Lowering Strain Rate Simultaneously Enhances Carbon- and Hydrogen-Induced Mechanical Degradation in an Fe-33Mn-1.1C Stee
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e quest for new steels lighter and stronger than conventional alloys has been ongoing as a part of the drive for improved energy efficiency. In 1888, Sir Robert Hadfield demonstrated the importance of the simultaneous addition of high concentrations of manganese and carbon in austenitic steels, resulting in an improved
IBRAHIM BURKAY TUG˘LUCA is with the Department of Mechanical Engineering, Kyushu University, Nishi-ku Fukuoka 9180395, Japan and also with the Department of Mechanical Engineering, Abdullah Gu¨l University, 38080 Kayseri, Turkey. MOTOMICHI KOYAMA and YUSAKU SHIMOMURA are with the Department of Mechanical Engineering, Kyushu University. Contact e-mail: [email protected] BURAK BAL is with the Department of Mechanical Engineering, Abdullah Gu¨l University. DEMIRCAN CANADINC is with the Department of Mechanical Engineering, Koc¸ University, Sariyer, Istanbul 34450, Turkey. EIJI AKIYAMA is with the Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Sendai 980-8577, Japan. KANEAKI TSUZAKI is with the Department of Mechanical Engineering, Kyushu University and also with the HYDROGENIOUS, Kyushu University, Motooka 744, Nishiku, Fukuoka 819-0395, Japan. Manuscript submitted May 25, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
work hardening rate and associated uniform elongation.[1] In this context, it is known that the major roles of manganese and carbon in work hardening are triggering deformation twinning[2,3] and dynamic strain aging (DSA).[4–6] Furthermore, austenitic steels containing high concentrations of manganese and carbon have been noted as hydrogen-resistant, high-strength steels used for hydrogen-energy-related infrastructures; this is due to the close-packed fcc structure, which exhibits a low diffusivity of hydrogen.[7] Thus, in light of these two energy-related aspects, the intrinsic effects of manganese, carbon, and hydrogen on strength and ductility have been of great concern for steel scientists and engineers. Regarding the effects of carbon, we have found that a high concentration of interstitial carbon degrades the ductility of austenitic high-manganese steels, even without hydrogen uptake, when the stacking fault energy is relatively high and the strain rate is below 103 s1.[8] For instance, an Fe-33Mn-1.1C* steel satisfies this *All chemical contents are provided in weight percentage, unless otherwise noted.
condition. The main cause of this behavior was determined to be deformation heterogeneity, associated with DSA-induced Portevin–Le Chatelier (PLC) effect. Moreover, even at a high strain rate of around 102 s1, where the PLC banding effect is not significant, hydrogen uptake causes remarkable mechanical degradation, which is associated with deformation localization.[9] In this context, our special interest in this study is to determine whether lowering the strain rate can simultaneously enhance the carbon and hydrogen-induced mechanical degradation in a high-manganese steel, which contains a high amount of interstitial carbon. According to a prev
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