Development of 1.2 GPa Ferrite-based Lightweight Steels via Low-temperature Tempering

• Published in: Korean Journal of Metals and Materials Vol. 59; no. 10; pp. 683 - 691
• Main Authors: Bae, Hyo Ju, Ko, Kwang Kyu, Park, Hyoung Seok, Jeong, Jae Seok, Kim, Jung Gi, Sung, Hyokyung, Seol, Jae Bok
• Format: Journal Article
• Language: English
• Published: 05.10.2021
• ISSN: 1738-8228; 2288-8241
• DOI: 10.3365/KJMM.2021.59.10.683

Previously reported low-Mn ferritic-based lightweight steels are potential candidates for industrial applications, however, they typically exhibit lower strength, with < 1 GPa and lower strength-ductility balance, than medium- and high-Mn austenitic lightweight steels. Herein, we introduce a low-temperature tempering-induced partitioning (LTP) treatment that avoids the strength-ductility dilemma of low-Mn ferriticbased steels. When the LTP process was performed at 330 oC for 665 s, the strength of typical ferritic base Fe-2.8Mn5.7Al0.3C (wt%) steel with heterogeneously sized metastable austenite grains embedded in a ferrite matrix, exceeded 1.1 GPa. Notably, the increased strength-ductility balance of the LTP-processed ferritic steel was comparable to that of the high-Mn based austenitic lightweight steel series. Using microscale to nearatomic scale characterization we found that the simultaneous improvement in strength and total elongation could be attributed to size-dependent dislocation movement, and controlled deformation-induced martensitic transformation.