Austenite reversion through subzero transformation and tempering of a boron-doped strong and ductile medium-Mn lightweight steel
- Authors
- Kim, Dae Woong; Yoo, Jisung; Sohn, Seok Su; Lee, Sunghak
- Issue Date
- 20-1월-2021
- Publisher
- ELSEVIER SCIENCE SA
- Keywords
- Medium-Mn lightweight Steel; (austenite plus ferrite plus martensite) triplex; microstructure; Subzero treatment; Transformation-induced plasticity (TRIP); Boron doping
- Citation
- MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, v.802
- Indexed
- SCIE
SCOPUS
- Journal Title
- MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING
- Volume
- 802
- URI
- https://scholar.korea.ac.kr/handle/2021.sw.korea/50082
- DOI
- 10.1016/j.msea.2020.140619
- ISSN
- 0921-5093
- Abstract
- Effects of subzero treatment and B doping on austenite reversion are investigated in quenched and tempered Fe-9Mn-5Al-0.3C and Fe-9Mn-5Al-0.3C-0.005B (wt.%) lightweight steels. In the as-quenched condition, the steel microstructure consist of a triplex structure of austenite, ferrite, and martensite. B doping leads to a reduction in the prior austenite grain size by grain boundary segregation and precipitation of boro-carbides, which increases the stability of austenite against the athermal martensitic transformation. After tempering at 200 degrees C for 2 h, nano-lath reverted austenite is formed by the C-enrichment instead of the carbide precipitation owing to the high Al content. This reversion effect is promoted further by the subzero treatment at -196 degrees C for 0.5 h prior to tempering, which enables the remaining austenite in the as-quenched state to transform and, thus, provides additional sites for austenite reversion. In addition, the subzero treatment and B doping result in the synergistic effect of the delay of crack initiation through the transformation of retained austenite in contact with ferrite and the improvement of bonding strength. Thus, the B-doped steel subjected to quenching, subzero treatment, and tempering exhibits a very high yield strength of approximately 1 GPa, the tensile strength of over 1.3 GPa, and an excellent elongation of 29.4%, which outperform the tensile properties of conventional austenitic or (austenite + ferrite) duplex lightweight steels.
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