Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23B—TURNING; BORING
  • B23B27/00—Tools for turning or boring machines; Tools of a similar kind in general; Accessories therefor
  • B23B27/14—Cutting tools of which the bits or tips or cutting inserts are of special material
  • B23B27/148—Composition of the cutting inserts
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C29/00—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides
  • C22C29/02—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides
  • C22C29/06—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbides, but not containing other metal compounds
  • C22C29/08—Alloys based on carbides, oxides, nitrides, borides, or silicides, e.g. cermets, or other metal compounds, e.g. oxynitrides, sulfides based on carbides or carbonitrides based on carbides, but not containing other metal compounds based on tungsten carbide
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/06—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the coating material
  • C23C14/0605—Carbon
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
  • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
  • C23C14/24—Vacuum evaporation
  • C23C14/32—Vacuum evaporation by explosion; by evaporation and subsequent ionisation of the vapours, e.g. ion-plating
  • C23C14/325—Electric arc evaporation
• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C16/00—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes
  • C23C16/22—Chemical coating by decomposition of gaseous compounds, without leaving reaction products of surface material in the coating, i.e. chemical vapour deposition [CVD] processes characterised by the deposition of inorganic material, other than metallic material
  • C23C16/26—Deposition of carbon only
  • C23C16/27—Diamond only
  • C23C16/271—Diamond only using hot filaments
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B22—CASTING; POWDER METALLURGY
  • B22F—WORKING METALLIC POWDER; MANUFACTURE OF ARTICLES FROM METALLIC POWDER; MAKING METALLIC POWDER; APPARATUS OR DEVICES SPECIALLY ADAPTED FOR METALLIC POWDER
  • B22F5/00—Manufacture of workpieces or articles from metallic powder characterised by the special shape of the product
  • B22F2005/001—Cutting tools, earth boring or grinding tool other than table ware
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23B—TURNING; BORING
  • B23B2224/00—Materials of tools or workpieces composed of a compound including a metal
• • C—CHEMISTRY; METALLURGY
  • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
  • C22C—ALLOYS
  • C22C1/00—Making non-ferrous alloys
  • C22C1/04—Making non-ferrous alloys by powder metallurgy
  • C22C1/05—Mixtures of metal powder with non-metallic powder
  • C22C1/051—Making hard metals based on borides, carbides, nitrides, oxides or silicides; Preparation of the powder mixture used as the starting material therefor

Definitions

• This disclosure relates to cemented carbide and cutting tools.
• cemented carbide alloys have been used as cutting tool materials. These alloys have a first hard phase primarily composed of tungsten carbide (WC), a second hard phase primarily composed of a compound containing multiple metal elements including tungsten and one or more elements selected from carbon, nitrogen, oxygen, and boron, and a binder phase primarily composed of an iron-group element.
• Patent Document 1 discloses a cutting tool in which a hard film such as a TiAlN film is formed on a substrate made of such a cemented carbide alloy.
• FIG. 1 is a diagram illustrating a typical example of the configuration of the cemented carbide according to the first embodiment.
• FIG. 2 is a schematic cross-sectional view of a cutting tool according to a second embodiment.
• FIG. 3 is a diagram illustrating a typical configuration example of a cutting tool according to the second embodiment.
• cutting tools having a thick coating formed on a substrate made of cemented carbide are used for cutting cemented carbide.
• the coating tends to peel off from inhomogeneous portions of the coating, resulting in a shortened tool life.
• the present disclosure therefore aims to provide a cemented carbide alloy that, when used as a cutting tool material, enables the cutting tool to have a longer life even when machining cemented carbide alloys, and a cutting tool equipped with the same.
• the cemented carbide of the present disclosure is a cemented carbide consisting of a first hard phase, a plurality of second hard phases, and a binder phase, the first hard phase is composed of a plurality of tungsten carbide particles;
• the particle diameter D10 of the tungsten carbide particles is 0.40 ⁇ m or more,
• the tungsten carbide particles have a particle size D90 of 2.00 ⁇ m or less
• the second hard phase is composed of at least one first compound selected from the group consisting of TaNbC, TaNbN, TaNbCN, TiCN, TiNbC, TiNbN, and TiNbCN;
• the cemented carbide contains the second hard phase in an amount of 0.30 vol% or more and 1.60 vol% or less, In a cross section of the cemented carbide, the median value of the distance between the centers of gravity of the two second hard phases that are closest to each other is 4 ⁇ m or more and 15
• This disclosure makes it possible to provide a cemented carbide alloy that, when used as a cutting tool material, enables the cutting tool to have a longer life, even when machining CFRP.
• the cemented carbide may contain 0.08% by mass or more and 0.5% by mass or less of chromium.
• Chromium is derived from chromium carbide ( Cr3C2 ), which is used as a grain growth inhibitor in the production of cemented carbide.
• cemented carbide contains chromium within the above range, the hardness of the cemented carbide is improved, and the life of cutting tools using the cemented carbide is further improved.
• the binder phase may contain one or both of iron and nickel.
• the cutting tool disclosed herein is a cutting tool comprising a substrate made of the cemented carbide alloy described in any one of (1) to (3) above, and a coating provided on the substrate.
• This disclosure makes it possible to provide cutting tools with long lifespans, even when machining cemented carbide.
• a ⁇ B means greater than or equal to A and less than or equal to B. If no unit is specified for A and only a unit is specified for B, the units for A and B are the same.
• a cemented carbide 4 is a cemented carbide 4 comprising a first hard phase 1, a plurality of second hard phases 2, and a binder phase 3,
• the first hard phase 1 is composed of a plurality of tungsten carbide particles,
• the particle diameter D10 of the tungsten carbide particles is 0.40 ⁇ m or more,
• the particle size D90 of the tungsten carbide particles is 2.00 ⁇ m or less
• the second hard phase 2 is made of at least one first compound selected from the group consisting of TaNbC, TaNbN, TaNbCN, TiCN, TiNbC, TiNbN, and TiNbCN;
• the cemented carbide 4 contains a second hard phase 2 in an amount of 0.30 vol% or more and 1.60 vol% or less, In the cross section of the cemented carbide 4, the median value of the distance between the centers
• the cemented carbide of embodiment 1 When used as a cutting tool material, the cemented carbide of embodiment 1 enables the cutting tool to have a longer life, even when machining cemented carbide. The reason for this is not clear, but is presumed to be as follows.
• a cutting tool When cemented carbide is used to machine cemented carbide, a cutting tool is generally used in which a coating is formed on a substrate made of cemented carbide. To achieve stable tool performance, it is essential that the coating structure is homogeneous. The inhomogeneous areas (e.g., unevenness) of the coating vary depending on the internal structure of the substrate. When the median value of the distance between the centers of gravity of the two closest second hard phases in the cross section of the cemented carbide is 4 ⁇ m or more and 15 ⁇ m or less, and the coefficient of variation of the distance between the centers of gravity is 1.20 or more and 1.90 or less, the homogeneity of the substrate and coating is improved. Therefore, a cutting tool using the cemented carbide of embodiment 1 as its material can have a long tool life, even when machining cemented carbide.
• the cemented carbide of the first embodiment is composed of a first hard phase, a plurality of second hard phases, and a binder phase.
• the cemented carbide may contain impurities as long as the effects of the present disclosure are not impaired. That is, the cemented carbide may be composed of a first hard phase, a plurality of second hard phases, a binder phase, and impurities. Examples of impurities include iron (Fe), molybdenum (Mo), calcium (Ca), silicon (Si), and sulfur (S).
• the impurity content of the cemented carbide (when there are two or more types of impurities, the total content of these impurities) may be 0% by mass or more and less than 0.1% by mass.
• the impurity content of the cemented carbide is measured by inductively coupled plasma emission spectroscopy (ICP optical emission spectroscopy). Shimadzu Corporation's "ICPS-8100" (trademark) can be used as the measuring device.
• the content of the second hard phase in the cemented carbide of embodiment 1 is 0.30% by volume or more and 1.60% by volume or less. This improves the adhesion resistance, heat resistance, and wear resistance of the cemented carbide.
• the content of the second hard phase in the cemented carbide may also be 0.40% by volume or more and 1.50% by volume or less, or 0.50% by volume or more and 1.40% by volume or less.
• the binder phase content of the cemented carbide of embodiment 1 is 8.0 vol% or more and 14.0 vol% or less. This improves the strength of the cemented carbide.
• the binder phase content of the cemented carbide may also be 8.1 vol% or more and 13.9 vol% or less, or 8.2 vol% or more and 13.8 vol% or less.
• the content of the first hard phase in the cemented carbide of embodiment 1 is the value obtained by subtracting the volumes of the second hard phase and binder phase from 100% by volume of the entire cemented carbide.
• the methods for measuring the content of the first hard phase, the content of the second hard phase, and the content of the binder phase of the cemented carbide are as follows.
• a cemented carbide alloy is cut out at an arbitrary position to expose a cross section, which is then polished to a mirror finish using a cross section polisher (manufactured by JEOL Ltd.).
• the machined surface of the cemented carbide is photographed using a scanning electron microscope (SEM) (Hitachi High-Technologies Corporation, "S-3400N” (trademark)) to obtain a backscattered electron image.
• SEM scanning electron microscope
• Six backscattered electron images are prepared. Each of the six backscattered electron images captures a different area. The location of the image can be set as desired.
• the observation conditions are a magnification of 5000x and an accelerating voltage of 10 kV.
• SEM-EDX energy dispersive X-ray analyzer
• (D1) The six backscattered electron images obtained in (B1) above are imported into a computer using image analysis software (ImageJ, version 1.51j8: https://imagej.nih.gov/ij/) and binarized to obtain six binarized images. After the images are imported, the binarization process is performed under conditions preset in the image analysis software by pressing the "Make Binary" button on the computer screen.
• the first region consisting of the first hard phase and the second region consisting of the second and third hard phases can be distinguished by the shade of color. For example, in the binarized image, the first hard phase is shown as a black region, and the second and third hard phases are shown as white regions.
• the average area percentage (area %) of the first hard phase for the six measurement fields, the average area percentage (area %) of the second hard phase for the six measurement fields, and the average area percentage (area %) of the binder phase for the six measurement fields correspond to the first hard phase content (volume %), second hard phase content (volume %), and binder phase content (volume %) of the cemented carbide, respectively.
• the D10 and D90 of tungsten carbide particles refer to the D10 (circle equivalent diameter at which the cumulative number-based frequency is 10%) and D90 (circle equivalent diameter at which the cumulative number-based frequency is 90%) of the equivalent area circle diameter (Heywood diameter) of the tungsten carbide particles in the cross section of the cemented carbide, respectively.
• the method for measuring D10 and D90 of tungsten carbide particles is as follows.
• (A2) Six binarized images are obtained using the same method as the method for measuring the content of the first hard phase, etc., of cemented carbide. Furthermore, to remove noise, the "Despeckle” button on the computer screen is pressed once, followed by the "Watershed” button. The grain boundaries of the first hard phase (tungsten particles) are also identified on the binarized images using the conditions preset in the image analysis software. The equivalent diameter of a circle with an area of 0.002 ⁇ m2 or more of tungsten carbide particles is measured by pressing "Analyze Particle" on the computer screen.
• the second hard phase comprises at least one first compound selected from the group consisting of TaNbC, TaNbN, TaNbCN, TiCN, TiNbC, TiNbN, and TiNbCN. This improves the adhesion resistance, heat resistance, and wear resistance of the cemented carbide.
• the ratio of the total number of Ta, Nb, and Ti atoms to the total number of C and N atoms of each of TaNbC, TaNbN, TaNbCN, TiCN, TiNbC, TiNbN, and TiNbCN is not limited to 1:1, and may include any conventionally known ratio as long as it does not impair the effects of the present disclosure.
• the second hard phase may consist of one first compound selected from the group consisting of TaNbC, TaNbCN, TiCN, and TiNbCN.
• the second hard phase may contain metal elements such as tungsten (W), chromium (Cr), and cobalt (Co) to the extent that the effects of the present disclosure are not impaired.
• the total content of W, Cr, and Co in the second hard phase may be 0% by mass or more and less than 0.1% by mass.
• the contents of W, Cr, and Co in the second hard phase are measured by ICP optical emission spectrometry.
• the composition of the second hard phase is measured as follows.
• (A3) An arbitrary position of the cemented carbide is thinned using an ion slicer (apparatus: IB09060CIS (trademark) manufactured by JEOL Ltd.) to prepare a sample with a thickness of 30 to 100 nm.
• the acceleration voltage of the ion slicer is 6 kV for thinning and 2 kV for finishing.
• STEM-HAADF high-angle annular dark field
• the imaging area for the STEM-HAADF image is set to the center of the sample, i.e., a position that does not include areas with properties clearly different from the bulk portion, such as near the surface of the cemented carbide (a position where the entire imaging area is the bulk portion of the cemented carbide).
• the measurement condition is an acceleration voltage of 200 kV.
• the median of the distance between the centers of gravity may be 5 ⁇ m or more and 13 ⁇ m or less, or 6 ⁇ m or more and 11 ⁇ m or less.
• the coefficient of variation of the distance between the centers of gravity may be 1.30 or more and 1.80 or less, or 1.40 or more and 1.70 or less.
• the distance d2 between the center of gravity C3 and the center of gravity C2 of another second hard phase 2 located closest to the center of gravity C3 corresponds to the distance between the centers of gravity of the two closest second hard phases.
• the center of gravity C2 of another second hard phase located closest to the center of gravity C3 means that the center of gravity C2 is the center of gravity closest to the center of gravity C3.
• the median of the distance between the centers of gravity of the two closest second hard phases in the cross section of the cemented carbide is the distance between the centers of gravity of the two closest second hard phases measured for each of all second hard phases within the measurement field of view, at which the cumulative frequency of the distance between the centers of gravity of the two closest second hard phases is 50%.
• the coefficient of variation of the distance between the centers of gravity of the second hard phases is the value obtained by dividing the standard deviation of the distance between the centers of gravity by the average value of the distance between the centers of gravity (standard deviation/average value).
• the average value of the distance between the centers of gravity means the arithmetic average of the distance between the centers of gravity of the two closest second hard phases measured for each of all second hard phases within the measurement field of view.
• the method for measuring the median value of the distance between the centers of gravity of the two most adjacent second hard phases in a cross section of a cemented carbide and the coefficient of variation of the distance between the centers of gravity is as follows.
• a position of the cemented carbide is cut out to expose a cross section.
• the cross section is polished using a cross-section polisher.
• the polished surface of the cemented carbide is photographed using an SEM to obtain a backscattered electron image.
• the observation conditions are a magnification of 1000x and an accelerating voltage of 10 kV.
• SEM-EDX energy dispersive X-ray analyzer
• C4 The backscattered electron image in which the second hard phases are identified is imported into a computer using image analysis software (Mac-View Version.5 (trademark) manufactured by Mountech Co., Ltd.), and the center of gravity of each second hard phase is identified under the following conditions, and the median value of the distance between the centers of gravity of the two closest second hard phases is measured.
• Acquisition mode Color difference Detection tolerance: 32, Detection accuracy: 0.5 Scanning: Density 10 x 1 time High cut: Enabled [110] Low cut: Inverted [150]
• (D4) Identify three visual fields in which 30 or more second hard phases can be confirmed. Based on all second hard phases in the three visual fields, measure the median of the distance between the centers of gravity of the two closest second hard phases and the coefficient of variation of the distance between the centers of gravity.
• the median of the distance between the centers of gravity of the two closest second hard phases measured above corresponds to the median of the distance between the centers of gravity of the two closest second hard phases in the cross section of the cemented carbide and the coefficient of variation of the distance between the centers of gravity.
• the binder phase contains 50% by mass or more of cobalt, which allows the cemented carbide to have excellent toughness.
• the cobalt content of the binder phase may be 50% by mass or more and 100% by mass or less, 60% by mass or more and 90% by mass or less, or 70% by mass or more and 80% by mass or less.
• the method for measuring the cobalt content of the binder phase is as follows.
• the region where the binder phase exists is identified in the element mapping image using the same methods as steps (A1) to (E1) of the method for measuring the content of the first hard phase, etc., of the cemented carbide described above.
• a rectangular measurement field of view measuring 24.9 ⁇ m x 18.8 ⁇ m is set in the element mapping image.
• the cobalt content is measured in the region where the binder phase exists in the measurement field.
• the average of the cobalt contents in the regions where the binder phase exists in the six measurement fields corresponds to the cobalt content of the binder phase.
• the binder phase may contain iron (Fe), nickel (Ni), etc., to the extent that the effects of the present disclosure are not impaired.
• the binder phase may contain cobalt and one or both of nickel and iron.
• the binder phase may consist of cobalt and one or both of nickel and iron.
• the cemented carbide of embodiment 1 may contain 0.08% by mass or more and 0.5% by mass or less of chromium.
• the chromium content of the cemented carbide may be 0.10% by mass or more and 0.48% by mass or less, or 0.12% by mass or more and 0.46% by mass or less.
• the chromium content of the cemented carbide is measured by ICP atomic emission spectrometry.
• the cemented carbide of the first embodiment can be produced through, for example, a preparation step, a mixing step, a molding step, a sintering step, and a cooling step.
• raw material powders are prepared.
• raw material powders include WC powder, TaNbC powder, TaNbN powder, TaNbCN powder, TiCN powder, TiNbC powder, TiNbN powder, TiNbCN powder, NbC powder, Ta2O5 powder, TiO2 powder, Co powder, Ni powder, and Fe powder.
• These raw material powders are appropriately selected based on the target composition of the cemented carbide.
• Chromium carbide ( Cr3C2 ) powder may be prepared as a grain growth inhibitor.
• the average particle size of the tungsten carbide (WC) powder is 1.0 ⁇ m or more and 1.8 ⁇ m or less.
• the TaNbC powder, TaNbN powder, TaNbCN powder, TiCN powder, TiNbC powder, TiNbN powder, TiNbCN powder, NbC powder, Ta2O5 powder, and TiO2 powder have an average particle size of 1 ⁇ m or more and 2 ⁇ m or less. These powders are raw material powders for the second hard phase.
• the average particle size of the Co powder, Ni powder, and Fe powder may be 0.1 ⁇ m or more and 5 ⁇ m or less.
• the average particle size of the raw material powders mentioned above is determined by the Fischer method.
• ⁇ Mixing process> In the mixing process, the raw material powders are mixed in a predetermined ratio to obtain a mixed powder. The mixing ratio of each raw material powder is adjusted appropriately depending on the target cemented carbide composition. A ball mill is used for mixing. The mixing conditions are a ball diameter of 6 mm, a rotation speed of 100 rpm, and a mixing time of 12 to 48 hours.
• the mixed powder is molded into a desired shape to obtain a molded body.
• the molding method and molding conditions are not particularly limited and may be any commonly used method and conditions.
• ⁇ Sintering process> the compact is first heated to 1365 to 1400°C and held there for 120 minutes.
• the heating rate above 1000°C is 1°C/min.
• the pressure here can be vacuum or N2 (flow rate 2 L/min, partial pressure 5 kPa).
• the compact is cooled to 1200°C at a temperature drop rate of -4.5 to -5.5°C/min to obtain a cemented carbide intermediate.
• the cemented carbide intermediate is subjected to HIP (Hot Isostatic Pressing). Specifically, the cemented carbide intermediate is subjected to a temperature of 1320°C and a pressure of 10 MPa for 60 minutes using Ar gas as the pressure medium. The cemented carbide intermediate is then slowly cooled to obtain the cemented carbide of embodiment 1.
• the temperature drop rate during slow cooling can be any general condition and is not particularly limited.
• the above conditions control the position at which the second hard phase precipitates, enabling the production of a cemented carbide according to the first embodiment, in which the median distance between the centers of gravity of the two closest second hard phases in the cross section of the cemented carbide is 4 ⁇ m to 15 ⁇ m, and the coefficient of variation of the distance between the centers of gravity is 1.20 to 1.90.
• Embodiment 2 Cutting tool
• the cutting tool 10 of Embodiment 2 includes a substrate 5 made of the cemented carbide of Embodiment 1 and a coating 6 provided on the substrate 5.
• the cutting tool of Embodiment 2 can have a long tool life even when machining cemented carbide. The reason for this is not clear, but is presumed to be as follows.
• a coating is provided on a substrate made of the cemented carbide of embodiment 1.
• the coating structure is homogeneous.
• the inhomogeneous areas (e.g., unevenness) of the coating vary depending on the internal structure of the substrate.
• the median value of the distance between the centers of gravity of the two closest second hard phases in the cross section of the cemented carbide is 4 ⁇ m or more and 15 ⁇ m or less, and the coefficient of variation of the distance between the centers of gravity is 1.20 or more and 1.90 or less, the homogeneity of the substrate and coating is improved. Therefore, the cutting tool of embodiment 2 can have a long tool life even when machining cemented carbide.
• the type of cutting tool is not particularly limited.
• Examples of cutting tools include cutting tools, drills, end mills, indexable cutting inserts for milling, indexable cutting inserts for turning, metal saws, gear cutting tools, reamers, taps, etc.
• the cutting tool 10 of embodiment 2 can demonstrate excellent effects, particularly in the case of a ball end mill.
• the substrate 5 of the cutting tool 10 shown in Figure 2 is made of the cemented carbide of embodiment 1.
• the coating may be disposed so as to cover the entire surface of the substrate, or it may be disposed so as to cover only a portion of the surface. If the coating is disposed so as to cover only a portion of the substrate, it is preferable that it be disposed so as to cover at least the surface of the portion of the substrate that is involved in cutting.
• the portion of the substrate that is involved in cutting refers to the region of the substrate that is within 0.5 mm of the cutting edge.
• the coating may be composed of a compound of one or more elements selected from the group consisting of metal elements of Groups 4, 5, and 6 of the periodic table, aluminum (Al), and silicon (Si), and one or more elements selected from the group consisting of carbon, nitrogen, oxygen, and boron. Examples include TiCN, Al2O3 , TiAlN, TiN, TiC, and AlCrN.
• the coating may also be composed of cubic boron nitride (cBN), diamond-like carbon, or diamond.
• the diamond may be either single crystal diamond or polycrystalline diamond.
• the coating may be single-layer or multi-layer.
• the thickness of the coating may be 1 ⁇ m or more and 20 ⁇ m or less, or 5 ⁇ m or more and 15 ⁇ m or less.
• the cutting tool of embodiment 2 is manufactured, for example, by the following method. First, a substrate made of the material of embodiment 1 is prepared. The surface of the substrate is etched with acid and alkali.
• a coating is formed on the substrate after the etching process to obtain the cutting tool of embodiment 2.
• the coating can be formed by a gas-phase method such as chemical vapor deposition (CVD) or physical vapor deposition (PVD).
• the coating When the coating is formed by the CVD method, it is easy to obtain a coating with excellent adhesion to the substrate.
• CVD methods include hot filament CVD.
• a cutting tool includes a substrate made of the cemented carbide of embodiment 1 and a coating provided on the substrate, The coating is made of diamond.
• Each sample of cemented carbide was prepared according to the following procedure. ⁇ Preparation process> The raw material powders prepared were WC powder, TaNbC powder (average particle size: 1 ⁇ m), TiCN powder (average particle size: 1 ⁇ m), NbC powder (average particle size: 1 ⁇ m), Ta2O5 powder (average particle size: 1 ⁇ m), TiO2 powder (average particle size: 1 ⁇ m), Cr3C2 powder (average particle size: 1 ⁇ m), Co powder (average particle size: 1 ⁇ m), Ni powder (average particle size: 1 ⁇ m), and Fe powder (average particle size: 1 ⁇ m).
• WC powders were prepared from A.L.M.T.
• TaNbC powder was prepared from H.C. "TaNbC 67/33" manufactured by Starck was prepared so as to have an average particle size of 1 ⁇ m.
• ⁇ Mixing process> The raw material powders were mixed in a ball mill or attritor in the proportions shown in Table 1 to obtain mixed powders.
• the mixing conditions for the "ball mill” were a ball diameter of 6 mm, a rotation speed of 100 rpm, and a mixing time of 24 hours.
• the mixing conditions for the "attritor” were a rotation speed of 250 rpm, and a mixing time of 1 hour.
• the cemented carbide intermediate was subjected to HIP treatment. Specifically, the cemented carbide intermediate was subjected to a temperature of 1320°C and a pressure of 10 MPa for 60 minutes using Ar gas as the pressure medium. It was then slowly cooled to obtain each cemented carbide sample.
• ⁇ D10 and D90 of particle size of tungsten carbide particles The particle sizes D10 and D90 of the tungsten carbide particles were measured for each cemented carbide sample. The specific measurement method is as described in embodiment 1. The results are shown in the "D10” and “D90” columns of "First hard phase” under "Cemented carbide” in Table 3.
• composition of the second hard phase in each cemented carbide sample was measured.
• the specific measurement method is as described in embodiment 1.
• the results are shown in the "Composition” column of "Second Hard Phase” in "Cemented Carbide” in Table 3.
• composition of binder phase The composition of the binder phase and the cobalt content of the binder phase were measured for each cemented carbide sample. The specific measurement method is as described in embodiment 1. The results are shown in the "Composition” and “Co Content” columns of "Binder Phase” under "Cemented Carbide” in Table 3.
• a 15 ⁇ m thick polycrystalline diamond coating was formed on the etched substrate by hot filament CVD to obtain each sample cutting tool (ball end mill).
• Each sample ball end mill was used to machine the inclined surface of cemented carbide. Machining conditions were: rotation speed 3000 rpm, table feed F 200 mm/min, depth of cut (axial direction) ap 0.05 mm, depth of cut (radial direction) ae 0.25 mm, dry machining. The cutting length until the surface of the workpiece deteriorated was measured. The longer the cutting length, the longer the tool life is considered to be. The results are shown in the "Cutting length” column under "Cutting test" in Table 3.
• the cemented carbide alloys and cutting tools of Samples 1 to 20 correspond to Examples.
• the cemented carbide alloys and cutting tools of Samples 21 to 31 correspond to Comparative Examples. It was confirmed that the cutting tools of the Examples had a longer tool life than the cutting tools of the Comparative Examples. It was confirmed that the cutting tools of the Examples had a long tool life when used to machine cemented carbide alloys. Although the cutting tools of the Examples had a large coating thickness, it is presumed that the coating was homogeneous and had strong adhesion between the substrate and the coating, which prevented surface deterioration due to film peeling.
• First hard phase 2.
• Second hard phase 3.
• Binding phase 4. Cemented carbide, 5.
• Base material 6. Coating, 10. Cutting tool.

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