JP2021151943A - cBN sintered body and cutting tool - Google Patents

Abstract

To provide a cubic boron nitride (cBN) sintered body and a cutting tool having crack propagation resistance and stability against thermal loads even in intermittent cutting process with depth of cut exceeding 0.1 mm.SOLUTION: A cBN sintered body and a cutting tool comprising 40 to 80 area% of cBN, and a binding phase comprising α and β phases, wherein the α phase is (Ti1-xVx) (C1-yNy) with an average composition of x=0.30-0.70, y=0.00-0.50, and 70-97 area% in the bound phase, and the β phase is a type of Al oxide, nitride, or boride with an average grain size of 0.05-0.40 μm, and 3-20 area% in the binder phase; and wherein the alpha phase has an A region and a B region, and the A region is (Ti1-xAVxA)(C1-yANyA), in which xA=0.10-0.30 and yA=0.00-0.50, and the B region is (Ti1-xBVxB)(C1-yBNyB) in which xB=0.70-0.90 and yB=0.00-0.50, and the sum of the A and B regions is more than 50 area% percent of the α phase.SELECTED DRAWING: Figure 1

Description

The present invention relates to a cubic boron nitride (hereinafter, may be referred to as cBN) -based sintered body and a cutting tool using the same.

Conventionally, the cBN sintered body has been widely used as a cutting tool material. Then, a cBN sintered body containing Ti, V and the like in addition to cBN which is a hard dispersion phase has been studied.

For example, Patent Document 1 describes a hard material consisting of one or more of titanium carbide, titanium nitride, titanium carbonitride, titanium / vanadium carbide, and titanium / vanadium carbonitride having an average particle size of 2 to 5 μm. A cutting tool containing 10 to 30% by volume of dispersed phase is described, and when an iron-based member such as steel or cast iron is cut with this cutting tool, an excellent surface finish having a surface roughness of 1.6 S or less is obtained. Moreover, it is said that the taper generated in the longitudinal direction is also extremely small.

Further, 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) (hereinafter, (A component): 10 to 40% by volume, one or more of Ti carbides, nitrides, and carbonitrides (hereinafter referred to as B component): 2 to 10% by volume, V carbides, nitrides One or more of the material and the carbide (hereinafter referred to as C component): 2 to 10% by volume, but B component + C component: 6 to 20% by volume, A component / B component + C component = A cutting tool made of a high-strength cBN-based sintered body composed of a cBN-based sintered body containing 1.5 to 7 and the rest consisting of cBN is described, and this cutting tool cuts hardened steel. Depth: It is said that high-speed intermittent cutting with a fine cut of 0.1 mm or less can be performed.

Further, for example, Patent Document 3 states that in a cutting tool composed of a cBN-based sintered body, when the bonding phase contains a composite nitride of at least one of V, Nb, and Ta and Ti, it is resistant to fracture. Improved properties and chipping resistance, and added V, Nb, Ta nitride or metal and reacting with cBN at the time of sintering to at least one orbital crystal in VB, NbB, TaB. It is said that the inclusion of boride increases thermal stability and improves wear resistance as well as chipping resistance.

Japanese Patent No. 2767890 Japanese Patent No. 3489297 Japanese Patent No. 4830571

As a result of examining the cutting tools described in these patent documents, the present inventor has found the following matters.

The cutting tool described in Patent Document 1 is intended to improve the surface finish of the work material and the problem that the columnar body is tapered in the longitudinal direction during cutting, but is a cBN-based sintered body. Since the particle size (particularly particles other than cBN) of the particles constituting the above is large, cutting work containing intermittent components or unstable cutting work (for example, cutting for a work material having an elongated shape or a thin work material) Cutting edge may be chipped or chipped when performing processing).

The cutting tools described in Patent Document 2 are shown to contain carbides, nitrides, carbonitrides of Ti, and carbides, nitrides, carbonitrides of V, which are of Ti and V. It is inferior in high-temperature strength to composite carbides or composite carbide nitrides, and there is a risk of destruction starting from these components due to the cutting heat when used as a cutting tool. In addition, it is a finding that the cutting tool is not chipped for minute cutting intermittent cutting with a cutting depth of 0.1 mm or less, but there is no mention of intermittent cutting when the cutting depth exceeds 0.1 mm, and there is room for improvement. There is.

The cutting tool described in Patent Document 3 has been shown to contain at least one orthocrystalline boronide among V, Nb and Ta, which are carbides or charcoal of V, Nb and Ta. The thermal stability is not sufficient as compared with nitrides, and the toughness of the cBN-based sintered body may decrease due to the cutting heat when used as a cutting tool.

The present invention has been made in view of such a situation, and has sufficient crack propagation resistance even in intermittent cutting with a cutting depth of more than 0.1 mm, and is thermally resistant to cutting. It is an object of the present invention to provide a cBN sintered body having high stability against a load and a cutting tool having excellent wear resistance, chipping resistance and fracture resistance of a cutting edge.

The present inventor has diligently studied the cBN sintered body and the CBN cutting tool in order to solve the above problems. As a result, two regions having different concentrations of the composite carbide or composite carbonitride of Ti and V are present in the bonded phase in a predetermined ratio, and further, Al having a predetermined average particle size is present in the bonded phase. When at least one of oxides, nitrides, and borides is present in a predetermined ratio, excellent high-temperature strength / high-temperature hardness and sufficient crack propagation resistance are exhibited, and cBN firing with high stability against a thermal load during cutting is performed. We have obtained a new finding that a body can be obtained, and if this cBN sintered body is used, a cutting tool having excellent wear resistance and chipping resistance of the cutting edge can be obtained.

The present invention is based on this finding and is as follows.
"(1) A cBN sintered body having a bonding phase with cubic boron nitride,
In the cross section of the cBN sintered body,
The cubic boron nitride occupies 40 to 80 area%.
The binding phase has an α phase and a β phase, and has an α phase and a β phase.
When the composition of the α phase is represented by the composition formula: (Ti _1-x V _x ) (C _1-y N _y ), the average composition thereof is x = 0.30 to 0.70, y = 0. It is .00 to 0.50 and is present in the bonded phase in an area% of 70 to 97.
The β phase is at least one of an oxide, nitride, and boride of Al having an average particle size of 0.05 to 0.40 μm, and is present in the bonded phase in an area of 3 to 20 area%.
Further, the α phase has an A region and a B region, and has an A region and a B region.
When the composition of the A region is represented by the composition formula: (Ti _1-xA V _xA ) (C _1-yA N _yA ), xA = 0.10 to 0.30, yA = 0.00 to 0. 50
When the composition of the B region is represented by the composition formula: (Ti _1-xB V _xB ) (C _1-yB N _yB ), xB = 0.70 to 0.90, yB = 0.00 to 0. 50
The sum of the ratios of the A region and the B region to the α phase is 50 area% or more.
A cBN sintered body characterized in that.
(2) The difference between the average composition x of V in the α phase and the average value xA _avg of the V content ratio xA in the A region is defined as x-xA _avg .
When the difference between the average composition x of V in the α phase and the average value xB _{avg of the V content ratio xB in the B region is xB avg} −x,
| (X-xA _avg )-(xB _avg- x) | is 0.20 or less.
The cBN sintered body according to (1) above.
(3) A cutting tool using the cBN sintered body according to (1) or (2) as a tool base. "

The cBN sintered body of the present invention has sufficient crack propagation resistance even in intermittent cutting with a cutting depth of more than 0.1 mm, is highly stable against a thermal load during cutting, and is also stable. A cutting tool using this cBN sintered body as a tool base is excellent in abrasion resistance and chipping resistance of the cutting edge.

It is a schematic diagram which shows an example of the sintered structure of the cBN sintered body of this invention, and the shape and size of each structure do not conform to the actual structure.

Hereinafter, the present invention will be described in detail. In the present specification, when the numerical range is expressed using "M to N" (both M and N are numerical values), the range includes the numerical values of the upper limit (N) and the lower limit (M). Moreover, the unit of the upper limit and the lower limit is the same. In addition, the numerical values include measurement tolerances.

The cBN sintered body of the present invention has the structure schematically shown in FIG. That is, this structure has a binding phase containing cBN particles 1, α-phases 2, 6, 7, and β-phase 3, and the α-phase has a region A and a region B. These will be described below.

Area ratio of cubic boron nitride (cBN) particles:
In any cross section of the cBN sintered body, the cBN particles preferably occupy 40-80 area%. When in this range, chipping is suppressed and fracture resistance is improved.
For the area ratio of the cBN particles, a portion of the cBN particles is extracted by image processing from the secondary electron image obtained by observing the structure with a scanning electron microscope described later, and the area ratio of the portion occupying one observation region is determined. This is performed for 3 observation regions (3 images), and the average value is taken as the area ratio of the cBN particles.

Average particle size of cBN particles:
The average particle size of the cBN particles, which is the hard dispersion phase used in the present invention, is not particularly limited, but is preferably in the range of 0.2 to 8.0 μm.
The cBN particles can enhance the fracture resistance of the cBN sintered body. At this time, if the average particle size of the cBN particles dispersed in the cBN sintered body is 0.2 to 8.0 μm, the uneven shape of the cutting edge caused by the cBN particles on the tool surface falling off during use as a cutting tool. Defects and chipping starting from It can suppress the propagation of cracks and have better fracture resistance.

Here, the average particle size of the cBN particles can be determined as follows.
An arbitrary cross section of the cBN sintered body is mirror-processed, and the mirror-surfaced surface is subjected to microstructure observation with a scanning electron microscope (SEM) to obtain a secondary electron image. Next, the portion of the cBN particles in the obtained image is extracted by image processing, and the average particle size is calculated based on the maximum length of each particle obtained by image analysis.

When extracting the cBN particle part in the image by image processing, in order to clearly judge the cBN particle and the bonding phase, the image displays 0 in black and 255 in white with 256 gradations in monochrome, and the cBN particle part. The binarization process is performed so that the cBN particles become black using the image of the pixel value in which the ratio of the pixel value of the above to the pixel value of the coupling phase portion is 2 or more.

Here, as a region for obtaining the pixel values of the cBN particle portion and the coupled phase portion, a region of about 0.5 μm × 0.5 μm is selected, and an average value obtained from at least three different locations within the same image region is obtained. It is preferable to use each contrast.

After the binarization treatment, a process for separating the portion where the cBN grains are considered to be in contact with each other, for example, a water shed is used to separate the cBN grains which are considered to be in contact with each other. Subsequently, image analysis is performed.

The portion (black portion) corresponding to the cBN particles in the image obtained after the binarization process is subjected to particle analysis, and the obtained maximum length is defined as the maximum length of each particle, and this is defined as the diameter of each particle. In the particle analysis for obtaining the maximum length, a value having a length larger than the two lengths obtained by calculating the ferret diameter for one cBN particle is taken as the maximum length, and that value is taken as the diameter of each particle. Assuming that each particle is an ideal sphere having this diameter, the cumulative volume is calculated by using the volume obtained by calculation as the volume of each particle.

Based on this cumulative volume, a graph is drawn with the vertical axis as the volume percentage [%] and the horizontal axis as the diameter [μm], and the diameter when the volume percentage is 50% is defined as the average particle size of the cBN particles in the region. This is performed for 3 observation regions (3 images), and the average value thereof is defined as the average particle size [μm] of cBN.

When performing this particle analysis, the length (μm) per pixel is set using the scale value known in advance by SEM. As an observation region used for image processing, when the average particle size of cBN particles is about 3 μm, a visual field region of about 15.0 μm × 15.0 μm is preferable.

Bonding phase:
The binding phase has an α phase and a β phase.

α phase:
The composition of the composite carbide of Ti and V or the composite carbonitride can be described by the composition formula: (Ti _1-x V _x ) (C _1-y N _y ) (0.00 <x <1.00, 0.00 ≦). When represented by y <1.00), the average composition of the α phase is x = 0.30 to 0.70, y = 0.00 to 0.50, and 70 to 97 area% is present in the bound phase. It is preferable to do so.
When x and y and the area% are set in this range, excellent strength is exhibited even under the high temperature brought about by the cutting process, and the stability of the cBN sintered body against a thermal load during the cutting process is increased, so that high-speed cutting is performed. Improves chipping resistance and fracture resistance at the time.

As schematically shown in FIG. 1, there are α phases having different compositions (atomic ratios of Ti and V). That is, the α phase 2 away from the A region and the B region, which will be described later, has a Ti / V of about 2/3 to 3/2, and the α phase 6 near the A region has a Ti / V of about 3/2 to 7 /. It is 3, and the α phase 7 in the vicinity of the B region has a Ti / V of about 3/4 to 2/3.

β phase:
The β phase is at least one of an oxide, nitride, and boride of Al having an average particle size of 0.05 to 0.40 μm, and is preferably present in the bonded phase in an area of 3 to 20 area%.
The reason for setting the average particle size to 0.05 to 0.40 μm is that within this particle size range, the growth of cracks propagating in the bonded phase can be suppressed, and intermittent cutting, in which a large impact is applied to the cutting edge during cutting, This is because it exhibits excellent chipping resistance without impairing wear resistance under high-load cutting conditions.
Further, the β phase is present in 3 to 20 area% in the bonded phase, so that it exhibits crack propagation resistance and excellent fracture resistance when used as a cutting tool.

Area A and Area B:
The α phase preferably has an A region having a low V concentration (high Ti concentration) and a B region having a high V concentration (low Ti concentration). By having two regions (A region and B region) with different V concentrations, plastic deformation of the coupling phase is suppressed under the condition of thermal load during cutting, and as a result, the cBN sintered body is formed. It can exert the effect of suppressing the decrease in hardness and toughness of the cutting tool, and gives the cutting tool excellent wear resistance and fracture resistance.

Here, the composition of the A region is expressed by the composition formula: (Ti _1-xA V _xA ) (C _1-yA N _yA ), xA = 0.10 to 0.30, yA = 0.00 to 0. .50 and the composition of the B region is xB = 0.70 to 0.90, yB = 0 when expressed by _{the composition formula: (Ti 1-xB} V _xB ) (C _1-yB N _yB). When the sum of the ratios of the A region and the B region to the α phase is 50 area% or more, the above-mentioned effect can be surely exhibited.

V concentration in A region and B region and average V concentration in α phase:
_{The difference between the average composition x of V in the α phase and the average value xA avg} of the V content in the A region xA is defined as x-xA _avg, and the average composition x of V in the α phase and the V content ratio xB in the B region When the difference from the average value xB _{avg is xB avg} −x, it is more preferable that | (x−xA _avg ) − (xB _avg −x) | is 0.20 or less.
The reason is that | (x-xA _avg )-(xB _avg- x) | is small, so that the repeated change of V concentration between the A region and the B region becomes clearer, and at the same time, the A region and the B region This is because the bias of the area ratio is also reduced, and as a result, the effect of suppressing plastic deformation at high temperature is enhanced, and the above-mentioned effect can be exhibited even more reliably.

Method for determining the composition of the bound phase and the area%:
When an arbitrary cross section of the cBN sintered body is mirror-processed and the cBN content is, for example, about 65% by volume and the average particle size is about 3 μm with respect to the mirror-processed surface, it is about 5.0 μm × 3.0 μm. It is preferable to select a region and use it as an observation region.

As one of the means for observing the structure of the cross section, B, C, N, O, Ti, V, and Al atoms are mapped by Auger electron spectroscopy (AES), and the part where only B and N overlap is cBN. It is defined as a particle, and the other part is defined as a binding phase.
The ratio of the α phase to the bonded phase is calculated by defining the portion where C, Ti, and V overlap as the α phase and dividing the area by the area of the bonded phase. Similarly, the ratio of the β phase is calculated by defining the portion where Al and at least one of B, N, and O overlap as the β phase, and dividing the area by the area of the coupling phase.

For the average composition of the α phase, draw straight lines that cross and traverse the mapped image at regular intervals, perform composition analysis on the point where the intersection is on the α phase, and use the average value as the α. The average composition of the phases. The measurement points for calculating this average value shall be at least 30 points, and the composition analysis shall be performed at all the intersections of the straight lines coming on the α phase.

Regarding the V and Ti concentrations in the A and B regions, check the V-dark part (Ti-light part) and V-light part (Ti-rich part) from the mapping results in advance, and include the peripheral parts. In addition, at least four line analyzes are performed on equiangular radial lines that pass through the approximate center of the dark and light parts, and the boundary between the parts that satisfy the conditions of A and B and the parts that do not meet the conditions ( (At least 8 points) are specified, and the areas connecting the boundary portions with straight lines are defined as the areas A and B, respectively, and the respective areas are obtained. This is carried out at all the locations checked in advance, and the total ratio of the area occupied by each region to the α phase is calculated.

Regarding the V concentration xA in the A region and the V concentration xB in the B region, each region defined by the above method is binarized by image processing and then binarized from the balance of moments. The position of the center of gravity of each of the above is obtained, and the V concentration in the composition of the position of the center of gravity is defined as xA and xB. Similarly, the N concentration yA in the A region and the N concentration yB in the B region are determined from the composition of the position of the center of gravity of each region. When binarizing, the A region and the B region are separately implemented. Also, when considering the balance of moments, the region that is binarized and painted black is treated as a two-dimensional rigid body, and its density is treated as uniform.

The average particle size of the β phase is the same as when the average particle size of the cBN particles described above was obtained after the part defined by the above method was image-processed and binarized to fill it with black. Is performed, and the average is calculated by using the ferret diameter of each particle as the particle size.

Production method:
The cBN powder as the raw material powder for the hard dispersed phase, the raw material powder for the α phase (for example, TiC powder, TiN powder, TiCN powder, VC powder, VN powder) and the raw material powder for the β phase (for example, TiC powder, TiN powder, TiCN powder, VC powder, VN powder) as the raw material powder for the bonded phase. for example, TiAl ₃ powder, _Al 2 _{O 3} powder, AlN powder), and other raw material powder (e.g., WC powder, TaC powder, preparing a NbC powder).

Next, when the α-phase raw material powder was blended in a predetermined ratio and compared by mass, a raw material having Ti more than V and a raw material having V more than Ti were obtained, and these blended raw materials were used to obtain a molded product. Is prepared, heat-treated in a vacuum atmosphere, crushed, and sieved to obtain two types of mixed heat-treated raw material powders.

Subsequently, these two types of mixed heat-treated raw material powders, β-phase raw material powders, and other raw material powders, if necessary, are pulverized and mixed with acetone by a ball mill, and further, a hard dispersed phase raw material is added. Mix to obtain sintered raw material powder.
Then, this sintered body raw material powder is molded, temporarily sintered, and main-sintered to prepare a cBN sintered body.

Next, an example will be described. The present invention is not limited to the examples.

(1) Preparation of raw materials The following raw materials were prepared.
(1-1) Hard dispersed phase: cBN powder with an average particle size of 0.5 to 8.0 μm (1-2) Bonded phase (1-2-1) α phase: Each average particle size is 0.3 to 2.5 μm TiC powder, TiN powder, TiCN powder, VC powder, VN powder (1-2-2) β phase: TiAl ₃ powder, Al ₂ O _{3 having an average particle size of 0.3 to 3.0 μm, respectively.} Powder, AlN powder (1-2-3) Others: WC powder, TaC powder, NbC powder with an average particle size of 0.3 to 3.0 μm, respectively.

(2) Preparation and mixing of raw materials (2-1) Adjustment of α-phase raw materials The α-phase raw materials of (1-2-1) above are mixed in a predetermined ratio (mass ratio of each component) shown in Table 1, that is, mass. Compared in The molded product was press-molded at a molding pressure of 1 MPa to a size of diameter: 50 mm × thickness: 3.0 mm, and the produced molded product was heat-treated while being held at 1600 ° C. in a vacuum atmosphere at a pressure of 1 Pa or less. Then, it was pulverized by grinding and compression, and sieved with a sieve having a mesh size of 45 μm to obtain two kinds of mixed heat-treated raw material powders that passed through the sieve.

(2-2) Crushing and mixing of prepared α-phase raw material, β-phase raw material, and other raw materials (2-1) Mixed and heat-treated raw material powder (Tirich α-phase raw material, V-rich α-phase raw material), Then, the β-phase raw material and other raw materials are filled in a ball mill container lined with cemented carbide together with cemented carbide balls and acetone at the ratios shown in Table 2, covered with a lid, and then mixed with crushing by a ball mill. Was done.

(2-3) Mixing with hard dispersed phase raw material cBN powder is added to the raw material pulverized and mixed in (2-2) so that the content ratio of cBN particles after sintering is 40 to 80% by volume. Then, the mixture was further mixed with a ball mill, and the mixed slurry was dried to separate the cemented carbide balls and the mixed powder to obtain a sintered raw material powder.

(3) Sintering The sintered raw material powder obtained in (2-3) was press-molded at a molding pressure of 1 MPa to a size of diameter: 50 mm × thickness: 1.5 mm to obtain a molded product. This molded product was temporarily sintered by raising the temperature to 1000 ° C. and holding it in a vacuum atmosphere of a pressure of 1 Pa or less, and then lowering the temperature to 750 ° C. and further holding the molded product. Then, it is charged into an ultra-high pressure sintering apparatus and sintered at a pressure of 5.5 GPa and a temperature of 1400 ° C., whereby the cBN sintered bodies 1 to 21 of Examples shown in Tables 3 and 4 (Example Baking). Bounds 1 to 21) were prepared.

In each step up to the sintering, it is preferable to prevent the raw material powder from being oxidized, and specifically, the raw material powder is handled in a non-oxidizing protective atmosphere.

For comparison, the same raw material powder as in the examples was prepared, and as shown in Tables 5 and 6, the raw materials were prepared and mixed according to the examples, and further subjected to sintering, and the matters specified in the present invention were obtained. Comparative Examples Sintered 1 to 15 shown in Tables 7 and 8 which are not satisfied were prepared.

Next, the example sintered bodies 1 to 21 and the comparative example sintered bodies 1 to 15 produced above were cut into predetermined dimensions by a wire electric discharge machine. Then, a brazing material is applied to the brazed portion (corner portion) of the insert body made of a WC-based cemented carbide (composition: Co: 5% by mass, TaC: 5% by mass, WC: remaining) having an insert shape of ISO standard CNGA120408. Insert of ISO standard CNGA120408 by brazing with (Cu: 26% by mass, Ti: 5% by mass, Ag: remaining, Ag alloy having a composition), polishing the upper and lower surfaces and the outer circumference, and performing honing treatment. Manufactures cBN-based ultra-high pressure sintered body cutting tools (referred to as Example tools) 1 to 21 of Examples having a shape, and cBN-based ultra-high pressure sintered body cutting tools (referred to as Comparative Example tools) 1 to 15 of Comparative Examples. bottom.

Next, cutting was performed on the tools 1 to 21 of the example and the tools 1 to 15 of the comparative examples under the following cutting conditions, and the number of interruptions until the tool life was reached was measured.

Work Material: Carburized Hardened Steel (JIS / SCM415, Hardness: HRC58-62) Equally spaced in the length direction 8 vertical grooved round bars Cutting speed: 180 m / min
Notch: 0.2 mm
Feed: 0.1 mm / rev
Therefore, a dry cutting test of high hardness steel was carried out.

The tool life is defined as the number of interruptions until the cutting edge of each tool reaches chipping or chipping, or the maximum amount of wear on the flank surface of the cutting edge reaches 150 μm. The presence or absence of wear and the amount of wear were confirmed.
Table 9 shows the results of the above cutting test.

From the results shown in Table 9, in the intermittent cutting process in which the cutting depth exceeds 0.1 mm, the sintered body of the example tool is more stable against thermal load than the comparative example tool. It is clear that it has sufficient crack propagation resistance and is excellent in abrasion resistance, chipping resistance, and chipping resistance.

When the cBN sintered body of the present invention is used as a tool base for a cutting tool, it has sufficient crack propagation resistance, is excellent in abrasion resistance, chipping resistance, and chipping resistance, and can extend the life of the tool. Since it is a thing, it is possible to fully and satisfactorily cope with high performance of the cutting machine, labor saving and energy saving of the cutting process, and cost reduction.

1 cBN
2 α phase (Ti / V is about 2/3 to 3/2)
3 β phase 4 A region 5 B region 6 α phase (Ti / V is about 3 / 2-7 / 3)
7 α phase (Ti / V is about 3/7 to 2/3)

Claims (3)

A cBN sintered body having a coupled phase with cubic boron nitride,
In the cross section of the cBN sintered body,
The cubic boron nitride occupies 40 to 80 area%.
The binding phase has an α phase and a β phase, and has an α phase and a β phase.
When the composition of the α phase is represented by the composition formula: (Ti _1-x V _x ) (C _1-y N _y ), the average composition thereof is x = 0.30 to 0.70, y = 0. It is .00 to 0.50 and is present in the bonded phase in an area% of 70 to 97.
The β phase is at least one of an oxide, nitride, and boride of Al having an average particle size of 0.05 to 0.40 μm, and is present in the bonded phase in an area of 3 to 20 area%.
Further, the α phase has an A region and a B region, and has an A region and a B region.
When the composition of the A region is represented by the composition formula: (Ti _1-xA V _xA ) (C _1-yA N _yA ), xA = 0.10 to 0.30, yA = 0.00 to 0. 50
When the composition of the B region is represented by the composition formula: (Ti _1-xB V _xB ) (C _1-yB N _yB ), xB = 0.70 to 0.90, yB = 0.00 to 0. 50
The sum of the ratios of the A region and the B region to the α phase is 50 area% or more.
A cBN sintered body characterized in that. The difference between the average composition x of V in the α phase and the average value xA _avg of the V content ratio xA in the A region is defined as x-xA _avg .
When the difference between the average composition x of V in the α phase and the average value xB _{avg of the V content ratio xB in the B region is xB avg} −x,
| (X-xA _avg )-(xB _avg- x) | is 0.20 or less.
The cBN sintered body according to claim 1. A cutting tool using the cBN sintered body according to claim 1 or 2 as a tool base.

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