Welding Metallurgy and Weldability

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.

• Preface xiiiAuthor Biography xvi1 Introduction 11.1 Fabrication-Related Defects 51.2 Service-Related Defects 61.3 Defect Prevention and Control 7References 82 Welding Metallurgy Principles 92.1 Introduction 92.2 Regions of a Fusion Weld 102.3 Fusion Zone 132.3.1 Solidification of Metals 152.3.1.1 Solidification Parameters 152.3.1.2 Solidification Nucleation 172.3.1.3 Solidification Modes 192.3.1.4 Interface Stability 222.3.2 Macroscopic Aspects of Weld Solidification 242.3.2.1 Effect of Travel Speed and Temperature Gradient 272.3.3 Microscopic Aspects of Weld Solidification 302.3.3.1 Solidification Subgrain Boundaries (SSGB) 322.3.3.2 Solidification Grain Boundaries (SGB) 332.3.3.3 Migrated Grain Boundaries (MGB) 342.3.4 Solute Redistribution 342.3.4.1 Macroscopic Solidification 352.3.4.2 Microscopic Solidification 372.3.5 Examples of Fusion Zone Microstructures 402.3.6 Transition Zone (TZ) 432.4 Unmixed Zone (UMZ) 452.5 Partially Melted Zone (PMZ) 482.5.1 Penetration Mechanism 502.5.2 Segregation Mechanism 532.5.2.1 Gibbsian Segregation 562.5.2.2 Grain Boundary Sweeping 562.5.2.3 Pipeline Diffusion 572.5.2.4 Grain Boundary Wetting 582.5.3 Examples of PMZ formation 582.6 Heat Affected Zone (HAZ) 602.6.1 Recrystallization and Grain Growth 612.6.2 Allotropic Phase Transformations 632.6.3 Precipitation Reactions 662.6.4 Examples of HAZ Microstructure 692.7 Solid-State Welding 702.7.1 Friction Stir Welding 722.7.2 Diffusion Welding 762.7.3 Explosion Welding 772.7.4 Ultrasonic Welding 79References 813 Hot Cracking 843.1 Introduction 843.2 Weld Solidification Cracking 853.2.1 Theories of Weld Solidification Cracking 853.2.1.1 Shrinkage-Brittleness Theory 863.2.1.2 Strain Theory 873.2.1.3 Generalized Theory 883.2.1.4 Modified Generalized Theory 893.2.1.5 Technological Strength Theory 903.2.1.6 Commentary on Solidification Cracking Theories 913.2.2 Predictions of Elemental Effects 943.2.3 The BTR and Solidification Cracking Temperature Range 973.2.4 Factors that Influence Weld Solidification Cracking 1023.2.4.1 Composition Control 1023.2.4.2 Grain Boundary Liquid Films 1093.2.4.3 Effect of Restraint 1103.2.5 Identifying Weld Solidification Cracking 1123.2.6 Preventing Weld Solidification Cracking 1163.3 Liquation Cracking 1193.3.1 HAZ Liquation Cracking 1193.3.2 weld metal Liquation Cracking 1223.3.3 Variables that Influence Susceptibility to Liquation Cracking 1233.3.3.1 Composition 1233.3.3.2 Grain Size 1243.3.3.3 Base Metal Heat Treatment 1253.3.3.4 Weld Heat Input and Filler Metal Selection 1253.3.4 Identifying HAZ and weld metal Liquation Cracks 1263.3.5 Preventing Liquation Cracking 127References 1284 Solid-State Cracking 1304.1 Introduction 1304.2 Ductility-dip Cracking 1304.2.1 Proposed Mechanisms 1334.2.2 Summary of Factors That Influence DDC 1394.2.3 Quantifying Ductility-Dip Cracking 1434.2.4 Identifying Ductility-Dip Cracks 1454.2.5 Preventing DDC 1474.3 Reheat Cracking 1494.3.1 Reheat Cracking in Low-Alloy Steels 1504.3.2 Reheat Cracking in Stainless Steels 1554.3.3 Underclad Cracking 1584.3.4 Relaxation Cracking 1604.3.5 Identifying Reheat Cracking 1614.3.6 Quantifying Reheat Cracking Susceptibility 1634.3.7 Preventing Reheat Cracking 1664.4 Strain-age Cracking 1684.4.1 Mechanism for Strain-age Cracking 1714.4.2 Factors That Influence SAC Susceptibility 1784.4.2.1 Composition 1784.4.2.2 Grain Size 1794.4.2.3 Residual Stress and Restraint 1794.4.2.4 Welding Procedure 1804.4.2.5 Effect of PWHT 1814.4.3 Quantifying Susceptibility to Strain-age Cracking 1824.4.4 Identifying Strain-age Cracking 1894.4.5 Preventing Strain-age Cracking 1894.5 Lamellar Cracking 1904.5.1 Mechanism of Lamellar Cracking 1914.5.2 Quantifying Lamellar Cracking 1954.5.3 Identifying Lamellar Cracking 1974.5.4 Preventing Lamellar Cracking 1984.6 Copper Contamination Cracking 2014.6.1 Mechanism for Copper Contamination Cracking 2014.6.2 Quantifying Copper Contamination Cracking 2034.6.3 Identifying Copper Contamination Cracking 2054.6.4 Preventing Copper Contamination Cracking 205References 2075 Hydrogen-Induced Cracking 2135.1 Introduction 2135.2 Hydrogen Embrittlement Theories 2145.2.1 Planar Pressure Theory 2165.2.2 Surface Adsorption Theory 2175.2.3 Decohesion Theory 2175.2.4 Hydrogen-Enhanced Localized Plasticity Theory 2185.2.5 Beachem’s Stress Intensity Model 2195.3 Factors That Influence HIC 2215.3.1 Hydrogen in Welds 2215.3.2 Effect of Microstructure 2245.3.3 Restraint 2285.3.4 Temperature 2305.4 Quantifying Susceptibility to HIC 2305.4.1 Jominy End Quench Method 2315.4.2 Controlled Thermal Severity Test 2345.4.3 The Y-Groove (Tekken) Test 2355.4.4 Gapped Bead-on-Plate Test 2365.4.5 The Implant Test 2375.4.6 Tensile Restraint Cracking Test 2435.4.7 Augmented Strain Cracking Test 2445.5 Identifying HIC 2455.6 Preventing HIC 2475.6.1 CE Method 2515.6.2 AWS Method 254References 2596 Corrosion 2636.1 Introduction 2636.2 Forms of Corrosion 2646.2.1 General Corrosion 2646.2.2 Galvanic Corrosion 2656.2.3 Crevice Corrosion 2676.2.4 Selective Leaching 2686.2.5 Erosion Corrosion 2686.2.6 Pitting 2686.2.7 Intergranular Corrosion 2716.2.7.1 Preventing Sensitization 2756.2.7.2 Knifeline Attack 2766.2.7.3 Low-Temperature Sensitization 2766.2.8 Stress Corrosion Cracking 2776.2.9 Microbiologically Induced Corrosion 2806.3 Corrosion Testing 2826.3.1 Atmospheric Corrosion Tests 2826.3.2 Immersion Tests 2826.3.3 Electrochemical Tests 284References 2867 Fracture and Fatigue 2887.1 Introduction 2887.2 Fracture 2907.3 Quantifying Fracture Toughness 2937.4 Fatigue 2977.5 Quantifying Fatigue Behavior 3057.6 Identifying Fatigue Cracking 3067.6.1 Beach Marks 3077.6.2 River Lines 3077.6.3 Fatigue Striations 3077.7 Avoiding Fatigue Failures 309References 3108 Failure Analysis 3118.1 Introduction 3118.2 Fractography 3128.2.1 History of Fractography 3128.2.2 The SEM 3138.2.3 Fracture Modes 3158.2.4 Fractography of Weld Failures 3208.2.4.1 Solidification Cracking 3208.2.4.2 Liquation Cracking 3238.2.4.3 Ductility-Dip Cracking 3268.2.4.4 Reheat Cracking 3268.2.4.5 Strain-Age Cracking 3318.2.4.6 Hydrogen-Induced Cracking 3328.3 An Engineer’s Guide to Failure Analysis 3338.3.1 Site Visit 3348.3.2 Collect Background Information 3358.3.3 Sample Removal and Testing Protocol 3368.3.4 Sample Removal, Cleaning, and Storage 3368.3.5 Chemical Analysis 3368.3.6 Macroscopic Analysis 3378.3.7 Selection of Samples for Microscopic Analysis 3388.3.8 Selection of Analytical Techniques 3388.3.9 Mechanical Testing 3398.3.10 Simulative Testing 3398.3.11 Nondestructive Evaluation Techniques 3408.3.12 Structural Integrity Assessment 3408.3.13 Consultation with Experts 3408.3.14 Final Reporting 3408.3.15 Expert Testimony in Support of Litigation 341References 3429 Weldability Testing 3439.1 Introduction 3439.2 Types of Weldability Test Techniques 3449.3 The Varestraint Test 3459.3.1 Technique for Quantifying Weld Solidification Cracking 3469.3.2 Technique for Quantifying HAZ Liquation Cracking 3509.4 The Cast Pin Tear Test 3549.5 The Hot Ductility Test 3579.6 The Strain-to-Fracture Test 3629.7 Reheat Cracking Test 3639.8 Implant Test for HAZ Hydrogen-Induced Cracking 3669.9 Gapped Bead-on-Plate Test for Weld Metal HIC 3679.10 O ther Weldability Tests 370References 371Appendix A 372Appendix B 374Appendix C 383Appendix D 388Index 396