JPH0357171B2 - - 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, and is synthesized under ultra-high pressure and high temperature. Currently, it is already used as abrasive grain for grinding, and also for cutting purposes.
Sintered bodies made by bonding CBN with metal Co, etc. are used in some parts. When this sintered body of CBN bonded with metal is used as a cutting tool, the bonding metal phase softens at high temperatures, resulting in a decrease in wear resistance, and the workpiece metal tends to weld, causing damage to the tool. There are drawbacks. The present invention provides a method for producing a new CBN sintered body suitable for tool applications such as cutting tools, which uses a hard metal compound as a binder phase that has high strength and excellent heat resistance, instead of a sintered body bonded with such metals. It is related to. The inventors first developed CBN into carbides, nitrides, and boron of group 4a, 5a, and 6a metals of the periodic table as a sintered body for tools that takes 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 a method for manufacturing sintered bodies that 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℃. Although it is possible to generate such high pressure and high temperature conditions with current ultra-high pressure and high temperature equipment, if the equipment is enlarged to an industrial scale, the number of service life of the high pressure and high temperature generating parts will be limited, making it impractical. In addition, although sintered bodies made only of CBN have high hardness,
Poor toughness when used as a tool. The inventors used CBN as a binder in periodic table 4a.
carbides, nitrides, carbonitrides of transition metals of the group Ti, Zr, Hf, W and/or WC, Al or intermetallic compounds of Al and Ti, Zr, Hf, AlN,
Find more suitable manufacturing conditions using one or more of AlB ₂ , Al ₂ O ₃ , Ti ₂ AlN, Zr ₂ AlN and one or more of Cu or an intermetallic compound of Cu and Ti, Zr, or Hf. As a result, 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), carbides of metals 4a, 5a, and 6a of the periodic table are used as binders.
If nitrides and carbonitrides are used and the particle size and composition of CBN and the distribution state of the binder phase are appropriately controlled, a high-performance sintered body that can be applied to applications such as interrupted cutting can be obtained. However, for example, when milling or turning a highly hardened hardened steel having a complicated shape, chipping of the cutting edge of the tool still occurs, which is a problem. The present inventors have conducted extensive research on the belief that in order to improve the toughness of sintered bodies, it is necessary to increase the bonding strength of CBN-CBN and CBN-bond phases, as well as improve the toughness of the bond phase itself. . the result,
As a binder for CBN, carbides, nitrides, and carbonitrides of Ti, Zr, and Hf, which are transition metals in group 4a of the periodic table, W and/or WC, and Al or Al are used.
Intermetallic compounds of Ti, Zr, Hf, AlN, AlB ₂ ,
If one or more of Al ₂ O ₃ , Ti ₃ AlN, Zr ₂ AlN and one or more of Cu or an intermetallic compound of Cu and Ti, Zr, Hf, etc. are used, a low CBN content area (30 volume We discovered that it is possible to improve not only the toughness of sintered bodies in the high CBN content region (80 volume %), but also the toughness of sintered bodies in the high CBN content region (80 volume %). Furthermore, the inventors have discovered that the above-mentioned binder is the main component.
We investigated various ways to improve the performance of CBN sintered bodies. As a result, when the carbides, nitrides, and carbonitrides of Ti, Zr, and Hf used in the production of sintered bodies are expressed as MCx, MNx, and M(CN)x, respectively, if 0.5≦x≦0.95 is used, It was found that sinterability was improved. In the present invention, by incorporating Cu and W or a compound of W into the sintered body, it has become possible to obtain a sintered body with excellent tool performance. to find out why
When examining the X-ray diffraction image of a sintered body that does not contain Cu, it was found that MC, MN, and M (CN) in the binder phase
A large amount of borides such as MB and MB ₂ were formed at the CBN interface. Furthermore, when we observed the fracture surface of this sintered body, we found that especially when the CBN content is high,
It was observed that there were places where CBN particles had fallen off. On the other hand, as a result of creating a sintered body by adding Cu to the composition of this CBN sintered body and examining the product and fracture surface,
The production of borides such as MB and MB ₂ is suppressed, and at the fracture surface, most of the CBN particles undergo intragranular fracture.
No CBN particles were observed to fall off. Usually MB,
Although borides such as MB ₂ have high hardness, they are brittle materials, so it is thought that if a large amount exists at the interface of CBN particles or the binder phase, it will easily 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 phase by containing Cu and suppressing the generation of boride. Furthermore, Cu is MCx in the sintered body,
MNx, M of surplus group 4a transition metal of M(CN)x
A low melting point liquid phase is formed by reacting with CBN, MC, MN,
Uniformly invades the interface with the binder phase such as M(CN),
M-Cu that has entered this interface has good affinity with CBN and the binder phases MC, MN, and M(CN).
CBN-CBN or CBN-MC, MN, M (C.
This is thought to be to increase the bonding strength with 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, these Cus do not exist as pure metals, but as MC, MN, M (C.
solid solution in the bonded phase such as N) or MCx,
Since MNx and M(CN)x react with excess M and Al and exist in the form of intermetallic compounds, no strength decrease occurs at high temperatures. However, when the Cu content exceeds 50% by weight in the binder phase, Cu becomes MC, MN, M(CN).
The hardness of the sintered body decreases because it exists in the sintered body in a pure metal state without solid solution in the binder phase or reaction with excess M and Al to form intermetallic compounds. becomes worse. On the other hand, the Cu content is 1%
If it is less than that, the above-mentioned effects such as boride suppression will not be enhanced. In addition, in the present invention, MCx, MNx, M
(CN) When the value of x of x exceeds 0.95, the surplus M
The reaction between M and Al and Cu is suppressed, and the toughness of the binder phase decreases.If M is less than 0.5, excess M remains in the binder phase, reducing the hardness. Next, let's consider the effect of containing W or W compounds. An indentation was made on the sintered body of the present invention using a Vickers hardness tester, and the state of crack propagation from the indentation portion was observed. For comparison, a sintered body having the composition of the sintered body of the present invention but not containing W was also investigated in the same manner. It was observed that the length of the crack in the sintered body of the present invention was about 1/2 of the length of the crack in the sintered body that did not contain W, and that the propagation of the crack was inhibited in the presence of W. In the sintered body of the present invention, it is presumed that the toughness is improved because cracks are difficult to propagate. Furthermore, a portion of W is dissolved in the carbides, nitrides, and carbonitrides of Ti, Zr, and Hf, which are the binders of CBN, improving the strength and wear resistance of the binder phase, and improving the toughness of the sintered body. It is thought that the wear resistance was improved. Ti, Zr, in the binder phase in the sintered body of the present invention,
The content of Hf carbide, nitride, carbonitride, a mixture thereof, or a mutual solid solution compound is preferably 30 to 91% by weight. Content is 30% by weight
If it is less than that, the strength and hardness of the binder phase will decrease, and both wear resistance and toughness will decrease. On the other hand, this content is 91
If it exceeds % by weight, the above-mentioned Al compound, W
Since the content of W, W compounds, and Cu compounds decreases, a sintered body with the target performance cannot be obtained. The content of W, WC, and WB ₂ in the sintered body of the present invention must be 3% by weight or more in the binder phase.
If the content of such W or W compounds is less than 3% by weight, the effect will not appear. Furthermore, if the content of W or W compounds exceeds 30% by weight, Ti, Zr,
The performance of Hf carbides, nitrides, and carbonitrides cannot be demonstrated. Furthermore, another factor that improves the performance of the sintered body of the present invention is that the Al or Al
It is possible that a compound is used. for example
If there is a phenomenon of dissolution of hard particles into the binder phase and re-precipitation 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, Al is included in the binder phase.
and intermetallic compounds of Ti, Zr, Hf, AlN, AlB ₂ ,
It was discovered that a phenomenon similar to this occurs when one or more of Al ₂ O ₃ , Ti ₃ AlN, and Zr ₂ AlN is present. MCx as a bonding material,
When Al or 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 phase. Also
If the content of Al exceeds 50% by weight in the binder phase, the strength of the binder phase 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 continuous phase. In particular, this sintered body is suitable for interrupted cutting of highly hard 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 powder 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. In the case of Al, the most preferred method is to use the binders MCx, MNx, M
Excess M of (CN)x is reacted with metal Al in advance to form an intermetallic compound of M-Al,
This method uses pulverization. In this case, extremely fine binder powder of 1 μm or less, which is made of an intermetallic compound of binder MCx, MNx, M(CN)x, and Al, can be easily obtained. In addition, an easily pulverized powder of an M-Al intermetallic compound synthesized by reacting the metal M and the metal Al in advance may be used. Another form of Al
It may also be added in the form of a nitrogen-containing compound such as AlN, Ti ₃ AlN, Zr ₂ AlN. In the case of Cu, the most preferable method is to infiltrate it by diffusion from the outside of the sintered body during sintering, or to add Ti, Zr,
It is added in the form of an intermetallic compound by reacting with Hf. 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 is
Most of it consists of extremely fine crystal grains of 1μ 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 at less than 70% by volume, with the remainder being
Bonding may be performed using an intermediate layer made of one of carbides, nitrides, and carbonitrides of Ti, Zr, and Hf, or a mixture thereof, or a mutual solid compound. Hereinafter, a more specific explanation will be given with reference to Examples. Example 1 A mixed powder consisting of 60% by volume CBN particles with an average particle size of 3 μm and binder powder was prepared. The binder powders are TiN _0.55 powder, WC powder, and Al in weight%.
A mixture of 60%, 10%, and 30% was heated in a vacuum furnace at 1000℃ for 30 minutes and then ground to an average particle size of 0.3μ.
It is made into a fine powder. 0.3 g of this mixed powder of CBN and binder was placed in a Mo container with an outer diameter of 14 mm and an inner diameter of 10 mm, after placing a cemented carbide of WC-6% Co composition (outer diameter of 10 mm, height of 2 mm). thickness on it
Cemented carbide with 3μ Cu vapor deposited (outer diameter 10mm, height 2
mm), a Mo stopper 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, and then the temperature was heated to 1250 degrees and held for 20 minutes. The removed sintered body was ground using a diamond grindstone until a highly hard sintered body appeared, and further polished using diamond paste. As a result of examining the elements contained in this sintered body using an X-ray microanalyzer, it was found that W, Al,
Cu and Ti were uniformly contained, and the Cu content was approximately 5% by weight in the binder phase. this
Cu was vapor-deposited on the cemented carbide and penetrated into it. Furthermore, as a result of investigating the products of this sintered body by X-ray diffraction, it was found that mainly CBN, TiN,
Although AlN etc. were detected, only a small amount of TiB ₂ etc. was detected. In addition, with the above composition
A sintered body containing no Cu was produced in the same manner, and the product was investigated by X-ray diffraction.
In addition to TiN and AlN, a large amount of TiB ₂ was present.
Cutting chips were made using these two types of sintered bodies. The work material used was SKD11 die steel (HRc60) with V-grooves at four locations in the circumferential direction. Cutting conditions are speed 100m/min, depth of cut 0.2mm,
Cutting was carried out at a feed rate of 0.35 mm until the cutting edge was damaged. While the sintered body of the present invention could be cut for 25 minutes,
The sintered body containing no Cu took 10 minutes. Also,
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. As a result, the machinable time was 2 minutes. Example 2 A binder powder shown in Table 1 was prepared. These compositions were obtained by subjecting binder powder to heat treatment and pulverization in the same manner as in Example 1.

[Table] A mixed powder having the composition shown in Table 2 was prepared by mixing this binder powder and CBN powder having an average particle size of 5 μm.

【table】

[Table] WC-10% was added to a Mo container in the same manner as in Example 1.
After placing a cemented carbide with a Co composition and filling it with finished powder, a Mo plug is placed and an ultra-high pressure and high temperature device is used.
50 kb, held at 1280°C for 20 minutes. The hardness measurement results for each are shown in Table 2. A~ which is a sintered body of the present invention
When the fracture surfaces of K were observed using a scanning electron microscope, it was found that CBN had undergone intragranular fracture in all of these sintered bodies. Next, these sintered bodies are cut, brazed onto one corner of a cemented carbide indexable chip, and then processed to create a cutting chip.In order to evaluate the cutting performance, first a single-flute cutout is made using a face milling machine. Intermittent cutting was performed with . The workpiece material is heat treated and has an outer diameter of 100mm.
It is HRc62 SKD11 die steel. The cutting speed is
200m/min, depth of cut 0.5mm, feed rate 0.07
Cut 3 times with mm/blade, then 3 times with 0.12mm/blade,
After that, the conditions were gradually increased to 0.19 mm/blade three times, and the state of defects in the sintered body was examined. For comparison, commercially available CBN contains approximately 90% by volume,
A sintered chip bonded with Co-based metal was also created and tested. The results are shown in Table 2. These cutting chips were also used to cut SNCM grade 9 steel (HRc54) after heat treatment. Cutting conditions are speed 120m/min, depth of cut 0.2mm, feed 0.5mm/min.
It is rev. Cutting was carried out until the tool flank wear width reached 0.2 mm. The results are also shown in Table 2. Furthermore, as a result of performing X-ray diffraction on the following sintered bodies A to P in Table 2 to examine the products, A contains CBN, (Ti, W)N, and a trace amount of W.
Peaks that appear to be AlN, AlB ₂ , Al ₂ O ₃ , TiB ₂ , WB ₂ , and TiCu; E indicates trace amounts of AlN, AlB ₂ , and CBN and ZrN;
Peaks thought to be ZrB ₂ , WB ₂ , and ZrTi; F is CBN, (Hf, W)N, W, and trace amounts of
Peaks thought to be AlN, AlB ₂ , WB ₂ , HfCu, G is CBN, Ti(C,N) and a trace amount of AlN,
Peaks thought to be AlB ₂ , WB ₂ , TiB ₂ , TiCu, H is CBN, (Ti, W) N, (Zr, W) N, and in addition to W, trace amounts of AlN, AlB ₂ , AlB ₂ , Al ₂ O ₃ , WB ₂ ,
Peaks thought to be TiB ₂ , TiCu, and ZrCu, I is CBN, and in addition to TiN, trace amounts of AlN, AlB ₂ ,
Example 3 In which peaks thought to be WB ₂ , W, TiB ₂ , and TiCu were observed, respectively. Binding material used in Example 2 using wurtzite-type boron nitride powder synthesized by the shock wave method with a particle size of 1 μ or less Powder (he) and wurtzite type boron nitride powder 75
% by volume, and the binder powder was mixed at a ratio of 25% by volume.
This powder was filled into a Mo container with the same configuration 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 Bitkers scale. Example 4 The binder powder shown in Table 3 was prepared. Binder powders having these compositions were heat-treated and pulverized in the same manner as in Example 1.

[Table] A mixed powder having the composition shown in Table 4 was prepared by mixing this binder powder and CBN powder having an average particle size of 8 μm.
A Mo container is coated with a mixed powder containing 30% CBN and the remainder being TiN and Al at a ratio of 5:1 by weight.
After placing a cemented carbide with a WC10%Co composition and filling it with finished powder, a Mo plug was placed on it, and an ultra-high pressure device was used to
50 kb, held at 1200°C for 20 minutes. The hardness of each is shown in Table 4. We also created cutting chips using these sintered bodies and used them to cut chilled cast iron. Cutting conditions are cutting speed 70m/min, depth of cut 0.5mm, feed 0.15mm/min.
rev, for 30 minutes. For comparison, commercially available
A sintered body with a CBN content of 90% by volume and Co as a binder was also tested. Table 4 shows the flank wear width of these tools.

【table】

【table】 [Brief explanation of drawings]

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 High-pressure phase type boron nitride powder with an average particle size of 10μ or less in a volume of 30% or more and 80% or less, and the remainder as a binder of Ti, Zr, and Hf, most of which have a particle size of 1μ or less. MCx for carbides, nitrides, and carbonitrides, respectively.
When expressed as MNx, M(CN)x, the value of x is
30-91% by weight of compound powder of 0.5 or more and 0.95 or less in the binder, 3-30% by weight of W and/or WC powder, and an intermetallic compound of Al or Al and Ti, Zr, or Hf. Or one or more powders of AlN, Ti ₃ AlN, Zr ₂ AlN and one or more powders of Cu or intermetallic compounds of Cu and Ti, Zr, Hf, each with 5 to 50% by weight of Al and 5 to 50% of Cu by weight. Mix 1 to 50% by weight, mold this into a powder or press mold, and then use an ultra-high pressure device to press at a pressure of 20kb or more and 70kb or less and a temperature of 900℃ or more and 1500℃.
A method for manufacturing a high-hardness sintered body for tools, which comprises sintering at temperatures below ℃. 2 High-pressure phase type boron nitride powder with an average particle size of 10 μ or less by volume of 30% or more and 80% or less, and the remaining binder as a binder consisting of Ti, Zr, Hf carbides, nitrides, and carbons with a particle size of 1 μ or less. Nitride as MCx, respectively
When expressed as MNx, M(CN)x, the value of x is
30-91% by weight of compound powder of 0.5 or more and 0.95 or less in the binder, 3-30% by weight of W and/or WC powder, and an intermetallic compound of Al or Al and Ti, Zr, or Hf. Or, mix one or more powders of AlN, Ti ₃ AlN, and Zr ₂ AlN at 5 to 50% by weight of Al, mold this into a powder form or press mold, and then use an ultra-high pressure device to apply a pressure of 20 kb or more to 70 kb or less. Temperature 900℃ or higher 1500℃
A method for manufacturing a high-hardness sintered body for tools, which comprises sintering the body as follows and infiltrating Cu from the outside of the sintered body by 1 to 50% by weight of Cu in the binder. 3. The method for producing a high-hardness sintered body for tools according to claim 1, wherein the high-pressure phase boron nitride is cubic boron nitride. 4. The method for producing a high-hardness sintered body for tools according to claim 2, wherein the high-pressure phase boron nitride is cubic boron nitride.