Creep rupture properties of Ni-Cr-W alloys for nuclear steel making in helium and reducing gas atmospheres

Creep rupture properties of Ni-Cr-W alloys developed for nuclear steel making, which precipitate α-W, were investigated in the temperature range from 900 0C to 1050 0C in He environment (He-2) which simulates the primary coolant of High Temperature Gas Cooled Reactor (HTGR), and at 900 0C in reducing gas environment which is to be used when direct steelmaking system is connected with the primary system of the HTGR. The results were discussed in terms of environmental factors such as carburization, decarburization and oxidation. It was found that the two alloys have the possibility to satisfy the target of R and D, that is, 'the alloy should have the 50000 h rupture strength of more than 1 kg/mm2'. Further, the degradation of the rupture strength in the alloy which has α-W as a main strengthener, did not appear in spite of severe decarburization of the alloy. (author)