中文摘要：

某超超临界660 MW机组的中压调节阀部分镍基螺栓（材料为GH783合金）发生断裂,通过宏观检验、金相检验、SEM及能谱分析、合金成分分析和力学性能检验,对螺栓失效原因进行分析。分析发现：在螺栓热紧过程中,其中3根螺栓中加热棒局部高温导致螺栓孔内壁材料烧损,裂纹萌生于内孔烧损处,并在正常服役条件下裂纹扩展导致螺栓发生断裂,致使剩余螺栓承受过高载荷及附加弯曲应力。螺栓服役过程中有因环境温度变化等产生的交变应力,以及材料本身在高温环境下性能的劣化,导致部分螺栓发生早期疲劳断裂及一次性脆断。在分析螺栓断裂基础上,提出规范热紧工艺、提高螺栓内外表面的加工精度和重新评估GH783合金材料螺栓在600℃下服役的可靠性等建议。

英文摘要：

The bolts in the tune door of a 660 MW ultra supercritical unit were broken after short-term service.These bolts were made of GH783 alloy,an anti-oxidized Ni low expansion superalloy.The fracture bolts were investigated by macroscopic examination,metallographic examination,SEM equipped energy spectrum analysis composition analysis and mechanical properties test.The results show that：in the bolt hot tightening process,three heating pipes were high temperature damaged and remained in the bolt holes which burned and damaged the bolt materials near the bolt holes.Cracks initiated in the burning sits and propagated under normal service conditions leading early fracture of the three bolts.After this,the size and distribution of the stress in the left bolts was changed and additional flexure stress was introduced.Some bolts were fatigue fractured under alternating stress due to the environmental temperature and loading change in the different order.Other bolts failed in the disposable brittle fracture.Some suggestions were also put forward such as regulating the hot tightening process,enhancing the machining quality of bolt outer and inner surface and re-assessing the service reliability of GH783 at 600 ℃.