35CrMoA螺栓失效分析和改进措施

Fracture Analysis and Optimization Measures of 35CrMoA Bolt

汽轮机运行时,转子上连接联轴器的高强度螺栓如果发生断裂,轻则需要停机维修,重则造成较大事故。为了找出某汽轮机35CrMoA钢制螺栓断裂失效的原因,对失效件的宏观断口形貌进行了观察,并采用光学显微镜、扫描电镜、X射线能谱仪、硬度计设备等对失效件的微观断口形貌、显微组织、硬度和化学成分等进行了理化试验和分析,结果表明早期淬火裂纹导致了该螺栓发生沿晶脆性断裂。杆部转接处在冷镦变形过程中形成了非正常组织,硬度为430~500 HV,远高于标准硬度,其经过淬火后扩展成淬火裂纹,最终导致螺栓断裂。提出了改进冷镦工艺并增加冷镦后的热处理的建议。研究成果可为冷镦工序后硬度异常问题的处理提供参考。

If the high-strength bolt used to connect the coupling of turbine rotor happens to break during the operation,the unit needs to be shut down for maintenance,severe damage may even occur.In order to find out the fracture cause of a 35CrMoA steel bolt used in steam turbine,the macroscopic morphology was observed.The microscopic morphology,hardness and chemical composition of the fractured part were observed and analyzed by means of optical microscope,scanning electron microscope,X-ray energy disperse Spectroscopy and hardness tester.The results showed that it was the early quenching crack that caused the intergranular brittle fracture.In the process of cold heading deformation,the abnormal structure was formed with hardness of 430~500 HV,which exceeded the hardness standard.After quenching,a crack was finally formed,leading to the fracture of the bolt.It is recommended to improve the cold heading process and add a heat treatment after it.The research results can provide reference for the problem of abnormal hardness after cold heading processes.