Effect of impurity antimony on the creep behavior of 2.25Cr-1Mo heat-resistant steel

The creep properties of 2.25Cr-1Mo steel samples, undoped and doped with Sb (0.05 wt%), are examined under different applied engineering stresses (150–400 MPa) and temperatures (773–873 K). The creep behavior follows a unified Monkman-Grant relation ε̇m×tr1.04=0.046 for both the undoped and Sb-doped steels, where ε̇m is the minimum creep rate in h−1 and tr is the rupture time in h. Under the same experimental conditions, the rupture time of the undoped steel is much longer than that of the Sb-doped steel, and meanwhile the minimum creep rate of the former is apparently smaller. Moreover, the threshold stress for creep is much lower for the Sb-doped steel than for the undoped one. This indicates that the impurity element Sb severely lowers the high temperature creep resistance of 2.25Cr-1Mo steel. As shown by boundary microanalysis, there is apparent grain or subgrain boundary segregation of Sb, which could promote the boundary sliding and the nucleation of cavities or microcracks, thereby leading to the creep property deterioration of the steel.