Cubic boron nitride sintered body and tools

Abstract

The cubic boron nitride sintered body comprises 40% by volume or more and 80% by volume or less of cubic boron nitride particles and 20% by volume or more and 60% by volume or less of a binder phase, wherein the average particle size d of the cubic boron nitride particles is 0.1 μm or more and 3 μm or less, and the binder phase is at least one element selected from a second group consisting of a simple substance of one element selected from a first group consisting of Group 4 elements, Group 5 elements, Group 6 elements, and aluminum in the periodic table, an alloy consisting of two or more elements selected from the first group, and an intermetallic compound consisting of two or more elements selected from the first group, or at least one element selected from the first group and at least one element selected from a third group consisting of nitrogen, carbon, boron, and oxygen. and at least one selected from a fourth group consisting of a first compound consisting of a first compound represented by formula (I) and a solid solution derived from said first compound, wherein a coefficient of variation Z of the area ratio of said cubic boron nitride particles in a cross section of said cubic boron nitride sintered body is 0.25 or less, and said coefficient of variation Z is obtained by providing a total of 260 square unit areas, each of which has a side length twice the average grain size d of said cubic boron nitride particles, in an image obtained by binarizing a backscattered electron image obtained by imaging a cross section of said cubic boron nitride sintered body at 5000 times magnification using a scanning electron microscope, calculating a standard deviation of the area ratio of said cubic boron nitride particles in each of said unit areas and an average of said area ratios, and dividing said standard deviation by said average.

Description

[Technical field]

[0001] The present disclosure relates to cubic boron nitride sintered bodies and tools. [Background technology]

[0002] Cubic boron nitride sintered bodies have conventionally been used as materials for tools such as cutting tools (Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2000-44347 A [Patent Document 2] JP 2002-302732 A [Patent Document 3] JP 2013-234335 A Summary of the Invention

[0004] The cubic boron nitride sintered body of the present disclosure is a cubic boron nitride sintered body comprising 40% by volume or more and 80% by volume or less of cubic boron nitride particles and 20% by volume or more and 60% by volume or less of a binder phase, the cubic boron nitride particles having an average particle size d of 0.1 μm or more and 3 μm or less, the binder phase being at least one element selected from a second group consisting of a simple substance of one element selected from a first group consisting of Group 4 elements, Group 5 elements, Group 6 elements, and aluminum in the periodic table, an alloy consisting of two or more elements selected from the first group, and an intermetallic compound consisting of two or more elements selected from the first group, or at least one element selected from the first group and at least one element selected from a third group consisting of nitrogen, carbon, boron, and oxygen. and at least one kind selected from a fourth group consisting of a first compound consisting of at least one kind of element and a solid solution derived from the first compound, and a coefficient of variation Z of the area ratio of the cubic boron nitride particles in a cross section of the cubic boron nitride sintered body is 0.25 or less, and the coefficient of variation Z is obtained by providing a total of 260 square unit areas, each of which has a side length twice the average grain size d of the cubic boron nitride particles, in a binarized image of a backscattered electron image obtained by imaging the cross section of the cubic boron nitride sintered body at 5000 times magnification using a scanning electron microscope, calculating a standard deviation of the area ratio of the cubic boron nitride particles in each of the 260 unit areas and an average of the area ratios, and dividing the standard deviation by the average. [Brief description of the drawings]

[0005] [Figure 1] FIG. 1 is a conceptual diagram showing a total of 260 unit regions in an image (second image) obtained by binarizing a backscattered electron image (first image) of one cross section of a cubic boron nitride sintered body. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] [Problem that this disclosure aims to solve] In recent years, the demand for heavy interrupted cutting has been increasing. Therefore, even when used as a material for cutting tools for heavy interrupted cutting, there is a demand for cubic boron nitride sintered bodies that can extend the life of the tools.

[0007] Therefore, an object of the present disclosure is to provide a cubic boron nitride sintered body that enables a longer tool life, particularly when used as a material for a cutting tool for heavy interrupted cutting, and a tool including the cubic boron nitride sintered body.

[0008] [Effects of this disclosure] According to the present disclosure, it is possible to provide a cubic boron nitride sintered body that enables a longer tool life, particularly when used as a material for cutting tools for heavy interrupted cutting, and a tool including the cubic boron nitride sintered body.

[0009] [Description of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be listed and described. (1) A cubic boron nitride sintered body according to the present disclosure is a cubic boron nitride sintered body comprising 40% by volume or more and 80% by volume or less of cubic boron nitride particles and 20% by volume or more and 60% by volume or less of a binder phase, wherein the average particle size d of the cubic boron nitride particles is 0.1 μm or more and 3 μm or less, and the binder phase is at least one element selected from a second group consisting of a simple substance of one element selected from a first group consisting of Group 4 elements, Group 5 elements, Group 6 elements, and aluminum in the periodic table, an alloy consisting of two or more elements selected from the first group, and an intermetallic compound consisting of two or more elements selected from the first group, or at least one element selected from a third group consisting of at least one element selected from the first group and nitrogen, carbon, boron, and oxygen. and at least one selected from a fourth group consisting of a first compound consisting of one kind of element and a solid solution derived from the first compound, wherein a coefficient of variation Z of the area ratio of the cubic boron nitride particles in a cross section of the cubic boron nitride sintered body is 0.25 or less, and the coefficient of variation Z is obtained by providing a total of 260 square unit areas, each of which has a side length twice the average grain size d of the cubic boron nitride particles, in a binarized image of a backscattered electron image obtained by imaging the cross section of the cubic boron nitride sintered body at 5000 times magnification using a scanning electron microscope, calculating a standard deviation of the area ratio of the cubic boron nitride particles in each of the unit areas and an average of the area ratios, and dividing the standard deviation by the average.

[0010] According to the present disclosure, it is possible to provide a cubic boron nitride sintered body that enables a longer tool life, particularly when used as a material for a cutting tool for heavy interrupted cutting, and a tool including the cubic boron nitride sintered body.

[0011] (2) In the above (1), the average particle size d of the cubic boron nitride particles may be 0.1 μm or more and 2 μm or less. This makes it possible to provide a cubic boron nitride sintered body that can extend the tool life of a cutting tool, particularly when the cubic boron nitride sintered body is used as a material for a cutting tool for heavy interrupted cutting, and a tool including the cubic boron nitride sintered body.

[0012] (3) In the above (1) or (2), the content of the cubic boron nitride particles in the cubic boron nitride sintered body may be 60 volume % or more and 70 volume % or less, and the content of the binder phase in the cubic boron nitride sintered body may be 30 volume % or more and 40 volume % or less. This makes it possible to provide a cubic boron nitride sintered body that can further extend the tool life of a cutting tool, particularly when used as a material for a cutting tool for heavy interrupted cutting, and a tool including the cubic boron nitride sintered body.

[0013] (4) In any of the above (1) to (3), the binder phase may contain at least one selected from the group consisting of titanium nitride, titanium boride, aluminum nitride, and aluminum oxide. This makes it possible to provide a cubic boron nitride sintered body that can extend the tool life of a cutting tool, particularly when the cubic boron nitride sintered body is used as a material for a cutting tool for heavy interrupted cutting, and a tool including the cubic boron nitride sintered body.

[0014] (5) In any one of the above (1) to (4), the total content of the cubic boron nitride particles and the binder phase in the cubic boron nitride sintered body may be 99% by volume or more. This makes it possible to provide a cubic boron nitride sintered body that can extend the tool life of a cutting tool, particularly when the cubic boron nitride sintered body is used as a material for a cutting tool for heavy interrupted cutting, and a tool including the cubic boron nitride sintered body.

[0015] (6) A tool according to the present disclosure includes the cubic boron nitride sintered body according to any one of (1) to (5) above.

[0016] According to the present disclosure, it is possible to provide a tool including a cubic boron nitride sintered body that enables a longer tool life, particularly when used as a material for a cutting tool for heavy interrupted cutting.

[0017] [Details of the embodiment of the present disclosure] A specific example of a cubic boron nitride sintered body and a tool according to an embodiment of the present disclosure (hereinafter also referred to as the "present embodiment") will be described below with reference to the drawings. In the drawings of the present disclosure, the same reference symbols represent the same or corresponding parts. Furthermore, dimensional relationships such as length, width, thickness, and depth have been appropriately changed for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0018] In this disclosure, an expression in the form "A to B" means the upper and lower limits of a range (i.e., A or more and B or less). When no unit is specified for A and a unit is specified only for B, the unit of A and the unit of B are the same.

[0019] In the present disclosure, when a compound or the like is represented by a chemical formula, unless the atomic ratio is particularly limited, it is intended to include any conventionally known atomic ratio, and should not necessarily be limited to only those within the stoichiometric range.

[0020] [Embodiment 1: Cubic boron nitride sintered body] A cubic boron nitride sintered body according to an embodiment of the present disclosure will be described with reference to Fig. 1. Fig. 1 is a conceptual diagram showing a total of 260 unit regions in an image (second image) obtained by binarizing a backscattered electron image (first image) of one cross section of a cubic boron nitride sintered body.

[0021] One embodiment of the present disclosure (hereinafter, also referred to as "the present embodiment") is a cubic boron nitride sintered body comprising 40 volume % to 80 volume % of cubic boron nitride particles and 20 volume % to 60 volume % of a binder phase, the cubic boron nitride particles having an average particle size d of 0.1 μm to 3 μm, and the binder phase being at least one element selected from a second group consisting of a simple substance of one element selected from a first group consisting of Group 4 elements, Group 5 elements, Group 6 elements, and aluminum in the periodic table, an alloy consisting of two or more elements selected from the first group, and an intermetallic compound consisting of two or more elements selected from the first group, or a compound selected from a third group consisting of at least one element selected from the first group and nitrogen, carbon, boron, and oxygen. and at least one element selected from a fourth group consisting of a first compound consisting of at least one element represented by formula (I) and a solid solution derived from the first compound, and a coefficient of variation Z of the area ratio of the cubic boron nitride particles in a cross section of the cubic boron nitride sintered body is 0.25 or less, and the coefficient of variation Z is obtained by providing a total of 260 square unit regions R1, each of which has a side length twice the average grain size d of the cubic boron nitride particles, in a binarized image of a backscattered electron image obtained by imaging the cross section of the cubic boron nitride sintered body at 5000 times magnification using a scanning electron microscope, calculating a standard deviation of the area ratio of the cubic boron nitride particles in each of the unit regions R1 and an average of the area ratios, and dividing the standard deviation by the average.

[0022] According to the present disclosure, it is possible to provide a cubic boron nitride sintered body that enables a longer tool life, particularly when used as a material for cutting tools for heavy interrupted cutting, and a tool including the cubic boron nitride sintered body.The reasons for this are presumably as follows.

[0023] The cubic boron nitride sintered body of this embodiment is a cubic boron nitride sintered body comprising 40% by volume or more and 80% by volume or less of cubic boron nitride particles and 20% by volume or more and 60% by volume or less of a binder phase, the average particle size d of the cubic boron nitride particles is 0.1 μm or more and 3 μm or less, and the variation coefficient Z of the area ratio of the cubic boron nitride particles in the cross section of the cubic boron nitride sintered body is 0.25 or less. This makes it easier for the cubic boron nitride particles to be sufficiently uniformly dispersed in the cubic boron nitride sintered body. As a result, since "regions that are likely to become the starting point of defects due to the relatively large amount of binder phase" are unlikely to occur, the cubic boron nitride sintered body can have excellent strength. Therefore, the cubic boron nitride sintered body of this embodiment improves the chipping resistance of the tool and enables the tool to have a longer life, particularly when used as a material for cutting tools for heavy interrupted cutting.

[0024] <Composition of cubic boron nitride sintered body> The cubic boron nitride sintered body comprises cubic boron nitride particles of 40 volume % or more and 80 volume % or less. From the viewpoint of improving chipping resistance, the lower limit of the content of the cubic boron nitride particles is 40 volume % or more, may be 50 volume % or more, or may be 60 volume % or more. From the viewpoint of improving sinterability, the upper limit of the content of the cubic boron nitride particles is 80 volume % or less, may be 75 volume % or less, or may be 70 volume % or less. The content of the cubic boron nitride particles may be 50 volume % or more and 75 volume % or less, or may be 60 volume % or more and 70 volume % or less.

[0025] The cubic boron nitride sintered body has a binder phase of 20 volume % or more and 60 volume % or less. From the viewpoint of improving sinterability, the lower limit of the binder phase content is 20 volume % or more, may be 25 volume % or more, or may be 30 volume % or more. From the viewpoint of improving fracture resistance, the upper limit of the binder phase content of the cubic boron nitride sintered body is 60 volume % or less, may be 50 volume % or less, or may be 40 volume % or less. The binder phase content of the cubic boron nitride sintered body may be 25 volume % or more and 50 volume % or less, or may be 30 volume % or more and 40 volume % or less.

[0026] In a cubic boron nitride sintered body, the content [volume %] of cubic boron nitride particles and the content [volume %] of the binder phase can be confirmed by observing the structure of the cubic boron nitride sintered body using a field emission scanning electron microscope (FE-SEM). The specific measurement method is as follows.

[0027] An arbitrary position of the cubic boron nitride sintered body is cut by ion milling to expose a cross section of the cubic boron nitride sintered body, and the cross section is polished. For the ion milling, a "Cross Section Polisher" (CP) manufactured by JEOL is used, the acceleration voltage is 5.5 kV, the protrusion amount is 20 μm, and the processing time is 5 hours or more. An adhesive such as C paste may be used to fix the cubic boron nitride sintered body. When the cubic boron nitride sintered body is used as a part of a tool, a part of the cubic boron nitride sintered body is cut out with a diamond grinding wheel, electroplated wire, or the like, to expose a sample including a cross section of the cubic boron nitride sintered body.

[0028] Next, the cross section is photographed at 2,000 to 50,000 times magnification with an FE-SEM to obtain an SEM image. Next, a backscattered electron image is obtained by using a semiconductor backscattered electron detector for the SEM image under conditions of 1024 x 768 pixels and an accelerating voltage of 1.5 kV. In addition, the brightness contrast is adjusted so that in the backscattered electron image, the area where the cubic boron nitride particles exist becomes the darkest black area (60 or less in the range of 0 to 255), and the area where the bonding phase exists becomes a gray or white area (100 to 255 in the range of 0 to 255). If the electrostatic charge is large, a conductive coating of 2 to 10 nm in thickness may be applied to the cross section.

[0029] Next, the backscattered electron image is binarized using image analysis software (Mitani Shoji Co., Ltd.'s "WinROOF 2018") so that only cubic boron nitride particles are extracted. The binarization threshold varies depending on the contrast, so it is set for each image. From the binarized image, the area ratio of pixels originating from the dark field (pixels originating from cubic boron nitride particles) to the area of ​​the measurement field is calculated. By regarding the calculated area ratio as volume %, the content [volume %] of cubic boron nitride particles in the cubic boron nitride sintered body can be obtained. The fact that the pixels originating from the dark field are originating from cubic boron nitride particles can be confirmed by performing elemental analysis of the cubic boron nitride sintered body using an energy dispersive X-ray spectrometer (EDX device) attached to the SEM.

[0030] The content [volume %] of the binder phase in the cubic boron nitride sintered body can be obtained by calculating the area ratio of pixels originating from the bright field (pixels originating from the binder phase) to the area of ​​the measurement field from the binarized image. The fact that the pixels originating from the bright field are originating from the binder phase can be confirmed by performing elemental analysis of the cubic boron nitride sintered body using an EDX device attached to the SEM.

[0031] The above-mentioned area percentages of the cubic boron nitride particles and the binder phase are measured in five mutually non-overlapping measurement fields, and the average of the area percentages of the cubic boron nitride particles and the binder phase in the five measurement fields is calculated. In the present disclosure, the average of the area percentages of the cubic boron nitride particles in the five measurement fields corresponds to the content [volume %] of the cubic boron nitride particles in the cubic boron nitride sintered body. In the present disclosure, the average of the area percentages of the binder phase in the five measurement fields corresponds to the content [volume %] of the binder phase in the cubic boron nitride sintered body.

[0032] As far as the applicant has measured, it has been confirmed that there is almost no variation in the measurement results even when the content of cubic boron nitride particles and binder phase in a cubic boron nitride sintered body is measured multiple times by arbitrarily setting five measurement fields of view on the same sample and following the above procedure.

[0033] The total content of the cubic boron nitride particles and the binder phase of the cubic boron nitride sintered body may be 99% by volume or more. This allows the cubic boron nitride sintered body to have a structure in which the cubic boron nitride particles are sufficiently and uniformly dispersed, thereby further improving the strength of the cubic boron nitride sintered body. The upper limit of the total content may be 100% by volume or less.

[0034] The total content of cubic boron nitride particles and binder phase in a cubic boron nitride sintered body can be determined by calculating the sum of the content [volume %] of cubic boron nitride particles and the content [volume %] of the binder phase.

[0035] The cubic boron nitride sintered body may contain other phases in addition to the cubic boron nitride particles and the binder phase, as long as the effect of the present disclosure is not impaired. Examples of other phases include WC, W, etc. 2 CoB 2 Examples include:

[0036] <Cubic boron nitride particles> <Average particle size d of cubic boron nitride particles> The average particle size d of the cubic boron nitride particles is 0.1 μm or more and 3 μm or less. This makes it easier to disperse the cubic boron nitride particles sufficiently uniformly in the cubic boron nitride sintered body, and therefore the strength of the cubic boron nitride sintered body can be improved. The average particle size d of the cubic boron nitride particles may be 0.1 μm or more and 2 μm or less, or may be 0.1 μm or more and 1 μm or less.

[0037] In the present disclosure, the average particle size d of cubic boron nitride particles is measured by the following procedure. First, a second image is obtained by the same method as the measurement method of "variation coefficient Z of area ratio of cubic boron nitride particles" described later. Next, the second image is subjected to watershed processing using image analysis software "ImageJ" (product name) to identify the positions of the grain boundaries of the cubic boron nitride particles in the second image, and the arithmetic average of the circle equivalent diameters (Heywood diameter: equivalent circle diameter of equal area) of each cubic boron nitride particle is calculated. Here, the cubic boron nitride particles in the image include cubic boron nitride particles that are in contact with the edge of the image.

[0038] The above measurement is performed in five mutually non-overlapping measurement fields. The arithmetic mean of the average particle diameters of the cubic boron nitride particles in the five measurement fields is calculated. In the present disclosure, the arithmetic mean of the average particle diameters in the five measurement fields corresponds to the average particle diameter d of the cubic boron nitride particles.

[0039] As far as the applicant has measured, it has been confirmed that there is almost no variation in the measurement results even when five measurement fields are arbitrarily set for the same sample and the average particle size d of cubic boron nitride particles is measured multiple times according to the above procedure.

[0040] <Coefficient of variation Z of area ratio of cubic boron nitride particles> In the cross section of the cubic boron nitride sintered body, the variation coefficient Z of the area ratio of the cubic boron nitride particles is 0.25 or less. This can improve the strength of the cubic boron nitride sintered body. In the cross section of the cubic boron nitride sintered body, the upper limit of the variation coefficient Z of the area ratio of the cubic boron nitride particles may be 0.24 or less, 0.23 or less, or 0.22 or less. In the cross section of the cubic boron nitride sintered body, the lower limit of the variation coefficient Z of the area ratio of the cubic boron nitride particles is not particularly limited, but may be 0 or more, 0.1 or more, 0.20 or more, or 0.21 or more. In the cross section of the cubic boron nitride sintered body, the coefficient of variation Z of the area ratio of cubic boron nitride particles may be 0 or more and 0.25 or less, 0.1 or more and 0.24 or less, or 0.20 or more and 0.23 or less.

[0041] A method for determining the coefficient of variation Z of the area ratio of cubic boron nitride particles in the cross section of a cubic boron nitride sintered body will be described. First, a total of 260 square unit regions R1, each having a side length twice the average particle diameter d of the cubic boron nitride particles, are provided in a binarized image (second image) of a backscattered electron image (first image) obtained by photographing the cross section of a cubic boron nitride sintered body at 5000 times magnification with a scanning electron microscope (Fig. 1). Next, based on the total of 260 unit regions R1, the standard deviation of the area ratio of the cubic boron nitride particles in each of the unit regions R1 and the average (arithmetic mean) of the area ratio are calculated, and the coefficient of variation Z is obtained by dividing the standard deviation by the average (arithmetic mean). More specifically, the size of the backscattered electron image is 300 μm 2 The backscattered electron image is captured with a contrast that allows the cubic boron nitride particles and the binder phase to be clearly distinguished. The binarization process is performed by binarizing the cubic boron nitride particle regions and the other regions using a program written in Python. In one second image, the unit regions R1 are arranged continuously along the first direction and the direction perpendicular to the first direction. The number of unit regions R1 in one second image is the maximum number that can be provided in the second image. If the number of unit regions R1 in only one second image is less than 260, further unit regions R1 are provided in other second images so that the total number of unit regions R1 becomes 260. If there is a second image in which the number of unit regions R1 is left over, the number of unit regions R1 is adjusted to 260 by selecting any unit region R1 in the second image.

[0042] As far as the applicant has measured, it has been confirmed that there is almost no variation in the measurement results even when the measurement field of view is arbitrarily set for the same sample and the measurement of the coefficient of variation Z of the area ratio of cubic boron nitride particles is performed multiple times according to the above procedure.

[0043] ≪Binding phase≫ <Composition of the binder phase> The binder phase includes at least one selected from the second group consisting of a simple substance of one element selected from the first group consisting of group 4 elements, group 5 elements, group 6 elements, and aluminum in the periodic table, an alloy consisting of two or more elements selected from the first group, and an intermetallic compound consisting of two or more elements selected from the first group, or at least one selected from the fourth group consisting of a first compound consisting of at least one element selected from the first group and at least one element selected from the third group consisting of nitrogen, carbon, boron, and oxygen, and a solid solution derived from the first compound. This allows the binder phase to have excellent binding strength to cubic boron nitride particles, so that the cubic boron nitride sintered body of this embodiment can improve the chipping resistance of the tool even when used as a material for cutting tools for heavy interrupted cutting. The binder phase may include at least one selected from the group consisting of titanium nitride, titanium boride, aluminum nitride, and aluminum oxide. This can further improve the chipping resistance of the tool, especially when used as a material for cutting tools for heavy interrupted cutting. The binder phase may contain, as a main component, at least one selected from a second group consisting of a simple substance of one element selected from a first group consisting of Group 4 elements, Group 5 elements, Group 6 elements, and aluminum in the periodic table, an alloy consisting of two or more elements selected from the first group, and an intermetallic compound consisting of two or more elements selected from the first group, or at least one selected from a fourth group consisting of a first compound consisting of at least one element selected from the first group and at least one element selected from a third group consisting of nitrogen, carbon, boron, and oxygen, and a solid solution derived from the first compound. Here, "contains as a main component" means that the total content of these components in the binder phase is 90 volume % or more.

[0044] In a cubic boron nitride sintered body, the composition of the binder phase can be identified by X-ray diffraction measurement (XRD).

[0045] [Embodiment 2: Manufacturing method of cubic boron nitride sintered body] The method for producing a cubic boron nitride sintered body according to this embodiment includes a preparation step, a pretreatment step, a mixing step, and a sintering step, in this order.

[0046] ≪Preparation process≫ In the preparation step, raw material powders are prepared, which include cubic boron nitride powder (hereinafter also referred to as "cBN powder") and binder phase raw material powder.

[0047] The cBN powder is a raw material powder of cubic boron nitride particles contained in a cubic boron nitride sintered body. The cBN powder may be produced by adding a catalyst (Li, Ca, Mg, and their nitrides, borides, and boron nitrides) to a hexagonal boron nitride powder, followed by heating and pressing, or a commercially available cBN powder may be prepared. The average particle size d of the cubic boron nitride particles contained in the cubic boron nitride sintered body depends on the average particle size of the cBN powder. Therefore, by setting the average particle size of the cBN powder within a desired range, the average particle size d of the cubic boron nitride particles contained in the cubic boron nitride sintered body can be set within a desired range.

[0048] The binder phase raw material powder includes at least one element selected from a second group consisting of a simple substance of one element selected from a first group consisting of Group 4 elements, Group 5 elements, Group 6 elements, and aluminum in the periodic table, an alloy consisting of two or more elements selected from the first group, and an intermetallic compound consisting of two or more elements selected from the first group, or at least one element selected from a fourth group consisting of a first compound consisting of at least one element selected from the first group and at least one element selected from a third group consisting of nitrogen, carbon, boron, and oxygen, and a solid solution derived from the first compound. The binder phase raw material powder may be produced by a conventionally known method, or a commercially available binder phase raw material powder may be prepared.

[0049] <Pretreatment process> In the pretreatment step, the cBN powder and the binder phase raw material powder are each subjected to a plasma treatment. More specifically, the cBN powder is exposed to a gas atmosphere containing Ar for 20 minutes to 40 minutes, and the binder phase raw material powder is heated to 1000° C. 2The mixture is exposed to a gas atmosphere containing the above for 20 minutes to 40 minutes. This makes it difficult for the particles to aggregate in the mixing step described below, thereby suppressing the generation of secondary particles.

[0050] ≪Mixing process≫ In the mixing step, the plasma-treated cBN powder and the plasma-treated binder phase raw material powder are mixed by wet ball mill mixing to obtain a mixed powder. The wet ball mill mixing is performed by simultaneously using balls with a diameter of 3 mm to 8 mm (hereinafter also referred to as "large diameter balls") and balls with a diameter of 1 mm to 2 mm (hereinafter also referred to as "small diameter balls"). This allows the large diameter balls to crush secondary particles that are still generated even after the pretreatment step to generate primary particles, while the small diameter balls can uniformly mix the primary particles. Therefore, the particles of the cBN powder can be sufficiently uniformly dispersed. Conventionally, the method of mixing raw material powders using large diameter balls and small diameter balls at the same time has not been adopted because it increases the manufacturing effort. In addition, examples of the above-mentioned solvent include ethanol, acetone, etc.

[0051] A ratio M2 / M1 of a total mass M2 of the small diameter balls to a total mass M1 of the large diameter balls may be 0.26 or greater and 0.40 or less.

[0052] <Sintering process> In the sintering step, the mixed powder is sintered to obtain a cubic boron nitride sintered body. More specifically, in the first step, the mixed powder is filled into a container and vacuum-sealed. Next, in the second step, the vacuum-sealed mixed powder is sintered using an ultra-high temperature and high pressure device.

[0053] In the sintering process, a first temperature rise in which the temperature is raised from 1200°C to 1300°C and a second temperature rise in which the temperature is raised from 1400°C to 1550°C are carried out in this order. In the first temperature rise, the temperature rise rate is 8°C / min to 12°C / min. In the second temperature rise, the temperature rise rate is 2°C / min to 5°C / min. This allows the temperature in the sintering process to be raised slowly, thereby suppressing the deformation of the heater caused by the temperature rise and the increase in the resistance value of the heater caused by the deformation. Therefore, the temperature during sintering can be controlled to the desired temperature range (i.e., 1400°C to 1550°C).

[0054] <Features of the manufacturing method of cubic boron nitride sintered body according to the present embodiment> In the above manufacturing method, in the pretreatment step, the cBN powder is exposed to a gas atmosphere containing Ar for 20 minutes to 40 minutes, and the binder phase raw material powder is heated to 1000° C. 2 The method is carried out by exposing the cBN powder to a gas atmosphere containing the above for 20 minutes or more and 40 minutes or less, simultaneously using the large diameter balls and the small diameter balls in the mixing step, and performing the first heating (heating rate: 8°C / min to 12°C / min) and the second heating (heating rate: 2°C / min to 5°C / min) in this order in the sintering step. This makes it possible to keep the particles of the cBN powder fine and sufficiently uniformly dispersed, and to control the temperature during sintering within a desired range. Therefore, since the cubic boron nitride particles can be sufficiently uniformly dispersed in the cubic boron nitride sintered body, the variation coefficient Z of the area ratio of the cubic boron nitride particles in the cross section of the cubic boron nitride sintered body can be controlled within a desired range. The present inventors have found, through extensive research, that the cubic boron nitride sintered body of the present disclosure can be realized by adopting such a manufacturing method.

[0055] [Embodiment 3: Tools] The tool according to this embodiment includes the cubic boron nitride sintered body described in the first embodiment.

[0056] According to the present disclosure, it is possible to provide a tool including a cubic boron nitride sintered body that can extend the tool's life, particularly when used as a material for a cutting tool for heavy interrupted cutting, for the reasons described in the first embodiment.

[0057] Each tool may be entirely made of cubic boron nitride sintered body, or only a part of it (for example, the cutting edge of a cutting tool) may be made of cubic boron nitride sintered body. Furthermore, a coating film may be formed on the surface of each tool. Examples of tools include cutting tools and wear-resistant tools.

[0058] Examples of cutting tools include drills, end mills, indexable cutting tips for drills, indexable cutting tips for end mills, indexable cutting tips for milling, indexable cutting tips for turning, metal saws, gear cutting tools, reamers, taps, cutting bits, and the like.

[0059] Examples of the wear-resistant tools include dies, scribers, scribing wheels, and dressers.

[0060] <Tool manufacturing method> The method for manufacturing a tool according to the present disclosure can be carried out in the same manner as a conventionally known method, except that the cubic boron nitride sintered body described in the first embodiment is used. EXAMPLES

[0061] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0062] <Production of cubic boron nitride sintered body> Cubic boron nitride sintered bodies according to Samples 1 to 17 and 101 to 107 were produced by carrying out the following steps in the following order.

[0063] <Preparation process> First, as raw material powders, cBN powder (particle size: same as d [μm] listed in Tables 2-1 and 2-2) and binder phase raw material powder (composition: same as the binder phase composition listed in Tables 2-1 and 2-2) were prepared.

[0064] <Pretreatment process> The cBN powder was exposed to a gas atmosphere containing Ar under the conditions shown in Tables 1-1 and 1-2, and the binder phase raw material powder was exposed to a gas atmosphere containing N 2 Plasma treatment was performed by exposing the sample to a gas atmosphere containing Ar under the conditions described in Tables 1-1 and 1-2. Note that "0" in the "Ar gas exposure time [min]" column in Tables 1-1 and 1-2 means that no exposure to a gas atmosphere containing Ar was performed. 2 If "0" is listed in the "Gas exposure time [min]" column, 2 This means that no exposure to a gas atmosphere containing

[0065] ≪Mixing process≫ A mixed powder was obtained by mixing the plasma-treated cBN powder and the plasma-treated binder phase raw material powder by wet ball mill mixing under the conditions shown in Tables 1-1 and 1-2. At that time, the volume ratio of the cBN powder content to the binder phase raw material powder content in the mixed powder was adjusted to be the same as the ratio of the cubic boron nitride particle content [volume %] shown in Tables 2-1 and 2-2 to the binder phase content [volume %] shown in Tables 2-1 and 2-2. Note that when a value is shown in both the "large diameter ball" column and the "small diameter ball" column, it means that the large diameter ball and the small diameter ball were used at the same time. When "-" is shown in the "small diameter ball" column, it means that the small diameter ball was not used.

[0066] <Sintering process> First, in the first step, the mixed powder was filled into a container and vacuum-sealed. Next, in the second step, the vacuum-sealed mixed powder was sintered under the conditions shown in Tables 1-1 and 1-2 using an ultra-high temperature and high pressure device to obtain a cubic boron nitride sintered body. In the first heating step, the heating rate was 3°C / min, and the temperature immediately after the first heating step was 1200°C to 1300°C. In the second heating step, the heating rate was 10°C / min, and the temperature immediately after the second heating step was 1400°C to 1550°C.

[0067] By the above procedure, cubic boron nitride sintered bodies according to Samples 1 to 17 and 101 to 107 were produced.

[0068] As conventional examples, a cubic boron nitride sintered body according to sample 108 was prepared by the same manufacturing method as No. 1 of Example 1 in Patent Document 1, a cubic boron nitride sintered body according to sample 109 was prepared by the same manufacturing method as invention product 1 in Patent Document 2, and a cubic boron nitride sintered body according to sample 110 was prepared by the same manufacturing method as the polycrystalline cBN material according to Example 1 in Patent Document 3.

[0069] [Table 1-1]

[0070] [Table 1-2]

[0071] [Table 2-1]

[0072] [Table 2-2]

[0073] <Characteristics evaluation of cubic boron nitride sintered body> <Composition of cubic boron nitride sintered body> For the cubic boron nitride sintered body of each sample, the content [volume %] of cubic boron nitride particles was obtained by the method described in embodiment 1. The results obtained are shown in the "content [volume %]" column of the "cBN particles" column in Tables 2-1 and 2-2. In addition, for the cubic boron nitride sintered body of each sample, the content [volume %] of the binder phase was obtained by the method described in embodiment 1. The results obtained are shown in the "content [volume %]" column of the "binder phase" column in Tables 2-1 and 2-2. In addition, for the cubic boron nitride sintered body of each sample, the total content [volume %] of cubic boron nitride particles and binder phase was obtained by the method described in embodiment 1. The results obtained are shown in the "cBN particle content + binder phase content [volume %]" column in Tables 2-1 and 2-2. For the cubic boron nitride sintered bodies of each sample, the total volume of the compounds listed in the "Composition" column of the "Binder Phase" column in Tables 2-1 and 2-2 and the volume of other impurities was 100% of the volume of the binder phase.

[0074] <Coefficient of variation Z of area ratio of cubic boron nitride particles> For the cubic boron nitride sintered body of each sample, the coefficient of variation Z of the area ratio of cubic boron nitride particles in the cross section of the cubic boron nitride sintered body was determined by the method described in embodiment 1. The results obtained are shown in the "Z" column of the "cBN particles" column in Tables 2-1 and 2-2.

[0075] <Average particle size d of cubic boron nitride particles> For the cubic boron nitride sintered bodies of the respective samples, the average particle size d of the cubic boron nitride particles was determined by the method described in embodiment 1. The results obtained are shown in the "d [μm]" column of the "cBN particles" column in Tables 2-1 and 2-2.

[0076] <Composition of the binder phase> The composition of the binder phase of each sample of the cubic boron nitride sintered body was determined by the method described in embodiment 1. The results are shown in the "Compound" column of the "Composition" column of the "Binder Phase" column in Tables 2-1 and 2-2.

[0077] <Cutting test> A cutting tool (shape: CNGA120408) was produced using the cubic boron nitride sintered body of each sample. Using the cutting tool, a cutting test was performed under the following cutting conditions. The following cutting conditions correspond to strong intermittent cutting. The cutting edge was observed every 345 m of cutting distance to check whether the cutting edge was chipped or not. The cutting distance at which a chip of 0.2 mm or more occurred was measured, and this cutting distance was taken as the life of the cutting tool. The results are shown in the "Life [km]" column of Tables 2-1 and 2-2. A cutting tool life of 2000 m or more means that the tool life is excellent. (Cutting conditions) Cutting speed: 100m / min. Feed speed: 0.2mm / rev. Depth of cut: 0.2 mm Coolant:DRY Cutting method: Strong intermittent cutting Lathe: LB400 (Okuma Corporation) Work material: Hardened steel (SCM415 U groove, hardness HRC60)

[0078] The cubic boron nitride sintered bodies of Samples 1 to 17 correspond to Examples. The cubic boron nitride sintered bodies of Samples 101 to 110 correspond to Comparative Examples. From the results of Tables 2-1 and 2-2, it was found that the cubic boron nitride sintered bodies of Samples 1 to 17 can extend the life of tools, especially when used as materials for cutting tools for heavy interrupted cutting, compared with the cubic boron nitride sintered bodies of Samples 101 to 110. In addition, from the results of Table 2-2, it was confirmed that the cubic boron nitride sintered body of the present application cannot be obtained by the manufacturing methods of cubic boron nitride sintered bodies of Patent Documents 1 to 3.

[0079] From the above, it was found that the cubic boron nitride sintered bodies according to Samples 1 to 17 enable a longer tool life, particularly when used as materials for cutting tools for heavy interrupted cutting.

[0080] Although the embodiments and examples of the present disclosure have been described above, it is intended from the outset that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways.

[0081] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered as limiting. The scope of the present invention is indicated by the claims, not by the embodiments and examples described above, and is intended to include the meaning equivalent to the claims and all modifications within the scope. [Explanation of symbols]

[0082] R1 unit area.

Claims

1. A cubic boron nitride sintered body comprising 40% to 80% by volume of cubic boron nitride particles and 20% to 60% by volume of a bonding phase, The average particle size d of the cubic boron nitride particles is 0.1 μm or more and 3 μm or less. The aforementioned bonded phase is At least one element selected from the second group, which consists of a first group consisting of group 4, group 5, group 6 elements of the periodic table and aluminum, an alloy consisting of two or more elements selected from the first group, and an intermetallic compound consisting of two or more elements selected from the first group, or The first compound comprises at least one element selected from the first group and at least one element selected from the third group consisting of nitrogen, carbon, boron, and oxygen, and at least one element selected from the fourth group consisting of solid solutions derived from the first compound. In the cross-section of the cubic boron nitride sintered body, the coefficient of variation Z of the area fraction of the cubic boron nitride particles is 0.25 or less. The coefficient of variation Z is obtained by, in the image after binarization of the backscattered electron image obtained by imaging the cross section of the cubic boron nitride sintered body with a scanning electron microscope at 5000x magnification, providing a total of 260 square unit regions in the image after binarization, where each side is twice the length of the average particle size d of the cubic boron nitride particles, and calculating the standard deviation and the average of the area ratios of the cubic boron nitride particles in each of the 260 unit regions, and dividing the standard deviation by the average, thereby obtaining a cubic boron nitride sintered body.

2. The cubic boron nitride sintered body according to claim 1, wherein the average particle size d of the cubic boron nitride particles is 0.1 μm or more and 2 μm or less.

3. The content of cubic boron nitride particles in the cubic boron nitride sintered body is 60% by volume or more and 70% by volume or less. The cubic boron nitride sintered body according to claim 1 or claim 2, wherein the content of the binding phase in the cubic boron nitride sintered body is 30% by volume or more and 40% by volume or less.

4. The cubic boron nitride sintered body according to claim 1 or claim 2, wherein the bonding phase comprises at least one selected from the group consisting of titanium nitride, titanium boride, aluminum nitride, and aluminum oxide.

5. The cubic boron nitride sintered body according to claim 1 or claim 2, wherein the total content of the cubic boron nitride particles and the binding phase in the cubic boron nitride sintered body is 99 volume percent or more.

6. A tool comprising a cubic boron nitride sintered body according to claim 1 or claim 2.

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