US2013309125A1PendingUtilityA1

Oxidation resistant ferritic stainless steels

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Assignee: ATI PROPERTIES INCPriority: Sep 3, 2003Filed: Jul 26, 2013Published: Nov 21, 2013
Est. expirySep 3, 2023(expired)· nominal 20-yr term from priority
Inventors:James M. Rakowski
C25F 3/00Y02E60/50C22C 38/50Y02P70/50C23C 8/18C22C 38/02C22C 38/06Y10T29/49108C22C 38/001H01M 8/021C22C 38/18C22C 38/58C22C 38/005C22C 38/04H01M 8/0223C25F 3/24H01M 8/0204
59
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Claims

Abstract

A method for making a ferritic stainless steel article having an oxidation resistant surface includes providing a ferritic stainless steel comprising aluminum, at least one rare earth metal and 16 to less than 30 weight percent chromium, wherein the total weight of rare earth metals is greater than 0.02 weight percent. At least one surface of the ferritic stainless steel is modified so that, when subjected to an oxidizing atmosphere at high temperature, the modified surface develops an electrically conductive, aluminum-rich, oxidation resistant oxide scale comprising chromium and iron and a having a hematite structure differing from Fe 2 O 3 , alpha Cr 2 O 3 and alpha Al2O3. The modified surface may be provided, for example, by electrochemically modifying the surface, such as by electropolishing the surface.

Claims

exact text as granted — not AI-modified
What is claimed is: 
     
         1 . A ferritic stainless steel comprising aluminum, at least one rare earth metal and 16 to less than 30 weight percent chromium, wherein the total weight of rare earth metals is greater than 0.02 weight percent, the ferritic stainless steel further comprising at least one modified surface, wherein when subjected to an oxidizing atmosphere at high temperature, the at least one modified surface develops an electrically conductive, aluminum-rich, oxidation resistant oxide scale comprising chromium and iron and a having a hematite structure differing from Fe 2 O 3 , alpha Cr 2 O 3  and alpha Al 2 O 3 . 
     
     
         2 . The ferritic stainless steel of  claim 1 , wherein lattice parameters a o  and c o  of the oxide scale differ from a o  and c o  of Fe 2 O 3 , alpha Cr 2 O 3  and alpha Al 2 O 3 . 
     
     
         3 . The ferritic stainless steel of  claim 1 , wherein the at least one modified surface develops the oxide scale when heated in an oxidizing atmosphere at a temperature in the range of 750° C. to 850° C. 
     
     
         4 . The ferritic stainless steel of  claim 1 , wherein the at least one modified surface develops the oxide scale when heated in an oxidizing atmosphere for at least 100 hours at a temperature in the range of 750° C. to 850° C. 
     
     
         5 . The ferritic stainless steel of  claim 1 , wherein the oxide scale is characterized by a o  in the range of 4.95 to 5.04 Å and c o  in the range of 13.58 to 13.75 Å. 
     
     
         6 . The ferritic stainless steel of  claim 1 , wherein the oxide scale is characterized by nominal lattice parameters a o =4.98 Å and c o =13.57 Å. 
     
     
         7 . The ferritic stainless steel of  claim 1 , wherein the at least one modified surface comprises at least one electrochemically modified surface. 
     
     
         8 . The ferritic stainless steel of  claim 7 , wherein the at least one electrochemically modified surface comprises at least one electropolished surface. 
     
     
         9 . The ferritic stainless steel of  claim 8 , wherein the at least one electropolished surface develops the oxide scale when heated in an oxidizing atmosphere for at least 100 hours at a temperature in the range of 750° C. to 850° C., and wherein the oxide scale is characterized by a o  in the range of 4.95 to 5.04 Å and c o  in the range of 13.58 to 13.75 Å. 
     
     
         10 . The ferritic stainless steel of  claim 9 , wherein the oxide scale is characterized by nominal lattice parameters a o =4.98 Å and c o =13.57 Å. 
     
     
         11 . A ferritic stainless steel comprising aluminum, at least one rare earth metal and 16 to less than 30 weight percent chromium, wherein the total weight of rare earth metals is greater than 0.02 weight percent, and wherein the ferritic stainless steel further comprises at least one electrochemically modified surface. 
     
     
         12 . The ferritic stainless steel of  claim 11 , wherein the at least one electrochemically modified surface is at least one electropolished surface. 
     
     
         13 . The ferritic stainless steel of  claim 12 , wherein the at least one electropolished surface develops an aluminum-rich oxide scale including iron and chromium and having a hematite structure, a o  in the range of 4.95 to 5.04 Å and c o  in the range of 13.58 to 13.75 Å when heated for at least 100 hours at 750° C. to 850° C. in an oxidizing atmosphere. 
     
     
         14 . The ferritic stainless steel of  claim 12 , wherein the oxide scale is characterized by nominal lattice parameters a o =4.98 Å and c o =13.57 Å. 
     
     
         15 . The ferritic stainless steel of  claim 11 , comprising 16 up to 19 weight percent chromium. 
     
     
         16 . The ferritic stainless steel of  claim 11 , comprising at least 0.2 weight percent aluminum. 
     
     
         17 . The ferritic stainless steel of  claim 11 , comprising 0.2 up to 1.0 weight percent aluminum. 
     
     
         18 . The ferritic stainless steel of  claim 11 , wherein the total weight of rare earth metals in the ferritic stainless steel is greater than 0.02 up to 1.0 weight percent. 
     
     
         19 . The ferritic stainless steel of  claim 11 , wherein the ferritic stainless steel comprises at least one rare earth metal selected from cerium, lanthanum, yttrium and hafnium. 
     
     
         20 . The ferritic stainless steel of  claim 11 , wherein the total weight of rare earth metals in the ferritic stainless steel is greater than 0.02 up to 1.0 weight percent. 
     
     
         21 . The ferritic stainless steel of  claim 11  comprising, in weight percent, 18 up to 22 chromium, 0.4 to 0.8 aluminum and 0.02 to 0.2 rare earth metals. 
     
     
         22 . The ferritic stainless steel of  claim 11 , further comprising, in weight percent, up to 3 nickel, up to 3 manganese, up to 0.7 silicon, up to 0.07 nitrogen, up to 0.07 carbon and up to 0.5 titanium. 
     
     
         23 . The ferritic stainless steel of  claim 11 , comprising, in weight percentages, about 22 chromium and about 0.6 aluminum, cerium and lanthanum, wherein the sum of the weights of cerium and lanthanum is up to about 0.10. 
     
     
         24 . The ferritic stainless steel of  claim 11 , comprising 16 to less than 30 weight percent chromium, at least 0.2 weight percent aluminum, and at least one rare earth metal, wherein the total weight of rare earth metals is greater than 0.02 up to 1.0 weight percent. 
     
     
         25 . The ferritic stainless steel of  claim 11 , wherein the at least one electrochemically modified surface exhibits improved resistance to oxidation when subjected to atmosphere and temperature conditions characteristic of the operating conditions in a solid oxide fuel cell. 
     
     
         26 . The ferritic stainless steel of  claim 12 , wherein the at least one electropolished surface has oxidation resistance in air at about 750° C. characterized by log k p  less than −9.1 g 2 /cm 4  h. 
     
     
         27 . The ferritic stainless steel of  claim 12 , wherein the at least one electropolished surface has oxidation resistance in air at about 850° C. characterized by log k p  less than −8.5 g 2 /cm 4  h. 
     
     
         28 . An article of manufacture comprising the ferritic stainless steel of  claim 1 . 
     
     
         29 . The article of manufacture of  claim 28 , wherein the article of manufacture is selected from a fuel cell, a solid oxide fuel cell, a planar solid oxide fuel cell, a fuel cell interconnect, a high-temperature manufacturing apparatus, a high-temperature handling apparatus, a calcining apparatus, a glass making apparatus, a glass handling apparatus and a heat exchanger component. 
     
     
         30 . An article of manufacture comprising the ferritic stainless steel of  claim 11 . 
     
     
         31 . The article of manufacture of  claim 30 , wherein the article of manufacture is selected from a fuel cell, a solid oxide fuel cell, a planar solid oxide fuel cell, a fuel cell interconnect, a high-temperature manufacturing apparatus, a high-temperature handling apparatus, a calcining apparatus, a glass making apparatus, a glass handling apparatus and a heat exchanger component.

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