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Processing, Microstructures and Properties of a Dual Phase Precipitation

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Processing, Microstructures and Properties of a Dual Phase Precipitation Processing, Microstructures and Properties of a Dual Phase Precipitation- Hardening PM Stainless Steel A Thesis Submitted to the Faculty of Drexel University by Christopher Schade in partial fulfillment of the requirements for the degree of Doctor of Philosophy July 2010 © Copyright 2010 Christopher Schade. All Rights Reserved . ii Dedications To Megan, Nicholas and Karen for their love and support and to my parents, Joe and JoAnn, for their faith and understanding. iii Acknowledgments I would like to express my gratitude to my advisors Prof. Roger D. Doherty and Prof. Alan Lawley for their guidance and support. I am grateful for many useful discussions and suggestions. I would like to thank the committee members Prof. Antonios Zavaliangos, Dr. Sim Narasimhan and Dr. Fred B. Fletcher for serving on my committee and providing me helpful suggestions in improving the quality of my thesis. I am grateful to Hoeganaes Corporation for not only the financial support but for providing encouragement and an environment for learning. I am also grateful to my colleagues at Lukens Steel and Hoeganaes many of whom provided technical discussions that helped with the research. Special thanks are due to Tom Murphy for assistance in many technical aspects of the thesis and Wing Hong Chen, Barry Diamond and Jerry Golin for helping me with the experimental work. Last, but by no means least, I thank Prof. Raj Mutharasan for his continued support of my Doctoral program despite many delays. His continued commitment to my education over the last twenty years is very much appreciated. iv Table of Contents LIST OF TABLES............................................................................................................. vi LIST OF FIGURES ......................................................................................................... viii ABSTRACT..................................................................................................................... xiii 1. INTRODUCTION ...........................................................................................................1 2. BACKGROUND .............................................................................................................6 2.1 Processing of PM Stainless Steels .....................................................................7 2.2 Part Fabrication..................................................................................................9 2.3 Dual Phase (DP) Stainless Steels.....................................................................11 2.4 Precipitation Hardening (PH) Stainless Steels.................................................17 2.5 Precipitation and Effect on Mechanical Properties..........................................20 2.6 Deformation Behavior in DP Steels.................................................................22 2.7 Yielding Behavior and Residual Stresses in DP Steels ...................................25 2.8 Deformation of PH Single Phase Alloys .........................................................28 2.9 Deformation of Precipitation Hardened DP Alloys.........................................35 2.10 Bauschinger Effect in DP Steels....................................................................41 2.11 Objective........................................................................................................46 3. EXPERIMENTAL METHODS.....................................................................................48 3.1 Powder Production...........................................................................................48 3.2 Chemical Analysis ...........................................................................................49 3.3 Mechanical Properties......................................................................................49 3.4 Metallography and Imaging.............................................................................50 v 3.5 Dilatometry ......................................................................................................53 3.6 Electrical Resistivity........................................................................................54 3.7 Compressive Yield Strength ............................................................................54 4. EXPERIMENTAL RESULTS.......................................................................................55 4.1 Material Development .....................................................................................55 4.2 Mechanical Properties......................................................................................68 4.2.1 Mechanical Properties of PM Alloys................................................68 4.2.2 Mechanical Properties of Cast Alloys...............................................74 4.2.3 Mechanical Properties versus Microstructure...................................76 4.3 Heat Treatment-Aging .....................................................................................86 4.3.1 Time Dependence .............................................................................86 4.3.2 Residual Stress Effects on Yield Stress and Strain Hardening.........93 4.3.3 Effect of Precipitation on Yield Stress and Strain Hardening ........102 4.4 Fractography ..................................................................................................120 4.5 Microindentation Hardness............................................................................129 5. DISCUSSION..............................................................................................................133 6. CONCLUSIONS..........................................................................................................144 7. RECOMMENDATIONS FOR FUTURE WORK ......................................................147 LIST OF REFERENCES.................................................................................................149 APPENDIX I ...................................................................................................................159 APPENDIX II ..................................................................................................................162 VITA................................................................................................................................167 vi List of Tables 1. Comparison of Chemistry of PM and Cast Stainless Steels (w/o) …………………9 2. Composition of Representative Wrought DP Stainless Steels (w/o)...........................17 3. Composition of ASTM A710 (w/o).............................................................................36 4. Composition of DP and Ferritic PM Stainless Steels (w/o).........................................55 5. Composition of Experimental DPPH Alloys (w/o) .....................................................56 6. Volume fraction of phases in 2 w/o Cu DPPH alloy quenched from sintering temperature (1260 0C) as a function of sintering time.................................................59 7. Chemistry of 1, 2 and 3 w/o Cu DPPH alloys measured by x-ray spectrometry and chemistry of the martensite and ferrite measured by EDX...................................60 8. Martensite v/o in experimental alloys as a function of sintering temperature and copper level (w/o) .................................................................................................62 9. Ac1 and Ac3 Transformation temperatures determined by dilatometry as a function of Cu content .................................................................................................64 10. Mechanical properties of DPPH PM stainless steels in the as sintered and aged conditions.....................................................................................................................68 11. Composition of 17-4 PH PM Stainless Steel (w/o) .....................................................73 12. Tensile properties of Cast DPPH alloys in the “sintered annealed” and aged condition ......................................................................................................................74 13. Tensile properties and resistivity measurements versus aging time on 2 w/o Cu DPPH alloy at aging temperatures of: (a) 316 oC, (b) 449 oC, (c) 538 oC and (d) 760 oC ..............................................................................................................88 14. Tensile properties and electrical resistivity versus aging time for 17-4 PH alloy at 538 oC aging temperature................................................................................89 15. Chemical composition of ferrite and martensite alloys derived from EDX measurements on 2 w/o Cu phase chemistries (w/o)...................................................90 16. Tensile properties and electrical resistivity measurements versus aging time in (a) all martensitic and (b) all ferritic DPPH alloys aged at 538 oC..............................91 17. Tensile properties and electrical resistivity versus aging time for copper free DPPH alloy aged at 538 oC..........................................................................................93 vii 18. Composition of wrought DP stainless steel (w/o)........................................................95 19. Composition of fully martensitic PM stainless steel (w/o)........................................108 20. Tensile properties of fully martensitic alloy as a function of aging temperature ......108 21. Chemical composition of super ferritic and martensitic alloys
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