1979 Volume 65 Issue 7 Pages 994-1003
Ni-Cr-Mo-W system alloys were investigated in order to develop a heat resistant alloy which may satisfy various properties required for heat exchanger tube materials of nuclear steel-making system.
In the first step, we investigated the effect of alloy elements on formability, high temperature strength, aging characteristics and weldability. And we selected some candidate alloy compositions in terms of creep rupture strength at 1000°C. Out of these alloys, Ni-0.07C-25Cr-5Mo-5W alloy turned out to be superior to other alloys when taking various properties.
In the second step, the effects of C and Cr contents on creep rupture strength at 1000°C were examined on this alloy. The creep rupture strength was found to increase when C content was reduced from 0.07% to 0.03% and Cr content was raised from 25% to 27.5% and solution treatment temperature was raised. In terms of various properties, Ni-0.03C-27.5Cr-5Mo-5W system alloy was chosen, which also proved resistant to helium environment.
In conclusion, we developed a candidate alloy with compositions of Ni-0.03C-27.5Cr-5Mo-5W which seemed to have high possibility of satisfying the creep rupture strength target, that is more than 1kg/mmmm2 at 1000°C and 5×104 hours in helium.