Extraction technique and evolution of carbides in serviced T91 steel

Carbide particles in T91 steel after service for different time were obtained by electrolytic extraction method and their phase,amount,morphology and composition were analyzed by SEM,XRD and EDS.The results show that the carbides in T91 steel exist mainly in two forms: M23C6,which is the majority,and MX.With increasing service time,the M23C6 carbides coarsen gradually along grain-boundary,while the MX carbides are relatively stable.No significant increase of size and amount of MC carbides are observed in the T91 steel even after service for 105296 hours.Morphologically,the initial rod-like carbides are spheroidized gradually.Mo,Cr,V in solid solution diffuse into M23C6,which leads to the increase of Mo,Cr,V and the decrease of Fe in the carbides as service time increases.