Temperature dependence of mechanical properties and deformation mechanism of Fe–25Mn–3Al–3Si alloy at high strain rate

Abstract

High-Mn steels exhibit an excellent combination of strength and ductility owing to the twinning induced plasticity (TWIP) effect or transformation induced plasticity (TRIP) effect, and have become an important material under service conditions of high strain rate and low temperature. However, the mechanical properties and deformation mechanism have not been fully understood during this extreme service conditions. Using impact test on Split Hopkinson Pressure Bar apparatus and microstructure characterization, the relationship among deformation temperature, mechanical properties and the underlying deformation mechanisms of high-Mn TRIP/TWIP steels during high strain rate (HSR) deformation was investigated. Our study shows that no matter the high temperature impact or low temperature impact, the Fe–25Mn–3Al–3Si alloy has good mechanical properties under large impact load and HSR deformation. Moreover, the strain hardening rate of the HSR impact samples at 300 °C are significantly higher than that at −80 °C and room temperature (RT). Detailed transmission electron microscopy results revealed that the strain rate has an important influence on the deformation mechanism of high-Mn TRIP/TWIP steel. Thus, TWIP effect also become the main deformation mechanism of Fe–25Mn–3Al–3Si alloy with a high SFE at 300 °C during HSR deformation. Higher strain rate and lower temperature can promote the formation of ε-martensite twinning (εT) and the occurrence of reversible transformation of ε-martensite ⇆ γ-austenite, which improve great the toughness of the alloy at low temperature (such as −80 °C). The models of reversible transformation are proposed based on the detailed microstructural characterization.