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Stellite is a hard-facing alloy resistant to wear, corrosion and high-temperature oxidation, invented by Elwood Haynes in the United States in 1907. It is a cobalt-based alloy (Co-Cr-W/Mo) containing considerable nickel, chromium and tungsten with small amounts of molybdenum, niobium, tantalum, titanium, lanthanum and sometimes iron. Depending on composition, Stellite can be made into welding wire and powders for hard-facing, thermal spraying and spray welding, as well as castings, forgings and powder-metallurgy parts.
By application, Stellite alloys fall into wear-resistant, high-temperature resistant, and wear plus aqueous-corrosion resistant families. Typical grades include Stellite 1, 4, 6, 8, 12, 20, 31 and 100. Unlike other superalloys strengthened by ordered precipitates, Stellite relies on a solid-solution-strengthened austenitic fcc matrix with distributed carbides; cast Stellite in particular is strengthened largely by carbides. All practical Stellite alloys are nickel-alloyed to stabilize the structure from room temperature to melting point, avoiding the hcp-to-fcc transformation of pure cobalt below 417 C. With its higher chromium content, Stellite shows excellent hot-corrosion resistance above 1000 C.
The Incoloy family includes Incoloy 800, 800H and 800AT - Ni-Fe-Cr alloys resistant to high-temperature oxidation and carburization. With about 32% nickel they resist chloride stress-corrosion cracking and are insensitive to sigma-phase precipitation, with excellent uniform corrosion resistance. In the solution-treated condition, 800H and 800AT offer excellent creep and stress-rupture strength, and all three are listed as structural materials in ASME Boiler and Pressure Vessel Code sections I, III and VIII. Their chemical compositions are identical except for carbon content, and 800AT additionally contains up to 1% Al+Ti. Alloy 800 is generally used up to about 593 C, while 800H and 800AT are used where higher creep and stress-rupture strength is required at similar temperatures.