JP7151722B2 - Tungsten carbide powder, tungsten carbide-cobalt metal composite powder, and cemented carbide - Google Patents

Description

The present disclosure relates to tungsten carbide powders, tungsten carbide-cobalt metal composite powders, and cemented carbides. This application claims priority based on Japanese Patent Application No. 2017-241878 filed on December 18, 2017. All the contents described in the Japanese patent application are incorporated herein by reference.

Japanese Patent Application Laid-Open No. 2007-262475 (Patent Document 1) discloses a cemented carbide powder containing WC powder and Co powder, wherein the WC powder has an average particle size of 50 to 200 nm, and the Co powder has a particle size of 100 nm or more. is 4% or less of the total number of Co powders.

In addition, International Publication No. _2009/001929 (Patent Document ₂ ) contains WC particles as a hard phase and Co as a binder phase, and includes _{Co3W3C , Co6W6C} , _Co2W4C and A cemented carbide containing at least one cobalt tungsten carbide particle selected from Co ₃ W ₉ C, wherein the Co ₃ W ₃ C peak, the Co ₆ W ₆ C peak in X-ray diffraction measurement using CuKα rays, When the maximum peak intensity of the Co ₂ W ₄ C peak and the Co ₃ W ₉ C peak is I ₁ and the maximum peak intensity of WC is I ₂ , "0<I ₁ /I ₂ ≤ 0.05 and wherein the WC grains have an average grain size of 0.3 μm or less and the cobalt tungsten carbide grains have an average grain size smaller than the WC grains.

JP 2007-262475 A WO2009/001929

A tungsten carbide powder according to an aspect of the present disclosure includes tungsten carbide particles having an average particle size of 50 nm or less, a transition metal element is dissolved in the tungsten carbide particles, and the transition metal element includes cobalt.

A tungsten carbide-cobalt metal composite powder according to an aspect of the present disclosure is a tungsten carbide-cobalt metal composite powder containing the above-described tungsten carbide particles and cobalt metal formed on the surface of at least part of the tungsten carbide particles. Contains composite particles.

A cemented carbide according to an aspect of the present disclosure includes tungsten carbide particles, in which a transition metal element is dissolved, the average particle size is 80 nm or less, and the maximum particle size is 100 nm or less. .

FIG. 1A is a photograph of a microscope image showing an example of a solid solution state of vanadium, which is a transition metal element other than tungsten, contained in tungsten carbide particles in a tungsten carbide powder of the present disclosure by high-angle scattering annular dark-field scanning transmission electron microscopy. is. FIG. 1B is a photograph of a microscopic image showing an example of a solid solution state of cobalt, which is a transition metal element other than tungsten, contained in tungsten carbide particles in the tungsten carbide powder of the present disclosure by high-angle scattering annular dark-field scanning transmission electron microscopy. is. FIG. 1C is a photograph of a microscope image showing an example of the distribution of tungsten contained in tungsten carbide particles in the tungsten carbide powder of the present disclosure by high angle scattering annular dark field scanning transmission electron microscopy. FIG. 2 is a flow chart illustrating an exemplary method for producing tungsten carbide powders and cemented carbides of the present disclosure.

[Problems to be Solved by the Present Disclosure]
The cemented carbide powder disclosed in JP-A-2007-262475 (Patent Document 1) and the cemented carbide disclosed in International Publication No. 2009/001929 (Patent Document 2) both contain tungsten and a transition metal element other than tungsten. It is formed using a composite carbide formed via a composite oxide containing as a raw material. In such composite carbides, tungsten and transition elements other than tungsten are separated or segregated in the stage of composite oxides, so even in the composite carbides formed, tungsten and transition elements other than tungsten are separated or segregated ( That is, a portion that is not solid-dissolved) remains. In order to promote solid solution between tungsten and transition elements other than tungsten in such composite carbides, heat treatment at a high temperature is further required. Such heat treatment increases the grain size of the composite carbide. A cemented carbide obtained from a composite carbide having a portion where tungsten and a transition element other than tungsten are separated or segregated, and a solid solution between tungsten and a transition element other than tungsten without a portion where tungsten and a transition element other than tungsten are separated or segregated However, cemented carbides obtained from composite carbides having a large grain size have a problem that their wear resistance is low although their hardness is high.

Accordingly, an object of the present disclosure is to provide a tungsten carbide powder, a tungsten carbide-cobalt metal composite powder, and a cemented carbide that can form a cemented carbide having both high hardness and high wear resistance.

[Effect of the present disclosure]
According to the present disclosure, it is possible to provide tungsten carbide powders, tungsten carbide-cobalt metal composite powders, cemented carbides, and methods for producing tungsten carbide powders that can form cemented carbides with both high hardness and wear resistance.

[Description of Embodiments of the Present Disclosure]
First, the embodiments of the present disclosure are listed and described. As used herein, the term "transition metal element" refers to a transition metal element other than tungsten (W).

[1] A tungsten carbide (WC) powder according to an aspect of the present disclosure includes tungsten carbide (WC) particles having an average particle size of 50 nm or less, the WC particles are dissolved with a transition metal element, and the transition metal element contains cobalt (Co). By sintering the WC powder of this embodiment, Co, which is one of the transition metal elements dissolved in the WC particles, precipitates as cobalt (Co) metal on the surfaces of the WC particles during sintering. Since a binder phase is formed by sintering, a uniform fine crystal phase is formed, and a cemented carbide with high hardness and wear resistance can be formed.

[2] In the WC powder, the transition metal element further includes at least one selected from the group consisting of vanadium (V), chromium (Cr), tantalum (Ta), niobium (Nb), and molybdenum (Mo). can contain. In such WC powder, in addition to Co, at least one selected from the group consisting of V, Cr, Ta, Nb, and Mo, which suppresses grain growth during sintering, is fixed to the WC grains as a transition metal element. As it melts, a harder and more wear-resistant cemented carbide with fine WC grains can be formed.

[3] The above-mentioned WC powder was measured by transmission electron microscope energy dispersive X-ray spectroscopy (TEM-EDX) at the center point of each of 20 WC particles in a transmission electron microscope (TEM) microscopic image. When the concentration of each contained transition metal element is measured, the inter-particle concentration variation represented by the difference between the maximum and minimum measured values can be 10% or less of the inter-particle average concentration. In such WC powder, the transition metal element is uniformly solid-dissolved in the WC particles such that the concentration variation between particles is 10% or less of the average concentration between particles, so that the hardness and wear resistance of fine WC particles are obtained. Cemented carbide can be formed with a higher

[4] The above-mentioned WC powder was obtained by TEM-EDX method at five points inside the WC particles arbitrarily selected on a straight line passing through the center of the WC particles in the TEM microscopic image. When the concentration of the metal element is measured, the intra-particle concentration variation represented by the difference between the maximum and minimum measured values can be set to 10% or less of the average intra-particle concentration. In such WC powder, the transition metal element is uniformly solid-dissolved in the WC particles such that the intra-particle concentration variation is 10% or less of the average intra-particle concentration. Cemented carbide can be formed with a higher

[5] A tungsten carbide (WC)-cobalt (Co) metal composite powder according to an aspect of the present disclosure includes WC particles of the WC powder and Co metal formed on the surface of at least part of the WC particles. and including. The WC—Co metal composite powder of the present embodiment is formed by depositing a Co metal having a size of nm order on the surface of WC particles having a size of nm order. Segregation (Co pool) of several micrometers or more of the element Co can be prevented, and a cemented carbide with higher hardness and wear resistance can be formed.

[6] A cemented carbide according to an aspect of the present disclosure includes WC particles, in which a transition metal element is dissolved, the average particle size is 80 nm or less, and the maximum particle size is 100 nm or less. be. The cemented carbide of this embodiment has high hardness and wear resistance because the transition metal element is dissolved in the WC particles and because it has fine WC particles.

[7] In the cemented carbide, the transition metal element may contain at least one selected from the group consisting of V, Cr, Ta, Nb, and Mo. In such a cemented carbide, in addition to Co, at least one selected from the group consisting of V, Cr, Ta, Nb, and Mo, which suppresses grain growth during sintering, is added to WC grains as a transition metal element. Since it is in solid solution, it has fine WC particles and higher hardness and wear resistance.

[8] When the concentration of each transition metal element contained in the WC particles is measured by the TEM-EDX method at the center point of each of the arbitrary 20 WC particles in the TEM microscopic image of the cemented carbide, In addition, the inter-particle concentration variation represented by the difference between the maximum and minimum measured values can be set to 10% or less of the average inter-particle concentration. Such a cemented carbide has fine WC particles because the transition metal element is uniformly solid-dissolved in the WC particles such that the concentration variation between particles is 10% or less of the average concentration between particles. Higher abrasion resistance.

[9] The above cemented carbide is obtained by the TEM-EDX method at five points inside the WC grain that are arbitrarily selected on a straight line passing through the center of the WC grain in the TEM microscopic image. When the concentration of the transition metal element is measured, the intra-particle concentration variation represented by the difference between the maximum and minimum measured values can be set to 10% or less of the average intra-particle concentration. Such a cemented carbide has fine WC particles because the transition metal element is uniformly solid-dissolved in the WC particles such that the intra-particle concentration variation is 10% or less of the average intra-particle concentration. Higher abrasion resistance.

[10] The cemented carbide may further include a cobalt (Co) metal phase, and the content of the Co metal phase may be 15 mass % or less. Such a cemented carbide has high hardness and wear resistance even when the content of the Co metal phase is as small as 2 mass % or less because the transition metal element is dissolved in the WC particles.

[11] The cemented carbide contains WC particles, in which a transition metal element is dissolved in a solid solution, the WC particles have an average particle size of 80 nm or less and a maximum particle size of 100 nm or less, and are When the concentration of each transition metal element contained in the WC particles was measured by the TEM-EDX method at the center point of each of the 20 WC particles in the microscopic image obtained by The concentration variation between particles represented by the difference is set to 10% or less of the average concentration between particles, and five points inside the WC particles arbitrarily selected on a straight line passing through the center of the WC particles in the TEM microscopic image. - When the concentration of each transition metal element contained in the tungsten carbide particles is measured by the EDX method, the intra-particle concentration variation represented by the difference between the maximum and minimum measured values is 10% of the average intra-particle concentration. can be: In such a cemented carbide, the transition metal element is dissolved in the WC particles and has fine WC particles, and the concentration variation between particles is 10% or less of the average concentration between particles, and the intra-particle Since the transition metal elements are uniformly solid-dissolved in the WC particles such that the concentration variation is 10% or less of the average concentration in the particles, the hardness and wear resistance are even higher.

[Details of Embodiments of the Present Disclosure]
<<Embodiment 1: Tungsten carbide powder>>
<Tungsten carbide powder>
The WC powder (tungsten carbide powder) according to the present embodiment contains WC particles having an average particle size of 50 nm or less, a transition metal element is dissolved in the WC particles, and the transition metal element includes Co. By sintering the WC powder of the present embodiment, Co, which is one type of transition metal element dissolved in the WC particles, precipitates as Co metal on the surface of the WC particles during sintering and bonds. Because of the phase formation, a uniform fine crystalline phase is formed to form cemented carbide with high hardness and wear resistance.

The average particle size of the WC particles is 50 nm or less, preferably 30 nm or less, from the viewpoint of increasing the hardness and wear resistance of the cemented carbide obtained by sintering. Moreover, the average particle size of the WC particles is preferably about 3 nm or more from the viewpoint of current technical limits in synthesizing fine particles. The average particle diameter of WC particles was obtained by TEM observation, from a visual field image containing 50 or more particles, by a linear intercept method (an arbitrary straight line was drawn on the visual field image, and the length of the line segment that the straight line crossed the WC particles was calculated. The same shall apply hereinafter.). Further, from the half width of the diffraction peak by XRD (X-ray diffraction) measurement, Scherrer's formula (1) below
D=(0.94λ)/(β cos θ) (1)
(In the formula, D: mean crystal grain size, λ: X-ray wavelength, β: half width [rad], θ: Bragg angle) can also be used to calculate the mean crystal grain size.

The WC particles contain a transition metal element as a solid solution, and the transition metal element includes Co. As a result, the Co solid solution in the WC particles precipitates as Co metal on the surface of the WC particles during sintering to form a uniform fine crystal phase, resulting in a cemented carbide with high hardness and wear resistance. can be formed. The solid solution of the transition metal element containing Co in the WC particles can be confirmed by the transition metal in a microscopic image (hereinafter also referred to as an HAADF-STEM image) obtained by a high-angle scattering annular dark field scanning transmission electron microscope (HAADF-STEM) method. It can be confirmed by the absence of elemental separation and/or segregation. From the viewpoint of forming a uniform fine crystal phase during sintering, the transition metal element containing Co is preferably dissolved uniformly in the WC particles. It can be confirmed by the TEM-EDX method, as described later, that the transition metal elements containing Co are uniformly dissolved in the WC particles.

The content of the transition metal element containing Co in the WC particles is preferably 0.5 mass% or more, more preferably 1 mass% or more, from the viewpoint of acting as a binder phase of the cemented carbide to be formed, and the strength of the cemented carbide to be formed. From the viewpoint of, 20 mass% or less is preferable, and 10 mass% or less is more preferable.

In the WC powder, the transition metal element is added to Co from the viewpoint of suppressing grain growth when sintering the WC powder and forming a cemented carbide with fine WC grains and higher hardness and wear resistance. , V, Cr, Ta, Nb, and Mo. The content of at least one transition metal element selected from the group consisting of V, Cr, Ta, Nb, and Mo should be 0.00, from the viewpoint of suppressing the grain growth of WC grains when cemented carbide is formed. It is preferably 1 mass% or more, more preferably 0.3 mass% or more, and from the viewpoint of increasing the bending strength of the cemented carbide to be formed, it is preferably 2.0 mass% or less, and more preferably 1.0 mass% or less.

The composition (type and content) of W and each transition metal element (that is, Co, V, Cr, Ta, Nb and Mo, etc.) contained in the WC powder was determined by ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry) method. Identify by Specifically, 0.1 g of WC powder is appropriately pulverized in an agate mortar. It was put into a platinum crucible together with an alkaline solvent consisting of 0.2 g of calcium carbonate and 0.5 g of boron oxide and melted at 1000°C. and then diluted to 200 ml with deionized water. This is introduced into an ICP analyzer, the light emitted from W and each transition metal element excited by Ar (argon) plasma is spectroscopically analyzed, and quantitative analysis is performed from the emission intensity.

The WC powder has a uniform solid solution of the transition metal element in the WC particles, and can be sintered to form a cemented carbide with fine WC particles and high hardness and wear resistance. , there is preferably no segregation and/or segregation of the respective transition metal elements contained in the WC particles. FIG. 1A shows an example of a solid solution state of V, which is a transition metal element other than W, contained in WC particles in the WC powder of the present embodiment by the HAADF-STEM method (Example II-1 described later). FIG. 1B shows an example of a solid solution state of Co, which is a transition metal element other than W, contained in WC particles in the WC powder of the present embodiment by the HAADF-STEM method (Example II-1 described later). FIG. 1C shows an example of the distribution state of W contained in WC particles in the WC powder of the present embodiment by the HAADF-STEM method (Example II-1 described later). Referring to FIGS. 1A, 1B and 1C, W and other transition metal elements Co and V contained in the WC grains are uniform in the WC grains without any separation and/or segregation within the WC grains. It can be seen that it is solid-dissolved in

In addition, WC powder can be sintered to form a cemented carbide with fine WC particles and high hardness and wear resistance by uniformly dissolving the transition metal element in the WC particles. TEM-EDX (transmission electron microscope energy dispersive X-ray spectroscopy) method at each center point of any 20 WC particles in the image (hereinafter also referred to as a TEM image) Each transition contained in the WC particles When the concentration of the metal element is measured, the inter-particle concentration variation represented by the difference between the maximum and minimum measured values is preferably 10% or less of the average inter-particle concentration. It is more preferably 8% or less, still more preferably 7% or less of the average inter-particle concentration, and particularly preferably 6% or less of the average inter-particle concentration. Here, since the inter-particle concentration variation of the transition metal element contained in 20 WC particles is measured, it is necessary that 20 or more WC particles are present within the field of view of the TEM image. Moreover, from the viewpoint of maintaining high accuracy of concentration measurement, the number of WC grains existing within the field of view of the TEM image is preferably 20 or more and 40 or less. The center of the WC grain refers to the intersection of the major axis and the minor axis of an ellipse drawn so as to circumscribe the WC grain, and is measured using a TEM image. Here, the concentration variation between particles means the difference between the maximum and minimum concentrations of the transition metal element at the central point of the 20 WC particles. The interparticle average concentration refers to the average concentration between the concentrations of the transition metal element at the center point of the 20 WC particles.

In addition, the WC powder can form a cemented carbide with fine WC particles and high hardness and wear resistance by sintering due to the uniform solid solution of the transition metal element in the WC particles. At five points inside the WC particle arbitrarily selected on a straight line passing through the center of the WC particle, the concentration of each transition metal element contained in the WC particle is measured by the TEM-EDX method. The intra-particle concentration variation represented by the difference between the maximum value and the minimum value is preferably 10% or less of the average intra-particle concentration, more preferably 8% or less of the average intra-particle concentration. is more preferably 7% or less, and particularly preferably 6% or less of the average intra-particle concentration. Here, the intra-particle concentration variation means the difference between the maximum value and the minimum value of the concentration of the transition metal element at the above five points. In addition, the average intra-particle concentration means the average value of the concentration of the transition metal element at the above five points).

<Method for producing tungsten carbide powder>
Referring to FIG. 2, the method for producing WC particles according to the present embodiment includes a tungsten oxide dissolving step S11 of dissolving tungsten oxide in ammonia water to prepare a first aqueous solution, and an organic An organic acid addition step S12 of preparing a second aqueous solution by dissolving an acid, and a first drying step S13 of preparing a dry solid by drying the second aqueous solution at a temperature lower than the decomposition temperature of the organic acid. and a dry solid dissolving step S14 of preparing a third aqueous solution by dissolving the dry solid in water again, and mixing an aqueous solution containing at least Co (cobalt) as a transition metal element into the third aqueous solution. a step S15 of adding a transition metal element to prepare a 4 aqueous solution; a second drying step S20 to prepare a carbide precursor by drying the fourth aqueous solution; and a carbonization step S30 of preparing a tungsten carbide (WC) powder by heat treating. In the WC powder production method of this embodiment, the WC powder is produced without forming a composite oxide in which W (tungsten) and transition metal elements other than W are separated or segregated in the process, so that the particle size is small. A WC powder in which a transition metal element containing Co is solid-dissolved is obtained. Such WC powders can form cemented carbides with finer WC grains and higher hardness and wear resistance.

(Step of dissolving tungsten oxide)
In the tungsten oxide dissolving step S11, a first aqueous solution is prepared by dissolving tungsten oxide in ammonia water. Ammonia water is not particularly limited, and commercially available ammonia water is sufficient as its kind, and its concentration may be, for example, 1 mass % or more and 20 mass % or less. Tungsten oxide is not particularly limited, and may be, for example _, WO3 or _WO2 . This dissolving operation can be performed at room temperature (eg, 25° C.).

(Step of adding organic acid)
In the organic acid addition step S12, a second aqueous solution is prepared by dissolving an organic acid in the first aqueous solution. The organic acid is not particularly limited, but preferably has a decomposition temperature of 100° C. or higher because the second aqueous solution is dried in a post-process to prepare a dry solid. The organic acid may be, for example, at least one selected from the group consisting of hydroxy acids, amino acids, polycarboxylic acids, and aminopolycarboxylic acids. More specifically, organic acids include hydroxy acids such as citric acid, gluconic acid and malic acid; amino acids such as alanine, arginine and aspartic acid; polycarboxylic acids such as oxalic acid, succinic acid and maleic acid; aminopolycarboxylic acid; may be at least one selected from; This dissolving operation can be performed at room temperature (eg, 25° C.).

(Primary drying process)
In the first drying step S13, a dry solid is prepared by drying the second aqueous solution at a temperature lower than the decomposition temperature of the organic acid. The drying method is not particularly limited, and a general constant temperature dryer may be used. The drying temperature should be lower than the decomposition temperature of the organic acid. For example, when the organic acid is citric acid (decomposition temperature 175°C), the drying temperature is 10 to 30°C lower than 175°C. The drying time is not particularly limited, and may be 24 to 48 hours. The resulting dry solid has a reduced ammonia content.

(Process of dissolving dry solid matter)
In the dry solid matter dissolving step S14, the dry solid matter is dissolved again in water to prepare a third aqueous solution. This dissolving operation can be performed at room temperature (eg, 25° C.). The third aqueous solution obtained by such dissolution becomes an acidic aqueous solution because organic acid ions are generated by the dissociation of the organic acid and the ammonia component is reduced as described above.

(Step of adding transition metal element)
In the step S15 of adding a transition metal element, a fourth aqueous solution is prepared by mixing an aqueous solution containing at least Co as a transition metal element into the third aqueous solution. The aqueous solution containing Co as a transition metal element is not particularly limited, and may be, for example, an aqueous solution containing a Co salt such as cobalt nitrate or cobalt chloride. In addition to Co, the transition metal element preferably further contains at least one selected from the group consisting of V, Cr, Ta, Nb, and Mo. At least one transition metal element selected from the group consisting of V, Cr, Ta, Nb, and Mo suppresses grain growth during sintering of the WC powder, so that the hardness and resistance of fine WC grains are improved. This is because a cemented carbide with higher wearability can be formed. Thus, a water-soluble composition, which is the fourth aqueous solution, is obtained.

(Secondary drying process)
In the secondary drying step S20, a carbide precursor is prepared by drying the fourth aqueous solution (aqueous solution composition). The drying method is not particularly limited, and a general constant temperature dryer may be used. From the viewpoint of preventing decomposition of the organic acid, the drying temperature is set lower than the decomposition temperature of the organic acid. For example, when the organic acid is citric acid (decomposition temperature 175°C), the drying temperature is 10 to 30°C lower than 175°C. The drying time is not particularly limited, and may be 24 to 48 hours. The product obtained in this way is called a carbide precursor because a carbide called WC powder is obtained in a post-process.

(Carbonization process)
The carbonization step S30 prepares tungsten carbide (WC) powder by heat-treating a carbide precursor in the presence of carbon in an inert gas atmosphere. The inert gas atmosphere is not particularly limited as long as it is an inert gas that does not interfere with the carbonization of the carbide precursor, and may be N ₂ (nitrogen) gas, Ar (argon) gas, or the like. Thus, the tungsten carbide powder according to Embodiment 1 is obtained.

<<Embodiment 2: Tungsten carbide-cobalt metal composite powder>>
<Tungsten carbide-cobalt metal composite powder>
The WC (tungsten carbide)-Co (cobalt) metal composite powder according to the present embodiment includes WC particles of the WC powder according to Embodiment 1 and Co metal formed on the surface of at least part of the WC particles. ,including. Since the WC—Co metal composite powder of the present embodiment is formed by depositing a Co metal having a size of nm order on the surface of WC particles having a size of nm order, transition It is possible to form a cemented carbide with higher hardness and wear resistance by preventing segregation (Co pool) of several micrometers or more of Co, which is a metal element. The content of the Co metal formed on the surface of the WC particles is 0.3 mass% or more and 2 mass% or less from the viewpoint of forming a cemented carbide with higher hardness and wear resistance by sintering the WC-Co metal composite powder. is preferable, and 0.5 mass% or more and 1.5 mass% or less is more preferable. When forming a cemented carbide with high bending strength, the content of Co metal formed on the surface of WC particles is preferably 5 mass% or more and 15 mass% or less, more preferably 6 mass% or more and 12 mass% or less. Here, the presence and content of the Co metal formed on the surface of the WC particles is confirmed by high-frequency inductively coupled plasma atomic emission spectrometry (ICP-AES) after dissolving the WC-Co metal composite powder in hydrochloric acid or nitric acid. and measure.

<Method for Producing Tungsten Carbide-Cobalt Metal Composite Powder>
A method for producing a WC (tungsten carbide)-Co (cobalt) metal composite powder according to the present embodiment includes a heat treatment step of heat-treating the WC powder according to the first embodiment at 200° C. or higher in a hydrogen atmosphere. Through this heat treatment step, the Co dissolved in the WC particles precipitates on the surfaces of the WC particles to form Co metal, thereby obtaining a WC-Co metal composite powder.

<<Embodiment 3: Cemented Carbide>>
<Cemented Carbide>
The cemented carbide according to the present embodiment contains WC particles, in which a transition metal element is dissolved, and has an average particle size of 80 nm or less and a maximum particle size of 100 nm or less. The cemented carbide of the present embodiment has high hardness and wear resistance because the transition metal element is dissolved in the WC particles. Among the transition metal elements, Co is uniformly precipitated as a Co metal on the interfaces of WC particles with a size of nm order to form a fine structure, so that the hardness and wear resistance are high. The transition metal elements dissolved in the WC grains and Co precipitated as Co metal at the interfaces of the WC grains are identified by the STEM-HAADF method.

The content of Co in the cemented carbide is preferably 0.1 mass% or more, more preferably 0.3 mass% or more, from the viewpoint of acting as a binder phase of the cemented carbide, and from the viewpoint of increasing the bending strength of the cemented carbide, 2.0 mass% or less is preferable, and 1.0 mass% or less is more preferable.

In cemented carbide, from the viewpoint of suppressing the growth of WC particles contained in the cemented carbide to form fine WC particles and further increasing hardness and wear resistance, in addition to Co, V, Cr, Ta, Nb, and at least one selected from the group consisting of Mo. The content of at least one transition metal element selected from the group consisting of V, Cr, Ta, Nb, and Mo is 0.00, from the viewpoint of suppressing the grain growth of WC grains during cemented carbide formation. It is preferably 1 mass% or more, more preferably 0.3 mass% or more, and from the viewpoint of increasing the bending strength of the cemented carbide, preferably 2.0 mass% or less, more preferably 1.0 mass% or less.

The composition (type and content) of W and each transition metal element (that is, Co, V, Cr, Ta, Nb and Mo, etc.) contained in the WC powder of the cemented carbide is determined by ICP-AES (Inductively Coupled Plasma- luminescence spectroscopy) method. Specifically, 0.1 g of cemented carbide is suitably pulverized in an agate mortar. It was put into a platinum crucible together with an alkaline solvent consisting of 0.2 g of calcium carbonate and 0.5 g of boron oxide and melted at 1000°C. and then diluted to 200 ml with deionized water. This is introduced into an ICP analyzer, the light emitted from W and each transition metal element excited by Ar (argon) plasma is spectroscopically analyzed, and quantitative analysis is performed from the emission intensity.

Cemented carbide has fine WC particles and higher wear resistance due to the uniform solid solution of transition metal elements in WC particles. Preferably there is no separation and/or segregation of W and the respective transition metal elements contained in the particles. In the HAADF-STEM image of the cemented carbide, it can be confirmed that Co among the transition metal elements is precipitated at the interfaces of the WC grains.

In addition, cemented carbide has fine WC particles and higher hardness and wear resistance due to the uniform solid solution of transition metal elements in WC particles. The difference between the maximum value and the minimum value of the concentration of each transition metal element contained in the WC grains measured by transmission electron microscope energy dispersive X-ray spectroscopy at each center point of the grains. The represented inter-particle concentration variation is preferably 10% or less of the average inter-particle concentration, more preferably 8% or less of the average inter-particle concentration, and preferably 7% or less of the average inter-particle concentration. More preferably, it is particularly preferably 6% or less of the average concentration between particles. Here, since the inter-particle concentration variation of the transition metal element contained in 20 WC particles is measured, it is necessary that 20 or more WC particles are present within the field of view of the TEM image. Moreover, from the viewpoint of maintaining high accuracy of concentration measurement, the number of WC grains existing within the field of view of the TEM image is preferably 20 or more and 40 or less. The center of the WC grain refers to the intersection of the major axis and the minor axis of an ellipse drawn so as to circumscribe the WC grain, and is measured using a TEM image. Here, the concentration variation between particles means the difference between the maximum and minimum concentrations of the transition metal element at the central point of the 20 WC particles. The interparticle average concentration refers to the average concentration between the concentrations of the transition metal element at the center point of the 20 WC particles.

In addition, cemented carbide has fine WC particles due to the uniform solid solution of transition metal elements in WC particles, and has higher hardness and wear resistance. The concentration of each transition metal element contained in the cemented carbide by the TEM-EDX method was measured at five points inside the WC grain arbitrarily selected on a straight line passing through the center of the WC grain. At this time, the intra-particle concentration variation represented by the difference between the maximum and minimum measured values is preferably 10% or less of the average intra-particle concentration, more preferably 8% or less of the average intra-particle concentration. It is more preferably 7% or less of the average intra-particle concentration, and particularly preferably 6% or less of the average intra-particle concentration. Here, the variation in the intra-particle concentration means the difference between the maximum value and the minimum value of the concentration of the transition metal element at the above five points. Further, the average intra-particle concentration means the average value of the concentration of the transition metal element at the above five points.

The average grain size of WC particles in the cemented carbide is 80 nm or less, preferably 65 nm or less, from the viewpoint of increasing the hardness and wear resistance of the cemented carbide. Moreover, the average grain size of WC grains in the cemented carbide is preferably about 15 nm or more from the viewpoint of not impairing the increase in hardness and wear resistance of the cemented carbide due to grain refinement of WC grains. Furthermore, the maximum grain size of WC particles in the cemented carbide is 100 nm or less, preferably 80 nm or less, from the viewpoint of increasing the hardness and wear resistance of the cemented carbide.

The grain size of the WC grains in the cemented carbide is calculated by the linear intercept method from a field image containing 50 grains or more by TEM observation. The average crystal grain size can also be calculated from the half-value width of the peak obtained by TEM-EDX measurement using the Scherrer's equation described above.

The cemented carbide may contain a cobalt (Co) metal phase, and the content of the Co metal phase is preferably 2 mass% or less, more preferably 1.5 mass% or less. In such a cemented carbide, the transition metal element dissolves in the WC particles, and/or Co, which is one of the transition metal elements, precipitates on the surface of the WC particles and becomes Co metal to cover the WC particles. Even if the content of is as small as 2 mass% or less, the hardness and wear resistance are high. Moreover, when forming a cemented carbide with high bending strength, 5 mass% or more and 15 mass% or less are preferable, and 6 mass% or more and 12 mass% or less are more preferable. The content of the transition metal element in the cemented carbide and the content of the Co metal phase among the transition metals can be measured by the ICP-AES method.

The cemented carbide according to the present embodiment contains WC particles, in which a transition metal element is dissolved in a solid solution, the WC particles have an average particle size of 80 nm or less and a maximum particle size of 100 nm or less, The maximum and minimum values of the measured values when the concentration of each transition metal element contained in the WC particles was measured by the TEM-EDX method at the center point of each of the 20 WC particles in the TEM microscopic image. The inter-particle concentration variation represented by the difference is 10% or less of the inter-particle average concentration, and 5 points inside the WC grain arbitrarily selected on a straight line passing through the center of the WC grain in the microscopic image by TEM , when the concentration of each transition metal element contained in the tungsten carbide particles is measured by the TEM-EDX method, the intra-particle concentration variation represented by the difference between the maximum value and the minimum value of the measured value is the average intra-particle concentration is particularly preferably 10% or less. Such a cemented carbide has a transition metal element containing Co dissolved in WC particles, has fine WC particles, and has an inter-particle concentration variation of 10% or less of the inter-particle average concentration, and Since the transition metal elements are uniformly solid-dissolved in the WC particles such that the variation in the intra-particle concentration is 10% or less of the average intra-particle concentration, the hardness and wear resistance are further increased.

<Method for producing cemented carbide>
Referring to FIG. 2, the cemented carbide manufacturing method according to the present embodiment comprises sintering at least one powder of the WC powder of Embodiment 1 and the WC—Co metal composite powder of Example 2 to produce a cemented carbide. It includes a sintering step S40 to prepare a hard alloy. In the sintering step S40, after pressing the WC powder and/or the WC—Co metal composite powder to form a powder body, the powder body is heated and pressed to form a cemented carbide, which is a sintered body. Prepare.

The method for forming the powdered material is not particularly limited, and may be CIP (cold isostatic pressing) or the like. In CIP, it is possible to pressurize at room temperature (for example, 25° C.) at a pressure of 150 MPa or more and 250 MPa or less. Before sintering the added powder, it can be heated at a temperature of 300° C. or more and 500° C. or less in an H ₂ (hydrogen) gas atmosphere for a time of 30 minutes or more and 2 hours or less. As a result, CoC (cobalt carbide) in the added powder becomes Co metal, so the added powder changes to a mixture of WC and Co metal. The Co metal becomes a liquid phase when the green compact is sintered, and Co liquid phase sintering proceeds, so that the cemented carbide can be expected to be densified. Here, Co metal may be mixed with the WC powder of Embodiment 1 or the WC—Co metal composite powder of Embodiment 2 within a range that the content of Co metal in the resulting cemented carbide is 2 mass % or less.

Cemented carbide is produced by heating and pressing the powder compact. For example, heating is performed in an argon gas atmosphere, a nitrogen gas atmosphere, a mixed gas atmosphere of argon gas and hydrogen gas, or a mixed gas atmosphere of nitrogen gas and hydrogen gas. The powder compact is heated to, for example, 1250° C. or higher and 1450° C. or lower. The heating time may be, for example, 30 minutes or more and 2 hours or less. A cemented carbide is produced by further heating and pressing the sintered body obtained by heating the green compact. The method of heating and pressurizing is not particularly limited, and may be HIP (hot isostatic pressing) or the like. In HIP, the heating temperature can be 1300° C. or higher and 1500° C. or lower, and the pressure can be 100 MPa or higher and 250 MPa or lower. Thus, the cemented carbide according to Embodiment 3 is obtained.

<Example I-1>
1. Preparation of tungsten carbide powder To 1 L of 10 mass% ammonia water (reagent manufactured by Wako Pure Chemical Industries, Ltd.), 200 g of WO3 powder ₍ F1 grade manufactured by A.L.M.T.), which is a tungsten oxide, is added and dissolved by stirring for 24 hours with a stirrer. A first aqueous solution was prepared by A second aqueous solution was prepared by adding 180 g of anhydrous citric acid to the first aqueous solution and dissolving it. By leaving the second aqueous solution in a thermostat at 150° C. for 24 hours, the second aqueous solution was dried (primary drying) to prepare a dry solid. The second aqueous solution was dried at 150°C, which is 30°C lower than the decomposition temperature of citric acid (180°C). A third aqueous solution was prepared by redissolving the dried solid in 1 L of water. This third aqueous solution was an acidic aqueous solution. A fourth aqueous solution was prepared by mixing 33 ml of an aqueous solution with a concentration of 500 g/L of cobalt nitrate (reagent manufactured by Wako Pure Chemical Industries, Ltd.) containing Co as a transition metal element into the third aqueous solution. A carbide precursor was prepared by leaving the fourth aqueous solution in a thermostat at 150° C. for 24 hours. By using an atmosphere exchange sintering furnace (NLA-2025D manufactured by Motoyama), the carbide precursor is placed in a carbon boat and heat-treated at 900 ° C. for 2 hours in an atmosphere in which nitrogen gas is flowed at 0.5 L / min. , WC (tungsten carbide) powder was prepared.

2. Preparation of Cemented Carbide 10 g of the WC powder obtained above was pulverized, molded at a pressure of 50 MPa using a tablet molding machine, sealed in a plastic bag under vacuum, and subjected to CIP (Cemented Carbide) at room temperature (25°C) at a pressure of 200 MPa. A green compact was obtained by isotropic hydrostatic pressure) treatment. The powder compact was heat-treated at 350° C. for 3 hours in an atmosphere in which hydrogen gas was flowed at 2 L/min. As a result, the Co carbide in the green compact becomes Co metal, so that the green compact changes into a mixture of WC and Co metal. A mixture of WC and Co metal was heat-treated at 1350° C. for 1 hour in an atmosphere of Ar gas, N ₂ gas, a mixed gas of Ar and H ₂ , or a mixed gas of N ₂ and H ₂ to obtain a Co liquid. Phase sintering occurred to prepare a WC—Co sintered body. A cemented carbide was prepared by HIPing (hot isostatic pressing) a tungsten carbide-cobalt sintered body at 1320° C. and 100 MPa in an Ar gas atmosphere.

3. Evaluation of physical properties The physical properties of the tungsten carbide powder and cemented carbide obtained above were measured and evaluated by the following methods, and the results are summarized in Table 1. Here, in Table 1, "<LOD" indicates less than 0.1 mass%, which is less than the limit of measurement by the TEM-EDX method.

(Evaluation of composition of WC powder and cemented carbide)
The composition of WC powder and cemented carbide was determined by the ICP-AES method. Specifically, 0.1 g of WC powder was appropriately pulverized in an agate mortar. It was put into a platinum crucible together with an alkaline solvent consisting of 0.2 g of calcium carbonate and 0.5 g of boron oxide and melted at 1000°C. and then diluted to 200 ml with deionized water. This is introduced into an ICP analyzer (ICPS-8100 manufactured by SHIMAZU or equivalent), and the light emitted from W and each transition metal element excited by Ar (argon) plasma is spectroscopically determined, and the emission intensity is A more quantitative analysis was performed.

(Evaluation of average grain size of WC powder and cemented carbide)
The average particle size of WC particles in the WC powder and cemented carbide was calculated by the linear intercept method from field images containing 50 or more particles by TEM observation. Further, from the half width of the diffraction peak by XRD measurement, the following Scherrer formula (1)
D=(0.94λ)/(β cos θ) (1)
(Wherein, D: average crystal grain size, λ: X-ray wavelength, β: half width [rad], θ: Bragg angle) It was also confirmed that the average crystal grain size calculated by .

(Presence or absence of solid solution of transition metal elements containing Co in WC powder and cemented carbide)
Whether or not a transition metal element containing Co is dissolved in the WC powder and the WC particles of the cemented carbide is determined by the HAADF-STEM image obtained by the HAADF-STEM method. Whether there is no difference in the contrast indicating the distribution of the elements (that is, whether the contrasts almost overlap), and whether there is no separation, precipitation or segregation (solid solution) or there is separation, precipitation or segregation of the transition metal elements (non-solid solution).

(Evaluation of transition metal element distribution in WC powder and cemented carbide)
(1) Evaluation of concentration variation between particles At the center point of each of the arbitrary 20 WC particles in the TEM microscopic image (TEM image) of the WC powder and cemented carbide, the WC particles are included by the TEM-EDX method. Calculating what percentage of the inter-particle concentration variation represented by the difference between the maximum value and the minimum value of the measured value when the concentration of each transition metal element is measured is relative to the average inter-particle concentration. The inter-particle density variation was evaluated by

(2) Evaluation of Intraparticle Concentration Variation At five points inside the WC particles arbitrarily selected on a straight line passing through the center of the WC particles in the TEM images of the WC powder and the cemented carbide, the WC particles were measured by the TEM-EDX method. When the concentration of each transition metal element contained in the particles is measured, the variation in the concentration inside the particles, which is expressed as the difference between the maximum and minimum values of the measured values, is the percentage of the average concentration inside the particles. By calculating, the intra-particle concentration variation was evaluated.

(Hardness of Cemented Carbide)
Using a Vickers hardness tester (HMV-G21 manufactured by SHIMAZU), the Vickers hardness was calculated from the indentation obtained when an indenter was pressed into the cemented carbide with a load of 100 g for 5 seconds.

(Wear resistance of cemented carbide)
Grinding and electrical discharge machining were applied to a cemented carbide manufactured in the shape of a round bar with a diameter of 8 mm and a length of 80 mm to form an outer peripheral portion. A nozzle for high-pressure water jet machining was produced by forming a tapered portion at a location where water is introduced and forming a through hole having a diameter of 0.5 mm in the longitudinal direction in the center of the cemented carbide. Using the manufactured nozzle, a test was conducted in which an iron plate was cut at a water pressure of 300 MPa using an aqueous slurry containing #120 garnet abrasive grains. The diameter of the nozzle through-hole was measured at regular time intervals to record the diameter change due to wear. Hydraulic cutting tests were performed on an initial through-hole diameter of 0.5 mm until the diameter increased by 0.1 mm. The life was evaluated as the time until the diameter of the through-hole reached 0.6 mm. The longer the life, the higher the wear resistance.

<Example I-2>
The WC powder prepared in Example I-1 above was treated with a high-pressure sintering apparatus (manufactured by KOBELCO) at a pressure of 7 GPa and a temperature of 1350° C. for 30 minutes to prepare a cemented carbide. WC powder and cemented carbide were produced in the same manner as in Example I-1, and their physical properties were evaluated in the same manner as in Example I-1. The results are summarized in Table 1.

<Example II-1>
When preparing the fourth aqueous solution, 1 g of vanadium (III) chloride powder ( WC powder and a cemented carbide were prepared in the same manner as in Example I-1, except that WO ₃ powder (corresponding to 0.5 mass% with respect to 200 g of WO 3 powder) was added, and their physical properties were measured in Example I-1. was evaluated in the same manner. The results are summarized in Table 1. Here, vanadium chloride (III) means vanadium chloride in which the valence of V (vanadium) ion is 3.

<Example II-2>
A WC powder and a cemented carbide were prepared in the same manner as in Example II-1, except that 1 g of vanadium (III) chloride powder was replaced with 1 g of chromium (III) chloride powder, and their physical properties were measured. It was evaluated in the same manner as I-1. The results are summarized in Table 1. Here, chromium (III) chloride means chromium chloride having a Cr (chromium) ion with a valence of 3.

<Example II-3>
WC powder and ultrafine powder were prepared in the same manner as in Example II-1, except that 0.6 g of vanadium (III) chloride powder and 0.4 g of chromium (III) chloride powder were used instead of 1 g of vanadium (III) chloride powder. Hard alloys were produced and their physical properties were evaluated in the same manner as in Example I-1. The results are summarized in Table 1.

<Example II-4>
A WC powder and a cemented carbide were prepared in the same manner as in Example II-1, except that 1 g of vanadium chloride (III) powder was replaced with 1 g of tantalum (V) chloride powder, and their physical properties were measured. It was evaluated in the same manner as I-1. The results are summarized in Table 1. Here, tantalum (V) chloride means tantalum chloride in which the Ta (tantalum) ion has a valence of 5.

<Example II-5>
A WC powder and a cemented carbide were prepared in the same manner as in Example II-1, except that 1 g of vanadium (III) chloride powder was replaced with 1 g of niobium (V) chloride powder, and their physical properties were measured. It was evaluated in the same manner as I-1. The results are summarized in Table 1. Here, niobium (V) chloride means niobium chloride in which the valence of Nb (niobium) ion is 5.

<Example II-6>
WC powder and cemented carbide were prepared in the same manner as in Example II-1, except that 1 g of vanadium (III) chloride powder was replaced with 1 g of molybdenum (V) chloride powder, and their physical properties were measured. It was evaluated in the same manner as I-1. The results are summarized in Table 1. Here, molybdenum (V) chloride means molybdenum chloride in which the valence of Mo (molybdenum) ion is 5.

<Comparative Example I>
For comparison with the above examples, 100 g of WC powder (WC02NRP grade manufactured by Allied Materials Co., Ltd.) and 2 g of Co metal powder manufactured by Kojundo Chemical Laboratory Co., Ltd. were added to an ethanol dispersion medium, mixed with an attritor, and the dry powder was tableted. After being molded in a container at a pressure of 50 MPa, it was vacuum-sealed in a plastic bag and subjected to CIP (cold isostatic pressing) treatment at room temperature (25° C.) and 200 MPa to obtain a green compact. A sintered body was prepared by heat-treating the powder compact at 1350° C. for 1 hour in an Ar gas atmosphere. A cemented carbide was prepared by subjecting this sintered body to HIP (hot isostatic pressing) treatment in an Ar gas atmosphere at a temperature of 1320° C. and a pressure of 100 MPa. The physical properties of the obtained cemented carbide were evaluated in the same manner as in Example I-1. The results are summarized in Table 1.

<Comparative Example II>
For comparison with the above examples, 10 g of cobalt nitrate and 5 g of ammonium vanadate (both from Wako Pure Chemical Industries, Ltd.) were added to 1 L of an aqueous ammonium metatungstate solution (MW-2 manufactured by Nippon Inorganic Chemical Industry Co., Ltd.) with a concentration of 50 mass%. 99% pure reagent) was dissolved. This mixed aqueous solution was converted into a mixed oxide powder having a particle size of about 10 μm using a spray pyrolysis apparatus (manufactured by Okawara Kakoki Co., Ltd.). WC powder was obtained by reducing and carbonizing this mixed oxide powder at 900° C. in a mixed gas (CO/H ₂ =1/4) atmosphere of carbon monoxide and hydrogen. A cemented carbide was prepared from this WC powder in the same manner as in Comparative Example 1. The physical properties of the obtained cemented carbide were evaluated in the same manner as in Example I-1. The results are summarized in Table 1.

Referring to Table 1, as shown in Examples I-1 to I-2 and II-1 to II-6, tungsten carbide (WC) particles having an average particle size of 50 nm or less were included, and the WC particles were transition metal particles. It was found that by sintering WC powder containing elements in solid solution and containing cobalt (Co) as a transition metal element, a cemented carbide with high hardness and wear resistance (for example, a long nozzle life) can be obtained. rice field.

<Example III-1>
1. Preparation of tungsten carbide powder To 1 L of 10 mass% ammonia water (reagent manufactured by Wako Pure Chemical Industries, Ltd.), 200 g of WO3 powder ₍ F1 grade manufactured by A.L.M.T.), which is tungsten oxide, is added and dissolved by stirring for 24 hours with a stirrer. A first aqueous solution was prepared by A second aqueous solution was prepared by adding 180 g of anhydrous citric acid to the first aqueous solution and dissolving it. By leaving the second aqueous solution in a thermostat at 150° C. for 24 hours, the second aqueous solution was dried (primary drying) to prepare a dry solid. The second aqueous solution was dried at 150°C, which is 30°C lower than the decomposition temperature of citric acid (180°C). A third aqueous solution was prepared by redissolving the dried solid in 1 L of water. This third aqueous solution was an acidic aqueous solution. A fourth aqueous solution was prepared by mixing 165 ml of an aqueous solution with a concentration of 500 g/L of cobalt nitrate (reagent manufactured by Wako Pure Chemical Industries, Ltd.) containing Co as a transition metal element into the third aqueous solution. A carbide precursor was prepared by leaving the fourth aqueous solution in a thermostat at 150° C. for 24 hours. By using an atmosphere exchange sintering furnace (NLA-2025D manufactured by Motoyama), the carbide precursor is placed in a carbon boat and heat-treated at 900 ° C. for 2 hours in an atmosphere in which nitrogen gas is flowed at 0.5 L / min. , WC (tungsten carbide) powder was prepared.

2. Preparation of Cemented Carbide 10 g of the WC powder obtained above was pulverized, molded at a pressure of 50 MPa using a tablet molding machine, sealed in a plastic bag under vacuum, and subjected to CIP (Cemented Carbide) at room temperature (25°C) at a pressure of 200 MPa. A green compact was obtained by isotropic hydrostatic pressure) treatment. The powder compact was heat-treated at 350° C. for 3 hours in an atmosphere in which hydrogen gas was flowed at 2 L/min. As a result, the Co carbide in the green compact becomes Co metal, so that the green compact changes into a mixture of WC and Co metal. A mixture of WC and Co metal was heat-treated at 1350° C. for 1 hour in an atmosphere of Ar gas, N ₂ gas, a mixed gas of Ar and H ₂ , or a mixed gas of N ₂ and H ₂ to obtain a Co liquid. Phase sintering occurred to prepare a WC—Co sintered body. A cemented carbide was prepared by HIPing (hot isostatic pressing) a tungsten carbide-cobalt sintered body at 1320° C. and 100 MPa in an Ar gas atmosphere.

3. Evaluation of physical properties In the same manner as in Example I-1, the composition of the WC powder and the cemented carbide was evaluated, the average grain size of the WC powder and the cemented carbide was evaluated, and the content of transition metal elements including Co in the WC powder and the cemented carbide was evaluated. The presence or absence of solid solution and the distribution of transition metal elements in the WC powder and cemented carbide were evaluated (evaluation of inter-particle concentration variation and evaluation of intra-particle concentration variation). Moreover, the bending strength of the cemented carbide obtained above was measured and evaluated by the following method. That is, the bending strength was measured according to Cemented Carbide Tool Association standard CIS026B "Testing method for bending strength (transverse rupture strength) of cemented carbide". The distance between fulcrums was 20 mm, the load point/fulcrum size was R1.6-R3.0, and the sample size was 4 mm×8 mm×25 mm. The results are summarized in Table 2.

<Example III-2>
When preparing the fourth aqueous solution, vanadium chloride powder of 0.5% was added to 165 ml of an aqueous solution having a concentration of 500 g/L of cobalt nitrate (reagent manufactured by Wako Pure Chemical Industries, Ltd.) containing Co as a mixed transition metal element to be mixed in the third aqueous solution. 8 g (equivalent to 0.4 mass% with respect to 200 g of _WO3 powder)
WC powder and cemented carbide were prepared in the same manner as in Example III-1 except that The results are summarized in Table 2.

<Example III-3>
When preparing the fourth aqueous solution, chromium (III) chloride powder1. A WC powder and a cemented carbide were prepared in the same manner as in Example III-1 except that 6 g (corresponding to 0.8 mass% with respect to 200 g of WO ₃ powder) was added, and their physical properties were evaluated as in Example III. -1 was evaluated in the same manner. The results are summarized in Table 2.

<Example III-4>
When preparing the fourth aqueous solution, vanadium chloride powder of 0.5% was added to 165 ml of an aqueous solution having a concentration of 500 g/L of cobalt nitrate (reagent manufactured by Wako Pure Chemical Industries, Ltd.) containing Co as a mixed transition metal element to be mixed in the third aqueous solution. Example except that 8 g (equivalent to 0.4 mass% with respect to 200 g of WO3 powder) and 1.6 g of chromium ( _III ) chloride powder (equivalent to 0.8 mass% with respect to 200 g of WO3 powder) _were added WC powder and cemented carbide were produced in the same manner as in III-1, and their physical properties were evaluated in the same manner as in Example III-1. The results are summarized in Table 2.

<Example III-5>
When preparing the fourth aqueous solution, vanadium chloride powder of 0.5% was added to 73 ml of an aqueous solution having a concentration of 500 g/L of cobalt nitrate (reagent manufactured by Wako Pure Chemical Industries, Ltd.) containing Co as a mixed transition metal element to be mixed in the third aqueous solution. A WC powder and a cemented carbide were prepared in the same manner as in Example III-1 except that 8 g (corresponding to 0.4 mass% with respect to 200 g of WO ₃ powder) was added, and their physical properties were measured in Example III. -1 was evaluated in the same manner. The results are summarized in Table 2.

<Example III-6>
When preparing the fourth aqueous solution, vanadium chloride powder of 0.5% was added to 91 ml of an aqueous solution having a concentration of 500 g/L of cobalt nitrate (reagent manufactured by Wako Pure Chemical Industries, Ltd.) containing Co as a mixed transition metal element to be mixed in the third aqueous solution. A WC powder and a cemented carbide were prepared in the same manner as in Example III-1 except that 8 g (corresponding to 0.4 mass% with respect to 200 g of WO ₃ powder) was added, and their physical properties were measured in Example III. -1 was evaluated in the same manner. The results are summarized in Table 2.

<Example III-7>
When preparing the fourth aqueous solution, vanadium chloride powder of 0.5% was added to 110 ml of an aqueous solution with a concentration of 500 g/L of cobalt nitrate (reagent manufactured by Wako Pure Chemical Industries, Ltd.) containing Co as a mixed transition metal element to be mixed in the third aqueous solution. A WC powder and a cemented carbide were prepared in the same manner as in Example III-1 except that 8 g (corresponding to 0.4 mass% with respect to 200 g of WO ₃ powder) was added, and their physical properties were measured in Example III. -1 was evaluated in the same manner. The results are summarized in Table 2.

<Example III-8>
When preparing the fourth aqueous solution, vanadium chloride powder of 0.5% was added to 220 ml of an aqueous solution with a concentration of 500 g/L of cobalt nitrate (reagent manufactured by Wako Pure Chemical Industries, Ltd.) containing Co as a mixed transition metal element to be mixed in the third aqueous solution. A WC powder and a cemented carbide were prepared in the same manner as in Example III-1 except that 8 g (corresponding to 0.4 mass% with respect to 200 g of WO ₃ powder) was added, and their physical properties were measured in Example III. -1 was evaluated in the same manner. The results are summarized in Table 2.

<Example III-9>
When preparing the fourth aqueous solution, 0.25 g of vanadium chloride powder was added to 256 ml of an aqueous solution having a concentration of 500 g/L of cobalt nitrate (reagent manufactured by Wako Pure Chemical Industries, Ltd.) containing Co as a mixed transition metal element to be mixed in the third aqueous solution. A WC powder and a cemented carbide were prepared in the same manner as in Example III-1 except that 8 g (corresponding to 0.4 mass% with respect to 200 g of WO ₃ powder) was added, and their physical properties were measured in Example III. -1 was evaluated in the same manner. The results are summarized in Table 2.

<Example III-10>
When preparing the fourth aqueous solution, 0.5 g of vanadium chloride powder was added to 275 ml of an aqueous solution with a concentration of 500 g/L of cobalt nitrate (reagent manufactured by Wako Pure Chemical Industries, Ltd.) containing Co as a mixed transition metal element to be mixed in the third aqueous solution. 8 g (equivalent to 0.4 mass% with respect to 200 g of _WO3 powder)
WC powder and cemented carbide were prepared in the same manner as in Example III-1 except that The results are summarized in Table 2.

<Example III-11>
When preparing the fourth aqueous solution, vanadium chloride powder of 0.5 g/L was added to 294 ml of an aqueous solution of cobalt nitrate (reagent manufactured by Wako Pure Chemical Industries, Ltd.) containing Co as a mixed transition metal element to be mixed in the third aqueous solution and having a concentration of 500 g/L. 8 g (equivalent to 0.4 mass% with respect to 200 g of _WO3 powder)
WC powder and cemented carbide were prepared in the same manner as in Example III-1 except that The results are summarized in Table 2.

<Comparative Example III>
For comparison with the above examples, 100 g of WC powder (WC02NRP grade manufactured by Allied Materials), 0.41 g of VC powder (OR10 grade manufactured by Allied Materials), and 2 g of Co metal powder manufactured by Kojundo Chemical Laboratory Co., Ltd. were dispersed in ethanol. After being put into a medium and mixed with an attritor, the dry powder was molded with a tableting machine at a pressure of 50 MPa, vacuum-sealed in a plastic bag, and subjected to CIP (cold isostatic pressing) at room temperature (25 ° C.) and 200 MPa. to obtain a green compact. A sintered body was prepared by heat-treating the powder compact at 1350° C. for 1 hour in an Ar gas atmosphere. A cemented carbide was prepared by subjecting this sintered body to HIP (hot isostatic pressing) treatment in an Ar gas atmosphere at a temperature of 1320° C. and a pressure of 100 MPa. The physical properties of the obtained cemented carbide were evaluated in the same manner as in Example III-1. The results are summarized in Table 2.

Referring to Table 2, as shown in Examples III-1 to III-10, tungsten carbide (WC) particles having an average particle size of 50 nm or less are included, and the WC particles are solid-dissolved with a transition metal element, and the transition The metal element contains cobalt (Co), and by sintering WC powder having a Co content of 5.0 mass% or more and 15 mass% or less, the content of Co metal precipitated on the surface of the WC particles is reduced to 5.0 mass%. It was found that a cemented carbide with high bending strength can be obtained at a content of 15 mass% or less.

The embodiments and examples disclosed this time are illustrative in all respects and should not be considered restrictive. The scope of the present invention is indicated by the scope of the claims rather than the above-described embodiments and examples, and is intended to include meanings equivalent to the scope of the claims and all modifications within the scope.

S11 Tungsten oxide dissolution step S12 Organic acid addition step S13 Primary drying step S14 Dry solid dissolution step S15 Transition metal element addition step S20 Secondary drying step S30 Carbonization step S40 sintering process.

Claims (5)

containing tungsten carbide particles having an average particle size of 50 nm or less,
A transition metal element is dissolved in the tungsten carbide particles,
A tungsten carbide powder, wherein the transition metal element includes cobalt. The tungsten carbide powder according to claim 1, wherein said transition metal element further includes at least one selected from the group consisting of vanadium, chromium, tantalum, niobium, and molybdenum. At the central point of each of the arbitrary 20 tungsten carbide particles in the transmission electron microscope image, the concentration of each transition metal element contained in the tungsten carbide particles is determined by transmission electron microscope energy dispersive X-ray spectroscopy. 3. The tungsten carbide powder according to claim 1 or 2, wherein the variation in concentration between particles, which is represented by the difference between the maximum and minimum measured values, is 10% or less of the average concentration between particles when measured. . said tungsten carbide particles by transmission electron microscope energy dispersive X-ray spectroscopy at five points inside said tungsten carbide particles arbitrarily selected on a straight line passing through the center of said tungsten carbide particles in a microscopic image by transmission electron microscope; When the concentration of each transition metal element contained in is measured, the intra-particle concentration variation represented by the difference between the maximum value and the minimum value of the measured value is 10% or less of the average intra-particle concentration. Tungsten carbide powder according to any one of claims 1 to 3. Tungsten carbide containing the tungsten carbide particles of the tungsten carbide powder according to any one of claims 1 to 4, and cobalt metal formed on the surface of at least part of the tungsten carbide particles - Cobalt metal composite powders.

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