On the continuous cooling transformation of deformed austenite and relationship to properties in medium-Mn steel

The continuous cooling tnsformation of deformed austenite and relationship to mechanical properties in medium-Mn steel was investigated by combining thermomechanical controlled processing and continuous cooling processes. The results indicated that the microstructure of experimental steel consists of lath martensite and a small amount of retained austenite. The stability of austenite was significantly improved by manganese, and martensite tnsformation occurred only during the slowly furnace-cooling process. The morphology of prior austenite gins changed from equiaxed recrystallization type to flat-elongated type with decreasing rolling tempeture. The martensitic tnsformation tempeture was decreased by the fgmentation of prior austenite gins and the stin hardening introduced by hot rolling, resulting in refined martensitic laths. The excellent mechanical properties were obtained in the steel rolled in the non-recrystallization region with combination of yield strength of 910 MPa, ultimate tensile strength of 1288 MPa and Vickers hardness number of 386.4 HV, which were mainly attributed to the refined martensitic laths, high density dislocation in matrix and high gin boundary length per unit area.