JP7068657B2 - Cutting tool made of cubic boron nitride base sintered body - Google Patents

Description

The present invention is a cBN made of a cubic boron nitride (hereinafter referred to as "cBN") based sintered body (hereinafter referred to as "cBN sintered body") having excellent chipping resistance and crater wear resistance. The present invention relates to a sintered body cutting tool (hereinafter referred to as “cBN tool”).

The cBN sintered body has high hardness and thermal conductivity next to diamond, and has low affinity with iron-based materials. Therefore, it is a tool for cutting iron-based work materials such as steel and cast iron. As a result, it has been widely used in the past.
However, the performance required for a cBN tool made of a cBN sintered body differs depending on the type of work material, processing conditions, etc., so some proposals have been made so far to meet the required performance. There is.

For example, Patent Document 1 contains a cBN component of 87% or more and 99% or less in volume% as a cBN sintered body for cutting iron-based difficult-to-cut materials such as hardened steel, FCD cast iron, and ADI cast iron. It is a cBN sintered body having a thermal conductivity of 100 W / m · K or more, and the molar ratio of B to N in the cBN component constituting the cBN sintered body is 1.10 or more and 1.17 or less. The outermost surface of the cBN sintered body containing at least one selected from Co compound, Al compound, W compound and oxygen compound and carbon as a binder component is a group 4a, 5a, 6a element and Al. It was coated with a heat-resistant film having a thickness of 0.5 μm to 12 μm composed of a compound of at least one element selected from among and at least one element selected from C, N, and O. A "cBN sintered body for high-quality surface texture processing" has been proposed.

Further, Patent Document 2 states that "a cBN sintered body having a cBN component of 60% or more and 95% or less in volume%, and the thermal conductivity of the cBN sintered body is 70 W / m · K or more. It has at least one selected from nitrides, carbides, and carbonitrides of group 4a, 5a, and 6a elements as a binder component, and an Al compound having a proportion in the binder of 20% or less in weight%. In the components other than the cBN component, the outermost surface of the cBN sintered body in which the ratio of the sum of the mole numbers of C and N to the sum of the mole numbers of the 4a, 5a, 6a elements M is 1.3 or more and 1.6 or less is From 0.5 μm consisting of a compound of at least one element selected from 4, 5a, 6a group elements and Al, and at least one element selected from C, N, O. A "cBN sintered body for high-quality surface texture processing" coated with a heat-resistant film having a thickness of 12 μm has been proposed.

Further, Patent Document 3 states that "a composite sintered body containing a cBN and a binder, the cBN is contained in the composite sintered body in an amount of 25% by volume or more and 80% by volume or less, and the binder is contained. , Ti-based compound group, and the Ti-based compound group contains at least one compound containing Ti, and is composed of two or more components including at least a first component and a second component. The particle size distribution of the Ti-based compound group in at least one cross section of the composite sintered body is divided into a predetermined particle size range on the horizontal axis, and the vertical axis is the particle size occupied by the particles in each particle size range. When shown by the distribution curve, the particle size distribution curve has a shape having two or more maximum values, and the particle size when showing the maximum maximum value among the maximum values is d ₁ , and the second largest maximum value. When the particle size indicating the value is d ₂ , the average particle size of the first component is d ₁ , the d ₁ is 0.05 μm or more and 0.15 μm or less, and the second component is. A composite sintered body having an average particle size of d ₂ and having d ₂ of 0.15 μm or more and 0.5 μm or less has been proposed.
Then, in the composite sintered body, the first component of the relatively fine particles constituting the binder reduces the crater wear resistance and toughness, but improves the impact chipping resistance, while the binder is used. The constituent second component of the relatively coarse grains lowers the impact chipping resistance, but improves the crater wear resistance and toughness. Therefore, the binder is a composite composed of the combination of the first component and the second component. The sintered body is said to have improved both impact chipping resistance and crater wear resistance.

Further, Patent Document 4 states that "a composite sintered body containing a cBN and a binder, the cBN is contained in the composite sintered body in an amount of 25% by volume or more and 80% by volume or less, and the binder is contained. , Ti-based compound group, the Ti-based compound group contains at least one compound containing Ti, and contains a first fine particle component composed of particles having a particle size of 0.1 μm or less. Further, the second fine particle component is contained together with the first fine particle component, and the second fine particle component is composed of particles having a particle size larger than 0.1 μm and 0.25 μm or less, and the first fine particle component and the second fine particle component. As the fine particle component, a composite sintered body that occupies 90% or more of the area occupied by the binder in at least one cross section of the composite sintered body is proposed. "
The first fine particle component having a particle size of 0.1 μm or less improves the fracture resistance, while the second fine particle component having a particle size larger than 0.1 μm and 0.25 μm or less improves wear resistance. Therefore, it is said that the fracture resistance and wear resistance of the composite sintered body are improved.

Japanese Patent No. 45288786 Japanese Patent No. 4704360 Japanese Patent No. 5504519 Japanese Unexamined Patent Publication No. 2011-207689

According to the cBN tool produced from the cBN sintered body proposed in Patent Documents 1 and 2, since the cBN sintered body has high thermal conductivity, high heat generated during cutting is generated from the cutting edge to other parts. Crater wear resistance is improved because heat is efficiently dissipated to and the temperature rise of the cutting edge during cutting can be suppressed, but on the other hand, intermittent cutting of high hardness steel (for example, HRC58-62) is performed. In, there is a problem that chipping is likely to occur and the tool life is shortened due to this.

Further, in the composite sintered body proposed in Patent Documents 3 and 4, by adjusting the particle size of the particles constituting the bonded phase of the composite sintered body, impact chipping resistance and crater wear resistance, or crater wear resistance, or We are trying to achieve both fracture resistance and wear resistance, but when a cutting tool made from this composite sintered body is used for intermittent cutting of high-hardness steel, the particle size that constitutes the bonded phase of the composite sintered body. The presence of small particles (first component of Patent Document 3 and first fine particle component of Patent Document 4) lowers the thermal conductivity of the composite sintered body and lowers the crater wear resistance. It cannot be said that both chipping resistance and crater wear resistance are sufficiently compatible.
Therefore, it is desired to develop a cBN tool that exhibits excellent crater wear resistance and chipping resistance even when subjected to intermittent cutting conditions of high-hardness steel.

In order to solve the above problems, the present inventors have carried out diligent research on a cBN sintered body having excellent crater wear resistance and chipping resistance, and obtained the following findings.

First, the cBN sintered body is mainly composed of cBN particles which are hard phase components and bonded phase components (for example, Ti compound particles such as TiN particles, TiC particles and TiCN particles), and the bonded phase particles are miniaturized. In this case, since the interface between the bonded phase particles increases, the thermal conductivity decreases and the crater wear resistance decreases as described above, while the decrease in thermal conductivity is tentatively compensated for and the resistance to craters. When the cBN content is increased in order to increase the crater wear resistance, the chipping resistance is lowered as described in Patent Documents 1 and 2.

Therefore, the present inventors have focused on the bonded phase structure of the cBN sintered body for enhancing both the crater wear resistance and the chipping resistance of the cBN tool, and obtained the following findings.
That is, when the particle size of the Ti compound particles constituting the bonded phase of the cBN sintered body is made finer, it is difficult to achieve both chipping resistance and crater wear resistance as described above, but cBN As the bonded phase structure of the sintered body, a W—Co phase in which the W component and the Co component coexist is formed in the bonded phase, and the W—Co phase is the interface of the Ti compound particles and the Ti compound particles and the cBN particles. When the structure structure that exists at the interface with and connects the cBN particles so as to form a heat conduction path between the cBN particles is formed, the heat conductivity of the cBN sintered body is improved, and as a result, the cBN tool is used. It was found that the crater wear resistance of the compound was improved.

That is, in the cBN sintered body, the present inventors form a W—Co phase in which the W component and the Co component coexist at the interface between the fine Ti compound particles and the interface between the Ti compound particles and the cBN particles, and When the W-Co phase has a structure that connects the cBN particles to each other so as to form a heat conduction path between the cBN particles, the cBN tool made of the cBN sintered body is accompanied by high heat generation and is attached to the cutting edge. Even when subjected to intermittent cutting conditions of high-hardness steel on which a high load acts, it exhibits excellent chipping resistance and at the same time excellent crater wear resistance, so it exhibits excellent cutting performance over a long period of use. In addition, it was found that the life of the tool can be extended.

Here, a W—Co phase in which the W component and the Co component coexist exists at the interface between the Ti compound particles constituting the bonded phase and the interface between the Ti compound particles and the cBN particles, and the W—Co phase is cBN. A cBN tool having a bonded phase structure that connects particles to each other and has a function of a heat conduction path can be manufactured, for example, as follows.
First, a powder for forming a bonded phase made of a Ti compound is crushed, and a mixed powder of nano W powder, nano Co powder, and cBN particle powder, which is a hard component of a cBN sintered body, is added to the crushed powder and then mixed. By producing a dust compact and then sintering the dust compact under ultra-high pressure sintering conditions, the interface between the bonded phase particles made of Ti compound particles and the interface between the Ti compound particles and the cBN particles are formed. , A cBN sintered body having a W—Co phase and a bonded phase structure in which the W—Co phase connects the cBN particles to each other and acts as a heat conduction path can be produced.
Next, the cBN sintered body produced above is brazed to the brazed portion (corner portion) of the WC-based cemented carbide insert body, and if necessary, polishing, honing, etc. are performed to at least the cutting edge. Can produce a cBN tool having a desired insert shape composed of the cBN sintered body.
Since the cBN tool produced above has a predetermined bonded phase structure, it has excellent chipping resistance when subjected to intermittent cutting conditions of high-hardness steel in which a high heat is generated and a high load acts on the cutting edge. Since it has both crater wear resistance and crater wear resistance, it exhibits excellent cutting performance over a long period of use and extends the life of the tool.

The present invention has been made based on the above findings.
"(1) Cubic boron nitride base firing in which at least the cutting edge is formed by a cubic boron nitride base sintered body containing cubic boron nitride particles as a hard phase and Ti compound particles as a bonded phase. In compound cutting tools
The average particle size of the Ti compound particles is 250 nm or less, and the average particle size is 250 nm or less.
At the interface between the Ti compound particles and the interface between the Ti compound particles and the cBN particles, a W—Co phase in which the W component and the Co component coexist is present.
The W—Co phase forms a heat transfer path by being present without interruption between cubic boron nitride particles.
When the cross section of the cubic boron nitride-based sintered body is observed by element mapping with a scanning electron microscope, the W-Co phase is not interrupted and is interconnected via the W-Co phase. A cutting tool made of a cubic boron nitride-based sintered body, characterized in that the number of boron particles is 20% or more of the total number of cubic boron nitride particles existing in the observation field .
(2) When the cross section of the cubic boron nitride base sintered body is observed by element mapping with a scanning electron microscope, the W-Co phases are not interrupted and are connected to each other via the W-Co phase. The cubic boron nitride base sintering according to (1) above, wherein the number of cubic boron nitride particles is 55 % or more of the total number of cubic boron nitride particles present in the observation field. Body cutting tool.
(3) The total content of W and Co constituting the W—Co phase in the cubic boron nitride base sintered body is 2% by mass or more and 10% by mass or less. The cutting tool made of a cubic boron nitride-based sintered body according to 1) or (2).
(4) The above-mentioned (1) to (3), wherein the Ti compound particles are any one or more selected from TiN particles, TiCN particles and TiC particles. Cutting tool made of cubic boron nitride based sintered body. "
It is characterized by.

In the cBN tool of the present invention, a W—Co phase in which the W component and the Co component coexist exists at the interface of the Ti compound particles constituting the bonded phase of the cBN sintered body and the interface between the Ti compound particles and the cBN particles. Since this W—Co phase exists without interruption between the cBN particles and has a bonded phase structure that forms a heat conduction path between the cBN particles, the cBN sintered body does not have to increase the cBN content. As a result, the crater wear resistance of the cBN tool can be improved without increasing the cBN content.
Further, in the cBN tool of the present invention, the W—Co phase formed at the interface of the Ti compound particles constituting the bonded phase of the cBN sintered body has a grain growth suppressing action of the Ti compound particles, and the bonded phase particles. The particle size of the bonded phase particles in the cBN sintered body can be reduced to, for example, an average particle size of 250 nm or less, thereby improving the chipping resistance of the cBN tool. Moreover, even if the bonded phase particles are fine, the thermal conductivity of the cBN sintered body does not decrease because the W—Co phase forms a heat conduction path between the cBN particles. As a result, the crater wear resistance of the cBN tool is not reduced.
Therefore, the cBN tool of the present invention is excellent in both chipping resistance and wear resistance even when it is subjected to cutting conditions in which a high heat is generated and a high load acts on the cutting edge, and the life of the tool can be extended.

The cross section of the cBN sintered body of the present invention is elementally mapped by SEM (scanning electron microscope. Magnification: 50,000 times) -EDS, and a schematic schematic diagram showing an image in which cBN particles are superimposed on an image in which W and Co are superimposed. Therefore, the shape and dimensions of each structure do not match the actual structure. It is a schematic schematic diagram for explaining the counting method of the cBN particles connected via the W—Co phase when observing the cross section of the cBN sintered body, (a) is the element mapping diagram of B and N, (a). b) is an elemental mapping diagram of W and Co, (c) is a mapping diagram in which (a) and (b) are superimposed (same as FIG. 1), and (d) is a mapping diagram in which all four cBN particles in the figure are W. -A schematic diagram showing that the three cBN particles in the figure are connected by the W-Co phase, but one cBN particle is not connected by the W-Co phase. Is.

The cBN tool of the present invention will be described below.

The cBN sintered body constituting at least the cutting edge of the cBN tool of the present invention contains cBN particles as a hard phase component and Ti compound particles such as TiC particles, TiN particles or TiCN particles as a main bonded phase component. ..
The main bonded phase component is Ti compound particles, but in addition to this, W compounds such as WC, which is an impurity component inevitably mixed in the manufacturing process, or Al ₂ O ₃ which is a reaction product during sintering. , AlN, TiAlN and the like are allowed to be contained in the bound phase.

Content of cBN particles in the cBN sintered body:
In the cBN sintered body of the present invention, when the content ratio of cBN particles in the cBN sintered body is less than 40% by volume, the unsintered portion where the cBN particles come into contact with each other and cannot sufficiently react with the bonded phase. Although the formation is reduced, on the other hand, the hardness of the cBN sintered body is lowered and the life as a tool is also shortened. Therefore, the content ratio of the cBN particles in the cBN sintered body is set to 40% by volume or more. Is preferable.
On the other hand, when the content ratio of the cBN particles exceeds 85% by volume, the cBN particles have a large number of parts in direct contact with each other and thus have high thermal conductivity, but when used as a cutting tool, they are contained in the sintered body. The content ratio of cBN particles in the cBN sintered body is preferably 85% by volume or less, because voids that are the starting points of cracks are likely to be generated and the fracture resistance is lowered.
Therefore, the content ratio of the cBN particles is preferably 40 to 85% by volume, more preferably 45 to 80% by volume.
Further, the content ratio of cBN particles suitable for reducing the content ratio of cBN particles to exhibit the best characteristics as a cBN tool is preferably 50 to 75% by volume, more preferably 50% by volume or more 60. It is in the range of volume% or less.

Measurement / calculation of the content ratio of cBN particles:
As for the content ratio of cBN particles in the cBN sintered body, the portion corresponding to the cBN particles in the secondary electron image obtained by observing the cross section of the cBN sintered body by SEM is extracted by image processing, and the cBN particles are extracted by image analysis. The area occupied by the cBN particles is calculated, and the area ratio of the cBN particles is calculated by dividing the value by the total area of the image. Then, by regarding this area ratio as a volume%, the content ratio (volume%) of the cBN particles can be measured.
Further, in this measurement, the average value of the values obtained by processing at least three images of the secondary electron images having a magnification of 5,000 obtained by SEM is defined as the content ratio (volume%) of the cBN particles.
The observation region used for image processing is preferably a square region having one side having a length of 5 times the average particle size of the cBN particles. For example, when the average particle size of the cBN particles is 3 μm, 15 μm × When the average particle size of the cBN particles is about 15 μm and the average particle size of the cBN particles is 6 μm, an observation region of about 30 μm × 30 μm is desirable.

Average particle size of cBN particles:
The average particle size of the cBN particles in the cBN sintered body of the present invention is not particularly limited, but is preferably in the range of 0.2 to 8 μm.
This is due to the following reasons.
When the cBN sintered body is used as the cutting edge of a cutting tool, cBN particles having an average particle size of 0.2 to 8 μm are dispersed in the sintered body, so that the cBN particles on the tool surface fall off during use of the tool. It is possible to suppress the occurrence of chipping starting from the uneven shape of the cutting edge that occurs. In addition, the propagation of cracks that propagate from the interface between the cBN particles and the bonded phase caused by the stress applied to the cutting edge during tool use, or cracks that propagate through the cBN particles, is caused by the cBN particles dispersed in the sintered body. It can be suppressed. Therefore, such a cutting tool has excellent fracture resistance.
Therefore, the average particle size of the cBN particles in the cBN sintered body of the present invention is preferably in the range of 0.2 to 8 μm, and more preferably in the range of 0.5 to 6 μm.

Measurement / calculation of average particle size of cBN particles:
The average particle size of the cBN particles can be measured and calculated as follows.
A predetermined region of the cross section of the cBN sintered body (for example, in the case of an average particle size of cBN particles of 3 μm, a region of 15 μm × 15 μm (5 times the average particle size of the cBN particles)) is observed with an SEM to obtain a secondary electron image. obtain. The obtained image is binarized and a portion corresponding to the cBN particles is extracted by image processing, and the maximum length of the portion corresponding to each particle extracted by image analysis is obtained as the diameter of each particle. From this diameter, the volume of each particle is calculated with each particle as a sphere. Based on the obtained volume of each particle, the integrated distribution of particle diameter is obtained. That is, for each particle, the sum of the volume and the volume of the particles having a diameter equal to or less than the diameter of the particles is obtained as an integrated value. For each particle, draw a graph with the volume percentage (%), which is the ratio of the total volume of all particles to the above integrated value, as the vertical axis and the diameter (μm) of each particle as the horizontal axis, and draw the volume percentage. The value of the particle diameter (median diameter) at which is 50% is taken as the average particle size of the cBN particles in one image. Then, the average value of the average particle size obtained by performing the above processing on at least three images is taken as the average particle size (μm) of the cBN particles of the cBN sintered body.

Bonded phase structure:
The cBN sintered body of the present invention contains Ti compound particles as a bonded phase, but when the cross section of the cBN sintered body is elementally analyzed using SEM-EDS (energy dispersive X-ray analysis method), the bonded phase is obtained. The presence of W component and Co component is detected at the interface of the constituent Ti compound particles and the interface between the Ti compound particles and the cBN particles.
From this, it can be seen that a W—Co phase in which the W component and the Co component coexist is formed at the interface of the Ti compound particles constituting the bonded phase and the interface between the Ti compound particles and the cBN particles.
The W-Co phase has a higher thermal conductivity than the Ti compound particles, and by being present without interruption between the cBN particles, it has a function as a heat transfer path, so that the thermal conductivity of the cBN sintered body is improved. At the same time, by suppressing the coarsening of the bonded phase particles, the strength of the cBN sintered body can be maintained and improved.
In order to improve the thermal conductivity of the cBN sintered body, when the cross section of the cBN sintered body is observed with an SEM (scanning electron microscope) and element mapping is obtained, they are interconnected via the W-Co phase. The number of cBN particles present is 20% or more, more preferably 55% or more, of the total number of cBN particles present in the observation field. If it is less than 20%, the effect of improving the thermal conductivity of the cBN sintered body cannot be expected.
In addition, the cross section of the cBN sintered body is qualitatively and quantitatively analyzed using EPMA (electron beam microanalyzer), and the W and Co contents (mass%) of the elements detected by the qualitative analysis are determined by the ZAF quantitative analysis method. When determined, the total content of W and Co in the entire cBN sintered body is 2% by mass or more and 10 when the total of Ti, Al, B, N, C, O, W and Co is 100% by mass. It is preferably mass% or less.
This is because when the total content of W and Co is less than 2% by mass, the effect of improving thermal conductivity cannot be obtained, while when it is 10% by mass or more, coarse agglomerates of the W—Co phase are formed. This is the starting point for chipping, and the chipping resistance is reduced.

Average particle size of Ti compound particles:
The size of the Ti compound particles constituting the bonded phase affects the strength and thermal conductivity of the cBN sintered body, and when the average particle size exceeds 250 nm, the thermal conductivity is improved, but on the other hand, the cBN sintered body The average particle size of the Ti compound particles is preferably 250 nm or less, and more preferably 50 to 200 nm, because it causes a decrease in strength and is likely to cause chipping when used as a cBN tool. preferable.
Even when the average particle size of the Ti compound particles is reduced to 250 nm or less or 50 to 200 nm and the length of the interface between the Ti compound particles is increased, in the present invention, between the cBN particles. The presence of the W—Co phase, which exists seamlessly and functions as a heat transfer path, prevents a decrease in the thermal conductivity of the cBN sintered body, and as a result, prevents a decrease in the crater wear resistance.

The average particle size of the Ti compound particles can be measured and calculated as follows, for example.
First, the observation region of the cross section of the cBN sintered body is observed using the crystal orientation analysis device attached to the TEM. More specifically, in order to observe Ti compound particles in a transmission electron microscope, a section polished to a thickness (50 nm) or less similar to the crystal grain size is set, and an electron beam accelerated to 200 kV is applied. By irradiating the section, observation is performed in the range of 400 nm × 500 nm.
The analysis method for obtaining the map data of the crystal orientation in the above range is as follows.
While the section is irradiated with an electron beam tilted at 0.5 to 1.0 degrees, the electron beam is scanned at an arbitrary beam diameter and interval, and the electron diffraction pattern is continuously captured for individual measurement. Analyze the crystal orientation of the points. The conditions for acquiring the diffraction pattern used in this measurement are a camera length of 20 cm, a beam size of 2.2 nm, and a measurement step of 2.0 nm.
Next, the analysis method for discriminating individual crystal grains from the obtained electron diffraction pattern is as follows.
First, when the crystal orientations of the adjacent points of the measurement points are separated by 5 degrees or more, the grain boundary is defined, and the portion other than the grain boundary is defined as a crystal grain, that is, a Ti compound particle.
This image is connected by 4 vertical × 4 horizontal to form an image of 1600 nm in length × 2000 nm in width, and the average particle size of Ti compound particles is obtained by the same procedure as the above-mentioned procedure for obtaining the average particle size of cBN particles. ..
Such measurements and calculations are carried out in a plurality of (three or more) observation regions, and the average value thereof is defined as the average particle size (nm) of the Ti-based compound particles.

Thermal conductivity of cBN sintered body κ:
The cBN sintered body of the present invention has excellent thermal conductivity due to having the above-mentioned bonded phase structure, and a specific method for measuring the thermal conductivity κ of the cBN sintered body is as follows.
First, a measurement sample is cut out from the cBN sintered body, the dimensions of the cut out measurement sample are measured, and then the density ρ is measured by the Archimedes method.
Then, the thermal diffusivity α and the specific heat capacity _CP are measured by the laser flash method using the Xe flash analyzer, and the thermal conductivity κ is calculated using the following equation.
Thermal conductivity κ (W / m ・ K)
= Thermal diffusivity α (mm ² / sec) × Density ρ (g / cm ³ ) × Specific heat capacity CP (J / ( _K · g))

Manufacture of cBN sintered body:
The cBN sintered body of the present invention preferably contains cBN particles having an average particle size of 0.2 to 8 μm, preferably Ti compound particles having an average particle size of 250 nm or less, and preferably has a volume ratio of cBN particles. It can be produced by producing a mixed powder containing 40 to 85% by volume (more preferably 50% by volume or more and 60% by volume or less) and sintering this under ultra-high pressure conditions.
First, raw material powders (TiN powder, TiCN powder, TiC powder, TiAl ₃ powder, Al ₂ O ₃ powder, etc.) constituting the bonded phase are prepared. These raw material powders are, for example, filled in a cemented carbide container together with cemented carbide balls and acetone, and pulverized and mixed by a ball mill.
After that, nano W powder (particle size: 800 nm or less) and nano Co powder (particle size: 30 nm or less) that form a W-Co phase in the cBN sintered body, and further, average particles that become the hard phase of the cBN sintered body. CBN particles having a diameter of 0.2 to 8 μm are added and further mixed by a ball mill to obtain a mixed powder.
Next, the mixed powder is sintered at ultra-high pressure for a predetermined time under a sintering condition of, for example, a pressure of 5 GPa or more and a temperature of 1200 to 1600 ° C. or higher, so that the interparticle interface of the Ti compound particles constituting the bonded phase is formed. In addition, a cBN sintered body having a bonded phase structure in which the W—Co phase is present can be produced.

FIG. 1 is an example of element mapping obtained by SEM observation of the cross section of the cBN sintered body of the present invention produced in the above step, and the W—Co phase is present at the interface of the Ti compound particles constituting the bonded phase. Is observed.
In addition, a trace amount of Al compound and W compound may be formed in the bound phase.

Then, the cBN sintered body produced above is brazed to the brazed portion (corner portion) of the WC-based cemented carbide insert body, and if necessary, polishing, honing, etc. are performed to at least the cutting edge. Can produce a cBN tool having a desired insert shape made of the cBN sintered body and having excellent fracture resistance and wear resistance.

Hereinafter, the cBN sintered body and the cBN tool of the present invention will be described based on examples.

First, TiN powder, TiCN powder, and TiC powder are prepared as raw material powders constituting the bonded phase, and one of the raw material powders selected from these is used as the raw material powder for forming the bonded phase.
Next, the raw material powder for forming the bonded phase selected above is filled in, for example, a cemented carbide container together with a cemented carbide ball and acetone, and pulverized and mixed by a ball mill for 96 hours to 120 hours.
Next, cBN particles having an average particle size of 3 μm are blended so that the content ratio of the cBN particle powder is in the range of 50 to 75% by volume when the total amount of the cBN particle powder and the Ti compound particle powder is 100% by volume. Further, a nano W powder having an average particle size of 500 nm to 900 nm and a nano Co powder having an average particle size of 20 nm to 40 nm were added as a W—Co phase, and then wet-mixed for 12 to 24 hours and dried.
Then, it was press-molded by a hydraulic press at a molding pressure of 1 MPa to a size of diameter: 50 mm × thickness: 1.5 mm to obtain a molded product.
Next, this molded product was held in a vacuum atmosphere at a pressure of 1 Pa at a predetermined temperature in the range of 1000 to 1300 ° C. for 30 to 60 minutes for heat treatment, and then charged into a normal ultra-high pressure sintering apparatus. The cBN sintered bodies 1 to 9 of the present invention were produced by ultra-high pressure high-temperature sintering under the conditions of pressure: 5 GPa and temperature: 1400 ° C.

Next, the upper and lower surfaces of the cBN sintered bodies 1 to 9 of the present invention produced above are polished with a diamond grindstone, divided by a wire discharge processing device, and further, Co: 5% by mass and TaC: 5% by mass. , WC: Remaining composition and in the brazed part (corner part) of the WC-based cemented carbide insert body having the shape of ISO standard CNGA120408, Cu: 26%, Ti: 5%, Ag: Remaining The cBN tools 1 to 9 of the present invention shown in Table 1 having an insert shape of ISO standard CNGA120408 by brazing using an Ag alloy brazing material having a composition consisting of the above, and further performing upper and lower surface and outer peripheral polishing and honing processing. Was produced.

For comparison, Comparative Examples cBN sintered bodies 1 to 7 were prepared using the same method as in Examples.
However, for Comparative Examples cBN sintered bodies 1 to 3, 6 and 7, the "step of adding nano W powder and nano Co powder" in the manufacturing process of the example was described in "Nano W powder and nano Co powder. Comparative Examples cBN sintered bodies 1 to 7 were produced by changing to the step of not adding.
Then, Comparative Examples cBN Tools 1 to 7 shown in Table 2 having an insert shape of ISO standard CNGA120408 were produced by the same method as in the examples.

The content ratio (volume%) of cBN particles was measured and calculated for the cBN sintered bodies 1 to 9 of the present invention and the cBN sintered bodies 1 to 7 of Comparative Examples produced above.
For the content ratio of cBN particles, the area corresponding to the cBN particles of the element mapping obtained by observing the cross section of the cBN sintered body by SEM-EDS was extracted by image processing, and the area occupied by the cBN particles was calculated by image analysis. The area ratio of the cBN particles was calculated by dividing the value by the total area of the image, and the content ratio (volume%) of the cBN particles was measured and calculated by regarding this area ratio as the volume%.
Further, in this measurement, the average value of the values obtained by processing at least three images of the secondary electron images having a magnification of 5,000 obtained by SEM was taken as the content ratio (volume%) of the cBN particles.
The observation region used for image processing is a square region having one side having a length five times the average particle size of the cBN particles (when the average particle size of the cBN particles is 3 μm, an observation region of about 15 μm × 15 μm). And said.
Tables 1 and 2 show the content ratio (volume%) of cBN particles.

Further, with respect to the cBN sintered bodies 1 to 9 of the present invention and the comparative examples cBN sintered bodies 1 to 7 produced above, in an observation region of 15 μm × 15 μm, by 50,000 times the scanning electron microscope (SEM) -EDS. The presence or absence of the W-Co phase was confirmed.
For example, FIG. 1 shows a schematic diagram of an example of elemental mapping obtained by observing a cross section of the cBN sintered body of the present invention with SEM (magnification: 50,000 times) -EDS, and shows an interface between Ti compound particles. It is confirmed that the W-Co phase is present in.
Next, when the presence of the W-Co phase was confirmed, the number of cBN particles connected via the W-Co phase was counted, and the ratio of the cBN particles present in the region to the total number was determined. ..
In addition, the cross section of the cBN sintered body is qualitatively and quantitatively analyzed using EPMA (electron beam microanalyzer), and the elements detected by the qualitative analysis are Ti, Al, B in the entire cBN sintered body by the ZAF quantitative analysis method. , N, C, O, W, and Co were measured, and the total content (% by mass) of W and Co was measured when the total was 100% by mass.
Tables 1 and 2 show the number ratio (%) of cBN particles connected via the W—Co phase and the total content (mass%) occupied by W and Co.

The specific measurement / calculation method of the number ratio of cBN particles connected via the W—Co phase is as follows.
Elemental mapping of W, Co, B, and N is performed on the cross section of the cBN sintered body with SEM (magnification: 50,000 times) -EDS. Then, black is acquired as 0 and white is acquired as a 256-step monochrome image of 255, and the Auto function of the Threathold tool of the image analysis software ImageJ is used so that the position where the element exists is white in each monochrome image. The elemental mapping image of each element is obtained by determining the threshold value and performing the binarization process.
As shown in FIG. 2A, B and N of the obtained images are overlapped, and the overlapped region is extracted to obtain an elemental mapping image of B and N. By the same method, as shown in FIG. 2B, W and Co are overlapped and the overlapped region is extracted to obtain an elemental mapping image of W and Co. The obtained FIG. 2A is an image in which cBN particles are extracted, and FIG. 2B is an image in which the W-Co phase is extracted. By superimposing FIGS. 2 (a) and 2 (b), FIG. 2 (c), which is an image in which the cBN particles and the W-Co phase are integrated, can be obtained.
Next, the obtained FIG. 2C is resized with image editing software (Adobe Photoshop) so that one pixel becomes a 2 nm square. The resized FIG. 2C is converted into a numerical matrix using graph creation software (HULINKS IGOR PRO). At this time, the pixel in the white area has a numerical value of 255, and the pixel in the black area has a numerical value of 0. In the resulting matrix, if any one of the eight pixels surrounding the pixel with the number 255 is the number 255, then the pixel with the number 255 is continuous, that is, the elements are continuously present. It is defined as being connected. In other words, if even one pixel having a numerical value of 0 exists between a pixel having a numerical value of 255 and a pixel having a numerical value of 255, it means that they are discontinuous and not connected.
Next, the method of obtaining the cBN particles connected via the W—Co phase from the numerical matrix is as follows.
Similar to FIG. 2 (c), FIG. 2 (a) is resized so that one pixel becomes a 2 nm square, and converted into a numerical matrix. All the pixels having the numerical value 255 of the matrix obtained here are the regions of the cBN particles, and one pixel is arbitrarily selected from the pixels having the numerical value 255.
For example, the numerical value of the pixel in FIG. 2 (c) at the same position as the pixel selected in FIG. 2 (a) is changed from 255 to 160. That is, the numerical value of one pixel in any one cBN region in FIG. 2C is changed from 255 to 160. Of the eight pixels surrounding this modified pixel, the pixel with a numerical value of 255 is replaced with 160. Here, the work of replacing the pixel whose numerical value is 255 out of the eight pixels surrounding the pixel replaced with 160 with 160 is repeated. The obtained matrix of numerical values of 0, 160 and 255 is output as an image. Since the numerical value 160 is gray, as shown in FIGS. 2 (d) and 2 (e), the gray BN particles are assumed to be cBN particles connected via the W-Co phase, and the number thereof. Is counted, and the ratio is calculated from the total number of cBN particles. The total number of cBN particles can be obtained by image analysis of FIG. 2 (a).
For example, in FIG. 2 (c), when the W-Co phase is interrupted, that is, there is a pixel having one or more numerical values of 0 between a pixel having a numerical value of 255 and a pixel having a numerical value of 255, which is discontinuous. In the case of, the cBN particles that are not connected as shown in FIG. 2 (e) remain black and are not converted to gray.
That is, in FIG. 2 (d), all four cBN particles are treated as being connected via the W—Co phase, while according to FIG. 2 (e), three of the four cBN particles are treated. The particles were treated as being connected via the W-Co phase, but the remaining one (cBN particles in the upper right of the figure) was not connected via the W-Co phase.
By using the Floor Fill Tool of the image analysis software ImageJ, it is possible to similarly discriminate the cBN particles connected to any one cBN particle via the W-Co phase.
The number ratio (% of the number) of cBN particles connected by the W-Co phase was measured at a magnification of 50,000 times, and the images were connected so as to be 8 μm in length × 12 μm in width to form one field of view, and then image processing and images. Perform analysis and use the average value of at least 3 fields of view.
Tables 1 and 2 show the number ratio (number%) of cBN particles connected by the W—Co phase.

The average particle size of Ti compound particles can be measured and calculated as follows.
First, the observation region of the cross section of the cBN sintered body is observed using the crystal orientation analysis device attached to the TEM. More specifically, in order to observe Ti compound particles in a transmission electron microscope, a section polished to a thickness (50 nm) or less similar to the crystal grain size is set, and an electron beam accelerated to 200 kV is applied. By irradiating the section, observation is performed in a range of 400 nm in length × 500 nm in width.
The analysis method for obtaining the map data of the crystal orientation in the above range is as follows.
While the section is irradiated with an electron beam tilted at 0.5 to 1.0 degrees, the electron beam is scanned at an arbitrary beam diameter and interval, and the electron diffraction pattern is continuously captured for individual measurement. Analyze the crystal orientation of the points. The conditions for acquiring the diffraction pattern used in this measurement are a camera length of 20 cm, a beam size of 2.2 nm, and a measurement step of 2.0 nm.
Next, the analysis method for discriminating individual crystal grains from the obtained electron diffraction pattern is as follows.
First, when the crystal orientations of the adjacent points of the measurement points are separated by 5 degrees or more, the grain boundary is defined, and the portion other than the grain boundary is defined as a crystal grain, that is, a Ti compound particle.
This image is connected by 4 vertical × 4 horizontal to form an image of 1600 nm in length × 2000 nm in width, and the average particle size of Ti compound particles is obtained by the same procedure as the above procedure for obtaining the average particle size of cBN particles.
Such measurements and calculations are carried out in a plurality of observation regions (three or more regions), and the average value thereof is defined as the average particle size (nm) of the Ti-based compound particles.
The results are shown in Tables 1 and 2.

Further, the thermal conductivity λ (W / m · K) of the cBN sintered bodies 1 to 9 of the present invention and the cBN sintered bodies 1 to 7 of Comparative Examples produced above were measured by the following methods.
A measurement sample is cut out from the cBN sintered body, the dimensions of the cut out measurement sample are measured, and then the density ρ is measured by the Archimedes method.
Then, the thermal diffusivity α and the specific heat capacity _CP are measured by the laser flash method using the Xe flash analyzer, and the thermal conductivity κ is calculated using the following equation.
Thermal conductivity κ (W / m ・ K)
= Thermal diffusivity α (mm ² / sec) × Density ρ (g / cm ³ ) × Specific heat capacity CP (J / ( _K · g))
Tables 1 and 2 show the measured values.

Further, the Vickers hardness (HV) was measured with a load of 5 kg on the cross-sectional polished surfaces of the cBN sintered bodies 1 to 9 of the present invention and the comparative examples cBN sintered bodies 1 to 7, and the measured values at 10 measurement points were averaged. By doing so, the hardness (HV) of the sintered body was determined.
Tables 1 and 2 show these values.

Then, with the cBN tools 1 to 9 of the present invention and the comparative examples cBN tools 1 to 7 screwed to the tip of the tool steel cutting tool with a fixing jig, the cutting conditions shown below are shown for each tool. A dry intermittent cutting test was conducted at the site, and the quality of chipping resistance and crater wear resistance as a cutting tool was evaluated.
《Cutting conditions》
Work material: JIS / SCM420 (HRC58-62) round bar
(However, there are two slits at equal intervals in the axial direction of the work material)
Cutting speed: 150m / min,
Feed: 0.15 mm / rev,
Notch: 0.15 mm,
A dry-type intermittent cutting test for outer peripheral machining was performed under the conditions of.
In the above intermittent cutting test, the number of impacts until chipping of the cutting edge was measured as an index of chipping resistance. (If the number of impacts is large, it is judged that the chipping resistance is excellent.)
In addition, as an index of crater wear resistance, the rake face 150 seconds after the start of cutting is observed with a laser microscope, and the maximum depth of crater wear is determined from the comparison with the rake surface before the start of cutting that was observed in advance. It was measured. (The smaller the maximum depth, the better the crater wear resistance.)
Tables 3 and 4 show the cutting test results.
The symbols in the crater wear quality determination column mean the following.
⊚: Excellent crater wear resistance (maximum crater wear depth is less than 20 μm)
◯: Good crater wear resistance (maximum crater wear depth is 20 μm or more and less than 30 μm)
Δ: Poor crater wear resistance (maximum crater wear depth is 30 μm or more and less than 40 μm)
X: Crater wear resistance is very poor (maximum crater wear depth is 40 μm or more).

According to the results shown in Tables 3 and 4, in the cBN tool of the present invention, the Ti compound particles in the bonded phase are fine particles, have excellent chipping resistance, and the cBN particles have the function of a heat conduction path. Since the cBN sintered body is connected via the W—Co phase, the cBN sintered body has good thermal conductivity and is excellent in crater wear resistance.
Therefore, excellent chipping resistance and crater wear resistance are exhibited over a long period of time even under cutting conditions in which high heat is generated and a high load acts on the cutting edge.
On the other hand, in the comparative example cBN tool, even if the bonded phase particles are fine, when the W—Co phase is not formed, the thermal conductivity is lowered and the crater wear resistance is lowered. Further, those in which the bonded phase particles are coarse-grained to improve the thermal conductivity have a short tool life due to the occurrence of chipping, and even in the case where the W—Co phase is formed, the bonded phase particles are coarse-grained. In this case, although the crater wear resistance is slightly improved, the chipping resistance is not sufficient.

Since the cBN tool of the present invention is excellent in chipping resistance and crater wear resistance, the life of the cutting tool can be extended.

Claims (4)

Cutting made of a cubic boron nitride base sintered body whose cutting edge is formed by a cubic boron nitride base sintered body containing cubic boron nitride particles as a hard phase and Ti compound particles as a bonded phase. In the tool
The average particle size of the Ti compound particles is 250 nm or less, and the average particle size is 250 nm or less.
At the interface between the Ti compound particles and the interface between the Ti compound particles and the cBN particles, a W—Co phase in which the W component and the Co component coexist is present.
The W—Co phase forms a heat transfer path by being present without interruption between cubic boron nitride particles.
When the cross section of the cubic boron nitride-based sintered body is observed by element mapping with a scanning electron microscope, the W-Co phase is not interrupted and is interconnected via the W-Co phase. A cutting tool made of a cubic boron nitride-based sintered body, characterized in that the number of boron particles is 20% or more of the total number of cubic boron nitride particles existing in the observation field . When the cross section of the cubic boron nitride-based sintered body is observed by element mapping with a scanning electron microscope, the W-Co phase is not interrupted and is interconnected via the W-Co phase. The cutting tool made of a cubic boron nitride-based sintered body according to claim 1, wherein the number of boron particles is 55 % or more of the total number of cubic boron nitride particles existing in the observation field. .. Claim 1 or 2 is characterized in that the total content of W and Co constituting the W—Co phase in the cubic boron nitride base sintered body is 2% by mass or more and 10% by mass or less. Cutting tool made of cubic boron nitride base sintered body described in. The cubic sinter method according to any one of claims 1 to 3, wherein the Ti compound particles are any one or more selected from TiN particles, TiCN particles and TiC particles. Cutting tool made of base sintered body.

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