Microstructure and mechanical properties of a mixed Si–Al TRIP-assisted steel subjected to continuous galvanizing heat treatments

Heat treatments with an isothermal bainitic transformation temperature of 465°C compatible with the continuous galvanizing process were performed on a 0.2C–1.5Mn–1.0Si–0.5Al (wt%) TRIP-assisted steel. The effect of intercritical annealing temperature and isothermal bainitic transformation (IBT) time at 465°C on mechanical properties and microstructure were determined. The best combination of strength and ductility was obtained for the lower intercritical annealing temperature of 750°C for an isothermal bainitic transformation time of 90s at 465°C. However, after intercritical annealing at a higher temperature of 797°C, optimum mechanical properties were obtained for a shorter isothermal bainitic transformation time of 60s at 465°C, likely due to the lower C content of the intercritical austenite bringing about faster transformation kinetics. It was concluded that varying the intercritical temperature and IBT time can play an important role in the development of a suitable process window to obtain the desired mechanical properties in low alloy TRIP-assisted steels given the constraints associated with the continuous galvanizing process.