Cubic boron nitride sintered body

Abstract

To provide a cubic boron nitride sintered body which has excellent abrasion resistance and defect resistance, and thereby can extend a tool life.SOLUTION: A cubic boron nitride sintered body contains cubic boron nitride and a bonding phase, wherein a content ratio of the cubic boron nitride is 30.0 vol.% or more and 70.0 vol.% or less with respect to the total amount of the sinter body, a content ratio of the bonding phase is 30.0 vol.% or more and 70.0 vol.% or less with respect to the total amount of the sinterd body, the bonding phase contains an Al compound and a Zr compound, the Al compound contains α type Al2O3 and the Zr compound contains ZrB2 and ZrO, when X-ray diffraction peak intensity of (110) plane of the α type Al2O3 is represented by Ial, X-ray diffraction peak intensity of (101) plane of the ZrB2 is represented by Izb, and X-ray diffraction peak intensity of (111) plane of the ZrO is represented by Izo, Izb / Izo is more than 0.30 and 5.00 or less, and Izb / Izo is 0.10 or more and 1.00 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a cubic boron nitride sintered body. [Background technology]

[0002] Cubic boron nitride (hereinafter referred to as "cBN") has a hardness second only to diamond and excellent thermal conductivity. Cubic boron nitride also has the characteristic of having a lower affinity with iron than diamond. Therefore, cubic boron nitride sintered bodies consisting of cubic boron nitride and a binder phase of metal or ceramic are used in cutting tools, wear-resistant tools, and the like.

[0003] In recent years, cutting conditions have become more stringent than ever before in order to increase machining efficiency, and there is a demand for longer tool life. In particular, in machining processes in which the cutting edge temperature of the tool becomes high during cutting, such as high-speed machining of gray cast iron, technologies have been proposed that can further improve wear resistance and fully meet these demands.

[0004] A conventional technique for producing cubic boron nitride sintered bodies used in cutting tools and the like is a sintered body made of cubic boron nitride, an oxide of Al, an oxide of Zr, and a boride of Zr. Specifically, for example, Patent Document 1 describes a sintered body made of cubic boron nitride: about 30 to about 70 volume % cubic boron nitride, a binder phase consisting of at least one selected from the group consisting of oxides, carbides, nitrides, and borides of Ti, Al, Zr, Y, Ce, Mg, and Ca, and their mutual solid solutions, and unavoidable impurities: the balance, and containing α-type Al2O3, ZrB2, ZrO2, and ZrO, and the X-ray diffraction intensity of the (110) plane of α-type Al2O3 is The present invention discloses a cubic boron nitride sintered body characterized in that, when the X-ray diffraction intensity of the (101) plane of ZrB2 is expressed as Ia, Izb is expressed as Izb, and the X-ray diffraction intensity of the (111) plane of ZrO is expressed as Izo, the ratio of Izb to Ia (Izb / Ia) satisfies 0.13≦(Izb / Ia)≦0.30, and the ratio of Izo to Ia (Izo / Ia) satisfies 0.05≦(Izo / Ia)≦0.20. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] International Publication No. 2011 / 059020 Summary of the Invention [Problem to be solved by the invention]

[0006] In recent years, there has been a demand for cubic boron nitride sintered bodies to be used in tools for machining "cast iron" that have even greater resistance to wear and chipping, and that can have a longer tool life.

[0007] An object of the present invention is to provide a cubic boron nitride sintered body that has excellent wear resistance and chipping resistance, thereby enabling an extension of tool life. [Means for solving the problem]

[0008] The present inventors have conducted extensive research into extending tool life and have discovered that the following features of the present invention, which are differences from Patent Document 1, affect the improved performance of the present invention. That is, the inventors discovered that when a cubic boron nitride sintered body has a specific structure, it is possible to improve its wear resistance and fracture resistance, and as a result, tool life can be extended, which led to the completion of the present invention.

[0009] The gist of the present invention is as follows. [1] A cubic boron nitride sintered body comprising cubic boron nitride and a binder phase, the content of the cubic boron nitride is 30.0% by volume or more and 70.0% by volume or less with respect to the total amount of the sintered body, the content of the binder phase is 30.0% by volume or more and 70.0% by volume or less with respect to the total amount of the sintered body, the binder phase includes an Al compound and a Zr compound; The Al compound contains α-type Al2O3, The Zr compounds include ZrB2 and ZrO, The X-ray diffraction peak intensity of the (110) plane of the α-type Al2O3 is I al The X-ray diffraction peak intensity of the (101) plane of the ZrB2 is I zb The X-ray diffraction peak intensity of the (111) plane of the ZrO is I zo When I zb / I al is greater than 0.30 and less than or equal to 5.00, I zb / I zo A cubic boron nitride sintered body, wherein the ratio is 0.10 or more and 1.00 or less. [2] The cubic boron nitride sintered body according to [1], wherein the content of the Zr compound is 10.0 volume % or more and 25.0 volume % or less with respect to the total amount of the sintered body. [3] The Zr compound further contains ZrO2, The ZrO2 includes cubic ZrO2 and / or tetragonal ZrO2, The X-ray diffraction peak intensity I of the (111) plane of the cubic ZrO2 zc and the X-ray diffraction peak intensity of (101) of the tetragonal ZrO2 I zt The sum of (I zc +I zt ) and I zo / (I zc +I zt ) is 0.50 or more and 3.00 or less. [4] The cubic boron nitride sintered body according to any one of [1] to [3], wherein the average particle size of the Zr compound is 50 nm or more and 300 nm or less. [5] The cubic boron nitride sintered body according to any one of [1] to [4], wherein the cubic boron nitride has an average particle size of 0.5 μm or more and 3.0 μm or less. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a cubic boron nitride sintered body that has excellent wear resistance and chipping resistance, thereby enabling an extension of tool life. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail, but the present invention is not limited to the following embodiment. The present invention can be modified in various ways without departing from the gist of the present invention.

[0012] [Cubic boron nitride sintered body] The cubic boron nitride sintered body of this embodiment is a cubic boron nitride sintered body containing cubic boron nitride (hereinafter also referred to as "cBN") and a binder phase, the content of cubic boron nitride is 30.0 volume % or more and 70.0 volume % or less with respect to the total amount of the sintered body, the content of the binder phase is 30.0 volume % or more and 70.0 volume % or less with respect to the total amount of the sintered body, the binder phase contains a compound having an Al element (hereinafter referred to as "Al compound") and a compound having a Zr element (hereinafter referred to as "Zr compound"), the Al compound contains α-type Al2O3 (hereinafter also simply referred to as "Al2O3"), the Zr compound contains ZrB2 and ZrO, and the X-ray diffraction peak intensity of the (110) plane of α-type Al2O3 is I al , the X-ray diffraction peak intensity of the (101) plane of ZrB2 is I zb , the X-ray diffraction peak intensity of the (111) plane of ZrO is I zo When I zb / I al is greater than 0.30 and less than or equal to 5.00, and I zb / I zo is between 0.10 and 1.00.

[0013] By providing the cubic boron nitride sintered body of this embodiment with the above-described configuration, it is possible to improve the wear resistance and chipping resistance, and as a result, the tool life can be extended. The factors that enable the cubic boron nitride sintered body of this embodiment to improve the wear resistance and fracture resistance of tools and extend their tool life are not fully understood, but the present inventors believe that the factors are as follows, although the factors are not limited to these. The cubic boron nitride sintered body of this embodiment has a cubic boron nitride content of 30.0% by volume or more, which improves the strength of the sintered body and improves chipping resistance. On the other hand, the cubic boron nitride sintered body of this embodiment has a cubic boron nitride content of 70.0% by volume or less, which relatively increases the binder phase content, thereby improving heat resistance and suppressing reactive wear. Furthermore, the cubic boron nitride sintered body of this embodiment has a binder phase content of 30.0% by volume or more, which improves heat resistance and suppresses reactive wear. On the other hand, the cubic boron nitride sintered body has a binder phase content of 70.0% by volume or less, which results in a relatively high cBN content, which improves the strength of the sintered body and improves its fracture resistance. The cubic boron nitride sintered body of this embodiment is I zb / I al When the value of the cubic boron nitride sintered body is greater than 0.30, reactive wear is suppressed, and the body has excellent wear resistance and chipping resistance. zb / I al When the value of I is 5.00 or less, the hardness of the binder phase at high temperatures is improved, and the wear resistance is excellent. zb / I zo When the value of I is 0.10 or more, reactive wear is suppressed, and the cubic boron nitride sintered body of this embodiment has excellent wear resistance and chipping resistance. zb / I zo When the ratio is 1.00 or less, the bond strength between particles is increased, and chipping resistance and fracture resistance are improved. As a result of the combined effects described above, the cubic boron nitride sintered body of this embodiment can improve wear resistance and chipping resistance, and extend the tool life.

[0014] The cubic boron nitride sintered body of this embodiment contains cBN and a binder phase. The cBN content is 30.0 volume % or more and 70.0 volume % or less with respect to the total amount of the sintered body. The binder phase content is 30.0 volume % or less and 70.0 volume % or less with respect to the total amount of the sintered body. In the cubic boron nitride sintered body of this embodiment, the total content of cBN and the binder phase is 100 volume %.

[0015] [Cubic boron nitride (cBN)] In the cubic boron nitride sintered body of this embodiment, the cubic boron nitride content is 30.0 volume % or more, which improves the strength of the sintered body and improves chipping resistance. On the other hand, in the cubic boron nitride sintered body of this embodiment, the cubic boron nitride content is 70.0 volume % or less, which relatively increases the content of the binder phase, thereby improving heat resistance and suppressing reactive wear. From the same perspective, the cubic boron nitride content is preferably 36.0 volume % or more and 65.2 volume % or less, and more preferably 40.8 volume % or more and 61.9 volume % or less.

[0016] In the cubic boron nitride sintered body of this embodiment, the average grain size of the cubic boron nitride (cBN) is preferably 0.5 μm or more and 3.0 μm or less. When the average grain size of the cBN is 0.5 μm or more, shedding of the cBN grains tends to be suppressed, and when the average grain size of the cBN is 3.0 μm or less, the chipping resistance of the cBN sintered body tends to be improved. From the same viewpoint, the average grain size of the cBN is more preferably 0.5 μm or more and 2.1 μm or less, and even more preferably 0.9 μm or more and 1.5 μm or less.

[0017] In this embodiment, the average particle size of cBN can be determined, for example, as follows. The cross-sectional structure of cubic boron nitride sintered body is photographed using an SEM. The area of ​​the cBN grain is determined by analyzing the photograph, and the diameter of a circle with the same area as this is calculated as the cBN grain size. The average value of the particle diameters of multiple cBN particles is determined as the average particle diameter of cBN. The average particle diameter of cBN can be determined from an image of the cross-sectional structure of a cubic boron nitride sintered body using commercially available image analysis software. More specifically, it can be determined by the method described in the Examples below.

[0018] [Binded phase] The cubic boron nitride sintered body of this embodiment has a binder phase content of 30.0 vol% or more, which improves heat resistance and suppresses reactive wear. On the other hand, the cubic boron nitride sintered body has a binder phase content of 70.0 vol% or less, which relatively increases the cBN content, thereby improving the strength and fracture resistance of the sintered body. From the same perspective, the binder phase content is preferably 34.8 vol% or more and 64.0 vol% or less, and more preferably 38.1 vol% or more and 59.2 vol% or less.

[0019] In the cubic boron nitride sintered body of this embodiment, the binder phase contains an Al compound and a Zr compound. The content of the Zr compound is preferably 10.0 volume % or more and 25.0 volume % or less relative to the total amount of the sintered body. When the content of the Zr compound in the cubic boron nitride sintered body of this embodiment is 10.0 volume % or more, the strength of the binder phase is improved and the chipping resistance tends to be excellent. On the other hand, when the content of the Zr compound in the cubic boron nitride sintered body of this embodiment is 25.0 volume % or less, the hardness of the binder phase at high temperatures is improved and the wear resistance tends to be excellent. From the same viewpoint, the content of the Zr compound is more preferably 11.1 volume % or more and 24.3 volume % or less, and even more preferably 14.4 volume % or more and 20.6 volume % or less relative to the total amount of the sintered body.

[0020] In the cubic boron nitride sintered body of this embodiment, the content of the Al compound is preferably 20.5 volume % or more and 49.2 volume % or less, more preferably 20.5 volume % or more and 45.1 volume % or less, and even more preferably 21.6 volume % or more and 42.1 volume % or less. When the content of the Al compound is within this range, the cubic boron nitride sintered body of this embodiment tends to have an excellent balance between the strength of the cubic boron nitride sintered body and hardness at high temperatures, and to have excellent chipping resistance and wear resistance.

[0021] The cubic boron nitride sintered body of this embodiment contains α-type Al2O3 as an Al compound. Although there are no particular limitations on Al compounds other than α-type Al2O3, examples include AlB2, AlN, and AlON, with AlB2 and AlN being preferred.

[0022] In the cubic boron nitride sintered body of this embodiment, the Zr compounds include ZrB2 and ZrO. Zr compounds other than ZrB2 and ZrO are not particularly limited, but include, for example, ZrO2, ZrC, and ZrN, with ZrO2 being preferred.

[0023] In the cubic boron nitride sintered body of this embodiment, the binder phase may contain elements other than the elements constituting the above-mentioned compounds. Specific examples of such elements include, but are not limited to, Si, Ti, Hf, V, Nb, Ta, Cr, Mo, W, Fe, Co, Ni, C, N, and O. The above elements may be contained as simple substances, alloys, or compounds. Examples of other simple substances, alloys, and compounds that may be contained in such binder phase include, but are not limited to, SiC, Si3N4, TiC, TiN, TiB2, NbC, NbN, TaC, TaN, Cr3C2, CrN, Cr2N, Mo2C, WC, and W2Co. 21 Examples include B6, Co3W3C, VC, VN, TaC, HfC, Mo, Fe, Co, CoAl, and Ni, with Cr2N, TiN, WC, VC, and TaC being preferred. These materials originate, for example, from cylinders and balls for ball mills, high-melting-point metal capsules used for filling, and may be unavoidably contained or may be added intentionally. In the cubic boron nitride sintered body of this embodiment, the content of other compounds is preferably 0.0 volume % or more and 10.0 volume % or less, more preferably 0.0 volume % or more and 5.0 volume % or less, and even more preferably 0.0 volume % or more and 3.0 volume % or less.

[0024] In the cubic boron nitride sintered body of this embodiment, the X-ray diffraction peak intensity of the (110) plane of α-type Al2O3 is I al , the X-ray diffraction peak intensity of the (101) plane of ZrB2 is I zb When I zb / I al The cubic boron nitride sintered body of this embodiment has a I zb / I al When the value of the cubic boron nitride sintered body is greater than 0.30, reactive wear is suppressed, and the body has excellent wear resistance and chipping resistance. zb / I al By making I 5.0 or less, the hardness of the binder phase at high temperatures is improved, and the wear resistance is excellent. zb / I al is more preferably 0.40 or more and 4.40 or less, and further preferably 0.78 or more and 3.52 or less.

[0025] In addition, the cubic boron nitride sintered body of this embodiment has an X-ray diffraction peak intensity of I in the (101) plane of ZrB2 in the binder phase. zb , the X-ray diffraction peak intensity of the (111) plane of ZrO is I zo When I zb / I zo is 0.1 or more and 1.0 or less. The cubic boron nitride sintered body of this embodiment has I zb / I zo When the value of I is 0.1 or more, reactive wear is suppressed, and the cubic boron nitride sintered body of this embodiment has excellent wear resistance and chipping resistance. zb / I zo By making I 1.0 or less, the bond strength between particles is increased, and chipping resistance and fracture resistance are improved. zb / I zois more preferably 0.15 or more and 0.89 or less, and further preferably 0.20 or more and 0.82 or less.

[0026] Furthermore, in the cubic boron nitride sintered body of this embodiment, it is preferable that the Zr compound further contains ZrO2. ZrO2 preferably contains cubic ZrO2 and / or tetragonal ZrO2. That is, ZrO2 preferably exists in the form of cubic ZrO2 only, tetragonal ZrO2 only, or a mixture of cubic ZrO2 and tetragonal ZrO2. When the Zr compound of the cubic boron nitride sintered body of this embodiment contains cubic ZrO2 and / or tetragonal ZrO2, the toughness of the sintered body tends to be improved and the fracture resistance tends to be excellent. In this embodiment, ZrO2 may be partially stabilized ZrO2 (PSZ) to which CeO2, Y2O3, MgO, CaO, and the like are added.

[0027] Furthermore, in the cubic boron nitride sintered body of this embodiment, when the Zr compound contains cubic ZrO2 and / or tetragonal ZrO2, the X-ray diffraction peak intensity I zc and (101) X-ray diffraction peak intensity of tetragonal ZrO2 I zt The sum of (I zc +I zt ), then I zo / (I zc +I zt ) is preferably 0.50 or more and 3.00 or less. The cubic boron nitride sintered body of this embodiment has I zo / (I zc +I zt ) is 0.50 or more, the hardness of the sintered body is improved and the wear resistance tends to be excellent. zo / (I zc +I zt When I is 3.00 or less, the toughness of the sintered body is improved and the fracture resistance tends to be excellent. zo / (I zc +I zt ) is more preferably 0.50 or more and 2.60 or less, and even more preferably 0.68 or more and 2.05 or less. In this embodiment, the X-ray diffraction peak intensity of each plane can be measured by the method described in the examples below.

[0028] Furthermore, in the cubic boron nitride sintered body of this embodiment, the average particle size of the Zr compound is preferably 50 nm or more and 300 nm or less. In the cubic boron nitride sintered body of this embodiment, when the average particle size of the Zr compound is 300 nm or less, the chipping resistance tends to be improved. On the other hand, in the cubic boron nitride sintered body of this embodiment, when the average particle size of the Zr compound is 50 nm or more, the manufacturing is easy. From the same viewpoint, the average particle size of the Zr compound is more preferably 62 nm or more and 297 nm or less, and even more preferably 103 nm or more and 272 nm or less. In this embodiment, the average particle size of the Zr compound can be measured by the method described in the examples below.

[0029] In the cubic boron nitride sintered body of this embodiment, the content (volume %) of cubic boron nitride and binder phase can be determined by analyzing a microstructure photograph of the cubic boron nitride sintered body taken with a scanning electron microscope (SEM) using commercially available image analysis software. More specifically, a mirror-polished surface of any cross section of the cubic boron nitride sintered body is obtained. Next, a backscattered electron image of the mirror-polished surface of the cubic boron nitride sintered body revealed by mirror polishing is observed using an SEM. The mirror-polished surface of the cubic boron nitride sintered body is magnified using an SEM at a magnification selected so that the cubic boron nitride particles are contained in an amount of 100 to 400. Using an energy dispersive X-ray analyzer (EDS) attached to the SEM, the black regions can be identified as cubic boron nitride, and the gray and white regions as binder phase. Then, a structural photograph of the cross section of the cubic boron nitride is taken using an SEM. Using commercially available image analysis software, the areas occupied by the cubic boron nitride and the binder phase are determined from the obtained structural photograph, and the content (volume %) is calculated from the areas. In this embodiment, the content ratios (volume %) of Al compounds, Zr compounds, and other materials can also be determined as follows. Specifically, first, as a prerequisite for determining the content ratios of each material, it is determined that the cubic boron nitride sintered body contains cubic boron nitride, Al compounds, Zr compounds, and other materials. For this purpose, the analysis using the backscattered electron image and EDS alone may not be sufficient. Here, by combining this with the results of XRD measurement, it is possible to identify the materials contained in the cubic boron nitride sintered body. Based on this information, it is possible to further identify each region on the backscattered electron image as cubic boron nitride, Al compounds, Zr compounds, and other materials from the results of elemental mapping using EDS, and the content ratios (volume %) can be determined by performing image analysis.

[0030] Here, the mirror-polished surface of a cubic boron nitride sintered body is a cross-section of a cubic boron nitride sintered body obtained by mirror-polishing the surface or any cross-section of a cubic boron nitride sintered body. A method for obtaining a mirror-polished surface of a cubic boron nitride sintered body can be, for example, a method of polishing with diamond paste.

[0031] The composition of the binder phase can also be identified using a commercially available X-ray diffractometer. For example, the composition of the binder phase can be identified by X-ray diffraction measurement using a 2θ / θ focused optical system with Cu-Kα radiation using an X-ray diffractometer (model "SmartLab") manufactured by Rigaku Corporation. Here, the measurement conditions are preferably, for example, those described in the examples below. Furthermore, analysis over a wide 2θ measurement range tends to enable detection of more peaks, making it possible to more reliably identify the materials contained in the sintered body. From this perspective, it is recommended to measure in the range of 2θ = 20 to 140°, for example. In this embodiment, the content ratios of cubic boron nitride and the binder phase, and the composition of the binder phase can also be measured by the methods described in the Examples below. Specifically, the composition of the binder phase can be identified by analyzing the results of measurement using an X-ray analyzer and the results of element mapping using EDS.

[0032] [Method for manufacturing sintered cubic boron nitride] The cubic boron nitride sintered body of this embodiment can be produced, for example, by the following method. As the raw material powder, for example, cBN powder, Al2O3 powder, Al powder, ZrO2 powder, etc. are prepared. Here, by appropriately adjusting the average particle size of the raw material cBN powder, it is possible to control the average particle size of cBN in the resulting cubic boron nitride sintered body to fall within the above-mentioned specific range. The method for reducing the average particle size of the Zr compound in the resulting cubic boron nitride sintered body is not particularly limited, but examples include reducing the proportion of ZrO2, the raw material for the Zr compound, among the binder phase materials (materials other than cBN) in the raw material powder, lowering the sintering temperature in the sintering step described below, increasing the proportion of Al powder in the raw material powder or the proportion of Al powder relative to the total of Al powder and Al2O3 powder, increasing the cBN content (volume %) in the cubic boron nitride sintered body, and reducing the average particle size of cBN in the cubic boron nitride sintered body. Among these, it is presumed that the sintering temperature and the cBN content (volume %) in particular have a significant effect on the average particle size of the Zr compound. Furthermore, by appropriately adjusting the ratio of each raw material powder, the content of cBN and binder phase in the resulting cubic boron nitride sintered body can be controlled within a desired range. Next, the prepared raw material powder is placed in a ball mill cylinder along with alumina balls, a hexane solvent, and paraffin and mixed (mixing process). After mixing, the raw material powder is filled into a high-melting-point metal capsule made of Zr (hereinafter simply referred to as "capsule") (filling process). After filling, a vacuum heat treatment is performed with the capsule open to remove moisture and organic components adsorbed on the surface of the raw material powder (drying process). After the vacuum heat treatment, the capsule is sealed, and the raw material powder filled in the capsule is sintered under high temperature and high pressure (sintering process). When filling the capsule, a substrate made of cemented carbide may be placed on the bottom. The sintering process conditions are, for example, a pressure of 7.7 to 8.5 GPa, a temperature of 1600 to 1700°C, and a time of 10 to 60 minutes.

[0033] In the binder phase used in this embodiment, the above-mentioned I zb / I al There are no particular limitations on the methods for increasing the cubic boron nitride sintered body, but examples include increasing the proportion of ZrO2 powder, which is the raw material for the Zr compound, among the binder phase materials (materials other than cBN) in the raw material powder in the above-mentioned manufacturing method of cubic boron nitride sintered body, increasing the sintering temperature in the sintering step, increasing the proportion of Al powder relative to the total of Al powder and Al2O3 powder in the raw material powder, increasing the content (volume %) of cBN in the cubic boron nitride sintered body, and reducing the average grain size of cBN in the cubic boron nitride sintered body. Among these, the proportion of ZrO2 powder, the sintering temperature, the content (volume %) of cBN, and the average grain size of cBN in the cubic boron nitride sintered body are particularly effective. zb / I al It is estimated that this will have a significant impact on

[0034] In the binder phase used in this embodiment, the above-mentioned I zb / I zo There are no particular limitations on the methods for reducing this, but examples include, in the above-mentioned manufacturing method of cubic boron nitride sintered body, a method of increasing the sintering temperature in the sintering step, a method of increasing the blending ratio of Al powder in the blending ratio of raw material powders or the blending ratio of Al powder to the total of Al powder and Al2O3 powder, a method of lowering the content (volume %) of cBN in the cubic boron nitride sintered body, and a method of reducing the average particle size of cBN in the cubic boron nitride sintered body. Among these, particularly preferred are a method of increasing the blending ratio of Al powder and the content (volume %) of cBN zb / I zo It is estimated that this will have a significant impact on

[0035] In the binder phase used in this embodiment, the above-mentioned I zo / (I zc +I zt) is not particularly limited, but examples include, in the above-mentioned method for producing a cubic boron nitride sintered body, a method of lowering the proportion of ZrO2 powder, which is the raw material for the Zr compound, among the binder phase materials (materials other than cBN) in the proportion of the raw material powder, a method of increasing the sintering temperature in the sintering step, a method of increasing the proportion of Al powder in the proportion of the raw material powder or the proportion of Al powder relative to the total of Al powder and Al2O3 powder, a method of increasing the content (volume %) of cBN in the cubic boron nitride sintered body, and a method of reducing the average particle size of cBN in the cubic boron nitride sintered body. Among these, particularly preferred are a method of increasing the sintering temperature, the proportion of Al powder, and the content (volume %) of cBN. zo / (I zc +I zt ) is expected to have a significant impact.

[0036] The cubic boron nitride sintered body of this embodiment may be used as a coated cubic boron nitride sintered body having a coating layer on its surface. Forming a coating layer on the surface of the cubic boron nitride sintered body further improves wear resistance. The coating layer is not particularly limited, but may contain, for example, at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Al, and Si, and at least one element selected from the group consisting of C, N, O, and B. The coating layer may have a single-layer structure or a laminated structure including two or more layers. When the coating layer has such a structure, the coated cubic boron nitride sintered body of this embodiment tends to have even more improved wear resistance.

[0037] Examples of compounds that form the coating layer include, but are not limited to, TiN, TiC, TiCN, TiAlN, TiSiN, and AlCrN. Among these, TiCN, TiAlN, and AlCrN are preferred. The coating layer may have a structure in which multiple layers with different compositions are stacked.

[0038] The thickness of each layer constituting the coating layer and the thickness of the entire coating layer can be measured from the cross-sectional structure of the coated cubic boron nitride sintered body using an optical microscope, SEM, transmission electron microscope (TEM), etc. The average thickness of each layer in the coated cubic boron nitride sintered body and the average thickness of the entire coating layer can be determined by measuring the thickness of each layer and the thickness of the entire coating layer from three or more cross sections in the vicinity of a position 50 μm from the cutting edge of the surface facing the metal evaporation source toward the center of said surface, and calculating the average value.

[0039] The composition of each layer constituting the coating layer can be measured from the cross-sectional structure of the coated cubic boron nitride sintered body using EDS or wavelength dispersive X-ray analyzer (WDS).

[0040] The method for producing the coating layer is not particularly limited, and examples thereof include chemical vapor deposition and physical vapor deposition methods such as ion plating, arc ion plating, sputtering, and ion mixing. Among these, the arc ion plating method is preferred because it provides superior adhesion between the coating layer and the cubic boron nitride sintered body.

[0041] The cubic boron nitride sintered body or coated cubic boron nitride sintered body of this embodiment has excellent wear resistance and chipping resistance, and is therefore preferably used as a cutting tool or a wear-resistant tool, and is particularly preferably used as a cutting tool. The cubic boron nitride sintered body or coated cubic boron nitride sintered body of this embodiment is more preferably used as a cutting tool for cast iron. When the cubic boron nitride sintered body or coated cubic boron nitride sintered body of this embodiment is used as a cutting tool or a wear-resistant tool, the tool life can be extended compared to conventional tools. [Example]

[0042] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0043] Example 1 [Preparation of raw powder] Raw material powders with the average particle size (μm) shown in Table 1 were prepared as the raw material for the cubic boron nitride sintered body. Among the raw material powders, ZrO2 was used, which consisted of secondary particles with an average particle size of 0.6 μm, formed by agglomeration of primary particles of partially stabilized zirconia with an average particle size of 40 nm, to which 3 mol% of Y2O3 had been added relative to the total ZrO2. The average particle size of the raw material powders was measured using the Fisher Sub-Sizer (FSSS) method according to the American Society for Testing and Materials (ASTM) standard B330. [Table 1]

[0044] [Mixing process] Each raw material powder was mixed in a ball mill cylinder together with alumina balls, hexane solvent, and paraffin to achieve the blending ratio (volume %) shown in Table 2. In Table 2, "-" indicates that the corresponding raw material was not included.

[0045] [Table 2]

[0046] [Filling process and drying process] The mixed raw material powder was filled into a high-melting-point metal capsule made of Ta (hereinafter also simply referred to as "capsule"). In order to remove moisture and organic components adsorbed on the surface of the filled raw material powder, a vacuum heat treatment was carried out with the capsule open. After the vacuum heat treatment, the capsule was sealed.

[0047] [Sintering process] The raw material powder packed in the capsule was then sintered under high temperature and high pressure under the sintering conditions shown in Table 3. The sintering time was 30 minutes.

[0048] [Table 3]

[0049] [Measurement and Analysis] The cubic boron nitride and binder phase contents (volume %) of the cubic boron nitride sintered body obtained by the sintering process were determined by analyzing the microstructure photographs of the cubic boron nitride sintered body taken with a scanning electron microscope (SEM) using commercially available image analysis software. More specifically, a mirror-polished surface of an arbitrary cross section of the cubic boron nitride sintered body was obtained. Next, a backscattered electron image of the mirror-polished surface of the cubic boron nitride sintered body revealed by mirror polishing was observed using the SEM. The mirror-polished surface of the cubic boron nitride sintered body was magnified at a magnification selected to contain 100 to 400 cubic boron nitride particles, and the backscattered electron image was observed using the SEM. An energy dispersive X-ray analyzer (EDS) attached to the SEM identified the black areas as cubic boron nitride and the gray and white areas as binder phase. Then, a microstructure photograph of the mirror-polished surface of the cubic boron nitride was taken using an SEM. Using commercially available image analysis software, the areas occupied by the cubic boron nitride and the binder phase were determined from the obtained microstructure photograph, and the content (volume %) was calculated from the areas. The results are shown in Table 5. Here, the mirror-polished surface of the cubic boron nitride sintered body was a cross-section of the cubic boron nitride sintered body obtained by mirror-polishing the surface or any cross-section of the cubic boron nitride sintered body. The mirror-polished surface (hereinafter also referred to as "cross-section") of the cubic boron nitride sintered body was obtained by polishing using diamond paste. Similarly, the content (volume %) of Al compound, Zr compound, and other materials was also determined as follows. Specifically, first, as a premise for determining the content of each material, it was determined that the cubic boron nitride sintered body contained cubic boron nitride, Al compound, Zr compound, and other materials. To this end, the backscattered electron image and EDS analysis were combined with the results of XRD measurement to identify the materials contained in the cubic boron nitride sintered body. Based on this information, the backscattered electron image and the results of elemental mapping using EDS were used to identify each region on the backscattered electron image as cubic boron nitride, Al compound, Zr compound, and other materials, and image analysis was performed to determine the content (volume %). The results are shown in Table 5.

[0050] Furthermore, the area of ​​the cBN particles was determined by image analysis using commercially available image analysis software for the structural photograph of the cubic boron nitride sintered body taken with the SEM, and the diameter of a circle with the same area as this area was taken as the particle size of the cBN particles. Next, the value D of the particle size of the cBN particles that satisfies the following formula was determined. 50 The results are shown in Table 4. (D 50 (Total area occupied by cBN particles with the following particle sizes) / (Area occupied by all cBN particles) = 0.5

[0051] The average particle size of Zr compounds can also be determined in the same way as the average particle size of cBN. Specifically, the area of ​​Zr compound particles was determined by image analysis using commercially available image analysis software for the structure photograph of the cubic boron nitride sintered body taken with the SEM, and the diameter of a circle with an area equal to this area was taken as the particle size of the Zr compound particles. Next, the particle size value D of the Zr compound particles that satisfies the relationship of the following formula was determined. 50 The results are shown in Table 4. (D 50 (Total area occupied by Zr compound particles having the following particle size) / (Area occupied by all Zr compound particles) = 0.5 The average particle size of the Zr compound was measured by mirror-polishing the cubic boron nitride sintered body as described above, then thermally etching the sample and observing it with an SEM as described above, and measuring the particle size of each Zr compound within the observed area. The thermal etching was carried out by heat treatment under the following conditions. Atmosphere: Vacuum below 1 Pa Heating rate: 10°C / min Temperature: 1200℃ Holding time: 30 minutes After the heat treatment, the sample was cooled to room temperature under an argon atmosphere of 250 kPa.

[0052] Furthermore, the composition of the binder phase was identified using an X-ray diffractometer (model "SmartLab") manufactured by Rigaku Corporation. Specifically, the composition of the binder phase was identified by analyzing the results of X-ray diffraction measurement using Cu-Kα radiation with a 2θ / θ focusing optical system under the following conditions and the element mapping results using EDS. <Measurement conditions> Output: 45kV, 200mA Entrance side Soller slit: 5° Divergence vertical slit: 2 / 3° Vertical divergence limiting slit: 5mm Scattering slit: 2 / 3° -Light receiving side solar slit: 5° Receiving slit: 0.3 mm Sampling width: 0.02° Scan speed: 1° / min 2θ measurement range: 30~90°

[0053] In addition, the X-ray diffraction peak intensity (I al ), the X-ray diffraction peak intensity of the (101) plane of ZrB2 (I zb ), the X-ray diffraction peak intensity of the (111) plane of ZrO (I zo ), the X-ray diffraction peak intensity of the (111) plane of cubic ZrO2 (I zc ) and the X-ray diffraction peak intensity of (101) of tetragonal ZrO2 (I zt ) and the sum (I zc +I zt ) to I zb / I al , I zb / I zo and I zo / (I zc +I zt ) were calculated for each crystal plane. The X-ray diffraction peaks for each crystal plane were identified based on the information in the Powder Diffraction File (hereinafter also referred to as "PDF") card number below. The values ​​obtained above are summarized in Table 6. In Table 6, "-" indicates that no clear peaks derived from ZrO were detected in the X-ray diffraction measurement, and I zo indicates that the value is "0". ·Cubic ZrO2(111):I zc PDF Card Number 71-6425 ·Tetragonal ZrO2(101):I zt PDF Card Number 68-0200 ZrO(111):I zo PDF Card Number 20-0684 ZrB2(101):I zb PDF Card Number 34-0423 α-type Al2O3(110):I al PDF Card Number 46-1212 The diffraction peak intensity of ZrO2 is I because the diffraction peak of cubic ZrO2 (111) and the diffraction peak of tetragonal ZrO2 (101) overlap. zc and I zt The sum of (I zc +I zt ) was used.

[0054] [Table 4]

[0055] [Table 5]

[0056] [Table 6]

[0057] [Cutting tool manufacturing] The obtained cubic boron nitride sintered body was cut using a laser processing machine to fit the insert shape specified in ISO standard SPGW120412 and the tool shape specified in ISO standard CNGA120408. The cut cubic boron nitride sintered body was joined by brazing to a base metal made of cemented carbide. The brazed tool was then honed to obtain a cutting tool.

[0058] [Cutting test 1] Continuous machining Using the obtained cutting tool, cutting test 1 was carried out under the following conditions. ·Work material: FC230, Workpiece shape: Cylindrical (outer diameter 90 mm, inner diameter 80 mm, length 100 mm) ·Cutting speed: 800m / min, Feed: 0.40mm / rev Cutting depth: 0.25mm Coolant: Water-soluble, Insert: ISO standard SPGW120412, using cBN sintered body at the cutting edge. Evaluation item: The machining time until the tool flank wear width exceeded 0.3 mm was defined as the tool life, and the machining time until the tool life was measured. In addition, the damage form at the end of the tool life was observed using an SEM. The damage form of "chipping" means that the chipping was small enough that machining could continue.

[0059] [Cutting test 2] Intermittent cutting Using the obtained cutting tool, cutting test 2 was carried out under the following conditions. ·Workpiece material: FC200, Workpiece shape: Round bar (120 mm, length 400 mm) with one groove on the outer surface, ·Cutting speed: 600m / min, Feed: 0.15mm / rev Cutting depth: 0.20mm Coolant: Water-soluble, Insert: ISO standard CNGA120408, with cBN sintered body at the cutting edge. Evaluation item: The tool life was determined when the cutting edge of the tool was chipped, and the number of impacts until the tool life was reached was measured.

[0060] The machining time until the tool life in Cutting Test 1 was evaluated as "A" for 20 minutes or more, "B" for 15 minutes or more but less than 20 minutes, and "C" for less than 15 minutes. Furthermore, the number of times until the tool life in Cutting Test 2 was evaluated as "A" for 1000 times or more, "B" for 750 times or more but less than 1000 times, and "C" for less than 750 times. Among these evaluations, "A" means the best, followed by "B" for the next best, and "C" for the worst. An evaluation of "A" or "B" for the machining time in Cutting Test 1 and an evaluation of "A" or "B" for the number of times in Cutting Test 2 indicate excellent cutting performance.

[0061] [Table 7]

[0062] From the results shown in Table 7, the evaluation of the processing time and the number of processing cycles of the inventive product were both "A" or "B", indicating that it has excellent wear resistance and fracture resistance. On the other hand, the evaluation of the processing time and the number of processing cycles of the comparative product were both "C", indicating that it has inferior wear resistance and / or fracture resistance compared to the inventive product. From the above results, it was found that the inventive product has excellent both wear resistance and chipping resistance, resulting in a long tool life. [Industrial Applicability]

[0063] The cubic boron nitride sintered body of the present invention has excellent wear resistance and chipping resistance, and can therefore extend the tool life compared to conventional tools, and in this respect has high industrial applicability.

Claims

1. A cubic boron nitride sintered body comprising cubic boron nitride and a binder phase, the content of the cubic boron nitride is 30.0% by volume or more and 70.0% by volume or less with respect to the total amount of the sintered body, the content of the binder phase is 30.0% by volume or more and 70.0% by volume or less with respect to the total amount of the sintered body, the binder phase includes an Al compound and a Zr compound; The Al compound is an α-type Al ２ O ３ Including, The Zr compound is ZrB ２ and ZrO, The α-type Al ２ O ３ The X-ray diffraction peak intensity of the (110) plane of ａｌ , the ZrB ２ The X-ray diffraction peak intensity of the (101) plane of ｚｂ , the X-ray diffraction peak intensity of the (111) plane of the ZrO is I ｚｏ When I ｚｂ / I ａｌ is greater than 0.30 and less than or equal to 5.00, I ｚｂ / I ｚｏ A cubic boron nitride sintered body, wherein the σ is 0.10 or more and 1.00 or less.

2. 2. The cubic boron nitride sintered body according to claim 1, wherein the content of said Zr compound is 10.0% by volume or more and 25.0% by volume or less with respect to the total amount of said sintered body.

3. The Zr compound further includes ZrO ２ Including, The ZrO ２ is cubic ZrO ２ and / or tetragonal ZrO ２ Including, The cubic ZrO ２ X-ray diffraction peak intensity I of the (111) plane ｚｃ and the tetragonal ZrO ２ X-ray diffraction peak intensity of (101) I ｚｔ The sum of (I ｚｃ +I ｚｔ ) and I ｚｏ / (I ｚｃ +I ｚｔ 3. The cubic boron nitride sintered body according to claim 1, wherein the value of (a) is 0.50 or more and 3.00 or less.

4. 3. The cubic boron nitride sintered body according to claim 1, wherein the average particle size of the Zr compound is 50 nm or more and 300 nm or less.

5. 3. The cubic boron nitride sintered body according to claim 1, wherein the average particle size of the cubic boron nitride is 0.5 μm or more and 3.0 μm or less.

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