Superplasticity of Medium Mn Lightweight Steel in the Intercritical Region

Abstract

The present study systematically investigated the superplastic deformation behavior of Fe–10Mn–4Al–(0.5, 1.5, and 3)Si–0.3C steels in the intercritical region. A moderate fraction of δ–ferrite (~30%) in the 1.5Si steel exhibited a high density of geometrically necessary dislocations and accommodated more strain during superplastic deformation, resulting in a significant elongation of ~1210%. Conversely, a high fraction of δ–ferrite (~60%) in the 3Si steel caused hardening due to enhanced grain coarsening and the formation of B2 precipitates, with strain gradually transferring into γ–austenite. The large grain size and low austenite fraction resulted in a reduced elongation of ~830%. Microstructural analysis revealed that dynamic γ→α transformation alleviates stress concentration caused by grain boundary sliding, thereby enhancing high–temperature tensile ductility in medium Mn lightweight steels.

Keywords: Medium Mn lightweight steel, superplasticity, δ-ferrite, Deformation-induced ferritic transformation, Dynamic recrystallization