Microstructure evolution and corrosion behaviour of an ASTM A213 T91 tube after long term creep exposure

Our investigations suggest remarkable changes in the core and the walls of the tube. In the bulk material, the recovery of the tempered martensitic matrix and the coarsening of the M23C6 carbides were observed, but the mechanical properties and the creep strength are still good. However, carburization/oxidation represents a major life time limiting factor by affecting about 20% of the tube thickness. The mechanisms of carburization, oxidation and microstructure evolution are here discussed.