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 mechanical stability of retained γ. Appling a faster cooling led to a remarkable increase of tensile properties without a loss of elongation. This increase was accompanied by a higher fraction of bainite as the cooling rate increased All the specimens showed a similar fraction and mechanical stability of γ. In-situ tensile EBSD experiment revealed the accelerated deformation-induced martensite transformation (DIMT) in the faster cooling rate condition. The increased flow stress from a larger bainite fraction brought 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.