Multistage serrated flow behavior of a medium-manganese high-carbon steel

The deformation mechanisms and the flow stress behavior of a medium-manganese high-carbon steel during cold deformation at a strain rate of 10×5 s^-1 were explored using a universal testing machine,an X-ray diffractometer,a field emission scanning electron microscope and a high-resolution transmission electron microscope.The results show that continuous step-up serrated flow behavior appears after the yielding point,and the true stress-strain curve is roughly divided into five stages based on distinctive densities and amplitudes of serration.The strengthening mechanisms of the experimental steel involve Cottrell atmosphere,twinning-induced plasticity(TWIP)efect and transformation-induced plasticity(TRIP)effect.TWIP effect is the dominant deformation mechanism,and deformation twins formed by TWIP effect comprise primary,secondary and nanotwins.Furthermore,TRIP effect arises in the local high-strain region.Carbon element plays a key role in the transformation of the deformation mechanism.A small amount of carbide precipitates around twin boundaries lead to the formation of local carbon-poor regions,and Md temperature and stacking fault energy of medium-manganese high-carbon steel are propitious to the occurrence of TRIP effect.In addition,the contributions of various deformation mechanisms to plasticity are calculated,and that of TWIP effect is the greatest.