JP7161670B2 - Cubic boron nitride-based sintered body and cutting tool - Google Patents

Description

The present invention provides a cubic boron nitride (hereinafter also referred to as "cBN")-based sintered body (hereinafter also referred to as "cBN sintered body") having excellent crack propagation resistance and toughness, and this cBN sintered body It relates to a cutting tool consisting of
In particular, a cBN sintered body with improved crack propagation resistance without reducing toughness by forming a binder phase structure in which Ti compound particles containing Al compound particles are present as the binder phase of the cBN sintered body. Further, it relates to a cBN sintered compact cutting tool that suppresses the occurrence of fractures by improving toughness and crack propagation resistance.

The cBN sintered body has a high hardness and thermal conductivity next to diamond, and has a low affinity with iron-based materials, so it is a tool for cutting iron-based work materials such as steel and cast iron. has been widely used as a
From the viewpoint of improving performance as a material for cutting tools, several proposals have been made to further improve the strength, heat resistance, toughness, hardness, etc. of cBN sintered bodies.

For example, Patent Document 1 discloses a composite sintered body containing cBN and a binder, wherein the cBN is contained in the composite sintered body at 25% by volume or more and 80% by volume or less, and the binder is A composite comprising a group of Ti-based compounds, wherein the group of Ti-based compounds contains at least one compound containing Ti, and is composed of two or more particle components having different average particle sizes. Sintered bodies have been proposed.
More specifically, for example, the Ti-based compound group is composed of two or more components including at least a first component and a second component, and the Ti-based compound group in at least one cross section of the composite sintered body When the particle size distribution is shown by a particle size distribution curve in which the horizontal axis is divided into predetermined particle size ranges and the vertical axis is the proportion of particles in each particle size range, the particle size distribution curve has a maximum value of 2 When the particle size of the case where there are more than _one and the maximum value among the maximum values is d1, the _average particle size of the _first component is d1, and d1 is 0.05 μm or more. 0.15 μm or less, and the particle diameter when the _second largest maximum value is shown is d2, the _second component has an _average particle diameter of d2, and d2 is 0.15 μm A composite sintered body having a thickness of 0.5 μm or less has been proposed.
This composite sintered body is used in cutting tools such as drills, end mills, indexable cutting inserts for drills, indexable cutting inserts for end mills, indexable cutting inserts for milling, and indexable cutting inserts for turning. It is said that when used, both the impact chipping resistance and the crater wear resistance are sufficiently improved, thereby prolonging the tool life.

Further, Patent Document 2 discloses a composite sintered body containing cBN and a binder for the purpose of providing a composite sintered body that achieves both fracture resistance and wear resistance at a high level, cBN is contained in the composite sintered body at 25% by volume or more and 80% by volume or less, the binding material includes a Ti-based compound group, and the Ti-based compound group includes at least one compound containing Ti. and includes a first fine grain component composed of particles having a grain size of 0.1 μm or less, wherein the first fine grain component is the area occupied by the binder in at least one cross section of the composite sintered body In addition, the Ti-based compound group includes a second fine particle component together with the first fine particle component, and the second fine particle component has a particle size of more than 0.1 μm and 0.25 μm or less. Composed of particles, the first fine grain component and the second fine grain component together occupy 90% or more of the area occupied by the binder in at least one cross section of the composite sintered body. body is suggested.

JP 2011-207688 A JP 2011-207689 A

In the cBN sintered bodies shown in Patent Documents 1 and 2, the binding phase of the cBN sintered body is composed of a Ti-based compound group, and the Ti-based compound group is composed of a first component and a second component having different particle sizes. By forming the composite, the binder phase has a mixed grain structure, and the impact chipping resistance, crater wear resistance, chipping resistance, and wear resistance are improved when the cBN sintered body is used as a cutting tool.
However, if the grains that make up the binder phase are simply made finer, the cracks that propagate along the grain boundaries of the binder phase will propagate linearly. , linear cracks propagating through grains occur.
Therefore, when the cBN sintered body shown in Patent Documents 1 and 2 is used as the cutting edge of a cutting tool and subjected to machining under heavy interrupted cutting conditions, intermittent and impactful high loads acting on the cutting edge Cracks generated by the sintered cBN propagate linearly in the cBN sintered body, which reduces the toughness, which causes chipping and shortens the tool life.
Therefore, the development of a cBN sintered body with excellent crack propagation resistance and toughness is desired.

Therefore, the inventors of the present invention have made intensive studies to solve the above problems and improve the crack propagation resistance of the cBN sintered body without lowering the toughness thereof, and obtained the following findings.

A conventional cBN sintered body is usually produced by mixing cBN powder, which is a hard phase component of the cBN sintered body, with, for example, TiN powder, TiAl ₃ powder, Al ₂ O ₃ powder, etc., which are binder phase forming components, in a ball mill. , which is sintered under high-pressure and high-temperature conditions.

The present inventors have found that by changing the conventional cBN sintered body manufacturing process, the cBN sintered body composed of cBN particles and a binder phase, for example, Al compound particles composed of Al ₂ O ₃ particles, etc. A cBN sintered body having a binder phase structure in which Ti compound particles were included in the grains was produced.
And the cBN sintered body having such a binder phase structure is similar to the conventional cBN sintered body containing approximately the same amount of Ti compound particles (however, the Ti compound particles do not contain Al compound particles). In comparison, the inventors have found that it has not only hardness, strength and heat resistance, but also excellent crack propagation resistance and toughness.

A major difference between the production process of the cBN sintered body according to the present invention and the conventional production process lies in the adjustment of raw material powder (details will be described later).
For example, as shown in FIG. 1, as a conventional general cBN sintered body manufacturing process, raw material powders for forming a binder phase (for example, Ti compound powder, metal Al powder, Al ₂ O ₃ powder, etc.) are prepared. Mixed in a ball mill, dried, vacuum sintered, pulverized in a ball mill to prepare a mixed powder (hereinafter, this mixed powder is referred to as "mixed powder A"), and then mixed powder A and a hard component. A cBN sintered body was produced by putting certain cBN particles into a cemented carbide pot, mixing them with a ball mill, and then sintering them at high pressure and high temperature.

However, in the present invention, a mixed powder containing Ti compound particles such as TiN particles in which Al compound particles such as Al ₂ O ₃ particles are encapsulated (hereinafter, this mixed powder is referred to as A step of producing a mixed powder B) is newly provided, and in the above conventional process, at the stage of putting the mixed powder A and cBN particles into a cemented carbide pot, the mixed powder B prepared above is added to the cemented carbide pot. A major feature of the present invention is that the cBN sintered body is produced by putting them into a manufacturing pot at the same time, mixing them by an ultrasonic method, and then sintering them at high pressure and high temperature.
FIG. 2 shows a schematic illustration of the process for producing a cBN sintered body according to the present invention.
Then, by producing a cBN sintered body by such a production process, as described above, Ti compound particles such as TiN particles containing Al compound particles such as Al ₂ O ₃ particles are present. A cBN sintered body having a binder phase structure can be produced, and the cBN sintered body having such a binder phase structure has hardness, strength, heat resistance, as well as excellent crack propagation resistance and toughness. be.

Furthermore, when the cutting edge of the cutting tool is composed of the cBN sintered body of the present invention, which has excellent crack propagation resistance and toughness as well as hardness, strength, and heat resistance, it can It is possible to suppress the occurrence of chipping in cutting and the like, and as a result, it is possible to obtain a cutting tool that exhibits excellent cutting performance over a long period of use.

The present invention has been made based on the above findings,
"(1) In a cubic boron nitride-based sintered body comprising cubic boron nitride particles and a binder phase, the binder phase contains Ti compound particles having an average particle size of 150 nm or more and 646 nm or less , and the Ti compound A cubic boron nitride-based sintered body characterized by having a binder phase structure in which, among particles, Ti compound particles containing Al compound particles are present.
(2) The volume ratio of the Ti compound particles containing the Al compound particles is 5% by volume or more and 60% by volume or less with respect to the total volume of the binding phase of the cubic boron nitride sintered body ( The cubic boron nitride-based sintered body according to 1).
(3) The volume ratio of the Al compound particles contained in the Ti compound particles to the Ti compound particles containing the Al compound particles is 3% by volume or more and 15% by volume or less (1) or ( The cubic boron nitride-based sintered body according to 2).
(4) The cubic boron nitride-based sintered body according to any one of (1) to (3), wherein the Ti compound particles have an average particle size of 150 nm or more and 500 nm or less.
(5) The cubic boron nitride-based sintered body according to any one of (1) to (4), wherein the Ti compound particles are TiN particles.
(6) A cubic boron nitride-based sintered body, wherein the cutting edge of the cutting tool is composed of the cubic boron nitride-based sintered body according to any one of (1) to (5). Solid cutting tool. ”
It is characterized by

The present invention is described below.

In the cBN sintered body of the present invention, the average particle size of the cBN particles is not particularly specified, but the average particle size of the cBN particles is preferably in the range of 0.3 to 12 μm.
By dispersing cBN particles with an average particle size of 0.3 μm to 12 μm in the sintered body, chipping caused by the uneven shape of the cutting edge caused by the falling off of the cBN particles from the tool surface during use of the tool is suppressed. In addition, cracks that develop from the interface between the cBN particles and the binder phase caused by the stress applied to the cutting edge during use of the tool, or cracks that propagate through the cBN grains are dispersed in the sintered body. This is because the chipping resistance can be improved by suppressing the
Further, the average particle size of the cBN particles used in the present invention is more preferably in the range of 0.5 to 8 μm, and still more preferably in the range of 0.5 to 5 μm.
Incidentally, the average particle size of the cBN particles, for example, for the cross-sectional structure of the cBN sintered body, the cBN sintered body structure is observed using SEM, the secondary electron image is obtained, and the cBN particles in the obtained image part is extracted by image processing, the maximum length of each cBN particle obtained by image analysis is obtained, this is used as the diameter of each particle, the diameter of the cBN particles is measured at multiple locations, and these measured values are averaged. is the average particle size of the cBN particles.

The content volume ratio of the cBN particles in the cBN sintered body of the present invention is not particularly limited, but when the content volume ratio of the cBN particles in the cBN sintered body is less than 40% by volume, the cBN particles The amount of unsintered portions that are in contact with each other and cannot sufficiently react with the binder phase is reduced, but on the other hand, the hardness of the cBN sintered body is lowered and the wear resistance is deteriorated.
On the other hand, when the content volume ratio of the cBN particles exceeds 95% by volume, when used as a cutting tool, voids that act as starting points for cracks are likely to form in the sintered body, resulting in reduced fracture resistance. Therefore, the content volume of cBN particles in the cBN sintered body is preferably 40 to 85% by volume.
Further, the content volume ratio of the cBN particles is more preferably 50 to 80% by volume. More preferably 50 to 75% by volume.
The volume ratio of the cBN particles in the cBN sintered body was obtained by observing the cross-sectional structure of the cBN sintered body with an SEM, extracting the cBN particles in the obtained secondary electron image by image processing, and performing image analysis. The area occupied by the cBN particles is calculated by , the ratio of the cBN particles in one image is obtained, and the average value of the values obtained by processing at least 3 images is obtained as the content volume ratio of the cBN particles. For example, when the cBN particles have an average particle size of 3 μm, the viewing area used for image processing is preferably about 15 μm×15 μm.

The cBN sintered body of the present invention is composed of cBN particles and Ti compound particles (for example, TiN particles) as a main binder phase. The binder phase contains, for example, Al ₂ O ₃ A bonded phase structure is formed in which Ti compound particles containing Al compound particles such as particles are present.
The Ti compounds referred to in the present invention are, for example, TiN, TiCN, and TiC, and the Al compounds are, for example, Al ₂ O ₃ and AlN.
In the present invention, the “Al compound particles enclosed in Ti compound particles” or “Ti compound particles enclosing Al compound particles” are, for example, Al compound particles of Al ₂ O ₃ and Ti compound particles of TiN. In some cases, in cross-sectional observation using a transmission electron microscope (TEM) (see FIG. 3(a)), element mapping is first performed for Al, O, Ti, and N, and then binarization processing is performed. (see FIGS. 3(b) to 3(e)), the overlapping region of Al and O is assumed to be Al ₂ O ₃ , and the overlapping region of Ti and N is assumed to be a Ti compound. Next, assuming that the TiN continuous region is a TiN particle, Al ₂ O ₃ that is not in contact with the boundary of the TiN particle and is present within the boundary of the TiN particle is specified, and this is referred to as a "Ti compound Al ₂ O ₃ particles enclosed in particles”, and Ti compound particles enclosing the Al ₂ O ₃ particles are defined as “Ti compound particles enclosing Al ₂ O ₃ particles”.

The cBN sintered body of the present invention having a binder phase structure in which Ti compound particles containing Al compound particles are dispersed in the binder phase contains approximately the same amount of Ti compound particles (however, the Ti compound particles are Al In addition to excellent hardness, strength and heat resistance, it has excellent crack propagation resistance and toughness as compared with a cBN sintered body containing no compound particles.
This is because the cracks generated in the cBN sintered body propagate mainly through grain boundaries when the Ti compound particles constituting the binding phase are fine grains, but when the Ti compound grains are coarse grains, It tends to propagate through grains. However, in the present invention, even if the Ti compound particles are coarse grains of 150 nm to 646 nm and the cracks are propagated and propagated through the grains instead of the grain boundaries, they are included in the Ti compound particles. This is because the Al compound contained therein stops and suppresses the propagation and progress of cracks that attempt to penetrate through the grains, thereby improving the crack propagation resistance without reducing the toughness.

The volume ratio of Ti compound particles (e.g., TiN particles) containing Al compounds (e.g., Al ₂ O ₃ particles) in the total volume of the binding phase of the cBN sintered body is 5% by volume or more and 60 volumes with respect to the binding phase. % or less, in a cutting tool using a cBN sintered body as a cutting edge, for example, a crack occurs in the cBN sintered body due to the intermittent and impactful high load during heavy interrupted cutting Also, since it is excellent in crack propagation resistance, the propagation and progress of cracks are suppressed, and the occurrence of defects and fractures is prevented.
However, if the volume ratio of the Ti compound particles containing the Al compound particles is less than 5% by volume of the binding phase of the cBN sintered body, the number of Ti compound particles containing Al compound particles that suppress crack propagation in the grains is small, an improvement in the effect of suppressing crack propagation cannot be expected. becomes excessive, and cracks may propagate starting from the Al compound particles, so the volume ratio of the Ti compound particles containing the Al compound particles to the binding phase of the cBN sintered body is 5% by volume or more and 60% by volume. It is preferable to:

In addition, the content of the Al compound particles contained in the Ti compound particles, that is, (the volume of the Al compound particles contained in the Ti compound particles) × 100/(the volume of the Ti compound particles containing the Al compound particles) is It is preferably 3% by volume or more and 15% by volume or less. This content is an average value calculated from Ti compound particles containing at least 10, preferably 50 or more Al compound particles.
This is because the Ti compound particles contain Al compound particles with an average volume ratio of 3% or more and 15% or less by volume in their interior, thereby suppressing the propagation and progress of cracks penetrating through the Ti compound particles. As a result, the toughness of the cBN sintered body is also improved.
However, if the average volume ratio of the Al compound particles included in the Ti compound particles is less than 3% by volume, the number of particles that suppress crack propagation is small, so crack propagation cannot be sufficiently suppressed, On the other hand, when the average volume ratio of the Al compound particles included in the Ti compound particles exceeds 15% by volume, the amount of the Al compound particles included in the Ti compound particles becomes excessive, so cracks form in the Al compound particles. There is a risk of spreading from the starting point.
Therefore, the content of the Al compound particles included in the Ti compound particles should be 3% by volume or more and 15% by volume or less.

The average particle size of the Ti compound particles that make up the binder phase of the cBN sintered body has a great effect on the impact chipping resistance, crater wear resistance, and toughness of the cBN sintered body, but it also affects how cracks propagate. effect.
In the present invention, the Ti compound particles are coarse grains and the average grain size is 150 nm or more and 646 nm or less, so that the cBN sintered body has crater wear resistance and toughness. By suppressing the intragranular propagation and development of cracks caused by the presence of Al compound particles contained in Ti compound particles in the binder phase (preferably 5% by volume or more and 60% by volume or less). , Crack propagation resistance is improved, and chipping resistance is improved under cutting conditions where a high load acts on the cutting edge of the tool.
Here, if the average particle diameter of the Ti compound particles constituting the binder phase is less than 150 nm, the cracks will propagate and progress along the grain boundaries. Even so, the effect of suppressing the propagation and progress of cracks is reduced. On the other hand, when the average particle size of the Ti compound particles constituting the binder phase exceeds 500 nm, the grain boundaries are reduced, and the crack propagation can be bypassed. Since the effect of suppressing the propagation and progress of the cBN sintered body is reduced, it is preferable that the average particle size of the Ti compound particles constituting the binding phase of the cBN sintered body is 150 nm or more and 500 nm or less.
The average particle size of the Ti compound particles can be measured and calculated, for example, as follows.
First, a cross-sectional observation region of the cBN sintered body is observed using a crystal orientation analyzer attached to the TEM. More specifically, in order to observe the Ti compound particles in a transmission electron microscope, a piece 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. Observation is performed in the range of 400 nm×500 nm by irradiating the section.
An analysis method for obtaining crystal orientation map data in the above range is as follows.
While precession irradiating the section with an electron beam inclined at 0.5 to 1.0 degrees, the electron beam is scanned at an arbitrary beam diameter and interval, and the electron beam diffraction pattern is continuously captured to perform individual measurements. Analyze the crystal orientation of a point. The diffraction pattern acquisition conditions 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 distinguishing individual crystal grains from the obtained electron beam diffraction pattern is as follows.
First, when the crystal orientations of adjacent points of measurement points are separated by 5 degrees or more, it is defined as a grain boundary, and the portion other than the grain boundary is defined as a crystal grain, that is, a Ti compound particle.
This image is connected with 4 vertical × 4 horizontal images to form an image of 1600 nm long × 2000 nm wide, and the average particle size of the Ti compound particles is obtained in the same procedure as described above for obtaining the average particle size of the cBN particles. .
Such measurements and calculations are performed in a plurality of (three or more) observation areas, and the average value is taken as the average particle diameter (nm) of the Ti-based compound particles.

As described above, the process of producing the cBN sintered body according to the present invention is, apart from the process of producing the raw material powder A for forming the binder phase of the conventional cBN sintered body (hereinafter referred to as "process A"), A step of producing mixed powder B containing Ti compound particles in which Al compound particles are encapsulated (hereinafter referred to as “step B”) is newly provided, and mixed powder A, mixed powder B and cBN particles are combined. It is characterized by providing a step of mixing by an ultrasonic method (hereinafter referred to as "step C").
A more specific description of each step with reference to FIG. 2 is as follows.
≪Step A≫
As shown as "conventional process ₍ process A)" in _FIG . After that, vacuum sintering is performed for a predetermined time (eg, 30 minutes) at a temperature range of 800 to 1200° C. (eg, 1000° C.) in a vacuum atmosphere of 1 Pa or less.
A mixed powder A is obtained by wet pulverizing with a ball mill to a desired particle size (for example, an average particle size of 100 to 1000 nm) and drying.
≪Step B≫
As shown in FIG. 2 as "the step of producing Ti compound particles containing Al compound particles (process B)", a Ti compound powder containing Al compound particles is produced by, for example, a metal method.
Specifically, in FIG. 2, Ti powder is first hydrogenated to produce titanium hydride, which is pulverized and then mixed with Al compound powder (for example, Al ₂ O ₃ powder) in a ball mill to obtain a slurry solution. get
The obtained slurry solution is taken out, dried, molded, and sintered in a predetermined sintering atmosphere at a temperature range of 800-1200° C. (eg, 1000° C.) for a predetermined time (eg, 30 minutes).
Here, when trying to produce a cBN sintered body having TiN as the main component of the binder phase, as is known in the metal method, the atmosphere may be a nitriding atmosphere, and TiC is used as a binder. When it is used as a phase main component, a carbonization treatment atmosphere may be used.
In the case of producing a cBN sintered body having TiCN as the main component of the binder phase, for example, TiN powder and TiC powder produced by the metal method are mixed and heat-treated at 1800 ° C. in a vacuum atmosphere. can synthesize TiCN powder.
Next, the sintered body is pulverized again with a ball mill or the like and then classified to prepare a mixed powder B composed of Ti compound particles containing an Al compound and having an average particle size of 100 to 1000 nm.
≪Step C≫
As shown as "process C" in FIG. 2, the mixed powder A prepared in step A, the mixed powder B prepared in step B, and the cBN particles that are the hard phase component of the cBN sintered body are mixed with an Al compound (for example, , Al ₂ O ₃ ) are mixed by an ultrasonic method so as not to break the Ti compound (for example, TiN) particles (the conventional ball mill method destroys the TiN particles including the Al compound), and dried. Then, for example, high pressure and high temperature sintering is performed for a predetermined time under sintering conditions of a pressure of 3 to 8 GPa and a temperature range of 1000 to 1800°C.
Here, the mixing conditions for the ultrasonic method are, for example, a slurry concentration of 7 wt % and an output of 180 W, and mixing is performed for 15 minutes at intervals of 15 seconds every 30 seconds.

In the present invention, as described above, in step B shown in FIG. 2, a mixed powder B composed of TiN particles containing Al compound particles in the grains is produced in a separate step, and in step C, (produced in step A). After mixing the mixed powder A, the mixed powder B and cBN particles by an ultrasonic method, high pressure and high temperature sintering is performed to obtain a cBN sintered body having a binder phase structure in which Ti compound particles containing Al compound particles are present. can be made.
A cBN sintered body having such a binder phase structure has excellent hardness, strength and heat resistance, as well as excellent toughness and crack propagation resistance.

Therefore, when the cutting edge of a cutting tool is made of the cBN sintered body of the present invention, which is excellent in hardness, strength, heat resistance, toughness, and crack propagation resistance, it can be used as a strong material such as alloy steel, which is subjected to a high load. Even in interrupted cutting, it is possible to suppress the occurrence of chipping due to the propagation and development of cracks, and as a result, it is possible to provide a cutting tool that exhibits excellent cutting performance over long-term use.
When using the cBN sintered body of the present invention as a cutting tool material, for example, the cBN sintered body is brazed to the brazing part (corner part) of the WC-based cemented carbide insert body, and if necessary, polished. By applying processing and honing processing, a cutting tool having a desired insert shape with a cBN sintered body as a cutting edge can be produced.

Whether or not Al compound particles are included in the Ti compound particles dispersed in the bonding phase of the cBN sintered body of the present invention, and whether the volume of the Ti compound particles including Al compound particles is determined by the bonding The volume ratio of the phase to the total volume and the average volume ratio of the Al compound particles contained in the Ti compound particles can be obtained as follows.
A cross section of the cBN sintered body is polished so that the thickness of the sample becomes 100 nm or less, and the binder phase region of the cBN sintered body is observed by TEM. The reason why the thickness of the sample is set to 100 nm or less is that if the particles are overlapped during TEM observation, it is impossible to determine whether the particles are contained particles or just overlapped particles.
The observation magnification is adjusted so that the diagonal length of the observation field is 10 times the obtained average particle diameter of the Ti compound particles (observation magnification 1), and the binding phase of the Ti compound particles containing the Al compound particles is measured. Measure the content. In determining the average particle diameter of the Ti compound particles, the particle diameters of the Ti compound particles are calculated from a field of view in which at least 10 Ti compound particles can be observed, and the average value is used. At an observation magnification of 1, it is not possible to accurately identify whether Al compound particles are included in the Ti compound particles, so the observation magnification is adjusted so that the diameter of the circumscribed circle of the Ti compound particles is 1/4 or more times the diagonal length of the observation field. In the field of view (observation magnification 2) adjusted as above, it is determined whether the Al compound particles are included in the Ti compound particles and the content of the included particles is measured.
FIG. 3A shows an example of TEM observation of a cross section of a cBN sintered body having a bond structure in which Al ₂ O ₃ particles are included in TiN particles. , TiN and Al ₂ O ₃ are the overlapping portions of Ti and N and Al and O in the mapping images obtained by binarization (see FIGS. 3B to 3E), respectively.
In the Al ₂ O ₃ particles contained in the TiN particles, from the superimposed image at an observation magnification of 2, the continuous region of TiN is regarded as the TiN particle, and is not in contact with the boundary of the TiN particle, and , identify the Al ₂ O ₃ grains present within the boundaries of the TiN grains and identify them as Al ₂ O ₃ grains encapsulated in the TiN grains. In addition, the content of TiN particles and Al ₂ O ₃ particles was measured by the same measurement method as the measurement method for obtaining the volume of the cBN particles from the binarized image, and the TiN particles in the field of view at an observation magnification of 1 Calculate the content of Al ₂ O ₃ particles included in the . The content of TiN particles containing Al ₂ O ₃ particles in the binder phase was obtained by extracting only TiN particles containing Al ₂ O ₃ particles from the binarized image using an observation magnification of 1. Then, the content is calculated by the same measuring method as that for determining the volume of the cBN particles.
The image processing software "imageJ" was used for the binarization processing, and the binarization processing was performed by setting the region including the element to black. A superimposed image of binarized images is obtained by, for example, when superimposing the images of Ti and N, by inverting the white and black regions of the image of N and subtracting the image of N from the image of Ti. .

The cBN sintered body of the present invention contains Ti compound particles in the binder phase, and has a binder phase structure in which Ti compound particles containing Al compound particles are present among the Ti compound particles. The content of the Ti compound particles containing the Al compound particles is 5% by volume or more and 60% by volume or less with respect to the total volume of the binding phase of the cBN sintered body, and the Ti compound particles containing the Al compound particles The content of the Al compound particles contained in the Ti compound particles is preferably 3% by volume or more and 15% by volume or less, so that hardness, strength, heat resistance, toughness, and crack propagation resistance are excellent.
Therefore, when the cutting edge of a cutting tool is made of the cBN sintered body of the present invention, it is possible to prevent defects caused by crack propagation and development in intermittent cutting of alloy steel, etc., where high loads are applied. The occurrence can be suppressed, resulting in excellent cutting performance over long-term use.

An example of the manufacturing process of a cBN sintered body by a conventional method is shown. An example of the production process of the cBN sintered body according to the present invention is shown. (a) shows an example of a TEM image (observation magnification of 2) of the cBN sintered body of the present invention, and (b) to (e) are respectively Al, N, O, Ti after binarization treatment A mapping image is shown.

The cBN sintered body of the present invention will be described below based on examples.

A cBN sintered body of the present invention was produced by steps A to C shown below.
≪Step A≫
As raw material powders for the binder phase of the cBN sintered body, Ti compound (see type in Table 1) powder, metal Al powder, and Al ₂ O ₃ powder having an average particle size in the range of 5 to 50 μm were prepared. Raw material powders were wet-mixed in a ball mill, dried, and then molded.
This compact was vacuum sintered by holding it at 1000° C. for 30 minutes in a vacuum of 1 Pa or less.
Next, this sintered body was wet pulverized in a ball mill and dried to prepare a mixed powder A having an average particle size of 150 to 700 nm (see "Step A" in Fig. 2).
The mixing or pulverization in the ball mill in the above step A and step B described later was carried out by enclosing the powder to be treated together with the cemented carbide balls and the organic solvent in a pot made of cemented carbide and then mixing or pulverizing.
≪Step B≫
In step B, which is a separate step from step A, raw material powder B was prepared as follows.
First, Ti powder is hydrogenated to produce hydrogenated Ti powder, which is mixed with Al compound (see type in Table 1) powder, and this mixed powder is nitrided in a _N2 gas atmosphere to obtain Al compound particles. TiN particles to be encapsulated were produced. Similarly, the mixed powder was carbonized to produce TiC particles containing Al compound particles.
Further, after TiN particles encapsulating Al compound particles and TiC particles encapsulating Al compound particles are prepared respectively, this is made into a mixed powder, and this is heat-treated in a vacuum at 1800 ° C. to encapsulate Al compound particles. TiCN particles were produced.
Next, this mixed powder is wet-pulverized in a ball mill, dried, and then centrifuged to collect a powder having a particle size of 150 to 700 nm to obtain a mixed powder B containing Ti compound particles encapsulating Al compound particles. (See “Step B” in FIG. 2).
≪Step C≫
The mixed powder A prepared in step A, the mixed powder B prepared in step B, and cBN particles having an average particle size of 3 μm are blended so that the cBN content is 50 vol%, for example, the slurry concentration is 7 wt%. Mix by an ultrasonic method under the condition that the output is 180 W and mix for 15 minutes at intervals of 15 seconds every 30 seconds. As sintering conditions, high pressure and high temperature sintering was performed at 6 GPa and 1500 ° C. to produce cBN sintered bodies 1 to 9 (referred to as "Examples 1 to 9") of the present invention shown in Table 1 (" Process C”).

For comparison, comparative cBN sintered bodies 1 to 5 (referred to as “Comparative Examples 1 to 5”) were produced by the following conventional steps (see “Step A” in FIG. 1).
First, Ti compound (see type in Table 1) powder, metal Al powder, and Al ₂ O ₃ powder were prepared, and these raw material powders were wet-mixed in a ball mill, dried, and then formed into a compact.
This compact was vacuum sintered by holding it at 1000° C. for 30 minutes in a vacuum of 1 Pa or less.
Next, this sintered body was wet pulverized in a ball mill and dried to prepare a mixed powder having an average particle size of 0.3 to 0.9 μm (for convenience, this powder will be referred to as “mixed powder A”). .
This mixed powder A and cBN particles having an average particle size of 3 μm are mixed in a ball mill so that the cBN content is 50 vol%, dried, and then subjected to a pressure of 3 to 6 GPa and a temperature range of 1000 to 1600 ° C. Comparative Examples 1 to 5 shown in Table 1 were produced by high pressure and high temperature sintering under sintering conditions.
That is, the manufacturing methods of Comparative Examples 1 to 5 are different in that the step B in the manufacturing method of the sintered bodies 1 to 9 of the present invention is not provided, and the mixing with cBN particles is performed by a ball mill instead of an ultrasonic method. ing.

In Examples 1 to 9 and Comparative Examples 1 to 5 prepared above, in order to facilitate evaluation of the influence of the binder phase on the cutting performance, the cBN particles had a constant average particle size of 3 μm. The content of the binder phase is increased to 50% by volume.
However, the average particle size and content of the cBN particles are not limited to the above, and can take various values.
The average particle diameter (μm) of the cBN particles in the cBN sintered body and the content ratio (vol %) of the cBN particles were calculated as follows.
Regarding the average particle size of the cBN particles, the cross-sectional structure of the cBN sintered body is observed with a scanning electron microscope (SEM) to obtain a secondary electron image, and the cBN particles in the obtained image are imaged. Extracted in the process, the maximum length of each particle obtained by image analysis was obtained, and the diameter of each particle was assumed to be the diameter of each particle, and the volume was calculated assuming that each particle was an ideal sphere.
The volume % of cBN particles was calculated using the average value of the diameters of cBN particles obtained from at least three images as the average particle size (μm) of cBN. The observation area used for image processing is preferably 15 μm×15 μm.
In addition, although the sintering conditions are constant at 6 GPa and 1500° C. in the examples, the superiority or inferiority of the cutting performance does not change depending on the sintering conditions.

The measurement and calculation of the average particle size of the Ti compound particles were performed as follows.
First, a cross-sectional observation region of the cBN sintered body is observed using a crystal orientation analyzer attached to the TEM. More specifically, in order to observe the Ti compound particles in a transmission electron microscope, a piece 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. Observation is performed in the range of 400 nm×500 nm by irradiating the section.
Next, map data of crystal orientation was obtained in the above range as follows.
While precession irradiating the section with an electron beam inclined at 0.5 to 1.0 degrees, the electron beam is scanned at an arbitrary beam diameter and interval, and the electron beam diffraction pattern is continuously captured to perform individual measurements. Analyze the crystal orientation of a point. The diffraction pattern acquisition conditions used for 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 distinguishing individual crystal grains from the obtained electron beam diffraction pattern is as follows.
First, when the crystal orientations of adjacent points of measurement points are separated by 5 degrees or more, it is defined as a grain boundary, and the portion other than the grain boundary is defined as a crystal grain, that is, a Ti compound particle.
This image is connected with 4 vertical × 4 horizontal images to form an image of 1600 nm long × 2000 nm wide, and the average particle size of the Ti compound particles is obtained in the same procedure as described above for obtaining the average particle size of the cBN particles. rice field.
Such measurements and calculations were performed in a plurality of (three or more) observation areas, and the average value was taken as the average particle size (nm) of the Ti-based compound particles.

In addition, identification of Ti compound particles containing Al compound particles in the binder phase, measurement of the volume ratio of Ti compound particles containing Al compound particles to the binding phase of the cBN sintered body, and Ti compound particles containing Al compound particles , the volume ratio of the Al compound particles included in the Ti compound particles was measured as follows.
The cross section of the cBN sintered body was polished so that the thickness of the sample became 100 nm or less, and the binder phase region of the cBN sintered body was observed by TEM. The reason why the thickness of the sample is set to 100 nm or less is that if the particles overlap during TEM observation, it is impossible to determine whether the particles are contained particles or just overlapped particles.
The observation magnification is adjusted so that the diagonal length of the observation field is 10 times the obtained average particle diameter of the Ti compound particles (observation magnification 1), and the binding phase of the Ti compound particles containing the Al compound particles is measured. Content was measured. However, at this observation magnification of 1, since it is not possible to accurately identify whether Al compound particles are included in the Ti compound particles, the observation magnification is set so that the diameter of the circumscribed circle of the Ti compound particles is 1/4 times the diagonal length of the observation field of view. In the field of view adjusted as above (observation magnification 2), TEM observation was performed to determine whether Al compound particles were included in the Ti compound particles and to measure the content of the included particles.
For example, when the Ti compound particles are TiN and the Al compound particles are Al ₂ O ₃ , elemental mapping of Ti, Al, O, and N is performed by TEM observation, and binarization is performed. The overlapped portions of the mapping images of Ti and N and Al and O were defined as TiN and Al ₂ O ₃ , respectively. In the Al ₂ O ₃ particles contained in the TiN particles, from the superimposed image at an observation magnification of 2, the continuous region of TiN is regarded as the TiN particle, and is not in contact with the boundary of the TiN particle, and , identified Al ₂ O ₃ particles present within the boundaries of the TiN grains, which were identified as Al ₂ O ₃ grains encapsulated within the TiN grains.
In addition, the volume ratio of Al ₂ O ₃ particles and TiN particles was measured by the same measurement method as the measurement method for obtaining the volume ratio of the cBN particles from the binarized image, and the TiN in the field of view at an observation magnification of 1 The volume ratio of Al ₂ O ₃ particles included in the particles was calculated. The volume ratio of the TiN particles encapsulating Al ₂ O ₃ particles to the binder phase is obtained by extracting only the TiN particles encapsulating Al ₂ O ₃ particles from the binarized image using an observation magnification of 1. Then, the volume ratio was calculated by the same measurement method as that for determining the volume of the cBN particles.
Table 1 shows these values.

Next, the upper and lower surfaces of the sintered bodies of Examples 1 to 9 and Comparative Examples 1 to 5 were polished using a diamond grindstone, divided by a wire electric discharge machine, and further Co: 5% by mass and TaC: 5% by mass. %, WC: Cu: 26%, Ti: 5%, Ag: 26%, Ti: 5%, and Ag: The cBN sintered cutting tool 1 of the present invention having an insert shape conforming to ISO standard CNGA120408 is obtained by brazing with an Ag alloy brazing material having a composition consisting of the remainder, polishing the upper and lower surfaces and the outer circumference, and performing honing. 9 and cBN sintered cutting tools 1 to 5 of comparative examples were produced.

Next, each of the various cutting tools described above was screwed to the tip of the tool steel bit with a fixing jig, and each tool was subjected to a dry heavy interrupted cutting test under the following cutting conditions. , the number of impacts until the cutting edge of the cBN sintered body was chipped, and the toughness and crack propagation resistance were evaluated.
Cutting conditions:
Work material: JIS SCr420 (HRC58-62) round bar (However, there are 4 slits at equal intervals in the axial direction of the work material)
Cutting speed: 240 m/min,
feed amount: 0.15mm/rev,
Cutting depth: 0.10mm
Condition: Dry In the above dry heavy interrupted cutting test, the number of interruptions (number of impacts) until chipping occurs on the cutting edge of the cutting tool or the number of interruptions (number of impacts) until the tool life expires due to chipping is defined as the tool life. , and the state of the cutting edge was confirmed by observing the cutting edge every 300 times of interruption.
Table 1 shows the cutting test results of cBN sintered cutting tools 1 to 9 of the present invention and cBN sintered cutting tools 1 to 5 of comparative examples.

As shown in Table 1, the cBN sintered body cutting tools 1 to 9 of the present invention are all excellent in toughness and crack propagation resistance of the cBN sintered body constituting the cutting edge, so chipping is observed. However, it does not break and exhibits excellent cutting performance over long-term use.
In particular, the volume ratio of the Ti compound particles containing the Al compound particles is 5% by volume or more and 60% by volume or less, and the volume ratio of the Al compound particles contained in the Ti compound particles is 3% by volume or more and 15% by volume or less, and further In Examples 1 to 5, in which the average particle size of the Ti compound particles was 150 nm or more and 500 nm or less, the number of impacts until reaching the end of life was remarkably large, indicating a long life.

On the other hand, in the cBN sintered cutting tools 1 to 5 of the comparative examples, since the toughness and crack propagation resistance of the cBN sintered body are inferior, it is clear that the life is shortened due to the occurrence of defects. be.
In particular, in Comparative Examples 1, 2, 4, and 5, although the average particle diameter of the Ti compound is within the range of 150 nm or more and 500 nm or less, which is preferable in the present invention, Ti compound particles containing Al compound particles It can be seen that the toughness and crack propagation resistance are inferior due to the absence of , and therefore the life is shortened due to chipping.

As described above, the cBN sintered body of the present invention is excellent in hardness, strength, heat resistance, crack propagation resistance and toughness. Therefore, for example, when used as a cBN cutting tool in which a high load acts on the cutting edge, it exhibits excellent resistance to abnormal damage such as chipping and breakage, and exhibits excellent cutting performance over a long period of use.

Claims (6)

In a cubic boron nitride-based sintered body composed of cubic boron nitride particles and a binder phase, the binder phase contains Ti compound particles having an average particle size of 150 nm or more and 646 nm or less , and moreover, among the Ti compound particles, A cubic boron nitride-based sintered body characterized by having a binder phase structure in which Ti compound particles containing Al compound particles are present. 2. The method according to claim 1, wherein the volume ratio of the Ti compound particles containing the Al compound particles is 5% by volume or more and 60% by volume or less with respect to the total volume of the binding phase of the cubic boron nitride sintered body. The cubic boron nitride-based sintered body described above. 3. The volume ratio of the Al compound particles contained in the Ti compound particles to the Ti compound particles containing the Al compound particles is 3% by volume or more and 15% by volume or less. A cubic boron nitride-based sintered body. The cubic boron nitride-based sintered body according to any one of claims 1 to 3, wherein the Ti compound particles have an average particle size of 150 nm or more and 500 nm or less. 5. The cubic boron nitride-based sintered body according to claim 1, wherein said Ti compound particles are TiN particles. Cutting made of cubic boron nitride-based sintered body, characterized in that the cutting edge of the cutting tool is composed of the cubic boron nitride-based sintered body according to any one of claims 1 to 5 tool.

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