Cemented carbide and cutting tool

Abstract

This cemented carbide includes a plurality of tungsten carbide particles and a binder phase. The cemented carbide contains the tungsten carbide particles and the binder phase in a total of 89 vol.% to 100 vol.%. The cemented carbide contains 0.5 vol.% to 25 vol.% of the binder phase. The binder phase contains cobalt of 40 mass% or more. The binder phase further contains at least one first element selected from the group consisting of boron, aluminum, silicon, phosphorus, sulfur, nickel, gallium, germanium, arsenic, and selenium, and the lattice constant of the cobalt is 3.560 Å or less.

Description

Cemented Carbide and Cutting Tools

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

[0002] Conventionally, cemented carbide alloys comprising a plurality of tungsten carbide particles and a binder phase have been used as materials for cutting tools (Patent Document 1).

[0003] JP 2013-170285 A

[0004] The cemented carbide of the present disclosure is a cemented carbide comprising a plurality of tungsten carbide particles and a binder phase, wherein the cemented carbide comprises a total of 89 volume % or more and 100 volume % or less of the tungsten carbide particles and the binder phase, and the cemented carbide comprises 0.5 volume % or more and 25 volume % or less of the binder phase, the binder phase comprising 40 mass % or more of cobalt, and the binder phase further comprising at least one first element selected from the group consisting of boron, aluminum, silicon, phosphorus, sulfur, nickel, gallium, germanium, arsenic, and selenium, and the lattice constant of the cobalt is 3.560 Å or less.

[0005] FIG. 1 is a schematic diagram of a cutting tool according to a second embodiment.

[0006] [Problem to be Solved by the Present Disclosure] In recent years, the development of thick copper printed circuit boards has been actively promoted as high current printed circuit boards used in electric vehicles, drones, etc. When machining thick copper printed circuit boards, cutting tools are prone to breakage in the early stages of cutting, and tool life tends to be shortened.

[0007] Therefore, an object of the present disclosure is to provide a cemented carbide alloy that enables a longer life of a cutting tool, particularly when used as a material for the cutting tool for drilling holes in thick copper printed circuit boards, and a cutting tool including the same.

[0008] [Effects of the Present Disclosure] According to the present disclosure, it is possible to provide a cemented carbide alloy that enables a longer life of a cutting tool, particularly when used as a material for the cutting tool for drilling holes in thick copper printed circuit boards, and a cutting tool including the same.

[0009] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be described. (1) A cutting tool of the present disclosure is a cemented carbide alloy including a plurality of tungsten carbide particles and a binder phase, wherein the cemented carbide contains the tungsten carbide particles and the binder phase in a total amount of 89 to 100 volume % of the cemented carbide particles and the binder phase, the cemented carbide contains 0.5 to 25 volume % of the binder phase, the binder phase contains 40 mass % or more of cobalt, the binder phase further contains at least one first element selected from the group consisting of boron, aluminum, silicon, phosphorus, sulfur, nickel, gallium, germanium, arsenic, and selenium, and the lattice constant of the cobalt is 3.560 Å or less.

[0010] According to the present disclosure, it is possible to provide a cemented carbide that enables a longer life of cutting tools, particularly when used as a material for cutting tools for drilling holes in thick copper printed circuit boards, and a cutting tool including the same. The reason for this is presumably as follows.

[0011] The cemented carbide of the present disclosure comprises a plurality of tungsten carbide particles (hereinafter also referred to as "WC particles") and a binder phase. The total content of the WC particles and binder phase in the cemented carbide is 89 volume % or more and 100 volume % or less. This allows the cemented carbide to have high hardness and strength, and cutting tools including the cemented carbide to have excellent wear resistance and breakage resistance.

[0012] The cemented carbide of the present disclosure contains a binder phase of 0.5% by volume or more and 25% by volume or less. The binder phase contains 40% by mass or more of cobalt. When the binder phase content of the cemented carbide is 0.5% by volume or more, the toughness of the cemented carbide is improved. When the binder phase content of the cemented carbide is 25% by volume or less, the hardness of the cemented carbide is improved. Therefore, a cutting tool including the cemented carbide can have excellent wear resistance and breakage resistance.

[0013] In the cemented carbide of the present disclosure, the binder phase further contains at least one first element selected from the group consisting of boron, aluminum, silicon, phosphorus, sulfur, nickel, gallium, germanium, arsenic, and selenium. By using a powder of the first element together with a tungsten carbide powder and a cobalt powder as raw materials and using predetermined manufacturing conditions when producing the cemented carbide, the binder phase contains the first element, and the lattice constant of the cobalt having an fcc structure in the binder phase can be made smaller than the lattice constant (3.569 Å) when cobalt exists alone.

[0014] In the cemented carbide of the present disclosure, the lattice constant of cobalt is 3.560 Å or less. In the cemented carbide of embodiment 1, the lattice constant of cobalt is smaller than the lattice constant of cobalt in conventional cemented carbide (3.569 Å) and closer to the lattice constant of tungsten carbide (WC) (2.8 to 2.9 Å). This increases the binding force between the tungsten carbide particles and cobalt, improving the interfacial strength between the WC particles and the binder phase and improving the rigidity of the cemented carbide. Furthermore, the thermal expansion characteristics of the cemented carbide are made uniform, improving resistance to thermal stress fracture. Furthermore, the cemented carbide of the present disclosure has improved tensile strength of the binder phase. Due to these effects, cutting tools including the cemented carbide have improved breakage resistance, especially in the early stages of cutting, and extended tool life.

[0015] Incidentally, in the past, a technical idea was adopted in which the lattice constant of cobalt was increased to improve the strength, heat resistance, and other properties of the cemented carbide, as described in, for example, Patent Document 1. The cemented carbide of the present disclosure is based on a technical idea opposite to that of the past, in which the lattice constant of cobalt is decreased to improve the properties of the cemented carbide, as described above.

[0016] (2) In the above (1), the lattice constant of the cobalt may be 3.530 Å or more and 3.550 Å or less. When the lattice constant of cobalt is 3.530 Å or more, the compressive strength of the binder phase is improved. When the lattice constant of cobalt is 3.550 Å or less, the rigidity and resistance to thermal stress fracture of the cemented carbide, as well as the tensile strength of the binder phase, are further improved. Therefore, a cutting tool including a cemented carbide has further improved breakage resistance in the early cutting stage and further improved tool life.

[0017] (3) In the above (1) or (2), the percentage of the mass M1 of the first element in the binder phase relative to the total mass M1+M2 of the first element M1 and the cobalt M2, {M1 / (M1+M2)} x 100, may be 0.1% or more and 25% or less. When {M1 / (M1+M2)} x 100 is 0.2% or more, the rigidity and resistance to thermal stress fracture of the cemented carbide, as well as the tensile strength of the binder phase, are further improved. Therefore, cutting tools including cemented carbide have further improved breakage resistance in the early stages of cutting and further improved tool life. When {M1 / (M1+M2)} x 100 is 25% or less, the strength and hardness of the cemented carbide are improved.

[0018] (4) In any of (1) to (3) above, the average particle size of the tungsten carbide particles may be 0.2 μm or more and 3 μm or less. When the average particle size of the WC particles is 0.2 μm or more, the strength of the cemented carbide is improved. When the average particle size of the WC particles is 3 μm or less, the hardness of the cemented carbide is improved. Therefore, the wear resistance of a cutting tool including the cemented carbide is improved, and the tool life is further extended.

[0019] (5) In any one of the above (1) to (4), the lattice constant of the cobalt is measured by wide-angle X-ray diffraction measurement.

[0020] (6) A cutting tool according to the present disclosure is a cutting tool having a cutting edge made of the cemented carbide according to any one of (1) to (5) above.

[0021] This makes it possible to provide a cutting tool that has a long tool life, especially when used to drill holes in thick copper printed circuit boards.

[0022] [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.

[0023] In the present disclosure, the notation in the form of "A to B" means 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.

[0024] 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.

[0025] In the present disclosure, when one or more numerical values ​​are listed as the lower limit and the upper limit of a numerical range, the combination of any one numerical value listed as the lower limit and any one numerical value listed as the upper limit is also considered to be disclosed.

[0026] In this disclosure, "comprises," "includes," "has," and variations thereof are open-ended terms. Open-ended terms may or may not include additional elements in addition to the required elements. The term "consisting of" is closed-ended. However, even a configuration expressed in closed terms may include additional elements that are normally incidental impurities or unrelated to the subject technology.

[0027] [Embodiment 1: Cemented Carbide] A cemented carbide according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") is a cemented carbide comprising a plurality of tungsten carbide particles and a binder phase, wherein the cemented carbide comprises 89 volume % or more and 100 volume % or less of the tungsten carbide particles and the binder phase in total, and the cemented carbide comprises 0.5 volume % or more and 25 volume % or less of the binder phase, the binder phase comprises 40 mass % or more of cobalt, and the binder phase further comprises at least one first element selected from the group consisting of boron, aluminum, silicon, phosphorus, sulfur, nickel, gallium, germanium, arsenic, and selenium, and the lattice constant of the cobalt is 3.560 Å or less.

[0028] <Composition of Cemented Carbide> The cemented carbide of embodiment 1 contains 89 to 100 volume % of tungsten carbide particles and a binder phase in total. The cemented carbide may contain 90 to 100 volume % of tungsten carbide particles and a binder phase in total, or 92 to 100 volume % of tungsten carbide particles and a binder phase in total.

[0029] The cemented carbide of embodiment 1 includes a binder phase in an amount of 0.5 to 25% by volume. The binder phase content of the cemented carbide may be 2 to 20% by volume, 3 to 18% by volume, or 4 to 15% by volume.

[0030] The cemented carbide of the first embodiment may be composed of a plurality of tungsten carbide particles and a binder phase. The cemented carbide of the first embodiment may be composed of a plurality of tungsten carbide particles, a binder phase, and impurities, as long as the effects of the present disclosure are not impaired.

[0031] In addition to the tungsten carbide particles and binder phase, the cemented carbide may contain other phases (not shown). The other phases may include carbides, nitrides, or carbonitrides containing at least one element selected from the group consisting of titanium (Ti), tantalum (Ta), niobium (Nb), zirconium (Zr), hafnium (Hf), and molybdenum (Mo). The compositions of the other phases may be, for example, TiCN, TaC, NbC, ZrC, HfC, and Mo. ２ C.

[0032] The content of other phases in the cemented carbide is permitted within a range that does not impair the effects of the present disclosure. The content of other phases in the cemented carbide may be more than 0 vol% and not more than 11 vol%, more than 0 vol% and not more than 10 vol%, or more than 0 vol% and not more than 8 vol%.

[0033] The cemented carbide of the first embodiment may be composed of a plurality of tungsten carbide particles, a binder phase, and other phases. The cemented carbide of the first embodiment may be composed of a plurality of tungsten carbide particles, a binder phase, other phases, and impurities, as long as the effects of the present disclosure are not impaired.

[0034] Examples of the impurities include iron (Fe) and calcium (Ca). The impurity content of the cemented carbide is acceptable within a range that does not impair the effects of the present disclosure. For example, the impurity content of the cemented carbide 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). The measuring device that can be used is the "ICPS-8100" (trademark) manufactured by Shimadzu Corporation.

[0035] The content of tungsten carbide particles in the cemented carbide of embodiment 1 may be 75% by volume or more and 99.5% by volume or less, 80% by volume or more and 98% by volume or less, 82% by volume or more and 97% by volume or less, or 85% by volume or more and 96% by volume or less.

[0036] The methods for measuring the content (volume %) of tungsten carbide particles in the cemented carbide and the content (volume %) of the binder phase in the cemented carbide are as follows.

[0037] (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.).

[0038] (B1) The mirror-finished surface of the cemented carbide is analyzed using an energy dispersive X-ray spectrometer (SEM-EDX) attached to a scanning electron microscope (apparatus: Carl Zeiss Gemini 450 (trademark)) to identify the elements contained in the cemented carbide.

[0039] (C1) The mirror-finished surface of the cemented carbide is photographed with a scanning electron microscope (SEM) to obtain a backscattered electron image. The photographed area is set at the center of the cross section of the cemented carbide, i.e., a position that does not include areas with properties clearly different from the bulk part, such as the surface vicinity of the cemented carbide (a position where the photographed area is entirely the bulk part of the cemented carbide). The observation magnification is 5000x. The measurement conditions are an acceleration voltage of 3 kV, a current value of 2 nA, and a working distance (WD) of 5 mm.

[0040] (D1) The photographed region of (C1) above is analyzed using SEM-EDX to identify the distribution of the elements identified in (B1) above in the photographed region, and an element mapping image is obtained.

[0041] (E1) The backscattered electron image obtained in (C1) above is imported into a computer and binarized using image analysis software (OpenCV, SciPy). In the binarized image, tungsten carbide particles are shown in white and the binder phase is shown in black. Note that the binarization threshold varies depending on the contrast, so it is set for each image.

[0042] (F1) By superimposing the elemental mapping image obtained in (D1) above on the binarized image obtained in (E1) above, the regions where tungsten carbide particles and binder phase exist are identified on the binarized image. Specifically, the regions shown in white in the binarized image and where tungsten (W) and carbon (C) exist in the elemental mapping image correspond to the regions where tungsten carbide particles exist. The regions shown in black in the binarized image and where cobalt (Co) exists in the elemental mapping image correspond to the regions where binder phase exists.

[0043] (G1) A rectangular measurement field of view of 24.9 μm × 18.8 μm is set in the binarized image, and the area percentages of the tungsten carbide particles and the binder phase are measured using the area of ​​the entire measurement field as the denominator using the image analysis software.

[0044] (H1) The measurement of (G1) above is carried out in five different, non-overlapping measurement fields. In the present disclosure, the average of the area percentages of tungsten carbide particles in the five measurement fields corresponds to the content (volume %) of tungsten carbide particles in the cemented carbide, and the average of the area percentages of the binder phase in the five measurement fields corresponds to the content (volume %) of the binder phase in the cemented carbide.

[0045] When the cemented carbide contains other phases in addition to the WC grains and binder phase, the content of the other phases in the cemented carbide can be obtained by subtracting the content (volume %) of the tungsten carbide grains and the content (volume %) of the binder phase measured by the above procedure from the total cemented carbide (100 volume %).

[0046] 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 when the cut-out location of the cross section of the cemented carbide, the photographing area described in (C1) above, and the measurement field of view described in (G1) above are arbitrarily set and the tungsten carbide particle content and the binder phase content of the cemented carbide are measured multiple times according to the above procedure.

[0047] <Tungsten Carbide Particles> In the cemented carbide of the first embodiment, the tungsten carbide particles include at least one of "pure WC particles (including WC containing no impurity elements and WC containing impurity elements below the detection limit)" and "WC particles containing impurity elements intentionally or unavoidably contained therein, as long as the effects of the present disclosure are not impaired." The impurity content of the tungsten carbide particles (when two or more elements constitute the impurities, the total concentration of these elements) is less than 0.1 mass%. The impurity element content of the tungsten carbide particles is measured by ICP optical emission spectrometry.

[0048] In embodiment 1, the average particle size of the tungsten carbide particles is not particularly limited. It has been confirmed that the cemented carbide of embodiment 1 enables a longer tool life when used as a cutting tool material, regardless of the average particle size of the tungsten carbide particles. From the viewpoint of improving tool life, the average particle size of the tungsten carbide particles may be 0.2 μm or more and 3 μm or less, 0.2 μm or more and 2.8 μm or less, or 0.8 μm or more and 2.5 μm or less.

[0049] The average particle size of tungsten carbide particles is measured as follows. Using the same method as (A1) to (G1) in the methods for measuring the tungsten carbide particle content and binder phase content of cemented carbide, a rectangular measurement field of 24.9 μm × 18.8 μm is set in the binarized image. Using the image analysis software, the circle-equivalent diameter (Heywood diameter: diameter equivalent to a circle with an equal area) of each of all tungsten carbide particles in the measurement field is measured. This measurement is performed in three different, non-overlapping measurement fields. In the present disclosure, the 50% cumulative particle size (circle-equivalent diameter) D50 on an area basis is calculated based on all tungsten carbide particles in the three measurement fields. This D50 corresponds to the average particle size of the tungsten carbide particles.

[0050] As long as measurements were performed on the same sample, it was confirmed that there was almost no variation in the measurement results even when the cut-out location of the cross section of the cemented carbide, the photographing area described in (C1) above, and the measurement field of view were arbitrarily set and the average particle size of tungsten carbide particles was measured multiple times according to the above procedure.

[0051] <Binder Phase> <Cobalt> In the cemented carbide of embodiment 1, the binder phase contains 40 mass% or more of cobalt. This allows the cemented carbide to have excellent toughness. The cobalt content of the binder phase may be 40 mass% or more but less than 100 mass%, 50 mass% or more but 90 mass% or less, or 60 mass% or more but 80 mass% or less.

[0052] The method for measuring the cobalt content of the binder phase is as follows. An elemental mapping image and a binarized image are obtained by the same methods as (A1) to (E1) of the method for measuring the tungsten carbide particle content and binder phase content of the cemented carbide described above. The elemental mapping image and the binarized image are superimposed to identify the region where the binder phase exists in the elemental mapping image. A rectangular measurement field of view of 24.9 μm × 18.8 μm is set in the elemental mapping image. The cobalt content is measured in the region where the binder phase exists in the measurement field of view. The above measurement is performed in five different, non-overlapping measurement fields of view. In the present disclosure, the average of the cobalt contents in the regions where the binder phase exists in the five measurement fields of view corresponds to the cobalt content of the binder phase.

[0053] As long as the measurement is performed on the same sample, it has been confirmed that there is almost no variation in the measurement results even when the cut-out location of the cross section of the cemented carbide, the photographing area described in (C1) above, and the measurement field of view are arbitrarily set and the cobalt content of the binder phase is measured multiple times according to the above procedure.

[0054] <<First Element>> In the cemented carbide of embodiment 1, the binder phase further contains at least one first element selected from the group consisting of boron, aluminum, silicon, phosphorus, sulfur, nickel, gallium, germanium, arsenic, and selenium.

[0055] The inclusion of the first element in the binder phase is confirmed by the following procedure. An element mapping image and a binarized image are obtained by the same methods as steps (A1) to (E1) of the method for measuring the tungsten carbide particle content and binder phase content of the cemented carbide described above. The element mapping image and the binarized image are superimposed to identify the region in which the binder phase exists in the element mapping image. If the first element is present in the region in which the binder phase exists in the element mapping, it is confirmed that the binder phase contains the first element.

[0056] In the binder phase of the cemented carbide of embodiment 1, the percentage of the mass M1 of the first element relative to the sum M1+M2 of the mass M1 of the first element and the mass M2 of cobalt, {M1 / (M1+M2)}×100, is 0.1% to 25%, or may be 0.2% to 25%, 0.4% to 10%, 0.6% to 7%, or 1.0% to 5%. Here, the units of the mass M1 and the mass M2 are the same. When the binder phase contains two or more types of first elements, the mass M1 of the first element means the total mass of all types of first elements.

[0057] The method for measuring the percentage {M1 / (M1+M2)} x 100 is as follows. An element mapping image and a binarized image are obtained using the same methods as steps (A1) to (E1) of the method for measuring the tungsten carbide particle content and binder phase content of the cemented carbide. The element mapping image and the binarized image are superimposed to identify the binder phase region in the element mapping image. A rectangular measurement field of view of 24.9 μm x 18.8 μm is set in the element mapping image. In the binder phase region in the measurement field of view, the percentage {m1 / (m1+m2)} x 100 of the mass m1 of the first element relative to the sum m1+m2 of the mass m1 of the first element and the mass m2 of cobalt is calculated. The above measurement is performed in five different, non-overlapping measurement fields of view. In the present disclosure, the average of the percentages {m1 / (m1+m2)}×100 in the five measurement fields corresponds to the "percentage {M1 / (M1+M2)}×100" in the binder phase of the cemented carbide.

[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 when the cut-out location of the cross section of the cemented carbide, the photographing area described in (C1) above, and the measurement field of view are arbitrarily set and the percentage {M1 / (M1+M2)}×100 is measured multiple times according to the above procedure.

[0059] In the cemented carbide of embodiment 1, the binder phase may contain, in addition to cobalt and the first element, at least one second element selected from the group consisting of iron (Fe) and chromium (Cr). The binder phase may consist of cobalt, the first element, and the second element. The binder phase may consist of cobalt, the first element, the second element, and inevitable impurities.

[0060] <Lattice constant of cobalt> In the cemented carbide of embodiment 1, the lattice constant of cobalt is 3.560 Å or less, or may be 3.559 Å or less, 3.556 Å or less, 3.553 Å or less, 3.552 Å or less, 3.550 Å or less, 3.549 Å or less, 3.557 Å or less, or 3.546 Å or less. The lattice constant of cobalt may be 3.530 Å or more, or 3.540 Å or more. The lattice constant of cobalt may be 3.530 Å or more and 3.560 Å or less.

[0061] In the present disclosure, the lattice constant of cobalt refers to the lattice constant of cobalt having an fcc structure. Generally, in cemented carbide, the main crystal structure of cobalt is an fcc structure. For example, in the cemented carbide of embodiment 1, more than 50 volume % of cobalt may have an fcc structure, or 60 volume % or more may have an fcc structure. It has been confirmed that in the cemented carbide of embodiment 1, as long as more than 50 volume % of cobalt has an fcc structure and the lattice constant of cobalt is 3.560 Å or less, the effects of the present disclosure derived from the lattice constant of cobalt can be obtained.

[0062] The method for measuring the lattice constant of cobalt is as follows. Wide-angle measurements are performed five times on the cemented carbide using an X-ray diffractometer (SmartLab (registered trademark) manufactured by Rigaku Corporation). The measurement conditions for the wide-angle measurements are as follows. The peaks derived from the fcc structure of cobalt (the peak derived from fcc (111) is present near 2θ = 44°, and the peak derived from fcc (200) is present near 2θ = 51°) in the X-ray diffraction pattern obtained by integrating the five measurements are analyzed to determine the lattice constant of cobalt. The measurement is performed at the center of the cross section of the cemented carbide. <Measurement conditions> X-ray used: Cu-Kα Incident optical system: CBO-f Excitation conditions: 45 kV / 200 mA Slit: 0.8 mm Receiving optical system: HyPix-3000 (two-dimensional) Scanning: 2θ-θ scan range: 2θ = 42°-53° Scan speed: 0.2° / min

[0063] It was confirmed that, as long as the measurements were performed on the same sample, there was almost no variation in the measurement results even when the lattice constant of cobalt was measured multiple times.

[0064] <Method for Manufacturing Cemented Carbide> The cemented carbide of embodiment 1 can be manufactured by carrying out a raw material powder preparation step, a mixing step, a molding step, a sintering step, a cooling and sintering step, and a HIP (Hot Isostatic Pressing) step in the above order. Each step will be described below.

[0065] <Preparation Step> The preparation step is a step of preparing a raw material powder for the cemented carbide. Examples of the raw material powder include tungsten carbide powder (hereinafter also referred to as "WC powder"), cobalt powder, first element powder, and alloy powder of the first element and cobalt. Examples of the first element powder include boron powder, aluminum powder, silicon powder, phosphorus powder, sulfur powder, nickel powder, gallium powder, germanium powder, arsenic powder, and selenium powder.

[0066] Further, iron powder, vanadium carbide powder, titanium carbonitride powder, etc. can be prepared as raw material powders. These raw material powders can be commercially available.

[0067] The average particle size of the raw material powder is not particularly limited and may be, for example, 0.5 to 5 μm. The average particle size of the raw material powder refers to the average particle size measured by the FSSS (Fisher Sub-Sieve Sizer) method. The average particle size is measured using a "Sub-Sieve Sizer Model 95" (trademark) manufactured by Fisher Scientific.

[0068] <Mixing Step> The mixing step is a step of mixing the raw material powders prepared in the preparation step in a predetermined ratio. By the mixing step, a mixed powder in which the raw material powders are mixed is obtained. The mixing ratio of the raw material powders is appropriately adjusted according to the target composition of the cemented carbide and within a range in which free carbon does not appear.

[0069] The raw material powders were mixed using a ball mill under the following mixing conditions: ball diameter: 2 mm, rotation speed: 100 rpm, and mixing time: 10 hours.

[0070] After the mixing step, the mixed powder may be granulated as necessary. Granulating the mixed powder makes it easier to fill the mixed powder into a die or mold during the molding step described below. A known granulation method can be applied to the granulation, and for example, a commercially available granulator such as a spray dryer can be used.

[0071] <Molding step> The molding step is a step of molding the mixed powder obtained in the mixing step into a shape for a cutting tool to obtain a molded body. The molding method and molding conditions in the molding step are not particularly limited and may be general methods and conditions.

[0072] <Sintering Step> The sintering step is a step of sintering the compact obtained in the compacting step to obtain a cemented carbide intermediate body. The sintering conditions are to hold the compact in a vacuum at 1350°C for 6 hours.

[0073] <Cooling and sintering step> The cooling and sintering step is a step in which cooling and sintering are repeatedly performed on the cemented carbide intermediate body after the sintering step. Specifically, the cemented carbide intermediate body is cooled to 800°C at -2°C / min, then heated to 1350°C and held at that temperature for 4 hours for sintering. This cooling and sintering step is repeated five times.

[0074] <HIP Step> The HIP step is a step of obtaining a cemented carbide by subjecting the cemented carbide intermediate body after the cooling and sintering steps to HIP. The HIP conditions are 100 MPa and 1250°C, and holding for 2 hours.

[0075] <Features of the manufacturing method of cemented carbide> In conventional cemented carbide, the first element has never been added. If the first element were added in the conventional manufacturing method of cemented carbide, the first element would generate impurities, resulting in a decrease in the performance of the cemented carbide. As a result of extensive research, the inventors have newly discovered that, in the manufacturing method of cemented carbide, by setting the amount of the first element added and the conditions of the mixing step, sintering step, cooling and sintering step, and HIP step as described above, it is possible to suppress the generation of impurities by the first element, promote the solid solution of the first element in the binder phase, and adjust the lattice constant of cobalt to within the range of the present disclosure.

[0076] [Embodiment 2: Cutting Tool] A cutting tool according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 2") is a cutting tool equipped with a cutting edge made of the cemented carbide of Embodiment 1. In this disclosure, the cutting edge refers to the portion involved in cutting. More specifically, the cutting edge refers to the region surrounded by the cutting edge ridge and an imaginary plane that is 0.5 mm or 2 mm away from the cutting edge ridge toward the cemented carbide.

[0077] 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. In particular, as shown in Figure 4, the cutting tool 10 of embodiment 2 can exhibit excellent effects in the case of small-diameter drills for machining copper-plated printed circuit boards. The cutting edge 11 of the cutting tool 10 shown in Figure 1 is made of the cemented carbide of embodiment 1.

[0078] In the cutting tool of Embodiment 2, the cemented carbide of Embodiment 1 may constitute the entire tool or may constitute a part of the tool. Here, "constitute a part" refers to a mode in which the cemented carbide of Embodiment 1 is brazed to a predetermined position of an arbitrary substrate to form a cutting edge.

[0079] The cutting tool of the second embodiment may further include a hard film that covers at least a part of the surface of the substrate made of cemented carbide. The hard film may be made of, for example, diamond-like carbon or diamond.

[0080] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0081] [Preparation of Cemented Carbide] Each sample of cemented carbide was prepared according to the following procedure. <Preparation Step> As raw material powders, WC powder (average particle size: as shown in Table 1), Co powder (average particle size: 1 μm), first element powder (average particle size: 1 μm), Fe powder (average particle size: 1 μm), VC powder (average particle size: 1 μm), and TiCN powder (average particle size: 1 μm) were prepared. As first element powders, boron powder, aluminum powder, silicon powder, phosphorus powder, sulfur powder, nickel powder, gallium powder, germanium powder, arsenic powder, and selenium powder were prepared. Each raw material powder was prepared in the proportion shown in Table 1. The proportion (mass %) of each raw material powder listed in Table 1 is the proportion when the total raw material powder is taken as 100 mass %. The "remainder" in the "mass %" column for "WC powder" refers to the value obtained by subtracting the proportion of raw material powders other than WC powder from the total raw material powder (100 mass %).

[0082]

[0083] <Mixing step> The raw material powders were mixed in a ball mill to obtain a mixed powder. The mixing conditions are as shown in the "Mixing" column in Table 2.

[0084] <Molding Step> The mixed powder was pressed to obtain a molded body in the shape of a round bar or an insert (CNMG120408N-GU).

[0085] <Sintering Step> The compact was sintered in a vacuum under the conditions shown in the "Sintering" column of Table 2 to obtain a cemented carbide intermediate.

[0086] <Cooling and Sintering Steps> The cemented carbide intermediate was subjected to the following step A or B. A: The cemented carbide intermediate was cooled to 800°C at -2°C / min, then heated to 1350°C and held for 4 hours for sintering. This cooling and sintering process was repeated five times. B: The cemented carbide intermediate was cooled to 800°C at -10°C / min, then rapidly cooled to room temperature.

[0087] <HIP Step> Next, the cemented carbide intermediate was subjected to HIP under the conditions shown in the "HIP" column of Table 2 to obtain a cemented carbide.

[0088]

[0089] [Evaluation of Cemented Carbide] <Content (volume %) of Tungsten Carbide Particles and Content (volume %) of Binder Phase in Cemented Carbide> The content (volume %) of tungsten carbide particles and the content (volume %) of binder phase in the cemented carbide of each sample were measured by the method described in embodiment 1. The results are shown in Table 3. Furthermore, the total content (WC particle + binder phase content) of the tungsten carbide particles and the binder phase in the cemented carbide is shown in Table 3. It was confirmed that cemented carbide alloys with a "WC particle + binder phase content" column of less than 100% by volume contained TiCN or VC.

[0090] <Cobalt Content in Binder Phase> The cobalt content in the binder phase of each cemented carbide sample was measured by the method described in embodiment 1. The results are shown in Table 3.

[0091] <Type of First Element and {M1 / (M1+M2)}×100> In the binder phase of the cemented carbide of each sample, the type and content of the first element, as well as the percentage {M1 / (M1+M2)}×100 of the mass M1 of the first element relative to the sum M1+M2 of the mass M1 of the first element and the mass M2 of cobalt, were measured by the method described in embodiment 1. The results are shown in Table 3. Samples with "-" in the "First Element" column indicate that they did not contain the first element.

[0092] <Average particle size of tungsten carbide particles> In each sample of cemented carbide alloy, the average particle size of tungsten carbide particles was measured by the method described in embodiment 1. The results are shown in Table 3.

[0093] <Lattice constant of cobalt> The lattice constant of cobalt in each cemented carbide sample was measured by the method described in embodiment 1. The results are shown in Table 3. It was confirmed that in all samples, more than 50% by volume of cobalt had an fcc structure.

[0094]

[0095] [Cutting Test 1] A round bar made of cemented carbide alloy from each sample was machined to produce a drill for machining printed circuit boards (PCB drills) with a cutting edge diameter of 0.1 mm. Using the PCB drill, a commercially available thick copper printed circuit board (thickness 0.6 mm) was drilled at a rotation speed of 100 krpm up to 100 hits. The above drilling was performed with 10 PCB drills, and the breakage rate was calculated. A lower breakage rate indicates better breakage resistance in the initial cutting stage of the cutting tool and a longer tool life. The results are shown in Table 4.

[0096] [Cutting test 2] A 5 μm thick TiCN layer and a 5 μm thick Al layer were formed by CVD on the surface of the cemented carbide insert (CNMG120408N-GU) of each sample. ２ O ３ The layers were formed in the above order to obtain surface-coated cutting tools. Using each sample of surface-coated cutting tool, a notched round bar made of SCM435 was turned. The cutting conditions were a cutting speed (vc) of 100 m / min, a feed rate (f) of 0.3 mm / rev, and a depth of cut (ap) of 1.5 mm, and the turning was performed for 2 minutes. The turning was performed on 10 surface-coated cutting tools, and the defect rate was calculated. A lower defect rate indicates better defect resistance in the initial cutting stage of the cutting tool and a longer tool life. The results are shown in Table 4.

[0097]

[0098] [Discussion] The cemented carbide alloys and cutting tools of Samples 1 to 20 correspond to Examples. The cemented carbide alloys and cutting tools of Samples 1-1 to 1-6 correspond to Examples. It was confirmed that the cutting tools of Samples 1 to 20 had longer tool life in drilling holes in thick copper printed circuit boards and turning notched round bars made of SCM435 than the cutting tools of Samples 1-1 to 1-6.

[0099] Although the embodiments and examples of the present disclosure have been described above, it is intended from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined and 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 above-described embodiments and examples, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0100] 10 cutting tool, 11 cutting edge

Claims

1. A cemented carbide alloy comprising a plurality of tungsten carbide particles and a binder phase, wherein the cemented carbide alloy contains a total of 89 to 100 volume % of the tungsten carbide particles and the binder phase, the cemented carbide alloy contains 0.5 to 25 volume % of the binder phase, the binder phase contains 40 mass % or more of cobalt, the binder phase further contains at least one first element selected from the group consisting of boron, aluminum, silicon, phosphorus, sulfur, nickel, gallium, germanium, arsenic, and selenium, and the lattice constant of the cobalt is 3.560 Å or less.

2. The cemented carbide according to claim 1, wherein the lattice constant of the cobalt is 3.530 Å or more and 3.550 Å or less.

3. The cemented carbide according to claim 1 or 2, wherein in the binder phase, the percentage of the mass M1 of the first element relative to the sum M1+M2 of the mass M1 of the first element and the mass M2 of the cobalt, {M1 / (M1+M2)}×100, is 0.1% or more and 25% or less.

4. A cemented carbide alloy according to any one of claims 1 to 3, wherein the average particle size of the tungsten carbide particles is 0.2 μm or more and 3 μm or less.

5. The cemented carbide according to any one of claims 1 to 4, wherein the lattice constant of the cobalt is measured by wide-angle X-ray diffraction measurement.

6. A cutting tool having a cutting edge made of the cemented carbide according to any one of claims 1 to 5.

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