工程用35CrMo钢的断裂失效与预防措施

Fracture Failure and Preventive Measures of 35CrMo Steel in Engineering

采用扫描电镜(SEM)、能谱分析仪(EDS)、金相显微镜(OM)和显微硬度计,对发生断裂的工程用35Cr Mo钢进行了断裂失效分析,并提出了相应的预防措施。结果表明,工程用钢基体组织为回火索氏体+少量铁素体;螺纹表面存在约18μm的脱碳层,螺纹根部有机械损伤和淬火裂纹;工程用钢的断裂失效形式为氢致延迟断裂,使用前的螺纹根部的机械损伤和淬火裂纹,使得在外加应力的作用下氢原子向裂纹尖端移动和富集,使局部氢浓度升高,使工程用钢发生氢致延迟断裂。裂纹起始于螺纹根部近表面的机械损伤或淬火裂纹处,并逐渐扩展至心部,在多源裂纹交汇处形成劈拉台阶,并最终造成断裂。

The fracture behavior of 35CrMo steel was analyzed with scanning electron microscopy （SEM）, energy spectrum analyzer （EDS）, optical microscope （OM） and microhardness tester, and put forward corresponding with the preventive measures. The results show that the microstructure of the steel matrix is tempered sorbite and a small amount of ferrite; there is about 18 μm decarburization screw on the tooth surface, and there are mechanical damage and quenching crack on screw tooth root; The failure mode of engineering steel is hydrogen induced delayed fracture, the mechanical damage before using the screw tooth root and the quenching crack makes hydrogen atoms move to the crack tip and enrichment by the external stress, local hydrogen concentration increase, which make the engineering steel hydrogen induce delayed fracture. The crack starts at the mechanical damage or quenching crack near the root of the tooth surface, and gradually expands to the heart, the splitting step is formed at the intersection of multisource cracks, and finally the engineering steel is broken.