1 μm以内。A technique coupled martensite transformation with severe plastic deformation (SPD) has been developed for rapid producing submicron grain medium carbon steel based on equal channel angular pressing (ECAP). Experiments were conduced on medium-carbon steel，and quenched steel was pressed at different tempering temperatures and time. The results indicted that the homogeneous supersaturated ferrites by martensite transformation was prepared for dynamic recrystallization and strain induced carbide precipitation, accumulated higher dislocation density in the crystal structure during ECAP at given tempering temperature urged to recrystallize and induced carbide particles to precipitate in dispersed phase. Homogeneous ultra-fined grain ferrites with fine carbide particles distributed grain boundaries could be achieved. These submicron microstructures possessed thermal stability and they remained grain size of less than 1 μm after annealing at 550℃ for 30 min. 