Achieving ultra-high elongation of 1401% in a warm-rolled medium Mn lightweight steel with dual-phase lamellar structure

Abstract

The present work reports a dual-phase lamellar structure to combine ultra-high superplastic elongation and relatively low deformation temperature in a novel Al-added medium Mn lightweight steel. The specimens were controlled rolling in a two-phase zone; Hence the microstructure contained a high-volume fraction of residual austenite in the ferrite matrix. The ultra-high elongation of 1401% was obtained at the deformation temperature of 775 °C, which is more than 50 °C lower than others reported of the cold-rolled sheets. Interestingly, near 800 °C, due to the enhanced DIFT effect, the ductility was reduced by temperature rise, which is opposite to the condition of the cold-rolled sheets. The ultrahigh elongation at 775 °C was ascribed to the continued recovery and recrystallization of the deformation-induced ferrite, which not only achieves dynamic grain refinement but also maintains the balance of stress distribution between the two phases.