Powder comprising 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

Powder containing tungsten carbide

[0001] The present disclosure relates to a powder containing tungsten carbide. This application claims priority to Japanese Patent Application No. 2024-009528, filed January 25, 2024. The entire contents of this Japanese patent application are incorporated herein by reference.

[0002] Conventionally, powders containing tungsten carbide are disclosed, for example, in Japanese Patent Laid-Open No. 8-117580 (Patent Document 1) and Japanese Patent Laid-Open No. 2013-60666 (Patent Document 2).

[0003] Japanese Patent Application Laid-Open No. 8-117580 Japanese Patent Application Laid-Open No. 2013-60666

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

[0005] FIG. 1 is a flowchart showing a method for producing a tungsten carbide-containing powder according to the present disclosure. FIG. 2 is a diagram of a powder 201 having crystals 202, illustrating the degree of single crystallinity. FIG. 3 is a graph showing the relationship between the FSSS average particle size and the degree of single crystallinity for tungsten carbide-containing powders produced by various methods. FIG. 4 is a graph illustrating the definition of half-width. FIG. 5 is a diagram showing XRD diffraction patterns of tungsten carbide-containing powders. FIG. 6 is a graph showing the relationship between the FSSS average particle size and the crystallite size for tungsten carbide-containing powders produced by various methods. FIG. 7 is a photograph showing porosity in a cemented carbide that occurs after sintering the cemented carbide. FIG. 8 is a graph showing the relationship between the mixing time during the production of a cemented carbide and the porosity area ratio. FIG. 9 is a graph showing the relationship between the average particle size of a powder containing coarse-grained tungsten carbide as a raw material and the porosity area ratio of the cemented carbide when the mixing time is 3 hours. FIG. 10 is a graph showing the relationship between the average particle size of the powder containing fine tungsten carbide particles, which is the raw material, and the porosity area ratio of the cemented carbide when the mixing time is 8 hours.

[0006] [Problem to be Solved by the Present Disclosure] There has been a demand for a powder containing tungsten carbide that enhances the uniformity of the cemented carbide structure and has excellent mixability.

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

[0008] (Outline of powder containing tungsten carbide) This invention provides a tungsten carbide powder that has few grain boundaries and is difficult to crush, and that can be dispersed in a short time during the mixing process for producing cemented carbide and can produce cemented carbide with a uniform structure.

[0009] Conventionally, WC-based cemented carbide has been widely used in various cutting tools, jigs and tools, machine parts, etc., due to its high hardness and excellent wear resistance. In recent years, the performance required for WC-based cemented carbide cutting tools has been increasing, with increasing demands for wear resistance and chipping resistance.

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

[0011] To achieve these improvements, it is important to homogenize the cemented carbide structure. Various innovations and improvements have been made to the mixing and sintering processes used to make cemented carbide. For example, in the case of attritor mixing, powder containing tungsten carbide is crushed during mixing, which promotes uniform powder granulation and also promotes uniform cemented carbide structure.

[0012] On the other hand, since the raw materials themselves are pulverized, dispersion takes time, which increases the mixing time and reduces productivity, and long mixing and pulverization can cause problems such as coarsening and agglomeration of the cobalt powder.

[0013] The pulverization of powder containing tungsten carbide during mixing basically occurs at the grain boundaries present in the powder containing tungsten carbide. Each particle of powder contains many crystals, and when mixed, pulverization begins at the grain boundaries between these crystals. In other words, the more grain boundaries there are in a powder, the longer it takes to pulverize and homogenize it, making it more likely to encounter the above-mentioned problems. Therefore, reducing the number of grain boundaries improves mixability.

[0014] FIG. 1 is a flow chart illustrating a method for producing a powder comprising tungsten carbide according to the present disclosure.

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

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

[0017] According to step 103, the powder containing tungsten carbide was crushed using a ball mill with a media size of φ20 mm. Finally, the powder 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.

[0019] 2, one powder 201 is an aggregate of crystals 202. In a powder containing tungsten carbide having an FSSS average particle size of 3.0 μm or more, the degree of single crystallinity is defined by the following formula:

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

[0021] The higher the single crystallinity, the faster the homogenization during mixing when producing the cemented carbide, so it is more preferable that the single crystallinity is 0.57 or more and 0.70 or less.

[0022] A powder containing tungsten carbide according to another aspect of the present disclosure is a powder containing tungsten carbide obtained by an FSSS method and having an average particle size of 0.50 μm or more and 3.0 μm or less, in which, where the average particle size of the powder containing tungsten carbide is X and the crystallite size of the powder containing tungsten is Y, X and Y satisfy the relationship 20X + 40≦1000·Y≦20X + 80. 1000·Y represents a value 1000 times Y. The same applies below.

[0023] The larger the crystallite size relative to the particle size of the powder, the faster the homogenization during mixing in producing the cemented carbide. Therefore, preferably, X and Y satisfy 20X+50≦1000·Y≦20X+80.

[0024] [Details of the embodiment of the present disclosure] (Powder containing tungsten carbide according to the first manufacturing method) In the first manufacturing method for producing a powder containing tungsten carbide, tungsten and carbon are mixed and then heated in a furnace under a vacuum atmosphere for carbonization. At this time, by controlling the carbonization temperature to an optimum temperature suited to the particle size of the tungsten powder, a powder containing tungsten carbide with an appropriate particle size and a high degree of single crystallinity can be obtained.

[0025] Tungsten powder having an average particle size of 0.3 to 10.0 μm as determined by the Fischer (FSSS) method and carbon powder having 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 blending ratio of tungsten powder to carbon powder is 93.8:6.2. Any type of mixer may be used for the mixing method, as long as the mixture is uniformly mixed.

[0026] The Fsss average particle size is measured using a Fisher Sub-Sieve Sizer Model 95 manufactured by Fisher Scientific.

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

[0028] Thereafter, the mixture 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 make the particle size of the powder containing tungsten carbide uniform, thereby producing a powder containing tungsten carbide.

[0029] The percentage of carbon (both free carbon not bonded to tungsten and carbon bonded to tungsten) in a powder containing tungsten carbide is measured by inspecting the carbon amount using, for example, a carbon measuring device (WC230) manufactured by LECO Corp. The percentage of tungsten carbide can be calculated using the formula "100 - (oxygen content + unavoidable impurity content + free carbon content)".

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

[0031] The inevitable impurities are impurities that are inevitably mixed into the powder containing tungsten carbide from at least one of the raw materials and the equipment during the manufacturing process, and specifically include aluminum, calcium, copper, magnesium, manganese, silicon, and tin. The free carbon content can be measured, for example, by collecting insoluble matter produced when the powder containing tungsten carbide is dissolved in a mixed acid consisting of nitric acid and phosphoric acid, and examining the insoluble matter using a carbon measuring device (WC230) manufactured by LECO Corporation.

[0032] The raw material composition of the produced 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 produced powder was confirmed 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 using an ICPS-8100CL ICP (Inductively Coupled Plasma) manufactured by Shimadzu Corporation. That is, 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 bodies in the alloy structure, a sound cemented carbide can be obtained by keeping the content of the unavoidable impurities within the above range.

[0033] The FSSS average particle size of the resulting powder containing tungsten carbide was measured. Powders having an FSSS average particle size of 3.0 μm or more are shown in Table 1. Powders having an FSSS average particle size of less than 3.0 μm are shown in Table 2.

[0034]

[0035]

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

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

[0038] (Tungsten Carbide-Containing Powder According to Second Manufacturing Method) In the second manufacturing method, a mixture is manufactured using the same procedure as in the first manufacturing method.

[0039] The mixture is poured onto a carbon tray to a thickness of 20 mm, and the powder containing tungsten carbide is carbonized by heat treatment at 1000 to 1800°C for 30 to 480 minutes in a hydrogen, nitrogen, argon, or vacuum atmosphere, thereby producing a powder containing tungsten carbide.

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

[0041] The FSSS average particle size of the resulting tungsten-containing powder was measured. Powders having an FSSS average particle size of 3.0 μm or more are shown in Table 1. Powders having an FSSS average particle size of less than 3.0 μm are shown in Table 2.

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

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

[0044] (Method for measuring the crystallinity of a powder containing tungsten carbide with an FSSS average particle size of 3.0 μm or more) A scanning electron microscope (SEM) is used to analyze the crystallinity of a powder containing tungsten carbide with an FSSS average particle size of 3.0 μm or more. First, a sample of the powder containing tungsten carbide to be measured is embedded in a resin such as epoxy resin. Embedding in resin makes it possible to polish the powder surface cleanly. The resin and embedding method used here can be any resin or method that will fix the sample.

[0045] The resin-embedded sample is roughly polished with sandpaper of 80 to 2000 grit, and then finished by polishing with diamond abrasive grains, etc. If the sample comes off the resin during this polishing, it is finally finished by ion milling.

[0046] The cross section of the polished powder containing tungsten carbide is observed with an SEM at a magnification of 3000x for 100 or more particles. The number of crystals contained in each particle is measured. The crystallinity is defined as the degree of single crystallinity using the following formula:

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

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

[0049] As shown in Table 1 and FIG. 3, it can be seen that the tungsten carbide-containing powders of Sample Nos. 1 to 5 produced by the first production method have a single crystallinity of 0.5 or more and 0.7 or less.

[0050] In contrast, the tungsten carbide-containing powders of sample numbers 11 to 27, which were produced by the second production method, have a single crystallinity in the range of 0.03 to 0.40. (Method for measuring the crystallinity of tungsten carbide-containing powders with an FSSS average particle size of 3.0 μm or less) An XRD (X-ray diffractometer) is used for crystallinity analysis of powders with an FSSS average particle size of 0.50 μm to 3.0 μm. The half-width at the peak value 2θ (°) = 84° in the data for tungsten carbide reference code 00-025-1047 from the ICDD (International Centre for Diffraction Data) is measured.

[0051] Figure 4 is a graph showing the definition of half-width. Figure 5 shows an 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 Empyrean was used as the analyzer, and the measurement conditions were set as shown in Table 3.

[0052]

[0053] The crystallinity evaluation is quantified as the crystallite size Y, and the calculation is expressed using the following Scherrer equation.

[0054] Y = 0.9 x 1.541 x 57.3 / (half width x 0.743 x 10000) The unit of half width is degrees. In this formula, the unit of Y is (μm).

[0055] Comparing the crystallite sizes of the tungsten carbide-containing powders produced by Production Method 1 and Production Method 2 in Table 2, the powder produced by Production Method 1 has a larger crystallite size than the powder produced by Production Method 2 for tungsten carbide-containing powders having similar FSSS particle sizes.

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

[0057] (Porosity Area Ratio of Cemented Carbide) The tungsten carbide-containing powders produced by Production Methods 1 and 2 were blended with 10 mass% Co powder and mixed in an attritor for 3 to 8 hours. Various mixtures mixed for 3 to 8 hours were press-molded at a pressure of 98 MPa. The compacts were sintered in vacuum at 1380°C for 1 hour. The size of the cemented carbide was 4 mm x 8 mm x 25 mm, and the porosity area ratio was determined by structural observation.

[0058] 7 is a photograph showing porosity in a cemented carbide alloy after it has been sintered. To measure the area ratio of porosity 401 on the surface 400 of the cemented carbide alloy, photographs of three or more locations on the cemented carbide alloy surface were taken at 100x magnification using an optical microscope. The porosity area ratio (porosity area / 700µm x 530µm) was determined within each area of ​​700µm x 530µm (2048 x 1536 pixels), and the average value was taken as the porosity area ratio on the cemented carbide alloy surface.

[0059] Fig. 8 is a graph showing the relationship between the mixing time during the production of cemented carbide and the porosity area ratio. Regarding the porosity area ratio of cemented carbide produced using as a raw material a powder containing tungsten carbide with an FSSS average particle size of 3 µm, as shown in Fig. 8, it was found that the porosity area ratio was stable with a shorter mixing time than in Production Method 2 for those with a single crystallinity of more than 0.50. This has the effect of increasing the productivity of the mixing process.

[0060] Furthermore, cemented carbides were produced and evaluated for all of the tungsten-containing powders in Tables 1 and 2 at mixing times of 3 hours and 8 hours.

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

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

[0063] As shown in FIGS. 9 and 10, it was confirmed that when a cemented carbide alloy is produced from a powder containing tungsten carbide produced by Production Method 1, the mixability is excellent, and therefore the porosity area ratio can be reduced.

[0064] The embodiments 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.

[0065] 201 Powder containing tungsten carbide, 202 Crystal, 400 Surface of cemented carbide, 401 Cavity.

Claims

1. A powder containing tungsten carbide obtained by the FSSS method, having an average particle size of 3.0 μm or more and 10.0 μm or less, and having a single crystallinity of 0.50 or more and 0.70 or less, the powder containing tungsten carbide.

2. A powder containing tungsten carbide obtained by the FSSS method, having an average particle size of 0.50 μm or more and 3.0 μm or less, where, when the average particle size of the powder containing tungsten carbide is X and the crystallite size of the powder containing tungsten carbide is Y, X and Y satisfy 20X + 40 ≤ 1000·Y ≤ 20X + 80, the powder containing tungsten carbide.

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