Creep Properties of Heat-Resistant Superalloys for Nuclear Plants in Helium

Abstract

In order to estimate the creep and rupture strengths of candidate alloys for the intermediate heat exchanger of VHTR, creep and stress rupture tests in impure helium were conducted on Hastelloy X, Inconel 617, Inconel 625, Incoloy 800 and Incoloy 807 at 900°C. The results were discussed in comparison with those in air and the alloys were examind from the point of view of the elevated temperature structural design.
The main results obtained are summarized as follows:
(1) No appreciable decrease in creep and rupture strengths in helium as compared with those in air is observed on Hastelloy X and Inconel 625. On the contrary, the creep and rupture strengths of Inconel 617 in helium decrease slightly as compared with those in air. Meanwhile, the creep and rupture strengths of Incoloy 800 in helium are remarkably lower than those in air. In the case of Incoloy 807, the creep strength to cause 1 percent total strain and that to initiate secondary creep increase remarkably in helium as compared with those in air. However, the creep strength to cause initiation of tertiary creep and the rupture strength in helium remarkably decrease as compared with those in air.
(2) The order of magnitude of the S_o value for each material in helium is as follows; Hastelloy X>Inconel 617>Incoloy 807>Inconel 625>Incoloy 800
Meanwhile, that of the S_t value in helium is; Inconel 617>Hastelloy X>Incoloy 807>Inconel 625>Incoloy 800.