超临界汽轮机中压调速汽阀2Cr12NiMo1W1V钢阀杆断裂原因分析

Causes Analysis on Rupture of 2Cr12NiMo1W1V Steel Reheat Interceptor Valve Stem of a Ultra-supercritical Turbine

通过宏观形貌分析、化学成分分析、力学性能测试、光学显微镜以及扫描电镜分析等方法对某超临界汽轮机中压调速汽阀2Cr12NiMo1W1V钢阀杆断裂原因进行了分析.结果表明:阀杆断裂的主要原因是其表面的渗氮层脆性超标,运行中当阀杆和与其紧密配合的阀碟发生挤压摩擦时,便会在应力集中的排汽孔处的渗氮层形成裂纹源,并在载荷作用下穿透渗氮层扩展至基体进而引发阀杆断裂;阀杆材料长期在超过其许用温度的环境下使用,造成蠕变老化,同时材料硬度偏高、塑性和韧性储备不足,都在一定程度上加速了裂纹的扩展,缩短了阀杆的使用寿命.
The rupture causes of a 2Cr12NiMo1W1V steel reheat interceptor valve stem of a ultra-supercritical turbine were analyzed by means of macro inspection,chemical compositions analysis,mechanical properties test,optical microscope and scanning electron microscope analysis.The results show that the excessive brittleness of nitriding layer of the valve stem was the main cause for the rupture.Cracks generated in the nitriding layer near exhaust steam holes when the valve stem extruded with the valve disc,then the cracks extended from nitriding layer to the base metal,and finally the valve stem was broken.On the other hand,the valve stem was used in high temperature environment for a long time where the temperature was higher than the designed value,which would reduce the ductility and plasticity and result in creep damage.So the cracks extending velocity was increased and the service life of the valve stem was shorten.

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