Revisiting the model for austenite grain size of M50 steel coupled with the carbide dissolution behavior

This study investigates the effects of time, temperature, and granular M 2 C carbides on the evolution of the average grain size of M50 steel. Based on classical theoretical models, it develops a predictive model for the average austenite grain size distribution. The research encompasses a temperature range of 1000 to 1200°C and an isothermal holding time range of 15 to 180 minutes, with the objective of examining the grain growth behavior of M50 high-temperature bearing steel under various isothermal conditions. The findings demonstrate that temperature is the predominant factor influencing the distribution of granular M 2 C carbides, which play a pivotal role in the migration of grain boundaries. When the temperature exceeds 1100°C, M 2 C carbides undergo significant dissolution, thereby reducing their pinning effect on the grain boundaries and causing the austenite grains in M50 high-temperature bearing steel to grow rapidly. The temperature range is categorized into low- and high-temperature zones, delineated by the threshold temperature for significant M 2 C carbide dissolution. In the low-temperature zone, the austenite grain size increases at a slow rate over time, while in the high-temperature zone, the grain size increases rapidly. The classical Arrhenius grain size distribution model was employed to re-model the time factor ( n ) with a linear equation and a log-normal function in the low and high-temperature zones, respectively. This was done to establish the relationship between the time factor and holding temperature, thereby enabling the model to dynamically reflect the influence of second-phase solute particles on grain size.