Method for reducing formation of electrically resistive layer on ferritic stainless steels

Patent metadata

Field	Value
Publication number	US-9580789-B2
Application number	US-201313873272-A
Country	US
Kind code	B2
Filing date	Apr 30, 2013
Priority date	Mar 6, 2007
Publication date	Feb 28, 2017
Grant date	Feb 28, 2017

Abstract

A method of reducing the formation of electrically resistive scale on a an article comprising a silicon-containing ferritic stainless subjected to oxidizing conditions in service includes, prior to placing the article in service, subjecting the article to conditions under which silica, which includes silicon derived from the steel, forms on a surface of the steel. Optionally, at least a portion of the silica is removed from the surface to placing the article in service. A ferritic stainless steel alloy having a reduced tendency to form silica on at least a surface thereof also is provided. The steel includes a near-surface region that has been depleted of silicon relative to a remainder of the steel.

First claim

I claim:

1. A method of reducing the tendency for formation of an electrically resistive silica layer on an article comprising a silicon-containing ferritic stainless steel when the article is subjected to high temperature conditions in use, the method comprising:
prior to placing the article in use, subjecting the article to an oxygen-containing atmosphere under conditions wherein silicon is selectively segregated from the steel to a surface of the steel without segregating chromium and other alloying elements in the steel to the surface of the steel,
wherein the oxygen-containing atmosphere is a gaseous atmosphere comprising oxygen at a partial pressure not greater than 1×10 −20 atmosphere; and
wherein the silicon is oxidized to form a silica layer on the surface of the steel and the silica layer is not removed from the surface.

2. The method of claim 1 , wherein subjecting the article to an oxygen-containing atmosphere under conditions wherein silicon is selectively segregated from the steel to a surface of the steel comprises:
heating the article in the oxygen-containing atmosphere.

3. The method of claim 2 , wherein the method depletes a portion of the silicon from a near-surface region of the steel.

4. The method of claim 3 , wherein the steel comprises at least 0.15 weight percent silicon.

5. The method of claim 3 , wherein the steel comprises, in weight percentages: 15 to 30 chromium; 0 to 6 molybdenum; up to 2 manganese; up to 1 nickel; up to 1 silicon; up to 1 aluminum; up to 0.1 carbon; up to 0.1 nitrogen; up to 1 titanium; up to 1 niobium; up to 1 zirconium; up to 1 vanadium; iron; and incidental impurities.

6. The method of claim 3 , wherein the steel is selected from the group consisting of AISI Type 430 stainless steel, AISI Type 439 stainless steel, AISI Type 441 stainless steel, AISI Type 444 stainless steel, and UNS S44627 stainless steel.

7. The method of claim 2 , wherein heating the article comprises heating the article at a temperature greater than a temperature to which the article will be subjected in service.

8. The method of claim 2 , wherein heating the article comprises heating the article at a temperature at least 100° C. greater than a temperature to which the article will be subjected in service.

9. The method of claim 2 , wherein heating the article comprises heating the article at a temperature at least 200° C. greater than a temperature to which the article will be subjected in service.

10. The method of claim 2 , wherein heating the article comprises heating the article at a temperature of at least 600° C.

11. The method of claim 2 , wherein heating the article comprises heating the article at a temperature in the range of 600° C. to 1100° C.

12. The method of claim 2 , wherein heating the article comprises heating the article at a temperature in the range of 600° C. to 1100° C.

13. The method of claim 2 , wherein the oxygen-containing oxidizing atmosphere is a gaseous atmosphere consisting essentially of hydrogen, a partial pressure of no more than 1×10 −20 atmosphere oxygen, and incidental impurities.

14. The method of claim 13 , wherein heating the article comprises heating the article at a temperature in the range of 600° C. to 1100° C.

15. The method of claim 2 , wherein heating the article in an oxygen-containing atmosphere comprises heating the article at a temperature of at least 600° C. for at least 2 minutes time-at-temperature.

16. The method of claim 2 , wherein the silica layer formed on the surface is a layer having a thickness of at least 0.5 microns per millimeter thickness of the article.

17. The method of claim 1 , wherein the article is selected from the group consisting of a mill product, a sheet, and a fuel cell interconnect.

18. A method of treating a fuel cell interconnect comprising a silicon-containing ferritic stainless steel to reduce the tendency for formation of an electrically resistive silica scale on a surface of the interconnect when subjected to high temperature conditions in service, the method comprising:
prior to placing the interconnect in service, subjecting the interconnect to an oxygen-containing atmosphere under conditions wherein silica including silicon derived from the stainless steel forms on a surface of the stainless steel and wherein chromium and other alloying elements in the steel do not segregate to the surface of the steel;
wherein the oxygen-containing atmosphere is a gaseous atmosphere comprising oxygen at a partial pressure not greater than 1×10 −20 atmosphere; and
wherein the silica is not removed from the surface of the stainless steel.

19. The method of claim 18 , wherein the stainless steel is a silicon-containing ferritic stainless steel comprising, in weight percentages: 15 to 30 chromium; 0 to 6 molybdenum; up to 2 manganese; up to 1 nickel; up to 1 silicon; up to 1 aluminum; up to 0.1 carbon; up to 0.1 nitrogen; up to 1 titanium; up to 1 niobium; up to 1 zirconium; up to 1 vanadium; iron; and incidental impurities.

20. The method of claim 18 , wherein the stainless steel is selected from the group consisting of AISI Type 430 stainless steel, AISI Type 439 stainless steel, AISI Type 441 stainless steel, AISI Type 444 stainless steel, and UNS S44627 stainless steel.

Assignees

• Ati Properties Llc

Inventors

• Rakowski James M

Classifications

• H01M2008/1293

  Fuel cells with solid oxide electrolytes · CPC title

• H01M8/0228

  in the form of layered or coated products · CPC title

• C21D3/02

  Extraction of non-metals · CPC title

• C21D1/74 Primary

  Methods of treatment in inert gas, controlled atmosphere, vacuum or pulverulent material · CPC title

• C21D6/008

  containing Si · CPC title