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A family of inexpensive, Al2O3-forming, high-creep strength austenitic stainless steels has been developed. The alloys are based on Fe-20Ni-14Cr-2.5Al weight percent, with strengthening achieved through nanodispersions of NbC. These alloys offer the potential to substantially increase the operating temperatures of structural components and can be used under the aggressive oxidizing conditions encountered in energy-conversion systems. Protective Al2O3 scale formation was achieved with smaller amounts of aluminum in austenitic alloys than previously used, provided that the titanium and vanadium alloying additions frequently used for strengthening were eliminated. The smaller amounts of aluminum permitted stabilization of the austenitic matrix structure and made it possible to obtain excellent creep resistance. Creep-rupture lifetime exceeding 2000 hours at 750 degrees C and 100 megapascals in air, and resistance to oxidation in air with 10% water vapor at 650 degrees and 800 degrees C, were demonstrated.

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Research Summary high-temperature AlloysHow would you… …describe the overall signifi cance of this paper?Alumina-forming austenitic stainless steels hold the potential to permit signifi cantly increased operating temperatures in aggressive high-temperature oxidizing environments encountered in energy conversion and chemical process industry applications.…describe this work to a materials science and engineering professional with no experience in your technical specialty?We have discovered that creepresistant, austenitic stainless steels capable of protective aluminumoxide scale formation, rather than conventionally used chromium-oxide scales, are feasible. This results in signifi cantly improved oxidation resistance and higher-temperature capability in many industrially relevant environments. …describe this work to a layperson?This paper describes the development of a new type of stainless steel with improved corrosion resistance for hightemperature use in power generation. The corrosion protection is derived from aluminum additions to the alloy instead of typically used chromium additions.Author's Note: Part of this research summary is based on a recent review paper (see Reference 1) and fi ndings fi rst reported in References 2-7.

A family of creep-resistant, alumina-forming austenitic (AFA) stainless steel alloys is under development for structural use in fossil energy conversion and combustion system applications. The AFA alloys developed to date exhibit comparable creep-rupture lives to state-of-the-art advanced austenitic alloys, and superior oxidation resistance in the~923 K to 1173 K (650°C to 900°C) temperature range due to the formation of a protective Al 2 O 3 scale rather than the Cr 2 O 3 scales that form on conventional stainless steel alloys. This article overviews the alloy design approaches used to obtain high-temperature creep strength in AFA alloys via considerations of phase equilibrium from thermodynamic calculations as well as microstructure characterization. Strengthening precipitates under evaluation include MC-type carbides or intermetallic phases such as NiAl-B2, Fe 2 (Mo,Nb)-Laves, Ni 3 Al-L1 2 , etc. in the austenitic single-phase matrix. Creep, tensile, and oxidation properties of the AFA alloys are discussed relative to compositional and microstructural factors.