Modeling of austenitic grain growth of 25CrMo4 steel for the high-speed railway axle during hot working

After hot deformation, the fine grains due to recrystallization are apt to grow up at high temperatures. The grain size affects directly the performance and quality of products, so it is of great significance to investigate the grain evolution. In this paper, 25CrMo4 steel samples are compressed until a strain of 0.6, under isothermal conditions using Gleeble-1500 at deformation temperatures in the range of 950-1100°C and at same strain rate 1.0 s^-1, and then the samples are held at deformation temperatures for 0, 10, 20 and 30 min. Microstructure is retained by using water quench. The grain growth model is expressed by a differential function of both temperature and holding time. The material constants in grain growth model are determined using genetic algorithm (GA) optimization technology from experimental data. A good agreement between predicted results and experimental data is obtained, which shows that the developed grain growth model enables the grain size evolution at various high temperatures to be well predicted.