Hardmetal and cutting tools

Abstract

A cemented carbide including a first phase, a second phase, and a third phase, the first phase being composed of a plurality of tungsten carbide particles, the content of the first phase in the cemented carbide being 65% by volume or more and 85% by volume or less, the arithmetic mean diameter a of the tungsten carbide particles being 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 satisfy the relationship of 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 based on the number of the tungsten carbide particles satisfy the relationship of the following formula II, c>0.34a+0.098 Formula II In the above formula II, the units of a and c are μm, a cemented carbide, wherein the second phase is made of cobalt, and the cobalt content of the cemented carbide is 3% by mass or more and 15% by mass or less; the third phase is made 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; and the total content of titanium, tantalum, niobium, and zirconium in the cemented carbide is 2% by mass or more and 8% by mass or less.

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 a phase composed of at least one composite compound of carbide, nitride, and carbonitride containing tungsten (W) and a metal element other than W, in addition to the hard phase mainly composed of WC, and improves chipping resistance by bonding WC particles and composite compound particles. [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 tungsten carbide particles have an arithmetic mean diameter a of 0.5 μm or more and 2.0 μm or less, The arithmetic mean diameter a and the standard deviation b of the particle diameter of the tungsten carbide particles satisfy 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 based on the number of the tungsten carbide particles satisfy the relationship of 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 consists of cobalt; The cobalt content 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 of titanium, tantalum, niobium and zirconium in the cemented carbide is 2% by mass or more and 8% by mass or less. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0005] [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.

[0006] 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.

[0007] [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.

[0008] [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 tungsten carbide particles have an arithmetic mean diameter a of 0.5 μm or more and 2.0 μm or less, The arithmetic mean diameter a and the standard deviation b of the particle diameter of the tungsten carbide particles satisfy 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 based on the number of the tungsten carbide particles satisfy the relationship of 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 consists of cobalt; The cobalt content 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 of titanium, tantalum, niobium and zirconium in the cemented carbide is 2% by mass or more and 8% by mass or less.

[0009] 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.

[0010] (2) In the above (1), a first image obtained by performing a binarization process on a backscattered electron image of a cross section of the cemented carbide includes a first region consisting of the first phase and a second region consisting of the second phase and the third phase, In the first image, an arithmetic mean diameter d of the second region may be 0.3 μm or more and 0.9 μm or less. The backscattered electron image is obtained by photographing a cross section of the cemented carbide at 5000 times magnification using a scanning electron microscope.

[0011] According to this, the presence of the second region with an appropriate grain size improves the wear resistance of the cemented carbide. If the grain size of the second region is small, there is a tendency for wear due to falling off to progress during cutting. If the grain size of the second region is large, that is, if there is variation in the location of the region, uneven wear tends to progress and wear resistance tends to decrease.

[0012] (3) In the above (1) or (2), the tungsten carbide particles may have an arithmetic mean diameter a of 0.8 μm or more and 1.6 μm or less, thereby further improving the tool life.

[0013] (4) In any one of the above (1) to (3), the cobalt content of the cemented carbide may be 4 mass % or more and 11 mass % or less, thereby further improving the tool life.

[0014] (5) A cutting tool according to the present disclosure is a cutting tool comprising the cemented carbide according to any one of (1) to (4) above. The cutting tool according to the present disclosure has excellent wear resistance and chipping resistance and can have a long tool life.

[0015] [Details of the embodiment of the present disclosure] Specific examples of the cemented carbide of the present disclosure are described below.

[0016] 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.

[0017] In the present disclosure, when a compound or the like is represented by a chemical formula, unless the atomic ratio is particularly limited, it is intended to include any conventionally known atomic ratio, and should not necessarily be limited to only those within the stoichiometric range.

[0018] In the present disclosure, when one or more numerical values ​​are 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.

[0019] [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 tungsten carbide particles have an arithmetic mean diameter a of 0.5 μm or more and 2.0 μm or less, The arithmetic mean diameter a and the standard deviation b of the particle diameter of the tungsten carbide particles satisfy 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 based on the number of the tungsten carbide particles satisfy the relationship of 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 consists of cobalt; The cobalt content 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 of titanium, tantalum, niobium and zirconium in the cemented carbide is 2% by mass or more and 8% by mass or less.

[0020] 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.

[0021] (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.

[0022] (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.

[0023] (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.

[0024] (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 satisfy the relationship of the following formula I. b<0.49a+0.063 Formula I The standard deviation b has a positive correlation with the arithmetic mean diameter a. Tungsten carbide particles that satisfy formula I exhibit high particle size uniformity regardless of the magnitude of the arithmetic mean diameter a. In the cemented carbide of the present disclosure, the arithmetic mean diameter a of the tungsten carbide particles and the 10% cumulative particle diameter c based on the number of the tungsten carbide particles satisfy the relationship represented by the following formula II. c>0.34a+0.098 Formula II Tungsten carbide particles satisfying formula II exhibit few fine particles, regardless of the magnitude of the arithmetic mean diameter a. 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 of the present disclosure, the tungsten carbide particles are uniformly present, so that the cutting heat generated during cutting is easily released to the outside of the cutting tool via the tungsten carbide particles. Therefore, the tool including the cemented carbide of the present disclosure has improved thermal conductivity, and is less likely to suffer from thermal wear even in high-speed cutting where the cutting edge temperature is likely to rise, and has excellent wear resistance.

[0025] <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).

[0026] <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 80 volume% or less, or may be 72 volume% or more and 84 volume% or less.

[0027] 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.

[0028] (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.

[0029] (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.

[0030] (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.

[0031] (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.

[0032] 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.

[0033] <Arithmetic mean diameter a of tungsten carbide particles> In the cemented carbide of the first embodiment, 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 means the arithmetic mean of the circle equivalent diameter of the WC particles measured on the surface or cross section of the cemented carbide based on the number of pieces. When the arithmetic mean diameter a of the WC particles is 0.5 μm or more, the cutting tool using the cemented carbide is less likely to suffer from shedding wear during use. When the arithmetic mean diameter a of the WC particles is 2.0 μm or less, the cemented carbide has excellent transverse strength, and the cutting tool using the cemented carbide can have excellent chipping resistance.

[0034] The lower limit of the arithmetic mean diameter a of the WC particles may be 0.50 μm or more, 0.60 μm or more, 0.70 μm or more, or 0.80 μm or more from the viewpoint of suppressing shedding wear. The upper limit of the arithmetic mean diameter a of the WC particles may be 2.00 μm or less, 1.80 μm or less, 1.60 μm or less, or 1.40 μm or less from the viewpoint of improving transverse rupture strength. The arithmetic mean diameter a of the WC particles may be 0.50 μm or more and 2.00 μm or less, 0.60 μm or more and 1.80 μm or less, 0.70 μm or more and 1.60 μm or less, 0.80 μm or more and 1.60 μm or less, or 0.80 μm or more and 1.40 μm or less.

[0035] In the present disclosure, the arithmetic mean diameter a of tungsten carbide particles is measured by the following procedures (A2) to (B2). (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.

[0036] (B2) Set one rectangular measurement field of view, 25.3 μm long x 17.6 μm wide, in each of the six binarized images obtained. Using image analysis software (ImageJ, version 1.51j8: https: / / imagej.nih.gov / ij / ), measure the circle equivalent diameter (Heywood diameter: diameter of a circle equivalent to an equal area) for each of the tungsten carbide particles (first phase) in the six measurement fields.

[0037] (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 arithmetic mean diameter a 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 arithmetic mean diameter a 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.

[0038] 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.

[0039] <Relationship between the arithmetic mean diameter a of tungsten carbide particles and the standard deviation b of the particle diameter of tungsten carbide particles> 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 diameters of the tungsten carbide particles have a relationship represented by the following formula I. b<0.49a+0.063 Formula I In formula I, a and b are in units of μm.

[0040] The particle size of the tungsten carbide particles contained in the cemented carbide satisfies the relationship of formula I, which indicates that the particle size of the tungsten carbide particles is highly uniform, regardless of the size of the arithmetic mean diameter a of the tungsten carbide particles. From the viewpoint of improving the uniformity of the particle size, the arithmetic mean diameter a and the standard deviation b may show the relationship of the following formulas IA and IB. b<0.49a+0.061 formula IA b<0.49a+0.059 Formula IB

[0041] In the present disclosure, the standard deviation b of the particle size of the tungsten carbide particles is measured by the following procedure. The circle equivalent diameter (Heywood diameter: equivalent circle diameter with equal area) is measured for each of all tungsten carbide particles (first phase) in the six measurement fields of view using the same method as (A2) to (B2) described in the measurement method for the arithmetic mean diameter a of tungsten carbide particles. The standard deviation b of the particle size of the tungsten carbide particles is calculated by the following formula based on all tungsten carbide particles in the six measurement fields of view except for tungsten carbide particles with circle equivalent diameters of 0.22 μm or less.

[0042]

number

[0043] 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 based on the number of particles satisfy the relationship represented by the following formula II. c>0.34a+0.098 Formula II In formula II, the units of a and c are μm. In the present disclosure, the 10% cumulative particle size c based on the number of tungsten carbide particles means the cumulative 10% particle size from the small diameter side in the cumulative particle size distribution based on the number of tungsten carbide particles.

[0044] The particle size of the tungsten carbide particles contained in the cemented carbide satisfies the relationship of formula II, which indicates that there are few fine tungsten carbide particles, regardless of the size of the arithmetic mean diameter a of the tungsten carbide particles. The arithmetic mean diameter a and the 10% cumulative particle size c may have the relationship of formula II-A and formula II-B below, from the viewpoint of reducing the fine tungsten carbide particles.

[0045] c>0.34a+0.099 Formula II-A c>0.34a+0.100 Formula II-B

[0046] In the present disclosure, the 10% cumulative particle size c based on the number of tungsten carbide particles is measured by the following procedure. The circle equivalent diameter (Heywood diameter: equivalent circle diameter of equal area) is measured for each of all tungsten carbide particles (first phase) in the six measurement fields of view using the same method as (A2) to (B2) described in the measurement method for the arithmetic mean diameter a of tungsten carbide particles. The 10% cumulative particle size c based on the number is determined based on all tungsten carbide particles in the six measurement fields of view, excluding tungsten carbide particles with circle equivalent diameters of 0.22 μm or less.

[0047] The cemented carbide of the first embodiment 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 third phase has a low thermal conductivity, when the cemented carbide including the third phase is used under cutting conditions in which the cutting edge temperature is likely to increase, such as high-speed machining, the cutting edge becomes hot, thermal wear is likely to progress, and the wear resistance of the cutting tool tends to decrease. In the cemented carbide of the first embodiment, the particle size distribution of the tungsten carbide particles satisfies the above formula I and formula II, so that the tungsten carbide particles can be uniformly present in the cemented carbide structure, and the cutting heat generated during cutting is likely to be released to the outside of the cutting tool through the tungsten carbide particles. Therefore, a tool including the cemented carbide of the present disclosure can have improved thermal conductivity, is less susceptible to thermal wear, and has excellent wear resistance, even while containing a third phase.

[0048] <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 constitute the first phase together.

[0049] 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).

[0050] <Cobalt content in cemented carbide> In the cemented carbide of the first embodiment, the cobalt content 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 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 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.

[0051] In this disclosure, the cobalt content 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 pulverized 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. Potentiometric titration is then performed with potassium ferricyanide (red ferricyanide) using platinum and saturated calomel (tungsten) electrodes. The measurement device used is the "AUT-501" manufactured by DKK-TOA Corporation.

[0052] <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.

[0053] 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).

[0054] The third phase may contain at least two elements selected from the group consisting of titanium, tantalum, niobium, zirconium and tungsten.

[0055] 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.

[0056] 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.

[0057] (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.

[0058] (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.

[0059] (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 %.

[0060] 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.

[0061] <Total content of titanium, tantalum, niobium and zirconium in cemented carbide> In the cemented carbide of the first embodiment, the total content 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 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 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 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 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 contained when the cemented carbide contains one or more and three or less elements selected from the group consisting of titanium, tantalum, niobium, and zirconium.

[0062] 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 measurement device for ICP emission spectrometry is Shimadzu Corporation's "ICPS-8100" (trademark).

[0063] <Arithmetic mean diameter of the second region> In the cemented carbide of the first embodiment, in a first image obtained by performing a binarization process on a backscattered electron image of a cross section of the cemented carbide, a first region consisting of a first phase and a second region consisting of a second phase and a third phase may be present, and the arithmetic mean diameter d of the second region in the first image may be 0.3 μm or more and 0.9 μm or less. The backscattered electron image is obtained by photographing the cross section of the cemented carbide at 5000 times magnification using a scanning electron microscope. The lower limit of the arithmetic mean diameter d of the second region may be 0.3 μm or more, 0.4 μm or more, or 0.5 μm or more from the viewpoint of improving wear resistance by suppressing particle shedding. The upper limit of the arithmetic mean diameter d of the second region may be 0.9 μm or less, 0.8 μm or less, or 0.7 μm or less from the viewpoint of improving wear resistance by suppressing uneven wear. 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.

[0064] In the present disclosure, the arithmetic mean diameter d of the second region is measured by the following procedures (A4) to (B4). (A4) Six images after binarization are obtained by the same method as (A1) to (C1) described in the measurement method for the content of the first phase in a cemented carbide.

[0065] (B4) A rectangular measurement field of view of 25.3 μm in length and 17.6 μm in width is set in each of the six images obtained after binarization processing. Using image analysis software (ImageJ, version 1.51j8: https: / / imagej.nih.gov / ij / ), the circle equivalent diameter (Heywood diameter: equivalent circle diameter of equal area) is measured for each of all second regions in the six measurement fields of view. The number-based arithmetic mean value of the circle equivalent diameter is calculated based on all second regions in the six measurement fields of view. In the present disclosure, the arithmetic mean value corresponds to the arithmetic mean diameter d of the second regions.

[0066] 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.

[0067] Chromium content The cemented carbide of the first embodiment may contain chromium (Cr). Chromium has a grain growth suppressing effect on tungsten carbide particles. In the cemented carbide, the percentage of the mass of chromium relative to the mass of cobalt may be 0% or more and 8% or less. This effectively prevents the raw material fine WC particles from remaining in the resulting cemented carbide, and effectively prevents the generation of coarse grains, 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 solubility limit of chromium in cobalt is exceeded, and chromium precipitates in the cemented carbide in the form of carbide or the like, which tends to deteriorate the chipping resistance of the cemented carbide.

[0068] In the cemented carbide, the upper limit of the percentage of the mass of chromium relative to the mass of cobalt may be 7% or less, or 6% or less, from the viewpoint of improving chipping resistance. In the cemented carbide, the lower limit of the percentage of the mass of chromium relative to the mass of cobalt may be 1% or more, or 2% or more, from the viewpoint of suppressing the generation of coarse grains. In the cemented carbide, the percentage of the mass of chromium relative to the mass of cobalt may be 1% or more, or 7% or less, or 2% or more, or 6% or less.

[0069] The chromium content of the cemented carbide is measured by ICP atomic emission spectrometry.

[0070] <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.

[0071] In the cemented carbide, 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, 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 0.5% or more, or 1% 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 0.5% or more and 5% or less, or 1% or more and 4% or less.

[0072] The zirconium content of the cemented carbide is measured by ICP atomic emission spectrometry.

[0073] <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.

[0074] <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.

[0075] <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 (NbC) powder, and zirconium carbide (ZrC) powder, which are raw materials of the third phase, are prepared (hereinafter, these are collectively referred to as "third phase raw material powders"). If necessary, chromium carbide (Cr3C2) powder can be prepared as a grain growth inhibitor. These raw powders can be commercially available.

[0076] As the tungsten carbide powder (hereinafter also referred to as "WC powder"), a tungsten carbide powder with a uniform particle size is prepared. Specifically, a WC powder with 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 device used in the FSSS method is "Sub-Sieve Sizer Model 95" (trademark) manufactured by Fisher Scientific. The particle size distribution of the WC powder is measured using a particle size distribution measuring device (trade name: MT3300EX) manufactured by Microtrac.

[0077] 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 particles 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 this 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 a Fisher Scientific "Sub-Sieve Sizer Model 95" (trademark).

[0078] ≪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.

[0079] The mixing method is a method that can maintain the particle size of the WC powder in a uniform state in the mixed powder after mixing. Specifically, a ball mill is used, the media diameter is made smaller than in the past, the rotation speed is made smaller, and the mixing time is shortened. This makes it possible to suppress the pulverization of the WC particles. The media diameter can be, for example, 5 mm or more and 10 mm or less. The rotation speed can be, for example, 15 rpm or more and 30 rpm or less. The mixing time can be, for example, 15 hours or more and 36 hours or less. If the mixing time is less than 15 hours, voids are likely to occur in the cemented carbide due to insufficient mixing.

[0080] If a mixing method with a strong crushing force (for example, an attritor) is used, even if the particle size of the raw material WC powder is uniform, the entire WC particles are finely crushed by mixing, the particle size of the WC powder after mixing 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 adopted.

[0081] 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.

[0082] ≪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.

[0083] <Sintering process> In the sintering step, the compact obtained in the molding step is sintered to obtain a cemented carbide. In the method for producing a cemented carbide of the present disclosure, the sintering temperature can be set to 1380°C or higher and 1500°C or lower. This can make the grain size of the WC particles in the cemented carbide uniform. In addition, the generation of fine WC particles and coarse WC particles is suppressed.

[0084] If the sintering temperature is lower than 1380°C, voids will be generated in the cemented carbide, reducing the chipping resistance of the cemented carbide, whereas if the sintering temperature is higher than 1500°C, the WC particles will coarsen due to grain growth, resulting in non-uniform grain sizes.

[0085] ≪Cooling process≫ The cooling step is a step of cooling the cemented carbide after the sintering is completed. The cooling conditions may be any general conditions and are not particularly limited.

[0086] [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.

[0087] 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.

[0088] The cemented carbide of the second embodiment may constitute the whole 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.

[0089] 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

[0090] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0091] <Preparation of cemented carbide> ≪Preparation process≫ The raw powder was prepared with the composition shown in the "Raw Powder" column of Table 1. Several tungsten carbide (WC) powders with 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 the "Raw Powder" column of Table 1, respectively.

[0092] The average particle size of the cobalt (Co) powder is 1.2 μm, the average particle size of the chromium carbide (Cr3C2) powder is 1.5 μm, the average particle size of the titanium carbide (TiC) powder is 1.5 μm, the average particle size of the titanium nitride (TiN) powder is 2.0 μm, the average particle size of the tantalum carbide (TaC) powder is 1.0 μm, the average particle size of the niobium carbide (NbC) powder is 1.1 μm, and the average particle size of the zirconium carbide (ZrC) powder is 1.5 μm.

[0093] ≪Mixing process≫ Each raw material powder was mixed in the blending amount shown in the "mass %" column of "Raw Materials" in Table 1 to produce a mixed powder. "Mas %" in the "Raw Materials" 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 a ball mill. The media diameter was 8 mm. The rotation speed and mixing time for 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 produce a granulated powder.

[0094] [Table 1]

[0095] ≪Molding process≫ The obtained granulated powder was press-molded to prepare a chip-shaped compact.

[0096] <Sintering process> The compact was placed in a sintering furnace and sintered in vacuum at the temperature and for the time shown in the "Temperature" and "Time" columns of "Sintering" in Table 2.

[0097] ≪Cooling process≫ After sintering was completed, the mixture was slowly cooled in an argon (Ar) gas atmosphere to obtain a cemented carbide alloy.

[0098] [Table 2]

[0099] <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 of the cemented carbide, and the total content of titanium, tantalum, niobium, and zirconium of the cemented carbide were measured. The specific measurement method is as described in embodiment 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 indicate that each sample contains all of Ti, Ta, Zr, and Nb.

[0100] <Arithmetic mean diameter of tungsten carbide particles a, standard deviation b, 10% cumulative particle diameter c> For each sample of cemented carbide, the arithmetic mean diameter a, standard deviation b, and 10% cumulative particle diameter c of the tungsten carbide particles were measured. The specific measurement method is as described in embodiment 1. The results are shown in the "Arithmetic mean diameter a," "Standard deviation b," and "10% cumulative particle diameter c" columns of "WC particles" in the "First phase" in Table 3.

[0101] Based on the "arithmetic mean diameter a," "standard deviation b," and "10% cumulative particle diameter c" of each sample, it was confirmed whether each sample satisfied the relationships of the following formulas I and II. b<0.49a+0.063 Formula I c>0.34a+0.098 Formula II The results are shown in the "Formula I" and "Formula II" columns of Table 3. In "Formula I", "Yes" indicates that the relationship of Formula I is satisfied, and "No" indicates that the relationship of Formula I is not satisfied. In "Formula II", "Yes" indicates that the relationship of Formula II is satisfied, and "No" indicates that the relationship of Formula II is not satisfied.

[0102] <Composition of the second phase> In all samples, the second phase was confirmed to consist of cobalt.

[0103] <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 4. It was confirmed that in all samples, the third phase was composed of the elements listed in Table 4 and did not contain tungsten carbide.

[0104] <Arithmetic mean diameter d of the second region> The arithmetic mean diameter d of the second region was measured for each sample. The specific measurement method is as described in embodiment 1. The results are shown in the "Arithmetic mean diameter d" column of "Second region" in "First image" in Table 4.

[0105] [Table 3]

[0106] [Table 4]

[0107] <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 0.35 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 in Table 5.

[0108] ≪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.

[0109] <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 5.

[0110] ≪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

[0111] In this embodiment, if the average wear amount Vb in cutting test 1 is 0.35 mm or less, and if the breakage rate in cutting test 2 is 25% or less, the tool life is determined to be long.

[0112] [Table 5]

[0113] <Consideration> The cemented carbide and cutting tools of Samples 1 to 22 correspond to Examples. The cemented carbide and cutting tools of Samples 101 to 112 correspond to Comparative Examples. Samples 1 to 22 have excellent wear resistance and chipping resistance, and showed long tool life in both Cutting Test 1 and Cutting Test 2. Samples 101, Samples 104 to 106, Sample 108, Sample 109, and Sample 112 had insufficient wear resistance and insufficient tool life in Cutting Test 1. Samples 102, Sample 103, Sample 107, Sample 110, and Sample 111 had insufficient chipping resistance and insufficient tool life in Cutting Test 2.

[0114] 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.

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 tungsten carbide particles have an arithmetic mean diameter a of 0.5 μm or more and 2.0 μm or less, The arithmetic mean diameter a and the standard deviation b of the particle diameter of the tungsten carbide particles satisfy 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 based on the number of the tungsten carbide particles satisfy the relationship of 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 comprises cobalt; The cobalt content 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 of titanium, tantalum, niobium and zirconium in the cemented carbide is 2% by mass or more and 8% by mass or less.

2. In a first image obtained by performing a binarization process on a backscattered electron image of a cross section of the cemented carbide, a first region consisting of the first phase and a second region consisting of the second phase and the third phase are present, 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, 2. The cemented carbide according to claim 1, wherein the backscattered 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 2, wherein the arithmetic mean diameter a of the tungsten carbide particles is 0.8 μm or more and 1.6 μm or less.

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

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