High Nb, Ta, and Al Creep- and Oxidation-Resistant Austenitic Stainless Steels

An austenitic stainless steel HTUPS alloy consisting essentially of, in weight percent:

• 15 to 30 Ni;
• 10 to 15 Cr;
• 2 to 3.5 Al;
• greater than 1, up to 5 total of at least one element selected from the group consisting of Nb and Ta;
• no more than 0.3 of combined Ti+V;
• up to 3 Mo;
• up to 3 Co;
• up to 1 W;
• up to 0.5 Cu;
• up to 4 Mn;
• up to 1 Si;
• 0.05 to 0.15 C;
• up to 0.15 B;
• up to 0.05 P;
• up to 1 total of at least one element selected from the group consisting of Y, La, Ce, Hf, and Zr;
• less than 0.05 N;
• and
• base Fe,
• wherein the weight percent Fe is greater than the weight percent Ni wherein said alloy forms an external continuous scale comprising alumina, nanometer scale sized particles distributed throughout the microstructure, said particles comprising at least one composition selected from the group consisting of NbC and TaC, and a stable essentially single phase fcc austenitic matrix microstructure, said austenitic matrix being essentially delta-ferrite-free and essentially BCC-phase-free.

An austenitic stainless steel HTUPS alloy consisting essentially of, in weight percent:

• 15 to 30 Ni;
• 10 to 15 Cr;
• greater than 3.5, up to 5 Al;
• greater than 1, up to 5 total of at least one element selected from the group consisting of Nb and Ta;
• no more than 0.3 of combined Ti+V;
• up to 3 Mo;
• up to 3 Co;
• up to 1 W;
• up to 0.5 Cu;
• up to 4 Mn;
• up to 1 Si;
• 0.05 to 0.15 C;
• up to 0.15 B;
• up to 0.05 P;
• up to 1 total of at least one element selected from the group consisting of Y, La, Ce, Hf, and Zr;
• less than 0.05 N;
• and
• base Fe,
• wherein the weight percent Fe is greater than the weight percent Ni wherein said alloy forms an external continuous scale comprising alumina, nanometer scale sized particles distributed throughout the microstructure, said particles comprising at least one composition selected from the group consisting of NbC and TaC, and a stable essentially single phase fcc austenitic matrix microstructure, said austenitic matrix being essentially delta-ferrite-free and essentially BCC-phase-free.