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The Microstructure, Hardness, Impact

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The Microstructure, Hardness, Impact THE MICROSTRUCTURE, HARDNESS, IMPACT TOUGHNESS, TENSILE DEFORMATION AND FINAL FRACTURE BEHAVIOR OF FOUR SPECIALTY HIGH STRENGTH STEELS A Thesis Presented to The Graduate Faculty of The University of Akron In Partial Fulfillment of the Requirements for the Degree Master of Science Manigandan Kannan August, 2011 THE MICROSTRUCTURE, HARDNESS, IMPACT TOUGHNESS, TENSILE DEFORMATION AND FINAL FRACTURE BEHAVIOR OF FOUR SPECIALTY HIGH STRENGTH STEELS Manigandan Kannan Thesis Approved: Accepted: _______________________________ _______________________________ Advisor Department Chair Dr. T.S. Srivatsan Dr. Celal Batur _______________________________ _______________________________ Faculty Reader Dean of the College Dr. C.C. Menzemer Dr. George.K. Haritos _______________________________ _______________________________ Faculty Reader Dean of the Graduate School Dr. G. Morscher Dr. George R. Newkome ________________________________ Date ii ABSTRACT The history of steel dates back to the 17th century and has been instrumental in the betterment of every aspect of our lives ever since, from the pin that holds the paper together to the automobile that takes us to our destination steel touch everyone every day. Pathbreaking improvements in manufacturing techniques, access to advanced machinery and understanding of factors like heat treatment and corrosion resistance have aided in the advancement in the properties of steel in the last few years. This thesis report will attempt to elaborate upon the specific influence of composition, microstructure, and secondary processing techniques on both the static (uni-axial tensile) and dynamic (impact) properties of the four high strength steels AerMet®100, PremoMetTM290, 300M and TenaxTM 310. The steels were manufactured and marketed for commercial use by CARPENTER TECHNOLOGY, Inc (Reading, PA, USA). The specific heat treatment given to the candidate steels determines its microstructure and resultant mechanical properties spanning both static and dynamic. Test specimens of the steels were precision machined and conformed to standards specified and prescribed by the American Society for Testing Materials (ASTM) for both tensile tests and Charpy V-Notch impact tests. Based on similarity of the secondary processing technique the candidate specialty steels were divided into two groups: (i) AerMet®100 and PremoMetTM290, (ii) 300M and TenaxTM310. The impact toughness response and resultant fracture behavior of the steels were studied at different temperatures ranging from -180°C to +170°C. Tensile tests iii were performed at room temperature and the final fracture behavior of the candidate steel was established at both the macroscopic and fine microscopic levels. The intrinsic microscopic mechanisms governing the impact toughness, quasi static deformation and final fracture behavior of each of the chosen high strength steels will be elaborated upon in light of the conjoint and mutually interactive influences of composition, intrinsic microstructural effects, and nature of loading. iv ACKNOWLEDGEMENTS First and foremost, I would like to thank my advisor Dr. T.S. Srivatsan. He was instrumental in every move I ever made in this university and I would be grateful all my life for the support rendered to me during my small stint in this university. I would like to thank Dr Celal Batur for awarding me with a Teaching assistant which helped me to complete my Master of Science degree in the Department of Mechanical Engineering. I would like to extend my sincere thanks to Dr. Craig Menzemer and Dr. Gregory Morscher for serving on my thesis committee. I would like to thank Michael Schmidt from Carpenter Technology,INC located at Reading Pennsylvania for providing the materials that made this research possible. Furthermore, I would like to give sincere thanks and recognition to the following individuals for their contribution in this research by way of knowledge and assistance: (i) Mr. Nurudeen Balogun and Mr. Udaykar Bathini (former graduate students) for assisting me during the initial stages of testing. (ii) Dr. Sergei F. Lyuksyutov(Associate professor in the department of physics) for his help with the atomic force microscope. (iii) Ms. Michelle Petraroli (Senior Research Technician, of the Timken Company) for assistance in microstructural observations v (iv) Mr. Clifford Bailey (Senior Engineering Technician, Department of Mechanical Engineering), for instruction and timely assistance with intricacies related to use of Mechanical Test Machine. (v) Mr. Thomas J. Quick (Research Associate, of the Department of Geology), for assistance with the use of the Scanning Electron Microscope. (vi) Mr. Stephen Gerbetz (Senior Engineering Technician, Department of Mechanical Engineering), (vii) Mr. Dale Ertley (Senior Engineering Technician) and Mr. Bill (Engineering Technician), of the College of Engineering Machine shop for assistance with the preparation of samples for scanning electron microscopy and optical microscopy. (viii) Mr. David McVaney (Senior Engineering Technician), for allowing me to use the hardness tester in the Civil Engineering Department. Above all I want to extend my gratitude to my parents, my brother and my dear friends for all their love and support throughout my life. vi TABLE OF CONTENTS Page LIST OF TABLES ix LIST OF FIGURES x CHAPTER I. Introduction 1 II. Review of the Literature 6 2.1 Processing and microstructure of Specialty steels 6 2.2 The impact fracture toughness of high strength 10 2.3 The tensile properties of high strength steels 13 III. The Test Materials 17 IV. Test Sample Preparation 4.1 Impact tests 21 4.2 Tensile tests 21 V. Experimental Procedures 5.1 Initial microstructure characterization 24 5.2 Characterization of Microstructure using Atomic Force 24 Microscopy (AFM). 5.3 Hardness testing 25 5.3.1 Macro-hardness tests 26 5.3.2 Micro-hardness tests 28 vii 5.4 Impact tests 30 5.5 Mechanical tests (tensile) 31 5.6 Failure-damage analysis 31 VI. Results and Discussion 6.1 Initial Microstructure 33 6.2 Initial Microstructure using the Atomic Force Microscope. 34 6.3 Hardness 6.3.1 Microhardness measurement 44 6.3.2 Macrohardness measurement 45 6.4 Impact Toughness 51 6.5 Dynamic Fracture 55 6.6 Tensile Properties 81 6.7 Tensile fracture behavior 89 VII. Conclusions 7.1 Impact Toughness 97 7.2 Tensile Deformation and Fracture Analysis 98 References 100 Appendix 105 APPENDIX A PROCEDURE FOR PERFORMING 105 THE TENSION TEST ON THE INSTRON-8500 SERVO HYDRAULIC TESTING MACHINE APPENDIX B PROCEDURE FOR PERFORMING LOOP 109 SHAPING FOR A GIVEN STRESS RATIO AND MATERIAL ON THE INSTRON-8500 SERVO HYDRAULIC TESTING MACHINE viii LIST OF TABLES Table Page 3.1 Nominal chemical composition of the chosen materials ………………..19 3.2 Primary and Secondary Processing history on the chosen ……………...20 High strength steels 5. 1 A compilation of the micro-hardness measurements made on the Specialty steels samples…………………………………………………26 5. 2 A compilation of the macrohardness measurements made on the Specialty steels samples............................................................................28 6. 1 The impact toughness properties of the four high strength steels in N-m….………………………………………………………………..55 6. 2 A compilation of the room temperature tensile properties of the test Materials………………………………………………………………...84 6. 3 A summary of the monotonic mechanical parameters of the candidate.. 86 ix LIST OF FIGURES Figure Page 4.1. A schematic showing dimensions of the Charpy V-Notch test specimen………22 4.2. A schematic of the cylindrical test specimen used for …………………………23 Mechanical testing(Tensile). 6.1. Optical micrographs showing the key micro-constituents of AerMet® 100 at three different magnifications .......................................................................... 36 6.2. Optical micrographs showing the key micro-constituents of PremoMetTM 290 at three different magnifications .............................................. 37 6.3. Optical micrographs showing the key micro-constituents of 300M at three different magnifications ........................................................................................ 38 6.4. Optical micrographs showing the key micro-constituents of Tenax TM 310 at three different magnifications ........................................................................... 39 6.5. Atomic force microscope image of the etched surface of AerMet® 100 showing profile and nature of roughness on a 10 μm x 10 μm section ................ 40 6.6. Atomic force microscope image of the etched surface of PremoMetTM 290 showing profile of roughness on a 10 μm x 10 μm section .................................. 41 6.7. Atomic force microscope image of the etched surface of 300M showing nature and profile of the roughness on a 10 μm x 10 μm section ......................... 42 6.8. Atomic force microscope image of the etched surface of TenaxTM 310 showing nature and profile of roughness on a 10 μm x 10 μm section ................ 43 6.9. A profile showing the variation of microhardness and macrohardness value across the length of AerMet® 100. ....................................................................... 46 6.10. A profile showing the variation of microhardness and macrohardness values across the length of PremoMetTM 290 .................................................................. 47 6.11. A profile showing the variation of microhardness and macrohardness values across the length of 300M ....................................................................................
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