US1977280A - Case-hardening - Google Patents

Description

Patented Oct. 16, 1934 I 1,977,280 CASE-HARDENING Augustus B. Kinzel, Beechhurst, Long Island, N. Y.', assignor to Electro Metallurgical Company, a corporation of West Virginia No Drawing.

Application August 21, 1931,

Serial No. 558,631

1 Claim.

The invention relates to the production of hard wear-resistant surface layers or cases on ferrous materials by the surface-carbonizing process, referring more particularly to an improvement in steels to be so case-hardened.

The value and utility of the case-hardened products of the carbonizing process are so well known and widely recognized as to require no expounding here. Such hardened materials find varied and valuable use in many fields, notably in the automotive and kindred industries, for mechanical parts which are subject to abrasion and wear.

In the carbonizing process it is customary to treat a low-carbon steel in such manner that the carbon content of the surface portions is increased. By subsequent quenching from an elevated temperature in the neighborhood of 800 C., the carbon-enriched surface portions are rendered extremely hard and wear-resistant, while the core or main body of the steel, having a lower carbon content, remains tough and ductile. The heat-treatment consisting of a quench from an elevated'temperature is considered an essential part of the surface-carbonizing. case hardening process.

One disadvantageous characteristic of the carbonized steels as heretofore produced has been that during the heat-treatment at elevated temperatures the metal of the core undergoes allotropic transformations which result, upon quenching to harden the case, in the development of internal strains and deformation of the article. This deformation is of obvious disadvantage, not only because it involves the departure of the fin-' ished article fromthe precise shape and dimensions desired, but also because it results in a general weakening of the entire structure. It is evident that a method which would materially'reduce this deformation would be of great value to the art.

It is the object of my invention to provide a means by which this distortion in case carbonized and hardened articles may be materially reduced,

' and I attain this object by the application of my discovery that low-carbon ferrous alloys containing alloyed additions in effective amounts of a certain class of non-ferrous metals which tend to inhibit the allotropic changes of iron in steels at carbonizing temperatures, may easily be carbonized; This is a surprising and remarkable discovery, inasmuch as it has heretofore been considered impossible and entirely out of the question to carbonize steels the iron of which is in the form of ferrite, the lower allotropic form.

The class of non-ferrous metals which are effective for the purpose of inhibiting the allotropic changes of iron, from ferrite to austenite, comprises a class which includes, for example, vanar dium, silicon, molybdenum, chromium, titanium, CJ

aluminum, beryllium, and tungsten. It is found by experiment that this class of' metals, when present in effective amounts either singly or in any proportions of any two or more in combination, serve to reduce substantially the distortion due to allotropic changes heretofore produced during the heat treatment of steels at temperatures of the order of those used in steel carbonizing.

The particular class .of low-carbon steels to which I prefer to apply my invention comprises those steels which contain about 0.10% or less of carbon, although my invention may be applied to steels containing somewhat more carbon.

I prefer also to carbonize the steels containing the alloyed additions to such degree that the surface portions contain about 0.90% or more of carbon, although my invention may be so applied as to produce beneficial results with more or less carbon enrichment. To secure the benefits of my invention to the fullest extent and with the greatest ease, a fairly wide spread is to be preferred between the amount of carbon in the core and in the surface portions, and it is to be. noted that this is the usual condition encountered in carbonizing practice.

Using a carbonizing steel containing less than about 0.10% carbon, which is to be carbonized to a surface carbon contentof 0.90% or more, I find that the following amounts of alloyed additions of representative metals of the prescribed class are to be recommended as the minimum amounts which must be present to secure satisfactorily the benefits of their inhibiting action: vanadium about 0.6%, silicon about 1.6%, molybdenum about 5%, chromium about 13%, titanium about 0.9%, aluminum about 2%, beryllium about 0.6%, and tungsten about 6%. When more than one metal is added to the steel, the minimum total may be figured on-the basis of their relative effects, since the individual effects are roughly additive. Greater amounts than those recommended may be used, the upper limit being governed by the degree of carbonization employed and the influence of the alloy on carbon penetration, but economic considerations will most frequently dictate the use of the minimum amounts. In the use of amounts much greater than the minimum, regard must also be had to the changes in physical characteristics of the core which will result from the use of large amounts of alloying metal. In no event should the iron content of the steel be below about I have determined by tests that the use of alloyed additions as above described materially reduces distortion according to the object of my invention. For example, a steel containing about 1% silicon, 0.5% vanadium, and 0.07% carbon was carbonized readily by one of the common methods to a surface carbon concentration of above 0.90%. A steel of similar carbon content, but without the alloyed additions of silicon and vanadium, was similarly carbonized to give a comparable case. Both test samples were quenched in the same manner from the same elevated temperature. The distortion of the sample containing the silicon and vanadium was found to be only about one tenth of the distortion of the unalloyed sample.

- Although I have described a number of spe- ;cific non-ferrous metals which may be used according to my invention, I do not wish to be limited to or by'them, but to the class of non-ferrous metals which will give the same result in the same way as those I have disclosed. Also, I do not wish to be limited to the specific ranges of carbon content in the carbonizing steel which I have recommended, for beneficial results may be secured through the application of my invention to steels of other carbon contents. Therefore, I wish to be limited only by the prior art and the appended claim.

I claim:

An article comprising an alloy steel body portion composed of more than 85% iron, less than about 0.10% carbon, and at least 0.60% vanadium; and a hardened surface portion containing more than about 0.90% carbon, said surface portion covering at least a part of the surface of said article.

AUGUSTUS B. KINZEL.