某发动机排气门在耐久试验中于头部发生径向开裂，通过化学成分分析、宏观检验及金相检验,对排气门开裂原因及过程进行了分析。结果表明: 由于气门锥面堆焊工艺不合理且未进行及时充分的去应力处理，导致堆焊层内残余应力较高，在机械应力及热应力的共同作用下，在堆焊层内靠近气门锥面处形成裂纹源并沿径向扩展。

The head of engine exhaust valve cracked in radial direction during the durability test. The cracking causes of exhaust valve were analyzed by chemical compositions analysis, macroscopic inspection and metallographic inspection. The results show that the weld overlaying technology of cone area of exhaust valve was not optimum, and the stress relief treatment was not in-time and complete. As a result of that, high residual stress remained in weld overlaying cladding. Under the combined action of mechanical stress and thermal stress, cracks were formed in weld overlaying cladding near the cone area and then propagated on radial direction.