JPH08112705A - Cutting tool made of silicon nitride substance sintered body and its manufacture - Google Patents

Abstract

PURPOSE: To provide a cutting tool made of a silicon nitride matter sintered body which is excellent in strength, toughness and chipping resistance and capable of high speed feeding. CONSTITUTION: A cutting tool is mainly composed of β-Si3 N4 minute particle being less than 3μm in diameter, cylindrical β-Si3 N4 large particle being more than 3μm in diameter, and the grain boundary phase of oxide and/or nitride- oxide. In the section of an sintered body, the area of β-Si3 N4 large particle is from 2 area % to 40 area % of the sectional area of silicon nitride substance sintered body, and the average aspect ratio (=major axis/minor axis) of β-Si3 N4 large particle in a section cut in parallel to a tool face 1 is larger more than 5% than the average aspect ratio of β-Si3 N4 large particle in a section cut perpendicularly to the tool face 1.

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 cutting tool suitable for use in a wide range of cutting operations such as turning, milling, drilling and shaping, and a method for producing the same. It is a thing.

[0002]

2. Description of the Related Art A sintered body containing silicon nitride as a main component is used as a cutting tool because it has high hardness at room temperature and high temperature and high mechanical strength. In particular, it shows excellent performance in cutting cast iron, cutting speed 500 m
A sufficiently practical tool life has been achieved even in high-speed cutting of over / min.

Since silicon nitride is a compound having a strong covalent bond, it is difficult to sinter, and liquid phase sintering using an oxide-based sintering aid has been carried out. In this case, the oxide-based sintering aid is usually added in an amount of 5 to 20 mol%, and the sintering aid and silica produced by the oxidation of silicon nitride form a glass phase in the grain boundary, and the sintering of silicon nitride is performed. Is promoting.

As a raw material powder of silicon nitride, a raw material powder mainly containing α type has been used. Here, the raw material powder containing α type as a main component is used (1) α type is a fine powder and has high sinterability, and (2) phase transition from α type to β type during sintering. Occurs, and the columnar crystal has a developed structure to improve strength and toughness, and the like.

Further, a method of improving fracture toughness by using α-type silicon nitride as a raw material powder to grow some particles to a length of several tens of microns (In-
in situ composition (for example, Cera
m. Eng. Sci. Proc. , Volume 10, Nos. 7-8,
632-645, p. 1989) and the like.

The silicon nitride sintered body using the α type as a starting material has a structure in which β type columnar crystals are developed by the phase transition from the α type to the β type, so that the fracture toughness value is improved,
The generated β-type columnar crystals had irregular sizes and large variations in strength, and there was a problem in reliability when used as mechanical parts. For example, the above In-situ co
In mposite, although the fracture toughness was improved to 10 MPa√m or more, the Weibull coefficient was 20 or less.

On the other hand, as the silicon nitride powder containing β-type as a main component, a high-purity sintered grade powder and a low-purity powder used as a raw material of a refractory are known. And
As a sintered body using a silicon nitride powder containing β type as a main component as a raw material, one disclosed in JP-A-58-151371 is known.

In the sintering of the silicon nitride powder containing β-type as the main component, the size of the β-type columnar crystals produced is relatively uniform, and the variation in strength is small.

However, since the silicon nitride powder containing β-type as the main component has coarse particles and a low α-phase content, a columnar structure cannot be obtained and a high-strength sintered body cannot be obtained. It was not used as a raw material powder for producing a sintered body.

On the other hand, in Japanese Patent Application Laid-Open No. 6-9274 and Japanese Patent Application No. 5-55792, a silicon nitride powder containing fine β-type as a main component is used as a raw material and under a high nitrogen partial pressure. It is stated that the high temperature sintering makes it possible to obtain a sintered body having high strength and excellent toughness even when a silicon nitride powder mainly composed of β-type is used as a raw material.

A cutting tool produced by using the silicon nitride sintered body obtained by these inventions is a silicon nitride produced by a raw material of α-type silicon nitride powder in milling of cast iron. It was confirmed that the same performance as the cutting tool made of the sintered body was exhibited. In particular, as described above, in the sintering of the silicon nitride powder containing β-type as the main component, the sizes of the β-type columnar crystals produced are relatively well matched.
It is possible to obtain a cutting tool having a small variation in strength and a stable strength.

[0012]

However, no matter which α-type or β-type silicon nitride powder is used as a raw material, in the cutting tool made of a silicon nitride-based sintered body produced by the conventional production method, In terms of chipping resistance at the cutting edge, there still remains the problem of inferior reliability as compared with cemented carbide tools.

[0013]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and uses β-type silicon nitride powder as a raw material, the type and amount of a sintering aid, a method for molding a green compact, and a firing process. By adjusting the conditions, etc., the size, density, and distribution of columnar crystals of several microns or tens of microns in the sintered body can be controlled, there is little variation in characteristics, and high feed with excellent chipping resistance at the cutting edge. It is an object of the present invention to provide a cutting tool made of a silicon nitride-based sintered body capable of being manufactured.

[0014]

As described in claim 1, a cutting tool made of a silicon nitride sintered body according to the present invention comprises β-Si ₃ N ₄ fine particles having a particle size of less than 3 μm, It is mainly composed of columnar β-Si ₃ N ₄ coarse particles having a particle size of 3 μm or more and an oxide and / or oxynitride grain boundary phase, and has β-Si ₃ N ₄ coarse particles in the cross section of the sintered body. The area is 2 area% or more and 40 area% or less of the cross-sectional area of the silicon nitride sintered body, and the average aspect ratio of the β-Si ₃ N ₄ coarse particles in the cross section cut in the direction parallel to the tool rake surface ( = Long axis / minor axis) is larger than the average aspect ratio of β-Si ₃ N ₄ coarse particles in a cross section cut in a direction perpendicular to the tool rake surface by 5% or more.

Further, in an embodiment of the cutting tool made of a silicon nitride sintered body according to the present invention, as described in claim 2, in the silicon nitride sintered body, among yttrium and neodymium, In addition to containing one type or two types in total of 0.2% by weight or more and 5.0% by weight or less,
It may contain oxygen in an amount of 0.5% by weight or more and 2.0% by weight or less. Further, as described in claim 3, magnesium, aluminum, One or more of yttrium, scandium, and lanthanoids are contained in a total amount of 0.2% by weight to 5.0% by weight, and at least 0.5% by weight to 2.0% by weight of oxygen. Can be one.

In the method for manufacturing a cutting tool made of a silicon nitride sintered material according to the present invention, as described in claim 4, nitriding mainly composed of β type containing 80% by weight or more of β type silicon nitride. Silicon powder is used as a raw material powder, and 0.5% by weight of one or two oxides selected from yttrium oxide and neodymium oxide is added to the silicon nitride raw material powder.
5.0 wt% or less is added, and columnar β-Si ₃ N ₄ particles having a particle size larger than that of the silicon nitride raw material powder and serving as nuclei for growing coarse particles are added, followed by molding. As a result, the axial direction of the columnar β-Si ₃ N ₄ particles serving as the nuclei is two-dimensionally oriented in the direction parallel to the tool rake face, and the pressure is set to 1 at 1 to 500 atm under nitrogen gas pressure.
Baking at a temperature between 800 ° C and 2100 ° C, particle size 3μ
β-Si ₃ N ₄ fine particles of less than m, columnar β-Si ₃ N ₄ coarse particles having a particle size of 3 μm or more, and a grain boundary phase of oxide and / or oxynitride, and sintered. In the cross section of the body, the area of the β-Si ₃ N ₄ coarse particles is 2 area% or more and 40 area% or less of the cross-sectional area of the silicon nitride sintered body, and in the cross section cut in the direction parallel to the tool rake surface. beta-Si ₃ average aspect ratio of N ₄ coarse particles (= major axis / minor axis) is 5 than the average aspect ratio of beta-Si ₃ N ₄ coarse particles in a cross section cut in a direction perpendicular to the tool rake face The feature is that the sintered body is made larger by at least%.

Similarly, in the method for manufacturing a cutting tool made of a silicon nitride sintered body according to the present invention, as described in claim 5, nitriding mainly of β type containing 80% by weight or more of β type silicon nitride. Silicon powder is used as a raw material powder, and 0.5% by weight of one or more oxides selected from aluminum oxide, magnesium oxide, yttrium oxide, scandium oxide, and lanthanoid oxides is added to the silicon nitride raw material powder. 5.0% by weight or less is added, and further,
After the columnar β-Si ₃ N ₄ particles having a particle size larger than that of the raw material powder of silicon nitride and serving as a core for the growth of coarse particles are added, the columnar β serving as the core is formed by molding.
-Si ₃ N ₄ particles are two-dimensionally oriented in the direction parallel to the tool rake face, and sintered at a temperature of 1800 ° C to 2100 ° C under a nitrogen gas pressure of 1 atm to 500 atm, and a particle size of 3 µm. Of β-Si ₃ N ₄ fine particles having a particle size of less than 3 μm, columnar β-Si ₃ N ₄ coarse particles having a particle size of 3 μm or more, and a grain boundary phase of an oxide and / or an oxynitride, and a sintered body. The area of β-Si ₃ N ₄ coarse particles is 2 area% or more of the cross-sectional area of the silicon nitride sintered body in the cross section of 40% or more.
The average aspect ratio (= major axis / minor axis) of β-Si ₃ N ₄ coarse particles in the cross section cut in the area% or less and parallel to the tool rake surface is in the direction perpendicular to the tool rake surface. It is characterized in that the sintered body has a structure in which the average aspect ratio of the β-Si ₃ N ₄ coarse particles in the cut section is 5% or more.

In the embodiment of the method for manufacturing a cutting tool made of a silicon nitride sintered body according to the present invention, as described in claim 6, the particle size is larger and coarser than the silicon nitride raw material powder. The addition amount of columnar β-Si ₃ N ₄ particles, which serve as nuclei for grain growth, is 0.5% by weight or more and 5.0
%, And as described in claim 7, a columnar β-Si _{3 having a} particle size larger than that of the silicon nitride raw material powder and serving as a nucleus for the growth of coarse particles.
After adding the N ₄ particles, a molding selected from a uniaxial powder molding press, an extrusion molding, and an injection molding is performed, so that the axial direction of the columnar β-Si ₃ N ₄ particles serving as the core is changed to a tool rake face. On the other hand, the two-dimensional orientation can be performed in the parallel direction.

Further, in an embodiment of the method for producing a cutting tool made of a silicon nitride sintered body according to the present invention, the method of claim 8
, The oxygen content in the sintered body becomes 0.5 wt% or more and 2.0 wt% or less at a temperature of 1800 ° C. or more and 2100 ° C. or less under a nitrogen gas pressure of 1 atm or more and 500 atm or less. Can be fired up to.

[0020]

The cutting tool made of a silicon nitride sintered body according to the present invention is made of a raw material containing silicon nitride powder mainly composed of β type as a main component, and a sintering aid suitable for the β type silicon nitride powder. After controlling the type and amount of molding, pay attention to the distribution of the number and size of coarse particles in the sintered body, and fire it under the firing conditions that can obtain a sintered body with coarse particles of uniform size. According to the invention, it is newly invented that a cutting tool having high strength and excellent toughness as well as excellent chipping resistance of the cutting edge can be obtained.

That is, the method for producing a cutting tool made of a silicon nitride sintered body according to the present invention is, as described in claims 4 and 5, a β-type main body containing 80% by weight or more of β-type silicon nitride. As a raw material powder, the silicon nitride raw material powder is used, and 0.5 weight% of one or two oxides selected from yttrium oxide and neodymium oxide is added to the raw material powder of silicon nitride. % Or more and 5.0% by weight or less, or as described in claim 5, one or two selected from aluminum oxide, magnesium oxide, yttrium oxide, scandium oxide, and lanthanoid group oxides. 0.5% by weight or more and 5.0% by weight or less of an oxide of at least one kind is added, and the particle size is larger than that of the raw material powder of silicon nitride as described in claims 4 and 5. And after the columnar β-Si ₃ N ₄ particles serving as nuclei for the growth of coarse particles are added, the core columnar β-Si ₃ N ₄ particles serving as the core are subjected to molding to form the axial direction of the tool rake face. 180 degrees under nitrogen gas pressure of 1 atm to 500 atm
Firing is performed at a temperature of 0 ° C. or higher and 2100 ° C. or lower.

In molding the powder, 0.5% by weight or more and 5.0% by weight or more of the above oxide is added to the silicon nitride raw material powder.
After the addition of not more than wt%, an appropriate amount of columnar β-Si ₃ N ₄ particles having a particle size larger than that of the silicon nitride raw material powder and serving as nuclei for growth of coarse particles is added, and more desirably As described, after adding 0.5 to 5.0% by weight, as described in claim 7, it is molded by a molding method such as uniaxial powder molding press, extrusion molding, injection molding, The axial direction of the columnar β-Si ₃ N ₄ particles to be two-dimensionally oriented parallel to the tool rake face.

The sintered body is a columnar β-S having a particle size of less than 3 μm.
i ₃ N ₄ fine particles and columnar β-Si ₃ having a particle size of 3 μm or more
It is mainly composed of N ₄ coarse particles and a grain boundary phase of oxide and / or oxynitride, and the area of β-Si ₃ N ₄ coarse particles is the silicon nitride sintered body when the cross section of the sintered body is observed. 2 area% to 40 area% of the cross-sectional area of, and the average aspect ratio [λ / |] of the β-Si ₃ N ₄ coarse particles in the cross section cut in the direction parallel to the tool rake surface ( lambda = major axis / minor axis) of, β-Si ₃ N ₄ in a cross section cut in a direction perpendicular to the tool rake face
It is larger than the average aspect ratio [λ⊥] of coarse particles by 5% or more, and is a columnar β-Si with respect to the tool rake face.
_The ratio of orientation of ₃ N ₄ coarse particles is higher than that in the direction perpendicular to the tool rake face.

Next, in the cutting tool of the present invention,
The reason for limiting the manufacturing process, organization, etc. as described above will be explained.

(1) Silicon Nitride Powder as Raw Material In this method, the starting raw material powder is a silicon nitride powder mainly composed of β type containing 80% by weight or more of β type. When a silicon nitride powder mainly composed of β type is used as a starting material, columnar crystals develop due to grain growth of the added β type silicon nitride. Therefore, by adjusting the particle size of the raw material powder, it is possible to use a raw material having a uniform core size for grain growth. When this raw material powder is fired under appropriate conditions, a material having uniform β-type coarse particles is obtained.

On the other hand, when the α type is used as a starting material, the α type first undergoes a phase transition to the β type in the firing process. In this process, β-type particles of several microns are generated, and the subsequent grain growth occurs according to the particle size distribution of the generated particles. The size of β-type particles generated by the phase transition is difficult to control and has large variations, so the size of β-type coarse particles varies. Therefore, if the β type is less than 80% by weight, nuclei are generated due to the phase transition, and the variations in strength increase, and as a result, the reliability as a cutting tool decreases. Therefore, the starting material powder is β
A silicon nitride powder containing 80% by weight or more of a mold is used.

(2) Kind and amount of sintering aid Yttrium oxide and neodymium oxide described in claim 4, or aluminum oxide, magnesium oxide, yttrium oxide, scandium oxide and lanthanoid described in claim 5. Oxide is an effective sintering aid for promoting the sintering of silicon nitride, but if the total addition amount of one or more of these is less than 0.5% by weight, a dense sintered body will be obtained. Can't get On the other hand, if the sintering aid is excessive, the grain boundary glass layer becomes thick, which greatly affects the wear resistance when used as a cutting tool. In the past, in most cases, a sintering aid exceeding 5.0% by weight was used, but as in the present invention, the amount of the sintering aid is 5.0% by weight or less. As described above, by setting the oxygen content of the sintered body to 2.0% by weight or less, the wear resistance as a cutting tool can be remarkably improved.

(3) Amount of columnar β-Si ₃ N ₄ particles In addition to the above-mentioned sintering aid, the silicon nitride raw material powder has a particle size larger than that of the silicon nitride raw material powder and is used for the growth of coarse particles. An appropriate amount of columnar β-Si ₃ N ₄ particles serving as nuclei is added. In this case, when the addition amount of the columnar β-Si ₃ N ₄ particles is small, the growth of the coarse particles is not sufficient, and as the addition amount increases, the strength and the fracture toughness tend to improve, and the Weibull coefficient also increases. If the amount of the added nuclei is too large, the density of the powder compact decreases, and as a result, it becomes difficult to densify the sintered body, so that the nuclei for growing coarse particles as described in claim 6. The amount of columnar β-Si ₃ N ₄ particles to be added is preferably 0.5% by weight or more and 5.0% by weight or less.

(4) Powder Forming In the present invention, in powder forming, columnar β-Si ₃ N ₄ particles having a particle size larger than that of the raw material powder and serving as nuclei for growing coarse particles are added to the silicon nitride raw material powder. After adding an appropriate amount of the columnar β-
The axial direction of the Si ₃ N ₄ particles is oriented two-dimensionally in the direction parallel to the tool rake face. At this time, as described in claim 7, uniaxial powder molding press, extrusion molding, injection molding It is preferable that the axial direction of the columnar β-Si ₃ N ₄ particles to be the core is two-dimensionally oriented in the direction parallel to the tool rake surface by performing the molding by a method such as molding.

As a result, as shown in FIG. 1, β-Si in a cross section cut in a direction parallel to the tool rake face 1
₃ N ₄ average aspect ratio of coarse particles [λ‖] (λ = major axis / minor axis) is the average of the columnar beta-Si ₃ N ₄ coarse particles in a cross section cut in a direction perpendicular to the tool rake face 1 The aspect ratio [λ⊥] is more than 5%, and the ratio of columnar β-Si ₃ N ₄ particles oriented to the tool rake face 1 is compared to the direction perpendicular to the tool rake face 1. As a result, the cutting edge strength is higher than in the past.

On the other hand, the average aspect ratio [λ / |] of the β-Si ₃ N ₄ coarse particles in the cross section cut in the direction parallel to the tool rake face 1 and the cut in the direction perpendicular to the tool rake face 1 When the average aspect ratio [λ⊥] of the β-Si ₃ N ₄ coarse particles in the cross section is approximately equal to each other and the difference is less than 5%, the results of the example of the present invention and the comparative example will be described later. As can be seen, the effects and advantages of the present invention are not fully exhibited.

(5) Sintering Conditions High temperature sintering at 1800 ° C. or higher is required for densifying β-type silicon nitride powder when the amount of sintering aid is relatively small. When the firing temperature is less than 1600 ° C., densification does not occur, and when the heat treatment temperature is less than 1800 ° C., densification is possible, but the growth of coarse particles is incomplete, and a structure in which fine particles and coarse particles are mixed is obtained. I can't. At the time of sintering, the nitrogen gas pressure needs to be equal to or higher than the decomposition pressure of silicon nitride in order to prevent decomposition of silicon nitride. The minimum nitrogen gas pressure required is 1600 ° C to 1750 ° C, 1 atm, 1
It is 2 atm at 800 ° C., 5 atm at 1900 ° C., and 10 atm at 2000 ° C.

When the pressure is lower than the predetermined pressure, silicon nitride undergoes thermal decomposition and releases nitrogen to become silicon. However, under a nitrogen gas pressure exceeding 500 atm, the high-pressure gas remains in the sintered body, and as a result, densification does not occur. Further, high temperature sintering exceeding 2100 ° C. causes remarkable grain growth and lowers strength. The firing time and heat treatment time vary depending on the temperature and the type and amount of the auxiliary agent, but in general,
The firing time is preferably the minimum time at which densification is achieved. Also,
The heat treatment time is determined in consideration of the size, density and distribution of the coarse particles, but normally it is preferably 30 minutes to 4 hours. As described in claim 8, nitrogen gas of 1 atm or more and 500 atm or less is used. It is desirable to fire at a temperature of 1800 ° C. or more and 2100 ° C. or less under pressure until the amount of oxygen in the sintered body becomes 0.5 wt% or more and 2.0 wt% or less.

(6) Microstructure of cutting tool Since cutting tools require chipping resistance, the toughness and strength of the cutting edge are important. The toughness of silicon nitride largely depends on the columnar coarse crystal grains contained in the sintered body structure. In order to satisfy the toughness required as a tool, as described in claim 1, columnar β-Si ₃ N ₄ fine particles having a particle size of less than 3 μm and columnar β having a particle size of 3 μm or more.
-Si ₃ N ₄ coarse particles are mainly composed of oxide and / or oxynitride grain boundary phases, and the area of the β-Si ₃ N ₄ coarse particles is determined by observing the cross section of the sintered body. It must be 2 area% or more and 40 area% or less of the cross-sectional area of the material sintered body.

[0035]

EXAMPLES Next, a cutting tool made of a silicon nitride sintered body according to the present invention will be specifically described by way of Examples together with Comparative Examples.

As a raw material for the fine powder of silicon nitride, the average particle size is 0.5 μm, the maximum particle size is 2 μm, and the β-type content is 100% by weight.
The silicon nitride powder of was used. Further, as the nuclei for the growth of particles that become coarse particles after sintering, the average minor axis particle size of 1.
0 μm, average major axis particle size 5 μm, β-type content 100% by weight
Columnar silicon nitride particles were used. Then, to the silicon nitride fine powder raw material, silicon nitride particles serving as nuclei for grain growth were added in the range of 0.5 to 5.0% by weight.

Using these silicon nitride raw material powders and sintering aids, a total of 16 types of silicon nitride raw material powders as shown in Examples 1 to 9 and Comparative Examples 1 to 7 of the table were prepared and shown below. It was thus sintered. Here, Examples 1 to 1
3, 6 to 9 and Comparative Examples 1, 2, 4, and 5 are cases where yttrium oxide and neodymium oxide were used as sintering aids, and Examples 4, 5, and Comparative Examples 3, 6 and 7 were yttrium oxide and When aluminum oxide was used as the sintering aid, the amount of the sintering aid added in Examples 1 to 9 and Comparative Examples 4 to 7 was within the scope of the claims of the present invention. The sintering aid added in Examples 1 to 3 is outside the scope of the claims of the present invention.

The silicon nitride raw material powder obtained as described above was mixed with the types and amounts of sintering aids shown in the table, and the mixture was pulverized by a wet ball mill containing ethanol for 94 hours and then spray dried in air. And dried to obtain a granulated powder.

Next, with respect to this granulated powder, Examples 1 to 7 were applied.
And for Comparative Examples 1 to 7, after performing the die molding with a uniaxial powder molding press at a pressure of 20 MPa, 200 M
By applying a rubber press at a pressure of Pa, 15 x 1
Molded bodies of 5 × 8 mm and 6 × 6 × 50 mm were obtained. In this uniaxial powder molding press, the columnar β-
The direction was such that the axis of the Si ₃ N ₄ particles was oriented parallel to the rake face of the throwaway tip (tool rake face 1 shown in FIG. 1).

On the other hand, in Examples 8 and 9, the silicon nitride raw material powder having the same composition as that of Example 6 was used, and the pillar-shaped β-form which becomes the core was formed by the doctor blade method and the injection molding method in the molding of the throwaway tip. The axis of the Si ₃ N ₄ particles makes the orientation of the throwaway tip remarkable in the rake face direction. That is, in Example 8, a thin film having a thickness of several 100 μm was formed from a raw material dispersed in ethanol by a doctor blade method, and the thin film was dried and then laminated to form a thin film. Further, in Example 9, the organic binder and the raw material powder were kneaded and molded by injection molding.

These molded bodies were fired at 1900 ° C. for 2 hours under a nitrogen gas pressure of 100 atm using a graphite gas pressure furnace, and then at 2000 ° C. under a nitrogen gas pressure of 300 atm.
Burned for hours. Then, each sintered body obtained here is
Surface grinding with a 0 mesh diamond wheel, JI
Throw away tip S defined by SB 4121
It was processed into a shape of NMN433 (SNMN120412) and subjected to a cutting experiment.

At the same time, the bending strength was measured by carrying out a room temperature three-point bending test according to JIS R 1601. Furthermore, the Weibull coefficient of strength was also obtained from the bending test data of 20 pieces. Furthermore, JIS
SEPB method according to R 1607 (3 x 40 m of test piece
A fracture toughness value was obtained by applying a Vickers indentation to the surface of m, generating a precrack from this, and breaking from this precrack.

Furthermore, the cross section cut in the direction parallel and the direction perpendicular to the tool rake face is plasma-etched,
The aspect ratios [λ / |] and [λ /] of the β-Si ₃ N ₄ coarse particles in each cross section were measured for 50 particles or more by image processing, and the average aspect ratio was determined. .

The average aspect ratio [λ / |] of the β-Si ₃ N ₄ coarse particles in the cross section parallel to the tool rake surface thus obtained and the average in the cross section perpendicular to the tool rake surface From the aspect ratio [λ⊥], the ratio ([λ‖] / [λ⊥]) was calculated.

The tool wear test by continuous cutting was carried out under the following conditions.

Machine tool: CNC lathe (Murata W & S, WSC-8II) Holder: PSBNL2020 Chip shape: SNMG433 (corner R1.2) Cutting speed: 300 m / min Depth of cut: 2 mm Feed: 0.3 mm / rev Work material is It is gray cast iron (FC20), and the size of the cut portion is φ150 mm × 150 mm. Further, in order to investigate the limit feed amount, the cutting speed and the cutting conditions were set constant, and the feed was 0.5 within the range of 0.3 to 1.0 mm / rev.
The feed amount at which the cutting edge of the cutting edge was generated was examined by increasing the value per mm / rev. 10 tests for each tool
This was carried out one by one, and a 10% failure point was obtained based on the Weibull distribution, and this was taken as the limit feed amount.

For each of the sintered bodies obtained in the examples and comparative examples, the density, mechanical properties, orientation ratio of coarse particles to the tool rake face, wear width VB on the flank surface after cutting test,
The table shows the results of examining the maximum chipping amount at the cutting edge and the limit feed amount.

[0048]

[Table 1]

[0049]

[Table 2]

[0050]

[Table 3]

[0051]

[Table 4]

As shown in the table, all the cutting tools of Examples 1 to 9 have a large Weibull coefficient of bending strength and a small variation in strength. Further, in each of the examples, the variation in the cutting edge strength is small, and as a result, the minimum strength is also large, so that the critical feed amount is as large as 0.6 mm / rev or more.

On the other hand, when α-type silicon nitride is used as the raw material powder as in the cutting tools of Comparative Examples 5 to 7, the average strength is large, but the strength varies widely, and as a result, the minimum strength is small. Has become. Therefore, the limit feed amount is small.

That is, according to the present invention, a tool suitable for high feed cutting of cast iron can be obtained.

In Examples 1, 6 and 7, the amount of silicon nitride particles serving as nuclei was different, but the tendency was that as the amount of silicon nitride particles serving as nuclei increased, the strength and fracture toughness increased. , The Weibull coefficient also increases. In the cutting test, both the flank wear amount and the maximum chipping amount at the cutting edge decrease.

On the other hand, in Comparative Example 4 in which no nucleus was added, the tool wear amount, the cutting edge chipping amount, and the limit feed amount were inferior to those of the examples. Further, as in Examples 8 and 9, by adopting a doctor blade method or an injection molding method capable of further strengthening the orientation of the columnar silicon nitride particles, which are the core, toward the tool rake surface, as compared with the uniaxial press molding, It becomes possible to obtain a cutting tool excellent in wear and edge strength.

When the amount of the sintering aid is excessive as in Comparative Examples 1 to 3, the tool wear amount is larger than that of the cutting tool of the example. This is because the grain boundary glass layer has a great influence on the wear of the silicon nitride sintered body cutting tool.

[0058]

The cutting tool made of a silicon nitride sintered body according to the present invention has a particle size of 3 μm as described in claim 1.
Of β-Si ₃ N ₄ fine particles having a particle size of less than 3 μm, columnar β-Si ₃ N ₄ coarse particles having a particle size of 3 μm or more, and a grain boundary phase of an oxide and / or an oxynitride, and a sintered body. The area of β-Si ₃ N ₄ coarse particles is 2 area% or more and 40 area% or less of the cross-sectional area of the silicon nitride sintered body, and β in the cross section cut in the direction parallel to the tool rake surface. -Si ₃ N ₄ coarse particles have an average aspect ratio (= long axis / minor axis) of 5% than the average aspect ratio of β-Si ₃ N ₄ coarse particles in a cross section cut in a direction perpendicular to the tool rake face. Because of the above-mentioned large structure, it is possible to provide a cutting tool made of a silicon nitride sintered body having less variation in characteristics and excellent in wear resistance and chipping resistance. For example, it is excellent in milling cutting of cast iron. Show cutting performance Results in significantly better effect that also it is possible to provide a ceramic indexable capable of achieving sufficient practical tool life in high-speed cutting.

In an embodiment of the cutting tool made of a silicon nitride sintered body according to the present invention, as described in claim 2, in the silicon nitride sintered body, one of yttrium and neodymium is contained. In addition to containing one type or two types in total of 0.2% by weight or more and 5.0% by weight or less,
By containing 0.5% by weight or more and 2.0% by weight or less of oxygen, it is possible to promote sintering of silicon nitride and obtain a dense and high-strength sintered body. As described in claim 3, one or more of magnesium, aluminum, yttrium, scandium, and lanthanoid are contained in the silicon nitride sintered body in a total amount of 0.2% by weight or more. By containing not less than 5.0% by weight and not less than 0.5% by weight and not more than 2.0% by weight of oxygen, the sintering of silicon nitride is promoted, resulting in a dense and high-strength sintering. It can be the body.

The method for manufacturing a cutting tool made of a silicon nitride sintered body according to the present invention is, as described in claims 4 and 5, a β-type main body containing 80% by weight or more of β-type silicon nitride. As a raw material powder, the silicon nitride raw material powder of 1 is selected from yttrium oxide and neodymium oxide as described in claim 4.
0.5% by weight or more and 5.0% by weight of one or two oxides
The following addition is made, or as described in claim 5, one or more oxides selected from the oxides of aluminum oxide, magnesium oxide, yttrium oxide, scandium oxide, and randanoid are added.
5 wt% or more and 5.0 wt% or less is added, and as described in claims 4 and 5, a columnar particle having a larger particle size than the silicon nitride raw material powder and serving as a nucleus for the growth of coarse particles. after addition of β-Si ₃ N ₄ particles, are oriented two-dimensionally in the direction parallel to the tool rake face in the axial direction of the columnar β-Si ₃ N ₄ particles as the said nuclear by performing molding,
1800 ° C under nitrogen gas pressure of 1 atm to 500 atm
The temperature is 2100 ° C. or lower, and β-Si ₃ N ₄ fine particles having a particle size of less than 3 μm and columnar β having a particle size of 3 μm or more.
-Si ₃ N ₄ coarse particles and an oxide and / or oxynitride grain boundary phase are mainly formed, and the area of the β-Si ₃ N ₄ coarse particles in the cross section of the sintered body is a silicon nitride sintered body. The average aspect ratio of the β-Si ₃ N ₄ coarse particles in the cross section of 2 area% or more and 40 area% or less of the cross sectional area of
The minor axis) is set to be a sintered body that is larger than the average aspect ratio of β-Si ₃ N ₄ coarse particles in the cross section cut in the direction perpendicular to the tool rake surface by 5% or more, so that there is a variation in characteristics. It is possible to manufacture a cutting tool made of a silicon nitride sintered body, which has a small amount and is excellent in wear resistance and chipping resistance.

Then, as described in claim 6,
By adjusting the amount of columnar β-Si ₃ N ₄ particles having a particle size larger than that of the raw material powder of silicon nitride and serving as nuclei for the growth of coarse particles to be 0.5% by weight or more and 5.0% by weight or less. It is possible to grow the coarse particles satisfactorily, improve the strength and fracture toughness, and increase the Weibull coefficient.

In addition, as described in claim 7, after adding columnar β-Si ₃ N ₄ particles having a particle size larger than that of the silicon nitride raw material powder and serving as nuclei for the growth of coarse particles, , A uniaxial powder molding press, an extrusion molding, or an injection molding is performed, whereby the axial direction of the core-shaped β-Si ₃ N ₄ particles is two-dimensionally parallel to the tool rake face. It becomes possible to orient,
As a result, the columnar β-Si _{3 with} respect to the tool rake face
Since the ratio of the N ₄ coarse particles being oriented is higher than that in the direction perpendicular to the tool rake face, it is possible to further increase the cutting edge strength.

Further, as described in claim 8,
1800 ° C under nitrogen gas pressure of 1 atm to 500 atm
Above 2100 ° C., the oxygen content in the sintered body is 0.5
By firing until the content becomes not less than wt% and not more than 2.0 wt%, the excellent effect that the cutting tool made of a silicon nitride sintered body having a high density and improved strength and fracture toughness and a large Weibull coefficient is produced. Be done.

[Brief description of drawings]

FIG. 1 is an explanatory view of a slope of a throwaway tip which is a silicon nitride sintered body cutting tool according to the present invention.

[Explanation of symbols]

 1 Tool rake face 2 Tool flank face

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Yusuke Okamoto 2 Takaracho, Kanagawa-ku, Yokohama, Kanagawa Nissan Motor Co., Ltd.

Claims (8)

[Claims] 1. β-Si ₃ N ₄ fine particles having a particle size of less than 3 μm, columnar β-Si ₃ N ₄ coarse particles having a particle size of 3 μm or more, and an oxide and / or oxynitride grain boundary phase. The area of the β-Si ₃ N ₄ coarse particles in the cross section of the sintered body is 2 area% of the cross-sectional area of the silicon nitride sintered body.
The average aspect ratio (= major axis / minor axis) of β-Si ₃ N ₄ coarse particles in a cross section cut in a direction parallel to the tool rake surface is 40% or less and 40 area% or less with respect to the tool rake surface. Β-Si ₃ in a cross section cut at right angles
A cutting tool made of a silicon nitride sintered body, characterized in that it is larger than the average aspect ratio of N ₄ coarse particles by 5% or more. 2. The silicon nitride sintered body contains one or two of yttrium and neodymium in a total amount of 0.2% by weight or more and 5.0% by weight or less,
The silicon nitride sintered body cutting tool according to claim 1, wherein the cutting tool contains 0.5% by weight or more and 2.0% by weight or less of oxygen. 3. A silicon nitride sintered body containing one or more of magnesium, aluminum, yttrium, scandium and lanthanoids in a total amount of 0.
2% by weight or more and 5.0% by weight or less and 0.5
The cutting tool made of a silicon nitride sintered body according to claim 1, wherein the cutting tool contains oxygen of 2.0% by weight or more and 2.0% by weight or less. 4. A β-type silicon nitride powder mainly containing β-type silicon nitride in an amount of 80% by weight or more is used as a raw material powder, and one or two kinds selected from yttrium oxide and neodymium oxide are contained in this silicon nitride raw material powder. 0.5 wt% or more and 5.0 wt% or less of the above oxide is added, and the columnar β-Si ₃ N ₄ has a particle size larger than that of the silicon nitride raw material powder and serves as a nucleus for the growth of coarse particles. After the particles are added, molding is performed to form a columnar β-
The axial direction of the Si ₃ N ₄ particles is two-dimensionally oriented in the direction parallel to the tool rake face, and the particles are fired at a temperature of 1800 ° C. to 2100 ° C. under a nitrogen gas pressure of 1 atm to 500 atm, and a particle size of less than 3 μm Of β-Si ₃ N ₄ fine particles, columnar β-Si ₃ N ₄ coarse particles having a particle size of 3 μm or more, and a grain boundary phase of oxide and / or oxynitride. The area of the β-Si ₃ N ₄ coarse particles in the cross section is 2 area% or more and 40 area% or less of the cross-sectional area of the silicon nitride sintered body, and β-in the cross section cut in the direction parallel to the tool rake surface. The average aspect ratio of Si ₃ N ₄ coarse particles (= long axis / minor axis) is 5% or more than the average aspect ratio of β-Si ₃ N ₄ coarse particles in a cross section cut in a direction perpendicular to the tool rake surface. To make a large sintered body Method for producing a silicon nitride sintered body cutting tool made according to symptoms. 5. A raw material powder is a β-type silicon nitride powder containing 80% by weight or more of β-type silicon nitride, and the silicon nitride raw material powder is oxidized with aluminum oxide, magnesium oxide, yttrium oxide, scandium oxide and lanthanoid. 0.5% by weight or more and 5.0% by weight or less of one or more oxides selected from
Further, after adding columnar β-Si ₃ N ₄ particles having a particle size larger than that of the silicon nitride raw material powder and serving as nuclei for the growth of coarse particles, the columnar β-Si serving as the nuclei are formed by molding. The axial direction of the Si ₃ N ₄ particles is two-dimensionally oriented in the direction parallel to the tool rake face, and the particles are fired at a temperature of 1800 ° C. to 2100 ° C. under a nitrogen gas pressure of 1 atm to 500 atm, and a particle size of less than 3 μm Of β-Si ₃ N ₄ fine particles, columnar β-Si ₃ N ₄ coarse particles having a particle size of 3 μm or more, and a grain boundary phase of oxide and / or oxynitride. The area of β-Si ₃ N ₄ coarse particles in the cross section is 2 area% of the cross-sectional area of the silicon nitride sintered body.
The average aspect ratio (= major axis / minor axis) of the β-Si ₃ N ₄ coarse particles in the cross section cut in the direction parallel to the tool rake surface is 40 area% or less and the tool rake surface Β-Si ₃ in a cross section cut at right angles
A method for producing a cutting tool made of a silicon nitride sintered body, characterized in that a sintered body having a larger average aspect ratio of N ₄ coarse particles by 5% or more. 6. A columnar β-Si _{3 having a} particle size larger than that of the silicon nitride raw material powder and serving as a nucleus for the growth of coarse particles.
The method for producing a cutting tool made of a silicon nitride sintered body according to claim 4 or 5, wherein the amount of N ₄ particles added is 0.5% by weight or more and 5.0% by weight or less. 7. A columnar β-Si _{3 having a} particle size larger than that of the silicon nitride raw material powder and serving as a nucleus for the growth of coarse particles.
After adding the N ₄ particles, a molding selected from a uniaxial powder molding press, an extrusion molding, and an injection molding is performed, so that the axial direction of the core-shaped β-Si ₃ N ₄ particles becomes a tool rake face. 7. A method for manufacturing a cutting tool made of a silicon nitride sintered body according to claim 4, wherein the two-dimensional orientation is made parallel to it. 8. Firing at a temperature of 1800 ° C. or more and 2100 ° C. or less under a nitrogen gas pressure of 1 atm or more and 500 atm or less until the amount of oxygen in the sintered body becomes 0.5 wt% or more and 2.0 wt% or less. The method for manufacturing a cutting tool made of a silicon nitride sintered body according to any one of claims 4 to 7.