中压主汽门阀盖螺栓断裂原因分析

Fracture analysis of the bolt on the RSV bonnet

中压主气门阀盖螺栓在运转两年后出现多根断裂，通过观察和分析20cr1Mo1VnbTiB高温螺栓断口的宏观及微观形貌，检验化学成分、测试力学性能，显微组织检验等方法，分析螺栓断裂原因。力学性能和化学成分符合要求，但螺纹根部粗糙度比较大，硬度为316 HBW2．5／187．5超过标准中规定的硬度252～302HBW上限值，金相组织是回火索氏体。分析结杲表明，螺纹根部粗糙，引起局部应力集中，全相组织不符合要求，硬度超过标准中的规定，晶粒粗大等是螺栓断裂的主要原因。在生产中，要加强高温紧固件性能检测，遵守拆装要求，定期喷涂防腐介质，以防此类事故发生。

Many bolts on the RSV bonnet are broken after two years work Through the macro and micro-analysis of the thread tooth surface and fracture, chemical compositions examination, mechanical properties test, microstructure exam-nation etc, the fracture of 20Cr1Mo1VnbTiB high temperature bolts is analyzed. Chemical composition and mechanical properties of bolt meet standards, but local stress concentration by rough machined is found, 316HBW2.5/187.5 hardness exceeds the upper limits of the standard hardness （252 302HBW）, the microstructure is tempered sorbite. The results show that main reasons caused fracture is Local stress concentration by rough machined, coarsening grain, excessive hardness, incorrect bolt MetaUographic microstructure etc. In production, the high temperature bolts performance testing is strengthened, the requirements of assembly and disassembly requirements is complied; the anti-corrosion medium is regular sprayed to prevent such occurrences.