低碳汽车齿轮钢20CrMnTi伪渗碳过程晶粒粗化行为

Grain coarsening behavior during pseudo carburizing process of low⁃carbon gear steel 20CrMnTi for automobile

设计了一种不含Nb元素的20CrMnTi齿轮钢,通过母相奥氏体晶粒尺寸统计、析出物分布规律分析,最终探明了伪渗碳温度对齿轮钢母相奥氏体晶粒尺寸的影响规律和机理。结果表明,不含Nb元素的20CrMnTi齿轮钢最高伪渗碳温度为970℃。相比于热轧态,经过伪渗碳处理后,(Ti,Mo)(C,N)颗粒中C含量减少,N含量增加,证实了第二相(Ti,Mo)(C,N)颗粒发生回溶、熟化,渗碳温度较高时(980℃),细小弥散颗粒的回溶和熟化更为明显。其次,伪渗碳温度为980℃时,细小弥散的第二相(Ti,Mo)(C,N)颗粒体积分数急剧下降,大尺寸第二相(Ti,Mo)(C,N)颗粒增多,减弱了对母相奥氏体晶粒的钉扎作用,导致晶粒发生异常长大。

A 20CrMnTi gear steel without Nb addition was designed,and the influence and mechanism of pseudo⁃carburizing temperature on its prior austenite grain size were studied through grain size measurement and precipitate distribution analysis.The results show that the maximum pseudo⁃carburizing temperature of the designed steel is 970℃.The C content in(Ti,Mo)(C,N)particles is reduced,while the N content is opposite after pseudo⁃carburizing treatment compared with the hot⁃rolled steel,which confirms the redissolution and ripening of the second phase(Ti,Mo)(C,N)particles,and being more obvious when the pseudo⁃carburizing temperature is higher(980℃).Moreover,the volume fraction of the fine dispersed second phase(Ti,Mo)(C,N)particles decreases sharply when the pseudo⁃carburizing temperature is 980℃,at which the large size second phase(Ti,Mo)(C,N)particles increases,thus weakening the pinning effect on prior austenite grains and resulting in the abnormal grain growth.