42CrMo钢螺栓表面线性缺陷产生原因OA

The 12.9-grade galvanized bolts used in marine equipment were found to have linear defects distributed along the axial direction on their surfaces during service.Macroscopic observation,chemical composition analysis,mechanical property testing,scanning electron microscopy and energy spectrum analysis,and metallographic examination were employed to analyze the causes of the linear defects on the bolt surfaces.The results show that the linear defects in the bolts originated from folding defects in the bolt rod material during production.The folds were filled with oxides,with decarburization occurring on both sides.During the bolt manufacturing process,surface defects were not removed,leading to their retention on the bolt surfaces.Subsequently,during the quenching and cooling process,the fold tips expanded,ultimately forming deep quenching cracks.