JP7405210B2 - cemented carbide - Google Patents

Description

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

JP 2007-262475A (Patent Document 1) discloses a cemented carbide powder containing WC powder and Co powder, in which 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. Disclosed is a cemented carbide powder in which the number of Co powders is 4% or less of the total number of Co powders.

Furthermore, International Publication No. 2009/001929 (Patent Document 2) contains WC particles as a hard phase, Co as a binder phase, and Co ₃ W ₃ C, Co ₆ W ₆ C, Co ₂ W ₄ C and A cemented carbide containing at least one type of cobalt tungsten carbide particles selected from Co ₃ W ₉ C, which has a Co ₃ W ₃ C peak, a 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. A superalloy is disclosed that satisfies the above requirements and discloses a cemented carbide in which the average particle size of the WC particles is 0.3 μm or less, and the average particle size of the cobalt tungsten carbide particles is smaller than the average particle size of the WC particles.

Japanese Patent Application Publication No. 2007-262475 International Publication No. 2009/001929

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

A tungsten carbide-cobalt metal composite powder according to one aspect of the present disclosure includes the above-described tungsten carbide particles and a cobalt metal formed on the surface of at least some of the tungsten carbide particles. Contains composite particles.

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

FIG. 1A is a photograph of a microscopic 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 the tungsten carbide powder of the present disclosure, obtained by high-angle scattering annular dark-field scanning transmission electron microscopy. It 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, obtained by high-angle scattering annular dark-field scanning transmission electron microscopy. It is. FIG. 1C is a photograph of a microscopic image showing an example of the distribution state of tungsten contained in tungsten carbide particles in the tungsten carbide powder of the present disclosure obtained by high-angle scattering annular dark-field scanning transmission electron microscopy. FIG. 2 is a flowchart illustrating an example of the method for manufacturing tungsten carbide powder and cemented carbide of the present disclosure.

[Problems to be solved by this 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 transition metal elements other than tungsten. It is formed using a composite carbide formed via a composite oxide containing as a raw material. In such a composite carbide, since tungsten and transition elements other than tungsten separate or segregate at the stage of forming a composite oxide, the composite carbide that is formed also has portions where tungsten and transition elements other than tungsten are separated or segregated ( In other words, the portion that is not dissolved in solid solution) remains. In order to promote solid solution of tungsten and a transition element other than tungsten in such a composite carbide, heat treatment at a high temperature is further required. Such heat treatment increases the particle size of the composite carbide. A cemented carbide obtained from a composite carbide that has a part where tungsten and a transition element other than tungsten are separated or segregated, and a cemented carbide obtained from a composite carbide that has a part where tungsten and a transition element other than tungsten are separated or segregated and are dissolved in solid solution with each other. However, all cemented carbides obtained from composite carbides with large particle sizes have a problem in that they have high hardness but low wear resistance.

Therefore, 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 wear resistance.

[Effects of this disclosure]
According to the present disclosure, it is possible to provide a tungsten carbide powder, a tungsten carbide cobalt metal composite powder, a cemented carbide, and a method for producing a tungsten carbide powder that can form a cemented carbide having both high hardness and wear resistance.

[Description of embodiments of the present disclosure]
First, embodiments of the present disclosure will be listed and described. In this specification, the term "transition metal element" refers to a transition metal element other than tungsten (W).

[1] The tungsten carbide (WC) powder according to one aspect of the present disclosure includes tungsten carbide (WC) particles having an average particle size of 50 nm or less, in which the WC particles have a transition metal element dissolved therein, and the WC particle has a transition metal element dissolved therein. contains cobalt (Co). When the WC powder of this embodiment is sintered, Co, which is one type of transition metal element solid-solved in the WC particles, is precipitated as cobalt (Co) metal on the surface of the WC particles during sintering. As a result, a uniform fine crystalline phase is formed and a cemented carbide with high hardness and wear resistance can be formed.

[2] In the above 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 be included. Such WC powder contains, in addition to Co, at least one transition metal element selected from the group consisting of V, Cr, Ta, Nb, and Mo, which suppresses particle growth during sintering, and is fixed to the WC particles. Because it is molten, a cemented carbide with fine WC particles and higher hardness and wear resistance can be formed.

[3] The above-mentioned WC powder was transformed into WC particles by transmission electron microscopy energy dispersive When the concentration of each included transition metal element is measured, the inter-particle concentration variation represented by the difference between the maximum value and the minimum value of the measured value can be set to 10% or less of the average inter-particle concentration. In such WC powder, the transition metal element is uniformly dissolved in the WC particles such that the inter-particle concentration variation is 10% or less of the average inter-particle concentration, so that the hardness and wear resistance of the fine WC particles are improved. It is possible to form a cemented carbide with higher hardness.

[4] The above-mentioned WC powder has five points inside the WC particle arbitrarily selected on a straight line passing through the center of the WC particle in the TEM microscopic image, and each transition contained in the WC particle is determined by the TEM-EDX method. When the concentration of a metal element is measured, the intra-particle concentration variation represented by the difference between the maximum value and the minimum value of the measured value can be made 10% or less of the average intra-particle concentration. In such WC powder, the transition metal element is uniformly dissolved in the WC particles such that the intra-particle concentration variation is 10% or less of the average intra-particle concentration, so that the hardness and wear resistance of the fine WC particles are improved. It is possible to form a cemented carbide with higher hardness.

[5] The tungsten carbide (WC)-cobalt (Co) metal composite powder according to one aspect of the present disclosure includes WC particles of the WC powder and Co metal formed on the surface of at least a part of the WC particles. and, including. The WC-Co metal composite powder of this embodiment is formed by precipitating Co metal in nm order size on the surface of WC particles in nm order size, so transition metal is removed during sintering. By preventing the segregation of the element Co (Co pool) in a size of several μm or more, a cemented carbide with higher hardness and wear resistance can be formed.

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

[7] In the cemented carbide, the transition metal element may include at least one selected from the group consisting of V, Cr, Ta, Nb, and Mo. In this cemented carbide, in addition to Co, at least one transition metal element selected from the group consisting of V, Cr, Ta, Nb, and Mo, which suppresses particle growth during sintering, is added to the WC particles. Since it is a solid solution, it has fine WC particles and has 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 20 arbitrary WC particles in the TEM microscopic image of the above cemented carbide, The inter-particle concentration variation, expressed as the difference between the maximum and minimum measured values, can be made 10% or less of the average inter-particle concentration. Such a cemented carbide has fine WC particles and has fine WC particles, and has hardness and More wear resistant.

[9] The above-mentioned cemented carbide is characterized in that each of the WC particles contained in the WC particles measured by the 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 a transition metal element is measured, the intra-particle concentration variation represented by the difference between the maximum value and the minimum measured value can be made 10% or less of the average intra-particle concentration. Such cemented carbide has fine WC particles, and has fine WC particles, and hardness and More wear resistant.

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

[11] The cemented carbide contains WC particles, the WC particles have a transition metal element dissolved therein, the WC particles have an average particle size of 80 nm or less, a maximum particle size of 100 nm or less, and TEM 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 microscopic image obtained by The inter-particle concentration variation represented by the difference is 10% or less of the average inter-particle concentration, and at five points inside the WC particle arbitrarily selected on a straight line passing through the center of the WC particle in the TEM microscopic image, TEM - When the concentration of each transition metal element contained in tungsten carbide particles is measured by the EDX method, the intra-particle concentration variation, expressed as the difference between the maximum and minimum measured values, is calculated as 10% of the average intra-particle concentration. It can be as follows. Such a cemented carbide has a transition metal element dissolved in solid solution in WC particles, has fine WC particles, and has a concentration variation among particles of 10% or less of the average concentration between particles, and a concentration within the particles. As the concentration variation is 10% or less of the average concentration within the particles, the transition metal element is uniformly dissolved in the WC particles, so that 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 includes WC particles having an average particle size of 50 nm or less, in which a transition metal element is dissolved in solid solution, and the transition metal element includes Co. By sintering the WC powder of this embodiment, Co, which is one type of transition metal element solid-solved in the WC particles, is precipitated as Co metal on the surface of the WC particles during sintering and bonded. Since the phase is formed, a uniform fine crystal phase is formed, and a cemented carbide with high hardness and wear resistance can be formed.

The average particle diameter 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. Further, the average particle diameter of the WC particles is preferably about 3 nm or more from the viewpoint of current technical limitations in fine particle synthesis. The average particle diameter of WC particles is determined by TEM observation using a field image containing 50 or more particles using the linear intercept method (drawing an arbitrary straight line on the field image and determining the length of the line segment where the straight line crosses the WC particles). This is a method for calculating the average particle diameter of WC particles (the same applies hereinafter). In addition, from the half-width of the diffraction peak by XRD (X-ray diffraction) measurement, the following Scherrer equation (1) can be used.
D=(0.94λ)/(βcosθ)...(1)
The average crystal grain size can also be calculated from (where D: crystal average grain size, λ: X-ray wavelength, β: half width [rad], θ: Bragg angle).

In the WC particles, a transition metal element is dissolved in solid solution, and the transition metal element contains Co. As a result, the Co dissolved in the WC particles precipitates as Co metal on the surface of the WC particles during sintering to form a uniform fine crystal phase, making it possible to create a cemented carbide with high hardness and wear resistance. Can be formed. The fact that transition metal elements including Co are dissolved in WC particles indicates that transition metal elements can be detected in microscopic images obtained by high-angle scattering annular dark-field scanning transmission electron microscopy (HAADF-STEM) (hereinafter also referred to as HAADF-STEM images). This can be confirmed by the absence of separation and/or segregation of elements. From the viewpoint of forming a uniform fine crystal phase during sintering, it is preferable that the transition metal element containing Co is uniformly dissolved in the WC particles. As will be described later, it can be confirmed by the TEM-EDX method that the transition metal elements including Co are uniformly dissolved in the WC particles.

The content of transition metal elements including 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 content can improve the strength of the cemented carbide to be formed. From this viewpoint, it is preferably 20 mass% or less, more preferably 10 mass% or less.

In the WC powder, transition metal elements are used in addition to Co, from the viewpoint of suppressing particle growth when sintering the WC powder to form a cemented carbide with fine WC particles and higher hardness and wear resistance. , V, Cr, Ta, Nb, and Mo. The content of at least one type of transition metal element selected from the group consisting of V, Cr, Ta, Nb, and Mo is set to 0.0000. 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 (i.e., Co, V, Cr, Ta, Nb, Mo, etc.) contained in the WC powder was determined using the ICP-AES (Inductively Coupled Plasma-Emission Spectrometry) method. Specify by. Specifically, 0.1 g of WC powder is appropriately ground in an agate mortar. 0.2 g of calcium carbonate and 0.5 g of boron oxide were placed in a platinum crucible together with an alkaline solvent and melted at 1000°C. After collecting at 60° C., dilute to 200 ml with ion-exchanged water. This is introduced into an ICP analyzer, and the light emitted from W excited by Ar (argon) plasma and the respective transition metal elements is spectrally analyzed, and quantitative analysis is performed based on the emission intensity.

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

In addition, WC powder can be used under TEM microscopy from the viewpoint that by sintering, a cemented carbide with fine WC particles and higher hardness and wear resistance can be formed by uniformly dissolving transition metal elements in WC particles. At the center point of each of 20 arbitrary WC particles in an image (hereinafter also referred to as a TEM image), each transition contained in the WC particles is determined by TEM-EDX (transmission electron microscopy energy dispersive X-ray spectroscopy). When measuring the concentration of a metal element, it is preferable that the interparticle concentration variation, expressed as the difference between the maximum and minimum measured values, is 10% or less of the average interparticle concentration, and It is more preferably 8% or less, even more preferably 7% or less of the interparticle average concentration, and particularly preferably 6% or less of the interparticle average concentration. Here, since the interparticle concentration variation of the transition metal element contained in 20 WC particles is measured, it is necessary that 20 or more WC particles exist within the field of view of the TEM image. Furthermore, from the viewpoint of maintaining high accuracy in concentration measurement, the number of WC particles present within the field of view of the TEM image is preferably 20 or more and 40 or less. The center of a WC particle refers to the intersection of the long axis and short axis of an ellipse drawn to circumscribe the WC particle, and is measured using a TEM image. Here, the inter-particle concentration variation refers to the difference between the maximum and minimum concentration values of the transition metal element at the center point of the 20 WC particles. The interparticle average concentration refers to the average concentration of the transition metal element at the center point of the 20 WC particles.

In addition, WC powder has the advantage of being able to form a cemented carbide with fine WC particles and higher hardness and wear resistance through sintering due to the uniform solid solution of transition metal elements in WC particles. The concentration of each transition metal element contained in the WC particles is measured by the TEM-EDX method at five points inside the WC particles arbitrarily selected on a straight line passing through the center of the WC particles. It is preferable that the intra-particle concentration variation expressed by the difference between the maximum value and the minimum value is 10% or less of the intra-particle average concentration, more preferably 8% or less of the intra-particle average concentration, and the intra-particle average concentration It is more preferably 7% or less of the intra-particle average concentration, and particularly preferably 6% or less of the average intra-particle concentration. Here, the intra-particle concentration variation refers to the difference between the maximum and minimum concentration values of the transition metal element at the above five points. In addition, the intra-particle average concentration refers to 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 preparing a first aqueous solution by dissolving tungsten oxide in aqueous ammonia, and a step S11 of dissolving tungsten oxide in which a first aqueous solution is An organic acid addition step S12 in which a second aqueous solution is prepared by dissolving the acid; and a first drying step S13 in which a dry solid is prepared by drying the second aqueous solution at a temperature lower than the decomposition temperature of the organic acid. A dry solid dissolving step S14 of preparing a third aqueous solution by redissolving the dry solid in water, and a third aqueous solution containing at least Co (cobalt) as a transition metal element in the third aqueous solution. A transition metal element addition step S15 for preparing a fourth aqueous solution, a second drying step S20 for preparing a carbide precursor by drying the fourth aqueous solution, and a step S20 for preparing a carbide precursor in the presence of carbon in an inert gas atmosphere. and a carbonization step S30 of preparing tungsten carbide (WC) powder by heat-treating. The method for producing WC powder of this embodiment produces WC powder without forming a composite oxide in which W (tungsten) and transition metal elements other than W separate or segregate during the process, so the particle size is small. A WC powder in which transition metal elements including Co are dissolved in solid solution is obtained. Such WC powder can form a cemented carbide having fine WC particles and higher hardness and wear resistance.

(Tungsten oxide melting process)
In the tungsten oxide dissolving step S11, a first aqueous solution is prepared by dissolving tungsten oxide in aqueous ammonia. There are no particular restrictions on the ammonia water, and commercially available ammonia water may be used as the type, and the concentration may be, for example, 1 mass% or more and 20 mass% or less. The tungsten oxide is not particularly limited, and may be, for example, WO ₃ or WO ₂ . This dissolution operation can be performed at room temperature (for example, 25°C).

(Organic acid addition step)
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 since the second aqueous solution is dried in a subsequent step to prepare a dry solid, it is preferable that the decomposition temperature is 100° C. or higher. The organic acid may be, for example, at least one type 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; and EDTA and the like. It may be at least one type selected from aminopolycarboxylic acids. This dissolution operation can be performed at room temperature (for example, 25°C).

(First 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 is 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 component.

(Dissolution process of dry solids)
In the dry solid matter dissolving step S14, a third aqueous solution is prepared by dissolving the dry solid matter in water again. This dissolution operation can be performed at room temperature (for example, 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 transition metal element addition step S15, a fourth aqueous solution is prepared by mixing an aqueous solution containing at least Co as a transition metal element with the third aqueous solution. The aqueous solution containing Co as a transition metal element is not particularly limited, and may be an aqueous solution containing a Co salt such as cobalt nitrate or cobalt chloride. In addition to Co, the transition metal element preferably further includes 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 particle growth during sintering of the WC powder, thereby increasing the hardness and resistance of fine WC particles. This is because a cemented carbide with higher wear resistance can be formed. In this way, a water-soluble composition, which is the fourth aqueous solution, is obtained.

(Second drying process)
In the second 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. The drying temperature is set lower than the decomposition temperature of the organic acid from the viewpoint of preventing decomposition 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. What is obtained in this way is called a carbide precursor because a carbide called WC powder is obtained in a post-process.

(Carbonization process)
In the carbonization step S30, tungsten carbide (WC) powder is prepared 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 does not interfere with carbonizing the carbide precursor, and may be N ₂ (nitrogen) gas, Ar (argon) gas, or the like. In this way, 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 the WC particles of the WC powder according to Embodiment 1 and the Co metal formed on the surface of at least a part of the WC particles. ,including. The WC-Co metal composite powder of this embodiment is formed by precipitating Co metal with a size on the nm order on the surface of WC particles with a size on the nm order, so transition occurs during sintering. Segregation (Co pool) of several micrometers or more of the metallic element Co can be prevented, and a cemented carbide with higher hardness and wear resistance can be formed. The content of 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 more preferably 0.5 mass% or more and 1.5 mass% or less. Further, when forming a cemented carbide with high bending strength, the content of Co metal formed on the surface of the 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 Co metal formed on the surface of the WC particles is confirmed by dissolving the WC-Co metal composite powder in hydrochloric acid or nitric acid and using high-frequency inductively coupled plasma emission spectroscopy (ICP-AES). and measure.

<Production method of tungsten carbide-cobalt metal composite powder>
The method for producing 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 Embodiment 1 at 200° C. or higher in a hydrogen atmosphere. Through this heat treatment step, Co dissolved in the WC particles is precipitated on the surface 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 includes WC particles, in which transition metal elements are dissolved in solid solution, and the average particle size is 80 nm or less and the maximum particle size is 100 nm or less. The cemented carbide of this embodiment has high hardness and wear resistance because the transition metal element is solidly dissolved in the WC particles. Among the transition metal elements, Co is uniformly precipitated as a Co metal at the interface of WC particles having a size on the order of nanometers, forming a fine structure, and therefore has high hardness and wear resistance. The transition metal element dissolved in the WC particles and the Co precipitated as Co metal at the interface of the WC particles 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. It is preferably 2.0 mass% or less, more preferably 1.0 mass% or less.

In cemented carbide, in addition to Co, V, Cr, Ta, Nb, It is preferable to further include at least one selected from the group consisting of and Mo. The content of at least one type of transition metal element selected from the group consisting of V, Cr, Ta, Nb, and Mo is set to 0.0000. 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, 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 (i.e., Co, V, Cr, Ta, Nb, Mo, etc.) contained in the WC powder of the cemented carbide is determined by ICP-AES (inductively coupled plasma). Identification by luminescence spectroscopy) method. Specifically, 0.1 g of cemented carbide is appropriately ground in an agate mortar. 0.2 g of calcium carbonate and 0.5 g of boron oxide were placed in a platinum crucible together with an alkaline solvent and melted at 1000°C. After collecting at 60° C., dilute to 200 ml with ion-exchanged water. This is introduced into an ICP analyzer, and the light emitted from W excited by Ar (argon) plasma and the respective transition metal elements is spectrally analyzed, and quantitative analysis is performed based on the emission intensity.

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

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

In addition, cemented carbide has microscopic TEM images (hereinafter referred to as TEM images) from the viewpoint that it has fine WC particles and has higher hardness and wear resistance due to the uniform solid solution of transition metal elements in WC particles. The concentration of each transition metal element contained in the cemented carbide was measured by the TEM-EDX method at five points inside the WC particles arbitrarily selected on a straight line passing through the center of the WC particles. It is preferable that the intra-particle concentration variation, expressed as the difference between the maximum and minimum measured values, is 10% or less of the average intra-particle concentration, and more preferably 8% or less of the average intra-particle concentration. It is preferably 7% or less of the intra-particle average concentration, more preferably 6% or less of the intra-particle average concentration. Here, the variation in intra-particle concentration refers to the difference between the maximum and minimum concentration of the transition metal element at the five points. In addition, the intra-particle average concentration refers to the average value of the concentration of the transition metal element at the above five points.

The average particle size of the 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. Further, the average particle diameter of the WC particles 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 the refinement of the WC particles. Further, the maximum particle size of the 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 particle size of the WC particles in the cemented carbide is calculated by the linear intercept method from a visual field image containing 50 or more particles by TEM observation. Further, the average crystal grain size can also be calculated from the half-value width of the peak obtained by TEM-EDX measurement using the above-mentioned Scherrer equation.

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 cemented carbide, transition metal elements are dissolved in solid solution in WC particles, and/or Co of the transition metal elements is precipitated on the surface of the WC particles to become Co metal and cover the WC particles, so that the Co metal phase is not formed. Even if the content 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, the amount is preferably 5 mass% or more and 15 mass% or less, and more preferably 6 mass% or more and 12 mass% or less. The content of the transition metal element and the Co metal phase among the transition metals in the cemented carbide can be measured by the ICP-AES method.

The cemented carbide according to the present embodiment includes WC particles, the WC particles have a transition metal element dissolved therein, 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 is measured by the TEM-EDX method at the center point of each of the 20 WC particles in the TEM microscopic image. Five points inside the WC particle are arbitrarily selected on a straight line passing through the center of the WC particle in a TEM microscopic image, and the inter-particle concentration variation represented by the difference is 10% or less of the average inter-particle concentration. When the concentration of each transition metal element contained in tungsten carbide particles is measured by the TEM-EDX method, the intra-particle concentration variation expressed as the difference between the maximum and minimum measured values is the intra-particle average concentration. It is particularly preferable that the amount is 10% or less. Such a cemented carbide has a transition metal element containing Co dissolved in solid solution in WC particles, has fine WC particles, and has such a structure that the inter-particle concentration variation is 10% or less of the average inter-particle concentration, and The transition metal element is uniformly dissolved in the WC particles so that the intra-particle concentration variation is 10% or less of the average intra-particle concentration, so that the hardness and wear resistance are even higher.

<Method for manufacturing cemented carbide>
Referring to FIG. 2, the method for manufacturing a cemented carbide according to the present embodiment includes sintering at least one type of powder of the WC powder of Embodiment 1 and the WC-Co metal composite powder of Example 2. It includes a sintering step S40 for preparing a hard metal. In the sintering step S40, a powdered body is formed by pressing the WC powder and/or the WC-Co metal composite powder, and then the cemented carbide as the sintered body is heated and pressed. Prepare.

The method for forming the powder is not particularly limited, and may be CIP (cold isostatic pressing) or the like. In CIP, pressure can be applied at room temperature (for example, 25° C.) at a pressure of 150 MPa or more and 250 MPa or less. Before sintering the powdered body, it can be heated in an H ₂ (hydrogen) gas atmosphere at a temperature of 300° C. or more and 500° C. or less for a period of 30 minutes or more and 2 hours or less. As a result, the CoC (cobalt carbide) in the powder becomes Co metal, so the powder changes into a mixture of WC and Co metal. Co metal turns into a liquid phase when the green compact is sintered, and Co liquid phase sintering progresses, so densification of the cemented carbide can be expected. 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 such that the content of Co metal in the obtained cemented carbide is 2 mass% or less.

Cemented carbide is manufactured by heating and pressurizing a compact. For example, the 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 green compact is heated to, for example, 1250°C or more and 1450°C or less. 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 pressurizing 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 more and 1500° C. or less, and the pressurizing pressure can be 100 MPa or more and 250 MPa or less. In this way, the cemented carbide according to Embodiment 3 is obtained.

<Example I-1>
1. Preparation of tungsten carbide powder Add 200 g of WO ₃ powder (F1 grade, manufactured by Allied Materials), which is a tungsten oxide, to 1 L of 10 mass% ammonia water (reagent manufactured by Wako Pure Chemical Industries, Ltd.), and stir with a stirrer for 24 hours to dissolve. A first aqueous solution was prepared. A second aqueous solution was prepared by adding 180 g of anhydrous citric acid to the first aqueous solution and dissolving it. The second aqueous solution was left in a thermostat at 150° C. for 24 hours to dry the second aqueous solution (first 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 dry solids 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 of cobalt nitrate (reagent manufactured by Wako Pure Chemical Industries, Ltd.) containing Co as a transition metal element with a concentration of 500 g/L 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. Using an atmosphere displacement sintering furnace (NLA-2025D manufactured by Motoyama), the carbide precursor was placed in a carbon boat and heat treated at 900°C for 2 hours in an atmosphere with nitrogen gas flowing at a rate of 0.5 L/min. , WC (tungsten carbide) powder was prepared.

2. Preparation of cemented carbide 10 g of the WC powder obtained above was crushed, molded using a tablet press at a pressure of 50 MPa, vacuum sealed in a plastic bag, and subjected to CIP (cooling) at a pressure of 200 MPa at room temperature (25°C). (isostatic hydrostatic pressure) to obtain a green compact. The green compact was heat-treated at 350° C. for 3 hours in an atmosphere in which hydrogen gas was flowing at 2 L/min. As a result, the Co carbide in the green compact becomes Co metal, and the green compact changes to a mixture of WC and Co metal. A mixture of WC and Co metal is 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 form a Co liquid. Phase sintering occurred and a WC-Co sintered body was prepared. A cemented carbide was prepared by subjecting a tungsten carbide-cobalt sintered body to HIP (hot isostatic pressing) 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 measurement limit by the TEM-EDX method.

(Evaluation of composition of WC powder and cemented carbide)
The compositions of the WC powder and cemented carbide were determined by the ICP-AES method. Specifically, 0.1 g of WC powder was appropriately ground in an agate mortar. 0.2 g of calcium carbonate and 0.5 g of boron oxide were placed in a platinum crucible together with an alkaline solvent and melted at 1000°C. After collecting at 60° C., dilute to 200 ml with ion-exchanged water. This was introduced into an ICP analyzer (ICPS-8100 manufactured by SHIMAZU or an equivalent device), and the light emitted from W excited in Ar (argon) plasma and each transition metal element was analyzed, and the emission intensity was measured. A more quantitative analysis was performed.

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

(Presence or absence of solid solution of transition metal elements including Co in WC powder and cemented carbide)
Whether or not transition metal elements including Co are dissolved in the WC powder and WC particles of cemented carbide can be determined by the presence of W and each transition metal contained in the WC particles in the HAADF-STEM image obtained by the HAADF-STEM method. Whether there is no difference in contrast indicating the distribution of elements (i.e., whether the contrasts almost overlap or not), and whether there is separation, precipitation, or segregation of transition metal elements (solid solution) or separation, precipitation, or segregation. Confirmation was made by whether (non-solid solution).

(Evaluation of distribution of transition metal elements in WC powder and cemented carbide)
(1) Evaluation of interparticle concentration variation At the center point of each of 20 arbitrary WC particles in a TEM microscopic image (TEM image) of WC powder and cemented carbide, the WC particles contained in the WC particles are determined by the TEM-EDX method. When measuring the concentration of each transition metal element, calculate what percentage of the inter-particle concentration variation, expressed as the difference between the maximum and minimum measured values, is relative to the average inter-particle concentration. The inter-particle concentration variation was evaluated.

(2) Evaluation of intra-particle concentration variation The TEM-EDX method was used to evaluate the WC particles 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 cemented carbide. When measuring the concentration of each transition metal element contained in particles, what percentage of the intra-particle concentration variation, expressed as the difference between the maximum and minimum measured values, is relative to the average intra-particle concentration? 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 at a load of 100 g for 5 seconds.

(Wear resistance of cemented carbide)
A cemented carbide prepared in the shape of a round bar with a diameter of 8 mm and a length of 80 mm was subjected to grinding and electrical discharge machining to form an outer peripheral portion. A nozzle for high-pressure water jet machining was produced by forming a tapered portion at the point where water is introduced, and forming a through hole with a diameter of 0.5 mm in the longitudinal direction in the center of the cemented carbide. Using the prepared 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 intervals, and changes in diameter due to wear were recorded. With respect to the initial diameter of the through hole of 0.5 mm, a hydraulic cutting test was conducted until the diameter increased by 0.1 mm. The time taken until the diameter of the through hole reached 0.6 mm was evaluated as the lifespan. The longer the life, the higher the wear resistance.

<Example I-2>
Except that the cemented carbide was produced by processing the WC powder prepared in Example I-1 above for 30 minutes at a pressure of 7 GPa and a temperature of 1350°C using a high-pressure sintering device (manufactured by KOBELCO). 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 cemented carbide were prepared in the same manner as in Example I-1, except that 0.5 mass% (equivalent to 200 g of WO ₃ powder) was added, and their physical properties were determined as in Example I-1. It was evaluated in the same manner. The results are summarized in Table 1. Here, vanadium (III) chloride means vanadium chloride whose V (vanadium) ion has a valence of 3.

<Example II-2>
WC powder and cemented carbide were produced in the same manner as in Example II-1, except that 1 g of chromium (III) chloride powder was used in place of 1 g of vanadium (III) chloride powder, and their physical properties were described in Example II-1. Evaluation was made in the same manner as I-1. The results are summarized in Table 1. Here, chromium (III) chloride means chromium chloride in which the valence of Cr (chromium) ions is 3.

<Example II-3>
WC powder and ultraviolet chloride 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 in place 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>
WC powder and cemented carbide were produced in the same manner as in Example II-1, except that 1 g of tantalum (V) chloride powder was used in place of 1 g of vanadium (III) chloride powder, and their physical properties were described in Example II-1. Evaluation was made 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>
WC powder and cemented carbide were produced in the same manner as in Example II-1, except that 1 g of niobium (V) chloride powder was used in place of 1 g of vanadium (III) chloride powder, and their physical properties were described in Example II-1. Evaluation was made in the same manner as I-1. The results are summarized in Table 1. Here, niobium chloride (V) means niobium chloride in which the valence of Nb (niobium) ions is 5.

<Example II-6>
WC powder and cemented carbide were produced in the same manner as in Example II-1, except that 1 g of molybdenum chloride (V) powder was used in place of 1 g of vanadium (III) chloride powder, and their physical properties were described in Example II-1. Evaluation was made in the same manner as I-1. The results are summarized in Table 1. Here, molybdenum chloride (V) means molybdenum chloride in which the valence of Mo (molybdenum) ions is 5.

<Comparative example I>
For comparison with the above example, 100 g of WC powder (WC02NRP grade manufactured by Allied Materials) and 2 g of Co metal powder manufactured by Kojundo Kagaku Kenkyusho were added to an ethanol dispersion medium, mixed with an attritor, and the dry powder was formed into tablets. After molding in a container at a pressure of 50 MPa, it was 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 green 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) at a temperature of 1320° C. and a pressure of 100 MPa in an Ar gas atmosphere. 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 example, 10 g of cobalt nitrate and 5 g of ammonium vanadate (all of which were manufactured by Wako Pure Chemical Industries, Ltd. 99% pure reagent) was dissolved. This mixed aqueous solution was made into mixed oxide powder with a particle size of about 10 μm using a spray pyrolysis device (manufactured by Okawara Kakoki Co., Ltd.). A WC powder was obtained by reducing and carbonizing this mixed oxide powder at 900° C. in a mixed gas atmosphere of carbon monoxide and hydrogen (CO/H ₂ =1/4). 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, the WC particles contain tungsten carbide (WC) particles with an average particle size of 50 nm or less, and the WC particles contain a transition metal. It has been found that cemented carbide with high hardness and wear resistance (for example, long nozzle life) can be obtained by sintering WC powder that contains cobalt (Co) as a transition metal element. Ta.

<Example III-1>
1. Preparation of tungsten carbide powder Add 200 g of WO ₃ powder (F1 grade, manufactured by Allied Materials), which is a tungsten oxide, to 1 L of 10 mass% ammonia water (reagent manufactured by Wako Pure Chemical Industries, Ltd.), and stir with a stirrer for 24 hours to dissolve. A first aqueous solution was prepared. A second aqueous solution was prepared by adding 180 g of anhydrous citric acid to the first aqueous solution and dissolving it. The second aqueous solution was left in a thermostat at 150° C. for 24 hours to dry the second aqueous solution (first 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 dry solids 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 of cobalt nitrate (reagent manufactured by Wako Pure Chemical Industries, Ltd.) containing Co as a transition metal element with a concentration of 500 g/L 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. Using an atmosphere displacement sintering furnace (NLA-2025D manufactured by Motoyama), the carbide precursor was placed in a carbon boat and heat treated at 900°C for 2 hours in an atmosphere with nitrogen gas flowing at a rate of 0.5 L/min. , WC (tungsten carbide) powder was prepared.

2. Preparation of cemented carbide 10 g of the WC powder obtained above was crushed, molded using a tablet press at a pressure of 50 MPa, vacuum sealed in a plastic bag, and subjected to CIP (cooling) at a pressure of 200 MPa at room temperature (25°C). (isostatic hydrostatic pressure) to obtain a green compact. The green compact was heat-treated at 350° C. for 3 hours in an atmosphere in which hydrogen gas was flowing at 2 L/min. As a result, the Co carbide in the green compact becomes Co metal, and the green compact changes to a mixture of WC and Co metal. A mixture of WC and Co metal is 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 form a Co liquid. Phase sintering occurred and a WC-Co sintered body was prepared. A cemented carbide was prepared by subjecting a tungsten carbide-cobalt sintered body to HIP (hot isostatic pressing) 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, evaluation of the composition of WC powder and cemented carbide, evaluation of average particle diameter of WC powder and cemented carbide, and evaluation of transition metal elements including Co in WC powder and cemented carbide were performed. 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 interparticle concentration variation and evaluation of intraparticle concentration variation). Further, 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 the "Test method for bending strength (transverse rupture strength) of cemented carbide" of the Cemented Carbide Tool Association standard CIS026B. The distance between fulcrums was 20 mm, the load point/fulcrum size was R1.6-R3.0, and the sample size was 4 mm x 8 mm x 25 mm. The results are summarized in Table 2.

<Example III-2>
When preparing the fourth aqueous solution, 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 mixed transition metal element to be mixed in the third aqueous solution is mixed with 0.0 ml of vanadium (III) chloride powder. WC powder and 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 evaluated as in Example III. -1 was evaluated in the same manner. The results are summarized in Table 2.

<Example III-3>
When preparing the fourth aqueous solution, chromium (III) chloride powder 1. WC powder and 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, 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 mixed transition metal element to be mixed in the third aqueous solution is mixed with 0.0 ml of vanadium (III) chloride powder. Example except that 8 g (corresponding to 0.4 mass% to 200 g of WO ₃ powder) and 1.6 g of chromium (III) chloride powder (corresponding to 0.8 mass% to 200 g of WO ₃ powder) were added. WC powder and cemented carbide were produced in the same manner as in Example 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, 73 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 is mixed with 0.0 ml of vanadium (III) chloride powder. WC powder and 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 evaluated as 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, 91 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 is mixed with 0.0 ml of vanadium (III) chloride powder. WC powder and 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 evaluated as 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, 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 is mixed with 0.0 ml of vanadium (III) chloride powder. WC powder and 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 evaluated as 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, 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 is mixed with 0.0 ml of vanadium (III) chloride powder. WC powder and 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 evaluated as 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, 256 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 is mixed with 0.0 ml of vanadium (III) chloride powder. WC powder and 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 evaluated as 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, 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 is mixed with 0.0 ml of vanadium (III) chloride powder. WC powder and 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 evaluated as in Example III. -1 was evaluated in the same manner. The results are summarized in Table 2.

<Example III-11>
When preparing the fourth aqueous solution, 294 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 is mixed with 0.0 ml of vanadium (III) chloride powder. WC powder and 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 evaluated as in Example III. -1 was evaluated in the same manner. The results are summarized in Table 2.

<Comparative Example III>
For comparison with the above example, 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 Kagaku Kenkyusho Co., Ltd. were dispersed in ethanol. The powder was poured into a medium, mixed with an attritor, and the dry powder was molded using a tablet molding machine at a pressure of 50 MPa, then vacuum sealed in a plastic bag and treated with CIP (cold isostatic isostatic pressing) at room temperature (25°C) and 200 MPa. A green compact was obtained. A sintered body was prepared by heat-treating the green 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) at a temperature of 1320° C. and a pressure of 100 MPa in an Ar gas atmosphere. 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, the WC particles contain tungsten carbide (WC) particles with an average particle size of 50 nm or less, and the WC particles have a transition metal element dissolved therein. The metal element includes cobalt (Co), and by sintering WC powder with 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 5.0 mass%. It has been found that a cemented carbide with high bending strength can be obtained with a content of 15 mass% or less.

The embodiments and examples disclosed herein are illustrative in all respects and should not be considered restrictive. The scope of the present invention is indicated by the claims rather than the embodiments and examples described above, and it is intended that equivalent meanings to the claims and all changes within the scope are included.

S11 Tungsten oxide dissolution step, S12 Organic acid addition step, S13 First drying step, S14 Dry solid matter dissolution step, S15 Transition metal element addition step, S20 Second drying step, S30 Carbonization step, S40 Sintering process.

Claims (5)

comprising tungsten carbide particles and further comprising a cobalt metal phase;
The tungsten carbide particles contain a transition metal element in solid solution, have an average particle size of 80 nm or less, and have a maximum particle size of 100 nm or less,
The cemented carbide, wherein the transition metal element is at least one selected from the group consisting of vanadium, chromium, tantalum, niobium, and molybdenum . At the center point of each of the arbitrary 20 tungsten carbide particles in the microscopic image obtained by a transmission electron microscope, the concentration of each transition metal element contained in the tungsten carbide particles is determined by energy dispersive X-ray spectroscopy using a transmission electron microscope. The cemented carbide according to claim 1 , wherein the interparticle concentration variation, expressed as the difference between the maximum and minimum measured values, is 10% or less of the average interparticle concentration. The tungsten carbide particles obtained by transmission electron microscopy energy dispersive X-ray spectroscopy at five points inside the tungsten carbide particles arbitrarily selected on a straight line passing through the center of the tungsten carbide particles in a microscopic image obtained by a transmission electron microscope. Claim 1: When the concentration of each transition metal element contained in the transition metal element is measured, the intra-particle concentration variation represented by the difference between the maximum and minimum measured values is 10% or less of the average intra-particle concentration. Or the cemented carbide according to claim 2 . The cemented carbide according to any one of claims 1 to 3, wherein the content of the cobalt metal phase is 15 mass% or less. comprising tungsten carbide particles and further comprising a cobalt metal phase;
The tungsten carbide particles have a transition metal element dissolved therein,
The transition metal element is at least one selected from the group consisting of vanadium, chromium, tantalum, niobium, and molybdenum,
The tungsten carbide particles have an average particle size of 80 nm or less and a maximum particle size of 100 nm or less,
At the center point of each of the arbitrary 20 tungsten carbide particles in the microscopic image obtained by a transmission electron microscope, the concentration of each transition metal element contained in the tungsten carbide particles is determined by energy dispersive X-ray spectroscopy using a transmission electron microscope. When measured, the interparticle concentration variation represented by the difference between the maximum and minimum measured values is 10% or less of the average interparticle concentration,
At five points inside the tungsten carbide particles arbitrarily selected on a straight line passing through the center of the tungsten carbide particles in a microscopic image obtained by a transmission electron microscope, the tungsten carbide particles are measured by energy dispersive X-axis spectroscopy using a transmission electron microscope. Cemented carbide, in which the intra-particle concentration variation, expressed as the difference between the maximum and minimum measured values, is 10% or less of the average intra-particle concentration when measuring the concentration of each transition metal element contained in the .

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