High strain rate superplasticity in a cold rolled Fe35Mn8Al0.3C low-density steel

The high temperature deformation of the 80% cold rolled Fe-35Mn-8Al-0.3C low-density steel were carried out under different deformation temperatures ranging from 700 to 900 °C and varied strain rates from 1× 10 -4 s -1 to 1×10 -1 s -1 . It was found that an excellent fracture elongation of 633% could be reached at initial deformation strain rate at 1×10 -2 s -1 under 800 °C. The microstructure was evolved from a banded cold rolled microstructure to an equiaxed grained microstructure, indicating a dynamic recrystallization taking place during high temperature deformation process. The average grain size of both β-Mn/γ phase and the fraction of γ-phase are increased with increasing of deformation temperature but decreased with the increasing of deformation strain rate. The superplasticity activation energy is found to be 125.9-185.3 kJ/mol and a strain rate sensitivity of 0.32-0.37 were detected based on the analysis on the stress-strain rate relationship, indicating a dislocation gliding associated grain boundary/phase boundary sliding mechanism. This research not only reveals the high strain rate superplasticity of the cold-rolled low-density steel, but also indicates that the combination of boundary sliding and dislocation glide could be a promising mechanism for achieving high strain rate superplasticity.