Optimization of Controlled Rolling and Cooling Process for 20CrMnTi Gear Steel Bar

The microstructure and hardness in different positions of 20CrMnTi gear steel bar produced by actual controlled rolling and cooling process were studied. The controlled rolling and cooling process of the bar was simulated by finite element method, and then the temperature and equivalent strain distribution of the bar was obtained. The optimal measures of controlled rolling and cooling process were put forward, and verified by tests. The results show that the microstructures of surface and 1/2 radius of bar consisted of ferrite and pearlite with actual controlled rolling and cooling process, while the microstructure of center consisted of ferrite, pearlite and a larger amount of bainite; the hardness of the center was significantly higher than that of other parts. The deformation of the bar during controlled rolling and cooling process mainly occurred at the surface and 1/2 radius, and the equivalent strain decreased with increasing distance from the surface of the bar. The temperature of the center of the bar was the highest, and the temperature of 1/2 radius and surface decreased in turn. The temperature of the center increased with the accumulation of rolling processing. The controlled rolling effect of the surface of the bar was the best, followed by that of 1/2 radius and center. When the final rolling temperature decreased from 880 ℃ to 840 ℃, the microstructures in different positions of the bar after controlled rolling and cooling process all consisted of ferrite and pearlite, and the hardnesses of surface, 1/2 radius and center were 182,188,190 HBW, respectively, indicating the uniformity of microstructure and hardness was improved obviously.