过冷奥氏体等温转变在转向轴齿预先热处理中的应用

Application of overcooling austenite isothermal transformation in pre-heat treatment for steering shaft tooth

采用理论分析和实验研究相结合的方法,对转向轴齿在预先热处理中存在金相组织不稳定和硬度分布不均匀的现象进行了研究。结果表明:过冷奥氏体在转变过程中的冷却速度、转变温度、转变时间等技术参数是决定其组织和性能的关键。根据过冷奥氏体等温转变过程中奥氏体分解的原理和机制,借助于可以控制风量大小、吹风时间的风冷室来控制其冷却速度,冷却结束后放入等温炉进行等温组织转变。最终得到了均匀分布的F+P显微组织,实现了轴齿锻件金相组织1~2级、同批次不同转向轴齿的硬度差值小于10 HB的技术指标,为后期渗碳淬火过程中减小齿轮的热处理变形提供了技术保障。

The phenomena of unstable metallographic structure and uneven hardness distribution of steering shaft tooth during pre-heat treatment were studied by combining theoretical analysis with experimental study. The results show that the cooling speed,transformation temperature and transformation time etc. of overcooling austenite during transformation process are the key factors to determine the microstructures and properties. According to the principle and mechanism of austenite decomposition in the process of isothermal transformation for overcooling austenite,the cooling speed was controlled by controlling air volume and blowing time in air cooling chamber,and after cooling,the isothermal structure transformation process was finished in isothermal furnace. Finally,the uniformly distributed F + P microstructures were obtained,and the technical specifications of metallographic structure grade 1-2 for steering gear forgings and hardness difference less than10 HB of different steering shaft teeth in the same batch were achieved,which provided technical guarantee for reducing heat treatment deformation of gears in subsequent carburizing and quenching process.