Welding Metallurgy

466 Pages·2002·8.877 MB·English

by  Sindo Kou

WELDING
METALLURGY
SECOND EDITION
WELDING
METALLURGY
SECOND EDITION
Sindo Kou
Professor and Chair
Department of Materials Science and Engineering
University of Wisconsin
A JOHN WILEY & SONS,INC.,PUBLICATION
Copyright © 2003 by John Wiley & Sons,Inc.All rights reserved.
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Library of Congress Cataloging-in-Publication Data
Kou,Sindo.
Welding metallurgy / Sindo Kou.–2nd ed.
p.cm.
“A Wiley-Interscience publication.”
Includes bibliographical references and index.
ISBN 0-471-43491-4
1. Welding. 2. Metallurgy. 3. Alloys. I. Title.
TS227 .K649 2002
671.5¢2–dc21
2002014327
Printed in the United States of America.
10 9 8 7 6 5 4 3 2 1
To Warren F.Savage
for his outstanding contributions to welding metallurgy
CONTENTS
Preface xiii
I INTRODUCTION 1
1 Fusion Welding Processes 3
1.1 Overview 3
1.2 Oxyacetylene Welding 7
1.3 Shielded Metal Arc Welding 11
1.4 Gas–Tungsten Arc Welding 13
1.5 Plasma Arc Welding 16
1.6 Gas–Metal Arc Welding 19
1.7 Flux-Core Arc Welding 22
1.8 Submerged Arc Welding 22
1.9 Electroslag Welding 24
1.10 Electron Beam Welding 27
1.11 Laser Beam Welding 29
References 33
Further Reading 34
Problems 34
2 Heat Flow in Welding 37
2.1 Heat Source 37
2.2 Analysis of Heat Flow in Welding 47
2.3 Effect of Welding Parameters 53
2.4 Weld Thermal Simulator 58
References 60
Further Reading 62
Problems 62
3 Chemical Reactions in Welding 65
3.1 Overview 65
3.2 Gas–Metal Reactions 68
3.3 Slag–Metal Reactions 82
References 92
vii
viii CONTENTS
Further Reading 95
Problems 95
4 Fluid Flow and Metal Evaporation in Welding 97
4.1 Fluid Flow in Arcs 97
4.2 Fluid Flow in Weld Pools 103
4.3 Metal Evaporation 114
4.4 Active Flux GTAW 116
References 117
Further Reading 119
Problems 120
5 Residual Stresses,Distortion,and Fatigue 122
5.1 Residual Stresses 122
5.2 Distortion 126
5.3 Fatigue 131
5.4 Case Studies 137
References 140
Further Reading 141
Problems 141
II THE FUSION ZONE 143
6 Basic Solidification Concepts 145
6.1 Solute Redistribution during Solidification 145
6.2 Solidification Modes and Constitutional Supercooling 155
6.3 Microsegregation and Banding 160
6.4 Effect of Cooling Rate 163
6.5 Solidification Path 166
References 167
Further Reading 168
Problems 169
7 Weld Metal Solidification I:Grain Structure 170
7.1 Epitaxial Growth at Fusion Boundary 170
7.2 Nonepitaxial Growth at Fusion Boundary 172
7.3 Competitive Growth in Bulk Fusion Zone 174
7.4 Effect of Welding Parameters on Grain Structure 174
7.5 Weld Metal Nucleation Mechanisms 178
7.6 Grain Structure Control 187
CONTENTS ix
References 195
Further Reading 197
Problems 197
8 Weld Metal Solidification II:Microstructure within Grains 199
8.1 Solidification Modes 199
8.2 Dendrite and Cell Spacing 204
8.3 Effect of Welding Parameters 206
8.4 Refining Microstructure within Grains 209
References 213
Further Reading 213
Problems 214
9 Post-Solidification Phase Transformations 216
9.1 Ferrite-to-Austenite Transformation in Austenitic Stainless
Steel Welds 216
9.2 Austenite-to-Ferrite Transformation in Low-Carbon,
Low-Alloy Steel Welds 232
References 239
Further Reading 241
Problems 241
10 Weld Metal Chemical Inhomogeneities 243
10.1 Microsegregation 243
10.2 Banding 249
10.3 Inclusions and Gas Porosity 250
10.4 Inhomogeneities Near Fusion Boundary 252
10.5 Macrosegregation in Bulk Weld Metal 255
References 260
Further Reading 261
Problems 261
11 Weld Metal Solidification Cracking 263
11.1 Characteristics,Cause,and Testing 263
11.2 Metallurgical Factors 268
11.3 Mechanical Factors 284
11.4 Reducing Solidification Cracking 285
11.5 Case Study:Failure of a Large Exhaust Fan 295
References 296
Further Reading 299
Problems 299
x CONTENTS
III THE PARTIALLY MELTED ZONE 301
12 Formation of the Partially Melted Zone 303
12.1 Evidence of Liquation 303
12.2 Liquation Mechanisms 304
12.3 Directional Solidification of Liquated Material 314
12.4 Grain Boundary Segregation 314
12.5 Grain Boundary Solidification Modes 316
12.6 Partially Melted Zone in Cast Irons 318
References 318
Problems 319
13 Difficulties Associated with the Partially Melted Zone 321
13.1 Liquation Cracking 321
13.2 Loss of Strength and Ductility 328
13.3 Hydrogen Cracking 328
13.4 Remedies 330
References 336
Problems 338
IV THE HEAT-AFFECTED ZONE 341
14 Work-Hardened Materials 343
14.1 Background 343
14.2 Recrystallization and Grain Growth in Welding 347
14.3 Effect of Welding Parameters and Process 349
References 351
Further Reading 352
Problems 352
15 Precipitation-Hardening Materials I:Aluminum Alloys 353
15.1 Background 353
15.2 Al–Cu–Mg and Al–Mg–Si Alloys 359
15.3 Al–Zn–Mg Alloys 367
15.4 Friction Stir Welding of Aluminum Alloys 370
References 371
Further Reading 372
Problems 372
16 Precipitation-Hardening Materials II:Nickel-Base Alloys 375
16.1 Background 375
CONTENTS xi
16.2 Reversion of Precipitate and Loss of Strength 379
16.3 Postweld Heat Treatment Cracking 384
References 390
Further Reading 392
Problems 392
17 Transformation-Hardening Materials:Carbon and
Alloy Steels 393
17.1 Phase Diagram and CCT Diagrams 393
17.2 Carbon Steels 396
17.3 Low-Alloy Steels 404
17.4 Hydrogen Cracking 410
17.5 Reheat Cracking 418
17.6 Lamellar Tearing 422
17.7 Case Studies 425
References 427
Further Reading 429
Problems 430
18 Corrosion-Resistant Materials:Stainless Steels 431
18.1 Classification of Stainless Steels 431
18.2 Austenitic Stainless Steels 433
18.3 Ferritic Stainless Steels 446
18.4 Martensitic Stainless Steels 449
18.5 Case Study:Failure of a Pipe 451
References 452
Further Reading 453
Problems 454
Index 455
PREFACE
Since the publication of the first edition of this book in 1987,there has been
much new progress made in welding metallurgy.The purpose for the second
edition is to update and improve the first edition.Examples of improvements
include (1) much sharper photomicrographs and line drawings;(2) integration
of the phase diagram,thermal cycles,and kinetics with the microstructure to
explain microstructural development and defect formation in welds;and (3)
additional exercise problems.Specific revisions are as follows.
In Chapter 1 the illustrations for all welding processes have been re-
drawn to show both the overall process and the welding area. In Chapter
2 the heat source efficiency has been updated and the melting efficiency
added. Chapter 3 has been revised extensively, with the dissolution of
atomic nitrogen, oxygen, and hydrogen in the molten metal considered and
electrochemical reactions added.Chapter 4 has also been revised extensively,
with the arc added, and with flow visualization, arc plasma dragging, and
turbulence included in weld pool convection. Shot peening is added to
Chapter 5.
Chapter 6 has been revised extensively, with solute redistribution and
microsegregation expanded and the solidification path added.Chapter 7 now
includes nonepitaxial growth at the fusion boundary and formation of non-
dendritic equiaxed grains.In Chapter 8 solidification modes are explained with
more illustrations. Chapter 9 has been expanded significantly to add ferrite
formation mechanisms,new ferrite prediction methods,the effect of cooling
rate, and factors affecting the austenite–ferrite transformation. Chapter 10
now includes the effect of both solid-state diffusion and dendrite tip under-
cooling on microsegregation. Chapter 11 has been revised extensively to
include the effect of eutectic reactions, liquid distribution, and ductility of
the solidifying metal on solidification cracking and the calculation of fraction
of liquid in multicomponent alloys.
Chapter 12 has been rewritten completely to include six different liquation
mechanisms in the partially melted zone (PMZ),the direction and modes of
grain boundary (GB) solidification,and the resultant GB segregation.Chapter
13 has been revised extensively to include the mechanism of PMZ cracking
and the effect of the weld-metal composition on cracking.
Chapter 15 now includes the heat-affected zone (HAZ) in aluminum–
lithium–copper welds and friction stir welds and Chapter 16 the HAZ of
Inconel 718.Chapter 17 now includes the effect of multiple-pass welding on
xiii