Grain-oriented electrical steel sheet and manufacturing method therefor

Abstract

A grain-oriented electrical steel sheet includes: a silicon steel sheet; an oxide layer formed of one or more kinds of Mg, Al, and Si that is formed on a surface of the silicon steel sheet; and an insulating coating layer that is formed on a surface of the oxide layer, in which an oxide of one or more kinds of Mg, Al, and Si having an equivalent circle diameter of 0.1 to 3.0 µm is present at a density of 0.010 to 0.200 grains / µm2 in the silicon steel sheet in a range of 10 µm in a sheet thickness direction from an interface between the silicon steel sheet and the oxide layer, on the surface side of the silicon steel sheet, flat grains where an average thickness in a direction perpendicular to the surface is 0.5 to 5.0 µm, an aspect ratio that is a ratio of a grain width in a direction parallel to the surface to the average thickness is 1.5 or more, and a deviation of a crystal orientation from Goss orientation is 10° or more are present, and in a cross section in the sheet thickness direction, the length of grain boundaries of the flat grains accounts for 70% or more of the length of the interface between the silicon steel sheet and the oxide layer.

Description

TECHNICAL FIELD

[0001] The present invention relates to a grain-oriented electrical steel sheet and a manufacturing method therefor.

[0002] Priority is claimed on Japanese Patent Application No. 2022-186165, filed November 22, 2022, the content of which is incorporated herein by reference.BACKGROUND ART

[0003] A grain-oriented electrical steel sheet is a soft magnetic material, and is mainly used as a core material of a transformer. The grain-oriented electrical steel sheet is a steel sheet in which, for example, 2.00 to 6.00% of Si is contained and the crystal orientation of the product is highly integrated in a { 110 }<001 > orientation. As the magnetic characteristics, the grain-oriented electrical steel sheet is required to have a high magnetic flux density represented by B8 value and a low iron loss represented by W17 / 50. In particular, recently, from the viewpoint of energy saving, a demand for a reduction in power loss of a transformer has increased, and a demand for a reduction in iron loss of the grain-oriented electrical steel sheet has increased.

[0004] In response to this demand, a so-called magnetic domain refinement technique for reducing the magnetic domain width present in the grain-oriented electrical steel sheet has been developed as a means of reducing the iron loss of the grain-oriented electrical steel sheet. Hereinafter, such a technique, that is, the technique for refining magnetic domains is referred to as a "magnetic domain control technique", and an effect of the magnetic domain control technique is also referred to as a "magnetic domain control effect".

[0005] For example, a method for refining magnetic domains (reducing the magnetic domain width) and reducing an eddy-current loss to reduce an iron loss by irradiating a surface of a grain-oriented electrical steel sheet after finish annealing with a laser beam is disclosed in Patent Document 1. However, the reduction in iron loss according to this method uses the magnetic domain refinement phenomenon mainly caused by thermal strain introduced into the steel sheet by the laser irradiation, and the method cannot be used for a wound core that requires stress relief annealing after forming a core for a transformer.

[0006] A wound core mainly used for a medium and small transformer is often manufactured by a core manufacturing method by mechanical forming. In this manufacturing method, in order to eliminate an increase in iron loss due to processing strain introduced into the steel sheet by forming, stress relief annealing (for example, at 800°C for about 2 to 4 hours) is generally performed after forming a core shape by machining. Due to the stress relief annealing, the strain introduced into the core by machining is reduced and eliminated, but the thermal strain introduced for the magnetic domain refinement into the steel sheet on which the magnetic domain control is performed by the laser irradiation is eliminated. Therefore, the grain-oriented electrical steel sheet on which the magnetic domain refinement is performed by the introduction of the thermal strain represented by laser irradiation cannot be applied to the wound core in general.

[0007] As a magnetic domain control technique in which the magnetic domain control effect is not lost even when the above-described stress relief annealing is performed, a "groove introduction type magnetic domain control technique" in which linear grooves are periodically formed in a direction intersecting a rolling direction is widely known. As such a groove introduction type magnetic domain control technique, a groove forming technique by machining, a groove forming technique by etching, a groove forming technique by laser irradiation, and the like are known. For example, Patent Document 2 discloses a groove forming technique by laser irradiation. However, these groove forming methods alone cannot sufficiently meet the demand for a reduction in iron loss that has been increasing in recent years.

[0008] In addition, as techniques for reducing iron loss using other methods, Patent Document 3 discloses a technique for forming sharp and fine unevenness on a sheet surface before decarburization annealing and activating the surface to form an oxide layer that is rich in silica after decarburization annealing.

[0009] In addition, Patent Document 4 discloses a technique of a steel sheet including an annealing film formed of an oxide containing Mg, Si, or Al as a major component on a surface to improve film characteristics and magnetic characteristics, in which in a crystal orientation distribution of steel sheet grains in a steel sheet portion within 3 µm from a boundary between the film and the steel sheet or in a mixed region of the film and the steel sheet grains, an abundance ratio of grains of a crystal orientation where a deviation angle from Goss orientation is within 10 degrees is 50% or less.

[0010] However, these methods cannot also sufficiently meet the demand for a reduction in iron loss that has been increasing in recent years.Citation ListPatent Document

[0011] Patent Document 1: Japanese Unexamined Patent Application, First Publication No. S56-51522 Patent Document 2: Japanese Unexamined Patent Application, First Publication No. 2005-59014 Patent Document 3: Japanese Unexamined Patent Application, First Publication No. S62-151522 Patent Document 4: Japanese Unexamined Patent Application, First Publication No. 2003-27194 SUMMARY OF INVENTIONTechnical Problem

[0012] As described above, it has been considered to improve magnetic flux density and to obtain the iron loss reduction effect corresponding to a degree of the improvement, but cannot also sufficiently meet the demand that has been increasing in recent years. In particular, for the grain-oriented electrical steel sheet (GO) that is suitable for application to a wound core that is manufactured after performing stress relief annealing during core working, the improvement of magnetic flux density and the iron loss reduction effect corresponding to the improvement cost cannot be sufficiently obtained.

[0013] Therefore, an object of the present invention is to provide a grain-oriented electrical steel sheet having excellent magnetic characteristics (a high magnetic flux density and low iron loss corresponding to the magnetic flux density) and a manufacturing method therefor. Preferably, an object of the present invention is to provide a grain-oriented electrical steel sheet having excellent magnetic characteristics (a high magnetic flux density and low iron loss corresponding to the magnetic flux density) and a manufacturing method therefor, the grain-oriented electrical steel sheet being manufactured without performing a non-heat-resistant magnetic domain control (the above-described magnetic domain control by thermal strain introduced into the steel sheet by laser irradiation of the sheet surface) assuming application to a core such as wound core on which stress relief annealing is performed.Solution to Problem

[0014] The present inventors investigated improvement of magnetic characteristics of a grain-oriented electrical steel sheet that is suitable for application to a wound core, that is, improvement of a magnetic flux density and iron loss reduction. As a result, it was found that, by allowing an oxide of one or more kinds of Mg, Al, and Si to be present at a predetermined density in the vicinity of the surface of a silicon steel sheet (base steel sheet) in the grain-oriented electrical steel sheet and further forming flat grains where a deviation angle of a crystal orientation from Goss orientation ({ 110}<001> orientation) is 10° or more on the surface side of the silicon steel sheet, the 180° magnetic domain width can be controlled to be small in terms of energy, and thus the eddy-current loss and the iron loss can be reduced.

[0015] In addition, the present inventors investigated the effect of manufacturing conditions. As a result, the following findings were obtained regarding the following points.

[0016] That is, Goss orientation where high magnetic characteristics are exhibited in the grain-oriented electrical steel sheet are highly integrated by allowing AlN, MnS, or the like called an inhibitor to be present as a precipitate in a grain boundary in a finish annealing step as a manufacturing step and exhibiting an abnormal grain growth phenomenon called "secondary recrystallization" utilizing the pinning effect of the precipitate. After completing the integration of Goss orientation in the steel sheet, that is, after covering the inside of the sheet surface with Goss orientation grains, the inhibitor of which the function ends is decomposed and oxidized by a temperature increase in the latter half of a finish annealing step and is removed from the inside of the steel sheet. That is, the decomposition and oxidation of the inhibitor before sufficient integration of Goss orientation in the steel sheet is not preferable. Further, by suppressing the decomposition and oxidation of the inhibitor at a higher temperature, Goss orientation can be highly integrated, that is, crystals having an orientation closer to ideal Goss orientation can be integrated. To that end, a method of improving the heat resistance of the precipitate of which the function as the inhibitor is used.

[0017] The present inventors found that, as the method of improving the heat resistance of the inhibitor, it is effective to allow an oxide that can suppress the decomposition and oxidation of the inhibitor during subsequent finish annealing to be present on the sheet surface in a decarburization annealing step that is typically performed during the manufacturing of the grain-oriented electrical steel sheet. Further, it was found that, by allowing the oxide that can suppress the decomposition and oxidation of the above-described inhibitor to be present on the sheet surface using the decarburization annealing step before finish annealing, flat grains where a deviation angle of a crystal orientation from Goss orientation is 10° or more can be formed in the vicinity of the interface between the oxide of the sheet surface and the steel sheet, and the flat grains contributes to the improvement of magnetic characteristics.

[0018] In addition, the present inventors found that, in order to form more preferable flat grains for improving magnetic characteristics, it is effective to form the oxide grains more densely, thick, and uniformly on the surface side of the cold rolled sheet for forming the base steel sheet in the decarburization annealing step, and in order to form the oxide grains densely, thick, and uniformly, it is effective to grind, before the decarburization annealing step, the cold rolled sheet under predetermined conditions for removing a reactant with the surface of the steel sheet that inhibits the uniform oxidation of the sheet surface during decarburization annealing.

[0019] In addition, it was found that, by combining the above-described steel sheet with the groove introduction type magnetic domain control technique under predetermined conditions, iron loss can be reduced.

[0020] The present invention has been made in view of the above findings. The gist of the present invention is as follows. [1] According to one aspect of the present invention, there is provided a grain-oriented electrical steel sheet including: a silicon steel sheet; an oxide layer formed of one or more kinds of Mg, Al, and Si that is formed on a surface of the silicon steel sheet; and an insulating coating layer that is formed on a surface of the oxide layer, in which an oxide of one or more kinds of Mg, Al, and Si having an equivalent circle diameter of 0.1 to 3.0 µm is present at a density of 0.010 to 0.200 grains / µm 2< in the silicon steel sheet in a range of 10 µm in a sheet thickness direction from an interface between the silicon steel sheet and the oxide layer, on the surface side of the silicon steel sheet, flat grains where the average thickness in a direction perpendicular to the surface is 0.5 to 5.0 µm, an aspect ratio that is the ratio of a grain width in a direction parallel to the surface to the average thickness is 1.5 or more, and the deviation of the crystal orientation from Goss orientation is 10° or more are present, and in a cross section in the sheet thickness direction, the length of grain boundaries of the flat grains accounts for 70% or more of the length of the interface between the silicon steel sheet and the oxide layer. [2] In the grain-oriented electrical steel sheet according to [1], the average of the average thicknesses of the flat grains may be more than 2.0 µm and 5.0 µm or less. [3] In the grain-oriented electrical steel sheet according to [1] or [2], the coverage of the oxide layer on surfaces of the flat grains forming the interface may be 50% or more. [4] In the grain-oriented electrical steel sheet according to [1] or [2], a plurality of grooves having a depth of 10 to 30 µm and extending in a direction of 80 to 100° with respect to a rolling direction may be present in the silicon steel sheet, and an interval of the groove adjacent to each other in the rolling direction may be 1.0 to 20.0 mm. [5] In the grain-oriented electrical steel sheet according to [3], a plurality of grooves having a depth of 10 to 30 µm and extending in a direction of 80 to 100° with respect to a rolling direction may be present in the silicon steel sheet, and an interval of the groove adjacent to each other in the rolling direction may be 1.0 to 20.0 mm. [6] In the grain-oriented electrical steel sheet according to [4], on a surface side of the groove of the silicon steel sheet, in-groove flat grains where an average diameter in a direction perpendicular to the surface of the groove is 0.5 to 5.0 µm, an aspect ratio that is the ratio of a grain width in a direction parallel to the surface to the average diameter is 2.0 or more, and the deviation of a crystal orientation from Goss orientation is 10° or more may be present, and in a cross section in the sheet thickness direction perpendicular to an extending direction of the groove, the length of grain boundaries of the in-groove flat grains may account for 70% or more of the length of an inner surface of the groove. [7] In the grain-oriented electrical steel sheet according to [5], on a surface side of the groove of the silicon steel sheet, in-groove flat grains where the average diameter in a direction perpendicular to the surface of the groove is 0.5 to 5.0 µm, an aspect ratio that is the ratio of a grain width in a direction parallel to the surface to the average diameter is 2.0 or more, and a deviation of a crystal orientation from Goss orientation is 10° or more may be present, and in a cross section in the sheet thickness direction perpendicular to an extending direction of the groove, the length of grain boundaries of the in-groove flat grains may account for 70% or more of the length of an inner surface of the groove. [8] In the grain-oriented electrical steel sheet according to [6], an average of the average diameters of the in-groove flat grains may be more than 2.0 µm and 5.0 µm or less. [9] In the grain-oriented electrical steel sheet according to [7], the average of the average diameters of the in-groove flat grains may be more than 2.0 µm and 5.0 µm or less.

[10] According to another aspect of the present invention, there is provided a manufacturing method for a grain-oriented electrical steel sheet, the manufacturing method including: a hot rolling step of heating and hot rolling a slab to obtain a hot rolled sheet; a hot rolled sheet annealing step of annealing the hot rolled sheet after the hot rolling step; a pickling step of pickling the hot rolled sheet after the hot rolled sheet annealing step; a cold rolling step of cold rolling the hot rolled sheet after the pickling step to obtain a cold rolled sheet; a grinding step of grinding a surface of the cold rolled sheet after the cold rolling step; a contact step of bringing the cold rolled sheet after the grinding step into contact with an aqueous solution of pH 4.0 to 10.0; a decarburization annealing step of performing decarburization annealing on the cold rolled sheet after the contact step; a finish annealing step of applying an annealing separator to the cold rolled sheet after the decarburization annealing step and performing finish annealing to form an oxide layer formed of one or more kinds of Mg, Al, and Si on a surface of the cold rolled sheet that is a base steel sheet; and an insulating coating forming step of forming an insulating coating layer on a surface of the oxide layer after the finish annealing step, in which in the grinding step, using abrasive grains having a Knoop hardness of 1000 or more and the maximum grain size of more than 50 µm and 500 µm or less or using abrasive paper, a roll, or a brush to which the abrasive grains are fixed, the surface of the cold rolled sheet is ground at a rolling reduction of 1.0 to 5.0 mm and a grinding speed of 500 mpm or more such that an amount of abrasion on at least one surface of the cold rolled sheet is 0.10 to 10.0 g / m 2< .

[11] The manufacturing method for a grain-oriented electrical steel sheet according to

[10] , may further include, before the grinding step, a groove forming step of forming a plurality of grooves having a depth of 10 to 30 µm and extending in a direction having an angle of 80 to 100° with respect to a rolling direction on the cold rolled sheet such that each of intervals in the rolling direction is 1.0 to 20 mm.

[12] In the manufacturing method for a grain-oriented electrical steel sheet according to

[11] , in the groove forming step, the grooves may be formed by removing a molten material from the surface of the cold rolled sheet while irradiating the surface of the cold rolled sheet with a laser beam to melt a part of the sheet surface. Advantageous Effects of Invention

[0021] According to the above-described aspects of the present invention, a grain-oriented electrical steel sheet having excellent magnetic characteristics and a manufacturing method therefor can be provided.BRIEF DESCRIPTION OF DRAWINGS

[0022] [FIG. 1] A schematic diagram illustrating a cross section of a grain-oriented electrical steel sheet according to the present embodiment. [FIG. 2] A schematic diagram illustrating a cross section of a grain-oriented electrical steel sheet according to the present embodiment when a groove is formed. [FIG. 3] A diagram illustrating a method for measuring the average thickness and the aspect ratio of a grain. [FIG. 4] A diagram illustrating a method for measuring the coverage of an oxide layer in flat grains. DESCRIPTION OF EMBODIMENTS

[0023] Hereinafter, a grain-oriented electrical steel sheet according to one embodiment of the present invention (grain-oriented electrical steel sheet according to the present embodiment) and a manufacturing method therefor will be described.<Grain-oriented electrical steel sheet>

[0024] As illustrated in FIG. 1, a grain-oriented electrical steel sheet 1 according to the present embodiment includes: a silicon steel sheet 11 (hereinafter, the base steel sheet or also simply referred to as the steel sheet); an oxide layer 21 formed of one or more kinds of Mg, Al, and Si, that is formed on a surface of the silicon steel sheet 11; and an insulating coating layer 31 that is formed on a surface of the oxide layer 21.

[0025] The oxide layer 21 and the insulating coating layer 31 may be formed on only one surface of the steel sheet but are preferably formed on both surfaces of the steel sheet from the viewpoints of insulation properties and the like.

[0026] Hereinafter, each of the elements will be described.[Silicon steel sheet](Oxide of one or more kinds of Mg, Al, and Si having an equivalent circle diameter of 0.1 to 3.0 µm are present at a density of 0.010 to 0.200 grains / µm 2< in a range of 10 µm in a sheet thickness direction from an interface between the silicon steel sheet and the oxide layer)

[0027] In the grain-oriented electrical steel sheet, decomposition and oxidation of inhibitors (precipitates present in grain boundaries of AlN or the like) during finish annealing is suppressed, and the inhibitors are allowed to be present at a high temperature. As a result, during secondary recrystallization, Goss orientation can be highly integrated, that is, crystals having a crystal orientation closer to ideal Goss orientation can be integrated, and the magnetic flux density can be improved. Therefore, iron loss can be reduced.

[0028] The sizes of the precipitates as the inhibitors are extremely small at several tens of nm to several hundreds of nm in terms of equivalent circle diameter. In addition, there is a distribution in the sizes. When there is a distribution in the sizes, decomposition and oxidation of an inhibitor having a small size is completed at a low temperature, and the effect as the inhibitor is lost. In this case, secondary recrystallization of Goss orientation closer to ideal Goss orientation is difficult, and it is difficult to improve the magnetic flux density. On the other hand, by controlling the size distribution of the inhibitors to be fixed (such that a different between the sizes is reduced), the object can be achieved. However, it is industrially very difficult.

[0029] On the other hand, as long as the inhibitors can be allowed to be present at a high temperature by suppressing decomposition and oxidation using any method even in a state where there is the size distribution of the inhibitors, secondary recrystallization of grains having a crystal orientation closer to ideal Goss orientation can be caused to occur. In addition, in order to suppress the decomposition and oxidation of the inhibitors, a method of using inhibitors having high heat resistance can be used. On the other hand, as a method of achieving the suppression without changing components or the like of the inhibitors, it is known that Si oxide grains (hereinafter, also referred to as Si-based pre-oxides) that are formed on the sheet surface or in a surface layer area of the steel sheet (in the steel) in a decarburization annealing step contribute to the suppression. The mechanism is a supposition but is presumed to be that the oxidation of the inhibitors occurs when a small amount of oxygen in a finish annealing atmosphere oxidizes AlN or the like on the sheet surface, and the above-described Si-based pre-oxide prevents and reduces the oxidation.

[0030] However, the formation state of the Si-based pre-oxide in each of parts of the surface of the silicon steel sheet is likely to be non-uniform. When the formation state is non-uniform, the effect of suppressing the decomposition and oxidation of the inhibitors varies depending on locations in the steel sheet surface, and the desired effect cannot be sufficiently obtained.

[0031] The present inventors investigated the reason why the formation state of the oxide layer after finish annealing is non-uniform at each of the parts of the surface. As a result, it was found that an Fe-based oxide on a surface of the silicon steel sheet (cold rolled sheet) before decarburization annealing or a reactant between an oil-based agent or an extreme pressure additive in a rolling oil used during cold rolling and surface metal of the steel sheet is non-uniformly present on the sheet surface, and the Fe-based oxide or the reactant inhibits the Si-based pre-oxide from being formed densely, thick, and uniformly in region of a predetermined thickness from the surface during decarburization annealing.

[0032] Since it is difficult to uniformly form the Fe-based oxide film or the reactant during cold rolling, the present inventors investigated a configuration of detoxifying a factor of inhibiting the formation of the Si-based pre-oxide. As a result, it was found that, by grinding the surface (at least one surface) of a cold rolled sheet before a decarburization annealing step to a certain degree to expose a clean metal surface using abrasive grains or using abrasive paper, a roll, or a brush to which the abrasive grains are fixed and bringing the cold rolled sheet into contact with an aqueous solution immediately after the grinding, The Fe-based oxide or the reactant that is the factor of inhibiting the formation of the Si-based pre-oxide can be removed from the surface of the steel sheet, and the Si-based pre-oxide can be formed at a predetermined number density in the region of the predetermined thickness from the surface of the steel sheet after the decarburization annealing step.

[0033] Based on this finding, in the grain-oriented electrical steel sheet according to the present embodiment, as illustrated in FIG. 1, an oxide 101 (oxide grains) that is an oxide of one or more kinds of Mg, Al and Si and having an equivalent circle diameter of 0.1 to 3.0 µm is present at a density of 0.010 to 0.200 grains / µm 2< in a range of 10 µm in a sheet thickness direction from an interface between the steel sheet (silicon steel sheet) 11 and the oxide layer 21, the oxide 101 being an oxide that is changed from the Si-based pre-oxide due to oxidation of the inhibitor in a step of finish annealing or the like or a solid phase reaction of an annealing separator. This oxide 101 may be an oxide (including a complex oxide) of one or more kinds of Mg, Al, and Si. Assuming manufacturing conditions described below, the oxide 101 is likely to be an oxide containing Mg, Al, and Si, for example, spinel (MgAl 2 O 4 ), alumina (Al 2 O 3 ), or mullite (2SiO 2 ·3Al 2 O 3 ).

[0034] When the number density of the oxide 101 is excessively small, the adhesion of the oxide layer 21 with the steel sheet deteriorates, and the formation of flat grains 102 described below is non-uniform. On the other hand, when the number density of the oxide 101 is excessively large, the area of the metal portion in the steel sheet 11 decreases, and thus the magnetic flux density decreases. In addition, the proportion of the flat grains 102 is also relatively small, and thus the effect of reducing iron loss is less likely to be obtained.

[0035] By uniformly forming the oxide 101 in a predetermined region, a variation depending on locations in the effect of suppressing the decomposition and oxidation of the inhibitors during finish annealing is reduced, and the magnetic flux density is improved in the grain-oriented electrical steel sheet 1. In addition, by appropriately forming the flat grains 102, the 180° magnetic domain width is reduced, and the iron loss reduction effect corresponding to the magnetic flux density is obtained.

[0036] In consideration of the process of the formation, the above-described oxide 101 is likely to be present in the flat grains 102 described below.(On the surface side of the silicon steel sheet, flat grains where an average thickness in a direction perpendicular to the surface is 0.5 to 5.0 µm, an aspect ratio that is a ratio of a grain width in a direction parallel to the surface to the average thickness is 1.5 or more, and a deviation of a crystal orientation from Goss orientation is 10° or more are present)(In a cross section in the sheet thickness direction, the length of grain boundaries of the flat grains accounts for 70% or more of the length of the interface between the silicon steel sheet and the oxide layer)

[0037] As described above, in the grain-oriented electrical steel sheet according to the present embodiment, by uniformly forming the Si-based pre-oxide on a surface layer area (range of 10 µm from the surface) of the silicon steel sheet (base steel sheet) mainly using a decarburization annealing step or the like, the decomposition and oxidation of the inhibitors during finish annealing are suppressed, and the inhibitors are allowed to be present at a high temperature. In this case, Goss orientation can be highly integrated, that is, crystals having a crystal orientation closer to ideal Goss orientation can be integrated, and thus the magnetic flux density is improved. That is, iron loss can be reduced.

[0038] On the other hand, the occurrence of secondary recrystallization at a higher temperature represents that secondary recrystallization occurs only for grains having a crystal orientation closer to ideal Goss orientation. In this case, the number of Goss orientation grains to be secondarily recrystallized is reduced, and thus the number of Goss orientation grains per unit area of the steel sheet is reduced. That is, the grain size per Goss orientation grain further increases.

[0039] The iron loss required for the grain-oriented electrical steel sheet is classified into hysteresis loss and eddy-current loss as the breakdown. The hysteresis loss is further reduced by improving the magnetic flux density. On the other hand, the eddy-current loss is classified into classical eddy current loss that is reduced by a decrease in sheet thickness and an increase in the specific resistance of the steel sheet and anomalous eddy current loss that is reduced by a decrease in the magnetic domain width formed in Goss orientation grains. The decrease in sheet thickness and the increase in the specific resistance of the steel sheet relating to the classical eddy current loss reduction is likely to affect productivity. Therefore, it is important to reduce the anomalous eddy current loss, that is, to reduce the magnetic domain width. In general, the magnetic domain width has a correlation with the grain size of Goss orientation. In general, by reducing the grain size, the magnetic domain width of the so-called 180° magnetic domain formed in the grain-oriented electrical steel sheet is also reduced.

[0040] That is, although the magnetic flux density is improved by controlling the above-described oxide, there is a concern that the anomalous eddy current loss increases due to an increase in grain size such that the iron loss reduction effect corresponding to the improvement of the magnetic flux density cannot be obtained.

[0041] Accordingly, the present inventors investigated a method for the iron loss reduction corresponding to the improvement of the magnetic flux density, that is, a method for reducing the magnetic domain width to solve the increase in grain size that occurs secondarily while improving the abundance frequency of ideal Goss orientation. As a result, it was found that, even when secondary recrystallization is caused to occur at a higher temperature as described above for only grains having a crystal orientation closer to ideal Goss orientation such that the grain size of the grains increases, by allowing flat grains where a deviation angle from Goss orientation is 10° or more to be present on the surface of the steel sheet, the 180° magnetic domain width can be controlled to be small in terms of energy, and an increase in eddy-current loss can be suppressed.

[0042] Specifically, as illustrated in FIG. 1, it was found that the eddy-current loss is reduced when the flat grains 102 where an average thickness in a direction perpendicular to the surface is 0.5 to 5.0 µm, an aspect ratio that is a ratio of a grain width in a direction parallel to the surface to the average thickness is 1.5 or more, and a deviation (deviation angle) of a crystal orientation from Goss orientation is 10° or more are present on the surface side of the base steel sheet 11 (when the flat grains 102 are present as grains forming the outermost layer of the silicon steel sheet 11).

[0043] In the grains where the average thickness is less than 0.5 µm, the aspect ratio is less than 1.5, or the deviation from Goss orientation is less than 10°, the effect of reducing the magnetic domain width cannot be sufficiently obtained, and iron loss cannot be sufficiently reduced.

[0044] On the other hand, the grains have the deviation from Goss orientation. Therefore, when the average thickness of the grains is more than 5.0 µm, magnetic characteristics deteriorate as a whole, that is, the magnetic flux density is reduced and iron loss increases.

[0045] The average of the average thicknesses of the flat grains is preferably more than 2.0 µm and 5.0 µm or less from the viewpoint of sufficiently obtaining the effect of reducing the magnetic domain width.

[0046] In addition, in order to sufficiently obtain the above-described magnetic domain refinement effect, in a cross section in the sheet thickness direction, the length of grain boundaries of the flat grains accounts for 70% or more of the length of the interface between the base steel sheet and the oxide layer.

[0047] When the proportion of the flat grains forming the interface is small, the effect of reducing the magnetic domain width is insufficient, and thus the effect of reducing iron loss cannot be sufficiently obtained.

[0048] In the manufacturing method for the grain-oriented electrical steel sheet, during finish annealing, fine Goss orientation grains present on the inside in the sheet thickness direction of the steel sheet grow while eroding peripheral grains having an orientation other than Goss orientation. As a result, the proportion of the Goss orientation grains (grains when a longitudinal direction of the silicon steel sheet is the <100> direction and a plane direction thereof is the <110> direction) with respect to a rolling direction and the width direction further increases across the sheet thickness surface from the inside in the sheet thickness direction.

[0049] In the grain-oriented electrical steel sheet according to the present embodiment, by allowing the oxide to be present discretely (at the predetermined number density) in the surface layer area of the silicon steel sheet as described above, during the growth of the Goss orientation grains present on the inside in the sheet thickness direction, fine flat grains remain in the steel sheet surface layer area without being encroached by the Goss orientation grains. As a result, it is considered that "the flat grains" that are verified as flat-shaped grains are formed.

[0050] The average thickness and the aspect ratio of the grains present on the surface side and the deviation of the crystal orientation can be measured using the following method. For example, a sample having a 20 mm square is cut from the steel sheet such that a surface parallel to the rolling direction (RD direction) is obtained as a cross section, and the sample is polished such that the cross section is a mirror surface. In addition, in a state where strain is applied to the steel sheet by the polishing, it is difficult to measure the crystal orientation. Therefore, the polished sample is formed not to have strain using a polishing material such as colloidal silica in a final step of polishing. Using the polished sample, a cross-section is observed with an FE-SEM, and subsequently the crystal orientation is measured by EBSD measurement. Regarding the FE-SEM, "SU_70" (manufactured by Hitachi High-Tech Corporation) is used as an example. Regarding the EBSD measurement, "Digiview" manufactured by TSL Solutions Co., Ltd. is used as an example. As a specific method, the following examples can be used. Using the FE-SEM, a range of the cross section including the base steel sheet, the oxide layer, and the insulating coating layer is observed at a magnification of 500-fold to obtain an electron microscopic image. An interface between the insulating coating layer described below and the oxide layer and an interface between the oxide layer and the steel sheet are identified based on a difference in electron density in the electron microscopic image. During the identification of the above-described interfaces, when an elemental analyzer (EDS) is attached to the FE-SEM, the interfaces can be more accurately identified based on a difference between the elemental species, such as P, B, O, or Fe, in the insulating coating layer, the oxide layer, and the silicon steel sheet.

[0051] Next, in the cross section in the same field of view, the crystal orientation of the steel sheet is measured by EBSD. Specifically, in the field of view at 500-fold where it is assumed that flat grains of 100 or more are included, a region with a cross section having a length of 200 µm in the rolling direction and a length of 70 µm in the sheet thickness direction is set as a target, and the crystal orientation is measured at a measurement point pitch of 0.25 µm. A boundary having a crystal orientation difference of 15° or more is identified as a grain boundary, and a range surrounded by this grain boundary is identified as a grain. When the number of grains is less than 100 in the field of view, the measurement is performed in an additional field of view.

[0052] Regarding the grains, the average thickness of the grains is obtained using a method illustrated in a) to d) as illustrated in FIG. 3. a) Imaginary lines (1) for determining both ends of a grain are drawn in the sheet thickness direction (normal direction) of the steel sheet. b) With respect to a distance L between both ends, imaginary lines (2) (lines between which a portion represents a 95% width of the grain) in the sheet thickness direction are drawn at a point of 2.5% of L from each of both ends of the grain. c) Regarding the portion (the 95% width portion of the grain) between the imaginary lines drawn in b), average lines (3) are drawn at an interface between the grain and the oxide layer and an envelope of the lower side (grain boundary opposite to the oxide layer) of the grain. d) The distance between the two average lines drawn in c) is obtained as a thickness t(4) (the average value of the five points in total including both ends, the center, and intermediate points between both ends and the center).

[0053] In addition, the range of both ends of the grain drawn in a) is obtained as the width of the grain to calculate the aspect ratio.

[0054] Among the grains, regarding all of grains where the average thickness is 0.5 to 5.0 µm and the aspect ratio is 1.5 or more, the crystal orientation of ferrite of Fe is measured. On a crystal orientation map called an IPF map where the measured crystal orientations are plotted, crystal orientations with respect to the rolling direction (RD direction) and the sheet surface normal direction (ND direction) are plotted. The average of orientation differences of the grains from Goss orientation is calculated to obtain the deviation from Goss orientation. When the deviation from Goss orientation is 10° or more, this grain is identified as a flat grain.

[0055] The average (simple average) of the average thicknesses of the flat grains can be obtained by the sum of the average thicknesses of the flat grains obtained as described above by the number of the flat grains.

[0056] Since the flat grain is flat in the rolling direction (longitudinal direction) and the width direction, a cross section in the sheet thickness direction may be observed using any method. A method of obtaining a surface of the above-described steel sheet parallel to the rolling direction (RD direction) as a cross section, obtaining the crystal orientation map by EBSD, and verifying the presence of "flat grain" is preferable due to the high accuracy. As another method for simply verifying the presence of "flat grain", a method of polishing a surface parallel to the rolling direction (RD direction) to obtain a smooth cross section and subsequently causing a grain boundary to appear using such as a so-called Nital method (nitric acid ethanol method, described in JIS-G-0553 (2019) or the like) can be used. However, in this method, the crystal orientation cannot be identified and needs to be measured separately by EBSD or the like. Therefore, in the present embodiment, a method of combining FE-SEM and EBSD described above is adopted.

[0057] In addition, a proportion of the length of grain boundaries of the flat grains in the length of the interface between the base steel sheet and the oxide layer can be obtained using the following method.

[0058] For example, in a field of view observed at a magnification of 500-fold, regarding the interface between the silicon steel sheet and the oxide layer, a region with a cross section having a length of 200 µm in the rolling direction is set as a target, and the SEM observation and the EBSD measurement are performed. Regarding five points, that is, the portion corresponding to an interface length of 1000 µm, the SEM observation and the EBSD measurement are performed. The proportion (percentage) of the length of the grain boundaries of flat grains where the average thickness is 0.5 to 5.0 µm, the aspect ratio is 1.5 or more, and the orientation difference from Goss orientation is 10° or more in the length (1000 µm) of the interface between the silicon steel sheet and the oxide layer is measured. The identification and the like of insulating coating layer, the oxide layer, the interface of the silicon steel sheet, and the flat grains can be performed in the same manner as described above.

[0059] During the measurement, in a measurement range B, the length of a portion where the oxide layer is formed on the surface of the silicon steel sheet is set as B' (when the oxide layer is formed on the entire area of the measurement range, B = B'). In this case, lengths of portions where flat grains are formed on the outermost layer of the silicon steel sheet and an interface between the silicon steel sheet and the oxide layer is a grain boundary between the flat grains are set as b1, b2,..., bi (in the drawing, i = 3), and the sum (Σbi) of the lengths b1 to bi is divided by B' (Σbi / B') that is the length of the portion where the oxide layer is formed on the surface of the silicon steel sheet to measure the proportion of the length of the grain boundaries of the flat grains in the length of the interface between the base steel sheet and the oxide layer.(Groove)

[0060] By periodically forming a linear groove in a direction intersecting the rolling direction, a magnetic domain control can be performed. In the grain-oriented electrical steel sheet according to the present embodiment, in order to obtain this effect, it is preferable that a groove G is formed on the surface of the base steel sheet 11 as illustrated in FIG. 2. Specifically, it is preferable that a plurality of grooves G having a depth (sheet thickness direction) of 10 to 30 µm and extending in a direction of 80 to 100° with respect to the rolling direction are present in the silicon steel sheet (base steel sheet) 11, and an interval between the grooves G adjacent to each other in the rolling direction is 1.0 to 20.0 mm. The interval between the grooves G adjacent to each other in the rolling direction is more preferably 2.0 to 10.0 mm.

[0061] When the size or the interval of the grooves is not in the above-described range, the sufficient effect cannot be obtained. The interval of the grooves refers to the distance from the center of the width of one groove to the center of the width of another groove adjacent thereto.

[0062] The shape of the groove is not particularly limited. For example, the cross section is a substantially rectangular shape or a substantially triangular shape. In addition, the cross section may be an arch shape or the like forming a part of a circle. The width of the groove is preferably about 0.5 times to 3.0 times the depth of the groove. When the width of the groove is less than 0.5 times the depth of the groove, the sufficient magnetic domain control effect cannot be obtained, and it is difficult to form the groove itself. On the other hand, when the width of the groove is more than 3.0 times the depth of the groove, the occupancy of the grooves of the sheet surface increases, and thus the magnetic flux density decreases. In contrast, since the magnetic domain control effect is saturated, the iron loss reduction effect cannot be obtained, which rather causes an increase in iron loss.

[0063] The anomalous eddy-current loss reduction effect by the above-described flat grains is also effective for a magnetic domain control material by the groove formation.

[0064] That is, when an inner surface (bottom surface, side surface) of the groove is the surface of the base steel sheet, as illustrated in FIG. 2, it is more preferable that, on a surface side of the groove of the base steel sheet, flat grains (in-groove flat grains) G102 where an average diameter in a direction perpendicular to the surface is 0.5 to 5.0 µm, an aspect ratio that is a ratio of a grain width in a direction parallel to the surface to the average diameter is 2.0 or more, and a deviation of a crystal orientation from Goss orientation is 10° or more are present (the in-groove flat grains G102 are present as grains forming the outermost layer of the groove of the silicon steel sheet), and that the length of grain boundaries of the in-groove flat grains G102 accounts for 70% or more of the length of the inner surface of the groove G in a cross section in the sheet thickness direction perpendicular to an extending direction because not only the magnetic domain refinement effect by the groove formation but also the eddy-current loss reduction effect by the in-groove flat grains G102 can be obtained.

[0065] The average of the average diameters of the in-groove flat grains G102 is more preferably more than 2.0 µm and 5.0 µm or less.

[0066] Whether or not the in-groove flat grains are present and the average diameter, the aspect ratio, and the deviation of the crystal orientation from Goss orientation thereof can be obtained in the same manner as that of the above-described flat grains of the surface of the base steel sheet.

[0067] Note that, when the groove provided on the surface of the steel sheet is, for example, curved instead of being linear, a cross section perpendicular to a tangent of the curve in an observation target portion appears. In this case, a deviation angle of the cross section from the rolling direction (RD direction) is measured and corrected when the crystal orientation of the flat grains is measured.

[0068] In addition, the proportion of the length of the grain boundaries of the in-groove flat grains in the length of the inner surface of the groove can be measured by performing the EBSD measurement of the cross section in the sheet thickness direction perpendicular to the extending direction of the groove in the same manner as that of the measurement of the flat grain on the surface side of the silicon steel sheet.(Chemical composition)

[0069] The chemical composition of the silicon steel sheet is not limited and may be the same as that of a base steel sheet of a well-known grain-oriented electrical steel sheet. For example, the chemical composition may be in the following ranges.

[0070] The chemical composition of the silicon steel sheet contains Si: 2.00 to 6.00% by mass%. The reason for this is to control the Goss texture where the crystal orientation is integrated in the {110}<001> orientation and to ensure favorable magnetic characteristics.

[0071] The other elements are not particularly limited, and the chemical composition is allowed to contain a well-known element in a well-known range instead of Fe. In addition, the remainder consists of Fe and impurities.

[0072] Representative content ranges (mass%) of representative elements other than Si are as follows. C: 0 to 0.0050%, Mn: 0 to 1.0%, S: 0 to 0.0150%, Se: 0 to 0.0150%, Al: 0 to 0.0650%, N: 0 to 0.0050%, Cu: 0 to 0.40%, Bi: 0 to 0.010%, B: 0 to 0.080%, P: 0 to 0.50%, Ti: 0 to 0.0150%, Sn: 0 to 0.10%, Sb: 0 to 0.10%, Cr: 0 to 0.30%, Ni: 0 to 1.0%, Nb: 0 to 0.030%, V: 0 to 0.030%, Mo: 0 to 0.030%, Ta: 0 to 0.030%, and W: 0 to 0.030%.

[0073] Since these optional elements may be contained depending on the object, it is not necessary to limit the lower limit, and these optional elements may not be substantially contained. In addition, even if these optional elements are contained as the impurity, the effects of the present invention are not impaired. Here, the impurity refers to an element that is unintentionally contained, and means an element that is mixed from ore as a raw material, scrap, a manufacturing environment, or the like when the base steel sheet is industrially manufactured.

[0074] The chemical composition of the silicon steel sheet is obtained using the following method.

[0075] The silicon steel sheet is decomposed by an acid such as hydrochloric acid to obtain a solution. Each of element solutions having a known concentration is analyzed by ICP (inductively coupled plasma) analysis to obtain a calibration curve. By analyzing the obtained solution, the content of the element can be determined and obtained.

[0076] When the oxide layer and / or the insulating coating layer is formed on the surface of the silicon steel sheet (when the grain-oriented electrical steel sheet includes the silicon steel sheet, the oxide layer, and the insulating coating layer), the measurement can be performed after removing the oxide layer and the insulating coating layer.

[0077] Specifically, when the insulating coating layer is formed, the insulating coating layer is removed by immersing the grain-oriented electrical steel sheet including the insulating coating layer in a sodium hydroxide aqueous solution containing NaOH: 30 to 50 mass% and H 2 O: 50 to 70 mass% at 80 to 90°C for 7 to 10 minutes. The grain-oriented electrical steel sheet from which the insulating coating layer has been removed is cleaned with water, and after water cleaning, dried with a warm air blower for slightly less than 1 minute.

[0078] When the oxide layer is formed, the oxide layer is removed by immersing the grain-oriented electrical steel sheet including the oxide layer in a hydrochloric acid aqueous solution containing 10 mass% of HCl at 80 to 90°C for 1 to 10 minutes. The immersed base steel sheet is cleaned with water, and after water cleaning, dried with a warm air blower for slightly less than 1 minute.

[0079] Through the above-described steps, the silicon steel sheet that is the base steel sheet can be extracted from the grain-oriented electrical steel sheet where the oxide layer and / or the insulating coating layer is formed.(Sheet thickness)

[0080] The sheet thickness of the silicon steel sheet of the grain-oriented electrical steel sheet according to the present embodiment is not limited and is preferably 0.15 to 0.35 mm. When the sheet thickness is more than 0.35 mm, the above-described classical eddy current loss increases due to the large sheet thickness, and iron loss increases. On the other hand, when the sheet thickness is less than 0.15 mm, the rolling efficiency decreases, which is disadvantageous in productivity and costs.[Oxide layer]

[0081] In the grain-oriented electrical steel sheet according to the present embodiment, the oxide layer formed of the oxide of one or more kinds of Mg, Al, and Si is formed on the surface of the base steel sheet.

[0082] The oxide layer is formed by a solid phase reaction of Mg and / or Al in the annealing separator and the Si-based pre-oxide formed on the sheet surface during finish annealing. For example, when the annealing separator containing MgO is used, a forsterite (Mg 2 SiO 4 ) coating layer is mainly formed as the oxide layer. In addition, AlN contained as the inhibitor in the steel is oxidized by oxygen in the annealing atmosphere on the surface of the silicon steel sheet in the latter half of finish annealing. Accordingly, spinel (MgAl 2 O 4 ), alumina (Al 2 O 3 ), or mullite (2SiO 2 ·3Al 2 O 3 ) is formed on the surface of the silicon steel sheet. Note that, when the annealing separator containing MgO as a major component is used, the oxide is formed as substantially spinel (MgAl 2 O 4 ).

[0083] By covering the surfaces of the flat grains with the oxide layer, an effect of improving the adhesion with the insulating coating layer formed as an upper layer of the oxide layer can be obtained. When the sufficient effect is obtained, the coverage of the oxide layer on the flat grains is preferably 50% or more.

[0084] The coverage can be obtained using the following method.

[0085] That is, the presence of the flat grains is identified by EBSD in the above-described manner. In addition, an FE-SEM image of each of the flat grains or an element analysis image obtained by performing elemental analysis on the FE-SEM image by EDS or the like is focused on. In a projection portion of the flat grains between the insulating coating layer and the flat grains or in a direction from the surface side of the flat grains to the inside of the steel sheet, the length of a portion where the oxide layer of one or more kinds of Mg, Al, and Si is present is measured. In the portion corresponding to an interface length of 1000 µm between the oxide layer or the insulating coating layer and the flat grains, the ratio of the length of the portion where the oxide layer is present is obtained as a percentage.

[0086] For example, in the state illustrated in FIG. 4, the coverage (%) can be obtained from (A1 + A2 + A3) / (a1 + a2 + a3) × 100.[Insulating coating layer]

[0087] In the grain-oriented electrical steel sheet according to the present embodiment, the insulating coating layer is formed (as the upper layer) on the surface of the oxide layer. This insulating coating layer is essential when the grain-oriented electrical steel sheet is used as a transformer. For use as a transformer, the grain-oriented electrical steel sheets are laminated and used. When a short-circuit occurs between the laminated steel sheets (silicon steel sheets), an eddy current is generated in a transformer core, which causes an increase in core iron loss. Therefore, by forming the insulating coating layer on the sheet surface to impart electrical insulation properties, the core iron loss of the transformer is reduced. In addition, by applying tension to the steel sheet in the insulating coating of the grain-oriented electrical steel sheet, the magnetic domain width can be reduced, and a reduction in anomalous eddy current loss and a reduction in iron loss can be achieved.

[0088] In addition, the insulating coating of the grain-oriented electrical steel sheet is required to have not only the above-described electrical insulation properties but also various properties such as corrosion resistance, heat resistance, and slippage necessary for forming a core. In consideration of these needs, as the insulating coating, for example, a coating species containing a phosphate and colloidal silica as a major component is used. In addition, in order to apply a higher tension to the steel sheet, a coating containing aluminum borate as a major component or a coating formed of aluminum borate and silica may also be used. Any of the coatings may be a well-known coating that is formed by applying a coating solution where the components in the coating are dissolved or dispersed to the surface of the oxide layer and baking the coating film.<Manufacturing Method>

[0089] The effect of the grain-oriented electrical steel sheet according to the present embodiment can be obtained regardless of the manufacturing method as long as the grain-oriented electrical steel sheet has the above-described characteristics, but a manufacturing method including the following step is preferable because such a manufacturing method enables stable manufacture.

[0090] The manufacturing method includes: (I) a hot rolling step of heating and hot rolling a slab to obtain a hot rolled sheet; (II) a hot rolled sheet annealing step of annealing the hot rolled sheet after the hot rolling step; (III) a pickling step of pickling the hot rolled sheet after the hot rolled sheet annealing step; (IV) a cold rolling step of cold rolling the hot rolled sheet after the pickling step to obtain a cold rolled sheet; (V) a grinding step of grinding a surface of the cold rolled sheet after the cold rolling step; (VI) a contact step of bringing the cold rolled sheet after the grinding step into contact with an aqueous solution of pH 4.0 to 10.0; (VII) a decarburization annealing step of performing decarburization annealing on the cold rolled sheet after the contact step; (VIII) a finish annealing step of applying an annealing separator to the cold rolled sheet after the decarburization annealing step and performing finish annealing to form an oxide layer formed of one or more kinds of Mg, Al, and Si on a surface of the cold rolled sheet that is a base steel sheet; and (IX) an insulating coating forming step of forming an insulating coating layer on a surface of the oxide layer after the finish annealing step.

[0091] In addition, the manufacturing method for a grain-oriented electrical steel sheet according to the present embodiment may further include one or more of the following steps.

[0092] The manufacturing method may further include, before the grinding step, (X) a groove forming step of forming a plurality of grooves having a depth of 10 to 30 µm and extending in a direction having an angle of 80 to 100° with respect to a rolling direction on the cold rolled sheet such that each of intervals in the rolling direction is 1.0 to 20.0 mm; and (XI) a nitriding treatment step of increasing the nitrogen content in the cold rolled sheet.

[0093] The manufacturing method for a grain-oriented electrical steel sheet according to the present embodiment is characterized in the grinding step, the contact step, and the groove forming step among the above-described steps. On the other hand, the hot rolling step, the hot rolled sheet annealing step, the cold rolling step, the decarburization annealing step, the nitriding treatment step, the finish annealing step, and the insulating coating forming step can be performed under well-known conditions.

[0094] Hereinafter, preferable conditions will be described. Known conditions can be applied to conditions that are not described.[Hot rolling step]

[0095] In the hot rolling step, a slab having a predetermined chemical composition (the chemical composition corresponding to the chemical composition of the silicon steel sheet of the grain-oriented electrical steel sheet according to the present embodiment) is heated and hot-rolled to obtain a hot rolled sheet.

[0096] The slab heating temperature is, for example, 1000 to 1400°C.

[0097] The chemical composition of the slab subjected to hot rolling may be determined depending on the desired chemical composition to be obtained as the grain-oriented electrical steel sheet in consideration of a change in chemical composition in each of the steps.

[0098] When the preferable chemical composition of the silicon steel sheet of the grain-oriented electrical steel sheet according to the present embodiment is obtained, for example, the chemical composition contains C: 0.040 to 0.100% and Si: 2.00 to 6.00% in the hot rolling stage by mass%, contains Al, Mn, Se, S, B, N, and the like in the predetermined ranges such that AlN, MnS, MnSe, and BN are formed as the inhibitors, and optionally contains elements such as Cu, Sn, Cr, Ni, Mo, Nb, Bi, Sb, P, Ti, V, Ta, and W.

[0099] A method for obtaining the slab is not limited. For example, molten steel having a predetermined chemical composition may be prepared to manufacture the steel using this molten steel. For example, the slab may be manufactured by a continuous casting method. Alternatively, optionally, an ingot is manufactured using molten steel, and then the ingot is subjected to blooming and rolling to manufacture the slab. The slab may be manufactured by other methods.

[0100] The thickness of the slab is not particularly limited and is, for example, 150 to 350 mm. The thickness of the slab is preferably 220 to 280 mm. As the slab, a so-called thin slab with a thickness of 10 to 70 mm may be used.

[0101] A so-called hot rolled sheet (hot-rolled steel sheet) can be obtained by hot rolling. The sheet thickness (finished sheet thickness) of the hot rolled sheet is not particularly limited. Note that the hot rolled sheet is subjected to hot rolled sheet annealing and cold rolling after pickling. It is known that a so-called cold rolling ratio affects the magnetic characteristics of the grain-oriented electrical steel sheet, and the sheet thickness of the hot rolled sheet is selected also in consideration of a cold rolling ratio necessary for the final sheet thickness. For example, when the final sheet thickness is 0.20 to 0.30 mm, the finished sheet thickness of the hot rolled sheet is preferably in a range of 2.0 to 4.0 mm.[Hot rolled sheet annealing step]

[0102] In the hot rolled sheet annealing step, the above-described hot rolled sheet after the hot rolling step is annealed. By performing such an annealing treatment, recrystallization occurs in the microstructure, and favorable magnetic characteristics can be realized.

[0103] In the hot rolled sheet annealing step of the present embodiment, the hot rolled sheet manufactured through the hot rolling step may be annealed according to a known method. A means of heating the hot rolled sheet at the time of annealing is not particularly limited, and a known heating method can be adopted. For example, so-called continuous annealing may be performed, or the hot rolled sheet may be formed in a coil shape to perform batch annealing. The annealing conditions are also not particularly limited, but for example, the hot rolled sheet can be annealed in a temperature range of 900 to 1200°C for 10 seconds to 5 minutes. In addition, the atmosphere is not particularly limited. However, it is preferable that the oxidation of the steel sheet is suppressed, and it is preferable that the annealing is performed in a non-oxidizing atmosphere such as nitrogen, argon, or hydrogen.[Pickling step]

[0104] In the pickling step, scale (oxide) produced on the sheet surface in hot rolling and hot rolled sheet annealing is removed. In the pickling step according to the present embodiment, a well-known method is used. As a pickling solution, a well-known acid such as hydrochloric acid, sulfuric acid, or nitric acid is used. In addition, optionally, a well-known pickling inhibitor, a pickling accelerator, or the like may be added to the pickling solution. Further, the pickling solution may be caused to permeate into an interface between the scale and the steel sheet before bringing the steel sheet into contact with the pickling solution such that a physical treatment such as shot blasting can also be performed on the steel sheet before pickling in order to improve the pickling efficiency.[Cold rolling step]

[0105] In the cold rolling step, the pickled steel sheet is cold rolled to obtain a cold rolled sheet. The cold rolling may be one time of cold rolling (a series of cold rolling without intermediate annealing). Before a final pass of the cold rolling step, cold rolling may be interrupted, at least one or more times of intermediate annealing may be performed, and a plurality of times of cold rolling may be performed with intermediate annealing interposed therebetween.

[0106] Conditions of the cold rolling may be determined with reference to a well-known method. The cold rolling ratio in the grain-oriented electrical steel sheet largely affects magnetic characteristics thereof. In particular, the effect of the final rolling reduction is large, and the final rolling reduction can be set to be 80 to 95%. The final rolling reduction is a cumulative rolling reduction of cold rolling, and when intermediate annealing is performed, the final rolling reduction is a cumulative rolling reduction of cold rolling after the final intermediate annealing.

[0107] When the intermediate annealing is performed, it is preferable to hold the intermediate annealing at a temperature of, for example, 800 to 1200°C for 5 to 180 seconds. The annealing atmosphere is not particularly limited, and it is preferable that the annealing is performed in a non-oxidizing atmosphere such as nitrogen, argon, or hydrogen in order to prevent the oxidation of the steel sheet. In addition, as the annealing method, any of continuous annealing or batch annealing in a coil shape may be used, or another method may be used. The number of times of intermediate annealing is preferably three or less in consideration of manufacturing cost.[Groove forming step]

[0108] In the groove forming step, grooves having a depth of 10 to 30 µm and extending in a direction having an angle of 80 to 100° with respect to a rolling direction are formed on the cold rolled sheet before the grinding step. A plurality of the grooves are formed such that each of intervals in the rolling direction is 1.0 to 20.0 mm. The interval in the rolling direction is more preferably 2.0 to 10.0 mm.

[0109] By forming the above-described grooves on the surface of the cold rolled sheet (base steel sheet), magnetic domains are refined due to the effect of the grooves when Goss orientation is recrystallized, and magnetic characteristics are improved. Specifically, the anomalous eddy current loss is reduced, and iron loss is reduced. When the direction, the interval, the shape, and the like of the grooves are outside the above-described ranges, the sufficient effect cannot be obtained.

[0110] The groove forming method is not particularly limited, and the following well-known methods can be used. Examples of the groove forming method include a method using a physical contact (for example, a method of scraping the sheet surface with a blade or the like, a method of performing roll transfer or press using a die with a blade), a method not using a physical contact (for example, a method of locally melting a part of the sheet surface with a laser or electron beam, a plasma, or the like and removing the molten material to the outside of the system), and a chemical method (a method of masking the sheet surface with a resin or the like, removing a part of the mask according to the groove shape to be formed, and bringing the mask-removed portion into contact with an acid or the like and erodes the steel sheet by etching to form the grooves).

[0111] Among these, the method not using a physical contact is superior to the method using a physical contact and the chemical method from the following viewpoint.

[0112] In the method using a physical contact, a blade or a die is brought into contact with the steel sheet. Therefore, strain is applied to the steel sheet, which causes deterioration in magnetic characteristics. In addition, in order to impart the grooves to the steel plate coil having a size of several thousands of m for introducing the grooves into the steel sheet at a pitch of 1.0 to 20.0 mm in the rolling direction, abrasion of the blade or the die becomes significant. Therefore, frequent replacement is necessary, which is a disadvantage of poor productivity.

[0113] In addition, regarding the chemical method, it is necessary to perform the multiple steps of masking the sheet surface with a resin, removing a part of the mask, and performing etching, which is a problem mainly in productivity. Further, a strongly acidic solution of about pH 1 such as hydrochloric acid is likely to be used for the etching, and the cost required for removing Fe dissolved in the strongly acidic solution or for treating a waste solution of the strongly acidic solution is also high.

[0114] The method not using a physical contact is a method of forming the grooves by irradiating the surface of the cold rolled sheet with a laser beam to melt a part of the sheet surface and removing the molten material from the surface. This method is highly advantageous in that, by using a high energy source having high straightness such as a laser, a high-level control of an irradiation position of the sheet surface can be performed such that the groove can be accurately formed at a predetermined point. In addition, the molten material produced from the steel sheet during the irradiation can be removed to the outside of the system by providing a suction duct in a laser irradiation unit, which does not affect the laser irradiation control. In addition, it is desirable that the molten material is removed without being attached to the sheet surface. Even if the molten material is attached to the sheet surface, the molten material can be removed from the sheet surface in the grinding step before the decarburization annealing step, and the sheet surface can be clearly maintained.

[0115] During the laser irradiation, a high-output laser that is generally industrially used, for example, a fiber laser, an YAG laser, a semiconductor laser, or a CO 2 laser can be used. In addition, the output type may be a pulsed laser or a continuous wave laser. In order to form the groove having a predetermined shape, it is preferable that the laser output is 200 to 3000 W, the focused spot diameter (diameter including 86% of the laser output) of the laser beam in the rolling direction is 10 to 1000 µm, the focused spot diameter of the laser beam in the sheet width direction is 10 to 1000 µm, and the laser scanning speed is in a range of 5 to 100 m / s. In addition, examples of the method of removing the molten material from the surface include spraying of assist gas. For example, by spraying air, CO 2 , argon, or the like to the irradiation portion while performing the laser irradiation, and providing a suction unit in the vicinity, the reattachment of the molten material to the sheet surface can be reduced.

[0116] The groove forming step is not necessary and can be skipped.[Grinding step]

[0117] In the grinding step, the surface of the cold rolled sheet after the cold rolling step (when the groove forming step is performed, the cold rolled sheet after the groove forming step) is ground. At this time, using abrasive grains having a Knoop hardness of 1000 or more and a maximum grain size of more than 50 µm and 500 µm or less or using abrasive paper, a roll, or a brush to which the abrasive grains are fixed, the surface of the cold rolled sheet is ground. When the coil-shaped cold rolled sheet is ground, it is preferable that the grinding is continuously performed using a pass line from the viewpoints of productivity and quality. In this case, a brush into which the abrasive grains are fixed is generally used. Of course, a sheet-shaped cold rolled sheet can be used instead of the coil. In this case, the grinding can also be performed using abrasive paper or the like.

[0118] As described above, by allowing the inhibitors (precipitates such as AlN present in the grain boundary) to be present at as a high temperature as possible during finish annealing, only grains having a crystal orientation closer to ideal Goss orientation are allowed to grow, and the magnetic flux density is improved.

[0119] However, the sizes of the inhibitors are extremely small at several tens of nm to several hundreds of nm and have a distribution. When the sizes have a distribution, the inhibitor having a small size starts to be decomposed at a low temperature. In this case, secondary recrystallization of only grains having a crystal orientation closer to Goss orientation (ideal Goss orientation) is difficult, and it is difficult to improve the magnetic flux density. On the other hand, it is industrially very difficult to control the sizes of the inhibitors to be fixed to a preferable size (such that a different between the sizes is reduced).

[0120] On the other hand, as long as the inhibitors can be allowed to be present at a high temperature by suppressing the decomposition and oxidation of the inhibitors, secondary recrystallization of only grains having a crystal orientation closer to ideal Goss orientation can be caused to occur. In addition, it is known that the above-described Si-based pre-oxide formed on the base steel sheet (the cold rolled sheet for forming the base steel sheet) in the decarburization annealing step contributes to the suppression of the decomposition and oxidation of the inhibitors.

[0121] However, the Si-based pre-oxide is likely to affect the previous step of the decarburization annealing step, and the formation state in each of parts of the surface of the sheet surface is likely to be non-uniform. When the formation state is non-uniform, the effect of suppressing the decomposition and oxidation of the inhibitors varies depending on locations in the steel sheet surface, and the desired effect cannot be obtained.

[0122] Therefore, in the manufacturing method for a grain-oriented electrical steel sheet according to the present embodiment, the formation state of the oxide layer after finish annealing is as uniform as possible in a region of a predetermined thickness from the surface of the steel sheet. Therefore, an Fe-based oxide or a reactant of an oil-based agent, an extreme pressure additive, or the like and the sheet surface, which are non-uniformly formed on the sheet surface by performing cold rolling or the like, is removed from the sheet surface before decarburization annealing by grinding the sheet surface.

[0123] Specifically, using abrasive grains having a Knoop hardness of 1000 or more and a maximum grain size of more than 50 µm and 500 µm or less or using abrasive paper, a roll, or a brush to which the abrasive grains are fixed, at least one surface of the steel sheet is ground to remove the Fe-based oxide film or the reactant from the sheet surface.

[0124] When the Knoop hardness is less than 1000, the hardness of the abrasive grains is insufficient for the steel sheet, and thus it is difficult to perform the grinding. In addition, the grinding efficiency decreases. In addition, when the maximum grain size of the abrasive grains is 50 µm or less, the grain size of the abrasive grains is small relative to the roughness of the sheet surface, and thus it is difficult to perform the grinding. In addition, the grinding efficiency decreases. On the other hand, when the maximum grain size is more than 500 µm, the grain size of the abrasive grains is excessively large relative to the roughness of the sheet surface. Therefore, surface scratches are likely to be conspicuous during grinding, and the quality of the external appearance of the product decreases. The upper limit of the Knoop hardness is not limited. However, hard abrasive grains are likely to be brittle, and a problem such as grinding failure is likely to occur when abrasive paper, a roll, or a brush including the abrasive grains is continuously used. Therefore, the upper limit of the Knoop hardness is preferably 8000 or less and more preferably 5000 or less. As the abrasive grains, alumina (Knoop hardness: about 2000), silicon carbide (Knoop hardness: about 2500), boron nitride (Knoop hardness: about 5000), diamond (Knoop hardness: about 7000), or the like is mainly used.

[0125] Specifically, the step of grinding the cold rolled sheet will be described by using an example where a brush roll containing the abrasive grains is used. In the brush roll, resin lining is performed on a surface of a metal roll to embed the above-described abrasive grains in fibers formed of an acrylic resin or the like, and the abrasive grains are embedded in a capillary shape in the resin layer surface of the roll surface. An example of application to a continuous pass line will be described. When the steel sheet is ground using the brush roll, the passing speed of the steel sheet is in a range of about 20 to 200 mpm (meter per minute), and at a position where the steel sheet and the brush roll are brought into contact with each other while moving the steel sheet, the brush roll that rotates in a direction facing a steel sheet passing direction is brought into contact with the steel sheet to grind the steel sheet. When the steel sheet is ground using the brush roll, the steel sheet is interposed between the brush roll and an idle roll, and the brush roll is rolled and pressed against the idle roll side for grinding the steel sheet in the pass line. At this time, the rolling reduction is 1.0 to 5.0 mm. When the rolling reduction is small, the amount of abrasion is small. On the other hand, when the rolling reduction increases to increase the amount of abrasion, the brush roll and the passing direction of the steel sheet face each other. Therefore, so-called "chattering" is likely to occur, in which the steel sheet cannot pass smoothly due to a frictional force between the steel sheet and the brush roll such that inching occurs. "Chattering" is not preferable because it causes the grinding of the sheet surface to be non-uniform, and thus this phenomenon should be avoided. Typically, a brush roll having a diameter of about 200 to 500 mm is used. The reason for this is as follows. When the diameter of the brush roll is excessively small, the abrasion of the brush or the abrasive grains is accelerated. When the diameter of the brush roll is excessively large, the metal roll excessively becomes large, and a large-scale facility is required. The brush grinds the steel sheet while rotating in the direction facing the passing direction of the steel sheet as described above. The passing speed of the steel sheet is in a range of 20 to 200 mpm as described above. In this case, the grinding speed (corresponding to the rotation speed in the case of the brush roll) is 500 mpm or more. When the grinding speed (corresponding to the rotation speed in the case of the brush roll) is small, the amount of abrasion is insufficient, and the Si-based pre-oxide cannot be sufficiently formed. Therefore, the formation of the flat grains is insufficient.

[0126] On the other hand, in the case of the brush roll, when the rotation speed is more than 2000 mpm, the frictional force between the brush roll and the steel sheet excessively increases. Therefore, the above-described "chattering" occurs, and also an overload is generated from a motor that drives the brush roll. Thus, the rotation speed of the brush roll is preferably 2000 mpm or less.

[0127] In addition, in order to sufficiently remove the Fe-based oxide film or the reactant that are non-uniformly formed on the surface of the cold rolled sheet, the amount of abrasion on at least one surface is 0.10 g / m 2< or more. On the other hand, when the amount of abrasion is more than 10.0 g / m 2< , the Fe-based oxide film or the reactant is sufficiently removed from the sheet surface, but the lifetime of the abrasive grains decreases or the occurrence of sludge becomes significant along with grinding. For this treatment, time and labor is required, which causes defects of the sheet surface due to pressing or the like. Therefore, the amount of abrasion is 10.0 g / m 2< or less.

[0128] The amount of abrasion can be verified from a difference in the weight of the steel sheet before and after grinding. The amount of abrasion is the amount of abrasion of one surface. When grinding is performed on both surfaces, the amount of abrasion of both surfaces is obtained, and the numerical value thereof is halved for convenience of description. From the viewpoint of removing the Fe-based oxide film or the reactant from all of the surfaces of the steel sheet, the amount of abrasion is preferably in a range of 0.30 g / m 2< or more and 3.0 g / m 2< or less.

[0129] When the groove formation is performed on the cold rolled sheet before the grinding step as described below, the depth of the groove is preferably 10 to 30 µm, and the sheet surface in the groove is ground. Therefore, the effect by grinding is also effective for the groove inner surface formed on the cold rolled sheet surface. Therefore, the flat grains (in-groove flat grains) are also formed on the inner surface side of the groove of the base steel sheet having undergone decarburization annealing and finish annealing.[Contact step]

[0130] In the contact step, the surface of the cold rolled sheet is brought into contact with an aqueous solution of pH 4.0 to 10.0 after the grinding step and before the decarburization annealing step. As a result, the abrasive grains attached to the sheet surface during grinding or steel sludge produced during grinding is removed. The aqueous solution may be ion exchange water or may contain a mineral such as Ca or Mg or may contain carbonic acid or silicic acid as a counter ion. In addition, about 0.01 wt% of an acid selected from sulfuric acid, nitric acid, phosphoric acid, carbonic acid, carboxylic acid, phosphonic acid, and the like may be added, and the pH may be adjusted with alkali metal, alkali earth metal, or the like to use the aqueous solution. In particular, carboxylic acid or phosphonic acid is highly effective for removing the abrasive grains or the sludge from the steel sheet. In the case of ion exchange water, from the viewpoint of preventing erosion, the electrical conductivity is preferably 0.1 to 10 µS / cm.

[0131] When the pH is less than 4.0, erosion of the steel sheet occurs due to etching of the sheet surface by an acidic aqueous solution. When the pH is more than 10.0, the oxidation of the ground metal surface is accelerated due to the action of an alkaline aqueous solution. Therefore, the effect decreases although the Fe-based oxide that is non-uniformly formed on the sheet surface is removed in the grinding step. In this case, the initial desired effect that is the uniform formation of the oxide layer and the oxide grains after finish annealing cannot be sufficiently obtained.

[0132] In order to achieve the above-described object, the contact time is preferably 0.1 to 60 seconds, more preferably 1 to 60 seconds, and still more preferably 5 to 60 seconds. The flow rate of the aqueous solution is preferably 1 to 100 L / min.

[0133] In addition, by performing the contact step, the abrasive grains or the sludge can be removed from the sheet surface, and factors of inhibiting the uniform formation of the oxide layer and the oxide grains after finish annealing can be avoided.

[0134] Even in the grinding step, the surface of the cold rolled sheet may be brought into contact with the aqueous solution. However, unless the contact step is performed after the grinding step, the above-described effect cannot be obtained.[Decarburization annealing step]

[0135] In the decarburization annealing step, decarburization annealing is performed on the cold rolled sheet after the grinding step. In the decarburization annealing, C that adversely affects magnetic characteristics is removed (decarburized) from the steel sheet, and the cold rolled sheet is primarily recrystallized.

[0136] Decarburization annealing conditions are not limited. Annealing is performed in a nitrogen / hydrogen mixed atmosphere for decarburization where oxygen potential is increased by humidification. In addition, it is necessary to form a primary recrystallized structure accordingly. Therefore, a humidification temperature (dew point) is determined from the viewpoint of an annealing temperature necessary for recrystallization and the oxygen potential where decarburization can be performed.

[0137] The annealing temperature is about 700 to 900°C, and soaking is performed for about 60 seconds because annealing is performed in a general continuous annealing step. As described above, annealing is performed in the humidified atmosphere where the oxygen potential is high for decarburization. Therefore, it is known that Si in the steel is formed as a layered oxide on the sheet surface and as oxide grains in the steel sheet (hereinafter, referred to as the Si-based pre-oxide as described above).[Nitriding treatment step]

[0138] In the nitriding treatment step, by increasing the nitrogen content in the steel sheet to increase the amount of a nitride, secondary recrystallization of grains having a crystal orientation closer to Goss orientation can be accelerated in the finish annealing step. In the nitriding treatment step, the nitrogen content in the steel sheet after the nitriding treatment is preferably 0.015 to 0.050 mass%. The nitriding treatment method is not limited, and a well-known method may be used.

[0139] The nitriding treatment step is not essential and may be skipped. It is preferable that the nitriding treatment is performed between the decarburization annealing step and the finish annealing step.[Finish annealing step]

[0140] In the finish annealing step, the annealing separator is applied to the cold rolled sheet after the decarburization annealing step (when the nitriding treatment is performed, after the nitriding treatment step), and finish annealing is performed to form an oxide layer formed of an oxide of one or more kinds of Mg, Al, and Si on the surface of the cold rolled sheet for forming the base steel sheet (silicon steel sheet).

[0141] In the finish annealing, since the annealing time is long, typically, the steel sheet is coiled in a coil shape and batch annealing is performed. Since the steel sheet temperature increases up to about 1200°C, the annealing separator is applied to the coil-shaped steel sheet such that bake hardening does not occur in the steel sheet. As the annealing separator, in general, MgO is mainly used. By performing finish annealing after applying the annealing separator, a solid phase reaction occurs between Mg in the annealing separator and the Si-based pre-oxide formed on the sheet surface in the decarburization annealing step, and thus an oxide layer formed of an oxide of one or more kinds of Mg and Si is formed on the surface of the cold rolled sheet. For example, when the annealing separator containing MgO is used, a forsterite (Mg 2 SiO 4 ) coating layer is mainly formed as the oxide layer. In addition, AlN contained as the inhibitor in the steel is oxidized by oxygen in the annealing atmosphere on the sheet surface in the latter half of finish annealing. At this time, the oxide is formed as spinel (MgAl 2 O 4 ), alumina (Al 2 O 3 ), or mullite (2SiO 2 ·3Al 2 O 3 ). When the annealing separator formed of only MgO is used, the oxide is formed as substantially spinel (MgAl 2 O 4 ).

[0142] In addition, in the finish annealing step, by secondarily recrystallizing primary recrystallized grains obtained by heating the steel sheet in the decarburization annealing step, grains having a crystal orientation close to Goss orientation are obtained, and by holding the steel sheet at an annealing temperature close to 1200°C for a predetermined time, precipitates in the steel, for example, a nitride (example: AlN) or a sulfide (example: MnS) of which the function as the inhibitor ends are removed (purified) not to adversely affect magnetic characteristics.

[0143] In the manufacturing method for a grain-oriented electrical steel sheet according to the present embodiment, in the cold rolled sheet subjected to finish annealing, the sizes of the inhibitors are controlled to be larger than usual and to be uniform. Therefore, secondary recrystallization of only grains close to Goss orientation (grains having an orientation close to Goss orientation occurs).

[0144] Finish annealing conditions are not limited. For example, the temperature is increased from room temperature in a range of 10 to 100 °C / h and is increased in a temperature range of 900 to 1000°C where secondary recrystallization in Goss orientation generally occurs at 5 to 20 °C / h to accelerate preferential growth in Goss orientation (secondary recrystallization). Next, the inhibitors of which the function ends are purified at about 1200°C (for example, 1150 to 1250°C) as described above. Next, the steel sheet is allowed to cool in a non-oxidizing atmosphere such as hydrogen or nitrogen, and the coil is extracted from a furnace.[Insulating coating forming step]

[0145] In the insulating coating forming step, an insulating coating layer is formed on a surface of the oxide layer after the finish annealing step.

[0146] For example, the insulating coating layer can be formed by applying a coating solution containing phosphoric acid or a phosphate, colloidal silica, and chromic anhydride or a chromate to the cold rolled sheet after finish annealing (base steel sheet + oxide layer) and baking and drying the coating film at 300 to 950°C for 10 seconds or longer. In addition, the atmosphere during baking is not particularly limited. However, it is preferable that the oxidation of the steel sheet is suppressed, and it is preferable that the annealing is performed in a non-oxidizing atmosphere such as nitrogen, argon, or hydrogen. As the coating species, a coating solution containing boric acid and alumina sol as a major component instead of the above-described phosphate, or a coating solution containing boric acid and an aluminosilicate (for example, kaolin mineral) as a major component can be used to form an insulating coating containing aluminum borate as a major component. By applying aluminum borate, a higher tension can be applied to the steel sheet, and thus iron loss can be reduced.

[0147] In this step, a function of flattening, by continuous annealing, the steel sheet that is coiled in a coil shape by batch annealing in the above-described finish annealing is also exhibited. That is, by performing continuous annealing while baking the insulating coating and applying a fixed tension to the steel sheet having a coil shape at about 800°C, a flat steel sheet is obtained. Therefore, this step is also called the flattening annealing step.

[0148] Through these steps, the grain-oriented electrical steel sheet including the silicon steel sheet (base steel sheet), the oxide layer, and the insulating coating layer can be obtained.Examples(Example 1)

[0149] Molten steel containing Si: 3.25 mass%, Mn: 0.13 mass%, S: 0.006 mass%, C: 0.050 mass%, acid-soluble Al: 0.025 mass%, and N: 0.007 mass% was continuously cast to obtain a slab having a thickness of 300 mm.

[0150] This slab was heated in an electric furnace adjusted in a nitrogen atmosphere at 1150°C for 60 minutes, and rough hot rolling was performed to obtain a steel sheet having a sheet thickness of 40 mm. Further, finish rolling was performed to obtain a hot rolled sheet having a sheet thickness of 2.3 mm.

[0151] Next, hot rolled sheet annealing of performing cooling after heating at 1100°C for 60 seconds in a continuous annealing furnace adjusted to a nitrogen atmosphere was performed.

[0152] The obtained steel sheet (hot rolled sheet) was pickled with 10% hydrochloric acid to remove scale of the steel sheet.

[0153] Next, cold rolling is performed to obtain a cold rolled sheet having a sheet thickness of 0.22 mm.

[0154] The surface of the obtained cold rolled sheet was ground using a brush containing various abrasive grains described in Table 1 while causing ion exchange water of pH = 2.5 to 12.0 to flow. In addition, after completion of the grinding, the surface was brought into contact with ion exchange water of pH = 2.5 to 12.0. Note that, as shown in Table 1, for comparison, some steel sheets were not ground, and some steel sheets were not brought into contact with ion exchange water after being ground. During the contact, the contact time was 5 seconds, and the flow rate of the aqueous solution was 10 L / min.

[0155] Regarding the steel sheet that was ground and was brought into contact with the aqueous solution (when both of the grinding and the contact with the aqueous solution were not performed, the cold rolled sheet after the cold rolling; or when the contact with the aqueous solution was not performed, the cold rolled sheet after the grinding step), a 1000 mm × 1000 mm sample was collected and was observed by visual inspection to evaluate the external appearance.

[0156] The determination criteria were as follows. 5: Very beautiful 4: Beautiful 3: Partially containing streak scratches 2: Containing unevenness due to attachment 1: Containing streak scratches on the entire surface

[0157] When the evaluation of the external appearance was 1, a general demand for the external appearance was not able to be satisfied, and the subsequent evaluation was not performed.

[0158] In addition, regarding the steel sheet that was ground and was brought into contact with the aqueous solution (when both of the grinding and the contact with the aqueous solution were not performed, the cold rolled sheet after the cold rolling; or when the contact with the aqueous solution was not performed, the cold rolled sheet after the grinding step), decarburization annealing was performed. The annealing atmosphere was a nitrogen 50% + hydrogen 50% atmosphere, and the oxygen potential (P H2O / P H2 ) was 0.33. Regarding the oxygen potential, the atmosphere was humidified to adjust the water content before being introduced into the furnace. In this atmosphere, decarburization annealing was performed by performing soaking at 850°C for 60 seconds.

[0159] Next, soaking is performed in a nitrogen-hydrogen-ammonia atmosphere at 750°C for 30 seconds to perform a nitriding treatment. At this time, the ammonia concentration was adjusted such that the nitrogen content after the nitriding treatment was 0.020 mass%.

[0160] Next, a water slurry of an annealing separator containing MgO as a major component was adjusted, and the annealing separator was applied to both surfaces of the steel sheet such that the adhesion amount of one surface after drying was 6 g / m 2< , and was dried. At this time, regarding the composition of the annealing separator, the amount of TiO 2 was 5 parts by weight with respect to MgO: 100 parts by mass, and the amount of FeCl 2 was 0.020 mass% in terms of Cl.

[0161] Next, as finish annealing, the steel sheet was put into a batch annealing furnace, was heated in a nitrogen 50% + hydrogen 50% atmosphere at an average heating rate of 20 °C / h, and was heated up to 1200°C. Next, the atmosphere was replaced with hydrogen 100%, soaking was performed for 20 h, and the temperature was decreased up to room temperature.

[0162] After completion of the finish annealing, the steel sheet was extracted from the furnace, and the annealing separator was removed by water cleaning. At this time, on the surface of the steel sheet (silicon steel sheet), a glass coating formed of forsterite and an oxide layer formed of granular spinel (MgAl 2 O 4 ), alumina (Al 2 O 3 ), and / or mullite formed between the glass coating and the steel sheet were formed.

[0163] A chemical containing an insulating coating component formed of aluminum phosphate, colloidal silica, and chromic anhydride was applied to the steel sheet (the steel sheet where the glass coating as the oxide layer was formed on the surface of the silicon steel sheet as the base steel sheet), and the steel sheet was heated to 800°C in a nitrogen atmosphere and was held for 30 seconds to perform baking. As a result, an insulating coating layer was formed. The adhesion amount of the insulating coating layer of one surface was 4.8 g / m 2< .

[0164] In addition, in the obtained silicon steel sheet (including the silicon steel sheet, the glass coating (oxide layer), and the insulating coating layer), the oxide in a range of 10 µm in the sheet thickness direction from the interface with the oxide layer and the flat grains were evaluated using the above-described method. Table 2 shows the results.

[0165] In the present example, as shown in the table, the oxide of one or more kinds of Mg, Al, and Si having an equivalent circle diameter of 0.1 to 3.0 µm in a range of 10 µm in the sheet thickness direction from the interface with the oxide layer was spinel (MgAl 2 O 4 ), alumina (Al 2 O 3 ), or mullite (2SiO 2 ·3Al 2 O 3 ), that is, an oxide containing Mg, Al, and Si.

[0166] 36 samples having a size of 30 mm in the sheet width direction × 280 mm in the rolling direction were collected by shearing from the obtained grain-oriented electrical steel sheet (including the silicon steel sheet, the glass coating (oxide layer), and the insulating coating layer), and stress relief annealing of holding the sample in a nitrogen atmosphere at 800°C for 2 h was performed on these samples.

[0167] Next, using a magnetic characteristic measurement method defined in the Epstein method described in JIS-C-2550-1:2011, a magnetic flux density (hereinafter, B8) during excitation at a magnetizing force of 800 A / m and an iron loss (hereinafter, W17 / 50) during excitation at an excitation frequency of 50 Hz and a magnetic flux density of 1.7 T were measured.

[0168] When B8 was 1.90 T or more and W17 / 50 was 0.85 W / kg or less, it was determined that magnetic characteristics were excellent. Table 2 shows the results.

[0169] In addition, a sample having a size of 300 mm in the rolling direction × 300 mm in the width direction was collected from the obtained grain-oriented electrical steel sheet, this sample was coiled around a round bar of SUS304 having a diameter of 20 mm (φ20 mm) and was uncoiled. Next, the insulating coating of a recessed portion of the inside for coiling was observed and adhesion of the insulating coating was evaluated.

[0170] The determination criteria were as follows. G (GOOD): No coating peeling P (POOR): Partial coating peeling B (BAD): Coating peeling on the entire surface

[0171] Table 2 shows the results. [Table 1]No.Brush RollPassing Speed mpmGrindingContactAfter Grinding + ContactRoll Diameter mmAbrasive GrainsGround SurfaceRotation Speed mpmPressing mmAqueous SolutionAmount of Abrasion of One Surface g / m 2< Surface External AppearanceKindKnoop HardnessMaximum Grain Size µmSolventAdditivepH1--------No ContactNo ContactNo Contact--2300Alumina20006030Both Surfaces10001.5No ContactNo ContactNo Contact0.4023300Alumina20004030Both Surfaces10001.5Pure Water-6.00.0844300Alumina20006030Both Surfaces10001.5Pure Water-6.00.4045300Alumina200012530Both Surfaces10001.5Pure Water-6.01.046300Alumina200015030Both Surfaces10001.5Pure Water-6.01.447300Alumina200020030Both Surfaces10001.5Pure Water-6.02.248300Alumina200050030Both Surfaces10001.5Pure Water-6.03.149300Alumina200080030Both Surfaces10001.5Pure Water-6.09.8310300Alumina2000100030Both Surfaces20001.5Pure Water-6.013.0111300Alumina20006030Both Surfaces10002.0Pure Water-6.00.50412300Alumina20006030Both Surfaces10002.5Pure Water-6.00.70413300Alumina20006030Both Surfaces10003.0Pure Water-6.01.0414300Silicon Carbide25006030Both Surfaces10001.5Pure Water-6.00.50415300Boron Nitride50006030Both Surfaces10001.5Pure Water-6.00.70416300Diamond70006030Both Surfaces10001.5Pure Water-6.00.80417300Alumina20006030Both Surfaces3001.5Pure Water-6.00.20418300Alumina20006030Both Surfaces301.5Pure Water-6.00.05419300Alumina20006030Both Surfaces50001.5Pure Water-6.02.3420300Alumina200012530Both Surfaces10001.5Pure WaterOxalic Acid2.511.0121300Alumina200012530Both Surfaces10001.5Pure WaterSodium Oxalate4.01.0522300Alumina200012530Both Surfaces10001.5Pure WaterSodium Phosphate5.01.0523300Alumina200012530Both Surfaces10001.5Pure WaterCalcium Carbonate8.01.0524300Alumina200012530Both Surfaces10001.5Pure WaterCalcium Hydroxide10.01.0425300Alumina200012530Both Surfaces10001.5Pure WaterMagnesium Hydroxide12.01.0426300Alumina20006030Both Surfaces10000.5Pure Water-6.00.4427300Alumina20006030Both Surfaces3002.5Pure Water-6.00.34 [Table 2] No.Flat GrainsOxide in Range of 10 µm from Interface between Base Steel Sheet and Oxide LayerOxide LayerMagnetic CharacteristicsAdhesion of Insulating CoatingLength Ratio %Average of Average Thicknesses µmKindDensity grains / (µm) 2< Coverage %Magnetic Flux Density B8 TIron Loss W17 / 50 W / kg1150.5Mg, Si, Al0.002301.870.89BComparative Example2600.5Mg, Si, Al0.008451.890.86PComparative Example3500.5Mg, Si, Al0.005401.890.87PComparative Example4700.8Mg, Si, Al0.010551.910.85GExample5802.1Mg, Si, Al0.050851.920.84GExample6802.5Mg, Si, Al0.080901.920.83GExample7803.6Mg, Si, Al0.100951.930.82GExample8804.5Mg, Si, Al0.150951.910.85GExample9805.0Mg, Si, Al0.210501.880.88GComparative Example10Not Evaluated due to Poor External AppearanceComparative Example11750.7Mg, Si, Al0.020801.910.85GExample12751.0Mg, Si, Al0.040851.910.84GExample13801.5Mg, Si, Al0.050901.920.83GExample14700.7Mg, Si, Al0.020851.920.85GExample15752.0Mg, Si, Al0.030851.920.84GExample16803.0Mg, Si, Al0.050901.920.83GExample17600.5Mg, Si, Al0.006401.890.86PComparative Example18500.5Mg, Si, Al0.003401.890.87PComparative Example19803.5Mg, Si, Al0.100901.930.82GExample20Not Evaluated due to Poor External AppearanceComparative Example21802.0Mg, Si, Al0.050851.920.84GExample22802.0Mg, Si, Al0.050851.920.84GExample23802.0Mg, Si, Al0.050901.920.84GExample24802.0Mg, Si, Al0.050851.920.84GExample25300.5Mg, Si, Al0.005451.880.86PComparative Example26700.5Mg, Si, Al0.006551.890.86PComparative Example27600.5Mg, Si, Al0.010601.890.86GComparative Example

[0172] In the results shown in Tables 1 and 2, in the examples where the grinding of the surface of the steel sheet and the contact with the aqueous solution were performed under conditions of the present invention, the oxide of one or more kinds of Mg, Al, and Si having an equivalent circle diameter of 0.1 to 3.0 µm was present at a density of 0.010 to 0.200 grains / µm 2< in a range of 10 µm in the sheet thickness direction from the interface between the silicon steel sheet and the oxide layer, and in a cross section in the sheet thickness direction, the length of grain boundaries of the flat grains accounted for 70% or more of the length of the interface between the silicon steel sheet and the oxide layer. In addition, as a result, magnetic characteristics were excellent in these examples.

[0173] On the other hand, in the examples where the contact with the predetermined aqueous solution was not performed or the grinding conditions were not preferable, the external appearance that was usually required was not satisfied, the oxide of the surface layer area was not sufficiently formed, or the flat grains were not sufficiently formed. In addition, as a result, magnetic characteristics were poor (some of external appearance defects were not evaluated).(Example 2)

[0174] Using the same molten steel and slab as those used in Example 1, the hot rolling, the hot rolled sheet annealing, the pickling, and the cold rolling were performed using the same method as that of Example 1 to obtain a cold rolled sheet having a sheet thickness of 0.22 mm.

[0175] One surface of the obtained cold rolled sheet was irradiated with a laser beam using a commercially available fiber laser under conditions of a laser output, a focused spot diameter (in the sheet width direction TD and the rolling direction RD) and a scanning speed shown in the tables. Argon as assist gas was sprayed during the laser irradiation such that molten material produced from the steel sheet during the laser irradiation was not re-attached to the steel sheet, a suction duct was provided at a position facing an assist gas ejection port, and dust derived from the molten material produced during the laser irradiation was collected. Due to the laser irradiation, linear grooves having a substantially triangular shape with a width and a depth shown in the tables as a cross-sectional projection shape were formed on the surface. The grooves extended in a direction shown in the tables and were periodically formed parallel to the rolling direction at an interval shown in the tables in the rolling direction.

[0176] Next, the surface of the cold rolled sheet where the grooves were formed was ground under conditions shown in Table 2 while causing ion exchange water of pH = 4.0 to 6.0 to flow on the surface of the steel sheet. Further, after completion of the grinding, the steel sheet was brought into contact with the ion exchange water of pH = 4.0 to 6.0. During the contact, the contact time was 5 seconds, and the flow rate of the aqueous solution was 10 L / min.

[0177] Next, the decarburization annealing, the nitriding treatment, the application of the annealing separator containing MgO as a major component, and the finish annealing were performed under the same conditions as those of Example 1.

[0178] As a result of removing the annealing separator by water cleaning after the finish annealing, a glass coating (oxide layer) was formed on the surface of the steel sheet.

[0179] A chemical containing an insulating coating component formed of aluminum phosphate, colloidal silica, and chromic anhydride was applied to the silicon steel sheet including the glass coating, and the steel sheet was heated to 800°C in a nitrogen atmosphere and was held for 30 seconds to bake the insulating coating. At this time, the adhesion amount of the insulating coating layer of one surface was 5.0 g / m 2< .

[0180] In addition, in the obtained silicon steel sheet (including the silicon steel sheet, the glass coating (oxide layer), and the insulating coating layer), the oxide in a range of 10 µm in the sheet thickness direction from the interface with the oxide layer and the flat grains were evaluated in the same manner as that of Example 1. In addition, in the present example, the in-groove flat grains were also evaluated.

[0181] 36 samples having a size of 30 mm in the sheet width direction × 280 mm in the rolling direction were collected by shearing from the obtained grain-oriented electrical steel sheet (including the silicon steel sheet, the glass coating (oxide layer), and the insulating coating layer), and stress relief annealing was performed on these samples in a nitrogen atmosphere at 800°C for 2 h.

[0182] Next, using a magnetic characteristic measurement method defined in the Epstein method described in JIS-C-2550-1:2011, a magnetic flux density (hereinafter, B8) during excitation at a magnetizing force of 800 A / m and an iron loss (hereinafter, W17 / 50) during excitation at an excitation frequency of 50 Hz and a magnetic flux density of 1.7 T were measured.

[0183] In addition, a sample having a size of 300 mm in the rolling direction × 300 mm in the width direction was collected from the obtained grain-oriented electrical steel sheet, this sample was coiled around a round bar of SUS304 having a diameter of 20 mm (φ20 mm) and was uncoiled. Next, the insulating coating of a recessed portion of the inside for coiling was observed to evaluate adhesion of the insulating coating.

[0184] The determination criteria were as follows. G (GOOD): No coating peeling P (POOR): Partial coating peeling B (BAD): Coating peeling on the entire surface [Table 3] No.Laser Irradiation ConditionsGroove FormationKindPower WFocused Spot (RD) µmFocused Spot (TD) µmScanning Speed m / sAssist GasGroove Depth µmGroove Width µmRolling Direction Pitch mmExtending Direction Angle with respect to Rolling Direction °KindFlow Rate L / min102Fiber20010.010.040Ar58156.082103Fiber20015.015.030Ar510206.082104Fiber45022.522.530Ar515306.082105Fiber80030.030.030Ar520406.082106Fiber125037.537.530Ar525506.082107Fiber180045.045.030Ar530606.082108Fiber20015.015.030Ar510206.075109Fiber20015.015.030Ar510206.080110Fiber20015.015.030Ar510206.085111Fiber20015.015.030Ar510206.090112Fiber20015.015.030Ar510206.095113Fiber20015.015.030Ar510206.0100114Fiber20015.015.030Ar510206.0105115Fiber45022.522.530Ar515300.582116Fiber45022.522.530Ar515301.082117Fiber45022.522.530Ar5153010.0082118Fiber45022.522.530Ar5153020.082119Fiber45022.522.530Ar5153025.082120Fiber45022.522.530Ar515306.082121Fiber80030.030.030Ar720406.082122Fiber80030.030.030Ar1020406.082 [Table 4] No.Brush RollPassing Speed mpmGrinding MethodContactAfter Grinding + ContactRoll Diameter mmAbrasive GrainsGround SurfaceRotation Speed mpmPressing mmAqueous SolutionAmount of Abrasion of One Surface g / m 2< Surface External AppearanceKindKnoop HardnessMaximum Grain Size µmSolventAdditivepH102300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04103300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04104300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04105300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04106300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04107300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04108300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04109300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04110300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04111300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04112300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04113300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04114300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04115300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04116300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04117300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04118300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04119300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04120300Alumina200012530Both Surfaces10001.5Pure WaterSodium Oxalate4.01.15121300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04122300Alumina200012530Both Surfaces10001.5Pure Water-6.01.04 [Table 5] No.Flat GrainsIn-Groove Flat GrainsOxide in Range of 10 µm from Surface of Base Steel SheetOxide LayerMagnetic CharacteristicsAdhesion of Insulating CoatingLength Ratio %Average of Average Thicknesses µmLength Ratio %Average of Average Diameters µmKindDensity grains / (µm) 2< Coverage %Magnetic Flux Density B8 TIron Loss W17 / 50 W / kg102801.5801.5Mg, Si, Al0.060851.900.80GInvention Example103801.5801.5Mg, Si, Al0.060851.890.76GInvention Example104801.5801.5Mg, Si, Al0.060851.880.75GInvention Example105801.5801.5Mg, Si, Al0.060851.880.74GInvention Example106801.5801.5Mg, Si, Al0.060901.880.73GInvention Example107801.5801.5Mg, Si, Al0.060951.870.75GInvention Example108801.5801.5Mg, Si, Al0.060951.910.78GInvention Example109801.5801.5Mg, Si, Al0.060951.900.76GInvention Example110801.5801.5Mg, Si, Al0.060951.880.75GInvention Example111801.5801.5Mg, Si, Al0.060951.870.74GInvention Example112801.5801.5Mg, Si, Al0.060951.880.75GInvention Example113801.5801.5Mg, Si, Al0.060951.900.76GInvention Example114801.5801.5Mg, Si, Al0.060951.910.78GInvention Example115801.5801.5Mg, Si, Al0.060851.860.80GInvention Example116801.5801.5Mg, Si, Al0.060851.870.73GInvention Example117801.5801.5Mg, Si, Al0.060851.880.74GInvention Example118801.5801.5Mg, Si, Al0.060851.900.75GInvention Example119801.5801.5Mg, Si, Al0.060851.910.80GInvention Example120801.5801.5Mg, Si, Al0.060851.880.74GInvention Example121801.5902.1Mg, Si, Al0.060851.880.73GInvention Example122801.5903.0Mg, Si, Al0.060851.880.72GInvention Example

[0185] As can be seen from Tables 3 to 5, in all of the cases, sufficient adhesion with the coating was obtained, and the iron loss was low at 0.85 W / kg or less. In the examples where the grooves were formed under the preferable conditions, the iron loss was further reduced to 0.76 W / kg or less.INDUSTRIAL APPLICABILITY

[0186] According to the present invention, a grain-oriented electrical steel sheet having excellent magnetic characteristics and a manufacturing method therefor can be provided. Therefore, industrial applicability is high.REFERENCE SIGNS LIST

[0187] 1 Grain-oriented electrical steel sheet 11 Silicon steel sheet 21 Oxide layer 31 Insulating coating layer 101 Oxide (oxide grains) 102 Flat grain G Groove t Thickness G102 In-groove flat grains

Claims

1. A grain-oriented electrical steel sheet comprising: a silicon steel sheet; an oxide layer formed of one or more kinds of Mg, Al, and Si that is formed on a surface of the silicon steel sheet; and an insulating coating layer that is formed on a surface of the oxide layer, wherein an oxide of one or more kinds of Mg, Al, and Si having an equivalent circle diameter of 0.1 to 3.0 µm is present at a density of 0.010 to 0.200 grains / µm2 in the silicon steel sheet in a range of 10 µm in a sheet thickness direction from an interface between the silicon steel sheet and the oxide layer, on the surface side of the silicon steel sheet, flat grains where an average thickness in a direction perpendicular to the surface is 0.5 to 5.0 µm, an aspect ratio that is a ratio of a grain width in a direction parallel to the surface to the average thickness is 1.5 or more, and a deviation of a crystal orientation from Goss orientation is 10° or more are present, and in a cross section in the sheet thickness direction, a length of grain boundaries of the flat grains accounts for 70% or more of a length of the interface between the silicon steel sheet and the oxide layer.

2. The grain-oriented electrical steel sheet according to claim 1, wherein an average of the average thicknesses of the flat grains is more than 2.0 µm and 5.0 µm or less.

3. The grain-oriented electrical steel sheet according to claim 1 or 2, wherein a coverage of the oxide layer on surfaces of the flat grains forming the interface is 50% or more.

4. The grain-oriented electrical steel sheet according to claim 1 or 2, wherein a plurality of grooves having a depth of 10 to 30 µm and extending in a direction of 80 to 100° with respect to a rolling direction are present in the silicon steel sheet, and an interval of the groove adjacent to each other in the rolling direction is 1.0 to 20.0 mm.

5. The grain-oriented electrical steel sheet according to claim 3, wherein a plurality of grooves having a depth of 10 to 30 µm and extending in a direction of 80 to 100° with respect to a rolling direction are present in the silicon steel sheet, and an interval of the groove adjacent to each other in the rolling direction is 1.0 to 20.0 mm.

6. The grain-oriented electrical steel sheet according to claim 4, wherein on a surface side of the groove of the silicon steel sheet, in-groove flat grains where an average diameter in a direction perpendicular to the surface of the groove is 0.5 to 5.0 µm, an aspect ratio that is a ratio of a grain width in a direction parallel to the surface to the average diameter is 2.0 or more, and a deviation of a crystal orientation from Goss orientation is 10° or more are present, and in a cross section in the sheet thickness direction perpendicular to an extending direction of the groove, a length of grain boundaries of the in-groove flat grains accounts for 70% or more of a length of an inner surface of the groove.

7. The grain-oriented electrical steel sheet according to claim 5, wherein on a surface side of the groove of the silicon steel sheet, in-groove flat grains where an average diameter in a direction perpendicular to the surface of the groove is 0.5 to 5.0 µm, an aspect ratio that is a ratio of a grain width in a direction parallel to the surface to the average diameter is 2.0 or more, and a deviation of a crystal orientation from Goss orientation is 10° or more are present, and in a cross section in the sheet thickness direction perpendicular to an extending direction of the groove, a length of grain boundaries of the in-groove flat grains accounts for 70% or more of a length of an inner surface of the groove.

8. The grain-oriented electrical steel sheet according to claim 6, wherein an average of the average diameters of the in-groove flat grains is more than 2.0 µm and 5.0 µm or less.

9. The grain-oriented electrical steel sheet according to claim 7, wherein an average of the average diameters of the in-groove flat grains is more than 2.0 µm and 5.0 µm or less.

10. A manufacturing method for a grain-oriented electrical steel sheet, the manufacturing method comprising: a hot rolling step of heating and hot rolling a slab to obtain a hot rolled sheet; a hot rolled sheet annealing step of annealing the hot rolled sheet after the hot rolling step; a pickling step of pickling the hot rolled sheet after the hot rolled sheet annealing step; a cold rolling step of cold rolling the hot rolled sheet after the pickling step to obtain a cold rolled sheet; a grinding step of grinding a surface of the cold rolled sheet after the cold rolling step; a contact step of bringing the cold rolled sheet after the grinding step into contact with an aqueous solution of pH 4.0 to 10.0; a decarburization annealing step of performing decarburization annealing on the cold rolled sheet after the contact step; a finish annealing step of applying an annealing separator to the cold rolled sheet after the decarburization annealing step and performing finish annealing to form an oxide layer formed of one or more kinds of Mg, Al, and Si on a surface of the cold rolled sheet that is a base steel sheet; and an insulating coating forming step of forming an insulating coating layer on a surface of the oxide layer after the finish annealing step, wherein in the grinding step, using abrasive grains having a Knoop hardness of 1000 or more and a maximum grain size of more than 50 µm and 500 µm or less or using abrasive paper, a roll, or a brush to which the abrasive grains are fixed, the surface of the cold rolled sheet is ground at a rolling reduction of 1.0 to 5.0 mm and a grinding speed of 500 mpm or more such that an amount of abrasion on at least one surface of the cold rolled sheet is 0.10 to 10.0 g / m2.

11. The manufacturing method for a grain-oriented electrical steel sheet according to claim 10, further comprising, before the grinding step, a groove forming step of forming a plurality of grooves having a depth of 10 to 30 µm and extending in a direction having an angle of 80 to 100° with respect to a rolling direction on the cold rolled sheet such that each of intervals in the rolling direction is 1.0 to 20 mm.

12. The manufacturing method for a grain-oriented electrical steel sheet according to claim 11, wherein in the groove forming step, the grooves are formed by removing a molten material from the surface of the cold rolled sheet while irradiating the surface of the cold rolled sheet with a laser beam to melt a part of the sheet surface.

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