SWRCH22A冷镦钢螺栓镦头开裂原因分析

Analysis of Cracking Reasons in the Cold Heading Process of SWRCH22A Steel

材质为SWRCH22A的冷镦钢盘条在经过拉拔、球化退火处理后冷镦加工成螺栓的过程中,部分螺栓头部出现开裂。对头部冷镦开裂的螺栓试样进行了宏观检测、非金属夹杂物检测、金相检测、扫描电镜及能谱检测分析,检测结果表明,螺栓头部开裂对应的螺杆部位近边缘存在大尺寸黑色夹渣。材料近边缘存在大尺寸夹渣会严重破坏材料基体的连续性,降低材料的韧塑性。在金属基体相对于夹渣发生流动时,夹渣与金属基体脱离并划伤基体而出现微裂纹及空隙,金属冷拔、冷镦变形会进一步加剧这些微裂纹及空隙的扩展。由此判断,材料近边缘大尺寸夹渣是导致材料镦头开裂的主要原因。

After drawing and spheroidizing annealing, the cold heading wire rod made of SWRCH22A is cracked in the process of cold heading into bolts. The cracked bolt specimens were tested by macroscopic examination, non-metallic inclusion detection, metallographic examination, scanning electron microscope and energy dispersive analysis. The results show that there are large size black slag inclusions near the edge of the screw. The existence of large size slag inclusion near edge will severely interrupt the material matrix and reduce the toughness and plasticity of the material. When the metal matrix is flowing relative to the slag, micro-cracks and voids appear in the metal matrix, because the slag inclusions are breaking away from the metal matrix and scratching the matrix. The cold drawing and cold heading deformation of the metal will further aggravate the propagation of these micro-cracks and voids. It is concluded that large size slag inclusions near the edge of the material is the main reason for the cracking of the header.