Influences of silicon on the work hardening behavior and hot deformation behavior of Fe–25 wt%Mn–(Si, Al) TWIP steel

Abstract

The influence of silicon on mechanical properties and hot deformation behavior of austenitic Fe–25wt%Mn TWIP steel was investigated by means of the comparison research between 25Mn3Al and 25Mn3Si3Al steel. The results show that the 25Mn3Si3Al steel has higher yield strength and higher hardness than that of 25Mn3Al steel because of the solution strengthening caused by Si atoms and possesses higher uniform deformation ability and tensile strength than that of 25Mn3Al steel due to the higher work hardening ability of 25Mn3Si3Al steel. 25Mn3Si3Al steel presents a clear four-stage curve of work hardening rate in course of cold compression. Quite the opposite, the 25Mn3Al steel presents a monotonic decline curve of work hardening rate. The difference of the work hardening behavior between 25Mn3Al and 25Mn3Si3Al steel can be attributed to the decline of stacking fault energy (SFE) caused by the addition of 3wt% Si. The dislocation glide plays an important role in the plastic deformation of 25Mn3Al steel even though the mechanical twinning is still one of the main deformation mechanisms. The 3wt% Si added into the 25Mn3Al steel blocks the dislocation glide and promotes the mechanical twinning, and then the dislocation glide characteristics cannot be observed in cold deformed microstructure of 25Mn3Si3Al steel. The hot compression tests reveal that the hot deformation resistance of the 25Mn3Si3Al steel is significantly higher than that of the 25Mn3Al steel due to the solid solution strengthening of silicon atoms. The hot deformation activation energies Q for the 25Mn3Si3Al and 25Mn3Al steels are determined respectively as 406 and 365kJ/mol using hyperbolic-sine constitutive equation. The dynamic recrystallization (DRX) is the most important softening mechanism for the two steels. Furthermore, the nucleation and growth of DRX grains of Fe–25wt%Mn TWIP steels are clearly retarded by the addition of 3wt% Si, especially at low deformation temperature and high strain rate, and these effects of Si can be gradually weakened as the increasing of temperature and decreasing of strain rate.