强度等级为530 MPa的绝缘子钢脚，其拉伸破坏负荷要求不小于615 kN。某公司生产的绝缘子钢脚在拉伸破坏负荷试验时负荷仅达到513 kN即发生断裂。通过断口分析、化学成分分析、金相检验等方法，对绝缘子钢脚拉伸破坏负荷不合格的原因进行了分析。结果表明：绝缘子钢脚在加工锻造球头时在球头与杆部交界处产生了折叠缺陷，该折叠缺陷在拉伸破坏负荷试验时受较大应力作用而产生脆性开裂，导致绝缘子钢脚断裂。

Insulator steel foot with strength grade 530 MPa requires a tensile failure load of not less than 615 kN. Insulator steel foot manufactured by a company was broken when the load reached 513 kN during the tensile failure load test. By means of fracture analysis, chemical composition analysis and metallographic examination, the causes of unqualified tensile failure load of insulator steel foot were analyzed. The results show that folding defect occurred at the junction of the ball head and the rod when the insulator steel foot was processed and forged. The folding defect were brittle cracks due to the large stress in the tensile failure load test, which eventually led to the fracture of the insulator steel foot.