Deformation behaviors and microstructure evolution of a novel multiphase medium Mn high Al lightweight steels with excellent strength-ductility combinations

The effects of phase constituents on the deformation behavior and the correlated mechanical properties at different solution temperatures were investigated in medium Mn high Al lightweight steels with different Al contents (Fe-12Mn-(6,8)-Al-1C). This study indicates that the mechanical properties of medium Mn high Al lightweight steels can be significantly enhanced though changing the content of Al and solution treatment. 6Al steel shows lower yield strength (YS) and tensile elongation (TEL) values than those of 8Al steel at the same temperature due to the unitary austenite phase. When Al is added to 8 wt%, both the precipitation of intergranular and intragranular x-carbide are promoted and the constituents of multiple phases (austenite + ferrite +x-carbide) result in ultra-high strengthening. The apparent strain partitioning causes by the different characteristics between different phases leads to the high initial strain hardening. During the deformation process, the sufficient formation of slip bands in austenite grains keeps the high strain hardening exponent and postponed the plastic stability, which also contribute to a pronounced ductility. The existence of multiple phases owing to the addition of Al is the key feature of excellent properties in the investigated lightweight steel.