Welding Metallurgy and Weldability

Describes the weldability aspects of structural materials used in a wide variety of engineering structures, including steels, stainless steels, Ni–base alloys, and Al–base alloys

Welding Metallurgy and Weldability describes weld failure mechanisms associated with either fabrication or service, and failure mechanisms related to microstructure of the weldment. Weldability issues are divided into fabrication and service related failures; early chapters address hot cracking, warm (solid–state) cracking, and cold cracking that occur during initial fabrication, or repair. Guidance on failure analysis is also provided, along with examples of SEM fractography that will aid in determining failure mechanisms. Welding Metallurgy and Weldability examines a number of weldability testing techniques that can be used to quantify susceptibility to various forms of weld cracking. 

Describes the mechanisms of weldability along with methods to improve weldability Includes an introduction to weldability testing and techniques, including strain–to–fracture and Varestraint tests Chapters are illustrated with practical examples based on 30 plus years of experience in the field

Illustrating the weldability aspects of structural materials used in a wide variety of engineering structures, Welding Metallurgy and Weldability provides engineers and students with the information needed to understand the basic concepts of welding metallurgy and to interpret the failures in welded components. 

John C. Lippold received his BS, MS, and PhD degrees in Materials Engineering from the Rensselaer Polytechnic Institute. Upon completion of his formal education, Dr. Lippold worked for seven years at Sandia National Laboratories as a member of the technical staff, specializing in stainless steel and high alloy weldability. From 1985 to 1995, Dr. Lippold worked for Edison Welding Institute. From 1995 to the present, he has been on the faculty of the Welding Engineering program at The Ohio State University and was recently named a College of Engineering Distinguished Faculty member.

Preface xiii

Author Biography xvi

1 Introduction 1

1.1 Fabrication–Related Defects, 5

1.2 Service–Related Defects, 6

1.3 Defect Prevention and Control, 7

References, 8

2 Welding Metallurgy Principles 9

2.1 Introduction, 9

2.2 Regions of a Fusion Weld, 10

2.3 Fusion Zone, 13

2.3.1 Solidification of Metals, 15

2.3.1.1 Solidification Parameters, 15

2.3.1.2 Solidification Nucleation, 17

2.3.1.3 Solidification Modes, 19

2.3.1.4 Interface Stability, 22

2.3.2 Macroscopic Aspects of Weld Solidification, 24

2.3.2.1 Effect of Travel Speed and Temperature Gradient, 27

2.3.3 Microscopic Aspects of Weld Solidification, 30

2.3.3.1 Solidification Subgrain Boundaries (SSGB), 32

2.3.3.2 Solidification Grain Boundaries (SGB), 33

2.3.3.3 Migrated Grain Boundaries (MGB), 34

2.3.4 Solute Redistribution, 34

2.3.4.1 Macroscopic Solidification, 35

2.3.4.2 Microscopic Solidification, 37

2.3.5 Examples of Fusion Zone Microstructures, 40

2.3.6 Transition Zone (TZ), 43

2.4 Unmixed Zone (UMZ), 45

2.5 Partially Melted Zone (PMZ), 48

2.5.1 Penetration Mechanism, 50

2.5.2 Segregation Mechanism, 53

2.5.2.1 Gibbsian Segregation, 56

2.5.2.2 Grain Boundary Sweeping, 56

2.5.2.3 Pipeline Diffusion, 57

2.5.2.4 Grain Boundary Wetting, 58

2.5.3 Examples of PMZ formation, 58

2.6 Heat Affected Zone (HAZ), 60

2.6.1 Recrystallization and Grain Growth, 61

2.6.2 Allotropic Phase Transformations, 63

2.6.3 Precipitation Reactions, 66

2.6.4 Examples of HAZ Microstructure, 69

2.7 Solid–State Welding, 70

2.7.1 Friction Stir Welding, 72

2.7.2 Diffusion Welding, 76

2.7.3 Explosion Welding, 77

2.7.4 Ultrasonic Welding, 79

References, 81

3 Hot Cracking 84

3.1 Introduction, 84

3.2 Weld Solidification Cracking, 85

3.2.1 Theories of Weld Solidification Cracking, 85

3.2.1.1 Shrinkage–Brittleness Theory, 86

3.2.1.2 Strain Theory, 87

3.2.1.3 Generalized Theory, 88

3.2.1.4 Modified Generalized Theory, 89

3.2.1.5 Technological Strength Theory, 90

3.2.1.6 Commentary on Solidification Cracking Theories, 91

3.2.2 Predictions of Elemental Effects, 94

3.2.3 The BTR and Solidification Cracking Temperature Range, 97

3.2.4 Factors that Influence Weld Solidification Cracking, 102

3.2.4.1 Composition Control, 102

3.2.4.2 Grain Boundary Liquid Films, 109

3.2.4.3 Effect of Restraint, 110

3.2.5 Identifying Weld Solidification Cracking, 112

3.2.6 Preventing Weld Solidification Cracking, 116

3.3 Liquation Cracking, 119

3.3.1 HAZ Liquation Cracking, 119

3.3.2 weld metal Liquation Cracking, 122

3.3.3 Variables that Influence Susceptibility to Liquation Cracking, 123

3.3.3.1 Composition, 123

3.3.3.2 Grain Size, 124

3.3.3.3 Base Metal Heat Treatment, 125

3.3.3.4 Weld Heat Input and Filler Metal Selection, 125

3.3.4 Identifying HAZ and weld metal Liquation Cracks, 126

3.3.5 Preventing Liquation Cracking, 127

References, 128

4 S olid–State Cracking 130

4.1 Introduction, 130

4.2 Ductility–dip Cracking, 130

4.2.1 Proposed Mechanisms, 133

4.2.2 Summary of Factors That Influence DDC, 139

4.2.3 Quantifying Ductility–Dip Cracking, 143

4.2.4 Identifying Ductility–Dip Cracks, 145

4.2.5 Preventing DDC, 147

4.3 Reheat Cracking, 149

4.3.1 Reheat Cracking in Low–Alloy Steels, 150

4.3.2 Reheat Cracking in Stainless Steels, 155

4.3.3 Underclad Cracking, 158

4.3.4 Relaxation Cracking, 160

4.3.5 Identifying Reheat Cracking, 161

4.3.6 Quantifying Reheat Cracking Susceptibility, 163

4.3.7 Preventing Reheat Cracking, 166

4.4 Strain–age Cracking, 168

4.4.1 Mechanism for Strain–age Cracking, 171

4.4.2 Factors That Influence SAC Susceptibility, 178

4.4.2.1 Composition, 178

4.4.2.2 Grain Size, 179

4.4.2.3 Residual Stress and Restraint, 179

4.4.2.4 Welding Procedure, 180

4.4.2.5 Effect of PWHT, 181

4.4.3 Quantifying Susceptibility to Strain–age Cracking, 182

4.4.4 Identifying Strain–age Cracking, 189

4.4.5 Preventing Strain–age Cracking, 189

4.5 Lamellar Cracking, 190

4.5.1 Mechanism of Lamellar Cracking, 191

4.5.2 Quantifying Lamellar Cracking, 195

4.5.3 Identifying Lamellar Cracking, 197

4.5.4 Preventing Lamellar Cracking, 198

4.6 Copper Contamination Cracking, 201

4.6.1 Mechanism for Copper Contamination Cracking, 201

4.6.2 Quantifying Copper Contamination Cracking, 203

4.6.3 Identifying Copper Contamination Cracking, 205

4.6.4 Preventing Copper Contamination Cracking, 205

References, 207

5 Hydrogen–Induced Cracking 213

5.1 Introduction, 213

5.2 Hydrogen Embrittlement Theories, 214

5.2.1 Planar Pressure Theory, 216

5.2.2 Surface Adsorption Theory, 217

5.2.3 Decohesion Theory, 217

5.2.4 Hydrogen–Enhanced Localized Plasticity Theory, 218

5.2.5 Beachem s Stress Intensity Model, 219

5.3 Factors That Influence HIC, 221

5.3.1 Hydrogen in Welds, 221

5.3.2 Effect of Microstructure, 224

5.3.3 Restraint, 228

5.3.4 Temperature, 230

5.4 Quantifying Susceptibility to HIC, 230

5.4.1 Jominy End Quench Method, 231

5.4.2 Controlled Thermal Severity Test, 234

5.4.3 The Y–Groove (Tekken) Test, 235

5.4.4 Gapped Bead–on–Plate Test, 236

5.4.5 The Implant Test, 237

5.4.6 Tensile Restraint Cracking Test, 243

5.4.7 Augmented Strain Cracking Test, 244

5.5 Identifying HIC, 245

5.6 Preventing HIC, 247

5.6.1 CE Method, 251

5.6.2 AWS Method, 254

References, 259

6 Corrosion 263

6.1 Introduction, 263

6.2 Forms of Corrosion, 264

6.2.1 General Corrosion, 264

6.2.2 Galvanic Corrosion, 265

6.2.3 Crevice Corrosion, 267

6.2.4 Selective Leaching, 268

6.2.5 Erosion Corrosion, 268

6.2.6 Pitting, 268

6.2.7 Intergranular Corrosion, 271

6.2.7.1 Preventing Sensitization, 275

6.2.7.2 Knifeline Attack, 276

6.2.7.3 Low–Temperature Sensitization, 276

6.2.8 Stress Corrosion Cracking, 277

6.2.9 Microbiologically Induced Corrosion, 280

6.3 Corrosion Testing, 282

6.3.1 Atmospheric Corrosion Tests, 282

6.3.2 Immersion Tests, 282

6.3.3 Electrochemical Tests, 284

References, 286

7 Fracture and Fatigue 288

7.1 Introduction, 288

7.2 Fracture, 290

7.3 Quantifying Fracture Toughness, 293

7.4 Fatigue, 297

7.5 Quantifying Fatigue Behavior, 305

7.6 Identifying Fatigue Cracking, 306

7.6.1 Beach Marks, 307

7.6.2 River Lines, 307

7.6.3 Fatigue Striations, 307

7.7 Avoiding Fatigue Failures, 309

References, 310

8 Failure Analysis 311

8.1 Introduction, 311

8.2 Fractography, 312

8.2.1 History of Fractography, 312

8.2.2 The SEM, 313

8.2.3 Fracture Modes, 315

8.2.4 Fractography of Weld Failures, 320

8.2.4.1 Solidification Cracking, 320

8.2.4.2 Liquation Cracking, 323

8.2.4.3 Ductility–Dip Cracking, 326

8.2.4.4 Reheat Cracking, 326

8.2.4.5 Strain–Age Cracking, 331

8.2.4.6 Hydrogen–Induced Cracking, 332

8.3 An Engineer s Guide to Failure Analysis, 333

8.3.1 Site Visit, 334

8.3.2 Collect Background Information, 335

8.3.3 Sample Removal and Testing Protocol, 336

8.3.4 Sample Removal, Cleaning, and Storage, 336

8.3.5 Chemical Analysis, 336

8.3.6 Macroscopic Analysis, 337

8.3.7 Selection of Samples for Microscopic Analysis, 338

8.3.8 Selection of Analytical Techniques, 338

8.3.9 Mechanical Testing, 339

8.3.10 Simulative Testing, 339

8.3.11 Nondestructive Evaluation Techniques, 340

8.3.12 Structural Integrity Assessment, 340

8.3.13 Consultation with Experts, 340

8.3.14 Final Reporting, 340

8.3.15 Expert Testimony in Support of Litigation, 341

References, 342

9 Weldability Testing 343

9.1 Introduction, 343

9.2 Types of Weldability Test Techniques, 344

9.3 The Varestraint Test, 345

9.3.1 Technique for Quantifying Weld Solidification Cracking, 346

9.3.2 Technique for Quantifying HAZ Liquation Cracking, 350

9.4 The Cast Pin Tear Test, 354

9.5 The Hot Ductility Test, 357

9.6 The Strain–to–Fracture Test, 362

9.7 Reheat Cracking Test, 363

9.8 Implant Test for HAZ Hydrogen–Induced Cracking, 366

9.9 Gapped Bead–on–Plate Test for Weld Metal HIC, 367

9.10 O ther Weldability Tests, 370

References, 371

Appendix A 372

Appendix B 374

Appendix C 383

Appendix D 388

Index 396

John C. Lippold received his BS, MS, and PhD degrees in Materials Engineering from Rensselaer Polytechnic Institute. Upon completion of his formal education, Dr. Lippold worked for seven years at Sandia National Laboratories, Livermore, CA, as a member of the technical staff, specializing in stainless steel and high alloy weldability. From 1985 to 1995, Dr. Lippold worked for Edison Welding Institute. From 1995 to the present, he has been on the faculty of the Welding Engineering program at The Ohio State University and was recently named a College of Engineering Distinguished Faculty member.