Microstructure and mechanical properties of C–Mn–Al–Si hot-rolled TRIP steels with and without Nb based on dynamic transformation

Two C–Mn–Al–Si TRIP steels with and without 0.038 (wt)% Nb addition were fabricated by a thermo-mechanical process based on dynamic transformation of undercooled austenite (DTUA), and the microstructures under the current process were refined significantly with homogeneous phase distribution, leading to better mechanical properties in comparison with the steels fabricated by the conventional hot-rolled process. Nb micro-addition further refined the microstructures, facilitated the formation of acicular ferrite and increased the stability of the retained austenite, in which carbon content and volume fraction were not affected apparently. As a result, the strengths of the steel with Nb addition were raised obviously without any deterioration of the elongations.