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Wednesday, June 05

Recent Development Activities for Creep-Resistant,
Alumina-Forming Austenitic Stainless Steel Alloys

Yukinori Yamamoto , Materials Science and Technology Division, ORNL
Materials and Chemistry Seminar Series
10:00 AM — 11:00 AM, Building 4500-N, Weinberg Auditorium
Contact: Adrian Sabau (sabaua@ornl.gov), 865.241.5145

Abstract

This talk will summarize our recent progress in development of creep-resistant, alumina-forming austenitic (AFA) stainless steel alloys at Oak Ridge National Laboratory. The AFA alloys possess a unique combination of an excellent oxidation resistance at elevated temperatures and a good creep resistance comparable to similar class of commercially available austenitic heat-resistant steel alloys, together with inexpensive material cost. The base alloy compositions are Fe-(14-19)Cr-(12-32)Ni-(2.5-4)Al-(1-3)Nb, wt%, with minor alloying additions of Mo, W, Si, Mn, Cu, P, C, and B, which are carefully balanced to achieve such unique properties. The formation of alumina-scales in AFA alloys results in superior oxidation resistance compared to conventional chromia-forming stainless steels, especially in water-vapor containing environments. Improved creep properties rely on nano-scale MC (M: mainly Nb) or M23C6 (M: mainly Cr) type carbide dispersions which are designed through a guidance of computational thermodynamic tools. Recent activities focus on the development of new types of AFA alloys. Cast versions of AFA alloys have been developed with creep resistance comparable to that of a traditional chromia-forming, cast austenitic stainless steel (HK) at temperatures up to 750oC. Wrought AFA alloys with additional strengthening from coherent Ni3(X) dispersion, so-called "Alumina-forming Fe-base Superalloy", have also been developed with drastically improved creep resistance in the range of 700oC to 750oC without losing alumina-scale formability. Activities for AFA commercialization with various commercial partners will also be presented.