采用直读光谱仪、显微维氏硬度计、光学显微镜和扫描电镜等仪器设备分别对1018钢渗碳处理的M3×6十字头自攻螺钉的化学成分、硬度、显微组织和断口形貌进行了分析，查明了螺钉断裂原因。结果表明：螺钉断裂属典型的脆性断裂，与其渗碳层深度超标，心部硬度又接近标准范围上限有关；螺钉断口还具有一定的氢脆断裂特征，是由于高的硬度和超标的渗碳层深度增加了螺钉的氢脆敏感性。最后根据螺钉断裂原因提出了改进措施。

The fracture reasons of the carburized 1018 steel M3×6 crosshead self-tapping screws were found out by analyzing their chemical compositions, hardness, microstructure and fracture morphology by direct reading spectrometry, Vickers hardness tester, optical microscope and scanning electron microscope (SEM). The results show that the fracture mode of the screws was typical brittle fracture, which should be due to the exceeded carburized layer depth and the core hardness being close to the upper limit of the standard range. At the same time, the fracture of the screws also showed some characteristics of hydrogen embrittlement fracture because the higher hardness and the exceeded carburized layer depth increased the susceptibility of the screws to hydrogen embrittlement. Finally, improvement measures were put forward according to the fracture reasons.