Cubic boron nitride sintered body

Abstract

The cubic boron nitride sintered body of the present disclosure contains 35-100 vol% inclusive of cubic boron nitride particles and 0-65 vol% inclusive of a binder material, wherein: the lattice constant of the cubic boron nitride particles is 3.6140-3.6161Å inclusive; the silicon content of the cubic boron nitride particles is 0.02 mass% or less; and the binder material contains at least one member selected from the group consisting of a compound, which comprises at least one element selected from the group consisting of the group 4 elements, the group 5 elements and the group 6 elements of the periodic table, aluminum, silicon, iron, cobalt and nickel, and at least one element selected from the group consisting of carbon, nitrogen, boron and oxygen, and a solid solution of the aforesaid compound.

Description

Technical Field

[0001] The present disclosure relates to a cubic boron nitride sintered body. This application claims priority based on International Application PCT / JP2021 / 039320 filed on October 25, 2021. All the descriptions contained in the international application are incorporated herein by reference.

Background Art

[0002] Cubic boron nitride (hereinafter also referred to as cBN) has hardness and thermal conductivity second only to diamond, and further has the characteristic of low reactivity with iron-based metals compared to diamond. For this reason, cubic boron nitride sintered bodies (hereinafter also referred to as cBN sintered bodies) containing cubic boron nitride particles (hereinafter also referred to as cBN particles) are widely used particularly for cutting iron-based difficult-to-machine materials (for example, Patent Documents 1 and 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

[0004] The cubic boron nitride sintered body of the present disclosure is a cubic boron nitride sintered body containing 35% by volume or more and 100% by volume or less of cubic boron nitride particles and 0% by volume or more and 65% by volume or less of a binder, wherein the lattice constant of the cubic boron nitride particles is 3.6140 Å or more and 3.6161 Å or less, the silicon content of the cubic boron nitride particles is 0.02% by mass or less, The binder contains at least one element selected from the group consisting of Group 4 elements, Group 5 elements, Group 6 elements, aluminum, silicon, iron, cobalt, and nickel in the periodic table, and at least one element selected from the group consisting of carbon, nitrogen, boron, and oxygen, and is a cubic boron nitride sintered body containing at least one selected from the group consisting of compounds composed of the above elements and solid solutions of the compounds.

Brief Description of Drawings

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Figure 1

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Embodiments for Carrying Out the Invention

[0006] [Problems to be Solved by the Present Disclosure] In recent years, from the perspective of cost reduction, the demand for high-efficiency machining has been increasing more and more. Therefore, when used as a tool material, a cubic boron nitride sintered body that can have a long tool life even in high-efficiency machining is desired.

[0007] [Effects of the Present Disclosure] The cubic boron nitride sintered body of the present disclosure can enable the tool to have a long life, especially in high-efficiency machining, when used as a tool material.

[0008] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. (1) The cubic boron nitride sintered body of the present disclosure is a cubic boron nitride sintered body containing 35% by volume or more and 100% by volume or less of cubic boron nitride particles and 0% by volume or more and 65% by volume or less of a binder, wherein the lattice constant of the cubic boron nitride particles is 3.6140 Å or more and 3.6161 Å or less, the silicon content of the cubic boron nitride particles is 0.02% by mass or less, and the binder contains at least one compound composed of at least one element selected from the group consisting of Group 4 elements, Group 5 elements, Group 6 elements, aluminum, silicon, iron, cobalt, and nickel in the periodic table and at least one element selected from the group consisting of carbon, nitrogen, boron, and oxygen, and at least one selected from the group consisting of solid solutions of the compounds.

[0009] When the cubic boron nitride sintered body of the present disclosure is used as a tool material, it can enable the tool to have a longer life, especially in high-efficiency machining.

[0010] (2) In the above (1), it is preferable that the lattice constant of the cubic boron nitride particles is 3.6142 Å or more and 3.6158 Å or less. According to this, the tool life is further improved.

[0011] (3) In the above (1) or (2), it is preferable that the lattice constant of the cubic boron nitride particles is 3.6145 Å or more and 3.6155 Å or less. According to this, the tool life is further improved.

[0012] (4) In any of the above (1) to (3), it is preferable that the silicon content of the cubic boron nitride particles is 0.01% by mass or less. According to this, the tool life is further improved.

[0013] (5) In any of the above (1) to (4), it is preferable that the silicon content of the cubic boron nitride particles is 0.001% by mass or less. According to this, the tool life is further improved.

[0014] (6) In any of the above (1) to (5), the content of the cubic boron nitride particles in the cubic boron nitride sintered body is preferably 40% by volume or more and 95% by volume or less. According to this, the tool life is further improved.

[0015] [Details of Embodiments of the Present Disclosure] The cubic boron nitride sintered body of the present disclosure will be described below. In this specification, the notation 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 there is a unit description only for B, the units of A and B are the same.

[0016] In this specification, when a compound or the like is represented by a chemical formula, when the atomic ratio is not particularly limited, it includes all conventionally known atomic ratios and should not necessarily be limited only to those within the stoichiometric range. For example, when "TiN" is described, the ratio of the number of atoms constituting TiN includes all conventionally known atomic ratios.

[0017] [Embodiment 1: Cubic Boron Nitride Sintered Body] ≪Cubic Boron Nitride Sintered Body≫ The cubic boron nitride sintered body according to an embodiment of the present disclosure (hereinafter also referred to as this embodiment) is a cubic boron nitride sintered body including 35% by volume or more and 100% by volume or less of cubic boron nitride particles and 0% by volume or more and 65% by volume or less of a binder, the lattice constant of the cubic boron nitride particles is 3.6140 Å or more and 3.6161 Å or less, the silicon content of the cubic boron nitride particles is 0.02% by mass or less, the binder includes at least one compound composed of at least one element selected from the group consisting of Group 4 elements, Group 5 elements, Group 6 elements, aluminum, silicon, iron, cobalt, and nickel in the periodic table and at least one element selected from the group consisting of carbon, nitrogen, boron, and oxygen, and at least one selected from the group consisting of solid solutions of the compound, and is a cubic boron nitride sintered body.

[0018] When the cubic boron nitride sintered body of the present embodiment is used as a tool material, it is possible to extend the life of the tool, especially in high-efficiency machining. The reason is presumed to be as follows (i) to (iii).

[0019] (i) The cubic boron nitride sintered body of the present embodiment contains cBN particles having high hardness, strength and toughness in an amount of 35% by volume or more and 100% by volume or less. Therefore, the cubic boron nitride sintered body has excellent wear resistance and chipping resistance, and the life of the tool using the cubic boron nitride sintered body is prolonged.

[0020] (ii) In the cubic boron nitride sintered body of the present embodiment, the lattice constant of the cubic boron nitride particles is 3.6140 Å or more and 3.6161 Å or less. The lattice constant of a general unit lattice of cubic boron nitride (hereinafter, the lattice constant of the unit lattice is simply referred to as the lattice constant) is 3.6162 Å. The lattice constant of the cBN particles used in the present embodiment is smaller than that of general cBN particles. In the cBN sintered body using cBN particles having a small lattice constant, the thermal conductivity of the cBN particles is high, and the occurrence of crater wear caused by cutting heat generated during cutting and the occurrence of chipping caused by the development of craters are suppressed, and the life of the tool using the cubic boron nitride sintered body is improved. The reason why the thermal conductivity of the cBN particles becomes high is not clear, but it is presumed that the covalent bond becomes stronger as the lattice constant becomes smaller, and the lattice vibration is more easily transmitted.

[0021] (iii) In the cubic boron nitride sintered body of the present embodiment, the silicon content of the cubic boron nitride particles is 0.02% by mass or less. Conventional cBN particles contain about 0.1% by mass of silicon as an impurity. Silicon has a lower thermal conductivity than cubic boron nitride. Since the content of silicon having a low thermal conductivity in the cBN particles used in the present embodiment is reduced, the thermal conductivity becomes high. Therefore, in the cBN sintered body having the cBN particles, the occurrence of crater wear caused by cutting heat generated during cutting and the occurrence of chipping caused by the development of craters are suppressed, and the life of the tool using the cubic boron nitride sintered body is improved.

[0022] <Composition of Cubic Boron Nitride Sintered Body> The cubic boron nitride sintered body of the present embodiment includes cubic boron nitride particles in an amount of 35% to 100% by volume and a binder in an amount of 0% to 65% by volume. Note that the cBN sintered body can contain unavoidable impurities resulting from raw materials, manufacturing conditions, etc., as long as the effects of the present disclosure are achieved.

[0023] The lower limit of the content of cBN particles in the cBN sintered body is 35% by volume or more from the viewpoint of improving hardness, preferably 40% by volume or more, and more preferably 45% by volume or more. The upper limit of the content of cBN particles in the cBN sintered body is 100% by volume or less. The cBN sintered body of the present embodiment can be composed of only cBN particles. The upper limit of the content of cBN particles in the cBN sintered body varies depending on the application, but is preferably 99% by volume or less, preferably less than 98% by volume, preferably 95% by volume or less, preferably 90% by volume or less, preferably 85% by volume or less, and more preferably 80% by volume or less. The content of cBN particles in the cBN sintered body is 35% to 100% by volume, preferably 35% to 99% by volume, preferably 35% to less than 98% by volume, preferably 40% to 95% by volume, preferably 40% to 90% by volume, preferably 40% to 85% by volume, and more preferably 45% to 80% by volume.

[0024] The lower limit of the content of the binder in the cBN sintered body is 0% by volume or more. The cBN sintered body of the present embodiment can contain no binder. From the viewpoint of ensuring the function as a binder, the lower limit of the content of the binder in the cBN sintered body is preferably 1% by volume or more, more preferably more than 2% by volume, still more preferably 5% by volume or more, yet more preferably 10% by volume or more, still more preferably 15% by volume or more, and even more preferably 20% by volume or more. The upper limit of the content of the binder in the cBN sintered body is 65% by volume or less from the viewpoint of improving hardness, preferably 60% by volume or less, and more preferably 55% by volume or less. The content of the binder in the cBN sintered body is 0% by volume or more and 65% by volume or less, preferably 1% by volume or more and 65% by volume or less, more preferably more than 2% by volume and 65% by volume or less, still more preferably 5% by volume or more and 60% by volume or less, yet more preferably 10% by volume or more and 60% by volume or less, still more preferably 15% by volume or more and 60% by volume or less, and even more preferably 20% by volume or more and 55% by volume or less.

[0025] The cBN sintered body of the present embodiment preferably contains cubic boron nitride particles of 35% by volume or more and less than 100% by volume and a binder of more than 0% by volume and 65% by volume or less, more preferably contains cubic boron nitride particles of 35% by volume or more and less than 98% by volume and a binder of more than 2% by volume and 65% by volume or less, still more preferably contains cubic boron nitride particles of 40% by volume or more and 95% by volume or less and a binder of 5% by volume or more and 60% by volume or less, and even more preferably contains cubic boron nitride particles of 45% by volume or more and 80% by volume or less and a binder of 20% by volume or more and 55% by volume or less.

[0026] The cBN sintered body of the present embodiment preferably comprises cubic boron nitride particles in an amount of 35% by volume or more and 100% by volume or less, and a binder in an amount of 0% by volume or more and 65% by volume or less. It is preferably composed of cubic boron nitride particles in an amount of 35% by volume or more and less than 100% by volume, and a binder in an amount of more than 0% by volume and 65% by volume or less. It is preferably composed of cubic boron nitride particles in an amount of 35% by volume or more and less than 98% by volume, and a binder in an amount of more than 2% by volume and 65% by volume or less. More preferably, it is composed of cubic boron nitride particles in an amount of 40% by volume or more and 85% by volume or less, and a binder in an amount of 15% by volume or more and 60% by volume or less. Even more preferably, it is composed of cubic boron nitride particles in an amount of 45% by volume or more and 80% by volume or less, and a binder in an amount of 20% by volume or more and 55% by volume or less. Even in these cases, as long as the cBN sintered body exhibits the effects of the present disclosure, it can contain unavoidable impurities resulting from raw materials, manufacturing conditions, etc.

[0027] The content rate (by volume) of cBN particles and the content rate (by volume) of the binder in the cBN sintered body can be confirmed by performing microstructure observation, elemental analysis, etc. on the cBN sintered body using an energy dispersive X-ray analyzer (EDX) (Octane Elect (Octane Elect) EDS system) attached to a scanning electron microscope (SEM) (manufactured by JEOL Ltd., "JSM-7800F" (product name)) (hereinafter also referred to as "SEM-EDX"). The specific measurement method is as follows.

[0028] First, cut an arbitrary position of the cBN sintered body to prepare a sample including the cross-section of the cBN sintered body. For preparing the cross-section, a focused ion beam apparatus, a cross-section polisher apparatus, etc. can be used. Next, observe the above cross-section with an SEM at a magnification of 5000 times to obtain a backscattered electron image. In the backscattered electron image, the region where cBN particles exist becomes a black region, and the region where the binder exists becomes at least one of a gray region and a white region. When the cBN sintered body consists only of cBN particles, the entire backscattered electron image becomes black or dark gray.

[0029] Next, binarization processing is performed on the above reflection electron image using image analysis software ("WinROOF" of Mitani Shosha Co., Ltd.). In the image after binarization processing, the region where cBN particles exist (the black region in the reflection electron image) becomes a dark field, and the region where the binder exists (at least either the gray region or the white region in the reflection electron image) becomes a bright field. A measurement region (15 μm × 20 μm) is set in the image after binarization processing. The area ratio of the pixels derived from the dark field (pixels derived from cBN particles, pixels derived from the black region in the reflection electron image) occupying the entire area of the measurement field of view is calculated. By regarding the calculated area ratio as volume%, the content rate (volume%) of cBN particles can be obtained.

[0030] The content rate (volume%) of the binder can be obtained by calculating the area ratio of the pixels derived from the bright field (the total of the pixels derived from the binder, the pixels derived from the gray region and the white region in the reflection electron image) occupying the entire area of the measurement field of view from the image after binarization processing.

[0031] The specific method of binarization processing will be described with reference to FIGS. 1 to 6. Note that FIGS. 1 to 6 are drawings shown for the purpose of explaining the method of binarization processing, and do not necessarily show the cubic boron nitride sintered body of the present embodiment.

[0032] FIG. 1 is an example of a reflection electron image obtained by observing a cBN sintered body with SEM. The reflection electron image is read into image processing software. The read image is shown in FIG. 2. As shown in FIG. 2, an arbitrary line Q1 is drawn in the read image.

[0033] Measure the concentration cross-section along line Q1 and read the GRAY value. Create a graph with line Q1 as the X coordinate and the GRAY value as the Y coordinate (hereinafter also referred to as the "concentration cross-section graph"). Figure 3 shows the reflected electron image of the cBN sintered body and the concentration cross-section graph of the reflected electron image. In Figure 3, the upper image is the reflected electron image, and the lower graph is the concentration cross-section graph. In Figure 3, the width of the reflected electron image coincides with the width of the X coordinate of the concentration cross-section graph (23.27 μm). Therefore, the distance from the left end of line Q1 in the reflected electron image to a specific position on line Q1 is indicated by the value of the X coordinate of the concentration cross-section graph.

[0034] Arbitrarily select three black regions where cBN particles are present in the reflected electron image of Figure 3. The black region is, for example, the portion indicated by the ellipse with the symbol c in the reflected electron image of Figure 4.

[0035] Read the GRAY value of each of the three black regions from the concentration cross-section graph. The GRAY value of each of the three black regions shall be the average value of the GRAY values in the three portions surrounded by the ellipse with the symbol c in the concentration cross-section graph of Figure 4. Calculate the average value of the GRAY values of each of the three portions. Let this average value be the GRAY value of cBN (hereinafter also referred to as G cbn either).

[0036] Arbitrarily select three regions where the binder shown in gray exists in the reflected electron image of Figure 3. The binder is, for example, the portion indicated by the ellipse with the symbol d in the reflected electron image of Figure 4.

[0037] Read the GRAY value of each of the three binders from the concentration cross-section graph. The GRAY value of each of the three binders shall be the average value of the GRAY values in the three portions surrounded by the ellipse with the symbol d in the concentration cross-section graph of Figure 4. Calculate the average value of the GRAY values of each of the three portions. Let this average value be the GRAY value of the binder (hereinafter also referred to as G binder either).

[0038] (G cbn +G binder) / 2 is defined as the GRAY value at the interface between the black region (cBN particles) and the binder. For example, in the concentration cross-sectional graph of FIG. 4, the GRAY value G of the black region (cBN particles) cbn is indicated by line G cbn , and the GRAY value G of the binder binder is indicated by line G binder . The GRAY value indicated by (G cbn +G binder ) / 2 is indicated by line G1.

[0039] As described above, in the concentration cross-sectional graph, by defining the interface between the black region (cBN particles) and the binder, the values of the X coordinate and the Y coordinate at the interface between the black region (cBN particles) and the binder can be read. The interface can be defined arbitrarily. For example, in the backscattered electron image at the top of FIG. 5, as an example of the region including the interface between the black region (cBN particles) and the binder, the region surrounded by the ellipse with the symbol e can be mentioned. In the concentration cross-sectional graph at the bottom of FIG. 5, the interface between the black region (cBN particles) and the binder within the region surrounded by the ellipse with the symbol e above is indicated by the arrow e. The tip of the arrow e indicates the position of the intersection of the concentration cross-sectional graph of the GRAY value and the line G1 indicating the GRAY value (G cbn +G binder ) / 2. The values of the X coordinate at the tip of the arrow e and the Y coordinate at the tip of the arrow e correspond to the values of the X coordinate and the Y coordinate at the interface between the black region (cBN particles) and the binder.

[0040] Binarization processing is performed using the values of the X coordinate and the Y coordinate at the interface between the black region (cBN particles) and the binder as thresholds. The image after the binarization processing is shown in FIG. 6. In FIG. 6, the region surrounded by the dotted line is the region where the binarization processing is performed. Note that the image after the binarization processing may include a white region (a portion whiter than the bright field, pixels derived from the binder) corresponding to the region that was white in the backscattered electron image before the binarization processing.

[0041] In Fig. 6, the area ratio of the pixels derived from the dark field (pixels derived from cBN particles, pixels derived from the black regions in the backscattered electron image) in the measurement field of view to the area of the measurement field of view is calculated. By regarding the calculated area ratio as volume %, the content (volume %) of cBN particles can be determined.

[0042] In Fig. 6, the content (volume %) of the binder can be determined by calculating the area ratio of the pixels derived from the bright field (the total of the pixels derived from the binder, the pixels derived from the gray and white regions in the backscattered electron image) in the measurement field of view to the area of the measurement field of view.

[0043] In the image after the binarization process, the fact that the dark field region indicates cBN particles and the bright field region indicates the binder is confirmed by analyzing the same region as the region photographed in the image after the binarization process using energy dispersive X-ray spectroscopy (SEM-EDX) to identify the elements contained in each of the dark field and the bright field.

[0044] According to the above measurement method, the measurement of the content (volume %) of cubic boron nitride particles in the cubic boron nitride sintered body is performed in five different measurement regions. The average of the measurement values in the five measurement regions is taken as the content (volume %) of cubic boron nitride particles in the cubic boron nitride sintered body of the present embodiment.

[0045] According to the above measurement method, the measurement of the content (volume %) of the binder in the cubic boron nitride sintered body is performed in five different measurement regions. The average of the measurement values in the five measurement regions is taken as the content (volume %) of the binder in the cubic boron nitride sintered body of the present embodiment.

[0046] As far as the applicant has measured, as long as the content (volume %) of cBN particles and the content (volume %) of the binder in the cBN sintered body are measured in the same sample, even if the selected location of the measurement field of view is changed and calculated multiple times, there is almost no variation in the measurement results, and it has been confirmed that it is not arbitrary even if the measurement field of view is set arbitrarily.

[0047] <Inevitable impurities> The cubic boron nitride sintered body of the present embodiment may contain inevitable impurities as long as the effects of the present disclosure are exhibited. Examples of the inevitable impurities include metal elements such as alkali metal elements (lithium (Li), sodium (Na), potassium (K), etc.) and alkaline earth metal elements (calcium (Ca), magnesium (Mg), etc.). When the cubic boron nitride sintered body contains inevitable impurities, the content of the inevitable impurities is preferably 0.1% by mass or less. The content of the inevitable impurities can be measured by secondary ion mass spectrometry (SIMS).

[0048] ≪Cubic boron nitride particles≫ <Lattice constant> In the cubic boron nitride sintered body of the present embodiment, the lattice constant of the cubic boron nitride particles is 3.6140 Å or more and 3.6161 Å or less. According to this, the thermal conductivity of the cBN particles is increased. Therefore, in the cBN sintered body containing the cBN particles, the occurrence of crater wear caused by cutting heat generated during cutting and the occurrence of defects caused by the development of craters are suppressed, and the tool life is improved.

[0049] The upper limit of the lattice constant of the cBN particles is 3.6161 Å or less, preferably 3.6158 Å or less, and more preferably 3.6155 Å or less from the viewpoint of improving the thermal conductivity. The lower limit of the lattice constant of the cBN particles is 3.6140 Å or more, preferably 3.6142 Å or more, and more preferably 3.6145 Å or more from the viewpoint of suppressing defects. The lattice constant of the cBN particles is 3.6140 Å or more and 3.6161 Å or less, preferably 3.6142 Å or more and 3.6158 Å or less, and more preferably 3.6145 Å or more and 3.6155 Å or less.

[0050] The lattice constant of the cBN particles is measured and calculated by the following procedure. <Measurement method> The cubic boron nitride sintered body is immersed in hydrofluoric acid (hydrofluoric acid (concentration: 60% by mass): nitric acid (concentration: 70% by mass) = 5:5 (volume ratio)) in a sealed container for 48 hours. As a result, all of the binder is dissolved in the hydrofluoric acid, and only the cubic boron nitride particles remain.

[0051] Recover the above-mentioned cubic boron nitride particles. Fill the cubic boron nitride particles into a capillary for X-ray crystal analysis with a diameter of 0.3 mm manufactured by TOHO (product name: Mark Tube), and use it as a sealed test specimen.

[0052] Prepare a powder made of cerium oxide (manufactured by High Purity Chemical Laboratory) as a standard sample for calculating the wavelength λ of synchrotron radiation. Fill the standard sample powder into a capillary for X-ray crystal analysis with a diameter of 0.3 mm manufactured by TOHO, and use it as a sealed standard sample.

[0053] Perform X-ray diffraction measurement on the sealed test specimen filled with the above-mentioned cubic boron nitride particles under the following conditions, and obtain a line profile of six or more diffraction peaks including at least four or more diffraction peaks on each of the (111), (200), (220), (311), (400), (331) azimuth planes, which are the main azimuths of cubic boron nitride, and two diffraction peaks on each of the (422) and (531) azimuth planes.

[0054] (X-ray diffraction measurement conditions) X-ray source: Synchrotron radiation Apparatus condition: Detector MYTHEN Energy: 18.000 keV (wavelength: 0.68881 Å) Camera length: 573 mm Measurement peaks: Six or more peaks including at least four or more diffraction peaks on each of the (111), (200), (220), (311), (400), (331) azimuth planes of cubic boron nitride, and two diffraction peaks on each of the (422) and (531) azimuth planes. However, when it is difficult to obtain a profile due to texture and orientation, the peaks with those Miller indices are excluded. Measurement condition: Ensure that there are at least five or more measurement points within the full width at half maximum. The basic configuration of this measurement is as described above. Since it is necessary to calculate the lattice constant with high precision, it is necessary to use at least synchrotron radiation. However, there is no problem as long as the X-ray diffraction profile of the above-mentioned azimuth planes can be obtained, and the present embodiment is not limited by the above-mentioned measurement conditions.

[0055] <Calculation method> The line profile obtained by the above X-ray diffraction measurement has the value of the diffraction angle 2θ shifted depending on the wavelength λ of the radiation used. Therefore, first, a standard sample for calculating the wavelength λ of the radiation is measured to calculate the wavelength λ. The procedure is as follows.

[0056] Regarding the sealed standard sample filled with the above cerium oxide, X-ray diffraction measurement is performed under the above X-ray diffraction measurement conditions to obtain the line profiles of seven diffraction peaks of the (111), (200), (220), (311), (222), (400), and (331) azimuthal planes of cerium oxide. The obtained line profiles are fitted with the sum of a pseudo-Voigt function and a background consisting of a linear function, and the central value 2θ0 of the pseudo-Voigt function is determined for each azimuthal plane. For each azimuthal plane (hkl), with the x-axis: h2 + k2 + l2 and the y-axis: sin2θ, after plotting seven points, the slope α of the straight line obtained by fitting with a linear function is obtained. Assuming the lattice constant a0 of cerium oxide is 0.541128 nm, the wavelength λ is calculated from the following formula (1). λ = 2a0√α (1)

[0057] After calculating the wavelength λ of the radiation, the lattice constant a of the cubic boron nitride particles encapsulated in the above sealed specimen is calculated as follows. Obtain the line profiles of six or more diffraction peaks including at least four or more diffraction peaks of the (111), (200), (220), (311), (400), and (331) azimuthal planes of cubic boron nitride, and two diffraction peaks of the (422) and (531) azimuthal planes. The line profiles are fitted with the sum of a pseudo-Voigt function and a background consisting of a linear function, and the central value 2θ0 of the pseudo-Voigt function is determined for each azimuthal plane. For each azimuthal plane (hkl), with the x-axis: h2 + k2 + l2 and the y-axis: sin2θ, after plotting, the slope β of the straight line obtained by fitting with a linear function is obtained. As the lattice constant a of the specimen, the lattice constant a of the cubic boron nitride particles encapsulated in the specimen is calculated from the following formula (2). a = λ / (2√β) (2)

[0058] In the same sample, even when the lattice constant of cBN particles in the cBN sintered body was measured and calculated multiple times according to the above measurement method and calculation method, it was confirmed that the obtained lattice constants were the same.

[0059] <Composition> In the cubic boron nitride sintered body of the present embodiment, the cubic boron nitride particles contain cubic boron nitride as a main component. Here, the fact that the cubic boron nitride particles contain cubic boron nitride as a main component means that the content rate of cubic boron nitride in the cubic boron nitride particles is 99% by mass or more. The content rate of components other than cubic boron nitride in the cubic boron nitride sintered body of the present embodiment is preferably 1% by mass or less, more preferably 0.5% by mass or less, and still more preferably 0.2% by mass or less. Examples of components other than cubic boron nitride include silicon, oxygen, lithium, magnesium, calcium, and the like.

[0060] The content rate of components other than cubic boron nitride (such as silicon, lithium, magnesium, calcium, etc.) in the cubic boron nitride particles can be measured by high-frequency inductively coupled plasma optical emission spectrometry (ICP method). Specifically, it can be measured by the same method as the method for measuring the silicon content rate described later.

[0061] The oxygen content rate of the cubic boron nitride particles is measured by gas analysis (measurement device: "EMGA-920" manufactured by Horiba, Ltd.).

[0062] ≪Silicon content rate≫ In the cubic boron nitride sintered body of the present embodiment, the silicon content rate of the cubic boron nitride particles is 0.02% by mass or less. According to this, the thermal conductivity of the cBN particles is increased. Therefore, in the cBN sintered body containing the cBN particles, the occurrence of crater wear caused by cutting heat generated during cutting and the occurrence of defects caused by the development of craters are suppressed, and the tool life is improved.

[0063] From the perspective of improving thermal conductivity, the upper limit of the silicon content in cBN particles is 0.02% by mass or less, preferably 0.01% by mass or less, and more preferably 0.001% by mass or less. Since it is preferable that the silicon content in cBN particles is as small as possible, the lower limit is not particularly limited. The lower limit of the silicon content in cBN particles can be, for example, 0% by mass or more. The silicon content in cBN particles is preferably 0% by mass or more and 0.02% by mass or less, more preferably 0% by mass or more and 0.01% by mass or less, and still more preferably 0% by mass or more and 0.001% by mass or less. cBN particles can be produced by adding a catalyst (Li, Ca, Mg, and their nitrides, borides, and boron nitrides) to hexagonal boron nitride powder and then performing heat and pressure treatment. At this time, Si is added in addition to the catalyst to promote the growth of cBN particles. Therefore, silicon may be contained in cBN particles as an inevitable impurity. Considering this point, the lower limit of the silicon content in cBN particles can be, for example, more than 0% by mass. The silicon content in cBN particles is preferably more than 0% by mass and 0.02% by mass or less, more preferably more than 0% by mass and 0.01% by mass or less, and still more preferably more than 0% by mass and 0.001% by mass or less.

[0064] The method for measuring the silicon content in cubic boron nitride particles is as follows. The cubic boron nitride sintered body is immersed in hydrofluoric acid (hydrofluoric acid (concentration: 60% by mass): nitric acid (concentration: 70% by mass) = 5:5 (volume ratio)) in a pressure vessel. As a result, all the binder is dissolved in hydrofluoric acid, and only cBN particles remain. After dissolving these cBN particles by the molten salt method, high-frequency inductively coupled plasma optical emission spectrometry (ICP method) (measurement device: Thermo Fisher iCAP6500) is performed to quantitatively measure the silicon content in cBN particles.

[0065] (Median diameter d50) The median diameter d50 of the equivalent circle diameter of the cubic boron nitride particles contained in the cubic boron nitride sintered body of the present embodiment (hereinafter, also referred to as "median diameter d50") is not particularly limited. For example, it is preferably 1 nm or more and 15000 nm or less, more preferably 10 nm or more and 12000 nm or less, and still more preferably 100 nm or more and 10000 nm or less. According to this, a tool using the cubic boron nitride sintered body can have a long tool life.

[0066] In this specification, the median diameter d50 of the equivalent circle diameter of cubic boron nitride particles (the equivalent circle diameter at which the cumulative frequency based on the number reaches 50%) is measured by the following method. In the same procedure as the method for measuring the content rate of cubic boron nitride particles in the above cubic boron nitride sintered body, binarization processing is performed on the reflection electron image of the cross section of the cubic boron nitride sintered body to extract the cubic boron nitride particles. The observation magnification is set to 5000 times. A measurement region (15 μm × 20 μm) is set in the image after binarization processing. In this measurement region, using the above image analysis software, the distribution of the equivalent circle diameter of each cubic boron nitride particle is calculated. From the distribution of the equivalent circle diameter of the cubic boron nitride particles, the median diameter d50 of the equivalent circle diameter of the cubic boron nitride particles in this measurement field of view is calculated. The measurement of the median diameter d50 of the equivalent circle diameter is performed in five different measurement regions. The average of the measured values in the five measurement regions is taken as the median diameter d50 of the equivalent circle diameter of the cubic boron nitride particles in the cubic boron nitride sintered body of this embodiment.

[0067] As long as the applicant has measured, as long as the median diameter d50 of the cubic boron nitride particles is measured in the same sample, even if the calculation is performed multiple times by changing the selection location of the measurement field of view in the cubic boron nitride sintered body, it has been confirmed that there is almost no variation in the measurement results and it is not arbitrary even if the measurement field of view is set arbitrarily.

[0068] ≪Binder≫ The cBN sintered body of this embodiment can contain a binder. The binder serves to make it possible to sinter cBN particles, which are difficult-to-sinter materials, at industrial-level pressure and temperature. Also, since its reactivity with iron is lower than that of cBN, it adds the function of suppressing chemical wear and thermal wear, particularly in the cutting of high-hardness hardened steel. Further, when the cBN sintered body contains a binder, the wear resistance and chipping resistance in the high-efficiency machining of high-hardness hardened steel are improved.

[0069] In the cBN sintered body of the present embodiment, the binder contains at least one element selected from the group consisting of Group 4 elements, Group 5 elements, Group 6 elements, aluminum, silicon, iron, cobalt, and nickel in the periodic table, and at least one element selected from the group consisting of carbon, nitrogen, boron, and oxygen. That is, the binder contains at least one selected from the group consisting of the above compounds and solid solutions of the above compounds. The binder has a high binding force to cBN particles. Therefore, the cubic boron nitride sintered body has excellent chipping resistance, and the life of a tool using the cubic boron nitride sintered body is prolonged.

[0070] In this specification, the Group 4 elements in the periodic table include titanium (Ti), zirconium (Zr), and hafnium (Hf). The Group 5 elements in the periodic table include vanadium (V), niobium (Nb), and tantalum (Ta). The Group 6 elements in the periodic table include chromium (Cr), molybdenum (Mo), and tungsten (W). Hereinafter, the elements contained in the Group 4 elements, Group 5 elements, Group 6 elements, aluminum, silicon, iron, cobalt, and nickel in the periodic table are also referred to as "first elements".

[0071] Examples of the compound (carbide) containing the above first element and carbon include titanium carbide (TiC), zirconium carbide (ZrC), hafnium carbide (HfC), vanadium carbide (VC), niobium carbide (NbC), tantalum carbide (TaC), chromium carbide (Cr3C2), molybdenum carbide (MoC), tungsten carbide (WC), silicon carbide (SiC), tungsten-cobalt carbide (W2Co3C).

[0072] Examples of the compound (nitride) containing the above-described first element and nitrogen include titanium nitride (TiN), zirconium nitride (ZrN), hafnium nitride (HfN), vanadium nitride (VN), niobium nitride (NbN), tantalum nitride (TaN), chromium nitride (Cr2N), molybdenum nitride (MoN), tungsten nitride (WN), aluminum nitride (AlN), silicon nitride (Si3N4), cobalt nitride (CoN), nickel nitride (NiN), titanium zirconium nitride (TiZrN), titanium hafnium nitride (TiHfN), titanium vanadium nitride (TiVN), titanium niobium nitride (TiNbN), titanium tantalum nitride (TiTaN), titanium chromium nitride (TiCrN), titanium molybdenum nitride (TiMoN), titanium tungsten nitride (TiWN), titanium aluminum nitride (TiAlN, Ti2AlN, Ti3AlN), zirconium hafnium nitride (ZrHfN), zirconium vanadium nitride (ZrVN), zirconium niobium nitride (ZrNbN), zirconium tantalum nitride (ZrTaN), zirconium chromium nitride (ZrCrN), zirconium molybdenum nitride (ZrMoN), zirconium tungsten nitride (ZrWN), hafnium vanadium nitride (HfVN), hafnium niobium nitride (HfNbN), hafnium tantalum nitride (HfTaN), hafnium chromium nitride (HfCrN), hafnium molybdenum nitride (HfMoN), hafnium tungsten nitride (HfWN), vanadium niobium nitride (VNbN), vanadium tantalum nitride (VTaN), vanadium chromium nitride (VCrN), vanadium molybdenum nitride (VMoN), vanadium tungsten nitride (VWN), niobium tantalum nitride (NbTaN), niobium chromium nitride (NbCrN), niobium molybdenum nitride (NbMoN), niobium tungsten nitride (NbWN), tantalum chromium nitride (TaCrN), tantalum molybdenum nitride (TaMoN), tantalum tungsten nitride (TaWN), chromium molybdenum nitride (CrMoN), chromium tungsten nitride (CrWN), molybdenum chromium nitride (MoCrN).

[0073] Examples of the compound (boride) containing the above-described first element and boron include titanium boride (TiB2), zirconium boride (ZrB2), hafnium boride (HfB2), vanadium boride (VB2), niobium boride (NbB2), tantalum boride (TaB2), chromium boride (CrB), molybdenum boride (MoB), tungsten boride (WB), aluminum boride (AlB2), cobalt boride (Co2B), and nickel boride (Ni2B).

[0074] Examples of the compound (oxide) containing the above-described first element and oxygen include titanium oxide (TiO2), zirconium oxide (ZrO2), hafnium oxide (HfO2), vanadium pentoxide (V2O5), niobium pentoxide (Nb2O5), tantalum pentoxide (Ta2O5), chromium oxide (Cr2O3), molybdenum oxide (MoO3), tungsten oxide (WO3), aluminum oxide (Al2O3), silicon oxide (SiO2), cobalt oxide (CoO), and nickel oxide (NiO).

[0075] Examples of the compound (carbonitride) containing the above-described first element, carbon, and nitrogen include titanium carbonitride (TiCN), zirconium carbonitride (ZrCN), hafnium carbonitride (HfCN), titanium niobium carbonitride (TiNbCN), titanium zirconium carbonitride (TiZrCN), titanium hafnium carbonitride (TiHfCN), titanium tantalum carbonitride (TiTaCN), and titanium chromium carbonitride (TiCrCN).

[0076] Examples of the compound (oxynitride) composed of the above-described first element, oxygen, and nitrogen include titanium oxynitride (TiON), zirconium oxynitride (ZrON), hafnium oxynitride (HfON), vanadium oxynitride (VON), niobium oxynitride (NbON), tantalum oxynitride (TaON), chromium oxynitride (CrON), molybdenum oxynitride (MoON), tungsten oxynitride (WON), aluminum oxynitride (AlON), and silicon oxynitride (SiON).

[0077] The solid solution of the above compound means a state in which two or more kinds of compounds are dissolved in each other's crystal structures, and includes interstitial solid solutions and substitutional solid solutions.

[0078] One kind of the above compound may be used, or two or more kinds may be used in combination.

[0079] In addition to the above compound, the binder may contain other components. Examples of the elements constituting the other components include manganese (Mn) and rhenium (Re).

[0080] The lower limit of the total content ratio of the above compound and the solid solution of the above compound in the binder is preferably 50% by volume or more, more preferably 60% by volume or more, and still more preferably 70% by volume or more. Since the higher the total content ratio of the above compound and the solid solution of the above compound in the binder, the better, it is not particularly limited, and for example, it can be 100% by volume or less. The total content ratio of the above compound and the solid solution of the above compound in the binder is preferably 50% by volume or more and 100% by volume or less, more preferably 60% by volume or more and 100% by volume or less, and still more preferably 70% by volume or more and 100% by volume or less.

[0081] The composition of the binder contained in the cBN sintered body can be specified by XRD (X-ray Diffraction).

[0082] The total content ratio of the above compound and the solid solution of the above compound in the binder is measured by the RIR method (Reference Intensity Ratio) using XRD.

[0083] <Use> The cubic boron nitride sintered body of this embodiment is preferably used for cutting tools, wear-resistant tools, grinding tools, etc.

[0084] The cutting tools, wear-resistant tools, and grinding tools using the cubic boron nitride sintered body of the present disclosure may each be entirely composed of the cubic boron nitride sintered body, or only a part thereof (for example, at least the cutting edge portion in the case of a cutting tool) may be composed of the cubic boron nitride sintered body. Further, a coating film may be formed on the surface of each tool.

[0085] Examples of cutting tools include drills, end mills, indexable cutting inserts for drills, indexable cutting inserts for end mills, indexable cutting inserts for milling, indexable cutting inserts for turning, hacksaws, tooth cutting tools, reamers, taps, cutting bits, and the like.

[0086] Examples of wear-resistant tools include dies, scribers, scribing wheels, dressers, and the like. Examples of grinding tools include grinding wheels and the like.

[0087] [Embodiment 2: Method for manufacturing cubic boron nitride sintered body] The cubic boron nitride sintered body of the present embodiment can be produced, for example, by the following method.

[0088] ≪Preparation of cubic boron nitride powder≫ The cubic boron nitride powder (hereinafter also referred to as cBN powder) is the raw material powder of the cBN particles contained in the cBN sintered body. The cBN powder may be produced by adding a catalyst (Li, Ca, Mg, and their nitrides, borides, boron nitrides) to hexagonal boron nitride powder and then performing heat treatment under pressure, or commercially available cBN powder may be prepared. The d50 (average particle size) of the cBN powder is not particularly limited, and for example, it can be 0.1 to 12.0 μm.

[0089] First, electron beam irradiation is performed on the above cBN powder. The conditions for electron beam irradiation can be, for example, an irradiation energy of 25 to 30 MeV and an irradiation time of 10 to 24 hours.

[0090] The cBN powder after electron beam irradiation is subjected to pressure heat treatment. The pressure heat treatment can be carried out using an ultra-high pressure and high temperature generating device. The ultra-high pressure and high temperature generating device can use a belt type, a multi-anvil type, a cubic type, etc. according to the desired generated pressure range. The pressure in the pressure heat treatment can be 5 to 15 GPa, the temperature can be 1000 to 2000 °C, and the holding time can be 1 to 60 minutes.

[0091] By performing the above electron beam irradiation and pressure heat treatment, the lattice constant of the cBN particles is reduced to 3.6161 Å or less.

[0092] Next, the cBN powder after the pressure heat treatment is heat-treated at an oxygen partial pressure of 1×10 -29 atm or less and at 800 to 1300 °C for 10 to 60 minutes (hereinafter, this step is also referred to as "heat treatment under low oxygen"). Thereby, the silicon content rate in the cBN particles can be reduced.

[0093] In the above, an example in which the pressure heat treatment and the heat treatment under low oxygen are performed in the above order after the electron beam irradiation is shown, but the order of the pressure heat treatment and the heat treatment under low oxygen is not limited to the above order. After the electron beam irradiation, the heat treatment under low oxygen may be performed, and then the pressure heat treatment may be performed.

[0094] ≪Preparation of Binder Raw Material Powder≫ When the cubic boron nitride sintered body contains a binder, a binder raw material powder is prepared. The binder raw material powder is the raw material powder of the binder contained in the cBN sintered body. The binder raw material powder can contain a compound composed of at least one element selected from the group consisting of group 4 elements, group 5 elements, group 6 elements, aluminum, silicon, iron, cobalt and nickel in the periodic table and at least one element selected from the group consisting of carbon, nitrogen, boron and oxygen.

[0095] The raw material powder of the binder can be prepared, for example, as follows. Mix TiN and Al, and heat-treat them in a vacuum at 1200 °C for 30 minutes to obtain a compound. Crush the compound to produce the raw material powder of the binder. In the X-ray diffraction measurement (XRD), peaks of TiN, Ti2AlN, TiAl3, etc. are confirmed in the raw material powder of the binder.

[0096] Note that the mixing and crushing methods of each powder are not particularly limited, but from the viewpoint of efficient and uniform mixing, mixing and crushing with media such as balls, and jet mill mixing and crushing are preferable. Each mixing and crushing method may be wet or dry.

[0097] <<Mixing step>> When the cubic boron nitride sintered body contains a binder, the cBN powder prepared above and the raw material powder of the binder are mixed using wet ball mill mixing with ethanol, acetone, etc. as a solvent to produce a mixed powder. The solvent is removed by natural drying after mixing. Thereafter, by performing heat treatment, impurities such as moisture adsorbed on the surface of the mixed powder are volatilized to clean the surface of the mixed powder.

[0098] <<Sintering step>> When the cubic boron nitride sintered body contains a binder, the above mixed powder is filled in a Ta (tantalum) container in contact with a WC-6%Co cemented carbide disk and vacuum-sealed. When the cubic boron nitride sintered body consists only of cubic boron nitride particles, the cBN powder prepared above is filled in a Ta (tantalum) container in contact with a WC-6%Co cemented carbide disk and vacuum-sealed. The vacuum-sealed mixed powder or cBN powder is held under the conditions of 3 to 12 GPa and 1100 to 2200 °C for 5 to 30 minutes using a belt-type ultrahigh pressure and high temperature generator to be sintered. Thereby, the cubic boron nitride sintered body of the present embodiment is produced.

[0099] [Appendix 1] The cubic boron nitride sintered body of the present disclosure preferably consists of 35% by volume or more and 100% by volume or less of cubic boron nitride particles and 0% by volume or more and 65% by volume or less of a binder. The cubic boron nitride sintered body of the present disclosure preferably comprises cubic boron nitride particles in an amount of 35% by volume or more and less than 100% by volume, and a binder in an amount of more than 0% by volume and 65% by volume or less. The cubic boron nitride sintered body of the present disclosure preferably comprises cubic boron nitride particles in an amount of 35% by volume or more and less than 98% by volume, and a binder in an amount of more than 2% by volume and 65% by volume or less. The cubic boron nitride sintered body of the present disclosure preferably comprises cubic boron nitride particles in an amount of 40% by volume or more and 85% by volume or less, and a binder in an amount of 15% by volume or more and 60% by volume or less. The cubic boron nitride sintered body of the present disclosure preferably comprises cubic boron nitride particles in an amount of 45% by volume or more and 80% by volume or less, and a binder in an amount of 20% by volume or more and 55% by volume or less. The cubic boron nitride sintered body of the present disclosure preferably consists of cubic boron nitride particles.

[0100] [Appendix 2] The cubic boron nitride sintered body of the present disclosure comprises cubic boron nitride particles, a binder, and inevitable impurities, and preferably contains cubic boron nitride particles in an amount of 35% by volume or more and 100% by volume or less, and a binder in an amount of 0% by volume or more and 65% by volume or less. The cubic boron nitride sintered body of the present disclosure comprises cubic boron nitride particles, a binder, and inevitable impurities, and preferably contains cubic boron nitride particles in an amount of 35% by volume or more and less than 100% by volume, and a binder in an amount of more than 0% by volume and 65% by volume or less. The cubic boron nitride sintered body of the present disclosure comprises cubic boron nitride particles, a binder, and inevitable impurities, and preferably consists of cubic boron nitride particles in an amount of 35% by volume or more and less than 98% by volume, and a binder in an amount of more than 2% by volume and 65% by volume or less. The cubic boron nitride sintered body of the present disclosure comprises cubic boron nitride particles, a binder, and inevitable impurities, and preferably contains cubic boron nitride particles in an amount of 40% by volume or more and 85% by volume or less, and a binder in an amount of 15% by volume or more and 60% by volume or less. The cubic boron nitride sintered body of the present disclosure comprises cubic boron nitride particles, a binder, and inevitable impurities, and preferably contains cubic boron nitride particles in an amount of 45% by volume or more and 80% by volume or less, and a binder in an amount of 20% by volume or more and 55% by volume or less. The cubic boron nitride sintered body of the present disclosure preferably consists of cubic boron nitride particles and inevitable impurities.

[0101] [Appendix 3] In the cubic boron nitride sintered body of the present disclosure, the silicon content of the cubic boron nitride particles is preferably more than 0% by mass and 0.02% by mass or less. In the cubic boron nitride sintered body of the present disclosure, the silicon content of the cubic boron nitride particles is preferably more than 0% by mass and 0.01% by mass or less. In the cubic boron nitride sintered body of the present disclosure, the silicon content of the cubic boron nitride particles is preferably more than 0% by mass and 0.001% by mass or less.

Examples

[0102] The present embodiment will be described in more detail by way of examples. However, the present embodiment is not limited by these examples.

[0103] [Test 1] ≪Preparation of cubic boron nitride powder≫ Known cubic boron nitride powder (d50 (average particle size) 3.2 μm) was prepared. At least one of electron beam irradiation, pressure heat treatment, and heat treatment under low oxygen was performed on the cBN powder. When two or more of electron beam irradiation, pressure heat treatment, and heat treatment under low oxygen were performed, they were performed in the above order.

[0104] The conditions for electron beam irradiation are as shown in the columns of "Energy (MeV)" and "Time (hr)" of "Electron Beam Irradiation" in Table 1. For example, in Sample 1, the cBN powder was irradiated with an electron beam at an irradiation energy of 27 MeV for 15 hours. The conditions for pressure heat treatment are as shown in the columns of "Pressure (GPa)", "Temperature (°C)", and "Time (min)" of "Pressure Heat Treatment" in Table 1. For example, in Sample 1, the cBN powder was subjected to a pressure heat treatment at a pressure of 6 GPa and a temperature of 1400 °C for 30 minutes. The conditions for heat treatment under low oxygen are as shown in the columns of "Oxygen Partial Pressure", "Temperature (°C)", and "Time (min)" of "Heat Treatment under Low Oxygen" in Table 1. For example, in Sample 1, the cBN powder was subjected to a heat treatment at an oxygen partial pressure of 1×10 -30 atm and a temperature of 1000 °C for 30 minutes. Note that the description of "-" in Table 1 indicates that the corresponding process was not performed.

[0105] ≪Preparation of Binder Raw Material Powder≫ The binder raw material powder was prepared according to the following procedure.

[0106] <Samples 1 to 7, Samples 13 to 19, Samples 1-1 to 1-5, Samples 1-7 to 1-9> TiN powder and Al powder were mixed at a mass ratio of 85:15, heat-treated in a vacuum atmosphere at 1200 °C for 30 minutes, and then mixed and pulverized with a wet ball mill to obtain a binder raw material powder.

[0107] <Sample 8> TiCN powder and Al powder were mixed at a mass ratio of 85:15, heat-treated in a vacuum atmosphere at 1200 °C for 30 minutes, and then mixed and pulverized with a wet ball mill to obtain a binder raw material powder.

[0108] <Samples 9, 1-6> WC powder, Co powder, and Al powder were mixed at a mass ratio of 3:8:1, heat-treated in a vacuum atmosphere at 1200 °C for 30 minutes, and then mixed and pulverized with a wet ball mill to obtain a binder raw material powder.

[0109] <Sample 10> TiO2 powder, Nb2O5 powder and C powder were mixed at a mass ratio of 57.19:16.79:26.02 and heat-treated at 2100 °C for 60 minutes in a nitrogen atmosphere to synthesize a single-phase compound with a TiNbCN composition. The single-phase compound was ground to a particle size of 0.5 μm by a wet grinding method to obtain TiNbCN powder. TiNbCN powder and Al powder were mixed at a mass ratio of 85:15, heat-treated at 1200 °C for 30 minutes in a vacuum atmosphere, and then mixed and ground by a wet ball mill to obtain a binder raw material powder.

[0110] <Sample 11> TiO2 powder, ZrO2 powder and C powder were mixed at a mass ratio of 58.35:15.88:25.77 and heat-treated at 2100 °C for 60 minutes in a nitrogen atmosphere to synthesize a single-phase compound with a TiZrCN composition. The single-phase compound was ground to a particle size of 0.5 μm by a wet grinding method to obtain TiZrCN powder. TiZrCN powder and Al powder were mixed at a mass ratio of 85:15, heat-treated at 1200 °C for 30 minutes in a vacuum atmosphere, and then mixed and ground by a wet ball mill to obtain a binder raw material powder.

[0111] <Sample 12> TiO2 powder, HfO2 powder and C powder were mixed at a mass ratio of 52.45:24.38:23.17 and heat-treated at 2100 °C for 60 minutes in a nitrogen atmosphere to synthesize a single-phase compound with a TiHfCN composition. The single-phase compound was ground to a particle size of 0.5 μm by a wet grinding method to obtain TiHfCN powder. TiHfCN powder and Al powder were mixed at a mass ratio of 85:15, heat-treated at 1200 °C for 30 minutes in a vacuum atmosphere, and then mixed and ground by a wet ball mill to obtain a binder raw material powder.

[0112] <Sample 20> TiO2 powder, Ta2O5 powder and C powder were mixed at a mass ratio of 51.47:25.12:23.42 and heat-treated at 2100 °C for 60 minutes in a nitrogen atmosphere to synthesize a single-phase compound with a TiTaCN composition. The single-phase compound was ground to a particle size of 0.5 μm by a wet grinding method to obtain TiTaCN powder. TiTaCN powder and Al powder were mixed at a mass ratio of 85:15, heat-treated at 1200 °C for 30 minutes in a vacuum atmosphere, and then mixed and ground by a wet ball mill to obtain a binder raw material powder.

[0113] <Sample 21> TiO2 powder, Cr2O3 powder and C powder were mixed at a mass ratio of 62.64:10.51:26.84 and heat-treated at 2100 °C for 60 minutes in a nitrogen atmosphere to synthesize a single-phase compound with a TiCrCN composition. The single-phase compound was ground to a particle size of 0.5 μm by a wet grinding method to obtain TiCrCN powder. TiCrCN powder and Al powder were mixed at a mass ratio of 85:15, heat-treated at 1200 °C for 30 minutes in a vacuum atmosphere, and then mixed and ground by a wet ball mill to obtain a binder raw material powder.

[0114] <Sample 22> WC powder, Co powder and Al powder were prepared at a mass ratio of 3:8:1. Zr powder was added to WC powder, Co powder and Al powder so that the total amount was 5% by mass, and the mixture was heat-treated at 1200 °C for 30 minutes in a vacuum, and then mixed and ground by a wet ball mill to produce a binder raw material powder containing WC, Co, Al and Zr.

[0115] <Sample 23> When producing the binder raw material powder, a cBN sintered body was produced in the same manner as in Sample 22, except that Ni powder and Nb powder were added instead of Zr powder. The mass ratio of Ni powder to Nb powder was Ni:Nb = 1:1.

[0116] <Sample 24> When producing the binder raw material powder, Zr powder was not added. When mixing the cBN powder and the binder powder, a cBN sintered body was produced in the same manner as in Sample 22, except that CrN powder was added. The addition amount of the CrN powder was adjusted so that the content ratio with respect to the entire binder was 5% by mass. The CrN powder was obtained by treating Cr2N (manufactured by Nippon Shinku Kinzoku Co., Ltd.) at 300 kPa and 900 °C for 3 hours in a nitrogen atmosphere.

[0117] <Sample 25> The binder raw material powder was not used. In the sintering process described below, the cBN powder was filled in a Ta (tantalum) container in a state sandwiched between Al plates and sintered.

[0118] ≪Mixing process≫ In the sample using the binder raw material powder, the cBN powder that had undergone at least one of the above electron beam irradiation, pressure heat treatment, and heat treatment under low oxygen and the binder raw material powder were mixed, and uniformly mixed by the wet ball milling method using ethanol to obtain a mixed powder. Then, degassing treatment was performed at 900 °C under vacuum to remove impurities such as surface moisture. The mixing ratio of the cBN powder and the binder raw material powder when producing the mixed powder was adjusted so that the ratio (volume %) of the cBN particles and the binder in the cubic boron nitride sintered body was the ratio described in the columns of "cBN particles (volume %)" and "binder (volume %)" of "cBN sintered body" in Table 2.

[0119] ≪Sintering process≫ Next, in the sample using the binder raw material powder, the mixed powder was filled in a Ta (tantalum) container in a state in contact with a WC-6%Co cemented carbide disk and vacuum sealed. The vacuum-sealed mixed powder was pressurized to 7 GPa at a pressure increase rate of 0.4 GPa / min using a belt-type ultrahigh pressure and high temperature generating device, and sintered by holding for 20 minutes under the conditions of 7 GPa and 1700 °C to obtain a cBN sintered body for each sample. In Sample 25 that did not use the binder raw material powder, the cBN powder was filled in a Ta (tantalum) container in a state sandwiched between Al plates and sintered to obtain a cBN sintered body.

[0120]

Table 1

[0121] ≪Evaluation≫ <Composition of cBN Sintered Body> The content rates (volume %) of cBN particles and the binder in the cBN sintered body were measured. Since the specific measurement method is the same as the method described in Embodiment 1, the description thereof will not be repeated. In each sample, the content rate (volume %) of cBN particles in the cBN sintered body is shown in the column of "cBN particles (volume %)" in "cBN sintered body" of Table 2, and the content rate (volume %) of the binder is shown in the column of "binder (volume %)" in "cBN sintered body" of Table 2.

[0122] <Composition of Binder> The composition of the binder in the cBN sintered body was measured. Since the specific measurement method is the same as the method described in Embodiment 1, the description thereof will not be repeated. The results are shown in the column of "binder" in "cBN sintered body" of Table 2. In all samples, the total content rate of the compounds described in the "binder" column of Table 2 in the binder was 50 volume % or more.

[0123] <Lattice Constant of cBN Particles> The lattice constant of cBN particles in the cBN sintered body was measured. Since the specific measurement method is the same as the method described in Embodiment 1, the description thereof will not be repeated. The results are shown in the column of "lattice constant of cBN particles (Å)" in "cBN sintered body" of Table 2.

[0124] <Silicon Content Rate of cBN Particles> The silicon content rate of cBN particles in the cBN sintered body was measured. Since the specific measurement method is the same as the method described in Embodiment 1, the description thereof will not be repeated. The results are shown in the column of "Si content rate of cBN particles (mass %)" in "cBN sintered body" of Table 2. In Table 2, the notation "<0.001" means that the silicon content rate is below the detection limit.

[0125] <Particle Size of cBN Particles> The median diameter d50 of the equivalent circle diameter of cBN particles in the cBN sintered body was measured. Since the specific measurement method is the same as the method described in Embodiment 1, the description thereof will not be repeated. In all samples, the median diameter d50 of the equivalent circle diameter of cBN particles was in the range of 1 nm or more and 15,000 nm or less.

[0126] <Cutting test> Using the cBN sintered body of each sample, a cutting tool (substrate shape: CNGA120408) was produced. Using this, a cutting test was carried out under the following cutting conditions. The following cutting conditions correspond to high-speed and high-efficiency machining of quenched steel. Cutting speed: 200 m / min. Feed rate: 0.2 mm / rev. Depth of cut: 0.2 mm Coolant: DRY Cutting method: Intermittent cutting Lathe: LB400 (manufactured by Okuma Corporation) Workpiece material: Quenched steel (SCM415 V-groove, hardness HRC60) Evaluation method: The cutting edge was observed every 0.5 km to confirm the presence or absence of cutting edge wear. The cutting distance at the time when a wear of 0.2 mm or more occurred was measured, and this cutting distance was defined as the tool life of the cutting tool. The results are shown in the column of "Tool life (km)" in Table 1.

[0127]

Table 2

[0128] <Discussion> Samples 1 to 25 correspond to examples, and samples 1-1 to 1-9 correspond to comparative examples. It was confirmed that Samples 1 to 25 (examples) had a longer tool life in high-efficiency machining than Samples 1-1 to 1-9 (comparative examples).

[0129] [Test 2] ≪Preparation of cubic boron nitride powder≫ A well-known cubic boron nitride powder (d50 (average particle size) 3.2 μm) was prepared. At least one of electron beam irradiation, pressure heat treatment, and heat treatment under low oxygen was performed on the cBN powder. When two or more of electron beam irradiation, pressure heat treatment, and heat treatment under low oxygen were performed, they were performed in the above order.

[0130] The conditions for electron beam irradiation are as shown in the columns of "Energy (MeV)" and "Time (hr)" of "Electron Beam Irradiation" in Table 3. The conditions for pressure heat treatment are as shown in the columns of "Pressure (GPa)", "Temperature (°C)", and "Time (min)" of "Pressure Heat Treatment" in Table 3. The conditions for heat treatment under low oxygen are as shown in the columns of "Oxygen Partial Pressure", "Temperature (°C)", and "Time (min)" of "Heat Treatment under Low Oxygen" in Table 3. Note that the description of "-" in Table 3 indicates that the corresponding process was not performed.

[0131] ≪Preparation of Binder Raw Material Powder≫ The binder raw material powder was prepared by the following procedure.

[0132] <Samples 2-1 to 2-7, Samples 2-9 to 2-18, Sample 2-29, Sample 2-30> WC powder, Co powder, and Al powder were mixed at a mass ratio of 3:8:1, heat-treated at 1200 °C for 30 minutes in a vacuum atmosphere, and then mixed and pulverized with a wet ball mill to obtain a binder raw material powder.

[0133] <Samples 2-19 to 2-27> For Samples 2-19 to 2-27, WC powder, Co powder, Al powder, and metal element powder were mixed at a mass ratio of 3:5:1:3, heat-treated at 1200 °C for 30 minutes in a vacuum atmosphere, and then mixed and pulverized with a wet ball mill to obtain a binder raw material powder. The metal element powder used was Cr powder for Sample 2-19, Mo powder for Sample 2-20, V powder for Sample 2-21, Nb powder for Sample 2-22, Ta powder for Sample 2-23, Ti powder for Sample 2-24, Zr powder for Sample 2-25, Hf powder for Sample 2-26, and Si powder for Sample 2-27.

[0134] <Sample 2-28> For the binder of Specimen 2-28, without using binder raw material powder, Al metal plates were placed above and below the cBN particles in the sintering process, and Al was infiltrated into the cBN during sintering to obtain AlN and AlB₂ as reaction products. <<Mixing Process>> The cBN powder that had undergone at least one of the above electron beam irradiation, pressure heat treatment, and heat treatment under low oxygen was mixed with the binder raw material powder, and uniformly mixed by a wet ball milling method using ethanol to obtain a mixed powder. Then, degassing treatment was performed at 900 °C under vacuum to remove impurities such as surface moisture. The mixing ratio of the cBN powder and the binder raw material powder when preparing the mixed powder was adjusted so that in the cubic boron nitride sintered body, the ratios (volume %) of the cBN particles and the binder were the same as those described in the columns of "cBN particles (volume %)" and "Binder (volume %)" of "cBN Sintered Body" in Table 4.

[0135] <<Sintering Process>> Next, for the specimens using the binder raw material powder, the mixed powder was filled into a Ta (tantalum) container in contact with a WC-6%Co cemented carbide disk and vacuum sealed. The temperature of the vacuum sealing was 850 °C or higher. The vacuum-sealed mixed powder was pressurized to 6 GPa at a pressure increase rate of 0.2 GPa / min using a belt-type ultrahigh pressure and high temperature generating device, and sintered by holding at 6 GPa and 1300 °C for 30 minutes to obtain the cBN sintered body of each specimen.

[0136] For Specimen 2-28, it was filled with Al metal plates placed above and below the cBN particles, and sintered to obtain a cBN sintered body.

[0137] <Specimens 2-8, 2-31> For Specimens 2-8 and 2-31, the cBN powder was filled into a Ta (tantalum) container in contact with a WC-6%Co cemented carbide disk and vacuum sealed. The temperature of the vacuum sealing was 850 °C or higher. The vacuum-sealed mixed powder was pressurized to 12 GPa at a pressure increase rate of 0.2 GPa / min using a belt-type ultrahigh pressure and high temperature generating device, and sintered by holding at 12 GPa and 2000 °C for 30 minutes to obtain the cBN sintered body of each specimen.

[0138] [Table 3]

[0139] [Evaluation] [Composition of cBN Sintered Body] The content rates (volume %) of cBN particles and the binder in the cBN sintered body were measured. Since the specific measurement method is the same as the method described in Embodiment 1, the description thereof will not be repeated. In each sample, the content rate (volume %) of cBN particles in the cBN sintered body is shown in the column of "cBN particles (volume %)" in "cBN sintered body" in Table 4, and the content rate (volume %) of the binder is shown in the column of "binder (volume %)" in "cBN sintered body" in Table 4.

[0140] [Composition of Binder] The composition of the binder in the cBN sintered body was measured. Since the specific measurement method is the same as the method described in Embodiment 1, the description thereof will not be repeated. The results are shown in the column of "binder" in "cBN sintered body" in Table 4. In all samples, the total content rate of the compounds described in the "binder" column of Table 4 in the binder was 50 volume % or more.

[0141] [Lattice Constant of cBN Particles] The lattice constant of cBN particles in the cBN sintered body was measured. Since the specific measurement method is the same as the method described in Embodiment 1, the description thereof will not be repeated. The results are shown in the column of "lattice constant (Å) of cBN particles" in "cBN sintered body" in Table 4.

[0142] [Silicon Content Rate of cBN Particles] The silicon content rate of cBN particles in the cBN sintered body was measured. Since the specific measurement method is the same as the method described in Embodiment 1, the description thereof will not be repeated. The results are shown in the column of "Si content rate (mass %) of cBN particles" in "cBN sintered body" in Table 4. In Table 4, the notation of "<0.001" means that the silicon content rate is below the detection limit.

[0143] [Particle Size of cBN Particles] The median diameter d50 of the equivalent circle diameter of cBN particles in the cBN sintered body was measured. Since the specific measurement method is the same as that described in Embodiment 1, the description thereof will not be repeated. In all samples, the median diameter d50 of the equivalent circle diameter of cBN particles was in the range of 1 nm or more and 15,000 nm or less.

[0144] <Cutting Test> Using the cBN sintered body of each sample, a cutting tool (substrate shape: CNGA120408) was fabricated. Using this, a cutting test was carried out under the following cutting conditions. The following cutting conditions correspond to high-speed and high-efficiency machining of sintered alloys. Cutting speed: 180 m / min. Feed rate: 0.14 mm / rev. Depth of cut: 0.18 mm Coolant: DRY Cutting method: Face intermittent cutting Lathe: LB4000 (manufactured by Okuma Corporation) Workpiece material: Sprocket shape (face cutting of sintered alloy DM-50 (quenched) manufactured by Sumitomo Electric Hardmetal Corporation, HV440) Evaluation method: The cutting edge was observed every 0.5 km to confirm the presence or absence of cutting edge wear. The cutting distance at the time when a wear of 0.2 mm or more occurred was measured, and this cutting distance was defined as the tool life of the cutting tool. The results are shown in the column of "Tool life (km)" in Table 4.

[0145]

Table 4

[0146] <Discussion> Samples 2-1 to 2-12, Samples 2-18 to 2-28 correspond to Examples. Samples 2-13 to 2-17, Samples 2-29 to 2-31 correspond to Comparative Examples. Samples 2-1 to 2-12, Samples 2-18 to 2-28 (Examples) were confirmed to have a longer tool life in high-efficiency machining compared to Samples 2-13 to 2-17, Samples 2-29 to 2-31 (Comparative Examples).

[0147] Although the embodiments and examples of the present disclosure have been described as above, it has been planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples or to make various modifications thereto. The embodiments and examples disclosed this time should be considered illustrative in all respects and not restrictive. The scope of the present invention is shown not by the above-described embodiments and examples but by the claims, and it is intended that all modifications within the meaning and scope equivalent to the claims be included.

Claims

Claim 1 A cubic boron nitride sintered body for tools, comprising cubic boron nitride particles in an amount of 35% by volume or more and 100% by volume or less, a binder in an amount of 0% by volume or more and 65% by volume or less, and inevitable impurities, wherein the lattice constant of the cubic boron nitride particles is 3.6140 Å or more and 3.6161 Å or less, the silicon content of the cubic boron nitride particles is 0% by mass or more and 0.02% by mass or less, and the binder contains at least one compound composed of at least one element selected from the group consisting of Group 4 elements, Group 5 elements, Group 6 elements, aluminum, silicon, iron, cobalt, and nickel in the periodic table and at least one element selected from the group consisting of carbon, nitrogen, boron, and oxygen, and at least one selected from the group consisting of solid solutions of the compounds. A cubic boron nitride sintered body for tools. Claim 2 The cubic boron nitride sintered body for tools according to claim 1, wherein the lattice constant of the cubic boron nitride particles is 3.6142 Å or more and 3.6158 Å or less. Claim 3 The cubic boron nitride sintered body for tools according to claim 1 or claim 2, wherein the lattice constant of the cubic boron nitride particles is 3.6145 Å or more and 3.6155 Å or less. Claim 4 The cubic boron nitride sintered body for tools according to claim 1 or claim 2, wherein the silicon content of the cubic boron nitride particles is 0% by mass or more and 0.01% by mass or less. Claim 5 The cubic boron nitride sintered body for tools according to claim 4, wherein the silicon content of the cubic boron nitride particles is 0% by mass or more and 0.001% by mass or less. Claim 6 The cubic boron nitride sintered body for tools according to claim 1 or claim 2, wherein the content of the cubic boron nitride particles in the cubic boron nitride sintered body for tools is 40% by volume or more and 95% by volume or less.

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