Microstructures and mechanical properties of Ti and Mo micro-alloyed medium Mn steel

Microstructures and tensile properties of a Ti and Mo micro-alloyed ultrafine-grained medium Mn TWIP-TRIP steel were investigated. The steel exhibits a superior combination of strength and ductility, i.e. 46800 MPa%, achieved by a high phase fraction of room temperature austenite with enhanced stability. Grain refinement is obtained from the formation of nano-sized (Ti, Mo)C precipitates by optimization of the intercritical annealing time and temperature after cold rolling. The intercritical annealing temperature dependence of the deformation mechanisms is investigated in detail. The localized deformation, pronounced when the TRIP effect is dominant, is related to the correlated strain-induced martensitic transformation of austenite islands.