某热电厂汽轮机组扩容检修时发现末级叶片出现早期断裂的质量问题。采用断口分析、金相检验、化学成分分析、表面硬化层工艺分析等方法，对汽轮机叶片的断裂原因进行了分析。结果表明：该汽轮机叶片的失效机理为疲劳断裂，叶片表面硬化层存在裂纹、气孔、局部未硬化等缺陷，降低了叶片的耐冲蚀能力，是叶片发生早期疲劳断裂的主要原因。

The quality problems of early fracture of last stage blades were found during the expansion and overhaul of the steam turbine unit in a thermal power plant. Methods of fracture analysis, metallographic examination, chemical composition analysis, technology analysis of hardened surface layer were used to analyze the fracture reasons of turbine blades. The results show that:the failure mechanism of steam turbine blades was fatigue fracture; defects of cracks, porosity, non-hardened part and so on existed in hardened layer of the blade surface and reduced the resistant ability of erosion, which was the main reason for the early fatigue fracture of blades.