Sulfidation-resistant alloy for coal gasification service. Quarterly report, September 1--November 30, 1977. [Fe--18Cr--5Al--1Mo--1Hf

Abstract

An Fe-18Cr-5Al-1Mo-1Hf alloy has been tested in synthetic coal gasification atmospheres at 500 and 1000 psi pressure. Resistance to attack is similar to that observed at atmospheric pressure. Tests also have been made at high pressure in a low P/sub O/sub 2//-high P/sub S/sub 2// atmosphere representative of low Btu gasification. The alloy did not resist attack under these conditions and has a transition to non-protective behavior with decreasing P/sub O/sub 2// and/or increasing P/sub S/sub 2//. A molybdenum alloy (TZM-Mo) is being screened for sulfidation resistance in coal gasification atmospheres. Initial tests at 1800/sup 0/F in the DOE/MPC gas mixture show a parabolic rate behavior with negligible attack. Extrapolation of the data indicates a potential loss of 0.2 mil in one year, with 1% H/sub 2/S in the gas. Samples will be exposed to a cumulative time of 4000 hr to obtain more accurate rate data. Impact tests indicate that Al and Si lower the notched impact toughness and raise the ductile to brittle transition temperature of Fe-Cr alloys with 17-19Cr. The addition of 1 to 2% Mo slightly improves impact behavior. An Fe-18Cr-5Al-1Mo-1Hf alloy is concluded to have the best combination of corrosion resistance and mechanical properties. This more » composition and an upper limit composition of 19Cr-6Al-2Mo-1Hf have been selected for the final Phase III evaluation. Two 50-lb ingots of each composition have been vacuum induction melted and cast successfully. « less