Nb微合金化对齿轮钢高温渗碳奥氏体晶粒度的影响

Influence of Nb microalloying on grain size of austenite in high-temperature carburized gear steel

通过Nb微合金化提高渗碳温度是当前发展高端齿轮钢的重要思路。以20Cr钢为基准成分,通过实验室熔炼、锻造以及977~1 134℃范围内高温伪渗碳实验,研究了0.02%、0.04%、0.06%、0.08%等不同Nb质量分数下渗碳后的奥氏体晶粒结构。在此基础上,依据热力学计算及析出颗粒熟化模型,对AlN、Nb(C,N)颗粒的钉扎强度进行估算并与晶粒尺寸建立联系,得到了适用于含Al、Nb齿轮钢的奥氏体晶粒度控制预测模型。最后,依据此模型分析了Nb含量对20Cr钢渗碳温度的影响,并基于高温渗碳目标提出了Nb微合金化的成分建议。

It is an important approach to develop the high-quality gear steels through Nb microalloying to increase the carburizing temperature. Based on 20 Cr steel, the influence of Nb addition of 0.02%, 0.04%, 0.06% and 0.08% on the prior austenite grain after carburizing was investigated with laboratory smelting, forging and high temperature pseudo-carburizing experiments in the range of 977—1 134 ℃. On this basis, according to the thermodynamic calculation and the kinetic modeling for precipitation particle ripening, the pinning strength of AlN and Nb(C,N) particles was estimated and used for establishing the relationship with the austenite grain size. Then, the predictive model for Al-and Nb-containing gear steels to control the austenite grain size was obtained. Finally, the influence of Nb content on the carburizing temperature of 20 Cr steel was analyzed based on the predictive model, and the composition suggestion for Nb microalloying was proposed for the target of high-temperature carburizing process.