Abstract:In this work, the stress rupture properties of a silicon-enhanced 9Cr ferritic/martensitic steel (denoted as H-Si steel) at 550℃, the microstructure and hardness of the grip and gauge sections from ruptured specimens were investigated by SEM, TEM, EBSD and Vickers hardness tester. A comprehensive investigation was conducted into the microstructure evolution of H-Si steel under the coupling effect of temperature and stress and its influence on the creep behavior. The results indicate that H-Si steel exhibits good stress rupture property 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 fractures. The grip section of H-Si steel exhibits relatively stable microstructure under different stresses, with a lath width ranging from 380 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 rapid decrease in dislocation density and significant widening lath. Correspondingly, the hardness drops obviously due to significantly decreasing dislocation strengthening and grain boundary strengthening. For instance, the hardness of the 167MPa@2252h sample decreased to 193 HV, which induces a lower high-temperature stress rupture property compared to P91 steel.