Cubic boron nitride sintered body

Abstract

To provide a cubic-crystalline boron nitride sintered body having excellent wear resistance and chipping resistance, thereby extending tool life.SOLUTION: A cubic-crystalline boron nitride sintered body contains cubic-crystalline boron nitride and a binder phase. A content ratio of the cubic-crystalline boron nitride is 81 vol.% or more and 95 vol.% or less, a content ratio of the binder phase is 5 vol.% or more and 19 vol.% or less, the binder phase contains a specific amount of each of a specific Al compound, V compound and CoW compound and a content ratio of the Al compound having a grain size of 0.1 μm or less is 10 vol.% or more and 50 vol.% or less with respect to a total of 100 vol.% of the Al compound.SELECTED DRAWING: None

Description

Technical Field

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

Background Art

[0002] Cubic boron nitride (hereinafter also referred to as "cBN") has high hardness second only to diamond and excellent thermal conductivity. In addition, cubic boron nitride has the characteristic of having a lower affinity for iron than diamond. Therefore, a cubic boron nitride sintered body composed of cubic boron nitride and a bonding phase of metal or ceramics is used for cutting tools, wear-resistant tools, and the like.

[0003] Since sintered metal has high formability and often has a complex shape, when processed by a tool, the tool is likely to be damaged by thermal shock. In addition, since sintered metal may contain hard particles, the tool is likely to wear. Therefore, cubic boron nitride is often used for processing sintered metal, and in particular, many studies have been made on cubic boron nitride sintered bodies having a high cubic boron nitride content.

[0004] For example, in Patent Document 1, cBN is 40 to 80 area%, the bonding phase has an α phase and a β phase, the α phase is (Ti 1-x V x )(C 1-y N y ) with an average composition of x = 0.30 to 0.70, y = 0.00 to 0.50, 70 to 97 area% in the bonding phase, the β phase is one of oxides, nitrides, and borides of Al with an average particle size of 0.05 to 0.40 μm, 3 to 20 area% in the bonding phase, the α phase has an A region and a B region, the A region is (Ti 1-xA V xA )(C 1-yA N yA ) with xA = 0.10 to 0.30, yA = 0.00 to 0.50, and the B region is (Ti 1-xB V xB )(C 1-yB N yB) where \(x_B = 0.70 - 0.90\), \(y_B = 0.00 - 0.50\), and a cBN sintered body is disclosed in which the sum of the A region and the B region is 50 area% or more of the \(\alpha\) phase.

[0005] Also, for example, in Patent Document 2, \((Ti 1-x V x )(C 1-y N y )(x: 0.1 - 0.4, y: 0.1 - 0.5): 10 - 40 vol%, one or more of carbides, nitrides, and carbonitrides of Ti: 2 - 10 vol%, one or more of carbides, nitrides, and carbonitrides of V: 2 - 10 vol%, provided that B component + C component: 6 - 20 vol%, A component / B component + C component = 1.5 - 7, and the balance is composed of cubic boron nitride. A high-strength cBN-based sintered body is disclosed, and the cBN-based sintered body cutting tool further contains one or more of \(Al_2O_3\), \(AlN\), and \(AlB_2\): 1 - 10 vol%.

[0006] Furthermore, for example, in Patent Document 3, a cBN sintered body containing 50 volume% or more of cBN particles and a binder phase containing Co, and in the binder phase, particles of a binder phase containing Co a W b (0 ≤ a ≤ 0.95, 0.05 ≤ b ≤ 1) are present, and a cutting tool such as a cutting insert including a cBN chip composed of the cBN sintered body or entirely composed of the cBN sintered body is disclosed.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0008] In recent years, in cutting, since even higher efficiency has been demanded, high speed, high feed rate, and deep cutting have become even more remarkable. Along with such a trend, in the high-speed machining of sintered metal, a cubic boron nitride sintered body having excellent wear resistance and chipping resistance and capable of having a long tool life is demanded.

[0009] Against such a background, in the cubic boron nitride sintered body described in Patent Document 1, the proportion of cubic boron nitride in the cubic boron nitride sintered body is low and the wear resistance is not yet sufficient. Further, in the cubic boron nitride sintered bodies described in Patent Document 2 and Patent Document 3, in the binder phase, both V and W are not included, and the toughness may not be sufficient, and the chipping resistance is likely to decrease.

[0010] The present invention has been made in view of the above circumstances, and an object thereof is to provide a cubic boron nitride sintered body capable of extending the tool life by having excellent wear resistance and chipping resistance.

Means for Solving the Problems

[0011] As a result of repeated studies on extending the tool life of coated cutting tools by the present inventor, it has been found that when the cubic boron nitride sintered body has a specific structure, its wear resistance and chipping resistance can be improved, and as a result, the tool life can be extended, and the present invention has been completed.

[0012] That is, the gist of the present invention is as follows. [1] A cubic boron nitride sintered body containing cubic boron nitride and a binder phase, The content ratio of the cubic boron nitride is 81% by volume or more and 95% by volume or less with respect to 100% by volume of the entire cubic boron nitride sintered body, The content ratio of the binder phase is 5% by volume or more and 19% by volume or less with respect to 100% by volume of the entire cubic boron nitride sintered body, The binder phase includes an Al compound, a V compound, and a CoW compound, The Al compound contains a compound composed of an Al element and at least one element selected from the group consisting of an N element, an O element, and a B element. The V compound contains a compound composed of at least one selected from the group consisting of a carbide, a nitride, and a carbonitride, with V as the main component. The CoW compound contains a compound composed of at least one selected from the group consisting of a carbide and a carbonitride, with CoW as the main component. The content ratio of the Al compound is 2% by volume or more and 40% by volume or less with respect to 100% by volume of the entire binder phase. The content ratio of the V compound is 50% by volume or more and 95% by volume or less with respect to 100% by volume of the entire binder phase. The content ratio of the CoW compound is 3% by volume or more and 35% by volume or less with respect to 100% by volume of the entire binder phase. A cubic boron nitride sintered body, wherein the content ratio of the Al compound having a particle size of 0.1 μm or less is 10% by volume or more and 50% by volume or less with respect to 100% by volume of the entire Al compound. [2] The cubic boron nitride sintered body according to [1], wherein the content ratio of the Al compound having a particle size exceeding 0.2 μm is 50% by volume or more and 80% by volume or less with respect to 100% by volume of the entire Al compound. [3] The cubic boron nitride sintered body according to [1] or [2], wherein the content ratio of the Al compound having a particle size exceeding 0.1 μm and being 0.2 μm or less is 20% by volume or less with respect to 100% by volume of the entire Al compound. [4] The cubic boron nitride sintered body according to any one of [1] to [3], wherein in the entire Al compound, the content ratio of the Al compound having a particle size of 0.1 μm or less is larger on a volume basis than the content ratio of the Al compound having a particle size exceeding 0.1 μm and being 0.2 μm or less. [5] The cubic boron nitride sintered body according to any one of [1] to [4], wherein the average particle size of the cubic boron nitride is 0.5 μm or more and 3.0 μm or less.

Advantages of the Invention

[0013] According to the present invention, a cubic boron nitride sintered body having excellent wear resistance and chipping resistance can be provided, thereby extending the tool life.

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments for carrying out the present invention (hereinafter, simply referred to as "the present embodiment") will be described in detail. However, the present invention is not limited to the following present embodiment. The present invention can be variously modified without departing from the gist thereof.

[0015] [Cubic Boron Nitride Sintered Body] The cubic boron nitride sintered body of the present embodiment is a cubic boron nitride sintered body containing cubic boron nitride (hereinafter, also referred to as "cBN") and a binder phase. The content ratio of cubic boron nitride is 81% by volume or more and 95% by volume or less with respect to 100% by volume of the entire cubic boron nitride sintered body. The content ratio of the binder phase is 5% by volume or more and 19% by volume or less with respect to 100% by volume of the entire cubic boron nitride sintered body. The binder phase contains an Al compound, a V compound, and a CoW compound. The Al compound contains a compound composed of Al element and at least one element selected from the group consisting of N element, O element, and B element. The V compound contains a compound composed of at least one selected from the group consisting of carbide, nitride, and carbonitride having V as a main component. The CoW compound contains a compound composed of at least one selected from the group consisting of carbide and carbonitride having CoW as a main component. The content ratio of the Al compound is 2% by volume or more and 40% by volume or less with respect to 100% by volume of the entire binder phase. The content ratio of the V compound is 50% by volume or more and 95% by volume or less with respect to 100% by volume of the entire binder phase. The content ratio of the CoW compound is 3% by volume or more and 35% by volume or less with respect to 100% by volume of the entire binder phase. The content ratio of the Al compound having a particle size of 0.1 μm or less is 10% by volume or more and 50% by volume or less with respect to 100% by volume of the entire Al compound.

[0016] By having the above-described configuration, the cubic boron nitride sintered body of the present embodiment can improve wear resistance and chipping resistance, and as a result, can extend the tool life. Although the factors by which the cubic boron nitride sintered body of the present embodiment improves wear resistance and chipping resistance and has a long tool life are not clear in detail, the present inventor considers the factors as follows. However, the factors are not limited to this. The cubic boron nitride sintered body of the present embodiment is excellent in wear resistance because the content ratio of cBN is 81% by volume or more. On the other hand, since the content ratio of cBN is 95% by volume or less, the exfoliation of cBN particles can be suppressed, and it is excellent in wear resistance. Further, in cutting, the surface roughness of the machined surface of the workpiece tends to be small, and the appearance after machining also tends to be good. Also, the cubic boron nitride sintered body of the present embodiment can suppress the exfoliation of cBN particles and is excellent in wear resistance because the content ratio of the bonding phase is 5% by volume or more. On the other hand, since the content ratio of the bonding phase is 19% by volume or less, the content ratio of cBN is relatively increased, and as a result of the improvement in hardness, it is excellent in wear resistance. In the cubic boron nitride sintered body of the present embodiment, the content ratio of the Al compound is 2% by volume or more with respect to 100% by volume of the entire bonding phase, so that Al oxide is formed, and the heat resistance is improved. On the other hand, when the content ratio of the Al compound is 40% by volume or less, the formation of Al nitride and Al boride can be reduced, and the wear resistance is excellent. Further, in the cubic boron nitride sintered body of the present embodiment, the content ratio of the V compound is 50% by volume or more with respect to 100% by volume of the entire bonding phase, so that the bonding strength between particles is improved, and the defect resistance is excellent. On the other hand, when the content ratio of the V compound is 95% by volume or less, the production of the cBN sintered body becomes easy. Furthermore, in the cubic boron nitride sintered body of the present embodiment, the content ratio of the CoW compound is 3% by volume or more with respect to 100% by volume of the entire bonding phase, so that the bonding strength between particles is improved, and the defect resistance is excellent. On the other hand, when the content ratio of the CoW compound is 35% by volume or less, a decrease in the hardness of the cBN sintered body can be suppressed, and the wear resistance is excellent. And, in the cubic boron nitride sintered body of the present embodiment, the content ratio of the Al compound having a particle size of 0.1 μm or less is 10% by volume or more with respect to 100% by volume of the entire Al compound, so that the contact area between the Al compound and the cBN particles increases, and as a result, the effect of removing oxygen on the surface of the cBN particles becomes high. As a result, the bonding strength between the cBN particles is improved, and the defect resistance is excellent. On the other hand, when the content ratio of the Al compound having a particle size of 0.1 μm or less is 50% by volume or less, the production of the cBN sintered body becomes easy. Due to the above-described effects combined, the cubic boron nitride sintered body of the present embodiment can improve the wear resistance and the defect resistance, and extend the tool life.

[0017] In the cubic boron nitride sintered body of the present embodiment, the content ratio of cBN is 81% by volume or more and 95% by volume or less with respect to 100% by volume of the entire cubic boron nitride sintered body, and the content ratio of the bonding phase is 5% by volume or more and 19% by volume or less with respect to 100% by volume of the entire cubic boron nitride sintered body. Note that, in the cubic boron nitride sintered body of the present embodiment, the total content ratio of cBN and the bonding phase is 100% by volume.

[0018] [Cubic boron nitride (cBN)] The cubic boron nitride sintered body of the present embodiment has excellent wear resistance due to the cBN content ratio being 81% by volume or more. On the other hand, since the cBN content ratio is 95% by volume or less, the detachment of cBN particles can be suppressed, and it has excellent wear resistance. Also, in cutting, the surface roughness of the machined surface of the workpiece tends to be small, and the appearance after machining is also good. From the same viewpoint, the cBN content ratio is preferably 82% by volume or more and 93% by volume or less, and more preferably 84% by volume or more and 92% by volume or less.

[0019] In the cubic boron nitride sintered body of the present embodiment, the content ratios (by volume) of cBN and the bonding phase can be obtained by photographing an arbitrary cross-section of the sintered body with a scanning electron microscope (SEM) and analyzing the photographed micrograph with commercially available image analysis software. Specifically, it can be obtained by the method described in the examples below.

[0020] In the cubic boron nitride sintered body of the present embodiment, the average particle size of cBN is preferably 0.5 μm or more and 3.0 μm or less. The cubic boron nitride sintered body of the present embodiment can suppress the detachment of cBN particles and tends to improve wear resistance because the average particle size of cBN is 0.5 μm or more. Also, the cubic boron nitride sintered body of the present embodiment tends to improve the defect resistance because the thickness of the bonding phase becomes thinner when the average particle size of cBN is 3.0 μm or less. From the same viewpoint, the average particle size of cBN is more preferably 0.7 μm or more and 2.5 μm or less.

[0021] As a method for measuring the average particle size of cBN, for example, an arbitrary cross-section of the sintered body is photographed with a scanning electron microscope (SEM), the area of cBN particles is obtained by analyzing the photographed micrograph with commercially available image analysis software, and the diameter of a circle with an area equal to this area can be taken as the particle size of cBN. The arithmetic mean of the particle sizes of a plurality of cBN particles thus obtained may be taken as the average particle size of cBN. Specifically, it can be obtained by the method described in the examples below.

[0022] [Bonding phase] The cubic boron nitride sintered body of the present embodiment can suppress the dropout of cBN particles and has excellent wear resistance because the content ratio of the bonding phase is 5% by volume or more. On the other hand, since the content ratio of the bonding phase is 19% by volume or less, the content ratio of cBN is relatively increased, and as a result of the improved hardness, the wear resistance is excellent. From the same viewpoint, the content ratio of the bonding phase is preferably 7% by volume or more and 18% by volume or less, and more preferably 8% by volume or more and 16% by volume or less.

[0023] In the cubic boron nitride sintered body of the present embodiment, the bonding phase contains an Al compound, a V compound, and a CoW compound. Further, the Al compound contains a compound composed of Al element and at least one element selected from the group consisting of N element, O element, and B element. Further, the V compound contains a compound composed of at least one selected from the group consisting of carbide, nitride, and carbonitride having V as a main component. Further, the CoW compound contains a compound composed of at least one selected from the group consisting of carbide and carbonitride having CoW as a main component. In the present specification, "having V as a main component" means that when the total metal elements in the compound are 100 atomic%, the content ratio of V element is 50 atomic% or more, and the content ratio may exceed 50 atomic%, may be 60 atomic% or more, or may be 70 atomic% or more. Further, "having CoW as a main component" means that the compound contains Co element and W element, and when the total metal elements in the compound are 100 atomic%, the total content ratio of Co element and W element is 50 atomic% or more, and the content ratio may exceed 50 atomic%, the content ratio may be 60 atomic% or more, may be 70 atomic% or more, or may be 80 atomic% or more. Further, in the CoW compound used in the present embodiment, the atomic ratio of W element to Co element (W element: Co element) is preferably in the range of 3:10 to 7:2.

[0024] The Al compound includes a compound composed of an Al element and at least one element selected from the group consisting of an N element, an O element, and a B element. As the Al compound, the components that the bonding phase may contain are not particularly limited. For example, Al2O3, AlN, AlB2, AlB 12 and the like can be mentioned. From the viewpoint of more effectively and surely achieving the effects of the present invention, the bonding phase preferably contains at least one selected from the group consisting of Al2O3, AlN, and AlB2 as the Al compound, more preferably contains at least one selected from the group consisting of Al2O3 and AlN, and particularly preferably contains only Al2O3.

[0025] In the Al compound, the content ratio of particles having a particle size of 0.1 μm or less (hereinafter also referred to as "fine particles") is 10% by volume or more and 50% by volume or less with respect to 100% by volume of the entire Al compound. In the cubic boron nitride sintered body of the present embodiment, since the content ratio of the fine particles is 10% by volume or more, the contact area between the Al compound and the cBN particles increases, so the effect of removing oxygen on the surface of the cBN particles becomes higher. As a result, the bonding strength between the cBN particles is improved and the defect resistance is excellent. On the other hand, when the content ratio of the fine particles is 50% by volume or less, the production of the cBN sintered body becomes easy. From the same viewpoint, the content ratio of the fine particles in the Al compound is preferably 11% by volume or more and 48% by volume or less, and more preferably 15% by volume or more and 35% by volume or less. In addition, in the present embodiment, the lower limit of the particle size of the fine particles is not particularly limited. For example, it is 0.01 μm. Also, in the present embodiment, minute particles that cannot be detected by the method described in the examples described later are not included in the particle content ratio.

[0026] In the Al compound, the content ratio of particles with a particle size exceeding 0.1 μm and equal to or less than 0.2 μm (hereinafter also referred to as "medium particles") is preferably 20% by volume or less with respect to 100% by volume of the entire Al compound. In the cubic boron nitride sintered body of the present embodiment, when the content ratio of the medium particles is 20% by volume or less, the effect of removing oxygen on the surface of the cBN particles and / or the effect of improving heat resistance can be obtained. As a result, it tends to be excellent in wear resistance and / or chipping resistance. From the same viewpoint, the content ratio of the medium particles in the Al compound is more preferably 14% by volume or less, and even more preferably 12% by volume or less.

[0027] In the entire Al compound, the content ratio of the Al compound (small particles) with a particle size of 0.1 μm or less is preferably larger on a volume basis than the content ratio of the Al compound (medium particles) with a particle size exceeding 0.1 μm and equal to or less than 0.2 μm. In the cubic boron nitride sintered body of the present embodiment, when the content ratio of the small particles is larger on a volume basis than the content ratio of the medium particles, the contact area between the Al compound and the cBN particles increases. Therefore, the effect of removing oxygen on the surface of the cBN particles is further improved, and as a result, it tends to be even more excellent in chipping resistance.

[0028] In the Al compound, the content ratio of particles with a particle size exceeding 0.2 μm (hereinafter also referred to as "large particles") is preferably 50% by volume or more and 80% by volume or less with respect to 100% by volume of the entire Al compound. In the cubic boron nitride sintered body of the present embodiment, when the content ratio of the large particles is 50% by volume or more, the heat resistance is improved, and thus the wear resistance tends to be improved. On the other hand, when the content ratio of the large particles is 80% by volume or less, the content ratio of the small particles or the medium particles relatively increases, and the contact area between the Al compound and the cBN particles increases. Therefore, the effect of removing oxygen on the surface of the cBN particles is further improved, and as a result, it tends to be even more excellent in chipping resistance. From the same viewpoint, the content ratio of the large particles in the Al compound is more preferably 61% by volume or more and 78% by volume or less, and even more preferably 62% by volume or more and 77% by volume or less.

[0029] As a method for measuring the particle size of Al compound particles, for example, an arbitrary cross-section of the sintered body is photographed with a scanning electron microscope (SEM), and the area of the Al compound particles in the bonding phase is obtained by analyzing the photographed micrograph with commercially available image analysis software. The diameter of a circle having the same area as this area can be defined as the particle size of each Al compound particle. From the particle sizes of the plurality of Al compound particles thus obtained, they can be classified into small particles, medium particles, and large particles, respectively. Specifically, it can be determined by the method described in the examples below.

[0030] The content ratio of the Al compound is 2% by volume or more and 40% by volume or less with respect to 100% by volume of the entire bonding phase. In the cubic boron nitride sintered body of the present embodiment, since the content ratio of the Al compound is 2% by volume or more with respect to 100% by volume of the entire bonding phase, Al oxide is formed, and the heat resistance is improved. On the other hand, since the content ratio of the Al compound is 40% by volume or less, the formation of Al nitride and Al boride can be reduced, and excellent wear resistance is achieved. From the same viewpoint, the content ratio of the Al compound is preferably 3% by volume or more and 36% by volume or less, and more preferably 4% by volume or more and 27% by volume or less with respect to 100% by volume of the entire bonding phase.

[0031] The V compound contains at least one compound selected from the group consisting of carbides (hereinafter also referred to as "V carbides"), nitrides (hereinafter also referred to as "V nitrides"), and carbonitrides (hereinafter also referred to as "V carbonitrides") having V as a main component. From the viewpoint of more effectively and surely achieving the effects of the present invention, it is preferable that the V compound contains V carbide. In addition, in the V compound, the metal elements contained in addition to V are not particularly limited, and examples include W, Co, Cr, Mo, Ta, Nb, Zr, Hf, Ni, etc. From the viewpoint of more effectively and surely achieving the effects of the present invention, it may contain at least two or more metal elements among W, Co, Cr, Mo, Ta, Nb, Zr, Hf, and Ni, it may contain at least W and Co, it may contain at least three or more metal elements among W, Co, Cr, Mo, Ta, Nb, Zr, Hf, and Ni, or it may contain at least W, Co, and Cr.

[0032] The content ratio of the V compound is 50% by volume or more and 95% by volume or less with respect to 100% by volume of the entire binding phase. In the cubic boron nitride sintered body of the present embodiment, since the content ratio of the V compound is 50% by volume or more with respect to 100% by volume of the entire binding phase, the bonding strength between particles is improved, and thus the defect resistance is excellent. On the other hand, when the content ratio of the V compound is 95% by volume or less, the production of the cBN sintered body becomes easy. From the same viewpoint, the content ratio of the V compound is preferably 54% by volume or more and 92% by volume or less, and more preferably 63% by volume or more and 84% by volume or less with respect to 100% by volume of the entire binding phase.

[0033] The content ratio of the metal element other than V contained in the V compound (hereinafter also simply referred to as "metal element other than V") is not particularly limited. For example, it is 0 atom% or more and less than 50 atom% with respect to 100 atom% of the total metal elements contained in the V compound. When the content ratio of the metal element other than V exceeds 0 atom% and becomes high, the toughness of the cubic boron nitride sintered body is improved, and it tends to be excellent in defect resistance. On the other hand, when the content ratio of the metal element other than V is less than 50 atom%, the hardness of the cubic boron nitride sintered body is improved, and it tends to be excellent in wear resistance. From the same viewpoint, the content ratio of the metal element other than V is preferably 4 atom% or more and 46 atom% or less, and more preferably 26 atom% or more and 39 atom% or less.

[0034] The CoW compound contains at least one compound selected from the group consisting of carbides (hereinafter also referred to as "CoW carbides") and carbonitrides (hereinafter also referred to as "CoW carbonitrides") mainly composed of CoW. From the viewpoint of making the effects of the present invention more effective and reliable, it is preferable that the CoW compound contains CoW carbide. In addition, in the CoW compound, the metal elements contained other than Co and W are not particularly limited, and examples thereof include V, Cr, Mo, Ta, Nb, Zr, Hf, Ni, etc. From the viewpoint of more effectively and surely achieving the effects of the present invention, it may contain at least one or more metal elements among V, Cr, Mo, Ta, Nb, Zr, Hf, and Ni, it may contain at least V, it may contain at least two or more metal elements among V, Cr, Mo, Ta, Nb, Zr, Hf, and Ni, or it may contain at least V and Cr.

[0035] The content ratio of the CoW compound is 3% by volume or more and 35% by volume or less with respect to 100% by volume of the entire binder phase. In the cubic boron nitride sintered body of the present embodiment, since the content ratio of the CoW compound is 3% by volume or more with respect to 100% by volume of the entire binder phase, the bonding strength between particles is improved, and thus it has excellent flaw resistance. On the other hand, since the content ratio of the CoW compound is 35% by volume or less, a decrease in the hardness of the cBN sintered body can be suppressed, and it has excellent wear resistance. From the same viewpoint, the content ratio of the CoW compound is preferably 4% by volume or more and 35% by volume or less, and more preferably 9% by volume or more and 13% by volume or less with respect to 100% by volume of the entire binder phase.

[0036] The content ratio of the metal elements contained other than Co and W in the CoW compound (hereinafter, also simply referred to as "metal elements other than Co and W") is not particularly limited. For example, it is 0 atomic% or more and less than 50 atomic% with respect to 100 atomic% of all the metal elements contained in the CoW compound. When the content ratio of the metal elements other than Co and W exceeds 0 atomic% and becomes high, the bonding strength between particles in the cubic boron nitride sintered body is improved, and it tends to have excellent flaw resistance. On the other hand, when the content ratio of the metal elements other than Co and W is less than 50 atomic%, the heat resistance of the cubic boron nitride sintered body is improved, and it tends to have excellent wear resistance. From the same viewpoint, the content ratio of the metal elements other than Co and W is preferably 3 atomic% or more and 48 atomic% or less, and more preferably 17 atomic% or more and 31 atomic% or less.

[0037] The composition of the bonding phase can also be identified using a commercially available X-ray diffractometer. For example, when performing X-ray diffraction measurement of a 2θ / θ focusing optical system using Cu-Kα rays under predetermined conditions using an X-ray diffractometer (product name "SmartLab") manufactured by Rigaku Corporation, the composition of the bonding phase can be identified. Specific conditions and the like can be carried out as described in the examples below. Also, when it is difficult to identify all of the composition of the bonding phase only with the X-ray analyzer, it may be specified by analyzing the result of the measurement by the X-ray analyzer and the elemental mapping result using an energy dispersive X-ray analyzer (EDS).

[0038] As a method for measuring the content ratio (atomic %) of each element in the bonding phase, for example, it can be obtained by taking a micrograph of the cubic boron nitride sintered body with a SEM equipped with an energy dispersive X-ray analyzer (EDS) and performing EDS analysis. More specifically, the method described in the examples below can be used.

[0039] [Method for manufacturing cubic boron nitride sintered body] The cubic boron nitride sintered body of the present embodiment can be manufactured, for example, by a method including the following steps (A) to (E). As a more specific method, it is advisable to use the method described in the examples below. Step (A): As raw material powders, cubic boron nitride (cBN) powder, VC powder, VN powder, Cr3C2 powder, Cr2N powder, WC powder, Co powder, Al powder, Mo2C powder, TaC powder, NbC powder, ZrC powder, HfC powder, Ni powder, etc. are prepared as necessary (preparation and weighing of raw material powders).

[0040] Step (B): A part of the Al powder prepared in step (A) is put into a cylinder for a ball mill together with cemented carbide balls, a hexane solvent, paraffin wax, and a dispersant, and mixed (first mixing step).

[0041] Step (C): The Al powder mixed in Step (B) and the remaining raw material powder prepared in Step (A) are put into a cylinder for ball milling together with cemented carbide balls, a hexane solvent, paraffin wax, and a dispersant and mixed (second mixing step). In accordance with the difference in the amount of raw material powder to be mixed, the cylinder used in this step is a cylinder different from that used in Step (B).

[0042] Step (D): The mixture obtained in Step (C) is filled into a high melting point metal capsule having a predetermined shape, and in order to remove moisture and other adhering components adsorbed on the surface of the filled raw material powder, vacuum heat treatment is performed with the capsule open (filling step and drying step).

[0043] Step (E): The capsule filled with the raw material powder is sintered by holding it at a temperature in the range of 1800 to 2100 °C and a pressure of 8.0 to 9.5 GPa for 30 to 40 minutes (high pressure sintering).

[0044] Each step of the method for producing a cubic boron nitride sintered body of the present invention has the following significance. In Step (A), by appropriately adjusting the average particle size of the cBN powder in the raw material, the average particle size of cBN in the obtained cubic boron nitride sintered body can be controlled within a predetermined range. When the average particle size of the raw material powder is increased, the average particle size of cBN in the sintered body becomes larger. Here, as the raw material of the binder phase, a combination of a part of each of the above raw material powders that has undergone the following treatment may be used. First, a part of each of the above raw material powders is mixed so as to have a specific blending ratio (mass %). The mixing is performed, for example, by putting each raw material powder together with cemented carbide balls, a hexane solvent, paraffin, and a dispersant into a cylinder for a ball mill. Then, the mixed raw material powder is heat-treated in a vacuum atmosphere, and the raw material after the heat treatment is put together with cemented carbide balls, a hexane solvent, paraffin, and a dispersant into a cylinder for a ball mill and pulverized, and the obtained pulverized product is used as the raw material powder material of the binder phase. When using the raw material powder material thus pre-combined in this way, it tends to be easy to set the content ratio (atomic ratio) of the metal elements contained other than V in the V compound and / or the metal elements contained other than Co and W in the CoW compound to a high value exceeding 0 atomic %. Examples of the raw material powder material pre-combined in this way include a raw material powder material obtained by combining at least two or more of VC powder, VN powder, Co powder, and WC powder, a raw material powder material obtained by combining at least three or more of VC powder, VN powder, Co powder, and WC powder, and a raw material powder material obtained by combining VC powder or VN powder, Co powder, and WC powder.

[0045] By appropriately adjusting the ratio of each raw material powder, the content ratios of cBN and the binder phase in the obtained cubic boron nitride sintered body can be controlled within the above-specified ranges. For example, when the blending ratio of cBN is increased, the content ratio (volume %) of cBN tends to increase. Also, for example, when the blending ratio of Al is increased, the content ratio (volume %) of the Al compound in the binder phase tends to increase. Further, when the ratio of the raw material powder containing the V element is increased, the content ratio (volume %) of the V compound in the binder phase tends to increase. Examples of the raw material powder containing the V element include VC powder, VN powder, Material A, Material B, Material D, etc. described in the examples below. The higher these blending ratios are, the higher the content ratio (volume %) of the V compound tends to be. Also, here, the effects of increasing the content ratio (volume %) of the V compound and the effect of increasing the ratio (atomic %) of V in the V compound are in the following order. (High) VC powder, VN powder > Material A, Material D > Material B (Low) Further, for example, when increasing the proportion of raw material powder containing Co element and / or W element, the content ratio (volume%) of CoW compound in the binder phase tends to increase. Examples of the raw material powder containing Co element and / or W element include WC powder, Co powder, Material B, Material C, Material E, etc. described in the examples to be described later. The higher these blending ratios, the higher the content ratio (volume%) of CoW compound tends to be. Here, the effect of increasing the content ratio (volume%) of CoW compound and the effect of increasing the ratio (atomic%) of V in CoW compound are in the following order. (High) WC powder, Co powder > Material C, Material E > Material B (Low)

[0046] As the Al powder to be mixed in step (B) (the first mixing step), for example, an amount of 15.0 mass% or more and 50.0 mass% or less, preferably 18.1 mass% or more and 47.5 mass% or less, may be used with respect to 100 mass% of the total Al powder prepared in step (A). Here, when increasing the amount of Al powder to be mixed in the first mixing step, the ratio (volume%) of small particles in the Al compound tends to increase, and the ratio (volume%) of large particles tends to decrease. Also, the mixing time in the first mixing step is, for example, 10 to 125 hours, preferably 15 to 120 hours. When increasing the mixing time in the first mixing step, the ratio (volume%) of small particles in the Al compound tends to increase, so the ratio (volume%) of small particles in the Al compound tends to be higher than the ratio (volume%) of medium particles.

[0047] The cubic boron nitride sintered body of the present invention and the coated cubic boron nitride sintered body of the present invention are excellent in wear resistance and chipping resistance, and thus are preferably applied to cutting tools and wear-resistant tools. Among them, the cubic boron nitride sintered body of the present invention and the coated cubic boron nitride sintered body of the present invention are more preferably applied to cutting tools.

Examples

[0048] Hereinafter, the present invention will be described in more detail by way of examples, but the present invention is not limited to these examples.

[0049] [Preparation of raw material powder] Cubic boron nitride (cBN) powder, VC powder, VN powder, Cr3C2 powder, Cr2N powder, WC powder, Co powder, Al powder, Mo2C powder, TaC powder, NbC powder, ZrC powder, HfC powder, and Ni powder were prepared. Their average particle sizes were 2.2 μm (VC powder), 2.6 μm (VN powder), 2.1 μm (Cr3C2 powder), 2.0 μm (Cr2N powder), 2.0 μm (WC powder), 1.5 μm (Co powder), 1.8 μm (Al powder), 3.0 μm (Mo2C powder), 2.4 μm (TaC powder), 2.1 μm (NbC powder), 2.5 μm (ZrC powder), 1.8 μm (HfC powder), and 1.5 μm (Ni powder), respectively, and the average particle size of the cBN powder was as shown in Table 2. The average particle size of the raw material powder was measured by the Fisher method (Fisher Sub-Sieve Sizer (FSSS)) described in ASTM Standard B330 of the American Society for Testing and Materials.

[0050] Furthermore, as raw materials for the binder phase, the raw material powders were blended so as to have the blending ratios (mass %) shown in Table 1, and were put into a cylinder for a ball mill together with cemented carbide balls, a hexane solvent, paraffin wax, and a dispersant, and mixed for 6 hours. Next, the mixed raw material powder was heat-treated under the condition of 1100 °C in a vacuum atmosphere, and then put into a cylinder for a ball mill again together with cemented carbide balls, a hexane solvent, paraffin wax, and a dispersant, and pulverized for 24 hours. Through such steps, Materials A to E as shown in Table 1 were obtained.

[0051]

Table 1

[0052]

Table 2

[0053] [First Mixing Step] The raw material powders prepared above were weighed so as to achieve the ratios shown in Tables 3 and 4. Next, a part of the weighed Al powder was put into a cylinder for a ball mill together with cemented carbide balls, a hexane solvent, paraffin wax, and a dispersant, and mixed for the mixing time shown in Table 5. Here, "Al (mass%)" shown in Table 5 represents a ratio with respect to 100 mass% of the entire weighed Al powder.

[0054] [Second Mixing Step] The Al powder mixed in the first mixing step and the weighed raw material powders other than the part of the Al powder were put into a cylinder for a ball mill different from that in the first mixing step together with cemented carbide balls, a hexane solvent, paraffin wax, and a dispersant, and mixed for 2 hours.

[0055] [Filling Step and Drying Step] The mixed raw material powders were filled into a high melting point metal capsule made of Ta. Next, vacuum heat treatment was performed with the capsule open to remove moisture and other adhering components adsorbed on the surface of the powder, and then the capsule was sealed.

[0056] [High-Pressure Sintering] Thereafter, the raw material powders filled in the capsule were sintered under high pressure. The conditions for high-pressure sintering were as shown in Tables 6 and 7.

[0057]

Table 3

[0058]

Table 4

[0059]

Table 5

[0060]

Table 6

[0061]

Table 7

[0062] [Measurement and Analysis] Regarding the cubic boron nitride sintered body obtained by high-pressure sintering, first, identification was performed using an X-ray diffractometer (product name: "SmartLab") manufactured by Rigaku Corporation. Specifically, X-ray diffraction measurement of the 2θ / θ focusing optical system using Cu-Kα rays was carried out under the following conditions. <Measurement Conditions> · Output: 45 kV, 200 mA, · Incident-side Soller slit: 5°, · Divergent vertical slit: 2 / 3°, · Divergent vertical limiting slit: 5 mm, · Scattering slit: 2 / 3°, · Receiving-side Soller slit: 5°, · Receiving slit: 0.3 mm, · Receiving slit: 0.3 mm, · Sampling width: 0.02°, · Scan speed: 1° / min, · 2θ measurement range: 30 to 90°. As a result, it was identified that the sintered body contains cubic boron nitride (cBN) and a bonding phase. As the bonding phase, it was identified that it contains an Al compound. The compositions of the identified cubic boron nitride and Al compound are shown in Tables 8 and 9. Regarding the V compound and CoW compound, further, by combining the results obtained by measurement under the above conditions with the elemental mapping results using an energy-dispersive X-ray analyzer (EDS) attached to a scanning electron microscope (SEM), the elements contained in each compound were identified. The identified elements are shown in Tables 10 and 11. Hereinafter, each measurement and analysis method will be described in more detail.

[0063] Regarding the cubic boron nitride sintered body obtained by high-pressure sintering, the content ratios (volume %) of cubic boron nitride and the bonding phase were determined by analyzing with commercially available image analysis software from the micrographs of the cubic boron nitride sintered body taken with a scanning electron microscope (SEM). More specifically, the cubic boron nitride sintered body was polished to obtain a mirror-polished surface from a cross-sectional structure at a position 500 μm deep from the surface and toward the inside. Next, using an SEM, the backscattered electron image of the mirror-polished surface of the cubic boron nitride sintered body was observed. At this time, the observation was performed with magnification at 10,000 times using an SEM. By using the energy dispersive X-ray analyzer (EDS) attached to the SEM, the black region was specified as cubic boron nitride, and the gray and white regions were specified as the bonding phase. Thereafter, three micrographs of the above-mentioned mirror-polished surface of cubic boron nitride were taken using an SEM. Using commercially available image analysis software, the occupied areas of cubic boron nitride and the bonding phase were determined from the obtained micrographs, and by dividing by the area occupied by the entire micrograph, the content ratios (volume %) of cubic boron nitride and the bonding phase were determined. The content ratios (volume %) of cubic boron nitride and the bonding phase were taken as the arithmetic mean of the values obtained by the above analysis in each of the three fields of view of the three micrographs taken. The results are shown in Tables 8 and 9. Here, the mirror-polished surface of the cubic boron nitride sintered body is a cross-section at a position 500 μm or more deep from the surface of the cubic boron nitride sintered body obtained by mirror-polishing the surface or an arbitrary cross-section of the cubic boron nitride sintered body. The polishing of the mirror-polished surface (hereinafter also referred to as a cross-section) was performed using diamond paste. In addition, the content ratio (volume %) of the Al compound in the bonding phase was determined by analyzing with commercially available image analysis software from the microstructure photograph in which the content ratios (volume %) of the above-mentioned cubic boron nitride and the bonding phase were determined. The backscattered electron image was observed in the same field of view as that in which the content ratios (volume %) of the cubic boron nitride and the bonding phase were determined. By using EDS, it was specified that among the gray region and the white region in the bonding phase, the dark gray region is the Al compound, and the light gray region and the white region are bonding phase materials other than the Al compound. Next, the area occupied by the Al compound and the area occupied by the bonding phase material other than the Al compound in the above microstructure photograph were determined, and by dividing by the area occupied by the entire bonding phase, the content ratio (volume %) of the Al compound in the bonding phase and the content ratio (volume %) of the bonding phase material other than the Al compound were determined. The same analysis was performed in three fields of view of each of the three microstructure photographs taken, and the weighted average of the obtained values was taken as the content ratio (volume %) of each compound. The content ratio (volume %) of the Al compound among the results is shown in Tables 8 and 9. In addition, the content ratios (volume %) of the V compound and the CoW compound in the binding phase were determined by combining elemental mapping using EDS. For the binding phase materials other than the Al compound specified in terms of the content ratio (volume %) of the Al compound, elemental mapping using EDS was performed. By analyzing the obtained mapping results, it was specified that the binding phase materials other than the Al compound are a V compound in which the content ratio of the V element is 50 atomic % or more based on 100 atomic % of the total detected metal elements, and a CoW compound in which the total content ratio of the Co element and the W element is 50 atomic % or more based on 100 atomic % of the total detected metal elements. Also, by analyzing the obtained mapping results, the area ratio occupied by each of the V compound and the CoW compound in the binding phase materials other than the Al compound was determined. The value obtained by analyzing this area ratio and the content ratio (volume %) of the binding phase materials other than the Al compound in the binding phase was taken as the content ratio (volume %) of the V compound and the CoW compound in the binding phase. These results are shown in Tables 8 and 9. For example, in Table 8, Invention Product 1 shows that the content ratio (volume %) of the binding phase materials other than the Al compound in the binding phase is 89 volume %, and the area ratio (V compound:CoW compound) occupied by the V compound and the CoW compound determined by mapping is 78:11. In addition, the composition of the V compound was determined by analysis using EDS. The same backscattered electron image as described above was observed, and point analysis using EDS was performed at an arbitrary point on the V compound on the mirror-polished surface specified by the above mapping, and the ratio of the V element to the total of all detected metal elements was determined. The same analysis was performed at 20 points, and the additive average value of the obtained ratios of the V element was taken as the content ratio (atomic %) of V in the V compound. At this time, the additive average value of the atomic ratio of the C element and the N element was also determined. When the C element is more than the N element with a C element:N element ratio of 8:2, it was regarded as a V carbide, when it is in the range of 8:2 to 2:8, it was regarded as a V carbonitride, and when the N element is more than the C element with a ratio of 2:8, it was regarded as a V nitride and distinguished from each other. These results and the elements other than V detected during the analysis using EDS are shown in Tables 10 and 11. The composition of the CoW compound was also determined in the same manner as that of the V compound. Similar to the above, at any point on the CoW compound on the mirror-polished surface, point analysis using EDS was performed, and the sum of the ratios of the Co element and the W element to the total of all detected metal elements was determined. The same analysis was performed at 20 points, and the arithmetic mean value of the sum of the ratios of the Co element and the W element obtained was taken as the total content ratio (atomic %) of Co and W in the CoW compound. At this time, the arithmetic mean value of the atomic ratio of the C element and the N element was also determined. When the C element was more than the N element at a C element:N element ratio of 8:2, it was designated as CoW carbide; when it was within the range of 8:2 to 2:8, it was designated as CoW carbonitride; and when the N element was more than the C element at a ratio of 2:8, it was designated as CoW nitride, and they were distinguished from each other. These results and the elements other than Co and W detected during the analysis using EDS are shown in Tables 10 and 11. In the point analysis for determining the composition of the CoW compound, the ratio of the W element to the Co element existed in the range of 3:10 to 7:2, and the ratio of the metal element to the non-metal element existed in the range of 3:1 to 12:1. Also, in the identification using an X-ray diffractometer, the peak presumed to be Co3W3C was most clearly present. Also, in the CoW compound of this example, it is presumed that the ratio of the W element to the Co element is close to a value of 1:1. Also, it is speculated that the CoW compound in this example mainly exists in a state where a part of the Co element and the W element in Co3W3C are substituted with other metal elements, and a part of the C element is substituted with the N element. In this analysis, although not used as a determination condition, in the point analysis for determining the composition of the V compound, the V compound existed in the range of 1:2 to 2:1 for the metal element to the non-metal element.

[0064] Also, by image analysis of the tissue photograph taken above, the area of Al compound particles present in the cross-sectional tissue was determined, and the diameter of a circle with an area equal to this area was defined as the particle size of the Al compound. Those with an Al compound particle size of 0.1 μm or less were defined as small particles, those with a size greater than 0.1 μm and 0.2 μm or less were defined as medium particles, and those with a size greater than 0.2 μm were defined as large particles. The sum of the areas occupied by small particles, the sum of the areas occupied by medium particles, and the sum of the areas occupied by large particles present in the cross-sectional tissue were determined, and by dividing by the area occupied by the entire Al compound, the content ratio (volume %) of each type of particle was calculated. Also, the respective content ratios obtained for small particles and medium particles were compared. These results are shown in Tables 12 and 13. Similarly, by image analysis of the tissue photograph taken above, the area of cBN particles present in the cross-sectional tissue was determined, and the diameter of a circle with an area equal to this area was defined as the particle size of the cBN particles. The arithmetic mean of the particle sizes of the cBN particles present in the cross-sectional tissue was determined and defined as the average particle size of cBN. As a result, it was the same as the average particle size of the cBN raw material powder shown in Table 2.

[0065]

Table 8

[0066]

Table 9

[0067]

Table 10

[0068]

Table 11

[0069]

Table 12

[0070]

Table 13

[0071] [Manufacture of Cutting Tool] The obtained cubic boron nitride sintered body was cut out into a tool shape with an insert shape defined by ISO standard CNGA120408 using a wire electrical discharge machining machine. The cut cubic boron nitride sintered body was joined to a base alloy made of cemented carbide by brazing. The brazed tool was subjected to honing to obtain a cutting tool.

[0072] [Cutting Test] A cutting test was conducted under the following conditions using the obtained cutting tool. ·Workpiece material: Case-hardened sintered metal (Material: JIS standard · FD-08N4C-39, hardness: HRA70), ·Workpiece material shape: Gear shape, φ45 mm (tooth thickness 8 mm) × 30 mm, ·Cutting speed: 250 m / min, ·Feed: 0.15 mm / rev, ·Depth of cut: 0.2 mm, ·Coolant: None (dry cutting), ·Evaluation item: The machining time until the flank wear width of the tool reached 0.15 mm or the cutting edge was damaged was defined as the tool life. The obtained results are shown in Table 14.

[0073]

Table 14

[0074] From the results shown in Table 14, it was found that the inventive product using a cubic boron nitride sintered body with a specific configuration has better chipping resistance and wear resistance than the comparative product without it, and has a long tool life.

Industrial Applicability

[0075] Since the cubic boron nitride sintered body of the present invention is excellent in wear resistance and chipping resistance, the tool life can be extended compared to the prior art, and thus it has high industrial applicability in that regard.

Claims

1. A cubic boron nitride sintered body containing cubic boron nitride and a binder phase, wherein the content ratio of the cubic boron nitride is 81% by volume or more and 95% by volume or less with respect to 100% by volume of the entire cubic boron nitride sintered body, the content ratio of the binder phase is 5% by volume or more and 19% by volume or less with respect to 100% by volume of the entire cubic boron nitride sintered body, the binder phase contains an Al compound, a V compound, and a CoW compound, the Al compound contains a compound composed of Al element and at least one element selected from the group consisting of N element, O element, and B element, the V compound contains a compound composed of at least one selected from the group consisting of carbide, nitride, and carbonitride having V as a main component, the CoW compound contains a compound composed of at least one selected from the group consisting of carbide and carbonitride having CoW as a main component, the content ratio of the Al compound is 2% by volume or more and 40% by volume or less with respect to 100% by volume of the entire binder phase, the content ratio of the V compound is 50% by volume or more and 95% by volume or less with respect to 100% by volume of the entire binder phase, the content ratio of the CoW compound is 3% by volume or more and 35% by volume or less with respect to 100% by volume of the entire binder phase, the content ratio of the Al compound having a particle size of 0.1 μm or less is 10% by volume or more and 50% by volume or less with respect to 100% by volume of the entire Al compound, the content ratio of the Al compound having a particle size exceeding 0.1 μm and being 0.2 μm or less is 20% by volume or less with respect to 100% by volume of the entire Al compound, the content ratio of the Al compound having a particle size exceeding 0.2 μm is 50% by volume or more and 80% by volume or less with respect to 100% by volume of the entire Al compound, a cubic boron nitride sintered body.

2. In the entire Al compound, the content ratio of the Al compound having a particle size of 0.1 μm or less is larger on a volume basis than the content ratio of the Al compound having a particle size exceeding 0.1 μm and being 0.2 μm or less, the cubic boron nitride sintered body according to Claim 1.

3. The average particle size of the cubic boron nitride is 0.5 μm or more and 3.0 μm or less, the cubic boron nitride sintered body according to Claim 1 or 2.

Images