Title:
Hard metal alloy and process of making the same
United States Patent 2119487


Abstract:
The present inventon relates to the production of hard metal alloys and it particularly relates to the production of alloys which may be utilized for making cutting tools, wear-resisting implements of various sorts, and so forth. It has been proposed to make hard metal bodies from combinations...



Inventors:
Padowicz, Henry N.
Application Number:
US9373436A
Publication Date:
05/31/1938
Filing Date:
07/31/1936
Assignee:
Sirian, Wire And Contact Compan
Primary Class:
Other Classes:
419/31, 419/33, 423/274, 427/217, 428/403
International Classes:
B22F1/02; C22C1/05
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Description:

The present inventon relates to the production of hard metal alloys and it particularly relates to the production of alloys which may be utilized for making cutting tools, wear-resisting implements of various sorts, and so forth.

It has been proposed to make hard metal bodies from combinations of tungsten carbide and cobalt which are sintered together at temperatures between 1500" C. and 1600° C. It has been found, however, that the hard metal alloys produced according to these processes are expensive and relatively difficult to manufacture and are not possessed of the most satisfactory qualities.

It is among the objects of the present invention to prepare an improved, hard metal alloy at low cost and of high quality in respect to strength, hardness, homogeneity and density. Another object is to provide an alloy which may be made uniform from batch to batch. Still another object is to provide an alloy which will have a sufficient degree of toughness and density to enable its wide utilization in connection with wear-resisting bodies, cutting tools or working implements which are to be employed in shaping or 26 cutting alloys of iron, steel, chromium, nickel, cobalt, and so forth. Other objects will become obvious from inspection of the following specification.

In accomplishing the objects of the present invention it has been found most suitable to prepare a finely divided,. pulverized or powdered tungsten or tungsten carbide, or a combination of both tungsten and. tungsten carbide. Tungsten carbide is preferably the predominant ingredient in the mass, or it should constitute the entire mass to be processed.

'Although in the preferred embodiment tungsten carbide alone is employed or compounded with finely divided tungsten, it is also possible to include in the combination or replace the tungsten with other refractory metals, such as molybdenum, chromium, tantalum, titanium, thorium, columbium, uranium, either in the form of the finely divided metals or their carbides, or both. Mixtures of tungsten and tantalum carbides may. readily be employed. Where the carbides are employed the metal is preferably compounded in the proportion of one mol. of the metal to one mol. of carbon.

With, this pulverized and finely divided tungsten carbide, with or without the additions above mentioned, is then mixed a concentrated solution of a cobalt salt, the preferred salt being a cobalt acetate. In lieu of a part or all of the co5s balt acetate it is possible to use other soluble salts, such as cobalt sulphate, cobalt chloride, or cobalt nitrate, or preferably the water soluble organic salts such as cobalt formate, cobalt tartrate, cobalt citrate, cobalt saccharate or cobalt lactate, and desirably the cobalt salt is used in the form of a concentrated water solution which may be saturated and even carry suspended particles of the cobalt salt.

In lieu of some or all of the cobalt compound or compounds above mentioned, it is possible to inelude the corresponding iron or nickel compounds. The proportioning of the hard metal, such as tungsten, or .of the additional metal such as cobalt, nickel or iron, or of the carbon, is pref*erably such that the refractory metal will constitute between 50% to 80% of the final alloy, or in some instances, between about 88% to 90% of the alloy; while the additional metal will constitute between about 10% and 11% of the alloy, or in some instances, more than 25% of the alloy; whiie the carbon will constitute up to 2% to 3% of the alloy, and even up to 10% to 15% in certain instances.

In preparing the alloy from the tungsten carbide and solution of the cobalt acetate, the fine- 95 ly divided tungsten carbide is mixed with the cobalt acetate solution and is evaporated until a paste or solid mass is obtained. This solid mass may then be finely ground and subjected to reduction, most desirably in an electric furnace in ng a hydrogen atmosphere. After this reduction operation has been completed the resultant mass may be.formed or pressed to desired shapes and then sintered to form a finished article ready for commercial use in cutting tools, drawing dies, wear-resisting parts, and so forth.

To give a specific example of one manner of carrying out the present invention, a pure, fine tungsten powder is mixed with finely divided sugar charcoal in the ratio of 184 parts of tungsten to 12 parts of carbon. This mixture is then fired in a carbon boat in an inert or reducing atmosphere at approximately 1450* C. for a length of time sufficient to form mono-tungsten carbide Sfromn the component materials. This material is then pulverized and milled. Cobalt acetate of the formula--Co(CSH30S)2.4H20 is then dissolved in water to form a concentrated solution and placed in an evaporating dish. This solution is heated and the mono-tungsten carbide is sprinkled into it in small quantities. This composite solution is evaporated to dryness, with constant stirring, and the dried mass is then pulverized and sifted through a 180 mesh sieve. This powder is then reduced in hydrogen. The resultant powder is then pressed and formed in the desired shapes for use as cutting tools, drawing dies, sand blast nozzles, and so forth.

As another example of making this new alloy, pulverized, finely powdered mono-tungsten carbide corresponding to the chemical formula WC is added to a cobalt acetate solution. This cobalt acetate solution is made by pulverizing C. P. cobalt acetate (Co(C2H302)2.4H20) and then weighing and dissolving the required amount in water to form a saturated solution. When the dissolution of the acetate has been completed, the solution is poured into an evaporating dish or other suitable container. In order to accelerate the process of dissolution of the acetate the solution Is heated. Tungsten carbide (WC) is then added in small quantities to this solution and the whole is evaporated to dryness with constant stirring.

This procedure takes approximately twenty hours. The resulting powder is sifted through.a 180 mesh sieve and reduced in an electric furnace in a hydrogen atmosphere. The temperature is gradually raised to 6000 C. in approximately three hours and held there until reduction is complete. 2s The resulting metal carbide powder made as above is then pressed and molded to the desired shapes. After sintering at suitable temperatures from 1400° C. to 15500 C., the finished article is ready for commercial use, i. e., cutting tools, drawing dies, wear-resistant parts, and so forth.

As a third example of making this new alloy, 1104 grams of pure tungsten powder and 72 grams of sugar charcoal are milled together. The mixture is loaded into carbon tubes and fired in an sb electric furnace with a reducing or hydrocarbon atmosphere, the temperature of the furnace being approximately 1450* C., which temperature is maintained for thirteen minutes. The material is then pushed into the cooling chamber with a reducing or hydrocarbon atmosphere and held there for approximately six minutes. The mono-tungsten carbide produced is crushed in a mortar and milled. Then 666.8 grams of cobalt acetate C. P. (Co(C2H302) 2.4H20) are pulverized and placed in 40 a 1-liter flask with 700 cc. of Water, and.after dissolution this solution is poured into an evaporating dish and heated. The mono-tungsten carbide is then sprinkled in small quantities into the solution and the solution containing the tungsten carbide is evaporated to dryness'with constant stirring. This procedure takes approximately twenty hours.

The powder is then sieved through a 180 mesh sieve, loaded in nickel boats and reduced in an electric furnace in a hydrogen atmosphere in accordance with the following schedule: Hours Volts 1/4 at 20 1%/ at 50 1/4 at 70 1/4 at 100.

14 at 130 and the temperature then reaches about 600" C., 65 which is maintained until reduction is complete.

The boat is then pushed into a cooler with a reducing atmosphere and held there for fifteen minutes.

As a fourth example of a manner of carrying 70 out the present invention, from 1% to 10% of titanium carbide or vanadium carbide or chromium carbide, or a combination of two of these materials or of. all three, may be combined with 60% to 75% of tungsten carbide and 10% to 25% 75 of tantalum carbide, these carbides being mixed together in finely divided condition or being prepared from mixtures of pure metals in finely divided form together with a pure form of finely divided carbon, such as sugar carbon. This mixture of carbides may then be combined with sufficient cobalt acetate or nickel. acetate, or a mixture of both, in the manner previously described to result in the production of an alloy containing 5% to 10% of cobalt or nickel or both.

As a fifth example of making this new alloy, tungsten and carbon may be combined together in such proportions as to result in the production of a final alloy containing 84.2% of tungsten and 5.5% of carbon, sufficient amounts of a cobalt or nickel compound being added to assure that the final alloy will contain about 10.3% cobalt or nickel or a combination of both.

In combining the tungsten with the carbon, the tungsten and carbon'mixture may be heated to a relatively high temperature, say up to 12000 C. in a reducing atmosphere containing hydrocarbon gases, such as benzene, acetylene, and so forth, which hydrocarbon gases appear to aid the production of carbides which most readily enter into homogeneous combinations with cobalt, nickel and/or iron.

In the above examples, instead of using cobalt, nickel or iron acetates in combination with the tungsten carbide, it is also possible to use the tartaric acid, or other organic acid salts of these metals. It is also possible to mix with the tungsten or other refractory metal carbides, some finely divided cobalt, nickel or iron which has been previously reduced, and often this mixture of finely divided, reduced cobalt, nickel or iron may replace part of the metal of the acetate or other soluble salt.

Some finely divided reduced cobalt, nickel or, in some cases, iron may be combined with the finely divided tungsten, tantalum, chromium, vanadium, or other refractory metal before the carburizing operation so that the carbides of the various metals in the final alloy are simultaneously produced.

Although both the high temperature treatments, namely the carburizing and the reduction, are carried out in reducing atmospheres it has been found most suitable to carry out the first operation in a hydrocarbon atmosphere, while the second operation is carried out in a hydrogen atmosphere. The final sintering operation may also be carried out in a substantially reducing atmosphere, preferably of hydrogen.

Many other changes could be effected in the particular features of process treatment disclosed, and in specific details thereof, without substantially departing from the invention intended to be defined in the claims, the specific description herein merely serving to illustrate certain elements by which, in one embodiment, the spirit of the invention may be effectuated.

What I claim is: 1. A process of preparing a hard metal alloy which comprises preparing a mixture including a tungsten carbide, mixing said carbide with an aqueous medium containing a concentrated dispersion of at least one water soluble, organic acid salt compound selected from the group consisting of the cobalt, nickel and iron compounds ,evaporating to dryness while continuously agitating, and heating the mixture in a reducing atmosphere.

2. A process of making tungsten-cobalt-car bide combinations which comprises incorporatini tungsten carbide with a solution of cobalt acetate with agitation, evaporating to dryness while continuing the agitation, pulverizing and sifting the dried mass and then reducing the dried mass in hydrogen.

3. A process of preparing tungsten-cobalt-carbide alloys which comprises incorporating the tungsten carbide in finely divided condition with a concentrated aqueous dispersion of a cobalt organic acid salt, evaporating to dryness while continuously agitating and heating in a reducing atmosphere.

4. A process of preparing hard metal alloys from tungsten carbides which comprises forming a pure tungsten powder, carburizing the metal powder, combining the carburized metal powder with a concentrated aqueous solution of cobalt acetate, evaporating to dryness while continuously agitating, powdering and heating in a reducing atmosphere.

5. A process of producing a hard metal alloy which comprises heating'finely divided tungsten with carbon in a hydrocarbon atmosphere, and then mixing the finely divided product with a water solution of an organic acid salt of a metal selected from the group consisting of cobalt and nickel, evaporating to dryness while continuously agitating, pulverizing and sifting, and then heating the combination in an atmosphere of hydrogen to form the alloy.

6. A process of preparing hard metal alloys which comprises drying a slurry containing, and then heating the resultant mixture of tungsten carbide and cobalt acetate in a hydrogen atmosphere.

7. A process of forming a hard metal alloy which comprises combining a finely divided tungsten carbide with a concentrated aqueous dispersion of a soluble compound of a metal selected from the group consisting of nickel, cobalt and iron, with agitation, evaporating to dryness while continuing the agitation, pulverizing the dried mass, sifting the pulverized material and then reducing in hydrogen.

8. A process of forming a hard metal alloy which comprises providing tungsten carbide, powdering the tungsten carbide, sprinkling the powdered tungsten carbide into a concentrated solution of cobalt acetate in proportiofs to give a final alloy containing between 10% and 10.5% of cobalt, evaporating to dryness while continuously agitating, pulverizing the dried mass, reducing the powder by heating in a hydrogen atmosphere, pressing and forming the powder into desired shapes, and then sintering.

9. In the process of preparing hard metal alloys, the step of combining a tungsten carbide with a solution of a cobalt salt, which comprises sprinkling the carbide into a concentrated solutiop of the cobalt salt until the proper proportions are obtained and then evaporating to dryness while continuously agitating.

10. A hard metal alloy comprising the reduction product of a tungsten carbide and a cobalt salt, particles of said carbide being encased in metallic cobalt and the encased particles being cemented together and being prepared by evaporating a slurry containing tungsten carbide and said salt to dryness, followed by pulverizing, pressing and sintering.

11. A hard metal alloy comprising a reduced mixture of tungsten carbide and cobalt acetate, particles of said carbide being encased in metallic cobalt and the encased particles being cemented together and being prepared by evaporating a slurry containing tungsten carbide and said salt to dryness, followed by pulverizing, pressing and sintering.

12. A hard metal alloy consisting of finely divided tungsten carbide~ the particles of which are each encased in, and cemented together by, a coating of an additional metal selected from the group consisting of iron, cobalt and nickel, said alloy being prepared by mixing the finely divided tungsten carbide with a solution of a water soluble salt of the additional metal to form a slurry followed by reduction to dryness while continuously agitating, reduction in hydrogen and sintering.

HENRY N. PADOWICZ. 46