powder containing tungsten carbide

Abstract

A powder comprising tungsten carbide having an average particle diameter obtained by the FSSS method of 3.0-10.0 μm, the powder having a single crystallinity of 0.50-0.70.

Description

Technical Field

[0001] The present disclosure relates to a powder containing tungsten carbide. This application claims priority based on Japanese Patent Application No. 2024-009528, filed on January 25, 2024. All the descriptions contained in the Japanese patent application are incorporated herein by reference.

Background Art

[0002] Conventionally, powders containing tungsten carbide have been disclosed, for example, in JP-A-8-117580 (Patent Document 1) and JP-A-2013-60666 (Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

[0004] The powder containing tungsten carbide of the present disclosure is a powder containing tungsten carbide having an average particle size of 3.0 μm or more and 10.0 μm or less obtained by the FSSS method, and having a single crystal degree of 0.50 or more and 0.70 or less.

Brief Description of the Drawings

[0005] [Figure 1] FIG. 1 is a flowchart showing a method for producing a powder containing tungsten carbide according to the present disclosure. [Figure 2] FIG. 2 is a view of a powder 201 having a crystal 202, shown for explaining the single crystal degree. [Figure 3] FIG. 3 is a graph showing the relationship between the FSSS average particle size and the single crystal degree of powders containing tungsten carbide produced by various production methods. [Figure 4]Figure 4 is a graph showing the definition of half-width. [Figure 5] Figure 5 shows the XRD diffraction pattern of a powder containing tungsten carbide. [Figure 6] Figure 6 is a graph showing the relationship between the FSSS average particle size and crystallite size of tungsten carbide-containing powders produced by various manufacturing methods. [Figure 7] Figure 7 is a photograph showing voids in cemented carbide that occur after the cemented carbide is manufactured by sintering. [Figure 8] Figure 8 is a graph showing the relationship between mixing time and void area ratio during cemented carbide manufacturing. [Figure 9] Figure 9 is a graph showing the relationship between the average particle size of the coarse-grained tungsten carbide powder used as the raw material and the porosity area ratio of the cemented carbide when the mixing time is 3 hours. [Figure 10] Figure 10 is a graph showing the relationship between the average particle size of the raw material, which is a powder containing fine tungsten carbide, and the porosity area ratio of the cemented carbide when the mixing time is 8 hours. [Modes for carrying out the invention]

[0006] [Issues this disclosure aims to address] There was a need for a powder containing tungsten carbide that would enhance the uniformity of the cemented carbide structure and provide excellent mixability.

[0007] [Description of Embodiments in this Disclosure] First, the embodiments of this disclosure will be listed and described.

[0008] (Overview of powder containing tungsten carbide) This invention provides a tungsten carbide powder with few grain boundaries and low pulverization resistance, which enables the mixing process for cemented carbide production to be dispersed in a short time and produces cemented carbide with a uniform structure.

[0009] Traditionally, WC-based cemented carbide has been widely used in various cutting tools, jigs and fixtures, and machine parts due to its high hardness and excellent wear resistance. In recent years, wear resistance and chipping resistance have become increasingly important performance characteristics for cutting tools made from WC-based cemented carbide.

[0010] Furthermore, the dimensional accuracy of cemented carbide used for molds is becoming increasingly stringent.

[0011] To achieve these improvements, homogenization of the cemented carbide structure is crucial. Various innovations and improvements are being made in the mixing and sintering processes, which are the steps involved in manufacturing cemented carbide. For example, in attritor mixing, the powder containing tungsten carbide is pulverized during mixing to promote the homogenization of the powder and thus the cemented carbide structure.

[0012] On the other hand, grinding the raw material itself takes time to disperse, increasing the mixing time and reducing productivity. Furthermore, prolonged mixing and grinding can lead to problems such as coarsening and aggregation of the cobalt powder.

[0013] The grinding of tungsten carbide-containing powders during mixing primarily occurs at the grain boundaries present in the tungsten carbide powder. Each powder particle contains numerous crystals, and grinding occurs at these grain boundaries during mixing. Therefore, powders with more grain boundaries take longer to grind and homogenize, making the aforementioned problems more likely to occur. To address this, reducing the number of grain boundaries improves mixability.

[0014] Figure 1 is a flowchart showing a method for producing a powder containing tungsten carbide according to this disclosure.

[0015] As shown in FIG. 1, in accordance with step S101, tungsten powder with an average particle size (FSSS average particle size) of 0.3 μm to 10.0 μm obtained by the FSSS method and carbon powder with an FSSS average particle size of 1.0 μm were prepared. These were mixed at 500 rpm for 10 minutes using a general mixer with stirring blades so that the mass mixing ratio was 93.8:6.2.

[0016] In accordance with step 102, the mixture was put onto a carbon tray to a thickness of 20 mm. It was heat-treated at 1850 to 2500 °C for 30 to 480 minutes in a hydrogen, nitrogen, argon or vacuum atmosphere. Thereby, a powder containing tungsten carbide was produced. The particle size of the obtained powder containing tungsten carbide varies depending on the size of the raw materials.

[0017] In accordance with step 103, the powder containing tungsten carbide was crushed using a ball mill with a media size of φ20 mm. Finally, it was mixed in a free-fall mixer for 30 minutes to make the particle size of the tungsten carbide powder uniform.

[0018] The powder containing tungsten carbide according to the present disclosure may contain 95% by mass or more of tungsten carbide in terms of mass ratio.

[0019] As shown in FIG. 2, one powder 201 is an aggregate of crystals 202. In a powder containing tungsten carbide with an FSSS average particle size of 3.0 μm or more, the single crystal degree is defined by the following formula.

[0020] Single crystal degree = number of a plurality of powders / total number of crystals in the plurality of powders The powder containing tungsten carbide according to one aspect of the present disclosure is a powder containing tungsten carbide with an average particle size of 3.0 μm or more and 10.0 μm or less obtained by the FSSS method, and having a single crystal degree of 0.50 or more and 0.70 or less.

[0021] The higher the single crystal degree, the faster the homogenization in the mixing during the production of the cemented carbide. Therefore, it is more preferable that the single crystal degree is 0.57 or more and 0.​

[0022] A tungsten carbide-containing powder according to another aspect of this disclosure is a tungsten carbide-containing powder obtained by the FSSS method with an average particle size of 0.50 μm or more and 3.0 μm or less, where X is the average particle size of the tungsten carbide-containing powder and Y is the crystallite size of the tungsten-containing powder, then X and Y satisfy 20X + 40 ≤ 1000·Y ≤ 20X + 80, where 1000·Y is 1000 times the value of Y. The same applies hereafter.

[0023] The larger the crystallite size is relative to the powder particle size, the faster homogenization occurs during mixing when manufacturing cemented carbide. Therefore, preferably, X and Y satisfy 20X + 50 ≤ 1000·Y ≤ 20X + 80.

[0024] [Details of the embodiments of this disclosure] (Powder containing tungsten carbide, manufactured according to the first method) In the first method for producing powder containing tungsten carbide, tungsten and carbon are mixed and then heated in a furnace under a vacuum atmosphere to perform a carbonization treatment. By controlling the carbonization temperature to an optimal level that matches the particle size of the tungsten powder, a powder containing tungsten carbide with an appropriate particle size and high single crystallinity can be obtained.

[0025] Tungsten powder with an average particle size of 0.3 to 10.0 μm according to the Fischer (FSSS) method and carbon powder with an average particle size of approximately 1.0 μm are mixed using a general mixer with stirring blades at a rotation speed of 500 rpm for approximately 10 minutes. At this time, the mass mixing ratio is tungsten powder:carbon powder = 93.8:6.2. Any type of mixer may be used for mixing, as long as the mixture is uniform.

[0026] The average Fss particle size was calculated using the Fisher Sub-Sieve Sizer Model 95 from Fisher Scientific.

[0027] The mixture is placed on a carbon tray to a thickness of 20 mm and heat-treated at 1850-2500°C for 30-480 minutes in a hydrogen, nitrogen, argon, or vacuum atmosphere to carbonize the tungsten. This produces a powder containing tungsten carbide.

[0028] Subsequently, the material was crushed using a ball mill with a media size of φ20 mm, and finally mixed in a free-fall mixer for 30 minutes to create a tungsten carbide-containing powder with uniform particle size.

[0029] The proportion of carbon (both free carbon not bound to tungsten and carbon bound to tungsten) in a powder containing tungsten carbide can be measured by examining the carbon content using, for example, a carbon analyzer (WC230) manufactured by LECO. The proportion of tungsten carbide can be calculated using the following formula: "100 - (oxygen content + unavoidable impurity content + free carbon content)".

[0030] The oxygen content can be measured, for example, using a LECO TC-600 oxygen / nitrogen analyzer by the "infrared absorption method" as specified in JIS H 1403 (2001), section 13.4.

[0031] Inevitable impurities are those that inevitably become mixed into the tungsten carbide powder during the manufacturing process from at least one of the raw materials and equipment. Specifically, these include aluminum, calcium, copper, magnesium, manganese, silicon, and tin. The free carbon content can be measured, for example, by collecting insoluble material generated when the tungsten carbide powder is dissolved in a mixed acid consisting of nitric acid and phosphoric acid, and then examining this insoluble material using a carbon analyzer (WC230) manufactured by LECO.

[0032] The raw material composition of the prepared powder was adjusted so that the free carbon content was 0.2% by mass or less. Furthermore, the content of the above-mentioned unavoidable impurities in each of the prepared powders was confirmed to be 10 ppm or less for aluminum, copper, magnesium, and manganese, and 20 ppm or less for calcium, silicon, and tin, using a Shimadzu ICPS-8100CL ICP (Inductively Coupled Plasma) instrument. In other words, the total content of the above-mentioned unavoidable impurities was 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 if the content of unavoidable impurities is within the above range.

[0033] The average FSSS particle size of the obtained tungsten carbide-containing powder was then measured. Table 1 shows powders with an average FSSS particle size of 3.0 μm or larger. Table 2 shows powders with an average FSSS particle size of less than 3.0 μm.

[0034] [Table 1]

[0035] [Table 2]

[0036] Sample numbers 1 to 5 in Table 1 are powders containing tungsten carbide produced by the first manufacturing method.

[0037] Sample numbers 31 to 41 in Table 2 are powders containing tungsten carbide produced by the first manufacturing method.

[0038] (Powder containing tungsten carbide, manufactured according to the second method) In the second method, the mixture is manufactured using the same procedure as in the first method.

[0039] The mixture is placed on a carbon tray to a thickness of 20 mm, and the powder containing tungsten carbide is placed inside. The tungsten is then carbonized by heat treatment at 1000-1800°C for 30-480 minutes in a hydrogen, nitrogen, argon, or vacuum atmosphere. This process produces powder containing tungsten carbide.

[0040] In the second method, the particle size of the tungsten carbide-containing powder is made uniform using the same procedure as in the first method. The tungsten carbide produced according to the second method has a similar composition to the tungsten carbide-containing powder produced by the first method.

[0041] The average FSSS particle size of the obtained tungsten-containing powder was then measured. Table 1 shows powders with an average FSSS particle size of 3.0 μm or larger. Table 2 shows powders with an average FSSS particle size of less than 3.0 μm.

[0042] Sample numbers 11 to 27 in Table 1 are powders containing tungsten carbide produced by the second manufacturing method.

[0043] Sample numbers 51 to 59 in Table 2 are powders containing tungsten carbide produced by the second manufacturing method.

[0044] (Method for measuring the crystallinity of powder containing tungsten carbide with an FSSS average particle size of 3.0 μm or more) For the crystallinity analysis of tungsten carbide powders with an FSSS average particle size of 3.0 μm or larger, a scanning electron microscope (SEM) is used. First, the tungsten carbide powder sample to be measured is embedded in a resin such as epoxy resin. Embedding in resin allows for smooth polishing of the powder surface. Any resin or embedding method that fixes the sample in place can be used.

[0045] The resin-embedded sample is roughly polished with 80-2000 grit sandpaper, and then finished with diamond abrasives. If the sample detaches from the resin during this polishing process, it is finished with ion milling.

[0046] Cross-sections of polished tungsten carbide powder are observed using a scanning electron microscope (SEM) at a magnification of 3000x, with over 100 particles being examined. This allows for the measurement of the number of crystals contained in each particle. Crystallinity is defined in the form of single crystallinity using the following formula.

[0047] Single crystallinity = Number of powders / Total number of crystals in the powders Table 1 shows the single crystallinity of the tungsten carbide powders for sample numbers 1 to 5 and 11 to 27.

[0048] Figure 3 is a graph showing the relationship between the FSSS average particle size and single crystallinity of tungsten carbide powders produced by various manufacturing methods.

[0049] As shown in Table 1 and Figure 3, the tungsten carbide powders from samples 1 to 5, produced by the first manufacturing method, have a single crystallinity of 0.5 to 0.7.

[0050] In contrast, the tungsten carbide powders from samples 11 to 27, produced by the second manufacturing method, show that their single crystallinity is in the range of 0.03 to 0.40. (Method for measuring the crystallinity of tungsten carbide powder with an FSSS average particle size of 3.0 μm or less) For crystallinity analysis of FSSS average grain size between 0.50 μm and 3.0 μm, XRD (X-ray diffraction) is used. The full width at half maximum (FWHM) at the peak value 2θ(°) = 84° is measured in the ICDD (International Centre for Diffraction Data) data for tungsten carbide with reference code 00-025-1047.

[0051] Figure 4 is a graph showing the definition of full width at half maximum. Figure 5 shows the XRD diffraction pattern of a powder containing tungsten carbide. From Figures 4 and 5, the crystal size of the powder containing tungsten carbide can be estimated (Figure 3). A PANalytical Enpyrean was used as the analyzer, and the measurement conditions were set as shown in Table 3.

[0052] [Table 3]

[0053] Crystallinity is quantified as crystallite size Y, and its calculation is expressed using Scherrer's formula as follows.

[0054] Y = 0.9 × 1.541 × 57.3 / (Half-Maximum width × 0.743 × 10000) The unit of the full width at half maximum is degrees. In this formula, the unit of Y is (μm).

[0055] Table 2 shows that, comparing the crystallite sizes of tungsten carbide powders produced by Method 1 or Method 2, for tungsten carbide powders with similar FSSS particle size, the powder produced by Method 1 has a larger crystallite size than the powder produced by Method 2.

[0056] Figure 6 is a graph showing the relationship between the FSSS average particle size and single crystallinity of tungsten carbide powders produced by various manufacturing methods. The relationship between the FSSS particle size (X) and crystallite size (Y) of the tungsten carbide powder produced by manufacturing method 1 was 20X + 40 ≤ 1000 · Y ≤ 20X + 80 (Figure 6).

[0057] (Novality ratio of cemented carbide) Powders containing tungsten carbide produced by methods 1 and 2 were mixed with 10% by mass of Co powder and mixed in an attritor for 3 to 8 hours. Various mixtures with mixing times of 3 to 8 hours were press-molded at a pressure of 98 MPa. The molded bodies were sintered in a vacuum at 1380°C for 1 hour. The size of the cemented carbide was set to 4 mm × 8 mm × 25 mm, and the area ratio of voids was determined by microstructural observation.

[0058] Figure 7 is a photograph showing voids in cemented carbide that occur after manufacturing by sintering. To measure the area ratio of voids 401 on the surface 400 of the cemented carbide, the surface of the cemented carbide is photographed at three or more locations using an optical microscope at 100x magnification. The area ratio of voids (area of ​​voids / 700μm × 530μm) is calculated for each area of ​​700μm × 530μm (2048 × 1536 pixels), and the average value is taken as the area ratio of voids on the surface of the cemented carbide.

[0059] Figure 8 is a graph showing the relationship between mixing time and void area ratio during cemented carbide manufacturing. Figure 8 shows that for cemented carbide alloys made from tungsten carbide powder with an average FSSS particle size of 3 μm, the void area ratio stabilized with a shorter mixing time compared to manufacturing method 2 when the single crystallinity exceeded 0.50. This has the effect of increasing the productivity of the mixing process.

[0060] Furthermore, cemented carbides were prepared and evaluated using all the tungsten-containing powders listed in Tables 1 and 2, after mixing times of 3 hours and 8 hours.

[0061] Figure 9 is a graph showing the relationship between the average particle size of the coarse-grained tungsten carbide powder used as the raw material and the porosity area ratio of the cemented carbide when the mixing time is 3 hours.

[0062] Figure 10 is a graph showing the relationship between the average particle size of the raw material, which is a powder containing fine tungsten carbide, and the porosity area ratio of the cemented carbide when the mixing time is 8 hours.

[0063] As shown in Figures 9 and 10, it was confirmed that when cemented carbide is produced from powder containing tungsten carbide manufactured by method 1, the mixture exhibits excellent mixability, thus reducing the void area ratio.

[0064] The embodiments 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 by 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]

[0065] 201 Tungsten carbide powder, 202 Crystal, 400 Surface of cemented carbide, 401 Pit.

Claims

1. A powder containing tungsten carbide with an average particle size of 3.0 μm or more and 10.0 μm or less, obtained by the FSSS method, It contains tungsten carbide with a single crystallinity of 0.50 or more and 0.70 or less. A tungsten carbide powder in which the cross-section of polished tungsten carbide powder is observed at a magnification of 3000x using a SEM for 100 or more particles, the number of crystals contained in each particle is measured, and the value obtained by dividing the total number of measured particles by the total number of crystals contained in the measured particles is the single crystallinity.

2. A powder containing tungsten carbide with an average particle size of 0.50 μm or more and 3.0 μm or less, obtained by the FSSS method, Let the average particle size of the tungsten carbide-containing powder be X μm, and the crystallite size of the tungsten carbide-containing powder be Y μm. Then X and Y satisfy 20X + 40 ≤ 1000 and Y ≤ 20X + 80, and the crystallite size is calculated as Y = 0.9 × 1.541 × 57.3 / (width at half maximum × 0.743 × 10000), and the width at half maximum is determined from the XRD diffraction pattern of the tungsten carbide-containing powder.

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