Discover the extraordinary progress that welding metallurgy has experienced over the last two decades
Welding Metallurgy, 3rd Edition is the only complete compendium of recent, and not-so-recent, developments in the science and practice of welding metallurgy. Written by Dr. Sindo Kou, this edition covers solid-state welding as well as fusion welding, which now also includes resistance spot welding. It restructures and expands sections on Fusion Zones and Heat-Affected Zones. The former now includes entirely new chapters on microsegregation, macrosegregation, ductility-dip cracking, and alloys resistant to creep, wear and corrosion, as well as a new section on ternary-alloy solidification. The latter now includes metallurgy of solid-state welding. Partially Melted Zones are expanded to include liquation and cracking in friction stir welding and resistance spot welding. New chapters on topics of high current interest are added, including additive manufacturing, dissimilar-metal joining, magnesium alloys, and high-entropy alloys and metal-matrix nanocomposites.
Dr. Kou provides the reader with hundreds of citations to papers and articles that will further enhance the reader’s knowledge of this voluminous topic. Undergraduate students, graduate students, researchers and mechanical engineers will all benefit spectacularly from this comprehensive resource.
The new edition includes new theories/methods of Kou and coworkers regarding:
· Predicting the effect of filler metals on liquation cracking
· An index and analytical equations for predicting susceptibility to solidification cracking
· A test for susceptibility to solidification cracking and filler-metal effect
· Liquid-metal quenching during welding
· Mechanisms of resistance of stainless steels to solidification cracking and ductility-dip cracking
· Mechanisms of macrosegregation
· Mechanisms of spatter of aluminum and magnesium filler metals,
· Liquation and cracking in dissimilar-metal friction stir welding,
· Flow-induced deformation and oscillation of weld-pool surface and ripple formation
· Multicomponent/multiphase diffusion bonding
Dr. Kou’s Welding Metallurgy has been used the world over as an indispensable resource for students, researchers, and engineers alike. This new Third Edition is no exception.
Table of Contents
Preface to Third Edition xxi
Part I Introduction 1
1 Welding Processes 3
1.1 Overview 3
1.1.1 Fusion Welding Processes 3
1.1.1.1 Power Density of Heat Source 4
1.1.1.2 Welding Processes and Materials 5
1.1.1.3 Types of Joints and Welding Positions 7
1.1.2 Solid-State Welding Processes 8
1.2 Gas Welding 8
1.2.1 The Process 8
1.2.2 Three Types of Flames 9
1.2.2.1 Neutral Flame 9
1.2.2.2 Reducing Flame 9
1.2.2.3 Oxidizing Flame 9
1.2.3 Advantages and Disadvantages 10
1.3 Arc Welding 10
1.3.1 Shielded Metal Arc Welding 10
1.3.1.1 Functions of Electrode Covering 10
1.3.1.2 Advantages and Disadvantages 11
1.3.2 Gas-Tungsten Arc Welding 11
1.3.2.1 The Process 11
1.3.2.2 Polarity 12
1.3.2.3 Electrodes 13
1.3.2.4 Shielding Gases 13
1.3.2.5 Advantages and Disadvantages 13
1.3.3 Plasma Arc Welding 14
1.3.3.1 The Process 14
1.3.3.2 Arc Initiation 14
1.3.3.3 Keyholing 15
1.3.3.4 Advantages and Disadvantages 15
1.3.4 Gas-Metal Arc Welding 16
1.3.4.1 The Process 16
1.3.4.2 Shielding Gases 16
1.3.4.3 Modes of Metal Transfer 17
1.3.4.4 Advantages and Disadvantages 18
1.3.5 Flux-Cored Arc Welding 18
1.3.5.1 The Process 18
1.3.6 Submerged Arc Welding 19
1.3.6.1 The Process 19
1.3.6.2 Advantages and Disadvantages 20
1.3.7 Electroslag Welding 20
1.3.7.1 The Process 20
1.3.7.2 Advantages and Disadvantages 21
1.4 High-Energy-Beam Welding 21
1.4.1 Electron Beam Welding 21
1.4.1.1 The Process 21
1.4.1.2 Advantages and Disadvantages 23
1.4.2 Laser Beam Welding 24
1.4.2.1 The Process 24
1.4.2.2 Reflectivity 24
1.4.2.3 Shielding Gas 25
1.4.2.4 Laser-Assisted Arc Welding 25
1.4.2.5 Advantages and Disadvantages 26
1.5 Resistance Spot Welding 26
1.6 Solid-State Welding 27
1.6.1 Friction Stir Welding 27
1.6.2 Friction Welding 29
1.6.3 Explosion and Magnetic-Pulse Welding 31
1.6.4 Diffusion Welding 31
Examples 32
References 33
Further Reading 34
Problems 35
2 Heat Flow in Welding 37
2.1 Heat Source 37
2.1.1 Heat Source Efficiency 37
2.1.1.1 Definition 37
2.1.1.2 Measurements 38
2.1.1.3 Heat Source Efficiencies in Various Welding Processes 41
2.1.2 Melting Efficiency 42
2.1.3 Power Density Distribution of Heat Source 43
2.1.3.1 Effect of Electrode Tip Angle 43
2.1.3.2 Measurements 43
2.2 Heat Flow During Welding 45
2.2.1 Response of Material to Welding Heat Source 45
2.2.2 Rosenthal’s Equations 45
2.2.2.1 Rosenthal’s Two-Dimensional Equation 46
2.2.2.2 Rosenthal’s Three-Dimensional Equation 47
2.2.2.3 Step-by-Step Application of Rosenthal’s Equations 48
2.2.3 Adams’ Equations 49
2.3 Effect of Welding Conditions 49
2.4 Computer Simulation 52
2.5 Weld Thermal Simulator 53
2.5.1 The Equipment 53
2.5.2 Applications 54
2.5.3 Limitations 54
Examples 54
References 57
Further Reading 59
Problems 59
3 Fluid Flow in Welding 61
3.1 Fluid Flow in Arcs 61
3.1.1 Sharp Electrode 61
3.1.2 Flat-End Electrode 63
3.2 Effect of Metal Vapor on Arcs 63
3.2.1 Gas-Tungsten Arc Welding 63
3.2.2 Gas-Metal Arc Welding 65
3.3 Arc Power- and Current-Density Distributions 68
3.4 Fluid Flow in Weld Pools 69
3.4.1 Driving Forces for Fluid Flow 69
3.4.2 Heiple’s Theory for Weld Pool Convection 71
3.4.3 Physical Simulation of Fluid Flow and Weld Penetration 72
3.4.4 Computer Simulation of Fluid Flow and Weld Penetration 75
3.5 Flow Oscillation and Ripple Formation 77
3.6 Active Flux GTAW 80
3.7 Resistance Spot Welding 81
Examples 84
References 85
Further Reading 88
Problems 88
4 Mass and Filler-Metal Transfer 91
4.1 Convective Mass Transfer in Weld Pools 91
4.2 Evaporation of Volatile Solutes 94
4.3 Filler-Metal Drop Explosion and Spatter 96
4.4 Spatter in GMAW of Magnesium 100
4.5 Diffusion Bonding 100
Examples 103
References 104
Problems 105
5 Chemical Reactions in Welding 107
5.1 Overview 107
5.1.1 Effect of Nitrogen, Oxygen, and Hydrogen 107
5.1.2 Protection Against Air 107
5.1.3 Evaluation of Weld Metal Properties 108
5.2 Gas-Metal Reactions 111
5.2.1 Thermodynamics of Reactions 111
5.2.2 Hydrogen 113
5.2.2.1 Magnesium 113
5.2.2.2 Aluminum 113
5.2.2.3 Titanium 116
5.2.2.4 Copper 116
5.2.2.5 Steels 116
5.2.3 Nitrogen 118
5.2.3.1 Steel 118
5.2.3.2 Titanium 121
5.2.4 Oxygen 121
5.2.4.1 Magnesium 121
5.2.4.2 Aluminum 121
5.2.4.3 Titanium 121
5.2.4.4 Steel 122
5.3 Slag-Metal Reactions 125
5.3.1 Thermochemical Reactions 125
5.3.1.1 Decomposition of Flux 125
5.3.1.2 Removal of S and P from Liquid Steel 126
5.3.2 Effect of Flux on Weld Metal Oxygen 127
5.3.3 Types of Fluxes, Basicity Index, and Weld Metal Properties 127
5.3.4 Basicity Index 128
5.3.5 Electrochemical Reactions 130
Examples 135
References 136
Further Reading 140
Problems 140
6 Residual Stresses, Distortion, and Fatigue 141
6.1 Residual Stresses 141
6.1.1 Development of Residual Stresses 141
6.1.1.1 Stresses Induced By Welding 141
6.1.1.2 Welding 141
6.1.2 Analysis of Residual Stresses 143
6.2 Distortion 145
6.2.1 Cause 145
6.2.2 Remedies 146
6.3 Fatigue 147
6.3.1 Mechanism 147
6.3.2 Fractography 147
6.3.3 S-N Curves 150
6.3.4 Effect of Joint Geometry 150
6.3.5 Effect of Stress Raisers 151
6.3.6 Effect of Corrosion 152
6.3.7 Remedies 152
6.3.7.1 Shot Peening 152
6.3.7.2 Reducing Stress Raisers 153
6.3.7.3 Laser Shock Peening 154
6.3.7.4 Use of Low-Transformation-Temperature Fillers 154
Examples 154
References 155
Further Reading 156
Problems 156
Part II The Fusion Zone 157
7 Introduction to Solidification 159
7.1 Solute Redistribution During Solidification 159
7.1.1 Directional Solidification 159
7.1.2 Equilibrium Segregation Coefficient k 159
7.1.3 Four Cases of Solute Redistribution 161
7.2 Constitutional Supercooling 166
7.3 Solidification Modes 168
7.4 Microsegregation Caused by Solute Redistribution 171
7.5 Secondary Dendrite Arm Spacing 174
7.6 Effect of Dendrite Tip Undercooling 177
7.7 Effect of Growth Rate 178
7.8 Solidification of Ternary Alloys 178
7.8.1 Liquidus Projection 178
7.8.2 Solidification Path 179
7.8.3 Ternary Magnesium Alloys 180
7.8.4 Ternary Fe-Cr-Ni Alloys 182
7.8.4.1 Fe-Cr-Ni Phase Diagram 182
7.8.4.2 Solidification Paths 185
7.8.4.3 Microstructure 186
Examples 189
References 191
Further Reading 193
Problems 193
8 Solidification Modes 195
8.1 Solidification Modes 195
8.1.1 Temperature Gradient and Growth Rate 195
8.1.2 Variations in Growth Mode Across Weld 197
8.2 Dendrite Spacing and Cell Spacing 200
8.3 Effect of Welding Parameters 201
8.3.1 Solidification Mode 201
8.3.2 Dendrite and Cell Spacing 202
8.4 Refining Microstructure Within Grains 203
8.4.1 Arc Oscillation 203
8.4.2 Arc Pulsation 205
Examples 205
References 206
Further Reading 207
Problems 207
9 Nucleation and Growth of Grains 209
9.1 Epitaxial Growth at the Fusion Line 209
9.2 Nonepitaxial Growth at the Fusion Line 212
9.2.1 Mismatching Crystal Structures 212
9.2.2 Nondendritic Equiaxed Grains 213
9.3 Growth of Columnar Grains 214
9.4 Effect of Welding Parameters on Columnar Grains 215
9.5 Control of Columnar Grains 218
9.6 Nucleation Mechanisms of Equiaxed Grains 219
9.6.1 Microstructure Around Pool Boundary 219
9.6.2 Dendrite Fragmentation 220
9.6.3 Grain Detachment 222
9.6.4 Heterogeneous Nucleation 222
9.6.5 Effect of Welding Parameters on Heterogeneous Nucleation 225
9.6.6 Surface Nucleation 228
9.7 Grain Refining 228
9.7.1 Inoculation 228
9.7.2 Weld Pool Stirring 229
9.7.2.1 Magnetic Weld Pool Stirring 229
9.7.2.2 Ultrasonic Weld Pool Stirring 229
9.7.3 Arc Pulsation 232
9.7.4 Arc Oscillation 232
9.8 Identifying Grain-Refining Mechanisms 233
9.8.1 Overlap Welding Procedure 233
9.8.2 Identifying the Grain-Refining Mechanism 235
9.8.3 Effect of Arc Oscillation on Dendrite Fragmentation 236
9.8.4 Effect of Arc Oscillation on Constitutional Supercooling 236
9.8.5 Effect of Composition on Grain Refining by Arc Oscillation 238
9.9 Grain-Boundary Migration 238
Examples 239
References 240
Further Reading 245
Problems 246
10 Microsegregation 247
10.1 Microsegregation in Welds 247
10.2 Effect of Travel Speed on Microsegregation 249
10.3 Effect of Primary Solidification Phase on Microsegregation 252
10.4 Effect of Maximum Solid Solubility on Microsegregation 253
Examples 259
References 261
Further Reading 262
Problems 262
11 Macrosegregation 263
11.1 Macrosegregation in the Fusion Zone 263
11.2 Quick Freezing of One Liquid Metal in Another 265
11.3 Macrosegregation in Dissimilar-Filler Welding 265
11.3.1 Bulk Weld-Metal Composition 265
11.3.2 Mechanism I 267
11.3.3 Mechanism II 270
11.4 Macrosegregation in Dissimilar-Metal Welding 279
11.4.1 Mechanism I 279
11.4.2 Mechanism II 283
11.5 Reduction of Macrosegregation 286
11.6 Macrosegregation in Multiple-Pass Welds 287
References 290
Further Reading 291
Problems 291
12 Some Alloy-Specific Microstructures and Properties 293
12.1 Austenitic Stainless Steels 293
12.1.1 Microstructure Evolution in Stainless Steels 293
12.1.2 Mechanisms of Ferrite Formation 294
12.1.3 Prediction of Ferrite Content 296
12.1.4 Effect of Cooling Rate 297
12.1.4.1 Changes in Solidification Mode 297
12.1.4.2 Dendrite Tip Undercooling 301
12.2 Low-Carbon, Low-Alloy Steels 301
12.2.1 Microstructure Development 301
12.2.2 Factors Affecting Microstructure 302
12.2.3 Weld Metal Toughness 306
12.3 Ultralow Carbon Bainitic Steels 306
12.4 Creep-Resistant Steels 308
12.5 Hardfacing of Steels 311
References 319
Further Reading 321
Problems 321
13 Solidification Cracking 323
13.1 Characteristics of Solidification Cracking 323
13.2 Theories of Solidification Cracking 323
13.2.1 Criterion for Cracking Proposed by Kou 327
13.2.2 Index for Crack Susceptibility Proposed by Kou 328
13.2.3 Previous Theories 330
13.3 Binary Alloys and Analytical Equations 331
13.4 Solidification Cracking Tests 334
13.4.1 Varestraint Test 334
13.4.2 Controlled Tensile Weldability Test 336
13.4.3 Transverse-Motion Weldability Test 337
13.4.4 Circular-Patch Test 341
13.4.5 Houldcroft Test 342
13.4.6 Cast-Pin Test 343
13.4.7 Ring-Casting Test 344
13.4.8 Other Tests 344
13.5 Solidification Cracking of Stainless Steels 345
13.5.1 Primary Solidification Phase 345
13.5.2 Mechanism of Crack Resistance 346
13.6 Factors Affecting Solidification Cracking 350
13.6.1 Primary Solidification Phase 350
13.6.2 Grain Size 350
13.6.3 Solidification Temperature Range 351
13.6.4 Back Diffusion 354
13.6.5 Dihedral Angle 355
13.6.6 Grain-Boundary Angle 359
13.6.7 Degree of Restraint 360
13.7 Reducing Solidification Cracking 360
13.7.1 Control of Weld Metal Composition 360
13.7.2 Control of Weld Microstructure 363
13.7.3 Control of Welding Conditions 365
13.7.4 Control of Weld Shape 366
Examples 367
References 370
Further Reading 376
Problems 376
14 Ductility-Dip Cracking 379
14.1 Characteristics of Ductility-Dip Cracking 379
14.2 Theories of Ductility-Dip Cracking 381
14.3 Test Methods 382
14.4 Ductility-Dip Cracking of Ni-Base Alloys 384
14.4.1 Grain-Boundary Sliding 384
14.4.2 Grain-Boundary Misorientation 386
14.4.3 Grain-Boundary Tortuosity and Precipitates 386
14.4.4 Grain Size 388
14.4.5 Factors Affecting Ductility-Dip Cracking 390
14.5 Ductility-Dip Cracking of Stainless Steels 390
Examples 392
References 394
Further Reading 396
Problems 396
Part III The Partially Melted Zone 399
15 Liquation in the Partially Melted Zone 401
15.1 Formation of the Partially Melted Zone 401
15.2 Liquation Mechanisms 403
15.2.1 Mechanism I: Alloy with Co > CSM 404
15.2.2 Mechanism II: Alloy with Co < CSM and no AxBy or Eutectic 405
15.2.3 Mechanism III: Alloy with Co < CSM and AxBy or Eutectic 405
15.2.4 Additional Mechanisms of Liquation 409
15.3 Directional Solidification of Liquated Material 411
15.4 Grain-Boundary Segregation 411
15.5 Loss of Strength and Ductility 413
15.6 Hydrogen Cracking 414
15.7 Effect of Heat Input 414
15.8 Effect of Arc Oscillation 415
Examples 416
References 417
Problems 418
16 Liquation Cracking 419
16.1 Liquation Cracking in Arc Welding 419
16.1.1 Crack Susceptibility Tests 421
16.1.1.1 Varestraint Testing 421
16.1.1.2 Circular-Patch Testing 422
16.1.1.3 Hot Ductility Testing 423
16.1.2 Mechanism of Liquation Cracking 423
16.1.3 Predicting Effect of Filler Metal on Crack Susceptibility 424
16.1.4 Factors Affecting Liquation Cracking 430
16.1.4.1 Filler Metal 430
16.1.4.2 Heat Source 430
16.1.4.3 Degree of Restraint 431
16.1.4.4 Base Metal 431
16.2 Liquation Cracking in Resistance Spot Welding 434
16.3 Liquation Cracking in Friction Stir Welding 434
16.4 Liquation Cracking in Dissimilar-Metal FSW 439
Examples 445
References 446
Problems 449
Part IV The Heat-Affected Zone 451
17 Introduction to Solid-State Transformations 453
17.1 Work-Hardened Materials 453
17.2 Heat-Treatable Al Alloys 455
17.3 Heat-Treatable Ni-Base Alloys 458
17.4 Steels 461
17.4.1 Fe-C Phase Diagram and CCT Diagrams 461
17.4.2 Carbon Steels 463
17.4.3 Dual-Phase Steels 470
17.5 Stainless Steels 471
17.5.1 Types of Stainless Steels 471
17.5.2 Sensitization of Unstabilized Grades 473
17.5.3 Sensitization of Stabilized Grades 473
17.5.4 σ-Phase Embrittlement 475
Examples 475
References 475
Problems 477
18 Heat-Affected-Zone Degradation of Mechanical Properties 479
18.1 Grain Coarsening 479
18.2 Recrystallization and Grain Growth 480
18.3 Overaging in Al Alloys 483
18.3.1 Al-Cu-Mg (2000-Series) Alloys 483
18.3.1.1 Microstructure and Strength 483
18.3.1.2 Effect of Welding Parameters or Process 488
18.3.2 Al-Mg-Si (6000-Series) Alloys 489
18.3.2.1 Microstructure and Strength 489
18.3.2.2 Effect of Welding Processes and Parameters 491
18.3.3 Al-Zn-Mg (7000-Series) Alloys 492
18.4 Dissolution of Precipitates in Ni-Base Alloys 494
18.5 Martensite Tempering in Dual-Phase Steels 498
Examples 500
References 500
Further Reading 502
Problems 502
19 Heat-Affected-Zone Cracking 505
19.1 Hydrogen Cracking in Steels 505
19.1.1 Cause 505
19.1.2 Appearance 506
19.1.3 Susceptibility Tests 507
19.1.4 Remedies 508
19.1.4.1 Preheating 508
19.1.4.2 Postweld Heating 509
19.1.4.3 Bead Tempering 509
19.1.4.4 Use of Low-H Processes and Consumables 509
19.1.4.5 Use of Lower-Strength Filler Metals 509
19.1.4.6 Use of Austenitic-Stainless-Steel Filler Metals 510
19.2 Stress-Relief Cracking in Steels 510
19.3 Lamellar Tearing in Steels 514
19.4 Type-IV Cracking in Grade 91 Steel 517
19.5 Strain-Age Cracking in Ni-Base Alloys 519
Examples 524
References 524
Further Reading 527
Problems 528
20 Heat-Affected-Zone Corrosion 529
20.1 Weld Decay of Stainless Steels 529
20.2 Weld Decay of Ni-Base Alloys 533
20.3 Knife-Line Attack of Stainless Steels 534
20.4 Sensitization of Ferritic Stainless-Steel Welds 536
20.5 Stress Corrosion Cracking of Austenitic Stainless Steels 537
20.6 Corrosion Fatigue of Al Welds 538
Examples 538
References 539
Further Reading 540
Problems 540
Part V Special Topics 541
21 Additive Manufacturing 543
21.1 Heat and Fluid Flow 543
21.2 Residual Stress and Distortion 545
21.3 Lack of Fusion and Gas Porosity 547
21.4 Grain Structure 550
21.5 Solidification Cracking 550
21.6 Liquation Cracking 553
21.7 Graded Transition Joints 558
21.8 Further Discussions 560
Examples 560
References 561
Further Reading 563
Problems 564
22 Dissimilar-Metal Joining 565
22.1 Introduction 565
22.2 Arc and Laser Joining 565
22.2.1 Al-to-Steel Arc Brazing 566
22.2.1.1 Effect of Lap Joint Gap 569
22.2.1.2 Effect of Heat Input 575
22.2.1.3 Effect of Ultrasonic Vibration 577
22.2.1.4 Effect of Preheating 578
22.2.1.5 Effect of Postweld Heat Treatment 578
22.2.1.6 Butt Joint 579
22.2.2 Al-to-Steel Laser Brazing 579
22.2.3 Al-to-Steel Laser Welding 580
22.2.4 Mg-to-Steel Brazing 582
22.2.5 Al-to-Mg Welding 583
22.3 Resistance Spot Welding 583
22.3.1 Al-to-Steel RSW 583
22.3.2 Mg-to-Steel RSW 586
22.3.3 Al-to-Mg RSW 588
22.4 Friction Stir Welding 589
22.4.1 Al-to-Cu FSSW 589
22.4.2 FSSW of Al to Galvanized Steel 592
22.4.3 Effect of Coating on Al-to-Steel FSSW 597
22.5 Other Solid-State Welding Processes 603
22.5.1 Friction Welding 603
22.5.2 Explosion Welding 606
22.5.3 Magnetic Pulse Welding 607
Examples 608
References 609
Further Reading 612
Problems 612
23 Welding of Magnesium Alloys 613
23.1 Spatter 613
23.1.1 Spatter in Mg GMAW 613
23.1.2 Mechanism of Spatter 614
23.1.3 Elimination of Spatter 614
23.1.4 Irregular Weld Shape and Its Elimination 617
23.2 Porosity 618
23.2.1 Porosity in Mg GMAW 618
23.2.2 Mechanisms of Porosity Formation and Elimination 620
23.2.3 Comparing Porosity in Al and Mg Welds 621
23.3 Internal Oxide Films 622
23.3.1 Mechanism 622
23.3.2 Remedies 624
23.4 High Crowns 625
23.4.1 Mechanism of High-Crown Formation 625
23.4.2 Reducing Crown Height 627
23.5 Grain Refining 628
23.5.1 Ultrasonic Weld Pool Stirring 628
23.5.2 Arc Pulsation 629
23.5.3 Arc Oscillation 629
23.6 Solidification Cracking 629
23.7 Liquation Cracking 629
23.7.1 A Simple Test for Crack Susceptibility 631
23.7.2 Effect of Filler Metals 634
23.7.3 Effect of Grain Size 636
23.8 Heat-Affected Zone Weakening 636
Examples 638
References 640
Further Reading 641
Problems 641
24 Welding of High-Entropy Alloys and Metal-Matrix Nanocomposites 643
24.1 High-Entropy Alloys 643
24.1.1 Solidification Microstructure 643
24.1.2 Weldability 644
24.2 Metal-Matrix Nanocomposites 646
24.2.1 Nanoparticles Increasing Weld Size 646
24.2.2 Nanoparticles Refining Microstructure 648
24.2.3 Nanoparticles Reducing Cracking During Solidification 650
24.2.4 Nanoparticles Allowing Friction Stir Welding 651
Examples 653
References 654
Further Reading 655
Problems 655
Appendix A: Analytical Equations for Susceptibility to Solidification Cracking 657
Index 659
