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Cyclic Stress Effect on Stress Corrosion Cracking of Duplex Stainless Steel in Chloride and Caustic Solutions

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Cyclic Stress Effect on Stress Corrosion Cracking of Duplex Stainless Steel in Chloride and Caustic Solutions CYCLIC STRESS EFFECT ON STRESS CORROSION CRACKING OF DUPLEX STAINLESS STEEL IN CHLORIDE AND CAUSTIC SOLUTIONS A Dissertation Presented to The Academic Faculty By Di Yang In Partial Fulfillment Of the Requirements for the Degree Doctor of Philosophy in the School of Mechanical Engineering Georgia Institute of Technology December, 2011 CYCLIC STRESS EFFECT ON STRESS CORROSION CRACKING OF DUPLEX STAINLESS STEEL IN CHLORIDE AND CAUSTIC SOLUTIONS Approved by: Dr. Preet M. Singh, Advisor School of Materials Science and Engineering Georgia Institute of Technology Dr. Richard W. Neu, Co-advisor School of Mechanical Engineering and Materials Science and Engineering Georgia Institute of Technology Dr. W. Steven Johnson School of Mechanical Engineering and Materials Science and Engineering Georgia Institute of Technology Dr. Naresh Thadhani School of Mechanical Engineering and Materials Science and Engineering Georgia Institute of Technology Dr. Hamid Garmestani School of Materials Science and Engineering Georgia Institute of Technology Date Approved: October 7, 2011 ACKNOWLEDGEMENTS Completing a Ph.D. study is like a long journey, and I would not have been able to complete this journey without the help and support of countless people over the past few years. I must first express my gratitude to my thesis advisor, Prof. Preet M. Singh, who opened the door to a whole new research area for me, corrosion, which I happen to like very much. This research work cannot be done without Dr. Singh’s guidance, support, encouragement and patience. His positive attitude for both research and life set a perfect role model for me. I would also like to thank my thesis co-advisor, Prof. Richard W. Neu for his assistance and guidance during my PhD study. The discussions with Dr. Neu on various topics have been extremely helpful to this study. I would like to thank my committee members, Dr. W. Steven Johnson, Dr. Hamid Garmestani and Dr. Naresh Thadhani for their valuable input and guidance to improve this work. I also greatly appreciate the corrosion group members, especially Mr. Jamshad Mahmood, who provided continuous support and help during the past few years. This research work was funded by the PSE Foundation Fellowship Program at Institute of Paper Science and Technology at Georgia Tech. The materials used in this study were graciously donated by Outokumpu. Lastly, and most importantly, I wish to thank my husband, Dr. Bate Bate, and my parents, Fan Yang and Liming Xiao. Their love, support, encouragement, and believe in me make this work possible, and I dedicate this thesis to them. III TABLE OF CONTENTS ACKNOWLEDGEMENTS III LIST OF TABLES VII LIST OF FIGURES IX SUMMARY XVI CHAPTER 1 INTRODUCTION ................................................................................................ 1 1.1 Research Objective ............................................................................................... 1 1.2 Overall Approach .................................................................................................. 2 CHAPTER 2 BACKGROUND .................................................................................................. 5 2.1 Duplex Stainless Steel .......................................................................................... 5 2.2 SCC ...................................................................................................................... 12 2.2.1 Definition of SCC ......................................................................................... 12 2.2.2 Classification of SCC .................................................................................... 15 2.2.3 Mechanisms of SCC ..................................................................................... 17 2.2.4 SCC of DSSs .................................................................................................. 26 2.3 Corrosion Fatigue ............................................................................................... 31 2.3.1 Definition and Characteristics ..................................................................... 31 2.3.2 Mechanisms of CF ....................................................................................... 31 2.3.3 Effect of Loading Parameters ...................................................................... 34 2.3.4 Relationship of SCC and CF ......................................................................... 36 2.4 Residual Stresses in DSSs ................................................................................... 37 2.4.1 Nature of Residual Stresses in DSSs ............................................................ 37 2.4.2 Quantification of Residual Stresses in DSSs ................................................ 38 2.4.3 Effect of Residual Stresses on SCC of DSSs ................................................. 42 2.4.4 Effect of Stresses on Corrosion and Electrochemical Behavior .................. 45 2.5 Effect of Cyclic Stresses on SCC of DSSs ............................................................. 46 2.5.1 Rate Sensitivity of SCC ................................................................................ 46 2.5.2 Effect of Cyclic Stresses on Crack Tip Creep ............................................... 49 2.5.3 Effect of Cyclic Stresses on SCC................................................................... 57 2.6 Motivation .......................................................................................................... 61 CHAPTER 3 EXPERIMENTAL PROCEDURES ........................................................................ 64 IV 3.1 Materials ............................................................................................................ 64 3.2 Sample Preparation ............................................................................................ 70 3.3 Testing Environments ......................................................................................... 71 3.4 Experimental Procedures ................................................................................... 72 3.4.1 Polarization Testing ..................................................................................... 72 3.4.2 SSRTs ........................................................................................................... 79 3.4.3 Static and Cyclic Creep Tests ....................................................................... 84 3.4.4 Low Frequency CF Tests .............................................................................. 91 3.4.5 Microhardness Measurement .................................................................... 92 CHAPTER 4 ENVIRONMENTAL EFFECT ON STRESS CORROSION CRACKING OF DUPELX STAINLESS STEEL 2205 ...................................................................................................... 94 4.1 Introduction........................................................................................................ 94 4.2 Results and Discussion ....................................................................................... 97 4.2.1 Effect of pH ................................................................................................. 97 4.2.2 Effect of Potential ..................................................................................... 104 4.2.3 Effect of Cold Working .............................................................................. 111 4.2.4 Crack Initiation .......................................................................................... 117 4.2.5 Threshold Stress/Strain for Crack Initiation .............................................. 124 4.3 Conclusions....................................................................................................... 129 CHAPTER 5 CYCLIC STRESS EFFECT ON CREEP BEHAVIOR OF DUPLEX STAINLESS STEEL 2205 ................................................................................................................................ 131 5.1 Introduction...................................................................................................... 131 5.2 Results and Discussion ..................................................................................... 134 5.2.1 Pure Static and Cyclic Creep Test Results ................................................. 136 5.2.2 Static Creep Analytical Model ................................................................... 144 5.2.3 Static-Cyclic Creep Test Results ................................................................ 148 5.2.4 Creep Strain Ratio ..................................................................................... 154 5.3 Conclusions....................................................................................................... 161 CHAPTER 6 CYCLIC STRESS EFFECT ON STRESS CORROSION CRACKING OF DUPLEX STAINLESS STEEL 2205 .................................................................................................... 163 6.1 Introduction...................................................................................................... 163 6.2 Results and Discussion ..................................................................................... 167 6.2.1 Low Frequency CF Behavior of DSS 2205 in Acidic Chloride Environment 168 V 6.2.2 Low Frequency CF Behavior of DSS 2205 in Caustic WL Environment ..... 188 6.2.3 Strain Distribution and Slip Dissolution Mechanism ................................ 201 6.2.4 Effect of Cold Working on CF of DSS 2205 ...............................................
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