JPS62983B2 - - Google Patents

Description

[Detailed description of the invention]

Cubic boron nitride (Cubic BN, hereinafter abbreviated as CBN) is a material with the second highest hardness after diamond.
Synthesized under ultra-high pressure and high temperature. Currently, CBN is already used as an abrasive grain for grinding, and CBN is also used for cutting purposes.
Sintered bodies made by bonding metals with metal such as Co are used in some cases. When this CBN bonded sintered body is used as a cutting tool, the wear resistance decreases due to the softening of the bonded metal phase at high temperatures, and the tool may be damaged because the workpiece metal tends to weld. There are some drawbacks. The present invention relates to a new CBN sintered body suitable for tool applications such as cutting tools, which has a binder phase of a hard metal compound with high strength and excellent heat resistance, rather than a sintered body bonded with such metals. It is. The inventors first developed CBN into carbides, nitrides, and borons of group 4a, 5a, and 6a metals of the periodic table as sintered bodies for tools that take advantage of CBN's characteristics of high hardness and extremely high thermal conductivity. We have developed a highly hard sintered body for tools bonded with compounds consisting of oxides and silicides and have applied for patents (Japanese Patent Application Laid-open Nos. 53-77811 and 53-139609).
issue). The inventors further conducted extensive studies in terms of wear resistance and toughness required of sintered bodies for tools, and arrived at the present invention, which is particularly suitable for cutting tool materials. As mentioned above, CBN is a material with high hardness and excellent heat resistance and wear resistance. Various attempts have been made to sinter only this CBN, but for example, as described in Japanese Patent Publication No. 39-8948,
It is over 70kb and needs to be sintered under ultra-high pressure and high temperatures of over 1900℃. Current ultra-high pressure and high temperature equipment can generate such high pressure and high temperature conditions, but if the equipment is scaled up on an industrial scale, it is not practical because the number of lifetimes of the high pressure and high temperature generation parts is limited. Furthermore, although a sintered body made only of CBN has high hardness, it has poor toughness when used as a tool. The inventors used the periodic table as a binder for CBN.
4a, 5a, 6a group carbides, nitrides, carbonitrides,
By finding more appropriate manufacturing conditions using a compound containing Al and a compound containing Cu and iron group metals, we can obtain a CBN sintered body with unprecedented wear resistance and toughness. I was able to do that. A similar study was also conducted on wurtzite boron nitride, which is another form of high-pressure phase boron nitride, and results similar to those obtained using CBN were obtained. A sintered body using CBN as a hard wear-resistant component will be described in detail below, but the same can be said when using a wurtzite type or a mixture of CBN and wurtzite type boron nitride. Possible uses of CBN sintered bodies as cutting tools include cutting high-hardness materials such as steel and cast iron (for example, hardened steel and high-hardness rolls), and machining difficult-to-cut materials such as super alloys. The same is true when cutting general steel, cast iron, etc., but especially for such applications, it is important that the tool material not only has high hardness and excellent wear resistance, but also excellent toughness. required. Although it cannot be said that the above-mentioned sintered body made of CBN bonded with metal Co has sufficient performance in terms of wear resistance and heat resistance, it is particularly suitable for cutting processes where intermittent impact is applied. It lacked toughness for its intended purpose and could hardly be used. As stated in the inventors' earlier application (Japanese Patent Application No. 113987-1987),
If carbides, nitrides, and carbonitrides of metals 4a, 5a, and 6a of the periodic table are used as binders, and the particle size and composition of CBN and the distribution state of the binder phase are appropriately controlled,
A high-performance sintered body can be obtained that can be applied to applications such as interrupted cutting. However, when milling a highly hardened steel having a complex shape, chipping of the tool edge still occurs, which is a problem. The inventors of the present invention have carried out extensive research in the belief that it is necessary to increase the bonding strength of CBN-CBN and CBN-bond materials in order to improve the toughness of the sintered body. As a result, if the binder phase of CBN is composed of nitrides, carbides, carbonitrides of metals of groups 4a, 5a, and 6a of the periodic table, a compound of Al, and a compound of Cu and iron group metals, the CBN can be reduced. It was discovered that it is possible to improve the toughness of sintered bodies not only in the CBN-containing region (30 volume %) but also in the high CBN content region (80 volume %). Furthermore, the inventors have discovered that the above-mentioned binder is the main component.
Various methods to improve the performance of CBN sintered bodies were investigated. As a result, when the carbides, nitrides, and carbonitrides of Groups 4a, 5a, and 6a of the periodic table used in the production of sintered bodies are expressed as MCx, MNx, and M(C,N)x, respectively, 0.5≦× It was found that the sinterability was improved by using ≦0.95. That is, CBN
It is desirable that there be surplus metal that contributes to the reaction with the particles, but if the value of x is less than 0.5, the hardness of the sintered body will decrease due to the excessive presence of free metal.
This is because if it exceeds 0.95, there will be too little free metal and no improvement in sinterability will be observed. In particular, when carbides and nitrides of Group 4a of the periodic table were used, the improvement in sinterability was remarkable. In the present invention, by incorporating Cu and iron group metals into the sintered body, it has become possible to obtain a sintered body with excellent tool performance. In order to investigate the reason for this, a sintered body containing no Cu or iron group metals was
When examining the line diffraction image, it was found that MC in the binder,
A large amount of borides such as MB and MB ₂ were formed at the interface between MN, M (CN) and CBN. Furthermore, when the fracture surface of this sintered body was observed, it was found that there were places where CBN particles had fallen off, especially when the CBN content was high. On the other hand, as a result of creating a sintered body by adding Cu and a small amount of iron group metal to the composition of this CBN sintered body and examining the products and fracture surfaces, it was found that the formation of borides such as MB and _MB2 was suppressed. , on the fracture surface,
Most of the CBN particles underwent intragranular fracture, and no CBN particles were observed to fall off. Borides such as MB and MB ₂ usually have high hardness, but are brittle materials, so if they are present in large quantities at the interface of CBN particles or binder, they are likely to become the source of fracture. Therefore, the sintered body of the present invention may have been able to improve the bonding strength at the interface between CBN and the binder by containing Cu and iron group metals and suppressing the generation of boride. Further, when a transition metal of No. 4a of the periodic table is used as M, even better performance is obtained, which is presumed as follows. Cu and iron group metals are
The surplus of MCx, MNx, and M(CN)x in the sintered body
Reacts with M, a group 4a transition metal, producing a low melting point liquid phase.
It penetrates uniformly into the interface between CBN and binding materials such as MC, MN, and M(CN). M that invaded this interface
Cu and M-iron group metals include CBN, MC as a binder phase,
Because of its good affinity with MN and M (CN), CBN-
This is thought to be to increase the bonding strength between CBN or CBN-MC, MN, and M (CN). Furthermore, as described above, the sintered body of the present invention can be sintered at a low temperature because a liquid phase with a low melting point appears during sintering. In the sintered body of the present invention, these Cu and iron group metals do not exist as pure metals, but as MC,
Solid solution in the binder phase of MN, M(CN), etc. or excess M or Al of MCx, MNx, M(CN)x
Because it reacts with the metal and exists in the form of an intermetallic compound, there is no decrease in strength at high temperatures. However, if the content of Cu and iron group metals exceeds 20% by weight in the binder,
Cu and iron group metals do not form a solid solution in the binder phase of HC, MN, and M (CN), or react with excess M and Al to form intermetallic compounds, and remain as pure metals in the sintered body. , the hardness of the sintered body decreases and tool performance deteriorates. On the other hand, if the content of Cu and iron group metals is less than 1%, the above-mentioned effect of suppressing the formation of boride is not observed. Further, the ratio of Cu to iron group metal is suitably in the range of 1/2 to 5.
If it is less than 1/2, the Cu content is too low and the generation of boride cannot be suppressed, while if it exceeds 5, the Cu content becomes too large and the hardness of the sintered body decreases. be. Another factor that improves the performance of the sintered body of the present invention is the use of an Al compound in the binder. For example, if there is a phenomenon of dissolution of hard particles into a binder phase and re-precipitation, such as in liquid phase sintering of WC-Co cemented carbide, a product with high bonding strength between the binder phase and the hard particles, or between the hard particles can be obtained. In the sintered body of the present invention, it has been found that a phenomenon similar to this occurs when an Al compound is present in the binder. MCx as a bonding material,
When an Al compound is added to MNx and M(CN)x, the sinterability improves as the amount increases, and a sintered body with high hardness can be obtained even when sintered at a low temperature. The effect of Al content is fully exhibited when the amount of Al added is 5% or more by weight in the binder. Also
If the Al content exceeds 30% by weight in the binder, the strength of the binder will decrease, which is undesirable, and the optimum content is 5% to 30%. In addition, the CBN content of the sintered body of the present invention is 30% by volume.
~80%. When the CBN content is 30% or less by volume, the hardness of the sintered body is low and the effect of CBN inclusion is not so great. Furthermore, the CBN content is 80% by volume.
% or less, especially 70% or less, the toughness of the sintered body is very good because the tough binder phase forms a connected phase. In particular, this sintered body is suitable for machining high-hardness work materials such as die steel and general hardened steel. Various methods can be considered for adding Al or Cu and iron group metals. The simplest method is to add Al or Cu and iron group metals to the mixed powder with CBN before sintering, but it is difficult to obtain fine powders of these metals of less than 1 μm, and coarse particles may affect the structure of the sintered body. tends to become uneven. In the case of Al, the most preferable method is to react the excess M of the binder MCx, MNx, M(CN)x with metallic Al in advance to form an intermetallic compound of M-Al, which is then pulverized and used. It's a method. In this case, the bonding materials MCx, MNx, M (C.
N) Extremely fine binder powder of 1μ or less consisting of an intermetallic compound of x and Al can be easily obtained. In addition, M synthesized by reacting metal M and metal Al in advance
- Easily pulverized powder of Al intermetallic compound may be used. AlN, another form of Al compound,
It may be added in the form of a nitrogen-containing compound such as Ti ₃ AlN or Zr ₂ AlN. In addition, in the case of Cu and iron group metals, the most preferable method is to infiltrate them from outside the sintered body by diffusion during sintering, or add them by reacting with the binder as in the case of adding Al above. . The grain size of the CBN crystal used in the present invention needs to be 10 μm or less in view of the performance of the sintered body as a tool. If the crystal grains are coarse, the strength of the sintered body will decrease, and especially when used as a cutting tool, a finer crystal grain will give a better machined surface. Another feature of the present invention is that the particle size of the binder phase consists of extremely fine crystal grains of 1 μm or less. As a result, the sintered body has a structure in which the binder phase is uniformly dispersed between the CBN particles, and a high-strength sintered body can be obtained. The production of the sintered body is carried out at a pressure of 20 kb or more and a temperature of 900°C or more using an ultra-high pressure and high temperature equipment used for diamond synthesis. Particularly preferred sintering pressure and temperature conditions are pressure 30kb to 70kb and temperature 1100℃.
~1500℃. The upper limits of these pressure and temperature conditions are all within the range of practical operating conditions for industrial scale ultra-high pressure, high temperature equipment. Further, the pressure and temperature conditions must be within the stable range of high-pressure phase type boron nitride shown in FIG. When using such an excellent sintered body as a cutting tool, the high hardness sintered body only needs to be used in the part that will become the cutting edge. Its performance can be fully demonstrated by bonding it to hard metal. However, if it is directly bonded to cemented carbide, the bonding strength may be weak and it may not be possible to use it for interrupted cutting, etc. if the CBN content is high. To obtain sufficient bonding strength, CBN should be contained less than 70% by volume, and the remainder should be one of carbides, nitrides, and carbonitrides of Ti, Zr, and Hf.
The bonding may be performed using an intermediate layer consisting of a seed, a mixture thereof, or a mutually solid compound. This will be explained in more detail below with reference to Examples. Example 1 A mixed powder consisting of 65% by volume CBN particles with an average particle size of 3 μm and binder powder was prepared. The binder powder consists of TiN _0.83 powder and Al powder at 80% by weight each _.
The mixture at a ratio of 20% was heated at 1000℃ in a vacuum furnace.
It was heated for 30 minutes and then ground to a fine powder with an average particle size of 0.3μ. When this binder powder was examined by X-ray diffraction, it was found that in addition to TiN, Ti ₃ AlN, TiAl ₃ ,
Compounds generated by the reaction of TiN and Al, such as TiAl, were detected, but metallic Al was not detected. this is
TiN _0. Relative excess Ti added to N in ₈₃
It is produced by reaction with Al. This mixed powder of CBN and binder was mixed with an outer diameter of 14 mm.
A cemented carbide with a WC-6% Co composition (outer diameter 10
mm, height 2 mm), and then filled with 0.30 g. A cemented carbide (outer diameter 10 mm, height 2 mm) on which 9Cu-1Ni alloy was vapor-deposited with a thickness of 2 μ was placed on top of this, a Mo stopper was placed, and the entire container was placed in an ultra-high pressure device used for diamond synthesis. . It was pressurized to a pressure of 50 kb, then heated to a temperature of 1250°C and held for 20 minutes. The removed sintered body was machined using a diamond grindstone to cut the Cu-Ni vapor-deposited cemented carbide until a high-hardness sintered body appeared, and then polished using diamond paste. When observed with an optical microscope, it was found to be a dense sintered body with no pores. This sintered body was firmly bonded to the cemented carbide via the CBN-containing bonding layer. The hardness was measured using a Bitkers hardness tester under a load of 5 kg and showed a value of approximately 3200. In addition, when we examined the elements contained in the sintered body using an X-ray microanalyzer, we found that Cu and Ni were evenly contained, and the total amount of Cu and Ni was approximately 3% of the weight of the binder. Ta. Furthermore, as a result of investigating the products of this sintered body by X-ray diffraction, CBN, TiN, AlN, etc. were found.
Only a small amount of bolide such as TiB ₂ was detected. A sintered body containing no Cu or iron group metals was produced in the same manner, and the product was examined by X-ray diffraction, but it was found that in addition to CBN, TiN, and AlN, a large amount of TiB ₂ was present. . These two types of sintered bodies were used to create chips for cutting and processing. A SKD11 die steel round bar with H _RC 60 was used as the work material. Cutting conditions are speed 100m/min, depth of cut 0.2mm
When cutting at a feed rate of 0.15 mm/rev. until the flank wear width was 0.2 mm, the sintered body of the present invention could be cut for 30 minutes, whereas the sintered body containing no Cu or Ni could be cut for 30 minutes.
It was hot in 23 minutes. For comparison, commercially available volume% is about 90%.
A chip made of a sintered body of CBN bonded with a metal mainly composed of Co was tested under the same conditions. As a result, the machining time was 15 minutes. Example 2 A binder powder shown in Table 1 was prepared.

[Table] Binder powders having these compositions were heat treated and pulverized in the same manner as in Example 1. This binder powder and CBN powder having an average particle size of 3 μm were mixed to prepare a mixed powder having the composition shown in Table 2.

[Table] In the same manner as in Example 1, a Mo container contained 50% CBN by volume and the remainder was Ti (CN) and Al by weight at 5:
A cemented carbide with a composition of WC-10%Co coated with a mixed powder containing 1 is placed on top of it, and a cemented carbide with a finished powder and 8Cu-2Ni alloy deposited in various thicknesses is placed on top of it, a Mo plug is placed, and the mixture is heated at ultra-high pressure and high temperature. 50kb was maintained at 1280°C for 20 minutes using the apparatus. The hardness measurement results for each are shown in Table 2. Furthermore, these sintered bodies were firmly bonded to the cemented carbide base material via an intermediate bonding layer containing CBN. The hardness increases as the CBN content increases, but even with the same CBN content, E with a Cu--Ni content of 26% is considerably lower in hardness than B. This is because some parts remain as pure Cu or Ni in the sintered body. Also, the sintered body of the present invention
When the fracture surfaces of ABCDEFGHI were observed, it was observed that CBN had undergone intragranular fracture in all of these sintered bodies. Next, these sintered bodies were cut and brazed onto one corner of a cemented carbide throw-away chip, and then processed to create a cutting chip. In order to evaluate the cutting performance, we first performed interrupted cutting with a single blade using a face milling machine. The workpiece material is heat-treated HRc62.
It is SKD11 die steel. The cutting speed was 200 m/min, the depth of cut was 0.5 mm, and the feed rate was gradually increased to 0.07 mm/tooth, 0.12 mm/tooth, and 0.19 mm/tooth, and the defect state of the sintered body was examined. For comparison, commercially available volume% is about 90%.
Cutting chips of a sintered body containing CBN and bonded with a metal mainly composed of Co, and a sintered body with the same composition as sintered body B but containing no Cu or Ni were also prepared and tested. ABCDEFGHI of the sintered body of the present invention did not break even at a feed rate of 0.19 mm/blade. On the other hand, commercially available sintered bodies using Co as a binder and sintered bodies containing no Cu or Ni were damaged at a feed rate of 0.19 mm/blade. We also created cutting chips made from BCE sintered bodies.
Heat-treated SNCM grade 9 steel (HRc54) was used as the work material, and cutting tests were conducted at a cutting speed of 120 m/min, depth of cut of 0.2 mm, and feed of 0.15 mm/rev. For comparison, a commercially available sintered body bonded with metal Co was also tested. The sintered body BC according to the present invention takes 30 minutes to reach a wear width of 0.2 mm on the tool flank.
While it was possible to cut for 40 minutes, E could cut for 10 minutes.
The Co-bonded sintered body reached the same wear width in 5 minutes. Example 3

[Table] A binder powder having the composition shown in Table 3 was prepared and subjected to heat treatment. These binder powders and an average particle size of 3μ
CBN particles were blended and mixed as shown in Table 4 by volume. Next, a container made of Mo was filled with the above finished powder, and a WC-10%Co powder containing 50% CBN by volume and the remainder TiN, HfN, and Al in a ratio of 5:4:1 by weight was coated on top of the finished powder. A cemented carbide of the same composition was placed, a Mo stopper was placed, and the entire container was placed in an ultra-high pressure device and sintered. When the products of these sintered bodies were examined by X-ray diffraction, almost no boride was observed. Furthermore, the results of measuring the hardness of these sintered bodies are shown in Table 4. Furthermore, these sintered bodies were firmly bonded to the cemented carbide base material via an intermediate bonding layer containing CBN. Chips were made using these sintered bodies and cut at a cutting speed of 60 m/min using chilled cast iron.
Cutting was performed for 30 minutes at a feed rate of 0.5 mm and a feed rate of 0.20 mm/rev.
For comparison, a test was conducted under the same conditions using a commercially available chip made of a sintered body in which approximately 90% CBN by volume was bonded with a metal containing Co as the main component. Table 4 also shows the results of observing the wear of the chips after cutting.

[Table] Solid Example 4 The binder powder shown in Table 5 was prepared and heat treated. These binder powders have an average particle size of 1μ.
The CBN powders were blended and mixed as shown in Table 6 by volume. Next, a container made of Mo was filled with the finished powder, a cemented carbide having a WC-6% Co composition was placed on top of the container, a plug made of Mo was placed, the container was placed in an ultra-high pressure device, and the container was sintered. When the products of these sintered bodies were examined by X-ray diffraction, almost no boride was observed.
Furthermore, when the fracture surfaces of these sintered bodies were observed, the fracture occurred within the CBN grains in all of the sintered bodies, and no areas of intergranular fracture were observed. Furthermore, Table 6 shows the hardness measurement results of these sintered bodies.

【table】

[Table] Example 5 Using wurtzite-type boron nitride powder synthesized by the shock wave method with a particle size of 1μ or less, 75% by volume of wurtzite-type boron nitride powder and binder were added to the binder powder used in Example 3. The powder was mixed in a proportion of 25% by volume. Mo
This powder was filled in a container made of aluminum with the same structure as in Example 1, and then sintered using an ultra-high pressure and high temperature device. The hardness of the sintered body was 3600 on the Pickers scale.

[Brief explanation of the drawing]

The figure is for explaining the manufacturing conditions of the sintered body of the present invention, and shows the thermodynamically stable region on the pressure-temperature phase diagram of high-pressure phase type boron nitride.

Claims (1)

[Scope of Claims] 1. Contains 30% to 80% by volume of high-pressure phase type boron nitride with an average particle size of 10μ or less, and the remaining binder phase is a carbide or nitride of a transition metal of 4a, 5a, or 6a of the periodic table. , one type of carbonitride or a mixture thereof or a mutual solid solution compound, and a compound of Al, and the content of Al in the binder phase is 5% or more and 30% or less by weight, and most of the bonded particles are It consists of fine particles of 1μ or less, and further contains Cu and iron group metal elements in the binder phase by 1% or more and 20% or less by weight, and the ratio of Cu to iron group metals is 1/2 to 5. Features: High hardness sintered body for tools. 2 The remaining binder phase is carbide of Ti, Zr, and Hf,
The high-hardness sintered body for tools according to claim 1, characterized in that it is made of one type of nitride, carbonitride, a mixture thereof, or a mutual solid solution compound, and a compound of Al. 3. The high-hardness sintered body for a tool according to claim 1, wherein the high-pressure phase type boron nitride is cubic boron nitride. 4 High-pressure phase type boron nitride powder with an average particle size of 10μ or less and carbides, nitrides, and carbonitrides of transition metals in the periodic table 4a, 5a, and 6a, respectively, are MCx, MNx, and M
(CN) When expressed as x, a compound powder with a value of x in the range of 0.5 to 0.95 and Al or an alloy or compound powder containing Al is 5 to 30% by weight of Al in the binder.
After mixing and molding into powder or molding, it is sintered using an ultra-high pressure and high temperature device at a pressure of 20 kb or more and a temperature of 900°C or more, and Cu and iron group metals or alloys or compounds containing these are extracted from the outside of the sintered body. A high-pressure phase type boron nitride, characterized in that Cu and iron group metals in the binder are infiltrated into the sintered body at a ratio of 1/2 to 5 in a range of 1% by weight or more and 20% by weight or less. Content is 30% by volume in sintered body
The above is a method for producing a high hardness sintered body for tools having a hardness of 80% or less. 5. The method for producing a high-hardness sintered body for tools according to claim 4, wherein M, which is the transition metal, is Ti, Zr, or Hf. 6. The method of manufacturing a high-hardness sintered body for tools according to claim 4, characterized in that a cubic boron nitride powder is used as the high-pressure phase boron nitride powder. 7 High-pressure phase type boron nitride powder with an average particle size of 10μ or less and carbides, nitrides, and carbonitrides of transition metals from Periodic Table 4a, 5a, and 6a were used as MCx, MNx, and M (C.
N) A compound powder with a value of x of 0.5 to 0.95 when expressed as x, and Al or an alloy or compound powder containing Al in a binder containing 5 to 30% by weight of Al and Cu and iron group metals or these. Alloy or compound powder in binder
1~20% by weight of Cu and iron group metals, 1/2~ by ratio
The content of high-pressure phase type boron nitride, which is characterized by mixing the mixture so that the content is within the range of 5. Volume % in sintered body
A method for manufacturing a high hardness sintered body for tools having a hardness of 30% or more and 80% or less. 8. The method for manufacturing a high-hardness sintered body for tools according to claim 7, wherein M, which is the transition metal, is Ti, Zr, or Hf. 9. The method for manufacturing a high-hardness sintered body for tools according to claim 7, characterized in that a cubic boron nitride powder is used as the high-pressure phase boron nitride powder.