US3859056A

US3859056A - Cemented carbide intermediate therefor and process for producing the same

Info

Publication number: US3859056A
Authority: US
Inventors: Akio Hara; Masaya Miyake; Mitsunori Kobayashi
Original assignee: Sumitomo Electric Industries Ltd
Current assignee: Sumitomo Electric Industries Ltd
Priority date: 1972-02-17
Filing date: 1973-01-31
Publication date: 1975-01-07
Anticipated expiration: 1992-01-07
Also published as: SE392882B; JPS4885406A; JPS518726B2; FR2172113A1; DE2304731C3; DE2304731B2; DE2304731A1; FR2172113B1

Abstract

In a process for producing a cemented carbide by powder metallurgy, oxidizable intermediate products are treated with a carboxylic acid or anhydride thereof having a molecular weight less than 200 to prevent oxidation. The intermediate products thus obtained are also described in detail.

Description

United States Patent [1 1 1111 3,859,056 Hara et al. 1 Jan. 7, 1975 CEMENTED CARBIDE INTERMEDIATE [56] References Cited THEREFOR AND PROCESS FOR UNITED STATES PATENTS PRODUCING THE SAME 2,698,232 12/1954 Golibersuch 75/204 x 75 Inventors; Akin H Masaya i 3,743,547 7/1973 Green [48/63 Mitsunori Kobayashi, all of Hyogo, Japan Primary ExaminerBenjamin R. Padgett [73] Assignee: Sumitomo Electric Industries, Ltd., A mm Examiner-R, E. Schafer Osaka, Japan Attorney, Agent, or Firm-Sughrue, Rothwell, Mion, 221 Filed: Jan. 31, 1973 & Macpcak [21] Appl. No.: 328,168

[57] ABSTRACT [30] Foreign Application Priority Data In a process for producing a cemented carbide by Feb. 17 1972 Japan 47-16838 Powd?r metallurgy Oxidizable intermediate PmduCtS are treated with a carboxylic acid or anhydride thereof 52 US. (:1 29/1s2.7, 29/l52.8 29/192, having a molecular Weight less than to 75/203 75/204 75 21 1 75/212: 75/221 Nation. The intermediate products thus obtained are 117/100 M, 117/100 B, ll7/l06 R, 117/127, also descflbed 117/161 UB, 148/63 [51] Int. Cl C22c 29/00, B22f H00 17 Claims, 1 Drawing Figure [58] Field of Search 75/204, 21 l, 212, 203,

75/221; 117/100 M, 100 B, 106 R, 127, 161 UB; 148/63; 29/l82.7, 182.8, 192

CEMENTED CARBIDE INTERMEDIATE THEREFOR AND PROCESS FOR PRODUCING THE SAME BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to an improvement in processes for producing a cemented carbides and to a process for producing intermediates used in the production of cemented carbides.

2. Description of the Prior Art Cemented carbides are hard alloys prepared by a powder metallurgy method in which the main components are one or two more carbides of a Group lV-a, V-a, or Vl-a metal in the periodic table, and one or two more powders of a Group VIII metal, present in minor proportion. Usually the carbide materials are about 70% or more of the cemented carbide.

Cemented carbides are evaluated for apparent porosity by ASTM Designation: B276-54 (Reapproved 1965 and the transverse rupture strength of cemented carbides by ASTM Designation: B406-70 (these were the test procedures used to analyze the properties in the Examples).

Unless otherwise indicated, the terms in the application have the standard powder metallurgy method provided in ASTM Designation: B243-70.

Several processes are known in the prior art for the production of cemented carbides. The raw materials for such a process generally comprise a powdered metal, a powdered alloy, a powdered carbide or a powdered carbide solid solution. Powdered metals or powdered alloys are generally formed by subjecting the oxide or hydride of the metal(s) involved to reduction or thermo-decomposition to obtain the powdered metal(s). Exemplary of the metals used in cement carbide formation processes are titanium, tantalum, tungsten, niobium, molybdenum, chromium, iron, cobalt and nickel.

The powdered carbides are generally obtained by treating the oxide or hydride of the metal involved to a reduction as described above, and then to carburization whereby the powdered carbides are obtained. Exemplary of such carbides are titanium carbide, tantalum carbide, tungsten carbide, molybdenum carbide and chromium carbide.

The powdered carbide solid solution is generally obtained by treating the oxide or hydride of the metal involved, the metal per se or a carbide thereof to mixing and heating in the presence of carbon, whereby a carbide solid solution is obtained such as tungsten titanium carbide, tungsten titanium tantalum carbide, etc.

Starting with one of the thus obtained powdered raw materials, which will hereafter often be referred to as starting powders, the first step in the prior art processes is generally a wet mixing followed by a drying. The purpose of the wet mixing, which is usually an intense mechanical mixing in the presence of a wetting liquid or wetting solution, i.e., a volatile lubricant, is to enable the mixture to be readily pressed into any desirable form. The powder after drying is often hereafter referred to as a mixture powder.

The mixture powder is pressed to provide a product which has sufficient strength to enable it to be handled and transferred. Pressing is generally a cold pressing under elevated pressure, and the product after pressing will hereafter often be referred to as a formed body.

The formed body may then be immediately subjected to final sintering to form the cemented carbide, but often is subjected to a preliminary sintering or further forming treatments. Usually the preliminary sintering is to provide strength to the formed body if it is to be molded or processed prior to final sintering, or to activate the material or remove organic binder if no further molding or processing steps are contemplated. The preliminary sintering is usually at a temperature of from 300 to 800 C. The product after preliminary sintering is hereafter often termed a preliminarily sintered body.

The preliminarily sintered body may be subjected to a forming or may then be directly final sintered to obtain the cemented carbide. Final sintering is at elevated temperatures as are used in the prior art, e.g., above 1,000C. and is often a vacuum sintering.

In the production of such cemented carbide, if the starting powder, the wet mixture of the starting powder, or the preliminarily sintered body is oxidized, the oxide film or hydroxide film formed will react with carbon in the carbide powder or free carbon during the subsequent sintering operation used to form such materials, thereby causing decarburization of the sintered body and resulting in an irregular carbon content in the resulting cemented carbide. While the problem can be encountered with the formed body, such is not usually the case since generally the formed body is quickly subjected to further sintering.

In the case that the carbon content in the cemented carbide is too greatly reduced, an abnormal phase is caused in the microstructure of the cemented carbide, which renders the alloy brittle and useless. However even if the cemented carbide exhibits a normal microstructure, the strength, toughness, hardness and wear resistance of the alloy are influenced by changes in the carbon content.

The optimum amounts of carbon in a cemented carbide are known to the art, and can be suitably determined by one skilled in the art. For instance, for a WC- (TiC-TaC)-Co alloy, where carbon is present in insufficient amounts, an anomalous phase, the 'r -phase results, and the alloy becomes very brittle. On the other hand, where excessive carbon is present, free carbon results, also causing the alloy to become brittle. The carbon content to maintain a normal cemented carbide matrix will obviously vary depending upon the composition of the cemented carbide. Usually, however, the carbon content is within the range of from about 0.06 to about 0.2 weight percent. If is preferred to control the carbon content to within i 0.02% of the above range.

The starting powder used for forming a cemented carbide is very reactive and easily oxidized due to the large specific surface area thereof. This increased reactivity is especially encountered immediately after preparation or reduction or during mixing with a wetting liquid or wetting solution when the material is cleaned and activated so as to be reactive with the oxygen and the moisture in the air and the mixing solution. Under certain circumstances, the powder becomes exothermic and is self-igniting.

The preliminarily sintered body surface, which has a large specific surface area and is activated by the preliminarily sintering treatment, is as easily oxidized as the starting powder.

Therefore, to obtain, a cemented carbide having an optimum carbon content it is important in the practical sense to consider that the starting powder and the intermediate sintered body are most easily oxidized before sintering, and decarburization of the resulting alloy due to such oxidation will be irregular.

Cemented carbides which have conventionally been produced using low temperature and low humidity conditions to prevent oxidation of the starting powder and the intermediate sintered body have shown a nonuniform degree of oxidation due to the influence of other treating conditions and the treating time.

On the other hand, to carry out all the steps for producing a cemented carbide under a vacuum or in an inert gas atmosphere to avoid oxidation, is ideal, but this is a very troublesome procedure.

Conventional procedures for treating the starting powder and the intermediate sintered product can be classified as follows:

1. A powder having the property of self-ignition was slightly oxidized or stuck together using a fat to stabilize the surface thereof and to facilitate handling. However, not only power thus treated but also powder exposed to air is oxidized to some extent. The higher the moisture contend in the air, the greater the oxidation of the powder. Accordingly, such powder must be stored in air having minimum moisture.

Although the storage of such cemented carbide starting powder under constant conditions is possible, ensuring the powder is not brought into contact with air during subsequent compressing and forming steps, i.e., during supply to a press or charging into a sintering furnace, is very difficult. The susceptability of the powder to absorb moisture and gases can be controlled so as to be in a narrow range if the powder is treated under constant temperature and humidity conditions, but other treating conditions and treating time influence the adsorption of mositure and gases. If the power is treated under conditions open to the atmosphere where temperature and moisture vary, the amount of the powder oxidized will be unstable and irregular.

2. The oxidation of the powder during mixing with the solution prior to pressing has been not taken into consideration, and means to solve this problem have been ignored. Powder oxidation during drying or the treatment to thermally expel the mixing solution can be eliminated by protecting the powder from exposure to air during the drying, e.g., by subjecting the powder to vacuum drying. The powder can be protected from oxygen between the successive pressing and sintering step by using a glove box, but this is very troublesome.

Another method of preventing the oxidation of the powder comprises coating the surface of the powder with a lubricant such as camphor, paraffin, glycol, Zn stearate, a resin or a like high molecular weight compound, but coating every particle of the powder is very difficult.

3. The treatment of the preliminarily sintered body has been carried out under constant temperature and humidity conditions in a manner similar to that described for the starting powder, but this treatment could not fully prevent the oxidation of the preliminarily sintered body. In addition, the degree of the oxidation varies with changes in other treating conditions and time.

The treatment of the preliminary sintered body may be carried out in vacuum or under an inert gas atmosphere, but again this is a very troublesome procedure.

SUMMARY OF THE INVENTION This invention thus has as its objects the elimination of the above described defects of the prior art and to provide an improved process for treating the starting powder, a wet mixture of the starting powder a formed body or a preliminarily sintered body used in the production of cemented carbide to prevent surface oxidation thereof.

One feature of this invention is to contact an oxidizable material used in the production of a cemented carbide, e.g.: (1) a Group IV-a, V-a or VIII metal, or a Group IV-a, V-a or VI-a carbide or a carbide solid solution, immediately after preparation, i.e., a starting powder; (2) a wet mixture of such metallic or carbide powders or a carbide solid solution, i.e., the mixture powder; (3) a formed body of such starting powders or such a wet mixture; or (4 preliminarily sintered body thereof, with a carboxylic acid or an anhydride thereof, having a molecular weight of less than 200, in an nonoxidizing atmosphere or in a vacuum, thereby adhering the carboxylic acid or the anhydride thereof to the surface of the starting powder or the like and preventing the oxidation thereof.

In one aspect of this invention, a starting powder of the cemented carbide, such as a powder of a Group IV-a, V-a or VI-a metal in the periodic table, or a carbide thereof, e.g., a WC, TiC or TaC powder, or a powder of a Group VIII metal of the periodic table, is exposed immediately after preparation, to a vaporized carboxylic acid having a molecular weight of less than 200 (or the anhydride thereof) in a vacuum or in a nonoxidizing atmosphere, to thereby adhere the carboxylic acid or the anhydride thereof to the powder surface.

In another aspect of this invention, a carboxylic acid having a molecular weight of less than 200 (or the anhydride thereof) is added to a wetting liquid or wetting solution while the starting powder and the solution are mixed with each other prior to the production of the formed body.

In third aspect of this invention, a carboxylic acid in the vaporized state having a molecular weight of less than 200 (or the anhydride thereof) is adhered to the surface of a preliminarily sintered body immediately after sintering in a vacuum or a non-oxidizing atmosphere.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a plot of adhered carboxylic acid versus molecular weight of the carboxylic acid.

DETAILED DESCRIPTION OF THE INVENTION According to one feature of the process of this invention, the cemented carbide starting powder has condensed thereon a vaporized carboxylic acid having a molecular weight less than 200, or by an anhydride thereof after the step of reducing the starting powder.

The vapor may be adhered to the reduced powder particles by introducing the vapor into the reducing meating the vapor into the pores of the body. As earlier indicated, this procedure is seldom necessary.

The carboxylic acid may be any unsaturated or saturated fatty acid or aromatic carboxylic acid with a molecular weight less than 200, but preferably is one which reacts with the surface of the powder particle and not with the interior of the powder particle.

Oleic acid and stearic acid can be used, but these do not fully permeate into the interior of a powder layer since these compounds have a high boiling point and must be heated to a high temperature to vaporize them and accordingly the molecular motion of the compounds becomes toviolent.

Therefore, the carboxylic acid or anhydride thereof must have a low molecular weight and a low boiling point, e.g., acetic acid, acrylic acid, propionic acid and acetic anhydride, each having the molecular weight of less than 200, provide favorable results.

An anhydride, such as acetic anhydride, having properties similar to the carboxylic acid can also be used. However, compounds having a substituting radical containing S,P, Cl, etc. in the carboxylic acid or anhydride material have an ill effect on the sintering treatment and should not be used.

From the drawing it is easily seen that the lower molecular weight carboxylic acids or anhydrides are preferred, and thus most preferred materials have a molecular weight of 120 150 or below.

If such a vaporized carboxylic acid or anhydride in a small amount is adhered to the surface of the powder particles, the surface activity of the powder particle is stabilized and successive treatments can be carried out in a short period of time to produce a uniform sintered body having a desired carbon content.

In the mixing of the starting powders with a wetting liquid solution, such as ethanol, acetone or benzene the carboxylic acid or the anhydride thereof can be added to the starting powder.

The wetting agent used can be in accordance with those used in the prior art, and any common organic liquid which is used to disperse materials can be used so long as it does not react with either the powders or carboxylic acid or anhydride (which will be easily apparent to one skilled in the art). Since the purpose of using the wetting liquid is to accomplish a physical process, i.e., to permit the powder particles to be easily contacted with each other and cleaned, the exact choice of the wetting liquid is not overly important, and generally alcohols, ketones and hydrocarbons (aliphatic or aromatic) are used in which the carboxylic acid or anhydride is dispersed or dissolved.

The carboxylic acid or the carboxylic anhydride is known to be easily adhered to a clean surface. The process of this invention is thus easily practiced when clean surfaces are caused by the grinding of the powder during the wet mixing treatment and the carboxylic acid or anhydride is well adhered to the clean surface of the powder particles which is easily oxidized and very reactive, to thereby protect the surface from oxidation.

The effect of the adhered carboxylic acid in preventing oxidation after a drying treatment was ascertained by empirical methods. As earlier indicated, the carboxylic acid used has a molecular weight less than 200. The empirical work on the treatment of coating the starting powder with various carboxylic acids having different molecular weight showed that the residual carbon content of the resultant super hard alloy increased rapidly as the molecular weight of the carboxylic acid used exceeded 200, as shown in the drawing.

While is is not completely definite, the inventors believe the carboxylic acid or anhydride is either adsorbed or chemically reacted with the powder, etc. in the various embodiments of this invention.

The reason for the rapid increase of residual carbon using materials of a molecular weight greater than 200 is believed to be that the carboxylic acid is cracked dur ing thermal decomposition thereof, and free carbon is apt to result.

Since the amount of carboxylic acid added to the starting powder is determined upon considering the number of molecules per unit surface area, the residual carbon amount is also increased with an increase in the molecular weight, i.e., from the equation A= E-M-S- W/N-s, A is in direct proportion to M, and therefore A increases with increased values of M. Since a rapid increase of the amount of residual carbon is detrimental in the production of the cemented carbide, the molecular weight of the carboxylic acid is accordingly, restricted to a value less than 200 for this additional reason.

Considering all of the above factors, the effective amount of carboxylic acid or the anhydride thereof in the mixing with a wetting solution is calculated by the equation below:

A Amount of carboxylic acid or anhydride (g);

M Molecular weight of the carboxylic acid or anhydride;

S BET value (m /g);

S Area occupied by a molecule of the carboxylic acid or anhydride (about 2 X 10 m W Amount of powder (g);

N Avogadro number;

E Safety coefficient (2 4).

Where the starting powders or preliminarily sintered body are subjected to contact with the vaporized carboxylic acid or anhydride thereof, good results can be obtained by contact under condition where the carboxylic acid or anhydride is present in an amount corresponding 60 of saturated vapor pressure.

In a further embodiment of the invention the vapor of the carboxylic acid or anhydride thereof is permeated into the fine pores of an intermediate sintered body before the final sintering treatment, whereby it reduces the surface energy of the active inner surface of the fine pores of the preliminarily sintered body, and makes the surface thereof resistant to oxidizing and prevents the formation of an oxide film and reaction with moisture in the pores, thereby preventing decarburization and oxidation during the final sintering treatment.

The permeation of the vapor of the carboxylic acid or the anhydride thereof into the fine pores of the preliminarily sintered body is carried out by introducing the vapor into a preliminary sintering furnace in which the preliminarily sintered body is contained and controlled the temperature in the furnace chamber to a temperature appropriate for the permeation. Alternatively, the preliminarily sintered body may be removed from the furnace and subjected to the vapor permeating treatment in a different container if the preliminarily sintered body is not oxidized too rapidly.

The carboxylic acid or the anhydride thereof is believed to combine with the metal surface or the metal carbide surface, and accordingly to be capable of preventing oxidation and decarburization during sintering. This effect is probably caused by the vaporized carboxylic acid combining with the surface of the metal or the metallic compound by a chemical adsorption or chemical reaction.

If it is assumed that a pore diameter for the intermediate sintered body more than about 10A in diameter tends to cause excess oxidation, the maximum size of the molecule of the carboxylic acid or the anhydride thereof must be smaller than 10 A to permeate into the pore. This assumption turned out to agree well empirical data. Therefore, the carboxylic acid or the anhydride thereof is restricted in accordance with the size of the molecule and the diameter of the pores in the preliminarily sintered body. Carboxylic acids and anhydrides thereof having a low molecular weight less than 200 as described in the Examples hereinafter provide most favorable results. Carboxylic acids and anhydrides thereof having a large molecular weight cannot fully permeat into the fine pores of the preliminarily sintered body.

On the other hand, since carboxylic acids and the anhydrides thereof having a high boiling point must be heated to a high temperature to be vaporized, the motion of the molecule becomes violent and accordingly the molecules are permeated into the fine pores of the preliminarily sintered body only with difficulty. Therefore, the carboxylic acid or the anhydride thereof must have a low boiling point and a low molecular weight. Accordingly, favorably results are obtained by the use of a compound having a molecular weight less than 200, e.g., acetic acid, acrylic acid, propionic acid and acetic anhydride as shown in the Examples.

Good results are obtained when the boiling point of the carboxylic acid or anhydride thereof which is utilized is less than about 200 C at 25 mm Hg, and for most preferred results the boiling point of the carboxylic acid or anhydride thereof which is utilized should be less than about 150 C at 25 mm Hg.

The carboxylic acid used may be a saturated or unsaturated fatty acid or an aromatic carboxylic acids, but must be reacted substantially only with the surface layer of the powder particles and not reacted with the interior of the particles. This is another reason for using carboxylic acids of a molecular weight less than 200. Excessive reaction can easily be determined, i.e., a n-phase will be formed or cavities will result. In such a case one should reduce the contact time, vapor pressure or temperature of operation, or reduce two or more of such parameters. While an important factor, as a general rule one must use treatment condition which are obviously excessive as compared to the illustrative discussion in the present invention to reach such an inferior product.

According to the above described three types of treatments, a cemented carbide having a desired carbon content can be produced with ease and at low cost.

Higher fatty acids and metallic salts thereof (oleic acid, stearic acid, laurylinic acid and their aluminum, calcium, magnesium, zinc, lead and sodium salts) are well known as rust-proofing agents for metallic articles. The rust-proofing mechanism of these compounds is believed to be similar to that of the lower fatty acids used in this invention, but such higher fatty acids are used together with an oil and fat. Besides, the molecular weight of the higher fatty acid is as large as possible to improve the adsorbing property, so that high amounts of residual carbon are caused as shown in Figure.

Thus, the control of the carbon content and the penetration into the fine pores are impossible if a higher fatty acid is applied to the process of this invention. Therefore, a higher fatty acid cannot be used for preventing the oxidation of the intermediate sintered body and for controlling the carbon content of the latter and the starting powder.

The optimum amounts of carbon in a cemented carbide are known to the art, and can be suitably determined by one skilled in the art. For instance, for a WC- (TiC-TaC)-Co alloy, where carbon is present in insufficient amounts, an anomalous phase, the "q-phase re sults, and the alloy becomes very brittle. On the other hand, where excessive carbon is present, free carbon results, also causing the alloy to become brittle. The carbon content to maintain a normal cemented carbide matrix will obviously vary depending upon the composition of the cemented carbide. Usually, however, the carbon content is within the range of from about 0.06 to about 0.2 weight percent. It is preferred to control the carbon content to within i 0.02% of the above range.

As particularly described above, the feature of this invention is to use solely a lower fatty acid having a molecular weight of less than 200 without the use of an oil or a fat, and to make use of the activity of the powder and the vapor permeability of the powder and the liquid dispersing property of the lower fatty acid having a low molecular weight, whereby the adsorption of the lower fatty acid to the powder surface is increased, the oxidation of the powder is inhibited and the carbon content of the resultant sintered body can be controlled.

Now, more specific embodiments of this invention will be described with reference to some Examples.

EXAM PLE l g of W oxide powder having a BET value of 9 m /g was reduced in an H gas atmosphere at 700 C for 20 min and cooled down to 100 C in the H atmosphere. Then, acetic anhydride vapor was introduced into the H gas (vapor pressure of acetic anhydride 180 mmHg.) until the temperature decreased to room temperature over one hour period. The metallic W powder thus obtained had adhered thereto 1.2 wt acetic anhydride and showed no temperature increase upon exposure to the atmosphere.

On the other hand, metallic W powder obtained by reducing in the same manner and cooling to the room temperature in the pure H gas atmosphere self-ignited upon exposure to air.

In the case that acetic anhydride vapor was replaced with acetic acid, propionic acid or butyric acid, the reduced metallic W powder again did not show a temperature elevation upon exposure to air.

In this embodiment the primary criterion for successful operation is that sufficient carboxylic acid or anhydride be present on the powder to prohibit oxidation thereof. The exact amount of carboxylic acid or anhydride which is required cannot be fixed with specificity because this will depend upon the severity of handling conditions to which the treated powder will be exposed. Usually, however, greater than about 0.2 weight percent of the carboxylic acid or anhydride will suffice, and in view of the relatively low cost of these materials usually from about 0.5 to 1.5 weight percent will be used. Greater amounts, of course, are acceptable but generally will not be necessary and, since they are generally not necessary will tend to render the process economically less attractive due to unnecessary application of the carboxylic acid or anhydride.

The temperature, time of application and vapor pressure of the carboxylic acid or anhydride are relatively non-critical and can be appropriately selected by one skilled in the art to bring sufficient amounts of the carboxylic or anhydride in the contact with powder. A simple test can be used to determine if the processing conditions are acceptable, that is, if the powder obtained self-ignites upon exposure to air, greater amounts of the carboxylic acid or anhydride or longer exposure times are needed. In view of the relatively low cost of the carboxylic acid or anhydride, it is usually easier to use relatively high vapor pressures of these components and a vapor pressure of about 100 to about 190 mm Hg will be used. Although very low vapor pressures can be used, for instance, as low as about 10 mm Hg, little will be gained by using such low vapor pressures considering the relatively low expense of the carboxylic acid or anhydride versus the extra care which is necessary to control such low vapor pressures.

The temperature of operation is usually less than about 350 C in order to avoid the necessity for high temperature resistant equipment, and operation will generally proceed quite adequately at from room temperature to 150 C. Considering the factor of hole-time in the apparatus, usually treatment for about one-half hour to about four hours will be used, and treatment in the general area of one hour is usually sufficient. While very low times, for instance, in the area of ten minutes, can be used with extra care of operation, considering the economics of the process usually the extra effort required by the process operator to use such low times will be economically undesirable.

EXAMPLE 2 50 g of Co oxide powder was reduced in H gas at 600 C for min. and cooled down to 100 C in an H gas atmosphere. Then, butyric acid vapor was introduced into the H gas atmosphere (vapor pressure of butyric acid 50 mm Hg) until the temperature was reduced to room temperature over a one hour period. The obtained Co powder had 0.8 wt.% butyric acid adhered thereto and did not show a temperature elevation after exposure to air, whereas Co powder obtained by reducing in the same manner but cooling in a pure H gas atmosphere self-ignited upon exposure to air.

In the case that butyric acid vapor was replaced with acetic anhydride, acetic acid or propionic acid vapor the reduced Co powder also showed no temperature elevation after exposure to air.

In the case of using butyric acid, generally lower vapor pressures are preferred, with from 30 60 mm Hg being generally used. In the case of butyric acid, usually from about 0.6 to 1.6 weight percent butyric acid adhered to the powder suffices for all practical commercial operations. Other conditions of operation and the factors to be considered in the treatment are as discussed in Example 1.

10 EXAMPLE 3 parts by weight of WC powder containing 0.04 wt.% oxygen, 6.11 wt.% fixed carbon and 0.06 wt.% free carbon was mixed with 10 wt. parts of Co powder containing 0.27 wt.% oxygen (500 g total powder) and the resulting mixture was blended in a ball mill with 300 cc acetone as a wetting agent for hours at 30 C. Acetic acid in an amount of 0.4 wt.% (2g) of the powder mixture was added to the acetone prior to blending. The resultant powder mixture, after thermally expelling the acetone, contained 0.12 wt.% 0 (excluding the combined oxygen of the butyric acid) upon oxygen analysis and contained 0.38 wt.% acetic acid.

This powder mixture was further compressed at 1 ton/cm pressure and sintered at 1,400 C under vacuum for 1 hour. The sintered body obtained showed a transverse rupture strength of 322 kg/mm (ASTM), and contained 5.49 wt.% fixed carbon and 0.00% free carbon.

On the other hand, powder mixture obtained in the same manner as described above except no acetic acid was added to the acetone contained 0.58 wt.% oxygen. The sintered body produced from this powder mixture contained 5.22 wt.% combined carbon and 0.00 wt.% free carbon, and resulted in a n-phase due to the lack of carbon.

In the case that carbon powder was added to the starting powder mixture in an amount of 0.25 wt.% of the latter, the vacuum-sintered body obtained by similar treatments of blending, drying and forming contained 5.48 wt.% combined carbon and 0.00 wt.% free carbon, and exhibited a normal microstructure but a low transverserupture strength, i.e., 247 kg/mm (ASTM).

In a manner similar to heretofore discussed for the powder embodiment in Examples 1 and2, the primary criterion which the mixing embodiment of the present invention must meet is that sufficient carboxylic acid or anhydride be adhered to the powder during the mixing treatment. As the discussion in the immediate proceeding paragraphs make clear, simple tests are also available in this embodiment to determine if the process conditions are effective, i.e., if a n phase results, one generally would additional carboxylic acid or anhydride to increase the amount thereof, or would increase the process time. These conditions can be easily determined by one skilled in the art in view of the present discussion considering the fact that the process variables for this embodiment are relatively uncomplicated.

Usually, considering the relatively low cost of the solvents used and the relatively low cost of the carboxylic acid or anhydride thereof, if insufficient protection is provided the amount of carboxylic acid or anhydride thereof in the solvent is increased. Considering these factors, seldom would one use less than 0.2 weight per cent of the carboxylic acid or anhydride, and generally from 0,4 to 0.6 weight percent, based on the amount of powder mixture, will suffice to provide good results. Greater amounts of carboxylic acid or anhydride can be used, of course and in certain instances where high solvent amounts are needed for some special process technique one would generally operate with greater amounts of carboxylic acid or anhydride. Most usually, however, no overly significant increase in results is encountered by using very high amounts of carboxylic ill acid or anhydride. The exact proportions can, of course, be determined by one skilled in the art depending upon the properties of final product.

In the above example, 0.38 weight percent of the carboxylic acid was adhered to the powder. This corresponded to 1.9 grams, and it can be seen that an extremely small amount of carboxylic acid (or, of course, the anhydride thereof) is effective for the purposes for the present invention. So as to provide a slight safety margin, one usually would not attempt to adhere much less than 0.2 weight percent of the carboxylic acid or anhydride, and so as to avoid excessive amounts of carboxylic acid or anhydride which leads to increased cost, and it will be found for most applications that an adhered amount of about 0.3 weight percent to about 0.6 weight percent is sufficient.

The temperature of operation is not overly critical and operation will generally be at room temperature. Seldom would any need exist to operate at temperatures greater than about 40 50 C.

The exact time of operation can vary over a wide range, and will depend primarily upon the degree of mixing achieved. This can easily be determined by one skilled in the art for the exact system under consideration.

EXAMPLE 4 90 wt. parts of WC powder containing 0.071 wt.% oxygen, 6.12 wt.% combined carbon and 0.02 wt.% free carbon, 5 wt. parts of TaC powder containing 0.04 wt.% oxygen, 6.21 wt.% combined carbon and 0.02 wt.% free carbon and 5 wt. parts of Co powder containing 0.31 wt.% oxygen (500 g total powder) were mixed with each other, and the powder mixture was blended in an oscillaing ball mill with 300 cc ethyl alcohol as the wetting agent for 6 hours. at 30 0. Acrylic acid monomer in an amount of 0.5 wt.% (2.5 g) of the powder mixture was added to the ethyl alcohol prior to ball milling.

Oxygen analysis of the resultant powder mixture after thermally expelling the ethyl alcohol by heating on a water bath showed that the carbon content of the powder mixture was 0.09 wt.% (excluding the combined oxygen of the acrylic acid monomer). The amount of acrylic acid adhered was 0.42 wt.% (21 g).

The powder mixture was further compressed at l ton/cm pressure and sintered at 1,450 C under vacuum for 1 hr. The sintered body obtained exhibited a transverse rupture strength of 225 kg/mm (ASTM) and contained 5.79 wt.% fixed carbon and 0.00 wt.% free carbon.

On the other hand, a powder mixture obtained in the same manner as described above except for omitting the acrylate monomer in the ethyl alcohol contained 0.36 wt.% oxygen. A sintered body produced from this powder mixture contained an undesirably small carbon content and n-phase formation resulted. In the case that carbon powder was added to the starting powder mixture in an amount of 0.14 wt.% of the latter, the resultant sintered body produced by blending, drying, compressing and vacuum-sintering in the same manner contained 5.77 wt.% combined carbon and 0.00 wt.% free carbon, and exhibited a normal microstructure but a low transverse rupture strength, e.g., 194 kg/rnm (ASTM).

The same basic criteria discussed with respect to Example 3 apply to Example 4, although generally one would add slightly greater amounts of acrylic acid to the mixture, for instance, greater than about 1.2 grams which corresponds to 0.24 weight percent.

EXAMPLE 5 wt. parts of TiC powder containing 0.05 wt.% oxygen, 19.95 wt.% combined carbon and 0.16 wt.% free carbon, 15 wt. parts of MoC powder containing 0.10 wt.% oxygen, 5,86 wt.% combined carbon and 0.09 wt.% free carbon, and 15 wt. parts of Ni powder containing 0.27 wt.% oxygen (200g total powders) were mixed with each other, and the powder mixture obtained was blended in a ball-mill with benzine (300 cc) as the wetting agent for 150 hr. at 30 c. Propionic acid in an amount of 0.5 wt.% (1 g) of the powder mixture was added to the benzine prior to blending. Oxygen analysis showed that the resultant powder mixture after thermally expelling the benzine contained 015 M5 oxygen (excluding the combined oxygen of the propionic acid). 0.41 wt.% (0.82 g) propionic acid was adhered to the powder mixture.

This powder mixture was compressed at 1 ton/cm pressure and vaccum-sintered at l,360 C for 1 hr.. The sintered alloy obtained exhibited transverse rupture strength of 222 kg/mm and contained 14.88% combined carbon and 0.00 free carbon.

On the other hand, a powder mixture obtained without the addition of the propionic acid to the benzine contained 0.61 wt.% oxygen. In order to compensate for the low carbon of the alloy after sintering, carbon powder was added to the mixture in an amount of 0.24 wt.% of the latter. After wet-blending, drying, compressing and sintering the carbon enriched powder mixture, the resultant sintered alloy contained 14.89 wt.% carbon but exhibited a low transverse rupture strength, e.g., 196 kg/mm (ASTM).

The same basic criterion discussed in Example 3 and Example 4 apply to Example 5. For propionic acid, the adhesion ratio (propionic acid added: propionic acid adhered) was about weight percent. Usually, one would thus provide a slight safety factor and adhere from about 0.4 to about 0.8 weight percent of propionic acid to the powder. Again, little is to be gained by using low amounts of the relatively inexpensive propionic acid, and though for certain specialized applications one might desire to use an amount approaching 0.25 weight percent, as a general rule the economics of the present process are not substantially benefited by using very low amounts of the carboxylic acid or anhydride, and the tendency will be to use greater amounts so as to insure sufficient carboxylic acid or anhydride is adhered to provide the necessary amount of protection.

EXAMPLE 6 A WC5% Co powder mixture was prepared in a ball mill, compressed and vacuum-sintered without preliminary sintering. The resultant sintered body contained 5.90 wt.% combined carbon and 0.01 wt.% free carbon.

A compressed body of the same composition was preliminarily vacuum-sintered at 700 C keeping the vacuum at 5 X 10 mm Hg. The resultant sintered body was then cooled to room temperature in a vacuum kept at the same level.

Acetic anhydride vapor obtained by heating the latter at 3040 C under a vacuum has then introduced into the vacuum-sintering furnace (vapor pressure=20mmI-Ig) for 30 min. at room temperature. About 0.5 wt.% acetic anhydride adhered thereto. The primininarily sintered body thus obtained was taken out from the furnace and charged into a constant temperature humidity container kept at 40C and 80% moisture. The treated body was again vacuum-sintered at 1,400C for 1 hr..

Another preliminarily sintered body not treated with acetic anhydride vapor was also subjected to a final sintering treatment in the same manner.

The sintered body which was treated with acetic anhydride vapor contained 5.82 wt.% combined carbon and 0.00 wt.% free carbon and was scarcely oxidized. In addition, no abnormal structure or cavities were observed, and the physical properties were favorable.

On the other hand, the sintered body which was not treated with acetic anhydride vapor was oxidized, and accordingly contained 5.44 wt.% combined carbon and 0.00 wt.% free carbon. Further, the n-phase was observed in the microstructure and many cavities were present. The pysical properties were inferior to the acetic anhydride vapor-treated material: The properties of these materials are shown in Table 1.

Table 1 sintered body treated with acetic anhydride sintered body not treated with acetic anhydride In a manner similar to the powder and wet mixing embodiments described earlier, one skilled in the art can easily determine when process conditions are optimum by applying a simple test similar to that described in the powder mixing embodiments, i.e., the formation of an abnormal structure such as the 1; -phase or cavity formation is a clear indication that additional carboxylic acid or anhydride thereof must be introduced into the preliminarily sintered body. Since this operation can generally be carried out in the sintering furnace, it will be understood by one skilled in the art that so long as the essential criterion of sufficient adhered carboxylic acid or anhydride is met, the exact process conditions selected are not overly critical in the sense that certain process conditions must necessarily be maintained within a certain range.

For case of operation, generally the vapor pressure of the carboxylic acid or anhydride will be greater than mm Hg. The use of lower pressures generally increases the process time, and since this is unnecessary and can be avoided merely by using slightly greater amounts of the carboxylic acid or anhydride vapor little is to be gained by such practice. As a general rule, a carboxylic acid or anhydride vapor pressure of 200 mm Hg permits sufficiently rapid operation without the necessity for any type of special high pressure apparatus. Of course, greater vapor pressure could be used, but this introduces an unnecessary complication into the process and will be seldom be used in actual commercial practice.

In a manner similar to the earlier embodiments, the general tendency in this embodiment will be to adhere greater amount of carboxylic acid or anhydride rather than lesser amounts. For example, seldom would one use amounts less than about 0.2 weight percent in view of the fact that additional amounts will provide a safety factor for any variations in process conditions which may inadvertently occur. Generally speaking, from about 0.3 to about 0.6 weight percent of adhered carboxylic acid or anhydride will suffice to protect the formed body for most ordinary handlings and treatments, but in certain instances one may, considering the low cost of the carboxylic acid or anhydride, wish to utilize greater amounts.

While generally the contacting treatment can take place in the area of room temperature, higher tempera tures can, of course, be used, though seldom will a temperature greater than 350C be needed. In fact, little is to be gained by operation for most materials outside the range of room temperature to about C.

The time of treating will, of course, depend upon the materials treated, the vapor pressure and the temperature of treatment, and considering hold-time in the apparatus and the relative high cost of cemented carbides, usually one will treat for about one third hour to about four hours. Greater times can be used, of course, but once a sufficient amount of carboxylic acid or anhydride is adhered nothing is to be gained by further treatment. On the other hand, while lower treatment times can be used seldom would one treat for less than 10 minutes, considering above factors, in order to provide a safety factor.

EXAMPLE 7 Sintered bodies identical to those in Example 6 were left in a room for 3 days instead of being stored in a constant temperature and humidity vessel, and both were then subjected to final sintering treatment as in Example 1. The test results are shown in Table 2 wherein the sintered body treated with acetic anhydride vapor showed better physical properties as compared to the sintered body not heated with acetic anhydride vapor.

Table 2 sintered body treated with acetic anhydride sintered body not treated with acetic anhydride EXAMPLE 8 A WC-Co powder mixture produced in the same manner as in Example 6 was compressed to form a 16 mm cube and a bending strength test piece. These materials were prelimary sintered at 700C for 30 minutes in a H gas atmosphere, and cooled therein to room temperature. Since the obtained preliminarily sintered body would be easily oxidized, acrylic acid monomer vapor (vapor pressure 200 mm Hg) was introduced into the H gas atmosphere for 30 min. at room temperature to adhere the vapor to the preliminarily sintered body in the H gas atmosphere. The amount of acrylic acid adhered was about 0.6 wt.%. The preliminarily sintered body thus treated was kept in a constant temperature and humidity vessel under the same conditions as in Example 6, and then vacuum sintered at 1,400C for 1 hour and 0.01 mm Hg pressure.

Another preliminarily sintered body not treated with acrylic acid (monomer) vapor was also subjected to final sintering treatment in the same manner.

The physical properties of both sintered bodies are shown in Table 3.

The trends indicated in the present example basically follow the discussion regarding Example 6. However, with acrylic acid a preferred vapor pressure will be in the range of from about 50 to about 300 mm Hg, with the tendency being to utilize vapor pressures near the higher end of this range. Seldom would one use vapor pressures as low as about mm Hg for the reasons advanced in Example 6.

In a manner similar to that in Example 6 the temperature and time of treatment can vary, with generally temperatures in the area of room temperatures being used, though higher temperatures, e.g., 40 to about 100C, can be used. With acrylic acid usually operation will be at a temperature less than about 150C.

The time of operation is selected in accordance with the principles set out in Example 6, with generally operations for about one half hour being selected as providing an adequate safety factor and yet not unduly increasing the hold time in the apparatus.

As shown in the earlier embodiments where acrylic acid as used, as compared to acetic acid, or butyric acid, the tendency will be to adhere somewhat greater amounts of acrylic acid, but usually an amount of from about 0.3 to about 1.2 weight percent adhered acrylic acid is sufficient for ordinary commercial practices. Usually one would not adhere as little as about 0.2

weight percent in order to provide a safety factor for the operation.

EXAMPLE 9 A preliminarily sintered body formed as in Example 6 was treated with acrylic acid (monomer) or a like carboxylic acid in lieu of acetic anhydride, and subjected to the final sintering treatment as described in Example 6. Carbon analysis of the thus obtained sintered bodies showed that sintered bodies treated with carboxylic acid were scarcely oxidized and the decrease of the carbon content of the latter was low, whereas a sintered body not treated with a carboxylic acid showed greatly increased oxidation and the reduction of the carbon content was also great, as shown in Table 4.

Whether the carboxylic acid or the anhydride thereof is fully penetrated into the pores of the intermediate sintered body to prevent its oxidation can be ascertained by cutting the sintered body after treatment and exposing the latter to an oxidizing atmosphere at high temperature and high humidity.

The action of various carboxylic acids or anhydrides thereof are compared below.

EXAMPLE 10 A compressed body produced from a WC5% Co alloy powder was subjected to preliminary sintering at 700C under 0.03 mm Hg vacuum. Then, the preliminarily sintered body was cooled to C while under vacuum. Then, a carboxylic acid vapor at 100C (or the anhydride thereof) selected from acetic acid, acetic an hydride, acrylic acid, propionic acid, butyric acid, propionic anhydride, isovaleric acid, crotonic acid, caproic acid and benzoic acid was introduced into the H gas atmosphere.

To test the action of each carboxylic acid or the anhydride thereof, two compressed powder bodies (cubes having 40 mm X 40 mm X 40mm size) were used as specimens. One of the specimens after being presintered was cut into two halves. Then, a pair of cut specimens, the uncut specimen treated by the carboxylic acid and another standard specimen not treated with the carboxylic acid (non-treated specimen) were charged into a constant temperature humidity vessel kept at 40C and 90% moisture for hr., taken out of the vessel and vacuum-sintered at 1,450C, for 1 hr. under 0.01 mm Hg vacuum. The results of carbon analysis of the sintered bodies obtained are shown in Table 5.

It will be apparent from Table 5 that the carbon content of the sintered body decreases as the oxidation thereof. Assuming that the carbon content of the uncut specimen is indicated as A and that of the untreated specimen is indicated as C, the large A-C value means that the oxidation inhibiting action of the corresponding carboxylic acid or the anhydride thereof used is strong. On the other hand, assuming that the carbon content of the cut specimen is indicated as B, a small A-B value means that the action of the corresponding carboxylic acid or the anhydride thereof to prevent the oxidation of the interior of the sintered body is strong. Therefore, a carboxylic acid or the anhydride thereof showing a large A-C value and a small A-B value is favorable.

molecular weight of less than 200 or an anhydride thereof to a starting powder of a Group lV-a, Group V-a or Group VI-a metal, a powder of an alloy containing such metals or a solid solution containing said metal, or a powder of a carbide of said metal.

2. A process for producing an intermediate product in the formation of a cemented carbide characterized by adhering an unsubstituted carboxylic acid having a molecular weight of less than 200, or an anhydride Table 5 carboxylic acid or the anhydride thereof A B C A-C A-B name boiling point molecular weight acetic acid 118C 60.05 5.56 5.56 4.57 0.99 0.00

acetic 140 102.06 5.51 5.48 4.55 0.96 0.03 anhydride acrylic acid 141 72.06 A 5.59 5.59 4.57 1.02 0.00

propionic 141 74.08 5.53 5.51 4.57 0.96 0.02 acid butyric: acid 162 88.10 5.47 5.31 4.57 0.82 0.21

propionic 168 130.16 5.39 5.18 4 57 0.82 0 21 anhydride isovaleric 174 102.13 5.42 5.25 4.56 0.86 0.17 acid crotonic 189 86.09 5.43 5.30 4.56 0.87 0.13 acid caproic 206 116.16 5.36 5.13 4 55 0.81 0 23 acid benzoic 250 122.12 5.32 5.06 4.57 0.75 0.26 acid It will be understood from Table 5 and the drawing that a carboxylic acid or the anhydride thereof having a molecular weight of less than 200, especially acetic acid, acetic anhydride, acrylic acid or propionic acid,

exhibit a large A-C value and a small A-B value and are 4 most suitable for use.

Although the effect of the carboxylic acid or the anhydride on the treatment of the starting powder or the intermediate sintered body is primarily influenced by the molecular weight of the acid or the anhydride, the 45 value of the boiling point also has an influence on the treatment.

In any case, the oxidation of (1 a starting powder for the super hard alloy, (2) a mixture of the starting powder, (3 a powder compressed body or (4) an intermediate sintered body can be prevented by adhering thereto a carboxylic acid having a molecular weight of less than 200, or the anhydride thereof. Therefore a cemented carbide having a desired carbon content can be produced irrespective of the length of the time period required for producing the latter or storing and shipping an intermediate product, without the use of any particular atmosphere gas or apparatus.

While the invention has been described in detail and I with reference to specific embodiments thereof, it will thereof, to a powder of a Group VIII metal or a powder of an alloy containing said metal.

3. A process for producing an intermediate product in the formation of a cemented carbide, according to the claim 1 characterized by adhering the unsubstituted carboxylic acid or anhydride thereof, in the vaporized state, to the starting powder immediately after preparation thereof.

4. A process for producing an intermediate product in the formation of a cemented carbide characterized by adhering an unsubstituted carboxylic acid having a molecular weight of less than 200, or an anhydride thereof, to a powder mixture containing both: (a) one or more powders of a Group lV-a, Group V-a or Group Vl-a metal, a powder of an alloy or a solid solution containing such a metal or a powder of a carbide of such a metal, and (b) one or more powders of Group VIII metal or an alloy thereof.

5. A process for producing an intermediate product according to claim 4 characterized in that the unsubstituted carboxylic acid or an anhydride thereof is adhered to the starting powder by adding the unsubstituted carboxylic acid or the anhydride thereof to a wet- 0 ting solution for mixing the powders.

6. A process for producing an intermediate product in the production of a cemented carbide characterized by compressing a powder mixture containing: (a) one or more powders of a Group IV-a, Group V-a or Group Vl-a metal, a powder of an alloy or a solid solution containing such a metal, and (b) one or more powders of a Group VIII metal and a powder of an alloy thereof, and adhering an unsubstituted carboxylic acid having a molecular weight of less than 200 or an anhydride thereof to the resultant compressed powder body.

7. A process for producing an intermediate product according to the claim 6 characterized in that the adherence of the unsubstituted carboxylic acid or the anhydride thereof to the compressed powder body is carried out by exposing the compressed powder body to the gaseous carboxylic acid or anhydride thereof.

8. A process for producing an intermediate product in the formation of a cemented carbide characterized by compressing a powder mixture containing (a) one or more powders of a Group IV-a, Group V-a or Group VI-a metal, a powder of an alloy or a solid solution containing such a metal; and (b) one or more powders of Group VIII metal or a powder of an alloy thereof, subjecting the resultant compressed powder body to preliminary sintering at a temperature lower than the final sintering temperature, and then adhering an unsubstituted carboxylic acid having a molecular weight of less than 200 or an anhydride thereof to the obtained preliminarily sintered body, which sintered body has fine pores in the surface thereof.

9. A process for producing an intermediate product according to claim 8 characterized in that the adherence of the unsubstituted carboxylic acid or the anhydride thereof to the intermediate sintered product is carried out by introducing gaseous carboxylic acid or the anhydride thereof into an intermediate sintering zone to penetrate the gas into the fine pores of the preliminarily sintered body.

10. In a process for producing cemented carbides comprising one or more carbides of a Group IV-a, V-a or VI-a metal and one or more metals from Group VIII involving a high temperature sintering operation, the improvement wherein the components of the cemented carbide are, in at least one processing sequence prior to final sintering, contacted with an unsubstituted carboxylic acid or anhydride thereof having a molecular weight less than 200, whereby oxidation is prevented.

11. In a process for producing cemented carbides comprising one or more carbides of a Group IV-a, V-a or VI'a metal and one or more metals from Group VIII by wet mixing and drying a starting powder of said carbides to form a mixture powder, pressing said mixture powder to form a formed body, optionally preliminarily sintering said formed body, and finally sintering said formed body, the improvement comprising applying an unsubstituted carboxylic acid or an anhydride thereof having a molecular weight less than 200 on an oxidizable material used to produce said cemented carbide to prevent oxidation.

12. A process comprising contacting an oxidizable material used in the production of cemented carbides by wet mixing and drying a starting powder of said carbides to form a mixture powder, pressing said mixture powder to form a formed body, optionally preliminarily sintering said formed body, and finally sintering said formed body, said material comprising a Group lV-a, V-a, VI-a or VIII metal, or a Group IV-a, V-a or VI-a carbide or a carbide solid solution, with an unsubstituted carboxylic acid or an anhydride thereof having a molecular weight of less than 200 to prevent oxidation of said material.

13. An intermediate product used in the formation of a cemented carbide comprising,

a starting powder of a Group IV-a, Group V-a or Group VI-a metal, a powder of an alloy containing such metals or a solid solution containing said metal, or a powder of a carbide of said metal having adhered thereto an unsubstituted carboxylic acid having a molecular weight of less than 200 or an anhydride thereof.

14. An intermediate product used in the formation of a cemented carbide comprising, a powder mixture containing both:

a. one or more powders of a Group IV-a, Group V-a of Group VI-a metal, a powder of an alloy or a solid solution containing such a metal or a powder of a carbide of such a metal, and

b. one or more powders of Group VIII metal or an alloy thereof having adhered thereto an unsubstituted carboxylic acid having a molecular weight of less than 200, or an anhydride thereof.

15. An intermediate product used in the formation of a cemented carbide comprising, a formed body containing:

a. one or more powders of a Group IV-a, Group V-a or Group VI-a metal, a powder of an alloy or a solid solution containing such a metal, and

b. one or more powders of a Group VIII metal or a powder of an alloy thereof having adhered thereto an unsubstituted carboxylic acid having a molecular weight ofless than 200, or an anhydride thereof.

16. An intermediate product used in the formation of a cemented carbide comprising,

a preliminarily sintered body having fine pores in the surface thereof, said body containing a. one or more powders of a Group VI-a, Group V-a or Group VI-a metal, a powder of an alloy or a solid solution containing such a metal, and

b. one or more powders of a Group VIII metal or a powder of an alloy thereof having adhered thereto an unsubstituted carboxylic acid having a molecular weight of less than 200, or an anhydride thereof.

17. The process of claim 11, wherein said applying is in a non-oxidizing atmosphere or in a vacuum.

Claims

1. S PROCESS FOR PRODUCING AN INTERMEDIATE PRODUCT IN THE FORMATION OF A CEMENTED CARBIDE CHARACTERIZED BY ADHERING AN UNSUBSTITUTED CARBOXYLIC ACID HAVING MOLECULAR WEIGHT OF LESS THAN 200 OR AN ANHYDRIDE THEREOF TO A STARTING POWDER OF A GROUP IV -A, GROUP V1-A METAL, A POWDER OF AN ALLOY CONTAINING SUCH METALS OR A SOLID SOLUTION CONTAINING SAID METAL, OR POWDER OF A CARBIDE OF SAID METAL.

2. A process for producing an intermediate product in the formation of a cemented carbide characterized by adhering an unsubstituted carboxylic acid having a molecular weight of less than 200, or an anhydride thereof, to a powder of a Group VIII metal or a powder of an alloy containing said metal.

4. A process for producing an intermediate product in the formation of a cemented carbide characterized by adhering an unsubstituted carboxylic acid having a molecular weight of less than 200, or an anhydride thereof, to a powder mixture containing both: (a) one or more powders of a Group IV-a, Group V-a or Group VI-a metal, a powder of an alloy or a solid solution containing such a metal or a powder of a carbide of such a metal, and (b) one or more powders of Group VIII metal or an alloy thereof.

5. A process for producing an intermediate product according to claim 4 characterized in that the unsubstituted carboxylic acid or an anhydride thereof is adhered to the starting powder by adding the unsubstituted carboxylic acid or the anhydride thereof to a wetting solution for mixing the powders.

6. A process for producing an intermediate product in the production of a cemented carbide characterized by compressing a powder mixture containing: (a) one or more powders of a Group IV-a, Group V-a or Group VI-a metal, a powder of an alloy or a solid solution containing such a metal, and (b) one or more powders of a Group VIII metal and a powder of an alloy thereof, and adhering an unsubstituted carboxylic acid having A molecular weight of less than 200 or an anhydride thereof to the resultant compressed powder body.

11. In a process for producing cemented carbides comprising one or more carbides of a Group IV-a, V-a or VI-a metal and one or more metals from Group VIII by wet mixing and drying a starting powder of said carbides to form a mixture powder, pressing said mixture powder to form a formed body, optionally preliminarily sintering said formed body, and finally sintering said formed body, the improvement comprising applying an unsubstituted carboxylic acid or an anhydride thereof having a molecular weight less than 200 on an oxidizable material used to produce said cemented carbide to prevent oxidation.

12. A process comprising contacting an oxidizable material used in the production of cemented carbides by wet mixing and drying a starting powder of said carbides to form a mixture powder, pressing said mixture powder to form a formed body, optionally preliminarily sintering said formed body, and finally sintering said formed body, said material comprising a Group IV-a, V-a, VI-a or VIII metal, or a Group IV-a, V-a or VI-a carbide or a carbide solid solution, with an unsubstituted carboxylic acid or an anhydride thereof having a molecular weight of less than 200 to prevent oxidation of said material.

13. An intermediate product used in the formation of a cemented carbide comprising, a starting powder of a Group IV-a, Group V-a or Group VI-a metal, a powder of an alloy containing such metals or a solid solution containing said metal, or a powder of a carbide of said metal having adhered thereto an unsubstituted carboxylic acid having a molecular weight of less than 200 or an anhydride thereof.

14. An intermediate product used in the formation of a cemented carbide comprising, a powder mixture containing both: a. one or more powders of a Group IV-a, Group V-a of Group VI-a metal, a powder of an alloy or a solid solution containing such a metal or a powder oF a carbide of such a metal, and b. one or more powders of Group VIII metal or an alloy thereof having adhered thereto an unsubstituted carboxylic acid having a molecular weight of less than 200, or an anhydride thereof.

15. An intermediate product used in the formation of a cemented carbide comprising, a formed body containing: a. one or more powders of a Group IV-a, Group V-a or Group VI-a metal, a powder of an alloy or a solid solution containing such a metal, and b. one or more powders of a Group VIII metal or a powder of an alloy thereof having adhered thereto an unsubstituted carboxylic acid having a molecular weight of less than 200, or an anhydride thereof.

16. An intermediate product used in the formation of a cemented carbide comprising, a preliminarily sintered body having fine pores in the surface thereof, said body containing a. one or more powders of a Group VI-a, Group V-a or Group VI-a metal, a powder of an alloy or a solid solution containing such a metal, and b. one or more powders of a Group VIII metal or a powder of an alloy thereof having adhered thereto an unsubstituted carboxylic acid having a molecular weight of less than 200, or an anhydride thereof.