某主动齿轮根部在紧固过程中发生断裂。采用宏观观察、化学成分分析、硬度测试、金相检验、扫描电镜分析等方法对主动齿轮断裂的原因进行了分析。结果表明:原材料存在过烧组织,导致部分晶界融化重熔,重熔区域存在Cr元素偏聚;晶界因过热析出大量铁素体,组织过烧和过热会使晶界结合力丧失,降低其塑性,最终导致主动齿轮发生断裂。

The root of a driving gear fractured during tightening. The fracture reasons of the driving gear were analyzed by means of macroscopic observation, chemical composition analysis, hardness testing, metallographic examination and scanning electron microscope analysis. The results show that the raw material had overburning structure, leading to partial grain boundary melting and remelting, there was segregation of Cr element in the remelted region. A large amount of ferrite precipitated from the grain boundary due to overheating. Overburning and overheating of the structure could cause the loss of grain boundary adhesion, reduced its plasticity, ultimately led to the fracture of the driving gear.