Welding Metallurgy and Weldability of Stainless Steels

 PREFACE xv

1 INTRODUCTION 1

1.1 Definition of a Stainless Steel 2

1.2 History of Stainless Steel 2

1.3 Types of Stainless Steel and Their Application 4

1.4 Corrosion Resistance 5

1.5 Production of Stainless Steel 6

References 7

2 PHASE DIAGRAMS 8

2.1 Iron–Chromium System 9

2.2 Iron–Chromium–Carbon System 10

2.3 Iron–Chromium–Nickel System 12

2.4 Phase Diagrams for Specific Alloy Systems 15

References 18

3 ALLOYING ELEMENTS AND CONSTITUTION DIAGRAMS 19

3.1 Alloying Elements in Stainless Steels 19

3.1.1 Chromium 20

3.1.2 Nickel 20

3.1.3 Manganese 21

3.1.4 Silicon 21

3.1.5 Molybdenum 22

3.1.6 Carbide-Forming Elements 22

3.1.7 Precipitation-Hardening Elements 23

3.1.8 Interstitial Elements: Carbon and Nitrogen 23

3.1.9 Other Elements 24

3.2 Ferrite-Promoting Versus Austenite-Promoting Elements 24

3.3 Constitution Diagrams 25

3.3.1 Austenitic–Ferritic Alloy Systems: Early Diagrams and Equivalency Relationships 25

3.3.2 Schaeffler Diagram 29

3.3.3 DeLong Diagram 33

3.3.4 Other Diagrams 34

3.3.5 WRC-1988 and WRC-1992 Diagrams 40

3.4 Austenitic–Martensitic Alloy Systems 43

3.5 Ferritic–Martensitic Alloy Systems 46

3.6 Neural Network Ferrite Prediction 50

References 52

4 MARTENSITIC STAINLESS STEELS 56

4.1 Standard Alloys and Consumables 57

4.2 Physical and Mechanical Metallurgy 59

4.3 Welding Metallurgy 63

4.3.1 Fusion Zone 63

4.3.2 Heat-Affected Zone 67

4.3.3 Phase Transformations 70

4.3.4 Postweld Heat Treatment 71

4.3.5 Preheat, Interpass, and Postweld Heat Treatment Guidelines 74

4.4 Mechanical Properties of Weldments 77

4.5 Weldability 77

4.5.1 Solidification and Liquation Cracking 78

4.5.2 Reheat Cracking 78

4.5.3 Hydrogen-Induced Cracking 79

4.6 Supermartensitic Stainless Steels 80

4.7 Case Study: Calculation of MS Temperatures of Martensitic Stainless Steels 84

References 86

5 FERRITIC STAINLESS STEELS 87

5.1 Standard Alloys and Consumables 88

5.2 Physical and Mechanical Metallurgy 92

5.2.1 Effect of Alloying Additions on Microstructure 95

5.2.2 Effect of Martensite 95

5.2.3 Embrittlement Phenomena 96

5.2.3.1 475°C Embrittlement 97

5.2.3.2 Sigma and Chi Phase Embrittlement 97

5.2.3.3 High-Temperature Embrittlement 98

5.2.3.4 Notch Sensitivity 103

5.2.4 Mechanical Properties 104

5.3 Welding Metallurgy 104

5.3.1 Fusion Zone 104

5.3.1.1 Solidification and Transformation Sequence 104

5.3.1.2 Precipitation Behavior 109

5.3.1.3 Microstructure Prediction 111

5.3.2 Heat-Affected Zone 112

5.3.3 Solid-State Welds 113

5.4 Mechanical Properties of Weldments 114

5.4.1 Low-Chromium Alloys 114

5.4.2 Medium-Chromium Alloys 116

5.4.3 High-Chromium Alloys 119

5.5 Weldability 123

5.5.1 Weld Solidification Cracking 123

5.5.2 High-Temperature Embrittlement 124

5.5.3 Hydrogen-Induced Cracking 126

5.6 Corrosion Resistance 126

5.7 Postweld Heat Treatment 130

5.8 Filler Metal Selection 132

5.9 Case Study: HAZ Cracking in Type 436 During Cold Deformation 132

5.10 Case Study: Intergranular Stress Corrosion Cracking in the HAZ of Type 430 135

References 137

6 AUSTENITIC STAINLESS STEELS 141

6.1 Standard Alloys and Consumables 143

6.2 Physical and Mechanical Metallurgy 147

6.2.1 Mechanical Properties 149

6.3 Welding Metallurgy 151

6.3.1 Fusion Zone Microstructure Evolution 153

6.3.1.1 Type A: Fully Austenitic Solidification 154

6.3.1.2 Type AF Solidification 155

6.3.1.3 Type FA Solidification 155

6.3.1.4 Type F Solidification 158

6.3.2 Interfaces in Single-Phase Austenitic Weld Metal 162

6.3.2.1 Solidification Subgrain Boundaries 162

6.3.2.2 Solidification Grain Boundaries 163

6.3.2.3 Migrated Grain Boundaries 163

6.3.3 Heat-Affected Zone 164

6.3.3.1 Grain Growth 165

6.3.3.2 Ferrite Formation 165

6.3.3.3 Precipitation 165

6.3.3.4 Grain Boundary Liquation 166

6.3.4 Preheat and Interpass Temperature and Postweld Heat Treatment 166

6.3.4.1 Intermediate-Temperature Embrittlement 167

6.4 Mechanical Properties of Weldments 168

6.5 Weldability 173

6.5.1 Weld Solidification Cracking 173

6.5.1.1 Beneficial Effects of Primary Ferrite Solidification 175

6.5.1.2 Use of Predictive Diagrams 177

6.5.1.3 Effect of Impurity Elements 179

6.5.1.4 Ferrite Measurement 181

6.5.1.5 Effect of Rapid Solidification 182

6.5.1.6 Solidification Cracking Fracture Morphology 186

6.5.1.7 Preventing Weld Solidification Cracking 189

6.5.2 HAZ Liquation Cracking 189

6.5.3 Weld Metal Liquation Cracking 190

6.5.4 Ductility-Dip Cracking 194

6.5.5 Reheat Cracking 196

6.5.6 Copper Contamination Cracking 199

6.5.7 Zinc Contamination Cracking 200

6.5.8 Helium-Induced Cracking 200

6.6 Corrosion Resistance 200

6.6.1 Intergranular Corrosion 201

6.6.1.1 Preventing Sensitization 204

6.6.1.2 Knifeline Attack 205

6.6.1.3 Low-Temperature Sensitization 205

6.6.2 Stress Corrosion Cracking 206

6.6.3 Pitting and Crevice Corrosion 208

6.6.4 Microbiologically Induced Corrosion 208

6.6.5 Selective Ferrite Attack 209

6.7 Specialty Alloys 211

6.7.1 Heat-Resistant Alloys 211

6.7.2 High-Nitrogen Alloys 214

6.8 Case Study: Selecting the Right Filler Metal 220

6.9 Case Study: What’s Wrong with My Swimming Pool? 223

6.10 Case Study: Cracking in the Heat-Affected Zone 224

References 225

7 DUPLEX STAINLESS STEELS 230

7.1 Standard Alloys and Consumables 231

7.2 Physical Metallurgy 234

7.2.1 Austenite–Ferrite Phase Balance 234

7.2.2 Precipitation Reactions 237

7.3 Mechanical Properties 237

7.4 Welding Metallurgy 238

7.4.1 Solidification Behavior 238

7.4.2 Role of Nitrogen 240

7.4.3 Secondary Austenite 244

7.4.4 Heat-Affected Zone 246

7.5 Controlling the Ferrite–Austenite Balance 250

7.5.1 Heat Input 251

7.5.2 Cooling Rate Effects 251

7.5.3 Ferrite Prediction and Measurement 253

7.6 Weldability 254

7.6.1 Weld Solidification Cracking 254

7.6.2 Hydrogen-Induced Cracking 254

7.6.3 Intermediate-Temperature Enbrittlement 255

7.6.3.1 Alpha-Prime Embrittlement 256

7.6.3.2 Sigma Phase Embrittlement 256

7.7 Weld Mechanical Properties 259

7.8 Corrosion Resistance 261

7.8.1 Stress Corrosion Cracking 261

7.8.2 Pitting Corrosion 261

References 262

8 PRECIPITATION-HARDENING STAINLESS STEELS 264

8.1 Standard Alloys and Consumables 265

8.2 Physical and Mechanical Metallurgy 267

8.2.1 Martensitic Precipitation-Hardening Stainless Steels 269

8.2.2 Semi-Austenitic Precipitation-Hardening Stainless Steels 274

8.2.3 Austenitic Precipitation-Hardening Stainless Steels 276

8.3 Welding Metallurgy 277

8.3.1 Microstructure Evolution 278

8.3.2 Postweld Heat Treatment 278

8.4 Mechanical Properties of Weldments 279

8.5 Weldability 280

8.6 Corrosion Resistance 285

References 285

9 DISSIMILAR WELDING OF STAINLESS STEELS 287

9.1 Applications of Dissimilar Welds 287

9.2 Carbon or Low-Alloy Steel to Austenitic Stainless Steel 288

9.2.1 Determining Weld Metal Constitution 288

9.2.2 Fusion Boundary Transition Region 291

9.2.3 Nature of Type II Boundaries 294

9.3 Weldability 296

9.3.1 Solidification Cracking 296

9.3.2 Clad Disbonding 298

9.3.3 Creep Failure in the HAZ of Carbon or Low-Alloy Steel 299

9.4 Other Dissimilar Combinations 301

9.4.1 Nominally Austenitic Alloys Whose Melted Zone Is Expected to Include Some Ferrite or to Solidify as
Primary Ferrite 301

9.4.2 Nominally Austenitic Alloys Whose Melted Zone Is Expected to Contain Some Ferrite, Welded to Fully
Austenitic Stainless Steel 301

9.4.3 Austenitic Stainless Steel Joined to Duplex Stainless Steel 302

9.4.4 Austenitic Stainless Steel Joined to Ferritic Stainless Steel 302

9.4.5 Austenitic Stainless Steel Joined to Martensitic Stainless Steel 302

9.4.6 Martensitic Stainless Steel Joined to Ferritic Stainless Steel 302

9.4.7 Stainless Steel Filler Metal for Difficult-to-Weld Steels 303

9.4.8 Copper-Base Alloys Joined to Stainless Steels 305

9.4.9 Nickel-Base Alloys Joined to Stainless Steels 306

References 307

10 WELDABILITY TESTING 309

10.1 Introduction 309

10.1.1 Weldability Test Approaches 310

10.1.2 Weldability Test Techniques 310

10.2 Varestraint Test 311

10.2.1 Technique for Quantifying Weld Solidification Cracking 312

10.2.2 Technique for Quantifying HAZ Liquation Cracking 316

10.3 Hot Ductility Test 319

10.4 Fissure Bend Test 323

10.5 Strain-to-Fracture Test 328

10.6 Other Weldability Tests 329

References 329

APPENDIX 1 NOMINAL COMPOSITIONS OF STAINLESS STEELS 331

APPENDIX 2 ETCHING TECHNIQUES FOR STAINLESS STEEL WELDS 343

AUTHOR INDEX 347

SUBJECT INDEX 353