Microstructure and mechanical properties of hot-rolled and heat-treated TRIP steel with direct quenching process

In the present study, a hot-rolled and heat-treated TRIP steel (Fe-0.25C-1.23Si-2.09Mn-2.92Al wt%) was successfully produced by a simple process that involved intercritical heat treatment (IHT) followed by direct quenching without bainite reaction step. The microstructure of the as-cast ingot, as-hot-rolled sheet and heat-treated sheet was studied and related to mechanical properties of the heat-treated sheet. It was observed that δ-ferrite was retained from the solidification stage and remained as a stable phase during different stages of processing because of the alloy design that included ~ 3 wt% Al. Banded structure was obtained in both as-hot-rolled sheet and heat-treated sheet. The microstructure of 770-820 °C heat-treated sheet consisted of δ-ferrite, retained austenite (RA), α-ferrite and martensite. Based on the alloy design and direct quenching process, ~ 20-30% volume fraction of RA was obtained in the heat-treated sheet. The 780 °C heat-treated sheet exhibited an excellent combination of tensile strength and total elongation of 880 MPa and 28%, respectively.