METALLURGY OF WELDING

London

Metallurgy of Welding 1. F. LANCASTER

GEORGE ALLEN & UNWIN Boston Sydney

First published as Metallurgy of welding, brazing and soldering in 1965 Third edition 1980

This book is copyright under the Berne Convention. All rights are reserved. Apart from any fair dealing for the purpose of private study, research, criticism or review, as permitted under the Copyright Act, 1956, no part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, electrical, chemical, mechanical, optical, photocopying, recording or otherwise, without the prior permission of the copyright owner. Enquiries shouldbe sent tothe publishers at the undermentioned address:

GEORGE ALLEN & UNWIN LTD 40 Museum Street, London WCIA lLU

© J. F. Lancaster, 1980 Softcover reprint of the hardcover 1st edition 1980

British Libory Cataloguing in Publication Data

Lancaster, John Frederick Metallurgy of welding. - 2nd ed. 1. Welding 2. Solder and soldering 3. Brazing I. Title II. Metallurgy of welding, brazing and soldering 671.5 TS227

ISBN 978-94-010-9508-2 ISBN 978-94-010-9506-8 (eBook) DOl 10.1007/978-94-010-9506-8

Typeset in 10 on 12 point Times by Alden Press Ltd.

Preface

This book is intended, like its predecessor (The metallurgy of welding, brazing and soldering), to provide a textbook for undergraduate and postgraduate students concerned with welding, and for candidates taking the Welding Institute examinations. At the same time, it may prove useful to practising engineers, metallurgists and welding engineers in that it offers a resume of information on welding metallurgy together with some material on the engineering problems associated with welding such as reliability and risk analysis.

In certain areas there have been developments that necessitated complete re-writing of the previous text. Thanks to the author's colleagues in Study Group 212 of the International Institute of Welding, understanding of mass flow in fusion welding has been radically transformed. Knowledge of the metallurgy of carbon and ferritic alloy steel, as applied to welding, has continued to advance at a rapid pace, while the literature on fracture mechanics accumulates at an even greater rate. In other areas, the welding of non-ferrous metals for example, there is little change to report over the last decade, and the original text of the book is only slightly modified. In those fields where there has been significant advance, the subject has become more quantitative and the standard of math­ematics required for a proper understanding has been raised. Mass flow in welding, for example, is not comprehensible without some knowledge of fluid dynamics, and fluid dynamics in turn is not comprehensible without a knowl­edge of vector analysis. In this and in other ways, welding technology will in the future, as it advances from a workshop subject to a full-fledged branch of engineering, demand higher standards of academic achievement from its students.

SI units are used throughout the book and a list of conversion factors is to be found in Appendix 2. Symbols are standardised so far as practicable and are listed in Appendix 1. The American Welding Society designations for welding processes have been used, although it is realised that in Europe (including the United Kingdom) there is a general preference for the older terms, TIG as opposed to GTA, for example. The AWS terms have been employed because they are more precise, have been standardised for a wider range of processes, and because A WS practice fmds increasing acceptance internationally, particularly in the oil, gas, petroleum and petrochemical industries, where welding is a key process in the manufacture of plant and equipment.

The author is glad to have the opportunity to thank Professor R. L. Apps, Professor C. E. Jackson and Dr. M. F. Jordan, for undertaking the onerous task

viii Preface

of reading and commenting on the fIrst draft of this book. The majority of the comments thus received were incorporated into the fmal text, thereby much improving its quality.

J. F. Lancaster

Contents

PREFACE

CHAPTER 1 INTRODUcrORY 1.1 Welding in ancient and medieval times 1.2 The advent of fusion welding 1.3 The theory of metal joining techniques 1.4 Welding engineering

CHAPTER 2 PROCESSES AND TYPES OF JOINT 2.1 The general character of welding, brazing, soldering and

adhesive jointing 2.2 The nature of welding processes

2.2.1 The classification of fusion welding processes 2.2.2 Heat source intensity 2.2.3 Heat input rate 2.2.4 Shielding methods

2.3 Types of fusion welded joint

CHAPTER 3 MASS AND HEAT FLOW IN WELDING 3.1 General 3.2 Mass flow: general 3.3 Mass flow from the electrode to the workpiece

3.3.1 The pinch instability 3.3.2 Other modes of instability

3.4 Mass flow in the weld pool 3.5 Heat flow: general

3.5.1 Heat sources 3.5.2 The welding arc

3.5.2.1 Electrode interactions 3.5.2.2 The arc column

3.5.3 Heat flow in the electrode 3.5.3.1 Time-dependent heat flow

3.5.4 Heat flow in the weld pool 3.5.5 Heat flow in the solid workpiece: theory 3.5.6 Heat flow in the solid workpiece: experimental

Page vii

1 1 2 4 4

6

6 6 7 7

13 14 16

19 19 20 21 22 26 29 31 31 32 33 35 39 39 41 41 45

CHAPTER 4 METALLURGICAL EFFECTS OF THE WELD THERMAL CYCLE 51

4.1 Metallurgical effects in the weld metal 51 4.1.1 Gas-metal reactions 51

4.1.1.1 Absorption 52 4.1.1. 2 Reaction 53 4.1.1.3 Evolution 55

x Contents

4.1.2 Dilution and uniformity of the weld deposit 58 4.1.3 Weld pool solidification 59 4.1.4 Weld cracking 63

4.1.4.1 Supersolidus cracking 64 4.1.4.2 Sub solidus cracking 67

4.2 Metallurgical effects in the parent metal and solidified weld metal 67 4.2.1 Microstructural changes in the heat-affected zone 67 4.2.2 Precipitation and embrittlement in the heat-affected zone 68 4.2.3 Contraction and residual stress 70

CHAPTER 5 SOLID-PHASE WELDING 74 5.1 Fundamentals 74

5.1.1 The cohesion and strength of metals 74 5.1.2 Surface deformation 76 5.1.3 Surface films 77 5.1.4 Recrystallisation 78 5.1.5 Diffusion 78

5.2 Processes 79 5.2.1 Pressure welding at elevated temperature 79 5.2.2 Diffusion bonding 82 5.2.3 Cold pressure welding 83 5.2.4 Friction welding 83 5.2.5 Explosive welding 84

CHAPTER 6 BRAZING, SOLDERING AND ADHESIVE BONDING 87 6.1 Physical aspects 87

6.1.1 Bonding 87 6.1.2 Surface energy and contact angle 88 6.1.3 Capillary action 91

6.2 Soldering and brazing 93 6.2.1 Wetting and spreading 93 6.2.2 Filling the joint 95 6.2.3 Solidification range 95

6.3 Soldering 95 6.3.1 Joint design 95 6.3.2 Solders 96 6.3.3 Fluxes 96 6.3.4 Soldering methods 97 6.3.5 Application to various metals 97

6.4 Brazing 97 6.4.1 Joint design 97 6.4.2 Brazing solders 98 6.4.3 Fluxes and protective atmospheres 98 6.4.4 Brazing methods 101 6.4.5 Bronze welding 102 6.4.6 Application to various metals 102

6.5 Adhesive bonding 103 6.5.1 Mechanical strength 104

6.5.1.1 Contact angle 104 6.5.1.2 Residual,stress and stress concentration factors 105

6.5.2 Bonding methods 106 6.5.2.1 Preparing the surface 106 6.5.2.2 Types of adhesive and the mode of application 107 6.5.2.3 Curing the joint 107

Contents xi

6.5.2.4 Testing 108 6.5.3 Applications 108

CHAPTER 7 CARBON AND FERRITIC-ALLOY STEELS 110 7.1 Scope 110 7.2 Metallurgy of the liquid weld metal 110

7.2.1 Gas-metal reactions 110 7.2.1.1 Reactions in the transferring drop 111 7.2.1.2 Reactions in the weld pool 111

7.2.2 Slag-metal reactions 112 7.2.2.1 The mechanics of slag-metal interaction 112 7.2.2.2 The chemistry of slag-metal interaction 114

7.2.3 Solidification and solidification cracking 116 7.3 Transformation and microstructure of steel 118

7.3.1 Transformation and microstructure of weld metal 120 7.3.2 Transformation and microstructure in the heat-

affected zone 121 7.4 The mechanical properties of the welded joint 126

7.4.1 The mechanical properties of weld metals 127 7.4.2 The mechanical properties of the heat-affected zone 129

7.4.2.1 The hardness of the HAZ 129 7.4.2.2 The fracture toughness of the HAZ 131

7.5 Stress intensification, embrittlement, and cracking of fusion welds below the solidus 134 7.5.1 Stress concentration 134 7.5.2 Embrittlement of fusion welds 134 7.5.3 The hydrogen embrittlement and cracking of welds in steel 135

7.5.3.1 Hydrogen attack 136 7.5.3.2 Hydrogen embrittlement 136 7.5.3.3 The solution of hydrogen 136 7.5.3.4 Cracking due to dissolved hydrogen 138 7.5.3.5 Hydrogen-induced cold cracking in welds 139 7.5.3.6 Testing for hydrogen-induced cold cracking 147 7.5.3.7 Measures to avoid hydrogen-induced cold cracking 150

7.5.4 Chevron cracking 152 7.5.5 Lamellar tearing 155 7.5.6 Reheat cracking 156

7.6 Welding problems with iron and steel products 160 7.6.1 Cast iron 160 7.6.2 Steels used primarily for their mechanical properties 162

7.6.2.1 Carbon and carbon-manganese steels 163 7.6.2.2 Microalloyed steels 164 7.6.2.3 Low-alloy normalised and tempered (NT) steels 167 7.6.2.4 Low-alloy quenched and tempered (QT) steels 170

7.6.3 Steels for subzero temperature use 172 7.6.4 Low-alloy corrosion- and heat-resisting steels 172 7.6.5 Ferritic and austenitic/ferritic chromium stainless steels 173

CHAPTER 8 AUSTENITIC AND HIGH-ALLOY STEELS 178 8.1 Scope 178 8.2 Metallurgy of the weld metal and heat-affected zone 178

8.2.1 Alloy constitution 178 8.2.2 Carbide precipitation 180 8.2.3 Solidification cracking in the weld deposit 182

xii Contents

8.2.4 Hot cracking in the heat-affected zone during welding 185 8.2.5 Reheat cracking 186

8.3 Corrosion 187 8.3.1 Intergranuiar corrosion 187 8.3.2 Stress corrosion cracking 190 8.3.3 Preferential corrosion of welds 191

8.4 Corrosion-resistant steels: alloys and welding procedures 192 8.5 Weld overlay cladding and dissimilar metal joints 193 8.6 Heat-resisting steels: alloys and welding procedures 194 8.7 Hardenable high-alloy steels 195

CHAPTER 9 NON-FERROUSMETALS 197 9.1 Aluminium and its alloys 197

9.1.1 Processes and materials 197 9.1.2 Porosity 198 9.1.3 Cracking 199 9.1.4 Mechanical properties 202 9.1.5 Alloys and welding procedures 204

9.2 Magnesium and its alloys 205 9.2.1 Alloys and welding procedures 205 9.2.2 Oxide film removal 206 9.2.3 Cracking 206 9.2.4 Mechanical properties 206 9.2.5 Corrosion resistance and fire risk 206

9.3 Copper and its alloys 207 9.3.1 Processes and materials 207 9.3.2 Heat input 207 9.3.3 Porosity 208 9.3.4 Cracking 209 9.3.5 Mechanical properties 209 9.3.6 Alloys and welding procedures 209

9.4 Nickel and its alloys 211 9.4.1 Cracking 211 9.4.2 Porosity 212 9.4.3 Mechanical properties 213 9.4.4 Corrosion resistance 213 9.4.5 Oxidation and creep resistance 216 9.4.6 Alloys and welding procedures 216

9.5 The reactive and refractory metals - beryllium, titanium, zirconium, niobium, molybdenum, tantalum and tungsten 216 9.5.1 Embrittlement due to gas absorption 217 9.5.2 Embrittlement due to recrystallisation 218 9.5.3 Porosity 219 9.5.4 Cracking 219 9.5.5 Tensile properties 219 9.5.6 Alloys and welding procedures 220

9.6 The low-melting metals: lead and zinc 221 9.6.1 Lead 221 9.6.2 Zinc 221

9.7 The precious metals: silver, gold, platinum 222 9.7.1 Silver 222 9.7.2 Gold 222 9.7.3 Platinum 222 9.7.4 Other platinum-group metals 222

C?ontents xiil

CHAPTER 10 THE BEHA VIOUR OF WELDS IN SER VIC?E 224 10.1 Reliability 224 10.2 Service problems associated with welding 226 10.3 Fast crack growth 226

10.3.1 General 226 10.3.2 Linear elastic-fracture mechanics (LEFM) 228 10.3.3 Alternative means of estimating or measuring fracture

toughness 233 10.4 Slow crack propagation 236 10.5 Corrosion of welds 239 10.6 Risk analysis 242

APPENDIX 1 SYMBOLS 244

APPENDIX 2 CONVERSION FACTORS 247

INDEX 249

List of tables

2.1 Fusion welding and cutting processes 2.2 Heat source intensities and type of penetration

3.1 IIW classification of metal transfer 3.2 Dominant forces in metal transfer 3.3 Electron work function and ionisation potential of pure metals 3.4 Temperature of the arc column in various gases 3.5 Dissociation of gases in the arc

5.1 Solid-phase welding processes

6.1 Surface free energy and surface tension of metals and adhesives 6.2 Furnace atmospheres for brazing 6.3 Shear strength of 12'5 mm redux bonded lap joints at room

temperature. Mechanical properties of redux (20 DC)

page 8 12

21 29 33 36 37

80

90 100

105

7.1 Fracture toughness (MN/m3/2 ) of weld HAZ in ASTM A533 (Mn-Mo) steel at - 196 DC 133

7.2 AWS requirements for moisture content of hydrogen-controlled electrode coatings 142

7.3 High-strength line pipe steel 166 7.4 Typical compositions of pearlite-reduced X 70 line pipe steel 167 7.5 Low-alloy high-tensile NT steels for welded fabrication 168 7.6 Low-alloy high-strength QT steels for welded fabrication 169 7.7 illtra high-strength maraging and QT steels for welded fabrication 171 7.8 Heat-resistant and corrosion-resistant chromium-molybdenum

steels 173 7.9 Chemical composition of ferritic and ferritic/austenitic stainless

~eels 175

8.1 Standard intergranular corrosion tests for stainless steels 189 8.2 Corrosion-resistant austenitic Cr-Ni steels 192 8.3 Heat-resistant austenitic Cr-Ni alloys 194

9.1 Nickel and nickel alloys 214

10.1 Alloy systems subject to stress corrosion cracking 240

METALLURGY OF WELDING