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AssigneeArmco Steel Corporation
InventorsJerry L. Arnold, Joseph A. Douthett
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Internally nitrided ferritic stainless steel cold reduced strip and sheet and products fabricated therefrom having an elevated temperature creep strength and oxidation resistance superior to AISI Type 316 austenitic stainless steel, and good room temperature formability. A non-hardenble AISI Type 400 series ferritic stainless steel containing a nitride former (titanium, zirconium, hafnium, columbium, vanadium, tantalum or rare earth metals) in excess of the amount required to react completely with residual nitrogen and carbon in the steel is reacted with nitrogen internally by heat treatment in a nitrogen-hydrogen atmosphere at a temperature of at least about 800.degree. C but below that at which austenite will form under conditions precluding formation of chromium nitrides, chromium oxides, and austenite.
Internally nitrided substantially fully ferritic stainless steel cold reduced strip and sheet and products fabricated therefrom comprising a non-hardenable AISI Type 400 series ferritic stainless steel containing a nitride former chosen from the group consisting of titanium, zirconium, hafnium, columbium, vanadium, tantalum and rare earth metals, said nitride former being present in excess of the amount required to react completely with residual nitrogen and carbon in said steel, said excess nitride former being reacted with nitrogen internally to a depth sufficient to obtain an elevated temperature creep strength superior to that of AISI Type 316 austenitic stainless steel, by the 982.degree. C Sag Test defined herein, and an oxidation resistance superior to that of AISI Type 316 austenitic stainless steel, by the Cyclic Oxidation Resistance Test defined herein, said nitrided strip, sheet and fabricated products exhibiting good room temperature formability, substantial freedom from chromium nitrides and chromium oxides, and containing less than about 5% austenite.
Internally nitrided substantially fully ferritic stainless steel cast products comprising, in weight percent, about 16% to about 26% chromium, about 0.4% to about 5% silicon;
A method of producing internally nitrided substantially fully ferritic stainless steel strip, sheet and fabricated products having elevated temperature creep strength and oxidation resistance superior to those of AISI Type 316 austenitic stainless steel, by the 982.degree. C Sag Test defined herein, and by the Cyclic Oxidation Resistance Test defined herein, respectively, together with good room temperature formability, comprising the steps of providing a cold reduced substantially fully ferritic non-hardenable AISI Type 400 series stainless steel containing a nitride forming element chosen from the group consisting of titanium, zirconium, hafnium, columbium, vanadium, tantalum and rare earth metals, the nitride-former being present in excess of the amount required to react completely with residual nitrogen and carbon in said steel, and subjecting said strip, sheet and fabricated products to a nitriding heat treatment in a nitrogen-hydrogen atmosphere at a temperature of at least about 800.degree. C but below the temperature at which austenite will form, in accordance with the following equation, wherein titanium is an exemplary nitride forming element:
Dependencies are inferred from the claim text.