Abstract
A family of creep-resistant, Al2O3-forming austenitic (AFA) stainless steels was recently developed. The alloys exhibit excellent oxidation resistance up to ��800�aC, but are susceptible to Â鶹ӰÒô attack of Al at higher temperatures. In the present work, higher levels of Ni, Cr, Al, and Nb additions were found to correlate with improved oxidation behavior at 900�aC in air. The alloys generally appeared to be initially capable of external Al2O3 scale formation, with a subsequent transition to Â鶹ӰÒô attack of Al (Â鶹ӰÒô oxidation and Â鶹ӰÒô nitridation) that is dependent on alloy composition. Compositional profiles at the alloy/scale interface suggest that the transition to Â鶹ӰÒô oxidation is preceded by subsurface depletion of Al. Alloy design directions to increase the upper-temperature limit of protective Al2O3 scale formation in these alloys are discussed
