A nickel-base superalloy that has excellent sulfidation resistance, high-temperature tensile properties and hot workability was developed as a material for the rotors of FCC gas expander turbines. The effect of Mo, Ti and/or AI additions on the sulfidation behavior of a Ni-20Cr-13.5Co alloy was investigated in H2-H2S mixtures at 873 K (600 C/1112 F). It was found that increasing the Al content in the alloy could improve the sulfidation resistance of AISI 685 (UNS N07001). Six kinds of forged alloy, in which the AI content was increased while Ti content was decreased, were manufactured. Sulfidation tests and high-temperature tensile tests of those alloys indicated that the 1.5Ti-3.0Al alloy has about twice the sulfidation resistance and almost equivalent tensile properties to those of AISI 685. Therefore, the 1.5Ti-3.0Al alloy was selected as the most suitable alloy for FCC gas expander rotors. A 1400 mm
diameter-expander rotor disk of this developed alloy was manufactured. Test specimens cut out of the disk rim showed that the disk had equivalent tensile properties both at room and elevated temperatures, and the same creep rupture strength as that of AISI 685.