超臨界汽輪機中壓調速汽閥2Cr12NiMo1W1V鋼閥桿斷裂原因分析

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

通過宏觀形貌分析、化學成分分析、力學性能測試、光學顯微鏡以及掃描電鏡分析等方法對某超臨界汽輪機中壓調速汽閥2Cr12NiMo1W1V鋼閥桿斷裂原因進行了分析.結果表明:閥桿斷裂的主要原因是其表面的滲氮層脆性超標,運行中當閥桿和與其緊密配合的閥碟發生擠壓摩擦時,便會在應力集中的排汽孔處的滲氮層形成裂紋源,并在載荷作用下穿透滲氮層擴展至基體進而引發閥桿斷裂;閥桿材料長期在超過其許用溫度的環境下使用,造成蠕變老化,同時材料硬度偏高、塑性和韌性儲備不足,都在一定程度上加速了裂紋的擴展,縮短了閥桿的使用壽命.
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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