JPS6330983B2 - - Google Patents

Description

[Detailed description of the invention]

This invention utilizes cubic boron nitride (Cubic Boron Nitride).
This is an ultra-high pressure sintered material with a high content of Nitride (hereinafter abbreviated as CBN) of over 70% by volume (hereinafter % indicates volume%), and the excellent properties originally brought about by CBN, that is, diamond. This is an ultra-high pressure sintered material that has the second highest hardness, excellent chemical stability, high thermal conductivity, and has high toughness and strength.
Excellent when used as a cutting tool for intermittent cutting of die steel and high-speed steel, which are particularly subject to severe thermal shock, high-speed cutting of ordinary cast iron and chilled cast iron, etc. at a cutting speed exceeding 500 m/min, and cutting such as milling. This article concerns a CBN-based ultra-high pressure sintered material that exhibits excellent performance. Previously, the same applicant filed a patent application No. 56-100980 (Japanese Unexamined Patent Publication No. 58-3903) in which titanium carbide (hereinafter referred to as TiC) was used as a binder phase forming component.
) and titanium carbonitride (hereinafter referred to as TiCN): 1 to 20%; CoAl, NiAl,
CBN-based ultra-high pressure sintering for cutting tools with a composition consisting of 1 to 20% intermetallic compound consisting of one or more of (Co, Ni) Al and 75 to 97% CBN and unavoidable impurities. I applied for a binding material. It is true that the CBN-based ultra-high pressure sintered material of this prior invention exhibits excellent performance when used as a cutting tool for milling die steel and high-speed steel, as well as cutting various difficult-to-cut materials. On the other hand, sufficient toughness is required for interrupted cutting when the workpiece material is, for example, high-hardness steel with grooves, or for cutting under conditions where severe thermal shock is repeatedly applied as the cutting speed increases. and showed no abrasion resistance. Therefore, the present inventors have determined that the above-mentioned prior invention
As a result of conducting research to obtain a CBN-based ultra-high pressure sintered material that has superior toughness and wear resistance compared to CBN-based ultra-high pressure sintered materials, we found that (a) CBN 70 In the case of CBN-based ultra-high-pressure sintered materials containing % or more, the content of binder phase-forming components that have plastic deformability is relatively small, so when manufacturing them, sufficient mechanical mixing is performed in the mixing process. Even if the binder phase-forming components are mixed uniformly, it is not possible to sufficiently cover each CBN particle with the binder phase-forming component, so the CBN-CBN particles may locally bridge together during ultra-high pressure sintering. The local effective pressure in this area is reduced, resulting in CBN
This is due to the fact that a part of the CBN is converted back into hexagonal boron nitride, which is a low-pressure phase, and that the components forming the bonded phase cannot pass through the physical gaps created between CBN and CBN particle bridges. The main causes of this are the generation of micropores and a decrease in grain boundary strength, which makes it difficult to provide sufficient saturation. (b) However, as a raw material powder, average particle size: 10 μm
The following CBN granules, ultrafine TiC powder of 0.2μm or less, TiCN powder of 1μm or less, and all of them 0.3μm or more, smaller in particle size than CBN powder, and with a melting point of 1400℃ or higher. Using intermetallic compound powder, these raw material powders are blended into a predetermined composition, mixed, and press-molded to form a green compact.The green compact is then heated at ¹²⁰⁰ m 5 to 60 to a specified temperature within the range of ~1400℃
When pre-sintering is carried out under conditions of holding for a minute, in the presence of the intermetallic compound, a reaction occurs between the surface of the CBN particles and the TiC powder that has been sufficiently activated by ultrafine particle formation, and the CBN particles and the binder phase Titanium diboride (hereinafter referred to as
TiB (shown as ₂ ) is now formed, and this
By forming the TiB ₂ intermediate layer, the frequency of bridging caused by CBN-CBN particles is suppressed as much as possible, and at the same time, the bond between the CBN particles and the binder phase becomes even stronger. When subjected to ultra-high-pressure sintering, the CBN-based ultra-high-pressure sintered material has significantly superior toughness and strength. The findings shown in (a) and (b) above were obtained. This invention was made based on the above knowledge, and uses CBN with an average particle size of 10 μm or less as a raw material powder.
Powder, ultra-fine TiC powder of 0.2 μm or less, TiCN powder of 1 μm or less, and all with an average particle size of 0.3 μm.
CoAl powder, NiAl powder, and (Co, Ni)Al powder as intermetallic compounds, which are finer than the CBN powder, are prepared, and these raw material powders are blended into a predetermined composition and heated under normal conditions. Mix with
After press-forming to make a green compact, this green compact is
Preliminary sintering is carried out in a vacuum of 10 ^-2 torr or more at a predetermined temperature within the range of 1200 to 1400°C for 5 to 60 minutes,
Then, by sintering this pre-sintered body under ultra-high pressure under normal conditions, TiC: 1 to 20% as a binder phase forming component, CoAl, NiAl,
and (Co, Ni)Al, an intermetallic compound consisting of one or more of two or more types: 1 to 10%, and if necessary, TiCN: 1 to 10% as a bonding phase forming component, The remainder consists of CBN as a dispersed phase forming component, TiB ₂ as an intermediate layer forming component, and unavoidable impurities (CBN: 70 to 95% content), and an intermediate layer of CBN and a binder phase. When the ratio of TiB ₂ to CBN _as When the number of contacts between CBN particles on a straight line is expressed as _Nc , and the number of contacts of CBN with the bonded phase on the same line is expressed as Nb, CBN contacts that satisfy 2Nc/Nb+2Nc=0.05 to 0.2 This is a high-strength CBN-based ultra-high-pressure sintered material for cutting tools with excellent toughness. Furthermore, in detail about the manufacturing method of the CBN-based ultra-high pressure sintered material of the present invention, the particle size of the ultra-fine TiC as the raw material powder reacts with the CBN particles during preliminary sintering to form TiB ₂ . This is an important factor that influences the amount of TiB 2 formed, and in order to ensure a sufficiently satisfactory amount of TiB ₂ formed, the average particle size must be 0.2 μm or less, preferably 0.05 to 0.1 μm. In other words, when the average particle size of TiC exceeds 0.2 μm, the reaction with the surface of CBN particles becomes insufficient, and CBN-
TiB ₂ as an intermediate layer that suppresses contact between CBN particles and strengthens the bond between CBN particles and the binder phase.
This is because the formation of is insufficient. In addition, by using ultrafine TiC powder as the raw material powder,
It is possible to coat the surfaces of individual CBN particles through normal mechanical mixing, and this also reduces the frequency of contact between CBN particles, so it is possible to reduce the frequency of contact between CBN particles during ultra-high pressure sintering. The generation of micropores is prevented, and the presence of the film-like TiC has the secondary effect of reducing the local effective pressure drop.
In connection with this, the average particle diameters of other raw material powders were set to 10μm or less for CBN powder and 1μm for TiCN.
The particle size of the intermetallic compound powder needs to be 0.3 μm or less, and if any particle size exceeds the above-mentioned particle size, it will not be possible to secure the desired high strength and high toughness. In other words, the average particle size of TiC powder, which is an essential component, is:
Since it is an ultrafine powder of 0.2 μm or less, if the particle size of TiCN powder or intermetallic compound powder, which are other binder phase forming components, becomes coarser than the above upper limit, the TiC powder activated during powder mixing will , it aggregates by itself, making it impossible to obtain a sintered material with a uniform structure. In addition, the intermetallic compound powder plays the role of an auxiliary agent that causes the surface part of the CBN particles to react.
In order to improve the coverage of the particles, it is necessary to make the particle size at least smaller than that of the CBN powder. However, when the intermetallic compound powder is pulverized to an average particle size of less than 0.3 μm by mechanical pulverization, the constituent components of the pulverization container become mixed into the pulverized powder, resulting in contamination of the sintered material. This is undesirable because it makes it worse. Furthermore, in the method for producing the CBN-based ultra-high pressure sintered material of the present invention, Co powder, Ni
CoAl powder and Al powder are mixed in appropriate amounts and subjected to preliminary sintering and ultra-high pressure sintering to produce CoAl,
It is not desirable to use NiAl or (Co, Ni)Al, and only CoAl, NiAl, and (Co, Ni) with a melting point of 1400°C or higher should be used as raw material powder.
It is necessary to use an intermetallic compound powder consisting of one or more types of Al. The first reason is that when mixed in the form of metal powder in the form of individual elements, Al, which has a low melting point and is highly reactive, melts quickly during preliminary sintering at a temperature of 1200 to 1400°C. , the liquid phase reaction immediately occurs with the CBN particles to form AlN and AlB ₂ , and the ultrafine TiC powder cannot participate in the reaction with the CBN particles, and the resulting AlN has a hardness. is the microvits hardness ( _M H _V )
The hardness of AlB 2 is low at around 1200, and the hardness of AlB ₂ is _M H _V :
Although it has a high hardness of about 2400, it is extremely brittle and has poor heat resistance, making it impossible to obtain ultra-high pressure sintered materials with high hardness and high toughness. In particular, since AlN is a stable compound with high vapor pressure, it acts as a sinterability inhibiting factor in the ultra-high pressure sintering process in the subsequent process.
The formation of these compounds is undesirable. The second reason is that Co-Al and Ni-Al2
As seen in the original alloy phase diagram, for example, an intermetallic compound with a weight ratio of Co/Al = 68/32: CoAl is 1645
℃, also the intermetallic compound of Ni/Al÷68/32:
NiAl has a high melting point of 1636°C, so it does not easily soften even when used under high-temperature conditions where the cutting tool edge temperature exceeds 1000°C. Moreover, ultra-high pressure sintered materials have excellent high-temperature wear resistance and welding resistance. Furthermore, the third reason is that when compounded in the form of metal powder in the form of individual elements, the average particle size: 0.2μ
It is impossible to sufficiently uniformly mix ultrafine TiC powder having a particle size of less than When mixed in the form of an intermediate compound, it not only becomes easier to grind, but also
The purpose is to enable uniform mixing and contribute to improved sinterability. From the above results, when producing the ultra-high pressure sintered material of the present invention, it is essential to use intermetallic compound powder as the raw material powder. In addition, when producing the CBN-based ultra-high pressure sintered material of the present invention, it is possible to mix and use TiB ₂ as a raw material powder from the beginning without forming it by preliminary sintering, but if TiB ₂ powder is blended, (a) TiB ₂ powder is uniformly dispersed together with ultrafine TiC particles, reducing the binding effect of the binder phase on CBN particles. (b) It is extremely difficult to obtain ultra-fine TiB ₂ powder, so relatively coarse-grained TiB ₂ powder is used, but since TiB ₂ powder itself is extremely hard, pulverization is difficult. Due to the difficulty, it was not possible to produce a dense sintered material, and in order to obtain a mixed powder with even finer grain size,
If pulverization is carried out for a long time, the sintered material becomes contaminated with the components constituting the pulverization container due to the hardness of the TiB ₂ powder, resulting in embrittlement. It is undesirable to mix TiB ₂ powder as a raw material powder because problems such as
Through the reaction with the powder, TiB ₂ is formed as an intermediate layer between the CBN particles and the binder phase, suppressing contact between CBN and CBN particles, and improving the bonding strength between the CBN particles and the binder phase. It is necessary to Next, regarding the CBN-based ultra-high pressure sintered material of the present invention, the reason why the preliminary sintering conditions and component composition are limited as described above will be explained. A Preliminary sintering conditions A part of CBN particles is decomposed to generate B and N, and ultrafine TiC particles are activated, and CBN
In order to efficiently form TiB ₂ , which constitutes the intermediate layer between the particles and the binder phase, the degree of vacuum in the pre-sintering atmosphere must be at least 10 ^-2 torr, preferably at least 10 ^-4 torr. Therefore, 10 ^-2 torr
TiB ₂ cannot be formed efficiently at low vacuums below 1200°C, and this also applies to the pre-sintering temperature.
Formation of TiB ₂ cannot be expected. On the other hand, the pre-sintering temperature is
When the temperature exceeds 1,400°C, CBN transforms back into a hexagonal system and is no longer able to exhibit the excellent properties of CBN particles. Also, regarding the preliminary sintering time, if the holding time is less than 5 minutes,
If the amount of TiB ₂ formed is not sufficient and on the other hand, it is held for a long time exceeding 60 minutes, the amount of TiB ₂ formed will be too large and the sintered material's toughness, especially fracture resistance, will deteriorate. , its retention time is 5~
It was set as 60 minutes. B Composition (a) CBN CBN forms a dispersed phase, and due to its own high hardness, excellent chemical stability, and high thermal conductivity, the sintered material has these excellent properties. However, if the content is less than 70%, it will not be possible to sufficiently impart the above characteristics to the sintered material, while if the content exceeds 95%, the sinterability will deteriorate significantly,
The content was set at 70-95% because CBN particles tend to fall off and cause a significant deterioration of wear resistance. (b) TiC TiC itself has a high melting point and high hardness, and has the effect of improving the wear resistance and heat resistance of sintered materials.As mentioned above, TiC reacts with CBN particles during pre-sintering. , has the effect of suppressing bridge formation between CBN-CBN particles, which causes toughness deterioration, and forming TiB ₂ , which improves the bonding between CBN particles and the binder phase, but if the content is less than 1%, the above-mentioned On the other hand, if the content exceeds 20%, the hardness of the sintered material will decrease and a tendency to embrittlement will appear, so the content should be reduced to 1%. ~20%. (c) Intermetallic compounds These components include
In addition to promoting the reaction between CBN particles and ultrafine TiC powder, it imparts these properties to sintered materials due to its own high toughness and excellent high-temperature wear resistance and welding resistance. However, if the content is less than 1%, the desired effect cannot be obtained;
If the content exceeds 10%, the hardness of the sintered material will tend to decrease, and the wear resistance will decrease in practical use.
Its content was set at 1 to 10%. (d) TiCN TiCN has the effect of significantly improving the heat resistance of sintered materials, and therefore is included as necessary, especially when used under cutting conditions that involve high-temperature heating. If the amount is less than 1%, the desired effect of improving heat resistance cannot be obtained, while if the content exceeds 10%, the hardness of the sintered material decreases and becomes brittle, as in the case of TiC. Therefore, the content is 1 to 10
%. (e) TiB ₂ TiB ₂ is formed as an intermediate layer between CBN particles and the binder phase during pre-sintering as described above, and is a hexagonal crystal system of CBN resulting from bridge formation between CBN-CBN particles. It has the effect of improving the toughness of the sintered material by suppressing the reverse conversion to CBN and the generation of micropores, and also increasing the bond strength between the CBN particles and the binder phase. but,
The amount of TiB ₂ formed is extremely small,
Since it cannot be measured by quantitative analysis or microscopic observation, the amount formed was measured by X-ray diffraction. That is, in X-ray diffraction, CBN
The peak height appearing on the (111) plane (hereinafter referred to as Xc
) and the peak height (hereinafter referred to as Xt) that appears on the (101) plane of TiB ₂ , and calculate Xt/Xc.
It is expressed as a percentage of Therefore, Xt/
If _the ratio _of Since the defectivity decreases, the content of TiB ₂ is increased by increasing Xt/Xc.
The ratio was set at 0.1 to 0.5. (f) Contact frequency of CBN As mentioned above, unless the contact between CBN particles is suppressed, it is not possible to obtain a sintered material with high toughness and high strength. The contact frequency of CBN particles was limited using the contact frequency of the particles. In other words, as shown in Figure 1, the number of contact points (● marks) between CBN particles on a straight line: Nc, and the number of contact points (● marks) between CBN particles on the same straight line
The number of contact points (○ marks) of the CBN particles with the binder phase: Nb was measured, and the value calculated by the formula: 2Nc/Nb+2Nc was taken as the contact frequency of the CBN particles. Therefore, if this value exceeds 0.2,
There will be too much contact between the CBN particles and it will not be possible to obtain a sintered material with the desired high toughness and strength, while if the value is less than 0.05, excessive pre-sintering will occur and the _TiB2 The amount formed becomes substantially too large, and on the other hand, the CBN particles themselves become thinner and thinner, and as a result, the properties provided by the CBN particles tend to deteriorate.
The CBN contact frequency was set at 0.05 to 0.2. The ultra-high pressure sintering conditions used to produce the CBN-based ultra-high pressure sintered material of this invention are: pressure: 70ton/cm ² , temperature: 1200-1500°C,
Holding time: Normal conditions are 10 to 60 minutes. Next, the sintered material of the present invention will be specifically explained with reference to Examples. Example As raw material powder, CBN particles with an average particle size of 3 μm,
Formed by chemical vapor deposition with a thickness of 0.08μm
TiC powder, 0.8μm TiCN powder, 1μm CoAl
Powder (Co/Al=70/30, weight ratio, same below),
1μm NiAl powder (Ni/Al=70/30), 1μm (Co, Ni)Al powder (Co/Ni/Al=35/35/30)
were prepared, these raw material powders were blended into the composition shown in Table 1, and after mixing in a ball mill,
At a pressure of 2ton/ ^cm2 , diameter 110mmφ x thickness: 1mm
Formed into a disk-shaped green compact with dimensions, then,
A part of this green compact is pre-sintered in a vacuum furnace under the conditions shown in Table 1 to obtain a pre-sintered body, and subsequently this pre-sintered body and a green compact without pre-sintering are was stacked on a tungsten carbide-based cemented carbide sintered alloy (Co: 12% by weight, WC: remainder) chip of the same size and inserted into an ultra-high pressure container, and the pressure:
Sintered materials 1 to 20 of the present invention and comparative sintered materials 1 to 20 were produced by ultra-high pressure sintering under the conditions of 50 ton/cm ² , temperature: 1300° C., and holding time: 15 minutes. In addition, comparative sintered materials 1 to 20

【table】

[Table] All of the samples were manufactured directly from the green compact by high-pressure sintering without pre-sintering. Next, the resulting sintered materials of the present invention 1-
Cutting chips were cut from 20 and comparative sintered materials 1 to 20, brazed to a tungsten carbide-based cemented carbide sintered alloy holder, and polished. Work material: die steel (SKD-11, hardness: H). _R C63), Cutter diameter: 160mm, Chip shape: JIS/SNP432, Cutting speed: 200m/min, Depth of cut: 0.5mm, Feed per tooth: 0.2mm, Cutting width: 100mm, High hardness steel milling under the following conditions. Test, Work material: die steel (SKD-11, hardness: H _R C60), depth of cut: 0.5 mm, feed: 0.1 mm, cutting speed: 60 m/min, dry high-hardness turning test under the following conditions, and Work material: Die steel with two cross-sectional grooves at symmetrical positions in the length direction (SKD-61, hardness: H _R C51)
An interrupted cutting test was conducted on a round bar of high hardness steel under the following conditions: depth of cut: 0.3 mm, feed rate: 0.1 mm/rev., cutting speed: 70 m/min, cutting time: 3 min. Flank wear width is 0.3
In addition, in the above turning test, the cutting time until the flank wear width of the cutting edge reaches 0.2 mm, and in the above intermittent cutting test, the number of breakages among the 6 test cutting edges was measured. did. The results of these measurements are shown in Table 1. Table 1 also shows the measurement results of the Vickers hardness (load: 1Kg), the X-ray height ratio of TiB ₂ /CBN, and the contact frequency of CBN. Binding material 1
-20 have excellent wear resistance during high-speed cutting and interrupted cutting of high-hardness steel, compared to comparative sintered materials 1-20, which are not pre-sintered and therefore do not have _TiB2 formation. and impact resistance (toughness). As mentioned above, the CBN _- based ultra-high pressure sintered material of the present invention has high hardness, high toughness, and
and have high strength, therefore,
This is used not only for milling of high-hardness steels such as die steel and high-speed steel, but also for interrupted cutting of the above-mentioned high-hardness steels, which are subject to severe thermal shock, as well as cutting speeds of 500 m/min for ordinary cast iron and chilled cast iron. When used as a cutting tool for high-speed cutting, etc., it exhibits excellent performance over a long period of time.

[Brief explanation of the drawing]

Figure 1 shows CBN in CBN-based ultra-high pressure sintered materials.
FIG. 2 is an explanatory diagram of contact frequency.

Claims (1)

[Claims] 1. Titanium carbide: 1 to 20 as a binder phase forming component
%, CoAl, NiAl,
An intermetallic compound consisting of one or more of (Co, Ni) Al and (Co, Ni) Al: 1 to 10%, and the rest is cubic boron nitride as a dispersed phase forming component and intermetallic compound as an intermediate layer forming component. Composition consisting of titanium diboride and unavoidable impurities (cubic boron nitride: 70-95%) (volume %)
In addition, when the ratio of titanium diboride to cubic boron nitride as an intermediate layer between cubic boron nitride and the binder phase is measured by X-ray diffraction, the peak height of the (101) plane of titanium diboride is /The peak height of the (111) plane of cubic boron nitride = 0.1 to 0.5, and further, the number of contacts between cubic boron nitride particles on a straight line is expressed as Nc, and the cubic boron nitride on the same straight line The number of contacts of boron with the bonded phase is
A cubic boron nitride-based ultra-high pressure sintered material for cutting tools with excellent toughness, characterized in that it has a contact frequency of cubic boron nitride that satisfies 2Nc/Nb+2Nc=0.05 to 0.2 when expressed as Nb. 2 Titanium carbide as a binder phase forming component: 1 to 20
%, CoAl, NiAl,
1 to 10% of an intermetallic compound consisting of one or more of (Co, Ni) Al, and 1 to 10% of titanium carbonitride as a bonding phase forming component, with the remainder being Composition (capacity %) consisting of cubic boron nitride as a dispersed phase forming component, titanium diboride as an intermediate layer forming component, and inevitable impurities (cubic boron nitride: 70 to 95% content)
In addition, when the ratio of titanium diboride to cubic boron nitride as an intermediate layer between cubic boron nitride and the binder phase is measured by X-ray diffraction, the peak height of the (101) plane of titanium diboride is /The peak height of the (111) plane of cubic boron nitride = 0.1 to 0.5, and further, the number of contacts between cubic boron nitride particles on a straight line is expressed as Nc, and the cubic boron nitride on the same straight line The number of contacts of boron with the bonded phase is
A cubic boron nitride-based ultra-high pressure sintered material for cutting tools with excellent toughness, characterized in that it has a contact frequency of cubic boron nitride that satisfies 2Nc/Nb+2Nc=0.05 to 0.2 when expressed as Nb.