Microstructural changes and the degradation of creep resistance due to creep damage have been studied on 1Cr 1Mo-1/4V steel crept for a duration of 9 500 h at 550°C. In particular, the effect of grain boundary void on the creep resistance has been examined on the creep damaged specimens, with and without a reheat treatment.
Metallographic observations have shown three types of microstructural changes with creep deformation: (1) coarsening of the carbide that usually occurs during tempering, (2) formation of voids and cracks, and (3) remarkable recovery in the vicinity of prior austenite grain boundaries.
It is found that the extent of carbide coarsening is a little even in the accelerating creep stage, and the effect of voids on the creep resistance is negligibly small.Progressive loss of the creep resistance is shown to be closely associated with the local recovery in the vicinity of prior austenite grain boundaries.
