JPH07233406A - Production of superfine powdery composite starting material for cemented carbide - Google Patents

Abstract

PURPOSE:To obtain superfine powdery composite starting material by an industrially advantageous dry process by reducing a mixture contg. tungsten oxide, cobalt oxide having a specified surface area and chromium oxide or further contg. vanadium oxide formed by a specified method. CONSTITUTION:A mixture contg. W oxide, Co oxide having >=7.5m<2>/g specific surface area and Cr oxide or further contg. V oxide is heated to form a multiple oxide. The V oxide is obtd. through a pretreating stage (a) in which a mixture contg. V oxide and Co oxide having >=7.5m<2>/g specific surface area is heated to form a multiple oxide and a pretreating stage (b) in which an oxide-metal combined body is formed by a partial reduction reaction. Tungsten and vanadium particles are acceleratedly made fine by the action of the Co oxide having >=7.5m<2>/g specific surface area and the obtd. multiple oxide has <=0.2mum particle diameter which is smaller than that of the starting materials.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an ultrafine composite raw material powder for a cemented carbide which is a suitable raw material for producing a high performance cemented carbide.

[0002]

2. Description of the Related Art Conventional ultrafine raw material powder for cemented carbide, that is, raw material powder for cemented carbide having a particle size of 0.5 μm or more, has been manufactured by a dry process. For example, in the case of cemented carbide raw material powder that does not contain vanadium,
First, a tungsten raw material such as tungsten oxide is reduced to obtain metallic tungsten, and then solid carbon is added to the metallic tungsten and carbonized to obtain tungsten carbide.

In this method, the grain size of the above-mentioned metal tungsten cannot be made smaller than that of the starting raw material, that is, the grain size of the tungsten carbide obtained in the subsequent carbonization treatment step. It cannot be smaller than the particle size. However, since the particle size of tungsten oxide that can be obtained as a tungsten raw material is about 0.5 μm even if it is the smallest, the raw material powder for cemented carbide cannot have a particle size smaller than 0.5 μm.

On the other hand, in the case of producing a raw material powder for a cemented carbide containing vanadium, a necessary amount of vanadium carbide is mixed with tungsten carbide and metallic cobalt which are the main components of the cemented carbide, and then, for example, an attritor or a pot mill is used. Then, the raw material powder for vanadium-containing cemented carbide is obtained by pulverizing and mixing for a long time. The smallest available vanadium carbide is about 1.2 μm,
Even if it is mechanically pulverized for a long time as in this method, the particle size of the obtained cemented carbide raw material powder is the smallest and is about 0.5 μm.

[0005]

By the way, in order to obtain a high-performance cemented carbide, an ultrafine grain raw material powder for a cemented carbide having a smaller grain size is required. As means for obtaining such ultrafine grain raw material powder for cemented carbide, conventionally, it is possible to carry out any of the following reaction steps (1) to (8) which is completely different from the above production method. Has been studied.

That is, in the case of obtaining a raw material powder containing no vanadium, (1) a tungsten complex and a cobalt complex are reacted in a liquid phase, (2) an ammonium salt of tungsten is freeze-dried, (3) tungsten hexachloride Is evaporated in an inert gas, and (4) molten tungsten trioxide is sprayed on a cooling body to cool it at a cooling rate of 10 ⁴ ° C / sec or more.

On the other hand, in the case of obtaining a raw material powder containing vanadium, (5) a tungsten complex, a cobalt complex and a vanadium complex are reacted in a liquid phase, (6) an ammonium salt of vanadium is added to an ammonium salt of tungsten, Lyophilize (7) Add vanadium chloride to tungsten hexachloride and evaporate in an inert gas. (8) Inject a molten mixed melt of tungsten trioxide and vanadium pentoxide into a cooling body for 10 ^{For example} , cooling at a rate of ⁴ ° C / sec or more.

However, since the above methods (1) to (8) are special methods which are completely different from the ordinary method for producing a raw material powder for cemented carbide having a particle size of 0.5 μm or more, they are applied to actual operations. In that case, there are many technical problems, and in addition, various devices for liquid phase reaction, freeze-drying, spray quenching, etc., which were not used in the conventional method for producing the raw material powder for cemented carbide, are required. It has poor properties and is extremely disadvantageous in industrialization.

On the other hand, as a manufacturing method for obtaining a tungsten powder by a dry process, (9) JP-B-49-188 is used.
There is a method described in Japanese Patent Laid-Open No. 92. This is tungstic acid (H ₂ WO ₄ ), ammonium paratungstate (S
_{(NH 4) 2 O · 12WO} 3 · 5H 2 O), tungsten trioxide (tungsten raw material such as WO _3), cobalt or cobalt salt (cobalt chloride or cobalt nitrate, etc.)
Is added to carry out a reduction reaction in a hydrogen stream to produce a tungsten powder having a fine particle size.

Since the tungsten manufacturing method (9) is located on an extension of the conventional method for obtaining a powder having a particle size of 0.5 μm or more, as in the conventional method, the tungsten having a particle size smaller than that of the starting tungsten material is used. No powder is obtained. Further, as a manufacturing method for obtaining uniform ultrafine WC powder of 0.5 μm or less obtained by crushing WC powder, (10) JP-A-3-
There is a method described in the method 208811.

In the method (10), WO ₃ powder having a particle size of 5 μm or less is mixed with 15.5 to 16.5% by weight of carbon powder having a particle size of 1.0 μm or less, and the mixture is added in N ₂ gas. At 137
After heating and reducing at a high temperature in the range of 0 to 1770K,
Carbonization is carried out in a hydrogen stream, and only WC is produced. The raw material powder for cemented carbide requires a cobalt component, and therefore it is necessary to separately reduce cobalt oxide and mix the obtained fine-grained metallic cobalt with the WC. However, in this case, there is a problem that a uniform powder cannot be obtained in mixing, which is unsuitable as a raw material powder for cemented carbide and has many manufacturing steps. Therefore, it is possible to make cobalt oxide coexist as a raw material from the beginning, but in this case, W obtained by coexistence of cobalt oxide
The particle size of C powder becomes large. Further, as a method for producing a WC-Co mixed powder, there is a method described in (11) JP-B-55-43485.

[0012] The method of (11) is a tungsten trioxide powder above specific surface area of 5 m ² / g, the raw material powder obtained by mixing carbon powder cobalt oxide powder over a specific surface area of 7m ² / g, carbon muffle furnace And heat it under atmospheric pressure,
It is to reduce and carbonize. In this method (11), the reduction temperature becomes higher than that of the reduction by hydrogen, the coarsening of the grains progresses before the reduction starts, and the grain size of the finally obtained powder becomes larger than 0.2 μm. There is a problem that it ends up.

The present invention has been made in view of the above-mentioned problems, and produces a fine ultrafine composite powder raw material for cemented carbide having a particle size of 0.2 μm or less even in an unpulverized state by the special method as described above. An object of the present invention is to provide a manufacturing method that can be performed by an industrially advantageous dry process without using

[0014]

The ultrafine composite raw material powder for cemented carbide according to the present invention comprises a tungsten oxide and a specific surface area.
A mixture containing 7.5 m ² / g or more of cobalt oxide and chromium oxide or a mixture of the following vanadium oxide raw materials is heated to form a composite oxide (hereinafter referred to as W composite oxide). The gist is to have a first step and a second step of reducing the W composite oxide to obtain a W—Cr—Co-based or W—Cr—Co—V-based metal composite.

As the vanadium oxide raw material, a mixture containing vanadium oxide and cobalt oxide having a specific surface area of 7.5 m ² / g or more is heated to form a composite oxide (hereinafter referred to as V composite oxide). It is obtained by going through a pretreatment step a and a pretreatment step b in which a partial reduction reaction is carried out to produce an oxide-metal composite. The amount of cobalt oxide added in the pretreatment step a is preferably 70% by weight or more.

If necessary, the reduction in the second step may be performed in the presence of solid carbon in a hydrogen atmosphere. If the intermediate raw material of the ultrafine composite raw material powder obtained through the first and second steps is further carbonized (third step) and cooled (fourth step), it becomes an ultrafine composite raw material powder for cemented carbide. It is more preferable to perform the cooling in the fourth step while suppressing the decarburization reaction.

[0017]

In the pretreatment step a of the present invention, by using a fine powder having a specific surface area of 7.5 m ² / g or more as the cobalt oxide, a V composite oxide having a particle diameter of 0.2 μm or less, that is, a particle diameter of 0.2 μm or less, A vanadium-containing powder having a small value is produced. At this time, the cobalt oxide having a specific surface area of 7.5 m ² / g or more is
It works to promote atomization of vanadium particles. Then, by subsequently promoting the reduction reaction in the reducing atmosphere (pretreatment step b), a vanadium oxide-cobalt oxide-metal cobalt composite (oxide-metal composite) having a small particle size is produced. That is, a fine vanadium-containing powder in which the cohesiveness between particles is eliminated is produced. Since the melting point of this oxide-metal composite is as high as 1200 ° C. or higher, no melt is formed during the heat treatment after the first step, and the powder particles do not become coarse. This oxide-metal composite is used as a vanadium oxide raw material.

In the first step of the present invention, a fine powder having a specific surface area of 7.5 m ² / g or more is used as the cobalt oxide, so that the grain size is 0.2 μ, which is finer than the starting material.
A complex oxide of m or less is produced. At this time, the cobalt oxide having a high specific surface area works to promote atomization of the tungsten particles, and the chromium oxide works to suppress sintering and improve grain uniformity. Cobalt oxide added to tungsten oxide and processed in an inert atmosphere 1st
In the process, a composite oxide of tungsten-cobalt is produced. At this time, when the specific surface area of the cobalt oxide is high, the cobalt oxide is highly active, and therefore, the particle size of the starting tungsten oxide is larger than that of the starting material. The finest tungsten-cobalt composite oxide is produced.

According to the experiments by the present inventors, in order to obtain a raw material powder for cemented carbide of 0.2 μm or less, it is sufficient if the specific surface area of the cobalt oxide to be added is 7.5 m ² / g or more. It has been found that the above object can be achieved by showing high activity.
Next, the W composite oxide having a fine particle size is subjected to a reduction treatment (second step), whereby W-Cr- finer than the starting material is obtained.
A Co-based or W-Cr-Co-V-based metal composite (hereinafter collectively referred to as a metal composite) is produced.

When a vanadium oxide raw material which has not been subjected to the pretreatment steps a and b of the present invention is used as a raw material for obtaining a vanadium-containing cemented carbide raw material powder of 0.2 μm or less, the following problems occur. . In other words, the most stable vanadium oxide in the atmosphere is vanadium pentoxide, but not only the industrially available raw material has a particle size of 0.5 μm or more, but also the particles are strongly aggregated. Even after mechanical pulverization for a long time, aggregated particles of about 1 to 3 μm remain. Further, since vanadium pentoxide has a low melting point of 690 ° C., when heat treatment such as reduction-carbonization treatment is performed, a vanadium pentoxide dioxide melt is produced during the reaction, and the powder particles become coarse.

The metal composite, which is an intermediate raw material obtained through the second step as described above, is heat-treated in a carburizing atmosphere (for example, a methane-hydrogen mixed atmosphere having a volume ratio of less than 15: 100) and subjected to predetermined treatment. The carbonization reaction is promoted at the temperature of (3rd step), and the subsequent cooling step is performed in a volume ratio (5: 100).
To (70: 100) in a methane-hydrogen mixed atmosphere while cooling while suppressing the decarburization reaction (fourth step) to finally obtain an ultrafine particle composite for cemented carbide with a particle size of 0.2 μm or less. A raw material powder is obtained.

The above-mentioned first step and pretreatment step a are carried out in an inert atmosphere, and argon, helium, etc. can generally be used, but in industrialization, it is desirable to carry out in a nitrogen atmosphere from the viewpoint of economy. . The second step and the pretreatment step b are carried out in a reducing atmosphere, and generally carbon monoxide or the like can be used, but it is preferable to carry out in a hydrogen atmosphere from the viewpoint of safety in industrialization.

The third step is carried out in a carburizing atmosphere,
Generally, carbon monoxide, carbon dioxide, etc. can be used,
In industrialization, it is desirable to carry out in a methane-hydrogen mixed atmosphere from the viewpoint of safety. The concentration in the atmosphere in this case is 1/100 to methane / hydrogen ratio in the case of a methane-hydrogen mixed gas.
In the case of 1/5, CO-CO ₂ mixed gas, the CO ₂ / CO ratio is preferably 1/2 to 1/100. The fourth step is preferably performed in a methane-hydrogen mixed atmosphere while maintaining a carburizing atmosphere.

Next, the case where the amount of powder to be processed is large will be described. As described above, it is recommended to carry out the reduction in the second step in a hydrogen atmosphere. However, when the amount of powder to be treated increases, a fine W composite oxide having a particle size of 0.2 μm or less produced in the first step. However, it is coarsened to about 0.4 μm due to the influence of water vapor generated during the reduction process.

Although it is conceivable to carry out the reduction step by the conventional methods (10) and (11), carbon is added to the oxide which is the starting material of the present invention, and this oxide / carbon mixture is added. When the reduction steps of (10) and (11) above are applied, the reduction temperature becomes higher than that of the reduction with hydrogen, and the coarsening of the grains progresses before the reduction begins, and finally it is obtained. The particle size of the powder becomes larger than 0.2 μm.

Therefore, the following method is recommended in the present invention. That is, in the first step, solid carbon is added to produce a composite oxide-carbon composite, and the composite oxide-carbon composite is subjected to the treatment in the second step. A metal composite or a metal composite / carbon composite is produced by the treatment in the first and second steps. By carbonizing and cooling the thus obtained intermediate raw material, an ultrafine composite raw material powder for cemented carbide having a particle diameter of 0.2 μm or less can be obtained.

When the composite oxide-carbon composite produced in the first step is reduced in the hydrogen atmosphere as described above (second step), the temperature is lower than the temperature at which the grain growth of the composite oxide particles starts. The reduction treatment can be performed with. At this time, carbon reacts with hydrogen to generate hydrocarbons. The produced hydrocarbon acts in a thermal equilibrium manner to suppress the generation of water vapor, which is the cause of the coarsening of the particles during reduction. Therefore, even when the amount of powder to be processed is large, a fine ultrafine composite raw material powder is finally obtained. Next, the suitable amount of each component contained in the generated ultrafine composite raw material powder for cemented carbide will be described.

<Tungsten carbide: 70 to 97% by weight
If it is less than 70% by weight (value converted to WC), W
Since the C / Co ratio becomes too small and the hardness and strength of the cemented carbide obtained by sintering the ultrafine composite raw material powder are remarkably reduced, the usefulness as the ultrafine composite raw material powder for cemented carbide is reduced. The lower limit is preferably 70% by weight. Also, 97% by weight
If it exceeds the above range, the WC / Co ratio becomes excessively large and the binder phase, cobalt, becomes insufficient, which makes it difficult to sinter when manufacturing a cemented carbide. That is, if it is attempted to sinter with a component composition of more than 97% by weight, the sintering temperature must be raised inevitably, and as a result, coarsening of the grains is brought about, so as an ultrafine composite raw material powder for cemented carbide. Is less useful. Therefore, the upper limit is preferably 97% by weight.

<Metallic cobalt: 3 to 30% by weight> If less than 3% by weight, the Co / WC ratio becomes too small, that is, WC / Co.
Since the ratio becomes too large and the usefulness as the ultrafine composite raw material powder for cemented carbide is reduced as described above, the lower limit is preferably 3% by weight. On the other hand, if it exceeds 30% by weight, the Co / WC ratio becomes excessively large, that is, the WC / Co ratio becomes excessively small, and the usefulness as the ultrafine composite raw material powder for cemented carbide is reduced as described above. Weight percent is preferred.

<Chromium Carbide: 1 to 20% by Weight Based on Cobalt (Value Converted to Cr ₂ C ₂ )> Less than 1% by weight based on cobalt, during sintering in the cemented carbide manufacturing process. On the other hand, since the effect of suppressing grain growth is reduced, on the other hand, if it exceeds 20% by weight, the Cr / Co ratio becomes excessively large, and after sintering, a large chromium carbide precipitates, which lowers the strength of the sintered body.
The above range is preferred.

<Vanadium carbide: 0 to cobalt
10% by weight (value converted to VC)> vanadium carbide is a component that acts to suppress grain growth during sintering in the cemented carbide manufacturing process. However, when vanadium carbide exceeds 10% by weight with respect to cobalt, the V / Co ratio becomes excessive, and large vanadium carbide precipitates after sintering to reduce the strength of the sintered body, so the above range is preferable. Next, the preferable blending amount of the raw materials used for obtaining the ultrafine composite raw material powder having the above-mentioned component contents will be described.
First, the case where no vanadium oxide raw material is added will be described.

<Cobalt Oxide in First Step> First
If the amount of cobalt oxide added in the step is less than 1% by weight with respect to tungsten oxide, the effect of promoting atomization of the W composite oxide decreases, so the lower limit is 1% with respect to tungsten oxide. % Is preferable. When Co in the ultrafine composite raw material powder obtained through the fourth step is less than 3% by weight, the usefulness as the ultrafine composite raw material powder for cemented carbide is reduced, which is not suitable. The desired component composition can be achieved by separately adding the deficiency in the form of metallic cobalt or the like. Regarding the upper limit value, it may be added so that Co in the finally obtained ultrafine composite raw material powder is 30% by weight or less. As the cobalt oxide, CoO, Co ₂ O ₃ , Co ₃ O ₄ or the like is used.

<Chromium Oxide> With respect to the sum of the amounts of tungsten oxide and cobalt oxide added in the first step,
If it is less than 0.1% by weight, the effect of suppressing the sintering of the W composite oxide is lowered and the effect of enhancing the grain uniformity is lowered, so the lower limit is set to the tungsten oxide and the cobalt oxide in the first step. It is preferably 0.1% by weight with respect to the sum of the added amounts of the substances. If the content of chromium carbide in the ultrafine composite raw material powder obtained through the fourth step is less than 1% by weight with respect to cobalt, the usefulness of the ultrafine composite raw material powder for cemented carbide decreases. Although it is unsuitable, a desired composition can be obtained by separately adding the insufficient amount in the form of fine chromium carbide or the like. For the upper limit,
Chromium carbide in the finally obtained ultrafine composite raw material powder may be added so that the content thereof is 20% by weight or less with respect to cobalt. In addition, as chromium oxide, Cr ₂ O ₃ , CrO ₂ ,
CrO ₃ , Cr ₂ O _5, etc. are used.

<Tungsten Oxide> The balance is tungsten oxide. WO ₃ , W as tungsten oxide
O ₂ , WO _2.72 or the like is used. Next, the case of adding the vanadium oxide raw material will be described.

<Cobalt Oxide in Pretreatment Step a>
The lower limit value is preferably 1% by weight or more with respect to the amount of vanadium oxide added in the pretreatment step a. 1% by weight based on the amount of vanadium oxide added in the pretreatment step a
If it is less than the above range, the effect of promoting atomization of vanadium particles is reduced.

1% by weight or more of cobalt oxide is sufficient for promoting the miniaturization of vanadium particles.
In order to ensure the uniformity of each component in the mixture after the process, it is desirable that the addition amount of cobalt oxide be 70% by weight or more. The amount of cobalt oxide added in the first step is the sum of the cobalt oxide contained in the vanadium oxide raw material and the cobalt oxide added from other sources, but the amount of cobalt oxide in the pretreatment step a is the amount of vanadium oxide. On the other hand, if the amount is sufficiently large, the amount of the vanadium oxide raw material added in the first step is relatively large, and vanadium is uniformly diluted in the vanadium oxide raw material. Even in mixed powder,
Since it works advantageously to uniformly disperse the vanadium component, it is preferable to increase the cobalt oxide content to 70% by weight or more as described above.

Regarding the upper limit value, Co is added so that Co in the finally obtained ultrafine composite raw material powder is 30% by weight or less, and the addition amount of the cobalt oxide in the first step after that is the first. 1% by weight of the amount of tungsten oxide added in the process
It is advisable to add them so as to satisfy the above conditions.

<Vanadium Oxide Raw Material> Regarding the amount of the oxide-metal composite produced through the pretreatment step b, that is, the vanadium oxide raw material in the first step, the ultrafine composite raw material powder finally obtained. The vanadium carbide may be added in an amount of 10% by weight or less with respect to metallic cobalt.

<Cobalt Oxide, Chromium Oxide, and Tungsten Oxide in the First Step> For cobalt oxide, chromium oxide, and tungsten oxide in the first step, vanadium oxide raw materials are not added to both the lower and upper limits. Is the same as. <Amount of solid carbon: 0.2 to 9% by weight> If less than 0.2% by weight, the effect of suppressing the generation of water vapor during reduction is reduced,
On the other hand, if it exceeds 9% by weight, carbon becomes excessive, and hydrogen, which is the reducing atmosphere in the second step, first reacts with carbon to form a hydrocarbon gas, which suppresses the progress of reduction of oxides.
The above range is desirable.

[0040]

EXAMPLES Next, the present invention will be described more specifically by way of examples. First, an example in the case where the vanadium oxide raw material is not added will be described. <Example 1> finally Cr ₃ C _2: 1 by weight%, Co: 5
As a raw material, WO ₃ powder, Cr ₂ O ₃ powder and a specific surface area of 54.7 m ² are obtained so as to obtain a mixed powder of wt% and the balance WC.
/ G of Co ₃ O ₄ powder was mixed. Mixed oxide powder 10
100g of deionized water and 5kg of cemented carbide balls in 0g
Was added and wet-mixed for 6 hours. After drying at 70 ° C, 2 g of mixed oxide powder was placed on an alumina boat, and the diameter was 10 cm,
It was inserted into a quartz reaction tube having a total length of 100 cm. This was heated to 700 ° C. over 90 minutes in a nitrogen atmosphere, and the particle size was reduced to 0.
A 1 μm W complex oxide was produced (first step). 700
Hydrogen was introduced into the tube when the temperature reached ℃, and the reduction reaction was allowed to proceed for 120 minutes to obtain a tungsten-chromium-cobalt-based metal composite (second step).

Further, the volume ratio of methane / hydrogen is 4/10.
It was heated to 900 ° C. while introducing methane so that it became 0, and the carbonization reaction was allowed to proceed for 60 minutes in that state (third step). Then, from 900 ° C. to room temperature, the volume ratio of methane was increased as shown in Table 1 below as the temperature decreased, and cooling was performed while controlling the decarburization reaction (fourth step).

[0042]

[Table 1]

The powder obtained by the above treatment is SE
By observation with M, it was confirmed that it was an ultrafine composite raw material powder having a particle size of 0.2 μm or less, and the amount of free carbon was 0.2% by weight.
It was below. <Examples 2 to 4 and Comparative Example 1> Next, the above Example 1 except that Co ₃ O ₄ is changed to one having various specific surface areas.
The same process was carried out. The results and the specific surface area of Co ₃ O ₄ are shown in Table 2.

[0044]

[Table 2]

The powder obtained in Comparative Example 1 was confirmed by SEM observation to be a fine-grain composite raw material powder having a particle size of 1.0 μm. Co ₃ O ₄ having such a small specific surface area
When using, the resulting ultrafine composite raw material powder had a large particle size. Obtained composite raw material powder (mainly WC)
The specific surface area of Co ₃ O ₄ is 7.5 m ² / g or more because the specific surface area of 4 m ² / g or more is sufficient as a raw material for obtaining a high-performance cemented carbide. I understand that if it is good.

<Embodiment 5> Next, the same treatment as in Embodiment 1 will be described except that the amount of cobalt oxide added is changed. In order to finally obtain a mixed powder of Cr ₃ C ₂ : 1% by weight, Co: 10% by weight, and the balance WC, W is used as a raw material.
O ₃ powder, Cr ₂ O ₃ powder and specific surface area of 54.7 m ² /
g of Co ₃ O ₄ powder was added, and the same treatment as in Example 1 was performed. The powder obtained from this Example 5 was SEM
It was confirmed by observation that it was an ultrafine composite raw material powder having a particle size of 0.1 μm.

<Comparative Example 2> For comparison with Example 1 described above,
After advancing the reduction reaction in the second step, it was heated to 900 ° C. in a nitrogen atmosphere, and when it reached 900 ° C., methane and hydrogen were added so that the volume ratio of methane / hydrogen became 4.5 / 100. After the introduction, the carbonization reaction was allowed to proceed for 60 minutes. Then, it cooled from 900 degreeC to room temperature in nitrogen atmosphere. The powder obtained in Comparative Example 2 was confirmed by SEM observation to be an ultrafine composite raw material powder having a particle size of 0.2 μm, but the amount of carbon in the obtained powder was non-uniform and free. The amount of carbon was 1.0% by weight or more.

In Comparative Example 2, the reduction reaction (second step)
After that, in the third step, the temperature was raised in a nitrogen atmosphere instead of in a methane-hydrogen mixed atmosphere, so a rapid exothermic reaction occurred between the powder and the atmosphere gas at the time of introducing methane / hydrogen gas,
As a result, it is considered that the amount of carbon in the obtained powder became non-uniform. Further, since the cooling (fourth step) after the carbonization reaction (third step) was performed in a nitrogen atmosphere instead of in a methane-hydrogen mixed atmosphere, a decarburization reaction preferentially occurs from the bonded carbon, and the amount of free carbon is increased. It is considered to have increased.

An example of adding a vanadium oxide raw material will be described below. <Example 6> As a raw material for the vanadium (V) component additive, C ² having a specific surface area of 50 m ² / g with respect to V ₂ O ₅ powder
o ₃ O ₄ powder 13.4 by mixing wt%, was mixed oxide powder. 20 g of this mixed oxide powder is added to 30 c of ionized water
c and 400 g of cemented carbide balls were blended and wet mixed for 6 hours. Then, after drying at 70 ° C., 2 g of this was placed on an alumina boat and had a diameter of 10 cm and a total length of 100 cm.
It was inserted into the quartz reaction tube. 90% of this in a nitrogen atmosphere
The temperature was raised to 600 ° C. over a period of time to produce a V composite oxide having a particle size of 0.1 μm (pretreatment step a).

When the temperature reached 600 ° C., hydrogen was introduced into the tube and the reduction reaction was allowed to proceed for 120 minutes (pretreatment step b). As a result, a vanadium oxide-cobalt oxide-metal cobalt composite (oxide-metal composite) having a particle size of 0.1 μm was produced. This is used as a vanadium oxide raw material for V component addition.

Then, finally Cr₃ C₂ : 0.5 weight
%, VC: 0.2% by weight, Co: 5% by weight, balance WC
To obtain a mixed raw material powder, WO is used as a raw material.₃ Powder,
Cr ₂ O₃ Powder, specific surface area 50m² / G of Co₃ O_Four 
Powder and vana obtained through the above pretreatment steps a and b
The raw material for the oxide of zinc was mixed. And these mixed powders
100g of powder and 100cc of ionized water and cemented carbide balls
5 kg was added and wet-mixed for 6 hours. And dry at 70 ℃
After drying, 2 g of this mixed oxide powder was placed on an alumina boat.
Insert it into a quartz reaction tube with a diameter of 10 cm and a total length of 100 cm.
I entered. This should be performed in a nitrogen atmosphere for 90 minutes at 700 ° C.
The temperature was raised to 0 to produce a W composite oxide having a particle size of 0.1 μm.
(First step). When the temperature reached 700 ° C, hydrogen was introduced into the tube.
Introduced, allowed to proceed with reduction reaction for 120 minutes, W-Cr-V
A -Co-based metal composite was obtained (second step).

Furthermore, the volume ratio of methane / hydrogen is 5/10.
It was heated to 900 ° C. while introducing methane so as to be 0, and the carbonization reaction was allowed to proceed for 70 minutes in that state (third step). Then, from 900 ° C. to room temperature, the volume ratio of methane was increased as shown in Table 1 above as in the case of Example 1 to cool while suppressing the decarburization reaction (No. 4).
Process). The powder obtained in this Example 6 was confirmed by SEM observation to be an ultrafine composite raw material powder having a particle size of 0.1 μm, and by elemental mapping analysis,
It was confirmed that V was uniformly dispersed.

Example 7 V₂ O_Five Specific surface to powder
Product is 11m² / G of Co₃ O_Four 6.83% by weight of powder
In this case, the same pretreatment steps a and b as those in Example 6 were performed.
Manufacture vanadium oxide raw material (oxide-metal composite)
It was Then finally Cr₃ C₂ 1% by weight, VC: 0.
5% by weight, 10% by weight of Co, the balance WC mixed raw material powder
As a raw material, WO₃ Powder, Cr₂ O ₃ powder
At the end, the specific surface area is 11m² / G of Co₃ O_Four Powder, and
The vanadium oxide raw material powder obtained above was blended, and
The same first to fourth steps as in Example 6 were performed. this
The powder obtained in Example 7 has a particle size of SEM observation.
It was confirmed to be 0.1 μm ultrafine composite raw material powder
It was

Comparative Example 3 For comparison with Example 6 above, finally, Cr ₃ C _{2 was} 0.5% by weight, and VC was 0.2.
As a raw material, a WO ₃ powder, a Cr ₂ O ₃ powder,
Co ₃ O ₄ powder having a specific surface area of 50 m ² / g and V ₂ O
₅ powders were blended, and the same treatments (reduction / carbonization treatment) as those in Example 6 were performed in the first to fourth steps.

According to SEM observation, the powder obtained in Comparative Example 3 was 1% in the ultrafine composite raw material powder having a particle size of 0.1 μm.
Aggregated particles and coarse particles of ˜3 μm were confirmed. In Comparative Example 3, only V ₂ O ₅ was added as the V component to be added,
It is used without going through the pretreatment steps a and b. Therefore, it is considered that a melt of the V ₂ O ₅ powder was generated after the first step, and aggregated particles and coarse particles of 1 to 3 μm were developed in the obtained powder.

Comparative Example 4 For comparison with Example 6 above, finally, Cr ₃ C _{2 was} 0.5% by weight, and VC was 0.2.
As a raw material, a WO ₃ powder, a Cr ₂ O ₃ powder,
Co ₃ O ₄ powder having a specific surface area of 50 m ² / g and vanadium carbide powder were mixed, and the first to fourth similar to Example 6 were prepared.
The process was processed.

The powder obtained in Comparative Example 4 was found by SEM observation to have coarse particles of 0.3 to 0.8 μm in the ultrafine composite raw material powder having a particle size of 0.1 μm. In Comparative Example 4, vanadium carbide is used as the V component to be added. This vanadium carbide is pulverized only to about 0.5 μm even after the mixing step in the first step. Therefore, it is considered that coarse particles of 0.3 to 0.8 μm remained in the obtained powder.

Since the powders produced in Comparative Examples 3 and 4 contained coarse particles, the vanadium oxide raw material (for adding V component) obtained through the pretreatment steps a and b of the present invention was used. It is understood that the oxide-metal complex) effectively acts to make the particles uniform and fine.

<Comparative Example 5> For comparison with Example 6 described above, the pretreatment steps a and b similar to those in Example 6 were performed without adding Co ₃ O ₄ powder to V ₂ O ₅ powder. Then, an oxide for adding V component (vanadium oxide raw material) was prepared.

Then finally Cr₃ C₂ : 0.5% by weight,
Mixing VC: 0.2 wt%, Co: 5 wt%, balance WC
As a raw material, WO is used to obtain the raw material powder.₃ Powder, Cr
₂ O ₃ Powder, specific surface area 50m² / G of Co₃ O_Four Powder
And oxide powder for adding V component obtained by the above-mentioned manufacturing method
And the treatments of the first to fourth steps similar to those of Example 6 above.
I went.

According to SEM observation, the powder obtained in Comparative Example 5 was 1% in the ultrafine composite raw material powder having a particle size of 0.1 μm.
Aggregated particles and coarse particles of ˜3 μm were confirmed. From the above Comparative Example 5 and Example 6, it can be seen that the V composite oxide obtained by adding the cobalt oxide acts to make the finally obtained powder uniform and fine.

<Comparative Example 6> For comparison with Example 6 described above, an experiment was carried out in Example 6 except that the pretreatment step b was omitted. That is, finally Cr ₃ C ₂ : 0.5
% By weight, VC: 0.2% by weight, Co: 5% by weight, balance W
In order to obtain a mixed raw material powder of C, WO ₃ powder, Cr ₂ O ₃ powder, Co ₃ having a specific surface area of 50 m ² / g are used as raw materials.
O ₄ powder and the composite oxide for V component addition obtained through only the pretreatment step a in Example 6 above were mixed as vanadium oxide raw materials, and the same first to fourth examples as in Example 6 above were mixed. The process was processed.

According to SEM observation, the powder obtained in Comparative Example 6 was 1% in the ultrafine composite raw material powder having a particle size of 0.1 μm.
Aggregated particles and coarse particles of ˜3 μm were confirmed. In Comparative Example 6, since the pretreatment step b was omitted when obtaining the V component addition powder, the agglomeration between the V component addition powders was not eliminated, and the melting of the V component addition powder was performed after the first step. Since the liquid was generated, it is considered that aggregated particles of 1 to 3 μm and coarse particles were expressed in the obtained powder.

An example of producing a cemented carbide by using the above-prepared ultrafine composite raw material powder for cemented carbide will be described below. To <Example 8> V ₂ O ₅ powder, a specific surface area of 11m ²
80% by weight of Co ₃ O ₄ powder / g was added, and pretreatment steps a and b similar to those in Example 6 were performed to prepare a vanadium oxide raw material (oxide-metal composite). Then, finally, Cr ₃ C ₂ : 1% by weight, VC: 0.5% by weight, Co:
As a raw material, WO ₃ was used so as to obtain a mixed raw material powder of 10% by weight and the balance WC (the same final component amount as in Example 7).
Powder, Cr ₂ O ₃ powder, Co having a specific surface area of 11 m ² / g
₃ O ₄ powder and the vanadium oxide raw material obtained through the pretreatment steps a and b were blended, and the same first to fourth steps as in Example 6 were performed. The ultrafine composite raw material powder obtained through the fourth step has a particle size of 0.1 μm by SEM observation.
Met.

Next, in order to produce a cemented carbide, this composite raw material powder is press-formed into a green compact with a surface pressure of 1 ton / cm ² (forming step), and the green compact is heated to a temperature of 135 in a vacuum atmosphere.
Sintering was performed under the condition of maintaining at 0 ° C. (sintering step) to produce a WC-based cemented carbide (sintered body). The structure of the surface of the obtained sintered body was observed by SEM, and it was found that 2 μ was found in the WC particles after sintering.
Although 3 to 5 coarse particles of about m were observed per 0.01 mm ² , the particle size was about 0.2 μm, which was good.

<Comparative Example 7> Comparison with Example 8 was made.
Therefore, Co in the pretreatment step a₃ O_Four Small amount of powder added
Cemented carbide is produced using the composite raw material powder of Example 7 above.
I made it. That is, the particle size of 0.1 μm obtained in Example 7 above.
Using the above ultrafine composite raw material powder,
After that, the cemented carbide (sintered body) was obtained by performing the sintering process. Got
The structure of the surface of the sintered body thus obtained was observed by SEM.
The particle size of the WC particles was as good as about 0.2 μm,
Coarse particles of 2 to 5 μm 0.01 mm ² Per 10
~ 15 were observed.

In Example 8 above, the amount of cobalt oxide added in the pretreatment step a was 80% by weight, which was a sufficiently large amount relative to vanadium oxide, but in Comparative Example 7, it was 6.83% by weight. And there were few. Thus, in the case of Comparative Example 7 in which the amount of cobalt oxide added in the pretreatment step a was small, the vanadium component in the obtained ultrafine composite raw material powder was contained in the ultrafine composite raw material powder obtained in Example 7. The uniformity is inferior to the dispersibility of vanadium. Therefore, it is considered that the grain growth suppressing effect during sintering was uneven, and a large amount of coarse particles appeared after sintering. Therefore, in order to secure the homogeneity of each component in the mixture after the first step and to further improve the composite raw material powder, the amount of cobalt oxide added in the pretreatment step a is large (preferably 70% or more). Is recommended.

Next, an example of a manufacturing method when the amount of powder to be treated is large will be described. <Example 9> V ₂ O as a raw material for the vanadium component additive
₅ powders were used, and the specific surface area was 50 m ² / g of C
o ₃ O ₄ powder was 13.4 wt% blend. 20 g of the mixed oxide powder was mixed with 30 cc of ionized water and 400 g of a cemented carbide ball, and wet mixed for 6 hours. And 70
After drying at 0 ° C., 2 g of this mixed oxide powder was placed on an alumina boat and inserted into a quartz reaction tube having a diameter of 10 cm and a total length of 100 cm. 90 to 600 ℃ in a nitrogen atmosphere
The temperature was raised in minutes, and a V composite oxide having a particle size of 0.1 μm was generated in the process (pretreatment step a).

When the temperature reached 600 ° C., hydrogen was introduced into the tube and the reduction reaction was allowed to proceed for 120 minutes (pretreatment step b). As a result, a vanadium oxide-cobalt oxide-metal cobalt composite (oxide-metal composite) for adding V component having a particle size of 0.1 μm, that is, a vanadium oxide raw material was produced.

Then, finally, Cr ₃ C ₂ : 0.5% by weight,
VC: 0.2% by weight, Co: 10.1% by weight, balance WC
Cr ₂ O ₃ as a raw material so that a mixed raw material powder of
Powder: 0.53% by weight, Co having a specific surface area of 50 m ² / g
₃ O ₄ powder: 11.6% by weight, vanadium oxide raw material powder obtained by the pretreatment steps a and b: 0.23% by weight, and the balance was WO ₃ powder. Then, 92.4 g of these mixed powders were mixed with solid carbon 7.
6 g, 100 cc of ion-exchanged water, and 5 kg of cemented carbide balls were mixed and wet-mixed for 6 hours. And 70 ° C
After being dried at 10, 10 g of the oxide / carbon mixed powder was placed on an alumina boat and inserted into a stainless steel tube having a diameter of 110 mm and a total length of 950 mm. 70% of this in a nitrogen atmosphere
The temperature was raised to 0 ° C. in 90 minutes, and in the process, a composite oxide-carbon composite having a particle size of 0.2 μm, that is, a W composite oxide was generated (first step). When the temperature reached 700 ° C., hydrogen was introduced into the tube containing the W composite oxide, the reduction reaction was allowed to proceed for 180 minutes, and a W—Cr—Co—V based metal composite (intermediate raw material) was obtained (No. 2 steps).

The intermediate raw material powder obtained in Example 9 was confirmed by SEM observation to be an ultrafine composite raw material powder having a particle size of 0.2 μm. Although a small amount of carbon may remain in the metal composite that has been subjected to the second step, this powder undergoes the carbonization step (third step) after the second step, so that the final cemented carbide is obtained. There is no problem as an ultrafine composite raw material powder for alloys.

Next, the WC obtained through the above second step
The r-Co-V-based metal composite or the metal composite / carbon composite (intermediate raw material) has a methane / hydrogen volume ratio of 4
It was heated to 900 ° C. while introducing methane so that the ratio became / 100, and the carbonization reaction was allowed to proceed for 60 minutes in that state (third step). Then, from 900 ° C. to room temperature, the volume of methane is increased as shown in Table 1 above as in the case of the above-mentioned Example 1 to cool while controlling the decarburization reaction, and then the ultrafine composite raw material powder for cemented carbide is obtained. Was obtained (4th step). The powder finally obtained in this Example 9 was confirmed by SEM observation to be an ultrafine composite raw material powder having a particle size of 0.2 μm, and trace elements were uniformly dispersed by elemental mapping analysis. Was confirmed.

<Comparative Example 8> In the case where the amount of powder to be treated next is large, as Comparative Example 8, the same pretreatment steps a, b and the same as in Example 9 except that solid carbon is not added. The process of the 1st and 2nd process was performed. The intermediate raw material powder obtained through the second step of Comparative Example 8 is SE
It was confirmed by M observation that the composite raw material powder had a particle size of 0.3 to 0.4 μm. Thus, when the reduction treatment was performed in a hydrogen atmosphere without adding solid carbon, the obtained composite powder had a large particle size. Subsequently, when this intermediate raw material powder was used to perform the same third and fourth steps as in Example 9, the obtained composite raw material powder for producing a cemented carbide had a particle size of 0.3 to It was confirmed to be a composite raw material powder of 0.4 μm.

<Examples 10 and 11, Comparative Examples 9 and 10> Next, in the case where the amount of powder was large, the same pretreatment steps a, b and as in Example 9 were used except that the amount of solid carbon added was variously changed. The 1st-4th process was performed and the ultrafine composite raw material powder for cemented carbide was obtained. Examples 10 and 11 and Comparative Examples 9 and 1
The particle size of the powder obtained in No. 0 was measured by SEM observation.
The results and the amount of solid carbon added are shown in Table 3.

[0075]

[Table 3]

As can be seen from Table 3, the powders obtained in Examples 10 and 11 are ultrafine composite raw material powders for cemented carbide having a particle size of 0.2 μm, and the powders obtained in Comparative Examples 9 and 10 Was confirmed to be a composite raw material powder having a particle size of 0.3 to 0.4 μm. When the amount of carbon added is large as in Comparative Examples 9 and 10, the hydrogen introduced in the second step first reacts with carbon to generate a hydrocarbon gas. Therefore, the reducing power of the oxide raw material by the hydrogen gas is therefore increased. Is weakened. Therefore, it is considered that the next temperature rising step (third step) is started before the reduction at 700 ° C. is completed, which causes coarsening of the grains.

<Comparative Examples 11 and 12> As a comparison with Example 9, a composite oxide-carbon composite (W composite oxide) obtained by completing the first step in Example 9 was carried out. Unlike Example 9, the reduction was carried out in a nitrogen atmosphere. That is, after completion of the first step, 850 ° C. in a nitrogen atmosphere (Comparative Example 1
1) and heated to 900 ° C. (Comparative Example 12) to 120
The reduction reaction was allowed to proceed for a minute to obtain an intermediate raw material powder. The reduction of the intermediate raw material powder obtained in Comparative Example 11 hardly progressed, and the reduction of the intermediate raw material powder obtained in Comparative Example 12 was almost completed.

Observation by SEM observation revealed that, in Comparative Examples 11 and 12 in which the reduction reaction proceeded in a nitrogen atmosphere, coarse particles of about 1 μm were contained in the powder having a particle size of 0.3 μm. confirmed. Comparative Examples 11 and 1
It can be seen from 2 that if the atmosphere during the reduction is a nitrogen atmosphere, grain coarsening will already proceed below the reduction start temperature.
By using the intermediate raw material powders of Comparative Examples 11 and 12,
The composite raw material powder for producing a cemented carbide obtained by performing the fourth step also contained coarse particles of about 1 μm.

In the above embodiment, the pretreatment step a
The first step and the first step were performed in a nitrogen atmosphere from the viewpoint of economy, but the present invention is not limited to this, and argon, helium, etc.
Any non-reducing atmosphere may be used.

Further, in the above embodiment, the pretreatment step b and the second step were carried out in a hydrogen atmosphere from the viewpoint of safety. However, the present invention is not limited to this, and if the atmosphere is a reducing atmosphere such as carbon monoxide. Good. However, when the method of adding solid carbon and treating in the second step is adopted when the amount of powder to be treated is large, the second step is performed in a hydrogen atmosphere. Further, in the third step, a mixed atmosphere of methane and hydrogen was used for safety, but the present invention is not limited to this, and a carburizing atmosphere such as carbon monoxide and carbon dioxide may be used. The present invention is not limited to the above-described embodiment, and various modifications and variations can be made without departing from the spirit of the invention.

[0081]

As described above, according to the manufacturing method of the present invention,
It is possible to obtain a fine ultrafine composite raw material powder for cemented carbide having a particle size of 0.2 μm or less in an unpulverized state. Moreover, a trace amount of the additive component is uniformly dispersed in this ultrafine composite raw material powder. In addition, since a dry process is adopted as the manufacturing process, there is no technical problem at the time of scale-up as in the past, no new equipment is required, and the economy is good.
Also, because it can be processed by a dry process, 0.2 μm
It has the advantage that it is not necessary to handle the composite metal active in the air during the following manufacturing process of the ultrafine composite raw material powder for cemented carbide and the manufacturing time can be shortened.

In the manufacturing method of the present invention, by increasing the specific surface area of the cobalt oxide as the additive raw material, regardless of the particle size of the tungsten raw material which occupies 70% or more of the raw material,
Since the particle size of the ultrafine composite powder becomes finer, the controllability as a manufacturing method is extremely good. Furthermore, by adopting a method in which the reduction in the second step is carried out in a hydrogen atmosphere in the presence of solid carbon, it is possible to suppress grain growth during reduction even in the case where the amount of powder processed is large, and it is possible to obtain a fine cemented carbide. A fine-grain composite raw material powder can be obtained.

Claims (5)

[Claims] 1. Tungsten oxide, specific surface area 7.5 m ²
/ G or more of a mixture containing cobalt oxide, chromium oxide, or a mixture of the following vanadium oxide raw material is heated to produce a complex oxide, and the complex oxide is reduced. A second step of obtaining a tungsten-chromium-cobalt-based or tungsten-chromium-cobalt-vanadium-based metal composite, and a method for producing an ultrafine composite raw material powder for cemented carbide. However, the vanadium oxide raw material includes a pretreatment step a in which a mixture containing vanadium oxide and cobalt oxide having a specific surface area of 7.5 m ² / g or more is heated to form a composite oxide, and a partial reduction is performed. It is obtained by going through a pretreatment step b in which a reaction is performed to form an oxide-metal composite. 2. The method for producing an ultrafine composite raw material powder for cemented carbide according to claim 1, wherein the amount of cobalt oxide added in the pretreatment step a is 70% by weight or more. 3. The method for producing an ultrafine composite raw material powder for cemented carbide according to claim 1, wherein the reduction in the second step is performed in a hydrogen atmosphere in the presence of solid carbon. 4. The method according to claim 1, further comprising a third step of carbonizing the metal composite produced by the reduction in the second step.
4. The method for producing an ultrafine composite raw material powder for cemented carbide according to any one of 3 above. 5. The method for producing an ultrafine composite raw material powder for cemented carbide according to claim 4, further comprising a fourth step of cooling after suppressing the decarburization reaction after passing through the third step.