采用化学成分分析、宏微观检验和力学性能测试手段，对失效盘齿轮进行了分析。结果表明，齿轮的渗碳层普遍存在深约25μm的黑色组织和较多的残余奥氏体，齿面、齿槽存在明显的加工刀痕，且齿根处有根切。以上几种缺陷的共同作用，使齿轮的疲劳强度大大降低，在外力较大的服役条件下，造成盘齿轮发生早期疲劳失效。

In this paper, a failure analysis of the plate gear is made by means of macroscopocal fracture observing, hardness testing, chemical composition analysis, microstructure examining and SEM. The result shows the things as follows-Firstly, generally there is approximate 25μm black structure and more residual austenite in the carburized layer. Secondly, the obvious cuter marks exists in the surface and trough of tooth; And last, a more obvious undercut occurs in the root of tooth. All these defects of above notably decrease the fatigue strength of the gear and are internal cause of the early stage fatigue failure of the plate-gear. Among others, the cuter marks and the black structure in the cuter marks is mainly cause. Because all defects of above has existed, when it serves at suffering a greater outside force, the early stage fatigue failure of plate-gear occurred.