Microstructural Evolution and Mechanical Properties of T122 Steel Tube in a 1000MW Ultra Supercritical Unit after Long-Term Service

The microstructures and mechanical properties of T122 steel used for superheater tube of the boiler in a 1000 MW ultra supercritical power plant after service for 83,000h at 590℃ were investigated, and compared with data of that served for 56,000h in previous studies. The results show that compared with T122 tube sample service for 56,000h, the tensile properties at room temperature and the size of precipitated phase exhibit few differences, but the lath martensites features are apparent, and the Brinell hardness value are obviously higher. SEM and TEM experiments show that the substructure is still dominated by lath martensite. A few lath martensites recover, subgrains appear and equiaxe, and the dislocation density in grains is relatively low. A large number of second-phase particles precipitated at boundaries of original austenite grains and lath martensite phases, which are mainly M₂₃C₆ and Laves phases.