Hardmetal and cutting tools

Abstract

A cemented carbide including a first phase, a second phase, and a third phase, wherein the first phase is composed of a plurality of tungsten carbide particles, the content of the first phase in the cemented carbide is 65% by volume or more and 85% by volume or less, the second phase is composed of cobalt, the cobalt content C5 of the cemented carbide is 3% by mass or more and 15% by mass or less, the third phase is composed of at least one element selected from the group consisting of titanium, tantalum, niobium, zirconium, and tungsten, and at least one of carbon and nitrogen, and the third phase does not contain tungsten carbide, the total content C of titanium, tantalum, niobium, and zirconium in the cemented carbide is 2% by mass or more and 8% by mass or less, and the Vickers hardness a of the cemented carbide is 12.5 GPa. the Vickers hardness a is measured at a point P1 in the cemented carbide at a distance of 5 μm from the surface of the cemented carbide in a normal direction to the surface, the cemented carbide includes a first region sandwiched between a virtual plane Q1 that is 5 μm away from the surface and a virtual plane Q4 that is 200 μm away from the surface, the first region has a second region sandwiched between a virtual plane Q2 that is 10 μm away from the surface and a virtual plane Q3 that is 50 μm away from the surface, in the first region, a point P2 exhibiting a Vickers hardness b that is the maximum value of the Vickers hardness is present in the second region, and a difference ba between the Vickers hardness b and the Vickers hardness a is 1.8 GPa or more.

Description

[Technical field]

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

[0002] Conventionally, cemented carbide having a hard phase mainly composed of tungsten carbide (WC) and a binder phase mainly composed of an iron group element is used as a material for cutting tools. The cemented carbide described in Patent Document 1 has, as a hard phase, a phase composed of at least one composite compound of carbide, nitride, and carbonitride containing tungsten (W) and a metal element other than tungsten, in addition to the hard phase mainly composed of WC. In this cemented carbide, the WC particles and the composite compound particles are bonded to improve the chipping resistance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2016-20541 A Summary of the Invention

[0004] The cemented carbide of the present disclosure is A cemented carbide comprising a first phase, a second phase, and a third phase, the first phase is comprised of a plurality of tungsten carbide particles; The content of the first phase in the cemented carbide is 65% by volume or more and 85% by volume or less, the second phase consists of cobalt; The cobalt content C5 of the cemented carbide is 3% by mass or more and 15% by mass or less, the third phase is composed of at least one element selected from the group consisting of titanium, tantalum, niobium, zirconium, and tungsten, and at least one of carbon and nitrogen; the third phase does not include tungsten carbide; The total content C of titanium, tantalum, niobium and zirconium in the cemented carbide is 2% by mass or more and 8% by mass or less, The Vickers hardness a of the cemented carbide is 12.5 GPa or more and 14.5 GPa or less, The Vickers hardness a is measured at a point P1 in the cemented carbide at a distance of 5 μm from the surface of the cemented carbide along the normal direction of the surface; The cemented carbide includes a first region sandwiched between a virtual plane Q1 that is 5 μm away from the surface and a virtual plane Q4 that is 200 μm away from the surface, The first region has a second region sandwiched between a virtual plane Q2 that is 10 μm away from the surface and a virtual plane Q3 that is 50 μm away from the surface, In the first region, a point P2 exhibiting a Vickers hardness b that is a maximum value of the Vickers hardness is present in the second region, The difference ba between the Vickers hardness b and the Vickers hardness a is 1.8 GPa or more. [Brief description of the drawings]

[0005] [Figure 1] FIG. 1 is a schematic diagram showing a cross section of the cemented carbide of the first embodiment. [Diagram 2] FIG. 2 is a graph showing an example of the relationship between the distance from the surface of the cemented carbide of embodiment 1 and the Vickers hardness, and an example of the relationship between the distance from the surface of the cemented carbide of embodiment 1 and each of the contents (mass%) of titanium, tantalum, niobium, and cobalt. [Diagram 3] FIG. 3 is a diagram for explaining a method for measuring the Vickers hardness of a cemented carbide. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] [Problem that this disclosure aims to solve] In recent years, work materials have become increasingly difficult to cut. Furthermore, the demand for improved processing efficiency has led to stricter processing conditions, such as increased cutting speeds, feed rates, and depths of cut.

[0007] Therefore, an object of the present disclosure is to provide a cemented carbide which, when used as a tool material, can provide a cutting tool that has excellent wear resistance and fracture resistance and can have a long tool life, and to provide a cutting tool having a long tool life.

[0008] [Effects of this disclosure] According to the present disclosure, it is possible to provide a cemented carbide which, when used as a tool material, can provide a cutting tool having excellent wear resistance and fracture resistance and a long tool life, as well as a cutting tool having a long tool life.

[0009] [Description of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be listed and described. (1) The cemented carbide disclosed herein is A cemented carbide comprising a first phase, a second phase, and a third phase, the first phase is comprised of a plurality of tungsten carbide particles; The content of the first phase in the cemented carbide is 65% by volume or more and 85% by volume or less, the second phase consists of cobalt; The cobalt content C5 of the cemented carbide is 3% by mass or more and 15% by mass or less, the third phase is composed of at least one element selected from the group consisting of titanium, tantalum, niobium, zirconium, and tungsten, and at least one of carbon and nitrogen; the third phase does not include tungsten carbide; The total content C of titanium, tantalum, niobium and zirconium in the cemented carbide is 2% by mass or more and 8% by mass or less, The Vickers hardness a of the cemented carbide is 12.5 GPa or more and 14.5 GPa or less, The Vickers hardness a is measured at a point P1 in the cemented carbide at a distance of 5 μm from the surface of the cemented carbide along the normal direction of the surface; The cemented carbide includes a first region sandwiched between a virtual plane Q1 that is 5 μm away from the surface and a virtual plane Q4 that is 200 μm away from the surface, The first region has a second region sandwiched between a virtual plane Q2 that is 10 μm away from the surface and a virtual plane Q3 that is 50 μm away from the surface, In the first region, a point P2 exhibiting a Vickers hardness b that is a maximum value of the Vickers hardness is present in the second region, The difference ba between the Vickers hardness b and the Vickers hardness a is 1.8 GPa or more.

[0010] When used as a tool material, the cemented carbide of the present disclosure can provide a cutting tool that has excellent wear resistance and chipping resistance and can have a long tool life.

[0011] (2) In (1) above, In the cemented carbide, a ratio C2 / C1 of a total mass content C2 of titanium, tantalum, niobium and zirconium at point P2 to a total mass content C1 of titanium, tantalum, niobium and zirconium at point P4, which is 200 μm away from the surface in a normal direction to the surface, may be 1.1 or more and 1.5 or less.

[0012] This indicates that the total mass content of titanium, tantalum, niobium, and zirconium is greater in areas with high Vickers hardness than in areas with low Vickers hardness. Titanium, tantalum, niobium, and zirconium can improve the oxidation resistance of cemented carbide. In cemented carbide with a ratio C2 / C1 of 1.1 to 1.5, the area showing Vickers hardness b is presumed to have excellent oxidation resistance.

[0013] (3) In (1) or (2) above, In the cemented carbide, a ratio C4 / C3 of the mass-based cobalt content C4 at point P1 to the mass-based cobalt content C3 at point P4, which is 200 μm away from the surface in a normal direction to the surface, may be 1.1 or more and 2.0 or less.

[0014] According to this, point P1, which is 5 μm away from the surface of the cemented carbide, has a higher cobalt content by mass than point P4, which is 200 μm away from the surface of the cemented carbide. A higher cobalt content tends to improve toughness. It is presumed that a cemented carbide with a ratio C4 / C3 of 1.1 or more and 2.0 or less has excellent toughness on the surface side due to the higher cobalt content on the surface side.

[0015] (4) In any of (1) to (3) above, The cobalt content C5 of the cemented carbide may be 4% by mass or more and 11% by mass or less, thereby further improving the tool life.

[0016] (5) In any of (1) to (4) above, A difference bc between the Vickers hardness b and a Vickers hardness c at a point P4 in the cemented carbide that is 200 μm away from the surface in the normal direction to the surface may be 0.3 GPa or more and 1.0 GPa or less.

[0017] According to this, the Vickers hardness c is greater than the Vickers hardness a and less than the Vickers hardness b. A cutting tool including this cemented carbide has an excellent balance between wear resistance and chipping resistance and can have stable cutting performance even when wear progresses from the surface side of the cutting tool during cutting.

[0018] (6) In any of (1) to (5) above, In the cemented carbide, a difference ca between a Vickers hardness c at a point P4 that is 200 μm away from the surface in a normal direction to the surface and the Vickers hardness a may be 1.2 GPa or more.

[0019] As a result, even if wear progresses from the surface side of the cutting tool as a result of cutting, the cutting tool can have an excellent balance between wear resistance and chipping resistance and can maintain stable cutting performance.

[0020] (7) A cutting tool according to the present disclosure is a cutting tool comprising the cemented carbide according to any one of (1) to (6) above. The cutting tool according to the present disclosure has excellent wear resistance and chipping resistance and can have a long tool life.

[0021] [Details of the embodiment of the present disclosure] 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. In addition, the dimensional relationships such as length, width, thickness, depth, etc. are appropriately changed for clarity and simplification of the drawings, and do not necessarily represent the actual dimensional relationships.

[0022] In this disclosure, an expression in the form "A to B" means the upper and lower limits of a range (i.e., A or more and B or less). 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.

[0023] 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.

[0024] In the present disclosure, when one or more numerical values ​​are described as the lower limit and the upper limit of a numerical range, a combination of any one numerical value described as the lower limit and any one numerical value described as the upper limit is also disclosed. For example, when a1 or more, b1 or more, and c1 or more are described as the lower limit, and a2 or less, b2 or less, and c2 or less are described 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 disclosed.

[0025] [Embodiment 1: Carbide] The cemented carbide according to one embodiment of the present disclosure (hereinafter also referred to as "embodiment 1") is A cemented carbide comprising a first phase, a second phase, and a third phase, the first phase is comprised of a plurality of tungsten carbide particles; The content of the first phase in the cemented carbide is 65% by volume or more and 85% by volume or less, the second phase consists of cobalt; The cobalt content C5 of the cemented carbide is 3% by mass or more and 15% by mass or less, the third phase is composed of at least one element selected from the group consisting of titanium, tantalum, niobium, zirconium, and tungsten, and at least one of carbon and nitrogen; the third phase does not include tungsten carbide; The total content C of titanium, tantalum, niobium and zirconium in the cemented carbide is 2% by mass or more and 8% by mass or less, The Vickers hardness a of the cemented carbide is 12.5 GPa or more and 14.5 GPa or less, The Vickers hardness a is measured at a point P1 in the cemented carbide, the point P1 being 5 μm away from the surface of the cemented carbide in the normal direction to the surface; The cemented carbide includes a first region sandwiched between a virtual plane Q1 that is 5 μm away from the surface and a virtual plane Q4 that is 200 μm away from the surface, The first region has a second region sandwiched between a virtual plane Q2 that is 10 μm away from the surface and a virtual plane Q3 that is 50 μm away from the surface, In the first region, a point P2 exhibiting a maximum Vickers hardness b is present in the second region, The difference ba between the Vickers hardness b and the Vickers hardness a is 1.8 GPa or more.

[0026] When used as a tool material, the cemented carbide of the present disclosure can provide a cutting tool that has excellent wear resistance and chipping resistance and can have a long tool life. The reason for this is not clear, but is presumed to be as follows.

[0027] (i) The cemented carbide of the present disclosure contains 65% by volume or more and 85% by volume or less of a first phase consisting of a plurality of tungsten carbide particles (hereinafter also referred to as "WC particles"). The tungsten carbide particles have high hardness and high thermal conductivity. Therefore, the cemented carbide of the present disclosure also has high hardness and high thermal conductivity, and a cutting tool including the cemented carbide can have excellent wear resistance.

[0028] (ii) The cemented carbide of the present disclosure contains 3% by mass or more and 15% by mass or less of cobalt. Cobalt has high toughness. Therefore, the cemented carbide of the present disclosure also has high toughness, and a cutting tool including the cemented carbide can have excellent chipping resistance.

[0029] (iii) The cemented carbide of the present disclosure includes a third phase consisting of at least one element selected from the group consisting of titanium, tantalum, niobium, zirconium, and tungsten, and at least one of carbon and nitrogen. The third phase can improve the reactivity and oxidation resistance of the cemented carbide. Therefore, a cutting tool including the cemented carbide has improved reactivity and oxidation resistance, which improves wear resistance.

[0030] (iv) The cemented carbide of the present disclosure has a Vickers hardness a of 12.5 GPa to 14.5 GPa at a point P1 5 μm away from the surface. The surface side of the cemented carbide has a relatively low hardness and appropriate toughness, so that a tool including the cemented carbide is prevented from chipping in the early stage of cutting.

[0031] (v) In the present disclosure, the point P2 showing the maximum Vickers hardness b in the first region is located in the second region at a distance of 10 μm or more and 50 μm or less from the surface. Furthermore, the difference ba between the Vickers hardness b and the Vickers hardness a is 1.8 GPa or more.

[0032] In the cemented carbide, a region exists in the second region, which is 10 μm or more and 50 μm or less from the surface, that exhibits a hardness 1.8 GPa or more higher than the hardness of point P1, which is further on the surface side than the second region. Even if the surface of the cemented carbide is worn away at the beginning of cutting, a cutting tool including the cemented carbide can have excellent wear resistance due to the region in the second region that is harder than the surface side.

[0033] <Phase 1> <Composition of Phase 1> In the cemented carbide of the first embodiment, the first phase is composed of a plurality of tungsten carbide particles. Here, 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 effect of the present disclosure is not impaired." Examples of impurities include iron (Fe), molybdenum (Mo), and sulfur (S).

[0034] <Content of first phase in cemented carbide> In the cemented carbide of the first embodiment, the content of the first phase of the cemented carbide is 65 volume% or more and 85 volume% or less. The lower limit of the content of the first phase of the cemented carbide is 65 volume% or more, may be 66 volume% or more, 70 volume% or more, 72 volume% or more, or 75 volume% or more, from the viewpoint of improving hardness. The upper limit of the content of the first phase of the cemented carbide is 85 volume% or less, may be 84 volume% or less, may be 80 volume% or less, or may be 78 volume% or less, from the viewpoint of improving toughness. The content of the first phase of the cemented carbide may be 70 volume% or more and 84 volume% or less, or may be 72 volume% or more and 80 volume% or less.

[0035] In the present disclosure, the content of the first phase in a cemented carbide is measured by the following procedure. (A1) Any surface or any cross section of a cemented carbide is mirror-finished. Examples of the mirror-finishing method include polishing with diamond paste, using a focused ion beam device (FIB device), using a cross-section polisher device (CP device), and a combination of these methods.

[0036] (B1) The machined surface of the cemented carbide is photographed with a scanning electron microscope ("S-3400N" manufactured by Hitachi High-Technologies Corporation) to obtain a backscattered electron image. Six backscattered electron images are prepared. The photographed areas of the six backscattered electron images are different. The photographed locations can be set arbitrarily. The observation conditions are 5000x magnification and 10kV accelerating voltage.

[0037] (C1) 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 / ), and binarized to obtain six images after binarization. The binarization is performed under conditions preset in the image analysis software by pressing the "Make Binary" button on the computer screen after importing the images. In the image after binarization, the first region consisting of the first phase and the second region consisting of the second and third phases can be distinguished by the shade of color. For example, in the image after binarization, the first phase is shown as a black region, and the second and third phases are shown as white regions.

[0038] (D1) In each of the six binarized images obtained, a rectangular measurement field of view measuring 25.3 μm in length and 17.6 μm in width is set. Using the image analysis software, the area percentage (area%) of the first phase is measured in each of the six measurement fields of view, with the entire measurement field of view being the denominator.

[0039] (E1) Calculate the average area percentage (area%) of the first phase obtained in six measurement fields. In the present disclosure, the average area percentage (area%) of the first phase obtained in six measurement fields is defined as the content (volume%) of the first phase in the cemented carbide.

[0040] As far as the applicant has measured, it has been confirmed that, as long as measurements are taken on the same sample, there is little variation in the measurement results even if the above-mentioned measurements are performed multiple times by changing the selected location of the measurement field of view, and that setting the measurement field of view arbitrarily is not arbitrary.

[0041] <Average particle size of tungsten carbide particles> In the cemented carbide of the first embodiment, the average particle size of the tungsten carbide particles is not particularly limited and can be any known average particle size used in cemented carbide. The average particle size of the tungsten carbide particles can be, for example, 0.5 μm or more and 2.0 μm or less, or 0.7 μm or more and 1.7 μm or less.

[0042] In this disclosure, the average particle size of tungsten carbide particles is measured by the following procedure. (A2) Six images after binarization are obtained by the same method as (A1) to (C1) described in the method for measuring the content of the first phase in a cemented carbide.

[0043] (B2) A rectangular measurement field of view, 25.3 μm long and 17.6 μm wide, is set in each of the six binarized images obtained. Using image analysis software (ImageJ, version 1.51j8: https: / / imagej.nih.gov / ij / ), the circle equivalent diameter (Heywood diameter: diameter of a circle equivalent to an equal area) of each of the tungsten carbide particles (first phase) in the six measurement fields is measured.

[0044] (C2) Based on all tungsten carbide particles in the six measurement fields of view, excluding tungsten carbide particles with a circle-equivalent diameter of 0.22 μm or less, calculate the number-based arithmetic mean value of the circle-equivalent diameter. In the present disclosure, the arithmetic mean value corresponds to the average particle size of the WC particles. The reason for excluding tungsten carbide particles with a circle-equivalent diameter of 0.22 μm or less when calculating the average particle size is that the inventors have confirmed that particles with a circle-equivalent diameter of 0.22 μm or less often correspond to noise that is erroneously detected as tungsten carbide particles in image analysis.

[0045] As far as the applicant has measured, it has been confirmed that, as long as measurements are taken on the same sample, there is little variation in the measurement results even if the above-mentioned measurements are performed multiple times by changing the selected location of the measurement field of view, and that setting the measurement field of view arbitrarily is not arbitrary.

[0046] <Phase 2> <Composition of the second phase> In the cemented carbide of embodiment 1, the second phase is made of cobalt. The second phase is a binder phase that bonds the tungsten carbide particles that make up the first phase.

[0047] In the present disclosure, "the second phase is composed of cobalt (Co)" also includes the case where "the second phase contains impurities together with cobalt, so long as the effect of the present disclosure is not impaired." Examples of impurities include manganese (Mn), magnesium (Mg), calcium (Ca), molybdenum (Mo), sulfur (S), and aluminum (Al).

[0048] <Cobalt content in cemented carbide> In the cemented carbide of the first embodiment, the cobalt content C5 of the cemented carbide is 3% by mass or more and 15% by mass or less. From the viewpoint of improving toughness, the lower limit of the cobalt content C5 of the cemented carbide is 3% by mass or more, may be 4% by mass or more, may be 5% by mass or more, or may be 6% by mass or more. From the viewpoint of improving hardness, the upper limit of the cobalt content C5 of the cemented carbide is 15% by mass or less, may be 11% by mass or less, or may be 9% by mass or less. The cobalt content of the cemented carbide may be 4% by mass or more and 11% by mass or less, or may be 5% by mass or more and 9% by mass or less.

[0049] In this disclosure, the cobalt content C5 of the cemented carbide is measured by cobalt titration. The cobalt titration is performed in accordance with the Japan Machine Tool Manufacturers Association standard (TAS0054:2017) or ISO3909:1976. Specifically, the procedure is as follows: A sample made of cemented carbide is crushed and passed through a 49 mesh sieve. The sample is dissolved in nitric acid and hydrofluoric acid, and ammonium citrate and aqueous ammonia are added. Then, potentiometric titration is performed with potassium ferricyanide (red ferricyanide) using platinum and saturated calomel (tungsten) electrodes. The measurement device used is "AUT-501" manufactured by DKK-TOA Corporation.

[0050] <Phase 3> <Composition of the third phase> In the cemented carbide of embodiment 1, the third phase is composed of at least one element selected from the group consisting of titanium, tantalum, niobium, zirconium, and tungsten, and at least one of carbon and nitrogen. The third phase does not contain tungsten carbide. The third phase can improve the reactivity resistance and oxidation resistance of the cemented carbide. Therefore, the cutting tool including the cemented carbide has improved reactivity resistance and oxidation resistance.

[0051] In the present disclosure, "the third phase is composed of at least one element selected from the group consisting of titanium, tantalum, niobium, zirconium, and tungsten, and at least one of carbon and nitrogen" also includes the case where "the third phase contains impurities as long as the effect of the present disclosure is not impaired." Examples of impurities include manganese (Mn), magnesium (Mg), calcium (Ca), molybdenum (Mo), sulfur (S), and aluminum (Al).

[0052] The third phase may contain at least two elements selected from the group consisting of titanium, tantalum, niobium, zirconium and tungsten.

[0053] The third phase may include at least one selected from the group consisting of titanium carbide (TiC), tantalum carbide (TaC), niobium carbide (NbC), titanium nitride (TiN), titanium carbonitride (TiCN), zirconium carbonitride (ZrCN), zirconium carbide (ZrC) and solid solutions derived from these compounds. Examples of the solid solutions include WTiCN, WTiTaCN, and WTiTaNbZrCN.

[0054] In the present disclosure, it is confirmed by the following procedure that the third phase is composed of at least one element selected from the group consisting of titanium, tantalum, niobium, zirconium, and tungsten, and at least one of carbon and nitrogen, and that the third phase does not contain tungsten carbide.

[0055] (A3) An arbitrary position of the cemented carbide is sliced ​​using an ion slicer (apparatus: 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 the thinning process and 2 kV for the finish process.

[0056] (B3) The above sample is observed at 50,000 times magnification with a scanning transmission electron microscope (STEM) (apparatus: JFM-ARM300F (trademark) manufactured by JEOL Ltd.) to obtain a STEM-HAADF (high-angle annular dark field scanning transmission electron microscope) image. The imaging area for the STEM-HAADF image is set to the center of the sample, that is, a position that does not include any part whose properties are clearly different from the bulk part, such as the vicinity of the surface of the cemented carbide (a position where the imaging area is entirely the bulk part of the cemented carbide). The measurement condition is an acceleration voltage of 200 kV.

[0057] (C3) A spot analysis is performed on the third phase present in the STEM-HAADF image using an EDX attached to the STEM (STEM-EDX), and the elements constituting the third phase are quantified. The spot size is set for each third phase to a range that includes only the third phase. When the result of quantifying the constituent elements satisfies the following (a) and (b), it is confirmed that the third phase is composed of at least one element selected from the group consisting of titanium, tantalum, niobium, zirconium, and tungsten, and at least one of carbon and nitrogen. (a) In the third phase, at least one element selected from the group consisting of titanium, tantalum, niobium, zirconium and tungsten, and at least one of carbon and nitrogen, are present. (b) The third phase contains no impurity elements other than titanium, tantalum, niobium, zirconium, tungsten, carbon and nitrogen, or the content of these impurity elements is less than 0.1 mass %.

[0058] When spot analysis of the third phase by the above EDX (STEM-EDX) detects only tungsten and carbon, and the carbon content relative to the total mass of tungsten and carbon is about 6.1 mass%, the third phase is determined to contain tungsten carbide. In other words, when spot analysis of the third phase by the above EDX (STEM-EDX) detects elements other than tungsten and carbon, the third phase is determined to not contain tungsten carbide.

[0059] <Total content C of titanium, tantalum, niobium and zirconium in cemented carbide> In the cemented carbide of the first embodiment, the total content C of titanium, tantalum, niobium and zirconium in the cemented carbide is 2% by mass or more and 8% by mass or less. The lower limit of the total content C of titanium, tantalum, niobium and zirconium in the cemented carbide is 2% by mass or more, may be 3% by mass or more, or may be 4% by mass or more, from the viewpoint of improving the reactivity resistance and oxidation resistance. The upper limit of the total content C of titanium, tantalum, niobium and zirconium in the cemented carbide is 8% by mass or less, may be 7% by mass or less, or may be 6% by mass or less, from the viewpoint of improving the thermal conductivity of the cemented carbide. The total content C of titanium, tantalum, niobium and zirconium in the cemented carbide is 2% by mass or more and 8% by mass or less, may be 3% by mass or more and 7% by mass or less, or may be 4% by mass or more and 6% by mass or less. Here, the third phase may contain at least two elements selected from the group consisting of titanium, tantalum, niobium, zirconium and tungsten. In the present disclosure, the total content C of titanium, tantalum, niobium, and zirconium in the cemented carbide means the total content of all of these elements when the cemented carbide contains all of titanium, tantalum, niobium, and zirconium, and means the total content of the elements when the cemented carbide contains one or more and three or less elements selected from the group consisting of titanium, tantalum, niobium, and zirconium.

[0060] In this disclosure, the total titanium, tantalum, niobium and zirconium content C of the cemented carbide is measured by ICP optical emission spectrometry.

[0061] <Vickers hardness> The Vickers hardness of the cemented carbide of the first embodiment will be described with reference to Figs. 1 and 2. Fig. 1 is a schematic diagram showing a cross section of the cemented carbide of the first embodiment. Fig. 2 is a graph showing an example of the relationship between the distance from the surface of the cemented carbide of the first embodiment and the Vickers hardness. In the graph of Fig. 2, the X-axis indicates the distance from the surface of the cemented carbide (unit: µm), and the Y-axis on the left side indicates the Vickers hardness (unit: GPa). Here, the "distance from the surface of the cemented carbide" is synonymous with the distance from the surface of the cemented carbide to the inner side along the normal direction of the surface of the cemented carbide (unit: µm). Note that Fig. 2 also shows an example of the relationship between the distance from the surface of the cemented carbide of the first embodiment and the respective contents (mass%) of titanium, tantalum, niobium, and cobalt. In this case, in the graph of Fig. 2, the X-axis indicates the distance from the surface of the cemented carbide (unit: µm), and the Y-axis on the right side indicates the contents (mass%) of each element.

[0062] The cemented carbide of the first embodiment has a Vickers hardness a of 12.5 GPa or more and 14.5 GPa or less at a point P1, which is 5 μm away from the surface S1 along the normal direction of the surface S1. In FIG. 1, the point P1 is located on a virtual plane Q1, which is 5 μm away from the surface S1 toward the inside of the cemented carbide. The surface side of the cemented carbide has a relatively low hardness and a moderate toughness, so that a tool including the cemented carbide is prevented from chipping in the early stage of cutting.

[0063] 1, the cemented carbide of the first embodiment includes a first region A1 between an imaginary plane Q1 that is 5 μm away from the surface S1 of the cemented carbide toward the inner side of the cemented carbide and an imaginary plane Q4 that is 200 μm away from the surface S1 of the cemented carbide toward the inner side of the cemented carbide. The first region A1 includes a second region A2 between an imaginary plane Q2 that is 10 μm away from the surface S1 of the cemented carbide toward the inner side of the cemented carbide and an imaginary plane Q3 that is 50 μm away from the surface S1 of the cemented carbide toward the inner side of the cemented carbide.

[0064] In the first region A1, a point P2 showing the maximum Vickers hardness, that is, Vickers hardness b, exists in the second region A2. Within the regionTherefore, even if the surface of the cemented carbide is worn away at the beginning of cutting, the cutting tool having the cemented carbide can cut the surface of the cemented carbide in the second region. Within the region The areas at the bottom that are harder than the surface provide excellent wear resistance.

[0065] If the position showing Vickers hardness b is within a region less than 10 μm away from the surface of the substrate, the region with relatively low hardness and moderate toughness near the surface of the substrate becomes small, and the effect of suppressing chipping at the initial stage of cutting tends to decrease.If the position showing Vickers hardness b is within a region more than 50 μm away from the surface of the substrate, the region with relatively low hardness becomes large, and the wear resistance of the cutting tool tends to decrease.

[0066] In the cemented carbide of the first embodiment, the lower limit of the Vickers hardness a is 12.5 GPa or more, may be 12.6 GPa or more, may be 12.9 GPa or more, or may be 13.0 GPa or more, from the viewpoint of suppressing the occurrence of excessive wear. The upper limit of the Vickers hardness a is 14.5 GPa or less, may be 14.4 GPa or less, may be 14.2 GPa or less, may be 14.1 GPa or less, or may be 14.0 GPa or less, from the viewpoint of improving the fracture resistance. The Vickers hardness a may be 12.6 GPa or more and 14.4 GPa or less, may be 12.9 GPa or more and 14.2 GPa or less, or may be 13.0 GPa or more and 14.0 GPa or less.

[0067] In the cemented carbide of the first embodiment, the lower limit of the difference ba between the Vickers hardness b and the Vickers hardness a is 1.8 GPa or more, and may be 2.0 GPa or more, 2.1 GPa or more, 2.3 GPa or more, or 2.6 GPa or more, from the viewpoint of increasing the hardness near the surface of the cemented carbide and improving the wear resistance of the cemented carbide. The upper limit of the difference ba may be 3.5 GPa or less, 3.4 GPa or less, 3.3 GPa or less, 3.2 GPa or less, or 3.1 GPa or less. The difference ba may be 1.8 GPa or more and 3.5 GPa or less, 2.0 GPa or more and 3.4 GPa or less, 2.1 GPa or more and 3.3 GPa or less, 2.3 GPa or more and 3.2 GPa or less, or 2.6 GPa or more and 3.1 GPa or less.

[0068] In the cemented carbide of embodiment 1, the lower limit of the Vickers hardness b may be 14.0 GPa or more, 14.3 GPa or more, more than 14.5 GPa, 14.6 GPa or more, or 14.8 GPa or more from the viewpoint of improving wear resistance. The upper limit of the Vickers hardness b may be 18.0 GPa or less, 17.9 GPa or less, or 17.8 GPa or less from the viewpoint of improving fracture resistance. The Vickers hardness b may be 14.0 GPa or more and 18.0 GPa or less, 14.3 GPa or more and 17.9 GPa or less, more than 14.5 GPa and 17.8 GPa or less, 14.6 GPa or more and 17.7 GPa or less, or 14.8 GPa or more and 17.6 GPa or less.

[0069] In the cemented carbide of embodiment 1, the difference bc between the Vickers hardness b and the Vickers hardness c at a point P4 located 200 μm away from the surface of the cemented carbide toward the inside of the cemented carbide along the normal direction of the surface may be 0.3 GPa or more and 1.0 GPa or less.

[0070] In the cemented carbide of embodiment 1, the lower limit of the difference bc between the Vickers hardness b and the Vickers hardness c may be 0.1 GPa or more, and from the viewpoint of the balance between the wear resistance and the chipping resistance inside the cemented carbide, it may be 0.3 GPa or more, 0.4 GPa or more, or 0.5 GPa or more. The upper limit of the difference bc may be 1.5 GPa or less, and from the viewpoint of the balance between the wear resistance and the chipping resistance inside the cemented carbide, it may be 1.0 GPa or less, 0.9 GPa or less, or 0.8 GPa or less. The difference bc may be 0.3 GPa or more and 1.0 GPa or less, 0.4 GPa or more and 0.9 GPa or less, or 0.5 GPa or more and 0.8 GPa or less.

[0071] In the cemented carbide of the first embodiment, the difference ca between the Vickers hardness c at a point P4, which is 200 μm away from the surface of the cemented carbide toward the inside of the cemented carbide along the normal direction of the surface, and the Vickers hardness a, may be 1.2 GPa or more. The lower limit of the difference ca may be 0.6 GPa or more, and from the viewpoint of the balance between the wear resistance and the chipping resistance inside the cemented carbide, may be 1.2 GPa or more, 1.5 GPa or more, 1.6 GPa or more, or 1.7 GPa or more. The upper limit of the difference ca is not particularly limited, but may be, for example, 2.8 GPa or less. The difference ca may be 1.2 GPa or more and 2.8 GPa or less, or 1.5 GPa or more and 2.6 GPa or less.

[0072] In the cemented carbide of embodiment 1, the lower limit of the Vickers hardness c may be 14.0 GPa or more, 14.2 GPa or more, more than 14.5 GPa, 14.6 GPa or more, or 14.8 GPa or more from the viewpoint of improving wear resistance. The upper limit of the Vickers hardness b may be 18.0 GPa or less, 17.9 GPa or less, or 17.8 GPa or less from the viewpoint of improving fracture resistance. The Vickers hardness b may be 14.0 GPa or more and 18.0 GPa or less, 14.3 GPa or more and 17.9 GPa or less, more than 14.5 GPa and 17.8 GPa or less, 14.6 GPa or more and 17.7 GPa or less, or 14.8 GPa or more and 17.6 GPa or less.

[0073] In this disclosure, the Vickers hardness of the cemented carbide is measured using a micro Vickers hardness tester (FM810 (trademark) manufactured by FutureTech Co., Ltd.) The measurement conditions are a test load of 500 g, a load holding time of 10 seconds, and a measurement temperature of 18°C ​​to 28°C.

[0074] In the present disclosure, the Vickers hardness of a cemented carbide is measured by the following procedure. The cemented carbide is embedded in a resin and polished with diamond paste to expose a cross section S2 having an angle θ of 5.7° with the surface S1 of the cemented carbide, as shown in FIG. 3, to obtain a measurement sample. When an arbitrary point B1 is set on the cross section S2 of the measurement sample, the shortest distance L2 between the surface S1 of the cemented carbide and the point B1 along the cross section S2 is 10 times the distance L1 between a virtual surface S11 on the same plane as the surface S1 and the point B1 along the normal direction of the surface S1. Based on this relationship, the Vickers hardness of the cemented carbide can be measured on the cross section S2 to obtain the Vickers hardness at a predetermined distance from the surface S1 of the cemented carbide.

[0075] In measuring the Vickers hardness, an indenter is pressed in a direction perpendicular to the cross section S2. The measurement position is set on an imaginary straight line that intersects with the surface S2 provided on the cross section S2. The points described in (a) and (b) below are set on the straight line, and the Vickers hardness is measured at each point. (a) A point at a distance of 5 μm from the virtual surface S11 along the normal direction of the surface S1. (b) Points at intervals of 10 μm along the normal direction of the surface S1, the distance from the imaginary surface S11 being 10 μm or more and 200 μm or less, including points at a distance of 10 μm from the imaginary surface S11 and points at a distance of 200 μm from the imaginary surface S11.

[0076] The above measurement is performed on each of three different imaginary straight lines. In the present disclosure, the average of the measured values ​​of the Vickers hardness of the cemented carbide at three points at the same distance L from the imaginary surface S11 corresponds to the Vickers hardness at the point at the distance L from the surface S1 of the cemented carbide.

[0077] As far as the applicant has measured, it has been confirmed that there is almost no variation in the measurement results even when the Vickers hardness is measured multiple times on the same sample by changing the measurement position.

[0078] <Total content by mass of titanium, tantalum, niobium and zirconium> The total mass-based content of titanium (Ti), tantalum (Ta), niobium (Ni) and zirconium (Zr) in the cemented carbide of the first embodiment will be described with reference to Figs. 1 and 2. Fig. 2 is a graph showing an example of the relationship between the distance from the surface of the cemented carbide of the first embodiment and the respective contents (mass%) of titanium, tantalum, niobium and cobalt. Fig. 2 shows a case in which the cemented carbide contains titanium, tantalum and niobium, but does not contain zirconium, among titanium, tantalum, niobium and zirconium. The cemented carbide of the first embodiment can contain at least one element of titanium, tantalum, niobium and zirconium.

[0079] In the cemented carbide of the first embodiment, the ratio C2 / C1 of the total mass content C2 of titanium, tantalum, niobium and zirconium at point P2 showing Vickers hardness b to the total mass content C1 of titanium, tantalum, niobium and zirconium at point P4 where the distance from the surface of the cemented carbide to the inner side of the cemented carbide along the normal direction of the surface is 200 μm may be 1.1 or more and 1.5 or less. This indicates that the total mass content of titanium, tantalum, niobium and zirconium is higher at the location where the Vickers hardness is high than at the location where the Vickers hardness is low. Titanium, tantalum, niobium and zirconium can improve the oxidation resistance of the cemented carbide. In the cemented carbide where the ratio C2 / C1 is 1.1 or more and 1.5 or less, it is presumed that the region showing Vickers hardness b has excellent oxidation resistance.

[0080] In the first embodiment, the lower limit of the ratio C2 / C1 may be 1.0 or more, and from the viewpoint of the balance between the wear resistance and the fracture resistance inside the cemented carbide, it may be 1.1 or more, or 1.2 or more. The upper limit of the ratio C2 / C1 may be 2.0 or less, and from the viewpoint of the balance between the wear resistance and the fracture resistance inside the cemented carbide, it may be 1.5 or less, or 1.4 or less. The ratio C2 / C1 may be 1.1 or more and 1.5 or less, or 1.2 or more and 1.4 or less.

[0081] For example, in the cemented carbide shown in Fig. 2, at point P4, the Ti content is 2.6 mass%, the Ta content is 3.3 mass%, the Nb content is 0.7 mass%, and the total content C1 of Ti, Ta, and Nb is 6.6 mass%. In Fig. 2, at point P2, the Ti content is 2.8 mass%, the Ta content is 4.1 mass%, the Nb content is 0.9 mass%, and the total content C2 of Ti, Ta, and Nb is 7.8 mass%. In the cemented carbide shown in Fig. 2, C2 / C1 is 1.2.

[0082] In the first embodiment, the lower limit of the total content C1 may be 2.0% by mass or more, 3.0% by mass or more, or 4.0% by mass or more. The upper limit of the total content C1 may be 8.0% by mass or less, 7.1% by mass or less, or 6.0% by mass or less. The total content C1 may be 2.0% by mass or more and 8.0% by mass or less, 3.0% by mass or more and 7.1% by mass or less, or 4.0% by mass or more and 6.0% by mass or less.

[0083] In the first embodiment, the lower limit of the total content C2 may be 2.0% by mass or more, 2.2% by mass or more, 2.4% by mass or more, 3.6% by mass or more, or 4.8% by mass or more. The upper limit of the total content C2 may be 16.0% by mass or less, 12.0% by mass or less, 11.0% by mass or less, or 10.0% by mass or less. The total content C2 may be 2.0% by mass or more and 16.0% by mass or less, 3.6% by mass or more and 12.0% by mass or less, or 4.8% by mass or more and 11.0% by mass or less.

[0084] In this disclosure, the total mass content C1 of titanium, tantalum, niobium and zirconium at point P4 and the total mass content C2 of titanium, tantalum, niobium and zirconium at point P2 are measured on the same cross section S2 of the cemented carbide as that used for measuring the Vickers hardness, using an energy dispersive X-ray spectrometer (SEM-EDX, Oxford Instruments' "EMAX-ACT") attached to a scanning electron microscope. The measurement conditions for EDX are an observation magnification of 3000 times and an acceleration voltage of 15 kV. The total content C1 and the total content C2 are measured on the same cross section of the cemented carbide as that used for measuring the Vickers hardness.

[0085] The procedure for measuring the total content C1 is as follows: In the cross section S2 of the cemented carbide, the total contents of titanium, tantalum, niobium, and zirconium are measured at three positions that are not overlapping with each other and are located at a distance of 200 μm from the surface of the cemented carbide toward the inside of the cemented carbide along the normal direction of the surface, and the average of the total contents at the three positions is calculated. The average corresponds to the total content C1.

[0086] The procedure for measuring the total content C2 is as follows. The total content of titanium, tantalum, niobium, and zirconium is measured at one location within 200 μm of the outer edge of the indentation (indentation) made by the indenter at the point where the Vickers hardness b was measured on the cross section S2 of the cemented carbide. The measurement is performed at a location within 200 μm of the outer edge of each of the three indentations, and the average of the total contents at the three locations is calculated. This average corresponds to the total content C2.

[0087] <Cobalt content> The mass-based content of cobalt (Co) in the cemented carbide of the first embodiment will be described with reference to Figs. 1 and 2. In the cemented carbide of the first embodiment, the ratio C4 / C3 of the mass-based cobalt content C4 at the surface S1 of the cemented carbide to the mass-based cobalt content C3 at a point P4 at a distance of 200 μm from the surface S1 of the cemented carbide to the inside of the cemented carbide along the normal direction of the surface S1 may be 1.1 or more and 2.0 or less. The mass-based cobalt content of the surface of the cemented carbide is higher than that at a point 200 μm away from the surface of the cemented carbide. A high cobalt content tends to improve toughness. It is presumed that a cemented carbide satisfying the ratio C4 / C3 of 1.1 or more and 2.0 or less has excellent toughness at the surface due to the high cobalt content at the surface.

[0088] In the cemented carbide of embodiment 1, the lower limit of the ratio C4 / C3 may be 1.1 or more, 1.2 or more, or 1.3 or more, from the viewpoint of improving the chipping resistance at the initial stage of cutting. The upper limit of the ratio C4 / C3 may be 2.0 or less, or 1.9 or less, from the viewpoint of the balance between the wear resistance and the chipping resistance inside the cemented carbide. The ratio C4 / C3 may be 1.2 or more and 1.9 or less, or 1.3 or more and 1.8 or less.

[0089] For example, in the cemented carbide shown in FIG. 2, the Co content C3 at point P4 is 6.2 mass%, the Co content C4 at the surface is 9.4 mass%, and C4 / C3 is 1.5. in be.

[0090] In the first embodiment, the lower limit of the cobalt content C3 may be 3 mass% or more, or 4 mass% or more. The upper limit of the cobalt content C3 may be 15 mass% or less, or 14 mass% or less. The cobalt content C3 may be 3 mass% or more and 15 mass% or less, or 4 mass% or more and 14 mass% or less.

[0091] In the first embodiment, the lower limit of the cobalt content C4 may be 3.9% by mass or more, 4% by mass or more, or 5% by mass or more. The upper limit of the cobalt content C4 may be 30% by mass or less, or 20% by mass or less. The cobalt content C4 may be 4% by mass or more and 30% by mass or less, or 5% by mass or more and 20% by mass or less.

[0092] <Zirconium content> The cemented carbide of the first embodiment may contain zirconium (Zr). Zirconium has the effect of improving the high-temperature hardness of the cemented carbide. In the cemented carbide, the percentage of the mass of zirconium relative to the mass of cobalt may be 0% or more and 6% or less. This improves the high-temperature hardness of the cemented carbide, thereby improving the tool life. In the cemented carbide, if the percentage of the mass of zirconium relative to the mass of cobalt exceeds 6%, the solid solubility limit of zirconium in cobalt is exceeded, and zirconium precipitates in the cemented carbide in the form of carbide or the like, which tends to deteriorate the chipping resistance of the cemented carbide.

[0093] In the cemented carbide, the upper limit of the percentage of the mass of zirconium relative to the mass of cobalt may be 6% or less, 5% or less, or 4% or less, from the viewpoint of a balance between fracture resistance and improved high-temperature hardness. In the cemented carbide, the lower limit of the percentage of the mass of zirconium relative to the mass of cobalt may be 1% or more, or 2% or more, from the viewpoint of improved high-temperature hardness. In the cemented carbide, the percentage of the mass of zirconium relative to the mass of cobalt may be 1% or more and 5% or less, or 2% or more and 4% or less.

[0094] The zirconium content of the cemented carbide is measured by ICP atomic emission spectrometry.

[0095] <Composition of cemented carbide> The cemented carbide of the first embodiment includes a first phase, a second phase, and a third phase. The cemented carbide of the first embodiment may be composed of a first phase, a second phase, and a third phase. The cemented carbide of the first embodiment may include other phases in addition to the first phase, the second phase, and the third phase, as long as the effect of the present disclosure is not impaired. Examples of other phases include chromium carbides. The cemented carbide of the first embodiment may include impurities in addition to the first phase, the second phase, and the third phase, as long as the effect of the present disclosure is not impaired. Examples of impurities include iron (Fe), molybdenum (Mo), sulfur (S), manganese (Mn), magnesium (Mg), calcium (Ca), and aluminum (Al). The content of impurities in the cemented carbide (when the impurities include two or more elements, the total concentration of the elements) may be less than 0.1% by mass. The content of impurities in the cemented carbide can be measured by ICP atomic emission spectrometry.

[0096] <Method of manufacturing cemented carbide> The cemented carbide of the first embodiment can be manufactured, for example, by carrying out the steps of preparing raw material powder, mixing, molding, sintering, and cooling in the above-mentioned order. Each step will be described below.

[0097] <Raw powder preparation process> In the raw powder preparation step, all raw powders of the materials constituting the cemented carbide are prepared. As raw powders, tungsten carbide powder, which is the raw material of the first phase, cobalt (Co) powder, which is the raw material of the second phase, titanium carbide (TiC) powder, titanium nitride (TiN) powder, tantalum carbide (TaC) powder, niobium carbide (NbN) powder, and zirconium carbide (ZrC) powder (hereinafter also referred to as "third phase raw material powder") are prepared. If necessary, chromium carbide (Cr3C2) powder can be prepared as a grain growth inhibitor. These raw powders can be commercially available.

[0098] The average particle size of the tungsten carbide powder (hereinafter also referred to as "WC powder") may be 1.5 μm or more and 6.0 μm or less. The average particle size of the cobalt powder may be 0.5 μm or more and 3.0 μm or less. The average particle size of the third phase raw material powder may be 0.5 μm or more and 4.0 μm or less. The average particle size of the chromium carbide powder may be 1.0 μm or more and 2.0 μm or less. In the present disclosure, the average particle size of these powders means the average particle size measured by the FSSS (Fisher Sub-Sieve Sizer) method. The average particle size is measured using a Fisher Scientific "Sub-Sieve Sizer Model 95" (trademark).

[0099] ≪Mixing process≫ In the mixing step, the raw material powders prepared in the preparation step are mixed to obtain a mixed powder. The content of each raw material powder in the mixed powder is appropriately adjusted in consideration of the content of each component of the first phase, the second phase, and the third phase of the cemented carbide.

[0100] The mixing method is not particularly limited, and a conventionally known method such as a ball mill or an attritor can be used. The mixing conditions are also not particularly limited, and conventionally known conditions can be used.

[0101] After the mixing step, the mixed powder may be granulated as necessary. By granulating the mixed powder, it becomes easier to fill the mixed powder into a die or a mold during the molding step described below. For granulation, a known granulation method can be applied, and for example, a commercially available granulator such as a spray dryer can be used.

[0102] ≪Molding process≫ The molding step is a step of forming the mixed powder obtained in the mixing step into a predetermined shape to obtain a molded body. The molding method and molding conditions in the molding step are not particularly limited and may be any general method and conditions. An example of the predetermined shape is a cutting tool shape.

[0103] <Sintering process> In the sintering step, the molded body obtained in the molding step is sintered to obtain a cemented carbide. First, when heating from the start of sintering to a temperature before the appearance of the liquid phase (for example, 1300°C), heating is performed under conditions of a low degree of vacuum in the sintering furnace (for example, 2 kPaG to 10 kPaG by introducing argon). Under these conditions, the raw material powder is heated in a state in which denitrification from the raw material powder is suppressed. Thereafter, while maintaining the same pressure conditions, the temperature is heated to about 1450°C (1400°C to 1450°C), and when it reaches about 1450°C, the inside of the sintering furnace is evacuated (pressure 0.1 kPaG) in a short time (for example, within 300 seconds). This operation causes denitrification from the powder to progress rapidly in a short time, making it difficult for titanium, tantalum, niobium, and zirconium present on the surface side of the cemented carbide to move toward the inside of the cemented carbide, and a region with high concentrations of titanium, tantalum, niobium, and zirconium can be formed in the surface region of the cemented carbide. This state is maintained for 20 to 40 minutes to sinter the compact, thereby obtaining a cemented carbide.

[0104] ≪Cooling process≫ The cooling step is a step of cooling the cemented carbide after the sintering is completed. The cooling rate to 1300°C is set to a gentle condition (for example, -2°C / min). This allows the cobalt to easily move to the surface of the cemented carbide, and a region with a high cobalt concentration can be formed on the surface of the cemented carbide.

[0105] [Embodiment 2: Cutting tool] The cutting tool of embodiment 2 includes the cemented carbide of embodiment 1. The cutting tool of embodiment 2 can include a cutting edge made of at least the cemented carbide of embodiment 1. In the present disclosure, the cutting edge means a portion involved in cutting, and in the cemented carbide, means the cutting edge ridge and a region of the cemented carbide within 0.5 mm of the cutting edge ridge toward the cemented carbide.

[0106] Examples of cutting tools include cutting tools, drills, end mills, indexable cutting tips for milling, indexable cutting tips for turning, metal saws, gear cutting tools, reamers, taps, and the like.

[0107] The cemented carbide of the second embodiment may constitute the entirety of these tools, or may constitute a part of them. Here, "constitute a part" refers to a mode in which the cemented carbide of the second embodiment is brazed to a predetermined position of any substrate to form a cutting edge, etc.

[0108] 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, for example, a film made of diamond-like carbon, diamond, Al2O3, or TiCN. The hard film may be a CVD film formed by a chemical vapor deposition method (CVD method). EXAMPLES

[0109] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0110] <Preparation of cemented carbide> <Raw powder preparation process> As raw material powders, powders having the compositions shown in the "Raw Material" column in Table 1 were prepared. The average particle size of the tungsten carbide (WC) powder was 3.2 μm, the average particle size of the cobalt (Co) powder was 1.2 μm, the average particle size of the chromium carbide (Cr3C2) powder was 1.5 μm, the average particle size of the titanium carbide (TiC) powder was 1.5 μm, the average particle size of the titanium nitride (TiN) powder was 2.0 μm, the average particle size of the tantalum carbide (TaC) powder was 1.0 μm, the average particle size of the niobium carbide (NbC) powder was 1.1 μm, and the average particle size of the zirconium carbide (ZrC) powder was 1.5 μm.

[0111] ≪Mixing process≫ Each raw material powder was mixed in the amount shown in the "Content (mass%)" column of "Raw Material" in Table 1 to prepare a mixed powder. "Mas%" in the "Raw Material" column of Table 1 indicates the percentage of the mass of each raw material powder with respect to the total mass of the raw material powders. Mixing was performed using an attritor. The mixing time was 8 hours. The obtained mixed powder was spray-dried to obtain a granulated powder.

[0112] ≪Molding process≫ The obtained granulated powder was press-molded to prepare a chip-shaped compact.

[0113] <Sintering process> The compact was placed in a sintering furnace and heated to sinter. The pressure in the sintering furnace when heating from the start of sintering to 1300°C was as shown in the "~1300°C Pressure" column of "Sintering" in Table 2. After that, the temperature was heated to 1450°C while maintaining the same pressure conditions.

[0114] For samples marked "Yes" in the "Vacuuming" column of "Sintering" in Table 2, the sintering furnace was evacuated to a vacuum (pressure 0.1 kPaG) within 300 seconds when the temperature reached 1450°C. This state was maintained for 20 to 40 minutes, and the compact was sintered to obtain a cemented carbide.

[0115] For samples with "None" written in the "Vacuuming" column of "Sintering" in Table 2, the pressure in the sintering furnace was set to 1 kPaG when the temperature reached 1450°C, and this condition was maintained for 20 to 40 minutes to sinter the compact and obtain a cemented carbide.

[0116] ≪Cooling process≫ After sintering, the samples were cooled slowly in an argon (Ar) gas atmosphere to obtain cemented carbide. The cooling rate to 1300°C for each sample is shown in the "Cooling rate" column of Table 2.

[0117] [Table 1]

[0118] [Table 2]

[0119] <Evaluation of cemented carbide> <Composition of cemented carbide> For each sample of cemented carbide, the first phase content of the cemented carbide, the cobalt content C5 of the cemented carbide, and the total content C of titanium, tantalum, niobium, and zirconium of the cemented carbide were measured. Here, the cobalt content C5 of the cemented carbide means the cobalt content in the entire cemented carbide, and the total content C of titanium, tantalum, niobium, and zirconium of the cemented carbide means the total content C of titanium, tantalum, niobium, and zirconium in the entire cemented carbide. The specific measurement method is as described in the first embodiment. The results are shown in the "first phase content" and "C5 (total)" of "Co content" of "Cemented carbide" in Table 3, and the "C (total)" of "Ti, Ta, Zr, Nb total content" in Table 4. The description of "Ti, Ta, Zr, Nb content" does not necessarily indicate that each sample contains all of Ti, Ta, Zr, and Nb.

[0120] <Average particle size of tungsten carbide particles> It was confirmed that the average particle size of the tungsten carbide particles was 0.5 μm or more and 2.0 μm or less in all samples.

[0121] <Composition of the second phase> In all samples, the second phase was confirmed to consist of cobalt.

[0122] <Composition of the third phase> In each sample, the elements contained in the third phase were identified by STEM-EDX. The specific identification method is as described in embodiment 1. The results are shown in the "Composition" column of "Third Phase" in Table 3. It was confirmed that in all samples, the third phase was composed of the elements listed in Table 3 and did not contain tungsten carbide.

[0123] <Vickers hardness> For each cemented carbide sample, the Vickers hardness was measured in a first region between an imaginary plane Q1 at a distance of 5 μm from the surface of the cemented carbide and an imaginary plane Q4 at a distance of 200 μm from the surface. The specific measurement method is as described in the first embodiment. The Vickers hardness a at point P1 at a distance of 5 μm from the surface is shown in the "a(P1)" column of "Vickers hardness" of "Cemented carbide" in Table 5. The Vickers hardness c at point P4 at a distance of 200 μm from the surface of the cemented carbide to the inside of the cemented carbide along the normal direction of the surface is shown in the "c(P4)" column of "Vickers hardness" of "Cemented carbide" in Table 5.

[0124] In all samples, it was confirmed that the point P2 showing the maximum Vickers hardness, Vickers hardness b, exists in the second region between the imaginary plane Q2, which is 10 μm away from the surface of the cemented carbide toward the inside of the cemented carbide, and the imaginary plane Q3, which is 50 μm away from the surface toward the inside of the cemented carbide. The Vickers hardness b is shown in the "b(P2)" column of "Vickers hardness" under "Cemented carbide" in Table 5. Based on the obtained "a", "b", and "c", "ba", "bc", and "ca" were calculated. The results are shown in Table 5.

[0125] <Total content by mass of titanium, tantalum, niobium and zirconium> For each sample of cemented carbide, the total mass content C1 of titanium, tantalum, niobium, and zirconium at point P4, which is 200 μm away from the surface of the cemented carbide toward the inside of the cemented carbide along the normal direction of the surface, and the total mass content C2 of titanium, tantalum, niobium, and zirconium at point P2, which shows Vickers hardness b, were measured. The specific measurement method is as described in embodiment 1. The results are shown in Table 1. 4 "Ti, Ta, Ni 、 The results are shown in the "C1 (P4)" and "C2 (P2)" columns of "Total Zr Content." Based on the obtained "C1" and "C2," "C2 / C1" was calculated. The results are shown in the "C2 / C1" column of Table 4.

[0126] <Cobalt content by mass> For each sample of cemented carbide, the mass-based cobalt content C3 at point P4, which is 200 μm from the surface of the cemented carbide toward the inside of the cemented carbide along the normal direction of the surface, and the mass-based total cobalt content C4 at point P1, which is 5 μm from the surface of the cemented carbide along the normal direction of the surface, were measured. The specific measurement method is as described in embodiment 1. The results are shown in the "C3(P4)" and "C4(P1)" columns of "Co content" in Table 3. "C4 / C3" was calculated based on the obtained "C3" and "C4". The results are shown in the "C4 / C3" column in Table 3.

[0127] [Table 3]

[0128] [Table 4]

[0129] [Table 5]

[0130] <Cutting test 1> Turning was performed under the following conditions using a cutting tool for each sample (tool model number: CNMG120408N-GU (manufactured by Sumitomo Electric Hardmetal Corp.)), and the average wear amount Vb (mm) on the flank side of the cutting tool after 15 minutes of cutting was measured. The smaller the average wear amount Vb (mm), the better the wear resistance and the longer the tool life. In Cutting Test 1, when the average wear amount Vb (mm) is 0.40 mm or less, it is judged that the wear resistance is excellent and the tool life is long. The results are shown in the "Cutting Test 1" column in Table 6.

[0131] ≪Cutting conditions≫ Work material: S45C Processing: Round bar external diameter turning Cutting speed: 350m / min Feed rate: 0.25mm / rev Depth of cut: 2.0mm Cutting fluid: Water-soluble cutting oil The above cutting conditions apply to high speed machining.

[0132] <Cutting test 2> Twenty cutting tools (tool model number: CNMG120408N-GU (Sumitomo Electric Hardmetal Corp.)) were prepared for each sample, and turning was performed using these under the following conditions, measuring the breakage rate (%) after 20 seconds of cutting. The smaller the breakage rate, the better the chipping resistance and the longer the tool life. In Cutting Test 2, a breakage rate of 25% or less is deemed to be a long tool life. The results are shown in the "Cutting Test 2" column in Table 6.

[0133] ≪Cutting conditions≫ Work material: SCM440 (grooved round bar) Processing: Intermittent turning of grooved round bar Cutting speed: 120m / min Feed rate: 0.15mm / rev Depth of cut: 2.0mm Cutting Fluid: None

[0134] In this embodiment, if the average wear amount Vb in cutting test 1 is 0.40 mm or less, and if the breakage rate in cutting test 2 is 25% or less, the tool life is determined to be long.

[0135] [Table 6]

[0136] <Consideration> The cemented carbide and cutting tools of Samples 1 to 17 correspond to Examples. The cemented carbide and cutting tools of Samples 101 to 113 correspond to Comparative Examples. Samples 1 to 17 have excellent wear resistance and chipping resistance, and showed long tool life in both Cutting Test 1 and Cutting Test 2. Samples 101, 104, and 107 had insufficient wear resistance, and insufficient tool life in Cutting Test 1. Samples 102, 103, 105, 106, and 108 to 113 had insufficient chipping resistance, and insufficient tool life in Cutting Test 2.

[0137] Although the embodiments and examples of the present disclosure have been described above, it is intended from the outset 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 as limiting. The scope of the present invention is indicated by the claims, not by the embodiments and examples described above, and is intended to include the meaning equivalent to the claims and all modifications within the scope. [Explanation of symbols]

[0138] A1 first region, A2 second region, S1 cemented carbide surface, Q1, Q2, Q3, Q4 virtual surfaces.

Claims

1. A cemented carbide comprising a first phase, a second phase, and a third phase, the first phase comprises a plurality of tungsten carbide particles; The content of the first phase in the cemented carbide is 65% by volume or more and 85% by volume or less, the second phase comprises cobalt; The cobalt content C5 of the cemented carbide is 3% by mass or more and 15% by mass or less, the third phase is composed of at least one element selected from the group consisting of titanium, tantalum, niobium, zirconium, and tungsten, and at least one of carbon and nitrogen; the third phase does not include tungsten carbide; The total content C of titanium, tantalum, niobium and zirconium in the cemented carbide is 2% by mass or more and 8% by mass or less, The Vickers hardness a of the cemented carbide is 12.5 GPa or more and 14.5 GPa or less, The Vickers hardness a is measured at a point P1 in the cemented carbide, the point P1 being 5 μm away from the surface of the cemented carbide in the normal direction to the surface; The cemented carbide includes a first region sandwiched between a virtual surface Q1 that is 5 μm away from the surface and a virtual surface Q4 that is 200 μm away from the surface, The first region has a second region sandwiched between a virtual surface Q2 that is 10 μm away from the surface and a virtual surface Q3 that is 50 μm away from the surface, In the first region, a point P2 exhibiting a Vickers hardness b that is a maximum value of the Vickers hardness is present in the second region, The difference b-a between the Vickers hardness b and the Vickers hardness a is 1.8 GPa or more.

2. In the cemented carbide, a ratio C2 / C1 of a total mass content C2 of titanium, tantalum, niobium and zirconium at the point P2 to a total mass content C1 of titanium, tantalum, niobium and zirconium at a point P4 at a distance of 200 μm from the surface along a normal direction to the surface is 1.1 or more and 1.5 or less. The cemented carbide according to claim 1.

3. 3. The cemented carbide according to claim 1, wherein a ratio C4 / C3 of the mass-based cobalt content C4 at the point P1 to the mass-based cobalt content C3 at a point P4 that is 200 μm away from the surface in a normal direction to the surface is 1.1 or more and 2.0 or less.

4. 3. The cemented carbide according to claim 1 or claim 2, wherein the cobalt content C5 of the cemented carbide is 4% by mass or more and 11% by mass or less.

5. The cemented carbide according to claim 1 or 2, wherein the difference b-c between the Vickers hardness b and the Vickers hardness c at a point P4 at a distance of 200 μm from the surface along the normal direction of the surface is 0.3 GPa or more and 1.0 GPa or less.

6. The cemented carbide according to claim 1 or claim 2, wherein the difference c-a between the Vickers hardness c at a point P4 at a distance of 200 μm from the surface along the normal direction of the surface and the Vickers hardness a is 1.2 GPa or more.

7. A cutting tool comprising the cemented carbide according to claim 1 or 2.

Images