JPS6270268A - Sintered body for high hardness tool - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Cubic boron nitride (Cubtc Boron N1tr)
IDE (hereinafter referred to as CBN) is expected to be used as a tool material in the future due to its properties such as high hardness and excellent thermal conductivity. Currently, a sintered body made of CBN crystals bonded with a metal mainly composed of Co is being used in one city for cutting purposes.

When this sintered body of CBN bonded with metal is used as a cutting tool, there are disadvantages such as a decrease in wear resistance due to the softening of the bonded metal phase at high temperatures, and damage to the tool because the work material metal is easily welded. There is.

In addition, most of the binder Co reacts with CBN, making it brittle.

It has changed into a boride and does not have the characteristics of tough CO.

The present invention relates to a new CBN sintered body suitable for tool applications such as cutting tools, which uses a hard metal compound as a binder phase with high strength and excellent heat resistance, rather than a sintered body bonded with such metals. be. Together, the present inventors have invented a sintered body for tools that can maximize the excellent characteristics of CBN, and have already applied for a patent. This application claims that carbides, nitrides, borides, silicides of transition metals in Groups 4a, 5a, and 6a of the periodic table, or mutual solid solution compounds of these, form a continuous phase and bind CBN crystals. The present invention provides a sintered body for a hard tool that is rich in heat resistance and abrasion resistance, maintains high thermal conductivity even at high temperatures, and has particularly excellent thermal shock properties.

The present inventors conducted cutting tests in various fields using the sintered body of the above application. As a result, we recognized the revolutionary tool properties and at the same time recognized the essential characteristics of CBN tools. This application is filed based on one of these recognitions. In the case of the above application, Altos and the like are excellent in terms of heat resistance and strength, as stated in the specification of the application, but were excluded because their thermal conductivity drops significantly at high temperatures. Those excluded for the same reason are AJ N, SiC, 5jsNn+BtC
It is. All of these materials are used as tool materials for cutting and grinding materials, or are attracting attention.

The reason why these compounds were excluded in the aforementioned application is that the heat resistance of CBN was noted and the application was mainly focused on applications where the cutting edge of the tool is exposed to high temperatures.

As mentioned earlier, after testing in various locations, we discovered that CBN is an extremely excellent material due to its excellent welding resistance, even in the low-speed cutting field where high-speed steel is currently used. . The cutting temperature in this case is 500-600℃
This is the range in which M2O, etc. has a sufficiently high thermal conductivity. Moreover, it can be said that other properties as a tool material, such as strength and hardness, are prioritized over thermal conductivity.

In particular, IJ zOx , 512N , , /V N with Cl5
When used as a binder for N, these are more stable than carbides-5 nitrides, borides, and silicides of group 4a, 5a, and 6a metals of the periodic table in terms of reactivity with workpiece metals. Depending on the type of work material to be machined and the machining conditions, it may have better wear resistance.

In addition, even when the cutting edge becomes hot, strength and thermal conductivity are more important than thermal conductivity.
It is not uncommon for the property of hardness to take precedence, and the present invention is of course applicable to such cases as well.

・This application supplements the above-mentioned application based on the above-mentioned purpose. The method for manufacturing a composite sintered body of the heat-resistant compound and CBN selected in this way is to first mix CBN powder and one or more of these heat-resistant compound powders using a means such as a ball mill. This is then molded into powder form or molded into a predetermined shape at room temperature, and then subjected to high pressure using an ultra-high pressure device.
Sinter under high temperature. The ultra-high pressure equipment used is a girdle type, belt type, etc. equipment used for diamond synthesis.

A graphite cylinder is used as the heating element, and talc, NaCj
A pressure medium such as pyrophyllite is placed around the graphite heating element.The sintering pressure and temperature conditions are as shown in Figure 1. Although it is desirable to carry out the process within the stability region of type boron nitride, this equilibrium line is not necessarily known accurately and is only a guideline.

Further, conditions can be changed depending on the type of heat-resistant compound to be combined with CBN. In FIG. 1, (^) indicates the stability region of cubic boron nitride, and (B) indicates the stability region of largely cubic boron nitride.

A very remarkable feature of the sintered body according to the present invention, which makes the present invention useful, is that the heat-resistant compound
i) Forming a continuous phase on the fiber. That is, in the sintered body of the present invention, the tough heat-resistant compound is as if it were WC.
Like the metallic Co phase which is the binder phase in -Co cemented carbide, it penetrates into the gaps between the high hardness CBN particles and forms a continuous binder phase, thereby imparting toughness to the sintered body. It is something that was given. As a result of experiments, it has become clear that in order to obtain a sintered body having such a structure, the content of CBN must be 80% or less by volume.

The lower limit of the amount of CBN phase in the sintered body according to the present invention is 30 by volume.
up to %. If it is less than this, the performance as a tool that takes advantage of the characteristics of CBN will not be exhibited. FIG. 2 shows the structure of a sintered body according to the present invention in which the volume is 60% CBN and the remainder is AIN.

Point in the middle of the figure (in the gaps between visible CBN particles, there is a white phase U)
N penetrates into the material to form a completely dense sintered body, and the MN phase continues to serve as a bonding phase for CBN particles. The reason for this structure is considered to be that MN, which is relatively easily deformed compared to CBN at high temperatures, invades between CBN particles during sintering.

When considered as a tool material, particularly in a cutting tool, the crystal grain size of the sintered body is preferably several microns or less. Fine powder of several microns or less than a micron contains a considerably large amount of oxygen. Generally, most of this oxygen exists on the powder surface in the form of a compound similar to hydroxide. This hydroxide-like compound decomposes when heated and comes out as a gas. When the material to be sintered is not sealed, it is not difficult to vent this gas out of the system. However, when sintering is performed under ultra-high pressure as in the present invention, it is almost impossible for the generated gas to escape outside the heating system. In general, it is common knowledge in the powder metallurgy industry to perform degassing treatment in advance in such cases, but this is a problem if the degassing temperature cannot be made high enough. This is exactly the case. That is, when considering the transformation of CBN into a low pressure phase, there is an upper limit to the heating temperature.

The degassing process of fine powder involves the following stages depending on the temperature. First, at low temperatures, physically adsorbed substances and hygroscopic moisture are removed, and then chemically adsorbed substances and hydroxides are decomposed. At the end, oxide remains. In case of CBN 1
Since it is stable up to about 000°C, it can be preheated to at least this temperature value. Therefore, it can be assumed that if the gas is heated and degassed in advance, the residual gas components will remain in the form of oxides.Conversely, since we do not want the gas components to remain in the sintered body as much as possible, we will remove all the water and hydrogen. Preferably, the removal is carried out as a preliminary treatment.

In the present invention, based on this idea, all degassing treatments at temperatures of 100° C. or higher are performed in vacuum.

In the sintered body according to the present invention, the heat-resistant compound described above is used as the CBN (71 bond), but if necessary, a metal phase other than the heat-resistant compound such as "i+Co+Fe" may be included as a third phase. It may be.

However, the main component of the binder phase is a heat-resistant compound phase,
The volume ratio of these metal phases in the sintered body must be equal to or less than that of the heat-resistant compound phase. Above that, the heat resistance of the sintered body
Wear resistance decreases and the performance as a tool is lost. Furthermore, the sintered body according to the present invention can be used in the synthesis of CBN, and can be used at high temperatures and
Elements believed to be soluble in hexagonal boron nitride and CBN under high pressure, such as alkali metals such as Li, primary alkaline earth metals, I'b, Sn, Sb, /
It may also contain V, Cd, Si, etc. as additives.

CBS used as a raw material for the sintered body of the present invention is synthesized under ultra-high pressure using hexagonal boron nitride as a raw material. Therefore, there is a possibility that most cubic boron nitride remains as an impurity in the CBN powder. In addition, even when sintering under ultra-high pressure, the CBN particles do not receive external pressure hydrostatically until the binder penetrates between the individual CBN particles, and the heating during this time causes the macrogonal boron nitride to form. There is also the possibility of reverse metamorphosis. - In such a case, it is believed that if an element that has a catalytic effect on the hexagonal boron nitride is added to the mixed powder, it will have the effect of preventing this reverse transformation. Based on this idea, experiments were conducted to confirm the effects particularly on AN and Si.

When a sintered body is polished and its structure is observed, it is found that the CBS particles are less likely to peel off on the polished surface in the sintered body containing JV and Si than in the sintered body, and the bond strength between the CBN particles and the binder phase is stronger. it is conceivable that. Furthermore, when comparing the performance as a cutting tool, the one containing Aj and Si was superior in both wear resistance and toughness. Note that such an effect appears when the sintered body contains M or Si in a weight percent of 0.1% or more.

The sintered body according to the present invention has high hardness and toughness, and has heat resistance and
It has excellent wear resistance and is suitable not only for cutting tools but also for tools such as wire drawing dies, peeling dies, and drill bits.

Examples will be described below.

Example 1 CBN powder with an average particle size of 7 μm and UN powder with an average particle size of 1 μm were blended at a volume ratio of 60% and 40%, respectively, and thoroughly mixed in a mortar. 2% camphor was added to this mixed powder, and it was molded to have an outer diameter of 10IIIAl and a height of 1.5+mm.

This was inserted into a stainless steel container. The container was heated in a vacuum furnace at 10 mm at a vacuum of 1100 mm Hg.
Degassed by heating to <RTIgt;C</RTI> for 20 minutes. This was charged into a girdle type ultra-high pressure device. Pyrophyllite was used as the pressure medium, and a graphite cylinder was used as the heater.

Note that Naα was filled between the graphite heater and the sample.

First, the pressure was raised to 55 Kb, and then the temperature was raised to 1400°C, held for 30 minutes, and then the temperature was lowered and the pressure was gradually lowered. The obtained sintered body had an outer diameter of about 10 mm and a thickness of about ll1lI. This was ground to a flat surface using a diamond grindstone, and further polished using diamond paste. When the polished surface was observed using an optical microscope, it exhibited the structure shown in FIG. That is, the hardness was measured using a micro Vickers hardness meter. The average value of hardness is 2800
Met. The sintered body was cut using a diamond cutting blade to create a cutting chip, which was brazed to a steel support. For comparison, a commercially available CBN sintered body made by bonding CBN with an average particle size of 3μ with metal Co and a JIS [Ko
Cutting tools of the same shape were made of cemented carbide.

Heat-treated SNCM grade 9 steel was used as the work material. The hardness of the work material is HRC54.

Cutting conditions are cutting speed 50m/win, depth of cut 0.1m
m.

The feed was set to 0.02+*@/rev. When a cutting test was conducted under these conditions, the alloy according to the present invention showed 1.
Although cutting was possible for 80 minutes, the cut surface deteriorated after 20 minutes with the CBN sintered tool bonded with metal Co. That is, the tool life of the present invention is nine times longer. Also, with cemented carbide tools, it was not possible to obtain a good work surface from the beginning.

Example 2 CBN powder and heat-resistant compound powder were mixed in the composition shown in Table 1. The CBS powder used had an average particle size of 4 microns, and was classified into micron powders with a particle size range of 3 to 6 microns, which is commercially available for ramping processing. As a result of analysis, approximately 6% by volume of diamond powder was mixed in this CBN.

A molded body of mixed powder was created in the same manner as in Example 1, and M.

After pretreatment in the same manner as in Example 1,
Sintering was performed using an ultra-high pressure device under the conditions shown in Table 1. The heating and holding time was 20 minutes in each case.

In both cases, dense sintered bodies were obtained.

Table 1 Cutting chips were prepared from this sintered body, and the cutting performance was evaluated under the same conditions as in the cutting test of Example 1. The machining time until the condition of the workpiece surface deteriorates is A and B.

C, D, E, F, G in order 40.20.180.200
．． The temperature was 120°40 for 20 minutes. That is, M, 0. The sintered body using CBN as a binder had good performance, and the sintered body with a volume percent of CBN of 60% had the highest performance. When the volume % of CBN becomes 70%, the performance is rather degraded.

Example 3 Using CBN powder with an average particle size of 7 μm, it was
A mixed powder having the percentage balance shown in Table 2 was prepared.

A mixed powder stamped body placed in an MO container in the same manner as in Example 1 was sintered under the conditions shown in Table 2. When the sintered bodies were polished with diamond paste and their textures were observed, they all showed a dense structure.

Example 4 2% M powder with an average particle size of 30 μm by weight was added to M2O powder with an average particle size of 1 μm, and CBN powder with an average particle size of 4 μm was blended at 65% and 35% by volume, respectively, as in Example 1. A sintered body having an outer diameter of 10 mm and a thickness of IRIll was prepared. However, the pressure during sintering was 50°C and the temperature was 1300°C.

A cutting tool was prepared in the same manner as in Example 1, and commercially available Al,
0. The cutting performance was compared with that of black ceramic made of 30% T1Cu. 550C was used as the work material, and the cutting speed was 40.
Cutting was carried out for 30 minutes at 0 m/min, depth of cut 2 mm, and % feed of 0.36 m5+/rotation. The flank wear width of black ceramic is 0.
301, whereas that of the present invention was CBN 65%.
0.21 mm for CB N 35%, 0.1 for CB N 35%
It was 9mm.

In addition, in the commercially available Co-bonded CBN sintered body, the cutting edge fell off after 2 minutes of cutting.

Example 5 CBIIJFA powder with an average particle size of 3μ and Ti with an average particle size of 1μ
c.

M N l) powder and Aj, 03 powder with an average particle size of 0.3μ were blended into the composition shown in Table 3.

Hereinafter, in the same manner as in Example 1, the outer diameter is ioam and the thickness is 1.51.
It was pressed and molded into a separately prepared disk made of WC-10%Co alloy with an outer diameter of 10 mm and a thickness of 3III11.
This was placed in a stainless steel container.

After heating and degassing in a vacuum furnace, the pressure is 50K using an ultra-high pressure device.
b. Sintered by holding at 14 degrees and 1200 degrees Celsius for 20 minutes. When the side surface of the sintered body was polished and observed, it was found that the layer containing CBN and having a thickness of about 1 square inch was firmly fixed to the cemented carbide disk by the connected binder phase. When the hardness of the sintered body containing CBN was measured using a Pinkers hardness tester under a load of 10 kg, it showed a value similar to that of the third barley. When the sintered body was brazed to a steel shank and a cutting performance test similar to that in Example 4 was conducted, it was found that during flank wear of the tool, L, L,
0.25.0.15.0.13.0 for Al, N, O noodles
．． 20. It was 0.16 mm.

Comparative Example: 40 uI-vol.% Wurtz type boron nitride (WBN), cubic boron nitride (CBN), balance Al, 0. Two types of sintered bodies were manufactured by the method described in the above example in combination with
The hardness and tool properties were compared.

FIG. 3 shows a microstructure photograph taken with an optical microscope at a magnification of 1500 times. The black areas in Figure 0 are aggregates of WBN crystals, which are also finely dispersed in the gray Al and Off phases.

In this way, the structure is completely different from that of a sintered body based on CBS.

〔hardness〕

Hv (10Kg) Knoop Hard (5Kg) CBN+
JV,○,:2380 2180wBN10Al,o,
: 1800 Unmeasurable [wear resistance] Carburized steel with a hardness (HRC) of 63 was used as the work material, and the speed was Lo.
om/min, depth of cut 0.2N, feed 0.1 tm
The wear width V when dry cutting is performed under the conditions of /rev is 2α minutes for CBN sintered body: 0.15++ m, W
The BN sintered bodies were 0.2 and 2.

C toughness] A round material with Ua made of the same material used in the above wear resistance test was used as the work material, and dry cutting was performed at a speed of 100 m/1 inch, depth of cut: 0.3 mm, feed rate of 0.41 mm/rev. However, while the CBN sintered body chipped in 32 seconds, the WBN sintered body of the comparative example chipped in 19 seconds.

[Brief explanation of drawings]

FIG. 1 relates to the manufacturing conditions of the sintered body of the present invention, and shows the stable existence region on the pressure and temperature phase diagram of cubic boron nitride. Figure 2 shows the structural characteristics of the sintered body of the present invention, and is a photograph of the sintered body detailed in Example 1 (magnification: 1
500 times). Black (The visible particles are cubic boron nitride crystal grains that form a continuous binder phase. 1,500 times magnification). Agent Patent attorney Senior representative's speech fL1゛f, "deprived. -I+, !φ = J Figure 1 Hen M cC) Procedural amendment form) % type % Commissioner of the Office Black 1 ) Akira Yudono -, Ha1, Indication of the case 1986 Patent Application No. 63386, Title of invention: Sintered body for high-hardness tools, Relationship with the person making the amendment Case Patent application Person Place
5-15 Kitahama, Higashi-ku, Osaka Name (213)
Tetsube Yojo, President of Sumitomo Electric Industries, Ltd.

Claims (3)

[Claims] (1) Contains cubic boron nitride in an amount of 80 to 30% by volume, with the remainder mainly consisting of Al_2O_3, AlN, Si_3N_4, a mixture thereof, or a mutual compound thereof, and the remainder is a sintered body. A sintered body for use in high-hardness tools that is characterized by a continuous binder phase in its structure. (2) Sintering for a high hardness tool according to claim (1), characterized in that the continuous binder phase in the sintered body contains a metal phase such as Ni, Fe, Co, etc. in addition to the above compound. Concretion. (3) The sintered body contains an alkali metal, an alkaline earth metal, or Pb, Sn, Sb, Al, Cd, or Si in addition to the above-mentioned compounds. Sintered body for hardness tools.