某火力发电厂汽轮机用20Cr1Mo1VNbTiB钢高温双头螺柱发生断裂。采用宏观观察、化学成分分析、金相检验、扫描电镜及能谱分析、力学性能测试等方法对螺柱断裂的原因进行分析。结果表明:螺柱的第一扣螺牙根部存在粗晶区,组织由回火贝氏体转变为马氏体相位的贝氏体,材料塑性、韧性下降,脆性增加,在高温应力和交变载荷的作用下,粗晶粒区发生沿晶开裂并不断扩展,最终导致螺柱发生脆性断裂。建议严格控制冶炼工艺和热处理工艺,规范螺柱安装、拆卸程序,采用无损检测、硬度测试等方法对螺柱进行出厂检验,以保证其使用性能。

The 20Cr1Mo1VNbTiB steel high temperature stud bolt used for steam turbine in a fossil-fuel power station fractured. The cause of bolt fracture was analyzed using methods such as macroscopic observation, chemical composition analysis, metallographic examination, scanning electron microscopy and energy spectrum analysis, mechanical property testing. The results show that there was a coarse grain zone at the root of the first thread of the stud. The microstructure changed from tempered bainite to martensite phase bainite. The plasticity and toughness of the material decreased, while the brittleness increased. Under the action of high temperature stress and alternating load, intergranular cracking and continuous expansion occurred in the coarse grain zone and finally led to brittle fracture of the stud. It was recommended to strictly control the smelting process and heat treatment process, standardized the installation and disassembly procedures of the studs, used non-destructive testing and hardness testing and other methods to carry out factory inspection of the studs to ensure their performance.