JPS644986B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Industrial Application) This invention has extremely excellent toughness and wear resistance, and is particularly suitable for use as a cutting tool for cutting cast materials, high-hardness steels such as die steel, and high-speed steel. The present invention relates to a method for producing cubic boron nitride (hereinafter referred to as CBN)-based sinter. [Conventional technology] Over the past few years, in the field of metal processing, there has been a rapid increase in the speed of cutting cast iron, and a rapid shift from grinding to cutting of high-hardness steels such as die steel and high-speed steel. , as the material that holds the key to its success or failure.
CBN-based sintered bodies have been developed. One of them is CBN of 80% by volume or less, silicon nitride (hereinafter referred to as Si ₃ N ₄ ), aluminum oxide (hereinafter referred to as Si ₃ N ₄ ) and aluminum oxide (hereinafter referred to as Al ₂ O ₃ ). One or two of the following:
There is a CBN-based sintered body obtained by ultra-high pressure sintering using a blended composition consisting of three to four components of titanium nitride (hereinafter referred to as TiN). [Problems to be solved by the invention] However, unlike general steel materials, cast iron, in most cases, has severe structural non-uniformity due to graphite precipitated inside or encroachment of foundry sand. On the other hand, die steel and high-speed steel are heat-treated steels, and have a high hardness as a whole with a Rockwell C hardness of 60 or more, and their surfaces exhibit a black crust. When cutting these materials, parts of different hardness must be removed at once, and strong shear stress acts on the cutting tool. When the above-mentioned conventionally known CBN-based sintered body is used for cutting cast iron, die steel, or high-speed steel, there is a drawback that the cutting edge is easily chipped due to insufficient toughness. In particular, when the cut is deep, the above-mentioned tendency is exacerbated, and furthermore, when the cutting mode is interrupted cutting, the cutting edge is easily chipped and cannot be used due to the impact applied. Therefore, the above-mentioned conventionally known cutting tools made of CBN-based sintered bodies are suitable for continuous cutting of cast iron or high-hardness steel under light load conditions.
That is, it was used only in a narrow range of applications, such as final finishing cutting. Therefore, an object of the present invention is to have extremely excellent toughness and wear resistance, and to exhibit excellent cutting performance when used as a cutting tool for high-hardness steel such as cast iron, die steel, and high-speed steel. The objective is to establish a method for manufacturing CBN-based sintered bodies. [Means for Solving the Problems] The present inventors have discovered that one of CBN, Si ₃ N ₄ and Al ₂ O ₃ or Type 2 and TiN 3
As a result of various studies on the reasons why the desired toughness and wear resistance could not be obtained for ultra-high pressure sintered products using a blended composition consisting of ~4 components, we found that the sintered bodies obtained by this method have a combination of CBN. Si ₃ N ₄ as material
Since the structure is a mixture of TiN and one or two of Al ₂ O 3 and Al 2 O ₃ (see Figure 1), the interfacial strength and toughness between these particles is low, and for this reason, the above sintering It was found that when the body is used as a cutting tool, the constituent particles tend to fall off or peel off, resulting in low wear resistance. On the other hand, the present inventors have previously filed an application for a method for producing dititanium aluminum nitride (hereinafter referred to as Ti ₂ AlN) (Japanese Patent Application No. 59-25768). This Ti ₂ AlN
After various studies on the properties of TiN, it was found that a rapid decomposition reaction occurs at temperatures above 1200°C, leading to the precipitation of TiN. Therefore, the present inventors blended Ti ₂ AlN in place of TiN in the above-mentioned blended composition consisting of one or two of CBN, Si ₃ N ₄ and Al ₂ O ₃ , and TiN. During high-pressure sintering, Ti ₂ AlN is decomposed to precipitate TiN.
When we considered the supply method, we surprisingly found that one or both of CBN, Si ₃ N ₄ and Al ₂ O ₃
Unlike the above-mentioned structure of the conventionally known sintered body obtained using a blended composition consisting of seeds and TiN, in the sintered body obtained by this method, the TiN precipitated during decomposition is separated from the CBN particles. ,
It wraps around the interface of Si ₃ N ₄ particles and/or Al ₂ O ₃ particles, and to be more specific, it mainly consists of TiN,
A sintered body can be obtained in which the binder phase, which also contains TiB ₂ (produced by the reaction between decomposed TiN and CBN), has a continuous structure and firmly bonds each particle (see Figure 2). Therefore, since this sintered body has high interfacial strength, it has excellent toughness, and when used as a cutting tool, particles do not fall off or peel off.
It has excellent wear resistance.Furthermore, even if the amount of CBN blended is higher than that of conventionally known products, the above-mentioned ~ holds true, and in this case, this and the large amount of CBN blended together. However, instead of Ti ₂ AlN, TiN and Ti and Al or TiN can be used to have the same composition.
When a combination of intermetallic compounds such as TiAl is used, AlN is formed during ultra-high pressure sintering with CBN, and this AlN component inhibits sinterability.
We have obtained the above knowledge that the wear resistance of the sintered body is reduced. This invention was made based on the above findings, and includes: one or both of silicon nitride powder and aluminum oxide powder: 3.5 to 15%, Ti ₂ AlN powder: 1.5 to 22%, CBN powder: remainder A composition having a compounding composition (the above, weight %) is mixed by a conventional method and press-molded to form a green compact, and this green compact can be used alone or with other green compacts or sintered bodies. This is a method for manufacturing a CBN-based sintered body for a cutting tool, which is characterized by performing ultra-high pressure sintering under stable temperature-pressure conditions for CBN in a superimposed state. Hereinafter, the configuration of the present invention will be explained in detail. () Particle size of raw material powder The average particle size of the Ti ₂ AlN powder is preferably in the range of 0.5 to 10 μm. The average particle size of the CBN powder is 1 to 20 μm, and the average particle size of the Si ₃ N ₄ powder and Al ₂ O ₃ powder is preferably equal to or smaller than the CBN powder, and preferably 0.5 μm or less. () Blend composition (a) Si ₃ N ₄ and Al ₂ O ₃ These components give a sintered body used as a cutting tool welding resistance (difficulty in welding of the workpiece to the cutting tool, i.e. , the cutting tool is less likely to react with the work material) and reduces strength loss at high temperatures, which in turn improves wear resistance and imparts heat resistance. If it is less than 3.5%, the desired effect described above cannot be obtained, while if it exceeds 15%, the resulting sintered body becomes brittle and its toughness decreases, so
It was set at 3.5% to 15%. (b) Ti ₂ AlN Ti ₂ AlN is a component that is blended to generate TiN through a decomposition reaction during ultra-high pressure sintering and, in turn, to generate a binder phase. In detail, this decomposed TiN reacts with CBN,
TiB ₂ is produced, and eventually Ti ₂ AlN is
This creates a bonded phase containing TiN or _TiB2 . This binder phase consists of CBN grains, Si ₃ N ₄ and
In order to form a continuous network structure between one or two types of Al ₂ O ₃ particles, CBN particles and Si ₃ N ₄
The strength of the interface with one or two particles of Al ₂ O ₃ and Al 2 O 3 increases, and the above components in the sintered body are firmly bonded. Its blending amount is 1.5%
If it is less than 22, the desired effect cannot be obtained;
%, the amount of binder phase produced is too large and wear resistance is impaired as a result, so the blending amount was set at 1.5 to 22%. Among them, 4 to 12
The best effect is obtained when the amount is within the range of %. () Mixing-press forming-ultra-high pressure sintering process These steps may be performed by conventional methods. For example, press molding may be performed at a molding pressure of about 1 to 5 t/cm ² . And before ultra-high pressure sintering
Preliminarily sintered at a temperature within the range of 200 to 800°C in a vacuum of 10 ^-4 torr or less or in an inert gas,
The strength of the powder compact may be increased. Other green compacts or sintered compacts to be superimposed during ultra-high pressure sintering include cemented carbide, cermet, etc. as in the conventional method. Stable temperature-pressure conditions for CBN during ultra-high pressure sintering are pressure 20-70kb, temperature 1200-1500℃, and holding time 10-1500℃.
It is 60 minutes. [Example] Hereinafter, the structure and effects of the present invention will be explained in detail by showing examples. Example As raw material powder, CBN powder with an average particle size of 3 μm,
Si ₃ N ₄ powder of 2 μm, Al ₂ O ₃ powder of 0.5 μm, and Ti ₂ AlN powder of 1 μm were blended into the compositions shown in Table 1 and mixed for 20 hours in a ball mill. , then press-formed at a pressure of 2t/cm ² to form a green compact, and this green compact is made into a cemented carbide sintered body (composition is
Sintered bodies 1 to 12 of the present invention are produced by stacking the WC-10% Co) disk on top of the disk, holding it for 30 minutes under the conditions shown in Table 1 in an ultra-high pressure device, and then cooling and lowering the pressure. did. For comparison, comparative sintered bodies 1 to 1 were prepared using a combination of compounds likely to produce Ti ₂ AlN without using Ti ₂ AlN, except that the other compounding compositions were the same as in the case of sintered body 5 of the present invention. 2, and comparative sintered bodies 3 to 8 whose blending composition deviates from that of the present invention.
A conventional sintered body using TiN instead of Ti ₂ AlN was similarly produced. For these sintered bodies of the present invention, comparative sintered bodies, and conventional sintered bodies, the amount of (TiN+TiB ₂ ) was determined from the intensity of the X-ray diffraction peak, and the values are shown in Table 1. The transverse rupture strengths of these sintered bodies were also measured and the values are also shown in Table 1. In addition, the structures of these sintered bodies were examined using an electron microscope, and a photograph showing the structure of the conventional sintered body is shown in FIG. 1, and a photograph showing the structure of the sintered body 4 of the present invention is shown in FIG. Ta. Next, sintered bodies 1 to 1 of the present invention manufactured in Examples
12. After cutting and brazing the comparative sintered bodies 1 to 8 and the conventional sintered body, they were respectively ground and polished to produce a cutting tool having the shape of SNP432. Using these cutting tools, cutting tests were conducted under the following conditions. <Cutting test conditions> Work material: Sintered high speed steel (Rockwell C hardness:
70) Cutting speed: 40 m/min Depth of cut: 0.1 mm Feed: 0.1 mm/rev. Then, the life is determined when the flank wear width reaches 0.1 mm, the time until the end of the life is measured, and the results are It is shown in Table 1. [Effects of the Invention] As shown in FIG. 2, the structure of the sintered body of the present invention consists of mainly TiN between CBN and one or two of Si ₃ N ₄ and Al ₂ O ₃ . On the other hand, as shown in Figure 1, the structure of conventional sintered bodies obtained using TiN is composed of Si ₃ N ₄ and Al ₂ as binding materials for CBN. It has a structure in which one or two of O ₃ and TiN are mixed. Therefore, as can be seen from Table 1, the sintered body of the present invention having the above-mentioned structure is superior to the conventional sintered body having the above-mentioned structure.
Combinations of compounds likely to produce Ti ₂ AlN

[Table] Comparative sintered bodies using the same composition and comparative sintered bodies whose composition deviates from the composition of the present invention have superior transverse rupture strength, and can be used, for example, in cutting sintered high-speed steel. When cut, the cutting edge will not chip, the cutting life is much longer, and the wear resistance is also much better. That is, according to the manufacturing method of the present invention, it has extremely excellent toughness and wear resistance, and is particularly suitable for use as a cutting tool for cutting cast materials, high-hardness steels such as die steel, and high-speed steel. Therefore, a CBN-based sintered body can be obtained.

[Brief explanation of drawings]

FIG. 1 is an electron micrograph showing the structure of a conventional sintered body, and FIG. 2 is an electron micrograph showing the structure of a sintered body obtained by the manufacturing method of the present invention (sintered body 4 of the present invention in Example). It is an electron micrograph shown.

Claims (1)

[Claims] 1. A composition consisting of one or two of silicon nitride powder and aluminum oxide powder: 3.5 to 15%, dititanium aluminum nitride powder: 1.5 to 22%, and cubic boron nitride powder: the remainder. A composition having the above composition (weight%) is mixed by a conventional method, press-formed to form a green compact, and this green compact is stacked alone or with another green compact or sintered body. 1. A method for producing a cubic boron nitride-based sintered body for a cutting tool, the method comprising sintering cubic boron nitride at a stable temperature and pressure under ultra-high pressure conditions.