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The Effect of Retained Austenite on the Distortion in Carburized SAE 8620 Steel

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The Effect of Retained Austenite on the Distortion in Carburized SAE 8620 Steel University of Windsor Scholarship at UWindsor Electronic Theses and Dissertations Theses, Dissertations, and Major Papers 1-1-2005 The effect of retained austenite on the distortion in carburized SAE 8620 steel. Haitao (Lily) He University of Windsor Follow this and additional works at: https://scholar.uwindsor.ca/etd Recommended Citation He, Haitao (Lily), "The effect of retained austenite on the distortion in carburized SAE 8620 steel." (2005). Electronic Theses and Dissertations. 7166. https://scholar.uwindsor.ca/etd/7166 This online database contains the full-text of PhD dissertations and Masters’ theses of University of Windsor students from 1954 forward. These documents are made available for personal study and research purposes only, in accordance with the Canadian Copyright Act and the Creative Commons license—CC BY-NC-ND (Attribution, Non-Commercial, No Derivative Works). Under this license, works must always be attributed to the copyright holder (original author), cannot be used for any commercial purposes, and may not be altered. Any other use would require the permission of the copyright holder. Students may inquire about withdrawing their dissertation and/or thesis from this database. For additional inquiries, please contact the repository administrator via email ([email protected]) or by telephone at 519-253-3000ext. 3208. THE EFFECT OF RETAINED AUSTENITE ON THE DISTORTION IN CARBURIZED SAE 8620 STEEL by Haitao (Lily) He A Thesis Submitted to the Faculty of Graduate Studies and Research through Engineering Materials in Partial Fulfillment of the Requirements for the Degree of Master of Applied Science at the University of Windsor Windsor, Ontario, Canada 2005 © 2005 Haitao (Lily) He Library and Archives Bibliotheque et 1*1 Canada Archives Canada Published Heritage Direction du Branch Patrimoine de I'edition 395 Wellington Street 395, rue Wellington OttawaONK1A0N4 OttawaONK1A0N4 Canada Canada Your file Votre reference ISBN: 978-0-494-57630-4 Our file Notre reference ISBN: 978-0-494-57630-4 NOTICE: AVIS: The author has granted a non­ L'auteur a accorde une licence non exclusive exclusive license allowing Library and permettant a la Bibliotheque et Archives Archives Canada to reproduce, Canada de reproduire, publier, archiver, publish, archive, preserve, conserve, sauvegarder, conserver, transmettre au public communicate to the public by par telecommunication ou par I'lntemet, preter, telecommunication or on the Internet, distribuer et vendre des theses partout dans le loan, distribute and sell theses monde, a des fins commerciales ou autres, sur worldwide, for commercial or non­ support microforme, papier, electronique et/ou commercial purposes, in microform, autres formats. paper, electronic and/or any other formats. The author retains copyright L'auteur conserve la propriete du droit d'auteur ownership and moral rights in this et des droits moraux qui protege cette these. Ni thesis. Neither the thesis nor la these ni des extraits substantiels de celle-ci substantial extracts from it may be ne doivent etre imprimes ou autrement printed or otherwise reproduced reproduits sans son autorisation. without the author's permission. In compliance with the Canadian Conformement a la loi canadienne sur la Privacy Act some supporting forms protection de la vie privee, quelques may have been removed from this formulaires secondaires ont ete enleves de thesis. cette these. While these forms may be included Bien que ces formulaires aient inclus dans in the document page count, their la pagination, il n'y aura aucun contenu removal does not represent any loss manquant. of content from the thesis. 1*1 Canada ABSTRACT The effects of retained austenite and other metallurgical parameters on the dimensional stability of carburized SAE 8620 steel have been investigated. The purpose is to find the optimum amount of retained austenite (RA) in SAE 8620 steel that is typically used in the carburized condition for powertrain applications in the automotive industry. A specially designed specimen, known as a Navy C-ring has been used for this study. The SAE 8620 steel was first normalized prior to machining the Navy C-ring specimens. The C-ring specimens were then heat treated by carburizing at one of two temperatures (6hrs at 1700°F & 4hrs at 1750°F) at four levels of carbon potential (0.9, 1.0, 1.1, 1.2) followed by quenching and tempering at one of two temperatures (300°F & 350°F). For every combination of heat treatment conditions, the distortion of the C-ring was evaluated by dimensional measurements of the ID, OD and gap width. XRD techniques were used to determine both the residual stress and the retained austenite. The retained austenite value for the as-carburized samples was also evaluated using an optical metallographic technique. Hardness profiles from the surface to the core were determined for the as-carburized samples using microhardness measurements. The carbon contents at the surface were measured using optical emission spectroscopy (OES). The amount of retained austenite and the residual stress increase with increasing carburizing temperature and carbon potential. The amount of retained austenite and the residual stress decrease with increasing tempering temperature. However, there is not a iii large change when the tempering temperature is increased from 300°F to350°F. Distortion is influenced both by the amount of retained austenite and the magnitude of the residual stress. With increasing retained austenite / residual stress, the distortion becomes more serious. Based on the distortion data (OD, ID & Flatness) for the quenched and tempered specimens, the optimum amount of retained austenite was about 25%. TO MY FATHER V ACKNOWLEDGEMENTS First I would like to acknowledge Dr. D. O. Northwood for his supervision, encouragement and patience. I would also like to acknowledge Dr. Xichen Sun for his technical suggestions and support particularly with respect to access to experimental facilities. The laboratory help of Mr. J. W. Robinson is also much appreciated. Secondly I would like to thank all staff and students of the Engineering Materials Group for their support and friendship during my studies. Finally I would like to express my sincere thanks to my mother, my husband, Xu Wang, and my son, Chee-Chee, for their selfless love and support. TABLE OF CONTENTS ABSTRACT m DEDICATION ACKNOWLEDGEMENTS VI LIST OF TABLES LIST OF FIGURES xm CHAPTER 1 INTRODUCTION 1 CHAPTER 2 LITERATURE REVIEW 3 2.1 Carburized SAE 8620 Steel 3 2.1.1 Carburizing 3 2.1.2 Properties & Applications 6 2.2 Retained Austenite 7 2.2.1 Origin of Retained Austenite 7 2.2.2 Range of Retained Austenite 10 2.2.3 Retained Austenite Profile and Hardness Profile 10 in Carburized Condition 2.2.4 Techniques for Measurement of Retained 15 Austenite 2.3 Residual Stress 19 2.3.1 Origin of Residual Stress 19 2.3.2 Residual Stress Pattern of Carburized and 21 Quenched Steel 2.3.3 Residual Stress Measurement by X-ray 24 Diffraction 2.4 Distortion in Heat Treatment 27 2.4.1 Types of Distortion 27 2.4.2 Distortion Caused by Changes in Metallurgical 28 Structure 2.4.3 Factors That Influence Distortion of Carburized 29 Parts 2.4.4 Control of Distortion of Carburized Parts 30 2.5 The Effect of Residual Stress on Distortion 32 2.6 The Effect of Retained Austenite on Distortion and Other 34 Properties 2.6.1 The Effect of Retained Austenite on Dimensional 35 Stability 2.7 Summary of Relationships between Heat Treatment 36 Processing Parameters, Retained Austenite, Residual Stresses and Distortion CHAPTER 3 EXPERIMENTAL DETAILS 38 3.1 Material 38 3.2 Pre-Heat Treatment, Carburizing and General Overview 38 of Processing 3.3 Material Characterization Techniques 45 3.3.1 Scanning Electron Microscopy 45 3.3.2 Optical Microscopy 45 3.3.3 X-ray Diffraction 46 3.3.4 Optical Metallography 47 3.3.5 Hardness Measurement 47 3.3.6 Optical Emission Spectroscopy 48 3.4 Dimensional Measurements 48 3.5 Summary of Experimental Procedures & Measurements 49 vui CHAPTER 4 THE EFFECT OF RETAINED AUSTENITE ON OD, 57 GAP AND FLATNESS DISTORTION OF SAE 8620 STEEL 4.1 Distortion 57 4.2 Retained Austenite and Residual Stress 60 4.3 Distortion vs. Retained Austenite and Residual Stress 61 4.4 Microstructure 77 CHAPTER 5 THE EFFECT OF RETAINED AUSTENITE ON ID, 86 THICKNESS, CYLINDRICITY AND ROUNDNESS DISTORTION OF SAE 8620 STEEL CHAPTER 6 HARDNESS PROFILES AND CARBON CONTENT 96 6.1 Hardness Profiles 96 6.2 Carbon Contents 97 CHAPTER 7 CONCLUSIONS AND RECOMMENDATIONS FOR 107 FUTURE WORK 7.1 Conclusions 107 7.2 Recommendations for Furture Work 110 APPENDIX 112 REFERENCES 133 VITA AUCTORIS 145 PRESENTATIONS & PUBLICATIONS RESULTING 146 FROM THIS THESIS LIST OF TABLES Chapter 2 Table 2.1 Compositions of case-hardening steels [3]. Table 2.2 Changes in volume during the phase transformations of austenite into different phases (Source: Ref. 57). Table 2.3 A Summary of the maximum residual stresses in surface heat-treated steels [40]. Chapter 3 Table 3.1 Chemical composition of as-received SAE 8620 steel. Table 3.2 SAE 8620 Navy C -ring heat treatment matrix. Table 3.3 Hardness Conversion Numbers for Steel [6]. Chapter 4 Table 4.1 Distortion values for Navy-C ring specimens subjected to various heat treatments. Table 4.2 Retained austenite and residual stresses in Navy C-ring specimens subjected to various heat treatment condition. Table 4.3 OD distortion vs. retained austenite and residual stress after quenching. Table 4.4 Gap width distortion vs. retained austenite and residual stress after quenching. Table 4.5 Flatness distortion vs. retained austenite and residual stress after quenching. Table 4.6 OD distortion vs. retained austenite and residual stress after 300°F/lhr tempering. Table 4.7 Gap width distortion vs. retained austenite and residual stress after 300°F/lhr tempering. Table 4.8 Flatness distortion vs.
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