Grain-oriented electrical steel sheet and method of manufacturing the same

Abstract

Magnetic domain subdivision by groove formation and magnetic domain subdivision by tension application are realized without increasing BF. In a oriented electrical steel sheet having a plurality of grooves arranged at a predetermined position on the steel sheet and having a forsterite film and an insulating film on both sides of the steel sheet, the Ra of the forsterite film at the center of the groove is 5.00 μm or more, and the average thickness of the insulating film at the bottom of the groove is 1.50 μm or more.

Description

Technology Field

[0001] The present invention relates to a oriented electrical steel sheet and a method for manufacturing the same, and in particular to a oriented electrical steel sheet suitable for iron core materials such as transformers and a method for manufacturing the same. Background Technology

[0002] Oriented electrical steel sheets, which possess a crystal structure in which the <001> orientation—the easy magnetization axis of iron—is highly ordered in the rolling direction of the steel sheet, are particularly utilized as core materials for power transformers. Here, transformers are broadly classified into laminated iron core transformers and wound iron core transformers based on their core structure. A laminated iron core transformer forms a core by laminating steel sheets cut into a predetermined shape. On the other hand, a wound iron core transformer forms a core by winding and laminating steel sheets. While various characteristics are required for a transformer core, a particularly important one is the reduction and minimization of iron loss. Consequently, there is a strong demand year after year for the development of transformer materials that possess the performance necessary to reduce such iron loss.

[0003] From the above perspective, low iron loss is important as a characteristic required for the oriented electrical steel sheets used as the core material. One technology for achieving low iron loss in oriented electrical steel sheets is magnetic domain segmentation technology. This magnetic domain segmentation technology includes heat-resistant and non-heat-resistant types. In the case of the aforementioned wound core, since strain-relief annealing is performed during the manufacturing process, heat-resistant magnetic domain segmentation technology is required for the oriented electrical steel sheets supplied to this wound core. As a heat-resistant magnetic domain segmentation technology, a method of forming grooves on the surface of the steel sheet is known.

[0004] For example, Patent Document 1 describes a technique for subdividing magnetic domains by forming a groove with a depth of more than 5 μm in the steel portion with a load of 882 to 2156 MPa (90 to 220 kgf / mm²) on a steel plate that has completed finish annealing, and then heat treating it at a temperature of 750°C or higher. Patent Document 2 proposes forming a groove with an asymmetric shape with respect to the center of the groove width in the groove width direction, and controlling the average depth of the groove, the arithmetic mean height Ra of the roughness curve forming the contour of the groove bottom region, and the average length RSm of the roughness curve element forming the contour of the groove bottom region. Patent Document 3 proposes controlling the depth of the groove, the groove width, the Ra value of the roughness of the groove bottom surface, and the Ra value of the roughness of the groove side surface to a specific range. Prior art literature

[0005] Japanese Patent Publication No. Sho 62-53579, International Publication No. 2016 / 171130, Japanese Patent Publication No. 2022-22494 The problem to be solved

[0006] When applying the aforementioned conventional technology, a certain level of iron loss is achieved, but the reality is that further reduction in iron loss is required. As a magnetic domain subdivision technology other than the method of forming grooves mentioned above, it is known that iron loss is reduced by subdividing magnetic domains through the application of tension to oriented electrical steel sheets. The application of tension to these steel sheets improves with increasing thickness of the forsterite film and the insulating film. On the other hand, if both of these films become thicker, there is a problem that when made into a transformer core, the volume ratio of the steel sheet within the transformer core, referred to as the stacking factor, decreases.

[0007] Here, the ratio of the iron loss value (transformer iron loss) when oriented electrical steel is used as the iron core of a transformer to the iron loss value of the material (oriented electrical steel) obtained from the Epstein test is generally referred to as the Building Factor (BF) or Destruction Factor (DF). Hereinafter, it will be collectively referred to as BF. Reducing this BF is also an item that must be considered as a characteristic required of oriented electrical steel. This BF increases as the aforementioned packing factor decreases. Therefore, from the perspective of reducing BF, it is desirable to make the film thickness thin.

[0008] The present invention has been made in consideration of the above circumstances and aims to propose a method for realizing magnetic domain segmentation by improving the surface tension of a steel plate in addition to magnetic domain segmentation by groove formation, without increasing BF. means of solving the problem

[0009] The inventors conducted repeated examinations to solve the above problem. As a result, they recognized that by thickening the insulating film formed in the groove, particularly on the bottom of the groove, the tension in the rolling direction generated in the part where the groove exists is improved, and the amount of magnetic charge generated on the wall of the groove increases. As a result, they recognized that magnetic domain subdivision is promoted and iron loss is reduced. They further recognized that according to this method, since the insulating film is thickened only in the part where the groove exists on the surface of the steel plate, the decrease in packing efficiency, which is a problem when the insulating film is thickened, does not occur.

[0010] Based on the above findings, the inventors attempted to form a thick insulating film in the grooves formed on the surface of a oriented electrical steel sheet by introducing a coating solution that forms an insulating film into the grooves and then performing planarization annealing. However, it was found that the adhesion of the insulating film was poor and it peeled off easily. Therefore, the inventors conducted repeated investigations to solve the problem of the film peeling. As a result, they recognized that by increasing the surface roughness of the forsterite film formed at a specific location in the groove to a certain degree, the adhesion of the insulating film additionally formed thereon is improved, and thus completed the present invention.

[0011] Furthermore, the inventors clearly demonstrated that damage to the forsterite film significantly affects the magnitude of the tension in the rolling direction within the groove. They also recognized that by suppressing this damage, a greater and more stable reduction in iron loss can be achieved.

[0012] Based on the above additional findings, the inventors identified that there are many cracks in the forsterite film formed on the surface of the oriented electrical steel sheet and explored a method to suppress these cracks. As a result, they recognized that damage to the forsterite film, represented by cracks, is mainly caused by the shape correction of the steel sheet during the flattening annealing after the final finishing annealing. They also recognized that by performing the final finishing annealing on a coil-shaped steel sheet wound with the grooved surface facing outward, the generation of tensile stress, which causes cracks introduced during the subsequent shape correction, is suppressed, thereby significantly reducing the frequency of crack occurrence, and thus came to complete a more suitable invention.

[0013] The gist of the present invention is as follows.

[0014] [1] A directional electrical steel sheet having a plurality of grooves that extend in a linear shape across the rolling direction of the steel sheet on one or both sides of the steel sheet and are spaced apart in the rolling direction, and having a forsterite film and an insulating film on both sides of the steel sheet in order from the surface side of the steel sheet.

[0015] A oriented electrical steel sheet having a surface roughness Ra of the forsterite film formed at the center of the groove in a cross-section orthogonal to the extension direction of the groove of 5.00 μm or more, and an average thickness of the insulating film at the bottom of the groove of 1.50 μm or more.

[0016] [2] The oriented electrical steel sheet described in [1], wherein the roughness coefficient of the forsterite film formed in the groove is 0.8 or less.

[0017] [3] A method for manufacturing a oriented electrical steel sheet, wherein a slab for an oriented electrical steel sheet is hot-rolled to form a hot-rolled sheet, and then, if necessary, annealed the hot-rolled sheet to form a hot-rolled annealed sheet, and then, one or more cold-rolls are performed on the hot-rolled sheet or the hot-rolled annealed sheet with intermediate annealing in between to form a cold-rolled sheet with a final thickness, and then, a decarburization annealing is performed on the cold-rolled sheet to form a decarburization annealed sheet, and then, an annealing separating agent mainly composed of MgO is applied to the surface of the decarburization annealed sheet, and then, a final finishing annealing is performed to form a finishing annealed sheet, and then, an insulating coating is applied to the finishing annealed sheet.

[0018] (1) Before applying the annealing separator, a plurality of grooves are formed on one or both sides of the hot-rolled plate, the hot-rolled annealing plate, the cold-rolled plate, or the decarburized annealing plate, extending in a linear shape in a direction across the rolling direction of the steel plate and arranged at intervals in the rolling direction.

[0019] (2) Applying the annealing separator to at least the surface of the decarburized annealing plate that has the groove formed therein, scraping off the annealing separator, and then applying the annealing separator to both sides of the decarburized annealing plate.

[0020] (3) A method for manufacturing a oriented electrical steel sheet, wherein the insulating coating is applied to at least the surface of the finishing annealing plate that has the groove formed therein, the insulating coating is scraped off, and then the insulating coating is applied to both sides of the finishing annealing plate.

[0021] [4] A method for manufacturing a directional electrical steel sheet as described in [3], using a doctor blade for scraping off the annealing separator and the insulating coating.

[0022] [5] A method for manufacturing a directional electrical steel sheet as described in [3] or [4], wherein the decarburized annealed sheet coated with the annealing separator is formed into a coil shape by placing the surface with the groove formed on the outer side of the coil and then performing the final finishing annealing. Effects of the invention

[0023] According to the present invention, in a groove formed on the surface of a oriented electrical steel sheet, the forsterite film is roughened and the insulating film is thickened, thereby creating strong tension in the rolling direction of the steel sheet and promoting magnetic domain segmentation. As a result, iron loss can be further reduced and a low BF can be realized.

[0024] In addition, according to the manufacturing method of the present invention, by applying an annealing separator to the grooves present on the surface of the decarburized annealed plate and additionally applying an insulating coating to the grooves present on the surface of the finished annealed plate, magnetic domain segmentation is promoted in the same manner as above. As a result, it is possible to achieve both a reduction in iron loss and a low BF.

[0025] Furthermore, according to the suitable invention, the degree of damage to the forsterite film is reduced, thereby further promoting magnetic domain subdivision. As a result, it is possible to achieve both lower iron loss and lower BF. Brief explanation of the drawing

[0026] Figure 1 is a cross-sectional view showing the grooves of a steel plate. FIG. 2 shows a groove in a steel plate and is a cross-sectional view at two positions separated in the extension direction. Specific details for implementing the invention

[0027] (Form for carrying out the invention)

[0028] Suitable embodiments of the present invention will be described in detail below. Furthermore, unless specifically stated otherwise, the notation "A to B" for numerical values ​​A and B shall mean "A or greater and B or less." In such notation, if a unit is attached only to numerical value B, said unit shall also apply to numerical value A.

[0029] (Oriented electrical steel sheets)

[0030] A oriented electrical steel sheet according to the present invention (hereinafter simply referred to as a steel sheet) has a plurality of grooves on one or both sides of the steel sheet that are extended in a linear shape in a direction traversing the rolling direction of the steel sheet (hereinafter simply referred to as the rolling direction) and arranged at intervals in the rolling direction, and on both sides of the steel sheet, a forsterite film and an insulating film are provided in order from the surface side of the steel sheet. In addition, it is important that the steel sheet of the present invention has an average thickness of the insulating film at the bottom portion of the grooves of 1.50 μm or more, and that the Ra of the surface of the forsterite film at the center of the grooves in a cross-section perpendicular to the extension direction of the grooves is 5.00 μm or more.

[0031] Furthermore, as a suitable oriented electrical steel sheet, it is preferable that the roughness coefficient of the forsterite film formed in the groove is 0.8 or less.

[0032] In addition, the oriented electrical steel sheet according to the present invention can be suitably obtained, for example, by the method for manufacturing the oriented electrical steel sheet according to the present invention described below.

[0033] [home]

[0034] The above grooves are preferably formed on the surface of the steel plate with a spacing of 1 mm or more between grooves in the rolling direction, more preferably 2 mm or more, 20 mm or less, and more preferably 10 mm or less. If this spacing is less than 1 mm, the magnetic domain segmentation effect may become saturated, and the effect of reducing eddy current loss may not be obtained. Furthermore, since hysteresis loss increases due to deformation, iron loss and BF are prone to increase, which is undesirable. On the other hand, if this spacing exceeds 20 mm, the magnetic domain segmentation effect decreases, resulting in insufficient improvement in iron loss and BF, which is undesirable. The preferred groove spacing is 1 to 20 mm, and more preferably 2 to 10 mm.

[0035] Although the pattern of groove formation is not particularly limited, it is preferable to have grooves on both sides of the steel plate—parallel to each other and in the same position on both sides—rather than on only one side, because this increases the magnetostatic energy in the grooves and strengthens the magnetic domain subdivision effect.

[0036] In addition, if the grooves on both sides of the steel plate are parallel to each other and positioned opposite each other on the front and back sides, the magnetic domain length in the rolling direction is shortened, so the magnetic energy increases, and the magnetic domain subdivision effect becomes stronger, which is desirable.

[0037] In addition, if grooves are positioned on both sides of the steel plate in a cross-sectional location, the magnetic energy at the intersecting points is high, and since the magnetic domain length in the rolling direction at non-intersecting points is shorter than in the parallel case, the magnetic energy increases, and the magnetic domain subdivision effect becomes stronger, which is desirable.

[0038] FIG. 1 is a cross-sectional view perpendicular to the extension direction of a groove (2) formed in a oriented electrical steel sheet (steel sheet) (1) according to one embodiment of the present invention. In FIG. 1, the groove (2) has a shape close to a cross-section trapezoid, but the shape of the groove (2) is not particularly limited and, for example, may have an arch cross-section. In one embodiment of the oriented electrical steel sheet of the present invention, the depth (D) of the groove (2) is preferably 10 μm or more, preferably 50 μm or less, and more preferably in the range of 10 μm to 50 μm.

[0039] Here, with reference to FIG. 1, the depth (D) of the groove (2) is the length of the perpendicular line drawn from the center of the opening width in the rolling direction of the groove (2) to the bottom portion (20). Also, the opening width is the distance (L) between the opening side edges of the two walls that divide the groove (2), in the extension line of the surface of the steel plate (1) that is virtually drawn at the opening of the groove (2).

[0040] If the depth (D) of the groove (2) is less than 10㎛, the amount of magnetic poles generated from the wall surface of the groove (2) is reduced, and there is a concern that a sufficient iron loss reduction effect may not be obtained. On the other hand, if the depth (D) exceeds 50㎛, the magnetic domains are subdivided, but the decrease in magnetic flux density due to groove formation is greater, and there is a concern that a sufficient iron loss reduction effect may not be obtained. A more preferable depth (D) is 15㎛ or more and 30㎛ or less, and even more preferably 15㎛ to 30㎛.

[0041] The oriented electrical steel sheet of the present invention, as illustrated in part of FIG. 1, has a forsterite film (3) and an insulating film (4) formed in order from the surface side on the front and back surfaces of a steel sheet (1) having the groove (2) on at least one side. When the steel sheet (1) has the groove (2) on both sides, the forsterite film (3) and the insulating film (4) are formed on the groove (2) on both sides of the steel sheet (1). When the steel sheet (1) has the groove (2) on one side, the forsterite film (3) and the insulating film (4) are formed on the groove (2) only on the corresponding side of the steel sheet (1). The forsterite film (3) and the insulating film (4) can be formed according to the general principles of the oriented electrical steel sheet in the steel sheet base portion excluding the groove (2). Meanwhile, regarding the groove (2), it is important to define the surface roughness of the forsterite film (3) and the average thickness of the insulating film (4) as follows.

[0042] [Surface roughness Ra of the forsterite film formed at the center of the groove in a cross-section orthogonal to the extension direction of the groove is 5.00 μm or more]

[0043] First, the “center of the groove in a cross-section perpendicular to the extension direction of the groove” is the position (center (21)) of the perpendicular line drawn down to the bottom portion (20) through the center of the opening width of the groove (2), as shown in FIG. 1. For the surface of the forsterite film (3) on this perpendicular line, the value measured as the arithmetic mean roughness Ra of the roughness curve over a predetermined distance (e.g., a length of 30 mm) along the extension direction of the groove (2) is the “surface roughness Ra of the forsterite film formed in the center of the groove in a cross-section perpendicular to the extension direction of the groove.” Hereinafter, it will also be simply referred to as the “surface roughness of the forsterite film.”

[0044] The surface roughness of the forsterite film described above will be explained in detail with reference to FIG. 2. FIG. 2 shows a top view of a steel plate (1) having a groove (2) on the right side of the drawing. Additionally, on the left side of the drawing, a cross-sectional view of the groove is shown corresponding to two different positions along the extension direction of the groove in the top view. That is, FIG. 2 shows the groove cross-sections corresponding to positions separated by a predetermined distance (t) in the extension direction of the groove (2) as cross-sections AA and BB. FIG. 2 shows the surface of the forsterite film (3) at the center of the rolling direction at each position separated by a predetermined distance (t) as d and d'. The unevenness of the surface of the forsterite film (3) on the straight line connecting these points d and d' can be measured as the arithmetic mean roughness Ra of the roughness curve. The predetermined distance (t) may be any length, but it is preferable to be about 30 to 50 mm. This is because achieving the condition locally is meaningless, and it needs to be achieved on average across the entire groove of the steel plate, and it is thought that it needs to be achieved in an area longer than at least one crystal grain width.

[0045] In addition, the definition of the arithmetic mean roughness Ra of the roughness curve shall conform to Japanese Industrial Standard JIS B0601 (2013).

[0046] It is important that the surface roughness Ra of the above forsterite film is 5.00 μm or more. That is, if the surface roughness Ra of the forsterite film is less than 5.00 μm, the adhesion of the insulating film on the forsterite film decreases, making it easy for the insulating film to peel off. Therefore, it is believed that by making Ra 5.00 μm or more, the surface area per unit groove of the forsterite film increases, resulting in a larger adhesion area with the insulating film and improved film adhesion. Preferably, Ra is 6.00 μm or more, and more preferably 7.00 μm or more.

[0047] Meanwhile, although there is no specific limit on the upper limit of Ra, if Ra exceeds 20.00 μm, there is a risk of causing embrittlement of the forsterite film itself. Therefore, it is desirable to make Ra 20.00 μm or less. More preferably, Ra is 15.00 μm or less, and even more preferably 10.00 μm or less.

[0048] [Method for Measuring Surface Roughness Ra of Forsterite Film]

[0049] Ra can be measured using a laser microscope (a 3D laser microscope using a confocal optical system based on a pinhole). That is, any one of the grooves formed in the oriented electrical steel sheet is selected, and two groove positions (A) and (B) are determined at a distance of, for example, t: 30 mm in the extension direction, as exemplified in FIG. 2. Then, the surface irregularity of the forsterite film on a straight line connecting surfaces d and d' of the forsterite film (3) corresponding to the rolling direction center of the bottom part (groove bottom surface) of the groove at each position is measured as the arithmetic mean roughness Ra of the roughness curve. The above measurements are performed for any 20 grooves, and the 20 obtained average values ​​are taken as the surface roughness Ra of the forsterite.

[0050] Here, when a sample is used for measurement before planarization annealing and the application of an insulating coating solution, it is acceptable to measure Ra as is. On the other hand, when a sample is used for measurement after the application of an insulating coating solution, it is acceptable to measure Ra after removing the insulating coating with an alkaline solution (e.g., sodium hydroxide solution).

[0051] [The roughness coefficient of the forsterite film formed in the groove is 0.8 or less]

[0052] It is preferable that the roughness coefficient of the forsterite film formed in the groove be 0.8 or less. If the roughness coefficient of the forsterite film present in the groove exceeds 0.8, it means that the porosity of the forsterite film is relatively large. As a result, the tension imparted by the insulating film on the forsterite film is not sufficiently reflected to the steel plate, and it is prone to causing deviations in characteristics such as iron loss and BF. Therefore, in order to further enhance the effect of improving tensile characteristics by applying a thick forsterite film formed in the groove, it is desirable to reduce the porosity of the forsterite film in the groove. Specifically, the roughness coefficient is preferably 0.8 or less, more preferably 0.6 or less, and even more preferably 0.4 or less.

[0053] Meanwhile, the lower limit of the roughness coefficient of the forsterite film formed in the groove is not particularly limited, but from the perspective of sufficiently covering the groove with the forsterite film, 0.05 or higher is preferred.

[0054] [Method for Measuring the Roughness Coefficient of a Forsterite Film Formed in a Groove]

[0055] First, for samples in which no grooves are formed and a forsterite film is formed, the specific surface area is measured by the gas adsorption method using Kr gas. Then, from the results, the true surface area, including minute surface irregularities, is calculated and divided by the apparent surface area assuming the surface is perfectly smooth. In this way, the surface roughness coefficient of the oriented electrical steel sheet with a forsterite film formed on the steel sheet surface other than the grooves is derived.

[0056] Next, for a sample containing a groove on which a forsterite film is formed, the specific surface area is measured by a gas adsorption method using Kr gas as described above, and the true surface area including minute surface irregularities is calculated. Subsequently, the apparent surface area of ​​the portion excluding the groove of the sample containing the groove is derived, and the true surface area of ​​the portion excluding the groove in the sample containing the groove is derived by multiplying it by the roughness coefficient of the sample excluding the groove derived earlier.

[0057] The difference between this result (the true surface area of ​​the portion excluding the groove in a sample containing the groove) and the true surface area derived from the specific surface area in a sample containing the groove is defined as the true surface area of ​​the groove portion. Then, by dividing this true surface area of ​​the groove portion by the apparent surface area of ​​the groove portion and further dividing by Ra, the roughness coefficient of the forsterite film formed in the groove is derived. Accordingly, the amount of micro-cracks that cannot be evaluated by surface roughness Ra can be evaluated.

[0058] In summary, the roughness coefficient of the forsterite film formed in the groove (unit: μm) －1 ) can be obtained by the following equation (1).

[0059] True surface area of ​​the groove / (Apparent surface area of ​​the groove × Ra)···(1)

[0060] Here, Ra is the surface roughness (μm) of the forsterite film formed at the center of the groove in a cross-section orthogonal to the extension direction of the groove, and can be measured by the aforementioned method.

[0061] [The average thickness of the insulating film at the bottom of the groove is 1.50㎛ or more]

[0062] It is also important that the average thickness of the insulating film at the bottom of the groove (groove bottom surface) is 1.50 μm or more. That is, if the average thickness of the insulating film at the above location is less than 1.50 μm, no additional improvement in iron loss is exhibited. Although the mechanism by which the effect is exhibited with an insulating film having an average thickness of 1.50 μm or more is not certain, it is thought that as the insulating film becomes thicker, the tension caused by the groove portion increases locally, thereby improving the magnetic domain segmentation effect. The average thickness of the insulating film at the bottom of the groove is preferably 1.70 μm or more.

[0063] In addition, although it varies depending on the thickness of the forsterite film formed in the groove, for example, the average thickness of the insulating film at the bottom of the groove is preferably 20 μm or less, and more preferably 10 μm or less.

[0064] [Method for measuring the average thickness of the insulating film at the bottom of the groove]

[0065] Using a scanning electron microscope, cross-section images along the rolling direction, including, for example, the groove cross-section of FIG. 1, are acquired in at least 30 fields of view, with a rolling direction width of 100 to 200 μm × the total thickness of the plate as one field of view. Preferably, cross-section images for at least 30 different grooves are acquired. By image analysis, the interface position between the forsterite film and the insulating film and the surface position of the insulating film are identified, and for each image, the average thickness of the insulating film at the bottom of the groove is calculated. In addition, the average of the acquired cross-section images is taken as the average thickness of the insulating film at the bottom of the groove.

[0066] In addition, in this measurement, the "bottom part" of the groove is determined to be the portion corresponding to the center of the opening width in the rolling direction described above, among the concave portions that partition the groove. In addition, the "side wall" of the groove is determined to be the portion excluding the "bottom part" among the concave portions that partition the groove, that is, the portion corresponding to each of the opening width in the rolling direction from both sides of the single edge of the steel plate surface that partitions the groove.

[0067] [Method for Evaluating the Adhesion of Insulating Films]

[0068] The adhesion of the aforementioned insulating film can be evaluated as peelability when the shape of the steel plate is deformed. Specifically, it can be evaluated by a bending peel test in which the steel plate is wound around a round bar and the minimum diameter at which film peeling does not occur is determined. The smaller the minimum diameter at which film peeling does not occur, the lower the peelability, and therefore the better the adhesion.

[0069] (Method for manufacturing grain-oriented electrical steel sheets)

[0070] The manufacturing method of the present invention comprises hot rolling a slab for a grain-oriented electrical steel sheet to form a hot-rolled plate, then, if necessary, performing hot-rolled plate annealing on the hot-rolled plate to form a hot-rolled annealed plate, then performing one or two or more cold rolling steps with intermediate annealing in between on the hot-rolled plate or the hot-rolled annealed plate to form a cold-rolled plate having a final plate thickness, then performing decarburization annealing on the cold-rolled plate to form a decarburization annealed plate, then applying an annealing separator mainly composed of MgO to the surface of the decarburization annealed plate, then performing final finishing annealing to form a finishing annealed plate, and then applying an insulating coating to the finishing annealed plate.

[0071] (1) Before applying an annealing separator, a plurality of grooves are formed on one or both sides of a hot-rolled plate, a hot-rolled annealed plate, a cold-rolled plate, or a decarburized annealed plate, extending in a linear shape across the rolling direction of the steel plate and arranged at intervals in the rolling direction.

[0072] (2) Applying an annealing separator to at least the grooved surface of the decarburized annealing plate, scraping off the annealing separator, and then applying an annealing separator to both sides of the decarburized annealing plate.

[0073] (3) It is important to apply an insulating coating to at least the grooved surface of the finishing annealing plate, then scrape off the insulating coating, and then apply an insulating coating to both sides of the finishing annealing plate.

[0074] According to the manufacturing method of the present invention, the oriented electrical steel sheet of the present invention described above can be obtained well, and thus, the same effect as the oriented electrical steel sheet of the present invention can be achieved.

[0075] In addition, a suitable manufacturing method may be the use of a doctor blade for scraping off the aforementioned annealing separator and insulating coating.

[0076] Another suitable manufacturing method is to perform final finishing annealing on a decarburized annealing plate coated with an annealing separator, by forming the decarburized annealing plate into a coil shape with the grooved surface positioned on the outer side.

[0077] Next, the method for forming the above-mentioned groove and the forsterite film and insulating film in the said groove will be described in detail.

[0078] [Method of forming a groove]

[0079] A linear groove is formed on one or both sides of a steel plate before the application of an annealing separator (i.e., before final finishing annealing), more specifically, a hot-rolled plate, a hot-rolled annealed plate, a cold-rolled plate, and a decarburized annealed plate. Among these, it is preferable to form a linear groove on a cold-rolled plate after final cold rolling and before decarburized annealing. Since the groove may be lost during cold rolling, there is no high necessity to form the groove before the final cold rolling. In addition, in order to form forsterite, it is necessary to form fayalite; since fayalite is typically formed during decarburized annealing, it is preferable to form the groove on a cold-rolled plate before decarburized annealing.

[0080] The grooves can be formed effectively by applying and attaching etching resist ink and then performing electrolytic etching treatment on the non-coated areas. When forming the groove pattern, the non-coated areas are formed by applying resist ink to, for example, the entire surface of one or both sides of a cold-rolled plate and then removing the ink by laser irradiation, or by forming them through resist printing. In particular, since it is important that a sufficient forsterite film is formed on the bottom of the grooves, it is essential to perform the groove formation before the application of an annealing release agent that forms the forsterite film and before the final finishing annealing.

[0081] Here, the groove is formed in a linear shape extending in a direction that crosses the rolling direction, that is, in a direction that has an angle along the rolling surface from the rolling direction. In this specification, "direction crossing the rolling direction" refers to the deviation of the linear groove from the direction perpendicular to the rolling direction, preferably within ±30°, and can be 0° (in the width direction of the steel plate). In addition, in this specification, "line shape" includes not only solid lines but also dotted lines and dashed lines.

[0082] Other characteristics of the groove can be the same as those described above for oriented electrical steel sheets.

[0083] [Application of Annealing Separator]

[0084] After applying an annealing separator to at least the grooved surface of the decarburized annealed plate (preliminary application), the annealing separator is scraped off, and an annealing separator is additionally applied to both sides of the decarburized annealed plate (main application). Thus, the annealing separator is applied twice to at least the grooved surface. The annealing separator is suitable for forming a forsterite film having a desired thickness, provided that the main component is MgO, the application amount is 8 g / m² or more per side of the steel plate, 15 g / m² or less, and within the range of approximately 8 to 15 g / m².

[0085] In addition, having MgO as the main component means that the annealing separator contains 75 mass% or more of MgO in terms of solid content. The same MgO content is also present in the forsterite film of the formed solid.

[0086] As a sequence for applying an annealing separator, an annealing separator (e.g., an MgO suspension) is applied (preliminary application) to at least the surface where the groove is formed, the suspension is scraped off, and then the MgO suspension is applied again to both sides (main application). Even if the preliminary annealing separator is scraped off, the suspension inside the groove is not scraped off, and the suspension scraped off from parts other than the groove flows into the groove through the scraping process, so it becomes possible to effectively apply a large amount of suspension to the groove. Using a doctor blade is suitable as the scraping means at that time. Although this application method is suitable, there is no problem with applying a large amount of suspension to the groove using other methods. In a known method (e.g., a roll coater) that does not perform scraping unlike the above method, it is difficult to apply a sufficient amount of suspension to the groove, and the forsterite film in the groove often becomes thin. If the foresterite film in the groove becomes thin, the roughness of the film decreases. Furthermore, it is difficult to increase the tensile strength applied to the steel plate, making it difficult to reduce iron loss and BF. On the other hand, according to the above method, by sufficiently spreading the annealing separator within the groove, the Ra of the foresterite film at a specific location in the groove after the subsequent final finishing annealing can be set to 5.00 μm or higher. Additionally, it is easy to reduce iron loss and achieve a low BF.

[0087] [Final Finishing Annealing]

[0088] Final finishing annealing is performed on a decarburized annealed plate coated with an annealing separator for the purpose of secondary recrystallization and the formation of a forsterite film. Final finishing annealing is often performed on a decarburized annealed plate wound into a coil shape. At this time, it is preferable to perform final finishing annealing on the decarburized annealed plate as a coil with the grooved surface positioned on the outer winding side. Since coil set occurs due to the final finishing annealing, shape correction may be performed in a subsequent process. Here, if a forsterite film is formed with a groove on the outer winding side, compressive stress is applied to the forsterite film in the groove when the shape is corrected to be flat by subsequent flattening annealing. Since tensile tension is the cause of damage such as cracks that increase the porosity of the forsterite film, damage to the forsterite film can be effectively avoided in this case. On the other hand, when a forsterite film is formed with a groove on the inner side, tensile stress is applied to the forsterite film in the groove when the shape is flattened; this introduces damage such as cracks into the forsterite film, making it prone to increasing porosity.

[0089] In addition, during the through process after the formation of the forsterite film, compressive stress is applied even when the finishing annealed sheet is bent in the opposite direction to the winding moisture, so the forsterite film is less likely to be damaged. Conversely, when the finishing annealed sheet is bent in the same direction as the winding moisture, tensile stress is applied, but the iron loss of the electrical steel sheet is reduced more effectively and stably by the amount of the winding moisture, and the increase in BF can be further prevented.

[0090] [Insulation Coating and Planarization Annealing]

[0091] After applying an insulating coating (preliminary coating) to at least the groove-forming surface of the finished annealed plate obtained in this way, the insulating coating is scraped off, and an insulating coating is additionally applied to both sides of the finished annealed plate (main coating). Thus, the insulating coating is applied twice to at least the groove-forming surface. An insulating coating refers to a coating that applies tension to the steel plate to reduce iron loss.

[0092] In addition, after the final finishing annealing, performing a planarization annealing to correct the shape is effective in improving the filling rate when processing the oriented electrical steel sheet into a core. For the planarization annealing, it is preferable to set the annealing temperature to 750°C or higher and 950°C or lower, within a range of approximately 750 to 950°C. Furthermore, it is suitable to perform the planarization annealing with an annealing time of 10 seconds or more and 200 seconds or less, within a range of approximately 10 to 200 seconds. It is preferable to form the insulating coating before or after the planarization annealing.

[0093] In one example of a process for forming an insulating film, an insulating coating solution containing, for example, colloidal silica and phosphate is applied over a forsterite film on the surface of a finishing annealed plate having at least a groove formed therein. A suitable application sequence may be to apply the insulating coating solution to at least the grooved surface (pre-application), then scrape off the insulating coating solution, and then apply the insulating coating solution again to both surfaces including the grooved surface (main application). Even when the pre-applied insulating coating solution is scraped off, the insulating coating solution inside the groove is not scraped off, and the insulating coating solution scraped off from parts other than the groove flows into the groove through the scraping process, so it becomes possible to effectively apply a large amount of insulating coating solution to the groove. It is suitable to use a doctor blade as the scraping means at that time. The above application method is merely a suitable example, and there is no problem with applying a large amount of coating solution to the groove by other methods. Unlike the above method, in known methods that do not perform scraping (e.g., roll coaters), it is difficult to apply a sufficient amount of insulating coating liquid to the grooves, and the insulating film in the grooves tends to become thin. If the insulating film in the grooves becomes thin, it is difficult to increase the tensile strength applied to the steel sheet, making it difficult to reduce iron loss and BF. On the other hand, according to the above method, by sufficiently spreading the insulating coating liquid within the grooves, the average thickness of the insulating film in the grooves of the final oriented electrical steel sheet can be made 1.50 μm or more. Furthermore, it is easy to reduce iron loss and achieve a low BF.

[0094] Typically, when an insulating film with a thickness of 1.50 μm is formed, adhesion (peelability) becomes a problem. However, in the present invention, as described above, the surface roughness of the forsterite film is controlled to be rougher than before, thereby ensuring that the peelability of the insulating film does not become a problem. Afterward, heat treatment can be performed at any temperature under suitable temperature conditions (e.g., 840 to 920°C). In this way, a oriented electrical steel sheet having a predetermined forsterite film and an insulating film inside the groove is finally obtained.

[0095] [Other processes]

[0096] The method for manufacturing the oriented electrical steel sheet of the present invention is not particularly limited to processes that are not directly related to the domain segmentation treatment. Recommended suitable compositional compositions and other manufacturing conditions are described below.

[0097] [Ingredient Composition]

[0098] It is preferable that the composition of the slab for grain-oriented electrical steel be such that secondary recrystallization occurs. In addition, when using an inhibitor, it is desirable to include appropriate amounts of Al and N, for example, if it is an AlN-based inhibitor, or Mn and S and / or Se, if it is a MnS·MnSe-based inhibitor. Of course, both inhibitors may be used in combination. In this case, the suitable contents of Al, N, S and / or Se are, respectively: Al: 0.01 to 0.04 mass%, N: 0.005 to 0.02 mass%, and S and / or Se: 0.005 to 0.03 mass% in total. Furthermore, during the final finishing annealing, Al, N, S, and Se are purified and reduced to the level of unavoidable impurities.

[0099] In addition, the present invention can also be applied to oriented electrical steel sheets that do not use inhibitors, with limited content of Al, N, S, and Se. In this case, it is preferable to limit the amounts of Al, N, S, and Se to Al: 100 mass ppm or less, N: 50 mass ppm or less, S: 50 mass ppm or less, and Se: 50 mass ppm or less, respectively.

[0100] The basic ingredients and optionally added ingredients other than those mentioned above are described as follows.

[0101] C: 0.08 mass% or less

[0102] If the C content exceeds 0.08 mass%, it becomes difficult to reduce C to 50 mass ppm or less, where magnetic aging does not occur during the manufacturing process, so it is desirable to keep it 0.08 mass% or less. On the other hand, regarding the lower limit, since secondary recrystallization is possible even in materials that do not contain C, there is no need to specifically form one, and 0 mass% is acceptable. In addition, during decarburization annealing, C is removed from the steel and reduced to a content amount that is an unavoidable impurity.

[0103] Si: 2.0–8.0 mass%

[0104] Si is an element effective for increasing the electrical resistance of steel and improving iron loss, but if the content does not meet 2.0 mass%, a sufficient iron loss reduction effect cannot be expected. On the other hand, if it exceeds 8.0 mass%, processability is significantly reduced, and magnetic flux density is also reduced. Therefore, the amount of Si is preferably 2.0 mass% or more, preferably 8.0 mass% or less, and more preferably in the range of 2.0 to 8.0 mass%.

[0105] Mn: 0.005–1.0 mass%

[0106] Mn is an element necessary for improving hot workability, but if the content is less than 0.005 mass%, the effect of its addition is insufficient. On the other hand, if Mn exceeds 1.0 mass%, the magnetic flux density of the product plate decreases. Therefore, the amount of Mn is preferably 0.005 mass% or more, preferably 1.0 mass% or less, and more preferably in the range of 0.005 to 1.0 mass%.

[0107] In addition to the basic components mentioned above, the following elements may be appropriately incorporated as components that improve magnetic properties.

[0108] At least one type selected from Ni: 0.03–1.50 mass%, Sn: 0.01–1.50 mass%, Sb: 0.005–1.50 mass%, Cu: 0.03–3.0 mass%, P: 0.03–0.50 mass%, Mo: 0.005–0.10 mass%, and Cr: 0.03–1.50 mass%.

[0109] Ni is a useful element for improving magnetic properties by improving the microstructure of hot-rolled sheets. However, when the content is less than 0.03 mass%, the effect of improving magnetic properties is small, while when it exceeds 1.50 mass%, secondary recrystallization becomes unstable and magnetic properties deteriorate. Therefore, it is preferable that the Ni content be 0.03 mass% or more, 1.50 mass% or less, and more preferable that it be in the range of 0.03 to 1.50 mass%.

[0110] In addition, Sn, Sb, Cu, P, Mo, and Cr are each elements useful for improving magnetic properties, but if they do not all meet the lower limit of each component mentioned above, the effect of improving magnetic properties is small. On the other hand, if the upper limit of each component mentioned above is exceeded, the development of secondary recrystallized grains is inhibited. Therefore, it is desirable to include each within the above range. In addition, the remainder other than the above components may be unavoidable impurities introduced during the manufacturing process and Fe.

[0111] Next, other manufacturing conditions regarding the method for manufacturing grain-oriented electrical steel sheets will be explained.

[0112] [Slab Heating]

[0113] A slab for a oriented electrical steel sheet having the above-described composition can be heated according to a conventional method. The heating temperature is preferably 1150°C or higher, preferably 1450°C or lower, and more preferably in the range of 1150°C to 1450°C.

[0114] [Hot Rolled]

[0115] After heating the above slab, hot rolling may be performed to produce a hot-rolled plate. After casting, hot rolling may be performed immediately without heating. In the case of a thin cast slab, hot rolling may be performed immediately, or hot rolling may be omitted. When hot rolling is performed, it is preferable to perform the rolling temperature of the final pass of rough rolling at 900°C or higher, and the rolling temperature of the final pass of finish rolling at 700°C or higher.

[0116] [Hot-rolled plate annealing]

[0117] After hot rolling, the hot-rolled sheet may be annealed as needed to produce a hot-rolled annealed sheet. At this time, in order to highly develop the Goss texture in the product sheet (oriented electrical steel sheet), the hot-rolled sheet annealing temperature is preferably 800°C or higher, preferably 1100°C or lower, and a range of 800°C to 1100°C is more suitable. If the hot-rolled sheet annealing temperature is below 800°C, the band structure from hot rolling remains, making it difficult to realize a finely divided primary recrystallized structure, which may hinder the development of secondary recrystallization. On the other hand, if the hot-rolled sheet annealing temperature exceeds 1100°C, the grain size after annealing becomes excessively coarsens, making it difficult to realize a finely divided primary recrystallized structure.

[0118] [Cold Rolled]

[0119] For a hot-rolled plate after hot rolling or a hot-rolled annealed plate after hot rolling annealing, one or two or more cold rolling steps are performed with intermediate annealing in between to produce a cold-rolled plate having a final plate thickness. The intermediate annealing temperature is preferably 800°C or higher, preferably 1150°C or lower, and more suitable to be 800°C or higher and 1150°C or lower. In addition, the intermediate annealing time is preferably 10 seconds or more, preferably 100 seconds or less, and preferably about 10 to 100 seconds.

[0120] As in the tactics, suitably, the aforementioned groove is formed in this cold-rolled plate.

[0121] [Detanning]

[0122] Decarburization annealing is performed on a cold-rolled sheet after cold rolling to produce a decarburized annealed sheet. In the decarburization annealing, the annealing temperature is preferably 750°C or higher, preferably 900°C or lower, and more preferably 750 to 900°C. In addition, the atmosphere oxidation properties (degree of oxidation) pH2O / PH2 is preferably 0.25 or higher, preferably 0.60 or lower, and more preferably 0.25 to 0.60. In addition, the annealing time is preferably 50 s or higher, preferably 300 s or lower, and more preferably 50 to 300 s.

[0123] [Text-detailing processing]

[0124] Regarding the processing of subdivision of the self-regulating part, it can follow the method of forming the groove of the tactical part.

[0125] In the magnetic domain refinement treatment, which is one of the features of the present invention, a linear groove is formed during any of the above-mentioned processes before applying an annealing separator. Methods for forming the linear groove include localized etching, scribing with a cutting tool, or rolling with a protrusion-attached roll. Among these, a preferred method is to form a linear groove by electrolytic etching in the non-attached area after applying an etching resist to the cold-rolled plate by printing, etc. Furthermore, since the formation of a predetermined forsterite film on the bottom of the groove is effective for magnetic domain refinement, the formation of the groove is performed before the application of the annealing separator that forms the forsterite film and before the final finishing annealing.

[0126] [Application of Annealing Separator]

[0127] The application of the annealing release agent is as described above. After decarburization annealing, the annealing release agent is applied using the aforementioned prescribed method, and a forsterite film is formed by the subsequent final finishing annealing.

[0128] [Final Finishing Annealing]

[0129] The final finishing annealing is as described in the tactic. After applying the annealing release agent, the final finishing annealing is performed for the purpose of secondary recrystallization and the formation of a forsterite film, thereby forming a finishing annealed plate. It is preferable that the annealing temperature of this final finishing annealing be 1100°C or higher, and the annealing time be 30 minutes or more.

[0130] In addition, as in the case of the tactic, it is desirable to perform final finishing annealing by forming the decarburized annealing plate into a coil shape with the grooved surface placed on the outer side.

[0131] [Insulation Coating and Planarization Annealing]

[0132] The insulating coating and planarization annealing are as described above. After the final finishing annealing, an insulating coating is applied using the method specified above to form an insulating film. Additionally, it is preferable to correct the shape by performing planarization annealing; however, the planarization annealing may be performed after the insulating coating, or the insulating coating may be applied after the planarization annealing.

[0133] Example 1

[0134] A steel slab (slab for oriented electrical steel sheets) was manufactured by continuous casting, comprising C: 0.07 mass%, Si: 3.4 mass%, Mn: 0.1 mass%, Ni: 0.2 mass%, Al: 240 mass ppm, S: 20 mass ppm, N: 90 mass ppm, and Se: 180 mass ppm, with the remainder being Fe and unavoidable impurities. The slab was heated to 1430°C and then hot-rolled to form a hot-rolled sheet with a thickness of 2.2 mm. The hot-rolled sheet was subjected to hot-rolling annealing at 1100°C for 20 seconds. Next, the hot-rolled annealed plate after the annealing was cold-rolled to an intermediate plate thickness of 0.40 mm, and then intermediate annealing was performed under conditions of oxidation degree P(H2O) / P(H2) = 0.40, temperature: 1000℃, and time: 70 seconds. Subsequently, after removing the surface subscale by hydrochloric acid cleaning of the hot-rolled annealed plate after the intermediate annealing, cold rolling was performed again to produce a cold-rolled plate with a final plate thickness of 0.23 mm.

[0135] After that, resist ink was applied to one or both sides of the cold-rolled plate, and a laser was irradiated onto the coated surface in a repeating line shape with a spacing of 3 mm in the rolling direction and also in the rolling direction, thereby peeling off the resist ink with a spacing of 3 mm in the rolling direction. The laser irradiation was performed using a single-mode fiber laser in a galvanometer scanner manner, and the resist ink was completely peeled off continuously from edge to edge in the width direction of the cold-rolled plate.

[0136] As shown in Table 1, the laser pattern, that is, the groove formation pattern, was performed in four ways: one side only (displacement with respect to the direction orthogonal to the rolling direction: 1 to 30°, indicated as "one side" in the table), both sides also parallel and staggered (the above-mentioned displacement: 1 to 30°, indicated as "both sides parallel and staggered" in the table), both sides also parallel and at the same position on the front and back (the above-mentioned displacement: 1 to 30°, indicated as "both sides at the same location" in the table), and both sides also cross on the front and back (the above-mentioned displacement: 1 to 30° each symmetrically with respect to the rolling direction, indicated as "both sides cross" in the table). After that, electrolytic etching was performed to form a groove with a depth (D): 25 μm and an approximate cross-section trapezoid. After electrolytic etching, the resist ink remaining on the steel plate was removed.

[0137] Next, decarburization annealing was performed at an oxidation degree P(H2O) / P(H2) = 0.44 and a cracking temperature of 820°C for 300 seconds, and then an annealing separator with MgO as the main component was applied to the surface of the decarburization annealing plate, and a final finishing annealing was performed at 1160°C for 10 hours for the purpose of secondary recrystallization, formation of a forsterite film, and purification.

[0138] At this time, the annealing separator was applied in two ways: by applying only with a conventional roll coater, and by applying according to the present invention (preliminary application: introducing the annealing separator into the groove by a roll coater + scraping off the annealing separator + main application: full surface application by a roll coater). In the table, the former is indicated as "no preliminary application and scraping," and the latter as "with preliminary application and scraping." In addition, to promote inflow into the groove, the viscosity of the annealing separator (suspension) was varied to 1000, 100, and 10 Pa·s, respectively. After the preliminary application of the annealing separator, the solution on the surface was scraped off using a doctor blade.

[0139] In addition, during the final finishing annealing, under the condition that the groove is formed only on one side of the decarburized annealing plate, the process was carried out under two conditions: a coil in which the groove is positioned on the outer side and a coil in which the groove is positioned on the inner side. Regarding the "position of the groove in the coil" in the table, the former is indicated as "outer" and the latter as "inner."

[0140] In addition, an insulating coating consisting of 60 mass% colloidal silica and aluminum phosphate was applied, and then baked at 850°C to form an insulating film, which was then prepared as each test specimen. The baking treatment of this insulating coating also serves as a planarization annealing.

[0141] At this time, the insulating coating liquid was applied using two methods: application by a conventional roll coater alone, and an application method according to the present invention (preliminary application: introducing the insulating coating into the groove by a roll coater + scraping off the insulating coating + main application: full surface application by a roll coater). In the table, the former is indicated as "no preliminary application and no scraping," and the latter as "with preliminary application and scraping." In addition, to promote inflow into the groove, the viscosity of the insulating coating liquid was varied to 1000, 100, and 10 Pa·s, respectively. After the preliminary application of the insulating coating liquid, the solution on the surface was scraped off using a doctor blade.

[0142] The surface roughness Ra of the forsterite film at the center of the groove of the oriented electrical steel sheet obtained in this way, the roughness coefficient of the forsterite film formed in the groove, and the average thickness of the insulating film at the bottom of the groove were measured according to the above and below methods.

[0143] First, the surface roughness Ra of the forsterite film was measured using a sample (finish annealing plate) prior to planarization annealing and the application of an insulating coating solution. For these samples, according to the aforementioned method for measuring surface roughness Ra, the distance (t) was set to 30 mm, and measurements of irregularities were performed at 20 random locations on the sample (for 20 different grooves) to obtain the Ra value. Then, the average value from these 20 locations was taken as the surface roughness Ra of the forsterite film formed at the center of the groove.

[0144] In addition, the annealing temperature during the final finishing annealing in which the forsterite film is formed is higher than the annealing temperature in which the insulating film is formed; therefore, the surface roughness of the forsterite film does not change before or after the formation of the insulating film.

[0145] In addition, the roughness coefficient of the forsterite film formed in the grooves was also measured using a finishing annealing plate, just as Ra was measured. Then, according to the roughness coefficient measurement method described above, 30g of a sample without grooves and 30g of a sample containing grooves were used for one analysis, and measurements were taken for 20 samples of each, with the average value taken as the result of the roughness coefficient. For the measurement, the automatic specific surface area and pore distribution measuring device TriStar (registered trademark) II series was used.

[0146] In addition, for the same reason as in the case of Ra, the roughness coefficient of the forsterite film does not change before and after the formation of the insulating film.

[0147] Next, the average thickness of the insulating film at the bottom of the groove was measured using a test specimen (oriented electrical steel sheet) after insulating coating combined with planarization annealing. For these test specimens, the average value of the insulating film thickness was obtained according to the aforementioned average thickness measurement method.

[0148] In addition, the above test specimen was sheared to a size of 30 mm × 280 mm, and then subjected to strain relief annealing (for the purpose of excluding the effect of shearing) under conditions of argon atmosphere and 800°C × 3 hours, and then subjected to self-measurement using the Epstein test method on the test specimen.

[0149] The evaluation of the adhesion (peelability) of the insulating film was performed by a bending peel test, in which a oriented electrical steel sheet having the film was wound onto a round bar as described above, and the minimum diameter (mm) at which peeling of the insulating film did not occur was determined. This test evaluates the adhesion of the insulating film in the groove, and the insulating film is more damaged in the case of tension than in compression. For this reason, during the test, the steel sheet was wound so that the groove was on the outside for evaluation.

[0150] Table 1 shows the surface roughness Ra (average value) of the forsterite film at the center of the groove, the thickness (average value) of the insulating film at the bottom of the groove, the roughness and roughness coefficient of the forsterite film in the groove, and the results of the evaluation of the adhesion (peelability) of the insulating film and the magnetic properties of the oriented electrical steel sheet.

[0151]

[0152]

[0153]

[0154]

[0155]

[0156]

[0157] As shown in Table 1, according to the present invention, when a forsterite film satisfying a predetermined surface roughness is formed in a groove, the insulating film on the forsterite film can be made thicker to a predetermined degree, thereby improving the adhesion (peelability) of the insulating film and obtaining an oriented electrical steel sheet with excellent magnetic properties.

[0158] Furthermore, in the method according to the present invention, a oriented electrical steel sheet is obtained that stably exhibits good magnetic properties without relying on the viscosity of the annealing separator (suspension) and the insulating coating solution. Furthermore, a oriented electrical steel sheet is obtained that stably exhibits good magnetic properties without relying on the pattern of the grooves formed.

[0159] As such, it is believed that by using the oriented electrical steel sheet of the present invention, which exhibits excellent adhesion despite the thick insulating film in the groove and also realizes low iron loss, the BF of the transformer can be reduced.

[0160] Among them, when the roughness coefficient of the forsterite film additionally satisfies 0.8 or less, even better magnetic properties are obtained.

[0161] In addition, regarding oriented electrical steel sheets in which grooves are formed on only one side, the roughness coefficient was smaller and iron loss was further reduced when the final finishing annealing was performed with the groove facing outward compared to when the final finishing annealing was performed with the groove facing inward.

[0162] In addition, regarding the oriented electrical steel sheet in which grooves are formed on both sides, the magnetic properties are better than those of the comparative example due to the magnetic domain subdivision effect caused by the grooves on the front and back surfaces. However, since the forsterite film formed on one side is prone to damage, the roughness coefficient tended to be higher than in the case where grooves are formed on only one side and the final finishing annealing is performed with the groove facing outward. As a result, due to the balance between the improvement of the magnetic domain subdivision effect from both sides and the increase in the roughness coefficient, the iron loss characteristics are almost equivalent to the case where grooves are formed on only one side and the final finishing annealing is performed with the groove facing outward. Explanation of the symbols

[0163] 1 : Grain-oriented electrical steel (steel sheet) 2 : Home 20 : Bottom part 21 : Center 3: Forsterite film 4: Insulating film

Claims

Claim 1 A oriented electrical steel sheet having a plurality of grooves on one or both sides of a steel sheet that are extended in a linear shape in a direction traversing the rolling direction of the steel sheet and arranged at intervals in the rolling direction, and having a forsterite film and an insulating film on both sides of the steel sheet in order from the surface side of the steel sheet, wherein the surface roughness Ra of the forsterite film formed at the center of the groove in a cross-section perpendicular to the extension direction of the groove is 5.00 μm or more, and the average thickness of the insulating film at the bottom of the groove is 1.50 μm or more. Claim 2 A oriented electrical steel sheet according to claim 1, wherein the roughness coefficient of the forsterite film formed in the groove is 0.8 or less. Claim 3 A method for manufacturing a oriented electrical steel sheet, wherein a slab for an oriented electrical steel sheet is hot-rolled to form a hot-rolled sheet, and subsequently, if necessary, annealing is performed on the hot-rolled sheet to form a hot-rolled annealed sheet, and then, one or more times with intermediate annealing in between, cold rolling is performed on the hot-rolled sheet or the hot-rolled annealed sheet to form a cold-rolled sheet having a final sheet thickness, and then, decarburization annealing is performed on the cold-rolled sheet to form a decarburization annealed sheet, and then, an annealing separating agent mainly composed of MgO is applied to the surface of the decarburization annealed sheet, and then, a final finishing annealing is performed to form a finishing annealed sheet, and then, an insulating coating is applied to the finishing annealed sheet, wherein, (1) before applying the annealing separating agent, on one or both sides of the hot-rolled sheet, the hot-rolled annealed sheet, the cold-rolled sheet or the decarburization annealed sheet, a linear shape extending in a direction transverse to the rolling direction of the steel sheet is also applied, and A method for manufacturing a oriented electrical steel sheet, comprising: forming a plurality of grooves spaced apart in the rolling direction; (2) applying an annealing separator to at least the groove-forming surface of the decarburized annealing sheet, scraping off the annealing separator, and then applying an annealing separator to both sides of the decarburized annealing sheet; (3) applying an insulating coating to at least the groove-forming surface of the finishing annealing sheet, scraping off the insulating coating, and then applying an insulating coating to both sides of the finishing annealing sheet. Claim 4 A method for manufacturing a oriented electrical steel sheet according to paragraph 3, wherein a doctor blade is used for scraping off the annealing separator and the insulating coating. Claim 5 A method for manufacturing a directional electrical steel sheet according to claim 3 or 4, wherein when performing final finishing annealing on the decarburized annealing sheet coated with the annealing separating agent, the decarburized annealing sheet is formed into a coil shape by placing the surface having the groove formed on the coil outer side and performing final finishing annealing.

Images