EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Changes in the martensite structure of 0.1%C-2%Si-5% Mn steel with decrease in the prior austenite grain size have been investigated. While prior austenite grain size in the range of 150 to 24 micro-meter led to the formation of martensite with a multi-packet and multi-block structure, a single packet and multi-block martensite structure formed from the prior austenite grain size of about 7 mico-meter. Furthermore, prior austenite grain size of about 2 micro-meter led to the formation of a single variant (single block) martensite structure. This microstructural analysis indicates that the critical prior austenite grain size to form martensite with a single variant structure is about 2 micro-meter. The tensile strength (TS, 1490 MPa), uniform elongation (UEL, 7.1%), and total elongation (TEL, 14.2%) of the single-variant martensite was found to be higher than that of the multi-packet multi-block martensite (TS = 1270 MPa, UEL = 6.2% and TEL = 13.6%). The improvement in mechanical properties of single-variant martensite was attributed to enhancement in its strain hardening rate as a result of change in the structure from the multi-variant to single variant.