Influence of final rolling temperature on microstructure and mechanical properties in a hot-rolled TWIP steel for cryogenic application

Three hot-rolled TWIP steels with different grain size were obtained by changing final rolling temperatures. The results show that the recrystallization microstructure can be obtained at the final rolling temperature range of 966-1083 °C and the grain size can be refined from 17.3 µm to 8.5 µm by decreasing final rolling temperature from 1083 °C to 966 °C. Moreover, the correlation between yield strength and grain size obeys Hall-Petch relation. However, surprisingly, the larger the grain size is, the higher the ultra low-temperature Charpy impact absorbed energy, and the reason may be is that the number fraction of austenite grains occupied by nano-twins formed in two or more twinning systems is relatively high for the steel with larger grain size, thereby leading to stronger dynamic grain refinement effect and heavier plastic deformation.