Austenite reversion through subzero transformation and tempering of a boron-doped strong and ductile medium-Mn lightweight steel

Dae Woong Kim, Jisung Yoo, Seok Su Sohn, Sunghak Lee

Research output: Contribution to journalArticlepeer-review

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 °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 °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.

Original languageEnglish
Article number140619
JournalMaterials Science and Engineering A
Volume802
DOIs
Publication statusPublished - 2021 Jan 20

Keywords

  • (austenite+ferrite+martensite) triplex microstructure
  • Boron doping
  • Medium-Mn lightweight Steel
  • Subzero treatment
  • Transformation-induced plasticity (TRIP)

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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