Microstructure Creep Rupture Ductility Relationship of Modified Alloy 800 at 600°C

Abstract

Low creep rupture ductility has been associated with the combination or interaction of gamma' strengthening and discontinuous grain boundary precipitation in Alloy 800 tested in the temperature range 500–600°C. The purpose of this paper was to compare a conventionally treated specimen of Alloy 800 that exhibited both gamma' and discontinuous precipitation with an unconventionally heat treated specimen of the same heat. The method used was to pre-age the specimen at 850° C for 150 h. This treatment modified the grain boundary distribution to discrete carbide particles in the grain boundaries. The result of the creep rupture test performed at 600° C showed that neither creep strength nor ductility was significantly different. This indicates that the presence of the fine dispersion of gamma' is sufficient to cause low ductility without the presence of discontinuous precipitation of M23C6 in the grain boundaries.