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

► The DTUA process is applied to the production of hot-rolled TRIP steels. ► Microstructures of TRIP steel based on DTUA are much finer and more homogeneous. ► Acicular ferrite is present in the Nb added TRIP steel based on DTUA. ► Film-formed retained austenite is stable in the Nb added TRIP steel based on DTUA. ► Strengths are raised without any deterioration of elongations with Nb-addition.