JP6256169B2 - Cubic boron nitride composite sintered body, method for producing the same, cutting tool, wear-resistant tool, and grinding tool - Google Patents

Description

  The present invention relates to a cubic boron nitride composite sintered body, a method for producing the same, and a cutting tool, an abrasion resistant tool, and a grinding tool including the cubic boron nitride composite sintered body.

  A cubic boron nitride (cBN) sintered body has a very high hardness and is excellent in thermal stability and chemical stability, and is therefore used in cutting tools and anti-wear tools.

  As a material for such a cBN sintered body, a cBN single crystal or a cBN polycrystal is used [for example, Japanese Patent Application Laid-Open No. 47-34099 (Patent Document 1), Japanese Patent Application Laid-Open No. 3-159964 (Patent Document 1). Document 2), Japanese Patent Publication No. 63-394 (Patent Document 3), Japanese Patent Application Laid-Open No. 8-47801 (Patent Document 4), Japanese Patent Application Laid-Open No. 11-335174 (Patent Document 5) and Japanese Patent Application Laid-Open No. 11-335175. See (Patent Document 6). ].

JP 47-34099 A JP-A-3-159964 Japanese Patent Publication No. 63-394 Japanese Patent Laid-Open No. 8-47801 Japanese Patent Laid-Open No. 11-335174 Japanese Patent Laid-Open No. 11-335175

  Conventionally, cBN sintered bodies used for cutting tools and the like are manufactured by sintering cBN powder together with a sintering aid or a binder under a pressure of about 4 to 5 GPa. That is, the cBN sintered body includes a binder and a sintering aid such as titanium nitride (TiN), titanium carbide (TiC), and cobalt (Co) in addition to the cBN powder.

  Normally, cBN powder as a raw material of a cBN sintered body is made of hexagonal boron nitride (hBN) at high temperature and high pressure using a nitride or boronitride of an alkali metal or alkaline earth metal as a catalyst. cBN single crystal converted to cBN.

  However, since the cBN sintered body contains about 10 to 40% by volume of a binder, it is inferior in hardness and thermal conductivity as compared with a cBN single crystal. Moreover, since a cBN single crystal contains a catalyst as an inclusion, the strength is not sufficient, and the strength tends to decrease particularly at high temperatures. Furthermore, cBN crystals also have the property of being easily cleaved. Therefore, in a cutting tool using a cBN sintered body, the tool blade edge may be worn or chipped due to cBN crystal grain destruction or microchipping due to cleavage.

  Therefore, cBN polycrystals containing no catalyst or binder have also been proposed (for example, Patent Documents 1 to 4). In these documents, a cBN polycrystal is produced by directly converting hBN to cBN without using a catalyst.

  However, since the method disclosed in Patent Documents 1 to 4 uses hBN or pyrolytic Boron Nitrde (pBN) having good crystallinity as a starting material, the conversion from the starting material to cBN is performed at 2100 ° C. The above high temperature is required. As a result, the crystal grain size of the cBN crystal grains constituting the polycrystal is increased to about 3 to 5 μm, the bonding force between the grains is weak, and the strength at high temperature is low.

  Based on the above, in order to improve the cutting performance and life of the cBN sintered body, a tougher cBN powder (raw material) is required. A candidate for such raw material is cBN polycrystalline abrasive. The cBN polycrystalline abrasive grains are partly used as grinding abrasive grains, and have improved strength compared to single crystal abrasive grains. However, in the conventional cBN polycrystalline abrasive grains, the primary particles (single crystals) constituting the polycrystals are coarse and irregular, with several μm to several tens of μm, and the strength is not sufficient.

  Patent Document 5 and Patent Document 6 are directed to the production of tough cBN powder. These documents disclose that a cBN single-phase polycrystal having high purity, high strength and excellent heat resistance is prepared, and pulverized to obtain a raw material for a sintered body.

  However, this method synthesizes cBN polycrystalline abrasive grains under high temperature and high pressure, and then synthesizes cBN polycrystalline abrasive grains and a binder as starting materials again under ultra high pressure and high temperature, which takes time and effort. Not economical. In addition, the cBN polycrystalline abrasive grains obtained by this method have insufficient bonding strength between the particles, low fracture resistance, and the strength is not yet sufficient.

  Then, in view of said subject, it aims at providing the cubic boron nitride compound sintered compact excellent in abrasion resistance and fracture resistance, and a cutting tool, an abrasion-resistant tool, and a grinding tool.

The cubic boron nitride composite sintered body according to one aspect of the present invention is
A cubic boron nitride polycrystal and a ceramic phase,
Containing the cubic boron nitride polycrystal in the range of 40 vol% or more and 80 vol% or less,
The cubic boron nitride polycrystal includes a cubic boron nitride single crystal having an average crystal grain size of 500 nm or less, and wurtzite boron nitride,
The cubic boron nitride polycrystal contains 0.01% by volume or more of the wurtzite boron nitride.

In addition, the method for producing a cubic boron nitride composite sintered body according to one aspect of the present invention,
A method for producing a cubic boron nitride composite sintered body containing a cubic boron nitride polycrystal in a range of 40 vol% to 80 vol%,
A first step of mixing a normal pressure boron nitride and a ceramic to obtain a mixture;
A second step of sintering the mixture under conditions of a pressure of 8 GPa or more and a temperature of 1500 ° C. or more and less than 2300 ° C.,
In the second step, the atmospheric boron nitride is directly converted into cubic boron nitride.

  According to the above, a cubic boron nitride composite sintered body excellent in wear resistance and fracture resistance is provided. This cubic boron nitride composite sintered body can be used for cutting tools, wear-resistant tools, and grinding tools.

It is a plane schematic diagram which shows an example of the sintered compact structure | tissue in the cubic boron nitride compound sintered compact which concerns on 1 aspect of this invention. It is a plane schematic diagram which shows an example of the sintered compact structure | tissue in the cubic boron nitride compound sintered compact which concerns on a reference example. It is a flowchart which shows the outline of the manufacturing method of the cubic boron nitride compound sintered compact which concerns on 1 aspect of this invention.

[Description of Embodiment of the Present Invention]
First, embodiments of the present invention will be listed and described.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor has started a mixture of normal pressure boron nitride (hereinafter also referred to as “normal pressure BN”) and ceramics, a pressure of 8 GPa or higher, and a temperature. Has found that a cBN composite sintered body containing a high-strength cBN polycrystal can be produced by directly converting normal pressure BN to cBN and simultaneously sintering with ceramics under the condition of 1500 ° C. or more and less than 2300 ° C. Thus, one embodiment of the present invention has been completed. That is, the cubic boron nitride composite sintered body according to one aspect of the present invention has the following configuration.

  [1] The cubic boron nitride composite sintered body includes a cubic boron nitride polycrystal and a ceramic phase, and contains the cubic boron nitride polycrystal in a range of 40% by volume to 80% by volume. The cubic boron nitride polycrystal includes a cubic boron nitride single crystal having an average crystal grain size of 500 nm or less and a wurtzite boron nitride, and the cubic boron nitride polycrystal includes the wurtzite Contains 0.01% by volume or more of type boron nitride.

  As described above, the composite sintered body containing the cBN polycrystal in the range of 40% by volume to 80% by volume has a sintered body structure in which the cBN polycrystal is dispersed in an island shape in the continuous ceramic phase. . In this sintered body structure, cBN single crystals, wurtzite boron nitride (wBN), and ceramics are firmly bonded to each other. Further, in the sintered body structure, cBN and wBN, and the cBN polycrystalline body and ceramics are firmly bonded to form a dense structure.

  Here, since the cBN single crystal constituting the cBN polycrystal is a fine crystal having an average crystal grain size of 500 nm or less, it is excellent in strength and toughness. In addition, wBN contained in the cBN polycrystalline body has an action of preventing the progress of cracks in the sintered body structure and improving toughness. Together with these, the cBN composite sintered body exhibits excellent wear resistance and fracture resistance.

Note that the average crystal grain size of the cBN single crystal is measured by a cutting method described later.
[2] The cubic boron nitride polycrystal preferably further contains a compressed hexagonal boron nitride in a range of 0.01% by volume to 0.5% by volume.

  This is because the presence of the compressed hBN at the above volume content has an effect of preventing the progress of cracks and improving the toughness.

  [3] The ceramic phase preferably contains one or more of carbides, nitrides, carbonitrides and borides of titanium (Ti), hafnium (Hf), zirconium (Zr) and tungsten (W). This is because such a ceramic phase is excellent in wear resistance.

  [4] The ceramic phase preferably further contains aluminum (Al). This is because the wear resistance is further improved.

One embodiment of the present invention also provides a method for producing a cBN composite sintered body.
[5] That is, the method for producing a cubic boron nitride composite sintered body is a method for producing a cubic boron nitride composite sintered body containing a cubic boron nitride polycrystal in a range of 40% by volume to 80% by volume. A first step of mixing atmospheric boron nitride and ceramics to obtain a mixture, and a second step of sintering the mixture under conditions of a pressure of 8 GPa or more and a temperature of 1500 ° C. or more and less than 2300 ° C. In the second step, atmospheric boron nitride is directly converted into cubic boron nitride.

  According to this manufacturing method, the cBN composite sintered body described in any one of the above [1] to [4] can be easily manufactured.

  “Direct conversion” means that the starting material is directly converted to cBN in the absence of a catalyst. The above production method sinters the mixture simultaneously with this direct conversion, which is a production method to be called “direct conversion sintering”. Through this direct conversion sintering, the intergranular bond in the cBN composite sintered body becomes strong. In addition, in the synthesized sintered body, the average grain size of the cBN single crystal can be controlled to 500 nm or less, and wBN can be generated.

One aspect of the present invention also relates to cutting tools, anti-wear tools and grinding tools.
[6] A cutting tool according to an aspect of the present invention includes the cubic boron nitride composite sintered body described in any one of [1] to [4].

  This cutting tool has excellent wear resistance and fracture resistance based on the properties of the above-described cBN composite sintered body.

  [7] A wear-resistant tool according to an aspect of the present invention includes the cubic boron nitride composite sintered body described in any one of [1] to [4].

  This wear-resistant tool has excellent wear resistance and fracture resistance based on the properties of the above-described cBN composite sintered body.

  [8] A grinding tool according to an aspect of the present invention includes the cubic boron nitride composite sintered body described in any one of the above [1] to [4].

  This grinding tool has excellent wear resistance and fracture resistance based on the properties of the above-described cBN composite sintered body.

  In these tools, the entire tool may be composed of a cBN composite sintered body, or a part thereof (for example, a cutting edge portion of a cutting tool) is composed of a cBN composite sintered body. May be.

[Details of the embodiment of the present invention]
Hereinafter, embodiments of the present invention (hereinafter also referred to as “this embodiment”) will be described in detail, but the present embodiment is not limited thereto.

<CBN composite sintered body>
The cBN composite sintered body of the present embodiment includes a cBN polycrystal and a ceramic phase. FIG. 1 is a schematic plan view showing an example of a sintered body structure in the cBN composite sintered body of the present embodiment. Such a sintered body structure can be confirmed by, for example, a scanning electron microscope (SEM).

  The cBN composite sintered body of the present embodiment contains the cBN polycrystal in the range of 40% by volume to 80% by volume. The cBN composite sintered body containing the cBN polycrystal within such a range has a structure in which the cBN polycrystals 10 are scattered in islands in the ceramic phase 2 continuous in a matrix form as shown in FIG. When such a cBN composite sintered body is applied to a cutting tool, the ceramic phase 2 is exclusively responsible for cutting the work material, and the cBN polycrystalline body 10 plays a role as a framework for supporting the sintered body structure. . The reactivity of the ceramic phase 2 with the metal (work material) can be controlled by its composition. Therefore, the cBN composite sintered body containing the cBN polycrystal with the volume content is effective for cutting high hardness steel such as hardened steel. The range of the volume content of the cBN polycrystal is more preferably 40% by volume to 60% by volume, and particularly preferably 50% by volume to 60% by volume.

(CBN polycrystal)
The cBN polycrystal 10 is composed of a cBN single crystal 1 having an average crystal grain size of 500 nm or less. Thus, since the cBN single crystal 1 is fine, the cBN polycrystal 10 is excellent in strength and toughness. FIG. 2 is a schematic plan view showing an example of a sintered body structure of a reference example (conventional). In this sintered body structure, the cBN single crystal 11 having a large crystal grain size is dispersed in the ceramic phase 12. In such a structure, the cBN single crystal 11 is broken or cleaved during cutting, so that the strength and toughness are not sufficient. On the other hand, the cBN polycrystalline body 10 composed of the fine cBN single crystal 1 as in the present embodiment shows the progress of the breakdown even if the cBN single crystal 1 is partially broken, etc. 10 can be stopped. Further, the fine cBN single crystal 1 itself is not easily broken and has high strength. Therefore, the cBN composite sintered body of this embodiment is excellent in wear resistance and fracture resistance as compared with the cBN sintered body shown in FIG.

  In this specification, as shown in FIG. 1, the cBN single crystal 1 constitutes the cBN polycrystalline body 10 and the cBN polycrystalline body 10 has a structure dispersed in the ceramic phase 2. A structure having a structure in which the cBN single crystal 11 is dispersed in the ceramic phase 12 as shown in FIG. 2 is referred to as a “cBN sintered body”.

(Average crystal grain size)
In the present embodiment, the average crystal grain size of the cBN single crystal needs to be 500 nm or less. The average crystal grain size is preferably less than 470 nm, more preferably 200 nm or less, and particularly preferably 100 nm or less. The lower limit is not particularly limited as the average crystal grain size is smaller from the viewpoint of strength, but the lower limit is preferably about 20 nm in consideration of productivity.

(Measuring method of average crystal grain size)
The average crystal grain size of the cBN single crystal is measured by a cutting method. The measurement procedure is as follows. First, a sintered body structure is imaged with an SEM to obtain an SEM image. Next, a circle is drawn in the SEM image, and further, eight straight lines are drawn radially from the center of the circle to the outer periphery of the circle (at this time, the angle formed by two adjacent straight lines is 45 °). Next, the number of times each straight line crosses the grain boundary (that is, the boundary between the cBN single crystals) in the circle is counted. Then, by dividing the length of the straight line by the number of crossings, the average intercept length is obtained, and the average crystal grain size can be calculated by multiplying the average intercept length by 1.128.

  In measurement, the imaging magnification of the SEM is desirably 30000 times. If it is less than 30000 times, the number of crystal grains contained in the image increases and it becomes difficult to discriminate grain boundaries. If it exceeds 30000 times, the number of crystal grains contained in the image becomes excessively small and accurate. This is because an average crystal grain size cannot be calculated.

  In order to be more accurate, it is also desirable to prepare a plurality of (for example, three separate locations) SEM images, calculate the average crystal grain size in each image, and set the average value as the average crystal grain size.

  The size of the circle (diameter of the circle) is determined in consideration of the number of cBN single crystals included in the circle. That is, a circle is drawn so that the number of crystal grain boundaries crossed by one straight line is 10 or more. The larger the number of grain boundaries that one straight line crosses, the more desirable from the viewpoint of measurement reliability. However, in order to avoid complicated operations, the upper limit of the number of crystal grain boundaries that one straight line crosses can be set to about 50, for example.

  If the average grain size of the cBN single crystal is 500 nm or less, if the circle of the SEM image taken at a magnification of 30000 times is the center of the circle and the largest possible circle is drawn to fit within the image, one The number of crystal grain boundaries crossed by the straight line is usually 10 or more. In addition, the crystal grain size distribution measured by the above procedure is generally close to a bell-shaped distribution (normal distribution) symmetrical about the average value (average crystal grain size). Therefore, the average crystal grain size in this specification can be said to be an average value based on a normal distribution.

(Wurtzite boron nitride)
The cBN composite sintered body of the present embodiment contains 0.01% by volume or more of wBN. By containing wBN, the progress of cracks is suppressed and the toughness is improved. The upper limit is not particularly limited as the content of wBN increases, but the upper limit is preferably about 60% by volume in consideration of the uniformity of the structure. The content of wBN is more preferably 0.1% by volume or more, particularly preferably 1.0% by volume or more, and most preferably 2.0% by volume or more.

  The volume content of cBN, wBN, and compressed hBN described later can be measured by a conventionally known method such as an X-ray diffraction method.

(Compressed hexagonal boron nitride)
The cBN polycrystal can contain compressed hBN in a range of 0.01 vol% to 0.5 vol%. The compression-type hBN is hBN that is compressed by applying stress from a surrounding substance (for example, cBN). For example, the plane distance of the (002) plane of the compression type hBN is shorter than the plane distance (0.333 nm) of normal hBN (normal pressure type hBN).

  The presence of compressed hBN that is 0.01% by volume or more and 0.5% by volume or less does not affect the strength of the cBN composite sintered body. In addition, it has the effect of preventing the growth of cracks and improving toughness. Further, by allowing the presence of the compression type hBN, sintering is possible in a wide temperature range, and productivity is improved. However, when the compression type hBN exceeds 0.5% by volume, the stress concentration in the compression type hBN becomes large, and the strength may decrease. Therefore, when the cBN composite sintered body further contains compression-type hBN, the upper limit is 0.5% by volume. The volume content of the compressed hBN is more preferably 0.01% by volume to 0.1% by volume, and particularly preferably 0.05% by volume to 0.1% by volume.

(Ceramics phase)
The ceramic phase is composed of one or more kinds of ceramics. The ceramic phase preferably contains at least one of Ti, Hf, Zr and W carbides, nitrides, carbonitrides and borides. It is because abrasion resistance improves by including these compounds. Specific examples of such compounds include TiC, TiN, TiCN, TiB ₂ , HfC, HfN, HfCN, HfB ₂ , ZrC, ZrN, ZrCN, ZrB ₂ , WC, W ₂ C, WB _{2 and the} like. The range of the volume content of the ceramic phase in the cBN composite sintered body is, for example, about 20% by volume to 60% by volume, preferably 40% by volume to 60% by volume, and more preferably 40% by volume to 50% by volume. % By volume or less.

  In the present specification, when a compound is represented by a chemical formula as described above, it is intended to include all conventionally known atomic ratios unless the atomic ratio is particularly limited, and is not necessarily limited to a stoichiometric range. For example, when “TiN” is described, the atomic ratio between “Ti” and “N” is not limited to 50:50, and any conventionally known atomic ratio is included.

The ceramic phase can further include Al. This is because the wear resistance is further improved. In the ceramic phase, for example, Al may constitute a nitride or boride such as AlN or AlB ₂ , or may constitute a complex compound with Ti or the like such as TiAlN.

<Method for producing cBN composite sintered body>
The above-mentioned cBN composite sintered body can be manufactured by the method described below. FIG. 3 is a flowchart showing an outline of the manufacturing method of the present embodiment. Referring to FIG. 3, the manufacturing method includes a first step (S101) and a second step (S102). Hereinafter, each step will be described.

(First step)
In the first step (S101), normal pressure BN and ceramics are mixed to obtain a mixture. In the first step, first, an atmospheric BN powder (for example, hBN powder) and a ceramic powder are prepared.

The ceramic powder is selected according to the composition of the target ceramic phase. For example, TiN _0.6 powder, TiC powder, HfN powder, ZrN powder, WC powder and the like can be used. You may mix Al powder with these.

  Next, these powder raw materials are mixed. At the time of mixing, the blending of each raw material is adjusted so that the volume content of the cBN polycrystalline body is 40% by volume or more and 80% by volume or less in the finally obtained cBN composite sintered body. For mixing, for example, a mixing device such as a ball mill or an attritor can be used. The mixing time is, for example, about 5 hours to 24 hours.

  In the mixture thus obtained, the hBN powder may contain an adsorbed gas such as boron oxide or moisture generated by the influence of surface oxidation during mixing. These impurities hinder direct conversion to cBN, or act as a catalyst to cause grain growth and weaken the bond between cBN single crystals. Therefore, it is preferable to remove impurities by performing a high-temperature purification treatment. For example, boron oxide and adsorbed gas are removed by heat treatment under conditions of 2050 ° C. or higher in nitrogen gas or 1650 ° C. or higher in vacuum. The mixture thus obtained has very few impurities and is suitable for direct conversion sintering.

(Second step)
In the second step (S102), the mixture is sintered under conditions where the pressure is 8 GPa or more and the temperature is 1500 ° C. or more and less than 2300 ° C. At this time, the normal pressure type BN is directly converted into cBN. That is, the mixture is sintered simultaneously with the conversion of hBN. As long as the pressure during sintering (hereinafter also referred to as “synthesis pressure”) is 8 GPa or more, cBN can be freely set within a thermodynamically stable range. However, considering the burden on the process, the upper limit of the combined pressure is, for example, about 20 GPa, preferably about 16 GPa.

  The range of sintering temperatures at which cBN can be synthesized varies with the synthesis pressure. For example, when the synthesis pressure is 10 GPa, the sintering temperature is suitably 1900 ° C. or more and less than 2300 ° C., and when the synthesis pressure is 20 GPa, the sintering temperature is suitably 1500 ° C. or more and less than 2300 ° C. Below these lower limit temperatures, conversion to cBN may be insufficient. In either case, when the sintering temperature is 2300 ° C. or higher, wBN is not generated. Accordingly, the sintering temperature range needs to be at least 1500 ° C. and less than 2300 ° C. The range of the sintering temperature is preferably 1800 ° C. or higher and 2200 ° C. or lower, and more preferably 1900 ° C. or higher and 2100 ° C. or lower.

  By executing the above steps, it is possible to appropriately control the bonding strength between the cBN single crystals or between the cBN polycrystal and the ceramic phase, and further the crystal grain size of the cBN single crystal. A cBN composite sintered body can be easily produced.

<Cutting tools, anti-wear tools and grinding tools>
Since the cBN composite sintered body of the present embodiment has excellent wear resistance and fracture resistance as described above, it can be used for cutting tools, wear resistant tools, and grinding tools.

  The cBN composite sintered body of the present embodiment can be widely applied to conventionally known cutting tools, wear-resistant tools, and grinding tools. The following can be illustrated as such a tool. Examples of the cutting tool include a cutting tool, a drill, an end mill, a milling cutting edge replacement cutting tip, a turning cutting edge replacement cutting tip, a metal saw, a gear cutting tool, a reamer, or a tap. Examples of the anti-wear tool include a die, a scriber, a scribing wheel, or a dresser. Furthermore, as a grinding tool, a grinding wheel etc. can be illustrated, for example.

  The cBN composite sintered body of the present embodiment may constitute the whole of these tools, or may constitute a part thereof. Here, “constituting a part” indicates, for example, a cutting tool in which a cBN composite sintered body is brazed to a predetermined position of a cemented carbide base material to form a cutting edge portion. .

  Hereinafter, although this embodiment is described in detail using an example, this embodiment is not limited to these.

[Production of cBN composite sintered body]
In the following manner, no. 1-No. 9, no. 11, no. 12 and no. 16-No. A cBN composite sintered body according to No. 18 was produced. No. 13-No. CBN sintered body according to No. 15 was procured. Here, no. 1-No. 9 corresponds to an example, and the other corresponds to a comparative example.

<No. 1-No. 12>
(First step)
First, hBN powder having an average particle size of 10 μm and various ceramics shown in Table 1 were prepared as starting materials (raw materials). Ceramics were blended at a mass ratio shown in Table 1, and hBN and ceramics were further mixed for 5 hours using a ball mill. This gave a mixture. Then, the mixture was heat-treated at a temperature of 2050 ° C. in a nitrogen atmosphere to remove impurities (high-temperature purification treatment).

(Second step)
The mixture subjected to the high-temperature purification treatment is put into a capsule made of a refractory metal, and kept for 20 minutes under the pressure and temperature conditions shown in Table 1 using an ultra-high pressure and high-temperature generator to convert the starting material hBN into cBN. And converted directly. In the mixing stage, the blending amounts of the hBN powder and the ceramic powder were adjusted so that the volume content of the cBN polycrystalline body in the composite sintered body became the value shown in Table 1 when hBN was converted to cBN.

  As shown in Table 1, each cBN composite sintered body obtained in this way contains cBN, high-pressure phase BN such as wBN, and nitrides, borides and the like generated by the reaction of ceramics and BN. It was.

  The composition of BN contained in each cBN composite sintered body (that is, the volume content of cBN, wBN and compressed hBN) and the composition of the ceramic phase were identified using an X-ray diffractometer. At this time, the X-ray source was Cu, and the characteristic X-ray was Kα ray (wavelength: 1.54 mm).

  The average crystal grain size of the cBN single crystal shown in Table 1 was measured by the cutting method as described above. At this time, the magnification of the SEM image was 30000 times. In this experiment, SEM images were taken at three different locations for one sample, the average crystal grain size was determined from each SEM image by a cutting method, and the arithmetic average value of the three values thus obtained was obtained. Was the average crystal grain size.

  During SEM observation, the ceramic phase was continuously connected in each cBN composite sintered body, and it was confirmed that the cBN polycrystals were bonded to each other via the ceramic phase.

<No. 13-No. 15>
No. 13-No. No. 15, a cutting chip made of a commercially available cBN sintered body was procured. These samples are manufactured using a cBN single crystal (powder) having an average particle diameter of 1000 to 2000 nm and ceramic powder as raw materials. Table 2 shows the composition of the ceramic phase, the content of the cBN single crystal, and the average crystal grain size of the cBN single crystal in these samples. The average crystal grain size and the ceramic phase composition in Table 2 were measured and identified by the methods described above.

<No. 16-No. 18>
No. 16-No. 18 was produced as follows. First, cBN polycrystalline powder and various ceramic powders having an average particle diameter of 2 to 4 μm were prepared as starting materials. This cBN polycrystalline powder is a powder made of a polycrystalline body (secondary particles) in which fine cBN single crystals having an average crystal grain size of 500 nm or less are aggregated. The composition of the ceramic powder used is as shown in Table 3. These raw materials were mixed for 5 hours using a ball mill to obtain a mixture. The obtained mixture was heat-treated in a vacuum at a temperature of 1000 ° C. to remove adsorbed gas such as moisture adhering to the powder surface (high purification treatment).

  The mixture of cBN polycrystalline body and ceramics that had been subjected to high purification treatment was put into a capsule made of a refractory metal, and held for 20 minutes under the pressure and temperature conditions shown in Table 3 using an ultrahigh pressure and high temperature apparatus. Thereby, a cBN composite sintered body was obtained. Table 3 shows the content of the cBN polycrystal and the composition of the ceramic phase in these samples. The compositions of BN and ceramic phase in Table 3 are those identified by the method described above.

[Manufacture of cutting tools and evaluation of cutting performance]
No. 1-No. 12 and no. 16-No. The cBN composite sintered body according to 18 was processed into a cutting chip. These cutting tips, and No. 13-No. Using the cutting tip (cBN sintered body) according to No. 15, a cutting test was performed under the following cutting condition A to evaluate the wear resistance. The results are shown in Table 4.

(Cutting condition A)
Cutting method: Dry cutting Work material: Round bar of hardened steel SCM415H (hardness: HRC58-62) Cutting speed: 100mm / min
Cutting depth: 0.2mm
Feed: 0.1 mm / rev.
Evaluation method: Amount of flank wear when cutting 5 km (unit: mm).

  Moreover, the chip | tip for cutting was used, the cutting test was done on the following cutting conditions B, and fracture resistance was evaluated. The results are shown in Table 4.

(Cutting condition B)
Cutting method: Dry cutting Work material: Round bar of hardened steel SCM415H (having 8 V-shaped grooves)
Cutting speed: 100 mm / min
Cutting depth: 0.2mm
Feed: 0.1 mm / rev.
Evaluation method: Cutting time until the cutting edge is lost (unit: minute).

〔Results and discussion〕
From Table 1 to Table 4, cBN composite sintered bodies (No. 11 and No. 12) that do not contain wBN, or cBN sintered bodies (No. 13 to No. 13) sintered using a cBN single crystal as a starting material (raw material). It can be seen that No. 15) does not have sufficient wear resistance and fracture resistance.

  On the other hand, the cBN polycrystal contains a cBN polycrystal and a ceramic phase, the cBN polycrystal is contained in the range of 40 vol% to 80 vol%, and the cBN polycrystal has an average crystal grain size of 500 nm or less. The cBN composite sintered body (No. 1 to No. 9) contains a single crystal and wBN, and the cBN polycrystalline body contains 0.01% by volume or more of wBN, and is excellent in wear resistance and fracture resistance. I understand that

  Further, from the results, a normal pressure type BN and ceramics were mixed to obtain a mixture, and the mixture was sintered, and at the same time, the normal pressure type BN was directly converted into cBN (No. 2). 1 to No. 9) were proved to be superior in wear resistance and fracture resistance to cBN composite sintered bodies (No. 16 to No. 18) simply sintered using cBN polycrystals as raw materials. I can say that. The reason for this is considered to be that through direct conversion sintering, wBN is generated and the intergranular bond between the cBN single crystal and cBN polycrystal and the ceramic phase is strengthened.

  In this experiment, evaluation was performed using a cutting tool. However, in view of the above results, it is presumed that the same result can be obtained even with an abrasion resistant tool or a grinding tool.

  As mentioned above, although this embodiment and an Example were described, it should be thought that embodiment and Example disclosed this time are illustrations in all points, Comprising: It is not restrictive. The scope of the present invention is shown not by the embodiments described above but by the scope of claims, and is intended to include meanings equivalent to the scope of claims and all modifications within the scope.

1,11 cBN single crystal 10 cBN polycrystal 2,12 ceramic phase

Claims (8)

A cubic boron nitride polycrystal and a ceramic phase,
Containing the cubic boron nitride polycrystal in a range of 40% by volume to 80% by volume;
The cubic boron nitride polycrystal includes a cubic boron nitride single crystal having an average crystal grain size of 500 nm or less, and wurtzite boron nitride,
The cubic boron nitride polycrystal contains 0.01% by volume or more of the wurtzite boron nitride ,
Having a sintered body structure in which the cubic boron nitride polycrystals are scattered like islands in the ceramic phase;
Cubic boron nitride composite sintered body.   2. The cubic boron nitride composite sintered body according to claim 1, wherein the cubic boron nitride polycrystal further contains compressed hexagonal boron nitride in a range of 0.01 volume% to 0.5 volume%. .   3. The cubic boron nitride composite sintered body according to claim 1, wherein the ceramic phase includes one or more of Ti, Hf, Zr, and W carbides, nitrides, carbonitrides, and borides.   The cubic boron nitride composite sintered body according to any one of claims 1 to 3, wherein the ceramic phase further contains Al. A method for producing a cubic boron nitride composite sintered body containing a cubic boron nitride polycrystal in a range of 40 vol% to 80 vol%,
A first step of mixing atmospheric pressure boron nitride and ceramics to obtain a mixture;
A second step of sintering the mixture under conditions of a pressure of 8 GPa or more and a temperature of 1500 ° C. or more and less than 2300 ° C.,
In the second step, the normal pressure type boron nitride is converted directly into cubic boron nitride, and sintered body tissue said cubic boron nitride polycrystals in the ceramic phase is dispersed in an island shape is formed,
The cubic boron nitride polycrystal is a method for producing a cubic boron nitride composite sintered body comprising a cubic boron nitride single crystal having an average crystal grain size of 500 nm or less and wurtzite boron nitride.   A cutting tool comprising the cubic boron nitride composite sintered body according to any one of claims 1 to 4.   A wear-resistant tool comprising the cubic boron nitride composite sintered body according to any one of claims 1 to 4.   A grinding tool comprising the cubic boron nitride composite sintered body according to any one of claims 1 to 4.

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