Effect of cooling rate on the final microstructure and tensile property in an Fe–Mn–Si–C-based multiphase TRIP steel

The effect of cooling rate on the formation of the final microstructure and the tensile property was studied in Fe–Mn–Si–C-based multiphase steel. Three different cooling rates of 5 °C/s, 10 °C/s, and 30 °C/s (CR5, CR10, and CR30) were applied from 800 °C to 400 °C and then the specimens held at 400 °C for 30 min. EPMA, EBSD, and TEM analyses clarified the constituent phases' volume fractions and the retained austenite's mechanical stability. Appling faster cooling led to a remarkable increase of tensile properties without loss of elongation. The increased bainite fraction was obtained as the cooling rate increased. All the specimens show a similar fraction and mechanical stability of γ. In-situ tensile EBSD experiment reveals the accelerated deformation-induced martensite transformation (DIMT) in the faster cooling rate condition. The increased flow stress from a larger bainite fraction brings faster DIMT kinetics and improves tensile properties. This study provides a detailed understanding of the influence of cooling rate on microstructural evolution and tensile properties.