Cemented carbide and cutting tool

Abstract

A cemented carbide containing a first phase, a second phase, and a third phase, the first phase comprising a plurality of tungsten carbide particles, the content of the first phase in the cemented carbide being 65-85 vol% inclusive, the arithmetic mean diameter a of the tungsten carbide particles being 0.5-2.0 [mu] m inclusive, and the third phase being a mixture of the first phase and the second phase. The arithmetic mean diameter a and the standard deviation b of the particle diameter of the tungsten carbide particles represent the relationship represented by formula I, b < 0.49 a + 0.063 in formula I, the units of a and b are [mu] m, the arithmetic mean diameter a and the 10% cumulative particle diameter c on the basis of the number of the tungsten carbide particles represent the relationship represented by formula II, c > 0.34 a + 0.098 in formula II, the units of a and c are [mu] m, and c > 0.34 a + 0.098 in formula II. The second phase is composed of cobalt, the cobalt content of the cemented carbide is 3-15 mass%, and 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 element selected from the group consisting of carbon and nitrogen, and does not contain tungsten carbide. The total content of titanium, tantalum, niobium, and zirconium in the cemented carbide is 2-8% by mass (inclusive).

Description

Technical Field

[0001] The present disclosure relates to cemented carbide and cutting tools. Background Art

[0002] In the past, cemented carbide having a hard phase with tungsten carbide (WC) as the main component and a bonding phase with an iron group element as the main component has been used as a material for cutting tools. In the cemented carbide described in Patent Document 1, as a hard phase, on the basis of a hard phase with WC as the main component, a phase consisting of at least one composite compound of carbides, nitrides and carbonitrides containing tungsten (W) and a metal element other than W is provided, and the defect resistance is improved by bonding WC particles with the composite compound particles.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2016-20541 Summary of the invention

[0006] The cemented carbide disclosed in the present invention is a cemented carbide comprising a first phase, a second phase, and a third phase, wherein:

[0007] The first phase is composed of a plurality of tungsten carbide particles,

[0008] The content of the first phase of the cemented carbide is 65 volume % or more and 85 volume % or less,

[0009] The arithmetic mean diameter a of the tungsten carbide particles is greater than or equal to 0.5 μm and less than or equal to 2.0 μm.

[0010] The arithmetic mean diameter a and the standard deviation b of the particle diameter of the tungsten carbide particles are expressed in the following formula (I):

[0011] b<0.49a+0.063 Formula I

[0012] In the formula I, the units of a and b are μm,

[0013] The arithmetic mean diameter a and the 10% cumulative particle diameter c of the tungsten carbide particles based on the number of particles are related by the following formula II:

[0014] c>0.34a+0.098 Formula II

[0015] In the above formula II, the units of a and c are μm,

[0016] The second phase is composed of cobalt,

[0017] The cobalt content of the cemented carbide is 3 mass % or more and 15 mass % or less,

[0018] 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.

[0019] The third phase does not contain tungsten carbide.

[0020] The total content rate of titanium, tantalum, niobium, and zirconium in the cemented carbide is 2% by mass or more and 8% by mass or less. Detailed Embodiments

[0021] [Problems to be Solved by the Present Disclosure]

[0022] In recent years, the difficulty of cutting materials to be cut in cutting has been increasing. Further, according to the requirement of improving machining efficiency, the cutting speed, feed rate, and depth of cut are increased, etc., and the machining conditions become stricter.

[0023] Therefore, an object of the present disclosure is to provide a cemented carbide for a cutting tool that can provide excellent wear resistance and chipping resistance and can have a long tool life when used as a tool material, and a cutting tool having a long tool life.

[0024] [Effects of the Present Disclosure]

[0025] According to the present disclosure, it is possible to provide a cemented carbide for a cutting tool that can provide excellent wear resistance and chipping resistance and can have a long tool life when used as a tool material, and a cutting tool having a long tool life.

[0026] [Description of Embodiments of the Present Disclosure]

[0027] First, the embodiments of the present disclosure will be listed and described.

[0028] (1) The cemented carbide of the present disclosure is a cemented carbide containing a first phase, a second phase, and a third phase, wherein

[0029] The first phase is composed of a plurality of tungsten carbide particles.

[0030] The content rate of the first phase of the cemented carbide is 65% by volume or more and 85% by volume or less.

[0031] The arithmetic average diameter a of the tungsten carbide particles is 0.5 μm or more and 2.0 μm or less.

[0032] The arithmetic average diameter a and the standard deviation b of the particle diameter of the tungsten carbide particles show the relationship of the following formula I.

[0033] b < 0.49a + 0.063 Formula I

[0034] In the formula I, the units of a and b are μm,

[0035] The arithmetic mean diameter a and the 10% cumulative particle diameter c of the tungsten carbide particles based on the number of particles are related by the following formula II:

[0036] c>0.34a+0.098 Formula II

[0037] In the above formula II, the units of a and c are μm,

[0038] The second phase is composed of cobalt,

[0039] The cobalt content of the cemented carbide is 3 mass % or more and 15 mass % or less,

[0040] 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.

[0041] The third phase does not contain tungsten carbide,

[0042] The total content of titanium, tantalum, niobium, and zirconium in the cemented carbide is 2 mass % or more and 8 mass % or less.

[0043] The cemented carbide disclosed herein can provide a cutting tool having excellent wear resistance and defect resistance and a long tool life when used as a tool material.

[0044] (2) In the above (1), it may be that, in a first image obtained by binarizing the reflected electron image of the cross section of the cemented carbide, there is a first region composed of the first phase and a second region composed of the second phase and the third phase,

[0045] In the first image, an arithmetic mean diameter d of the second region is 0.3 μm or more and 0.9 μm or less. The reflected electron image is obtained by photographing a cross section of the cemented carbide at 5000 times magnification using a scanning electron microscope.

[0046] Thus, by having a second region with a moderate particle size, the wear resistance of the cemented carbide is improved. When the particle size in the second region is small, there is a tendency to easily aggravate the wear caused by shedding during cutting. When the particle size in the second region is large, in other words, when there is a deviation in the location, there is a tendency to easily aggravate partial wear and easily reduce wear resistance.

[0047] (3) In the above (1) or (2), the arithmetic mean diameter a of the tungsten carbide particles may be 0.8 μm or more and 1.6 μm or less. This further improves the tool life.

[0048] (4) In any one of (1) to (3) above, the cobalt content of the cemented carbide may be 4 mass % or more and 11 mass % or less. This further improves the tool life.

[0049] (5) The cutting tool of the present disclosure is a cutting tool comprising the cemented carbide according to any one of (1) to (4). The cutting tool of the present disclosure is excellent in wear resistance and defect resistance and can have a long tool life.

[0050] [Details of the embodiments of the present disclosure]

[0051] Specific examples of the cemented carbide disclosed in the present invention will be described below.

[0052] In the present disclosure, the expression of the form "A to B" refers to the upper and lower limits of the range (i.e., greater than A and less than B). When there is no unit recorded in A and only the unit is recorded in B, the unit of A is the same as the unit of B.

[0053] In the present disclosure, when a compound or the like is represented by a chemical formula, unless there is a particular limitation on the atomic ratio, all conventionally known atomic ratios are included, and the atomic ratio is not necessarily limited to the atomic ratio within the stoichiometric range.

[0054] In the present disclosure, when more than one numerical value is recorded as the lower limit and the upper limit of the numerical range, a combination of any numerical value recorded as the lower limit and any numerical value recorded as the upper limit is also disclosed. For example, when more than a1, more than b1, and more than c1 are recorded as the lower limit, and less than a2, less than b2, and less than c2 are recorded as the upper limit, more than a1 and less than a2, more than a1 and less than b2, more than a1 and less than c2, more than b1 and less than a2, more than b1 and less than b2, more than b1 and less than c2, more than c1 and less than a2, more than c1 and less than b2, more than c1 and less than c2 are disclosed.

[0055] [Embodiment 1: Cemented Carbide]

[0056] A cemented carbide according to one embodiment of the present disclosure (hereinafter also referred to as “embodiment 1”) is a cemented carbide including a first phase, a second phase, and a third phase, wherein:

[0057] The first phase is composed of a plurality of tungsten carbide particles,

[0058] The content of the first phase of the cemented carbide is 65 volume % or more and 85 volume % or less,

[0059] The arithmetic mean diameter a of the tungsten carbide particles is greater than or equal to 0.5 μm and less than or equal to 2.0 μm.

[0060] The arithmetic mean diameter a and the standard deviation b of the particle diameter of the tungsten carbide particles are expressed in the following formula (I):

[0061] b<0.49a+0.063 Formula I

[0062] In the formula I, the units of a and b are μm,

[0063] The arithmetic mean diameter a and the 10% cumulative particle diameter c of the tungsten carbide particles based on the number of particles are related by the following formula II:

[0064] c>0.34a+0.098 Formula II

[0065] In the above formula II, the units of a and c are μm,

[0066] The second phase is composed of cobalt,

[0067] The cobalt content of the cemented carbide is 3 mass % or more and 15 mass % or less,

[0068] 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.

[0069] The third phase does not contain tungsten carbide,

[0070] The total content of titanium, tantalum, niobium, and zirconium in the cemented carbide is 2 mass % or more and 8 mass % or less.

[0071] When the cemented carbide disclosed in the present invention is used as a tool material, it is possible to provide a cutting tool that is excellent in wear resistance and defect resistance and can have a long tool life. The reason for this is not clear, but it is presumed as follows.

[0072] (i) The cemented carbide disclosed herein contains 65% by volume or more and 85% by volume or less of a first phase composed 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 disclosed herein also has high hardness and high thermal conductivity, and a cutting tool having the cemented carbide can have excellent wear resistance.

[0073] (ii) The cemented carbide disclosed herein contains 3% by mass or more and 15% by mass or less of cobalt. Cobalt has high toughness. Therefore, the cemented carbide disclosed herein also has high toughness, and a cutting tool having the cemented carbide can have excellent defect resistance.

[0074] (iii) The cemented carbide disclosed herein 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 resistance and oxidation resistance of the cemented carbide. Therefore, the reactivity resistance and oxidation resistance of the cutting tool having the cemented carbide are improved, thereby improving the wear resistance.

[0075] (iv) In the cemented carbide of the present disclosure, the arithmetic mean diameter a of the tungsten carbide particles is 0.5 μm or more and 2.0 μm or less, and the arithmetic mean diameter a and the standard deviation b of the particle diameter of the tungsten carbide particles are related by the following formula (I).

[0076] b<0.49a+0.063 Formula I

[0077] The standard deviation b is positively correlated with the arithmetic mean diameter a. This indicates that the tungsten carbide particles satisfying Formula I have high uniformity in particle size regardless of the size of the arithmetic mean diameter a.

[0078] In the cemented carbide disclosed herein, the arithmetic mean diameter a of the tungsten carbide particles and the 10% cumulative particle diameter c of the tungsten carbide particles on a number basis are related by the following formula II.

[0079] c>0.34a+0.098 Formula II

[0080] This indicates that the tungsten carbide particles satisfying Formula II have a small number of fine particles regardless of the size of the arithmetic mean diameter a.

[0081] When the particle size of the tungsten carbide particles satisfies Formula I and Formula II, the tungsten carbide particles can be uniformly present in the cemented carbide structure. In the cemented carbide disclosed in the present invention, since the tungsten carbide particles are uniformly present, the cutting heat generated by the cutting process is easily released to the outside of the cutting tool via the tungsten carbide particles. Therefore, the thermal conductivity of the tool having the cemented carbide disclosed in the present invention is improved, and even in high-speed processing where the tip temperature is easily increased, thermal wear is not easily generated, and excellent wear resistance can be achieved.

[0082] <First phase>

[0083] The composition of the first phase

[0084] In the cemented carbide of embodiment 1, the first phase is composed of a plurality of tungsten carbide particles. Here, the tungsten carbide particles include not only "pure WC particles (WC that does not contain any impurity elements, but also WC whose content of impurity elements is less than the detection limit)", but also "WC particles that contain impurities within the range that does not impair the effect of the present disclosure". Examples of impurities include iron (Fe), molybdenum (Mo), and sulfur (S).

[0085] 《Content ratio of the first phase of cemented carbide》

[0086] In the cemented carbide of embodiment 1, the content of the first phase of cemented carbide is more than 65 volume % and less than 85 volume %. From the viewpoint that hardness improves, the lower limit of the content of the first phase of cemented carbide is more than 65 volume %, can be more than 66 volume %, can be more than 70 volume %, can be more than 72 volume %, can also be more than 75 volume %. From the viewpoint that toughness improves, the upper limit of the content of the first phase of cemented carbide is less than 85 volume %, can be less than 84 volume %, can be less than 80 volume %, can also be less than 78 volume %. The content of the first phase of cemented carbide can be more than 70 volume % and less than 80 volume %, can also be more than 72 volume % and less than 84 volume %.

[0087] In the present disclosure, the content of the first phase of cemented carbide is measured by the following procedure.

[0088] (A1) Mirror finishing is performed on any surface or any cross section of the cemented carbide. As the mirror finishing method, for example, a method of grinding by diamond paste, a method using a focused ion beam device (FIB device), a method using a cross-section polishing device (CP device) and a method of combining these can be cited.

[0089] (B1) A reflected electron image is obtained by photographing the processed surface of cemented carbide using a scanning electron microscope ("S-3400N" manufactured by Hitachi High-Technologies Co., Ltd.). Six reflected electron images are prepared. The photographing areas of the six reflected electron images are different. The photographing part can be set arbitrarily. The conditions are set to an observation magnification of 5000 times and an acceleration voltage of 10 kV.

[0090] (C1) The six reflected electron images obtained by the above (B1) are imported into a computer through image analysis software (ImageJ, version 1.51j8: https: / / imagej.nih.gov / ij / ), and binarized to obtain six binarized images. The binarization process is performed by clicking the "Make Binary" display on the computer screen after importing the image, and the conditions pre-set for the image analysis software are performed. In the binarized image, the first area composed of the first phase and the second area composed of the second phase and the third phase can be identified by the depth of color. For example, in the binarized image, the first phase is represented by the black area, and the second phase and the third phase are represented by the white area.

[0091] (D1) Set a measurement field of view in the form of a rectangle with a length of 25.3 μm and a width of 17.6 μm in each of the six obtained binarized images. Using the above-mentioned image analysis software, in each of the six measurement fields of view, measure the area percentage (area %) of the first phase with the entire measurement field of view as the denominator.

[0092] (E1) Calculate the average of the area percentages (area %) of the first phase obtained in the six measurement fields of view. In the present disclosure, the average of the area percentages (area %) of the first phase obtained in the six measurement fields of view is defined as the content ratio (volume %) of the first phase of the cemented carbide.

[0093] It was confirmed that as long as it is within the range measured by the applicant and as long as the measurement is carried out on the same specimen, even if the selection position of the measurement field of view is changed and the above-mentioned measurement is carried out multiple times, the deviation of the measurement results is small, and even if the measurement field of view is arbitrarily set, it will not change randomly.

[0094] 《Arithmetic mean diameter a of tungsten carbide particles》

[0095] In the cemented carbide of Embodiment 1, the arithmetic mean diameter a of the tungsten carbide particles is 0.5 μm or more and 2.0 μm or less. In the present disclosure, the arithmetic mean diameter a of the tungsten carbide particles refers to the arithmetic mean based on the number of equivalent circle diameters of WC particles measured on the surface or cross-section of the cemented carbide. If the arithmetic mean diameter a of the WC particles is 0.5 μm or more, it is difficult for peeling wear to occur in a cutting tool using the cemented carbide. If the arithmetic mean diameter a of the WC particles is 2.0 μm or less, the cemented carbide has excellent flexural strength, and a cutting tool using the cemented carbide can have excellent resistance to chipping.

[0096] From the viewpoint of suppressing peeling wear, the lower limit of the arithmetic mean diameter a of the WC particles can be 0.50 μm or more, can be 0.60 μm or more, can be 0.70 μm or more, or can be 0.80 μm or more. From the viewpoint of improving flexural strength, the upper limit of the arithmetic mean diameter a of the WC particles can be 2.00 μm or less, can be 1.80 μm or less, can be 1.60 μm or less, or can be 1.40 μm or less. The arithmetic mean diameter a of the WC particles can be 0.50 μm or more and 2.00 μm or less, can be 0.60 μm or more and 1.80 μm or less, can be 0.70 μm or more and 1.60 μm or less, can be 0.80 μm or more and 1.60 μm or less, or can be 0.80 μm or more and 1.40 μm or less.

[0097] In the present disclosure, the arithmetic mean diameter a of the tungsten carbide particles is measured by the following steps (A2) to (B2).

[0098] (A2) Six images after binarization processing are obtained by the same method as (A1) to (C1) described in the method for measuring the content of the first phase of cemented carbide.

[0099] (B2) A rectangular measurement field of 25.3 μm in length and 17.6 μm in width was set in each of the six binarized images. The equivalent circle diameter (Heywood diameter: equivalent circle diameter of equal area) was measured for each of all tungsten carbide particles (first phase) in the six measurement fields using image analysis software (ImageJ, version 1.51j8: https: / / imagej.nih.gov / ij / ).

[0100] (C2) Based on all tungsten carbide particles except tungsten carbide particles with an equivalent circle diameter of 0.22 μm or less in the six measurement fields, the arithmetic mean of the number of equivalent circle diameters is calculated. In the present disclosure, the arithmetic mean is equivalent to the arithmetic mean diameter a of the WC particles. The reason for removing tungsten carbide particles with an equivalent circle diameter of 0.22 μm or less when calculating the arithmetic mean diameter a is because the present inventors have determined and confirmed that particles with an equivalent circle diameter of 0.22 μm or less are equivalent to the number of noises that are mistakenly detected as tungsten carbide particles in image analysis.

[0101] It was confirmed that as long as the measurement was performed within the range measured by the applicant and the measurement was performed on the same sample, there was little variation in the measurement results even if the selected site of the measurement field was changed and the measurement was performed multiple times, and there was no random change even if the measurement field was arbitrarily set.

[0102] 《Relationship between the arithmetic mean diameter a of tungsten carbide particles and the standard deviation b of the particle size of tungsten carbide particles》

[0103] In the cemented carbide of the first embodiment, the arithmetic mean diameter a of the tungsten carbide particles and the standard deviation b of the particle diameter of the tungsten carbide particles are related by the following formula (I).

[0104] b<0.49a+0.063 Formula I

[0105] In Formula I, the unit of a and b is μm.

[0106] The particle sizes of the multiple tungsten carbide particles included in the cemented carbide satisfy the relationship of formula I, which indicates that the particle size of the tungsten carbide particles has high uniformity regardless of the size of the arithmetic mean diameter a of the tungsten carbide particles. From the perspective of improving the uniformity of the particle size, the arithmetic mean diameter a and the standard deviation b can also be shown in the relationship of the following formulas IA and IB.

[0107] b<0.49a+0.061Formula IA

[0108] b<0.49a+0.059Formula IB

[0109] In the present disclosure, the standard deviation b of the particle size of tungsten carbide particles is determined by the following steps. The equivalent circle diameter (Heywood diameter: equal area equivalent circle diameter) is measured for each of all tungsten carbide particles (first phase) in six measurement fields of view by the same method as (A2) to (B2) described in the method for measuring the arithmetic mean diameter a of tungsten carbide particles. Based on all tungsten carbide particles in the six measurement fields of view, except for tungsten carbide particles with an equivalent circle diameter of 0.22 μm or less, the standard deviation b of the particle size of tungsten carbide particles is calculated by the following formula.

[0110] [Mathematical formula 1]

[0111]

[0112] In the above formula, s represents the standard deviation b, n represents the number of tungsten carbide particles, and x i represents the equivalent circle diameter of each tungsten carbide particle, It represents the arithmetic mean diameter a of tungsten carbide particles.

[0113] In the cemented carbide of the first embodiment, the arithmetic mean diameter a of the tungsten carbide particles and the 10% cumulative particle diameter c of the tungsten carbide particles on a number basis are related by the following formula II.

[0114] c>0.34a+0.098 Formula II

[0115] In Formula II, the unit of a and c is μm. In the present disclosure, the 10% cumulative particle size c of tungsten carbide particles based on number refers to the cumulative 10% particle size from the smaller diameter side in the cumulative particle size distribution based on number of tungsten carbide particles.

[0116] The particle sizes of the multiple tungsten carbide particles contained in the cemented carbide satisfy the relationship of formula II, which indicates that there are fewer tiny tungsten carbide particles regardless of the size of the arithmetic mean diameter a of the tungsten carbide particles. From the perspective of reducing the number of tiny tungsten carbide particles, the arithmetic mean diameter a and the 10% cumulative particle size c can also be shown in the relationship of the following formulas II-A and II-B.

[0117] c>0.34a+0.099Formula II-A

[0118] c>0.34a+0.100 Formula II-B

[0119] In the present disclosure, the 10% cumulative particle size c of the tungsten carbide particles on a number basis is measured by the following steps. The equivalent circle diameter (Heywood diameter: equal area equivalent circle diameter) is measured for each of all tungsten carbide particles (first phase) in the six measurement fields of view by the same method as (A2) to (B2) described in the method for measuring the arithmetic mean diameter a of the tungsten carbide particles. The 10% cumulative particle size c on a number basis is calculated based on all tungsten carbide particles in the six measurement fields of view except for tungsten carbide particles with an equivalent circle diameter of 0.22 μm or less.

[0120] The cemented carbide of embodiment 1 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. Here, the third phase does not include tungsten carbide. The third phase is added for the purpose of improving the reactivity resistance and oxidation resistance of the cemented carbide. However, since the thermal conductivity of the third phase is low, when the cemented carbide including the third phase is used under cutting conditions such as high-speed machining where the tip temperature is easily increased, the tip temperature becomes high, thermal wear is easily advanced, and the wear resistance of the cutting tool tends to decrease. In the cemented carbide of embodiment 1, since the particle size distribution of the tungsten carbide particles satisfies the above-mentioned formula I and formula II, the tungsten carbide particles can be uniformly present in the cemented carbide structure, and the cutting heat generated by the cutting process is easily released to the outside of the cutting tool through the tungsten carbide particles. Therefore, even if the tool of the cemented carbide disclosed in the present invention includes the third phase, the thermal conductivity is improved, thermal wear is not easily generated, and excellent wear resistance can be achieved.

[0121] <Phase 2>

[0122] The composition of the second phase

[0123] In the cemented carbide of Embodiment 1, the second phase is composed of cobalt. The second phase is a bonding phase that bonds tungsten carbide particles constituting the first phase.

[0124] In the present disclosure, “the second phase is composed of cobalt (Co)” also includes the case where “the second phase contains cobalt and impurities within a range that does not impair the effects of the present disclosure.” Examples of impurities include manganese (Mn), magnesium (Mg), calcium (Ca), molybdenum (Mo), sulfur (S), and aluminum (Al).

[0125] 《Cobalt content of cemented carbide》

[0126] In the cemented carbide of embodiment 1, the cobalt content of cemented carbide is more than 3 mass % and less than 15 mass %. From the viewpoint that toughness improves, the lower limit of the cobalt content of cemented carbide is more than 3 mass %, can be more than 4 mass %, can be more than 5 mass %, can also be more than 6 mass %. From the viewpoint that hardness improves, the upper limit of the cobalt content of cemented carbide is less than 15 mass %, can be less than 11 mass %, can also be less than 9 mass %. The cobalt content of cemented carbide can be more than 4 mass % and less than 11 mass %, can also be more than 5 mass % and less than 9 mass %.

[0127] In the present disclosure, the cobalt content of cemented carbide is determined by cobalt titration. The cobalt titration is performed in accordance with the Japan Machine Tool Industry Association Standard (TAS0054: 2017) or ISO3909: 1976. Specifically, it is performed by the following steps. The sample composed of cemented carbide is crushed and passed through a 49-mesh sieve. After dissolving the sample in nitric acid and hydrofluoric acid, adding ammonium citrate and ammonia water, a platinum and saturated calomel (tungsten) electrode is used to perform potentiometric titration using potassium ferrocyanide (red blood salt). The measuring device used is "AUT-501" manufactured by DKK East Asia.

[0128] <Phase 3>

[0129] The composition of the third phase

[0130] 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 and oxidation resistance of the cemented carbide. Therefore, the reactivity and oxidation resistance of the cutting tool equipped with the cemented carbide are improved.

[0131] 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 within a range that does not impair the effects of the present disclosure.” Examples of impurities include manganese (Mn), magnesium (Mg), calcium (Ca), molybdenum (Mo), sulfur (S), and aluminum (Al).

[0132] The third phase may also contain at least two elements selected from the group consisting of titanium, tantalum, niobium, zirconium, and tungsten.

[0133] The third phase may include, for example, 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 solution include WTiCN, WTiTaCN, and WTiTaNbZrCN.

[0134] 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.

[0135] (A3) Use an ion microtome (device: IB09060CIS (trademark) manufactured by JEOL Ltd.) to slice any position of the cemented carbide to prepare a sample with a thickness of 30 to 100 nm. The acceleration voltage of the ion microtome is 6 kV for the thinning process and 2 kV for the finishing process.

[0136] (B3) The sample was observed at 50,000 times using a scanning transmission electron microscope (STEM) (device: JFM-ARM300F (trademark) manufactured by JEOL Ltd.) to obtain a STEM-HAADF (high-angle annular dark fields scanning transmission electron microscope) image. The shooting area of ​​the STEM-HAADF image was set to the central part of the sample, i.e., the position of the part where the properties are obviously different from the main part, such as the surface vicinity of the cemented carbide, which does not include the cemented carbide (the shooting area is the position of the main part of the cemented carbide). The measurement condition is an acceleration voltage of 200 kV.

[0137] (C3) For the third phase present in the STEM-HAADF image, point analysis is performed by EDX (STEM-EDX) attached to STEM to quantify the elements constituting the third phase. For each third phase, the point size is set within a range that only includes the third phase. As a result of quantifying the constituent elements, 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 when the following (a) and (b) are satisfied.

[0138] (a) At least one element selected from the group consisting of titanium, tantalum, niobium, zirconium, and tungsten, and at least one of carbon and nitrogen exist in the third phase.

[0139] (b) No impurity elements other than titanium, tantalum, niobium, zirconium, tungsten, carbon, and nitrogen are confirmed in the third phase, or the content of these impurity elements is less than 0.1 mass %.

[0140] As a result of performing point analysis on the third phase by the EDX (STEM-EDX), when only tungsten and carbon are detected and the content of carbon relative to the total mass of tungsten and carbon is about 6.1 mass %, it is judged that the third phase contains tungsten carbide. In other words, as a result of performing point analysis on the third phase by the EDX (STEM-EDX), when elements other than tungsten and carbon are confirmed, it is judged that the third phase does not contain tungsten carbide.

[0141] 《Total content of titanium, tantalum, niobium and zirconium in cemented carbide》

[0142] In the cemented carbide of embodiment 1, the total content of titanium, tantalum, niobium and zirconium in the cemented carbide is more than 2 mass % and less than 8 mass %. From the viewpoint of improving reactivity and oxidation resistance, the lower limit of the total content of titanium, tantalum, niobium and zirconium in the cemented carbide is more than 2 mass %, which can be more than 3 mass %, or more than 4 mass %. From the viewpoint of improving the thermal conductivity of the cemented carbide, the upper limit of the total content of titanium, tantalum, niobium and zirconium in the cemented carbide is less than 8 mass %, which can be less than 7 mass %, or less than 6 mass %. The total content of titanium, tantalum, niobium and zirconium in the cemented carbide is more than 2 mass % and less than 8 mass %, which can be more than 3 mass % and less than 7 mass %, or more than 4 mass % and less than 6 mass %. Here, the third phase can also include at least two elements selected from the group consisting of titanium, tantalum, niobium, zirconium and tungsten. In the present disclosure, when the cemented carbide contains all of titanium, tantalum, niobium and zirconium, the total content of titanium, tantalum, niobium and zirconium in the cemented carbide refers to the total content of all these elements, and when the cemented carbide contains one or more and three or less elements selected from the group consisting of titanium, tantalum, niobium and zirconium, the total content of titanium, tantalum, niobium and zirconium in the cemented carbide represents the total content of the contained elements.

[0143] In the present disclosure, the total content of titanium, tantalum, niobium, and zirconium in the cemented carbide is measured by ICP emission spectrometry. In the present disclosure, the measuring apparatus for ICP emission spectrometry is "ICPS-8100" (trademark) manufactured by Shimadzu Corporation.

[0144] <Arithmetic mean diameter of the second area>

[0145] In the cemented carbide of Embodiment 1, in a first image obtained by binarizing a reflected electron image of a cross-section of the cemented carbide, there is a first region composed of a first phase and a second region composed of a second phase and a third phase. In the first image, the arithmetic mean diameter d of the second region may also be 0.3 μm or more and 0.9 μm or less. The reflected electron image is obtained by photographing a cross-section of the cemented carbide at a magnification of 5000 times using a scanning electron microscope. From the viewpoint of improving wear resistance due to suppression of particle detachment, the lower limit of the arithmetic mean diameter d of the second region may be 0.3 μm or more, may be 0.4 μm or more, or may be 0.5 μm or more. From the viewpoint of improving wear resistance due to suppression of uneven wear, the upper limit of the arithmetic mean diameter d of the second region may be 0.9 μm or less, may be 0.8 μm or less, or may be 0.7 μm or less. The arithmetic mean diameter d of the second region may be 0.4 μm or more and 0.8 μm or less, or may be 0.5 μm or more and 0.7 μm or less.

[0146] In the present disclosure, the arithmetic mean diameter d of the second region is measured by the following steps (A4) to (B4).

[0147] (A4) Six binarized images are obtained by the same method as (A1) to (C1) described in the method for measuring the content ratio of the first phase of the cemented carbide.

[0148] (B4) A rectangular measurement field of 25.3 μm in length × 17.6 μm in width is set in each of the six obtained binarized images. Using image analysis software (ImageJ, version 1.51j8: https: / / imagej.nih.gov / ij / ), for each of all the second regions in the six measurement fields, the equivalent circle diameter (Heywood diameter: equivalent circle diameter of equal area) is measured. Based on all the second regions in the six measurement fields, the arithmetic mean value on a number basis of the equivalent circle diameters is calculated. In the present disclosure, this arithmetic mean value corresponds to the arithmetic mean diameter d of the second region.

[0149] It has been confirmed that as long as it is within the range measured by the applicant and as long as the measurement is performed on the same specimen, even if the selection position of the measurement field is changed and the above measurement is performed multiple times, the deviation of the measurement result is small, and even if the measurement field is arbitrarily set, it will not change randomly.

[0150] 《Chromium content ratio》

[0151] The cemented carbide of embodiment 1 can contain chromium (Cr). Chromium has a grain growth inhibitory effect on tungsten carbide particles. In the cemented carbide, the percentage of the mass of chromium relative to the mass of cobalt can also be more than 0% and less than 8%. Thus, it is possible to effectively suppress the tiny WC particles of the raw material from remaining as they are in the obtained cemented carbide, and it is possible to effectively suppress the generation of coarse particles, thereby improving the tool life. In the cemented carbide, if the percentage of the mass of chromium relative to the mass of cobalt exceeds 8%, the solid solubility limit of chromium to cobalt is exceeded, and chromium is precipitated into the cemented carbide in the form of carbides, etc., and the defect resistance of the cemented carbide tends to deteriorate.

[0152] From the viewpoint of improving defect resistance, in cemented carbide, the upper limit of the percentage of the mass of chromium relative to the mass of cobalt can be 7% or less, or 6% or less. In cemented carbide, from the viewpoint of suppressing the generation of coarse particles, the lower limit of the percentage of the mass of chromium relative to the mass of cobalt can be 1% or more, or 2% or more. In cemented carbide, the percentage of the mass of chromium relative to the mass of cobalt can be 1% or more and 7% or more, or 2% or more and 6% or less.

[0153] The chromium content of the cemented carbide was measured by ICP emission spectrometry.

[0154] 《Zirconium content》

[0155] The cemented carbide of embodiment 1 can contain zirconium (Zr). Zirconium has the effect of improving the high temperature hardness of cemented carbide. In cemented carbide, the percentage of the mass of zirconium relative to the mass of cobalt can also be more than 0% and less than 6%. Thus, since the high temperature hardness of cemented carbide is improved, the tool life is improved. In cemented carbide, if the percentage of the mass of zirconium relative to the mass of cobalt exceeds 6%, the solid solubility limit of zirconium to cobalt is exceeded, and zirconium is precipitated into cemented carbide in the form of carbides, etc., and the defect resistance of cemented carbide tends to deteriorate.

[0156] In cemented carbide, from the viewpoint of balancing defect resistance and high temperature hardness improvement, the upper limit of the percentage of the mass of zirconium relative to the mass of cobalt may be 5% or less, or 4% or less. In cemented carbide, from the viewpoint of high temperature hardness improvement, the lower limit of the percentage of the mass of zirconium relative to the mass of cobalt may be 0.5% or more, or 1% or more. In cemented carbide, the percentage of the mass of zirconium relative to the mass of cobalt may be 0.5% or more and 5% or 1% or more and 4% or less.

[0157] The zirconium content of the cemented carbide was measured by ICP emission spectrometry.

[0158] <Composition of cemented carbide>

[0159] The cemented carbide of embodiment 1 includes a first phase, a second phase, and a third phase. The cemented carbide of embodiment 1 may also be composed of a first phase, a second phase, and a third phase. Without prejudice to the effect of the present disclosure, the cemented carbide of embodiment 1 may include other phases on the basis of including the first phase, the second phase, and the third phase. As other phases, for example, chromium carbides may be cited. Without prejudice to the effect of the present disclosure, the cemented carbide of embodiment 1 may include impurities on the basis of including the first phase, the second phase, and the third phase. Impurities may include, for example, 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 elements constituting the impurities are two or more, it is their total concentration.) may also be less than 0.1% by mass. The content of impurities in the cemented carbide may be determined by ICP emission spectrometry.

[0160] <Method of manufacturing cemented carbide>

[0161] The cemented carbide of the first embodiment can be produced by, for example, performing a raw material powder preparation step, a mixing step, a molding step, a sintering step, and a cooling step in the above order.

[0162] 《Raw material powder preparation process》

[0163] In the raw material powder preparation step, all raw material powders of the materials constituting cemented carbide are prepared. As raw material powders, tungsten carbide powder as a raw material for the first phase, cobalt (Co) powder as a raw material for the second phase, titanium carbide (TiC) powder, titanium nitride (TiN) powder, tantalum carbide (TaC) powder, niobium carbide (NbC) powder, and zirconium carbide (ZrC) powder as raw materials for the third phase are prepared (hereinafter, these are collectively referred to as "third phase raw material powders"). Chromium carbide (Cr) can be prepared as a grain growth inhibitor as needed. 3 C 2 ) powder. These raw material powders can use commercially available raw material powders.

[0164] As tungsten carbide powder (hereinafter, also referred to as "WC powder"), tungsten carbide powder with uniform particle size is prepared. Specifically, a WC powder having an average particle size of 1.5 μm or more and 6.0 μm or less and a particle size distribution in which the ratio d10 / d90 of the 10% cumulative particle size d10 on a volume basis to the 90% cumulative particle size d90 on a volume basis is 0.2 or more and 0.5 or less is prepared. In the present disclosure, the particle size of each WC particle contained in the WC powder is measured by the FSSS (Fisher Sub-Sieve Sizer) method. The measuring machine used for the FSSS method is the "Sub-Sieve Sizer model 95" (trademark) manufactured by Fisher Scientific. The distribution of the particle size of the WC powder is measured using a particle size distribution measuring device (trade name: MT3300EX) manufactured by Microtrac.

[0165] The average particle size of the cobalt powder can be set to be greater than 0.5 μm and less than 3.0 μm. The average particle size of the third phase raw material particles can be set to be greater than 0.5 μm and less than 4.0 μm. The average particle size of the chromium carbide powder can be set to be greater than 1.0 μm and less than 2.0 μm. In the present disclosure, the average particle size of these powders refers to the average particle size measured by the FSSS (Fisher Sub-Sieve Sizer) method. The average particle size is measured using the "Sub-Sieve Sizer model 95" (trademark) manufactured by Fisher Scientific.

[0166] 《Mixing process》

[0167] 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.

[0168] As a mixing method, a method that can maintain a uniform particle size of the WC powder in the mixed powder after mixing is used. Specifically, a ball mill is used to make the medium diameter smaller than before, reduce the rotation speed, and shorten the mixing time. In this way, the crushing of the WC particles can be suppressed. The medium diameter can be set to, for example, more than 5 mm and less than 10 mm. The rotation speed can be set to, for example, more than 15 rpm and less than 30 rpm. The mixing time can be set to, for example, more than 15 hours and less than 36 hours. If the mixing time is less than 15 hours, it is easy to produce voids in the cemented carbide due to insufficient mixing.

[0169] If a mixing method with a strong crushing force (e.g., a grinder) is used, even if the particle size of the raw material WC powder is uniform, the WC particles as a whole are finely crushed by mixing, and the particle size of the mixed WC powder becomes fine, and coarse particles are generated due to grain growth during sintering. Therefore, in the manufacturing method of this embodiment, a mixing method with a strong crushing force is not used.

[0170] The mixed powder may be granulated as required after the mixing step. Granulation of the mixed powder makes it easy to fill the mixed powder into a die or mold during the forming step described later. For granulation, a known granulation method may be applied, for example, a commercially available granulator such as a spray dryer may be used.

[0171] 《Forming process》

[0172] The forming step is a step of forming the mixed powder obtained in the mixing step into a predetermined shape to obtain a formed body. The forming method and forming conditions in the forming step can be general methods and conditions, and are not particularly limited. As the predetermined shape, for example, a cutting tool shape can be cited.

[0173] 《Sintering process》

[0174] In the sintering step, the formed body obtained in the forming step is sintered to obtain a cemented carbide. In the method for manufacturing a cemented carbide disclosed herein, the sintering temperature can be set to 1380° C. or higher and 1500° C. or lower. Thus, the particle size of the WC particles in the cemented carbide can be made uniform. In addition, the generation of fine WC particles and coarse WC particles can be suppressed.

[0175] If the sintering temperature is lower than 1380° C., voids are generated in the cemented carbide, and the defect resistance of the cemented carbide is reduced. If the sintering temperature exceeds 1500° C., the WC particles are coarsened due to grain growth, and the particle size of the WC particles becomes non-uniform.

[0176] 《Cooling process》

[0177] The cooling step is a step of cooling the cemented carbide after sintering. The cooling conditions may be general conditions and are not particularly limited.

[0178] [Embodiment 2: Cutting Tool]

[0179] The cutting tool of embodiment 2 is provided with the cemented carbide of embodiment 1. The cutting tool of embodiment 2 can include at least a cutting edge formed of the cemented carbide of embodiment 1. In the present disclosure, the cutting edge refers to a portion involved in cutting, and in cemented carbide, refers to the cutting edge ridge and an area within 0.5 mm from the cutting edge ridge to the cemented carbide side.

[0180] Examples of the cutting tool include a cutting tool, a drill, an end mill, an indexable cutting insert for milling, an indexable cutting insert for turning, a metal saw, a gear cutting tool, a reamer, a tap, and the like.

[0181] The cemented carbide of the second embodiment may constitute the whole of these tools or a part thereof. Here, "constituting a part" means that the cemented carbide of the second embodiment is welded to a predetermined position of any base material to form a cutting edge portion.

[0182] The cutting tool of the second embodiment may further include a hard film covering at least a portion of the surface of the substrate composed of cemented carbide. As the hard film, for example, diamond-like carbon, diamond, Al 2 O 3 Or a film composed of TiCN. The hard film may also be a CVD film formed by a chemical vapor deposition method (CVD method).

[0183] Example

[0184] The present embodiment will be described in more detail by way of examples, but the present embodiment is not limited to these examples.

[0185] <Production of cemented carbide>

[0186] 《Preparation process》

[0187] As raw material powder, powders of the composition shown in the "Raw Material Powder" column of Table 1 were prepared. For tungsten carbide (WC) powder, a plurality of tungsten carbide (WC) powders having different average particle sizes and particle size distributions were prepared. The average particle size and d10 / d90 of the WC powder are shown in the "Average Particle Size (μm)" and "d10 / d90" columns of "WC" in "Raw Material Powder" of Table 1, respectively.

[0188] The average particle size of cobalt (Co) powder is 1.2 μm, and the chromium carbide (Cr 3 C 2 ) powder has an average particle size of 1.5 μm, the average particle size of titanium carbide (TiC) powder is 1.5 μm, the average particle size of titanium nitride (TiN) powder is 2.0 μm, the average particle size of tantalum carbide (TaC) powder is 1.0 μm, the average particle size of niobium carbide (NbC) powder is 1.1 μm, and the average particle size of zirconium carbide (ZrC) powder is 1.5 μm.

[0189] 《Mixing process》

[0190] The raw material powders were mixed in the amounts shown in the "mass %" column of "Raw Materials" in Table 1 to prepare mixed powders. The "mass %" in the "Raw Materials" column of Table 1 represents the percentage of the mass of each raw material powder relative to the total mass of the raw material powders. The mixing was performed using a ball mill. The media diameter was set to 8 mm. The rotation speed and mixing time in each sample are as shown in the "rotation speed" and "time" columns of "mixing" in Table 2. The obtained mixed powder was spray-dried to form a granulated powder.

[0191] Table 1

[0192]

[0193] 《Forming process》

[0194] The obtained granulated powder was press-molded to produce a blade-shaped compact.

[0195] 《Sintering process》

[0196] The compact was placed in a sintering furnace and sintered in a vacuum at the temperature and time shown in the "Temperature" and "Time" columns of "Sintering" in Table 2.

[0197] 《Cooling process》

[0198] After sintering, the material was slowly cooled in an argon (Ar) atmosphere to obtain a cemented carbide.

[0199] Table 2

[0200]

[0201] <Evaluation of cemented carbide>

[0202] 《Composition of Cemented Carbide》

[0203] For each sample of cemented carbide, the first phase content of the cemented carbide, the cobalt content of the cemented carbide, and the total content of titanium, tantalum, niobium, and zirconium in the cemented carbide were measured. The specific measurement method is shown in the description of Implementation Example 1. The results are shown in the "First Phase Content", "Co Content", and "Total Content of Ti, Ta, Zr, and Nb" columns of "Cemented Carbide" in Table 3. The description of "Ti, Ta, Zr, and Nb Content" does not necessarily mean that each sample contains all of Ti, Ta, Zr, and Nb.

[0204] 《Arithmetic mean diameter a, standard deviation b, 10% cumulative particle size c of tungsten carbide particles》

[0205] For each sample of cemented carbide, the arithmetic mean diameter a, standard deviation b, and 10% cumulative particle size c of the tungsten carbide particles were measured. The specific measurement method is as described in Implementation Example 1. The results are shown in the "arithmetic mean diameter a", "standard deviation b", and "10% cumulative particle size c" columns of the "WC particles" of the "first phase" in Table 3.

[0206] Based on the “arithmetic mean diameter a”, “standard deviation b” and “10% cumulative particle size c” of each sample, it was confirmed whether the relationship of the following formula I and formula II was satisfied in each sample.

[0207] b<0.49a+0.063 Formula I

[0208] c>0.34a+0.098 Formula II

[0209] The results are shown in the "Formula I" and "Formula II" columns of Table 3. In "Formula I", "yes" means that the relationship of Formula I is satisfied, and "no" means that the relationship of Formula I is not satisfied. In "Formula II", "yes" means that the relationship of Formula II is satisfied, and "no" means that the relationship of Formula II is not satisfied.

[0210] The composition of the second phase

[0211] In all samples, it was confirmed that the second phase was composed of cobalt.

[0212] The composition of the third phase

[0213] In each sample, the elements contained in the third phase were determined by STEM-EDX. The specific determination method is as described in Implementation Example 1. The results are shown in the "Composition" column of "Third Phase" in Table 4. In all samples, it was confirmed that the third phase was composed of the elements described in Table 4 and that the third phase did not contain tungsten carbide.

[0214] 《Arithmetic mean diameter d of the second region》

[0215] In each sample, the arithmetic mean diameter d of the second region was measured. The specific measurement method is as described in Embodiment 1. The results are shown in the "arithmetic mean diameter d" column of the "second region" of the "first image" in Table 4.

[0216] Table 3

[0217]

[0218] Table 4

[0219]

[0220] <Cutting test 1>

[0221] The cutting tool (tool model: CNMG120408N-GU (manufactured by Sumitomo Electric Hardmetal Co., Ltd.)) of each sample was used for turning under the following conditions, and the average wear amount Vb (mm) of the flank side of the cutting tool after cutting for 15 minutes 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 0.35 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 of Table 5.

[0222] 《Cutting conditions》

[0223] Cutting material: S45C

[0224] Processing: Round bar outer diameter turning

[0225] Cutting speed: 350m / min

[0226] Feed rate: 0.25mm / rev

[0227] Cutting amount: 2.0mm

[0228] Cutting fluid: water-soluble cutting oil

[0229] The above cutting conditions are equivalent to high-speed machining.

[0230] <Cutting test 2>

[0231] 20 cutting tools of each sample (tool model: CNMG120408N-GU (manufactured by Sumitomo Electric Hardmetal Co., Ltd.)) were prepared, and turning was performed under the following conditions, and the breakage rate (%) after cutting for 20 seconds was measured. The smaller the breakage rate, the better the defect resistance and the longer the tool life. In cutting test 2, when the breakage rate was 25% or less, the tool life was judged to be long. The results are shown in the "Cutting Test 2" column of Table 5.

[0232] 《Cutting conditions》

[0233] Cutting material: SCM440 (round bar with grooves)

[0234] Processing: intermittent turning of the outer diameter of a grooved round bar

[0235] Cutting speed: 120m / min

[0236] Feed rate: 0.15mm / rev

[0237] Cutting amount: 2.0mm

[0238] Cutting fluid: None

[0239] In the present embodiment, when the average wear amount Vb in the cutting test 1 is 0.35 mm or less and the breakage rate in the cutting test 2 is 25% or less, it is determined that the tool life is long.

[0240] Table 5

[0241]

[0242] <Investigation>

[0243] The cemented carbides and cutting tools of samples 1 to 22 correspond to the examples. The cemented carbides and cutting tools of samples 101 to 112 correspond to the comparative examples. Samples 1 to 22 have excellent wear resistance and defect resistance, and show long tool life in both cutting test 1 and cutting test 2. The wear resistance of samples 101, 104 to 106, 108, 109, and 112 is insufficient, and the tool life is insufficient in cutting test 1. The defect resistance of samples 102, 103, 107, 110, and 111 is insufficient, and the tool life is insufficient in cutting test 2.

[0244] As mentioned above, although the embodiment and the example of this disclosure were described, it is also planned that the configurations of each embodiment and the example described above may be appropriately combined or variously modified.

[0245] The embodiments and examples disclosed herein are illustrative in all aspects and are not restrictive. The scope of the present invention is indicated by the claims rather than the embodiments and is intended to include all modifications within the scope and meaning equivalent to the claims.

Claims

1. A cemented carbide, comprising a first phase, a second phase, and a third phase. in, The first phase is composed of a plurality of tungsten carbide particles, The content of the first phase of the cemented carbide is 65 volume % or more and 85 volume % or less, The arithmetic mean diameter a of the tungsten carbide particles is greater than or equal to 0.5 μm and less than or equal to 2.0 μm. The arithmetic mean diameter a and the standard deviation b of the particle diameter of the tungsten carbide particles are expressed in the following formula (I): b<0.49a+0.063 Formula I In the formula I, the units of a and b are μm, The arithmetic mean diameter a and the 10% cumulative particle diameter c of the tungsten carbide particles based on the number of particles are related by the following formula II: c>0.34a+0.098 Formula II In the above formula II, the units of a and c are μm, The second phase is composed of cobalt, The cobalt content of the cemented carbide is 3 mass % or more and 15 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 contain tungsten carbide, The total content of titanium, tantalum, niobium, and zirconium in the cemented carbide is 2 mass % or more and 8 mass % or less.

2. The cemented carbide according to claim 1, in, In a first image obtained by binarizing the reflected electron image of the cross section of the cemented carbide, there is a first region composed of the first phase and a second region composed of the second phase and the third phase. In the first image, the arithmetic mean diameter d of the second region is greater than or equal to 0.3 μm and less than or equal to 0.9 μm, The reflected electron image is obtained by photographing a cross section of the cemented carbide at 5000 times magnification using a scanning electron microscope.

3. The cemented carbide according to claim 1 or claim 2, in, The arithmetic mean diameter a of the tungsten carbide particles is greater than or equal to 0.8 μm and less than or equal to 1.6 μm.

4. The cemented carbide according to any one of claims 1 to 3, in, The cobalt content of the cemented carbide is 4 mass % or more and 11 mass % or less.

5. A cutting tool, in, The cutting tool includes the cemented carbide according to any one of claims 1 to 4 .

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