Creep Rupture Properties of Superalloys Developed for Nuclear Steelmaking

Creep rupture tests on six candidate alloys for intermediate heat exchangers of high-temperature gas-cooled reactors were carried out at 1173 to 1323 K in helium with small amounts of H₂, CH₄, CO, and C0₂, and at 1173K in H₂ + 15% CO + 5% C0₂. The creep rupture strengths of each alloy were scarcely different at 1173 K in both environments. At higher temperatures in helium environments, the degradation of the creep rupture strengths appeared in carbide-strengthened alloys because of decarburization. The alloy, which mainly uses α-W as a strengthener, showed stable creep rupture strength up to 1323 K in spite of severe decarburization.