Method for forming grooves on the surface of a metal strip and method for manufacturing a directionally electromagnetic steel sheet

Abstract

A method for forming grooves on the surface of a metal strip, wherein a coating agent for forming a resist film is applied to a roller, the roller is irradiated with a laser while being scanned in the axial direction of the roller or in a direction inclined with respect to the axial direction, the coating agent for forming a resist film on the portion irradiated with the laser is removed, the roller is brought into contact with at least one side of the metal strip, or the roller is brought into contact with a pinch roller so that the pinch roller is brought into contact with at least one side of the metal strip, a non-coated area is set as the portion corresponding to the portion where the coating agent for forming a resist film is removed, the coating agent for forming a resist film is transferred onto at least one side of the metal strip, the coating agent for forming a resist film is dried, a resist film having the non-coated area is formed on at least one side of the metal strip, and an etching process is performed on the non-coated area of the metal strip to form grooves.

Description

Technical Field

[0001] The present disclosure relates to a method for forming grooves on the surface of a metal strip such as a grain-oriented electromagnetic steel sheet for a core or the like used in electrical equipment such as transformers, and a method for manufacturing a grain-oriented electromagnetic steel sheet using the groove forming method. Background Art

[0002] Grain-oriented electromagnetic steel sheets are mainly used as materials for cores inside transformers. In order to improve the energy use efficiency of transformers, it is required to reduce the iron loss of grain-oriented electromagnetic steel sheets. As a technique for reducing the iron loss of grain-oriented electromagnetic steel sheets, a technique for refining the magnetic domain structure by forming irregularities such as grooves on the steel sheet surface can be cited. As a method for forming grooves on the steel sheet surface, a method of pressing a gear-shaped roll against the steel sheet surface, a method of locally melting the base iron of the steel sheet using a laser beam, and a method of forming grooves in the uncoated portion of the steel sheet surface by etching the uncoated portion of the steel sheet surface with chemical etching or electrolytic etching using a resist film are known. Among them, the method using a resist film is an advantageous method for effectively forming deep grooves and has the advantage of having a high magnetic domain refining effect. However, in the method using a resist film, as in other methods, it is an extremely important issue to form grooves with high precision and uniformity.

[0003] In the method of forming grooves using a resist film, as a particularly industrially advantageous method, there is the following technique: a part of the resist film uniformly coated on the steel sheet surface is locally removed by a laser beam, and the steel sheet surface of the portion where the film has been removed is etched by chemical etching or electrolytic etching to form grooves (Patent Document 1). Under appropriately maintained conditions, the laser beam maintains a very uniform beam shape, so very uniform grooves can be formed. On the other hand, as clarified by the present inventors in their research so far, there is a risk in this method that the laser beam irradiated to remove the resist film causes deformation and melting of the base iron, damaging the magnetic properties of the final product sheet. In contrast, Patent Document 2 discloses the following technique: by using a high-output laser (output power of 1.5 kW or more) to remove the resist film in a short time, heat diffusion in the base iron during irradiation is suppressed, and high magnetic properties are obtained.

[0004] Prior Art Documents

[0005] Patent Documents

[0006] Patent Document 1: Japanese Patent No. 6332185 Specification

[0007] Patent Document 2: Japanese Patent No. 6172403 Specification Summary of the Invention

[0008] However, when the flatness of the metal strip is low, it is difficult to form uniform grooves in the width direction by the technique of locally removing a part of the resist film with a laser beam and etching the steel sheet surface of the laser-removed part to form grooves as described above. For example, when the metal strip is a grain-oriented electrical steel sheet, especially in a steel sheet with a high Si content, shape defects such as edge wave shape (edge elongation) and edge cracks are likely to occur at the ends in the width direction (rolling orthogonal direction; TD) of the steel sheet. There is a risk that the resist film remains without being removed due to unfocused laser in such shape defect parts.

[0009] Therefore, an object of the present disclosure is to provide a technique for forming uniform grooves in the width direction of a metal strip even when shape defect parts occur in the metal strip, and further to provide a grain-oriented electrical steel sheet having extremely excellent magnetic properties.

[0010] That is, the main configuration of the present disclosure is as follows.

[0011] [1] A method for forming grooves on the surface of a metal strip, comprising coating a coating agent for forming a resist film on a roller,

[0012] then, irradiating the roller with a laser while scanning the roller in the axial direction of the roller or in a direction inclined with respect to the axial direction, and removing the coating agent for forming a resist film in the part irradiated with the laser,

[0013] then, bringing the roller into contact with at least one side of the metal strip, or bringing the roller into contact with a nip roller clamped between the roller and the metal strip so that the nip roller is in contact with at least one side of the metal strip, setting the part corresponding to the part where the coating agent for forming a resist film has been removed as a non-coated area, and transferring the coating agent for forming a resist film to at least one side of the metal strip,

[0014] then, drying the coating agent for forming a resist film to form a resist film having the non-coated area on at least one side of the metal strip,

[0015] then, performing an etching treatment on the non-coated area of the metal strip to form grooves.

[0016] [2] The method for forming grooves on the surface of a metal strip according to the above [1], wherein the luminance index L* of the resist film in the CIELAB color space (CIE 1976 L*a*b* color space) is 0 to 70, and the output power of the laser is less than 2.0 kW.

[0017] [3] The method for forming grooves on the surface of a metal strip according to the above [1] or [2], wherein the laser has a top hat type intensity distribution.

[0018] [4] A method for producing a grain-oriented electrical steel sheet, comprising hot-rolling a steel billet to produce a hot-rolled steel sheet,

[0019] Next, the hot-rolled steel sheet or the hot-rolled annealed steel sheet obtained by annealing the hot-rolled steel sheet is subjected to cold rolling once or twice or more with intermediate annealing to obtain a cold-rolled steel sheet.

[0020] Next, the cold-rolled steel sheet is subjected to primary recrystallization annealing to obtain a primary recrystallized sheet.

[0021] Next, the primary recrystallized sheet is subjected to secondary recrystallization annealing to obtain a secondary recrystallized sheet.

[0022] A groove is formed on the surface of any of the hot-rolled steel sheets by the groove forming method described in any one of [1] to [3].

[0023] According to the present disclosure, it is possible to provide a technology for forming uniform grooves in the width direction of a metal strip even when a shape defect occurs in the metal strip, and further provide a grain-oriented electromagnetic steel sheet having extremely excellent magnetic properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is a diagram showing the results of forming grooves on the surface of a steel plate using a conventional technique.

[0025] Figure 2 This is a diagram showing the results of investigating the hardness distribution of the steel sheet base iron near the laser irradiation portion under the condition that high magnetic properties cannot be obtained.

[0026] Figure 3 It is a diagram showing a conventional method of transferring a covering agent for forming a resist film.

[0027] Figure 4 It is a diagram showing an example of a method of transferring the covering agent for forming a resist film according to the present disclosure.

[0028] Figure 5 It is a diagram showing an example of a method of transferring the covering agent for forming a resist film according to the present disclosure. DETAILED DESCRIPTION

[0029] First, the experiment that led to the development of the present disclosure is described. It should be noted that in the following description, "%" and "ppm" indicating the content of the component elements of the steel plate refer to "mass %" and "mass ppm" respectively unless otherwise specified. In addition, in this specification, the numerical range expressed by "to" refers to a range that includes the numerical values ​​described before and after "to" as the lower limit and upper limit.

[0030] <Experiment 1>

[0031] First, by the existing method of locally removing a part of the resist film uniformly coated on the surface of the steel sheet with a laser beam and etching the surface of the steel sheet at the part where the resist film has been removed (hereinafter also referred to as the laser removal part), grooves are formed on the surface. First, a cold-rolled steel sheet (C: 0.048%, Mn: 0.10%, P: 0.005%, S: 0.002%, Al: 0.008%, N: 42 ppm, Ti+Nb+V+Zr+Ta<0.001%) for forming grooves is produced. The steel slab with the above composition is subjected to hot rolling to produce a hot-rolled steel sheet. Then, hot-rolled sheet annealing is carried out at 1000°C, and then cold rolling is carried out to obtain a cold-rolled steel sheet with a thickness of 0.22 mm and a width of 1200 mm. The cold-rolled steel sheet is cut in half along the width direction to obtain a cold-rolled steel sheet with a width of 600 mm. In this cold-rolled steel sheet, a shape defect of edge elongation is observed at one end in the width direction on one side. A coating agent for forming a resist film mainly composed of an aqueous alkyd resin is uniformly coated on both the front and back surfaces of the cold-rolled steel sheet to form a resist film. Then, while scanning the cold-rolled steel sheet in a direction crossing the rolling direction, a laser is irradiated to locally remove the resist film. A laser irradiation device with a diameter of 100 μm and an output power of 1.8 kW is used for laser irradiation. Then, the surface of the steel sheet at the laser removal part is etched to form linear grooves on the surface of the cold-rolled steel sheet. The resist films remaining on both the front and back surfaces of the cold-rolled steel sheet are completely removed after etching. An optical microscope is used to measure the groove width of the linear grooves formed on the cold-rolled steel sheet. The results are shown in Figure 1 .

[0032] In Figure 1 , the distribution of the groove width in the width direction (rolling orthogonal direction; TD) of the 600-mm-wide steel sheet is shown. Edge elongation occurs at the width direction position of 560 mm to 600 mm of the steel sheet. Thus, hereinafter, the part where edge elongation exists is also referred to as the edge elongation part. Uniform groove widths are formed at positions without edge elongation up to 540 mm in the width direction, but a part of the resist film (groove width 0 μm in the figure) is not removed at the edge elongation part.

[0033] In order to form uniform grooves in the width direction of the end portion of a metal strip as well, the present inventors conducted in-depth research. First, the present inventors considered that by increasing the output power of the laser, the resist film can be reliably removed even in a portion with poor shape of the metal strip where the focus of the laser is likely to deviate. However, in a laser with high output power, it is difficult to reduce the diameter of the laser. It is known that the narrower the groove width, the better the magnetic properties of a directionally electromagnetic steel sheet in which magnetic domains are refined by forming grooves. In the method of locally removing a part of the resist film uniformly coated by a laser beam, in order to form a narrow groove, it is most effective to reduce the beam diameter for removing the resist film. However, since the beam diameter tends to increase as the output power increases, it is difficult to achieve both high output power of the laser and a narrow groove width. Countermeasures such as increasing the number of laser setting stations and scanning a low-output power laser with a small diameter at a slow speed on the steel sheet to remove the resist film are effective, but on the other hand, other problems such as an increase in equipment cost and maintenance cost cannot be avoided.

[0034] <Experiment 2>

[0035] In addition, the present inventors found that in the existing method of locally removing a part of the resist film uniformly coated on the surface of a steel sheet by a laser beam and etching the surface of the steel sheet in the laser removal portion, when using a high-output power laser to form grooves on the surface of the steel sheet, depending on the type of the resist film, high magnetic properties may not be obtained sometimes.

[0036] Under the condition of not obtaining high magnetic properties, the hardness distribution of matrix iron on the surface of the steel sheet near the laser irradiation part was investigated. First, a flat cold-rolled steel sheet with a width of 500 mm for laser irradiation was fabricated (C: 0.048%, Mn: 0.10%, P: 0.005%, S: 0.002%, Al: 0.008%, N: 42 ppm, Ti + Nb + V + Zr + Ta < 0.001%). The steel billet with the above composition was hot-rolled to obtain a hot-rolled steel sheet. Then, the hot-rolled steel sheet was annealed at 1050 °C, and then cold-rolled to obtain a cold-rolled steel sheet with a thickness of 0.22 mm. An anti-corrosion coating agent for forming an anti-corrosion film was uniformly coated on both sides of the cold-rolled steel sheet using an intaglio roller to form an anti-corrosion film. As the anti-corrosion coating agent for forming the anti-corrosion film, a coating agent mainly composed of an aqueous alkyd resin was used. Then, while scanning in the transverse direction (TD) orthogonal to the rolling direction of the cold-rolled steel sheet, laser was irradiated to locally remove the anti-corrosion film. Here, for laser irradiation, a laser irradiation device with a diameter of 80 μm and an output power of 1.8 kW was used. Then, the surface of the steel sheet in the laser removal part was etched to form linear grooves on the surface of the cold-rolled steel sheet. Then, the anti-corrosion films remaining on both sides of the steel sheet were removed. After removing the anti-corrosion film, the hardness of the matrix iron on the surface of the steel sheet near the laser irradiation part was measured. The hardness was measured using micro-Vickers hardness. Each point in the figure is the average value of 15 measurement points. The reference of the hardness is the value at the position 1 mm away from the laser irradiation part in the rolling direction (RD) (laser non-irradiation part). The ratio of the hardness change of the matrix iron at each measurement point to the hardness value of the laser non-irradiation part was investigated. It should be noted that the measurement of the hardness of the matrix iron was carried out after sampling the plate before etching and completely removing the anti-corrosion films on both sides of the steel sheet. The results are shown in Figure 2 . The RD position in the figure represents the position of the rolling direction (RD) with the laser irradiation center on the steel sheet as the origin at the central part in the width direction of the steel sheet. It can be seen from this figure that a significant hardness reduction was observed on the surface of the steel sheet in the laser irradiation part. It is considered that through high-output power laser irradiation, the matrix iron is heated, the rolling structure is restored, and the hardness is reduced.

[0037] Next, for the cold-rolled steel sheet with the above-mentioned linear grooves formed and the cold-rolled steel sheet without linear grooves sampled from the cold-rolled steel sheet before forming the above-mentioned linear grooves as its comparison material, a primary recrystallization annealing with decarburization annealing was respectively carried out at 860 °C to obtain primary recrystallized plates. Then, the primary recrystallized plates were subjected to secondary recrystallization annealing at a maximum temperature of 1200 °C to obtain secondary recrystallized plates. Furthermore, for the cold-rolled steel sheet without grooves, after secondary recrystallization annealing, linear grooves were formed on the surface of the steel sheet under the same conditions of high-output power laser as above. Then, after annealing the two steel sheets for the purpose of flattening and forming an insulating tension film, the iron loss (W 17 / 50) As a result, it can be seen that the iron loss of the grooved steel sheet formed on the cold-rolled steel sheet is 0.005 W / kg higher than that of the grooved steel sheet formed on the secondary recrystallization annealed sheet. Here, the iron loss of each steel sheet is measured according to the evaluation method of "iron loss in the central part in the width direction" described later. Based on these results, the inventors of the present invention believe that the tissue change corresponding to the above hardness reduction has a certain influence on the deterioration of the magnetic properties of the grain-oriented electrical steel sheet.

[0038] Furthermore, the inventors of the present invention considered that in order to remove the resist film equally in the shape defective part of the metal strip as in the shape good part, after applying the coating agent for forming the resist film, the shape defective part of the metal strip is mechanically crushed and corrected using a special jig to make it flat. However, when mechanically correcting the shape of the shape defective part, there is a risk of wear of the resist film. Therefore, the inventors of the present invention have conducted in-depth research on the method of uniformly forming a resist pattern for forming a groove in the width direction at the coating stage of the coating agent for forming the resist film. Moreover, the inventors of the present invention came up with the following configuration: by irradiating a laser on the roller coated with the coating agent for forming the resist film, a resist pattern having a part where the coating agent for forming the resist film has been removed by the laser (hereinafter also referred to as the laser removal part) is formed on the roller surface, and the roller is brought into contact with the steel sheet to transfer the resist pattern from the roller to the steel sheet. Then, the following idea was completed: according to this configuration, no thermal influence such as hardness reduction is generated on the metal strip, a good resist pattern can be formed also in the shape defective part of the metal strip, and further, a uniform groove can be formed in the width direction of the metal strip.

[0039] At the coating stage of the coating agent for forming the resist film, as a method of forming a resist pattern for forming a groove, there is known a method of coating the coating agent for forming the resist film in a pattern on an intaglio roller and transferring the coating agent for forming the resist film on the surface of the intaglio roller to the surface of the metal strip by intaglio offset printing. However, it is described in the known documents such as Patent Document 2 above that it is difficult to uniformly form a groove by this method. As Figure 3 shown, in intaglio offset printing, the transfer of the coating agent 10 for forming the resist film from the intaglio roller 20 to the surface of the metal strip 50 conveyed in the conveying direction A is carried out via the offset roller 21. At this time, the shape of the coating agent 10 for forming the resist film transferred to the surface of the offset roller 21 is as Figure 3 shown, and becomes a convex bowl shape facing the outside of the offset roller 21. As a result, if the coating agent 10 for forming the resist film is transferred to the surface of the metal strip 50, there is a risk that the resist pattern on the surface of the metal strip 50 becomes uneven.

[0040] In contrast, in the present disclosure, as Figure 4As shown, a laser irradiation device 40 or the like irradiates a laser on a roller 30 uniformly coated with a coating agent 10 for forming a resist film, forming a resist pattern having a laser removal portion 60 of the coating agent 10 for forming a resist film from which the laser irradiation portion has been removed, and transferring the formed resist pattern from the surface of the roller 30 to the surface of a metal strip 50 conveyed in the conveying direction A. Thus, the resist pattern can be transferred from the surface of the roller 30 to the surface of the metal strip 50 before the shape of the coating agent 10 for forming a resist film changes, and a uniform resist pattern can be formed.

[0041] Hereinafter, the best mode of the present disclosure will be described. It should be noted that the present disclosure is not limited to the following embodiments. The groove forming method according to this embodiment is a method of forming a groove on the surface of a metal strip as follows:

[0042] Coat a coating agent for forming a resist film on a roller;

[0043] Next, while scanning the above roller in the axial direction of the roller or a direction inclined with respect to the axial direction, irradiate a laser to remove the coating agent for forming a resist film in the portion irradiated with the laser;

[0044] Next, bring the above roller into contact with at least one side surface of the metal strip, or bring the above roller into contact with a nip roller clamped between the above roller and the above metal strip so that the nip roller is in contact with at least one side surface of the above metal strip, and set the portion corresponding to the portion from which the coating agent for forming a resist film has been removed as an uncoated area, and transfer the coating agent for forming a resist film to at least one side surface of the above metal strip;

[0045] Next, dry the coating agent for forming a resist film to form a resist film having the above uncoated area on at least one side surface of the metal strip;

[0046] Next, perform an etching process on the uncoated area of the metal strip to form a groove.

[0047] As described below, a coating agent 10 for forming a resist film is coated on the surface of the metal strip 50. First, the coating agent 10 for forming a resist film is uniformly coated on the roller 30 by a method such as bringing the roller 30 into contact with the inside of a container filled with the coating agent 10 for forming a resist film. It should be noted that as Figure 4As shown, the resist film forming coating agent 10 can also be applied to the other roller 22, and then the other roller 22 is brought into contact with the roller 30, whereby the resist film forming coating agent 10 is applied to the roller 30. The details of the resist film forming coating agent 10 will be described later. When using the other roller 22, gravure cells can be formed on the other roller 22 in the same manner as in the existing gravure offset printing method. However, in order to coat the coating agent 10 more evenly on the roller 30, it is more preferable not to form gravure cells on the other roller 22. In addition, gravure cells can be formed on the roller 30. However, when no gravure cells are formed, even when the roller 30 is brought into contact with the metal strip 50 as in the past, there is no need to consider the change in the cell shape due to the wear of the roller 30. Therefore, instead of using the method of transferring the resist film forming coating agent 10 on the surface of one roller (the gravure roller 20 in the gravure offset printing method) to another roller (the offset roller 21 in the gravure offset printing method) and transferring the resist film forming coating agent 10 to the surface of the metal strip through the other roller as in the existing gravure offset printing method, a method can be used in which the resist film forming coating agent 10 attached to one roller 30 is transferred to the surface of the metal strip 50 without passing through the other roller.

[0048] As described later, in order to form linear grooves extending in a direction crossing the rolling direction of the metal strip 50, a laser is irradiated while scanning in the axial direction of the roller 30 or in a direction inclined with respect to the axial direction, and a resist pattern of the resist film forming coating agent 10 having a laser removal portion 60 is formed on the roller 30 along the axial direction of the roller 30 or in a direction inclined with respect to the axial direction. When the laser is scanned in a direction inclined with respect to the axial direction of the roller 30, the direction of the scanned laser is preferably within 45° with respect to the axial direction of the roller 30 corresponding to the direction orthogonal to the rolling direction (TD) of the metal strip 50. By making the direction of the scanned laser within 45° with respect to the axial direction of the roller 30, through the etching process described later, grooves having an angle of 45° or less with respect to the direction orthogonal to the rolling direction (TD) of the metal strip 50 can be formed. Therefore, in the case where the metal strip is a directional electromagnetic steel sheet, the magnetic domain structure can be appropriately refined and the iron loss can be reduced. In addition, in order to form the grooves with high precision, it is preferable to control the beam scanning in synchronization with the rotation of the roller 30. When a polygon mirror is used for laser deflection, it is preferable to synchronize the rotation of the polygon mirror with the rotation of the roller. The laser conditions will be described later. The laser is preferably irradiated at a position close to the position where the roller 30 contacts the surface of the metal strip 50. By irradiating the laser at a position close to the position where the roller 30 contacts the surface of the metal strip 50, even when the viscosity of the resist film forming coating agent 10 is low, after forming a pattern on the resist film forming coating agent 10 using the laser, an even resist pattern can be formed even when the shape of the resist film forming coating agent 10 is likely to change due to surface tension and gravity.

[0049] After forming a resist pattern of the resist film forming coating agent 10 having the laser removal portion 60 on the roller 30, the roller 30 is brought into contact with one or both sides of the metal strip 50, and the coating agent 10 for forming the resist film on the surface of the roller 30 is transferred (coated) onto one or both sides of the metal strip. The laser removal portion 60 on the roller 30 corresponds to the non-coated region 70 on the metal strip 50. In one example, as Figure 4 shown, the roller 30 is rotated while being in contact with the metal strip 50 conveyed in the conveying direction A. At this time, it is preferable to adjust the amount of the coating agent 10 for forming the resist film on the roller by a doctor blade or the like, or to adjust the pressing pressure of the roller 30 so that the film thickness of the resist film becomes uniform within the surface of the metal strip 50.

[0050] In addition to the method of directly bringing the roller 30 on which the resist pattern is formed into contact with the surface of the metal strip 50 as described above, it is also possible to, as Figure 5 shown, bring the roller 30 into contact with the holding roller 31 (such as the existing offset roller 21 etc.) held between the roller 30 and the metal strip, transfer the coating agent 10 for forming the resist film which is uniformly attached to the roller 30 and has a pattern to the holding roller 31, and then bring the holding roller 31 into contact with the surface of the metal strip 50 to further transfer the coating agent 10 for forming the resist film transferred from the roller 30 to the holding roller 31 to the surface of the metal strip 50. In this case, the coating agent 10 for forming the resist film remains in a uniform state and is transferred from the roller 30 to the holding roller 31. Therefore, it is possible to prevent the coating agent 10 for forming the resist film from becoming a convex bowl shape as in the existing method of transferring the coating agent accumulated in the gravure cell to the offset roller. Thus, by transferring the coating agent 10 for forming the resist film to the surface of the metal strip 50 via the holding roller 31, the viscosity of the coating agent 10 for forming the resist film can be increased, and in addition, the amount of attachment of the coating agent 10 for forming the resist film can be adjusted. It should be noted that the number of the holding rollers 31 held between the roller 30 and the metal strip 50 is not particularly limited. For example, after bringing the roller 30 into contact with the holding roller 31 and transferring the coating agent 10 for forming the resist film to the holding roller 31, the holding roller 31 may be further brought into contact with a second holding roller (not shown) held between the holding roller 31 and the metal strip 50 to transfer the coating agent 10 for forming the resist film to the second holding roller. Then, the second holding roller may be brought into contact with the surface of the metal strip 50 to further transfer the coating agent 10 for forming the resist film transferred to the second holding roller to the surface of the metal strip 50.

[0051] The resist film 10 is preferably formed on the front and back surfaces of the metal strip 50, but the resist pattern having the non-coated region 70 for forming the groove as described above may be formed on at least one side of the metal strip 50.

[0052] Since heat accumulates in the roller 30 due to laser irradiation, it is preferable that the roller 30 is always cooled. The roller 30 is preferably made of a metal with a high thermal conductivity to prevent heat accumulation.

[0053] After transferring the coating agent 10 for forming a resist film onto the surface of the metal strip 50, the coating agent 10 for forming a resist film is dried before the etching treatment described below to form a resist film on the surface of the metal strip 50. For the drying of the coating agent 50 for forming a resist film, the drying temperature is preferably 180 to 300 °C, but the drying method is not particularly limited. For example, the coating agent 50 for forming a resist film can be dried by blowing hot air or the like. Next, by subjecting the metal strip 10 to an etching treatment, the portion of the surface of the metal strip that is not covered with the resist film is etched. The etching can be performed by either chemical etching or electrolytic etching. In the case of electrolytic etching, it is preferable that the electrolytic solution is an aqueous solution of NaCl or KCl. After the etching treatment, the resist film is removed from the surface of the metal strip 50, whereby a metal strip with grooves formed thereon is obtained. The removal of the resist film is preferably carried out using an alkali or an organic solvent.

[0054] The grooves formed on the surface of the metal strip 50 are linear grooves extending in a direction crossing the rolling direction of the metal strip 50. The shape of the grooves can be adjusted by adjusting the resist pattern on the roll 30. Here, in the case where the metal strip 50 is a directionally oriented electromagnetic steel sheet, from the viewpoint of refining the magnetic domain structure to reduce iron loss, it is preferable that the angle formed by the linear grooves with respect to the rolling orthogonal direction (TD) of the metal strip is within 45°. Here, one groove does not necessarily have to extend over the entire width in the direction crossing the rolling direction of the metal strip 50, and two or more laser irradiation devices can also be used to irradiate the laser, and the grooves can be extended over the entire width through multiple grooves. In addition, in the case of manufacturing a directionally oriented electromagnetic steel sheet, in order to more effectively reduce iron loss, the grooves are preferably formed repeatedly at periodic intervals in the rolling direction of the metal strip 50. The shape of the linear grooves can be adjusted according to the laser beam shape and etching conditions, but in the case of a directionally oriented electromagnetic steel sheet, the groove width is preferably 30 μm to 200 μm, and the depth is preferably 10 μm to 40 μm. When grooves are formed on the surface of the directionally oriented electromagnetic steel sheet, the groove width is more preferably 100 μm or less. In addition, the linear grooves are preferably formed periodically in the rolling direction of the metal strip. In the case of a directionally oriented electromagnetic steel sheet, the periodic interval of the linear grooves is preferably 1 mm to 30 mm. By making the periodic interval of the linear grooves 1 mm or more, the volume occupied by the matrix iron in the directionally oriented electromagnetic steel sheet can be better ensured, and a better magnetic flux density can be obtained. In addition, by making the periodic interval of the linear grooves 30 mm or less, a higher magnetic domain refinement effect can be obtained. In addition, when the linear grooves are formed periodically, the groove intervals do not need to be uniform within the metal strip 50, and the groove intervals can be adjusted within the above range (1 mm to 30 mm) by changing the irradiation conditions of the laser on the roll 30 according to the position of the metal strip 50 in the rolling direction.

[0055] Laser

[0056] The resist film-forming coating agent 10 coated on the roll 30 is locally heated and vaporized and removed by using a laser beam. Generally, since the metal strip 50 having a width of 1 m or more is irradiated with a laser, multiple laser irradiation devices are mostly used, but the number of laser irradiation devices is preferably 3 or less. More preferably, it is 2 or less. By making the number of laser irradiation devices less than 3, the time required for equipment maintenance can be shortened, and the productivity can be improved. On the other hand, by making the number of laser irradiation devices more than 1, the beam characteristics can be made more uniform over the entire area of the laser scanning area. In addition, for high-speed scanning on the roll, the scanning of the laser is preferably performed by the rotational drive of a polygon mirror. In addition, in order to prevent the resist film-forming coating agent 10 locally removed from contaminating the laser beam path, it is preferable to recover the removed resist film-forming coating agent into a dust collector by air supply or the like. By not contaminating the laser beam path, it is possible to prevent the characteristics of the laser beam from being changed by the resist film-forming coating agent 10 locally removed.

[0057]

[0057] The output power of the laser is preferably 2.0 kW or less. By setting the output power of the laser to 2.0 kW or less, the temperature rise of the roll 30 can be suppressed, and melting of the roll 30 can be better prevented. In addition, in the case of a low-output-power laser, compared with a high-output-power laser, a laser beam with a smaller power diameter can be output. Therefore, when forming a linear groove on the surface of the directionality electromagnetic steel sheet, the width of the formed groove can be made narrower, and the iron loss can be further reduced, which is advantageous compared with a high-output-power laser.

[0058]

[0058] The laser preferably has a flat-top intensity distribution. In the case of using a laser with a Gaussian intensity distribution, the coating agent 10 for forming the resist film near the laser removal portion deteriorates due to heat and is difficult to transfer to the metal strip 50. A laser with a flat-top intensity distribution can be obtained by a conventionally known method. For example, a resonator for multimode can be used, or a beam shaping element can be used to shape the laser into a flat-top intensity distribution. Here, the flat-top shape means that in the beam distribution intensity distribution (a graph with the horizontal axis being the beam position / distance and the vertical axis being the intensity), when the distance between two points corresponding to 2 / 3 times the maximum value of the beam intensity is defined as the beam diameter r, and the distance between two points corresponding to 1 / 2 times the maximum value of the beam intensity is defined as the beam diameter R, the beam shape satisfying the condition that the beam diameter r > the beam diameter R × 0.64 is satisfied.

[0059]

[0059] The beam diameter in the direction orthogonal to the scanning direction of the laser on the surface of the roll 30 is preferably 200 μm or less. By reducing the beam diameter in the direction orthogonal to the scanning direction of the laser on the roll 30 to 200 μm or less, the removal width of the coating agent 10 for forming the resist film can be reduced. As a result, the width of the groove formed after etching can be made narrower, and further, the iron loss of the directionality electromagnetic steel sheet having the groove formed therein can be further reduced. The beam diameter in the direction orthogonal to the scanning direction of the laser on the surface of the metal strip 50 is more preferably 150 μm or less, and even more preferably 100 μm or less. The lower limit of the beam diameter is not particularly limited, but in order to form a groove width of 30 μm or more, the beam diameter in the direction orthogonal to the scanning direction of the laser on the roll surface is preferably 30 μm or more. The ratio of the major axis to the minor axis (major axis diameter / minor axis diameter) of the laser is not particularly limited, but if it is excessively increased, the removal ability of the coating agent 10 for forming the resist film is reduced, so the upper limit is 5.0. It is considered that the reduction in the removal ability of the coating agent 10 for forming the resist film when the ratio of the major axis to the minor axis of the laser is increased is due to the reduction in the power density of the laser represented by the output power / beam area. It should be noted that for the beam diameter shown in this specification, in the case of a laser having a Gaussian intensity distribution (here, a laser having a distribution with the beam diameter r ≤ the beam diameter R × 0.64), it is 1 / e of the maximum value of the beam intensity in the intensity distribution 2The distance between two points corresponding to a multiple is a value represented by the half-value width in the case of a laser having a flat-top intensity distribution.

[0060] As the laser, a fiber laser is preferably used. By using a fiber laser, a laser beam with a smaller diameter can be irradiated. As the fiber laser, a fiber laser with a minor axis diameter of 200 μm or less is preferably used.

[0061] The higher the scanning speed of the laser on the roll 30, the more beneficial it is for improving productivity. To improve productivity, the scanning speed of the laser on the roll 30 is preferably 400 / (number of laser irradiation devices) m / s or more. On the other hand, in order to sufficiently heat the coating agent 10 for forming the resist film by laser irradiation and appropriately form the desired groove, when the number of laser irradiation devices is 3, the upper limit of the scanning speed of the laser is preferably 400 m / s, and when the number of laser irradiation devices is 2, the upper limit of the scanning speed of the laser is preferably 600 m / s.

[0062] Resist film and coating agent for forming resist film

[0063] In order to prevent corrosion of the surface of the metal strip 50 in the etching process, the coating agent 10 for forming a resist film having a non-coated area 70 is transferred to the surface of the metal strip 50 to form a resist film. The hue of the resist film preferably has an L* value of 0 to 70 in the CIELAB color space (CIE 1976 L*a*b* color space) numerically represented by the spectral reflectance measured by a spectrophotometer. By reducing the L* value, a low-output power laser can be produced, melting of the roll 30 can be prevented, and a groove with a narrow width can be formed on the surface of the metal strip 50, thereby providing a grain-oriented electrical steel sheet with extremely excellent magnetic properties. The brightness index L* of the resist film is preferably 65 or less, more preferably 60 or less.

[0064] The resist film is preferably a film (organic type) mainly composed of any one of an alkyd resin, an epoxy resin, and a polyethylene resin, but is not limited thereto. For example, an inorganic coating that becomes a tension film of a grain-oriented electrical steel sheet can be used as the resist film. The thickness of the resist film is preferably 0.1 μm to 4 μm. If the thickness of the resist film is too thick, in addition to increasing costs, the amount of deformation near the resist defect part increases during transfer from the roll to the steel sheet. Therefore, the thickness of the resist film is preferably as small as possible within the range where the coating agent for forming the resist film can be uniformly coated and etching can be normally performed.

[0065] The adjustment of the brightness index L* value of the resist film can be carried out by adjusting the blending amount of the pigment component in the coating agent 10 for forming the resist film. For example, in a solvent containing an alkyd resin in part, at least one of a white pigment and a black pigment can be adjusted within a range where the total amount in terms of solid content is 0.01% to 95% by mass relative to all the solid components contained in the coating agent 10 for forming the resist film. Considering cost, the total amount in terms of solid content of the white pigment and the black pigment is more preferably 0.01% to 30% by mass relative to all the solid components contained in the coating agent for forming the resist film. As the black pigment, known black substances such as titanium oxide, iron phosphide, and carbon can be used. In addition, as the white pigment, known white substances such as oxides of zinc and titanium can be used.

[0066] As long as the effects of the present disclosure are not impaired, the coating agent for forming the resist film of the present disclosure may contain other components. As other components, for example, surfactants, rust inhibitors, lubricants, defoamers, antioxidants, leveling agents, etc. can be cited. These other components are added to further improve the performance of the resist film and the uniform coating property of the coating agent for forming the resist film. From the viewpoint of sufficiently maintaining the performance of the resist film, the total blending amount of these other components is preferably 95% by mass or less in terms of solid content relative to all the solid components (in the blending ratio in the dry film) contained in the coating agent for forming the resist film.

[0067] (Inorganic coating)

[0068] As described above, the resist film can be an inorganic coating that becomes the tension film of the grain-oriented electrical steel sheet. For the film composition, an insulating tension film for grain-oriented electrical steel sheets disclosed in a known document (for example, International Publication No. WO2015 / 064472A1) can be used as the base, but most of the known insulating tension films for grain-oriented electrical steel sheets are colorless and transparent, so the hue needs to be adjusted separately. For example, an inorganic coating liquid containing 20 to 80% by mass of phosphate (such as magnesium phosphate, aluminum phosphate, calcium phosphate, etc.) in terms of solid content, 0 to 10% by mass of chromium oxide in terms of solid content, and 20 to 50% by mass of silica in terms of solid content can be used as the base, and the brightness index L* value of the film can be adjusted by blending pigment components such as black pigments and white pigments in the same manner as the above-mentioned organic resist to form an insulating tension film.

[0069] Metal strip

[0070] The type of the metal strip 50 in which the groove is formed by the groove forming method of the present disclosure is not particularly limited. In the case of a grain-oriented electrical steel sheet, the iron loss is reduced by forming grooves on the sheet surface. As described above, according to this groove forming method, the thermal influence of laser irradiation on the steel sheet can be reduced, and grooves with a narrow width can be formed on the surface even in a portion with a defective shape of the metal strip 50. Therefore, by forming grooves on the sheet surface using this groove forming method, the iron loss of the grain-oriented electrical steel sheet can be effectively reduced.

[0071] In addition, the final steel composition of the grain-oriented electrical steel sheet is not particularly limited and may be a known steel composition, but preferably contains C: 30 ppm or less, Si: 1 to 7%, P: 0.1% or less, Mn: 0.1% or less, S: less than 10 ppm, N: 20 ppm or less. If C is contained in an excessive amount, magnetic aging impairs the iron loss, so it is preferably less than 30 ppm. Si increases the resistivity and reduces the iron loss, so it is preferably contained in an amount of 1% or more. P also increases the resistivity, so from the viewpoint of reducing the iron loss, it is not a problem to contain it, but if the content is large, there is a risk of impairing the manufacturability. In addition, in order to reduce the saturation magnetic flux density, the content of P is preferably 0.1% or less. If Mn and S are contained in excessive amounts, precipitates such as MnS are formed to deteriorate the iron loss, so they are preferably within the above ranges. N precipitates silicon nitride or the like during stress relief annealing to impair the iron loss, so it is preferably not contained as much as possible. For other components, based on existing knowledge, it is not a problem to add them in such a way that the crystal orientation after secondary recrystallization becomes sharpened to the Goss orientation, but in the case of forming a forsterite film, Cr that promotes anchoring is preferably as little as possible, preferably 0.1% or less. In addition, elements such as Ti, Nb, V, Zr, and Ta deteriorate the iron loss by forming carbides and nitrides, so the total is preferably 0.01% or less.

[0072] When assembling the iron core of a transformer, in order to improve the interlayer insulation, it is preferable to finally apply an insulating tension film to the outermost layer of the grain-oriented electrical steel sheet. In addition, the thickness of the finally obtained metal strip is preferably in the range of 0.10 to 0.35 mm. In the case of manufacturing a grain-oriented electrical steel sheet, a non-heat-resistant type magnetic domain refinement treatment can be further performed by laser irradiation or the like.

[0073] Manufacturing method of grain-oriented electrical steel sheet

[0074] In one example, the manufacturing method of the grain-oriented electrical steel sheet using the groove forming method of the present disclosure is as follows:

[0075] The steel slab is hot-rolled to produce a hot-rolled steel sheet;

[0076] Next, the above hot-rolled steel sheet or a hot-rolled annealed sheet obtained by subjecting the above hot-rolled steel sheet to hot-rolled sheet annealing is subjected to cold rolling one time or two or more times with an intermediate annealing therebetween to produce a cold-rolled steel sheet;

[0077] Next, the above cold-rolled steel sheet is subjected to a primary recrystallization annealing to produce a primary recrystallized sheet;

[0078] Next, the above primary recrystallized sheet is subjected to a secondary recrystallization annealing to produce a secondary recrystallized sheet;

[0079] A groove is formed on the surface of any of the above steel sheets after hot rolling by the above groove forming method. It should be noted that in the primary recrystallization annealing, decarburization for reducing carbon in the steel sheet and nitriding for increasing nitrogen can also be performed concurrently. In addition, the secondary recrystallization annealing mentioned here refers to annealing for selectively abnormally growing Goss-oriented grains. The secondary recrystallization annealing can concurrently serve as a process for forming a forsterite film and a process for purifying elements in the steel.

[0080] The groove formation on the steel sheet surface is carried out at any stage after hot rolling. The metal strip to be the object of groove formation can be a hot-rolled steel sheet after hot rolling, a hot-rolled annealed sheet obtained by subjecting the hot-rolled steel sheet to hot-rolled sheet annealing, a cold-rolled steel sheet after cold rolling once, a cold-rolled steel sheet before or after an intermediate annealing when the cold rolling is two or more times with an intermediate annealing therebetween, or a cold-rolled steel sheet after cold rolling after the intermediate annealing, a primary recrystallized sheet after primary recrystallization annealing, or a secondary recrystallized sheet after secondary recrystallization annealing. It should be noted that in the case of performing rolling processing after groove formation, the groove sometimes disappears. Therefore, the groove formation is preferably carried out on a cold-rolled steel sheet after cold rolling once, a cold-rolled steel sheet after cold rolling after the last intermediate annealing when the cold rolling is two or more times with an intermediate annealing therebetween, a primary recrystallized sheet after primary recrystallization annealing, and a secondary recrystallized sheet after secondary recrystallization annealing. In addition, the groove formation can be carried out in multiple stages after hot rolling.

[0081] Examples

[0082] · Manufacturing of Metal Strip

[0083] A hot-rolled steel sheet is produced by subjecting a 3.4% Si steel slab (C: 0.050%, Mn: 0.05%, P: 0.01%, S: 0.002%, Al: 0.014%, N: 70 ppm, Ti + Nb + V + Zr + Ta < 0.002%) to hot rolling. Next, the steel sheet annealed at 1050°C is subjected to cold rolling to produce a cold-rolled steel sheet with a thickness of 0.22 mm, and a metal strip with a groove formation width of 1200 mm is produced. In this steel sheet, a shape defect part with edge elongation is confirmed at a position about 50 mm in the width direction from the end in the width direction.

[0084] Form an anti-corrosion agent pattern of the coating agent for forming an anti-corrosion film on one side of the steel sheet by any one of the following methods (1) to (3).

[0085] (1) After uniformly coating the coating agent for forming an anti-corrosion film on the steel sheet, irradiate the laser while scanning in the direction orthogonal to the rolling direction of the metal strip, and locally remove the coating agent for forming an anti-corrosion film in the laser irradiation part to form a laser removal part.

[0086] (2) As shown in Figure 3 , after uniformly coating the coating agent for forming an anti-corrosion film on the roll 30, irradiate the laser while scanning in the axial direction of the roll 30 (corresponding to the direction orthogonal to the rolling direction of the metal strip), and locally remove the coating agent for forming an anti-corrosion film in the laser irradiation part to form a laser removal part. Then, press the roll 30 against the steel sheet, thereby transferring the coating agent for forming an anti-corrosion film to the steel sheet.

[0087] (3) As shown in Figure 4 , after uniformly coating the coating agent for forming an anti-corrosion film on the roll 30, irradiate the laser while scanning in the axial direction of the roll 30 (corresponding to the direction orthogonal to the rolling direction of the metal strip), and locally remove the coating agent for forming an anti-corrosion film in the laser irradiation part to form a laser removal part. Then, transfer the coating agent for forming an anti-corrosion film on the roll 30 to the steel sheet through the sandwiching roll 31.

[0088] As the anti-corrosion agent pattern, regions where the coating agent for forming an anti-corrosion film is not coated are linearly provided at a repetition interval of 3.3 mm in the rolling direction along the direction orthogonal to the rolling direction of the steel sheet. The composition of the coating agent for forming an anti-corrosion film (in terms of solid content) is shown in Table 1. On the other side of the steel sheet, the coating agent for forming an anti-corrosion film is coated over the entire surface. The coating thickness of the coating agent for forming an anti-corrosion film on both the front and back sides of the steel sheet is approximately 1 μm. After coating, the coating agent for forming an anti-corrosion film is dried under the conditions of 220 °C and 30 seconds to form an anti-corrosion film on both the front and back sides of the steel sheet.

[0089] [Table 1]

[0090] Table 4

[0091]

[0092] <Measurement of the brightness index L* of the anti-corrosion film>

[0093] For the formed anti-corrosion film, measure the brightness index L* in the CIELAB color space (CIE 1976 L*a*b* color space). The brightness index L* is numerically expressed by the spectral reflectance measured with a spectrophotometer. The measurement results are shown in Table 2.

[0094] <Evaluation of resist removal property>

[0095] The laser removability of the resist film was evaluated by visually judging the appearance of the peeling line after laser irradiation. The judgment criteria are as follows. It should be noted that if it is ○, it is judged as qualified. The results are shown in Table 2.

[0096] (Judgment criteria)

[0097] ○: The peeling area of the laser irradiation part is 95% or more

[0098] ×: The peeling area of the laser irradiation part is less than 95%

[0099] Next, electrolytic etching was performed on the steel plate. The electrolytic solution was NaCl, and the current density was adjusted in advance to form the desired groove. After etching, the resist films remaining on both the front and back sides of the steel plate were removed with an aqueous NaOH solution. The liquid temperature of the aqueous NaOH solution was maintained at 50 - 70°C. Then, the steel plate was washed with water, followed by surface cleaning, and grooves were formed on the surface. After subjecting the cold-rolled steel plate with linear grooves to recrystallization annealing at 860°C to obtain a primary recrystallized plate, the primary recrystallized plate was subjected to secondary recrystallization annealing at a maximum temperature of 1200°C to obtain a secondary recrystallized plate. A phosphate-based coating agent for forming an insulating tension film was applied to the secondary recrystallized plate, and annealing was performed at a maximum temperature of 860°C for the purpose of flattening the steel plate and forming an insulating tension film, thereby producing a grain-oriented electrical steel sheet with a thickness of 0.22 mm. Table 2 shows the irradiation conditions of the laser. The characteristics of this grain-oriented electrical steel sheet were evaluated as follows. The evaluation results are shown in Table 2.

[0100] <Measurement of groove width>

[0101] · Groove width at the center in the width direction

[0102] For the groove width at the center in the width direction of the steel plate, it is defined as: 10 test pieces with a width of 80 mm and a length of 300 mm were collected at the center in the width direction of the steel plate, and the average value of the groove widths measured at 200 arbitrary points in the rolling direction of each specimen, a total of 200 points, using an optical microscope.

[0103] · Groove width at end 1 in the width direction

[0104] For the groove width at end 1 in the width direction of the steel plate, it is defined as: 10 test pieces with a width of 80 mm and a length of 300 mm were collected at the end on the DR side (drive side of the cold rolling mill) of the steel plate, and the average value of the groove widths measured at 200 arbitrary points in the rolling direction of the DR side end of each specimen, a total of 200 points, using an optical microscope.

[0105] · Groove width at end 2 in the width direction

[0106] For the groove width at the end 2 in the width direction of the steel sheet, it is set as follows: 10 test pieces with a width of 80 mm and a length of 300 mm are collected from the end on the OP side (the operator side of the cold rolling mill) of the steel sheet, and the average value of the groove widths measured using an optical microscope at 200 points in total at any 20 points in the rolling direction at the end on the OP side of each specimen is taken.

[0107] <Measurement of iron loss W 17 / 50 >

[0108] ·Iron loss at the central part in the width direction

[0109] For the iron loss at the central part in the width direction of the steel sheet, 2 SST test piece specimens with a width of 100 mm and a length of 320 mm are cut out from the central part in the width direction of the steel sheet along the rolling direction, obtaining a total of 40 SST test piece specimens. Using these 40 SST test piece specimens for a single-sheet magnetic test, the iron loss: W 17 / 50 (W / kg) is measured at a maximum magnetic flux density of 1.7 T and a frequency of 50 kHz. If the iron loss W 17 / 50 is 0.72 W / kg or less, the iron loss W 17 / 50 is evaluated as excellent.

[0110] ·Iron loss at the end in the width direction

[0111] One piece is cut out from each of the two end parts in the width direction of the steel sheet along the rolling direction, obtaining a total of 40 SST test piece specimens with a width of 100 mm. It should be noted that there is a tendency of uneven plate thickness at the outermost ends in the width direction of the steel sheet, so here the part 30 mm inside from the outermost end is treated as the end. Using these 40 SST test pieces for a single-sheet magnetic test, the iron loss: W 17 / 50 (W / kg) is measured at a maximum magnetic flux density of 1.7 T and a frequency of 50 kHz. If the iron loss W 17 / 50 is 0.72 W / kg or less, the iron loss W 17 / 50 is evaluated as excellent.

[0112]

[0113] Industrial availability

[0114] The grain-oriented electrical steel sheet manufactured by using the groove forming method of the present disclosure also exhibits good magnetic properties after annealing such as stress relief annealing, and can also be applied to wound transformers. If the grain-oriented electrical steel sheet manufactured by using this groove forming method is used for a transformer, the energy use efficiency can be improved, so it is industrially useful.

[0115] Symbol description

[0116] 10 Coating agent for forming resist film

[0117] 20 Gravure roll

[0118] 21 Offset roll

[0119] 22 Other roll

[0120] 30 Roll

[0121] 31 Clamping roll

[0122] 40 Laser irradiation device

[0123] 50 Metal strip

[0124] 60 Laser removal section

[0125] 70 Non-coated area

[0126] A Conveying direction

Claims

1. A method for forming grooves on the surface of a metal strip, comprising coating a coating agent for forming a resist film on a roll. Next, while scanning the roll in the axial direction of the roll or in a direction inclined with respect to the axial direction, irradiate the roll with a laser, and remove the coating agent for forming a resist film in the portion irradiated with the laser. Irradiate the laser at a position close to the position where the roll contacts the surface of the metal strip. The output power of the laser is 2.0 kW or less, the intensity distribution is a flat-top type or a Gaussian type, and the beam diameter in the direction orthogonal to the scanning direction of the roll surface is 200 μm or less. Next, bring the roll into contact with at least one side of the metal strip, or bring the roll into contact with a pinch roll clamped between the roll and the metal strip so that the pinch roll is in contact with at least one side of the metal strip. Set the portion corresponding to the portion where the coating agent for forming a resist film is removed as an uncoated area, and transfer the coating agent for forming a resist film to at least one side of the metal strip. Next, dry the coating agent for forming a resist film to form a resist film having the uncoated area on at least one side of the metal strip. Next, perform an etching process on the uncoated area of the metal strip to form grooves.

2. The method for forming a groove on the surface of a metal strip according to claim 1, wherein, The brightness index L* of the resist film in the CIELAB color space, i.e., the CIE 1976 L*a*b* color space, is 0 to 70.

3. A method for manufacturing a directional electromagnetic steel sheet, comprising hot-rolling a steel slab to obtain a hot-rolled steel sheet. Next, perform cold rolling on the hot-rolled steel sheet or on a hot-rolled and annealed sheet obtained by subjecting the hot-rolled steel sheet to hot-rolled sheet annealing once or two or more times with an intermediate annealing therebetween to obtain a cold-rolled steel sheet. Next, perform primary recrystallization annealing on the cold-rolled steel sheet to obtain a primary recrystallized sheet. Next, perform secondary recrystallization annealing on the primary recrystallized sheet to obtain a secondary recrystallized sheet. On the surface of any of the steel sheets after hot rolling, form grooves by using the groove forming method according to claim 1 or 2.

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