某火电机组高压主汽阀双头螺柱在检修时发生断裂。采用宏观观察、化学成分分析、扫描电镜分析、金相检验和力学性能测试等方法对螺柱的断裂原因进行了分析。结果表明:该螺柱的晶粒粗大,冲击韧度低,服役时间较长,产生了黑色网状奥氏体晶界异常组织,导致材料脆化,缺口敏感性和脆化倾向增大,在检修期间受拆卸冲击力的作用,螺柱发生了脆性断裂。

The double head stud of high pressure main steam valve of a thermal power unit fractured during maintenance. The fracture reasons of the stud were analyzed by means of macroscopic observation, chemical composition analysis, scanning electron microscope analysis, metallographic examination and mechanical property test. The results show that the grain of the stud was coarse, the impact toughness was low, the service time was long, and the abnormal structure of the black mesh austenite grain boundary was produced, which led to the embrittlement of the material, the notch sensitivity and the embrittlement tendency were increased. During the overhaul, the stud was brittle fracture due to the impact force of disassembly.