Iron-chromium-aluminum alloy and article and method therefor

Claim 2

A hot workable ferritic stainless steel alloy resistant to thermal cyclic oxidation and scaling at elevated temperatures and suitable for forming thereon an adherent textured aluminum oxide surface, the alloy consisting essentially of, by weight, 8.0-25.0% chromium, 3.0-8.0% aluminum, and an addition of at least 0.002% and up to 0.05% from the group consisting of cerium and lanthanum, neodymium and praseodymium, a total of all rare earths up to 0.060%, up to 4.0% silicon, 0.06% to 1.0% manganese and normal steelmaking impurities of less than 0.050% carbon, less than 0.050% nitrogen, less than 0.020% oxygen, less than 0.040% phosphorus, less than 0.030% sulfur, less than 0.50% copper, less than 1.0% nickel, and the sum of calcium and magnesium less than 0.005%, the remainder being iron.

Claim 3

The alloy as set forth in claim 1 stabilized with zirconium additions in amounts up to ##EQU7##

Claim 4

The alloy as set forth in claim 1 or 2 including niobium for stabilization and elevated temperature creep strength, in amounts up to ##EQU8##

Claim 5

The alloy as set forth in claim 1 wherein the rare earth addition is selected from the group consisting of cerium and lanthanum.

Claim 6

The alloy as set forth in claim 1 or 4 wherein minimum total amounts of the rare earth additions selected from the group consisting of cerium, lanthanum, or mixtures thereof are proportional to the chromium content as expressed by ##EQU9##

Claim 7

The alloy as set forth in claim 1 wherein minimum amounts of aluminum are based on the chromium content as expressed by ##EQU10##

Claim 8

The alloy as set forth in claim 1 having up to 3% silicon.

Claim 9

The alloy as set forth in claim 1 having about 0.10 to 0.50% manganese.

Claim 10

A hot workable ferritic stainless steel alloy resistant to thermal cyclic oxidation and scaling at elevated temperatures and suitable for forming thereon an adherent textured aluminum oxide surface, the alloy consisting essentially of, by weight, 12.0-23.0% chromium, from ##EQU11## up to 8.0% aluminum, and at least [%CR/2200]% of an addition from the group consisting of cerium and lanthanum, a total of all rare earths up to 0.050%, up to 3.0% silicon, 0.10 to 0.50% manganese, and normal steelmaking impurities of less than 0.030% carbon, less than 0.030% nitrogen, less than 0.010% oxygen, less than 0.030% phosphorus, less than 0.020% sulfur, less than 0.4% copper, less than 0.4% nickel, the sum of calcium and magnesium being less than 0.003%, the remainder being iron.

Claim 11

A hot workable ferritic stainless steel alloy resistant to thermal cyclic oxidation and scaling at elevated temperatures and suitable for forming thereon an adherent textured aluminum oxide surface, the alloy consisting essentially of, by weight, 12.0-23.0% chromium, from ##EQU11## up to 8.0% aluminum, and at least [%CR/2200]% of an addition from the group consisting of cerium and lanthanum, a total of all rare earths up to 0.050%, up to 3.0% silicon, 0.10 to 0.50% manganese, and normal steelmaking impurities of less than 0.030% carbon, less than 0.030% nitrogen, less than 0.010% oxygen, less than 0.030% phosphorus, less than 0.020% sulfur, less than 0.4% copper, less than 0.4% nickel, the sum of calcium and magnesium being less than 0.003%, the remainder being iron.

Claim 12

The alloy as set forth in claim 9 stabilized with zirconium additions in amounts up to ##EQU12##

Claim 13

The alloy as set forth in claim 9 or 10 including niobium for stabilization and elevated temperature creep strength, in amounts up to ##EQU13##

Claim 14

An oxidation resistant catalytic substrate comprising a hot workable ferritic stainless steel alloy having an adherent textured aluminum oxide surface thereon, said alloy being resistant to thermal cyclic oxidation and scaling at elevated temperatures, said alloy consisting essentially of, by weight, 8.0-25.0% chromium, 3.0-8.0% aluminum, and an addition of at least 0.002% and up to 0.050% from the group consisting of cerium, lanthanum, neodymium and praseodymium, a total of all rare earths up to 0.060%, up to 4.0% silicon, 0.06 to 1.0% manganese and normal steelmaking impurities of less than 0.050% carbon, less than 0.050% nitrogen, less than 0.020% oxygen, less than 0.040% phosphorus, less than 0.030% sulfur, less than 0.50% copper, less than 1.0% nickel, and the sum of calcium and magnesium less than 0.005%, the remainder being iron.

Claim 15

An oxidation resistant catalytic substrate comprising a hot workable ferritic stainless steel alloy having an adherent textured aluminum oxide surface thereon, said alloy being resistant to thermal cyclic oxidation and scaling at elevated temperatures, said alloy consisting essentially of, by weight, 8.0-25.0% chromium, 3.0-8.0% aluminum, and an addition of at least 0.002% and up to 0.050% from the group consisting of cerium, lanthanum, neodymium and praseodymium, a total of all rare earths up to 0.060%, up to 4.0% silicon, 0.06 to 1.0% manganese and normal steelmaking impurities of less than 0.050% carbon, less than 0.050% nitrogen, less than 0.020% oxygen, less than 0.040% phosphorus, less than 0.030% sulfur, less than 0.50% copper, less than 1.0% nickel, and the sum of calcium and magnesium less than 0.005%, the remainder being iron.

Claim 16

The substrate as set forth in claim 12 wherein the steel is stabilized with zirconium additions up to ##EQU14##

Claim 17

The substrate as set forth in claim 12 or 13 wherein the steel includes niobium additions in the melt composition up to ##EQU15## for stabilization and elevated temperature creep strength.

Claim 18

The substrate as set forth in claim 12 wherein the rare earth addition is from the group consisting of cerium and lanthanum.

Claim 19

The substrate as set forth in claim 12 or 15 wherein minimum total amounts of the rare earth additions selected from the group consisting of cerium, lanthanum, or mixtures thereof are proportional to the chromium content as expressed by ##EQU16##

Claim 20

The substrate as set forth in claim 12 or 16 wherein minimum amounts of aluminum are based on the chromium content as expressed by ##EQU17##

Claim 21

The substrate as set forth in claim 12 having up to 3% silicon.

Claim 22

The substrate as set forth in claim 12 having about 0.10 to 0.50% manganese.

Claim 23

An oxidation resistant catalytic substrate comprising a hot workable ferritic stainless steel alloy having an adherent textured aluminum oxide surface thereon, said alloy being resistant to thermal cyclic oxidation and scaling at elevated temperatures, said alloy consisting essentially of, by weight, 12.0-23.0% chromium, ##EQU18## up to 8% aluminum, and at least [%CR/2200]% of an addition from the group consisting of cerium and lanthanum, a total of all rare earths up to 0.050%, up to 3.0% silicon, 0.10 to 0.50% manganese and normal steelmaking impurities of less than 0.030% carbon, less than 0.030% nitrogen, less than 0.010% oxygen, less than 0.030% phosphorus, less than 0.020% sulfur, less than 0.40% copper, less than 0.40% nickel, and the sum of calcium and magnesium less than 0.003%, the remainder being iron.

Claim 24

An oxidation resistant catalytic substrate comprising a hot workable ferritic stainless steel alloy having an adherent textured aluminum oxide surface thereon, said alloy being resistant to thermal cyclic oxidation and scaling at elevated temperatures, said alloy consisting essentially of, by weight, 12.0-23.0% chromium, ##EQU18## up to 8% aluminum, and at least [%CR/2200]% of an addition from the group consisting of cerium and lanthanum, a total of all rare earths up to 0.050%, up to 3.0% silicon, 0.10 to 0.50% manganese and normal steelmaking impurities of less than 0.030% carbon, less than 0.030% nitrogen, less than 0.010% oxygen, less than 0.030% phosphorus, less than 0.020% sulfur, less than 0.40% copper, less than 0.40% nickel, and the sum of calcium and magnesium less than 0.003%, the remainder being iron.

Claim 25

The substrate as set forth in claim 20 stabilized with zirconium additions in amounts up to ##EQU19##

Claim 26

The substrate as set forth in claim 20 or 21 including niobium for stabilization and elevated temperature creep strength in amounts up to ##EQU20##

Claim 27

A catalyst system comprising an oxidation resistant catalytic substrate of claims 12 or 20.