Cubic boron nitride sinter and cutting tool including the same

Abstract

The cubic boron nitride sintered body comprises cubic boron nitride particles in an amount of 85% by volume or more and less than 100% by volume, and the balance is a binder. The binder comprises WC, Co and Al compounds, and the binder comprises W2Co 21 B6. When I A It is defined as the X-ray diffraction intensity of the (111) plane of cubic boron nitride particles. B is defined as the X-ray diffraction intensity of the (100) plane of WC, and I C Defined as W2Co 21 When the X-ray diffraction intensity of the (420) plane of B6 is C with I A Ratio I C / I A Greater than 0 and less than 0.10, and I C with I B Ratio I C / I B Greater than 0 and less than 0.40.

Description

[0001] This application is a divisional application of application No. 201980061110.X filed on September 18, 2019, with the title of “Cubic Boron Nitride Sintered Body and Cutting Tool Including the Cubic Boron Nitride Sintered Body”. TECHNICAL FIELD

[0002] The present disclosure relates to a cubic boron nitride sintered body and a cutting tool including the cubic boron nitride sintered body. This application claims priority to Japanese Patent Application No. 2018-174694 filed on September 19, 2018, the entire contents of which are incorporated herein by reference. BACKGROUND

[0003] A cubic boron nitride sintered body (hereinafter also referred to as “cBN sintered body”) is a high-hardness material used for cutting tools and the like. The cBN sintered body is generally made of cubic boron nitride particles (hereinafter also referred to as “cBN particles”) and a binder, and tends to have different properties depending on the content ratio of the cBN particles.

[0004] Therefore, in the field of cutting processing, different types of cBN sintered bodies are appropriately applied to cutting tools depending on the material of a workpiece, the required processing accuracy, and the like. For example, a cBN sintered body (hereinafter also referred to as “high-cBN sintered body”) in which the content ratio of cubic boron nitride (hereinafter also referred to as “cBN”) is high can be suitably used for cutting sintered alloys and the like.

[0005] However, sudden breakage tends to occur in high-cBN sintered bodies. It is considered that the sudden breakage is caused by the weak bonding strength between the cBN particles and the peeling of the cBN particles resulting therefrom. For example, WO 2005 / 066381 (Patent Literature 1) discloses a technique of suppressing the occurrence of sudden breakage in high-cBN sintered bodies by appropriately selecting a binder.

[0006] LIST OF CITATIONS

[0007] PATENT LITERATURE

[0008] Patent Literature 1: WO 2005 / 066381 SUMMARY

[0009] The cubic boron nitride sintered body according to one aspect of the present disclosure is a cubic boron nitride sintered body including cubic boron nitride particles in an amount of greater than or equal to 85 vol% and less than 100 vol%, and a binder in the balance, wherein the binder includes WC, Co, and an Al compound, the binder includes W2Co 21 B6, and when I A represents the X-ray diffraction intensity of the (111) plane of the cubic boron nitride particles, I Brepresents the X-ray diffraction intensity of the (100) plane of WC, and I C W2Co 21 When the X-ray diffraction intensity of the (420) plane of B6 is C with I A Ratio I C / I A Greater than 0 and less than 0.10, and I C with I B Ratio I C / I B Greater than 0 and less than 0.40.

[0010] A cubic boron nitride sintered body according to another aspect of the present disclosure is a cubic boron nitride sintered body comprising 85 volume % or more and less than 100 volume % of cubic boron nitride particles, with the balance being a binder, wherein the binder comprises WC, Co, and an Al compound, and the binder does not contain W2Co 21 B6.

[0011] A cutting tool according to one aspect of the present disclosure is a cutting tool including the above-described cubic boron nitride sintered body. DETAILED DESCRIPTION

[0012] [Problems to be solved by the present disclosure]

[0013] In recent years, with the rapid increase in the functionality of machine components, cutting workpieces used as such components has become increasingly difficult. Consequently, the problem of increased costs due to shortened cutting tool life has become significant. Therefore, further improvements in high-cBN sintered bodies are desired. In light of this, the present disclosure aims to provide a cubic boron nitride sintered body with a long lifespan and a cutting tool incorporating the same.

[0014] [Beneficial Effects of the Present Disclosure]

[0015] According to the cubic boron nitride sintered body described above, it can have a long life, and a cutting tool including the cubic boron nitride sintered body can also have a long life.

[0016] [Description of Embodiments of the Present Disclosure]

[0017] To achieve a cBN sintered body with a longer lifespan, the inventors initially decided to use a binder raw material powder containing WC (tungsten carbide), Co (cobalt), and Al (aluminum) as the binder raw material in high-cBN sintered bodies. This was because, through their research to date, the inventors had discovered that using this binder raw material powder resulted in an excellent cBN sintered body. However, the inventors believed that further improvements in this cBN sintered body and achieving a breakthrough required a different approach than conventional techniques, such as improving the binder ratio.

[0018] Therefore, to find the optimal method, the inventors first sintered a mixed powder of the aforementioned binder raw material powder and a cBN raw material powder, which serves as the raw material for cBN particles, to produce a cBN sintered body. In cBN sintered bodies, the cBN particles tend to be bound together in relatively large quantities. This is because during sintering, boron (boron) and nitrogen (nitrogen) dissolve and diffuse from the surface of the cBN raw material powder near Co. The dissolved boron and nitrogen then precipitate and reach adjacent cBN particles. In this specification, this function performed by the binder is also referred to as a "catalytic function."

[0019] Next, the present inventors conducted XRD (X-ray diffraction measurement) and ICP (inductively coupled plasma spectroscopy) to examine the composition of the compounds contained in the above cBN sintered body and found that W2Co 21 The presence of B6, which is an unexpected compound. 21 The mechanism of B6 is not yet clear, but the reasons are speculated as follows.

[0020] WC also exists in the region where the dissolution (diffusion) and reprecipitation of B and N occur as described above. This WC participates in the dissolution (diffusion) and reprecipitation described above. This causes C (carbon) to separate from WC, and Co and B to enter the portion from which C is separated. As a result, unintended reactants such as W2Co are generated. 21 B6.

[0021] Here, the inventors make the assumption that W2Co 21 B6 acts as the starting point for the shedding of cBN particles because, according to the above-mentioned presumed generation mechanism, it is speculated that W2Co is more brittle than other binders such as WC. 21 B6 is a brittle material with significantly inferior mechanical properties such as hardness and strength, and is 21 B6 adjacent cBN particles have disordered crystal structure. Based on the above assumptions, the inventors have repeatedly considered to find a way to suppress W2Co 21 The method of generating B6.

[0022] As a result, the present inventors found that by attaching an organic substance to a cBN raw material powder to produce an organic cBN powder, and using the organic cBN powder to produce a cBN sintered body, W2Co 21 B6 generation is suppressed. In addition, as supporting facts for the above hypothesis, in the cBN sintered body in which W2Co 21 B6 generation is suppressed, the cBN particle dropouts are significantly suppressed.

[0023] The present disclosure was completed based on the above findings. In the following, aspects of the present disclosure will be described in an enumerated form.

[0024] [1] A cubic boron nitride sintered body according to one aspect of the present disclosure is a cubic boron nitride sintered body containing greater than or equal to 85 vol% and less than 100 vol% of cubic boron nitride particles, and the balance being a binder, wherein the binder contains WC, Co, and an Al compound, the binder contains W2Co 21 B6, and when I A represents the X-ray diffraction intensity of the (111) plane of the cubic boron nitride particles, I B represents the X-ray diffraction intensity of the (100) plane of WC, and I C represents the X-ray diffraction intensity of the (420) plane of W2Co 21 B6, and when I C / I A / I C / I A is greater than 0 and less than 0.10, and I C / I B / I C / I B is greater than 0 and less than 0.40.

[0025] From the content (content ratio) of the cBN particles, the cBN sintered body is a "high cBN sintered body" in which cBN particle dropouts are likely to occur. In a conventional high cBN sintered body, the ratio I C / I A and the ratio I C / I B do not satisfy the above ranges. This is because, since a relatively large amount of W2Co 21 B6 is present in the conventional high cBN sintered body, the ratio I C / I A is greater than 0.10 and the ratio I C / I BIt should be noted that in the specification of the present application, “conventional high cBN sintered body” refers to a high cBN sintered body obtained by a conventional manufacturing method (i.e., a method without the attachment of organic matter) using a binder raw material powder containing WC, Co, and Al compounds as a raw material of the binder.

[0026] In contrast, unlike conventional high cBN sintered bodies, in the cBN sintered body according to the present disclosure, the C / I A Less than 0.10 and greater than I C / I B That is, compared with the conventional high cBN sintered body, the W2Co 21 The lower the content of B6, the longer the lifespan. This is likely because W2Co, which is the starting point for cBN particles to fall off in the cBN sintered body, 21 The B6 content is lower, so the frequency of shedding of cBN particles occurs less frequently.

[0027] [2] In cubic boron nitride sintered body, the ratio of I C / I A Greater than 0 and less than 0.05, and greater than I C / I B is greater than 0 and less than 0.20. In this case, the cubic boron nitride sintered body can have a longer life.

[0028] [3] A cubic boron nitride sintered body according to one aspect of the present disclosure is a cubic boron nitride sintered body comprising 85% by volume or more and less than 100% by volume of cubic boron nitride particles, with the remainder being a binder, wherein the binder comprises WC, Co, and an Al compound, and the binder does not contain W2Co 21 B6. In this case, the cubic boron nitride sintered body can have a longer life.

[0029] [4] A cutting tool according to one aspect of the present disclosure is a cutting tool including the above-mentioned cubic boron nitride sintered body. The cutting tool can have a long life.

[0030] [Details of the embodiment of the present disclosure]

[0031] An embodiment of the present disclosure (hereinafter referred to as the "present embodiment") will be described below, but the present embodiment is not limited thereto. It should be noted that in this specification, expressions in the form of "A to Z" refer to the lower and upper limits of a range (i.e., A or more and Z or less), and when A does not have any units and Z alone has units, the units of A and Z are the same.

[0032] <First Embodiment: cBN Sintered Body>

[0033] The cBN sintered body according to the present embodiment contains cBN particles of 85% by volume or more and less than 100% by volume, and the balance is a binder. That is, the cBN sintered body according to the present embodiment is a so-called high-cBN sintered body. It should be noted that the cBN sintered body can contain unavoidable impurities resulting from the raw material used, the manufacturing conditions, and the like. In this case, it is understood that the unavoidable impurities are contained in the binder.

[0034] The content ratio (volume %) of the cBN particles in the cBN sintered body is approximately equal to the content ratio (volume %) of the cBN raw material powder for the mixed powder described later, because the volume change amount caused by the attachment of organic matter or the like is very small with respect to the volume of the cBN powder itself. Therefore, by controlling the content ratio of the cBN raw material powder for the mixed powder, the content (content ratio) of the cBN particles in the cBN sintered body prepared can be made to be within a desired range.

[0035] In addition, the content ratio (volume %) of the cBN particles in the cBN sintered body can also be confirmed by performing organization observation, elemental analysis, or the like on the cBN sintered body using quantitative analysis by ICP, an energy dispersive X-ray analyzer (EDX) attached to a scanning electron microscope (SEM), or an EDX attached to a transmission electron microscope (TEM). In the present embodiment, the content ratio of the cBN particles in the cBN sintered body is determined by the method using the SEM described later, unless there is a particular reason.

[0036] For example, in the case of using the SEM, the content ratio (volume %) of the cBN particles can be determined as follows. First, the cBN sintered body is cut at an arbitrary position to produce a sample including a cross section of the cBN sintered body. To produce the cross section, a focused ion beam device, a cross section polisher device, or the like can be used. Then, the cross section is observed with the SEM at a magnification of 2000 times to obtain a reflected electron image. In the reflected electron image, the region where the cBN particles exist is shown as a black region, and the region where the binder exists is shown as a gray region or a white region.

[0037] Then, the reflected electron image is subjected to a binarization process using image analysis software (for example, "WinROOF" by Mitani Corporation), and the area ratio of each is calculated from the image subjected to the binarization process. By taking the calculated area ratio as the volume percentage, the content ratio (volume %) of the cBN particles can be determined. It should be noted that the volume percentage of the binder can also be determined at the same time.

[0038] <<cBN particles>>

[0039] cBN particles have high hardness, strength and toughness, and play the role of skeleton in cBN sintered body. 50 (Average particle size) is not particularly limited, and may be, for example, 0.1 μm to 10.0 μm. 50 The smaller the particle size, the higher the hardness of the cBN sintered body. There is also a trend that the smaller the particle size variation, the more uniform the properties of the cBN sintered body. For example, the D 50 It is preferably 0.5 μm to 4.0 μm.

[0040] The D of cBN particles was determined as follows 50 First, a sample comprising a cross-section of a cBN sintered body is prepared according to the above-described method for determining the cBN particle content, and a reflected electron image is obtained. Then, the equivalent circular diameter of each black area in the reflected electron image is calculated using image analysis software. Preferably, the equivalent circular diameters of at least 100 cBN particles are calculated by observing at least five fields of view.

[0041] Subsequently, the equivalent circle diameters are arranged in ascending order from the smallest value to the largest value to obtain the cumulative distribution. The particle size at which the cumulative area in the cumulative distribution reaches 50% is defined as D 50 It should be noted that the equivalent circle diameter refers to the diameter of a circle having the same area as the measured area of ​​the cBN particle.

[0042] <<Binding Agent>>

[0043] The binder's function is to sinter cBN particles, a difficult-to-sinter material, at industrial-level pressures and temperatures. Furthermore, because the binder's reactivity with iron is lower than that of cBN, the binder imparts to the cBN sintered body the effect of suppressing chemical and thermal wear during the cutting of high-hardness hardened steel. Furthermore, the inclusion of a binder in the cBN sintered body improves wear resistance during the efficient machining of high-hardness hardened steel.

[0044] In this embodiment, the binder contains WC, Co, and an Al compound. Here, "Al compound" refers to a compound containing Al as a constituent element. Examples of Al compounds include CoAl, Al2O3, AlN, AlB2, and composite compounds thereof. A binder containing WC, Co, and an Al compound is believed to be particularly effective in extending the life of the cBN sintered body according to this embodiment for the following reasons.

[0045] First, since Co and Al have catalytic functions, they can promote the growth of the neck of the cBN particles during the sintering step described later. Second, it is speculated that WC can effectively bring the thermal expansion coefficient of the binder close to that of the cBN particles.

[0046] In addition to the WC, Co, and Al compounds, the binder can contain W2Co 21 B6. However, in the cBN sinter, it is preferable that the W2Co 21 B6be contained in the binder in a small amount, and more preferably that the binder not contain the W2Co 21 B6. The present inventors have confirmed that when the W2Co 21 B6is contained in the binder in a small amount, the cBN sinter can have a long lifetime, and when the binder does not contain the W2Co 21 B6, the cBN sinter can have a longer lifetime.

[0047] In addition, in addition to the WC, Co, and Al compounds, the binder can contain Co3W3C and Co4W2C. As with the W2Co 21 B6, it is preferable that the amount in the binder be small, and more preferably that the binder not contain the Co3W3C and Co4W2C.

[0048] It should be noted that the description "the binder does not contain the W2Co 21 B6" means that when the X-ray diffraction intensity measurement described later is performed on the cBN sinter, an X-ray peak from the (420) plane of the W2Co 21 B6is not observed. Similarly, the description "the binder does not contain the Co3W3C" means that when the measurement described above is performed, an X-ray peak from the (333) plane of the Co3W3C is not observed. The description "the binder does not contain the Co4W2C" means that when the measurement described above is performed, an X-ray peak from the (221) plane of the Co4W2C is not observed.

[0049] The composition of the binder contained in the cBN sinter can be determined by combining XRD and ICP. Specifically, first, a test piece having a thickness of about 0.45 mm to 0.50 mm is cut out from the cBN sinter. The cut test piece is subjected to XRD analysis, whereby the compounds, metals, etc. are determined from the X-ray diffraction peaks. Then, the test piece is immersed in a mixture of nitric acid and hydrofluoric acid (mixed acid having a volume mixing ratio of concentrated nitric acid (60%): distilled water: concentrated hydrofluoric acid (47%) = 2:2:1) in a closed container to obtain an acid-treated liquid in which the binder is dissolved. The acid-treated liquid is subjected to ICP analysis, and quantitative analysis is performed on each of the metal elements. Then, the composition of the binder is determined by analyzing the results of the XRD and the results of the ICP analysis.

[0050] In addition to the WC, Co, and Al compounds, the binder in the present embodiment can contain other binders. Examples of elements suitable as the other binders include Ni, Fe, Cr, Mn, Ti, V, Zr, Nb, Mo, Hf, Ta, Re, etc.

[0051] <<X射线衍射强度比> >

[0052] In the cBN sintered body according to the present embodiment, the binder contains W2Co 21 In the case of B6, when I A represents the X-ray diffraction intensity of the (111) plane of cBN particles, I B represents the X-ray diffraction intensity of the (100) plane of WC, and I C W2Co 21 The X-ray diffraction intensity of the (420) plane of B6 is higher than that of C / I A Less than 0.10, and greater than I C / I B Less than 0.40.

[0053] In one aspect of this embodiment, C / I A Can be greater than 0 and less than 0.10, and is greater than I C / I B It can be greater than 0 and less than 0.40.

[0054] The ratio I is calculated as follows C / I A and ratio I C / I B First, a test piece with a thickness of about 0.45 mm to 0.50 mm was cut out from the cBN sintered body. XRD analysis was performed on five or more arbitrary points of the cut test piece to measure the X-ray diffraction intensity of the (111) surface of the cBN particles, the X-ray diffraction intensity of the (100) surface of the WC, and the X-ray diffraction intensity of the W2Co 21 The X-ray diffraction intensity of the (420) surface of B6 is calculated. Then, the average value of each X-ray diffraction intensity measured at each point is calculated, and each average value is defined as I A , I B and I C The measurement conditions are as follows. The above-mentioned ratios are calculated based on the three values ​​obtained.

[0055] X-ray diffraction apparatus: "SmartLab" (trade name) manufactured by Rigaku Corporation

[0056] Characteristic X-ray: Cu-Kα

[0057] Tube voltage: 45kV

[0058] Tube current: 200mA

[0059] X-ray diffraction method: θ-2θ method

[0060] X-ray irradiation range: Using a pinhole collimator, the X-rays were irradiated to an area with a diameter of about 0.3 mm.

[0061] <<Functions and Effects>>

[0062] According to the cBN sintered body of the present embodiment, a long life can be achieved. The reason is presumed to be as follows. Although W2Co 21 B6 becomes the starting point of the shedding of cBN particles, but the W2Co 21 The B6 content is lower, so the shedding of cBN particles is suppressed, thereby achieving a long life.

[0063] In the cBN sintered body according to the present embodiment, it is preferable that the C / I A Less than 0.05, and higher than I C / I B Less than 0.20, more preferably 1 C / I A Greater than 0 and less than 0.05, and greater than I C / I B Greater than 0 and less than 0.20. More preferably, the ratio C / I A and ratio I C / I B All are 0, that is, the binder does not contain W2Co 21 B6. In this case, the starting point of the falling off of the cBN particles is further reduced, and therefore, the cBN sintered body according to the present embodiment can have a longer life.

[0064] <Second embodiment: cutting tool>

[0065] The cutting tool according to this embodiment includes the cBN sintered body described above. In one aspect of this embodiment, the cutting tool includes the cBN sintered body as a substrate. In addition, the cutting tool according to this embodiment may have a film located on a portion or all of the surface of the cBN sintered body serving as the substrate.

[0066] There are no particular limitations on the shape and use of the cutting tool according to this embodiment. Examples of the cutting tool include drills, end mills, replaceable cutting inserts for drills, replaceable cutting inserts for end mills, replaceable cutting inserts for milling, replaceable cutting inserts for turning, metal saws, gear cutting tools, reamers, taps, crankpin milling inserts, and the like.

[0067] Furthermore, the cutting tool according to this embodiment is not limited to a cutting tool made entirely of a cBN sintered body, but also includes a cutting tool in which only a portion (particularly the cutting edge portion (cutting blade portion), etc.) is made of a cBN sintered body. For example, the cutting tool according to this embodiment also includes a cutting tool in which only the cutting edge portion of a base (support body) composed of cemented carbide or the like is composed of a cBN sintered body. In this case, the cutting edge portion is literally considered to be a cutting tool. In other words, even when the cBN sintered body occupies only a portion of the cutting tool, the cBN sintered body is also referred to as a cutting tool.

[0068] Since the cutting tool according to the present embodiment includes the above-described cBN sintered body, the cutting tool can have a long life.

[0069] <Third Embodiment: Method for Manufacturing cBN Sintered Body>

[0070] A method for producing a cBN sintered body according to the present embodiment will be described. The method for producing a cBN sintered body according to the present embodiment is a method for producing the cBN sintered body according to the first embodiment.

[0071] Specifically, the method for producing a cBN sintered body according to this embodiment includes at least: a step of producing organic cBN powder formed by attaching an organic substance to a cBN raw material powder (producing step); a step of mixing the organic cBN powder with a binder raw material powder containing WC, Co, and Al to produce a mixed powder composed of 85% by volume or more and less than 100% by volume of the organic cBN powder and the remainder of the binder raw material powder (producing step); and a step of sintering the mixed powder to obtain a cBN sintered body (sintering step). Each step will be described in detail below.

[0072] <<Production steps>>

[0073] This step is a step of producing organic cBN powder formed by attaching an organic substance to cBN raw material powder.

[0074] The cBN raw material powder is a raw material powder of cBN particles to be included in a cBN sintered body. Examples of a method for attaching an organic substance to the cBN raw material powder include a method using supercritical water, a method performing plasma treatment, and the like.

[0075] (Method using supercritical water)

[0076] The following describes a method using supercritical water. This method involves, for example, introducing cBN raw material powder and an organic substance into supercritical water. This process can produce organic cBN powder. It should be noted that in this specification, supercritical water refers to water in a supercritical or subcritical state.

[0077] Examples of methods for introducing cBN raw material powder and organic matter into supercritical water include sequentially introducing the cBN raw material powder and the organic matter, sequentially introducing the organic matter and the cBN raw material powder into supercritical water, and simultaneously introducing the cBN raw material powder and the organic matter into supercritical water. These methods clean the surface of the cBN raw material powder through contact with the supercritical water. Furthermore, through contact between the organic matter and the cBN raw material powder having a cleaned surface (hereinafter also referred to as the "cleaned surface"), the organic matter adheres to the cleaned surface of the cBN raw material powder.

[0078] (By performing plasma treatment)

[0079] A method for plasma treatment will now be described. This method involves attaching organic matter to the cBN raw material powder through plasma treatment. A specific example involves exposing the cBN raw material powder to a first carbon-containing gas atmosphere in a plasma generator, followed by exposing the cBN raw material powder to a second ammonia-containing gas atmosphere. The first gas can be CF₄, CH₄, C₂H₂, or the like. The second gas can be a mixed gas of N₂ and H₂, NH₃, or the like.

[0080] These methods expose the cBN raw material powder to a first gas atmosphere, etching the surface of the cBN raw material powder to form a clean surface, and then attaching carbon (first gas) to the clean surface. By continuously exposing the cBN raw material powder with carbon attached to it to a second gas atmosphere, the carbon is capped with ammonia. Consequently, organic matter containing carbon and nitrogen is attached to the clean surface.

[0081] As described above, organic cBN powder can be produced by either a method using supercritical water or a method using plasma treatment. In this step, the method using supercritical water is preferred because it easily homogenizes the organic matter adhering to the cBN raw material powder, thereby easily homogenizing the organic cBN powder.

[0082] In this step, the average particle size of the cBN raw material powder is not particularly limited. From the perspective of forming a cBN sintered body having high strength, high wear resistance, and high fracture resistance, the average particle size of the cBN raw material powder is preferably 0.1 μm to 10 μm, more preferably 0.5 μm to 5.0 μm.

[0083] When this step is performed using supercritical water, examples of preferably used organic substances include amines and hydrocarbon compounds having 5 or more carbon atoms. Among these, hexylamine, capronitrile, paraffin wax, and hexane are more preferred, with hexylamine being even more preferred. The present inventors have confirmed that the use of these organic substances significantly reduces the shedding of cBN particles from the cBN sintered body. When this step is performed using plasma treatment, examples of organic substances to be attached include amines, hydrogen fluoride, and the like.

[0084] The preferred amount of organic matter attached to the cBN raw material powder varies depending on the particle size of the cBN raw material powder. For example, when using hexylamine as the organic matter, it is preferable to attach 50 to 2000 ppm of hexylamine to a cBN raw material powder with an average particle size of 1 to 10 μm, and preferably to attach 100 to 5000 ppm of hexylamine to a cBN raw material powder with an average particle size of 0.1 to 1 μm. In this case, the desired cBN sintered body tends to be produced more efficiently. For example, the amount of organic matter attached to the organic cBN powder can be measured by gas chromatography-mass spectrometry.

[0085] In this embodiment, it is believed that only enough carbon to replenish or suppress the shedding of C (carbon) from WC is present in the organic cBN powder after undergoing the second step of sintering, described later. Furthermore, the amount of organic matter adhering to the cBN raw material powder tends to decrease during subsequent steps (e.g., the purification and preparation steps described later). Therefore, even if the amount of organic matter adhering to the cBN raw material powder is not as high as described above (e.g., an excessive amount), it is believed that a sufficient amount of carbon can be retained in the organic cBN powder after undergoing the second step through appropriate preparation during various subsequent treatments.

[0086] <<Purification Step>>

[0087] When the organic cBN powder obtained through the above-described preparation steps is used in the following manufacturing steps, it is preferable to remove impurities from the organic cBN powder. Examples of impurities include unreacted organic matter. Removing unreacted organic matter can suppress undesirable reactions during the preparation and / or sintering steps.

[0088] For example, when supercritical water is used, organic cBN powder is obtained in the form of a slurry. In this case, the unreacted organic matter can be separated from the organic cBN powder by centrifuging the slurry.

[0089] Alternatively, the organic cBN raw material powder extracted from supercritical water, or the organic cBN raw material powder extracted from supercritical water and subsequently subjected to the above-described centrifugal separation, may be subjected to a heat treatment (e.g., at 850° C. or higher in a vacuum). This can remove impurities such as moisture adsorbed on the surface of the organic cBN powder.

[0090] The inventors initially worried that any organic matter adhering to the cBN raw material powder might volatilize and / or disappear when the organic cBN powder is heat-treated. However, surprisingly, observation of the organic cBN powder using Auger electron spectroscopy confirmed that, despite the decomposition of the organic matter during heat treatment, carbon remains uniformly on the surface of the organic cBN powder. This carbon is believed to originate from the organic matter.

[0091] Specifically, it has been confirmed that heat treatment of organic cBN powder removes impurities from the surface of the organic cBN powder, and also yields surface-modified organic cBN powder with carbon uniformly attached to the surface. Although the mechanism is unclear, the present inventors believe that the organic matter strongly bonds to the clean surface due to the high activity of the clean surface formed by treatment with supercritical water, plasma, or the like, and that this strong bonding is related to the surface modification of the organic cBN powder.

[0092] <<Preparation Steps>>

[0093] This step involves mixing organic cBN powder with a binder raw material powder containing WC, Co, and Al to produce a mixed powder consisting of 85% to 100% by volume of organic cBN powder and the remainder of the binder raw material powder. The organic cBN powder is obtained through the above-described production steps, and the binder raw material powder is the raw material for the binder to be included in the cBN sintered body.

[0094] The binder raw material powder can be prepared as described below. First, WC powder, Co powder and Al powder are prepared. Then, these powders are mixed to have a predetermined ratio and heat treated under vacuum (for example, 1200°C) to produce an intermetallic compound. The intermetallic compound is crushed by a wet ball mill, a wet bead mill, etc. to prepare a binder raw material powder containing WC, Co and Al. It should be noted that although there is no particular limitation on the method of mixing these powders, from the viewpoint of effectively and uniformly mixing these powders, ball mill mixing, bead mill mixing, planetary mill mixing, jet mill mixing, etc. are preferred. Each mixing method can be wet mixing or dry mixing.

[0095] The organic cBN powder and the prepared binder raw material powder are preferably mixed using a wet ball mill using ethanol, acetone, or the like as a solvent. After mixing, the solvent is removed by natural drying. Impurities such as moisture adsorbed on the surface are preferably subsequently removed by heat treatment (e.g., at 850°C or above in a vacuum). This allows the organic matter to decompose, as described above, and the carbon derived from the organic matter to remain uniformly on the surface of the organic cBN powder, resulting in a surface-modified organic cBN powder. In this way, a mixed powder is prepared.

[0096] In addition to WC, Co, and Al, the binder raw material powder may contain other elements. Examples of elements suitable as other elements include Ni, Fe, Cr, Mn, Ti, V, Zr, Nb, Mo, Hf, Ta, Re, etc.

[0097] <<Sintering Step>>

[0098] This step is a step of sintering the mixed powder to obtain a cBN sintered body. In this step, the mixed powder is exposed to high temperature and high pressure conditions for sintering, thereby producing a cBN sintered body.

[0099] Specifically, as a first step, the mixed powder is placed in a container and vacuum-sealed, preferably at a temperature of 850°C or higher. This temperature is higher than the melting point of the sealing material and is sufficient to decompose organic matter adhering to the organic cBN powder and allow carbon derived from the organic matter to remain uniformly on the surface of the organic cBN powder.

[0100] Then, as a second step, the vacuum-sealed mixed powder is sintered using an ultrahigh-temperature, high-pressure apparatus. While there are no particular restrictions on sintering conditions, 5.5 to 8 GPa, 1500°C or higher and less than 2000°C are preferred. From the perspective of a balance between cost and sintering performance, 6 to 7 GPa and 1600°C to 1900°C are particularly preferred.

[0101] When heat treatment (heat treatment in the purification step and / or heat treatment in the preparation step) is performed before this step, the surface-modified organic cBN powder, in which carbon remains uniformly on the surface of the organic cBN powder, is subjected to the first step. When heat treatment is not performed before this step, the surface-modified organic cBN powder is produced by the first step (i.e., vacuum sealing). Consequently, carbon is uniformly present on the surface of the organic cBN powder that undergoes the second step. The mixed powder containing this organic cBN powder is subjected to the second step to produce a cBN sintered body.

[0102] <<Functions and Effects>>

[0103] According to the method for producing a cBN sintered body of the present embodiment described above, a cBN sintered body having a long life can be produced. The reason for this is presumably as follows.

[0104] When the organic cBN powder is sintered, the carbon derived from organic matter uniformly adheres to the surface of the organic cBN powder to supplement the shedding of C (carbon) from WC, or the presence of carbon derived from organic matter suppresses the shedding of C from WC. Therefore, the incorporation of Co and B into WC is also suppressed. As a result, the W2Co 21 Generation of B6.

[0105] That is, the W2Co in the cBN sintered body is 21 B6 has a lower content or does not contain W2Co 21 B6, which considers W2Co 21 B6 is the starting point for cBN particles to fall off. Therefore, the cBN sintered body can have a long life.

[0106] The above description includes the features pointed out below.

[0107] (Note 1)

[0108] A cubic boron nitride sintered body comprising 85% by volume or more and less than 100% by volume of cBN particles, with the remainder being a binder, wherein

[0109] The binder contains WC, Co and Al compounds,

[0110] The binder may contain W2Co 21 B6, and

[0111] The binder contains W2Co 21 In the case of B6, when I A represents the X-ray diffraction intensity of the (111) plane of cubic boron nitride, I B represents the X-ray diffraction intensity of the (100) plane of WC, and I C W2Co 21 When the X-ray diffraction intensity of the (420) plane of B6 is

[0112] I C with I A Ratio I C / I A Less than 0.10, and

[0113] I C with I B Ratio I C / I B Less than 0.40.

[0114] (Note 2)

[0115] The cubic boron nitride sintered body according to Supplementary Note 1, wherein

[0116] Than I C / I A Less than 0.05, and

[0117] Than I C / I B Less than 0.20.

[0118] (Note 3)

[0119] The cubic boron nitride sintered body according to Supplementary Note 1 or 2, wherein the binder does not contain W2Co 21 B6.

[0120] (Note 4)

[0121] A cutting tool comprising the cubic boron nitride sintered body according to any one of Supplementary Notes 1 to 3.

[0122] [Example]

[0123] Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto.

[0124] <Experimental Example 1>

[0125] First, organic cBN powder was prepared. Specifically, supercritical water was prepared using a supercritical water synthesis apparatus ("MOMI Super mini" manufactured by ITEC Co., Ltd.) under the following conditions.

[0126] Pressure: 40MPa

[0127] Temperature: 388°C

[0128] Flow rate: 2ml / min

[0129] Then, a stock solution of hexylamine was continuously introduced into the apparatus to a concentration of 6.7% by weight in the supercritical water. Furthermore, a cBN raw material powder with an average particle size of 2.5 μm was continuously introduced into the apparatus to a concentration of 8% by weight in the supercritical water. Thus, the cBN raw material powder and hexylamine, an organic substance, were introduced into the supercritical water.

[0130] After 120 minutes of supercritical water treatment, the temperature and pressure inside the apparatus were returned to normal, the supercritical water treatment was terminated, and the resulting slurry was collected. The slurry was centrifuged (10,000 rpm for 10 minutes) to separate the excess hexylamine that had not adhered to the cBN raw material powder. The concentrated slurry was dried (-90°C for 10 hours) to collect approximately 15 g of supercritical water-treated powder.

[0131] In this manner, organic cBN powder was produced. When the produced organic cBN powder was subjected to gas chromatography-mass spectrometry analysis, the presence of 321 ppm of hexylamine (attached to the cBN powder) relative to the cBN powder was confirmed.

[0132] Next, a binder raw material powder was prepared to serve as the raw material for the binder. Specifically, WC powder, Co powder, and Al powder were prepared and mixed in a weight ratio of WC:Co:Al = 50:43:7. It should be noted that the average particle size of each powder was 2 μm. The mixed powder was heat-treated (at 1200°C for 30 minutes under vacuum) to homogenize it, and then pulverized using a cemented carbide ball mill. This yielded a binder raw material powder with an average particle size of 1 μm.

[0133] Organic cBN powder and the obtained binder raw material powder were mixed in a ratio of 85:15 (volume %) and uniformly mixed using ethanol using wet ball milling. The mixed powder was then heat-treated at 900°C under vacuum. Auger electron spectroscopy analysis of the heat-treated organic cBN powder confirmed the presence of carbon on its surface. In this manner, a mixed powder was produced.

[0134] The resulting mixed powder was then sintered to produce a cBN sintered body. Specifically, the mixed powder was placed in a Ta container in contact with a WC-6% Co cemented carbide disk and Co foil, and then vacuum-sealed. Using a belt-type ultrahigh-pressure, high-temperature generator, the mixture was sintered at 7.0 GPa and 1700°C for 15 minutes. This produced a cBN sintered body.

[0135] <Experimental Example 2>

[0136] A cBN sintered body was produced using the same method as in Experimental Example 1, except that the concentration of hexylamine introduced was 8.2% by weight, and the organic cBN powder and binder raw material powder were mixed in a ratio of 95% (organic cBN powder:binder raw material powder) to 5% (volume %). Gas chromatography-mass spectrometry analysis of the organic cBN powder revealed the presence of 439 ppm of hexylamine relative to the cBN.

[0137] <Experimental Example 3>

[0138] A cBN sintered body was produced using the same method as in Experimental Example 1, except that the concentration of hexylamine introduced was 9.5% by weight, and the organic cBN powder and binder raw material powder were mixed in a ratio of 92:8 (volume %). Gas chromatography-mass spectrometry analysis of the organic cBN powder revealed the presence of 557 ppm of hexylamine relative to the cBN.

[0139] <Experimental Example 4>

[0140] A cBN sintered body was produced using the same method as in Experimental Example 1, except that the concentration of hexylamine introduced was 20.0% by weight, and the organic cBN powder and binder raw material powder were mixed in a ratio of 92:8 (volume %). Gas chromatography-mass spectrometry analysis of the organic cBN powder revealed the presence of 1278 ppm of hexylamine relative to the cBN.

[0141] <Experimental Example 5>

[0142] Organic cBN powder was produced using plasma treatment instead of supercritical water. Specifically, a plasma modification device (a low-pressure plasma device, FEMTO, manufactured by Dienner) was used to etch the surface of the cBN raw material powder under a CF4 atmosphere. The atmosphere inside the device was then switched to an NH3 atmosphere to treat the etched cBN raw material powder. A cBN sintered body was produced using the same method as in Experimental Example 1.

[0143] <Experimental Example 6>

[0144] A cBN sintered body was manufactured by the same method as in Experimental Example 2, except that the above-mentioned plasma treatment was performed instead of the method using supercritical water.

[0145] <Experimental Example 7>

[0146] A cBN sintered body was manufactured by the same method as in Experimental Example 3, except that the above-mentioned plasma treatment was performed instead of the method using supercritical water.

[0147] <Experimental Example 8>

[0148] A cBN sintered body was manufactured by the same method as in Experimental Example 4, except that the above-mentioned plasma treatment was performed instead of the method using supercritical water.

[0149] <Experimental Example 11>

[0150] A cBN sintered body was produced by the same method as in Experimental Example 3, except that the cBN raw material powder was not subjected to the supercritical water treatment.

[0151] <Experimental Example 12>

[0152] A cBN sintered body was produced by the same method as in Experimental Example 3, except that the cBN raw material powder was not subjected to supercritical water treatment and the sintering temperature was changed to 1800°C.

[0153] <Experimental Example 13>

[0154] A cBN sintered body was produced by the same method as in Experimental Example 1, except that the organic cBN powder and the binder raw material powder were mixed at a ratio of organic cBN powder:binder raw material powder = 70:30 (volume %).

[0155] <Experimental Example 14>

[0156] A cBN sintered body was produced by the same method as in Experimental Example 1, except that the treatment with supercritical water was not performed, and only the cBN raw material powder was used without mixing the binder raw material powder.

[0157] In this manner, cBN sintered bodies were produced in Experimental Examples 1 to 8 and Experimental Examples 11 to 14. Here, Experimental Examples 1 to 8 correspond to Examples, and Experimental Examples 11 to 14 correspond to Comparative Examples.

[0158] <Characteristics Evaluation>

[0159] 《X-ray diffraction intensity ratio》

[0160] The ratio I in each cBN sintered body was calculated by the above-mentioned method using the above-mentioned X-ray diffraction apparatus. C / I A and ratio I C / I B Table 1 shows the results. It should be noted that I A , I B and I C Each is an average value of measurement results at five arbitrary points in each test piece.

[0161] <<Composition of the binder>>

[0162] From each produced cBN sintered body, test pieces with a length of 6 mm, a width of 3 mm, and a thickness of 0.45 mm to 0.50 mm were cut and subjected to XRD analysis. Each test piece was then immersed in a sealed container at 140°C in a mixture of nitric and hydrofluoric acid (a mixture with a volume ratio of concentrated nitric acid (60%): distilled water: concentrated hydrofluoric acid (47%) = 2:2:1) for 48 hours to obtain an acid-treated solution containing each binder. The acid-treated solution was subjected to ICP analysis. The composition of each binder was then determined based on the results of the XRD and ICP analyses. Table 1 shows the results.

[0163] <<Hardness>>

[0164] Each cBN sintered body was measured using a Vickers hardness tester at a load of 50 kgf, and the Vickers hardness (Hv) was calculated from the length of the diagonal line of the indentation. Table 1 shows the results.

[0165] <<Cutting Test>>

[0166] Cutting tools (base material shape: DNGA150408, cutting edge treatment: T01225) were made using each of the produced cBN sintered bodies. Cutting tests were conducted using each cutting tool under the following cutting conditions:

[0167] Cutting speed: 170m / min

[0168] Feed speed: 0.07mm / rev

[0169] Cutting depth: 0.1mm

[0170] Coolant: Dry

[0171] Cutting method: interrupted cutting

[0172] Lathe: LB400 (manufactured by Okuma)

[0173] Workpiece: sintered component (hardened sintered alloy D-40, manufactured by Sumitomo Electric Industries, Ltd., hardness of hardened cutting portion: 40 HRC).

[0174] Each cutting edge was observed every 0.3 km of cutting distance to measure the amount of cutting edge fallout. Cutting edge fallout is defined as the distance the cutting edge has retreated from its pre-cutting ridgeline due to wear. If the cutting edge is damaged, the amount of cutting edge fallout is defined as the size of the damage. The cutting distance at which the cutting edge fallout exceeds 0.05 mm was measured. It should be noted that this cutting distance was defined as an indicator of the life of each cutting tool. Table 1 shows the results.

[0175] [Table 1]

[0176]

[0177] The volume percentage of cBN particles in each cBN sintered body is also shown in Table 1. Columns indicated by "-" in Table 1 indicate that each value is less than or equal to the detection limit.

[0178] With reference to Table 1, the presence of WC, Co, and Al compounds was confirmed in Experimental Examples 1 to 8 and Experimental Examples 11 to 13. It should be noted that since no clear peak of the Al compound was detected in XRD, it is presumed that the Al compound is a composite compound made of multiple Al compounds. In addition, the presence of W2Co was confirmed in Experimental Examples other than Experimental Example 3 and Experimental Example 4 (i.e., Experimental Examples 1, 2, 5 to 8 and Experimental Examples 11 to 13). 21 B6 and Co3W3C.

[0179] Although W2Co was not confirmed in Experimental Examples 3 and 4, 21 The reason for the formation of B6 and Co3W3C is not clear, but it is considered that an appropriate amount of carbon adheres to the organic cBN powder, thereby appropriately suppressing the generation of these compounds.

[0180] In addition, as shown in Experimental Examples 1 to 8, when the ratio C / I A Less than 0.10 and higher than I C / I B When the value is less than 0.40, high hardness and long cutting distance are achieved. The length of the cutting distance means the extension of the life of the cBN sintered body. In addition, in Experimental Examples 2 to 4, 7 and 8, the C / I A Less than 0.05 and less than I C / I B Less than 0.20, and in this case, a particularly long life is achieved. In particular, in Experimental Example 3, each ratio is 0, that is, the cBN sintered body does not contain W2Co 21 In this case, B6 has been confirmed to have a particularly long lifespan.

[0181] In contrast, Experimental Examples 11 to 14 showed significantly lower results in terms of hardness and life compared to Experimental Examples 1 to 8. The reasons for these results are considered to be as follows. In Experimental Examples 11 and 12, since organic matter was not attached, a large amount of W2Co was generated. 21 B6, as a result, cBN particles frequently fell off and had low hardness. In Experimental Example 13, due to the low proportion of cBN particles (i.e., the cBN sintered body was not a high-cBN sintered body), its hardness and life were insufficient. In Experimental Example 14, due to the lack of a binder, the cBN particles were not sintered sufficiently.

[0182] It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in all aspects. The scope of the present invention is defined by the scope of the claims, rather than by the above embodiments, and is intended to include all changes within the meaning and scope equivalent to the scope of the claims.

Claims

1. A cubic boron nitride sintered body comprising 85% by volume or more and less than 100% by volume of cubic boron nitride particles, the remainder being a binder, wherein The binder comprises an Al compound, WC and Co, The binder comprises W2Co 21 B6, and When I A represents the X-ray diffraction intensity of the (111) plane of the cubic boron nitride particles, I B represents the X-ray diffraction intensity of the (100) plane of the WC, and I C Indicates the W2Co 21 When the X-ray diffraction intensity of the (420) plane of B6 is I C With the I A Ratio I C / I A is greater than 0 and less than 0.10, and I C With the I B Ratio I C / I B Greater than 0 and less than 0.

40.

2. The cubic boron nitride sintered body according to claim 1, wherein The D of the cubic boron nitride particles 50 It is not less than 0.5 μm and not more than 4.0 μm.

3. The cubic boron nitride sintered body according to claim 1 or 2, wherein The Al compound is at least any one of CoAl, Al2O3, AlN, AlB2, and composite compounds thereof.

4. The cubic boron nitride sintered body according to claim 1 or 2, wherein The binder includes at least either Co3W3C or Co4W2C.

5. A cubic boron nitride sintered body comprising 85% by volume or more and less than 100% by volume of cubic boron nitride particles, with the remainder being a binder, wherein The binder comprises an Al compound, WC and Co, and The binder does not contain W2Co 21 B6, The D of the cubic boron nitride particles 50 It is not less than 0.5 μm and not more than 4.0 μm.

6. The cubic boron nitride sintered body according to claim 5, wherein The Al compound is at least any one of CoAl, Al2O3, AlN, AlB2, and composite compounds thereof.

7. The cubic boron nitride sintered body according to claim 5 or 6, wherein The binder does not contain any of Co3W3C and Co4W2C. 8 . A cutting tool comprising the cubic boron nitride sintered body according to claim 1 .

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