High-strain rate and low-temperature superplasticity of Si-added medium-Mn steel

This study investigated the superplastic behavior of Fe-10Mn-(3.5 and 5.5)Si (wt%) steels through tensile testing at temperatures ranging from 823 K to 973 K with relatively high strain rates of 1 × 10 -2 s -1 and 1 × 10 -1 s -1 . Both steels exhibited superplastic elongation exceeding 300% at deformation temperatures ( T s ) lower than those reported for previously developed superplastic steels. Notably, at a strain rate of 1 × 10 -1 s -1 , the 5.5Si specimen achieved superplastic elongation at 923 K–approximately 100 K lower than the previously reported minimum T s of 1023 K. Microstructural analysis revealed that the enhanced superplastic performance was primarily due to active interphase boundary sliding between recrystallized α-ferrite and reverted γ-austenite grains. In the 5.5Si specimen, this sliding was further promoted by the dissolution of Si-rich bands–composed of δ-ferrite and (Fe,Mn) 3 Si intermetallic compounds–which increased the hardness difference between the α-ferrite and γ-austenite grains.