cemented carbide

Abstract

A cemented carbide comprising tungsten carbide particles and a binding phase, wherein the cemented carbide comprises a total of 80% or more of the tungsten carbide particles and the binding phase, the cemented carbide comprising 0.1% or more and 20% or less of the binding phase, the tungsten carbide particles comprising a first region and a second region, the first region being a region at a distance of 0 nm or more and 50 nm or less from the surface of the tungsten carbide particles, the second region being a portion of the tungsten carbide particles after removing the first region, the first region and the second region respectively comprising a first metal element, the first metal element being at least one selected from the group consisting of titanium, niobium and tantalum, the ratio R1 of the number of atoms of the first metal element in the first region to the total number of atoms of the first metal element and the number of atoms of tungsten being R1 being at least 1.30 times the ratio R2 of the number of atoms of the first metal element in the second region to the total number of atoms of the first metal element and the number of atoms of tungsten being R2, wherein R2 is 2.0% or more and 10.0% or less, and the binding phase comprising cobalt.

Description

Technical Field

[0001] This disclosure relates to cemented carbide. Background Technology

[0002] For a long time, cemented carbide containing tungsten carbide (WC) particles and a bonding phase mainly composed of iron group elements (e.g., Fe, Co, Ni) has been used as a raw material for cutting tools (Patent Document 1, Patent Document 2). The properties required for cutting tools include strength (e.g., bending strength), toughness (e.g., fracture toughness), hardness (e.g., Vickers hardness), resistance to plastic deformation, and wear resistance.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2016-098393

[0006] Patent Document 2: Japanese Patent Application Publication No. 2021-110010 Summary of the Invention

[0007] The cemented carbide disclosed herein is a cemented carbide comprising tungsten carbide particles and a bonding phase, wherein,

[0008] The cemented carbide comprises a total of more than 80% by volume of the tungsten carbide particles and the bonding phase.

[0009] The cemented carbide contains more than 0.1% by volume and less than 20% by volume of the bonding phase.

[0010] The tungsten carbide particle consists of a first region and a second region.

[0011] The first region is the area between 0 nm and 50 nm from the surface of the tungsten carbide particle.

[0012] The second region is the portion of the tungsten carbide particle after the first region has been removed.

[0013] The first region and the second region each contain a first metallic element.

[0014] The first metallic element is selected from at least one of the group consisting of titanium, niobium, and tantalum.

[0015] The ratio R1 of the number of atoms of the first metal element in the first region to the total number of atoms of the first metal element and the number of atoms of tungsten is more than 1.30 times the ratio R2 of the number of atoms of the first metal element in the second region to the total number of atoms of the first metal element and the number of atoms of tungsten.

[0016] The R² is above 2.0% and below 10.0%.

[0017] The combined phase contains cobalt. Attached Figure Description

[0018] Figure 1 This is a schematic cross-sectional view of a cemented carbide according to one embodiment of the present disclosure.

[0019] Figure 2 This is a HAADF (high-angle annular dark field) image of a cross-section of a cemented carbide according to one embodiment of this disclosure. Detailed Implementation

[0020] [The problem this disclosure aims to solve]

[0021] In recent years, the machining of workpieces has become increasingly difficult, and the operating conditions of cutting tools have become more demanding. Therefore, there is a need to improve the various properties of cemented carbide used as the base material for cutting tools. Especially in the machining of end mills made of steel, titanium, and chromium-nickel-iron alloys (high-efficiency machining), to extend tool life, it is required that the tungsten carbide particles in the cemented carbide possess excellent hardness.

[0022] [The Effects of This Disclosure]

[0023] According to this disclosure, it is possible to provide a cemented carbide containing tungsten carbide particles with excellent hardness.

[0024] [Description of embodiments of this disclosure]

[0025] First, embodiments of this disclosure will be described.

[0026] (1) The cemented carbide disclosed herein is a cemented carbide comprising tungsten carbide particles and a bonding phase, wherein,

[0027] The cemented carbide comprises a total of more than 80% by volume of the tungsten carbide particles and the bonding phase.

[0028] The cemented carbide contains more than 0.1% by volume and less than 20% by volume of the bonding phase.

[0029] The tungsten carbide particle consists of a first region and a second region.

[0030] The first region is the area between 0 nm and 50 nm from the surface of the tungsten carbide particle.

[0031] The second region is the portion of the tungsten carbide particle after the first region has been removed.

[0032] The first region and the second region each contain a first metallic element.

[0033] The first metallic element is selected from at least one of the group consisting of titanium, niobium, and tantalum.

[0034] The ratio R1 of the number of atoms of the first metal element in the first region to the total number of atoms of the first metal element and the number of atoms of tungsten is more than 1.30 times the ratio R2 of the number of atoms of the first metal element in the second region to the total number of atoms of the first metal element and the number of atoms of tungsten.

[0035] The R² is above 2.0% and below 10.0%.

[0036] The combined phase contains cobalt.

[0037] In the cemented carbide disclosed herein, tungsten carbide particles can exhibit excellent hardness.

[0038] (2) Preferably, R1 is more than 1.40 times R2. As a result, it can have better hardness.

[0039] (3) Preferably, R2 is 3.0% or more and 8.0% or less. As a result, it can have better hardness.

[0040] (4) Preferably, R1 is 2.6% or more and 13.0% or less. As a result, it can have better hardness.

[0041] (5) Preferably, the vanadium content in the cemented carbide is 1.0 atm% or less. This suppresses the reduction in grain boundary strength between tungsten carbide particles caused by vanadium.

[0042] [Details of the embodiments disclosed herein]

[0043] Hereinafter, a specific example of a cemented carbide according to one embodiment of the present disclosure (hereinafter also referred to as "this embodiment") will be described with reference to the accompanying drawings. In the drawings of this disclosure, the same reference numerals denote the same or equivalent parts. In addition, the dimensional relationships such as length, width, thickness, and depth have been appropriately changed for the sake of clarity and simplification of the drawings, and do not necessarily represent the actual dimensional relationships.

[0044] In this specification, expressions such as "A~B" refer to the upper and lower limits of a range (i.e., above A and below B). If no unit is recorded in A but only in B, the unit of A is the same as the unit of B.

[0045] In this specification, when compounds are represented by chemical formulas, all conventionally known atomic ratios are included unless otherwise specified, and are not necessarily limited to atomic ratios within the stoichiometric range. For example, when referred to as "WC", the ratio of the number of atoms constituting WC includes all conventionally known atomic ratios.

[0046] [Implementation Method 1: Hard Alloy]

[0047] like Figure 1 As shown, the cemented carbide involved in this embodiment is a cemented carbide 3 containing tungsten carbide particles 1 and a bonding phase 2, wherein,

[0048] The cemented carbide 3 comprises tungsten carbide particles 1 totaling more than 80% by volume and the bonding phase 2.

[0049] The cemented carbide 3 contains more than 0.1% by volume and less than 20% by volume of the bonding phase 2.

[0050] The tungsten carbide particle consists of a first region and a second region.

[0051] The first region is the area between 0 nm and 50 nm from the surface of the tungsten carbide particle.

[0052] The second region is the portion of the tungsten carbide particle after the first region has been removed.

[0053] The first region and the second region each contain a first metallic element.

[0054] The first metallic element is selected from at least one of the group consisting of titanium, niobium, and tantalum.

[0055] The ratio R1 of the number of atoms of the first metal element in the first region to the total number of atoms of the first metal element and the number of atoms of tungsten is more than 1.30 times the ratio R2 of the number of atoms of the first metal element in the second region to the total number of atoms of the first metal element and the number of atoms of tungsten.

[0056] The R² is above 2.0% and below 10.0%.

[0057] Phase 2 contains cobalt.

[0058] In the cemented carbide 3 of this embodiment, the tungsten carbide particles can exhibit excellent hardness. The reason for this is speculated as follows.

[0059] The ratio R1 of the number of atoms of the first metal element in the first region to the total number of atoms of the first metal element and the number of atoms of tungsten is at least 1.30 times that of R2 of the number of atoms of the first metal element in the second region to the total number of atoms of the first metal element and the number of atoms of tungsten, where R2 is at least 2.0% and less than 10.0%. As a result, strain occurs in the crystal structure of the tungsten carbide particles 1 in both the surface region (first region) and the internal region (second region), thereby increasing the hardness of the tungsten carbide particles 1.

[0060] <Composition of cemented carbide>

[0061] The cemented carbide of this embodiment is a cemented carbide comprising tungsten carbide particles and a bonding phase. Furthermore, this cemented carbide comprises a total of 80% by volume or more of the tungsten carbide particles and the bonding phase. Therefore, the cemented carbide of this embodiment can possess excellent hardness. Preferably, the cemented carbide comprises a total of 82% by volume or more of the tungsten carbide particles and the bonding phase, more preferably 84% by volume or more, and even more preferably 86% by volume or more. Preferably, the cemented carbide comprises a total of 100% by volume or less of the tungsten carbide particles and the bonding phase. Furthermore, from a manufacturing point of view, the cemented carbide may comprise a total of 98% by volume or less, or 99% by volume or less of the tungsten carbide particles and the bonding phase. Preferably, the cemented carbide comprises a total of 80% by volume or more and 100% by volume or less of the tungsten carbide particles and the bonding phase, more preferably 82% by volume or more and 100% by volume or less, and even more preferably 84% by volume or more and 100% by volume or less.

[0062] The cemented carbide of this embodiment can be composed of tungsten carbide particles and a bonding phase. In addition to tungsten carbide particles and a bonding phase, the cemented carbide of this embodiment may also contain other phases besides tungsten carbide particles and the bonding phase described above. Examples of such other phases include carbides or nitrides of titanium (Ti), niobium (Nb), tantalum (Ta), etc. The cemented carbide of this embodiment can be composed of tungsten carbide particles, a bonding phase, and other phases. The content of other phases in the cemented carbide is permitted within a range that does not impair the effects of this disclosure. For example, the content of other phases in the cemented carbide is preferably 0% by volume or more and 20% by volume or less, more preferably 0% by volume or more and 18% by volume or less, and even more preferably 0% by volume or more and 16% by volume or less.

[0063] The cemented carbide of this embodiment may contain impurities. Examples of such impurities include iron (Fe), molybdenum (Mo), calcium (Ca), silicon (Si), and sulfur (S). The impurity content of the cemented carbide is permitted within a range that does not impair the effects of this disclosure. For example, the impurity content of the cemented carbide is preferably 0% by mass or more and less than 0.1% by mass. The impurity content of the cemented carbide is determined by ICP-based inductively coupled plasma emission spectroscopy (measurement device: Shimadzu Corporation "ICPS-8100" (trademark)).

[0064] The lower limit of the tungsten carbide particle content in the cemented carbide of this embodiment is preferably 60% by volume or more, 62% by volume or more, or 64% by volume or more. The upper limit of the tungsten carbide particle content in the cemented carbide of this embodiment is preferably 99.9% by volume or less, 99% by volume or less, or 98% by volume or less. The tungsten carbide particle content in the cemented carbide of this embodiment is preferably 60% by volume or more and 99.9% by volume or less, 62% by volume or more and 99% by volume or less, or 64% by volume or more and 98% by volume or less.

[0065] The cemented carbide of this embodiment contains 0.1% by volume or more and 20% by volume or less of a binding phase. Therefore, the cemented carbide of this embodiment can exhibit excellent hardness. Furthermore, the cemented carbide preferably contains 1% by volume or more of the aforementioned binding phase, more preferably 2% by volume or more, and even more preferably 3% by volume or more. Furthermore, the cemented carbide preferably contains 18% by volume or less of the aforementioned binding phase, more preferably 16% by volume or less, and even more preferably 14% by volume or less. Furthermore, the cemented carbide preferably contains 1% by volume or more and 18% by volume or less of the aforementioned binding phase, more preferably 2% by volume or more and 16% by volume or less, and even more preferably 3% by volume or more and 14% by volume or less.

[0066] The cemented carbide of this embodiment is preferably composed of 60% by volume or more and 99.9% by volume or less of tungsten carbide particles and 0.1% by volume or more and 20% by volume of a binding phase. The cemented carbide of this embodiment is preferably composed of 62% by volume or more and 99% by volume or less of tungsten carbide particles and 1% by volume or more and 18% by volume of a binding phase. The cemented carbide of this embodiment is preferably composed of 64% by volume or more and 98% by volume of tungsten carbide particles and 2% by volume or more and 16% by volume of a binding phase.

[0067] The methods for determining the content (volume %) of tungsten carbide particles and the content (volume %) of the cemented carbide bonding phase are as follows.

[0068] (A1) Cut any point on the cemented carbide to expose the cross-section. The cross-section is then mirror-finished using a cross-section polishing machine (manufactured by Nippon Egis Corporation).

[0069] (B1) The mirror-finished surfaces of cemented carbide were analyzed using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDX) (device: Gemini 450 (trademark) manufactured by Carl Zeiss) to determine the elements contained in the cemented carbide.

[0070] (C1) The mirror-finished surface of cemented carbide was photographed using a scanning electron microscope (SEM) to obtain a reflected electron image. The image was captured in the central part of the cross-section of the cemented carbide, excluding areas near the surface where the carbide's properties are significantly different from the bulk portion (the entire image area represents the bulk portion of the cemented carbide). The magnification was 5000x. The measurement conditions were an accelerating voltage of 3kV, a current of 2nA, and a working distance (WD) of 5mm.

[0071] (D1) For the area captured in (C1) above, an energy dispersive X-ray analyzer (SEM-EDX) with SEM attached is used to analyze the area to determine the distribution of the elements identified in (B1) above, and an element mapping image is obtained.

[0072] (E1) The reflected electron image obtained in (C1) above is imported into a computer and binarized using image analysis software (OpenCV, SciPy). In the binarized image, tungsten carbide particles are shown in white, and the bound phase is shown in gray to black. Furthermore, the binarization threshold varies depending on the contrast; therefore, a threshold is set for each image.

[0073] (F1) By overlaying the elemental mapping image obtained in (D1) above with the binarized image obtained in (E1) above, the respective regions where tungsten carbide particles and the bonding phase exist are determined on the binarized image. Specifically, regions shown in white in the binarized image and containing tungsten (W) and carbon (C) in the elemental mapping image correspond to the regions where tungsten carbide particles exist. Regions shown in gray to black in the binarized image and containing cobalt (Co) in the elemental mapping image correspond to the regions where the bonding phase exists.

[0074] (G1) In the image after binarization, a rectangular field of view of 24.9 μm × 18.8 μm is defined. Using the image analysis software described above, the area percentage of each tungsten carbide particle and the bonding phase is measured using the total area of ​​the field of view as the denominator.

[0075] (H1) The above (G1) determination is performed in five different non-overlapping measurement fields. In this specification, the average area percentage of tungsten carbide particles in the five measurement fields corresponds to the content (volume %) of tungsten carbide particles in cemented carbide, and the average area percentage of the bound phase in the five measurement fields corresponds to the content (volume %) of the bound phase in cemented carbide.

[0076] In cases where cemented carbide contains other phases in addition to WC particles and the bonding phase, the content of other phases in the cemented carbide can be obtained by subtracting the content of tungsten carbide particles (volume%) and the content of the bonding phase (volume%) as determined by the above steps from the total cemented carbide (100 vol%).

[0077] The following situation has been confirmed: as long as the measurement is within the range of the applicant's measurement and is performed on the same sample, even if the cutting part of the cemented carbide profile is arbitrarily set and the imaging area described in (C1) is arbitrarily set on the profile, and the content of tungsten carbide particles and the content of the bonding phase of the cemented carbide are measured multiple times according to the above steps, the deviation of the measurement results is very small. Even if the cutting part of the cemented carbide profile is arbitrarily set and the imaging area of ​​the reflected electron image is arbitrarily set, the results will not change arbitrarily.

[0078] Tungsten carbide particles

[0079] The aforementioned tungsten carbide particle is composed of a first region and a second region. The first region is a region located at a distance of 0 nm or more and 50 nm or less from the surface of the tungsten carbide particle. The second region is the portion of the tungsten carbide particle after the first region has been removed.

[0080] (First metallic element)

[0081] The first region and the second region described above each contain a first metallic element, which is at least one selected from the group consisting of titanium, niobium, and tantalum. From the viewpoint of enabling the tungsten carbide particles to possess high hardness, the first metallic element is preferably titanium.

[0082] The ratio R1 of the number of atoms of the first metal element in the first region to the total number of atoms of the first metal element and the number of atoms of tungsten is at least 1.30 times that of the ratio R2 of the number of atoms of the first metal element in the second region to the total number of atoms of the first metal element and the number of atoms of tungsten. This increases the hardness of the tungsten carbide particles, thus enabling the cemented carbide containing such tungsten carbide particles to exhibit excellent hardness. Furthermore, R1 is preferably at least 1.40 times that of R2, more preferably at least 1.50 times, and even more preferably at least 1.60 times. Additionally, R1 is preferably at least 4.0 times that of R2, more preferably at least 3.8 times, and even more preferably at least 3.6 times. Furthermore, R1 is preferably at least 1.30 times and less than 4.0 times that of R2, more preferably at least 1.40 times and less than 3.8 times, and even more preferably at least 1.50 times and less than 3.6 times.

[0083] The aforementioned R1 can also be expressed as the formula "R1 = [(number of atoms of the first metallic element in the first region) / {(number of atoms of tungsten in the first region) + (number of atoms of the first metallic element in the first region)}] × 100". Similarly, the aforementioned R2 can be expressed as "R2 = [(number of atoms of the first metallic element in the second region) / {(number of atoms of tungsten in the second region) + (number of atoms of the first metallic element in the second region)}] × 100". Furthermore, "R1 is more than 1.30 times R2" can also be expressed as the formula "R1 / R2 ≥ 1.30".

[0084] The aforementioned R2 is 2.0% or more and 10.0% or less. This generates lattice strain in the cemented carbide, thereby increasing its hardness. Furthermore, the aforementioned R2 is preferably 3.0% or more, more preferably 3.5% or more, and even more preferably 4.0% or more. Additionally, the aforementioned R2 is preferably 8.0% or less, more preferably 7.5% or less, and even more preferably 7.0% or less. Furthermore, the aforementioned R2 is preferably 3.0% or more and 8.0% or less, more preferably 3.5% or more and 7.5% or less, and even more preferably 4.0% or more and 7.0% or less.

[0085] The aforementioned R1 is preferably 2.6% or more and 13.0% or less. This generates lattice strain in the cemented carbide, thereby further increasing the hardness of the cemented carbide. Furthermore, the aforementioned R1 is preferably 2.8% or more, more preferably 3.0% or more. Furthermore, the aforementioned R1 is preferably 12.8% or less, more preferably 12.6% or less. Furthermore, the aforementioned R1 is preferably 2.8% or more and 12.8% or less, more preferably 3.0% or more and 12.6% or less.

[0086] (Methods for determining R1 and R2)

[0087] The method for determining R1 and R2 for each tungsten carbide particle is shown in (A2) to (G2) below.

[0088] (A2) Samples were collected from cemented carbide and sliced ​​to a thickness of 30-100 nm using an argon ion slicer (“IB09060CIS” manufactured by Nippon Electron Ltd. (trademark)) under an accelerating voltage of 2 kV.

[0089] (B2) Next, the slice was observed at 200,000x magnification using a TEM (Transmission Electron Microscopy) (JFM-ARM300F manufactured by Nippon Electronics Corporation, a trademark) at an accelerating voltage of 200V, thus obtaining the first image (not shown).

[0090] (C2) In this first image, the surface S of the tungsten carbide particles is arbitrarily selected. Furthermore, the method for determining the surface S of the tungsten carbide particles in the first image is as follows: That is, elemental mapping analysis based on EDX (Energy Dispersive X-ray Spectroscopy) is performed on the aforementioned first image to analyze the distribution of cobalt. In the obtained elemental mapping image, the lines representing regions with high cobalt concentrations correspond to the surface S of the tungsten carbide particles.

[0091] (D2) Next, arbitrarily select a tungsten carbide particle from the first image. Within this tungsten carbide particle, use image processing software (OpenCV, SciPy) to determine the region (first region) that is 0 nm or more and 50 nm or less from the surface S of the tungsten carbide particle, and the portion after removing the first region (second region). In the first image, draw a line segment L that crosses the tungsten carbide particle. Line segment L is a line segment connecting two points on the surface S of the tungsten carbide particle, and it passes through both the first region and the second region. It was confirmed that as long as line segment L passes through both the first region and the second region, it will not affect the following measurement results.

[0092] (E2) Positioning a line segment L that traverses the aforementioned tungsten carbide particles near the center of the image, and observing at 25 millionx magnification, a second image is obtained. If the line segment L is too long to be captured in a single second image, multiple consecutive second images (HAADF images) are obtained to include the entire line segment L. An example of a second image is shown below. Figure 2It can be understood that in the second image, line segment L is located near the center of the image, and different tungsten carbide particles exist on the left and right sides of the paper, with the surface S of the tungsten carbide particle as the boundary. Figure 2 In the second image, the following elemental line analysis is performed on the tungsten carbide particles located on the left side of the paper, with the aforementioned S as the boundary.

[0093] Next, in the second image, EDX-based elemental line analysis is performed along the aforementioned line segment to analyze the distribution of the first metallic element and the distribution of tungsten. The beam diameter is set to 0.3 nm or less, and the scan interval is set to 0.1–0.7 nm. Thus, the aforementioned elemental line analysis can be performed in the region from a point on the surface of the tungsten carbide particle to a point on the opposite side of the surface.

[0094] (F2) Based on the results of elemental line analysis, for the region (first region) between 0 nm and 50 nm from the surface of the tungsten carbide particles, the average number of atoms of the first metal element and the average number of atoms of tungsten are calculated. Then, the calculated average number of atoms of the first metal element is divided by the sum of the average number of atoms of the first metal element and the average number of atoms of tungsten to calculate R1.

[0095] (G2) Furthermore, based on the results of the elemental line analysis described above, for the portion (second region) after removing the first region from the tungsten carbide particles, the average number of atoms of the first metal element and the average number of atoms of tungsten are calculated. Then, the average number of atoms of the first metal element is divided by the sum of the average number of atoms of the first metal element and the average number of atoms of tungsten to calculate R2.

[0096] (Average particle size)

[0097] In this embodiment, the lower limit of the average particle size of the tungsten carbide particles is preferably 0.1 μm or more, 0.2 μm or more, or 0.3 μm or more. The upper limit of the average particle size of the tungsten carbide particles is preferably 3.5 μm or less, 3.0 μm or less, or 2.5 μm or less. Specifically, the average particle size of the tungsten carbide particles is preferably 0.1 μm or more and 3.5 μm or less, 0.2 μm or more and 3.5 μm or less, 0.3 μm or more and 3.5 μm or less, 0.1 μm or more and 3.0 μm or less, 0.2 μm or more and 3.0 μm or less, 0.3 μm or more and 3.0 μm or less, 0.1 μm or more and 2.5 μm or less, 0.2 μm or more and 2.5 μm or less, or 0.3 μm or more and 2.5 μm or less. Therefore, the cemented carbide has high hardness, and the wear resistance of the tool containing this cemented carbide is improved. Furthermore, the tool can exhibit excellent resistance to breakage.

[0098] In this specification, the average particle size of tungsten carbide particles refers to the D50 of the equivalent circular diameter (Heywood diameter) of the WC particles contained in the cemented carbide (the median particle size D50 is the equivalent circular diameter with a cumulative frequency of 50% based on the number of particles). The method for determining the average particle size of tungsten carbide particles is as follows.

[0099] (A3) Using the same method as (A1) to (F1) for determining the content of tungsten carbide particles and the content of the bound phase in the above-mentioned cemented carbide, the region where tungsten carbide particles exist is determined on the binarized image.

[0100] (B3) In the image after binarization, a rectangular field of view of 24.9 μm × 18.8 μm is defined. Using the image analysis software described above, the outer edge of each tungsten carbide particle in the field of view is determined, and the equivalent circle diameter (Heywood diameter: equivalent diameter of a circle with equal area) of each tungsten carbide particle is calculated.

[0101] (C3) Based on all tungsten carbide particles in the above-mentioned field of view, calculate the D50 of the equivalent diameter of the tungsten carbide particle's equal area circle.

[0102] The following conditions have been confirmed: as long as the measurement is within the range of the applicant's measurement and is performed on the same sample, even if the cutting part of the cemented carbide cross-section is arbitrarily set, the shooting area described in (C1) is arbitrarily set on the cross-section, and the measurement field of view described in (B2) is arbitrarily set, and the average particle size of tungsten carbide particles is measured multiple times according to the above steps, the deviation of the measurement results is very small. Even if the cutting part of the cemented carbide cross-section is arbitrarily set, the shooting area of ​​the image is arbitrarily set, and the measurement field of view is arbitrarily set, the results will not change arbitrarily.

[0103] (Hardness of tungsten carbide particles)

[0104] The hardness of the tungsten carbide particles is preferably 31 GPa or higher and 33 GPa or lower. The hardness of the tungsten carbide particles in cemented carbide can be determined by the following method. First, the surface of the cemented carbide is ground using a cross-section polishing (CP) processing apparatus (“IB-19500CP cross-section sample preparation apparatus” (trademark) manufactured by Nippon Egis Corporation), thereby exposing the tungsten carbide particles. Next, for any single tungsten carbide particle, the hardness is measured using a nanoindenter (“TI980” (trademark) manufactured by Bruker Hysitron) under the following measurement conditions.

[0105] (Measurement conditions for nanoindentation)

[0106] Maximum load: 3mN

[0107] • Load: 5s

[0108] Hold: 2 seconds

[0109] • Unloading: 5s

[0110] ·N:10

[0111] Similarly, the hardness of any other nine tungsten carbide particles was measured. Then, for the ten tungsten carbide particles whose hardness was measured, the average hardness was calculated, thereby determining the hardness of the tungsten carbide particles.

[0112] "Combination Phase"

[0113] The aforementioned binder phase contains cobalt. This imparts excellent toughness to the cemented carbide. The cobalt content of the binder phase is preferably 90% by mass or more and 100% by mass or less, 92% by mass or more and 100% by mass or less, 94% by mass or more and 100% by mass or less, or 100% by mass. The cobalt content of the binder phase is determined by ICP (Inductively Coupled Plasma) luminescence analysis (measuring device: Shimadzu Corporation's "ICPS-8100" (trademark)). Furthermore, as long as the binder phase contains a level of cobalt detectable by ICP luminescence analysis, it functions as a binder phase regardless of its cobalt content.

[0114] In addition to cobalt, the aforementioned bonding phase may also include nickel (Ni), chromium (Cr), iron (Fe), aluminum (Al), ruthenium (Ru), rhenium (Re), etc. This bonding phase can be composed of cobalt and at least one element selected from the group consisting of nickel, chromium, iron, aluminum, ruthenium, and rhenium. The bonding phase can also consist of cobalt, at least one element selected from the group consisting of nickel, chromium, iron, aluminum, ruthenium, and rhenium, and unavoidable impurities. Examples of unavoidable impurities include, for example, manganese (Mn), magnesium (Mg), calcium (Ca), molybdenum (Mo), sulfur (S), and titanium (Ti).

[0115] <Atomic vanadium content in cemented carbide>

[0116] The atomic number basis content of vanadium in the cemented carbide is preferably 1.0 atm% or less. This suppresses the reduction in grain boundary strength between tungsten carbide particles caused by vanadium. Furthermore, the upper limit of the atomic number basis content of vanadium in the cemented carbide is more preferably 0.8 atm% or less, and even more preferably 0.6 atm% or less. From a manufacturing point of view, the lower limit of the atomic number basis content of vanadium in the cemented carbide can be 0.1 atm% or more, 0.2 atm% or more, or 0.3 atm% or more. Furthermore, the atomic number basis content of vanadium in the cemented carbide is preferably 0 atm% or more and 1.0 atm% or less, more preferably 0 atm% or more and 0.8 atm% or less, and even more preferably 0 atm% or more and 0.6 atm% or less. Additionally, vanadium is present at the interfaces between tungsten carbide particles.

[0117] The atomic number basis of vanadium in cemented carbide was determined by ICP (Inductively Coupled Plasma) luminescence analysis (measuring device: Shimadzu Corporation "ICPS-8100" (trademark)).

[0118] [Implementation Method 2: Method for Manufacturing Hard Alloy]

[0119] The cemented carbide raw material of this embodiment can be manufactured by sequentially performing the following steps: raw material powder preparation, mixing, forming, sintering, and cooling. Each step will be described below.

[0120] <Pre-treatment process>

[0121] The pretreatment step is a process of obtaining tungsten carbide (WC) powder containing the aforementioned first metal element. First, a mixture is obtained by mixing tungsten oxide (WO3) powder, the first metal element powder, and carbon (C) powder. Here, the first metal element powder is 1.0% by mass or more and 1.5% by mass or less, and the carbon (C) powder is 10% by mass or more and 30% by mass or less. Examples of the aforementioned first metal element powder include titanium oxide (TiO2), niobium oxide (Nb2O5) powder, and tantalum oxide (Ta2O5). Next, by heating the mixture at 1300°C for 30 to 90 minutes, tungsten carbide powder containing the aforementioned first metal element (hereinafter also referred to as "WC powder containing the first metal element") can be obtained. Commercially available products can be used for the tungsten oxide (WO3) powder, the first metal element powder, and the carbon powder.

[0122] <Preparation Process>

[0123] The preparation process involves preparing the raw material powders that constitute the raw materials for cemented carbide. Examples of raw material powders include WC powder and cobalt (Co) powder, which contain the first metallic element. Further examples of raw material powders include chromium carbide (Cr3C2) powder and vanadium carbide (VC) powder, which act as grain growth inhibitors. Commercially available products can be used for cobalt powder, chromium carbide powder, and vanadium carbide powder.

[0124] <Mixed Processes>

[0125] The mixing process is a process of mixing the raw material powders prepared in the preparation process in a predetermined proportion. Through the mixing process, a mixed powder is obtained by mixing the raw material powders.

[0126] The proportion of WC powder containing the first metallic element in the mixed powder can, for example, be 80% by mass or more and 99.9% by mass or less. Furthermore, the proportion of cobalt powder in the mixed powder can, for example, be 0.1% by mass or more and 20% by mass or less. Additionally, the proportion of chromium carbide powder in the mixed powder can, for example, be 0.1% by mass or more and 2% by mass or less. Furthermore, the proportion of vanadium carbide powder in the mixed powder can, for example, be 0.1% by mass or more and 2% by mass or less.

[0127] A wet bead mill (LMZ06, manufactured by Ashizawa Finetech Co., Ltd., trademark) can be used for mixing the various raw material powders. The mixing time can be set to more than 2 hours and less than 20 hours. This allows the raw material powders to be finely crushed and pulverized.

[0128] Furthermore, the mixed powder can be granulated as needed after the mixing process. Granulation of the mixed powder facilitates filling the die or mold during the subsequent forming process. Known granulation methods can be used for granulation, such as commercially available granulators like spray dryers.

[0129] <Forming Process>

[0130] The forming process is the process of shaping the mixed powder obtained in the mixing process into a shape for use as a rotary tool (e.g., a round bar) to obtain a molded body. The forming method and forming conditions in the forming process are not particularly limited as long as general methods and conditions are used.

[0131] <Sintering Process>

[0132] The sintering process is a process of sintering the formed body obtained from the forming process by applying pressure during sintering (Hot Isostatic Pressing) to obtain a cemented carbide intermediate.

[0133] The sintering temperature is preferably above 1320°C and below 1500°C, more preferably above 1330°C and below 1450°C, and even more preferably above 1340°C and below 1420°C.

[0134] In addition, the sintering time is preferably 30 minutes or more and 120 minutes or less, more preferably 45 minutes or more and 90 minutes or less.

[0135] In addition, the vacuum degree (pressure) during sintering is preferably above 0.1 kPa and below 10 MPa.

[0136] Furthermore, there are no particular limitations on the atmosphere during sintering; examples of such atmospheres include N2 gas atmosphere or inactive gas atmospheres such as Ar.

[0137] Cooling Process

[0138] The cooling process is the process of cooling the cemented carbide intermediate after the sintering process. For example, the cemented carbide intermediate can be rapidly cooled to 1000°C in Ar gas.

[0139] <Features of the cemented carbide manufacturing method of this embodiment>

[0140] In the cemented carbide obtained by the above-described manufacturing method, the ratio R1 of the number of atoms of the first metal element in the first region to the total number of atoms of the first metal element and the number of atoms of tungsten is at least 1.30 times the ratio R2 of the number of atoms of the first metal element in the second region to the total number of atoms of the first metal element and the number of atoms of tungsten, and R2 is at least 2.0% and less than 10.0%. The reason for this is speculated as follows.

[0141] By preparing a powder of the first metallic element as a raw material, the first metallic element can be incorporated into the cemented carbide. However, simply mixing the raw material powder and sintering it tends to make it difficult for the first metallic element to diffuse into the tungsten carbide particles contained in the cemented carbide. On the other hand, by combining the following steps: obtaining tungsten carbide powder pre-containing the first metallic element in a pretreatment step; pulverizing the mixed powder using a bead mill in a mixing step; and sintering at a low temperature while applying pressure in a sintering step, the diffusion of the first metallic element in the tungsten carbide particles is easily promoted, thus making it easier for the first metallic element to diffuse into the tungsten carbide particles contained in the cemented carbide.

[0142] The inventors of this invention, through in-depth research, have discovered a new method to obtain a cemented carbide by combining the following steps: obtaining tungsten carbide powder pre-containing the aforementioned first metallic element in a pretreatment step; using a bead mill in a mixing step; and sintering under pressure at a low temperature in a sintering step. This allows for the production of a cemented carbide in which "the ratio R1 of the number of atoms of the first metallic element in the first region to the total number of atoms of the first metallic element and the number of atoms of tungsten is 1.30 times or more than R2 of the ratio R2 of the number of atoms of the first metallic element in the second region to the total number of atoms of the first metallic element and the number of atoms of tungsten, where R2 is 2.0% or more and 10.0% or less".

[0143] <Tools>

[0144] The cemented carbide used in this embodiment can be used as a tool material. Examples of such tools include cutting tools, drills, end mills, indexable cutting inserts for milling, indexable cutting inserts for turning, metalworking saws, gear cutting tools, reamers, or taps.

[0145] The cemented carbide of this embodiment can form the entirety of these tools or it can form a part of them. Here, "forms a part" means, for example, the cemented carbide of this embodiment is brazed to a predetermined position on any substrate to form the tool tip.

[0146] The aforementioned tool may also include a hard coating that covers at least a portion of the surface of a substrate made of cemented carbide. For example, diamond-like carbon or diamond can be used as the hard coating.

[0147] Example

[0148] This embodiment will be described in more detail through examples. However, this embodiment is not limited to these examples.

[0149] The Making of Hard Alloy

[0150] The cemented carbide samples were fabricated following the steps outlined below.

[0151] <Pre-treatment process>

[0152] To prepare the cemented carbide samples 1 to 17, tungsten oxide (WO3) powder (manufactured by Xiamen Tungsten Co., Ltd.), titanium oxide (TiO2) powder (first metal element powder), niobium oxide (Nb2O5) powder (first metal element powder), tantalum oxide (Ta2O5) powder (first metal element powder), and carbon powder were mixed as raw material powders according to the composition described in Table 1 to obtain a mixture. Next, the mixture was heated at 1300°C for 30 to 90 minutes to obtain tungsten carbide powder containing the aforementioned first metal element.

[0153] <Preparation Process>

[0154] In order to prepare cemented carbide samples 1 to 17 and samples 101 to 109, the following raw material powders were prepared: WC powder containing the first metal element, cobalt (Co) powder, chromium carbide (Cr3C2) powder, vanadium carbide (VC) powder, tungsten carbide (WC) powder not containing the first metal element (hereinafter also referred to as "WC (without first metal element)") ("WC04NR" (trade name) manufactured by Allied Material Co., Ltd.), and titanium carbonitride (TiCN) powder.

[0155] Table 1

[0156]

[0157] <Mixed Processes>

[0158] Next, the prepared raw material powders were mixed in a bead mill for 12 hours according to the formula recorded in Table 2, thereby producing a mixed powder.

[0159]

[0160] <Forming Process>

[0161] Next, the obtained mixed powder is stamped to form a cylindrical shaped body.

[0162] <Sintering Process>

[0163] Next, sintering HIP (hot isostatic pressing) was performed under the conditions described in Table 2, thereby producing a cemented carbide intermediate. Furthermore, the "N2→Ar" description in Table 2 refers to changing the atmosphere from N2 gas (10 kPa) to Ar gas (the pressure of Ar gas is the pressure described in the "s-HIP pressure [MPa]" column of Table 2).

[0164] Cooling Process

[0165] Next, the cemented carbide intermediate after the sintering process was rapidly cooled to 1000 °C in Ar gas.

[0166] Through the above, cemented carbides of Specimens 1 to 17 and cemented carbides of Specimens 101 to 109 were produced. The cemented carbides of Specimens 1 to 17 correspond to the examples, and the cemented carbides of Specimens 101 to 109 correspond to the comparative examples.

[0167] "Manufacture of Cutting Tools"

[0168] The obtained round bar made of cemented carbide was processed to produce an end mill (cutting tool) with a diameter of 3 mm.

[0169] "Characteristic Evaluation of Cemented Carbide"

[0170] <Ratio of the total volume of tungsten carbide particles and the volume of the binder phase to the volume of the cemented carbide>

[0171] For the cemented carbides of Specimens 1 to 17 and Specimens 101 to 109, the ratio of the total volume of tungsten carbide particles and the volume of the binder phase to the volume of the cemented carbide was determined by the method described in Embodiment 1. The obtained results are respectively described in the column of "WC particles + binder phase [volume %]" in Table 3.

[0172]

[0173] <Ratio of the volume of the binder phase to the volume of the cemented carbide>

[0174] For the cemented carbides of Specimens 1 to 17 and Specimens 101 to 109, the ratio of the volume of the binder phase to the volume of the cemented carbide was determined by the method described in Embodiment 1. The obtained results are respectively described in the column of "Binder phase [volume %]" in Table 3.

[0175] <Cobalt content in the binder phase>

[0176] In the cemented carbides of Specimens 1 to 17, Specimens 101 to 102, and Specimens 104 to 109, the cobalt content in the binder phase was determined by the method described in Embodiment 1. As a result, in all of the above specimens, the cobalt content in the binder phase was 90 mass% or more.

[0177] <R1 and R2, R1 / R2>

[0178] For the cemented carbide samples 1 to 17 and 101 to 109, R1 was determined using the method described in Embodiment 1. The results are recorded in the "R1 [%]" column of Table 2. Furthermore, for the cemented carbide samples 1 to 17 and 101 to 109, R2 was determined using the method described in Embodiment 1. The results are recorded in the "R2 [%]" column of Table 3. Based on the obtained R1 and R2, R1 / R2 was calculated. The result is shown in the "R1 / R2" column of Table 3.

[0179] <Average particle size of tungsten carbide particles>

[0180] For the cemented carbide samples 1 to 17 and 101 to 109, the average particle size of the tungsten carbide particles was determined using the method described in Example 1. The results are recorded in the "Average particle size of WC particles [μm]" column of Table 3.

[0181] <Atomic vanadium content in cemented carbide>

[0182] For the cemented carbides of samples 1 to 17 and samples 101 to 109, the atomic percentage of vanadium in the cemented carbides was determined using the method described in Embodiment 1. The results are recorded in the "V content [atm%]" column of Table 3.

[0183] <Hardness of tungsten carbide particles>

[0184] For the cemented carbide samples 1 and 101, the hardness of the tungsten carbide particles was determined using the method described in Example 1. The hardness of the WC particles in sample 1 was 33 GPa. The hardness of the WC particles in sample 101 was 29 GPa. In the cemented carbide samples 2 to 17, the hardness of the tungsten carbide particles was confirmed to be 31 GPa or higher. Furthermore, in the cemented carbide samples 101 to 109, the hardness of the tungsten carbide particles was confirmed to be less than 30 GPa.

[0185] <Cutting Test>

[0186] Using end mills for each sample, cutting was performed under the following cutting conditions, and the cutting distance until a defect of 100 μm or more was produced in the end mill was measured. The following cutting conditions are equivalent to end mill machining of titanium alloys (high-efficiency machining). The longer the cutting distance, the longer the tool life. The results are recorded in the "Cutting Test [m]" column of Table 3.

[0187] (Cutting conditions)

[0188] Workpiece to be machined: 64 titanium (Ti) alloy

[0189] Cutting speed Vc: 150m / min

[0190] Feed rate Fz for each cutting edge: 0.2mm / t

[0191] Cutting depth Ap: 1.0mm

[0192] Cutting width Ae: 0.5mm

[0193] Cutting fluid: Available (wet type)

[0194] Investigation

[0195] The carbide end mills (cutting tools) of Specimens 1 to 17 correspond to the Examples. Additionally, the carbide end mills (cutting tools) of Specimens 101 to 109 correspond to the Comparative Examples. It was confirmed that the carbide end mills (cutting tools) of Specimens 1 to 17 (Examples) have a longer tool life, especially in the machining (high-efficiency machining) of end mills made of steel, titanium, chromium-nickel-iron alloys, etc., compared to the carbide end mills (cutting tools) of Specimens 101 to 109 (Comparative Examples).

[0196] The embodiments and examples of this disclosure have been described above, but it is also intended from the outset that the above-described embodiments and examples may be appropriately combined or modified.

[0197] The embodiments and examples disclosed herein should be considered exemplary in all respects, and not restrictive. The scope of the invention is defined not by the foregoing embodiments and examples, but by the claims, and is intended to include all modifications equivalent to and within the scope of the claims.

[0198] Explanation of reference numerals in the attached figures

[0199] 1: Tungsten carbide particle; 2: Binding phase; 3: Hard alloy; R1: The ratio of the number of atoms of the first metal element in the first region to the total number of atoms of the first metal element and the number of atoms of tungsten; R2: The ratio of the number of atoms of the first metal element in the second region to the total number of atoms of the first metal element and the number of atoms of tungsten; L: A line segment crossing the tungsten carbide particle; S: The surface of the tungsten carbide particle.

Claims

1. A cemented carbide comprising tungsten carbide particles and a bonding phase, wherein, The cemented carbide comprises a total of 80% by volume or more of the tungsten carbide particles and the bonding phase. The cemented carbide comprises more than 0.1 vol% and less than 20 vol% of the bonding phase. The tungsten carbide particles are composed of a first region and a second region. The first region is the area between 0 nm and 50 nm from the surface of the tungsten carbide particles. The second region is the portion of the tungsten carbide particles after the first region has been removed. The first region and the second region each contain a first metallic element. The first metallic element is at least one selected from the group consisting of titanium, niobium, and tantalum. The ratio R1 of the number of atoms of the first metal element in the first region to the total number of atoms of the first metal element and the number of atoms of tungsten is more than 1.30 times the ratio R2 of the number of atoms of the first metal element in the second region to the total number of atoms of the first metal element and the number of atoms of tungsten. The R² value is greater than 2.0% and less than 10.0%. The bonding phase contains cobalt.

2. The cemented carbide according to claim 1, wherein, R1 is more than 1.40 times R2.

3. The cemented carbide according to claim 1 or 2, wherein, The R2 is above 3.0% and below 8.0%.

4. The cemented carbide according to claim 1 or 2, wherein, The R1 is above 2.6% and below 13.0%.

5. The cemented carbide according to claim 1 or 2, wherein, The R1 is above 2.8% and below 12.8%.

6. The cemented carbide according to claim 1 or 2, wherein, The vanadium content of the cemented carbide is less than 1.0 atm%.

7. The cemented carbide according to claim 1 or 2, wherein, The vanadium content of the cemented carbide is less than 0.8 atm%.

8. The cemented carbide according to claim 1 or 2, wherein, R1 is less than 4.0 times R2.

9. The cemented carbide according to claim 1 or 2, wherein, The average particle size of the tungsten carbide particles is greater than 0.1 μm and less than 3.5 μm.

10. The cemented carbide according to claim 1 or 2, wherein, The hardness of the tungsten carbide particles is above 31 GPa and below 33 GPa.

11. The cemented carbide according to claim 1 or 2, wherein, The cobalt content of the combined phase is 90% by mass or more and 100% by mass or less.

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