高温ガス炉近似ヘリウム雰囲気におけるハステロイＸＲのクリープおよび破断挙動

Abstract

Creep and rupture tests were conducted on Hastelloy XR (a modified version of the conventional Hastelloy X) at 1, 073, 1, 173 and 1, 273K in simulated high-temperature gas-cooled reactor helium. The test section of creep testing machine was designed and constructed with special care for impurity chemistry in helium. A device for counting Moire patterns was developed for contamination-free creep strain measurement. The test results up to 10, 000h showed no significant degradation in creep properties. Comparing the data on the stresses to rupture, to cause 1% total strain and to the onset of tertiary creep, the stress to cause 1% total strain is judged to be the dominant factor for the allowable stress (St) in the ASME Code. Carbon analysis for ruptured specimen showed that caburization was limited to the region near the ruptured portion and slight carbon intrusion occurred only in the early stage of exposure. Surface cracks were not responsible for creep-rupture, because they were blunted at the depth of approximately 100μm from the specimen surface at 1, 173K and 200μm at 1, 273K. Internally formed cracks were initiated at the sites of carbide precipitation at grain boundary, growing nearly perpendicular to the stress axis. Recrystallization observed was localized at 1, 173K but became pronounced at 1, 273K. Creep deformation enhanced coasening of the grain boundary carbide under tensile stress.