cubic boron nitride sintered body

Abstract

The cubic boron nitride sintered body comprises a binder material and 80% to 96% cubic boron nitride particles by volume. The binder material includes tungsten carbide, cobalt, and aluminum compounds. The hardness Hb of the cubic boron nitride sintered body and the hardness Ha of the acid-treated cubic boron nitride sintered body satisfy Ha / Hb≥0.40. The acid-treated cubic boron nitride sintered body is obtained by acid treating the cubic boron nitride sintered body and substantially removing the binder material from the cubic boron nitride sintered body.

Description

Technical Field

[0001] This disclosure relates to cubic boron nitride sintered bodies. Background Technology

[0002] As a high-hardness material used in cutting tools, cubic boron nitride sintered bodies (hereinafter also referred to as "cBN sintered bodies") are available. Cubic boron nitride sintered bodies are typically composed of cubic boron nitride particles (hereinafter also referred to as "cBN particles") and a bonding material, and their properties tend to vary depending on the proportion of cubic boron nitride particles contained in them.

[0003] Therefore, in the field of machining, different types of cubic boron nitride sintered bodies suitable for cutting tools are used depending on the material of the workpiece and the required machining accuracy. For example, cubic boron nitride sintered bodies with a high proportion of cubic boron nitride (hereinafter also referred to as "cBN") particles (hereinafter also referred to as "High-cBN sintered bodies") can be appropriately used for cutting sintered alloys, etc.

[0004] However, High-cBN sintered bodies are prone to sudden defects. These sudden defects are believed to be caused by weak bonding between cubic boron nitride particles, leading to particle detachment. For example, International Patent Publication No. 2005 / 066381 (Patent Document 1) discloses a technique for suppressing the generation of sudden defects in High-cBN sintered bodies through appropriate selection of bonding materials.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: International Publication No. 2005 / 066381 Summary of the Invention

[0008] The cubic boron nitride sintered body disclosed herein comprises a bonding material and 80% by volume and 96% by volume of cubic boron nitride particles, wherein,

[0009] The bonding material comprises tungsten carbide, cobalt, and aluminum compounds.

[0010] The hardness Hb of the cubic boron nitride sintered body and the hardness Ha of the acid-treated cubic boron nitride sintered body satisfy Ha / Hb≥0.40. The acid-treated cubic boron nitride sintered body is obtained by acid treating the cubic boron nitride sintered body and substantially removing the bonding material from the cubic boron nitride sintered body. Attached Figure Description

[0011] Figure 1This is a figure showing an example of the SEM-EDS analysis results of the cubic boron nitride sintered body (before acid treatment) of this disclosure.

[0012] Figure 2 This is a figure illustrating an example of the SEM-EDS analysis results of the cubic boron nitride sintered body of this disclosure after acid treatment. Detailed Implementation

[0013] [The problem this disclosure aims to solve]

[0014] In recent years, with the rapid increasing functionality of mechanical components, the machining difficulty of the workpieces used in these components is accelerating. Consequently, the increased costs caused by the shortened lifespan of cutting tools have become significant. Therefore, further improvements to High-cBN sintered bodies are desired. In view of this, the object of this disclosure is to provide a cubic boron nitride sintered body that enables long tool life when used as a tool material.

[0015] [The Effects of This Disclosure]

[0016] Tools using the cubic boron nitride sintered body disclosed herein can have a longer tool life.

[0017] [Description of embodiments of this disclosure]

[0018] Firstly, in order to achieve a cubic boron nitride sintered body with a further extended lifespan, the inventors of this invention used a binder powder containing WC (tungsten carbide), Co (cobalt), and Al (aluminum) as the binder material in the High-cBN sintered body. This is because, through the inventors' research to date, it has been discovered that when using such a binder powder, the binding force of the binder to the cubic boron nitride particles is particularly high, resulting in a cubic boron nitride sintered body with excellent wear resistance and chip resistance.

[0019] However, in High-cBN sintered bodies, the amount of binder material is significantly less than the amount of cubic boron nitride particles, thus there is a tendency for the binder material to be widely distributed among the cubic boron nitride particles. Therefore, the inventors of this invention believe that optimizing the binder material alone cannot achieve a breakthrough in extending the lifespan of High-cBN sintered bodies.

[0020] Therefore, the inventors of this invention significantly changed their thinking from conventional methods of improving the bonding force between the bonding material and cubic boron nitride particles. After conducting in-depth research on whether there were methods to improve the bonding force between cubic boron nitride particles, the cubic boron nitride sintered body of this disclosure was obtained.

[0021] This disclosure has been completed as described above. Hereinafter, embodiments of this disclosure will be described.

[0022] (1) The cubic boron nitride sintered body of this disclosure comprises a bonding material and cubic boron nitride particles comprising more than 80% by volume and less than 96% by volume, wherein,

[0023] The bonding material comprises tungsten carbide, cobalt, and aluminum compounds.

[0024] The hardness Hb of the cubic boron nitride sintered body and the hardness Ha of the acid-treated cubic boron nitride sintered body satisfy Ha / Hb≥0.40. The acid-treated cubic boron nitride sintered body is obtained by acid treating the cubic boron nitride sintered body and substantially removing the bonding material from the cubic boron nitride sintered body.

[0025] When the cubic boron nitride sintered body disclosed herein is used as a tool material, it enables the tool to have a long service life.

[0026] (2) Preferably, Ha and Hb satisfy Ha / Hb≥0.53. This improves tool life.

[0027] (3) Preferably, Ha and Hb satisfy Ha / Hb≥0.55. This further improves tool life.

[0028] (4) Preferably, the thermal diffusivity Kb of the cubic boron nitride sintered body before acid treatment and the thermal diffusivity Ka of the cubic boron nitride sintered body after acid treatment satisfy Ka / Kb≥0.60. This further improves tool life.

[0029] (5) Preferably, Ka and Kb satisfy Ka / Kb≥0.90. As a result, the tool life is further improved.

[0030] (6) Preferably, Ka and Kb satisfy Ka / Kb≥0.95. As a result, the tool life is further improved.

[0031] (7) Preferably, the bending test strength Tb of the cubic boron nitride sintered body before acid treatment and the bending test strength Ta of the cubic boron nitride sintered body after acid treatment satisfy Ta / Tb≥0.30. This further improves tool life.

[0032] (8) Preferably, the Ta and the Tb satisfy Ta / Tb≥0.35. As a result, the tool life is further improved.

[0033] (9) Preferably, the Ta and the Tb satisfy Ta / Tb≥0.40. As a result, the tool life is further improved.

[0034] (10) Preferably, the average particle size of the cubic boron nitride is 0.4 μm or more and 5 μm or less. As a result, the tool life is further improved.

[0035] (11) Preferably, the average particle size of the cubic boron nitride is 0.5 μm or more and 3.5 μm or less. As a result, the tool life is further improved.

[0036] [Details of the embodiments disclosed herein]

[0037] Hereinafter, one embodiment of the present disclosure (hereinafter referred to as "this embodiment") will be described. However, this embodiment is not limited thereto. Furthermore, in this specification, expressions in the form of "A to Z" refer to the upper and lower limits of a range (i.e., above A and below Z). When no unit is specified in A and only in Z, the unit of A is the same as the unit of Z.

[0038] <Implementation Method 1: Cubic Boron Nitride Sintered Body>

[0039] The cubic boron nitride sintered body of this embodiment is a cubic boron nitride sintered body containing a bonding material and 80% to 96% cubic boron nitride particles by volume.

[0040] The bonding material contains tungsten carbide, cobalt, and aluminum compounds.

[0041] The hardness Hb of the cubic boron nitride sintered body and the hardness Ha of the acid-treated cubic boron nitride sintered body satisfy Ha / Hb≥0.40. The acid-treated cubic boron nitride sintered body is obtained by acid treating the cubic boron nitride sintered body and substantially removing the bonding material in the cubic boron nitride sintered body.

[0042] When the cubic boron nitride sintered body of this embodiment is used as a tool material, it enables the tool to have a long service life. The reasons for this are presumably as described in (i) and (ii) below.

[0043] (i) The cubic boron nitride sintered body of this embodiment contains 80% by volume and 96% by volume of cubic boron nitride particles with excellent strength and toughness. Therefore, the cubic boron nitride sintered body can also have excellent strength and toughness. Consequently, this cubic boron nitride sintered body has excellent wear resistance and chipping resistance, and tools using this cubic boron nitride sintered body can have a long tool life.

[0044] (ii) In the cubic boron nitride sintered body of this embodiment, the bonding material includes tungsten carbide, cobalt, and an aluminum compound. In such a bonding material, the bonding force to the cubic boron nitride particles is particularly high. Therefore, this cubic boron nitride sintered body exhibits excellent wear resistance and chipping resistance, and tools using this cubic boron nitride sintered body can have a long tool life.

[0045] (iii) In the cubic boron nitride sintered body of this embodiment, the hardness Hb of the cubic boron nitride sintered body and the hardness Ha of the acid-treated cubic boron nitride sintered body satisfy Ha / Hb≥0.40. This acid-treated cubic boron nitride sintered body is obtained by acid treating the cubic boron nitride sintered body and substantially removing the bonding material from it. Such a cubic boron nitride sintered body exhibits high bonding strength between the cubic boron nitride particles. Therefore, the cubic boron nitride sintered body is less prone to particle detachment during tool use, exhibiting excellent wear resistance and chip resistance. Tools using this cubic boron nitride sintered body can have a longer tool life.

[0046] (composition)

[0047] The cubic boron nitride sintered body according to this embodiment comprises a binder material and 80% to 96% by volume of cubic boron nitride particles. That is, the cubic boron nitride sintered body according to this embodiment is a so-called High-cBN sintered body. Furthermore, the cubic boron nitride sintered body may contain unavoidable impurities due to the raw materials used, manufacturing conditions, etc. The proportion (mass%) of unavoidable impurities in the cubic boron nitride sintered body can be set to 1% by mass or less. The cubic boron nitride sintered body according to this embodiment may be composed of cubic boron nitride particles, a binder material, and unavoidable impurities.

[0048] The lower limit of the content (volume %) of cubic boron nitride particles in the cubic boron nitride sintered body is 80 vol% or more, and can be set to 81 vol% or more or 82 vol% or more. The upper limit of the content (volume %) of cubic boron nitride particles in the cubic boron nitride sintered body is 96 vol% or less, and can be set to 95 vol% or less or 94 vol% or less. The content (volume %) of cubic boron nitride particles in the cubic boron nitride sintered body can be set to 81 vol% or more and 95 vol% or less, or 82 vol% or more and 94 vol% or less.

[0049] The lower limit of the content (volume %) of the binder material in the cubic boron nitride sintered body can be set to 4% or more, 5% or more, or 6% or more. The upper limit of the content (volume %) of the binder material in the cubic boron nitride sintered body can be set to less than 20% or 19% or 18% or less. The content (volume %) of the binder material in the cubic boron nitride sintered body can be set to 4% or more and less than 20% or 5% or more and less than 19% or 6% or more and less than 18% or less.

[0050] The proportion (volume %) of cubic boron nitride in the cubic boron nitride sintered body can be confirmed by quantitative analysis using inductively coupled plasma atomic emission spectrometry (ICP), energy-dispersive X-ray diffraction (EDX) with a scanning electron microscope (SEM), or EDX with a transmission electron microscope (TEM), through microstructural observation and elemental analysis of the cubic boron nitride sintered body. In this embodiment, unless there is a specific reason, the proportion of cubic boron nitride particles in the cubic boron nitride sintered body is determined by the SEM method described later.

[0051] Using SEM, the content (volume %) of cubic boron nitride particles can be determined as follows: First, a sample containing a cross-section of the cubic boron nitride sintered body is prepared by cutting it at any point. The cross-section can be prepared using a focused ion beam apparatus, a cross-section polishing machine, etc. Next, the cross-section is observed using SEM at 2000x magnification to obtain a reflected electron image. In the reflected electron image, areas containing cubic boron nitride particles are represented by black areas, while areas containing bonding material are represented by gray or white areas. The magnification is adjusted appropriately according to the particle size, and the average value obtained from observing and analyzing at least five fields of view is taken as the content percentage.

[0052] Next, the reflected electron image was binarized using image analysis software (e.g., WinROOF from Mitani Corporation). The area ratios of the black regions (regions containing cubic boron nitride particles) and the white regions (regions containing the binding phase) were calculated from the binarized image. By treating the calculated area ratios as volume percentages, the content (volume %) of the cubic boron nitride particles could be determined. Furthermore, the volume % of the binding material could also be calculated simultaneously.

[0053] (Cubic boron nitride particles)

[0054] Cubic boron nitride particles possess high hardness, strength, and toughness, serving as a framework within the cubic boron nitride sintered body. From the viewpoint of improving tool life, the D50 (average particle size) of the cubic boron nitride particles is preferably 0.4 μm or more and 5 μm or less, more preferably 0.5 μm or more and 3.5 μm or less.

[0055] The D50 of the cubic boron nitride particles is determined as follows. First, a sample containing a cross-section of a sintered cubic boron nitride body is prepared according to the method described above for determining the content of cubic boron nitride particles, and a reflected electron image is obtained. Next, the equivalent circle diameter (diameter of a circle with equal area) of each black region in the reflected electron image is calculated using image analysis software. Preferably, the equivalent circle diameter of more than 100 cubic boron nitride particles is calculated by observing more than five fields of view.

[0056] Next, the equivalent circle diameters are arranged in ascending order from minimum to maximum to determine the cumulative distribution. The particle size with a cumulative area of ​​50% in the cumulative distribution is designated as D50. Furthermore, the equivalent circle diameter refers to the diameter of a circle with an area equal to the area of ​​the measured cubic boron nitride particle.

[0057] (Based on the materials)

[0058] The bonding material enables the sintering of cubic boron nitride particles, which are difficult to sinter, under industrial-grade pressure and temperature.

[0059] In the cubic boron nitride sintered body of this embodiment, the bonding material includes WC, Co, and Al compounds. Here, "Al compound" refers to a compound containing Al as a constituent element. Examples of Al compounds include CoAl, Al₂O₃, AlN, and AlB₂, as well as their composite compounds. This bonding material containing WC, Co, and Al compounds is considered particularly effective for extending the lifespan of the cubic boron nitride sintered body according to this embodiment for the following reasons.

[0060] First, due to the catalytic properties of Co and Al, the sintering process in manufacturing cubic boron nitride sintered bodies can promote neck growth between cubic boron nitride particles. Second, it is speculated that WC is effective in bringing the coefficient of thermal expansion of the bonding material close to that of the cubic boron nitride particles. Furthermore, the aforementioned catalytic function refers to the diffusion or precipitation of B (boron) and / or N (nitrogen) constituting the cubic boron nitride particles via Co or Al. Third, metallic components such as Co enhance toughness, and an appropriate amount of bonding material improves resistance to chipping.

[0061] The composition of the binder material in a cubic boron nitride sintered body can be determined by combining XRD (X-ray diffraction) and ICP (inductively coupled plasma chromatography). Specifically, firstly, a test piece with a thickness of approximately 0.45–0.50 mm is cut from the cubic boron nitride sintered body. XRD analysis is performed on this test piece to identify the compounds and metals determined by the X-ray diffraction peaks. Next, the test piece is immersed in a fluoronitric acid solution (a mixed acid consisting of concentrated nitric acid (60%), distilled water, and concentrated hydrofluoric acid (47%) in a volume ratio of 2:2:1) in a sealed container to obtain an acid treatment solution containing dissolved binder material. ICP analysis is then performed on this acid treatment solution to quantitatively analyze each metal element. Finally, the composition of the binder material is determined by analyzing the results of both the XRD and ICP analyses.

[0062] In this embodiment, the binding material may include other binding materials besides WC, Co, and Al compounds. Preferably, the elements constituting these other binding materials are Ni, Fe, Cr, Mn, Ti, V, Zr, Nb, Mo, Hf, Ta, Re, etc.

[0063] (hardness)

[0064] In the cubic boron nitride sintered body of this embodiment, the hardness Hb of the cubic boron nitride sintered body before acid treatment and the hardness Ha of the cubic boron nitride sintered body after acid treatment satisfy Ha / Hb≥0.40. This acid-treated cubic boron nitride sintered body is obtained by acid treating the cubic boron nitride sintered body and substantially removing the bonding material from it. Here, the hardness Hb (GPa) of the cubic boron nitride sintered body before acid treatment is measured according to the following steps: The cubic boron nitride sintered body is machined to a thickness of 0.5 mm to prepare test sample A. Using a force sensor micro Vickers hardness tester manufactured by FUTURE-TECH, the hardness of test sample A (the cubic boron nitride sintered body before acid treatment) is measured under a load of 5 kg. The hardness is measured at six locations, and the average hardness of these six locations is taken as the hardness Hb of the cubic boron nitride sintered body before acid treatment.

[0065] The hardness Ha of the acid-treated cubic boron nitride sintered body was determined according to the following steps. An acid solution was prepared with a volume ratio of hydrochloric acid (95%): nitric acid (95%): hydrofluoric acid (95%): water = 2:1:1:2. The test sample A was immersed in the acid solution heated to 140°C and subjected to acid treatment for 48 hours in a sealed container. The acid-treated test sample B (cubic boron nitride sintered body) was then removed from the acid solution. For test sample B, the hardness was measured at six locations using the same method as for the hardness Hb of the cubic boron nitride sintered body before acid treatment. The average hardness of these six locations was taken as the hardness Ha of the acid-treated cubic boron nitride sintered body.

[0066] Furthermore, within the scope of the applicant's measurements, it was confirmed that as long as the measurements were performed on the same sample, even if the measurement site was changed and the above-mentioned hardness Ha and hardness Hb were measured multiple times, the measurement results were almost without deviation, and even if the measurement site was arbitrarily set, the results would not change arbitrarily.

[0067] While the acid treatment described above can substantially remove the binding material from the cubic boron nitride sintered body, some binding material components may remain after the acid treatment. The reasoning is as follows: Acid treatment involves immersing the cBN sintered body in an acid solution. Therefore, it is assumed that if multiple cBN particles within the cBN sintered body form a region that the acid solution cannot penetrate (also known as a triple point), binding material components will remain after acid treatment. Alternatively, it is assumed that if substances such as alumina, which are insoluble in acid solutions, are present in the cBN sintered body, binding material components will also remain after acid treatment. Therefore, as long as an amount of binding material sufficient to evaluate the bonding strength between the CBN particles is removed, it can be considered that the binding material of the cubic boron nitride sintered body has been substantially removed.

[0068] Confirmation that the acid treatment effectively removed the bonding material from the cubic boron nitride sintered body can be performed according to the following steps. To observe the test sample A (cBN sintered body before acid treatment) using a SEM (device: JSM-7800F, Nippon Electronics Manufacturing Co., Ltd., trademark), the surface was ground (#2000). A line scan was performed using the SEM, including the center of the test surface. The line width was 100 μm or more. A line width of 100 μm or more reduces the deviation of cBN particles and bonding material in the test area.

[0069] An example of SEM-EDS analysis results of the cubic boron nitride sintered body of this embodiment before and after acid treatment is shown below. Figure 1 (before acid treatment) and Figure 2 (After acid treatment). In Figure 1 as well as Figure 2 In the diagram, the horizontal axis represents the measurement location (μm) in the sample, and the vertical axis represents the proportion of the element present (wt%). For example... Figure 1 as well as Figure 2 As shown, the presence of Al (aluminum), W (tungsten), Cr (chromium), Co (cobalt), B (boron), and N (nitrogen) was confirmed in this cubic boron nitride sintered body. Among these elements, carbon and nitrogen originate from cubic boron nitride particles, while tungsten, aluminum, chromium, and cobalt originate from the bonded phase.

[0070] like Figure 2 As shown, the elements other than N (nitrogen) and B (boron) in the acid-treated cubic boron nitride sintered body (in...) Figure 2 The proportions of W (tungsten), Al (aluminum), Cr (chromium), and Co (cobalt) in the sintered body all decrease. This is because, after acid treatment, the binding material components of the cubic boron nitride sintered body dissolve into the acid treatment solution.

[0071] In the aforementioned line scan, the proportion (mass%) of cobalt (Co) in the cubic boron nitride sintered body was calculated. Specifically, the average value X1 (mass%) of the proportion (mass%) of cobalt (Co) in the region where the cubic boron nitride sintered body was being analyzed was determined. The region where the cubic boron nitride sintered body was being analyzed was determined by the fact that the combined proportion (at%) of boron and nitrogen, which are constituent elements of cubic boron nitride, was greater than that of other binding material components.

[0072] Next, sample B (acid-treated cBN sintered body) was subjected to a line scan using the same method as sample A described above, employing SEM. During this line scan, the proportion (mass%) of cobalt (Co) in the cubic boron nitride sintered body was calculated. Specifically, the average value x2 (mass%) of the proportion of cobalt (Co) in the region where the cubic boron nitride sintered body was being analyzed was measured. The region where the cubic boron nitride sintered body was being analyzed was determined by the fact that the combined proportion (at%) of boron and nitrogen, which are constituent elements of cubic boron nitride, was greater than that of other binding material components.

[0073] When X2 / X1 is below 0.20, it is confirmed that the bonding material of the cubic boron nitride sintered body is substantially removed through the above acid treatment. Therefore, the hardness measurement of the acid-treated cBN sintered body with X2 / X1 below 0.20 is equivalent to the measurement of the bonding force between cBN particles.

[0074] Furthermore, when X2 / X1 exceeds 0.20, by appropriately adjusting the acid treatment time to exceed 48 hours, it is possible to reduce X2 / X1 to below 0.20.

[0075] Cubic boron nitride sintered bodies satisfying Ha / Hb≥0.40 exhibit a smaller decrease in hardness after acid treatment. During acid treatment, the bonding material components of the cubic boron nitride sintered body dissolve into the acid treatment solution. Therefore, the smaller decrease in hardness after acid treatment indicates a strong bond between the cubic boron nitride particles. Consequently, tools made from this cubic boron nitride sintered body are less prone to particle detachment during tool use, exhibiting excellent wear resistance and chip resistance, resulting in a longer tool life.

[0076] When conventional cubic boron nitride sintered bodies are used to process sintered alloys, cubic boron nitride particles are prone to detachment during processing, the tool tip becomes blunt, and there is a tendency for burrs and cloudiness to form on the processed parts. In the cubic boron nitride sintered body of this embodiment, as described above, the cubic boron nitride particles have strong bonding forces and are less prone to detachment, thus enabling the machined parts to have good surface quality.

[0077] The Ha / Hb ratio satisfies Ha / Hb≥0.40, preferably Ha / Hb≥0.53, and more preferably Ha / Hb≥0.55. The upper limit of Ha / Hb can be set to 1 or less, for example. Ha / Hb can be set to 1≥Ha / Hb≥0.40, 1≥Ha / Hb≥0.53, or 1≥Ha / Hb≥0.55.

[0078] Ha can be set to, for example, above 14 GPa and below 24 GPa, above 15 GPa and below 23 GPa, or above 16 GPa and below 24 GPa.

[0079] Hb can be set to, for example, above 34 GPa and below 45 GPa, above 35 GPa and below 44 GPa, or above 37 GPa and below 43 GPa.

[0080] (thermal diffusivity)

[0081] In the cubic boron nitride sintered body of this embodiment, the thermal diffusivity Kb of the cubic boron nitride sintered body before acid treatment and the thermal diffusivity Ka of the cubic boron nitride sintered body after acid treatment preferably satisfy Ka / Kb≥0.60. This acid-treated cubic boron nitride sintered body is obtained by acid treating the cubic boron nitride sintered body and substantially removing the binding material from the cubic boron nitride. Here, the thermal diffusivity Kb (mm²) of the cubic boron nitride sintered body before acid treatment is... 2The following determination was performed: a cubic boron nitride sintered body was cut into an isosceles triangle with a base of 3.9 mm, a vertices of 80°, and a thickness of 0.5 mm to prepare a test sample C. The test sample C was measured using a xenon flash analyzer (trade name LFA467HyperFlashu) manufactured by NETZSCH.

[0082] Thermal diffusivity Ka (mm) of cubic boron nitride sintered body after acid treatment 2 The determination of the thermal diffusivity Ka (mm²) was performed according to the following steps. The above-mentioned test sample C was acid-treated to prepare the acid-treated test sample D (cubic boron nitride sintered body). The thermal diffusivity Ka (mm²) was then determined using the apparatus used in the determination of the above-mentioned test sample C. 2 The test was conducted using a method involving acid treatment ( / s). The specific method for acid treatment is the same as that used in the hardness test described above, and therefore will not be repeated.

[0083] Cubic boron nitride sintered bodies satisfying Ka / Kb≥0.60 also exhibit a smaller decrease in thermal diffusivity after acid treatment. This indicates excellent thermal conductivity between cubic boron nitride particles. Tools using this cubic boron nitride sintered body, especially in cast iron machining, show reduced damage caused by thermal cracking and have a longer tool life.

[0084] Ka / Kb is preferably Ka / Kb≥0.60, more preferably Ka / Kb≥0.90, and even more preferably Ka / Kb≥0.95. The upper limit of Ka / Kb can be set to 1 or less, for example. Ka / Kb can be set to 1≥Ka / Kb≥0.60, 1≥Ka / Kb≥0.90, or 1≥Ka / Kb≥0.95.

[0085] Ka can be set to 20mm, for example. 2 / s or higher and 62mm 2 / s or less, 30mm 2 / s or higher and 60mm 2 / s or less, 40mm 2 / s or higher and 58mm 2 / s or less.

[0086] Kb can be set to 39mm for example. 2 / s or higher and 65mm 2 / s or less, 42mm 2 / s or higher and 62mm 2 / s or less, 50mm 2 / s or higher and 60mm 2 / s or less.

[0087] (Bending test strength)

[0088] In the cubic boron nitride sintered body of this embodiment, the bending test strength Tb of the cubic boron nitride sintered body before acid treatment and the bending test strength Ta of the cubic boron nitride sintered body after acid treatment preferably satisfy Ta / Tb≥0.30. This acid-treated cubic boron nitride sintered body is obtained by acid treating the cubic boron nitride sintered body and substantially removing the binding material from it. Here, the bending test strength b (GPa) of the cubic boron nitride sintered body before acid treatment is measured as follows: a test specimen E is prepared by cutting the cubic boron nitride sintered body into plates of 0.5mm×2mm×5.8mm. For this test specimen E, a three-point bending tester is used to measure the bending test strength (GPa) at a span of 4mm and a stroke speed of 0.5mm / min. The average bending test strength of ten test specimens E is taken as the bending test strength Tb (GPa) of the cubic boron nitride sintered body.

[0089] The determination of the bending strength Ta (GPa) of the acid-treated cubic boron nitride sintered body was performed according to the following steps. The test specimen E was acid-treated to prepare the acid-treated test specimen F (cubic boron nitride sintered body). The bending strength was measured using a three-point bending tester under conditions of a span of 4 mm and a stroke speed of 0.5 mm / min. The average bending strength of ten test specimens F was taken as the bending strength Ta (GPa) of the acid-treated cubic boron nitride sintered body. The specific method of acid treatment is the same as that used in the hardness determination above, and therefore will not be repeated.

[0090] Cubic boron nitride sintered bodies satisfying Ta / Tb ≥ 0.30 also exhibit a smaller decrease in flexural strength after acid treatment. This indicates strong bonding between the cubic boron nitride particles. Consequently, this cubic boron nitride sintered body demonstrates excellent resistance to chipping, especially in the processing of high-strength sintered alloys.

[0091] The Ta / Tb ratio is preferably Ta / Tb ≥ 0.30, more preferably Ta / Tb ≥ 0.35, and even more preferably Ta / Tb ≥ 0.40. The upper limit of Ta / Tb can be set to 1 or less, for example. Ta / Tb can be set to 1 ≥ Ta / Tb ≥ 0.30, 1 ≥ Ta / Tb ≥ 0.35, or 1 ≥ Ta / Tb ≥ 0.40.

[0092] Ta can be set to, for example, above 0.35 GPa and below 1.2 GPa, above 0.5 GPa and below 1.1 GPa, or above 0.65 GPa and below 1.0 GPa.

[0093] Tb can be set to, for example, above 1.2 GPa and below 3.0 GPa, above 1.5 GPa and below 2.7 GPa, or above 1.7 GPa and below 2.5 GPa.

[0094] <Implementation Method 2: Method for Manufacturing Cubic Boron Nitride Sintered Body>

[0095] The method for manufacturing the cubic boron nitride sintered body of Embodiment 1 described above will be explained. However, the method for manufacturing the cubic boron nitride sintered body is not limited to the following methods. The method for manufacturing the cubic boron nitride sintered body of Embodiment 2 may include, for example, a "cubic boron nitride powder processing step," in which particulate cubic boron nitride particles (hereinafter also referred to as "particulate cBN particles") are attached to coarse cubic boron nitride particles (hereinafter also referred to as "coarse cBN particles") to obtain cubic boron nitride raw material powder (hereinafter also referred to as "cBN raw material powder"); a "mixed powder preparation step," in which the cubic boron nitride raw material powder is mixed with a binder material raw material powder containing WC, Co, and Al to prepare a mixed powder; and a "sintering step," in which the mixed powder is sintered to obtain a cubic boron nitride sintered body.

[0096] (Cubic boron nitride powder processing process)

[0097] Prepare coarse-grained cubic boron nitride powder (average particle size 0.2–8 μm, hereinafter referred to as "coarse-grained cBN powder") and fine-grained cBN powder (average particle size 0.05–0.1 μm, hereinafter referred to as "fine-grained cBN powder"). The volume ratio of fine-grained cBN powder to coarse-grained cBN powder can be set to 20:80 to 1:99.

[0098] (Electrostatic adsorption)

[0099] PSS (poly(diallyldimethylammonium chloride)) was added to particulate cBN powder and allowed to stand for 30 minutes. PDDA (poly(sodium 4-styrenesulfonate)) was added to coarse cBN powder and allowed to stand for 30 minutes. After washing both the particulate and coarse cBN powders, they were mixed in a planetary mill for 10 minutes to obtain a slurry. The slurry was allowed to dry for 24 hours to obtain cBN raw material powder.

[0100] In the obtained cBN raw material powder, fine cBN particles adhere to the surface of coarse cBN particles through electrostatic adsorption. The presence of fine cBN particles with excellent sinterability among the coarse cBN particles strengthens the bonding force between them during sintering. Therefore, the resulting cBN sintered body maintains high hardness even after acid treatment.

[0101] (Ion implantation)

[0102] The cBN raw material powder obtained through the above electrostatic adsorption can be ion implanted. In ion implantation, for example, an ion implantation device (Sumitomo Heavy Industries' "SHX-II" (trademark)) is used to irradiate ions with an energy of 0.2 to 60 keV. Cobalt ions, calcium ions, nickel ions, iron ions, aluminum ions, etc., can be used as ions.

[0103] By adding elements to the surface of cBN particles through ion irradiation, the trace oxide layer and the boron-nitrogen bonds (BN bonds) existing on the cBN particle surface become unstable. This promotes the dissolution and re-precipitation of cobalt and other substances during the subsequent sintering process, thereby further strengthening the bonding force between coarse-grained cBN particles. Therefore, the resulting cBN sintered body exhibits high hardness even after acid treatment.

[0104] (Ammonia treatment)

[0105] The cBN raw material powder obtained by the above electrostatic adsorption can be subjected to ammonia treatment. In the ammonia treatment, for example, the cBN raw material powder is placed in an ammonia atmosphere heated to 100-1400°C and left for 30-540 minutes.

[0106] By subjecting the cBN particles to prolonged ammonia treatment, it can be predicted that oxygen on the surface of the cBN particles will be decomposed, and nitrogen (N) and hydrogen (H) will be modified at the atomic level on the cBN particle surface. In the sintering process described later, this further promotes the bonding between cBN particles. Therefore, the resulting cBN sintered body can still exhibit high hardness and high flexural strength even after acid treatment.

[0107] (Powder preparation process)

[0108] The cBN raw material powder obtained above is mixed with a binder material raw material powder containing WC, Co, and Al to form a mixed powder. The binder material raw material powder is the raw material for the binder material of the cubic boron nitride sintered body.

[0109] The raw material powder for the bonding material can be prepared as follows: First, prepare WC powder, Co powder, and Al powder. Next, mix the powders in a predetermined ratio and heat-treat them under vacuum (e.g., 1200°C) to create an intermetallic compound. The intermetallic compound is then pulverized using a wet ball mill, wet bead mill, or similar method to prepare a raw material powder containing WC, Co, and Al. Furthermore, there are no particular limitations on the mixing method of the powders; however, from the viewpoint of efficient and homogeneous mixing, ball mill mixing, bead mill mixing, planetary mill mixing, and jet mill mixing are preferred. Each mixing method can be wet or dry.

[0110] The cBN raw material powder and the binder raw material powder are preferably mixed using a wet ball mill with ethanol, acetone, or similar solvents. After mixing, the solvent is removed by natural drying. Subsequently, it is preferable to remove impurities such as moisture adsorbed on the surface by heat treatment (e.g., at 850°C or higher under vacuum).

[0111] In addition to WC, Co, and Al, the raw material powder of the above-mentioned bonding material may also contain other elements. Preferred other elements include Ni, Fe, Cr, Mn, Ti, V, Zr, Nb, Mo, Hf, Ta, and Re.

[0112] (Sintering process)

[0113] The mixed powder obtained above is filled into a container and then vacuum-sealed. The vacuum sealing temperature is preferably above 850°C. This is a temperature exceeding the melting point of the sealing material.

[0114] Next, the vacuum-sealed mixed powder is sintered using an ultra-high temperature and high pressure apparatus to obtain a cubic boron nitride sintered body. There are no particular restrictions on the sintering conditions. For example, sintering can be carried out for 15 minutes at a pressure of 4.5–10 GPa and a temperature above 1200°C and below 1900°C.

[0115] During sintering, if the mixed powder is subjected to high pressure and high temperature, and pressure changes from low to high are repeatedly performed, the surface defects of the cBN particles are damaged, resulting in highly active new surfaces and strengthening the bonding force between cBN particles. This effect is particularly significant when micro-sized cBN particles are attached to coarse-sized cBN particles through electrostatic adsorption. Therefore, the resulting cBN sintered body can maintain high hardness and high thermal diffusivity even after acid treatment.

[0116] Example

[0117] The present embodiment will be further described in detail through examples. However, the present embodiment is not limited to these examples.

[0118] [Example 1]

[0119] <Sample 1-1>

[0120] (Powder preparation process)

[0121] Prepare the binder material powder. Prepare WC powder, Co powder, and Al powder, and mix them in a weight percentage ratio of WC:Co:Al = 43:40:17. The average particle size of each powder is 2 μm. The powders are then heat-treated (under vacuum, 950°C, for 30 minutes) to homogenize them, followed by micronization using a hard ball mill. This yields a binder material powder with an average particle size of 1 μm.

[0122] cBN raw material powder (average particle size 1 μm) and binder raw material powder were mixed at a volume ratio of cBN raw material powder: binder raw material powder = 95:5, and uniformly mixed using a wet ball milling method with ethanol. Subsequently, to remove surface moisture and other impurities, the mixed powder was subjected to degassing heat treatment at 900°C under vacuum. Through these operations, a mixed powder was prepared.

[0123] (Sintering process)

[0124] Next, a cubic boron nitride sintered body was fabricated by sintering the obtained mixed powder. Specifically, the mixed powder was filled into a Ta container in contact with a disk made of WC-6%Co hard alloy and then vacuum-sealed. Using a belt-type ultra-high pressure and high temperature generator, it was sintered at 7.0 GPa and 1700 °C for 15 minutes. This produced the cubic boron nitride sintered body.

[0125] <Sample 1-2>

[0126] (cBN powder processing process)

[0127] First, prepare cBN raw material powder. Prepare coarse cBN powder (average particle size of 1 μm) and fine cBN powder (average particle size of 0.1 μm) at a volume ratio of coarse cBN powder to fine cBN powder of 8:1.

[0128] PSS reagent was added to the particulate cBN powder and allowed to stand for 30 minutes. PDDA reagent was added to the coarse cBN powder and allowed to stand for 30 minutes. Afterwards, the particulate and coarse cBN powders were washed and then mixed in a planetary mill for 10 minutes to obtain a slurry. The slurry was allowed to stand for 24 hours to dry, yielding the cBN raw material powder.

[0129] When the obtained cBN raw material powder was observed using SEM, it was confirmed that micro-sized cBN particles were attached (electrostatically adsorbed) on the surface of the coarse cBN particles.

[0130] (Powder preparation process)

[0131] Next, the raw material powder for the binder was prepared. WC powder, Co powder, and Al powder were prepared and blended in a weight ratio of WC:Co:Al = 43:40:17. Furthermore, the average particle size of each powder was 2 μm. The powder was then heat-treated (under vacuum, 950°C, for 30 minutes) to homogenize it, and subsequently micronized using a hard ball mill. This yielded a raw material powder for the binder with an average particle size of 1 μm.

[0132] cBN raw material powder and binder raw material powder were mixed at a volume ratio of cBN raw material powder: binder raw material powder = 95:5, and uniformly mixed using a wet ball milling method with ethanol. Subsequently, to remove surface moisture and other impurities, the mixed powder was subjected to degassing heat treatment at 900°C under vacuum. SEM observation of the heat-treated cBN raw material powder confirmed the presence of fine cBN particles adhering to the surface of coarse cBN particles. Through these operations, a mixed powder was prepared.

[0133] (Sintering process)

[0134] Next, a cubic boron nitride sintered body was prepared by sintering the obtained mixed powder. Specifically, the mixed powder was filled into a Ta container in contact with a disk made of WC-6%Co hard alloy and then vacuum-sealed. Using a belt-type ultra-high pressure and high temperature generator, it was sintered at 7.0 GPa and 1700 °C for 15 minutes. This produced the cubic boron nitride sintered body.

[0135] <Samples 1-3>

[0136] Except for the following aspects, cubic boron nitride sintered bodies were prepared by the same method as those of samples 1-2.

[0137] The volume ratio of coarse cBN powder to fine cBN powder in the "cBN powder processing procedure" is set to the volume ratio recorded in the "coarse:fine (volume ratio)" column of "electrostatic adsorption" in "cBN powder processing" of Table 1.

[0138] The cBN raw material powder and the binder raw material powder are blended at a ratio of cBN raw material powder: binder raw material powder = 80:20 by volume%.

[0139] <Sample 1-11>

[0140] cBN raw material powder and binder raw material powder were mixed at a ratio of cBN raw material powder: binder raw material powder = 97:3 by volume. Otherwise, cubic boron nitride sintered bodies were prepared by the same method as those for samples 1-3.

[0141] <Sample 1-12>

[0142] The cBN raw material powder and the binder raw material powder were mixed at a ratio of cBN raw material powder: binder raw material powder = 65:35 by volume. Otherwise, cubic boron nitride sintered bodies were prepared by the same method as those used for samples 1-3.

[0143] <Samples 1-4, Samples 1-5, Samples 1-13 to Samples 1-19>

[0144] In samples 1-4, 1-5, and 1-13 to 1-19, cubic boron nitride sintered bodies were prepared by the same method as in sample 1-2, except for the aspects described below.

[0145] The volume ratio of coarse cBN powder to fine cBN powder in the "cBN powder processing procedure" is as shown in the "coarse:fine (volume ratio)" column of "electrostatic adsorption" in Table 1 for "cBN powder processing".

[0146] Set the pressure in the "Sintering Process" to the pressure recorded in the "Pressure (GPa)" column of the "Sintering Process" in Table 1.

[0147] The average particle size of the coarse cBN powder is set to the particle size recorded in the "Coarse cBN Particle Size (μm)" column of "Raw Materials" in Table 1.

[0148] <Sample 1-6 to Sample 1-10>

[0149] Except for the following aspects, cubic boron nitride sintered bodies of samples 1-6 to 1-10 were prepared by the same method as those of samples 1-2.

[0150] Perform the "cBN powder processing step" according to the following steps. Prepare coarse cBN powder (average particle size of 1 μm) and fine cBN powder (average particle size of 0.1 μm) in a volume ratio of coarse cBN powder to fine cBN powder of 8:1.

[0151] PSS reagent was added to the particulate cBN powder and allowed to stand for 30 minutes. PDDA reagent was added to the coarse cBN powder and allowed to stand for 30 minutes. Afterwards, the particulate and coarse cBN powders were washed and then mixed in a planetary mill for 10 minutes to obtain a slurry. The slurry was allowed to stand for 24 hours to dry, yielding the cBN raw material powder.

[0152] The obtained cBN raw material powder was irradiated with an ion implantation device at an energy of 100 keV to the elements listed in the "Implanted Elements" column of "CBN Powder Treatment" in Table 1. For example, in samples 1-6, cobalt (Co) was irradiated.

[0153] When observing the irradiated cBN raw material powder using TEM-EELS, it was confirmed that micro-sized cBN particles were attached (electrostatically adsorbed) on the surface of coarse cBN particles, and Co was further present near the surface.

[0154] <Sample 1-20>

[0155] Except as described below, cubic boron nitride sintered bodies of samples 1-20 were prepared in the same manner as samples 1-4.

[0156] In the "mixed powder production process", cBN raw material powder is mixed with binder raw material powder at a ratio of 60:40.

[0157] <Sample 1-21>

[0158] Except as described below, cubic boron nitride sintered bodies of samples 1-20 were prepared in the same manner as samples 1-4.

[0159] In the "mixed powder manufacturing process", cBN raw material powder is mixed with binder raw material powder at a ratio of 97:3.

[0160] In the "sintering process", a disk made of hard alloy is not used for sintering.

[0161] <Evaluation>

[0162] (Containment of cubic boron nitride)

[0163] The content of cubic boron nitride in each cubic boron nitride sintered body was determined using SEM. The specific measurement method is described in Example 1, and therefore will not be repeated. The results are shown in the "cBN content (volume %)" column of "cBN sintered body" in Table 1.

[0164] In samples 1-1 to 1-19, the proportion of cubic boron nitride in the sintered cubic boron nitride body was less than the proportion of cBN raw material powder in the mixed powder. In these samples, the mixed powder was sintered in contact with a cemented carbide disk during the sintering process. Therefore, it is presumed that the cemented carbide component flowed into the mixed powder during sintering, and the mixing ratio of cBN raw material powder in the mixed powder changed to the ratios recorded in Table 1.

[0165] <Composition of the bonding material>

[0166] Test pieces with a length of 6 mm, a width of 3 mm, and a thickness of 0.45–0.50 mm were cut from each cubic boron nitride sintered body, and XRD analysis was performed on the test pieces. Next, in a sealed container, each test piece was immersed in a fluoronitric acid solution (a mixed acid with a volume ratio of concentrated nitric acid (60%): distilled water: concentrated hydrofluoric acid (47%) = 2:2:1) at 140 °C for 48 hours to obtain an acid-treated solution containing the bonding material. ICP analysis was performed on this acid-treated solution. The composition of the bonding material was then determined based on the results of the XRD and ICP analyses.

[0167] At least WC, Co, and Al compounds were confirmed to be present in all samples. Furthermore, no significant peaks were detected in the XRD for the Al compounds. This is presumably because the use of a Cu X-ray source in the XRD apparatus resulted in significant background noise caused by Co, making it impossible to detect the small amount of Al compounds.

[0168] <Hardness>

[0169] The hardness Hb (GPa) of each cubic boron nitride sintered body before acid treatment was measured. The hardness Ha (GPa) of each cubic boron nitride sintered body after acid treatment was measured. The specific measurement method is described in Example 1, and therefore will not be repeated. The Ha / Hb of each sample was calculated based on the above Ha and Hb. The results are shown in the "Ha / Hb" column of "cBN sintered body" in Table 1.

[0170] Furthermore, when measuring the X2 / X1 ratio in each acid-treated test sample (cubic boron nitride sintered body), the X2 / X1 ratio was 0.09 or less in all test samples, confirming that the binding material in the cubic boron nitride was substantially removed. The detailed method for measuring X2 / X1 is described in Embodiment 1, and therefore will not be repeated.

[0171] <Cutting Test: Cutting of Sintered Alloys>

[0172] Cutting tools were fabricated using the prepared cubic boron nitride sintered bodies (substrate shape: TNGA160404, tool tip treatment T01225). Cutting tests were conducted using these tools under the following cutting conditions.

[0173] Cutting speed: 180 m / min.

[0174] Feed rate: 0.1 mm / rev.

[0175] Incision: 0.2mm

[0176] Coolant: DRY

[0177] Cutting method: Continuous end face cutting

[0178] Lathe: LB4000 (manufactured by OKUMA Co., Ltd.)

[0179] Workpiece to be cut: Cylindrical sintered component (end face cutting of sintered alloy D-40 manufactured by Sumitomo Electric Sintered Alloy Co., Ltd.: HRB75)

[0180] Evaluation method: The tool tip was observed at cutting distances of 0.1 km, and the flank wear was measured. The cutting distance at the point where the maximum flank wear reached 200 μm or more was measured. Regarding the cutting distance, a graph was plotted for each sample with the cutting distance (km) on the horizontal axis and the maximum flank wear on the vertical axis. A graph was obtained by interpolating the graphs using straight lines. The value of 200 μm was then read from the graph. A longer cutting distance indicates a longer tool life. The results are shown in the "Cutting Distance (km)" column of "Cutting Test" in Table 1.

[0181] Table 1

[0182]

[0183] <Inspection>

[0184] Samples 1-1, 1-20, and 1-21 correspond to comparative examples. Samples 1-2 to 1-19 correspond to examples. It was confirmed that samples 1-2 to 1-19 (examples) have a longer tool life compared to samples 1-1, 1-20, and 1-21 (comparative examples).

[0185] [Example 2]

[0186] <Sample 2-1>

[0187] In sample 2-1, a cubic boron nitride sintered body was prepared using the same method as in samples 1-4.

[0188] <Sample 2-2 to Sample 2-5>

[0189] In samples 2-2 to 2-5, cubic boron nitride sintered bodies were prepared by the same method as in sample 2-1, except for the aspects described below.

[0190] In the "Sintering Process", the pressure was increased to 7 GPa and then heated to 1700 °C. Subsequently, during a 15-minute sintering time, the pressure was varied as described in the "Pressure Distribution (GPa)" section of Table 2 for the "Sintering Process". For example, in sample 2-2, the pressure was varied in the manner of 7 GPa → 6 GPa → 7 GPa during the 15-minute sintering time.

[0191] <Sample 2-6>

[0192] The cBN raw material powder and the binder raw material powder were mixed at a ratio of cBN raw material powder: binder raw material powder = 80:20 by volume. Otherwise, cubic boron nitride sintered bodies were prepared by the same method as those for samples 2-5.

[0193] <Sample 2-7>

[0194] cBN raw material powder and binder raw material powder were mixed at a ratio of cBN raw material powder: binder raw material powder = 65:35 by volume. Otherwise, cubic boron nitride sintered bodies were prepared by the same method as those for samples 2-5.

[0195] <Sample 2-8>

[0196] cBN raw material powder and binder raw material powder were mixed at a ratio of cBN raw material powder: binder raw material powder = 97:3 by volume. Otherwise, cubic boron nitride sintered bodies were prepared by the same method as for samples 2-5.

[0197] <Evaluation>

[0198] For each cubic boron nitride sintered body, the content of cubic boron nitride, the composition of the bonding material, and the hardness were measured. The measurement methods were the same as in Example 1, so their descriptions will not be repeated.

[0199] The content of cubic boron nitride in each sample is shown in the "cBN content (volume %)" column of "cBN sintered body" in Table 2.

[0200] Regarding the composition of the bonding materials, it was confirmed that at least WC, Co, and Al compounds were present in all samples. Furthermore, no significant peaks were detected in the Al compounds using XRD, suggesting that the Al compounds are a composite of multiple Al compounds.

[0201] The Ha / Hb of each sample is shown in the "Ha / Hb" column of "cBN sintered body" in Table 2.

[0202] Thermal diffusivity

[0203] Thermal diffusivity (Kb / mm) of each cubic boron nitride sintered body before acid treatment 2 The thermal diffusivity Ka (mm) of each cubic boron nitride sintered body after acid treatment was measured. 2 The measurement was performed using a method described in Embodiment 1, and therefore will not be repeated. The Ka / Kb of each sample was calculated based on the aforementioned Ka and Kb. The results are shown in the "Ka / Kb" column of "cBN sintered body" in Table 2.

[0204] Furthermore, when measuring the X2 / X1 ratio in each acid-treated test sample (cubic boron nitride sintered body), it was confirmed that in all test samples, the X2 / X1 ratio was 0.09 or less, indicating that the binding material in the cubic boron nitride was substantially removed. The detailed method for measuring X2 / X1 is described in Embodiment 1, and therefore will not be repeated.

[0205] <Cutting Test: Evaluation of Cast Iron Grinding (Residual WET)>

[0206] Cutting tools were fabricated using the prepared cubic boron nitride sintered bodies (substrate shape: SNGN090308LE, retainers: RM3080R, SNGN090308, tool tip treatment T01225). Cutting tests were conducted using these tools under the following cutting conditions.

[0207] Cutting speed: 1000 m / min.

[0208] Feed rate: 0.15 mm / rev.

[0209] Incision: 0.4mm

[0210] Coolant: Emulsion 96 diluted 20 times with water.

[0211] Equipment: NEXUS 530C-II HS (manufactured by Yamazaki Mazak Co., Ltd.)

[0212] Workpiece to be machined: Simultaneously machining two FC250 pearlite plates

[0213] Evaluation method: The tool tip is checked every 20 passes, and any chipping or defects exceeding 100μm are considered part of the tool life. The removal volume per pass is calculated as the kerf depth (0.4mm) multiplied by the area of ​​the cutting surface of the workpiece (cm²). 2 The calculation is based on 2 × 10⁻² (pieces). A longer removal volume indicates a longer tool life. The results are shown in Table 2, under "Cutting Test," in the "Removal Volume (cm²)" section. 3 In the column “)”.

[0214] Table 2

[0215]

[0216] <Inspection>

[0217] Samples 2-1 to 2-8 are equivalent to the examples, and all of them were found to have a long tool life.

[0218] Among them, samples 2-2 to 2-8 were confirmed to satisfy Ka / Kb≥0.60, exhibiting exceptionally long tool life. It is speculated that this is because in these samples, the pressure was repeatedly changed from high pressure to low pressure during the sintering process, thus promoting the bonding between the coarse cBN particles due to electrostatic adsorption of the micro-cBN particles.

[0219] [Example 3]

[0220] <Sample 3-1>

[0221] In sample 3-1, a cubic boron nitride sintered body was prepared using the same method as in samples 1-4.

[0222] <Sample 3-2 to Sample 3-6>

[0223] In samples 3-2 to 3-6, cubic boron nitride sintered bodies were prepared by the same method as in sample 3-1, except for the aspects described below.

[0224] In the "cBN powder processing step", the cBN raw material powder obtained by electrostatic adsorption is subjected to ammonia treatment. The temperature and time of the ammonia treatment are shown in the "Temperature, Time" column of "Ammonia Treatment" in Table 3.

[0225] Set the pressure in the "Sintering Process" to the pressure recorded in the "Pressure (GPa)" column of the "Sintering Process" in Table 3.

[0226] <Sample 3-7>

[0227] The cBN raw material powder and the binder raw material powder were mixed at a ratio of cBN raw material powder: binder raw material powder = 80:20 by volume. Otherwise, cubic boron nitride sintered bodies were prepared by the same method as those for samples 3-6.

[0228] <Sample 3-8>

[0229] cBN raw material powder and binder raw material powder were mixed at a ratio of cBN raw material powder: binder raw material powder = 65:35 by volume. Otherwise, cubic boron nitride sintered bodies were prepared by the same method as those for samples 3-6.

[0230] <Sample 3-9>

[0231] cBN raw material powder and binder raw material powder were mixed at a ratio of cBN raw material powder: binder raw material powder = 97:3 by volume. Otherwise, cubic boron nitride sintered bodies were prepared by the same method as those for samples 3-6.

[0232] <Evaluation>

[0233] For each cubic boron nitride sintered body, the content of cubic boron nitride, the composition of the bonding material, and the hardness were measured. The measurement methods were the same as in Example 1, so their descriptions will not be repeated.

[0234] The content of cubic boron nitride in each sample is shown in the "cBN content (volume %)" column of "cBN sintered body" in Table 3.

[0235] Regarding the composition of the bonding materials, it was confirmed that at least WC, Co, and Al compounds were present in all samples. Furthermore, no significant peaks were detected in the Al compounds using XRD, suggesting that the Al compounds are a composite of multiple Al compounds.

[0236] The Ha / Hb of each sample is shown in the "Ha / Hb" column of "cBN sintered body" in Table 3.

[0237] <Bending Test Strength>

[0238] The bending strength Tb (GPa) of each cubic boron nitride sintered body before acid treatment was measured. The bending strength of each cubic boron nitride sintered body after acid treatment was set as Ta (GPa). The specific measurement method is described in Embodiment 1, so it will not be repeated here. Based on the above Ta and Tb, the Ta / Tb of each sample was calculated. The results are shown in the "Ta / Tb" column of "cBN sintered body" in Table 3.

[0239] Furthermore, when measuring the X2 / X1 ratio in each acid-treated test sample (cubic boron nitride sintered body), it was confirmed that in all test samples, the X2 / X1 ratio was 0.09 or less, indicating that the binding material in the cubic boron nitride was substantially removed. The detailed method for measuring X2 / X1 is described in Embodiment 1, and therefore will not be repeated.

[0240] <Cutting Test: Cutting of High-Strength Sintered Alloy>

[0241] Cutting tools were fabricated using the prepared cBN sintered bodies (substrate shape: CNGA120408, tool tip treatment T01225). Cutting tests were conducted using these tools under the following cutting conditions.

[0242] Cutting speed: 170 m / min.

[0243] Feed rate: 0.1 mm / rev.

[0244] Incision: 0.13mm

[0245] Coolant: DRY

[0246] Cutting method: Intermittent end face cutting

[0247] Lathe: LB4000 (manufactured by OKUMA Co., Ltd.)

[0248] Workpiece to be cut: Sprocket (end face cutting of Sumitomo Electric Industries DM-50 (quenched) sintered alloy manufactured by Sumitomo Electric Industries: HV440)

[0249] Evaluation method: The tool tip was observed every 0.5 km, and the wear on the flank face was measured. The cutting distance was measured at the time point when the width of the flank face defect reached 100 μm or more. The longer the cutting distance, the longer the tool life. The results are shown in the "Cutting Distance (km)" column of "Cutting Test" in Table 3.

[0250] Table 3

[0251]

[0252] <Inspection>

[0253] Samples 3-1 to 3-9 are equivalent to the examples, and all of them were found to have a long tool life.

[0254] Among them, samples 3-4 to 3-9 were confirmed to have a Ta / Tb ≥ 0.35, resulting in an exceptionally long tool life. The reason for this is speculated to be that the prolonged ammonia treatment further reduces the oxygen content on the CBN surface, thereby increasing the bonding strength between CBN particles.

[0255] The embodiments and examples of this disclosure have been described above, but it is also intended from the outset that the above-described embodiments and examples may be appropriately combined or modified.

[0256] The embodiments and examples disclosed herein should be considered exemplary in all respects, and not restrictive. The scope of the invention is defined not by the foregoing embodiments and examples, but by the claims, and is intended to include all modifications equivalent to and within the scope of the claims.

Claims

1. A cubic boron nitride sintered body, comprising a binder and 80% by volume and 96% by volume of cubic boron nitride particles, wherein, The bonding material comprises tungsten carbide, cobalt, and aluminum compounds. The hardness Hb of the cubic boron nitride sintered body and the hardness Ha of the acid-treated cubic boron nitride sintered body satisfy Ha / Hb≥0.

40. The acid-treated cubic boron nitride sintered body is obtained by acid treating the cubic boron nitride sintered body and substantially removing the bonding material from the cubic boron nitride sintered body.

2. The cubic boron nitride sintered body according to claim 1, wherein, The Ha and the Hb satisfy Ha / Hb≥0.

53.

3. The cubic boron nitride sintered body according to claim 2, wherein, The Ha and the Hb satisfy Ha / Hb≥0.

55.

4. The cubic boron nitride sintered body according to any one of claims 1 to 3, wherein, The thermal diffusivity Kb of the cubic boron nitride sintered body before acid treatment and the thermal diffusivity Ka of the cubic boron nitride sintered body after acid treatment satisfy Ka / Kb≥0.

60.

5. The cubic boron nitride sintered body according to claim 4, wherein, The Ka and the Kb satisfy Ka / Kb≥0.

90.

6. The cubic boron nitride sintered body according to claim 5, wherein, The Ka and the Kb satisfy Ka / Kb≥0.

95.

7. The cubic boron nitride sintered body according to any one of claims 1 to 3, wherein, The bending test strength Tb of the cubic boron nitride sintered body before acid treatment and the bending test strength Ta of the cubic boron nitride sintered body after acid treatment satisfy Ta / Tb≥0.

30.

8. The cubic boron nitride sintered body according to claim 7, wherein, The Ta and the Tb satisfy Ta / Tb≥0.

35.

9. The cubic boron nitride sintered body according to claim 8, wherein, The Ta and the Tb satisfy Ta / Tb≥0.

40.

10. The cubic boron nitride sintered body according to any one of claims 1 to 3, wherein, The cubic boron nitride particles have an average particle size of 0.4 μm or more and 5 μm or less.

11. The cubic boron nitride sintered body according to claim 10, wherein, The cubic boron nitride particles have an average particle size of 0.5 μm or more and 3.5 μm or less.

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