Hard coating for rolling tools, rolling tools, and method for forming coatings on rolling tools

Abstract

To provide a hard coating suitable for a rolling tool with an improved abrasion resistance in rolling processing for an alloy steel object to be processed such as a chromium-molybdenum steel, a rolling tool with the hard coating coated, and a film deposition method for the rolling tool.SOLUTION: A first layer as a hard coating with a composition represented by AlaTibN (0.66≤a≤0.67, 0.33≤b≤0.34, where a and b represent an atomic ratio of Al and Ti, respectively) and a second layer as a hard coating with a composition represented by AlcCrdTieSifN (0.48≤c≤0.49, 0.25≤d≤0.26, 0.20≤e≤0.21, 0.04≤f≤0.05, where c, d, e and f represent an atomic ration of Al, Cr, Ti and Si, respectively) are formed. When a diffraction intensity ratio of a (200) plane is I(200) and that of a (111) plane is I(111), a relationship of I(200) / I(111)>6 is satisfied in an X-ray diffraction intensity of the hard coating.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a hard coating applied to the surface of a thread rolling tool such as a tap, a thread rolling tool coated with the hard coating, and a method for forming the coating on the thread rolling tool. [Background technology]

[0002] In recent years, coatings (hard films) for cutting tools have been shifting from conventional TiN and TiCNN to TiAlN and AlCrN films, which prioritize heat resistance.

[0003] Furthermore, it is known that these hard coatings can improve wear resistance by arranging the (111) plane, which has a high atomic density in X-ray diffraction intensity, parallel to the tool material (see Patent Documents 1 and 2).

[0004] On the other hand, for hard coatings used in rolling tools such as taps and forming racks, wear resistance and sliding properties against the workpiece are required. Therefore, the tool surface is not coated with a hard coating (so-called untreated), or the hard coating is mainly formed by nitriding, or by dissolution methods of TiN, TiCN, CrN, etc. (See Patent Documents 3 and 5).

[0005] Furthermore, when hard coatings such as TiAlN or AlCrN are applied to rolling tools such as taps, sputtering methods are used instead of the arc method mainly used for cutting tools, in order to prioritize the smoothness of the hard coating surface (see Patent Document 4). [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Patent No. 3452726 [Patent Document 2] Patent No. 5945950 [Patent Document 3] Japanese Patent Publication No. 2006-68822 [Patent Document 4] Patent No. 5951040 [Patent Document 5] Utility Model Publication No. 3027780 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, while hard coatings such as TiAlN and AlCrN have strong wear resistance in the film thickness direction and the film surface direction, they have the problem that the hard coating will rupture if the usage limit is exceeded. When these hard coatings are applied to cutting tools, even if the hard coating ruptures, only the cutting edge itself will wear down, and the impact on the workpiece material will be relatively small.

[0008] Furthermore, in the case of thread rolling tools, damage to one thread affects other threads, making it difficult to apply hard coatings such as TiAlN and AlCrN to the tool coating. Since arc ion plating is the mainstream method for applying hard coatings such as TiAlN and AlCrN, droplets (clumps of hard coating material) are generated on the surface of the hard coating. These droplets increase the processing load on the workpiece during thread rolling and become the starting point for the hard coating to break down.

[0009] Furthermore, because the threads of thread rolling tools are subjected to repeated loads during the rolling process, high-toughness powder metallurgy high-speed tool steel or low-hardness materials are used, which leads to a decrease in the wear resistance of the thread rolling tools.

[0010] Therefore, the object of the present invention is to provide a hard coating that is optimal for rolling tools, which improves wear resistance even when rolling workpieces made of alloy steel such as chromium-molybdenum steel, a rolling tool coated with the hard coating, and a method for forming a coating on a rolling tool. [Means for solving the problem]

[0011] The hard coating for rolling tools of the present invention is a hard coating consisting of at least two layers that is applied to the surface of a rolling tool material made of high-speed tool steel. The hard coating is made of Al a Ti bA first layer which is a hard film represented by a composition of N(0.66 ≦ a ≦ 0.67, 0.33 ≦ b ≦ 0.34: a and b represent the atomic ratios of Al and Ti), and Al c Cr d Ti e Si f It is formed from a second layer which is a hard film represented by a composition of N(0.48 ≦ c ≦ 0.49, 0.25 ≦ d ≦ 0.26, 0.20 ≦ e ≦ 0.21, 0.04 ≦ f ≦ 0.05: c, d, e, and f represent the atomic ratios of Al, Cr, Ti, and Si).

[0012] Also, regarding the X-ray diffraction intensity of the hard film, when the diffraction intensity ratio of the (200) plane is I(200) and the diffraction intensity ratio of the (111) plane is I(111), the relationship I(200) / I(111) > 6 holds. Regarding the thickness of the hard film, when the thickness of the first layer is t 1、 and the thickness of the second layer is t2, the ratio of the thicknesses is preferably in the range of t1:t2 = 50:50 to 95:5. Furthermore, regarding the forging tool material coated with the hard film, it is preferably a melted high-speed tool steel with a surface hardness of 67 HRC or more on the Rockwell C scale. Note that the thickness t1 of the first layer can also be made larger than the thickness t2 of the second layer (t1 > t2).

[0013] Next, regarding the invention of the forging tool, it can be a forging tap coated with the above-mentioned hard film for forging tools. In that case, regarding the film-forming method of a forging tool made of high-speed tool steel, first, a first polishing step of polishing the surface of the forging tool material made of high-speed tool steel, a film-forming step of coating the surface of the forging tool material with a hard film by arc ion plating using a film-forming apparatus having a target inside after the first polishing step, and finally, a second polishing step of polishing the surface of the hard film after the film-forming step can be formed.

[0014] Regarding the hard film to be coated, Al a Ti b A first layer composed of a hard film represented by a composition of N(0.66 ≦ a ≦ 0.67, 0.33 ≦ b ≦ 0.34: a and b represent the atomic ratios of Al and Ti), and Al c Cr d Tie Si f A second layer made of a hard film having a composition of N (0.48 ≦ c ≦ 0.49, 0.25 ≦ d ≦ 0.26, 0.20 ≦ e ≦ 0.21, 0.04 ≦ f ≦ 0.05: c, d, e, f represent the atomic ratios of Al, Cr, Ti, and Si) can be formed from.

Advantages of the Invention

[0015] The hard film of the present invention is an optimal hard film for forging tools, and has the effect of improving wear resistance even in forging processes for workpieces made of alloy steels such as chromium molybdenum steel.

Brief Description of the Drawings

[0016] [Figure 1] It is the forging test result of Example 1. [Figure 2] It is the forging test result of Example 2. [Figure 3] It is the forging test result of Example 3. [Figure 4] It is the forging test result of Example 4. [Figure 5] It is the forging test result of Example 5. [Figure 6] It is the forging test result of Example 6.

Modes for Carrying Out the Invention

[0017] A hard film for a forging tool (hereinafter referred to as a hard film), which is an embodiment of the present invention, and a forging tool coated with the hard film will be described. First, the hard film is a hard film to be coated on the surface of a forging tool material made of high-speed tool steel such as a broach or a tap. In particular, it is preferable to coat the hard film on the surface of a tap material for forging.

[0018] Regarding the composition of the hard film, as the first layer of the hard film, Al a Ti bA hard coating represented by the composition N (0.66≦a≦0.67, 0.33≦b≦0.34: a and b represent the atomic ratios of Al and Ti), with Al as the second layer of the hard coating. c Cr d Ti e Si f It is formed from a hard coating represented by the composition N(0.48≦c≦0.49,0.25≦d≦0.26,0.20≦e≦0.21,0.04≦f≦0.05: c, d, e, f represent the atomic ratios of Al, Cr, Ti, and Si). That is, the hard coating is laminated in the order of the first layer, then the second layer, from the surface side of the rolling tool material.

[0019] Al is used as the first hard coating on the surface side of the rolling tool material. a Ti b By coating the rolling tool material with a hard coating represented by the composition N (0.66≦a≦0.67, 0.33≦b≦0.34: a and b represent the atomic ratios of Al and Ti), adhesion between the hard coating and the rolling tool material is ensured, while a second hard coating containing Si is applied to the outermost surface of the rolling tool material as Al c Cr d Ti e Si f By coating the workpiece with a hard coating represented by the composition N(0.48≦c≦0.49,0.25≦d≦0.26,0.20≦e≦0.21,0.04≦f≦0.05: c,d,e,f represent the atomic ratios of Al, Cr, Ti, and Si), the hard coating provides both hardness and lubrication between the workpiece and the rolling tool during the rolling process.

[0020] The crystal orientation of the hard coating is defined as I(200) / I(111)>6 based on the X-ray diffraction intensity. In other words, in X-ray diffraction, the peak intensity I(200) from the (200) plane is stronger than the peak I(100) from the (100) plane, and the relationship I(200) / I(111)>6 holds true.

[0021] In X-ray diffraction, by making the peak I(200) from the (200) plane stronger than the peak I(100) from the (100) plane, the orientation of the (100) plane is strengthened, causing the crystal cleavage plane to become parallel to the substrate surface. As a result, damage to the hard coating can be directed in the plane direction of the hard coating rather than in the thickness direction. The crystal structure of this hard coating is presumed to be a cubic NaCl type structure, and the cleavage plane is presumed to be the (100) plane.

[0022] Furthermore, the rolling tool material that covers the hard coating is preferably a melted high-speed tool steel with a surface hardness of 67 HRC or higher on the Rockwell C scale, from the viewpoint of mitigating deformation of the rolling tool during rolling and suppressing the occurrence of fatigue fracture in the hard coating.

[0023] Next, we will explain the method for depositing a hard coating onto a rolling tool material (hereinafter referred to as the "deposition method"). First, this deposition method consists of a first polishing step of polishing the surface of a rolling tool material made of high-speed tool steel, a deposition step of coating the surface of the rolling tool material with a hard coating using the arc ion plating method with a deposition apparatus equipped with a target inside after the first polishing step, and a second polishing step of polishing the surface of the hard coating after the deposition step.

[0024] First, the first polishing process aims to reduce the surface roughness of the rolling tool material by polishing it in the circumferential direction (processing direction) of the rolling tool material before the film formation process in which a hard film is applied to the surface of the rolling tool material, and at the same time, to enable the workpiece to undergo rapid plastic deformation during the rolling process.

[0025] Next, the second polishing process aims to reduce the starting points for damage to the hard film surface by removing droplets that formed on the surface of the hard film during the arc ion plating process through a polishing treatment after the film formation process. [Examples]

[0026] (Example 1) To confirm the effect of the type of hard coating applied to the surface of the thread rolling tool (thread rolling tap) on the thread rolling process, a thread rolling test was conducted, and the test results are explained with reference to the drawings. Figure 1 shows the type of test specimen used in the thread rolling test of this embodiment, the hardness of the base material, and the test results.

[0027] In this embodiment, the thread rolling test involved coating a thread rolling tap (M12×1.75) with various hard coatings and measuring the number of holes that could be rolled under the following thread rolling conditions. • Workpiece material: Chromium molybdenum steel (SCM440H) • Lubricant: Water-soluble cutting fluid ·Processing speed: 10m / min • Effective screw length: 18mm (1.5D) • Pilot hole diameter: 11.2mm

[0028] The hard coatings used in the rolling process tests of this embodiment were three types: TiCN (test specimens 1A to 1C in Figure 1), AlTiN (atomic ratio Al:Ti = 67:33, test specimens 1D to 1H in Figure 1), and AlCrTiSiN (atomic ratio AlCrTiSi = 48:26:21:5, test specimens 1E to 1H in Figure 1). Of these, four types of test specimens were prepared with a thickness ratio of AlTiN hard coating to AlCrTiSiN hard coating of 10:90 (test specimen 4E), 40:60 (test specimen 4F), 50:50 (test specimen 4G), and 90:10 (test specimen 4H).

[0029] Furthermore, as shown in Figure 1, the hard coating of TiCN (test specimens 1A to 1C in Figure 1) was applied to the base material surface of the tap for rolling using the dissolution method, while AlTiN and AlCrTiSiN (test specimens 1D to 1H in Figure 1) were applied using the arc method. The values ​​calculated from the results of X-ray diffraction measurements of each hard coating formed by these coating methods, namely the X-ray diffraction intensity of the hard coating, are also shown in Figure 1, along with the I(200) / I(111) value (hereinafter referred to as the X-ray intensity ratio) when the diffraction intensity ratio of the (200) plane is I(200) and the diffraction intensity ratio of the (111) plane is I(111).

[0030] As shown in Figure 1, the results of this test showed that specimens 1A to 1C, coated only with a hard TiCN film, could be rolled to produce 910 to 1400 holes under the rolling conditions described above. Furthermore, specimens 1D to 1F, coated only with a hard AlTiN film and specimens 1D to 1F, laminated with hard AlTiN and AlCrTiSiN films, could be rolled to produce 1120 to 1680 holes under the rolling conditions described above.

[0031] In contrast, test specimens 4G (where the hard coatings of AlTiN and AlCrTiSiN were laminated together, and the thickness ratio of the AlTiN and AlCrTiSiN coatings was 50:50), and test specimens 1G and 1H (where the ratio was 90:10), were able to roll-form 2061 to 2240 holes under the aforementioned rolling conditions. The number of holes these produced was approximately 1.3 times the number of holes produced in test specimens 1A to 1F.

[0032] (Example 2) Next, similar to Example 1, a rolling test was conducted to confirm the effect of the type of hard coating applied to the surface of the rolling tool (tap for rolling) on ​​the rolling process. The test results will be explained using the drawings. Figure 2 shows the type of test specimen, the hardness of the base material, and the test results used in the rolling test of this example.

[0033] In this embodiment, the thread rolling test was conducted in the same manner as in Embodiment 1, by coating a thread rolling tap (M12 × 1.75) with various hard coatings and measuring the number of holes that could be rolled under the following thread rolling conditions. ·Work material: Carbon steel (S50C) • Lubricant: Water-soluble cutting fluid ·Processing speed: 30m / min • Effective screw length: 18mm (1.5D) • Pilot hole diameter: 11.2mm

[0034] The hard coatings used in the rolling process tests of this embodiment consisted of four types: TiCN (test specimen 2A in Figure 2), AlCrN (test specimen 2B in Figure 2), AlTiN (test specimen 2C in Figure 2), and a composite coating of AlTiN (atomic ratio Al:Ti=67:33) and AlCrTiSiN (atomic ratio AlCrTiSi=48:26:21:5, test specimens 2D and 2E in Figure 2).

[0035] In this context, for the aforementioned composite coatings (test specimens 2D and 2E), test specimens were prepared by distinguishing between a hard coating of AlTiN and a hard coating of AlCrTiSiN, with a thickness ratio of 50:50 for test specimen 2D and 90:10 for test specimen 2E.

[0036] Furthermore, as shown in Figure 2, the hard coating of TiCN (test specimen 2A in Figure 2) was applied to the base material surface of the tap for thread rolling using the dissolution method, while AlCrN, AlTiN, and AlCrTiSiN (test specimens 2B to 2E in Figure 2) were applied using the arc method.

[0037] Figure 2 also shows the values ​​calculated from the results of X-ray diffraction measurements of each hard coating formed by these coating methods, namely the X-ray diffraction intensity of the hard coating, specifically the I(200) / I(111) value (hereinafter referred to as the X-ray intensity ratio) when the diffraction intensity ratio of the (200) plane is I(200) and the diffraction intensity ratio of the (111) plane is I(111).

[0038] As shown in Figure 2, the results of this test show that specimen 2A, coated only with a hard coating of TiCN, specimen 2B, coated only with a hard coating of AlCrN, and specimen 2C, coated only with a hard coating of AlTiN, were able to produce 5091, 4352, and 7934 holes, respectively, under the rolling conditions described above.

[0039] In contrast, test specimens 2D and 2E, which were laminated with the inventive hard coatings of AlTiN and AlCrTiSiN, and with the thickness ratio of the AlTiN hard coating to the AlCrTiSiN hard coating being 50:50 and 90:10 respectively, were able to be rolled to produce 8164 and 9100 holes, respectively, under the aforementioned rolling conditions.

[0040] (Example 3) Next, a rolling test was conducted to confirm the effect of differences in the surface hardness of the base material of the rolling tool (rolling tap) on adhesion to a specific hard coating. The test results will be explained using the drawings. Figure 3 shows the type of test specimen, the hardness of the base material, and the test results used in the rolling test of this embodiment.

[0041] In the rolling process test of this embodiment, the test specimens used were prepared by coating the base material surface of molten high-speed tool steel with two types of hard coatings: AlTiN (atomic ratio Al:Ti = 67:33) and AlCrTiSiN (atomic ratio AlCrTiSi = 48:26:21:5), with the AlTiN hard coating and the AlCrTiSiN hard coating in a ratio of 90:10 in thickness. The molten high-speed tool steel used as the base material for the test specimens consisted of two types: specimen 3A with a surface hardness of 66.8 HRC on the Rockwell C scale and specimen 3B with a surface hardness of 68.5 HRC.

[0042] In this embodiment, the thread rolling test involved coating a thread rolling tap (M6×1) with the aforementioned hard coating and measuring the number of holes that could be rolled under the following thread rolling conditions. ·Work material: Carbon steel (S50C) • Lubricant: Water-soluble cutting fluid ·Processing speed: 30m / min • Effective screw length: 12mm (2D) • Pilot hole diameter: 5.55mm

[0043] As shown in Figure 3, the results of this test show that specimen 3A, whose base material (molded high-speed tool steel) for thread rolling had a surface hardness of 66.8 HRC on the Rockwell C scale, produced 7,525 holes. In contrast, specimen 3B, whose base material (molded high-speed tool steel) for thread rolling had a surface hardness of 68.5 HRC on the Rockwell C scale, produced 10,949 holes, which is approximately 1.5 times the number of holes produced by specimen 3A.

[0044] (Example 4) Next, similar to Example 3, a rolling test was conducted to confirm the effect of differences in surface hardness of the base material of the rolling tool (rolling tap) on adhesion to a specific hard coating. The test results will be explained using the drawings. Figure 4 shows the type of test specimen, the hardness of the base material, and the test results used in the rolling test of this example.

[0045] The hard coatings used on the test specimens in the rolling process test of this embodiment were the same as in Example 3, consisting of two types of hard coatings: AlTiN (atomic ratio Al:Ti = 67:33) and AlCrTiSiN (atomic ratio AlCrTiSi = 48:26:21:5). These coatings were applied to the surface of the base material of the molten high-speed tool steel so that the ratio of the thicknesses of each coating was 90:10. The molten high-speed tool steel used as the base material of the test specimens was also the same as in Example 3, with two types of specimens: specimen 4A with a surface hardness of 66.8 HRC on the Rockwell C scale and specimen 4B with a surface hardness of 68.5 HRC.

[0046] In this embodiment, the thread rolling test involved coating a thread rolling tap (M12×1.75) with the aforementioned hard coating and measuring the number of holes that could be rolled under the following thread rolling conditions. • Workpiece material: Chromium molybdenum steel (SCM440H) • Lubricant: Water-soluble cutting fluid ·Processing speed: 10m / min • Effective screw length: 18mm (1.5D) • Pilot hole diameter: 11.2mm

[0047] As shown in Figure 4, the results of this test show that specimen 4A, whose base material (molded high-speed tool steel) for the thread rolling tap had a surface hardness of 66.8 HRC on the Rockwell C scale, produced 1876 holes. In contrast, specimen 4B, whose base material (molded high-speed tool steel) for the thread rolling tap had a surface hardness of 68.5 HRC on the Rockwell C scale, produced 2774 holes, which is approximately 1.5 times the number of holes produced by specimen 3A.

[0048] (Example 5) Next, a rolling test was conducted to investigate the effect of surface roughness of the base material before and after coating the tool (tap for rolling) with a hard coating on the rolling process. The number of polishing cycles was as follows: the base material surface was polished before coating the tool with the hard coating (1st time), and the surface of the hard coating was polished after coating (2nd time). The test results for this example are shown in Figure 5.

[0049] Furthermore, polishing was classified into rough polishing and finish polishing according to the surface roughness. Before coating, rough polishing was performed when the base material surface had Ra: 0.100~0.130 μm and Rz: 0.500~1.00 μm, and finish polishing was performed when Ra: 0.050~0.100 μm and Rz: 0.100~0.500 μm. After coating, rough polishing was performed when the hard film surface had Ra: 0.100~0.130 μm and Rz: 0.500~2.000 μm, and finish polishing was performed when Ra: 0.0500~0.100 μm and Rz: 0.300~0.500 μm.

[0050] Polishing before coating aims to remove grinding marks from the base material surface and increase surface roughness, thereby reducing the starting point of damage during the rolling process. Polishing after coating removes droplets (small clumps of coating components). If droplets are present on the surface of a hard coating, they can act as spikes during rolling, piercing the workpiece and increasing machining resistance, leading to tool damage. Therefore, removing droplets and increasing surface roughness reduces machining resistance and simultaneously reduces the starting point of damage, thereby improving performance.

[0051] The hard coating used on the test specimens in the rolling process test of this embodiment was the same as in Example 4, using two types of hard coatings: AlTiN (atomic ratio Al:Ti = 67:33) and AlCrTiSiN (atomic ratio AlCrTiSi = 48:26:21:5). The AlTiN hard coating and the AlCrTiSiN hard coating were applied to the surface of the base material of the melted high-speed tool steel so that the ratio of the thicknesses of each was 90:10.

[0052] Furthermore, in the rolling process test in this embodiment, the aforementioned hard coating was applied to a rolling tap (M12×1.75) in the same manner as in Embodiment 4, and the number of holes that could be rolled under the following rolling conditions was measured. • Workpiece material: Chromium molybdenum steel (SCM440H) • Lubricant: Water-soluble cutting fluid ·Processing speed: 10m / min • Effective screw length: 18mm (1.5D) • Pilot hole diameter: 11.2mm

[0053] As shown in Figure 5, the results of this test were that specimens 5A and 5B, which were only roughly polished before the hard coating was applied to the rolling tool material, had 280 and 1607 processed holes, regardless of whether the surface of the hard coating was roughly polished (specimen 5A) or finish polished (specimen 5B) after the hard coating was applied. Furthermore, specimen 5C, which was only roughly polished before the hard coating was applied and then the surface of the hard coating was finish polished after the hard coating was applied, had 1763 processed holes.

[0054] Based on these test results, the number of machined holes in test specimens 5D and 5E, which underwent rough polishing and finish polishing before and after coating with a hard film, was 1820 and 2061, respectively. From these test results, it was found that polishing the surface of the hard film after coating the tool material, and achieving a surface roughness of Ra < 0.1 μm and Rz < 0.6 μm, increases the number of holes that can be machined by rolling.

[0055] (Example 6) Similar to Example 5, a rolling test was conducted to investigate the effect of the surface roughness of the base material on the rolling process before and after coating the rolling tap with a hard coating. The number of polishing cycles was as follows: the surface of the base material was polished before coating the tool with the hard coating (1st time), and the surface of the hard coating was polished after coating (2nd time). The test results for this example are shown in Figure 6.

[0056] Furthermore, polishing was classified into rough polishing and finish polishing according to the surface roughness. Before coating, rough polishing was performed when the base material surface had Ra: 0.100~0.130 μm and Rz: 0.500~1.00 μm, and finish polishing was performed when Ra: 0.050~0.100 μm and Rz: 0.100~0.500 μm. After coating, rough polishing was performed when the hard film surface had Ra: 0.100~0.130 μm and Rz: 0.500~2.000 μm, and finish polishing was performed when Ra: 0.0500~0.100 μm and Rz: 0.300~0.500 μm.

[0057] The hard coating used on the test specimens in the rolling process test of this embodiment was the same as in Example 5, using two types of hard coatings: AlTiN (atomic ratio Al:Ti = 67:33) and AlCrTiSiN (atomic ratio AlCrTiSi = 48:26:21:5). The AlTiN hard coating and the AlCrTiSiN hard coating were applied to the surface of the base material of the melted high-speed tool steel so that the ratio of each thickness was 90:10.

[0058] In this embodiment, the thread rolling test was conducted in the same manner as in Embodiment 5, by coating a thread rolling tap (M12 × 1.75) with the aforementioned hard coating and measuring the number of holes that could be rolled under the following thread rolling conditions. ·Work material: Carbon steel (S50C) • Lubricant: Water-soluble cutting fluid ·Processing speed: 30m / min • Effective screw length: 18mm (1.5D) • Pilot hole diameter: 11.2mm

[0059] As shown in Figure 6, the results of this test were that specimen 6A, which was not polished at all before or after coating the rolling tool material with a hard film, and specimen 6B, which underwent rough polishing and finish polishing before coating with the hard film, both had 0 processed holes. On the other hand, specimen 6C, which underwent only rough polishing before and after coating with the hard film, and specimen 6D, which underwent rough polishing and finish polishing only after coating with the hard film, had 2014 holes and 5040 holes, respectively.

[0060] In contrast to these test results, the number of processed holes in test specimen 6E, which underwent only rough polishing before applying the hard coating and then both rough and finish polishing after applying the hard coating, and in test specimen 6F, which underwent both rough and finish polishing before and after applying the hard coating, were 9100 holes and 10202 holes, respectively. From these test results, it was found that polishing the surface of the hard coating after applying it to the tool material, and achieving a surface roughness of Ra < 0.1 μm and Rz < 0.5 μm, increases the number of holes that can be processed by rolling.

Claims

1. A hard coating consisting of at least two layers that covers the surface of a rolling tool material made of high-speed tool steel, wherein the hard coating is Al ａ Ti ｂ The first layer is a hard coating represented by the composition N (0.66 ≤ a ≤ 0.67, 0.33 ≤ b ≤ 0.34: a and b represent the atomic ratios of Al and Ti), and Al ｃ Cr ｄ Ti ｅ Si ｆ A hard coating for rolling tools, formed from a second layer which is a hard coating represented by the composition N (0.48 ≤ c ≤ 0.49, 0.25 ≤ d ≤ 0.26, 0.20 ≤ e ≤ 0.21, 0.04 ≤ f ≤ 0.05: c, d, e, f represent the atomic ratios of Al, Cr, Ti, and Si), wherein the X-ray diffraction intensity of the hard coating is such that I(200) / I(111) > 6, where I(200) is the diffraction intensity ratio of the (200) plane and I(111) is the diffraction intensity ratio of the (111) plane.

2. The thickness t of the first layer １ and the thickness t of the second layer ２ have a ratio of t １ : t ２ = 50:50 to 95:5, and the hard film for a forging tool according to claim 1 is characterized by this.

3. The hard coating for rolling tools according to claim 1 or 2, characterized in that the rolling tool material is a melted high-speed tool steel with a surface hardness of 67 HRC or higher on the Rockwell C scale.

4. A rolling tool characterized by being coated with a hard coating for rolling tools as described in any one of claims 1 to 3.

5. The rolling tool according to claim 4, characterized in that the rolling tool is a tap for rolling.

6. The process comprises: a first polishing step of polishing the surface of a rolling tool material made of high-speed tool steel; a film deposition step of coating the surface of the rolling tool material with a hard film using an arc ion plating method with a target inside the film deposition apparatus after the first polishing step; and a second polishing step of polishing the surface of the hard film after the film deposition step. The hard coating consists of a first layer made of a hard coating represented by the composition Al a Ti b N (0.66 ≤ a ≤ 0.67, 0.33 ≤ b ≤ 0.34: a and b represent the atomic ratios of Al and Ti), and Al c Cr d Ti e Si f A method for forming a film on a rolling tool, comprising: a second layer made of a hard film represented by the composition N (0.48 ≤ c ≤ 0.49, 0.25 ≤ d ≤ 0.26, 0.20 ≤ e ≤ 0.21, 0.04 ≤ f ≤ 0.05: c, d, e, f represent the atomic ratios of Al, Cr, Ti, and Si), wherein the X-ray diffraction intensity of the hard film is such that I(200) / I(111) > 6, when the diffraction intensity ratio of the (200) plane is represented as I(200) and the diffraction intensity ratio of the (111) plane is represented as I(111).

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