Unified Kinetics Modeling of Isothermal Bainite Transformation in 60Si2CrA Steel

In this study, isothermal bainite transformation kinetics in hypo-eutectoid steel 60Si2CrA was investigated. Isothermal transformation at temperature ranging from [528 K (255 °C)] to [653 K (380 °C)] after austenitization was performed on a quenching dilatometer. Based on the dilation data, a shear bainite kinetics model was established using the internal state variable (ISV) approach. The model is coupling with bainite phase nucleation and growth, and the incubation time is characterized by the proposed normalized bainite nucleus radius and normalized radius growth rate. Material constants within the unified kinetics model were calibrated with genetic algorithm (GA)-based optimization methodology using GA toolbox in MATLAB. Furthermore, fairly close agreement between model predicted and tested data was achieved, and predicted evolution of ISVs in the model was illustrated. The proposed shear-type bainite kinetics model may be applied to other hypo-eutectoid steels.