Structure and mechanical properties of DP-type and TRIP-type sheets obtained after the thermomechanical processing

The chemical composition of the C-Mn-Si steel with Nb and Ti microadditions was established. The rolling and cooling conditions of the thermomechanical processing of DP-type and TRIP-type sheets were developed. The conditions of the thermomechanical processing were selected on a basis of the determined DTTTc-diagram of plastically deformed undercooled austenite and dissolution kinetics of TiN and NbC in the austenite. It was found that thermomechanically processed sheets have more fine-grained structure and better mechanical properties than after the classical underhardening or isothermal quenching from the temperature slightly higher than Ac1 of the investigated steel.