US1706130A - Heat-resisting material - Google Patents

Description

Patented Mar. 19, 1929.

UNITED STATES WILLIAM E. RUDER, OF SCHENECTADY, NEW YORK, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

HEAT-RZESISTING- MATERIAL.

No Drawing.

My invention relates to heat resisting materials and has for its object the provision of a metal, which may be an alloy, capable of withstanding exceptionally high temperatures for long periods of time without appreciable deleterious effects from oxidation and corrosion.

Aluminum added to various alloys of iron, such as iron and chromium, iron and nickel or an alloy of iron with both chromium and nickel, produces an alloy having exceptional heat resisting qualities. It may e exposed to very high temperatures, in the neighborhood of 1200 C. for long periods of time without showing appreciable oxidation or corrosion. Such an alloy is described and claimed in a copending application Serial No. 478,422 to Gerald R. Brophy, filed June 17, 1921, Patent Number 1,638,805, of June 28, 1927, and assigned to the same assignee as this invention. The aluminum, however, tends to make the alloy somewhat hard and brittle and thereby reduces its malleability and ductility so that more or less difiiculty is experienced in working it or drawing it into wire.

In one of its aspects my invention relates to the production of metallic articles which are shaped by drawing or otherwise working the metal and which must be capable of withstanding high temperatures. In carrying out my invention I complete the drawing or other working operations of the metal before adding the aluminum, the metal then being easily worked. Thereafter, a surface protective coating of an aluminum alloy is formed on the completed article.

In accordance with my invention I form the article from a base metal consisting of an alloy of iron with another metal, such as chromium or nickel. Preferably an iron chromium alloy is used such as is sometimes known as stainless iron or steel. This alloy may contain from 10 to 30% or more of chromium and may be freely drawn or worked into the desired shape. After the article. is formed, it is subjected to a heat treatment in the presence of aluminum whereby the aluminum is caused to penetrate or alloy with the surface of the article so as to form a protective coating or surface layer of an alloy of iron, chromium and aluminum.

The aluminum may be applied and caused to penetrate the surface of the article in any suitable manner. For example where the shape of the article permits, it may be placed Application filedl September 14, 1925. Serial No. 56,204.

in an oven and surrounded by a powdered mixture of aluminum with sal ammoniac and zinc. The oven is then closed and slowly rotated, a temperature of about 450 C. being maintained. This treatment is continued for about two hours after which the article is taken out and fired at a temperature of 700 to 800 C. for about 15 or 20 minutes. This process is described and claimed in Patent No. 1,155,974 to Van Aller. For wires, however, also for certain tubes, the aluminum may be more satisfactorily applied by means of the dipping process in accordance with which the Wire is passed through a bath of molten aluminum and thereafter fired at a suitable temperature, as described and claimed in Patent #1,409,0l7 to Ortiz.

Furthermore, for complicated shapes or fabricated articles, such as gas mantles, it may be desirable to apply the aluminum by means of a spraying process whereby the powdered aluminum is mixed with a suitable liquid binder. Such a process is described and claimed in a copending application, Serial No. 19,999 to Goodwin H. Howe, filed April 1, 1925, Patent Number 1,655,269 of anuary 3, 1928, and assigned to the same assignee as this invention. In accordance with this process the powdered aluminum is mixed with a solution of nitro-cellulose and amyl acetate or wood alcohol and the mixture applied to the surface of the article by means of a brush or by spraying, care being taken to apply an even coating, and the surface of the article having been thoroughly cleaned by pickling or sand blasting. After the binder has dried, the article is fired at a suitable temperature, which may be from 750 to 900 C. for about an hour.

Any suitable process of applying the aluminum to the surface of the article may be used, the important feature of my invention being that the aluminum is not mixed with the other metals upon the formation of the alloy as has heretofore been the practice, but is added subsequently after the drawing or working operation has been performed.

The chromium seems to have the effect of dimlnishing considerably the rate of diffusion of the aluminum into the interior of the base metal of the article which would ordinarily take place after continued use if a base metal of iron alone were used. This diffusion or penetration of the aluminum tends to gradually decrease the proportion of aluminum at the surface and thus gradually leaves the surface unprotected so that destructive oxidation would eventually take place it preventive measures were not taken.

It will be understood that my invention is {not limited in respect to the particular metals employed or to their proportions or methods of handling except in so far as it is limited by the scope of the claims annexed hereto.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. A heat resisting metallic article consisting predominantly of iron having a surface layer alloyed with aluminum to form a. heat resisting coating and an interior portion substantially free from aluminum and containing a material preventing penetration of the aluminum into the interior of the article upon exposure to high temperatures.

2. A heat resisting metallic article consistiron, ch -omium and aluminum, the interior portions of said article being composed of a malleable alloy of iron and chromium;

4. A heat resisting metallic article made of a malleable alloy of iron and chromium having, its surface metal alloyed with aluminum to form a protective coatin In witness whereof, I have hereunto set my hand this 11th day of September, 1925.

WILLIAM E, RUDER.