Strength and toughness of Fe-1.2Mn-0.3Cr-1.4Ni-0.4Mo-C tempered steel plate in three cooling processes

Microstructure and mechanical properties of the Fe-1.2Mn-0.3Cr-1.4Ni-0.4Mo-C tempered steel plate in three cooling processes (direct quenching, accelerated cooling + air cooling and air cooling) after hot rolling were investigated in this paper. The lath-martensite is obtained by direct quenching, whereas granular bainite, lath bainite, retained austenite and M/A constituents are observed in other two cooling processes. Meanwhile, the lath-martensite with higher cooling rate after hot-rolling could enhance the intensity of {332} < 113 > texture, which is beneficial for the strength and toughness of the steel. After tempering at 680 degrees C, the difference of yield strength is mainly caused by grain boundary strengthening and precipitation strengthening. The higher proportion of high misorientation boundary, stronger intensity of {332} < 113 > texture, weaker intensity of {001} < 110 > texture and fewer of M/A constituents (or retained austenite) will improve the impact toughness. All in all, the steel with optimum combination of strength and toughness is obtained by using direct quenching to room temperature after hot rolling.