DEVELOPMENT OF Co-FREE Ni-BASE SUPERALLOY FOR HTGR.

Abstract

The effects of Cr, W and Mo as solution strengthening elements for austenite matrix and of Y and Zr as grain boundary affecting elements on the creep rupture strength and on the microstructure of Ni-base superalloys have been investigated. For the matrix composition, 18%Cr-15%W-0. 5%Mo-Ni is found to be optimum. Creep rupture strength of this alloy is improved by the addition of proper amounts of Y and Zr. The alloy composition is as follows: 18%Cr-15%W-0. 5%Mo-0. 02%Y-0. 02%Zr-0. 05%Al-0. 2%Ti-Ni. The creep rupture strength of this alloy in helium environment simulated in HTGR Is comparable with that in air at 1000 degree C at 3. 5 kg/mm**2.