CREEP-PROPERTIES WITH SHORT-PERIOD EXCESSIVE LOADINGS ON A NICKEL-BASE HEAT-RESISTANT ALLOY HASTELLOY-XR

A series of constant load & temperature creep tests and constant tempe rature creep tests with short period excessive loadings was carried ou t on a nickel-base heat-resistant alloy Hastelloy XR, which was develo ped for applications in the High-Temperature Engineering Test Reactor (HTTR), at temperatures ranging from 900 to 1,000-degrees-C. The exces sive loading levels were set at the design stress intensity values Sm for Hastelloy XR indicated in the HTTR high-temperature structural des ign code. Five to six time excessive loadings did not cause significan t changes of the minimum creep rate or the time to onset of tertiary c reep. Excessive loadings repeated around ten times did not cause signi ficant changes of the time to rupture or the rupture elongation. The r esults suggest that the design stress intensity values Sm for Hastello y XR have been determined reasonably.