Surface effect induced phase transformation by Mn removal during annealing and its textures in cold-rolled high manganese transformation-induced plasticity steel

The surface effect induced transformation texture during vacuum annealing of cold-rolled high manganese transformation-induced plasticity (TRIP) steels was studied. Due to Mn removal occurring at the surface layer, γ → δ diffusional phase transformation leads to the formation of hard pancake-shaped ferrite grains due to solution strengthening at the surface and the centre layer remains as austenite + martensite after annealing. In the case of slow heating, {112}/{111}<110> textures for the surface ferrite were strengthened with the increase in temperature and holding time, indicating an inheritance of rolling textures. By increasing the heating rate of annealing, the rotated cube texture was developed in surface ferrite. This kind of multiphase sandwich structure with hard ferrite surface layer and tough austenite dominant centre can increase tensile strength and should also improve deep drawing properties, therefore providing new possibility of controlling properties for the application of high manganese TRIP steel.