Ni-Cr-W系固溶強化型超耐熱合金の合金設計

抄録

For the purpose of developing cobalt-free tube materlals for the heat-exchanger of nuclear steel-making process, an alloy design has been conducted with respect to the Ni-Cr-W system.
Theoretically promising composition ranges in the Ni-Cr-W system are determined by the conditions that average electron vacancy number N_v is smaller than Barrows' critical electron vacancy number N^c and that lattice parameter a is greater than 3.580 Å. some compositions in the above mentioned range have been examined experimentally and 23% Cr-18%W has been determined as the best composition from the creep rupture strength point of view.
Effects of carbon and magnesium on the creep rupture strength of 23%Cr-18%W-Ti-Zr-Bal. Ni alloy have been studied. The long-term creep rupture strength decreases with the increase of carbon content in the range from 0.03% to 0.14%. Up to 90 ppm magnesium does not significantly affect the creep rupture strength of the alloy at 1000°C, but about 160 ppm magnesium significantly reduces the creep rupture strength at that temperature.
In conclusion, 23%Cr-18%W- (0.3%Ti) - (0.05%Zr) -0.03%C-Bal. Ni alloy has a high possibility of satisfying the creep rupture strength target, that is more than 1kg/mmmm² at 1000°C and 10⁵ hours.