Cemented carbide and tool containing the same

Abstract

A superhard alloy comprising tungsten carbide particles and a bonding phase, wherein the total content of the tungsten carbide particles and the bonding phase in the superhard alloy is 80% by volume or more, and the content of the bonding phase in the superhard alloy is 0.1% by volume or more and 20% by volume or less. In a histogram showing the distribution of the orientation difference between adjacent pairs of two adjacent tungsten carbide particles in the superhard alloy, a first peak exists at the level of orientation difference of 29.5° or more but less than 30.5°. The level on the horizontal axis of the histogram represents the orientation difference, and the width of the level is 1.0°. The frequency on the vertical axis of the histogram represents the ratio of the number of adjacent pairs belonging to each level to the total number of adjacent pairs in the superhard alloy.

Description

Cemented carbide and tool including the same The present invention relates to a cemented carbide and a tool including the same. A cemented carbide including tungsten carbide particles and a cobalt-containing binder phase is widely used as a material for cutting tools (Patent Document 1). [Prior Art Document] [Patent Document] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-132570 The cemented carbide of the present invention includes tungsten carbide particles and a binder phase. The total content of the tungsten carbide particles and the binder phase in the cemented carbide is 80% by volume or more. The content of the binder phase in the cemented carbide is 0.1% by volume or more and 20% by volume or less. In a histogram showing the distribution of the azimuth difference between adjacent pairs of two adjacent tungsten carbide particles in the cemented carbide, there is a first peak in the class where the azimuth difference is 29.5° or more and less than 30.5°. The class on the horizontal axis of the histogram represents the azimuth difference, and the width of the class is 1.0°. The frequency on the vertical axis of the histogram represents the ratio of the number of adjacent pairs belonging to each class to the number of all adjacent pairs in the cemented carbide. The tool of the present invention is a tool including the above cemented carbide. [Problems to be Solved by the Invention] In recent years, the requirement for cost reduction has become increasingly strict. For example, in high-efficiency machining, tools with long service life are also required. Therefore, an object of the present invention is to provide a cemented carbide and a tool using the same that can achieve a long service life of the tool when used as a tool material. [Effects of the Invention] A tool including the cemented carbide of the present invention can have a long tool life. [Description of Embodiments of the Invention] First, the embodiments of the present invention are listed and described. (1) The cemented carbide of the present invention includes tungsten carbide particles and a binder phase. The total content of the tungsten carbide particles and the binder phase in the cemented carbide is 80% by volume or more. The content of the binder phase in the cemented carbide is 0.1% by volume or more and 20% by volume or less. In a histogram showing the distribution of the azimuth difference between adjacent pairs of two adjacent tungsten carbide particles in the cemented carbide, there is a first peak in the class where the azimuth difference is 29.5° or more and less than 30.5°. The class on the horizontal axis of the histogram represents the azimuth difference, and the width of the class is 1.0°. The frequency on the vertical axis of the histogram represents the ratio of the number of adjacent pairs belonging to each class to the number of all adjacent pairs in the cemented carbide. A tool including the cemented carbide of the present invention can have a long tool life. (2) The frequency of the grade with an azimuth difference of more than 29.5° and less than 30.5° is preferably 0.010 or more and 0.2 or less. The tool containing the cemented carbide can suppress the propagation of cracks generated during the use of the tool. Therefore, the tool life is further improved. (3) In the above histogram, it is preferable that there is a second peak in the grade with an azimuth difference of 89.5° or more and less than 90.5°. Thereby, the matching between particles is good, the strength of the particle interface is high, and the strength of the cemented carbide is improved. (4) The above histogram is preferably produced by the following method: performing EBSD (Electron Back Scatter Diffraction) analysis on the cross-section of the above cemented carbide, and measuring the azimuth difference between all adjacent pairs of tungsten carbide particles existing within a measurement field of view of a rectangle of 85 μm × 115 μm provided on the above cross-section. (5) The tool of the present invention is a tool containing the above cemented carbide. The tool of the present invention can have a long tool life. [Detailed content of the embodiment of the invention] Hereinafter, with reference to the drawings, specific examples of the cemented carbide of the present invention and the tool using the same will be described. In the drawings of the present invention, the same reference numerals denote the same parts or corresponding parts. Also, the dimensional relationships such as length, width, thickness, depth, etc. are appropriately changed for the clarity and simplification of the drawings, and do not necessarily represent the actual dimensional relationships. In this specification, the expression in the form of "A to B" means the upper and lower limits of the range (that is, A or more and B or less). When there is no unit description for A and only a unit is described for B, the unit of A is the same as the unit of B. When a compound or the like is represented by a chemical formula in this specification, when the atomic ratio is not particularly limited, it is regarded as including all known atomic ratios, and should not necessarily be limited only to the stoichiometric range. [Embodiment 1: Cemented carbide] The cemented carbide of an embodiment of the present invention (hereinafter, also referred to as "this embodiment" or "Embodiment 1") contains tungsten carbide particles and a binder phase. The total content ratio of the tungsten carbide particles and the binder phase in the cemented carbide is 80% by volume or more. The content ratio of the binder phase in the cemented carbide is 0.1% by volume or more and 20% by volume or less. In a histogram showing the distribution of the azimuth difference between adjacent pairs of two tungsten carbide particles in the cemented carbide, there is a first peak in the grade with an azimuth difference of 29.5° or more and less than 30.5°. The grade on the horizontal axis of the histogram represents the azimuth difference, and the width of the grade is 1.0°. The frequency on the vertical axis of the histogram represents the ratio of the number of adjacent pairs belonging to each grade to the number of all adjacent pairs in the cemented carbide. The tool containing the cemented carbide of the present embodiment can have a longer tool life. The reasons are presumably as described in (i) and (ii) below. (i) In the cemented carbide of the present embodiment, the total content rate of tungsten carbide particles (hereinafter, also referred to as "WC particles") and the binder phase is 80% by volume or more, and the content rate of the binder phase in the cemented carbide is 0.1% by volume or more and 20% by volume or less. Thereby, the cemented carbide can have hardness and wear resistance suitable for tools. (ii) In the histogram showing the distribution of the azimuth difference between adjacent pairs of two adjacent tungsten carbide particles in the cemented carbide of the present embodiment, there is a first peak in the grade where the azimuth difference is 29.5° or more and less than 30.5°. Therefore, the tungsten carbide particles in the cemented carbide structure have anisotropy, and the propagation of cracks generated by the use of the tool containing the cemented carbide can be suppressed. <Composition of Cemented Carbide> The cemented carbide of Embodiment 1 contains tungsten carbide particles and a binder phase. In the cemented carbide of Embodiment 1, the lower limit of the total content rate of tungsten carbide particles and the binder phase is preferably 80% by volume or more, 82% by volume or more, 84% by volume or more. In the cemented carbide of Embodiment 1, the upper limit of the total content rate of tungsten carbide particles and the binder phase is preferably 100% by volume or less. In the cemented carbide of Embodiment 1, the total content rate of tungsten carbide particles and the binder phase is preferably 80% by volume or more and 100% by volume or less, 82% by volume or more and 100% by volume or less, 84% by volume or more and 100% by volume or less. In Embodiment 1, the lower limit of the content rate of tungsten carbide particles in the cemented carbide can be set to 60% by volume or more, 62% by volume or more, 64% by volume or more, 70% by volume or more. The upper limit of the content rate of tungsten carbide particles in the cemented carbide can be set to 99.9% by volume or less, 99% by volume or less, 98% by volume or less, 95% by volume or less. The content rate of tungsten carbide particles in the cemented carbide can be set to 60% by volume or more and 99.9% by volume or less, 62% by volume or more and 99.9% by volume or less, 64% by volume or more and 99.9% by volume or less, 70% by volume or more and 99.9% by volume or less, 60% by volume or more and 99% by volume or less, 62% by volume or more and 99% by volume or less, 64% by volume or more and 99% by volume or less, 70% by volume or more and 99% by volume or less, 60% by volume or more and 98% by volume or less, 62% by volume or more and 98% by volume or less, 64% by volume or more and 98% by volume or less, 70% by volume or more and 98% by volume or less, 60% by volume or more and 95% by volume or less, 62% by volume or more and 95% by volume or less, 64% by volume or more and 95% by volume or less, 70% by volume or more and 95% by volume or less. In Embodiment 1, the content of the binder phase in the cemented carbide is 0.1% by volume or more and 20% by volume or less. Thereby, the toughness of the cemented carbide is improved. The lower limit of the content of the binder phase in the cemented carbide can be set to 0.1% by volume or more, 0.5% by volume or more, 1% by volume or more, 2% by volume or more. The upper limit of the content of the binder phase in the cemented carbide can be set to 20% by volume or less, 18% by volume or less, 16% by volume or less, 14% by volume or less. The content of the binder phase in the cemented carbide can be set to 0.1% by volume or more and 20% by volume or less, 0.5% by volume or more and 20% by volume or less, 1% by volume or more and 20% by volume or less, 2% by volume or more and 20% by volume or less, 0.1% by volume or more and 18% by volume or less, 0.5% by volume or more and 18% by volume or less, 1% by volume or more and 18% by volume or less, 2% by volume or more and 18% by volume or less, 0.1% by volume or more and 16% by volume or less, 0.5% by volume or more and 16% by volume or less, 1% by volume or more and 16% by volume or less, 2% by volume or more and 16% by volume or less, 0.1% by volume or more and 14% by volume or less, 0.5% by volume or more and 14% by volume or less, 1% by volume or more and 14% by volume or less, 2% by volume or more and 14% by volume or less. The cemented carbide of Embodiment 1 preferably contains tungsten carbide particles and a binder phase. As long as the effects of the invention are not impaired, the cemented carbide may contain, in addition to tungsten carbide particles and a binder phase, hard phase particles other than tungsten carbide and / or impurities. Examples of the hard phase particles include carbides, nitrides, carbonitrides, oxides, and solid solutions or composites thereof containing at least one selected from the group consisting of titanium, niobium, tantalum, zirconium, molybdenum, chromium, and vanadium. Examples of the impurities include iron, molybdenum, calcium, silicon, sulfur, and the like. The cemented carbide may contain tungsten carbide particles, a binder phase, and impurities. The cemented carbide may contain tungsten carbide particles, a binder phase, and hard phase particles. The cemented carbide may contain tungsten carbide particles, a binder phase, hard phase particles, and impurities. In Embodiment 1, the cemented carbide may contain hard phase particles. The lower limit of the content of the hard phase particles in the cemented carbide can be set to 0% by volume or more, 0.1% by volume or more, 0.2% by volume or more. The upper limit of the content of the hard phase particles in the cemented carbide can be set to 20% by volume or less, 18% by volume or less, 16% by volume or less. The content of the hard phase particles in the cemented carbide can be set to 0% by volume or more and 20% by volume or less, 0.1% by volume or more and 20% by volume or less, 0.2% by volume or more and 20% by volume or less, 0% by volume or more and 18% by volume or less, 0.1% by volume or more and 18% by volume or less, 0.2% by volume or more and 18% by volume or less, 0% by volume or more and 16% by volume or less, 0.1% by volume or more and 16% by volume or less, 0.2% by volume or more and 16% by volume or less. The methods for measuring the content of tungsten carbide particles, the content of the binder phase, and the content of hard phase particles in the cemented carbide are as described in the following (A1) to (H1). (A1) Cut any position of the cemented carbide to expose the cross-section. Mirror-finish the cross-section using a cross-section polisher (manufactured by JEOL Ltd.). (B1) Analyze the mirror-finished surface of the cemented carbide using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) (device: Gemini450 (trademark) manufactured by Carl Zeiss), and identify the elements contained in the cemented carbide. (C1) Take a backscattered electron image by photographing the mirror-finished surface of the cemented carbide using a scanning electron microscope (SEM). The photographing area of the captured image is set at the central part of the cross-section of the cemented carbide, that is, at a position that does not include parts with significantly different shapes from the main body part such as near the surface of the cemented carbide (all photographing areas are set at the position of the main body part of the cemented carbide). The observation magnification is 5000 times. The measurement conditions are an acceleration voltage of 3 kV, a current value of 2 nA, and a working distance (WD) of 5 mm. (D1) Analyze the photographing area in the above (C1) using an energy dispersive X-ray analyzer attached to SEM (SEM-EDX), identify the distribution of the elements identified in the above (B1) in the photographing area, and obtain an element mapping image. (E1) Import the backscattered electron image obtained in the above (C1) into a computer, and perform binarization processing using image analysis software (OpenCV, SciPy). The binarization processing is performed in such a way that only the hard phase particles are extracted among the tungsten carbide particles, the binder phase, and the hard phase particles in the backscattered electron image. Since the binarization threshold varies depending on the contrast, it is set for each image separately. (F1) Overlap the element mapping image obtained in the above (D1) with the binarized image obtained in the above (E1), thereby identifying the existence regions of the tungsten carbide particles, the binder phase, and the hard phase particles on the binarized image. Specifically, it is represented by white in the binarized image, and the region where tungsten (W) and carbon (C) exist in the element mapping image corresponds to the existence region of the tungsten carbide particles. It is represented by black in the binarized image, and the region where at least one element selected from the group consisting of titanium, niobium, tantalum, zirconium, molybdenum, chromium, and vanadium exists in the element mapping image corresponds to the existence region of the hard phase particles. It is represented by white in the binarized image, and the region where at least one element selected from the group consisting of iron, cobalt, and nickel exists in the element mapping image corresponds to the existence region of the binder phase. (G1) In the binarized image described above, set a measurement field of view of a rectangle with a size of 24.9 μm × 18.8 μm. Using the above image analysis software, with the area of the entire measurement field of view as the denominator, measure the area percentage of each of the tungsten carbide particles, the binder phase, and the hard phase particles. (H1) Conduct the measurement in (G1) above in 5 different non-overlapping measurement fields of view. In this specification, the average value of the area percentage of the tungsten carbide particles in the 5 measurement fields of view corresponds to the content rate (volume %) of the tungsten carbide particles in the cemented carbide, the average value of the area percentage of the binder phase in the 5 measurement fields of view corresponds to the content rate (volume %) of the binder phase in the cemented carbide, and the average value of the area percentage of the hard phase particles in the 5 measurement fields of view corresponds to the content rate (volume %) of the hard phase particles in the cemented carbide. Regarding the measurements conducted by the applicant, it was confirmed that as long as the same specimen is measured, even if the cutting position of the cross-section of the cemented carbide is arbitrarily set, the shooting area described in (C1) above is arbitrarily set on the cross-section, the 5 measurement fields of view described in (H1) above are arbitrarily set, and the content rates of the tungsten carbide particles, the binder phase, and the hard phase particles in the cemented carbide are measured multiple times in the above order, the deviation of the measurement results is also small. Even if the cutting position of the cross-section of the cemented carbide is arbitrarily set, the shooting area of the backscattered electron image is arbitrarily set, and the measurement field of view is arbitrarily set, the results will not become random. The content rate of impurities in the cemented carbide (when there are two or more kinds of impurities, it is the sum of their content rates) is preferably 0 mass% or more and less than 0.1 mass%. The content rate of impurities in the cemented carbide is measured by ICP emission analysis (Inductively Coupled Plasma Emission Spectroscopy, inductively coupled plasma emission analysis (measurement device: Shimadzu Corporation "ICPS-8100" (trademark))). <Tungsten Carbide Particles> ≪Composition≫ Tungsten carbide particles (hereinafter, also referred to as "WC particles") are particles containing tungsten carbide. As long as the effects of the invention are not impaired, the WC particles may contain iron (Fe), molybdenum (Mo), calcium (Ca), silicon (Si), sulfur (S), etc. The content rate of iron (Fe), molybdenum (Mo), calcium (Ca), silicon (Si), sulfur (S) in the WC particles (when there are two or more kinds, it is the sum of their content rates) is preferably 0 mass% or more and less than 0.1 mass%. The content rate of iron (Fe), molybdenum (Mo), calcium (Ca), silicon (Si), sulfur (S) in the WC particles is measured by ICP emission analysis. ≪Average particle size≫ The lower limit of the average particle size of the tungsten carbide particles in Embodiment 1 is preferably 0.1 μm or more, 0.2 μm or more, 0.3 μm or more. The upper limit of the average particle size of the tungsten carbide particles is preferably 3.5 μm or less, 3.0 μm or less, 2.5 μm or less. The average particle size of the tungsten carbide particles is preferably 0.1 μm or more and 3.5 μm or less, 0.2 μm or more and 3.5 μm or less, 0.3 μm or more and 3.5 μm or less, 0.1 μm or more and 3.0 μm or less, 0.2 μm or more and 3.0 μm or less, 0.3 μm or more and 3.0 μm or less, 0.1 μm or more and 2.5 μm or less, 0.2 μm or more and 2.5 μm or less, 0.3 μm or more and 2.5 μm or less. Thereby, the cemented carbide has high hardness, and the wear resistance of the tool including the cemented carbide is improved. Further, the tool can have excellent fracture resistance. In this specification, the average particle size of the tungsten carbide particles means the D50 (the circular equivalent diameter at which the cumulative frequency based on the number reaches 50%, the median particle size D50) of the equivalent circle diameter (Heywood diameter) of the WC particles contained in the cemented carbide. The method for measuring the average particle size of the tungsten carbide particles is as described below. (A2) By the same method as (A1) to (F1) of the method for measuring the content ratio of tungsten carbide particles, the content ratio of the binder phase, and the content ratio of hard phase particles of the above cemented carbide, the existence region of the tungsten carbide particles is specified on the binarized image. (B2) In the above binarized image, a rectangular measurement field of 24.9 μm × 18.8 μm is set. Using the above image analysis software, the outer edge of each tungsten carbide particle in the measurement field is specified, and the circular equivalent diameter (Heywood diameter: equivalent circle diameter) of each tungsten carbide particle is calculated. (C2) Based on all the tungsten carbide particles in the above measurement field, D50 of the equivalent circle diameter of the tungsten carbide particles is calculated. Regarding the measurement performed by the applicant, it was confirmed that as long as the same specimen is measured, even if the cutting position of the cross section of the cemented carbide is arbitrarily set, the shooting area described in (C1) above is arbitrarily set on the cross section, and the measurement field described in (B2) above is arbitrarily set, and the average particle size of the tungsten carbide particles is measured multiple times in the above order, the deviation of the measurement results is small, and even if the cutting position of the cross section of the cemented carbide is arbitrarily set, the shooting area of the captured image is arbitrarily set, and the measurement field is arbitrarily set, the result will not become random. <Combined Phase> The cemented carbide of the present embodiment includes a combined phase. The combined phase preferably contains at least one first element selected from the group consisting of iron, cobalt, and nickel. The content ratio of the first element in the combined phase (when the first element contains two or more elements, it is the sum of their content ratios) is preferably 90% by mass or more and 100% by mass or less, 95% by mass or more and 100% by mass or less, 98% by mass or more and 100% by mass or less, 100% by mass. In the present embodiment, the combined phase preferably contains cobalt as a main component. Here, the combined phase containing cobalt as a main component means that the content ratio of cobalt in the combined phase is 90% by mass or more and 100% by mass or less. In the present embodiment, the combined phase may contain tungsten (W), chromium (Cr), vanadium (V), titanium (Ti), niobium (Nb), tantalum (Ta), etc. in addition to the first element. The composition of the combined phase can be measured by ICP emission spectrometry (equipment used: "ICPS-8100" (trademark) manufactured by Shimadzu Corporation). <Distribution of the azimuth difference between adjacent pairs> In the histogram showing the distribution of the azimuth difference between two adjacent pairs of the tungsten carbide particles in the cemented carbide of Embodiment 1, a first peak exists in the grade where the azimuth difference is 29.5° or more and less than 30.5°. Here, the grade on the horizontal axis of the histogram represents the azimuth difference, and the width of the grade is 1.0°, and the frequency on the vertical axis of the histogram represents the ratio of the number of adjacent pairs belonging to each grade to the number of all adjacent pairs in the cemented carbide. Thereby, the tungsten carbide particles in the cemented carbide structure have anisotropy, and the propagation of cracks generated by using a tool including the cemented carbide can be suppressed. The adjacent pairs in Embodiment 1 will be described with reference to FIG. 1. FIG. 1 is a schematic enlarged view of the cemented carbide of Embodiment 1. First, among the plurality of tungsten carbide particles 1 in FIG. 1, one WC particle is arbitrarily selected. In FIG. 1, one arbitrarily selected tungsten carbide particle is represented by the symbol a. There are three adjacent tungsten carbide particles (hereinafter, also referred to as "WC particle b", "WC particle c", "WC particle d") represented by the symbols b, c, and d in the tungsten carbide particle represented by the symbol a. That is, when WC particle a is used as a reference, there are three adjacent pairs: the adjacent pair of WC particle a and WC particle b, the adjacent pair of WC particle a and WC particle c, and the adjacent pair of WC particle a and WC particle d. For WC particle a, the azimuth difference between adjacent pairs is measured for each of the three adjacent pairs. The above histogram in the cemented carbide of Embodiment 1 will be described with reference to FIG. 2. FIG. 2 is an example of the above histogram in the cemented carbide of Embodiment 1. In the histogram of FIG. 2, the horizontal axis grades represent the azimuth difference between adjacent pairs of the two adjacent tungsten carbide particles in the cemented carbide, and the width of the grade is 1.0°. In the horizontal axis, the grades are arranged in ascending order of azimuth difference. The vertical axis frequency of the histogram represents the ratio of the number of adjacent pairs belonging to each grade to the number of all adjacent pairs in the cemented carbide. The numerical value on the horizontal axis of FIG. 2 represents the lower limit value of the grade. For example, the grade of the line represented by 26.5 is an azimuth difference of 26.5° or more and less than 27.5°. In the histogram of FIG. 2, there is a first peak represented by symbol A in the grade of azimuth difference of 29.5° or more and less than 30.5°. In this specification, in the histogram, the existence of the first peak in the grade of azimuth difference of 29.5° or more and less than 30.5° means that the frequency of the grade of azimuth difference of 29.5° or more and less than 30.5° satisfies the following condition (a). (a) The frequency of the grade of azimuth difference of 29.5° or more and less than 30.5° is 1.2 times or more the maximum value of the frequencies of 10 grades in the range of azimuth difference of 24.5° or more and less than 29.5° and the range of azimuth difference of 30.5° or more and less than 35.5°. In FIG. 2, the frequency of the grade of azimuth difference of 29.5° or more and less than 30.5° is 0.026. In FIG. 2, the 10 grades in the range of azimuth difference of 24.5° or more and less than 29.5° and the range of azimuth difference of 30.5° or more and less than 35.5° are 5 grades within the range represented by symbol a1 and 5 grades within the range represented by symbol a2. The maximum value of the frequencies of these 10 grades is the frequency 0.007 of the grade of azimuth difference of 28.5° or more and less than 29.5°. The frequency 0.026 of the grade of azimuth difference of 29.5° or more and less than 30.5° is 3.7 times the maximum value 0.007 of the frequencies of the above 10 grades. Therefore, the histogram shown in FIG. 2 satisfies the above condition (a). In the above histogram of the cemented carbide of Embodiment 1, from the viewpoint of improving the effect of suppressing crack propagation, the lower limit of the frequency of the grade of azimuth difference of 29.5° or more and less than 30.5° is preferably 0.010 or more, 0.011 or more, 0.012 or more. There is no particular limitation on the upper limit of the frequency of the grade of azimuth difference of 29.5° or more and less than 30.5°, and it can be set to 0.2 or less, for example. The frequency of the grade of azimuth difference of 29.5° or more and less than 30.5° is preferably 0.010 or more and 0.2 or less, 0.011 or more and 0.2 or less, 0.012 or more and 0.2 or less. In the above histogram of the cemented carbide of Embodiment 1, the frequency of the grade of azimuth difference of 29.5° or more and less than 30.5° is preferably 1.2 times or more, 2 times or more, 3 times or more the maximum value of the frequencies of the above 10 grades. In the columnar diagram of the cemented carbide of Embodiment 1, it is preferable that a second peak exists in the range where the azimuth difference is 89.5° or more and less than 90.5°. Thereby, the matching between particles is good, the strength of the particle interface is high, and the strength of the cemented carbide is improved. In the columnar diagram of FIG. 2, a second peak indicated by symbol B exists in the range where the azimuth difference is 89.5° or more and less than 90.5°. In this specification, in the columnar diagram, the existence of a second peak in the range where the azimuth difference is 89.5° or more and less than 90.5° means that the frequency of the range where the azimuth difference is 89.5° or more and less than 90.5° satisfies the following condition (b). (b) The frequency of the range where the azimuth difference is 89.5° or more and less than 90.5° is 1.5 times or more the maximum value of the frequencies of 8 ranges within the range where the azimuth difference is 85.5° or more and less than 89.5°, and the range where the azimuth difference is 90.5° or more and less than 94.5°. In FIG. 2, the frequency of the range where the azimuth difference is 89.5° or more and less than 90.5° is 0.267. In FIG. 2, the 8 ranges within the range where the azimuth difference is 85.5° or more and less than 89.5°, and the range where the azimuth difference is 90.5° or more and less than 94.5° are 4 ranges within the range indicated by symbol b1 and 4 ranges within the range indicated by symbol b2. The maximum value of the frequencies of these 8 ranges is the frequency 0.094 of the range where the azimuth difference is 88.5° or more and less than 89.5°. The frequency 0.267 of the range where the azimuth difference is 89.5° or more and less than 90.5° is 2.8 times the maximum value 0.094 of the frequencies of the above 8 ranges. Therefore, the columnar diagram shown in FIG. 2 satisfies the above condition (b). In the columnar diagram of the cemented carbide of Embodiment 1, from the viewpoint of improving the effect of suppressing crack propagation, the lower limit of the frequency of the range where the azimuth difference is 89.5° or more and less than 90.5° is preferably 0.10 or more, 0.12 or more, 0.14 or more. There is no particular limitation on the upper limit of the frequency of the range where the azimuth difference is 89.5° or more and less than 90.5°, and it can be set to 0.3 or less, for example. The frequency of the range where the azimuth difference is 89.5° or more and less than 90.5° is preferably 0.10 or more and 0.3 or less, 0.12 or more and 0.3 or less, 0.14 or more and 0.3 or less. In the columnar diagram of the cemented carbide of Embodiment 1, the frequency of the range where the azimuth difference is 89.5° or more and less than 90.5° is preferably 1.5 times or more, 1.7 times or more, 2.0 times or more the maximum value of the frequencies of the above 8 ranges. In this specification, the above columnar diagram is produced in the following order. (A3) Cut an arbitrary position of the cemented carbide to expose a cross-section. Mirror-process the cross-section using a cross-section polisher (manufactured by JEOL Ltd.). (B3) Observe the above mirror-finished surface using a scanning electron microscope (SEM, device: Gemini450 (trademark) manufactured by Carl Zeiss) equipped with an electron backscatter diffraction device (EBSD device: Symmetry (trademark) manufactured by Oxford), and perform EBSD analysis on the obtained observation image. Set it at the central part of the cross-section of the cemented carbide, that is, at a position that does not include parts with significantly different properties from the main body near the surface of the cemented carbide (all shooting areas are set at the positions of the main body part of the cemented carbide). The measurement area is set as a rectangular area of 85 μm × 115 μm on the above mirror-finished surface. The measurement conditions are set as: acceleration voltage 15 kV, current value 20 nA, 40 nm / step size, exposure time 0.1 - 1 ms, and measurement time 1 - 2 hours. (C3) Use commercially available software (AZtecCrystal (trademark) manufactured by Oxford) to analyze the above EBSD analysis results, and specify the crystal orientation of each tungsten carbide particle contained in the above measurement area. Here, the crystal orientation of each specified tungsten carbide particle is the crystal orientation observed when looking down from the normal direction of the mirror-finished surface at each tungsten carbide particle on the mirror-finished surface of the cemented carbide. Based on the crystal orientation of each obtained tungsten carbide particle, measure the orientation difference between adjacent pairs for all WC particles in the above measurement area. When a part of a WC particle appears outside the measurement area, that WC particle is set as the object for measuring the orientation difference. In this specification, two WC particles being adjacent means that at least a part of one WC particle is in contact with at least a part of another WC particle. When both of the two adjacent measurement points of EBSD are identified as WC, and at the boundary of these two measurement points (corresponding to the interface of the WC particles), when the difference in crystal orientation is 10° or more, these two measurement points are determined to be different WC particles. (D3) Perform the above measurement of the orientation difference in three different measurement areas. Based on the total of the measurement results of these three measurement areas, use the above software to create a histogram showing the distribution of the orientation difference between adjacent pairs of two adjacent tungsten carbide particles in the above three measurement areas. This histogram corresponds to the histogram of the cemented carbide of Embodiment 1. Regarding the measurements performed by the applicant, it was confirmed that as long as the same specimen is measured, even if the cutting position of the cross-section of the cemented carbide is arbitrarily set, the shooting area and measurement area described in (B3) above are arbitrarily set on the cross-section, and the histogram is created in the above order, the deviation of the histogram is small. Even if the cutting position of the cross-section of the cemented carbide is arbitrarily set, the shooting area of the captured image is arbitrarily set, and the measurement area is arbitrarily set, the result will not become random. <Method for manufacturing cemented carbide> The cemented carbide of Embodiment 1 can be produced, for example, by the following method. Prepare raw material powders. Prepare tungsten carbide (WC) powder as the raw material for tungsten carbide particles. As the raw material for the binder phase, cobalt (Co) powder, iron (Fe) powder, and nickel (Ni) powder can be cited. As the raw material for the hard phase particles, TiC powder, TiN powder, TiCN powder, NbC powder, TaC powder, ZrC powder, Mo 2 C powder, TiO 2 powder, Nb 2 O 5 powder and solid solutions or composites thereof. As the grain growth inhibitor, chromium carbide (Cr 3 C 2 ) powder and vanadium carbide (VC) powder can be used. The average particle diameter of the tungsten carbide (WC) powder can be set to 0.1 μm or more and 3.5 μm or less. The average particle diameter of the cobalt (Co) powder can be set to 0.5 μm or more and 3.5 μm or less. The average particle diameter of the iron (Fe) powder can be set to 0.5 μm or more and 3.5 μm or less. The average particle diameter of the nickel (Ni) powder can be set to 0.5 μm or more and 3.5 μm or less. The average particle diameter of the chromium carbide (Cr 3 C 2 ) powder can be set to 0.5 μm or more and 3.5 μm or less. The average particle diameter of the vanadium carbide (VC) powder can be set to 0.5 μm or more and 3.5 μm or less. The so-called average particle diameter of the above raw material powders means the median diameter d50 of the number basis of the equivalent spherical diameter of the raw material powders. The average particle diameter of the raw material powders is measured using a particle size distribution measuring device (trade name: MT3300EX) manufactured by Microtrac. Next, mix the raw material powders to obtain a mixed powder. A grinder or a ball mill can be used for mixing. When using a grinder for mixing, the mixing time can be set to 4 hours or more and 18 hours or less. When using a ball mill for mixing, the mixing time can be set to 4 hours or more and 72 hours or less. Next, after forming the mixed powder into a desired shape, perform high-pressure pressing to obtain a formed body. The pressure of the high-pressure pressing is set to 100 MPa or more. Next, heat the formed body in a vacuum to 800 °C to degrease it. Subsequently, the defatted green body is subjected to CIP (Cold Isostatic Pressing). The pressure of CIP is set to 392 MPa, and the processing time is set to 60 to 600 minutes. Subsequently, the green body after CIP is heated to 1000 °C in a vacuum and then sintered to obtain a sintered body. The sintering conditions can be set as follows: in an argon atmosphere, heated to 1380 °C at 7 MPa and a heating rate of 10 °C per minute, and the holding time at 1380 °C is set to 2 hours. A nitrogen atmosphere can also be used instead of the argon atmosphere. Subsequently, the above sintered body is rapidly cooled in an argon atmosphere. Subsequently, the sintered body after cooling is subjected to HIP (HIP: Hot Isostatic Pressing) to obtain a cemented carbide. The conditions of this HIP can be set as follows: held at 1330 °C and 200 MPa for 2 hours. [Embodiment 2: Tools] The tool of this embodiment includes the cemented carbide of Embodiment 1. As such a tool, for example, a cutting tool, a drill, an end mill, an indexable cutting insert for milling, an indexable cutting insert for turning, a saw for metal, a gear cutting tool, a reamer, or a tap, etc. can be exemplified. The cemented carbide of this embodiment can form the whole of these tools or a part thereof. Here, the so-called "forming a part" means a form in which the cemented carbide of this embodiment is brazed to a specific position of an arbitrary base material to form a tool tip portion, etc. ≪Hard coating≫ The cutting tool of this embodiment may further include a hard coating covering at least a part of the surface of a base material containing cemented carbide. As the hard coating, for example, diamond-like carbon or diamond can be used. [Examples] This embodiment will be more specifically described by way of examples. However, this embodiment is not limited by these examples. [Production of cemented carbide] <Specimens 1 to 8> WC powder (average particle size 0.8 μm), Co powder (average particle size 1 μm), TiCN powder (average particle size 1 μm), NbC powder (average particle size 1 μm), TaC powder (average particle size 1 μm), ZrC powder (average particle size 1 μm), Mo 2 C powder (average particle size 1 μm) is prepared as raw material powders. The raw material powders are mixed at the ratios described in the "Raw Material Powders" column of Table 1 to obtain a mixed powder. For example, in Specimen 1, in 100% by volume of the mixed powder, WC powder is 99.9% by volume and Co powder is 0.1% by volume. When using two or more powders as the hard phase raw material powders, the amounts of these powders are those obtained by equally dividing the whole (by volume) of the hard phase raw material powders. For example, in Specimen 5, the whole of the hard phase raw material powders is 20% by volume, and the details are 10% by volume of TiCN powder and 10% by volume of NbC powder. The mixing is carried out using a grinder. The mixing time when using the grinder for mixing is 8 hours. The obtained mixed powder is press-formed into a tool shape (model SEET13T3AGSN-G (Sumitomo Electric Hardmetal Corporation)), and then hot isostatically pressed to obtain a formed body. The pressure for hot isostatic pressing is set to 100 MPa. Subsequently, the formed body is heated to 800 °C in a vacuum to degrease it. Subsequently, the degreased formed body is subjected to CIP. The pressure for CIP is set to 392 MPa, and the treatment time is set to 60 minutes. Subsequently, the formed body after CIP is heated to 1000 °C in a vacuum and then sintered to obtain a sintered body. The sintering conditions are set as follows: in an argon atmosphere, heated to 1380 °C at 7 MPa and a heating rate of 10 °C per minute, and the holding time at 1380 °C is 2 hours. Subsequently, the above sintered body is quenched in an argon atmosphere. Subsequently, the sintered body after cooling is subjected to HIP to obtain a cemented carbide. The conditions for HIP are set as follows: held at 1330 °C and 200 MPa for 2 hours. <Specimens a to c> The raw material powders are mixed at the ratios described in the "Raw Material Powders" column of Table 1 to obtain a mixed powder. The mixing is carried out using a grinder. The mixing time when using the grinder for mixing is 8 hours. The obtained mixed powder is press-formed into a tool shape (model SEET13T3AGSN-G (Sumitomo Electric Hardmetal Corporation)). Hot isostatic pressing is not carried out. Subsequently, the formed body is heated to 800 °C in a vacuum to degrease it. CIP after degreasing is not carried out. Subsequently, the degreased formed body is heated to 1000 °C in a vacuum and then sintered to obtain a sintered body. The sintering conditions are set as follows: in an argon atmosphere, heated to 1380 °C at 7 MPa and a heating rate of 10 °C per minute, and the holding time at 1380 °C is 2 hours. Subsequently, the sintered body is rapidly cooled in an argon atmosphere. Subsequently, the sintered body after cooling is subjected to HIP to obtain a cemented carbide. The conditions for this HIP are set as follows: maintaining at 1330 °C and 200 MPa for 2 hours. [Table 1] [Evaluation] <Cemented Carbide> <<Composition of Cemented Carbide>> The volume percentages of WC particles, binder phase, and hard phase particles in the cemented carbide of each specimen are measured. The specific measurement method is as described in Embodiment 1. The results are shown in the columns of "Volume %" of "WC Particles", "Volume %" of "Binder Phase", and "Volume %" of "Hard Phase Particles" in Table 2 under "Cemented Carbide". The compositions of the binder phase and hard phase particles are specified based on elemental mapping images. The results are shown in the columns of "Composition" of "Binder Phase" and "Composition" of "Hard Phase Particles" in Table 2. <<Distribution of Orientation Differences between Adjacent Pairs>> The distribution of orientation differences between adjacent pairs in the cemented carbide of each specimen is measured to create a histogram. The specific measurement method is as described in Embodiment 1. Based on this histogram, the frequency A of the peak in the grade where the orientation difference is 29.5° or more and less than 30.5°, the range where the orientation difference is 24.5° or more and less than 29.5°, and the maximum value a1 of the frequencies of 10 grades where the orientation difference is 30.5° or more and less than 35.5°, the frequency B of the peak in the grade where the orientation difference is 89.5° or more and less than 90.5°, the range where the orientation difference is 85.5° or more and less than 89.5°, and the maximum value b1 of the frequencies of 8 grades within the range where the orientation difference is 90.5° or more and less than 94.5° are obtained. The results are shown in the columns of "Frequency A", "Frequency a1", "Frequency B", and "Frequency b1" in "Histogram" in Table 2. The notation "None" in the column of "Frequency A" indicates that there is no peak in the grade where the orientation difference is 29.5° or more and less than 30.5°. Furthermore, the ratio "A / a1" of frequency A to frequency a1 and the ratio "B / b1" of frequency B to frequency b1 are calculated. The results are shown in the columns of "A / a1" and "B / b1" in "Histogram" in Table 2. When "A / a1" is 1.2 or more, it is determined that there is a first peak (denoted as "Yes" in Table 2). When "B / b1" is 1.5 or more, it is determined that there is a second peak (denoted as "Yes" in Table 2). <Tool> The tool of each specimen is installed on a cutting machine (model WGC4100R (Sumitomo Electric Hardmetal Corporation)) and S45C block material ( Milling of a 6 mm through hole. The processing conditions are set as follows: cutting speed Vc of 250 m / min, table feed F of 0.45 mm / min, depth of cut (axial) ap of 2.0 mm, depth of cut (radial) ae of 50 mm, and dry machining. Measure the machining length until a defect starting from a crack appears in the tool. The maximum machining length is set to 900 mm. The longer the machining length, the better the defect resistance and the longer the tool life. The results are shown in the "Life" column of "Tool" in Table 2. "No defect" in the "Life" column indicates that no defect appears at the time point of a machining length of 900 mm. [Table 2] [Discussion] The cemented carbides and tools of Specimens 1 to 8 correspond to the examples, and the cemented carbides and tools of Specimens a to c correspond to the comparative examples. It was confirmed that the tools of Specimens 1 to 8 (examples) have a longer life than the tools of Specimens a to c (comparative examples). As described above, the embodiments and examples of the present invention have been described. However, initially, it was also intended to appropriately combine the configurations of the above-described embodiments and examples, or make various changes. It should be considered that the embodiments and examples disclosed this time are illustrative in all aspects and not restrictive. The scope of the present invention is represented by the claims and not by the above-described embodiments and examples, and is intended to include meanings equivalent to the claims and all changes within the scope. 1: Tungsten carbide particle 2: Bonding phase A: First peak B: Second peak FIG. 1 is a schematic enlarged view of the cemented carbide of Embodiment 1. FIG. 2 is an example of a histogram showing the distribution of the azimuth difference between adjacent pairs including two adjacent tungsten carbide particles in the cemented carbide of Embodiment 1. A: First peak B: Second peak

Claims

1. A superhard alloy comprising tungsten carbide particles and a bonding phase, wherein the total content of the tungsten carbide particles and the bonding phase in the superhard alloy is 80% by volume or more, and the content of the bonding phase in the superhard alloy is 0.1% by volume or more and 20% by volume or less. In a histogram representing the distribution of the orientation difference between adjacent pairs of two adjacent tungsten carbide particles in the superhard alloy, a first peak exists at the level of orientation difference of 29.5° or more but less than 30.5°. The level on the horizontal axis of the histogram represents the orientation difference, and the width of the level is 1.0°. The frequency on the vertical axis of the histogram represents the ratio of the number of adjacent pairs belonging to each level to the total number of adjacent pairs in the superhard alloy.

2. For the superhard alloy of claim 1, the frequency of the above-mentioned orientation difference of 29.5° or more but less than 30.5° is 0.010 or more and 0.2 or less.

3. The superhard alloy of claim 1 or 2, wherein in the above bar chart, there is a second peak at the level of azimuth difference of 89.5° or more but less than 90.5°.

4. For the superhard alloy as requested in item 1 or 2, wherein the above bar chart is produced by performing EBSD analysis on the cross section of the superhard alloy and measuring the orientation difference between adjacent pairs of all tungsten carbide particles present in the measurement field of view of an 85 μm × 115 μm rectangle set on the cross section.

5. The superhard alloy of claim 1 or 2, wherein the bonding phase comprises at least one first element selected from the group consisting of iron, cobalt and nickel.

6. A tool comprising any one of claims 1 to 5 of a superhard alloy.

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