Effect of Design Factors on Thermal Fatigue Cracking of Die Casting Dies

Effect of Design Factors on Thermal Fatigue Cracking of Die Casting Dies
Final Technical Report
David Schwam
John F. Wallace
Sebastian Birceanu
Department of Materials Science
Case Western Reserve University
Cleveland, Ohio
TABLE OF CONTENTS
Content Page
TABLE OF CONTENTS 2
LIST OF TABLES 4
LIST OF FIGURES 5
ACKNOWLEDGEMENTS 8
ABSTRACT 9

1. Introduction 10
   1.1. Die Failure Modes 10
   1.2. Thermal Fatigue Failure Mechanisms 11
   1.3. Thermal Shock and Thermal Fatigue Resistance Evaluation Factors 16
   1.4. Thermal and Physical Properties that Affect Thermal Fatigue Resistance 7
   1.4.1. Thermal Conductivity 7
   1.4.2. Thermal Expansion Coefficient 8
   1.5. Mechanical Properties that Affect Thermal Fatigue Resistance 9
   1.5.1. Elastic Modulus and Strength 9
   1.6. The Effect of Thermal Cycling on Microstructural Stability 10
   1.7. The Temperature-Time Effect on the Structure of Martensitic Steel 20
   2Content Page
   1.7.1. Martensitic Transformation in Steel – Brief Overview 20
   1.7.2. Tempering of Martensite 22
2. Materials and Experimental Procedures 26
   2.1. Materials 26
   2.2. The Thermal Fatigue Test 27
   2.2.1. Specimens and Equipment 27
   2.2.2. Thermal Fatigue Cracks Evaluation Procedure 28
   2.2.3. Temperature Measurement 29
   2.2.4. Microhardness Measurement 30
   2.2.5. Scanning Electron Microscopy 30
3. Results and Discussion 39
   3.1. Softening During Thermal Cycling and Thermal Fatigue Resistance 39
   3.1.1. The Influence of Immersion Time on Softening and Thermal Fatigue
   dsadasdasCracking 40
   3.1.2. The Influence of Cooling Line Diameter on Softening and Thermal
   sadadadadFatigue Cracking
   47
   3.2. Stress Analysis at the Specimen Surface and Around the Cooling Line 51
   3.3. Microstructure Degradation that Promotes Softening During Thermal
   sasdsdCycling 52
4. Conclusions 59
5. Bibliography 99
   3LIST OF TABLES
   Table Page
   2.1. Chemical Composition of Experimental Material – Premium Grade H13 31
   2.2. Typical Properties of Premium Grade H13 32
   2.3. Characteristics of the Tested Specimens 33
   3.1. Measurement Data For Different Immersion Times 44
   3.2. Immersion Time Effect on Hardness Variation Across the Surface 45
   3.3. Measurement Data For Different Cooling Line Diameters 49
   3.4. Cooling Line Diameter Effect on Hardness Variation Across the Surface 50
   4LIST OF FIGURES
   Figures Page
   1.1. Hysteresis Loop at the Surface of a Material Subjected to Cyclic Heating
   aaaaand Cooling 15
   2.1. CCT Diagram for H13 steel 35
   2.2. The Reference Specimen for Thermal Fatigue Test 36
   2.3. The Thermal Fatigue Test Equipment 37
   2.4. Temperature Measurement 38
   3.1. Relationship between Tensile Properties and Hardness 61
   3.2. The Effect of Thermal Cycling on Crack Area-Different Immersion Times 63
   3.3.The Effect of Thermal Cycling on Crack Length- Different Immersion Times 64
   3.4. The Effect of Thermal Cycling on Microhardness Distribution Across the
   aaaaSurface- Different Immersion Times 65
   3.5. The Effect of Temperature on Crack Area-Different Immersion Times 66
   3.6. The Effect of Temperature on Crack Length-Different Immersion Times 67
   3.7. Effect of Elevated Temperature on Tensile Strength 68
   3.8. The Effect of Hardness Recovery on Thermal Fatigue Cracking 70
   3.9. Relationship Between Total Crack Area and Average Maximum Crack
   aaaaLength 71
   3.10. The Relationship Between Maximum Crack Length and Microhardness at
   aaaaaMaximum Crack Length 72
   3.11. The Effect of Temperature on Microhardness-Different Immersion Times 73
   3.12. The Effect of Microhardness at Average Maximum Crack Length on Crack
   aaaaaArea 74
   5Figures
   Page
   3.13. The Effect of Microhardness at Average Maximum Crack Length on Crack
   aaaaaLength-Different Immersion Times 75
   3.14. Microhardness Profile at the Corner of 12 Seconds Immersed Specimen 76
   3.15. Tempering Curve for H13 77
   3.16. Maximum Temperature Cycle for 1.5″ Cooling Line Specimen After 12
   aaaaaSeconds Immersion Time 78
   3.17. The Effect of Thermal Cycling on Crack Area-Different Cooling Line
   aaaaaDiameters 79
   3.18. The Effect of Thermal Cycling on Crack Length-Different Cooling Line
   aaaaaDiameters 80
   3.19. The Effect of Thermal Cycling on Microhardness Distribution Across the
   aaaaaSurface-Different Cooling Line Diameters 81
   3.20. The Effect of Temperature on Crack Area-Different Cooling Line
   aaaaaDiameters 82
   3.21. The Effect of Temperature on Crack Length-Different Cooling Line
   aaaaaDiameters 83
   3.22. The Effect of Temperature on Microhardness-Different Cooling Line
   aaaaaDiameters 84
   3.23. The Effect of Microhardness at Average Maximum Crack Length on Crack
   aaaaaArea-Different Cooling Line Diameters 86
   3.24. The Effect of Microhardness at Average Maximum Crack Length on Crack
   aaaaaLength-Different Cooling Line Diameters 87
   3.25. The Effect of Immersion Time on Temperature 88
   3.26.The Effect of Cooling Line Diameter on Temperature 89
   3.27. Cracks at the Corner of H13 Specimen 90
   3.28. Crack at the Cooling Line of H13 Specimen 90
   3.29. Stress Modeling at the Corner and Cooling Line 91
   6Figures
   Page
   3.30. Effect of Volume Percent Primary Carbides on the Transverse Charpy Vnotch Impact Toughness of H13 92
   3.31. Microstructure Sampling at the Corner of 12 Seconds Immersion Specimen 93
   3.32 a. The Effect of Temperature on Microstructure – Unaffected 94
   3.32 b. The Effect of Temperature on Microstructure – 0.2” from Corner 94
   3.32 c. The Effect of Temperature on Microstructure – 0.1” from Corner 94
   3.32 d. The Effect of Temperature on Microstructure – 0.06” from Corner 94
   3.32 e. The Effect of Temperature on Microstructure – Corner 94
   3.33.Temperature Influence on Carbide Size and Distribution-Photomontage 95
   3.34. Effect of Austenitizing Temperature on the Weight Percentage of Isolated
   aaaaaCarbide Residues in H13 Steel 96
   3.35. Small Carbide in Softened H13 97
   3.36. Large Carbide in Softened H13 98

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