Abstract: In the carburizing process of gear steel， AlN is often used to control the growth of austenite grains. however， the large amount of AlN precipitation will deteriorate its thermoplasticity and crack sensitivity， and AlN remelts during high temperature carburizing at 1 050 ℃， the pinning effect is weakened . By designing steel grades at different AlN concentration product （［%Al］［%N］） and Zr microalloying， to study the effect of AlN and Zr microalloying on the growing behavior of thermoplastic and carburization grains of 20 Cr gear steel. The results show that： for 20Cr series gear steel， increasing the AlN concentration product will deteriorate the hot ductility and make the plastic trough （750-900 ℃） to move to the high temperature zone. However， the low AlN concentration product or Ostwald ripening phenomenon during carburizing process will weaken the grain boundary pinning effect of AlN. Therefore， it is more appropriate to control ［%Al］［%N］ in steel at the lower limit between 2.9×10^-4-5.1×10^-4. In addition， the Zr in gear steel will preferentially precipitate coarse ZrN during the solidification process， resulting in a decrease in the amount of AlN precipitation and weakening the effect of pinning grain boundaries. Therefore， it is necessary to control the content of N elements to avoid the influence of coarse high temperature precipitation phase on AlN.

Key words: Gear Steel, AlN, Hot Ductility, Grain Size, Zr Microalloying

摘要： 齿轮钢渗碳过程常采用AlN控制奥氏体晶粒长大，然而，AlN大量析出将恶化其热塑性和裂纹敏感性，且1 050 ℃高温渗碳时AlN回溶，钉扎作用减弱。通过设计不同AlN浓度积（［%Al］［%N］）以及Zr微合金化的钢种，研究AlN和Zr微合金化对于20Cr系齿轮钢热塑性和渗碳处理奥氏体晶粒长大行为的影响，结果表明：对于20Cr系齿轮钢，提高AlN浓度积会使其热塑性恶化，塑性低谷（750～900 ℃）向高温区移动。而渗碳过程钢中AlN浓度积较低或Ostwald熟化现象，均会减弱AlN的钉扎晶界效果。因此，将钢中的［%Al］［%N］控制在2.9×10^-4～5.1×10^-4之间偏下限控制较为合适。此外，齿轮钢中的Zr在凝固过程中会优先析出粗大的Zr（C，N），而造成AlN析出量减少，削弱钉扎晶界的效果。故需要对N元素含量进行控制，避免粗大高温析出相的出现对AlN造成影响。

关键词: 齿轮钢, AlN, 热塑性, 晶粒度, Zr微合金化