JP5340028B2 - Cutting tools - Google Patents

Description

  The present invention relates to a cutting tool made of a silicon nitride sintered body.

  A silicon nitride sintered body has high hardness and is stable at high temperatures, and thus has excellent wear resistance and oxidation resistance, and is used as a cutting tool.

  In such a cutting tool comprising a silicon nitride sintered body, for example, Patent Document 1 discloses a silicon nitride sintered body having an absolute value of residual stress of 42 to 55 MPa, and the absolute value of residual stress is set to 45 MPa or less. By doing so, it is described that high strength at room temperature and high temperature can be achieved.

In Patent Document 2, the surface of the sintered body is surface ground using a # 140 diamond grindstone, then polished using a diamond disk having an abrasive grain size of 45 μm, and further using Fe ₂ O ₃ powder. A silicon nitride sintered body subjected to mechanochemical polishing is disclosed, and it is disclosed that the residual stress of the sintered body, which was 100 MPa before processing, can be reduced to 10 to 40 MPa due to a difference in processing method.

  Further, in Patent Document 3, after grinding the surface of the silicon nitride-based sintered body, the compressive stress is increased on the surface of the sintered body by heat treatment in the atmosphere to recover the strength reduced by the grinding process. It is disclosed that it can be achieved.

JP-A-8-319166 JP-A-7-069736 JP 7-299708 A

  However, like the silicon nitride sintered bodies described in Patent Documents 1 to 3, the method for controlling the overall residual stress of the sintered body optimizes the tool performance when used as a cutting tool. That wasn't true.

  Accordingly, an object of the present invention is to provide a cutting tool made of a silicon nitride-based sintered body having high fracture resistance in consideration of the optimum residual stress as a cutting tool.

The cutting tool of the present invention is composed of a silicon nitride sintered body mainly composed of silicon nitride and containing an RE element compound (wherein RE is at least one element of rare earth elements), and intersecting ridge lines between a rake face and a flank face. In a cutting tool in which a part is a cutting edge and a nose is formed on the cutting edge located between two adjacent flank faces, the 2D method (two-dimensional X-ray diffraction: full Debye fitting method) ), The residual stress σ11 in the direction parallel to the rake face and from the center of the rake face toward the nose closest to the measurement point is a compressive stress of 10 MPa to 30 MPa (σ ₁₁ = −10). is MPa ~-30MPa), the residual stress sigma ₂₂ for parallel and the sigma ₁₁ direction perpendicular to the rake face is 10MPa or less compressive stress (σ ₂₂ = -10 MP Characterized in that it is a ~0MPa).

  Here, it is desirable that the arithmetic average roughness (Ra) on the rake face of the silicon nitride sintered body is 0.2 to 0.6 μm.

  Further, it is desirable that the silicon nitride sintered body contains Mg and the Mg concentration on the surface of the rake face is present in a ratio of 60 to 90% by mass with respect to the Mg concentration of the entire sintered body.

According to the cutting tool of the present invention, at the nose of the rake face, the residual stress σ ₁₁ in the direction from the center of the rake face toward the nose closest to the measurement point is 10 MPa to the compressive stress. 30 MPa (σ ₁₁ = −10 MPa to −30 MPa), and the residual stress σ _{22 in the} direction parallel to the rake face and perpendicular to the σ ₁₁ direction is 10 MPa or less (σ ₂₂ = −10 MPa− 0 MPa), the chipping resistance during cutting is improved.

  Here, the arithmetic average roughness (Ra) on the rake face of the silicon nitride sintered body is preferably 0.2 to 0.6 μm from the viewpoint of chipping resistance.

  In addition, the silicon nitride sintered body contains Mg, and the Mg concentration on the surface of the rake face is present at a ratio of 60 to 90% by mass with respect to the Mg concentration of the entire sintered body. Desirable in terms of strength, wear resistance, and chipping resistance.

It is a schematic perspective view about an example of the cutting tool of this invention.

  The cutting tool 1 of the present invention is a silicon nitride sintered body (hereinafter simply referred to as “sintering”) that contains silicon nitride as a main component and contains an RE element compound (wherein RE is at least one element of rare earth elements (yttrium and lanthanoid elements)). Abbreviated to body.)

Then, according to the present invention, at the rake face of the nose, parallel to the rake face 2 and 10 MPa residual stress sigma ₁₁ in the direction toward the closest nose to the measurement point from the center of the rake face 2 is in compressive stress ˜30 MPa (σ ₁₁ = −10 MPa to −30 MPa), and the residual stress σ _{22 in the} direction parallel to the rake face 2 and perpendicular to the σ ₁₁ direction is 10 MPa or less (σ ₂₂ = −10 MPa) as a compressive stress. ~ 0 MPa). Thereby, the chipping resistance of the cutting tool 1 is improved.

Incidentally, the measurement of residual stress in the present invention, the measurement position, as shown in the perspective view of FIG. 1, is measured at position P. In the present invention, the residual stress is measured using a 2D method (multiaxial stress measurement method / full Debye fitting method). In addition, as the X-ray diffraction peak used for the measurement of the residual stress, the (323) plane peak that appears when the value of 2θ is 141.7 ° is used. In calculating the residual stress, the Poisson's ratio of silicon nitride = 0.27 and Young's modulus = 306000 MPa are used. Further, as conditions for X-ray diffraction measurement, residual stress is measured by irradiating a mirror-finished rake face with CuKα ray as an X-ray source and irradiating under the conditions of output = 45 kV and 110 mA.

  Here, the arithmetic average roughness (Ra) on the rake face 2 of the cutting tool 1 is preferably 0.2 to 0.6 μm from the viewpoint of the strength of the sintered body, wear resistance, and chipping resistance.

  In addition, the sintered body forming the cutting tool 1 contains Mg, and the Mg concentration on the surface of the rake face 2 is present at a ratio of 60 to 90% by mass with respect to the Mg concentration of the entire sintered body. Desirable in terms of strength, wear resistance and chipping resistance.

  Here, in the present invention, the content ratio of RE element on the surface of the sintered body is constant within a range of 5% with respect to the content ratio inside the sintered body, and the content ratio of magnesium element is a sintered body. It is desirable that the surface area is less than 5% with respect to the content ratio inside the bonded body. As a result, the reason is unknown, but the wear resistance on the surface of the sintered body is high and the fracture resistance on the surface of the sintered body is high. The content ratio in the sintered body in the present invention is the content of each element by an area analysis using an electron beam microanalyzer (EPMA) in a region of depth 50 μm × width 50 μm near the center of the sintered body. It is a value obtained by measuring a ratio and performing this surface analysis for three arbitrary locations and taking an average value, which is almost the same as the overall composition of the sintered body.

  The sintered body further includes an aluminum compound and oxygen, and the content ratio of the aluminum element in the surface region is within a range of 10% with respect to the content ratio in the sintered body, and the surface region. The content ratio of oxygen in is preferably in the range of 15% with respect to the content ratio in the sintered body.

Here, the desirable overall composition of the sintered body is 94.5 to 99.5% by mass of silicon nitride, 0.1 to 4.5% by mass of RE element oxide in terms of RE ₂ O ₃ , and magnesium oxide to MgO. 0.3 to 2.5% by mass in terms of conversion, 0 to 0.6% by mass in terms of aluminum oxide in terms of Al ₂ O ₃ , 0.1 to 4.5% by mass in terms of residual oxygen in terms of silica (SiO ₂ ), It is desirable that the periodic table Group 6 element silicide is composed of 0 to 2% by mass in that the hardness and high-temperature strength of the sintered body can be increased and the wear resistance of the sintered body can be increased. Note that it is desirable that the RE element compound, the magnesium compound, and the aluminum compound are all present as oxides in that the silicon nitride can be firmly bonded to each other and the content ratio of silicon nitride can be increased.

Furthermore, the content of the RE element oxide is 0.5 to 4.5% by mass in terms of RE ₂ O ₃ and further 1 to 2.5% by mass for densification of the sintered body. It is desirable. The content of magnesium oxide is 0.35 to 2.0% by mass in terms of MgO in order to densify the sintered body at a lower temperature by lowering the liquid phase generation temperature of the sintering aid, It is desirable that it is 0.4-1.0 mass%. The content of aluminum oxide is calculated in terms of Al ₂ O ₃ in order to suppress a decrease in wear resistance due to a decrease in the liquid phase generation temperature of the sintering aid, a densification of the sintered body, and a decrease in oxidation resistance. It is desirable that the content be 0.2 to 0.55 mass%, and further 0.3 to 0.5 mass%. The remaining oxygen is considered to be present as an impurity of silicon nitride and as silica (SiO ₂ ), but its content is reduced in the liquid phase formation temperature of the sintering aid, the denseness of the sintered body In order to realize a sintered body with improved oxidation resistance and wear resistance, it is desirable that the content be 0.1 to 4.5% by mass in terms of SiO ₂ , especially 1.0 to 2.5%. It is desirable to set it as the mass%, and also 1.5-2 mass%.

In addition, when lanthanum (La) is contained as an essential element as the RE element, the sintered body can be densified at a lower temperature than when lanthanum (La) is not included, so that crystals in the sintered body grow abnormally. Crystal without atomization. For example, the average major axis of six silicon nitrides is suppressed to 10 μm or less from the larger major axis with a relative density of 99% or higher and a field of view of 0.015 mm ² by atmospheric pressure firing at 1730 to 1780 ° C. Is possible. As a result, the hardness and strength of the sintered body can be improved.

Here, the RE compound, the magnesium compound, the aluminum compound, and silica (SiO ₂ ) form a grain boundary phase. The grain boundary phase may have a structure in which a part of the grain boundary phase is precipitated, but the hardness and high temperature strength of the sintered body are increased by reducing the existence ratio of the grain boundary phase itself to 4% by mass or less. In order to increase the bondability of the silicon nitride crystal while reducing the absolute amount of the grain boundary phase, the grain boundary phase is desirably present in an amorphous state.

  Although silicon nitride exists as a main crystal, the silicon nitride crystal is mainly composed of β-silicon nitride crystal and, if desired, a part thereof contains a little aluminum to form β-sialon. Is desirable. Further, a part of the β-silicon nitride crystal may be an α-silicon nitride crystal, but it is desirable not to include the α-silicon nitride crystal in order to increase hardness and strength.

  Moreover, the periodic table group 6 element silicide can suppress the decrease in high-temperature strength and can blacken the color of the sintered body. Examples of the Periodic Table Group 6 element silicide include chromium silicide, molybdenum silicide, and tungsten silicide. It is desirable to use it. The periodic table group 6 element silicide particles are present dispersed in the grain boundary phase of the silicon nitride sintered body.

  Further, it is desirable that the surface region exists over a depth of 100 to 500 μm from the surface in terms of enhancing the fracture resistance while maintaining the wear resistance on the surface of the sintered body.

  Next, the manufacturing method of the sintered body described above will be described.

First, as starting materials, for example, silicon nitride (Si ₃ N ₄ ) powder, hydroxide (RE (OH) ₂ ) or oxide (RE ₂ O ₃ ), and aluminum oxide (Al ₂ O ₃ ) of RE element Magnesium hydroxide (Mg (OH) ₂ ) is prepared. If necessary, silicon dioxide (SiO ₂ ) and periodic table group 6 element silicide powders are prepared.

As the silicon nitride raw material, any of α-silicon nitride powder, β-silicon nitride powder, or a mixture thereof can be used. These particle sizes are preferably 1 μm or less, particularly 0.5 μm or less. Inevitable oxygen exists as silicon oxide in the silicon nitride raw material. Therefore, the composition is adjusted on the assumption that the oxide present in the silicon nitride raw material is present as silica (SiO ₂ ). When the oxygen content is insufficient, silica (SiO ₂ ) powder is added.

Oxide powder may be used as a raw material for the RE element. For example, in the case of lanthanum (La), lanthanum hydroxide (La (OH) ₂ ) has high hygroscopicity because lanthanum oxide (La ₂ O ₃ ) has high hygroscopicity. It is preferable to use a compound having a low water absorption and changing to lanthanum oxide (La ₂ O ₃ ) during the firing process. Magnesium oxide (MgO) or magnesium carbonate (MgCO ₃ ) may be used as the magnesium (Mg) raw material, but magnesium oxide (MgO) has high water absorption, and magnesium carbonate (MgCO ₃ ) generates carbon dioxide gas. Therefore, it is preferable to use a compound such as magnesium hydroxide (Mg (OH) ₂ ) that has low water absorption, does not generate carbon dioxide, and changes to magnesium oxide (MgO) during the firing process.

  The raw material for forming the periodic table group 6 element silicide may be any of the oxides, carbides, silicides, nitrides, etc. of the periodic table group 6 element, but it is oxidized because it is inexpensive and easily obtains a fine powder. It is desirable to use a product.

  Next, a binder or a solvent is appropriately added to the mixed powder obtained by weighing these raw materials, mixed and pulverized, and dried and granulated by a spray drying method or the like. And after shape | molding this granulated powder in arbitrary shapes by a well-known shaping | molding means, it bakes at the temperature of 1650-1800 degreeC by a normal-pressure baking method, a gas pressure baking method, a hot press method etc. in nitrogen atmosphere, for example. .

  The specific conditions for this firing are that the molded body is placed in a firing bowl made of a silicon nitride sintered body, and Si and Mg components are placed in the firing bowl so that the sealing state of the firing bowl is so high. Close and set in the firing furnace. Then, after replacing the inside of the firing furnace with 1 atm of nitrogen, the temperature increase was started at 5 to 15 ° C./min, and the temperature increase rate in the temperature range of 1400 to 1500 ° C. was changed to 1 to 5 ° C./min. The heating rate from 1500 ° C. to the firing temperature of 1650 to 1800 ° C. is changed again to 5 to 15 ° C./min. And it is set as the conditions which hold | maintain at 1650-1800 degreeC of a calcination temperature for 5 to 10 hours, cool down to 1100 degreeC by 10-50 degreeC / min, and then cool to room temperature. Further, during the firing, the atmosphere in the furnace is adjusted to be maintained at 1 atm of nitrogen by degassing or additionally introducing nitrogen gas. As a result, magnesium volatilizes moderately on the surface and RE element does not volatilize, densifying the sintered body, and obtaining a sintered body having a low magnesium concentration and the same RE element concentration on the surface. It is done.

In addition, the Si and Mg components put together with the molded body in the baking pot include methods of putting in the state of Si powder, SiO ₂ powder, Si ₃ N ₄ powder, MgCO ₃ powder, Mg (OH) ₂ powder, and these The powder is placed around the molded body, spread on the lower surface of the molded body, or fired in a state where the molded body is embedded in the powder, thereby generating SiO gas and MgO gas in the firing atmosphere and sintering. The method of promoting is mentioned.

  Furthermore, in order to obtain the concentration distribution of each element on the surface of the sintered body as described above, it is necessary to sufficiently raise the temperature up to the inside of the fired product in the temperature range where the diffusion of the element begins. It becomes possible by setting the temperature rising rate between 1 to 5 ° C./min and setting the temperature decreasing rate from the firing temperature to 1100 ° C. to 10 to 50 ° C./min. In addition, after firing at 1650 ° C. to 1850 ° C. in a nitrogen atmosphere, hot isostatic firing is performed at 9.8 MPa to 294 MPa and 1500 to 1700 ° C. to form dense and abnormal grain growth of silicon nitride crystal grains This is desirable in that a silicon nitride-based sintered body with improved chipping resistance that is suppressed can be obtained.

  And the grinding process is given to the sintered compact mentioned above. In the polishing process, a first grinding is performed in a certain direction along the shape of the cutting tool 1 with a rough grindstone (a direction parallel to the cutting edge ridge line), and then the second grinding is performed in a direction perpendicular to the cutting edge ridge line with a fine grinding stone. Polish. An example of a specific condition is that, in the first polishing, the arithmetic average roughness (Ra) of the rake face 2 is set to # 100 to # 300 with the grade of the grindstone being either polishing using an elastic grindstone or brush polishing. ) Is polished to 3 μm or less. Then, it grind | polishes until the arithmetic mean roughness (Ra) of the rake face 2 is set to 0.1-1 micrometer by making grinding | polishing stone grade # 400- # 1000 by grinding | polishing using an elastic grindstone, and brush grinding | polishing. As a result, the residual stress that becomes the cutting tool 1 with high fracture resistance in cutting can be optimized according to the direction, and the tool life can be extended. In order to eliminate damage such as microcracks that are likely to occur in the first polishing, it is preferable to polish a thickness of 30 μm or more, more preferably 50 μm or more in the second polishing.

It may be subjected to hard coating layer of TiN and _Al 2 _O 3, TiAlN or the like on the surface of the sintered body.

As starting materials, silicon nitride (Si ₃ N ₄ ) powder having an average particle size of 0.3 μm, RE element compound (lanthanum hydroxide (La (OH) ₂ ), yttrium oxide (Y ₂ O) having an average particle size of 1.2 μm ₃ ), ytterbium oxide (Yb ₂ O ₃ ), erbium oxide (Er ₂ O ₃ ) powder, aluminum oxide (Al ₂ O ₃ ) powder having an average particle size of 0.7 μm, and average particle size 5 μm of magnesium hydroxide (Mg (OH) ₂ ) powder was prepared in the ratio shown in Table 1, and after adding a binder and a solvent, it was pulverized and mixed in an attritor mill for 72 hours. In Table 1, for the lanthanum hydroxide (La (OH) ₂ ) powder and the magnesium hydroxide (Mg (OH) ₂ ) powder, oxides ((La ₂ O ₃ and MgO) present in the sintered body are used. ).

  Thereafter, the solvent was removed by drying to prepare a granulated powder, and this granulated powder was press-molded into a cutting tool shape of SNGN120212 at a pressure of 98 MPa.

When this molded body is set in a baking pot, it is set in the state shown in Table 1 using a mixed powder of at least one of Si ₃ N ₄ powder, Si powder, and SiO ₂ powder and Mg (OH) ₂ powder. The lid was put on and placed in a firing furnace in a state where it was placed in a carbon cylinder. Then, the inside of the firing furnace was replaced with 1 atm of nitrogen, and after degreasing, the temperature was raised to 1400 ° C. at a rate of temperature rise of 10 ° C./min. The atmosphere during firing was controlled to 1 atm of nitrogen. Thereafter, hot isostatic pressing (HIP) was performed under the conditions of 1600 ° C., 2 hours, and 196 MPa, and the surface of the sintered body was ground under the conditions shown in Table 2 to obtain a cutting tool.

About the obtained silicon nitride sintered body, the rake face is ground to a thickness of 0.5 mm to obtain a mirror state, and then the 2D method (apparatus: X-ray diffraction D8 DISCOVER with GADDS Super Speed, made by BrukerAXS, radiation source: CuK The residual stress of silicon nitride was measured using _α , collimator diameter: 0.8 mmφ, and measurement diffraction line: 141.7 ° (Si ₃ N ₄ (323) plane).

  Moreover, the electron beam microanalyzer (EPMA) measurement was performed on the surface of the sintered compact, and the content ratio of each component in the surface region was measured. In addition, the surface analysis of EPMA was performed at any three locations in the 50 μm depth × 50 μm width region near the center of the sintered body, and the average value of the content ratio was determined as the content ratio inside the sintered body. It was compared with the content ratio on the surface of the bonded body. Further, the structure was observed in the cross section of the sintered body including the surface, and the distribution state of the content ratio of each component was confirmed by EPMA, and the thickness of the surface region was calculated. Regarding the measurement of the oxygen content, the depth of the surface region confirmed by EPMA was polished from the surface of the sintered body, and this region was collected as a powder to obtain a sample of the surface region. A 3 mm thick portion was collected as a powder by polishing and used as a sample in the inner region. The amount of oxygen in these samples was measured by infrared absorption oxygen analysis, and the ratio was calculated. The results are shown in Table 2.

Furthermore, cutting performance was evaluated under the following conditions using a cutting tool made of the obtained silicon nitride sintered body.
Work material: FCD-450 Block material Cutting speed: 500 m / min Feed amount: 0.2 mm / rev
Cutting depth: 2.0mm
Cutting conditions: Dry cutting evaluation items: After 10 passes, the flank wear amount and chipping state of the cutting edge were confirmed by microscopic observation.
The results are shown in Table 3.

  According to the results shown in Tables 1 to 3, sample Nos. Within the scope of the present invention. Nos. 1 to 5 all showed cutting performance with a small amount of wear and little chipping of the blade edge. On the other hand, sample No. which is a sample outside the scope of the present invention. 6 to 8 had poor chipping resistance.

1 Tool (throw away tip)
2 Rake face 3 Relief face 4 Cutting edge 5 Nose σ ₁₁ direction Parallel to the rake face and the direction from the center of the rake face to the nose closest to the measurement point σ ₂₂ direction Parallel to the rake face and perpendicular to the σ ₁₁ direction direction

Claims (3)

Consists of a silicon nitride-based sintered body mainly composed of silicon nitride and containing an RE element compound (wherein RE is at least one element of rare earth elements), with the crossing ridge line portion between the rake face and the flank face as a cutting edge and adjacent In a cutting tool in which a nose is formed on the cutting blade located between the two flank surfaces
When the residual stress is measured by the 2D method at the nose of the rake face, the residual stress σ ₁₁ in the direction parallel to the rake face and from the center of the rake face toward the nose closest to the measurement point is 10 as a compressive stress. MPa to 30 MPa (σ ₁₁ = −10 MPa to −30 MPa), and the residual stress σ _{22 in the} direction parallel to the rake face and perpendicular to the σ ₁₁ direction is 10 MPa or less (σ ₂₂ = −10 Cutting tool that is MPa to 0 MPa ).   The cutting tool according to claim 1, wherein the arithmetic average roughness (Ra) of the rake face of the silicon nitride sintered body is 0.2 to 0.6 µm.   The cutting according to claim 1 or 2, wherein the silicon nitride sintered body contains Mg, and the Mg concentration on the surface of the rake face is in a ratio of 60 to 90 mass% with respect to the Mg concentration of the entire sintered body. tool.