JP2011207690A - Composite sintered compact - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite sintered compact which achieves a longer tool life.SOLUTION: The composite sintered compact comprises cubic boron nitride and a binder. The cubic boron nitride is included by 20 to 80 vol.% in the composite sintered compact. The binder comprises a Ti compound and an auxiliary binder component. The auxiliary binder component is composed of either or both of an Al compound and an Si compound. Also, the ratio of the total of the outlines of the auxiliary binder component to the total of the outlines of the grains of the cubic boron nitride is 1.4 to 2.8 in at least one cross-section of the composite sintered compact.

Description

  The present invention relates to a composite sintered body containing cubic boron nitride.

  Cubic boron nitride has the second highest hardness and excellent thermal conductivity after diamond, and has a lower affinity with iron than diamond. Therefore, a sintered body containing cubic boron nitride is conventionally hardened steel. And has been used for finish cutting of cast iron.

  For example, Japanese Patent Laid-Open No. 53-077811 (Patent Document 1) discloses a cubic boron nitride sintered body containing 40 to 80% by volume of cubic boron nitride, with the Ti-based ceramic binder remaining. Has been. However, this sintered body has not obtained a sufficient tool life for high-efficiency cutting such as intermittent cutting, heavy cutting and high-speed cutting, and further improvement has been desired. Therefore, in order to improve the toughness and heat resistance of such a sintered body, it is possible to enhance the bonding force and improve the dispersibility by improving the binder and coating the cubic boron nitride particles with ceramics. It has been planned.

  For example, Japanese Patent Application Laid-Open No. 07-172924 (Patent Document 2) discloses a sintered body made of a cubic boron nitride, a binder mainly composed of ceramics, and inevitable impurities for the purpose of further improving fracture resistance. Thus, there has been proposed a composite sintered body in which cubic boron nitride particles are surrounded by a titanium-containing compound phase and aluminum oxide has a particle size of 1 μm or less.

JP-A-53-077781 Japanese Patent Application Laid-Open No. 07-172924

  Various improvements related to the composition and particle size of the binder have been made as suggested above, but the performance required for high-efficiency processing and multi-product processing in recent years has become extremely high, and further improvement in performance has been achieved. It has been demanded. That is, it is required to further improve the fracture resistance and the life stability against the fracture under severer cutting conditions and machining with different environments from continuous cutting to intermittent cutting.

  This invention is made | formed in view of such a condition, The place made into the objective is to provide the composite sintered compact which achieves a longer tool life.

  The composite sintered body of the present invention is a composite sintered body containing cubic boron nitride and a binder, and the cubic boron nitride is contained in the composite sintered body in an amount of 20% by volume to 80% by volume. The binder includes a Ti compound and an auxiliary binder component, and the auxiliary binder component is composed of one or both of an Al compound and an Si compound, and at least one of the composite sintered body. In the cross section, the ratio of the total outline of the auxiliary binder component particles to the total outline of the cubic boron nitride particles is 1.4 or more and 2.8 or less. Such a ratio is preferably 1.7 or more and 2.2 or less.

  Here, the auxiliary binder component is preferably contained in the composite sintered body in an amount of 3% by volume to 30% by volume, and the average particle size thereof is preferably 0.001 μm to 1.5 μm.

  In addition, in at least one section of the composite sintered body, the auxiliary binder component that contacts the cubic boron nitride is preferably contained in the composite sintered body in an amount of 6.5% by volume to 24% by volume. . Further, in each particle of the auxiliary binder component, (area) / (square of outline) is preferably 0.25 or more.

  Moreover, it is preferable that the said composite sintered compact contains either W, Co, and the compound containing W or Co in 2 mass% or less.

  The composite sintered body of the present invention has an excellent effect that a longer tool life can be achieved by having the above-described configuration.

Hereinafter, the present invention will be described in more detail.
<Composite sintered body>
The composite sintered body of the present invention includes cubic boron nitride and a binder. Such a composite sintered body may contain other components as long as it contains the above two components, and may contain inevitable impurities due to raw materials used, production conditions, and the like.

  Such a composite sintered body of the present invention can be used for various tools including cutting tools and is also useful as various industrial materials. In particular, when used as a cutting tool including at least a part of the composite sintered body of the present invention, the effect of the present invention is effectively exhibited, especially for iron-based high hardness materials such as hardened steel, bearing steel, and die steel. Effective in cutting.

  Examples of such cutting tools include drills, end mills, drill tip changeable cutting tips, end mill tip replacement cutting tips, milling tip replacement cutting tips, turning tip replacement cutting tips, metal saws, teeth A cutting tool, a reamer, a tap, a pin milling tip for a crankshaft, and the like can be given.

  When the composite sintered body of the present invention is used for such a cutting tool, it is not limited to the case of constituting the entire tool, but only a part thereof (particularly a cutting edge part (cutting edge part)). Is also included. For example, the case where only the cutting edge part of the base material made of cemented carbide or the like is composed of the composite sintered body of the present invention is also included.

<Cubic boron nitride>
The cubic boron nitride contained in the composite sintered body of the present invention has long been used as a machining tool because of its excellent hardness and thermal conductivity. In the present invention, the cubic boron nitride is contained in the composite sintered body in an amount of 20% by volume to 80% by volume. More preferably, it is 40 volume% or more and 75 volume% or less.

  When the proportion of cubic boron nitride is less than 20% by volume, the proportion of high-strength cubic boron nitride is small, the strength necessary for machining is insufficient, and it is easily lost. Also, mechanical wear may develop. On the other hand, when the proportion of cubic boron nitride exceeds 80% by volume, the proportion of the binder is relatively reduced, so that the heat resistance is insufficient and the wear resistance is lowered.

  Such volume% can be achieved by setting the volume% of the cubic boron nitride powder used in the production of the composite sintered body within the above range. By using quantitative analysis by inductively coupled high-frequency plasma spectroscopy) or SEM (scanning electron microscope) or TEM (transmission electron microscope), it can be measured by tissue observation, elemental analysis, or the like. In particular, the structure of the composite sintered body is observed using SEM, the cubic boron nitride and the binder are distinguished from the difference in contrast, and the area ratio is calculated by image analysis. It is preferable to measure by considering. Thereby, the volume% of the below-mentioned binder (auxiliary binder component) can be obtained simultaneously.

<Binder>
The binding material of the present invention mainly has an action of retaining the above cubic boron nitride, and may contain any other conventionally known component as long as it contains a Ti compound and an auxiliary binding material component. There is no problem.

  In such a binder, since the Ti compound has a high hardness, it is excellent in wear resistance and has an effect of suppressing defects caused by impact. However, the bonding strength with cubic boron nitride and other binder components is weak, and the toughness as a composite sintered body is lowered. For this reason, there is a possibility that it becomes a starting point of microchipping generated in the composite sintered body, and the effect for suppressing propagation of microchipping is not sufficient.

  On the other hand, the auxiliary binder component composed of one or both of the Al compound and the Si compound has a strong bonding force with cubic boron nitride, Ti compound, and other binders, and exhibits an effect of improving toughness. . However, the hardness is low and the wear resistance tends to be deteriorated, and the effect on the defect due to impact is low.

  The binding material of the present invention is intended to achieve both wear resistance and fracture resistance by using such a Ti compound and an auxiliary binding material component in a complementary manner. However, such auxiliary binder components are considered to exist between cubic boron nitride and Ti compounds or between Ti compounds in the composite sintered body. For this reason, if the surface area of the auxiliary binder component is appropriate with respect to the surface area of cubic boron nitride, the strength and toughness are improved without deteriorating the wear resistance of the composite sintered body by strengthening the bonding force. In addition, it can be expected that the fracture resistance is improved. Further, when the auxiliary auxiliary binder component is dispersed in the binder component, higher fracture resistance can be expected. However, if the surface area of the auxiliary binder component is excessive with respect to the surface area of the cubic boron nitride, the wear resistance deteriorates and the performance varies. On the contrary, if the surface area is too small, the bonding strength and Since the toughness is lowered, the fracture resistance is deteriorated.

  The present invention has been made on the basis of the above findings, and as a result of intensive studies aimed at optimizing the surface area of the auxiliary binder component, it is most effective in achieving both wear resistance and fracture resistance. The present invention has been completed by finding the existence form determined by the content, particle size, shape, and degree of dispersion of the auxiliary binder component to be investigated, and further studying. The details will be described below.

<Auxiliary binder component>
The auxiliary binder component of the present invention is composed of one or both of an Al compound and an Si compound, and in at least one cross section of the composite sintered body, the total outline of the cubic boron nitride particles The ratio of the total outline of the auxiliary binder component particles is 1.4 or more and 2.8 or less. As a result, the composite sintered body of the present invention is a very strong and densely sintered body, which can achieve both high wear resistance and fracture resistance, thereby enabling a very long tool life. It is. For this reason, the composite sintered body of the present invention has succeeded in realizing a long life particularly in machining of an iron-based high hardness material. The ratio is more preferably 1.7 or more and 2.2 or less.

Here, the Al compound referred to in the present invention refers to a compound containing at least Al. The auxiliary binder component of the present invention can contain one or more of such Al compounds. Examples of such Al compounds include AlN, AlB ₂ , Al ₂ O ₃ , TiAl ₃ , Ti ₂ AlN, and the like, and solid solutions containing two or more thereof.

In the past, aluminum oxide, which is easily available as an Al source, was often used as a raw material, but aluminum oxide is excellent in oxidation resistance, but the fracture resistance is not sufficient for cutting a high-hardness material, Further, since the thermal conductivity is low, the cutting edge portion becomes high temperature, the cubic boron nitride is thermally damaged, and the wear resistance may be deteriorated. Therefore, it is preferable to use powder of Al alone (that is, Al powder) instead of Al ₂ O ₃ as a raw material for the Al compound.

On the other hand, the Si compound referred to in the present invention means a compound containing at least Si. The auxiliary binder component of the present invention can contain one or more of such Si compounds. Examples of such Si compounds include SiC, Si ₃ N ₄ , SiB _{2 and the} like, and solid solutions containing two or more thereof. Such Si compounds include Si alone.

  In addition, when Al compound or Si compound contains Ti, in this invention, it shall be contained in an auxiliary binder component instead of Ti compound.

  Further, “particle outline” means a contour line along the outer periphery (grain boundary) of the particles observed in the cross section of the composite sintered body, and “total” means the outline for each particle. This is the sum of the lengths obtained for a line.

  Such a contour line can be obtained as follows. That is, at least one section of the composite sintered body was photographed at 10,000 to 50,000 times using SEM, and the cubic boron nitride particles were visually observed along the contrast of light and shade on the obtained photograph. The grain boundaries of the grains constituting the grain boundaries and the auxiliary binder component are traced. In this case, the contrast between light and shade is determined by separately obtaining the color of the target cubic boron nitride and the compound constituting the auxiliary binder component by analysis using EDS (energy dispersive X-ray analysis). be able to. Then, by analyzing the image of the trace, the outline can be specified and the length can be obtained. However, for example, if cubic boron nitrides having the same contrast in density are in contact with each other and different contrasts are not confirmed at the grain boundaries, the grain boundaries between the cubic boron nitrides are not included in the total outline. To do. Moreover, the average particle diameter of an auxiliary | assistant binder component can also be calculated | required by said method. That is, when the auxiliary binder component is not circular but has an indefinite shape, the length of the portion with the largest diameter (length) is defined as the particle size, and the length of each of a plurality (preferably 20) of the particles is the length. The average value is measured as the average particle size.

  In the present invention, as described above, in at least one cross section of the composite sintered body, the ratio of the total outline of the auxiliary binder component particles to the total outline of the cubic boron nitride particles is 1.4 or more and 2 The reason for adopting this rule is as follows.

  That is, when the particles constituting the auxiliary binder component are coarse or agglomerated (especially when they are present at the cutting edge portion serving as an action point at the time of cutting), the wear resistance is reduced. Conversely, if the particles that make up the auxiliary binder component are too fine, they are oxidized during the production (mixing and sintering) stage of the composite sintered body and exist stably as an oxide, thus improving the bond strength and toughness. Will contribute less. For this reason, it is important to define the particle size of the auxiliary binder component, but a desired effect cannot be expected simply by defining the particle size.

  For example, if the entire surface of cubic boron nitride is covered with an auxiliary binder component, when machining a workpiece having a complicated shape, the impact is increased due to intermittent machining or the like, and therefore exists at the cutting edge portion. The composite sintered body may fall off. In addition, the bonding force between the bonding materials is weak, and micro-chipping occurs in the bonding material having a weak bonding force due to impact, and the processed surface of the workpiece is streaked or clouded.

  Therefore, it is not sufficient to specify the particle size of the auxiliary binder component, and the mixing ratio and dispersion state of cubic boron nitride and the auxiliary binder component, the shape of the particles constituting the auxiliary binder component, and the like are taken into consideration. There is a need.

  From the above viewpoint, the present invention is the most effective in achieving both fracture resistance and wear resistance as a result of intensive studies on the existence form of the auxiliary binder component, that is, the blending amount, particle size, and shape (surface area). The above-mentioned provisions are the ones that find out and define the existence forms of the auxiliary binder components.

  That is, according to the present invention, in at least one section of the composite sintered body, the ratio of the total outline of the auxiliary binder component particles to the total outline of the cubic boron nitride particles is 1.4 or more and 2.8. This provision is characterized by the following: the provisions indexed the optimal surface area ratio between cubic boron nitride and auxiliary binder component depending on the content, particle size, shape and dispersibility of the auxiliary binder component It is considered a thing. Therefore, this rule is fundamentally different from those that merely define the average particle size of the auxiliary binder component or the content, and in addition to the particle size distribution and dispersion state of the auxiliary binder component, the auxiliary binder component The shape of each particle that constitutes is also considered comprehensively.

  Here, when the ratio of the total outline of the auxiliary binder component particles to the total outline of the cubic boron nitride particles is less than 1.4, the auxiliary binder component content is small and the particle size is Phenomenon such as large, close to spherical shape, agglomerated, or unevenly present on the outer periphery of cubic boron nitride becomes a complex factor, and the auxiliary binder component of the surface area of cubic boron nitride This means that the ratio of the surface area is small, indicating a reduction in chipping resistance and wear resistance. When the ratio exceeds 2.8, the auxiliary binder component content is large, the particle size is small, the shape is complicated, the individual particles are present, and the auxiliary material is present in the binder. Phenomenon such as a large amount of binder component becomes a complex factor, which means that the ratio of the surface area of the auxiliary binder component to the surface area of cubic boron nitride is large, resulting in a reduction in fracture resistance and wear resistance. Indicates. A more preferable range of the ratio is 1.7 or more and 2.2 or less.

  The auxiliary binder component of the present invention is preferably contained in the composite sintered body in an amount of 3% by volume to 30% by volume, and the average particle size is preferably 0.001 μm to 1.5 μm.

  When the content is less than 3% by volume, the surface area of the auxiliary binder component becomes smaller than the surface area of the cubic boron nitride, and the bonding strength of the cubic boron nitride and the binder cannot be strengthened. Even in the processing of the load, the strength of the composite sintered body is insufficient, and both wear resistance and fracture resistance are deteriorated. If it exceeds 30% by volume, the amount necessary for strengthening the bonding strength of cubic boron nitride and the binder is exceeded, and the auxiliary binder component becomes surplus in the composite sintered body, thereby reducing the wear resistance. When the average particle size of the auxiliary binder component is less than 0.001 μm, the auxiliary binder component is likely to aggregate and may reduce the wear resistance. When it exceeds 1.5 μm, the wear resistance and fracture resistance May be reduced.

  The content is more preferably 6% by volume or more and 13% by volume or less, and the average particle diameter is more preferably 0.02 μm or more and 0.5 μm or less.

<Ti compound>
The Ti compound contained in the binder of the present invention refers to a compound containing at least Ti. The binding material of the present invention can contain one or more of such Ti compounds.

Examples of such a Ti compound include TiC, TiCN, TiN, TiB ₂ , and solid solutions containing two or more thereof. Further, as such a Ti compound, at least one element selected from the group consisting of Ti, Zr, Si, Hf, V, and Cr, and at least selected from the group consisting of nitrogen, carbon, boron, and oxygen is used. A compound composed of one kind of element can be mentioned as a suitable compound. Such Ti compounds also include Ti alone.

  Such a Ti compound is preferably contained in the composite sintered body in an amount of 5 to 77% by volume, more preferably 15 to 60% by volume. Moreover, it is preferable to set it as 0.2-3.0 micrometers, and, as for the average particle diameter of Ti compound, it is more preferable to set it as 0.4-1.5 micrometers.

<Auxiliary binder component in contact with cubic boron nitride>
In at least one cross section of the composite sintered body, it is preferable that an auxiliary binder component contacting the cubic boron nitride is contained in an amount of 6.5% by volume or more and 24% by volume or less in the composite sintered body. As a result, the auxiliary binder component that strengthens the bonding force is present not only on the surface of the cubic boron nitride, but also on the surface of the Ti compound and other binder components. Defect resistance can be improved.

  When the auxiliary binder component in contact with the cubic boron nitride is less than 6.5% by volume, the effect of increasing the bonding force with respect to the surface area of the cubic boron nitride tends to be hardly exhibited, or a Ti compound or the like In some cases, the amount of the auxiliary binder component present between these binder components is small, and the fracture resistance due to impact tends to be reduced. When the volume exceeds 24% by volume, there is a tendency that many auxiliary binder components having a large particle diameter are present on the surface of cubic boron nitride, or auxiliary binders existing between binder components such as Ti compounds. There are cases where the amount of the component is large and the wear resistance tends to deteriorate.

  The amount of the auxiliary binder component that contacts the cubic boron nitride is more preferably 8% by volume or more and 15% by volume or less.

<(Area) of each particle of auxiliary binder component / (square of outline)>
In each particle of the auxiliary binder component, it is preferable that (area) / (square of outline) of the particle is 0.25 or more. The (area) / (outline squared) of each particle of the auxiliary binder component is an index indicating the degree of the complicated shape of the auxiliary binder component.

  For example, in the case of a simple sphere, the above value is 1 / 4π (about 0.0796). The value of 1 / 4π indicates that the particle has the smallest surface area. When the value is greater than 1 / 4π, the surface of the particle has irregularities and has a complicated shape. In other words, it indicates that the particles have an elliptical spherical shape, or that a plurality of particles are combined to form an elliptical spherical shape or a complicated shape.

  In order to increase the binding strength of cubic boron nitride and other binder components in small amounts where the auxiliary binder component can maintain good wear resistance, the auxiliary binder component has an elliptical or complex particle shape. By showing, it is effective to increase the surface area with a small amount, and it is preferable that (area) / (square of outline) of the particles is 0.25 or more.

  When the above value is less than 0.25, the auxiliary binder component is dispersed in the composite sintered body in a nearly spherical shape, and is sufficient to increase the bonding strength of cubic boron nitride and other binders. In some cases, the fracture resistance due to impact is reduced.

<W and Co>
It is preferable that any of W, Co, and a compound containing W or Co is contained in the composite sintered body at 2% by mass or less.

  In the composite sintered body, when the W and Co components having a relatively low melting point are sintered at an ultrahigh pressure and high temperature, grain growth may occur selectively as a component having a low melting point. The sintered body component in contact with these components having a low melting point may induce grain growth. In particular, the auxiliary binder component having a low melting point tends to induce grain growth. When grain growth is induced, the auxiliary binder component approaches a spherical shape, so that it is not suitable as a shape of the auxiliary binder component that increases the surface area with a small amount. For this reason, the fracture resistance due to impact is lowered, and the grains are coarsened by grain growth, so that the wear resistance is also lowered.

  Therefore, in the present invention, when a compound containing W, Co, and W or Co is contained, it is preferable that any one of W, Co, and a compound containing W or Co is contained in an amount of 2% by mass or less. More preferably, the total content of the compound containing W and Co is 2% by mass or less.

<Manufacturing method>
The composite sintered body of the present invention can be produced, for example, as follows. That is, first, a raw material powder for a binder is prepared. This is obtained by pulverizing the raw material powder with a pulverizer such as a ball mill. In the present invention, it was found that an auxiliary binder component having a hardness lower than that of the Ti compound can be selectively deformed and atomized by controlling the pulverization conditions in order to obtain the desired particle size and shape of the binder ( The raw material powder obtained by pulverizing only the raw material powder for the binder thus obtained is hereinafter referred to as “raw material powder A”).

  That is, for example, when a ball mill is used as a pulverizer, it is important to control the particle diameter and shape of the raw material powder by variously controlling the ball diameter, pulverization time, and stirring speed. This is because the particle size and shape of the raw material powder are usually reflected in the particle size and shape of the particles constituting the auxiliary binder component in the composite sintered body.

For this reason, it is preferable that the diameter of the ball is about 0.1 to 8.0 mm and the pulverization time is about 30 to 140 hours. Further, as the container and the ball, those made of cemented carbide can be adopted, but instead of this, by using a thing made of high hardness ceramics such as ZrO ₂ , contamination of impurities can be reduced.

  On the other hand, in place of the ball mill, it is preferable to use a high-pressure homogenizer that crushes / mixes particles by the collision of the shearing force when the liquid is pressurized to a high pressure and exits the nozzle because the contamination of impurities can be reduced. In this case, the particle diameter and shape can be controlled by setting the nozzle diameter of the high-pressure homogenizer to about 0.3 to 1.0 mm and controlling the pressure to 20 to 250 MPa.

  Next, a raw material powder obtained by separately uniformly mixing cubic boron nitride and the raw material powder of the auxiliary binder component by the above-described method or the like is prepared (this raw material powder is hereinafter referred to as “raw material powder B”). The above raw material powder A is further uniformly mixed. As the mixing method, the above-described ball mill, high-pressure homogenizer, or the like can be used. And after making the raw material powder prepared in this way into a desired shape, after carrying out a fixed heat processing in a vacuum furnace, it can sinter and can obtain the composite sintered compact of this invention. In this case, it is necessary to employ sintering conditions that do not cause grain growth of the binder obtained above. In order to strengthen the bonding strength of the composite sintered body, it is conceivable to increase the sintering conditions (pressure and temperature). However, depending on the balance between pressure and temperature, the low melting point component selectively causes grain growth. There is a case. In the present invention, since the melting point of the auxiliary binder component is lower than that of the Ti compound, grain growth of the auxiliary binder component is likely to occur. In particular, the Al compound induces grain growth when it comes into contact with other binder components having lower melting points or unavoidable impurities, and therefore may cause grain growth even under lower sintering conditions.

  When the auxiliary binder component causes grain growth in this way, it approaches a spherical shape with a small surface area rather than the target shape, and further becomes coarse, so that the bonding strength of the composite sintered body becomes insufficient, Wearability may be deteriorated or microcracks may be developed. For this reason, it is preferable to employ | adopt the conditions of hold | maintaining for about 10 to 120 minutes by the pressure of about 3-10 GPa at the temperature of about 700-2000 degreeC as sintering conditions, for example. Thereby, the composite sintered compact sintered firmly and densely can be manufactured.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited to these.

First, as a raw material powder for a binder, TiN powder for Ti compound (average particle size: 2.5 μm), TiC powder (average particle size: 3.0 μm), TiCN powder (average particle size: 3.0 μm), Al powder (average particle size: 2.0 μm) for auxiliary binder components, Si ₃ N ₄ powder (average particle size: 3.0 μm), and HfC powder (average particle size: 3.0 μm) for other components The compositions shown in Table 1 and Table 2 were blended and mixed (“mass ratio” in Tables 1 and 2 is (Al powder): (Si ₃ N ₄ powder or HfC powder)) Indicates mass ratio). Thereafter, the powder was heat-treated at 1000 ° C. for 30 minutes in a vacuum.

  Subsequently, the raw material powder that has undergone the above treatment is pulverized under the conditions shown in Tables 3 and 4 (ball diameter and pulverization time) using a ball mill consisting of a cemented carbide container and a cemented carbide ball. As a result, a binder ("Raw Material Powder A") was obtained.

Subsequently, separately prepared raw material powder for cubic boron nitride (having the average particle diameter shown in Tables 1 and 2) and the auxiliary binder component Al powder and Si ₃ N ₄ powder used above were uniformly mixed. The raw material powder B is obtained, and this and the raw material powder A obtained above are shown in Tables 5 and 6, and the cubic boron nitride contained in the finally obtained composite sintered body and the auxiliary It mixed uniformly by the volume ratio used as content (volume%) of a binder component. Note that the volume ratio of the raw material powder of the cubic boron nitride and the binder is substantially equal to the volume ratio in the finally obtained composite sintered body.

  And the mixed powder obtained by making it above was made into the desired shape, and this was hold | maintained for 20 minutes at 1000 degreeC in the vacuum furnace, and degassed. Further, this powder was filled into a cemented carbide capsule and sintered for 60 minutes under the sintering conditions (pressure and temperature) shown in Tables 3 and 4 to produce a composite sintered body of the present invention (Example) No. 1-32). Similarly, Comparative Example No. 1 and Comparative Example No. 1 2 composite sintered body was also produced. On the other hand, Comparative Example No. For the composite sintered body 3, the binder powder obtained by pulverizing only the binder component (“raw powder A”) and the cubic boron nitride raw powder were directly and uniformly mixed (that is, the above “ It was produced without going through the process of obtaining the raw material powder B). For the composite sintered body of Comparative Example 4, only TiN powder as a binder was pulverized under the conditions shown in Table 4 ("Raw Material Powder A"), cubic boron nitride raw material powder and auxiliary binder. The powder in which the components were uniformly mixed (“raw material powder B”) was heat-treated at 500 ° C. and again mixed again (the auxiliary binder component is contained only in “raw material powder B”).

  Next, the surface of each composite sintered body produced as described above was chemically polished, and then observed with a SEM at 2000 times. Then, by performing binarization processing on the observed image from the difference in contrast using image processing software (trade name: WinROOF, manufactured by Mitani Corporation), cubic boron nitride regions (particles) and binders Regions (particles) were identified, and the total area of each was calculated. This area ratio was taken as the content (volume%) of cubic boron nitride in the composite sintered body. The results are shown in Tables 5 and 6. Note that the threshold value when performing the binarization process was adjusted so that the interface between the cubic boron nitride and the binder determined from the observation image (structure photograph) was separated.

  Furthermore, in the same manner, four visual fields were observed at 50,000 times for each composite sintered body. Then, by using the same image processing software as described above for each observation image (tissue photograph), binarization processing is performed from the contrast of light and shade, and the cubic boron nitride region and the auxiliary binder component region And the total area of the auxiliary binder component was calculated and used as the content (volume%) of the auxiliary binder component in the sintered body. Further, the auxiliary binder component present in the binder component not in contact with cubic boron nitride was removed, and the content (volume%) of the auxiliary binder component in contact with cubic boron nitride was calculated. These results are shown in Tables 5 and 6. The numerical values in parentheses in the column of auxiliary binder component content in Tables 5 and 6 indicate the content (% by volume) of the auxiliary binder component in contact with cubic boron nitride.

  Then, the same software calculates the total outline of cubic boron nitride particles (regions) and the total outline of auxiliary binder component particles (regions) to obtain cubic boron nitride particles. The ratio of the sum of the contour lines of the auxiliary binder component particles to the sum of the contour lines was determined. The results are shown in Tables 5 and 6 ("Outline line ratio" column). In addition, since the tissue observation region of 50,000 times is very narrow, it is desirable to obtain the ratio by selecting four or more fields of average tissue portions. Moreover, the average particle diameter was computed by calculating | requiring simultaneously each particle size (length which becomes the longest) of an auxiliary | assistant binder material in the above. The results are shown in Tables 5 and 6.

  Note that the binarization threshold in this case was adjusted so that the interface was separated from the tissue photograph in the same manner as in the above case. In this case, for example, cubic boron nitrides having the same contrast in density are in contact with each other, and unless a different contrast is confirmed at the grain boundaries, the grain boundaries between the cubic boron nitrides are not included in the total outline. It was.

  In addition, Example No. 21, 22, and 32, the contour line and its area are calculated for each particle of the auxiliary binder component by the same software as used above, and (area) / (outline (Square) was calculated, and the average value of the results was defined as (area) / (square of outline) of each composite sintered body. The results are shown in Example No. 21 is 0.1, Example No. 22 is 0.25, Example No. 32 was 0.3. In this case, since the observation region of the tissue is narrow, it is desirable to select four fields or more and to average 50 or more auxiliary binder particles.

  Furthermore, Example No. 1-32 and Comparative Example No. For the composite sintered bodies 1 to 4, the total content of W, Co, and the compound containing W or Co contained therein was determined by ICP (inductively coupled plasma) analysis. All except 31 was 2% by mass or less. Example No. 31 was 5 mass% or less.

  And the cutting tool (ISO model number: CNGA120408) was shape | molded using each composite sintered compact produced as mentioned above. The arrangement of each composite sintered body in this cutting tool is an isosceles triangle with an apex angle of 80 ° (the tip is attached with a round (R)) and a side of 2 mm, and a thickness of 1 A total of two triangular prisms having a shape of 2 mm are arranged at each corner.

  Then, using this cutting tool, two types of cutting tests were performed under the following cutting conditions. The cutting test A can evaluate the fracture resistance due to the impact of the composite sintered body, and the cutting test B can evaluate the toughness of the composite sintered body. In the cutting test A, the hardness of the work material is high, and the composite sintered body is subjected to intermittent impact, so that the fracture life due to the impact can be evaluated. In the cutting test B, crater wear progresses, so the composite sintered body Microcracks are generated in the crater wear part where the strength of the cracks decreases, and it is possible to evaluate the defect life in which the cracks propagate and are lost.

<Cutting test A (intermittent cutting)>
Cutting speed: Vc = 120 m / min.
Feed: f = 0.1 mm / rev.
Cutting depth: ap = 0.1mm
Coolant: Dry type Work material: SKD11-6V (HRC64)
Diameter 100mm x length 300mm
There are six V-shaped grooves in the axial direction.

<Cutting test B (continuous cutting)>
Cutting speed: Vc = 200 m / min.
Feed: f = 0.2 mm / rev.
Cutting depth: ap = 0.1mm
Coolant: Dry Work material: SCM415
Diameter 100mm x length 300mm.

  The results of each cutting test are shown in Tables 5 and 6. The results show the time until chipping by intermittent cutting for the cutting test A, and the longer the time, the longer the tool life. The cutting test B represents the distance until the chip is broken, and the longer the distance, the longer the tool life.

  As is clear from Tables 5 and 6, it was confirmed that the tool life of the example of the present invention was clearly extended as compared with the comparative example. This is considered to be a result that both the fracture resistance and the wear resistance are sufficiently improved.

  Although the embodiments and examples of the present invention have been described as described above, it is also planned from the beginning to appropriately combine the configurations of the above-described embodiments and examples.

  It should be understood that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

Claims (7)

A composite sintered body containing cubic boron nitride and a binder,
The cubic boron nitride is contained in the composite sintered body in an amount of 20% by volume to 80% by volume,
The binder includes a Ti compound and an auxiliary binder component,
The auxiliary binder component is composed of any one or both of an Al compound and an Si compound, and the total amount of outlines of the cubic boron nitride particles in at least one section of the composite sintered body, A composite sintered body in which the total ratio of the contour lines of the particles of the auxiliary binder component is 1.4 or more and 2.8 or less.   2. The composite sintered body according to claim 1, wherein a ratio of a total outline of the auxiliary binder component particles to a total outline of the cubic boron nitride particles is 1.7 or more and 2.2 or less. .   The composite sintered body according to claim 1, wherein the auxiliary binder component is contained in the composite sintered body in an amount of 3% by volume to 30% by volume.   The composite sintered body according to claim 1, wherein the auxiliary binder component has an average particle size of 0.001 μm to 1.5 μm.   The auxiliary binder component that contacts the cubic boron nitride in at least one section of the composite sintered body is contained in the composite sintered body in an amount of 6.5% by volume to 24% by volume. 5. The composite sintered body according to any one of 4 above.   6. The composite sintered body according to claim 1, wherein in each particle of the auxiliary binder component, (area) / (square of outline) is 0.25 or more.   The composite sintered body according to any one of claims 1 to 6, wherein the composite sintered body contains 2% by mass or less of any of W, Co, and a compound containing W or Co.