JPS6326189B2 - - Google Patents

Description

[Detailed description of the invention] Cubic boron nitride (CBN) is second in hardness to diamond, has high thermal conductivity, and has excellent chemical stability at high temperatures, so it is attracting attention as a wear-resistant material for metal processing. It is used as grinding abrasive grains and cutting tools.

The inventors also paid attention to this CBN, and as a result of prototyping and researching various CBN sintered bodies, they invented a sintered body for tools that can maximize the excellent characteristics of CBN, and filed a patent application. (Japanese Patent Application No. 53-77811) This invention combines CBN crystals by forming a continuous phase of carbides, nitrides, borides, silicides, or mutual solid solution compounds of transition metals of groups A, A, and A of the periodic table. The present invention provides a sintered body for high-hardness tools that is rich in heat resistance and abrasion resistance, maintains high thermal conductivity even at high temperatures, and is particularly rich in thermal shock properties.

The inventors further conducted various cutting tests using these sintered bodies, and found that CBN is extremely effective even in low-speed cutting, where high-speed steel is used, due to its excellent welding resistance. discovered that it is a substance that

Therefore, CBN sintering using titanium nitride, a type of the invented sintered body, as a binder is used for so-called automatic lathe work of small precision parts that use high-speed steel or ultrafine-grained cemented carbide made of fine tungsten carbide. When we tested the final product, we found that it had excellent welding resistance, resulting in a beautiful glossy finished surface, but on the other hand, the dimensional accuracy was not very good, and the joints between the surfaces should not form an R shape. Because the part was said to have an R-shape, it was not possible to show particularly superior performance compared to the normally used tool.

As a result of conducting various investigations to clarify the cause of this, it was discovered that there was a problem with sharpness (obtaining a sharp cutting edge), which is a particularly necessary characteristic for tools used in such applications. Ta.

In other words, as a result of enlarging and observing the ground cutting edge of the CBN sintered body, the test sintered body had a lot of edge loss, and there was a clear difference from the ultrafine-grained cemented carbide. Therefore, it was thought that the problems such as the above-mentioned dimensional accuracy were caused by the sharpness of the edge.

Therefore, we thought that these problems could be overcome by making the CBN particles in the sintered body extremely fine, so we tried making a prototype of such a sintered body. Now, as a method for producing a CBN sintered body, for example, as shown in Japanese Patent Publication No. 52-43846, it is possible to mix CBN powder with Al, Co, Ni, Fe, etc., which becomes a catalyst for CBN synthesis, or to mix these powders together. metal plate
There is a method of hot pressing under high temperature and high pressure conditions where CBN is stabilized by placing it in contact with CBN powder.

However, in this method, sintering is performed in the presence of a liquid phase of these metals, so if the raw CBN powder is 1 μm or less, the surface energy is large, and grain growth of CBN particles occurs during sintering. One problem is that the desired fine-grained sintered body cannot be obtained, and the other is that these metal phases, which are the binder of the sintered body, have a high affinity with the work material.
This is not preferable because it inhibits the excellent welding resistance of CBN.

As another method for producing a CBN sintered body, as mentioned above, the CBN sintered body is prepared by mixing a powder made of a ceramic material and a CBN powder, which was applied by the inventors.
There is a method of hot pressing under high temperature and high pressure that is stable.

According to this method, grain growth of CBN particles in the sintered body does not occur, and a uniform and fine sintered body can be obtained, and the ceramic used as a binder generally has a good affinity with the work material. Poor, excellent welding resistance
It is thought that this will be a sintered body that takes advantage of the characteristics of CBN. Therefore, we actually use particles with a particle size of 1 μm or less as raw materials.
When CBN particles and various ceramic powders were mixed and sintered under high temperature and pressure, most of the particles were 1μm in size.
We were able to obtain a dense sintered body with a fine microstructure in which the following CBN particles were uniformly dispersed. Using the various ceramic bonded sintered bodies obtained, we again conducted tests using the automatic lathe operation described above.
It was discovered that the best performance was obtained when using a carbide mainly composed of WC containing Al and Cu, or a binder containing an iron group metal. The reason why the one using WC as the main binder showed the best performance is thought to be as follows.

In general, in automatic lathe work for small parts, the workpiece is a few mm to 30mm in diameter, and there are mechanical restrictions on the rotation speed of the workpiece, so the cutting speed cannot be freely selected, and many In some cases, it is necessary to cut at a low speed of less than 10 m/min. For this reason, the temperature of the cutting edge of the tool during cutting is low, and therefore tool wear is mainly due to mechanical scraping action, with very little wear due to chemical reactions. Furthermore, due to mechanical constraints, the amount of tool feed per revolution of the workpiece is also small, typically 0.1 to 0.5 when cutting with a carbide tool.
While the feed rate is generally mm/rev,
For automatic lathes, 0.01mm/rev or less is normal.
It is well known that even in the case of such minute feed, mechanical scraping wear is the main cause. For these reasons, it can be said that materials with high hardness, excellent strength, and toughness, rather than chemical stability, are suitable for tool materials used in applications such as automatic lathe work. WC has the highest hardness among various ceramic materials, and is well known as a material with excellent strength and toughness, and this is probably why products using WC as a binder showed excellent performance. .

In addition, the coefficient of thermal expansion of WC, which is an important factor in making a composite sintered body with CBN, has a value that is almost close to that of CBN, and it is also bonded in that it does not leave any undesirable internal residual stress in the sintered body. It is suitable as a material.

In addition to WC, there is (Mo, W)C, which has the same crystal structure as WC and is obtained by replacing part or most of W with Mo. One of the inventors, along with another researcher, conducted detailed research on the properties of cemented carbide using this compound, and found that, for example, (Mo ₇ W ₃ )C and (Mo ₅ W ₅ )C
The hardness, rigidity, and wear resistance of carbide expressed as
It was confirmed that the properties such as thermal conductivity and thermal expansion coefficient are almost similar to WC. In the following explanation, only WC will be described, but in the present invention, this (Mo, W)C carbide can be used in exactly the same way as WC.

The sintered body for tools of the present invention is a sintered body having a uniform structure in which CBN particles of 1 μm or less are bonded by carbide of 1 μm or less and mainly composed of WC. The hard component, CBN particles, are extremely fine and uniformly dispersed, so when ground into a cutting tool, the cutting edge is extremely sharp and has no irregularities. In this way, in order to obtain good edge sharpness by grinding, the WC in the binder must also be 1 μm or less. Furthermore, the particle size of WC in CBN and binder is 0.5μ
It is most preferable to make it less than m. The fine structure not only improves the cutting edge but also has the advantage of improving toughness and strength, which are important for tools.

In addition, at the cutting speed of about 10 m/min, which is common in automatic lathe work, a built-up cutting edge may develop on the cutting edge during cutting, the workpiece surface may be peeled off due to deposits remaining, and the dimensional accuracy of the workpiece may deteriorate. may become worse,
CBN has low affinity with the workpiece material and has excellent adhesion resistance, resulting in good dimensional accuracy and a beautiful finished surface. Furthermore, because WC is used as the binder, which has high strength and toughness, it is resistant to mechanical scraping and wear, and is a strong sintered body with little breakage even when the cutting edge angle is sharp.

The CBN content in the sintered body of the present invention is 80~80 in terms of capacity.
It is 20% and can be changed depending on the application. In particular, for tools for interrupted cutting that require toughness and may sacrifice wear resistance to some extent, a tool with a large amount of bonding material is selected. When the CBN content is less than 20%, there seems to be little merit in terms of cost and life of tools manufactured using ultra-high pressure equipment, such as the sintered body of the present invention.

Now, why does the sintered body having the composition of the present invention have a uniform structure consisting of ultrafine CBN particles of 1 μm or less?
Furthermore, whether a sintered body with excellent tool performance could be obtained is estimated as follows.

CBN particles have extremely high hardness and are difficult to deform. Therefore, even if CBN particles are compressed under ultra-high pressure, voids remain between the particles. The finer the CBN particles, the higher the porosity, but in the sintered body of the present invention, as mentioned above, the CBN volume content is 80 to 20%.
There are always fine grains of WC between the CBN particles, and by sintering these under ultra-high pressure, the WC deforms and it is possible to obtain a completely dense and uniform sintered body. In addition, in the sintered body of the present invention, a binder such as WC is always present around the CBN particles.
It is thought that because there is no contact between CBN, CBN grain growth does not occur even if a liquid phase of Al or Cu alloy is generated, and a sintered body with fine grains of 1 μm or less can be obtained.

Furthermore, the sintered body of the present invention improves its sinterability and tool performance by containing Cu and Al, and the reason for this will be discussed.

In order for CBN particles to firmly adhere to the binder, CBN
A reaction must occur between the particles and the binder, but in the sintered body of the present invention, the CBN particles react with the binder WC and iron group metal M to form M _x W _y B _z
is formed, and the CBN particles strongly adhere to the binder.
However, if this M _x W _y B _z phase becomes too thick at the interface of CBN particles, the boride is extremely brittle, and cracks will occur in the boride, making the CBN particles easy to fall off and resulting in poor tool performance. In particular, when the sintered body of the present invention is made of ultrafine CBN particles of 1 μm or less, the surface area of CBN is large and boride is likely to be formed, so it is difficult to control the formation of boride by adjusting the sintering conditions. Cu or this compound suppresses the formation of these borides, but by including Cu or this compound in the binder, a boride layer with an optimal thickness is formed, increasing the adhesive strength between CBN and the binder. it is conceivable that. The reason why boride generation is suppressed is not clear, but one reason may be that WC and CBN have low solubility in Cu or iron group metals containing Cu. Fe group metal is 1 in the binder phase.
If it is less than 10%, the amount of boride formed is too small.
If it exceeds the amount, the amount of boride formed increases, and CBN particles tend to fall off.

Next, the effect of Al can be considered as follows.
For example, in liquid phase sintering of WC-Co cemented carbide, if there is a phenomenon of dissolution of hard particles into the binder phase and re-precipitation, it is possible to obtain hard particles of the binder phase or a product with high bonding strength between the hard particles. However, in the sintered body of the present invention, WC-
It is thought that a phenomenon similar to that in the case of Co occurred and the adhesion strength between the CBN particles and the binder improved.

The content of Cu in the sintered body of the present invention is preferably 1 to 30% by weight in the binder. If the Cu content is less than 1%, the generation of boride cannot be suppressed, resulting in poor tool performance. On the other hand, the Cu content
If it exceeds 30%, the hardness of the sintered body decreases, making it impossible to obtain a high-strength sintered body. Further, the content of Al in the binder is preferably 1 to 30% by weight. If the Al content is less than 1%, the effect of the Al content is not recognized, and if it exceeds 30%, the hardness decreases as in the case of Cu.

In carrying out the present invention, such
When a sintered body is composed of CBN powder, WC powder, Cu, and Al, it is convenient to mix the former in a wet ball mill using a cemented carbide ball and a pot lined with cemented carbide. Alternatively, an attritor or vibrating mill may be used, which has almost the same function as a wet ball mill.

Since CBN is hard, a considerable amount of abrasion powder gets mixed in from the balls and lining. It is convenient to use this as it is as a binder component. In particular, it is more convenient if the ball and the inner lining have the same composition as the cemented carbide used to form the bonding material.

Alternatively, only CBN powder and WC powder may be mixed in a wet ball mill as described above without mixing Cu and Al, and Cu and Al or Cu may be introduced into the sintered body from the outside during sintering.

Although WC does not have to be the main component, it is most preferable to use WC from the standpoint of utilizing its excellent properties such as toughness and high thermal conductivity.

TiC as other carbide to replace part of WC,
ZrC, HfC, TaC, NbC, etc. can be used.

As the raw material CBN powder for the sintered body of the present invention, the particle size is
A material having a diameter of 1 μm or more may be used by pulverizing it using a cemented carbide ball or pot as described above.

With fine CBN powder of 1μm or less as in the present invention,
When it is necessary to mix WC uniformly, the method using a pole mill is most suitable as described above, but in this case, even if cemented carbide balls and pots are used, the bonding metal contained in the cemented carbide may be mixed. will be mixed in. In this case, there is no problem if the amount of the bonding metal mixed in is small, but if it is too much, the bonding metal
CBN reacts at low temperatures and produces a large amount of M-W-B boride when the bonding metal is M.
CBN particles fall off during cutting, reducing tool performance.
If the amount of this mixture is large, the metal components can be dissolved in a hydrochloric acid solution after grinding and mixing CBN and WC.

Since the raw material powder used in the present invention is extremely fine, it has a large amount of adsorbed gas. Therefore, it is usually necessary to heat, degas, and sinter in a vacuum at a temperature of 300° C. or higher.

Degassing at a temperature below 300°C is not practical as it requires a long time.

Examples will be described below.

Example 1 Using ultrafine CBN powder with a particle size of 1 μm or less,
Grinding was carried out using acetone as a solvent using a WC-7%Co cemented carbide ball and a pot lined with a cemented carbide having the same composition. The amount of CBN added was 5 g, but after pulverizing for 100 hours, the weight increased to 9.3 g. This increased amount is the fine cemented carbide powder mixed in from the pots and balls. From this, the composition of this powder is estimated to contain 70% CBN by volume. When this powder was observed using a scanning electron microscope, it was found that it was entirely composed of extremely fine powder of 1 μm or less. This mixed powder was placed in a Mo container with an outer diameter of 14 mm and an inner diameter of 10 mm.
After placing the cemented carbide of the composition, 0.65g was filled. On top of this, a 30 μm thick Al-Cu alloy (weight ratio Al:Cu=
1:2) was placed, a stopper made of Mo was placed, and the entire container was placed in an ultra-high pressure device used for diamond synthesis.
The pressure was increased to 50 kb, then heated to a temperature of 1250°C and held for 20 minutes. When the obtained sintered body was polished using diamond paste and its structure was examined, it was found to be a sintered body with extremely fine particles consisting of CBN particles of 0.5 μm or less. Furthermore, as a result of examining this sintered body using an X-ray microanalyzer, it was found that Al and Cu were uniformly contained in the sintered body, and the content was 3% and 6%, respectively, in terms of the weight of the binder. It was %. Next, the composition of this sintered body was investigated by X-ray diffraction, and it was found that in addition to CBN and WC, a small amount of Co _x W _y
Peaks of B _z , AlB ₂ , and AlN were observed.

For comparison, we also prototyped a sintered body with the above-mentioned composition that did not contain Cu, and investigated it by X-ray diffraction.
Besides CBN, WC, large amounts of Co _x W _y B _z , AlB ₂ and small amounts of AlN were detected. Next, a cutting tool made of the two types of sintered bodies and WC-based ultrafine cemented carbide was prepared, and lead free-cutting steel was cut at a cutting speed of 50 m/min, depth of cut of 0.3 mm, and feed rate of 0.01 mm/rev using water-insoluble cutting oil. A cutting test was conducted using As a result, with the ultra-fine grained cemented carbide, the roundness of the right-angled corner of the cutting edge when viewed from the rake face direction reached 15 μm after 15 minutes of cutting time, whereas with the sintered body of the present invention, it took 300 minutes of cutting to reach the same state. It was hot. Furthermore, the sintered body containing no Cu could be cut for 20 minutes.

Example 2 5 g of CBN raw powder and 1.5 g of Al--Cu alloy (weight ratio 1:2) powder were pulverized and mixed for 150 hours using the cemented carbide pot and ball used in Example 1. After mixing, the powder weighed 20.8 g. Estimating the composition of the powder from this, CBN accounts for 52% by volume.
Contains WC-Co with the balance being 90% by weight and 3.3%
It consisted of Al and 6.7% Cu. This powder was embossed to have an outer diameter of 10 mm and a thickness of 2.0 mm, and then degassed at 1000°C for 1 hour. This stamped body has an outer diameter of 14 mm and an inner diameter of 10 mm.
After placing it in a Mo container, place a 10mm outer diameter on top of it.
A WC-10% Co cemented carbide was placed, a Mo stopper was placed, and the same procedure as in Example 1 was carried out at a pressure of 55 kb and a temperature of 1300°C for 10 min.
Hold for minutes. The composition of the obtained sintered body was investigated by X-ray diffraction and found that it contained CBN, WC, and a small amount of Co _x W _y
B _z , AlN, and AlB ₂ were detected. Note that Cu is a pure metal and no peak is found, so it is thought that it exists as some kind of compound. The hardness of this sintered body was 3300. A cutting tool was prepared from this sintered body in the same manner as in Example 1, and an S45C round bar was cut. In addition, cutting speed 10m/min, depth of cut 0.5mm,
Cutting was performed for 200 minutes at a feed rate of 0.03 mm/rev. for comparison
Cutting tests on JIS classification P40 cemented carbide and ultra-fine grained cemented carbide were also conducted at the same time. As a result, the flank wear width of the sintered body of the present invention was 0.05 mm, whereas the flank wear width of P40 cemented carbide and ultrafine cemented carbide were respectively
They were 0.05mm and 0.23.

Example 3 4 _g of CBN powder was pulverized for 20 hours using a ball and pot made of ( _Mo7W3 )C-10%Co-5%Ni alloy. The weight after crushing was 14g. The metal components in this powder were removed by pickling.

This powder contains 67% CBN and 33% (Mo ₇ W ₃ )C by volume.
This includes: This powder has an outer diameter of 14 mm and an inner diameter of
WC-6 with an outer diameter of 10 mm and a thickness of 3 mm in a 10.0 mm Mo container.
After placing %Co, 0.5g was filled. 50μm above this
Place an Al-Cu alloy (1:1 by weight) plate with a thickness of
55 kb and held at a temperature of 1500°C for 10 minutes. The amounts of Cu and Al contained in the obtained sintered body were respectively 10% and 9% by weight in the binder. The structure of the sintered body was an ultrafine-grained alloy of (Mo ₇ W ₃ )C with a uniform structure of 1 μm or less. A cutting tool was made using this sintered body in the same manner as in Example 1.
A cutting test was conducted on SUS303 for 60 minutes using a cutting speed of 50 m/min, depth of cut of 0.2 mm, feed rate of 0.01 mm/rev, and water-insoluble cutting oil. For comparison, ultrafine-grained cemented carbide was also tested at the same time. As a result, the flank wear width of the sintered body of the present invention was 0.1 mm, while that of the ultrafine cemented carbide was 0.3 mm.

Claims (1)

[Claims] 1 High-pressure phase boron nitride with a particle size of 1 μm or less by volume
The content of Al in the binder phase is 80 to 20%, and the remainder of the binder phase is composed of fine particles of 1 μm or less, or a compound of (Mo, W)C, Al that has the same crystal structure as WC, and Cu. is 1-30% by weight,
A sintered body for small precision parts and micromachining tools, characterized by a Cu content of 1 to 30% by weight. 2 Volume of high-pressure phase boron nitride with a particle size of 1 μm or less
The remaining binder phase is composed of fine particles of 1 μm or less in WC or a compound of (Mo, W)C, Al, Cu, and iron group metals with the same crystal structure as WC. Precision small parts micromachining tool characterized by Al content of 1 to 30% by weight, Cu content of 1 to 30% by weight, and iron group metal content of 1 to 10% by weight. sintered body.