Effects of microstructure on material properties of modified 9Cr-1Mo steel subject to creep-fatigue

The creep-fatigue properties of modified 9Cr-1Mo steel were studied to elucidate the effects of the microstructure on specimens deformed by fatigue and creep-fatigue via stress holding for 30 min at 550°C. First, creep-fatigue behaviors up to 7.8% nominal strains were obtained with respect to the deformation conditions. Next, the micro Vickers hardness values were determined to measure the creep-fatigue properties of the deformed materials. Electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) were used to determine the grain diameters and grain average misorientations (GAMs) and distributions of dislocations and precipitates, respectively. These observations explained the creep-fatigue properties of the deformed specimens. The differences in the properties of materials subjected to fatigue and creep-fatigue are discussed both macroscopically and microscopically.