Structure-mechanical property relationship in a low-C medium-Mn ultrahigh strength heavy plate steel with austenite-martensite submicro-laminate structure

We elucidate structure-property relationship in a 0.1C-5Mn-0.4Mo hot rolled steel that was directly water-quenched and intercritically tempered at 650 °C. Tempering in the intercritical region for optimum time was critical in obtaining elongation of 25.0% and reduction in area of 65.4%. Moreover, the tensile strength was 875 MPa and the impact energy at test temperature of −60 °C was significantly high at 165.3 J. The microstructure of water-quenched steel consisted of lath martensite, needle-shaped cementite, and about 1% retained austenite. The superior combination of strength, ductility, and toughness subjected to tempering for optimal time of 30 min is attributed to the dissolution of cementite, recovery of martensitic structure, and formation of approximately 13% reversed austenite with appropriate mechanical stability.