对阀杆进行宏观检查、金相显微组织观察、化学成分分析、硬度测试试验和拉伸试验,结果表明:该阀杆因为同时受到交变应力和附加弯曲应力的共同作用,在阀杆外表面处产生微裂纹,微裂纹逐渐扩展,致使阀杆的有效承载面积逐步缩小,直至发生断裂。阀杆断裂的主要原因是:阀杆的硬度偏高,强度偏低,力学性能不符合要求,而且长期在高应力的交替作用下导致其发生疲劳断裂。 The stem of the valve macro-examination, metallographic microstructure observation, chemical composition analysis, hardness test and tensile test results show that: the valve stem by both the alternating stress and additional bending stress of the joint action at the valve stem outer surface Produce microcracks, microcracks gradually expanded, resulting in the effective bearing area of ​​the valve stem gradually reduced until it breaks. Stem stem fracture is the main reason: the stem of the high hardness, low strength, mechanical properties do not meet the requirements, and long-term high stress in the alternate cause fatigue fracture occurs.