Medium Mn steels (4-12 wt% Mn) have shown to exhibit a combined Twinning Induced Plasticity and Transformation Induced Plasticity (TWIP+TRIP) effect, allowing for large elongations (>30%) and high strain hardening rates (2-3 GPa). However, the tensile behaviour of cold rolled medium Mn steels has not been investigated in detail.
In this study, tensile tests were conducted on a novel 8 wt% medium Mn steel in the as-annealed and cold rolled conditions. Compared to the as-annealed steel, the cold rolled steels (10-20% reduction) showed a large increase in strength and strain hardening rate without a significant loss in ductility. Microstructural changes during plastic deformation were investigated using Electron Backscatter Diffraction (EBSD) and Transmission Electron Microscopy (TEM). It was found that at a similar equivalent strain, cold rolling introduced a larger density of defects compared to uniaxial tensile strain, resulting in increased transformation from austenite to martensite.