JP2009067637A - Cubic boron nitride sintered compact and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-hardness sintered compact which has a high cBN content and is capable of fully exhibiting the characteristic properties, such as high hardness and high thermal conductivity, which is inherent in cBN, and thus is applicable also to high-speed cutting of a hardly cut material and can achieve a long tool lifetime. <P>SOLUTION: The cubic boron nitride sintered compact is a sintered compact based on cubic boron nitride, wherein at least one element selected from the group consisting of F, Cl, Br and I is contained, and the concentration of the element is 50 ppb to 100 ppm by wt.%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a sintered body containing cubic boron nitride (cBN) (hereinafter referred to as a cBN sintered body) and a method for producing the same, and more specifically, cubic boron nitride sintered having excellent lifetime. It is about the body.

  cBN (Cubic Boron Nitride) has the second highest hardness and thermal conductivity after diamond, and is characterized by low reactivity with ferrous metals compared to diamond. This is useful for cutting hardened steel and cast iron. A cBN sintered body containing cBN is frequently used. A sintered body having a structure in which cBN particles are dispersed in a Ti ceramic binder is useful for cutting hardened steel.

  On the other hand, for cutting difficult-to-cut materials, a cBN sintered body with a high cBN particle content and a skeletal structure in which the particles are brought into contact with each other and applied, taking full advantage of the high hardness and high thermal conductivity of cBN. Is done. If the thermal conductivity of the tool material is high, an increase in the cutting edge temperature can be suppressed, so that a decrease in strength due to a temperature change of the tool material can be reduced, and the tool life is improved. For example, as shown in Patent Document 1, a cBN sintered body that is sintered by reacting and bonding cBN particles with an Al-based alloy as a catalyst is known. Patent Document 2 discloses a method for obtaining a cBN sintered body even at a relatively low pressure by improving the sinterability by adjusting the composition of the Al-based alloy.

  Further, in Patent Document 3, a skeletal structure in which cBN particles are bonded to each other, which is formed only from cBN particles and Al, and is composed of cBN and aluminum nitride and aluminum diboride which are reaction products between cBN and Al. A method of manufacturing a sintered body having the above is disclosed.

  However, in order to obtain a sintered body having a high content of cBN and a skeleton structure, the cBN particles are in contact with each other. Therefore, it is necessary to cause the cBN particles to react with each other and sinter them. In many cases, the cBN particles are stable in a temperature range of up to about 2000 ° C. even under high pressure, so that the reaction is difficult. Many defects are introduced into the reaction parts between the cBN particles, or unreacted parts are often left only by contact. When used as a tool, it becomes a starting point for chipping and particle dropping, and a sufficient tool life cannot be obtained.

In addition, since a metal having a catalytic action remains as a metal between the cBN skeleton structures in the sintered body, the mechanical strength is extremely lowered at a high temperature corresponding to the cutting edge temperature at the time of cutting, and the desired tool life in the market. Is not obtained.
Japanese Examined Patent Publication No. 52-43846 Japanese Examined Patent Publication No. 57-59228 Japanese Examined Patent Publication No. 63-20792

  The object of the present invention is to solve the above-mentioned problems of a sintered body having a high cBN content, to fully exhibit the characteristics of cBN such as high hardness and high thermal conductivity, and can be applied to high-speed cutting of difficult-to-cut materials, The object is to provide a high hardness sintered body capable of achieving a long tool life.

As a result of diligent research, the present inventors have an excellent catalytic effect on hydrogen halide, an effect of promoting strong bond formation between particles by solid-phase sintering of cBN particles, and generating a tough cBN sintered body. Found that there is. Further, the effect was exhibited even at a lower temperature and a lower pressure than the region where cBN was stable, and a high-strength cubic boron nitride sintered body that was industrially inexpensive could be obtained. That is, the present invention adopts the following configuration.

(1) A sintered body containing cubic boron nitride as a main component, wherein the sintered body contains one or more elements selected from the group consisting of F, Cl, Br, and I, and the concentration is wt. A cubic boron nitride sintered body characterized by being 50 ppb or more and 100 ppm or less.
(2) A sintered body containing cubic boron nitride as a main component, wherein the sintered body contains one or more elements selected from the group consisting of F, Cl, Br, and I, and the concentration is wt. A cubic boron nitride sintered body characterized by being 50 ppb or more and 10 ppm or less.
(3) The cubic boron nitride sintered body according to the above (1) or (2), wherein the cubic boron nitride has an average particle size of 0.5 μm or more and 5 μm or less.
(4) The cubic boron nitride sintered body according to any one of (1) to (3), wherein the cubic boron nitride has a volume content of 70% or more.
(5) The cubic boron nitride sintered body according to any one of the above (1) to (4), wherein the cubic boron nitride sintered body has a thermal conductivity of 100 W / (m · K) or more. Sintered body.
(6) A sintered body mainly composed of cubic boron nitride, wherein the cubic boron nitride sintered body is selected from the group consisting of elements IV, VI, VIII to X in the periodic table and Al The cubic nitriding according to any one of the above (1) to (5), comprising any one or more of a simple substance, a mutual solid solution, carbide, nitride, carbonitride, boride and oxide Boron sintered body.
(7) A cubic boron nitride sintered body characterized by sintering cubic boron nitride powder after heat treatment in hydrohalic acid, which is an aqueous solution of hydrogen halide comprising HF, HCl, HBr, and HI. Manufacturing method.

  Since the cBN sintered body according to the present invention has a strong bond strength between the cBN particles, the thermal conductivity of the sintered body is high, and there is an effect of suppressing the temperature rise and strength deterioration at the time of high-load cutting. In addition, since the sintered body has high mechanical strength, chipping and wear during cutting are suppressed, and the tool life is greatly extended compared to conventional materials.

The cBN sintered body according to the present invention contains one or more elements of the group consisting of F, Cl, Br, and I in the sintered body, and the concentration is 50 ppb or more and 100 ppm or less in wt%. It is characterized by. The concentration is more preferably 50 ppb or more and 10 ppm or less in terms of wt%.
When the concentration of the element in the sintered body is less than 50 ppb, there are too few joint points where the bond between cBN is strengthened, so this effect improves the properties of the sintered body and does not provide the desired tool characteristics. . If it exceeds 100 ppm, the halogen is segregated at the cBN grain boundaries, resulting in a decrease in thermal conductivity and, consequently, an increase in cutting edge temperature during cutting, resulting in poor tool characteristics.
Moreover, in the case of cutting with a very high cutting edge load, a slight decrease in thermal conductivity greatly affects the wear resistance and fracture resistance, and the expected tool performance cannot be obtained. As described above, since the residual halogen concentrates at the grain boundaries, if the halogen species content exceeds 10 ppm, the thermal conductivity tends to decrease. The concentration in is more preferably 10 ppm or less.

  The cBN sintered body according to the present invention is characterized in that an average particle diameter of cubic boron nitride as a main component is 0.5 μm to 5 μm. When the average particle size is less than 0.5 μm, the scattering effect due to the grain boundary of the cBN particles becomes large, and the desired thermal conductivity of the sintered body cannot be obtained. On the other hand, if it exceeds 5 μm, the fracture resistance of cBN particles in high-load cutting is remarkably lowered, which does not meet the object of the present invention. A more preferable average particle diameter is 0.5 to 0.2 μm.

  The cBN sintered body according to the present invention is characterized in that cubic boron nitride as a main component thereof is 70% or more by volume. When the filling rate is lower than 70%, the contact area between the cBN particles in the sintered body that is sintered using the finished powder in which the binder and the cBN particles are uniformly mixed is reduced, and sufficient thermal conductivity is obtained. I cannot expect improvement. The higher the volume content of cBN particles, the better.

  The cBN sintered body according to the present invention has a thermal conductivity of 100 W / (m · K) or more. When the thermal conductivity is less than 100 W / (m · K), the cutting edge temperature increases during high-load cutting, leading to deterioration of cutting edge strength and cutting performance.

  In addition, the cBN sintered body according to the present invention is a simple element of elements selected from the group consisting of IV, VI, VIII to X group elements of the periodic table, Fe, Co, Ni, and Al, mutual solid solution, carbide, It is preferable to include any one or more of nitride, carbonitride, boride, and oxide as a binder. These binders can strengthen the bond between the cBN particles. Specifically, Co, Al, WC, TiN, etc. can be preferably used.

  The cBN sintered body according to the present invention is obtained by sintering cBN powder in a hydrohalic acid, which is an aqueous solution of hydrogen halide comprising HF, HCl, HBr, and HI, and then sintering under a predetermined temperature and pressure condition. It can manufacture by the manufacturing method characterized by these. When the catalytic effect of hydrogen halide is used as in the present invention, 5.5 to 6.5 GPa and 1400 to 1700 ° C. when the binder is included, and 6.0 to 7.0 GPa when the binder is not included. It becomes possible to sinter the cBN particles under pressure temperature conditions of 1600 to 1900 ° C.

When the cBN particles are kept under high temperature and high pressure where cBN is stably present, a diffusion reaction occurs at the contact point, and a sintered body of cBN alone in which the particles are bonded to each other is obtained. However, voids are generated at the locations corresponding to the triple points of the particles, and the generated pressure is reduced, so that hBN, which is a stable isotope at low pressure, is generated. When hBN is present at the grain boundary, the strength of the sintered body becomes extremely low, so that the performance as a tool is significantly reduced. By adding a substance having a catalytic effect that promotes the hBN-cBN conversion reaction, it is possible to convert hBN produced at the triple point to cBN at a lower temperature and lower pressure than the stable temperature and pressure range of cBN. NH ₂ group-containing substances such as alkali metal nitride (H180525) and melamine used for synthesizing cBN abrasive grains as a catalyst for promoting hBN-cBN conversion reaction are known (H120202).

Hereinafter, the present invention will be specifically described by way of examples.
[Sintered body preparation]
Several kinds of cBN particles having different average particle diameters were kept in 37 wt% -HCl at 150 ° C. for a predetermined time (shown in Table 1) to obtain HCl-treated cBN powder.

<Examples 1, 2, 3, 7, 8 Comparative Example-4, 5>
The above-mentioned HCl-treated cBN powder was filled into a cemented carbide container and sintered at a pressure of 6.5 GPa and a temperature of 1800 ° C. to sinter a cBN sintered body containing no binder.

<Example-4>
CBN particles having an average particle diameter of 2 μm were held in 37 wt% -HF at 150 ° C. for a predetermined time to obtain HF-treated cBN powder. The HF-treated cBN powder was filled into a cemented carbide container and sintered at a pressure of 6.5 GPa and a temperature of 1800 ° C. to sinter a cBN sintered body containing no binder.

<Example-5, 6, 9 Comparative Example-6>
Using cemented carbide pot and ball, binder powder made of Co, Al and WC (
(Weight ratio in bonding: Co-65%, Al-34%, and WC-1%) and HCl-treated cBN powders having different average particle diameters are mixed, filled into a cemented carbide container, and a pressure of 6.0 GPa And sintered at a temperature of 1600 ° C.

<Example-10>
TiN powder and Al powder were uniformly mixed at a mass ratio of 80:20, and then this mixed powder was heat-treated at 1200 ° C. for 30 minutes in a vacuum oven. Thereafter, the heat-treated mixed powder was pulverized with a ball mill composed of a cemented carbide pot and a cemented carbide ball to obtain a raw material powder for a binder.
The binder raw material powder and the cubic boron nitride powder subjected to heat treatment in HCl having an average particle diameter of 5 μm are uniformly mixed in a mixing ratio such that the cubic boron nitride powder is 68% by volume using the above-mentioned ball mill. Mixed. Thereafter, the mixed powder was degassed by being held at 900 ° C. for 30 minutes in a vacuum furnace.
Next, after the degassed mixed powder was filled into a molybdenum capsule, the temperature was increased to 6 GPa-1500 ° C. simultaneously with pressurization, and this pressure temperature condition was maintained again for 5 minutes.

<Comparative Example-1>
A cemented carbide container is filled with cBN powder that has not been heat-treated in HCl having an average particle diameter of 2 μm, and sintered at a pressure of 6.5 GPa and a temperature of 1800 ° C. to sinter a cBN sintered body that does not contain a binder. It was.
<Comparative Example-2>
Using cemented carbide pots and balls, a binder powder composed of Co, Al, and WC (weight ratio during bonding: Co-65%, Al-34%, and WC-1%) and an average particle diameter of 2 μm Was mixed with cBN powder that had not been treated with HCl, filled into a cemented carbide container, and sintered at a pressure of 6 GPa and a temperature of 1600 ° C.
<Comparative Example-3>
The same procedure as in Example 10 was performed except that cBN powder having an average particle diameter of 5 μm and not treated with HCl was used.

[Sintered body composition / impurity analysis]
The sintered body obtained by the above method was subjected to quantitative analysis of constituent elements using glow discharge mass spectrometry.
In this method, electrolysis is provided between a sample as an electrode and a counter electrode to cause glow discharge, and the sample is ionized by sputtering to perform ion mass spectrometry. Calibration with a standard sample is not required, and the solid sample can be analyzed easily and easily.
From the mass ratio determined by this analysis method, the volume content was determined on the assumption that the binder was a metal layer for those having a cBN content of 85% or more. In addition, the residual halogen concentration was quantitatively analyzed.
For those with a cBN volume content of 68%, there were many assumptions for calculating the cBN content from the analysis value, and therefore, the evaluation was made with the amount charged.
The results are shown in Table 1.

[Cutting evaluation]
The cBN sintered body is processed, a cutting tip having a shape of ISO standard SNGA120408 is created, cutting evaluation is performed under the following conditions, and tool life is evaluated.
Work material: Ductile cast iron FCD450 round bar Outside diameter turning Cutting conditions: Cutting speed V = 35 m / min.
Incision d = 0.15 mm,
Feed f = 0.2 mm / rev. Wet,
Life judgment: The cutting edge wear state is observed every 100 m of cutting length, and the ridgeline of the cutting edge is worn by 200 μm or more from the cutting edge ridgeline before cutting by observation from the flank, or cutting cannot be continued due to a sharp chipping of the cutting edge. The cutting state was defined as the life and the cutting length until reaching the life was measured.
Table 2 shows comparative values when the tool life under the above-mentioned cutting conditions is 1 with a cutting tip prepared using the sintered body of Comparative Example 1.

The sintered body using the cBN powder subjected to the heat treatment in hydrogen halide showed a longer tool life than the sintered body prepared using the untreated cBN powder (for example, Comparative Example 1). On the other hand, Examples 1 to 4, Comparative Examples 2 to 5 to 9, and Comparative Example 3 to Example 10 all have a longer tool life).
On the other hand, Comparative Examples 4 to 6 use cBN powder that has been heat-treated in hydrogen halide. However, since the concentration of the halogen species is not in the range of 50 ppb to 100 ppm, the tool life is longer than that of the untreated one. Slightly short and inferior in performance.

In this example, only the method of incorporating cBN particles into the sintered body by heat treatment in hydrogen halide is shown, but the method of adding hydrogen halide to the sintered powder is limited to this. Alternatively, diluted hydrogen halide may be added to the finished powder.

Claims (7)

  A sintered body mainly composed of cubic boron nitride, wherein the sintered body contains at least one element selected from the group consisting of F, Cl, Br, and I, and the concentration thereof is 50 ppb at wt%. A cubic boron nitride sintered body characterized by being 100 ppm or less.   A sintered body mainly composed of cubic boron nitride, wherein the sintered body contains at least one element selected from the group consisting of F, Cl, Br, and I, and the concentration thereof is 50 ppb at wt%. A cubic boron nitride sintered body characterized by being 10 ppm or less.   3. The cubic boron nitride sintered body according to claim 1, wherein an average particle diameter of the cubic boron nitride is 0.5 μm or more and 5 μm or less.   The cubic boron nitride sintered body according to any one of claims 1 to 3, wherein the cubic boron nitride has a volume content of 70% or more.   The cubic boron nitride sintered body according to any one of claims 1 to 4, wherein the cubic boron nitride sintered body has a thermal conductivity of 100 W / (m · K) or more.   A sintered body mainly composed of cubic boron nitride, wherein the cubic boron nitride sintered body is an element selected from the group consisting of groups IV, VI, VIII to X of the periodic table and Al. The cubic boron nitride sintered body according to any one of claims 1 to 5, comprising any one or more of a simple substance, a mutual solid solution, a carbide, a nitride, a carbonitride, a boride, and an oxide.   A method for producing a cubic boron nitride sintered body comprising sintering cubic boron nitride powder after heat treatment in hydrohalic acid which is an aqueous solution of hydrogen halide comprising HF, HCl, HBr, and HI .