TWI896784B - Superhard alloy and cutting tool having the same - Google Patents

Abstract

The present invention is a superhard alloy having a first phase composed of a plurality of tungsten carbide particles and a second phase containing cobalt. In an image obtained by photographing the superhard alloy using a scanning electron microscope, the ratio of the first phase is 78 area % or more and less than 100 area %, and the ratio of the second phase is more than 0 area % and less than 22 area %. When the circular equivalent diameter of each of the tungsten carbide particles in the image is calculated, the average value of the circular equivalent diameter is 0.5 μm or more and 1.2 μm or less, the number-based ratio of the tungsten carbide particles with a circular equivalent diameter of 0.3 μm or less is 10% or less, and the number of the tungsten carbide particles with a circular equivalent diameter of more than 1.8 μm is less than 10%. The number-based ratio of the tungsten carbide particles having a diameter of 0.01 μm is less than 2%, and the mass-based content of the cobalt in the cemented carbide exceeds 0% by mass and is 10% by mass or less.

Description

Superhard alloy and cutting tool having the same

The present invention relates to a superhard alloy and a cutting tool comprising the same.

In the opening of the printed circuit board, Small diameter holes of 1 mm or less are the mainstream. Therefore, as super-hard alloys used in tools such as small diameter drills, so-called micro-hard alloys are used, in which the hard phase includes tungsten carbide particles with an average particle size of 1 μm or less (for example, Japanese Patent Publication No. 2007-92090 (Patent Document 1), Japanese Patent Publication No. 2012-52237 (Patent Document 2), and Japanese Patent Publication No. 2012-117100 (Patent Document 3)). [Prior Art Literature] [Patent Literature]

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

The superhard alloy of the present invention comprises a first phase composed of a plurality of tungsten carbide particles and a second phase containing cobalt. In an image of the superhard alloy taken with a scanning electron microscope, the ratio of the first phase is 78% by area or more and less than 100% by area, and the ratio of the second phase is more than 0% by area and less than 22% by area. When the circular equivalent diameter of each of the tungsten carbide particles in the image is calculated, the average value of the circular equivalent diameter is 0.5 μm or more and 1.2 μm or less. The number-based ratio of the tungsten carbide particles having a circular equivalent diameter of 0.3 μm or less is 10% or less. The number of particles having a circular equivalent diameter exceeding 1.8 μm is less than 10%. The number-based ratio of the tungsten carbide particles with a diameter of μm is less than 2%. The mass-based content of the cobalt in the cemented carbide exceeds 0% by mass and is less than 10% by mass.

The cutting tool of the present invention has a cutting tip made of the above-mentioned superhard alloy.

[Problem to be Solved by the Present Invention] In recent years, with the expansion of 5G (fifth generation mobile communication systems), data capacity is increasing. Consequently, printed circuit boards (PCBs) are required to have even higher heat resistance. To improve the heat resistance of PCBs, the industry is developing technologies that enhance the heat resistance of the resins and glass fillers that comprise them. However, this approach makes PCBs difficult to cut.

Therefore, an object of the present invention is to provide a superhard alloy and a cutting tool having the same, wherein the superhard alloy can extend the life of the tool when used as a tool material, especially in the micromachining of printed circuit boards.

[Effects of the Invention] The superhard alloy of the present invention, when used as a tool material, can extend the tool life, particularly in micromachining of printed circuit boards.

[Description of the Implementation Methods of the Present Invention] First, we will explain the implementation methods of the present invention. (1) The superhard alloy of the present invention has a first phase composed of a plurality of tungsten carbide particles and a second phase containing cobalt, and in an image obtained by photographing the superhard alloy using a scanning electron microscope, the ratio of the first phase is 78 area % or more and less than 100 area %, and the ratio of the second phase is more than 0 area % and less than 22 area %, when the circular equivalent diameter of each of the tungsten carbide particles in the image is calculated, the average value of the circular equivalent diameter is 0.5 μm or more and 1.2 μm or less, the number-based ratio of the tungsten carbide particles having a circular equivalent diameter of 0.3 μm or less is 10% or less, the circular equivalent diameter exceeds 1.8 The number-based ratio of the tungsten carbide particles with a diameter of μm is less than 2%. The mass-based content of the cobalt in the cemented carbide exceeds 0% by mass and is less than 10% by mass.

When the superhard alloy of the present invention is used as a tool material, especially in the micro-machining of printed circuit boards, it can extend the life of the tool.

(2) In the above image, the ratio of the second phase is preferably not less than 5 area % and not more than 12 area %. This further extends the tool life.

(3) The chromium content of the above-mentioned superhard alloy is preferably not less than 0.15 mass% and not more than 1.0 mass%. This further extends the tool life.

(4) The ratio of chromium to cobalt is preferably 5% to 10% by mass. This further extends the tool life.

(5) The mass-based content of vanadium in the above-mentioned superhard alloy is preferably 0 ppm or more and less than 2000 ppm. This further extends the tool life.

(6) The mass-based content of vanadium in the above-mentioned superhard alloy is preferably 0 ppm or more and less than 100 ppm. This further extends the tool life.

(7) The cutting tool of the present invention has a cutting tip comprising the above-mentioned superhard alloy. The cutting tool of the present invention has a longer tool life.

(8) The above-mentioned cutting tool is preferably a rotary tool for processing printed circuit boards. The cutting tool of the present invention is suitable for fine processing of printed circuit boards.

[Details of the Embodiments of the Invention] The following describes specific embodiments of the cemented carbide and cutting tool of the present invention with reference to the accompanying drawings. In the drawings of the present invention, identical reference numerals denote identical or equivalent parts. Dimensional relationships, such as length, width, thickness, and depth, are modified for clarity and simplicity and do not necessarily represent actual dimensional relationships.

In this specification, the notation "A-B" refers to the upper and lower limits of a range (i.e., A is greater than and B is less than). When the unit is not specified in A and only in B, the unit of A is the same as the unit of B.

In this specification, when compounds are represented by chemical formulas, unless otherwise specified, the atomic ratios include all known atomic ratios and are not necessarily limited to atomic ratios within the stoichiometric range. For example, when "WC" is described, the ratios of the number of atoms constituting WC include all known atomic ratios.

To develop a super-hard alloy that extends tool life, the inventors investigated tool damage patterns during micromachining of printed circuit boards using tools containing conventional micro-hard alloys. They discovered that tungsten carbide particles in conventional micro-hard alloys detach and wear away during tool use. Further research into this shedding wear revealed that tungsten carbide particles with a diameter of 0.3 μm or less are particularly susceptible to shedding.

Therefore, the inventors of the present invention speculate that in order to achieve a longer tool life, it is more important to reduce the content of tungsten carbide particles with a particle size of 0.3 μm or less, which are easily detached during tool use, in the micro-hard alloy.

In order to reduce the content of tungsten carbide particles with a particle size of less than 0.3 μm in fine-grained super-hard alloys, consideration is given to promoting the grain growth of fine-grained tungsten carbide particles (with a particle size of approximately 0.2 μm) in the raw material during its manufacturing process. For example, consideration is given to not adding vanadium and chromium, which have a grain growth-inhibiting effect, when sintering the fine-grained tungsten carbide particles used as the raw material, or to sintering at high temperatures. However, if these methods are adopted, coarse tungsten carbide particles with a particle size of approximately 2 μm or more will be produced due to abnormal grain growth. These coarse tungsten carbide particles are the main cause of the reduction in strength of fine-grained super-hard alloys.

On the other hand, if vanadium and chromium are added as in the previous method of manufacturing micro-grained super-hard alloy in order to suppress abnormal grain growth, there is a tendency that the micro-grained tungsten carbide particles used as the raw material will remain directly in the obtained micro-grained super-hard alloy.

In light of the above circumstances, the inventors conducted intensive research into raw materials, composition, and manufacturing conditions that could reduce the content of tungsten carbide particles with a diameter of 0.3 μm or less in super-hard alloys and inhibit the formation of coarse tungsten carbide particles. This resulted in the development of the super-hard alloy of the present invention. The following details the super-hard alloy of the present invention and cutting tools incorporating the same.

[Embodiment 1: Superhard alloy] The superhard alloy of the present invention has a first phase composed of a plurality of tungsten carbide particles and a second phase containing cobalt. In an image of the superhard alloy taken with a scanning electron microscope, the ratio of the first phase is 78% by area or more and less than 100% by area, and the ratio of the second phase is more than 0% by area and less than 22% by area. When the circular equivalent diameter of each tungsten carbide particle in the image is calculated, the average value of the circular equivalent diameter is 0.5 μm or more and 1.2 μm or less. The number-based ratio of tungsten carbide particles with a circular equivalent diameter of 0.3 μm or less is 10% or less. The number of particles with a circular equivalent diameter exceeding 1.8 μm is less than 10%. The number-based ratio of μm tungsten carbide particles is less than 2%. The mass-based content of cobalt in the cemented carbide exceeds 0% and is less than 10%.

The superhard alloy of the present invention, when used as a tool material, can extend the life of the tool, particularly in micromachining of printed circuit boards. The reasons for this are not yet clear, but are speculated as follows (i) to (v).

(i) In the super-hard alloy of the present invention, the ratio of the first phase composed of a plurality of tungsten carbide particles is 78% by area or more and less than 100% by area, and the ratio of the second phase containing cobalt is greater than 0% by area and less than 22% by area. This allows the hardness and wear resistance required for printed circuit board processing to be achieved, suppressing variations in tool life. (ii) In the super-hard alloy of the present invention, the average equivalent diameter of the tungsten carbide particles (hereinafter also referred to as "WC particles") is 0.5 μm or more and 1.2 μm or less. When the average equivalent diameter of the tungsten carbide particles is 0.5 μm or more, the super-hard alloy is less likely to experience shedding wear during use, and thus exhibits excellent wear resistance. If the average equivalent diameter of the tungsten carbide particles is 1.2 μm or less, the superhard alloy can have higher hardness and excellent wear resistance, as well as higher bending strength and excellent fracture resistance.

(iii) In the super-hard alloy of the present invention, the number-based ratio of tungsten carbide particles with a circular equivalent diameter of 0.3 μm or less is less than 10%. This makes it less likely for the super-hard alloy to suffer from shedding wear during use, and the super-hard alloy can have excellent wear resistance.

(iv) In the super-hard alloy of the present invention, the number-based ratio of the tungsten carbide particles having a circular equivalent diameter exceeding 1.8 μm is less than 2%. As a result, the super-hard alloy can have higher bending strength and excellent fracture resistance.

(v) The cobalt content of the super-hard alloy is greater than 0% by mass and less than 10% by mass. This allows the super-hard alloy to have higher hardness and excellent wear resistance.

<Phase 1> (Composition of Phase 1) Phase 1 is composed of a plurality of tungsten carbide particles. Tungsten carbide herein includes not only pure WC (including WC without any impurity elements or WC with impurity elements below the detection limit) but also WC that intentionally or unavoidably contains other impurity elements, to the extent that the effects of the present invention are not impaired. The concentration of impurities in the tungsten carbide (or the combined concentration of two or more impurity elements when the impurities are present) is less than 0.1% by mass relative to the total amount of the tungsten carbide and the impurities. The content of impurity elements in the first phase was measured using inductively coupled plasma (ICP) emission spectroscopy (ICP) (measurement equipment: Shimadzu Corporation "ICPS-8100" (trademark)).

(Equivalent Circle Diameter of Tungsten Carbide Particles) In images of the super-hard alloy of the present invention taken with a scanning electron microscope, the average equivalent circle diameter of the tungsten carbide particles is 0.5 μm or greater and 1.2 μm or less. When the average equivalent circle diameter of the tungsten carbide particles is 0.5 μm or greater, the super-hard alloy is less likely to experience shedding wear during use, resulting in excellent wear resistance. When the average equivalent circle diameter of the tungsten carbide particles is 1.2 μm or less, the super-hard alloy exhibits higher hardness and excellent wear resistance, as well as higher bending strength and excellent fracture resistance.

The lower limit of the average value of the equivalent circular diameter of the tungsten carbide particles is preferably 0.5 μm or greater, 0.55 μm or greater, or 0.60 μm or greater. The upper limit of the average value of the equivalent circular diameter of the tungsten carbide particles is preferably 1.2 μm or less, 1.1 μm or less, or 1.0 μm or less. The average value of the equivalent circular diameter of the tungsten carbide particles is 0.5 μm or greater and 1.2 μm or less, preferably 0.55 μm or greater and 1.1 μm or less, and 0.60 μm or greater and 1.0 μm or less.

The equivalent circular diameter of tungsten carbide particles is measured in the order of (A1) to (C1) below. (A1) Mirror finishing is performed on any surface or cross-section of the cemented carbide. Examples of mirror finishing methods include polishing with diamond plaster, using a focused ion beam apparatus (FIB apparatus), using a cross-section polisher apparatus (CP apparatus), and combinations thereof.

(B1) The processed surface of the cemented carbide was photographed using a scanning electron microscope (S-3400N, manufactured by Hitachi High-Technologies Corporation). The conditions were 5000x magnification, 10 kV accelerating voltage, and backscattered electron imaging. An example of an image of the cemented carbide of the present invention obtained using a scanning electron microscope is shown in Figure 1.

(C1) Use image analysis software (ImageJ, version 1.51j8: https://imagej.nih.gov/ij/) to import the image obtained in (B1) into a computer and perform binarization. After importing the image, click "Make Binary" on the computer screen to perform the binarization process (binarization is performed under the pre-set conditions in the image analysis software). A rectangular measurement field of view measuring 25.3 μm in length and 17.6 μm in width is set in the binarized image. Calculate the equivalent circular diameter (Heywood diameter: the diameter of a circle of equal area) of the tungsten carbide particles within this measurement field. The first phase, composed of tungsten carbide particles, and the second phase, composed of cobalt, can be distinguished by the color depth in the image captured above. Figure 2 shows the image obtained by binarizing the image in Figure 1. In Figure 2, the black area represents the first phase, and the white area represents the second phase. White lines represent grain boundaries.

The applicant has determined that, as long as the same sample is measured, the difference in the measurement results is small even if the selected location of the measurement field of view is changed and the equivalent circular diameter of tungsten carbide particles in super-hard alloy is measured multiple times. Even if the measurement field of view is arbitrarily set, the difference does not change arbitrarily.

(Distribution of Tungsten Carbide Particles by Equivalent Circle Diameter) In images of the cemented carbide of the present invention taken with a scanning electron microscope, the number-based proportion of tungsten carbide particles with an equivalent circle diameter of 0.3 μm or less was less than 10%. This reduces the risk of shedding and wear associated with use, resulting in excellent wear resistance for the cemented carbide.

The number-based ratio of tungsten carbide particles having a circle-equivalent diameter of 0.3 μm or less is 10% or less, preferably 9% or less, or 8% or less. The lower limit of the number-based ratio of tungsten carbide particles having a circle-equivalent diameter of 0.3 μm or less is not particularly limited, and may be, for example, 0% or more, 2% or more, or 4% or more. The number-based ratio of tungsten carbide particles having a circle-equivalent diameter of 0.3 μm or less may be 0% or more and 10% or less, 0% or more and 9% or less, 0% or more and 8% or less, 2% or more and 10% or less, 2% or more and 9% or less, 2% or more and 8% or less, 4% or more and 10% or less, 4% or more and 9% or less, or 4% or more and 8% or less.

In this specification, the number-based ratio of tungsten carbide particles with a circular equivalent diameter of 0.3 μm or less in an image of a cemented carbide film obtained by scanning electron microscopy is calculated in the following order (D1) and (E1).

(D1) Prepare three images (corresponding to three measurement fields) of the cemented carbide alloy using a scanning electron microscope, following the sequence of steps (A1) and (B1) for measuring the equivalent circular diameter of tungsten carbide particles described above. Perform the image processing (binarization) described in step (C1) for measuring the equivalent circular diameter of tungsten carbide particles described above on each of the three measurement fields. The size of one measurement field is a rectangle measuring 25.3 μm in length and 17.6 μm in width.

(E1) Calculate the number-based ratio of tungsten carbide particles with a circle-equivalent diameter of 0.3 μm or less in each of the three measurement fields relative to the total number of tungsten carbide particles in each field of view. The average of the number-based ratios in the three measurement fields is defined as the number-based ratio of tungsten carbide particles with a circle-equivalent diameter of 0.3 μm or less in the cemented carbide.

The applicant has determined that, as long as the same sample is measured, the difference in the measurement results of the ratio of the number of tungsten carbide particles with a circular equivalent diameter of 0.3 μm or less in super-hard alloy is small even if the selected location of the measurement field of view is changed and the measurement results are measured multiple times. Even if the measurement field of view is arbitrarily set, the difference does not change arbitrarily.

In images of the present invention's super-hard alloy taken with a scanning electron microscope, the number of tungsten carbide particles exceeding 1.8 μm in diameter was less than 2%. This demonstrates the super-hard alloy's high bending strength and excellent damage resistance.

The number-based ratio of tungsten carbide particles with a circle-equivalent diameter exceeding 1.8 μm is less than 2%, preferably 1% or less, or 0.5% or less. The lower limit of the number-based ratio of tungsten carbide particles with a circle-equivalent diameter exceeding 1.8 μm is not particularly limited, and may be, for example, 0% or more, 0.1% or more, or 0.2% or more. The number-based ratio of tungsten carbide particles with a circle-equivalent diameter exceeding 1.8 μm may be 0% or more and less than 2%, 0% or more and less than 1%, 0% or more and less than 0.5%, 0.1% or more and less than 2%, 0.1% or more and less than 1%, 0.1% or more and less than 0.5%, 0.2% or more and less than 2%, 0.2% or more and less than 1%, or 0.2% or more and less than 0.5%.

In this specification, the number-based ratio of tungsten carbide particles with a circular equivalent diameter exceeding 1.8 μm in an image of cemented carbide obtained by scanning electron microscopy is calculated according to the following sequence (F1) and (G1).

(F1) Prepare three images (corresponding to three measurement fields) of the cemented carbide alloy using a scanning electron microscope, following the sequence of steps (A1) and (B1) for measuring the equivalent circular diameter of tungsten carbide particles described above. Perform the image processing (binarization) described in step (C1) for measuring the equivalent circular diameter of tungsten carbide particles described above on each of the three measurement fields. The size of one measurement field is a rectangle measuring 25.3 μm in length and 17.6 μm in width.

(G1) Calculate the ratio of tungsten carbide particles with a circle-equivalent diameter exceeding 1.8 μm to the total number of tungsten carbide particles in each of the three measurement fields. The average of these ratios is used as the number-based ratio of tungsten carbide particles with a circle-equivalent diameter exceeding 1.8 μm in the cemented carbide.

The applicant has determined that, as long as the same sample is measured, the difference in the measurement results of the ratio of the number of tungsten carbide particles with a circular equivalent diameter exceeding 1.8 μm in a super-hard alloy is small even if the selected location of the measurement field of view is changed and the measurement results are measured multiple times. Even if the measurement field of view is arbitrarily set, the difference does not change arbitrarily.

<Second Phase> The second phase contains cobalt. It is a bonding phase that binds the tungsten carbide particles that make up the first phase together.

Here, "the second phase contains cobalt (Co)" means that the main component of the second phase is Co. "The main component of the second phase is Co" means that the mass ratio of cobalt in the second phase is 90% to 100% by mass. The mass ratio of cobalt in the second phase can be measured by inductively coupled plasma (ICP) optical emission spectroscopy (using the "ICPS-8100" (trademark) manufactured by Shimadzu Corporation).

In addition to cobalt, the second phase may also contain iron elements such as nickel, and dissolved substances in the alloy (chromium (Cr), tungsten (W), vanadium (V), etc.).

<Composition of Supercarbide> (Composition) Supercarbide has a first phase composed of multiple tungsten carbide particles and a second phase composed of cobalt. Images of the supercarbide taken with a scanning electron microscope show that the first phase accounts for 78% to 100% by volume, while the second phase accounts for 0% to 22% by volume. This ensures the hardness and wear resistance required for printed circuit board processing, minimizing variations in tool life.

If the ratio of the first phase in the cemented carbide is 78% by volume or greater, the hardness of the cemented carbide increases. The lower limit of the ratio of the first phase in the cemented carbide can be set to 78% by volume or greater and 88% by volume or greater. The upper limit of the ratio of the first phase in the cemented carbide can be set to less than 100% by volume and less than 95% by volume. The ratio of the first phase in the cemented carbide can be set to 78% by volume or greater and less than 100% by volume, 88% by volume or greater and less than 95% by volume.

If the proportion of the second phase in the cemented carbide is 22% by volume or less, the hardness of the cemented carbide increases. The lower limit of the proportion of the second phase in the cemented carbide can be set to more than 0% by volume and more than 5% by volume. The upper limit of the proportion of the second phase in the cemented carbide can be set to less than 22% by volume and less than 12% by volume. The proportion of the second phase in the cemented carbide can be set to more than 0% by volume and less than 22% by volume, and more than 5% by volume and less than 12% by volume.

In an image of the cemented carbide taken with a scanning electron microscope, the ratio of the first phase is preferably not less than 88 area% and not more than 95 area%, and the ratio of the second phase is preferably not less than 5 area% and not more than 12 area%.

The area ratios of the first phase and the second phase in the cemented carbide are measured in the order of (A2) to (C2) below.

(A2) Prepare five images (equivalent to five measurement fields) of the cemented carbide alloy using a scanning electron microscope, following the sequence of steps (A1) and (B1) for measuring the equivalent circular diameter of tungsten carbide particles described above. Perform the image processing (binarization) described in step (C1) for measuring the equivalent circular diameter of tungsten carbide particles described above on each of the five measurement fields. The size of one measurement field is a rectangle measuring 25.3 μm in length by 17.6 μm in width.

(B2) In each of the five measurement fields, using the entire measurement field as the denominator, determine the area ratio of the first phase to the second phase.

(C2) The average of the area ratios of the first phase obtained in the five measurement fields is set as the area ratio of the first phase in the cemented carbide. The average of the area ratios of the second phase obtained in the five measurement fields is set as the area ratio of the second phase in the cemented carbide.

(Valium Content) The vanadium content of the cemented carbide of the present invention is preferably 0 ppm by mass or greater and less than 2000 ppm by mass. Specifically, the cemented carbide of the present invention preferably (a) contains no vanadium, or (b) if it contains vanadium, the vanadium content is less than 2000 ppm by mass.

Vanadium has been used in the production of previously ultrafine-grained cemented carbide alloys due to its ability to inhibit grain growth. However, when vanadium is added to inhibit grain growth, the tungsten carbide particles used as the raw material tend to remain in the resulting cemented carbide alloy.

The inventors of this invention have conducted intensive research on manufacturing conditions, resulting in the discovery of new manufacturing conditions that effectively prevent the retention of fine tungsten carbide particles, the raw material, in the resulting superhard alloy, even when no vanadium is added or when a trace amount of vanadium is added. These conditions can also effectively suppress the formation of coarse particles. Details of these manufacturing conditions are described below.

The upper limit of the vanadium content in cemented carbide is less than 2000 ppm, preferably less than 100 ppm. Since the lower the vanadium content in cemented carbide, the better, the lower limit is 0 ppm. The vanadium content in cemented carbide can be set to 0 ppm or more but less than 2000 ppm, or 0 ppm or more but less than 100 ppm.

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

(Cobalt Content) The cobalt content of the cemented carbide of the present invention is greater than 0% by mass and less than 10% by mass. This allows the cemented carbide to possess high hardness and excellent wear resistance.

The upper limit of the cobalt content in the cemented carbide is preferably 9% by mass or less and 8% by mass or less. The lower limit of the cobalt content in the cemented carbide is preferably 1% by mass or more and 2% by mass or more. The cobalt content in the cemented carbide is preferably 1% by mass or more and 9% by mass or less and 2% by mass or more and 8% by mass or less.

The cobalt content in cemented carbide was determined by ICP emission spectrometry.

(Chromium Content) The superhard alloy of the present invention contains chromium (Cr). The chromium content of the superhard alloy is preferably 0.15% by mass to 1.0% by mass. Chromium inhibits the grain growth of tungsten carbide particles. The inventors have conducted research and discovered that a chromium content of 0.15% by mass to 1.0% by mass in the superhard alloy effectively prevents the fine tungsten carbide particles used as the raw material from remaining in the resulting superhard alloy, and also effectively suppresses the formation of coarse particles.

The upper limit of the chromium content in the cemented carbide is preferably 0.95% by mass or less and 0.90% by mass or less. The lower limit of the chromium content in the cemented carbide is preferably 0.20% by mass or more and 0.25% by mass or more. The chromium content in the cemented carbide is preferably 0.20% by mass or more and 0.95% by mass or less and 0.25% by mass or more and 0.90% by mass or less.

The chromium content in cemented carbide was determined by ICP emission spectrometry.

(Cobalt to Chromium Ratio) In the superhard alloy of the present invention, the ratio of chromium to cobalt is preferably 5% to 10% by mass. Chromium inhibits the grain growth of tungsten carbide particles. Furthermore, by forming a solid solution in cobalt, it promotes lattice strain in the cobalt. Therefore, when the superhard alloy contains chromium in the above ratio, its fracture resistance is further improved.

On the other hand, if the amount of chromium is too high, it may precipitate as carbides, becoming a starting point for damage. If the ratio of chromium to cobalt is between 5% and 10%, chromium carbides are less likely to precipitate, resulting in improved damage resistance.

Furthermore, if the ratio of chromium to cobalt is 10% or less, the degree of grain growth inhibition is appropriate, and the amount of tungsten carbide particles with a circle equivalent diameter exceeding 1.2 μm in the superhard alloy can be prevented from becoming excessive.

The lower limit of the ratio of chromium to cobalt is preferably 5% or more, more preferably 7% or more. The ratio of chromium to cobalt is preferably 10% or less, more preferably 9% or less. The ratio of chromium to cobalt can be set to 5% or more and 10% or 7% or more and 9% or less.

<Method for Manufacturing Superhard Carbide> The superhard carbide of this embodiment can typically be manufactured by sequentially performing a raw material powder preparation step, a mixing step, a forming step, a sintering step, and a cooling step. Each step is described below.

The preparation step involves preparing the raw material powders for all materials that make up the cemented carbide alloy. Essential raw material powders include tungsten carbide powder, the raw material for the first phase, and cobalt (Co) powder, the raw material for the second phase. Chromium carbide (Cr ₃ C ₂ ) powder can also be prepared as a grain growth inhibitor, if necessary. Commercially available tungsten carbide, cobalt, and chromium carbide powders can be used.

Prepare tungsten carbide powder with an average particle size of 0.5 μm to 1.5 μm. In this specification, the average particle size of the raw material powder refers to the average particle size measured using the Fisher Sub-Sieve Sizer (FSSS) method. This average particle size is measured using a "Sub-Sieve Sizer Model 95" (trademark) manufactured by Fisher Scientific.

The ratio (d20/d80) of the 20% volume particle size (d20) to the 80% volume particle size (d80) of the tungsten carbide powder is preferably 0.2 or higher and 1 or lower. This tungsten carbide powder has a uniform particle size and contains a low content of fine tungsten carbide particles with a particle size of 0.3 μm or less. Therefore, when using this tungsten carbide powder to produce superhard alloys, the formation of coarse tungsten carbide particles due to dissolution and reprecipitation during the sintering step can be suppressed. Furthermore, the content of fine tungsten carbide particles in the resulting superhard alloy can be reduced.

In this specification, the volume particle size distribution of tungsten carbide powder is measured using a Microtrac particle size distribution analyzer (trade name: MT3300EX). The 20% volume particle size (d20) refers to the particle size at which the volume of the particles comprising the tungsten carbide powder, in ascending order, accounts for 20% of the total volume. The 80% volume particle size (d80) refers to the particle size at which the volume of the particles comprising the tungsten carbide powder, in ascending order, accounts for 80% of the total volume.

In the super-hard alloy manufacturing method of the present invention, vanadium carbide (VC) powder, which has a high grain growth inhibition effect and is commonly used in the production of previous micro-particle super-hard alloys, is not used, or even if it is used, it is only used in trace amounts (for example, the mass-based content in the raw material powder is less than 2000 ppm). In the super-hard alloy manufacturing method of the present invention, the content of micro-particle tungsten carbide particles with a particle size of 0.3 μm or less in the raw material powder is reduced during the raw material preparation stage. Therefore, regardless of the amount of vanadium (V) added, the area ratio of micro-particle tungsten carbide particles in the super-hard alloy can be suppressed to a low level. Furthermore, because the content of micro-particle tungsten carbide particles is reduced during the raw material preparation stage, the grain growth of these micro-particle tungsten carbide particles can be further reduced when vanadium (V) is not added, thereby further reducing the micro-particle tungsten carbide particles in the super-hard alloy. On the other hand, because the amount of fine tungsten carbide particles in the raw material powder is relatively small, abnormal grain growth to the extent that coarse tungsten carbide particles would be produced does not occur. This mechanism of action is a new discovery by the inventors.

The average particle size of cobalt powder can be set to 0.5 μm to 1.5 μm. The average particle size of chromium carbide powder can be set to 1.0 μm to 2.0 μm. The average particle size is measured using a "Sub-Sieve Sizer Model 95" manufactured by Fisher Scientific.

Mixing Step The mixing step involves combining the raw material powders prepared in the preparation step. This step creates a mixed powder.

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

The ratio of the cobalt powder in the mixed powder can be set to, for example, more than 0 mass % and not more than 10 mass %.

The ratio of the chromium carbide powder in the mixed powder can be set to, for example, 0.17 mass % to 1.15 mass %.

The mixed powder is mixed using a ball mill. The mixing time can be set to 15 to 36 hours. These conditions can prevent the raw material powder from pulverizing and maintain the uniformity of the raw material powder particle size.

After the mixing step, the mixed powder can be granulated as needed. Granulating the mixed powder facilitates filling the die or mold with the mixed powder during the molding step described below. Granulation can be performed using known granulation methods, such as a commercially available granulator such as a spray dryer.

Forming Step The forming step involves forming the mixed powder obtained in the mixing step into a specific shape to produce a compact. The forming method and conditions in the forming step are not particularly limited; conventional methods and conditions may be employed. An example of a specific shape is the shape of a cutting tool (e.g., a small-diameter drill).

Sintering Step The sintering step involves sintering the formed body obtained in the forming step to produce a superhard alloy. In the superhard alloy production method of the present invention, the sintering temperature can be set to 1350-1450°C. This suppresses the formation of coarse tungsten carbide particles and reduces the content of fine tungsten carbide particles in the resulting superhard alloy.

If the sintering temperature is lower than 1350°C, grain growth is suppressed, and the content of fine tungsten carbide particles in the resulting super-hard alloy tends to increase. On the other hand, if the sintering temperature exceeds 1450°C, abnormal grain growth tends to occur.

Cooling Step The cooling step involves cooling the sintered cemented carbide. There are no specific cooling conditions; standard cooling conditions will suffice.

The present invention's super-hard alloy production method allows for the production of super-hard alloys that suppress abnormal grain growth and reduce the content of fine-grained tungsten carbide particles, even without the use of vanadium carbide (VC) powder, which has a high grain growth-inhibiting effect and is commonly used in the production of previous micro-grained super-hard alloys. Even when VC powder is used, it is only in trace amounts (e.g., less than 2000 ppm by mass in the raw material powder). This discovery is the result of intensive research by the inventors.

[Embodiment 2: Cutting Tool] The cutting tool of the present invention comprises a cutting tip made of the aforementioned super-hard alloy. In this specification, the cutting tip refers to the portion of the super-hard alloy involved in cutting, specifically the area of the super-hard alloy enclosed by the cutting tip edge and a hypothetical plane measured 2 mm from the cutting tip edge to the side of the super-hard alloy, along a perpendicular line tangent to the cutting tip edge.

Examples of cutting tools include cutting tools, drills, end mills, replaceable cutting tips for milling, replaceable cutting tips for turning, metal saws, gear cutting tools, hinges, and taps. The cutting tool of the present invention is particularly effective when used as a small-diameter drill for processing printed circuit boards.

The super-hard alloy of this embodiment can constitute the whole of these tools or a part thereof. Here, "constituting a part" means that the super-hard alloy of this embodiment is brazed to a specific position of any base material to form the tip of the tool.

Hard Coating The cutting tool of this embodiment may further include a hard coating covering at least a portion of the surface of the substrate made of a cemented carbide. Diamond-like carbon or diamond, for example, may be used as the hard coating.

[Note 1] In the superhard alloy of the present invention, the average equivalent diameter of the tungsten carbide particles is preferably not less than 0.55 μm and not more than 1.1 μm. In the superhard alloy of the present invention, the average equivalent diameter of the tungsten carbide particles is preferably not less than 0.60 μm and not more than 1.0 μm.

[Note 2] In the super-hard alloy of the present invention, the ratio of tungsten carbide particles with a circle-equivalent diameter of 0.3 μm or less, based on number, is preferably 0% or more and 10% or less. In the super-hard alloy of the present invention, the ratio of tungsten carbide particles with a circle-equivalent diameter of 0.3 μm or less, based on number, is preferably 0% or more and 9% or less. In the super-hard alloy of the present invention, the ratio of tungsten carbide particles with a circle-equivalent diameter of 0.3 μm or less, based on number, is preferably 0% or more and 8% or less.

[Note 3] In the super-hard alloy of the present invention, the number-based ratio of tungsten carbide particles with a circle-equivalent diameter exceeding 1.8 μm is preferably 0% or more and less than 2%. In the super-hard alloy of the present invention, the number-based ratio of tungsten carbide particles with a circle-equivalent diameter exceeding 1.8 μm is preferably 0% or more and less than 1%. In the super-hard alloy of the present invention, the number-based ratio of tungsten carbide particles with a circle-equivalent diameter exceeding 1.8 μm is preferably 0% or more and less than 0.5%.

[Note 4] In an image of the cemented carbide of the present invention photographed using a scanning electron microscope, the ratio of the first phase is preferably 88% by area to 95% by area. In an image of the cemented carbide of the present invention photographed using a scanning electron microscope, the ratio of the second phase is preferably 5% by area to 12% by area. In an image of the cemented carbide of the present invention photographed using a scanning electron microscope, the ratio of the first phase is preferably 88% by area to 95% by area, and the ratio of the second phase is preferably 5% by area to 12% by area.

[Note 5] The vanadium content of the cemented carbide of the present invention is preferably 0 ppm or more and less than 2000 ppm by mass. The vanadium content of the cemented carbide of the present invention is preferably 0 ppm or more and less than 100 ppm by mass.

[Note 6] The cobalt content of the cemented carbide of the present invention is preferably not less than 1% by mass and not more than 9% by mass. The cobalt content of the cemented carbide of the present invention is preferably not less than 2% by mass and not more than 8% by mass.

[Note 7] The chromium content of the cemented carbide of the present invention is preferably not less than 0.20 mass% and not more than 0.95 mass%. The chromium content of the cemented carbide of the present invention is preferably not less than 0.25 mass% and not more than 0.90 mass%.

[Note 8] In the superhard alloy of the present invention, the ratio of chromium to cobalt is preferably not less than 7% and not more than 9% by mass. [Example]

The present embodiment is described in more detail with reference to the following examples, but the present embodiment is not limited to these examples.

By varying the type of raw material powder, mixing ratio, and manufacturing conditions, super-hard alloy samples 1 to 17 were produced. Small-diameter drills with tool tips incorporating these super-hard alloys were manufactured and evaluated.

Sample Preparation (Preparation Steps) Prepare raw material powders with the compositions shown in the "Raw Materials" column of Table 1. Prepare several tungsten carbide (WC) powders with different average particle sizes. The average particle sizes of the WC powders are shown in the "Average Particle Size (μm)" column of the "WC Powder" section of Table 1. The average particle size of the Co powder is 1.0 μm. The average particle size of the _{Cr₃C₂ powder} is 1.5 μm. The average particle size of the VC powder is 0.9 μm. The average particle size of the raw material powders was measured using a "Sub-Sieve Sizer Model 95" (trademark) manufactured by Fisher Scientific.

For WC powders from Samples 1 to 13, the ratio of the 20% volume particle size (d20) to the 80% volume particle size (d80) (d20/d80) was measured. The results showed that all samples had a d20/d80 ratio between 0.2 and 1. For WC powders from Samples 14 to 17, the d20/d80 ratio was measured. The results showed that all samples had a d20/d80 ratio between 0.1 and 0.2. The d20/d80 ratios of the WC powders were measured using a Microtrac particle size distribution analyzer (trade name: MT3300EX).

(Mixing Step) Mix the raw material powders in the amounts listed in the "Mass %" column under "Raw Materials" in Table 1 to produce a mixed powder. The "Mass %" in the "Raw Materials" column in Table 1 represents the ratio of each raw material powder to the total mass of the raw material powders. Mixing is performed using a ball mill or attritor. The mixing time is as specified in the "Mixer/Time" column under "Mixing Step" in Table 1. The resulting mixed powder is spray dried to produce a granulated powder.

(Forming step) The obtained granulated powder is pressurized to form 3.4 mm round rod shaped molded body.

(Sintering Step) The formed body is placed in a sintering furnace and sintered in a vacuum. The sintering temperature and time are as shown in the "Temperature/Time" column of the "Sintering Step" in Table 1.

(Cooling Step) After sintering, the alloy is slowly cooled in an argon (Ar) atmosphere to obtain a super-hard alloy.

[Table 1] Table 1 Sample No. raw material Mixing step Sintering steps WC powder Co powder Cr ₃ C ₂ powder VC powder Mixer/time Temperature/time Average particle size (μm) Mass% Average particle size (μm) Mass% Average particle size (μm) Mass% Mass% 1 0.9 94.54 1.0 5 1.5 0.46 - Ball mill/15 hours 1420℃/1 hour 2 0.7 94.54 1.0 5 1.5 0.46 - Ball mill/15 hours 1420℃/1 hour 3 1.4 94.54 1.0 5 1.5 0.46 - Ball mill/15 hours 1420℃/1 hour 4 0.9 94.44 1.0 5 1.5 0.46 0.10 Ball mill/15 hours 1420℃/1 hour 5 0.9 94.34 1.0 5 1.5 0.46 0.20 Ball mill/15 hours 1420℃/1 hour 6 0.9 90.17 1.0 9 1.5 0.83 - Ball mill/15 hours 1420℃/1 hour 7 0.9 96.72 1.0 3 1.5 0.28 - Ball mill/15 hours 1420℃/1 hour 8 0.9 97.82 1.0 2 1.5 0.18 - Ball mill/15 hours 1420℃/1 hour 9 0.9 94.88 1.0 5 1.5 0.12 - Ball mill/15 hours 1420℃/1 hour 10 0.9 93.62 1.0 5 1.5 1.38 - Ball mill/15 hours 1420℃/1 hour 11 0.9 94.83 1.0 5 1.5 0.17 - Ball mill/15 hours 1420℃/1 hour 12 0.9 93.85 1.0 5 1.5 1.15 - Ball mill/15 hours 1420℃/1 hour 13 0.9 94.53 1.0 5 1.5 0.46 0.01 Ball mill/15 hours 1420℃/1 hour 14 1.0 94.54 1.0 5 1.5 0.46 - Grinder/9 hours 1420℃/1 hour 15 0.5 94.54 1.0 5 1.5 0.46 - Ball mill/15 hours 1470℃/1 hour 16 2.0 94.54 1.0 5 1.5 0.46 - Ball mill/15 hours 1420℃/1 hour 17 0.9 88.08 1.0 11 1.5 0.92 - Ball mill/15 hours 1420℃/1 hour

<Evaluation> For each sample of cemented carbide, the average value and distribution of the circular equivalent diameter of tungsten carbide particles, the area ratio of the first and second phases, the mass-based vanadium content, the mass-based cobalt content, and the mass-based ratio of the chromium phase to the cobalt were measured.

(Average Value of the Circle Equivalent Diameter of Tungsten Carbide Particles) For each sample of cemented carbide, the average value of the circle equivalent diameter of the tungsten carbide particles was measured. Since the specific measurement method is described in Example 1, its description is not repeated here. The results are shown in the "Average Value" column under "Circle Equivalent Diameter of WC Particles" in Table 2.

(Distribution of Tungsten Carbide Particles by Equivalent Circle Diameter) For each sample of cemented carbide, the number-based ratio of tungsten carbide particles with an equivalent circle diameter of 0.3 μm or less and the number-based ratio of tungsten carbide particles with an equivalent circle diameter of more than 1.8 μm were calculated. The specific measurement and calculation methods are described in Example 1 and will not be repeated here.

The results are shown in Table 2 under the "Circular Equivalent Diameter of WC Particles" column, under the "Ratio of WC Particles Less Than 0.3 μm (%)" and the "Ratio of WC Particles Exceeding 1.8 μm (%)" columns.

(Volume Ratio of Phase 1 and Phase 2) For each sample of cemented carbide, the area ratio of Phase 1 to Phase 2 was measured in images captured using a scanning electron microscope. The specific measurement method is described in Example 1 and will not be repeated here. The results are shown in the "Area %" column for "Phase 1" and the "Area %" column for "Phase 2" in Table 2.

(Valvium content by mass, cobalt content by mass, and chromium ratio to cobalt by mass) For each sample of cemented carbide, the vanadium content by mass, the cobalt content by mass, and the chromium ratio to cobalt by mass were measured. The specific measurement methods are described in Example 1 and are not repeated here. The results are shown in the "V" (ppm), "Co" (mass %), "Cr" (mass %), and "Cr/Co" (%) columns of Table 2.

<Cutting test> The round rod of each sample is processed to make the cutting edge 0.35 mm small diameter drill. Currently, the mainstream method is to simply press the blade into the stainless steel handle to form the drill, but for the purpose of evaluation, A drill was made by sharpening the tip of a 3.4 mm round rod. This drill was used to drill holes in commercially available automotive printed circuit boards. The drilling conditions were set at a rotational speed of 155 krpm and a feed rate of 2.5 m/min. The wear of the drill after drilling 10,000 holes was calculated based on the reduction in the drill diameter. Three drills were used for drilling. The average wear of the three drills is shown in the "Wear (μm)" column of Table 2. The condition of the tool tip after drilling was observed. The results are shown in the "Tool Tip Condition" column of Table 1.

The smaller the wear, the longer the tool life of the drill. If "-" is entered in the "Wear (μm)" column, it means that two or more drills were damaged immediately after the start of processing, and wear measurement was unavailable. Furthermore, if "1 damaged" is entered in the "Tool Tip Condition" column, the average wear of two undamaged drills is shown in the "Wear (μm)" column in Table 2. If "Fine chipping" is entered in the "Tool Tip Condition" column, it indicates that fine chipping has occurred at the tool tip.

[Table 2] Table 2 Sample No. super carbide Cutting test WC particle equivalent diameter Phase 1 Phase 2 V Co Cr Cr/Co Wear loss (μm) Tip status Average value (μm) Ratio below 0.3 μm (%) Ratio exceeding 1.8 μm (%) Area% Area% ppm Mass% Mass% % 1 0.7 7 1.2 89.3 10.7 0 5 0.40 8.0 13.0 Normal wear 2 0.5 9 0.8 89.1 10.9 0 5 0.40 8.0 14.6 Normal wear 3 1.2 4 1.8 89.5 10.5 0 5 0.40 8.0 14.2 Normal wear 4 0.6 8 0.5 89.3 10.7 810 5 0.40 8.0 14.2 Normal wear 5 0.5 9 0.2 89.3 10.7 1620 5 0.40 8.0 14.5 Normal wear 6 0.7 6 1.4 80.9 19.1 0 9 0.72 8.0 15.5 Normal wear 7 0.7 6 1.0 93.6 6.4 0 3 0.24 8.0 13.8 Normal wear 8 0.7 6 0.9 95.8 4.2 0 2 0.16 8.0 14.0 tiny debris 9 1.0 3 1.8 89.2 10.8 0 5 0.10 2.0 14.5 Normal wear 10 0.5 10 0.4 89.3 10.7 0 5 1.2 24.0 14.9 Normal wear 11 1.0 5 1.6 89.4 10.6 0 5 0.15 3.0 14.6 Normal wear 12 0.6 9 0.6 89.3 10.7 0 5 1.0 20.0 14.0 Normal wear 13 0.7 7 1.0 89.3 10.7 81 5 0.40 8.0 13.4 Normal wear 14 0.9 6 4.8 89.3 10.7 0 5 0.40 8.0 16.2 1 damaged 15 0.5 11 5.8 89.5 10.5 0 5 0.40 8.0 - 2 damaged 16 1.7 0.5 32 89.1 10.9 0 5 0.40 8.0 - 3 damaged 17 0.7 6 1.9 76.7 23.3 0 11 0.88 8.0 16.9 Normal wear

<Discussion> Samples 1 through 13 are examples, and samples 14 through 17 are comparative examples. It was confirmed that samples 1 through 13 exhibited less wear and longer tool life than samples 14 through 17.

It was confirmed that although the raw material powders of Samples 1 to 13 did not contain vanadium carbide powder, which is commonly used as a grain growth inhibitor, or even if vanadium carbide powder was contained, the content was only a trace amount of less than 2000 ppm. However, the ratio of WC particles with a circular equivalent diameter of 1.8 μm or more in the obtained superhard alloys did not reach 2%, and grain growth was suppressed.

The above describes the embodiments and examples of the present invention. However, it is initially intended that the above embodiments and examples may be appropriately combined or modified in various ways. The embodiments and examples disclosed herein are to be considered in all respects as illustrative and non-restrictive. The scope of the present invention is defined by the claims, not by the above embodiments and examples, and is intended to encompass all modifications within the meaning and scope of the claims.

Figure 1 shows an example of an image of the cemented carbide of the present invention captured using a scanning electron microscope. Figure 2 shows the image of Figure 1 after binarization processing.

Claims (8)

A superhard alloy, comprising a first phase and a second phase, wherein the first phase is composed of a plurality of tungsten carbide particles, and the second phase contains cobalt, and in an image of the superhard alloy photographed by a scanning electron microscope, the ratio of the first phase is greater than 78 area % and less than 100 area %, and the ratio of the second phase is greater than 0 area % and less than 22 area %, and in calculating the ratio of each tungsten carbide particle in the image, In the case of particles with an equivalent circular diameter, the average value of the equivalent circular diameter is 0.5 μm or more and 1.2 μm or less, the number-based ratio of the tungsten carbide particles with an equivalent circular diameter of 0.3 μm or less is 10% or less, the number-based ratio of the tungsten carbide particles with an equivalent circular diameter exceeding 1.8 μm is less than 2%, and the mass-based content of cobalt in the cemented carbide exceeds 0% and is 10% or less. The superhard alloy of claim 1, wherein in the above image, the ratio of the second phase is not less than 5 volume % and not more than 12 volume %. For the superhard alloy of claim 1 or claim 2, the chromium content of the superhard alloy is not less than 0.15% by mass and not more than 1.0% by mass. The superhard alloy of claim 3, wherein the ratio of the chromium to the cobalt is not less than 5% and not more than 10% by mass. For the superhard alloy of claim 1 or 2, the mass-based content of vanadium in the superhard alloy is 0 ppm or more and less than 2000 ppm. For example, the superhard alloy of claim 5, wherein the mass-based content of vanadium in the superhard alloy is greater than 0 ppm and less than 100 ppm. A cutting tool having a cutting tip comprising the superhard alloy according to any one of claims 1 to 6. The cutting tool of claim 7, wherein the cutting tool is a rotary tool for processing printed circuit boards.