Microstructural evolution and mechanical behaviour of Fe-30Mn-C steels with various carbon contents

A Fe-30Mn-0.6C sheet steel was decarburised and/or annealed to obtain four Fe-30Mn-C alloys with carbon contents of 0.06, 0.2, 0.4 and 0.6 wt-%. The primary deformation products were found to be mechanical twins for the 0.2C, 0.4C and 0.6C alloys and a combination of mechanical twins and ε-martensite for the 0.06C alloy. Both the ε-martensite and mechanical twin formation kinetics increased sigmoidally with true strain such that the final twin volume fraction increased with increasing alloy SFE and C content, where the latter finding disagrees with some of the accepted models for high-Mn twinning induced plasticity steels. Moreover, the activation stress for twin formation was found to increase linearly with alloy SFE, per a model previously proposed by the present authors.