汽轮机高压主汽阀阀杆断裂原因分析

摘要

某火电厂300MW亚临界燃煤发电机组汽轮机1号高压汽门阀杆发生断裂，截止到断裂发生，机组累计运行4．6万小时。将断裂的高压主汽门阀杆取样进行化学成分分析，符合2Cr12NiMo1W1V 材质的成分范围，化学成分正常。通过金相组织观察，阀杆表层为渗氮处理的细晶马氏体组织，心部为低碳板条马氏体组织，组织正常。但是在取样部位多处看到周向裂纹，裂纹边缘呈黑色，中间有白色腐蚀产物，说明裂纹内表面已经发生高温氧化和应力腐蚀，初步断定裂纹的产生是表面磨削加工时的残余应力所致。最后对断口进行扫描电镜分析，发现表层断口已经被高温氧化皮覆盖，心部为光洁的解理断口，未发现韧窝和疲劳断裂的贝壳状花纹，排除了阀杆异常运行导致循环应力疲劳断裂的可能性。%A 300MW sub-critical coal-fired thermal power plant steam turbine generator set No .1 high pressure steam valve stem is fractured .The turbine unit has been running 46 000 hours before the crack happened .The chemical component was examined which was in the standard range .We observed the metallographic structure of the broken stem to find the nitriding treatment of fine grain martensite structure at surface area and lath martensite at central section ,healthy structure condition . We also found the existing of circumferential oxidized cracks with white corrosion production .According to that ,we believe it was caused by residual stress when grinding .Finally,SEM was used to observed the fracture to further confirm our ideas .