基于减小热处理畸变的20CrMnMoH高性能齿轮预先热处理工艺

采用理论分析和实验研究相结合的方法,对20CrMnMoH齿轮钢在预先热处理过程中产生贝氏体非平衡组织的现象进行了分析研究。结果表明:20CrMnMoH齿轮钢在常规预先热处理过程中的冷却速度无法控制,过冷奥氏体进行非平衡组织转变,容易得到贝氏体等非平衡组织。根据贝氏体等非平衡组织的组织遗传效应,结合过冷奥氏体等温转变的原理和机制,设计了两次等温正火预先热处理工艺,首次等温正火预先热处理完成了非平衡组织到平衡组织的转变,二次等温正火预先热处理实现了晶粒的细化和均匀化。通过工艺优化控制实现了齿轮锻件的金相组织为1~2级、同批次不同齿轮锻件硬度差≤5 HB的技术指标。成品齿轮的精度可以达到6级,验证了预先热处理对减小齿轮热处理畸变、提高齿轮精度的有效性。

Pre-heat treatment process of 20CrMnMoH high performance gear based on reducing heat treatment distortion

The phenomenon of non-equilibrium microstructure for bainite produced in the pre-heat treatment process of gear steel 20CrMnMoH was analzed and studied by the method combining theoretical analysis and experimental research. The results show that the cooling rate of gear steel 20CrMnMoH in the conventional pre-heat treatment process cannot be controlled,and the undercooled austenite is easily transformed into bainite and other nonequilibrium structures. According to the structure genetic effects of bainite and other non-equilibrium microstructure,combining with the principle and mechanism of isothermal transformation for undercooled austenite,two times of preheat treatment process for isothermal normalizing were designed. Furthermore,the first pre-heat treatment of isothermal normalizing completes the transformation from the non-equilibrium microstructure to the equilibrium microstructure,and the second pre-heat treatment of isothermal normalizing realizes grain refinement and homogenization. Through the process optimization and control,the technical indicators of the metallographic structure of 1-2 grades for gear forgings and the hardness difference of different gear forgings in the same batch ≤5 HB are achieved. The accuracy of finished gear is detected up to level 6,which verifies the effectiveness of pre-heat treatment to reduce the heat treatment distortion of gear and improve the accuracy of gear.