Cubic boron nitride sintered compact and tool

Abstract

This cubic boron nitride sintered compact comprises 40-80 vol% of cubic boron nitride particles and 20-60 vol% of a binder phase. The average particle diameter d of the cubic boron nitride particles is 0.1-3 µm. The binder phase contains: at least one selected from a second group consisting of elementary substances of one element selected from a first group consisting of aluminum, group-4 elements, group-5 elements, and group-6 elements in the periodic table, alloys formed of two or more elements selected from the first group, and intermetallic compounds formed of two or more elements selected from the first group; or at least one selected from a fourth group consisting of first compounds formed 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 solid solutions derived from the first compounds. In a cross section of the cubic boron nitride sintered compact, the coefficient of variation Z of area ratios of the cubic boron nitride particles is 0.25 or less. The coefficient of variation Z is obtained by: providing, in a binarized image of a backscattered electron image obtained by imaging the cross section of the cubic boron nitride sintered compact by using a scanning electron microscope at a magnification of 5000, a total of 260 unit regions each in a shape of a square in which the length of one side is two-fold of the average particle diameter d of the cubic boron nitride particles; calculating, on the basis of the total of 260 unit regions, the average of the area ratios and the standard deviation of the area ratios of the cubic boron nitride particles in each of the unit regions; and dividing the standard deviation by the average.

Description

Cubic boron nitride sintered body and tools

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

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

[0003] JP 2000-44347 A JP 2002-302732 A JP 2013-234335 A

[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, 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 element selected from a fourth group consisting of a first compound consisting of at least one element and a solid solution derived from the first compound, and the coefficient of variation 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, 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 particle 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 5000x magnification using a scanning electron microscope, calculating the standard deviation of the area ratio of the cubic boron nitride particles in each of the 260 unit areas and the average of the area ratios, and dividing the standard deviation by the average.

[0005] 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 a cross section of a cubic boron nitride sintered body.

[0006] [Problem to be Solved by the Present Disclosure] In recent years, there has been an increasing demand for heavy interrupted cutting processes, and therefore, there is a demand for a cubic boron nitride sintered body that can extend the life of cutting tools, particularly when used as a material for such 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 cutting tools for heavy interrupted cutting, and a tool including the cubic boron nitride sintered body.

[0008] [Effects of the Present 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] [Explanation of the embodiment of the present disclosure] First, the embodiment of the present disclosure will be listed and explained. (1) A cubic boron nitride sintered body of the present disclosure is a cubic boron nitride sintered body comprising 40 to 80 volume % of cubic boron nitride particles and 20 to 60 volume % of a binder phase, wherein the average particle size d of the cubic boron nitride particles is 0.1 μm to 3 μm, 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 said first compound, wherein the 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 particle size d of said cubic boron nitride particles, in a binarized image of a backscattered electron image obtained by imaging the cross section of said cubic boron nitride sintered body at 5000x magnification using a scanning electron microscope, calculating the standard deviation of the area ratio of said cubic boron nitride particles in each of said 260 unit areas and the average of said area ratios, and dividing said standard deviation by said 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 cutting tools 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 further extend the tool life of cutting tools, particularly when used as a material for cutting tools 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% by volume or more and 70% by volume or less, and the content of the binder phase in the cubic boron nitride sintered body may be 30% by volume or more and 40% by volume or less. This makes it possible to provide a cubic boron nitride sintered body that can further extend the tool life of cutting tools, particularly when used as a material for cutting tools 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 further extend the tool life of cutting tools, particularly when used as a material for cutting tools for heavy interrupted cutting, and a tool including the cubic boron nitride sintered body.

[0014] (5) In any 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, thereby providing a cubic boron nitride sintered body that can further extend the tool life of cutting tools, particularly when used as a material 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 containing 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.

[0017] [Details of the embodiment of the present disclosure] Specific examples of a cubic boron nitride sintered body and a tool according to one 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 changed as appropriate for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0018] In the present disclosure, the expression "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and when no unit is specified for A and a unit is specified only for B, the units of A and 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 one 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 a 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% 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 cubic boron nitride particles have an average particle size d of 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 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 selected from the group consisting of a first compound and a solid solution derived from the first compound, wherein the coefficient of variation 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, and the coefficient of variation Z is obtained by providing a total of 260 square unit regions R1, each having a side length twice the average particle 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 5000x magnification using a scanning electron microscope, calculating the standard deviation of the area ratio of the cubic boron nitride particles in each of the 260 unit regions R1 and the 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 presumed to be as follows.

[0023] The cubic boron nitride sintered body of this embodiment is a cubic boron nitride sintered body comprising 40 to 80 volume % cubic boron nitride particles and 20 to 60 volume % binder phase, wherein the average particle size d of the cubic boron nitride particles is 0.1 μm to 3 μm, and the coefficient of variation 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, "regions that are likely to become the starting point of defects due to the presence of a relatively large amount of binder phase" are less likely to occur, and 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, especially 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 40 volume % or more and 80 volume % or less of cubic boron nitride particles. From the viewpoint of improving fracture resistance, the lower limit of the content of cubic boron nitride particles is 40 volume % or more, or may be 50 volume % or more, or 60 volume % or more. From the viewpoint of improving sinterability, the upper limit of the content of cubic boron nitride particles is 80 volume % or less, or may be 75 volume % or less, or may be 70 volume % or less. The content of 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, or may be 25 volume % or more, or 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, or 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 [vol %] of cubic boron nitride particles and the content [vol %] 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] A cubic boron nitride sintered body is cut at an arbitrary position by ion milling to expose a cross section of the cubic boron nitride sintered body, and the cross section is polished. Ion milling is performed using a JEOL "Cross Section Polisher" (CP), with an acceleration voltage of 5.5 kV, a protrusion of 20 μm, and a processing time of 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 part of a tool, a portion of the cubic boron nitride sintered body is cut out using a diamond grinding wheel or electrodeposited wire, etc., to expose a sample including a cross section of the cubic boron nitride sintered body.

[0028] Next, an SEM image is obtained by photographing the cross section at 2,000x to 50,000x magnification using an FE-SEM. A backscattered electron image is then obtained using a semiconductor backscattered electron detector under conditions of 1024 x 768 pixels and an acceleration voltage of 1.5 kV. In the backscattered electron image, the brightness contrast is adjusted so that the areas where cubic boron nitride particles exist appear as the darkest black areas (60 or less in the range of 0 to 255) and the areas where the binder phase exists appear as gray or white areas (100 to 255 in the range of 0 to 255). If the electrostatic charge is significant, 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 Corporation'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 determined. 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 determined by calculating the area ratio of pixels derived from the bright field (pixels derived from the binder phase) to the area of ​​the measurement field from the binarized image. The fact that the pixels derived from the bright field are derived 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 area percentages of the cubic boron nitride particles and binder phase are measured in five non-overlapping measurement fields, and the average of the area percentages of the cubic boron nitride particles and 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 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 five measurement fields are arbitrarily set for the same sample and the content of cubic boron nitride particles and binder phase in a cubic boron nitride sintered body is measured multiple times according to the above procedure.

[0033] The total content of cubic boron nitride particles and binder phase in the cubic boron nitride sintered body may be 99% by volume or more. This allows the cubic boron nitride sintered body to contain a structure in which 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 this 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 effects of the present disclosure are not impaired. Examples of other phases include WC, W, and the like. 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 using a method similar to the method for measuring the "coefficient of variation Z of the area ratio of cubic boron nitride particles" described below. Next, the second image is subjected to a watershed process using image analysis software "ImageJ" (trade name), thereby identifying the positions of the grain boundaries of the cubic boron nitride particles in the second image and calculating the arithmetic mean of the circle-equivalent diameters (Heywood diameter: diameter equivalent to a circle with an equal area) of each cubic boron nitride particle. Note that the cubic boron nitride particles in the image include cubic boron nitride particles that are adjacent to the edges of the image.

[0038] The above measurement is performed in five 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 coefficient of variation Z of the area ratio of 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 coefficient of variation Z of the area ratio of 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 coefficient of variation Z of the area ratio of 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] The 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 now be described. First, a backscattered electron image (first image) obtained by photographing the cross section of a cubic boron nitride sintered body at 5000x magnification using a scanning electron microscope is binarized to obtain a second image. A total of 260 square unit regions R1, each with a side length twice the average particle size d of the cubic boron nitride particles, are provided in the second image (FIG. 1). Next, based on the 260 unit regions R1, the standard deviation of the area ratio of the cubic boron nitride particles in each unit region 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. ２The 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 using a program written in Python to binarize the cubic boron nitride particle regions and other regions. In one second image, the unit regions R1 are arranged consecutively along both the first direction and a direction perpendicular to the first direction. The number of unit regions R1 in one second image is the maximum number that can be included in the second image. If the number of unit regions R1 in one second image is less than 260, additional unit regions R1 are added in other second images so that the total number of unit regions R1 reaches 260. If there is a second image with a remainder of the unit regions R1, any unit region R1 in the second image is selected to adjust the total number of unit regions R1 to 260.

[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 carried out multiple times according to the above procedure.

[0043] <Binder Phase> <Binder Phase Composition> The binder phase includes at least one element selected from Group 2, which includes a simple substance of one element selected from Group 1, consisting of Groups 4, 5, and 6 elements, and aluminum, an alloy of two or more elements selected from Group 1, and an intermetallic compound of two or more elements selected from Group 1; or at least one element selected from Group 4, which includes a first compound consisting of at least one element selected from Group 1 and at least one element selected from Group 3, consisting of nitrogen, carbon, boron, and oxygen, and a solid solution derived from the first compound. This provides the binder phase with excellent bonding strength to cubic boron nitride particles, thereby improving the chipping resistance of cutting tools, especially when used as a material for heavy interrupted cutting. The binder phase may include at least one element selected from the group consisting of titanium nitride, titanium boride, aluminum nitride, and aluminum oxide. This further improves the chipping resistance of the tool, particularly when used as a material for cutting tools for heavy interrupted cutting. The binder phase may contain, as a main component, at least one element selected from Group 2, which consists of a simple substance of one element selected from Group 1, which consists of Group 4 elements, Group 5 elements, and Group 6 elements of the periodic table, and aluminum, an alloy consisting of two or more elements selected from Group 1, and an intermetallic compound consisting of two or more elements selected from Group 1, or at least one element selected from Group 4, which consists of a first compound consisting of at least one element selected from Group 1 and at least one element selected from Group 3, which consists of nitrogen, carbon, boron, and oxygen, and a solid solution derived from the first compound. Here, "contained as a main component" means that the total content of these components in the binder phase is 90% by 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: Method for manufacturing cubic boron nitride sintered body] The method for manufacturing 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 Step> In the preparation step, raw material powders are prepared, including cubic boron nitride powder (hereinafter also referred to as "cBN powder") and binder phase raw material powder.

[0047] cBN powder is a raw material powder of cubic boron nitride particles contained in a cubic boron nitride sintered body. cBN powder may be produced by adding a catalyst (Li, Ca, Mg, and their nitrides, borides, and boron nitrides) to hexagonal boron nitride powder and then heating and pressing, or 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 contains 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] In the pretreatment step, the cBN powder and the binder phase raw material powder are each subjected to 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 a temperature of 1000°C. ２The mixture is exposed to a gas atmosphere containing the above-mentioned component 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 process, the plasma-treated cBN powder and the plasma-treated binder phase raw material powder are mixed by wet ball milling to obtain a mixed powder. 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 remain even after the pretreatment process to generate primary particles, while the small diameter balls uniformly mix the primary particles. Therefore, the cBN powder particles can be sufficiently uniformly dispersed. Conventionally, the method of simultaneously using large diameter balls and small diameter balls to mix raw material powders has not been adopted due to the increased manufacturing effort. Examples of the solvent include ethanol and acetone.

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

[0052] <Sintering Step> 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 apparatus.

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

[0054] <<Features of the manufacturing method of cubic boron nitride sintered body of this embodiment>> In the manufacturing method described above, in the pretreatment step, cBN powder is exposed to a gas atmosphere containing Ar for 20 minutes to 40 minutes, and the binder phase raw material powder is ２ the cBN powder is exposed to a gas atmosphere containing the large-diameter balls for 20 to 40 minutes; the large-diameter balls and the small-diameter balls are used simultaneously in the mixing step; and the first temperature increase (heating rate: 8°C / min to 12°C / min) and the second temperature increase (heating rate: 2°C / min to 5°C / min) are performed in this order in the sintering step. This allows the cBN powder particles to be kept fine and sufficiently uniformly dispersed, and the sintering temperature to be controlled within a desired range. Therefore, since the cubic boron nitride particles can be sufficiently uniformly dispersed in the cubic boron nitride sintered body, the coefficient of variation 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 inventors have found, through extensive research, that the cubic boron nitride sintered body of the present disclosure can be realized by employing such a manufacturing method.

[0055] Third Embodiment: Tool A 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 containing 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, for the reasons described in embodiment 1.

[0057] Each tool may be entirely made of cubic boron nitride sintered body, or only a part of it (for example, the cutting edge in the case 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, and cutting bits.

[0059] Examples of the wear-resistant tool include a die, a scriber, a scribing wheel, and a dresser.

[0060] <Tool Manufacturing Method> The tool manufacturing method of 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.

[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] <<Preparation of Cubic Boron Nitride Sintered Body>> Cubic boron nitride sintered bodies according to Samples 1 to 17 and 101 to 107 were prepared by carrying out the following steps in the following order.

[0063] <Preparation Step> 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 Step> 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 entered in the "Gas exposure time [min]" column, ２ This means that no exposure to a gas atmosphere containing

[0065] <Mixing Step> A mixed powder was obtained by mixing the plasma-treated cBN powder and the plasma-treated binder phase raw material powder using a wet ball mill under the conditions shown in Tables 1-1 and 1-2. The volumetric 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 listed in both the "large diameter balls" and "small diameter balls" columns, it means that both large diameter balls and small diameter balls were used simultaneously. A "-" in the "small diameter balls" column means that small diameter balls were not used.

[0066] <Sintering Step> 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 using an ultra-high temperature and high pressure apparatus under the conditions shown in Tables 1-1 and 1-2 to obtain a cubic boron nitride sintered body. Note that, in the first temperature increase, the temperature increase rate was 3°C / min, and the temperature immediately after the first temperature increase was 1200°C to 1300°C. Furthermore, in the second temperature increase, the temperature increase rate was 10°C / min, and the temperature immediately after the second temperature increase 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] Furthermore, 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]

[0070]

[0071]

[0072]

[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 [vol %] of cubic boron nitride particles was determined by the method described in Embodiment 1. The results obtained are shown in the "Content [vol %]" column of the "cBN Particles" column in Tables 2-1 and 2-2. Furthermore, for the cubic boron nitride sintered body of each sample, the content [vol %] of the binder phase was determined by the method described in Embodiment 1. The results obtained are shown in the "Content [vol %]" column of the "Binder Phase" column in Tables 2-1 and 2-2. Furthermore, for the cubic boron nitride sintered body of each sample, the total content [vol %] of cubic boron nitride particles and binder phase was determined 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 sum of the volumes of the compounds shown in the "composition" column of the "binder phase" column in Tables 2-1 and 2-2 and the volumes 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 body of each sample, 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 Binder Phase> For each sample of cubic boron nitride sintered body, the composition of the binder phase was determined by the method described in Embodiment 1. The results obtained are shown in the "Compound" column under "Composition" in 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. A cutting test was carried out using the cutting tool under the following cutting conditions. The following cutting conditions correspond to heavy intermittent cutting. The cutting edge was observed every 345 m of cutting distance to check for chipping of the cutting edge. The cutting distance at which chipping 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 in Table 2-1 and Table 2-2. A cutting tool life of 2000 m or more means an excellent tool life. (Cutting Conditions) Cutting speed: 100 m / min. Feed rate: 0.2 mm / rev. Depth of cut: 0.2 mm Coolant: DRY Cutting method: Heavy intermittent cutting Lathe: LB400 (Okuma Corporation) Workpiece: 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. The results in Tables 2-1 and 2-2 show that the cubic boron nitride sintered bodies of Samples 1 to 17 enable longer tool life, particularly when used as materials for cutting tools for heavy interrupted cutting, compared to the cubic boron nitride sintered bodies of Samples 101 to 110. The results in Table 2-2 also confirm that the cubic boron nitride sintered body of the present application cannot be obtained by the methods for manufacturing 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 of Samples 1 to 17 can extend the life of cutting tools, especially when used as materials for heavy interrupted cutting.

[0080] Although the embodiments and examples of the present disclosure have been described above, it is originally intended 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 limiting. The scope of the present invention is defined by the claims, not by the embodiments and examples described above, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0082] R1 unit area.

Claims

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; 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 and 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; 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; The coefficient of variation Z is obtained by providing a total of 260 square unit areas, each having a side length twice the average particle diameter d of the cubic boron nitride particles, in a binarized image of a backscattered electron image obtained by imaging a cross section of the cubic boron nitride sintered body at 5000x 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 ratio, and dividing the standard deviation by the average.

2. The cubic boron nitride sintered body according to claim 1, wherein the average particle size d of said cubic boron nitride particles is 0.1 μm or more and 2 μm or less. 　 the content of the cubic boron nitride particles in the cubic boron nitride sintered body is 60% by volume or more and 70% by volume or less; 3. The cubic boron nitride sintered body according to claim 1, wherein the content of said binder phase in said 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, wherein the binder 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, wherein the total content of the cubic boron nitride particles and the binder phase in the cubic boron nitride sintered body is 99% by volume or more. 　 A tool comprising the cubic boron nitride sintered body according to any one of claims 1 to 5.

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