在对某经过调质处理的40MnBH钢轴头进行机械加工时,发现该轴头内孔表面存在轴向和环向裂纹,采用宏观观察、磁粉检验、金相检验、扫描电镜分析等方法研究了裂纹产生的原因。结果表明:该裂纹为淬火裂纹,裂纹的产生原因是冲孔异常使内孔表面形成环向折叠,并产生了局部应力集中。对冲孔模具及锻造工艺进行改进,可以避免该类问题再次发生。

Axial and circumferential cracks were found on the surface of the inner hole of a quenched and tempered 40MnBH steel shaft head during machining. The cause of the crack was analyzed by macroscopic observation, magnetic particle inspection, metallographic examination and scanning electron microscope analysis. The results show that the crack was a quenching crack, and the cause of the crack was the local stress concentration caused by the annular folding of the inner hole surface caused by the abnormal punching. The improvement of punching die and forging process could avoid the recurrence of such problems.