某汽轮机高压主汽阀门杆在机组运行过程中发生断裂。采用宏观观察、化学成分分析、金相检验、扫描电镜分析和力学性能测试等方法,对该门杆的断裂原因进行了分析。结果表明:门杆材料的热处理工艺不当,造成了材料的组织异常、强度不合格、冲击韧性偏低;门杆与套筒之间为过盈配合,在表面生成氧化皮的情况下,过盈度进一步增大,在较大的拉应力作用下,产生了应力集中,门杆的“十字”形通孔处发生过载开裂,最终导致门杆断裂。

The high pressure main steam valve stem of a turbine broke during the operation of the unit. The fracture reasons of the stem were analyzed by means of macro observation, chemical composition analysis, metallographic examination, scanning electron microscope analysis and mechanical property test. The results show that the improper heat treatment process of the stem material results in the abnormal structure, unqualified strength and low impact toughness of the material. There was an interference fit between the stem and the sleeve. In the case of oxide skin formed on the surface, the interference degree was further increased. Under the action of large tensile stress, stress concentration was generated, and overload cracking occurred at the cross hole of the stem, which eventually led to the fracture of the stem.