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Chemistry, Design, and Processing of Two-Stage TRIP Steel

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Chemistry, Design, and Processing of Two-Stage TRIP Steel Scholars' Mine Doctoral Dissertations Student Theses and Dissertations Spring 2018 Chemistry, design, and processing of two-stage TRIP steel Daniel M. Field Follow this and additional works at: https://scholarsmine.mst.edu/doctoral_dissertations Part of the Metallurgy Commons Department: Materials Science and Engineering Recommended Citation Field, Daniel M., "Chemistry, design, and processing of two-stage TRIP steel" (2018). Doctoral Dissertations. 2672. https://scholarsmine.mst.edu/doctoral_dissertations/2672 This thesis is brought to you by Scholars' Mine, a service of the Missouri S&T Library and Learning Resources. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. i CHEMISTRY, DESIGN, AND PROCESSING OF TWO-STAGE TRIP STEEL by DANIEL MORYE FIELD A DISSERTATION Presented to the Faculty of the Graduate School of the MISSOURI UNIVERSITY OF SCIENCE AND TECHNOLOGY In Partial Fulfillment of the Requirements for the Degree DOCTOR OF PHILOSOPHY in METALLURGICAL ENGINEERING 2018 Approved David C. Van Aken, Advisor Matthew J. O’Keefe Ronald J. O’Malley William G. Fahrenholtz Julia E. Medvedeva ii iii PUBLICATION DISSERTATION OPTION This dissertation has been prepared in the form of three manuscripts for publication. Paper I, pages 18-53 were published February 2017 online and in print in Metallurgical and Materials Transactions A volume 48A, May 2017. Paper II, pages 54- 92 has been prepared to the Metallurgical and Materials Transactions A format and was submitted for review September 2017, and accepted with minor revisions. Paper III, pages 93-136 have been prepared in the style utilized by the Materials & Design. The Introduction, Literature Review, and Proposed Future Alloy Design provide supplemental information and discussion to the dissertation topic and have been formatted to Missouri University of Science and Technology specification. iv ABSTRACT A regular solution model was developed to calculate the chemical driving force γα→ γα→ for α-martensite formation, ∆GChem . A model for the strain energy, ∆Gstr , was formulated utilizing the Young’s modulus (E), lattice misfit squared (δ2), and molar volume (Ω) which opposed the chemical driving force for α-martensite formation. The α γα→→ γα M S was determined at a temperature at which ∆GGChem +∆ str =0 . In conjunction with a previously developed ε-martensite model, a means of predicting the volume fraction of γ-austenite was determined; and it was shown that for values of ΔMs < 0, defined as Msε – Msα produced the greatest amounts of retained γ-austenite in the as quenched microstructure. These models were tested, and confirmed, with a new alloy formulated to produce a steel with chromium replacing the traditional aluminum to obtain a ΔMs = - 100 C° that exhibited the two-stage TRIP behavior. From this substitution the dynamic strain aging response could be mitigated through M23(C,N)6 precipitation trapping carbon and nitrogen. The work hardening behavior of these steels was found to be due to the Stage II (ε→α) martensitic reaction and not the dynamic strain aging of the steels. Eight medium-Mn steels were processed and it was found that when the intrinsic stacking fault energy was less than 10.5 mJ/m2 the two-stage TRIP response was activated. Empirical relationships for the strength and ductility were determined for the two-stage TRIP steels. The developed models have been used to optimize alloy composition and a designed steel with composition Fe-13.8Mn-1.0Si-3.0Cr-0.15C-0.003N (wt. pct.) is recommended for future investigation. v ACKNOWLEDGMENTS This work has been supported by the Kent D. Peaslee Steel Manufacturing Research Center (PSMRC) as part of the project development of New 3rd Generation Advanced High Strength Steels. First and foremost I would like to express my extreme gratitude to my wife Melissa Field for being a supporting and understanding partner. Throughout this entire process she has supported me with her unwavering faith in me and being a sounding board for my troubles. I also appreciate all of the sacrifices my wife and children have made to make it possible for me to finish my degree. I am enormously grateful to Dr. David. C. Van Aken for his guidance, instruction, and encouragement during my time as a student and a researcher. His dedication to education has been an inspiration. I would like to thank Dr. Ronald J. O’Malley, Dr. Matthew J. O’Keefe, Dr. William G. Fahrenholtz, and Dr. Julia E. Medvedeva for their role as committee members. Further gratitude is extended to Todd M. Link at U.S. Steel, Eric Gallo of Nucor Steel, Narayan Pottore and Bernard Chukwulebe of ArcelorMittal, and Luis Garza of AK Steel for their advice, support, and technical discussion as acting industry representatives of the Kent D. Peaslee Steel Manufacturing Research Center. I would like to extend my appreciation to the staff of the Materials Research Center including Dr. Clarissa Wisner and Dr. Jingjing Qing for their guidance and training in electron microscopy and Dr. Eric Bohannon for conducting numerous X-ray diffraction experiments in support of this project. I also wish to thank Dr. Mingzhi Xu for his assistance in the research foundry, assisting with the casting of the alloys investigated, and Dr. Mario Buchely for his assistance with hot rolling and high strain rate testing of the alloys. I also acknowledge my colleagues, Scott Pisarik for his initial ground work on the two-stage TRIP steels as well as Terrell Webb, Seth Rummel, Viraj Athavale, and Jie Wan. The Materials Science and Engineering Department staff of Teneke Hill and Denise Eddings were integral in their daily help in overcoming life’s daily hurdles. Undergraduate student assistance was provided by Travis Zerna, Jackson Riley, and Sonya Snyder, who have helped me be in two or more places at once. vi TABLE OF CONTENTS Page PUBLICATION DISSERTATION OPTION.................................................................... iii ABSTRACT ....................................................................................................................... iv ACKNOWLEDGMENTS .................................................................................................. v LIST OF ILLUSTRATIONS ............................................................................................. ix LIST OF TABLES ........................................................................................................... ixv SECTION 1. INTRODUCTION ...................................................................................................... 1 2. LITERATURE REVIEW ........................................................................................... 5 2.1. THERMODYNAMICS ...................................................................................... 5 2.1.1. ε-martensite, Stage I (γ→ε). ................................................................... 5 2.1.2. α-martensite, (γ→α). .............................................................................. 7 2.2. STRAIN AGING ................................................................................................ 9 2.2.1. Static Strain Aging. ................................................................................ 9 2.2.2. Dynamic Strain Aging. ......................................................................... 10 2.3. MECHANICAL BEHAVIOR .......................................................................... 13 2.3.1. Deformation Response. ........................................................................ 13 2.3.2. Effect of Chemistry. ............................................................................. 16 PAPER I. ON THE PREDICTION OF α-MARTENSITE TEMPERATURES IN MEDIUM MANGANESE STEELS ........................................................................ 18 ABSTRACT............................................................................................................. 19 I. INTRODUCTION ................................................................................................ 20 A. Regular Solution Model of γ→α Martensitic Transformation .................... 25 B. Experimental Procedure ............................................................................... 26 II. RESULTS ........................................................................................................... 29 A. Incorporation of Young’s Modulus and Application of SFE Model to α Calculate M S .............................................................................................. 31 III. DISCUSSION .................................................................................................... 34 IV CONCLUSION .................................................................................................. 47 vii ACKNOWLEGEMENTS ........................................................................................ 48 APPENDIX .............................................................................................................. 48 REFRENCES ........................................................................................................... 51 II. DYNAMIC STRAIN AGING PHENOMENA AND TENSILE RESPONSE OF MEDIUM-MN TWO-STAGE TRIP STEEL ................................................... 54 ABSTRACT............................................................................................................. 55 I. INTRODUCTION
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