某轿车变速器中间轴在进行耐久性试验时发生断裂。采用化学成分分析、金相检验、扫描电镜观察及硬度测定等方法对失效件进行了分析。结果表明：齿根表面淬火层非淬硬组织过深和硬度过低,造成中间轴齿轮承载能力下降,最终导致在耐久性试验中发生弯曲疲劳断裂。并提出了改进意见。

The intermediate shaft for certain car transmission has ruptured in durability test. The chemical composition analysis,metallography examination,scan electricity lens observation and hardness measurement for failed parts have been conducted.All above results show that decrease of carrying capacity for intermediate shaft gear resulting from not over depth of non-quenching part of tooth root surface and not good hardness distribution but low surface hardness,caused bending fatigue overload rupture in durability test. Some improvement comments were given out.