JPH0764638B2 - Manufacturing method of cubic boron nitride based ultra high pressure sintered body for cutting tool - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention has a cubic boron nitride excellent in wear resistance (particle drop resistance) and particularly suitable for use as a cutting tool for finishing cast iron. The present invention relates to a method for manufacturing a base ultra-high pressure sintered body (hereinafter referred to as CBN).

[Conventional technology]

In recent years, for finishing of cast iron, a cutting tool that cuts at a high cutting speed of 500 m / min. Has been used, and a CBN-based ultra-high pressure sintered body has come to be used for this. As an ultra-high pressure sintered body, for example, 4a group of the periodic table, 5a group,
And carbides of 6a group elements, nitrides, borides, silicides, Al
One or more of ₂ O ₃ , MgO, AlN, and Si ₃ N ₄ : 20
-80% by weight, CBN and unavoidable impurities: the rest is proposed (Japanese Patent Publication No. 57-3631).
(See the official gazette).

[Problems to be solved by the invention]

However, among the above conventional CBN-based ultra-high pressure sintered bodies,
If a CBN-based ultra-high pressure sintered body composed of titanium carbide (hereinafter referred to as TiC) and CBN and unavoidable impurities is used as a cutting tool for finishing work, for example, for drilling cast iron, 3.2 The limit is to obtain the surface roughness of S.
The dimensional accuracy and surface roughness obtained in the grinding of cast iron are inferior, and therefore, in the present situation where the grinding of cast iron is shifting to the cutting with higher processing efficiency, the above CBN-based ultra-high pressure sintering However, when used as a cutting tool for finishing cast iron, it is not possible to obtain satisfactory dimensional accuracy and surface roughness.Therefore, the conventional CBN-based ultra-high pressure sintered body is suitable as a cutting tool for finishing. In order for such a CBN-based ultra-high pressure sintered body to be used for finishing of cast iron, at least 1.
It needs to be finished to a surface roughness of 6S.

[Means for solving problems]

Therefore, the present inventors have conducted various studies to solve the problems of the conventional CBN-based ultra-high pressure sintered body as described above, and as a result, (1) a CBN-based super-compound composed of TiC particles and CBN particles When TiC particles and CBN particles contact each other in a high-pressure sintered body (hereinafter, also referred to as a sintered body), a glass phase with weak bonding strength is easily formed at the interface.
Since the grain boundary strength is reduced by the rise of the cutting edge temperature during cutting, the particles cannot be sufficiently held on the cutting edge surface, whereby the particles fall off from the surface prematurely and there are relatively large particles. Since a concave portion is formed, when the material rich in the glass phase is used as a cutting tool, the surface roughness of the product is reduced. (2) On the other hand, stable titanium boride (at the interface between the TiC particles and the CBN particles ( Below, TiB ₂ ) is formed and this stable
Contrary to the above, the reaction phase rich in TiB ₂ maintains the grain boundary strength sufficiently and firmly holds the particles even when the cutting edge temperature rises, so that the particles do not fall off from the cutting edge surface and gradually The surface of the cutting edge is kept relatively smooth during cutting as it wears out and the recesses do not occur on its surface, and therefore, when the CBN-based ultra-high pressure sintered body rich in the reaction phase is used as a cutting tool. (3) In order to reduce the formation of the glass phase at the grain interface and increase the formation of the TiB ₂ -rich reaction phase at the grain interface, it is necessary to improve the dimensional accuracy and surface roughness of the product. The particle size of the CBN particles should be the same, and the mixing ratio based on the volumes of both should be as equal as possible. In order to meet the requirements described in (3), raw powder The average particle size of both TiC powder and CBN powder is 0.5 to 5μ, and the average particle size ratio between them is kept within the range of 0.5 to 2.0. Then, TiC powder: 40 to 60%, CBN powder: rest, and (5) Among impurities contained in the sintered body according to (4), a mixture such as a ball mill is used. Impurities consisting of iron group metal and W, which are mixed by the device or mixed for other reasons, are removed from the mixed powder and the content thereof is suppressed to 0.5% by volume or less, the resulting sintered body is Since the toughness is improved and the welding resistance at high temperatures, and therefore the wear resistance, is improved, such a heat-resistant sintered body has excellent dimensional accuracy and surface even in high-speed cutting exposed to high temperatures. Roughness can be maintained, above (1) to (5 Than it was to obtain the results of a study it is shown in.

This invention was made based on the above research results,
A method for producing a CBN-based ultra-high pressure sintered body that has excellent "particle detachment resistance" and is particularly suitable for use as a cutting tool that can improve the dimensional accuracy and surface roughness of products in the finishing of cast iron. For the purpose of providing, TiC powder and CBN powder each having an average particle size of 0.5 to 5μ are used as raw material powders, and both of these powders are TiC powder: 40 to 60% by volume, CBN powder: rest, And mix them in the mixed powder in proportion to each other and the condition that the average particle diameter ratio of these two powders satisfies 0.5 to 2.
By removing impurities consisting of one or more of Fe, Ni, Co, and W so that the content of the impurities in the mixed powder is 0.5% by volume or less, the TiC particles are substantially separated from each other. Characterized by a method for producing a CBN-based ultra-high pressure sintered body for a cutting tool, which has a structure in which a TiB ₂ -rich reaction phase exists at the interface between these TiC particles and CBN particles without contact between CBN particles and CBN particles Is.

Next, the reason why the manufacturing conditions are limited as described above in the method of the present invention will be described.

A. Blend composition TiC powder has the effect of imparting wear resistance to the sintered body, but if the proportion is less than 40% (volume%, the same applies below), wear resistance will be insufficient and The amount of TiC particles relative to the CBN particles becomes too small, the contact between CBN particles increases, whereby the formation of the glass phase becomes remarkable and the wear resistance of the sintered body further decreases, and the ratio is
If it exceeds 60%, the amount of CBN particles will be too small, the thermal conductivity of the sintered body will be insufficient, welding will easily occur at the cutting edge, and the contact between TiC particles will increase, which also causes the above-mentioned glass. The formation of phases becomes remarkable and the wear resistance of the sintered body decreases, and in any case, when this is used for finishing of cast iron, the dimensional accuracy and surface roughness of the product will decrease. Therefore, the ratio was set to 40-60%.

Of the impurities mixed in the mixed powder, the impurities composed of the iron group metal and W combine with B at the time of sintering to partially form a liquid phase, which promotes the growth of TiC particles and thereby the sintered body. B component contained in the sintered body in a state of being combined with the impurities is easily diffused in the work material by being exposed to high temperature during cutting, resulting in welding resistance of the cutting edge. These impurities are removed from the mixed powder in order to impart special heat resistance and strength and to make it suitable for high speed cutting as well, since it has the effect of decreasing the heat resistance and rapidly increasing its wear. And its content is 0.5%
It is important to keep below.

B. Average particle size When the average particle size of CBN powder and TiC powder is less than 0.5 μ, the particles in the sintered body become too small and the same kind of particles tend to agglomerate with each other.
The contact between particles or TiC particles increases, which facilitates the formation of a glass phase that reduces the grain boundary strength.
If the average particle size of the CBN powder exceeds 5μ, the CBN particles in the sintered body itself become brittle, and the strength and wear resistance of the sintered body decrease, which may deteriorate the dimensional accuracy and surface roughness of the product. In addition, in order to avoid the formation of the glass phase, it is necessary to make the average particle size of the TiC powder equal to that of the CBN powder.
The average particle size of both iC powder and CBN powder was set to 0.5 to 5 μm.

C. Average particle size ratio Even if the average particle size of TiC powder and CBN powder is within the above range,
The mutual average particle size ratio is less than 0.5, or 2.0
If it exceeds, the contact interface between TiC particles and CBN particles in the sintered body will decrease, and the proportion of the glass phase formed at the interface between particles of the same type will increase, causing the aforementioned inconvenience, The average particle size ratio between the TiC powder and the CBN powder was set to 0.5 to 2.0.

Incidentally, when carrying out the method of the present invention, a normal ultra-high pressure sintering method, that is, first as a raw material powder, both have an average particle size of 0.5 to 2.0 prepared CBN powder and TiC powder, From these raw material powders, those having an average particle size ratio of TiC powder and CBN powder within the range of 0.5 to 2.0 are appropriately selected and mixed into a predetermined composition and mixed, and then, for example, mixed powder preparation In order to remove the impurities mixed in from a mixing device such as a ball mill, for example,
A method in which a magnet is mixed with a solvent such as acetone or is gently rotated in a slurry-like mixed powder to thereby adsorb the iron group metal and W bound thereto to the magnet, or a mixed powder. After being dried, the impurities are removed by utilizing a method such as pickling and selectively dissolving the impurities to reduce the content of impurities of the iron group metal and W to 0.5% or less. If necessary, insert it into a metal container together with a WC-based cemented carbide plate, etc. in the mixed powder state or the green compact state,
It is heated to a temperature of 800 to 1200 ° C, vacuum degassed and sealed, and then this sealed container is attached to an ultrahigh pressure and high temperature generator, then the pressure and temperature are raised, pressure: 40 to 70 Kb, temperature:
The basic steps consist of holding the pressure and temperature in the range of 1200-1600 ° C for a few minutes to a few tens of minutes, then cooling and finally releasing the pressure.

Furthermore, in using the CBN-based ultra-high pressure sintered body produced by the method of the present invention as a cutting tool, alone or in combination with a high-rigidity sintered body such as WC-based cemented carbide or cermet. In this state, it may be used as a throw-away tip, or these tips may be attached to the tip of a holder made of WC-based cemented carbide or hardened steel by brazing.

〔Example〕

 Next, the method of the present invention will be described with reference to examples.

As raw material powder, average particle size: 0.6μ, 1.0μ, 2.5μ, 4.0μ,
And CBN powder having 6.0μ, the same 0.3μ, 1.5μ, 2.5μ,
And a TiC powder having 5.0 μm are prepared, and these raw material powders are mixed with the compounding compositions shown in Table 1, respectively,
A ball mill is used to mix in acetone for 5 to 40 hours to obtain a mixed powder containing impurities of iron group metal and W mainly from the mixing device in the range of 1 to 3%, and then mixed with this acetone to form a slurry. A cylindrical permanent magnet whose surface was covered with a Teflon sheet (Teflon is a trademark of DuPont, USA) was inserted into the mixed powder, and gently rotated in the slurry-like mixed powder to form an iron group metal. A mixed powder was prepared by adsorbing and removing the impurities consisting of W, whereby the content of this impurity was reduced as shown in Table 1, and then 2 t of the mixed powder thus prepared was prepared.
After molding into a disk-shaped green compact having a diameter of 13 mm and a thickness of 1.5 mm at a pressure of on / cm ² , these green compacts were placed in the container of the ultrahigh pressure and high temperature generator. , Pressure: 50Kb, temperature: 1500
C., holding time: Carrying out the method 1 to 8 of the present invention by performing ultra-high pressure sintering under the conditions of 5 minutes, and having the same component composition as the blending composition, and substantially the same average as the raw material powder. A CBN-based ultra-high pressure sintered body composed of TiC particles and CBN particles each having a particle size was manufactured.

For comparison, as shown in Table 1, the compounding composition,
The same conditions except that one of the average particle sizes of TiC powder and CBN powder and the ratio of the average particle sizes to each other is outside the scope of the present invention (indicated by * in Table 1). Comparative methods 1 to 5 were performed to produce a CBN-based ultrahigh pressure sintered body.

Next, for the various CBN-based ultra-high pressure sintered bodies obtained as a result of this, the toughness fracture value was measured for the purpose of evaluating the toughness, and the welding resistance and wear resistance at high temperatures were evaluated. For the purpose of assessing the dimensional accuracy and surface roughness obtained in the finishing of cast iron with valuation, cutting chips are cut from each of the above sintered bodies, brazed to a WC-based cemented carbide holder, and after polishing finish, Work material: cast iron (FC25), cutting speed: 700 m / min., Depth of cut: 0.3 mm, feed: 0.04 mm / rev., Cutting time: 20 mm. The flank wear width was measured, and the surface roughness of the product after cutting was measured. The results of these measurements are shown in Table 2.

〔The invention's effect〕

From the results shown in Tables 1 and 2, the CBN-based ultra-high pressure sintered bodies produced by the methods 1 to 8 of the present invention have high toughness, wear resistance, and heat resistance. In addition to exhibiting excellent cutting performance in cutting, it is possible to manufacture a product having excellent dimensional accuracy and surface roughness in finish processing of cast iron, while as shown in Comparative Methods 1 to 5, the compounding composition In the CBN-based ultra-high pressure sintered body manufactured under the condition that any one of the average particle diameter of the powder and the average particle diameter ratio of the powder is out of the range of the present invention, the dimensional accuracy and surface roughness are inferior. You can see that

As described above, according to the method of the present invention, in particular, having excellent “particle detachment resistance”, and having excellent heat resistance and toughness, and therefore when used as a cutting tool for finishing cast iron, It is possible to manufacture a CBN-based ultra-high pressure sintered body that can secure excellent dimensional accuracy and surface roughness even with high-speed cutting.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Itaro Tajima 1-2-97 Kitabukuro-cho, Omiya-shi, Saitama Inside Central Research Laboratory, Mitsubishi Metals Co., Ltd. (56) References JP-A-61-14763 (JP, A)

Claims (1)

[Claims] 1. A method for producing a cubic boron nitride-based ultra-high pressure sintered body, wherein titanium carbide powder and cubic boron nitride powder each having an average particle diameter of 0.5 to 5 μ are used as raw material powders. The powder is compounded in the following ratios: titanium carbide powder: 40 to 60% by volume, cubic boron nitride powder: rest, and an average particle size ratio of titanium carbide powder / cubic boron nitride powder of 0.5 to 2 is satisfied. At the same time, impurities such as one or more of Fe, Ni, Co, and W mixed in the mixed powder are removed to reduce the content of the impurity in the mixed powder to 0.5% by volume or less. As a result, there is substantially no contact between the titanium carbide particles and the cubic boron nitride particles, and the cubic structure has a structure in which a titanium boride-rich reaction phase exists at the interface between the titanium carbide particles and the cubic boron nitride particles. Crystalline boron nitride-based ultra-high pressure firing Preparation of cutting tools for cubic boron nitride based ultra-high-pressure sintered body, which comprises manufacturing the body.