Structure dependence of the TRIP phenomenon in Si-Mn bulk steel

Experimental simulations of thermomechanical processing (TM) using press forging of cylindrical specimens of C–Si–Mn TRIP (transformation induced plasticity) steel were performed. The aim was to understand the effect of the hot deformation introduced in the austenite recrystallization, nonrecrystallization and intercritical temperature regions on the austenite conditioning and microstructure evolution of the studied steel. The microstructures resulting from a variety of TM processing were characterized by light and scanning electron microscopy. Volume fraction of retained austenite was evaluated by neutron diffraction. It was found that the choice of applied strain and temperature of deformation prior transformation had strong impact on transformation kinetics, final multiphase (ferrite, bainite and retained austenite) structure characteristics and mechanical properties of TRIP steel. A good combination of strength and ductility was achieved in the material with refined microstructure and sufficient volume fraction of retained austenite.