汽轮机调速汽阀高温紧固螺栓断裂失效分析

Fracture failure analysis of high-temperature fastening bolt for turbine control valve

某火电厂在机组检修期间发现汽轮机中压调速汽阀高温紧固螺栓断裂失效。为了确定失效原因,避免类似事件再次发生,利用直读光谱仪、光学显微镜、扫描电镜、摆锤式冲击试验机对断裂螺栓的宏观形貌、断口微观形貌、化学成分、显微组织、力学性能等进行了测试分析。结果表明,此次高温紧固螺栓断裂的主要原因为20Cr1Mo1VTiB钢螺栓在制造阶段的锻造温度过高或淬火温度过高造成组织晶粒粗大,引起材料冲击性能降低,在中压调速汽阀频繁动作产生的冲击载荷作用下沿粗晶部位开裂,并以脆性解理断裂方式扩展,直至螺栓整体断裂。

High temperature fastening bolt of the steam turbine IP governing valve was broken and failed during the unit maintenance in A thermal power plant.In order to determine the cause of failure and avoid the recurrence of similar events,macro morphology,fracture micro morphology,chemical composition,microstructure and mechanical properties of the fractured bolt were tested and analyzed by direct reading spectrometer,optical microscope,scanning electron microscope and pendulum impact tester.The results show that the main reason for the fracture of high temperature fastening bolt made of 20Cr1Mo1VTiB steel is that the forging temperature of the bolt in the manufacturing stage is too high or the quenching temperature is too high,which results in the coarse grain structure and the impact property of the material is reduced.Under the impact load generated by the frequent action of the turbine control valve,the bolt cracks along the coarse grain region and extends in the form of brittle cleavage fracture until the bolt is completely broken.