High temperature deformation behavior of two as-cast high-manganese TWIP steels

The high-temperature behavior of two as-cast high-manganese steels with different levels of carbon (0.49 and 0.07 wt%) has been studied by employing hot compression tests at different temperatures (900, 1000 and 1100 °C) and strain rates (0.01, 0.1, 1 and 10/s). Microstructures of the deformed specimens have been examined using SEM-EBSD. The steels are compared in terms of their flow stress level, activation energy of deformation, critical stress and strain for the initiation of softening, and extent of grain refinement. The two steels behave quite differently: flow stress levels at small strains are higher for the high-carbon steel than for the low-carbon one but softening, starting at very small strains, is very pronounced in the former, whereas only slight softening is observed for the low-carbon steel. This peculiar behavior of the high-carbon steel is due to the localization of strain along segregation bands and possibly the presence of ferrite at high temperatures in the highly segregated regions of the cast structure. Effective grain refinement occurs by dynamic recrystallization in both the steels.