Carbide tool

Abstract

This carbide tool is such that a cemented carbide composed of a WC phase and a Co-containing binder phase is used, wherein the average particle diameter Xμm of the WC phase and the total amount Y mass% of the binder phase satisfy relationships (1), (2), and (3): Relationship (1): X ≤ 1.2; Relationship (2): 2 ≤ Y; Relationship (3): −6.7X + 6 ≤ Y ≤ −14X + 38, and Cr and / or V are contained at an amount of 2-20 mass% in terms of carbide relative to the total amount of the binder phase.

Description

carbide tools

[0001] The present invention relates to a cemented carbide tool.

[0002] In the major trend towards a decarbonized society, the electrification of automobiles and other vehicles plays a major role. Lightweight and high performance are required for the motors used in electric vehicles. Iron cores for motors and other devices are often made by laminating multiple sheets of electromagnetic steel to achieve low iron loss and high magnetic flux density. Amorphous alloy foil, in particular, exhibits excellent mechanical properties, magnetic properties, corrosion resistance, and other characteristics. Because its magnetic properties are particularly excellent, using amorphous alloy foil instead of regular electromagnetic steel sheet is expected to significantly improve performance.

[0003] While the electromagnetic steel sheets used in the iron cores of motors and other devices are generally 100 to 500 μm thick, amorphous metal foils are about 10 to 100 μm thick, requiring multiple punching processes. However, when high-hardness, high-strength metal foils such as amorphous alloy foils are repeatedly punched into a predetermined shape, the punching tools wear out rapidly, resulting in a short tool life.

[0004] Japanese Patent Application Laid-Open No. 2021-130131 (Patent Document 1) discloses a method for obtaining amorphous alloy pieces by forming a plastically worked groove that becomes a punched outline of a predetermined shape on the surface of an amorphous alloy ribbon and punching along the plastically worked groove using a punching punch and die. By forming a plastically worked groove that becomes a punched outline of a predetermined shape on the surface of an alloy foil, the punching load is reduced and tool life is improved.

[0005] Furthermore, when punching amorphous alloy foil, multiple sheets of alloy foil are sometimes stacked to ensure productivity, but as the number of layers increases, the punching load increases and the quality of the punched material also decreases. Japanese Patent Application Laid-Open No. 2023-8048 (Patent Document 2) discloses a punching method for punching amorphous electromagnetic steel sheets using a die and punch, in which an elastic coating is applied to the amorphous electromagnetic steel sheets before punching to reduce the punching load. By applying an elastic coating between the alloy foils in this laminated material, the punching load is suppressed and tool wear is reduced.

[0006] There have also been attempts to devise the shape of punching tools. Japanese Patent No. 7129048 (Patent Document 3) discloses a shearing method for amorphous alloy foils, in which a punch used to punch multiple laminated amorphous alloy foils is provided with a first edge formed on the punch tip surface and a second edge formed on the punch side surface, and the horizontal distance from the first edge to the punch side surface and the vertical distance from the second edge to the punch tip surface are set to predetermined distances. The tip of the punching tool is shaped in a predetermined shape so that when punching multiple laminated amorphous alloy foils, a product with no cracks and high dimensional stability can be obtained.

[0007] JP 2021-130131 A JP 2023-8048 A Patent No. 7129048

[0008] However, the manufacturing method of Patent Document 1 requires the pre-forming of a plastically processed groove that will become a punched outline of a predetermined shape, which requires a special processing tool and increases the number of steps. Furthermore, the punching method of Patent Document 2 requires the step of producing a laminated material in which an elastic coating is applied between alloy foils. The shearing method of Patent Document 3 requires the tip of the punching tool to be shaped to a predetermined shape, which limits the flexibility of processing.

[0009] As described above, studies have been conducted on the processing of amorphous alloy foils and the shapes of punching tools, but no studies have been conducted on cemented carbide alloys that are suitable as materials for tools that continuously punch out high-hardness, high-strength metal foils (single layer or multi-layered foils) into a predetermined shape.

[0010] SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a cemented carbide tool suitable for continuously punching out a high-hardness, high-strength metal foil (single layer or multi-layer laminate) into a predetermined shape.

[0011] The present invention relates to a cemented carbide that is optimal for punching tools for punching high-hardness, high-strength metal foils (single layer or multi-layer laminates), such as amorphous alloy foils. In order to solve the above-mentioned problems, the present invention conducted a detailed investigation into the wear and damage patterns of punching tools for amorphous alloy foils and attempted to improve them.

[0012] The most important point is that when punching amorphous alloy foils, the hardness and wear resistance of the cemented carbide used in the punching tool are not necessarily proportional. Until now, the wear resistance of punching tools has been discussed in terms of the hardness of the tool material. In other words, to improve the wear resistance of punching tools, a cemented carbide with high hardness is selected, but this also reduces toughness and chipping resistance. In this study, we focused on the fact that the wear caused by adhesion of the alloy foil to the punching tool when punching amorphous alloy foils is highly dependent on the WC phase grain size of the cemented carbide used in the punching tool, and that punching tools made of cemented carbide with finer WC phase grains tend to have better wear resistance.

[0013] When punching conventional metal foils with a thickness of about 250 μm, such as electromagnetic steel sheets, using lubricating oil, the amount of workpiece material that adheres to the punching tool is small. As a result, the stress when the adhered material is pulled off during punching is also small, and the larger the WC grain size, the better the supporting force of the binder phase. Therefore, when comparing cemented carbides with the same hardness but different WC grain sizes, cemented carbides with a relatively larger WC phase grain size have better wear resistance and do not shed particles.

[0014] On the other hand, if lubricating oil is used when punching amorphous alloy foil with a thickness of approximately 10 to 100 μm, core adhesive lamination cannot be performed. On the other hand, if amorphous alloy foil is punched without using lubricating oil, a large amount of material adheres to the punching tool from the workpiece. Because amorphous alloys are hard and strong, the stress when the adhered material is peeled off is very large. Therefore, even WC phases with large particle sizes and high support strength by the binder phase fall off due to the stress when the adhered material is peeled off, causing wear on the punching tool.

[0015] Based on the above findings, the inventors conducted extensive research and found that cemented carbide with a smaller WC phase grain size loses less volume when the metal foil falls off, resulting in a smaller total volume loss (i.e., wear loss) due to repeated shedding. That is, when punching high-hardness, high-strength metal foils (single-layer or multi-layer laminates), cemented carbide with a smaller WC grain size has lower wear resistance, even when compared with cemented carbide with comparable hardness. As a result, the inventors discovered that by using an ultrafine-grain cemented carbide with a small WC grain size, which has a higher hardness within the range in which the punching tool does not chip under specified punching conditions, for a punching tool, superior wear resistance and chipping resistance can be achieved compared to conventional cemented carbide punching tools.

[0016] That is, one embodiment of the present invention provides a cemented carbide tool for punching, which comprises a WC phase and a binder phase containing Co, wherein an average grain size of the WC phase is X μm and a total amount of the binder phase, Y mass %, satisfies the following formulas (1), (2), and (3): X≦1.2 ... (1) 2≦Y ... (2) −6.7X+6≦Y≦−14X+38 ... (3), and wherein the tool contains 2 to 20 mass % of Cr and / or V, calculated as carbides, relative to the total amount of the binder phase.

[0017] The total amount Y mass % of the binder phase preferably satisfies the following formula (4): −7X+12≦Y (4), and more preferably satisfies the following formulas (5) and (6): X≦0.9 (5) −11X+22≦Y (6).

[0018] In the cemented carbide tool according to one embodiment of the present invention, the total amount Y mass % of the binder phase preferably satisfies the following formulas (7) and (8): X≦0.7 (7) −6.7X+9.1≦Y (8).

[0019] In one embodiment of the present invention, the cemented carbide tool preferably contains at least one element selected from the group consisting of Groups 4 to 6 of the periodic table other than Cr and V, the total content of the elements being 0.2 to 5 mass% in terms of carbides, and the cemented carbide tool preferably contains a compound phase made of carbides and / or carbonitrides of the elements, the particle size of which is 0.02 to 2 μm.

[0020] In the cemented carbide tool according to one embodiment of the present invention, the binder phase preferably contains at least one of Ni and Fe.

[0021] Such a cemented carbide tool can be suitably used as a tool for punching metal foil having a thickness of 10 to 100 μm and a hardness of 700 HV or more, and the metal foil is preferably an amorphous alloy foil.

[0022] In the cemented carbide tool according to one embodiment of the present invention, after a punching test is conducted 500 times or more on a laminated material made of five layers of amorphous alloy foil, each having a thickness of 25 μm and a hardness of 900 HV, with a clearance of 5% t and without lubrication, the surface roughness Ra of the cutting edge is preferably 0.1 μm or less.

[0023] The cemented carbide tool according to one embodiment of the present invention is preferably coated with a hard coating.

[0024] According to the present invention, a cemented carbide tool suitable for continuously punching out a high-hardness, high-strength metal foil (single layer or multi-layer laminate) into a predetermined shape can be obtained.

[0025] FIG. 2 is a schematic diagram showing the measurement positions of the line roughness Ra of the worn portion.

[0026] A cemented carbide tool for punching according to one embodiment of the present invention comprises a WC phase and a binder phase containing Co, wherein an average grain size of the WC phase is X μm and a total amount of the binder phase is Y mass % and satisfies the following formulas (1), (2), and (3): X≦1.2 ... (1) 2≦Y ... (2) −6.7X+6≦Y≦−14X+38 ... (3), and wherein the tool contains 2 to 20 mass % of Cr and / or V, calculated as carbides, relative to the total amount of the binder phase.

[0027] The average grain size X of the WC phase is 1.2 μm or less. The average grain size X of the WC phase is determined by the Fullman equation based on the structure of an arbitrary cross section of the cemented carbide. If the average grain size X of the WC phase exceeds 1.2 μm, the WC phase is likely to wear away when punching a high-hardness, high-strength metal foil (single layer or multi-layer laminate), making it difficult to obtain sufficient wear resistance for a punching tool. The average grain size X of the hard phase is preferably 0.9 μm or less, more preferably 0.7 μm or less, even more preferably 0.6 μm or less, and particularly preferably 0.4 μm or less.

[0028] The total amount Y (mass%) of the binder phase is 2 or more and satisfies the following formula (3): -6.7X+6≦Y≦-14X+38 (3). Here, the total amount Y of the binder phase means the sum of the components added as binder phase components in the binder phase, and does not include components that are solid-solved after being added as other components. If the total amount Y of the binder phase (mass%) is less than 2 or less than -6.7X+6, the toughness of the cemented carbide decreases, and the chipping resistance of the punching tool decreases. If the total amount Y of the binder phase (mass%) is more than -14X+38, the hardness of the cemented carbide is insufficient, and the wear resistance of the punching tool decreases. The total amount Y (mass%) of the binder phase is preferably at least −6.7X + 9.1, more preferably at least −6.7X + 9.6, even more preferably at least −6.7X + 10.1, even more preferably at least −7X + 12, and particularly preferably at least −11X + 22.

[0029] The binder phase preferably contains at least one of Ni and Fe in addition to the main component Co. At least one of Ni and Fe may be contained in 30 mass% of the total amount of the binder phase, and 20 mass% can further enhance the advantages without degrading the properties. Components that can be used as binder phases, such as Al and Cu, may also be contained. These components correspond to the components added as binder phase components described above. Furthermore, metal elements that constitute the hard phase can be solid-dissolved in the binder phase of cemented carbide. When components other than Co are contained as binder phase components as described above, Co is preferably contained in an amount of 70 mass% or more, more preferably 80 mass% or more, of the total amount of the binder phase.

[0030] The cemented carbide of the present invention contains 2 to 20 mass% Cr and / or V, calculated as carbide, relative to the binder phase. Adding 2 to 20 mass% Cr, calculated as carbide, inhibits WC grain growth during sintering and improves corrosion resistance. Adding 2 to 20 mass% V, calculated as carbide, provides an even greater grain growth inhibition effect than Cr. The amount of Cr and / or V added is preferably 3 to 18 mass%, more preferably 4 to 15 mass%, calculated as carbide.

[0031] It may contain at least one element selected from the group consisting of Groups 4 to 6 of the periodic table other than Cr and V. The total content of the above elements is preferably 0.2 to 5 mass% in terms of carbide. The total content of the above elements is more preferably 0.5 to 4 mass%, and even more preferably 1 to 3 mass%, in terms of carbide. These components can also be dissolved in the binder phase.

[0032] It preferably contains a compound phase consisting of carbides and / or carbonitrides of the above elements, with the particle size of the compound phase being 0.02 to 2 μm. The compound phase may be composed of a plurality of compounds present alone or may form a solid solution phase. Examples of the solid solution phase include (Ta, Nb)C, (W, Ti)C, (W, Cr, Ti)C, (W, Ti)CN, and (W, Ti, Nb)C. The particle size of the compound phase is more preferably 0.05 to 1 μm.

[0033] A cemented carbide tool according to one embodiment of the present invention emphasizes improved chipping resistance and preferably satisfies the following formula (4): −7X+12≦Y (4) By reducing the WC phase grain size of the cemented carbide and increasing the amount of the binder phase mainly composed of Co, chipping is less likely to occur at the cutting edge even when continuously punching high-hardness, high-strength metal foil (single layer or multi-layer laminate) into a predetermined shape, and a more suitable cemented carbide metal foil punching tool can be obtained.

[0034] To further improve chipping resistance and wear resistance over conventional products, the cemented carbide tool according to one embodiment of the present invention more preferably satisfies the following formulas (5) and (6): X≦0.9 (5) −11X+22≦Y (6). Such a cemented carbide tool is particularly suitable for punching multiple laminated metal foils with high hardness and strength, and is less likely to chip at the cutting edge even when the punching load increases, thereby suppressing wear at the cutting edge of the punching tool. In other words, it is advantageous when punching under high load conditions or with a tool with a shape that is prone to chipping.

[0035] Furthermore, a cemented carbide tool according to one embodiment of the present invention emphasizes improved wear resistance while ensuring sufficient chipping resistance, and preferably satisfies the following formulas (7) and (8): X≦0.7 (7) -6.7X+9.1≦Y (8). Wear resistance can be further improved by reducing the WC phase grain size of the cemented carbide to 0.7 μm. A WC phase grain size of 0.6 μm or less is more preferable for superior wear resistance, and 0.4 μm or less is even more preferable. Furthermore, if the average grain size of the WC phase, X μm, and the total amount of the binder phase, Y mass%, satisfy the relationship -6.7X+9.6≦Y, the cutting edge of the punching tool is less likely to chip, enabling stable machining, which is more preferable, and -6.7X+10.1≦Y is even more preferable.

[0036] The surface of the cemented carbide tool according to one embodiment of the present invention may be coated with a hard film depending on the application, thereby extending the tool life. The method for applying the hard film is not particularly limited, and known coating methods such as DLC, PVD, and CVD can be used.

[0037] Furthermore, the surface of the cemented carbide tool according to one embodiment of the present invention can be treated by shot peening, laser peening, etc. Any commonly used method can be used for shot peening and laser peening.

[0038] An example of a method for manufacturing a cemented carbide tool of the present invention is described below. However, the method for manufacturing a cemented carbide tool of the present invention is not limited to the following, and any ordinary method for manufacturing cemented carbide tools, such as metal foil punching tools, can be applied. Raw material powders are wet-mixed in a ball mill or the like and then dried to prepare a molding powder that will serve as the raw material for cemented carbide. The molding powder is molded by a method such as die molding or cold isostatic pressing (CIP). The resulting molded body is sintered in a vacuum or inert atmosphere at a temperature above the liquid phase appearance temperature. The liquid phase appearance temperature of the molded body is the temperature at which a liquid phase appears during the sintering temperature rise process and is measured using a differential thermal analyzer. The upper limit of the sintering temperature is preferably the liquid phase appearance temperature + 100°C or less. The resulting sintered body may further be subjected to HIP treatment.

[0039] The cemented carbide tool of the present invention can be used to continuously punch high-hardness, high-strength metal foils, such as amorphous alloy foils, into predetermined shapes. The cemented carbide tool of the present invention is effective for workpieces with a hardness of approximately 200 HV or higher, more effective for workpieces with a hardness of 500 HV or higher, and even more effective for workpieces with a hardness of 700 HV or higher. The thickness of the workpiece is not particularly limited; for example, it can be applied to general metal sheets with a thickness of 100 to 500 μm, such as electromagnetic steel sheets. However, it is suitable for metal foils with a thickness of approximately 10 to 100 μm, and particularly suitable for metal foils with a thickness of approximately 25 to 50 μm. Depending on the workpiece's workability, punching can be performed in single or multilayer form, and the punching method can be optimized. It is particularly suitable for punching amorphous alloy foils without the use of lubricating oil. Furthermore, wear on the punching tool can be reduced even when punching multiple layers of high-hardness, high-strength metal foils, such as amorphous alloy foils, stacked together. Therefore, the metal foil punching tool of the present invention can be suitably used when punching a plurality of laminated amorphous alloy foils without using lubricating oil.

[0040] When the WC phase of the cemented carbide alloy falls off the wear surface of a cemented carbide tool, the area becomes depressed, and the sharp corners of the WC particles tend to protrude from the surrounding area, increasing the roughness of the wear surface. As a result, the friction force between the workpiece and the wear surface during punching also increases, making the wear surface more susceptible to wear. In other words, it was found that the wear surface of a cemented carbide tool with small wear surface roughness experiences less friction with the workpiece during punching and is less susceptible to wear.

[0041] Specifically, after a punching test of 500 or more times with a 5% clearance and no lubrication on a laminate consisting of five 25 μm-thick, 900 HV-hardness amorphous alloy foils, the surface roughness Ra of the cutting edge is preferably 0.1 μm or less. Here, the measurement method for the surface roughness Ra of the cutting edge is explained using Figure 1. The surface roughness Ra of the cutting edge refers to the linear roughness Ra measured in the direction perpendicular to the punching direction at a position A / 2 from the tool end face, where the worn portion is the side surface around the cutting edge of the cemented carbide tool after the punching test, as shown in Figure 1(1). The distance from the tool end face to the edge of the worn portion (the length perpendicular to the tool end face) is defined as A. The cutoff λc is 8 μm, and the rest of the measurement conforms to JIS B 0601. If it is difficult to measure by avoiding adhered materials, the surface roughness Ra of the cutting edge may be measured at a position between A / 8 and A / 2 from the tool end face.

[0042] Furthermore, if the cutting edge has been subjected to C-surface machining (Fig. 1(2)) or R-machining (Fig. 1(3)), the line roughness Ra (cut-off λc is 8μm, and the rest conforms to JIS B 0601) in the direction perpendicular to the punching direction at the worn part position (positions indicated by arrows in Fig. 1(2) and Fig. 1(3)) corresponding to the boundary between the machined part and the side part shall be used. If it is difficult to measure by avoiding adhered matter, or if the cutting edge has been machined but the boundary between the machined part and the side part is not clear, follow the measurement position for the tool in Fig. 1(1).

[0043] The line roughness Ra is preferably measured at three or more locations over a measurement length of 258 μm or more, avoiding or removing any adhered material, so that the total measurement length is 1,000 μm or more. To facilitate measurement while avoiding adhered material, the A / 2 position is preferably located at a position 10 μm or more from the tool end face. After the punching test, the surface roughness Ra of the cutting edge is preferably 0.06 μm or less, and even more preferably 0.04 μm or less.

[0044] The metal foil punching tool of the present invention exhibits superior wear resistance and chipping resistance when punching using a lubricating oil. It also exhibits excellent performance with laminated materials such as those disclosed in Patent Document 2. It can exhibit excellent performance not only with amorphous alloys but also with nanocrystalline alloys, and even better performance when punching ordinary electromagnetic steel sheets. Furthermore, it can be used not only for punching motor cores, but also for punching foils and thin plates used in various applications.

[0045] In the following examples, performance evaluations were carried out using tools manufactured by grinding, demonstrating that the cemented carbide tool of the present invention exhibits excellent performance under various punching conditions. Note that punching tools with complex shapes may be manufactured by electrical discharge machining. In this case, for example, if the tool is made of a cemented carbide alloy that emphasizes improved chipping resistance, defects that occur during electrical discharge machining, which can lead to chipping during punching, can be minimized, thereby demonstrating excellent tool performance.

[0046] The present invention will be described in more detail with reference to inventive products, but the present invention is not limited thereto.

[0047] Example 1: WC powder (0.07-1.4 μm), Co powder (1.3 μm), Ni powder (2.5 μm), VC powder (2.2 μm), TaC powder (1.2 μm), Cr3C2 powder (2.3 μm), and Mo2C powder (3.4 μm) with different particle sizes were used as raw material powders, which were blended according to the composition shown in Table 1, wet mixed, and dried to obtain a mixed powder. This mixed powder was pressure-molded, vacuum sintered at 1320-1400°C, and then subjected to HIP treatment to produce a sintered body (cemented carbide).

[0048]

[0049] The WC phase grain size, binder phase amount, transverse rupture strength, and Vickers hardness of the cemented carbide alloys of invention products 1 to 15 and comparison products 1 to 5 were determined by the following methods. The results are shown in Table 2.

[0050] (WC Phase Grain Size) The average grain size X of the WC phase in the cemented carbide alloys of invention products 1 to 15 and comparison products 1 to 5 was determined by Fullman's formula based on the structure of an arbitrary cross section of the cemented carbide alloy.

[0051] (Binder Phase Amount) The binder phase amount Y of the cemented carbide alloys of the invention products 1 to 15 and the comparative products 1 to 5 was determined as a mass ratio of the blend composition.

[0052] (Transverse Rupture Strength) The transverse rupture strength (MPa) of the cemented carbide alloys of invention products 1 to 15 and comparison products 1 to 5 was determined by transverse rupture strength measurement (three-point bending test) according to the method of JIS B4104.

[0053] (Vickers Hardness) The Vickers hardness (HV) of the cemented carbide alloys of the invention products 1 to 15 and the comparative products 1 to 5 was measured using a Vickers hardness tester HV30.

[0054]

[0055] Punching tools with a 5 mm square shape were fabricated by grinding using the cemented carbide alloys of Invention Products 1 to 15 and Comparative Products 1 to 4. Corresponding dies were also fabricated using cemented carbide (WC-1.0%Cr3C2-15Co, WC phase grain size 1.4 μm). Using these punching tools, punching tests were conducted on amorphous alloy foil (25 μm thick). Because tool life trends vary depending on the punching conditions, punching tests were conducted under the following two conditions (Test A and Test B). Note that Comparative Product 5 had a low binder phase content (Y) of 1 mass%, which resulted in the formation of pores, so a punching test was not conducted. (1) Test A: A single-layer amorphous alloy foil (25 μm thick, hardness 900 HV) was punched with a clearance of 10% t and without lubrication. (2) Test B: Five of the above amorphous alloy foils were simply stacked (total thickness 125 μm) and punched with a clearance of 5% t and without lubrication.

[0056] After the test, the cutting edge of each punching tool was observed and evaluated for wear resistance and chipping resistance. The wear resistance was evaluated as ◯ for small wear, △ for some wear but still usable, and × for large wear. The chipping resistance was evaluated as ◯ for no chipping or breakage, △ for small chipping, and × for relatively large breakage. The results are shown in Table 3.

[0057]

[0058] (1) Regarding Test A: Comparative Samples 1 and 2 had poor wear resistance because the WC phase grain size was larger than 1.2 μm. Comparative Sample 3 had a WC phase grain size smaller than 1.2 μm, but the binder phase content was 27% by mass, which was high relative to the WC phase grain size, resulting in very low hardness and poor wear resistance. Comparative Sample 4 had a WC phase grain size of 0.25 μm, but the binder phase content was 39% by mass, which was high relative to the WC phase grain size, resulting in very low hardness and poor wear resistance. Invention Samples 1 to 5 and 14 experienced minor chipping due to their high hardness, but this was not a problem for use. Furthermore, because the WC phase grain size was smaller than 1.2 μm and the hardness was high, the wear resistance was excellent. Invention Samples 6 to 9, 11, and 12 had a moderate hardness, so no chipping or chipping was observed, and because the WC phase grain size was smaller than 1.2 μm, they also had excellent wear resistance. Invention samples 10 and 13 had relatively low hardness due to the WC phase grain size of 1.0 μm and 0.90 μm, respectively, close to 1.2 μm, so they were worn to some extent but still usable. Invention sample 15 had a small WC phase grain size of 0.25 μm, but a large binder phase content of 34 mass%, so they were relatively low hardness, so they were worn to some extent but still usable.

[0059] (2) Regarding Test B: Comparative Sample 1 experienced minor chipping due to its high hardness, but this was not a problem for use. Furthermore, its WC phase grain size was larger than 1.2 μm, resulting in poor wear resistance. Comparative Sample 2 showed no chipping or chipping, but its WC phase grain size was larger than 1.2 μm and its hardness was low, resulting in poor wear resistance. Comparative Sample 3 had a WC phase grain size smaller than 1.2 μm, but the binder phase content was high at 27% by mass relative to the WC phase grain size, resulting in very low hardness and poor wear resistance. Comparative Sample 4 had a small WC phase grain size of 0.25 μm, but the binder phase content was high at 39% by mass relative to the WC phase grain size, resulting in very low hardness and poor wear resistance. Invention Samples 1 to 4 and 14 experienced large chipping early in the punching process due to their excessive hardness. Furthermore, because they became unusable early, quantitative comparison of wear amounts was not possible. Invention products 5 and 6 had excellent wear resistance because the WC phase grain size was smaller than 1.2 μm, but large chips occurred because the hardness was too high. Invention products 7, 8, and 10 had high hardness, so minor chipping occurred, but this was not a problem for use. They also wore to a certain extent, but were usable. Invention product 9 had a small WC phase grain size of 0.24 μm, so they also had excellent wear resistance. They also wore to a certain extent, but this was not a problem for use. Invention products 11 to 13 and 15 had low hardness, so they wore to a certain extent, but were usable.

[0060] Example 2 In punching test B performed in Example 1, the surface roughness Ra of each worn portion of the cutting edge was measured after 500 shots and 1000 shots for Invention Products 5, 7, and 9, and Comparative Product 2. The measurement positions were the line roughness at the predetermined positions described above, and measurements were taken at four locations over a measurement length of 258 μm using a laser microscope OLS4100 (manufactured by Olympus Corporation), avoiding adhered material or after removing the adhered material. A cutoff λc of 8 μm was used, and values ​​calculated in accordance with JIS B 0601 for other areas were averaged. The results are shown in Table 4.

[0061]

[0062] Invention product 5 had a surface roughness Ra of 0.1 μm or less on the punch cutting edge and a high hardness of HV1530, so it had excellent wear resistance. Invention product 7 had some wear on the surface roughness of the punch cutting edge, but was still usable. Invention product 9 had excellent wear resistance because the surface roughness Ra of the punch cutting edge was very small. Comparison product 2 had a surface roughness Ra of more than 0.1 μm on the punch cutting edge, so it had poor wear resistance.

Claims

1. A cemented carbide tool for punching, comprising a WC phase and a binder phase containing Co, wherein the average grain size of the WC phase is X μm and the total amount of the binder phase is Y mass % and satisfies the following formulas (1), (2), and (3): X≦1.2 ... (1) 2≦Y ... (2) -6.7X+6≦Y≦-14X+38 ... (3), and wherein the cemented carbide tool contains 2 to 20 mass % of Cr and / or V, calculated as carbides, relative to the total amount of the binder phase.

2. The cemented carbide tool according to claim 1, characterized in that the total amount Y mass % of the binder phase satisfies the following formula (4): -7X+12≦Y (4).

3. The cemented carbide tool according to claim 2, characterized in that the total amount Y mass % of the binder phase satisfies the following formulas (5) and (6): X≦0.9 ... (5) -11X+22≦Y ... (6).

4. The cemented carbide tool according to claim 1, characterized in that the total amount Y of the binder phase (mass %) satisfies the following formulas (7) and (8): X≦0.7 (7) -6.7X+9.1≦Y (8).

5. A cemented carbide tool according to any one of claims 1 to 4, characterized in that it contains at least one element selected from the group consisting of Groups 4 to 6 of the periodic table other than Cr and V, and the total content of said elements is 0.2 to 5 mass% in terms of carbide.

6. A cemented carbide tool according to any one of claims 1 to 5, characterized in that the binder phase contains at least one of Ni and Fe.

7. The cemented carbide tool according to any one of claims 1 to 6, characterized in that it is a tool for punching metal foil having a thickness of 10 to 100 µm and a hardness of 700 HV or more.

8. The cemented carbide tool according to any one of claims 7 to 8, wherein the metal foil is an amorphous alloy foil.

9. A cemented carbide tool according to any one of claims 1 to 8, characterized in that after a punching test is conducted 500 times or more on a laminated material made of five layers of amorphous alloy foil, each having a thickness of 25 µm and a hardness of 900 HV, with a clearance of 5% t and without lubrication, the surface roughness Ra of the cutting edge is 0.1 µm or less.

10. The cemented carbide tool according to any one of claims 1 to 9, characterized in that it is coated with a hard coating.

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