Abstract:The stress rupture properties at 550 ℃ and the microstructure and hardness of the grip and gauge sections from ruptured specimens of a silicon-enhanced 9Cr ferritic/martensitic steel (denoted as H-Si steel) were investigated by SEM, TEM, EBSD and Vickers hardness tester. A comprehensive investigation was conducted, which included the microstructure evolution of H-Si steel under the coupling effect of temperature and stress and its influence on the creep behavior. The results show that H-Si steel exhibits good stress rupture properties and the stress rupture life is 2252 h under the conditions of 550 ℃ and 167 MPa. The fracture modes under experimental stress conditions are all ductile fracture. The grip section of H-Si steel exhibits relatively stable microstructure under different stresses, with a lath width ranging from 380 nm to 440 nm and the hardness being approximately 230 HV. However, the microstructure of the gauge section undergoes obvious degradation due to the stress, with the rapid decrease in dislocation density and the significant widening of laths. Correspondingly, the hardness drops obviously due to significantly decreasing dislocation strengthening and interface strengthening. The hardness of the 167 MPa@2252 h specimen decreases to 193 HV, which induces a lower high-temperature stress rupture property compared to 9Cr-1Mo-V-Nb martensitic steel (P91).