Evolution of deformation twins with strain rate in a medium-manganese wear-resistant steel Fe–8Mn–1C–1.2Cr–0.2V

Abstract

Microstructure evolutions of the medium-manganese wear-resistant steel Fe–8Mn–1C–1.2Cr–0.2V\xa0(in wt.%) with stacking-fault energy of 22\xa0mJ\xa0m−2 during deformation at strain rate ranging of 10−2–1\xa0s−1 were analyzed by means of X-ray diffraction, field emission scanning electron microscopy and high-resolution transmission electron microscopy. The results indicate that the twinning-induced plasticity effect is the main strengthening mechanism of the studied steel, whilst the transformation-induced plasticity effect only occurs at high strain rate. With an increase in strain rate, volume fraction of the deformation twins, in particular that of the secondary twins, increases significantly along with decreasing average size. When applied strain rate is higher than 10−1\xa0s−1, the parallel deformation twins are turned into a crossing morphology, and the original straight twin boundaries exhibit a ladder feature, which is attributed to the interactions between regular dislocations and twin dislocations at the twin boundary. The critical strain, a key indicator of the initiation of deformation twin, decreases with increasing strain rate. In addition, the ductility and strength of medium-manganese wear-resistant steel Fe–8Mn–1C–1.2Cr–0.2V are mainly determined by the shape and volume fraction of deformation twins.