Alumina-Forming Austenitic Alloys Resist High-Temperature Corrosion

Oak Ridge National Laboratory (ORNL) has developed a new class of high temperature alumina-forming austenitic (AFA) stainless steel (SS) alloys that deliver both superior corrosion and creep resistance for many industrial environments. The alloys' composition range includes Fe (35 to 63 wt%), Ni (12 to 35 wt%), Cr (12 to 15 wt%), Al (2.5 to 4 wt%), Nb (0.6 to 3 wt%), and manganese (Mn) (0.0 to 5 wt%). The Al, Cr, Mn, and Ni are balanced to maintain the austenitic microstructure, and carbide precipitates are incorporated for creep strength. the AFA alloys exhibited superior high-temperature corrosion resistance vs. chromia-formers in water vapor, steam, and sulfidation/oxidation conditions. Creep data for AFA alloys relative to tabulated data for commercial chromia forming wrought and cast alloys were also collected. The wrought AFA alloys showed creep strength properties comparable to advanced commercial austenitic SS. The AFA SS alloys are also being evaluated under a wide range of sulfidation carburization, nitridation, and molten salt/deposit conditions. Overall, the AFA SS alloy family showed high-temperature corrosion resistance advantages for many, but not all, energy conversion, combustion system, and chemical/petrochemical process environments.