JP2000218411A - Cubic boron nitride sintered cutting tool - Google Patents

Abstract

(57) [Summary] [PROBLEMS] While maintaining mechanical properties and thermal properties, cBN particles fall off during cutting of high hardness hardened steel or cast iron, tool wear and chipping due to abrasion and falling off of the binder. The present invention provides a cubic boron nitride sintered compact cutting tool with high performance. A cubic boron nitride having an average particle diameter of 1 μm or less is contained in an amount of 30 to 90% by volume and a cubic boron nitride having an average particle diameter of 2 to 10 μm in an amount of 10 to 70% by volume. The particle diameter is defined as fine-grained cubic boron nitride <bonding material <coarse-grained cubic boron nitride.
a, a carbide, a nitride, a carbonitride, a boride and a composite compound thereof containing at least one group a, 5a or 6a element;
By using at least one of 1N, Al ₂ O _3, and an iron group metal, both excellent wear resistance and excellent fracture resistance can be achieved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cutting tool made of a cubic boron nitride sintered body having both high wear resistance and high fracture resistance.

[0002]

2. Description of the Related Art Cubic Boro Nitride (Cubic Boro)
nNitride (hereinafter abbreviated as cBN) has the hardness next to diamond and does not have the affinity for ferrous metals unlike diamond. Therefore, it is used particularly for grinding tools and cutting tools of hardened steel and cast iron. ing.

[0003] As a cutting tool using such cBN, a cBN bonded with a metal such as cobalt (Co) or a cBN sintered body bonded with a ceramic such as titanium carbide (TiC) has been used. (Special Publication 52-43
846, etc.).

[0004]

SUMMARY OF THE INVENTION Problems to be Solved by the Invention
In the case of a sintered tool, the amount of binder is kept as small as possible so as not to impair the wear resistance and heat resistance, and the remaining cBN
To form a directly connected tissue. However, when cutting a high hardness hardened steel or cast iron with such a sintered body, there is a problem that the tool wear greatly progresses due to the drop of cBN particles during the cutting.

On the other hand, in the case of a sintered body having a structure in which a large amount of a binder is added and cBN particles are dispersed in the binder in order to suppress the shedding of cBN particles, the mechanical properties and thermal properties of the binder particles are lower than those of the cBN particles. Due to inferior characteristics, there is a disadvantage that abrasion and detachment of the binder cause tool wear and chipping.

[0006]

Means for Solving the Problems The present inventor has conducted intensive studies to simultaneously solve tool wear due to cBN particle falling off and wear of the bonding material and tool wear and chipping due to falling off. By controlling the average particle size of the fine cBN particles, the coarse cBN particles, and the remaining binder, the cBN particles having excellent abrasion resistance and fracture resistance are contained uniformly. The inventors have found that a sintered body can be obtained, and have reached the present invention.

That is, the cubic boron nitride sintered body constituting the tool of the present invention is composed of 30 to 90% by volume of fine cBN particles having an average particle size of 1 μm or less and coarse cBN particles having an average particle size of 2 to 10 μm.
Cubic boron nitride sintering characterized in that the binder contains 10 to 70% by volume of particles and the average particle size of the remaining 4% to 65% by volume of binder is fine cBN <binder <coarse cBN. Body.

[0008] Further, the bonding material is used in the periodic table 4a, 5a
a, carbides, nitrides containing at least one group 6a element,
A cubic boron nitride sintered body characterized by containing carbon nitride, boride, a composite compound thereof, and at least one of AlN, Al ₂ O ₃ and an iron group metal as main components.

The cubic boron nitride sintered body has an average particle size of 1 μm.
The reason for containing 30 to 90% by volume of fine cBN particles less than m is that the wear resistance is reduced when the fine particle cBN content is less than 30% by volume, and when the content exceeds 90% by volume, cBN cannot be held by the binder, and the cBN particles fall off. Is caused.

Fine cBN particles having an average particle diameter of 1 μm or less are 50 to 50 μm.
Desirably, the content is 80% by volume. Average particle size 2-1
The content of 10 μm by volume of coarse cBN of 0 μm is as follows.
If the coarse cBN content is less than 10% by volume, the fracture resistance decreases,
If it exceeds 70% by volume, cBN particles may fall off.

The coarse cBN having an average particle size of 2 to 10 μm is 10
It is desirable that the content be contained by 50 to 50% by volume. The reason why the average particle size of the remaining binder is fine cBN <binder <coarse cBN is that if the average particle size of the remaining binder is binder <fine cBN, the binder can hold the coarse cBN particles. Gone, cB
This is because N particles fall off, and when coarse grain cBN <the binder, tool wear and chipping due to the abrasion and the fall of the binder occur.

Further, as the binder, the periodic table 4a, 5
a, carbides, nitrides containing at least one group 6a element,
Carbon nitrides, borides, and composite compounds thereof are included because such compounds have high hardness and toughness, and have improved wear resistance and chipping resistance.

The reason that at least one of AlN, Al ₂ O ₃ and iron group metal is contained is that these compounds are cBN
This is because it has an action of firmly holding the particles.

A specific method for producing such a cubic boron nitride sintered body of the present invention is as follows. First, as a raw material powder, a fine cBN particle having an average particle diameter of 1 μm or less,
10 μm coarse cBN, Ti, V, Cr, Zr, N
b, Mo, Hf, Ta, W, at least one metal, carbide, nitride, carbonitride, boride and composite compounds thereof, AlN, Al ₂ O ₃ , Fe, Ni, Co
Are prepared and weighed to a specific composition, and mixed with, for example, a ball mill made of cemented carbide.

Then, if necessary, it is formed into a predetermined shape. Well-known molding means such as press molding, injection molding, casting molding, extrusion molding and the like can be used for molding.
Next, the compact is sintered at a high temperature and a high pressure as disclosed in, for example, Japanese Patent Publication No. 39-8948.

That is, a pressure of 4 GPa or more and a temperature of 1300 ° C.
The above is maintained for 15 to 60 minutes to obtain the cubic boron nitride sintered body of the present invention. The pressure is preferably 4 to 6 GPa, and the temperature is preferably 1300 to 1800 ° C.

In the present invention, the volume% is obtained from a value obtained by converting the mass of the added cBN from the density. Also,
The usual conversion method for sintered bodies is SEM (electron micrograph)
Is calculated based on the addition ratio of a known sample.

The average particle size of cBN is determined by adding cB
This is the particle size of the N particles. This is because the cBN particle size hardly changes even after sintering. The usual conversion method for a sintered body is to calculate the particle size of an SEM (electron micrograph).

Incidentally, the presence or absence of cBN particles having a particle size of 1 μm to 2 μm did not significantly affect the performance of the cutting tool.

[0020]

Embodiments of the present invention will be described below in detail.

As raw material powders, cBN powder, Ti,
Metals of V, Cr, Zr, Nb, Mo, Hf, Ta, W,
Carbide, nitride, carbonitride, boride, Al powder, Al ₂
O ₃ powder and at least one powder of Ni and Co metals are prepared, weighed so that the composition of the sintered body becomes the composition shown in Table 1, and mixed with a cemented carbide ball mill for 10 hours. did.

Next, the mixed powder is subjected to a pressure of 1 ton / cm ^2.
This compact was fired by holding it at a pressure of 5.0 GPa and a temperature of 1400 ° C. for 30 minutes using an ultra-high pressure and high temperature apparatus to obtain a cubic boron nitride sintered body of the present invention. Obtained.

Then, the cubic boron nitride sintered body is taken out, ground, mirror-finished, and scanned with a scanning electron microscope (SEM).
The tissue was observed at. As a result, Table 1 shows the respective average particle diameters and the average particle diameters of the binders of the obtained fine cBN particles and coarse cBN particles.

Further, a tool was produced using these sintered bodies, and a continuous cutting test and an intermittent cutting test were performed under the following conditions. Table 1 shows the results.

[0025]

[0026]

[Table 1]

Sample No. 1 has a small amount of fine cBN of 10% by volume. In Sample No. 2, the average particle size of the binder was larger than the average particle size of coarse cBN.

Sample No. 7 has a small amount of fine cBN of 29% by volume. Sample No. 9 has an average particle size of the binder smaller than the average particle size of the fine cBN particles.

In sample No. 13, the fine cBN content was as large as 92% by volume, while the coarse cBN content was as small as 2% by volume.

Sample No. 20 has a large content of fine cBN of 95% by volume, while there is no coarse cBN. Further, the average particle size of the binder is smaller than the average particle size of the fine cBN particles.

Sample No. 21 has a small coarse cBN of 1.8 μm. Sample No. 26 has a binder having an average particle size of coarse cBN.
Is larger than the average particle size.

Sample No. 27 has an average particle size of coarse cBN of 1
It is as large as 1 μm. Sample No. 28 has a large average particle size of fine cBN of 1.1 μm.
The average particle size of N is as large as 3.0 μm.

Sample No. 30 has no fine cBN.

With respect to the samples outside the scope of the present invention, Sample Nos. 13, 20, and 21 were lost in the intermittent cutting test.

On the other hand, other comparative examples outside the scope of the present invention, that is, sample Nos. 1, 2, 7, and 26 to 30 have a large wear width of 0.20 mm or more in any of the continuous cutting tests, Abrasion was insufficient.

On the other hand, the sample numbers other than those described above and those of the products of the present invention, except for sample number 24, had a small wear width of 0.20 mm or less in the continuous cutting test, and showed no breakage in the intermittent cutting test. Since it did not occur, good abrasion resistance and fracture resistance were shown.

Sample No. 24 had only SiC as the binder and did not have any defects, but had low wear resistance.

[0038]

As described above, the cubic boron nitride sintered body of the present invention has 30 to 90% by volume of fine cubic boron nitride having an average particle size of 1 μm or less and coarse particles having an average particle size of 2 to 10 μm. Cubic boron nitride is contained in an amount of 10 to 70% by volume, and the remaining binder has an average particle size of fine cubic boron nitride <Binder <
Coarse-grained cubic boron nitride, and in particular, the binder is a carbide, nitride, carbonitride, boride, or a composite compound thereof containing at least one element from Groups 4a, 5a, and 6a of the periodic table; and Al by ₂ O ₃ and be at least one of iron group metals, it is possible to combine the excellent performance of wear resistance and chipping resistance.

Claims (2)

[Claims] 1. When the total composition is 100% by volume, 30 to 90% by volume of fine cubic boron nitride having an average particle size of 1 μm or less.
And 5 to 70 coarse cubic boron nitride having an average particle size of 2 to 10 μm.
% Of the binder and 4 to 65% by volume of the binder, and the average particle size of the binder is in relation to the average particle sizes of the fine cubic boron nitride and the coarse cubic boron nitride. A cubic boron nitride sintered compact cutting tool characterized by satisfying an inequality of boron nitride <bonding material <coarse-grained cubic boron nitride. 2. The method according to claim 1, wherein the bonding material is a periodic table No. 4a, 5a,
Carbides, nitrides, carbonitrides, borides and composite compounds thereof containing at least one group 6a element, AlN and Al
_2. The cubic boron nitride sintered compact cutting tool according to claim 1, wherein ₂ O ₃ and at least one of iron group metals are the main components.