Cemented carbide and cutting tool

Abstract

The present invention is a cemented carbide, comprising a hard phase that comprises a plurality of tungsten carbide particles and a binder phase that includes cobalt. The hard phase content ratio in the cemented carbide is at least 91.5% by mass and no more than 97% by mass; the cobalt content ratio is at least 3% by mass and no more than 8.5% by mass; the mean particle diameter of the hard phase is at least 0.15 μm and no more than 0.50 μm; and the mean particle diameter of the binder phase is at least 0.10 μm and no more than 0.25 μm. In a histogram showing the distribution of particle diameters of the hard phase, the number N1 of grades with frequencies that are at least 50% of the maximum frequency Fmax is at least 7 and no more than 10; the grades on the horizontal axis of the histogram show the particle diameters of the hard phase; the width of each grade is 0.05 μm; the frequency, on the vertical axis, shows the number-base percentage of the hard phase belonging to each grade relative to all of the hard phase; and the proportion D10 / D90, which is the area-base 10% cumulative particle diameter D10 of the binder phase to the area-base 90% cumulative particle diameter D90, is at least 0.23.

Description

Cemented Carbide and Cutting Tools

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

[0002] In drilling printed circuit boards, small-diameter holes of 1 mm or less are the norm, and so-called fine-grain 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 (see, for example, Patent Documents 1 to 3).

[0003] JP 2007-92090 A JP 2012-52237 A JP 2012-117100 A

[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 mass % or more and 97 mass % or less, the content of cobalt in the cemented carbide is 3 mass % or more and 8.5 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 a histogram showing the grain size distribution of the hard phase is the number N1 of classes having frequencies equal to or greater than 50% of the maximum frequency Fmax is 7 or more and equal to or less than 10, 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 of the hard phases 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.

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

[0006] [Problem to be Solved by the Present Disclosure] In recent years, with the expansion of 5G (fifth generation mobile communication systems), the amount of information being transmitted has been increasing. Therefore, printed circuit boards are required to have even higher heat resistance. To improve the heat resistance of printed circuit boards, technologies have been developed to improve the heat resistance of resins and glass fillers that make up printed circuit boards. However, this has led to printed circuit boards becoming increasingly difficult to cut. As printed circuit boards become more difficult to cut, the tool life of drills that use cemented carbide as a tool material 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] Effect of the Present Disclosure The cemented carbide of the present disclosure makes it possible to provide a cutting tool having a long tool life, particularly in the micromachining of printed circuit boards.

[0009] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. (1) A cemented carbide according to the present disclosure is a cemented carbide comprising a hard phase made 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 a histogram showing the grain size distribution of the hard phase is wherein the number N1 of classes having frequencies equal to or greater than 50% of the maximum frequency Fmax is 7 or more and equal to or less than 10, 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 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.

[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 allows the cemented carbide to have hardness and wear resistance suitable for micromachining 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 a histogram showing the distribution of the grain sizes of the hard phases of the cemented carbide of the present disclosure, the number N1 of classes having frequencies equal to or greater than 50% of the maximum frequency Fmax is 7 to 10. This increases the uniformity of the distribution of contact points between the hard phases, suppresses the shedding of hard phase particles, and improves chipping resistance. Furthermore, the characteristic of the binder phase, described below, having a D10 / D90 of 0.23 or more can be achieved.

[0015] In the cemented carbide of the present disclosure, 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. 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 ratio 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, the remaining fine tungsten carbide particles of the raw material can be effectively prevented from remaining in the resulting cemented carbide, and the generation of coarse grains can be effectively suppressed, thereby improving 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 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 one 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 of "A to B" means A or more and B or less, and when no unit is specified for A and a unit is specified only 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 the present disclosure, when one or more numerical values ​​are listed as the lower limit and the upper limit of a numerical range, the combination of any one numerical value listed as the lower limit and any one numerical value listed as the upper limit is also considered to be 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 closed-ended. However, even a configuration expressed in closed terms may include additional elements that are normally incidental impurities or unrelated to the subject technology.

[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 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 mass % or more and 97 mass % or less, the content of the cobalt in the cemented carbide is 3 mass % or more and 8.5 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 the grain size distribution of the hard phase is In the histogram shown in FIG. 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, 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 with respect 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.

[0030] <Composition of Cemented Carbide> <Hard Phase and Binder Phase Content> The cemented carbide of embodiment 1 comprises a hard phase composed 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 also 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) 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 mass% or more and 1.0 mass% or less, 0.4 mass% or more and 0.9 mass% or less, or 0.5 mass% or more and 0.8 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 mass% or less, may be 0 mass% or more and 0.15 mass% or less, or may be more than 0 mass% and 0.1 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 any cross section of the cemented carbide. Examples of mirror-finishing methods include polishing with diamond paste, using a focused ion beam (FIB) device, using a cross-section polisher (CP) device, and combinations of these.

[0041] Step B1. The processed surface of the cemented carbide is photographed using a scanning electron microscope ("S-3400N" manufactured by Hitachi High-Technologies Corporation). Three images are prepared. The photographed areas of the three images are different. The photographed locations can be set arbitrarily. The conditions are observation magnification 10,000x, accelerating voltage 10 kV, and backscattered electron images.

[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 subjected to binarization processing. After importing the images, the binarization processing is performed under 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, followed by Watershed, which allows the grain boundaries of the crystal grains to be identified under conditions preset in the image analysis software. Analyze Particle to 0.002 μm ２ The above particles are measured. Although the threshold value for the binarization process can be manually adjusted, this procedure does not employ manual adjustment. In this procedure, the binarization process is performed by pressing the "Make Binary" button, as described above.

[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: A rectangular measurement field of view measuring 960 pixels in height and 1280 pixels in width is set in each of the three binarized images. Using the image analysis software, the circle-equivalent diameter (Heywood diameter: diameter equivalent to a circle with an equal area) of each of the hard phases (black regions) in the three measurement fields is measured.

[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 Grain Size Distribution> In the histogram showing the grain size distribution 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 to 10, or may be 8 to 10, or may be 9 to 10. If N1 is 6 or less, the uniformity of the distribution of contact points between the 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 sizes of hard phases in cemented carbide is created by the following procedure. The grain sizes (circle equivalent diameters) of all hard phases (black regions) in the three measurement fields are measured using the same methods as in the above-mentioned steps A1 to D1 for measuring the average grain size of hard phases. 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 sizes of the hard phases, 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 having 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 in the optical microscope image. The grain size is measured in an area of ​​1 mm at an observation magnification of 1000 times. ２The 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] <Binder Phase> <Binder Phase Composition> 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 spectrometry.

[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 Grain Size of 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 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 watershedding 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) is measured for each of all binder phases (white areas) in the three measurement fields. The 50% cumulative grain size (circle-equivalent diameter) D50 on an area basis is calculated based on all binder phases in the three measurement fields. This D50 corresponds to the average grain size of the binder phase.

[0053] <D10 / D90 of Binder 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. Using the same method as the above-described method for measuring the average particle size of the binder phase, the particle size (equivalent circle diameter) of all binder phases (white regions) in the three measurement fields is measured. The 10% cumulative particle size (equivalent circle diameter) D10 and the 90% cumulative particle size (equivalent circle diameter) D90 are calculated based on all binder phases in the three measurement fields. Next, D10 is divided by D90 to obtain D10 / D90.

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

[0056] <Preparation Step> 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 a raw material for the hard phase, and cobalt (Co) powder, which is a raw material for the binder phase. Furthermore, chromium carbide (Cr) powder is used as a grain growth inhibitor. ３ C ２) powder and vanadium carbide (VC) powder may be prepared. Commercially available tungsten carbide powder, cobalt powder, chromium carbide powder, and vanadium carbide powder may 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 grain size d20 to the 80% cumulative grain size 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 grain size and a low content of fine WC grains having a grain size 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 grains due to dissolution and reprecipitation is suppressed in the sintering process.

[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 average particle size of the chromium carbide powder may be 0.7 μm or more and 3.5 μm or less, and the average particle size of the vanadium carbide powder may be 0.1 μm or more and 1.2 μm or less.

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

[0062] <Mixing Step> The mixing step is a step of mixing the raw material powders prepared in the preparation step. By the mixing step, a mixed powder in which the raw material powders are mixed is obtained.

[0063] The total content 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 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 set to 15 hours or more and 36 hours or less. 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] <Granulation 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 the Co powder. In the granulation process, a spray drying method is generally used from the viewpoint of productivity. 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 rotation speed of the granulating blade is 200 rpm, and the processing time is 30 minutes. This gives the granulated powder sufficient uniformity and a particle size that is easy to handle during molding. After removal, the mixture is thoroughly dried.

[0069] <<Shaping Step>> The molding step is a step of molding the mixed powder obtained in the mixing step into a predetermined shape to obtain a molded body. The molding method and molding conditions in the molding step are not particularly limited, and general methods and conditions may be used. An example of the predetermined shape is a cutting tool shape (e.g., the shape of a small-diameter drill).

[0070] <Sintering Process> The sintering process is a process in which the compact obtained in the molding process 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 Step>> The cooling step is a step of cooling the cemented carbide after the sintering is completed. The cooling rate may be a conventionally known cooling rate.

[0072] <Features of the manufacturing method> One way to improve the chipping resistance of 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 results in the formation of a coarse binder phase in part of the cemented carbide, which deteriorates 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, and furthermore, by allowing the relatively fine first WC particles to enter the gaps formed by a plurality of relatively coarse second WC powders, 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, agitation granulation was adopted in the granulation process to promote the penetration of WC particles. This allows a fine binder phase to be uniformly dispersed in the structure of the cemented carbide, and the cemented carbide has good chipping resistance.

[0075] [Embodiment 2: Cutting Tool] A 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 a portion involved in cutting. More specifically, the cutting edge refers to a region surrounded by a 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 inserts for milling, indexable cutting inserts for turning, metal saws, gear cutting tools, reamers, taps, etc. In particular, as shown in Figure 3, the cutting tool 10 of the second embodiment is highly effective in the case of small-diameter drills for machining printed circuit boards. The cutting edge 11 of the cutting tool 10 shown in Figure 3 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 an arbitrary substrate to form a cutting edge.

[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.

[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] [Production of cemented carbide] <Preparation step> As raw material powders, a first WC powder, a second WC powder, a Co powder, and a Cr powder were mixed. ３ C ２ The average particle sizes of the first WC powder, the second WC powder, and the Co powder used in each sample are shown in Table 1. The d20 / d80 ratios of all the first WC powders and all the second WC powders were 0.2 or more and 1 or less. ３ C ２ The average particle size of the powder was 1.5 μm, and the average particle size of the VC powder was 0.8 μm.

[0082] <Mixing Step> 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 with respect to the total mass of the mixed powder. Mixing was carried out for 20 hours using a ball mill.

[0083] <Granulation step> 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 200 rpm, and the processing time was 30 minutes. "Spray drying" in Table 2 refers to a conventionally known spray drying method.

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

[0085] <Sintering Step> 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 Step> After sintering, the cemented carbide was cooled to obtain each sample of cemented carbide.

[0087]

[0088]

[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 N1 of classes having a frequency of 50% or more of the maximum frequency Fmax in a histogram showing the distribution of grain sizes of the hard phase, and the number of hard phases having a grain size of 5 μm or more per unit area were measured by the method described in embodiment 1. The results are shown in Table 3.

[0091]

[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]

[0094] [Cutting test] A round bar made of cemented carbide alloy of each sample was machined to prepare 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 a commercially available automotive printed circuit board, and chipping resistance and breakage resistance were evaluated. The chipping resistance evaluation test conditions were a rotation speed of 200 krpm and a feed rate of 2 m / min. The breakage resistance evaluation test conditions were 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] [Discussion] 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 correspond to Examples. These small diameter drills 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 intended from the beginning that the configurations of the above-described embodiments and examples may be appropriately combined and 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 above-described embodiments and examples, and is intended to include meanings equivalent to the claims and all modifications within the scope of the claims.

[0099] 10 cutting tool, 11 cutting edge

Claims

1. 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 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 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, in a histogram showing the distribution of grain sizes of the hard phases, 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 sizes of the hard phases, and the width of the classes is 0.05 μm, and the frequency on the vertical axis of the histogram indicates the percentage of the hard phases belonging to each class based on the number of the hard phases relative to all of the hard phases, A cemented carbide, wherein 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.

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

3. The cemented carbide according to claim 1 or 2, wherein the number N1 of classes 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. A cemented carbide according to any one of claims 1 to 5, wherein the cobalt content of the binder 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 the hard phases having a grain size of 5 μm or more per unit area is 1 / mm ２ 7. The cemented carbide according to any one of claims 1 to 6, wherein:

8. A cutting tool comprising the cemented carbide according to any one of claims 1 to 7.

Images