JPH0377151B2 - - Google Patents

Description

[Detailed description of the invention]

(a) Technical field The present invention relates to the performance of a high-hardness sintered body containing cubic boron nitride as a main component used for cutting tools, etc., and in particular to improving the welding resistance, toughness, and wear resistance. (b) Technical background Cubic boron nitride (hereinafter abbreviated as CBN) is a substance with the highest hardness next to diamond, and also has excellent thermal conductivity and low reactivity with iron group metals at high temperatures. It is a substance that is synthesized under ultra-high pressure and high temperature. Various attempts have been made to sinter only this CBN; for example, as described in Japanese Patent Publication No. 39-8948,
As mentioned above, it is necessary to sinter at ultra-high pressure and high temperature of 1900℃ or higher. Although current ultra-high pressure and high temperature equipment can generate such high pressure and high temperature conditions, when the equipment is scaled up on an industrial scale, the number of service life of the high pressure and high temperature generating section is limited, making it impractical. In addition, some sintered bodies made of CBN particles bonded with metal are commercially available for cutting purposes, but when used as cutting tools, the bonding metal phase softens at high temperatures, resulting in a decrease in wear resistance and The disadvantage is damage to the tool due to welding of the material. (C) Disclosure of the Invention The present inventors have conducted repeated research in order to develop a material that has not only excellent welding resistance but also excellent toughness and wear resistance. As a result, 20 to 85 volume% of CBN particles with a size of 2 to 100 μm
Contains 20 to 90% by volume of ultrafine CBN particles with the remainder of the binder having an average particle size of 1 μm or less, Periodic Table 4a, 5a,
It has been discovered that a sintered body consisting of 5-50% by volume of carbides, carbonitrides, nitrides or solid solutions or mixtures of crystals of group 6a transition metals and 5-30% by volume of Al achieves this goal. First, the reason why the sintered body of the present invention has excellent toughness is considered as follows. The transverse rupture strength of a CBN sintered body decreases as the grain size increases, as shown in FIG. Fine-grained CBN sintered bodies have high transverse rupture strength and excellent toughness, so the cutting edge is less prone to breakage, but the bonding strength of individual particles is weak, so in the case of abrasive wear, individual particles may break during cutting. It is thought that the wear resistance is poor because it easily falls off. On the other hand, coarse grain
Although the CBN sintered body has excellent wear resistance because the bonding force between individual CBN particles is strong, once a crack occurs, it is likely to propagate and cause the cutting edge to break. The sintered body of the present invention has CBN particles of 2 μm or more and 100 μm or less held in an ultrafine CBN sintered body of 1 μm or less. It has the high toughness of a fine-grained CBN sintered body. Furthermore, the sintered body of the present invention uses ultrafine CBN particles as a binder, and carbides and nitrides of groups 4a, 5a, and 6a of the periodic table.
Since it contains carbonitrides, it has excellent wear resistance and welding resistance. Next, if the addition of Al causes the phenomenon of dissolution of hard particles into the binder phase and re-precipitation, as in liquid phase sintering of WC-Co cemented carbide, the binder phase and the hard particles will be separated. Alternatively, a product with high bonding strength between hard particles can be obtained, but it is thought that a phenomenon similar to this occurs in the sintered body of the present invention due to the presence of Al in the binder. Furthermore, these Al compounds have high hardness.
No decrease in strength occurs because AlB ₂ and AlN are generated. The coarse CBN particles used in the sintered body of the present invention are 2 μm
The above is good. When the thickness is less than 2 μm, problems occur in wear resistance. Moreover, when the thickness exceeds 100 μm, the toughness decreases. The content of CBN with a size of 2 μm or more and 100 μm or less is by volume.
20-85% is preferred. In particular, if wear resistance is required, it is sufficient to increase the content of CBN particles with a size of 2 μm or more and 100 μm or less, but this content is determined by the volume of the sintered body.
If it exceeds 85%, the cutting edge may break during cutting. Further, although the content can be reduced, if the content is less than 20% by volume, wear resistance becomes a problem. The particle size of the ultrafine CBN particles in the binder is 1 μm or less, preferably
0.5μm or less is good. The particle size of fine CBN particles is 1μm
If it exceeds this, the toughness will decrease. The content of fine CBN particles in the binder is by volume,
20-90% is preferred. The content of fine CBN particles is
If it is less than 20%, the wear resistance of the binder phase will decrease,
The binder phase wears out prematurely, and coarse CBN particles larger than 2 μm fall off. On the other hand, when the content of fine CBN particles exceeds 90%,
The bonding material becomes brittle, or the periodic table 4a,
As the content of carbides, nitrides, and carbonitrides of groups 5a and 6a decreases, CBN grains of 1 μm or less grow and the toughness decreases. Carbides and nitrides of groups 4a, 5a, and 6a of the periodic table,
The content of carbonitride is preferably 5% to 50% by volume;
If it exceeds %, the above effect will not be produced because the amount of fine CBN will decrease. Below 5%, periodic table 4a, 5a,
Group 6a carbides, nitrides, and carbonitrides are not effective and performance deteriorates. In addition, the Al content is preferably 5% to 30% by volume.
If it exceeds 30%, the strength of the binder phase weakens and cutting performance deteriorates. If it is less than 5%, the effect of Al will not be produced. When manufacturing sintered bodies, CBN with a thickness of 1 μm or less is prepared in advance.
The particles and one or more of carbides, nitrides, carbonitrides, solid solutions or mixture powders of transition metals of groups 4a, 5a, and 6a of the periodic table, and Al powder are uniformly mixed using a means such as a ball mill. mix,
Subsequently, it is mixed with CBN particles of 2 μm to 100 μm. This Al may be infiltrated during sintering without being mixed in advance. The mixed powder is placed in an ultra-high pressure device and sintered under conditions where the high-pressure phase type boron nitride is stable. When using such an excellent sintered body as a cutting tool, the high hardness sintered body is only needed in the part that will become the cutting edge.
Its performance can be fully demonstrated by bonding it to cemented carbide, which has excellent thermal conductivity. 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 must 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. In addition, we conducted a similar study on wurtzite boron nitride, which is another form of high-pressure phase boron nitride.
Similar results were obtained using CBN. Examples will be described below. Example 1 CBN powder with a particle size of 0.5μ, TiC and Al powder were pulverized and mixed in a volume ratio of 6:3:1 using a pot and ball made of WC-Co hard alloy. This mixed powder and CBN powder having an average particle size of 10 μm were mixed at a volume ratio of 4:6. This finished powder has an inner diameter of 10 mm and an outer diameter of 14 mm.
It was filled into a container made of Mo. Next, this container was placed in an ultra-high pressure device, and a pressure of 50 kb was first applied, followed by heating to 1300°C and holding for 20 minutes. When we took out the Mo container, removed the Mo, and observed the structure of the sintered body, we found that CBN with an average particle size of 10 μm was uniformly dispersed, and a binder containing ultrafine CBN particles was present around it. was. Next, a chip for a cutting tool was made using this sintered body, and a cutting test was conducted. For comparison, a similar chip was made from a sintered body of commercially available CBN particles bonded with metal, and a cutting test was conducted. The workpiece material is SKD11 with an outer diameter of 100 mm and four grooves around the circumference.
Using die steel (HRC=62), cutting speed 100m/
min, depth of cut 0.3 mm, feed rate 0.3 mm/rev, dry test, the product of the present invention could be cut for 22 minutes before the cutting edge broke, whereas the commercially available product could cut after 10 minutes. The cutting edge was missing. Example 2 A binder powder shown in Table 1 was prepared. Ultra fine particles
The CBN used had an average particle size of 0.5 μm.

[Table] Table 2 shows this binder and CBN particles with an average particle size of 4 μm.
A finished powder was prepared by mixing in the proportions shown below.

[Table] These finished powders were sintered in the same manner as in Example 2. However, No. 1 and No. 3 are not the sintered bodies of the present invention. Next, cutting chips were prepared from these sintered bodies in the same manner as in Example 1, and a cutting test was conducted. The work material and conditions are the same as in Example 1. Table 2 shows the machining time until breakage. Also, with an outer diameter of 100 mm
Cutting speed of SKD11 die steel (HRC=62) 100m/
Min, depth of cut 0.2 mm, feed 0.1 mm/rev, dry cutting, and flank wear width was measured after 20 minutes of cutting time. The results are shown in Table 2. Example 3 Wurtzite type boron nitride powder with an average particle size of 1 μm or less was used as ultrafine CBN, mixed to the same composition as No. C of Example 2, and sintered in the same manner as Example 1. When a cutting chip was prepared and a cutting test was conducted, it was possible to cut for 20 minutes before the cutting edge broke. Example 4 Coarse-grained CBN with average particle sizes of 50 μm and 80 μm were mixed to the same composition as No. C of Example 2, and after sintering in the same manner as in Example 1, cutting chips were prepared. When a cutting test was conducted, cutting was possible for 18 minutes and 15 minutes, respectively, before the cutting edge broke.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between rupture force and grain size of a CBN sintered body.

Claims (1)

[Claims] 1. Contains 20 to 85% by volume of high-pressure phase type boron nitride particles of 2 to 100 μm, and the remaining binder has an average particle size of 1 μm.
The following ultrafine high-pressure phase boron nitride particles 20-90% by volume
and carbides, nitrides, carbonitrides, or solid solutions or mixtures thereof of transition metals of Groups 4a, 5a, and 6a of the periodic table with a diameter of 1 μm or less, and 5 to 50% by volume of Al5.
High hardness sintered body for tools consisting of ~30% by volume. 2 The binder is 20-90% by volume of ultrafine high-pressure phase boron nitride particles with an average particle size of 1 μm or less, periodic table 4a, 5a,
5-50% by volume of carbides of group 6a transition metals and Al5-
The high hardness sintered body for tools according to claim 1, which comprises 30% by volume. 3 The binder is 20 to 90 volume % of ultrafine high-pressure phase boron nitride particles with an average particle size of 1 μm or less, 5 to 50 volume % of Ti carbides, nitrides, and carbonitrides, and 5 to 30 volume % of Al.
A high-hardness sintered body for a tool according to claim 1 or 2, comprising: 4 Claims 1 to 3, characterized in that the high-pressure phase boron nitride is cubic boron nitride.
A high-hardness sintered body for tools according to any of the items listed below. 5 High-pressure phase type boron nitride powder of 2 to 100 μm, ultrafine high-pressure phase type boron nitride powder of 1 μm or less, carbides, nitrides, carbonitrides of transition metals of groups 4a, 5a, and 6a of the periodic table of 1 μm or less, or these A mixed powder of Al powder and at least one solid solution or mixed crystal powder of Ultra-fine high-pressure phase type boron nitride particles containing 20-85% by volume of high-pressure phase type boron nitride particles, the remainder being 1 μm or less, 20-90% by volume,
5-50% by volume of carbides, nitrides, carbonitrides, or solid solutions or mixtures of transition metals of Groups 4a, 5a, and 6a of the periodic table of 1 μm or less, and Al5-
A method for manufacturing a high-hardness sintered body for tools made of a binder composed of 30% by volume. 6 Use a high-pressure phase type boron nitride powder of 2 to 100 μm, an ultrafine high-pressure phase type boron nitride powder of 1 μm or less, a carbide of a transition metal of group 4a, 5a, or 6a of the periodic table of 1 μm or less, and a mixed powder of Al. A method for producing a high-hardness sintered body for tools according to claim 5, characterized in that: 7 Ti carbide, nitride,
7. The method for manufacturing a high-hardness sintered body for tools according to claim 5 or 6, characterized in that carbonitride is used. 8. The method for producing a high-hardness sintered body for tools according to any one of claims 5 to 7, wherein the high-pressure phase boron nitride is cubic boron nitride.