Gear shaft of 16MnCr5 steel is an important moving part to transfer torque in truck steering, which fatigue design life is 50,000 times. However, the lifetime of the test results is only about half in two design life. The microstructure, slag inclusion, phase composition and microhardness profiles of failure gear shaft were characterized by the optical microscope, scanning electron microscope and microhardness tester, respectively. The results show that cracks appeared at the fillet of the top, pitch circle and root of the gear. The size and distribution of slag inclusions in16MnCr5 steel also have a certain effect on the initiation of surface cracks of gears. The surface hardness of carburizing quenching hardening layer is low. After the heat treatment, a non-martensitic microstructure is formed, and machining hardening occurs on the right tooth surface, which seriously affects the contact fatigue degree of the gear.

中文翻译：

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夹杂物引起的16MnCr5齿轮轴断裂及热处理工艺

16MnCr5钢齿轮轴是卡车转向中传递扭矩的重要运动部件，疲劳设计寿命为5万次。然而，测试结果的寿命只有两个设计寿命的一半左右。分别采用光学显微镜、扫描电子显微镜和显微硬度计对失效齿轮轴的显微组织、夹渣、物相成分和显微硬度曲线进行了表征。结果表明，齿轮顶部圆角、分度圆和根部均出现裂纹。 16MnCr5钢中夹渣的尺寸和分布对齿轮表面裂纹的萌生也有一定的影响。渗碳淬火硬化层表面硬度低。热处理后形成非马氏体显微组织，右侧齿面发生加工硬化，严重影响齿轮的接触疲劳程度。