Cemented carbide material for cutting tool, and cutting tool

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 a cutting tool and to the cutting tool. [Background technology]

[0002] Cemented carbide alloys comprising tungsten carbide particles and a binder phase containing cobalt are widely used as materials for cutting tools (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-132570 Summary of the Invention [Problem to be solved by the invention]

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

[0005] The present disclosure provides a cemented carbide material for a cutting tool, comprising: The cemented carbide material comprises tungsten carbide particles and a binder phase, The cemented carbide material contains three or less pores having a circular equivalent diameter of less than 0.2 μm in a rectangular measurement field of view of 24.9 μm × 18.8 μm, The measurement field of view is a cemented carbide material for a cutting tool, and is provided at the center of the cross section of the cemented carbide material.

[0006] The present disclosure provides a cutting tool made of cemented carbide, The cemented carbide comprises tungsten carbide particles and a binder phase; The cemented carbide contains three or less pores having a circular equivalent diameter of less than 0.2 μm in a rectangular measurement field of view of 24.9 μm × 18.8 μm, The measurement field of view is provided within an area S1 on a cross section of the cemented carbide including the cutting edge of the cutting tool, The region S1 is a region in the cross section of the cemented carbide that is 100 μm or less away from the cutting edge and 0.5 μm or more and 30 μm or less away from the surface of the cutting tool. [Effects of the Invention]

[0007] According to the present disclosure, it is possible to provide a cutting tool having a long tool life. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing an example of an image of the cemented carbide material of the first embodiment taken with a scanning electron microscope. [Figure 2] FIG. 2 is a diagram for explaining the position of the measurement field of the cemented carbide material of the first embodiment. [Figure 3] FIG. 3 is a diagram for explaining a method for setting a measurement field of view for the cemented carbide of the cutting tool of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described. (1) The present disclosure provides a cemented carbide material for a cutting tool, comprising: The cemented carbide material comprises tungsten carbide particles and a binder phase, The cemented carbide material contains three or less pores having a circular equivalent diameter of less than 0.2 μm in a rectangular measurement field of view of 24.9 μm × 18.8 μm, The measurement field of view is a cemented carbide material for a cutting tool, and is provided at the center 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) The average particle size of the tungsten carbide particles is preferably 0.80 μm or more and 3.00 μm or less, which further improves the tool life of the cutting tool.

[0012] (3) The tungsten carbide particles preferably have an average particle size of more than 1.00 μm and not more than 3.00 μm, which further improves the tool life of the cutting tool.

[0013] (4) The cemented carbide material preferably contains 85.0 to 95.5 volume % of the tungsten carbide particles and 0.5 to 15.0 volume % of the binder phase, which further improves the tool life of the cutting tool.

[0014] (5) The present disclosure provides a cutting tool made of cemented carbide, The cemented carbide comprises tungsten carbide particles and a binder phase; The cemented carbide contains three or less pores having a circular equivalent diameter of less than 0.2 μm in a rectangular measurement field of view of 24.9 μm × 18.8 μm, The measurement field of view is provided within an area S1 on a cross section of the cemented carbide including the cutting edge of the cutting tool, The region S1 is a region in the cross section of the cemented carbide that is 100 μm or less away from the cutting edge and 0.5 μm or more and 30 μm or less away from the surface of the cutting tool.

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

[0016] [Details of the embodiments of the present disclosure] Specific examples of the cemented carbide material for cutting tools and cutting tools of 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 or corresponding parts. Furthermore, dimensional relationships such as length, width, thickness, and depth have been appropriately changed for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0017] In this specification, the expression "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and when no unit is specified for A and a unit is specified only for B, the unit of A and the unit of B are the same.

[0018] In this specification, a pore having a diameter of less than 0.2 μm is also referred to as a “first pore,” and a pore having a diameter of 0.2 μm or more is also referred to as a “second pore.” The first pore and the second pore are collectively referred to as a “pore.”

[0019] In this specification, a cutting tool refers to a tool that does not rotate itself but rotates a workpiece to perform cutting or other processing, or a tool that rotates around an axis of rotation that does not pass through the tool itself to perform cutting or other processing. In addition, when the tip of a drill or end mill is replaceable, the cutting tool also includes the tip (indexable cutting tip for drill, indexable cutting tip for end mill).

[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 comprises tungsten carbide particles and a binder phase, The cemented carbide material contains three or less pores with a circular equivalent diameter of less than 0.2 μm in a rectangular measurement field of view of 24.9 μm × 18.8 μm, The measurement field of view is a cemented carbide material for cutting tools, and is provided in the center of the cross section of the cemented carbide material.

[0021] <Pore> The cemented carbide material of this embodiment contains three or less pores (first pores) with 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 located in the center of the cross section of the cemented carbide material. A cemented carbide material having three or less first pores in the measurement field has excellent strength. Therefore, a cutting tool using this cemented carbide material has improved chipping resistance, fracture resistance and / or breakage resistance, and therefore extended tool life.

[0022] The number of first pores in the 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 the first pores is preferably 0 to 3, preferably 0 to 2, preferably 0 to 1, and most preferably 0.

[0023] The cemented carbide material of this embodiment preferably does not contain second pores with an equivalent circle diameter of 0.2 μm or more in the measurement field. This allows the cemented carbide material to have high strength. Therefore, a cutting tool using the cemented carbide material has improved chipping resistance, fracture resistance and / or breakage resistance, and thus a longer tool life.

[0024] In this specification, the methods for measuring the number of first pores and second pores in the above-mentioned measurement field of view of the cemented carbide material are as follows (A1) to (H1).

[0025] (A1) A cemented carbide material is cut through the vicinity of its center of gravity to expose a cross section, which is then mirror-polished. Examples of mirror-polishing methods include polishing with diamond paste, using a focused ion beam (FIB) device, using a cross-section polisher (CP) device, and combinations of these methods.

[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 a photographed image. The photographed area of ​​the photographed image is set to the center of the cross section of the cemented carbide material, that is, a position that does not include areas with properties clearly different from the bulk part, such as the surface vicinity of the cemented carbide material (a position where the entire photographed area is the bulk part of the cemented carbide material). The observation magnification is 5000x.

[0028] FIG. 1 is an example of an image of a cemented carbide material 1 of this embodiment taken with a scanning electron microscope. In the scale at the bottom right of FIG. 1, the length of a straight line indicates 1 μm. In FIG. 1, the cemented carbide material 1 includes pores 2. Note that, as shown in FIG. 1, the pores 2 may be very small and difficult to identify in the image taken with the scanning electron microscope. However, as will be explained in (F1) below, the pores can be identified by superimposing the image taken with the scanning electron microscope after binarization processing on an element mapping image.

[0029] (D1) The imaging region of (C1) above is analyzed using energy dispersive X-ray spectroscopy (SEM-EDX) to identify the distribution of the elements identified in (B1) above in the imaging region, and an elemental mapping image is obtained. In the elemental mapping image, no elements are present in the pore region.

[0030] (E1) The photographed image obtained in (C1) above is imported into a computer, and image processing and binarization are performed using image analysis software (ImageJ, version 1.51j8: https: / / imagej.nih.gov / ij / ). Specifically, after importing the photographed image into the computer, the "Make Binary" button on the computer screen is pressed, and binarization processing is performed under the conditions preset in the image analysis software. In the image after binarization processing, the tungsten carbide particles are shown in the lightest color (white), and the binder phase and pores are shown in black.

[0031] (F1) By superimposing the elemental mapping image obtained in (D1) above on the binarized image obtained in (E1) above, the pore presence region is identified on the binarized image. Specifically, among the regions shown in black in the binarized image, the regions where no elements are present in the elemental mapping image correspond to the pore presence region.

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

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

[0034] As far as the applicant has measured, as long as measurements are made on the same sample, even if the cut-out location of the cross section of the cemented carbide material is arbitrarily set, the photographing area described in (C1) above is arbitrarily set on the cross section, and the number of first pores and second pores is measured multiple times according to the procedures (B1) to (H1) above, there is little variation in the measurement results, and it has been confirmed that arbitrarily setting the cut-out location of the cross section of the cemented carbide material and arbitrarily setting the photographing area of ​​the photographed image will not be arbitrary.

[0035] For example, as shown in Figure 2, a total of five shooting 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 that are the same distance from the central part A, and the numbers of first pores and second pores were measured at each of the five locations according to the above procedures (B1) to (H1). It was confirmed that there was little variation in the measurement results, and that arbitrarily setting the shooting area for the captured image would not be 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 containing no impurity elements, or may be tungsten carbide containing impurity elements as long as the effects of the present disclosure are not impaired. The content of impurities contained in tungsten carbide (when two or more elements constitute the impurities, the total concentration of these elements) is preferably less than 0.1 mass% relative to the total amount of WC particles. The content of impurities in the WC particles is measured by ICP (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 more 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, which further improves the tool life.

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

[0039] (A2) By superimposing an elemental mapping image obtained by the same method as (A1) to (E1) described in the method for measuring the number of first pores and second pores in the above measurement field of view of a cemented carbide material on the image after binarization processing, the region where tungsten carbide particles exist is identified on the image after binarization processing. Specifically, the region shown in the lightest color (white) in the image after binarization processing and 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. Using the image analysis software, the circle-equivalent diameter (Heywood diameter: diameter equivalent to a circle with an equal area) of each tungsten carbide particle in the measurement field of view is calculated.

[0041] As far as the applicant has measured, as long as measurements are made on the same sample, even when the cut-out location of the cross section of the cemented carbide material is arbitrarily set, the photographing 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, there is little variation in the measurement results, and it has been confirmed that arbitrarily setting the cut-out location of the cross section of the cemented carbide material and arbitrarily setting the photographing area of ​​the photographed image are not arbitrary.

[0042] <Binded phase> The cemented carbide of this embodiment includes a binder phase. The binder phase preferably includes cobalt as a main component. Here, "the binder phase includes cobalt as a 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 atomic emission spectroscopy (instrument used: Shimadzu Corporation's "ICPS-8100" (trademark)).

[0043] In addition to cobalt, the binder phase may include chromium, vanadium, nickel, tungsten, titanium, niobium, tantalum, and the like.

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

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

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

[0047] The cemented carbide material may contain 85.0 to 99.5 volume % tungsten carbide particles and 0.5 to 15.0 volume % binder phase. The cemented carbide material may contain 88.0 to 99.5 volume % tungsten carbide particles and 0.5 to 12.0 volume % binder phase. The cemented carbide material may contain 90.0 to 99.5 volume % tungsten carbide particles and 0.5 to 10 volume % binder phase. The cemented carbide material may contain 85.0 to 95.0 volume % tungsten carbide particles and 5.0 to 15.0 volume % binder phase. The cemented carbide material may include 88.0 to 95.0 volume % tungsten carbide particles and 5.0 to 12.0 volume % binder phase. The cemented carbide material may include 90.0 to 95.0 volume % tungsten carbide particles and 5.0 to 10.0 volume % binder phase.

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

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

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

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

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

[0053] As far as the applicant has measured, as long as measurements are made on the same sample, even when the cut-out location of the cross section of the cemented carbide material is arbitrarily set, the photographing area described in (C1) above is arbitrarily set on the cross section, and the area percentages of tungsten carbide particles, binder phase, hard phase particles, and impurities are measured multiple times according to the procedures in (A3) and (B3) above, there is little variation in the measurement results, and it has been confirmed that arbitrarily setting the cut-out location of the cross section of the cemented carbide material and arbitrarily setting the photographing area of ​​the photographed image are not arbitrary.

[0054] <Method of manufacturing cemented carbide materials for cutting tools> The cemented carbide material for cutting tools of this embodiment can be manufactured by carrying out the steps of preparing raw material powder, mixing, granulating, molding, sintering, HIP treatment, and cooling in the above order. Each step will be described below.

[0055] ≪Preparation process≫ The preparation step is a step of preparing raw material powders of materials constituting the cemented carbide material. Examples of raw material powders include tungsten carbide powder, which is a raw material for tungsten carbide particles, cobalt (Co) powder, which is a raw material for the binder phase, and chromium carbide (Cr3C2) powder, which is a grain growth inhibitor. Further examples include vanadium carbide (VC) powder, which is a grain growth inhibitor, and niobium carbide (NbC) powder, which is a raw material for the hard phase particles. 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 the tungsten carbide powder can be 0.7 μm or more and 5.0 μm or less. The average particle size of the cobalt powder can be 0.8 μm or more and 1.2 μm or less. The average particle size of the niobium carbide powder can be 0.5 μm or more and 2.0 μm or less. The average particle size of the chromium carbide powder can be 1.0 μm or more and 2.0 μm or less. The average particle size of the vanadium carbide powder can be 0.5 μm or more and 1.0 μm or less. In this specification, the average particle size of the raw material powder means the 50% cumulative number particle size (median diameter d50) of the equivalent spherical diameter. The average particle size is measured using a particle size distribution analyzer manufactured by Microtrac (product name: MT3300EX).

[0057] ≪Mixing process≫ The mixing step is a step of mixing the raw material powders prepared in the preparation step, and a mixed powder in which the raw material powders are mixed is obtained by the mixing step.

[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] The raw material powders can be mixed using an attritor or a ball mill. The mixing time in an attritor can be 7 hours or more and 15 hours or less. The mixing time in a ball mill can be 30 hours or more and 60 hours or less.

[0060] ≪Pelletization process≫ The mixed powder obtained by mixing is dried in a hot water bath to obtain a dry 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 mixed solution is sprayed onto the dry raw material powder to granulate it. Hereinafter, the mixed solution sprayed onto the dry raw material powder will also be referred to as the binder.

[0061] ≪Molding process≫ The compacting step is a step of compacting the mixed powder obtained in the mixing step into a shape for a cutting tool to obtain a compact. The compacting method and conditions in the compacting step are not particularly limited and may be any general method and conditions.

[0062] <Sintering process> The sintering step is a step of sintering the compact obtained in the compacting step to obtain a cemented carbide material. The sintering step can be performed in the following manner.

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

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

[0065] <HIP processing process> The HIP treatment step is a step in which the sintered cemented carbide material is subjected to HIP (Hot Isostatic Pressing) treatment. For example, the cemented carbide material can be subjected to a temperature of 1370°C and a pressure of 100 to 200 MPa for 120 minutes using Ar gas as a pressure medium.

[0066] ≪Cooling process≫ The cooling step is a step of cooling the cemented carbide material after the HIP treatment, for example, by rapidly cooling the cemented carbide material after the HIP treatment in Ar gas.

[0067] <Features of the manufacturing method of the cemented carbide material according to the present embodiment> In the cemented carbide material obtained by the above manufacturing method, the number of pores with an equivalent circle diameter of less than 0.2 μm is 3 or less 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] It is believed that pores in the cemented carbide material are formed by the evaporation of the binder during the sintering process. In the above manufacturing method, a mixed solution of polyethylene oxide and glycerin is used as the binder during the granulation process, and the sintering process involves heating at a slow temperature increase rate while applying pressure. The binder has a large molecular weight and is therefore not easily evaporated. Therefore, in the above manufacturing method, the binder vaporizes almost simultaneously inside and near the surface of the compact during the temperature increase in the sintering process, and the binder does not remain inside the compact but is easily expelled to the outside. Furthermore, in the above manufacturing method, the compact is held at the maximum temperature (1400°C) in an Ar gas atmosphere (140 kPaG) for a certain period of time (120 minutes). The pressurized state is held for a certain period of time. Pressurizing the compact at a high temperature causes the structure to flow and the pores to become smaller. Therefore, pores are unlikely to exist inside the cemented carbide material after sintering, and the number of pores is reduced throughout. Furthermore, even if pores exist, their size is very small. As a result of extensive investigations, the present inventors have newly discovered that by using a mixed solution of polyethylene oxide and glycerin as a binder and heating at a slow temperature increase rate while applying pressure in the sintering process, it is possible to obtain a cemented carbide material having 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.

[0069] On the other hand, in conventional methods for manufacturing cemented carbide materials, granulation is performed by spray drying from the viewpoint of efficiency, 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. Note that 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, from the viewpoint of efficiency, the temperature rise rate during sintering is set to 10 to 20°C / min, and sintering at the maximum temperature is performed under reduced pressure or vacuum. Therefore, while the binder near the surface of the compact is easily vaporized during temperature rise, the binder inside the compact is less likely to vaporize. Therefore, the cemented carbide material after sintering is prone to have pores inside, which makes the structure non-uniform.

[0070] [Embodiment 2: Cutting Tool] 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 less pores having a circular equivalent diameter of less than 0.2 μm in a rectangular measurement field of view of 24.9 μm × 18.8 μm, The measurement field of view is provided within an area S1 on a cross section of the cemented carbide including the cutting edge of the cutting tool, The region S1 is a region in the cross section of the cemented carbide that is 100 μm or less away from the cutting edge and 0.5 μm or more and 30 μm or less away from the surface of the cutting tool.

[0071] Examples of cutting tools of this embodiment include indexable cutting tips for drills, indexable cutting tips for end mills, indexable cutting tips for milling, and indexable cutting tips for turning. The cutting tool of this embodiment may be entirely made of the above-mentioned cemented carbide alloy. Alternatively, a part of the cutting tool may be made of the above-mentioned cemented carbide alloy. Here, "a part of the cutting tool made of the above-mentioned cemented carbide alloy" refers to an embodiment in which the above-mentioned cemented carbide alloy is attached to a predetermined position of any substrate to form a cutting edge.

[0072] <Pore> The cemented carbide constituting the cutting tool of this embodiment contains three or less pores (first pores) with an equivalent circle 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. Therefore, the cutting tool of this embodiment has improved chipping resistance, fracture resistance and / or breakage resistance, and thus improved tool life.

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

[0074] The cutting tool of this embodiment preferably does not contain pores (second pores) having a circle-equivalent diameter of 0.2 μm or more in a rectangular measurement field of view of 24.9 μm × 18.8 μm, which provides the cutting tool with high strength, improved chipping resistance, and improved fracture resistance and / or breakage resistance, and an extended tool life.

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

[0076] (A4) The cutting tool is cut out so that a cross section including the cutting edge is exposed, and the cross section is mirror-finished. Examples of mirror-finishing methods include polishing with diamond paste, using a focused ion beam (FIB) device, using a cross-section polisher (CP) device, and combinations of these methods.

[0077] (B4) The mirror-finished cross section of the cemented carbide is analyzed using energy dispersive X-ray spectroscopy (SEM-EDX) to identify the elements contained in the cemented carbide.

[0078] (C4) The cross section of the cemented carbide is photographed using a scanning electron microscope. When photographing, the photographing area is set so as to include the cutting edge 4 of the cutting tool 3, as shown in Figure 3. The observation magnification is set to 5000x.

[0079] (D4) The imaging region of (C4) above is analyzed using energy dispersive X-ray spectroscopy (SEM-EDX), the distribution of the elements identified in (B4) above in the imaging region is identified, and an elemental mapping image is obtained. In the elemental mapping image, no elements are present in the pore region.

[0080] (E4) The image obtained in (C4) above is imported into a computer, and image processing and binarization are performed using image analysis software (ImageJ, version 1.51j8: https: / / imagej.nih.gov / ij / ). Specifically, after importing the image into the computer, the "Make Binary" button on the computer screen is pressed, and binarization is performed under the conditions preset in the image analysis software. In the image after binarization, the tungsten carbide particles are shown in the lightest color (white), and the binder phase and pores are shown in black.

[0081] (F4) By superimposing the elemental mapping image obtained in (D4) above on the binarized image obtained in (E4) above, the pore presence region is identified on the binarized image. Specifically, among the regions shown in black in the binarized image, the regions where no elements are present in the elemental mapping image correspond to the pore presence region.

[0082] (G4) A rectangular measurement field of view measuring 24.9 μm × 18.8 μm is set in the obtained image after binarization processing. The method for setting the measurement field of view will be explained using FIG. 3. The cutting edge 4 is identified in the image after binarization processing. In the image, a region S2 of the cemented carbide alloy that is 100 μm or less away from the cutting edge 4 is identified. As shown in FIG. 3, if an arc R1 with a diameter of 100 μm is drawn with the cutting edge 4 as its center, region S2 corresponds to the region inside the arc R1.

[0083] Next, in the image, a region S3 of the cemented carbide at a distance of 0.5 μm to 30 μm from the tool surface is identified. As shown in FIG. 3, when a line L1 at a distance of 0.5 μm from the tool surface and a line L2 at a distance of 30 μm from the tool surface are drawn, region S3 corresponds to the region surrounded by lines L1 and L2. In the image, the measurement field of view is set within region S1 where regions S2 and S3 overlap. In FIG. 3, region S1 is indicated by diagonal lines. In the measurement field of view, the circle-equivalent diameter of the pore (Heywood diameter: diameter equivalent to a circle with an equal area) is calculated using the image analysis software based on the number of pixels in the region identified as a pore in the measurement field of view.

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

[0085] As far as the applicant has measured, as long as measurements are made on the same sample, even if the cut-out location of the cemented carbide cross section is arbitrarily set according to the procedure (A4) above, and the position of the measurement field is arbitrarily set according to the procedures (B4) to (H4) above, and the number of first pores and second pores is measured multiple times, there is little variation in the measurement results, and it has been confirmed that arbitrarily setting the cut-out location of the cemented carbide cross section and arbitrarily setting the position of the measurement field is not arbitrary.

[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 the first embodiment.

[0087] ≪Average particle size≫ In this embodiment, the average particle size (median diameter D50 of the equivalent circle diameter) of the tungsten carbide particles is preferably 0.80 μm or more and 3.00 μm or less, more preferably more 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, which further improves the tool life.

[0088] In this specification, the average particle size of tungsten carbide particles contained in the cemented carbide of a cutting tool refers to the D50 (median diameter D50, the diameter equivalent to a circle with an equivalent area) of the WC particles contained in the cemented carbide (Heywood diameter) at which the cumulative frequency based on the number of particles is 50%). The methods 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 with an equivalent area) are as follows (A5) to (B5).

[0089] (A5) By superimposing an elemental mapping image obtained by the same method as (A4) to (E4) described in the method for measuring the number of first pores and second pores in a cemented carbide alloy for a cutting tool on the 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 and where tungsten (W) and carbon (C) exist in the elemental mapping image corresponds to the region where tungsten carbide particles exist.

[0090] (B5) As in (G4), a rectangular measurement field of view measuring 24.9 μm × 18.8 μm is set in the image after the binarization process. Using the image analysis software, the circle-equivalent diameter (Heywood diameter: diameter equivalent to a circle with an equal area) of each tungsten carbide particle in the measurement field is calculated.

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

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

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

[0094] The methods for measuring the respective contents (volume %) of tungsten carbide particles and binder phase in the cemented carbide of the cutting tool are as follows (A6) to (B6).

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

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

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

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

[0099] <Cutting tool manufacturing method> The cutting tool of this embodiment can be obtained, for example, by processing the cemented carbide material for the cutting tool of embodiment 1. During processing, the cemented carbide material is processed so as not to include any portion, such as the vicinity of the surface thereof, whose properties are clearly different from those of the bulk portion.

[0100] [Appendix 1] The present disclosure provides a cemented carbide material for a cutting tool, comprising: The cemented carbide material comprises tungsten carbide particles and a binder phase, The cemented carbide material contains three or less pores having a circular equivalent 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 having a circular equivalent diameter of 0.2 μm or more, The measurement field of view is a cemented carbide material for a cutting tool, and is provided at the center of the cross section of the cemented carbide material.

[0101] [Appendix 2] The present disclosure provides a cutting tool made of cemented carbide, The cemented carbide comprises tungsten carbide particles and a binder phase; The cemented carbide contains three or less pores having a circular equivalent 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 having a circular equivalent diameter of 0.2 μm or more, The measurement field of view is provided within an area S1 on a cross section of the cemented carbide including the cutting edge of the cutting tool, The region S1 is a region in the cross section of the cemented carbide that is 100 μm or less away from the cutting edge and 0.5 μm or more and 30 μm or less away from the surface of the cutting tool. [Example]

[0102] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

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

[0104] The tungsten carbide powders used were 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 A.L.M.T. Corp. The tungsten carbide powder used in each sample is shown in the "WC powder" column in Table 1.

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

[0106] ≪Mixing process≫ The raw material powders were mixed in the amounts shown in the "Mixed Powder (mass%)" column of Table 1 to prepare mixed powders. For example, the notation "2.0NbC-6.0Co-balance WC" in the "Mixed Powder (mass%)" column for Sample 1 indicates that the NbC powder content in the mixed powder was 2.0 mass%, the Co powder content was 6.0 mass%, and the balance (92.0 mass%) was 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 / hour" column of Table 1. For example, the mixing time for Sample 1 was 7 hours.

[0107] ≪Pelletization process≫ The mixed powder obtained by mixing was dried in a hot water bath to obtain a dry raw material powder. A mixed solution was prepared by mixing polyethylene oxide (weight average molecular weight (Mw): approximately 100,000) and glycerin at a volume ratio of 1:1. The mixed solution was sprayed onto the dry raw material powder to granulate it.

[0108] ≪Molding process≫ The resulting granulated powder was press-molded to prepare a compact.

[0109] <Sintering process> The compact was placed in a sintering furnace and heated to 800°C in a vacuum (1.0 Pa or less) at the heating rate shown in the "Heating Rate (°C / min)" column under "Sintering Process" in Table 1. Ar gas was then introduced into the sintering furnace, and the compact was heated to 1400°C under an Ar gas atmosphere (7 MPaG) at the heating rate shown in the "Heating Rate (°C / min)" column under "Sintering Process" in Table 1. The pressure inside the sintering furnace was then reduced to 1400°C under an Ar gas atmosphere (140 kPaG), and the compact was held at 1400°C for the time shown in the "Holding Time (min)" column under "Sintering Process" in Table 1, to obtain a cemented carbide material.

[0110] <HIP processing 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 a pressure shown in the "HIP treatment" column in Table 1 for 60 minutes using Ar gas as a pressure medium.

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

[0112] <Cutting tool manufacturing> The cemented carbide materials of Samples 1 to 7, 1-1 and 1-2 were machined to produce indexable cutting inserts for turning (shape: CNMG120408N-GU).

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

[0114] [Table 1]

[0115] [evaluation] <Cemented carbide material> For each sample of cemented carbide material before processing into a cutting tool, 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> The content (volume %) of tungsten carbide particles and binder phase of each cemented carbide material sample was measured. The specific measurement method is described in embodiment 1, and therefore the description will not be repeated. The content (volume %) of binder phase is shown in the "volume %" column of "Binder Phase" in Table 2. In all samples, the total of the volume % of WC particles, the volume % of binder phase, and the volume % of pores was 100 volume %.

[0117] <Average particle size of tungsten carbide particles> The average particle size of the tungsten carbide particles was measured for each sample of cemented carbide material. The specific measurement method is described in embodiment 1, and therefore the description will not be repeated. The results are shown in the "Average particle size (μm)" column of "WC particles" under "Cemented carbide material" in Table 2.

[0118] <Composition of binder phase> The elements contained in the binder phase of each cemented carbide material sample were measured by ICP atomic emission spectroscopy. It was confirmed that the binder phase of all samples contained 90 mass % or more of cobalt.

[0119] Number of pores For each sample of cemented carbide material, the number of pores (first pores) with a circle-equivalent diameter of less than 0.2 μm and the number of pores (second pores) with a circle-equivalent diameter of 0.2 μm or more were measured in a rectangular measurement field of view of 24.9 μm × 18.8 μm. The specific measurement method is described in embodiment 1, and therefore the description thereof will not be repeated. The results are shown in the "Less than 0.2 μm (number)" and "0.2 μm or more (number)" columns of "Number of pores" for "Cemented carbide material" in Table 2.

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

[0121] <Average particle size of tungsten carbide particles> The average particle size of tungsten carbide particles was measured for each sample of cemented carbide cutting tool. The specific measurement method is described in embodiment 2, so the description will not be repeated. The results are shown in the "Average particle size (μm)" column of "WC particles" under "Cutting tool" in Table 2.

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

[0123] <Composition of cemented carbide> It was confirmed that the composition of the cemented carbide material of the cutting tool was the same as the composition of the cemented carbide material before being processed into the cutting tool in all samples.

[0124] <Cutting test> <Indexable cutting inserts for turning> Using indexable cutting inserts for turning of Samples 1 to 7, 1-1, and 1-2, cutting tests were conducted under the following conditions. The following cutting conditions correspond to intermittent cutting. The time (min) until a fracture of 2 mm or more occurred was measured. The results are shown in the "Tool life" column under "Cutting tool" in Table 2. The longer the time until a fracture occurs, the longer the tool life. Work material: SCM435 round bar with notch Cutting speed vc: 120m / min Feed per revolution f: 2.0 mm / rev Cutting depth ap: 1.5 mm Cutting fluid: Yes (WET)

[0125] <Replaceable cutting tip for drill> Using the indexable drill cutting inserts for Sample 8 and Samples 1-3, through-holes were drilled into S50C blocks under the following conditions. The number of holes drilled (holes) until the difference from the target hole diameter of 20 nm exceeded 0.1 mm was measured. The results are shown in the "Tool life" column under "Cutting tool" in Table 2. The greater the number of holes drilled, the longer the tool life. Workpiece: S50C block material, 50mm thick in the drilling direction Cutting speed vc:150m / min Feed per revolution f: 0.10 mm / rev Cutting fluid: Yes (WET) Holder model number: WDX2003DS25

[0126] [Table 2]

[0127] <Consideration> The indexable cutting inserts for turning of Samples 1 to 7 correspond to Examples, and the indexable cutting inserts for turning of Samples 1-1 and 1-2 correspond to Comparative Examples. It was confirmed that the indexable cutting inserts for turning of Samples 1 to 7 (Examples) have a longer tool life than the indexable cutting inserts for turning of Samples 1-1 and 1-2 (Comparative Examples).

[0128] The indexable cutting inserts for turning of Samples 1-1 and 1-2 were chipped and severely damaged in the early stages of machining.

[0129] The indexable drill cutting tip of Sample 8 corresponds to an example, and the indexable drill cutting tips of Samples 1-3 correspond to comparative examples. It was confirmed that the indexable drill cutting tip of Sample 8 (example) had a longer tool life than the indexable drill cutting tips of Samples 1-3 (comparative examples).

[0130] Although the embodiments and examples of the present disclosure have been described above, it is originally intended that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways. The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims rather than the above-described embodiments and examples, and it is intended to include any modifications within the scope of the claims that are equivalent to the claims. [Explanation of symbols]

[0131] 1. Cemented carbide material 2 Pore 3 cutting tools 4 cutting edge

Claims

1. A cemented carbide material for cutting tools, The cemented carbide material comprises tungsten carbide particles and a binder phase, The cemented carbide material contains three or less pores having a circular equivalent diameter of less than 0.2 μm in a rectangular measurement field of view of 24.9 μm × 18.8 μm, The cemented carbide material for cutting tools, wherein the measurement field of view is provided in the center of a cross section of the cemented carbide material.

2. 2. The cemented carbide material for cutting tools according to claim 1, wherein the tungsten carbide particles have an average particle size of 0.80 μm or more and 3.00 μm or less.

3. 3. The cemented carbide material for cutting tools according to claim 1 or 2, wherein the tungsten carbide particles have an average particle size of more than 1.00 μm and not more than 3.00 μm.

4. 4. The cemented carbide material for a cutting tool according to claim 1, wherein the cemented carbide material comprises 85.0 volume % or more and 95.5 volume % or less of the tungsten carbide particles and 0.5 volume % or more and 15.0 volume % or less of the binder phase.

5. A cutting tool made of cemented carbide, The cemented carbide comprises tungsten carbide particles and a binder phase; The cemented carbide contains three or less pores having a circular equivalent diameter of less than 0.2 μm in a rectangular measurement field of view of 24.9 μm × 18.8 μm, the measurement field of view is provided within an area S1 on a cross section of the cemented carbide including the cutting edge of the cutting tool, The region S1 is a region in a cross section of the cemented carbide that is 100 μm or less away from the cutting edge and 0.5 μm or more and 30 μm or less away from the surface of the cutting tool.

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