cemented carbide

Abstract

A cemented carbide including tungsten carbide particles and a binder phase, wherein the cemented carbide includes the tungsten carbide particles and the binder phase in total of 80% by volume or more, the cemented carbide includes the binder phase of 0.1% by volume or more and 20% by volume or less, the tungsten carbide particles are composed of a first region and a second region, the first region is a region of 0 nm or more and 50 nm or less from a surface of the tungsten carbide particle, the second region is a portion in the tungsten carbide particle after the first region is removed, the first region and the second region each include a first metal element, the first metal element is at least one selected from the group consisting of titanium, niobium, and tantalum, a proportion R1 of an atomic number of the first metal element in the first region with respect to a total of an atomic number of the first metal element and an atomic number of tungsten is 0.70 times or more and less than 1.30 times a proportion R2 of an atomic number of the first metal element in the second region with respect to a total of an atomic number of the first metal element and an atomic number of tungsten, the R2 is 2.0% or more and 10.0% or less, and the binder phase includes cobalt.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a cemented carbide. BACKGROUND

[0002] Conventionally, a cemented carbide having tungsten carbide (WC) particles and a binder phase mainly composed of an iron group element (e.g., Fe, Co, Ni) has been used as a raw material for cutting tools (Patent Literature 1, Patent Literature 2). The cemented carbide for cutting tools is required to have strength (e.g., bending strength), toughness (e.g., fracture toughness), hardness (e.g., Vickers hardness), plastic deformation resistance, wear resistance, and the like.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

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

[0006] Patent Literature 2: Japanese Patent Application Publication No. 2021-110010 SUMMARY

[0007] The cemented carbide of the present disclosure is a cemented carbide including tungsten carbide particles and a binder phase, in which

[0008] The cemented carbide includes the tungsten carbide particles and the binder phase in total of 80 vol% or more,

[0009] The cemented carbide includes the binder phase in an amount of 0.1 vol% or more and 20 vol% or less,

[0010] The tungsten carbide particles are composed of a first region and a second region,

[0011] The first region is a region of 0 nm or more and 50 nm or less from a surface of the tungsten carbide particle,

[0012] The second region is a portion of the tungsten carbide particle after the first region is removed,

[0013] The first region and the second region each include a first metal element,

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

[0015] A ratio R1 of an atomic number of the first metal element in the first region to a total of the atomic number of the first metal element and an atomic number of a tungsten element is 0.70 times or more and less than 1.30 times a ratio R2 of an atomic number of the first metal element in the second region to a total of the atomic number of the first metal element and the atomic number of the tungsten element,

[0016] R2 is 2.0% or more and 10.0% or less,

[0017] The binding phase contains cobalt. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a diagram schematically showing a cross section of a cemented carbide of one embodiment of the present disclosure.

[0019] Figure 2 is a HAADF (high-angle annular dark field) image of a cross section of a cemented carbide of one embodiment of the present disclosure. DETAILED DESCRIPTION

[0020] [PROBLEMS TO BE SOLVED BY THE PRESENT DISCLOSURE]

[0021] In recent years, in cutting processing, difficulty in cutting of a workpiece has been increasing, and the use conditions of a cutting tool have become severe. Thus, a cemented carbide used as a base material of a cutting tool is also required to have various properties improved. In particular, in end mill processing (intermittent processing) of steel, titanium, Inconel, and the like, in order to be able to make the tool long in life, tungsten carbide particles in the cemented carbide are required to have excellent toughness (strength).

[0022] [EFFECTS OF THE PRESENT DISCLOSURE]

[0023] According to the present disclosure, it is possible to provide a cemented carbide containing tungsten carbide particles having excellent toughness (strength).

[0024] [EXPLANATION OF EMBODIMENTS OF THE PRESENT DISCLOSURE]

[0025] First, one embodiment of the present disclosure will be described.

[0026] (1) The cemented carbide of the present disclosure is a cemented carbide containing tungsten carbide particles and a binding phase, in which

[0027] The cemented carbide contains the tungsten carbide particles and the binding phase in total of 80 vol% or more,

[0028] The cemented carbide contains the binding phase in an amount of 0.1 vol% or more and 20 vol% or less,

[0029] The tungsten carbide particles are composed of a first region and a second region,

[0030] The first region is a region from the surface of the tungsten carbide particle by 0 nm or more and 50 nm or less,

[0031] The second region is a portion in the tungsten carbide particle after the first region is removed,

[0032] The first region and the second region each contain a first metal element,

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

[0034] The proportion R1 of the number of atoms of the first metal element in the first region with respect to the total of the number of atoms of the first metal element and the number of atoms of tungsten is 0.70 times or more and less than 1.30 times the proportion R2 of the number of atoms of the first metal element in the second region with respect to the total of the number of atoms of the first metal element and the number of atoms of tungsten,

[0035] The R2 is 2.0% or more and 10.0% or less,

[0036] The combined phase contains cobalt.

[0037] In the cemented carbide of the present disclosure, tungsten carbide particles can have excellent toughness (strength).

[0038] (2) Preferably, the R1 is 0.75 times or more and 1.25 times or less the R2. Thereby, more excellent toughness can be obtained.

[0039] (3) Preferably, the R2 is 3.0% or more and 8.0% or less. Thereby, more excellent toughness can be obtained.

[0040] (4) Preferably, the R1 is 2.6% or more and 12% or less. Thereby, more excellent toughness can be obtained.

[0041] (5) Preferably, the cemented carbide has a vanadium content of 1.0 at% or less on an atomic basis. Thereby, reduction in grain boundary strength between tungsten carbide particles caused by vanadium can be suppressed.

[0042] [Details of Embodiments of the Present Disclosure]

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

[0044] In the present specification, the expression in the form of "A to B" means the upper limit and the lower limit of the range (i.e., A or more and B or less), and in the case where the unit is not described in A but only described in B, the unit of A is the same as the unit of B.

[0045] In the present specification, in the case of expressing a compound or the like by a chemical formula, all atomic ratios conventionally known are included, and the atomic ratio is not necessarily limited to only the stoichiometric range, unless specifically limited. For example, in the case of being described as "WC", the atomic ratio of the atoms constituting WC includes all atomic ratios conventionally known.

[0046] [Embodiment 1: Cemented carbide]

[0047] As shown in Figure 1 the cemented carbide according to the present embodiment is a cemented carbide 3 including tungsten carbide particles 1 and a binder phase 2, in which

[0048] the cemented carbide 3 includes the tungsten carbide particles 1 and the binder phase 2 in total of 80% by volume or more,

[0049] the cemented carbide 3 includes the binder phase 2 in an amount of 0.1% by volume or more and 20% by volume or less,

[0050] the tungsten carbide particles 1 are composed of a first region and a second region,

[0051] the first region is a region of 0 nm or more and 50 nm or less from the surface of the tungsten carbide particles 1,

[0052] the second region is a portion of the tungsten carbide particles after the first region is removed,

[0053] the first region and the second region each include a first metal element,

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

[0055] a proportion R1 of the number of atoms of the first metal element in the first region with respect to the total of the number of atoms of the first metal element and the number of atoms of tungsten is 0.70 times or more and less than 1.30 times a proportion R2 of the number of atoms of the first metal element in the second region with respect to the total of the number of atoms of the first metal element and the number of atoms of tungsten,

[0056] the R2 is 2.0% or more and 10.0% or less,

[0057] the binder phase 2 includes cobalt.

[0058] In the cemented carbide 3 of the present embodiment, the tungsten carbide particles can have excellent toughness (strength). The reason is presumed as follows.

[0059] The proportion R1 of the number of atoms of the first metal element in the first region with respect to the total of the number of atoms of the first metal element and the number of atoms of tungsten in the first region is 0.70 times or more and less than 1.30 times the proportion R2 of the number of atoms of the first metal element in the second region with respect to the total of the number of atoms of the first metal element and the number of atoms of tungsten in the second region, the R2 being 2.0% or more and 10.0% or less. Thus, since the first metal element is moderately contained in the surface region (first region) and the internal region (second region) in the tungsten carbide particle 1, lattice strain is generated in the tungsten carbide particle 1. As a result, since the lattice strain, the toughness (strength) of the tungsten carbide particle 1 can be improved.

[0060] <Composition of the cemented carbide>

[0061] The cemented carbide of the present embodiment is a cemented carbide containing tungsten carbide particles and a binder phase. In addition, the cemented carbide contains the tungsten carbide particles and the binder phase in a total of 80% by volume or more. Thus, the cemented carbide of the present embodiment can have excellent toughness. The cemented carbide preferably contains the tungsten carbide particles and the binder phase in a total of 82% by volume or more, more preferably 84% by volume or more, and further preferably 86% by volume or more. The cemented carbide preferably contains the tungsten carbide particles and the binder phase in a total of 100% by volume or less. Furthermore, from the viewpoint of manufacturing, the cemented carbide can contain the tungsten carbide particles and the binder phase in a total of 98% by volume or less, 99% by volume or less. The cemented carbide preferably contains the tungsten carbide particles and the binder phase in a total of 80% by volume or more and 100% by volume or less, more preferably 82% by volume or more and 100% by volume or less, and further preferably 84% by volume or more and 100% by volume or less.

[0062] The cemented carbide of the present embodiment can be composed of tungsten carbide particles and a binder phase. The cemented carbide of the present embodiment can further contain tungsten carbide particles and other phases other than the binder phase described above, in addition to the tungsten carbide particles and the binder phase. As the other phases, carbonitrides or nitrides of titanium (Ti), tantalum (Ta), niobium (Nb), or the like can be exemplified. The cemented carbide of the present embodiment can be composed of tungsten carbide particles, a binder phase, and other phases. The content rate of the other phases of the cemented carbide is allowed within a range not impairing the effects of the present disclosure. For example, the content rate of the other phases of 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 further preferably 0% by volume or more and 16% by volume or less.

[0063] The cemented carbide of the present embodiment can contain impurities. As the impurities, iron (Fe), molybdenum (Mo), calcium (Ca), silicon (Si), and sulfur (S) can be listed. The content of the impurities in the cemented carbide is allowed within a range that does not impair the effects of the present disclosure. For example, the content of the impurities in the cemented carbide is preferably 0 mass% or more and less than 0.1 mass%. The content of the impurities in the cemented carbide is measured by ICP emission analysis (measuring device: Shimadzu Corporation "ICPS-8100" (trademark)).

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

[0065] The cemented carbide of the present embodiment contains 0.1 vol% or more and 20 vol% or less of the binder phase. Thereby, the cemented carbide of the present embodiment can have excellent toughness. In addition, the cemented carbide preferably contains 1 vol% or more of the binder phase, more preferably 2 vol% or more, and further preferably 3 vol% or more. In addition, the cemented carbide preferably contains 18 vol% or less of the binder phase, more preferably 16 vol% or less, and further preferably 14 vol% or less. In addition, the cemented carbide preferably contains 1 vol% or more and 18 vol% or less of the binder phase, more preferably 2 vol% or more and 16 vol% or less, and further preferably 3 vol% or more and 14 vol% or less.

[0066] The cemented carbide of the present embodiment is preferably composed of 60 vol% or more and 99.9 vol% or less of tungsten carbide particles and 0.1 vol% or more and 20 vol% or less of the binder phase. The cemented carbide of the present embodiment is preferably composed of 62 vol% or more and 99 vol% or less of tungsten carbide particles and 1 vol% or more and 18 vol% or less of the binder phase. The cemented carbide of the present embodiment is preferably composed of 64 vol% or more and 98 vol% or less of tungsten carbide particles and 2 vol% or more and 16 vol% or less of the binder phase.

[0067] The measurement method of the content of tungsten carbide particles (vol%) in the cemented carbide and the content of the binder phase (vol%) in the cemented carbide is as described below.

[0068] (A1) Cut any position of the cemented carbide to expose a cross section. Mirror finish the cross section by a cross section polisher (manufactured by JEOL Ltd.).

[0069] (B1) Analyze the mirror finished surface of the cemented carbide using a scanning electron microscope-energy dispersive X-ray spectrometry (SEM-EDX) (device: Gemini450 (trademark) manufactured by Carl Zeiss) to determine the elements contained in the cemented carbide.

[0070] (C1) Take a photograph of the mirror finished surface of the cemented carbide by a scanning electron microscope (SEM) to obtain a reflection electron image. The photographing region for taking the image is set at a position of the central part of the cross section of the cemented carbide, i.e., a part where the characteristics are obviously different from the bulk part, such as the vicinity of the surface of the cemented carbide (the photographing region is entirely a position of the bulk part of the cemented carbide). The observation magnification is 5000 times. The measurement conditions are an acceleration voltage of 3 kV, a current value of 2 nA, and a working distance (WD) of 5 mm.

[0071] (D1) Analyze the photographing region of the above (C1) using an energy dispersive X-ray analysis device (SEM-EDX) attached to the SEM to determine the distribution of the elements determined in the above (B1) in the photographing region to obtain an element mapping image.

[0072] (E1) Introduce the reflection electron image obtained in the above (C1) into a computer and perform a binarization process using an image analysis software (OpenCV, SciPy). In the image after the binarization process, the tungsten carbide particles are shown in white and the binder phase is shown in gray to black. In addition, the threshold value for the binarization varies depending on the contrast, and therefore the threshold value is set for each image.

[0073] (F1) Determine the presence regions of the tungsten carbide particles and the binder phase on the image after the binarization process by superimposing the element mapping image obtained in the above (D1) on the image after the binarization process. Specifically, the region where tungsten (W) and carbon (C) are present in the element mapping image corresponds to the presence region of the tungsten carbide particles in the image after the binarization process, which is shown in white. The region where cobalt (Co) is present in the element mapping image corresponds to the presence region of the binder phase in the image after the binarization process, which is shown in gray to black.

[0074] (G1) Set one measurement field of a rectangle of 24.9 pm x 18.8 pm in the image after the binarization process. Determine the area percentage of the tungsten carbide particles and the binder phase each using the image analysis software described above with the area of the entire measurement field as the denominator.

[0075] (H1) The measurement of (G1) above is performed in five mutually non-overlapping different measurement fields. In the present specification, the average of the area percentages of tungsten carbide particles in the five measurement fields corresponds to the content (vol%) of tungsten carbide particles in the cemented carbide, and the average of the area percentages of the binder phase in the five measurement fields corresponds to the content (vol%) of the binder phase in the cemented carbide.

[0076] In the case where the cemented carbide contains other phases in addition to the WC particles and the binder phase, the content of the other phases in the cemented carbide can be obtained by subtracting the content (vol%) of the tungsten carbide particles and the content (vol%) of the binder phase, which are determined according to the above-described procedure, from the entirety of the cemented carbide (100 vol%).

[0077] It was confirmed that, as long as the measurement is performed in the range of the applicant's measurement, and as long as the measurement is performed in the same test sample, even if the cutting position of the cross section of the cemented carbide is arbitrarily set, and the imaging region described in (C1) above is arbitrarily set on the cross section, the determination of the content of the tungsten carbide particles and the content of the binder phase of the cemented carbide is performed several times according to the above-described procedure, the deviation of the measurement results is small, and even if the cutting position of the cross section of the cemented carbide is arbitrarily set, and the imaging region of the reflected electron image is arbitrarily set, the results do not change at will.

[0078] Tungsten carbide particles

[0079] The tungsten carbide particles described above are composed of a first region and a second region. In addition, the first region is a region of 0 nm or more and 50 nm or less from the surface of the tungsten carbide particles. In addition, the second region is a portion of the tungsten carbide particles after the first region is removed.

[0080] First metal element

[0081] The first region and the second region described above each contain a first metal element, and the first metal element is at least one selected from the group consisting of titanium, niobium, and tantalum. From the viewpoint of imparting high toughness (strength) to the tungsten carbide particles described above, the first metal 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 of the number of atoms of the first metal element and the number of atoms of the tungsten element is 0.70 times or more and less than 1.30 times the ratio R2 of the number of atoms of the first metal element in the second region to the total of the number of atoms of the first metal element and the number of atoms of the tungsten element. Thus, the toughness of the tungsten carbide particles can be improved, and therefore the cemented carbide including such tungsten carbide particles can have excellent toughness. In addition, the R1 is preferably 0.75 times or more, more preferably 0.8 times or more, the R2. In addition, the R1 is preferably 1.25 times or less, more preferably 1.2 times or less, the R2. In addition, the R1 is preferably 0.75 times or more and 1.25 times or less, more preferably 0.8 times or more and 1.2 times or less, the R2.

[0083] The R1 can also be expressed by the calculation formula "R1 = [(number of atoms of the first metal element in the first region) / {(number of atoms of the tungsten element in the first region) + (number of atoms of the first metal element in the first region)}] x 100". In addition, the R2 can also be expressed by the calculation formula "R2 = [(number of atoms of the first metal element in the second region) / {(number of atoms of the tungsten element in the second region) + (number of atoms of the first metal element in the second region)}] x 100". In addition, "R1 is 0.70 times or more and less than 1.30 times the R2" can also be expressed by the calculation formula "0.70 ≤ R1 / R2 < 1.30".

[0084] The R2 is preferably 2.0% or more and 10.0% or less. Thus, a lattice strain is generated in the cemented carbide, and therefore the toughness of the cemented carbide can be improved. In addition, the R2 is preferably 3.0% or more, more preferably 3.5% or more, further preferably 4.0% or more. In addition, the R2 is preferably 8.0% or less, more preferably 7.0% or less, further preferably 6.0% or less. In addition, the R2 is preferably 3.0% or more and 8.0% or less, more preferably 3.5% or more and 7.0% or less, further preferably 4.0% or more and 6.0% or less.

[0085] The R1 is preferably 2.6% or more and 12% or less. Thus, a lattice strain is generated in the cemented carbide, and therefore the toughness of the cemented carbide can be further improved. In addition, the R1 is preferably 2.8% or more, more preferably 3.0% or more. In addition, the R1 is preferably 12.8% or less, more preferably 12.5% or less. In addition, the R1 is preferably 2.8% or more and 12.8% or less, more preferably 3.0% or more and 12.5% or less.

[0086] (R1 and R2 measurement method)

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

[0088] (A2) A sample is collected from the cemented carbide, and a slice is prepared by slicing the sample into a thickness of 30 to 100 nm using an argon ion slicer ("IB09060CIS" (trademark) manufactured by JEOL Ltd.) under conditions where the acceleration voltage is 2 kV.

[0089] (B2) Next, the slice is observed at 200,000 times using a TEM (Transmission Electron Microscopy) ("JFM-ARM300F" (trademark) manufactured by JEOL Ltd.) under conditions where the acceleration voltage is 200 V, thereby obtaining a first image (not shown).

[0090] (C2) In the first image, the surface S of the tungsten carbide particle is arbitrarily selected. In addition, in the first image, the method for determining the surface S of the tungsten carbide particle is as described below. That is, element mapping analysis based on EDX (Energy Dispersive x-ray Spectroscopy) is performed on the above first image, and the distribution of cobalt is analyzed. In the obtained element mapping image, the line indicating the region where the concentration of cobalt is high corresponds to the surface S of the tungsten carbide particle.

[0091] (D2) Next, one tungsten carbide particle in the first image is arbitrarily selected, and using image processing software (OpenCV, SciPy), a region (first region) from the surface S of the tungsten carbide particle that is 0 nm or more and 50 nm or less and a portion (second region) excluding the first region are determined. In the first image, a line segment L that passes through the tungsten carbide particle is drawn. The line segment L is a line segment that connects two points on the surface S of the tungsten carbide particle and passes through both the first region and the second region. It is confirmed that as long as the line segment L passes through both the first region and the second region, the determination results below will not be affected.

[0092] (E2) The line segment L that passes through the above tungsten carbide particle is positioned so as to pass near the center of the image, the observation magnification is changed to 25 million times, and observation is performed, thereby obtaining a second image. In the case where the length of the above line segment L is long and is not accommodated in the field of view of one second image, a plurality of continuous second images (HAADF images) are obtained so as to include the entire line segment L. One example of the second image is shown in Figure 2It is understood that, in the second image, the line segment L is located near the center of the image, and different tungsten carbide particles exist on the left and right sides toward the paper surface with the surface S of the tungsten carbide particle as a boundary. Figure 2 In the second image, regarding the tungsten carbide particle located on the left side toward the paper surface with the above S as a boundary, the following elemental line analysis is performed.

[0093] Next, in the second image, EDX-based elemental line analysis is performed along the above line segment, and the distribution of the first metal element and the distribution of the tungsten element are analyzed. The beam diameter at this time is set to be 0.3 nm or less, and the scanning interval is set to be 0.1-0.7 nm. Thus, in the region from a point on the surface of the tungsten carbide particle to a point on the opposite surface, the above elemental line analysis can be performed.

[0094] (F2) According to the results of the elemental line analysis, for a region (first region) of 0 nm or more and 50 nm or less from the surface of the tungsten carbide particle, the average value of the atomic number of the first metal element and the average value of the atomic number of the tungsten element are calculated. Next, the average value of the atomic number of the first metal element is divided by the sum of the average value of the atomic number of the first metal element and the average value of the atomic number of the tungsten element, and the value thus obtained is multiplied by 100, thereby calculating the above R1.

[0095] (G2) In addition, according to the results of the above elemental line analysis, for a portion (second region) of the tungsten carbide particle after removing the above first region, the average value of the atomic number of the first metal element and the average value of the atomic number of the tungsten element are calculated. Next, the average value of the atomic number of the first metal element is divided by the sum of the average value of the atomic number of the first metal element and the average value of the atomic number of the tungsten element, and the value thus obtained is multiplied by 100, thereby calculating the above R2.

[0096] (Average particle diameter)

[0097] The lower limit of the average particle diameter of the tungsten carbide particles in the present embodiment 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 diameter of the tungsten carbide particles is preferably 3.5 μm or less, 3.0 μm or less, or 2.5 μm or less. The average particle diameter 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. Thus, the cemented carbide has high hardness, and the tool containing the cemented carbide has improved wear resistance. In addition, the tool can have excellent chipping resistance.

[0098] In the present specification, the average particle diameter of the tungsten carbide particles refers to the D50 (equivalent circle diameter at which the cumulative frequency on a number basis is 50%, median particle diameter D50) of the equivalent circle diameter of area of the WC particles contained in the cemented carbide. The average particle diameter of the tungsten carbide particles is measured as described below.

[0099] (A3) The presence area of the tungsten carbide particles is determined on the image after the binarization treatment by the same method as in (A1) to (F1) of the measurement method of the content of the tungsten carbide particles and the content of the binder phase of the cemented carbide described above.

[0100] (B3) One measurement field of a rectangle of 24.9 μm x 18.8 μm is set in the image after the binarization treatment described above. The outer edge of each tungsten carbide particle in the measurement field is determined using the image analysis software described above, and the equivalent circle diameter (Heywood diameter: equivalent circle diameter of area) of each tungsten carbide particle is calculated.

[0101] (C3) The D50 of the equivalent circle diameter of area of the tungsten carbide particles is calculated based on all the tungsten carbide particles in the measurement field described above.

[0102] It was confirmed that, as long as the measurement was performed within the range measured by the applicant, as long as the measurement was performed in the same test sample, even if the cutting position of the cross section of the cemented carbide was arbitrarily set, the photographing area described in (C1) above was arbitrarily set on the cross section, and the measurement field described in (B2) above was arbitrarily set, the measurement of the average particle diameter of the tungsten carbide particles was performed several times according to the steps described above, and the deviation of the measurement results was small. Even if the cutting position of the cross section of the cemented carbide was arbitrarily set, the photographing area of the photographed image was arbitrarily set, and the measurement field was arbitrarily set, the results did not change at will.

[0103] (Elastic modulus of tungsten carbide particles)

[0104] The elastic modulus of the tungsten carbide particles is preferably 450 GPa or greater and 465 GPa or less. In the cemented carbide, the elastic modulus of the tungsten carbide particles can be determined by the following method. First, the surface of the cemented carbide is polished using a cross-section polisher (CP) processing device (IB-19500 CP section sample making device (trademark) manufactured by JEOL Ltd.), thereby exposing the tungsten carbide particles. Next, for an arbitrary one of the tungsten carbide particles, the elastic modulus is determined using a nanoindenter (TI980 (trademark) manufactured by Bruker Hysitron Inc.) by the following measurement conditions.

[0105] (Measurement conditions of the nanoindenter)

[0106] • Maximum load: 3 mN

[0107] • Load: 5 s

[0108] • Hold: 2 s

[0109] • Unload: 5 s

[0110] • N: 10

[0111] Similarly, the elastic modulus is determined for other nine arbitrary tungsten carbide particles. Next, for the ten tungsten carbide particles for which the elastic modulus is determined, the average of the elastic modulus is calculated, thereby obtaining the elastic modulus of the tungsten carbide particles.

[0112] The binder phase contains cobalt. Thereby, the cemented carbide can be imparted with excellent toughness. In addition, the content of cobalt of the binder phase is preferably 90 mass% or greater and 100 mass% or less, 92 mass% or greater and 100 mass% or less, 94 mass% or greater and 100 mass% or less, 100 mass%. The content of cobalt of the binder phase is determined by ICP (Inductively Coupled Plasma) emission analysis (measurement device: ICPS-8100 (trademark) manufactured by Shimadzu Corporation). In addition, as long as cobalt is contained in the binder phase to a degree that can be detected by ICP emission analysis, the binder phase functions as a binder phase regardless of the content of cobalt of the binder phase.

[0113] The above-described combined phase can further include nickel (Ni), chromium (Cr), iron (Fe), aluminum (Al), ruthenium (Ru), rhenium (Re), or the like in addition to cobalt. The combined phase can be composed of cobalt and at least one selected from the group consisting of nickel, chromium, iron, aluminum, ruthenium, and rhenium. The combined phase can be composed of cobalt, at least one selected from the group consisting of nickel, chromium, iron, aluminum, ruthenium, and rhenium, and unavoidable impurities. As the unavoidable impurities, for example, manganese (Mn), magnesium (Mg), calcium (Ca), molybdenum (Mo), sulfur (S), titanium (Ti), or the like can be exemplified.

[0114] [Atomic number-based content of vanadium in cemented carbide]

[0115] The atomic number-based content of vanadium in the cemented carbide is preferably 1.0 at% or less. Thereby, the reduction in the grain boundary strength between tungsten carbide particles caused by vanadium can be suppressed. Further, the upper limit of the atomic number-based content of vanadium in the cemented carbide is more preferably 0.8 at% or less, and further preferably 0.6 at% or less. Further, from the viewpoint of manufacturing, the lower limit of the atomic number-based content of vanadium in the cemented carbide can be 0.1 at% or more, 0.2 at% or more, 0.3 at% or more. Further, the atomic number-based content of vanadium in the cemented carbide is preferably 0 at% or more and 1.0 at% or less, more preferably 0 at% or more and 0.8 at% or less, and further preferably 0 at% or more and 0.6 at% or less. In addition, vanadium exists at the interface between tungsten carbide particles.

[0116] The atomic number-based content of vanadium in the cemented carbide is measured by ICP (Inductively Coupled Plasma) emission analysis (measuring device: "ICPS-8100" (trademark) manufactured by Shimadzu Corporation).

[0117] [Embodiment 2: Method for manufacturing cemented carbide]

[0118] The cemented carbide raw material of the present embodiment can be manufactured by sequentially performing a raw material powder preparation step, a mixing step, a molding step, a sintering step, and a cooling step. Hereinafter, each step will be described.

[0119] [Pre-treatment step]

[0120] The pre-treatment step is a step of obtaining tungsten carbide (WC) powder containing the above first metal element. First, a mixture is obtained by mixing 75 mass% or more and 97 mass% or less of tungsten (W) powder, 0.1 mass% or more and 10 mass% or less of the first metal element powder, and 3 mass% or more and 15 mass% or less of carbon (C) powder. As the first metal element powder, titanium oxide (TiO2), niobium oxide (Nb2O5), and tantalum oxide (Ta2O5) can be listed. Next, by heating the mixture at 1500°C for 4 hours, tungsten carbide powder containing the above first metal element (hereinafter, also referred to as "WC powder containing the first metal element") can be obtained. The tungsten (W) powder, the first metal element powder, and the carbon powder can be commercially available products.

[0121] <Preparation step>

[0122] The preparation step is a step of preparing raw material powder of a material constituting a hard alloy raw material. As the raw material powder, the above WC powder containing the first metal element and cobalt (Co) powder can be listed. Further, as the raw material powder, chromium carbide (Cr3C2) powder and vanadium carbide (VC) powder as a crystal grain growth inhibitor can be listed. The cobalt powder, the chromium carbide powder, and the vanadium carbide powder can be commercially available products.

[0123] <Mixing step>

[0124] The mixing step is a step of mixing each of the raw material powders prepared in the preparation step at a predetermined ratio. By the mixing step, mixed powder in which each of the raw material powders is mixed can be obtained.

[0125] The proportion of the above WC powder containing the first metal element in the mixed powder can be, for example, 80 mass% or more and 99.9 mass% or less. In addition, the proportion of the cobalt powder in the mixed powder can be, for example, 0.1 mass% or more and 20 mass% or less. In addition, the proportion of the chromium carbide powder in the mixed powder can be, for example, 0.1 mass% or more and 2 mass% or less. In addition, the proportion of the vanadium carbide powder in the mixed powder can be, for example, 0.1 mass% or more and 2 mass% or less.

[0126] In the mixing of each of the raw material powders, a wet-type bead mill ("LMZ06" (trademark) manufactured by Ashizawa Finetech Co., Ltd.) can be used. The mixing time can be 2 hours or more and 20 hours or less. Thereby, the raw material powders can be finely broken and pulverized.

[0127] Further, after the mixing step, the mixed powder can be granulated as needed. By granulating the mixed powder, it is easy to fill the mixed powder into a die or a mold at the forming step described later. In the granulation, a publicly known granulation method can be applied, and for example, a commercially available granulator such as a spray dryer can be used.

[0128] <forming step>

[0129] The forming step is a step of forming the mixed powder obtained in the mixing step into a shape (for example, a round bar shape) for a rotary tool to obtain a formed body. The forming method and the forming conditions in the forming step are not particularly limited as long as a general method and conditions are adopted.

[0130] <the sintering step>

[0131] The sintering step is a step of sintering the formed body obtained through the forming step by a sintering HIP (Hot Isostatic Pressing) (Sinter-HIP) treatment capable of performing pressurization at the time of sintering to obtain a cemented carbide intermediate.

[0132] The sintering temperature is preferably 1320°C or higher and 1500°C or lower, more preferably 1330°C or higher and 1450°C or lower, and further preferably 1340°C or higher and 1420°C or lower.

[0133] Further, the sintering time is preferably 30 minutes or longer and 120 minutes or shorter, and more preferably 45 minutes or longer and 90 minutes or shorter.

[0134] Further, the degree of vacuum (pressure) at the time of sintering is preferably 0.1 kPa or higher and 10 MPa or lower.

[0135] Further, the atmosphere at the time of sintering is not particularly limited, and as the atmosphere, an N2 gas atmosphere or an Ar or the like non-active gas atmosphere can be cited.

[0136] <the cooling step>

[0137] The cooling step is a step of cooling the cemented carbide intermediate after the sintering step. For example, the above cemented carbide intermediate can be rapidly cooled to 1000°C in an Ar gas.

[0138] <Features of the method for producing a cemented carbide of the present embodiment>

[0139] In the cemented carbide obtained by the production method described above, the proportion R1 of the number of atoms of the first metal element in the first region with respect to the total of the number of atoms of the first metal element and the number of atoms of tungsten is 0.70 times or more and less than 1.30 times the proportion R2 of the number of atoms of the first metal element in the second region with respect to the total of the number of atoms of the first metal element and the number of atoms of tungsten, and the R2 is 2.0% or more and 10.0% or less. The reason is presumed as follows.

[0140] By preparing a first metal element powder as a raw material of the first metal element, it is possible to include the first metal element in the cemented carbide. However, there is a tendency that the first metal element is difficult to diffuse into tungsten carbide particles included in the cemented carbide, only by simply mixing the raw material powder and performing sintering. On the other hand, by combining the following processes: in a pretreatment process, obtaining tungsten carbide powder containing the first metal element in advance; in a mixing process, using a bead mill to strongly pulverize the mixed powder; and in a sintering process, performing sintering at a low temperature while applying pressure, it is easy to promote diffusion of the first metal element into tungsten carbide particles, and thus the first metal element is easily diffused into tungsten carbide particles included in the cemented carbide.

[0141] As a result of intensive studies by the inventors of the present application, it has been newly found that by combining the following processes: in a pretreatment process, obtaining tungsten carbide powder containing the first metal element in advance; in a mixing process, using a bead mill; and in a sintering process, performing sintering at a low temperature while applying pressure, it is possible to obtain a cemented carbide in which "the proportion R1 of the number of atoms of the first metal element in the first region with respect to the total of the number of atoms of the first metal element and the number of atoms of tungsten is 0.70 times or more and less than 1.30 times the proportion R2 of the number of atoms of the first metal element in the second region with respect to the total of the number of atoms of the first metal element and the number of atoms of tungsten, and the R2 is 2.0% or more and 10.0% or less".

[0142] <Tool>

[0143] The cemented carbide of the present embodiment can be used as a tool material. As the tool, for example, cutting tools, drills, end mills, indexable cutting inserts for milling, indexable cutting inserts for turning, bench saws, gear cutting tools, reamers, taps, and the like can be exemplified.

[0144] The cemented carbide of the present embodiment can constitute the entirety of these tools, or can constitute a part. Here, "constitute a part" means a manner in which the cemented carbide of the present embodiment is brazed to a predetermined position of an arbitrary base material to form a tip portion, and the like.

[0145] The tool can further have a hard film that coats at least a portion of the surface of the substrate composed of cemented carbide. As the hard film, for example, diamond-like carbon or diamond can be used.

[0146] Embodiments

[0147] The present embodiment will be further specifically described by way of examples. However, the present embodiment is not limited to these examples.

[0148] Manufacture of Cemented Carbide

[0149] The cemented carbide of each sample was manufactured in accordance with the following steps.

[0150] <Pre-treatment Step>

[0151] In order to manufacture the cemented carbide of Sample 1 to Sample 16, as the raw material powder, a mixture was obtained by mixing tungsten (W) powder ("A20" (trademark) manufactured by ALMT Corporation), titanium oxide (Ti02) powder (first metal element powder), niobium oxide (Nb205) powder (first metal element powder), tantalum oxide (Ta205) powder (first metal element powder), and carbon powder in the composition described in Table 1. Next, the mixture was heated at 1500°C for 4 hours, thereby obtaining tungsten carbide powder containing the above-described first metal element.

[0152] <Preparation Step>

[0153] In order to manufacture the cemented carbide of Sample 1 to Sample 16, and Sample 101 to Sample 108, as the raw material powder, the above-described 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 above-described first metal element (hereinafter, also referred to as "WC (without first metal element)") ("WC04NR" (trade name) manufactured by Allied Material Corporation), titanium carbonitride (TiCN) powder were prepared.

[0154] Table 1

[0155]

[0156] <Mixing Step>

[0157] Next, the prepared each raw material powder was mixed using a bead mill for 12 hours in the blend described in Table 2, thereby manufacturing a mixed powder.

[0158]

[0159] <Shaping Step>

[0160] Next, the obtained mixed powder was subjected to press forming, whereby a formed body in a round bar shape was produced.

[0161] <annealing step>

[0162] Next, sintering HIP (sintering hot isostatic pressing) treatment was performed under the conditions described in Table 2, whereby cemented carbide intermediates were produced. Further, the description of "N2→Ar" in Table 2 means that the atmosphere was changed from N2 gas (10 kPa) to Ar gas (the pressure of the Ar gas was the pressure described in the column of "s-HIP pressure [MPa]" in Table 2).

[0163] <cooling step>

[0164] Next, the cemented carbide intermediate after the sintering step was rapidly cooled to 1000°C in Ar gas.

[0165] By the above, cemented carbides of Samples 1 to 16, and cemented carbides of Samples 101 to 108 were produced. The cemented carbides of Samples 1 to 16 correspond to Examples, and the cemented carbides of Samples 101 to 108 correspond to Comparative Examples.

[0166] <Production of cutting tools>

[0167] The obtained round bar composed of cemented carbide was processed, whereby a end mill (cutting tool) having a diameter of 3 mm was produced.

[0168] <Property evaluation of cemented carbide>

[0169] <Proportion of the sum of the volume of tungsten carbide particles and the volume of binder phase to the volume of cemented carbide>

[0170] For the cemented carbides of Samples 1 to 16, and Samples 101 to 108, the proportion of the sum of the volume of tungsten carbide particles and the volume of binder phase to the volume of the cemented carbide was calculated by the method described in Embodiment 1. The obtained results are described in the column of "WC particles + binder phase [vol%]" in Table 3, respectively.

[0171]

[0172] <Proportion of the volume of binder phase to the volume of cemented carbide>

[0173] For the cemented carbides of Samples 1 to 16, and Samples 101 to 108, the proportion of the volume of binder phase to the volume of the cemented carbide was calculated by the method described in Embodiment 1. The obtained results are described in the column of "binder phase [vol%]" in Table 3, respectively. ​

[0174] <Content of cobalt in the binder phase>

[0175] The content of cobalt in the binder phase was calculated by the method described in Embodiment 1 for the cemented carbides of Test Samples 1 to 16 and Test Samples 101 to 108. The results obtained are described in the column of "Content of cobalt in the binder phase [mass%]" in Table 3, respectively.

[0176] <R1 and R2, R1 / R2>

[0177] R1 was calculated by the method described in Embodiment 1 for the cemented carbides of Test Samples 1 to 16 and Test Samples 101 to 108. The results obtained are described in the column of "R1 [%]" in Table 3, respectively. In addition, R2 was calculated by the method described in Embodiment 1 for the cemented carbides of Test Samples 1 to 16 and Test Samples 101 to 108. The results obtained are described in the column of "R2 [%]" in Table 3, respectively. Based on the obtained R1 and R2, R1 / R2 was calculated. The results are shown in the column of "R1 / R2" in Table 3.

[0178] <Average particle diameter of tungsten carbide particles>

[0179] The average particle diameter of tungsten carbide particles was calculated by the method described in Embodiment 1 for the cemented carbides of Test Samples 1 to 16 and Test Samples 101 to 108. The results obtained are described in the column of "Average particle diameter of WC particles [μm]" in Table 3, respectively.

[0180] <Content of vanadium on an atomic number basis of the cemented carbide>

[0181] The content of vanadium on an atomic number basis of the cemented carbide was calculated by the method described in Embodiment 1 for the cemented carbides of Test Samples 1 to 16 and Test Samples 101 to 108. The results obtained are described in the column of "Content of V [atm%]" in Table 3, respectively.

[0182] <Elastic modulus of tungsten carbide particles>

[0183] The elastic modulus of the cemented carbide was calculated by the method described in Embodiment 1 for the cemented carbides of Test Sample 1 and Test Sample 101. The elastic modulus of the WC particles of Test Sample 1 was 465 GPa. The elastic modulus of the WC particles of Test Sample 101 was 449 GPa. In the cemented carbides of Test Samples 2 to 12, it was confirmed that the elastic modulus of the tungsten carbide particles was 450 GPa or more. In addition, in the cemented carbides of Test Samples 102 to 108, it was confirmed that the elastic modulus of the tungsten carbide particles was less than 450 GPa.

[0184] <Cutting test>

[0185] Using the end mill of each sample, cutting was performed under the following cutting conditions, and the cutting distance until a defect of 100 μm or more occurred in the end mill was measured. The following cutting conditions correspond to end mill machining (high efficiency machining) of a titanium alloy. The longer the cutting distance, the longer the tool life. The results obtained are respectively described in the column of "cutting test [m]" in Table 3.

[0186] (Cutting conditions)

[0187] Workpiece: Inconel aged material Hole forming material

[0188] Cutting speed Vc: 40 m / min

[0189] Feed per tooth Fz: 0.1 mm / t

[0190] Depth of cut Ap: 1.0 mm

[0191] Width of cut Ae: 0.5 mm

[0192] Cutting fluid: Yes (wet)

[0193] Investigation

[0194] The cemented carbide end mill (cutting tool) of Samples 1 to 16 (Examples) corresponds to the Examples. In addition, the cemented carbide end mill (cutting tool) of Samples 101 to 108 (Comparative Examples) corresponds to the Comparative Examples. It was confirmed that the cemented carbide end mill (cutting tool) of Samples 1 to 16 (Examples) has a longer tool life than the cemented carbide end mill (cutting tool) of Samples 101 to 108 (Comparative Examples), particularly in end mill machining (interrupted machining) of steel, titanium, Inconel, and the like.

[0195] The embodiments and examples of the present disclosure have been described as above, but it is also intended from the outset to appropriately combine or variously modify the configurations of the above-described embodiments and examples.

[0196] The embodiments and examples of the present disclosure should be considered to be examples in all aspects, rather than limiting. The scope of the present invention is not represented by the above-described embodiments and examples, but by the claims, and is intended to include the meaning equivalent to the claims, and all modifications within the scope.

[0197] Explanation of reference numerals

[0198] 1: tungsten carbide particle; 2: binder phase; 3: cemented carbide; R1: ratio of the number of atoms of the first metal element in the first region to the total of the number of atoms of the first metal element and the number of atoms of tungsten element; R2: ratio of the number of atoms of the first metal element in the second region to the total of the number of atoms of the first metal element and the number of atoms of tungsten element; L: line segment crossing the tungsten carbide particle; S: 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% or more of the tungsten carbide particles and the bonding phase. The cemented carbide comprises 0.1% by volume and less than 20% by volume 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 0.70 times and less 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 0.75 times and less than 1.25 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 12%.

5. The cemented carbide according to claim 1 or 2, wherein, The R1 is above 2.8% and below 11.8%.

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 more than 0.8 times and less than 1.2 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 elastic modulus of the tungsten carbide particles is above 450 GPa and below 465 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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