SWRCH22A盘条生产的十字头螺钉在进行扭力和攻速测试时发生断裂。通过对盘条和螺钉的组织和断口进行分析, 探讨了断裂的原因。结果表明: 在螺钉生产的搓丝过程中形成的齿间严重表面裂纹是造成螺钉断裂的根本原因。此外, 盘条冷镦前球化退火工艺不良造成表面严重脱碳并形成粗大铁素体, 而后表面过度渗碳处理致使螺钉表层严重脆化, 并在渗碳层下形成铁素体+马氏体过渡层组织和沿晶渗碳体, 螺钉表面裂纹在最大剪切应力作用下通过沿晶断裂最终导致螺钉失效。

Crosshead screws made of SWRCH22A wire rod were fractured in the torque force and drilling tests. The fracture reason was discussed by means of the microstructure of wire rod and screw examination and the fracture mode analysis.The results showed that severe surface cracks formed in the teeth valleys of screw during threading process were the main reason for the fracture. In addition, poor protection of spheroidizing annealing resulted in severe decarburization and coarse ferrite grain in wire rod surface; and then the following excessive carburization treatment made the surface layer highly brittle. Meanwhile, a transitional zone consisting of ferrite, martensite and carbide network formed below the brittle carburized layer. Thus, the cracks in surface could easily propagate intergranularly under the maximum shear stress around screw surface and finally caused the screw failure during torque force test.