US1910532A - Hard metal - Google Patents

Description

Fatented May 23, 1933 ares FATEZNT BRUNO FETKENHEUER, DECEASED, LATE 0F BERLIN-SIEMENSSTADT, GERMANY, BY

HELENE FETKENHEUER, NEE JllRGE-NS, ADMINISTRATRIX, OF BERLIN-SIEMENS- STADT, GERMANY, ASSIGNOR TO DEUTSCHE EDELS'IAHLWERKE AKTIENGESELL- SCI-IAFT, OF KREFELD, GERMANY, A CORPORATION OF GERMANY HARD METAL No Drawing. Application filed August 21, 1931, Serial No. 558,560, and in Germany August 21, 1930.

The invention relates to the composition and making of a so-called hard metal. According to the invention, the hard metal consists for the greater part of titanium car bide and contains besides a carrier metal or substance, i. e. a metal or substance in which the titanium carbide is embedded or which serves as a binding material for the titanium carbide. The carrier metal, also called auxiliary metal, may consist of a single metal or of a plurality of metals or of alloys or mixtures of same.

Compared with tungsten or Wolfram carbide, the use of which for making hard metals is already known, titanium carbide has considerable advantages. In the first place, its unit of weight is substantially cheaper, and then it has a considerably lower specific gravity. As, when it is used for tools etc, the volume of the quantity employed and not its weight is the major consideration, the price of the tools is thereby still more reduced. The hardness of titanium carbide is not less than that of tungsten carbide. On the contrary, it is possible with the same percentage of auxiliary metal to obtain a greater hardness of the finished article or body than is the case with a corresponding article containing Wolfram carbide.

Titanium carbide is able in combination with a whole series of auxiliary metals to form exceedingly homogeneous bodies capable of great mechanical resistance. Such metals are in the first place cobalt and iron; alloys or mixtures of cobalt and'iron may also be used. There are, besides, other metals which give excellent results.

Nickel for example alon or in combination with other metals is also suitable for this purpose. Furthermore, for example, alloys of cobalt, chromium and tungsten (alloys resembling stellite), with or without the addition of carbon, may be advantageously used. In a hard metal tool element containing titanium carbide in amounts of, say, 60% or higher, small percentages of carbide from the group consisting of molybdenum carbide, tantalum carbide, and tungsten carbide, ma advantageously be used in addition to the stated amount of the titanium carbide. .In

that case. however, only a small fraction of the whole carbide mass may be replaced, if the good properties of the carbide component are not to be too much impaired. The addition of, for example, 10 to 20 per cent of tungsten carbide, molybdenum carbide or tantalum carbide is quite permissible.

To utilize fully the excellent properties of the titanium carbide, it is, however, necessary to make a relatively large portion, i. e. at least two thirds of the whole mass consist of titanium carbide. Bodies containing about 85 per cent of titanium carbide have proved particularly suitable. The carbide content may, however, be increased far beyond that value, for instance up to 95 per cent. An increase in the percentage of the carbide generally has the effect of increasing the hardness of the finished body, but the greater the carbide content, the mor diflicult it becomes to obtain a strong binding of the carbide mass. The higher the carbide content, the higher must the temperature be raised to obtain the solidification of the finished body. Temperatures of over 2000 C. may even be required. The difiiculties consist partly in the fact that the titanium carbide, owing to its relatively low specific gravity and the greater volume resulting therefrom and to the greater total surface of the same weight of powder, requires a relatively larger quantity of auxiliary metal to fill up the interstices between the carbide particles than is the case with the other heavier carbides.

It has, however, been found that these difficult-ies can be well surmounted by choosing the solidifying temperatures" correspondingly take place between the titanium carbide and the other substances with which it comes into contact,-for example, with the oxygen or nitrogen of the atmosphere. Under circumstances this is liable to impair the properties of the finished body considerably. Care must, therefore, be taken to avoid the presence of oxygen and nitrogen especially during the heating. For this reason the heatmg will mostly be performed in a hydrogen atmosphere or in another indifferent atmosphere or in a vacuum. It is also important to keep away even small traces of oxygen or nitrogen, as a satisfactory binding of the mass through the auxiliary metal would otherwise be out of question owing to the individual carbide particles covering themselves with layers of oxide or nitride, thus preventing the contact between the carbide and the auxiliary metal.

Instead of bringing the bodies directly into their ultimate form and finishing them by the means of heat, it is also possible to make bodies which for the time are only heated to a low temperature, for, instance up to just below the melting point of the auxiliary metal or only a little above that temperature. Bodies of this kind may then still be relatively easily machined. They can be brought into the desired shape by cutting or dealing otherwise with them and the bodies so obtained then be finished by heating them to the higher solidifying temerature. Instead of employing the auxiliary metals themselves, chemical compounds of these auxiliary metals may be used. In that case the compounds are either ground to powder or dissolved and then mixed with the titanium carbide and heated in a reducing atmosphere, so that an intimate mixture of the titanium carbide with the auxiliary metal results. By this means, after the chemical compound is destroyed, a finer distribution of the auxiliary metal and a more intimate binding is obtained through the further heating. It is, for example, possible to employ the oxides" or the oxalates of the auxiliary metals and carry out the reduction with hydrogen, in as pure a state as possible, at relatively low temperatures, for instance at the temperature at which the mass begins to get red hot, and only after that to continue the heating, under exclusion of oxygen and nitrogen. The process for making a hard metal may be carried out as follows. The carbide powder, either all together without or with only a small addition of auxiliary metal, is pressed into the form of bodies which are then sintered at a high temperature.

The sintered body is then brought into contact with the remaining quantity of the auxiliary metal with which it is to be impregnated and heated to the final solidifyin temperature. It is naturally presupposed that the sintered body of the carbide still possesses a suflicient porosity. The auxiliary metal may, for example in the form of a solid coherentbody, be laid on the previously sintered body of carbide and then heated with same in vacuo. The auxiliary metal is then absorbed by the previously sintered carbide body and evenly distributed.

' What is claimed is:

A hard metal tool element containing from about 60% to about 85% titanium carbide, from about 10% to about 20% tantalum carbide, and the remainder substantially from about 5% to about 20% of auxiliary metal taken from the group consisting of cobalt, iron and nickel.

In testimony whereof I ailix my signature.

HELENE FETKENHEUER, ne JilRGENS, Administratriw of Estate of Bruno Fetkenheuer,

Deceased.