18CrNiMo7-6钢制齿轮渗碳后等温淬火组织及性能

Austempering microstructure and properties of carburized 18CrNiMo7-6 steel gear

利用JMatPro软件对渗碳后的18CrNiMo7-6钢制齿轮表面Ms点进行模拟计算,基于模拟结果对齿轮进行了180℃等温盐浴淬火处理,研究了等温盐浴淬火处理齿轮的组织和性能,并和普通油浴淬火处理进行了横向对比。结果表明:渗碳齿轮经180℃等温淬火处理,表层获得下贝氏体,少量马氏体以及残留奥氏体的复相组织,并由表及里逐渐过渡至心部的马氏体组织;相比于普通油浴淬火,盐浴淬火所形成的心部存在少量的贝氏体组织能够降低齿轮的裂纹敏感性,提高综合力学性能;等温盐浴淬火齿轮的表面生成了约20%的残留奥氏体,导致齿轮表面硬度较低,但经深冷处理,能够有效控制等温盐浴淬火后齿轮表面的残留奥氏体含量,并且显著提高表面硬度;通过试验齿轮的单齿弯曲疲劳检测,180℃等温盐浴淬火齿轮服役性能显著高于普通油浴淬火齿轮。

JMatPro software was used to simulate and calculate the Ms points on the surface of 18 CrNiMo7-6 steel gear after carburizing treatment.Based on the simulation results,the gear was austempered in salt bath at 180℃,the microstructure and properties of the gearso treated were studied and compared with that of the ordinary oil bath quenching.The results show that after 180℃austempering,complex microstructures composed of lower bainite,a small amount of martensite and residual austenite are obtained in the surface layer of the carburized gear,and transiting graduallyfrom the surface to the martensite microstructure in the center.Compared with the ordinary oil bath quenching,a small amount of bainite formed in the center during austempering can reduce the crack sensitivity and improve the comprehensive mechanical propertiesof the gear.About 20%residual austenite is generated in the surface of the austempered gear,which lowers the surface hardness of the gear.However,cryogenic treatment can effectively control the residual austenite content in the surface of the austempered gear,and significantly improves the surface hardness.It is confirmed from the single tooth bending fatigue test that the service performance of the 180℃austempered gear is significantly higher than that of ordinary oil bath quenching gear.