Cemented Carbide and Cutting Tools

Abstract

A cemented carbide alloy comprising a hard phase consisting of a plurality of tungsten carbide particles and a binder phase containing cobalt, wherein the content of the hard phase in the cemented carbide alloy is 91.5% by mass or more and 97% by mass or less, the content of the cobalt is 3% by mass or more and 8.5% by mass or less, the average grain size of the hard phase is 0.15 μm or more and 0.50 μm or less, and the average grain size of the binder phase is 0.10 μm or more and 0.25 μm or less, and in a histogram showing the grain size distribution of the hard phase, The number N1 of classes having frequencies of 50% or more of the maximum frequency Fmax is 7 or more and 10 or less, the classes on the horizontal axis of the histogram indicate the grain sizes of the hard phases, and the width of the classes is 0.05 μm, the frequencies on the vertical axis indicate the percentage of the hard phases belonging to each class based on the number relative to all the hard phases, and the ratio D10 / D90 of the 10% cumulative grain size D10 on an area basis to the 90% cumulative grain size D90 on an area basis of the binder phase is 0.23 or more.

Description

[Technical Field]

[0001] The present disclosure relates to cemented carbides and cutting tools. [Background technology]

[0002] The mainstream drilling of holes in printed circuit boards is small diameter holes of 1 mm or less. For this reason, so-called fine-grained cemented carbide alloys, in which the hard phase is made of tungsten carbide particles with an average particle size of 1 μm or less, are used as cemented carbide alloys for tools such as small diameter drills (for example, Patent Documents 1 to 3). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-92090 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-52237 [Patent Document 3] Japanese Patent Application Laid-Open No. 2012-117100 Summary of the Invention

[0004] The cemented carbide of the present disclosure is a cemented carbide comprising a hard phase consisting of a plurality of tungsten carbide particles and a binder phase containing 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 cobalt in the cemented carbide is 3% by mass or more and 8.5% by mass or less, the average grain size of the hard phase is 0.15 μm or more and 0.50 μm or less, and the average grain size of the binder phase is 0.10 μm or more and 0.25 μm or less, and in a histogram showing the distribution of the grain sizes of the hard phase, grains having a frequency of 50% or more of the maximum frequency Fmax are the number N1 of classes in the histogram is 7 or more and 10 or less, the classes on the horizontal axis of the histogram indicate the grain sizes of the hard phases, and the width of the classes is 0.05 μm, the frequency on the vertical axis of the histogram indicates the percentage of the hard phases belonging to each class based on the number relative to all of the hard phases, and the ratio D10 / D90 of the 10% cumulative grain size D10 on an area basis to the 90% cumulative grain size D90 on an area basis of the binder phase is 0.23 or more. [Brief explanation of the drawings]

[0005] [Figure 1] FIG. 1 is a diagram showing an example of a cutting tool (small diameter drill) according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0006] [Problem to be solved by this disclosure] In recent years, with the expansion of 5G (fifth generation mobile communication systems), the amount of information being transmitted has been increasing. This has led to a demand for even higher heat resistance in printed circuit boards. To improve the heat resistance of printed circuit boards, technologies have been developed to improve the heat resistance of the resins and glass fillers that make up printed circuit boards. However, this has also made printed circuit boards more difficult to cut. As printed circuit boards become more difficult to cut, the tool life of drills made of cemented carbide alloys tends to decrease.

[0007] Therefore, an object of the present disclosure is to provide a cemented carbide alloy that, when used as a tool material, enables a longer tool life, particularly in the micromachining of printed circuit boards, and a cutting tool including the same.

[0008] [Effects of this disclosure] The cemented carbide of the present disclosure makes it possible to provide cutting tools with long tool life, particularly in the micromachining of printed circuit boards.

[0009] [Description of the embodiments of the present disclosure] First, embodiments of the present disclosure will be listed and described. (1) The presently disclosed cemented carbide is a cemented carbide comprising a hard phase consisting of a plurality of tungsten carbide particles and a binder phase containing 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 cobalt in the cemented carbide is 3% by mass or more and 8.5% by mass or less, the average grain size of the hard phase is 0.15 μm or more and 0.50 μm or less, the average grain size of the binder phase is 0.10 μm or more and 0.25 μm or less, and in a histogram showing the distribution of grain sizes of the hard phase, a frequency of 50% or more of the maximum frequency Fmax is the number N1 of classes having numbers is 7 or more and 10 or less, the classes on the horizontal axis of the histogram indicate the grain sizes of the hard phases, and the width of the classes is 0.05 μm, the frequencies on the vertical axis of the histogram indicate the percentages of the hard phases belonging to each class based on the number relative to all the hard phases, and the ratio D10 / D90 of the 10% cumulative grain size D10 on an area basis to the 90% cumulative grain size D90 on an area basis of the binder phase is 0.23 or more.

[0010] The cemented carbide of the present disclosure makes it possible to provide a cutting tool with a long tool life, particularly in the micromachining of printed circuit boards. The reason for this is not clear, but is presumed to be as follows.

[0011] The cemented carbide of the present disclosure comprises a hard phase consisting of a plurality of tungsten carbide particles and a binder phase containing cobalt. The cemented carbide has a hard phase content of 91.5% by mass or more and 97% by mass or less. The cemented carbide has a cobalt content of 3% by mass or more and 8.5% by mass or less. This means that the cemented carbide is likely to have hardness and wear resistance suitable for microfabrication of printed circuit boards.

[0012] In the cemented carbide of the present disclosure, the average grain size of the hard phase is 0.15 μm or more and 0.50 μm or less. When the average grain size of the hard phase is 0.15 μm or more, the cemented carbide tends to have toughness suitable for microfabrication of printed circuit boards. When the average grain size of the hard phase is 0.50 μm or less, the cemented carbide tends to have hardness suitable for microfabrication of printed circuit boards.

[0013] In the cemented carbide of the present disclosure, the average grain size of the binder phase is 0.10 μm or more and 0.25 μm or less, which makes the structure of the cemented carbide more homogeneous and improves chipping resistance.

[0014] In the histogram showing the distribution of the grain size of the hard phase of the cemented carbide of the present disclosure, the maximum frequency Fmax The number N1 of classes having a frequency of 50% or more of the above is 7 or more and 10 or less. This increases the uniformity of the distribution of contact points between hard phases, suppresses the shedding of hard phase particles, and improves chipping resistance. Furthermore, it is possible to achieve the characteristic of a D10 / D90 ratio of 0.23 or more for the binder phase, which will be described later.

[0015] In the cemented carbide of the present disclosure, the ratio D10 / D90, which is the 10% cumulative grain size D10 on an area basis to the 90% cumulative grain size D90 on an area basis of the binder phase, is 0.23 or more. Generally, when the average grain size of the binder phase is 0.10 μm or more and 0.25 μm or less, it is difficult to uniformly disperse the binder phase. In the cemented carbide of the present disclosure, since D10 / D90 is 0.23 or more, the binder phase is uniformly dispersed without localized aggregation, and the cemented carbide can have stable chipping resistance.

[0016] (2) In the above (1), the D10 / D90 may be 0.25 or more, which allows the binder phase to be dispersed more uniformly and the cemented carbide to have more stable chipping resistance.

[0017] (3) In the above (1) or (2), the number of classes N1 may be 8 or more and 10 or less. This makes the distribution of contact points between hard phases and the dispersion of the binder phase more uniform, and the cemented carbide can have more stable chipping resistance.

[0018] (4) In any of the above (1) to (3), the cemented carbide may contain 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 prevent the fine tungsten carbide particles of the raw material from remaining as they are in the resulting cemented carbide, and it is also possible to effectively prevent the generation of coarse grains, thereby improving the tool life.

[0019] (5) In any of the above (1) to (4), the cemented carbide may contain 0.3 mass% or less of vanadium. Vanadium has a grain growth inhibitory effect. When the vanadium content of the cemented carbide is 0.3 mass% or less, the raw material fine tungsten carbide particles can be effectively prevented from remaining as they are in the resulting cemented carbide, and the generation of coarse grains can be effectively suppressed, thereby improving the tool life.

[0020] (6) In any one of the above (1) to (5), the content of cobalt in the binder phase may be 85% by mass or more and 99.9% by mass or less, thereby improving the toughness of the cemented carbide.

[0021] (7) In any of the above (1) to (6), the number of the hard phases having a grain size of 5 μm or more per unit area in the cross section of the cemented carbide is 1 / mm 2 This further improves the breakage resistance of the cemented carbide.

[0022] (8) A cutting tool according to the present disclosure is a cutting tool comprising any one of the cemented carbide alloys described above in (1) to (7). The cutting tool according to the present disclosure has a long tool life, particularly in micromachining of printed circuit boards.

[0023] [Details of the embodiments of the present disclosure] Specific examples of the cemented carbide and cutting tool of the present disclosure will be described below with reference to the drawings. In the drawings of the present disclosure, the same reference numerals represent the same or corresponding parts. Furthermore, dimensional relationships such as length, width, thickness, and depth have been appropriately changed for clarity and simplification of the drawings, and do not necessarily represent actual dimensional relationships.

[0024] In the present disclosure, the notation in the form "A to B" means greater than or equal to A and less than or equal to B, and when no unit is specified for A and only a unit is specified for B, the unit of A and the unit of B are the same.

[0025] In the present disclosure, when a compound or the like is represented by a chemical formula, unless the atomic ratio is particularly limited, it is intended to include any conventionally known atomic ratio, and should not necessarily be limited to only those within the stoichiometric range.

[0026] In this disclosure, when one or more numerical values ​​are listed as the lower limit and upper limit of a numerical range, the combination of any one numerical value listed in the lower limit and any one numerical value listed in the upper limit is also disclosed.

[0027] In this disclosure, "comprises," "includes," "has," and variations thereof are open-ended terms. Open-ended terms may or may not include additional elements in addition to the required elements. The term "consisting of" is a closed term. However, even if a configuration is expressed in closed terms, it may not include impurities that normally accompany it. Things It may include.

[0028] It has been confirmed that, as long as measurements are made on the same sample, there is almost no variation in the measurement results even if measurements are made multiple times by changing the selected location of the measurement field of view.

[0029] [Embodiment 1: Cemented Carbide] One embodiment of the present disclosure (hereinafter also referred to as "Embodiment 1") is a cemented carbide alloy comprising a hard phase composed of a plurality of tungsten carbide particles and a binder phase containing 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 cobalt in the cemented carbide is 3% by mass or more and 8.5% by mass or less, the average grain size of the hard phase is 0.15 μm or more and 0.50 μm or less, the average grain size of the binder phase is 0.10 μm or more and 0.25 μm or less, in a histogram showing the grain size distribution of the hard phase, the number N1 of classes having a frequency of 50% or more of the maximum frequency Fmax is 7 or more and 10 or less, The classes on the horizontal axis of the histogram indicate the grain size of the hard phase, and the width of the classes is 0.05 μm. The frequencies on the vertical axis of the histogram indicate the percentage of the hard phases belonging to each class based on the number of the hard phases relative to all the hard phases. The ratio D10 / D90 of the 10% cumulative grain size D10 on an area basis to the 90% cumulative grain size D90 on an area basis of the binder phase is 0.23 or more.

[0030] <Composition of cemented carbide> <Hard phase and binder phase content> The cemented carbide of the first embodiment is composed of a hard phase consisting of a plurality of tungsten carbide particles and a binder phase containing cobalt. That is, the total content of the hard phase and binder phase in the cemented carbide is 100% by mass. As long as the effects of the present disclosure are not impaired, the cemented carbide may contain inevitable impurities in addition to the hard phase and binder phase. That is, the cemented carbide may be composed of a hard phase, a binder phase, and inevitable impurities. Examples of inevitable impurities include iron, molybdenum, and sulfur. The content of the inevitable impurities in the cemented carbide (when there are two or more types of impurities, the total content of these impurities) may be 0% by mass or more and less than 0.1% by mass. The content of inevitable impurities in the cemented carbide is measured by ICP (Inductively Coupled Plasma) optical emission spectrometry (measuring device: Shimadzu Corporation "ICPS-8100" (trademark)).

[0031] The content of the hard phase in the cemented carbide of embodiment 1 is 91.5 mass % or more and 97 mass % or less, or may be 92 mass % or more and 96 mass % or less, or may be 94 mass % or more and 95 mass % or less.

[0032] The hard phase content of a cemented carbide is measured by analyzing a cross section of the cemented carbide using an energy dispersive X-ray spectrometer (SEM-EDX) attached to a scanning electron microscope. The measurement is performed in six different, non-overlapping measurement fields. In the present disclosure, the average of the hard phase contents in the six measurement fields corresponds to the hard phase content of the cemented carbide. The cobalt content of the cemented carbide, which will be described later, is also measured using the same method.

[0033] The binder phase content of the cemented carbide of embodiment 1 may be 3% by mass or more and 8.5% by mass or less, 4% by mass or more and 8% by mass or less, or 5% by mass or more and 6% by mass or less.

[0034] The content of the binder phase in the cemented carbide is a value obtained by subtracting the content of the hard phase from the total cemented carbide (100 mass %).

[0035] <Cobalt content> The cobalt content of the cemented carbide of embodiment 1 is 3 mass % or more and 8.5 mass % or less, or may be 4 mass % or more and 8 mass % or less, or may be 5 mass % or more and 6 mass % or less.

[0036] ≪Chromium content≫ The chromium content of the cemented carbide of embodiment 1 may 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 measured by ICP atomic emission spectroscopy.

[0037] <Vanadium content> The vanadium content of the cemented carbide of embodiment 1 is 0.3% by mass or less, may be 0% by mass or more and 0.15% by mass or less, or may be more than 0% by mass and 0.1% by mass or less. The vanadium content of the cemented carbide is measured by ICP atomic emission spectrometry.

[0038] <Hard phase> <Hard phase composition> The hard phase of the cemented carbide of embodiment 1 is composed of a plurality of tungsten carbide particles. Here, the tungsten carbide particles include not only "pure WC particles (including WC containing no impurity elements and WC containing impurity elements below the detection limit)" but also "WC particles containing impurity elements intentionally or unavoidably contained therein, as long as the effects of the present disclosure are not impaired." The content of impurity elements in the hard phase (when two or more elements are included as impurities, the total content of these elements) is less than 0.1% by mass. The content of impurity elements in the hard phase is measured by ICP atomic emission spectroscopy.

[0039] <Average grain size of hard phase> The average grain size of the hard phase of the cemented carbide of embodiment 1 is 0.15 μm or more and 0.50 μm or less, or may be 0.20 μm or more and 0.45 μm or less, or may be 0.25 μm or more and 0.40 μm or less.

[0040] In the present disclosure, the average grain size of the hard phase is measured by the following procedure. Step A1: Mirror-finish any surface or cross section of the cemented carbide. Mirror-finishing methods include, for example, polishing with diamond paste, using a focused ion beam (FIB) device, using a cross-section polisher (CP) device, and a combination of these methods.

[0041] Step B1. Photograph the machined surface of the cemented carbide alloy using a scanning electron microscope (Hitachi High-Technologies Corporation, "S-3400N"). Prepare three images. Each of the three images captures a different area. The photographed location can be set as desired. The observation conditions are a magnification of 10,000x, an accelerating voltage of 10 kV, and a backscattered electron image.

[0042] Step C1. The three backscattered electron images obtained in Step B1 are imported into a computer using image analysis software (ImageJ, version 1.51j8: https: / / imagej.nih.gov / ij / ) and binarized. After importing the images, the binarization process is performed under the conditions preset in the image analysis software by pressing the "Make Binary" button on the computer screen. Furthermore, to remove noise, Despeckle is performed once, and then Watershed is performed, which allows the grain boundaries to be identified under the conditions preset in the image analysis software. Analyze Particle to 0.002 μm 2 The above particles are measured. Although the threshold setting for the binarization process can be adjusted manually, manual adjustment is not used in this procedure. In this procedure, as described above, the binarization process is performed by pressing the "Make Binary" display.

[0043] In the binarized image, the hard phase and the binder phase can be distinguished by the shade of color. For example, in the binarized image, the hard phase is shown as a black area and the binder phase is shown as a white area.

[0044] Step D1: Set a rectangular measurement field of view measuring 960 pixels in height and 1280 pixels in width in each of the three binarized images. Using the image analysis software, measure the circle-equivalent diameter (Heywood diameter: diameter of a circle with equal area) of each of the hard phases (black areas) in the three measurement fields.

[0045] Step E1: Calculate the 50% cumulative grain size (circle equivalent diameter) D50 on an area basis based on all hard phases in the three measurement fields. This D50 corresponds to the average grain size of the hard phases.

[0046] <Hard phase particle size distribution> In the histogram showing the distribution of grain sizes of the hard phase of the cemented carbide of embodiment 1, the number N1 of classes having a frequency of 50% or more of the maximum frequency Fmax is 7 or more and 10 or less, and 8 or more and 10 or less. It may be 9 or less, or may be 9 or more and 10 or less. If N1 is 6 or less, the uniformity of the distribution of contact points between hard phases decreases. If N1 is 11 or more, the amount of coarse hard phases increases, and breakage resistance decreases.

[0047] A histogram showing the distribution of grain size of the hard phase of cemented carbide is created by the following procedure. The grain size (circle equivalent diameter) is measured for each of all hard phases (black areas) in the three measurement fields using the same method as steps A1 to D1 for measuring the average grain size of the hard phase described above. A histogram is created based on the grain sizes of all hard phases measured in the three measurement fields, with the horizontal axis representing classes and the vertical axis representing frequency. The classes on the horizontal axis of the histogram indicate the grain size of the hard phase, and the width of the classes is 0.05 μm. The vertical axis of the histogram represents the percentage of hard phases belonging to each class based on the number of hard phases relative to all hard phases.

[0048] <Number of hard phases with a grain size of 5 μm or more per unit area> In the cross section of the cemented carbide of embodiment 1, the number of hard phases having a grain size of 5 μm or more per unit area is 1 / mm 2 The grain size of the hard phases is measured by etching the cross section of the cemented carbide with Murakami's reagent and then measuring the cross section of the cemented carbide in an optical microscope image. The grain size here is the major axis of each hard phase measured on the optical microscope image. The grain size is measured at an observation magnification of 1000 times and an area of ​​1 mm 2 The area is observed and the number of hard phases with a grain size of 5 μm or more is counted. It is desirable that the measurement field is continuous.

[0049] <Binded phase> <Composition of binder phase> The binder phase of the cemented carbide of embodiment 1 contains cobalt. The cobalt content of the binder phase may 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 of the binder phase is measured by ICP atomic emission spectroscopy.

[0050] The binder phase of the cemented carbide of embodiment 1 may contain, in addition to cobalt, iron (Fe), nickel (Ni), dissolved substances in the alloy (chromium (Cr), tungsten (W), vanadium (V), etc.). The binder phase may consist of cobalt, at least one selected from the group consisting of iron, nickel, chromium, tungsten, and vanadium, and inevitable impurities. Examples of inevitable impurities include manganese (Mn), magnesium (Mg), calcium (Ca), molybdenum (Mo), sulfur (S), titanium (Ti), and aluminum (Al). The presence of iron (Fe), nickel (Ni), dissolved substances in the alloy (chromium (Cr), tungsten (W), vanadium (V), etc.), and inevitable impurities in the binder phase can be identified by performing elemental mapping on a cross section of the cemented carbide using an energy dispersive X-ray analyzer (EDS).

[0051] <Average particle size of the binder phase> The average grain size of the binder phase of the cemented carbide of embodiment 1 is 0.10 μm or more and 0.25 μm or less, or may be 0.12 μm or more and 0.24 μm or less, or may be 0.15 μm or more and 0.22 μm or less.

[0052] In the present disclosure, the average grain size of the binder phase is measured by the following procedure. Three images after binarization are obtained in the same manner as in procedures A1 to C1, except that in procedure B1 for measuring the average grain size of the hard phase, the observation magnification is changed to 3,000x and watershed processing is not required. The same measurement field as in procedure D1 is set in each image. Using the image analysis software, the grain size (circle-equivalent diameter) of all the binder phases (white areas) in the three measurement fields is measured. The 50% cumulative grain size (circle-equivalent diameter) D50 on an area basis is calculated based on all the binder phases in the three measurement fields. This D50 corresponds to the average grain size of the binder phase.

[0053] <D10 / D90 of bonded phase> In the cemented carbide of embodiment 1, the ratio D10 / D90 of the 10% cumulative grain size D10 on an area basis to the 90% cumulative grain size D90 on an area basis of the binder phase is 0.23 or more, or may be 0.23 or more and 0.5 or less, 0.25 or more, or 0.25 or more and 0.4 or less.

[0054] In the present disclosure, the average particle size of the binder phase is measured by the following procedure. The particle size (circle-equivalent diameter) of all binder phases (white regions) in the three measurement fields is measured using the same method as the above-mentioned method for measuring the average particle size of the binder phase. The 10% cumulative particle size (circle-equivalent diameter) D10 and the 90% cumulative particle size (circle-equivalent diameter) D90 are calculated based on all binder phases in the three measurement fields. Then, D10 is divided by D90 to obtain D10 / D90.

[0055] <Method of manufacturing cemented carbide> The cemented carbide of embodiment 1 can be manufactured by carrying out the steps of preparing raw material powder, mixing, granulating, compacting, sintering, and cooling in the above order. Each step will be described below.

[0056] ≪Preparation process≫ The preparation step is a step of preparing raw material powders of all materials constituting the cemented carbide. The raw material powders include tungsten carbide powder, which is the raw material for the hard phase, and cobalt (Co) powder, which is the raw material for the binder phase. In addition, chromium carbide (Cr3C2) powder and vanadium carbide (VC) powder may be prepared as grain growth inhibitors. Commercially available tungsten carbide powder, cobalt powder, chromium carbide powder, and vanadium carbide powder can be used.

[0057] As the tungsten carbide powder, a first WC powder having an average particle size of 0.1 μm or more and 0.3 μm or less and a second WC powder having an average particle size of 0.4 μm or more and 0.8 μm or less are prepared.

[0058] The ratio d20 / d80 of the 20% cumulative particle diameter d20 to the 80% cumulative particle diameter d80 on a volume basis of each of the first WC powder and the second WC powder is 0.2 or more and 1 or less. Such WC powder has a uniform particle diameter and contains a small amount of fine WC particles with a particle diameter of 0.02 μm or less. When such first WC powder and second WC powder are used to produce a cemented carbide, the generation of coarse WC particles due to dissolution and reprecipitation during the sintering process is suppressed.

[0059] The average particle size of the cobalt powder is 0.3 μm or more and 1.0 μm or less. By using fine Co, the density of the granulated powder can be increased in the subsequent granulation process. Furthermore, the particle size of the binder phase in the sintered cemented carbide becomes finer.

[0060] The chromium carbide powder may have an average particle size of 0.7 μm or more and 3.5 μm or less, and the vanadium carbide powder may have an average particle size of 0.1 μm or more and 1.2 μm or less.

[0061] In this disclosure, the average particle size of the raw material powder is measured by the FSSS (Fisher Sub-Sieve Sizer) method. The measuring device used is a Fisher Scientific "Sub-Sieve Sizer Model 95" (trademark). The particle size of each WC particle contained in the WC powder is measured using a particle size distribution analyzer (MT3300EX (trademark)) manufactured by Microtrac.

[0062] ≪Mixing process≫ The mixing step is a step of mixing the raw material powders prepared in the preparation step, and a mixed powder in which the raw material powders are mixed is obtained by the mixing step.

[0063] The total proportion of the first WC powder and the second WC powder in the mixed powder may be 90% by mass or more and 98% by mass or less, and 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.

[0064] The proportion of the cobalt powder in the mixed powder may be more than 2 mass % and not more than 8.5 mass %.

[0065] The content of the chromium carbide powder in the mixed powder may be 0.3% by mass or more and 1.5% by mass or less, and the content of the vanadium carbide powder in the mixed powder may be 0% by mass or more and 0.3% by mass or less.

[0066] The mixing is carried out using a ball mill. The mixing time is between 15 and 36 hours. Under these conditions, pulverization of the raw material powder can be suppressed, and the powder can be sufficiently mixed while maintaining the uniformity of the particle size of the raw material powder.

[0067] ≪Pelletization process≫ In the granulation process, a binder is added to the mixed powder, and the mixture is granulated by an agitation granulation method to obtain a granulated powder. By using the agitation granulation method, an external force is applied to the mixed powder, compressing the WC powder and Co powder. From the viewpoint of productivity, the spray drying method is generally used in the granulation process. The granulated powder obtained by the agitation granulation method has fewer gaps and a higher density than the granulated powder obtained by the spray drying method. This granulated powder is easy to fill into a die or mold during the molding process described below. Furthermore, this granulated powder allows for good adhesion of hard phase particles to each other in the cemented carbide after the sintering process, resulting in an alloy structure in which the binder phase is finely dispersed.

[0068] In the agitation granulation method, 5% by weight of binder solution is added to the mixed powder, the granulating blade rotation speed is set to 200 rpm, and the processing time is set to 30 minutes. This gives the granulated powder sufficient uniformity and a particle size that is easy to handle during molding. After removal, it is thoroughly dried.

[0069] ≪Molding process≫ The molding process is Granulation Obtained in the process Granulated powder This is a process of forming the powder into a predetermined shape to obtain a molded body. The forming method and forming conditions in the forming process are not particularly limited and may be general methods and conditions. An example of the predetermined shape is a cutting tool shape (for example, the shape of a small-diameter drill).

[0070] <Sintering process> The sintering step is a step in which the compact obtained in the molding step is sintered to obtain a cemented carbide. The sintering temperature can be 1350 to 1400°C, and the sintering time can be 30 to 90 minutes. This can broaden the particle size distribution of the equivalent circle diameter of WC particles in the cemented carbide. It also suppresses the generation of coarse WC particles. It also reduces the content of fine tungsten carbide particles in the resulting cemented carbide.

[0071] ≪Cooling process≫ The cooling step is a step of cooling the cemented carbide after sintering is completed. The cooling rate may be a conventionally known cooling rate.

[0072] <Features of the manufacturing method> One way to improve chipping resistance in cemented carbide is to reduce the size of the binder phase. One way to reduce the size of the binder phase is to atomize the raw WC powder. However, the finer the WC powder, the more susceptible it is to agglomeration, which inhibits the smooth movement of WC particles during the sintering process. This leads to the formation of coarse binder phases in parts of the cemented carbide, which causes a deterioration in chipping resistance and breakage resistance.

[0073] As a result of extensive research, the inventors have succeeded in suppressing the aggregation of WC particles due to the atomization of the WC powder by using a relatively fine first WC powder and a relatively coarse second WC powder in a predetermined ratio. Furthermore, by allowing the relatively fine first WC particles to enter the gaps formed by the plurality of relatively coarse second WC powder particles, the binder phase is refined and the dispersibility of the binder phase is improved.

[0074] However, the above-mentioned WC powder particle size adjustment alone was not enough to suppress the aggregation of WC particles. Therefore, a further agitation granulation method was adopted in the granulation process to promote the penetration of WC particles. This allows a fine binder phase to be uniformly dispersed throughout the cemented carbide structure, giving the cemented carbide good chipping resistance.

[0075] [Embodiment 2: Cutting Tool] The cutting tool of embodiment 2 includes a cutting edge made of the cemented carbide of embodiment 1. In this disclosure, the cutting edge refers to the portion involved in cutting. More specifically, the cutting edge refers to the region surrounded by the cutting edge ridge and an imaginary plane that is 0.5 nm or 2 mm away from the cutting edge ridge toward the cemented carbide.

[0076] Examples of cutting tools include cutting tools, drills, end mills, indexable cutting tips for milling, indexable cutting tips for turning, metal saws, gear cutting tools, reamers, taps, etc. 1 As shown in FIG. 1, the cutting tool 10 of the second embodiment can exhibit excellent effects when used as a small-diameter drill for machining printed circuit boards. 1 The cutting edge 11 of the cutting tool 10 shown in FIG. 1 is made of the cemented carbide of the first embodiment.

[0077] The cemented carbide of embodiment 1 may constitute the entire cutting tool of embodiment 2, or may constitute a part of the cutting tool. Here, "constitute a part" refers to a mode in which the cemented carbide of embodiment 1 is brazed to a predetermined position of any substrate to form a cutting edge, etc.

[0078] The cutting tool of the second embodiment may further include a hard film that covers at least a part of the surface of the substrate made of cemented carbide. The hard film may be made of, for example, diamond-like carbon or diamond.

[0079] The cutting tool of the second embodiment can be obtained by forming the cemented carbide of the first embodiment into a desired shape. [Example]

[0080] The present embodiment will be described in more detail with reference to examples, although the present embodiment is not limited to these examples.

[0081] [Preparation 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 sizes of the first WC powder, second WC powder, and Co powder used in each sample are shown in Table 1. The d20 / d80 ratios of all first WC powders and all second WC powders were 0.2 or more and 1 or less. The average particle size of the Cr3C2 powder was 1.5 μm. The average particle size of the VC powder was 0.8 μm.

[0082] <Mixing process> A mixed powder was prepared by mixing the raw material powders in the amounts shown in Table 1. In Table 1, "mass %" indicates the proportion of each raw material powder relative to the total mass of the mixed powder. Mixing was carried out using a ball mill for 20 hours.

[0083] <Granulation process> The mixed powder was granulated by the method described in "Granulation method" in Table 2 to obtain a granulated powder. "Stirring" in Table 2 refers to the stirring granulation method. In the stirring granulation method, 5% by weight of binder solution was added to the mixed powder, the rotation speed of the granulating blade 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.

[0084] <Forming process> The obtained granulated powder was press-molded to prepare a compact in the shape of a round bar with a diameter of 6 mm.

[0085] <Sintering process> The compact was placed in a sintering furnace and sintered for 60 minutes at the temperature shown in the "Sintering temperature" column in Table 2 to obtain a cemented carbide.

[0086] <Cooling process> After sintering, the cemented carbide was cooled to obtain each sample of cemented carbide.

[0087] [Table 1]

[0088] [Table 2]

[0089] [Evaluation of cemented carbide] The hard phase content, cobalt content, chromium content, and vanadium content of each cemented carbide sample were measured by the method described in embodiment 1. The results are shown in Table 3.

[0090] For each sample of cemented carbide, the average grain size of the hard phase, the number of classes N1 having a frequency of 50% or more of the maximum frequency Fmax in the histogram showing the distribution of grain sizes of the hard phase, and The number of hard phases having a size of 1 μm or more per unit area was measured by the method described in embodiment 1. The results are shown in Table 3.

[0091] [Table 3]

[0092] For each sample of cemented carbide, the cobalt content of the binder phase, the average grain size of the binder phase, and the D10 / D90 of the binder phase were measured by the method described in embodiment 1. The results are shown in Table 4.

[0093] [Table 4]

[0094] [Cutting test] Each sample of cemented carbide was machined into a round bar to produce a small-diameter drill (a rotary tool for machining printed circuit boards) with a cutting diameter of 0.15 mm. The drill was used to drill holes in commercially available automotive printed circuit boards, and the chipping resistance and breakage resistance were evaluated. The chipping resistance evaluation test was performed under conditions of a rotation speed of 200 krpm and a feed rate of 2 m / min. The breakage resistance evaluation test was performed under conditions of a rotation speed of 120 krpm and a feed rate of 2 m / min.

[0095] Five small-diameter drills were used in each evaluation test. Holes were drilled with each small-diameter drill, and the number of small-diameter drills that chipped or broke within 6,000 hits was counted. The results are shown in Table 4. In this cutting test, if one or fewer small-diameter drills chipped in the chipping resistance evaluation test and no drills broke in the breakage resistance evaluation test, the small-diameter drill was determined to have a long tool life.

[0096] [Consideration] The cemented carbide alloys and small diameter drills (cutting tools) of Samples 1 to 15 correspond to Examples. It was confirmed that these small diameter drills have a long tool life in the micromachining of printed circuit boards.

[0097] The cemented carbide alloys and small diameter drills (cutting tools) of Samples 1-1 to 1-10 are comparison These small diameter drills have had insufficient tool life in the micromachining of printed circuit boards.

[0098] Although the embodiments and examples of the present disclosure have been described above, it is originally intended that the configurations of the above-described embodiments and examples may be appropriately combined or modified in various ways. The embodiments and examples disclosed herein are illustrative in all respects and should not be considered limiting. The scope of the present invention is defined by the claims, not by the embodiments and examples described above, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims. [Explanation of symbols]

[0099] 10 Cutting tool, 11 Cutting edge

Claims

1. A cemented carbide alloy comprising a hard phase consisting of multiple tungsten carbide particles and a bonding phase containing 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. The average particle size of the binding phase is 0.10 μm or more and 0.25 μm or less. In the histogram showing the particle size distribution of the hard phase, the number of classes N1 having a frequency of 50% or more of the maximum frequency Fmax is 7 or more and 10 or less. The horizontal axis of the histogram represents the particle size of the hard phase, and the width of the class 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 class relative to all of the hard phases. A cemented carbide in which the ratio D10 / D90 of the 10% cumulative particle size D10 on an area basis to the 90% cumulative particle size D90 on an area basis of the bonding phase is 0.23 or more.

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

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

4. The cemented carbide alloy according to claim 1 or claim 2, wherein the cemented carbide alloy contains 0.3% by mass or more and 1.0% by mass or less of chromium.

5. The cemented carbide alloy according to claim 1 or claim 2, wherein the cemented carbide alloy contains 0.3% by mass or less of vanadium.

6. The cemented carbide according to claim 1 or claim 2, wherein the cobalt content of the bonding phase is 85% by mass or more and 99.9% by mass or less.

7. In the cross-section of the cemented carbide, the number of hard phase particles with a grain size of 5 μm or more per unit area is 1 particle / mm². ２ The cemented carbide according to claim 1 or claim 2, which is as follows:

8. A cutting tool comprising the cemented carbide alloy according to claim 1 or claim 2.

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