Compositional effects on the creep ductility of a low alloy steel

The role which P plays in determining the creep ductility of 2.25Cr-1Mo steel is examined by notched bar creep rupture tests on high purity material selectively doped with combinations of Mn, Si and P. The impurity concentrations, hardness and grain size were carefully controlled. The ductility of as-tempered samples containing dopants was found to be higher than those without dopants; however the ductility of step cooled samples containing Mn and P was found to be lower than as-tempered samples. It is suggested that P, when segregated to the prior austenite grain boundaries, enhances the nucleation of grain boundary cavities while retarding their growth. Mechanisms for each process are proposed.