Effect of Si content on low-temperature superplasticity in Fe–10Mn steel

Abstract

We systematically investigated the effect of Si on the low-temperature superplasticity of 50% and 80% cold-rolled Fe–10Mn-(0.2–5.5)Si steels through tensile testing at 763 K with strain rates of 1 × 10−3 s−1 and 1 × 10−4 s−1. Superplasticity was achieved through interphase boundary sliding between fine recrystallized α grains and reverted γ grains in most specimens, except for the 50% and 80% cold-rolled 0.2Si specimens and the 50% cold-rolled 2.4Si specimen at the strain rate of 1 × 10−3 s−1. Notably, at the strain rate of 1 × 10−4 s−1, the 80% cold-rolled 3.5Si specimen exhibited the highest elongation of 948% even at the low temperature of 763 K. The increased cold reduction and Si content enhanced superplasticity by raising stored energy, a driving force of recrystallization of the α phase and dynamic α′-to-γ reverse transformation. Additionally, Si enhanced interphase boundary sliding by increasing the difference in hardness between the α and γ phases. However, the 50% cold-rolled 5.5Si specimen, which contained δ ferrite-(Fe,Mn)3Si compound constituents, exhibited similar elongation to the 50% cold-rolled 3.5Si specimen due to the dynamic α′-to-γ reverse transformation occurring rapidly only up to a strain of ∼100%. Therefore, it is believed that a Si content of 3.5 wt% is ideal for enhancing low-temperature superplasticity in Fe–10Mn steel.

Keywords

• Low-temperature superplasticity
• Medium-Mn steel
• Interphase boundary sliding
• Solid-solution strengthening
• Dynamic reverse transformation