Cubic boron nitride sintered body and cutting tool

Abstract

A cubic boron nitride sintered body comprising 40% to 85% by volume of cubic boron nitride particles and 15% to 60% by volume of a binder, wherein the binder includes at least one element selected from the group consisting of Group 4, Group 5, Group 6 elements of the periodic table and aluminum, and at least one element selected from the group consisting of nitrogen, carbon, boron, and oxygen, and at least one solid solution derived from the compound, and the Raman spectrum of the cubic boron nitride sintered body is a Raman shift of 10⁴⁸ cm⁻¹. -1 The above is 1062cm. -1 The first peak is located below, and the Raman shift is 1076 cm. -1 Over 1090cm -1 This is a cubic boron nitride sintered body having one or both of the second peaks shown below.

Description

[Technical Field]

[0001] This disclosure relates to a cubic boron nitride sintered body and a cutting tool. [Background technology]

[0002] One high-hardness material used in cutting tools and the like is cubic boron nitride sintered body (hereinafter also referred to as "cBN sintered body"). Cubic boron nitride sintered body typically consists of cubic boron nitride particles (hereinafter also referred to as "cBN particles") and a binder, and its properties tend to differ depending on the cBN particle content. For this reason, in the field of cutting processes, the type of cubic boron nitride sintered body applied to the cutting tool is selected depending on the material of the workpiece, the required machining accuracy, etc.

[0003] For example, as shown in Patent Document 1, a cubic boron nitride sintered body with a low content of cubic boron nitride (hereinafter also referred to as "cBN") can be suitably used for cutting hardened steel and the like. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2005-187260 [Overview of the project]

[0005] The cubic boron nitride sintered body of this disclosure comprises 40% to 85% by volume of cubic boron nitride particles and 15% to 60% by volume of a binder, wherein the binder includes at least one element selected from the group consisting of Group 4, Group 5, Group 6 elements of the periodic table and aluminum, and at least one element selected from the group consisting of nitrogen, carbon, boron, and oxygen, and at least one solid solution derived from the compound, and the Raman spectrum of the cubic boron nitride sintered body has a Raman shift of 10⁴⁸ cm⁻¹. -1 The above is 1062cm. -1The first peak located below, or the Raman shift of 1076 cm. -1 Over 1090cm -1 This is a cubic boron nitride sintered body having one or both of the second peaks shown below. [Modes for carrying out the invention]

[0006] [Issues this disclosure aims to address] In recent years, various initiatives have been underway to achieve carbon neutrality, which means reducing greenhouse gas emissions such as carbon dioxide to zero overall, from the perspective of improving the global environment. In machining, too, there is a demand for technologies that can contribute to achieving carbon neutrality.

[0007] For example, in the machining of hardened steel, high-speed machining can contribute to energy savings during product manufacturing and thus contribute to achieving carbon neutrality.

[0008] Therefore, the present disclosure aims to provide a cubic boron nitride sintered body and a cutting tool equipped therewith that enable the extension of the lifespan of cutting tools, especially when used as a material for cutting tools for high-speed machining of hardened steel.

[0009] [Effects of this disclosure] According to this disclosure, it is possible to provide a cubic boron nitride sintered body that enables the extended lifespan of cutting tools, especially when used as a material for cutting tools for high-speed machining of hardened steel, and a cutting tool equipped therewith.

[0010] [Description of Embodiments in this Disclosure] First, the embodiments of this disclosure will be listed and described. (1) The cubic boron nitride sintered body of the present disclosure is a cubic boron nitride sintered body comprising 40% by volume or more and 85% by volume or less of cubic boron nitride particles and 15% by volume or more and 60% by volume or less of a binder, wherein the binder comprises at least one element selected from the group consisting of Group 4 elements, Group 5 elements, Group 6 elements, and aluminum in the periodic table, and at least one element selected from the group consisting of nitrogen, carbon, boron, and oxygen, and a compound composed of the above elements, and at least one selected from the group consisting of solid solutions derived from the above compounds, and the Raman spectrum of the cubic boron nitride sintered body has a first peak present at a Raman shift of 1048 cm -1 or more and 1062 cm -1 or less, and a second peak present at a Raman shift of 1076 cm -1 or more and 1090 cm -1 or less, or both.

[0011] According to the present disclosure, it is possible to provide a cubic boron nitride sintered body that enables the extension of the life of a cutting tool, particularly even when used as a material for a cutting tool for high-speed machining of hardened steel.

[0012] (2) In the above (1), the Raman spectrum has the first peak, and the first peak may be present at a Raman shift of 1052 cm -1 or more and 1058 cm -1 or less.

[0013] According to this, the life of a cutting tool using the cubic boron nitride sintered body as a material is further improved.

[0014] (3) In the above (1) or (2), the Raman spectrum has the first peak, and the full width at half maximum of the first peak may be 15 cm -1 or more and 50 cm -1 or less.

[0015] According to this, the life of a cutting tool using the cubic boron nitride sintered body as a material is further improved.

[0016] (4) In any of (1) to (3) above, the Raman spectrum has the second peak, and the second peak has a Raman shift of 1080 cm. -1 1086cm -1 It may also exist in the following places.

[0017] According to this, the lifespan of cutting tools using the cubic boron nitride sintered body as a material will be further improved.

[0018] (5) In any of (1) to (4) above, the Raman spectrum has the second peak, and the full width at half maximum of the second peak is 15 cm. -1 More than 50cm -1 The following is also acceptable.

[0019] According to this, the lifespan of cutting tools using the cubic boron nitride sintered body as a material will be further improved.

[0020] (6) In any of (1) to (5) above, the cubic boron nitride particles contain either or both magnesium and calcium, and the total content of magnesium and calcium in the cubic boron nitride particles may be 0.001% by mass or more and 0.1% by mass or less.

[0021] According to this, the lifespan of cutting tools using the cubic boron nitride sintered body as a material will be further improved.

[0022] (7) In any of (1) to (6) above, the cubic boron nitride particles contain either lithium or barium, and the total content of lithium and barium in the cubic boron nitride particles may be 0.001% by mass or more and 0.1% by mass or less.

[0023] According to this, the lifespan of cutting tools using the cubic boron nitride sintered body as a material will be further improved.

[0024] (8) The cutting tool of this disclosure is a cutting tool comprising a cubic boron nitride sintered body as described in any of (1) to (7) above.

[0025] According to this disclosure, it is possible to provide cutting tools that have a long tool life, especially when used for high-speed machining of hardened steel.

[0026] [Details of the embodiments of this disclosure] In this disclosure, the notation "A~B" means an upper and lower limit of the range (i.e., A or greater and B or less), and if there is no unit specified for A, but a unit is specified only for B, then the unit for A and the unit for B are the same.

[0027] In this disclosure, when compounds and the like are represented by chemical formulas, unless otherwise specified, the atomic ratios should include all conventionally known atomic ratios and should not necessarily be limited to those within the stoichiometric range.

[0028] In cubic boron nitride sintered bodies containing cubic boron nitride particles and a ceramic-based binder, the cubic boron nitride particles are thought to form the framework and contribute to fracture resistance. To date, improvements to the cBN particles themselves have been made by modifying the synthesis catalyst and controlling impurity levels and crystallinity to improve toughness. These improvements were made in a way that did not impair the inherent properties of the cBN particles. While the binder contributes to wear resistance, it is a brittle material and therefore often becomes the starting point for fractures. Improvements to the binder have been made through microstructure control and impurity reduction.

[0029] In developing a cubic boron nitride sintered body that enables longer tool life, particularly when used as a material for cutting tools for machining hardened steel, the inventors investigated the mechanism by which conventional tools using cubic boron nitride sintered bodies reach the end of their lifespan.

[0030] When cutting hardened steel with cutting tools made from conventional cubic boron nitride sintered bodies, crater wear is prone to occur near the cutting edge. Detailed analysis of the mechanism of crater wear using a scanning transmission electron microscope with atomic resolution revealed that cBN particles are selectively worn away by abrasion and micro-fracture, and that the worn areas of the cBN particles are worn down smoothly at the atomic level. Furthermore, it was discovered that the binder undergoes plastic flow into the depressions created by the selective wear of the cBN particles, and that this repeated process causes the crater wear to progress.

[0031] Considering that the cBN particles are abraded smoothly at the atomic level, the inventors considered that suppressing heat generation at the atomic level in the cBN particles and the surrounding binder would be effective. Therefore, they conducted a detailed investigation of the correlation between the Raman spectrum of a cubic boron nitride sintered body, obtained by Raman spectroscopy capable of acquiring lattice vibration energy, and crater abrasion. As a result, they found that the amount of Raman shift of the peak originating from cubic boron nitride varies depending on the raw material of the cBN particles, the type of binder, and the ultra-high pressure sintering conditions, and that this Raman shift amount correlates with crater abrasion resistance. Based on this finding, they completed the cubic boron nitride sintered body according to this disclosure. Specific examples of the cubic boron nitride sintered body and its manufacturing method according to this disclosure are described below.

[0032] [Embodiment 1: Cubic boron nitride sintered body] A cubic boron nitride sintered body according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") comprises 40% to 85% by volume of cubic boron nitride particles and 15% to 60% by volume of a binder, wherein the binder includes at least one element selected from the group consisting of Group 4, Group 5, Group 6 elements of the periodic table and aluminum, and at least one element selected from the group consisting of nitrogen, carbon, boron, and oxygen, and at least one solid solution derived from the compound, and the Raman spectrum of the cubic boron nitride sintered body has a Raman shift of 10⁴⁸ cm⁻¹. -1 The above is 1062cm. -1 The first peak located below, or the Raman shift of 1076 cm.-1 Over 1090cm -1 This is a cubic boron nitride sintered body having one or both of the second peaks shown below.

[0033] The cubic boron nitride sintered body of this disclosure enables extended tool life, especially when used as a material for cutting tools for high-speed machining of hardened steel. The reasons for this are presumed to be as follows (i) to (iii).

[0034] (i) The cubic boron nitride sintered body of this disclosure contains 40% to 85% by volume of cBN particles, which have high hardness, strength, and toughness. Therefore, the cBN sintered body can also have excellent strength and toughness. Accordingly, cutting tools using the cubic boron nitride sintered body as a material can have excellent wear resistance and fracture resistance even in high-speed machining of hardened steel, resulting in a longer tool life.

[0035] (ii) In the cubic boron nitride sintered body of the present disclosure, The binder is, The compound comprises at least one element selected from the group consisting of Group 4, Group 5, Group 6 elements of the periodic table and aluminum, and at least one element selected from the group consisting of nitrogen, carbon, boron, and oxygen, as well as at least one element selected from the group consisting of solid solutions derived from the compound.

[0036] The above-mentioned binder possesses excellent heat resistance and reactivity with the workpiece, and also improves the bonding strength between cBN particles. Therefore, cutting tools using a cubic boron nitride sintered body containing the above-mentioned binder as the material can exhibit excellent wear resistance and fracture resistance even in high-speed machining of hardened steel, resulting in a longer tool life.

[0037] (iii) When the inventors investigated in detail the correlation between the Raman spectral spectrum of the cubic boron nitride sintered body and crater wear, they found that the Raman spectrum of the cubic boron nitride sintered body had a Raman shift of 10⁴⁸ cm⁻¹. -1 The above is 1062cm. -1 The first peak is located below, and the Raman shift is 1076 cm. -1Over 1090cm -1 It has been confirmed that when one or both of the second peaks shown below are present, tools made from the cubic boron nitride sintered body are less prone to crater wear caused by micro-fracture of cBN particles and smooth wear at the atomic level. This is presumed to be because atomic (lattice) vibrations in the cBN particles in the cubic boron nitride sintered body are suppressed, resulting in reduced thermal wear. In addition, this also includes the effect of improved strength due to the application of compressive stress to the cBN particles.

[0038] The Raman spectrum of the cubic boron nitride sintered body disclosed herein is a Raman shift of 10⁴⁸ cm⁻¹. -1 The above is 1062cm. -1 The first peak is located below, and the Raman shift is 1076 cm. -1 Over 1090cm -1 Because it possesses one or both of the second peaks shown below, tools made from this cubic boron nitride sintered body are less prone to crater wear, and the progression of flank wear and boundary damage at the cutting edge associated with the detachment of the cutting edge is suppressed, resulting in a longer tool life. In particular, in the finishing of the sliding surfaces of bearing components, the formation of a machined altered layer is suppressed, dimensional accuracy is maintained, and tool life is extended.

[0039] In the Raman spectrum of a cubic boron nitride sintered body containing a conventional ceramic binder, the Raman shift was 10⁶³ cm⁻¹. -1 1066cm or more -1 The following peak originates from cubic boron nitride, with a Raman shift of 1048 cm⁻¹. -1 The above is 1062cm. -1 The first peak is located below, and the Raman shift is 1076 cm. -1 Over 1090cm -1 There is no second peak below.

[0040] The above describes how the cutting tool using the cubic boron nitride sintered body of Embodiment 1 has a long tool life in high-speed machining of hardened steel, but the workpiece material is not limited to this. Examples of workpiece materials include carburized and hardened steel (SCM415H, SCr420H), high-frequency hardened steel (S45C), bearing steel (SUJ2), and ductile cast iron (FCD450, FCD700).

[0041] <Composition of cubic boron nitride sintered body> The cubic boron nitride sintered body of Embodiment 1 comprises cubic boron nitride particles of 40% to 85% by volume and a binder of 15% to 60% by volume.

[0042] The cBN particle content of the cubic boron nitride sintered body may be 45% to 75% by volume, 50% to 70% by volume, or 55% to 65% by volume.

[0043] The binder content of the cubic boron nitride sintered body may be 25% to 55% by volume, 30% to 50% by volume, or 35% to 45% by volume.

[0044] The cBN particle content (volume %) and binder content (volume %) in a cubic boron nitride sintered body can be confirmed by performing microstructural observation, elemental analysis, etc., on the cubic boron nitride sintered body using an energy-dispersive X-ray analyzer (EDX) (Octane Elect EDS system) (hereinafter also referred to as "SEM-EDX") attached to a scanning electron microscope (SEM) (JEOL Ltd.'s "JSM-7800F" (product name)). The specific measurement method is as follows.

[0045] A sample containing the cross-section of a cubic boron nitride sintered body is prepared by cutting the body at an arbitrary position. A focused ion beam apparatus, a cross-section polisher apparatus, etc., can be used to prepare the cross-section. Next, the above cross-section is observed at 5000x magnification using a scanning electron microscope (SEM) to obtain a backscattered electron image. In the backscattered electron image, regions where cBN particles are present appear as black regions, and regions where the binder is present appear as gray or white regions.

[0046] Next, the above backscattered electron image is subjected to binarization using image analysis software (WinROOF from Mitani Corporation). The binarization threshold is set for each image as it varies depending on the contrast. From the binarized image, the area ratio of pixels originating from the dark field (pixels originating from cBN particles) to the area of ​​the measurement field of view is calculated. By considering the calculated area ratio as a volume percentage, the cBN particle content (volume percentage) in the cubic boron nitride sintered body can be determined. The fact that pixels originating from the dark field originate from cBN particles can be confirmed by performing elemental analysis of the cubic boron nitride sintered body using SEM-EDX.

[0047] By calculating the area ratio of pixels originating from the brightfield (pixels originating from the binder) to the area of ​​the measurement field of view from the binarized image, the binder content (volume %) in the cubic boron nitride sintered body can be determined. The fact that pixels originating from the brightfield are derived from the binder can be confirmed by performing elemental analysis of the cubic boron nitride sintered body using SEM-EDX.

[0048] It has been confirmed that even when measuring the cBN particle content (volume %) and binder content (volume %) multiple times in the same cubic boron nitride sintered body by changing the selected measurement area, there is almost no variation in the measurement results.

[0049] The cubic boron nitride sintered body of Embodiment 1 may consist of cubic boron nitride particles in an amount of 40% to 85% by volume and a binder in an amount of 15% to 60% by volume. The cubic boron nitride sintered body of Embodiment 1 may contain unavoidable impurities as long as the effects of the present disclosure are not impaired. The cubic boron nitride sintered body of Embodiment 1 may consist of cubic boron nitride particles in an amount of 40% to 85% by volume, a binder in an amount of 15% to 60% by volume and unavoidable impurities.

[0050] Inevitable impurities are components that are not present in the starting materials but are inevitably introduced as impurities during the manufacturing process. The content of unavoidable impurities may be 0.1% by mass or less. The content of unavoidable impurities can be measured by high-frequency induction plasma emission spectrometry (ICP analysis) and inert gas fusion spectrometry (gas analysis).

[0051] <Cubic boron nitride particles> ≪Magnesium, calcium, lithium, and barium content of cubic boron nitride particles≫ In Embodiment 1, the cubic boron nitride particles mainly consist of cubic boron nitride. The content of cubic boron nitride in the cubic boron nitride particles can be 99.9% by mass or more.

[0052] In the cubic boron nitride sintered body of Embodiment 1, the cubic boron nitride particles contain either or both magnesium and calcium, and the total content of magnesium and calcium in the cubic boron nitride particles may be 0.001% by mass or more and 0.1% by mass or less. According to this, the life of the cutting tool using the cubic boron nitride sintered body as a material is further improved. The reason for this is presumed to be as follows: Either or both magnesium and calcium enter the crystal lattice of the cubic boron nitride, causing the crystal lattice around the magnesium and calcium atoms to expand locally, resulting in lattice distortion in minute regions. This lattice distortion is responsible for the local energy dissipation at the crack tip of the cubic boron nitride particles caused by mechanical and thermal stress during intermittent cutting, thereby suppressing crack propagation. As a result, crater wear during intermittent cutting is further reduced, further improving the life of the cutting tool.

[0053] The total magnesium and calcium content of the cubic boron nitride particles may be 0.01% by mass or more and 0.1% by mass or less, or 0.04% by mass or more and 0.1% by mass or less. In this disclosure, the total magnesium and calcium content of the cubic boron nitride particles means the magnesium or calcium content if the cubic boron nitride particles contain only magnesium or calcium.

[0054] In the cubic boron nitride sintered body of Embodiment 1, the cubic boron nitride particles may contain magnesium in an amount of 0.001% by mass or more and 0.1% by mass or less. This further improves the lifespan of cutting tools using the cubic boron nitride sintered body as a material. The magnesium content of the cubic boron nitride particles may be 0.01% by mass or more and 0.1% by mass or less, or 0.04% by mass or more and 0.1% by mass or less.

[0055] In the cubic boron nitride sintered body of Embodiment 1, the cubic boron nitride particles may contain calcium in an amount of 0.001% by mass or more and 0.1% by mass or less. This further improves the lifespan of cutting tools using the cubic boron nitride sintered body as a material. The calcium content of the cubic boron nitride particles may be 0.01% by mass or more and 0.1% by mass or less, or 0.04% by mass or more and 0.1% by mass or less.

[0056] In the cubic boron nitride sintered body of Embodiment 1, the cubic boron nitride particles contain either or both lithium and barium, and the total content of lithium and barium in the cubic boron nitride particles may be 0.001% by mass or more and 0.1% by mass or less. According to this, the life of the cutting tool using the cubic boron nitride sintered body as a material is further improved. The reason for this is presumed to be as follows: In the cubic boron nitride particles, lithium, which has a smaller atomic radius than boron and nitrogen, is substituted for boron and nitrogen, causing the crystal lattice around the lithium atom to shrink locally. On the other hand, barium, which has a larger atomic radius than boron, nitrogen, magnesium, and calcium, is substituted for boron and nitrogen, or penetrates between the crystal lattices, causing the crystal lattice around the barium atom to expand locally significantly. These factors further enhance lattice distortion in micro-regions, promoting local energy dissipation at the crack tip of cubic boron nitride particles generated by mechanical and thermal stresses during intermittent cutting, thereby suppressing crack propagation. As a result, crater wear during intermittent cutting is further reduced, leading to an improved cutting tool life.

[0057] The total content of lithium and barium in the cubic boron nitride particles may be 0.01% by mass or more and 0.1% by mass or less, or 0.04% by mass or more and 0.1% by mass or less. In this disclosure, the total content of lithium and barium in the cubic boron nitride particles means the content of lithium or barium if the cubic boron nitride particles contain only lithium or barium.

[0058] In the cubic boron nitride sintered body of Embodiment 1, the cubic boron nitride particles may contain lithium in an amount of 0.001% by mass or more and 0.1% by mass or less. This further improves the lifespan of cutting tools using the cubic boron nitride sintered body as a material. The lithium content of the cubic boron nitride particles may be 0.01% by mass or more and 0.1% by mass or less, or 0.04% by mass or more and 0.1% by mass or less.

[0059] In the cubic boron nitride sintered body of Embodiment 1, the cubic boron nitride particles may contain barium in an amount of 0.001% by mass or more and 0.1% by mass or less. This further improves the lifespan of cutting tools using the cubic boron nitride sintered body as a material. This is presumed to be because, in addition to the suppression of crack propagation by strain introduction mentioned above, the barium acts as a getter for trace amounts of oxygen dissolved as impurities in the cBN particles, thereby improving the thermal conductivity of the cBN particles. The barium content of the cubic boron nitride particles may be 0.01% by mass or more and 0.1% by mass or less, or 0.04% by mass or more and 0.1% by mass or less.

[0060] In the cubic boron nitride sintered body of Embodiment 1, the cubic boron nitride particles contain magnesium and calcium, or both, and lithium and barium, and the total content of magnesium and calcium in the cubic boron nitride particles is 0.001% by mass or more and 0.1% by mass or less, and the total content of lithium and barium in the cubic boron nitride particles may be 0.001% by mass or more and 0.1% by mass or less. According to this, the lifespan of cutting tools using the cubic boron nitride sintered body as a material is further improved. In this case, the total content of magnesium and calcium in the cubic boron nitride particles may be 0.01% by mass or more and 0.1% by mass or less, or 0.04% by mass or more and 0.1% by mass or less, and the total content of lithium and barium in the cubic boron nitride particles may be 0.01% by mass or more and 0.1% by mass or less, or 0.04% by mass or more and 0.1% by mass or less.

[0061] The magnesium, calcium, lithium, and barium content of cubic boron nitride particles is measured by ICP.

[0062] Abundance ratio of boron-10 and boron-11 in cubic boron nitride particles In the cubic boron nitride sintered body of Embodiment 1, the boron contained in the cubic boron nitride particles is the isotope boron 10 (hereinafter referred to as " 10 Also written as "B". ) and boron-11 (hereinafter referred to as " 11 Also written as "B". ) can consist of the following. The cubic boron nitride sintered body of Embodiment 1 is composed of cubic boron nitride particles 10 B and 11 The ratio of B to B is 10 B: 11 B = 10:90 to 0:100, or, 10 B: 11 The material may also contain cubic boron nitride particles with a B ratio of 90:10 to 100:0. This further improves the lifespan of cutting tools using the cubic boron nitride sintered body as a material.

[0063] In the above cubic boron nitride particles 10 B and 11 The relative abundance of B is 10 B: 11 B = 4:96 to 1:99, or 10 B: 11 B=96:4 to 99:1 is also acceptable. In all cubic boron nitride particles contained in a cubic boron nitride sintered body. 10 B and 11 The ratio of B to B may be within the aforementioned range. Furthermore, in conventional cubic boron nitride sintered bodies, 10 B and 11 The relative abundance of B is roughly 10 B: 11 B = 20:80.

[0064] In this disclosure, cubic boron nitride particles are included 10 B and 11 The relative abundance of B is measured by time-of-flight secondary ion mass spectrometry (TOF-SIMS).

[0065] ≪Average particle size of cubic boron nitride particles≫ In the cubic boron nitride sintered body of Embodiment 1, the average particle size of the cubic boron nitride particles is not particularly limited and can be the general average particle size used in conventional cubic boron nitride sintered bodies. The particle size of the cubic boron nitride particles may be, for example, 0.1 μm or more and 10 μm or less.

[0066] In this disclosure, the average particle size of cubic boron nitride particles is measured by the following procedure. The cross-section of the cBN sintered body is exposed and polished using the same method as the procedure for measuring the content of cubic boron nitride particles in a cubic boron nitride sintered body.

[0067] Next, the polished surface is observed at 10,000x magnification using a scanning electron microscope (SEM) to obtain an SEM image. A rectangular measurement field of view of 12 μm × 15 μm is set within the SEM image. The SEM image is processed using image analysis software (WinROOF ver. 7.4.5 from Mitani Corporation) to obtain the equivalent circle diameter of each cBN particle observed within the measurement field of view. The arithmetic mean of the equivalent circle diameters of all cBN particles within the measurement field of view is calculated. This arithmetic mean corresponds to the average particle size of the cBN particles in the measurement field of view.

[0068] The above measurements are performed in five non-overlapping measurement fields. The arithmetic mean of the average particle size of cBN particles in the five measurement fields is calculated. In this disclosure, the arithmetic mean of the average particle size of the five measurement fields corresponds to the average particle size of cubic boron nitride particles.

[0069] It has been confirmed that even when measuring the average particle size of cubic boron nitride particles multiple times in the same cubic boron nitride sintered body by arbitrarily setting five measurement fields and following the procedure described above, there is almost no variation in the measurement results.

[0070] <Binding material> The binder plays a role in enabling the sintering of cBN particles, which are difficult to sinter, at industrial-level pressures and temperatures. In the cubic boron nitride sintered body of Embodiment 1, the binder is mainly composed of a ceramic-based binder, and because its reactivity with iron is lower than that of cBN, it adds the function of suppressing chemical and thermal wear during the cutting of high-hardness hardened steel. When the cBN sintered body contains this binder, the wear resistance during high-speed machining of high-hardness hardened steel is improved.

[0071] In the cubic boron nitride sintered body of Embodiment 1, the binder includes a compound (hereinafter also referred to as "first compound") consisting of at least one element selected from the group consisting of Group 4, Group 5, Group 6 elements of the periodic table and aluminum, and at least one element selected from the group consisting of nitrogen, carbon, boron, and oxygen, as well as at least one selected from the group consisting of solid solutions derived from the compound.

[0072] In this disclosure, Group 4 elements of the periodic table include titanium (Ti), zirconium (Zr), and hafnium (Hf). Group 5 elements of the periodic table include vanadium (V), niobium (Nb), and tantalum (Ta). Group 6 elements of the periodic table include chromium (Cr), molybdenum (Mo), and tungsten (W). Hereinafter, elements included in Group 4, Group 5, and Group 6 will also be referred to as "primary metallic elements."

[0073] Examples of compounds containing a primary metallic element and nitrogen (nitrides) include titanium nitride (TiN), zirconium nitride (ZrN), hafnium nitride (HfN), vanadium nitride (VN), niobium nitride (NbN), tantalum nitride (TaN), chromium nitride (CrN), molybdenum nitride (MoN), tungsten nitride (WN), titanium zirconium nitride (TiZrN), titanium hafnium nitride (TiHfN), titanium vanadium nitride (TiVN), and titanium niobium nitride. (TiNbN), Titanium Tantalum Nitride (TiTaN), Titanium Chromium Nitride (TiCrN), Titanium Molybdenum Nitride (TiMoN), Titanium Tungsten Nitride (TiWN), Zirconium Hafnium Nitride (ZrHfN), Zirconium Vanadium Nitride (ZrVN), Zirconium Niobium Nitride (ZrNbN), Zirconium Tantalum Nitride (ZrTaN), Zirconium Chromium Nitride (ZrCrN), Zirconium Molybdenum Nitride (ZrMoN), Zirconium NibN Um tungsten (ZrWN), hafnium vanadium nitride (HfVN), hafnium niobium nitride (HfNbN), hafnium tantalum nitride (HfTaN), hafnium chromium nitride (HfCrN), hafnium molybdenum nitride (HfMoN), hafnium tungsten nitride (HfWN), vanadium niobium nitride (VNbN), vanadium tantalum nitride (VTaN), vanadium chromium nitride (VCrN), vanadium molybdenum nitride (VMoN), nitride Examples include vanadium tungsten (VWN), niobium tantalum nitride (NbTaN), niobium chromium nitride (NbCrN), niobium molybdenum nitride (NbMoN), niobium tungsten nitride (NbWN), tantalum chromium nitride (TaCrN), tantalum molybdenum nitride (TaMoN), tantalum tungsten nitride (TaWN), chromium molybdenum nitride (CrMoN), chromium tungsten nitride (CrWN), and molybdenum tungsten nitride (MoWN).

[0074] Examples of compounds (carbides) containing a primary metallic element and carbon include titanium carbide (TiC), zirconium carbide (ZrC), hafnium carbide (HfC), vanadium carbide (VC), niobium carbide (NbC), tantalum carbide (TaC), chromium carbide (Cr3C2), molybdenum carbide (MoC), and tungsten carbide (WC).

[0075] Examples of compounds (borides) containing a primary metallic element and boron include titanium boride (TiB2), zirconium boride (ZrB2), hafnium boride (HfB2), vanadium boride (VB2), niobium boride (NbB2), tantalum boride (TaB2), titanium zirconium boride ((TiZr)B2), titanium hafnium boride ((TiHf)B2), titanium vanadium boride ((TiV)B2), titanium niobium boride ((TiNb)B2), titanium tantalum boride ((TiTa)B2), chromium boride (CrB), molybdenum boride (MoB), and tungsten boride (WB).

[0076] Examples of compounds (oxides) containing a primary metallic element and oxygen include titanium oxide (TiO2), zirconium oxide (ZrO2), hafnium oxide (HfO2), vanadium oxide (V2O5), niobium oxide (Nb2O5), tantalum oxide (Ta2O5), chromium oxide (Cr2O3), molybdenum oxide (MoO3), and tungsten oxide (WO3).

[0077] Examples of compounds containing primary metallic elements, carbon, and nitrogen (carbonitrides) include titanium carbonitride (TiCN), zirconium carbonitride (ZrCN), hafnium carbonitride (HfCN), titanium niobium carbonitride (TiNbCN), titanium zirconium carbonitride (TiZrCN), titanium hafnium carbonitride (TiHfCN), titanium tantalum carbonitride (TiTaCN), and titanium chromium carbonitride (TiCrCN).

[0078] Examples of compounds (oxynitrides) consisting of a primary metallic element, oxygen, and nitrogen include titanium oxynitride (TiON), zirconium oxynitride (ZrON), hafnium oxynitride (HfON), vanadium oxynitride (VON), niobium oxynitride (NbON), tantalum oxynitride (TaON), chromium oxynitride (CrON), molybdenum oxynitride (MoON), and tungsten oxynitride (WON).

[0079] Examples of first compounds containing aluminum include aluminum nitride (AlN), titanium aluminum nitride (TiAlN, Ti2AlN, Ti3AlN), aluminum boride (AlB2), aluminum oxide (Al2O3), titanium aluminum carbide (TiAlC, Ti2AlC, Ti3AlC), titanium aluminum carbonitride (TiAlCN, Ti2AlCN, Ti3AlCN), aluminum oxynitride (AlON), and SiAlON.

[0080] A solid solution derived from a primary compound refers to a state in which two or more primary compounds are dissolved within each other's crystal structures, and includes interstitial solid solutions and substitutional solid solutions.

[0081] The first compound may be a single type, or a combination of two or more types may be used.

[0082] The binder may consist of only one or more compounds selected from the group consisting of the first compound and solid solutions derived from the first compound. Furthermore, the binder may consist of at least 99.9% by volume of one or more compounds selected from the group consisting of the first compound and solid solutions derived from the first compound, with the remainder being the remaining portion.

[0083] Here, "residue" refers to unavoidable impurities in the binder. The content of unavoidable impurities in the binder can be 0.1% by mass or less.

[0084] The composition of the binder can be identified using X-ray diffraction. The specific measurement method is as follows:

[0085] Cut the cubic boron nitride sintered body with a diamond grinding wheel and electroplated wire or the like so that the measurement points are exposed, and polish the cut surface. If the cubic boron nitride sintered body is used as part of a tool, cut out the portion of the cubic boron nitride sintered body with a diamond grinding wheel and electroplated wire or the like, and polish the cut surface. Set five measurement points arbitrarily on the polished surface.

[0086] The X-ray diffraction spectrum of the polished surface described above is obtained using an X-ray diffractometer (Rigaku "MiniFlex600" trademark). The conditions for the X-ray diffractometer at this time are as follows. Characteristic X-ray: Cu-Kα (wavelength 1.54Å) Tube voltage: 45kV Tube current: 40mA Filter: Multi-layer mirror Optics: Concentration method X-ray diffraction method: θ-2θ method.

[0087] Based on the obtained X-ray diffraction spectrum, the composition of the binder is identified.

[0088] <Raman Spectroscopic Spectrum> The Raman spectrum of the cubic boron nitride sintered body of Embodiment 1 is a Raman shift of 10⁴⁸ cm⁻¹. -1 The above is 1062cm. -1 The first peak is located below, and the Raman shift is 1076 cm. -1 Over 1090cm -1 The following has one or both of the second peaks present. The Raman spectrum is obtained by taking the Raman shift (cm) on the X axis. -1 The coordinate system is shown with the Y-axis representing intensity (au). Both the first and second peaks originate from cubic boron nitride.

[0089] In this disclosure, "The Raman spectrum is Raman shift 1048 cm²." -1 The above is 1062cm. -1 "Having the first peak located below" means a Raman shift of 1048 cm. -1 The above is 1062cm. -1 A peak was observed within the following range, and the Raman shift at the peak's maximum intensity was 1048 cm². -1 The above is 1062cm. -1 This means the following: In this disclosure, "the Raman spectrum is a Raman shift of 1076 cm²." -1 Over 1090cm -1 "Having a second peak located below" means a Raman shift of 1076 cm. -1 The above 1090 cm -1 A peak was observed within the following range, and the Raman shift at the peak's maximum intensity was 1076 cm². -1 Over 1090cm -1 This means the following:

[0090] The Raman spectrum of the cubic boron nitride sintered body of Embodiment 1 has a first peak, the first peak having a Raman shift of 1052 cm⁻¹. -1 More than 1058cm -1 The following may also exist: In this disclosure, "the first peak is a Raman shift of 1052 cm." -1 More than 1058cm -1 "Existing below" means that the Raman shift at the maximum intensity of the first peak is 1052 cm. -1 More than 1058cm -1 This means that the lifespan of cutting tools using the cubic boron nitride sintered body as a material will be further improved. This is presumed to be because the lattice vibrations of the cBN particles themselves in the cubic boron nitride sintered body are further suppressed, resulting in a reduction in thermal wear during cutting, and because compressive stress is applied to the cBN particles, improving their strength.

[0091] The Raman spectrum of the cubic boron nitride sintered body of Embodiment 1 has a first peak, and the full width at half maximum of the first peak is 15 cm². -1 More than 50cm -1 The following is also acceptable. According to this, the lifespan of cutting tools using the cubic boron nitride sintered body as a material is further improved. This is presumed to be because the balance between the toughness and strength of the cubic boron nitride particles is improved. The full width at half maximum of the first peak is broadened from the starting material due to the external stress during ultra-high pressure sintering, improving the crystal's resistance to cleavage. On the other hand, if the full width at half maximum of the first peak becomes excessive, the crystallinity decreases, and the inherent strength of the cubic boron nitride sintered body is reduced. The full width at half maximum of the first peak is 15 cm. -1 More than 50cm -1 The following conditions provide a good balance between improving the crystal's cleavage resistance and increasing the strength of the cubic boron nitride sintered body. From this perspective, the full width at half maximum of the first peak is 25 cm. -1 More than 35cm -1It may also be 25 cm or less, -1 or 30 cm or more. -1 It may also be 30 cm or less.

[0092] The Raman spectrum of the cubic boron nitride sintered body of Embodiment 1 has a second peak, and the second peak may be present at a Raman shift of 1080 cm -1 or more and 1086 cm -1 or less. In the present disclosure, "the second peak is present at a Raman shift of 1080 cm -1 or more and 1086 cm -1 or less" means that the Raman shift at the maximum intensity of the second peak is 1080 cm -1 or more and 1086 cm -1 or less. According to this, the life of the cutting tool using the cubic boron nitride sintered body as a material is further improved. The reason for this is presumably that the lattice vibration of the cBN particles themselves in the cubic boron nitride sintered body is more suppressed, and as a result, the thermal wear during cutting is further reduced. In addition, compressive stress is applied to the cBN particles, improving their strength.

[0093] The Raman spectrum of the cubic boron nitride sintered body of Embodiment 1 has a second peak, and the full width at half maximum of the second peak may be 15 cm -1 or more and 50 cm -1 [[ID=2)]]or less. According to this, the life of the cutting tool using the cubic boron nitride sintered body as a material is further improved. The reason for this is presumably that the balance between the toughness and strength of the cubic boron nitride particles is improved. The full width at half maximum of the second peak expands more than that at the starting material due to the external stress during ultra-high pressure sintering, improving the crystal's cleavage resistance. On the other hand, if the full width at half maximum of the second peak becomes too large, the crystallinity decreases, and the strength originally possessed by the cubic boron nitride sintered body decreases. When the full width at half maximum of the second peak is 15 cm -1 or more and 50 cm -1 or less, the effect of improving the crystal's cleavage resistance and the strength of the cubic boron nitride sintered body are improved in a well-balanced manner. From this perspective, the full width at half maximum of the second peak may be 25 cm[[ID=))]] -1 or more and 35 cm -1 or less, or it may also be 25 cm -1 or more and 30 cm -1 or less.

[0094] In this disclosure, the Raman spectrum of a cubic boron nitride sintered body is obtained by performing Raman spectroscopy on the cubic boron nitride sintered body. The specific method of Raman spectroscopy is as follows: First, the polished surface obtained by mirror polishing the cubic boron nitride sintered body with an Ar ion beam cross-section polisher is irradiated with a laser with a wavelength of 532 nm as excitation light. The measurement is performed at room temperature (25°C). The magnification is 100x and the spot diameter is 0.5 μm. At each of 10 arbitrary locations where at least a portion of the cBN particles are within the spot, a 900 cm⁻¹ measurement is performed. -1 ~1200cm -1 The Raman spectrum is measured within the specified range. The peak shapes of the Raman spectra obtained at each measurement point are peak-fitted using a Lorentz function, and the Raman shift and full width at half maximum (FWHM) of the peak with the maximum intensity are calculated.

[0095] In this disclosure, of the 10 locations where Raman spectra were measured, at least one Raman spectrum was found to have a Raman shift of 10⁴⁸ cm⁻¹. -1 The above is 1062cm. -1 The first peak is located below, and the Raman shift is 1076 cm. -1 Over 1090cm -1 If one or both of the following second peaks are present, the Raman spectrum of a cubic boron nitride sintered body has a Raman shift of 10⁴⁸ cm⁻¹. -1 The above is 1062cm. -1 The first peak is located below, and the Raman shift is 1076 cm. -1 Over 1090cm -1 It is determined that one or both of the following secondary peaks are present. At least one of the 10 Raman spectra has a Raman shift of 10⁴⁸ cm⁻¹. -1 The above is 1062cm. -1 The first peak is located below, and the Raman shift is 1076 cm. -1 Over 1090cm -1As long as the cubic boron nitride sintered body has one or both of the second peaks shown below, it has been confirmed that it can extend the lifespan of cutting tools, especially when used as a material for cutting tools for high-speed machining of hardened steel.

[0096] From the viewpoint of further extending the lifespan of cutting tools, in the cubic boron nitride sintered body of Embodiment 1, at least 5 of the 10 locations where Raman spectra were measured showed a Raman shift of 10⁴⁸ cm⁻¹. -1 The above is 1062cm. -1 The first peak is located below, and the Raman shift is 1076 cm. -1 Over 1090cm -1 It may have one or both of the following second peaks. From the viewpoint of further extending the life of the cutting tool, in the cubic boron nitride sintered body of Embodiment 1, all 10 Raman spectra measured at 10 locations had a Raman shift of 1048 cm⁻¹. -1 The above is 1062cm. -1 The first peak is located below, and the Raman shift is 1076 cm. -1 Over 1090cm -1 It may have one or both of the following second peaks.

[0097] The Raman shift of the first peak was 1052 cm. -1 More than 1058cm -1 The following conditions must be met: the first peak has a full width at half maximum of 15 cm. -1 More than 50cm -1 The following conditions must be met: the Raman shift of the second peak is 1080 cm. -1 1086cm -1 It exists as follows, and the half-width of the second peak is 15 cm. -1 More than 50cm -1 The following conditions are also determined by the same criteria as above (at least one Raman spectrum out of 10 has a Raman shift within the range, or the full width at half maximum is within the range).

[0098] From the viewpoint of further extending the lifespan of cutting tools, in the cubic boron nitride sintered body of Embodiment 1, at least 5 of the 10 Raman spectra measured had a first peak, and the full width at half maximum of each of the 5 first peaks was 15 cm². -1 More than 50cm -1 The following is also acceptable. From the viewpoint of further extending the lifespan of the cutting tool, in the cubic boron nitride sintered body of Embodiment 1, of the 10 locations where Raman spectra were measured, all 10 Raman spectra had a first peak, and the full width at half maximum of each of the 10 first peaks was 15 cm. -1 More than 50cm -1 The following is also acceptable.

[0099] From the perspective of further extending the lifespan of cutting tools, in the cubic boron nitride sintered body of Embodiment 1, at least 5 of the 10 Raman spectra measured had a second peak, and the full width at half maximum of each of the 5 second peaks was 15 cm². -1 More than 50cm -1 The following is also acceptable. From the viewpoint of further extending the lifespan of cutting tools, in the cubic boron nitride sintered body of Embodiment 1, out of 10 locations where Raman spectra were measured, all 10 Raman spectra had a second peak, and the full width at half maximum of each of the 10 second peaks was 15 cm. -1 More than 50cm -1 The following is also acceptable.

[0100] <Method for manufacturing cubic boron nitride sintered bodies> An example of a method for manufacturing the cubic boron nitride sintered body of Embodiment 1 is described below. <<Process for obtaining cubic boron nitride powder>> 10 B and 11 For the total of B 10 B or 11 Using boric acid (hereinafter also referred to as "boric acid") in which the percentage of B's ​​abundance is 90% or more, and a nitrogen source, cubic boron nitride powder is obtained.

[0101] Boron, which makes up boric acid, 10 B and 11 It can consist of B.10 B and 11 The relative abundance of B is 10 B: 11 B can be 10:90 to 0:100. 10 B: 11 B can also be 4:96 to 1:99. 10 B: 11 B can be 90:10 to 100:0, or, 10 B: 11 B=96:4 to 99:1 is also acceptable. 10 B and 11 The ratio of B to B is maintained in the cubic boron nitride sintered body produced using the boric acid. That is, in boric acid 10 B and 11 The ratio of B to B in the cubic boron nitride sintered body made using the boric acid 10 B and 11 It is identical to B.

[0102] The boric acid mentioned above has the general formula (B2O3)·(H2O). x The mixture may contain one or more compounds represented by [x=0~3]. Specifically, examples include ortho-boric acid (H3BO3), meta-boric acid (HBO2), tetra-boric acid (H2B4O7), and boric anhydride (B2O3). Among these, ortho-boric acid is preferred because it is readily available.

[0103] The nitrogen source may consist of at least one selected from the group comprising nitrogen compounds such as ammonium chloride, dicyandiamide, melamine, urea, and ammonia, and nitrogen.

[0104] Methods A and B below are examples of how to obtain cubic boron nitride powder using boric acid and a nitrogen source. Details of Methods A and B are described below.

[0105] ≪Method A≫ In Method A, a first mixed powder is obtained containing boric acid, ammonium chloride (NH4Cl) as a nitrogen source, and either or both magnesium and calcium. The mixing can be carried out in a glove box.

[0106] Next, hexagonal boron nitride is synthesized by heat treatment of the first mixed powder at a pressure of 1 MPa or less and a temperature between 400°C and 1400°C for 60 minutes or more and 900 minutes or less. The molded body obtained by molding the first mixed powder can also be heat-treated. The heat treatment can be carried out using a pressurized furnace. The molded body after heat treatment may be washed by immersing it in aqua regia at 150°C for 24 hours to recover the hexagonal boron nitride.

[0107] Next, the mixture of hexagonal boron nitride and catalyst is subjected to a heat treatment at 4 GPa to 7 GPa and 1400°C to 1800°C for 5 minutes to 600 minutes, thereby converting the hexagonal boron nitride to cubic boron nitride and obtaining cubic boron nitride powder. The mixture of hexagonal boron nitride and catalyst can be obtained by mixing the catalyst with hexagonal boron nitride in a glove box at a molar ratio of 20% or more. The heat treatment can be performed using an ultra-high pressure generator with the mixed powder filled into molybdenum capsules.

[0108] The catalyst may include at least one selected from the group consisting of alkali metals, alkaline earth metals, alkali metal nitrides, alkaline earth metal nitrides, alkali metal boronites, and alkaline earth metal boronites. Alkali metals include lithium (Li), sodium (Na), potassium (K), rubidium (Rb), and cesium (Cs). Alkaline earth metals include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), and barium (Ba). The catalyst may also include at least one selected from the group consisting of, for example, lithium nitride (Li3N), barium nitride (Ba3N2), magnesium nitride (Mg3N2), magnesium boronite (Mg3B2N4), lithium boronite (Li3BN2), lithium calcium boronite (Li3CaBN2), and lithium silicon nitride (Li8SiN4).

[0109] ≪Method B≫ In Method B, first, boric acid and melamine as a nitrogen source are mixed to obtain a second mixed powder. The second mixed powder is then subjected to a heat treatment in an ammonia atmosphere at 600°C to 1200°C for 5 minutes to 180 minutes to reduce and homogenize it, and then subjected to a heat treatment in a nitrogen atmosphere at 1600°C to 2200°C for 5 minutes to 180 minutes to synthesize hexagonal boron nitride. The heat treatment can be carried out using an atmospheric furnace. The second mixed powder after heat treatment may be washed by immersion in aqua regia at 150°C for 24 hours to recover the hexagonal boron nitride.

[0110] Next, a mixture of hexagonal boron nitride and a catalyst is subjected to a heat treatment at 4 GPa to 7 GPa and 1400°C to 1800°C for 5 minutes to 600 minutes, thereby converting the hexagonal boron nitride to cubic boron nitride and obtaining cubic boron nitride powder. The mixture of hexagonal boron nitride and a catalyst can be obtained by mixing the catalyst with hexagonal boron nitride in a glove box at a molar ratio of 20% or more. The heat treatment can be performed using an ultra-high pressure generator with the mixed powder filled into molybdenum capsules. The catalyst can be the one described in Method A above.

[0111] The resulting cubic boron nitride powder may be subjected to grinding in a ball mill and classification in a classifier to adjust the particle size.

[0112] <<Process for obtaining a cubic boron nitride sintered body>> Next, a mixed powder for sintering, containing cubic boron nitride powder and binder raw material powder, is sintered to obtain a cubic boron nitride sintered body.

[0113] The binder raw material powder is the raw material powder for the binder contained in the cubic boron nitride sintered body. The binder raw material powder can be prepared, for example, as follows: A powder consisting of a compound (first compound) made of at least one element selected from the group consisting of Group 4, Group 5, and Group 6 elements of the periodic table (first metallic element) and at least one element selected from the group consisting of nitrogen, carbon, boron, and oxygen (hereinafter also referred to as "first compound powder") is mixed with a powder consisting of the first metallic element to obtain a mixed powder. The mixed powder is heat-treated under vacuum at 1800°C for 60 minutes and then pulverized to obtain the binder raw material powder. If the binder contains aluminum, the heat-treated mixed powder is pulverized, aluminum powder is mixed in, and heat-treated under vacuum at 1500°C for 30 minutes to obtain the binder raw material compound. The binder raw material compound is pulverized to obtain the binder raw material powder.

[0114] Examples of the first compound powders mentioned above include TiN powder, TiCN powder, TiNbCN powder, TiTaCN powder, and TiZrCN powder. Examples of the first metal powders include Ti powder and Al powder.

[0115] There are no particular restrictions on the mixing and grinding methods for each powder. Ball mills or jet mills can be used to ensure efficient and homogeneous mixing. Each mixing and grinding method may be wet or dry.

[0116] The cubic boron nitride powder prepared in the above-mentioned process for obtaining cubic boron nitride powder and the binder raw material powder are mixed using a wet ball mill with ethanol or acetone as a solvent to produce a mixed powder for sintering. The solvent is removed by natural drying after mixing. Subsequently, by heat treatment at 900°C in a vacuum, impurities such as moisture adsorbed on the surface of the mixed powder for sintering can be volatilized, and the surface of the mixed powder for sintering can be cleaned. The cubic boron nitride powder may contain 10% by mass or more of the cubic boron nitride powder prepared in the above-mentioned process for obtaining cubic boron nitride powder.

[0117] The mixed powder for the sintered body described above is placed in contact with a WC-6%Co cemented carbide disc and filled into a tantalum (Ta) container, which is then vacuum-sealed. The vacuum-sealed mixed powder for the sintered body is then subjected to heat treatment using a belt-type ultra-high pressure high-temperature generator at a pressure of 3 GPa to 4.5 GPa and a temperature of 500°C to 800°C for 10 to 30 minutes (first stress adjustment step), followed by heat treatment at a pressure of 5.5 GPa to 8 GPa and a temperature of 1300°C to less than 1800°C for 5 to 60 minutes (main sintering step), and then heat treatment at a pressure of 3 GPa to 4.5 GPa and a temperature of 500°C to 800°C for 10 to 30 minutes (second stress adjustment step). After that, the mixture is slowly cooled to room temperature and the pressure is released to obtain a cubic boron nitride sintered body. The first stress adjustment step, the main sintering step, and the second stress adjustment step are performed continuously during ultra-high pressure sintering.

[0118] <Features of the manufacturing method for the cubic boron nitride sintered body according to this disclosure> In conventional methods for manufacturing cubic boron nitride sintered bodies, when sintering a mixed powder of cubic boron nitride powder and binder raw material powder, for example, the process involves pressurizing to 5-10 GPa at room temperature, then raising the temperature to 1300-2000°C, maintaining the pressure for a certain period, and finally cooling to room temperature before depressurizing. In this sintering method, excessive compressive stress is introduced to the cBN particles and binder when pressurized at room temperature, and this compressive stress is partially relieved as sintering progresses during heating. During cooling after sintering, further compressive stress is applied to the cBN particles due to the difference in thermal expansion coefficients between the cBN particles and the binder, and then, during depressurization, the compressive stress of the cBN particles is relieved due to the difference in Young's modulus between the cBN particles and the binder. Therefore, stress remains in the cBN particles within the cubic boron nitride sintered body. In conventional cubic boron nitride sintered bodies, the Raman shift fluctuates due to stress generated in the cBN particles, lattice vibrations caused by the mass difference of boron isotopes within the cBN particles, and lattice vibrations caused by impurities. The Raman shift of the peak originating from cubic boron nitride is approximately 1063 cm⁻¹. -1 From 1066cm -1 It fluctuates within the range.

[0119] As a result of diligent research, the inventors have found that when sintering a mixed powder for a sintered body containing cubic boron nitride powder with appropriately controlled isotopic abundance and impurity levels, and a binder raw material powder, first, before solid-phase sintering progresses, a heat treatment is performed at a pressure of 3 GPa to 5 GPa and a temperature of 500°C to 1000°C for 10 to 30 minutes (first stress adjustment step). This softens the binder, which has lower hardness than the cBN particles, and allows it to flow into the gaps between the cBN particles, thereby sufficiently transmitting pressure to the cBN particles and increasing the compressive stress applied to the cBN particles. Furthermore, they have found that by performing a heat treatment at a pressure of 3 GPa to 5 GPa and a temperature of 500°C to 800°C for 10 to 30 minutes after this sintering step (second stress adjustment step), the decrease in compressive stress caused by the difference in thermal expansion coefficient and Young's modulus between the cBN particles and the binder can be mitigated. As a result, it became easier to precisely control the Raman shift in the Raman spectrum of the cubic boron nitride sintered body so that it falls within a desired range. We found that this suppresses atomic (lattice) vibrations in the cBN particles within the cubic boron nitride sintered body, imparts compressive stress to the cBN particles, and improves the strength of the cBN particles.

[0120] Factors that influence the Raman shift of peaks originating from cubic boron nitride include those contained in cBN particles. 10 B and 11 The relative abundance of B, as well as the effects of lattice vibrations and lattice strains caused by impurities, should also be considered. Therefore, in the method for producing a cubic boron nitride sintered body of this disclosure, the raw materials are: 10 B and 11 By using boric acid with a controlled ratio of B, magnesium and calcium act as catalysts to promote the reduction and nitridation of boric acid. The resulting hexagonal boron nitride is then converted to cubic boron nitride using various catalysts. This allows for precise control of trace amounts of catalyst elements derived from the raw materials used, enabling the catalyst elements to be dissolved in the cubic boron nitride crystals at the atomic level through substitution or penetration.

[0121] Furthermore, regarding the cubic boron nitride particles used in the production of conventional cubic boron nitride sintered bodies described in Patent Document 1, etc. 10 B and11 The relative abundance of B is 10 B: 11 B = 20:80.

[0122] [Embodiment 2: Cutting Tools] The cubic boron nitride sintered body of Embodiment 1 is suitable for use as a material for cutting tools, wear-resistant tools, grinding tools, heat dissipation materials, and the like. The cutting tool according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 2") is a cutting tool comprising the cubic boron nitride sintered body of Embodiment 1.

[0123] The cutting tool, wear-resistant tool, and grinding tool comprising the cubic boron nitride sintered body of Embodiment 1 may each be composed entirely of the cubic boron nitride sintered body, or only a part thereof (for example, the cutting edge portion in the case of a cutting tool) may be composed of the cubic boron nitride sintered body. In this disclosure, the cutting edge portion means the portion involved in cutting. More specifically, the cutting edge means the region enclosed by the cutting edge ridge and a hypothetical plane at a distance of 0.5 mm from the cutting edge ridge to the cemented carbide side. Furthermore, a coating film may be formed on the surface of each tool. The cubic boron nitride sintered body of Embodiment 1 may also be used as the base material for coated tools.

[0124] Examples of cutting tools include drills, end mills, replaceable cutting tips for drills, replaceable cutting tips for end mills, replaceable cutting tips for milling machines, replaceable cutting tips for turning machines, metal saws, gear cutting tools, reamers, taps, and cutting tools.

[0125] Examples of wear-resistant tools include dies, scribers, scribing wheels, and dressers. Examples of grinding tools include grinding wheels. [Examples]

[0126] This embodiment will be described in more detail by reference to examples. However, this embodiment is not limited by these examples.

[0127] [Consideration 1] <Fabrication of cubic boron nitride sintered bodies> <<Process for obtaining cubic boron nitride powder>> For samples 1-1 to 1-10 and samples 1-12 to 1-18, cubic boron nitride powder was obtained using the following procedure. 10 B and 11 Boric acid (H3BO3) with a controlled ratio of B was prepared. 10 B and 11 The relative abundance of boron isotopes is shown in the "Bore Isotope Abundance Ratio" column under "Preparation of cBN Powder" in Table 1.

[0128] Using the boric acid described above, cubic boron nitride powder was prepared according to Method A below. The method used for each sample is shown in the "Preparation Method" column of "Preparation of cBN Powder" in Table 1.

[0129] ≪Method A≫ In a glove box, H3BO3:Mg:NH4Cl were weighed and mixed in a molar ratio of 1:4:2 to obtain the first mixed powder. The molded body of the first mixed powder was heated in a pressurized furnace at a pressure of 1 MPa or less, at a heating rate of 20°C / min over 1 hour to 1200°C, held at 1200°C for 14 hours, and then cooled to room temperature over 1 hour to obtain a molded body containing hexagonal boron nitride. Subsequently, the molded body was washed by immersion in aqua regia at 150°C for 24 hours to recover the hexagonal boron nitride. Hereafter, the above process will also be referred to as the hexagonal boron nitride synthesis process.

[0130] Next, a mixture of hexagonal boron nitride and Li3N in a glove box at a molar ratio of hexagonal boron nitride:Li3N = 10:3 was filled into molybdenum capsules, and cubic boron nitride was synthesized by heat treatment at 5 GPa and 1600°C for 180 minutes using an ultra-high pressure generator. The cubic boron nitride was then crushed in a ball mill and classified in a classifier, and in all samples, the average particle size of the cBN particles in the cBN sintered body was adjusted to 4.5 μm to obtain cubic boron nitride powder. Hereafter, the above process will also be referred to as the cubic boron nitride synthesis process.

[0131] For sample 1-11, commercially available cubic boron nitride powder with the same average particle size as the cubic boron nitride powder prepared by method A above was used.

[0132] For sample 1-19, the cBN powder used in sample 1-5 of Patent Document 1 (Japanese Patent Publication No. 2005-187260) was prepared and adjusted to the same average particle size as the cubic boron nitride powder produced by Method A above.

[0133] For samples 1-20, cBN powder was prepared according to method B below. ≪Method B≫ 10 B and 11 The ratio of B to B 10 B: 11 A mixed powder was obtained by weighing and mixing boric acid (H3BO3) powder and melamine (C3H6N6) powder in a molar ratio of H3BO3:C3H6N6=2:1 with a B=0:100 ratio. The mixed powder was heat-treated at 900°C for 100 minutes under an ammonia atmosphere to reduce and homogenize it, and then heat-treated at 2000°C for 1 hour under a nitrogen atmosphere to obtain a molded body containing hexagonal boron nitride. The molded body was then washed by immersion in aqua regia at 150°C for 24 hours to recover the hexagonal boron nitride. Cubic boron nitride was synthesized from the obtained hexagonal boron nitride using the same method as in Method A, and the resulting powder was crushed in a ball mill and classified in a classifier to adjust the average particle size of the cBN particles in the cBN sintered body to 4.5 μm, thereby obtaining cubic boron nitride powder.

[0134] <Process for obtaining a cubic boron nitride sintered body> A mixed powder was obtained by mixing one type of first compound powder selected from the group consisting of TiN powder, TiCN powder, TiNbCN powder, TiTaCN powder, and TiZrCN powder with Ti powder in a mass ratio of 7:3. The type of powder used for each sample is shown in the "Powder Type" column of "Preparation of Binder Raw Material Powder" in Table 1.

[0135] The mixed powder was heat-treated at 1800°C for 60 minutes under vacuum, then pulverized to obtain binder raw material powder. For samples containing aluminum as a binder, the heat-treated mixed powder was pulverized, aluminum powder was mixed in, and the mixture was heat-treated at 1500°C for 30 minutes under vacuum to obtain the binder raw material compound. The amount of aluminum powder added was adjusted so that the aluminum content of the binder raw material compound matched the "Al content" column in "Preparation of Binder Raw Material Powder" in Table 1. The binder raw material compound was pulverized to obtain binder raw material powder. Pulverization was performed using a ball mill. The average particle size of the binder raw material powder was 0.5 μm.

[0136] [Table 1]

[0137] The cubic boron nitride powder prepared above and the binder raw material powder were mixed using a wet ball mill mixing method with ethanol or acetone as a solvent to produce a mixed powder for sintered bodies. The mass ratio of cubic boron nitride powder to binder raw material powder in the mixed powder for sintered bodies was adjusted so that the cBN particle content and binder content in the produced cubic boron nitride sintered body matched those listed in the "Content" column for "cBN Particles" and "Content" column for "Binder" in Table 3.

[0138] The mixed powder for the sintered body described above was placed in contact with a WC-6%Co cemented carbide disc and filled into a tantalum (Ta) container, which was then vacuum-sealed. The vacuum-sealed mixed powder for the sintered body was heat-treated using a belt-type ultra-high pressure high-temperature generator under the conditions described in the "First Stress Adjustment Process" column of Table 2 (First Stress Adjustment Process), followed by heat treatment under the conditions described in the "Main Sintering Process" column of Table 2 (Main Sintering Process), and then heat treatment under the conditions described in the "Second Stress Adjustment Process" column of Table 2. After that, the mixture was slowly cooled to room temperature and the pressure was released to obtain a cubic boron nitride sintered body. The first stress adjustment process, the main sintering process, and the second stress adjustment process were performed continuously during ultra-high pressure sintering. For samples marked "-" in the "First Stress Adjustment Process" column, the first stress adjustment process was not performed. For samples marked "-" in the "Second Stress Adjustment Process" column, the second stress adjustment process was not performed, and the mixture was slowly cooled to room temperature and the pressure was released to obtain a cubic boron nitride sintered body.

[0139] [Table 2]

[0140] [Table 3]

[0141] <Evaluation of cubic boron nitride sintered bodies> In the cubic boron nitride sintered bodies of each sample, the content of cubic boron nitride particles and the content of the binder were measured. The specific measurement method is as described in Embodiment 1. The results are shown in Table 3, in the "Content of cBN particles" and "Content of binder" columns for "cBN sintered body".

[0142] In the cubic boron nitride sintered body of each sample, the cubic boron nitride particles are contained 10 B and 11 The abundance of B was measured by TOF-SIMS. In samples 1-1 to 1-10, samples 1-12 to 1-18, and 1-20, B was found in cubic boron nitride particles. 10 B and 11 The relative abundance of B in boric acid 10B and 11 The abundance of B was maintained. In samples 1-11 and 1-19, the cubic boron nitride particles were contained within them. 10 B and 11 The ratio of B to B was 20:80.

[0143] The composition of the binder was identified in the cubic boron nitride sintered bodies of each sample. The specific identification method is as described in Embodiment 1. The results are shown in the "Composition" column of "Binder" under "cBN Sintered Body" in Table 3. In all samples, it was confirmed that the binder consisted of the compounds listed in the "Composition" column. Note that the "Al compound" listed in the "Composition" column includes AlN, AlB2, and Al2O3. The "Zr compound" listed in the "Composition" column includes ZrB2 and (TiNb)B2.

[0144] Raman spectra were measured for the cubic boron nitride sintered bodies of each sample. In the Raman spectra, the Raman shift was 10⁴⁴ cm⁻¹. -1 More than 1100cm -1 The peaks present in the following locations were identified, and the Raman shift at the peak intensity and the full width at half maximum of each peak were measured. The specific method for measuring the Raman spectrum is as described in Embodiment 1.

[0145] The "Raman Shift" column in the "Raman Spectrum" section of Table 3 contains the following values. Similarly, the "Raman Shift" columns in Tables 4 and 5 also contain the following values.

[0146] (i) Of the Raman spectra measured at 10 locations on a cubic boron nitride sintered body, the Raman shift of 10⁴⁸ cm⁻¹ -1 The above is 1062cm. -1 If there is one Raman spectrum with the peaks listed below, the Raman shift value of that peak is the number in the "Raman Shift" column of the table. Of the Raman spectra measured at 10 locations, the Raman shift is 1048 cm⁻¹. -1 The above is 1062cm. -1 If there are two or more Raman spectra with the peaks shown below, the Raman shift is 1052 cm⁻¹. -1More than 1058cm -1 The Raman shift values ​​in the "Raman Shift" column of the table represent the peaks in the Raman spectra that have peaks located below or closest to this range. Raman shift 1052 cm² -1 More than 1058cm -1 If multiple peaks exist below, the Raman shift is 1052 cm. -1 More than 1058cm -1 The Raman shift value of the peak closest to the average value of the Raman shifts listed below is the value in the "Raman Shift" column of the table.

[0147] (ii) Of the Raman spectra measured at 10 locations in the cubic boron nitride sintered body, the Raman shift of 1076 cm⁻¹ -1 Over 1090cm -1 If there is one Raman spectrum with a peak as shown below, the Raman shift value of that peak is the number in the "Raman Shift" column of the table. Of the Raman spectra measured at 10 locations, the Raman shift is 1076 cm⁻¹. -1 Over 1090cm -1 If there are two or more Raman spectra with the peaks shown below, the Raman shift is 1080 cm. -1 1086cm -1 The Raman shift values ​​in the "Raman Shift" column of the table are those of Raman spectra with peaks located below or closest to this range. Raman shift 1080 cm -1 1086cm -1 If multiple peaks exist below, the Raman shift is 1080 cm. -1 1086cm -1 The Raman shift value of the peak closest to the average value of the Raman shifts listed below is the value in the "Raman Shift" column of the table.

[0148] (iii) All Raman spectra measured at 10 locations in the cubic boron nitride sintered body showed a Raman shift of 10⁴⁸ cm⁻¹. -1 The above is 1062cm. -1 The first peak and Raman shift of 1076 cm are located below. -1Over 1090cm -1 If none of the following secondary peaks are present, the Raman shift value of any one of the peaks in the Raman spectrum is the value in the "Raman Shift" column of the table.

[0149] The Raman shift shown in Table 3 is 1048 cm². -1 The above is 1062cm. -1 The Raman spectrum is considered to have a first peak in the following cases: The Raman shift shown in Table 3 is 1076 cm⁻¹. -1 Over 1090cm -1 In the following cases, the Raman spectrum is judged to have a second peak.

[0150] In Table 3, the "Half Width at Half Max" column for the "Raman Spectrum" shows the half width at half maximum for peaks exhibiting the Raman shift indicated in the "Raman Shift" column.

[0151] In the cubic boron nitride sintered bodies of each sample, the content of magnesium, calcium, lithium, and barium in the cBN particles was measured by ICP. Values ​​below 0.001% by mass are below the detection limit.

[0152] The magnesium content of samples 1-1 to 1-10 and samples 1-12 to 1-19 was between 0.001% by mass and 0.1% by mass, and the lithium content was between 0.001% by mass and 0.1% by mass. These samples did not contain calcium or barium.

[0153] The magnesium content of samples 1-11 exceeded 0.1% by mass. Samples 1-11 did not contain calcium, lithium, or barium.

[0154] The lithium content of samples 1-20 was between 0.001% by mass and 0.1% by mass. Samples 1-20 did not contain magnesium, calcium, or barium.

[0155] <Cutting Test 1> Cutting tools (base shape: CNGA120408, cutting edge treatment T01225) were fabricated using cubic boron nitride sintered bodies of each sample. Cutting tests were then conducted using these tools under the following cutting conditions. The following cutting conditions correspond to high-speed machining of hardened steel.

[0156] Cutting speed: 200m / min. Feed rate: 0.1 mm / rev. Cutting depth: 0.2mm Coolant: WET Cutting method: Continuous cutting Lathe: LB400 (manufactured by Okuma Corporation) Workpiece material: SCM415H, hardness of the hardened cut section: 62HRC

[0157] The lifespan of the cutting tool was defined as the cutting distance at which the damage width of the cutting edge exceeded 0.2 mm. The results are shown in the "Cutting Distance" column of "Cutting Test 1" in Table 3. A longer cutting distance indicates superior wear resistance and fracture resistance.

[0158] Furthermore, the amount of crater wear at the cutting edge was measured using a three-dimensional measuring machine at a cutting distance of 4 km. The results are shown in the "Wear Volume" column of "Cutting Test 1" in Table 3. A smaller wear volume indicates better resistance to crater wear. The entry "Defect" in the "Wear Volume" column means that the cubic boron nitride sintered body was damaged at a cutting distance of less than 0.5 km.

[0159] In cutting test 1, the cutting distance was 7.0 km or more, and the wear volume was 600,000 μm³. 3 The following conditions indicate that the tool has a long lifespan:

[0160] The cubic boron nitride sintered bodies of Samples 1-2 to 1-10, and Samples 1-12 to 1-17 and 1-20, correspond to the examples. Cutting tools made using these cubic boron nitride sintered bodies as materials were confirmed to have a long tool life.

[0161] The cubic boron nitride sintered bodies of Samples 1-1, 1-11, and 1-18 to 1-19 are comparative examples. Cutting tools made using these cubic boron nitride sintered bodies as materials exhibited insufficient tool life.

[0162] Generally, crater wear is affected by the cBN content, the particle size of the cBN particles, and the type of binder. Comparing Sample 1-11 (Comparative Example), which has the same cBN content, average particle size of cBN particles, and binder, with Samples 1-3 to 1-6 and Samples 1-12 to 1-15 and Sample 1-20 (Examples), the amount of crater wear is significantly reduced in Samples 1-3 to 1-6 and Samples 1-12 to 1-15 and Sample 1-20 (Examples). Samples 1-4, 1-7, and 1-10, which differ only in the binder, all show similar amounts of crater wear, and are significantly reduced compared to Sample 1-11 (Comparative Example). In the manufacturing method of the Examples, 10 B and 11 By using boric acid with a controlled ratio of B and performing a first and second stress adjustment step during the sintering of the mixed powder for the sintered body, the Raman shift of the peak originating from cubic boron nitride is precisely controlled to fall within a desired range. As a result, the atomic-level vibration of the cBN particles themselves is suppressed, and the mutual diffusion between the atoms of the cBN particles and the atoms of the workpiece is greatly reduced. In addition, the atomic-level heat generation of the surrounding binder is suppressed. Consequently, in the micro-region, not only the heat resistance of the cBN particles but also the surrounding binder in contact with the cBN particles is improved, which is thought to have led to the suppression of crater wear during cutting. In particular, the fact that a significant performance improvement effect is obtained even when the cBN content is 50% and the binder accounts for half suggests that controlling the Raman spectrum of the cubic boron nitride sintered body within the range of this disclosure has a positive effect on the binder as well, and it can be said that a very unique phenomenon has been discovered that occurs when combined with this binder. In addition, it is presumed that a synergistic effect is also involved, where compressive stress is applied to the cBN particles, improving their strength and suppressing micro-fractures of the cBN particles.

[0163] [Consideration 2] <Fabrication of cubic boron nitride sintered bodies> In Study 2, the average particle size of the cubic boron nitride powder, the binder raw material powder, the mass ratio of cBN particle powder to binder raw material powder in the mixed powder for the sintered body, the first stress adjustment step, the main sintering step, and the second stress adjustment step were all the same as for Samples 1-16, except that the method for preparing the cubic boron nitride powder was changed. The preparation methods for the cubic boron nitride powder in each sample are as follows.

[0164] In Sample 2-1, in the hexagonal boron nitride synthesis step of Method A described in Study 1, the molar ratio of Mg in the first mixed powder was changed so that the Mg content of the cubic boron nitride particles in the cubic boron nitride sintered body matched the Mg content listed in the "Mg, Ca, Li, Ba content" column for "cBN sintered body" in Table 4. The cBN powder was prepared under the same conditions as Method A, except that a heat treatment at 1500°C with a pressure of 5.5 GPa was performed for 600 minutes in the cubic boron nitride synthesis step.

[0165] In Sample 2-2, cBN powder was prepared under the same conditions as Sample 2-1, except that the Mg was replaced with Ca in the hexagonal boron nitride synthesis process in Sample 2-1, and the Ca content of the cubic boron nitride particles in the cubic boron nitride sintered body was changed to match the Ca content listed in the "Mg, Ca, Li, Ba Content" column for "cBN Sintered Body" in Table 4.

[0166] In samples 2-1 and 2-2, the synthesis rate of cubic boron nitride particles was slowed down, significantly suppressing the incorporation of Li components into the cubic boron nitride particles and controlling the Li content to below the detection limit (0.001 mass%).

[0167] In samples 2-3 to 2-8, hexagonal boron nitride was synthesized under the same conditions as in method A of Study 1, except that the molar ratio of Mg in the first mixed powder was changed in the synthesis step of method A of Study 1 so that the Mg content of the cubic boron nitride particles in the cubic boron nitride sintered body matched the Mg content listed in the "Mg, Ca, Li, Ba content" column for "cBN sintered body" in Table 4.

[0168] For samples 2-3 to 2-5, cBN powder was then prepared under the same conditions as method A in Study 1, except that the mixing ratio of hexagonal boron nitride and Li3N was changed in the synthesis step of cubic boron nitride powder method A in Study 1 so that the Li content of cubic boron nitride particles in the cubic boron nitride sintered body matched the Li content listed in the "Mg, Ca, Li, Ba content" column for "cBN sintered body" in Table 4.

[0169] For samples 2-6 to 2-8, cBN powder was then prepared under the same conditions as method A in Study 1, except that in the synthesis step of cubic boron nitride powder using method A in Study 1, Ba3N2 was used instead of Li3N, and the mixing ratio of hexagonal boron nitride and Ba3N2 was changed so that the Ba content of the cubic boron nitride particles in the cubic boron nitride sintered body matched the Ba content listed in the "Mg, Ca, Li, Ba content" column for "cBN sintered body" in Table 4.

[0170] For sample 2-9, cBN powder was prepared according to method B below. ≪Method B≫ 10 B and 11 The ratio of B to B 10 B: 11 A second mixed powder was obtained by weighing and mixing boric acid (H3BO3) powder with a B=5:95 ratio and melamine (C3H6N6) powder in a molar ratio of H3BO3:C3H6N6=2:1. The second mixed powder was heat-treated at 900°C for 100 minutes under an ammonia atmosphere to reduce and homogenize it, and then heat-treated at 2000°C for 1 hour under a nitrogen atmosphere to obtain a molded body containing hexagonal boron nitride. The molded body was then washed by immersion in aqua regia at 150°C for 24 hours to recover the hexagonal boron nitride.

[0171] Next, hexagonal boron nitride and Li3N were mixed in a glove box in a molar ratio of 10:3, filled into molybdenum capsules, and subjected to a heat treatment at 5.5 GPa and 1500°C for 60 minutes using an ultra-high pressure generator to synthesize cubic boron nitride powder.

[0172] The cubic boron nitride powder was ground using a ball mill and then classified using a classifier. In all samples, the average particle size of the cBN particles in the cBN sintered body was adjusted to 4.5 μm.

[0173] [Table 4]

[0174] <Evaluation of cubic boron nitride sintered bodies> In the cubic boron nitride sintered bodies of each sample, the content of cubic boron nitride particles and the content of the binder were measured. The specific measurement method is as described in Embodiment 1. The results are shown in the "Content of cBN Particles" and "Content of Binder" columns of "cBN Sintered Body" in Table 4.

[0175] In the cubic boron nitride sintered body of each sample, the cubic boron nitride particles are contained 10 B and 11 The abundance of B was measured by TOF-SIMS. In all samples, the abundance of B contained in cubic boron nitride particles was measured. 10 B and 11 The relative abundance of B is determined by the amount of boric acid in the raw material. 10 B and 11 The ratio of abundance to B was identical.

[0176] The composition of the binder was identified in the cubic boron nitride sintered bodies of each sample. The specific identification method is as described in Embodiment 1. The results are shown in the "Composition" column of "binder" under "cBN sintered body" in Table 4. It was confirmed that in all samples, the binder consisted of the compound listed in the "Composition" column.

[0177] Raman spectra were measured for the cubic boron nitride sintered bodies of each sample. These are shown in the "Raman Shift" and "Half-Maximum Width" columns of Table 4.

[0178] In the cubic boron nitride sintered bodies of each sample, the magnesium, calcium, lithium, and barium content of the cBN particles was measured by ICP. The results are shown in the "Mg, Ca, Li, Ba Content" column of "cBN Sintered Body" in Table 4.

[0179] <Cutting Test 2> Cutting tools (base shape: CNGA120408, cutting edge treatment T01225) were fabricated using cubic boron nitride sintered bodies of each sample. Cutting tests were then conducted using these tools under the following cutting conditions. The following cutting conditions correspond to high-speed intermittent machining of hardened steel.

[0180] Cutting speed: 200m / min. Feed rate: 0.15 mm / rev. Cutting depth: 0.3mm Coolant: DRY Cutting method: Intermittent cutting Lathe: LB400 (manufactured by Okuma Corporation) Workpiece material: SCM415H, hardness of the hardened cut surface: 62HRC, with 5 V-grooves on the outer circumference.

[0181] The lifespan of the cutting tool was defined as the cutting distance at which the damage width of the cutting edge exceeded 0.1 mm. The results are shown in the "Cutting Distance" column of "Cutting Test 2" in Table 4. In Cutting Test 2, a cutting distance of 2.0 km or more is considered to indicate a long tool life.

[0182] [Consideration] The cubic boron nitride sintered bodies of Samples 2-1 to 2-9 correspond to the examples. Cutting tools made using the cubic boron nitride sintered bodies of Samples 2-1 to 2-9 as materials were confirmed to have a long tool life.

[0183] Samples 2-1 and 2-3 to 2-8, which contain Mg, had longer lifetimes than samples 2-2 and 2-9, which do not contain Mg, and it was observed that the lifetime tended to increase with increasing Mg content. This is because trace amounts of Mg form solid solutions between the crystal lattices of cBN particles, 10 B and 11It is presumed that by using boric acid with the abundance ratio controlled with respect to B and performing the first stress adjustment step and the second stress adjustment step when sintering the mixed powder for the sintered body, the Raman shift of the peak derived from cubic boron nitride falls within a desired range, resulting in further improved performance.

[0184] In addition to Mg, Samples 2-3 to 2-8 containing Li or Ba had longer lifetimes than Samples 2-1 and 2-2 that did not contain Li and Ba. Furthermore, Sample 2-7 containing 0.04 mass% each of Mg and Ba had the longest lifetime. From these results, it is also presumed that for Li and Ba, coexisting with Mg and Ca further promotes lattice strain in the microregion, promotes local energy dissipation at the crack tip of cubic boron nitride particles generated by mechanical stress and thermal stress during interrupted cutting, suppresses crack propagation, and thus further reduces crater wear during interrupted cutting, resulting in improved cutting performance.

[0185] Note that in Patent Document 1 (Japanese Patent Application Laid-Open No. 2005-187260), it is described that Li, Ca, and Ba promote bonding by a catalytic action at the contact portion of cBN particles, and Mg forms oxides in the cBN particles and at the interface, preventing heat conduction without a catalytic action. Therefore, the forms of existence of Mg, Li, Ca, and Ba in the cubic boron nitride sintered bodies of Samples 2-1 to 2-9 and the effects obtained by the existence of Mg, Li, Ca, and Ba are completely different from the forms of existence of Li, Ca, Ba, and Mg contained in the cubic boron nitride sintered body of Patent Document 1 and the effects obtained by the existence of Li and Mg.

[0186] [Study 3] <Production of Cubic Boron Nitride Sintered Body> In Samples 3-1 to 3-5, two types of cubic boron nitride powders prepared according to Method A and commercially available cubic boron nitride powder were prepared. In each cubic boron nitride, 10 B and 11 The abundance ratio of B and 10 B: 11B was 100:0, 0:100, or 20:80 (commercial product). In Samples 3-1 to 3-5, cubic boron nitride sintered compacts of each sample were produced in the same manner as in Sample 1-16, except that these powders were blended such that the mass ratios of the three types of cubic boron nitride powders were those shown in Table 5, and the average particle size of the cubic boron nitride powder, the raw material powder of the binder, the mass ratio of the cBN particle powder to the raw material powder of the binder in the mixed powder for sintering, the first stress adjustment step, the main sintering step, and the second stress adjustment step were the same as those in Sample 1-16.

[0187] Sample 3-6 was produced in the same process as Sample 1-11, except that the content ratio of the cubic boron nitride powder in Sample 1-11 was changed to 70 vol% and the Al content of the binder was changed to 15 mass%.

[0188]

Table 5

[0189] <Cutting Test 3> Cutting tools (substrate shape: CNGA120408, cutting edge treatment T01225) were produced using the cubic boron nitride sintered compacts of each sample. Using these tools, a cutting test was conducted under the following cutting conditions. The following cutting conditions are applicable to high-speed machining of difficult-to-cut cast iron.

[0190] Cutting speed: 350 m / min. Feed rate: 0.2 mm / rev. Depth of cut: 0.2 mm Coolant: WET Cutting method: continuous cutting, outside diameter turning Lathe: LB400 (manufactured by Okuma Corporation) Workpiece material: ductile cast iron (FCD450 round bar)

[0191] The cutting distance at the time when the damage width of the cutting edge exceeded 0.1 mm was defined as the tool life of the cutting tool. The results are shown in the "Cutting Distance" column of "Cutting Test 3" in Table 5. A longer cutting distance indicates a longer tool life.

[0192] Raman spectra were measured for the cubic boron nitride sintered bodies of each sample. These are shown in the "Raman Shift" and "Half-Maximum Width" columns of Table 4.

[0193] In samples 3-1 to 3-3, the Raman shift of the peak in all Raman spectra obtained at any 10 locations was 1048 cm⁻¹. -1 The above is 1062cm. -1 Below or 1076cm -1 Over 1090cm -1 It fell within the following range.

[0194] In samples 3-4, the Raman shift of the peak in the Raman spectra obtained at 5 out of 10 arbitrary locations was 1048 cm⁻¹. -1 The above is 1062cm. -1 Below or 1076cm -1 Over 1090cm -1 It fell within the following range.

[0195] In samples 3-5, the Raman spectrum obtained at one of the ten random locations showed a peak Raman shift of 1048 cm⁻¹. -1 The above is 1062cm. -1 Below or 1076cm -1 Over 1090cm -1 It fell within the following range.

[0196] In comparative example sample 3-6, the Raman shift of the peak in the Raman spectra obtained at 10 arbitrary locations was 1048 cm⁻¹. -1 The above is 1062cm. -1 Below or 1076cm -1 Over 1090cm -1 No Raman spectra were found within the following range.

[0197] Samples 3-1 to 3-5 (Examples) had a longer lifetime than Sample 3-6 (Comparative Example), and in Raman spectra acquired at any 10 locations, the Raman shift of the peaks in the Raman spectra acquired at one or more locations was 1048 cm⁻¹. -1 The above is 1062cm. -1 Below or 1076cm-1 Over 1090cm -1 This indicates that an improvement in tool life can be achieved as long as it falls within the following range.

[0198] As described above, the embodiments and examples of this disclosure have been explained, but it is also intended from the outset that the configurations of each of the embodiments and examples described above may be combined or modified in various ways as appropriate. The embodiments and examples disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than the embodiments and examples described above, and all modifications within the scope of the claims are intended to be included in the meaning of equivalents and within the scope.

Claims

1. A cubic boron nitride sintered body comprising 40% to 85% by volume of cubic boron nitride particles and 15% to 60% by volume of a binder, The binder comprises a compound consisting of at least one element selected from the group consisting of Group 4, Group 5, Group 6 elements of the periodic table and aluminum, and at least one element selected from the group consisting of nitrogen, carbon, boron, and oxygen, and at least one solid solution derived from the compound. The Raman spectrum of the cubic boron nitride sintered body is a Raman shift of 1048 cm⁻¹. －１ The above is 1062 cm. －１ The first peak is located below, and the Raman shift is 1076 cm. －１ 1090cm －１ A cubic boron nitride sintered body having one or both of the following second peaks.

2. The Raman spectrum has the first peak, The aforementioned first peak corresponds to a Raman shift of 1052 cm. －１ 1058cm or more －１ The cubic boron nitride sintered body according to claim 1, as described below.

3. The Raman spectrum has the first peak, The full width at half maximum of the first peak is 15 cm. －１ More than 50cm －１ The cubic boron nitride sintered body according to claim 1 or claim 2, which is as follows:

4. The Raman spectrum has the second peak, The second peak is present at a Raman shift of 1080 cm －１ or higher and 1086 cm －１ or lower, and is the cubic boron nitride sintered body according to claim 1 or claim 2.

5. The Raman spectrum has the second peak, The full width at half maximum of the second peak is 15 cm. －１ More than 50cm －１ The cubic boron nitride sintered body according to claim 1 or claim 2, which is as follows:

6. The cubic boron nitride particles contain either or both magnesium and calcium. The cubic boron nitride sintered body according to claim 1 or claim 2, wherein the total content of magnesium and calcium in the cubic boron nitride particles is 0.001% by mass or more and 0.1% by mass or less.

7. The cubic boron nitride particles contain either or both lithium and barium. The cubic boron nitride sintered body according to claim 1 or claim 2, wherein the total content of lithium and barium in the cubic boron nitride particles is 0.001% by mass or more and 0.1% by mass or less.

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

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