JPH04104934A - Sintered material for machine tool - Google Patents

Abstract

PURPOSE:To obtain the subject sintered material having a high abrasion resistance and excellent in toughness at a low cost by blending a specified crystal grain with a continuous ceramics bond phase. CONSTITUTION:A crystal grain (A) of a carbide, nitride (e.g. TiN), boride, silicide or carbonitride of a transition metal belonging to 4a, 5a or 6a groups of the periodic table is selected from single crystal grains and crystal grains prepared by coprecipitation method. A bonding phase material (B) composed of a low reactive ceramics, etc., having a resistance to grain boundary separation from (A) component is then selected from Al2O3, ZrO2, etc. (A) and (B) components are then blended and the resultant mixture is sintered at 800-2400 deg.C using the hot-pressing method, etc., thus producing the objective sintered material for machine tools having <=0.01% volume ratio occupied by crystal grain boundary and composed of 20-80vol% crystal grain of >=99.99wt.% purity and the remainder consisting of the continuous ceramics bond phase.

Description

[Detailed description of the invention] <Industrial use public funds> The present invention is a sintered material for tools used in cutting and plastic working of high hardness materials such as hardened steel and cemented carbide, or heat resistant alloys. Regarding.

<Conventional technology> When processing high-hardness materials such as hardened steel, nickel-based heat-resistant alloys, and cobalt-based heat-resistant alloys, carbide powder of high-melting point metals such as tungsten is generally processed using iron, cobalt, nickel, and other ferrous metals. Cemented carbide bonded by sintering has been used.

In recent years, in addition to the fact that the above-mentioned cemented carbide is being used not only as a tool but also as a workpiece, in order to meet the strict requirements for machining conditions, sintered carbide, which is made by bonding hard grains with ceramics, has been developed as a higher-performance tool. Products using crystalline diamond, cubic boron nitride (hereinafter referred to as CBN) sintered bodies, etc. have been developed.

Sintered diamond is made by sintering diamond powder at high temperature and pressure using cemented carbide as a binder, but it is fundamentally unsuitable for processing materials such as steel, which has a strong affinity with carbon. In this regard, CBN sintered bodies containing CBN as hard particles, which has a hardness second only to diamond, have little reaction with ferrous metals, so they can be used for all workpieces other than diamonds, especially hardened steel and cemented carbide. In addition to high-hardness materials, it is effective for processing nickel-based heat-resistant alloys, cobalt-based heat-resistant alloys, etc.

Conventional CBN sintered bodies are made by mixing CBN powder with ceramics such as titanium carbide or titanium nitride, which serve as a binder phase, either alone or in combination, and by adding metal components to improve sinterability. High temperature (1300~1800℃), high pressure (30
It is manufactured by sintering at ~80 Kb (kilobars). In addition to the above materials, known binder phase materials include carbides of silicon and zirconium, nitrides of silicon and zirconium, and intermetallic compounds of aluminum and titanium and intermetallic compounds of aluminum and zirconium. There is.

<Problems to be Solved by the Invention> CBN sintered tools have come to be used in place of conventional grindstones (grinding) for precision cutting of hardened steel. The features of CBN sintered tools as cutting tools are high wear resistance and high finished surface accuracy (roughness). It is expressed because it is contained in tools at a rate of .

Although such a CBN sintered tool in which hard CBN grains are dispersed in a ceramic binder phase has excellent features as a cutting tool, it has various problems as described below. It should be noted that diamond sintered tools and CBN sintered tools have similar manufacturing methods, and the problems that arise from this are also similar, so diamond sintered tools also have the following problems. .

First of all, CBN grains are expensive. The particle size of the CBN grains that are usually added is 0.5 to 6 μm, and they are manufactured by ultra-high pressure synthesis similar to the synthesis of diamond. This method uses a pressure of 50-70Kb and a temperature of 1500-1700℃.
The process involves growing crystals using specialized ultra-high pressure synthesis equipment, and the synthesis process takes a long time, making the product CBN grains expensive.

The second problem is that the CBN grains and the ceramic binder phase must be sintered under ultra-high pressure, which is also related to the method for manufacturing the CBN grains described above. That is, C.B.
When N grains are heated under atmospheric pressure, a phase transformation occurs from around 1200℃, changing from cubic to macrogonal (CBN changes to hBN).
This is because the resulting hBN is boron nitride (BN) with a graphite structure and has low hardness and cannot be used as a tool material. On the other hand, in order to integrally sinter the CBN grains and the ceramic binder phase, it is necessary to
This is because it is necessary to heat above 1200° C. where phase transformation of N grains occurs. Therefore, it is necessary to heat and sinter under ultra-high pressure using the ultra-high pressure synthesis equipment described above.

Generally, the conditions for sintering CBN sintered tool material are pressure 40
~60 Kb, and the temperature is 1400 to 1800°C. However, in ultra-high pressure synthesis, the size of the sintered body that can be produced in one operation is small and sintering takes a long time, making the tools expensive and the applied light. The current situation is that these are limited.

In this way, CB, which is a typical example of a hard particle dispersion type sintered tool,
N sintered tools have excellent features as tools, but there are still problems to be solved in order to further expand the field of application in the future. Therefore, it is desired to develop a new hard grain dispersed sintered tool using hard grains instead of CBN grains, which have the same excellent features as CBN sintered tools.

In view of these circumstances, the present invention aims to provide a sintered material for tools that has high wear resistance, excellent toughness, and is inexpensive. The sintered material for tools according to the present invention to be achieved contains 20 to 80 volume % of crystal grains in which the volume ratio occupied by grain boundaries is 0.01% or less and the purity is 99.99% or more, and the remainder is ceramic. It is characterized by consisting of a continuous bonded phase.

The present invention will now be described in comparison with a CBN sintered tool, which is a typical example of a conventional hard grain dispersed sintered tool.

First, the wear condition of a conventional CBN sintered tool will be explained with reference to the drawings. FIG. 5 (b) schematically shows the state of wear on the flank and rake surfaces of a CBN sintered tool when cutting hardened steel. As shown in both figures, during the cutting process, the CBN grains 11 on the tool cutting edge 10 are broken within the grains or fallen off from the binder phase 12, and these broken pieces or fallen CBN grains 11 are connected to the workpiece 13 and the flank surface 10m.
When passing through the boundary with the flank surface 10a, a streak a is left on the flank surface 10a, and it is thought that this streak a determines the flank wear width (v,), that is, the wear resistance. In addition, in the figure, 10b
indicates the rake face. In the process of breakage or falling off of the CBN grains 11, the part of the bonding phase 12 at the cutting edge that has the function of supporting the CBN grains 11, which is in contact with the work material 13, retreats due to wear, and the external force ( When the cutting force, thermal stress, etc.) exceeds the force that breaks or supports the CBN grains 11, the CBN grains 11 break, the CBN grains 11 and the binder phase 12 separate at the grain boundary, or the binder phase 12 breaks. It is thought that due to the cutting damage, 1) CBN grains fall off from the cutting edge portion 10;

From this, in tools where the wear resistance of the hard grains is several times higher than that of the binder phase, only the binder phase wears out selectively, causing the hard grains to protrude from the binder phase, making it difficult to withstand external forces. This is thought to lead to breakage and falling off of the hard grains, and it is thought that breakage and falling off become more likely to occur, causing the flank surface to wear out faster as described above.

In other words, when focusing mainly on the wear resistance of tools, it cannot be said that the higher the wear resistance of the hard grains relative to the binder phase, the better; the properties of hard grains such as tensile strength and toughness are superior. This is very important.

Furthermore, cutting tests using CBN sintered tools have shown that in tools with dispersed hard particles, the CBN particles maintain the surface roughness of the workpiece with high accuracy, and increase the hardness of the tool to improve the cutting edge. It was found that this helps reduce deformation.

In particular, the former is a feature as important as wear resistance.

Therefore, the hard particles should not have significantly higher abrasiveness than the binder phase, and although they do not need to have significantly higher hardness, they will have a higher hardness than the binder phase at the cutting edge temperature (800 to 1000°C). Materials that have hardness, high tensile strength, and toughness are suitable because they do not cause breakage.A hard grain dispersion type tool using such hard grains has high wear resistance and It is thought that highly accurate surface roughness can be obtained.

The hard particles used in the present invention meet these conditions. In addition, since the hard particles must not react with the work material, the standard free energy of formation of both (
ΔGT″cat/ma1) needs to be a positive value.

In the present invention, crystal grains in which the volume ratio occupied by grain boundaries is 0.01% or less and the purity is 99.99% or more refer to single crystal grains or similar polycrystalline grains. Moreover, here, the polycrystalline grains similar to single crystal grains refer to polycrystalline grains manufactured by, for example, a coprecipitation method.

Specific materials for the hard particles include periodic table Nos. 4a and 5J.
Examples include carbides, nitrides, silicides, silicides, carbides, and oxides of group 1 and 6a transition metals, and oxides of aluminum.

In addition, diamond and CBN, which has the second highest hardness,
As mentioned above, it is expensive and requires high pressure (30 to 7
0 Kb) and its hardness is significantly higher than that of other ceramic intermetallic compounds, so it is not included in the hard grains in the present invention.

On the other hand, although ceramics are used as the composite metal phase, considering the above-mentioned wear mechanism, it is considered necessary to have the following four characteristics.

In other words, in order to increase the wear resistance of the binder phase and suppress the receding speed of the binder phase at the cutting edge due to wear, it is necessary to: ■ have high hardness at the cutting edge temperature during cutting; rust.

low reactivity with iron group metals, etc.).

In addition, in order to prevent the hard particles from falling off due to peeling at the grain boundaries between the hard grains and the binder phase, it is necessary to: ■ Mutual diffusion 2 reaction between the hard grains and strong adhesion; In order to be sound as a material, it is required to have good sinterability (densification occurs at low sintering temperatures) and high strength and toughness.

Therefore, it is preferable to use ceramics having these characteristics as the binder phase. Let's consider this in detail below.

FIG. 1 shows the hardness of various binder phases of CBN sintered tools, and generally shows the hardness of the periodicity table 4a.

5m, carbides, silicides, and nitrides of group 6a transition metals have high hardness. In particular, titanium nitride (hereinafter referred to as TiN) is included and has high hardness, and aluminum oxide (hereinafter referred to as alumina or AI!203) is The hardness shows a high value.

Figure 2 shows the cutting edge temperature (800 to 10
Free energy of formation (ΔGT
' ca 1 /mol).

If such free energy of formation is used as an index of reactivity with iron etc., it will be 4a and 5a of the periodic table.

It is assumed that oxides such as carbides, nitrides, some silicides, alumina, and zirconium oxide (hereinafter referred to as ZrO or zirconia) of Group 6a transition metals have low reactivity, and these are difficult to bond with. Can be used as phase material.

Regarding ■, the standard free energy of formation (ΔGT.caj
/moj), and for (2), a healthy binder phase can be obtained by adding an auxiliary agent that promotes sintering to the main component of the binder phase.

In order to manufacture the hard grain dispersed sintered tool according to the present invention from the binder phase material selected in this manner and the hard grains described above, a hot pressing method, an ultra-high pressure sintering method, or the like is applied.

In the case of the hot press method, first, the binder phase material and hard particles are mixed in a ball mill or the like, and the mixture is compacted into a predetermined shape using a powder molding press using a mold. next,
This compression molded body is loaded into a graphite mold of a hot press, and a temperature of 800 to 2400° C. and a pressure of ~IKb are applied in a vacuum or an inert atmosphere, and held for several minutes to several hours to produce a sintered body.

Also, the ultra-high pressure sintering method is a similar method for manufacturing CBN sintered tool materials. In this method, a powder compact obtained in the same manner as the hot press method is wrapped in metal foil such as zirconium, and then wrapped in a powder compact of salt that serves as a pressure medium, and this is assembled into a graphite fitting. , loaded into a belt-type device used for diamond synthesis via a pressure medium such as pyroferrite, and heated to a temperature of 800 to 1800°C.
A pressure of 40 to 60 Kb is applied and maintained for several minutes to several hours to produce a sintered body.

The sintered body of the present invention thus obtained is sintered to a higher density, especially when produced by ultra-high pressure sintering method.
When this is used as a cutting tool, the wear resistance is improved by 5 to 10%.

As mentioned above, the sintered material for tools of the present invention manufactured by the hot press method or the ultra-high pressure sintering method is a sintered body in which hard particles are dispersed and arranged in the binder phase, so that it can be used to harden steel, etc. The aim is to combine high wear resistance and high precision surface roughness in cutting of high hardness materials, so considering its function, the binder phase should form a continuous phase on the sintered body structure. is required. In other words, by making the binder phase a continuous phase, it is possible for the binder phase to grip the hard particles sufficiently firmly and to have high toughness as a sintered body, so that it has the desired performance as a tool. leading to.

In order to make the binder phase a continuous phase in this way, it is necessary to reduce the content of hard particles to 80% by volume. On the other hand, the effect of dispersing hard particles is that the content is 20% by volume.
The content of hard particles needs to be in the range of 20 to 80% by volume, since the hard particles are not exhibited when divided.

Similarly, in order to make the binder phase a continuous phase, it is necessary to coordinate the binder phase material around the hard particles. , it is necessary to satisfy the condition that the surface of the hard particles is contained in the powder of the binder phase material, for example, the particle size of the powder of the binder phase material is made smaller than the particle size of the hard particles. is achieved.

On the other hand, the powder of the binder phase material that is industrially produced has a particle size of 0-2 μm to 1 μm, so based on the above conditions, the particle size of the hard particles should be twice the particle size of the powder of the binder phase material. If so, a particle size larger than 0.4 μm is required. Also, the finished surface roughness of the work material is R6. If it is 3.2 μm or less,
Since the particle size of the hard particles is considered to be 10 μm or less, the range of the particle size of the hard particles is preferably 0.4 μm to 1 μm.
It becomes 0 μm.

In Figure 3, single-crystal alumina grains with a volume of 40% are used as hard grains, and the remainder is titanium nitride (TiN) 50% as a binder phase.
Volume % and alumina (AZ203) are set to 10 volume %, and the structure is shown when this is made into a sintered body using an ultra-high pressure sintering method. As shown in the figure, TiN, which appears as a white phase, coordinates between the gaps between the gray single crystal alumina grains, forming a completely dense sintered body, and the TiN continuously forms the single crystal alumina grains. It is the bonded phase of

Figure 4 (al indicates the result of machining the sintered body shown in Figure 3 into a tool shape and subjecting it to a cutting test. Here, the workpiece material is hardened steel (SUJ2, hardness H, O62 ), cutting conditions are cutting speed 100m/5in1 feed 0.1wa
/rev1 This is a microscopic photograph of the cutting edge after cutting under the same conditions with a depth of cut of 0.1+m.

For comparison, Figures 4(b) and 4(e) show micrographs of the cutting edge of a conventional CBN sintered tool and a tool sintered with only a binder phase composition, which were subjected to cutting tests in the same manner. . Note that the binder phase of the CBN sintered tool is the same as that of the above example ((a
), and the CBN content was 40% by volume.

Looking at these results, (b) shows the edge wear pattern of the Naro CBN sintered tool with a sharp linear cutting edge.
On the other hand, (cl) has a rounded cutting edge, and the central part of the cutting edge undergoes plastic deformation and takes on a new shape.

In contrast, the tool of the present invention (a
1 showed a cutting edge wear pattern very similar to that of a CBN sintered tool, and it was confirmed that single-crystal alumina dispersed in the binder phase as hard grains had the same function as CBN grains.

Example of implementation Hereinafter, the present invention will be explained based on examples.

(Example 1) As hard particles, single crystal Aj 0 grains with an average particle size of 3 μm, T i N powder with an average particle size of 1 μm, and average particle size of 0.2 μm
of Al2O3 powder at 40%, 50%, and 1 by volume, respectively.
The mixture was mixed in a mortar at a ratio of 0%. Add 1% lubricant to this powder, and use a powder molding press to obtain an outer diameter of 4 cm and a thickness of 1.5 cm.
A green compact was obtained.

This was first heated in a vacuum furnace at a vacuum level of 10-Q Torr at 80°C.
It was heated at 0° C. for 2 hours to remove wax. This green compact has a thickness of 2
It was wrapped in 0 μm zirconium foil and sintered at ultra-high pressure using a belt-type ultra-high pressure device. At this time, Pyrofluorite was used as the pressure sealing gasket, and Kurofune Cylindrical was used as the gasket. The space between the graphite heater and the sample compact was filled with a compact formed by pressurizing common salt. Ultra-high pressure sintering involves first increasing the pressure to 55 Kb, then increasing the temperature to 1650°C and
It was held for a minute, then the temperature was lowered and the pressure was gradually released. The obtained sintered body was dense with an outer diameter of about 4 wm and a thickness of about 1 mm. After processing this into a flat surface using a diamond grindstone, the tool was created by adhering it to the corner of an alumina indexable tip using brazing.

For comparison, a ceramic tool with 3 μm CBN grains added as hard grains and a ceramic tool with only a binder phase composition without hard grains were created. In addition, for ceramic tools, the raw material powder is the aforementioned TiN and alumina in a volume of 8
The ratios were 3% and 17%, and 1% of lubricant was added to the ratios, and a tool was prepared in the same manner as described above.

The cutting test was conducted under the same conditions using the hard particle dispersion type tool and the ceramic tool of this example. The conditions are cutting speed 10
0 m/win, feed 1) 0.1111111/r
e V % Depth of cut 0.1m, workpiece material is hardened steel (SUJ
2. Hardness H. 6.2).

As a result, the tool of this example had a flank wear width of 0.17 m at a cutting distance of +4 m, and a surface roughness of the workpiece of 1.6 to 2 m.
．． In contrast, the flank wear width of the ceramic tool with the binder phase composition was 0.22 to 0.26 m, and the surface roughness of the workpiece was 2.6 to 3.6 m. That is,
Addition of hard particles improved wear resistance and surface roughness accuracy of the workpiece.

On the other hand, CBN sintered tools have a flank wear width of 0.2 to 0.2.
4 wan, the surface roughness of the workpiece is 2.0 to 2.5 μm
Even when compared with the CBN sintered tool, the tool of this example showed superior characteristics.

(Example 2) Single crystal A with the same composition as Example 1 and an average grain size of 3 μm
A tool was produced by sintering a mixed powder of TiN powder, 0340% by volume, 5% by volume of AIIto3 powder, and 10% by volume of AIIto3 powder with an average particle diameter of 1 μm using a hot press method instead of ultra-high pressure sintering.

The hot pressing conditions were vacuum (10-2 Torr), humidity 1650°C, pressure 1000 kgf/cj, and sintering was performed by holding for 1 hour. A throw-away tool was cut out from the obtained sintered body using a diamond cutter and subjected to a cutting test. When 7 tests were conducted under the same cutting conditions as in Example 1, the flank wear width was 0.18 m at cutting distance 4.
, the surface roughness of the work material is 1.8 to 2.4 μm, which is inferior to the tool of the present invention made by ultra-high pressure sintering, but the CBN sintered tool has the same binder phase composition as described in Example 1. It showed the same or better characteristics compared to .

(Example 3) The hard grains and powders having the binder phase composition shown in Table 1 were mixed separately.

The average particle size of the hard particles used was 0.4 μm to 10 μm, and single crystals prepared by the Bridgman method, the Bernoulli method, etc. were crushed and used as single crystal grains. In addition to single crystal grains, high purity polycrystal grains prepared by a coprecipitation method were also used for Ar1.

Sintering was performed using the hot press method as in Example 2, but
The obtained sintered bodies were dense in all cases.

Table 2 also shows purity of alumina: 99, 5-9.
9. A comparison between 95% polycrystalline grain and single grain addition is shown. As shown in the wood table, it can be seen that the wear resistance is 20 to 30% worse when polycrystalline grains are added compared to single crystal grains. The reason for this is presumed to be that the impurities contained in polycrystalline grains are located at grain boundaries, which have a low melting point and therefore have low hardness at high temperatures. Therefore, in the present invention, the volume ratio occupied by grain boundaries is 0.01% or less, and the purity is 9.9%.
It is necessary to use crystal grains of 99% or more.

Table 1 <Effects of the Invention> As explained above, the sintered material for tools of the present invention has a volume ratio of 0.01% or less to grain boundaries and a purity of 9.
Since it contains 9.99% or more of crystal grains as hard grains, 20 to 80% by volume, the wear resistance and surface roughness accuracy of the workpiece material are improved compared to ceramic tools consisting only of binder phase composition, and CBN sintered It has the same performance as a bonded tool, and can be manufactured at a lower cost than a CBN sintered tool.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram showing the hardness of the binder phase material of the CBN sintered tool, Figure 2 is an explanatory diagram showing the reactivity of the binder phase material of the CBN sintered tool with the work material, and Figures 3 and 4 are Figure (al, (
b), (cl is a micrograph showing the particle structure on the surface of the sintered body, Fig. 5 (al is a schematic diagram explaining the wear of a CBN sintered tool, and Fig. 5 (b) is an enlarged view of part A) In the drawings, reference numeral 10 indicates the cutting edge of the tool, and as shown in the examples in Table 2, the sintered body according to the present invention has high hardness and high wear resistance, so it is suitable for cutting of high-hardness materials such as hardened steel. In addition to tools, it is also suitable for mold materials for plastic working (drawing dies, press dies, etc.). 0a is the flank surface, Ob is the rake surface, 1 is the CBN grain, 2 is the binder phase, 3 is the It is the work material.

Claims (3)

[Claims] (1) 20 to 80% by volume of crystal grains in which the volume ratio occupied by grain boundaries is 0.01% or less and the purity is 99.99% or more
1. A sintered material for tools, characterized in that the remaining part consists of a continuous bonding phase of ceramics. (2) The sintered material for tools according to claim 1, wherein the crystal grains are single crystal grains or crystal grains produced by a coprecipitation method. (3) The sintered material for tools according to claim 1, wherein the crystal grains are carbides, nitrides, silicides, silicides, or carbides of transition metals of Groups 4a, 5a, and 6a of the periodic table. .