Powder containing tungsten carbide

Abstract

The present disclosure provides a powder containing tungsten carbide having a uniform particle diameter.　One aspect of the present invention is a powder containing tungsten carbide having a mode value in a cross-sectional particle diameter distribution chart of 24.0% or more as prepared by analyzing a feature amount of primary particles by image analysis of a cross-sectional SEM image of the powder containing tungsten carbide.　One aspect of the present invention is a powder containing tungsten carbide satisfying E / D<0.9, wherein, when a feature amount of primary particles is analyzed by image analysis of a cross-sectional SEM image of the powder containing tungsten carbide, D is a simple average of particle diameters of the primary particles and E is an area-weighted standard deviation of the particle diameters.

Description

Powder containing tungsten carbide

[0001] The present disclosure relates to a powder containing tungsten carbide. This application claims priority to Japanese Patent Application No. 2024-112251, filed on July 12, 2024. The entire contents of said Japanese Patent Application are incorporated herein by reference.

[0002] Conventionally, powders containing tungsten carbide and cemented carbides produced therefrom have been disclosed, for example, in JP-A-8-117580 (Patent Document 1), JP-A-2009-242181 (Patent Document 2), JP-A-2013-60666 (Patent Document 3), JP-A-2005-335997 (Patent Document 4), JP-A-2018-165233 (Patent Document 5), JP-A-2006-151806 (Patent Document 6), and JP-A-2023-127129 (Patent Document 7).

[0003] JP 8-117580 A JP 2009-242181 A JP 2013-60666 A JP 2005-335997 A JP 2018-165233 A JP 2006-151806 A JP 2023-127129 A

[0004] The powder containing tungsten carbide has a mode value of 24.0% or more in a cross-sectional particle size distribution diagram prepared based on an analysis of the feature quantities of primary particles by image analysis in a cross-sectional SEM image of the powder containing tungsten carbide.

[0005] FIG. 1 is a SEM photograph of a cross section of powder 100 containing tungsten carbide according to Sample No. 1. FIG. 2 is a SEM photograph of a cross section of powder 100 containing tungsten carbide according to Sample No. 2. FIG. 3 is a SEM photograph of a cross section of powder 100 containing tungsten carbide according to Sample No. 3. FIG. 4 is a SEM photograph of a cross section of powder 100 containing tungsten carbide according to Sample No. 4. FIG. 5 is a diagram showing the results of image analysis of the SEM photograph of a cross section of powder 100 containing tungsten carbide according to Sample No. 1. FIG. 6 is a diagram showing the results of image analysis of the SEM photograph of a cross section of powder 100 containing tungsten carbide according to Sample No. 2. FIG. 7 is a diagram showing the results of image analysis of the SEM photograph of a cross section of powder 100 containing tungsten carbide according to Sample No. 3. Fig. 8 is a diagram showing the results of image analysis of an SEM photograph of a cross section of powder 100 containing tungsten carbide according to sample number 4. Fig. 9 is a graph showing the relationship between particle size and frequency of powder 100 containing tungsten carbide according to sample numbers 1 to 4.

[0006] [Problem to be Solved by the Present Disclosure] Conventional powders containing tungsten carbide have had problems with uniformity of particle size.

[0007] <Powder of the present disclosure> The present disclosure provides a powder containing tungsten carbide with a uniform particle size. According to the present disclosure, in a powder containing tungsten carbide and a cemented carbide alloy mainly composed of cobalt, the particle size of the tungsten carbide in the alloy is uniform, and the particles can be densely arranged. Since fine particles and abnormal particles are reduced, a cemented carbide alloy with high hardness and strength and high thermal conductivity due to densification can be produced.

[0008] Cemented carbide alloys have been used in cutting tools, jigs, and other applications due to their high hardness and excellent wear resistance. In recent years, with the growth of the IT field, the miniaturization of workpieces has led to the miniaturization of tools themselves, and dimensional accuracy has become increasingly important. The cemented carbide alloys used in high-precision tools contain powder containing fine tungsten carbide particles. While these alloys are highly hard, the fine particles are prone to generating abnormal particles due to Ostwald ripening during the sintering process, which reduces the strength of the alloy.

[0009] The present disclosure solves the above problems by providing a powder containing tungsten carbide with a uniform primary particle size.

[0010] In the process of mixing the tungsten powder and carbon powder before carbonization, mixing is usually performed once for 10 minutes. In contrast, in the present disclosure, after 15 minutes of mixing, the mixed powder is recovered and re-introduced into the mixer. This process is repeated until the mixed powder is uniformly mixed. It is desirable to repeat this process three or more times.

[0011] If there are areas where the tungsten powder and carbon powder are not mixed uniformly, the degree of particle growth during carbonization will vary. For example, if the powder adheres to the walls or ceiling of the mixer during mixing, the mixture will be poor.

[0012] By mixing multiple times and recovering and re-adding the mixed powder, the effects of adhesion are reduced and the powder is mixed uniformly.

[0013] <Manufacturing Method> (1) Reduction: Hydrogen reduction is performed using tungsten trioxide as a raw material to obtain a lower grade tungsten oxide. (2) Sieving: The obtained lower grade tungsten oxide is sieved to remove coarse agglomerated particles, and the powder that remained on the sieve and the powder that remained on the sieve are recovered. (3) Repeating Reduction and Sieving: The above steps are repeated until agglomerates and coarse particles are removed and a uniformly sized tungsten-containing powder is obtained. (4) Mixing: The tungsten-containing powder obtained above is mixed uniformly with carbon powder having an average particle size of approximately 1.0 μm as determined by the FSSS method. The mixing ratio, by mass, is as follows:

[0014] Mixing mass ratio: tungsten-containing powder: carbon powder = 93.8:6.2 However, it is not necessary to strictly adhere to this mixing ratio, and it is sufficient if the mixing ratio of the carbon powder is between 6.1 and 6.5.

[0015] It is not necessary to strictly adhere to the mass ratio when mixing, but if either powder is excessively insufficient, unreacted tungsten powder and carbon powder will remain, reducing the quality of the alloy. A mixer with stirring blades is used for mixing. For example, the mixing conditions are as follows:

[0016] Agitator blade rotation speed: 500 rpm, rotation time: 15 minutes. This 15-minute mixing is repeated at least three times, resulting in a total of 45 minutes or more of mixing. This results in a homogeneous mixture. (5) Heat Treatment (Carbonization) The mixture is placed in a carbon container and heat-treated at 1200°C to 2500°C in a hydrogen, nitrogen, argon, or vacuum atmosphere. More specifically, the mixed powder is filled into a designated carbon container and heat-treated in a vacuum or hydrogen atmosphere at 1200°C to 2500°C for 30 to 480 minutes for carbonization. The optimal temperature profile and heat treatment time must be selected depending on the particle size of the tungsten-containing powder. An inappropriate temperature profile and heating time can result in the generation of unreacted tungsten-containing powder or carbon powder, or abnormal grain growth due to solid-phase sintering of the powders, resulting in a decrease in alloy quality.

[0017] After carbonization, the powder particles are bonded together by heat, so they are crushed using the Nara method or an atomizer. After that, they are mixed in a double cone mixer to make the powder uniform.

[0018] The content of unavoidable impurities in the powder was adjusted to 10 ppm or less for each of aluminum, copper, magnesium, and manganese, and 20 ppm or less for each of calcium, silicon, and tin. That is, the total content of the unavoidable impurities was 100 ppm or less. As long as the unavoidable impurities were not of a size that would cause them to become foreign bodies in the alloy structure, a sound cemented carbide could be obtained by keeping the content of the unavoidable impurities within the above range. (6) Pulverization: By pulverizing the powder using a heat-treated powder pulverizer and mixing it using an appropriate mixer, a powder containing tungsten carbide with a uniform primary particle size was obtained.

[0019] <Evaluation Overview> Image analysis was used to analyze the particle size components. The powder containing tungsten carbide embedded in resin was cross-sectionally processed by ion milling, and the cross section was observed using an SEM.

[0020] 1 to 4 are SEM photographs of cross sections of powders 100 containing tungsten carbide according to sample numbers 1 to 4.

[0021] The particle size of the primary particles of the powder can be measured by image analysis of the photographs shown in Figures 1 to 4. Figures 5 to 8 show the results of image analysis of SEM photographs of cross sections of powders 100 containing tungsten carbide according to Sample Nos. 1 to 4.

[0022] The particle size of the primary particles of the powder can be measured from Figures 5 to 8. The resin used is Clearepoxy 2 base resin and Clearepoxy 2 hardener, manufactured by Sankei Co., Ltd. In addition, as a pretreatment for cross-section processing, flattening and cross-sectioning are performed using #600 and #2000 abrasive paper.

[0023] The cross-section of the sample was processed by ion milling using an IM4000II ion milling device (Hitachi High-Tech Corp.) Argon ions were used as the milling ions, and the acceleration voltage was 6 kV.

[0024] A field emission scanning electron microscope JSM7900F (JEOL) was used for cross-sectional observation, with an acceleration voltage of 7.0 kV and a magnification of 5000. ImageJ was used for image analysis of SEM images, and after appropriate preprocessing, particles were analyzed using the Analyze → Particles function.

[0025] An example of preprocessing using ImageJ is shown below. - Noise reduction using the Process → Smooth function. - Binarization using Image → Adjust → Threshold. The value calculated by the Auto function is used as the threshold. If the binarized image deviates from the original image, set an appropriate threshold yourself. - Particle area determination using Process → Binary → Watershed. To improve the accuracy of the analysis, analyze more than 1,000 particles. The analysis results are displayed as particle cross-sectional area, and the Heywood diameter (diameter equivalent to a circle with a projected area) is used to convert to particle size. Table 1 is used for the histogram classes. Note that the range from the upper limit to the lower limit of each class in Table 1 is uneven. However, if the upper and lower limits of each class i are displayed as logarithms with a base of 10, the difference between them is 0.157. In other words, the following equation holds:

[0026] log １０ (Upper limit of class i)-log １０(Lower limit of rank i) = 0.157

[0027]

[0028] In the above table, for example, Class 1 indicates a particle size of 0 μm or more and less than 0.03000 μm. The powder containing tungsten carbide according to the present disclosure has a mode of 24.0% or more in a cross-sectional particle size distribution diagram prepared based on an image analysis of the feature quantities of primary particles in a cross-sectional SEM image of the powder containing tungsten carbide.

[0029] In the powder containing tungsten carbide thus configured, there are many specific particle sizes, and therefore when this powder is used to produce a cemented carbide, a cemented carbide with high strength and high thermal conductivity can be obtained.

[0030] Preferably, when D10, D50, and D90 of the particle size distribution of primary particles obtained by image analysis of a cross-sectional SEM image of a powder containing tungsten carbide are defined as A, B, and C, the relationship (C−A) / B≦1.4 is satisfied.

[0031] Preferably, the powder containing tungsten carbide has an average particle size measured by FSSS method of 0.3 to 60 μm.

[0032] Preferably, the content of carbon not bonded to tungsten is 0.30 mass % or less, and the value obtained by subtracting the amount of unbonded carbon from the total carbon amount in the reactant is 5.8 to 6.3 mass % or less.

[0033] Preferably, the powder containing tungsten carbide has 1000 or more particles containing tungsten carbide.

[0034] Preferably, the powder containing tungsten carbide has particle sizes distributed in 10 or more sections in a cross-sectional particle size distribution diagram.

[0035] The powder containing tungsten carbide according to the present disclosure satisfies E / D<0.9 when the feature quantities of primary particles are analyzed by image analysis in a cross-sectional SEM image of the powder containing tungsten carbide, and the simple average particle diameter of the primary particles is defined as D and the area-weighted standard deviation of the particle diameters is defined as E.

[0036] In the powder containing tungsten carbide, the value of E / D, which is the coefficient of variation, is less than 0.9, and therefore the powder contains tungsten carbide of uniform particle size, resulting in improved strength after sintering.

[0037] Preferably, the powder containing tungsten carbide has an average particle size measured by FSSS method of 0.3 to 60 μm.

[0038] Preferably, the content of carbon not bonded to tungsten is 0.30% by mass or less, and the value obtained by subtracting the amount of unbonded carbon from the total carbon amount in the reactants is 5.8 to 6.3% by mass or less. [Details of the embodiment of the present disclosure] <Preparation of powder> Powders containing tungsten carbide of sample numbers 1, 3, 5, 6, 10, 12 and 13 were prepared.

[0039] Raw materials: WO ２．９ The powder was used. The coarse powder portion was removed by sieving it through a sieve with openings of 90 to 100 μm. The fine powder portion was removed by sieving it through a sieve with openings of 40 to 50 μm (Step 1).

[0040] The powder was packed into a metal boat. The powder layer thickness was set to 50 mm or less. A pusher-type reduction furnace was used to carry out reduction treatment in a hydrogen atmosphere at 640 to 650°C to obtain WO ２ A powder was obtained (Step 2).

[0041] The obtained WO ２ The powder was sieved using a sieve with 20 to 30 μm openings to remove coarse powder and agglomerated powder (step 3). For example, classification can be performed using a classifier (Turbo Screener manufactured by Freund Turbo Corporation). The device is not limited to this, as long as it can classify particles to 30 μm or less.

[0042] The undersize powder was further reduced in a pusher-type reduction furnace under conditions of a hydrogen atmosphere, 800 to 820°C, and a layer thickness of 10 mm or less, to obtain a powder containing tungsten (step 4).

[0043] The tungsten-containing powder and carbon powder were mixed at a mass ratio of 93.8:6.2. The mixing was performed with a stirring blade rotation speed of 500 rpm for 15 minutes. This mixing was repeated three times. The mixed powder was filled into a specified carbon container and subjected to a heat treatment in a vacuum atmosphere at 1200°C to 2500°C for 30 to 480 minutes, thereby carrying out a carbonization treatment. This resulted in a powder containing tungsten carbide, sample number 1 (step 5).

[0044] Powders containing tungsten carbide were prepared as sample numbers 2, 4, 7 to 9, 11, 14, and 15. ２．９ Powder was used. The raw materials were packed into a specified container to a layer thickness of 30 mm or less. Reduction treatment was performed using a pusher-type reduction furnace under conditions of a hydrogen atmosphere and a reduction temperature of 800°C to 820°C, yielding a tungsten-containing powder. The manufacturing methods of Sample Nos. 1, 3, 5, 6, 10, 12, and 13 differed from those of Sample Nos. 2, 4, 7 to 9, 11, 14, and 15 in that the manufacturing methods of Sample Nos. 1, 3, 5, 6, 10, 12, and 13 included sieving in step 1, whereas Sample Nos. 2, 4, 7 to 9, 11, 14, and 15 did not. The manufacturing methods of Sample Nos. 1, 3, 5, 6, 10, 12, and 13 included a lower reduction temperature in step 2. Only the manufacturing methods of Sample Nos. 1, 3, 5, 6, 10, 12, and 13 included steps 3 to 5.

[0045] <Image Observation of Powder> Image analysis is used to analyze the uniform particle size. Resin-embedded powder containing tungsten carbide was cross-sectionally processed by ion milling. The cross-section was then observed using SEM (Figures 1 to 4) and image analysis (Figures 5 to 8) to measure the primary particle size of the powder. The resin used was Clearepoxy 2 base resin and Clearepoxy 2 hardener, manufactured by Sankei Co., Ltd. Additionally, pre-processing for cross-section processing involved flattening and cross-sectioning using #600 and #2000 grit abrasive paper. An IM4000II ion milling system (Hitachi High-Tech Corporation) was used to cross-section the sample using ion milling. Argon ions were used for milling, with an accelerating voltage of 6 kV. Cross-section observation was performed using a JSM7900F field emission scanning electron microscope (JEOL) at an accelerating voltage of 7.0 kV and a magnification of 5000x. ImageJ was used to analyze SEM images, and after appropriate preprocessing, the particles were analyzed using the Analyze → Particles function. Examples of appropriate preprocessing using ImageJ include: - Noise reduction using the Process → Smooth function - Binarization using Image → Adjust → Threshold The value calculated by the Auto function is used as the binarization threshold. If the binarized image deviates from the original image, set an appropriate threshold yourself. - Particle regions are determined using Process → Binary → Watershed To improve the accuracy of the analysis, more than 1,000 particles were analyzed. The analysis results are displayed as particle cross-sectional area, and the Heywood diameter (diameter equivalent to a circle with a projected area) was used to convert to particle size.

[0046] The particle size distributions for Samples Nos. 1 to 4 are shown in Table 2 and FIG.

[0047]

[0048] The class hierarchy was derived using the following Sturgess formula: Number of classes = 1 + log ２ (n): (n is the number of samples) In sample numbers 1 to 4, the number of samples n was set to 1000 or more.

[0049] In sample number 1, the minimum particle size was 0.03 μm (class 2) and the maximum particle size was 1.60 μm (class 12). The class width was determined by the following formula: １０ (Maximum particle size)-log １０ (minimum particle size)} / 11≈0.157 Therefore, for sample numbers 1 to 4, the class width of the particle size after logarithmic transformation was set to 0.157.

[0050] That is, in the present disclosure, the class layers are derived using the Sturgess equation, and the class width can be calculated using the following equation using the number of classes calculated using the Sturgess equation, the maximum particle diameter in the sample, and the minimum particle diameter in the sample.

[0051] Class width = {log10(maximum particle size) - log10(minimum particle size)} / number of classes calculated using Sturgess' formula By dividing the range from the maximum particle size to the minimum particle size equally into classes on a logarithmic graph with a base of 10, the upper and lower limits of the particle size for each class can be determined.

[0052] From Table 2 and FIG. 9, it was confirmed that the powder containing tungsten carbide of sample number 1 contained more particles of a specific particle size (more than 0.379575335 μm and 0.545446277 μm or less) than the powder containing tungsten carbide of sample number 2.

[0053] From FIG. 9, it can be seen that the mode value of the particle size distribution of the powder containing uniform-sized tungsten carbide of sample number 1 is larger than that of the powder containing tungsten carbide of sample number 2, exceeding 24%.

[0054] Furthermore, particle size uniformity was evaluated using D10, D50, and D90 of the particle size distribution. Particle size uniformity was evaluated using the sharpness of the particle size distribution as an index, and was calculated as particle size uniformity = (D90 - D10) / D50. The number of particles with a particle size of D10 or less is 10% of the total number of particles. The number of particles with a particle size of D50 or less is 50% of the total number of particles. The number of particles with a particle size of D90 or less is 90% of the total number of particles.

[0055]

[0056] From Table 3, it can be seen that the uniform grain WC of Sample Nos. 1 and 3 has a low proportion of coarse grains relative to D50 and has high grain uniformity.

[0057] It was found that the width of the particle size distribution of sample No. 1 was narrower than that of sample No. 2. The high particle uniformity suppresses Ostwald ripening during sintering, and suppresses the occurrence of particles with abnormal grain growth.

[0058] <Measurement of Coefficient of Variation> According to the above <Image Observation of Powder>, the simple average of particle diameters was determined for Sample Nos. 5 to 15. The results are shown in Table 4.

[0059]

[0060] The "simple average D" in Table 4 is the simple arithmetic average of all particle diameters for each sample number.

[0061] The determined particle diameter was weighted by area to determine the area-weighted standard deviation.

[0062]

[0063] E is the area-weighted standard deviation, xi is the particle size of each particle constituting each sample number, bi is the area of ​​each particle constituting each sample number, D is the simple average value of the particles constituting each sample number, and n is the number of particles constituting each sample number.

[0064] The area-weighted standard deviation represents the variation of the particles being analyzed. It can be normalized by dividing the area-weighted standard deviation by the simple average value D of the particles. This normalized value is the coefficient of variation. A coefficient of variation of less than 0.9 is defined as uniform-grained WC.

[0065] <Results of Transverse Rupture Strength Test> To measure the transverse rupture strength, a cemented carbide alloy was produced by mixing a powder containing tungsten carbide (sample number 1) and a cobalt powder in a mass ratio of 90:10 and sintering the mixture. Similarly, a cemented carbide alloy was produced by mixing a powder containing tungsten carbide (sample number 2) and a cobalt powder in a mass ratio of 90:10 and sintering the mixture. Ten samples were produced from each cemented carbide alloy, and the transverse rupture strength of each of the ten samples was measured.

[0066] Transverse rupture strength was measured in accordance with the Japan Machine Tool Manufacturers' Association standard TAS 0050:2017 (formerly CIS026B).

[0067]

[0068] The ten cemented carbide samples produced from sample number 1 are numbered N=1 to N=10 in ascending order of transverse rupture strength, and the transverse rupture strengths of N=2 to N=10 are shown in Table 4. N=1 is not included in the table because it may be an abnormal value.

[0069] The ten cemented carbide samples produced from sample number 2 are numbered N=1 to N=10 in ascending order of transverse rupture strength, and the transverse rupture strengths of N=2 to N=10 are shown in Table 4. N=1 is not included in the table because it may be an abnormal value.

[0070] From Table 5, it was confirmed that the cemented carbide produced from sample number 1 had a greater transverse rupture strength than the cemented carbide produced from sample number 2.

[0071] <Results of Thermal Conductivity> The thermal conductivity was determined for the cemented carbide alloys produced from sample numbers 1 and 2. As a result, the thermal conductivity of the cemented carbide alloy produced from sample number 1 was 97.2 W / m·K, while the thermal conductivity of the cemented carbide alloy produced from sample number 2 was 90.9 W / m·K. It was found that the cemented carbide alloy produced from sample number 1 had more densely arranged particles than the cemented carbide alloy produced from sample number 2, and therefore had improved thermal conductivity within the cemented carbide alloy.

[0072] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the above-described embodiments, and is intended to include meanings equivalent to the claims and all modifications within the scope thereof.

[0073] 100 Powder containing tungsten carbide.

Claims

1. A powder containing tungsten carbide, in which the feature quantities of primary particles are analyzed by image analysis in a cross-sectional SEM image of the powder, and the mode value of the cross-sectional particle size distribution diagram created based on the analysis is 24.0% or more.

2. The powder containing tungsten carbide according to claim 1, wherein, when D10, D50 and D90 of the particle size distribution of the primary particles obtained by image analysis of a cross-sectional SEM image of the powder containing tungsten carbide are defined as A, B and C, respectively, the relationship (C-A) / B≦1.4 is satisfied.

3. The powder containing tungsten carbide according to claim 1 or 2, wherein the powder containing tungsten carbide has an average particle size measured by FSSS method of 0.3 to 60 μm.

4. A powder containing tungsten carbide according to claim 1 or 2, in which the content of carbon not bonded to tungsten is 0.30% by mass or less, and the value obtained by subtracting the amount of unbonded carbon from the total carbon content of the reactants is 5.8 to 6.3% by mass or less.

5. The powder containing tungsten carbide according to claim 1 or 2, wherein the particle sizes are distributed in 10 or more sections in the cross-sectional particle size distribution diagram.

6. A powder containing tungsten carbide, wherein the feature quantities of primary particles are analyzed by image analysis in a cross-sectional SEM image of the powder containing tungsten carbide, and where D is the simple average particle diameter of the primary particles and E is the area-weighted standard deviation of the particle diameters, the powder satisfies E / D<0.

9.

7. The powder containing tungsten carbide according to claim 6, wherein the powder containing tungsten carbide has an average particle size measured by FSSS method of 0.3 to 60 μm.

8. A powder containing tungsten carbide according to claim 6 or 7, in which the content of carbon not bonded to tungsten is 0.30% by mass or less, and the value obtained by subtracting the amount of unbonded carbon from the total carbon amount in the reactants is 5.8 to 6.3% by mass or less.

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