20SiMn2MoVA钢高强度螺栓磁粉探伤时，发现有多条长短不一的裂纹。采用宏观分析、力学性能试验、化学成分分析、金相检验等方法对裂纹产生的原因进行了分析。结果表明：该高强度螺栓表面存在的裂纹属于锻造折叠缺陷，锻造过程中锻压工艺和变形量不均匀引起锻造流线不畅而形成飞边，最终导致锻造折叠缺陷的产生。

Several cracks with different lengths were found on the surface of 20SiMn2MoVA steel high strength bolt when magnetic particle inspection. Macroscopic analysis, mechanical properties test, chemical composition analysis and metallographic examination were used to analyze the causes of cracks. The results show that the cracks on the surface of the high strength bolt belonged to forging folding defect. In the forging process, the uneven forging process and deformation caused the forging streamline to be blocked and the edge fin to be formed, which eventually led to the formation of forging folding defects.