Initiation of high temperature creep voids in notched components

High temperature creep damage is caused by voids generated at grain boundary at elevated temperatures. Creep void formation is greatly influenced by stress-state as well as metallurgical factors. In this paper, the notched components of 2.25%Cr-1% Mo steel, of which microstructure was prepared to be characteristic of the heat-affected zone in the welded joint by heat treatments, was creep-tested at 630°C. Then the creep void density and total length of creep voids to grain boundary length fraction were measured in the area of 1 × 1 mm² settled around the notch root in association with the inclined angle of grain boundary against loading axis and the stress state around the root of notch, which was calculated using inelastic finite element method. Consequently, it was found that creep void tended to initiate much more at the grain boundary more perpendicular to loading axis and with the greater normal stress, and seemed to originate and grow almost independent of the shear stress on the grain boundary. The much easier initiation and growth of creep voids at welded joint and/ or notch roots are considered to be due to the much higher normal stress to the grain boundary developed under the greater stress triaxiality.