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Effects of Ni and Cu addition on cryogenic-temperature tensile and Charpy impact properties in austenitic 22Mn-0.45C-1Al steels

Title
Effects of Ni and Cu addition on cryogenic-temperature tensile and Charpy impact properties in austenitic 22Mn-0.45C-1Al steels
Authors
Kim, B.Lee, S.Kim, D.W.Jo, Y.H.Bae, J.Sohn, S.S.Lee, S.
Date Issued
30-Jan-2020
Publisher
ELSEVIER SCIENCE SA
Abstract
Austenitic high-Mn steels present a dominant deformation mechanism of TWinning Induced Plasticity (TWIP) or TRansformation Induced Plasticity (TRIP), which effectively enables be used for various cryogenic applications. This mechanism affects significantly tensile or impact properties, and can be carefully tuned by adjusting alloying compositions; however, the alloying effects of Ni and Cu have not been studied yet. In the present study, the steels were fabricated by adding Ni or Cu and their microstructural evolutions were examined for the quasi-statically-tensioned and dynamically-Charpyimpacted specimens. In the room-temperature tensile deformation, many twins were populated without any martensite. At cryogenic temperature, however, epsilon- and alpha'-martensite were formed together with twins in the 22Mn-0.45C-1Al (Base) and 1-wt.%-Ni-added (INi) steels, whereas they were not in the 1-wt.%-Cu-added (ICu) steel. This TWIP or TRIP amount showed a good correlation with the stacking fault energy (SFE) calculated by considering Mn-segregation bands, and affected the tensile ductility. At cryogenic temperature, the TRIP occurred in the Base and 1Ni steels as SFEs of low-Mn bands decreased down to the TRIP range, whereas it did not in the 1Cu steel, and thus the Base and 1Ni steels showed the lower ductility than the 1Cu steel. For the cryogenic-temperature Charpy impact test, the martensite was not formed even at the heavily-deformed area near the notch tip as the time was not enough for inducing the martensitic transformation, while twins were populated. Since the twin fraction near the notch-tip area increased in the order of the 1Cu, 1Ni, and Base steels, it was expected that the Charpy impact energy increased in this order, but the Base steel showed the lowest energy because of the precipitation of fine M23C6-type carbides on grain boundaries. (C) 2019 Elsevier B.V. All rights reserved.
Keywords
STACKING-FAULT ENERGY; MECHANICAL-PROPERTIES; DEFORMATION-BEHAVIOR; TRIP/TWIP STEELS; GRAIN; MN; DEPENDENCE; STRENGTH; MICROSTRUCTURE; SEGREGATION
URI
http://oasis.postech.ac.kr/handle/2014.oak/100433
ISSN
0925-8388
Article Type
Article
Citation
JOURNAL OF ALLOYS AND COMPOUNDS, vol. 815, 2020-01-30
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 LEE, SUNG HAK
Dept of Materials Science & Enginrg
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