US2207708A - Hard metal alloy process - Google Patents

Description

Patented July 16, 1940 UNITED STATES HARD METAL ALLOY PROCESS Clarence W. Balke and Claire C. Balke, Highland Park, Ill., assignors to Ram'et Corporation of America, North Chicago, 111., a corporation of Illinois No Drawing.

4 Claims.

This invention relates to a method of manufacturing hard metal alloys consisting of one or more carbides which form the major portion of the alloy, and are cemented by auxiliary metal 5 taken substantially from the iron group and forming the balance of the alloy.

Such alloys are generally used for tools or tool elements in other working appliances which are subjected in operation to mechanical wear. The carbides employed are generally those of tungsten, tantalum, columbium, zirconium, boron, silicon, molybdenum, vanadium and chromium, which are known as hard and wear-resistant, while the auxiliary metal is generally taken from the iron group and may be supplemented by manganese and sometimes metals of the sixth group. It should also be pointed out that in addition to the carbides of the above enumerated elements, borides, nitrides and silicides may in some cases be substituted. The exact composition of the material treated is not the most significant part of our invention, and it is, therefore, to be understood that the foregoing is by way of example only, and not by way of limitation.

It is an object of our invention to reduce the cost of manufacture of hard metal bodies by improvement of the method of manufacture.

It is a further object of our invention to improve the uniformity of hard metal bodies whereby to reduce waste and make more definite and certain the results which can be obtained.

According to common practice, the metal carbide or carbides used in hard metal bodies are obtained from any suitable source, and the so-called hinder or auxiliary metal is similarly obtained from any suitable source. These are reduced to an intimate mixture of fine powders in which the particle size is considerably finer than 200 mesh. The carbide and binder may be reduced to powder form either jointly or separately. However obtained, the powder is pressed either with or without a small amount of an organic binder and pressed under exceedingly great pressure. Because of the high pressure required, it is commonly obtained by hydraulic means. The resultant pressed body is heated to a relatively low temperature of the order of 700 or 800 deg. C.

This operation effects the preliminary bindingwithout at the same time making the body so hard that it cannot be shaped with ordinary available tools. Then after the partially bound body is brought to the final shape required, due regard, however, being had for the fact that the body will utimately shrink to a considerable degree, and therefore must be made a g r than the Application September 20, 1939, Serial No. 295,755

final desired shape; then after a final sintering operation is carried on, either in vacuum or some indifferent gas such as hydrogen at a high temperature of the order of 1400 to 1500 degrees, the common trade practice has heretofore been to place the shaped bodies in carbon boxes and in order to prevent contact between the bodies when a number of relatively small ones are placed in a single box, they are usually packed in loose graphite powder or coarsely granular alumina. The selection of the packing material depends largely upon the character of treatment it is desired to give the. bodies. If graphite powder is used, the tendency is for the bodies to absorb additional amounts of carbon, and if equilibrium is not had in the body, there is a tendency for a case of a more highly carburized material to grow on the body. On the other hand, if alumina is employed, there is a slight tendency to decarburize the pressed body. In an effort to maintain some form of equilibrium, it has been suggested that slightly additional amounts of carbon may be added to parts of the pressed bodies, or in some cases, slight deficiencies of carbon are deliberately employed in the body in order that the final product will reach the desired state of equilibrium.

We have found that all of the difiiculties can be easily and simply overcome and a sintered product obtained which is constant in quality, by the employment of a different character of packing material. In place of the graphite or alumina which has heretofore been used, we em ploy a coarsely granular carbide of a refractory 'metal of the fourth or fifth group, particularly tantalum carbide. This material is highly inert under the conditions, and because it is closely chemically allied to the materials employed in producing the hard carbide, there is not the slightest tendency on its part to react with the hard bodies being sintered.

This carbide is not easily wet by the binder metal of the bodies, and therefore serves to separate the bodies without thermally insulating them. Compared with the graphitepowder or alumina, it has a relatively much greater thermal conductivity and, therefore, quickly aids the bodies in reaching an equilibrium temperature during the variation of temperature during the sintering' process. We have found that compared to the prior hard materials employed that surprisingly uniform results are obtained. An extremely fine carbide powder is not wholly satisfactory. We prefer to employ coarse material since it allows the gaseous atmosphere, whether it be a gas or a vacuum, to circulate freely around the bodies without any difficulty.

We have found that the carbides of the nonradio-active refractory metals of the fourth and fifth groups of the periodic charttitanium, zirconium, hafnium, vanadium, columbium and tantalum, are suitable for this purpose. The employment of pure carbides is not at all essential. Mixed carbides made up of any two or more of the foregoing elements are also suitable.

Tungsten carbide and other carbides of the sixth group have been tried, but we find them to be unsatisfactory because of the ease with which they are wetted by the binder metal. This causes the carbide grains to adhere to the shaped body, and in some cases to draw part of it out of the body by capillarity. That is, of course, unsatisfactory.

The exact method of practicing our invention 7 of at least one nonradioactive refractory metal of the fourth or fifth group, the particles being of sumcient size to permit free flow of gas through the interstices thereof.

.2. In the process of making hard metal bodies, that improvement in the sintering process which includes surrounding the bodies during the sintering operation with loose particles of a carbide selected from the group consisting of tantalum carbide, columbium carbide, and tantalum-columbium carbide, the particles being of sumcient size as to permit free flow of gas through the interstices thereof. v

3. In the process of making hard metal bodies, that improvement in the sintering operation which includes separating the bodies from any adjacent body during the sintering operation by means of loose particles of a carbide of at least 7 one nonradioactive refractory metal of the fourth.

or fifth group, particles being of sufllcientsize as to permit free flow of gas through the interstices thereof.

4. In the process of making hard metal bodies, that improvement in the sintering operation :which includesseparating the hard metal bodies from adjacent bodies during the sintering operation with'loose particles of tantalum carbide, the particles being of sufficient size as to permit free flow of gas through the interstices thereof.

CLARENCE W. BALKE.

CLAIRE C. BALKE.