JP5275744B2 - Cutting insert, silicon nitride cutting tool, and method of manufacturing silicon nitride sintered body used for cutting insert - Google Patents

Description

  The present invention relates to a silicon nitride sintered body and a cutting tool formed of the silicon nitride sintered body.

  Conventionally, cast iron has been used as a material for automobile parts and the like. A silicon nitride sintered tool is widely used for processing cast iron. The silicon nitride sintered body tool has high fracture resistance, wear resistance, thermal shock resistance and the like when cutting cast iron (for example, cited reference 1).

  In recent years, metal parts such as automobile parts are being converted from cast iron to aluminum alloy for the purpose of reducing the weight of the parts. When an aluminum alloy is cut using a conventionally used silicon nitride sintered body tool, since a defect occurs in the silicon nitride sintered body tool, for example, a diamond sintered body tool, A carbide tool having a surface coated with a hard carbon film or the like is used (for example, cited reference 2 and cited reference 3). The diamond sintered body tool has the advantage of high wear resistance and long life, and can provide good cutting performance because of low reactivity between the aluminum alloy and the diamond sintered body. Coated carbide tools have the advantages of excellent wear resistance and low manufacturing costs.

Japanese Patent Laid-Open No. 11-139876 JP 2003-145316 A JP 11-291104 A

  However, the diamond sintered body tool has high reactivity with cast iron, so there is a problem that wear resistance is reduced when cutting a material made of aluminum alloy and cast iron, and there is a problem that cost is high because it is expensive. . Also, when performing high-efficiency high-speed cutting, the carbide tool has a problem of shortening the life due to increased wear when the cutting edge shape is sharply formed, or when a coating such as hard carbon is formed on the surface layer Further, there arises a problem of peeling of the coating film when cutting an aluminum alloy or a material made of aluminum alloy and cast iron.

  The above-described problems are not limited to automobile parts, but are also problems that occur when cutting materials made of aluminum alloys and aluminum alloys and cast iron used in various machines and devices.

  The present invention has been made in view of the above-described problems, and provides a silicon nitride sintered body tool having high wear resistance and fracture resistance at the time of cutting an aluminum alloy, a material made of aluminum alloy and cast iron. Objective.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
A silicon nitride-based sintered body produced by adding a sintering aid to silicon nitride and sintering, the main crystal phase comprising α-type silicon nitride and β-type silicon nitride, and the sintering And a proportion of the α-type silicon nitride in the silicon nitride-based sintered body is 35% or less, and two of the silicon nitride sintered body. A silicon nitride sintered body characterized in that the proportion of β-type silicon nitride having a major axis diameter of 2 μm or more in a dimensional cross-section is 10% or less.

  According to the silicon nitride sintered body of Application Example 1, the composition of the silicon nitride sintered body is such that the proportion of α-type silicon nitride in the silicon nitride-based sintered body is 35% or less, and the silicon nitride-based sintered body The proportion of the particle area of β-type silicon nitride having a major axis diameter of 2 μm or more on the two-dimensional cross section of the sintered body is 10% or less. Accordingly, since β-type silicon nitride particles having a needle shape are present in the composition of the silicon nitride sintered body, the effect of crack deflection in which β-type silicon nitride provides resistance to crack propagation can be obtained. In addition, the β-type silicon nitride is entangled with each other, so that toughness is improved. Therefore, the wear resistance and fracture resistance of the silicon nitride sintered body can be improved. Further, since the ratio of β-type silicon nitride having a major axis diameter of 2 μm or more is 10% or less, a sharp cutting edge useful for processing an aluminum alloy and a material made of aluminum alloy and cast iron can be obtained. Further, the fact that the α-type silicon nitride is 35% or less means that fine α-type silicon nitride is present appropriately, so that the β-type silicon nitride particles are coarsened. The effect of crack deflection can be obtained without causing the toughness to be improved.

[Application Example 2]
In the silicon nitride sintered body of Application Example 1, the major axis diameter of the β-type silicon nitride is 7 μm or less. According to the silicon nitride sintered body of Application Example 2, a sharp cutting edge useful for processing an aluminum alloy and a material made of the aluminum alloy and cast iron can be obtained.

[Application Example 3]
In the silicon nitride sintered body of Application Example 1 or Application Example 2, the ratio of the grain boundary phase on the two-dimensional cross section of the silicon nitride sintered body is 3 area% to 9 area%. According to the silicon nitride sintered body of Application Example 3, since sintering can be performed at a temperature lower than the conventional firing temperature of silicon nitride (about 1700 ° C. to 1900 ° C.), the particle shape of the silicon nitride sintered body is fine and Thus, a dense silicon nitride sintered body having a needle-like structure can be obtained.

[Application Example 4]
In the silicon nitride sintered body according to any one of Application Examples 1 to 3, the sintering aid includes magnesium (Mg) and a rare earth element. According to the silicon nitride sintered body of Application Example 4, magnesium is used as a sintering aid. Since magnesium can lower the liquid phase generation temperature with other sintering aids that form grain boundary phases and silicon oxide containing silicon nitride as an impurity, it suppresses the coarsening of silicon nitride particles, and Can be densified. In addition, rare earth elements react with other sintering aids to form grain boundary phases, densifying the sintered body, and forming silicon nitride needle-like particles to improve the mechanical properties of the silicon nitride sintered body. Can be improved. In addition, sintering aids containing ytterbium elements have a large effect of improving the sinterability of silicon nitride among sintering aids containing various rare earth elements, especially when combined with sintering aids containing magnesium elements. , Sinterability is further improved. Therefore, the silicon nitride particles can be made fine and acicular.

[Application Example 5]
In the silicon nitride sintered body of Application Example 4, the sintering aid contains 2 to 5% by weight of the magnesium (Mg) in terms of magnesium oxide (MgO), and ytterbium oxide (Yb) as a rare earth element. 3 to 11% by weight in terms of (Yb2O3). According to the silicon nitride sintered body of Application Example 5, the sintering aid contains 2 to 5% by weight of magnesium (Mg) in terms of magnesium oxide (MgO), and ytterbium (Yb) contains ytterbium oxide (Yb2O3). ) 3 to 11% by weight in terms of conversion. Therefore, segregation of the sintering aid and coarsening of the β-type silicon nitride can be suppressed, and a fine silicon nitride sintered body having a fine and needle-like structure can be obtained.

[Application Example 6]
A silicon nitride tool comprising a silicon nitride sintered body comprising a main crystal phase composed of α-type silicon nitride and β-type silicon nitride, and a grain boundary phase containing the sintering aid as a component In the silicon nitride sintered body, the proportion of α-type silicon nitride in the silicon nitride-based sintered body is 35% or less, and the major axis diameter on the two-dimensional cross section of the silicon nitride-based sintered body A silicon nitride-based tool characterized in that the proportion of the particle area of β-type silicon nitride having a diameter of 2 μm or more is 10% or less.

  According to the silicon nitride tool of Application Example 6, the proportion of α-type silicon nitride in the silicon nitride-based sintered body is 35% or less, and the long axis on the two-dimensional cross section of the silicon nitride-based sintered body The silicon nitride sintered body is characterized in that the proportion of the particle area of β-type silicon nitride having a diameter of 2 μm or more is 10% or less. Accordingly, a silicon nitride tool having high wear resistance and high fracture resistance can be provided.

[Application Example 7]
A cutting insert comprising a silicon nitride sintered body comprising a main crystal phase composed of α-type silicon nitride and β-type silicon nitride, and a grain boundary phase containing the sintering aid as a component, In the silicon nitride sintered body, the ratio of the silicon nitride-based sintered body to the α-type silicon nitride is 35% or less, and the major axis diameter of the silicon nitride-based sintered body on the two-dimensional cross section is 2 μm. A cutting insert in which the proportion of the particle area of the β-type silicon nitride is 10% or less.

  According to the cutting insert of Application Example 7, the ratio of the silicon nitride-based sintered body to the α-type silicon nitride is 35% or less, and the major axis diameter on the two-dimensional section of the silicon nitride-based sintered body is A silicon nitride sintered body characterized in that the ratio of the particle area of β-type silicon nitride of 2 μm or more is 10% or less is formed as a material. Therefore, it is possible to provide a cutting insert having high wear resistance and high fracture resistance.

[Application Example 8]
The cutting insert of Application Example 7 is characterized in that the surface is coated with an amorphous carbon film. According to the cutting insert of Application Example 8, the wear resistance and fracture resistance can be further improved.

[Application Example 9]
A silicon nitride cutting tool comprising: a mounting means for mounting a cutting insert; and the cutting insert of Application Example 7 or Application Example 8 mounted on the mounting means.

  According to the silicon nitride cutting tool of Application Example 9, the proportion of the silicon nitride-based sintered body in the α-type silicon nitride is 35% or less, and the long axis on the two-dimensional cross section of the silicon nitride-based sintered body The silicon nitride sintered body is characterized in that the proportion of the particle area of β-type silicon nitride having a diameter of 2 μm or more is 10% or less. Therefore, a silicon nitride cutting tool having high wear resistance and high fracture resistance can be provided.

[Application Example 10]
The silicon nitride cutting tool of Application Example 6 or Application Example 9 is characterized in that it is used for cutting an aluminum alloy material and a material composed of an aluminum alloy and cast iron. According to the silicon nitride cutting tool of Application Example 10, in cutting of an aluminum alloy material and a material composed of an aluminum alloy and cast iron, cutting having superior cutting performance as compared with conventional silicon nitride cutting tools and carbide tools. Tools can be provided.

[Application Example 11]
A method for producing a silicon nitride sintered body, in which a silicon nitride powder having an average particle size of 0.5 μm and an α-type silicon nitride occupying 95% or more and a sintering aid is a total of 100% by weight. The powder formed as a result of the mixing is molded to form a molded body, and the molded body is first fired at about 1500 ° C. to about 1550 ° C., and the primary fired molding is performed. A method for producing a silicon nitride sintered body, wherein the body is subjected to secondary firing at about 1450 ° C to about 1550 ° C.

  According to the method for producing a silicon nitride sintered body of Application Example 11, the green body is primarily fired at about 1500 ° C. to about 1550 ° C., and the primary fired green body is about 1450 ° C. to about 1550 ° C. Preferably, the silicon nitride sintered body is manufactured by performing secondary firing at about 1475 ° C. to about 1525 ° C. Therefore, since sintering can be performed at a temperature lower than the firing temperature of conventional silicon nitride, the particle shape of the silicon nitride sintered body can be made fine and acicular. Therefore, a high-strength silicon nitride sintered body can be manufactured.

[Application Example 12]
A method for manufacturing a silicon nitride cutting tool, in which a silicon nitride powder having an average particle size of 0.5 μm and an α-type silicon nitride occupying 95% or more and a sintering aid total 100% by weight. The powder formed as a result of the mixing is molded to form a molded body, the molded body is primarily sintered at about 1500 ° C., and the primary fired molded body is about A silicon nitride cutting tool which is subjected to secondary sintering at 1450 ° C. to about 1550 ° C., more preferably at about 1475 ° C. to about 1525 ° C., and the silicon nitride sintered body obtained by the secondary sintering is processed into a cutting tool. Manufacturing method.

  According to the silicon nitride cutting tool manufacturing method of Application Example 12, a cutting tool is manufactured by processing a silicon nitride sintered body generated by sintering at a temperature lower than the firing temperature of conventional silicon nitride. . Therefore, a cutting tool can be manufactured with a high-strength silicon nitride sintered body having a fine needle-like particle composition and a needle-like structure. Therefore, a silicon nitride cutting tool having high wear resistance and high fracture resistance can be provided.

  In the present invention, the various aspects described above can be applied by appropriately combining or omitting some of them.

A. First embodiment:
The silicon nitride sintered body, cutting insert, and silicon nitride cutting tool of the first embodiment will be described below with reference to the drawings as appropriate.

A1. Production method:
FIG. 1 is a flowchart for explaining a method of manufacturing a silicon nitride cutting tool in the first embodiment. FIG. 2 is an explanatory view illustrating a cutting insert in the first embodiment. FIG. 3 is a front view showing the silicon nitride cutting tool in the first embodiment. FIG. 4 is a plan view showing the silicon nitride cutting tool in the first embodiment. The cutting insert shown in FIG. 2 is an insert manufactured by the manufacturing method shown in FIG. 3 and 4 show the silicon nitride cutting tool with the cutting insert attached.

  A silicon nitride powder having an average particle size of 0.5 μm and an α ratio of 95% and a sintering aid are blended to a total of 100% by weight, and the blended powder is mixed with ethanol in a ball mill for about 40 hours. Then, a mixture (slurry) is produced, and then the slurry is granulated by hot water drying to form a powder (step S10). In the first embodiment, the α rate represents the proportion of α-type silicon nitride powder contained in all powders to be blended. Hereinafter, in this specification, α-type silicon nitride is referred to as α-type silicon nitride. In the first embodiment, magnesium (Mg) and a rare earth element are used as the sintering aid, and in particular, ytterbium (Yb) is used as the rare earth. In the sintering aid of the first example, magnesium (Mg) is contained in an amount of 2 to 5% by weight in terms of magnesium oxide (MgO), and ytterbium (Yb) is 3 to 11% in terms of ytterbium oxide (Yb2O3). %include. In addition, the silicon nitride sintered body used for processing the aluminum alloy is a silicon nitride sintered body for the purpose of cast iron processing in order to make the silicon nitride particles in the sintered body structure fine and acicular. On the other hand, it is preferable to add a large amount of sintering aid, and magnesium (Mg) and ytterbium (Yb) are about 7 wt% to about 15 wt% in total in terms of magnesium oxide (MgO) and ytterbium oxide (Yb 2 O 3). %, Preferably about 7 wt% to about 13 wt%.

  Next, the granulated powder is molded by cold isostatic pressing (CIP) molding at 1500 kgf / cm @ 2 (step S12).

  Subsequently, the molded body molded by CIP molding is subjected to primary firing (step S14). Specifically, the compact is stored at about 1500 ° C. to 1550 ° C. for 2 hours under a nitrogen (N 2) atmosphere of 1 atm.

  Subsequently, the primary fired compact is secondarily fired (step S16). Specifically, the primary fired molded body is held at about 1450 ° C. to about 1550 ° C., more preferably about 1475 ° C. to about 1525 ° C. for about 4 hours in a nitrogen (N 2) atmosphere of 1000 atm. . As a result, the silicon nitride sintered body of the first embodiment is obtained.

  Next, the obtained silicon nitride sintered body is polished into a predetermined tool shape to obtain a cutting insert (step S18). In the first embodiment, as shown in FIG. 2, the predetermined tool shape is the ISO standard and SNGN432 size (vertical 12.7 mm, horizontal 12.7 mm, height 4.76 mm, no honing). In the first embodiment, the cutting edge of the cutting insert 2 is not chamfered, but chamfering (for example, a chamfering width of 0.3 mm and a chamfering angle of 25 °) is performed to form a chamfered portion. May be. As shown in FIGS. 3 and 4, the cutting insert 2 is set on a cutting tool with a holder (milling cutter) 4 to obtain a silicon nitride cutting tool (step S20). The surface of the cutting insert 2 may be coated with amorphous carbon. The amorphous carbon coating can suppress welding when the aluminum alloy is cut.

  The silicon nitride cutting tool (milling cutter) 4 equipped with the cutting insert 2 will be described. As shown in FIGS. 3 and 4, the milling cutter 4 has a substantially cylindrical cutter body main body (holder) 5, along the outer periphery of the tip side (processing surface side: front side of FIG. 3), Recessed cutting portions 6 are provided at six locations. That is, along the outer periphery on the front end side of the holder 5, concave mounting portions 7 are provided at six locations, and the cutting insert 2 and the alloy steel cartridge 8 for mounting the cutting insert 2 in the mounting portion 7, A member such as a wedge 9 made of the same alloy steel is arranged to constitute the cutting portion 6. One cutting insert 2 is attached to one mounting portion 7 of the milling cutter 4. 3 and 4, some members such as the cutting insert 2 are omitted in order to clarify the structure of the silicon nitride cutting tool.

  FIG. 5 is a schematic diagram showing the crystal composition of the silicon nitride sintered body in the first embodiment. FIG. 5A shows the crystal composition after secondary firing. FIG. 5B shows the diameter of β-type silicon nitride. The crystal composition 100 includes an α-type silicon nitride 101 that is fine particles and a crystal phase 110 that includes β-type silicon nitride (hereinafter referred to as β-type silicon nitride) 103 that is needle-like particles. And a grain boundary phase 120 containing a sintering aid component, which is present between the α-type silicon nitride and β-type silicon nitride particles. In the first example, the major axis diameter and minor axis diameter of the β-type silicon nitride particles were determined by mirror-polishing the silicon nitride sintered body, etching, and photographing the structure with a scanning electron microscope (SEM) (FIG. 5 ( a)) A photographed image is image-analyzed and measured. The photographed image corresponds to a two-dimensional cross section of the silicon nitride sintered body. As shown in FIG. 5 (b), the largest width portion of one particle of β-type silicon nitride is the major axis diameter (X) of the particle, and the largest width in a direction substantially perpendicular to the major axis. The portion where is small is the minor axis diameter (Y) of the particles. In the first example, the ratio of the grain boundary phase 120 on the two-dimensional cross section of the silicon nitride sintered body is 3 area% to 9 area%. According to the above manufacturing method, sintering can be performed at a temperature lower than the conventional firing temperature of silicon nitride (about 1700 ° C. to 1900 ° C.). When the firing temperature of silicon nitride increases, relatively large particles in the sintered body absorb surrounding fine particles and become further coarsened. Therefore, by lowering the firing temperature of silicon nitride, the coarseness of the particles In other words, it is possible to make the particles finer (in the case of silicon nitride, the grains grow in a columnar shape, so that they become acicular). Therefore, the silicon nitride sintered body can be a fine silicon nitride sintered body having a fine and acicular structure.

  In the silicon nitride sintered body of the first embodiment, the α ratio in the silicon nitride-based sintered body is 35% or less, and the major axis diameter on the two-dimensional section of the silicon nitride-based sintered body is 2 μm or more. The proportion of the β-type silicon nitride particle area is 10% or less. The α ratio is more preferably 25% or less, and the proportion of the particle area of β-type silicon nitride having a major axis diameter of 2 μm or more is more preferably 5% or more. The major axis diameter of β-type silicon nitride is preferably 7 μm or less. The α ratio in the silicon nitride-based sintered body means the abundance of the α phase (α-type silicon nitride phase) in the cooled silicon nitride sintered body. Here, the α ratio of the silicon nitride-based sintered body being 35% or less means the following. That is, usually, when a sintering aid is added to the raw material α-type silicon nitride powder and fired, it is in phase with the β phase (β-type silicon nitride phase) of the high temperature layer during the temperature rising and during the temperature holding. This means that the α phase is present in a ratio of 35% or less in the sintered body after cooling.

  The α rate of the silicon nitride-based sintered body is expressed by the following formula 1. In Equation 1, the X-ray diffraction intensity of the index (hkl) of α-type silicon nitride is expressed as α (hkl), and the X-ray diffraction intensity of the index (hkl) of β-type silicon nitride is expressed as β (hkl).

  The reason why the α ratio of the silicon nitride-based sintered body is set to 35% or less is as follows. That is, when the α ratio of the silicon nitride-based sintered body is higher than 35%, the sintered body structure itself is refined, but the ratio of acicular β-type silicon nitride is small, so the effect of crack deflection is reduced. This is because the toughness is lowered and the wear resistance and fracture resistance are lowered.

  The ratio of the particle area of β-type silicon nitride having a major axis diameter of 2 μm or more on the two-dimensional cross section of the silicon nitride-based sintered body is set to 10% or less for the following reason. That is, when acicular β-type silicon nitride is present, the strength is improved by becoming a resistance to the crack propagation of the silicon nitride sintered body, and the acicular β-type silicon nitride is entangled with each other, and the strength is further improved. . Therefore, high wear resistance and fracture resistance can be obtained. Further, by setting the major axis diameter of β-type silicon nitride to 2 μm or less, it is possible to obtain a sharp cutting edge effective for cutting an aluminum alloy and a material made of aluminum alloy and cast iron.

  Further, on the two-dimensional cross section of the silicon nitride-based sintered body, the ratio of the particle area of β-type silicon nitride having a major axis diameter of 2 μm or more is set to 5% or more, so that the β type having a major axis diameter of 2 μm or more The abrasion resistance and fracture resistance of the silicon nitride-based sintered body can be improved as compared with the case where the proportion of the silicon nitride particle area is less than 5%.

  In addition, the presence of particles having a major axis diameter larger than 7 μm in β-type silicon nitride means that a large amount of β-type silicon nitride having a larger major axis diameter exists as a whole and that the α ratio is low. Therefore, it is considered that the wear resistance and fracture resistance of the silicon nitride-based sintered body are lowered. Therefore, by producing a silicon nitride sintered body so that the major axis diameter of β-type silicon nitride is 7 μm or less, a sharp cutting edge useful for processing an aluminum alloy and a material made of aluminum alloy and cast iron is obtained. Can do.

  According to the silicon nitride sintered body of the first embodiment described above, the composition of the silicon nitride sintered body is such that the ratio of α-type silicon nitride in the silicon nitride-based sintered body is 35% or less, and The ratio of the particle area of β-type silicon nitride having a major axis diameter of 2 μm or more is 10% or less. Accordingly, since β-type silicon nitride particles having a needle shape are present in the composition of the silicon nitride sintered body, β-type silicon nitride provides resistance to crack propagation, and β-type silicon nitride is Toughness is improved by intertwining each other. Therefore, the wear resistance and fracture resistance of the silicon nitride sintered body can be improved. Further, since the ratio of the particle area of β-type silicon nitride having a major axis diameter of 2 μm or more is 10% or less, a sharp cutting edge useful for processing an aluminum alloy and a material made of aluminum alloy and cast iron can be obtained. Further, the fact that the α-type silicon nitride is 35% or less means that fine α-type silicon nitride is present appropriately, so that the β-type silicon nitride particles are coarsened. The effect of crack deflection can be obtained without causing the toughness to be improved.

  In the silicon nitride sintered body of the first embodiment, the proportion of the particle area of β-type silicon nitride having a major axis diameter of 2 μm or more on the two-dimensional cross section of the silicon nitride-based sintered body is 5% or more. It is. According to the silicon nitride sintered body of Application Example 1, 5% to 10% of β-type silicon nitride having a major axis diameter of 2 μm or more is included in the composition of the silicon nitride sintered body. Therefore, β-type silicon nitride particles having a needle shape can be appropriately present in the composition of the silicon nitride sintered body, and toughness can be improved.

  Moreover, according to the silicon nitride sintered body of the first embodiment, the sintering aid contains 0.5 to 5 wt% of magnesium (Mg) in terms of magnesium oxide (MgO), and ytterbium (Yb ) Is contained in an amount of 3 to 11% by weight in terms of ytterbium oxide (Yb2O3). Therefore, since it can be fired at a temperature of about 1450 ° C. to 1550 ° C. (lower than the firing temperature of conventional silicon nitride), the phase transition of α-type silicon nitride to β-type silicon nitride is suppressed, and β-type Expansion of the silicon nitride diameter is suppressed. Therefore, a fine silicon nitride sintered body having a fine and needle-like structure can be obtained.

A2. Evaluation of cutting performance:
The performance of the silicon nitride sintered body produced by the above production method will be described below in comparison with a comparative example. FIG. 6 is images showing the structures of the silicon nitride sintered body of the first embodiment and the conventional silicon nitride sintered body, respectively. FIG. 7 is a schematic diagram for explaining milling in the first embodiment. Table 1 shows the composition (wt%) of the silicon nitride sintered bodies (Example Samples 1 to 8) obtained by the above-described manufacturing method and the silicon nitride sintered bodies of Comparative Examples (Comparative Example Samples 9 to 14). ) Primary firing temperature (° C.), secondary firing temperature (° C.), proportion (%) of β-type silicon nitride having a major axis diameter of 2 μm or more in the two-dimensional cross section of the silicon nitride sintered body, The maximum major axis diameter (μm) of silicon nitride, the α ratio (%) of the silicon nitride sintered body, and the grain boundary phase amount (area%) are shown. Table 1 also shows the fracture resistance evaluated by the method described later in the column “Deficiency”. Hereinafter, in this specification, samples 1 to 8 of the silicon nitride sintered body obtained by the manufacturing method of the examples are referred to as example samples 1 to 8, and samples 9 to 14 of the silicon nitride sintered body as a comparative example. Are referred to as Comparative Samples 9-14.

  In Table 1, the major axis diameter and minor axis diameter of the silicon nitride particles are obtained by mirror-polishing a silicon nitride sintered body, etching, photographing the structure with a scanning electron microscope (SEM), and enlarging the magnification by 5000 times. Was measured by image analysis. Further, the amount of grain boundary phase in the silicon nitride sintered body is obtained by observing the mirror-polished surface of the cross section obtained by cutting the central portion of the silicon nitride sintered body by SEM, and then converting the obtained structure photograph into two gradations, It was measured by analyzing with image analysis software. In this embodiment, WinROOF manufactured by Mitani Corporation was used as the image processing software. Further, the α ratio of the silicon nitride sintered body was calculated using the calculation formula shown in the above-described formula 1.

  Table 2 shows the measurement results of the characteristics of Example Samples 1 to 3 and conventional silicon nitride sintered bodies (Comparative Samples 9, 13, and 14) as comparative examples.

  In Table 2, as properties, strength (MPa), toughness (MPa / m0.5), hardness (Hv), and thermal conductivity (W / mK) were measured. The measurement method and value of each characteristic will be described. The strength was measured by three-point bending strength measurement based on JIS R1601. Fracture toughness was measured by the IF method based on JISR1607. Hardness was measured by the Vickers hardness test method based on JISR1610. The thermal conductivity was measured by a laser flash method based on JIS R1611.

  6A shows the structure of the silicon nitride sintered body of Example Sample 3, and FIG. 6B shows the structure of the silicon nitride sintered body of Comparative Example Sample 9. In FIG. 6, the black area represents the crystal phase, and the white area represents the grain boundary phase. As shown in FIGS. 6A and 6B, the silicon nitride sintered body of Example Sample 3 has a fine needle shape as compared with the silicon nitride sintered body of Comparative Sample 9. It has become. By adopting such a particle shape, the fine needle-like β-type silicon nitrides are entangled with each other and the strength and hardness are improved. Moreover, toughness is substantially maintained.

  The cutting inserts of Example Samples 1 to 8 and Comparative Example Samples 9 to 14 are set in a holder for a 6-tooth milling cutter for face milling shown in FIG. 4, and cutting is performed under the following cutting test conditions. Abrasion resistance and fracture resistance were evaluated. The cutting insert 2 was not subjected to honing (chamfering) processing. Specifically, in the evaluation test, as shown in FIG. 7, the milling cutter 4 is attached to the rotating shaft 4a, and the aluminum alloy 200 to be cut is fixed to the table. The surface 200a of the aluminum alloy 200 is cut by moving the milling cutter 4 in a direction perpendicular to the rotation shaft 4a (in the direction of arrow R2 in FIG. 7) while rotating the rotation shaft 4a as indicated by the arrow R1. . Hereinafter, in this specification, the number of times the milling cutter 4 has scanned the work material (aluminum alloy in the first embodiment) 200 in the direction of the arrow R2 is referred to as “pass”. For example, when the milling cutter 4 scans the work material 200 twice, the number of passes is represented by two. In Table 1, in the column of “defect”, defect resistance is shown, and “A” is attached to a sample having 10 or more passes until the defect is generated by this cutting test. Samples 2 to 9 were marked with “B”, and samples with 1 or 0 passes were marked with “C”.

<Cutting test conditions>
・ Work material: Aluminum alloy (AC4A-T6)
Cutting speed: 1000 m / min.
・ Feeding speed: 0.1 mm / blade ・ Incision depth: 1 mm
・ Cutting oil: wet (uses water-soluble coolant)

  As shown in Table 1, excellent fracture resistance was obtained in Example Samples 1 to 8, whereas defects were generated in Comparative Example Samples 9 to 14 in 1 to 9 passes.

  FIG. 8 is a graph showing the evaluation results on the amount of wear (mm) of the flank of the tool edge by the continuous cutting test of the aluminum alloy for the silicon nitride cutting tool in the first example. FIG. 8 shows the amount of wear on the flank face of the tool edge by a continuous cutting test of an aluminum alloy using the cutting insert of Example Sample 3 as an example of the example and the cemented carbide tool (type K carbide) as a comparative example. The evaluation result about (mm) was shown. Table 3 shows the flank of the cutting edge of the cutting edge of a continuous cutting test of an aluminum alloy using the cutting inserts of Example Samples 1 to 8 and Comparative Example Sample 10 and the cutting inserts of a carbide tool (type K carbide). The evaluation results for the amount of wear (mm) and the occurrence of defects were shown.

  Each of FIG. 8 and Table 3 represents the result of an evaluation test performed under the following cutting test conditions. In the graph 300 of FIG. 8, the vertical axis represents the amount of wear (mm) of the flank of the cutting insert, and the horizontal axis represents the number of passes of cutting. In the graph 300, as an example, the wear amount of the cutting insert of Example Sample 3 and the wear amount of the cutting insert of the carbide tool (K-type carbide) are shown. In addition, in the cutting insert formed by the silicon nitride sintered body of the comparative example sample, it is lost within 9 passes, and it is difficult to measure the wear amount. Therefore, as a comparative example, a carbide tool (K type carbide) ) Was used. The amount of wear of each sample and carbide tool in Table 3 is an example. In Table 3, the column of “defect” indicates defect resistance. “A” is attached to a sample in which no defect is generated by this cutting test, and defect is generated for a sample in which the defect has occurred. The number of passes is listed. In addition, a continuation test was further performed on samples in which no defects occurred, and “S” was assigned to samples in which defects did not occur even at the time of 40 passes.

<Cutting test conditions>
・ Work material: Aluminum alloy (AC4A-T6)
Cutting speed: 1000 m / min.
・ Feeding speed: 0.1 mm / blade ・ Incision depth: 1 mm
・ Cutting oil: wet (uses water-soluble coolant)
・ Number of passes: 30 passes

  As shown in the graph 300, the cutting insert of the example sample 3 and the cutting insert of the cemented carbide tool (K type carbide) as a comparative example wear with the increase in the number of passes of the cutting process. The amount of wear of this cutting insert is smaller than that of a cutting insert of a carbide tool (K-type carbide). For example, when 30 passes are completed, the wear amount of the cutting insert of Example Sample 3 is about 1/3 of the cutting insert of the carbide tool.

  As shown in Table 3, excellent fracture resistance was obtained with the example samples. Also, excellent wear resistance was obtained for carbide tools (K-type carbide). In addition, about the comparative example sample 10, since the defect | deletion generate | occur | produced in the 7th pass, the abrasion loss at the time of a defect generation | occurrence | production was shown.

  As described above, according to the silicon nitride cutting tool of the first embodiment, in cutting an aluminum alloy, a cutting tool having superior cutting performance compared to conventional silicon nitride cutting tools and carbide tools is provided. it can.

B. Second embodiment:
In the second embodiment, a material made of aluminum alloy and cast iron is used as a work material in the performance evaluation test. In the second embodiment, the sample for producing the silicon nitride sintered body, the silicon nitride sintered body, the cutting insert, and the method for manufacturing the silicon nitride cutting tool are the same as in the first embodiment.

B1. Evaluation of cutting performance:
FIG. 9 is an explanatory view illustrating a work material in the second embodiment. FIG. 10 is a schematic diagram for explaining milling in the second embodiment. FIG. 11 is a graph showing the results of the abrasion resistance test in the second example. As shown in FIGS. 9 and 10, the work material 500 of the second embodiment has a rectangular column shape smaller than the aluminum alloy 510 between the two rectangular columnar aluminum alloys 510 and the two aluminum alloys 510. This is an aluminum alloy / cast iron composite member in which two cast irons 520 are arranged. Hereinafter, the work material 500 is referred to as an aluminum alloy / cast iron composite member 500. The cutting edge of Example Samples 1 to 8, Comparative Example Sample 10 (see Table 1 described in the first example) and carbide (K-type carbide) cutting inserts are shown in FIG. The aluminum alloy / cast iron composite member 500 shown in FIG. 9 was cut under the cutting test conditions shown below, and the wear resistance and fracture resistance were evaluated. As in the first embodiment, the milling cutter 4 is moved in the direction perpendicular to the rotating shaft 4a (the direction of the arrow R2 in FIG. 10) while rotating the rotating shaft 4a of the milling cutter 4 as indicated by the arrow R1. Thus, the surface of the aluminum alloy / cast iron composite member 500 is cut.

  FIG. 11 shows continuous cutting of an aluminum alloy / cast iron composite member 500 using the cutting insert of Example Sample 3 and a cemented carbide tool (K-type carbide) as a comparative example, an alumina + SiC whisker-based tool, and Comparative Sample 10. The evaluation result about the abrasion amount (VB) of the tool blade edge by the test was shown. Table 4 shows the clearance of the tool edge by the continuous cutting test of the aluminum alloy / cast iron composite member 500 using the cutting inserts of Example samples 1 to 8, the comparative example sample 10, and the carbide tool (K-type carbide). The evaluation result about the abrasion amount (mm) of a surface and generation | occurrence | production of a defect | deletion was shown.

  Each of FIG. 11 and Table 4 represents the result of an evaluation test performed under the following cutting test conditions. In the graph 600 of FIG. 11, the vertical axis represents the wear amount (mm) of the flank of the cutting insert, and the horizontal axis represents the number of passes of cutting. The amount of wear of the silicon nitride sintered body and the cemented carbide tool in each sample in Table 3 is an example. In Table 4, the “Deficit” column shows flaw resistance, and “A” is attached to a sample in which no deficiency occurs by this cutting test, and deficiency occurs for a sample in which a deficiency has occurred. The number of passes is listed.

(Cutting test conditions)
Work material: Aluminum alloy (AC4A-T6) + cast iron (FC200)
Work material ratio: Aluminum alloy (56 percent), cast iron (13 percent), idling (31 percent)
Cutting speed: 1000 m / min.
・ Feeding speed: 0.1 mm / blade ・ Incision depth: 0.5 mm
・ Cutting oil: wet (uses water-soluble coolant)
・ Number of passes: 10 passes

  As shown in the graph 600, with the increase in the number of cutting passes, the cutting insert of Example Sample 3 is also a carbide tool (K type carbide) as a comparative example, an alumina + SiC whisker-based tool, and a comparative sample 10 Although it is worn, the amount of wear of the cutting insert of Example Sample 3 is smaller than that of the carbide tool (K type carbide), the alumina + SiC whisker-based tool, and the comparative sample 10. For example, a carbide tool (K type carbide) has a large wear surface roughness at the end of the first pass, and an alumina + SiC whisker tool has a large wear surface roughness at the end of the third pass. The wear is so great that the test must be finished in the third pass, that is, the wear is so difficult that it is difficult to compare the wear resistance with Example Sample 3. The comparative sample 10 has a defect at the sixth pass, and the wear amount at the time when the tenth pass is finished is larger than that of the cutting insert of the example sample 3.

  Further, as shown in Table 4, excellent fracture resistance was obtained in Example Samples 1 to 6. Also, excellent wear resistance was obtained for carbide tools (K-type carbide). In addition, with respect to the comparative sample 10, defects occurred in the sixth pass. In addition, the carbide tool (K type carbide) finished the test in one pass because the wear surface of the work material was very rough.

  The silicon nitride sintered body of the second embodiment described above has the same effect as that of the first embodiment. Moreover, according to the silicon nitride cutting tool of the second embodiment, it is superior to conventional silicon nitride cutting tools and carbide tools in cutting an aluminum alloy / cast iron composite member made of an aluminum alloy and cast iron. A cutting tool having high cutting performance can be provided.

  As mentioned above, although the various Example of this invention was described, this invention is not limited to these Examples, A various structure can be taken in the range which does not deviate from the meaning.

The flowchart explaining the manufacturing method of the silicon nitride cutting tool in 1st Example. Explanatory drawing which illustrates the cutting insert in 1st Example. The front view showing the silicon nitride cutting tool in 1st Example. The top view showing the silicon nitride cutting tool in 1st Example. The schematic diagram showing the composition of the crystal | crystallization of the silicon nitride sintered compact in 1st Example. The image showing the structure | tissue of the silicon nitride sintered compact of 1st Example, and the conventional silicon nitride sintered compact, respectively. The schematic diagram explaining the milling process in 1st Example. The graph showing the abrasion resistance test result in 1st Example. Explanatory drawing which illustrates the work material in 2nd Example. The schematic diagram explaining the milling process in 2nd Example. The graph showing the abrasion resistance test result in 2nd Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 2 ... Cutting insert 4 ... Milling cutter 4a ... Rotating shaft 5 ... Holder 6 ... Cutting part 7 ... Mounting part 8 ... Cartridge 9 ... Wedge 100 ... Crystal composition 101 ... alpha silicon nitride 103 ... beta silicon nitride 110 ... crystal phase 120 ... Grain boundary phase 200 ... Aluminum alloy 200a ... Surface 300 ... Graph 500 ... Aluminum alloy / cast iron composite member 510 ... Aluminum alloy 520 ... Cast iron 600 ... Graph

Claims (5)

A cutting insert comprising a silicon nitride sintered body produced by adding a sintering aid to silicon nitride and sintering,
The silicon nitride sintered body is
a main crystal phase composed of α-type silicon nitride and β-type silicon nitride;
A grain boundary phase containing the sintering aid as a component, and
The proportion of α-type silicon nitride in the silicon nitride-based sintered body is 35% or less, and the long-axis diameter is 2 μm or more on the two-dimensional section of the silicon nitride-based sintered body. The proportion of the silicon nitride particle area is 10% or less,
The sintering aid contains 2 to 5% by weight of magnesium (Mg) in terms of magnesium oxide (MgO), and 3 to 11% by weight of ytterbium (Yb) in terms of ytterbium oxide (Yb2O3) as a rare earth element,
A cutting insert used for cutting an aluminum alloy material and a material made of an aluminum alloy and cast iron. The cutting insert according to claim 1,
A cutting insert in which the maximum major axis diameter of the β-type silicon nitride is 7 μm or less. The cutting insert according to claim 1 or 2,
The cutting insert whose ratio which the said grain boundary phase occupies on the two-dimensional cross section of the said silicon nitride sintered compact is 3 area%-9 area%.   A silicon nitride cutting tool comprising the cutting insert according to any one of claims 1 to 3. A method for producing a silicon nitride sintered body used for the cutting insert according to any one of claims 1 to 3,
A silicon nitride powder having an average particle size of 0.5 μm and α-type silicon nitride occupying 95% or more and a sintering aid are blended and mixed so that the total amount is 100 wt%,
Molding the powder produced as a result of the mixing to produce a molded body,
The molded body is first fired at 1500 ° C. to 1550 ° C.,
The primary sintered molded body to secondary baking at 1 450 ° C. to 1 550 ° C., the manufacturing method of the silicon nitride sintered body.

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