metal

Fe–Cr–Ni–B

PL 6467 Fe–V–Cr–Mo

Argon, helium, carbon dioxide, air, and nitrogen are used as transporting gas. Type of gas does not affect the process of coating formation when surfacing is performed using self-fluxing powders. When using non-self-fluxing powders, it is necessary to use inert gases, because the oxidation of powders and as a consequence—the formation of pores and non-fusion of particles in the beads are taking place.

7.3.2 Filler Wires Filler wires and rods are used due to their wide range, which allows us to choose the material for different operating conditions of the surfaced part. The chemical composition of wires and rods corresponds to the composition of steels of different alloying systems, aluminum- and titanium-based alloys (Table 7.8) and copper. Titanium-based wires are used for surfacing of titanium alloys, for example, in medical and dental prosthetics. Aluminum-based wires are used for repair surfacing of products and tooling made of aluminum and its alloys. Copper-based wires are used to eliminate defects in parts made of copper and copper alloys, such as copper mold inserts.

7.4 Procedures of Laser Surfacing Laser surfacing parameters: • power of laser radiation in continuous mode (kW), • laser pulse energy (kJ), pulse duration (ms), pulse frequency (Hz) in pulsed mode,

≤ 0.30 –

≤ 0.40 –

≤ 0.25 –

≤ 0.10

≤ 0.08

≤ 0.08

LPW Ti 64

LPW Ti64 Gd5

LPW Ti 64Gd23

≤ 0.20 –

≤ 0.10 1.80–2.20

≤ 0.08

≤ 0.05

LPW CP Ti

LPW Ti 6242

Mo

Fe

Mass fraction of elements,%

C

Alloy brand

–

–

–

0.06–0.10

–

Si

3.50–4.50

3.50–4.50

3.50–4.50

–

–

V

–

–

–

3.60–4.40

–

Zr

Table 7.7 Chemical composition of titanium-based powders for laser surfacing [1]

5.50–6.50

5.50–6.75

5.50–6.75

5.50–6.50

–

Al

≤ 0.13

≤ 0.20

0.13–0.18

≤ 0.20

≤ 0.18

O2

≤ 0.012

≤ 0.015

≤ 0.012

≤ 0.012

≤ 0.015

H2

Others

≤ 0.03 –

≤ 0.05 –

≤ 0.04

≤ 0.05 1.80–2.20 Sn ≤ 0.005 Yt

≤ 0.03 –

N2

144 7 Laser Surfacing

7.4 Procedures of Laser Surfacing

145

Table 7.8 Brands and characteristics of filler wires and rods produced by Castolin for laser surfacing [1] Brand, standard, type of deposited metal, hardness

The material on which the surfacing is performed

LaserTech 45273 LA; 1.5424; Recommended for materials: 35CrMo8, 5XGM (1.2311)a ; EN 1668: W2Mo; ISO 21952: 40CrMnMoS86 (1.2312); 21MnCr5 (1.2162); GS20MoNi33 13 WMoSi; HRC 38–42 (1.2728) LaserTech 45301 LA; 1.2567; 3X2B4F; X32WCrV5; HRC 42–48

4X5MFC (1.2343); 4X5MF1C (1.2344); 4X5M3F, X38CrMoV5-3, (1.2367); X37CrMoW5 (1.2606); 20XH4M (1.2764); 45X2H4M, X45NiCrMoV (1.2767)

LaserTech 45303 LA; 1.3348; Recommended for materials: high-speed steels 1.3316; HS2-9-2; P2M9F2; HRC ~ 62 11P3AM3F2 (1.3333); HS 6-3-2 (1.3339); P6M5F3, HS 6-5-3 (1.3344); P2M9F, HS 2-9-1 (1.3346) LaserTech 45351 LA; 1.4718; EN 14700: S Fe6; 45X9C3; X45CrSi9-3; HRC ~ 60

X210Cr12 (1.2080); X155CrMoV12 1 (1.2379); X210CrW12 (1.2436); X165CrMoV12 1 (1.2601) and the like—X12MF, X153CrMoV12 (1.2379); Z160

LaserTech 45353 LA; 1.4115; X20CrMo171; HRC ~ 40

X33CrS16 (1.2085) and others of this type

LaserTech 45355 LA; 1.6356; X2NiCoMo18-9-5 and martensitic-aging Maraging steels X2NiCoMoTi 18 1; HRC ~ 35 LaserTech 45366 LA; EN 14700: S Fe3; EN: X37CrMoV5-1; HRC 53–58

40X13 (1.2083); 40CrMnMo7 (1.2311); 40CrMnMoS8 6 (1.2312); X38CrMoV5, 4X5MFC (1.2343), X40CrMoV5, 4X5MF1C (1.2344); X37CrMoW5-1 (1.2606), X19NiCrMo4, 20XH4M (1.2764); 45X2H4M

X38CrMoV5 1 (1.2343); X40CrMoV5 1 (1.2344, 1.2082); LaserTech 45367 LA; DIN 8555: WSG-3-GZ-45-T; HRC X38CrMoV5 3 (1.2606) 42–46 LaserTech 45368 LA; DIN 8555:WSG-3-GZ-40-T; HRC 38–42

X38CrMoV5-3 (1.2367)

LaserTech 45369 LA; 1.4122; X39CrMo17-1; 39X17M; HRC ~ 48

X17CrNi16-2 (1.4057); steel groups 300 (307, 308, 309, 316 etc.)

LaserTech 45553 LA; 1.4576; ISO 14343-A: W 19 12 3 Nb

X6CrNiMoTi 17 12 2 (1.4571); X10CrNiMoTi 18 12 (1.4573, 1.4580); G-X5CrNiMoNb 18 10 (1.4581), GX10CrNiMoNb18-12 (1.4583)

LaserTech 45612 LA; 2.4806; SG-NiCr20Nb; ISO 18274: NiCr20Mn3Nb

NiCr15Fe, Inconel 600 (2.4816, 2.4817); NiCr23Fe (2.4851); X10NiCrAlTi32-21, X10NiCrAlTi32-20, Incoloy 800H (1.4876); 304N (1.6907)

LaserTech 45860 LA; W. Nr ~ Titanium and its alloys 3.706; DIN 1737:WSG Ti 2 LaserTech 45651 LA; 2.4654; DIN: NiCr19Co14Mo4Ti

Nickel and its alloys

LaserTech 45802 LA; W. Nr 3.7036; EN AW-AlMg5

Aluminum alloys: AlMg1, AlMg2, AlMg3, AlMg5, AlMgMn, AlMgSi1, AlZnMg1

a Material

index according to EN standards is given in brackets

146

7 Laser Surfacing

• diameter of the focused beam, or shape and size of the beam spot (mm), • distance of the beam focus from the surface of the surfaced part (mm), • laser beam scanning parameters—shape (rectangular, trapezoidal, sinusoidal), amplitude (mm), frequency (Hz), • surfacing speed (mm/s), • filler powder particle size (μm) and its mass flow rate (g/s), • diameter of the filler wire (mm), wire feeding speed (cm/min) and angle of inclination of the filler wire (deg), • composition and consumption of shielding and transporting gas (l/min), • bead width (mm) and bead overlap (% of bead width). Derivative parameters are: • heat input—energy spent on melting the elementary volume of metal per unit length of the bead (J/mm), • power density—the ratio of radiation power to the area of heating spot (J/mm2 ), • powder utilization factor—the ratio of the mass of powder spent on the formation of the bead to the overall mass of spent powder. The power of laser radiation and deposition rate have the greatest effect on the geometric dimensions of the deposited beads. As the laser power increases from 1.5 to 3.5 kW, the width and height of the beads increase as the heating of the base metal increases and the utilization rate of the powder increases to 78%. When increasing the deposition rate from 8.3 to 50.0 mm/s, the width of the beads decreases twice, the height—by 4 times because the irradiation time of the unit per unit decreases, the amount of powder fed to the processed zone decreases, the melted zone decreases, and powder utilization factor decreases. In the pulsed mode, the formation of the deposited bead is significantly affected by the frequency of the pulses. Compared with the continuous process, the pulsed input of energy leads to the melting of certain volumes of metal-pools. The distance S between pools depends on the parameters of the pulsed mode: ( ) S = V c τpu + τpa

(7.1)

where Vc —surfacing speed, τpu —pulse duration table, τpa —pause duration. EXAMPLE 1 parameters of manual laser surfacing of the upper decorative layer with a thickness of 0.3–0.4 mm of the joint of pipes 33.9 × 3.2 mm diameter: • • • • • •

filler wire—Ø 0.6 mm, 45273 La Castolin Eutectic, energy of the laser pulse—11.5 J, laser pulse power—185 W, pulse frequency—20 Hz, pulse duration—9.5 ms, surfacing speed—1.0 cm/min,

References

147

• shielding gas—argon of high purity, • consumption of shielding gas—6 l/min. EXAMPLE 2 parameters of automated laser surfacing of steel extruder automated laser surfacing of steel extruder 14crmov 6–9 [1]: • • • • • • • •

filler powder—Stellite 6 diameter of the nozzle for feeding of filler powder—1.5 mm, mass consumption of filler powder–110 mg/sec, angle of inclination of the powder feeding nozzle- - - 45°, power of laser radiation—1100 W, diameter of laser beam spot—3 mm, distance from the nozzle tip to the surface—9.5 mm, distance of the beam focus from the surface of the part—200 mm, • consumption of argon for transporting of powder—4.8 l/min, • surfacing step—0.9 mm.

References 1. P bcev I.A., Cenqenkov I.K., Typyk .B. Haplavka. Matepialy, texnologii, matematiqeckoe modelipovanie. - g.Glivice (Gliwice), Pol xa: Izd-vo Cilezckogo ´ askiej), 2015. – 590 c politexniqeckogo inctityta (Wydawnictwo Politechniki Sl˛ 2. EN 14700:2014 Welding consumables—welding consumables for hard-facing. https://www.iso. org/standards.html

Chapter 8

Other Methods of Coating Production

Abstract Schemes of cladding processes by rolling and extrusion, which are used to obtain bimetallic sheets, plates, strips, pipes, rods, are given. Features of explosion cladding for the production of bimetallic plates, sheets, pipes, parts due to plastic deformation during high-speed movement of the workpiece are presented. An analysis of explosion cladding according to two schemes is given: angular and parallel. Directions for using these processes are indicated. Schemes of electrical resistance cladding carried out by welding steel wires, powders or strips to the surfaces of cylindrical and flat parts due to heating with powerful current pulses and simultaneous plastic deformation, are considered. The parameters of these processes and fields of application are indicated. Furnace surfacing of composite powders by impregnation of solid refractory tungsten carbides with a binder alloy under vacuum furnace heating conditions is considered. This provides deposited layers high wear resistance due to the high density of the composite powder. Considered features of electron beam surfacing, which ensures minimal mixing of the filler and base metals and the possibility of precise regulation of heating and melting of the base and filler metals. Friction cladding occurs by heating to a plastic state due to the friction of the additive material against the surface of the part, which is provided by high-speed rotation and pressing. The processes of plating with additive monolithic material and additive granular material are described. The parameters of these processes are provided. Prospective schemes of cladding with additive granular material are considered.

8.1 Rolling and Extrusion Cladding Rolling cladding—obtaining bimetallic sheets, plates, tapes, pipes, rods due to joint deformation when rolling strips or tapes in the hot state (basic method) or in the cold state (for highly plastic materials). Depending on the mechanical properties of the constituent layers of the workpieces, cladding is divided into: . rolling of packages, . roll rolling.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 I. Ryabtsev et al., Surfacing and Additive Technologies in Welded Fabrication, https://doi.org/10.1007/978-3-031-34390-2_8

149

150

8 Other Methods of Coating Production

Rolling of packages can be assembled according to different schemes (Fig. 8.1) depending on the functional purpose of the product. Packages for rolling cladding are made of: . . . .

multilayer ingots, workpieces obtained by multilayer surfacing, pre-sealed welded packages, multilayer workpieces obtained by explosion welding.

Roll rolling (Fig. 8.2) is used to obtain bimetals of small thickness. The layers included in such bimetal must have sufficiently high ductility.

2 1 b

a

3 c

d

Fig. 8.1 Diagrams of folding metals into packages for cladding by rolling sheets (a asymmetric two-layer package, b symmetrical two-sided package, c asymmetric package with a connecting sublayer, and d symmetrical two-sided package with a connecting sublayer): 1—base layer, 2—clad layer, 3—connecting sublayer

2

P 3 5

4

1

4

3

P

2

Fig. 8.2 Diagram of system for three-layer cold rolling: 1—unfolder with a roll of the main layer strip, 2—unfolder with a roll of the clad layer strip, 3—guide rollers, 4—working rolls of a rolling mill, 5—roll of three-layer strip

8.2 Explosion Cladding

2

151

3

4

5

6 1

P

Fig. 8.3 Extrusion cladding diagram: 1—part in the initial state, 2—matrix, 3—container, 4— workpiece, 5—press stamp, 6—punch

In comparison with package rolling roll rolling: . significantly increases productivity, . reduces time consumption, . provides ability of automation of technological process. Extrusion cladding (Fig. 8.3)—obtaining bimetallic round and shaped profiles by jointly pushing the materials to be joined through a hole in the tool (matrix). The joint formation is achieved due to preheating and intensive plastic deformation. Powders, granules, material of solid section are used as a clad material.

8.2 Explosion Cladding Explosion cladding—obtaining bimetallic plates, sheets, pipes, elements due to plastic deformation during high-speed movement of the workpiece (plate, sheet), rapidly coming towards a stationary workpiece or mutual countermovement of workpieces. Explosion cladding of plates and sheets (Fig. 8.4) is carried out according to two diagrams: (1) Angular (Fig. 8.4a): The workpiece (plate, sheet) of the clad metal (1) is located at a small contact angle α = 2–10° to the main workpiece (2). On the surface of the clad workpiece explosive charges (4) are placed. A detonator is installed near the top of the corner to explode the charge. The blast wave creates high pressure, and the clad workpiece is thrown at high speed (400–800 m/sec) towards the main workpiece. The workpieces are joined as a result of high-speed plastic deformation. The joint is formed at an angle of impact. The presence of the angle of contact ensures the extrusion of the remnants of the surface oxide films (5) in the direction of propagation of the explosion. The angular scheme is used when cladding workpieces of considerable thickness with a small surface area, such as slabs to be further rolled.

152

8 Other Methods of Coating Production

6

4

α

1 2 3

β

D a 5

γ

h

b Fig. 8.4 Diagrams of explosion cladding process of plates and sheets (a angular, and b parallel): 1—clad plate, 2—main plate, 3—flat base, 4—explosive charge, 5—remnants of extruded surface oxide films, 6—joint macrostructure

(2) Parallel (Fig. 8.4b): The workpiece (plate, sheet) of clad metal is located parallel to the main workpiece at a distance h. The impact angle γ is formed due to the double bend of the flying workpiece. The parallel diagram is simpler and more universal, it is used for cladding with thin sheets. Explosion cladding of pipes (Fig. 8.5) is carried out according to the angular diagram. When cladding the inner surface, the conical workpiece (1) of clad metal is placed inside the pipe (2). In this case, the angle of inclination of the cone is equal to the angle of contact α. The charge of the explosive (3) is placed inside the conical workpiece. The most important property of explosives is their ability to detonate. Detonation is a chain reaction that propagates with a constant velocity D for given charge parameters (Fig. 8.4). The constancy of the detonation velocity D ensures the quasistationary nature of the cladding process. The detonation velocity varies widely D = 1500–8000 m/sec. Ammonites, ammonals, tolls with D ≤ 3200 m/sec are used for explosion joining processes. The detonation front moves continuously from the initiation point to the end of the charge area.

8.2 Explosion Cladding Fig. 8.5 Diagram of preparation for explosion cladding of pipes: 1—conical workpiece made of clad metal, 2—pipe, 3—explosive charge

153

2

1

3

α

During explosion the chemical energy of the explosive is converted into: . mechanical energy of plate throwing, due to which plastic deformation and heating of the joining surfaces takes place, . thermal energy for heating of detonation products and environment, . mechanical energy of blast waves in the environment and metals. The joints are formed due to plastic deformation and heating of the surfaces. Explosive waves cause the wave nature of mechanical displacements and, therefore, the formation of waves of plastic deformations of the surface layers in joint area (6) are formed (Fig. 8.4). Due to the rapidity of deformation, 3D diffusion processes do not have time to develop, as a result explosion can be used to connect dissimilar metals and alloys. Before cladding, the surfaces of the parts must be cleaned and degreased. The process is performed in adapted soundproofed rooms (on sites, in swimming pools, chambers), or under foam. Areas of use: . plating of low-carbon structural steels with corrosion-resistant plastic steels of 12X18H9T type to produce bimetals for the petrochemical industry and agriculture, . plating of low-carbon steels with low-plastic tool steels such as P6M5, X6F1, X12 for mechanical engineering, . cladding of large products, such as turbine blades, structural elements of reactors with special alloys for heavy industry.

154

8 Other Methods of Coating Production

8.3 Electric Resistance Weld Cladding Electric resistance weld cladding—welding of steel wires, powders, or tapes to the surfaces of cylindrical and flat parts by heating with powerful current pulses and simultaneous plastic deformation. The scheme of electric resistance weld cladding of shaft with wire is shown in Fig. 8.6. Shaft (1) rotates. The guide sleeve (2) and the pressing roller (3) provide a spiral supply of wire (4). The welding current is supplied to the shaft and to the pressing roller. In the area of contact of the wire with the shaft a contact resistance appears, and heat is released. At the same time, a force F is applied to the clamping roller, which plastically deforms the heated wire. Heating and intense plastic deformation destroy the oxide films in the shaft-wire contact. A solid clad layer (5) is formed in the form of spiral overlapping beads. Diagram of electric resistance weld cladding of a flat part with powder is shown in Fig. 8.7. Powder (1) is applied to the surface of part (2) and rolled by current-supply rollers (3). The rollers are pressed by force F. In the area of contact of the powder with the upper roller a contact resistance appears, and heat is released. The powder is heated to a temperature of 0.8–0.9 melting point, deformed, connected to the part, and sintered. A clad layer (4) is formed with a porosity of 3–5% and high tear strength. Wear-resistant, refractory, hard-alloy powders are used for resistance weld cladding of knives of graders and bulldozers, cutting parts for agricultural machinery, shafts, bushings, etc. Fig. 8.6 Diagram of electric resistance weld cladding of shaft with a wire: 1—shaft, 2—guide sleeve, 3—pressing roller, 4—wire, 5—clad layer

4

2

Vc

1 5

3

F

Vc

F

8.5 Electron-Beam Surfacing Fig. 8.7 Diagram of electric resistance weld cladding of flat part with powder: 1—part, 2—powder, 3—current-carrying rollers, 4—clad layer

155

F 1

4

F

3

2

Vc

Vc 3

F 8.4 Furnace Surfacing Furnace surfacing of composite powders—impregnation of solid refractory tungsten carbides with a binder alloy under vacuum furnace heating. Part (1) (Fig. 8.8) with process shell (2) is installed on the pallet of the furnace (3). The wall of the process shell and the surface of the part have a gap between them equal to the thickness of the layer to be deposited. The gap is filled with composite powder (4). The part is closed with a lid (5). On top of the part crushed pieces of binder alloy (6) (e.g., cupronickel) is placed. The tray is lifted to the furnace (7). The air is pumped out of the furnace by a vacuum pump (8). When heated to 1150 °C, the binder alloy melts, flows into the gap and seeps through the composite powder. Due to the high density of the composite powder, the deposited layer is characterized by high wear resistance. The method is used in the metallurgical industry as well as in the manufacture of plain bearings for submersible oil pumps and other parts of drilling equipment.

8.5 Electron-Beam Surfacing Electron beam—the flow of accelerated electrons moving along close trajectories, the cross-sectional size of which is small compared to the length in the direction of flow. The electron beam can create energy of high density. The electronic gun (Fig. 8.9) creates an electron beam and consists of a vacuum housing (1), cathode assembly (2, 3, 4), anode (5) with an aperture for the electron beam, a magnetic lens (6) and a system of deflection of the electron beam (7).

156

8 Other Methods of Coating Production

6

5

8

1 2 4 7

3 Fig. 8.8 Furnace surfacing diagram: 1—surfaced part, 2—technological shell, 3—the pallet of the furnace, 4—composite powder, 5—cover, 6—pieces of binder alloy, 7—induction furnace, 8—air pumping system

Cathode (3) is heated to high temperatures. Because of thermoelectron emission, free electrons emerge from the heated metal and create an electron cloud around cathode (3). Cathode is located inside the control electrode (4), which forms and seals the electron cloud. Electrons of the electron cloud move in an electric field from cathodes (3, 4) to anode (5). Voltage between the cathodes and anode reaches tens of thousands of volts, so the electrons on the way to the anode gain significant speed and energy. The flow of electrons accelerates, passes through the hole in the center of the anode and is focused by magnetic lens (6). An electron beam is formed. The direction of the electron beam is controlled by the magnetic deviation system (7). The electron beam is directed to the deposited part (8). The part is moved by the manipulator (9). To ensure the free movement of electrons and to prevent the formation of an arc discharge between the electrodes in vacuum chamber (10), a deep vacuum (of the order of 1–10–2 Pa) is created by the vacuum system (11, 12, 13, 14). Surfacing is performed by filler solid or flux-cored wire. Flux-cored wire may contain alloying component only, as the surfacing is performed in a vacuum. Efficiency of electron-beam surfacing technology increases the use of loading vacuum chambers at the inlet and outlet of the main vacuum chamber, which are separated by shutters. At the time of surfacing, the inlet chamber is loaded, the

8.6 Friction Stir Surface Cladding

157

2 3

4

1 5 6

15 +

7 13

12

11 8

10

14 9

Fig. 8.9 Diagram of electron-beam system: 1—vacuum housing of the electronic gun, 2—heater, 3—cathode, 4—control electrode, 5—anode, 6—magnetic lens, 7—magnetic deviation system, 8—deposited part, 9—drive manipulator, 10—vacuum chamber, 11, 12—shutters, 13—diffusion pump, 14—forvacuum pump, 15—high voltage DC source

outlet chamber is unloaded and both chambers are pumped to a deep vacuum. After surfacing, the shutters are opened, and the parts are replaced. The surfacing of strips is carried out by continuous movement through two vacuum locks installed on the inlet and outlet sides of the main vacuum chamber. The main advantages of electron-beam surfacing are minimal mixing of filler and base metals and the ability to accurately control the heating and melting of base and filler metals.

8.6 Friction Stir Surface Cladding Friction stir surface cladding is performed by heating to a plastic state due to the friction of the filler material on the surface of the part, which is provided by high-speed rotation and pressing. The surface of the part can be flat (Fig. 8.10), or cylindrical (Fig. 8.10a and 8.11). The filler material can be monolithic (in the form of a cast, rolled or pressed rod)—Fig. 8.10, or granular (in the form of powder or shavings)—Fig. 8.11. During friction stir cladding with monolithic filler material (Fig. 8.10) the tip of the filler rod (2) is pressed to the surface of the part (1) with a force of F. The filler rod is rotated with an angular velocity ω. As a result of friction, thermal energy is

158

8 Other Methods of Coating Production 1

3

Vcr

F

Vcl 2

a

F

ω

3

ω 2

1

Vc

b

Fig. 8.10 Diagram of friction stir cladding with monolithic filler rod (a on a cylindrical surface, and b on a flat surface): 1—part, 2—filler rod, 3—clad bead

ω

ω

4 5

5

1

ω

1 1 3 2 5

3 3 2 2

4

F a

F

b

F

c

Fig. 8.11 Diagrams of cladding with filler granular material: (a cladding of the outer surface according to the direct scheme, b cladding of the inner surface according to the indirect scheme, and c cladding of the end surface according to the direct scheme), 1—part, 2—filler granular material (powder), 3—clad metal in a plastic state, 4—refractory tool, 5—auxiliary sleeve

8.6 Friction Stir Surface Cladding

159

released at the place of contact. The tip of the filler rod and the contact surface of the part are heated. The metal at the end of the filler rod becomes plastic. In the presence of pressure created by force F, the formation of metal bonds—the connection of the filler rod tip and the surface layer of the part in the contact zone—begins. The surface of the part is moved relative to the tip of the filler rod with a linear welding speed Vc —a clad bead (3) is formed. Part of plastic metal from the filler rod tip is extruded in radial directions with the formation of a mushroom-shaped head. It must be removed with a chisel during cladding. The main parameters of the friction stir cladding are: . angular velocity ω, . pressure created by the force F on the friction surface, . cladding speed Vc . Parameter values are mostly determined by the physical properties of the base material, primarily the coefficient of friction, as well as the melting point of the filler metal. EXAMPLE: FRICTION STIR CLADDING OF STEEL AND CAST-IRON PARTS WITH NON-FERROUS ALLOYS SUCH AS BRONZE AND BRASS. OPTIMAL PARAMETERS OF CLADDING: . ANGULAR VELOCITY Ω (RPM) IS DETERMINED FROM THE CONDITION OF PROVIDING A LINEAR SPEED OF MOVEMENT OF THE EDGE POINTS OF THE ROD TIP WITH A DIAMETER OF D (MM) IN THE RANGE OF (2.5–6) 103 MM/SEC, I.E. FROM THE CONDITION: ω=

(5 . . . 12)103 D

(8.1)

. PRESSURE ON THE ROD TIP 20–60 MPA. . CLADDING SPEED VCL OF LONGITUDINAL MOVEMENT OF THE ROD IS 0.65D PER ONE FULL ROTATION OF THE CYLINDRICAL PART (THIS ENSURES THE APPLICATION OF A SOLID LAYER OF DEPOSITED METAL WITH BEADS OVERLAPPING BY 1/3 OF THEIR WIDTH). Cladding with filler granular material (Fig. 8.11) is provided by the friction of the granules of the material with each other during their relative movement under pressure. Heating, compaction, sintering of granules and the formation of a clad layer are taking place. Cladding with granular filler material is performed according to two diagrams: (1) Direct (Fig. 8.11a and c)—a part itself is a rotating body and initial friction surface. Heating begins at the point of contact of the powder with the part. Heat distribution occurs by two mechanisms: . due to heat transfer,

160

8 Other Methods of Coating Production

. by engaging in the movement and, consequently, the friction of more distant volumes of powder. In the direct scheme, a part should be a more refractory element of the friction pair (usually made of steel or cast iron). (2) Indirect (Fig. 8.11b)—refractory tool is a rotating body and the initial friction surface. The heating of the contact area of the powder with the part and, consequently, the formation of the joint is due to the heat propagating from the contact area of powder with the refractory tool. During cladding with filler granular material, the greatest friction force, and therefore the greatest release of thermal energy and heating, occurs in the zone of maximum pressure—at the end of the rotating body. In this zone the sintered filler metal heated to a plastic state is formed. When plating the side surfaces, the clad metal in the plastic state is displaced under pressure into the gap between the part and the auxiliary sleeve (Fig. 8.11a), or into the gap between the part and the refractory tool (Fig. 8.11b). The size of the gap is equal to the thickness of the clad layer. During cladding according to the direct diagram, the part stops after completion of the formation of plastic clad layer on the entire surface of the rotation. The clad layer cools down, the process ends. During cladding according to the indirect diagram, after formation of the plastic clad layer on the entire surface of the part the refractory tool is removed without stopping the rotation. The clad layer cools down, the process ends.

Chapter 9

Additive Technologies

Abstract The principles of additive manufacturing are considered as the creation of three-dimensional objects by connecting materials layer by layer without the use of pre-made, as a rule, based on the data of digital computer 3D models. The classification of additive manufacturing technologies according to the methods of forming and fixing the next layer to be attached and according to the type of energy source for fixing the layer to be attached is given. The fundamental differences between additive technologies and surfacing technologies are indicated. The structural scheme of laser additive manufacturing for forming on the bed is described: (Bed Deposition) as layer-by-layer deposition by laser scanning of the plane above the surface of the previously applied layer of powder and turning on the laser over the points falling into the cross-section of the part. The parameters of laser additive manufacturing process are provided and the requirements for powders for additive manufacturing are indicated. The differences between electron beam additive technologies and laser technologies are indicated. The scheme of the industrial system for electric arc additive manufacturing by direct formation (Direct Deposition) of the hemisphere is considered. The key tasks of electric arc additive technologies are explained, namely, ensuring manipulation of the torch along a given trajectory in accordance with the program, which ensures the creation of the product and the minimization of the stress-deformed state of the part. Recommendations for the selection of electrode (filler) materials for electric arc additive manufacturing are provided.

9.1 Terminology and Classification There are three strategic directions for the development of technologies to produce metal parts (Fig. 9.1): (1) Subtracting technology—creating parts from larger workpieces by removing “excess” material. Subtractors include machining (cutting, milling, drilling, turning, planning, grinding) and thermal cutting. (2) Forming technologies—creating parts by providing a metal workpiece of the required shape and size. Forming technologies include rolling, stamping, bending, welding, surfacing. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 I. Ryabtsev et al., Surfacing and Additive Technologies in Welded Fabrication, https://doi.org/10.1007/978-3-031-34390-2_9

161

162

9 Additive Technologies

TECHNOLOGIES FOR MANUFACTURING OF METAL PARTS

Subtractive

Formative

Additive

Fig. 9.1 Technologies of metal parts production

(3) Additive technologies—creating three-dimensional objects by joining materials layer by layer without the use of workpieces, usually based on data from digital computer 3D models. Classification of additive technologies. (a) According to methods of forming and fixing of the next added layer: • Bed Deposition—forming a part on the technological surface by scanning the plane, turning on the heat source and melting the filler material at points that fall into the cross section of the part (Fig. 9.2). • Direct Deposition—direct formation of the part by moving the specified floating pool (Fig. 9.3). Heat energy from various sources and filler material are fed directly to the point of formation of the part. (b) By type of energy source to fix the added layer: • • • •

Laser melting, Electron beam melting, Wire arc additive manufacturing, Plasma additive manufacturing.

(c) By type of material for construction of the part: • made of metallic materials (powders, wires), • from liquid materials. The fundamental differences between additive technologies and surfacing technologies are given in Table 9.1.

9.1 Terminology and Classification

163

6

X

Y

11 3

4

5

12

2 9

1

10

7

8

Fig. 9.2 Diagram of laser bed deposition additive technology: 1—powder bed, 2—powder supply, 3—sintered detail, 4—laser, 5—laser beam, 6—X–Y scanning system, 7—build platform, 8—build platform piston, 9—powder dispenser platform, 10—powder dispenser piston, 11—recoated arm, 12—mini-pool

X Z 5

1

3 4 6

2

Y

Fig. 9.3 Direct deposition wire arc additive manufacturing system for hemisphere manufacturing: 1—hemisphere, 2—faceplate, 3—torch, 4—electrode wire, 5—beam, 6—rack

Fabrication of a part layer by layer using additive technologies provides exceptional opportunities: • creation of gradient materials—parts with variable cross-sectional and thickness properties by changing the composition of the powder (filler wire) during the formation of layers,

164

9 Additive Technologies

Table. 9.1 Differences between additive technologies and surfacing technologies Additive technologies

Surfacing

• Involve the manufacture of parts from “zero” • Is performed on the surface of parts—new to the final shape and size (manufacturing surfacing), or worn after a certain period of operation (restorative surfacing) • Are performed by robotic systems using a three-dimensional computer model (CAD-model)

• Involves automated, mechanizing manual technologies

• Do not require machining of manufactured parts, or it is minimized

• Requires mandatory machining of surfaced parts (except for parts in which machining is not provided by the specifications)

• Are based on the use of concentrated energy sources

• Is based on the use of wide range of energy sources

• creation of light and rigid mesh structures and structures with multi-hollow walls, which cannot be made by casting or machining.

9.2 Laser and Electron Beam Melting Laser melting—layer-by-layer surfacing by laser scanning of the plane above the surface of the pre-applied layer of powder and the inclusion of the laser over the points that fall into the cross section of the part. The industrial system for laser melting (Fig. 9.2) consists of a powder bed (1) and a powder supply (2). In the initial state, the build platform (7) is in the uppermost position, the powder dispenser platform (9) is in the lowest position. The powder supply is filled to the top with powder. The upper plane of the powder is aligned with the layer-by-layer application device—recoated arm (11). The cycle consists of the stage of filling the powder layer and the stage of spot surfacing of the powder layer. At the stage of filling the powder layer the powder dispenser piston (10) moves up the platform of the powder dispenser (9) by a distance equal to the thickness of one surfacing layer. Piston (8) moves down the build platform (7) by a distance equal to the thickness of one welded layer. The recoated arm (11) is moved from the extreme left position of the powder supply to the extreme right position of the build platform. In this way, a layer of surfacing powder is transferred from the powder supply to the build platform. At the stage of spot surfacing of the powder layer the X–Y coordinate system (6) scans the laser (4) in a plane above the surface of the powder layer. Pulsed laser is switched on at the scan points that fall into the cross section of the part. The volume of the metal is melted with a height equal to the thickness of the bulk powder and

9.2 Laser and Electron Beam Melting

165

a cross-sectional diameter equal to the diameter of the laser beam (5). A floating mini-pool (12) is formed. After laser scanning of the plane, the step of filling the next layer of powder is repeated. Parameters of laser melting: • laser power (kW), • laser pulse energy (kJ), pulse duration (msec.), pulse frequency (Hz) in pulse mode, • diameter of the focused beam or size of the heating spot (μm), • distance from the focus of the beam to surface distance (mm), • scanning speed along the X axis (mm/sec), • scanning step—moving along the Y axis when reaching the extreme position (μm), • particle size distribution of additive powder—particle size (μm), • composition of the protective environment. Power of laser radiation and size of the heating spot are selected depending on the configuration of the part: • decreased—in the manufacture of small and thin-walled elements, • increased—in the manufacture of massive elements. Lasers with a power of about 5 kW provide a fairly high productivity—rate of layer formation can reach 1 kg/h. at the sizes of a heating spot of 15–25 microns. The particle size distribution of the filler powder and scanning step are chosen depending on the configuration of the part and the requirements for surface quality. Reducing the particle size distribution of the filler powder and reducing the scanning step provide: • more relief processing of small elements of the part, • smoother surface of the part. Laser melting powders consist of two groups: • powders for laser surfacing (Sect. 7.3.1), • powders from new materials of special purpose which are produced by powder metallurgy technologies. Metal powders with a particle size of 10–100 μm are used. The general requirement for powders for additive technologies is the spherical shape of the particles. This ensures maximum density and good “fluidity” of powders in filler supply systems. Gas pores in the deposited layers are the main problem of laser melting. The cause of gas pores is the low density of the powder, the presence of internal pores in the particles and process parameters. For example, for aluminum alloys porosity can reach 4–5%, for titanium alloys—up to 2%, for steels—up to 0.2%. Porosity can be lowered by means of heat treatment, pressure treatment (including hot isostatic

166

9 Additive Technologies

pressing) and re-melting of the layers. As a result, the porosity is reduced by an order of magnitude, but manufacturing time of the part increases twice. Laser melting is unique for the manufacture of: (a) Parts made of new materials. New materials with a wide range of required characteristics are obtained by powder metallurgy technologies. Laser melting significantly expands the possibilities of manufacturing parts immediately after the development of a new powder material. (b) Parts of complex spatial configuration. Laser melting do not limit the geometry of the part and, apparently, provide an opportunity to make assemblies in one operation. At the same time at the points of contact of the two parts the laser is not turned on and a gap is provided. Disadvantages of laser melting Advantages of laser melting are are • High efficiency and environmental friendliness due to the absence of waste. The powder that remains on the building • High cost and complexity of platform after the part is made is filled into the powder supply equipment, including • High productivity due to the exclusion of operations of layer-by-layer scanning preparation, assembling and machining of parts software • Limited overall dimensions of parts

Electron beam melting differs from lasers ones with using an electron-beam gun as a source of energy to fix the adjoining layer and the need to perform the process in a vacuum chamber (Sect. 8.5). Electron beam creates a heating spot 0.2–1.0 mm in size, which is more than an order of magnitude larger than the laser beam. Therefore, in terms of surface cleanliness and manufacturing accuracy, Electron beam melting are inferior to laser ones. Advantages of electron beam melting are: • High productivity—7–18 kg/h. when using powerful electron-beam guns, which allows manufacturing of massive parts, • Possibility of using a wide range of filler materials (metal powders, wires, rods) of stainless and tool steels, nickel and cobalt alloys, etc., • No requirements for additional protection against oxidation, as the process of forming the part takes place in a high vacuum. .

9.4 Calculation of Stress–Strain State

167

9.3 Wire Arc Additive Manufacturing Wire Arc Additive Manufacturing—manufacturing of a new product of the required shape and size by multilayer electric arc surfacing. The key tasks of wire arc additive manufacturing are: (a) Ensuring that the torch is manipulated on a given trajectory according to the program that ensures creation of the product. The main unit of the manufacturing system for wire arc additive manufacturing is the torch manipulating mechanism. It is advisable to use robots to produce oversized parts. Portals are used to make large products. An example of the wire arc additive manufacturing system of the hemisphere is given on Fig. 9.3. The hemisphere (1) grows on the faceplate (2), which provides movement along the Y axis with the deposition rate. The imposition of parallel rollers is provided by moving the torch (3) on the beam (4) (X axis). The formation of the next layer is provided by moving the beam up rack (5) (Z axis). (b) Minimization of the stress–strain state of the part being manufactured can be ensured by: • in-process heating (local or general) parts to temperatures of 100–500 ºC depending on the material and design of the product (larger products are heated to higher temperatures), • use of CMT surfacing (Sect. 2.6), which provides minimal thermal impact on the product. Electrode (filler) materials for wire arc additive manufacturing include two groups: • materials for electric arc surfacing (Sects. 2.8.2 and 2.8.3)—used for the manufacture of parts that are operated in conditions of friction, aggressive environment, high temperatures, • welding materials (solid and flux-cored wires made of low-carbon low-alloy steels). Only wires of small diameter—up to 1.6 mm are used in wire arc additive manufacturing.

9.4 Calculation of Stress–Strain State Uneven heating during layer-by-layer application of molten metal in additive manufacturing forms a stress–strain state, which can lead to residual deformations or cracks in the finished parts.

168

9 Additive Technologies

The method of calculating the stress–strain state of parts can be based on the theory of growing bodies [1], which most closely simulates the process of multilayer formation. Mechanical behavior of the material is described by the Bodner-Partom model [2], which includes the following relations in the rectangular Cartesian coordinate system: • Law of flow and equation of plastic non-compression: p

e

p

´ i j = ´ i j + ´ i j ; ´ kk = 0; i, j = x, y, z

(9.1)

• Prandtl-Reiss flow law: p ´ij



   1 K 0 + K 2n = 1 exp − Si j √ 2 3J2 J22 D0

(9.2)

where: 1 Si j Si j ; 2 1 Si j = σi j − δi j σkk ; σkk = σx x + σ yy + σzz 3 J2 =

• Evolution equation for the isotropic strengthening parameter K: '

K = m 1 (K 1 − K )W0 ; K (0) = 0 .

(9.3)

p

where W = σij ε˙ ij , D0 , K0 , K1 , m1 —model parameters p

• Hooke’s law: σkk = 3K v (εkk − 3α(θ − θ0 ));   p si j = 2G ei j − εi j ;

(9.4)

1 ei j = εi j − εkk δi j 3 where G, K v , α—shear modulus, volumetric compression modulus and linear thermal expansion coefficient. The relations are supplemented by universal equations of quasi-static equilibrium and thermal conductivity, as well as boundary and initial conditions. There are two possible models of the process of building a product by multilayer formation: • the first—bead formation of layers (Fig. 9.4a),

9.4 Calculation of Stress–Strain State 1 1 1

2 2 2

3 3 4 3 4 2 5 6 3 4 15 6

7 7

8 n 8 n

169

3

a

2

1

b

Fig. 9.4 Process diagrams of building the product by multilayer formation: a bead formation of layers (numbers indicate the numbers of beads in the order of their application in each layer), b continuous formation of layers (numbers in circles indicate the numbers of layers)

• the second—simultaneous formation of layers (Fig. 9.4b). Time interval between the connections of these beads or layers, their size, material temperature, cooling time, etc. are selected from the condition of equivalence to geometric, energy and other parameters of the technological process of formation. The finite element method is used to simulate bodies growing in the process of formation. The finite element grid (FE grid) covers both the part that is formed and all the layers that will be formed. Thus, the number of FE-grid nodes does not change in the process of numerical simulation. Areas of formation are initially attributed to the properties of the thermoelastic material with the following characteristics: E = 0; ν = 0.5; α = 0

(9.5)

where E—elasticity modulus, v—Poisson’s ratio, α—coefficient of linear thermal expansion. The value of Poisson’s ratio is chosen from the condition of non-compression of the formed material. At the same time only deformation of shape changing can take place. Thermophysical properties of the “void” of the FE-grid are assumed to be the same as those of the formed metal. Thus, the element is “empty” only in terms of mechanics. In the process of formation, the “empty” elements of the FE-grid will be filled with the melt of the formed material. It is important to keep in mind that in the process of filling the elements (formation) the whole FE-grid is deformed—both the part and the “empty” elements. Let’s assume that at the time of filling some empty element of the FE grid adjacent to the building surface has a deformation. Let it be filled with a melt of a material that has a temperature and is unstressed at the time of filling. Then in the formed element: 6i j = 0, i, j = x, y, z when t = t ∗

(9.6)

170

9 Additive Technologies

Condition (9.6) in terms of defining equations can be written as:   6i j ε ∗kl , θ ∗ = 0i n t he F E − gr i d el ement △V t ∗ i , j , k, l ↔ x, y, z

(9.7)

Equation (9.7) indicates the absence of stresses (condition (9.6)) in the formed element △V , which has initial deformation ε ∗i j at filling temperature θ ∗ . It is assumed that non-elastic deformation of surfaced material at the moment of time t * of grid element filling is absent: p ε i j t ∗ = 0i n t he F E − gr i d el ement △V (t ∗ )

(9.8)

For conditions (9.2) and (9.3) to be satisfied, it is necessary to modify Hooke’s equation for isotropic material (9.4) at t > t * as follows:   p s i j = 2G f e i j − ε i j − e∗i j ;  6kk = 2K f (ε kk − ε kk ∗ 3α f θ − θ ∗

(9.9)

and to assume in Eqs. (9.2) and (9.3):  p ε i j t ∗ = 0; K t ∗ = 0;   K0 t ∗ = K0 f θ ∗ ;

(9.10)

The lower index f indicates that the parameters refer to the material of the formed layer. Thus, to satisfy condition (9.6) in the growing surface layer, for all elements of the formed material the defining Eqs. (9.1)–(9.4) are individualized by those specific values of deformation εij * and temperature θ * at which they were filled at the time t = t* . A common example is the spiral formation of the side surface of the cylinder. In the longitudinal section, the scheme of filling the formed layer with separate beads (Fig. 9.4a) is shown in Fig. 9.5. Let the beginning of the formation of the Nth roller correspond to the time t = t N . The process sequence is as follows: (1) In the time interval (tN , tN + tQ ) (where tQ —effective operating time of the heating source) simultaneous heating is going in: (a) the “empty” area (3) with evenly distributed volumetric heat source with power QK (index K—formation), (b) the adjacent region (4) with an electric arc, which is a volumetric heat source of power QL (index L—arc). (2) At the moment of time t = tN + tQ both sources are turned off and “filling” of area (3) is happening, which means the replacement in this area of “empty” material with properties (1) with material described by the system of Eqs. (9.1)–(9.4)

9.4 Calculation of Stress–Strain State

171 δ1

a 3

2

b δ2

r

4 1

z Fig. 9.5 Diagram of filling the Nth bead: 1—part, 2—previously formed (N −1) bead, 3—area corresponding to the current Nth bead and to be filled (before filling—”empty” area), 4—heated areas of the part (δ2) and the pre-bead (δ1)

taking into account modifications (9) and (10), where εij * and θ* —deformation and temperature at the nodal points of region (3) at the time of filling. (3) In the time interval (tN+Q + t N+1 ) cooling is happening due to thermal conductivity into the part and heat exchange with the environment. (4) At the moment of time t = t N+1 a new mechanically “empty” element is joined and the process is repeated. (5) The heat Q going into the part during the formation is determined by the ratio:  Q = ηT η E + ηY I U△t 1 = Q E + QY

(9.11)

where ηT —effective power coefficient, ηE —efficiency of heating of parts with the ˛ E and O ˛ Y —heat, which, arc, ηY —efficiency of heating of parts with the filler metal, O respectively, is transmitted to the part from the arc and from the filler metal: Q E = ηT η E I U△t 1 ; QY = ηT ηY I U△t 1

(9.12)

where △t1 —the surfacing time of several beads, which is determined based on the geometric dimensions of the surface formed and the surfacing rate. Corresponding volumetric capacities of heat sources are calculated by the formulas: QE =

QE QY ; QY = V Et Q VY t Q

(9.13)

where VE —the volume of the area in which the heat source acts, obtained by rotating a flat figure (4) or (3) of the meridional section around the axis of the part, VY —the

172

9 Additive Technologies

volume of the area obtained by rotating figure (3) (Fig. 9.5), tQ —effective time of heating source operating. The following values of geometric parameters are accepted for filling diagram (Fig. 9.5): δ1 = 10−3 i, δ 2 = 0, 5 × 10−3 i, parameters a and b are determined by the width and height of the bead. Values δ1 , δ 2 and tQ are selected by numerical experiment under the condition of approximate equality of temperatures in volumes VE and VY at the time of filling the area of the bead (3) with molten material.

References 1. Apyt n n H.X., Dpozdov A.D., Haymov B. . Mexanika pactywix v zkoyppygoplactiqnyx tel. – M.: Hayka, 1987. – 471 c 2. Bodner SR (2000) Unified plasticity – an engineering approach (final report), faculty of mechanical engineering, Technion – Israel Inst. of Techn. Haifa 32000, Israel, 105p

Chapter 10

Structure and Properties of Surfaced Metal of Different Alloying Systems

Abstract The classification of surfacing materials in accordance with the EN 14700 standard is given, which divides surfacing materials into 30 groups, including: 18 groups of iron-based steels and alloys (Fe1-Fe17; Fe20); 5 groups of nickel-based alloys (Ni1-Ni4; Ni20); 3 groups of cobalt-based alloys (Co1-Co3); 1 group of chromium-based alloys (Cr1); 2 groups of copper-based alloys (Cu1; Cu2); 1 group of alloys based on aluminum (Al1). The surfacing methods that are recommended for the respective groups of surfacing materials are listed. For each group of materials, along with chemical composition, structure and hardness, mechanical properties and performance characteristics are determined. For each group of surfacing materials, the phase composition of the structures is provided, which is illustrated with appropriate symbols and explanations. Examples of application of all groups of materials in conditions of various types of wear are given. An algorithm is provided that allows the developer to choose the most effective coating material depending on the products’ operating conditions and type of wear.

10.1 General Classification of Surfacing Metals of Different Alloying Systems and Typical Applications According to EN 14700:2014 World companies produce a wide range of surfacing materials of various chemical compositions—mainly steels and cast irons, less—non-ferrous alloys. To systematize the chemical composition and properties of the standard EN 14700: 2014 [1] divides the surfacing materials into 30 groups (Table 10.1). • • • • • •

18 groups of steels and alloys iron-based (Fe1-Fe17, Fe20), 5 groups of nickel-based alloys (Ni1-Ni4, Ni20), 3 groups of cobalt-based alloys (Co1-Co3), 1 group of chromium-based alloys (Cr1), 2 groups of copper-based alloys (Cu1, Cu2), 1 group of aluminum-based alloys (Al1).

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 I. Ryabtsev et al., Surfacing and Additive Technologies in Welded Fabrication, https://doi.org/10.1007/978-3-031-34390-2_10

173

–

≤ 20

–

≤ 0.3

ckpv

cgtz

Fe17

Fe20

10–40

gz

Fe16

25–40

20–40

4–8

1.5–4.5

3–7

g (c)

g

Fe14

≤7

≤ 1.5

g

Fe13

Fe15

17–32

17–27

≤ 0.3

≤ 0.12

cnz

c n (z)

Fe11

≤ 20

17–22

≤ 1.2

≤ 0.25

Fe12

k p (n)

c k p z (n)

Fe9

Fe10

5–20

0.2–2

gpt

Fe8

≤ 10

11–30

≤ 2.5

≤ 0.2

gps

cpt

Fe6

Fe7

≤ 0.1

≤ 0.5

cpstw

Fe5

≤5 –

–

8–20

≤ 10

≤3

– –

≤2

≤4 ≤2

≤3 ≤3

≤4 ≤4

≤4

≤4

≤4

≤ 1,5

≤3

≤3

≤3

3–8

≤2

≤5

≤3 9–20

≤2

≤3

3–5

≤3

≤3

≤1

≤ 10

≤5

≤4

≤1

Mo

≤4

9–26

8–20

7–11

≤5

–

≤6

–

17–22

≤3 ≤3

≤5 ≤4

1–15

2–10

0.1–0.5

0.2–1.5

st

s t (p)

Fe3

Fe4

≤ 4.5 ≤ 3.0

≤3 ≤ 1.0

≤ 3.5

Mn

≤ 7.0

≤ 0.4

0.4–1.5

p

p (g) (s)

Fe1

Ni

Cr

Mass fraction of elements (%)

C

Fe2

Properties

Alloy symbol

–

≤ 0.3

≤ 10

–

–

–

–

–

–

–

≤2

–

–

–

≤ 20

≤ 10

≤1

≤1

W

–

–

≤ 10

–

–

–

–

–

–

≤1

≤2

≤1

–

–

≤4

≤ 1.5

≤1

≤1

V

–

–

≤ 10

≤ 10

–

–

≤ 1.5

≤ 1.5

≤ 1.5

–

≤ 10

≤1

≤ 10

–

–

≤3

–

–

Nb

B A S E

B A S E

Fe

10–15

–

–

–

–

–

–

–

–

–

–

–

10–15

≤5

≤ 13

≤1

–

Co

Table. 10.1 Classification (alloy symbol) and chemical composition of surfacing metals according to EN 14700:2014 [1]

–

–

–

–

–

–

–

–

–

–

–

–

–

–

–

≤1

–

Cu

–

–

–

–

–

–

–

–

–

–

–

–

≤1

–

–

–

–

Al

(continued)

WC

Si

Si, B

Si, B

Si

Si, B, Ti

Si

Si, Cu

Si

Si, Ti

Si, Ti

Si, N

Si, Ti

Si, Ti

Si, Ti

Si, Ti

Si, Ti

Si, Ti

Others

174 10 Structure and Properties of Surfaced Metal of Different Alloying Systems

–

Any other agreed composition

–

–

≤ 0.5

Z

–

–

10–35

–

cn

Al1

–

≤ 15

≤6

–

c (n)

≤6 –

≤1 ≤2

–

Cu2

–

1–5

–

gn

c (n)

Base

≤1

≤2

≤4

Cr1

20–35

1–3

≤ 10 –

0.1–2 0.1–2

–

≤ 30

≤6

10–30

≤6

Mo

≤ 10

–

≤ 1.5

≤1

≤ 1.5

≤1

Mn

≤4

B A S E

Ni

Cu1

t z (c) (s)

Co3

20–35

20–35

0.6–3

≤ 0.6

cktz

t z (c) (s)

Co1

Co2

–

–

cgtz

Ni20

≤ 15

1–20

≤1

≤ 0.1

cpt

c k p tz

Ni3

Ni4

15–30

14–30

≤1

≤ 0.1

cpt

ckptz

Ni1

Cr

C

Mass fraction of elements (%)

Ni2

Properties

Alloy symbol

Table. 10.1 (continued)

–

–

–

–

6–15

4–10

≤ 15

–

≤8

≤2

≤8

≤2

W

–

–

–

15–30

–

–

–

–

≤1

≤1

≤1

≤1

V

–

–

–

–

–

–

≤1

–

≤5

–

≤5

–

Nb

–

≤5

≤5

≤5

≤5

≤5

≤5

–

≤3

≤5

≤ 10

≤5

Fe

–

–

–

B A S E

–

≤ 15

–

≤5

–

Co

≤6

B A S E

–

–

–

–

–

–

–

–

Cu

Base

≤9

7–15

–

–

–

–

≤3

–

–

–

Al

Si

Sn

Sn

Si, B, Zr

Si

Si

Si

WC

Si, Ti

Si, B

Si, Ti

Si, B

Others

10.1 General Classification of Surfacing Metals of Different Alloying … 175

176

10 Structure and Properties of Surfaced Metal of Different Alloying Systems

Chemical composition and structure of the surfacing materials determine mechanical properties and performance characteristics of coating (below the designation of properties is given in accordance with Table 10.1). Hardness is a property of the material to resist the penetration of another, harder body. The main units of hardness are HRC and HB. HRC (Rockwell hardness)—is determined by the relative depth of indentation of the diamond cone into the surface of the material. HRC is a dimensionless quantity used for solid materials. The maximum value is HRC 67. HB (Brinell hardness)—is defined as the ratio of the force applied to the ball to the area of the part of the sphere that is the imprint. The unit of measurement is MPa (or N/m2 ). HB is used for soft materials. Within one group of surfacing metals the hardness depends on wear resistance, abrasion resistance, preservation of the cutting edge of cutting tools, etc., so hardness is one of the main characteristics of the deposited metal. Strength—the property of the material to resist destruction, as well as irreversible changes in shape under external loads. It is determined by the tensile strength (MPa)—the level of maximum stresses at which failure occurs. For composite materials, the strength of the matrix material, which keeps the particles of the reinforcing phase in the deposited layer on the surface of the reinforced part, is of great importance. Strength of the particles themselves, their ability to resist breakage and chipping are important as well. In addition, strength ensures preservation of the cutting edge of cutting tools. Plasticity—the property of materials under the impact of external forces to change their shape and size and retain deformation after the elimination of these forces, i.e., the property to deform plastically. Plasticity is determined by the residual elongation at break (%). Strengthening during operation (k) is a property of metal, which is the loss of plasticity of surface layers as a result of plastic deformation under the action of operational factors, primarily impact loads and temperatures. Operational hardening increases the hardness of the surface but reduces its toughness. The property of the deposited metal to strengthen under impact loads is used in surfacing of parts that are operated in conditions of shock-abrasive wear or friction with impact loads. Cutting edge preservation (s) is a complex ability of the material which is characterized by high hardness and high strength at the same time. Preserving the cutting edge is important for cutting tools. Resistance to chipping (z) is a complex ability of the material which is characterized by high toughness and high strength. Resistance to chipping is important for parts that operate under impact loads and abrasive wear. Impact toughness (p) is a property of a material to absorb mechanical energy during deformation and fracture under the action of impact load. Impact toughness is defined as the energy lost to form a unit of free surface in the event of impact failure of a notched specimen (J/cm2 ). High toughness is important when surfaced parts operate under fatigue and impact loads. Nonmagnetic material (n) is a material with no effect of partial ordering of the directions of magnetic moments of individual atoms or magnetic domains when an

10.1 General Classification of Surfacing Metals of Different Alloying …

177

external magnetic field is applied. The use of non-magnetic surfacing materials eliminates the possibility of using magnetic powder method and the method of magnetic anisotropy for non-destructive testing of parts. Wear resistance—ability of a material to resist destruction of the friction surface, which is accompanied by a change in the size and shape of the part. Wear resistance is characterized by the amount of wear during the test for friction of metal on metal with a certain pressure. Wear is determined by the loss of volume (mm3 /km) or the loss of mass (g/km) of metal per unit of friction distance. Materials with high hardness and durability usually have high wear resistance. High wear resistance is the main requirement for surfacing friction pairs. Abrasion resistance (g)—a type of wear resistance when the action of solid particles, usually of mineral origin (sand, ore, granite, etc.) exists. Gas-abrasion resistance is a type of abrasion resistance when solid particles move in a gas stream. Hydro-abrasion resistance is a type of abrasion resistance when solid particles move in a fluid flow. High abrasion resistance should be ensured when surfacing parts of agricultural and road-building machines, mining equipment, metallurgical equipment, etc. Resistance against cavitation (v)—ability of the material to resist destruction from the surface under repeated impact loads and chipping of plastic zones that occur during the formation and closure of cavitation bubbles in the liquid. Resistance to cavitation is important when surfacing propellers, impellers of turbines, steam turbine blades, etc. Heat resistance (t)—ability of a material to retain mechanical properties at high temperatures. Heat resistance must be ensured when surfacing equipment for the needs of metallurgical, heat and power, chemical industries, etc. Corrosion resistance (c)—ability of a material to resist destruction under electrochemical processes (anodic—transition of metal ions into solution with the formation of excess electrons in the metal, cathodic—transition of free electrons into solution by reducing positive ions of depolarizer and transition of excess electrons from anode to cathode zone) and chemical process (creation of chemical compounds, primarily oxides and hydroxides of metals). Corrosion resistance is characterized by the magnitude of corrosion rate. Corrosion rate is determined by the loss of metal mass per unit time per unit surface area of corrosion—g/(m2 h.) or by reducing the thickness of the product per unit time—mm/year. The rate of electrochemical corrosion is also determined by corrosion current density—A/mm2 . Corrosion resistance is the most important characteristic when choosing surfacing materials for equipment that is operated in aggressive working environments and (or) at elevated temperatures. Dispersion hardening (w)—increase in hardness and strength during aging and tempering of alloys due to release of supersaturated solid solutions of dispersed (small) particles of the new solid phase. Common properties of surfacing materials’ groups according to EN 14700: 2014 [1] are given in Table 10.2.

1

4

4

1

Fe11

Fe12

Fe13

4

4

Fe9

1–2

Fe8

Fe10

1–2

2

Fe7

1

4

3

3

1

2

1

2

1

Fe5

2–3

Fe6

2

Fe4

2

2

3–4

3

Fe2

Fe3

2–3

3–4

2

1

1

1–2

4

4

1–2

2–3

1

1–2

2

4

4

Thermal

Temperature resistance

Impact resistance

Mechanical

Friction resistance

Properties

Fe1

Alloy symbol

4

4

4

1

4

4

1–2

2–3

1

1–2

2

4

4

4

1

1

2

2–3

3

1–2

4

2

3

3

4

4

Corrosion resistance Resistance to thermal shocks

4

1

1

1

1–2

2–3

1

2–3

1

2–3

2

2

1

Crack resistance

4

1

1

2

3

3–4

1–2

3–4

1

3–4

2

3

1

Ability to process

Martensitic/ austenitic + FeB

Austenitic

Austenitic

Austenitic

–

150–250

–

180–200

200–250

–

Martensitic + carbides Austenitic

250–450

Ferritic/ martensitic

– –

Martensitic

–

Martensitic + carbides Martensitic + carbides

–

–

150–450

HB

Hardness

Martensitic (carbides)

Martensitic

Ferritic/ martensitic

Micro-structure

(continued)

55–65

–

–

38–42

40–50

50–65

–

48–55

30–40

55–65

40–55

30–58

–

HRC

Table. 10.2 Common properties of groups (alloy symbol) and structure of surfacing materials according to EN 14700:2014 [1] (1—excellent, 2—good, 3—acceptable, 4—unacceptable)

178 10 Structure and Properties of Surfaced Metal of Different Alloying Systems

Properties

1

2–3

2

2–3

Ni3

Ni4

2

2–3

2

1–2

2–3

Ni1

3

Ni2

2–3

4

1

Fe16

1

4

1

Fe15

Fe17

3–4

1

Fe14

Fe20

Impact resistance

Mechanical

Friction resistance

Alloy symbol

Table. 10.2 (continued)

2

2

1

2

3

2

1

2

3

Temperature resistance

Thermal

1

3

1

3

4

2

4

4

4

Resistance to thermal shocks

2

2

2

2

3

1

3

3

2

Corrosion resistance

1

2

1

3

4

1

4

4

4

Crack resistance

2

2

2

3

4

1

4

4

4

Ability to process

Ni-based alloy

Ni-based alloy

Ni-based alloy

Ni-based alloy

Solid material in Fe-matrix

Austenitic

Martensitic/ austenitic + carbides

Martensitic/ austenitic + carbides

Martensitic/ austenitic + carbides

Micro-structure

200–400

–

200–400

–

–

150–350

–

–

–

HB

Hardness

(continued)

–

45–60

–

45–60

50–60

40–55

60–70

55–65

40–60

HRC

10.1 General Classification of Surfacing Metals of Different Alloying … 179

Properties

2–3

1

Cr1

3

3

1

Al1

2–3

2

3–4

3–4

Cu1

2–3

Cu2

1–2

1–2

Co2

1

2–3

Co1

Co3

2

Impact resistance

1

Friction resistance

Mechanical

Ni20

Alloy symbol

Table. 10.2 (continued)

3

4

4

4

1

1

1

2

Temperature resistance

Thermal

3

4

3

4

1–2

1–2

1–2

3

Resistance to thermal shocks

1

2

1

1

2

2

1

2

Corrosion resistance

2–3

2–3

3

2–3

2–3

2–3

1

1–2

Crack resistance

3–4

3

2

2

3–4

3–4

1

4

Ability to process

200–400

–

–

250–350

1500–2800 HV

HB

Hardness

150–300 HV –

600–700 HV –

Austenitic + inclusion

–

–

45–60

35–50

40–45

45–55

HRC

α-solid solution + intermetallic phase

Alloy Cu–Al–Mn 200–300

Alloy Cu–Al

Co-based alloy

Co-based alloy

Co-based alloy

Solid material in Ni-matrix

Micro-structure

180 10 Structure and Properties of Surfaced Metal of Different Alloying Systems

10.1 General Classification of Surfacing Metals of Different Alloying …

181

Algorithm of choosing of surfacing materialof choosing of surfacing material according EN 14700:2014 [1]. (1) According to operating conditions (type of interaction of part surface with working medium) and type of wear, choose the group (alloy symbol in Table 10.3) of the deposited material from Table 10.3. To facilitate the choice, the table shows examples of surfaced parts. (2) Determine properties of the selected group (alloy symbol) of the deposited material and assess the degree of satisfaction with the properties according to Table 10.2. If the properties of the deposited material do not satisfy choose another group according to Table 10.3. (3) According to the chemical composition of the group choose a specific material for surfacing. It is possible to solve the reverse problem—to check whether selected surfacing material meets the requirements. Algorithm for checking the suitability of a certain surfacing material for operation in specified conditions according to EN 14700: 2014 [1]. (1) According to Table 10.1, determine to which group (alloy symbol) the deposited material belongs by its chemical composition. (2) According to Table 10.2, determine the properties of a particular group of deposited material. Decide whether the properties are satisfactory. (3) According to Table 10.3, determine whether the chosen group of deposited material can be operated under specified conditions (by type of interaction of part surface with working medium and type of wear). To ensure uniformity of designation, EN 14700: 2014 [1] divides the electrode and filler materials into types with the following assignment of letter symbols. • • • • • • •

E—coated electrodes, S—solid wires and rods, T—flux cored wires and rods, R—cast rods, B—cold-rolled strips, C—sintered rods, powder and metal-ceramic strips, P—metal powders.

When designating the surfacing material, the symbol of the group (alloy symbol) is indicated according to Table 10.1 after the type designation. For example, a solid wire (S) with a chemical composition corresponding to the group with alloy symbol Fe7: “Solid wire EN 14700 S Fe7”.

182

10 Structure and Properties of Surfaced Metal of Different Alloying Systems

Table. 10.3 Application of groups (alloy symbol) of surfacing metals depending on types of wear according to EN 14700:2014 [1] Types of contact interaction Solid body—solid body; Friction of solid bodies; Boundary friction; Combined friction Type of wear

Examples of parts with surfacing

Alloy designation

Friction wear

Guides, rails

Fe1, Fe2, Fe3, Cu1, Cu2

Wear and tear Impact wear

Blacksmithing hammer

Fe9, Fe10, Al 1,Ni2, Ni4

Valve rocker arm, cams

Fe1, Fe2, Fe3

Tram rails, switches

Fe9, Fe10

Rolling wear Friction wear

Trolley wheel

Fe1, Fe2, Fe3, Fe9

Railroad rails

Fe1, Fe9, Fe10

Rolling and impact Rollers for continuous casting wear Roller rollers Thermal fatigue Leading rollers, drums

Cold sliding friction with impacts wear High temperature sliding friction with impacts wear

Fe7 Fe3, Fe6, Fe7, Fe8 Fe3

Forging and pressing stamps

Fe3, Fe4, Fe6, Fe8, Co1, Co2, Co3, Ni2, Ni4

Cold cutting knives, cutting stamps

Fe4, Fe5, Fe8, Co1, Co2, Co3

Hot cutting knives

Fe4, Fe3, Co2, Ni2, Ni4

Stamp tooling

Fe4, Fe3, Co2, Ni2, Ni4

Jaw crusher, hammer crusher

Fe6, Fe8, Fe9, Fe14, Fe15

Types of contact interaction Solid body—solid body with abrasive layer

Sliding friction with impacts wear

Stirrer blades

Fe6, Fe8, Fe9

Parts of crushers

Fe6, Fe8, Fe9, Fe13, Fe14, Fe15 (continued)

10.1 General Classification of Surfacing Metals of Different Alloying …

183

Table. 10.3 (continued) Bandages for cement crusher rollers Fe6, Fe8 Details of mills for grinding ore and Fe6, Fe8, Fe13, Fe14, Fe15, Fe16 coal Grid-irons, shale-shakers

Fe13, Fe14, Fe15

Hammers of coal mills

Fe8, Fe13, Fe14, Fe15

Wear-resistant sheets

Fe13, Fe14, Fe15

Plowshares, knives for construction and road machines

Fe15, Fe20, Ni20

Types of contact interaction Solid body—abrasive particles, high surface tension and impacts

Sliding friction with impacts wear

Bunkers, gutters

Fe14, Fe15, Fe20, Ni20

Wear-resistant sheets

Fe14, Fe15, Ni1, Ni2, Ni3, Ni4, Ni20

Parts of extruders

Fe14, Fe15, Fe20, Ni1, Ni3, Ni20, Co2, Co3, Cr1

Types of contact interaction Solid body—solid body with abrasive layer, high surface pressure

Cutting wear

(continued)

184

10 Structure and Properties of Surfaced Metal of Different Alloying Systems

Table. 10.3 (continued) Worms, augers of conveyors

Fe14, Fe15, Fe20, Ni1, Ni3, Ni20, Co2, Cr1

Knives, buckets teeth for construction and road machines

Fe15, Fe20, Ni20

Teeth of rippers, working bodies of cultivators

Fe6, Fe2, Fe8

Plowshares

Fe2, Fe6, Fe8, Fe20, Ni20

Parts of faucets

Fe6, Fe8, Fe14, Fe20, Nil, Ni3, Ni20

Stamps of brick presses

Fe6, Fe8, Fe14, Ni1, Ni3

Parts of mills

Fe14

Types of contact interaction Solid body—abrasive parts in a gas flow

Gas-abrasive wear Blast furnace valves T ≥ 500 °C Contact belt of the cone and the blast furnace bowl Details of blast furnace feeding devices

Fe6, Fe7, Fe8 Fe6, Fe3, Fe8, (Fe16) Fe15, Fe16

Parts of heating furnaces

Fe7, Co1,Co2

Parts of fans, exhausters

Fe10, Fe15, Fe16, Fe20, Ni1, Ni2, Ni3, Ni4, Ni20

Parts of crushers, shale shakers

Fe15, Fe16

Impellers of pumps, wear-resistant sheets

Fe14, Fe15, Fe20, Ni1, Ni3, Ni20 (continued)

10.1 General Classification of Surfacing Metals of Different Alloying … Table. 10.3 (continued) Types of contact interaction Solid body—abrasive parts in a flow of liquid

Hydro-abrasive wear, erosion

Erosion corrosion

Parts of pulp pipelines, wear-resistant sheets

Fe14, Fe15

Parts of dredges, excavators, dredgers

Fe6, Fe8

Parts of pumps for pumping liquids

Fe6, Fe7, Fe8, Ni1, Ni3

Parts of faucets

Fe6, Fe7, Fe8

Propeller blades

Cu1, Cu2

Hydroturbine

Fe7, Fe17, Cu1

Types of contact interaction Solid body—liquid

Corrosion Cavitation * * * * * * *

Chemical equipment

Fe7, Fe11, Fe12

Sealing surfaces of shut-off valves

Fe7, Co1, Co2, Co3

Hydro turbine

Fe17, Fe7, Co1, Co2, Co3, Fe11

Solid body-solid body, friction of solid bodies, boundary friction, combined friction Solid body—solid body with abrasive layer Solid body—abrasive particles, high surface tension and impacts Solid body—solid body with abrasive layer, high surface pressure Solid body—abrasive parts in a gas flow Solid body—abrasive parts in a flow of liquid Solid body—liquid

185

186

10 Structure and Properties of Surfaced Metal of Different Alloying Systems

10.2 Unalloyed and Low-Alloyed Steels with Carbon Content up to 0.4% (Fe1 Group) Surfaced layers of unalloyed and low-alloy steels with carbon content up to 0.4% (Table 10.4) have low hardness, so they are most widely used to restore the geometric dimensions of parts without giving the deposited layer any special properties, including hardening. They are also used as a plastic sublayer when surfacing high-alloy steels with special properties. The primary structure of deposited metal consists of columnar crystallites, oriented, as a rule, normal to the fusion surface of the base and surfaced metals. The size of the primary crystallites is small due to the high crystallization rate (they are much smaller than crystallites in steel castings of the same chemical composition). The microstructure of the surfaced metal is ferrite-pearlite or pearlite-ferrite (Fig. 10.1) [2]. If the carbon content is more than 0.25% formation of needle troostite and martensite is possible. The most favorable structure is formed at a cooling rate of 10–40 ºC/sec. in the temperature range 540–550 ºC [3, 4]. Increasing the cooling rate for steels with carbon content higher than 0.25% can lead to formation of an increased amount of martensite in the deposited layer, increase in hardness and cracking. When surfacing massive parts, preheating up to 200–250 ºC is required. When surfacing parts of small mass heating from heat sources (so-called auto heating) is enough. The following methods are used for surfacing of non-alloy and low-alloy steels with carbon content up to 0.4%: manual metal arc surfacing with coated electrodes, arc surfacing in protective gases with solid wire, self-protective flux cored wire (strip), submerged arc surfacing. Oxy-gas surfacing with rods or electroslag surfacing with wire are used less often. Table. 10.4 Chemical composition of deposited layers of low-alloyed steels with carbon content up to 0.4% and their hardness after surfacing Brand of surfacing steel

Mass fraction of elements in the deposited layer (%) C

Mn

Si

Cr

10G2

0.10

2.00

0.40

–

Hardness of the deposited layer, HB 230–260

10G4

0.12

4.00

0.40

–

320–360

18XGC

0.18

0.90

1.10

0.80

270–300

30XGC

0.30

1.00

1.00

1.00

290–350

30X4G

0.30

1.40

0.50

4.00

350–450

10G2XC

0.10

1.50

0.40

1.00

260

15G2X2C

0.15

1.50

0.80

1.50

360

20G2X3C

0.20

2.00

0.80

3.00

400

10.3 Surfaced Unalloyed and Low-Alloyed Steels with Carbon Content …

1

1

1

2 2

a

187

c

b Fig. 10.1 Structure of the surfaced metal × 200 with carbon content of up to 0.4% (a Ferritic structure at C = 0.04%, b Ferritic-sorbitol structure at C = 0.2%, c Sorbitol-ferritic structure at C = 0 0.4%): 1—ferrite, 2—sorbitol

10.3 Surfaced Unalloyed and Low-Alloyed Steels with Carbon Content Above 0.4% (Fe2 Group) Surfaced unalloyed and low-alloyed steels with a carbon content above 0.4% (Table 10.5) are wear-resistant due to high carbon content and, therefore, have high hardness. Increase in toughness is achieved by nickel alloying, and the increase in hardenability—by manganese and chromium alloying. These materials are used to restore and strengthen rollers, rolls of the straightening machines, brake pulleys, crankshafts. They are also used to strengthen tools for hot and cold deformation of metal (knives, dies), working bodies of road and construction machines (knives of bulldozers, scrapers, graders, etc.). Due to the low total content of alloying elements wear-resistant coatings made of this group metals have low cost. Structurally unalloyed and low-alloyed steels with a carbon content above 0.4% are pre-eutectoid or close to pre-eutectoid. After annealing they have pearlitic structure (Fig. 10.2) [2]. After hardening—martensitic structure with a certain amount of residual austenite. Carbide phase—cementite and carbide Me23 C6 . The presence of hardening structures (martensite) and, in some cases, layers of high chromium ledeburite eutectic cause structural stresses. This is the reason for the high susceptibility of the deposited metal to formation of cold cracks.

188

10 Structure and Properties of Surfaced Metal of Different Alloying Systems

Table. 10.5 Chemical composition of surfaced layers corresponding to low-alloyed steels with carbon content above 0.4% and their hardness after surfacing Brand of surfacing steel

Mass fraction of elements in the deposited layer (%) C

Mn

Si

Cr

Mo

Ni

HRC

Others

40X3G2MF

0.40

1.80

0.50

3.50

0.40

–

0.20 V

37–42

50XHM

0.50

0.60

0.40

0.80

–

1.40

–

40–50

50XFA

0.50

50X3CT

0.50

60X3

0.60

0.60 0,50 0.40

0.40

1.00

–

–

0.20 V

43–50

1.00

3.00

–

–

0.20 Ti

40–50

0.20

3.00

–

–

–

46–55

70X3GCMH

0.70

0.50

0.70

3.00

0.60

0.50

–

52–58

40X3G2MC

0.40

1.50

0.70

2.50

0.50

–

–

45

50X6GMC

0.50

1.20

0.70

6.00

0.70

–

–

55

1

1

a

b

Fig. 10.2 Pearlitic structure of surfaced metal × 200 (a at carbon content 0.6%, b at carbon content 0.8%): 1—pearlite

To prevent cracks, preheating up to 200–250 ºC is required. After surfacing part tempering or slow cooling in the thermostat or in the flux is recommended. The following methods are used for surfacing of unalloyed and low-alloyed steels with carbon content over 0.4%: manual metal arc surfacing with coated electrodes, arc surfacing in shielding gases with solid wire, self-protective flux cored wire (strip), submerged arc surfacing. Oxy-gas surfacing with rods or electroslag surfacing with wire are used less often.

10.4 Surfaced Chrome-Tungsten, Chrome-Molybdenum, and Other …

189

10.4 Surfaced Chrome-Tungsten, Chrome-Molybdenum, and Other Heat-Resistant Tool Steels (Fe3 Group) Surfaced metals such as chromium tungsten, chromium-molybdenum, and other heat-resistant tool steels (Table 10.6) are widely used to strengthen parts of metallurgical equipment operating in cyclical thermal changes, high dynamic loads in combination with abrasive wear (rolls for hot rolling, knives for hot cutting, hot stamping stamps, rollers of hot rolling, etc.). Tungsten provides the highest hardness at elevated temperatures and sufficient heat resistance. At the same time, the toughness of tungsten-alloyed steels is relatively low. Molybdenum and chromium provide sufficient hardness and heat resistance (replace tungsten), while significantly increasing the toughness. The reason is that the toughness increases with increasing coagulation (enlargement) of carbides released during tempering. During tempering of tungsten-containing steels Me6 C and Me3 C carbides are released from the solid solution. During tempering of molybdenumcontaining steels larger Me23 C6 carbides are isolated along with Me6 C carbides [3] Thus, molybdenum and chromium carbides have a greater ability to coagulate than tungsten carbides. Increase of toughness and heat resistance of steel by alloying with molybdenum is also enhanced by enrichment of boundary zones of the grains with molybdenum and by corresponding complication of carbide particles’ separation at the grain boundaries. Molybdenum and chromium also increase the ultimate strength. Table. 10.6 Chemical composition of surfaced layers corresponding to chromium-tungsten, chromium-molybdenum and other heat-resistant tool steels and their hardness after surfacing Brand of surfacing steel

Mass fraction of elements in the deposited layer (%)

HRC

C

Mn

Si

Cr

Mo

W

V

Ni

Ti

30X2M2HF

0.30

0.7

0.8

2.0

2.0

–

0.4

1.0

–

44–50

30X4M3B2F

0.30

0.7

0.7

4.0

2.5

2.0

0.5

–

–

44–52

30X5B2G2M

0.30

1.8

1.0

5.0

0.5

2.0

–

–

–

50–60

35X7MF

0.35

0.7

0.6

6.0

1.0

–

0.4

–

–

50–52

35B9X3CF

0.35

0.8

0.9

3.0

–

9.0

0.3

–

–

44–50

50X4B3F

0.50

0.8

0.5

4.0

–

3.2

0.3

–

–

46–52

25X6BG2M

0.25

2.0

0.8

6.5

1.5

1.5

–

–

–

44

50X6BG2M

0.50

2.0

0.8

6.5

1.5

1.5

–

–

–

55

30X2B4F

0.30

0.3

0.4

2.4

–

4.0

0.6

0.2

–

45

30X6B2M2F

0.30

0.8

0.6

6.5

2.0

2.0

0.6

–

–

52

22X5M4G

0.22

1.0

0.5

5.0

3.8

–

–

–

0.25

45

35X7M2G

0.35

1.20

0.50

6.8

2.2

–

–

–

0.30

55

190

10 Structure and Properties of Surfaced Metal of Different Alloying Systems

Fig. 10.3 Structure of deposited metal × 500 of heat-resistant tool steel 35B9X3CF: 1—martensite, 2—residual austenite, 3—carbide inclusions

3 2

1

Tool steel usually contains 1.0–4.0% molybdenum. Chromium content in them is recommended to be limited to 5.0% (otherwise a decrease in heat resistance is possible) [3]. Carbon increases strength, hardness, and resistance of steel against abrasive wear. At the same time, it reduces thermal resistance and toughness. Carbon content in heat-resistant tool steels is 0.3–0.5%. Nickel increases strength, toughness, and thermal stability of steel. However, when nickel content is more than 2.0% probability of hot cracks in the deposited metal increases sharply during surfacing [5]. The structure of surfaced heat-resistant tool steels (Fig. 10.3) depending on the cooling conditions consists of martensite, residual austenite, and carbides of different composition. Heat-resistant tool steels are susceptible to cracking during surfacing. Surfacing is carried out with pre- and sometimes in-process heating. The heating temperature is 400–450 ºC. Heating is carried out by industrial frequency current, gas flame or in furnaces. After surfacing it is necessary to provide slow cooling of the surfaced part in the furnace, thermostat or in the flux. In case when machining by cutting is needed a full cycle of heat treatment should be performed: “annealing → machining → hardening → tempering”. The following methods are used for surfacing of heat-resistant tool steels: manual metal arc surfacing with coated electrodes, arc surfacing in shielding gases, submerged arc surfacing, oxy-gas surfacing, electroslag surfacing with coated electrodes, flux-cored electrodes, powders as electrode and filler materials. cold-rolled and sintered strips, fractions and other non-compact materials, rods of various cross-sections, as well as liquid filler material.

10.5 Surfaced High-Speed Steels (Fe4 Group)

191

10.5 Surfaced High-Speed Steels (Fe4 Group) Surfaced layers of high-speed steels (Table 10.7) are alloyed with tungsten and molybdenum (basic alloying), as well as with chromium, cobalt, vanadium. They combine high heat resistance (600–700 ºC) with high hardness (HRC ≥ 63) and high resistance to plastic deformation. The main application of high-speed steels is the manufacture of cutting tools. Heat resistance of high-speed steels is provided by alloying with tungsten or tungsten with molybdenum and quenching at high temperatures—1200 to 1300 °C [3]. The carbon content is 0.7–1.0%. The main carbide in this alloying scheme is M6 C type. To ensure high heat resistance a large proportion of carbides should be converted into a solid solution during high temperature quenching. Subsequent tempering increases the hardness to maximum values due to release of dispersed carbides, the size of which is much smaller than of those in annealed steel. Tempering to secondary hardness also causes transformation of residual austenite into martensite. As a result, the steel acquires martensitic-carbide structure. Alloying with chromium leads to the appearance of carbides of Cr23 C6 type. While quenching these carbides are completely soluble in the matrix. This leads to saturation of solid solution with chromium and carbon and increases ability to harden (level of hardness during quenching) and the ability to calcine (depth at which hardness increases during quenching) of high-speed steel. Vanadium is a traditional alloying element for high-speed steels. It forms carbide VC and is also a part of M6 C and M23 C6 carbide groups. During high-temperature tempering vanadium is released in the form of VC carbide. This increases secondary hardness and heat resistance but reduces toughness of the steel. Table. 10.7 Chemical composition of high-speed steel surfaced layers Brand of surfacing steel

Mass fraction of elements in the deposited layer (%) C

Cr

Mo

P9

0.90

3.0

≤ 1.0

W 9.0

V

Co

2.2

–

P12

0.85

3.3

≤ 1.0

12.5

1.7

–

P18 (X75WCrV18-4-1)

0.75

4.0

≤ 1.0

18.0

1.2

–

P6M3

0.90

3.2

3.2

6.0

2.2

–

P6M5 (HS6-5-2)

0.85

4.0

5.0

6.0

2.0

–

P6M5K5 (HS6-5-2-5)

0.85

4.0

5.0

6.5

2.0

5.0

P18F2K5

0.90

4.0

≤ 1.0

18.0

2.0

5.5

90X4M8B2F

0.90

4.5

8.0

2.0

1.2

–

90X5M7B2F2

0.90

5.0

7.0

2.0

1.7

–

192

10 Structure and Properties of Surfaced Metal of Different Alloying Systems

a

1

1

2

2

3

3

b

Fig. 10.4 Martensitic-austenitic structure of surfaced metal × 320 of P6M5 high-speed steel (a coarse-grained at cooling rate 10–25 °C/sec., b fine-grained at cooling rate 50–100 °C/sec.): 1—martensite, 2—residual austenite, 3—carbides

Cobalt in high-speed steel helps to increase hardness and heat resistance due to formation of Co7 W6 intermetallic. However, alloying with cobalt significantly increases the cost of surfacing materials. To ensure the optimal structure of surfaced metal the cooling rate after surfacing should be 50–100 ºC/sec with a subsequent decrease in speed to 1–5 ºC/sec in the range of temperatures of martensitic transformation. This hardens the deposited metal from liquid state and provides a fine-grained martensitic-austenitic structure with a continuous, fine mesh of carbide eutectic and primary carbides along the grain boundaries (Fig. 10.4) [6]. Martensitic-austenitic structure determines susceptibility of the deposited metal to cracking. To prevent cracks pre-heating and in-process heating of surfaced parts to a temperature of 400–700 ºC and slow cooling in the furnace after surfacing are used. The following methods are used for surfacing of high-speed steels: plasma-powder surfacing with 10P6M5 high-speed steel powder, coated electrodes, which provide 80B18X4F, 90B10X5F, 105B6X5M3F3, 10K15B7M5X3CF and 90H4B2FM8 deposited metal types, electroslag surfacing with liquid filler material (high-speed steel with a carbon content of about 2%) [7, 8].

10.6 Surfaced Low-Carbon Chromium Steels (Fe7 Group)

193

10.6 Surfaced Low-Carbon Chromium Steels (Fe7 Group) Surfaced low-carbon chromium steels contain up to 0.2% carbon and 4–30% chromium (Table 10.8). Surfacing, depending on the alloying, provides the properties of the surfaced layer in a wide range: • • • •

wear resistance at different types of wear, corrosion resistance, high strength, heat resistance.

Low-carbon chromium steels are used to restore and strengthen plungers of hydraulic presses and hydraulic cylinders, rollers of machines for continuous casting of billets, parts of general industrial, energy, oil and gas fittings, etc. Structure of deposited metal of low-carbon chromium steels varies in a wide range: • ferritic, • martensitic–ferritic, • martensitic-austenitic with different content of chromium carbides (Fig. 10.5). Phase composition of the surfaced metal structure of low-carbon chromium steels depends on the content of alloying elements: ferritizers (Cr, Si, Mo, Ti, Nb, Al, W, V) and austenitizers (Ni, C, N, B, Mn, Co, Cu). Phase composition is determined by the following algorithm. (1) Calculate equivalent content of chromium [Cr]: [Cr] = Cr + 1.5Si + 2Mo + 5Ti + 2Nb + 2Al + 1.5W + V

(10.1)

Table. 10.8 Chemical composition of surfaced layers corresponding to low-carbon chromium steels and their hardness after surfacing Brand of surfacing steel

Mass fraction of elements in the deposited layer (%) C

Mn

Si

Cr

Mo

Ni

HRC

Others

10X13 (X10Cr13)

0.10

0.8

0.6

13.0

–

–

–

34–40

10X13M

0.15

0.8

0.7

13.0

0.8

–

–

32–35

10X15H3

0.12

1.1

0.5

15.0

–

3.0

–

38–42

08X13H4M

0.08

1.0

0.6

13,5

0.5

4.0

–

38

12X13H2MF

0.12

0.8

0.6

13.0

0.8

2.0

0.2 V

45–50

20X13

0.20

0.6

0.6

13.0

–

–

–

42–48

20X17

0.20

0.6

0.6

17.0

–

–

–

45–50

08X17

0.08

0.9

0.7

17.5

–

–

–

20

194

10 Structure and Properties of Surfaced Metal of Different Alloying Systems

Fig. 10.5 Structure of deposited metal × 250 of 20 × 17 low-carbon chromium steel: 1—ferrite, 2—chromium carbides

1

2 where Cr, Si, Mo, Ti, Nb, Al, W, V—content of the corresponding alloying element in steel, %. (2) Calculate equivalent content of Nickel [Ni]: [Ni] = Ni + 30C + 30N + 10B + 0.5Mn

(3)

• • • • • •

• •

(10.2)

where Ni, C, N, B, Mn—content of the corresponding alloying element in steel, %. Intersection on the Schaeffler diagram (Fig. 10.6) of the value of chromium equivalent (abscissa axis) and the value of nickel equivalent (ordinate axis) indicates the area of phase composition of the structure: A—austenitic structure zone, A + M—zone of austenitic-martensitic structure, M—martensitic structure zone, F + M—zone of ferritic-martensitic structure, M + F—zone of martensitic–ferritic structure, A + F—zone of austenitic-ferrite structure (zone is divided into sectors depending on the share of ferrite. In each sector the share of ferrite in percent is indicated), A + F + M—zone of austenitic-ferritic-martensitic structure, F—zone of ferritic structure.

There are usually no difficulties in surfacing low-carbon chromium steels. In the case of restoration and strengthening of massive parts, preheating to 250–350 °C and slow cooling after surfacing are required. The surfacing of low-carbon chromium steels is carried out with all methods using coated electrodes, flux-cored and solid wires, powders, cold-rolled and sintered strips, powders, and other non-compact materials such as electrode or filler materials.

10.7 Surfaced Chromium Steels with Increased Carbon Content (Fe8 Group)

195

[Ni],% 36

32 28

A

24 20 16 8 4 0

A+F

A+M

12

A +F+M

M

F+ M

M+F 8

4

12

16

F 20

24

28

32

[Cr], %

Fig. 10.6 Schaeffler diagram

10.7 Surfaced Chromium Steels with Increased Carbon Content (Fe8 Group) Surfaced chromium steels with increased carbon content contain 0.2–2.0% C and 5–18% Cr (Table 10.9). Depending on the content of carbon and chromium, chromium steel is used for surfacing cold cutting knives (30X13), cold and hot stamping stamps (50X9C3), Table. 10.9 Chemical composition of surfaced layers corresponding to chromium steels with increased carbon content and their hardness after surfacing Brand of surfacing steel

Mass fraction of elements in the deposited layer (%)

HRC

C

Mn

Si

Cr

Mo

Ni

Others

30X13

0.30

0.6

0.6

13.0

–

–

–

45–50

35X12B3F

0.35

1.2

0.5

12.0

–

–

3.0 W; 0.8 V

50–55

50X9G3

0.50

3.0

0.6

9.0

–

–

–

52–58

65X11H3

0.65

0.4

0.6

11.0

–

3.0

–

25–32

200X12M

1.80

0.6

0.6

12.0

0.8

–

–

40–44

200X12BF

1.80

0.6

0.6

12.0

–

–

1.0 W; 0.3 V

40–44

50X8C2

0.50

1.5

2.5

8.5

–

–

–

59

180X6T5MF

1.80

1.2

0.7

6.5

0.8

–

5.0 Ti; 0.2 V

57

130X6B6

1.30

0.9

1.0

6.5

–

–

6.5 Nb

50–65

196

10 Structure and Properties of Surfaced Metal of Different Alloying Systems

Fig. 10.7 Surfaced metal structure (× 500) of 200X12BF chromium steel with increased carbon content: 1—martensite, 2—residual austenite, 3—alloyed ledeburite

2 3

1 parts operated in conditions of abrasive wear (200X12M, 200X12BF, 50X8C2, 180X6T5MF, 130X6B6). The structure of deposited metal is martensitic or martensitic-austenitic with inclusion of chromium carbides. When the content of carbon is more than 1% and that of chromium is more than 10%, a ledeburite eutectic is formed in the structure (Fig. 10.7) [5]. Metal has high wear resistance in abrasive wear. Surfacing with chromium steels with increased carbon content is carried out with preheating. The surfaced parts should be cooled slowly in a thermostat or an oven. The greatest difficulty is the surfacing of steels of 200X12M, 200X12BF type. Preheating to 500 ºC is required to prevent cracks. After surfacing, the part is placed in an oven at a temperature of 700 ºC and cooled together with the oven [9] It is recommended to do a full cycle of heat treatment: “annealing → quenching → tempering”. The surfacing of low-carbon chromium steels with increased carbon content is carried out with all methods using coated electrodes, flux-cored electrodes, fluxcored and solid wires, flux-cored strips and non-compact materials as electrode or filler materials.

10.8 Surfaced High-Manganese Austenitic Steels (Fe9 Group)

197

10.8 Surfaced High-Manganese Austenitic Steels (Fe9 Group) Typical high-manganese austenitic steel is Hadfield steel (mangalloy) with a content of 11–14.5% Mn and 0.9–1.3% C, as well as steels similar in composition with additional Cr, Mo or Ni alloying (Table 10.10). A feature of these steels is work hardening—ability to harden under the influence of impact loads. As a result, the hardness of the surface layer of the part made of G13 steel increases from HB 180– 250 to HB 450–500. Steel acquires high resistance to abrasive wear with intense impact loads. Surfaced materials of high-manganese austenitic steel type are used to restore crossroads, parts of crushing and sintering equipment, as well as to correct defects of castings in G13 type steels. After surfacing high-manganese austenitic steel should have a purely austenitic structure (Fig. 10.8) [10]. This is achieved only at high cooling rates in the temperature range 800–500 ºC (with slow cooling at the grain boundaries, cementite is released, the toughness of metal is significantly reduced, cracks may appear). Surfacing with parameters that provide high cooling rate are used. Sometimes the surfaced parts are cooled with water. Alloying with Nickel is used to increase the stability of austenite. Electric arc surfacing is used for high-manganese austenitic steels with coated electrodes, flux-cored and solid wires as electrode materials. Table. 10.10 Chemical composition of surfaced layers corresponding to high-manganese austenitic steels and their hardness after surfacing and work hardening Brand of surfacing steel

Mass fraction of elements in the deposited layer (%) C

Mn

Si

Ni

Cr

Hardness after surfacing, HB

Hardness after slander, HB

Mo

G13

1.0

13.0

0.6

–

–

–

220–280

450–500

G13H4

0.8

13.0

0.5

4.0

–

–

170–230

400–450

G13X4H3M3

0.8

14.0

0.5

3.4

3.8

3.4

160–200

420–460

G13X25H3

0.6

13.0

0.5

2.6

24.5

–

250–310

450–500

G16X14

0.4

16.0

0.5

–

14.0

–

240

460

G14X2H

0.6

14.0

0.7

1.0

2.0

–

220–230

380–485

198

10 Structure and Properties of Surfaced Metal of Different Alloying Systems

Fig. 10.8 Surfaced metal structure × 260 of high-manganese austenitic steel (1%C and 14% Mn): 1—austenite, 2—carbides in small quantities

1

2 10.9 Surfaced Chromium-Nickel, Chromium-Nickel-Manganese Stainless Austenitic Steels (Fe10, Fe11, Fe12 Groups) Surfaced chromium-nickel, chromium-nickel-manganese stainless austenitic steels (Table 10.11) are widely used in chemical, nuclear and power engineering to ensure corrosion and cavitation resistance of parts. Chromium-nickel, chromium-nickel-manganese austenitic steels have high resistance to chemical and general electrochemical uniform and non-uniform corrosion. An exception may be the type of general electrochemical selective corrosion— intergranular corrosion. Complex chromium carbides are precipitated at the grain boundaries in the deposited austenitic metal at critical temperatures (500–800 ºC). Chromium for the formation of carbides is provided by diffusion from the grain zones adjacent to the boundaries. As a result, the adjacent areas are depleted of chromium. The processes of corrosion dissolution of metal are localized in the chromium-depleted zones of grains. Measures to prevent intergranular corrosion. • Reduction of carbon content in the deposited metal to the solubility limit of carbon in austenite (up to 0.02–0.03%). At this concentration, carbon remains in solid solution at any temperature, and carbide precipitation does not occur.

10.9 Surfaced Chromium-Nickel, Chromium-Nickel-Manganese Stainless …

199

Table. 10.11 Chemical composition of surfaced layers corresponding to chromium-nickel, chromium-nickel-manganese stainless austenitic steels Brand of surfacing steel

Mass fraction of elements in the deposited layer (%) C

Mn

Si

Cr

Ni

Mo

Ti

Others

06X19H9T

≤ 0.08 1.5

0.6

19.0

9.0

–

0.5

–

07X19H10B

0.08

≤ 0.7

19.0

9.5

–

–

1.5 Nb

1.5

05X19H9F3C2

≤ 0.07 1.5

1.5

19.0

9.0

–

–

2.5 V

08X20H9C2BT

≤ 0.1

1.5

2.0

20.0

9.0

–

0.7

0.8 Nb; 0.5 Al

10X16H25AM6

0.1

1.5

≤ 0.6

16.0

25.0

6.0

–

0.1 N2

07X25H13

≤ 0.09 1.5

0.7

25.0

13.0

–

–

–

02X20H11G2B

≤ 0.02 1.5

≤ 0.6

20.0

11.0

–

–

0.8 Nb

04X20H14M3

≤ 0.04 1.5

≤ 0.6

20.0

14.0

3.0

–

–

03X23H28M3D3T

≤ 0.03

≤ 0.55 24.0

28.0

3.0

0.7

3.0 Cu

X6CrNiTi18-10

≤ 0.08 –

≤ 0.55

–

17–19

9–12

–

0.7

–

X19H9G6

0.10

0.5

19.0

9.0

–

–

–

6.0

28X24H16G6

0.28

5.4

0.3

24.8

16.5

–

–

–

09X23H9G6C2

0.09

6.3

2.5

23.1

9.4

–

–

–

• Alloying of surfaced metal with strong carbide-forming elements—titanium, vanadium, niobium, zirconium, tantalum. These elements bind carbon into strong carbides and prevent the formation of chromium carbides. When surfacing pure austenitic stainless steels, there is a high possibility of hot cracks. This is due to the peculiarities of the conditions of crystallization of austenitic deposited metal [11]. • • • •

Highly developed trans-crystalline directional primary microstructure, Significant casting shrinkage of the crystallized metal, Significant tensile stresses acting on the surfacing pool during crystallization, Multicomponent alloying, which increases the likelihood of small amounts of low-melting eutectic components at the dendritic boundary at the time of crystallization.

To prevent formation of hot cracks it is recommended to use a surfaced metal with a two-phase austenitic-ferritic structure (Fig. 10.9) [11]. Formation of a twophase structure in the surfaced metal reduces grain size. It is possible to partially or completely re-crystallize the primary trans-crystalline structure and eliminate the conditions for the formation of hot cracks. To obtain a two-phase austenitic-ferritic structure in the surfaced metal it is necessary to provide the required ratio of austenitizers and ferritizers in accordance with the Schaeffler diagram (Fig. 10.6).

200

10 Structure and Properties of Surfaced Metal of Different Alloying Systems

Fig. 10.9 Austenitic-ferritic structure of surfaced metal × 500 of X20H9 chromium-nickel stainless steel: 1—ferrite, 2—austenite

1

2 Deposited metal with high ferrite content is susceptible to sigmatization (appearance of fragile components in the metal structure) in the temperature range of 450– 850 °C, which leads to reduction of plasticity. Therefore, for critical structures, the ferrite content in the deposited metal should be at the level of 2–3%. In steels with a high content of austenite it is difficult to obtain a two-phase structure. To prevent the formation of hot cracks the content of harmful impurities (sulfur, phosphorus, lead) should be minimized, as well that of elements that contribute to the formation of fusible eutectics outside the crystallites (silicon, aluminum, titanium, niobium). When choosing surfacing materials it is necessary to consider the structure and properties of the metal in the alloying zone, which depends on the mixing of the deposited metal with the base metal. The following methods are used for surfacing of chromium-nickel, chromium-nickel-manganese stainless austenitic steels. • Manual metal arc surfacing with coated electrodes, • Automated and mechanized surfacing in shielding gas and automated submerged arc surfacing with solid and flux-cored wires, flux-cored, solid and sintered strips, • Electroslag surfacing.

10.10 Surfaced High-Chromium High-Alloyed Cast Irons (Fe14, Fe15, Fe16 …

201

10.10 Surfaced High-Chromium High-Alloyed Cast Irons (Fe14, Fe15, Fe16 Groups) Surfaced high-chromium high-alloyed cast irons (Table 10.12) contain more than 2% C and are used to increase the wear resistance of parts operated at normal and high temperatures in abrasive, gas-abrasive, and hydro-abrasive wear: blast furnace valves, contact surfaces of cones and bowls of filling furnaces. High-chromium high-alloyed cast irons are also surfaced on rolled rolls with electroslag method. Structure of surfaced high-chromium high-alloyed cast irons consists of martensite, residual austenite, ledeburite and free chromium carbides Cr7 C3 , Cr23 C6 (Fig. 10.10) [10]. Niobium and tungsten carbides appear in the structure if metal is alloyed with these elements. Table. 10.12 Chemical composition of surfaced layers corresponding to high-chromium highalloyed cast irons and their hardness after surfacing Brand of surfacing cast iron

Mass fraction of elements in the deposited layer (%) C

Mn

Si

Cr

Mo

V

HRC

Others

250X10B8C2

2.5

0.4

2.0

10.0

–

–

8.0 Nb

50–58

250X30C2GP

2.5

1.0

2.0

30.0

–

–

1.5 B

50–58

250X25G3C3F2H2

2.5

1.0

3.0

25.0

–

1.6

1.6 Ni

52–56

300X25C3H2G2

3.0

2.0

3.0

25.0

–

–

2.0 Ni

50–56

300X28C4H4

3.0

1.0

3.5

28.0

–

–

4.0 Ni

50–56

350X10B8G2

3.5

2.0

1.0

10.0

–

–

8.0 Nb

54–60

350X26G2P2

3.5

2.0

1.0

26.0

–

–

2.0 B

58–63

400X20B7M7H5B2F

4.0

0.4

0.4

20.0

7.0

1.0

7.0 Nb; 5.0 Ni; 2.0 W

54–60

Brand of surfacing cast iron

Mass fraction of elements in the deposited layer (%)

HRC

C

Mn

Si

Cr

Mo

V

Others

400X26H2C2BM

4.0

1.0

1.5

26.0

0.1

–

1.5 Ni; 0.3 W

53–58

400X38G3

4.0

3.0

1.0

38.0

–

–

–

50–54

450X20B7M6B2C2

4.5

0.4

2.0

20.0

6.0

1.0

7.0 Nb; 2.0 W

55–62

500X38H2G2C2

5.0

2.0

2.0

38.0

–

–

1.5 Ni

55–60

500X27GC

5.0

1.3

1.5

27.0

–

–

–

61

500X22B7C

5.0

0.5

1.0

22.0

–

–

7.0 Nb

63

550X22B6M6B2C2F

5.5

0.5

1.5

22.0

5.5

1.0

6.0 Nb; 2.0 W

65

550X16B6CFP

5.5

0.5

1.3

16.0

–

6.0

6.5 Nb; 1.0 B

66

202

10 Structure and Properties of Surfaced Metal of Different Alloying Systems

Fig. 10.10 Surfaced metal structure × 260 of 450 × 25 high-chromium high-alloyed cast iron: 1—austenitic base, 2—large-sized carbides Cr7 C3 , 3—small-sized carbides Cr23 C6 [10]

1

2 3 Boron alloying provides solid borides and carbide borides in the structure, which increase the wear resistance of the surfaced metal [5, 10]. Wear resistance of the surfaced metal increases significantly with increased quantities of carbides with their uniform distribution (in case of excessive quantities of carbides they crumble). The following methods are used for surfacing of high-chromium high-alloyed cast irons: manual metal arc surfacing with coated electrodes, automated and mechanized surfacing in shielding gas with flux-cored wires and flux-cored strips, plasma-powder surfacing, induction surfacing with powder, electroslag surfacing.

10.11 Surfaced Nickel-Based Alloys Alloyed with Chromium, Boron, and Silicon (Ni1, Ni3 Groups) Surfaced nickel alloys alloyed with chromium, boron, and silicon (Table 10.13) have high wear resistance at normal and elevated temperatures under conditions of friction of metal on metal and high heat resistance. Alloys also have high corrosion resistance in solutions of some acids (acetic, formic, citric), caustic soda and other aggressive media. Nickel alloys alloyed with chromium, boron and silicon are used for surfacing of disks, wedges, spools, and seats of armature, shafts, protective sleeves, sealing rings and support disks of centrifugal pumps, camshafts, valves, and seats of internal combustion engines, parts of metallurgical equipment [6, 12].

10.11 Surfaced Nickel-Based Alloys Alloyed with Chromium, Boron …

203

Table. 10.13 Chemical composition of surfaced layers corresponding to nickel alloys alloyed with chromium, boron and silicon and their hardness after surfacing Brand of surfacing alloy

Mass fraction of elements in the deposited layer (%) C

Si

Cr

B

Fe

Others

H97CP

–

2.0

–

1.2

≤ 0.5

–

HRC

HB 150-180

H96C2P

–

2.5

–

1.5

≤ 0.5

–

HB 200-250

H94C5P2

–

3.5

–

2.0

≤ 0.5

–

34–42

H92C4P3

–

4.5

–

3.0

≤ 0.5

–

59

25X5H90C3P

0.25

3.0

5

1.25

≤ 3.0

–

20–30

25X8H85C5P3

0.25

4.5

7.5

3.0

≤ 3.0

–

56–62

40X10H80C2P2

0.4

2.5

10

2.0

≤ 5.0

–

35–40

50X11H65B16C3P2

0.5

3.25

11.5

2.5

–

16.0 W

50

50X16H67C4P4M3D3

0.5

4.0

16

4.0

2.5

3.0 Cu; 3.0 Mo

60

60X12H70C3P2

0.5

3.0

15

2.1

≤ 5.0

–

35–45

60X25H55C5P

0.6

5.0

25

0.9

8–10

–

45–48

80X14H70C4P3

0.7

3.5

16

2.8

≤ 5.0

–

45–50

100X17H70C4P4

1.0

4.0

18

3.8

≤ 5.0

–

55–60

100X26H65C4P4

1.0

4,0

26

3.5

≤ 3.0

–

50–55

With the increase of carbon, boron, and silicon content, the hardness of the deposited metal increases. The structure of the alloy changes from pre-eutectic to super-eutectic. The pre-eutectic structure consists of an α-solid solution based on Nickel and a complex eutectic. The super-eutectic structure consists of α-solid solution based on Nickel, complex eutectic, as well as borides, complex carbides such as M23 C6 and carbide borides (Fig. 10.11) [6]. Surfaced metal with pre-eutectic and eutectic structures is used mainly for operation in friction pairs and at significant impact loads, with super-eutectic structure—in abrasive wear. Carbon in nickel–chromium-silicon-boron alloys is present mainly in the form of M7 C3 and M23 C6 type carbides. Alloying with boron in the range of 1–4% increases the wear resistance of the surfaced metal, reduces melting temperature of alloys, and provides them an ability to self-flux. In addition, boron and silicon contribute to the excellent formation of the deposited layer. Alloying with iron up to 5% changes the metal structure. Increasing the concentration of iron to 20% leads to a decrease in the amount of eutectic components due to increased solubility of carbon, boron and silicon in solid solution enriched with iron. Self-fluxing (ability to clean the surface of the base metal from oxide films) combined with low melting point is an important technological property of chromium-nickel alloys with boron and silicon. First of all, proper self-fluxing is

204

10 Structure and Properties of Surfaced Metal of Different Alloying Systems

Fig. 10.11 Surfaced metal structure × 320 of 60X12H70C3P2 nickel alloy deposited with plasma-powder method

important when surfacing preheated parts, when the surface is covered with an oxide film. B2 O3 and SiO2 react with the oxides of the base metal and reduce the metals. Conditions are created for good wetting of the surface. Plasma-powder surfacing and oxy-gas surfacing with filler rods are used for surfacing of nickel alloys alloyed with chromium, boron, and silicon, as well as, to a lesser extent, manual metal arc surfacing with coated electrodes and mechanized surfacing in shielding gas. Materials for surfacing are produced mainly in the form of powders, including self-fluxing Ni–Cr–Si–B–C alloys.

10.12 Surfaced Nickel-Based Alloys Alloyed with Molybdenum and Chromium (Ni2 Group) Surfaced nickel alloys alloyed with molybdenum and chromium (Table 10.14) have high heat resistance, good resistance to thermal fatigue and corrosion, and little susceptibility to cracking during surfacing. Surfacing materials made of nickel alloys alloyed with molybdenum and chromium are available in the form of coated electrodes, solid and flux-cored wires, solid and flux-cored strips and powders.

10.13 Surfaced Carbide-Based Alloys (Fe20, Ni20 Groups)

205

Table. 10.14 Chemical composition of welded layers corresponding to nickel alloys alloyed with molybdenum and chromium Brand of surfacing alloy

Mass fraction of elements in the deposited layer (%) C

Mn

Si

Cr

Mo

Others

Ni B A S E

H65M30

–

–

30.0

–

5.0

–

H65M15X15

–

15.0

15.0

–

5.0

–

15.0

18.0

7.0

2.5

–

2.0 Al

H60X20M8B4T2

–

20.0

8.0

1.5

7.5

3.5 Nb

H55X18B5M3

–

18.0

3.0

–

18.5

5.0 Nb

H62M16X15B4GC

2.3

15.5

16.0

–

3.0

4.4 W; 1.0 Mn; 0.6 Si

11.5

13.0

6.0

3.0

2.2

2.0 Al 0.8 W

H55X18K15M7T2

H61X13K12M6T3

2

2B

10.13 Surfaced Carbide-Based Alloys (Fe20, Ni20 Groups) Surfaced carbide-alloys are used for surfacing of drill cones, filling devices of blast furnaces, other parts that undergo intense abrasive wear [13–15]. The most common is the surfacing of cast tungsten carbide (relite)—a eutectic alloy of WC and W2 C carbides. Relite is used in the form of grains of different sizes or as a filler in steel tubes or as “tape relite”. The weight of the steel shell is about 40%, and the weight of carbide grains—60%. In addition to the relite chromium carbides Cr7 C3 , Cr23 C6 are used in carbide compositions as a solid component. Carbide compositions are characterized by the absence of the initial chemical composition. During solidification carbides do not crystallize from the melt but are introduced into the alloy-bond as prepared grains of the desired size and shape. In the process of surfacing carbide grains are only partially soluble in liquid metal. Carbide grains retain their original composition and structure in the deposited layer. Wear of carbide compositions is selective. The bonding alloy wears out faster. Wear-resistant carbide grains protrude above the surface of the part and absorb the main load. As the bonding alloy wears, the carbide grains protrude above the matrix. The bending load on the grains increases, which leads to breakage and chipping of carbides. To ensure high wear resistance of the carbide composition, carbides must have high hardness and strength. The bonding alloy must possess high resistance to abrasive wear and ensure strong fixation of carbide grains. Induction surfacing, gas surfacing, furnace surfacing are used for surfacing of carbide-based alloys.

206

10 Structure and Properties of Surfaced Metal of Different Alloying Systems

10.14 Surfaced Cobalt Alloys Alloyed with Chromium and Tungsten (Co1, Co2, Co3 Groups) Surfaced cobalt alloys alloyed with chromium and tungsten, the so-called stellites (Table 10.15) are designed for surfacing of fittings, valves and seats of internal combustion engines, tools for hot deformation of metal, knives for cutting cellulose, pump sleeves. The deposited metal has high wear resistance at normal and elevated temperatures, heat resistance, scale resistance, corrosion resistance. Chromium provides cobalt alloys with scale resistance, increases hardness, strength, and heat resistance. It should be noted that when chromium content is more than 34% inter-metal cobalt-chromium compounds are formed, which leads to embrittlement of alloys. Tungsten contributes to the increase of heat resistance and hardness. Tungsten content varies in a wide range from 3 to 25% depending on the purpose of the alloy. The carbon content does not exceed 2.5%. Carbon increases hardness. The effect of carbon is especially noticeable at high concentrations of chromium. Small (0.5–1.5%) additives of boron, manganese, etc. are also introduced in satellite. Boron provides the surfaced metal with increased hardness and wear resistance, as well as resistance to formation of hot cracks. However, boron reduces corrosion resistance in solutions of some acids 6, 12]. The structure of cobalt alloys alloyed with chromium and tungsten consists of a cobalt-based solid solution with a face-centered cubic lattice and carbides, mainly of M7 C3 , M23 C6 and M6 C types. Along with chromium and tungsten, carbides also contain cobalt. The alloys’ structure is eutectic and super-eutectic. Exceptions are soft and plastic 110K63X30B5C2H type alloys. They have a pre-eutectic structure with a small amount of carbide eutectic located along the grain boundaries of solid solution [6, 16]. Table. 10.15 Chemical composition of deposited layers corresponding to cobalt alloys alloyed with chromium and tungsten and their hardness after surfacing Brand of surfacing alloy Mass fraction of elements in the deposited layer (%)

HRC

C

Si

Cr

W

Ni

Fe

110K63X30B5C2H

1.1

2.5

30.0

4.5

1.2

≤ 2.0 –

Others 40–45

150K60X30B4H3C2

1.5

2.0

30.0

4.5

≤ 2.0

≤ 3.0 –

42–46

180K40X25B12H22C

1.8

1.5

25.0

12.0

22.0

≤ 2.0 –

42–48

190K62X29B5C2

1.9

2.0

30.0

4.5

–

≤ 2.0 0.2 Mn

44–48

190K60X30B9H2C

1.9

1.0

30.0

9.0

1.2

≤ 2.0 0.1 B; 0.8 Mn

46–52

250K55X30B12H3C

2.5

1.0

30.0

12.0

≤ 2.0

≤ 3.0 –

52–54

14K50X20B8H10G2C

0.14

0.8

20.0

8.0

10.0

3.0

1.5 Mn

29

110K60X29B4GC

1.1

1.0

29.0

4.5

–

4.0

1.0 Mn

40

10.14 Surfaced Cobalt Alloys Alloyed with Chromium and Tungsten (Co1 …

a

207

c

b Fig. 10.12 Structure of surfaced metal × 300 (stellite): a manual metal arc surfacing, b plasmapowder surfacing (powder fraction 200–250 μm), c plasma-powder surfacing (mixture of powders of two fractions—160–200 microns (70%) and 500–630 microns (30%)

In the case of manual metal arc surfacing with coated electrodes and in case of plasma-powder surfacing, the metal has a directional structure typical for surfacing (Fig. 10.12a, b). The fine-grained structure, which is more desirable, can be obtained by changing the particle size distribution of the powder and the effective thermal power of plasma arc. At the same time the directed growth of columnar crystallites is suppressed (Fig. 10.12c). Hardness of stellites varies from HRC 32 to HRC 66 depending on the composition of the solid solution and the carbide eutectic, as well as on presence of carbide, boride, and carbide-boride phases. Heat treatment does not affect the hardness of stellites. The exception is long exposure to temperatures above 700 ºC which leads to dispersion hardening and increased hardness. Strengthening of stellites during aging is associated either with formation of intermetallic CoCr or with the emergence of supersaturated solid solution of secondary fine carbides. Disadvantages of cobalt alloys alloyed with chromium and tungsten. • Susceptibility to cracking during surfacing, • Limited ability to obtain good performance properties when iron content in the deposited layer is less than 6%, • Difficulty of rolling the electrode wire or strip which complicates mechanization of the surfacing process, • Shortage and high cost of cobalt and tungsten.

208

10 Structure and Properties of Surfaced Metal of Different Alloying Systems

Manual metal arc surfacing with coated electrodes, gas surfacing with filler rods, mechanized surfacing in shielding gas, plasma-powder surfacing are used for cobalt alloys alloyed with chromium and tungsten.

10.15 Surfaced Copper-Based Alloys (Cu1 Group) Copper-based alloys have high corrosion resistance in seawater and in most inorganic and organic acids, as well as low coefficient of friction. The most common alloys are bronzes (Table 10.16)—alloys of copper with tin, aluminum, silicon. CuAl8 Mn11 Fe3 Ni2 alloy is highly resistant to erosion, cavitation and corrosion in seawater and is used to repair worn propellers, agitator blades and pump impellers. CuAl8 alloy is used for surfacing of ship propellers, pump housings and impellers, steel expansion couplings and valve seats. CuAl13 Fe4 alloy is used for surfacing of guide cutting machines. Manganese significantly increases hardness, strength, corrosion resistance and resistance to abrasive wear of aluminum bronze by dissolving up to 10% Mn in α-Cu [17]. Iron and nickel also increase hardness, strength, and resistance to abrasive wear. Brass—alloys of copper with zinc (Table 10.17) are used less often than bronzes for surfacing parts of friction pairs, as well as parts operated in seawater. Gas surfacing of brass is also used to repair steel and cast-iron castings, pumps, water turbine blades [18]

Table. 10.16 Chemical composition of bronze-type surfaced layers and their hardness after surfacing Brand of surfacing alloy CuAl8 CuAl9Fe3 CuAl11Fe3

Mass fraction of elements in the deposited layer (%) Mn

Fe

Ni

Si

Zn

HB

Cu

Al

Sn

B A S E

8.0

0.5

0.5

0.4

–

–

–

150

9.0

0.5

3.5

0.4

–

–

–

210

11.5

0.5

3.5

0.4

–

–

–

320

CuAl9Ni5Fe2

9.0

1.0

2.0

4.8

–

–

–

210

CuAl11Ni5Fe2

11.5

1.0

2.0

4.8

–

–

–

320

CuAl9Fe4

9.0

–

4.0

–

–

–

–

210

CuAl11Fe4

11.5

–

4.0

–

–

–

–

320

CuAl13Fe4

13.5

–

4.0

–

–

–

–

420

CuAl8Ni5Fe4Mn

8.5

1.5

4

5

–

–

–

170

CuAl8Mn11Fe3Ni2

8.0

11.5

3.0

2.0

–

–

–

210

CuSn6

≤ 0.1 –

≤ 0.2

≤ 0.2 –

≤ 0.2 5.5–7.0

75–85

CuSi3Mn1

–

–

–

0.1

95

1.0

3.0

0.1

References

209

Table. 10.17 Chemical composition of brass-type surfaced layers and their hardness after surfacing Brand of surfacing alloy

Mass fraction of elements in the deposited layer (%) Cu

Al

Ni

Zn

HB

Sn

CuZn30

70

–

–

30

–

70

CuZn39Sn1

60

–

–

39

1

70–80

CuZn18Al2

80

2

–

18

–

80–90

CuZn42Ni10

48

–

10

42

–

120

References 1. EN 14700:2014 Welding consumables – Welding consumables for hard-facing. - https://www. iso.org/standards.html 2. Gyl ev A.P. Metallovedenie. – M.: Metallypgi , 1977. – 647 c 3. Gellep .A. Inctpymental nye ctali. M.: Metallypgi , 1983. – 527 c 4. Pozn k L.A. Inctpymental nye ctali. - Kiev: Haykova dymka, 1996. - 488 c 5. Fpymin I.I. Avtomatiqecka lektpodygova naplavka. – Xap kov: Metallypgizdat, 1961. – 421 c 6. Gladki P.B., Pepepletqikov E.F., P bcev I.A. Plazmenna naplavka. – Kiev: kotexnologi , 2007. – 292 c 7. lektpoxlakova naplavka / Kyckov .M., Ckopoxodov B.H., P bcev I.A., Capyqev I.C. // – M.: «Hayka i texnologi », 2001. – 180 c 8. XH M - kak cpocob polyqeni tonko ctpyktypy naplavlennogo clo iz byctpope ywe ctali /B.I.Medovap, A.B.Qepnec, L.B.Medovap i dp. //Ppoblemy cpecial no lektpometallypgii. - 1997. - № 1. - C. 3–4 9. Poxodn I.K. Gop qie (kpictallizacionnye) tpewiny ppi naplavke vycokoyglepodictyx vycokoxpomictyx ctale //Gop qie tpewiny v cvapnyx coedineni x, clitkax i otlivkax. – M.: AH CCCP, 1959. – C. 68–92 10. Livxic L.C., Gpinbepg H.A., Kypkymelli .G. Ocnovy legipovani naplavlennogo metalla. – M.: Maxinoctpoenie, 1969. - 188 c 11. . Texnologi lektpiqecko cvapki metallov i cplavov plavleniem. Pod pedakcie B.E. Patona. – M.: Maxinoctpoenie, 1974. – 768 c 12. Pepepletqikov E.F. Plazmenna naplavka// Cvapwik. – 2000. – № 2. – C. 8–11 13. zvenko .A., ydpa A.P., Fpymin E.I. Ob iznaxivanii kompozicionnyx cplavov//Bycokoppoizvoditel nye ppoceccy naplavki i naplavoqnye matepialy. – Kommynapck: KMK, 1973. – C.103–107 14. Uppoqnenie kompozicionnym cplavom detale zagpyzoqnogo yctpo ctva domenno peqi ob emom 5000 m3/D.A.Dydko, B.I.Makcimoviq, I.B.Heteca i dp.//Cvapoqnoe ppoizvodctvo.– 1976. – № 2. – C. 10–12 15. Haplavka kompozicionnym cplavom detale metallypgiqeckogo obopydovani / B.D.Kydinov, B.B.Filimonov, C.A.Xevnov, I.B.Heteca //Avtomatiqecka cvapka. – 1985. – № 5. – C. 48–50 16. Cobaltbased alloys for surfacing. The Paton Weld J 2015. 56:101–106 17. Dobrza´nski LA (2006) Materiały in˙zynierskie i projektowanie materiałowe. Podstawy nauki o materiałach i metaloznawstwo. Warszawa, WNT, 1596 pp 18. . Pałasz J (1970) Poradnik spawacza gazowego. Warszawa, WNT, 299 pp

Chapter 11

Surfacing and Additive Manufacturing Imperfections

Abstract The classification of the most common imperfections of surfacing and additive technologies according to the ISO 6520 standard is provided. Mechanisms, causes of formation and measures to prevent hot cracks, cold cracks, reheating cracks during surfacing, gas pores, lack of fusion, deviation of the shape of the surfacing beads are described. The recommended methods of non-destructive testing of imperfections of surfacing and additive technologies are listed.

11.1 General Information Imperfection—an inconsistency in the weld (or base) metal, or deviation from the required geometry. Unacceptable imperfection is called defect. The appearance of imperfections depends on the chemical composition of the base and deposited metals, surfacing methods and technology (including the preparation of surfacing materials and products, surfacing parameters, use of pre- and in-process heating, personnel qualifications). Imperfections of surfacing and additive manufacturing are similar in nature to welding ones, so the classification according to ISO 6520-1 [1] is applicable for them. ISO 6520-1 classifies imperfections into six main groups (in imperfection identification, the main group is the first digit of the imperfection identification number): (1) (2) (3) (4) (5) (6)

cracks (100–106), cavities (201–203), solid inclusions (301–304), lack of fusion and penetration (401–403), imperfect shape and dimensions (501–521), miscellaneous imperfections (601–618).

In each main group imperfections are divided into subgroups by orientation (longitudinal, transverse), location (in the deposited bead, on fusion boundary, in heat affected zone, in base metal metal), or by quantity (single, group) [2]. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 I. Ryabtsev et al., Surfacing and Additive Technologies in Welded Fabrication, https://doi.org/10.1007/978-3-031-34390-2_11

211

212

11 Surfacing and Additive Manufacturing Imperfections

ISO 6520-1 describes imperfections that may occur in structures fabricated using fusion welding technologies, including those with high density heating sources. Therefore, it can be used without restrictions for surfacing and additive manufacturing technologies based on such processes and using metallic filler materials in the form of wires or strips. At the same time, its use is limited in cases where a coating or a part is made by sintering powders, especially if the powder contains non-metallic components. Technical specification ISO/TS 17845: 2004 provides a more general classification of imperfections. It includes imperfections caused by welding and related processes (including metallurgical) for metallic and non-metallic materials. However, the ISO 6520-1 standard is more convenient for practical use, as it is directly related to quality control standards, such as ISO 5817. In the text below the numerical designations for imperfections are given in accordance with ISO 6520-1. The most common imperfections of surfacing and additive manufacturing are: . cracks—all types, . cavities—gas pores (2011–2014, 2017), . lack of fusion—between separate beads (4012), between the bead and the base metal (4011), . imperfect shape—all types. Various methods of non-destructive testing are used to detect imperfections in surfacing and additive manufacturing, such as: visual, radiographic, ultrasonic, penetrant, magnetic powder, eddy current method. Testing techniques and evaluation criteria are given in the corresponding standards. Non-destructive testing methods have certain limitations and peculiarities of application, which must be considered when choosing them. Visual testing identifies only surface imperfections and, depending on the testing technique, may require pre-machining of the surface in the control area. Radiographic testing makes it possible to identify imperfections at any depth, but the effectiveness of control depends on the orientation of the imperfection relative to the direction of transmission and on the imperfection’s dimensions. Ultrasonic testing requires mandatory surface pre-machining in the control area. Same as radiography, it makes it possible to identify internal imperfections, but the effectiveness of control depends on the orientation of the imperfection and its disclosure (in the case of cavity-type imperfections). Penetrant testing detects surface hollow imperfections and requires mandatory mechanical surface preparation before inspection. Magnetic powder testing can only be used for ferromagnetic materials. In addition to superficial, it allows to detect imperfections located close to the surface. The method, depending on the technique, may require pre-machining the surface. The eddy current method allows to detect imperfections on the surface and with a small depth and requires prior machining of the control area. The method is used exclusively for electrically conductive materials.

11.2 Cracks

213

11.2 Cracks Crack (Fig. 11.1)—disruption of the interatomic bonds of the crystal lattice of metal with the formation of free surfaces (crack surfaces). According to the mechanism of formation, the most common cracks are [2]. (1) Hot cracks—occur either in solid–liquid state during crystallization or in solid state at high temperatures at the stage of predominant intergranular deformation in temperature intervals of brittleness (temperature intervals during crystallization and cooling of weld metal in which the plastic properties of metal decrease to the level of minimum plasticity). A combination of two physical effects causes formation of hot cracks: abrupt loss of plasticity of the metal in the temperature range of brittleness, effect of temporary tensile welding deformations that occur during cooling of the welded joint. A crack occurs if the rate of high-temperature welding deformation exceeds the deformation capacity of the metal in a certain temperature range of brittleness. (2) Cold cracks—occur during cooling to temperatures usually below 200 °C. Two conditions cause formation of cols cracks: reduction of the plastic properties of base metal due to the influence of alloying elements and/or effect of diffused hydrogen, ensuring the inflow of energy for crack formation due to residual

1012

1021

1023 1014

1024 1013 1001

1011

x500

Fig. 11.1 Types of cracks during surfacing: 1001—microcracks, 1011—longitudinal and 1021— transverse in the bead, 1012—longitudinal along the fusion boundary, 1013—longitudinal and 1023—transverse in the heat affected zone, 1014—longitudinal and 1024—transverse in the base metal

214

11 Surfacing and Additive Manufacturing Imperfections

stresses. The presence of a stress concentrator, especially an imperfection, facilitates formation of cracks. (3) Reheating cracks—occur during multilayer surfacing. The reason for formation of reheating cracks is release of excess phases (most often carbides) from supersaturated solid solution of metal and alloys. As a result, the hardness and strength increase, but toughness and ductility decrease. Cracks are a common type of surfacing imperfections for the following reasons. (1) Surfaced metal (in many cases base metal as well) has high content of carbon and alloying elements, which leads to: . structural transformations accompanied by volume changes (martensitic transformations) and formation of stresses of the second type (at the grain level) and the third type (at the level of the crystal lattice), . presence of temperature intervals of brittleness, which creates conditions for formation of hot cracks, . high brittleness of the metal, which creates conditions for formation of cold cracks. (2) A feature of the technology is the high cooling rate of the deposited bead on the base metal, which is not deformed. This leads to large deformations during crystallization process in the temperature range of brittleness. In addition, there is a high level of residual tensile stresses in the deposited bead. Cracks during surfacing are the most dangerous type of imperfection, for the following reasons. (a) Cracks are the largest stress concentrators. (b) Surfaced parts are operated in conditions of fatigue and impact loads and (or) aggressive working environments, at high temperatures. All operational factors initiate additional micro-level fracture processes at the crack tip (accumulation of damage in case of fatigue loads or anodic dissolution and hydrogen embrittlement in case of corrosion) and significantly reduce the critical length of crack propagation. However, cracks may be acceptable in cases when the part does not carry the load and presence of cracks does not lead to chipping of the deposited layer. This applies to cracks that do not go into the base metal or are not oriented parallel to the fusion surface. Examples of parts where cracks may be allowed are blast furnace cones, leaks for transporting abrasive materials, hoppers and other parts operated in abrasive wear conditions. These parts are surfaced with materials of groups Fe13–Fe16 and Fe20 (Sect. 10). Methods of non-destructive testing of surfacing and additive manufacturing cracks: . visual (for long surface cracks), . penetrant (for surface cracks), . radiographic,

11.3 Gas Pores

215

. ultrasonic, . eddy currents (after machining the surface of the deposited layer), . magnetic powder. The main way to prevent formation of cracks during surfacing is pre- and inprocess heating of the part.

11.3 Gas Pores Gas pores (Fig. 11.2)—spherical cavities in the deposited bead formed by trapped gas released during crystallization. The mechanism of gas pore formation consists of the following stages [2]. . Gases enter surfacing zone and dissolve in the liquid metal of the surfacing pool. Such gases are: hydrogen—from moisture contained in flux, in coating of the electrodes, in rust and scale on the surface and on the surfacing wire, in protective gases and in the air, nitrogen—from the air, carbon dioxide—during the combustion of pollutants (lubricants, etc.) on the surface of the part, on the surfacing materials, violation of surfacing parameters when using CO2 as a protective gas. . As the temperature of the surfacing pool decreases, solubility of gases in the metal decreases and, as a result, gas is released in the form of bubbles.

2017 2011 2013 2014 2012 x50

Fig. 11.2 Types of gas pores in the weld metal: 2011—gas pore, 2012—evenly distributed porosity, 2013—group of pores, 2014—linear porosity, 2017—surface pore

216

11 Surfacing and Additive Manufacturing Imperfections

. Some gas bubbles float to the surface of the liquid metal and are removed from the surfacing pool. The pores are formed by another part of gas bubbles, which do not have time to emerge and remain in the bead after crystallization. Single gas pores of a certain size or gas pores in parts operated in abrasive wear conditions without significant force load may be permissible. Methods of non-destructive testing for surfacing and additive manufacturing gas pores: . visual (for surface pores), . radiographic, . ultrasonic. Measures to prevent the formation of gas pores are aimed at preventing gases from entering the surfacing pool and facilitating gas release and removal during crystallization: . improving the protection of the surfacing zone, . cleaning of surfacing materials from moisture (calcination of coated electrodes, drying of flux, cleaning of protective gases), . cleaning of the surface from rust, scale, and grease before surfacing, . increasing the time of the weld metal in the liquid state, for example, by reducing the rate of deposition, . reduction of the contact surface of the arc with air and possibility of nitrogen entering the welding zone, for example by reducing the arc length, . reduction of sulfur impurities in the base metal, . use of external magnetic fields for stirring metal of the surfacing pool.

11.4 Lack of Fusion Lack of fusion (Fig. 11.3)—absence of joint due to lack of melting between the bead and the base metal (4011) or between the separate beads (4012). Lack of fusion is caused by: . incorrect surfacing parameters (low current, high surfacing speed)—the main reason, . increasing surface contamination, poor surface preparation of previous layers. Lack of fusion is the most dangerous in parts that work under fatigue loads. Methods of non-destructive testing for lack of fusion: . ultrasonic, . radiographic, . eddy currents.

11.5 Imperfect Bead Shape

217

4011

4012

Fig. 11.3 Lack of fusion: 4011—between bead and base metal, 4012—Between separate beads in multilayer surfacing

11.5 Imperfect Bead Shape Imperfect bead shape is the most numerous groups of surfacing imperfections. The most common subgroups are (Fig. 11.4): . uneven width of the bead (513), . uneven surface of the bead (514). Uneven width of the bead is caused by: . long arc length, . unstable surfacing parameters, . low personnel qualifications, 513 514

Fig. 11.4 Imperfect bead shape: 513—uneven bead width, 514—uneven bead surface

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11 Surfacing and Additive Manufacturing Imperfections

. improper equipment characteristics, for example use of a power source with constant voltage or constant current with flatter output slope characteristic during manual metal arc surfacing. Uneven surface of the bead is caused by: . uneven surfacing speed, . low personnel qualifications, . high ductility of liquid flux (in submerged arc surfacing). The following subgroups also belong to imperfect bead shape: . undercut (501)—deepening in the base metal or in the previous bead on the border with the surfacing bead (occurs due to poor heat dissipation, high arc voltage, high surfacing speed), . excess penetration (504)—occurs due to excessive local heating, for example due to high arc current, . burn-through (510)—leakage of the surfacing pool with the formation of a through hole in the bead (imperfection in thin-walled parts when, for example, the arc current is exceeded or the surfacing speed is reduced), . poor arc restart (517)—local surface roughness in place of restarting of surfacing (occurs due to low current or voltage), . bulking (520)—deviation of the shape and size of the surfaced product, which occurs as a result of residual welding stresses and strains. The following products are mainly subject to bulking: sheet metal products (due to low rigidity and, as a result, loss of stability under the action of longitudinal and transverse shrinkage forces), products made of aluminum and its alloys (due to the relatively high coefficient of thermal expansion), products made of high-alloy austenitic steels (due to higher coefficient of thermal expansion and lower thermal conductivity compared to carbon steels). . incorrect dimensions of the bead (521)—deviation of convexity and width of the bead from the standard dimensions due to violation of the surfacing parameters, low personnel qualification. Non-destructive testing of imperfect bead shape is performed with visual method.

11.6 Less Common Surfacing and Additive Manufacturing Imperfections Solid inclusions (third group of imperfections)—foreign substances in the weld metal of small volume of non-metallic or metallic origin. Solid inclusions are classified into four subgroups depending on the composition of the substance that forms the inclusion: . slag inclusions (301),

11.6 Less Common Surfacing and Additive Manufacturing Imperfections

219

Fig. 11.5 Slag inclusions

301

. flux inclusions (302), . oxide inclusions (303), . metal inclusions (304)—tungsten (3041), copper (3042) or inclusions of other metals (3043). Slag inclusions (Fig. 11.5) can be formed in the weld metal during manual metal arc surfacing, surfacing with self-protective flux-cored wires and during automated submerged arc surfacing. Solid inclusions are caused by: . poor surface cleaning before surfacing, . incorrect choice of flux and electrode coating, which does not provide sufficient slag removal and separation of slag crust, . high rate of deposition, low current (short time of the metal remaining in the liquid state does not give inclusions enough time to float until the crystallization process ends), . low personnel qualifications, . Methods of non-destructive testing of solid inclusions: – – – – –

visual (for surface inclusions), radiographic, ultrasonic, eddy currents, magnetic powder.

Miscellaneous imperfections (sixth group of imperfections) include 14 subgroups, 4 of which are important for surfacing: . accidental arc (601)—local damage to the base metal surface adjacent to the deposited layer due to accidental striking of the arc, . spatter (602)—drops of metal formed during the surfacing process and welded to the surface of the hardened weld layer or to the base metal, . tempering colors (610)—a thin painted oxide film on the surface in the welding (surfacing) zone, for example, when welding stainless steel, the appearance of which is due to heating during surfacing and/or insufficient protection, for example, when welding (surfacing) titanium,

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11 Surfacing and Additive Manufacturing Imperfections

. slag residues (615)—slag that is not completely removed from the surface of the weld or weld metal. The main causes of miscellaneous imperfections are: . low personnel qualifications, . wrong choice of welding materials: shielding gas, flux, electrode coating etc. Non-destructive testing of miscellaneous surfacing imperfections is performed with visual method.

References 1. ISO 6520:2015 Classification of imperfections in metallic fusion welds, with explanations. https://www.iso.org/standards.html, https://www.iso.org/standards.html 2. Fomichov S, Skachkov I, Chvertko E, Minakov S, Banin A (2021) Quality management in welded fabrication. In: Part of international welding engineers textbook series under the editorship of borys paton, vol 1. Kyiv, Polytechnica, 222 P

Chapter 12

Procedures’ Qualification for Surfacing and Additive Manufacturing

Abstract The definition of qualification of procedures for surfacing and additive technologies is given. The mandatory qualification is substantiated based on the provision of controlled conditions of surfacing and additive technologies in accordance with the ISO 9001 standard. Mandatory documented information regarding the certification of welding (surfacing) procedures in accordance with ISO 15607, 15613 and ISO 15614 standards is listed: “Preliminary welding procedure specification” (pWPS); “Welding Procedure Qualification Protocol” (WPQR); “Welding procedure specification” (WPS); “System operating procedure” (SOP). The requirements for control samples for surfacing are given. Recommendations are given on the preparation of the “Program of testing control samples” and the use of non-destructive and destructive testing methods. The structure of the “Welding Procedure Qualification Protocol” (WPQR) is provided, explanations and recommendations on the use of test results are given.

12.1 Definitions of Procedure Qualification Provision of controlled conditions and traceability are the main requirements of ISO 9001 standard [1] for manufacturing. Controlled conditions are provided when eight ISO 9001 mandatory requirements for manufacturing are met, one of which is validation of production processes when the result cannot be confirmed by direct monitoring or measurement. Such processes are called special. Welding, surfacing and additive manufacturing are considered as special processes, as there are no means of control that can quantify changes in structure and properties, stress–strain state, imperfections. The influence of welding and related processes on the quality of the product is detected only during operation. Procedures’ qualification (systematic, formalized confirmation of compliance of procedures with certain requirements) for welding, surfacing and additive manufacturing is a common form of process validation and is regulated by ISO 15607 [2], 15613 [3] and ISO 15614 [4]—the basic standard.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 I. Ryabtsev et al., Surfacing and Additive Technologies in Welded Fabrication, https://doi.org/10.1007/978-3-031-34390-2_12

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Standards use the following terminology (common for welding, surfacing and additive manufacturing): • welding (surfacing) procedure—established procedure for performing welds (surfaced beads), which includes instructions for the welding (surfacing) process, base and welding (surfacing) materials, preparation for welding (surfacing), preheating, if necessary, method and control of welding (surfacing), heat treatment and necessary equipment, • preliminary Welding Procedure Specification (pWPS)—a specification that contains parameter values of the welding procedure to be qualified, • Welding Procedure Qualification Record (WPQR)—a record containing all the necessary data for the qualification of preliminary welding procedure specification (pWPS), • Welding Procedure Specification (WPS)—a specification that contains values of parameters of the welding procedure that ensure repeatability in production and was qualified by one of the standard methods, • System Operating Procedure (SOP)—a specification that contains simplified welding procedure specification in a form suitable for use in specific shop conditions. Surfacing procedure qualification should be carried out before implementing it in production. It is recommended that qualification of surfacing procedures is carried out by an independent accredited body.

12.2 Control Samples After preliminary specification (pWPS) was developed it is necessary to test the surfacing procedure in accordance with ISO 15614 [4] on standard control samples made of plates (Fig. 12.1) or pipes. The surfacing of control samples is performed in accordance with the manufacturer’s “Preliminary Surfacing Procedure Specification” (pWPS) in the presence of an expert appointed by an expert body. In case when design features of the product change the heat dissipation and temperature-related structural and deformation processes, the surfacing conditions cannot be reproduced by standard samples. ISO 15613 standard [3] allows testing of non-standard welded control samples, which in shape and size mimics the product. Surfacing procedure qualification is based on pre-production testing. In this case, it is necessary to agree with the expert body on the methodology of preparation of non-standard control samples, the scope of tests and requirements for test results.

223

≥250 ≥150

≥3

12.3 Program of Control Samples’ Testing

2 1 ≥200

t

≥400 Fig. 12.1 Welded control sample—plate: 1—sublayer, (applied if required), 2—layer numbers according to pWPS or the total thickness of the deposited layer, t is the base metal thickness

12.3 Program of Control Samples’ Testing Control samples surfaced according to pWPS requirements are to be tested. Testing includes non-destructive and destructive methods (Table 12.1) in the following sequence: Table 12.1 Surfaced control samples’ testing program Specimen

Testing

Testing volume

Note

All types of surfacing except wear-resistant

Visual testing Ultrasound testing Detection of surface cracks Side bending Macrostructure analysis Microstructure analysis Chemical analysis Contents of delta-ferrite/ferrite number FN Hardness measurement

100% 100% 100% 2 specimens 1 specimen 1 specimen 1 specimen 1 specimen 1 measurement

– a b c – d – a d

Wear-resistant surfacing

Visual testing Detection of surface cracks Macrostructure analysis Microstructure analysis Hardness measurement

100% 100% 1 specimen 1 specimen 1 measurement

– b – – d

a—according to corresponding standards if applicable; b—penetrant or magnetic particle testing; c—transversal bending can be replaced with ultrasound testing; two additional macrostructure analysis specimens; d—not required for metals Group 1 ISO15608

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12 Procedures’ Qualification for Surfacing and Additive Manufacturing

Fig. 12.2 Diagram of cutting samples from the welded control sample—plates for destructive methods’ testing

3

2

1

2

3

(a) Heat treatment after surfacing—if required by pWPS. (b) Non-destructive testing: • visual testing, • ultrasonic testing—if required by standards, • detection of surface cracks by penetrant or magnetic powder testing. (c) In case of positive results of non-destructive testing—cutting samples and testing with destructive methods (Fig. 12.2): • 1—area for cutting: sample for research of macrostructures, sample for chemical analysis and determination of delta-ferrite content, sample for research of microstructure with hardness measurement, samples for repeated research, • 2—area for cutting the sample for transverse bending tests, • 3—uncontrolled area of at least 25 mm of weld metal. Samples for macrostructure and microstructure research should be prepared and etched on one side to clearly identify the fusion line, heat affected zone and deposited layers. Samples for macrostructure studies should include base metal that has not been affected by surfacing. Hardness should be measured by the Vickers method under HV10 or HV5 load. In case of wear-resistant surfacing at least five measurements should be made on the surface of the control sample. Hardness is defined as the arithmetic average value of five measurements. Hardness in heat affected zone should not exceed the permissible maximum values (Table 12.2). In the case of wear-resistant surfacing, the maximum values of the deposited layer hardness should be determined. When tested for side bending, the specimen shall not have single cracks larger than 3 mm in any direction. Cracks appearing during the test at the edges of the sample are not taken into account.

12.4 Welding Procedure Qualification Record (WPQR)

225

Table 12.2 Maximum permissible hardness values in heat affected zone (HV 10 load) Group of steels according to 15,608

Without heat treatment With heat treatment

1—Non-alloyed and fine-grained steels

380

320

2—Thermo mechanically treated steels

380

320

3—Quenched and precipitation hardened steels

450

380

4—Low vanadium alloyed steels Cr–Mo–(Ni)

380

320

5—Steels free of vanadium Cr–Mo (C ≤ 0035%) 380

320

6—High vanadium alloyed Cr–Mo–(Ni) steels

–

350

12.4 Welding Procedure Qualification Record (WPQR) If the tests do not reveal unacceptable imperfections (defects), the expert body draws up a surfacing procedure qualification record—WPQR. WPQR contains the following sections: • qualification range of surfacing procedure specification, • information on the technology of surfacing and heat treatment of the control sample, • test results of the control sample. In the Qualification range section of the WPQR the following should be indicated: • surfacing process according to ISO 4063 [5], • operational purpose of surfacing (wear-resistant, corrosion-resistant or other), • structure of the deposited layer (single-layer or multilayer, number of layers). Qualification range of the surfacing procedure determines possible limits of deviation from the parameters of surfacing and processing of the control sample. For all purposes of surfacing, except wear-resistant, the qualification of singlelayer surfacing applies to multilayers, provided that each layer is deposited by the same technology. For wear-resistant surfacing, the qualification of single-layer surfacing does not apply to multilayer surfacing. Qualification of multilayer surfacing does not apply to single-layer surfacing. Qualification of multilayer surfacing with the number of layers N applies only to multilayer surfacing with the number of layers from N to (N + 4). Base metal thickness. When the base metal thickness of the control sample (flat sample) is t < 25 mm the qualification range of the surfacing procedure is limited with products 0.8–1.5 t thick. When t ≥ 25 mm the qualification range includes products with a thickness of more than 25 mm. When surfacing the tubular sample, qualification applies to all pipes with diameters above 0.75 of the outer diameters of the control sample. Minimum qualified thickness of the deposited layer. For wear-resistant surfacing with machining of the weld layer the minimum qualified thickness is the distance between the fusion line and the treated surface of the control specimen at which the

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12 Procedures’ Qualification for Surfacing and Additive Manufacturing

hardness measurement was performed. For other surfacing purposes the minimum certified thickness is the distance between the fusion line and the treated surface of the control sample on which the chemical analysis was performed. Brand of electrode (filler) material in surfacing qualification extends to other electrode (filler) materials, if they have equivalent mechanical properties, the same type of coating, the same nominal chemical composition and hydrogen content as indicated in the relevant standard on electrode (filler) material. Surfacing current, its type and polarity in the qualification range of the surfacing procedure are regulated by the amount of heat introduced during surfacing in accordance with EN 1011-1 [6]. The upper limit for the amount of heat input for each layer may be set 25% higher than that during surfacing of the control sample. The lower limit may be set 10% below the amount of heat input during surfacing of the control sample. Surfacing position in the qualification range of the surfacing procedure must completely coincide with the position in which the surfacing of the control sample was carried out. Preheating temperature, interpass temperature and post-surfacing heat treatment in the qualification range of the surfacing procedure must completely coincide with the parameters of surfacing and treatment of the control sample. Adding, canceling, or changing the heat treatment parameters is not allowed.

References 1. ISO 9001:2015 Quality management systems. Requirements. https://www.iso.org/standards. html 2. ISO 15607:2019 Specification and qualification of welding procedures for metallic materials — General rules. https://www.iso.org/standards.html 3. ISO 15613:2004 Specification and qualification of welding procedures for metallic materials — qualification based on pre-production welding test. https://www.iso.org/standards.html 4. ISO 15614-1:2017 Specification and qualification of welding procedures for metallic materials — welding procedure test — Part 1: Arc and gas welding of steels and arc welding of nickel and nickel alloys. https://www.iso.org/standards.html, https://www.iso.org/standards.html 5. ISO 4063:2009 Welding and allied processes — nomenclature of processes and reference numbers. https://www.iso.org/standards.html 6. EN 1011-1:2009 Welding - recommendations for welding of metallic materials – Part 1 - General guidance for arc welding. https://www.iso.org/standards.html