Abstract
In order to clarify the strengthening mechanism due to grain boundary carbide precipitation, creep behavior and dislocation substructure developed during creep of 15Cr-25Ni steels with different carbon content have been studied at 850 and 950°C under stresses of 14.7-79.2 MPa. With the grain boundary carbide precipitation, creep resistance and rupture life increased markedly, showing significant grain boundary precipitation strengthening by carbide. The minimum creep rate of γ single phase steel was independent on grain size, while it increased with increasing grain size in the steels with grain boundary carbide precipitation. With grain boundary carbide precipitation, dislocation density near grain boundary increased, but little difference in dislocation substructure within grains was observed in both steels. This suggests that grain boundary carbide strongly obstructs dislocation annihilation at grain boundaries, and therefore markedly increase the creep resistance. It is also suggested that the minimum creep rate of the steel with the grain boundary precipitation is controlled by recovery process near the grain boundaries instead of recovery at subboundaries which control the creep rate of γ single phase steel.
