US1736921A

US1736921A - Case nitrification of steel

Info

Publication number: US1736921A
Application number: US254162A
Authority: US
Inventors: Augustus B Kinzel
Original assignee: ELECTRO METALLURG CO
Current assignee: ELECTRO METALLURG CO; ELECTRO METALLURGICAL Co
Priority date: 1928-02-13
Filing date: 1928-02-13
Publication date: 1929-11-26
Anticipated expiration: 1946-11-26

Description

Patented Nov. 26, 1929.-

UNITED STATES PATENT OFFICE aueusrus 3. xINzEL, or BAYSIDE, mew YORK, Ass1enon. 'ro-nnmo METALLUR- GICL'L COMPANY, A CORPORATION or wear 'vmemm case mrnrrrcarron or swam.

HoDrawing. Application filed. February 13, 1928,

, 5 ammonia.

This application is a continuation in art of my application, Serial No. 214,447, led

alloys containing at least a critical amount August 20, 1927', which relates to methods of nitrogenizin articles consisting of ferrous of vanadium to produce thereon a hard sur face containig vanadium and nitrogen.

Some of the ferrous materials which otherwise have desirable properties for use in machine parts or other structural elementscannot be used where they are subject to wear because a wearing surface of satisfactory hardness cannot be given them economically. For such purpose, a surface hardness of 700 Brinell is desired and a hardness of 900 Brinell or higher is preferred.

I have discovered that surfaces of such degree of hardness can be produced by nitrogenizing ferrous articles in which the vanadium content is confined to the surface. I

have also discovered that the hardness of the nitrogenized coating can be'regulated to a considerable extent by varying the content of vanadium not present as carbide in the surface layer. That is to say, when the con tent of uniformly distributed non-carbide vanadium (designated herein unbound vanadium) is insuflicient to bring about maximum hardening, the hardness of the nitrogenized coating can be increased by increasing the concentration of unbound vana- 'dium in the surface layer of the article.

.The layer of hard'nitrogenized material is usually thin and the hardness is greater with larger amounts of unbound vanadium up to about 0.5% of unbound vanadium. I have discovered that when the surfaces of ferrous articles are enriched in vanadium'up to or beyond the critical amount and then the articles are subjected to heat in the presence of ammonia or other nitrogenizing compounds at temperatures of about 500 to 580 C. the desired surface hardness is produced without materially affecting the properties of the core of the material.

Serial No. 254,162. Renewed June 24, 1929.

I usually prefer to remove carbon from the surface of the material, if carbon is present, and then to incorporate vanadium into the surface before nitrogenizing, but decarburizing of the surface is not always necessary, and may be omitted where only a small addition of vanadium is required to produce the desired vanadium-containing hardening constituent. Decarburization may also be omitted where only a small amount of carbon is present or where a relatively large addition of vanadium is practicable to overcome the effect of carbon. I usually prefer to heat the article in the presence of hydrogen to effect the-surface decarburizavanadium in a neutral or reducing atmosphere to affect the introduction of vanadium,

but other means of decarburization and other means of incorporating vanadium into the surface skin may be used. Decarburization alone will sufliciently increase the concentration of unbound vanadium in some cases where the article is composed of alloy relatively rich in vanadium. I

My invention will be more fully understood by referring to the following examples. An article containing 0.5% vanadium; and 1.0 carbon was heated in an atmosphere of hydrogen to 700 C. for 2 hours. Ammonia gas was substituted for the hydrogen and a temperature of 510 C. was maintained for about 16 hours.- The surface of this piece hada hardness corresponding to about 900 Brinell. Another piece of the same steelwas treated in'like manner inthe presence of ammonia without decarburizing the surface. Much less hardness was im arted to the second piece than to the piece in which the ratio of vanadium to carbon was increased.

The critical amount of vanadium as stated in my prior application is about 0.3% to 0.5% unbound vanadium In the practice of my present invention, only the surface layer is enriched with vanadium to the extent required for producing the desired hardening effect when the article is nitrogenized.

The presence of vanadium in the original material is not necessary to produce the desired hardening surface as will appear from the temperature was reduced to 510 C. and

the heating was continued for 16 hdurs in the presence of ammonia. The surface of this piece was harder than 900 Brinell and there was no material change in the properties of the core of the material.

Should I prefer to use aluminum instead of vanadium as the nitrifiable element I may do so. A ferrous alloy may be aluminized in any desired manner but I prefer to heat the ferrous alloy in contact with aluminum powder under neutral or reducing conditions at a temperature of about 500 to 800 C. I have obtained satisfactory results when the ferrous alloy was treated with aluminum for one half to two hours at 550 C., but other temperatures and times may be used. If, by chance, the concentration of aluminum in the surface becomes too great, I may reduce it to the desired value by soaking the ferrous alloy at a suitable temperature, as for example about 900 C. The surface-aluminized ferrous alloy is then heated to about 500 to 580 C. in the presence of a substance, such as ammonia, that yields nitrogen to the material. This treatment provides a hard nitrogenized compound only as a surface layer and the properties of the core of the material will not be detrimentally affected. The nitrogenization preferably is carried out at a temperature not materially above 580 (3., and under these conditions there is no serious embrittling of the interior portions of the member treated.

I have previously described the use of aluminum as a nitrifiable element in my copending application Serial No. 209,184, filed July 28, 1927, from which this description is taken.

In the foregoing examples, the content of unbound vanadium in the surface of the ar-' ticle was increased to the point where a very high degree of hardness was produced when the piece was nitrogenized, but other degrees of hardness may be produced by regulating the times and temperatures of treatment with the decarburizing agent, the vanadium introducing agent, and with the nitrogenizing agent.

a partial decarburization at the surface will produce an enrichment in unbound vanadium and a treatment with the nitrogenizing agent will then produce the desired hardening. Other modifications within the scope of my invention will suggest themselves to those skilled in the art. Therefore, I desire to be limited only by the prior art and by the invent-ion as defined in the annexed claims.

I claim as my invention:

1. The method ofmaking a hardened surface coating on an article composed of fer rous material which comprises enriching the surface of the article in unbound vanadium and then subjecting the article to heat in the presence of a material that yields nitrogen to the coating.

2. The method of making a hard surface coating on an article composed of ferrous material which comprises heating in anonoxidizing atmosphere in the presence of vanadium, thereby introducing vanadium in a surface layer and then heating in the presence of a material that yields nitrogen to the material.

3. The method of making a hard surface coating on .an article composed of ferrous material which comprises heating in an nonoxidizing atmosphere in the presence of vanadium, thereby introducing vanadium in the surface lager and then heating to about 500 to 580 in the presence of ammonia.

4. The method of making a hard surface coating on an article composed of ferrous material which comprises decarburizing a surface layer, enriching said layer in unbound vanadium and then heating in the presence of a material that yields nitrogen to the article.

5. The method of making a hard surface coating on an article composed of a ferrous material which comprises successively heating the article in the presence of a decarburizing agent and vanadium in a nonoxidizing atmosphere to temperatures sufficient to decarburize a surface layer and to introduce vanadium therein and then heating to about 500 to 580 C. in the presence of ammonia.

6. The method of making a hard surface coating on an article composed of .a ferrous material which comprises heating the article in the presence of hydrogen to a temperature sufiicient to remove carbon from at least a surface layer thereof, heating in the presence of vanadium to a temperature suflicient to introduce vanadium in the surface and then heating to 500 to 580 C. in the presence of ammonia.

7. The method of making a hard surface coating on an article composed of a ferrous material which comprises heating the article to about 700 C. for about 2 hours in the presence of hydrogen, heating in the presence of vanadium to about 900 C. for 2 hours and then heating in the presence of ammonia to about 500 to 580 C. for a time suflicient to make a hard surface layer on the article.

8..The method of making a hard surface coating on anarticle containin iron, va-

nadium and carbon which comprises depriving only a surface layer of the alloy article of carbon ,to enrich the surface in unbound vanadium and then heating in the presence of a material that ields nitrogen.

9. The method of with vanadium to an extent equal to or greater than the critical amount suflicient to form a hardened nitrogenized compound which comprises heating in the presence of a nitrogen containing compound to about 500 to 580 C.

10. An articlecomposed -of a core of ferrous metal and a surface layer enriched with vanadium, said surface layer being integral with the core and containing a constltuent that is formed by nitrogenizing a ferrosvanadium alloy containing vanadium in solid solution.

11. An article composed of a core of ferrous metal and a surfacelayer enriched with vanadium, said surface layer being integral with the core and containing a constituent that is formed by nitrogenizing a ferro-vanadium alloy containing vanadium in excess of that required to form carbides.v

12. An article composed of a core of ferrous metal and a surface layer enriched with vanadium and .containing unbound vanadium in excess of .3%, said layer'being integral with the core and containing nitro; gen, and said core being softer than the exterior portion.

13. The method of making a hardened surface coating on an article composedof a ferrous material which comprises modifying the surface of the article with respect to its content of a nitrifiable alloy constituent so as to produce a surface layer containing at least a critical amount of the nitrifiable alloy and subjecting the article to heat in the presence of a material that yields nitrogen to the coatin 14. An art1cle composed of a core of ferrous material and a surface layer enriched with a nitrifiable alloy constituent, said surface layer being integral with the core and containing a constituent that is formed by nitrogenizing a ferrous alloy containin a nitrogenizable constituent in solid solutlon.

I testimony whereof, I afiix in Si ature.

AUGUSTUS B. I ZEL.

making a hard surface coating on an article composed of ferrous 7 material which has a surface layer enriched