Carbide alloy materials and cutting tools for cutting tools

Abstract

To provide a cemented carbide material for a cutting tool that can extend the life of the cutting tool when used as a material for the cutting tool, and a cutting tool including the same.SOLUTION: The cemented carbide material for a cutting tool includes tungsten carbide particles and a binder phase, and has three or less pores having an equivalent circle diameter of less than 0.2 μm in a rectangular measurement field of 24.9 μm×18.8 μm, the measurement field being provided in a central portion of a cross section of the cemented carbide material.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a cemented carbide material for cutting tools and a cutting tool.

Background Art

[0002] Cemented carbide comprising tungsten carbide particles and a binder phase containing cobalt is widely used as a material for cutting tools (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In recent years, the demand for cost reduction has become increasingly severe, and cutting tools with a long tool life are required. Therefore, an object of the present disclosure is to provide a cemented carbide material for cutting tools that enables the extension of the tool life of a cutting tool when used as a material for the cutting tool, and a cutting tool including the same.

Means for Solving the Problems

[0005] The present disclosure is a cemented carbide material for cutting tools, wherein the cemented carbide material includes tungsten carbide particles and a binder phase, the cemented carbide material contains three or fewer pores having an equivalent circle diameter of less than 0.2 μm in a rectangular measurement field of 24.9 μm × 18.8 μm, and the measurement field is provided at the center of the cross section of the cemented carbide material, and it is a cemented carbide material for cutting tools.

[0006] The present disclosure is a cutting tool made of cemented carbide, wherein the cemented carbide includes tungsten carbide particles and a binder phase, The aforementioned cemented carbide contains three or fewer pores with an equivalent circular diameter of less than 0.2 μm in a rectangular measurement field of view measuring 24.9 μm × 18.8 μm. The measurement field is provided within a region S1 on the cross-section of the cemented carbide, including the cutting edge of the cutting tool. The region S1 is a cutting tool in which, in the cross-section of the cemented carbide, the distance from the cutting edge is 100 μm or less, and the distance from the surface of the cutting tool is 0.5 μm or more and 30 μm or less. [Effects of the Invention]

[0007] This disclosure makes it possible to provide cutting tools with a long tool life. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 shows an example of an image of the cemented carbide material of Embodiment 1 taken with a scanning electron microscope. [Figure 2] Figure 2 is a diagram illustrating the position of the measurement field of view for the cemented carbide material in Embodiment 1. [Figure 3] Figure 3 is a diagram illustrating the method for setting the measurement field of view in a cemented carbide cutting tool according to Embodiment 2. [Modes for carrying out the invention]

[0009] [Description of Embodiments in this Disclosure] First, the embodiments of this disclosure will be listed and described. (1) This disclosure relates to cemented carbide materials for cutting tools, The cemented carbide material comprises tungsten carbide particles and a binder phase, The aforementioned cemented carbide material contains three or fewer pores with an equivalent circular diameter of less than 0.2 μm in a rectangular measurement field of view measuring 24.9 μm × 18.8 μm. The measurement field is a cemented carbide material for cutting tools, provided in the central part of the cross-section of the cemented carbide material.

[0010] According to the present disclosure, it is possible to provide a cutting tool having a long tool life.

[0011] (2) Preferably, the average particle size of the tungsten carbide particles is 0.80 μm or more and 3.00 μm or less. According to this, the tool life of the cutting tool is further improved.

[0012] (3) Preferably, the average particle size of the tungsten carbide particles is more than 1.00 μm and 3.00 μm or less. According to this, the tool life of the cutting tool is further improved.

[0013] (4) Preferably, the cemented carbide material contains 85.0% by volume or more and 95.5% by volume or less of the tungsten carbide particles and 0.5% by volume or more and 15.0% by volume or less of the binder phase. According to this, the tool life of the cutting tool is further improved.

[0014] (5) The present disclosure is a cutting tool made of cemented carbide, The cemented carbide includes tungsten carbide particles and a binder phase, The cemented carbide contains 3 or less pores having an equivalent circle diameter of less than 0.2 μm in a rectangular measurement field of 24.9 μm × 18.8 μm, The measurement field is provided in a region S1 on the cross-section of the cemented carbide including the cutting edge of the cutting tool, The region S1 is a region on the cross-section of the cemented carbide where the distance from the cutting edge is 100 μm or less and the distance from the surface of the cutting tool is 0.5 μm or more and 30 μm or less.

[0015] The cutting tool of the present disclosure can have a long tool life.

[0016] [Details of Embodiments of the Present Disclosure] Specific examples of the cemented carbide material for cutting tools and cutting tools according to the present disclosure will be described below with reference to the drawings. In the drawings of the present disclosure, the same reference numerals represent the same parts or corresponding parts. In addition, dimensional relationships such as length, width, thickness, depth, etc. are appropriately changed for the sake of clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0017] In this specification, the notation in the form of "A to B" means the upper and lower limits of the range (that is, A or more and B or less). When there is no unit description for A and there is a unit description only for B, the units of A and B are the same.

[0018] In this specification, pores with a diameter less than 0.2 μm are also referred to as "first pores", and pores with a diameter of 0.2 μm or more are also referred to as "second pores". The first pores and the second pores are collectively also referred to as "pores".

[0019] In this specification, a cutting tool means a tool that does not rotate itself but rotates a workpiece to perform machining such as cutting, or a tool that rotates around a rotation axis that does not pass through itself to perform machining such as cutting. Further, when the tip portions of a drill or an end mill are replaceable, the tip portions (drill tip replacement type cutting tips, end mill tip replacement type cutting tips) are also included in the cutting tool.

[0020] [Embodiment 1: Cemented Carbide Material for Cutting Tools] One embodiment of the present disclosure (hereinafter also referred to as "the present embodiment") is a cemented carbide material for a cutting tool, The cemented carbide material includes tungsten carbide particles and a binder phase, The cemented carbide material contains 3 or less pores with an equivalent circle diameter less than 0.2 μm in a rectangular measurement field of 24.9 μm × 18.8 μm, The measurement field is provided at the central portion of the cross section of the cemented carbide material for a cutting tool.

[0021] <Pore> The cemented carbide material of this embodiment contains three or fewer pores (first pores) with an equivalent circle diameter of less than 0.2 μm in a rectangular measuring field of view measuring 24.9 μm × 18.8 μm, and this measuring field is located in the center of the cross-section of the cemented carbide material. The cemented carbide material having three or fewer first pores in this measuring field has excellent strength. Therefore, cutting tools using this cemented carbide material have improved chipping resistance, as well as fracture resistance and / or breakage resistance, resulting in improved tool life.

[0022] The number of first pores in the above measurement field of the cemented carbide material is 3 or less, preferably 2 or less, preferably 1 or less, and most preferably 0. The number of first pores is preferably 0 to 3, preferably 0 to 2, preferably 0 to 1, and most preferably 0.

[0023] In this embodiment, it is preferable that the cemented carbide material does not contain a second pore with an equivalent circular diameter of 0.2 μm or more in the measurement field described above. This results in a cemented carbide material with high strength. Consequently, cutting tools using this cemented carbide material exhibit improved chipping resistance, as well as fracture and / or breakage resistance, leading to improved tool life.

[0024] In this specification, the method for measuring the number of first and second pores in the above measurement field of a cemented carbide material is as follows (A1) to (H1).

[0025] (A1) The cemented carbide material is cut so as to pass near its center of gravity, exposing the cross-section, and the cross-section is polished to a mirror finish. Examples of methods for mirror polishing include polishing with diamond paste, using a focused ion beam (FIB) device, using a cross-section polisher (CP) device, and methods combining these.

[0026] (B1) The mirror-finished surface of the cemented carbide material is analyzed using energy-dispersive X-ray spectroscopy (SEM-EDX) to identify the elements contained in the cemented carbide material.

[0027] (C1) The mirror-finished surface of the cemented carbide material is photographed with a scanning electron microscope to obtain an image. The imaging area of ​​the image is set to the central part of the cross-section of the cemented carbide material, that is, a position that does not include parts that clearly have different properties from the bulk portion, such as the vicinity of the surface of the cemented carbide material (a position where the entire imaging area is the bulk portion of the cemented carbide material). The observation magnification is set to 5000x.

[0028] Figure 1 is an example of a scanning electron microscope image of the cemented carbide material 1 of this embodiment. In the lower right scale of Figure 1, the length of the straight line is 1 μm. In Figure 1, the cemented carbide material 1 contains pores 2. As shown in Figure 1, pores 2 are very small and may be difficult to identify in the scanning electron microscope image. However, as explained in (F1) below, it is possible to identify the pores by superimposing the binarized image of the scanning electron microscope image with an elemental mapping image.

[0029] (D1) The imaging area described in (C1) above is analyzed using scanning electron microscopy (SEM-EDX) to determine the distribution of the elements identified in (B1) above within the imaging area and to obtain an elemental mapping image. In the elemental mapping image, no elements are present in the pore regions.

[0030] (E1) The captured image obtained in (C1) above is imported into a computer, and image processing is performed using image analysis software (ImageJ, version 1.51j8: https: / / imagej.nih.gov / ij / ) to perform binarization. Specifically, after importing the captured image into the computer, pressing the "MakeBinary" button on the computer screen executes the binarization process according to the conditions pre-set in the image analysis software. In the image after binarization, tungsten carbide particles are shown in the lightest color (white), and the binding phase and pores are shown in black.

[0031] (F1) By overlaying the elemental mapping image obtained in (D1) above with the binarized image obtained in (E1) above, the regions where pores exist are identified on the binarized image. Specifically, among the regions shown in black in the binarized image, the regions where elements are absent in the elemental mapping image correspond to the regions where pores exist.

[0032] (G1) In the obtained binarized image, one rectangular measurement field of view of 24.9 μm × 18.8 μm is set. Based on the number of pixels in the area identified as a pore within the measurement field of view, the equivalent circle diameter of the pore (Heywood diameter: equivalent circle diameter of an equal area) is calculated using the image analysis software described above.

[0033] (H1) Based on the calculation results in (G1) above, the number of first pores with an equivalent circle diameter of less than 0.2 μm and the number of second pores with an equivalent circle diameter of 0.2 μm or more in the measurement field are measured.

[0034] As far as the applicant has measured, as long as the measurements are performed on the same sample, the variation in the measurement results is small even when the cutting location of the cross-section of the cemented carbide material is arbitrarily set, the imaging area described in (C1) above is arbitrarily set on the cross-section, and the number of first and second pores is measured multiple times according to the procedures in (B1) to (H1) above. It has been confirmed that arbitrarily setting the cutting location of the cross-section of the cemented carbide material and arbitrarily setting the imaging area of ​​the captured image does not result in arbitrary results.

[0035] For example, as shown in Figure 2, five imaging areas were set on the cross-section of the cemented carbide material 1, including the central part A and positions A1, A2, A3, and A4, each at the same distance from the central part A. Even when the number of first and second pores was measured at each of these five locations according to the procedures (B1) to (H1) above, the variation in the measurement results was small, confirming that the imaging area of ​​the captured image could be arbitrarily set without being arbitrary.

[0036] <Tungsten carbide particles> ≪Composition≫ Tungsten carbide particles (hereinafter also referred to as "WC particles") are particles made of tungsten carbide. Here, the tungsten carbide may be pure tungsten carbide that does not contain impurity elements, or it may be tungsten carbide that contains impurity elements, as long as the effects of this disclosure are not impaired. The content of impurities contained in the tungsten carbide (if there are two or more elements constituting the impurities, their total concentration) is preferably less than 0.1 mass% of the total amount of WC particles. The content of impurities in the WC particles is measured by ICP emission spectrometry (Inductively Coupled Plasma) Emission Spectroscopy (measuring device: Shimadzu Corporation "ICPS-8100" trademark).

[0037] ≪Average particle size≫ The average particle size of the tungsten carbide particles is preferably 0.80 μm or more and 3.00 μm or less, more preferably between 1.00 μm and 3.00 μm, and even more preferably between 1.00 μm and 2.50 μm. This further improves tool life.

[0038] In this specification, the average particle size of tungsten carbide particles contained in the cemented carbide material refers to the equivalent circle diameter (Heywood diameter) D50 of the WC particles contained in the cemented carbide material (the equivalent circle diameter at which the cumulative frequency based on the number of particles reaches 50%, the median diameter D50). The method for measuring the particle diameter of each particle to calculate the average particle size of the WC particles is as follows (A2) to (B2).

[0039] (A2) By superimposing the elemental mapping image obtained by the same method as (A1) to (E1) described in the method for measuring the number of first and second pores in the above measurement field of the cemented carbide material with the image after binarization, the region where tungsten carbide particles exist is identified on the binarized image. Specifically, the region shown in the lightest color (white) in the binarized image, where tungsten (W) and carbon (C) exist in the elemental mapping image, corresponds to the region where tungsten carbide particles exist.

[0040] (B2) A rectangular measurement field of view measuring 24.9 μm × 18.8 μm is set in the image after the binarization process described above. The equivalent circle diameter (Heywood diameter: equivalent circle diameter of an equal area) of each tungsten carbide particle in the measurement field of view is calculated using the image analysis software described above.

[0041] As far as the applicant has measured, as long as the measurements are performed on the same sample, the variation in the measurement results is small even when the cutting location of the cross-section of the cemented carbide material is arbitrarily set, the imaging area described in (C1) above is arbitrarily set on the cross-section, and the average particle size of tungsten carbide particles is measured multiple times according to the procedures in (A2) and (B2) above. It has been confirmed that arbitrarily setting the cutting location of the cross-section of the cemented carbide material and arbitrarily setting the imaging area of ​​the captured image does not result in arbitrary results.

[0042] <Binded phase> The cemented carbide of this embodiment includes a binder phase. Preferably, the binder phase contains cobalt as its main component. Here, "containing cobalt as its main component" means that the cobalt content in the binder phase is 90% by mass or more and 100% by mass or less. The cobalt content in the binder phase can be measured by ICP emission spectrometry (equipment used: Shimadzu Corporation's "ICPS-8100" trademark).

[0043] The bonding phase can include, in addition to cobalt, chromium, vanadium, nickel, tungsten, titanium, niobium, tantalum, and others.

[0044] <Composition of cemented carbide material> The cemented carbide material of this embodiment preferably contains 85.0% to 95.5% by volume of tungsten carbide particles and 0.5% to 15.0% by volume of a binder phase. This further improves the tool life of cutting tools using the cemented carbide material.

[0045] The lower limit of the tungsten carbide particle content in cemented carbide material can be 85.0 volume% or more, 88.0 volume% or more, or 90.0 volume% or more. The upper limit of the tungsten carbide particle content in cemented carbide material can be 99.5 volume% or less, or 95.0 volume% or less. The tungsten carbide particle content in cemented carbide material can be 85.0 volume% or more and 99.5 volume% or less, 88.0 volume% or more and 99.5 volume% or less, 90.0 volume% or more and 99.5 volume% or less, 85.0 volume% or more and 95.0 volume% or less, 88.0 volume% or more and 95.0 volume% or less, or 90.0 volume% or more and 95.0 volume% or less.

[0046] The lower limit of the binder phase content in cemented carbide material can be 0.5 volume% or more, or 5.0 volume% or more. The upper limit of the binder phase content in cemented carbide material can be 15.0 volume% or less, 12.0 volume% or less, or 10.0 volume% or less. The binder phase content in cemented carbide material can be 0.5 volume% or more and 15.0 volume% or less, 5.0 volume% or more and 15.0 volume% or less, 0.5 volume% or more and 12.0 volume% or less, 5.0 volume% or more and 12.0 volume% or less, 0.5 volume% or more and 10.0 volume% or less, or 5.0 volume% or more and 10.0 volume% or less.

[0047] The cemented carbide material may contain 85.0% to 99.5% by volume of tungsten carbide particles and 0.5% to 15.0% by volume of the binder phase. The cemented carbide material may contain 88.0% to 99.5% by volume of tungsten carbide particles and 0.5% to 12.0% by volume of the binder phase. The cemented carbide material may contain 90.0% to 99.5% by volume of tungsten carbide particles and 0.5% to 10% by volume of the binder phase. The cemented carbide material may contain 85.0% to 95.0% by volume of tungsten carbide particles and 5.0% to 15.0% by volume of the binder phase. The cemented carbide material may contain tungsten carbide particles in an amount of 88.0% to 95.0% by volume, and a binder phase in an amount of 5.0% to 12.0% by volume. The cemented carbide material may contain tungsten carbide particles in an amount of 90.0% to 95.0% by volume, and a binder phase in an amount of 5.0% to 10.0% by volume.

[0048] The cemented carbide material may consist of tungsten carbide particles and a binder phase. In addition to tungsten carbide particles and the binder phase, the cemented carbide material may contain hard phase particles other than tungsten carbide and / or impurities. Examples of such hard phase particles include titanium, niobium, and tantalum. The impurity content of the cemented carbide material may be 0.1% by mass or less. The cemented carbide material may consist of tungsten carbide particles, a binder phase, and impurities. The cemented carbide material may consist of tungsten carbide particles, a binder phase, hard phase particles, and impurities.

[0049] The methods for measuring the respective content (volume %) of tungsten carbide particles and the binding phase in cemented carbide materials are as follows (A3) to (B3).

[0050] (A3) By superimposing the elemental mapping image obtained by the same method as (A1) to (E1) described in (A3) for measuring the number of first and second pores in the above measurement field of the cemented carbide material with the image after binarization, the regions where tungsten carbide particles exist and the regions where the bonding phase exists are identified on the binarized image. Specifically, the regions shown in the lightest color (white) in the binarized image, where tungsten (W) and carbon (C) exist in the elemental mapping image, correspond to the regions where tungsten carbide particles exist. The regions shown in black in the binarized image, where cobalt (Co) exists in the elemental mapping image, correspond to the regions where the bonding phase exists.

[0051] (B3) A rectangular measurement field of view of 24.9 μm × 18.8 μm is set in the image after the binarization process described above. Using the image analysis software described above, the area percentages of the tungsten carbide particles and the binder phase are measured with the area of ​​the entire measurement field of view as the denominator. In this specification, the area percentage of the tungsten carbide particles corresponds to the tungsten carbide particle content (volume %) of the cemented carbide material, and the area percentage of the binder phase corresponds to the binder phase content (volume %) of the cemented carbide material.

[0052] If the cemented carbide material contains hard phase particles in addition to WC particles and the binder phase, the region where the hard phase particles exist is identified in (A3) above, and their area percentage is measured in (B3) above. The area percentage of the hard phase particles corresponds to the hard phase particle content (volume %) of the cemented carbide material.

[0053] As far as the applicant has measured, as long as the measurements are performed on the same sample, the variation in measurement results is small even when the cutting location of the cross-section of the cemented carbide material is arbitrarily set, the imaging area described in (C1) above is arbitrarily set on the cross-section, and the area percentage measurements of tungsten carbide particles, binder phase, hard phase particles, and impurities are performed multiple times according to the procedures in (A3) and (B3) above. It has been confirmed that arbitrarily setting the cutting location of the cross-section of the cemented carbide material and arbitrarily setting the imaging area of ​​the captured image does not result in arbitrary results.

[0054] <Manufacturing method for cemented carbide material for cutting tools> The cemented carbide material for cutting tools according to this embodiment can be manufactured by performing the following steps in the order described above: preparation of raw material powder, mixing, granulation, molding, sintering, HIP treatment, and cooling. Each step will be described below.

[0055] ≪Preparation process≫ The preparation process involves preparing the raw material powders for the cemented carbide material. Examples of raw material powders include tungsten carbide powder, which is the raw material for tungsten carbide particles; cobalt (Co) powder, which is the raw material for the binder phase; and chromium carbide (Cr3C2) powder, which is a grain growth inhibitor. Furthermore, vanadium carbide (VC) powder, which is also a grain growth inhibitor, and niobium carbide (NbC) powder, which is the raw material for hard phase particles, can also be used. Commercially available tungsten carbide powder, cobalt powder, chromium carbide powder, vanadium carbide powder, and niobium carbide powder can be used.

[0056] The average particle size of tungsten carbide powder can be between 0.7 μm and 5.0 μm. The average particle size of cobalt powder can be between 0.8 μm and 1.2 μm. The average particle size of niobium carbide powder can be between 0.5 μm and 2.0 μm. The average particle size of chromium carbide powder can be between 1.0 μm and 2.0 μm. The average particle size of vanadium carbide powder can be between 0.5 μm and 1.0 μm. In this specification, the average particle size of the raw material powder refers to the 50% cumulative particle size of the equivalent sphere diameter (median diameter d50). This average particle size is measured using a particle size distribution analyzer (product name: MT3300EX) manufactured by Microtrac.

[0057] ≪Mixing process≫ The mixing process involves mixing the individual raw material powders prepared in the preparation process. The mixing process yields a mixed powder in which the individual raw material powders are combined.

[0058] The proportion of tungsten carbide powder in the mixed powder can be, for example, 84% by mass or more and 99.5% by mass or less. The proportion of cobalt powder in the mixed powder can be, for example, 0.5% by mass or more and 15% by mass or less. The proportion of niobium carbide powder in the mixed powder can be, for example, 0% by mass or more and 5% by mass or less. The proportion of chromium carbide powder in the mixed powder can be, for example, 0.1% by mass or more and 1.2% by mass or less. The proportion of vanadium carbide powder in the mixed powder can be, for example, 0% by mass or more and 0.2% by mass or less.

[0059] An attritor or ball mill can be used to mix each raw material powder. The mixing time in an attritor can be between 7 and 15 hours. The mixing time in a ball mill can be between 30 and 60 hours.

[0060] ≪Pelletization process≫ The mixed powder obtained by mixing is dried by a water bath to obtain dried raw material powder. A mixed solution is prepared by mixing polyethylene oxide (weight-average molecular weight (Mw): approximately 100,000) and glycerin in a volume ratio of 1:1. The above dried raw material powder is granulated by spraying this mixed solution onto it. Hereinafter, the mixed solution sprayed onto the dried raw material powder will also be referred to as the binder.

[0061] ≪Molding process≫ The molding process involves shaping the mixed powder obtained in the mixing process into a form suitable for a cutting tool to obtain a molded body. The molding method and conditions in the molding process can be general methods and conditions, and are not particularly limited.

[0062] ≪Sintering Process≫ The sintering process is a process in which the molded body obtained in the molding process is sintered to obtain cemented carbide material. The sintering process can be carried out according to the following procedure.

[0063] The molded body is placed in a sintering furnace and heated to 800°C in a vacuum (1.0 Pa or less) at a heating rate of 0.5 to 1.0°C / min.

[0064] Next, Ar gas is introduced into the sintering furnace, and the material is heated to 1400°C at a heating rate of 0.5-1.0°C / min under an Ar gas atmosphere (7 MPaG). Subsequently, the pressure inside the sintering furnace is reduced, and the material is held at 1400°C for 120 minutes under an Ar gas atmosphere (140 kPaG) to obtain cemented carbide material.

[0065] ≪HIP Treatment Process≫ The HIP treatment process is a process of applying HIP (Hot Isostatic Pressing) to cemented carbide material after sintering. For example, a temperature of 1370°C and a pressure of 100-200 MPa can be applied to the cemented carbide material for 120 minutes using Ar gas as the pressure medium.

[0066] ≪Cooling process≫ The cooling process involves cooling the cemented carbide material after HIP treatment. For example, the cemented carbide material can be rapidly cooled in Ar gas after HIP treatment.

[0067] Features of the manufacturing method for cemented carbide material in this embodiment The cemented carbide material obtained by the above manufacturing method has three or fewer pores with an equivalent circle diameter of less than 0.2 μm in a rectangular measurement field of view of 24.9 μm × 18.8 μm. The reason for this is presumed to be as follows.

[0068] Pores in cemented carbide material are presumed to be formed when the binder vaporizes during the sintering process. In the above manufacturing method, a mixed solution of polyethylene oxide and glycerin is used as the binder in the granulation process, and the material is heated at a slow heating rate under pressure during the sintering process. This binder has a large molecular weight and does not vaporize easily. Therefore, in the above manufacturing method, vaporization of the binder occurs almost simultaneously inside and near the surface of the molded body during the heating process, and the binder does not remain inside the molded body but is easily discharged to the outside. Furthermore, in the above manufacturing method, the material is held at the maximum temperature (1400°C) and in an Ar gas atmosphere (140kPaG) for a certain period of time (120 minutes). It is held under pressure for a certain period of time. By pressurizing the molded body at a high temperature, the structure flows, and the pores become smaller. Therefore, in the cemented carbide material after sintering, pores are less likely to exist inside, and the number of pores is reduced overall. Also, even if pores are present, their size is minute. The inventors have newly discovered, through diligent research, that by using a mixed solution of polyethylene oxide and glycerin as a binder and heating under pressure and at a slow heating rate during the sintering process, it is possible to obtain a cemented carbide material with three or fewer pores having an equivalent circle diameter of less than 0.2 μm in a rectangular measurement field of view of 24.9 μm × 18.8 μm.

[0069] On the other hand, in conventional methods for manufacturing cemented carbide materials, granulation is performed by spray drying for efficiency reasons, and polyethylene glycol, which is suitable for spray drying, is used as a binder. Polyethylene glycol has a small molecular weight and is easily vaporized. However, polyethylene oxide used in this embodiment cannot be used for spray drying because it causes clogging of the spray dryer. Furthermore, in conventional methods for manufacturing cemented carbide materials, the heating rate during sintering is set to 10-20°C / min for efficiency reasons, and sintering at the maximum temperature is performed under reduced pressure or vacuum. As a result, the binder near the surface of the molded body is easily vaporized during heating, but the binder inside the molded body is not easily vaporized. Therefore, in cemented carbide materials after sintering, pores tend to exist inside, and the structure tends to be non-uniform.

[0070] [Embodiment 2: Cutting Tools] This embodiment is a cutting tool made of cemented carbide, The cemented carbide comprises tungsten carbide particles and a binder phase, The cemented carbide contains three or fewer pores with an equivalent circular diameter of less than 0.2 μm in a rectangular measurement field of view measuring 24.9 μm × 18.8 μm. The measurement field is provided within a region S1 on the cross-section of the cemented carbide, including the cutting edge of the cutting tool. The region S1 is a cutting tool in which the distance from the cutting edge is 100 μm or less and the distance from the surface of the cutting tool is 0.5 μm or more and 30 μm or less in the cross-section of the cemented carbide.

[0071] Examples of cutting tools in this embodiment include replaceable tip cutting inserts for drills, replaceable tip cutting inserts for end mills, replaceable tip cutting inserts for milling, replaceable tip cutting inserts for turning, and the like. The cutting tool in this embodiment may be entirely made of the above-mentioned cemented carbide. Alternatively, only a part of it may be made of the above-mentioned cemented carbide. Here, "a part of it being made of the above-mentioned cemented carbide" indicates an embodiment in which the above-mentioned cemented carbide is attached to a predetermined position on any base material to form a cutting edge.

[0072] <Pore> The cemented carbide alloy constituting the cutting tool of this embodiment contains three or fewer pores (first pores) with an equivalent circular diameter of less than 0.2 μm within a rectangular measurement field of view of 24.9 μm × 18.8 μm. This improves the strength of the cutting tool. Consequently, the cutting tool of this embodiment has improved chipping resistance, as well as fracture and / or breakage resistance, resulting in an improved tool life.

[0073] The number of first pores in the above measurement field of view of the cutting tool is preferably 3 or less, preferably 2 or less, preferably 1 or less, and most preferably 0. The number of first pores is preferably 0 to 3, preferably 0 to 2, preferably 0 to 1, and most preferably 0.

[0074] In this embodiment, it is preferable that the cutting tool does not contain pores (second pores) with an equivalent circular diameter of 0.2 μm or more in a rectangular measuring field of view of 24.9 μm × 18.8 μm. This results in a cutting tool with high strength, improved chipping resistance, and improved fracture and / or breakage resistance, thus extending tool life.

[0075] In this specification, the method for measuring the number of first and second pores in the measurement field of the cemented carbide constituting the cutting tool is as follows (A4) to (H4).

[0076] (A4) Cut the cutting tool so that the cross-section including the cutting edge is exposed, and then polish the cross-section to a mirror finish. Examples of methods for mirror polishing include polishing with diamond paste, using a focused ion beam (FIB) device, using a cross-section polisher (CP) device, and methods combining these.

[0077] (B4) The cross-section of the cemented carbide alloy, which has been polished to a mirror finish, is analyzed using energy-dispersive X-ray spectroscopy (SEM-EDX) to identify the elements contained in the cemented carbide alloy.

[0078] (C4) The above cross-section of the cemented carbide is photographed using a scanning electron microscope. When taking the photograph, the imaging area is set so that the cutting edge 4 of the cutting tool 3 is included, as shown in Figure 3. The observation magnification is 5000x.

[0079] (D4) The imaging area described in (C4) above is analyzed using scanning electron microscopy (SEM-EDX) to determine the distribution of the elements identified in (B4) above within the imaging area and to obtain an elemental mapping image. In the elemental mapping image, no elements are present in the pore regions.

[0080] (E4) The captured images obtained in (C4) above are imported into a computer and image processing is performed using image analysis software (ImageJ, version 1.51j8: https: / / imagej.nih.gov / ij / ) to perform binarization. Specifically, after importing the images into the computer, pressing the "MakeBinary" button on the computer screen executes the binarization process according to the conditions pre-set in the image analysis software. In the image after binarization, tungsten carbide particles are shown in the lightest color (white), and the binding phase and pores are shown in black.

[0081] (F4) By overlaying the elemental mapping image obtained in (D4) above with the binarized image obtained in (E4) above, the regions where pores exist are identified on the binarized image. Specifically, among the regions shown in black in the binarized image, the regions where elements are absent in the elemental mapping image correspond to the regions where pores exist.

[0082] (G4) In the resulting binarized image, set one rectangular measurement field of view measuring 24.9 μm × 18.8 μm. The method for setting this measurement field of view will be explained using Figure 3. Identify the cutting edge 4 in the binarized image. In the above image, identify the cemented carbide region S2 that is 100 μm or less from the cutting edge 4. As shown in Figure 3, region S2 corresponds to the area inside the arc R1 with a diameter of 100 μm drawn with the cutting edge 4 as the center.

[0083] Next, in the image above, region S3 of cemented carbide is identified, where the distance from the tool surface is between 0.5 μm and 30 μm. As shown in Figure 3, region S3 corresponds to the area enclosed by line L1, where the distance from the tool surface is 0.5 μm, and line L2, where the distance from the tool surface is 30 μm. In the image above, the measurement field of view is set within region S1, where regions S2 and S3 overlap. In Figure 3, region S1 is indicated by a diagonal line. In this measurement field of view, the equivalent circular diameter of the pore (Heywood diameter: equivalent circular diameter of an equal area) is calculated using the image analysis software based on the number of pixels in the pore and identified region within the measurement field of view.

[0084] (H4) Based on the calculation results in (G4) above, the number of first pores with an equivalent circle diameter of less than 0.2 μm and the number of second pores with an equivalent circle diameter of 0.2 μm or more in the measurement field are measured.

[0085] As far as the applicant has measured, as long as the measurements are performed on the same sample, the variation in the measurement results is small even when the cutting location of the cemented carbide cross-section is arbitrarily set according to the procedure in (A4) above, and the position of the measurement field is arbitrarily set according to the procedure in (B4) to (H4) above, and the number of first and second pores is measured multiple times. It has been confirmed that arbitrarily setting the cutting location of the cemented carbide cross-section and the position of the measurement field does not result in arbitrary results.

[0086] <Tungsten carbide particles> ≪Composition≫ The composition of the tungsten carbide particles in this embodiment can be the same as the composition of the tungsten carbide particles described in Embodiment 1.

[0087] ≪Average particle size≫ In this embodiment, the average particle size of the tungsten carbide particles (median diameter D50 of the equivalent diameter of an equal-area circle) is preferably 0.80 μm or more and 3.00 μm or less, more preferably greater than 1.00 μm and 3.00 μm or less, and even more preferably 1.00 μm or more and 2.50 μm or less. This further improves tool life.

[0088] In this specification, the average particle size of tungsten carbide particles contained in the cemented carbide of a cutting tool means the equivalent circle diameter (Heywood diameter) D50 of the WC particles contained in the cemented carbide (the equivalent circle diameter where the cumulative frequency based on the number of particles reaches 50%, the median diameter D50). The method for measuring the particle size of each particle to calculate the average particle size of the WC particles (median diameter D50 of the equivalent circle diameter) is as follows (A5) to (B5).

[0089] (A5) By superimposing an elemental mapping image obtained by the same method as (A4) to (E4) described in (A5) Method for measuring the number of first and second pores in cemented carbide cutting tools with a binarized image, the region where tungsten carbide particles exist is identified on the binarized image. Specifically, the region shown in the lightest color (white) in the binarized image, where tungsten (W) and carbon (C) are present in the elemental mapping image, corresponds to the region where tungsten carbide particles exist.

[0090] (B5) In the image after the binarization process described above, set one rectangular measurement field of view of 24.9 μm × 18.8 μm, similar to (G4) above. Using the image analysis software described above, calculate the equivalent circle diameter (Heywood diameter: equivalent circle diameter of an equal area) of each tungsten carbide particle in the measurement field of view.

[0091] As far as the applicant has measured, as long as the measurements are performed on the same sample, even when the cutting location of the cemented carbide cross-section is arbitrarily set according to the procedure in (A4) above, and the position of the measurement field is arbitrarily set according to the procedure in (B4) to (H4) above, and the average particle size of tungsten carbide particles is measured multiple times, the variation in the measurement results is small, and it has been confirmed that arbitrarily setting the cutting location of the cemented carbide cross-section and the position of the measurement field does not result in arbitrary results.

[0092] <Binded phase> The composition of the bonding phase in this embodiment can be the same as the composition of the bonding phase described in Embodiment 1.

[0093] <Composition of cemented carbide> The composition of the cemented carbide in this embodiment (such as the content of tungsten carbide particles, the content of the binder phase, and the constituent components) can be the same as the composition of the cemented carbide material described in Embodiment 1.

[0094] The method for measuring the respective content (volume %) of tungsten carbide particles and the binding phase in the cemented carbide of the above-mentioned cutting tool is as follows (A6) to (B6).

[0095] (A6) By superimposing an elemental mapping image obtained by the same method as (A4) to (E4) described in (A6) Method for measuring the number of first and second pores in cemented carbide cutting tools with a binarized image, the regions where tungsten carbide particles and the regions where the bonding phase exists are identified on the binarized image. Specifically, the regions shown in the lightest color (white) in the binarized image, where tungsten (W) and carbon (C) are present in the elemental mapping image, correspond to the regions where tungsten carbide particles exist. The regions shown in black in the binarized image, where cobalt (Co) is present in the elemental mapping image, correspond to the regions where the bonding phase exists.

[0096] (B6) In the image after the binarization process described above, a rectangular measurement field of view of 24.9 μm × 18.8 μm is set in the same location as in (G4) above. Using the image analysis software described above, the area percentages of the tungsten carbide particles and the binder phase are measured with the area of ​​the entire measurement field of view as the denominator. In this specification, the area percentage of the tungsten carbide particles corresponds to the tungsten carbide particle content (volume %) of the cemented carbide, and the area percentage of the binder phase corresponds to the binder phase content (volume %) of the cemented carbide.

[0097] As far as the applicant has measured, as long as the measurements are performed on the same sample, the variation in the measurement results is small even when the cutting location of the cemented carbide cross-section is arbitrarily set according to the procedure in (A4) above, and the position of the measurement field is arbitrarily set according to the procedure in (B4) to (H4) above, and the measurement of the tungsten carbide particle content and the binder phase content is performed multiple times. It has been confirmed that arbitrarily setting the cutting location of the cemented carbide cross-section and the position of the measurement field does not result in arbitrary results.

[0098] The cutting tool according to this embodiment may further include a hard coating that covers at least a portion of the surface of a substrate made of cemented carbide. For example, diamond-like carbon or diamond can be used as the hard coating.

[0099] <Manufacturing method for cutting tools> The cutting tool of this embodiment can be obtained, for example, by machining the cemented carbide material for the cutting tool of Embodiment 1. During machining, the machining process should be carried out in a way that does not include parts that have properties clearly different from the bulk portion, such as the area near the surface of the cemented carbide material.

[0100] [Note 1] This disclosure relates to cemented carbide materials for cutting tools, The cemented carbide material comprises tungsten carbide particles and a binder phase, The aforementioned cemented carbide material contains three or fewer pores with an equivalent circle diameter of less than 0.2 μm in a rectangular measurement field of view of 24.9 μm × 18.8 μm, and does not contain any pores with an equivalent circle diameter of 0.2 μm or more. The measurement field is a cemented carbide material for cutting tools, provided in the central part of the cross-section of the cemented carbide material.

[0101] [Note 2] This disclosure relates to a cutting tool made of cemented carbide, The cemented carbide comprises tungsten carbide particles and a binder phase. The cemented carbide alloy contains three or fewer pores with an equivalent circular diameter of less than 0.2 μm in a rectangular measurement field of 24.9 μm × 18.8 μm, and does not contain any pores with an equivalent circular diameter of 0.2 μm or more. The measurement field is provided within a region S1 on the cross-section of the cemented carbide, including the cutting edge of the cutting tool. The region S1 is a cutting tool in which the distance from the cutting edge is 100 μm or less and the distance from the surface of the cutting tool is 0.5 μm or more and 30 μm or less in the cross-section of the cemented carbide. [Examples]

[0102] This embodiment will be described in more detail by reference to examples. However, this embodiment is not limited by these examples.

[0103] <Manufacturing of cemented carbide materials> The cemented carbide material for each sample was prepared using the following procedure. Three cemented carbide materials were prepared for each sample. ≪Preparation process≫ As raw material powders, we prepared tungsten carbide (WC) powder, cobalt (Co) powder, niobium carbide (NbC) powder, and chromium carbide (Cr3C2) powder.

[0104] As tungsten carbide powder, we used tungsten carbide powders "WC08" (average particle size 0.7-0.9 μm), "WC20" (average particle size 1.8-2.2 μm), "WC30" (average particle size 2.8-3.3 μm), and "WC40" (average particle size 3.7-4.4 μm) manufactured by Allied Material Co., Ltd. The tungsten carbide powder used in each sample is shown in the "WC Powder" column of Table 1.

[0105] The average particle size of the cobalt (Co) powder is 1 μm, the average particle size of the niobium carbide (NbC) powder is 1 μm, and the average particle size of the chromium carbide (Cr3C2) powder is 1 μm. The Co powder, NbC powder, and Cr3C2 powder are commercially available. The average particle size of the raw material powders was measured using a particle size distribution analyzer (product name: MT3300EX) manufactured by Microtrac.

[0106] ≪Mixing process≫ The raw material powders were mixed in the proportions shown in the "Mixed Powder (mass%)" column of Table 1 to prepare the mixed powder. For example, the notation "2.0NbC-6.0Co-remainder WC" in the "Mixed Powder (mass%)" column for Sample 1 indicates that the NbC powder content in the mixed powder is 2.0 mass%, the Co powder content is 6.0 mass%, and the remainder (92.0 mass%) is WC powder. Mixing was performed using an attritor (indicated as "ATR" in Table 1). The mixing time in the attritor is shown in the "Mixing / Time" column of Table 1. For example, the mixing time for Sample 1 was 7h (7 hours).

[0107] ≪Pelletization process≫ The mixed powder obtained by mixing was dried by a water bath to obtain dried raw material powder. A mixed solution was prepared by mixing polyethylene oxide (weight-average molecular weight (Mw): approximately 100,000) and glycerin in a volume ratio of 1:1. The above dried raw material powder was granulated by applying this mixed solution by spraying.

[0108] ≪Molding process≫ The obtained granulated powder was press-molded to produce a molded body.

[0109] ≪Sintering Process≫ The molded body was placed in a sintering furnace and heated to 800°C in a vacuum (1.0 Pa or less) at the heating rate indicated in the "~800°C" column of the "Sintering Process" in Table 1. Subsequently, Ar gas was introduced into the sintering furnace and heated to 1400°C in an Ar gas atmosphere (7 MPaG) at the heating rate indicated in the "800°C~1400°C" column of the "Sintering Process" in Table 1. Then, the pressure inside the sintering furnace was reduced to an Ar gas atmosphere (140 kPaG), and the body was held at 1400°C for the time indicated in the "1400°C" column of the "Sintering Process" in Table 1 to obtain cemented carbide material.

[0110] ≪HIP Treatment Process≫ Next, the sintered cemented carbide material was subjected to HIP treatment. Specifically, the cemented carbide material was subjected to a temperature of 1370°C and the pressure described in the "HIP Treatment" column of Table 1 for 60 minutes, using Ar gas as the pressure medium.

[0111] ≪Cooling process≫ Next, the cemented carbide material was cooled after the HIP treatment.

[0112] <Manufacturing of cutting tools> The cemented carbide materials of Samples 1 to 7, Sample 1-1, and Sample 1-2 were processed to produce replaceable cutting tips (shape: CNMG120408N-GU) for turning.

[0113] The cemented carbide materials of sample 8 and samples 1-3 were processed to produce replaceable cutting tips for drills (tip model number: WDXT063006-G).

[0114] [Table 1]

[0115] [evaluation] <Superhard alloy material> For each sample of cemented carbide material before processing into cutting tools, the volume percentage of tungsten carbide particles and binder phase, the average particle size of tungsten carbide particles, the composition of the binder phase, and the number of pores were measured.

[0116] ≪Volume % of tungsten carbide particles and binder phase≫ For each cemented carbide material sample, the content (volume %) of tungsten carbide particles and the binder phase was measured. The specific measurement method is described in Embodiment 1, so it will not be repeated here. The content (volume %) of the binder phase is shown in the "Volume %" column of "Binder Phase" in Table 2. In all samples, the sum of the volume % of WC particles, the volume % of the binder phase, and the volume % of pores was 100 volume %.

[0117] ≪Average particle size of tungsten carbide particles≫ The average particle size of tungsten carbide particles was measured for each cemented carbide material sample. The specific measurement method is described in Embodiment 1, so it will not be repeated here. The results are shown in the "Average Particle Size (μm)" column of "WC Particles" under "Cemented Carbide Material" in Table 2.

[0118] ≪Composition of the bonded phase≫ For each cemented carbide material sample, the elements contained in the binder phase were measured by ICP emission spectroscopy. In all samples, it was confirmed that the binder phase contained 90% or more cobalt by mass.

[0119] ≪Number of pores≫ For each cemented carbide material sample, the number of pores with an equivalent circle diameter of less than 0.2 μm (first pores) and the number of pores with an equivalent circle diameter of 0.2 μm or more (second pores) were measured within a rectangular measurement field of view measuring 24.9 μm × 18.8 μm. The specific measurement method is described in Embodiment 1, so that explanation will not be repeated. The results are shown in the "Less than 0.2 μm (pores)" and "0.2 μm or more (pores)" columns of "Number of Pores" under "Cemented Carbide Material" in Table 2.

[0120] <Cutting tools> For each sample of the cemented carbide cutting tool, the average particle size of tungsten carbide particles, the number of pores, and the composition of the cemented carbide were measured.

[0121] ≪Average particle size of tungsten carbide particles≫ The average particle size of tungsten carbide particles was measured for the cemented carbide cutting tools of each sample. The specific measurement method is described in Embodiment 2, so it will not be repeated here. The results are shown in the "Average Particle Size (μm)" column of "WC Particles" under "Cutting Tools" in Table 2.

[0122] ≪Number of pores≫ For each sample of cemented carbide cutting tool, the number of pores with an equivalent circle diameter of less than 0.2 μm (first pores) and the number of pores with an equivalent circle diameter of 0.2 μm or more (second pores) were measured within a rectangular measurement field of 24.9 μm × 18.8 μm. The specific measurement method is described in Embodiment 2, so that explanation will not be repeated. The results are shown in the "Less than 0.2 μm (pores)" and "0.2 μm or more (pores)" columns of "Number of Pores" under "Cutting Tool" in Table 2.

[0123] ≪Composition of cemented carbide≫ In all samples, it was confirmed that the composition of the cemented carbide material of the cutting tool was identical to the composition of the cemented carbide material before processing into the cutting tool.

[0124] <Cutting Test> <<Interchangeable cutting inserts for turning>> Cutting tests were conducted using the replaceable tip cutting inserts for turning, samples 1-7, 1-1, and 1-2, under the following conditions. The following cutting conditions correspond to intermittent cutting. The time (min) until a chip of 2 mm or more occurred was measured. The results are shown in the "Tool Life" column of "Cutting Tool" in Table 2. A longer time until chipping occurs indicates a longer tool life. Workpiece material: Notched SCM435 round bar Cutting speed vc:120m / min Feed rate per revolution f: 2.0 mm / rev Cutting depth ap: 1.5mm Cutting fluid: Yes (WET)

[0125] ≪Replaceable cutting tips for drills≫ Using the replaceable drill tips of Sample 8 and Samples 1-3, through-hole drilling was performed on S50C block material under the following conditions. The number of drilled holes (holes) was measured until the difference from the target hole diameter of 20 nm exceeded 0.1 mm. The results are shown in the "Tool Life" column of "Cutting Tool" in Table 2. A higher number of drilled holes indicates a longer tool life. Workpiece material: S50C block material, 50mm thickness in the drilling direction Cutting speed vc:150m / min Feed rate per revolution f: 0.10 mm / rev Cutting fluid: Yes (WET) Holder model number: WDX2003DS25

[0126] [Table 2]

[0127] <Consideration> The replaceable tip cutting inserts for turning in Samples 1 to 7 correspond to the Examples, while the replaceable tip cutting inserts for turning in Samples 1-1 and 1-2 correspond to the Comparative Examples. It was confirmed that the replaceable tip cutting inserts for turning in Samples 1 to 7 (Examples) had a longer tool life compared to the replaceable tip cutting inserts for turning in Samples 1-1 and 1-2 (Comparative Examples).

[0128] The replaceable cutting inserts for turning in samples 1-1 and 1-2 suffered chipping and severe breakage during the initial stages of machining.

[0129] The replaceable tip cutting chip for drills in Sample 8 corresponds to the Example, while the replaceable tip cutting chips for drills in Samples 1-3 correspond to the Comparative Examples. It was confirmed that the replaceable tip cutting chip for drills in Sample 8 (Example) had a longer tool life compared to the replaceable tip cutting chips for drills in Samples 1-3 (Comparative Examples).

[0130] As described above, embodiments and examples of this disclosure have been explained, but it is also intended from the outset that the configurations of each of the above embodiments and examples may be combined as appropriate or modified in various ways. The embodiments and examples disclosed herein should be considered in all respects to be illustrative and not restrictive. The scope of the present invention is indicated by the claims rather than the embodiments and examples described above, and all modifications within the meaning and scope of the claims are intended to be included. [Explanation of Symbols]

[0131] 1. Carbide alloy material 2 pore 3 cutting tools 4 cutting edge

Claims

1. A cemented carbide material for cutting tools, The aforementioned cemented carbide material contains 85.0% to 95.5% by volume of tungsten carbide particles and 0.5% to 15.0% by volume of a binder phase. When a binarized image of a first image obtained by photographing the central part of the cross-section of the cemented carbide material at a scanning electron microscope at an observation magnification of 5000x is superimposed with an elemental mapping image obtained by analyzing the same region as the first image using energy-dispersive X-ray spectroscopy, if a region shown in black in the binarized image where no elements are present in the elemental mapping image is identified as a pore, In one rectangular measurement field of 24.9 μm × 18.8 μm provided in the image after the binarization process, the number of pores with an equivalent circle diameter of less than 0.2 μm is 0 or more and 3 or less. In the aforementioned measurement field, no pores with an equivalent circular diameter of 0.2 μm or more existed. The average particle size of the tungsten carbide particles is 0.80 μm or more and 3.50 μm or less. The cemented carbide material for cutting tools has an average particle size of tungsten carbide particles, with a median diameter D50 of the equivalent diameter of the equiarea circle of the tungsten carbide particles.

2. The cemented carbide material for cutting tools according to claim 1, wherein the average particle size of the tungsten carbide particles is greater than 1.00 μm and less than or equal to 3.50 μm.

3. A cutting tool made of cemented carbide, The cemented carbide alloy contains 85.0% to 95.5% by volume of tungsten carbide particles and 0.5% to 15.0% by volume of a binder phase. When a binarized image of a first image obtained by photographing the cross-section of the cemented carbide, including the cutting edge of the cutting tool, at a viewing magnification of 5000x using a scanning electron microscope, is superimposed with an elemental mapping image obtained by analyzing the same region as the first image using energy-dispersive X-ray spectroscopy, and when a region shown in black in the binarized image where no elements are present in the elemental mapping image is identified as a pore, In a single rectangular measurement field measuring 24.9 μm × 18.8 μm provided in the image after the binarization process, the number of pores with an equivalent circle diameter of less than 0.2 μm is between 0 and 3. In the aforementioned measurement field, no pores with an equivalent circular diameter of 0.2 μm or more existed. The measurement field of view is provided within the region S1 on the cross-section, The region S1 is a region in the cross-section where the distance from the cutting edge is 100 μm or less, and the distance from the surface of the cutting tool is 0.5 μm or more and 30 μm or less. The average particle size of the tungsten carbide particles is 0.80 μm or more and 3.50 μm or less. A cutting tool in which the average particle size of the tungsten carbide particles is the median diameter D50 of the equivalent diameter of the equiarea circle of the tungsten carbide particles.

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