Warm ductility enhanced by austenite reversion in ultrafine-grained duplex steel

The current work investigated the relationship between microstructure and warm deformation properties in a strong but ductile Mn-rich steel. A cold-rolled Fe-11.3Mn-0.068C-0.3Si-1.1Al-0.25Mo-0.01P-0.01S-0.0003N (in wt. %) steel was deformed isothermally after inter-critical annealing at temperatures from 550 °C to 720 °C. Deformation at 650 °C led to exceptional ductility, corresponding to total elongation of over 100%. The microstructure was characterized by electron backscattered diffraction, transmission Kikuchi diffraction, and transmission electron microscopy. It was found that the rate of austenite reversion can be accelerated by deformation, and that the transformation makes strained austenite into equiaxed grains. Exceptional ductility can be achieved when warm deformation is accompanied by austenite reversion. This research will provide metallurgical principles for warm deformation of steel under reversed transformation.