JP2020131293A - Cutting tool made of cubic crystal boron nitride-based sintered body - Google Patents

Abstract

To provide a cBN tool which is excellent in chipping resistance and crater abrasion resistance.SOLUTION: At least a blade tip of a cBN tool is formed from a cBN sintered body which contains cBN particles as a hard phase and contains Ti compound particles as a binder phase. In the cBN tool, an average particle diameter of the Ti compound particle is 250nm or less, there is a W-Co-Fe phase, in which W component, Co component and Fe component co-exist, on a boundary face of the Ti compound particles, and the W-Co-Fe phase exists between the cBN particles and thus constitutes a heat transmission path. When element mapping of a cross section of the cBN sintered body is performed with SEM, a number ratio of cBN particles, which are connected to one another via the W-Co-Fe phase, is 20% or more of the total number of cBN particles in an observation view.SELECTED DRAWING: Figure 3

Description

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

The cBN sintered body has high hardness and thermal conductivity next to diamond, and has a low affinity for iron-based materials. Therefore, it is a tool for cutting iron-based work materials such as steel and cast iron. 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 in order to meet the required performance. There is.

For example, Patent Document 1 states that a cBN sintered body for cutting iron-based difficult-to-cut materials such as hardened steel, FCD cast iron, and ADI cast iron has a cBN component of 87% or more and 99% or less in volume%. 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, and 6a elements M is 1.3 or more and 1.6 or less is 0.5 μm to be composed of a compound of at least one element selected from 4, 5a, 6a 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 is set. When the particle size showing 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 in which the average particle size is d ₂ and the d ₂ is 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 second component of the relatively coarse grains that composes reduces 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 , Ti-based compound group, and the Ti-based compound group contains a first fine particle component composed of particles having a particle size of 0.1 μm or less and containing at least one compound containing Ti. 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 for 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 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 abrasion resistance of the composite sintered body are improved.

Japanese Patent No. 4528786 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. Since heat is efficiently dissipated to and the rise in cutting edge temperature during cutting can be suppressed, sinter wear resistance is improved, but on the other hand, intermittent cutting of high hardness steel (for example, HRC58-62) is performed. In the above, 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 Although we are trying to achieve both fracture resistance and wear resistance, 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 (the first component of Patent Document 3 and the 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 it is subjected to intermittent cutting of high hardness steel.

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

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), but when the bonded phase particles are miniaturized. As described above, since the interface between the bonded phase particles increases, the thermal conductivity decreases and the crater wear resistance decreases, while tentatively compensating for the decrease in thermal conductivity and crater wear resistance. When the cBN content is increased in order to enhance the properties, 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 in order to improve 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 abrasion resistance as described above, but cBN As the bonded phase structure of the sintered body, a W-Co-Fe phase having excellent thermal conductivity in which the W component, the Co component and the Fe component coexist in the bonded phase is formed, and further, this W-Co-Fe phase is formed. , When a bonded phase structure existing at the interface of the Ti compound particles and thermally connecting the cBN particles via the W—Co—Fe phase is formed, the decrease in thermal conductivity of the cBN sintered body is suppressed. As a result, it has been found that the sinter abrasion resistance of the cBN tool is improved.

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

Here, at the interface of the Ti compound particles constituting the bonded phase, there is a W—Co—Fe phase in which the W component, the Co component, and the Fe component coexist, and the W—Co—Fe phase communicates with each other of the cBN particles. A cBN tool having a coupled phase structure having the function of a heat conduction path that is thermally connected can be manufactured, for example, as follows.

First, a powder for forming a bonded phase made of a Ti compound is pulverized so that the particle size is 30 nm or more and 250 nm or less, and the finely pulverized powder contains nano W powder, nano Co powder, nano Fe powder, and cBN. A mixed powder of cBN particle powder, which is a hard component of the sintered body, is added and then mixed to prepare a powder compact, and then the powder compact is sintered under ultra-high pressure sintering conditions. Bonded phase composed of Ti compound particles A bonded phase structure in which a W-Co-Fe phase exists at the interface of the powder and the W-Co-Fe phase acts as a thermal conduction path that thermally connects the cBN particles to each other. A cBN sintered body having the above 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, or the like is 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 coupled 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. It also has crater wear resistance, 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 bonding phase. In the body cutting tool
The average particle size of the Ti compound particles is 250 nm or less.
At the interface of the Ti compound particles, there is a W—Co—Fe phase in which the W component, the Co component, and the Fe component coexist.
The W—Co—Fe phase is made of a cubic boron nitride-based sintered body, which is characterized in that a heat transfer path is formed by connecting cubic boron nitride particles to each other and existing without interruption. Cutting tools.
(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—Fe phases are not interrupted and are mutually interposed via the W—Co—Fe phase. The number of cubic boron nitride particles connected to the above (1) is 20% or more of the total number of cubic boron nitride particles present in the observation field. Cutting tool made of base sintered body.
(3) The total content of W, Co, and Fe constituting the W—Co—Fe phase in the cubic boron nitride base sintered body is 2% by mass or more and 10% by mass or less, and The cutting tool made of a cubic boron nitride-based sintered body according to (1) or (2) above, wherein the Fe content is 0.03% by mass or more and 1.0% by mass or less.
(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-Fe phase in which the W component, the Co component, and the Fe component coexist exists at the interface of the Ti compound particles constituting the bonded phase of the cBN sintered body, and this W-Co Since the −Fe phase has a bonded phase structure that acts as a heat conduction path between the cBN particles by connecting the cBN particles to each other and existing without interruption, cBN sintering is performed without increasing the cBN content. The thermal conductivity of the body can be improved, and as a result, the sinter abrasion 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—Fe phase formed at the interface of the Ti compound particles constituting the bonded phase of the cBN sintered body has a grain growth suppressing effect of the Ti compound particles and is bonded. Since the coarsening of the phase particles is suppressed, 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. Even if the bonded phase particles are fine, the W—Co—Fe phase forms a heat conduction path between the cBN particles, so that the heat conductivity of the cBN sintered body is lowered. 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 abrasion resistance, and the life of the tool can be extended even when it is subjected to intermittent cutting conditions in which high heat is generated and a high load acts on the cutting edge.

An image obtained by cross-section of the cBN sintered body of the present invention by a scanning electron microscope (hereinafter referred to as "SEM"; magnification: 50,000 times) -energy dispersive X-ray spectroscopy (hereinafter referred to as "EDS"). (A) to (c) are element mapping diagrams of W, Co, and Fe, respectively, and (d) and (e) are B, respectively, showing an example of an element mapping diagram obtained by binarizing the above. It is an element mapping diagram of N. In each of the images, the region where the element exists is a white region. (A) is a schematic schematic diagram showing the structure state of cBN particles obtained by superimposing element mapping diagrams of B and N, and (b) is obtained by superimposing element mapping diagrams of W, Co and Fe. It is a schematic schematic diagram which shows the structure state of the W—Co—Fe phase. It is a schematic schematic diagram which shows the structure state of the cBN sintered body prepared by superimposing FIG. 2 (a) and FIG. 2 (b). FIG. 3A is a schematic explanatory view for determining whether or not cBN particles are connected via the W—Co—Fe phase in the cBN sintered body having the structure shown in FIG. 3, and FIG. The state in which the cBN particles are connected via the −Co—Fe phase is shown, and (b) is a schematic description showing the state in which the cBN particles in the upper right of the figure are not connected via the W—Co—Fe phase. It is a figure. It should be noted that FIGS. 2 to 4 above are schematic views for facilitating the understanding of the present invention and do not directly correspond to the element mapping diagram of FIG.

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 also contains Ti compound particles such as TiC particles, TiN particles or TiCN particles as a main bonding phase component. ..
The main bonding phase component is Ti compound particles, but in addition to this, an impurity component that is inevitably mixed in during the manufacturing process, or Al such as Al ₂ O ₃ , AlN, and TiAlN, which are reaction products during sintering. It is permissible for compounds and the like to be contained in the binding phase.

Content ratio of cBN particles in the cBN sintered body:
In the cBN sintered body of the present invention, when the content ratio of the cBN particles in the cBN sintered body is less than 40% by volume, 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 reduced and the life as a tool is also shortened. Therefore, the content ratio of 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. Since voids that are the starting points of cracks are likely to be generated and the fracture resistance is lowered, the content ratio of cBN particles in the cBN sintered body is preferably 85% by volume or less.
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 and exhibiting the best characteristics as a cBN tool is preferably 50 to 75% by volume, more preferably 60% by volume. The range is 70% by volume or less.

Measurement / calculation of the content ratio of cBN particles:
Regarding 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 ratio of the cBN particles is calculated by calculating the area occupied by the cBN particles and dividing the value by the total image area. Then, by regarding this area ratio as a volume%, the content ratio (volume%) of the cBN particles can be measured.
Further, in the present invention, 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 five 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, the 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 grow from the interface between the cBN particles and the bonding phase caused by the stress applied to the cutting edge during tool use, or cracks that grow 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 measurement / calculation of the average particle size of the cBN particles can be obtained 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 by 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 size 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 values obtained by performing the above processing on at least three images is defined as the average particle size (μm) of the cBN particles of the cBN sintered body.

Bonded phase structure:
In the cBN sintered body of the present invention containing Ti compound particles as a bonding phase, when the cross section of the cBN sintered body is elementally analyzed by SEM-EDS, for example, an element mapping diagram as shown in FIG. 1 can be obtained.
1 (a) to 1 (e) show an example of an element mapping diagram for a cross section of the cBN sintered body of the present invention acquired by SEM-EDS at a magnification of 50,000, while FIG. 1 (a) shows W, ( b) is an element mapping diagram for Co, (c) is Fe, (d) is B, and (e) is N.

FIG. 2 (a) is obtained by superimposing the mapping diagrams of the B component and the N component (see FIGS. 1 (d) and 1 (e)) using the element mapping diagrams as shown in FIGS. 1 (a) to 1 (e). ) Can be confirmed as a schematic diagram of the cBN particles in the cBN sintered body of the present invention, and a mapping diagram of the W component, the Co component, and the Fe component (FIG. 1 (a)). By superimposing (b) and (c), the presence of the W—Co—Fe phase in the bonded phase of the cBN sintered body of the present invention can be determined as shown in the schematic diagram of FIG. 2 (b). You can check.

Further, by further superimposing the element mapping diagrams shown in FIGS. 2A and 2B, the structure of the cBN sintered body of the present invention can be confirmed as shown in the schematic diagram of FIG. ..
Note that FIGS. 2 and 3 are schematic views for easily understanding the existence of the W—Co—Fe phase in the bonded phase and the structural state of the cBN sintered body, and the element mapping of FIG. It should be noted that it does not correspond directly to the figure.

From FIGS. 2 and 3, in the cBN sintered body of the present invention, the W—Co—Fe phase in which the W component, the Co component, and the Fe component coexist is at the interface of the Ti compound particles constituting the bonding phase. , CBN particles are connected to each other and exist without interruption, but it is understood that the W-Co-Fe phase is not formed (does not exist) so as to surround (surround) the cBN particles. Will be done.

The W-Co-Fe phase has a higher thermal conductivity than the Ti compound particles, exists seamlessly between the cBN particles, and has a function as a heat transfer path connecting the cBN particles, so that the cBN firing is performed. The thermal conductivity of the body is improved.
Further, the W-Co-Fe phase suppresses coarsening of the bonded phase particles under high temperature and high pressure sintered conditions, and thus contributes to the maintenance of a fine bonded phase structure of the cBN sintered body.

In order to improve the thermal conductivity of the cBN sintered body, when the cross section of the cBN sintered body is observed by SEM and the element mapping is obtained, the cBN particles connected to each other via the W—Co—Fe phase. The number of cBN particles 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 greatly improving the thermal conductivity of the cBN sintered body cannot be expected.

In addition, the cross section of the cBN sintered body was subjected to qualitative and quantitative analysis using an electron probe microanalyzer (hereinafter referred to as "EPMA"), and the elements detected by the qualitative analysis were subjected to W, Co and Fe by the ZAF quantitative analysis method. When the content (% by mass) of is determined, W and Co occupying the total of Ti, Al, B, N, C, O, W, Co, and Fe in the entire cBN sintered body as 100% by mass. The total content of Fe is preferably 2% by mass or more and 10% by mass or less, and the Fe content is preferably 0.03% by mass or more and 1.0% by mass or less.
This is because if the total content of W, Co and Fe is less than 2% by mass, the effect of improving thermal conductivity cannot be obtained, while if it is 10% by mass or more, the coarse agglomerates of the W—Co—Fe phase Is formed, which is the starting point of chipping, and the chipping resistance is reduced.
In particular, when the Fe content in the W—Co—Fe phase is 0.03% by mass or more, the effect of improving thermal conductivity is large, but when the Fe content exceeds 1.0% by mass, the formation tendency of coarse agglomerates The content of Fe in the W—Co—Fe phase is preferably 0.03% by mass or more and 1.0% by mass, because this becomes the starting point of chipping.

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 250 nm or less, preferably 30 nm or more and 200 nm or less, because it causes a decrease in strength and is likely to cause chipping when used as a cBN tool. Is desirable.
In the present invention, even when the average particle size of the Ti compound particles is refined to 250 nm or less, or 30 nm or more and 200 nm or less, and the length of the interface between the Ti compound particles is increased, the Ti compound is used. Since the W—Co—Fe phase having a function as a heat transfer path is present at the interface of the particles, the decrease in thermal conductivity of the cBN sintered body is prevented, and as a result, the decrease in crater wear resistance is prevented. To.

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 a crystal orientation analyzer attached to a transmission electron microscope (hereinafter, referred to as “TEM”). More specifically, in order to observe Ti compound particles, a section polished to a thickness equal to or less than the crystal particle size is set in the TEM, and the section is irradiated with an electron beam accelerated to 200 kV. Then, the 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 precession-irradiating the section 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 obtain 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 measurement / calculation is carried out in a plurality of observation regions (three or more locations), and the average value 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 the presence of the W—Co—Fe phase in the bonded phase, but a specific method for measuring the thermal conductivity κ of the cBN sintered body is For example, it 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 an Xe flash analyzer, and the thermal conductivity κ is calculated using the following formula.
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 blended so as to be 40 to 85% by volume (more preferably 60% by volume or more and 70% 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. For example, these raw material powders are filled in a cemented carbide container together with cemented carbide balls and acetone, and pulverized and mixed by a ball mill.
Then, nano W powder (particle size: 800 nm or less), nano Co powder (particle size: 30 nm or less), and nano Fe powder (particle size: 100 nm or less) forming a W—Co—Fe phase in the cBN sintered body, Further, cBN particles having an average particle size of 0.2 to 8 μm, which is a hard phase of the cBN sintered body, 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 sintering conditions of, for example, a pressure of 5 GPa or higher and a temperature of 1200 to 1600 ° C. or higher, so that the interparticle interface of the Ti compound particles constituting the bonded phase In addition, a cBN sintered body having a bonded phase structure in which the W—Co—Fe 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.
Further, from FIG. 2 (b) showing a schematic diagram of the W—Co—Fe phase in the cBN sintered body and FIG. 3 showing a schematic diagram of the cBN sintered body structure, the Ti compound particles constituting the bonded phase It is observed that the W—Co—Fe phase is present at the interface of the cBN particles without interruption by connecting the cBN particles to each other.
On the other hand, it is understood by the explanation described later that the W-Co-Fe phase does not exist (is not formed) so as to surround (surround) the cBN particles.

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, or the like is performed to at least the cutting edge. However, it is possible to manufacture a cBN tool having a desired insert shape composed of the cBN sintered body and having excellent fracture resistance and abrasion 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 cemented carbide balls 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. Then, 12 hours after adding the nano W powder having an average particle size of 500 nm to 900 nm, the nano Co powder having an average particle size of 20 nm to 40 nm, and the nano Fe powder having an average particle size of 60 nm to 80 nm as the W—Co—Fe phase. Wet-mixed for ~ 24 hours and dried.
Then, a molded product was obtained by press molding with a hydraulic press at a molding pressure of 1 MPa to a size of diameter: 50 mm × thickness: 1.5 mm.
Next, the molded product was heat-treated by holding it at a predetermined temperature in the range of 1000 to 1300 ° C. for 30 to 60 minutes in a vacuum atmosphere at a pressure of 1 Pa, and then charged into a normal ultra-high pressure sintering apparatus. The cBN sintered bodies 1 to 10 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 11 of the present invention produced above are polished with a diamond grindstone, divided by a wire electric discharge machine, and further, Co: 5% by mass and TaC: 5% by mass. , WC: In the brazed part (corner part) of the WC-based cemented carbide insert body having the remaining composition and the shape of ISO standard CNGA120408, Cu: 26%, Ti: 5%, Ag: Remaining The cBN tools 1 to 12 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 circumference polishing and honing processing. Was produced.

For comparison, Comparative Examples cBN sintered bodies 1 to 7 were prepared using almost the same method as in Examples.
However, as shown in Table 2, Comparative Examples cBN sintered bodies 1 to 6 satisfy the condition of "adding nano W powder, nano Co powder, and nano Fe powder" in the manufacturing process of the above example. Not.
Further, in Comparative Example 7, the average particle size of the Ti compound particles of the cBN sintered body does not satisfy the conditions specified in the present invention.
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 Examples.

The content ratio (volume%) of cBN particles was measured and calculated for the cBN sintered bodies 1 to 12 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 portion 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 defined as the content ratio (volume%) of the cBN particles.
The observation area used for image processing is a square area 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 area of about 15 μm × 15 μm). And said.
Tables 1 and 2 show the content ratio (volume%) of the cBN particles.

Further, with respect to the cBN sintered bodies 1 to 12 of the present invention and the cBN sintered bodies 1 to 7 produced above, the W-Co-Fe phase was increased by 50,000 times that of SEM-EDS in an observation region of 15 μm × 15 μm. The existence of was confirmed.
For example, as shown in the schematic diagram of FIG. 2B, Ti compound particles are obtained by elemental mapping obtained by observing a cross section of the cBN sintered body of the present invention with SEM (magnification: 50,000 times) -EDS. It was confirmed that the W-Co-Fe phase was present at the mutual interface and that the cBN particles were connected to each other and existed without interruption. Further, as is clear from FIG. 2B, it was confirmed that the periphery of the cBN particles was not covered (surrounded) by the W—Co—Fe phase.
Next, the number of cBN particles connected to each other without interruption via the W—Co—Fe phase was counted, and the ratio of the cBN particles existing in the region to the total number was determined.
In addition, the cross section of the cBN sintered body is subjected to qualitative and quantitative analysis using EPMA, and the elements detected by the qualitative analysis are subjected to the ZAF quantitative analysis method, and W, Co, Fe, which are contained in the entire cBN sintered body. When the total content of B, N and Ti, Al, C, O is 100% by mass, W accounts for the total content of W, Co, Fe, B, N, Ti, Al, C, O. And the ratio of the total content of Co and Fe (mass%) and the ratio of the content of Fe (% by mass) were measured.
Tables 1 and 2 show the number ratio (%) of cBN particles connected via the W—Co—Fe phase, the total content (mass%) of W, Co, and Fe, and the content of Fe (mass%). ) Is shown.

The specific measurement / calculation method of the number ratio of cBN particles connected via the W—Co—Fe phase is as follows.
Elemental mapping of W, Co, Fe, B, and N is performed on the cross section of the cBN sintered body with SEM (magnification: 50,000 times) -EDS, and each mapping image shows the part where the target element does not exist in black and the part where the target element exists. Is white, black is 0, and white is acquired as a 256-step monochrome image of 255, and the Auto function of the Threat tool of the image analysis software ImageJ is set so that the position where the element exists is white in each monochrome image. By determining the threshold value using the above and performing the binarization process, an element mapping image of each element as shown in FIG. 1 is obtained.

By superimposing B and N of the obtained images and extracting the overlapping regions, an elemental mapping image of B and N (see the schematic diagram of FIG. 2A) is obtained. In the same manner, W, Co, and Fe are overlapped and the overlapping region is extracted to obtain an element mapping image of W, Co, and Fe (see the schematic diagram of FIG. 2B).
By superimposing the element mapping image of B and N and the element mapping image of W, Co and Fe, an image in which the cBN particles and the W—Co—Fe phase are integrated (see the schematic diagram of FIG. 3) is obtained.

Next, the size of FIG. 3 is resized with image editing software (Adobe Photoshop) so that one pixel is 2 nm square. The resized FIG. 3 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 contiguous, that is, the elements are continuously present. It is defined as being connected. In other words, if even one pixel having the numerical value 0 exists between the pixel having the numerical value 255 and the pixel having the numerical value 255, it means that they are discontinuous and not connected.

Next, the method of obtaining the cBN particles connected via the W—Co—Fe phase from the numerical matrix is as follows.
In FIG. 4A, the size is changed so that one pixel becomes a 2 nm square as in FIG. 3, and converted into a numerical matrix. The pixel having the numerical value 255 of the matrix obtained here is the region of the cBN particle and the W—Co—Fe phase, and one pixel is arbitrarily selected from the cBN region among the pixels having the numerical value 255.
The numerical value of the pixel of FIG. 4A at the same position as the pixel selected in FIG. 3 is changed from, for example, 255 to 160. That is, the numerical value of one pixel in any one cBN region in FIG. 4A is changed from 255 to 160. Of the eight pixels surrounding the modified pixel, all pixels with a numerical value of 255 are replaced with 160. Here, the work of replacing all the pixels having a numerical value of 255 out of the eight pixels surrounding each pixel replaced with 160 with 160 is repeated. The finally obtained matrix of numerical values of 0, 160, and 255 is output as an image. Since the numerical value 160 becomes gray when output as an image, the obtained image becomes an image of three colors of white, black, and gray as shown in FIGS. 4A and 4B. In the obtained image, it is assumed that the gray BN particles are cBN particles connected via the W-Co—Fe phase, the number of the cBN particles 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. 2A.

For example, when the W-Co-Fe phase is interrupted, that is, between a pixel having a numerical value of 255 and a pixel having a numerical value of 255, one or more pixels having a numerical value of 0 exist and are discontinuous. In this case, the cBN particles that are not connected as shown in FIG. 4 (b) (cBN particles in the upper right corner of FIG. 4 (b)) are not converted to gray.
That is, in FIG. 4A, all three cBN particles are treated as being connected via the W—Co—Fe phase, while according to FIG. 4B, among the three cBN particles, The two particles are connected via the W-Co-Fe phase, but the remaining one (cBN particles in the upper right corner of FIG. 4B) is not connected via the W-Co-Fe phase. I handled it.
In the image processing performed in paragraph 0051, for example, by using the Flod Fill Tool of the image analysis software ImageJ, cBN particles connected to any one cBN particle via the W-Co-Fe phase can be obtained. It can be determined in the same way.
The number ratio (% number) of cBN particles connected by the W—Co—Fe 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 was performed. And image analysis is performed, and the average value of at least 3 fields of view is used.
Tables 1 and 2 show the number ratio (number%) of cBN particles connected by the W—Co—Fe phase.

The average particle size of the 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 a crystal orientation analyzer attached to the TEM. More specifically, in order to observe Ti compound particles, a section polished to a thickness equal to or less than the crystal particle size is set in the TEM, and the section is irradiated with an electron beam accelerated to 200 kV. Then, the observation is performed in the 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 precession-irradiating the section 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 obtain 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 measurement / calculation is carried out in a plurality of observation regions (3 regions or more), 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 12 of the present invention and the cBN sintered bodies 1 to 7 of Comparative Examples prepared above was 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 an Xe flash analyzer, and the thermal conductivity κ is calculated using the following formula.
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 12 of the present invention and the cBN sintered bodies 1 to 7 of Comparative Examples, 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 12 of the present invention and the comparative examples cBN tools 1 to 7 screwed to the tip of the tool steel tool with a fixing jig, the cutting conditions shown below are applied to 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 5 slits at equal intervals in the axial direction of the work material)
Cutting speed: 150 m / min,
Feed: 0.15 mm / rev,
Notch: 0.15 mm,
A dry intermittent cutting test of outer circumference processing 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 surface 150 seconds after the start of cutting is observed with a laser microscope, and the maximum depth of crater wear is determined by comparing 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: Inferior 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 depth of crater wear is 40 μm or more)

According to the results shown in Tables 3 and 4, in the cBN tools 1 to 12 of the present invention, the Ti compound particles in the bonding phase are fine particles and have excellent chipping resistance, and the cBN particles have mutual heat conduction paths. Since the cBN sintered body is connected via a functional W—Co—Fe 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 Comparative Examples cBN Tools 1 to 7, the average particle size of the Ti compound particles constituting the bonded phase is outside the range of the present invention, or the W—Co—Fe phase is not formed. Therefore, it is inferior in chipping resistance and crater wear resistance, and has a short tool life.
In the cBN tool 11 of the present invention, the Fe content in the W—Co—Fe phase is out of the preferable range specified in the present invention, and in the cBN tool 12 of the present invention, W + Co + Fe in the W—Co—Fe phase. Since the total content is out of the preferable range specified in the present invention, the number of impacts until chipping of the cutting edge is smaller than that of the cBN tools 1 to 10 of the present invention, and the chipping resistance is slightly reduced. Excellent crater wear resistance.
However, when the cBN tools 11 and 12 of the present invention are compared with the cBN tools 1 to 7 of the comparative examples, the cBN tools 11 and 12 of the present invention are superior in terms of both chipping resistance and crater wear resistance. it is obvious.

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-based sintered body in which at least the cutting edge is formed by a cubic boron nitride-based sintered body containing cubic boron nitride particles as a hard phase and Ti compound particles as a bonding phase. In the tool
The average particle size of the Ti compound particles is 250 nm or less.
At the interface of the Ti compound particles, there is a W—Co—Fe phase in which the W component, the Co component, and the Fe component coexist.
The W—Co—Fe phase is made of a cubic boron nitride-based sintered body, which is characterized in that a heat transfer path is formed by connecting cubic boron nitride particles to each other and existing without interruption. Cutting tools. 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-Fe phase is not interrupted and is connected to each other via the W-Co-Fe phase. The cubic boron nitride group sintering according to claim 1, wherein the number of cubic boron nitride particles present is 20% or more of the total number of cubic boron nitride particles present in the observation field. Body cutting tool. The total content of W, Co, and Fe constituting the W—Co—Fe phase in the cubic boron nitride base sintered body is 2% by mass or more and 10% by mass or less, and Fe is contained. The cutting tool made of a cubic boron nitride-based sintered body according to claim 1 or 2, wherein the amount is 0.03% by mass or more and 1.0% by mass or less. The cubic nitriding 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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