TW202346614A - 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 [mu]m 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 invention relates to a cemented carbide and a cutting tool using the same.

Among the openings of printed circuit boards, openings with a diameter of ϕ1 mm or less are the mainstream. Therefore, as cemented carbide used for tools such as small-diameter drills, so-called fine-grained cemented carbide containing tungsten carbide particles with a hard phase having an average particle diameter of 1 μm or less is used (for example, Patent Documents 1 to 3). . [Previous Patent Document] [Patent Document]

[Patent Document 1] Japanese Patent Application Publication No. 2007-92090 [Patent Document 2] Japanese Patent Application Publication No. 2012-52237 [Patent Document 3] Japanese Patent Application Publication No. 2012-117100

Superhard alloy of the present invention It has a first phase containing tungsten carbide particles and a second phase containing cobalt as a main component, and The total content of the above-mentioned first phase and the above-mentioned second phase in the above-mentioned cemented carbide is 97% by volume or more, The average circular equivalent diameter of the above-mentioned tungsten carbide particles is 0.8 μm or less, The cobalt content of the above-mentioned cemented carbide is not less than 3% by mass and not more than 10% by mass, The vanadium content of the above-mentioned cemented carbide is not less than 0.01% by mass and not more than 0.30% by mass, 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 is 15 atomic % or less.

The cutting tool of the present invention has a cutting edge made of the above-mentioned cemented carbide.

[Problems to be solved by this invention]

In recent years, with the expansion of 5G (fifth generation mobile communication system), the capacity of information has continued to increase. Therefore, printed circuit boards are required to have higher heat resistance. In order to improve the heat resistance of printed circuit boards, a technology has been developed to improve the heat resistance of resin or glass fillers constituting printed circuit boards. On the other hand, this makes the printed circuit board more difficult to cut. Therefore, in the microprocessing of printed circuit boards, cutting tools tend to be easily worn or broken.

Therefore, an object of the present invention is to provide a cemented carbide and a cutting tool having a longer tool life, especially when used as a material for cutting tools used in micromachining of printed circuit boards. of cutting tools. [Effects of the present invention]

The cemented carbide according to the present invention can provide a cutting tool that has a long tool life, especially when used for micromachining of printed circuit substrates.

[Description of embodiments of the present invention] First, embodiments of the present invention will be described with examples. (1) Super hard alloy of the present invention It has a first phase containing tungsten carbide particles and a second phase containing cobalt as a main component, and The total content of the above-mentioned first phase and the above-mentioned second phase in the above-mentioned cemented carbide is 97% by volume or more, The average circular equivalent diameter of the above-mentioned tungsten carbide particles is 0.8 μm or less, The cobalt content of the above-mentioned cemented carbide is not less than 3% by mass and not more than 10% by mass, The vanadium content of the above-mentioned cemented carbide is not less than 0.01% by mass and not more than 0.30% by mass, 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 is 15 atomic % or less.

The cemented carbide according to the present invention can provide a cutting tool that has a long tool life, especially when used for micromachining of printed circuit substrates.

(2) In the above (1), preferably, the cemented carbide has a third phase containing third phase particles containing 10 atomic % or more of vanadium, and The content of the third phase in the above-mentioned cemented carbide exceeds 0% by volume and is less than 1% by volume, The maximum value of the circle equivalent diameter of the third phase particles is 0.5 μm or less.

Thereby, there are no coarse third-phase particles with a circle-equivalent diameter exceeding 0.5 μm that may become the starting point of breakage, so the breakage resistance of cutting tools using this cemented carbide is improved.

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

This can prevent the interface strength between WC particles and Co particles from decreasing due to the presence of chromium in the interface region. Therefore, in this cemented carbide, it is difficult for WC particles to fall off due to a reduction in interface strength, and cutting tools using this cemented carbide can have excellent wear resistance and breakage resistance.

(4) The cutting tool of the present invention is provided with a cutting edge containing the cemented carbide in any one of the above (1) to (3).

The cutting tool of the present invention can also have a longer tool life, especially when used for micro-machining of printed circuit substrates.

[Details of embodiments of the present invention] Hereinafter, specific examples of the cemented carbide and cutting tool of the present invention will be described with reference to the drawings. In the drawings of the present invention, the same reference characters represent the same or equivalent parts. In addition, in order to clarify and simplify the drawings, dimensional relationships such as length, width, thickness, and depth have been appropriately changed, and they do not necessarily represent actual dimensional relationships.

In the present invention, the notation in the form of "A～B" means the upper and lower limits of the range (that is, A is above A and B is below). When A does not record the unit and only B records the unit, the unit of A is the same as the unit of B. The units are the same.

In the present invention, when the lower limit and the upper limit of a numerical range are each described with more than one numerical value, it is deemed to also disclose the combination of any one numerical value described in the lower limit and any one numerical value described in the upper limit. For example, when a1 or more, b1 or more, c1 or more are described as the lower limit, and a2 or less, b2 or less, c2 or less are described as the upper limit, it is deemed to also reveal that a1 or more, a2 or less, a1 or more, b2 or less, a1 or more below c2, above b1 but below a2, above b1 but below b2, above b1 but below c2, above c1 but below a2, above c1 but below b2, above c1 but below c2.

In the present invention, when a compound or the like is represented by a chemical formula, unless the atomic ratio is specifically limited, it is deemed to include all previously known atomic ratios, and is not necessarily limited to atomic ratios within the stoichiometric range.

In the crystallographic description in the present invention, [] is used to represent individual orientations, ＜＞ is used to represent collective orientations, () is used to represent individual planes, and {} is used to represent collective planes. In addition, when the crystallographic index is negative, it is usually expressed by placing a "-" (dash) above the number. However, in the present invention, a negative sign is placed before the number.

[Embodiment 1: Cemented carbide] Cemented carbide according to one embodiment of the present invention (hereinafter also referred to as “this embodiment”) It has a first phase containing tungsten carbide particles and a second phase containing cobalt as a main component, and The total content of the first phase and the second phase of the cemented carbide is 97% by volume or more, The average circular equivalent diameter of the tungsten carbide particles is 0.8 μm or less, The cobalt content of the cemented carbide is not less than 3% by mass and not more than 10% by mass, The vanadium content of the cemented carbide is not less than 0.01% by mass and not more than 0.30% by mass, 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 is 15 atomic % or less.

The cemented carbide according to this embodiment can provide a cutting tool that has a long tool life, especially when used for micromachining of printed circuit boards. The reason is not yet clear, but it is speculated to be as follows (i) to (v).

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

(ii) In the cemented carbide according to this embodiment, the average value of the circle equivalent diameter of the WC particles is 0.8 μm or less. Thereby, the cemented carbide has higher hardness, and cutting tools using the cemented carbide can have excellent wear resistance. In addition, the cemented carbide has excellent strength, and cutting tools using the cemented carbide can have excellent breakage resistance.

(iii) The cobalt content of the cemented carbide according to this embodiment is 3% by mass or more and 10% by mass or less. As a result, cemented carbide has higher hardness and strength. Cutting tools using this cemented carbide can have excellent wear resistance and breakage resistance.

(iv) The vanadium content of the cemented carbide according to this embodiment is 0.01 mass% or more and 0.30 mass% or less. Thereby, the generation of coarse WC particles is suppressed, and the structure of the cemented carbide becomes densified. Therefore, the cemented carbide has excellent hardness and strength, and cutting tools using the cemented carbide can have excellent wear resistance and breakage resistance.

(v) In the cemented carbide of this embodiment, 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 is 15 atomic % or less. This suppresses the formation of a vanadium-densified layer in which vanadium is concentrated in the interface region. Therefore, it is possible to suppress a decrease in the interface strength between the WC particles and the second phase due to the vanadium thickened layer. Therefore, in this cemented carbide, it is difficult for WC particles to fall off due to a reduction in interface strength, and cutting tools using this cemented carbide can have excellent wear resistance and breakage resistance.

＜Composition of cemented carbide＞ ＜＜Content ratio of the 1st phase, 2nd phase and 3rd phase>> The cemented carbide according to this embodiment includes a first phase containing 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. Thus, the cemented carbide has high hardness and strength, and cutting tools using the cemented carbide can have excellent wear resistance and breakage resistance.

The lower limit of the total content rate of the first phase and the second phase of the cemented carbide is 97 volume % or more, preferably 98 volume % or more, more preferably 99 volume % or more. The upper limit of the total content rate of the first phase and the second phase of cemented carbide is preferably 100 volume % or less. The total content rate of the first phase and the 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 still more preferably 99 volume % or more and 100 volume % the following. The cemented carbide preferably contains a first phase and a second phase.

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

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

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

When the cemented carbide contains the third phase, the content rate of the third phase of the cemented carbide is preferably more than 0% by volume and 1% by volume or less. This can prevent the cemented carbide from being reduced in fracture resistance due to the presence of the third phase. The lower limit of the content rate of the third phase of cemented carbide exceeds 0 volume %. The upper limit of the content rate of the third phase of cemented carbide is preferably 1 volume % or less, more preferably 0.8 volume % or less, and still more preferably 0.7 volume % or less. When the cemented carbide contains the third phase, the content rate 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. Furthermore, it is more preferable that it exceeds 0 volume% and is 0.7 volume% or less.

The cemented carbide of this embodiment may contain unavoidable impurities other than the first phase, the second phase, and the third phase as long as it exhibits the effects of the present invention. 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 rate of this unavoidable impurity in cemented carbide can be measured using ICP luminescence analysis (Inductively Coupled Plasma, Inductively Coupled Plasma) Emission Spectroscopy (measuring device: Shimadzu Corporation "ICPS-8100" (trademark)) .

The content ratio of each of the first phase, the second phase and the third phase of the cemented carbide is measured in the order of (A1) to (D1) below.

(A1) Use an ion microtome, etc. to cut a thin slice sample with a thickness of less than 50 nm from the cemented carbide, and perform mirror processing on the surface of the thin slice sample. Examples of methods of mirror processing include: polishing using diamond paste, methods using focused ion beam equipment (FIB equipment), methods using cross-section polishing equipment (CP equipment), and methods combining these wait.

(B1) For the mirror-finished surface of the above-mentioned thin slice sample, use EDX (Energy Dispersive X-ray Spectroscopy) with a transmission electron microscope (TEM: Transmission Electron Microscopy) to conduct tungsten (W), Element mapping of cobalt (Co), chromium (Cr), and vanadium (V) to obtain the mapping image of each element. The measurement conditions were set to an observation magnification of 100,000 times and an acceleration voltage of 200 kV. The number of pixels in the element mapping is set to 125×125. Prepare 5 fields of view mapping images of this element. The shooting areas of the element mapping images of the 5 fields of view are different. The shooting area can be set arbitrarily.

In the above element mapping image, a region containing more than 70 atomic % of tungsten relative to the total number of atoms of tungsten (W), cobalt (Co), chromium (Cr), and vanadium (V) corresponds to the existence of the first phase. area. In the above element mapping image, the region containing more than 70 atomic % of cobalt relative to the total number of atoms of tungsten, cobalt, chromium, and vanadium corresponds to the region where the second phase exists. In the above element mapping image, a region containing more than 10 atomic % of vanadium relative to the total number of atoms of tungsten, cobalt, chromium, and vanadium corresponds to the region where the third phase exists. Furthermore, the condensed layer of vanadium present in the interface region between the tungsten carbide particles and the second phase, and the condensed layer of vanadium present in the interface region between the second phases, have several atoms (for example, 1 to 5 atoms). (left or right) layer with a certain thickness, so it was not detected under the observation magnification of 100,000 times.

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

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

In the applicant's measurement, it was confirmed that as long as the same sample is measured, even if the selected part of the measurement area is changed and the above measurement is performed a plurality of times, the deviation of the measurement result is small, and even if the measurement field of view is arbitrarily set, the measurement result will not be consistent. It is arbitrary.

＜＜Phase 1＞ ＜＜Composition of the first phase＞＞ The first phase contains tungsten carbide particles. Here, tungsten carbide particles include not only "pure WC particles (WC that does not contain any impurity elements, but also WC whose content of impurity elements does not reach the detection limit)", but also "within the range that does not impair the effects of the present invention. , WC particles that intentionally or unavoidably contain impurity elements inside." The content rate of the impurities in the first phase (when there are two or more elements constituting the impurities, the total concentration thereof) is less than 0.1% by mass. The content rate of impurity elements in the first phase can be measured by ICP luminescence analysis.

＜＜Average of equivalent circle diameters of tungsten carbide particles＞＞ In this embodiment, the average value of the circular equivalent diameter of the tungsten carbide particles (hereinafter also referred to as the "average particle diameter of the WC particles") is 0.8 μm or less. Thereby, the cemented carbide has higher hardness, and cutting tools using the cemented carbide can have excellent wear resistance. In addition, the cemented carbide has excellent strength, and cutting tools using the cemented carbide can have excellent breakage resistance. In the present invention, the average value of the equivalent circular diameter of tungsten carbide particles means the arithmetic mean of the numerical basis of the equivalent circular diameter of WC particles measured on the cross-section of cemented carbide.

From the viewpoint of improving wear resistance, the lower limit of the average particle diameter of WC particles is preferably 0.2 μm or more, more preferably 0.3 μm or more, and further 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 WC particles is 0.8 μm or less, preferably 0.5 μm or less, more preferably 0.6 μm or less, and still more preferably 0.4 μm or less. 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, further preferably 0.2 μm or more and 0.5 μm or less.

The average value of the circle-equivalent diameter of the tungsten carbide particles is measured according to the following procedures (A2) to (D2). (A2) Mirror processing of any cross-section of cemented carbide. Examples of mirror processing methods include: polishing using diamond paste, using a focused ion beam device (FIB device), a method using a cross-section polisher device (CP device), and a combination of these methods wait.

(B2) Photograph the machined surface of cemented carbide using a scanning electron microscope ("S-3400N" manufactured by Hitachi High-Technology Co., Ltd.). Prepare 3 captured images. The shooting area of each of the 3 captured images is different. The shooting area can be set arbitrarily. The conditions were set to an observation magnification of 10,000 times, an accelerating voltage of 10 kV, and a reflected electron image.

(C2) Use image analysis software (ImageJ, version 1.51j8: https://imagej.nih.gov/ij/) to input the three reflection electron images obtained in (B2) above into the computer and perform binarization. handle. Binarization processing is performed under the conditions preset in the above image analysis software by clicking the "Make Binary" display on the computer screen after inputting the image. In the binarized image, the first phase and the second phase can be distinguished according to the intensity of the color. For example, in the binarized image, the first phase is represented by a black area and the second phase is represented by a white area. Furthermore, when the cemented carbide contains a third phase, the third phase is represented by the same color tone (white) as the second phase in the image after the binarization process.

(D2) For the three captured images obtained, use the above-mentioned image analysis software to measure the equivalent circular diameter (Heywood diameter: equal-area circle diameter) of all tungsten carbide particles (black areas) in the three captured images. . Calculate the arithmetic average of the number-based equivalent diameters of all tungsten carbide particles in the three measurement fields of view. In the present invention, the arithmetic mean value is equivalent to the mean value of the circle-equivalent diameter of the WC particles.

In the applicant's measurement, it was confirmed that as long as the same sample is measured, even if the selected part of the measurement area is changed and the above measurement is performed a plurality of times, the deviation of the measurement result is small, and even if the measurement field of view is arbitrarily set, the measurement result will not be consistent. It is arbitrary.

＜Phase 2＞ The second phase contains cobalt as a main component. The second phase is a bonded phase in which the tungsten carbide particles of the first phase are bonded to each other.

In the present invention, "the 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 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 may be 70 mass% or more, 80 mass% or more, or 90 mass% or more. The upper limit of the percentage may be set to less than 100% by mass. The percentage may be 70 mass% or more and less than 100 mass%, 80 mass% or more but less than 100 mass%, or 90 mass% or more but less than 100 mass%.

It was confirmed that in the second phase of the cemented carbide of the present invention, as long as the percentage of cobalt relative to the total of tungsten, chromium, vanadium and cobalt is 70 mass % or more, the second phase functions as a binding phase without impairing the original component. The effect of the invention.

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

In addition to cobalt, the second phase may also include chromium (Cr), tungsten (W), vanadium (V), iron (Fe), nickel (Ni), carbon (C), etc. The second phase may include: cobalt; and at least one selected from the group consisting of chromium, tungsten, vanadium, iron, nickel and carbon. The second phase may include: cobalt; at least one 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), aluminum (Al), and the like. When the second phase contains vanadium, it is assumed that the vanadium content rate of the second phase does not exceed 5 atomic %. That is, the vanadium content rate of the second phase can be set to 5 atomic % or less.

＜Phase 3＞ ＜＜Composition of the third phase＞＞ The cemented carbide of this embodiment has a third phase containing third phase particles containing 10 atomic % or more of vanadium, and the content of the third phase in the cemented carbide exceeds 0% by volume and is 1% by volume. Hereinafter, the maximum value of the circular equivalent diameter of the third phase particles is preferably 0.5 μm or less. Thereby, there are no coarse third-phase particles with a circle equivalent diameter exceeding 0.5 μm that may become the starting point of breakage, so the breakage resistance of cutting tools using this cemented carbide is improved.

The third phase contains third phase particles containing 10 atomic % or more of vanadium. It is speculated that the third phase originates from the fine precipitation phase of vanadium (V) in vanadium carbide (VC) added as a grain growth inhibitor in the cemented carbide manufacturing process. In the present invention, the vanadium-densified layer having a certain thickness on the order of several atoms does not correspond to the third phase.

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

In addition to vanadium, the third phase particles may also contain tungsten, cobalt, chromium, carbon, etc. The third phase particles may include: vanadium; and at least one selected from the group consisting of tungsten, cobalt, chromium, and carbon. The third phase particles may include: vanadium; at least one 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, aluminum, and the like.

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 may be 20 atomic % or more, or 30 atomic % or more. The upper limit of the percentage can be set to 100 atomic % or less. The percentage may 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 in the third phase particles relative to the total of tungsten, chromium, vanadium and cobalt is as follows.

First, perform element mapping analysis in the same order as (A1) to (B1) for measuring the content rates of the first phase, second phase and third phase of cemented carbide to obtain element mapping in five fields of view. images. In each element mapping image, a region containing 10 atomic % or more of vanadium relative to the total number of atoms of tungsten, cobalt, chromium, and vanadium is specified. This region corresponds to phase 3 particles.

The specified third phase particles were magnified to an observation magnification of 2 million times, and through EDX point analysis, the percentage of the number of atoms of vanadium in the third phase particles relative to the total number of atoms of tungsten, cobalt, chromium and vanadium (below , also written as "vanadium content rate of third phase particles") was measured. This measurement was performed on five third-phase particles. The average value of the vanadium content of the five third phase particles was calculated. This average value corresponds to the percentage of vanadium in the third phase particles in the present invention relative to the total of tungsten, chromium, vanadium and cobalt.

In the applicant's measurement, it was confirmed that as long as the same sample is measured, even if the selected part of the measurement area is changed and the above measurement is performed a plurality of times, the deviation of the measurement result is small, and even if the measurement field of view is arbitrarily set, the measurement result will not be consistent. It is arbitrary.

＜＜The maximum value of the circle equivalent diameter of the third phase particle＞＞ In this embodiment, the maximum value of the circular equivalent diameter of the third phase particles (hereinafter also referred to as the "maximum value of the third phase particles") is preferably 0.5 μm or less.

When the cemented carbide has a third phase, the upper limit of the maximum value of the third phase particles is preferably 0.5 μm or less, more preferably 0.4 μm or less, further preferably 0.3 μm or less, still more preferably 0.2 μm or less. , the best value is below 0.1 μm. The lower limit of the maximum value of the circular equivalent diameter of the third phase particles is not particularly limited, but may be set to exceed 0 μm. The maximum value of the circle equivalent diameter of the third phase is preferably more than 0 μm and less than 0.5 μm, more preferably more than 0 μm and less than 0.4 μm, still more preferably more than 0 μm and less than 0.3 μm, still more preferably It is more than 0 μm and not more than 0.2 μm, and particularly preferably it is more than 0 μm and not more than 0.1 μm.

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

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

(B3) Using the above-mentioned image analysis software, measure the circular equivalent diameter (Heywood diameter: equal-area circle diameter) of all third-phase particles in the five measurement areas. The maximum value of the equivalent circular diameter of all the third phase particles in the five measurement fields is equivalent to the maximum value of the equivalent circular diameter of the third phase particles in the present invention.

In the applicant's measurement, it was confirmed that as long as the same sample is measured, even if the selected part of the measurement area is changed and the above measurement is performed a plurality of times, the deviation of the measurement result is small, and even if the measurement field of view is arbitrarily set, the measurement result will not be consistent. It is arbitrary.

＜＜Cobalt content＞＞ The cobalt content of the cemented carbide according to this embodiment is 3% by mass or more and 10% by mass or less. As a result, cemented carbide has higher hardness and strength. Cutting tools using this cemented carbide can have excellent wear resistance and breakage resistance.

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

The cobalt content in cemented carbide can be determined by ICP luminescence spectrometry.

＜＜Vanadium content＞＞ The vanadium content of the cemented carbide according to this embodiment is 0.01% by mass or more and 0.30% by mass or less. Thereby, the generation of coarse WC particles is suppressed, and the structure of the cemented carbide becomes densified. Therefore, the cemented carbide has excellent hardness and strength, and cutting tools 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 rate of cemented carbide is 0.01 mass% or more, preferably 0.05 mass% or more, and more preferably 0.10 mass% or more. From the viewpoint of suppressing a decrease in interface strength, the upper limit of the vanadium content rate of cemented carbide is 0.30 mass% or less, preferably 0.20 mass% or less. The vanadium content rate of the cemented carbide is preferably 0.01 mass% or more and 0.20 mass% or less, and further preferably 0.10 mass% or more and 0.20 mass% or less.

The vanadium content of cemented carbide can be measured by ICP luminescence spectrometry.

＜＜Chromium content＞＞ The cemented carbide of this embodiment may contain chromium (Cr). The chromium content of the cemented carbide according to this embodiment is preferably 0.2 mass% or more and 0.8 mass% or less. Chromium has the effect of inhibiting the grain growth of tungsten carbide particles. When the chromium content of the cemented carbide is within the above range, the fine tungsten carbide particles of the raw material can be effectively suppressed from directly remaining in the obtained cemented carbide, and the generation of coarse particles can be effectively suppressed, thereby improving the tool. lifespan.

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

The chromium content of cemented carbide can be measured by ICP luminescence spectrometry.

<Vanadium content rate in interface region> In the cemented carbide of this embodiment, 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 (hereinafter also referred to as "WC/second phase interface region") It is 15 atomic % or less. This suppresses the formation of a vanadium-densified layer in which vanadium is concentrated in the interface region. Therefore, it is possible to suppress a decrease in the interface strength between the WC particles and the second phase due to the vanadium thickened layer. Therefore, in this cemented carbide, it is difficult for WC particles to fall off due to a reduction in interface strength, and cutting tools using this cemented carbide can have excellent wear resistance and breakage resistance. Furthermore, the amount of vanadium thickened layer in the above-mentioned interface of the previous cemented carbide was relatively large, and the interface strength showed a decreasing trend.

In cemented carbide, when there is a vanadium-densified layer 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 A vanadium-densified layer may also exist in the interface region (hereinafter, also referred to as "WC/WC interface region"). In the cemented carbide of this embodiment, it was confirmed that when the maximum value of the vanadium content rate in the WC/second phase interface region is 15 atomic % or less, the maximum value of the vanadium content rate in the WC/WC interface region is also 15 atomic% or less. Therefore, if the maximum value of the vanadium content rate in the WC/second phase interface region is 15 atomic % or less, the maximum value of the vanadium content rate in the WC/WC interface region is also 15 atomic % or less, so that the WC/second phase interface region can have a maximum vanadium content rate of 15 atomic % or less. Inhibits the formation of vanadium thickened layer in the WC interface area. Therefore, it is also possible to suppress a decrease in the interface strength between WC particles due to the vanadium thickened layer.

The upper limit of the maximum value of the vanadium content in the WC/second phase interface region is preferably 15 atomic % or less, more preferably 14 atomic % or less, further preferably 13 atomic % or less, still more preferably 12 atomic % or less. , particularly preferably 11 atomic % or less. The lower limit of the maximum vanadium content rate 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 vanadium content in the WC/second phase interface region is preferably 1 atomic % or more and 15 atomic % or less, more preferably 1 atomic % or more and 12 atomic % or less, and still more preferably 2 atomic % or more and 15 atomic % or more. or less, and more preferably 2 atomic % or more and 12 atomic % or less.

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

(A4) Use an ion microtome, etc. to cut a thin sample with a thickness of less than 50 nm from the cemented carbide. The surface of the thin sample was mirror-finished. Examples of methods of mirror processing include: polishing using diamond paste, methods using focused ion beam equipment (FIB equipment), methods using cross-section polishing equipment (CP equipment), and methods combining these wait.

(B4) Use a transmission electron microscope (TEM) to observe the mirror-processed surface of the above-mentioned thin slice sample to obtain the electron diffraction image of the WC particles. Set the observation magnification to 2 million times.

(C4) In the electron diffraction image, identify the (0001) crystal plane of WC particles. By using EDX (Energy Dispersive X-ray Spectroscopy) with TEM, the orientation of [11-20] or [10-10] of the WC particles self-identified to the (0001) crystal plane was carried out. Line analysis was performed on the interface region between the (0001) crystal plane of the WC particle and the second phase adjacent to the WC particle in the observed situation. In line analysis, the atomic number percentage (atomic %) of each of tungsten (W), cobalt (Co), chromium (Cr) and vanadium (V) is measured. The atomic number percentage means the atomic number percentage of each element when the total atomic number of W, Co, Cr, and V is 100 atomic %.

The specific sequence of line analysis will be explained using Figure 1. Figure 1 schematically shows a transmission electron microscope (TEM) image of the above-mentioned thin slice sample. In FIG. 1 , the measurement area R of the line analysis is a rectangular area represented by the symbol R.

As shown in Figure 1 , in 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, select a substantially straight line and the length of the substantially straight line portion It is the part above 25 nm. Line analysis is performed along the direction perpendicular to the approximately straight line portion (arrow B direction in Figure 1). The distance for line analysis is 20 nm from the WC particle side and the second phase side, centered on the substantially straight line portion. The width of the line analysis is 25 nm and the step pitch is 0.4 nm. Furthermore, as shown in FIG. 1 , the measurement region R of the line analysis is set so as not to include the third phase particles 3 .

Based on the line analysis results, the maximum value of the vanadium percentage (atomic %) was calculated when the total number of atoms of W, Cr, V, and Co was 100 atomic %. This maximum value is regarded 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 above-mentioned measurement (C4) was performed in the interface region between the (0001) crystal plane and the second phase of five different WC particles. Calculate the average value of the vanadium content in the five interface areas. 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 invention. Therefore, in cemented carbide, when the average value of the vanadium content in the above five interface regions is 15 atomic % or less, the interface region between the (0001) crystal plane of the tungsten carbide particles of the cemented carbide and the second phase The maximum vanadium content is less than 15 atomic %.

In the applicant's measurement, it was confirmed that as long as the same sample is measured, even if the selected part of the measurement area is changed and the above measurement is performed a plurality of times, the deviation of the measurement result is small, and even if the measurement field of view is arbitrarily set, the measurement result will not be consistent. It is arbitrary.

It was confirmed that in the interface region between the (0001) crystal plane and the second phase of the tungsten carbide particles of the cemented carbide of the present invention, as long as the maximum percentage of vanadium relative to the total of tungsten, chromium, vanadium and cobalt is 15 atomic % below, the decrease in interface strength is suppressed without impairing the effect of the present invention.

＜Chromium content rate in 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. This suppresses the formation of a chromium-condensed layer in which chromium is concentrated in the interface region. Therefore, it is possible to suppress a decrease in the interface strength between the WC particles and the second phase due to the chromium-concentrated layer. Therefore, in this cemented carbide, it is difficult for WC particles to fall off due to a reduction in interface strength, and cutting tools using this cemented carbide can have excellent wear resistance and breakage resistance.

In cemented carbide, when there is a condensed layer of chromium in the WC/second phase interface region, the (0001) crystal plane of the WC particle and other WC adjacent to the (0001) crystal plane of the WC particle There may also be a thickened layer of chromium in the interface area of the particles (WC/WC interface area). In the cemented carbide of this embodiment, it was confirmed that when the maximum value of the chromium content rate in the WC/second phase interface region is 20 atomic % or less, the maximum value of the chromium content rate in the WC/WC interface region is also 20 atomic % or less. Therefore, if the maximum value of the chromium content rate in the WC/second phase interface region is 20 atomic % or less, the maximum value of the chromium content rate in the WC/WC interface region is also 20 atomic % or less. At the WC/WC interface In this area, the formation of a chromium-densified layer where chromium is concentrated is suppressed. Therefore, it is possible to suppress a decrease in the interface strength between WC particles due to the chromium-concentrated layer.

The upper limit of the maximum value of the chromium content rate in the WC/second phase interface region is preferably 20 atomic % or less, more preferably 18 atomic % or less, further preferably 16 atomic % or less, still more preferably 15 atomic % or less. , particularly preferably 14 atomic % or less. The lower limit of the maximum chromium content rate 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 rate 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 still more preferably 2 atomic % or more and 20 atomic % or more. or less, and more preferably 2 atomic % or more and 15 atomic % or less.

The maximum value of the chromium content in the WC/second phase interface region is calculated by combining W, Cr, and V in the above-mentioned measurement methods (A4) to (D4) of the vanadium content in the WC/second phase interface region. The percentage of chromium (atomic %) when the total atomic number of W, Cr, V, and Co is 100 atomic % is used instead of the percentage of vanadium (atomic %) when the total atomic number of W, Cr, V, and Co is 100 atomic %. %) obtained.

In the applicant's measurement, it was confirmed that as long as the same sample is measured, even if the selected part of the measurement area is changed and the above measurement is performed a plurality of times, the deviation of the measurement result is small, and even if the measurement field of view is arbitrarily set, the measurement result will not be consistent. It is arbitrary.

It was confirmed that in the interface region between the (0001) crystal plane and the second phase of the tungsten carbide particles of the cemented carbide of the present invention, as long as the maximum percentage of chromium relative to the total of tungsten, chromium, vanadium and cobalt is 20 atomic % below, the decrease in interface strength is suppressed without impairing the effect of the present invention.

＜Manufacturing method of cemented carbide＞ In order to reduce the vanadium content in the interface region between the (0001) crystal plane of the cemented carbide tungsten carbide particles and the second phase, it is considered to reduce the amount of vanadium added as a grain growth inhibitor. However, if the added amount of vanadium is reduced, the grain growth suppressing effect is insufficient, and abnormal grain growth occurs in WC particles. This becomes the main factor that reduces the strength of cemented carbide. The inventors of the present invention have conducted intensive research, and as a result have newly discovered a method of manufacturing cemented carbide. This method of manufacturing cemented carbide can suppress the generation of coarse WC particles, so a sufficient amount of vanadium can be added, and the above-mentioned interface area can be made The vanadium content in the product decreases. Hereinafter, the details of the manufacturing method of the cemented carbide according to this embodiment will be described.

Typically, the cemented carbide of this embodiment can be produced by sequentially performing a raw material powder preparation step, a mixing step, a shaping step, a sintering step (including a pre-sintering step and a main sintering step), repeated heat treatment steps, and a cooling step. Each step is explained below.

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

The average particle diameter 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 20% cumulative volume particle diameter d20 and 80% cumulative volume particle diameter d80 of 0.2 or more and 1 or less. The particle size of this kind of WC powder is uniform, and the content of fine WC particles is small. Therefore, if the WC powder is used to produce cemented carbide, the generation of coarse WC particles due to dissolution and re-precipitation during the sintering step can be suppressed. The above "20% cumulative volume particle size d20" means the cumulative 20% particle size from the small diameter side in the cumulative particle size distribution based on the volume of the crystal grains. The above "80% cumulative volume particle size d80" means the cumulative 80% particle size from the small diameter side in the cumulative particle size distribution based on the volume of the crystal grains.

The average particle diameter 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 fully diffused in the mixed powder in the subsequent pre-sintering step. The average particle diameter of the chromium carbide powder can be 1.0 μm or more and 2.0 μm or less.

In the present invention, 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 diameter can be measured using "Sub-Sieve Sizer Model 95" (trademark) manufactured by Fisher Scientific. The particle size distribution of the above-mentioned WC powder can be measured using a particle size distribution measuring device (trade name: MT3300EX) manufactured by Microtrac.

＜＜Mixing Steps＞＞ The mixing step is a step of mixing the respective raw material powders prepared in the preparation step. Through the mixing step, a mixed powder obtained by mixing each raw material powder is obtained. The content rate of each raw material powder in the mixed powder can be appropriately adjusted taking into account the content rate of each component such as the first phase, the second phase, and the third phase of the cemented carbide.

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

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

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

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

Use a ball mill for mixing. The mixing time can be set from 15 hours to 36 hours. Thereby, the pulverization of the raw material powder can be suppressed, and the VC powder can be fully 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, the mixed powder can be easily filled into a die or mold in the following molding step. In the granulation, a known granulation method can be applied, for example, a commercially available granulator such as a spray dryer can be used.

＜＜Forming steps＞＞ The molding step is a step of molding the mixed powder obtained in the mixing step into a predetermined shape to obtain a formed body. The forming method and forming conditions in the forming step can adopt general methods and conditions and are not particularly limited. As the predetermined shape, for example, a cutting tool shape (such as the shape of a small-diameter drill) can be used.

＜＜Sinter step＞＞ The sintering step includes a pre-sintering step and a formal sintering step. In the pre-sintering step, the formed body is maintained at a sintering temperature of 800 to 1000°C for 2 hours. The environment adopts vacuum. The sintering temperature of 800 to 1000°C is the temperature range in which grain growth does not occur in WC. By keeping the WC in a temperature range where grain growth does not occur for 2 hours, the VC in the mixed powder can be diffused into the entire cobalt. Thus, in the formal sintering step, VC exerts a uniform grain growth inhibition effect throughout the cemented carbide, thereby inhibiting the generation of coarse WC particles.

Then, proceed to the formal sintering step. In the formal sintering step, the formed body after the pre-sintering step is maintained in an argon (Ar) environment at a sintering temperature of 1350-1450°C for 1 to 2 hours to obtain a cemented carbide. Thereby, the generation of coarse WC particles is suppressed. In addition, the content of fine WC particles in the obtained cemented carbide can be reduced.

By performing the pre-sintering step and the main sintering step, vanadium can be fully solid-soluble in cobalt.

＜＜Repeated heat treatment steps＞＞ Then, the cemented carbide obtained in the sintering step is quenched. With a cooling rate of -60°C/min or above, quench from the temperature in the formal sintering step to 1100°C where VC precipitates in solid phase, and maintain at 1100°C for 30 minutes. By such rapid cooling, the movement of vanadium dissolved in cobalt, which is likely to occur during cooling, is suppressed. Therefore, in 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) is uniformly formed. A large area (corresponding to the "vanadium thickened layer"), and/or a fine precipitated phase of VC (hereinafter also referred to as "VC fine precipitated phase"). Hereinafter, the step of quenching the cemented carbide to 1100°C at a cooling rate of -60°C/min or more and maintaining it at 1100°C for 30 minutes is also referred to as the "quenching step".

Then, the cemented carbide is heated to 1250°C and maintained at 1250°C for 10 to 20 minutes. By setting the holding time at 1250°C to less than 20 minutes, the vanadium in the vanadium thickened layer with a large surface area can be preferentially dissolved in the cobalt. On the other hand, the solid solution of vanadium in the VC fine precipitated phase into cobalt is suppressed, so that at least part of the VC fine precipitated phase can remain in the alloy. Hereinafter, the step of heating the cemented carbide to 1250°C and maintaining it at 1250°C for 10 to 20 minutes is also referred to as the "heat treatment step".

Then, the cemented carbide is quenched to 1100°C at a cooling rate of -60°C/min or more, and maintained at 1100°C for 30 minutes (equivalent to a quenching step). Thereby, during the heat treatment step, the movement of vanadium dissolved in cobalt is suppressed. Therefore, in the cemented carbide, a vanadium thickened layer and/or a VC fine precipitated phase are uniformly formed.

The above-described quenching step and heat treatment step are alternately repeated two or more times each. As a result, the maximum value of the vanadium concentration in the vanadium thickened layer existing in the WC/second phase interface region and the WC/WC interface region becomes smaller. 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 (0001) crystal plane of the WC particles are adjacent to the (0001) crystal plane of the WC particles. The vanadium content rate in the interface region of the WC particles decreases. Furthermore, even when the cemented carbide contains VC particles, the VC particles are relatively fine and uniformly dispersed in the cemented carbide.

＜＜Cooling step＞＞ Then, the cemented carbide after repeated heat treatment steps is cooled. The cooling conditions can be general conditions and are not particularly limited.

According to the above-mentioned manufacturing method of cemented carbide, abnormal grain growth of WC particles is suppressed, so it is possible to obtain a cemented carbide that does not contain coarse WC particles and has a reduced vanadium content in the interface region. This super hard alloy 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 invention, the tool tip refers to the part involved in cutting, which means the distance between the tool tip ridge line and the perpendicular line from the tool tip ridge line to the cemented carbide side along the tangent line of the tool tip ridge line in cemented carbide is 2 mm. The area enclosed by the imaginary surface.

Examples of cutting tools include cutting tools, drills, end mills, interchangeable cutting inserts for milling, interchangeable cutting inserts for turning, metal saws, gear cutting tools, and reamers. Or screw tapping, etc. As shown in FIG. 2 , the cutting tool 10 of the present embodiment can particularly exhibit excellent effects when used as a small-diameter drill for processing printed circuit boards. The cutting tool tip 11 of the cutting tool 10 shown in FIG. 2 contains the cemented carbide of the first embodiment.

The cemented carbide in this embodiment can constitute the entirety of these tools, or can also constitute a part. Here, "constituting a part" means a state in which the cemented carbide of the present embodiment is brazed to a predetermined position on an arbitrary base material to form a tip portion.

＜＜Hard film＞＞ The cutting tool of this embodiment may further include a hard film covering at least part of the surface of the base material containing cemented carbide. As the hard film, for example, diamond-like carbon or diamond can be used.

[Note 1] The total content of the first phase and the second phase in the cemented carbide of the present invention is preferably not less than 97% by volume and not more than 100% by volume. The content of the first phase in the cemented carbide of the present invention is preferably 82 volume % or more and 95 volume % or less. The content of the second phase in the cemented carbide of the present invention 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 invention is preferably more than 0% by volume and 0.8% by volume or less.

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

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

[Note 4] The cobalt content of the cemented carbide of the present invention is preferably 4% by mass or more and 10% by mass or less. The cobalt content of the cemented carbide of the present invention is preferably 3% by mass or more and 9% by mass or less.

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

[Note 6] In the cemented carbide of the present invention, 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 is preferably 1 atomic % or more and 15 atomic % or less. In the cemented carbide of the present invention, 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 is preferably 1 atomic % or more and 12 atomic % or less.

[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 rate 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. [Example]

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

In this example, the mixing ratio of the raw material powder and the manufacturing conditions were changed to produce cemented carbide samples 1 to 12 and 1-1 to 1-10. A small-diameter drill equipped with a tip containing this cemented carbide was produced and evaluated.

＜Preparation of sample＞ ＜＜Preparation step＞＞ As raw material powder, prepare a powder having the composition shown in the "Mixed Powder" column of Table 1. The average particle size of WC powder is 0.4 μm, and d20/d80 is above 0.3. The average particle size of Co powder is 1 μm, the average particle size of VC powder is 0.3 μm, and the average particle size of Cr ₃ C ₂ powder is 1 μm. WC powder, Co powder, Cr ₃ C ₂ powder and VC powder are commercial products.

＜＜Mixing Steps＞＞ Mix each raw material powder according to the compounding amount shown in "mass %" of "Mixed Powder" in Table 1 to prepare a mixed powder. The "mass %" in the "Mixed Powder" column of Table 1 represents the ratio of each raw material powder to the total mass of the raw material powders. Mixing was performed by means of a ball mill for 15 hours. The obtained mixed powder was dried using a spray dryer to prepare granulated powder.

＜＜Forming steps＞＞ The obtained granulated powder was press-molded to produce a rod-shaped molded body with a diameter of 3.4 mm.

＜＜Sinter step＞＞ Next, the formed body is subjected to a pre-sintering step. The molded body was put into a sintering furnace and maintained in a vacuum at the temperature listed in the "Temperature" column of "Pre-sintering" in Table 1 for 2 hours. The record "None" in the "Pre-sintering" column of Table 1 indicates that the pre-sintering step was not performed.

Then, the formal sintering step is performed. In an Ar environment, the formed body after the pre-sintering step was maintained at the temperature recorded in the "Temperature" column of "Full sintering" in Table 1 for 1 hour to obtain a cemented carbide.

＜＜Repeated heat treatment steps＞＞ Next, the cemented carbide obtained in the sintering step was alternately subjected to a quenching step and a heat treatment step twice each. That is, a quenching step, a heat treatment step, a quenching step, and a heat treatment step are performed in this order.

In the quenching step, the cemented carbide is quenched to 1100°C at a cooling rate of -60°C/min or more, and maintained at 1100°C for 30 minutes. In the heat treatment step, the cemented carbide is 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 step＞＞ Then, in an argon (Ar) gas environment, the cemented carbide after repeated heat treatment steps is slowly cooled to obtain the cemented carbide of each sample.

[Table 1] Table 1 Sample No. mixed powder Mixing step pre-sintered Formal sintering Repeated heat treatment WC powder Co powder VC powder Cr ₃ C ₂ powder time temperature time temperature time yes/no mass % mass % mass % mass % hr ℃ hr ℃ hr 1 89.53 10.00 0.01 0.46 15 1000 2 1420 1 have 2 96.17 3.00 0.37 0.46 15 1000 2 1420 1 have 3 96.30 3.00 0.24 0.46 15 1000 2 1420 1 have 4 91.30 8.00 0.24 0.46 15 1000 2 1420 1 have 5 91.17 8.00 0.37 0.46 15 1000 2 1420 1 have 6 96.30 3.00 0.24 0.46 15 800 2 1420 1 have 7 89.17 10.00 0.37 0.46 15 1000 2 1420 1 have 8 91.30 8.00 0.24 0.46 15 1000 2 1420 1 have 9 95.84 3.00 0.24 0.92 15 1000 2 1420 1 have 10 96.17 3.00 0.37 0.46 15 800 2 1420 1 have 11 91.30 3.00 0.24 0.69 15 1000 2 1420 1 have 12 96.17 3.00 0.01 0.46 15 1000 2 1420 1 have 1-1 96.17 3.00 0.37 0.46 15 without - 1420 1 have 1-2 98.17 1.00 0.37 0.46 15 1000 2 1420 1 have 1-3 87.17 12.00 0.37 0.46 15 1000 2 1420 1 have 1-4 96.54 3.00 0 0.46 15 1000 2 1420 1 have 1-5 96.05 3.00 0.49 0.46 15 1000 2 1420 1 have 1-6 96.17 3.00 0.37 0.46 15 1000 2 1500 1 have 1-7 96.17 3.00 0.37 0.46 15 1000 2 1420 1 without 1-8 96.17 3.00 0.37 0.46 15 without - 1420 1 without 1-9 89.53 10.00 0.01 0.46 15 without - 1420 1 have 1-10 96.17 3.00 0.01 0.46 15 1000 2 1420 1 without

＜Evaluation of Cemented Carbide＞ For the cemented carbide of each sample, the content rates of the first phase, the second phase and the third phase of the cemented carbide were measured (shown in Table 2 as "1st phase (volume %)", "2nd phase (volume %)" %)", "3rd phase (volume %)" column), the cobalt content rate of cemented carbide (shown in the "Co (mass %)" column in Table 2), the vanadium content rate of cemented carbide (shown in In the "V (mass %)" column in Table 2), the percentage of cobalt in the second phase relative to the total of tungsten, chromium, vanadium and cobalt (shown in "Co/Second Phase (mass %)" in Table 2 )" column), the average value of the circular equivalent diameter of WC particles (shown in the "WC particle average particle diameter (μm)" column in Table 2), the maximum value of the circular equivalent diameter of the third phase particles (shown in the 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 (shown in Table 2 "WC/ The maximum value of the chromium content rate in the interface area (shown in the "Cr Max (atomic %)" column of "Interface Area" in Table 2 middle). The measurement method of each item is as shown in Embodiment 1. The results are shown in Table 2.

＜Cutting test＞ The round rod of each sample was processed to produce a small diameter drill (rotary tool for printed circuit board processing) with a tool diameter of ϕ0.2 mm. Currently, it is mainstream to form a drill by inserting only the blade into the stainless steel shank. However, for evaluation, the drill was produced by sharpening the front end of a φ3.4 mm round rod. Use this drill to drill holes in commercially available printed circuit boards for vehicles.

In the wear resistance evaluation test, the conditions for drilling were set to a rotation speed of 160 krpm and a feed speed of 2.7 m/min. The width of the wear mark (μm) was measured on the drill after 10,000 holes were drilled. The width of the wear mark in this example will be described using FIG. 3 . FIG. 3 is a view from the front end side of the small-diameter drill produced in this embodiment. As shown in Figure 3, the width of the above-mentioned wear mark means the width L1 of the wear mark W at a distance of 0.08 mm from the center C of the drill. The results are shown in the column "Wear resistance of cutting test (μm)" in Table 2. In this example, when the width of the wear mark is 22 μm or less, the wear resistance is judged to be good, and when the width of the wear mark is 20 μm or less, the wear resistance is judged to be even better.

In the fracture resistance evaluation test, the conditions for drilling were set to a rotation speed of 100 krpm and a feed speed of 3.6 m/min. Carry out a maximum of 5,000 holes and measure the number of holes until breakage. The results are shown in the "Break resistance of cutting test (times)" column of Table 2. The result of 5000 times means that no breakage occurred at the time of 5000 times of drilling. In this example, when the number of drillings until breakage is 3,000 or more, the breakage resistance is judged to be good, and when the number of drillings is 5,000, the breakage resistance is judged to be even better.

[Table 2] Table 2 Sample No. super carbide WC particles Phase 3 WC/second phase interface area Cutting test Phase 1 Phase 2 Phase 3 Phase 1 + Phase 2 Co V Co/Phase 2 average particle size maximum particle size Vmax Crmax Wear resistance Resistance to breakage Volume % Volume % Volume % Volume % mass % mass % mass % μm μm atom% atom% μm Second-rate 1 82.0 18.0 0.0 100.0 10 0.01 93 0.8 0 2 15 21.8 5000 2 94.0 5.0 0.8 99.0 3 0.30 90 0.3 0.5 12 15 19.3 3790 3 94.0 5.0 0.0 99.0 3 0.20 86 0.3 0.4 10 15 19.2 5000 4 85.0 15.0 0.0 100.0 8 0.20 85 0.4 0.2 10 15 19.6 5000 5 84.0 15.0 0.5 99.0 8 0.30 92 0.2 0.2 9 14 19.9 5000 6 94.0 5.0 0.5 99.0 3 0.20 90 0.3 0.5 9 15 19.2 3852 7 82.0 18.0 0.0 100.0 10 0.30 90 0.3 0.3 10 14 21.2 5000 8 84.0 15.0 0.6 99.0 8 0.20 93 0.5 0.4 11 15 19.5 4501 9 94.0 5.0 0.3 99.0 3 0.20 83 0.4 0.2 11 twenty two twenty one 4167 10 94.0 5.0 0.7 99.0 3 0.30 90 0.3 0.5 15 16 20.3 3548 11 94.0 5.0 0.3 99.0 3 0.20 83 0.4 0.2 11 20 19.6 4088 12 94.0 5.0 0.6 99.0 3 0.01 88 0.3 0.4 10 15 19.2 3804 1-1 91.0 5.0 1.3 96.0 3 0.30 96 0.3 1.0 13 15 20.8 1657 1-2 95.0 2.0 1.0 97.0 1 0.30 85 0.3 0.7 4 9 damaged 1 1-3 78.0 22.0 0.0 100.0 12 0.30 93 0.3 0.4 10 12 23.1 5000 1-4 95.0 5.0 0.0 100.0 3 0 91 0.9 0 0 14 21.9 2523 1-5 93.0 5.0 0.6 98.0 3 0.40 89 0.3 0.9 17 0 22.3 947 1-6 94.0 5.0 0.5 99.0 3 0.30 90 1.0 0.9 12 14 19.5 1095 1-7 94.0 5.0 0.6 99.0 3 0.30 92 0.3 0.2 17 16 22.4 2874 1-8 92.0 5.0 1.0 97.0 3 0.30 90 0.6 0.9 18 twenty one 22.6 761 1-9 82.0 18.0 0.0 100.0 10 0.01 93 0.9 0 2 20 22.1 1382 1-10 94.0 5.0 0.6 99.0 3 0.01 89 0.3 0.3 16 twenty four 22.1 2020

＜Discussion＞ The cemented carbide and cutting tools of Samples 1 to 12 are equivalent to the 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 are equivalent to comparative examples. It was confirmed that the wear resistance and/or breakage resistance of these samples were insufficient.

As mentioned above, the embodiments and examples of the present invention have been described. However, appropriate combinations or various changes of the configurations of the above-described embodiments and examples are initially intended. It should be considered that the implementation modes and examples disclosed this time are illustrative in all respects and are not intended to be limiting. The scope of the present invention is shown by the scope of the patent application, rather than by the above-mentioned embodiments and examples, and is intended to include meanings equivalent to the scope of the patent application and all changes within the scope.

(0001):Crystalline surface 1: Tungsten carbide particles 2: Phase 2 3: 3rd phase particles 10:Cutting tools 11: Tip of the knife B: Direction C:Drill center L1: Width R: Measurement area W: Wear marks

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

(0001):Crystalline surface

1: Tungsten carbide particles

2: Phase 2

3: 3rd phase particles

B: Direction

R: Measurement area

Claims (4)

A cemented carbide having a first phase containing tungsten carbide particles and a second phase containing cobalt as a main component, and The total content of the above-mentioned first phase and the above-mentioned second phase in the above-mentioned cemented carbide is 97% by volume or more, The average circular equivalent diameter of the above-mentioned tungsten carbide particles is 0.8 μm or less, The cobalt content of the above-mentioned cemented carbide is not less than 3% by mass and not more than 10% by mass, The vanadium content of the above-mentioned cemented carbide is not less than 0.01% by mass and not more than 0.30% by mass, 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 is 15 atomic % or less. The cemented carbide of claim 1, wherein the cemented carbide has a third phase, and the third phase contains third phase particles containing more than 10 atomic % of vanadium, The content of the third phase in the above-mentioned cemented carbide exceeds 0% by volume and is less than 1% by volume, The maximum value of the circle equivalent diameter of the third phase particles is 0.5 μm or less. For example, in the cemented carbide of Claim 1 or Claim 2, the maximum chromium content rate in the above-mentioned interface region is 20 atomic % or less. A cutting tool having a tip including the cemented carbide according to any one of claims 1 to 3.