Method for forming linear groove, method for manufacturing grain-oriented electrical steel sheet, and device for forming linear groove

Abstract

Provided is a method for forming a linear groove in which etching is used to form a linear groove in the surface of a steel sheet and through which a linear groove having a narrow and uniform shape can be formed while suppressing, in particular, deterioration of magnetic characteristics in a grain-oriented electrical steel sheet that result from laser irradiation for removing a resist. The present invention is a method for forming a linear groove that includes a resist application step for applying a resist to the surface of a steel sheet having a final sheet thickness, a laser irradiation step for periodically performing, in the rolling direction of the steel sheet, laser scanning for removing the resist in a portion irradiated with a laser by radiating the laser while scanning in a direction transverse to the rolling direction of the steel sheet, and an etching step for forming a linear groove by etching the portion of the steel sheet from which the resist was removed. In the laser irradiation step, removal of the resist is performed by laser scanning the surface of the steel sheet which is wound around a support roll.

Description

Method for forming linear grooves, method for manufacturing grain-oriented electrical steel sheets, and apparatus for forming linear grooves

[0001] The present invention relates to a method for forming linear grooves, a method for manufacturing grain-oriented electrical steel sheets, and a linear groove forming apparatus.

[0002] Grain-oriented electrical steel sheets, which have excellent magnetic properties, are mainly used as core materials for transformers, and there is a need to reduce iron loss in order to improve the energy efficiency of transformers. Methods for reducing iron loss in grain-oriented electrical steel sheets include methods to highly align the secondary recrystallized grains in the steel sheet to the Goss orientation (sharpening), methods to increase the film tension, methods to thin the steel sheet, and methods to process the surface of the steel sheet.

[0003] The technology for reducing iron loss through surface processing of steel sheets involves introducing non-uniform strain to the surface of the steel sheet using physical methods to subdivide the width of magnetic domains and reduce iron loss. One such method involves forming grooves on the surface of a finish-annealed steel sheet using a toothed roll. This method subdivides the magnetic domains on the surface of the steel sheet by forming grooves, thereby reducing iron loss in the steel sheet. Furthermore, it has been found that even if heat treatment such as strain-relieving annealing is performed after groove formation, the introduced grooves do not disappear, thus maintaining the iron loss reduction effect. However, this method has problems: the groove shape tends to become non-uniform due to severe wear of the toothed roll, and manufacturing costs increase if the roll is heated to a high temperature or lubricant is applied to suppress wear of the toothed roll.

[0004] Therefore, a method has been developed to form linear grooves on the surface of a steel plate by etching, without using mechanical means such as toothed rolls. Specifically, a resist ink is applied in a pattern to the surface of the steel plate before the forsterite coating is formed, and then grooves are formed on the surface of the steel plate by selectively etching the areas where the resist ink is not applied using methods such as electrolytic etching. With this method, there is almost no mechanical wear on the equipment, making maintenance easier compared to methods using toothed rolls.

[0005] Incidentally, it is known that the magnetic properties of steel plates with such linear grooves formed on them are greatly influenced by the shape of the linear grooves. Furthermore, it is understood that not only the depth and width of the grooves, but also detailed shapes such as the curvature of the groove cross-section affect iron loss. Therefore, when forming linear grooves using the etching method described above, variations in the shape of the resist, which functions as an etching mask, result in variations in the groove shape, and consequently, variations in the magnetic properties of the steel plate. To address this, techniques have been proposed to improve the coating accuracy of the resist in methods for forming linear grooves by etching, thereby suppressing variations in the magnetic properties of the steel plate.

[0006] For example, Patent Document 1 proposes a technique for forming linear grooves of uniform shape by controlling the temperature of the resist ink and the steel plate to a constant level when applying the resist. By keeping the temperature constant, fluctuations in the viscosity of the resist ink are suppressed, and as a result, variations in groove shape are suppressed.

[0007] Patent Document 2 proposes a technique for controlling conditions such as the viscosity of the resist ink used and the mesh pattern of the gravure roll within a specific range when applying resist using gravure offset printing. This suppresses the generation of halftone dots caused by gravure cells formed on the surface of the gravure roll and improves the accuracy of the resist pattern.

[0008] While the methods proposed in Patent Documents 1 and 2 show some improvement in the shape accuracy of the resist, variations in shape still persist in the linear grooves formed by these methods. As an alternative measure to improve the accuracy of resist pattern formation, Patent Document 3 describes forming a resist pattern using a laser. Specifically, after uniformly applying the resist to the entire surface of the steel plate, the resist is instantly evaporated or sublimated by irradiating the areas where coating is unnecessary with a laser, selectively removing the resist from the irradiated areas. With such a method, the shape of the areas from which the resist is removed is not affected by variations in the gravure cell, and it is expected that linear grooves with a uniform shape can be formed.

[0009] JP 11-279646 JP 07-032575 JP International Publication No. 2017-017908

[0010] Patent Document 3 further investigated the effects of laser irradiation-based resist removal on grain-oriented electrical steel sheets (base metal) and revealed that controlling the output, beam diameter, resist film thickness, etc., is important. However, it was found that even with control of these parameters, problems such as not being able to obtain the desired peeling width or not being able to sufficiently reduce variations in groove shape are not completely resolved.

[0011] The present invention has been made in view of the above circumstances, and aims to provide a method for forming linear grooves on the surface of a steel sheet using etching, which can form narrow, uniform linear grooves while suppressing the deterioration of the magnetic properties of grain-oriented electrical steel sheets, in particular, that occurs with laser irradiation for resist removal. Furthermore, the present invention aims to provide a method for manufacturing grain-oriented electrical steel sheets that includes this method. The present invention also aims to provide a linear groove forming apparatus suitable for carrying out the above linear groove forming method.

[0012] The inventors of the present invention have further investigated the effects of laser irradiation on resist removal, particularly on grain-oriented electrical steel sheets (base metal), and have obtained the following findings: (1) As the groove width increases, the amount of electrolysis increases, leading to an increase in hysteresis loss; therefore, from the viewpoint of iron loss, a smaller groove width is preferable. (2) In order to make the groove width as narrow as possible, it is important to lower the laser output. In order to set the laser output even lower, it is necessary to make it easier to peel off the resist with a laser. In order to improve the laser peelability of the resist, it is effective to wrap it around a support roll and irradiate it with a laser while applying tensile stress to the resist peeling surface.

[0013] Furthermore, the inventors conducted further studies and obtained the following findings: (3) In order to further narrow the groove width and further suppress variations in groove width, it is important to suppress the heat diffusion distance introduced into the steel plate during laser irradiation as much as possible. To suppress heat diffusion, it is important to minimize the heat diffusion time. Although the output and scanning speed have a large effect on heat input, even if the ratio of output to scanning speed is the same, if the scanning speed is slow, it will lead to an increase in groove width and increased variation, so it is preferable to adopt a fast scanning speed.

[0014] Based on the above findings, we conducted a detailed study on the conditions for resist removal by laser irradiation and completed the present invention. That is, the gist of the present invention is as follows: [1] A linear groove formation method comprising: a resist coating step of coating a steel sheet surface having a final thickness; a laser irradiation step of periodically performing laser scanning in the rolling direction of the steel sheet, in which a laser is irradiated while scanning in a direction transverse to the rolling direction of the steel sheet to remove the resist from the irradiated portion; and an etching step of etching the portion of the steel sheet from which the resist has been removed to form a linear groove, wherein in the laser irradiation step, the removal of the resist is carried out by performing laser scanning on the steel sheet surface of the steel sheet wrapped around a support roll. [2] The linear groove formation method of [1], wherein in the laser irradiation step, the laser scanning speed is 200 m / sec or more. [3] A method for manufacturing grain-oriented electrical steel sheets, comprising: a hot rolling step of hot rolling a steel slab to obtain a hot-rolled steel sheet; a cold rolling step of cold rolling the hot-rolled steel sheet, or a hot-rolled annealed steel sheet obtained by hot-rolling the hot-rolled steel sheet, once or two or more times with an intermediate annealing in between, to obtain a cold-rolled steel sheet; and an annealing step of primary recrystallization annealing the cold-rolled steel sheet to obtain a primary recrystallized sheet, and then secondary recrystallization annealing the primary recrystallized sheet to obtain a secondary recrystallized sheet, wherein linear grooves are formed between the cold rolling step and the annealing step by the linear groove forming method of [1] or [2]. [4] A linear groove forming apparatus comprising: a cleaning unit for cleaning the surface of a steel plate; a resist application unit for applying a resist to the surface of the steel plate; a laser irradiation unit for irradiating the surface of the steel plate wrapped around a support roll with a laser to remove the resist from the irradiated portion; an etching unit for etching the portion of the steel plate from which the resist has been removed; and a resist removal unit for removing the resist remaining on the surface of the steel plate, all arranged in this order.

[0015] According to the present invention, in a method for forming linear grooves on the surface of a steel sheet using etching, narrow linear grooves can be formed in a uniform shape, making it possible to fully enjoy the magnetic domain refinement effect caused by groove formation, and thus obtain a grain-oriented electrical steel sheet with excellent iron loss characteristics.

[0016] This is a schematic diagram of laser scanning on a steel plate surface without a support roll. It shows the relationship between laser power and laser peeling width. It also shows the relationship between laser peeling width and groove width. Finally, it shows the relationship between laser peeling width and iron loss. This is a schematic diagram of laser scanning on a steel plate surface with a support roll. It shows the relationship between support roll diameter and minimum peeling width. It also shows the relationship between scanning speed and laser peeling width.

[0017] First, we will explain the experimental results that clarified the relationship between groove width and iron loss. In the experiment, as shown in Figure 1, a known cold-rolled sheet (steel plate) 1 with a thickness of 0.23 mm and a resist coating on its surface was passed through the sheet in the direction of the arrow (Y direction), and laser irradiation was performed using a laser irradiation device 2, scanning in a direction perpendicular to the rolling direction, repeatedly at intervals of 5 mm in the rolling direction (Y direction), to form laser-peeled sections 3. At that time, the beam diameter was 40 μm, the scanning speed was 10 m / sec, and the output was varied between 20 and 300 W. The beam diameter was determined by measuring the intensity profile using a CCD camera type fixed beam profiler (LaseView-LHB series manufactured by Kokyo Co., Ltd.), and the profile width at the position where the intensity was 0.135 times the maximum intensity was used. Laser irradiation was performed using a single-mode fiber laser (Trumpf TruFiber P manufactured by Trumpf) with a galvanometer scanner method, with a scanning width of 200 mm and a scanning interval of 5 mm. Figure 2 shows the relationship between laser output and the width of the laser-peeled section 3 (width in the Y direction). Under all conditions, the resist was successfully removed, but it was observed that the laser removal width decreased as the power output decreased. The laser removal width was determined by taking a sample after removal, observing the area around the removed portion using a laser microscope (a 3D laser microscope with a pinhole confocal optical system) in a flat state, and measuring the distance of the area where the resist had been removed. This measurement was performed at 20 locations, and the average value of the results obtained from these 20 locations was taken as the removal width.

[0018] Next, an electrolytic etching treatment was performed on a sample of the cold-rolled sheet 1 in which the resist peeled portion 3 was formed, to remove the resist from the entire surface of the steel sheet, and a grain-oriented electrical steel sheet was manufactured using a known method. Specifically, a method was adopted in which decarburization annealing was performed, MgO was applied and secondary recrystallization annealing was performed, and then planarization annealing was performed by applying an insulating coating. The relationship between the groove width and the laser peeled width of the obtained product sheet was investigated. In addition, iron loss W at a magnetic flux density of 1.7 T and excitation frequency of 50 Hz in accordance with JIS C2556 was investigated. 17／50 The material was evaluated using a single-plate magnetic tester. The samples used were those with a B8 of 1.90T, which were measured magnetically before grooving. The groove depth was adjusted to be the same by controlling the electrolytic etching process time. The groove width was determined by observing the area around the delamination with a laser microscope (a 3D laser microscope using a pinhole confocal optical system), identifying the deepest groove depth, and defining the groove width as the distance between the groove walls at 50% of the deepest point. This measurement was performed at 20 locations, and the average of the results obtained from these 20 locations was used as the groove width.

[0019] Figure 3 shows the relationship between laser peeling width and groove width, and Figure 4 shows the relationship between laser peeling width and iron loss. From Figures 3 and 4, it can be seen that there is a correlation between laser peeling width and groove width, and that the smaller the laser peeling width (groove width), the better the iron loss. The reason why iron loss increases as the laser peeling width (groove width) increases is that hysteresis loss increases with increasing electrolysis.

[0020] Next, we investigated whether it was possible to reduce the laser peeling width even under the same laser irradiation conditions. As a result, we found that by scanning the laser beam across the surface of the cold-rolled sheet 1 wrapped around a support roll, laser peeling was possible with lower power. Figure 5 shows a schematic diagram of laser scanning across the surface of the cold-rolled sheet 1 wrapped around a support roll. Here, the diameter of the support roll was changed from 100 mm to 1000 mm, and the surface of the cold-rolled sheet 1 was irradiated with a laser while it was wrapped around the support roll. The beam diameter was 100 μm and the scanning speed was 10 m / sec, and the minimum peeling width was determined while changing the power for each condition. Figure 6 shows the relationship between the support roll diameter and the minimum peeling width. The minimum peeling width is the laser peeling width when irradiated at the lowest power that does not leave any resist residue. It was newly discovered that the laser peeling width can be narrowed by irradiating with a laser while wrapped around a support roll. The reason for this is not clear, but it is presumed that tensile stress is applied to the laser irradiation surface when wrapped around the roll.

[0021] Next, with the aim of further reducing the laser delamination width, the relationship between laser scanning speed, output power, and laser delamination width was investigated. It was assumed that the laser delamination state changes depending on the input energy density. Since the input energy density is determined by the laser scanning speed and laser output power, the laser delamination width obtained under each condition was evaluated while keeping the input energy density constant and varying the laser scanning speed and laser output power. Here, experiments were conducted and evaluated under two conditions: without winding onto a support roll and with winding onto a 500 mm support roll, with a laser diameter of 70 μm, and a constant laser output to scanning speed ratio (laser output power / scanning speed) of 5 W·sec / m.

[0022] Figure 7 shows the relationship between scanning speed and laser delamination width. Even with the same energy density, a faster scanning speed tended to result in a smaller laser delamination width. While the reason for this is not entirely clear, thermal diffusion distance is a very important influencing factor for laser delamination width. It is speculated that the influence of the input time on this thermal diffusion distance is greater than that of the thermal energy, and therefore, shortening the laser irradiation time resulted in a shorter thermal diffusion distance.

[0023] Based on the above results, a method for carrying out the present invention will be specifically described. Note that the following description represents a preferred embodiment of the present invention, and the present invention is not limited in any way by the following description.

[0024] In the method of the present invention, the following processes (1) to (4) are sequentially applied to the surface of a steel sheet having a final thickness: (1) resist film formation process (2) laser irradiation process (3) etching process (4) resist removal process

[0025] [Steel Sheet] The type of steel sheet used in the present invention is not limited, but the linear groove formation method of the present invention is particularly useful for reducing iron loss in grain-oriented electrical steel sheets. When applied to grain-oriented electrical steel sheets, steel sheets at an intermediate stage in the manufacturing process of grain-oriented electrical steel sheets, such as those that have been cold-rolled to the final thickness of the grain-oriented electrical steel sheet, can be used. Examples include cold-rolled steel sheets, primary recrystallized steel sheets, secondary recrystallized steel sheets, etc., with cold-rolled steel sheets being preferred.

[0026] The component composition (including, for example, the component composition of the steel material) when manufacturing grain-oriented electrical steel sheets is not particularly limited and can be any component composition. From the viewpoint of reducing iron loss in grain-oriented electrical steel sheets, it is preferable to have a component composition containing Si in the range of 2.0 to 8.0 mass%, and in addition, from the viewpoint of treadability, it is more preferable to have a component composition containing Si in the range of 2.5 to 4.5 mass%.

[0027] The following are suitable component compositions other than Si for manufacturing grain-oriented electrical steel sheets. However, the present invention is not limited to the following component compositions, and the effects of the present invention can be enjoyed with any component composition used when manufacturing grain-oriented electrical steel sheets.

[0028] C: 0.01 to 0.08% by mass. C is an element effective for improving the structure during primary recrystallization. To obtain its effect, the C content is preferably 0.01% by mass or more. On the other hand, since it is easy to reduce C to an amount that does not cause magnetic aging during primary recrystallization annealing, the C content is preferably 0.08% by mass or less. The C content is more preferably 0.03% by mass or more and more preferably 0.07% by mass or less.

[0029] Mn: 0.005 to 1.0% by mass. Mn is an element effective for improving hot workability. To obtain its effect, the Mn content is preferably 0.005% by mass or more. On the other hand, from the point of avoiding a decrease in magnetic flux density, the Mn content is preferably 1.0% by mass or less. The Mn content is more preferably 0.01% by mass or more and more preferably 0.2% by mass or less.

[0030] Also, regarding the component composition in the case of manufacturing a grain-oriented electrical steel sheet, the basic components other than the above components are different depending on whether an inhibitor is used to cause secondary recrystallization or not.

[0031] When an inhibitor is used to cause secondary recrystallization, it is made into a component containing various inhibitor-forming components. For example, when using an AlN-based inhibitor, it is preferable to contain Al and N in the ranges of Al: 0.01 to 0.065% by mass and N: 0.005 to 0.012% by mass, respectively. Also, when using an MnS·MnSe-based inhibitor, it is preferable to contain Se and / or S in the ranges of S: 0.005 to 0.03% by mass and Se: 0.005 to 0.03% by mass, respectively.

[0032] On the other hand, when an inhibitor is not used to cause secondary recrystallization, it is preferable to reduce Al, N, S, and Se, which are inhibitor-forming components, to Al: 0.0100% by mass or less, N: 0.0050% by mass or less, S: 0.0050% by mass or less, and Se: 0.0050% by mass or less, respectively.

[0033] In addition, regarding the component composition in the production of grain-oriented electrical steel sheets, for the purpose of further improving magnetic properties, in addition to the above basic components, Ni: 0.03 to 1.50% by mass, Sn: 0.01 to 1.50% by mass, Sb: 0.005 to 1.50% by mass, Cu: 0.03 to 3.0% by mass, P: 0.03 to 0.50% by mass, Mo: 0.005 to 0.10% by mass, and Cr: 0.03 to 1.50% by mass, one or more selected from the group consisting of may be contained.

[0034] Ni is an element useful for improving magnetic properties by improving the hot-rolled sheet structure. From the point of fully obtaining this effect, when Ni is contained, the Ni content is preferably 0.03% by mass or more. On the other hand, from the point of stably developing secondary recrystallized grains and suppressing deterioration of magnetic properties, the Ni content is preferably 1.50% by mass or less. Also, Sn, Sb, Cu, P, Mo, and Cr are elements useful for improving magnetic properties. From the point of fully obtaining this effect, when these elements are contained, the content is preferably not less than the above lower limit value. Also, from the point of development of secondary recrystallized grains, the content is preferably not more than the above upper limit value.

[0035] In the component composition in the production of grain-oriented electrical steel sheets, the balance other than the above components is Fe and unavoidable impurities. Note that C is decarburized during primary recrystallization annealing, and Al, N, S, and Se are purified during secondary recrystallization annealing (finish annealing). Therefore, in the steel sheet after secondary recrystallization annealing (finish annealing), the content of these components is reduced to the level of unavoidable impurities.

[0036] When a film is formed on the surface of the steel sheet, etching may be inhibited. Therefore, a film insoluble or hardly soluble in an etching solution (electrolytic solution), such as a forsterite film or a tension-applying film, is not formed on the surface of the steel sheet, and the resist described later is directly applied to the surface of the steel sheet.

[0037] [Resist Coating Process] A resist (resist ink) is applied to the surface of the steel sheet prior to laser irradiation. The resist functions as an etching resist to prevent the steel sheet from being etched in the etching process described later. Any material can be used as the resist as long as it can prevent the etching of the steel sheet, but a resist mainly composed of a thermosetting resin is preferred. Examples of thermosetting resins include alkyd resins, epoxy resins, melamine resins, etc. These may be used alone or in combination of two or more. UV curability and electron beam curability, as used in the semiconductor field, are not necessarily required. In addition, although there is an equipment challenge of increasing the size of the apparatus, the insulating film that is usually formed on the surface of the electrical steel sheet may be used as the resist. In this case, the coating can be carried out according to the prior art. Drying can also be carried out according to the prior art.

[0038] The application of the resist to the steel plate surface can be carried out by any method without particular limitations, but it is preferable to use a roll coater method, and more preferably a gravure printing method using a gravure roll. When using a gravure printing method, it is preferable to install a doctor blade above the gravure roll to uniformize the amount of ink on the gravure roll in order to ensure a constant film thickness.

[0039] The resist formation pattern in the present invention is not particularly limited and can be any pattern as long as it can ultimately form the desired linear grooves. However, in the present invention, it is preferable to apply the resist to the entire surface of the steel plate in order to partially remove the resist by laser irradiation.

[0040] The basis weight (coating amount) of the resist is 1.0 to 10.0 g / m². 2 A basis weight of 1.0 g / m² is preferred. 2 With the above specifications, it is easy to avoid insufficient resist resistance causing dielectric breakdown during electrolytic etching, and the basis weight is 10.0 g / m². 2The following conditions are advantageous for laser resist stripping. Here, the basis weight of the resist is the value before laser stripping and after drying, and is derived from the weight difference of the object to be coated and the coating area before and after resist coating.

[0041] After applying the resist, it is preferable to dry the resist before the next laser irradiation step. The drying method is not particularly limited, and for example, hot air drying, vacuum drying, etc., can be used. In the case of hot air drying, the drying temperature is preferably 150 to 350°C. In the case of vacuum drying, the pressure is preferably 10 Pa or less, and the drying time is preferably 5 seconds or more.

[0042] [Laser Irradiation Process] Next, the surface of the steel sheet coated with resist is irradiated with a laser while scanning it in a direction transverse to the rolling direction of the steel sheet. This laser irradiation locally heats and vaporizes the resist in the irradiated area, causing it to be removed, and as a result, a resist-removed area is formed where the steel sheet surface (base metal) is exposed. The exposed steel sheet portion in the resist-removed area is selectively etched in the etching process described later to form linear grooves.

[0043] The dimensions of the linear grooves formed by etching affect the magnetic properties of the final product, the grain-oriented electrical steel sheet. A narrower groove width is preferable.

[0044] Here, the groove width of the linear groove and the laser peeling width are correlated and are approximately the same; therefore, the laser peeling width is controlled so that it matches the groove width of the linear groove, as described later. As mentioned above, a narrower groove width for the linear groove is preferable, and a narrower laser peeling width is also preferable. In order to form a narrower groove, it is necessary to make the laser peeling width as small as possible.

[0045] The method the inventors focused on to narrow the laser peeling width is to reduce the laser output as much as possible. When the laser output is high, heat is transferred to a wide area around it by thermal conduction. This heat causes the resist to peel off, so the laser peeling width becomes larger than the beam diameter. The key to further reducing the laser output is to improve the laser peelability of the resist. To improve this laser peelability, the linear groove forming method of the present invention irradiates the resist with a laser while it is wrapped around a support roll. The tensile stress on the surface of the steel plate generated when it is wrapped around the support roll contributes to improving the laser peelability of the resist.

[0046] The support roll is installed so that its axis of rotation coincides with the width direction of the steel plate. Then, while applying tension to the steel plate, it is pressed against the support roll, causing it to wrap around the support roll and pass over it. This applies tensile stress to the laser irradiation surface, improving laser peelability. The material of the support roll is not particularly limited and may be metal, but it is preferable to use a rubber roll or a metal roll with rubber wrapped around the surface, as these are less prone to scratches.

[0047] When wrapping the steel plate, the steel plate is made to contact the support roll with its entire width in the axial direction at least a portion of its circumference. For example, the starting point of contact between the support roll and the steel plate (P in Figure 5) １ ) and the center of the rotation axis are connected by a line segment and the end point of contact of the support roll with the steel plate (P in Figure 5). ２ The steel plate can be brought into contact with the support roll such that the angle between the line segment connecting the support roll and the center of the rotation axis (the angle shown as θ in Figure 5) is between 1° and 180°, preferably between 5° and 90°.

[0048] The support roll diameter is not specifically defined, but from the viewpoint of improving laser peelability, it is preferably 600 mm or less, more preferably 300 mm or less. Furthermore, if the roll diameter is too small, the tensile stress increases, which can damage the resist in areas that are not laser peeled, and it may not be possible to secure the required resistability. Therefore, it is preferably 50 mm or more, and more preferably 100 mm or more.

[0049] In addition, increasing the laser scanning speed and shortening the irradiation time are also effective in improving the laser peelability of the resist. This is presumably the result of suppressing the spread of the thermal energy introduced into the steel sheet to the surroundings by shortening the irradiation time. From the viewpoint of improving the laser peelability, the scanning speed is preferably 200 m / sec or more, more preferably 500 m / sec or more. Also, from the viewpoints of the installation cost and maintenance cost of the irradiation equipment, it is preferably 3000 m / sec or less, more preferably 2000 m / sec or less.

[0050] The tension applied to the steel sheet can be 1.0 kg / mm 2 or more, preferably 2.0 kg / mm 2 or more. Also, if the tension is too strong, the steel sheet will undergo plastic deformation. Therefore, from the viewpoint of suppressing this, it can be 5.0 kg / mm 2 or less, preferably 3.5 kg / mm 2 or less.

[0051] In the laser irradiation process, the laser scanning is performed on the surface of the steel sheet in the contact area with the support roll.

[0052] The laser scanning is preferably performed linearly. Also, the laser scanning direction may be a direction crossing the rolling direction. However, from the viewpoint of enhancing the effect of reducing the iron loss, it is preferable that the angle of the laser scanning direction with respect to the width direction of the steel sheet is 40° or less, more preferably 20° or less. More preferably, the laser is scanned in the width direction of the steel sheet (the direction perpendicular to the rolling direction).

[0053] Laser scanning is performed periodically in the rolling direction of the grain-oriented electrical steel sheet. In other words, laser scanning is repeated so that resist removal areas are formed at regular intervals in the rolling direction. The interval of resist removal areas in the rolling direction (hereinafter referred to as "resist removal area interval") is preferably 1 mm or more and 20 mm or less. Since the interval of linear grooves formed by etching in the rolling direction (hereinafter referred to as "linear groove interval") is correlated with the interval of resist removal areas, setting the interval of resist removal areas within the above range allows for a suitable range for the linear groove interval, further improving the magnetic properties of the grain-oriented electrical steel sheet. The interval of resist removal areas is more preferably 2 mm or more, and more preferably 10 mm or less.

[0054] The type of laser can be appropriately selected from the viewpoints of iron loss characteristics and productivity. From the viewpoint of iron loss characteristics, a narrow groove width is advantageous, so it is preferable to use a laser device with high beam focusing capabilities to narrow the laser peeling width. On the other hand, from the viewpoint of productivity, high-speed laser scanning is required. When laser scanning is performed at high speed, it is preferable to use a laser device with higher output to ensure the energy density required for peeling. To achieve both beam focusing capability and laser output, it is preferable to use a single-mode fiber laser. From the viewpoint of high speed, it is preferable to perform laser scanning by rotating a mirror such as a galvanometer mirror or polygon mirror.

[0055] Since the resist is gasified or powdered and removed by laser irradiation, it is preferable to have a dust collector and exhaust gas cleaning device that collects the removed resist by blowing air or suction. However, in order to prevent the steel plate from vibrating and causing the focus to shift, the airflow rate when blowing air or suctioning should be 100 m³. 3 It is preferable that the airflow rate be less than or equal to / min. The lower limit of the airflow rate is not particularly limited, but 10m 3 It is preferable to set it to 1 / min or more.

[0056] The laser beam diameter is preferably 100 μm or less, and more preferably 50 μm or less. A smaller beam diameter is advantageous for narrowing the laser delamination width. There is no particular lower limit to the beam diameter, but if the laser delamination width is too narrow, the formed groove width will be narrow, and the magnetic flux leaking from the groove wall surface will enter the groove wall surface on the opposite side through the air gap, which may reduce the amount of magnetic poles generated and reduce the magnetic domain subdivision effect. Therefore, it is preferable to set the beam diameter to 10 μm or more.

[0057] For continuous lasers, the laser output is preferably 3000W or less, more preferably 2000W or less. When using pulsed lasers, the output is preferably 500W or less, more preferably 300W or less.

[0058] The laser peeling width is preferably 200 μm or less, more preferably 100 μm or less, because if it is too wide, the groove width increases, which in turn increases the void space and reduces the magnetic permeability, leading to deterioration of hysteresis loss. If the lower groove width becomes too narrow, the magnetic flux leaking from the groove wall surface can enter the opposite groove wall surface through the void space, potentially reducing the amount of magnetic poles generated and decreasing the magnetic domain subdivision effect. Therefore, it is preferable to set it to 10 μm or more.

[0059] Other than the conditions mentioned above, the laser irradiation conditions are not particularly limited and can be carried out by conventional methods.

[0060] [Etching Process] After the laser irradiation process is completed, etching is performed to form linear grooves on the surface of the steel plate. The etching method is not particularly limited as long as it can etch the steel plate, and any method can be used, but it is preferable to use at least one of chemical etching and electrolytic etching. From the viewpoint of controlling the amount of etching, it is more preferable to use electrolytic etching. In the case of chemical etching, for example, FeCl ３ HNO ３ HCl and H ２ SO ４ An aqueous solution containing at least one selected from the group consisting of the following can be used as the etching solution. In the case of electrolytic etching, for example, NaCl, KCl, CaCl ２ and NaNO ３An aqueous solution containing at least one selected from the group consisting of the above can be used as an etching solution (electrolyte).

[0061] Furthermore, it is preferable to stir the etching solution when etching. By stirring the etching solution, unevenness in the temperature and concentration of the electrolyte in the etching tank can be eliminated, allowing for more uniform etching. In addition, the etching efficiency can be improved by increasing the flow rate of the electrolyte in the tank. The method of stirring is not particularly limited, and for example, mechanical stirring or stirring by circulating the etching solution can be used. When mechanical stirring is performed, it is preferable to use a stirring member made of resin, taking into consideration its resistance to the etching solution. When stirring by circulation, for example, an etching solution nozzle can be provided in the etching tank, and the etching solution can be ejected from the nozzle using a pump or the like.

[0062] When etching is performed by electrolytic etching, current can be applied to the steel plate in any way. For example, current can be applied directly or indirectly using a radial cell type etching tank or a horizontal cell type etching tank. The electrolytic conditions should be adjusted as appropriate depending on the steel plate to be processed and the electrolyte used, but for example, the current density can be set to 1 to 100 A / dm². 2 It can be adjusted within the range.

[0063] The shape of the linear grooves formed by etching can be adjusted by the laser beam shape and etching conditions. However, from the viewpoint of the magnetic properties of the final product, grain-oriented electrical steel sheet, a narrower groove width is preferable, specifically 150 μm or less, and preferably 100 μm. The lower limit of the groove width is not particularly limited, but for example, it can be 10 μm or more. A deeper groove depth is preferable, specifically 10 μm or more, and preferably 10 μm or more. The groove depth can be, for example, 40 μm or less.

[0064] Other etching conditions are not particularly limited and can be carried out by conventional methods.

[0065] As described above, linear grooves can be formed on the surface of the steel sheet. In the linear groove forming method of the present invention, conditions other than those described above are not particularly limited and can be carried out by conventional methods. For example, the method for removing the resist remaining on the surface of the steel sheet after the etching process is not particularly limited and can be carried out using an alkaline aqueous solution (e.g., an aqueous NaOH solution).

[0066] <Method for Manufacturing Grain-Grain Electrical Steel Sheets> The linear groove formation method of the present invention can be suitably applied to the manufacture of grain-grain electrical steel sheets. The present invention also relates to a method for manufacturing grain-grain electrical steel sheets.

[0067] The present invention provides a method for manufacturing grain-oriented electrical steel sheets, comprising the following steps (1) to (3), wherein linear grooves are formed in the steel sheet between step (2) cold rolling and step (3) annealing, using the linear groove forming method of the present invention. (1) Hot rolling step (2) Cold rolling step (3) Annealing step

[0068] [Hot Rolling Process] The hot rolling process is a process in which a steel slab is subjected to hot rolling to produce a hot-rolled steel sheet. The composition of the steel slab is not particularly limited as long as it is a component composition used in the manufacture of grain-oriented electrical steel sheets, and any component composition can be used. The description of the component composition of the steel sheet used in the linear groove forming method of the present invention applies.

[0069] The conditions for hot rolling are not particularly limited and can be carried out by conventional methods.

[0070] [Cold Rolling Process] The cold rolling process is a process in which a hot-rolled steel sheet obtained in the hot rolling process, or a hot-rolled annealed steel sheet obtained by hot-rolling the hot-rolled steel sheet, is subjected to cold rolling once or two or more times with an intermediate annealing in between, in order to produce a cold-rolled steel sheet.

[0071] The conditions for cold rolling are not particularly limited and can be carried out by conventional methods.

[0072] [Annealing Process] The annealing process involves first performing primary recrystallization annealing on a cold-rolled steel sheet to form a primary recrystallized sheet, and then performing secondary recrystallization annealing on the primary recrystallized sheet to form a secondary recrystallized sheet.

[0073] The conditions for primary and secondary recrystallization annealing are not particularly limited and can be carried out by conventional methods.

[0074] The manufacturing process for grain-oriented electrical steel sheets other than those described above is not particularly limited and can be carried out by conventional methods. For example, a tension coating can be applied to the surface of the steel sheet after secondary recrystallization annealing to form a baked tension film. In addition, a magnetic domain refinement treatment can be performed on the surface of the steel sheet after secondary recrystallization annealing by irradiating it with a laser, plasma, or electron beam to impart strain to the surface of the steel sheet.

[0075] <Linear Groove Forming Apparatus> The apparatus for carrying out the linear groove forming method of the present invention is not particularly limited in terms of other configurations, as long as it can perform each of the above steps, and can be used with any configuration. For example, the following apparatus is preferable: A linear groove forming apparatus having the following components arranged in this order: a cleaning unit for cleaning the surface of a steel plate; a resist application unit for applying a resist to the surface of the steel plate; a laser irradiation unit for irradiating the surface of the steel plate of the steel plate wrapped around a support roll with a laser to remove the resist from the irradiated portion; an etching unit for etching the portion of the steel plate from which the resist has been removed; and a resist removal unit for removing the resist remaining on the surface of the steel plate.

[0076] The cleaning section, resist coating section, etching section, and resist removal section are not particularly limited, and known apparatus can be used for each.

[0077] The laser irradiation unit is equipped with a support roll. The support roll is installed so that its axis of rotation coincides with the width direction of the steel plate. The above examples and preferred descriptions apply to the support roll.

[0078] The laser is not particularly limited, and any known laser can be used. The laser-related conditions described in the linear groove formation method can be applied.

[0079] From the viewpoint of productivity, the linear groove forming apparatus is preferably a continuous processing apparatus capable of continuously processing steel sheets (grain-oriented electrical steel sheets) supplied as coils. From this perspective, it is preferable to arrange the discharge section for discharging the coiled steel sheets and the welding section for joining the coils together in this order, before the cleaning section. Furthermore, it is preferable to arrange the cutting section for cutting the steel sheets to the desired coil size after the resist removal process.

[0080] A linear groove forming apparatus is preferably equipped with a looper to maintain a constant sheet metal speed in the laser irradiation section. For example, when welding coils together, if the sheet metal speed decreases at a certain point in the line, it will also decrease in the laser irradiation section, resulting in a temporary increase in irradiation energy. This can cause fluctuations in the resulting groove width and variations in the iron loss characteristics of the grain-oriented electrical steel sheet. By installing a looper to maintain a constant sheet metal speed, fluctuations in the sheet metal speed in the laser irradiation section can be suppressed, thereby suppressing variations in the magnetic properties of the grain-oriented electrical steel sheet. Specifically, the looper is preferably installed between the welding section (optional) and the resist coating section, and between the resist removal section and the cutting section.

[0081] The linear groove forming apparatus preferably includes a dust collector and exhaust gas cleaning device for recovering the pulverized and gasified peeled resist film. The dust collector and exhaust gas cleaning device are preferably located in the laser irradiation section.

[0082] Furthermore, it is preferable that the linear groove forming apparatus be equipped with an imaging unit to monitor the groove width and depth after the resist stripping process following groove formation. In other words, forming deep, uniformly shaped linear grooves using the linear groove forming apparatus is important from the viewpoint of improving the magnetic properties of grain-oriented electrical steel sheets. However, if a malfunction occurs in any one of the groove forming processes—resist coating, laser stripping, electrolytic etching, or resist ink removal—the desired grooves cannot be obtained. In such a situation, it is effective to install a sensor to monitor the groove shape after the resist stripping process in order to detect the abnormality as quickly as possible.

[0083] Next, the present invention will be specifically described based on examples. The following examples illustrate preferred examples of the present invention, and the present invention is not limited in any way by these examples. Embodiments of the present invention can be modified as appropriate within the scope of the spirit of the present invention, and all such modifications are included within the technical scope of the present invention.

[0084] To evaluate the effects of laser irradiation conditions, linear grooves were formed on the surface of grain-oriented electrical steel sheets under multiple conditions. The grain-oriented electrical steel sheet had a composition of C: 0.05 mass%, Si: 3.25 mass%, Mn: 0.01 mass%, Al: 0.029 mass%, N: 0.012 mass%, S: 0.005 mass%, and Se: 0.012 mass%, with the remainder being Fe and unavoidable impurities. A steel slab containing inhibitor-forming components was hot-rolled and cold-rolled according to conventional methods to produce a 0.27 mm cold-rolled steel sheet. Subsequently, a resist ink mainly composed of epoxy resin was uniformly applied to the entire surface of the steel sheet using gravure offset printing. The basis weight of the resist was 3.0 g / m². 2 That's what I decided.

[0085] After applying the resist ink, the sheet was dried at 330°C for 40 seconds. Then, under the conditions shown in Table 1, the laser was irradiated onto the steel sheet while scanning the laser irradiation device linearly in the width direction. The laser scanning was performed periodically in the rolling direction at 3.5 mm intervals. In this experiment, three single-mode fiber laser irradiation devices (Trumpf TruFiber P) were installed side-by-side in the width direction of the steel sheet, and irradiated onto a coil with a width of 1120 mm. The support rolls used had a roll diameter of 300 mm, were made of metal, and had rubber rolls wrapped around the surface. The steel sheet was then subjected to a tension of 2.0 kg / mm². 2 While applying pressure, the steel plate was wrapped around the support roll, pressing it against it. Table 1 shows the starting point of contact between the support roll and the steel plate (P in Figure 5). １ ) and the center of the rotation axis are connected by a line segment and the end point of contact of the support roll with the steel plate (P in Figure 5). ２ This indicates the angle formed by the line segment connecting the center of the rotation axis and the object (the angle shown as θ in Figure 5; in Table 1, the contact angle θ).

[0086] Next, linear grooves were formed on each sample by electrolytic etching. A 25% NaCl aqueous solution was used as the electrolyte, and the current density was pre-adjusted so that all samples had a groove depth of 20 μm. The electrolytic conditions were: electrolyte temperature: 20°C, current density: 4–24 A / dm 2 The current was applied for 2 minutes. After etching was complete, the resist remaining on both the front and back surfaces of the steel plate was removed with an aqueous NaOH solution. The temperature of the aqueous NaOH solution was maintained at 50-70°C. After that, the plate was rinsed with water and the surface was cleaned.

[0087] Subsequently, primary recrystallization annealing (decarburization annealing), secondary recrystallization annealing (final finishing annealing), and tensile coating formation were performed on all samples under the same conditions. After that, the samples were cut out, and the groove width, presence or absence of groove breaks, and iron loss W were measured. 17 / 50 Each of these was measured. The measurement results are shown in Table 1. The groove width was determined by observing the area around the delamination portion of the groove using a laser microscope (a 3D laser microscope using a pinhole confocal optical system), and the deepest groove depth was determined. The groove width was defined as the distance between the groove walls on both sides at 50% of the depth of the deepest portion. The above measurements were performed at 20 locations, and the average value of the results obtained from these 20 locations was used as the groove width. The presence or absence of groove breaks was determined by observing the groove formation section with a total length of 1 m using an optical microscope. Iron loss W 17 / 50 This is based on JIS C 2550-1, and the iron loss W at an excitation flux density of 1.7T and frequency of 50Hz was determined by the Epstein test. 17 / 50 We measured it.

[0088] As can be seen from the results shown in Table 1, in Nos. 1 and 2 (comparative examples), where laser irradiation was performed without winding the resist onto a support roll, the resist could not be peeled uniformly, and the resist remained partially in the area where grooves were to be formed. As a result, grooves were not formed in the areas where the resist remained, resulting in discontinuous groove formation, the predetermined magnetic domain subdivision effect could not be obtained, and the magnetic properties were insufficient. No. 3 (comparative example) is an example without winding onto a support roll, and although the resist was peeled uniformly by increasing the output, the high output caused heat transfer to increase the laser peeling width, resulting in a very large groove width, leading to hysteresis loss degradation and insufficient iron loss characteristics. No. 4 (comparative example) is also an example without winding onto a support roll, and although the groove width was suppressed compared to No. 3, which had a slower scanning speed, the absolute value of the groove width was too large, and the magnetic properties were insufficient. On the other hand, for Nos. 5 to 10, which are within the scope of the present invention, good peelability was obtained, so the ink was peeled cleanly even at low output, and no groove breaks occurred. Furthermore, due to the low power output, thermal diffusion is suppressed, the groove width is very narrow, and the degradation of hysteresis loss is suppressed, resulting in good iron loss characteristics.

[0089]

[0090] According to the present invention, in a method for forming linear grooves on the surface of a steel sheet using etching, narrow linear grooves can be formed in a uniform shape, making it possible to fully enjoy the magnetic domain refinement effect caused by groove formation, and thus obtain a grain-oriented electrical steel sheet with excellent iron loss characteristics, which has high industrial utility.

[0091] 1. Cold-rolled sheet (steel plate) coated with resist 2. Laser irradiation device 3. Laser peeling section P １ Point P where the support roll begins to contact the steel plate. ２ End point of contact between the support roll and the steel plate

Claims

1. A method for forming linear grooves, comprising: a resist coating step of applying a resist to the surface of a steel sheet having a final thickness; a laser irradiation step of periodically performing laser scanning in the rolling direction of the steel sheet, where a laser is irradiated while scanning the steel sheet in a direction transverse to the rolling direction to remove the resist from the irradiated portion; and an etching step of etching the portion of the steel sheet from which the resist has been removed to form linear grooves, wherein in the laser irradiation step, the removal of the resist is performed by performing laser scanning on the surface of the steel sheet wrapped around a support roll.

2. The linear groove forming method according to claim 1, wherein the scanning speed of the laser in the laser irradiation step is 200 m / sec or more.

3. A method for manufacturing a grain-oriented electrical steel sheet, comprising: a hot rolling step of hot rolling a steel slab to obtain a hot-rolled steel sheet; a cold rolling step of cold rolling the hot-rolled steel sheet, or a hot-rolled annealed steel sheet obtained by hot-rolling the hot-rolled steel sheet, once or two or more times with an intermediate annealing in between, to obtain a cold-rolled steel sheet; and an annealing step of primary recrystallization annealing the cold-rolled steel sheet to obtain a primary recrystallized sheet, and then secondary recrystallization annealing the primary recrystallized sheet to obtain a secondary recrystallized sheet, wherein linear grooves are formed between the cold rolling step and the annealing step by the linear groove forming method described in claim 1 or 2.

4. A linear groove forming apparatus comprising: a cleaning unit for cleaning the surface of a steel plate; a resist application unit for applying a resist to the surface of the steel plate; a laser irradiation unit for irradiating the surface of the steel plate wrapped around a support roll with a laser to remove the resist from the irradiated portion; an etching unit for etching the portion of the steel plate from which the resist has been removed; and a resist removal unit for removing the resist remaining on the surface of the steel plate, all arranged in this order.

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