WO2023228328A1 - Cemented carbide and cutting tool using same - Google Patents

Abstract

This cemented carbide comprises: a first phase comprising tungsten carbide particles; and a second phase including cobalt as a main component. The total content of the first phase and the second phase in the cemented carbide is 97 vol% or more, the average value of the circle-equivalent diameters of the tungsten carbide particles is 0.8 μm or less, the cobalt content of the cemented carbide is 3-10 mass%, the vanadium content of the cemented carbide is 0.01-0.30 mass%, and the maximum value of the vanadium content in an interface region between the second phase and the (0001) crystal planes of the tungsten carbide particles is 15 at% or less.

Description

Cemented carbide and cutting tools using it

The present disclosure relates to a cemented carbide and a cutting tool using the same.

When drilling holes in printed circuit boards, the mainstream is to drill holes with a small diameter of φ1 mm or less. For this reason, so-called fine-grained cemented carbide, in which the hard phase consists of tungsten carbide particles with an average particle size of 1 μm or less, is used as the cemented carbide used in tools such as small-diameter drills (for example, Patent Document 1 to Patent Document 1) Reference 3).

Japanese Patent Application Publication No. 2007-92090 Japanese Patent Application Publication No. 2012-52237 Japanese Patent Application Publication No. 2012-117100

The cemented carbide of the present disclosure is
A cemented carbide comprising a first phase consisting of tungsten carbide particles and a second phase containing cobalt as a main component,
The total content of the first phase and the second phase of the cemented carbide is 97% by volume or more,
The average value of the equivalent circle diameter of the tungsten carbide particles is 0.8 μm or less,
The cobalt content of the cemented carbide is 3% by mass or more and 10% by mass or less,
The vanadium content of the cemented carbide is 0.01% by mass or more and 0.30% by mass or less,
The cemented carbide has a maximum vanadium content of 15 atomic % or less in the interface region between the (0001) crystal plane of the tungsten carbide particles and the second phase.

A cutting tool of the present disclosure includes a cutting edge made of the above-mentioned cemented carbide.

FIG. 1 is a diagram for explaining a method for measuring the vanadium content in the WC/second phase interface region. FIG. 2 is a diagram showing an example of a cutting tool (small diameter drill) of this embodiment. FIG. 3 is a diagram for explaining the width of wear scars measured in Examples.

[Problems that this disclosure seeks to solve]
In recent years, with the expansion of 5G (fifth generation mobile communication system), the capacity of information is increasing. For this reason, printed circuit boards are required to have even higher heat resistance. In order to improve the heat resistance of printed circuit boards, techniques have been developed to improve the heat resistance of resins and glass fillers that constitute printed circuit boards. On the other hand, this has made it increasingly difficult to cut printed circuit boards. For this reason, in micromachining of printed circuit boards, cutting tools tend to wear out or break easily.

Therefore, the present disclosure provides a cemented carbide that can provide a cutting tool with a long tool life even when used as a material for a cutting tool used particularly for micromachining of printed circuit boards, and a cutting tool equipped with the same. The purpose is to provide

[Effects of this disclosure]
According to the cemented carbide of the present disclosure, it is possible to provide a cutting tool that has a long tool life, especially when used for micromachining of printed circuit boards.

[Description of embodiments of the present disclosure]
First, embodiments of the present disclosure will be listed and described.
(1) The cemented carbide of the present disclosure is
A cemented carbide comprising a first phase consisting of tungsten carbide particles and a second phase containing cobalt as a main component,
The total content of the first phase and the second phase of the cemented carbide is 97% by volume or more,
The average value of the equivalent circle diameter of the tungsten carbide particles is 0.8 μm or less,
The cobalt content of the cemented carbide is 3% by mass or more and 10% by mass or less,
The vanadium content of the cemented carbide is 0.01% by mass or more and 0.30% by mass or less,
The cemented carbide has a maximum vanadium content of 15 atomic % or less in the interface region between the (0001) crystal plane of the tungsten carbide particles and the second phase.

According to the cemented carbide of the present disclosure, it is possible to provide a cutting tool with a long tool life, especially when used for micromachining of printed circuit boards.

(2) In (1) above, the cemented carbide includes a third phase consisting of third phase particles containing 10 atomic % or more of vanadium,
The content of the third phase of the cemented carbide is more than 0% by volume and not more than 1% by volume,
The maximum value of the equivalent circle diameter of the third phase particles is preferably 0.5 μm or less.

According to this, since there are no coarse third phase particles with an equivalent circle diameter of more than 0.5 μm, which can become a starting point for breakage, the breakage resistance of a cutting tool using the cemented carbide is improved.

(3) In (1) or (2) above, the maximum value of the chromium content in the interface region is preferably 20 atomic % or less.

According to this, the decrease in the interface strength between the WC particles and the Co particles due to the presence of chromium in the interface region is suppressed. Therefore, in the cemented carbide, WC particles are unlikely to fall off due to a decrease in interfacial strength, and a cutting tool using the cemented carbide can have excellent wear resistance and breakage resistance.

(4) The cutting tool of the present disclosure is a cutting tool including a cutting edge made of the cemented carbide according to any one of (1) to (3) above.

The cutting tool of the present disclosure can have a long tool life, especially when used for micromachining of printed circuit boards.

[Details of embodiments of the present disclosure]
Specific examples of the cemented carbide and cutting tool of the present disclosure will be described below with reference to the drawings. In the drawings of this disclosure, the same reference numerals indicate the same or corresponding parts. Further, dimensional relationships such as length, width, thickness, depth, etc. have been appropriately changed for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

In the present disclosure, the notation in the format "A to B" means the upper and lower limits of the range (i.e., from A to B), and if there is no unit described in A and a unit is described only in B, then The unit and the unit of B are the same.

In this disclosure, if one or more numerical values are stated as the lower limit and upper limit of the numerical range, any one numerical value stated in the lower limit and any one numerical value stated in the upper limit. It is assumed that combinations of the above are also disclosed. For example, if the lower limit is a1 or more, b1 or more, c1 or more, and the upper limit is a2 or less, b2 or less, c2 or less, a1 or more and a2 or less, a1 or more and b2 or less, a1 or more and c2 or less, b1 or more and a2 or less, b1 or more and b2 or less, b1 or more and c2 or less, c1 or more and a2 or less, c1 or more and b2 or less, and c1 or more and c2 or less are disclosed.

In the present disclosure, when a compound or the like is expressed by a chemical formula, unless the atomic ratio is specifically limited, it includes all conventionally known atomic ratios, and should not necessarily be limited to only those in the stoichiometric range.

In the crystallographic description in the present disclosure, individual orientations are indicated by [], collective orientations are indicated by <>, individual planes are indicated by (), and collective planes are indicated by {}, respectively. Also, the fact that the crystallographic index is negative is usually expressed by adding a "-" (bar) above the number, but in this disclosure, a negative sign is added in front of the number. .

[Embodiment 1: Cemented carbide]
The cemented carbide of one embodiment of the present disclosure (hereinafter also referred to as "this embodiment") is
A cemented carbide comprising a first phase consisting of tungsten carbide particles and a second phase containing cobalt as a main component,
The total content of the first phase and the second phase of the cemented carbide is 97% by volume or more,
The average value of the equivalent circle diameter of the tungsten carbide particles is 0.8 μm or less,
The cobalt content of the cemented carbide is 3% by mass or more and 10% by mass or less,
The vanadium content of the cemented carbide is 0.01% by mass or more and 0.30% by mass or less,
The cemented carbide has a maximum vanadium content of 15 atomic % or less in the interface region between the (0001) crystal plane of the tungsten carbide particles and the second phase.

According to the cemented carbide of this embodiment, it is possible to provide a cutting tool with a long tool life, especially when used for micromachining of printed circuit boards. Although the reason for this is not clear, it is presumed to be as described in (i) to (v) below.

(i) The cemented carbide of this embodiment includes a first phase consisting of a plurality of tungsten carbide particles (hereinafter also referred to as "WC particles") and a second phase containing cobalt as a main component. The total content of the first phase and second phase of the cemented carbide is 97% by volume or more. According to this, the cemented carbide has high hardness and strength, and a cutting tool using the cemented carbide can have excellent wear resistance and breakage resistance.

(ii) In the cemented carbide of this embodiment, the average value of the equivalent circle diameter of the WC particles is 0.8 μm or less. According to this, the cemented carbide has high hardness, and a cutting tool using the cemented carbide can have excellent wear resistance. Further, the cemented carbide has excellent strength, and a cutting tool using the cemented carbide can have excellent breakage resistance.

(iii) The cobalt content of the cemented carbide of this embodiment is 3% by mass or more and 10% by mass or less. According to this, cemented carbide has high hardness and strength. A cutting tool using the cemented carbide can have excellent wear resistance and breakage resistance.

(iv) The vanadium content of the cemented carbide of this embodiment is 0.01% by mass or more and 0.30% by mass or less. According to this, the generation of coarse WC particles is suppressed, and the structure of the cemented carbide is made dense. Therefore, the cemented carbide has excellent hardness and strength, and a cutting tool using the cemented carbide can have excellent wear resistance and breakage resistance.

(v) In the cemented carbide of the present embodiment, the maximum vanadium content in the interface region between the (0001) crystal plane of the tungsten carbide particles and the second phase is 15 atomic % or less. According to this, the formation of a vanadium-concentrated layer in which vanadium is present in a concentrated manner is suppressed in the interface region. Therefore, a decrease in the interfacial strength between the WC particles and the second phase due to the vanadium concentrated layer is suppressed. Therefore, in the cemented carbide, WC particles are unlikely to fall off due to a decrease in interfacial strength, and a cutting tool using the cemented carbide can have excellent wear resistance and breakage resistance.

<Composition of cemented carbide>
≪Content rate of 1st phase, 2nd phase and 3rd phase≫
The cemented carbide of this embodiment includes a first phase consisting of tungsten carbide particles and a second phase containing cobalt as a main component. The total content of the first phase and second phase of the cemented carbide is 97% by volume or more. According to this, the cemented carbide has high hardness and strength, and a cutting tool using the cemented carbide can have excellent wear resistance and breakage resistance.

The lower limit of the total content of the first phase and second phase of the cemented carbide is 97 volume % or more, preferably 98 volume % or more, and more preferably 99 volume % or more. The upper limit of the total content of the first phase and second phase of the cemented carbide is preferably 100% by volume or less. The total content of the first phase and second phase of the cemented carbide is preferably 97 volume% or more and 100 volume% or less, more preferably 98 volume% or more and 100 volume% or less, and even more preferably 99 volume% or more and 100 volume% or less. preferable. Preferably, the cemented carbide consists of a first phase and a second phase.

From the viewpoint of improving hardness, the lower limit of the content of the first phase of the cemented carbide is preferably 82 volume % or more, more preferably 85 volume % or more, and even more preferably 87 volume % or more. The upper limit of the content of the first phase of the cemented carbide is less than 100 vol%, and from the viewpoint of improving breakage resistance, it is preferably 95 vol% or less, more preferably 94 vol% or less, and even more preferably 93 vol% or less. It is preferably 90% by volume or less, and even more preferably 90% by volume or less. The content of the first phase of the cemented carbide is preferably 82 volume% or more and 95 volume% or less, more preferably 85 volume% or more and 93 volume% or less, and even more preferably 87 volume% or more and 90 volume% or less.

From the viewpoint of improving breakage resistance, the lower limit of the content of the second phase of the cemented carbide is preferably 5% by volume or more, more preferably 7% by volume or more, and even more preferably 9% by volume or more. From the viewpoint of improving hardness, the upper limit of the second phase content of the cemented carbide is preferably 18 vol% or less, more preferably 16 vol% or less, and even more preferably 14 vol% or less. The content of the second phase of the cemented carbide is preferably 5 volume% or more and 18 volume% or less, more preferably 7 volume% or more and 16 volume% or less, and even more preferably 9 volume% or more and 14 volume% or less.

In addition to the first phase and the second phase, the cemented carbide of this embodiment can include a third phase consisting of third phase particles containing 10 atomic % or more of vanadium.

When the cemented carbide includes a third phase, the content of the third phase of the cemented carbide is preferably more than 0% by volume and not more than 1% by volume. According to this, the decrease in breakage resistance of the cemented carbide due to the presence of the third phase is suppressed. The lower limit of the content of the third phase of the cemented carbide is more than 0% by volume. The upper limit of the third phase content of the cemented carbide is preferably 1% by volume or less, more preferably 0.8% by volume or less, and even more preferably 0.7% by volume or less. When the cemented carbide includes a third phase, the content of the third phase of the cemented carbide is preferably more than 0 volume% and 1 volume% or less, more preferably more than 0 volume% and 0.8 volume% or less, and 0 volume%. More preferably, it is more than 0.7% by volume.

The cemented carbide of this embodiment can contain unavoidable impurities in addition to the first phase, second phase, and third phase as long as the effects of the present disclosure are exhibited. Examples of the unavoidable impurities include iron, molybdenum, and sulfur. The content of the unavoidable impurities in the cemented carbide is preferably less than 0.1% by mass. The content of the inevitable impurities in the cemented carbide is measured by ICP emission spectroscopy (measurement device: Shimadzu Corporation "ICPS-8100" (trademark)).

The content of each of the first phase, second phase, and third phase of the cemented carbide is measured according to the following procedures (A1) to (D1).

(A1) A thin sample with a thickness of 50 nm or less is cut from cemented carbide using an ion slicer or the like, and the surface of the thin sample is mirror-finished. Examples of mirror finishing methods include a method of polishing with diamond paste, a method of using a focused ion beam device (FIB device), a method of using a cross section polisher device (CP device), and a method of combining these.

(B1) The mirror-finished surface of the thin sample was subjected to EDX (Energy Dispersive X-ray Spectroscopy) with a transmission electron microscope (TEM). Tungsten (W) , cobalt (Co), chromium (Cr), and vanadium (V) to obtain a mapping image of each element. The measurement conditions are an observation magnification of 100,000 times and an acceleration voltage of 200 kV. The number of pixels for element mapping is 125×125. Five visual fields of the elemental mapping images are prepared. The photographing regions of the elemental mapping images of the five fields of view are different from each other. The imaging area can be set arbitrarily.

In the above elemental mapping image, the region containing 70 atomic percent or more of tungsten is the region where the first phase exists, based on the total number of atoms of tungsten (W), cobalt (Co), chromium (Cr), and vanadium (V). Applicable. In the above elemental mapping image, a region containing 70 atomic % or more of cobalt with respect to the total number of atoms of tungsten, cobalt, chromium, and vanadium corresponds to the region where the second phase exists. In the above elemental mapping image, the region containing vanadium at 10 atomic % or more with respect to the total number of atoms of tungsten, cobalt, chromium, and vanadium corresponds to the region where the third phase exists. Note that the vanadium concentrated layer existing in the interface area between the tungsten carbide particles and the second phase and the vanadium concentrated layer existing in the interface area between the second phases have a concentration of several atoms (for example, about 1 to 5 atoms). ), it is not detected at 100,000x magnification because it is layered with a certain thickness.

(C1) Regarding the elemental mapping images of 5 fields of view of each element obtained in (B1) above, using image analysis software (ImageJ, version 1.51j8: https://imagej.nih.gov/ij/), The area percentage of each of the first phase, second phase, and third phase is measured using the entire visual field as the denominator.

(D1) Calculate the average value of the area % of the first phase obtained in 5 visual fields. The average value corresponds to the content (volume %) of the first phase of the cemented carbide. The average value of the area % of the second phase obtained in 5 fields of view is calculated. This average value corresponds to the content rate (volume %) of the second phase of the cemented carbide. The average value of the area % of the third phase obtained in 5 fields of view is calculated. The average value corresponds to the content rate (volume %) of the third phase of the cemented carbide.

As far as the applicant has measured, as long as the measurement is performed on the same sample, even if the above measurement is performed multiple times by changing the selected measurement area, there is little variation in the measurement results, and the measurement field of view can be set arbitrarily. However, it was confirmed that this was not arbitrary.

<Phase 1>
≪Composition of the first phase≫
The first phase consists of tungsten carbide particles. Here, tungsten carbide particles include not only "pure WC particles (including WC containing no impurity elements and WC whose content of impurity elements is below the detection limit)" but also "pure WC particles (including WC containing no impurity elements and WC whose content of impurity elements is less than the detection limit)". It also includes "WC particles in which impurity elements are intentionally or unavoidably contained, as long as they do not damage the particles." The content of impurities in the first phase (if there are two or more elements constituting the impurities, their total concentration) is less than 0.1% by mass. The content of impurity elements in the first phase is measured by ICP emission spectrometry.

≪Average equivalent circle diameter of tungsten carbide particles≫
In the present embodiment, the average equivalent circle diameter of the tungsten carbide particles (hereinafter also referred to as "average particle diameter of WC particles") is 0.8 μm or less. According to this, the cemented carbide has high hardness, and a cutting tool using the cemented carbide can have excellent wear resistance. Further, the cemented carbide has excellent strength, and a cutting tool using the cemented carbide can have excellent breakage resistance. In the present disclosure, the average value of the equivalent circle diameter of tungsten carbide particles means the arithmetic mean of the number-based equivalent circle diameter of WC particles measured on a cross section of the cemented carbide.

From the viewpoint of improving wear resistance, the lower limit of the average particle size of the WC particles is preferably 0.2 μm or more, more preferably 0.3 μm or more, and even more preferably 0.4 μm or more. From the viewpoint of improving wear resistance and breakage resistance, the upper limit of the average particle diameter of the WC particles is 0.8 μm or less, preferably 0.5 μm or less, more preferably 0.6 μm or less, and even more preferably 0.4 μm or less. preferable. The average particle diameter of the WC particles is preferably 0.2 μm or more and 0.8 μm or less, more preferably 0.2 μm or more and 0.6 μm or less, and even more preferably 0.2 μm or more and 0.5 μm or less.

The average value of the equivalent circle diameter of tungsten carbide particles is measured by the following procedures (A2) to (D2).
(A2) Mirror-finishing an arbitrary cross section of the cemented carbide. Examples of mirror finishing methods include a method of polishing with diamond paste, a method of using a focused ion beam device (FIB device), a method of using a cross section polisher device (CP device), and a method of combining these.

(B2) Photograph the machined surface of the cemented carbide using a scanning electron microscope (“S-3400N” manufactured by Hitachi High-Technologies Corporation). Prepare three images. The photographing areas of the three photographed images are different. The imaging area can be set arbitrarily. The conditions are: observation magnification of 10,000 times, acceleration voltage of 10 kV, and backscattered electron image.

(C2) The three backscattered electron images obtained in (B2) above were imported into a computer using image analysis software (ImageJ, version 1.51j8: https://imagej.nih.gov/ij/) and binarized. Perform processing. The binarization process is executed under conditions preset in the image analysis software by pressing the "Make Binary" display on the computer screen after capturing the image. In the image after the binarization process, the first phase and the second phase can be distinguished by color shading. For example, in an image after binarization processing, the first phase is shown as a black area, and the second phase is shown as a white area. Note that when the cemented carbide includes a third phase, the third phase is shown in the same color tone (white) as the second phase in the image after the binarization process.

(D2) Using the above-mentioned image analysis software on the three obtained images, the circle-equivalent diameter (Heywood diameter: Measure the area circle equivalent diameter). The arithmetic mean value based on the number of circle-equivalent diameters of all tungsten carbide particles in the three measurement fields of view is calculated. In the present disclosure, the arithmetic mean value corresponds to the average value of the equivalent circle diameter of the WC particles.

As far as the applicant has measured, as long as the measurement is performed on the same sample, even if the above measurement is performed multiple times by changing the selected measurement area, there is little variation in the measurement results, and the measurement field of view can be set arbitrarily. However, it was confirmed that it was not arbitrary.

<Phase 2>
The second phase contains cobalt as a main component. The second phase is a binding phase that binds the tungsten carbide particles of the first phase.

In the present disclosure, "a second phase containing cobalt as a main component" means that in the second phase, the percentage of cobalt relative to the total of tungsten, chromium, vanadium, and cobalt is 70% by mass or more. In the second phase, the lower limit of the percentage of cobalt relative to the total of tungsten, chromium, vanadium, and cobalt can be 70% by mass or more, 80% by mass or more, or 90% by mass or more. The upper limit of the percentage can be less than 100% by mass. The percentage can be 70% by mass or more and less than 100% by mass, 80% by mass or more and less than 100% by mass, or 90% by mass or more and less than 100% by mass.

In the second phase of the cemented carbide of the present disclosure, as long as the percentage of cobalt with respect to the total of tungsten, chromium, vanadium, and cobalt is 70% by mass or more, the second phase functions as a binder phase, and the effects of the present disclosure are achieved. It has been confirmed that there is no damage to the

The percentage of cobalt relative to the total of tungsten, chromium, vanadium, and cobalt in the second phase can be measured by ICP emission spectrometry (equipment used: "ICPS-8100" (trademark) manufactured by Shimadzu Corporation).

In addition to cobalt, the second phase can include chromium (Cr), tungsten (W), vanadium (V), iron (Fe), nickel (Ni), carbon (C), etc. The second phase can consist of cobalt and at least one member selected from the group consisting of chromium, tungsten, vanadium, iron, nickel, and carbon. The second phase can include cobalt, at least one member selected from the group consisting of chromium, tungsten, vanadium, iron, nickel, and carbon, and impurities. Examples of the impurities include manganese (Mn), magnesium (Mg), calcium (Ca), molybdenum (Mo), sulfur (S), titanium (Ti), and aluminum (Al). If the second phase includes vanadium, it is assumed that the vanadium content of the second phase does not exceed 5 at.%. That is, the vanadium content of the second phase can be 5 at % or less.

<Phase 3>
≪Composition of third phase≫
The cemented carbide of the present embodiment includes a third phase consisting of third phase particles containing 10 atomic % or more of vanadium, and the content of the third phase of the hard alloy is more than 0 vol. % and 1 vol. % or less. The maximum value of the equivalent circle diameter of the third phase particles is preferably 0.5 μm or less. According to this, since there are no coarse third phase particles having an equivalent circle diameter of more than 0.5 μm, which can become a starting point for breakage, the breakage resistance of a cutting tool using the cemented carbide is improved.

The third phase consists of third phase particles containing 10 atomic % or more of vanadium. The third phase is presumed to be a fine precipitated phase of vanadium (V) derived from vanadium carbide (VC) added as a grain growth inhibitor in the manufacturing process of cemented carbide. In the present disclosure, a vanadium enriched layer having a certain thickness on the order of several atoms does not correspond to the third phase.

In the present disclosure, "third phase particles containing 10 atomic % or more of vanadium" means that in the third phase particles, the percentage of vanadium with respect to the total of tungsten, chromium, vanadium, and cobalt is 10 atomic % or more. .

In addition to vanadium, the third phase particles can include tungsten, cobalt, chromium, carbon, etc. The third phase particles can be made of vanadium and at least one selected from the group consisting of tungsten, cobalt, chromium, and carbon. The third phase particles can include vanadium, at least one member selected from the group consisting of tungsten, cobalt, chromium, and carbon, and impurities. Examples of the impurities include iron, nickel, manganese, niobium, magnesium, calcium, molybdenum, sulfur, titanium, and aluminum.

In the third phase particles, the lower limit of the percentage of vanadium relative to the total of tungsten, chromium, vanadium, and cobalt is 10 atomic % or more, and can be 20 atomic % or more, or 30 atomic % or more. The upper limit of the percentage can be 100 atomic % or less. The percentage can be 10 atomic % or more and 100 atomic % or less, 20 atomic % or more and 100 atomic % or less, or 30 atomic % or more and 100 atomic % or less.

The method for measuring the percentage of vanadium relative to the total of tungsten, chromium, vanadium, and cobalt in the third phase particles is as follows.

First, an elemental mapping analysis was performed using the same procedure as (A1) to (B1) of the method for measuring the content of each of the first, second, and third phases of cemented carbide, and elemental mapping images of five fields of view were obtained. get. In each elemental mapping image, a region containing 10 atomic % or more of vanadium is specified based on the total number of atoms of tungsten, cobalt, chromium, and vanadium. This region corresponds to third phase particles.

The identified third phase particles were magnified to an observation magnification of 2,000,000 times, and EDX point analysis was performed to calculate the percentage of the number of vanadium atoms (hereinafter referred to as "the percentage of the number of vanadium atoms relative to the total number of atoms of tungsten, cobalt, chromium, and vanadium" in the third phase particles). Measure the vanadium content (also referred to as "vanadium content of three-phase particles"). The measurements are carried out on five third phase particles. The average value of the vanadium content of the five third phase particles is calculated. The average value corresponds to the percentage of vanadium relative to the sum of tungsten, chromium, vanadium, and cobalt in the third phase particles in the present disclosure.

As far as the applicant has measured, as long as the measurement is performed on the same sample, even if the above measurement is performed multiple times by changing the selected measurement area, there is little variation in the measurement results, and the measurement field of view can be set arbitrarily. However, it was confirmed that it was not arbitrary.

≪Maximum value of equivalent circle diameter of third phase particles≫
In the present embodiment, the maximum value of the equivalent circle diameter of the third phase particles (hereinafter also referred to as "maximum value of the third phase particles") is preferably 0.5 μm or less.

When the cemented carbide includes a third phase, the upper limit of the maximum value of the third phase particles is preferably 0.5 μm or less, preferably 0.4 μm or less, preferably 0.3 μm or less, more preferably 0.2 μm or less, More preferably, it is 0.1 μm or less. The lower limit of the maximum value of the equivalent circle diameter of the third phase particles is not particularly limited, and can be set to exceed 0 μm. The maximum value of the equivalent circle diameter of the third phase is preferably more than 0 μm and not more than 0.5 μm, preferably more than 0 μm and not more than 0.4 μm, preferably more than 0 μm and not more than 0.3 μm, more preferably more than 0 μm and not more than 0.2 μm, and 0 μm More preferably, it is more than 0.1 μm or less.

The maximum value of the equivalent circle diameter of the third phase particles is measured by the following steps (A3) to (B3).

(A3) Using the same procedure as (A1) to (C1) of the method for measuring the content of each of the first phase, second phase, and third phase of the cemented carbide described above, for the elemental mapping image of 5 fields of view, Analyze using the above image analysis software (ImageJ) to identify the third phase.

(B3) Using the above image analysis software, measure the equivalent circle diameter (Heywood diameter: equal area circle equivalent diameter) for each of all third phase particles in the five measurement regions. The maximum value of the equivalent circle diameter of all the third phase particles in the five measurement fields corresponds to the maximum value of the equivalent circle diameter of the third phase particles in the present disclosure.

As far as the applicant has measured, as long as the measurement is performed on the same sample, even if the above measurement is performed multiple times by changing the selected measurement area, there is little variation in the measurement results, and the measurement field of view can be set arbitrarily. However, it was confirmed that it was not arbitrary.

≪Cobalt content rate≫
The cobalt content of the cemented carbide of this embodiment is 3% by mass or more and 10% by mass or less. According to this, cemented carbide has high hardness and strength. A cutting tool using the cemented carbide can have excellent wear resistance and breakage resistance.

From the viewpoint of improving breakage resistance, the lower limit of the cobalt content of the cemented carbide is 3% by mass or more, preferably 4% by mass or more. From the viewpoint of improving hardness, the upper limit of the cobalt content of the cemented carbide is 10% by mass or less, preferably 9% by mass or less, and more preferably 8% by mass or less. The cobalt content of the cemented carbide is preferably 4% by mass or more and 10% by mass or less, more preferably 3% by mass or more and 9% by mass or less, and even more preferably 3% by mass or more and 8% by mass or less.

The cobalt content in the cemented carbide is measured by ICP emission spectrometry.

≪Vanadium content≫
The vanadium content of the cemented carbide of this embodiment is 0.01% by mass or more and 0.30% by mass or less. According to this, the generation of coarse WC particles is suppressed, and the structure of the cemented carbide is made dense. Therefore, the cemented carbide has excellent hardness and strength, and a cutting tool using the cemented carbide can have excellent wear resistance and breakage resistance.

From the viewpoint of suppressing the generation of coarse WC particles, the lower limit of the vanadium content of the cemented carbide is 0.01% by mass or more, preferably 0.05% by mass or more, and more preferably 0.10% by mass or more. The upper limit of the vanadium content of the cemented carbide is 0.30% by mass or less, preferably 0.20% by mass or less, from the viewpoint of suppressing a decrease in interfacial strength. The vanadium content of the cemented carbide is preferably 0.01% by mass or more and 0.20% by mass or less, and more preferably 0.10% by mass or more and 0.20% by mass or less.

The vanadium content of the cemented carbide is measured by ICP emission spectrometry.

≪Chromium content≫
The cemented carbide of this embodiment can contain chromium (Cr). The chromium content of the cemented carbide of this embodiment is preferably 0.2% by mass or more and 0.8% by mass or less. Chromium has the effect of inhibiting grain growth of tungsten carbide particles. When the chromium content of the cemented carbide is within the above range, it is possible to effectively prevent the fine tungsten carbide particles of the raw material from remaining as they are in the obtained cemented carbide, and to effectively prevent the generation of coarse grains. can be suppressed to improve tool life.

The lower limit of the chromium content of the cemented carbide is preferably 0.2% by mass or more, more preferably 0.3% by mass or more. The upper limit of the chromium content of the cemented carbide is preferably 0.8% by mass or less, more preferably 0.5% by mass or less. The chromium content of the cemented carbide is preferably 0.2% by mass or more and 0.8% by mass or less, and more preferably 0.3% by mass or more and 0.5% by mass or less.

The chromium content of the cemented carbide is measured by ICP emission spectroscopy.

<Vanadium content in the interface region>
In the cemented carbide of this embodiment, the maximum vanadium content in the interface region between the (0001) crystal plane of the tungsten carbide particles and the second phase (hereinafter also referred to as "WC/second phase interface region") The value is 15 atomic % or less. According to this, the formation of a vanadium-concentrated layer in which vanadium is present in a concentrated manner is suppressed in the interface region. Therefore, a decrease in the interfacial strength between the WC particles and the second phase due to the vanadium concentrated layer is suppressed. Therefore, in the cemented carbide, WC particles are unlikely to fall off due to a decrease in interfacial strength, and a cutting tool using the cemented carbide can have excellent wear resistance and breakage resistance. In addition, conventional cemented carbide has a large amount of vanadium concentrated layer at the interface, which tends to reduce the interface strength.

In a cemented carbide, when a vanadium enriched layer exists in the WC/second phase interface region, the (0001) crystal plane of the WC particle and other WC particles adjacent to the (0001) crystal plane of the WC particle There is a possibility that a vanadium-concentrated layer also exists in the interface region with the WC/WC interface region (hereinafter also referred to as "WC/WC interface region"). In the cemented carbide of the present embodiment, when the maximum vanadium content in the WC/second phase interface region is 15 atomic % or less, the maximum vanadium content in the WC/WC interface region is also 15 atomic % or less. This has been confirmed. Therefore, if the maximum value of the vanadium content in the WC/second phase interface region is 15 atomic % or less, the maximum value of the vanadium content in the WC/WC interface region is also 15 atomic % or less, and the WC/WC interface region The formation of a vanadium-enriched layer is suppressed. Therefore, a decrease in the interfacial strength between WC particles due to the vanadium concentrated layer is also suppressed.

The upper limit of the maximum vanadium content in the WC/second phase interface region is preferably 15 atom % or less, preferably 14 atom % or less, more preferably 13 atom % or less, even more preferably 12 atom % or less, and 11 atom %. The following are even more preferred. The lower limit of the maximum vanadium content in the WC/second phase interface region is not particularly limited, but may be, for example, 1 atomic % or more or 2 atomic % or more. The maximum value of vanadium content in the WC/second phase interface region is preferably 1 atom % or more and 15 atom % or less, more preferably 1 atom % or more and 12 atom % or less, and even more preferably 2 atom % or more and 15 atom % or less. , 2 atomic % or more and 12 atomic % or less is even more preferable.

The maximum value of vanadium content in the WC/second phase interface region is measured by the following steps (A4) to (D4).

(A4) Cut a thin sample with a thickness of 50 nm or less from cemented carbide using an ion slicer or the like. The surface of the thin sample is mirror-finished. Examples of mirror finishing methods include a method of polishing with diamond paste, a method of using a focused ion beam device (FIB device), a method of using a cross section polisher device (CP device), and a method of combining these.

(B4) Observe the mirror-finished surface of the thin sample with a transmission electron microscope (TEM) to obtain an electron diffraction image of the WC particles. The observation magnification is 2 million times.

(C4) In the electron diffraction image, the (0001) crystal plane of the WC particle is identified. When observed from the [11-20] or [10-10] orientation of the WC grain where the (0001) crystal face has been identified, the (0001) crystal face of the WC grain and the adjacent to the WC grain. Line analysis is performed on the interface region with the second phase using EDX (Energy Dispersive X-ray Spectroscopy) accompanied by TEM. In the line analysis, the percentage (atomic %) of the number of atoms is measured for each of tungsten (W), cobalt (Co), chromium (Cr), and vanadium (V). The percentage of the number of atoms means the percentage of the number of atoms of each element when the total number of atoms of W, Co, Cr, and V is 100 atomic %.

The specific procedure for line analysis will be explained using FIG. 1. FIG. 1 schematically shows a transmission electron microscope (TEM) image of the thin sample. In FIG. 1, the measurement region R for line analysis is a rectangular region indicated by the symbol R. In FIG.

As shown in FIG. 1, the interface between the (0001) crystal plane of the WC particle 1 and the second phase 2 adjacent to the (0001) crystal plane of the WC particle 1 is approximately straight, and , select a portion where the length of the substantially straight portion is 25 nm or more. Line analysis is performed in the direction perpendicular to the substantially straight line portion (direction of arrow B in FIG. 1). The distance of the line analysis is 20 nm from the substantially straight line portion to the WC particle side and the second phase side, respectively. The width of the line analysis is 25 nm, and the step interval is 0.4 nm. Note that, as shown in FIG. 1, the measurement region R of the line analysis is set so that the third phase particles 3 are not included.

Based on the line analysis results, the maximum percentage of vanadium (atomic %) is calculated when the total number of atoms of W, Cr, V, and Co is 100 atomic %. This maximum value is defined as the maximum value of the vanadium content in the interface region between the (0001) crystal plane of the WC particles and the second phase.

(D4) The measurement in (C4) above is performed in the interface region between the (0001) crystal plane of five different WC particles and the second phase. The average vanadium content of the five interface regions is calculated. This average value corresponds to the maximum value of the vanadium content in the interface region between the (0001) crystal plane of the tungsten carbide particles and the second phase in the cemented carbide of the present disclosure. Therefore, in a cemented carbide, if the average value of the vanadium content in the five interface regions is 15 atomic % or less, the cemented carbide has a structure in which the (0001) crystal plane of the tungsten carbide particles and the second phase The maximum value of vanadium content in the interface region is 15 atomic % or less.

As far as the applicant has measured, as long as the measurement is performed on the same sample, even if the above measurement is performed multiple times by changing the selected measurement area, there is little variation in the measurement results, and the measurement field of view can be set arbitrarily. However, it was confirmed that this was not arbitrary.

In the interface region between the (0001) crystal plane of the tungsten carbide particles of the cemented carbide of the present disclosure and the second phase, the maximum percentage of vanadium with respect to the total of tungsten, chromium, vanadium and cobalt is 15 atomic % or less. It has been confirmed that as long as there is a reduction in interfacial strength, the effects of the present disclosure are not impaired.

<Chromium content in the interface area>
In the cemented carbide of this embodiment, the maximum value of the chromium content in the interface region between the (0001) crystal plane of the tungsten carbide particles and the second phase is preferably 20 atomic % or less. According to this, the formation of a chromium-enriched layer in which chromium is concentrated in the interface region is suppressed. Therefore, a decrease in the interfacial strength between the WC particles and the second phase due to the chromium-enriched layer is suppressed. Therefore, in the cemented carbide, WC particles are unlikely to fall off due to a decrease in interfacial strength, and a cutting tool using the cemented carbide can have excellent wear resistance and breakage resistance.

In a cemented carbide, when a chromium enriched layer exists in the WC/second phase interface region, the (0001) crystal plane of the WC particle and the other WC adjacent to the (0001) crystal plane of the WC particle A chromium-enriched layer may also exist in the interface region with particles (WC/WC interface region). In the cemented carbide of this embodiment, when the maximum value of the chromium content in the WC/second phase interface region is 20 at% or less, the maximum value of the chromium content in the WC/WC interface region is also 20 at% or less. This has been confirmed. Therefore, if the maximum value of the chromium content in the WC/second phase interface region is 20 atom % or less, the maximum value of the chromium content in the WC/WC interface region is also 20 atom % or less, and the WC/WC interface region In this case, the formation of a chromium-enriched layer in which chromium is present is suppressed. Therefore, a decrease in the interfacial strength between WC particles due to the chromium-concentrated layer is also suppressed.

The upper limit of the maximum value of the chromium content in the WC/second phase interface region is preferably 20 atom % or less, preferably 18 atom % or less, more preferably 16 atom % or less, even more preferably 15 atom % or less, and 14 atom %. The following are even more preferred. The lower limit of the maximum chromium content in the WC/second phase interface region is not particularly limited, but may be, for example, 1 atomic % or more or 2 atomic % or more. The maximum value of the chromium content in the WC/second phase interface region is preferably 1 atomic % or more and 20 atomic % or less, more preferably 1 atomic % or more and 15 atomic % or less, and even more preferably 2 atomic % or more and 20 atomic % or less. , more preferably 2 at % or more and 15 at % or less.

The maximum value of the chromium content in the WC/second phase interface region is determined by the number of atoms of W, Cr, V, and Co in the methods (A4) to (D4) for measuring the vanadium content in the WC/second phase interface region. Calculate the percentage (atomic %) of chromium when the total number of atoms of W, Cr, V, and Co is 100 atomic % instead of the percentage (atomic %) of vanadium when the total number of atoms is 100 atomic %. It can be obtained by

As far as the applicant has measured, as long as the measurement is performed on the same sample, even if the above measurement is performed multiple times by changing the selected measurement area, there is little variation in the measurement results, and the measurement field of view can be set arbitrarily. However, it was confirmed that this was not arbitrary.

In the interface region between the (0001) crystal plane of the tungsten carbide particles of the cemented carbide of the present disclosure and the second phase, the maximum percentage of chromium with respect to the total of tungsten, chromium, vanadium and cobalt is 20 atomic % or less. It has been confirmed that as long as there is a reduction in interfacial strength, the effects of the present disclosure are not impaired.

<Method for manufacturing cemented carbide>
In order to reduce the vanadium content in the interface region between the (0001) crystal plane of the tungsten carbide particles of the cemented carbide and the second phase, it is necessary to reduce the amount of vanadium added as a grain growth inhibitor. Conceivable. However, when the amount of vanadium added is reduced, the effect of suppressing grain growth is insufficient and WC grains grow abnormally. This causes a decrease in the strength of the cemented carbide. As a result of extensive studies, the present inventors have discovered that, in order to suppress the generation of coarse WC particles, a sufficient amount of vanadium can be added, while at the same time reducing the vanadium content in the interface region. I found a new method. The details of the method for manufacturing cemented carbide of this embodiment will be described below.

The cemented carbide of this embodiment typically undergoes a raw material powder preparation process, a mixing process, a molding process, a sintering process (including a preliminary sintering process and a main sintering process), a repeated heat treatment process, and a cooling process. It can be manufactured by performing the steps in the above order. Each step will be explained below.

≪Preparation process≫
The preparation step is a step of preparing all the raw material powders of the materials constituting the cemented carbide. The raw material powders include tungsten carbide powder (hereinafter also referred to as "WC powder") which is the raw material for the first phase, cobalt powder (hereinafter also referred to as "Co powder") which is the raw material for the second phase, and a grain growth inhibitor. Examples include vanadium carbide powder (hereinafter also referred to as "VC powder"). Further, if necessary, chromium carbide powder (hereinafter also referred to as "Cr ₃ C ₂ powder"), which is a grain growth inhibitor, can be prepared. Commercially available tungsten carbide powder, cobalt powder, vanadium carbide powder, and chromium carbide powder can be used.

The average particle size of the tungsten carbide powder can be 0.2 μm or more and 1.0 μm or less. The WC powder preferably has a ratio d20/d80 of its 20% cumulative volume particle diameter d20 to its 80% cumulative volume particle diameter d80 of 0.2 or more and 1 or less. Such WC powder has a uniform particle size and has a small content of fine WC particles. Therefore, when a cemented carbide is produced using the WC powder, the generation of coarse WC particles due to dissolution and reprecipitation is suppressed in the sintering process. The above-mentioned "20% cumulative volume particle diameter d20" means the cumulative 20% particle diameter from the small diameter side in the volume-based cumulative particle size distribution of crystal grains. The above-mentioned "80% cumulative volume particle diameter d80" means the cumulative 80% particle diameter from the small diameter side in the volume-based cumulative particle size distribution of crystal grains.

The average particle size of the cobalt powder can be 0.5 μm or more and 1.5 μm or less. The average particle size of the vanadium carbide powder can be 0.1 μm or more and 0.5 μm or less. By using fine VC powder, the VC powder can be sufficiently diffused into the mixed powder in the subsequent preliminary sintering step. The average particle size of the chromium carbide powder can be 1.0 μm or more and 2.0 μm or less.

In the present disclosure, the average particle size of the above-mentioned raw material powder means the average particle size measured by the FSSS (Fisher Sub-Sieve Sizer) method. The average particle size is measured using a "Sub-Sieve Sizer Model 95" (trademark) manufactured by Fisher Scientific. The particle size distribution of the above-mentioned WC powder is measured using a particle size distribution measuring device manufactured by Microtrac (trade name: MT3300EX).

≪Mixing process≫
The mixing step is a step of mixing the raw material powders prepared in the preparation step. Through the mixing step, a mixed powder in which each raw material powder is mixed is obtained. The content of each raw material powder in the mixed powder is appropriately adjusted in consideration of the content of each component such as the first phase, second phase, and third phase of the cemented carbide.

The content of tungsten carbide powder in the mixed powder can be, for example, 88.85% by mass or more and 99.83% by mass or less.

The content of cobalt powder in the mixed powder can be, for example, 3% by mass or more and 10% by mass or less.

The content of vanadium carbide powder in the mixed powder can be, for example, 0.01% by mass or more and 0.37% by mass or less.

The content of the chromium carbide powder in the mixed powder can be, for example, 0.20% by mass or more and 0.92% by mass or less.

A ball mill is used for mixing. The mixing time can be 15 hours or more and 36 hours or less. According to this, pulverization of the raw material powder can be suppressed, and the VC powder can be sufficiently dispersed in the mixed powder while maintaining the particle size of the raw material powder.

After the mixing step, the mixed powder may be granulated if necessary. By granulating the mixed powder, it is easy to fill the mixed powder into a die or mold during the forming process described later. A known granulation method can be applied to the granulation, and for example, a commercially available granulation machine such as a spray dryer can be used.

≪Molding process≫
The molding step is a step of molding the mixed powder obtained in the mixing step into a predetermined shape to obtain a molded body. The molding method and molding conditions in the molding step are not particularly limited as long as they may be general methods and conditions. Examples of the predetermined shape include a cutting tool shape (for example, the shape of a small diameter drill).

≪Sintering process≫
The sintering process includes a preliminary sintering process and a main sintering process. In the preliminary sintering step, the compact is held at a sintering temperature of 800 to 1000° C. for 2 hours. The atmosphere is vacuum. A sintering temperature of 800 to 1000° C. is a temperature range in which WC grain growth does not occur. By maintaining the temperature in a temperature range where WC grain growth does not occur for 2 hours, the VC in the mixed powder can be diffused throughout the cobalt. Thereby, in the main sintering process, VC exhibits a uniform grain growth suppressing effect throughout the cemented carbide, and the generation of coarse WC particles is suppressed.

Next, the main sintering process is performed. In the main sintering step, the compact after the preliminary sintering step is held at a sintering temperature of 1350 to 1450° C. for 1 to 2 hours in an argon (Ar) atmosphere to obtain a cemented carbide. According to this, generation of coarse WC particles is suppressed. Moreover, the content of fine WC particles in the obtained cemented carbide can be reduced.

By performing the preliminary sintering step and the main sintering step, vanadium can be sufficiently dissolved in cobalt.

≪Repeated heat treatment process≫
Subsequently, the cemented carbide obtained in the sintering process is rapidly cooled. It is rapidly cooled from the temperature in the main sintering step to 1100° C. at which VC precipitates as a solid phase at a cooling rate of −60° C./min or higher, and held at 1100° C. for 30 minutes. Such rapid cooling suppresses the movement of vanadium dissolved in cobalt, which tends to occur during cooling. Therefore, in the cemented carbide, the vanadium content in the interface region between WC particles and the second phase (WC/second phase interface region) or the interface region between WC particles (WC/WC interface region) A large region (corresponding to a "vanadium concentrated layer") and/or a fine VC precipitate phase (hereinafter also referred to as "VC fine precipitate phase") are uniformly formed. Hereinafter, the process of rapidly cooling the cemented carbide to 1100°C at a cooling rate of -60°C/min or higher and holding it at 1100°C for 30 minutes will also be referred to as a "quenching process".

Subsequently, the cemented carbide is heated to 1250°C and held at 1250°C for 10 to 20 minutes. By setting the holding time at 1250° C. to 20 minutes or less, vanadium in the vanadium concentrated layer having a large surface area can be preferentially dissolved in cobalt. On the other hand, solid solution of vanadium in the VC fine precipitated phase into cobalt is suppressed, and at least a part of the VC fine precipitated phase can remain in the alloy. Hereinafter, the process of heating the cemented carbide to 1250°C and holding it at 1250°C for 10 to 20 minutes will also be referred to as a "heat treatment process."

Subsequently, the cemented carbide is rapidly cooled to 1100°C at a cooling rate of -60°C/min or higher, and held at 1100°C for 30 minutes (corresponding to the rapid cooling process). This suppresses the movement of vanadium dissolved in cobalt in the heat treatment step. Therefore, a vanadium concentrated layer and/or a VC fine precipitated phase are uniformly formed in the cemented carbide.

The above quenching step and heat treatment step are alternately repeated two or more times. As a result, the maximum value of the vanadium concentration in the WC/second phase interface region and the vanadium concentrated layer present in the WC/WC interface region is finally reduced. That is, the vanadium content in the interface region between the (0001) crystal plane of the tungsten carbide particles of the cemented carbide and the second phase, and the vanadium content in the (0001) crystal plane of the WC particle and the (0001) of the WC particle. The vanadium content in the interface region with the WC grains adjacent to the crystal plane is reduced. Furthermore, even when the cemented carbide contains VC particles, the VC particles are fine and uniformly dispersed in the cemented carbide.

≪Cooling process≫
Subsequently, the cemented carbide after the repeated heat treatment process is cooled. The cooling conditions are not particularly limited and may be general conditions.

According to the above method for manufacturing a cemented carbide, abnormal grain growth of WC particles is suppressed, so a cemented carbide that does not contain coarse WC particles and has a reduced vanadium content in the interface region can be obtained. It will be done. The cemented carbide has excellent wear resistance and breakage resistance.

[Embodiment 2: Cutting tool]
The cutting tool of this embodiment includes a cutting edge made of the cemented carbide of Embodiment 1. In the present disclosure, the cutting edge means a part involved in cutting, and in cemented carbide, the distance between the cutting edge ridgeline and the perpendicular line of the tangent to the cutting edge ridgeline from the cutting edge ridgeline to the cemented carbide side is 2 mm. It means an area surrounded by a certain virtual surface.

Examples of the cutting tool include a cutting tool, a drill, an end mill, an indexable cutting tip for milling, an indexable cutting tip for turning, a metal saw, a gear cutting tool, a reamer, or a tap. In particular, as shown in FIG. 2, the cutting tool 10 of this embodiment can exhibit excellent effects when used as a small-diameter drill for processing printed circuit boards. The cutting edge 11 of the cutting tool 10 shown in FIG. 2 is made of the cemented carbide of the first embodiment.

The cemented carbide of this embodiment may constitute the entirety of these tools, or may constitute a part thereof. Here, "constituting a part" refers to a mode in which the cemented carbide of this embodiment is brazed to a predetermined position of an arbitrary base material to form a cutting edge part.

≪Hard membrane≫
The cutting tool according to this embodiment may further include a hard film that covers at least a portion of the surface of the base material made of cemented carbide. As the hard film, for example, diamond-like carbon or diamond can be used.

[Additional note 1]
The total content of the first phase and second phase of the cemented carbide of the present disclosure is preferably 97% by volume or more and 100% by volume or less.
The content of the first phase of the cemented carbide of the present disclosure is preferably 82 volume % or more and 95 volume % or less.
The content of the second phase in the cemented carbide of the present disclosure is preferably 5% by volume or more and 18% by volume or less.
The content of the third phase in the cemented carbide of the present disclosure is preferably more than 0 volume % and 0.8 volume % or less.

[Additional note 2]
In the cemented carbide of the present disclosure, the average value of the equivalent circle diameter of the tungsten carbide particles is preferably 0.2 μm or more and 0.8 μm or less.
In the cemented carbide of the present disclosure, the average value of the equivalent circle diameter of the tungsten carbide particles is preferably 0.2 μm or more and 0.6 μm or less.

[Additional note 3]
In the second phase of the cemented carbide of the present disclosure, the percentage of cobalt relative to the total of tungsten, chromium, vanadium, and cobalt is preferably 70% by mass or more.

[Additional note 4]
The cobalt content of the cemented carbide of the present disclosure is preferably 4% by mass or more and 10% by mass or less.
The small Alto content of the cemented carbide of the present disclosure is preferably 3% by mass or more and 9% by mass or less.

[Additional note 5]
The chromium content of the cemented carbide of the present disclosure is preferably 0.2% by mass or more and 0.8% by mass or less.
The chromium content of the cemented carbide of the present disclosure is preferably 0.3% by mass or more and 0.5% by mass or less.

[Additional note 6]
In the cemented carbide of the present disclosure, the maximum vanadium content in the interface region between the (0001) crystal plane of the tungsten carbide particles and the second phase is preferably 1 atomic % or more and 15 atomic % or less.
In the cemented carbide of the present disclosure, the maximum vanadium content in the interface region between the (0001) crystal plane of the tungsten carbide particles and the second phase is preferably 1 atomic % or more and 12 atomic % or less.

[Additional note 7]
The maximum value of the chromium content in the interface region between the (0001) crystal plane of the tungsten carbide particles and the second phase is preferably 1 atomic % or more and 20 atomic % or less.
The maximum value of the chromium content in the interface region between the (0001) crystal plane of the tungsten carbide particles and the second phase is preferably 1 atomic % or more and 15 atomic % or less.

This embodiment will be described in more detail with reference to Examples. However, this embodiment is not limited to these Examples.

In this example, cemented carbide alloys of Samples 1 to 12 and Samples 1-1 to 1-10 were produced by changing the blending ratio of raw material powders and manufacturing conditions. A small-diameter drill with a cutting edge made of the cemented carbide was manufactured and evaluated.

<Preparation of sample>
≪Preparation process≫
A powder having the composition shown in the "mixed powder" column of Table 1 was prepared as a raw material powder. The average particle size of the WC powder is 0.4 μm, and d20/d80 is 0.3 or more. The average particle size of the Co powder is 1 μm, the average particle size of the VC powder is 0.3 μm, and the average particle size of the Cr ₃ C ₂ powder is 1 μm. WC powder, Co powder, Cr ₃ C ₂ powder and VC powder are commercially available products.

≪Mixing process≫
Each raw material powder was mixed in the amount shown in "mass%" of "mixed powder" in Table 1 to produce a mixed powder. "Mass %" in the "Mixed powder" column of Table 1 indicates the ratio of each raw material powder to the total mass of the raw material powders. Mixing was carried out in a ball mill for 15 hours. The obtained mixed powder was dried using a spray dryer to obtain a granulated powder.

≪Molding process≫
The obtained granulated powder was press-molded to produce a round bar-shaped compact with a diameter of 3.4 mm.

≪Sintering process≫
Subsequently, the compact was subjected to a preliminary sintering step. The compact was placed in a sintering furnace and held in vacuum for 2 hours at the temperature listed in the "temperature" column of "preliminary sintering" in Table 1. The description "None" in the "Preliminary Sintering" column of Table 1 indicates that the preliminary sintering step was not performed.

Next, the main sintering process was performed. The compact after the preliminary sintering step was held in an Ar atmosphere at the temperature listed in the "temperature" column of "main sintering" in Table 1 for 1 hour to obtain a cemented carbide.

≪Repeated heat treatment process≫
Subsequently, the cemented carbide obtained in the sintering process was alternately subjected to a quenching process and a heat treatment process twice. That is, the quenching step, the heat treatment step, the quenching step, and the heat treatment step were performed in the above order.

In the quenching step, the cemented carbide was rapidly cooled to 1100°C at a cooling rate of -60°C/min or higher, and held at 1100°C for 30 minutes. In the heat treatment step, the cemented carbide was heated to 1250°C and held at 1250°C for 20 minutes.

The description "None" in the "Repeated heat treatment" column of Table 1 indicates that the repeated heat treatment step was not performed.

≪Cooling process≫
Subsequently, the cemented carbide after the repeated heat treatment process was slowly cooled in an argon (Ar) gas atmosphere to obtain each sample of cemented carbide.

<Evaluation of cemented carbide>
Regarding the cemented carbide of each sample, the content of the first phase, second phase, and third phase of the cemented carbide (in Table 2, "first phase (volume %)", "second phase (volume %)", ), the cobalt content of the cemented carbide (shown in the "Co (mass%)" column in Table 2), the vanadium content of the cemented carbide (shown in the "Co (mass%)" column in Table 2), 2, the percentage of cobalt relative to the total of tungsten, chromium, vanadium, and cobalt in the second phase (indicated in the "Co/Second Phase (mass %)" column in Table 2), ), the average value of the equivalent circle diameter of the WC particles (shown in the "WC particle average particle diameter (μm)" column in Table 2), the maximum value of the equivalent circle diameter of the third phase particles (in Table 2 ), the maximum value of the vanadium content in the interface region between the (0001) crystal plane of the tungsten carbide particles and the second phase (indicated in the "WC /Second phase interface region" in the "V maximum (atomic %)" column), the maximum value of the chromium content in the interface region (in Table 2, "Cr maximum (atomic %)" in "interface region") ) was measured. The measurement method for each item is as shown in Embodiment 1. The results are shown in Table 2.

<Cutting test>
The round bars of each sample were processed to produce small-diameter drills (rotary tools for processing printed circuit boards) with a blade diameter of φ0.2 mm. Currently, it is common practice to form a drill by press-fitting only the blade portion into a stainless steel shank, but for evaluation purposes, a drill was fabricated by cutting the tip of a φ3.4 mm round bar. The drill was used to drill holes in a commercially available in-vehicle printed circuit board.

In the wear resistance evaluation test, the drilling conditions were a rotation speed of 160 krpm and a feed rate of 2.7 m/min. After drilling 10,000 holes, the width (μm) of the wear scar was measured for the drill. The width of the wear scar in this example will be explained using FIG. 3. FIG. 3 is a view from the tip side of the small diameter drill produced in this example. The width of the wear mark means the width L1 of the wear mark W at a location at a distance of 0.08 mm from the drill center C, as shown in FIG. The results are shown in the "Cutting test wear resistance (μm)" column of Table 2. In this example, when the width of the wear mark is 22 μm or less, the wear resistance is determined to be good, and when the width of the wear mark is 20 μm or less, the wear resistance is determined to be better.

In the breakage resistance evaluation test, the drilling conditions were a rotation speed of 100 krpm and a feed rate of 3.6 m/min. A maximum of 5000 holes were drilled and the number of holes punched until breakage was measured. The results are shown in the "Breakage resistance of cutting test (times)" column of Table 2. A result of 5000 times means that no breakage occurred after 5000 holes were punched. In this example, if the number of holes to be punched before breakage is 3000 times or more, it is determined that the breakage resistance is good, and if the number of holes to be drilled is 5000 times, it is determined that the breakage resistance is better.

<Consideration>
The cemented carbide and cutting tools of Samples 1 to 12 correspond to Examples. It was confirmed that these samples had excellent wear resistance and breakage resistance.

The cemented carbide and cutting tools of Samples 1-1 to 1-10 correspond to comparative examples. It was confirmed that these samples had insufficient wear resistance and/or breakage resistance.

Although the embodiments and examples of the present disclosure have been described above, it is planned from the beginning that the configurations of the above-described embodiments and examples may be combined as appropriate or variously modified.
The embodiments and examples disclosed herein are illustrative in all respects and should not be considered restrictive. The scope of the present invention is indicated by the claims rather than the embodiments and examples described above, and it is intended that equivalent meanings to the claims and all changes within the scope are included.

1 Tungsten carbide particles, 2 Second phase, 3 Third phase particles, R Measurement area, 10 Cutting tool, 11 Cutting edge, C Drill center, W Wear marks.

Claims (4)

1. A cemented carbide comprising a first phase consisting of tungsten carbide particles and a second phase containing cobalt as a main component,
   The total content of the first phase and the second phase of the cemented carbide is 97% by volume or more,
   The average value of the equivalent circle diameter of the tungsten carbide particles is 0.8 μm or less,
   The cobalt content of the cemented carbide is 3% by mass or more and 10% by mass or less,
   The vanadium content of the cemented carbide is 0.01% by mass or more and 0.30% by mass or less,
   A cemented carbide, wherein the maximum vanadium content in the interface region between the (0001) crystal plane of the tungsten carbide particles and the second phase is 15 atomic % or less.
2. The cemented carbide includes a third phase consisting of third phase particles containing 10 atomic % or more of vanadium,
   The content of the third phase of the cemented carbide is more than 0% by volume and not more than 1% by volume,
   The cemented carbide according to claim 1, wherein the third phase particles have a maximum equivalent circle diameter of 0.5 μm or less.
3. The cemented carbide according to claim 1 or 2, wherein the maximum value of the chromium content in the interface region is 20 atomic % or less.
4. A cutting tool comprising a cutting edge made of the cemented carbide according to any one of claims 1 to 3.

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