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在主机厂做试验时,20CrMnTi凸轮轴大小端键槽发生断裂。通过对断裂部位进行化学成分检测并借助光学显微镜和扫描电镜对20CrMnTi凸轮轴的组织、裂纹形态以及凸轮轴大、小键槽横截面的硬度进行分析,发现,该材料的化学成分、金相组织及硬度均符合相关技术标准要求。大端裂纹起源于键槽底部,慢慢累积而导致最终断裂,锥度处有明显的磨损痕迹,表明该处受力最大;小端裂纹起源于键槽底部,无明显扩展区,属于瞬间断裂;两端键槽底部均无明显倒角,加大了零件应力集中倾向,是造成凸轮轴断裂的一个原因。

Failure Analysis on Fracture of 20CrMnTi Cam Shaft

During the experiment in the host plant, big and small key slot of 20CrMnTi cam shaft were fractured. Chemical analysis on fracture position of cam shaft, optical microscopy and scanning electron microscopy analysis on the microstructure and crack shape, hardness test of the cam shaft big key slot cross section and small key slot cross section were carried out. The results show that the chemical composition, microstructure and hardness are all in accordance with the requirements of the related technical standard. Big crack originated from the slot bottom, accumulated and led to final fracture. Obvious wear occurred at the position of conical degree, indicating the maximum loading there. Small crack originated from the slot bottom and no significant expansion area occured, so it belongs to the instantaneous fracture. At both of the keyway bottoms there are no obvious chamfer, which increases the tendency of stress concentration, and thus results into the fracture of cam shaft.