Cemented Carbide and Cutting Tools

Abstract

This cemented carbide has a hard phase containing W and C and a binder phase containing an iron-group metal. In addition, the binder phase has a fractal dimension of 0.7 or greater when in a dispersed state.

Description

[Technical Field]

[0001] Disclosed embodiments relate to cemented carbides and cutting tools. [Background technology]

[0002] BACKGROUND ART In recent years, there has been an increasing need for micromachining tools for electronic devices, such as extremely small diameter drills for drilling holes in printed circuit boards (hereinafter also referred to as PWB drills) (see, for example, Patent Document 1).

[0003] In addition, in recent years, printed circuit boards, which are processed components, have become lighter, thinner, shorter, and smaller, and as the demand for higher electrical reliability increases, higher heat resistance, heat dissipation, and rigidity are required. To meet these demands, efforts are being made to increase the inorganic filler content in the glass fiber reinforced resin, which is the constituent material of printed circuit boards, and to increase the density of the glass fiber. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-122934 Summary of the Invention

[0005] The cemented carbide of the present disclosure has a hard phase containing W and C and a binder phase containing an iron-group metal, and the binder phase has a fractal dimension of 0.7 or more in its dispersed state. [Brief explanation of the drawings]

[0006] [Figure 1] FIG. 1 is a diagram schematically showing the configuration of a PWB drill according to an embodiment. [Figure 2] FIG. 2 is a diagram showing a binarized image of an SEM photograph of a cemented carbide alloy that was fired at a temperature rise rate of 2° C. / min. [Figure 3]FIG. 3 is a diagram showing a binarized image of an SEM photograph of a cemented carbide alloy that was fired at a temperature rise rate of 6 (° C. / min). [Figure 4] FIG. 4 is a diagram showing the relationship between the rate of temperature rise during firing treatment, the fractal dimension of the dispersed state of the binder phase, and the particle size of the hard phase. [Figure 5] FIG. 5 is a diagram showing the relationship between the fractal dimension of the dispersed state of the binder phase and the standard deviation of the Vickers hardness at multiple points. [Figure 6] FIG. 6 is a diagram showing the relationship between the fractal dimension of the dispersed state of the binder phase and the process capability index CPK of the degree of deviation of hole positions. DETAILED DESCRIPTION OF THE INVENTION

[0007] Hereinafter, embodiments of the cemented carbide and cutting tool disclosed in the present application will be described with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described below.

[0008] In recent years, there has been an increasing need for micromachining tools for electronic devices, such as extremely small diameter drills for drilling holes in printed circuit boards (hereinafter also referred to as PWB drills).

[0009] In addition, in recent years, printed circuit boards, which are processed components, have become lighter, thinner, shorter, and smaller, and as the demand for higher electrical reliability increases, higher heat resistance, heat dissipation, and rigidity are required. To meet these demands, efforts are being made to increase the inorganic filler content in the glass fiber reinforced resin, which is the constituent material of printed circuit boards, and to increase the density of the glass fiber.

[0010] However, with the above-mentioned conventional technology, as the amount of inorganic filler or glass fiber in the printed circuit board increases, the cutting edge of the PWB drill can easily wear unevenly when cutting the printed circuit board, which can lead to problems such as poor hole position accuracy, poor surface roughness, and breakage of the PWB drill.

[0011] Therefore, there is a need to develop a technology that can overcome the above-mentioned problems and reduce uneven wear during cutting in PWB drills.

[0012] <PWBドリル> First, the configuration of a PWB drill 1 according to an embodiment will be described with reference to Fig. 1. Fig. 1 is a diagram schematically showing the configuration of a PWB drill 1 according to an embodiment.

[0013] As shown in Figure 1, the PWB drill 1 according to the embodiment has a cutting portion 2, a shank portion 3, and a connecting portion 4. The cutting portion 2 has a long cylindrical shape, and the tip of the cylindrical shape is sharpened. In addition, one or more spiral chip discharge flutes 2a are formed on the side surface of the cutting portion 2, extending from the tip end to the base end.

[0014] The cutting portion 2 according to the embodiment is made of cemented carbide having a hard phase containing W (tungsten) and C (carbon) and a binder phase containing an iron group metal (at least one of Co (cobalt), Ni (nickel) and Fe (iron)).

[0015] The shank portion 3 has, for example, a cylindrical shape with an outer diameter larger than that of the cutting portion 2. The shank portion 3 is made of, for example, stainless steel, etc. This allows the manufacturing cost of the PWB drill 1 to be reduced compared to when the entire PWB drill 1 is made of cemented carbide.

[0016] The connecting portion 4 connects the cutting portion 2 and the shank portion 3, which have different outer diameters, and has a first tapered portion 4a, a second tapered portion 4b, and a cylindrical portion 4c.

[0017] The first tapered portion 4a is formed integrally with the shank portion 3, and the outer diameter gradually decreases toward the tip. That is, the first tapered portion 4a is formed of the same material (stainless steel, etc.) as the shank portion 3.

[0018] The second tapered portion 4b is formed integrally with the cutting portion 2, and the outer diameter gradually increases with increasing distance from the tip. That is, the second tapered portion 4b is formed of the same material (super hard alloy) as the cutting portion 2.

[0019] A part of the cylindrical portion 4c is integral with the first tapered portion 4a, and the rest is integral with the second tapered portion 4b. The cemented carbide and the stainless steel are joined at a joining surface 4d located on the cylindrical portion 4c, connecting the cutting portion 2 and the shank portion 3.

[0020] The PWB drill 1 according to the embodiment is not limited to the example shown in FIG. 1, and may have any configuration as long as at least the cutting edge 2 is made of cemented carbide.

[0021] In this embodiment, the fractal dimension of the dispersion state of the binder phase in the hard phase is 0.7 or more in the cemented carbide constituting the cutting portion 2. The value of the fractal dimension of the dispersion state of the binder phase indicates the dispersion state of the binder phase in the sintered body, so the higher the value of the fractal dimension of the dispersion of the binder phase, the more uniform the dispersion of the binder phase.

[0022] The uniformity of the binder phase dispersion correlates with the variation in the Vickers hardness of the sintered body. Specifically, the more uniform the binder phase dispersion, the smaller the variation in the Vickers hardness of the sintered body from a microscopic perspective, and the smaller the standard deviation. Therefore, by having a high fractal dimension, the dispersion state of the binder phase becomes uniform, and the formation of non-uniform parts in the hard phase in the cemented carbide can be reduced.

[0023] Therefore, according to the embodiment, the variation in hardness in the cemented carbide can be reduced, and uneven wear during cutting can be reduced.

[0024] In an embodiment, the cemented carbide constituting the cutting portion 2 may have a fractal dimension of 0.8 or more in the dispersion state of the binder phase in the hard phase, which can further reduce the formation of non-uniform portions in the hard phase in the cemented carbide.

[0025] Therefore, according to the embodiment, the variation in hardness in the cemented carbide can be further reduced, and uneven wear during cutting can be further reduced.

[0026] In the embodiment, the cemented carbide constituting the cutting portion 2 has a thickness of 400 (μm 2 The standard deviation of the Vickers hardness measured at multiple points in the cutting edge region may be 2.5 or less. By reducing the variation in hardness in a small region such as the cutting edge, uneven wear during cutting can be further reduced.

[0027] In addition, in the embodiment, the degree of deviation of the hole position when the tip of the cutting portion 2 drills a hole in a member such as a printed circuit board may be 2.45 or more in terms of process capability index CPK. In this way, the accuracy of the hole position is improved, which further reduces uneven wear during cutting, thereby achieving a longer life of the PWB drill 1. [Example]

[0028] Examples of the present disclosure will be specifically described below. Note that, although the examples described below show cemented carbide alloys using cobalt as a binder phase, the present disclosure is not limited to the following examples.

[0029] First, various powders were blended together to make a total of 100 wt% containing 75-98.9 wt% tungsten carbide (WC) powder with an average particle size of 0.1-1 μm, 1-20 wt% cobalt powder, 0.1-5 wt% carbide powder of at least one element selected from Groups 4A, 5A, and 6A of the periodic table, and other unavoidable impurities. In the present disclosure, metallic tungsten (W) powder or carbon black (C) may also be blended as desired.

[0030] Next, water or an organic solvent and, if desired, an organic binder are added to the prepared mixed powder and mixed, and the mixture is pulverized and mixed by a known method such as a ball mill or a vibration mill, and then dried in a spray dryer to form granules.

[0031] Next, this granular mixed powder was molded into a predetermined cutting tool shape as shown in FIG. 1 by a known molding method such as press molding, casting, extrusion molding, or cold isostatic pressing.

[0032] Next, this compact was fired in a firing furnace in a vacuum or in a non-oxidizing atmosphere such as Ar or N2 at a firing temperature of 1350 to 1450°C for 0.5 to 5 hours, and then HIP sintering was carried out at a temperature 5 to 50°C lower than the firing temperature, at a pressure of 5 to 20 MPa, and for 0.5 to 3 hours to produce cemented carbide for cutting tools in the examples and comparative examples.

[0033] In the present disclosure, the maximum firing temperature itself was all set to the same temperature, but the temperature rise rate just before the firing temperature reached the maximum temperature was varied to control the crystalline state within the cemented carbide. In addition, in the comparative example, the firing temperature was allowed to reach the maximum temperature without changing the temperature rise rate.

[0034] Specifically, for the cemented carbide of the example, the temperature of the sintering furnace was first increased at a heating rate V1, and then the heating rate was changed to V2 just before the maximum temperature was reached. At this time, the heating rate V2 was set to be smaller than the heating rate V1. Furthermore, for the cemented carbide of the example, the firing temperature was allowed to reach the maximum temperature at a constant heating rate V0. More specifically, the heating rates V0 and V1 were set to 8 (°C / min). Furthermore, three cemented carbide alloys were prepared as examples, with heating rates V2 of 2 (°C / min), 4 (°C / min), and 6 (°C / min).

[0035] Here, changing the heating rate immediately before means changing the heating temperature when the firing temperature reaches approximately 80 to 99% of the maximum temperature. For example, if the maximum temperature is 1400°C and the heating rate is changed when the firing temperature reaches 1358°C, the heating temperature will be changed when the firing temperature reaches 97% of the maximum temperature (=1358°C / 1400°C). In this case, it can be said that the heating rate immediately before is changed.

[0036] In the present disclosure, the crystalline state in the cemented carbide is controlled by changing the heating rate immediately before the firing temperature reaches the maximum temperature, but the control of the crystalline state is not limited to this method. If the fractal dimension of the dispersion state of the binder phase in the hard phase can be increased, the crystalline state in the cemented carbide may be controlled, for example, by changing the particle size distribution in the mixed powder, or by adding an organic substance different from the organic substance contained in the solvent when adding water or an organic solvent to the mixed powder and mixing it.

[0037] In the present disclosure, if desired, a coating film may be formed on the surface of the prepared cemented carbide substrate, such as titanium carbide (TiC), titanium nitride (TiN), titanium carbonitride (TiCN), titanium-aluminum composite nitride (TiAlN), or aluminum oxide (Al2O3).

[0038] Furthermore, as a method for forming such a coating film, known film formation methods such as chemical vapor deposition methods (thermal CVD, plasma CVD, organic CVD, catalytic CVD, etc.) and physical vapor deposition methods (ion plating, sputtering, etc.) can be used.

[0039] Next, predetermined locations of the obtained cemented carbide for cutting tools were polished, and the polished surfaces were photographed using a field emission scanning electron microscope (FE-SEM) manufactured by JEOL under the following conditions: magnification: 2000x, acceleration voltage: 10 (kV), brightness: 581, contrast: 4630, with five fields of view per sample.

[0040] The photographs were then analyzed using the computer software "ImageJ" (developed by Wayne Rasband, National Institutes of Health). Specifically, the photographs were first imported into ImageJ, and then binarized into the hard and bonded phases using "Trainable Weka Segmentation" in ImageJ.

[0041] In this binarization process, one photograph was selected from the photographs taken, and at least four areas were extracted from the Co (black area) and the hard phase (other areas), and the binarization conditions were determined. These conditions were applied to the remaining four photographs, and binarization was performed on each of the five photographs.

[0042] Next, this binarized image was subjected to fractal analysis by the box counting method using "Fractal Box Count..." in ImageJ. In this case, the box sizes for division were set to 5, 6, 7, 8, 9, and 10. The fractal value was calculated for each of the five photographs mentioned above, and the five obtained fractal values ​​were averaged to identify the fractal dimension of the cemented carbide to be evaluated.

[0043] In addition, using ImageJ, the average value of the circle-equivalent diameter (hereinafter also referred to as particle diameter) of the crystal grain size of the hard phase in the photograph was calculated.

[0044] Furthermore, the hardness distribution in a micro area of ​​the obtained cemented carbide for cutting tools was measured. Specifically, a micro Vickers hardness tester was used to measure the hardness distribution in a micro area of ​​400 μm. 2 The hardness was measured at a total of 100 points at intervals of about 2 μm in the vertical and horizontal directions in a measurement area (for example, 20 μm square), and similar tests were also performed on five fields of view per sample.

[0045] The obtained hardness distribution of the plurality of Vickers hardnesses was then plotted as a histogram and approximated to a normal distribution, and the standard deviation of the Vickers hardness was calculated.

[0046] The obtained cemented carbide for cutting tools was also evaluated for the degree of hole position deviation when drilling holes in a component using the process capability index (CPK). Specifically, six PWB drills 1 with a drill diameter of 150 μm and a printed wiring board substrate were prepared. Next, 10,000 holes per drill were drilled into the prepared printed wiring board substrate using the prepared PWB drills 1.

[0047] Next, measure the distance between the drilled hole and the target center position and use this as hole position accuracy data. Then, calculate the average value and standard deviation of the measured hole position accuracy data. Finally, use the calculated average value and standard deviation to calculate the process capability index CPK using the following formula (1). CPK = (specification value - mean value) / (3 × standard deviation) (1)

[0048] In this disclosure, the process capability index CPK is calculated using a standard value of 75 (μm). In addition, in this disclosure, the process capability index CPK for six drills is measured and then averaged to determine the overall process capability index CPK.

[0049] FIG. 2 is a diagram showing a binarized image of an SEM observation photograph of a cemented carbide sintered at a heating rate of 2 (°C / min), and FIG. 3 is a diagram showing a binarized image of an SEM observation photograph of a cemented carbide sintered at a heating rate of 6 (°C / min).

[0050] As shown in FIGS. 2 and 3, it can be seen that the dispersion state of the binder phase (black portion) is improved by lowering the rate of temperature rise until the maximum temperature is reached.

[0051] FIG. 4 is a diagram showing the relationship between the rate of temperature rise during firing treatment, the fractal dimension of the dispersed state of the binder phase, and the particle size of the hard phase.

[0052] As shown in Figure 4, by setting the heating rate V2 until the maximum temperature is reached lower than the initial heating rate V1, the fractal dimension, which indicates the dispersion state of the binder phase, is improved (i.e., the dispersion state of the binder phase is improved). In particular, it can be seen that the fractal dimension increases as the heating rate V2 decreases.

[0053] When the heating rate V2 is smaller than the heating rate V1, it is possible to ensure a long firing time just before reaching the maximum temperature, which has a significant impact on the dispersion state of the binder phase, while avoiding an excessive increase in the time required for the entire firing process. This is thought to promote uniformity in the dispersion state of the binder phase and make it easier to efficiently increase the fractal dimension. In particular, the smaller the heating rate V2, the longer the firing time just before reaching the maximum temperature. This is thought to promote more uniformity in the dispersion state of the binder phase and make it easier to increase the fractal dimension.

[0054] The heating rate V2 may be constant or may be varied. For example, the heating rate V2 may be divided into a first stage represented by a constant heating rate V21 and a second stage represented by a constant heating rate V22 (however, different from V21). In this case, the heating rate V22 may be smaller than the heating rate V21. When the heating rate V2 gradually decreases in this manner, a longer firing time can be ensured just before the maximum temperature, which has a significant effect on the dispersion state of the binder phase. This is thought to further promote uniform dispersion of the binder phase and facilitate an increase in the fractal dimension.

[0055] Furthermore, when the temperature rise rate V2 is configured in multiple stages as described above and the temperature rise rate in each stage is constant, the temperature control of the sintering furnace is easier than when the temperature rise rate V2 changes continuously. Therefore, for example, it is easy to avoid variations in the fractal dimension due to the position of the cemented carbide in the sintering furnace and variations in the sintering process due to operators. In other words, the fractal dimension of the cemented carbide is stable and reproducibility is good.

[0056] Furthermore, in the present disclosure, since the maximum temperature itself is kept constant, it can be seen that even if the heating rate immediately before reaching the maximum temperature is changed, the particle size of the hard phase hardly changes, which makes it possible to control the dispersion state of the binder phase without changing the hardness characteristics of the cemented carbide.

[0057] Fig. 5 is a diagram showing the relationship between the fractal dimension of the dispersed state of the binder phase and the standard deviation of the Vickers hardness at multiple points. As shown in Fig. 5, by setting the fractal dimension to 0.7 or more, the standard deviation of the Vickers hardness can be reduced to a good value.

[0058] That is, in the embodiment, by setting the fractal dimension to 0.7 or more, the hardness distribution in a minute region can be made uniform, and uneven wear during cutting can be reduced.

[0059] In addition, in the embodiment, by setting the fractal dimension to 0.8 or more, the standard deviation of the Vickers hardness can be reduced to a better value, which makes it possible to make the hardness distribution in a microscopic area more uniform, thereby further reducing uneven wear during cutting.

[0060] In the present disclosure, the upper limit of the fractal dimension may be 2 or less, and preferably 1 or less, from the viewpoint of manufacturing efficiency and the like.

[0061] Furthermore, in the embodiment, by setting the standard deviation of the Vickers hardness at a plurality of points to 2.5 or less, the hardness distribution in a minute region can be made uniform, thereby reducing uneven wear during cutting.

[0062] Figure 6 shows the relationship between the fractal dimension of the binder phase dispersion state and the process capability index CPK of the hole position deviation. As shown in Figure 6, by setting the fractal dimension to 0.7 or more, the process capability index CPK can be improved to a good value.

[0063] That is, in the embodiment, by setting the fractal dimension of the dispersed state of the binder phase to 0.7 or more, the accuracy of the hole position can be improved. Therefore, according to the embodiment, uneven wear during cutting can be reduced, and the life of the PWB drill 1 can be extended.

[0064] In addition, in the embodiment, by setting the fractal dimension of the dispersed state of the binder phase to 0.8 or more, the process capability index CPK can be further improved, and therefore, according to the embodiment, the life of the PWB drill 1 can be further extended.

[0065] Furthermore, in the embodiment, by setting the process capability index CPK to 2.45 or more, uneven wear during cutting can be reduced, and therefore the life of the PWB drill 1 can be extended.

[0066] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications are possible without departing from the spirit of the present invention. For example, in the above embodiments, an example was shown in which the above-mentioned cemented carbide was used in a PWB drill, but the present disclosure is not limited to such an example, and the above-mentioned cemented carbide may be used in various cutting tools such as tips.

[0067] Further advantages and other aspects may readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described above. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. [Explanation of symbols]

[0068] 1 PWB drill 2 Blade part 3 Shank 4 Connecting part

Claims

1. a hard phase containing W and C; a binder phase containing an iron group metal; and The fractal dimension of the dispersed state of the binder phase is 0.7 or more and 2 or less. Cemented carbide.

2. The fractal dimension of the dispersed state of the binder phase is 0.8 or more. The cemented carbide according to claim 1.

3. 400 (μm ２ The standard deviation of the Vickers hardness measured at multiple points in the 3. The cemented carbide according to claim 1 or 2.

4. One end of the cemented carbide according to claim 1 or 2 in a long cylindrical shape is joined to a shank portion, and the other end is sharpened. cutting tools.

5. The degree of deviation of the hole position when the other end portion drills a hole in a member is 2.45 or more in terms of process capability index CPK. The cutting tool according to claim 4.

Images