Grain-oriented electrical steel sheet and its manufacturing method

Abstract

The present invention provides a grain-oriented electrical steel sheet and a manufacturing method thereof in which the thickness of an insulating coating layer formed on grooves is controlled depending on the thickness of a forsterite layer, thereby improving magnetic properties and hot rolling characteristics. [Solution] The grain-oriented electrical steel sheet of the present invention has grooves with bottoms and sides located on the surface of the electrical steel sheet, a metal oxide layer located on the grooves, and an insulating layer located on the metal oxide layer, and the steel sheet includes normal grooves in which the metal oxide layer located on the bottom and sides has a thickness of more than 0.5 μm, and defective grooves in which the metal oxide layer located on the sides or bottom has a thickness of 0.5 μm or less, and the thickness of the insulating layer located on the normal grooves is 0.5 μm or more and less than 1.5 μm, and the thickness of the insulating layer located on the defective grooves is 1.5 to 10 μm.

Description

[Technical field]

[0001] The present invention relates to a grain-oriented electrical steel sheet and a manufacturing method thereof, and more particularly to a grain-oriented electrical steel sheet in which the thickness of an insulating coating layer formed on a groove is controlled according to the thickness of a forsterite layer, thereby improving magnetic properties and hot rolling characteristics, and a manufacturing method thereof. [Background technology]

[0002] In order for grain-oriented electrical steel sheets to be used as the core of highly efficient transformers, it is preferable to use an iron core material having excellent core loss and insulation properties for the electrical steel sheets, which minimizes losses in electronic devices. Grain-oriented electrical steel sheets are produced by arranging the secondary recrystallized grains in the Goss orientation ({110} <001> ) orientation, the iron loss characteristics in the rolling direction are superior to those in the direction perpendicular to the rolling direction, making it a functional steel sheet for electronic devices. In particular, the magnetic domain refinement technology in grain-oriented electrical steel improves iron loss by reducing the 180° magnetic domain width in secondary crystal grains when a magnetic field is applied, and is applied to products of various thicknesses. When low-loss plates are laminated to improve the efficiency of transformer cores, it is necessary to improve insulation properties and minimize stray field. That is, when low-loss steel sheets are laminated, if the insulation properties of the plates deteriorate and leakage flux increases, the excitation voltage of the core increases, which is undesirable because it requires current to be passed at a level higher than the designed magnetic flux density. Summary of the Invention [Problem to be solved by the invention]

[0003] An object of the present invention is to provide a grain-oriented electrical steel sheet and a manufacturing method thereof, more specifically, to provide a grain-oriented electrical steel sheet and a manufacturing method thereof in which the thickness of the insulating coating layer formed on the grooves is controlled according to the thickness of the forsterite layer, thereby improving magnetic properties and hot rolling characteristics. [Means for solving the problem]

[0004] The grain-oriented electrical steel sheet of the present invention is characterized in that a groove having a bottom and sides is located on a surface of the electrical steel sheet, a metal oxide layer is located on the groove, and an insulating layer is located on the metal oxide layer, the steel sheet includes normal grooves in which the metal oxide layer located on the bottom and sides has a thickness of more than 0.5 μm, and defective grooves having defective portions in which the metal oxide layer located on the sides or bottom has a thickness of 0.5 μm or less, the insulating layer located on the normal grooves has a thickness of 0.5 μm to 4.0 μm, and the insulating layer located on the defective grooves has a thickness of 1.5 to 10 μm.

[0005] The defect groove may include a side defect groove having a defect on a side and a bottom defect groove having a defect on a bottom, and the thickness of the insulating layer located on the side defect groove may be 1.5 to 6 μm, and the thickness of the insulating layer located on the bottom defect groove may be 2.0 to 10 μm. It is preferable that the thickness of the insulating layer located on the side of the normal groove is 0.5 μm to 2.0 μm, and the thickness of the insulating layer located on the bottom of the normal groove is 1.0 μm to 4.0 μm.

[0006] It is preferable that the thickness of the insulating layer located on the side of the side defect groove is 1.5 μm or more and less than 4.0 μm, and the thickness of the insulating layer located on the bottom of the side defect groove is 4.0 μm to 6.0 μm. It is preferable that the thickness of the insulating layer located on the side of the bottom defect groove is 2.0 μm or more and less than 5.0 μm, and the thickness of the insulating layer located on the bottom of the bottom defect groove is 5.0 μm to 10.0 μm.

[0007] It is preferable that the steel sheet is divided into sections in a direction perpendicular to the rolling direction, and the thickness of the insulating layer for each section is determined according to the thickness of the metal oxide layer located on the groove included in each section. It is preferable that the steel sheet is divided into sections in the rolling direction, and the thickness of the insulating layer for each section is determined according to the thickness of the metal oxide layer located on the groove included in each section.

[0008] The bottom of the groove may be at least 0.7 of the total groove depth and the sides of the groove may be at least 0.7 of the total groove depth. The defective grooves can account for 10-80% of the grooves in the steel plate. The grooves are formed linearly, and 2 to 10 grooves may be positioned discontinuously in the direction perpendicular to the rolling direction.

[0009] The groove is formed linearly and preferably forms an angle of 75 to 88° with respect to the vertical direction of the rolling. The groove depth is preferably 3 to 30 μm.

[0010] The method for producing a grain-oriented electrical steel sheet of the present invention is characterized by including the steps of producing a cold-rolled sheet, forming a groove having a bottom and sides on a surface of the cold-rolled sheet, applying an annealing separator to the cold-rolled sheet and annealing the sheet at a high temperature to form a metal oxide layer, measuring the thickness of the metal oxide layer located on the bottom and sides of the groove, and applying an insulating layer-forming composition having a viscosity adjusted according to the measured thickness of the metal oxide layer to form an insulating layer.

[0011] In the step of forming the insulating layer, in the case of a normal groove in which the thickness of the metal oxide layer located on the bottom and sides exceeds 0.5 μm, it is preferable to adjust the viscosity of the insulating layer-forming composition to more than 80 cps, and in the case of a defective groove having a defective portion in which the thickness of the metal oxide layer located on the side or bottom is 0.5 μm or less, it is preferable to adjust the viscosity of the insulating layer-forming composition to 80 cps or less. In the step of forming an insulating layer, in the case of a side defect groove having a defect portion in which the thickness of the metal oxide layer located on the side is 0.5 μm or less, it is preferable to adjust the viscosity of the insulating layer-forming composition to 20 to 80 cps, and in the case of a bottom defect groove having a defect portion in which the thickness of the metal oxide layer located on the bottom is 0.5 μm or less, it is preferable to adjust the viscosity of the insulating layer-forming composition to less than 20 cps.

[0012] In the step of measuring the thickness of the metal oxide layer, the thickness is measured by dividing the metal oxide layer into sections in the direction perpendicular to the rolling direction, and in the step of forming the insulating layer, the insulating layer-forming composition can be applied to the sections in the direction perpendicular to the rolling direction. In the step of measuring the thickness of the metal oxide layer, the thickness can be measured by dividing the area into sections in the rolling direction, and in the step of forming the insulating layer, the insulating layer-forming composition can be applied to the area divided in the rolling direction. Effect of the Invention

[0013] According to the present invention, the grain-oriented electrical steel sheet of the present invention can improve insulation properties by forming an insulating layer with an appropriate thickness even if defects occur in the metal oxide layer. Even if no defects occur in the metal oxide layer, the space factor can be improved by forming the insulating layer with an appropriate thickness. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a schematic diagram of a rolled surface (ND surface) of a grain-oriented electrical steel sheet according to one embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram of a groove cross section according to one embodiment of the present invention. [Diagram 3] FIG. 2 is a schematic diagram of a normal groove cross section according to one embodiment of the present invention. [Figure 4] FIG. 2 is a schematic diagram of a side defect groove cross section according to one embodiment of the present invention. [Diagram 5] FIG. 2 is a schematic diagram of a bottom defect groove cross section according to one embodiment of the present invention. [Figure 6] This shows the case where the sections are divided in the direction perpendicular to the rolling direction. [Figure 7] This shows the case where the sections are divided in the rolling direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Terms such as first, second and third are used to describe various parts, components, regions, layers and / or sections, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer or section from another part, component, region, layer or section. Thus, a first part, component, region, layer or section described below can be referred to as a second part, component, region, layer or section without departing from the scope of the present invention. The terminology used herein is for the purpose of referring to particular embodiments only and is not intended to limit the invention. As used herein, the singular form includes the plural form unless the phrase clearly indicates otherwise. As used in the specification, the meaning of "comprising" embodies the specified features, regions, integers, steps, operations, elements and / or components and does not exclude the presence or addition of other features, regions, integers, steps, operations, elements and / or components.

[0016] When an element is referred to as being "on" or "on" another element, it may be immediately on or above the other element, or there may be other elements between them. In contrast, when an element is referred to as being "directly on" another element, there are no other elements between them. Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention belongs. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the currently disclosed content, and are not interpreted in an ideal or very formal sense unless otherwise defined.

[0017] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention may be embodied in various different forms and should not be construed as being limited to the embodiments set forth herein.

[0018] Fig. 1 is a schematic diagram of the rolled surface (ND surface) of a grain-oriented electrical steel sheet according to one embodiment of the present invention. Fig. 2 is a schematic diagram of a groove cross section according to one embodiment of the present invention. Fig. 3 is a schematic diagram of a normal groove cross section according to one embodiment of the present invention. As shown in Figures 1 to 3, a grain-oriented electrical steel sheet 10 according to an embodiment of the present invention has a groove 20 located on the surface of the electrical steel sheet, the groove 20 including a bottom portion 21 and a side portion 22. As shown in Figure 3, a metal oxide layer 30 and an insulating layer 40 are sequentially located on the groove 20.

[0019] The metal oxide layer 30 is formed through a reaction between an annealing separator and an oxide layer on the surface of the steel sheet during the secondary recrystallization annealing process in the manufacturing process of the grain-oriented electrical steel sheet. Ideally, the metal oxide layer 3-0 should be formed uniformly, but since the metal oxide layer 30 is affected by various process variables, it is not easy to form the metal oxide layer uniformly. Furthermore, when grooves 20 are formed in the steel sheet as in one embodiment of the present invention, it is very difficult to form a uniform metal oxide layer 30 on the grooves 20. The metal oxide layer 30 is widely known, and therefore a detailed description thereof will be omitted. As an example, the metal oxide layer 30 may be Forsterite (Mg2SiO4).

[0020] In the actual process, defects occur in which the thickness of the metal oxide layer 30 located above the grooves 20 is thin in some places, and if the insulating layer 40 applied to such defective grooves is formed in the same way as for normal grooves, the insulating properties of the defective grooves will be very weak. On the other hand, it is possible to form an insulating layer 40 with a large thickness over the entire steel sheet in anticipation of the formation of defective grooves, but in this case, the space factor will deteriorate. In one embodiment of the present invention, normal grooves and defective grooves are distinguished from each other based on the thickness of the metal oxide layer 30, and insulating layers 40 of different thicknesses are formed in each of the grooves, thereby improving both the insulating properties and the space factor at the same time.

[0021] Specifically, normal grooves and defective grooves can be classified as follows: A normal groove refers to a groove in which the thickness of the metal oxide layer 30 located on the bottom 21 and sides 22 exceeds 0.5 μm. An example of a normal groove is shown in Figure 3. As shown in Figure 3, the metal oxide layer 30 is formed uniformly on the bottom 21 and sides 22, and there are no defects with a thickness of 0.5 μm or less.

[0022] Meanwhile, a defective groove means a groove having a defect d in which the thickness of the metal oxide layer on the side 22 or bottom 21 is 0.5 μm or less. Examples of defective grooves are shown in Figures 4 and 5. As shown in Figures 4 and 5, defect d exists on the side 22 or bottom 21. Defective grooves can be further divided into side defective grooves in which defect d exists on the side 22 and bottom defective grooves in which defect d exists on the bottom 21. A side defective groove is shown in Figure 4, and a bottom defective groove is shown in Figure 5. In one embodiment of the present invention, when defect d exists on both the bottom 21 and side 22, it is classified as a bottom defective groove.

[0023] Since the metal oxide layer 30 is properly formed in the normal grooves, it is not necessary to increase the thickness of the insulating layer 40. In fact, if the insulating layer 40 is excessively thick, there is a risk of the space factor deteriorating. The insulating layer located on the normal grooves preferably has a thickness of 0.5 μm to 4.0 μm. More specifically, the insulating layer located on the normal grooves preferably has a thickness of 0.5 μm or more and less than 1.5 μm. Furthermore, the insulating layer located on the normal grooves more preferably has a thickness of 0.7 μm to 1.2 μm.

[0024] Since the defective grooves have defects in the metal oxide layer 30, the insulating layer 40 must be thick. Specifically, the insulating layer located on the defective groove has a thickness of 1.5 to 10 μm. More specifically, the insulating layer located on the defective groove preferably has a thickness of 3 to 7 μm. The thickness of the insulating layer 40 on the groove 20 may vary even within the groove 20, and in one embodiment of the present invention, the thickness of the insulating layer 40 refers to the average thickness relative to the groove width. Among the defect grooves, the bottom defect groove can have suitable insulating properties by making the insulating layer 40 thicker. Specifically, the insulating layer 40 located on the side defect grooves preferably has a thickness of 1.5 to 6 μm, and the insulating layer 40 located on the bottom defect groove preferably has a thickness of 2.0 to 10 μm. More specifically, the insulating layer 40 located on the side defect grooves more preferably has a thickness of 2 to 4 μm, and the insulating layer 40 located on the bottom defect groove more preferably has a thickness of 5 to 7 μm.

[0025] In both normal and defective grooves, the thickness of the bottom portion 21 is greater than that of the side portion 22, which helps improve insulation. Specifically, the thickness of the insulating layer on the side portion 21 is less than 20% of the groove depth H. The thickness of the insulating layer on the bottom portion 21 is 20 to 80% of the groove depth H. Specifically, the insulating layer located on the side 22 of the normal groove preferably has a thickness of 0.5 to 2.0 μm. More specifically, it is more preferable that the thickness is 0.5 μm or more and less than 1.5 μm. The insulating layer located on the bottom 21 of the normal groove preferably has a thickness of 1.5 μm to 4.0 μm. More specifically, it is more preferable that the thickness is 1.5 to 2.0 μm. On the other hand, it is particularly preferable that the insulating layer located on the side 22 of the normal groove has a thickness of 0.6 μm to 1.0 μm, and it is particularly preferable that the insulating layer located on the bottom 21 of the normal groove has a thickness of 1.7 μm to 1.8 μm.

[0026] The insulating layer located on the side 22 of the side defect groove has a thickness of 1.5 μm or more and less than 4.0 μm, and the insulating layer located on the bottom of the side defect groove has a thickness of 4.0 μm to 6.0 μm. More specifically, the insulating layer located on the side 22 of the side defect groove more preferably has a thickness of 1.5 μm to 3.0 μm, and the insulating layer located on the bottom of the side defect groove more preferably has a thickness of 5.0 μm to 6.0 μm. Moreover, it is preferable that the insulating layer located on the side portion 22 of the bottom defect groove has a thickness of 2.0 μm or more and less than 5.0 μm, and the insulating layer located on the bottom portion 11 of the bottom defect groove has a thickness of 5.0 μm to 10.0 μm. More specifically, it is more preferable that the insulating layer located on the side portion 22 of the bottom defect groove has a thickness of 2.0 μm to 3.0 μm, and it is more preferable that the insulating layer located on the bottom portion 11 of the bottom defect groove has a thickness of 7.0 μm to 9.0 μm.

[0027] The bottom 21 and side 22 of the groove are specifically shown in Fig. 2. As shown in the figure, the bottom 21 of the groove is a portion having a depth of 0.7 or more of the total groove depth H, and the side 22 of the groove is a portion having a depth of less than 0.7 of the total groove depth H. The steel sheet is divided into sections in the vertical direction of rolling, and the thickness of the insulating layer for each section is determined according to the thickness of the metal oxide layer 30 located on the grooves included in each section. The thickness of the metal oxide layer 30 varies depending on process variables, and does not vary abruptly along the vertical direction of rolling of the steel sheet. Therefore, there is no significant problem even if the steel sheet is divided into sections in the vertical direction of rolling, and the thickness of the insulating layer 40 located on the grooves included in each section is unified. In this case, the thickness of the insulating layer 40 is determined according to the thickness of the metal oxide layer 30 of any groove present within the section.

[0028] It is also possible to divide the steel sheet into sections in the rolling direction and determine the thickness of the insulating layer for each section depending on the thickness of the metal oxide layer located on the grooves included in each section. There is no significant problem even if the steel sheet is divided into sections in the rolling direction and the thickness of the insulating layer 40 located on the grooves included in each section is unified. In this case, the thickness of the insulating layer 40 is determined depending on the thickness of the metal oxide layer 30 of any groove present in the section.

[0029] 6 and 7 show cases where the thickness of the insulating layer 40 is determined by dividing the area into sections in the direction perpendicular to the rolling direction or in the rolling direction. Any groove (dotted circle) within the area can be selected and the thickness of the metal oxide layer on the groove (dotted circle) can be measured to represent the thickness of the insulating layer 40 for all grooves within the area. It is also possible to divide the insulating layer into sections in the direction perpendicular to or along the rolling direction, and determine the thickness of the insulating layer for each section according to the thickness of the metal oxide layer located on the grooves included in each section.

[0030] The defective groove is 10 The ratio of defective grooves may be up to 80%. As mentioned above, it is most ideal that no defective grooves are generated, but in actual processes, defective grooves are generated within the above range. Here, the ratio of defective grooves is the combined ratio of bottom defective grooves and side defective grooves. The grooves are formed linearly, with 2 to 10 of the grooves being arranged discontinuously in the rolling direction. Figure 1 shows a case where 4 of the grooves are formed discontinuously. The grooves are formed linearly, with an angle of 75 to 88 degrees in the rolling direction. The appropriate angle can further improve the iron loss. The groove depth is preferably 3 to 30 μm. An appropriate depth can further improve the core loss.

[0031] A method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention includes the steps of: preparing a cold-rolled sheet; forming a groove including a bottom and a side on a surface of the cold-rolled sheet; applying an annealing separator to the cold-rolled sheet and annealing the sheet at a high temperature to form a metal oxide layer; measuring the thickness of the metal oxide layer located on the bottom and the side of the groove; and adjusting the viscosity of an insulating layer-forming composition according to the measured thickness of the metal oxide layer and applying the composition to form an insulating layer.

[0032] First, a cold-rolled steel sheet is manufactured. The alloy components and manufacturing method of the cold-rolled steel sheet can be variously applied to the alloy components and manufacturing method of the grain-oriented electrical steel sheet, and are not particularly limited. As an example, the cold-rolled sheet may contain, based on the total composition of 100% by weight, O: 0.0020-0.0080%, Si: 2.5-6.0%, C: 0.02-0.10%, Al: 0.02-0.04%, Mn: 0.05-0.20%, N: 0.002-0.012%, S: 0.001%-0.010%, and P: 0.01-0.08%, with the balance being Fe and impurities (Ni, Cr, Sb, and rare earth metals, the total weight of which is within 0.1%).

[0033] Next, a groove having a bottom and sides is formed in the surface of the cold rolled sheet. The method of forming the grooves is not particularly limited and may be applied in various ways. As an example, the grooves may be formed by laser irradiation. In this case, a laser beam having an average output of several kilowatts is used. Since the laser beam is widely known, a detailed description thereof will be omitted. The annealing separator is applied to the cold-rolled sheet and then annealed at high temperature to form a metal oxide layer. Annealing separators and high-temperature annealing are widely known in the field of grain-oriented electrical steel sheets, so a detailed explanation is omitted. As an example, MgO can be used as the annealing separator. During the high-temperature annealing process, MgO combines with the oxide layer on the steel sheet surface to form forsterite.

[0034] The thickness of the metal oxide layer located on the bottom and sides of the groove is measured. At this stage, the groove is classified into a normal groove and a defective groove. The defective groove is further subdivided and classified into a side defective groove and a bottom defective groove. The thickness measurement method is not limited and can be applied in various ways, for example, an optical microscope method, an electron microscope method, a GDS method, etc. can be used. Then, an insulating layer-forming composition having a viscosity adjusted according to the measured thickness of the metal oxide layer is applied to form an insulating layer.

[0035] Specifically, in the step of forming the insulating layer, in the case of a normal groove in which the thickness of the metal oxide layer located on the bottom and sides exceeds 0.5 μm, it is preferable to adjust the viscosity of the insulating layer-forming composition to exceed 80 cps, and in the case of a defective groove having a defective portion in which the thickness of the metal oxide layer located on the side or bottom is 0.5 μm or less, it is preferable to adjust the viscosity of the insulating layer-forming composition to 80 cps or less. Various methods can be used to adjust the viscosity of the insulating layer-forming composition. For example, the viscosity can be adjusted by adjusting the amount of solvent in the composition. Alternatively, the viscosity can be adjusted by changing the types of components in the composition. That is, the composition may contain inorganic particles, and in this case, the viscosity can be adjusted by adjusting the specific surface area of ​​the inorganic particles. Various other methods can also be used without limitation. The above viscosities are based on a temperature of 25°C.

[0036] When the viscosity is low, a thick insulating layer can be formed on the groove. Conversely, when the viscosity is high, a thin insulating layer can be formed on the groove. In one embodiment of the present invention, the thickness of the insulating layer can be adjusted by using the viscosity of the insulating layer-forming composition. The thickness of the insulating layer has been described above, so a duplicated description will be omitted. In the case of a side defect groove in which the thickness of the metal oxide layer located on the side is 0.5 μm or less, the viscosity of the insulating layer-forming composition is preferably adjusted to 20 to 80 cps, whereas in the case of a bottom defect groove in which the thickness of the metal oxide layer located on the bottom is 0.5 μm or less, the viscosity of the insulating layer-forming composition is preferably adjusted to less than 20 cps.

[0037] In the step of measuring the thickness of the metal oxide layer, the thickness is measured by dividing the metal oxide layer into sections in the direction perpendicular to the rolling direction, and in the step of forming the insulating layer, the insulating layer-forming composition can be applied to the sections in the direction perpendicular to the rolling direction. In the step of measuring the thickness of the metal oxide layer, the thickness can be measured by dividing the area into sections in the rolling direction, and in the step of forming the insulating layer, the insulating layer-forming composition can be applied to the area divided in the rolling direction.

[0038] Various types of insulating layer forming compositions can be used without limitation. For example, an insulating layer forming composition containing silica and a metal phosphate can be used. The present invention will be described in more detail with reference to the following examples, which are merely illustrative of the present invention and are not intended to limit the present invention. EXAMPLES

[0039] Example 1 A cold-rolled sheet with a thickness of 0.27 mm was prepared by cold rolling. A 1.5 kW Gaussian mode continuous wave laser was irradiated onto this cold-rolled sheet to form grooves with a depth of 15 μm. After the grooves were formed, decarburization-nitriding annealing was performed, MgO was applied, and high-temperature annealing was performed. The above process was performed so that all of the metal oxide layers formed on the grooves in the specimen had defects at their bottoms. Thereafter, an insulating layer-forming composition containing silica and Al phosphate, the viscosity of which was adjusted to 15 cps, was applied to form an insulating layer. The thickness of the insulating layer, core loss (W17 / 50) and leakage current were measured and are shown in Table 1 below.

[0040] Example 2 The same procedure as in Example 1 was carried out, and the above process was carried out so that the metal oxide layer formed on the grooves in the specimen had defects on all sides. The viscosity was adjusted to 50 cps to form an insulating layer. The thickness of the insulating layer, core loss (W17 / 50) and leakage current were measured and are shown in Table 1 below.

[0041] Comparative Example 1 The same procedure as in Example 1 was carried out, and the viscosity was adjusted to 100 cps to form an insulating layer. The thickness of the insulating layer, core loss (W17 / 50) and leakage current were measured and are shown in Table 1 below. [Table 1]

[0042] As shown in Table 1, it can be confirmed that even if bottom defect grooves and side defect grooves are formed, if the insulating layer is formed with an appropriate thickness, a steel sheet with excellent iron loss and insulation properties can be obtained. On the other hand, it can be confirmed that if the insulating layer is formed thinly even though bottom defect grooves are formed as in Comparative Example 1, the iron loss and insulation properties become inferior.

[0043] The present invention is not limited to the embodiments, and can be manufactured in various different forms, and a person skilled in the art to which the present invention pertains can understand that the present invention can be embodied in other specific forms without changing the technical idea or essential features of the present invention. Therefore, it should be understood that the embodiments described above are illustrative in all respects and are not limiting. [Explanation of symbols]

[0044] 10: Grain-oriented electrical steel sheet 20: Groove 21: Bottom 22: Side 30: Metal oxide layer 40: Insulating layer d: Defect H: Groove depth

Claims

1. a groove having a bottom and a side is located on a surface of the electrical steel sheet; a metal oxide layer located on the groove; an insulating layer overlying the metal oxide layer; The steel plate includes a normal groove having a metal oxide layer located on the bottom and sides that is more than 0.5 μm thick and no defect having a thickness of 0.5 μm or less, and a defective groove having a metal oxide layer located on the side or bottom that is less than 0.5 μm thick, The thickness of the insulating layer located on the normal groove is 0.5 μm to 4.0 μm. the thickness of the insulating layer located on the defect groove is 1.5 to 10 μm; A grain-oriented electrical steel sheet, characterized in that the bottom of the groove has a depth of 0.7 or more of the total depth of the groove, and the side of the groove has a depth of less than 0.7 of the total depth of the groove.

2. the defect grooves include side defect grooves having defects on their sides and bottom defect grooves having defects on their bottoms; the thickness of the insulating layer located on the side defect groove is 1.5 to 6 μm; 2. The grain-oriented electrical steel sheet according to claim 1, wherein the thickness of the insulating layer located on the bottom defect groove is 2.0 to 10 μm.

3. 3. The grain-oriented electrical steel sheet according to claim 1, wherein the insulating layer located on the side of the normal groove has a thickness of 0.5 μm to 2.0 μm, and the insulating layer located on the bottom of the normal groove has a thickness of 1.0 μm to 4.0 μm.

4. 3. The grain-oriented electrical steel sheet according to claim 2, wherein a thickness of the insulating layer located on a side of the side defect groove is 1.5 μm or more and less than 4.0 μm, and a thickness of the insulating layer located on a bottom of the side defect groove is 4.0 μm to 6.0 μm.

5. 3. The grain-oriented electrical steel sheet according to claim 2, wherein a thickness of the insulating layer located on a side of the bottom defect groove is 2.0 μm or more and less than 5.0 μm, and a thickness of the insulating layer located on a bottom of the bottom defect groove is 5.0 μm to 10.0 μm.

6. 6. The grain-oriented electrical steel sheet according to claim 1, wherein the steel sheet is divided into sections in a rolling perpendicular direction, and a thickness of the insulating layer for each section is determined according to a thickness of a metal oxide layer located on a groove included in each section.

7. 6. The grain-oriented electrical steel sheet according to claim 1, wherein the steel sheet is divided into sections in a rolling direction, and a thickness of the insulating layer for each section is determined according to a thickness of a metal oxide layer located on a groove included in each section.

8. The grain-oriented electrical steel sheet according to any one of claims 1 to 7, characterized in that the defective grooves account for 10 to 80% of all grooves in the steel sheet.

9. The grain-oriented electrical steel sheet according to any one of claims 1 to 8, characterized in that the grooves are formed linearly, and 2 to 10 of the grooves are positioned intermittently in the rolling direction perpendicular thereto.

10. The grain-oriented electrical steel sheet according to any one of claims 1 to 9, characterized in that the grooves are formed linearly and form an angle of 75 to 88° with respect to the rolling direction.

11. The grain-oriented electrical steel sheet according to any one of claims 1 to 10, characterized in that the total depth of the groove is 3 to 30 µm.

12. producing a cold rolled sheet; forming a groove having a bottom and a side in a surface of the cold rolled sheet; applying an annealing separator to the cold-rolled sheet and annealing the sheet at a high temperature to form a metal oxide layer; measuring the thickness of the metal oxide layer located on the bottom and sides of the groove; and The method includes applying an insulating layer-forming composition having a viscosity adjusted according to the measured thickness of the metal oxide layer to form an insulating layer, In the step of forming the insulating layer, In the case of a normal groove in which the thickness of the metal oxide layer located on the bottom and sides exceeds 0.5 μm and there is no defect part with a thickness of 0.5 μm or less, the viscosity of the insulating layer-forming composition is adjusted to exceed 80 cps, and the thickness of the insulating layer is 0.5 μm to 4.0 μm; In the case of a defect groove having a defect portion in which the thickness of the metal oxide layer located on the side or bottom is 0.5 μm or less, the viscosity of the insulating layer-forming composition is adjusted to 80 cps or less, and the thickness of the insulating layer is 1.5 to 10 μm; a bottom of the groove has a depth of 0.7 or more of the total depth of the groove, and a side of the groove has a depth of less than 0.7 of the total depth of the groove.

13. In the step of forming the insulating layer, In the case of a side defect groove having a defect in which the thickness of the metal oxide layer located on the side is 0.5 μm or less, the viscosity of the insulating layer forming composition is adjusted to 20 to 80 cps, and the thickness of the insulating layer is 1.5 to 6 μm; 13. The method for producing a grain-oriented electrical steel sheet according to claim 12, wherein in the case of a bottom defect groove having a defect portion in which a thickness of a metal oxide layer located on the bottom is 0.5 μm or less, the viscosity of the insulating layer-forming composition is adjusted to less than 20 cps, and the thickness of the insulating layer is 2.0 to 10 μm.

14. In the step of measuring the thickness of the metal oxide layer, the thickness is measured at sections in a rolling direction; The method for producing a grain-oriented electrical steel sheet according to claim 12 or 13, wherein in the forming of the insulating layer, the insulating layer-forming composition is applied to separate sections in a direction perpendicular to the rolling direction.

15. In the step of measuring the thickness of the metal oxide layer, the thickness is measured at sections in a rolling direction; The method for producing a grain-oriented electrical steel sheet according to claim 12 or 13, wherein in the step of forming the insulating layer, the insulating layer-forming composition is applied to separate sections in the rolling direction.

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