JP6075803B2 - Silicon nitride sintered body and cutting tool - Google Patents

Description

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

  Silicon nitride-based sintered bodies have high hardness and are stable at high temperatures, so they have excellent wear resistance and oxidation resistance, and are used as heat engine parts such as gas turbines and turbo rotors, and as cutting tools. ing.

In such a silicon nitride sintered body, attempts have been made to improve the characteristics by modifying the surface of the sintered body. For example, in Patent Document 1, when Raman spectroscopic analysis is performed on a member surface of a silicon nitride sintered body, a peak intensity X1 of a peak appearing at 206 ± 10 cm ⁻¹ and a peak intensity X2 of a peak appearing at 1584 ± 20 cm ⁻¹ are obtained. It is disclosed that the ratio X2 / X1 is 0.001 to 0.5. In Patent Document 2, in the Raman spectroscopic analysis chart, the peak intensity of the Si peak appearing at 521 ± 10 cm ⁻¹ is H ₁ , and the peak intensity of the silicon nitride peak appearing at 206 ± 10 cm ⁻¹ is the ratio of H ₂ , H ₁ / A silicon nitride sintered body in which H ₂ is larger inside than the surface is disclosed.

JP 2001-80978 A JP 2000-143350 A

However, the peak of 206cm ^-1 in the Raman spectroscopic analysis chart described in Patent Documents 1 and 2, the peak of 521 cm ^-1, in the silicon nitride sintered body obtained by adjusting the peak intensity ratio of a peak of 1584 cm ^-1, sintered The body has insufficient chipping resistance, and further improvement in chipping resistance has been demanded.

  An object of the present invention is to provide a silicon nitride sintered body and a cutting tool with improved fracture resistance.

The silicon nitride sintered body of the present invention is a silicon nitride sintered body mainly composed of silicon nitride, and the peak intensity of the Si peak appearing at 521 ± 10 cm ⁻¹ in the Raman spectroscopic analysis chart is H ₁ , 206. When the peak intensity of the silicon nitride peak appearing at ± 10 cm ⁻¹ is H ₂ and the ratio H ₁ / H ₂ of the peak intensity is P, the P value (P _s ) in the surface layer region including the surface is larger than 0 In addition, in the cross section including the surface, which is smaller than the P value (P _i ) inside, the brightness V in the color display method defined in JISZ8721 is 3 or more smaller on the inner side than the surface side. When the portion is a boundary, the Si peak has a portion where the peak position of the Si peak shifts to the high angle side from the boundary toward the center of the silicon nitride sintered body.

  Moreover, the cutting tool of this invention comprises the said silicon nitride sintered body.

According to the present invention, the Si peak is observed in the Raman spectroscopic analysis chart, the peak intensity of the Si peak appearing at 521 ± 10 cm ⁻¹ is H ₁ , and the peak intensity of the silicon nitride peak appearing at 206 ± 10 cm ⁻¹ is H _{2. When} the peak intensity ratio H ₁ / H ₂ is P, the P value (P _s ) is smaller than the internal P value (P _i ), that is, the Si peak is smaller or detected in the surface layer region. Not. As a result, hardness is high on the surface and small chipping is generated, but wear resistance is high, so it can be used without problems in the processing conditions of silicon nitride sintered bodies that do not require much smoothness of the cutting surface, such as rough machining. Can continue. Moreover, since the peak position of the Si peak is shifted toward the high angle side toward the inside, a tensile stress is applied to the metal Si inside, and a compressive stress is applied to the metal Si compared to the inside on the surface. Become. That is, the silicon nitride particles present together with the metal Si are in a state where compressive stress is applied inside. Further, since the content of metal Si in the surface layer region is smaller than that in the inside, the silicon nitride particles on the surface are not so much tensile stressed and the fracture resistance is not lowered. Even if small chipping occurs on the surface, it is possible to suppress the development of large cracks inside from this. As a result, the fracture resistance of the silicon nitride sintered body is improved.

In one embodiment of the silicon nitride sintered body of this invention, it is a microscope picture about the cross section containing the surface. 2 is a Raman spectroscopic analysis chart in a range of ⁰ to 2000 cm ⁻¹ of the silicon nitride sintered body of FIG. 1. 2 is a Raman spectroscopic analysis chart in a range of 480 to 580 cm ⁻¹ of the silicon nitride sintered body of FIG. 1.

  According to one embodiment of the silicon nitride sintered body (hereinafter simply referred to as “sintered body”) of the present invention, the sintered body 1 is mainly composed of silicon nitride and includes an RE element (either yttrium or a rare earth element). 1 type or more), magnesium, and aluminum are contained as oxides. In the present invention, “mainly composed of silicon nitride” refers to a state in which silicon nitride is present in the sintered body 1 by 50 volume% or more, particularly 90 volume% or more.

  According to this embodiment, the silicon nitride crystal is composed of a β-silicon nitride crystal phase, and although not shown, in the cross-sectional photograph obtained by observing the cross section of the sintered body 1 with a scanning electron microscope, the aspect ratio is 3 or more. Further, the elongated crystals having a major axis diameter of 1 to 3 μm are present in an area of 20% by area or more based on the total amount of silicon nitride crystals. Thus, a predetermined internal stress can be applied to the silicon nitride crystal, and the internal stress applied to the metal Si existing together with the silicon nitride crystal can be set within a predetermined range.

  Moreover, according to this embodiment, the color of the surface 4 of the sintered body 1 is lighter than the inside 2 as shown in the metal micrograph of the cross section including the surface 4 of the sintered body 1 shown in FIG. It is high.

The sintered body 1 has a surface layer region 3 including a surface 4. The surface layer region 3 is the peak of the silicon nitride peak appearing at H ₁ and 206 ± 10 cm ⁻¹ in the peak intensity of the Si peak appearing at 521 ± 10 cm ⁻¹ in the Raman spectroscopic analysis chart of the sintered body 1 shown in FIGS. When the intensity is H ₂ and the peak intensity ratio H ₁ / H ₂ is P, the P value (P _s ) in the surface layer region 3 is smaller than the P value (P _i ) in the interior 2. Further, the peak position of the Si peak is shifted to the high angle side in the interior 2 as compared with the peak position in the surface layer region 3. 2 and 3, the legends 100, 300. . . Represents the position where Raman spectroscopic analysis was performed, and is the depth (μm) from the surface 4 of the sintered body 1.

  Accordingly, the surface layer region 3 has high hardness and small chipping is generated, but wear resistance is high. Therefore, the use of the cutting tool made of the silicon nitride-based sintered body 1 in which the smoothness of the cutting surface is not so required as in roughing can be continued without problems.

  Moreover, in this embodiment, the peak position of the Si peak is shifted to the higher angle side in the interior 2 than in the surface layer region 3. In the present embodiment, the peak position of the Si peak is gradually shifted toward the high angle side from the surface layer region 3 toward the inside 2. As a result, compressive stress is applied to the metal Si in the surface layer region 3, and tensile stress is applied to the metal Si in the interior 2. That is, compressive stress is applied to the silicon nitride particles present together with the metal Si in the interior 2. In addition, since the metal Si content in the surface layer region 3 is small, the silicon nitride particles are not subjected to a large tensile stress, so that the fracture resistance in the surface layer region 3 does not decrease so much. Further, even if small chipping occurs in the surface layer region 3, since the progress of cracks can be suppressed in the interior 2, the sintered body 1 does not reach a large defect, and the sintered body 1 has high fracture resistance. It is.

In the present embodiment, together with the _{P i} are 2 to 10, less than 2 _{P s} is 0 or more. As a result, it is possible to achieve both improvement in wear resistance in the surface layer region 3 and improvement in chipping resistance in the interior 2.

Further, the sintered body 1, a half of a value intermediate position M of _{P i} (around 620 cm ^-1 in the sintered body of FIG. 1) is present in the surface region 3. In the present embodiment, the intermediate position M exists at a depth of 100 to 1000 μm from the surface 4. As a result, the balance between the wear resistance in the surface layer region 3 and the fracture resistance in the interior 2 can be optimized.

When the sintered body 1 is used as a cutting tool, the P value (P _s ) is smaller than the P value (P _i ) in the interior 2 at any position of the cutting blade, rake face, and flank face of the cutting tool. The surface layer region 3 is preferably present. As a result, the wear resistance and chipping resistance in the vicinity of the cutting edge during cutting are high, and the wear resistance and chipping resistance against chips are also high on the rake face and flank face. According to this embodiment, the intermediate position M of the surface layer region 3 in the cutting edge exists deeper from the surface than the intermediate position M in the rake face and the flank face. As a result, the wear resistance of the cutting blade to which the greatest impact is applied can be increased. In the present embodiment, the depth of the intermediate position M on the cutting edge is 1.0 to 3.5 times the depth of the intermediate position M on the rake face and the flank face.

  The range of the cutting edge of the cutting tool is defined as a region having a width of 500 μm from the intersecting ridge line between the rake face and the flank face. Therefore, the range of the rake face is a region extending from the center of the rake face such as the main surface of the cutting tool to the position of 500 μm from the cross ridge line that is the end of the cutting edge, and the range of the flank face is a clearance of the side face of the cutting tool. This is a region extending from the center of the surface to the position of 500 μm from the intersecting ridge line that is the end of the cutting edge.

  In the present embodiment, there is a boundary X in which the brightness V in the color display method defined in JISZ8721 of the sintered body 1 is smaller by 3 or more on the inner 2 side than on the surface 4 side. This boundary X exists in the surface layer region 3 and exists at a position within 20% of the depth from the surface of the intermediate position M ± intermediate position M. That is, it is considered that the change in the peak intensity of the Si peak is reflected in the color of the sintered body 1. And since it is a bright color tone in the surface layer area | region 3 of the sintered compact 1, it becomes easy to find a foreign material and a defect, and becomes the sintered compact 1 with high intensity | strength reliability.

  The silicon nitride-based sintered body (sintered body 1) of this embodiment is mainly composed of silicon nitride, contains RE element (any one or more of yttrium or rare earth element), magnesium, aluminum, and silicon oxide. Contains metal Si.

The overall composition of the sintered body 1 is 94.5 to 99.5% by mass of silicon nitride, 0.1 to 4.5% by mass of RE element in terms of RE ₂ O ₃ , and 0.005 in terms of magnesium in terms of MgO. 3 to 2.5% by mass, aluminum is 0 to 1.5% by mass in terms of Al ₂ O ₃ , part of silicon is 0.1 to 4.5% by mass in terms of SiO ₂ , periodic table group 6 element silicidation A thing is contained at 0-2 mass%. With this composition, the wear resistance and fracture resistance of the sintered body 1 as a whole can be increased. Moreover, in this embodiment, the content rate of the magnesium element in the surface 4 of the sintered compact 1 is 0.1-1.0 mass%. As a result, the hardness and high-temperature strength of the sintered body in the surface layer region 3 can be increased, and the wear resistance of the sintered body 1 can be increased. Note that the RE element, magnesium and aluminum all exist as oxides, and part of silicon also exists as silicon oxide (SiO ₂ ). Thereby, silicon nitride can be firmly bonded with a small amount, and the content ratio of silicon nitride can be increased.

In the present embodiment, the RE element content 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 1. is there. The content of magnesium 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. 4 to 1.0% by mass.

In this embodiment, the content of aluminum is Al ₂ 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 0.2 to 1.0% by mass in terms of O ₃ , and further 0.3 to 0.8% by mass. The remaining oxygen is present as an impurity of silicon nitride and is present as silicon oxide (SiO ₂ ). However, the content of silicon present as SiO ₂ is reduced in the liquid phase formation temperature of the sintering aid and sintered. In order to maintain the densification of the body 1 and realize the sintered body 1 with improved oxidation resistance and wear resistance, it is 0.1 to 4.5% by mass in terms of SiO ₂ , particularly 1.0 to ₂ %. 0.5% by mass, and further 1.5-2% by mass. Metal Si is contained as a Si component other than the above silicon nitride and silicon oxide, but the content of metal Si is greater than 0 and 0.5% by mass or less. The content ratio is so small that no peak is detected.

In addition, if 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 1 grow abnormally. Crystals can be atomized without any problems. For example, the average major axis of the six silicon nitrides is suppressed to 10 μm or less from the larger major axis with a relative density of 99% or more and a field of view of 0.015 mm ² by atmospheric pressure firing at 1730 to 1780 ° C. It becomes possible. As a result, the hardness and strength of the sintered body 1 can be improved.

  Here, RE, magnesium, aluminum, and part of silicon basically form a grain boundary phase as an oxide. A part of the grain boundary phase may be precipitated as crystals, but the hardness and high-temperature strength of the sintered body 1 are increased by reducing the proportion of the grain boundary phase itself to 4% by mass or less. Therefore, in order to increase the bonding property of the silicon nitride crystal while reducing the absolute amount of the grain boundary phase, in this embodiment, the grain boundary phase exists in an amorphous state.

  Although silicon nitride exists as a main crystal, the silicon nitride crystal may be mainly composed of β-silicon nitride crystal, and if desired, a part thereof may contain aluminum to form β-sialon. . Further, a part of the β-silicon nitride crystal may be an α-silicon nitride crystal, but in this embodiment, the α-silicon nitride crystal is not included in order to increase hardness and strength.

  Moreover, the periodic table group 6 element silicide can suppress the fall of high temperature intensity | strength, and can also blacken the color of a sintered compact. Examples of periodic table group 6 element silicides include chromium silicide, molybdenum silicide, and tungsten silicide, but tungsten silicide is used because it can be present as fine particles in the fired body using a fine oxide raw material. 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.

  In addition, the inside 2 of the sintered body 1 refers to a range in which the difference from the P value at the center which is the center of the thickness of the sintered body 1 is less than 0.2, and the surface 4 side of the inside 2 is a surface layer region. 3 is defined. In this embodiment, the surface layer region 3 exists from the surface 4 to a depth of 100 to 1500 μm. Thereby, the fracture resistance can be enhanced while maintaining the wear resistance on the surface 4 of the sintered body 1.

  The content ratio in the interior 2 is the same as the content ratio of each element measured by area analysis using an electron beam microanalyzer (EPMA) in a region of 50 μm depth × 50 μm width including the center of the sintered body 1 The average value is obtained by conducting this surface analysis at two arbitrary locations near the center (total of three locations), which is almost the same as the overall composition of the sintered body 1.

  Further, in this embodiment, the magnesium content ratio in the surface layer region 3 of the sintered body 1 is gradually lower than the inside, and the magnesium content ratio on the surface 4 is the content ratio in the interior 2 of the sintered body 1. On the other hand, the RE element content ratio in the surface layer region 3 is in the range of 70 to 85% and the content ratio in the sintered body 1 is in the range of 85 to 115%. In the surface layer region 3 of the sintered body 1, the content ratio of magnesium gradually decreases with respect to the inside 2, so that the sintering does not easily proceed in the surface layer region 3, and the shrinkage amount of the sintered body 1 due to firing is smaller than that of the inside 2. Therefore, a compressive stress is generated on the surface 4 of the sintered body 1 and chipping in the surface layer region 3 can be suppressed.

  In addition, although the silicon nitride sintered body of this embodiment can be suitably used as a cutting tool, it can also be suitably used as a structural material that requires other wear resistance and fracture resistance.

Further, a coating layer may be provided on the surface of the sintered body 1. As the coating layer, TiC, TiN, TiCN, Al ₂ O ₃ , TiAlN, or the like can be suitably used. As the first layer in contact with the sintered body 1, any of TiC, TiN, and TiCN is suitable. According to this embodiment, since the amount of metal Si on the surface of the sintered body 1 is small, the adhesion of the first layer to the sintered body 1 is good, and the cutting tool is not easily worn.

(Production method)
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 in the silicon nitride raw material. Therefore, the composition is adjusted by considering that oxygen present in the silicon nitride raw material exists as silicon oxide (SiO ₂ ). When the oxygen content is insufficient, silicon oxide (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, in this embodiment, a compound that has low water absorption, does not generate carbon dioxide gas, and changes into magnesium oxide (MgO) during the firing process, such as magnesium hydroxide (Mg (OH) ₂ ), is used.

  The raw material for forming the Group 6 element silicide of the periodic table may be any of the oxide, carbide, silicide, nitride, etc. of the Group 6 element of the periodic table, but in this embodiment, a fine powder can be obtained at low cost. Oxides are used because they are easily formed.

  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 1650-1950 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 the Si and Mg components are placed in the firing bowl so that the lid of the firing bowl is sealed. Close in low condition and set in firing furnace. In addition, the state which closes the lid | cover of a baking pot in the state where the sealing state is not so high refers to the state where gas can go in and out so that the atmosphere in a baking pot may become the same as the atmosphere in a baking furnace. Then, after replacing the inside of the firing furnace with 0.1 MPa (1 atm) of nitrogen, 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 1 to 5 ° C./min. After changing to minutes, the heating rate from 1500 ° C. to the first firing temperature of 1650 to 1820 ° C. is changed again to 5 to 15 ° C./min. And it adjusts so that the atmosphere in a furnace may be maintained by nitrogen 0.1MPa by degassing or introducing nitrogen gas additionally, and hold | maintains at the 1st baking temperature for 2 to 12 hours. Next, the temperature is increased from the first baking temperature to a second baking temperature of 1680 to 1950 ° C., which is 30 ° C. or higher, at a temperature rising rate of 5 to 15 ° C./min. The pressure is maintained at 10 MPa for 0.5 to 3 hours. Thereafter, the temperature is lowered to 1100 ° C. at 10 to 50 ° C./min, and then cooled to room temperature. At this time, by performing the two-stage firing of the first firing temperature and the second firing temperature, the sintered state of silicon nitride (Si ₃ N ₄ ) on the surface and inside of the sintered body is optimized, and the firing is performed. It is possible to optimize the wear resistance and fracture resistance on the surface and inside of the bonded body.

Incidentally, Si and Mg components put together molded body during the firing bowl, a metal Si powder, SiO ₂ powder, _Si 3 _{N 4} powder, MgO powder, Mg _(OH) method to put in ₂ powder state and the like, these By placing the powder around the molded body, laying it on the lower surface of the molded body, or firing the molded body itself embedded in the above powder, SiO gas and MgO gas are generated in the firing atmosphere. The method of adjusting the balance of the sintered state in the surface and inside of a bonded body is mentioned.

  Further, once the firing is completed, hot isostatic firing may be performed at 9.8 MPa to 294 MPa and 1500 to 1700 ° C., thereby suppressing the abnormal growth of the silicon nitride crystal particles that are dense. A silicon nitride based sintered body with improved chipping resistance is obtained.

Moreover, although the sintered body mentioned above is ground according to the target performance, as long as it grinds in the state where the surface layer area | region prescribed | regulated by this invention remains, the effect of this invention is not lost. And since the said sintered compact is excellent in hardness and toughness, it can be adapted for structural members, but it is particularly suitably used as a cutting tool that requires wear resistance and fracture resistance. It may be subjected to coating of TiN and _Al 2 _O 3, TiAlN or the like on the surface of the sintered body.

In order to form a first layer made of TiC, TiN, or TiCN as a coating layer in contact with the sintered body, the sintered body is immersed in pure water and subjected to ultrasonic cleaning, and then the sample is subjected to CVD. Set in the device. Then, heated to 800 to 1050 ° C. in vacuo, titanium tetrachloride (TiCl ₄₎ as a reaction gas composition from 0.5 to 10% by volume gas, nitrogen _{(N 2)} gas 0 to 60% by volume, methane (CH ₄ ) Adjust a mixed gas consisting of 0 to 20% by volume of gas, 0 to 3% by volume of acetonitrile (CH ₃ CN) gas, and the remaining hydrogen (H ₂ ) gas so that the pressure is 8 to 50 kPa. It introduce | transduces in a chamber and forms into a film.

In order to form an Al ₂ O ₃ layer as an upper layer of the first layer, ₃ to 20% by volume of aluminum chloride (AlCl ₃ ) gas, 0.5 to 10% by volume of hydrogen chloride (HCl) gas, dioxide dioxide A mixed gas composed of 0.01 to 20% by volume of carbon (CO ₂ ) gas and the remaining hydrogen (H ₂ ) gas is used, and the film forming temperature is 960 to 1100 ° C. and the pressure is 5 to 25 kPa. If the film is formed under these conditions, κ-Al ₂ O ₃ is basically generated, but α-Al ₂ O ₃ may also be generated.

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 ), cerium oxide (Ce ₂ O ₃ ) powder, and aluminum oxide (Al ₂ O ₃ ) having an average particle size of 0.7 μm ) Powder and magnesium hydroxide (Mg (OH) ₂ ) powder having an average particle size of 2.5 μm were prepared in a proportion such that the composition of the sintered body is as shown in Table 2, and after adding a binder and a solvent, an attritor mill And ground for 72 hours. 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, metal Si powder, and SiO ₂ powder and Mg (OH) ₂ powder. Then, it was covered and placed in a firing furnace in a state where it was placed in a carbon cylinder. Then, the inside of the firing furnace is replaced with 0.1 MPa of nitrogen, and after degreasing, the temperature is increased to 1400 ° C. at a rate of temperature increase of 10 ° C./min, 1400-1500 ° C. is increased at 2 ° C./min, and 1500 ° C. or higher Was heated at a rate of 10 ° C./min, and then fired in the order of firing 1 and firing 2 in Table 1. The atmosphere during firing was the atmosphere shown in Table 1. The rate of temperature increase between firing 1 and firing 2 was 10 ° C./min. The cooling rate after firing was 20 ° C./min. The surface of this sintered body was subjected to 0.3 mm thickness grinding (double-head processing and peripheral processing) to obtain a silicon nitride sintered body.

The obtained silicon nitride sintered body is subjected to electron beam microanalyzer (EPMA) measurement on the surface of the sintered body, the content ratio of each component in the surface layer region is measured, and the ratio of RE element, magnesium element, aluminum element is determined. In terms of oxide, the content ratio in the surface region of Table 2 is described. For the measurement of the amount of SiO ₂ , the depth of the surface layer region measured by EPMA is polished from the surface of the sintered body, and this region is collected as a powder to obtain a sample of the surface layer region. The oxygen amount of these samples was measured by analysis, and the remaining oxygen excluding the oxygen amount existing as an oxide such as RE ₂ O ₃ , MgO, Al ₂ O ₃ was calculated in terms of SiO ₂ .

In addition, the EPMA surface analysis was performed at three arbitrary locations in the 50 μm thick × 50 μm wide region near the center (position at a depth of about 2000 to 2500 μm from the surface) inside the sintered body. The average value of the ratio was taken as the content ratio inside the sintered body. The content ratio in the interior of the sintered body was expressed as the overall composition of the sintered body, compared with the content ratio on the surface, and shown in Table 2 as the ratio. Regarding the measurement of the amount of SiO ₂ , a 3 mm thick portion at the center of the sintered body was collected as a powder by polishing to obtain samples in the inner region, and the oxygen content of these samples was determined by infrared absorption oxygen analysis. Measured, and the remaining oxygen excluding the amount of oxygen present as an oxide such as RE ₂ O ₃ , MgO, Al ₂ O ₃ was calculated in terms of SiO ₂ . The results are shown in Table 2.

In addition, for the cross section of the cutting tool, perform Raman spectroscopic analysis under the following conditions,
Laser Raman spectrometer HR-800
Laser wavelength: 514.53 nm
Grating: 600 objective lenses: × 50
Detector: CCD
Measurement fraction: 100-2000 / cm
From the measured Raman chart, the peak intensity ratio for a predetermined peak and the presence or absence of a peak shift from the surface to the inside were confirmed, and the depth of the intermediate position M in the surface layer region was determined. In addition, when measuring the depth of the intermediate position M on the rake face and the flank face, the depth from the surface of the sintered body was changed and measured at a position away from the intersecting ridge line by 1000 μm. When measuring the depth of the intermediate position M on the cutting edge, the depth was measured by changing the depth on a straight line forming an angle of 45 degrees with the rake face and the flank face from the position of the intersecting ridge line.

Furthermore, cutting performance was evaluated under the following conditions using a cutting tool made of the obtained silicon nitride sintered body.
Workpiece: FCD-450 block material (shape in which through-holes with a diameter of 40 mm are arranged in parallel at intervals of 68 mm)
Cutting speed: 500 m / min Feed amount: 0.5 mm / rev
Cutting depth: 2.0mm
Cutting condition: Wet cutting evaluation item: The chipping state of the cutting edge after processing 100 pieces was observed with a digital scope. Moreover, the number of machining until the end of the tool life was confirmed.
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. 4 to 8 all showed cutting performance with good wear resistance with a small amount of wear and little chipping of the cutting edge. On the other hand, Sample No. baked only in the normal pressure atmosphere. 10. Sample No. with no mixed powder placed in the baking pot. 11. Sample No. 1 with a firing time of firing 1 shorter than 2 hours. In either case, P _i is the same as P _s or P _i is larger than P _s . Sample No. fired only in a pressurized atmosphere. 12, the peak position of the Si peak was shifted to the low angle side inside. All of these samples were greatly chipped and became inoperable due to chipping. Sample No. 1 to 3 and 9 are outside the scope of the present invention.

  Sample No. In 1, 3-7, and 9, the brightness V in the color display method defined in JISZ8721 includes the inside with respect to the surface side including the surface at the intermediate position ± 20% in the Raman spectroscopic analysis measurement. There was a boundary X that was 3 or more smaller on the inner side.

Sample No. 1 of Example 1 For 1 and 10, a coating layer was formed on the surface by chemical vapor deposition (CVD). The first TiN layer is formed using the remaining mixed gas composition at a film forming temperature of 1010 ° C., a gas pressure of 30 kPa, and TiCl ₄ : 2.0, N ₂ : 30, H ₂ : Was formed at a gas pressure of 9 kPa, AlCl ₃ : 1.5, HCl: 2, CO ₂ : 4, H ₂ : the remaining Al ₂ O ₃ layer was formed using the remaining mixed gas composition. The third TiN layer was formed using the remaining mixed gas composition at a film forming temperature of 880 ° C., a gas pressure of 16 kPa, and TiCl ₄ : 2.0, N ₂ : 33, H ₂ : The temperature is 1005 ° C., the gas pressure is 9 kPa, AlCl ₃ : 1.5, HCl: 2, CO ₂ : 4, H ₂ S: 0.3, H ₂ : Al in the fourth layer using the remaining mixed gas the ₂ O ₃ layer was deposited, deposition temperature 1010 ° C., gas pressure at _{15kPa, TiCl 4: 3.0, CH} 4: 7, _2: was deposited TiC layer of the fifth layer using a mixed gas composition of the residual. Then, the surface of the coating layer was brushed for 30 seconds from the rake face side, and sample No. 14 and 15 cutting tools were produced.

Using the obtained cutting tool, cutting performance was evaluated under the following conditions.
Workpiece material: FCD-450 Sleeve material Cutting speed: 500 m / min Feed amount: 0.5 mm / rev
Cutting depth: 2.0mm
Cutting condition: Wet cutting evaluation item: The chipping state of the cutting edge after processing 100 pieces was observed with a digital scope. In addition, the number of processing until the cutting was continued and the cutting became impossible was confirmed.

  Sample No. Sample No. 1 using the sintered body of No. 1 was used. In No. 14, when the cutting edge was observed after processing 100 pieces, no peeling of the coating layer was observed, and up to 500 pieces could be processed. In contrast, sample no. Sample No. 10 using the sintered body of No. 10. In No. 15, peeling of the coating layer was observed in the observation of the cutting blade after 100 pieces were processed, and the number of processing was 200.

1 Sintered body (silicon nitride based sintered body)
2 Inside 3 Surface region 4 Surface

Claims (10)

A silicon nitride sintered body mainly composed of silicon nitride, wherein the peak intensity of the Si peak appearing at 521 ± 10 cm ⁻¹ is H ₁ and the peak of the silicon nitride peak appearing at 206 ± 10 cm ⁻¹ in the Raman spectroscopic analysis chart. When the intensity is H ₂ and the peak intensity ratio H ₁ / H ₂ is P,
The P value (P _s ) in the surface layer region including the surface is larger than 0 and smaller than the P value (P _i ) inside,
In the cross section including the surface, when the brightness V in the color display method defined in JISZ8721 is a boundary that is 3 or more smaller on the inner side than the surface side,
A silicon nitride based sintered body having a portion where the peak position of the Si peak shifts to the high angle side from the boundary toward the center of the silicon nitride based sintered body. Wherein _{P i} with is 2-10, the _{P s} is less than 2 in a claim 1 silicon nitride sintered body according. The P intermediate position M to be half the value of _i, according to claim 1 or 2 silicon nitride sintered body according to present in the surface layer region of a depth of 100~1000μm from said surface. The silicon nitride based sintered body according to claim 3, wherein the boundary is a position within 20% of a depth of the intermediate position M ± the intermediate position M from the surface.   The silicon nitride based sintered body according to any one of claims 1 to 4, which contains RE element (any one or more of yttrium and rare earth elements), magnesium, aluminum, and silicon as oxides and metal Si. The total composition contains 94.5 to 99.5% by mass of silicon nitride, and in the balance, the RE element is 0.1 to 4.5% by mass in terms of RE ₂ O ₃ and magnesium is 0.3 in terms of MgO. ~ 2.5 mass%, aluminum is 0 to 0.6 mass% in terms of Al ₂ O ₃ , silicon is 0.1 to 4.5 mass% in terms of SiO ₂ , and periodic table group 6 element silicide is 0 to The silicon nitride based sintered body according to claim 5, containing 2% by mass. The magnesium content ratio on the surface is in the range of 70 to 85% with respect to the internal content ratio, and the RE element content ratio on the surface is in the range of 85 to 115% with respect to the internal content ratio. The silicon nitride based sintered body according to claim 6, wherein the silicon nitride sintered body is inside.   The silicon nitride-based sintered body according to any one of claims 1 to 7, wherein the first layer in contact with the surface of the coating layer is made of any one of TiC, TiN, and TiCN. .   A cutting tool comprising the silicon nitride sintered body according to any one of claims 1 to 8.   The cutting tool according to claim 9, wherein an intermediate position M of the surface layer region in the cutting edge exists at a position deeper from the surface than the intermediate position M in the rake face and the flank face.