Prediction of bainite start temperature in alloy steels with different grain sizes

Bainite microstructure in alloy steels yields materials with an excellent combination of mechanical properties such as high strength and toughness, resistance to creep and fatigue, and hydrogen embrittlement. During cooling, bainite transformation is initiated at the bainite start (Bs) temperature, which is the highest isothermal temperature at which upper bainite is observed, and ceases when the temperature reaches the martensite start (Ms) temperature. They reported that the bainite volume fraction calculated by considering the decrease in Bs temperature as the PAGS decreased showed a good match with the experimentally measured volume fraction of bainite. This implies that variation in PAGS directly affects the Bs temperature and changes the transformation kinetics and volume fraction of bainite, thereby influencing the mechanical properties of the final material.