US2081049A - Sintered hard carbide composition - Google Patents

Description

-' suitable as addition agents.

Patented May 18, 1937 UNITED STATES PATENT OFFICE SINTERED HARD CARBIDE COMPOSITION New York No Drawing. 'Application September 28, 1935, Serial No. 42,712

5 Claims. (01. 75-136) In fabricating hard carbides, such as the carbides of tungsten, tantalum, titanium, and the like, into tool bits, dies, and similar articles, certain limitations are encountered that are well known to those skilled in the art., The carbides in finely powdered form-are usually compressed into briquettes or other required shapes and highly heated. If the heating is carried to complete fusion, a porous, brittle, coarsely crystalline mass usually results which is lacking in strength and wholly unsuitable for the required purpose. If the heating is stopped somewhat short of fusion, porosity is usually avoided but a weak coarsely crystalline structure results that is unsuitable for tools. To overcome these difiiculties a small proportion of a comparatively low melting point metal such as cobalt is added to the carbide powder. This fuses and cements the carbide grains together.

An object of the present invention is to provide a sintered pure hard carbide composition having a strong fine grained structure.

Another object of this invention is to provide a means of sintering carbides into strong tough bodies without adding soft or low melting point diluents.

In general the process of my invention consists of modifying the carbide to be sintered, by adding to it a very small percentage of a second hard carbide, suitably chosen. If the modified carbide is then heated within a certain definite and fairly narrow range of temperatures, a strong, hard, fine grained body is produced that is well adapted for tool bits, dies, and the like .The process which I employ in making tool bits consisting principally of tungsten carbide may be employed to illustrate my invention. Tungsten carbide powder is used having a content of about 5.5% carbon. This is mixed with another metallic carbide in the proportion of about 99 parts of tungsten carbide to one part of the second carbide. The second carbide may be a carbide of tantalum, molybdenum, columbium or titanium. All carbides however are not For example, zirconium carbide seems to dissociate when heated in contact with tungsten carbide, and produces ing in a ball mill for several hours. The resulting mixture is then sifted through bolting cloth and compressed into briquettes or other shapes suitable to the intended purpose. The exact degree of pressure employed is comparatively unimportant. Pressures from three tons to ten tons per square inch have been employed without producing significant difi'erences in result.

The briquettes are heated in a furnace having a reducing atmosphere which may be produced by passing carbon monoxide or hydrogen through the furnace, preferably the latter. For the heating operation the briquettes are preferably placed in a carbon cylinder, between two slabs of pure tungsten carbide, one on top and one on the bottom of the briquette. This arrangement insures even heating and prevents warping. By holding the briquette out of contact with the carbon cylinder any change in the carbon content of the briquettes is prevented.

The required temperature to which the briquettes are heated is of considerable importance and should be ascertained by trial for each mix ture, and. carefully controlled. In this specific example (99% tungsten carbide and 1% columbium carbide) the preferred temperature is about 2200 C. to 2300 C. Specifically, a temperature of 2225 C. has proved to be the most satisfactory. A heating period of about one-half hour is usually sufficient.

As a result of the foregoing treatment the briquettes shrink about to and are found to have a very fine and solid texture. The hardness of the heat treated material is about 1600- 1800 Brinell and the strength about 100,000 lbs. per square inch. This strength, while less than that of pure tungsten carbide cemented with cobalt, is ample for many commercial purposes.

The proportion of the second carbide or modifying agent employed may be increased to as much as 5%. While such increase lowers the hardness the resulting product has uses in special fields.

If the carbide addition is greater than 1% a somewhat lower temperature than 2200 C. preferably should be employed. Although in general I prefer to employ tungsten carbide with only one additional carbide, a plurality of such additional carbides may be employed. The total of such additional carbides however should not exceed 5% in Weight of the total content of the resulting composition.

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

1. A sintered alloy containing about 99% tung- 5. A sintered alloy containing 99% to 95% tungsten carbide, the remainder of the alloy consisting of one or more of the carbides from the group consisting of coiumbium carbide, tantalum carbide, molybdenum carbide and titanium carbide.

HUGH S. COOPER.