The effect of carbon content on the microstructure and mechanical properties of high-Mn steels

In Fe-22wt% Mn steels, the Stacking Fault Energy (SFE) strongly influences the transformation products produced and the mode by which deformation occurs. Low SFE alloys favor forming ε-martensite while higher SFE alloys tend to form twins, both which act as barriers for dislocation motion. By varying the carbon content within the steel, the SFE was altered to include formation of ε-martensite, twinning or both. A specific look into carbon contents of 0.6 wt%, 0.4 wt%, and 0.2 wt% alloys is examined and for the 0.6C alloy, the initial microstructure was fully austenitic, the mechanical tests show high uniform elongation, high work hardening rate, and the alloy deformed by mechanical twinning. The 0.4C alloy also had a fully austenitic initial microstructure, with lower uniform elongation and relatively lower work hardening rate. Twinning was observed and ε-martensite formation may also result at high strains. The 0.2C steel comprised an initial dual-phase microstructure of ε-martensite and austenite. A high work hardening rate was attributed to the transformation of ε-martensite and yielded low uniform elongation. It was seen that as the carbon content is decreased, the deformation mode was transferred from twinning to ε-martensite formation.