某自动扶梯主驱动链条外链板在运行过程中断裂失效。采用宏观检验、化学成分分析、硬度测试、非金属夹杂物检验以及金相检验等方法对外链板的断裂原因进行了分析。结果表明：外链板表面打印字头底部过渡圆角尖锐并存在折叠缺陷，同时部分原材料存在表面脱碳缺陷，导致外链板打印字头底部过渡圆角处应力集中以及材料表面抗疲劳性能降低；在多重应力的作用下外链板表面打印字头底部缺陷处萌生疲劳裂纹，裂纹不断扩展最终导致外链板疲劳断裂失效。

The outer chain plate of an escalator main drive chain fractured during operation. The fracture causes of the outer chain plate were analyzed by macroscopic inspection, chemical composition analysis, hardness test, non-metallic inclusion inspection and metallographic examination. The results show that the surface printed word bottom of the outer chain plate had a sharp corner and folding defect, and there was surface decarburization on some raw material surface of the outer chain plate, which resulted in stress concentration at word bottom of the outer chain plate and decrease of the fatigue resistance of the material surface. Under the action of multiple stresses, the fatigue crack source originated from the bottom defect of the outer chain plate, and the cracks continuously expanded, which eventually led to fatigue fracture failure of the outer chain plate.