Shearing die and manufacturing method for the same

Abstract

To provide a shearing die having a hard coating on a surface thereof, in which the hard coating is excellent in durability and the hard coating can still be suppressed from peeling off even when high-strength materials such as high tensile strength steel are subjected to shearing.SOLUTION: In a shearing die, a surface of a base material of a die is coated with a hard coating made of at least one selected from Ti-system nitride, carbide and carbonitride. A film thickness of the hard coating is 2 μm or more. In the base material of the die, 0.2% proof stress determined in a compression test is 2300 MPa or more, and a Charpy impact value at 23°C is 10 J / cm2 or more. With respect to a complex having the hard coating formed on the base material of the die, when Vickers hardness HV0.5 specified in JISZ2244-1 is defined as composite hardness, the composite hardness is 900 HV0.5 or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a shearing die and a method for manufacturing the same. [Background technology]

[0002] Dies used in plastic processing such as forging and press working have traditionally been made of cold die steel, hot die steel, high-speed tool steel, cemented carbide, etc. as their base material. Plastic processing is classified as cold processing, which is processing performed at around room temperature, and warm or hot processing, which is processing performed at temperatures above 400°C. In these plastic processing processes, adhesive wear between the die surface and the workpiece becomes a problem for dies made of any steel material. Therefore, wear resistance is required for the friction surface of the die. In particular, as the strength of workpiece materials increases, even greater wear resistance is required for dies.

[0003] In recent years, with the advancement of surface modification technology, there has been an increase in the use of molds with improved wear resistance by forming a hard coating on the mold surface. Methods for applying hard coatings include CVD (chemical vapor deposition), PVD (physical vapor deposition), TRD (thermal reactive deposition diffusion), and PCVD (plasma chemical vapor deposition). PVD and PCVD in particular are widely used because they require application temperatures of 500°C or less, resulting in minimal dimensional change in the mold and eliminating the need for heat treatment after coating.

[0004] For example, Patent Document 1 discloses a coated die for shearing, which has a hard coating made of AlCrSi nitride on the surface of the die substrate. This die has a hard coating thickness of 0.3 μm to 2.0 μm, and the ratio of the hard coating thickness on the edge of the die to the hard coating thickness on the flat surface of the die is 0.60 to 1.40. The die of Patent Document 1 is said to enable high-precision shearing of thin, high-hardness materials and to provide excellent durability. Furthermore, Patent Document 2 discloses a die for punching electromagnetic soft iron, which is made of a sintered member mainly composed of WC and contains 6% or less by mass of Co, and has a hard coating on its surface containing Al, Cr, and N. The die of Patent Document 2 is said to prevent adhesion of electromagnetic soft iron to the die surface during punching, thereby suppressing die wear due to adhesion. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2022-117438 [Patent Document 2] Patent No. 6878999 Summary of the Invention [Problem to be solved by the invention]

[0006] On the other hand, high-strength steel sheets, such as high-tensile steel, are becoming more common in order to reduce the weight of automobiles and improve collision safety. When processing these high-strength steel sheets, the load on the dies increases, resulting in a shorter die life. Therefore, even for dies used to process high-strength steel sheets, hard coatings are often formed on the surface to improve wear resistance. However, when the workpiece material is high-strength, such as high-tensile steel, premature peeling occurs even when a hard coating is formed, preventing the die from achieving sufficient life.

[0007] Therefore, the present application aims to provide a shearing die having a hard coating on its surface, which prevents peeling of the hard coating even when high-strength materials such as high-tensile steel are sheared, and which has excellent durability of the hard coating. [Means for solving the problem]

[0008] The means for solving the above problems are as follows.

[0009] (1) A shearing die in which a hard coating of at least one of a Ti-based nitride, a Ti-based carbide, and a Ti-based carbonitride is coated on the surface of the die substrate, The hard coating has a thickness of 2 μm or more, The mold substrate has a 0.2% yield strength of 2300 MPa or more in a compression test and a Charpy impact value of 10 J / cm at 23°C. 2 That's all, A shearing mold characterized in that, when the Vickers hardness HV0.5 specified in JIS Z 2244-1 is defined as the composite hardness of a composite in which the hard coating is formed on the mold substrate, the composite hardness is 900 HV0.5 or more.

[0010] (2) The die for shearing according to (1) above, wherein the hard coating is TiN.

[0011] (3) The shearing die according to (1) above, wherein the die substrate is any one of cold die steel, hot die steel, high-speed tool steel, and powder high-speed tool steel.

[0012] (4) The shearing die according to (1), characterized in that the Charpy impact value is a Charpy impact value measured using a test piece made from the die base material, the test piece having a width of 10 mm, a height of 10 mm, and a length of 55 mm, and having an arc-shaped C-shaped notch at the center with a radius of 10 mm and a depth of 2 mm.

[0013] (5) The shearing die according to (1) above, wherein the hard coating is a PVD coating formed by a PVD method.

[0014] (6) A method for manufacturing a shearing die in which a hard coating is coated on the surface of a die substrate, comprising: The 0.2% yield strength in the compression test is 2300 MPa or more, and the Charpy impact value at 23°C is 10 J / cm 2 On the mold substrate as described above, the hard coating formed of at least one of a Ti-based nitride, a Ti-based carbide, and a Ti-based carbonitride is formed to a thickness of 2 μm or more, A method for manufacturing a mold for shearing, characterized in that, when the Vickers hardness HV0.5 specified in JIS Z 2244-1 is defined as the composite hardness of a composite in which the hard coating is formed on the mold substrate, the composite hardness is set to 900 HV0.5 or more.

[0015] (7) The method for manufacturing a die for shearing according to (6) above, wherein the hard coating is made of TiN.

[0016] (8) The method for manufacturing a die for shearing according to (6) above, wherein the die substrate is any one of cold die steel, hot die steel, high-speed tool steel, and powder high-speed tool steel.

[0017] (9) The method for manufacturing a mold for shear processing according to (6) above, characterized in that the Charpy impact value is a Charpy impact value measured using a test piece made from the mold base material, which is 10 mm wide, 10 mm high, and 55 mm long, and has an arc-shaped C-shaped notch at the center with a radius of 10 mm and a depth of 2 mm.

[0018] (10) The method for manufacturing a die for shearing processing according to (6) above, wherein the hard coating is formed by a PVD method. [Effects of the Invention]

[0019] In a shearing die having a hard coating on its surface, peeling of the hard coating is suppressed even when high-strength materials such as high-tensile steel are sheared, making it possible to provide a shearing die having a hard coating with excellent durability. [Brief explanation of the drawings]

[0020] [Figure 1] FIG. 1 is a diagram showing the shape and dimensions of a test piece for a Charpy impact test. [Figure 2] FIG. 2 is a schematic diagram showing a method for measuring composite hardness. DETAILED DESCRIPTION OF THE INVENTION

[0021] A shearing die (hereinafter simply referred to as "die") of this embodiment will be described. The die of this embodiment is a shearing die that requires wear resistance. The die of this embodiment is used for, for example, press working, forging, etc. The die of this embodiment has a die substrate and a hard coating.

[0022] (About mold substrate) The mold substrate of the mold of this embodiment will be described. The mold substrate of this embodiment preferably has a 0.2% yield strength in a compression test (hereinafter also referred to as "0.2% compressive yield strength") of 2300 MPa or more. Having a 0.2% compressive yield strength of 2300 MPa or more of the mold substrate makes the tool surface less likely to be dented, and can suppress peeling of the hard coating. For the same reason, the 0.2% compressive yield strength is preferably 2400 MPa or more, and more preferably 2500 MPa or more. The upper limit of the 0.2% compressive yield strength is not particularly limited, but can be set to 3800 MPa or less. The 0.2% compressive yield strength of this embodiment is the 0.2% compressive yield strength measured by a compression test using a compression testing machine based on the standard ASTM-E9-19 (Standard Test Method for Compression Tests of Metallic Materials at Room Temperature). Details of the measurement conditions will be explained in the test method of the examples.

[0023] The mold substrate has a Charpy impact value of 10 J / cm at room temperature (23°C). 2 It is recommended that the Charpy impact value is 10J / cm or more.2 By satisfying this condition, the desired toughness can be ensured, and chipping of the hard coating and cracking of the mold can be suppressed. Furthermore, the Charpy impact value is 10 J / cm or more. 2 Ensuring a Charpy impact value of 15J / cm or more has the effect of suppressing the progression of adhesion after chipping has occurred. 2 It is preferable that the temperature is 20 J / cm or more. 2 The upper limit of the Charpy impact value is not particularly limited, but is preferably 100 J / cm 2 The following can be used. The Charpy impact value in this embodiment is measured by a Charpy impact test. For the Charpy impact test, a test piece shown in FIG. 1 is prepared from a mold substrate (steel material) that does not contain a hard coating and used for measurement. This test piece has dimensions of 10 mm width, 10 mm height, and 55 mm length. The test piece has an arc-shaped C-notch in the center with a radius of 10 mm (10R) and a depth of 2 mm. Details of the measurement conditions will be explained in the test method in the examples.

[0024] The steel material constituting the mold substrate is preferably a high-strength tool steel. In particular, it is preferable to use a steel material that undergoes secondary hardening during tempering. Examples of steel materials that undergo secondary hardening during tempering include cold die steel, hot die steel, high-speed tool steel, and powder high-speed tool steel. By using these steel materials, softening of the substrate during coating application can be suppressed. Furthermore, it is preferable to use a tool steel with higher toughness as the steel material for the mold substrate. This is because cracking and chipping of the mold can be further suppressed.

[0025] Die steel is an alloy containing chromium, manganese, molybdenum, vanadium, etc. When used in dies and molds, die steel can be hardened by quenching and tempering. Die steel is a material with good hardness and wear resistance, little quench distortion, and excellent toughness. Cold die steel contains more carbon than hot die steel, and is more likely to lose hardness when heated than hot die steel.

[0026] High-speed tool steel is a steel material used for cutting tools and general-purpose tools, and is also called high-speed steel. High-speed tool steel may be powdered high-speed steel (powdered high-speed tool steel) or molten high-speed steel. Powdered high-speed steel is formed by sintering powdered material under pressure. Powdered high-speed steel has excellent toughness and wear resistance. Molten high-speed steel is formed by rolling material melted in an electric furnace. Molten high-speed steel has excellent wear resistance and cost.

[0027] Among these tool steels, the use of tool steels with high toughness can suppress die cracking and chipping. From this perspective, it is preferable to use cold die steels that are mainly composed of Fe and contain 0.9 mass% or less of C and 9 mass% or less of Cr. Such cold die steels have excellent toughness due to their low primary carbide content. It is more preferable that the C content of such cold die steels be 0.6 mass% or more and the Cr content be 5 mass% or more. It is preferable to use powder high-speed steels (powdered high-speed tool steels) that are mainly composed of Fe and contain 1.0 to 1.3 mass% of C and 9 mass% or less of Cr. Such powder high-speed steels have excellent toughness due to their small primary carbide size of 1 μm to 2 μm. It is more preferable that the Cr content of such powder high-speed steels be 3.5 mass% or more.

[0028] (Hard coating) Next, the hard coating will be described. The hard coating is formed on the surface of the mold. The hard coating needs to be formed at least on the portion of the entire mold that comes into contact with the workpiece during shearing, but it may also be formed on other portions, or on the entire mold. In order to achieve the desired composite hardness of the mold described below, the film thickness of the hard coating should be 2 μm or more, and preferably 3 μm or more.

[0029] The hard coating can be formed of at least one of Ti-based nitrides, carbides, and carbonitrides. The hardness of the material constituting the hard coating is preferably 1000 HV or more in Vickers hardness. TiN is preferred as the material for such hard coatings, as it contains fewer droplets.

[0030] The composite hardness of a mold provided with the above hard coating is preferably 900 HV0.5 or more in Vickers hardness. In this embodiment, the composite hardness refers to the Vickers hardness HV0.5 of the composite consisting of the hard coating and the mold substrate. Specifically, the composite hardness is the Vickers hardness measured when a hardness test is conducted on the surface of the mold substrate on which the hard coating is formed under load conditions (test load 500 gf (4.903 N)) in accordance with the hardness symbol HV0.5 specified in JIS Z 2244-1. Details of the measurement method will be explained in the test method of the examples. The composite hardness is an index that indicates the resistance of the mold surface to dents; the higher the hardness, the more resistant the mold surface to dents. A composite hardness of 900 HV0.5 or more makes the mold surface less dented, and peeling of the hard coating can be suppressed. For the same reason, the composite hardness is preferably 950 HV0.5 or more, and more preferably 1000 HV0.5 or more.

[0031] (Method for manufacturing a die for shearing) A method for manufacturing a shearing die will now be described. First, a die substrate is prepared. Steel material, which has been annealed as necessary, is processed (roughly processed) to form a die of the desired shape. The formed die is then heat-treated as necessary. Heat treatment can be carried out under appropriate conditions depending on the type of steel material. For example, quenching and tempering can be performed as heat treatment. After heat treatment, finish processing can be carried out as necessary. The die substrate is prepared by heat treatment or the like so that the above-mentioned 0.2% compressive yield strength and Charpy impact value meet the specified standards.

[0032] Next, a hard coating is formed on the prepared mold substrate. The hard coating is formed to a thickness of 2 μm or more. The method for forming the hard coating is not particularly limited. For example, CVD (chemical vapor deposition), PVD (physical vapor deposition), TRD (thermal reactive deposition diffusion), and PCVD (plasma chemical vapor deposition) can be used. Of these, PVD and PCVD require the mold to be heated to a temperature of 500°C or less during film formation. Therefore, PVD and PCVD are preferred because they minimize dimensional change in the mold and eliminate the need for heat treatment after film formation. PVD methods include vacuum deposition, sputtering, and ion plating. Ion plating is preferred from the perspective of the wide range of applicable materials and mold dimensional accuracy. From the perspectives of dimensional accuracy and hardness, a treatment temperature of 500°C or less is preferred. For each film formation method, a hard coating of Ti-based nitride, carbide, or carbonitride can be formed on the mold substrate using a known method. For example, in the case of ion plating, if the ion plating process is carried out using Ti as the target and nitrogen gas as the reactive gas, a hard coating of TiN can be formed.

[0033] By forming a hard coating on the mold substrate as described above, the composite hardness of the mold, which is a composite of the hard coating and mold substrate, is set to 900 HV0.5 or more. By manufacturing a mold substrate using the above-mentioned steel material so that the compressive 0.2% proof stress and Charpy impact value satisfy the above-mentioned conditions and forming a hard coating using the above-mentioned method, a mold with a composite hardness of 900 HV0.5 or more can be obtained. This completes the method for manufacturing a shearing mold of this embodiment.

[0034] According to the above-described embodiment, a shearing die having excellent durability and suppressing peeling of the hard coating can be provided. The inventors of the present application discovered that chipping (fracture) of the hard coating during shearing of high-strength materials causes adhesion of the workpiece, resulting in peeling of the hard coating. In response to this, by using a die substrate that satisfies the above-described predetermined conditions for 0.2% compressive yield strength and Charpy impact value, forming a predetermined hard coating, and forming a die having a predetermined composite hardness, chipping of the hard coating can be effectively suppressed. By suppressing chipping, adhesion originating from the chipped portion with the workpiece is suppressed, thereby suppressing adhesive wear. As a result, peeling of the hard coating can be effectively suppressed. Therefore, according to the present embodiment, a shearing die having excellent durability and suppressing peeling of the hard coating can be provided. [Example]

[0035] Examples are provided to explain the embodiments in more detail. Test specimens and dies (punches) were prepared as follows for the steels Nos. 1 to 5 (cold die steel, high-speed tool steel, and powder high-speed tool steel) shown in Table 1. A steel similar to SKD11 was used for the cold die steels Nos. 1 to 3, SKH51 for the high-speed tool steel No. 4, and a steel similar to SKH40 for the powder high-speed tool steel No. 5. First, rough machining was performed using annealed steels to prepare rough-machined specimens for the test specimens and die substrates. These rough-machined specimens were then heat-treated. For the cold die steels (Samples Nos. 1 to 3), the cold die steels were air-quenched at 1030°C to 1050°C and tempered at 500°C to 600°C. For the high-speed tool steel (Sample No. 4), the steels were quenched at 1200°C and tempered at 560°C. The powder high-speed tool steel (sample No. 5) was salt bath quenched at 1180 to 1200°C and tempered at temperatures of 560 to 600°C. The test pieces after the above heat treatment (test pieces before hard coating formation) were subjected to the compression test and Charpy impact test described below.

[0036] Furthermore, a 3 μm-thick TiN hard coating was formed on the heat-treated test pieces and die substrate by the PVD method (ion plating). The test pieces and die with the hard coating were subjected to a composite hardness measurement test, a hard coating chipping resistance evaluation test, and a die evaluation test, which will be described later. The shape and dimensions of the test pieces used for each test are shown in the explanation of the test methods below.

[0037] (Compression test) A compression test was performed on the test piece before the hard coating was formed under the following conditions to measure the 0.2% compressive yield strength. Two test pieces were prepared and the measurement was carried out twice, and the average value was taken as the 0.2% compressive yield strength of the test piece. -Standard: ASTM-E9-19 - Testing machine: Universal testing machine - Test piece dimensions: φ6 x 12 mm (round bar test piece) - Strain measurement: strain gauge -Temperature: 23℃±5 - Initial strain rate: 4.5 x 10 -4 s -1 - Number of measurements: 2

[0038] (Charpy impact test) The test specimens were subjected to a Charpy impact test under the conditions shown below to measure the Charpy impact values. Test specimens having the shape shown in Figure 1 were prepared and the test was carried out. - Testing machine capacity: 300J - Test piece dimensions: 10 x 10 x 55 mm, 10 mm R-C 2 mm notch -Temperature: 23℃±5

[0039] (Composite hardness measurement test) The composite hardness of the die (punch surface) on which the hard coating was formed was measured at room temperature (23°C ± 5°C) using a micro Vickers hardness tester (FM-700, manufactured by Future Tech Co., Ltd.). As shown in the schematic diagram in Figure 2, the test was performed by pressing an indenter into the surface of the die on which the hard coating was formed with a test load of 500 gf (HV0.5). The average value of five tests was calculated as the composite hardness of the test piece.

[0040] (Hard coating chipping resistance evaluation test) To evaluate the chipping resistance of hard coatings, scratch tests were conducted on test specimens (plate-shaped test specimens measuring 22 × 50 × 6 mm) coated with hard coatings. In the scratch test, a diamond indenter was pressed against the test specimen, and the indenter was moved relative to the test specimen while increasing the load, scratching the coating surface. The applied load (critical load) at which peeling of the coating occurred was measured. The chipping resistance of the coating was evaluated based on the measured critical load. A CSR1000 tester (manufactured by Rhesca Corporation) was used. The test was performed with an indenter radius of 200 μm, an initial load of 5 N, a final load of 155 N, and an indenter scanning speed of 10 mm / min. Delamination was detected by measuring the sound of the coating breaking with an acoustic emission (AE) sensor. The critical load was defined as the load at which the AE sensor's count rate reached 50 counts / s or higher. A higher critical load indicates less chipping and therefore higher chipping resistance. In this way, by evaluating the critical load using AE, it is possible to evaluate chipping strength.

[0041] (Mold evaluation test) The produced die was used as a punch to press a steel plate (workpiece), and the occurrence of peeling of the hard coating was evaluated. The test conditions were as follows: - Press machine: 80t crank press - Punching speed: 50 shots / min - Number of shots: 500 shots - Steel plate: 1.2GPa high tensile strength, plate thickness 1.6mm - Punching diameter: φ20mm - Ratio of clearance between punch and die to steel plate thickness: Clearance / steel plate thickness x 100 = 3% - Lubrication: No lubrication - Punch material: Molds for the examples and comparative examples - Die material: Commercially available cold die steel - Punch surface roughness: Ra≦0.05μm - Damage area evaluation: The entire circumference of the cutting edge of the punch (die) was checked under a microscope at 50x magnification, and the total area of ​​the part where the coating had peeled off was measured. -Microscope used to measure the damage area: Keyence VHX-7000 - Damage area judgment criteria: (damage area) <10mm 2 :◎, (damage area)<11mm 2 :〇, 11mm 2 ≦(damage area): × The criteria are 11mm 2 In the above cases, the tool life will be shortened. 2 If it is less than 10mm, it is passed (○). 2 Cases where the value was less than this were marked as ◎.

[0042] The steel types used in the examples and comparative examples and the test results are shown in Table 1 below.

[0043] [Table 1]

[0044] All of Samples Nos. 2, 3, and 5 met the standards set forth in the embodiments for 0.2% compressive yield strength, Charpy impact value, and composite hardness HV0.5. The test examples of Samples Nos. 3 and 5 had higher critical loads than the comparative examples, superior chipping resistance of the hard coating, and smaller damaged areas. Among the test examples using the same cold die steel substrate, the test example of Sample No. 2 had a higher critical load and a smaller damaged area than Comparative Example 1, confirming its superior chipping resistance. When observing the test specimens after the scratch test and the punch surfaces after the die evaluation test, chipping of the coating was observed in all of Samples Nos. 1-5. However, the punches of Samples Nos. 2, 3, and 5, which met the standards set forth in the embodiments, tended to have less chipping than Samples Nos. 1 and 4.

[0045] For sample No. 1, the 0.2% compressive yield strength of the mold substrate was less than 2300 MPa, indicating low strength. Consequently, the composite hardness was also less than 900 HV0.5. As a result, the damage area in the mold evaluation test was also larger than the standard. For sample No. 4, the 0.2% compressive yield strength and composite hardness of the mold substrate met the standards, and the critical load value was also higher than that of sample No. 1. However, the Charpy impact value did not meet the standard. As a result, it is presumed that the occurrence of chipping itself was suppressed to a certain extent, but the insufficient Charpy impact value did not sufficiently suppress the progression of adhesion after chipping occurred, and the damage area in the final mold evaluation test was larger than the standard.

Claims

1. A shearing die having a die substrate surface coated with a hard coating of at least one of a Ti-based nitride, a Ti-based carbide, and a Ti-based carbonitride, The hard coating has a thickness of 2 μm or more, The mold base material has a 0.2% yield strength of 2300 MPa or more in a compression test and a Charpy impact value of 10 J / cm at 23°C. ２ That's all, A shearing die characterized in that, when a Vickers hardness HV0.5 defined in JIS Z 2244-1 of a composite in which the hard coating is formed on the die substrate is defined as composite hardness, the composite hardness is 900 HV0.5 or more.

2. 2. The shearing die according to claim 1, wherein the hard coating is made of TiN.

3. 2. The shearing die according to claim 1, wherein the die substrate is any one of cold die steel, hot die steel, high-speed tool steel, and powder high-speed tool steel.

4. 2. The shearing mold according to claim 1, wherein the Charpy impact value is a Charpy impact value measured using a test piece made from the mold base material, the test piece having a width of 10 mm, a height of 10 mm, and a length of 55 mm, and having an arc-shaped C-shaped notch at the center with a radius of 10 mm and a depth of 2 mm.

5. 2. The shearing die according to claim 1, wherein the hard coating is a PVD coating formed by a PVD method.

6. A method for manufacturing a shearing mold in which a hard coating is coated on the surface of a mold base material, comprising: The 0.2% yield strength in the compression test is 2300 MPa or more, and the Charpy impact value at 23°C is 10 J / cm ２ On the mold substrate as described above, the hard coating formed of at least one of a Ti-based nitride, a Ti-based carbide, and a Ti-based carbonitride is formed to a thickness of 2 μm or more, A method for manufacturing a shearing mold, characterized in that, when a Vickers hardness HV0.5 specified in JIS Z 2244-1 is defined as the composite hardness of a composite in which the hard coating is formed on the mold substrate, the composite hardness is 900 HV0.5 or more.

7. 7. The method for manufacturing a die for shearing processing according to claim 6, wherein the hard coating is made of TiN.

8. 7. The method for manufacturing a die for shearing according to claim 6, wherein the die substrate is any one of cold die steel, hot die steel, high-speed tool steel, and powder high-speed tool steel.

9. 7. The method for manufacturing a die for shearing processing according to claim 6, wherein the Charpy impact value is a Charpy impact value measured using a test piece made from the die base material, the test piece having a width of 10 mm, a height of 10 mm, and a length of 55 mm, and having an arc-shaped C-shaped notch at the center with a radius of 10 mm and a depth of 2 mm.

10. 7. The method for manufacturing a die for shearing processing according to claim 6, wherein the hard coating is formed by a physical vapor deposition method.

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