Composite Sintered Body and Tool Using the Same

Abstract

A composite sintered body is composed of cubic boron nitride particles, and hexagonal boron nitride particles, or hexagonal boron nitride particles and wurtzite-type boron nitride particles. The dislocation density of the cubic boron nitride particles is 1×10<supgt;15< / supgt> / m<supgt;2< / supgt> or more and 1×10<supgt;17< / supgt> / m<supgt;2< / supgt> or less. The median particle size d50 of the equivalent circle diameter of the cubic boron nitride particles is 10 nm or more and 500 nm or less. The volume-based content rate Vc of the cubic boron nitride particles, the volume-based content rate Vh of the hexagonal boron nitride particles, and the volume-based content rate Vw of the wurtzite-type boron nitride particles satisfy the relationship of Formula 1 below. Formula 1: 0.015 ≤ (Vh + Vw) / (Vc + Vh + Vw) ≤ 0.5.

Description

Technical Field

[0001] The present disclosure relates to a composite sintered body and a tool using the composite sintered body. Background Art

[0002] Cubic boron nitride (hereinafter, also referred to as "cBN") has a hardness second only to diamond and is also excellent in thermal stability and chemical stability. Therefore, cubic boron nitride sintered bodies are used as materials for tools.

[0003] As the cubic boron nitride sintered body, a sintered body containing about 10 to 40% by volume of a binder is used. However, the binder is the cause of reducing the strength and thermal diffusivity of the sintered body.

[0004] To solve this problem, the following methods have been developed: Without using a binder, by directly converting hexagonal boron nitride into cubic boron nitride under ultrahigh pressure and high temperature while performing sintering, a cubic boron nitride sintered body not containing a binder is obtained (Japanese Patent Application Laid-Open No. 2004-250278 (Patent Document 1), Japanese Patent Application Laid-Open No. 11-246271 (Patent Document 2), Japanese Patent Application Laid-Open No. 2014-34487 (Patent Document 3)).

[0005] Prior Art Documents

[0006] Patent Documents

[0007] Patent Document 1: Japanese Patent Application Laid-Open No. 2004-250278

[0008] Patent Document 2: Japanese Patent Application Laid-Open No. 11-246271

[0009] Patent Document 3: Japanese Patent Application Laid-Open No. 2014-34487 Summary of the Invention

[0010] The composite sintered body of the present disclosure is composed of

[0011] cubic boron nitride particles,

[0012] and hexagonal boron nitride particles, or and hexagonal boron nitride particles and wurtzite boron nitride particles,

[0013] the dislocation density of the cubic boron nitride particles is 1×10 15 / m 2 or more and 1×10 17 / m 2 or less,

[0014] the median particle size d50 of the equivalent circle diameter of the cubic boron nitride particles is 10 nm or more and 500 nm or less,

[0015] The volume-based content rate Vc of the cubic boron nitride particles, the volume-based content rate Vh of the hexagonal boron nitride particles, and the volume-based content rate Vw of the wurtzite boron nitride particles satisfy the relationship of the following formula 1,

[0016] Formula 1: 0.015 ≤ (Vh + Vw) / (Vc + Vh + Vw) ≤ 0.5.

[0017] The tool of the present disclosure is a tool using the above composite sintered body. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Figure 1 is a pressure-temperature phase diagram of boron nitride.

[0019] Figure 2 Figure 2 is a diagram for explaining an example of the manufacturing method of the composite sintered body of the present disclosure.

[0020] Figure 3 Figure 3 is a diagram for explaining another example of the manufacturing method of the composite sintered body of the present disclosure.

[0021] Figure 4 Figure 4 is a diagram for explaining another example of the manufacturing method of the composite sintered body of the present disclosure. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] [Problems to be Solved by the Present Disclosure]

[0023] When a die is made of a cubic boron nitride sintered body, adhesion (adhere) is likely to occur on the wire due to friction during wire drawing. Therefore, wire breakage may occur during wire drawing, or damage may occur on the surface of the obtained wire.

[0024] Therefore, an object of the present invention is to provide a composite sintered body that, when used as a tool material, particularly in wire drawing, can have a long tool life without deteriorating the surface state of the wire.

[0025] [Effects of the Present Disclosure]

[0026] According to the present disclosure, a composite sintered body can be provided that, when used as a tool material, particularly in wire drawing, can have a long tool life without deteriorating the surface state of the wire.

[0027] [Description of Embodiments of the Present Disclosure]

[0028] First, embodiments of the present disclosure will be listed and described. ​​​​​​​​

[0029] (1) The composite sintered body of the present disclosure is composed of

[0030] cubic boron nitride particles,

[0031] and hexagonal boron nitride particles, or and hexagonal boron nitride particles and wurtzite boron nitride particles,

[0032] the dislocation density of the cubic boron nitride particles is 1×10 15 / m 2 or more and 1×10 17 / m 2 or less,

[0033] the median particle size d50 of the equivalent circle diameter of the cubic boron nitride particles is 10 nm or more and 500 nm or less,

[0034] the volume-based content Vc of the cubic boron nitride particles, the volume-based content Vh of the hexagonal boron nitride particles, and the volume-based content Vw of the wurtzite boron nitride particles satisfy the relationship of Formula 1 below,

[0035] Formula 1: 0.015 ≤ (Vh + Vw) / (Vc + Vh + Vw) ≤ 0.5.

[0036] When the composite sintered body of the present disclosure is used as a tool material, especially in wire drawing, it can also have a long tool life without deteriorating the surface state of the wire.

[0037] (2) The dislocation density of the cubic boron nitride particles is preferably 1×10 15 / m 2 or more and 3×10 16 / m 2 or less. Thereby, it is difficult to cause welding to the wire, and the tool life is further improved.

[0038] (3) The dislocation density of the cubic boron nitride particles is preferably 1×10 15 / m 2 or more and 5×10 15 / m 2 or less. Thereby, it is difficult to cause welding to the wire, and the tool life is further improved.

[0039] (4) The median particle size d50 of the equivalent circle diameter of the cubic boron nitride particles is preferably 10 nm or more and 300 nm or less. Thereby, it is difficult to cause damage to the surface of the wire, the deterioration of the surface state of the wire is suppressed, and the tool life is further improved.

[0040] (5) The median particle size d50 of the equivalent circle diameter of the cubic boron nitride particles is preferably 10 nm or more and 100 nm or less. Thereby, it is difficult to cause damage to the surface of the wire rod, deterioration of the surface state of the wire rod is suppressed, and the tool life is further improved.

[0041] (6) Preferably, the volume-based content Vc of the cubic boron nitride particles, the volume-based content Vh of the hexagonal boron nitride particles, and the volume-based content Vw of the wurtzite boron nitride particles satisfy the relationship of the following formula 2.

[0042] Formula 2: 0.03 ≤ (Vh + Vw) / (Vc + Vh + Vw) ≤ 0.4

[0043] Thereby, the slidability between the tool and the wire rod is improved, deterioration of the surface state of the wire rod is suppressed, and the tool life is further improved.

[0044] (7) Based on mass, the total content of the alkali metal element and the alkaline earth metal element in the composite sintered body is preferably 10 ppm or less. The tool using this composite sintered body can have excellent tool life.

[0045] (8) The dislocation density is preferably calculated using the modified Williamson-Hall method and the modified Warren-Averbach method. The correlation between this dislocation density and the performance of the composite sintered body is good.

[0046] (9) The dislocation density is preferably measured using synchrotron radiation as the X-ray source. The correlation between this dislocation density and the performance of the composite sintered body is good.

[0047] (10) The tool of the present disclosure is a tool using the above composite sintered body. The tool of the present disclosure can have a long tool life without deteriorating the surface state of the wire rod especially in wire drawing.

[0048] [Details of the Embodiment of the Present Disclosure]

[0049] A specific example of the composite sintered body and the tool using the composite sintered body according to an embodiment of the present disclosure will be described.

[0050] In this specification, the expression in the form of "A to B" means the upper and lower limits of the range (that is, A or more and B or less). When no unit is described for A and only a unit is described for B, the unit of A is the same as the unit of B.

[0051] [Embodiment 1: Composite Sintered Body]

[0052] One embodiment of the present disclosure relates to a composite sintered body composed of cubic boron nitride particles, and hexagonal boron nitride particles, or hexagonal boron nitride particles and wurtzite boron nitride particles. The dislocation density of the cubic boron nitride particles is 1×10 15 / m 2 or more and 1×10 17 / m 2 or less. The median particle size d50 of the equivalent circle diameter of the cubic boron nitride particles is 10 nm or more and 500 nm or less. The volume-based content rate Vc of the cubic boron nitride particles, the volume-based content rate Vh of the hexagonal boron nitride particles, and the volume-based content rate Vw of the wurtzite boron nitride particles satisfy the relationship of the following formula (1),

[0053] Formula (1): 0.015 ≤ (Vh + Vw) / (Vc + Vh + Vw) ≤ 0.5.

[0054] When the composite sintered body of the present disclosure is used as a tool material, especially in wire drawing, it can also have a long tool life without deteriorating the surface state of the wire. Although the reason is unclear, it is speculated as follows (i) to (iv).

[0055] (i) The composite sintered body of the present disclosure is composed of cubic boron nitride particles, and hexagonal boron nitride particles, or hexagonal boron nitride particles and wurtzite boron nitride particles, and substantially does not contain binders, sintering aids, catalysts, etc. Therefore, the strength and thermal diffusivity of the composite sintered body are improved. As a result, the tool using this composite sintered body is difficult to adhere due to the generation of frictional heat even in wire drawing and can have a long tool life.

[0056] (ii) In the composite sintered body of the present disclosure, the dislocation density of the cubic boron nitride particles is 1×10 15 / m 2 or more and 1×10 17 / m 2 or less. The cubic boron nitride particles have high hardness, excellent toughness, high crystallinity, and high thermal diffusivity. Therefore, the tool using the composite sintered body containing the cubic boron nitride particles has excellent wear resistance even in wire drawing and is difficult to adhere due to the generation of frictional heat and can have a long tool life.

[0057] (iii) In the composite sintered body of the present disclosure, the median particle size d50 of the equivalent circle diameter of the cubic boron nitride particles is 10 nm or more and 500 nm or less. The composite sintered body containing the cubic boron nitride particles has improved toughness while having excellent strength, and thus can have excellent crack propagation resistance. Therefore, the tool using this composite sintered body is difficult to crack even in wire drawing and can have a long tool life.

[0058] (iv) In the composite sintered body of the present disclosure, the volume-based content rate Vc of cubic boron nitride particles, the volume-based content rate Vh of hexagonal boron nitride particles, and the volume-based content rate Vw of wurtzite boron nitride particles satisfy the relationship of the following formula 1.

[0059] Formula 1: 0.015 ≤ (Vh + Vw) / (Vc + Vh + Vw) ≤ 0.5

[0060] That is, in the composite sintered body of the present disclosure, the ratio of the total of hexagonal boron nitride particles and wurtzite boron nitride particles to the total of cubic boron nitride particles, hexagonal boron nitride particles, and wurtzite boron nitride particles is 1.5% by volume or more and 50% by volume or less. Hexagonal boron nitride and wurtzite boron nitride have a small frictional resistance during wire drawing, and thus can impart slidability to the composite sintered body. Therefore, the composite sintered body containing hexagonal boron nitride particles and wurtzite boron nitride particles in the above ratio has excellent slidability, and even during wire drawing processing, it is difficult to cause burn adhesion or wire breakage due to the generation of frictional heat, and can have a long tool life.

[0061] Furthermore, hexagonal boron nitride and wurtzite boron nitride are softer than cubic boron nitride, and thus have excellent crack propagation resistance. Therefore, a tool using this composite sintered body is difficult to generate cracks even during wire drawing processing and can have a long tool life.

[0062] Furthermore, in the composite sintered body of the present disclosure, the ratio of cubic boron nitride particles to the total of cubic boron nitride particles, hexagonal boron nitride particles, and wurtzite boron nitride particles is 50% by volume or more and 98.5% by volume or less. As described in (ii) above, cubic boron nitride particles have high hardness, excellent toughness, high crystallinity, and high thermal diffusivity. Therefore, a tool using the composite sintered body containing the cubic boron nitride particles in the above ratio has excellent wear resistance even during wire drawing processing, and is difficult to cause burn adhesion due to the generation of frictional heat, and can have a long tool life.

[0063] It should be noted that the above has described the case where the composite sintered body of the present disclosure has a long tool life during wire drawing processing, but the processing method is not limited thereto. Examples of the processing method include cutting tools. By improving the lubricity, the adhesion of the cutting tool to the material to be cut can be reduced, and the cutting resistance can be further reduced.

[0064] <Composition>

[0065] The composite sintered body of the present disclosure is composed of cubic boron nitride (hereinafter, also referred to as "cBN") particles, and hexagonal boron nitride (hereinafter, also referred to as "hBN") particles, or hexagonal boron nitride particles and wurtzite boron nitride (hereinafter, also referred to as "wBN") particles. That is, the composite sintered body of the present disclosure can be in the following manner (a) or (b).

[0066] (a) It is composed of cubic boron nitride particles and hexagonal boron nitride particles.

[0067] (b) It is composed of cubic boron nitride particles, hexagonal boron nitride particles, and wurtzite boron nitride particles.

[0068] It should be noted that in this specification, the hexagonal boron nitride contained in the composite sintered body of the present disclosure is defined to include ordinary "hexagonal boron nitride" and / or "compressed hexagonal boron nitride". Compressed hexagonal boron nitride refers to hexagonal boron nitride that has a crystal structure similar to that of ordinary hexagonal boron nitride and has a c-axis plane spacing smaller than the plane spacing (0.333 nm) of ordinary hexagonal boron nitride. Compressed hexagonal boron nitride has the same lubricity as ordinary hexagonal boron nitride. Therefore, in this specification, ordinary hexagonal boron nitride and compressed hexagonal boron nitride are regarded as the same, and the hexagonal boron nitride contained in the composite sintered body of the present disclosure is defined to include "hexagonal boron nitride" and / or "compressed hexagonal boron nitride".

[0069] Within the range showing the effects of the present disclosure, the composite sintered body may also contain inevitable impurities. As inevitable impurities, for example, hydrogen, oxygen, carbon, alkali metal elements (such as lithium (Li), sodium (Na), potassium (K), etc.), and alkaline earth metal elements (such as calcium (Ca), magnesium (Mg), strontium (Sr), barium (Ba), etc.) and other metal elements can be listed. When the composite sintered body contains inevitable impurities, the content of the inevitable impurities is preferably 0.5% by volume or less. The content of the inevitable impurities can be measured by secondary ion mass spectrometry (SIMS).

[0070] Based on mass, the total content of alkali metal elements (lithium (Li), sodium (Na), potassium (K)) and alkaline earth metal elements (calcium (Ca), magnesium (Mg), strontium (Sr), barium (Ba)) in the composite sintered body is preferably 10 ppm or less. This total content can be measured by secondary particle mass spectrometry (SIMS).

[0071] Among the above-mentioned inevitable impurities, alkali metal elements and alkaline earth metal elements have a catalytic effect on the phase transformation between hexagonal boron nitride and cubic boron nitride. When the total content of alkali metal elements and alkaline earth metal elements in the composite sintered body is 10 ppm or less, for a tool using this composite sintered body, in a machining environment, even when the interface between the tool and the material to be cut is exposed to high temperature and high pressure, the expansion of tool damage caused by the transformation of a part of the cubic boron nitride constituting the tool into hexagonal boron nitride can be well suppressed. The lower limit of the total content of alkali metal elements and alkaline earth metal elements in the hexagonal boron nitride polycrystal is preferably 0 ppm. That is, the total content of alkali metal elements and alkaline earth metal elements in the hexagonal boron nitride polycrystal is preferably 0 ppm or more and 10 ppm or less.

[0072] Conventional cubic boron nitride sintered bodies are produced, for example, as described in Japanese Patent Laid-Open No. 2006-201216, starting from cBN abrasive grains. Here, the total content of catalyst components (alkali metal elements, alkaline earth metal elements) remaining in the cBN abrasive grains (the content of catalyst components in 1 mole of cBN) is 2.4×10 -4 ~13.5×10 -4 moles. Therefore, it is obvious to those skilled in the art that the total content of catalyst components in a conventional cubic boron nitride sintered body obtained by sintering the cBN abrasive grains is 0.01 mass% (100 ppm) or more.

[0073] On the other hand, as will be described later, the composite sintered body of the present disclosure is obtained by the following method: using hexagonal boron nitride or pyrolytic boron nitride as a starting material, without using a catalyst, heating and pressurizing the hexagonal boron nitride or the pyrolytic boron nitride to convert it into cubic boron nitride. Therefore, based on mass, the content of catalyst components in the composite sintered body can be set to 10 ppm or less.

[0074] Based on mass, the total content of silicon (Si) and aluminum (Al) in the composite sintered body is preferably 50 ppm or less. This total content is measured by secondary ion mass spectrometry (SIMS). Thus, for a tool using this composite sintered body, in a machining environment, even when the interface between the tool and the material to be cut is exposed to high temperature and high pressure, the expansion of tool damage caused by the reaction of a part of the cubic boron nitride constituting the tool with Si or Al can be well suppressed.

[0075] The composite sintered body substantially does not contain a binder, a sintering aid, a catalyst, etc. Thus, the strength and thermal diffusivity of the composite sintered body are improved.

[0076] The lower limit of the content rate of cubic boron nitride particles in the composite sintered body is preferably 50% by volume or more, more preferably 60% by volume or more, and still more preferably 70% by volume or more. The upper limit of the content rate of cubic boron nitride particles in the composite sintered body is preferably 98.5% by volume or less, more preferably 97% by volume or less, and still more preferably 95% by volume or less. The content rate of cubic boron nitride particles in the composite sintered body is preferably 50% by volume or more and 98.5% by volume or less, more preferably 60% by volume or more and 97% by volume or less, and still more preferably 70% by volume or more and 95% by volume or less.

[0077] The lower limit of the content rate of hexagonal boron nitride particles in the composite sintered body is preferably 1.5% by volume or more, more preferably 3% by volume or more, and still more preferably 5% by volume or more. The upper limit of the content rate of hexagonal boron nitride particles in the composite sintered body is preferably 50% by volume or less, more preferably 40% by volume or less, and still more preferably 30% by volume or less. The content rate of hexagonal boron nitride particles in the composite sintered body is preferably 1.5% by volume or more and 50% by volume or less, more preferably 3% by volume or more and 40% by volume or less, and still more preferably 5% by volume or more and 30% by volume or less.

[0078] The lower limit of the content rate of wurtzite boron nitride particles in the composite sintered body is preferably 1.5% by volume or more, more preferably 3% by volume or more, and still more preferably 5% by volume or more. The upper limit of the content rate of wurtzite boron nitride particles in the composite sintered body is preferably 40% by volume or less, more preferably 30% by volume or less, and still more preferably 20% by volume or less. The content rate of wurtzite boron nitride particles in the composite sintered body is preferably 1.5% by volume or more and 40% by volume or less, more preferably 3% by volume or more and 30% by volume or less, and still more preferably 5% by volume or more and 20% by volume or less.

[0079] In the composite sintered body of the present disclosure, the volume-based content rate Vc of cubic boron nitride particles, the volume-based content rate Vh of hexagonal boron nitride particles, and the volume-based content rate Vw of wurtzite boron nitride particles satisfy the relationship of the following formula 1.

[0080] Formula 1: 0.015 ≤ (Vh + Vw) / (Vc + Vh + Vw) ≤ 0.5

[0081] In the composite sintered body satisfying the relationship of the above formula 1, the total of the hexagonal boron nitride particles and the wurtzite boron nitride particles is 1.5% by volume or more and 50% by volume or less with respect to the total of the cubic boron nitride particles, the hexagonal boron nitride particles, and the wurtzite boron nitride particles. Hexagonal boron nitride and wurtzite boron nitride have low frictional resistance during wire drawing, and thus slidability can be imparted to the composite sintered body. Therefore, the composite sintered body containing hexagonal boron nitride and wurtzite boron nitride in the above ratio has excellent slidability, and it is difficult to cause seizure or wire breakage due to the generation of frictional heat even during wire drawing processing, and a long tool life can be achieved.

[0082] Furthermore, hexagonal boron nitride and wurtzite boron nitride are softer than cubic boron nitride, and thus excellent crack propagation resistance can be achieved. Thereby, a tool using this composite sintered body is difficult to generate cracks even during wire drawing processing, and a long tool life can be achieved.

[0083] Furthermore, in the composite sintered body of the present disclosure, the ratio of the cubic boron nitride particles with respect to the total of the cubic boron nitride particles, the hexagonal boron nitride particles, and the wurtzite boron nitride particles is 50% by volume or more and 98.5% by volume or less. Cubic boron nitride particles have excellent toughness while having high hardness, and also have high crystallinity and high thermal diffusivity. Therefore, a tool using the composite sintered body containing the cubic boron nitride particles in the above ratio has excellent wear resistance even during wire drawing processing, and it is difficult to cause seizure due to the generation of frictional heat, and a long tool life can be achieved.

[0084] The volume-based content rate Vc of the cubic boron nitride particles, the volume-based content rate Vh of the hexagonal boron nitride particles, and the volume-based content rate Vw of the wurtzite boron nitride particles preferably satisfy the relationship of the following formula 2, and more preferably satisfy the relationship of the following formula 3.

[0085] Formula 2: 0.03 ≤ (Vh + Vw) / (Vc + Vh + Vw) ≤ 0.4

[0086] Formula 3: 0.05 ≤ (Vh + Vw) / (Vc + Vh + Vw) ≤ 0.3

[0087] The volume-based content rate Vh of the hexagonal boron nitride particles and the volume-based content rate Vw of the wurtzite boron nitride particles preferably satisfy the relationship of the following formula 4, and more preferably satisfy the relationship of formula 5.

[0088] Formula 4: 0.05 ≤ Vh / (Vh + Vw) ≤ 1

[0089] Formula 5: 0.1 ≤ Vh / (Vh + Vw) ≤ 0.95

[0090] Thereby, the composite sintered body has high slidability and excellent crack propagation resistance.

[0091] The volume-based content rates (volume %) of cubic boron nitride particles, hexagonal boron nitride particles, and wurtzite boron nitride particles in the composite sintered body can be measured by X-ray diffraction. The specific measurement method is as described below.

[0092] Cut the composite sintered body with a diamond grinding stone electrodeposition wire, and use the cut surface as the observation surface.

[0093] Obtain the X-ray spectrum of the cut surface of the composite sintered body using an X-ray diffractometer (manufactured by Rigaku Corporation, "MiniFlex600" (trade name)). The conditions of the X-ray diffractometer at this time are as described below.

[0094] Characteristic X-ray: Cu-Kα (wavelength )

[0095] Tube voltage: 45 kV

[0096] Tube current: 40 mA

[0097] Filter: Multilayer mirror

[0098] Optical system: Focusing method

[0099] X-ray diffraction method: θ-2θ method

[0100] In the obtained X-ray spectrum, measure the following peak intensities A, peak intensity B, and peak intensity C.

[0101] Peak intensity A: The peak intensity of hexagonal boron nitride obtained by removing the background from the peak intensities near diffraction angles 2θ = 26° and 28.5°. When there are two peaks, one near 26° and the other near 28.5°, the sum of the peak intensities of the two is used as the peak intensity of hexagonal boron nitride.

[0102] Peak intensity B: The peak intensity of wurtzite boron nitride obtained by removing the background from the peak intensity near diffraction angle 2θ = 40.8°.

[0103] Peak intensity C: The peak intensity of cubic boron nitride obtained by removing the background from the peak intensity near diffraction angle 2θ = 43.5°.

[0104] The content fraction of hexagonal boron nitride particles is obtained by calculating the value of peak intensity A / (peak intensity A + peak intensity B + peak intensity C). The content fraction of wurtzite boron nitride particles is obtained by calculating the value of peak intensity B / (peak intensity A + peak intensity B + peak intensity C). The content fraction of cubic boron nitride particles is obtained by calculating the value of peak intensity C / (peak intensity A + peak intensity B + peak intensity C). Hexagonal boron nitride, compressed hexagonal boron nitride, wurtzite boron nitride, and cubic boron nitride all have the same degree of electron weight. Therefore, the above X-ray peak intensity ratio can be regarded as the volume ratio in the composite sintered body. In addition, the content of inevitable impurities is trace, so it will not affect the calculation of the content fraction (volume%) of cubic boron nitride particles, hexagonal boron nitride particles, and wurtzite boron nitride particles in the composite sintered body.

[0105] <Dislocation density of cubic boron nitride particles>

[0106] In the composite sintered body of the present disclosure, the dislocation density of cubic boron nitride particles is 1×10 15 / m 2 or more and 1×10 17 / m 2 or less. The cubic boron nitride particles have excellent toughness while having high hardness, and have high crystallinity and large thermal diffusivity. Therefore, a tool using the composite sintered body containing the cubic boron nitride particles has excellent wear resistance even in wire drawing processing, and is difficult to cause seizure with the generation of frictional heat, and can have a long tool life.

[0107] From the viewpoint of improving toughness and thermal diffusivity, the upper limit of the dislocation density of cubic boron nitride particles is preferably 3×10 16 / m 2 or less, more preferably 5×10 15 / m 2 or less. From the viewpoint of maintaining high hardness and excellent wear resistance, the lower limit of the dislocation density of cubic boron nitride is preferably 1×10 15 / m 2 or more. The dislocation density of cubic boron nitride particles is preferably 1×10 15 / m 2 or more and 3×10 16 / m 2 or less, further preferably 1×10 15 / m 2 or more and 5×10 15 / m 2 or less.

[0108] In this specification, the dislocation density is calculated according to the following steps.

[0109] Prepare a test piece composed of a composite sintered body. The dimensions of the test piece are as follows: the observation surface is 2.0 mm × 2.0 mm, and the thickness is 1.0 mm. Grind the observation surface of the test piece.

[0110] Perform X-ray diffraction measurement on the observation surface of the test piece under the following conditions, and obtain the line profiles of the diffraction peaks from the respective orientation planes of the main orientations (111), (200), (220), (311), (400), and (331) of cubic boron nitride.

[0111] (X-ray diffraction measurement conditions)

[0112] X-ray source: synchrotron radiation

[0113] Instrument conditions: detector NaI (fluorescence cut by appropriate ROI)

[0114] Energy: 18 keV (wavelength: )

[0115] Diffraction crystal: Si(111)

[0116] Incident slit: width 5 mm × height 0.5 mm

[0117] Receiving slit: double slit (width 3 mm × height 0.5 mm)

[0118] Mirror: platinum-coated mirror

[0119] Incident angle: 2.5 mrad

[0120] Scanning method: 2θ-θ scanning

[0121] Measured peaks: six peaks of (111), (200), (220), (311), (400), and (331) of cubic boron nitride. However, in cases where it is difficult to obtain the profile through texture and orientation, the peaks with this crystal plane index are excluded.

[0122] Measurement conditions: Set more than 9 measurement points in the full width at half maximum. The peak top intensity is 2000 counts or more. Since the peak tail is also used for analysis, set the measurement range to about 10 times the full width at half maximum.

[0123] The line profile obtained by the above X-ray diffraction measurement has a shape that includes both the true broadening caused by physical quantities such as the inhomogeneous strain of the specimen and the broadening caused by the apparatus. To obtain the inhomogeneous strain and the grain size, the component caused by the apparatus is removed from the measured line profile to obtain the true line profile. The true line profile is obtained by the following method: fitting the obtained line profile and the line profile caused by the apparatus using a pseudo-Voigt function and subtracting the line profile caused by the apparatus. As a standard sample for removing the diffraction line broadening caused by the apparatus, LaB6 is used. In addition, when using synchrotron radiation with high parallelism, the diffraction line broadening caused by the apparatus can be regarded as 0.

[0124] The dislocation density is calculated by analyzing the obtained true line profile using the modified Williamson-Hall method and the modified Warren-Averbach method. The modified Williamson-Hall method and the modified Warren-Averbach method are well-known line profile analysis methods for obtaining the dislocation density.

[0125] The formula of the modified Williamson-Hall method is expressed by the following formula (I).

[0126] [Mathematical formula 1]

[0127]

[0128] (In the above formula (I), ΔK represents the half-value width of the line profile, D represents the grain size, M represents the configuration parameter, b represents the Burgers vector, ρ represents the dislocation density, K represents the scattering vector, O(K 2 C) represents the higher-order term of K 2 C, and C represents the average value of the contrast factor.

[0129] C in the above formula (I) is expressed by the following formula (II).

[0130] C = C h00 [1 - q(h 2 k 2 + h 2 l 2 + k 2 l 2 ) / (h 2 + k 2 + l 2 ) 2 (II)

[0131] In the above formula (II), the calculation code ANIZC is used, and the slip system is <110>{111}, and the elastic stiffness C 11is 8.44 GPa, C 12 is 1.9 GPa, C 44 Find the contrast factors C for screw dislocations and edge dislocations respectively, with the contrast factor C for screw dislocations being 0.203 and that for edge dislocations being 0.212. For the coefficient q related to the contrast factor, the value for screw dislocations is 1.65 and that for edge dislocations is 0.58. It should be noted that the ratio of screw dislocations is fixed at 0.5 and the ratio of edge dislocations is fixed at 0.5. h00 and the coefficient q related to the contrast factor. Regarding the contrast factor C h00 For screw dislocations, it is 0.203, and for edge dislocations, it is 0.212. Regarding the coefficient q related to the contrast factor, for screw dislocations, it is 1.65, and for edge dislocations, it is 0.58. It should be noted that the ratio of screw dislocations is fixed at 0.5 and the ratio of edge dislocations is fixed at 0.5.

[0132] In addition, a relationship of the following formula (III) is established using the contrast factor C between dislocations and non-uniform strain.

[0133] <ε(L) 2 >=(ρCb 2 / 4π)ln(R e / L) (III)

[0134] (In the above formula (III), R e represents the effective radius of the dislocation.)

[0135] Based on the relationship of the above formula (III) and the Warren - Averbach formula, it can be expressed in the case of the following formula (IV). As a modified Warren - Averbach method, the dislocation density ρ and the grain size can be obtained.

[0136] lnA(L) = lnA S (L) - (πL 2 ρb 2 / 2)ln(R e / L)(K 2 C) + O(K 2 C) 2 (IV)

[0137] (In the above formula (IV), A(L) represents the Fourier series, A S (L) represents the Fourier series related to the grain size, and L represents the Fourier length.)

[0138] Details of the modified Williamson-Hall method and the modified Warren-Averbach method are described in T. Ungar and A. Borbely, “The effect of dislocation contrast on x-ray linebroadening: A new approach to line profile analysis,” Appl. Phys. Lett., Vol. 69, No. 21, pp. 3173, 1996; and T. Ungar, S. Ott, P. Sanders, A. Borbely, J. Weertman, “Dislocations, grain size and planar faults in nanostructured copper determined by high resolution X-ray diffraction and a new procedure of peak profile analysis,” Acta Mater., Vol. 46, No. 10, pp. 3693-3699, 1998.

[0139] <Median particle diameter d50 of cubic boron nitride particles>

[0140] In the composite sintered body of the present disclosure, the median particle diameter d50 (hereinafter also referred to as “particle diameter”) of the equivalent circle diameter of the cubic boron nitride particles is 10 nm or more and 500 nm or less. The composite sintered body containing the cubic boron nitride particles can have excellent strength, improved toughness, and excellent crack propagation resistance. Therefore, a tool using the composite sintered body is hardly cracked even in wire drawing processing and can have a long tool life.

[0141] From the viewpoint of ensuring excellent strength and toughness, the upper limit of the median particle diameter d50 of the equivalent circle diameter of the cubic boron nitride particles is 500 nm or less, preferably 100 nm or less. From the manufacturing viewpoint, the lower limit of the median particle diameter d50 of the equivalent circle diameter of the cubic boron nitride particles is 10 nm or more. The median particle diameter d50 of the equivalent circle diameter of the cubic boron nitride particles is preferably 10 nm or more and 300 nm or less, more preferably 10 nm or more and 100 nm or less.

[0142] (Method for measuring median particle diameter d50)

[0143] In this specification, the median particle size d50 of the circular equivalent diameters of the multiple cubic boron nitride particles contained in the composite sintered body refers to the value obtained by respectively measuring the median particle size d50 of the multiple cubic boron nitride particles at five arbitrarily selected measurement points and calculating their average value.

[0144] It should be noted that, as measured by the applicant, it can be confirmed that as long as the median particle size d50 is measured for the same specimen, even if the calculation is performed multiple times by changing the selection position of the measurement field of view of the composite sintered body, there is almost no deviation in the measurement results, and even if the measurement field of view is arbitrarily set, the measurement results are not random.

[0145] When the composite sintered body is used as part of a tool, a part of the composite sintered body is cut out using a diamond grinding wheel electroplated wire or the like, the cut cross-section is polished, and five measurement points are arbitrarily set on the polished surface.

[0146] Hereinafter, the method for measuring the median particle size d50 of the circular equivalent diameters of the multiple cubic boron nitride particles at each measurement point will be specifically described.

[0147] The composite sintered body is cut using a diamond grinding wheel electroplated wire or the like so that the measurement points are exposed, and the cut surface is polished. The measurement points on the polished surface are observed using SEM (JSM-7500F (trade name) manufactured by JEOL Ltd.) to obtain an SEM image. The size of the measurement field of view is set to 12 μm × 15 μm, and the observation magnification is set to 10,000 times.

[0148] For each of the five SEM images, in the state where the grain boundaries of the grains observed within the measurement field of view are separated, the distribution of the circular equivalent diameters of the cubic boron nitride particles is calculated using image processing software (Win Roof ver.7.4.5).

[0149] The median particle size d50 is calculated with the entire measurement field of view as the denominator. The median particle size d50 is calculated based on the distribution of the circular equivalent diameters of the cubic boron nitride particles.

[0150] [Embodiment 2: Tool]

[0151] The tool of the present disclosure is a tool using the composite sintered body of Embodiment 1. Specifically, it is preferably used for cutting tools, wear-resistant tools, grinding tools, etc.

[0152] The entirety of each of the cutting tool, wear-resistant tool, and grinding tool using the composite sintered body of the present disclosure may be composed of the composite sintered body, or only a part thereof (for example, in the case of a cutting tool, the cutting edge part) may be composed of the composite sintered body. In addition, a coating film may be formed on the surface of each tool.

[0153] As cutting tools, examples include: drill bits, end mills, indexable cutting inserts for drill bits, indexable cutting inserts for end mills, indexable cutting inserts for milling, indexable cutting inserts for turning, metal saws, gear cutting tools, reamers, taps, turning tools, etc.

[0154] As wear-resistant tools, examples include: dies, scribers, scriber wheels, trimmers, etc. As grinding tools, examples include grindstones, etc.

[0155] [Embodiment 3: Manufacturing method of composite sintered body]

[0156] Use Figures 1 to 4 A specific example of the manufacturing method of the composite sintered body of the present disclosure will be described. Figure 1 is the pressure-temperature phase diagram of boron nitride. Figures 2 to 4 are respectively diagrams for explaining an example of the manufacturing method of the composite sintered body of the present disclosure.

[0157] First, in order to facilitate understanding of the manufacturing method of the composite sintered body, the pressure-temperature phase diagram of boron nitride will be described. As Figure 1 shown, boron nitride exists in the following three phases: hexagonal boron nitride, which is the stable phase at normal temperature and pressure; cubic boron nitride, which is the stable phase at high temperature and high pressure; and wurtzite boron nitride, which is the metastable phase during the transition from hexagonal boron nitride to cubic boron nitride.

[0158] The boundaries of each phase can be represented by a linear function. In this specification, the temperature and pressure within the stable region of each phase can be represented by a linear function.

[0159] In this specification, when the temperature is set to T (°C) and the pressure is set to P (GPa), the temperature and pressure within the stable region of wurtzite boron nitride (denoted as "wBN stable region" in Figure 1 ) are defined as the temperature and pressure that simultaneously satisfy the following formula (1) and formula (2).

[0160] Formula (1): P ≥ -0.0037T + 11.301

[0161] Formula (2): P ≤ -0.085T + 117

[0162] In this specification, when the temperature is set to T (°C) and the pressure is set to P (GPa), the temperature and pressure within the stable region of hexagonal boron nitride (denoted as "hBN stable region" in Figure 1 ) are defined as the temperature and pressure that simultaneously satisfy the following formula A and formula B, or the temperature and pressure that simultaneously satisfy the following formula C and formula D.

[0163] Formula A: P ≤ -0.0037T + 11.301

[0164] Formula B: P ≤ -0.085T + 117

[0165] Formula C: P ≤ 0.0027T + 0.3333

[0166] Formula D: P ≥ -0.085T + 117

[0167] In this specification, when the temperature is set to T (°C) and the pressure is set to P (GPa), the temperature and pressure within the stable region of cubic boron nitride (denoted as "cBN stable region" in Figure 1 ) are defined as the temperature and pressure that simultaneously satisfy Formula D and Formula E below.

[0168] Formula D: P ≥ -0.085T + 117

[0169] Formula E: P ≥ 0.0027T + 0.3333

[0170] In the method for manufacturing the composite sintered body of the present disclosure, hexagonal boron nitride or pyrolytic boron nitride is used as a raw material. By subjecting hexagonal boron nitride or pyrolytic boron nitride to heat and pressure treatment until the temperature and pressure within the stable region of cubic boron nitride, at least a part of the raw material can be converted into cubic boron nitride. The inventors of the present invention have intensively studied the path of temperature and pressure during the heat and pressure treatment, as well as the holding time at a certain temperature and a certain pressure, and newly discovered the heat and pressure conditions under which the composite sintered body of the present disclosure can be obtained.

[0171] Hereinafter, Figures 2 to 4 the details of each step of the method for manufacturing the composite sintered body of the present disclosure will be described. It should be noted that in Figures 2 to 4 , the arrow indicates the heat and pressure path. Figures 2 to 4 The path shown is an example and is not limited thereto.

[0172] <Preparation Step>

[0173] Prepare hexagonal boron nitride powder or pyrolytic boron nitride as the raw material of the composite sintered body. The purity (content rate of hexagonal boron nitride) of the hexagonal boron nitride powder is preferably 98.5% or more, more preferably 99% or more, and most preferably 100%. There is no particular limitation on the particle size of the hexagonal boron nitride powder, but for example, it can be set to 0.1 μm or more and 10 μm or less.

[0174] The particle size of pyrolytic boron nitride becomes very fine due to thermal decomposition, making it difficult for crystal grains to grow. Therefore, when pyrolytic boron nitride is used as a raw material, the particle size of the cubic boron nitride particles in the resulting composite sintered body tends to be small. Either pyrolytic boron nitride produced by a conventionally known synthesis method or commercially available pyrolytic boron nitride can be used.

[0175] <Heating and Pressurizing Step>

[0176] Next, subject hexagonal boron nitride powder or pyrolytic boron nitride to temperatures and pressures within the stable region of wurtzite boron nitride, and heat and pressurize it to temperatures and pressures within the stable region of cubic boron nitride.

[0177] Appropriately adjust the heating and pressurizing path to obtain the composite sintered body of Embodiment 1. For example, as Figure 2 shown, starting from the starting point (25°C, 0 GPa) of hexagonal boron nitride powder or pyrolytic boron nitride, apply pressure while maintaining the temperature (arrow A1), then heat while maintaining the pressure (arrow A2), then apply pressure while maintaining the temperature (arrow A3), and then heat while maintaining the pressure (arrow A4) to reach temperatures and pressures within the stable region of cubic boron nitride, thereby obtaining the composite sintered body of the present disclosure. In the Figure 2 heating and pressurizing path, during the second pressurization shown by arrow A3, the heating and pressurizing path enters the stable region of wurtzite boron nitride.

[0178] In addition, as Figure 3 shown, starting from the starting point (25°C, 0 GPa) of hexagonal boron nitride powder or pyrolytic boron nitride, heat while maintaining the pressure (arrow B1), then apply pressure while maintaining the temperature (arrow B2), and then heat while maintaining the pressure (arrow B3) to reach temperatures and pressures within the stable region of cubic boron nitride, thereby obtaining the composite sintered body of the present disclosure. In the Figure 3 heating and pressurizing path, during the first pressurization shown by arrow B2, the heating and pressurizing path enters the stable region of wurtzite boron nitride.

[0179] Figure 4 Shows the heating and pressurizing paths indicated by arrow C1 and arrow C3, and the heating and pressurizing paths indicated by arrow C2 and arrow C4. As Figure 4 shown, starting from the starting point (25°C, 0 GPa) of hexagonal boron nitride powder or pyrolytic boron nitride, apply pressure while maintaining the temperature (arrow C1, arrow C2), then heat while maintaining the pressure (arrow C3, arrow C4) to reach temperatures and pressures within the stable region of cubic boron nitride, thereby obtaining the composite sintered body of the present disclosure. In the Figure 4 heating and pressurizing path, during the first heating shown by arrow C3 or the first pressurization shown by arrow C2, the heating and pressurizing path enters the stable region of wurtzite boron nitride.

[0180] In Figures 2 to 4In any of the heating and pressurization paths shown, the temperature in the stable region of cubic boron nitride finally reached can be set, for example, to 1200 °C or higher and less than 2500 °C, and the pressure can be set to 6 GPa or higher and 20 GPa or lower. The holding time at this temperature and this pressure can be set to 1 minute or longer and 30 minutes or shorter. Thereby, not all of the raw material is converted into cubic boron nitride, and hexagonal boron nitride particles, or hexagonal boron nitride particles and wurtzite-type boron nitride particles can remain in the composite sintered body.

[0181] By increasing the holding time in the stable region of cubic boron nitride, the dislocation density of the cubic boron nitride particles in the composite sintered body can be increased. In addition, by Figures 2 to 4 holding for 3 minutes or longer at the temperature and pressure between the boundary (P = -0.0037T + 11.301) between the stable region of hexagonal boron nitride and the stable region of wurtzite-type boron nitride in the stable region of wurtzite type shown and the dotted line represented by P = -0.0037T + 11.5, the dislocation density of cubic boron nitride in the composite sintered body can be increased.

[0182] <Supplementary Note>

[0183] The above description includes the embodiments described in the following supplementary notes.

[0184] (Supplementary Note 1)

[0185] A composite sintered body composed of

[0186] cubic boron nitride particles,

[0187] and hexagonal boron nitride particles, or hexagonal boron nitride particles and wurtzite-type boron nitride particles,

[0188] the dislocation density of the cubic boron nitride particles is 1×10 15 / m 2 or more and 1×10 17 / m 2 or less,

[0189] the median particle size d50 of the equivalent circle diameter of the cubic boron nitride particles is 10 nm or more and 500 nm or less,

[0190] the volume-based content rate Vc of the cubic boron nitride particles, the volume-based content rate Vh of the hexagonal boron nitride particles, and the volume-based content rate Vw of the wurtzite-type boron nitride particles satisfy the relationship of Formula 1 below,

[0191] Formula 1: 0.015 ≤ (Vh + Vw) / (Vc + Vh + Vw) ≤ 0.5.

[0192] (Supplementary Note 2)

[0193] The composite sintered body according to Note 1, the volume-based content rate Vh of the hexagonal boron nitride particles and the volume-based content rate Vw of the wurtzite-type boron nitride particles satisfy the relationship of Formula 4 below,

[0194] Formula 4: 0.05 ≤ Vh / (Vh + Vw) ≤ 1.

[0195] Examples

[0196] The present embodiment will be described in more detail by way of examples. However, the present embodiment is not limited to these examples.

[0197] [Example 1]

[0198] In Example 1, hexagonal boron nitride was used as a raw material to produce a composite sintered body, and the relationship between the composition (composition, median grain size, dislocation density) of the composite sintered body and the tool life during wire drawing of stainless steel wire using a die made of the composite sintered body was studied.

[0199] <Production of composite sintered body>

[0200] Composite sintered bodies of Specimens 1 to 17 were produced according to the following steps.

[0201] (Preparation process)

[0202] 6 g of hexagonal boron nitride powder (“DENKA boron nitride” (trade name) manufactured by DENKA Company, particle size 5 μm) was prepared. The above-mentioned hexagonal boron nitride powder was put into a molybdenum capsule and set in a high-pressure high-temperature generating device.

[0203] (Heating and pressurizing process)

[0204] [Specimens 1 to 6, Specimen 8, Specimen 9]

[0205] Using the high-pressure high-temperature generating device, the above-mentioned hexagonal boron nitride powder was heated or pressurized from the temperature and pressure described in the “starting point” of Table 1 to the temperature and pressure described in the “reached temperature” and “reached pressure” columns of the “first stage”.

[0206] Subsequently, it was heated or pressurized to the temperature and pressure described in the “reached temperature” and “reached pressure” columns of the “second stage” of Table 1 and held for the length described in the “holding time” column. When the “holding time” is recorded as “0”, it is immediately transferred to the “third stage” described later.

[0207] Subsequently, raise the temperature and pressure to the temperature and pressure recorded in the "Reached Temperature" and "Reached Pressure" columns of the "Third Stage" in Table 1, and maintain for the length of time recorded in the "Holding Time" column. When the "Holding Time" is recorded as "0", immediately proceed to the "Fourth Stage" described below.

[0208] Subsequently, raise the temperature to the temperature and pressure recorded in the "Reached Temperature" and "Reached Pressure" columns of the "Fourth Stage" in Table 1, and maintain for the length of time recorded in the "Holding Time" column, thereby obtaining a composite sintered body.

[0209] [Specimens 7, 11 to 17]

[0210] Using an ultra-high pressure and high temperature generating device, starting from the temperature and pressure recorded in the "Temperature" and "Pressure" columns of the "Starting Point" in Table 1 for the above hexagonal boron nitride powder, raise the temperature or pressure to the temperature and pressure recorded in the "Reached Temperature" and "Reached Pressure" columns of the "First Stage", and maintain for the length of time recorded in the "Holding Time" column. When the "Holding Time" is recorded as "0", immediately proceed to the "Third Stage" described below.

[0211] Subsequently, raise the temperature or pressure to the temperature and pressure recorded in the "Reached Temperature" and "Reached Pressure" columns of the "Second Stage" in Table 1, and maintain for the length of time recorded in the "Holding Time" column. When the "Holding Time" is recorded as "0", immediately proceed to the "Third Stage" described below.

[0212] Subsequently, raise the temperature or pressure to the temperature and pressure recorded in the "Reached Temperature" and "Reached Pressure" columns of the "Third Stage" in Table 1, and maintain for the length of time recorded in the "Holding Time" column, thereby obtaining a composite sintered body.

[0213] [Specimen 10]

[0214] Using an ultra-high pressure and high temperature generating device, starting from the temperature and pressure recorded in the "Temperature" and "Pressure" columns of the "Starting Point" in Table 1 for the above hexagonal boron nitride powder, raise the pressure to the temperature and pressure recorded in the "Reached Temperature" and "Reached Pressure" columns of the "First Stage".

[0215] Subsequently, raise the temperature to the temperature and pressure recorded in the "Reached Temperature" and "Reached Pressure" columns of the "Second Stage" in Table 1, and maintain for the length of time recorded in the "Holding Time" column, thereby obtaining a composite sintered body.

[0216] The heating and pressing paths of Specimens 1 to 12 passed through the stable region of wurtzite boron nitride. The temperature at which each specimen entered the stable region of wurtzite boron nitride is shown in the column of "wBN stable region entry temperature" in Table 1. The heating and pressing paths of Specimens 13 to 17 did not pass through the stable region of wurtzite boron nitride. In this case, "none" is indicated in the column of "wBN stable region entry temperature" in Table 1.

[0217] <Evaluation>

[0218] (Determination of composition)

[0219] In the composite sintered body obtained above, the respective content ratios (volume %) of cubic boron nitride particles, hexagonal boron nitride particles, and wurtzite boron nitride particles were measured by X-ray diffraction. The specific method of X-ray diffraction is as shown in Embodiment 1, so the description thereof will not be repeated. The results are shown in the columns of "cBN volume %", "hBN volume %", and "wBN volume %" in Table 1. In addition, based on these results, the value of (Vh + Vw) / (Vc + Vh + Vw) was calculated. The results are shown in the column of "Vh+Vw / Vc+Vh+Vw" in Table 1.

[0220] It should be noted that in all specimens, no components other than cBN, hBN, and wBN were identified.

[0221] (Determination of dislocation density)

[0222] By analyzing the line profile obtained by X-ray diffraction using the modified Williamson-Hall method and the modified Warren-Averbach method, the dislocation density of the cubic boron nitride particles in the composite sintered body obtained above was calculated. The specific calculation method of the dislocation density is as shown in Embodiment 1, so the description thereof will not be repeated. The results are shown in the column of "cBN dislocation density" in Table 1.

[0223] (Determination of median diameter d50)

[0224] For the cubic boron nitride particles contained in the composite sintered body obtained above, the median diameter d50 of the equivalent circle diameter was measured. The specific method is as shown in Embodiment 1, so the description thereof will not be repeated. The results are shown in the column of "median diameter d50" in Table 1.

[0225] (Wire drawing test)

[0226] For the obtained composite sintered body, a through hole was formed by laser irradiation to fabricate a mold in which the central portion of the mold was composed of the composite sintered body and the periphery was coated with metal. The minimum value of the diameter of the through hole was 0.1 mm.

[0227] Using the above-mentioned die, a wire drawing test was conducted on a wire (wire diameter : 110 μm, material: SUS304). No lubricant was used during wire drawing. The wire drawing speed was 150 m / minute, and the area reduction rate was 17%.

[0228] Under the above conditions, wire drawing was carried out, and the wire drawing time until the surface roughness Ra of the wire reached 0.020 μm was determined as the tool life. The surface roughness Ra of the wire was measured using a laser microscope ("VK-X100" (trademark) manufactured by KEYENCE Corporation) based on ISO25178. The tool life of each specimen is expressed as the ratio when the tool life during wire drawing under the same conditions as above using a die made of commercially available single-crystalline diamond (manufactured by Sumitomo Electric Hardmetal) is set to "1". The results are shown in the "Tool Life" column of Table 1. The larger the value, the more difficult it is to cause deterioration of the surface state of the wire, and the longer the tool life.

[0229] [Table 1]

[0230]

[0231] <Discussion>

[0232] Specimens 1 to 12 correspond to the examples. Specimens 13 to 17 correspond to the comparative examples.

[0233] It can be confirmed that: compared with the comparative examples (Specimens 13 to 17), the die of the examples (Specimens 1 to 12) is less likely to cause deterioration of the surface state of the wire, and has a longer tool life.

[0234] In Specimens 13 to 15 (comparative examples), the dislocation density of cubic boron nitride particles is less than 1×10 15 / m 2 , and the tool life is shorter than that of the examples. It is speculated that the reason is that as the hardness of the cubic boron nitride particles decreases, the wear resistance of the composite sintered body decreases, and the surface state of the wire is easily deteriorated.

[0235] In Specimen 16 (comparative example), the content rate of cubic boron nitride particles is 100 vol%, and (Vh + Vw) / (Vc + Vh + Vw) is 0 (i.e., less than 0.0015), and the tool life is shorter than that of the examples. It is considered that the reason is that the composite sintered body does not contain hexagonal boron nitride and wurtzite boron nitride, so the slidability of the composite sintered body decreases, the frictional heat increases as the resistance increases, and wear proceeds rapidly, and galling is likely to occur.

[0236] In sample 17 (comparative example), the content rate of cubic boron nitride particles was 100 vol%, (Vh+Vw) / (Vc+Vh+Vw) was 0 (i.e., less than 0.0015), and the median particle size d50 of the equivalent circle diameter of the cubic boron nitride particles was 720 nm (i.e., exceeding 500 nm), and the tool life was also shorter than that of the examples. It is speculated that the reason is that the composite sintered body does not contain hexagonal boron nitride and wurtzite boron nitride, so the slidability of the composite sintered body is reduced, the frictional heat increases with the increase of resistance, wear proceeds rapidly, seizure is likely to occur, and since the particle size of the cubic boron nitride particles is large, the strength and toughness are reduced, the composite sintered body is likely to have defects, and the surface state of the wire is likely to deteriorate.

[0237] [Example 2]

[0238] In Example 2, pyrolytic boron nitride was used as a raw material to produce a composite sintered body, and the relationship between the composition of the composite sintered body (composition, median particle size of grains, dislocation density) and the tool life when using a die made of the composite sintered body for wire drawing of stainless steel wire was studied.

[0239] <Production of composite sintered body>

[0240] Composite sintered bodies of Samples 2-1 to 2-9 were produced according to the following steps.

[0241] (Preparation process)

[0242] 6 g of pyrolytic boron nitride was prepared. The pyrolytic boron nitride was placed in a molybdenum casing and set in a ultra-high pressure and high temperature generating device.

[0243] (Heating and pressurization process)

[0244] [Sample 2-3, Sample 2-6]

[0245] Using the ultra-high pressure and high temperature generating device, the above-mentioned pyrolytic boron nitride was pressurized from the temperature and pressure recorded in the "Temperature" and "Pressure" columns of the "Starting point" in Table 2 to the temperature and pressure recorded in the "Reached temperature" and "Reached pressure" columns of the "First stage". The holding time for each sample was 0 minutes and it was immediately transferred to the "Second stage" described below.

[0246] Subsequently, the temperature was raised to the temperature and pressure recorded in the "Reached temperature" and "Reached pressure" columns of the "Second stage" in Table 2.

[0247] Subsequently, the pressure was raised to the temperature and pressure recorded in the "Reached temperature" and "Reached pressure" columns of the "Third stage" in Table 2 and held for the length recorded in the "Holding time" column. When "0" was recorded in the "Holding time", it was immediately transferred to the "Fourth stage" described below.

[0248] Subsequently, the temperature was raised to the temperature and pressure recorded in the "Reached Temperature" and "Reached Pressure" columns of the "Fourth Stage" in Table 2, and maintained for the length recorded in the "Holding Time" column, thereby obtaining a composite sintered body.

[0249] [Specimens 2-2, 2-7, 2-8]

[0250] Using a ultra-high pressure and high temperature generating device, the above hexagonal boron nitride powder was started from the temperature and pressure recorded in the "Temperature" and "Pressure" columns of the "Starting Point" in Table 2, and the pressure was raised to the temperature and pressure recorded in the "Reached Temperature" and "Reached Pressure" columns of the "First Stage".

[0251] Subsequently, the temperature was raised to the temperature and pressure recorded in the "Reached Temperature" and "Reached Pressure" columns of the "Second Stage" in Table 2, and maintained for the length recorded in the "Holding Time" column. When the "Holding Time" is recorded as "0", it is immediately transferred to the "Third Stage" described below.

[0252] Subsequently, the temperature and / or pressure was raised to the temperature and pressure recorded in the "Reached Temperature" and "Reached Pressure" columns of the "Third Stage" in Table 2, and maintained for the length recorded in the "Holding Time" column, thereby obtaining a composite sintered body.

[0253] [Specimens 2-1, 2-4, 2-5, 2-9]

[0254] Using a ultra-high pressure and high temperature generating device, the above hexagonal boron nitride powder was started from the temperature and pressure recorded in the "Temperature" and "Pressure" columns of the "Starting Point" in Table 2, and the pressure was raised to the temperature and pressure recorded in the "Reached Temperature" and "Reached Pressure" columns of the "First Stage", and maintained for the length recorded in the "Holding Time" column. When the "Holding Time" is recorded as "0", it is immediately transferred to the "Second Stage" described below.

[0255] Subsequently, the temperature was raised to the temperature and pressure recorded in the "Reached Temperature" and "Reached Pressure" columns of the "Second Stage" in Table 2, and maintained for the length recorded in the "Holding Time" column, thereby obtaining a composite sintered body.

[0256] The pressure and temperature increase paths of Specimens 2-1 to 2-6 and 2-9 passed through the stable region of wurtzite boron nitride. The temperature at which each specimen entered the stable region of wurtzite boron nitride is shown in the column of "wBN Stable Region Entry Temperature" in Table 2. The pressure and temperature increase paths of Specimens 2-7 and 2-8 did not pass through the stable region of wurtzite boron nitride.

[0257] <Evaluation>

[0258] (Determination of composition, determination of dislocation density, determination of median particle size d50)

[0259] By the same method as in Example 1, the composition of the obtained composite sintered body was determined, the dislocation density of cubic boron nitride particles was determined, and the median particle size d50 was determined. The results are shown in the columns of "cBN volume %", "hBN volume %", "wBN volume %", "Vh+Vw / Vc+Vh+Vw", "cBN dislocation density", and "median particle size d50" in Table 2.

[0260] (Wire drawing test)

[0261] For the obtained composite sintered body, a through-hole was formed by laser irradiation to fabricate a die. The minimum value of the diameter of the through-hole was 0.1 mm. Using this die, a wire drawing test was carried out under the same conditions as in Example 1. The results are shown in the column of "tool life" in Table 2.

[0262] [Table 2]

[0263]

[0264] <Discussion>

[0265] Specimens 2-1 to 2-6 correspond to the examples. Specimens 2-7 to 2-9 correspond to the comparative examples.

[0266] It can be confirmed that the tool life of the die in the examples (Specimens 2-1 to 2-6) is longer than that in the comparative examples (Specimens 2-7 to 2-9).

[0267] In Specimens 2-7 and 2-8 (comparative examples), the dislocation density of cubic boron nitride particles is less than 1×10 15 / m 2 , and the tool life is shorter than that in the examples. It is speculated that the reason is that as the hardness of cubic boron nitride particles decreases, the wear resistance of the composite sintered body decreases, and the surface state of the wire is likely to deteriorate.

[0268] In Specimen 2-9 (comparative example), the median particle size d50 of the equivalent circle diameter of cubic boron nitride particles is 550 nm (i.e., exceeding 500 nm), and the tool life is shorter than that in the examples. It is speculated that the reason is that the particle size of cubic boron nitride particles is large, so the strength and toughness decrease, the composite sintered body is likely to have defects, and the surface state of the wire is likely to deteriorate. It should be noted that although the temperature and pressure increase path of Specimen 2-9 passes through the stable region of wurtzite boron nitride, the temperature in the stable region of cubic boron nitride finally reached is as high as 2500 °C, so excessive grain growth occurred.

[0269] [Example 3]

[0270] In Example 3, hexagonal boron nitride was used as a raw material to fabricate a composite sintered body, and the relationship between the composition of the composite sintered body (composition, total content of alkali metals and alkaline earth metals, median grain size, dislocation density) and the tool life during wire drawing of stainless steel wire using a die made of the composite sintered body was studied.

[0271] <Fabrication of Composite Sintered Body>

[0272] Composite sintered bodies of Specimen 3-1 and Specimen 3-2 were fabricated according to the following steps.

[0273] (First Step)

[0274] [Specimen 3-1]

[0275] 6 g of hexagonal boron nitride powder (median grain size d50: 5 μm) was prepared. The hexagonal boron nitride powder was placed in a molybdenum capsule and set in a ultrahigh pressure and high temperature generating device.

[0276] [Specimen 3-2]

[0277] 6 g of cubic boron nitride powder (median grain size d50: 5 μm) containing a total amount of alkali metals and alkaline earth metals more than 10 ppm was prepared. The cubic boron nitride powder was maintained at a temperature of 1900 °C for 1 hour in an argon atmosphere to reversely transform cubic boron nitride into hexagonal boron nitride, thereby obtaining hexagonal boron nitride powder. The hexagonal boron nitride powder was placed in a molybdenum capsule and set in a ultrahigh pressure and high temperature generating device.

[0278] (Heating and Pressurizing Step)

[0279] Using the ultrahigh pressure and high temperature generating device, the above-mentioned hexagonal boron nitride powder was started from the temperature and pressure recorded in the "Temperature" and "Pressure" columns of the "Starting Point" in Table 3, and the pressure was increased to the pressure recorded in the "Reached Pressure" column of the "First Stage" while maintaining the temperature.

[0280] Subsequently, the temperature was increased to the temperature recorded in the "Reached Temperature" column of the "Second Stage" in Table 3 while maintaining the pressure.

[0281] Subsequently, the pressure was increased to the pressure recorded in the "Reached Pressure" column of the "Third Stage" in Table 3 while maintaining the temperature.

[0282] Subsequently, the temperature was increased to the temperature recorded in the "Reached Temperature" column of the "Fourth Stage" in Table 3 while maintaining the pressure, and the length recorded in the "Holding Time" column was maintained, thereby obtaining a composite sintered body.

[0283] <Evaluation>

[0284] (Measurement of composition, dislocation density, and median grain size d50)

[0285] Using the same method as in Example 1, the composition of the obtained composite sintered body was measured, the dislocation density of cubic boron nitride particles was measured, and the median grain size d50 was measured. The results are shown in the columns of "cBN volume %", "hBN volume %", "wBN volume %", "Vh+Vw / Vc+Vh+Vw", "cBN dislocation density", and "median grain size d50" in Table 3.

[0286] (Measurement of total content of alkali metal elements and alkaline earth metal elements)

[0287] The total content of alkali metal elements and alkaline earth metal elements in the obtained composite sintered body was measured by SIMS. The total content of alkali metal elements and alkaline earth metal elements is shown in the column of "alkali metal / alkaline earth metal content" in Table 3.

[0288] (Wire drawing test)

[0289] For the obtained composite sintered body, a through-hole was formed by laser irradiation to fabricate a die in which the central portion of the die was composed of the composite sintered body and the periphery was coated with metal. The minimum value of the diameter of the through-hole was 0.1 mm.

[0290] Using the above die, a wire drawing test was carried out on a wire (wire diameter : 110 μm, material: SUS304). No lubricant was used during wire drawing. The wire drawing speed was 250 m / min, and the area reduction rate was 17%.

[0291] Wire drawing was carried out under the above conditions, and the wire drawing time until the surface roughness Ra of the wire reached 0.020 μm was determined as the tool life. The surface roughness Ra of the wire was measured using a laser microscope ("VK-X100" (trademark) manufactured by KEYENCE Corporation) based on ISO25178. The tool life of each specimen is expressed as the ratio when the tool life during wire drawing under the same conditions as above using a die made of commercially available single crystal diamond (manufactured by Sumitomo Electric Hardmetal) is set to "1". The results are shown in the column of "tool life" in Table 3. The larger the value, the more difficult it is to cause deterioration of the surface state of the wire, and the longer the tool life.

[0292] [Table 3]

[0293]

[0294] <Discussion>

[0295] Samples 3-1 and 3-2 correspond to the examples. It can be confirmed that the tool life of the die of Sample 3-1 is longer than that of Sample 3-2. It is believed that this is because the content of alkali metal elements and alkaline earth metal elements in the composite sintered body of Sample 3-1 is 10 ppm or less, and even in die drawing under conditions where the friction part is likely to become high temperature, it is difficult for the alkali metal elements and alkaline earth metal elements to transform from cubic boron nitride to hexagonal boron nitride, thereby effectively suppressing the expansion of tool damage.

[0296] As mentioned above, although the embodiment and the example of the present disclosure have been described, it is initially intended that the configurations of the above-mentioned respective embodiments and the examples may be appropriately combined or various modifications may be made.

[0297] The embodiments and examples disclosed herein are illustrative in all aspects and are not restrictive. The scope of the present disclosure is indicated by the claims rather than the embodiments and is intended to include all modifications within the meaning and scope equivalent to the claims.

Claims

1. A composite sintered body, which is composed of cubic boron nitride particles and hexagonal boron nitride particles, or which is composed of cubic boron nitride particles, hexagonal boron nitride particles and wurtzite-type boron nitride particles, The dislocation density of the cubic boron nitride particles is 1×10 15 / m 2 or more and 1×10 17 / m 2 or less. wherein the median particle size d50 of the equivalent circle diameter of the cubic boron nitride particles is 10 nm or more and 500 nm or less, and the volume-based content Vc of the cubic boron nitride particles, the volume-based content Vh of the hexagonal boron nitride particles, and the volume-based content Vw of the wurtzite-type boron nitride particles satisfy the relationship of the following formula 2, Formula 2: 0.03 ≤ (Vh + Vw) / (Vc + Vh + Vw) ≤ 0.

4.

2. The composite sintered body according to claim 1, wherein, The dislocation density of the cubic boron nitride particles is 1×10 15 / m 2 or more and 3×10 16 / m 2 or less.

3. The composite sintered body according to claim 1 or claim 2, wherein, The dislocation density of the cubic boron nitride particles is 1×10 15 / m 2 or more and 5×10 15 / m 2 or less.

4. The composite sintered body according to claim 1 or claim 2, wherein, the median particle size d50 of the equivalent circle diameter of the cubic boron nitride particles is 10 nm or more and 300 nm or less.

5. The composite sintered body according to claim 1 or claim 2, wherein, the median particle size d50 of the equivalent circle diameter of the cubic boron nitride particles is 10 nm or more and 100 nm or less.

6. The composite sintered body according to claim 1 or claim 2, wherein, based on mass, the total content of alkali metal elements and alkaline earth metal elements in the composite sintered body is 10 ppm or less.

7. The composite sintered body according to claim 1 or claim 2, wherein, the dislocation density is calculated using the modified Williamson-Hall method and the modified Warren-Averbach method.

8. The composite sintered body according to claim 1 or claim 2, wherein, the dislocation density is measured using synchrotron radiation as an X-ray source.

9. A tool which uses the composite sintered body according to any one of claims 1 to 8.

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