Creep ductility of 1CrMoV rotor steel

Abstract

The creep ductility of 1CrMoV steels at a given temperature is high at high stresses responsible for high strain rates and ductile rupture, and low at lower stresses responsible for low strain rates and constrained cavity growth at grain boundaries. The magnitudes of ductility in the high and low stress regimes and the time to, and strain rate at, the transition between the two is determined by the chemical composition and the adopted quality heat treatment procedure of the steel. The basis for a material pedigree function forming part of a creep ductility model for 1CrMoV rotor steel is presented. Low ductility 1CrMoV steels are expected to be extremely notch sensitive. While this appears to be true for medium to high strength heats of the alloy, it is not necessarily the case for lower strength heats. There is not a simple inverse relationship between creep ductility and creep strength. Increasingly, creep-fatigue lifetime predictions for high temperature 1CrMoV power plant components subjected to thermo-mechanical transients employ a creep ductility exhaustion methodology to determine the creep damage accumulated per cycle. A creep ductility model of the type developed in the paper is suitable for forming the basis of such an approach.