High temperature intergranular crack growth under cyclic loading in martensitic 2·25Cr–1Mo steel

Abstract

Mechanisms of subcritical high temperature intergranular crack growth have been studied during fatigue loading in air and in vacuum for coarse grained martensitic 2·25Cr–1Mo steel. The crack increment per cycle, da/dN, is increased greatly under high mean stress conditions as the cyclic frequency is reduced. In addition, fatigue crack growth rates as a function of frequency can be predicted accurately from baseline fatigue data (obtained at low mean stresses) and static crack growth resistance curves. The cyclic and static components of crack growth appear to be essentially independent. The importance of the average value of stress intensity over the fatigue cycle, K_mean, has been identified, but more accurate predictions can be made if the value of static stress intensity is integrated over the fatigue cycle. More generally, these cyclic-static crack growth mechanisms may have some potential use for modelling fatigue-creep interactions.

MST/1112