Cemented carbide and cutting tool

Abstract

Provided is a cemented carbide which comprises a plurality of tungsten carbide grains and a binder phase, wherein: the cemented carbide contains the tungsten carbide grains and the binder phase in a combined amount of 89% by volume or more; the cemented carbide contains the binder phase in an amount of 1.8% by volume to 20.0% by volume inclusive; the binder phase contains 80% by mass or more cobalt; the cemented carbide includes a first region that is located at a distance of 15 μm or less from the surface and a second region that is located at a distance of more than 15 μm from the surface; and the ratio R1 / R2 of the ratio R1 of an area S1(hcp) of cobalt having an hcp structure to the sum of the area S1(hcp) and an area S1(fcc) of cobalt having an fcc structure in the binder phase in the first region to the ratio R2 of an area S2(hcp) of cobalt having an hcp structure to the sum of the area S2(hcp) and an area S2(fcc) of cobalt having an fcc structure in the binder phase in the second region is 1.8 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] Japanese Patent Application Laid-Open No. 2004-131769

[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 of the tungsten carbide particles and the binder phase, the cemented carbide comprises 1.8 volume % or more and 20 volume % or less of the binder phase, the binder phase comprises 80 mass % or more of cobalt, the cemented carbide comprises a first region within 15 μm from the surface and a second region more than 15 μm from the surface, and an area S1 of cobalt having an hcp structure in the binder phase of the first region （ｈｃｐ） and the area S1 of cobalt having an fcc structure （ｆｃｃ） The area S1 with respect to the sum of （ｈｃｐ） Ratio R1 and area S2 of cobalt having a hcp structure in the binder phase of the second region （ｈｃｐ） and the area S2 of cobalt having an fcc structure （ｆｃｃ） The area S2 with respect to the sum of （ｈｃｐ） The ratio R1 / R2 is 1.8 or less.

[0005] Fig. 1 is a schematic cross-sectional view of a cemented carbide according to embodiment 1. Fig. 2 is a schematic view of a cutting tool according to embodiment 2.

[0006] [Problem to be Solved by the Present Disclosure] In recent years, workpiece materials have become increasingly difficult to cut in cutting processes, and the conditions under which cutting tools are used have become more severe. Therefore, improvements in various properties are being sought for cemented carbide alloys used as the substrate of cutting tools. In particular, there is a need for cemented carbide alloys that enable tool life extension, even when used as materials for cutting tools for interrupted cutting of high-hardness materials, and cutting tools equipped with such cemented carbide alloys.

[0007] [Effects of the Present Disclosure] According to the present disclosure, it is possible to provide a cemented carbide alloy that enables a longer tool life, particularly when used as a material for cutting tools for intermittent machining of high-hardness materials, and a cutting tool including the same.

[0008] [Description of the embodiment of the present disclosure] First, the embodiment of the present disclosure will be listed and described. (1) 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 contains the tungsten carbide particles and the binder phase in a total of 89% by volume or more, the cemented carbide contains the binder phase in an amount of 1.8% by volume or more and 20% by volume or less, the binder phase contains 80% by mass or more of cobalt, the cemented carbide comprises a first region within 15 μm from the surface and a second region more than 15 μm from the surface, and the area S1 of the cobalt having a hcp structure in the binder phase of the first region （ｈｃｐ） and the area S1 of cobalt having an fcc structure （ｆｃｃ） The area S1 with respect to the sum of （ｈｃｐ） Ratio R1 and area S2 of cobalt having a hcp structure in the binder phase of the second region （ｈｃｐ） and the area S2 of cobalt having an fcc structure （ｆｃｃ） The area S2 with respect to the sum of （ｈｃｐ） The ratio R1 / R2 is 1.8 or less.

[0009] According to the present disclosure, it is possible to provide a cemented carbide that enables a longer tool life, especially when used as a material for cutting tools for interrupted machining of high-hardness materials.

[0010] (2) In the above (1), the ratio R1 / R2 may be 1.2 or more and 1.5 or less, which improves the balance between the deformation resistance and strength of the binder phase of the cemented carbide, and allows a cutting tool including the cemented carbide to have a longer tool life.

[0011] (3) In the above (1) or (2), the binder phase may further contain at least one first element selected from the group consisting of silicon, phosphorus, germanium, tin, rhenium, ruthenium, osmium, iridium, and platinum, thereby improving the balance between the deformation resistance and strength of the binder phase of the cemented carbide, and enabling a cutting tool including the cemented carbide to have a longer tool life.

[0012] (4) In the above (3), 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, may be 1% or more and 6% or less. This allows the binder phase to have both superior hardness and superior toughness, and therefore allows a cutting tool including a cemented carbide containing the binder phase to have a longer tool life.

[0013] (5) 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 (4) above.

[0014] According to the present disclosure, it is possible to provide a cutting tool that has a long tool life, especially when used for interrupted cutting of high-hardness materials.

[0015] [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.

[0016] In the present disclosure, the notation in the form of "A to B" means the upper and lower limits of a range (i.e., A or more and B or less), and when no unit is specified for A and a unit is specified only for B, the units of A and B are the same.

[0017] 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.

[0018] In the present disclosure, when one or more numerical values ​​are recited as the lower limit and the upper limit of a numerical range, a combination of any one numerical value recited as the lower limit and any one numerical value recited as the upper limit is also considered to be disclosed. For example, when a1 or more, b1 or more, and c1 or more are recited as the lower limit and a2 or less, b2 or less, and c2 or less are recited as the upper limit, a1 or more and a2 or less, a1 or more and b2 or less, a1 or more and c2 or less, b1 or more and a2 or less, b1 or more and b2 or less, b1 or more and c2 or less, c1 or more and a2 or less, c1 or more and b2 or less, and c1 or more and c2 or less are considered to be disclosed.

[0019] [Embodiment 1: Cemented Carbide] A cemented carbide according to one embodiment of the present disclosure will be described with reference to Figure 1. A cemented carbide 3 according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") is a cemented carbide 3 including a plurality of tungsten carbide particles 1 and a binder phase 2, wherein the cemented carbide 3 contains 89 volume % or more of the tungsten carbide particles 1 and the binder phase 2 in total, the cemented carbide 3 contains 1.8 volume % or more and 20 volume % or less of the binder phase 2, the binder phase 2 contains 80 mass % or more of cobalt, the cemented carbide 3 includes a first region within 15 μm from the surface and a second region more than 15 μm from the surface, and the area S1 of the cobalt having the hcp structure in the binder phase 2 of the first region （ｈｃｐ） and the area S1 of cobalt having an fcc structure （ｆｃｃ） The area S1 for the sum of （ｈｃｐ） The ratio R1 and the area S2 of cobalt having an hcp structure in the binder phase 2 of the second region （ｈｃｐ） and the area S2 of cobalt having an fcc structure （ｆｃｃ） The area S2 for the sum of （ｈｃｐ） The ratio R1 / R2 is 1.8 or less.

[0020] The cemented carbide of the first embodiment can provide a cemented carbide that enables a longer tool life, even when used as a material for cutting tools for interrupted cutting of particularly high-hardness materials, and a cutting tool including the cemented carbide. The reason for this is not clear, but is presumed to be as follows.

[0021] The cemented carbide of the first embodiment comprises a plurality of tungsten carbide particles (hereinafter also referred to as "WC particles") and a binder phase, and the total content of the WC particles and binder phase in the cemented carbide is 89 volume % or more. As a result, the cemented carbide has high hardness and strength, and a cutting tool including the cemented carbide can have excellent wear resistance and chipping resistance.

[0022] The cemented carbide of the first embodiment contains a binder phase of 1.8 to 20 volume % and the binder phase contains 80 mass % or more of cobalt, which provides high hardness and strength, and allows a cutting tool including the cemented carbide to have excellent wear resistance and chipping resistance.

[0023] In the cemented carbide of embodiment 1, the area S1 of cobalt having an hcp structure in the binder phase of the first region （ｈｃｐ） and the area S1 of cobalt having an fcc structure （ｆｃｃ） The area S1 for the sum of （ｈｃｐ） The ratio R1 and the area S2 of cobalt having an hcp structure in the binder phase of the second region （ｈｃｐ） and the area S2 of cobalt having an fcc structure （ｆｃｃ） The area S2 for the sum of （ｈｃｐ） The ratio R1 / R2 of the ratio R2 is 1.8 or less. The first region on the surface side of the cemented carbide has a higher proportion of the hcp structure in the binder phase than the second region on the inner side of the cemented carbide, thereby improving the deformation resistance of the binder phase on the surface side of the cemented carbide. As a result, cutting tools equipped with the cemented carbide have improved plastic deformation resistance at the initial stage of cutting. The second region on the inner side of the cemented carbide has a higher proportion of the fcc structure in the binder phase than the first region, thereby improving the strength of the inner side of the cemented carbide. As a result, cutting tools equipped with the cemented carbide can have excellent fatigue strength even when the interior of the cemented carbide is exposed during cutting. The cemented carbide of embodiment 1 has an improved balance between the deformation resistance and strength of the binder phase, and cutting tools equipped with the cemented carbide have improved fracture resistance during high-load processing such as intermittent processing of high-hardness materials, resulting in a long tool life.

[0024] <Composition of Cemented Carbide> The cemented carbide of embodiment 1 contains tungsten carbide particles and a binder phase in a total amount of 89% by volume or more. This increases the hardness of the cemented carbide. The cemented carbide may contain tungsten carbide particles and a binder phase in a total amount of 89% by volume or more and 100% by volume or less, 90% by volume or more and 100% by volume or less, 91% by volume or more and 100% by volume or less, or 92% by volume or more and 100% by volume or less.

[0025] The cemented carbide of the first embodiment contains 1.8 to 20 volume percent of a binder phase, which can enhance the hardness and toughness of the cemented carbide. The binder phase content of the cemented carbide may be 2.0 to 19.0 volume percent, 3.0 to 18.0 volume percent, or 4.0 to 17.0 volume percent.

[0026] The cemented carbide of the first embodiment may be composed of a plurality of tungsten carbide particles and a binder phase. In this case, the cemented carbide may contain impurities within a range that does not impair the effects of the present disclosure.

[0027] 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, CrC, etc. ３ C ２ and Mo ２ C.

[0028] The cemented carbide of the first embodiment may be composed of tungsten carbide particles, a binder phase, and other phases. In this case, the cemented carbide may contain impurities within a range that does not impair the effects of the present disclosure.

[0029] The content of other phases in the cemented carbide is permissible within a range that does not impair the effects of the present disclosure. For example, the content of other phases in the cemented carbide may be 0 vol% or more and 11 vol% or less, more than 0 vol% and 11 vol% or less, more than 0 vol% and 7 vol% or less, or more than 0 vol% and 4 vol% or less.

[0030] The cemented carbide of embodiment 1 may contain impurities. Examples of impurities include iron (Fe), calcium (Ca), silicon (Si), and sulfur (S). The impurity content of the cemented carbide is acceptable as long as it 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.

[0031] The content of tungsten carbide particles in the cemented carbide of embodiment 1 may be 67% by volume or more and 98.2% by volume or less, 70% by volume or more and 97% by volume or less, or 75% by volume or more and 96% by volume or less.

[0032] 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.

[0033] (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.).

[0034] (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.

[0035] (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 to 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 entire photographed area is 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.

[0036] (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.

[0037] (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 gray to black. Note that the binarization threshold varies depending on the contrast, so it is set for each image.

[0038] (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 gray to black in the binarized image and where cobalt (Co) exists in the elemental mapping image correspond to the regions where binder phases exist.

[0039] (G1) A rectangular measurement field of view of 24.9 μm × 18.8 μm is set in the image after the binarization process. Using the image analysis software, the area percentages of the tungsten carbide particles and the binder phase are measured, with the area of ​​the entire measurement field being used as the denominator.

[0040] (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.

[0041] 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 %).

[0042] 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.

[0043] The cemented carbide of embodiment 1 may contain 1% by mass or more of cobalt. The cobalt content of the cemented carbide may be 1.0% by mass or more and 20% by mass or less, 2.0% by mass or more and 15% by mass or less, or 3.0% by mass or more and 12% by mass or less.

[0044] The method for measuring the cobalt content of a cemented carbide alloy is as follows. Analysis is performed using SEM-EDX to obtain an elemental mapping image using the same methods as (A1) to (D1) of the method for measuring the tungsten carbide particle content and binder phase content of a cemented carbide alloy described above. Based on the elemental mapping image, the cobalt region in the cemented carbide alloy is identified, and the cobalt content is measured. The measurement is performed in five different, non-overlapping imaging regions. In the present disclosure, the average of the cobalt contents in the five imaging regions corresponds to the cobalt content of the cemented carbide alloy.

[0045] 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 and the photographing area described in (C1) above were arbitrarily set and the cobalt content of the cemented carbide was measured multiple times according to the above procedure.

[0046] <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.

[0047] In the first embodiment, the average particle size of the tungsten carbide particles is not particularly limited. The average particle size of the tungsten carbide particles can be, for example, 0.1 μm or more and 3.5 μm or less. It has been confirmed that the cemented carbide of the first embodiment enables the tool to have a long life when used as a cutting tool material, regardless of the average particle size of the tungsten carbide particles.

[0048] <Binder Phase> In the cemented carbide of embodiment 1, the binder phase contains 80 mass% or more of cobalt. This allows the cemented carbide to have excellent toughness. The cobalt content of the binder phase may be 80 mass% or more and 100 mass% or less, 80 mass% or more and less than 100 mass%, or 90 mass% or more and less than 100 mass%.

[0049] 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.

[0050] 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.

[0051] In the cemented carbide of embodiment 1, the binder phase may further contain at least one first element selected from the group consisting of silicon, phosphorus, germanium, tin, rhenium, ruthenium, osmium, iridium, and platinum, thereby improving the deformation resistance of the binder phase.

[0052] 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.

[0053] In the binder phase of the cemented carbide of embodiment 1, the percentage of the mass M1 of the first element relative to the total mass M1 + M2 of the first element and the cobalt, {M1 / (M1+M2)} × 100, may be 1% or more and 6% or less. Here, M1 and M2 have the same units. This allows the binder phase to have both superior hardness and superior toughness, thereby enabling a cutting tool including a cemented carbide containing the binder phase to have a longer tool life. Here, when the binder phase contains two or more types of first elements, the mass M1 of the first element refers to the total mass of all types of first elements. The percentage {M1 / (M1+M2)} × 100 may be 2% or more and 5% or less, or 3% or more and 4% or less.

[0054] 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.

[0055] 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.

[0056] 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, nickel, and chromium. 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. Examples of the inevitable impurities include iron, nickel, and sulfur.

[0057] <Ratio R1 / R2> The cemented carbide of embodiment 1 includes a first region within 15 μm from the surface and a second region more than 15 μm from the surface, and the area S1 of cobalt having an hcp (hexagonal close-packed) structure in the binder phase of the first region （ｈｃｐ） and the area S1 of cobalt having an fcc (face-centered cubic) structure （ｆｃｃ） The area S1 for the sum of （ｈｃｐ） The ratio R1 and the area S2 of cobalt having a hcp structure in the binder phase of the second region （ｈｃｐ） and the area S2 of cobalt having an fcc structure （ｆｃｃ） The area S2 for the sum of （ｈｃｐ） The ratio R1 / R2 is 1.8 or less. （ｈｃｐ） / (S1 （ｈｃｐ） +S1 （ｆｃｃ） ) and the ratio R2 is S2 （ｈｃｐ） / (S2 （ｈｃｐ） +S2 （ｆｃｃ） ) Area S1 （ｈｃｐ） , area S1 （ｆｃｃ） , area S2 （ｈｃｐ） and area S2 （ｆｃｃ） The units are the same.

[0058] R1 / R2 may be 1.2 or more and 1.8 or less, 1.2 or more and 1.7 or less, 1.2 or more and 1.6 or less, 1.2 or more and 1.5 or less, 1.2 or more and 1.4 or less, or 1.2 or more and 1.3 or less.

[0059] R1 may be 0.5 or more and 1.0 or less, 0.6 or more and 0.9 or less, or 0.7 or more and 0.8 or less. When the ratio R1 is 0.5 or more and 1.0 or less, the plastic deformation resistance of the cutting tool at the initial stage of cutting is improved.

[0060] R2 may be 0.3 or more and 0.6 or less, 0.35 or more and 0.55 or less, or 0.4 or more and 0.5 or less. When the ratio R2 is 0.3 or more and 0.6 or less, the fatigue strength of the cutting tool is improved.

[0061] In the present disclosure, R1 / R2 is measured by the following procedure.

[0062] (A2) The cemented carbide is cut along the normal to its main surface to expose a cross section. If the surface of the cemented carbide does not have a flat area, the cemented carbide is cut from any point on the surface in a direction toward the center of gravity of the cemented carbide to expose a cross section. The cross section is mirror-polished using a cross-section polisher (manufactured by JEOL Ltd.).

[0063] (B2) The mirror-finished surface of the cemented carbide is observed using a scanning electron microscope (SEM device: Carl Zeiss "Gemini 450" (trademark)) equipped with an electron backscatter diffraction device (EBSD device: Oxford "Symmetry" (trademark)). EBSD analysis is performed on the obtained observation image. The observation image is acquired so as to include a region sandwiched between the surface of the cemented carbide and a virtual plane that is 50 μm away from the surface toward the interior of the cemented carbide. In the observation image, a rectangular first measurement field of 11.5 μm × 8.5 μm is set in a first region within 15 μm from the surface. In the observation image, a rectangular second measurement field of 11.5 μm × 8.5 μm is set in a second region greater than 15 μm from the surface. The observation magnification is 10,000 times. The measurement conditions are an acceleration voltage of 15 kV, a current value of 20 nA, 0.02 μm / step, an exposure time of 1.5 to 3 ms, and a measurement time of 10 to 20 minutes.

[0064] (C2) The EBSD analysis results are analyzed using commercially available software (AZtecCrystal (trademark) manufactured by Oxford University Press, Oxford, USA), and the crystal structure of cobalt contained in the binder phase is identified in each of the first and second measurement fields, resulting in a color map. The crystal structure of cobalt identified here is the crystal structure observed when the cobalt appearing on the mirror-finished surface of the cemented carbide is viewed in plan view from the normal direction of the mirror-finished surface.

[0065] (D2) Using the above software, the area S of cobalt having an hcp structure in the bonded phase of each of the first measurement field and the second measurement field is calculated. （ｈｃｐ） and the area S of cobalt having an fcc structure （ｆｃｃ） The area S for the sum of （ｈｃｐ） For example, based on a color map, image A showing tungsten carbide particles in white and cobalt having an hcp structure in black, and image B showing tungsten carbide particles in white and cobalt having an fcc structure in black are output, and the ratio R can be measured based on image A and image B.

[0066] (E2) The above-mentioned ratio R is measured in three mutually non-overlapping first measurement fields and three mutually non-overlapping second measurement fields. In the present disclosure, the average of the ratios R in the three first measurement fields is determined as the area S1 of cobalt having an hcp structure in the binder phase of the first region of the cemented carbide. （ｈｃｐ） and the area S1 of cobalt having an fcc structure （ｆｃｃ） The area S1 for the sum of （ｈｃｐ） In the present disclosure, the average of the ratios R in the three second measurement fields corresponds to the area S2 of cobalt having a hcp structure in the binder phase of the second region of the cemented carbide. （ｈｃｐ） and the area S2 of cobalt having an fcc structure （ｆｃｃ） The area S2 for the sum of （ｈｃｐ） This corresponds to the ratio R2.

[0067] (F2) Based on the ratio R1 and the ratio R2 obtained in (E2) above, calculate R1 / R2.

[0068] 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 cemented carbide cross section, the acquisition area of ​​the observation image described in (B2) above, and the measurement field of view were arbitrarily set and R1 / R2 was measured multiple times according to the above procedure.

[0069] <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, and a sintering step in the above order. Each step will be described below.

[0070] <Preparation Step> The preparation step is a step of preparing raw material powders of materials constituting the cemented carbide. Examples of raw material powders include tungsten carbide powder (hereinafter also referred to as "WC powder"), cobalt (Co) powder, first element powder, and alloy powder of the first element and cobalt. Examples of first element powders include silicon (Si) powder, phosphorus (P) powder, germanium (Ge) powder, tin (Sn) powder, rhenium (Re) powder, ruthenium (Ru) powder, osmium (Os) powder, iridium (Ir) powder, and platinum (Pt) powder. Examples of raw material powders include nickel (Ni) powder, niobium carbide (NbC) powder, tungsten carbide (TaC) powder, titanium carbonitride (TiCN) powder, and chromium carbide (Cr ３ C ２ ) powders, etc. can be prepared. These raw material powders can be commercially available. The average particle size of these raw material powders is not particularly limited and can be, for example, 0.5 to 2 μm. The average particle size of the raw material powders 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.

[0071] <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 depending on the target composition of the cemented carbide.

[0072] The raw material powders can be mixed using a conventionally known mixing method such as an attritor, a ball mill, or a bead mill. Conventional known mixing conditions can also be used. The mixing time can be, for example, from 2 hours to 20 hours.

[0073] 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.

[0074] <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.

[0075] <Sintering Step> The sintering step is a step of sintering the compact obtained in the compacting step to obtain a cemented carbide intermediate. The sintering conditions are as follows: The compact is placed in a sintering furnace and maintained at 7 MPa and 1360°C for 2 hours.

[0076] The cooling step is a step of cooling the cemented carbide intermediate body after the sintering step. Specifically, the cemented carbide intermediate body is released from the sintering furnace into the atmosphere and rapidly cooled to room temperature at a temperature decreasing rate of −100° C. / min, thereby obtaining the cemented carbide of the first embodiment.

[0077] <Features of the Manufacturing Method of the Cemented Carbide of the First Embodiment> In the manufacturing method of the cemented carbide of the first embodiment, the sintering step is performed by holding the cemented carbide intermediate body under conditions of 7 MPa and 1360°C for 2 hours. In addition, in the cooling step, rapid cooling is performed at a temperature drop rate of -100°C / min. This cooling rate is faster than conventional cooling rates. Under these conditions, the area S1 of cobalt having a hcp structure in the binder phase of the first region of the cemented carbide is （ｈｃｐ） and the area S1 of cobalt having an fcc structure （ｆｃｃ） The area S1 for the sum of （ｈｃｐ） The ratio R1 and the area S2 of cobalt having a hcp structure in the binder phase of the second region （ｈｃｐ） and the area S2 of cobalt having an fcc structure （ｆｃｃ） The area S2 for the sum of （ｈｃｐ） The cemented carbide of embodiment 1 can be manufactured in which the ratio R1 / R2 of the ratio R1 to the ratio R2 is 1.8 or less. The present inventors have found, as a result of extensive investigations, that the cemented carbide of the present disclosure can be realized by employing such a sintering step and cooling step.

[0078] [Embodiment 2: Cutting Tool] A cutting tool according to one embodiment of the present disclosure (hereinafter also referred to as "Embodiment 2") includes 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.

[0079] 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 2, the cutting tool 10 of the second embodiment is particularly effective in the case of an end mill. The cutting edge 11 of the cutting tool 10 shown in Figure 2 is made of the cemented carbide of the first embodiment.

[0080] 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.

[0081] 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.

[0082] The cutting tool of the second embodiment can be obtained by forming the cemented carbide of the first embodiment into a desired shape.

[0083] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0084] [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: 1 μm), Co powder (average particle size: 1 μm), first element powder, TiCN powder (average particle size: 1 μm), and Ni powder (average particle size: 1 μm) were prepared. As first element powders, silicon (Si) powder (average particle size: 1 μm), phosphorus (P) powder (average particle size: 1 μm), germanium (Ge) powder (average particle size: 1 μm), tin (Sn) powder (average particle size: 1 μm), rhenium (Re) powder (average particle size: 1 μm), ruthenium (Ru) powder (average particle size: 1 μm), osmium (Os) powder (average particle size: 1 μm), iridium (Ir) powder (average particle size: 1 μm), and platinum (Pt) powder (average particle size: 1 μm) were prepared.

[0085] <Mixing Step> A mixed powder was obtained by mixing the raw material powders for 10 hours using an attritor in the proportions shown in Table 1. The proportion (mass %) of each raw material powder shown in Table 1 is the proportion when the total mixed powder is taken as 100 mass %.

[0086]

[0087] <Molding Step> The mixed powder was pressed to obtain a round bar-shaped molded body.

[0088] <Sintering step> The compact was placed in a sintering furnace and held at the pressure shown in the "Holding pressure" column and the temperature shown in the "Holding temperature" column of "Sintering step" in Table 2 for the time shown in the "Holding time" column. This resulted in a cemented carbide intermediate. The "vac" in the "Holding pressure" column means in a vacuum.

[0089] <Cooling Step> The cemented carbide intermediate body after the sintering step was released from the sintering furnace to the atmosphere and cooled at the temperature decreasing rate shown in the "Cooling Step" column of Table 2, to obtain each sample of cemented carbide.

[0090]

[0091] [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. Specific measurement methods are as described in Embodiment 1. The results are shown in the "WC Particle Content" and "Binder Phase Content" columns of "Cemented Carbide" in Table 3. Furthermore, the total content of tungsten carbide particles and binder phase in the cemented carbide is shown in the "WC Particle + Binder Phase Content" column of "Cemented Carbide" in Table 3. In Table 3, cemented carbides with a "WC Particle + Binder Phase Content" column of less than 100 vol% were confirmed to further contain TiCN.

[0092]

[0093] <Cobalt Content in Binder Phase> The cobalt content in the binder phase of each cemented carbide sample was measured. The specific measurement method is as described in Embodiment 1. The results are shown in the "Co content" column of "Binder phase" in Table 4.

[0094] <{M1 / (M1+M2)}×100> In the binder phase of each sample of cemented carbide, the type of first element and the percentage {M1 / (M1+M2)}×100 of the mass of the first element M1 relative to the total mass M1 of the first element M1 and the mass M2 of cobalt M1 were measured. The specific measurement method was as described in embodiment 1. The results are shown in the "First element" column and the "{M1 / (M1+M2)}×100" column of "Binder phase" in Table 4. A "-" in the "First element" column indicates that the sample did not contain the first element.

[0095] <Ratio R1 / R2> In each sample of cemented carbide, the area S1 of cobalt having an hcp (hexagonal close-packed) structure in the binder phase of the first region within a distance of 15 μm from the surface （ｈｃｐ） and the area S1 of cobalt having an fcc (face-centered cubic) structure （ｆｃｃ） The area S1 for the sum of （ｈｃｐ） The ratio R1 and the area S2 of cobalt having a hcp structure in the binder phase in the second region at a distance from the surface of more than 15 μm （ｈｃｐ） and the area S2 of cobalt having an fcc structure （ｆｃｃ） The area S2 for the sum of （ｈｃｐ）The ratio R1 / R2 of the ratio R1 to the ratio R2 of the ratio R1 was measured. The specific measurement method is as described in embodiment 1. R1, R2 and the ratio R1 / R2 are shown in the "R1", "R2" and "R1 / R2" columns of "bonded phase" in Table 4.

[0096] [Cutting Test] A round bar made of cemented carbide alloy from each sample was machined to produce a ball end mill with a blade diameter of 3 mm. The ball end mill was used to perform intermittent side cutting of a workpiece made of SDK61 (with equally spaced 2 mm diameter holes). The cutting conditions were a cutting speed Vc of 100 m / min, a feed rate fz of 0.05 mm / tooth, an axial depth of cut ap of 0.05 mm, and a radial depth of cut ae of 0.05 mm, all in dry condition. The cutting length until chipping occurred on the cutting tool was measured. A longer cutting length indicates a longer tool life. The results are shown in the "Cutting Length" column of the "Cutting Test" section in Table 4. The above cutting conditions correspond to the intermittent cutting of high-hardness materials.

[0097]

[0098] [Discussion] The cemented carbide alloys and cutting tools of Samples 1 to 19 correspond to Examples. The cemented carbide alloys and cutting tools of Samples 101 to 106 correspond to Comparative Examples. It was confirmed that the cutting tools of Samples 1 to 19 had longer tool life than the cutting tools of Samples 101 to 106.

[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 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 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] 1 tungsten carbide particles, 2 binder phase, 3 cemented carbide, 10 cutting tool, 11 cutting edge.

Claims

1. 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 of the tungsten carbide particles and the binder phase, the cemented carbide comprises 1.8 volume % or more and 20 volume % or less of the binder phase, the binder phase comprises 80 mass % or more of cobalt, the cemented carbide comprises a first region within a distance of 15 μm from the surface and a second region beyond a distance of 15 μm from the surface, and the area S1 of cobalt having a hcp structure in the binder phase of the first region （ｈｃｐ） and the area S1 of cobalt having an fcc structure （ｆｃｃ） The area S1 with respect to the sum of （ｈｃｐ） and the area S2 of cobalt having a hcp structure in the binder phase of the second region. （ｈｃｐ） and the area S2 of cobalt having an fcc structure （ｆｃｃ） The area S2 with respect to the sum of （ｈｃｐ） The ratio R1 / R2 of the ratio R1 to the ratio R2 is 1.8 or less.

2. The cemented carbide according to claim 1, wherein the ratio R1 / R2 is greater than or equal to 1.2 and less than or equal to 1.

5.

3. The cemented carbide according to claim 1 or claim 2, wherein the binder phase further comprises at least one first element selected from the group consisting of silicon, phosphorus, germanium, tin, rhenium, ruthenium, osmium, iridium, and platinum.

4. The cemented carbide according to claim 3, wherein in the binder phase, the percentage of the mass M1 of the first element to the sum M1+M2 of the mass M1 of the first element and the mass M2 of cobalt, {M1 / (M1+M2)}×100, is 1% or more and 6% or less.

5. A cutting tool having a cutting edge made of the cemented carbide according to any one of claims 1 to 4.

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