局部非马氏体沿晶界向内延伸的形成原因和预防措施

Cause of local non-martensite extending inwards from grain boundary and its countermeasure

利用金相显微镜、扫描电镜对渗碳齿轮局部非马氏体沿晶界向内延伸形成原因进行了分析,并提出预防措施。结果表明,造成局部非马氏体沿晶界向内延伸超差的原因是由于钢材次表层非金属夹杂与表层非马氏体连接,使Si元素与夹杂物中的氧化性组分接触后继续沿晶界氧化偏析形成。在钢材冶炼过程中提高钢材纯净度,减少非金属氧化物夹杂,在零件热处理过程中控制表层非马氏体的深度可预防此现象发生。

By means of metallographic examination,and scanning electron microscope,the cause of local non-martensite extending inwards from the grain boundary of carburized gear was analyzed,and a solution was provided. The results show that the connection of non-martensite with nonmetallic inclusions at steel subsurface is the main cause,then Si element will contact with the oxidable composition in the inclusions and continues to oxidize and to segregate along the grain boundary. Increasing purity of steel during the steel making process,deceasing the nonmetallic oxidable inclusions and controlling the depth of non-martensite by the heat treatment can prevent those problems.