阅读说明：本技术 硬质合金以及具备该硬质合金的切削工具 (Cemented carbide and cutting tool provided with same ) 是由 广濑和弘 山川隆洋 于 2020-03-31 设计创作，主要内容包括：一种硬质合金,具备由多个碳化钨颗粒构成的第1相以及包含钴的第2相,当通过对采用扫描电子显微镜拍摄硬质合金而得的图像进行图像处理以计算碳化钨颗粒各自的圆当量直径时,圆当量直径为0.3μm以上1.0μm以下的碳化钨颗粒的基于个数的比例为50％以上,当通过以频率为纵轴且以等级为横轴的直方图来表示碳化钨颗粒的圆当量直径的分布时,频率是碳化钨颗粒的个数,等级是圆当量直径以0.1μm的间隔按升序进行划分的,在横轴中,将超过0.3μm且为0.6μm以下的范围定义为第1范围,将超过0.6μm且为1.0μm以下的范围定义为第2范围,第1范围和第2范围分别具有至少一个极大频率,在存在于第1范围内的极大频率当中,最大的第1极大频率相对于碳化钨颗粒的总数的比例为10％以上,在存在于第2范围内的极大频率当中,最大的第2极大频率相对于碳化钨颗粒的总数的比例为10％以上。(A cemented carbide comprising a1 st phase composed of a plurality of tungsten carbide particles and a2 nd phase containing cobalt, wherein when an image obtained by imaging the cemented carbide with a scanning electron microscope is subjected to image processing to calculate the equivalent circular diameter of each of the tungsten carbide particles, the proportion of the tungsten carbide particles having an equivalent circular diameter of 0.3 μm or more and 1.0 μm or less is 50% or more by number, and when the distribution of the equivalent circular diameter of the tungsten carbide particles is represented by a histogram having a frequency as a vertical axis and a scale as a horizontal axis, the frequency is the number of the tungsten carbide particles, the scale is a division of the equivalent circular diameter in ascending order at intervals of 0.1 μm, in the horizontal axis, a range exceeding 0.3 μm and being 0.6 μm or less is defined as a1 st range, a range exceeding 0.6 μm and being 1.0 μm or less is defined as a2 nd range, and each of the 1 st and 2 nd ranges has at least one maximum frequency, among the maximum frequencies existing in the 1 st range, the ratio of the largest 1 st maximum frequency to the total number of tungsten carbide particles is 10% or more, and among the maximum frequencies existing in the 2 nd range, the ratio of the largest 2 nd maximum frequency to the total number of tungsten carbide particles is 10% or more.)

1. A cemented carbide comprising a1 st phase composed of a plurality of tungsten carbide particles and a2 nd phase containing cobalt,

wherein when an image obtained by imaging the cemented carbide with a scanning electron microscope is image-processed to calculate the circle-equivalent diameters of the tungsten carbide particles, the proportion of the tungsten carbide particles having the circle-equivalent diameters of 0.3 μm to 1.0 μm is 50% or more on a number basis,

when the distribution of the circle-equivalent diameter of the tungsten carbide particles is represented by a histogram having a frequency as a vertical axis and a scale as a horizontal axis,

the frequency is the number of the tungsten carbide particles,

the ranks are divided in ascending order at intervals of 0.1 μm by the circle-equivalent diameter,

in the horizontal axis, a range exceeding 0.3 μm and being 0.6 μm or less is defined as a1 st range, a range exceeding 0.6 μm and being 1.0 μm or less is defined as a2 nd range,

said 1 st range and said 2 nd range each having at least one maximum frequency,

a ratio of the largest 1 st maximum frequency to the total number of the tungsten carbide particles is 10% or more among maximum frequencies existing in the 1 st range,

among the maximum frequencies existing in the 2 nd range, the ratio of the largest 2 nd maximum frequency to the total number of the tungsten carbide particles is 10% or more.

2. The cemented carbide according to claim 1, wherein the cemented carbide comprises 75% by area or more and less than 100% by area of the 1 st phase and more than 0% by volume and 20% by area or less of the 2 nd phase in an image taken by a scanning electron microscope.

3. The cemented carbide according to claim 1 or 2, wherein the cemented carbide comprises 5 area% or more and 12 area% or less of the 2 nd phase in an image taken by a scanning electron microscope.

4. The cemented carbide of any one of claims 1 to 3, wherein the cemented carbide comprises chromium,

the ratio of the chromium to the cobalt is 5% to 10% by mass.

5. The cemented carbide of any one of claims 1 to 4, wherein, when the cemented carbide comprises vanadium, the vanadium content in the cemented carbide on a mass basis is less than 100 ppm.

6. The hard metal according to any one of claims 1 to 5, wherein a proportion by number of the tungsten carbide particles having the circle-equivalent diameter of 0.3 μm or less is 7% or less.

7. The cemented carbide according to any one of claims 1 to 6, wherein a ratio of the 2 nd maximum frequency to the 1 st maximum frequency is 0.8 or more and 1.2 or less.

8. The cemented carbide of any one of claims 1 to 7,

when, in the horizontal axis, a range exceeding 0.4 μm and being 0.6 μm or less is defined as a3 rd range and a range exceeding 0.6 μm and being 0.8 μm or less is defined as a 4 th range,

said 3 rd range having said 1 st maximum frequency,

the 4 th range has the 2 nd maximum frequency.

9. A cutting tool having a cutting edge made of the cemented carbide according to any one of claims 1 to 8.

10. The cutting tool according to claim 9, wherein the cutting tool is a rotary tool for processing a printed circuit substrate.

Technical Field

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

Background

The holes drilled in the printed circuit board are mainly drilled with a small diameter of 1mm or less. Therefore, as a cemented carbide used for a tool such as a small-diameter drill, a so-called particulate cemented carbide in which a hard phase is composed of tungsten carbide particles having an average particle diameter of 1 μm or less is used (for example, japanese patent laid-open nos. 2007 and 92090 (patent document 1), 2012 and 52237 (patent document 2), 2012 and 117100 (patent document 3)).

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2007-92090

Patent document 2: japanese laid-open patent publication No. 2012-52237

Patent document 3: japanese patent laid-open publication No. 2012-117100

Disclosure of Invention

The disclosed hard alloy is provided with: a1 st phase composed of a plurality of tungsten carbide particles, and a2 nd phase containing cobalt,

wherein when the equivalent circle diameter of each of the tungsten carbide particles is calculated by image processing of an image obtained by imaging the cemented carbide with a scanning electron microscope, the proportion of the tungsten carbide particles having the equivalent circle diameter of 0.3 μm to 1.0 μm is 50% or more on a number basis,

when the distribution of the circle-equivalent diameters of the above tungsten carbide particles is represented by a histogram having a frequency as a vertical axis and a scale as a horizontal axis,

the frequency is the number of the tungsten carbide particles,

the above-mentioned rank is a division of the circle-equivalent diameter in ascending order at intervals of 0.1 μm, and in the above-mentioned horizontal axis, a range exceeding 0.3 μm and being 0.6 μm or less is defined as a1 st range, a range exceeding 0.6 μm and being 1.0 μm or less is defined as a2 nd range,

the 1 st range and the 2 nd range each have at least one maximum frequency, and among the maximum frequencies existing in the 1 st range, the ratio of the largest 1 st maximum frequency to the total number of the tungsten carbide particles is 10% or more,

among the maximum frequencies existing in the 2 nd range, the ratio of the maximum 2 nd maximum frequency to the total number of the tungsten carbide particles is 10% or more.

The cutting tool of the present disclosure is a cutting tool including a cutting edge made of the cemented carbide.

Brief description of the drawings

Fig. 1 is an example of a captured image of a cemented carbide of the present disclosure obtained by a scanning electron microscope.

Fig. 2 is an image obtained by performing image processing on the captured image of fig. 1.

Fig. 3 is a view showing an example of the circle-equivalent diameter distribution of tungsten carbide particles in the cemented carbide of the present disclosure.

Fig. 4 is a view showing another example of the circle-equivalent diameter distribution of tungsten carbide particles in the cemented carbide of the present disclosure.

Fig. 5 is a view showing another example of the circle-equivalent diameter distribution of tungsten carbide particles in the cemented carbide of the present disclosure.

Fig. 6 is a view showing another example of the circle-equivalent diameter distribution of tungsten carbide particles in the cemented carbide of the present disclosure.

Detailed Description

[ problem to be solved by the present disclosure ]

In recent years, with the development of 5G (5 th generation mobile communication system), the capacity of information has been increasing. Therefore, the printed circuit board is required to have further heat resistance. In order to improve the heat resistance of the printed circuit board, techniques for improving the heat resistance of a resin or glass filler constituting the printed circuit board have been developed. On the other hand, cutting of the printed circuit board becomes difficult.

Accordingly, an object of the present disclosure is to provide a cemented carbide that can improve the tool life even when used as a tool material, particularly in the fine processing of a printed circuit board, and a cutting tool provided with the cemented carbide.

[ Effect of the present disclosure ]

The cemented carbide of the present disclosure can improve tool life when used as a tool material, particularly in fine processing of printed circuit substrates.

[ description of embodiments of the present disclosure ]

First, embodiments of the present disclosure are listed for explanation.

(1) The disclosed hard alloy is provided with: a1 st phase composed of a plurality of tungsten carbide particles, and a2 nd phase containing cobalt,

wherein when the equivalent circle diameter of each of the tungsten carbide particles is calculated by image processing of an image obtained by imaging the cemented carbide with a scanning electron microscope, the proportion of the tungsten carbide particles having the equivalent circle diameter of 0.3 μm to 1.0 μm is 50% or more on a number basis,

when the distribution of the circle-equivalent diameters of the above tungsten carbide particles is represented by a histogram having a frequency as a vertical axis and a scale as a horizontal axis,

the frequency is the number of the tungsten carbide particles,

the above-mentioned rank is a division of the above-mentioned circle-equivalent diameter in ascending order at intervals of 0.1 μm,

in the above horizontal axis, a range exceeding 0.3 μm and not more than 0.6 μm is defined as a1 st range, a range exceeding 0.6 μm and not more than 1.0 μm is defined as a2 nd range,

the 1 st range and the 2 nd range each have at least one maximum frequency,

among the maximum frequencies existing in the 1 st range, the ratio of the maximum 1 st maximum frequency to the total number of the tungsten carbide particles is 10% or more,

among the maximum frequencies existing in the 2 nd range, the ratio of the maximum 2 nd maximum frequency to the total number of the tungsten carbide particles is 10% or more.

The cemented carbide of the present disclosure can improve tool life when used as a tool material, particularly in fine processing of printed circuit substrates.

(2) The image of the cemented carbide taken by a scanning electron microscope preferably includes 75% by area or more and less than 100% by area of the 1 st phase and more than 0% by volume and 20% by area or less of the 2 nd phase. Thereby, the tool life is further improved.

(3) The cemented carbide preferably contains the 2 nd phase in an area of 5 to 12% by area in an image taken by a scanning electron microscope. Thereby, the tool life is further improved.

(4) The cemented carbide described above contains chromium and,

the ratio of the chromium to the cobalt is preferably 5% to 10% by mass. This improves the fracture resistance of the cemented carbide, and further improves the tool life.

(5) When the cemented carbide contains vanadium, the content of the vanadium in the cemented carbide on a mass basis is preferably less than 100 ppm. Thereby, the strength of the cemented carbide is improved.

(6) The proportion of the tungsten carbide particles having a circle-equivalent diameter of less than 0.3 μm on a number basis is preferably 7% or less. Thereby, the tool life is further improved.

(7) The ratio of the 2 nd maximum frequency to the 1 st maximum frequency is preferably 0.8 to 1.2. Thereby, the tool life is further improved.

(8) When, in the above horizontal axis, a range exceeding 0.4 μm and being 0.6 μm or less is defined as a3 rd range and a range exceeding 0.6 μm and being 0.8 μm or less is defined as a 4 th range, it is preferable that the 3 rd range has the 1 st maximum frequency and the 4 th range has the 2 nd maximum frequency. Thereby, the tool life is further improved.

(9) The cutting tool of the present disclosure is a cutting tool including a cutting edge made of the cemented carbide. The cutting tool of the present disclosure has a long tool life.

(10) The cutting tool is preferably a rotary tool for processing a printed circuit board. The cutting tool of the present disclosure is suitable for fine processing of a printed circuit substrate.

[ details of embodiments of the present disclosure ]

Specific examples of the cemented carbide and the cutting tool of the present disclosure are described below with reference to the drawings. In the drawings of the present disclosure, the same reference numerals denote the same parts or equivalent parts. In addition, dimensional relationships such as length, width, thickness, depth, and the like are appropriately changed for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

In the present specification, unless otherwise specified, the expression "a to B" means the upper limit to the lower limit (i.e., a is not less than a and not more than B) of the range, and when no unit is described in a and only a unit is described in B, the unit of a and the unit of B are the same.

In the present specification, in the case of a compound represented by a chemical formula or the like, when the atomic ratio is not particularly limited, all conventionally known atomic ratios are included, and are not necessarily limited to the atomic ratio within the stoichiometric range. For example, when it is referred to as "WC", the ratio of the number of atoms constituting WC includes all conventionally known atomic ratios.

In order to obtain a cemented carbide capable of improving the tool life, the present inventors have studied the form of tool damage in the case of fine processing of a printed circuit board using a tool made of a conventional particulate cemented carbide, and have obtained the following findings.

As a substrate used for a printed circuit board, a glass epoxy substrate obtained by impregnating an epoxy resin into a glass fabric obtained by weaving glass fibers into a cloth shape, a glass polyimide substrate obtained by impregnating a polyimide resin into a glass fabric, or the like is used.

When a printed circuit board is finely processed using a tool composed of a conventional particulate cemented carbide, it is confirmed that cobalt, which is a bonding phase of the cemented carbide, is locally worn away due to resin and glass fibers in the printed circuit board, so that tungsten carbide particles (hereinafter also referred to as "WC particles") are exposed, and the WC particles fall off.

Therefore, in order to achieve a long tool life, the present inventors presume that the following is important: reducing the amount of cobalt (Co) exposed to the tool surface during machining, and improving the binding force of WC particles to each other. In addition, since WC particles in cemented carbide directly participate in cutting of a printed circuit board, the present inventors have estimated that the following are also important in order to maintain precision of fine processing: WC particles appear continuously and densely on the tool surface.

In order to reduce the interface of WC with each other where Co is present and to reduce the amount of cobalt exposed to the tool surface during machining, it may be considered to increase the particle size of WC particles in cemented carbide and to reduce the amount of cobalt. However, if the particle size of WC particles is increased and the amount of cobalt is reduced, the strength is reduced and fracture easily occurs during processing.

Based on the above findings, the present inventors have intensively studied and, as a result, have newly found that the binding force between WC particles can be improved by controlling the particle size of the WC particles, thereby obtaining the cemented carbide of the present disclosure. The cemented carbide of the present disclosure and a cutting tool provided with the cemented carbide will be described in detail below.

Embodiment 1: cemented carbide

The disclosed hard alloy is provided with: a1 st phase composed of a plurality of tungsten carbide particles, and a2 nd phase containing cobalt,

when an image obtained by imaging a cemented carbide with a scanning electron microscope is subjected to image processing to calculate the circle-equivalent diameters of the tungsten carbide particles, the proportion of the tungsten carbide particles having a circle-equivalent diameter of 0.3 μm or more and 1.0 μm or less on a number basis is 50% or more, when a distribution of the circle-equivalent diameters of the tungsten carbide particles is represented by a histogram having a frequency as a vertical axis and a scale as a horizontal axis, the frequency is the number of the tungsten carbide particles, the scale is a division of the circle-equivalent diameters in ascending order at intervals of 0.1 μm, in the horizontal axis, a range exceeding 0.3 μm and 0.6 μm or less is defined as a1 st range, a range exceeding 0.6 μm and 1.0 μm or less is defined as a2 nd range, the 1 st range and the 2 nd range each have at least one maximum frequency, among the maximum frequencies existing in the 1 st range, the proportion of the largest 1 st maximum frequency to the total number of the tungsten carbide particles is 10% or more, among the maximum frequencies existing in the 2 nd range, the ratio of the largest 2 nd maximum frequency to the total number of tungsten carbide particles is 10% or more.

The cemented carbide of the present disclosure can improve tool life when used as a tool material, particularly in fine processing of printed circuit substrates. The reason for this is not clear, but is presumed to be as described in (i) and (ii) below.

(i) In the cemented carbide of the present disclosure, the proportion of tungsten carbide particles having a circle-equivalent diameter of 0.3 μm or more and 1.0 μm or less is 50% or more on a number basis. This makes the cemented carbide structure uniform, and suppresses a decrease in precision of fine machining accompanying use, thereby increasing the tool life.

(ii) In the cemented carbide of the present disclosure, the WC particles have at least one maximum frequency in a distribution of circle-equivalent diameters in a range (1 st range) where the particle diameter exceeds 0.3 μm and is 0.6 μm or less and a range (2 nd range) where the particle diameter exceeds 0.6 μm and is 1.0 μm or less, respectively. The ratio of each of the maximum frequency in the 1 st range (1 st maximum frequency) and the maximum frequency in the 2 nd range (2 nd maximum frequency) to the total number of tungsten carbide particles in the cemented carbide is 10% or more.

Thus, the cemented carbide has a structure in which WC grains having a large circle-equivalent diameter form a skeleton, and gaps are filled between the WC grains having a small circle-equivalent diameter. In this cemented carbide, since WC particles are bonded to each other, wear resistance is improved by suppressing the fall-off of the WC particles. Further, by suppressing abrasion, an increase in cutting resistance is suppressed, and fracture resistance is improved. This increases the tool life.

Furthermore, in the cemented carbide, the amount of cobalt exposed to the tool surface during machining is less than in conventional particulate cemented carbides. Therefore, wear of cobalt is less likely to occur during machining, the falling off of WC particles can be suppressed, and the tool life becomes long.

< phase 1 >

(composition of phase 1)

Phase 1 is composed of tungsten carbide particles. Here, tungsten carbide includes not only "pure WC (including WC containing no impurity element and WC containing an impurity element below the detection limit)" but also "WC containing other impurity elements intentionally or inevitably in the inside thereof within a range not impairing the effect of the present disclosure". The concentration of impurities contained in tungsten carbide (the total concentration of two or more elements constituting the impurities, if any) is less than 0.1 mass% relative to the total amount of the tungsten carbide and the impurities. The content of the impurity element in the phase 1 was measured by ICP Emission Spectroscopy (Inductively Coupled Plasma) Emission Spectroscopy (measuring apparatus: ICPS-8100 (trade Mark) manufactured by Shimadzu corporation).

(distribution of circle-equivalent diameter of tungsten carbide particles)

The tungsten carbide particles have a proportion of tungsten carbide particles having a circle-equivalent diameter of 0.3 to 1.0 [ mu ] m based on the number of the tungsten carbide particles of 50% or more. This makes the cemented carbide structure uniform, and suppresses a decrease in precision of fine machining accompanying use, thereby increasing the tool life.

When the amount of cobalt in the cemented carbide is constant, if the proportion of coarse tungsten carbide particles having a circle equivalent diameter of more than 1 μm is increased, the hardness is decreased and the wear resistance tends to be decreased, and if the proportion of fine tungsten carbide particles having a circle equivalent diameter of less than 0.3 μm is increased, the exfoliation of the tungsten carbide particles is promoted and the wear resistance tends to be decreased. In the cemented carbide of the present disclosure, the proportion of tungsten carbide particles having a circle-equivalent diameter of 0.3 μm or more and 1.0 μm or less based on the number is 50% or more, and thus, excellent wear resistance can be obtained.

From the viewpoint of improving the uniformity of the cemented carbide structure, the proportion of tungsten carbide particles having a circle-equivalent diameter of 0.3 μm to 1.0 μm on a number basis is 50% or more, preferably 70% or more. The upper limit of the proportion of tungsten carbide particles having a circle-equivalent diameter of 0.3 μm to 1.0 μm on a number basis is not particularly limited, and may be, for example, 100% or less, 90% or less, or 80% or less. The proportion of tungsten carbide particles having a circle-equivalent diameter of 0.3 μm to 1.0 μm on a number basis may be 50% to 100%, 60% to 90%, or 70% to 80%.

The proportion of tungsten carbide particles having a circle-equivalent diameter of less than 0.3 μm on a number basis is preferably 7% or less. Tungsten carbide particles with a circle-equivalent diameter of less than 0.3 μm contribute less to the improvement of the strength of the cemented carbide and to the reduction of the amount of cobalt exposed to the tool surface during machining. Therefore, by reducing the proportion of tungsten carbide particles having a circle-equivalent diameter of less than 0.3 μm on a number basis, the tool life becomes longer.

The proportion of tungsten carbide particles having a circle-equivalent diameter of less than 0.3 μm on a number basis is preferably 0% to 7%, more preferably 0% to 5%. The proportion of tungsten carbide particles having a circle-equivalent diameter of less than 0.2 μm on a number basis is preferably 0% to 3%.

The circle-equivalent diameter of the tungsten carbide particles was measured by the following procedures (a1) to (C1).

(A1) And performing mirror surface processing on any surface or any section of the hard alloy. Examples of the mirror finishing method include a diamond polishing method, a method using a focused ion beam apparatus (FIB apparatus), a method using a cross-section polishing apparatus (CP apparatus), and a method combining these methods.

(B1) And shooting the processed surface of the hard alloy by using a scanning electron microscope. The observation magnification was 5000 times. Fig. 1 shows an example of a captured image of the cemented carbide of the present disclosure obtained by a scanning electron microscope. In the scale at the lower right of fig. 1, one scale indicates 1 μm.

(C1) The captured image obtained in (B1) above was introduced into a computer, and image processing was performed using image analysis software (ImageJ: https:// image. nih. gov/ij /), to calculate the equivalent circular diameter (Heywood diameter: equivalent circular diameter). The 1 st phase composed of tungsten carbide particles and the 2 nd phase containing cobalt can be identified by the shade of color in the above-described captured image. Fig. 2 shows an image obtained by image processing of the captured image of fig. 1. In fig. 2, the black area is phase 1, and the white area is phase 2. White lines indicate grain boundaries. In the scale at the lower right of fig. 2, one scale indicates 1 μm.

In the present specification, the proportion of tungsten carbide particles having a circle-equivalent diameter of 0.3 μm to 1.0 μm in the cemented carbide based on the number is calculated by the following steps (D1) and (E1).

(D1) The image processing described above (C1) was performed in 3 measurement fields. The dimensions of 1 measurement visual field were set to be rectangles having a length of 25.3 μm × a width of 17.6 μm.

(E1) The ratio of tungsten carbide particles having a circle-equivalent diameter of 0.3 μm or more and 1.0 μm or less to the total number of tungsten carbide particles in the measurement field of view was calculated for each of the 3 measurement fields of view. The average value of these is the ratio of tungsten carbide particles having a circle-equivalent diameter of 0.3 μm to 1.0 μm in the cemented carbide on a number basis.

As measured by the applicant, it was confirmed that, in the range where the same sample was measured, even when the ratio of tungsten carbide particles having a circle-equivalent diameter of 0.3 μm to 1.0 μm in cemented carbide on the basis of the number was measured a plurality of times by changing the selection position of the measurement visual field, the variation in the measurement results was small, and the measurement visual field was not changed arbitrarily even when the measurement visual field was set arbitrarily.

The distribution of the circle-equivalent diameter of the tungsten carbide particles contained in the cemented carbide of the present disclosure satisfies the following (a). Further, when the distribution of the circle-equivalent diameters of the tungsten carbide particles contained in the cemented carbide of the present disclosure is represented by a histogram with the frequency as the vertical axis and the rank as the horizontal axis, the following (b) and (c) are satisfied. Here, the frequency is the number of tungsten carbide particles, and the rank is divided in ascending order at intervals of 0.1 μm in the circle-equivalent diameter.

(a) The proportion of tungsten carbide particles having a circle-equivalent diameter of 0.3 to 1.0 [ mu ] m is 50% or more on a number basis.

(b) In the horizontal axis, when a range exceeding 0.3 μm and being 0.6 μm or less is defined as a1 st range, and a range exceeding 0.6 μm and being 1.0 μm or less is defined as a2 nd range, the 1 st range and the 2 nd range respectively have at least one maximum frequency.

(c) Among the maximum frequencies existing in the 1 st range, the ratio of the largest 1 st maximum frequency to the total number of tungsten carbide particles is 10% or more, and among the maximum frequencies existing in the 2 nd range, the ratio of the largest 2 nd maximum frequency to the total number of tungsten carbide particles is 10% or more.

In the present specification, the histogram is produced by the following steps (a2) and (B2).

(A2) The circle-equivalent diameter of the tungsten carbide particle was calculated by the steps (a1) to (C1) described in the method for measuring the circle-equivalent diameter of the tungsten carbide particle. The determination of the circle-equivalent diameter of the tungsten carbide particles was carried out in 3 measurement fields.

(B2) Based on the circle-equivalent diameters of all the tungsten carbide particles measured in the 3 measurement fields, a histogram was created with the frequency as the vertical axis and the rank as the horizontal axis. The frequency is the number of tungsten carbide particles, and the ranks are divided in ascending order at intervals of 0.1 μm in circle-equivalent diameter.

In this specification, the maximum frequency means any of a frequency of a level higher than the level to which the frequency belongs by one step (the side on which the equivalent circle diameter is smaller) and a frequency of a level higher than the level to which the frequency belongs by one step (the side on which the equivalent circle diameter is larger).

Note that the rank one step lower than the rank to which the maximum frequency belongs and the rank one step higher than the rank to which the maximum frequency belongs may be ranks other than the 1 st range or other than the 2 nd range. Specifically, when the maximum frequency in the 1 st range belongs to a rank exceeding 0.3 μm and being 0.4 μm or less, the rank of the lower rank is more than 0.2 μm and being 0.3 μm or less outside the 1 st range. When the maximum frequency in the 2 nd range belongs to a rank exceeding 0.9 μm and being 1.0 μm or less, a rank of a higher rank is exceeding 1.0 μm and being 1.1 μm or less outside the 2 nd range.

By satisfying the above (a) to (c), it is possible to suppress a decrease in precision of fine machining accompanying use, to improve strength, to improve fracture resistance, to suppress the dropping of WC particles, and to prolong the tool life.

The above (a) to (c) will be described with reference to fig. 3 to 6. Fig. 3 to 6 are each an example of a graph showing a circle-equivalent diameter distribution of tungsten carbide particles in the cemented carbide of the present disclosure. In fig. 3 to 6, the horizontal axis represents the ranks obtained by dividing the circle equivalent diameters in ascending order at intervals of 0.1 μm, and the vertical axis represents the proportion (%) of the tungsten carbide particles belonging to each rank with respect to the total number of tungsten carbide particles.

In fig. 3 to 6, the form "C to D" indicates that the number exceeds C and is D or less. Specifically, the form of "0 to 0.1" on the horizontal axis of FIGS. 3 to 6 means more than 0 μm and not more than 0.1 μm, and the form of "0.1 to 0.2" means more than 0.1 μm and not more than 0.2 μm.

The shapes in fig. 3 to 6 can be regarded as the shapes of histograms when the horizontal axis has the same level definition and the vertical axis has the same frequency as the number of tungsten carbide particles. Therefore, the above (a) to (c) can be described using the shapes shown in fig. 3 to 6. In fig. 3 to 6, the vertical axis represents the percentage (%) of the tungsten carbide particles belonging to each grade based on the number of all the tungsten carbide particles, but hereinafter, for convenience of explanation, the vertical axis in fig. 3 to 6 may be represented as a frequency.

(FIG. 3)

In fig. 3, the proportion of tungsten carbide particles having a circle-equivalent diameter of 0.3 μm to 1.0 μm is 50% or more (about 72%) by number. Therefore, the circle-equivalent diameter distribution of the tungsten carbide particles shown in fig. 3 satisfies the above (a).

In fig. 3, the frequency of a rank having a circle equivalent diameter of more than 0.4 μm and 0.5 μm or less is higher than the frequency of a rank one step lower than the rank to which the frequency belongs (the circle equivalent diameter of more than 0.3 μm and 0.4 μm or less), and the frequency of a rank one step higher than the rank to which the frequency belongs (the circle equivalent diameter of more than 0.5 μm and 0.6 μm or less). That is, in FIG. 3, the 1 st range (circle equivalent diameter exceeding 0.3 μm and 0.6 μm or less) has one maximum frequency.

In fig. 3, the frequency of a level higher than the frequency by one level (the circle equivalent diameter exceeds 0.6 μm and is 0.7 μm or less) and the frequency of a level higher than the frequency by one level (the circle equivalent diameter exceeds 0.8 μm and is 0.9 μm or less) are higher than the frequency by one level (the circle equivalent diameter exceeds 0.7 μm and is 0.8 μm or less). That is, in FIG. 3, the 2 nd range (circle equivalent diameter exceeding 0.6 μm and 1.0 μm or less) has one maximum frequency.

As can be seen from the above, the circle-equivalent diameter distribution of the tungsten carbide particles shown in fig. 3 satisfies the above (b).

In fig. 3, the maximum frequency existing in the 1 st range (i.e., the 1 st maximum frequency) is a frequency in the order that the circle-equivalent diameter exceeds 0.4 μm and is 0.5 μm or less. The proportion of the tungsten carbide particles of the 1 st maximum frequency to the total number is 10% or more (about 14.3%).

In fig. 3, the maximum frequency existing in the 2 nd range (i.e., the 2 nd maximum frequency) is a frequency in the order that the circle-equivalent diameter exceeds 0.7 μm and is 0.8 μm or less. The proportion of the tungsten carbide particles of the 2 nd maximum frequency to the total number is 10% or more (about 12.6%).

As can be seen from the above, the circle-equivalent diameter distribution of the tungsten carbide particles shown in fig. 3 satisfies the above (c).

(FIG. 4)

In fig. 4, the proportion of tungsten carbide particles having a circle-equivalent diameter of 0.3 μm to 1.0 μm is 50% or more (about 72.1%) by number. Therefore, the circle-equivalent diameter distribution of the tungsten carbide particles shown in fig. 4 satisfies the above (a).

In fig. 4, the frequency of a rank having a circle equivalent diameter of more than 0.5 μm and 0.6 μm or less is higher than the frequency of a rank one step lower than the rank to which the frequency belongs (the circle equivalent diameter of more than 0.4 μm and 0.5 μm or less), and the frequency of a rank one step higher than the rank to which the frequency belongs (the circle equivalent diameter of more than 0.6 μm and 0.7 μm or less). That is, in FIG. 4, the 1 st range (circle equivalent diameter exceeding 0.3 μm and 0.6 μm or less) has one maximum frequency.

In fig. 4, the frequency of a rank having a circle equivalent diameter of more than 0.7 μm and 0.8 μm or less is higher than the frequency of a rank one step lower than the rank to which the frequency belongs (the circle equivalent diameter of more than 0.6 μm and 0.7 μm or less), and the frequency of a rank one step higher than the rank to which the frequency belongs (the circle equivalent diameter of more than 0.8 μm and 0.9 μm or less). In fig. 4, the frequency of the rank having the circle equivalent diameter of more than 0.9 μm and 1.0 μm or less is higher than the frequency of the rank one step lower than the frequency (the circle equivalent diameter of more than 0.8 μm and 0.9 μm or less) and the frequency of the rank one step higher than the frequency (the circle equivalent diameter of more than 1.0 μm and 1.1 μm or less). That is, in fig. 4, the 2 nd range (circle equivalent diameter exceeding 0.6 μm and 1.0 μm or less) has two maximum frequencies.

As can be seen from the above, the circle-equivalent diameter distribution of the tungsten carbide particles shown in fig. 4 satisfies the above (b).

In fig. 4, the maximum frequency existing in the 1 st range (i.e., the 1 st maximum frequency) is a frequency in the order that the circle-equivalent diameter exceeds 0.5 μm and is 0.6 μm or less. The proportion of the tungsten carbide particles of the 1 st maximum frequency to the total number is 10% or more (about 13.4%).

In fig. 4, the maximum frequency existing in the 2 nd range (i.e., the 2 nd maximum frequency) is a frequency in the order that the circle-equivalent diameter exceeds 0.7 μm and is 0.8 μm or less. The proportion of the tungsten carbide particles of the 2 nd maximum frequency to the total number is 10% or more (about 12.7%).

As can be seen from the above, the circle-equivalent diameter distribution of the tungsten carbide particles shown in fig. 4 satisfies the above (c).

(FIG. 5)

In fig. 5, the proportion of tungsten carbide particles having a circle-equivalent diameter of 0.3 μm to 1.0 μm is 50% or more (about 73.5%) by number. Therefore, the circle-equivalent diameter distribution of the tungsten carbide particles shown in fig. 5 satisfies the above (a).

In fig. 5, the frequency of a rank having a circle equivalent diameter of more than 0.3 μm and 0.4 μm or less is higher than the frequency of a rank one step lower than the rank to which the frequency belongs (the circle equivalent diameter of more than 0.2 μm and 0.3 μm or less), and the frequency of a rank one step higher than the rank to which the frequency belongs (the circle equivalent diameter of more than 0.4 μm and 0.5 μm or less). That is, in FIG. 5, the 1 st range (circle equivalent diameter exceeding 0.3 μm and 0.6 μm or less) has one maximum frequency.

In fig. 5, the frequency of the rank having the circle equivalent diameter of more than 0.7 μm and 0.8 μm or less is higher than the frequency of the rank one step lower than the rank to which the frequency belongs (the circle equivalent diameter of more than 0.6 μm and 0.7 μm or less) and the frequency of the rank one step higher than the rank to which the frequency belongs (the circle equivalent diameter of more than 0.8 μm and 0.9 μm or less). In fig. 5, the frequency of the rank having the circle equivalent diameter of more than 0.9 μm and 1.0 μm or less is higher than the frequency of the rank one step lower than the frequency (the circle equivalent diameter of more than 0.8 μm and 0.9 μm or less) and the frequency of the rank one step higher than the frequency (the circle equivalent diameter of more than 1.0 μm and 1.1 μm or less). That is, in fig. 5, the 2 nd range (circle equivalent diameter exceeding 0.6 μm and 1.0 μm or less) has two maximum frequencies.

As can be seen from the above, the circle-equivalent diameter distribution of the tungsten carbide particles shown in fig. 5 satisfies the above (b).

In fig. 5, the maximum frequency existing in the 1 st range (i.e., the 1 st maximum frequency) is a frequency in the order that the circle-equivalent diameter exceeds 0.3 μm and is 0.4 μm or less. The proportion of the tungsten carbide particles of the 1 st maximum frequency to the total number is 10% or more (about 11.8%).

In fig. 5, the maximum frequency existing in the 2 nd range (i.e., the 2 nd maximum frequency) is a frequency in the order that the circle-equivalent diameter exceeds 0.7 μm and is 0.8 μm or less. The proportion of the tungsten carbide particles of the 2 nd maximum frequency to the total number is 10% or more (about 12.2%).

As can be seen from the above, the circle-equivalent diameter distribution of the tungsten carbide particles shown in fig. 5 satisfies the above (c).

(FIG. 6)

In fig. 6, the proportion of tungsten carbide particles having a circle-equivalent diameter of 0.3 μm to 1.0 μm is 50% or more (about 72.6%) by number. Therefore, the circle-equivalent diameter distribution of the tungsten carbide particles shown in fig. 6 satisfies the above (a).

In fig. 6, the frequency of a rank having a circle equivalent diameter of more than 0.4 μm and 0.5 μm or less is higher than the frequency of a rank one step lower than the rank to which the frequency belongs (the circle equivalent diameter of more than 0.3 μm and 0.4 μm or less), and the frequency of a rank one step higher than the rank to which the frequency belongs (the circle equivalent diameter of more than 0.5 μm and 0.6 μm or less). That is, in FIG. 6, the 1 st range (circle equivalent diameter exceeding 0.3 μm and 0.6 μm or less) has one maximum frequency.

In fig. 6, the frequency of a rank having a circle equivalent diameter of more than 0.6 μm and 0.7 μm or less is higher than the frequency of a rank one step lower than the rank to which the frequency belongs (the circle equivalent diameter of more than 0.5 μm and 0.6 μm or less), and the frequency of a rank one step higher than the rank to which the frequency belongs (the circle equivalent diameter of more than 0.7 μm and 0.8 μm or less). That is, in fig. 6, the 2 nd range (circle equivalent diameter exceeding 0.6 μm and 1.0 μm or less) has one maximum frequency.

As can be seen from the above, the circle-equivalent diameter distribution of the tungsten carbide particles shown in fig. 6 satisfies the above (b).

In fig. 6, the maximum frequency existing in the 1 st range (i.e., the 1 st maximum frequency) is a frequency in the order that the circle-equivalent diameter exceeds 0.4 μm and is 0.5 μm or less. The proportion of the tungsten carbide particles of the 1 st maximum frequency to the total number is 10% or more (about 14.2%).

In fig. 6, the maximum frequency existing in the 2 nd range (i.e., the 2 nd maximum frequency) is a frequency in the order that the circle-equivalent diameter exceeds 0.6 μm and is 0.7 μm or less. The proportion of the tungsten carbide particles of the 2 nd maximum frequency to the total number is 10% or more (about 12.4%).

As can be seen from the above, the circle-equivalent diameter distribution of the tungsten carbide particles shown in fig. 6 satisfies the above (c).

In the horizontal axis of the histogram representing the circle-equivalent diameter distribution of the tungsten carbide particles of the present disclosure, when a range exceeding 0.4 μm and being 0.6 μm or less is defined as a3 rd range and a range exceeding 0.6 μm and being 0.8 μm or less is defined as a 4 th range, preferably, the 3 rd range has a1 st maximum frequency and the 4 th range has a2 nd maximum frequency. Thereby, the tool life is further improved.

The ratio of the 2 nd maximum frequency to the 1 st maximum frequency is preferably 0.8 to 1.2. Thereby, the tool life is further improved. It is presumed that the reason is that the bonding by the contact of the tungsten carbide particles is important, and if the difference between the maximum frequency existing in the 1 st range and the maximum frequency existing in the 2 nd range becomes large, the contact of the tungsten carbide particles in the cemented carbide becomes small as a result.

< phase 2 >

The phase 2 comprises cobalt. The 2 nd phase is a bonding phase in which tungsten carbide particles constituting the 1 st phase are bonded to each other.

Here, the phrase "the 2 nd phase contains cobalt (Co)" means that the main component of the 2 nd phase is Co. "the main component of the 2 nd phase is Co" means that the mass ratio of Co in the 2 nd phase is 90 mass% or more and 100 mass% or less. The mass ratio of Co in the 2 nd phase can be measured by ICP emission spectrometry (using a device: ICPS-8100 (trade mark) manufactured by Shimadzu corporation).

The 2 nd phase may contain, in addition to cobalt, an iron group metal such as nickel, and a solute (Cr, W, etc.) in the alloy.

< composition of cemented carbide >

(composition)

The hard alloy is provided with: a1 st phase composed of a plurality of tungsten carbide particles, and a2 nd phase containing cobalt. Preferably, the cemented carbide includes a1 st phase of 75 area% or more and less than 100 area% and a2 nd phase of more than 0 area% and 20 area% or less in an image taken by a scanning electron microscope.

When the proportion of the 2 nd phase in the cemented carbide is 20 area% or less, the tungsten carbide particles of fine particles having a circle-equivalent diameter of 0.6 μm or less can be suppressed from dissolving in the cobalt of the 2 nd phase, and the reduction of the tungsten carbide particles having a circle-equivalent diameter of more than 0.3 μm and 0.6 μm or less can be suppressed. In addition, the amount of cobalt exposed to the tool surface during machining is further reduced. Thereby, the tool life is further improved.

Preferably, the cemented carbide includes 5 area% or more and 12 area% or less of the 2 nd phase in an image taken by a scanning electron microscope. Thus, the hardness and wear resistance required for processing the printed circuit board can be exhibited, and the occurrence of variations in tool life can be suppressed.

The lower limit of the proportion of the 1 st phase in the cemented carbide may be 75% by area or more, or 85% by area or more. The upper limit of the proportion of the 1 st phase in the cemented carbide may be set to less than 100% by area, or 95% by area or less. The proportion of the 1 st phase in the cemented carbide may be 75% by area or more and less than 100% by area, or 85% by area or more and 95% by area or less.

The lower limit of the proportion of the 2 nd phase in the cemented carbide may be set to more than 0 area%, or 5 area% or more. The upper limit of the proportion of the 2 nd phase in the cemented carbide may be 20 area% or less, or 12 area% or less. The proportion of the 2 nd phase in the cemented carbide may be more than 0 area% and 2 area% or less, or 5 area% or more and 12 area% or less.

The area ratio of each of the 1 st phase and the 2 nd phase in the cemented carbide was measured by the following procedures (a3) to (C3).

(A3) The same procedures as (a1) and (B1) described in the above method for measuring the equivalent circle diameter of tungsten carbide particles were used to obtain a captured image of the cross section of the cemented carbide.

(B3) The captured image obtained in (A3) above was introduced into a computer, and image analysis software (ImageJ: https:// image. nih. gov/ij /) was used to perform image processing, and the area ratios of the 1 st phase and the 2 nd phase were measured using the entire measurement field (rectangle 25.3. mu. m. long. by 17.6. mu.m wide) as a denominator. The 1 st and 2 nd phases can be identified by the shade of color in the above-described captured image.

(C3) The image processing (B3) is performed in 5 measurement fields. The average of the area ratios of the 1 st phase obtained in the 5 measurement fields was defined as the area ratio of the 1 st phase in the cemented carbide. The average of the area ratios of the 2 nd phase obtained in the 5 measurement fields was defined as the area ratio of the 2 nd phase in the cemented carbide.

(chromium content)

The cemented carbide contains chromium, and the ratio of chromium to cobalt on a mass basis is preferably 5% to 10%. Chromium has the effect of inhibiting grain growth of tungsten carbide particles. Further, solid solution in cobalt promotes the generation of lattice strain of cobalt. Thus, if the cemented carbide contains chromium in the above-described ratio, the fracture resistance is further improved.

On the other hand, if the amount of chromium is too large, chromium precipitates as carbide, which may become a starting point of cracking. When the ratio of chromium to cobalt on a mass basis is 5% or more and 10% or less, precipitation of chromium carbide is less likely to occur, and the effect of improving fracture resistance can be obtained.

When the mass ratio of chromium to cobalt is 10% or less, the degree of the effect of suppressing grain growth becomes appropriate, and the amount of tungsten carbide grains having a circle-equivalent diameter of more than 1.0 μm in the cemented carbide can be prevented from becoming too large.

The lower limit of the mass-based ratio of chromium to cobalt is preferably 5% or more, and more preferably 7% or more. The ratio of chromium to cobalt on a mass basis is preferably 10% or less, more preferably 9% or less. The ratio of chromium to cobalt on a mass basis may be 5% to 10% or 7% to 9%.

The contents of cobalt and chromium in the cemented carbide were measured by ICP emission spectroscopy.

(vanadium)

When the cemented carbide contains vanadium, the vanadium content of the cemented carbide on a mass basis is preferably less than 100 ppm.

Vanadium has an effect of suppressing grain growth, and is therefore used in the production of conventional ultrafine cemented carbide. If vanadium is present during grain growth of the tungsten carbide grains, it is considered that the growth of the tungsten carbide grains is suppressed by precipitation of vanadium on the surfaces of the tungsten carbide grains or by short-term intervention of vanadium in the growth surfaces of the tungsten carbide grains.

Therefore, when vanadium is added, an effect of suppressing grain growth can be obtained, but since tungsten carbide exists at the interface of tungsten carbide particles and cobalt and the interface of tungsten carbide particles with each other, wettability reduction and strength reduction may occur. Therefore, the smaller the vanadium content in the tungsten carbide, the higher the affinity between the tungsten carbide particles and cobalt and the affinity between the tungsten carbide particles can be maintained, and the strength of the cemented carbide can be improved.

The vanadium content in the cemented carbide is preferably 100ppm or less, more preferably 10ppm or less. Since the lower the vanadium content in the cemented carbide, the better, the lower limit thereof is preferably 0 ppm. It should be noted that several ppm of vanadium may be detected accidentally during the manufacturing process. The vanadium content in the cemented carbide may be set to 0ppm to 100ppm or less, or 0ppm to 10 ppm.

The vanadium content in the cemented carbide was determined by ICP emission spectroscopy.

< method for producing cemented carbide >

The cemented carbide of the present embodiment can be usually produced by sequentially performing a raw material powder preparation step, a mixing step, a forming step, a sintering step, and a cooling step. Hereinafter, each step will be described.

< preparation step >)

The preparation step is a step of preparing all raw material powders of the material constituting the cemented carbide. The raw material powder includes a raw material of the 1 st phase (i.e., tungsten carbide powder) and a raw material of the 2 nd phase (cobalt (Co) powder) as essential raw material powders. Further, chromium carbide (Cr) may be prepared as required₃C₂) The powder is used as granule growth inhibitor. Further, Vanadium Carbide (VC) powder may be prepared as long as the effects of the present disclosure can be exhibited. Commercially available tungsten carbide powder, cobalt powder, chromium carbide powder, and vanadium carbide powder can be used.

As for the tungsten carbide powder, (a) a tungsten carbide powder having an average particle size of 0.4 μm to 1.2 μm (hereinafter, also referred to as "1 st tungsten carbide powder") and (b) a tungsten carbide powder having an average particle size of 0.8 μm to 1.2 μm (hereinafter, also referred to as "2 nd tungsten carbide powder") were prepared. The 1 st tungsten carbide powder having an average particle diameter smaller than that of the 2 nd tungsten carbide powder was prepared. In the present specification, the average particle diameter of the raw material powder refers to the median diameter d50 of the circle-equivalent diameter. The average particle diameter was measured by using a particle size distribution measuring apparatus (trade name: MT3300EX) manufactured by マイクロトラック.

The average particle diameter of the cobalt powder may be 0.8 μm or more and 1.2 μm or less. The average particle diameter of the chromium carbide powder may be 1.0 μm or more and 2.0 μm or less. The average particle diameter of the vanadium carbide powder may be 0.5 μm or more and 1.0 μm or less.

< mixing step >)

The mixing step is a step of mixing the respective raw material powders prepared by the preparation step. Through the mixing step, a mixed powder in which the respective raw material powders are mixed is obtained.

The proportion of the 1 st tungsten carbide powder in the mixed powder may be, for example, 30 mass% to 94.6 mass%.

The ratio of the 2 nd tungsten carbide powder in the mixed powder may be, for example, 30 mass% or more and 64.6 mass% or less.

The mixing ratio of the 1 st tungsten carbide powder to the 2 nd tungsten carbide powder may be set, for example, on a mass basis, to the 1 st tungsten carbide powder: the 2 nd tungsten carbide powder is 2:1 to 1: 2.

The proportion of the cobalt powder in the mixed powder may be, for example, 2.8 mass% or more and 10 mass% or less.

The ratio of the chromium carbide powder in the mixed powder may be, for example, 0.2 mass% or more and 1.2 mass% or less.

The proportion of the vanadium carbide powder in the mixed powder may be, for example, 0 mass% or more and 0.2 mass% or less.

The mixed powder was mixed using a ball mill. The mixing time may be 20 hours to 48 hours.

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 mold or a die in a molding step described later. For the granulation, a known granulation method may be used, and for example, a commercially available granulator such as a spray dryer may be used.

< Forming step >

The molding step is a step of molding the mixed powder obtained by the mixing step into a predetermined shape to obtain a molded body. The forming method and forming conditions in the forming step may be general methods and conditions, and are not particularly limited. The predetermined shape may be, for example, a shape of a cutting tool (for example, a shape of a small-diameter drill).

< sintering step >)

The sintering step is a step of sintering the formed body obtained by the forming step to obtain a cemented carbide. In the method for producing a cemented carbide according to the present disclosure, the sintering temperature may be set to a normal sintering temperature (1350 to 1500 ℃) for cemented carbide.

Although cemented carbide is generally sintered at 1350 to 1500 ℃, fine tungsten carbide particles have a large surface area and are easily dissolved in cobalt, and thus are likely to cause an abnormal structure due to dissolution and re-precipitation. Therefore, in sintering of fine tungsten carbide particles, in order to suppress re-precipitation by dissolution, sintering is performed in a low temperature region of 1350 to 1380 ℃ where the solid solubility limit of tungsten carbide with respect to cobalt is low. However, in the cemented carbide sintered in the low temperature region, the tungsten carbide particles do not undergo particle growth, and therefore the surfaces of the tungsten carbide particles are in a crushed state by the pulverization and mixing in the previous step. Therefore, the bonding force between the interface between the tungsten carbide particles and cobalt and the interface between the tungsten carbide particles is low, and the wear resistance and fracture resistance tend to decrease.

On the other hand, in the method for producing a cemented carbide according to the present disclosure, the generation of fragments of ultrafine tungsten carbide particles generated by grinding and mixing of raw materials is suppressed, and the effect of suppressing the particle growth by chromium is exhibited to the maximum. It has also been found that: by maintaining the distribution of coarse particles and fine particles having peaks of similar particle sizes in the microstructure, abnormal particle growth can be suppressed even in a temperature range in which particle growth normally occurs. Therefore, in the method for manufacturing a cemented carbide of the present disclosure, even when the tungsten carbide particles are sintered at a higher temperature than usual, generation of abnormal structures can be suppressed, and the wear resistance and fracture resistance of the cemented carbide can be improved by increasing the bonding force between the interfaces between the tungsten carbide particles and cobalt and between the tungsten carbide particles. The above-mentioned novel findings are the results of intensive studies by the present inventors.

< Cooling step >)

The cooling step is a step of cooling the cemented carbide after completion of sintering. The cooling conditions may be any conditions, and are not particularly limited.

Embodiment 2: cutting tools ]

The cutting tool of the present disclosure includes a cutting edge composed of the cemented carbide described above. In the present specification, the cutting edge refers to a portion relating to cutting, and in cemented carbide, refers to a region surrounded by a cutting edge ridge line thereof and an imaginary plane having a distance of 2mm moving from a perpendicular line of the cutting edge ridge line along a tangent line of the cutting edge ridge line to the cemented carbide side.

Examples of the cutting tool include a turning tool, a drill, an end mill, a cutting insert for milling, a cutting insert for turning, a metal saw, a gear cutting tool, a reamer, and a tap. In particular, when the cutting tool of the present disclosure is a small-diameter drill for processing a printed circuit board, excellent effects can be exerted.

The cemented carbide of the present embodiment may constitute all or part of these tools. Here, "constituting a part" means a mode of forming a cutting edge portion by brazing the cemented carbide of the present embodiment to a predetermined position of an arbitrary base material, and the like.

< hard film >)

The cutting tool according to the present embodiment may further include a hard film covering at least a part 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.

Examples

This embodiment mode will be further specifically described by way of examples. However, the present embodiment is not limited to these examples.

[ example 1]

In example 1, cemented carbides of samples 1 to 24 were produced by changing the kind and the mixture ratio of the raw material powders. A small-diameter drill provided with a cutting edge made of the cemented carbide was produced and evaluated.

< preparation of sample >)

(preparation step)

As the raw material powder, powder having a composition shown in the column of "raw material" in table 1 was prepared. A plurality of tungsten carbide (WC) powders having different average particle sizes were prepared. The average particle size of the tungsten carbide (WC) powder is shown in the column "average particle size (μm)" of "1 st WC powder" in table 1.

Cobalt (Co) powder having an average particle size of 1 μm, Vanadium Carbide (VC) powder having an average particle size of 0.8 μm, and chromium carbide (Cr)₃C₂) The average particle size of the powder was 1 μm. Co powder, VC powder and Cr₃C₂The powder is commercially available. The average particle diameter of the raw material powder was measured by using a particle size distribution measuring apparatus (trade name: MT3300EX) manufactured by マイクロトラック.

(mixing step)

The raw material powders were mixed in the blending amounts shown in table 1 to prepare mixed powders. The "% by mass" in the column of "raw material" in table 1 represents the ratio of each raw material powder to the total mass of the raw material powders. Mixing was carried out by a ball mill for 20 hours. The resulting mixed powder was spray-dried to obtain a granulated powder.

(shaping step)

The obtained granulated powder was press-molded to prepare a round rod-shaped compact having a diameter of 3.4 mm.

(sintering step)

The formed body was placed in a sintering furnace and held at 1400 ℃ for 1 hour in vacuum to be sintered.

(Cooling step)

After completion of the sintering, it was slowly cooled in an argon (Ar) gas atmosphere, thereby obtaining a cemented carbide.

[ Table 1]

< evaluation >

For each sample of cemented carbide, the distribution of the circle-equivalent diameter of the tungsten carbide particles, the area ratios of the 1 st and 2 nd phases, the mass-based ratio of chromium to cobalt, and the mass-based content of vanadium were measured.

(distribution of circle-equivalent diameter of tungsten carbide particles)

The distribution of the circle-equivalent diameters of the tungsten carbide particles was measured for each of the cemented carbides of the samples, and the ratio of the number-based tungsten carbide particles having a circle-equivalent diameter of 0.3 μm to 1.0 μm, the ratio of the 1 st maximum frequency to the total number of tungsten carbide particles, the ratio of the 2 nd maximum frequency to the total number of tungsten carbide particles, and the ratio of the 2 nd maximum frequency to the 1 st maximum frequency were calculated. Since the specific measurement method and calculation method have already been described in embodiment 1, the description thereof will be omitted.

The results are shown in the columns "circle equivalent diameter 0.3-1.0 μm proportion (%)", "grade (μm)" and "proportion (%)" of "1 st maximum frequency", "grade (μm)" and "proportion (%)" of "2 nd maximum frequency", and "2 nd maximum frequency/1 st maximum frequency" of table 1, respectively.

If the maximum frequency is not present in the 1 st range (exceeding 0.3 μm and being 0.6 μm or less) or the 2 nd range (exceeding 0.6 μm and being 1.0 μm or less), it is represented by "-". If the maximum frequency is present outside the 1 st range (exceeding 0.3 μm and being 0.6 μm or less) or outside the 2 nd range (exceeding 0.6 μm and being 1.0 μm or less), the level of the maximum frequency is shown in parentheses ().

(volume ratio of phase 1 to phase 2)

For each sample of cemented carbide, the area ratio of the 1 st phase and the 2 nd phase in an image taken by a scanning electron microscope was measured. Since the specific measurement method has already been described in embodiment 1, the description thereof is omitted. The results are shown in the columns "phase 1 (% by area)" and "phase 2 (% by area)" of table 1.

(mass-based ratio of chromium to cobalt, mass-based content of vanadium)

For each sample of cemented carbide, the mass-based ratio of chromium to cobalt and the mass-based content of vanadium were measured. Since the specific measurement method has already been described in embodiment 1, the description thereof is omitted. The results are shown in the columns "Cr/Co (%)" and "V (ppm)" in Table 1.

< cutting test >

The round bar of each sample was processed to prepare a small-diameter drill having a blade diameter of 0.35 mm. Currently, only the blade is pressed into a stainless steel shank to form a drill, but for evaluation, the drill is made by machining the tip of a round bar of 3.4mm in diameter into the blade. The drill was used to drill a commercially available printed circuit board for mounting on a vehicle. The drilling conditions were 155krpm in rotation speed and 2.5 m/min in feed speed. The wear amount of the drill after 10000 drilling was calculated from the decrease in the drill diameter. And 3 drill bits are adopted for drilling. The average value of the wear amounts of the 3 drill bits is shown in the column "wear amount (μm)" in table 1. In addition, the state of the cutting edge after the drilling was observed. The results are shown in the column "cutting edge state" in table 1.

The smaller the amount of wear, the longer the tool life of the drill bit. When the column "wear amount (μm)" is written as "-", it means that all of the 3 drills were broken immediately after the start of machining, and the wear amount could not be measured. In addition, if the column of "cutting edge state" is described as "1 breakage", the average value of the wear amount of 2 pieces that are not broken is shown in the column of "wear amount (μm)" in table 1. If the column "cutting edge state" is referred to as "minor breakage", it indicates that minor breakage has occurred at the cutting edge.

< remarks >

Samples 3, 5 to 9, and 13 to 24 correspond to examples.

Samples 1, 4 and 12 had no maximum frequency (2 nd maximum frequency) in the 2 nd range, and corresponded to comparative examples. Sample 12 has a maximum frequency in the order of more than 1.0 μm and 1.1 μm or less.

Samples 2, 10 and 11 had no maximum frequency (1 st maximum frequency) in the 1 st range, and corresponded to comparative examples. In sample 2, the maximum frequency was present in a scale exceeding 0.2 μm and not more than 0.3 μm, and the proportion of the maximum frequency based on the number was 10.1%.

It was confirmed that the wear amount of samples 3, 5 to 9, and 13 to 24 (examples) was smaller and the tool life was longer than those of samples 1, 2, 4, 10, and 12 (comparative examples). In sample 11 (comparative example), 3 drills broke immediately after the start of machining, and the wear amount could not be measured.

As described above, although the embodiments and examples of the present disclosure have been described, it is clear from the beginning that the configurations of the embodiments and examples can be appropriately combined or variously modified.

The embodiments and examples disclosed herein are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is indicated not by the above-described embodiments and examples but by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.