| The main way to improve the efficiency and reduce the coal consumption is improving steam parameters of the power plant boiler. More strict requirements are put forward for power plant boiler material. T92 steel becomes the main candidate material of ultra-supercritical utility boiler for its excellent high-temperature corrosion resistance and high-temperature creep resistant performance. In order to guarantee the safety of the unit operation, the law of high temperature creep should be studied.The creep tests of T92 steel on both smooth and notched specimens were carried out under different stress levels at 650℃ to research the creep properties of the steel under high temperature and multiaxial stress state. In order to research the change of microstructure and the influence of precitipates on creep strength, SEM and TEM are used to observe the fracture morphology and the microstructure and precipitates transformation. The composition and transformation of precipitates were analyzed by means of EDS. Through long-term creep process, certain changes will happen to the hardness of material. Hardness tester is used to detect the hardness of material after creep. Finite element analysis is adopted to study the influence of multiaxial stress state on creep behavior. The results show that the presence of notch weaken plastic deformation of steel, with the increase of notch acuity ratio, the deformation is smaller. The notched specimens and smooth specimens have different fracture mechanism. The main precipitates consist of M23C6 carbides, MX carbonitrides and Laves phase during creep process. The presence of notch contributes to the precipitation of Laves phase. The hardness value in smooth specimens is on a rise as a whole from the center to the edge, while on a decline in the notched specimens. Von Mises stress seems to be the primary cause of cavities nucleation, thus leading to the initiation of crack and further to fracture. |
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