cutting tools

Abstract

A cemented carbide alloy comprising a first hard phase, a plurality of second hard phases, and a binder phase, wherein the first hard phase comprises a plurality of tungsten carbide particles, the tungsten carbide particles having a particle size D10 of 0.40 μm or more and a particle size D90 of 2.00 μm or less, and the second hard phase comprises at least one selected from the group consisting of TaNbC, TaNbN, TaNbCN, TiCN, TiNbC, TiNbN, and TiNbCN. the cemented carbide is composed of a first compound of a type, the cemented carbide contains the second hard phase in an amount of 0.30 volume % or more and 1.60 volume % or less, the median value of the distance between the centers of gravity of two of the second hard phases that are closest to each other in a cross section of the cemented carbide is 4 μm or more and 15 μm or less, and the coefficient of variation of the distance between the centers of gravity is 1.20 or more and 1.90 or less, the binder phase contains 50 mass % or more of cobalt, and the cemented carbide contains the binder phase in an amount of 8.0 volume % or more and 14.0 volume % or less.

Description

[Technical Field]

[0001] The present disclosure relates to cemented carbides and cutting tools. [Background technology]

[0002] Conventionally, cemented carbide alloys having a first hard phase mainly composed of tungsten carbide (WC), a second hard phase mainly composed of a compound containing multiple metal elements including tungsten and one or more elements selected from carbon, nitrogen, oxygen, and boron, and a binder phase mainly composed of an iron-group element have been used as materials for cutting tools.Patent Document 1 discloses a cutting tool in which a hard film such as a TiAlN film is formed on a substrate made of such a cemented carbide alloy. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2017 / 191744 Summary of the Invention

[0004] The cemented carbide of the present disclosure is a cemented carbide consisting of a first hard phase, a plurality of second hard phases, and a binder phase, the first hard phase is composed of a plurality of tungsten carbide particles; The particle diameter D10 of the tungsten carbide particles is 0.40 μm or more, The tungsten carbide particles have a particle size D90 of 2.00 μm or less, the second hard phase is composed of at least one first compound selected from the group consisting of TaNbC, TaNbN, TaNbCN, TiCN, TiNbC, TiNbN, and TiNbCN; The cemented carbide contains the second hard phase in an amount of 0.30% by volume or more and 1.60% by volume or less, In the cross section of the cemented carbide, the median value of the distance between the centers of gravity of the two most adjacent second hard phases is 4 μm or more and 15 μm or less, the coefficient of variation of the distance between the centers of gravity is 1.20 or more and 1.90 or less, The binder phase contains 50% by mass or more of cobalt, The cemented carbide contains the binder phase in an amount of 8.0% by volume or more and 14.0% by volume or less. [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 1 is a diagram illustrating a typical example of the configuration of the cemented carbide according to the first embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view of a cutting tool according to a second embodiment. [Figure 3] FIG. 3 is a diagram illustrating a typical configuration example of a cutting tool according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0006] [Problem to be solved by this disclosure] For example, cutting tools having a thick coating formed on a substrate made of cemented carbide are used for cutting cemented carbide. When cemented carbide is cut using such cutting tools, the coating tends to peel off from inhomogeneous portions of the coating, resulting in a shortened tool life.

[0007] Therefore, an object of the present disclosure is to provide a cemented carbide alloy that, when used as a material for a cutting tool, enables the cutting tool to have a longer life even when machining cemented carbide alloys, and a cutting tool including the cemented carbide alloy.

[0008] [Effects of this disclosure] According to the present disclosure, it is possible to provide a cemented carbide alloy that, when used as a material for a cutting tool, enables the cutting tool to have a longer life even when machining cemented carbide alloys, and a cutting tool including the cemented carbide alloy.

[0009] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described. (1) The cemented carbide of the present disclosure is a cemented carbide consisting of a first hard phase, a plurality of second hard phases, and a binder phase, the first hard phase is composed of a plurality of tungsten carbide particles; The particle diameter D10 of the tungsten carbide particles is 0.40 μm or more, The tungsten carbide particles have a particle size D90 of 2.00 μm or less, the second hard phase is composed of at least one first compound selected from the group consisting of TaNbC, TaNbN, TaNbCN, TiCN, TiNbC, TiNbN, and TiNbCN; The cemented carbide contains the second hard phase in an amount of 0.30% by volume or more and 1.60% by volume or less, In the cross section of the cemented carbide, the median value of the distance between the centers of gravity of the two most adjacent second hard phases is 4 μm or more and 15 μm or less, the coefficient of variation of the distance between the centers of gravity is 1.20 or more and 1.90 or less, The binder phase contains 50% by mass or more of cobalt, The cemented carbide contains the binder phase in an amount of 8.0% by volume or more and 14.0% by volume or less.

[0010] According to the present disclosure, it is possible to provide a cemented carbide that, when used as a material for cutting tools, enables the cutting tools to have a longer life even when machining CFRP.

[0011] (2) In the above (1), the cemented carbide may contain 0.08% by mass or more and 0.5% by mass or less of chromium.

[0012] Chromium is derived from chromium carbide (Cr3C2), which is used as a grain growth inhibitor in the production of cemented carbide. When cemented carbide contains chromium within the above range, the hardness of the cemented carbide is improved, further improving the life of cutting tools using the cemented carbide. (3) In the above (1) or (2), the binder phase may contain one or both of iron and nickel.

[0013] This improves the toughness of the cemented carbide, and further improves the life of cutting tools using the cemented carbide.

[0014] (4) A cutting tool according to the present disclosure is a cutting tool including a substrate made of the cemented carbide according to any one of (1) to (3) above, and a coating provided on the substrate.

[0015] According to the present disclosure, it is possible to provide a cutting tool having a long life even when machining cemented carbide.

[0016] [Details of the embodiments of the present disclosure] Specific examples of the cemented carbide and cutting tool 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 the present disclosure, the notation in the form "A to B" means greater than or equal to A and less than or equal to B, and when no unit is specified for A and only a unit is specified for B, the unit of A and the unit of B are the same.

[0018] In the present disclosure, when a compound or the like is represented by a chemical formula, unless the atomic ratio is particularly limited, it is intended to include any conventionally known atomic ratio, and should not necessarily be limited to only those within the stoichiometric range.

[0019] In this disclosure, when one or more numerical values ​​are listed as the lower limit and upper limit of a numerical range, the combination of any one numerical value listed in the lower limit and any one numerical value listed in the upper limit is also disclosed.

[0020] [Embodiment 1: Cemented Carbide] As shown in FIG. 1 , a cemented carbide 4 according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") is a cemented carbide 4 comprising a first hard phase 1, a plurality of second hard phases 2, and a binder phase 3, The first hard phase 1 is composed of a plurality of tungsten carbide particles, The particle size D10 of the tungsten carbide particles is 0.40 μm or more, The particle size D90 of the tungsten carbide particles is 2.00 μm or less, the second hard phase 2 is made of at least one first compound selected from the group consisting of TaNbC, TaNbN, TaNbCN, TiCN, TiNbC, TiNbN, and TiNbCN; The cemented carbide 4 contains a second hard phase 2 in an amount of 0.30 vol% or more and 1.60 vol% or less, In the cross section of the cemented carbide 4, the median value of the distance between the centers of gravity of the two closest second hard phases 2 is 4 μm or more and 15 μm or less, The coefficient of variation of the distance between the centers of gravity is 1.20 or more and 1.90 or less, The binder phase 3 contains 50 mass % or more of cobalt, The cemented carbide 4 is a cemented carbide 4 containing a binder phase 3 in an amount of 8.0 volume % or more and 14.0 volume % or less.

[0021] When used as a material for cutting tools, the cemented carbide of embodiment 1 enables the cutting tools to have a longer life even when machining cemented carbide. The reason for this is not clear, but is presumed to be as follows.

[0022] When cemented carbide is used to machine cemented carbide, a cutting tool is generally used in which a coating is formed on a substrate made of cemented carbide. To obtain stable tool performance, it is essential that the coating structure is homogeneous. The inhomogeneous portions (e.g., unevenness) of the coating vary depending on the internal structure of the substrate. When the median value of the distance between the centers of gravity of the two closest second hard phases in the cross section of the cemented carbide is 4 μm or more and 15 μm or less, and the coefficient of variation of the distance between the centers of gravity is 1.20 or more and 1.90 or less, the homogeneity of the substrate and the coating is improved. Therefore, a cutting tool using the cemented carbide of embodiment 1 as its material can have a long tool life even when machining cemented carbide.

[0023] <Composition of cemented carbide> The cemented carbide of the first embodiment is composed of a first hard phase, multiple second hard phases, and a binder phase. The cemented carbide may contain impurities as long as the effects of the present disclosure are not impaired. That is, the cemented carbide may be composed of a first hard phase, multiple second hard phases, a binder phase, and impurities. Examples of impurities include iron (Fe), molybdenum (Mo), calcium (Ca), silicon (Si), and sulfur (S). The impurity content of the cemented carbide (when there are two or more types of impurities, the total content of these impurities) may be 0% by mass or more and less than 0.1% by mass. The impurity content of the cemented carbide is measured by inductively coupled plasma emission spectroscopy (ICP optical emission spectroscopy). A Shimadzu "ICPS-8100" (trademark) measurement device may be used.

[0024] The content of the second hard phase in the cemented carbide of embodiment 1 is 0.30% by volume or more and 1.60% by volume or less. This improves the adhesion resistance, heat resistance, and wear resistance of the cemented carbide. The content of the second hard phase in the cemented carbide may be 0.40% by volume or more and 1.50% by volume or less, or 0.50% by volume or more and 1.40% by volume or less.

[0025] The cemented carbide of embodiment 1 has a binder phase content of 8.0 volume % or more and 14.0 volume % or less. This improves the strength of the cemented carbide. The binder phase content of the cemented carbide may be 8.1 volume % or more and 13.9 volume % or less, or 8.2 volume % or more and 13.8 volume % or less.

[0026] The content of the first hard phase in the cemented carbide of embodiment 1 is the value obtained by subtracting the volumes of the second hard phase and binder phase from 100% by volume of the entire cemented carbide.

[0027] The methods for measuring the content of the first hard phase, the content of the second hard phase, and the content of the binder phase of the cemented carbide are as follows. (A1) A cemented carbide alloy is cut out at an arbitrary position to expose a cross section, which is then polished to a mirror finish using a cross section polisher (manufactured by JEOL Ltd.).

[0028] (B1) The machined surface of the cemented carbide is photographed using a scanning electron microscope (SEM) (Hitachi High-Technologies Corporation, "S-3400N" (trademark)) to obtain a backscattered electron image. Six backscattered electron images are prepared. Each of the six backscattered electron images captures a different area. The photographed location can be set arbitrarily. The observation conditions are a magnification of 5000x and an accelerating voltage of 10 kV.

[0029] (C1) The photographed area in (B1) above is subjected to elemental analysis using an energy dispersive X-ray analyzer attached to an SEM (SEM-EDX) to obtain an elemental mapping image.

[0030] (D1) The six backscattered electron images obtained in (B1) above are imported into a computer using image analysis software (ImageJ, version 1.51j8: https: / / imagej.nih.gov / ij / ), where they are binarized to obtain six binarized images. The binarization process is performed under preset conditions in the image analysis software by clicking the "Make Binary" button on the computer screen after importing the images. In the binarized image, the first region consisting of the first hard phase and the second region consisting of the second and third hard phases can be distinguished by their different shades of color. For example, in the binarized image, the first hard phase is shown as a black region, and the second and third hard phases are shown as white regions.

[0031] (E1) By superimposing the element mapping image obtained in (C1) above on the binarized image obtained in (D1) above, the regions where the first hard phase, the second hard phase, and the binder phase exist are identified on the binarized image. Specifically, the regions shown in black in the binarized image and where tungsten (W) and carbon (C) exist in the element mapping image correspond to the regions where the first hard phase exists. The regions shown in white in the binarized image and where titanium (Ti) or tantalum (Ta) exist in the element mapping image correspond to the regions where the second hard phase exists. The regions shown in white in the binarized image and where cobalt exists in the element mapping image correspond to the regions where the binder phase exists.

[0032] (F1) One rectangular measurement field of view of 25.3 μm × 17.6 μm is set in each of the six images after binarization. Using the image analysis software, the area percentage (area%) of each of the first hard phase, second hard phase, and binder phase is measured in each of the six measurement fields, with the area of ​​the entire measurement field being used as the denominator. In the present disclosure, the average area percentage (area%) of the first hard phase in the six measurement fields, the average area percentage (area%) of the second hard phase in the six measurement fields, and the average area percentage (area%) of the binder phase in the six measurement fields correspond to the content (volume%) of the first hard phase, the content (volume%) of the second hard phase, and the content (volume%) of the binder phase in the cemented carbide, respectively.

[0033] As long as measurements are made on the same sample, it has been confirmed that there is almost no variation in the measurement results even if the above measurement is performed multiple times by changing the selected location of the measurement field.

[0034] <1st hard phase> ≪Composition≫ In the cemented carbide of the first embodiment, the first hard phase is composed of a plurality of tungsten carbide particles (hereinafter also referred to as "WC particles"). The tungsten carbide particles include not only "pure WC particles (including WC containing no impurity elements and WC with impurity elements below the detection limit)" but also "WC particles containing impurities therein, as long as the effects of the present disclosure are not impaired." Examples of impurities include iron (Fe), molybdenum (Mo), and sulfur (S).

[0035] <Tungsten carbide particle diameter> The tungsten carbide particles have a particle size D10 of 0.40 μm or more and a particle size D90 of 2.00 μm or less, which provides the cemented carbide with high hardness and improves the wear resistance of cutting tools containing the cemented carbide.

[0036] The tungsten carbide particles may have a D10 of 0.42 μm or more, or 0.44 μm or more, and a D90 of 1.98 μm or less, or 1.96 μm or less.

[0037] In the present disclosure, the D10 and D90 of tungsten carbide particles refer to the D10 (circle equivalent diameter at which the cumulative number-based frequency is 10%) and D90 (circle equivalent diameter at which the cumulative number-based frequency is 90%) of the equivalent area circle diameter (Heywood diameter) of the tungsten carbide particles in the cross section of the cemented carbide, respectively.

[0038] In the present disclosure, the method for measuring D10 and D90 of tungsten carbide particles is as follows. (A2) Six images after binarization are obtained using the same method as the method for measuring the content of the first hard phase, etc., in cemented carbide. Furthermore, to remove noise, the "Despeckle" display on the computer screen is pressed once, and then the "Watershed" display is pressed, and the grain boundaries of the first hard phase (tungsten particles) are also identified on the images after binarization under the conditions preset in the image analysis software. By pressing "Analyze Particle" on the computer screen, the area is reduced to 0.002 μm. 2 The equivalent diameter of a circle having the same area as the above tungsten carbide particles is measured.

[0039] (B2) In each of the six binarized images, a rectangular measurement field of 25.3 μm × 17.6 μm is set. Using the image analysis software, the area of ​​the six measurement fields is determined to be 0.002 μm. 2 Based on all of the above tungsten carbide particles, the equivalent diameters D10 and D90 of the circles with equal area of ​​the tungsten carbide particles are measured. In the present disclosure, the D10 and D90 measured above correspond to the D10 and D90 of the tungsten carbide particles.

[0040] Although the threshold setting for the binarization process can be manually adjusted, this measurement method does not use manual adjustment. In this measurement method, as described above, binarization is performed by pressing the "Make Binary" button. 2 The reason for measuring the equivalent circle diameter of the tungsten carbide particles is that the inventors have measured the area of ​​0.002 μm 2 This is because it has been confirmed that particles smaller than this size are often noise that is mistakenly detected as tungsten carbide particles in image analysis.

[0041] As long as measurements are made on the same sample, it has been confirmed that there is almost no variation in the measurement results even if the above measurement is performed multiple times by changing the selected location of the measurement field.

[0042] <Second hard phase> ≪Composition≫ In embodiment 1, the second hard phase comprises at least one first compound selected from the group consisting of TaNbC, TaNbN, TaNbCN, TiCN, TiNbC, TiNbN, and TiNbCN. This improves the adhesion resistance, heat resistance, and wear resistance of the cemented carbide. In the present disclosure, the ratio of the total number of Ta, Nb, and Ti atoms to the total number of C and N atoms in each of TaNbC, TaNbN, TaNbCN, TiCN, TiNbC, TiNbN, and TiNbCN is not limited to 1:1, and may include any conventionally known ratio as long as it does not impair the effects of the present disclosure.

[0043] The second hard phase may be made of one first compound selected from the group consisting of TaNbC, TaNbCN, TiCN, and TiNbCN.

[0044] The second hard phase may contain metal elements such as tungsten (W), chromium (Cr), and cobalt (Co) within a range that does not impair the effects of the present disclosure. The total content of W, Cr, and Co in the second hard phase may be 0% by mass or more and less than 0.1% by mass. The contents of W, Cr, and Co in the second hard phase are measured by ICP optical emission spectroscopy.

[0045] The composition of the second hard phase was measured as follows. (A3) An arbitrary position of the cemented carbide is thinned using an ion slicer (device: IB09060CIS (trademark) manufactured by JEOL Ltd.) to prepare a sample with a thickness of 30 to 100 nm. The acceleration voltage of the ion slicer is 6 kV for thinning and 2 kV for finish processing.

[0046] (B3) The above sample is observed at 50,000x magnification using a scanning transmission electron microscope (STEM) (JFM-ARM300F (trademark) manufactured by JEOL Ltd.) to obtain a STEM-HAADF (HAADF: high-angle annular dark field) image. The imaging area for the STEM-HAADF image is set to the center of the sample, i.e., a position that does not include areas with properties clearly different from the bulk part, such as the vicinity of the surface of the cemented carbide (a position where the entire imaging area is the bulk part of the cemented carbide). The measurement condition is an acceleration voltage of 200 kV.

[0047] (C3) Next, elemental mapping analysis is performed on the STEM-HAADF image using EDX attached to the STEM to obtain an elemental mapping image. In the elemental mapping image, regions where tantalum (Ta) or titanium (Ti) and one or both of carbon (C) and nitrogen (N) exist are identified as the second hard phase, and the composition of the second hard phase is identified.

[0048] As long as measurements are made on the same sample, it has been confirmed that there is almost no variation in the measurement results even if the above measurement is performed multiple times by changing the selected location of the measurement field.

[0049] <Distance between centers of gravity of the second hard phase and coefficient of variation of the distance between centers of gravity> The cemented carbide of embodiment 1 includes a plurality of second hard phases. Each second hard phase is composed of one first compound particle or an aggregate of a plurality of first compound particles. When the second hard phase is composed of an aggregate of a plurality of first compound particles, the plurality of first compound particles may be composed of one type of first compound particle or two or more types of first compound particles.

[0050] In a cross section of the cemented carbide of embodiment 1, the median value of the distance between the centers of gravity of the two closest second hard phases is 4 μm or more and 15 μm or less, and the coefficient of variation of the distance between the centers of gravity is 1.20 or more and 1.90 or less. When the median value of the distance between the centers of gravity of the two closest second hard phases is 4 μm or more and the coefficient of variation of the distance between the centers of gravity is within the above range, unevenness of the coating is reduced when a coating is provided on a substrate made of the cemented carbide of embodiment 1. When the median value of the distance between the centers of gravity of the two closest second hard phases is 15 μm or less and the coefficient of variation of the distance between the centers of gravity is within the above range, homogeneity of the coating is improved when a coating is provided on a substrate made of the cemented carbide of embodiment 1.

[0051] The median of the distance between the centers of gravity may be 5 μm or more and 13 μm or less, or may be 6 μm or more and 11 μm or less. The coefficient of variation of the distance between the centers of gravity may be 1.30 or more and 1.80 or less, or may be 1.40 or more and 1.70 or less.

[0052] In the present disclosure, the distance between the centers of gravity of two closest second hard phases is the distance between the center of gravity of one second hard phase and the center of gravity of another second hard phase located closest to the center of gravity in the cross section of the cemented carbide. For example, in FIG. 1, when a second hard phase 2 having a center of gravity C1 is used as a reference, the distance d1 between the center of gravity C1 and the center of gravity C2 of another second hard phase 2 located closest to the center of gravity C1 corresponds to the distance between the centers of gravity of the two closest second hard phases. In this case, "the center of gravity C2 of another second hard phase located closest to the center of gravity C1" means that the center of gravity located closest to the center of gravity C1 is the center of gravity C2. Furthermore, when the center of gravity C3 of a second hard phase 2 having a center of gravity C3 is used as a reference, the distance d2 between the center of gravity C3 and the center of gravity C2 of another second hard phase 2 located closest to the center of gravity C3 corresponds to the distance between the centers of gravity of the two closest second hard phases. In this case, "the center of gravity C2 of another second hard phase located at a position closest to the center of gravity C3" means that the center of gravity located at a position closest to the center of gravity C3 is the center of gravity C2.

[0053] In the present disclosure, the median of the distance between the centers of gravity of the two closest second hard phases in the cross section of the cemented carbide is the distance between the centers of gravity of the two closest second hard phases measured for each of all second hard phases within the measurement field of view, where the cumulative frequency of the distance between the centers of gravity of the two closest second hard phases is 50%. In the present disclosure, the coefficient of variation of the distance between the centers of gravity of the second hard phases is the value obtained by dividing the standard deviation of the distance between the centers of gravity by the average value of the distance between the centers of gravity (standard deviation / average value). In the present disclosure, the average value of the distance between the centers of gravity means the arithmetic average of the distance between the centers of gravity of the two closest second hard phases measured for each of all second hard phases within the measurement field of view.

[0054] In the present disclosure, the median value of the distance between the centers of gravity of the two most adjacent second hard phases in a cross section of a cemented carbide and the coefficient of variation of the distance between the centers of gravity are measured as follows. (A4) A position of the cemented carbide is cut out to expose a cross section. The cross section is polished using a cross-section polisher. The polished surface of the cemented carbide is photographed using an SEM to obtain a backscattered electron image. The observation conditions are a magnification of 1000x and an accelerating voltage of 10 kV.

[0055] (B4) The photographed area in (A4) above is subjected to elemental analysis using an energy dispersive X-ray analyzer (SEM-EDX) attached to an SEM to obtain an element mapping image. By superimposing the backscattered electron image and the element mapping image, the second hard phase is identified on the backscattered electron image.

[0056] (C4) The backscattered electron image in which the second hard phases are identified is imported into a computer using image analysis software (Mountech Co., Ltd.'s "Mac-View Version.5" (trademark)), and the center of gravity of each second hard phase is identified under the following conditions, and the median value of the distance between the centers of gravity of the two closest second hard phases is measured. Acquisition mode: Color difference Detection tolerance: 32, detection accuracy: 0.5 Scanning: Density 10 x 1 time High Cut: Enabled

[0110] Low Cut: Inverted

[0150]

[0057] (D4) Identify three visual fields in which 30 or more second hard phases can be confirmed. Based on all second hard phases in the three visual fields, measure the median of the distance between the centers of gravity of the two closest second hard phases and the coefficient of variation of the distance between the centers of gravity. In the present disclosure, the median of the distance between the centers of gravity of the two closest second hard phases measured above corresponds to the median of the distance between the centers of gravity of the two closest second hard phases in the cross section of the cemented carbide and the coefficient of variation of the distance between the centers of gravity.

[0058] As long as measurements are made on the same sample, it has been confirmed that there is almost no variation in the measurement results even if the above measurement is performed multiple times by changing the selected location of the measurement field.

[0059] <Binded phase> ≪Composition≫ In the cemented carbide of embodiment 1, the binder phase contains 50% by mass or more of cobalt, which allows the cemented carbide to have excellent toughness. The cobalt content of the binder phase may be 50% by mass or more and 100% by mass or less, 60% by mass or more and 90% by mass or less, or 70% by mass or more and 80% by mass or less.

[0060] The method for measuring the cobalt content of the binder phase is as follows: The region where the binder phase exists is identified in the element mapping image using the same methods as (A1) to (E1) of the method for measuring the content of the first hard phase, etc., of the cemented carbide described above. One rectangular measurement field of view of 24.9 μm × 18.8 μm is set in the element mapping image. The cobalt content is measured in the region where the binder phase exists in the measurement field of view. In the present disclosure, the average of the cobalt contents in the region where the binder phase exists in the six measurement fields of view corresponds to the cobalt content of the binder phase.

[0061] As long as measurements are made on the same sample, it has been confirmed that there is almost no variation in the measurement results even if the above measurement is performed multiple times by changing the selected location of the measurement field.

[0062] The binder phase may contain iron (Fe), nickel (Ni), etc., as long as the effects of the present disclosure are not impaired. The binder phase may contain cobalt and one or both of nickel and iron. The binder phase may consist of cobalt and one or both of nickel and iron.

[0063] <Chrome> The cemented carbide of embodiment 1 may contain 0.08% by mass or more and 0.5% by mass or less of chromium. The chromium content of the cemented carbide may be 0.10% by mass or more and 0.48% by mass or less, or 0.12% by mass or more and 0.46% by mass or less. The chromium content of the cemented carbide is measured by ICP atomic emission spectrometry.

[0064] <Manufacturing method> The cemented carbide of the first embodiment can be produced, for example, through a preparation step, a mixing step, a molding step, a sintering step, and a cooling step.

[0065] <Preparation process> In the preparation step, raw material powders are prepared. Examples of raw material powders include WC powder, TaNbC powder, TaNbN powder, TaNbCN powder, TiCN powder, TiNbC powder, TiNbN powder, TiNbCN powder, NbC powder, Ta2O5 powder, TiO2 powder, Co powder, Ni powder, and Fe powder. These raw material powders are appropriately selected based on the target composition of the cemented carbide. Chromium carbide (Cr3C2) powder may be prepared as a grain growth inhibitor.

[0066] The average particle size of the tungsten carbide (WC) powder is 1.0 μm or more and 1.8 μm or less.

[0067] The TaNbC powder, TaNbN powder, TaNbCN powder, TiCN powder, TiNbC powder, TiNbN powder, TiNbCN powder, NbC powder, Ta2O5 powder, and TiO2 powder have an average particle size of 1 μm or more and 2 μm or less. These powders are raw material powders for the second hard phase.

[0068] The average particle size of the Co powder, Ni powder, and Fe powder may be 0.1 μm or more and 5 μm or less.

[0069] The average particle size of the raw material powder is determined by the Fischer method.

[0070] <Mixing process> In the mixing process, the raw material powders are mixed in a predetermined ratio to obtain a mixed powder. The mixing ratio of each raw material powder is adjusted appropriately depending on the target cemented carbide composition. A ball mill is used for mixing. The mixing conditions are a ball diameter of 6 mm, a rotation speed of 100 rpm, and a mixing time of 12 to 48 hours.

[0071] <Forming process> In the molding step, the mixed powder is molded into a desired shape to obtain a molded body. The molding method and molding conditions are not particularly limited and may be any commonly used method and conditions.

[0072] <Sintering process> In the sintering process, the compact is first heated to 1365 to 1400°C and held there for 120 minutes. The temperature rise rate above 1000°C is 1°C / min. The pressure here can be vacuum or N2 (flow rate 2 L / min, partial pressure 5 kPa). Next, the compact is cooled to 1200°C at a temperature drop rate of -4.5 to -5.5°C / min to obtain a cemented carbide intermediate.

[0073] Next, the cemented carbide intermediate is subjected to HIP (Hot Isostatic Pressing). Specifically, the cemented carbide intermediate is subjected to a temperature of 1320°C and a pressure of 10 MPa for 60 minutes using Ar gas as a pressure medium. Then, the cemented carbide intermediate is slowly cooled to obtain the cemented carbide of embodiment 1. The temperature drop rate during the slow cooling is not particularly limited and may be any general condition.

[0074] <Features of the method for manufacturing a cemented carbide according to the first embodiment> In the method for producing a cemented carbide according to the first embodiment, the above mixing conditions are employed to prevent excessive pulverization of the raw powder of WC particles and the second hard phase, thereby controlling the particle size. Furthermore, the heating rate at 1000°C or higher is 1°C / min, which is slower than a typical heating rate, and the heating rate is controlled to -4.5 to -5.5°C / min. The above conditions control the position at which the second hard phase precipitates, allowing the production of a cemented carbide according to the first embodiment, in which the median value of the distance between the centers of gravity of the two closest second hard phases in the cross section of the cemented carbide is 4 μm or more and 15 μm or less, and the coefficient of variation of the distance between the centers of gravity is 1.20 or more and 1.90 or less. This was discovered by the present inventors after extensive research.

[0075] [Embodiment 2: Cutting Tool] A cutting tool according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 2") will be described with reference to FIG. 2. As shown in FIG. 2, the cutting tool 10 of Embodiment 2 includes a substrate 5 made of the cemented carbide of Embodiment 1 and a coating 6 provided on the substrate 5. The cutting tool of Embodiment 2 can have a long tool life even when machining cemented carbide. The reason for this is not clear, but is presumed to be as follows.

[0076] In the cutting tool of embodiment 2, a coating is provided on a substrate made of the cemented carbide of embodiment 1. To obtain stable tool performance, it is essential that the coating structure is homogeneous. The inhomogeneous portions (e.g., unevenness) of the coating vary depending on the internal structure of the substrate. When the median value of the distance between the centers of gravity of the two closest second hard phases in the cross section of the cemented carbide is 4 μm or more and 15 μm or less, and the coefficient of variation of the distance between the centers of gravity is 1.20 or more and 1.90 or less, the homogeneity of the substrate and the coating is improved. Therefore, the cutting tool of embodiment 2 can have a long tool life even when machining cemented carbide.

[0077] The type of cutting tool is not particularly limited. Examples of cutting tools include cutting tools, drills, end mills, indexable cutting inserts for milling, indexable cutting inserts for turning, metal saws, gear cutting tools, reamers, taps, etc. As shown in Figure 3, the cutting tool 10 of embodiment 2 can exhibit excellent effects, particularly in the case of a ball end mill. The substrate 5 of the cutting tool 10 shown in Figure 2 is made of the cemented carbide of embodiment 1.

[0078] The coating may be disposed so as to cover the entire surface of the substrate, or may be disposed so as to cover only a portion of the surface. When the coating is disposed so as to cover only a portion of the substrate, it is preferable that the coating be disposed so as to cover at least the surface of the portion of the substrate involved in cutting. In the present disclosure, the portion of the substrate involved in cutting refers to a region of the substrate that is within 0.5 mm of the cutting edge.

[0079] The coating may be a compound of one or more elements selected from the group consisting of metal elements of Groups 4, 5, and 6 of the periodic table, aluminum (Al), and silicon (Si), and one or more elements selected from the group consisting of carbon, nitrogen, oxygen, and boron. Examples include TiCN, Al2O3, TiAlN, TiN, TiC, and AlCrN. The coating may also be composed of cubic boron nitride (cBN), diamond-like carbon, or diamond. The diamond may be either single crystal or polycrystalline.

[0080] The coating may be a single layer or a multilayer, and the thickness of the coating may be 1 μm or more and 20 μm or less, or 5 μm or more and 15 μm or less.

[0081] The cutting tool of the second embodiment is produced, for example, by the following method: First, a substrate made of the material of the first embodiment is prepared. The surface of the substrate is etched with acid and alkali.

[0082] A coating is formed on the substrate after the etching treatment to obtain the cutting tool of embodiment 2. The coating can be formed by a gas phase method such as chemical vapor deposition (CVD) or physical vapor deposition (PVD).

[0083] When the coating is formed by the CVD method, it is easy to obtain a coating with excellent adhesion to the substrate. Examples of CVD methods include hot filament CVD. For example, when forming a diamond coating, the film formation conditions for the hot filament CVD method may be a temperature of 650 to 800°C, a pressure of 500 Pa, and a gas flow ratio of H2 / CH4 of 100 / 1 to 5.

[0084] If the coating is formed by the PVD method, compressive residual stress is imparted to the coating, which makes it easier to increase its toughness.

[0085] [Appendix 1] A cutting tool according to the present disclosure includes a substrate made of the cemented carbide of embodiment 1 and a coating provided on the substrate, A cutting tool, wherein the coating is made of diamond. [Example]

[0086] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0087] [Preparation of cemented carbide] Each sample of cemented carbide was prepared according to the following procedure. <Preparation process> The raw powders prepared were WC powder, TaNbC powder (average particle size: 1 μm), TiCN powder (average particle size: 1 μm), NbC powder (average particle size: 1 μm), Ta2O5 powder (average particle size: 1 μm), TiO2 powder (average particle size: 1 μm), Cr3C2 powder (average particle size: 1 μm), Co powder (average particle size: 1 μm), Ni powder (average particle size: 1 μm), and Fe powder (average particle size: 1 μm).The WC powders prepared were WC08 (average particle size: 0.8 μm), WC10 (average particle size: 1.0 μm), WC12 (average particle size: 1.2 μm), WC15 (average particle size: 1.5 μm), and WC20 (average particle size: 2.0 μm) manufactured by A.L.M.T.C., with the average particle size indicated in parentheses. The TaNbC powder was prepared using "TaNbC 67 / 33" manufactured by HC Starck, with an average particle size of 1 μm.

[0088] <Mixing process> The raw material powders were mixed in a ball mill or attritor in the proportions shown in Table 1 to obtain mixed powders. The mixing conditions for the "ball mill" were a ball diameter of 6 mm, a rotation speed of 100 rpm, and a mixing time of 24 hours. The mixing conditions for the "attritor" were a rotation speed of 250 rpm, and a mixing time of 1 hour.

[0089] [Table 1]

[0090] <Forming process> The mixed powder was pressed to obtain a round bar-shaped compact.

[0091] <Sintering process> The compact was heated to the temperature shown in the "Hold" column under "Sintering" in Table 2 and held at that temperature for the time shown in the "Hold" column. The heating rate above 1000°C was as shown in the "Hold Rate Above 1000°C" column. The pressure during holding was vacuum (vac) or N2 (flow rate 2 L / min, partial pressure 5 kPa, shown as "N2 (2 L-5 kPa)" in the table).

[0092] Next, the temperature was decreased to 1200°C at the temperature decreasing rate shown in the "Temperature decreasing rate" column in Table 2, to obtain a cemented carbide intermediate.

[0093] Next, the cemented carbide intermediate was subjected to HIP treatment. Specifically, the cemented carbide intermediate was subjected to a temperature of 1320°C and a pressure of 10 MPa for 60 minutes using Ar gas as a pressure medium. After that, it was slowly cooled to obtain each cemented carbide sample.

[0094] [Table 2]

[0095] [Evaluation of cemented carbide] <Content of secondary hard phase and binder phase in cemented carbide> The content of the second hard phase and the content of the binder phase of the cemented carbide of each sample were measured. The specific measurement method is as described in embodiment 1. The results are shown in the "Content" column of "Second Hard Phase" and the "Content" column of "Binder Phase" of "Cemented Carbide" in Table 3. In all samples, the components other than the second hard phase and binder phase were the first hard phase.

[0096] <D10 and D90 diameters of tungsten carbide particles> The particle sizes D10 and D90 of the tungsten carbide particles were measured for each cemented carbide sample. The specific measurement method is as described in embodiment 1. The results are shown in the "D10" and "D90" columns of "First hard phase" under "Cemented carbide" in Table 3.

[0097] <Composition of the second hard phase> The composition of the second hard phase in each cemented carbide sample was measured. The specific measurement method is as described in embodiment 1. The results are shown in the "Composition" column of "Second hard phase" under "Cemented carbide" in Table 3.

[0098] <Median and coefficient of variation of the area of ​​the secondary hard phase> In the cross section of each cemented carbide sample, the median of the distance between the centers of gravity of the two most adjacent second hard phases and the coefficient of variation of the distance between the centers of gravity were measured. The specific measurement method is as described in embodiment 1. The results are shown in the "Median of the distance between the centers of gravity" and "Coefficient of variation of the distance between the centers of gravity" columns of "Second hard phase" under "Cemented carbide" in Table 3.

[0099] <Binder phase composition> The composition of the binder phase and the cobalt content of the binder phase of each cemented carbide sample were measured. The specific measurement method is as described in embodiment 1. The results are shown in the "Composition" and "Co content" columns of "Binder phase" under "Cemented carbide" in Table 3.

[0100] <Chromium content in cemented carbide> The chromium content of the cemented carbide of each sample was measured. The specific measurement method is as described in embodiment 1. The results are shown in the "Cr content" column of "Cemented carbide" in Table 3.

[0101] [Table 3]

[0102] [Cutting tool manufacturing] A round bar made of cemented carbide for each sample was machined to produce a base material with a ball end mill shape (model number: SDCB2R050-0150). The surface of the base material was etched with acid and alkali.

[0103] After etching, a 15 μm thick polycrystalline diamond coating was formed on the substrate using the hot filament CVD method to obtain cutting tools (ball end mills) for each sample. The deposition conditions for the hot filament CVD method were 700°C, 500 Pa, and the gas flow ratio of H2 / CH4 = 100 / 1.

[0104] Each sample ball end mill was used to machine the inclined surface of cemented carbide. The machining conditions were a rotation speed of 3000 rpm, table feed F of 200 mm / min, cutting depth (axial) ap of 0.05 mm, cutting depth (radial) ae of 0.25 mm, and dry machining. The cutting length until the surface of the workpiece deteriorated was measured. The longer the cutting length, the longer the tool life is considered to be. The results are shown in the "Cutting length" column of "Cutting test" in Table 3.

[0105] [Consideration] The cemented carbide alloys and cutting tools of Samples 1 to 20 correspond to Examples. The cemented carbide alloys and cutting tools of Samples 21 to 31 correspond to Comparative Examples. It was confirmed that the cutting tools of the Examples had a longer tool life than the cutting tools of the Comparative Examples. It was confirmed that the cutting tools of the Examples had a long tool life when used to machine cemented carbide alloys. Although the cutting tools of the Examples had a thick coating, it is presumed that the coating was homogeneous and had strong adhesion between the substrate and the coating, which prevented surface deterioration due to film peeling.

[0106] 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, not by the embodiments and examples described above, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims. [Explanation of symbols]

[0107] 1 First hard phase, 2 Second hard phase, 3 Binding phase, 4 Cemented carbide, 5 Base material, 6 Coating, 10 Cutting tool.

Claims

1. A cemented carbide comprising a first hard phase, a plurality of second hard phases, and a binder phase, the first hard phase is composed of a plurality of tungsten carbide particles; The particle diameter D10 of the tungsten carbide particles is 0.40 μm or more, The tungsten carbide particles have a particle size D90 of 2.00 μm or less, the second hard phase is composed of at least one first compound selected from the group consisting of TaNbC, TaNbN, TaNbCN, TiCN, TiNbC, TiNbN, and TiNbCN; The cemented carbide contains the second hard phase in an amount of 0.30 vol% or more and 1.60 vol% or less, In a cross section of the cemented carbide, the median value of the distance between the centers of gravity of the two second hard phases that are closest to each other is 4 μm or more and 15 μm or less, the coefficient of variation of the distance between the centers of gravity is 1.20 or more and 1.90 or less, The binder phase contains 50% by mass or more of cobalt, The cemented carbide contains the binder phase in an amount of 8.0 volume % or more and 14.0 volume % or less.

2. 2. The cemented carbide according to claim 1, wherein the cemented carbide contains 0.08% by mass or more and 0.5% by mass or less of chromium.

3. 3. A cemented carbide according to claim 1 or claim 2, wherein the binder phase comprises one or both of iron and nickel.

4. A cutting tool comprising a substrate made of the cemented carbide according to claim 1 or 2 and a coating provided on the substrate.

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