In-situ neutron diffraction investigation on the martensite transformation, texture evolution and martensite reversion in high manganese TRIP steel

In order to reveal the behaviors of two kinds of martensites (epsilon-M and alpha'-M) transformation during TRIP and reversion process and to separate transformation textures from rolling textures during the TRIP process, the phase transformation and texture evolution during cold rolling and the subsequent heating in high manganese TRIP steel were investigated by time-of-flight neutron diffraction measurement. The results show that the TRIP process occurred mainly at the rolling reductions ranging from 0% to 60%. The transformation of gamma -> epsilon-M and epsilon-M -> alpha'-M didn't occur synchronously and the transformation of gamma -> epsilon-M was easier and occurred earlier. The cube-oriented gamma grains transformed to martensite most easily showing an orientation dependence and the gamma grains with other orientations tend to form preferentially the {100} orientation in alpha'-M phase demonstrating a strong variant selection during the TRIP process below the 60% rolling reduction. The {113}<010> texture of alpha'-M rotated toward a more stable orientation {112}<010> with increasing reduction and a shift of texture components from rotated cube and alpha-fibre to the gamma-fibre occurred at higher rolling reduction. The epsilon-M texture was characterized by a constant {0001} peaks 20 degrees-tilted toward RD at any reduction related with a high Schmid factor for basal slip. For the 60% rolled sample, the reversion of epsilon-M and alpha'-M to gamma-phase occurred at temperatures ranging from 300 degrees C to 500 degrees C and 500 degrees C to 700 degrees C, respectively. During heating, the deformed alpha'-M did not change its texture until decomposition and swallowing-up by austenite, and the retained and newly nucleated gamma grains inherited their initial Goss and brass orientations until their recrystallization and replacing by Goss texture. This weak Goss texture remained during further heating to 900 degrees C and subsequent cooling. In addition, the transformation of both kinds of thermally-induced martensites during cooling can only occurred below 200 degrees C.