Description of the Related Art Tungsten carbide (stoichiometric percentage 6.13% carbon) is conventionally manufactured from the carburization of tungsten powder. The tungsten powder is in turn typically obtained from tungsten bearing ores such as Scheelite and Wolframite which are mechanically treated by known means to make the recovery of tungsten possible. The exact process used to extract the tungsten powder depends upon the type of ore from which the powder is derived.

Tungsten powder may be obtained from Scheelite by hydrochloric acid leaching to produce tungstic acid and calcium chloride. The tungstic acid may then be heated in air to convert the tungstic acid to tungstic oxide which is further hydrogen reduced in a furnace to produce tungsten powder.

Alternatively, tungsten powder may also be obtained from Wolframite by reaction of the ore with sodium hydroxide at approximately 100 degrees centigrade to form sodium tungstate. The sodium tungstate may then be treated with hydrochloric acid to produce tungstic acid and sodium chloride. The

tungstic acid may be further treated with ammonium hydroxide to form ammonium paratungstate and then heated to produce tungstic oxide. The tungstic oxide formed by this process may also be hydrogen reduced as previously described. The tungsten powder produced from the tungsten containing ores according to the processes as described above is typically of a size smaller than 15 micron.

It is well known that tungsten powder particle size is critical to successful sintering and subsequent metal working operations. The size of the tungsten powder particles determines the grain size of tungsten carbide produced therefrom, which in turn influences the strength and toughness of cemented carbides produced from the tungsten carbide.

One known method for producing tungsten carbide has been to subject tungsten powder to carburization with finely divided carbon powder at about 1400-1700 degrees centigrade. Tungstic oxide or tungstic acid may also be used in place of the tungsten powder to produce tungsten carbide. Still yet another method of producing tungsten carbide is by thermochemical treatment of the tungsten ores to directly produce macrocrystalline tungsten carbide. Macrocrystalline tungsten carbide refers to crystal particles having a size typically larger than 15 micron. As used herein the process for producing macrocrystalline tungsten carbide may be any suitable process such as but not limited to the alumino thermit process or the menstruum process.

The menstruum process is a process for the formation of tungsten carbide within a melt of auxiliary metals. The process requires the addition of external energy which often is supplied by the use of inductive coils. For a more detailed description of the menstruum process reference is made to Eloff,

Production of Metal Carbides, 7 Metals Handbook, Ninth Edition 156-159 (1984) , incorporated herein by reference.

The alumino thermit process is a self sustaining reaction in which macrocrystalline tungsten carbide is produced from a blend of tungsten ore concentrates. The blend contains at least 55 weight percent tungsten, and more preferably, at least 57 weight percent tungsten. Preferably, the individual tungsten sources constituting the blend also each contains greater than 55 weight percent tungsten. In addition, the blend contains less than or equal to 0.03 weight percent Ti, 0.03 weight percent Ta and 0.03 weight percent Nb. Preferably, the blend of tungsten ore concentrates contains both wolframite and scheelite ore concentrates.

More particularly, macrocrystalline tungsten carbide is produced by the steps of: (1) providing a reaction charge constituted of the foregoing blend of tungsten ore concentrates, calcium carbide, metallic aluminum, up to 0.43 kilograms of iron oxide per kilogram of tungsten in the charge, and 0.04 to 0.31 kilograms of metallic iron per kilogram of tungsten in the charge;

(2) proportioning the reaction charge to provide, upon ignition, a self-sustaining exothermic reaction to develop a calculated operating temperature within the charge of about 4372° to about 4500°F with production of a crystal mass of crystalline tungsten monocarbide containing residual calcium carbide and metallic aluminum in amounts providing a reducing condition at the end of the reaction;

(3) disposing a first portion of the reaction charge in a kiln and igniting it;

(4) progressively feeding the rest of said reaction charge into the kiln at a rate to maintain a continuous substantially smooth reaction;

(5) separating the crystal mass from the slag products of the reaction; and

(6) recovering crystalline tungsten monocarbide from the crystal mass.

In an alternate embodiment of this process, a heater charge of metallic aluminum, iron oxide and calcium carbide may be placed in the kiln and ignited prior to introducing the reaction charge.

For a more detailed understanding of the production of macrocrystalline tungsten carbide reference is made to United States Patent Nos. 3,379,503 and 4,834,963 assigned to Kennametal Inc. and incorporated herein by reference.

One known use of the tungsten carbide powder produced in the manner described above is in infiltration type operations in the formation of an article such as a drill bit. In the formation of a drill bit, hard wear resistant objects such as diamonds are initially positioned about the interior surface of a mold cavity. A powdered tungsten carbide such as P-90 matrix powder available from Kennametal Inc. is then placed in the mold thereby surrounding the wear resistant objects and partially filling the mold cavity. A tungsten shoulder powder is then added to the mold completely filling the mold cavity. A binder metal which will wet the carbide powder in the molten state is added, and the mold and its contents are then heated to an infiltration temperature above the melting point of the binder. As it approaches the infiltration temperature, the binder melts and flows into the interstices between the powder granules. Upon hardening, the unfinished composite product typically includes a top excess alloy layer, an intermediate infiltrated tungsten shoulder powder layer, and a

bottom infiltrated matrix powder such as P-90. The excess alloy and the shoulder powder may then be machined to a finished state. It will be appreciated that products of this type are widely used in the fabrication and hardsurfacing of oil field drill bits and similar tools normally subjected to severe abrasion or erosion.

The previously known tungsten powder used as a shoulder powder and which is infiltrated with a metallic binder to form composite products as described in the preceding paragraph is adequate for many purposes but further improvements in the characteristics of powdered tungsten are desired. Through the use of the present invention it is possible to provide a decarburized tungsten carbide powder possessing improved characteristics.

As used herein decarburized tungsten carbide refers to either partially or totally decarburized tungsten carbide of either a macrocrystalline or finer particle size. However, in a preferred form of the invention the decarburized tungsten carbide is decarburized macrocrystalline tungsten carbide.

An object of the present invention is to provide a shoulder powder of decarburized tungsten carbide exhibiting enhanced wetability, machinability, and infiltration characteristics. Another object of the present invention is to produce decarburized tungsten carbide which exhibits extremely high purity, high surface area, and uniform particle size and shape. Another object of this invention is to produce decarburized tungsten carbide having enhanced sinterability in terms of reaching a desired sintered density under comparable conditions of time and/or temperature, and/or pressure in comparison to other sinterable powders having about the same particle size and/or particle size distribution. A further object is to provide a process which enables the attainment of

the forgoing objects. Yet another object of the present invention is to provide a process for producing decarburized tungsten carbide on a continuous basis. Another object of the present invention is to provide a process for producing varying levels of decarburization of tungsten carbide whose physical characteristics are determined by simple and controllable process parameters.

SUMMARY OF THE INVENTION Briefly, according to this invention, there is provided a process for the production of varying levels of decarburized tungsten carbide powder of either fine particle size or macrocrystalline particle size. The tungsten carbide may have only a portion of the carbon removed therefrom to form decarburized tungsten carbide having a plurality of layers including at least one intermediate layer of ditungsten carbide or the tungsten carbide may have all of the carbon removed therefrom to form tungsten. The process includes the steps of forming a carburized tungsten powder and then reacting wet hydrogen with the carburized tungsten powder at an elevated temperature to produce a decarburized tungsten carbide powder. The process may be conducted in either a walking beam furnace, pusher type furnace, batch type furnace or a rotary furnace and the like. It will be appreciated that although the tungsten carbide powder is preferably a macrocrystalline tungsten carbide produced by the alumino thermit process or menstruum process as described above, the tungsten carbide may also be produced by any means known in the art. BRIEF DESCRIPTION OF THE DRAWINGS Further features and other objects and advantages of this invention will become clear from the following detailed description made with reference to the drawings in which:

Figure 1 is a longitudinal sectional view of a furnace including trays or boats having tungsten carbide contained therein;

Figure 2 is a photomicrograph, magnified to 500x and dilute Murakami etch treated, of an agglomeration of totally decarburized tungsten carbide powder crystals produced in accordance with the present invention; and

Figure 3 is a photomicrograph, magnified to 500x and dilute Murakami etch treated, of partially decarburized tungsten carbide powder crystals produced in accordance with the present invention having a relative concentration estimated in the central core of approximately 50 v/o (volume percent) WC, intermediate layer of approximately 20 v/o ₂ C and an external layer of approximately 30 v/o W.

DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to the drawings, the method of the present invention will be described. Initially, it should be understood that tungsten carbide powder of any desired particle size may be used in accordance with the present invention for subsequent decarburization. However, to obtain large decarburized macrocrystalline tungsten carbide particles the alumino thermit process or menstruum process is preferred. The alumino thermit process is described and set forth in United States Patent Nos. 3,379,503 and 4,834,963 assigned to Kennametal Inc. and in E. N. Smith, "Macro Process for Direct Production of Tungsten Monocarbide," Metal Powder Report, Vol. 35, No. 2, (February 1980) Pages 53, 54. The menstruum process is described and set forth in Eloff, Production of Metal Carbides, 7 Metals Handbook, Ninth Edition 156-159 (1984) . It will be appreciated that although most any suitable process may be used to produce the tungsten carbide crystals initially employed in the present invention, the

alumino thermit process offers the advantage of not requiring the preparation of a tungsten powder from a tungsten containing ore and then separately carburizing the tungsten powder to produce a tungsten carbide for subsequent decarburization.

Whichever process for preparing tungsten carbide is used, the tungsten carbide powder crystals so produced are loaded on to trays 10 or boats as shown in Figure 1. The trays 10 may be of most any design well known in the art and may be formed of either a ceramic or molybdenum sheet material or of any suitable known material. Preferably, the trays 10 are of a type having side rails and are covered with a shield made of ceramic or molybdenum to prevent contamination of the tungsten carbide contained therein.

The trays 10 containing tungsten carbide are then heated by charging the trays to the furnace where they are longitudinally pushed through the furnace. The furnace 18 may be of any suitable type such as a walking beam furnace, batch type furnace, pusher type furnace or a rotary furnace and the like. As shown in Figure 1, the furnace 18 is a Hayes pusher type furnace and is of a design well known in the art. A pusher type furnace 18 is a continuous furnace widely used for sintering. The Hayes pusher type furnace 18 includes a furnace chamber 20 having an entrance 22, a front section 23, a rear section 24, a cooling section 25, a discharge end 26, and a gas inlet 28 at the discharge end of the furnace chamber 20 and a gas exit 27 at the entrance of the furnace chamber 20. The furnace chamber 20 is further divided into approximately six separate temperature zones (not shown) for carefully controlled stage heating. It will be appreciated that the heating condition of six separate temperature zones is not a limitation to the practice of the present invention. For example, the tungsten powder may be carefully heated at one temperature in a pressure

vessel in batches or as a continuous feed to achieve substantially the same result.

In the operation of the furnace 18, trays 10 are successively charged to the furnace so that the front end 30 of each tray 10 engages the rear end 32 of the tray immediately preceding. As shown, the trays enter the furnace through entrance 22 to front section 23 and are conveyed along a ceramic hearth 12. The front section 23 preheats and purges the powder under pressure as it is advanced to the furnace chamber 20.

After the powder passes through the furnace chamber 20, the powder enters the rear section 24 for retarded cooling before entering the cooling section 25 and subsequent exit from the furnace 18 via discharge end 26 along rollers 14. By continuously charging the trays 10 to the furnace, each tray is progressively advanced through the furnace 18. Wet hydrogen gas is introduced through a gas inlet 28 and flows generally through the furnace chamber 20 counter to the direction of movement of the trays 10. The hydrogen gas may be introduced through the gas inlet 28 at a preferred flow rate of 600 cubic feet per hour but may vary from approximately as low as 350 cubic feet per hour to as high as approximately 900 cubic feet per hour. It will be appreciated that the flow rate of hydrogen introduced into the furnace chamber 20 may be varied to achieve various desired levels of decarburized tungsten carbide as more fully described herein. As the trays 10 are advanced through the furnace 18 the trays are exposed to the wet hydrogen gas and increasing temperatures within the furnace chamber 20. The temperature that each tray 10 is exposed to increases from approximately 1000 degrees fahrenheit to approximately 2600 degrees fahrenheit. At a temperature of at least 1800 degrees fahrenheit, the tungsten carbide in each tray 10 begins to decarburize. It is believed that the wet hydrogen

gas at the elevated temperature penetrates the tungsten carbide crystal from the external surface of the crystal inward thereby bonding with and liberating the most outwardly positioned carbon as methane gas. Moreover, it is believed that the water vapor within the furnace chamber 20 is reduced thereby freeing oxygen which also combines with the carbon and may enhance the liberation of carbon and subsequent bonding of the carbon and hydrogen. It will be appreciated that no appreciable decarburization of tungsten carbide was observed when tungsten carbide was exposed to only hydrogen gas at an elevated temperature in a water vapor free environment. It is believed that as the time period that the tungsten carbide crystals are exposed to free wet hydrogen within the furnace chamber 20 increases, the hydrogen penetrates further into the interstices of the crystal structure to react with and liberate previously unreacted carbon from the tungsten carbide crystal. Figure 3, as confirmed by optical microscopy, is illustrative of decarburized tungsten carbide crystals produced in accordance with one aspect of the present invention. More particularly, Figure 3 shows decarburized tungsten carbide having an inner layer of tungsten carbide, an intermediate layer of ditungsten carbide and an outer layer of tungsten.

The level of decarburization of the tungsten carbide within each tray 10 may be controlled by varying such process parameters as the depth of tungsten carbide within each tray, the residence time of the tungsten carbide within the furnace chamber 20, hydrogen concentration, and water vapor concentration. More particularly, the level of decarburization may be increased by decreasing the depth of tungsten carbide within each tray, and/or increasing the residence time of the tungsten carbide within the furnace chamber 20, and/or increasing the hydrogen and water vapor concentration. Similarly, the level of decarburization

may be decreased by increasing the depth of tungsten carbide within each tray, and/or decreasing the residence time of the tungsten carbide within the furnace chamber 20, and/or decreasing the hydrogen and water vapor concentration. Tungsten carbide crystals having various levels of decarburization have proven advantageous when machining a composite product formed by infiltration. More particularly, an outer layer of decarburized tungsten carbide has proven to be much easier to machine than an outer layer of much harder tungsten carbide crystal.

It is believed that the following reaction occurs between the tungsten carbide and the wet hydrogen gas within the furnace chamber 20 to form tungsten carbide having varying levels of decarburization.

WC + H ₂ + H ₂ 0 WxCy + CH ₄ + CO

Wherein x=l or 2 and y=0 or 1. Furthermore, in accordance with yet another aspect of the present invention, when complete decarburization of tungsten carbide to tungsten powder is achieved, the following reaction is believed to occur.

2WC + H ₂ + H ₂ 0 2W + CH ₄ + CO The gaseous products formed by the reaction of wet hydrogen gas and tungsten carbide and any unreacted wet hydrogen gas are then exhausted from the furnace chamber 20 through a gas exit 27 located near the furnace entrance 22. It will be appreciated that the decarburized tungsten carbide powder may be screened to obtain particles of selected sizes after the trays complete one pass through the furnace and then, if desired, reloaded into the trays for further decarburization. The invention will be further clarified by a consideration of the following examples, which are

intended to be purely exemplary of the use of the invention.

Example 1 Approximately 25 Kg. of -80 mesh size tungsten carbide powder produced in accordance with the process described in U. S. Patent No. 4,834,963 was loaded into approximately 12 ceramic trays as described above. The Hayes furnace, of the type previously described above, was divided longitudinally into six temperature zones of equal length. The temperature zones within the furnace chamber were as follows; zone 1: 1000 degrees fahrenheit; zone 2: 2425 degrees fahrenheit; zone 3: 2525 degrees fahrenheit; zone 4: 2600 degrees fahrenheit; zone 5: 2600 degrees fahrenheit; and zone 6: 2600 degrees fahrenheit. The rate of advancement or "push" of each tray through the furnace chamber was approximately two hours thereby requiring about 48 hours for any one tray to advance from the entrance of the furnace chamber to the exit of the furnace chamber. As used herein the term "push" refers to the time required for a tray to advance one full length of the tray. As the trays advanced through the furnace, water contained within a water bottle at a temperature of 140 degrees fahrenheit and hydrogen gas were introduced into the furnace chamber. Similarly, the hydrogen gas was introduced through gas inlets into the furnace chamber at a flow rate of 600 cubic feet per hour counter to the direction of movement of the trays. After the trays completed one pass through the furnace the tungsten carbide was evaluated and then screened to -100 mesh in size to deaglomerate it and then reloaded into the trays. The reloaded trays were again cycled through the furnace chamber to further decarburize the tungsten carbide. X-ray diffraction analysis and metallographic examination were then conducted on samples of the powder from each tray. As shown in Figure 2 and

confirmed by X-ray diffraction analysis and metallographic examination, individual tungsten carbide crystals had been reduced to multiple small crystals of tungsten metal with no remaining intact crystals of tungsten carbide.

Example 2 Approximately 500 Kg. of -80 mesh size tungsten carbide powder produced in accordance with the process described in U. S. Patent No. 4,834,963 was loaded into approximately 275 ceramic boats, covered and placed on ceramic trays of approximately 17 inches in length having side rails to a level depth of approximately 0.25 inches. The ceramic boats and covers are used to prevent contamination of the powder therein. The trays and boats were introduced in sequence into a Hayes pusher furnace. The Hayes furnace, of the type previously described above, was divided longitudinally into six temperature zones of equal length. The temperature zones within the furnace chamber were set as follows; zone 1: 1000 degrees fahrenheit; zone 2: 2425 degrees fahrenheit; zone 3: 2525 degrees fahrenheit; zone 4: 2600 degrees fahrenheit; zone 5: 2600 degrees fahrenheit; and zone 6: 2600 degrees fahrenheit. The maximum optical pyrometer reading was at 2615 degrees fahrenheit. The rate of advancement or "push" of each tray through the furnace chamber was approximately one hour thereby requiring about 24 hours for any one tray to advance from the entrance of the furnace chamber to the exit of the furnace chamber. As used herein the term "push" refers to the time required for a tray to advance one full length of the tray. As the trays advanced through the furnace, water contained within a water bottle at a temperature of 140 degrees fahrenheit and hydrogen gas were introduced into the furnace chamber. Similarly, the hydrogen gas was introduced through gas inlets into the furnace chamber at a flow rate of 600 cubic feet

per hour counter to the direction of movement of the trays. After the trays completed one pass through the furnace the tungsten carbide was screened to -100 mesh in size to deaglomerate it and then reloaded into the ceramic boats. The reloaded boats and trays were again cycled through the furnace chamber to further decarburize the tungsten carbide.

X-ray diffraction analysis and metallographic examination were then conducted on samples of the powder from each tray. As shown in Figure 3 and confirmed by metallographic examination, only partial decarburization of the tungsten carbide occurred. It is estimated, by optical microscopy, that the particle shown in Figure 3 contains relative concentrations of 50 v/o WC, 30 v/o W and 20 v/o W ₂ C. It will be appreciated that the decarburization process proceeded from total decarburization of particles of the smallest size which were most effectively exposed to the decarburization conditions to partial decarburization of larger tungsten carbide particles.

The decarburized tungsten carbide powder was then separated to selected U. S. Sieve series sizes of -80 to +200 mesh, -60 to +325 mesh, -80 to +325 mesh, and -100 to +325 mesh. Samples of each of the separated decarburized tungsten carbide powder were then tested to determine their properties. The tests conducted were as follows: sieve analysis to determine the size distribution of solid particles expressed as weight percent; apparent density and tap density using standard ASTM B 212 and ASTM B 527 (American Society for Testing and Materials) methods to determine the weight per unit volume of uncompacted powder and to determine the weight per unit volume of powder when the receptacle is tapped or vibrated; , hall flow as measured by ASTM B 213 to determine the time required for a powder sample of a standard weight to flow under atmospheric conditions through a funnel into a cavity

of a container; angle of repose and tap to determine the ability of the powder to flow around corners and the like by tilting a container filled with powder and measuring the angle at which the powder begins to slide both as the container is tapped and not tapped.

Further properties such as hardness, relative strength, and percent infiltration properties were determined based upon a "coin" prepared using infiltration techniques. The infiltration test "coin" specifications were as follows: coin size 1 1/2 in. diameter x 1/4 inch thick, cold pressure 570 psi, time at temperature 20 minutes, infiltration temperature 1150 degrees centigrade, infiltrant Cu, Ni, Zn alloy, hot pressure 640 psi, mold material graphite. Hardness measurements of both the top face and bottom face of the coin were determined using a Rockwell hardness testing machine. Break strength was determined by measuring the minimum force required to fracture the coin using a a 2.7 cm diameter steel ball bearing and a 3.02 cm inside diameter steel ring with a hydraulic bench press.

The measured properties were as follows:

TABLE I

MEASURED PROPERTIES

Example 3 Approximately 4 lbs. of -80 mesh size tungsten carbide powder produced in accordance with the process described in U. S. Patent No. 4,834,963 was loaded into one ceramic tray of as described above. The Hayes furnace, of the type previously described above, was divided longitudinally into six temperature zones of equal length. The temperature zones within the furnace chamber were set as follows; zone l: 1300 degrees fahrenheit; zone 2: 1400 degrees fahrenheit; zone 3: 1500 degrees fahrenheit; zone 4: 1600 degrees fahrenheit; zone 5: 1700 degrees fahrenheit; and zone 6: 1700 degrees fahrenheit. The maximum optical pyrometer reading was at 1800 degrees fahrenheit. The rate of advancement or "push" of the loaded tray and empty trays was approximately two hours thereby requiring about 48 hours for any one tray to advance from the entrance of the furnace chamber to the exit of the furnace chamber. As used herein the term "push" refers to the time required for a tray to advance one full length of the tray. As the trays advanced through the furnace, water contained within a water bottle at a temperature of 140 degrees fahrenheit and hydrogen gas were introduced into the furnace chamber. Similarly, the hydrogen gas was introduced through gas inlets into the furnace chamber at a flow rate of 600 cubic feet per hour counter to the direction of movement of the trays.

Chemical analysis was then conducted on samples of the powder from the loaded tray. Analysis showed that the total carbon was 6.04 percent, free carbon was 0.01 percent and the oxygen was 0.02 percent. It is obvious from this analysis that, at a maximum optical pyrometer temperature of 1800 degrees fahrenheit, little decarburization has taken place. The stoichio etric carbon level for fully carburized tungsten carbide is 6.13 percent.

Example 4 Approximately 4 lb Kg. of -80 mesh size tungsten carbide powder produced in accordance with the process described in U. S. Patent No. 4,834,963 was loaded into one ceramic tray as described above. The Hayes furnace, of the type previously described above, was divided longitudinally into six temperature zones of equal length. The temperature zones within the furnace chamber were set as follows; zone 1: 2175 degrees fahrenheit; zone 2: 2400 degrees fahrenheit; zone 3: 2600 degrees fahrenheit; zone 4: 2700 degrees fahrenheit; zone 5: 2845 degrees fahrenheit; and zone 6: 2765 degrees fahrenheit. The maximum optical pyrometer reading was at 2840 degrees fahrenheit. The rate of advancement or "push" of each tray through the furnace chamber was approximately two hours thereby requiring about 48 hours for any one tray to advance from the entrance of the furnace chamber to the exit of the furnace chamber. As used herein the term "push" refers to the time required for a tray to advance one full length of the tray. As the trays advanced through the furnace, water contained within a water bottle at a temperature of 140 degrees fahrenheit and hydrogen gas were introduced into the furnace chamber. Similarly, the hydrogen gas was introduced through gas inlets into the furnace chamber at a flow rate of 600 cubic feet per hour counter to the direction of movement of the trays.

Chemical analysis was then conducted on samples of the powder from the loaded tray. Analysis showed that the total carbon was 2.99 percent, the free carbon was 0.035 percent and the oxygen was 0.03 percent. It is obvious from this analysis that, at a maximum optical temperature of 2840 degrees fahrenheit and in the presence of 600 cubic feet per hour of wet hydrogen gas, a significant amount of decarburization of the tungsten carbide has taken place.

Example 5 Approximately 4 lbs. of -80 mesh size tungsten carbide powder produced in accordance with the process described in U. S. Patent No. 4,834,963 was loaded into approximately one ceramic tray as described above. The Hayes furnace, of the type previously described above, was divided longitudinally into six temperature zones of equal length. The temperature zones within the furnace chamber were set as follows; zone 1: 2100 degrees fahrenheit; zone 2: 2550 degrees fahrenheit; zone 3: 2730 degrees fahrenheit; zone 4: 2895 degrees fahrenheit; zone 5: 2888 degrees fahrenheit; and zone 6: 2885 degrees fahrenheit. The maximum optical pyrometer reading was at 2900 degrees fahrenheit. The rate of advancement or "push" of each tray through the furnace chamber was approximately two hours thereby requiring about 48 hours for any one tray to advance from the entrance of the furnace chamber to the exit of the furnace chamber. As used herein the term "push" refers to the time required for a tray to advance one full length of the tray. As the trays advanced through the furnace, water contained within a water bottle at a temperature of 140 degrees fahrenheit and hydrogen gas were introduced into the furnace chamber. Similarly, the hydrogen gas was introduced through gas inlets into the furnace chamber at a flow rate of 350 cubic feet per hour counter to the direction of movement of the trays.

Chemical analysis was then conducted on samples of the powder from the loaded tray. Analysis showed that the total carbon was 0.01 percent, the free carbon was 0.03 percent and the oxygen was 0.08 percent. It is obvious that, at a maximum optical temperature of 2900 degrees fahrenheit and in the

presence of wet hydrogen gas flowing at 350 cubic feet per hour, the tungsten carbide is almost completely decarburized.

Having described presently preferred embodiments of the invention, it is to be understood that it may be otherwise embodied within the scope of the appended claims.