Creep rupture behavior and microstructural evolution of modified 9Cr–1Mo heat-resistant steel

High-temperature creep rupture behavior of modified 9Cr–1Mo steel used for steam cooler was investigated at temperature of 838 and 923 K and stress ranging from 100 to 250 MPa. Based on the analysis of creep rate–time curves, it is found that the creep rupture life decreases with the increase in the applied stress and temperature. The creep damage tolerance factor has been identified as a value of 8. In the normalized and tempered condition, the studied steel shows typical martensitic microstructure with Cr-rich M₂₃C₆ and Nb- or V-rich MX precipitates. Moreover, the Laves phase has been found along the grain boundaries. The fracture morphology characterized by field emission scanning electron microscope is adopted to reveal the creep failure mechanisms. The investigated results indicate the occurrence of the transgranular fracture under all the creep test conditions.