Growth of Creep Cavities in 12% Cr Steels

The nucleation and growth of creep cavities will eventually occupy a considerable fraction of the grain boundary. This will lead to microcracks and intergranular fracture thus controlling the ductility of the component. The traditional approach to predicting this type of failure is to simulate cavities with only one size. Assumptions of an instant nucleation with symmetrically placed cavities make all cavities equally sized. It has been observed, in 12% Cr steels as well as in other commercial alloys that cavities nucleate during all stages of creep. Creep cavities get randomly placed mostly at grain boundaries directed transverse to the loading direction. With continuous nucleation a size distribution of cavities appears, which is compared to observed average cavity size. Constraints on cavity growth are introduced, which reduces the growth rate. This is needed in order to explain the cavity growth of 12% Cr steels. Furthermore, creep rupture will be derived based on the area fraction of cavities, thus explaining the intergranular failure.