Cubic boron nitride sintered body and cutting tool including the same

Abstract

A cubic boron nitride sintered body comprises 70 volume% or more and less than 100 volume% of cubic boron nitride particles and a binder, wherein the binder comprises at least one first metal element selected from the group consisting of titanium, zirconium, vanadium, niobium, hafnium, tantalum, chromium, rhenium, molybdenum, and tungsten, as constituent elements, and cobalt and aluminum, wherein the cubic boron nitride sintered body has a first interface region formed by an interface between the cubic boron nitride particles and the binder and a region sandwiched by a first imaginary line passing through a point 10 nm away from the interface toward the binder, and when the element present at the highest concentration among the first metal elements in the first interface region is designated as the first element, the atomic concentration of the first element in the first interface region is higher than the atomic concentration of the first element in the binder outside the first interface region.

Description

Technology Field

[0001] The present disclosure relates to a cubic boron nitride sintered body and a cutting tool comprising the same. The present application claims priority based on Japanese Patent Application No. 2020-130673 filed on July 31, 2020. All contents of the said Japanese patent application are incorporated herein by reference. Background Technology

[0002] Cubic boron nitride sintered bodies (hereinafter also referred to as "cBN sintered bodies") are high-hardness materials used in cutting tools and the like. CBN sintered bodies are typically composed of cubic boron nitride particles (hereinafter also referred to as "cBN particles") and a binder, and their properties tend to differ depending on the content ratio of the cBN particles.

[0003] For this reason, in the field of cutting processes, the types of cBN sintered bodies applied to cutting tools are distinguished and used according to the material of the workpiece and the required machining precision. For example, a cBN sintered body with a high content of cubic boron nitride (hereinafter also referred to as "cBN") (hereinafter also referred to as "High-cBN sintered body") can be suitablely used for cutting sintered alloys, etc.

[0004] However, High-cBN sintered bodies tend to be prone to sudden defects. This is thought to be due to the weak bonding force between cBN particles, causing the cBN particles to detach. For example, International Publication No. 2005 / 066381 (Patent Document 1) discloses a technique for suppressing the occurrence of sudden defects in High-cBN sintered bodies by selecting an appropriate binder. Prior art literature

[0005] Patent Document 1: International Publication No. 2005 / 066381

[0006] A cubic boron nitride sintered body according to one embodiment of the present disclosure is a cubic boron nitride sintered body comprising 70 volume% or more and less than 100 volume% of cubic boron nitride particles and a binder, wherein the binder comprises, as constituent elements, at least one first metal element selected from the group consisting of titanium, zirconium, vanadium, niobium, hafnium, tantalum, chromium, rhenium, molybdenum, and tungsten, and cobalt and aluminum, and wherein the cubic boron nitride sintered body has a first interface region formed by an interface between the cubic boron nitride particles and the binder and a region sandwiched by a first imaginary line passing through a point 10 nm away from the interface toward the binder, and wherein, when the element present at the highest concentration among the first metal elements in the first interface region is the first element, the atomic concentration of the first element in the first interface region is such that, except for the first interface region The atomic concentration of the first element in the binder is higher than that of the first element.

[0007] A cutting tool according to one embodiment of the present disclosure comprises the cubic boron nitride sintered body. Specific details for implementing the invention

[0008] [Problems to be solved by the present disclosure]

[0009] Recently, due to the rapid increase in the functionality of machine parts, the difficulty of machining workpieces used as machine parts is accelerating. Consequently, the problem of increased costs resulting from the shortened lifespan of cutting tools is becoming a reality. For this reason, further improvement of High-cBN sintered bodies is required. Taking this into account, the present disclosure aims to provide a cubic boron nitride sintered body that enables a long lifespan and a cutting tool comprising the same.

[0010] [Effects of the present disclosure]

[0011] According to the present disclosure, a cubic boron nitride sintered body that enables a long lifespan and a cutting tool including the same can be provided.

[0012] [Description of embodiments of the present disclosure]

[0013] In order to solve the above problem, the inventors carefully examined the cause of the short lifespan of the High-cBN sintered body and found that due to the low affinity of cobalt (Co) in the binder with the cBN particles, the bonding strength at the interface between the cBN particles and the binder is weakened, causing the detachment of cBN particles during cutting. Based on the above findings, the inventors devised a method to improve the bonding strength between the cBN particles and the binder by sintering the cBN particles and the binder after presenting a metal element with high affinity for the cBN particles at a high concentration around the cBN particles at the interface between the cBN particles and the binder. Accordingly, the inventors arrived at the present disclosure, which enables the suppression of the detachment of cBN particles during cutting and thereby enables a long lifespan. Furthermore, it was discovered that when a metal element with high affinity for the cBN particles is present at a high concentration at the interface between the cBN particles and the binder, thermal shrinkage based on the heat generated during cutting is mitigated, thereby suppressing thermal cracking. Thus, the stability against defects in the present disclosure has been significantly improved. Below, the first embodiment of the present disclosure will be described.

[0014] [1] A cubic boron nitride sintered body according to one aspect of the present disclosure is a cubic boron nitride sintered body comprising 70 volume% or more and less than 100 volume% of cubic boron nitride particles and a binder, wherein the binder comprises at least one first metal element selected from the group consisting of titanium, zirconium, vanadium, niobium, hafnium, tantalum, chromium, rhenium, molybdenum, and tungsten, as constituent elements, and cobalt and aluminum, and the cubic boron nitride sintered body has a first interface region formed by an interface between the cubic boron nitride particles and the binder and a region formed by a first imaginary line passing through a point 10 nm away from the interface toward the binder, and when the element present at the highest concentration among the first metal elements in the first interface region is the first element, the atomic concentration of the first element in the first interface region is the first interface The atomic concentration of the first element in the binder outside the region is higher than that of the first element. When a cubic boron nitride sintered body having this characteristic is applied to a cutting tool, it can achieve a long lifespan for the cutting tool.

[0015] [2] The above cubic boron nitride sintered body has a second interface region formed by the interface and a second virtual line passing through a point 2 nm away from the interface toward the binder side, and in the second interface region, the atomic concentration of the first element is preferably 0.7 atomic% or more and 10 atomic% or less. By doing so, the long life of the cutting tool can be more sufficiently realized.

[0016] [3] It is preferable that the cubic boron nitride sintered body contains 85 volume% or more and 95 volume% or less of the cubic boron nitride particles. By doing so, the cubic boron nitride sintered body with a very high content of cBN particles can achieve a long lifespan for the cutting tool.

[0017] [4] It is preferable that the first metal element be at least one selected from the group consisting of zirconium, niobium, chromium, molybdenum, and tungsten. This allows for a longer lifespan to be more fully realized for the cutting tool.

[0018] [5] It is preferable that the first metal element be zirconium. This allows for a longer lifespan to be more fully realized for the cutting tool.

[0019] [6] A cutting tool according to one aspect of the present disclosure comprises the cubic boron nitride sintered body. A cutting tool having these features can achieve a long lifespan.

[0020] [Details of embodiments of the present invention]

[0021] Hereinafter, an embodiment of the present invention (hereinafter also referred to as "this embodiment") will be described. However, this embodiment is not limited thereto. Furthermore, in this specification, notations in the form of "A to B" indicate upper and lower limits of a range (i.e., A or greater and B or less). If a unit is not specified in A and a unit is specified only in B, the unit of A and the unit of B are the same. Additionally, when a compound, etc. is represented by a chemical formula in this specification, unless the atomic ratio is specifically limited, it shall include all conventionally known atomic ratios and shall not necessarily be limited only to those within the stoichiometric range.

[0022] [Cubic Boron Nitride Sintered Body (cBN Sintered Body)]

[0023] A cubic boron nitride sintered body (cBN sintered body) according to the present embodiment is a cBN sintered body comprising 70 volume% or more and less than 100 volume% of cubic boron nitride particles (cBN particles) and a binder. The binder comprises, as a constituent element, at least one first metal element selected from the group consisting of titanium, zirconium, vanadium, niobium, hafnium, tantalum, chromium, rhenium, molybdenum, and tungsten, as well as cobalt and aluminum. The cBN sintered body has a first interface region consisting of an interface between the cBN particles and the binder and a region sandwiched between them by a first imaginary line passing through a point 10 nm away from the interface toward the binder. When the element present at the highest concentration among the first metal elements in the first interface region is designated as the first element, the atomic concentration of the first element in the first interface region is higher than the atomic concentration of the first element in the binder outside the first interface region. A cBN sintered body having this characteristic can achieve a long lifespan for a cutting tool when applied to the cutting tool.

[0024] Cubic Boron Nitride (cBN) Particles

[0025] The cBN sintered body according to the present embodiment comprises cBN particles in an amount of 70 volume% or more and less than 100 volume% as described above. It is preferable that the cBN sintered body contains cBN particles in an amount of 70 volume% or more and 99 volume% or less. It is also preferable that the cBN sintered body contains cBN particles in an amount of 85 volume% or more and 95 volume% or less. That is, the cBN sintered body is a so-called High-cBN sintered body. The cBN particles have high hardness, strength, and toughness, and serve as a framework within the cBN sintered body. The content (volume%) of cBN particles in the cBN sintered body is substantially the same amount as the content (volume%) of the cBN raw material powder used in the mixed powder described later. In addition, although the material inside the capsule containing the above-mentioned mixed powder may melt during ultra-high pressure sintering, the amount of the molten material is minimal; therefore, the content of cBN particles in the cBN sintered body and the content of cBN raw powder in the mixed powder can be considered substantially the same. In this way, by controlling the content of the cBN raw powder used in the mixed powder, the content of cBN particles in the cBN sintered body can be prepared within a desired range.

[0026] The content (volume %) of cBN particles in a cBN sintered body can be confirmed by performing quantitative analysis by inductively coupled high-frequency plasma spectroscopy (ICP) on the cBN sintered body, structural observation using an energy dispersive X-ray analyzer (EDX) equipped with a scanning electron microscope (SEM) or EDX equipped with a transmission electron microscope (TEM), and elemental analysis.

[0027] For example, when using SEM, the content (volume %) of cBN particles can be determined as follows. First, a sample containing a cross-section of the cBN sintered body is prepared by cutting at an arbitrary location on the cBN sintered body. A focused ion beam device, a cross-section polisher device, etc., may be used to prepare the cross-section. Subsequently, a reflected electron image is obtained by observing the cross-section at 2000x magnification using SEM. In the reflected electron image, the region where cBN particles are present appears as a black region, and the region where the binder is present appears as a gray region or a white region, respectively.

[0028] Next, binarization processing is performed on the above-mentioned reflected electron image using image analysis software (e.g., "WinROOF" of Mitani Shoji Bushiki Kaisha), and each area ratio is calculated from the image after this binarization processing. Subsequently, by assuming that the above-mentioned area ratio is continuous in the depth direction of the cross-section, the above-mentioned area ratio can be obtained as the content (volume %) of cBN particles in the cBN sintered body. In addition, the content (volume %) of the binder described later can be obtained simultaneously by this measurement method.

[0029] D based on the area of ​​cBN particles 50 (Average particle size) is not particularly limited and can be, for example, 0.1 to 10 μm. Typically D 50 The smaller the α, the higher the hardness of the cBN sintered body tends to be, and the smaller the variation in grain size, the more homogeneous the properties of the cBN sintered body tend to be. D of the cBN particles 50 It is preferable to make the size 0.5 to 4 μm.

[0030] D of cBN particles 50The result is obtained as follows. First, a reflected electron image is obtained by preparing a sample containing a cross-section of a cBN sintered body in accordance with the cBN particle content measurement method described above. Next, the circle equivalent diameter of each black region in the reflected electron image is calculated using the image analysis software described above. In this case, it is preferable to calculate the circle equivalent diameters of 100 or more cBN particles by observing at least 5 fields of view.

[0031] Next, the cumulative distribution is obtained by arranging the equivalent diameters of each circle in ascending order from the minimum to the maximum. In the cumulative distribution, the particle size at which the cumulative area is 50% is D. 50 It becomes. Here, the circle equivalent diameter refers to the diameter of a circle having the same area as the area of ​​the measured cBN particle.

[0032] <Binder: Composition other than cBN particles>

[0033] The cBN sintered body according to the present embodiment comprises a binder as described above. Additionally, the cBN sintered body may contain unavoidable impurities resulting from the raw materials used, manufacturing conditions, etc. In this case, the cBN sintered body may consist of cBN particles, a binder, and unavoidable impurities. As for the content (volume%) of the binder, it is preferable to have more than 0 volume% and less than or equal to 30 volume%, more preferable to have more than 1 volume% and less than or equal to 30 volume%, and even more preferable to have 5 to 15 volume%. The binder plays a role in enabling cBN particles, which are difficult-to-sinter materials, to be sintered at an industrial-level pressure temperature.

[0034] The above binder comprises at least one first metal element selected from the group consisting of titanium (Ti), zirconium (Zr), vanadium (V), niobium (Nb), hafnium (Hf), tantalum (Ta), chromium (Cr), rhenium (Re), molybdenum (Mo), and tungsten (W) as constituent elements, as well as cobalt (Co) and aluminum (Al). It is preferable that Al be included in the binder as an Al compound. Examples of Al compounds include CoAl, Al2O3, AlN, AlB2, and composite compounds thereof. Additionally, it is preferable that W be included in the binder as WC (tungsten carbide). For the following reasons, these components in the binder are considered to be particularly effective in extending the lifespan of the cBN sintered body.

[0035] First, since Co and Al have catalytic functions, they can promote the bonding of cBN particles in the sintering process described later. Second, WC is presumed to be effective in bringing the coefficient of thermal expansion of the binder close to the coefficient of thermal expansion of the cBN particles. In addition, the catalytic function of Al refers to the function of promoting the diffusion or precipitation of B (boron) and N (nitrogen) constituting the cBN particles through Al.

[0036] Thirdly, when the binder includes the first metal element as a constituent element, the first metal element has a high affinity with the cBN particles, so the bonding strength at the interface between the cBN particles and the binder can be improved.

[0037] Here, it is preferable that the first metal element is at least one selected from the group consisting of zirconium, niobium, chromium, molybdenum, and tungsten. It is more preferable that the first metal element is zirconium. By doing so, the bonding strength at the interface between the cBN particles and the binder can be more sufficiently improved.

[0038] The composition of the binder can be determined by combining XRD (X-ray diffraction measurement) and ICP. Specifically, first, a test specimen with a thickness of approximately 0.45 to 0.5 mm is cut from a cBN sintered body, and by performing XRD analysis on this specimen, compounds, metals, etc., determined from the X-ray diffraction peaks are identified. Subsequently, the specimen is immersed in hydrofluoric acid (a mixed acid with a volume ratio of concentrated nitric acid (60%):distilled water:concentrated hydrofluoric acid (47%) = 2:2:1) in a sealed container to obtain an acid treatment solution in which the binder is dissolved. In addition, ICP analysis is performed on the acid treatment solution to quantitatively analyze each metal element. Finally, the composition of the binder can be determined by interpreting the results of the XRD and the ICP analysis.

[0039] Examples of unavoidable impurities that may be included in the cBN sintered body according to the present embodiment include iron, magnesium, calcium, sodium, lithium, etc. The above unavoidable impurities may be included in the cBN sintered body as impurities alone in an amount of 0.01 mass% or less, or as a total amount of all impurities in an amount of 0.1 mass% or less. In this specification, regarding "unavoidable impurities" that may be included in the cBN sintered body, they are treated as a third component other than cBN and binder.

[0040] <Atomic concentration of the first element in the first interface region>

[0041] The cBN sintered body according to the present embodiment has a first interface region formed by the interface between the cBN particles and the binder, and a region sandwiched between the interface and a first virtual line passing through a point 10 nm away from the interface toward the binder. When the element present at the highest concentration among the first metal elements in the first interface region is designated as the first element, the atomic concentration of the first element in the first interface region is higher than the atomic concentration of the first element in the binder outside the first interface region. Accordingly, the cBN sintered body can have a metal element with high affinity for the cBN particles present at a high concentration around the cBN particles, thereby improving the bonding strength between the cBN particles and the binder. The atomic concentration of the first element in the first interface region and the atomic concentration of the first element in the binder outside the first interface region can each be determined by analyzing using an energy-dispersive X-ray analysis device (TEM-EDX) equipped with a transmission electron microscope. The analysis method using TEM-EDX is described below.

[0042] (Analysis by TEM-EDX)

[0043] <Measurement of atomic concentration of the first element in the first interface region>

[0044] First, a sample is taken from a cBN sintered body, and an argon ion slicer is used to prepare a thinned section with a thickness of 30 to 100 nm from the sample. Next, the section is photographed using a TEM (transmission electron microscope) at a magnification such that at least 10 and no more than 30 cBN particles corresponding to the average particle size of the cBN particles in the sintered body are observed in one field of view, thereby obtaining a first image. Additionally, from the first image, one region including the interface between the cBN particles and the binder (hereinafter also referred to as the "interface region") is arbitrarily selected. At this time, if the structure of the arbitrarily selected interface region is tilted in the depth direction with respect to the field of view, the interface region is excluded from selection or the section is finely adjusted so that the structure of the interface region tilted in the depth direction becomes perpendicular to the field of view. This is because if the structure of the interface region is tilted in the depth direction relative to the field of view, the structure of the interface becomes unclear, and there is a concern that the distance from the interface between the cBN particle and the binder described later cannot be properly measured. Subsequently, a position is determined so that the selected interface region passes near the center of the image, and by changing the observation magnification to 2 million times and observing, a second image of size 100 nm × 100 nm is obtained. In the second image, the interface region exists in such a way that it extends from one end of the image, through near the center of the image, to the other end (the other end) opposite to the one end.

[0045] Next, the interface between the cBN particle and the binder is identified from the interface region in the second image, and a first virtual line is established passing through a point 10 nm away from the interface toward the binder. In this way, a first interface region sandwiched between the interface and the first virtual line is formed within the second image. Additionally, for the first interface region in the second image, elemental line analysis by EDX is performed in a direction approximately perpendicular to the first virtual line. In this case, the beam spot diameter is set to 0.3 nm or less, and the scan interval is set to 0.1 to 0.7 nm.

[0046] Next, based on the element line analysis above, the atomic concentration (atomic %) of each element included as the first metal element in the first interface region is determined. Here, the concentration of each element included as the first metal element is defined as the average value (average concentration) of the atomic concentrations of each element obtained for each beam spot. Additionally, the atomic concentration (atomic %) of each element included as the first metal element is determined by setting the total elements measured within the beam spot, i.e., within the measurement field of view, to 100 atomic %). In this way, the first element present at the highest concentration among the first metal elements in the first interface region can be identified. For example, it is preferable that the first element present at the highest concentration among the first metal elements in the first interface region is 0.7 to 10 atomic %) or less.

[0047] <Measurement of atomic concentration of the first element in the binder other than the first interface region>

[0048] Meanwhile, the atomic concentration of the first element in the binder other than the first interface region can be obtained, for example, by the following method. That is, virtual lines passing through points 15 nm and 30 nm away from the specified interface towards the binder side in the interface region within the second image are respectively set (hereinafter, each is also referred to as "virtual line A" and "virtual line B"). By doing so, a region sandwiched between virtual line A and virtual line B (hereinafter also referred to as "binder region other than the first interface region") is formed within the second image. Subsequently, for the binder region other than the first interface region, elemental line analysis by EDX is performed in a direction approximately perpendicular to either virtual line A or virtual line B. In this case as well, the beam spot diameter is set to 0.3 nm or less, and the scan interval is set to 0.1 to 0.7 nm. Thus, the concentration (atomic %) of the first element in the binder region other than the first interface region can be obtained from the element line analysis above (in addition, the atomic concentration of the first element in this case is also the average value (average concentration) of the concentration of each element obtained for each beam spot). For example, it is preferable that the first element in the binder region other than the first interface region be 0.01 to 0.3 atomic %) or less.

[0049] Here, in this specification, the atomic concentration of the first element in the first interface region and the atomic concentration of the first element in the binder other than the first interface region are defined as the average concentration obtained by averaging each atomic concentration from the second image in six fields of view in order to suppress measurement errors. That is, a second image in six fields of view is prepared from the cBN sintered body used as a sample, and the TEM-EDX analysis described above is performed on the second image to obtain the atomic concentration of the first element in six first interface regions and the atomic concentration of the first element in the binder other than the first interface region, respectively, and the average concentration is determined.

[0050] <Atomic concentration of the first element in the second interface region>

[0051] The cBN sintered body according to the present embodiment has a second interface region formed by the interface and a region sandwiched between the interface and a second virtual line passing 2 nm away from the interface toward the binder side, and it is preferable that the atomic concentration of the first element in the second interface region is 0.7 atomic% or more and 10 atomic% or less. By doing so, the bonding strength between the cBN particles and the binder at the interface between the cBN particles and the binder can be more sufficiently improved.

[0052] The atomic concentration of the first element in the second interface region can be obtained by the same method as obtaining the atomic concentration of the first element in the first interface region. That is, in the second interface region, the atomic concentration (atomic %) of the first element in the second interface region can be obtained by performing element line analysis using the EDX described above in a direction approximately perpendicular to the second virtual line.

[0053] <Action>

[0054] In the cBN sintered body according to the present embodiment, when the element present at the highest concentration among the first metal elements in the first interface region is used as the first element, the atomic concentration of the first element in the first interface region is higher than the atomic concentration of the first element in the binder outside the first interface region. In this case, it is inferred that the cBN sintered body can suppress the detachment of cBN particles during cutting by increasing the bonding strength between the cBN particles and the binder for the following reasons, thereby achieving a long lifespan. That is, since the first interface region is the interface between the cBN particles and the binder and the adjacent region, in the cBN sintered body according to the present embodiment, it means that among the first metal elements with high affinity for cBN particles in the said region, the atomic concentration of the first element is particularly high around the cBN particles. Accordingly, it is thought that during sintering, a large amount of the first element reacts with the cBN particles, and thereby the bonding strength at the interface between the cBN particles and the binder is greatly improved. In particular, when the atomic concentration of the first element in the above-mentioned second interface region is 0.7 atomic% or more and 10 atomic% or less, the first element becomes highly concentrated in the immediate vicinity of the interface between the cBN particles and the binder, so it is thought that the bonding strength at the interface between the cBN particles and the binder is significantly improved. From the above, it is inferred that the cBN sintered body according to the present embodiment can suppress the detachment of cBN particles during cutting, thereby enabling a long lifespan.

[0055] [Cutting Tool]

[0056] The cutting tool according to the present embodiment comprises the cBN sintered body. Specifically, it is preferable that the cutting tool comprises the cBN sintered body as a substrate. A film may be coated on part or all of the surface of the cBN sintered body serving as the substrate.

[0057] The shape and use of the cutting tool according to the present embodiment are not particularly limited. For example, the shape and use of the cutting tool may include a drill, an end mill, a cutting chip with an interchangeable blade for a drill, a cutting chip with an interchangeable blade for an end mill, a cutting chip with an interchangeable blade for milling, a cutting chip with an interchangeable blade for turning, a metal saw, a gear cutting tool, a reamer, a tap, a chip for milling a crankshaft pin, etc.

[0058] Furthermore, the cutting tool according to the present embodiment is not limited to the entire tool being made of a cBN sintered body, but also includes cases where only a part of the tool (particularly the blade portion (cutting edge portion), etc.) is made of a cBN sintered body. For example, a cutting tool according to the present embodiment includes cases where only the blade portion of a base (support) made of cemented carbide, etc., is composed of a cBN sintered body. In this case, the blade portion may be considered as a cutting tool based on the wording. In other words, even if the cBN sintered body occupies only a part of the cutting tool, the cBN sintered body is referred to as a cutting tool.

[0059] The cutting tool according to the present embodiment may include a coating that covers at least the blade portion. In this case, the coating may be formed on the blade portion of the cBN sintered body by a conventionally known method. The method for forming the coating may include physical vapor deposition methods such as ion plating, arc ion plating, sputtering, and ion mixing. Additionally, the coating may be formed by chemical vapor deposition. The composition of the coating is not particularly limited, and any conventionally known coating may be adopted. For example, the composition of the coating may include AlTiSiN, AlCrN, TiZrSiN, CrTaN, HfWSiN, CrAlN, TiN, TiBNO, TiCN, TiCNO, TiB2, TiAlN, TiAlCN, TiAlON, TiAlONC, Al2O3, etc.

[0060] Since the cutting tool according to the present embodiment includes the cBN sintered body, it is possible to suppress the detachment of cBN particles during cutting, thereby enabling a long lifespan.

[0061] [Method for manufacturing a cubic boron nitride sintered body]

[0062] Regarding the method for manufacturing a cBN sintered body according to the present embodiment, there are no particular limitations as long as a cBN sintered body as described above, which enables long life when applied to a cutting tool, can be obtained. However, from the perspective of yield, etc., it is preferable to obtain a cBN sintered body by, for example, the following manufacturing method. The inventors have discovered that in a process for manufacturing a cBN sintered body, a raw material powder of a binder containing a first metal element capable of increasing bonding strength with cBN particles as described below is prepared, impurities in the binder are removed, and the surface of the cBN particles is made N-rich, thereby allowing the first metal element to be present in a high concentration around the cBN particles, and thus a cBN sintered body capable of long life can be manufactured. Here, in this specification, "making the surface of the cBN particles N-rich" means increasing the concentration of nitrogen (N) element on the surface of the cBN particles or imparting N-containing functional groups on the surface of the cBN particles.

[0063] Specifically, the method for manufacturing a cBN sintered body according to the present embodiment preferably comprises: a process (first process) for preparing a binder raw material powder that increases the bonding strength between cBN particles and the binder raw material powder and for removing impurities by heat-treating the binder raw material powder in a low-oxygen atmosphere; a process (second process) for preparing a cBN raw material powder and for making the surface of the cBN particles in the cBN raw material powder N-rich; a process (third process) for preparing a mixed powder consisting of 70 volume% or more and less than 100 volume% of cBN powder and the remainder of the binder raw material powder by mixing the binder raw material powder and the cBN raw material powder; and a process (fourth process) for obtaining a cBN sintered body by sintering the mixed powder. Each process will be described in detail below.

[0064] Process 1

[0065] The first process is a process of preparing a binder raw material powder to increase the bonding strength between cBN particles and the binder raw material powder, and removing impurities by heat-treating the binder raw material powder in a low-oxygen atmosphere. The binder raw material powder can be prepared as follows. First, for example, WC powder, Co powder, and Al powder are prepared by manufacturing them using a conventionally known method or by obtaining them from the market. In addition, it is preferable to prepare a powder of a nitride, carbide, carbonitride, or hydride of at least one first metal element selected from the group consisting of Ti, Zr, V, Nb, Hf, Ta, Cr, Re, Mo, and W as a constituent element in the binder raw material powder by manufacturing it using a conventionally known method or by obtaining it from the market. Subsequently, each of the above-described powders is mixed in a predetermined ratio under inert atmosphere conditions, and then the binder raw material powder can be prepared by grinding it using a wet ball mill, a wet bead mill, etc., under inert atmosphere conditions. By performing the mixing and grinding of each powder under inert atmosphere conditions, the incorporation of oxygen and the oxidation of each powder element can be prevented.

[0066] Here, regarding the Al content in the binder raw material powder, it is set to 20 to 40 mass%, and it is preferable to increase the amount of Al in this type of binder compared to conventional binders. As a result, the Co in the binder is alloyed, making it easier for the first element to diffuse near the interface with the cBN particles than Co during sintering. The mixing method of each powder is not particularly limited, but from the perspective of mixing efficiently and homogeneously, it is preferable to use ball mill mixing, bead mill mixing, planetary mill mixing, or jet mill mixing. Each mixing method may be wet or dry.

[0067] In addition, in the first process, impurities are removed by heat-treating the binder raw material powder in a low-oxygen atmosphere. Specifically, it is preferable to perform a reduction treatment on the binder raw material powder. For example, the binder raw material powder is heated under an argon atmosphere with a low oxygen partial pressure to perform a reduction treatment. At this time, the heating temperature is preferably 700 to 900°C. By doing so, impurities such as oxygen can be further removed from the binder raw material powder.

[0068] Process 2

[0069] The second process is a process of preparing cBN raw material powder and making the surface of the cBN particles in the cBN raw material powder N-rich. As the cBN raw material powder, commercially available cBN powder may be used, or cBN powder obtained from B and N by a conventionally known ultra-high pressure synthesis method may be used. It has been confirmed by the inventors that oxides are present on the surface of this cBN powder. This is thought to be due to the fact that the cBN powder synthesized under ultra-high pressure undergoes a washing treatment or is exposed to the atmosphere. For this reason, it is desirable to reduce the amount of oxides by making the surface of the cBN particles in the cBN raw material powder N-rich.

[0070] As a method for making the surface of cBN particles N-rich, heat treatment in a gas atmosphere containing ammonia can be cited. Specifically, this is a method of exposing the cBN raw material powder to a gas atmosphere containing ammonia. By exposing the cBN raw material powder to a gas atmosphere containing ammonia, oxygen is reduced on the surface of the cBN particles, and at the same time, the surface of the cBN particles can be made N-rich.

[0071] In the second process, the average particle size of the cBN particles is not particularly limited. From the perspective of forming a cBN sintered body that is high strength and possesses excellent wear resistance and fracture resistance, the average particle size of the cBN particles is preferably 0.1 to 10 μm, and more preferably 0.5 to 5 μm. By the above, it is possible to obtain a cBN raw material powder containing N-rich cBN particles while reliably removing the oxide film formed on the surface of the cBN particles.

[0072] Here, when manufacturing a cBN sintered body containing, for example, Zr as a first metal element constituting the binder, it is preferable to prepare the cBN raw material powder described above in the second process and then coat the cBN raw material powder with Zr. This makes it easier to selectively place the Zr component around the cBN particles. This is not limited to Zr, and the same can be said for other first metal elements. That is, by preparing the cBN raw material powder described above in the second process and then coating the cBN raw material powder with the first metal element, it is possible to make it easier to selectively place the first metal element around the cBN particles. Specific coating methods for the first metal element, including Zr, may utilize at least one of sputtering, the AlP method, the HIPIMS method, the CVD method, and the arc plasma powder method (APD method).

[0073] Process 3

[0074] The third process is a process for preparing a mixed powder consisting of 70 volume% or more and less than 100 volume% of cBN powder and the remainder of the binder raw material powder by mixing the binder raw material powder and the cBN raw material powder. Specifically, in the third process, it is preferable to prepare the mixed powder by performing wet ball mill mixing using ethanol, acetone, etc., as a solvent with respect to the binder raw material powder and the cBN raw material powder. After preparing the mixed powder, the solvent is removed by natural drying. In addition, it is preferable to perform heat treatment (e.g., at 850°C or higher under vacuum) on the mixed powder, as this can remove impurities such as moisture adsorbed on the surface.

[0075] Process 4

[0076] The fourth process is a process for obtaining a cBN sintered body by sintering the above-mentioned mixed powder. In this process, a cBN sintered body is manufactured by sintering the above-mentioned mixed powder under high temperature and high pressure conditions. Specifically, in the fourth process, the vacuum-sealed above-mentioned mixed powder is sintered using an ultra-high temperature and high pressure device. The temperature condition for sintering is preferably 1500°C or higher and less than 2000°C, and more preferably 1600°C to 1900°C. The holding time is preferably 10 to 50 minutes. The sintering pressure condition is not particularly limited, but is preferably 5.5 to 8 GPa. By the above, a cBN sintered body can be manufactured.

[0077] <Effects of Action>

[0078] The method for manufacturing a cBN sintered body according to the present embodiment can manufacture a cBN sintered body capable of long lifespan by undergoing each of the above-described processes.

[0079] Examples

[0080] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited thereto.

[0081] [Preparation of Samples]

[0082] cBN sintered bodies of samples 1 to 41 were prepared according to the following procedure.

[0083] <Sample 1>

[0084] (Process 1)

[0085] First, commercially available WC powder, Co powder, Al powder, and Zr carbide powders were prepared. Next, each of the aforementioned powders was blended by ball milling in a mass ratio of WC:Co:Al:ZrC to 22:45:28:5. At this time, the average particle size of each powder was 2 μm. Furthermore, the powder blended in the above mass ratio was subsequently ground by ball milling to prepare the binder raw material powder. Subsequently, the binder raw material powder was subjected to a reduction treatment by heating under an argon atmosphere with a low oxygen partial pressure. The binder raw material powder was prepared as described above. The reduction treatment (heat treatment) was performed at 1×10 -29 The ultra-low oxygen conditions were set to atm or lower, the holding temperature was set to 800℃, and the heat treatment holding time was set to 3 hours.

[0086] (Process 2)

[0087] cBN raw material powder with an average particle size of 2 μm was prepared by a conventionally known ultra-high pressure synthesis method. In addition, the cBN raw material powder was subjected to a reduction treatment under the following heat treatment conditions in an ammonia atmosphere to make the surface of the cBN particles N-rich.

[0088] <Heat Treatment Conditions>

[0089] Ammonia flow rate: 0.5 L / min

[0090] Nitrogen flow rate: 5 L / min

[0091] Pressure inside the furnace: Atmospheric pressure

[0092] Furnace temperature: 700℃

[0093] Duration: 3 hours.

[0094] (Process 3)

[0095] The above cBN raw material powder and the above binder raw material powder were mixed in a volume ratio of 60:40, with the cBN raw material powder to binder raw material powder being uniformly mixed by a wet ball milling method using ethanol. Afterward, the solvent was removed by natural drying, and the above mixed powder was heat-treated under a vacuum at 900°C. By the above, a mixed powder was prepared.

[0096] (Process 4)

[0097] A cBN sintered body was prepared by sintering the above-mentioned mixed powder. Specifically, the above-mentioned mixed powder was placed in contact with a WC-6% Co cemented carbide disc and filled into a Ta (tantalum) container and vacuum sealed. Subsequently, this was sintered for 20 minutes under conditions of 6.5 GPa and 1650°C using a belt-type ultra-high pressure high temperature generator. From the above, the cBN sintered body of Sample 1 was prepared.

[0098] <Sample 2>

[0099] In the third process, the cBN raw material powder and binder raw material powder were mixed in a volume ratio of 70:30, except that the cBN sintered body of Sample 2 was prepared in the same manner as Sample 1.

[0100] <Sample 3>

[0101] In the third process, the cBN raw material powder:binder raw material powder was mixed in a volume ratio of 80:20, except that the cBN sintered body of Sample 3 was prepared in the same manner as Sample 1.

[0102] <Sample 4>

[0103] In the third process, cBN raw material powder:binder raw material powder was mixed in a volume ratio of 91:9, except that the cBN sintered body of Sample 4 was prepared in the same manner as Sample 1.

[0104] <Sample 5>

[0105] In the third process, the cBN raw material powder:binder raw material powder was mixed in a volume ratio of 95:5, except that the cBN sintered body of Sample 5 was prepared in the same manner as Sample 1.

[0106] <Sample 6>

[0107] In the third process, the cBN raw material powder:binder raw material powder was mixed in a volume ratio of 99:1, except that the cBN sintered body of Sample 6 was prepared in the same manner as Sample 1.

[0108] Sample 7

[0109] In the third process, the cBN raw material powder and the binder raw material powder were not mixed, and thus 100 mass% of the cBN raw material powder was sintered in the fourth process. Except for this, the cBN sintered body of Sample 7 was produced in the same manner as Sample 1.

[0110] <Sample 8>

[0111] The cBN sintered body of Sample 8 was prepared in the same manner as Sample 1, except that in the third process, the above-described first and second processes were not carried out, and a binder raw material powder was prepared by mixing the above-described WC powder, Co powder, Al powder, and Zr carbide powder in a mass ratio of WC:Co:Al:ZrC of 22:45:28:5, and cBN powder obtained by ultra-high pressure synthesis was prepared, and these were mixed in a volume ratio of cBN powder to binder raw material powder of 91:9 to obtain a mixed powder. In addition, when the second image obtained from Sample 8 was analyzed by TEM-EDX, W was not detected in the first interface region and the second interface region. The cause was presumed to be that the first and second processes were not carried out, and a mixed powder was obtained from the above-described binder raw material powder and the above-described cBN powder in the third process.

[0112] <Sample 9>

[0113] In the first process, a binder raw material powder was prepared by mixing the above WC powder, Co powder, and Al powder in a mass ratio of WC:Co:Al of 35:45:20, and in the second process, Zr was coated on the cBN raw material powder by the APD method under the following coating conditions, except that a cBN sintered body of Sample 9 was produced in the same manner as Sample 4.

[0114] <Coverage Conditions>

[0115] Coating device: Nanoparticle forming device APD-P manufactured by Advance Rico Co., Ltd.

[0116] Target: Zirconium

[0117] Introductory Gas: 10 -4 Introduce argon gas after vacuuming Pa.

[0118] Discharge voltage: 150 V

[0119] Discharge frequency: 6 Hz

[0120] Capacitor capacitance: 1080 μF

[0121] Shot count: 1000

[0122] Processed powder amount: 25 g

[0123] Powder container rotation speed: 50 rpm.

[0124] <Sample 10>

[0125] Regarding the cBN raw material powder prepared in the second process, the cBN sintered body of Sample 10 was produced in the same manner as Sample 9, except that the number of shots in the coating condition for coating Zr by the APD method was set to 50,000.

[0126] <Sample 11>

[0127] In the case of the first broadcast

[0128] <Sample 12>

[0129] In the second process, regarding the cBN raw material powder prepared, the cBN sintered body of Sample 12 was produced in the same manner as Sample 11, except that the number of shots in the coating condition for coating Zr by the APD method was set to 100,000.

[0130] <Sample 13>

[0131] Regarding the cBN raw material powder prepared in the second process, the cBN sintered body of Sample 13 was produced in the same manner as Sample 11, except that the number of shots in the coating condition for coating Zr by the APD method was set to 200,000.

[0132] <Sample 14>

[0133] In the first process, the WC powder, the Co powder, and the Al powder were prepared, and each of the powders described above was mixed in a mass ratio of WC:Co:Al of 38:42:20. Except for this, the cBN sintered body of Sample 14 was produced in the same manner as Sample 4.

[0134] <Sample 15>

[0135] In the first process, the above WC powder, the above Co powder, the above Al powder, and commercially available metal Cr powder were prepared, and each of the above powders was mixed in a mass ratio of WC:Co:Al:Cr to be 22:44:25:9, except that the cBN sintered body of Sample 15 was produced in the same manner as Sample 4.

[0136] <Sample 16>

[0137] In the first process, the above WC powder, the above Co powder, the above Al powder, and commercially available Hf carbide powder were prepared, and each of the above powders was mixed in a mass ratio such that WC:Co:Al:HfC was 22:46:25:7, except that the cBN sintered body of Sample 16 was produced in the same manner as Sample 4.

[0138] <Sample 17>

[0139] In the first process, the above WC powder, the above Co powder, the above Al powder, and commercially available Ta carbide powder were prepared, and each of the above powders was mixed in a mass ratio such that WC:Co:Al:TaC was 22:46:26:6, except that the cBN sintered body of Sample 17 was produced in the same manner as Sample 4.

[0140] <Sample 18>

[0141] In the first process, the above WC powder, the above Co powder, the above Al powder, and commercially available Mo carbide powder were prepared, and each of the above powders was mixed in a mass ratio of WC:Co:Al:MoC to be 20:47:25:8, except that the cBN sintered body of Sample 18 was produced in the same manner as Sample 4.

[0142] <Sample 19>

[0143] In the first process, the above WC powder, the above Co powder, the above Al powder, and commercially available Ti carbide powder were prepared, and each of the above powders was mixed in a mass ratio of WC:Co:Al:TiC to be 20:46:25:9, except that the cBN sintered body of Sample 19 was prepared in the same manner as Sample 4.

[0144] <Sample 20>

[0145] In the first process, the above WC powder, the above Co powder, the above Al powder, and commercially available V carbide powder were prepared, and each of the above powders was mixed in a mass ratio of WC:Co:Al:VC to be 20:47:25:8, except that the cBN sintered body of Sample 20 was produced in the same manner as Sample 4.

[0146] <Sample 21>

[0147] In the first process, the above WC powder, the above Co powder, the above Al powder, and commercially available Nb carbide powder were prepared, and each of the above powders was mixed in a mass ratio such that WC:Co:Al:NbC was 20:44:30:6, except that the cBN sintered body of Sample 21 was produced in the same manner as Sample 4.

[0148] <Sample 22>

[0149] In the first process, the above WC powder, the above Co powder, the above Al powder, and commercially available Re carbide powder were prepared, and each of the above powders was mixed in a mass ratio such that WC:Co:Al:ReC was 23:45:25:7, except that the cBN sintered body of Sample 22 was produced in the same manner as Sample 4.

[0150] <Sample 23>

[0151] A cBN sintered body of Sample 23 was produced in the same manner as Sample 1, except that the above-described first and second processes were not carried out, and in the third process, a binder raw material powder was prepared by mixing the above-described WC powder, Co powder, Al powder, and commercially available W powder in a mass ratio of WC:Co:Al:W of 22:45:28:5, and cBN powder obtained by ultra-high pressure synthesis was prepared, and these were mixed in a volume ratio of cBN powder to binder raw material powder of 91:9 to obtain a mixed powder.

[0152] <Sample 24>

[0153] The cBN sintered body of Sample 24 was produced in the same manner as Sample 23, except that the first and second processes described above were not carried out, and in the third process, the binder raw material powder was prepared by mixing the WC powder, Co powder, Al powder, and Cr powder in a mass ratio such that WC:Co:Al:Cr is 22:45:28:5.

[0154] <Sample 25>

[0155] Except for not carrying out the first and second processes described above and preparing a binder raw material powder in the third process such that the mass ratio of WC powder, Co powder, Al powder, and commercially available Hf powder is 22:45:28:5, the cBN sintered body of Sample 25 was produced in the same manner as Sample 23.

[0156] <Sample 26>

[0157] The cBN sintered body of Sample 26 was produced in the same manner as Sample 23, except that the first and second processes described above were not carried out, and in the third process, the binder raw material powder was prepared by mixing the WC powder, Co powder, Al powder, and commercially available Ta powder in a mass ratio such that WC:Co:Al:Ta is 22:45:28:5.

[0158] <Sample 27>

[0159] Except for not carrying out the first and second processes described above, and preparing a binder raw material powder in the third process by mixing the WC powder, Co powder, Al powder, and commercially available Mo powder in a mass ratio of WC:Co:Al:Mo of 22:45:28:5, the cBN sintered body of Sample 27 was produced in the same manner as Sample 23.

[0160] <Sample 28>

[0161] The cBN sintered body of Sample 28 was produced in the same manner as Sample 23, except that the first and second processes described above were not carried out, and in the third process, a binder raw material powder was prepared by mixing the WC powder, Co powder, Al powder, and commercially available Ti powder in a mass ratio of WC:Co:Al:Ti of 22:45:28:5.

[0162] <Sample 29>

[0163] Except for not carrying out the first and second processes described above and preparing a binder raw material powder in the third process such that the mass ratio of WC powder, Co powder, Al powder, and commercially available V powder is 22:45:28:5, the cBN sintered body of Sample 29 was produced in the same manner as Sample 23.

[0164] <Sample 30>

[0165] A cBN sintered body of Sample 30 was produced in the same manner as Sample 23, except that the first and second processes described above were not carried out, and in the third process, a binder raw material powder was prepared by mixing the WC powder, Co powder, Al powder, and commercially available Nb powder in a mass ratio such that WC:Co:Al:Nb is 22:45:28:5.

[0166] Sample 31

[0167] The cBN sintered body of Sample 31 was produced in the same manner as Sample 23, except that the first and second processes described above were not carried out, and in the third process, a binder raw material powder was prepared by mixing the WC powder, Co powder, Al powder, and commercially available Re powder in a mass ratio of WC:Co:Al:Re of 22:45:28:5.

[0168] <Sample 32>

[0169] In the first process, the cBN sintered body of Sample 32 was prepared by the same method as Sample 4, except that the binder raw material powder was prepared by mixing each of the above WC powder, Co powder, Al powder, and Zr carbide powder in a mass ratio of WC:Co:Al:ZrC to 20:43:28:9.

[0170] <Sample 33>

[0171] In the first process, the cBN sintered body of Sample 33 was prepared by the same method as Sample 4, except that the binder raw material powder was prepared by mixing the WC powder, Co powder, Al powder, and commercially available W powder in a mass ratio of WC:Co:Al:W of 20:43:28:9.

[0172] <Sample 34>

[0173] In the first process, the cBN sintered body of Sample 34 was prepared by the same method as Sample 4, except that the binder raw material powder was prepared by mixing each of the above WC powder, Co powder, Al powder, and Cr powder in a mass ratio of WC:Co:Al:Cr of 20:43:28:9.

[0174] <Sample 35>

[0175] In the first process, the cBN sintered body of Sample 35 was prepared by the same method as Sample 4, except that the binder raw material powder was prepared by mixing the WC powder, Co powder, Al powder, and commercially available Hf powder in a mass ratio of WC:Co:Al:Hf of 20:43:28:9.

[0176] <Sample 36>

[0177] In the first process, the cBN sintered body of Sample 36 was prepared by the same method as Sample 4, except that the binder raw material powder was prepared by mixing the WC powder, Co powder, Al powder, and commercially available Ta powder in a mass ratio of WC:Co:Al:Ta of 20:43:28:9.

[0178] Sample 37

[0179] In the first process, the cBN sintered body of Sample 37 was prepared by the same method as Sample 4, except that the binder raw material powder was prepared by mixing the WC powder, Co powder, Al powder, and commercially available Mo powder in a mass ratio of WC:Co:Al:Mo of 20:43:28:9.

[0180] <Sample 38>

[0181] In the first process, the cBN sintered body of Sample 38 was prepared by the same method as Sample 4, except that the binder raw material powder was prepared by mixing the WC powder, Co powder, Al powder, and commercially available Ti powder in a mass ratio of WC:Co:Al:Ti of 20:43:28:9.

[0182] <Sample 39>

[0183] In the first process, the cBN sintered body of Sample 39 was prepared by the same method as Sample 4, except that the binder raw material powder was prepared by mixing the WC powder, Co powder, Al powder, and commercially available V powder in a mass ratio of WC:Co:Al:V of 20:43:28:9.

[0184] <Sample 40>

[0185] In the first process, the cBN sintered body of Sample 40 was prepared by the same method as Sample 4, except that the binder raw material powder was prepared by mixing the WC powder, Co powder, Al powder, and commercially available Nb powder in a mass ratio of WC:Co:Al:Nb of 20:43:28:9.

[0186] Sample 41

[0187] In the first process, the cBN sintered body of Sample 41 was prepared by the same method as Sample 4, except that the binder raw material powder was prepared by mixing the WC powder, Co powder, Al powder, and commercially available Re powder in a mass ratio of WC:Co:Al:Re of 20:43:28:9.

[0188] 〔evaluation〕

[0189] <Atomic concentration of the first element in the first interface region, the second interface region, and the binder other than the first interface region>

[0190] For each cBN sintered body of Samples 1 to 13 above, a smooth surface was produced by cutting at an arbitrary location and polishing the exposed surface. Then, sections were prepared by thinning to a thickness of 50 nm using an argon ion slicer. Subsequently, analysis was performed on the second image (100 nm × 100 nm) using the TEM-EDX method described above. The beam diameter of the TEM-EDX was set to 0.2 nm, and the scan interval was set to 0.6 nm. From the obtained measurements, the atomic concentration of the first element in the first interface region, the second interface region, and the binder other than the first interface region was determined, respectively, according to the method described above. The results are shown in Table 1. Samples 2 to 6 and Samples 9 to 13 are examples, and Sample 1 and Samples 7 to 8 are comparative examples.

[0191] In addition, for each cBN sintered body of samples 14 to 41, a second image (100 nm × 100 nm) was obtained in the same manner as for each cBN sintered body of samples 1 to 13, and the second image was analyzed by TEM-EDX. From the obtained measurements, the atomic concentration of the first element in the first interface region, the second interface region, and the binder other than the first interface region was determined, respectively, according to the method described above. The results are shown in Table 2. Samples 14 to 22 and samples 32 to 41 are all examples, and samples 23 to 31 are comparative examples. In addition, in Table 2, the results of sample 4 (example) and sample 8 (comparative example) are also specified to show the results of the cutting test described later.

[0192] <1st Cutting Test>

[0193] A cutting tool (substrate shape: SNGN090308, blade treatment T01225) for each sample was manufactured from each cBN sintered body of Samples 1 to 13 above. Using this, a cutting test (first cutting test) was performed under the following cutting conditions.

[0194] <Cutting Conditions>

[0195] Cutting speed: 1450 m / min.

[0196] Feed rate: 0.2 mm / rev.

[0197] Cut: 0.3 mm

[0198] Coolant: WET

[0199] Coolant: Emulsion 96 (diluted 20 times with water)

[0200] Cutter: RM3080R (Manufactured by Sumitomo Electric Vehicle Co., Ltd.)

[0201] Cutting method: Intermittent cutting

[0202] Lathe: NEXUS 530-II HS (Manufactured by Yamazaki Corporation)

[0203] Workpiece: FC250.

[0204] The blade was observed at every 0.5 km of cutting distance, and the amount of blade detachment was measured. The amount of blade detachment was defined as the width of retraction due to wear from the blade ridge position prior to cutting. In the case of chipping, the size of the chipping was defined as the amount of detachment. The cutting distance at which the amount of blade detachment exceeded 0.1 mm was measured. Furthermore, the above cutting distance was defined as the life of the cutting tool. The results are shown in Table 1. It can be evaluated that the longer the cutting distance, the longer the life of the cutting tool.

[0205] <2nd Cutting Test>

[0206] A cutting tool (substrate shape: TNGA160404, blade processing T01225) for each sample was fabricated from each cBN sintered body of the above samples 4, 8, and 14 to 41. Using this, a cutting test (second cutting test) was performed under the following cutting conditions.

[0207] <Cutting Conditions>

[0208] Cutting speed: 300 m / min.

[0209] Feed rate: 0.2 mm / rev.

[0210] Cut: 0.1 mm

[0211] Coolant: DRY

[0212] Cutting method: Continuous cutting

[0213] Lathe: LB400 (Manufactured by Okuma Kabushiki Kaisha)

[0214] Workpiece: Sintered part (Quenched Sintered Alloy D40 manufactured by Sumitomo Electric Company, Hardness of quenched cutting section: HRB75).

[0215] The blade was observed at every 0.1 km of cutting distance to measure the amount of blade wear. The cutting distance at which the amount of blade wear exceeded 100 μm was measured. In addition, the above cutting distance was defined as the lifespan of the cutting tool. The results are shown in Tables 2 to 4. It can be evaluated that the longer the cutting distance, the longer the lifespan of the cutting tool.

[0216]

[0217]

[0218]

[0219]

[0220] [Consideration]

[0221] According to Table 1, it can be understood that the cutting tools obtained from each cBN sintered body of Samples 2 to 6 and Samples 9 to 13, which are examples, have a longer lifespan compared to the cutting tools obtained from the cBN sintered bodies of Sample 1 and Samples 7 to 8, which are comparative examples.

[0222] According to Tables 2 to 4, it can be understood that the cutting tools obtained from each of the cBN sintered bodies of Sample 4, Samples 14 to 22, and Samples 32 to 41, which are examples, have a longer lifespan compared to the cutting tools obtained from the cBN sintered bodies of Sample 8 and Samples 23 to 31, which are comparative examples.

[0223] Although the embodiments and examples of the present disclosure have been described above, it is also intended from the outset to appropriately combine the configurations of each of the above-described embodiments and examples.

[0224] The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the invention is defined by the claims, not by the embodiments and examples described above, and is intended to include all modifications within the meaning and scope equivalent to the claims.

Claims

Claim 1 A cubic boron nitride sintered body comprising 70 volume% or more and less than 100 volume% of cubic boron nitride particles and a binder, wherein the binder comprises, as constituent elements, at least one first metal element selected from the group consisting of titanium, zirconium, vanadium, niobium, hafnium, tantalum, chromium, rhenium, molybdenum, and tungsten, and cobalt and aluminum, and wherein the cubic boron nitride sintered body has a first interface region formed by an interface between the cubic boron nitride particles and the binder and a region sandwiched by a first imaginary line passing 10 nm away from the interface toward the binder, and wherein, when the element present at the highest concentration among the first metal elements in the first interface region is defined as the first element, the atomic concentration of the first element in the first interface region is higher than the atomic concentration of the first element in the binder outside the first interface region. Boron nitride sintered body. Claim 2 The cubic boron nitride sintered body according to claim 1, wherein the cubic boron nitride sintered body has a second interface region formed by the interface and a region sandwiched between the interface and a second virtual line passing 2 nm away from the interface toward the binder side, and the atomic concentration of the first element in the second interface region is 0.7 atomic% or more and 10 atomic% or less. Claim 3 A cubic boron nitride sintered body according to claim 1 or 2, wherein the cubic boron nitride sintered body comprises 85 volume% or more and 95 volume% or less of the cubic boron nitride particles. Claim 4 A cubic boron nitride sintered body according to claim 1 or 2, wherein the first metal element is at least one selected from the group consisting of zirconium, niobium, chromium, molybdenum, and tungsten. Claim 5 A cubic boron nitride sintered body according to claim 1 or 2, wherein the first metal element is zirconium. Claim 6 A cutting tool comprising a cubic boron nitride sintered body as described in claim 1 or 2.

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