Effect of strain rate on tensile and serration behaviors of an austenitic Fe-22Mn-0.7C twinning-induced plasticity steel

In this study tensile and serration behaviors of an austenitic Fe-22Mn-0.7C twinning-induced plasticity steel was investigated in terms of dynamic strain aging and deformation twinning. Under quasi-static strain rate range, serrated flow and, negative strain-rate dependence of flow stress were found during room-temperature tensile testing. The serrated flow is closely related to dynamic strain aging induced by the interaction of dislocation and interstitial carbon. In order to understand the flow stress contribution of strain hardening rate and strain rate sensitivity, strain rate jumping test was performed. The results showed that the negative strain-rate dependence of flow stress was more dependent on strain hardening rate factor than strain rate sensitivity factor by dynamic strain aging. EBSD and TEM analysis revealed that the higher strain hardening rate at lower strain rate was attributed to the higher fraction and finer thickness of deformation twin. The localized stress accompanied by dynamic strain aging plays an important role in twinning process since it decreases effective stacking fault energy and promotes deformation twinning in localized region at lower strain rate.