JPH07172923A - Production of hard sintered material having high tenacity for tool - Google Patents

Abstract

PURPOSE:To produce a sintered material excellent in tenacity, chipping resistance, strength, hardness, abrasion resistance and workability and useful as a material for e.g. a tool to cut hard steel, cast ion, a heat resistant alloy, an iron-reinforced building material, etc., at a low pressure at low cost. CONSTITUTION:A powdery raw material containing (A) 30-70vol.% of cubic baron nitride, (B) 20-50vol.% of powdery aluminum oxide and (C) 10-30vol.% of at least one kind selected from carbides and nitrides of transition metals of the groups 4a, 5a and 6a of the Periodic Table is sintered at 1100-1250 deg.C at a pressure of 5-20kb.

Description

Detailed Description of the Invention

[0001]

The present invention relates to a method for producing a sintered body which has excellent toughness, strength and wear resistance and is suitable as a cutting tool material such as high hardness steel, cast iron, heat resistant alloys and building materials with reinforcing bars. Regarding

[0002]

BACKGROUND OF THE INVENTION Cubic boron nitride (hereinafter referred to as cBN) is a material having the second highest hardness after diamond, has excellent thermal conductivity, and at the same time, is an iron-based metal at high temperatures. Since the reactivity of is extremely smaller than that of diamond,
Recently, it has been particularly noted as a cutting tool material such as high hardness steel, cast iron, and heat resistant alloy.

However, since the conventional cBN sintered body is usually sintered under an ultrahigh pressure of 50 kb or more, a cutting tool using this is several tens of thousands as compared with ceramics, cermet and cemented carbide tools. There was a problem that it would be more than double the price. In addition, this tool has a problem that chipping wear or breakage of the cutting edge sometimes occurs because an impact force acts on the cutting edge of the tool during cutting of high hardness steel, cast iron, heat-resistant alloy, etc., particularly intermittent cutting.

[0004] Yoshida et al.
When this is sintered, even if the pressure and temperature conditions are such that cBN is not stable (metastable), at a low temperature of 1200 ° C. or lower, the phase transition rate of cBN is remarkably suppressed, so that the bonding It has been reported that it is possible to densify the cBN-containing inorganic composite sintered body to some extent by applying a pressure effective only for promoting densification of the phase-forming inorganic material (29th). Abstracts of the 1st High-Volume Debate Conference (1
1988), JP-A-2-302371).

However, this pressure is 2000 MPa.
Even under the condition that the sintering is performed at a temperature not exceeding 1500 ° C., the sintering conditions are different depending on the raw materials, so that it is not always possible to obtain a high hardness sintered body. Moreover, the hardness was not yet sufficient. Therefore, a sintered body having excellent characteristics such as toughness, fracture resistance, strength, wear resistance, and workability, which can be economically obtained, and which is suitable as a cutting tool material has been desired.

[0006]

Under these circumstances, the inventors of the present invention have conducted extensive studies and as a result, have found that cBN and aluminum oxide powder, carbides or nitrides of transition metals of Groups 4a, 5a and 6a of the Periodic Table. 1100 of the combined raw material powder
By sintering at a temperature of ˜1250 ° C. and a size of 5 to 20 kb, which is significantly lower than that of a conventional cBN sintered body, a high toughness hard sintered body for a tool having excellent characteristics, which solves the above problems, is obtained. Therefore, the present invention has been completed.

That is, the present invention provides the following (A)-
(C): (A) Cubic boron nitride powder 30 to 70% by volume, (B) Aluminum oxide powder 20 to 50% by volume, (C) Carbides and nitriding of transition metals of Groups 4a, 5a and 6a of the periodic table. A high toughness hard sintered body for tools, characterized in that a raw material powder containing one or more kinds selected from the group of 10 to 30% by volume is sintered at a temperature of 1100 to 1250 ° C. and a pressure of 5 to 20 kb. The present invention provides a method for manufacturing the same.

The (A) cBN powder used in the present invention is not particularly limited, but its average particle size is 100 μm.
The following are preferred. If the average particle size exceeds 100 μm, the cutting edge strength tends to decrease. cB
Since the N powder has a remarkable hardness second only to diamond, it is useful for improving the hardness and wear resistance of the sintered body and for strengthening the sintered body by dispersing it in the binder phase.

The cBN powder is mixed in the raw material powder in an amount of 30 to 70% by volume, preferably 45 to 65% by volume. If it is less than 30% by volume, a sintered body having sufficient hardness and wear resistance derived from the properties peculiar to cBN cannot be obtained, and if it exceeds 70% by volume, the above binder phase forming a continuous network is densified. It is difficult to obtain a dense and high-hardness sintered body.

This cBN powder is the same substance as one of the components (B) and (C) described below, which forms a binder phase, that is,
Aluminum oxide powder and Periodic Table Nos. 4a, 5a, 6
The surface is preferably coated with one or more components selected from carbides and nitrides of Group a transition metals. By coating in this way, cBN
Improves the wettability of the substance that forms the binder phase with the powder, eliminates the parts where the cBN that is difficult to plastically deform directly contacts, and the voids between the cBN particles due to the plastic deformation of the substance that easily forms the binder phase and that is easily plastically modified. To densify it to enable a sintered body with excellent mechanical properties. The pressure applied during sintering also has the function of promoting this densification.

The coating method is not particularly limited, and for example, PVD method, CVD method and the like can be applied. The coating amount is preferably 0.5 to 15% by volume, and particularly preferably 5 to 10% by volume, based on the cBN powder. If it is less than 0.5% by volume, a sufficient coating effect cannot be obtained, and if it exceeds 15% by volume, a free substance which is not coated on the cBN powder is produced, which is not preferable.

The aluminum oxide powder (B) is mixed in the raw material powder in an amount of 20 to 50% by volume, preferably 25 to 40% by volume. If it is less than 20% by volume, the mixing ratio of (A) or (C), which is a hardly sinterable component, becomes large, and cBN such as 1100 to 1250 ° C., which is the sintering temperature of the present invention.
It does not undergo densification at low temperatures, which has a very slow phase transition rate, and does not take advantage of the unique features of aluminum oxide such as oxidation resistance and chemical stability. On the other hand, when it exceeds 50% by volume, the blending ratio of the component (A) or (C) in the raw material powder becomes small, so that the wear resistance and the high temperature characteristics deteriorate,
A good sintered body cannot be obtained.

(C) Periodic Table Nos. 4a and 5 used in the present invention
Examples of the carbides and nitrides of the a and 6a group transition metals include TiC, ZrC, WC, TaC, VC, MoC and Ti.
N, ZrN, TaN, etc. are mentioned. These may be used alone or in combination of two or more, and further, solid solution powders thereof may be used. These components (C) are mixed in the raw material powder in an amount of 10 to 30% by volume, preferably 15 to 25% by volume. When the content is less than 10% by volume, when used as a cutting tool, the high temperature characteristics (hardness, strength, thermal conductivity, thermal expansion coefficient) characteristic of these compounds and the easy workability due to the electrical conductivity are utilized. Not 3
If it exceeds 0% by volume, the proportion of these refractory metal compounds having high sinterability in the binder phase increases, which hinders the densification of the binder phase, which is not preferable.

Further, in the present invention, metallic aluminum powder can be mixed in the raw material powder. This metallic aluminum acts as a sintering aid, promotes densification by viscous flow at the time of sintering, and AlN is generated during sintering, and has a function of firmly bonding the sintered body in the process. However, it is possible to obtain a sintered body that is more excellent in density and toughness. When metallic aluminum powder is used, it is preferable to add 0.1 to 10% by volume, especially 1 to 5% by volume to the raw material powder. If the content exceeds 10% by volume, metallic aluminum remains and the hardness of the sintered body decreases, which is not preferable.

Further, the raw material powder may further contain silicon carbide whiskers. The silicon carbide whiskers used here may be either α-type or β-type, and are preferably those having a purity of 98% or more, a length of 100 μm or less, and an aspect ratio of about 10 to 30. By using such a silicon carbide whisker, a tougher sintered body can be obtained. When silicon carbide whiskers are used, it is preferable to add 1 to 20% by volume, especially 5 to 15% by volume to the raw material powder. If the content exceeds 20% by volume, the proportion of the refractory silicon carbide whiskers with high melting point which occupy the binder phase increases and the densification of the binder phase is hindered.

In the present invention, first, the above (A)-
A raw material powder is prepared by mixing components including (C). This raw material powder is used as it is or after treatment such as embossing molding, using a high temperature and high pressure generator such as a piston cylinder type high temperature and high pressure generator, 1100 to 1250 ° C., 5 to 20 kb.
Sintering in the metastable region of thermodynamically cBN.

If the sintering temperature is less than 1100 ° C., the sintered body will not be densified, and if it exceeds 1250 ° C., a significant cB will occur.
A phase transition of N occurs, a large amount of mechanically weak hexagonal boron nitride (hBN) is generated, and the hardness and wear resistance inherent to cBN are impaired. It is particularly preferable to sinter at 1150 to 1200 ° C.

When the sintering pressure is less than 5 kb, it is 1100.
In the temperature range of ~ 1250 ° C, the effect of the pressure that contributes to the densification of the binder phase does not sufficiently act, so that a high hardness and high density sintered body cannot be obtained, and it is surprising that the sintering pressure exceeds 20 kb. In addition, the toughness and strength of the sintered body decrease. 20 kb
Although the reason why the toughness and strength of the sintered body obtained at a sintering pressure exceeding 10 is deteriorated has not been completely clarified, it is presumed that the reason is as follows. That is, when the sintering pressure is high, the cBN and the binder phase particles constituting the sintered body are plastically deformed, and at the same time, a considerable amount of strain and intragranular fracture are introduced. Due to this strain and the existence of intragranular fracture,
It is considered that the resistance to the elongation of cracks, which determines the toughness of the sintered body, was remarkably lowered, and the toughness and strength were lowered.
Therefore, it is necessary to set the sintering pressure to 5 to 20 kb, and it is particularly preferable to sinter at 5 to 15 kb.

Further, at the time of sintering, the raw material powders may be laminated and arranged on the cemented carbide raw material substrate, and these may be simultaneously sintered and joined. As a cemented carbide raw material for the substrate, W
C-Co and the like, which are excellent in toughness, rigidity, and thermal conductivity, and are suitable for use as a cutting tool,
It is also excellent in brazability with tool base materials. In the present invention, since the sintering temperature is as low as 1100 to 1250 ° C., the liquid phase found in the ordinary cemented carbide sintering process is
Although it does not appear in the cemented carbide substrate, it is sufficiently solid-phase sintered because it is sintered under high pressure. Further, since the liquid phase does not appear during sintering, the hard layer is altered because the liquid phase such as Co does not enter the raw material for forming the cBN-containing hard layer laminated on the cemented carbide. Also, there is no decrease in wear resistance due to the remarkable promotion of the phase transition of cBN due to the penetration of liquid phase such as Co. The thickness of the sintered body forming the hard layer may be appropriately determined in consideration of use, economy and tool strength, and is preferably 0.5 to 10 mm, more preferably 0.5 to 2 mm.

In the sintered body obtained according to the present invention, the components (B) and (C) form a binder phase, and this binder phase is cB.
The N particles are continuously distributed to form a strong network, and the state thereof significantly affects the toughness of the sintered body. Then, according to the present invention, a sintered body having excellent toughness, fracture resistance, strength, hardness, wear resistance and workability can be obtained.

[0021]

EXAMPLES Next, the present invention will be further described with reference to examples, but the present invention is not limited to these examples.

Example 1 Raw materials having the compositions shown in Tables 1 to 6 were mixed to prepare raw material powders, which were fired at the pressures and temperatures shown in Tables 1 to 6.
The cBN powder used as a raw material had an average particle size of about 3 μm, but other particle sizes did not show much particle size dependence, and the physical properties were almost the same. As the various compounds used for the binder phase and the aluminum raw material powder, commercially available products having an average particle diameter of several μm or less are used, and the silicon carbide whiskers have a length of about 10 μm.
A film having a micrometer and an aspect ratio of about 20 was used. Also,
The coating of the cBN powder was performed by the CVD method.
When the surface condition of the coated particles was observed with an electron microscope, it was confirmed that all the particles were uniformly coated.

The relative density, Vickers hardness, fracture toughness value (K _1c ) and bending strength of the obtained sintered body were measured. The results are shown in Tables 1 to 6. (Measurement method) Relative density: Measured according to JIS C 2141 (Testing method for ceramic materials for electrical insulation). Vickers hardness: JIS C with an indenter load of 500 g
2141 (Vickers hardness test method). Fracture toughness value (K _1c ): Performed based on the IF method of JIS R 1607 (Fracture toughness test method for fine ceramics), and the sample was sufficiently polished. Bending strength: 1mm x 1.3mm x 12mm by cutting the sintered body
A square test piece of (± 0.1 mm) was prepared. The produced test piece was measured for three-point bending strength according to JIS R 1601 (bending strength test method for fine ceramics). The span between the fulcrums was 10 mm.

[0024]

[Table 1]

[0025]

[Table 2]

[0026]

[Table 3]

[0027]

[Table 4]

[0028]

[Table 5]

[0029]

[Table 6]

As is clear from the results of Tables 1 to 6, the sintered body obtained according to the present invention showed high relative density, Vickers hardness, fracture toughness and bending strength.

Example 2 Sample Nos. Shown in Tables 1 to 6 9, 14, 21, 23, 2
5, 29, 35 and 39 and the raw materials having the compositions shown in Comparative Examples 4 and 11 were mixed to obtain a preform having a diameter of 20 mm and a thickness of 2 mm. This molded body and a diameter of 20 produced in advance
A WC-Co cemented carbide preform having a thickness of 2 mm and a thickness of 2 mm was placed in a piston cylinder type ultrahigh pressure apparatus. A graphite heater was used as the heating element, and roxite and hexagonal boron nitride were used as the solid pressure medium. The sintering conditions are shown in Tables 1 to 6
As shown in Fig. 1 at a pressure of 10 kb and a temperature of 1150 ° C.
Hold for 0 minutes to sinter. The recovered sintered body is cBN
The hard layer containing C and the cemented carbide portion were firmly integrated.

This cBN / cemented carbide simultaneous sintered body was cut by electric discharge machining and bladed to produce TNGN16030.
The shape of the cutting tool was 4 (ISO mm nominal). In addition,
For comparison, commercially available cBN sintered bodies (Comparative Examples 19 and 20) were prepared. As the work material, SK4 (HRC61) is used, and in order to evaluate the intermittent cutting performance, as shown in FIG.
Four cylinders with an outer diameter of 50 mm and a length of 250 mm are arranged at equal intervals on the circumference.
Two grooves were formed. The cutting conditions are as follows. Cutting speed: 120 m / min Depth of cut: 0.5 mm Feed: 0.1 mm / revolution Using a general-purpose lathe and cutting under the above cutting conditions, the life is reached when the flank wear width reaches 0.3 mm, until then. Table 7 shows the tool life as time.

[0033]

[Table 7]

As is clear from the results shown in Table 7, the chips using the sintered body obtained according to the present invention had a long tool life. Further, in the case of the tip using the sintered body obtained by the present invention, the wear state of the tool flank was steady wear, whereas in the case of the tip using the comparative sintered body, the flank face When the wear width was about 0.1 mm, the cutting edge of the tool was chipped.

Example 3 The same sintered body as in Example 2 was processed in the same manner to produce chips. For comparison, in addition to the same tip as in Example 2, commercially available K10 type cemented carbide and diamond sintered body tools were prepared. As the work material, an outer diameter of 50 mm, as shown in Fig. 2,
SS made by forming four grooves at regular intervals on the circumference of a cylindrical cement mortar with a length of 200 mm and processing them
The material (iron plate) was fixed with an adhesive. The cutting conditions are as follows. Cutting speed: 50 m / min Depth of cut: 0.5 mm Feed: 0.1 mm / revolution Using a general-purpose lathe, cutting under the above cutting conditions, the life is reached when the flank wear width becomes 0.3 mm, until then Table 8 shows the tool life as time.

[0036]

[Table 8]

The chips using the sintered body obtained according to the present invention had a longer tool life than those using the comparative sintered body. Further, in the case of the chip using the sintered body of the present invention, the wear state of the tool flank was steady wear, whereas the chips using the comparative sintered body (Comparative Examples 4, 11, 19, 20) In this case, the tool edge was chipped when the wear width of the flank was 0.1 mm or less. In the case of a commercially available diamond sintered body tool, no breakage of the tool edge was observed,
As compared with the sintered material chip of the present invention, the wear rate was faster, and when the cutting edge was observed in detail, a reaction between diamond and iron in the work material was recognized. Further, in the case of the commercially available K10 type cemented carbide, the wear rate was remarkably high, and the cutting edge was broken within 30 seconds.

[0038]

INDUSTRIAL APPLICABILITY According to the present invention, it is excellent in toughness, fracture resistance, strength, hardness, wear resistance and workability, and is useful as a cutting tool material such as high hardness steel, cast iron, heat resistant alloys and building materials with reinforcing bars. An excellent sintered body can be economically obtained under a low pressure.

[Brief description of drawings]

FIG. 1 is a view showing a hardened steel round bar for performing interrupted cutting.

FIG. 2 is a drawing showing a work material in which an iron plate is embedded in a round bar of cement mortar.

[Explanation of symbols]

 1 SK4 (HRC; 60) 2 Cement mortar 3 SS material

Claims (5)

[Claims] 1. The following (A) to (C): (A) Cubic boron nitride powder 30 to 70% by volume, (B) Aluminum oxide powder 20 to 50% by volume, (C) Periodic table 4a, A raw material powder containing 10 to 30% by volume of one or more selected from carbides and nitrides of 5a and 6a group transition metals is sintered at a temperature of 1100 to 1250 ° C. and a pressure of 5 to 20 kb. A method for producing a high toughness hard sintered body for a tool, which is characterized. 2. The method for producing a high toughness hard sintered body for a tool according to claim 1, wherein the raw material powder further contains 0.1 to 10% by volume of aluminum metal powder. 3. The method for producing a high toughness hard sintered body for a tool according to claim 1, wherein the raw material powder further contains 1 to 20% by volume of silicon carbide whiskers. 4. The cubic boron nitride powder (A) is coated with aluminum oxide and one or more selected from carbides and nitrides of transition metals of Groups 4a, 5a and 6a of the Periodic Table. Item 5. A method for producing a high toughness hard sintered body for a tool according to any one of Items 1 to 3. 5. The method for producing a high toughness hard sintered body for a tool according to claim 1, wherein the raw material powder is laminated and arranged on a cemented carbide raw material substrate and sintered.