Cemented carbide and cutting tool

Abstract

A cemented carbide comprising a hard phase and a binder phase, the hard phase comprising a plurality of tungsten carbide particles, the binder phase comprising cobalt, the content of the hard phase in the cemented carbide being 91.5-97% by mass (inclusive), the content of the cobalt in the cemented carbide being 3-8.5% by mass (inclusive), and the hard phase comprising a plurality of tungsten carbide particles. The average particle diameter of the hard phase is 0.15 [mu] m or more and 0.50 [mu] m or less, the average particle diameter of the binder phase is 0.10 [mu] m or more and 0.25 [mu] m or less, and in a histogram representing the distribution of the particle diameters of the hard phase, the number N1 of levels having frequencies of 50% or more of the maximum frequency Fmax is 7 or more and 10 or less, and the number N3 of levels having frequencies of 50% or more of the maximum frequency Fmax is 7 or more and 10 or less. The level of the horizontal axis of the histogram represents the particle size of the hard phases and the width of the level is 0.05 [mu] m, and the frequency of the vertical axis of the histogram represents the percentage of the number of the hard phases belonging to each level for all of the hard phases. The ratio (D10 / D90) of the 10% cumulative particle diameter (D10) on the basis of the area to the 90% cumulative particle diameter (D90) on the basis of the area of the binder phase is 0.23 or more.

Description

Technical Field

[0001] This disclosure relates to cemented carbide and cutting tools. Background Technology

[0002] In printed circuit board openings, small-diameter openings of φ1mm or less are the mainstream. Therefore, as cemented carbide for tools such as small-diameter drill bits, so-called micro-particle cemented carbide (e.g., Patent Documents 1 to 3) is used, in which the hard phase is composed of tungsten carbide particles with an average particle size of 1μm or less.

[0003] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 2007-92090; Patent Document 2: Japanese Patent Application Publication No. 2012-52237; Patent document 3: Japanese Patent Application Publication No. 2012-117100. Summary of the Invention

[0004] The cemented carbide disclosed herein is a cemented carbide composed of a hard phase and a bonding phase. The hard phase consists of a plurality of tungsten carbide particles, and the bonding phase contains cobalt. The hard phase content of the cemented carbide is 91.5% by mass or more and 97% by mass or less, the cobalt content of the cemented carbide is 3% by mass or more and 8.5% by mass or less, the average particle size of the hard phase is 0.15 μm or more and 0.50 μm or less, and the average particle size of the bonding phase is 0.10 μm or more and 0.25 μm or less. (The last sentence appears to be incomplete and possibly refers to a different material.) In the histogram of the distribution, the number N1 of the grades with more than 50% of the maximum frequency Fmax is 7 or more and less than 10. The grade on the horizontal axis of the histogram represents the particle size of the hard phase, and the width of the grade is 0.05 μm. The frequency on the vertical axis of the histogram represents the percentage of the hard phase belonging to each grade for all the hard phases. The ratio D10 / D90 of the 10% cumulative particle size D10 of the bound phase on an area basis to the 90% cumulative particle size D90 on an area basis is 0.23 or more. Attached Figure Description

[0005] Figure 1 This is a diagram showing an example of a cutting tool (small-diameter drill bit) according to Embodiment 2. Detailed Implementation

[0006] [The problem this disclosure aims to solve] In recent years, with the expansion of 5G (fifth-generation mobile communication system), the capacity of information has been continuously increasing. Therefore, there is a growing demand for improved heat resistance in printed circuit boards (PCBs). To improve the heat resistance of PCBs, technologies have been developed to enhance the heat resistance of the resins and glass fillers that constitute the PCBs. On the other hand, this has led to an increasing difficulty in machining PCBs. Due to the increased difficulty in machining PCBs, there is a tendency for a reduction in tool life for drills using cemented carbide as the tool material.

[0007] Therefore, the purpose of this disclosure is to provide a cemented carbide that enables long tool life when used as a tool material, especially in the micromachining of printed circuit boards, and a cutting tool incorporating the cemented carbide.

[0008] [The Effects of This Disclosure] The cemented carbide disclosed herein can provide cutting tools with a long tool life, particularly in the micromachining of printed circuit boards.

[0009] [Description of embodiments of this disclosure] First, embodiments of this disclosure will be described.

[0010] (1) The cemented carbide disclosed herein is a cemented carbide composed of a hard phase and a bonding phase, wherein the hard phase is composed of a plurality of tungsten carbide particles, and the bonding phase contains cobalt, wherein the content of the hard phase in the cemented carbide is 91.5% by mass or more and 97% by mass or less, the content of the cobalt in the cemented carbide is 3% by mass or more and 8.5% by mass or less, the average particle size of the hard phase is 0.15 μm or more and 0.50 μm or less, and the average particle size of the bonding phase is 0.10 μm or more and 0.25 μm or less. (The last sentence appears to be incomplete and possibly refers to a different document.) In the histogram of the distribution, the number N1 of the grades with more than 50% of the maximum frequency Fmax is 7 or more and less than 10. The grade on the horizontal axis of the histogram represents the particle size of the hard phase, and the width of the grade is 0.05 μm. The frequency on the vertical axis of the histogram represents the percentage of the hard phase belonging to each grade for all the hard phases. The ratio D10 / D90 of the 10% cumulative particle size D10 of the bound phase on an area basis to the 90% cumulative particle size D90 on an area basis is 0.23 or more.

[0011] According to the cemented carbide disclosed herein, cutting tools with long tool life can be provided, particularly in the micromachining of printed circuit boards. The reason for this is not yet clear, but it is speculated as follows.

[0012] The cemented carbide disclosed herein comprises a hard phase and a bonding phase, wherein the hard phase consists of a plurality of tungsten carbide particles and the bonding phase contains cobalt. The content of the hard phase in the cemented carbide is 91.5% by mass or more and 97% by mass or less. The content of cobalt in the cemented carbide is 3% by mass or more and 8.5% by mass or less. Therefore, the cemented carbide readily possesses hardness and wear resistance suitable for the micromachining of printed circuit boards.

[0013] In the cemented carbide disclosed herein, the average grain size of the hard phase is 0.15 μm or more and 0.50 μm or less. If the average grain size of the hard phase is 0.15 μm or more, the cemented carbide readily possesses toughness suitable for the microfabrication of printed circuit boards. If the average grain size of the hard phase is 0.50 μm or less, the cemented carbide readily possesses hardness suitable for the microfabrication of printed circuit boards.

[0014] In the cemented carbide disclosed herein, the average grain size of the bonding phase is 0.10 μm or more and 0.25 μm or less. As a result, the microstructure of the cemented carbide is easily made uniform, and its resistance to chipping is improved.

[0015] In the histogram representing the grain size distribution of the hard phase in the cemented carbide of this disclosure, the number N1 of the grades having a frequency of 50% or more of the maximum frequency Fmax is 7 or more and 10 or less. This increases the uniformity of the distribution of the junctions between the hard phases, suppresses the shedding of hard phase particles, and thus improves the resistance to chipping. Furthermore, it is possible to achieve the characteristic that the bonding phase has a D10 / D90 ratio of 0.23 or higher, as described later.

[0016] In the cemented carbide of this disclosure, the ratio D10 / D90, which is the 10% cumulative grain size D10 based on area to the 90% cumulative grain size D90 based on area, is 0.23 or more. Generally, when the average grain size of the bonding phase is 0.10 μm or more and 0.25 μm or less, it becomes difficult to achieve uniform dispersion of the bonding phase. In the cemented carbide of this disclosure, since D10 / D90 is 0.23 or more, the bonding phase does not locally aggregate but is uniformly dispersed, and the cemented carbide can exhibit stable resistance to chipping.

[0017] (2) Alternatively, in (1) above, the D10 / D90 ratio is 0.25 or higher. This results in a more uniform dispersion of the bonding phase, enabling the cemented carbide to exhibit more stable resistance to chipping.

[0018] (3) Alternatively, in (1) or (2) above, the number N1 of the grades is 8 or more and 10 or less. As a result, the distribution of the junctions between the hard phases and the dispersion of the bonding phases become more uniform, and the cemented carbide can have more stable resistance to chipping.

[0019] (4) Alternatively, in any of (1) to (3) above, the cemented carbide contains 0.3% by mass or more and 1.0% by mass or less of chromium. Chromium has the effect of inhibiting the grain growth of tungsten carbide particles. When the chromium content of the cemented carbide is 0.3% by mass or more and 1.0% by mass or less, it is possible to effectively inhibit the retention of particulate tungsten carbide particles from the raw material in the obtained cemented carbide, and it is possible to effectively inhibit the generation of coarse particles, thereby improving tool life.

[0020] (5) Alternatively, in any of (1) to (4) above, the cemented carbide contains 0.3% by mass or less of vanadium. Vanadium has the effect of inhibiting grain growth. When the vanadium content of the cemented carbide is 0.3% by mass or less, it can effectively inhibit the residual of particulate tungsten carbide particles from the raw material in the obtained cemented carbide, and can effectively inhibit the generation of coarse particles, thereby improving tool life.

[0021] (6) Alternatively, in any of (1) to (5) above, the cobalt content of the bonding phase is 85% by mass or more and 99.9% by mass or less. As a result, the toughness of the cemented carbide is improved.

[0022] (7) Alternatively, in any of (1) to (6) above, the number of hard phases with a particle size of 5 μm or more in the cross-section of the cemented carbide is 1 per unit area / mm. 2 Therefore, the folding resistance of cemented carbide is further improved.

[0023] (8) The cutting tool of this disclosure is a cemented carbide cutting tool having any one of (1) to (7) above. The cutting tool of this disclosure can also have a long tool life, especially in the micro-machining of printed circuit boards.

[0024] [Details of the embodiments disclosed herein] Hereinafter, specific examples of the cemented carbide and cutting tools of this disclosure will be described with reference to the accompanying drawings. In the drawings of this disclosure, the same reference numerals denote the same or equivalent parts. In addition, dimensional relationships such as length, width, thickness, and depth have been appropriately modified for the clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0025] In this disclosure, expressions in the form "A~B" refer to A above and B below, where there is no unit recorded in A but only in B, and the units of A and B are the same.

[0026] In this disclosure, when compounds are represented by chemical formulas, all previously known atomic ratios are included without specifically limiting the atomic ratios, and are not necessarily limited to atomic ratios within the stoichiometric range.

[0027] In this disclosure, when more than one value is recorded as the lower limit and the upper limit of the numerical range, a combination of any value recorded in the lower limit and any value recorded in the upper limit is also disclosed.

[0028] In this disclosure, "possessing," "comprising," "having," and variations thereof are open-ended terms. Open-ended terms may include additional elements beyond the essential elements, or they may not include any. The phrase "consisting of" is a closed-ended term. However, even a composition expressed in a closed-ended term may include commonly implied impurities or additional elements unrelated to the target technology.

[0029] The following has been confirmed: Regarding the measured values ​​described in this disclosure, as long as the measurements are performed on the same sample, even if the selected location of the measurement field of view is changed and multiple measurements are performed, there is almost no deviation in the measurement results.

[0030] [Implementation Method 1: Hard Alloy] One embodiment of this disclosure (hereinafter also referred to as "Embodiment 1") is a cemented carbide composed of a hard phase and a bonding phase, wherein the hard phase is composed of a plurality of tungsten carbide particles, and the bonding phase contains cobalt. The hard phase content of the cemented carbide is 91.5% by mass or more and 97% by mass or less, the cobalt content of the cemented carbide is 3% by mass or more and 8.5% by mass or less, the average particle size of the hard phase is 0.15 μm or more and 0.50 μm or less, and the average particle size of the bonding phase is 0.10 μm or more and 0.25 μm or less. In the histogram of the particle size distribution of the hard phase, the number N1 of the grades with more than 50% of the maximum frequency Fmax is 7 or more and less than 10. The grades on the horizontal axis of the histogram represent the particle size of the hard phase, and the width of the grades is 0.05 μm. The frequency on the vertical axis of the histogram represents the percentage of the number of hard phases belonging to each grade for all hard phases. The ratio D10 / D90 of the 10% cumulative particle size D10 of the bound phase on an area basis to the 90% cumulative particle size D90 on an area basis is 0.23 or more.

[0031] <Composition of cemented carbide> Content of hard phase and bound phase The cemented carbide of Embodiment 1 consists of a hard phase and a bonding phase. The hard phase is composed of multiple tungsten carbide particles, and the bonding phase contains cobalt. That is, the total content of the hard phase and the bonding phase in the cemented carbide is 100% by mass. Without impairing the effects of this disclosure, the cemented carbide may also contain unavoidable impurities in addition to the hard phase and the bonding phase. That is, the cemented carbide may consist of a hard phase, a bonding phase, and unavoidable impurities. Examples of unavoidable impurities include iron, molybdenum, and sulfur. The content of unavoidable impurities in the cemented carbide (the sum of their contents when there are two or more impurities) may be 0% by mass or more and less than 0.1% by mass. The content of unavoidable impurities in the cemented carbide is determined by ICP (Inductively Coupled Plasma) luminescence analysis (measuring device: Shimadzu Corporation "ICPS-8100" (trademark)).

[0032] The hard phase content of the cemented carbide in Embodiment 1 is 91.5% by mass or more and 97% by mass or less, or it may be 92% by mass or more and 96% by mass or less, or it may be 94% by mass or more and 95% by mass or less.

[0033] The content of the hard phase in the cemented carbide was determined by analyzing the cross-section of the cemented carbide using an energy-dispersive X-ray spectrometer (SEM-EDX) attached to a scanning electron microscope. Measurements were performed in six distinct fields of view. In this disclosure, the average content of the hard phase in the six fields of view corresponds to the content of the hard phase in the cemented carbide. The cobalt content in the cemented carbide, described later, was also determined using the same method.

[0034] The content of the bonding phase in the cemented carbide of Embodiment 1 can be 3% or more by mass and 8.5% or less by mass, or 4% or more by mass and 8% or less by mass, or 5% or more by mass and 6% or less by mass.

[0035] The content of the bonding phase in cemented carbide is obtained by subtracting the content of the hard phase from the total cemented carbide (100% by mass).

[0036] Cobalt Content The cobalt content of the cemented carbide in Embodiment 1 is 3% by mass or more and 8.5% by mass or less, or it may be 4% by mass or more and 8% by mass or less, or it may be 5% by mass or more and 6% by mass or less.

[0037] Chromium Content The chromium content of the cemented carbide in Embodiment 1 can be 0.3% by mass or more and 1.0% by mass or less, 0.4% by mass or more and 0.9% by mass or less, or 0.5% by mass or more and 0.8% by mass or less. The chromium content of the cemented carbide is determined by ICP-based luminescence spectrophotometry.

[0038] Vanadium Content The vanadium content of the cemented carbide in Embodiment 1 is 0.3% by mass or less, or it can be 0% by mass or more and 0.15% by mass or less, or it can be greater than 0% by mass and 0.1% by mass or less. The vanadium content of the cemented carbide is determined by ICP-based spectroscopy.

[0039] <Hard phase> Composition of the hard phase The hard phase of the cemented carbide in Embodiment 1 is composed of multiple tungsten carbide particles. Here, the tungsten carbide particles include not only "pure WC particles (WC completely free of impurity elements, but also WC with impurity element content below the detection limit)," but also "WC particles that intentionally or unavoidably contain impurity elements within them without impairing the effects of this disclosure." The impurity element content of the hard phase (the total content of two or more elements constituting the impurities) is less than 0.1% by mass. The impurity element content of the hard phase is determined by ICP-based luminescence spectrophotometry.

[0040] Average particle size of the hard phase The average grain size of the hard phase in the cemented carbide of Embodiment 1 is 0.15 μm or more and 0.50 μm or less, or it may be 0.20 μm or more and 0.45 μm or less, or it may be 0.25 μm or more and 0.40 μm or less.

[0041] In this disclosure, the average particle size of the hard phase is determined by the following steps.

[0042] Step A1. Perform mirror finishing on any surface or cross-section of the cemented carbide. Examples of mirror finishing methods include grinding with diamond polishing paste, using a focused ion beam (FIB) device, using a cross-section polishing (CP) device, and combinations thereof.

[0043] Step B1. Take images of the machined surface of the cemented carbide using a scanning electron microscope (S-3400N manufactured by Hitachi High Technology Co., Ltd.). Prepare three images. The three images should cover different areas. The image location can be arbitrarily set. Set the conditions to 10,000x magnification, 10kV accelerating voltage, and reflected electron image.

[0044] Step C1. Using image analysis software (ImageJ, version 1.51j8: https: / / imagej.nih.gov / ij / ), the three reflected electron images obtained in Step B1 are read into the computer and binarized. Binarization is performed after the images are read by pressing the "Make Binary" button on the computer screen, under the pre-set conditions of the image analysis software. Further, to remove noise, after one Despeckle operation, Watershed is performed, thereby identifying grain boundaries under the pre-set conditions of the aforementioned image analysis software. In Analyze Particle, for 0.002 μm... 2 The particles described above are measured. Furthermore, the threshold setting in the binarization process can be manually adjusted, but this step does not use manual adjustment. In this step, as described above, binarization is performed by pressing the "Make Binary" button.

[0045] In the binarized image, hard phases and bound phases can be distinguished by their color intensity. For example, in the binarized image, hard phases are represented by black areas, and bound phases are represented by white areas.

[0046] Step D1. In each of the three binarized images, set a rectangular measurement field of view of 960 pixels in height and 1280 pixels in width. Using the image analysis software described above, measure the equivalent circle diameter (Heywood diameter: equivalent circle diameter with equal area) for all hard phases (black areas) in the three measurement fields.

[0047] Step E1. Calculate the 50% cumulative particle size (equivalent circle diameter) D50 based on area, using all hard phases in the three measurement fields. This D50 corresponds to the average particle size of the hard phase.

[0048] Particle size distribution of hard phases In the histogram representing the grain size distribution of the hard phase in the cemented carbide of Embodiment 1, the number N1 of grades having a frequency of 50% or more of the maximum frequency Fmax is 7 or more and 10 or less, or it may be 8 or more and 10 or less, or it may be 9 or more and 10 or less. If N1 is 6 or less, the uniformity of the distribution of the junctions between the hard phases decreases. If N1 is 11 or more, the number of coarse hard phases increases, and the resistance to breakage decreases.

[0049] A histogram representing the grain size distribution of the hard phase in cemented carbide was constructed according to the following steps. The grain size (equivalent circle diameter) of all hard phases (black areas) in three measurement fields was measured using the same method as steps A1 to D1 described above for determining the average grain size of the hard phase. Based on the grain size of all hard phases measured in the three measurement fields, a histogram was constructed with grade as the horizontal axis and frequency as the vertical axis. The grade on the horizontal axis of the histogram represents the grain size of the hard phase, and the width of the grade is 0.05 μm. The frequency on the vertical axis of the histogram represents the percentage of hard phases belonging to each grade for all hard phases.

[0050] Number of hard phase particles with a diameter of 5 μm or larger per unit area In the cross-section of the cemented carbide in Embodiment 1, the number of hard phase particles with a diameter of 5 μm or more per unit area can be 1 particle / mm. 2 The following describes the particle size of the hard phase. After etching the cross-section of the cemented carbide using Murakami reagent, the cross-section was measured using an optical microscope. The particle size here refers to the major axis of each hard phase as measured in the optical microscope image. At a magnification of 1000x, a 1 mm² area was analyzed. 2 The observation area was examined to determine the amount of hard phase particles larger than 5 μm. A continuous field of view was desired.

[0051] <Binding Phase> Composition of the bound phase The cemented carbide of Embodiment 1 contains cobalt as a binder phase. The cobalt content in the binder phase can be 85% by mass or more and 99.9% by mass or less, 87% by mass or more and 99% by mass or less, or 90% by mass or more and 98% by mass or less. The cobalt content in the binder phase is determined by ICP-N (Inductively Coupled Plasma) spectroscopy.

[0052] In addition to cobalt, the bonding phase of the cemented carbide in Embodiment 1 may also contain iron (Fe), nickel (Ni), and dissolved substances in the alloy (chromium (Cr), tungsten (W), vanadium (V), etc.). The bonding phase may consist of cobalt, at least one selected from the group consisting of iron, nickel, chromium, tungsten, and vanadium, and unavoidable impurities. Examples of unavoidable impurities include manganese (Mn), magnesium (Mg), calcium (Ca), molybdenum (Mo), sulfur (S), titanium (Ti), and aluminum (Al). Furthermore, the presence of iron (Fe), nickel (Ni), dissolved substances in the alloy (chromium (Cr), tungsten (W), vanadium (V), etc.), and unavoidable impurities in the bonding phase can be determined by performing elemental mapping on the cross-section of the cemented carbide using an energy-dispersive X-ray analyzer (EDS).

[0053] Average particle size of the bound phase The average particle size of the bonding phase of the cemented carbide in Embodiment 1 is 0.10 μm or more and 0.25 μm or less, or it may be 0.12 μm or more and 0.24 μm or less, or it may be 0.15 μm or more and 0.22 μm or less.

[0054] In this disclosure, the average particle size of the bound phase is determined according to the following steps. In step B1, which measures the average particle size of the hard phase, except that the magnification is changed to 3,000x and watershed is not required, three binarized images are obtained using the same method as in steps A1 to C1. The same measurement field of view as in step D1 is set in each image. Using the image analysis software described above, the particle size (equivalent circle diameter) of all bound phase (white area) in the three measurement fields is measured. Based on all bound phase in the three measurement fields, the 50% cumulative particle size (equivalent circle diameter) D50 based on area is calculated. This D50 corresponds to the average particle size of the bound phase.

[0055] D10 / D90 of the binding phase In the cemented carbide of Embodiment 1, the ratio D10 / D90 of the cumulative particle size D10 of the bonding phase based on area to the cumulative particle size D90 of the bonding phase based on area is 0.23 or more, or it may be 0.23 or more and 0.5 or less, or it may be 0.25 or more, or it may be 0.25 or more and 0.4 or less.

[0056] In this disclosure, the average particle size of the bound phase is determined according to the following steps. Using the same method as described above for determining the average particle size of the bound phase, the particle size (equivalent circle diameter) of all bound phases (white areas) in three measurement fields is measured. Based on all bound phases in the three measurement fields, the 10% cumulative particle size (equivalent circle diameter) D10 and the 90% cumulative particle size (equivalent circle diameter) D90 are calculated. Then, D10 / D90 is obtained by dividing D10 by D90.

[0057] <Manufacturing Methods of Hard Alloys> The cemented carbide manufacturing method of Embodiment 1 can be carried out by sequentially performing the following steps: raw material powder preparation, mixing, granulation, forming, sintering, and cooling. Each step will be described below.

[0058] Preparation Process The preparation process involves preparing all the raw material powders that constitute the cemented carbide material. Examples of raw material powders include tungsten carbide powder as the hard phase and cobalt (Co) powder as the bonding phase. Furthermore, chromium carbide (Cr3C2) powder and vanadium carbide (VC) powder can be prepared as grain growth inhibitors. Commercially available products can be used for tungsten carbide powder, cobalt powder, chromium carbide powder, and vanadium carbide powder.

[0059] As tungsten carbide powder, a first WC powder with an average particle size of 0.1 μm or more and 0.3 μm or less, and a second WC powder with an average particle size of 0.4 μm or more and 0.8 μm or less are prepared.

[0060] The ratio of the 20% cumulative particle size d20 to the 80% cumulative particle size d80, based on volume, for both the first and second WC powders, is d20 / 80, which is greater than 0.2 and less than 1. Such WC powders have uniform particle size and a low content of WC particles with a diameter of 0.02 μm or less. If such first and second WC powders are used to manufacture cemented carbides, the formation of coarse WC particles due to dissolution and re-precipitation is suppressed during the sintering process.

[0061] The cobalt powder has an average particle size of 0.3 μm or more and 1.0 μm or less. By using fine Co, the particle density of the granulated powder in the subsequent granulation process can be increased. Furthermore, in the sintered cemented carbide, the particle size of the bonding phase becomes fine.

[0062] The average particle size of chromium carbide powder can be greater than 0.7 μm and less than 3.5 μm. The average particle size of vanadium carbide powder can be greater than 0.1 μm and less than 1.2 μm.

[0063] In this disclosure, the average particle size of the raw material powder was determined by the FSSS (Fisher Sub-Sieve Sizer) method. The measuring apparatus used was the "Sub-Sieve Sizer Model 95" (trademark) manufactured by Fisher Scientific. The particle size of each WC particle contained in the WC powder was determined using a particle size distribution measuring apparatus (MT3300EX (trademark)) manufactured by Microtrac.

[0064] Mixed Processes The mixing process is the process of mixing the various raw material powders prepared in the preparation process. Through the mixing process, a mixed powder is obtained by combining the various raw material powders.

[0065] The total proportion of the first WC powder and the second WC powder in the mixed powder can be above 90% by mass and below 98% by mass. The mass ratio of the first WC powder to the second WC powder in the mixed powder is first WC powder : second WC powder = 1 : 4 to 1 : 1.

[0066] The proportion of cobalt powder in the mixed powder can be greater than 2% by mass and less than 8.5% by mass.

[0067] The proportion of chromium carbide powder in the mixed powder can be 0.3% by mass or more and 1.5% by mass or less. The proportion of vanadium carbide powder in the mixed powder can be 0% by mass or more and 0.3% by mass or less.

[0068] The mixing is carried out using a ball mill. The mixing time is set to be more than 15 hours and less than 36 hours. Under these conditions, the pulverization of the raw material powder can be suppressed, and the powder can be thoroughly mixed while maintaining the uniformity of the particle size of the raw material powder.

[0069] Granulation Process In the granulation process, a binder is added to the mixed powder, and granulation is performed using a stirring granulation method to obtain granulated powder. By applying external force to the mixed powder using the stirring granulation method, the WC powder and Co powder are compressed. From a production standpoint, spray drying is generally used in the granulation process. Granulated powder obtained by stirring granulation has fewer gaps and higher density compared to granulated powder obtained by spray drying. This granulated powder is easily filled into the die or mold during the forming process described later. Furthermore, in the cemented carbide after the sintering process, the hard phase particles of this granulated powder are well assembled with each other, resulting in an alloy microstructure with a finely dispersed bound phase.

[0070] In the stirred granulation method, a binder solution of 5% by weight can be added relative to the mixed powder. The rotation speed of the granulation blades is set to 200 rpm, and the processing time is set to 30 minutes. This results in sufficiently uniform granulated powder, forming a particle size that is easy to handle during molding. After removal, allow it to dry thoroughly.

[0071] Molding Process The forming process is the process of shaping the mixed powder obtained in the mixing process into a predetermined shape to obtain a molded body. The forming method and conditions in the forming process are not particularly limited, as long as general methods and conditions are used. For example, a predetermined shape can be exemplified by the shape of a cutting tool (e.g., the shape of a small-diameter drill bit).

[0072] Sintering Process The sintering process is a process of obtaining cemented carbide by sintering the formed body obtained in the forming process. The sintering temperature can be set to 1350~1400℃, and the sintering time can be set to 30~90 minutes. This allows for a wider particle size distribution of the equivalent circular diameter of WC particles in the cemented carbide. Furthermore, it suppresses the formation of coarse WC particles. Additionally, it reduces the content of fine tungsten carbide particles in the obtained cemented carbide.

[0073] Cooling Process The cooling process is the process of cooling the hard alloy after sintering. The cooling rate can be a conventionally known cooling rate.

[0074] Characteristics of Manufacturing Methods To improve the chipping resistance of cemented carbide, methods to reduce the binding phase are considered. One method to reduce the binding phase is to micronize the WC powder in the raw material. However, the finer the WC powder, the more susceptible it is to agglomeration, which hinders the smooth movement of WC particles during the sintering process. As a result, coarse binding phases are formed in a portion of the cemented carbide, leading to a decrease in chipping resistance and folding resistance.

[0075] The inventors of this invention conducted in-depth research and, by using a more fine first WC powder and a more coarse second WC powder in a predetermined ratio, suppressed the aggregation of WC particles caused by the micronization of the WC powder. Furthermore, by allowing the more fine first WC particles to enter the gaps formed by the multiple coarser second WC powders, the bound phase becomes finer, and the dispersibility of the bound phase is improved.

[0076] However, the study of WC powder particle size alone is insufficient to fully suppress WC particle aggregation. Therefore, by further employing a stirring granulation method during the granulation process, the integration of WC particles is promoted. This allows the fine bonding phase to be uniformly dispersed within the cemented carbide structure, resulting in excellent chipping resistance.

[0077] [Implementation Method 2: Cutting Tool] The cutting tool of Embodiment 2 includes a cutting tip made of cemented carbide as in Embodiment 1. In this disclosure, the cutting tip refers to the portion involved in cutting. More specifically, the cutting tip refers to the region surrounded by a cutting tip ridge and an imaginary surface extending from the cutting tip ridge toward the cemented carbide side at a distance of 0.5 nm or 2 mm.

[0078] Examples of cutting tools include cutting tools, drills, end mills, indexable cutting inserts for milling, indexable cutting inserts for turning, metalworking saws, gear cutting tools, reamers, or taps. In particular, as shown in FIG3, when the cutting tool 10 of Embodiment 2 is a small-diameter drill bit for printing circuit board processing, it exhibits excellent performance. The cutting tip 11 of the cutting tool 10 shown in FIG3 is made of cemented carbide as in Embodiment 1.

[0079] The cemented carbide of Embodiment 1 can form the entirety of the cutting tool of Embodiment 2, or it can form a part thereof. Here, "forms a part thereof" means, for example, a method in which the cemented carbide of Embodiment 1 is brazed at a predetermined position on any substrate to form the cutting tip.

[0080] The cutting tool of embodiment 2 may also include a hard coating that covers at least a portion of the surface of a substrate made of cemented carbide. For example, diamond-like carbon or diamond can be used as the hard coating.

[0081] The cutting tool of Embodiment 2 can shape the cemented carbide of Embodiment 1 into the desired shape.

[0082] Example The present embodiment will be further described in detail through the examples. However, the present embodiment is not limited to these examples.

[0083] [Making of cemented carbide] <Preparation Process> As raw material powders, first WC powder, second WC powder, Co powder, Cr3C2 powder, and VC powder were prepared. The average particle size of the first WC powder, second WC powder, and Co powder used in each sample is shown in Table 1. The d20 / 80 of all first WC powders and all second WC powders was 0.2 or more and 1 or less. The average particle size of Cr3C2 powder was 1.5 μm. The average particle size of VC powder was 0.8 μm.

[0084] <Mixed Processes> The raw material powders were mixed according to the proportions shown in Table 1 to prepare a mixed powder. The "mass %" in Table 1 indicates the ratio of the mass of each raw material powder to the total mass of the mixed powder. The mixing was carried out using a ball mill for 20 hours.

[0085] <Granulation Process> The mixed powder was granulated using the method described in Table 2, "Granulation Method," to obtain granulated powder. "Stirring" in Table 2 refers to the stirred granulation method. In the stirred granulation method, 5% by weight of a binder solution was added relative to the mixed powder, the rotation speed of the granulation blades was set to 200 rpm, and the processing time was set to 30 minutes. "Spray Drying" in Table 2 refers to the conventionally known spray drying method.

[0086] <Forming Process> The obtained granulated powder is pressed into a cylindrical shape with a diameter of 6 mm to form a molded body.

[0087] <Sintering Process> The shaped body was placed in a sintering furnace and sintered for 60 minutes at the temperature shown in the "Sintering Temperature" column of Table 2, thereby obtaining cemented carbide.

[0088] Cooling Process The cemented carbide samples were obtained by cooling the cemented carbide after sintering.

[0089] [Table 1]

[0090] [Table 2]

[0091] [Evaluation of cemented carbide] The content of the hard phase, cobalt, chromium, and vanadium in the cemented carbide of each sample was determined using the method described in Embodiment 1. The results are shown in Table 3.

[0092] In each cemented carbide sample, the number N1 of the classes with frequencies of 50% or more of the maximum frequency Fmax in the histogram representing the average grain size of the hard phase, and the number of hard phase particles with a grain size of 5 μm or more per unit area were measured using the method described in Example 1. The results are shown in Table 3.

[0093] [Table 3]

[0094] In each cemented carbide sample, the cobalt content of the bonding phase, the average particle size of the bonding phase, and the D10 / D90 ratio of the bonding phase were measured using the method described in Example 1. The results are shown in Table 4.

[0095] [Table 4]

[0096] [Cutting Test] A small-diameter drill bit (rotary tool for printed circuit board processing) with a cutting diameter of φ0.15 mm was fabricated from a round bar made of cemented carbide for each sample. The drill bit was used to drill holes in commercially available automotive printed circuit boards, and its chipping resistance and breakage resistance were evaluated. The chipping resistance evaluation test conditions were set at a rotational speed of 200 krpm and a feed rate of 2 m / min. The breakage resistance evaluation test conditions were set at a rotational speed of 120 krpm and a feed rate of 2 m / min.

[0097] Five small-diameter drill bits were used in each evaluation test. Holes were drilled using each small-diameter drill bit, and the number of small-diameter drill bits that chipped or broke up to 6000 hits was measured. The results are shown in Table 4. In this cutting test, if fewer than one small-diameter drill bit chipped in the chipping resistance evaluation test and zero drill bits broke in the breakage resistance evaluation test, the small-diameter drill bit was judged to have a long tool life.

[0098] [Inspection] The carbide samples 1 to 15 and the small-diameter drill bits (cutting tools) are equivalent to the examples. It was confirmed that these small-diameter drill bits have a long tool life in the micromachining of printed circuit boards.

[0099] The cemented carbide samples 1-1 to 1-10 and the small-diameter drill bits (cutting tools) are equivalent to the examples. These small-diameter drill bits have insufficient tool life in the micromachining of printed circuit boards.

[0100] The embodiments and examples of this disclosure have been described above, but it is also intended from the outset that the above-described embodiments and examples may be appropriately combined or modified.

[0101] The embodiments and examples disclosed herein should be considered exemplary in all respects, and not restrictive. The scope of the invention is defined not by the foregoing embodiments and examples, but by the claims, and is intended to include all modifications equivalent to and within the scope of the claims.

[0102] Explanation of reference numerals in the attached figures 10: Cutting tool; 11: Tool tip.

Claims

1. A cemented carbide which is a cemented carbide composed of a hard phase composed of a plurality of tungsten carbide particles and a binder phase containing cobalt, wherein, the content rate of the hard phase of the cemented carbide is 91.5 mass% or more and 97 mass% or less, the content rate of the cobalt of the cemented carbide is 3 mass% or more and 8.5 mass% or less, the average particle diameter of the hard phase is 0.15 μm or more and 0.50 μm or less, the average particle diameter of the binder phase is 0.10 μm or more and 0.25 μm or less, in a histogram representing a distribution of particle diameters of the hard phase, the number N1 of ranks having a frequency of 50% or more of the frequency of the rank having the maximum frequency Fmax is 7 or more and 10 or less, the ranks of the horizontal axis of the histogram represent the particle diameters of the hard phase, and the width of the ranks is 0.05 μm, the frequency of the vertical axis of the histogram represents the percentage of the number of the hard phase belonging to each rank on the basis of the number of the hard phase as a whole, the proportion D10 / D90 of the 10% cumulative particle diameter D10 of the binder phase on an area basis with respect to the 90% cumulative particle diameter D90 on an area basis is 0.23 or more.

2. The cemented carbide according to claim 1, wherein, the D10 / D90 is 0.25 or more.

3. The cemented carbide according to claim 1 or 2, wherein, the number N1 of the ranks is 8 or more and 10 or less.

4. The cemented carbide according to any one of claims 1 to 3, wherein, the cemented carbide contains 0.3 mass% or more and 1.0 mass% or less of chromium.

5. The cemented carbide according to any one of claims 1 to 4, wherein, the cemented carbide contains 0.3 mass% or less of vanadium.

6. The cemented carbide according to any one of claims 1 to 5, wherein, the content rate of the cobalt of the binder phase is 85 mass% or more and 99.9 mass% or less.

7. The cemented carbide according to any one of claims 1 to 6, wherein, In the cross section of the cemented carbide, the number of the hard phase having a particle size of 5 μm or more per unit area is 1 / mm2 2 The following.

8. A cutting tool, wherein, the cutting tool is provided with the cemented carbide according to any one of claims 1 to 7.

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