JPH03107441A - High hardness sintered body for tool - Google Patents

Abstract

PURPOSE:To manufacture the high hardness sintered body for tools excellent in strength and wear resistance and suitable as a nose for cutting cast iron by sintering the powder of cubic boron nitride with the mixed fine powder of Al and the carbides of specified metals as a binder. CONSTITUTION:The powder of high hardness cubic boron nitride, 60 to 85vol.%, having a particle size distribution in which the ones having <=1mum average particle size are regulated to 35 to 85wt.% and the ones having 3 to 6mum one are regulated to 20 to 65wt.% is mixed with 15 to 40vol.% ones having the shape of fine powder and having the average particle size less than 1/3 that in the above cubic boron nitride and having the following compsn. as a binder at the time of sintering. The mixture is subjected to deaeration under heating in a vacuum furnace, is thereafter subjected to pressing and is sintered, e.g. at 1400 deg.C. As for the compsn. of the binder, carbides constituted of 3 to 15wt.% Al and the balance one or more kinds among TiC2 and (Ti.M)C2 (where M denotes the 4a, 5a and 6a group transition metallic elements in a periodic table and 0.55<=z<=0.8 is satisfied) are used. The high hardness sintered body of cubic boron nitride series for tools suitable for cutting hard cast iron, hardened steels and heat-resistant alloys can be obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a sintered body for a high hardness tool used for cutting cast iron using cubic boron nitride (cubic BN, hereinafter referred to as cBN).

<Prior Art> High-hardness sintered bodies containing cBN are used in various cutting tools.

An example of this type of sintered body suitable for cutting tools is disclosed in Japanese Patent Application Laid-open No. 53
-77811.

That is, in this prior art, cBN is contained at 80 to 40% by volume.
%, and the remainder consists mainly of carbides, nitrides, borides, silicides, or mixtures or mutual solid solution compounds of group V, group 8 transition metal elements in the periodic table, and this compound is sintered. Disclosed are continuous bonded phases in conjunctive tissue.

In this sintered body for high-hardness tools, the bonding compounds include carbides, nitrides,
Borides, silicides, or mutual solid solution compounds thereof are used, and since these compounds have excellent high hardness, the sintered bodies generally exhibit high performance as cutting tools.

However, even with this sintered body, there is a problem that, in applications where particularly severe impact forces are applied, such as interrupted cutting of high-hardness hardened steel, the cutting edge breaks off during cutting and its life is relatively short.

This chipping of the cutting edge is caused by insufficient strength of the cutting edge, or by wear, especially crater wear, occurring on the cutting edge.

As a sintered body for obtaining a cutting tool with improved strength and wear on the cutting edge, Japanese Patent Application Laid-Open No. 62-228450
No. Publication is known.

<Problem to be solved by the invention> The above-mentioned Japanese Patent Laid-Open No. 53-77811 and Japanese Patent Laid-open No. 62-
It has been confirmed in the above-mentioned commercial products that the high-hardness sintered body for tools disclosed in Japanese Patent No. 228450 generally exhibits high performance when used in cutting tools.

However, when used as a cutting tool, there are still problems depending on the application.

For example, when cutting high-strength graphite cast iron or high-speed cutting of gray cast iron, there are problems such as rapid wear on the cutting edge, shortening its lifespan, or crater wear on the cutting edge, causing the cutting edge to break. It was still left behind.

Therefore, an object of the present invention is to provide a sintered body for a high-hardness tool that has even better strength and wear resistance than the conventional cBN sintered body described above and is suitable as a cutting edge for cutting cast iron. .

<Means for Solving the Problems> As a result of intensive studies to achieve the above object, the present inventors found that cBN in the form of a mixed powder consisting of 60 to 85% by volume of cBN and the remainder of the binder as shown below is stable. It was discovered that if sintered under ultra-high pressure conditions, a sintered body for high hardness tools with superior wear resistance than conventional cBN sintered bodies could be obtained.

That is, it contains 3 to 15% by weight of M, and the remainder is TiCz, (
Ti, M) Compounds represented by Cz (However, M is a transition metal element of group 11., ■, ■ of the periodic table excluding Ti, and 0.55≦Z≦0.8) One or more types and unavoidable This is a sintered body obtained by ultra-high-pressure sintering of a mixed powder obtained by mixing a binder containing impurities with cBN in the above ratio.

<Function> The reason why the sintered body of the present invention has excellent strength and wear resistance is presumed to be due to the following reasons.

In order to improve the strength and wear resistance of the sintered body, it is necessary to have a high content of cBN and a strong bond between the cBN and the binder.
Furthermore, the binder phase after sintering must have excellent wear resistance.

In this invention, by containing 3 to 15% by weight of M and a Ti compound in excess of the stoichiometric composition in the binder, the M and Ti compounds react with cBN during sintering under high temperature and high pressure, and aluminum boride It is thought that the aluminum compound or aluminum reacts with the carbide or boride of Ti to firmly bond cBN and the binder or the binders together.

In this invention, the reason why the cBN content is set to 60 to 85% by volume is that if it is less than 60% by volume, the strength and hardness in the sintered body will decrease. In addition, there is a relatively large amount of binder phase (for example, mechanical wear of the binder phase part occurs when cutting high hardness parts such as high hardness graphite contained in cast iron that is the workpiece material or pearlite base material in the matrix). may develop more quickly and cracks may occur more easily due to impact.

On the other hand, when the cBN content exceeds 85% by volume, the cBN particles almost contact each other, and cracks occur in the contact areas between the particles during interrupted cutting where high pressure is applied to high-strength work materials or cutting edges. This is because the strength of the sintered body decreases.

In addition, the content of M in the binder is 3 to 15% by weight.
is preferred.

When the content of M is 3% by weight without swirling, the reaction between M and cBN is insufficient, and the holding power of the cBN crystal by the binder becomes weak. On the other hand, the content of M is 15% by weight in the binder.
Exceeding this is not preferable because although the bonding strength between cBN and the binder increases, the hardness of the binder itself decreases and wear resistance decreases.

That is, if the binder phase in the sintered body contains a large amount of aluminum nitride or aluminum boride, JP-A-62-228450
As disclosed in the publication, excellent bonding strength is obtained, but the wear resistance is lower than that of the above-mentioned aluminum nitride and aluminum boride, which are produced by containing a large amount of M. TiCz, (T
i, M) The relative content of the Ti compound represented by Cz decreases, making it impossible to obtain sufficient wear resistance when cutting cast iron.

For this purpose, the optimum amount of M in the binder is 3 to 15% by weight.

Further, A2 is aluminum oxide in addition to the above-mentioned aluminum nitride and aluminum boride compounds.

However, although the presence of a trace amount was confirmed by X-ray diffraction, this does not pose any hindrance to the present invention.

Regarding Ti carbide TiCz, (Ti, M)Cz,
It is thought that free Ti forms borides such as TiBz and is strongly bonded to cBN.

The value of Z in the above TiC:z, (TiM)Cz is 0
．． It is preferable that 55≦Z≦0.8.

If the Z value is less than 0.55, the amount of free Ti increases and the bonding strength increases, but the strength and hardness of the bonding material itself decreases, which is not preferable.

Furthermore, when the Z value exceeds 0.8, the hardness of the binder itself becomes high, but the amount of free TiO becomes insufficient and the bonding strength decreases.

Furthermore, Periodic Table No. 11a, ■, ■ contained in the binder.

2 to 10% by weight of WC in the binder among group transition metal elements
It was confirmed that the abrasion resistance was improved by containing the compound.

Furthermore, by containing one or more iron group metal elements in the binder, the strength and hardness of the binder can be further increased.
The properties of the sintered body are further improved.

This is thought to be due to the high wettability between iron group metal elements and borides such as TiB2 and IRB2, which causes the borides in the sintered body to bond more strongly.

In particular, it has been found that when W is used as M in the above TiCz and (TiM)Cz, the wear resistance and strength of the binder are improved and exhibit good properties.

In the sintered body of the present invention, cBN crystals are bonded to each other through a binder phase made of the binder as described above, and fine grains of cBN
It has a tissue filled with BN.

Generally, cBN sintered bodies are abraded because cBH has excellent abrasion resistance, so it is thought that the bonding material wears out preferentially and cBN falls off.

Therefore, it is preferable that the binder phase is uniformly dispersed by using fine particles of the binder for cBN particles in which the ratio of the particle diameters of the cBN particles and the binder is preferably 3:1 or less.

Further, if the average particle size of cBN exceeds 4 gm, the size of the binder phase becomes large and this portion is preferentially worn out, so it is preferable that the average particle size is 4 pm or less.

Furthermore, 35 to 80% by weight of cBN powder of 1 um or less,
20-65% by weight of cBN powder of 3 gm or more and 6 μm or less
By containing fine cBN particles in the gaps between coarse cBN particles,
Filled with BN particles, the structure is made uniform, preferential wear of the binder phase is avoided, and wear resistance is further improved.

<Example> Hereinafter, this invention will be explained in detail with reference to Examples.

Example I A carbide or carbonitride powder containing Ti and M powder were mixed, and the mixture was mixed using a cemented carbide pot and ball to have a composition shown in Table 1 with an average particle size of 0.8 μm or less. A binder powder was prepared.

In Table 1, samples Nos. 011 to 8 indicate the samples of this example,
Sample Nos. 9 to 15 show samples of comparative examples.

In the comparative examples, underlined values indicate compositions that deviate from the compositions of the present invention.

Table 1 Each binder powder shown in the above table has an average particle size of 2°5 to 4.
．． OL1m of cBN powder was mixed at a volume ratio of 32:6 g.

Next, the obtained mixed powder was inserted into a container made of Mo, and the container was placed in a vacuum furnace at a vacuum level of 1000 Torr.
It was degassed by heating for 20 minutes at a temperature of .degree. Next, 55Kb
The sintering was carried out at a pressure of 1400°C and a temperature of 1400°C.

Next, when the obtained sintered bodies were identified by X-ray diffraction, peaks of carbides or carbonitrides containing cBN and Ti were observed in all the sintered bodies. In addition to the above-mentioned substances, peaks thought to be TiB2, Ai'Bz, AJN, and W borides, carbides, or W were observed.

Next, when the compositions of these sintered bodies were observed using a scanning electron microscope, it was found that the fine cBN particles were bonded to each other via a bonding phase.

Next, each of the above sintered bodies was processed into a cutting tip, and a workpiece of spheroidal graphite cast iron FCD45 was turned. The cutting conditions were a cutting speed of 320 m/min, a depth of cut of 0.3 mm, and a feed rate of 0.18 mm/rev, and cutting was carried out in a wet manner for 30 minutes using a water-soluble cutting fluid. This result is the second
As shown in the table.

Table 2 Example 2 91% by weight of TiCo, y and 9% by weight of M powder were mixed using a cemented carbide pot and ball to produce a binder having the average particle size shown in Table 3. Next, after blending this binder with cBN powder having the particle size and content shown in Table 3,
It was filled into a Mo container and sintered for 20 minutes at a pressure of 45 Kb and a pressure of 1300''.

Next, the obtained sintered body is processed into a cutting tip,
Spheroidal graphite cast iron F with grooves with a U-shaped cross section at two locations on the outer periphery
Cutting speed: 250 m/min, depth of cut: 0.3 mm, a cylindrical workpiece made of CD65 material (hardness H, = 240).
Wet turning was carried out under the cutting conditions of a feed rate of 0.15 mm/rev and the use of water-soluble cutting fluid.

The results are shown in Table 3.

Comparative Examples in Table 1 <Effects of the Invention> As explained above, according to the present invention, by mixing cBN with Ti carbide and M, which have excellent high-temperature strength, and sintering it under ultra-high pressure, cBN can be Contains 85% by volume,
A sintered body for high-hardness tools containing Ti carbide, carbonitride, and aluminum boride can be obtained, and this sintered body can be used for cutting high-strength graphite cast iron and high-speed cutting of gray cast iron. It is effective as a chip for

Further, since the sintered body of the present invention has high hardness, it can be suitably used for cutting hardened steel and heat-resistant alloys.

Claims (2)

[Claims] (1) A sintered body obtained by ultra-high pressure sintering of a mixed powder consisting of 60 to 85% by volume of cubic boron nitride powder and the remainder a binder, the binder being 3 to 15% by weight of Al. and the remainder is TiCz, (Ti, M)Cz (where M is Ti
It is a transition metal element in groups IVa, Va, and VIa of the periodic table, excluding 0.55≦Z≦0.8. ) and unavoidable impurities. (2) The average particle size of the cubic boron nitride powder of the sintered body is 4 μm or less, and 35 to 80% by weight of cubic boron nitride powder of at least 1 μm or less, and 3 to 6 μm cubic boron nitride powder. The sintered body for a high-hardness tool according to claim 1, which contains 20 to 65% by weight of boron powder. (3) The sintered body for a high-hardness tool according to claim (1) or (2), wherein the average particle size of the binder is less than 1/3 of the particle size of the cubic boron nitride powder.