Morphology of the creep crack tip in P92 steel and its relation to microstructure

The region around the tip of a creep crack obtained using an interrupted test on a C(T) specimen of the 9 wt.% Cr power plant alloy P92 has been examined using electron backscatter diffraction to study the relationship between the crack morphology and the martensitic substructure. Nucleation of voids was found to occur primarily on prior austenite grain and packet boundaries. This agrees well with previous results in which minimum creep rate decreased with increasing prior austenite grain size for small prior austenite grains. Growth and coalescence of voids to form a continuous crack appears to occur by recovery, recrystallisation and eventual rupture of the bridging regions between the voids.