5th International High Manganese Steel Conference - HMNS 2022

The changes in the martensite structure of 0.1-0.2%C-2%Si-5-7% Mn steels with a decrease in the prior austenite grain size were investigated. Particularly, the austenite grain size, at which the single variant martensite was formed, was investigated. When the prior austenite grain size was 2 micrometers, martensite with a single variant (single block) structure was formed. These results indicate that the critical prior austenite grain size to form martensite with a single variant structure is 2 micrometers. The tensile strength (TS >1500 MPa), uniform elongation (UEL, 8%), and total elongation (TEL >14%) of the single-variant martensite were superior to that of the multi-packet multi-block martensite (TS = 1350 MPa, UEL = 6% and TEL = 13%). The superior properties of the single-variant martensite are a result of enhancement of its strain hardening rate due to the structural change. Synchrotron radiation analysis clarified the change in dislocation density with decreasing prior austenite grain size.