JPH09301773A - Silicon nitride sintered body for tools - Google Patents

Abstract

(57) An object of the present invention is to provide a silicon nitride sintered body for a tool, which has a low porosity, is excellent in wear resistance and fracture resistance particularly at high temperatures, and is suitable for a cutting tool and the like. SOLUTION: When the silicon nitride sintered body is 100% by weight, 0.16 to 2.1% by weight of magnesium element and 0.7 to 4.8% by weight of ytterbium element are contained,
A silicon nitride sintered body for a tool is obtained in which the total amount of these magnesium element and ytterbium element is 6.2% by weight or less. Further, 0.64% by weight or less, especially 0.32% mixed from the aluminum oxide mixing tool used for mixing the raw materials
A silicon nitride sintered body for tools containing an aluminum element in an amount of at least wt% is obtained. This sintered body has a large grain size of β-Si ₃ N
₄ is a specific amount or less, and microcracks are unlikely to occur.
Further, when the surface has a plurality of coating layers made of Al ₂ O ₃ , AlON, TiN, etc., the abrasion resistance is particularly excellent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon nitride sintered body for a tool, which has excellent wear resistance especially at high temperatures and is suitable for a machine tool, particularly a cutting tool.

[0002]

2. Description of the Related Art Conventionally, a silicon nitride sintered body has a heat resistance,
Because of its excellent thermal shock resistance and abrasion resistance, its application as a structural material for various heat engines and a material for cutting tools is being promoted. However, silicon nitride is not easy to sinter because it has high heat resistance, and is generally fired using a sintering aid. This sintering aid is usually an oxide and is present in the sintered body as a grain boundary glass phase having a softening point lower than the decomposition temperature of silicon nitride. Therefore, there is a problem that the grain boundary glass phase is softened at a high temperature and causes deterioration of high temperature characteristics such as high temperature hardness of the sintered body, such as wear resistance.

In order to solve the above problems, it has hitherto been proposed to use a sintering aid having a high melting point for the purpose of forming a glass phase having a high softening point (JP-A-4-209).
763, JP-A-4-240162, and U.S. Pat. No. 5,382,273). Further, it is also effective to reduce the total amount of the sintering aid and reduce the generated grain boundary glass phase. However, in general, when a sintering aid having a high melting point is used, the sinterability is inferior to that when a sintering aid having a low melting point is used. Therefore, in order to obtain a dense sintered body by using a sintering aid having a high melting point, the total amount of the sintering aid must be increased even if the high temperature characteristics are sacrificed to some extent.

[0004]

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems. Even if a sintering aid component having a high melting point is contained and the content thereof is smaller than in the conventional case, It is an object of the present invention to provide a silicon nitride sintered body for a tool which is dense and has excellent high temperature characteristics such as wear resistance particularly at high temperatures.

[0005]

Among the sintering aids used for firing silicon nitride, oxides of rare earth elements are generally well known as those that form a grain boundary glass phase having a high softening point. There is. Since rare earth elements have similar chemical properties to each other, they are often treated collectively as rare earth elements. However, when considered as a sintering aid for silicon nitride, the sinterability is different, and the characteristics of the obtained sintered body are not always similar.

The present inventors have advanced the selection of the optimum rare earth element, paying particular attention to the sinterability and the wear resistance of the obtained sintered body as a tool material and the like. As a result, by using a sintered body containing a magnesium component and a ytterbium component as a sintering aid component, even if the content thereof is relatively small, it is dense and has excellent wear resistance. It has been found that an excellent sintered body can be obtained.

The silicon nitride sintered body for a tool of the first invention is a silicon nitride sintered body containing a magnesium element and a ytterbium element, and when the silicon nitride sintered body is 100% by weight, the above magnesium element and the above The ytterbium element is 0.16 to 2.0 wt% and 0.7 to
4.85% by weight, and the total amount of the magnesium element and the ytterbium element is 6.2% by weight or less. The tool silicon nitride sintered body of the first invention may or may not contain an oxygen element. Further, it may contain a very small amount of oxygen element.

The silicon nitride sintered body for a tool of the fifth invention is a silicon nitride sintered body containing a magnesium component and a ytterbium component, and when the silicon nitride sintered body is 100% by volume, the above magnesium component is used. And the above ytterbium component, converted to oxides, are each 0.25
Is 3.0% by volume and 0.3% by volume to 2.0% by volume, and the total amount of the magnesium component and the ytterbium component is 4.0% by volume or less.

As the silicon nitride raw material powder for obtaining the above "silicon nitride sintered body", one having an oxygen amount of about 1 to 2% as an impurity and a small amount of other impurities is usually used. Further, a large proportion of α-Si ₃ N ₄ , for example, α
What is generally preferred as a raw material powder having a crystallization rate of 95% or more can be used without particular limitation.

The above "magnesium element" forms a grain boundary glass phase in the form of an oxide together with other metal elements such as ytterbium, aluminum and silicon. Magnesium oxide produces a grain boundary glass phase having a low softening point in the presence of oxygen (usually present as silicon oxide) contained as an impurity in the silicon nitride raw material and the raw material of other components forming the grain boundary glass phase. Therefore, when it is contained in a large amount, the high temperature characteristics of the obtained sintered body are deteriorated, and it is not suitable for a tool material that requires wear resistance at high temperatures. On the other hand, since a glass phase having a low softening point is generated, the effect of improving the sinterability is great even if the amount of the sintering aid containing the magnesium element used is small. Therefore, it is possible to reduce the total amount of the grain boundary glass phase including the glass phase formed of another sintering aid, and it is possible to suppress the deterioration of the high temperature characteristics due to the small amount.

In the first invention, the above "magnesium element" is "0.16 to 2.0% by weight", preferably 0.1.
The reason why the content is 7 to 1.98% by weight is that if the content is less than 0.16% by weight, the sintered body will not be sufficiently dense. Also,
If it exceeds 2.0% by weight, the softening of the grain boundary glass phase at high temperature becomes severe, the hardness of the sintered body decreases, and the wear resistance becomes poor. Further, in the fifth invention, the content of the “magnesium component” is “0.25 to 3.0% by volume” in “converted to oxide”, and when the upper and lower limit values are not met, The same problem as in the first invention occurs. In the first invention, the content of the magnesium element is 0.17
The range is preferably 1.0 to 1.0% by weight, more preferably 0.17 to 0.7% by weight. Further, in the fifth invention, the magnesium component is 0.25 to 1.5% by volume, particularly 0.25 to 1.0%.
A range of volume% is preferred. When the content of the magnesium element or the magnesium component is within this range, the sintered body is dense and has excellent wear resistance at high temperatures.

Further, the sintering aid containing the ytterbium element has a great effect of improving the sinterability of silicon nitride among the sintering aids containing various rare earth elements. In particular, when combined with a sintering aid containing a magnesium element, the sinterability is further improved. Therefore, it is very suitable for the purpose of reducing the total amount of the sintering aid and thus the amount of the grain boundary glass phase. When used as a material for a cutting tool, it is required to have both wear resistance and fracture resistance, and in this respect, the sintering aid containing the ytterbium element is suitable.

In a silicon nitride sintered body containing a magnesium component and a rare earth element component in the grain boundary glass phase, if the type of the rare earth element changes, the resulting sintered body also has wear resistance and chipping resistance as a cutting tool. Change. For example, when the yttrium component, the dysprosium component, etc. are contained, the cutting tool obtained has relatively high fracture resistance and low wear resistance. In addition, when the ytterbium component is contained, the fracture resistance is slightly lower than that of the cutting tool containing the yttrium component, the dysprosium component, etc., but the wear resistance is considerably excellent. Therefore, in order to obtain the object of the present invention, in particular, a silicon nitride sintered body for a tool having excellent wear resistance at high temperatures, it is preferable to use a sintered body containing a ytterbium component as a rare earth element.

In the first invention, the above "ytterbium element" is "0.7 to 4.85% by weight", preferably 0.
The reason why the content is 75 to 4.83% by weight is that if it is less than 0.7% by weight, the strength of the sintered body is lowered and the fracture resistance and the like are insufficient. On the other hand, if it exceeds 4.85% by weight, the wear resistance of the sintered body particularly at high temperatures is deteriorated. Further, in the fifth invention, the "ytterbium component" is "0.3 to 2.0% by volume" in terms of oxide, and when the upper and lower limit values are not satisfied, the same as in the first invention. Cause problems. In the first invention, the ytterbium element content is particularly preferably in the range of 0.75 to 3.0% by weight. Also, the third
In the invention, the ytterbium component is 0.3 to 1.2.
A range of volume% is preferred. When the content of the ytterbium element or the ytterbium component is within this range, the sinterability is good, and the deterioration of the wear resistance at high temperatures can be suppressed.

In the first aspect of the invention, the total amount of the magnesium element and the ytterbium element is "6.2% by weight or less", preferably 6.15% by weight or less.
If it exceeds 2% by weight, the hardness of the sintered body, especially at high temperature,
This is because the strength decreases and the wear resistance and the like become insufficient.
Furthermore, in the fifth invention, the total amount of the magnesium component and the ytterbium component is "4.0 vol% or less", and when it exceeds 4.0 vol%, the same problem as in the first invention occurs. This total amount is “5.2 as in the third invention.
"% By weight or less", particularly 5.17% by weight or less, and "2.5% by volume or less" as in the sixth invention is preferable, and if the total amount is within this range, the denseness is high, and A sintered body excellent in hardness and strength at high temperatures can be obtained.

In addition, in the silicon nitride sintered body of the first invention, when the "oxygen element" is contained, the "2.1" is provided as in the second invention.
It is preferably 5% by weight or less ”. Further, in the silicon nitride sintered body of the third invention, when it contains the “oxygen element”, it is preferably “1.74 wt% or less” as in the fourth invention. In the second invention, the content of this oxygen element is
0.73 to 2.15% by weight, 0.73 in the fourth invention
It is preferably about 1.74% by weight. If the oxygen element contents exceed their respective upper limits, the wear resistance of the sintered body decreases.

In order to obtain a cutting tool having excellent wear resistance, it is important that the silicon nitride sintered body has a low porosity, in other words, a high density. In the present invention, since the total amount of the grain boundary glass phase is very small, that is, the sintering aid used is small, it is necessary to raise the firing temperature in order to enhance the sinterability and reduce the porosity. There is. However, if a general α-type silicon nitride raw material is used and the firing temperature is simply raised, a part of the crystal grains grow abnormally, mainly using β-type silicon nitride contained in the raw material in a small amount as a nucleus. . This abnormally grown particle easily causes microcracks in the particle,
In addition, the abnormally grown particles themselves are the origin of fracture, which causes the strength of the sintered body to decrease.

Therefore, in the silicon nitride sintered body for a tool of the present invention, the total cross-sectional area of "β-Si ₃ N ₄ particles" observed in the cut surface is set to 100% as in the seventh invention. In this case, the total cross-sectional area of "particles having a minor axis diameter of 1 μm or more" is "less than 10% by volume", and "major axis diameter is 10 μm".
The total cross-sectional area of "particles of m or more" is preferably "less than 4% by volume".

10% by volume of particles having a minor axis diameter of 1 μm or more
Or more, or if the major axis diameter is 10μm or more of the particles 4% by volume or more, on cooling after _{firing, β-Si 3 N 4 β} -Si 3 as internal microcracks particles generated
The amount of N ₄ increases, which is not preferable. Particles having a minor axis diameter of 1 μm or more are less than 5% by volume, particularly less than 3% by volume, and particles having a major axis diameter of 10 μm or more are less than 3% by volume, particularly 2% by volume.
If it is less than the above range, there is almost no decrease in strength due to microcracks, which is more preferable. In the sintered silicon nitride for tools of the present invention, particles having a minor axis diameter of 1 μm or more are preferably 2
~ 8% by volume, especially 1 to 4% by volume, and the major axis diameter is 10μ.
The particles of m or more are 1 to 4% by volume, and particularly 1.4 to 3.6% by volume.

The silicon nitride sintered body for a tool of the eighth invention is a silicon nitride sintered body containing magnesium element, ytterbium element and aluminum element, and when the silicon nitride sintered body is 100% by weight, the above magnesium The element and the ytterbium element are each 0.16 to 1.0.
0% by weight, preferably 0.17 to 1.00% by weight and 0.7 to 3.0% by weight, preferably 0.75 to 2.94.
% By weight, and the aluminum element is 0.64
It is characterized by being less than or equal to weight% (however, 0 weight% is not included). The tool silicon nitride sintered body of the first invention may or may not contain an oxygen element. Further, it may contain a very small amount of oxygen element.

The silicon nitride sintered body for a tool according to the twelfth invention is a silicon nitride sintered body containing a magnesium component, a ytterbium component and an aluminum component, and when the silicon nitride sintered body is 100% by volume, The above-mentioned magnesium component and the above-mentioned ytterbium component are 0.25-1.5 volume% and 0.3-1.
It is 2% by volume, and the aluminum component is 1.0% by volume or less (however, 0% by volume is not included) in terms of oxide.

In the present invention, the mixing of the raw material powders should be carried out by a method that does not contain impurities that would reduce the wear resistance of the obtained sintered body. Most preferably, they are mixed using a silicon nitride mixing tool. However, since a silicon nitride mixing tool is very expensive, a resin or aluminum oxide mixing tool may be used. When a resin is used, the resin mixed in the mixture of the raw material powders is volatilized during firing and does not remain in the sintered body, so there is no problem.

A part of aluminum oxide forms a solid solution with silicon nitride in the sintered body. Therefore, if the mixing amount is small, the wear resistance is not significantly decreased by the increase of the grain boundary glass phase, and rather, the chipping resistance and the sinterability are improved. Therefore, when using a mixing tool made of aluminum oxide, in consideration of the decrease in wear resistance, by reducing the amount of the sintering aid containing magnesium element or ytterbium element in an amount equivalent to the content of aluminum oxide, silicon nitride or It is possible to obtain a sintered body having the same performance as when a resin-made mixing tool is used.

Therefore, in the above eighth invention, the amounts of magnesium element and ytterbium element are reduced as compared with the case of the first invention. In the twelfth invention described above, the magnesium component and the ytterbium component are
The amount is reduced as compared with the case of the fifth invention. The total amount of the elemental aluminum or the aluminum component mixed from the mixing tool and the amount obtained from the sintering aid is “0.64% by weight or less” in the eighth invention,
In the invention, it is adjusted to be "1.0% by volume or less". If the amount of this aluminum element or aluminum component exceeds the upper limit value, it is not possible to obtain a sintered body having the same performance as in the case of using a mixing tool made of silicon nitride or a resin, and wear resistance and the like decrease. .

Further, in the tenth invention, the upper limit of the magnesium element is lowered and the aluminum element is set to 0.3.
It is as high as 2 to 0.64% by weight. In addition, in the thirteenth invention, the upper limit of the magnesium component is lowered and the aluminum component is increased to 0.5 to 1.0% by volume. As a result, it is possible to obtain a sintered body in which the deterioration of wear resistance is sufficiently suppressed and the fracture resistance is greatly improved. This aluminum element is preferably 0.45% by weight or more, and particularly preferably 0.51% by weight or more. Further, the aluminum component is preferably 0.7% by volume or more, and particularly preferably 0.8% by volume or more. As described above, when the amount of aluminum element or aluminum component is large, it is possible to obtain a sintered body having both excellent wear resistance and chipping resistance.

In addition, in the silicon nitride sintered body of the eighth invention, when the "oxygen element" is contained, as in the ninth invention, "2.1
2% by weight or less "is preferable. Further, in the silicon nitride sintered body of the tenth invention, when it contains the “oxygen element”, it is preferably “1.96% by weight or less” as in the eleventh invention. The content of this oxygen element is preferably about 0.73 to 2.12% by weight in the ninth invention and about 0.87 to 1.96% by weight in the eleventh invention. If the oxygen element contents exceed their respective upper limits, the wear resistance of the sintered body decreases.

The main purpose of the present invention is to improve the wear resistance, but depending on the application, purpose, etc., a sintered body having particularly excellent fracture resistance can be formed. When the aluminum element (aluminum component) is not contained, the magnesium element is about 2.0% by weight (the magnesium component is about 3.0% by volume) and the ytterbium element is 2.4 to 7.2% by weight (the ytterbium component is 1% by weight). .0 to 3.0% by volume) makes it possible to obtain a silicon nitride sintered body for a tool having a number of processing peaks of 68 or more in a cutting test and having extremely excellent fracture resistance. In addition, magnesium element 0.19 ~
1.07% by weight (0.3 to 1.6% by volume of magnesium component) and 2.43 to 3.16% by weight of ytterbium element (1.0 to 1.3% by volume of ytterbium component). Even if the composition is such that 0.51 to 0.70% by weight of aluminum element (0.8 to 1.1% by volume of aluminum component) is added, the number of processing peaks in the cutting test is 68 or more. It is possible to obtain a sintered body having excellent chipping resistance.

In the present invention, the total amount of the magnesium element and the ytterbium element is not more than 5.2% by weight, preferably 5.17% by weight, as in the third invention.
Hereafter, if the total amount is 4.2% by weight or less, a sintered body having high denseness and excellent hardness and strength at high temperature can be obtained. Further, as in the sixth invention,
The total amount of the magnesium component and the ytterbium component is 2.5% by volume or less, and further, the total amount is 2.0% by volume.
Even if it is the following, a sintered body having similarly excellent characteristics can be obtained. Further, when aluminum element or aluminum component is contained, similarly, a sintered body having high denseness and excellent hardness, strength and the like can be obtained. As described above, in the silicon nitride sintered body of the present invention, as in the fourteenth invention, the "porosity" is "0.06% by volume or less", particularly 0.02% by volume or less, and wear resistance and the like. It is possible to obtain a sintered body having excellent properties.
The porosity can be reduced to about 0.01% by volume.

Generally, when cutting a casting with a silicon nitride-based tool, a coating layer made of a material having a high hardness is provided on the surface of the sintered body under the condition of abrasive wear such as intermittent processing such as milling. However, the effect hardly appears. On the other hand, in the case of machining in which rubbing wear is the deciding factor of tool life, such as continuous machining in turning, it is necessary to improve wear resistance and welding resistance by providing the above coating layer. You can Also in the present invention, it is preferable to provide a specific coating layer as in the fifteenth invention for the purpose of use in a continuous turning machining line.

In the fifteenth invention, "Al ₂ O ₃ ,
At least one coating layer made of AlON, TiN, TiC, and TiCN ”is provided. These coating layers may be only one layer, but 2
The number of layers can be set to 10 to 10, and particularly about 3 to 8 can provide a tool having excellent wear resistance and a long life. In addition, the "outermost layer" of the coating layer has a high hardness T
It is preferably iN. Furthermore, the total thickness of the coating layer can be 1.0-8.0 μm, in particular the first
As in the fifth invention, the range of “1.5 to 6 μm” is preferable. When the total thickness is 1.5 μm or more, the wear amount is sufficiently reduced and the tool life can be extended. If the total thickness exceeds 6 μm, the coating layer may peel off and the tool life may not be sufficiently extended.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described specifically with reference to examples. As the silicon nitride raw material powder, the average particle size was 0.
5 μm, α-type crystallization rate 95% or more, oxygen content 1.5% by weight
Of powder was used. As the sintering aid, magnesium oxide powder having an average particle size of 0.3 to 0.4 μm and ytterbium oxide powder having an average particle size of 0.5 to 1.5 μm were used.

Each of the above powders was mixed with ethanol as a solvent in the composition shown in Tables 1, 2 and 3 using a resin container and silicon nitride spherule, or an aluminum oxide container and aluminum oxide spherule. Crushed and mixed for 16 hours. Then, an organic binder was added and the mixture was molded by a die press to obtain a molded body having a shape for the tool SNGN120408. Next, after degreasing this molded body, it was fired under the conditions of temperature and pressure shown in Tables 1 to 3 to obtain silicon nitride sintered bodies of Experimental Examples 1 to 27 shown in Tables 4, 5 and 6. In addition, Experimental Examples 1 to 12
22 to 27, a resin container and a silicon nitride ball were used, and in Experimental Examples 13 to 21, an aluminum oxide container and an aluminum oxide ball were used.

[0033]

[Table 1]

[0034]

[Table 2]

[0035]

[Table 3]

[0036]

[Table 4]

[0037]

[Table 5]

[0038]

[Table 6]

In Tables 2 and 3, the analytical value (*) of aluminum oxide is a value obtained by analyzing the amount of aluminum oxide in the base powder after pulverization and mixing by the fluorescent X-ray method.
This value is (volume) weight% when the total amount of magnesium oxide, ytterbium oxide, and silicon nitride is 100 (volume) weight%. In addition, the upper column of the analytical value column of Tables 4 to 6 is the weight% of each element of Mg, Yb and Al in the sintered body, and the lower column is the volume% of the oxide of each element based on the numerical values of the upper column. It is a converted value. In the present invention, most of the sintered bodies have a porosity of 0.06% or less and are almost completely densified. Therefore, after converting the weight% of each element into the weight% of the oxide, this weight% Can be theoretically numerically converted to volume% as follows.

The constituents of the sintered body are 1, 2, ...
Assuming that there is a kind, the weight% of the components 1, 2, ... N is W ₁ ,
W ₂ , ... W _n , the volume% of the oxide is V ₁ , V ₂ ,
· · · V _n, each specific gravity of the oxide _{d 1, d 2, ··· d} n
, The volume% of the oxide of the component k is V _k = (W _k / d _k ) / (W ₁ / d ₁ + W ₂ / d ₂ +
.. W _n / d _n ) can be obtained. For example, in the present invention, since the specific gravities of MgO, Yb ₂ O ₃ and Si ₃ N ₄ are 3.65, 9.17 and 3.20, respectively, VMgO = (WMgO / 3.65) / (WMgO / 3.65+
_{WYb 2 O 3 /9.17+WSi 3 N 4} /3.20), and _{VYb 2 O 3 = (WYb 2} O 3 /9.17)/(WMgO /3.6
5 + WYB by _{2 O 3 /9.17+WSi 3 N 4 /3.20} ), it is possible to calculate the volume percent MgO and Yb ₂ O _3, respectively. Incidentally, when aluminum oxide is contained, it can be converted in the same manner.

The porosity of the sintered body of each experimental example measured by CIS006B (corresponding international standard ISO 4505) was 0.06 except for Experimental Examples 6, 18, and 23.
It was less than volume% and the sintered body was sufficiently densified.
Further, the cross section of the sintered body was observed by SEM at a magnification of 1000 times for 5 fields of view. As a result, the total cross-sectional area of β-Si ₃ N ₄ particles having a major axis diameter of 10 μm or more is β-Si ₃
1.4% of Experimental Example 23 relative to the total cross-sectional area of N ₄ particles
To 4.3% of Experimental Example 27. In many experimental examples 1 to 2, 7 to 10, 20 and 23, 2.
It is 0% or less, and it can be seen that in these sintered bodies, the amount ratio of β-Si ₃ N ₄ having a large major axis diameter is particularly low.

The method of the cutting test will be described below. Cutting test (flank wear amount) After precisely polishing the obtained sintered body, a cutting test was performed for 10 seconds by a dry method under the following conditions. The shape of the work material is cylindrical as shown in FIG. In FIG. 1, L1 is 260
mm, L2 is 300 mm, and the wall thickness is 20 mm. L3 is 100 mm. In addition, the maximum amount of wear generated when entering and leaving the black skin of the cast sand of the work material by one-pass cutting was measured and set as the flank wear amount VB (abrasive wear test). Work Material: FC200 Cutting Speed: 300 m / min Feed: 0.34 mm / rev Depth of Cut: 1.5 mm Blade Edge: 0.15 mm x 20 °

Cutting Test (Fracture Resistance) The fracture resistance was evaluated under the following conditions, and the number of processed peaks was used as an index of the fracture resistance. Work Material: FC200 Cutting Speed: 150 m / min Feed: 0.8 mm / rev Depth of Cut: 2.0 mm Blade Edge: 0.08 mm x 20 ° Cutting Time: Until Defect

In this cutting test, the work material has a cylindrical shape, and as shown in FIG. 2 which is a front view of the work material after the cutting test, one work material has ten work ridges. To make.
In FIG. 2, L4 is 10 mm, L5 is 5 mm, L
6 is about 50 mm, L7 is 200 mm, R1 is 32
It is 0 mm. In this cutting test, the cutting diameter per cutting was 2 mm, so the outer diameter decreased by 4 mm, and
Since the surface is smoothed by cutting in mm, the outer diameter is reduced by 5 mm in total by one cutting. By repeating this, the same work material is used until the outer diameter reaches 280 mm. still,
The results of the above cutting test are also shown in Tables 1, 2 and 3. In the cutting test and the cutting test described later, the tool-shaped sintered body of SNGN120408 was used by being fixed to a holder of product number CSBR2525N12Q specified by ISO.

According to the results of Table 4, Table 5 and Table 6, the difference in the number of processing peaks is clear between Experimental Example 1 and Experimental Example 2, and if the ytterbium element is less than the lower limit value, the fracture resistance is poor. Further, it can be seen that in Experimental Example 4 in which the ytterbium element amount ratio is high, the wear resistance is inferior to that in Experimental Example 3. On the other hand, in Experimental Example 6 in which the magnesium element is less than the lower limit value, not only a sufficiently dense sintered body cannot be obtained, but also the wear resistance and the fracture resistance are greatly reduced as compared with Experimental Example 3 having the same composition. . Further, in both Experimental Example 11 and Experimental Example 12, the total amount is close to the upper limit value and the oxygen element content is large, but it is found that the wear resistance is more deteriorated when the magnesium element amount ratio is high. .

Further, the magnesium element and the ytterbium element are almost constant, and the aluminum element is 0.31.
In Experimental Examples 13 to 17 in the range of ~ 0.69% by weight,
It can be seen that in the case of Experimental Examples 14 to 16, the wear resistance and the fracture resistance are well balanced and a sintered body having excellent performance can be obtained. On the other hand, it can be seen that in Experimental Example 13 in which the aluminum element is less than the lower limit value of the eighth invention, the fracture resistance decreases, and in Experimental Example 17 in which the aluminum element exceeds the upper limit value, the abrasion resistance is inferior.

Further, even if the aluminum element and the ytterbium element are in proper amounts, the experimental example 18 in which the magnesium element is less than the lower limit value is not sufficiently densified, and is more resistant than the experimental example 15 having the same composition. It can be seen that both wear resistance and fracture resistance are greatly reduced. In addition, Experimental Example 19 in which the total amount of the magnesium element and the ytterbium element exceeded the upper limit value of the third invention and the oxygen element content was large.
Then, both the wear resistance and the fracture resistance are slightly lowered. On the other hand, in Experimental Example 20 in which the ytterbium element was less than the lower limit value of the first invention, even if the aluminum element and the magnesium element were in appropriate amounts, the fracture resistance was significantly decreased, and in Experimental Example 21 in which the ytterbium element amount ratio was high, It can be seen that the wear resistance decreases.

In Experimental Example 22 in which the ytterbium element exceeds the upper limit of the first invention and the oxygen element content is large, the wear resistance is very poor. Further, in Experimental Example 23, since the firing temperature was low, it was found that the porosity was 0.6% by volume, the densification of the sintered body was not sufficient, and both wear resistance and fracture resistance were poor. Furthermore, in Experimental Examples 24 and 25, yttrium element and dysprosium element are contained as rare earth elements, respectively, but the abrasion resistance is very inferior as compared with Experimental Example 10 containing the same amount of ytterbium element. There is. Also, since the firing temperature was high, β-S
It can be seen that the experimental example 27 in which the i ₃ N ₄ particles abnormally grow and is out of the range of the seventh invention is inferior in fracture resistance to the experimental example 26 having the same composition.

According to the results of Experimental Examples 11 and 12 in Table 2 and Experimental Example 22 in Table 3, the flank wear amount is 1.48 to
Since it is 1.88 mm, it cannot be said that the abrasion resistance is sufficient. However, the number of processing peaks in the cutting test is 69 to 82.
It can be seen that this is a sintered body that is extremely excellent in fracture resistance. Also, in Experimental Examples 15 to 17 and 19 and 21 in Table 2, the wear resistance is lowered, but the number of processed peaks is 68 to
It can be seen that the number of sintered compacts is 78, which is a very excellent fracture resistance.

Further, in the present invention, a silicon nitride raw material powder containing no oxygen element is used as an impurity, and Mg ₃ N ₂ , Mg ₂ Si, ytterbium nitride and ytterbium silicide are used as sintering aids, It is also possible to obtain a silicon nitride sintered body for a tool containing no oxygen element by mixing these powders with a resin container in a silicon nitride ball and firing them in a non-oxidizing atmosphere (capsule HIP method).
This silicon nitride sintered body containing no oxygen element also has excellent performance.

Next, on the surface of the sintered body of Experimental Example 15,
Experimental examples 28 to 34 were prepared by providing 3 to 8 coating layers made of various oxides, nitrides and the like described in the invention. In these experimental examples, wear resistance was evaluated by the following cutting test method. Table 7 shows the types of oxides forming the coating layer, the order of lamination, the thickness of each layer, and the total thickness of the coating layer. The results of the flank wear amount are also shown.

[0052]

[Table 7]

Cutting test (evaluation of flank wear where the effect of the coating is apt to appear) Under the following conditions, the wear resistance is evaluated using the work material ground from the casting sand, and the maximum flank wear amount VB Was used as an index of wear resistance (rubbing wear test). The shape of the work material is cylindrical. In FIG. 3, L8 is about 50 mm, L9
Is 195 mm and R2 is 320 mm. The tool moves from right to left in FIG. Moreover, this work material was repeatedly used. Work material: FC200 Cutting speed: 100 m / min Feed: 0.1 mm / rev Cutting depth: 1.0 mm Cutting edge: 0.20 mm x 20 ° Cutting time: 20 minutes

According to the results of Table 7, in any of Experimental Examples 28 to 34 in which the coating layer was provided, the flank wear amount was smaller than that of the sintered body of Experimental Example 15 having no coating layer, which was excellent. It can be seen that it has abrasion resistance. Further, in Experimental Examples 29 to 33 which are within the scope of the fifteenth invention, the wear amount is 1/2 or less as compared with the case of Experimental Example 15,
Especially excellent in abrasion resistance. On the other hand, in Experimental Example 28 in which the total thickness of the coating layer is 1.3 μm, which is below the lower limit of the fifteenth invention, it can be seen that the effect of the coating is slightly small. The total thickness of the coating layer is 6.3 μm
In Experimental Example 34 in which the upper limit of the fifteenth invention was exceeded, the coating layer peeled off at the beginning of the cutting test, and the effect of the coating decreased.

[0055]

EFFECTS OF THE INVENTION In the first and fifth aspects of the invention, a sintered body having a small amount of grain boundary glass phase containing a specific element is used, so that the compact has a high density and is particularly excellent in wear resistance at high temperatures. It is possible to obtain a silicon nitride sintered body for a tool which is suitable as a material for a tool or the like. In addition, in the seventh invention, a β-Si ₃ N ₄ having a large size in the sintered body is set to a specific amount or less, whereby a silicon nitride sintered body for a tool having excellent performance can be obtained.

Further, in the eighth and twelfth inventions, when a mixing tool made of aluminum oxide is used for mixing the raw material powder, aluminum oxide mixed into the raw material or aluminum produced by a sintering aid containing an aluminum element is used. By specifying the amounts of the components and adjusting the amounts of the other sintering aid components to the amounts commensurate with this mixed amount, it is possible to obtain a silicon nitride sintered body for tools which also has excellent compactness and wear resistance. Obtainable.

[Brief description of drawings]

FIG. 1A is a cross-sectional view of a work material for measuring a flank wear amount. Further, (B) is a vertical cross-sectional view of the work material for measuring the flank wear amount.

FIG. 2 is a front view of a work material after a cutting test for evaluating fracture resistance.

FIG. 3 is a front view of a work material when a flank wear amount is measured in order to confirm an effect of coating.

Claims (15)

[Claims] 1. A silicon nitride sintered body containing a magnesium element and a ytterbium element, wherein the magnesium element and the ytterbium element are each 0.16 to 2.25 when the silicon nitride sintered body is 100% by weight. 0
%, And 0.7 to 4.85% by weight, and the total amount of the magnesium element and the ytterbium element is 6.2% by weight or less. 2. The silicon nitride sintered body for a tool according to claim 1, which contains 2.15% by weight or less of oxygen element. 3. The total amount of the magnesium element and the ytterbium element is 5.2% by weight or less.
A silicon nitride sintered body for a tool as described. 4. The silicon nitride sintered body for a tool according to claim 3, which contains 1.74% by weight or less of an oxygen element. 5. A silicon nitride sintered body containing a magnesium component and a ytterbium component, wherein the magnesium component and the ytterbium component are converted into oxides when the silicon nitride sintered body is 100% by volume, It is respectively 0.25 to 3.0% by volume and 0.3 to 2.0% by volume, and the total amount of the magnesium component and the ytterbium component is 4.0% by volume or less. Silicon nitride sintered body for tools. 6. The total amount of the magnesium component and the ytterbium component is 2.5 vol% or less.
A silicon nitride sintered body for a tool as described. 7. β-Si ₃ N observed on a cut surface
_When the total of the cross-sectional areas of the ₄ particles is 100%, the total of the cross-sectional areas of the particles having a minor axis diameter of 1 μm or more is less than 10% and the cross-sectional area of the particles having a major axis diameter of 10 μm or more. The silicon nitride sintered body for tools according to claim 1, wherein the total is less than 4%. 8. A silicon nitride sintered body containing a magnesium element, a ytterbium element and an aluminum element,
When the silicon nitride sintered body is set to 100% by weight, the magnesium element and the ytterbium element are 0.16 to 1.00% by weight and 0.7 to 3.0% by weight, respectively.
And the aluminum element is 0.64% by weight.
The following (however, 0% by weight is not included) is the silicon nitride sintered body for tools characterized by the above-mentioned. 9. The silicon nitride sintered body for a tool according to claim 8, which contains 2.12% by weight or less of oxygen element. 10. The magnesium element is 0.16 to
0.67% by weight, the above aluminum element is 0.32
The silicon nitride sintered body for a tool according to claim 8, which is 0.64% by weight. 11. The silicon nitride sintered body for a tool according to claim 10, which contains 1.96% by weight or less of oxygen element. 12. In a silicon nitride sintered body containing a magnesium component, a ytterbium component and an aluminum component, the magnesium component and the ytterbium component are converted into oxides when the silicon nitride sintered body is 100% by volume. And 0.25 to 1.5% by volume and 0.3 to 1.2% by volume, respectively, and the aluminum component is 1.0% by volume or less (provided that 0
Volume% is not included. ) Is a silicon nitride sintered body for a tool. 13. The magnesium component is 0.25 to 0.25.
1.0% by volume, the aluminum component is 0.5 to 1.0
The silicon nitride sintered body for a tool according to claim 12, which has a volume percentage. 14. The silicon nitride sintered body for a tool according to claim 1, which has a porosity of 0.06% by volume or less. 15. Al ₂ O ₃ , AlON, Ti on the surface
7. At least one coating layer made of one of N, TiC and TiCN, wherein the outermost coating layer is made of TiN, and the total thickness of the coating layer is 1.5 to 6 μm. Any one of 1 to 14
A silicon nitride sintered body for a tool according to the item.