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

Technical Field

[0001] The present disclosure relates to powders containing tungsten carbide. This application claims priority based on Japanese Patent Application No. 2024-112251, filed on July 12, 2024. All the descriptions contained in the Japanese patent application are incorporated herein by reference.

Background Art

[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).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Summary of the Invention

[0004] For powders containing tungsten carbide, the mode of the cross-sectional particle size distribution diagram created based on the analysis of primary particle characteristics by image analysis in a cross-sectional SEM image of the tungsten carbide powder is 24.0% or higher. [Brief explanation of the drawing]

[0005] [Figure 1] Figure 1 is a SEM image of a cross-section of powder 100 containing tungsten carbide, according to sample number 1. [Figure 2] Figure 2 is a SEM image of a cross-section of powder 100 containing tungsten carbide, according to sample number 2. [Figure 3] Figure 3 is a SEM image of a cross-section of powder 100 containing tungsten carbide, according to sample number 3. [Figure 4] Figure 4 is a SEM image of a cross-section of powder 100 containing tungsten carbide, according to sample number 4. [Figure 5] Figure 5 shows the results of image analysis of a cross-sectional SEM photograph of powder 100 containing tungsten carbide, according to sample number 1. [Figure 6] Figure 6 shows the results of image analysis of a cross-sectional SEM photograph of powder 100 containing tungsten carbide, according to sample number 2. [Figure 7] Figure 7 shows the results of image analysis of a cross-sectional SEM photograph of powder 100 containing tungsten carbide, according to sample number 3. [Figure 8] Figure 8 shows the results of image analysis of a cross-sectional SEM photograph of powder 100 containing tungsten carbide, according to sample number 4. [Figure 9] Figure 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. [Modes for carrying out the invention]

[0006] [Issues this disclosure aims to address] Conventional powders containing tungsten carbide had problems with particle size uniformity.

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

[0008] Cemented carbides have been used in cutting tools, jigs, etc. because of their high hardness and excellent wear resistance. In recent years, with the growth of the IT field, as the processing target has become smaller, the tool itself has become smaller, and its dimensional accuracy has been emphasized. Powders containing fine tungsten carbide are used for cemented carbides used in high-precision tools. Although the alloy has high hardness, fine particles are likely to generate abnormal particles due to Ostwald ripening in the sintering process, leading to a decrease in alloy strength.

[0009] In the present disclosure, the above problem is solved by providing a powder containing tungsten carbide with a uniform primary particle size.

[0010] In the mixing step of tungsten powder before carbonization and carbon powder, usually mixing is performed once for 10 minutes. In contrast, in the present disclosure, after mixing for 15 minutes, the mixed powder is recovered and re-introduced into the mixer. This is repeated until the mixed powder is uniformly mixed. It is desirable to repeat this 3 times or more.

[0011] If there are parts where tungsten powder and carbon powder are not uniformly mixed, the grain growth during carbonization will vary. For example, the parts adhering to the wall surface and ceiling of the mixer during mixing have poor mixing conditions.

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

[0013] <Manufacturing method> (1) Reduction Hydrogen reduction is carried out using tungsten trioxide as a raw material to obtain lower tungsten oxides. (2) Sieving The obtained lower tungsten oxides are sieved to remove coarse agglomerated particles, and the undersize and oversize powders are recovered. (3) Repeated reduction and sieving The above steps are repeated until powders containing homogeneous tungsten are obtained by removing agglomerates and coarse particles. (4) Mixing The powder containing tungsten obtained as above and carbon powder with an average particle size of about 1.0 μm by the FSSS method are mixed to be uniform. The blending content during mixing is in terms of mass ratio and is set to the following ratio.

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

[0015] Although it is not necessary to strictly adhere to the mass ratio during mixing, if either powder is excessively insufficient, unreacted tungsten powder and carbon powder will remain, deteriorating the alloy quality. A mixer with a stirring blade is used for mixing. The mixing conditions are as follows, for example.

[0016] Stirring blade rotation speed: 500 rpm Rotation time: 15 minutes This 15-minute mixing is repeated three or more times. The total mixing time is 45 minutes or more. Thereby, a homogeneous mixture is obtained. (5) Heat treatment (carbonization) The mixture is put into a carbon container and heat-treated at 1200 °C to 2500 °C in a hydrogen, nitrogen, argon or vacuum atmosphere More specifically, the carbonization process is carried out by filling a designated carbon container with the mixed powder and heat-treating it in a vacuum or hydrogen atmosphere at 1200°C to 2500°C for 30 to 480 minutes. The optimal temperature profile and heat treatment time must be selected depending on the particle size of the tungsten-containing powder. If the temperature profile and heating time are not appropriate, unreacted tungsten-containing powder or carbon powder may be generated, or abnormal grain growth may occur due to solid-phase sintering of the powders, degrading the quality of the alloy.

[0017] After carbonization, the powder particles are bonded together by heat, so they are pulverized using the Nara method or an atomizer. Then, the powder is mixed using a double-cone mixer to ensure uniformity.

[0018] The content of unavoidable impurities in the powder is adjusted to be 10 ppm or less for each of aluminum, copper, magnesium, and manganese, and 20 ppm or less for each of calcium, silicon, and tin. In other words, the total content of the above unavoidable impurities is 100 ppm or less. As long as the unavoidable impurities are not of a size that would cause them to become foreign matter in the alloy structure, a sound cemented carbide can be obtained by keeping the content of unavoidable impurities within the above range. (6) Crushing By grinding the tungsten carbide in a heat-treated pulverizer and mixing it in a suitable mixer, a powder containing tungsten carbide with a uniform primary particle size was obtained.

[0019] <Evaluation Summary> Image analysis was used to analyze the uniform particle size. Powder containing resin-embedded tungsten carbide was cross-sectionally processed by ion milling, and the cross-section was observed using a scanning electron microscope (SEM).

[0020] Figures 1 to 4 are SEM images of cross-sections of powder 100 containing tungsten carbide, according to sample numbers 1 to 4.

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

[0022] Figures 5 to 8 allow for the measurement of the particle size of the primary particles in the powder. The resin used is Clearpoxy 2 main component and Clearpoxy 2 hardener, manufactured by Sankei Co., Ltd. Furthermore, as a pretreatment before cross-sectional processing, the surface and cross-section are prepared using #600 and #2000 grit sandpaper.

[0023] For cross-sectional processing of the sample using ion milling, an IM4000II ion milling system (Hitachi High-Tech Corporation) was used. Argon ions were used for milling, and the acceleration voltage was set to 6kV.

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

[0025] An example of preprocessing using ImageJ is shown below. • Process → Noise reduction using the Smooth function. • Binarization using Image → Adjust → Threshold Use the value calculated by the Auto function as the threshold. If the binarized image deviates too much from the original image, set an appropriate threshold yourself. The particle region is determined by Process → Binary → Watershed. To improve the accuracy of the analysis, more than 1000 particles were analyzed. The analysis results were displayed as particle cross-sectional area, and the Heywood diameter (equivalent diameter of the projected area circle) was used to convert them to particle size. The histogram classes are as shown in Table 1. Note that in Table 1, the width from the upper limit to the lower limit of each class is non-uniform. However, when the upper and lower limits of each class i are expressed on a base-10 logarithmic scale, the difference between them is 0.157. That is, the following equation holds:

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

[0027] [Table 1]

[0028] In the table above, for example, class 1 represents a size of 0 μm or more and less than 0.03000 μm. The tungsten carbide-containing powder of this disclosure has a mode of 24.0% or higher in the cross-sectional particle size distribution diagram created by analyzing the features of primary particles using image analysis in a cross-sectional SEM image of the tungsten carbide-containing powder.

[0029] In a powder containing tungsten carbide configured in this way, a large number of specific particle sizes are present. Therefore, when a cemented carbide is made using this powder, a cemented carbide with high strength and high thermal conductivity can be obtained.

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

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

[0032] 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 amount of carbon in the reactant is 5.8 to 6.3% by mass or less.

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

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

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

[0036] In powders containing tungsten carbide, the coefficient of variation (E / D) is less than 0.9. This indicates that the powder contains tungsten carbide with a homogeneous particle size, resulting in improved strength after sintering.

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

[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 amount of carbon in the reactant is 5.8 to 6.3% by mass or less. [Details of the embodiments of this disclosure] <Preparation of powder> Powders containing tungsten carbide were prepared using sample numbers 1, 3, 5, 6, 10, 12, and 13.

[0039] WO 2.9 Powder was used. The coarse powder was removed by sieving with a mesh size of 90-100 μm. The fine powder was removed by sieving with a mesh size of 40-50 μm (Step 1).

[0040] The powder was packed into a designated metal boat. At this time, the thickness of the powder layer was kept to 50 mm or less. Using a pusher-type reduction furnace, the reduction treatment was carried out under conditions of a hydrogen atmosphere and 640-650°C to obtain WO2 powder (Step 2).

[0041] The obtained WO2 powder was sieved using a sieve with a mesh size of 20-30 μm to remove coarse and agglomerated powder (Step 3). For example, classification can be performed using a classifier (Freund Turbo Turbo Screener). The apparatus is not limited to this as long as it can classify particles of 30 μm or less.

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

[0043] Tungsten-containing powder and carbon powder were mixed in 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 designated carbon container and subjected to carbonization treatment by heat treatment in a vacuum atmosphere at 1200°C to 2500°C for 30 to 480 minutes. This yielded tungsten carbide-containing powder of sample number 1 (step 5).

[0044] Powders containing tungsten carbide were prepared from samples 2, 4, 7 through 9, 11, 14, and 15. In preparing these, WO was used as a raw material. 2.9 Powder was used. The raw materials were packed into a designated container so that the layer thickness was 30 mm or less. A reduction treatment was carried out using a pusher-type reduction furnace under conditions of a hydrogen atmosphere and a reduction temperature of 800°C to 820°C to obtain a powder containing tungsten. The differences in the manufacturing methods between samples 1, 3, 5, 6, 10, 12 and 13 and samples 2, 4, 7 to 9, 11, 14 and 15 are that in the manufacturing methods of samples 1, 3, 5, 6, 10, 12 and 13 there is sieving in step 1, whereas in samples 2, 4, 7 to 9, 11, 14 and 15 there is no sieving; in the manufacturing methods of samples 1, 3, 5, 6, 10, 12 and 13 the reduction temperature is lower in step 2; and steps 3 to 5 are present only in the manufacturing methods of samples 1, 3, 5, 6, 10, 12 and 13.

[0045] <Image observation of powder> Image analysis is used to analyze the uniform particle size. Powder containing resin-embedded tungsten carbide is cross-sectionally processed by ion milling, and the cross-section is observed with SEM (Figures 1 to 4), followed by image analysis (Figures 5 to 4). Figure 8) shows how the particle size of the primary particles in the powder can be measured. For the resin, we used Clearpoxy 2 main agent and Clearpoxy 2 hardener manufactured by Sankei Co., Ltd. Furthermore, as a pretreatment for cross-sectional processing, we performed flat and cross-sectional surface preparation using #600 and #2000 grit sandpaper. Ion mill For cross-sectional processing of samples using a ring, the IM4000II ion milling system (Nippon Co., Ltd.) is used. (High-tech) was used. Argon ions were used for milling, and the acceleration voltage at that time was The voltage is set to 6kV. A field emission scanning electron microscope JSM7900F (JEOL) is used for cross-sectional observation. The acceleration voltage was set to 7.0kV and the observation magnification to 5000x. ImageJ was used for image analysis of the SEM images, and after appropriate preprocessing, the particles were analyzed using the Analyze→Particles function. Examples of appropriate preprocessing using ImageJ include the following. • Process → Noise reduction using the Smooth function. • Binarization using Image → Adjust → Threshold The Auto function calculates the threshold value for binarization. If the binarized image deviates too much from the original image, you need to manually set an appropriate threshold. The particle region is determined by Process → Binary → Watershed. To improve the accuracy of the analysis, more than 1000 particles were analyzed. The analysis results were displayed as particle cross-sectional area, and the Heywood diameter (equivalent to the projected area circle diameter) was used to convert them to particle size.

[0046] The particle size distribution for samples 1 to 4 is shown in Table 2 and Figure 9.

[0047] [Table 2]

[0048] The class strata were derived using Sturges' formula, which is as follows. Number of classes = 1 + log2(n): (n is the sample size) For sample numbers 1 to 4, the sample size 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, the class width for the logarithmically transformed particle size was set to 0.157 for samples 1 to 4.

[0050] In other words, in this disclosure, the class layers are derived using Sturges' equation, and the class width can be determined using the following formula, which utilizes the number of classes obtained by Sturges' equation, the maximum particle size in the sample, and the minimum particle size in the sample.

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

[0052] Table 2 and Figure 9 show that the tungsten carbide powder of sample number 1 had a higher proportion of particles of a specific size (greater than 0.379575335 μm and less than or equal to 0.545446277 μm) compared with the tungsten carbide powder of sample number 2.

[0053] Figure 9 shows that the mode of the particle size distribution for the uniformly sized tungsten carbide powder of sample number 1 is significantly larger than that of the tungsten carbide powder of sample number 2, exceeding 24%.

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

[0055] [Table 3]

[0056] Table 3 shows that the uniform-grained WC samples 1 and 3 have a lower proportion of coarse grains compared to D50, indicating high uniformity.

[0057] Sample No. 1 was found to have a narrower particle size distribution than Sample No. 2. Its high uniformity suppresses Ostwald growth during sintering, thus preventing the generation of abnormally grown particles.

[0058] <Measurement of the coefficient of variation> Following the <Powder Image Observation> procedure described above, the simple average particle size was calculated for samples 5 through 15. The results are shown in Table 4.

[0059] [Table 4]

[0060] In Table 4, "Simple Average D" refers to the simple arithmetic mean of all particle sizes for each sample number.

[0061] The area-weighted standard deviation was calculated by applying area weighting to the determined particle size.

[0062]

number

[0063] E is the area-weighted standard deviation, xi is the particle size of each individual particle constituting each sample number, bi is the area of ​​each individual 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 variability of the particles being analyzed. It can be normalized by dividing the area-weighted standard deviation by the simple mean value D of the particles. This normalized value is the coefficient of variation. A coefficient of variation less than 0.9 is defined as uniform particle WC.

[0065] <Results of the bending strength test> To measure the bending strength, a cemented carbide alloy was prepared by mixing tungsten carbide powder (sample number 1) with cobalt powder in a mass ratio of 90:10 and sintering the mixture. Similarly, a cemented carbide alloy was prepared by mixing tungsten carbide powder (sample number 2) with cobalt powder in a mass ratio of 90:10 and sintering the mixture. Ten samples were prepared from each cemented carbide alloy, and the bending strength of these ten samples was measured.

[0066] The bending strength measurement was performed in accordance with the Japan Machine Tool Builders Association standard TAS 0050:2017. TAS 0050:2017 (formerly CIS026B)

[0067] [Table 5]

[0068] Table 4 shows the bending strengths of 10 cemented carbide samples prepared from sample number 1, with N=1 to N=10 listed in descending order of bending strength. N=1 is not included in the table because it may be an outlier.

[0069] Table 4 shows the bending strengths of 10 cemented carbide samples prepared from sample number 2, with N=1 to N=10 representing the samples in increasing order of bending strength. N=1 may be an outlier and is therefore not included in the table.

[0070] Table 5 shows that the cemented carbide produced from sample number 1 had a greater bending strength compared to the cemented carbide produced from sample number 2.

[0071] <Thermal conductivity results> The thermal conductivity of cemented carbide alloys prepared from sample numbers 1 and 2 was determined. The results showed that the thermal conductivity of the cemented carbide alloy prepared from sample number 1 was 97.2 W / m·K, while the thermal conductivity of the cemented carbide alloy prepared from sample number 2 was 90.9 W / m·K. It was found that the thermal conductivity of the cemented carbide alloy prepared from sample number 1 was improved compared to the cemented carbide alloy prepared from sample number 2, due to the denser arrangement of the particles.

[0072] The embodiments and examples disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than the embodiments described above, and all modifications within the scope of the claims are intended to be included in the meaning of equivalents and within the scope. [Explanation of symbols]

[0073] 100 Powder containing tungsten carbide.

Claims

1. In a cross-sectional SEM image of a powder containing tungsten carbide, the mode of the cross-sectional particle size distribution diagram created by analyzing the feature quantities of 1000 or more primary particles using image analysis is 24.0% or higher, the average particle size of the tungsten carbide-containing powder by the FSSS method is 0.3 to 60 μm, and the upper and lower limits of each class i in the cross-sectional particle size distribution diagram are: A powder containing tungsten carbide that satisfies the relationship shown by log 10 (upper limit of class i) - log 10 (lower limit of class i) = 0.

157.

2. In a cross-sectional SEM image of a powder containing tungsten carbide, the mode of the cross-sectional particle size distribution diagram created by analyzing the characteristics of more than 1000 primary particles by image analysis is 24.0% or higher, the average particle size of the tungsten carbide-containing powder by the FSSS method is 0.3 to 60 μm, and the number of classes in the cross-sectional particle size distribution diagram is calculated as: Number of classes = 1 + log 2 (n) : (n is the number of samples). The class width is calculated as {log 10 (maximum particle size) - log 10 (minimum particle size)} / number of classes for powders containing tungsten carbide.

3. The powder containing tungsten carbide according to claim 2, wherein the number of grades is 11.

4. A tungsten carbide-containing powder according to any one of claims 1 to 3, wherein when the particle size distributions D10, D50, and D90 of the primary particles obtained by image analysis of a cross-sectional SEM image of the tungsten carbide-containing powder are denoted as A, B, and C, the powder satisfies (C - A) / B ≤ 1.

4.

5. A powder containing tungsten carbide according to any one of claims 1 to 3, wherein the content of unbonded carbon is 0.30% by mass or less and the value obtained by subtracting the amount of unbonded carbon from the total amount of carbon in the reactant is 5.8 to 6.3% by mass.

6. The powder containing tungsten carbide according to any one of claims 1 to 3, wherein the particle size is distributed into 10 or more sections in the cross-sectional particle size distribution diagram.

Images