Method for forming grooves on the surface of a metal strip and method for manufacturing a grain-oriented electrical steel sheet

Abstract

The present invention provides a grain-oriented magnetic steel sheet in which even a low-output laser can reduce the thermal effect of laser irradiation on a metal strip and in which a resist film is removed well to form a groove with a narrow width on the surface of the metal strip, and in which the magnetic characteristics are extremely excellent. A method for forming a groove on the surface of a metal strip includes forming a resist film with a brightness index L* of 0 to 70 on at least one side of the metal strip, then irradiating a laser with an output power of less than 1.5 kW while scanning in a direction that crosses the rolling direction of the metal strip, removing the resist film from the portion that was irradiated by the laser, and then performing etching treatment on the portion of the metal strip from which the resist film was removed to form a groove. The brightness index L* refers to the L* value in the CIELAB color space (CIE 1976 L*a*b* color space).

Description

TECHNICAL FIELD

[0001] The present disclosure relates to a method of forming grooves on a surface of a metal strip such as a grain-oriented magnetic steel sheet used for a core of an electrical device such as a transformer, and a method of manufacturing a grain-oriented magnetic steel sheet using the groove forming method. BACKGROUND

[0002] A grain-oriented magnetic steel sheet is mainly used as a material for a core inside a transformer. In order to improve the energy use efficiency of a transformer, low iron loss of a grain-oriented magnetic steel sheet is required. As one of the techniques for making a grain-oriented magnetic steel sheet low in iron loss, a technique of refining a magnetic domain structure by forming a concave-convex portion such as a groove on a steel sheet surface can be cited. As a method of forming a groove on a steel sheet surface, a method of pressing a gear-like roller against a steel sheet surface, a method of locally melting a steel sheet base iron using a laser beam, and a method of forming a groove in an uncoated portion of a resist film on a steel sheet surface by etching the uncoated portion of the resist film using chemical etching or electrolytic etching, and the like are known. Among them, the method using a resist film is an advantageous method of efficiently forming a deep groove, and has the advantage of having a high magnetic domain refining effect. However, in the method using a resist film, as with other methods, it is an extremely important problem to form a groove with high precision and uniformity.

[0003] In the method of forming a groove using a resist film, as a method that is particularly advantageous in industry, a technique of locally removing a portion of a resist film that is uniformly coated on a steel sheet surface using a laser beam, and forming a groove by etching the steel sheet surface of the portion from which the film is removed using chemical etching or electrolytic etching is known (Patent Literature 1). Under appropriate maintenance conditions, a laser beam maintains a very uniform beam profile, and thus a very uniform groove can be formed. On the other hand, as clarified by the present inventors and the like in research to date, in this method, there is a risk that the laser irradiated in order to remove the resist film deforms and melts the base iron, and impairs the magnetic properties of the final product sheet. In contrast, in Patent Literature 2, a technique of removing a resist film in a short time by using a high output power laser (output power of 1.5 kW or more), thereby suppressing heat diffusion in the base iron during irradiation, and obtaining high magnetic properties is disclosed.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent No. 6332185

[0007] Patent Literature 2: Japanese Patent No. 6172403 SUMMARY

[0008] However, it is known that the narrower the groove width, the better the magnetic properties of the grain-oriented magnetic steel sheet using groove refinement. In the method of locally removing a portion of the uniformly applied resist film using 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, there is a tendency that the higher the output power, the larger the beam diameter, and therefore in the technology disclosed in the above-described Patent Document 2, it is difficult to reduce the groove width formed to 200 μm or less. A countermeasure of increasing the number of laser settings to remove the resist film at a slow speed on the steel sheet by a low-output laser is effective, but on the other hand, it is not possible to avoid other problems such as an increase in equipment cost and maintenance cost. That is, in order to further reduce the groove width, even a low-output laser needs to remove the resist film as with a high-output laser that has been used all the time.

[0009] In addition, the present inventors and others have found as a result of their own research that in a case where laser irradiation for removing the resist film reduces the hardness of the base iron, the iron loss of the grain-oriented magnetic steel sheet obtained finally deteriorates. From this, the present inventors and others have considered that by reducing the thermal influence of laser irradiation on the metal strip steel including reduction in the hardness of the base iron, it is possible to further improve the magnetic properties.

[0010] Therefore, the object of the present disclosure is to provide a grain-oriented magnetic steel sheet in which even a low-output laser can reduce the thermal influence of laser irradiation on the metal strip steel, and in which the resist film is removed well to form a groove with a narrow width on the surface of the metal strip steel, and in which the magnetic properties are extremely excellent.

[0011] That is, the gist of the present disclosure is constituted as follows.

[0012] [1] A method of forming a groove on a surface of a metal strip steel, in which a resist film having a lightness index L* of 0 to 70 is formed on at least one side of the metal strip steel,

[0013] Next, the above-described resist film is irradiated with a laser having an output power of less than 1.5 kW while being scanned in a direction that crosses the rolling direction of the above-described metal strip steel, and the resist film of the portion irradiated with the laser is removed,

[0014] Next, the portion of the above-described metal strip steel from which the resist film is removed is subjected to etching treatment to form a groove.

[0015] wherein the above-described lightness index L* refers to the L* value in the CIELAB color space (CIE 1976 L*a*b* color space).

[0016] [2] The method of forming a groove on a surface of a metal strip steel according to the above-described [1], in which the removal width of the above-described resist film is 200 μm or less, and the scanning speed of the above-described laser is 111 m / s or more.

[0017] [3] The method of forming a groove on a surface of a metal strip steel according to any one of the above [1] or [2], wherein a beam diameter in a direction orthogonal to a scanning direction of the laser on the surface of the metal strip steel is 200 μm or less.

[0018] [4] The method of forming a groove on a surface of a metal strip steel according to any one of the above [1] to [3], wherein the laser is a fiber laser having a beam diameter in a direction orthogonal to a scanning direction of the laser of 200 μm or less.

[0019] [5] The method of forming a groove on a surface of a metal strip steel according to any one of the above [1] to [4], wherein a surface roughness Ra in a rolling orthogonal direction of the metal strip steel is 0.5 μm or less before forming the resist film.

[0020] [6] A method of manufacturing a grain-oriented magnetic steel sheet, hot-rolling a steel slab to produce a hot-rolled steel sheet,

[0021] then, cold-rolling the hot-rolled steel sheet or a hot-rolled annealed sheet obtained by subjecting the hot-rolled steel sheet to a hot-rolled sheet annealing once or two or more times with an intermediate annealing therebetween to produce a cold-rolled steel sheet,

[0022] then, subjecting the cold-rolled steel sheet to a primary recrystallization annealing once to produce a primary recrystallization sheet,

[0023] then, subjecting the primary recrystallization sheet to a secondary recrystallization annealing to produce a secondary recrystallization sheet;

[0024] forming a groove on a surface of any one of the sheets after the hot-rolling by the groove forming method according to any one of the above [1] to [5].

[0025] According to the present disclosure, it is possible to provide a grain-oriented magnetic steel sheet in which even a low-output power laser can reduce a thermal influence of laser irradiation on a metal strip steel, and a resist film is removed well to form a groove having a narrow width on a surface of the metal strip steel, and furthermore, magnetic characteristics are extremely excellent. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a graph showing a result of analyzing a hardness distribution of a steel sheet base iron in the vicinity of a laser irradiation portion under a condition where high magnetic characteristics are not obtained.

[0027] Figure 2 is a graph showing a correlation between a brightness index L* of a resist film and an iron loss W 17 / 50 of a grain-oriented magnetic steel sheet.

[0028] Figure 3is a graph showing the correlation of the brightness index L* of the resist film and the output power of the laser required to remove the resist film.

[0029] Figure 4 is a graph showing the removal width distribution of the resist film in the rolling orthogonal direction (TD) at the brightness index L* = 44 of the resist film.

[0030] Figure 5 is a graph showing the correlation of the brightness index L* of the resist film and the iron loss W 17 / 50 of the grain-oriented magnetic steel sheet when the surface roughness Ra of the steel sheet in the rolling orthogonal direction (TD) before forming the resist film is greater than 0.5 μm. DETAILED DESCRIPTION

[0031] First, an experiment that became the impetus for developing the present disclosure will be described. Note that in the following description, "%" and "ppm" indicating the content of the component elements of the steel sheet mean "mass %" and "mass ppm", respectively, unless otherwise specified. In addition, in the present specification, a numerical range indicated using "~" means a range including the numerical values recited before and after the "~" as lower limit values and upper limit values.

[0032] <Experiment 1>

[0033] The inventors thought of changing the requirements of the resist film. Also, various resist films were formed on the surface of a steel sheet, linear grooves were formed on the surface of the steel sheet, and the obtained magnetic flux densities were compared. First, a 500 mm wide cold-rolled steel sheet (C: 0.048%, Mn: 0.07%, P: 0.007%, S: 0.002%, Al: 0.010%, N: 50 ppm, Ti+Nb+V+Zr+Ta < 0.001%) on which linear grooves were formed was prepared. A steel billet having the above-mentioned composition was subjected to hot rolling to produce a hot-rolled steel sheet, and then, a hot-rolled annealed sheet obtained by subjecting the hot-rolled steel sheet to hot-rolled sheet annealing at 1050°C was subjected to cold rolling at 300°C or lower to produce a 0.22 mm thick cold-rolled steel sheet. A resist film forming agent was uniformly applied to the surface of the cold-rolled steel sheet using a gravure roll to form a resist film. As the resist film forming agent, an agent in which a water-based alkyd resin was used as the main body and the composition of black and white pigments was changed was used. Next, a high output power laser was irradiated while scanning in a direction orthogonal to the rolling direction (RD) of the cold-rolled steel sheet (rolling orthogonal direction: TD), and the resist film was partially removed. Next, the cold-rolled steel sheet was subjected to etching treatment, and the surface of the steel sheet in the portion from which the resist film had been removed by the laser (hereinafter, also referred to as the laser-removed portion) was etched to form linear grooves on the surface of the cold-rolled steel sheet. Next, the resist film remaining on the cold-rolled steel sheet was completely removed. Next, the cold-rolled steel sheet on which the linear grooves had been formed was subjected to primary recrystallization annealing including decarburization annealing at 860°C to produce a primary recrystallized sheet, and further subjected to secondary recrystallization annealing at a maximum temperature of 1200°C to produce a secondary recrystallized sheet. Next, the secondary recrystallized sheet was subjected to annealing at a maximum temperature of 860°C for the purpose of planarization of the steel sheet and formation of an insulating tension film to produce a grain-oriented magnetic steel sheet having a sheet thickness of 0.22 mm. The iron loss characteristics of each grain-oriented magnetic steel sheet thus formed with linear grooves were evaluated. For the iron loss, single sheet magnetic tests were performed using 30 pieces of an SST test piece having a width of 100 mm and a length of 320 mm, and the iron loss was measured at a maximum magnetic flux density of 1.7 T and a frequency of 50 kHz: W 17 / 50 (W / kg). As a result, it was found that depending on the type of the resist film, high magnetic characteristics were not obtained at times.

[0034] Here, under conditions in which high magnetic characteristics were not obtained, the formation of the resist film and the laser irradiation were additionally performed, and the hardness distribution of the base iron of the surface of the steel sheet in the vicinity of the laser-irradiated portion was analyzed. The results are shown in Figure 1The RD position in the figure indicates the position of the center of the width of the steel sheet in the rolling direction (RD) from the center of the laser irradiation on the steel sheet. Here, a laser irradiation device with a diameter of 80 μm and an output of 1.8 kW was used to irradiate the laser on the steel sheet. The hardness of the base iron was measured in the same manner as described above in the cold-rolled steel sheet having the resist film without etching after the resist film was removed. The hardness of the base iron was measured using a micro Vickers hardness tester, and the points in the figure are the average values of 15 measurement points. In addition, the reference for the hardness was the value at a position 1 mm away from the laser irradiation portion in the rolling direction (RD) (portion not irradiated with the laser), and the proportion of the change in the hardness of the base iron of each measurement point with respect to the hardness value of the portion not irradiated with the laser was analyzed. According to this figure, a significant decrease in the hardness was observed in the steel sheet surface of the laser irradiation portion compared to the portion not irradiated with the laser, and it was considered that this decrease in the hardness had some influence on the deterioration of the magnetic properties of the grain-oriented magnetic steel sheet.

[0035] <Experiment 2>

[0036] The inventors and others analyzed the correlation between the type of resist film and the magnetic properties (W 17 / 50 ) of the grain-oriented magnetic steel sheet finally obtained by changing the type of resist film. First, a 500 mm wide cold-rolled steel sheet (C: 0.048%, Mn: 0.07%, P: 0.007%, S: 0.002%, Al: 0.010%, N: 50 ppm, Ti+Nb+V+Zr+Ta <0.001%) having linear grooves was produced. A steel billet having the above-described composition was subjected to hot rolling to produce a hot-rolled steel sheet, and then a hot-rolled annealed sheet obtained by annealing the hot-rolled sheet at 1050°C was subjected to cold rolling to obtain a cold-rolled steel sheet. Then, linear grooves were formed in the cold-rolled steel sheet under the conditions described below, and after a primary recrystallization annealing was performed at 860°C to obtain a primary recrystallization sheet, a secondary recrystallization annealing was performed at a maximum temperature of 1200°C on the primary recrystallization sheet to obtain a secondary recrystallization sheet. In order to planarize the steel sheet and form an insulating tension film, the secondary recrystallization sheet was annealed at a maximum temperature of 860°C to produce a grain-oriented magnetic steel sheet having a thickness of 0.22 mm.

[0037] In the formation of the above-described linear grooves, a resist film formation coating agent was applied to the surface of the grain-oriented magnetic steel sheet to form a resist film. At this time, as the resist film formation coating agent, a coating agent in which a water-based alkyd resin was used as the main body and the composition of black and white pigments was changed was used, and a plurality of grain-oriented magnetic steel sheets having resist films with different compositions were obtained.

[0038] Next, the resist film is partially removed by irradiating laser light in the rolling direction (TD) of each of the oriented electromagnetic steel sheets while scanning. Then, the surface of the steel sheet at the laser-removed portion is etched to form linear grooves on the surface of the oriented electromagnetic steel sheet. Next, the resist film remaining on the surface of the steel sheet is removed. The surface roughness Ra of the oriented electromagnetic steel sheet coated with the resist film-forming coating agent is 0.1 μm in the rolling direction (TD). The laser light for removing the resist film is irradiated using one laser irradiation device having a diameter of 120 μm. The output power of the laser light is determined by a preliminary test according to the type of the resist film. That is, the output power of the laser light is increased by 100 W every time the laser light is irradiated, and the appearance of the laser-irradiated portion is visually observed to determine the lowest output power of the laser light under the condition in which the resist film is removed at an area ratio of 95% or more with respect to the irradiated area of the laser light. The output power of the laser light required for removing each resist film is determined, and the laser light is irradiated at the output power. Here, the irradiated area of the laser light is the product of the diameter of the beam in the scanning direction orthogonal to the rolling direction and the distance of the laser scanning.

[0039] The oriented electromagnetic steel sheet after the planarization and the formation of the insulating tension film was subjected to a single-sheet magnetic test using three SST test pieces each having a width of 100 mm and a length of 320 mm, and the maximum magnetic flux density was measured. The iron loss was measured at a frequency of 50 kHz: 1.7 T, W 17 / 50 (W / kg).

[0040] The correlation between the brightness index L* value (hereinafter, also simply referred to as L* value) of the resist film in the CIELAB color space (CIE 1976 L*a*b* color space) in which the spectral reflectance measured by a spectrophotometer is numerically converted and the magnetic characteristics of the oriented electromagnetic steel sheet was found. Figure 2 As shown in Figure 2 According to the present experiment, it was found that when the L* value of the resist film was 70 or less, the iron loss W 17 / 50 of the oriented electromagnetic steel sheet after the formation of grooves was significantly reduced.

[0041] Figure 3 The correlation between the brightness index L* of the resist film and the output power of the laser light required for removing the resist film found above is shown in Table 1. The present inventors found that, as shown in Figure 3 the lower the L* value, the lower the output power of the laser light required for removing the resist film. Furthermore, the present inventors found that if the L* value of the resist film was less than 70, the resist film could be removed without using laser light under high output power conditions. That is, if the resist film can be removed using low output power laser light, the diameter of the beam can be reduced, and a groove having a narrow width can be formed, and furthermore, the magnetic characteristics of the oriented electromagnetic steel sheet can be improved.

[0042] <Experiment 3>

[0043] The removal width distribution of the resist film in the rolling orthogonal direction (TD) at L* = 44 of Experiment 2 described above was found. The results are shown in FIG. 6. Figure 4 As is apparent from this figure, by reducing the L* value, no significant decrease in the removal width of the laser irradiation end portion was found, and the resist film could be uniformly removed. Note that the removal width of the resist film was analyzed by observing each position in the rolling orthogonal direction (TD) with an optical microscope.

[0044] <Experiment 4>

[0045] Furthermore, the present inventors analyzed the influence on the iron loss by increasing the surface roughness Ra of the grain-oriented magnetic steel sheet before forming the resist film and changing the type of the resist film. First, a 500 mm wide cold-rolled steel sheet (C: 0.043%, Mn: 0.07%, P: 0.002%, S: 0.001%, Al: 0.009%, N: 45 ppm, Ti + Nb + V + Zr + Ta < 0.001%) in which linear grooves were formed was produced. A steel billet having the above-described composition was subjected to hot rolling to produce a hot-rolled steel sheet, and then a hot-rolled annealed sheet in which the hot-rolled sheet was annealed at 1050°C was subjected to cold rolling to obtain a cold-rolled steel sheet. Linear grooves were formed in the cold-rolled steel sheet, and then primary recrystallization annealing was performed at 860°C to obtain a primary recrystallization sheet, and secondary recrystallization annealing was performed at a maximum temperature of 1200°C on the primary recrystallization sheet to obtain a secondary recrystallization sheet. Then, for the purpose of flattening the steel sheet and forming an insulating tension film, the secondary recrystallization sheet was annealed at a maximum temperature of 860°C to obtain a grain-oriented magnetic steel sheet having a sheet thickness of 0.22 mm.

[0046] In the formation of the linear grooves described above, a resist film formation coating agent was applied to the surface of the grain-oriented magnetic steel sheet to form a resist film. As the resist film formation coating agent, a coating agent in which the composition of black and white pigments was changed was used as in Experiment 2, and a plurality of grain-oriented magnetic steel sheets on which resist films of different compositions were formed were obtained. As in Experiment 2, laser light was irradiated in the rolling orthogonal direction (TD) of each of the grain-oriented magnetic steel sheets after the formation of the resist film, the steel sheet surface of the laser light removal portion was etched, and linear grooves were formed on the surface of the grain-oriented magnetic steel sheet, and the resist film remaining on the steel sheet surface was removed. The surface roughness Ra of the surface of the grain-oriented magnetic steel sheet on which the resist film formation coating agent was applied was 0.55 μm in the rolling orthogonal direction (TD). The laser light for removing the resist film was irradiated using one laser light irradiation device having a diameter of 120 μm. The laser output power was adjusted to each resist film of different brightness as in Experiment 2.

[0047] For the iron loss of the directionally solidified electromagnetic steel sheet after planarization and formation of the insulating tension coating, a single sheet magnetic test was performed using three SST test pieces each having a width of 100 mm and a length of 320 mm, and the iron loss was measured at a maximum magnetic flux density of 1.7 T and a frequency of 50 kHz: W 17 / 50 (W / kg). The results are shown in Figure 5 .

[0048] It was found that in the case where the surface roughness Ra of the directionally solidified electromagnetic steel sheet before formation of the resist coating was large, even if the L* value of the resist coating was low, the iron loss was not always low. Figure 5 is a graph showing the correlation of the L* value of the resist coating when the surface roughness Ra of the directionally solidified electromagnetic steel sheet before formation of the resist coating was 0.55 μm in the rolling orthogonal direction with the iron loss W 17 / 50 of the directionally solidified electromagnetic steel sheet after formation of the grooves. By comparison with Figure 2 , it was found that when the surface roughness Ra of the directionally solidified electromagnetic steel sheet before formation of the resist coating was 0.55 μm in the rolling orthogonal direction, the effect of low iron loss was small even if the L* value was 70 or less, as compared with the case where the surface roughness Ra was 0.1 μm.

[0049] Hereinafter, an embodiment of the present disclosure will be described. It should be noted that the present disclosure is not limited to the following embodiment. The groove formation method according to the present embodiment is a method of forming grooves on a metal strip surface, which includes the following steps:

[0050] forming a resist coating on at least one surface of the metal strip,

[0051] Next, the resist coating is irradiated with laser light having an output power of less than 1.5 kW while scanning in a direction that crosses the rolling direction of the metal strip, and the resist coating of the portion irradiated with the laser light is removed,

[0052] Next, the portion of the metal strip from which the resist coating has been removed is subjected to etching treatment to form grooves.

[0053] wherein the L* value of the resist coating in the CIELAB color space is 0 to 70.

[0054] Resist coating and coating agent for resist coating formation

[0055] First, a resist film is formed on at least one side of the metal strip. The resist film is formed to prevent corrosion of the surface of the metal strip during the etching process. It is extremely important for the present disclosure that the color tone of the resist film has an L* value of 0 to 70 in the CIELAB color space (CIE 1976 L*a*b* color space) numerically expressed by the spectrophotometer. As described above, by reducing the L* value, even with low output power laser, the thermal impact on the metal strip can be reduced, a narrow width groove can be formed on the surface of the metal strip, and further a grain-oriented magnetic steel sheet with extremely excellent magnetic properties can be provided. The brightness index L* of the resist film is preferably 65 or less, and more preferably 60 or less. It should be noted that the lower limit of the brightness index L* of the resist film is not particularly limited as long as it is 0 or more.

[0056] The brightness index of the resist film was L* = 79 and L* = 44, and whether the base iron hardness of the laser scanned portion of the steel sheet after the laser removed the resist film was reduced by 1% or more with respect to the hardness value of the laser non-irradiated portion was investigated. The results are shown in Table 1. The resist film was formed on a cold-rolled steel sheet (C: 0.042%, Mn: 0.14%, P: 0.003%, S: 0.002%, Al: 0.11%, N: 54 ppm, Ti+Nb+V+Zr+Ta <0.001%) having a width of 500 mm. The cold-rolled steel sheet was produced by hot-rolling a steel billet to produce a hot-rolled steel sheet, and then cold-rolling a hot-rolled annealed sheet that had been annealed at 1050°C to produce a cold-rolled steel sheet. The laser was irradiated on the steel sheet in a 200 μm diameter while scanning in the 500 mm width direction of the steel sheet. Among them, the laser output power was adjusted in advance in such a way that 95% or more of the resist film was removed in the entire width of the laser scanned portion with respect to the irradiation area of the laser. The position in the table indicates the position in the laser scanning direction with the central portion of the width direction of the steel sheet scanned by the laser as the origin. The hardness of the steel sheet was measured at the laser scanned portion at the origin and at ±50, ±100, ±150, and ±245 mm from the origin. The hardness of the base iron was measured using a micro Vickers hardness tester, and the hardness at each position was the average of 15 measurement points. The reference for the hardness was the value at a position 1 mm away from the laser irradiated portion in the rolling direction (RD) (laser non-irradiated portion), and whether the base iron hardness of each measurement point was reduced by 1% or more with respect to the hardness value of the laser non-irradiated portion was investigated. In the above two conditions, the hardness change distribution with respect to the laser non-irradiated portion was measured at each rolling direction position Figure 1 The hardness change distribution with respect to the laser non-irradiated portion is shown, but a hardness change of 1% or more was found only at the width direction central position (laser irradiated portion) of L* = 79, and the hardness change was less than 1% at the other positions.

[0057] [Table 1]

[0058] Table 1

[0059]

[0060] The underlined range is outside the scope of the present application.

[0061] As shown in Table 1, in the case of the resist film having a brightness index L* = 44, the hardness of the base iron did not decrease by more than 1% relative to the hardness of the portion not irradiated with the laser, regardless of the position in the laser scanning direction. In contrast, in the case of the resist film having a brightness index L* = 79, the hardness of the base iron decreased by more than 1% relative to the hardness of the portion not irradiated with the laser, at the central portion of the steel sheet in the width direction (origin: position 0 mm). Note that in the case of a high L* value, an attempt was made to remove the resist film using a low output power laser of 1.5 W or less, but the resist film was not completely removed at the position 245 mm in the width direction. In order to remove the resist film over the entire width, a high laser output power of 1.8 kW was required. In contrast, in the case of a low L* value, the resist film was removed over the entire width using a laser output power of 1.0 kW. The detailed reason is not clear, but it is inferred that in the case of a high L* value of the resist film, the laser absorption ability of the resist film decreases, particularly at the deflection end portion of the laser beam in the laser scanning direction, and thus a higher output power laser is required.

[0062] The resist film is preferably a film (organic system) in which any one of an alkyd-based resin, an epoxy-based resin, and a polyvinyl-based resin is used as a main component, but is not limited thereto. For example, an inorganic coating layer 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 generally 0.1 μm to 8 μm. If the thickness of the resist film is too thick, the cost increases, and thus the thickness of the resist film is preferably as small a value as possible within a range in which the coating agent for forming a resist film can be uniformly applied and etching can be normally performed.

[0063] The adjustment of the brightness index L* value of the resist film can be performed by adjusting the blending amount of the pigment component in the coating agent for forming a resist film. For example, at least one of a white pigment and a black pigment can be adjusted in a range in which the proportion of the total amount of the solid components, in terms of solid components, to the entire solid components contained in the coating agent for forming a resist film becomes 0.01 mass% to 95 mass% in a solvent containing an alkyd-based resin. More preferably, the proportion of the total amount of the solid components, in terms of solid components, of the white pigment and the black pigment to the entire solid components contained in the coating agent for forming a resist film is 0.01 mass% to 30 mass% from the cost aspect. As the black pigment, a well-known black substance such as titanium oxide, iron phosphide, carbon, or the like can be used. In addition, as the white pigment, a well-known white substance such as an oxide of zinc, titanium, or the like can be used.

[0064] The resist film-forming coating agent of the present disclosure can contain other components as long as the effects of the present disclosure are not impaired. As the other components, for example, a surfactant, a rust preventive, a lubricant, an antifoaming agent, an antioxidant, a leveling agent, and the like can be mentioned. These other components are added in order to further improve the properties of the resist film and the uniformity of the application of the resist film-forming coating agent. From the viewpoint of sufficiently maintaining the properties of the resist film, the total amount of these other components is preferably 95% by mass or less in terms of solid content with respect to the total solid content (in terms of the blending ratio in the dried film) contained in the resist film-forming coating agent.

[0065] (Inorganic coating)

[0066] As described above, the resist film can be an inorganic coating that becomes a tension film of a grain-oriented magnetic steel sheet. As the film composition, a known insulating tension film for a grain-oriented magnetic steel sheet (for example, International Publication No. WO2015 / 064472A1) can be used as the base, but since the known insulating tension film for a grain-oriented magnetic steel sheet is mostly colorless and transparent, it is necessary to adjust the color tone additionally. For example, an inorganic coating liquid containing 20 to 80% by mass of a phosphate (Mg phosphate, Al phosphate, Ca phosphate, or the like) 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 silicon dioxide in terms of solid content can be used as the base, and the brightness index L* value of the film is adjusted by the blending of a pigment component such as a black pigment, a white pigment, or the like, as with the above-described organic resist, to form an insulating tension film.

[0067] Groove forming method

[0068] In the groove forming method, first, the above-described resist film-forming coating agent is applied to the surface of the metal strip or both the surface and the back surface to form a resist film. The application of the resist film-forming coating agent can be performed using a known method, but it is preferable to apply the resist film-forming coating agent uniformly to the surface of the metal strip or both the surface and the back surface. The application of the resist film-forming coating agent can be performed using, for example, a gravure roll.

[0069] The resist film is dried before the etching treatment described later. It is preferable to dry the resist film before the laser irradiation described later. When the resist film is dried, the drying temperature is preferably 180 to 300°C, and the method of drying is not particularly limited. For example, the resist film is dried by blowing hot air or the like.

[0070] Next, the resist film is irradiated with a laser having an output power of less than 1.5 kW while scanning in a direction transverse to the rolling direction of the metal strip, and the resist film in the portion irradiated with the laser is removed. As described above, in the present disclosure, by making the lightness index L* of the resist film 70 or less, the resist film can be removed with a narrow width using a low-output laser having an output power of less than 1.5 kW. Next, the portion of the metal strip from which the resist film has been removed is subjected to etching treatment, and a groove is formed in the portion of the metal strip surface from which the resist film has been removed. The etching can be performed by either of chemical etching and electrolytic etching. In the case of electrolytic etching, the electrolyte is preferably an aqueous solution of NaCl or KCl. After the etching treatment, the resist film is removed from the metal strip surface, thereby obtaining a metal strip having a groove formed therein. The removal of the resist film is preferably performed using an alkali or an organic solvent.

[0071] laser

[0072] In order to remove the resist film formed on the metal strip surface by local heating and vaporization, a laser beam is used. Generally, since the metal strip having a width of 1 m or more is irradiated with a laser, a plurality of laser irradiation devices are often used, but the number of laser irradiation devices is preferably 3 or less. More preferably, the number is 2 or less. By making the number of laser irradiation devices less than 3, the time required for maintenance of the equipment 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 profile can be made more uniform over the entire region of the laser scanning field. In addition, in order to scan at high speed on the metal strip, the scanning of the laser is preferably performed by rotational driving of a polygon mirror. In addition, in order to prevent the resist film removed locally from contaminating the beam path of the laser, it is preferable to collect the removed resist film into a dust collector by air blowing or the like. By not contaminating the beam path of the laser, the change in the properties of the laser beam due to the resist film removed locally can be prevented.

[0073] Output power of the laser: less than 1.5 kW

[0074] Generally, the higher the laser output power, the more advantageous in the removal of the resist film, but if it is too high, the metal strip of the laser irradiation portion melts, and the groove shape can become uneven. Also, for example, in the case of irradiating a once-recrystallized sheet of a grain-oriented magnetic steel sheet with a laser, by irradiating a laser of high output power, a slight strain can be introduced to the base iron. This slight strain becomes a driving force for the growth of the crystal grains other than the Goss orientation at the time of secondary recrystallization, and can hinder the sharpening of the Goss orientation. Therefore, it is preferable to be able to remove the resist film with a low output power laser. In the present disclosure, by making the lightness index L* of the resist film 70 or less, the output power of the laser can be reduced to less than 1.5 kW. The output power of the laser is preferably 1.4 kW or less, more preferably 1.25 kW or less. The lower limit of the output power of the laser is not particularly limited as long as it is an output power capable of removing the resist film, and from the viewpoint of more appropriately removing the resist film, the output power of the laser is preferably 0.3 kW or more, more preferably 1.0 kW or more. Also, the irradiation energy per unit scan length of the laser is influenced by the beam diameter and the like, and when the beam diameter is 200 μm, it is preferably 7.5 J / m or more, and when the beam diameter is 100 μm, it is preferably 4.0 J / m or more. As described below, the appropriate scan speed of the laser on the metal strip is preferably 111 m / s or more, and in this case, the irradiation energy per unit scan length of the laser can be made lower compared to the case where the scan speed is low.

[0075] The beam diameter in the direction orthogonal to the direction of scanning of the laser onto the surface of the metal strip is preferably 200 μm or less. By making the beam diameter in the direction orthogonal to the direction of scanning of the laser onto the surface of the metal strip 200 μm or less, the removal width of the resist film can be made narrow. Thereby, the groove width formed after etching can be made narrower, and furthermore, the iron loss of the grain-oriented magnetic steel sheet in which the groove is formed can be further reduced. The beam diameter in the direction orthogonal to the direction of scanning of the laser onto the surface of the metal strip is more preferably 120 μm or less, and further preferably 80 μm or less. The ratio of the long axis to the short axis of the laser (long axis diameter / short axis diameter) is not particularly limited, but if it is excessively increased, the removal ability of the resist film decreases, and therefore the upper limit is 5.0. It is considered that if the ratio of the long axis to the short axis of the laser is increased, the removal ability of the resist film decreases due to a decrease in the power density of the laser represented by the output power / beam area. Note that the beam diameter shown in the present specification is the distance between 2 points in the laser beam profile that correspond to 1 / e2 of the maximum value of the beam intensity. 2

[0076] ​As the laser, an optical fiber laser is preferably used. By using an optical fiber laser, a laser beam having a smaller diameter can be irradiated. As the optical fiber laser, an optical fiber laser having a beam diameter of 200 μm or less in a direction orthogonal to the scanning direction of the laser is preferably used. In the case where the diameter is 200 μm or less or the laser beam is elliptical, an optical fiber laser having a beam diameter of 200 μm or less in a direction orthogonal to the scanning direction of the laser and a beam diameter in a direction orthogonal to the scanning direction of the laser smaller than the beam diameter in the scanning direction is preferably used.

[0077] Scanning speed of laser: 111 m / s or more

[0078] The greater the scanning speed of the laser on the metal strip, the more advantageous it is in terms of increasing productivity. For example, in the case where a metal strip having a width of 1200 mm is formed with linear grooves at intervals of 3 mm in the rolling direction of the metal strip using three laser irradiation devices at a line speed of 50 mpm, the scanning speed of the laser becomes 111 m / s or more. On the other hand, in order to sufficiently heat the resist film by laser irradiation and appropriately form the desired grooves, the upper limit of the scanning speed of the laser when the number of laser irradiation devices is three is preferably 400 m / s, and the upper limit of the scanning speed of the laser when the number of laser irradiation devices is two is preferably 600 m / s.

[0079] Scanning angle of laser on metal strip:

[0080] The laser is irradiated while being scanned in a direction crossing the rolling direction of the metal strip when the resist film is removed. The scanning angle of the laser is not particularly limited as long as it is in a direction crossing the rolling direction of the metal strip, and when the present groove forming method is used for the production of a grain-oriented magnetic steel sheet, the laser is preferably irradiated while being scanned in such a manner that the angle (0 to 90°) formed by the orthogonal direction to the rolling direction of the metal strip and the scanning direction of the laser becomes 45° or less. This is because the iron loss can be particularly appropriately reduced by making the angle formed by the orthogonal direction to the rolling direction of the metal strip and the scanning direction of the laser 45° or less. In addition, the repeating interval in the rolling direction of the laser removal portion is preferably 1 mm to 30 mm. By making the repeating interval in the rolling direction of the laser removal portion 1 mm or more, the number of laser irradiation devices required for removing the resist film and the maintenance time proportional thereto can be saved, and the productivity can be further improved. By making the repeating interval in the rolling direction of the laser removal portion 30 mm or less, the iron loss can be particularly appropriately reduced.

[0081] When the present groove forming method is used for the production of a grain-oriented magnetic steel sheet, the groove width formed on the surface of the metal strip is preferably 200 μm or less from the viewpoint of further improving the magnetic properties of the grain-oriented magnetic steel sheet after the groove is formed. The groove width formed on the surface of the metal strip is further preferably 100 μm or less.

[0082] Metal strip

[0083] According to the groove forming method of the present disclosure, the kind of the metal strip steel in which the groove is formed is not particularly limited. In the grain-oriented magnetic steel sheet, by forming a groove on the surface of the steel sheet, the iron loss thereof can be reduced. As described above, according to the present groove forming method, the heat influence of the laser irradiation on the steel sheet can be reduced, and a groove with a narrow width can be formed on the surface of the steel sheet, and thus by forming a groove on the surface of the steel sheet using the present groove forming method, the iron loss of the grain-oriented magnetic steel sheet can be effectively reduced.

[0084] Grain-oriented magnetic steel sheet

[0085] In the grain-oriented magnetic steel sheet, the surface roughness Ra in the rolling orthogonal direction of the metal strip steel before the resist agent is applied is preferably 0.5 μm or less. By making the surface roughness Ra in the rolling orthogonal direction of the metal strip steel 0.5 μm or less, the iron loss of the final grain-oriented magnetic steel sheet can be further reduced. The surface roughness Ra in the rolling orthogonal direction of the metal strip steel before the resist agent is applied is more preferably 0.4 μm or less, and further preferably 0.3 μm or less.

[0086] In addition, the final steel composition of the grain-oriented magnetic steel sheet is not particularly limited, and can be a publicly 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, and N: 20 ppm or less. If C is excessively contained, the magnetic aging can impair the iron loss, and thus it is preferable to be less than 30 ppm. Si improves the electrical resistivity and reduces the iron loss, and thus it is preferable to be contained at 1% or more. P also improves the electrical resistivity, and thus it is not problematic to be contained from the viewpoint of reducing the iron loss, but if the content is large, the manufacturability can be impaired, and 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 excessively contained, precipitates such as MnS are formed, which deteriorate the iron loss, and thus it is preferable to be within the above range. N precipitates as silicon nitride or the like at the time of stress relief annealing, which impairs the iron loss, and thus it is preferable not to be contained as much as possible. As for other components, based on the existing knowledge, it is not problematic to be added in a manner that the crystal orientation after secondary recrystallization is sharpened to the Goss orientation, but in the case where a forsterite film is formed, Cr, which develops anchoring, is preferably contained as little as possible, and is preferably 0.1% or less. In addition, Ti, Nb, V, Zr, and Ta elements deteriorate the iron loss by forming carbides and nitrides, and thus it is preferable that the total content thereof is 0.01% or less.

[0087] At the time of assembling the core of the 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 magnetic steel sheet. In addition, the sheet thickness of the final metal strip steel is preferably in the range of 0.10 to 0.35 mm. In the case of manufacturing the grain-oriented magnetic steel sheet, a non-heat-resistant type magnetic domain refinement treatment can be further applied by laser irradiation or the like.

[0088] Manufacturing method of directional electromagnetic steel sheet

[0089] In one example, the method for manufacturing a directional electromagnetic steel sheet using the groove forming method of this disclosure is as follows:

[0090] Hot-rolled steel plates are produced by hot rolling steel billets.

[0091] Next, the hot-rolled steel sheet or the hot-rolled annealed sheet obtained by hot-rolling and annealing the hot-rolled steel sheet is subjected to one or more cold rolling processes with intermediate annealing to produce a cold-rolled steel sheet.

[0092] Next, the cold-rolled steel sheet is subjected to a single recrystallization annealing process to produce a single recrystallized sheet.

[0093] Next, the above-mentioned primary recrystallization plate is subjected to secondary recrystallization annealing to produce a secondary recrystallization plate;

[0094] Linear grooves are formed on the surface of any of the hot-rolled steel sheets using the groove-forming method described above. It should be noted that primary recrystallization annealing can also serve to reduce carbon decarburization or increase nitrogen nitriding in the steel sheet. Furthermore, secondary recrystallization annealing, as mentioned here, refers to annealing used to selectively induce abnormal growth of Goss-oriented grains. Secondary recrystallization annealing can also serve as a process for forming a magnesium olivine coating and for purifying elements in the steel.

[0095] The groove formation on the surface of the steel sheet can be performed at any stage after hot rolling. The metal strip to which the groove formation is applied can be a hot-rolled steel sheet after hot rolling, a hot-rolled annealed sheet obtained by hot rolling and annealing a hot-rolled steel sheet, a cold-rolled steel sheet after cold rolling once, a cold-rolled steel sheet before or after intermediate annealing when cold rolling twice or more with intermediate annealing in between, a cold-rolled steel sheet after cold rolling after intermediate annealing, a first recrystallized sheet after first recrystallization annealing, or a second recrystallized sheet after second recrystallization annealing. It should be noted that if rolling is performed after the groove formation, the groove may sometimes disappear. Therefore, groove formation is preferably performed on a cold-rolled steel sheet after cold rolling once, a cold-rolled steel sheet after cold rolling after the final intermediate annealing when cold rolling twice or more with intermediate annealing in between, a first recrystallized sheet after first recrystallization annealing, or a second recrystallized sheet after second recrystallization annealing. Furthermore, groove formation can be performed at multiple stages after hot rolling.

[0096] The grooves are linear grooves extending in a direction transverse to the rolling direction of the metal strip. In this case, when the metal strip is a grain-oriented magnetic steel sheet, the angle of the linear grooves with respect to the transverse direction (TD) of the metal strip is preferably within 45° from the viewpoint of reducing the iron loss by refining the magnetic domain structure. In this case, one groove does not necessarily extend over the entire width in the direction transverse to the rolling direction of the metal strip, and a plurality of grooves can be formed by irradiating laser light using two or more laser irradiation devices. In addition, when the grain-oriented magnetic steel sheet is manufactured, the grooves are preferably repeatedly formed at periodic intervals in the rolling direction of the metal strip in order to more effectively reduce the iron loss. The shape of the linear grooves can be adjusted according to the laser beam shape or etching conditions, but in the case of the grain-oriented magnetic steel sheet, the groove width is preferably 30 μm to 200 μm, and the depth is preferably 10 μm to 40 μm. In addition, the linear grooves are preferably periodically formed in the rolling direction of the metal strip. In the case of the grain-oriented magnetic steel sheet, the periodic interval of the linear grooves is preferably 1 mm to 30 mm. By setting the periodic interval of the linear grooves to 1 mm or more, the volume of the base iron in the grain-oriented magnetic steel sheet can be more appropriately ensured, and a more appropriate magnetic flux density can be obtained. In addition, by setting the periodic interval of the linear grooves to 30 mm or less, a higher magnetic domain refinement effect can be obtained.

[0097] Example

[0098] [Example 1]

[0099] Manufacture of the grain-oriented magnetic steel sheet having linear grooves

[0100] A hot-rolled steel sheet was manufactured by subjecting a steel billet (C: 0.050%, Mn: 0.06%, P: 0.01%, S: 0.002%, Al: 0.014%, N: 70 ppm, Ti + Nb + V + Zr + Ta < 0.001%) containing 3.4% Si to hot rolling, and then a cold-rolled steel sheet having a sheet thickness of 0.22 mm was manufactured by subjecting a hot-rolled annealed sheet obtained by subjecting the hot-rolled sheet to hot-rolled sheet annealing at 1050°C to cold rolling, and then a primary recrystallized sheet was obtained by subjecting the cold-rolled steel sheet to primary recrystallization annealing at 860°C, and then a secondary recrystallized sheet having a sheet thickness of 0.22 mm was obtained by subjecting the primary recrystallized sheet to secondary recrystallization annealing at a maximum temperature of 1200°C, and a metal strip having grooves was manufactured.

[0101] Measurement of the surface roughness Ra in the transverse direction

[0102] The surface roughness Ra in the transverse direction of the metal strip before the resist film was formed was measured based on JIS B 0031 (1994). The results are shown in Table 3.

[0103] Next, the resist film formation coating agent of the composition (solid component conversion) shown in Table 2 was applied to both sides on a secondary recrystallization plate in a manner such that the thickness of each side after sintering became 2 μm, and sintering was performed at a temperature of 830°C. As the other component, titanium oxide was used.

[0104] [Table 2]

[0105] Table 2

[0106]

[0107] Measurement of Brightness Index L* of Resist Film

[0108] The brightness index L* in the CIELAB color space (CIE 1976 L*a*b* color space) was measured for the formed resist film. The brightness index L* was numerically evaluated using the spectral reflectance measured by a spectrophotometer. The measurement results are shown in Table 3.

[0109] Next, laser irradiation was performed while scanning the surface and the back surface of the steel plate in the rolling orthogonal direction (TD), and the resist film was removed in a linear shape periodically at 5 mm intervals in the rolling direction.

[0110] Measurement of Maximum Value of Removal Width of Resist Film

[0111] The maximum value of the removal width of the resist film was analyzed by observing the removal width of the resist film on both surfaces of the steel plate in the rolling orthogonal direction (TD) using an optical microscope. The measurement results are shown in Table 3.

[0112] Evaluation of Heat Influence of Laser Irradiation on Metal Strip Steel

[0113] The presence or absence of the heat influence of laser irradiation on the metal strip steel was determined by how much percentage the Vickers hardness of the base iron of the laser irradiated portion decreased from the laser non-irradiated portion in the average value of at least 15 or more measurement points after laser irradiation. If the Vickers hardness of the laser irradiated portion decreased by 1% or more from the laser non-irradiated portion, it was judged that there was heat influence due to laser irradiation. If the Vickers hardness of the laser irradiated portion did not decrease by 1% or more from the laser non-irradiated portion, it was judged that there was no heat influence due to laser irradiation. Here, the Vickers hardness measurement was performed using a steel plate prepared separately from the steel plate on which etching was performed, on the base iron after the resist film was removed after laser irradiation. The evaluation results are shown in Table 3.

[0114] Next, the steel sheet from which the resist film was partially removed was electrolytically etched. The electrolyte was NaCl, and the current density was adjusted in advance to form grooves of a desired depth. After etching, the surface of the steel sheet was cleaned, and further a film composed of inorganic matter having a one-side thickness of 0.3 μm was coated at 300°C on the laser-irradiated surface to produce a grain-oriented magnetic steel sheet having grooves formed on the surface. The laser-irradiation conditions are shown in Table 3. In addition, the grain-oriented magnetic steel sheet having grooves formed on the surface was subjected to the following property evaluations. The evaluation results are shown in Table 3.

[0115] Evaluation of Resist Removability

[0116] The laser removability of the resist film was evaluated by visually determining the appearance of the peeling line after laser irradiation and using the area ratio of the peeling area of the laser-irradiated portion to the irradiated area. Here, the irradiated area of the laser was obtained by multiplying the diameter of the laser in the direction orthogonal to the scanning direction by the distance of the laser scanning. Note that if the peeling area of the laser-irradiated portion was 95% or more, it was rated as "O". The evaluation results are shown in Table 3.

[0117] Evaluation Criteria

[0118] O: The peeling area of the laser-irradiated portion was 95% or more

[0119] X: The peeling area of the laser-irradiated portion was less than 95%

[0120] Measurement of Iron Loss W 17 / 50

[0121] For the iron loss, single sheet magnetic tests were performed using 30 pieces of SST test pieces each having a width of 100 mm and a length of 320 mm, and the iron loss W (W / kg) at a maximum magnetic flux density of 1.7 T and a frequency of 50 kHz was measured. Note that if the iron loss W was 0.710 W / kg or less, the magnetic properties were good, and if it was 0.700 W / kg or less, the magnetic properties were even better. The measurement results are shown in Table 3. 17 / 50 17 / 50

[0122]

[0123] [Example 2]

[0124] Production of Grain-oriented Magnetic Steel Sheet Having Linear Grooves

[0125] ​​​As a metal strip, a hot-rolled steel sheet was produced by hot-rolling a steel billet containing 3.4% Si (C: 0.050%, Mn: 0.06%, P: 0.01%, S: 0.002%, Al: 0.014%, N: 70 ppm, Ti + Nb + V + Zr + Ta < 0.001%) and then a cold-rolled steel sheet having a sheet thickness of 0.22 mm was produced by cold-rolling a hot-rolled annealed sheet obtained by annealing the hot-rolled sheet at 1050°C. The surface roughness Ra in the rolling normal direction of the cold-rolled steel sheet (metal strip) before forming the resist film was measured in the same manner as in Example 1. The results are shown in Table 5.

[0126] Next, a resist film forming agent having a composition shown in Table 4 (solid content conversion) was applied to both the front and back surfaces of the cold-rolled steel sheet in a thickness of 2 μm by a gravure offset printing method, and then dried at 220°C for 30 seconds to form a resist film. The brightness index L* of the resist film was measured in the same manner as in Example 1. The results are shown in Table 4.

[0127] [Table 4]

[0128] Table 4

[0129]

[0130] Next, the resist film was removed in a linear shape by laser irradiation to the steel sheet surface with an interval of 3.3 mm in the rolling direction (RD). Then, electrolytic etching was performed on the steel sheet from which the resist film was partially removed. The electrolyte was NaCl, and the current density was previously adjusted to form grooves of a desired depth. After the electrolytic etching was performed, the resist film remaining on both the front and back surfaces of the steel sheet was removed with an aqueous NaOH solution. The liquid temperature of the aqueous NaOH solution was maintained at 50 to 70°C. Thereafter, the steel sheet was washed with water, and then surface cleaning was performed to form grooves on the surface. The laser irradiation conditions are shown in Table 5. Only the conditions of No. 17 used an elliptical light beam, and the others used an isometric (circular) light beam. Only No. 20 was not a fiber laser, but a CO2laser was used. After a cold-rolled steel sheet on which linear grooves were formed was subjected to primary recrystallization annealing at 860°C to obtain a primary recrystallization sheet, secondary recrystallization annealing was performed on the primary recrystallization sheet at a maximum temperature of 1200°C to obtain a secondary recrystallization sheet. For the purpose of planarization of the steel sheet and formation of an insulating tension film, the secondary recrystallization sheet was subjected to annealing at a maximum temperature of 860°C to produce a grain-oriented magnetic steel sheet having a sheet thickness of 0.22 mm. The grain-oriented magnetic steel sheet was evaluated for characteristics in the same manner as in Example 1. The evaluation results are shown in Table 5.

[0131]

[0132] Industrial applicability

[0133] The grain-oriented magnetic steel sheet manufactured using the groove forming method of the present disclosure also exhibits good magnetic characteristics after annealing such as stress relief annealing, and can be applied to a transformer of a core type. If the grain-oriented magnetic steel sheet manufactured using the groove forming method of the present disclosure is applied to a transformer, energy use efficiency can be improved, and thus is useful in industry.

Claims

1. A method for forming grooves on the surface of a metal strip, wherein a resist film with a brightness index L* of 0 to 70 is formed on at least one side of the metal strip. Next, the resist film is scanned in a direction traversing the rolling direction of the metal strip while being irradiated with a laser with an output power of 0.3 kW or more and less than 1.5 kW, and the portion of the resist film irradiated by the laser is removed in a linear motion. Next, the portion of the metal strip where the resist film has been removed is etched to form a groove. in, The brightness index L* refers to the L* value in the CIELAB color space, i.e., the CIE 1976 L*a*b* color space.

2. The method for forming a groove on the surface of a metal strip according to claim 1, wherein, The width of the resist film removal is less than 200 μm, and the laser scanning speed is greater than 111 m / s.

3. The method for forming a groove on the surface of a metal strip according to claim 1, wherein, The diameter of the laser beam on the surface of the metal strip in a direction orthogonal to the scanning direction of the laser is less than 200 μm.

4. The method for forming a groove on the surface of a metal strip according to claim 2, wherein, The diameter of the laser beam on the surface of the metal strip in a direction orthogonal to the scanning direction of the laser is less than 200 μm.

5. The method for forming a groove on the surface of a metal strip according to any one of claims 1 to 4, wherein, The laser is a fiber laser with a beam diameter of less than 200 μm in a direction orthogonal to the laser scanning direction.

6. The method for forming a groove on the surface of a metal strip according to any one of claims 1 to 4, wherein, Before the formation of the resist film, the surface roughness Ra of the metal strip in the rolling orthogonal direction is less than 0.5 μm.

7. The method for forming a groove on the surface of a metal strip according to claim 5, wherein, Before the formation of the resist film, the surface roughness Ra of the metal strip in the rolling orthogonal direction is less than 0.5 μm.

8. A method for manufacturing a directional electromagnetic steel sheet, comprising hot rolling a steel billet to produce a hot-rolled steel sheet. Next, the hot-rolled steel sheet or the hot-rolled annealed sheet obtained by hot-rolling and annealing the hot-rolled steel sheet is subjected to one or more cold rolling processes, with intermediate annealing, to produce a cold-rolled steel sheet. Next, the cold-rolled steel sheet is subjected to a single recrystallization annealing process to produce a single recrystallized plate. Next, the primary recrystallization plate is subjected to secondary recrystallization annealing to produce a secondary recrystallization plate; A groove is formed on the surface of any hot-rolled steel plate using the groove forming method according to any one of claims 1 to 7.

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