The creep strength of a 20%Cr-25%Ni-Nb steel containing controlled particle dispersions

Abstract

AbstractA 20%Cr-25%Ni-Nb steel subjected to mechanical working and precipitation strengthening was creep-tested at a temperature of 1073 K in the stress range 25–180 MPa. Coarse and fine NbCN precipitate distributions were investigated. At stresses less than that to bow dislocations between precipitates each alloy exhibited a linear dependence of creep rate on stress. At high stresses, increases occurred in stress dependence, n, from 1 to 9.5 in the coarse and from 1 to 10.3 in the fine distribution materials. Dislocation densities measured on samples strained in secondary creep also showed a marked transition in behaviour above and below the yield stress for bowing. Below YS the densities were independent of stress; above YS the density could be described by the relation: σA=σB+αμb(P A½−P o½), where σA is the applied stress, σp the YS due to bowing between particles, σA the dislocation line tension factor, μ the shear modulus, b the Burgers vector, P A the dislocation density in secondary creep, and P o ...