JP2954996B2 - Sintered materials for tools - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a sintered material for a tool used in cutting or plastic working of a hard material such as hardened steel or cemented carbide, or a heat-resistant alloy. About.

<Prior art> When machining hardened steel or a high-hardness material such as a nickel-base heat-resistant alloy or a cobalt-base heat-resistant alloy, generally, a carbide powder of a high-melting point metal such as tungsten is mixed with an iron-based metal such as iron, cobalt or nickel. Sintered cemented carbide has been used.

In recent years, in addition to the above-mentioned cemented carbide being used not as a tool but as an object to be machined, and in order to respond to strict requirements for machining conditions, as a more sophisticated tool, a hard grain bonded with ceramics has been used. Those using sintered diamond, sintered cubic boron nitride (hereinafter referred to as CBN), and the like have been developed. Sintered diamond is
Although diamond particles are sintered under a high temperature and a high pressure using a cemented carbide as a binder, they are fundamentally unsuitable for processing of steel or the like having a strong affinity for carbon. In this regard, the CBN sintered body in which CBN with the hardness next to diamond is added as hard grains has little reaction with iron-based metals, and therefore, all the objects to be processed other than diamond, especially hardened steel and cemented carbide, etc. It is effective for processing nickel-based heat-resistant alloys, cobalt-based heat-resistant alloys, and the like, in addition to hard materials.

Conventional CBN sintered bodies are prepared by mixing ceramics such as titanium carbide or titanium nitride, which serves as a binder phase, alone or in combination with the CBN powder, adding a metal component to improve sinterability, (1300-1800 ° C) and high pressure (30-80Kb (kilobar)). In addition, as the material of the binder phase, in addition to the above, silicon or zirconium carbide or silicon or zirconium nitride, furthermore, an intermetallic compound of aluminum and titanium, an intermetallic compound of aluminum and zirconium, and the like are known. I have.

<Problems to be Solved by the Invention> CBN sintered tools are increasingly used for precision cutting of hardened steel instead of conventional grinding wheels (grinding). The features of CBN sintered tools as cutting tools are that they have high wear resistance and high finish area (roughness).
This feature is made up of 40 CBN grains, which have the hardness next to diamond
It is manifested because it is contained in tools at a rate of ~ 60% by volume.

A CBN sintered tool in which hard CBN grains are dispersed in a binder phase of ceramics has excellent characteristics as a cutting tool, but has the following various problems. Note that the diamond sintering tool and the CBN sintering tool are similar in manufacturing method, and the problems caused thereby are also the same. Therefore, the diamond sintering tool also has the following problems.

First, CBN grains are expensive. The particle size of the CBN particles usually added is 0.5 to 6 μm, and is produced by ultra-high pressure synthesis as in the synthesis of diamond. This method grows crystals at a pressure of 50 to 70 Kb and a temperature of 1500 to 1700 ° C. Using a special ultra-high pressure synthesis equipment and requiring a long time for synthesis, the product CBN grains are expensive. It has become something.

Secondly, the sintering of the CBN particles and the ceramic binder phase must be performed under an ultra-high pressure, although it is related to the above-mentioned method for producing the CBN particles. In other words, when CBN grains are heated under atmospheric pressure, a phase transformation occurs around 1200 ° C and changes from cubic to large crystals (CBN undergoes a phase transformation to hBN), and the resulting hBN is boron nitride (BN ), Which has low hardness and cannot be used as a tool material. On the other hand, in order to integrally sinter the CBN particles and the ceramic binder phase, it is necessary to heat the CBN particles to 1200 ° C. or more at which phase transformation occurs. For this reason, it is necessary to heat and sinter under ultra-high pressure using the above-mentioned ultra-high pressure synthesis equipment.

Generally, the conditions for sintering CBN sintered tool materials are pressures of 40 to 6
0Kb, temperature 1400-1800 ℃, but in ultra-high pressure synthesis, the size of the sintered body that can be manufactured in one operation is small and sintering requires a long time, so the tool becomes expensive and the application destination is limited. It is the present situation that is done.

Thus, CB which is a representative example of the hard grain dispersion type sintered tool
N-sintered tools have excellent features as tools, but there are various problems in expanding their application fields in the future. Therefore, C, which has the same excellent features as CBN sintered tools,
There is a demand to develop a new hard grain dispersion type sintering tool using hard grains instead of BN grains.

In view of such circumstances, an object of the present invention is to provide an inexpensive sintered material for tools having high wear resistance, excellent toughness, and low cost.

<Means for Solving the Problems> A sintered material for a tool according to the present invention that achieves the above objects,
A single-crystal alumina having a grain size of 1 to 10 μm
It is characterized by containing 40 to 80% by volume, with the balance being a continuous binder phase of ceramics.

Here, the present invention will be described in comparison with a CBN sintered tool, which is a representative of conventional hard grain dispersion type sintered tools.

First, the state of wear of a conventional CBN sintered tool will be described with reference to the drawings. FIGS. 5 (a) and 5 (b) schematically show the state of wear of the flank and rake face of a CBN sintered tool when cutting hardened steel. As shown in both figures, in the cutting process, the CBN grains 11 of the tool tip 10 are broken or fallen off from the binder phase 12 in the grains, and the broken pieces or the dropped CBN grains 11 form the work material 13 and the flank 10a. When passing through the boundary of the flank, a streak a is left on the flank 10a, and it is considered that the streak a determines the flank wear width (V _B ), that is, the wear resistance. In the drawings, 10b indicates a rake face. In the process in which the CBN grains 11 are broken or dropped,
Work material of the binder phase 12 of the cutting edge having the function of carrying the grains 11
At the stage where the part in contact with 13 recedes due to wear and the external force (cutting force, thermal stress, etc.) exceeds the force to split or support the CBN grain 11, the CBN grain 11 breaks, It is considered that the CBN particles fall off the cutting edge portion 10 due to the separation at the grain boundary with the C12 or the breakage of the binder phase 12.

For this reason, in a tool in which the wear resistance of hard grains is several times higher than that of the binder phase, only the binder phase is selectively worn, and the hard grains protrude from the binder phase, which cannot withstand external force. It is considered that the hard particles are likely to be broken or dropped, and rather the break or drop is liable to occur, so that the flank is considered to be quickly worn as described above.

That is, when focusing mainly on the wear resistance of the tool,
It cannot be said that the higher the wear resistance of the hard grains with respect to the binder phase, the better, and it is important that the hard grains have excellent properties such as tensile strength and toughness.

Furthermore, from cutting tests using CBN sintered tools, in tools with hard grains dispersed, CBN grains maintain the surface roughness of the work material with high accuracy, and increase the hardness of the tool to increase the cutting edge It turned out that it was helpful in reducing deformation. In particular, the former is as important a feature as the abrasion resistance.

Therefore, as hard grains, those that are not significantly higher in wear resistance than the binder phase, that is, the hardness does not need to be significantly higher, but have a higher hardness than the binder phase at the cutting edge temperature (800 to 1000 ° C) during cutting. A material that has high tensile strength and toughness is suitable because it has high wear resistance and high precision surface roughness. Is considered to be obtained.

The hard particles used in the present invention meet such conditions. Since the hard grains must not react with the work material, the change in standard free energy of formation (ΔG _T゜ cal / mol) of both must be a positive value.

Here, the crystal grain in which the volume ratio occupied by the crystal grain boundary is 0.01% or less and the purity is 99.99% or more means a single crystal grain or a polycrystal grain equivalent thereto. In addition, the polycrystal grain equivalent to the single crystal grain here means a polycrystal grain produced by, for example, a coprecipitation method.

As a specific material of the hard grains, periodic table 4a, 5a, 6a
Examples thereof include carbides, nitrides, borides, silicides, carbonitrides and oxides of group transition metals, and oxides of aluminum.

In addition, diamond and CBN with hardness next to this
Is expensive as mentioned above, high pressure during sintering (30-70K
b) and the hardness is much higher than other ceramics and intermetallics.
It is not included in the hard grains in the present invention.

On the other hand, although ceramics is used as the combination phase, it is considered that it is necessary to have the following four characteristics in view of the wear mechanism described above.

That is, in order to increase the wear resistance of the binder phase and to suppress the retreat speed of the binder phase at the cutting edge due to wear, the hardness at the cutting edge temperature during cutting is high, and the work material (steel, And low reactivity with iron group metals).

Also, in order to make it difficult for the hard grains and the binder phase to fall off due to peeling at the grain boundaries, they must diffuse and react with each other and firmly adhere to each other. In order to be sound, good sinterability (densification at low sintering temperature) and high strength and toughness are required.

Therefore, it is preferable to use ceramics having such properties as the binder phase. The following is a concrete consideration.

FIG. 1 shows the hardness of various binder phases of a CBN sintered tool. In general, carbides, borides and nitrides of transition metals of Groups 4a, 5a and 6a of the periodic table have high hardness. In particular, titanium nitride (hereinafter referred to as TiN) is contained therein and has high hardness,
In addition, aluminum oxide (hereinafter referred to as alumina or Al ₂ O ₃ ) has a high hardness at a temperature (800 to 1000 ° C.) at the cutting edge during cutting.

Figure 2 shows the cutting edge temperature (800-1000
Free energy of formation (ΔG _T゜ cal /
mol).

When such free energy of formation is used as an index of reactivity with iron or the like, carbides, nitrides, some borides, alumina, and zirconium oxide (hereinafter, ZrO _{2) of} transition metals of Groups 4a, 5a, and 6a of the periodic table are used. Or zirconia) is presumed to have low reactivity, and these can be used as materials for the combined phase.

In addition, the standard free energy of formation (ΔG _T゜ cal / mo
The evaluation can be made according to l). About the above, a sound binder phase can be obtained by adding an auxiliary agent for promoting sintering to the main component of the binder phase.

In order to manufacture the hard grain dispersion type sintering tool according to the present invention from the binder phase material selected as described above and the hard grains described above, a hot press method or an ultra-high pressure sintering method is applied.

In the case of using the hot press method, first, the binder phase material and the hard particles are mixed by a ball mill or the like, and the mixture is compacted by a powder compacting press using a mold into a predetermined shape. Next, this green compact was loaded into a graphite mold of a hot press,
A sintered body is manufactured by applying a temperature of 800 to 2400 ° C. and a pressure of 1 Kb in a vacuum or an inert atmosphere, and holding for several minutes to several hours.

Further, the ultra-high pressure sintering method is a method similar to that for producing a CBN sintered tool material. In this method, the green compact obtained in the same manner as the hot press method is wrapped with a metal foil such as zirconium, and further wrapped with a green compact of a salt serving as a pressure medium, and this is incorporated into a graphite heater ring. A belt-type apparatus used for diamond synthesis is charged via a pressure medium such as pyroferrite, and the temperature is set to 800 to 1800 ° C and the pressure is set to 40 ° C.
6060 Kb is applied and held for several minutes to several hours to produce a sintered body.

The sintered body of the present invention obtained in this way sinters at a higher density especially when manufactured by the ultra-high pressure sintering method, but when it is used as a cutting tool, it has a 5-10% resistance. Abrasion is improved.

As described above, the sintered material for a tool of the present invention produced by the hot press method or the ultra-high pressure sintering method is a sintered body in which hard grains are dispersed and arranged in a combined phase to obtain hardened steel or the like. In order to achieve high wear resistance and high-precision surface roughness in the cutting of high hardness materials, the bonding phase must be a continuous phase on the sintered body structure in view of its function. Required. In other words, by making the binder phase a continuous phase, it becomes possible for the binder phase to grip hard particles sufficiently firmly, and to have high toughness as a sintered body, and to have the expected performance as a tool. Leads to. In order to make the binder phase a continuous phase, the content of the hard particles must be 80% or less by volume. On the other hand, since the effect of dispersing the hard particles is not exhibited when the content is less than 40% by volume, the content of the hard particles needs to be in the range of 40 to 80% by volume.

Similarly, in order to make the binder phase a continuous phase, it is necessary to coordinate the material of the binder phase around the hard grains, and for this purpose, when the hard grains and the powder of the binder phase material are mixed, ,
It is necessary to satisfy the condition that the surface of the hard particles contains the powder of the binder phase material.For example, by making the particle size of the powder of the binder phase material smaller than the particle size of the hard particles. Achieved.

On the other hand, since the particle size of the binder phase material produced industrially is 0.2 μm to 1 μm, the particle size of the hard particles is twice as large as the powder particle size of the binder phase material. Then, a particle size larger than 0.4 μm is required. When the surface roughness of the work material is R _max 3.2 μm or less, the particle size of the hard particles is considered to be 10 μm or less, so the range of the particle size of the hard particles is preferably 1 μm to 10 μm. .

FIG. 3 shows that 40% by volume of single crystal alumina particles are used as hard particles, and 50% by volume of titanium nitride (TiN) and 10% by volume of alumina (Al ₂ O ₃ ) are used as a binder phase. It shows the structure when a sintered body is formed by a sintering method.
As shown in the figure, TiN of a white-looking phase is coordinated in the gaps between the single-crystal alumina grains that appear gray, forming a completely dense sintered body, and TiN is continuously bonded to the single-crystal alumina grains. Are in phase.

FIG. 4 (a) shows the results of processing the sintered body shown in FIG. 3 into a tool shape and subjecting it to a cutting test. here,
Workpiece is hardened steel (SUJ2, hardness H _RC 62), the cutting conditions are photomicrographs of the cutting edge portion after cutting under the same conditions of cutting speed 100 m / min, Feed 0.1 mm / rev, cut 0.1 mm.

For comparison, micrographs of the cutting edge of the conventional CBN sintered tool and a tool sintered only with the binder phase composition when subjected to a cutting test are shown in FIGS. 4 (b) and 4 (c). . The binder phase of the CBN sintered tool is the same as in the above embodiment ((a)
), And the CBN content was 40% by volume.

Looking at these results, (b) shows the cutting edge wear form of the CBN sintered tool with a sharp linear cutting edge,
On the other hand, in (c), the cutting edge portion is rounded, and the central portion of the cutting edge is plastically deformed and has a different form.

On the other hand, the tool (a) of the present invention using single-crystal alumina shows a cutting edge wear pattern very similar to a CBN sintered tool, and the single-crystal alumina dispersed in the binder phase as hard grains is the same as the CBN grains. It was confirmed that it had a function.

<Examples> Hereinafter, the present invention will be described based on examples.

(Example 1) As hard particles, single-crystal Al ₂ O ₃ particles having an average particle size of 3 μm, TiN powder having an average particle size of 1 μm, and Al ₂ O ₃ powder having an average particle size of 0.2 μm were respectively 40% and 50% by volume. %, 10% and mixed in a mortar. A 1% lubricant was added to this powder, and a powder compact having a diameter of 4 mm and a thickness of 1.5 mm was formed by a powder compacting press.

This is first done in a vacuum furnace at 800 ° C with a vacuum of 10 ^-2 Torr.
Heated for hours and dewaxed. This green compact was wrapped in a zirconium foil having a thickness of 20 μm, and was subjected to ultra-high pressure sintering using a belt type ultra-high pressure device. At this time, pyroferrite was used as a gasket for pressure sealing, and a graphite cylinder was used as a heater. Between the graphite heater and the sample green compact, a green compact formed by pressing salt was filled. In ultra-high pressure sintering, the pressure was first raised to 55 Kb, then the temperature was raised to 1650 ° C and held for 30 minutes, after which the temperature was lowered and the pressure was gradually reduced. The obtained sintered body was a dense one having an outer diameter of about 4 mm and a thickness of about 1 mm. This was processed into a flat surface with a diamond grindstone, and then bonded to the corner of an alumina indexable insert by brazing to form a tool.

For comparison, a ceramic tool was prepared by adding only 3 μm of CBN particles as hard particles and by using only the binder phase composition without including the hard particles. For ceramic tools, the raw material powder contains the aforementioned TiN and alumina in 83% by volume.
And a 17% ratio, and 1% of a lubricant was added thereto to obtain a tool in the same manner as described above.

The cutting test was performed under the same conditions for the hard grain dispersion type tool of the present embodiment and the ceramic tool. Conditions are cutting speed 10
0 m / min, Feed 0.1 mm / rev, cuts 0.1 mm, the workpiece was hardened steel (SUJ2, hardness H _RC 62).

As a result, the tool of the present example had a flank wear width of 0.17 mm at a cutting distance of 4 km and a surface roughness of the work material of 1.6 to 2.0 μm, whereas the flank face of a ceramic tool having a binder phase composition Wear width 0.22-0.26mm, surface roughness of work material 2.6-3.6
μm. That is, the addition of the hard particles improved the wear resistance and the surface roughness accuracy of the work material.

On the other hand, the CBN sintered tool has a flank wear width of 0.2 to 0.24 mm, and the surface roughness of the work material is 2.0 to 2.5 μm. It showed better properties.

(Example 2) Single crystal having the same composition as that of Example 1 and having an average particle size of 3 µm
Sintered by hot pressing instead of ultra-high pressure sintering a mixed powder of 40% by volume of Al ₂ O _3, 50% by volume of TiN powder having an average particle size of 1 μm, and 10% by volume of Al ₂ O ₃ powder having an average particle size of 0.2 μm And created a tool.

Hot pressing conditions are vacuum (10 ^-2 Torr) medium temperature 1650
C., the pressure was set to 1000 kgf / cm ^2, and the mixture was held for 1 hour for sintering.
A throw-away tool was cut out from the obtained sintered body with a diamond cutter and subjected to a cutting test. When a test was conducted under the same cutting conditions as in Example 1, the flank wear width was 0.18 mm at a cutting distance of 4 km, and the surface roughness of the work material was 1.8 to 2.4 μm.
Although it is inferior to the tool of the present invention prepared by ultra-high pressure sintering, it exhibited the same or better characteristics than the CBN sintered tool of the same binder phase composition described in Example 1.

(Example 3) The hard particles and the powder of the binder phase composition shown in Table 1 were separately mixed.

The average grain size of the hard grains used is 3 to 10 μm (0.4 μm
Is a reference example), and a single crystal prepared by a Bridgman method, a Bernoulli method, or the like was used by pulverization and used as single crystal grains. For reference, a single crystal as well as high-purity polycrystalline grains prepared by a coprecipitation method were used as Al ₂ O ₃ .

The sintering was performed by the hot press method as in Example 2, but the obtained sintered bodies were dense in each case.

In Table 1, Nos. 2 to 4 and 6 to 8 correspond to this test example, while Nos.
5, 9 to 15 show reference examples.

Table 2 shows that alumina has a purity of 99.5 to 99.95.
5 shows a comparison between the addition of a single crystal grain and the addition of a single crystal grain of the same type. As shown in this table, it can be seen that the abrasion resistance is lower by 20 to 30% when polycrystalline grains are added than when single crystal grains are added. The reason is presumed to be that impurities contained in the polycrystalline grains are present at the grain boundaries, which have a low melting point, and thus have low hardness at high temperatures. Therefore, in the present invention, it is necessary to use crystal grains whose volume ratio occupied by crystal grain boundaries is 0.01% or less and whose purity is 99.99% or more.

As shown in the above examples, the sintered body according to the present invention has high hardness and high wear resistance. Therefore, in addition to cutting tools for hardened materials such as hardened steel, for example, molds for plastic working (drawing) Dies, press dies, etc.).

<Effects of the Invention> As described above, the sintered material for a tool according to the present invention is a single-crystal alumina having a grain size of 1 to 10 μm,
It is a sintered material for tools characterized by containing up to 80% by volume and the remainder consisting of a continuous binder phase of ceramics.
Abrasion resistance and surface roughness accuracy of the work material are improved compared to ceramic tools consisting only of the binder phase composition, and they have the same performance as CBN sintered tools, and are inexpensive compared to CBN sintered tools It can be manufactured.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an explanatory view showing the hardness of a binder phase material of a CBN sintered tool, and FIG. 2 is an explanatory view showing the reactivity of a binder phase material of a CBN sintered tool with a work material. , FIGS. 3 and 4 (a), (b),
(C) is a micrograph showing the particle structure of the sintered body surface, and FIG.
FIG. 5A is a schematic diagram for explaining the wear of a CBN sintered tool, and FIG.
FIG. 2B is an enlarged view of the portion A. In the drawing, 10 is a tool edge, 10a is a flank, 10b is a rake face, 11 is a CBN grain, 12 is a binder phase, and 13 is a work material.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tetsuo Ichizaki, Hiroshima 4-6-22 Kannon Shinmachi, Nishi-ku, Hiroshima-shi, Hiroshima In-house Hiroshima Research Laboratory Mitsubishi Heavy Industries, Ltd. No. Mitsubishi Heavy Industries, Ltd. Nagasaki Laboratory (72) Inventor Fukushi Yamada 2-5-1 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Heavy Industries, Ltd. (56) References JP-A-64-52668 (JP, A) Hei 2-501209 (JP, A)

Claims (1)

(57) [Claims] 1. A single-crystal alumina having a particle size of 1 to 10 μm.
A sintered material for a tool, comprising 40 to 80% by volume of m crystal grains, and a balance consisting of a continuous binder phase of ceramics.