JPS6241306B2 - - 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 sintered body of CBN bonded with metal is used as a cutting tool, the wear resistance decreases due to the softening of the bonded metal phase at high temperatures, and the workpiece metal easily adheres to the tool, resulting in damage to the tool. 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 suitable manufacturing conditions using Al-containing compounds and Cu-based compounds,
We were able to obtain a CBN sintered body with unprecedented wear resistance and toughness. 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 the binder, and the particle size and composition of CBN and the distribution state of the binder phase are appropriately controlled, it is possible to perform such interrupted cutting. A high-performance sintered body that can be used for various purposes can be obtained. 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-binder in order to improve the toughness of the sintered body. As a result, we found that 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 Cu, the CBN content is in the low content region (30% by volume). ) as well as high CBN content regions (80
It has been discovered that it is also possible to improve the toughness of the sintered body (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, x≦0.95 It was found that the sinterability was improved by using the following. 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 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, we examined the X-ray diffraction image of a sintered body that does not contain Cu, and found that MC, MN, M (C/N) and CBN in the binder.
A large amount of borides such as MB and MB ₂ were formed at the interface. 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 examining the product and fracture surface of a sintered body created by adding Cu to the composition of this CBN sintered body, it was found that MB,
The generation of borides such as MB ₂ was suppressed, and at the fracture surface, most of the CBN particles were intragranularly fractured, 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 suppressing the generation of boride. In addition, when a transition metal from periodic table 4a is used as M, even better performance is obtained;
It is estimated as follows. Cu is MCx in the sintered body,
MNx, M(C/N)x reacts with excess M of group 4a transition metal to form a low melting point liquid phase, resulting in CBN and MC,
It penetrates uniformly into the interface with binders such as MN and M(C/N). M-Cu that has entered this interface has good affinity with CBN and the binder phases MC, MN, and M(C/N), so it
This is thought to be to increase the bonding strength with MN and M(C/N). 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, Cu does not exist as a blunt metal, but as MC, MN, M
(C/N), etc. as a solid solution in the binder phase, or
Because it reacts with excess M and Al in MCx, MNx, and M(C/N)x and exists in the form of intermetallic compounds, no strength decrease occurs at high temperatures. However, if the Cu content exceeds 50% by weight in the binder, Cu and iron group metals may dissolve in the binder phase of MC, MN, and M (C/N) or react with excess M and Al. Since the metal does not completely form intermetallic compounds and exists in the sintered body in a pure metal state, the hardness of the sintered body decreases and tool performance deteriorates. Furthermore, if the content is less than 1%, the effect of adding Cu will not be apparent. 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 in which hard particles are dissolved in a binder phase and reprecipitated, 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,
As Al compounds are added to MNx and M(C/N)x, the sinterability improves as the amount increases.
A highly hard sintered body can be obtained even when sintered at low temperatures. 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 content of Al exceeds 50% by weight in the binder, the strength of the binder decreases, which is not preferable, and the optimum content is 5% to 50%. In addition, the CBN content of the sintered body of the present invention is 30% by volume.
~80%. When the CBN content is less than 30% 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 interrupted cutting of high-hardness work materials such as die steel and general hardened steel. Various methods of adding Al or Cu can be considered. Al or Al in the mixed powder with CBN before sintering
The method of adding Cu is the simplest, but it is difficult to obtain fine powders of these metals with a size of 1 μm or less, and coarse particles tend to make the structure of the sintered body non-uniform. The most preferable method is to use sintered materials MCx, MNx, and M for Al.
This is a method in which the excess M of (C.N)x is reacted with metal Al in advance to form an intermetallic compound of M-Al, which is then pulverized and used. In this case, extremely fine binder powder of 1 μm or less, which is made of an intermetallic compound of binders MCx, MNx, M(C·N)x, and Al, can be easily obtained. In addition, metal M and metal
An easily pulverized powder of an M-Al intermetallic compound synthesized by reacting Al may also be used. yet another form
It may be added in the form of a nitrogen-containing compound such as AlN, Ti ₃ AlN, Zr ₂ AlN, which is an Al compound. In the case of Cu, the most preferable method is to infiltrate Cu from the outside of the sintered body by diffusion during sintering, or to add it by reacting with a binder in the same way as when adding Al. 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 bond 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 _0.55 powder and Al powder at 70% by weight each _.
The mixture at a ratio of 30% was heated to 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 ₂ 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 ₅₅
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. Cemented carbide (outer diameter
10 mm, height 2 mm), a Mo stopper was placed, and the entire container was placed in an ultra-high pressure device used for diamond synthesis. Pressure is increased to 50kb and then temperature is increased to 1250℃.
and held for 20 minutes. The removed sintered body was ground using a diamond grindstone to grind the Cu-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 with a load of 5 kg, and the result was approx.
It showed a value of 3500. In addition, when we investigated the elements contained in the sintered body using an X-ray microanalyzer, we found that
Cu was uniformly contained, and the amount was approximately 3% of the weight of the binder. Furthermore, the products of this sintered body were investigated by X-ray diffraction, and the results showed that CBN, TiN,
AlN etc. were present, but only a small amount of borides such as TiB ₂ were detected. A sintered body containing no Cu was produced in the same manner, and the product was examined by X-ray diffraction. It was found that in addition to CBN, TiN, and AlN, large amounts of TiB ₂ and AlB ₂ were present in the product. Chips for cutting were made using these two types of sintered bodies. 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, feed 0.15mm/rev., and flank wear width 0.2mm.
The sintered body of the present invention could be cut for 40 minutes, while the sintered body containing no Cu could be cut for 23 minutes. For comparison, commercially available volume% is approximately 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】

[Table] WC-10% in which a mixed powder containing 50% CBN by volume and the balance containing Ti (C/N) and Al at a ratio of 5:1 by weight was applied to a Mo container in the same manner as in Example 1. Co
A cemented carbide of the same composition is placed, and a cemented carbide on which finished powder and Cu have been vapor-deposited with various film thicknesses is placed, a Mo plug is placed, and 50kb is heated at 1250℃ for 20 minutes using an ultra-high pressure and high temperature device.
Hold for minutes. The hardness measurement results for each are shown in Table 2. Moreover, these sintered bodies were firmly bonded to the cemented carbide base material via the intermediate bonding layer. Among J, K, L, and M listed as comparative examples, J, which has a low CBN content, is inferior in wear resistance. In general,
The hardness increases as the CBN content increases, but even with the same CBN content, K and L, which have a large amount of Cu and Al, have significantly lower hardness than B. Furthermore, M with less Al has poor wear resistance. Also, the sintered body of the present invention
When the fracture surfaces of ABCDEFGHI were observed, CBN was found to have 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 cutting performance,
First, interrupted cutting was performed with a single blade using a face milling machine. Work material is heat treated HRc62 SKD11
It is 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 whose main component is Co, and a sintered body N that has the same composition as sintered body B but does not contain Cu 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, the commercially available sintered body using Co as a binder broke at a feed rate of 0.07 mm/blade, and the sintered body N, which does not contain Cu, broke at a feed rate of 0.19 mm/blade. In addition, using these cutting chips, the cutting speed was increased using SNCM grade 9 steel (HRc ₅₄ ) after heat treatment.
Cutting tests were conducted at 120 m/min., 0.2 mm depth of cut, and 0.15 mm/rev. Table 2 shows the cutting time until the flank wear width of the tool reaches 0.2 mm. 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 5μ
CBN powder was formulated as shown in Table 4. Next, fill the Mo container with the above finished powder and place it on top.
A cemented carbide with a WC-10% Co composition was placed, a Mo stopper was placed, and the entire container was placed in an ultra-high pressure device and sintered. When these sintered bodies were examined by X-ray diffraction, the occurrence of boride was extremely small. Furthermore, the results of measuring the hardness of these sintered bodies are shown in Table 4. Create chips using these sintered bodies,
Chilled cast iron was cut for 30 minutes at a cutting speed of 60 m/min, depth of cut of 0.5 mm, and feed of 0.20 mm/rev. For comparison, commercially available CBN with a volume percentage of approximately 90% is used.
Tests were conducted under the same conditions using a chip made of a sintered body bonded with Co-based metal. Table 4 also shows the results of observing the wear of the chips after cutting.

【table】

[Table] Example 4 Binding material powders shown in Table 5 were prepared and subjected to heat treatment. 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 composition of WC-6% Co 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, little boride was found. 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 1 μ or less, 75% by volume of wurtzite-type boron nitride powder and binder were added to the binder powder used in Example 2. The powder was mixed in a proportion of 25% by volume. Mo
After filling this powder into a container made of
A cemented carbide on which Cu was deposited was placed, a Mo stopper was placed, and the material was sintered using ultra-high pressure and high temperature equipment. 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 boron nitride with an average particle size of 10μ or less, and the remaining binder phase is a carbide or nitride of a periodic table 4a, 5a, or 6a transition metal. , one type of carbonitride or a mixture thereof, or a mutual solid solution compound and a compound of Al, the content of Al in the binder phase is 5 to 50% by weight, and most of the binder particles of the binder are It consists of fine particles of 1μ or less, and further contains 1 to 50% by weight of Cu in the binder phase.
containing a carbide or nitride of the transition metal, the remainder being a carbide or nitride of the transition metal,
A high-hardness sintered body for tools, characterized in that it is made of one type of carbonitride, a mixture thereof, or a mutual solid solution compound. 2 The remainder of the binder phase is carbides 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, or a mixture thereof, or a mutual solid solution compound. 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, as MCx, MNx, and M
When expressed as (C/N)x, a compound powder with a value of x of 0.95 or less is mixed with Al or an alloy or compound powder containing Al, and after molding into a powder form or molding, an ultra-high pressure and high temperature equipment is used. The content of high-pressure phase type boron nitride is 30% by volume in the sintered body.
% or more and 80% or less, the remainder of the binder phase contains 5 to 50% by weight of Al, 1 to 50% of Cu by weight, and the remainder of the binder phase is a carbide, nitride, or carbonitride of the transition metal. A method for producing a high-hardness sintered body for tools, which is made of one type or a mixture thereof, or a mutual solid solution compound. 5. The method for manufacturing 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 10 μ or less and carbides, nitrides, and carbonitrides of transition metals in the periodic table 4a, 5a, and 6a, respectively, as MCx, MNx, and M
When expressed as (C/N)x, a compound powder with a value of x of 0.95 or less, Al or an alloy or compound powder containing Al, and Cu powder are mixed, and after molding into powder or molding, ultra-high pressure equipment is used. The content of high-pressure phase type boron nitride, which is characterized by sintering at a pressure of 20 kb or more and a temperature of 900°C or more, is expressed as volume % in the sintered body.
30% to 80%, the remaining binder phase contains 5 to 50% by weight of Al and 1 to 50% by weight of Cu,
The remainder of the binder phase is a carbide or nitride of the transition metal,
A method for producing a high hardness sintered body for tools comprising one type of carbonitride, a mixture thereof, or a mutual solid solution compound. 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.