对某BM4输出轴使用断裂失效件进行了理化检验和失效分析。结果表明：该输出轴断裂失效主要是由于工件在渗碳淬火过程中, 淬透性严重不足, 造成基体组织存在大量的粒状贝氏体和块状铁素体, 从而使材料强度大幅度降低; 另输出轴原材料中大量存在的非金属夹杂物也增加了材料的脆性; 而原材料严重的带状组织, 使材料的横向抗拉强度进一步降低; 上述因素综合作用最终造成输出轴在承载时发生早期断裂失效。

The physical and chemical test and failure analysis were done to the BM4 output shaft which fractured during service. The results show that the fracture of the output shaft was mainly caused by the serious insufficient hardenability during the carburizing and quenching process, which resulted in the existence of a lot of granular bainite and blocky ferrite in the matrix microstructure and a considerable reduction of strength of the material. At the same time, the presence of a large number of non-metallic inclusions in the raw material also increased the brittleness of the material. The serious banded structure further reduced the transversal tensile strength of the material. The combined action of the above mentioned factors ultimately led to the early fracture failure of the output shaft in bearing.