JP6933017B2 - Cubic boron nitride base sintered body and cutting tool - Google Patents

Description

The present invention is a cubic boron nitride (hereinafter, also referred to as “cBN”)-based sintered body (hereinafter, also referred to as “cBN sintered body”) having high hardness, high strength, and heat resistance, and particularly having excellent toughness. With respect to the cutting tool made of the cBN sintered body, in particular, _{the hardness, strength, and heat resistance of the Al 2} O ₃ particles, which are the components of the bonding phase of the cBN sintered body, because they have a structure containing Ti compound particles. The present invention relates to a cBN sintered body having improved toughness without lowering the toughness, and a cutting tool made of a cBN sintered body having improved toughness to suppress the occurrence of abnormal damage such as chipping and chipping.

The cBN sintered body has a 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.
From the viewpoint of improving the performance as a material for cutting tools, some proposals have been made conventionally for further improving the strength, heat resistance, toughness, hardness and the like of the cBN sintered body.

For example, Patent Document 1 contains 20 to 80% by volume of a hard phase cBN as a tool material having a low affinity with iron-based work materials such as steel and cast iron, and the balance is 4a and 5a in the periodic table. , 6a, a cutting tool made of a cBN sintered body having a ceramic compound such as a carbide, a nitride, or a boride as a bonding phase has been proposed. It is said to have high strength and excellent heat resistance and abrasion resistance.

Further, in Patent Document 2, by adding a simple substance of Zr, Si, Hf, Ge, W, Co and a trace amount of a compound to the bonded phase of the cBN sintered body, the bonded phase in the cBN sintered body is added. _{It has been proposed to control the particle size of the Al 2} O ₃ particles contained as a component, thereby improving the heat resistance without lowering the strength of the cBN sintered body.

Further, in Non-Patent Document 1, a nanocomposite material in which toughness, which is a weak point of ceramics, is improved by forming composite ceramic particles (nanocomposites) in which nano-sized ceramic particles are dispersed in a matrix grain of ceramics. Has been proposed. For example, a nanocomposite material in which TiN particles having a diameter of 5 nm are encapsulated in _{Si 3} N _{4 matrix particles by a chemical vapor deposition method has been introduced.}

Japanese Unexamined Patent Publication No. 53-77811 International Publication No. 2008/093577

"New Design Concept of structural Ceramics-Ceramic Nanocomposites-Koichi NIIHARA" (100th Anniversary Issue of Academic Journal of the Ceramic Society of Japan) 99 [10] 974-982 (1991)

In the cBN sintered body shown in Patent Document 1, since a ceramic compound is used as the bonding phase, the strength, heat resistance, and wear resistance are improved as compared with the case where a metal such as Co is used as the bonding phase. Is recognized. However, when this cBN sintered body is used as a cutting tool for intermittent cutting of alloy steel or the like in which a high load acts on the cutting edge, it cannot be said that the toughness is sufficient. There is a problem that abnormal damage occurs and the life is reached in a short period of time.
Further, in the cBN sintered body proposed in Patent Document 2, trace particles of Zr, Si, Hf, Ge, W, and Co are added in order to control the particle size of _{Al 2} O _{3 particles.} However, the addition of these particles does not impair the heat resistance of the _{Al 2} O _{3 particles.} However, since Al ₂ O ₃ particles are brittle components in the bound phase, the toughness cannot be improved yet. Further, there is a problem that the strength of the cBN sintered body is lowered due to the formation of impurities in the bonded phase by the added trace particles.

Therefore, the present inventors have solved the above problems and conducted intensive studies to improve the toughness without lowering the hardness, strength, and heat resistance of the cBN sintered body, and obtained the following findings. ..

In the conventional cBN sintered body, cBN powder, which is a hard phase component of the cBN sintered body, is usually _{mixed with, for example, TiN powder, TiAl 3} powder, Al ₂ O ₃ powder, etc., which are bonding phase forming components, in a ball mill. , This is manufactured by the process of sintering under high pressure and high temperature conditions.

_{By changing the conventional process for producing the cBN sintered body, the present inventors and others have created Al 2} O ₃ particles in which Ti compound particles are encapsulated in the cBN sintered body composed of the cBN particles and the bonded phase. It has been found that a cBN sintered body having a bonded phase structure in which is dispersed in the bonded phase can be produced.
The cBN sintered body having such a bonded phase structure is a _{conventional cBN containing substantially the same amount of Al 2} O ₃ particles (however, Ti compound particles are not included in _{the Al 2} O _{3 particles).} They found that they have excellent toughness in addition to being superior in hardness, strength, and heat resistance as compared to sintered bodies.

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

However, in the present invention, apart from the above-mentioned conventional step, _{a mixed powder containing Al 2} O ₃ particles containing Ti compound particles in the particles (hereinafter, this mixed powder is referred to as “mixed powder B”) is produced. In the above-mentioned conventional step, at the stage of charging the mixed powder A and the cBN particles into the cemented carbide pot, the mixed powder B produced above is simultaneously charged into the cemented carbide pot. A major feature of the present invention is that a cBN sintered body is produced by mixing by an ultrasonic method and then sintering at high pressure and high temperature.
FIG. 2 shows a schematic explanatory view of a process for producing a cBN sintered body according to the present invention.
Then, by producing the cBN sintered body by such a production step, as described above, the Al ₂ O ₃ particles in which the Ti compound particles are encapsulated in the particles are dispersed and exist in the bonding phase. A cBN sintered body having a structure can be produced, and the cBN sintered body having such a bonded phase structure is excellent in hardness, strength, heat resistance and toughness.
Further, when the cutting edge portion of the cutting tool is composed of the cBN sintered body of the present invention having excellent hardness, strength, heat resistance and toughness, in intermittent cutting of alloy steel or the like on which a high load acts. , The occurrence of abnormal damage such as chipping and chipping can be suppressed, and as a result, a cutting tool that exhibits excellent cutting performance over a long period of use can be obtained.

The present invention has been made based on the above findings.
"(1) In a cubic boron nitride based sintered body composed of cubic boron nitride particles and a bonded phase, the content of the cubic nitride boron particles is 40 of the cubic boron nitride based sintered body. not less than vol% 85 vol% or less, wherein the binder phase comprises _Al 2 _{O 3} particles, moreover, among the _Al 2 _{O 3} particles, there are _Al 2 _{O 3} particles containing the Ti N particles, wherein the content of Al ₂ O ₃ particles containing the TiN particles, cubic boron nitride containing groups sintered body characterized by having a 5 vol% to 50 vol% der Ru binder phase structure of the binder phase.
( 2 ) The content of the Ti N particles contained in the Al ₂ O ₃ particles is 3% by volume or more and 25% by volume or less with respect to the Al ₂ O ₃ particles containing the Ti N particles (2). The cubic boron nitride based sintered body according to 1).
( 3 ) Cutting made of 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 (1) or (2). tool. "
It is characterized by.

The present invention will be 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.
This suppresses chipping starting from the uneven shape of the cutting edge that occurs when cBN particles on the tool surface fall off during tool use because cBN particles with an average particle size of 0.3 μm to 12 μm are dispersed in the sintered body. In addition to this, the cBN particles that propagate from the interface between the cBN particles and the bonding phase, which are generated by the stress applied to the cutting edge during tool use, or the cracks that propagate through the cBN particles are dispersed in the sintered body. This is because the fracture resistance can be improved by suppressing the particles.
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 even more preferably in the range of 0.5 to 5 μm.
Regarding the average particle size of the cBN particles, for example, with respect to the cross-sectional structure of the cBN sintered body, the cBN sintered body structure was observed using SEM to obtain a secondary electron image, and the cBN particles in the obtained image were obtained. The part of is extracted by image processing, the maximum length of each cBN particle obtained by image analysis is obtained, it is used as the diameter of each particle, the diameter of the cBN particle is measured at a plurality of places, and these measured values are averaged. The average particle size of the cBN particles is set according to.

The content ratio of cBN particles in the cBN sintered body of the present invention is not particularly limited, but when the content ratio of cBN particles in the cBN sintered body is less than 40% by volume, the cBN particles are separated from each other. Although the number of unsintered portions that come into contact with each other and cannot sufficiently react with the bonded phase is reduced, on the other hand, the hardness of the cBN sintered body is reduced and the wear resistance is deteriorated.
On the other hand, when the content ratio of cBN particles exceeds 95% by volume, when used as a cutting tool, voids that are the starting points of cracks are likely to be generated in the sintered body, and the fracture resistance is lowered. Therefore, the content of cBN particles in the cBN sintered body is preferably 40 to 85% by volume.
Further, the content of the more preferable cBN particles is 50 to 80% by volume. More preferably, it is 50 to 75% by volume.
The content of cBN particles in the cBN sintered body is determined by observing the cross-sectional structure of the cBN sintered body by SEM, extracting the portion of 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, the ratio occupied by the cBN particles in one image is obtained, and the average value of the values obtained by processing at least three images is obtained as the content of the cBN particles. As the observation region used for image processing, for example, when the average particle size of cBN particles is 3 μm, a visual field region of about 15 μm × 15 μm is desirable.

The cBN sintered body of the present invention is composed of cBN particles and a bonded phase, and Al ₂ O ₃ particles are dispersed and present in the _{bonded phase, and the Al 2 O 3 particles are used as the Al 2} O ₃ particles. Al ₂ O ₃ is present _Al 2 _{O 3} particles inside enclosing Ti compound particles made of, for example TiN particles bonded phase structure is formed.
The term "Ti compound particles contained in Al ₂ O _{3 particles" or "Al 2} O ₃ particles containing Ti compound particles" in the present invention means, for example, when the Ti compound particles are TiN. In cross-sectional observation using a transmission electron microscope (TEM) (see FIG. 3A), first, element mapping for Al, O, Ti, and N is performed, and then binarization processing is performed (FIG. 3 (Fig. 3). b)-(e), it is assumed that the region where Al and O overlap is Al ₂ O ₃ (see FIG. 4), and the region where Ti and N overlap is a Ti compound (for example, TiN). (See Fig. 4). Then, a region that is continuous _{for Al} 2 _{O 3} is _Al 2 _{O 3} particles, not in contact with the boundary of the _Al 2 _{O 3} particles, and are present within the boundaries of _Al 2 _{O 3} particles Ti the compound was identified, which was defined as "Al ₂ O ₃ contained been Ti compound particles to particles", also the Al ₂ O ₃ particles containing the Ti compound particles containing the "Ti compound particles Al _It is defined as "2 O ₃ particles" (see FIG. 4).

The cBN sintered body of the present invention having a bonded phase structure in which _{Al 2} O ₃ particles containing Ti compound _{particles are dispersed in the bonded phase has approximately the same amount of Al 2} O ₃ particles (however, Al _2). O ₃ particles, as compared with the cBN sintered body containing no enclosing Ti compound particles), provided excellent hardness, strength, heat resistance and toughness.
This is the _Al 2 _{O 3} particles and say fragile component in the binder phase of the cBN sintered body, by containing a large Ti compound particles in the thermal expansion rate than _Al 2 _{O 3,} in a _Al 2 _{O 3} particles Crack generation can be suppressed, and as a result, _{the toughness of Al 2} O ₃ particles is improved. Further, Ti compound particles contained in _Al 2 _{O 3} particles, since _Al is sufficiently small compared to 2 _{O 3} particles not impair the heat resistance inherent is _Al 2 _{O 3} particles, cBN sintered body The heat resistance of is maintained and improved.
Further, _{by dispersing such Al 2} O ₃ particles in the bonded phase, cBN sintering having excellent toughness is not impaired without impairing the effect of suppressing abnormal grain growth of the Ti compound which is the main bonded phase of the cBN sintered body. You can get a body.
Further, by enclosing the Ti compound _Al 2 _{O 3} particles, the uniformity of the crystallinity or the like of the _Al 2 _{O 3} particles, and suppress abnormal grain growth of _Al 2 _{O 3} particles, and controls the particle shape At the same time, it is possible to suppress a decrease in strength due to particle destruction due to inhomogeneity in the particles.

_{The content volume ratio of the Al 2} O ₃ particles containing the Ti compound particles dispersed in the bonded phase of the cBN sintered body affects the characteristics (particularly toughness) of the cBN sintered body. _{When the content of Al 2} O ₃ particles containing compound particles occupies 5% by volume or more and 50% by volume or less with respect to the bonded phase, a high load is applied to the cBN sintered body (for example, intermittent cutting during intermittent cutting). Even if cracks occur in the cBN sintered body due to the action of a target and shocking mechanical high load), the propagation and propagation of the cracks are suppressed, so that the occurrence of breakage is prevented.
_{Therefore, the content of the Al 2} O ₃ particles containing the Ti compound particles with respect to the bonded phase of the cBN sintered body is preferably 5% by volume or more and 50% by volume or less.

Further, _Al 2 _{O 3} content particles contained a Ti compound particles, i.e., _(Al 2 _{O 3} volumes of encapsulated the Ti compound particles in the _{particle) × 100 / (Al 2 O} 3 enclosing a Ti compound particles The volume of the particles) is preferably 3% by volume or more and 40% by volume or less. This content is an average value calculated from _{Al 2} O ₃ particles containing at least 10, preferably 50 or more Ti compound particles.
This is because the Al ₂ O ₃ particles contain Ti compound particles of 3% by volume or more and 40% by volume or less in an average volume ratio, thereby _{improving the toughness of the Al 2} O ₃ particles themselves, and as a result, This is because the toughness of the cBN sintered body is also improved.
However, when _{the average volume ratio of the Ti compound particles contained in the Al 2} O ₃ particles exceeds 25% by volume, the cracks penetrate and propagate inside the contained Ti compound particles themselves, or Since cracks may propagate at the interface between the contained Ti compound particles and Al ₂ O ₃ , the effect of suppressing crack propagation / propagation is reduced.
Further, when _{the average volume ratio of the Ti compound particles contained in the Al 2} O ₃ particles is less than 10% by volume, particularly less than 3% by volume, _{the toughness improving effect of the Al 2} O ₃ particles themselves is reduced, and as a result, the toughness improving effect is reduced. The toughness improving effect of the cBN sintered body tends to decrease.
Therefore, in the bonded phase of the cBN sintered body, _{the average volume ratio of the volume of the Ti compound particles contained in the Al 2} O ₃ particles to the volume of the Al ₂ O ₃ particles containing the Ti compound particles is 3% by volume. It is preferably 40% by volume or more, more preferably 3% by volume or more and 25% by volume or less, and further preferably 10% by volume or more and 25% by volume or less.

As described above, the process for producing the cBN sintered body according to the present invention is different from the process for producing the raw material powder A for forming the bonded phase of the conventional cBN sintered body (hereinafter referred to as “step A”). _{A new step (hereinafter referred to as “step B”) for producing a mixed powder B containing Al 2} O ₃ particles in which Ti compound particles are encapsulated is provided, and the mixed powder A, the mixed powder B, and the cBN particles are provided. It is characterized in that a step (hereinafter, referred to as “step C”) of mixing and is provided by an ultrasonic method.
A more specific description of each step with FIG. 2 is as follows.
≪Process A≫
As shown as the “conventional step (step A)” in FIG. 2, the Ti compound powder, the metal Al powder, and the Al ₂ O ₃ powder, which are the bonding phase forming components of the cBN sintered body, are wet-mixed with a ball mill and dried / molded. After that, vacuum sintering is performed for a predetermined time (for example, 30 minutes) in a temperature range of 800-1200 ° C. (for example, 1000 ° C.) in a vacuum atmosphere of 1 Pa or less.
It is pulverized and dried to a desired particle size (for example, an average particle size of 0.3 to 1 μm) by wet pulverization with a ball mill to obtain a mixed powder A.
≪Process B≫
As shown in FIG. 2 as " _{Step of producing Al 2} O ₃ particles containing Ti compound particles (step B)", Ti compound powder (this powder is mainly used in the final cBN sintered body, Al ₂ O ₃ is a powder for forming a Ti compound particles contained in the particle, for example, wet milling the TiN powder) in a ball mill.
Then, the metal Al powder is additionally added, and the Ti compound powder and the metal Al powder are mixed by a ball mill to obtain a slurry solution.
The obtained slurry solution is taken out, dried, molded, and vacuum sintered in a vacuum atmosphere of 1 Pa or less in a temperature range of 800-1200 ° C. (for example, 1000 ° C.) for a predetermined time (for example, 30 minutes).
This sintered body is crushed again with a ball mill or the like and then classified, and only powder having a diameter of 10% or less (also referred to as “d10”) in the particle size distribution is collected and used as mixed powder B.
≪Process C≫
As shown as "step C" in FIG. 2, a Ti compound is contained in the mixed powder A prepared in step A, the mixed powder B prepared in step B, and cBN particles which are the hard phase components of the cBN sintered body. The Al ₂ O ₃ particles were mixed by an ultrasonic method so as not to destroy _{the Al 2 O 3 particles (the conventional ball mill method destroys the Al 2} O ₃ particles containing a Ti compound), dried, and then, for example, 3 to 3 to A cBN sintered body having the bonded phase structure of the present invention can be formed by high-pressure high-temperature sintering for a predetermined time under a pressure of 8 GPa and a sintering condition in a temperature range of 1000 to 1800 ° C.
Here, the mixing conditions by the ultrasonic method are, for example, mixing at a slurry concentration of 7 wt% with an output of 180 W for 15 minutes at intervals of 15 seconds every 30 seconds.

In the non-patent document 1 mentioned as a prior art document, composite ceramic particles (nanocomposite) in which nano-sized ceramic particles are dispersed in a ceramic matrix grain are produced, for example, by a chemical evaporation method. , A technique for improving the toughness of ceramics has been proposed, but a conventional manufacturing method (for example, a manufacturing method including the manufacturing process shown in FIG. 1) using such composite ceramic particles (nanocomposite) itself as a raw material powder). When the cBN sintered body is produced in the above case, when the composite ceramic particles, the powder for forming a bonded phase (for example, TiN powder, TiAl ₃ powder, Al ₂ O ₃ powder, etc.) and the cBN particles are mixed with a ball mill, the composite ceramics are used. Since the particles are destroyed, it is practically difficult to prepare a cBN sintered body in which nano-sized ceramic particles are encapsulated in the matrix grains of the composite ceramic particles.
Therefore, even if the composite ceramic particles (nanocomposite) shown in Non-Patent Document 1 are used, the toughness of the cBN sintered body cannot be improved by the conventional method for producing the cBN sintered body.

However, in the present invention, in step B shown in FIG. 2, _{composite ceramic particles composed of Al 2} O ₃ particles containing Ti compound particles in the particles are produced as mixed powder B in a separate step, and in step C, ( _{Al 2} O ₃ particles are present in the bonded phase by mixing the mixed powder A (produced in step A), the mixed powder B, and the cBN particles by an ultrasonic method and then sintering at high pressure and high temperature. As the Al ₂ O ₃ particles, a cBN sintered body having a bonded phase structure in which _{Al 2} O ₃ particles containing Ti compound particles are present at least dispersed can be produced.
The cBN sintered body having such a bonded phase structure is excellent in hardness, strength and heat resistance, and also has excellent toughness.

Therefore, when the cutting edge of the cutting tool is composed of the cBN sintered body of the present invention having excellent hardness, strength, heat resistance and toughness, even in intermittent cutting of alloy steel or the like on which a high load acts. It is possible to suppress the occurrence of abnormal damage such as chipping and chipping, and as a result, it is possible to provide a cutting tool that exhibits excellent cutting performance over a long period of use.
When the cBN sintered body of the present invention is used as a cutting tool material, for example, the cBN sintered body is brazed to the brazed portion (corner portion) of the WC-based cemented carbide insert body and polished as necessary. By performing processing and honing processing, it is possible to produce a cutting tool having a desired insert shape using a cBN sintered body as a cutting edge.

Whether or not Ti compound particles are included in _{the Al 2} O ₃ particles dispersed in the bonded phase of the cBN sintered body of the present invention, and _{whether or not the Al 2} O ₃ particles containing Ti compound particles are included. The volume ratio of the volume to the total volume of the bonded phase, and the average volume ratio of the Ti compound particles contained in the _{Al 2} O _{3 particles can be determined as follows.}
The cross section of the cBN sintered body is polished so that the sample thickness is 100 nm or less, and the bonded phase region of the cBN sintered body is observed by TEM. Here, the reason why the sample thickness is set to 100 nm or less is that if the particles are overlapped during TEM observation, it cannot be determined whether the particles are contained particles or particles that are just overlapped.
The observation magnification is adjusted so that the diagonal length of the observation field is _{10 times the average particle size of the obtained Al 2} O ₃ particles (observation magnification 1), and the Al ₂ O ₃ particles containing Ti compound particles are contained. The content of the particles with respect to the bound phase is measured. Upon obtaining the average particle size of the Al ₂ O ₃ particles, _Al 2 _{O 3} particles calculates the particle size of _Al 2 _{O 3} particles from the field of view that can be at least 10 observations, and its average value. Since it is not possible to accurately identify whether the Ti compound particles are contained in the _{Al 2} O ₃ particles at the observation magnification of 1 observation magnification, _{the diameter of the circumscribing circle of the Al 2} O ₃ particles is 1/4 of the diagonal length of the observation field. In the field of view adjusted to be more than double (observation magnification 2), _{it is specified whether the Ti compound particles are contained in the Al 2} O ₃ particles, and the content of the contained particles is measured.
In the TEM observation (see FIG. 3 (a)), elemental mapping of Ti, Al, O, and N is performed, and the mapping image obtained by binarization (see FIGS. 3 (b) to (e)) and Ti. The overlapping portions of N, Al and O are designated as TiN and Al ₂ O ₃ (see FIG. 4). In Al ₂ O ₃ particles encapsulated the Ti compound particles, the superimposed observation magnification 2 image, a region that is continuous _{for Al} 2 _{O 3} is _Al 2 _{O 3} particles, the _Al 2 _{O 3} The Ti compound particles that are not in contact with the boundary of the particles and are present within the boundary of the Al ₂ O ₃ particles are specified, and this is specified as the Ti compound particles contained in the _{Al 2} O _{3 particles.} Further, in the binarization processing the measuring method to determine the volume of the cBN particles from an image similar to the measuring method, Al ₂ O ₃ content of particles and Ti compound was measured, Al ₂ in the observation magnification 1 field O ₃ calculates the amount of Ti compound particles are contained in the particles. Content relative binding phase of Al ₂ O ₃ particles of the enclosing Ti compound particles, observation magnification 1 with only Al ₂ O ₃ particles of the enclosing Ti compound particles from said binarizing the image Is extracted, and the content is calculated by the same measuring method as the measuring method for determining the volume of the cBN particles.
For the binarization process, the image processing software "imageJ" was used, and the binarization process was performed with the region containing the element as black. Further, the superposed image of the binarized image can be obtained by, for example, when superimposing the Ti and N images, inverting the white and black regions of the N image and subtracting the N image from the Ti image. ..

CBN sintered body of the present invention comprises _Al 2 _{O 3} particles to binder phase, moreover, among the _Al 2 _{O 3} particles, a binder phase _{tissue Al} 2 _{O 3} particles containing the Ti compound particles are present _{The content of the Al 2} O ₃ particles containing the Ti compound particles is 5% by volume or more and 50% by volume or less with respect to the total volume of the bonded phases of the cBN sintered body, and Ti the content of the compound particles Ti compound particles contained in _Al 2 _{O 3} particles to _Al 2 _{O 3} particles containing a preferably, since it is 3 vol% to 25 vol%, the hardness, strength, heat resistance It also has excellent toughness.
Therefore, when the cutting edge portion of the cutting tool is made of the cBN sintered body of the present invention, the occurrence of abnormal damage such as chipping and chipping is suppressed in intermittent cutting of alloy steel or the like on which a high load acts. As a result, it exhibits excellent cutting performance over a long period of use.

An example of the manufacturing process of the cBN sintered body by the conventional method is shown. An example of the manufacturing process of the cBN sintered body by this invention is shown. (A) shows an example of a TEM image (observation magnification 2) of the cBN sintered body of the present invention, and (b) to (e) are after binarization treatment for Al, N, O, and Ti, respectively. The mapping image is shown. _{"Al 2} O ₃ particles containing Ti compound particles" and " _{Ti compound contained in Al 2} O ₃ particles" obtained by superimposing the mapping images after the binarization treatment of FIGS. 3 (b) to 3 (e). Indicates "particle".

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

The cBN sintered body of the present invention was produced by the steps A to C shown below.
≪Process A≫
As the raw material powder for the bonded phase of the cBN sintered body, TiN powder, metal Al powder, and Al ₂ O ₃ powder having an average particle size in the range of 5 to 50 μm are prepared, and these raw material powders are wet-mixed in a ball mill. After drying, a molded product was prepared.
This molded product was vacuum sintered by holding it at 1000 ° C. for 30 minutes in a vacuum of 1 Pa or less.
Then, this sintered body was wet-pulverized in a ball mill and dried to prepare a mixed powder A having an average particle size of 0.3 to 0.9 μm (see “Step A” in FIG. 2).
In the mixing or crushing with a ball mill in the above step A and the step B described later, a cemented carbide ball and an object to be treated were sealed together with an organic solvent in a cemented carbide pot for mixing or crushing.
≪Process B≫
The raw material powder B was produced as follows in step B, which is a step different from the above step A.
TiN powder and metallic Al powder were prepared as Ti compound powder, and first, the Ti compound powder was wet-pulverized in a ball mill.
Then, the metal Al powder was put into the ball mill, the Ti compound powder and the metal Al powder were wet-mixed, a slurry solution was collected, dried, and then a molded product was prepared.
Then, vacuum sintering was performed in which the molded product was held at 1000 ° C. for 30 minutes in a vacuum of 1 Pa or less.
Then, this sintered body is wet-pulverized in a ball mill and dried to prepare a mixed powder, and then centrifugation is performed to collect a powder having a particle size of 10% or less, and this is mixed powder. It was designated as B (see "Step B" in FIG. 2).
≪Process 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%. The mixture is mixed by an ultrasonic method under the condition that the mixture is mixed at an output of 180 W at intervals of 15 seconds every 30 seconds for 15 minutes, dried, and then at a pressure of 3 to 6 GPa and in a temperature range of 1000 to 1600 ° C. The cBN sintered bodies 1 to 5 of the present invention (referred to as "Examples 1 to 5") shown in Table 1 were produced by high-pressure high-temperature sintering at 6 GPa and 1500 ° C., which is one of the sintering conditions (FIG. See "Step C" in 2).

For comparison, cBN sintered bodies 1 to 3 (referred to as “Comparative Examples 1 to 3”) of Comparative Example were produced by the following conventional steps (see “Step A” in FIG. 1).
First, as the raw material powder for the bonded phase of the cBN sintered body, TiN powder, TiC powder, metal Al powder, and Al ₂ O ₃ powder having an average particle size in the range of 5 to 50 μm are prepared, and these raw material powders are used. After wet mixing in a ball mill and drying, a molded product was prepared.
This molded product was vacuum sintered by holding it at 1000 ° C. for 30 minutes in a vacuum of 1 Pa or less.
Then, this sintered body was wet-ground 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 is referred to as “mixed powder A”). ..
The mixed powder A and cBN particles having an average particle size of 3 μm are mixed with a ball mill so that the cBN content is 50 vol%, dried, and then at a pressure of 3 to 6 GPa and in a temperature range of 1000 to 1600 ° C. Comparative Examples 1 to 3 shown in Table 1 were produced by high-pressure high-temperature sintering under sintering conditions.
That is, the production methods of Comparative Examples 1 to 3 do not provide the step B in the production methods of the sintered bodies 1 to 5 of the present invention, and the mixing with the cBN particles is performed by a ball mill instead of the ultrasonic method. Is different.

In Examples 1 to 5 and Comparative Examples 1 to 3 prepared above, in order to facilitate the evaluation of the influence of the bonded phase on the cutting performance, the average particle size of the cBN particles is kept constant at 3 μm, and the cBN particles are used. The content ratio of is as small as 50% by volume to increase the content ratio of the bound phase.
However, the average particle size and content ratio of the cBN particles are not limited to the above, and various values can be taken.
The average particle size (μm) of the cBN particles and the content ratio (vol%) of the cBN particles in the cBN sintered body can be 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. The part of the cBN particles in the obtained image is extracted by image processing, the maximum length of each particle obtained by image analysis is obtained, and this is used as the diameter of each particle, and the volume assuming that each particle is an ideal sphere. To calculate.
The volume% of the cBN particles is calculated by using the average value of the diameters of the cBN particles obtained from at least three images as the average particle size (μm) of the cBN. The observation area used for image processing is preferably 15 μm × 15 μm.
Further, in the embodiment, the sintering condition is set to 6 GPa 1500 ° C., but the superiority or inferiority of the cutting performance does not change depending on the sintering condition.

Further, specific _Al 2 _{O 3} particles containing the Ti compound particles in the binding phase, measurement of the content of _Al 2 _{O 3} particles containing the Ti compound particles to the binder phase of the cBN sintered body, containing the Ti compound particles for Al ₂ O ₃ particles, measurement of the content of the Ti compound particles contained in the _Al 2 _{O 3} particles, also containing the _Al 2 _{O 3} particles (Ti compound particles contained in the binder phase of the cBN sintered body The content of (including those with and without inclusion) was measured as follows.
The cross section of the cBN sintered body was polished so that the sample thickness was 100 nm or less, and the bonded phase region of the cBN sintered body was observed by TEM. Here, the sample thickness is set to 100 nm or less because if the particles are overlapped during TEM observation, it cannot be determined whether the particles are contained particles or particles that are just overlapped.
The observation magnification is adjusted so that the diagonal length of the observation field is _{10 times the average particle size of the obtained Al 2} O ₃ particles (observation magnification 1), and the Al ₂ O ₃ particles containing Ti compound particles are contained. The content of the compound with respect to the bound phase is measured. However, since it is not possible to accurately identify whether the Ti compound particles are contained in the _{Al 2} O ₃ particles at the observation magnification of 1 observation magnification, _{the diameter of the circumscribing circle of the Al 2} O ₃ particles is the diagonal length of the observation field. In a visual field adjusted to 1/4 times or more (observation magnification 2), it is specified whether or not Ti compound particles are contained in _{Al 2} O _{3 particles, and the content of the contained particles is measured.}
In TEM observation, elemental mapping of Ti, Al, O, and N is performed, and the overlapping portions of Ti and N, and Al and O of the mapping image obtained by binarization are overlapped with TiN and Al ₂ O _{3, respectively.} And. In Al ₂ O ₃ particles encapsulated the Ti compound particles, the superimposed observation magnification 2 image, a region that is continuous _{for Al} 2 _{O 3} is _Al 2 _{O 3} particles, the _Al 2 _{O 3} The Ti compound particles that are not in contact with the boundary of the particles and are present within the boundary of the Al ₂ O ₃ particles are specified, and this is specified as the Ti compound particles contained in the _{Al 2} O _{3 particles.} Further, in the binarization processing the measuring method to determine the volume of the cBN particles from an image similar to the measuring method, Al ₂ O ₃ content of particles and Ti compound was measured, Al ₂ in the observation magnification 1 field O ₃ calculates the amount of Ti compound particles are contained in the particles. Content relative binding phase of Al ₂ O ₃ particles of the enclosing Ti compound particles, observation magnification 1 with only Al ₂ O ₃ particles of the enclosing Ti compound particles from said binarizing the image Is extracted, and the content is calculated by the same measuring method as the measuring method for determining the volume of the cBN particles.
Table 1 shows these values.

Then, the upper and lower surfaces of the sintered bodies of Examples 1 to 5 and Comparative Examples 1 to 3 were polished with a diamond grindstone, divided by a wire electric discharge machine, and further, Co: 5% by mass and TaC: 5 mass. %, WC: Cu: 26%, Ti: 5%, Ag: by mass% on the brazed part (corner part) of the WC-based cemented carbide insert body having the remaining composition and the shape of ISO standard CNGA120408. The cBN sintered body cutting tool 1 of the present invention having an insert shape of ISO standard CNGA120408 by brazing using an Ag alloy brazing material having the remaining composition, and further performing upper and lower surface and outer circumference polishing and honing processing. ~ 5 and cBN sintered body cutting tools 1 to 3 of the comparative example were prepared, respectively.

Next, with all of the above-mentioned various cutting tools screwed to the tip of the tool steel cutting tool with a fixing jig, each tool was subjected to a wet intermittent cutting test under the following cutting conditions. The quality of the toughness of the cBN sintered body was evaluated.
Cutting conditions:
Work material: JIS / SCr420 (HRC58-62) round bar (however, there are two slits at equal intervals in the axial direction of the work material)
Cutting speed: 200 m / min. ,
Feed amount: 0.05 rev / mm,
Cut amount: 0.10 mm
Condition: Wet In the above wet intermittent cutting test, the tool life is the number of interruptions (impacts) until the cutting edge of the cutting tool chips or breaks, and the maximum number of interruptions (impacts) is 5500. A processing test was carried out.
The cutting edge was observed every 100 times of interruption (number of impacts), and the presence or absence of chipping of the cutting edge and the presence or absence of defects were observed.
The cutting test results of the cBN sintered body cutting tools 1 to 5 of the present invention and the cBN sintered body cutting tools 1 to 3 of the comparative example are shown in the columns of Examples 1 to 5 and Comparative Examples 1 to 3 in Table 1, respectively. show.

As shown in Table 1, all of the cBN sintered body cutting tools 1 to 5 of the present invention have excellent toughness of the cBN sintered body constituting the cutting edge, so that abnormal damage such as chipping and chipping occurs. Demonstrates excellent cutting performance over long-term use.
Further, as is clear from the comparison between Examples 1 and 5 and Comparative Example 1, the comparison between Examples 2 and 3 and Comparative Example 2, and the comparison between Example 4 and Comparative Example 3, the sintered body Even if the content of the Al ₂ O ₃ particles in the particle is about the same, in the present invention, the cutting performance is remarkably improved by containing the Ti compound particles in the _{Al 2} O _{3 particles.} Recognize.

On the other hand, in the cBN sintered body cutting tools 1 to 3 of the comparative example, the Ti compound particles are not included in _{the Al 2} O _{3 particles existing in the bonding phase of the cBN sintered body constituting the cutting edge.} Therefore, it is clear that the toughness of the cBN sintered body is not sufficient, and as a result, the life is reached in a short period of time due to the occurrence of abnormal damage such as chipping and chipping.

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

Claims (3)

In the cubic nitrided boron-based sintered body composed of the cubic boron nitride particles and the bonded phase, the content of the cubic nitrided boron particles is 40% by volume or more of 85% by volume or more of the cubic nitrided boron-based sintered body. or less% by volume, said binder phase comprises _Al 2 _{O 3} particles, moreover, among the _Al 2 _{O 3} particles, there are _Al 2 _{O 3} particles containing the Ti N particles, containing the TiN particles the content of Al ₂ O ₃ particles, cubic boron nitride containing groups sintered body characterized by having a 5 vol% to 50 vol% der Ru binder phase structure of the binder phase. For _Al 2 _{O 3} particles containing the Ti N particles, the content of Ti N particles contained in _Al 2 _{O 3} particles to claim 1, characterized in that 25% by volume or less 3% or more by volume The described cubic boron nitride based sintered body. A cutting tool made of 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 claim 1 or 2.

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