Abstract
The main objective of this study was to clarify the effects of microstructural change on minimum creep rate and rupture life of Hastelloy X, and was also to develop a creep life prediction method from the microstructural observations. For this purpose, long-time aging at 750 to 900°C up to 104hr was used for making different degraded microstructural materials. The accomplishments of this study were as follows;(1) During the aging, carbides of M12C, M6C, and M23C6, and an intermetallic compound of μ phase were precipitated at the grain boundaries and in the grains. Intergranular precipitates strengthened the creep resistance, but intragranular ones weakened, which was not commonly expected.(2) The minimum creep rate (em) of the aged Hastelloy X at 850°C was explained as a function of grain boundary coverage ratio of precipitates (ρ), volume fraction of intragranular precipitates (V), aging temperature (Ta), and applied stress (σ). The equation was as followed.em=[e*0+A1(1-ρ)(V-V0)2exp(-QD/κTa)]σn(3) Creep rupture life was also explained from the minimum creep rate by using the Monkman-Grant equation for the aged degraded Hastelloy X.
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