Low-Temperature Superplastic Deformation of Cold-Rolled Fe–5.6Mn–1.1Al–0.2C Steel

cold-rolled low Al-added medium Mn steel was employed to investigate the low-temperature superplastic deformation at a relatively high initial strain rate of 10 –2 s −1 . The values of tensile ductility were measured to be 560 to 1170 pct at temperatures ranging from 655 °C to 745 °C. A maximum tensile elongation of 1170 pct was obtained at 745 °C and 10 –2 s −1 , which is the highest low-temperature-high-strain-rate superplasticity in the reported medium Mn steels. The superplastic flow behavior and deformation mechanisms of the low Al-added medium Mn steel were studied in detail by comparing the microstructural changes at various stages during both tensile deformation and isothermal annealing. In contrast to isothermal annealing, tensile deformation accelerated the dynamic recrystallization, phase transformation and partitioning of solid solution elements Mn/Al in austenite and ferrite, respectively. The representative microstructural features (equiaxed grains, random texture and sluggish grain growth) together with m ≈ 0.5 and Q ≈ Q_gb indicate that Rachinger-type grain boundary sliding (GBS) was the predominant deformation mechanism which is accommodated through the movement of lattice dislocation.