Grain-oriented electrical steel sheet and method for producing same

Abstract

This grain-oriented electrical steel sheet comprises: a silicon steel sheet; an oxide layer that is formed on the surface of the silicon steel sheet and contains one or more oxides from among Mg, Al, and Si; and an insulating coating layer which is formed on the surface of the oxide layer, and in which at least one oxide of Mg, Al, and Si having an equivalent circle diameter of 0.1-3.0 [mu] m is present at a density of 0.010-0.200 / [mu] m2 within a range of 5 [mu] m in the sheet thickness direction from the interface between the silicon steel sheet and the oxide layer. Flat crystal grains are present on the surface side of the silicon steel sheet, and in a cross-section in the sheet thickness direction, the length of the grain boundary of the flat crystal grains, which is the length of the interface between the silicon steel sheet and the oxide layer, is 50% or more; a plurality of linear thermal strains extending in a direction at an angle of 80-100 degrees with respect to the rolling direction are formed on the surface of the silicon steel sheet at intervals of 1.0-20.0 mm with respect to the rolling direction.

Description

Technical Field

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

[0002] This application claims priority based on Japanese Patent Application No. 2022-186166 filed on November 22, 2022, and incorporates its content herein. Background Art

[0003] Grain-oriented electrical steel sheets are soft magnetic materials and are mainly used as core materials for transformers. For example, a grain-oriented electrical steel sheet contains 2.00 to 6.00% Si and has a highly concentrated crystal orientation of the product in the {110}<001> orientation. As its magnetic properties, a high magnetic flux density represented by the B8 value and a low iron loss represented by W17 / 50 are required. In particular, recently, from the viewpoint of energy saving, the requirement for reducing the power loss of transformers has increased, and the requirement for reducing the iron loss of grain-oriented electrical steel sheets has increased.

[0004] Iron loss is roughly divided into two loss components: hysteresis loss and eddy current loss. Furthermore, eddy current loss can be divided into classical eddy current loss and anomalous eddy current loss.

[0005] For example, in order to reduce classical eddy current loss, methods such as increasing the resistance of grain-oriented electrical steel sheets and reducing the thickness of the silicon steel sheet used as the base steel sheet are known.

[0006] However, in these methods, the productivity decreases, so they are not preferred, and sufficient iron loss improvement effects cannot be obtained only by these measures.

[0007] In order to reduce hysteresis loss, it is important to increase the magnetic flux density. It is effective to control the crystal orientation in the steel sheet to an orientation close to the Goss orientation through cold rolling and control of inhibitors.

[0008] For example, Patent Document 1 describes that by performing decarburization annealing to form a silica-rich oxide layer, decomposition and disappearance of inhibitors can be suppressed, and recrystallization of grains having a crystal orientation close to the Goss orientation (hereinafter referred to as Goss-oriented grains) can be stably generated.

[0009] According to the above method, although the magnetic flux density is increased, the number of recrystallized Goss-oriented grains becomes smaller, so the number of Goss-oriented grains per unit area of the steel sheet becomes smaller. That is, the grain diameter of each Goss-oriented grain becomes larger, and as a result, the magnetic domain width (hereinafter referred to as the magnetic domain width) of the 180° magnetic domains formed within the Goss-oriented grains and contributing to the magnetic properties of the grain-oriented electrical steel sheet becomes larger. In this case, even though the hysteresis loss is reduced due to the increase in the magnetic flux density, the abnormal eddy current loss increases due to the increase in the magnetic domain width, so as a result, the iron loss is offset, and it may not be possible to obtain an iron loss reduction effect commensurate with the increase in the magnetic flux density.

[0010] Therefore, a method of reducing the magnetic domain width and reducing the abnormal eddy current loss in a state of enjoying the effect of reducing the hysteresis loss brought about by the increase in the magnetic flux density has been proposed. As a commonly used method, there is a method of periodically imparting thermal strain in the rolling direction on the surface of the grain-oriented electrical steel sheet, and these methods commonly use high-energy sources such as lasers and electron beams.

[0011] As an example, Patent Document 2 discloses a method for manufacturing a grain-oriented electrical steel sheet, which has the following steps: irradiating the surface of the grain-oriented electrical steel sheet while scanning the focused continuous-wave laser in a direction inclined from the rolling direction of the grain-oriented electrical steel sheet; and having a step of repeating while staggering the part where the continuous-wave laser is scanned at a predetermined interval. When the average power of the continuous-wave laser is represented by P (W), the scanning speed is represented by Vc (mm / s), the predetermined interval is represented by PL (mm), and the average irradiation energy density Ua is defined as Ua = P / (Vc × PL) (mJ / mm 2 ), the magnetic domains are controlled by irradiating the laser that satisfies 1.0 mm ≤ PL ≤ 3.0 mm and 0.8 mJ / mm 2 ≤ Ua ≤ 2.0 mJ / mm 2 .

[0012] In Patent Document 2, it is disclosed that it is possible to easily reduce the iron loss in both the rolling direction and the width direction of the grain-oriented electrical steel sheet while ensuring high productivity.

[0013] In addition, Patent Document 3 discloses a method for manufacturing a grain-oriented electrical steel sheet, which improves the iron loss characteristics by scanning and irradiating a continuously oscillating laser beam, which is substantially perpendicular to the rolling direction of the steel sheet and forms linear circulating magnetic domains at substantially constant intervals.

[0014] In Patent Document 3, a TEM00 mode in which the laser intensity distribution in a cross section perpendicular to the beam transport direction has a maximum intensity near the optical axis center is shown. The condensing diameter d [mm] in the rolling direction of the irradiation beam, the scanning line speed V [mm / sec] of the laser beam, and the average output P [W] of the laser are in the range of 0 < d ≤ 0.2 and 0.001 ≤ P / V ≤ 0.012, thereby obtaining an oriented electrical steel sheet with reduced iron loss.

[0015] In order to reduce iron loss, it is required to improve the above-mentioned magnetic flux density technology and improve the magnetic domain control technology. However, in recent years, compared with the progress of the high magnetic flux density technology, the progress of the magnetic domain control technology lags behind, and there is a problem that the reduction of iron loss commensurate with the high magnetic flux density cannot be fully achieved.

[0016] Prior Art Documents

[0017] Patent Documents

[0018] Patent Document 1: Japanese Patent Laid-Open No. 62-151522

[0019] Patent Document 2: Japanese Patent No. 4669565

[0020] Patent Document 3: Japanese Patent No. 4510757 Summary of the Invention

[0021] Problems to be Solved by the Invention

[0022] As described above, the improvement of the magnetic flux density and the reduction effect of iron loss commensurate with the increased amount have been studied, but it cannot be said to be sufficient for the increasingly high requirements in recent years. The so-called thermal strain-imparting type magnetic domain control material (hereinafter simply referred to as magnetic domain control material) that intentionally imparts thermal strain by irradiating an oriented electrical steel sheet with laser, electron beam, plasma, etc. suitable for laminated iron cores to reduce the magnetic domain width and reduce iron loss is also insufficient, and the room for reducing iron loss has been studied.

[0023] Therefore, the subject of the present invention is to provide an oriented electrical steel sheet having excellent magnetic properties, namely high magnetic flux density and low iron loss commensurate with its magnetic flux density, in a magnetic domain control material, and a manufacturing method thereof.

[0024] Means for Solving the Problems

[0025] The inventors mainly studied the improvement of the magnetic properties of the magnetic domain control material for the grain-oriented electromagnetic steel sheet suitable for the laminated core, that is, the increase in magnetic flux density and the reduction of iron loss. As a result, it was found that by forming grains (hereinafter referred to as "flat grains") that are flat and have a deviation angle of 10° or more from the Goss orientation ({110}<001> orientation) on the surface side of the silicon steel sheet (base material steel sheet) included in the grain-oriented electromagnetic steel sheet, the 180° magnetic domain width can be controlled to a small state in terms of energy. Therefore, even when the same thermal strain as before is applied, the eddy current loss can be further reduced compared to the past, and as a result, the iron loss can be further reduced.

[0026] In addition, the inventors studied the influence of manufacturing conditions. As a result, the following aspects were understood.

[0027] That is, in the final annealing process of the manufacturing process of the grain-oriented electromagnetic steel sheet, the Goss orientation that exhibits high magnetic properties allows precipitates such as AlN and MnS, which are called inhibitors, to exist at the crystal grain boundaries in the form of precipitates, and highly aggregates by an abnormal grain growth phenomenon called "secondary recrystallization" that utilizes the pinning effect of these precipitates. After the aggregation of the Goss orientation in the steel sheet is completed, that is, when the steel sheet surface is almost covered with Goss-oriented grains, the acting inhibitor is decomposed and oxidized by the temperature rise in the latter half of the final annealing process and removed from the steel sheet. That is, it is not preferable for the decomposition and oxidation of the inhibitor to occur before the Goss orientation in the steel sheet is sufficiently aggregated. Furthermore, for the inhibitor, by suppressing the decomposition and oxidation to a higher temperature, the Goss orientation can be more highly aggregated, that is, crystals closer to the ideal Goss orientation can be aggregated. Therefore, a method of improving the heat resistance of the precipitate that exhibits the inhibitor effect is used.

[0028] The inventors found that as a method of improving the heat resistance of the inhibitor, it is effective to make an oxide that can suppress the decomposition and oxidation of the inhibitor during the subsequent final annealing exist on the steel sheet surface in the decarburizing annealing process that is usually performed in the manufacture of the grain-oriented electromagnetic steel sheet. Furthermore, it was found that by using the decarburizing annealing process before the final annealing to make an oxide that can suppress the decomposition and oxidation of the above-mentioned inhibitor exist on the steel sheet surface, flat grains can be generated near the interface between the steel sheet surface oxide and the steel sheet.

[0029] In addition, the inventors found that in order to generate flat grains that are more preferable for improving magnetic properties, it is effective to form oxide particles more densely, thicker, and uniformly on the surface side of the cold-rolled sheet that becomes the base material steel sheet in the decarburizing annealing process. In order to form the oxide particles densely, thicker, and uniformly, it is effective to grind the cold-rolled sheet under specified conditions before the decarburizing annealing process in order to remove the reactants on the surface of the steel sheet that hinder the uniform oxidation of the steel sheet surface during decarburizing annealing.

[0030] In addition, in the case of a grain-oriented electrical steel sheet, thermal strain is sometimes intentionally imparted by irradiating laser light, electron beams, plasma, etc., to perform magnetic domain control. However, since the magnetic domain width of the above-described grain-oriented electrical steel sheet is small before magnetic domain control is performed, by combining with these techniques, excellent magnetic properties, namely, high magnetic flux density and reduced iron loss, can be further achieved through a synergistic effect.

[0031] The present invention has been completed in view of the above-described viewpoints. The gist of the present invention is as follows.

[0032] [1] A grain-oriented electrical steel sheet according to one embodiment of the present invention includes: a silicon steel sheet; an oxide layer formed on the surface of the silicon steel sheet and containing one or more oxides of Mg, Al, and Si; and an insulating coating layer formed on the surface of the oxide layer. In the silicon steel sheet, within a range of 5 μm in the plate thickness direction from the interface between the silicon steel sheet and the oxide layer, one or more oxides 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 per μm. 2 Flat grains are present on the surface side of the silicon steel sheet. The average thickness of the flat grains in the direction perpendicular to the surface is 0.5 to 5.0 μm, the aspect ratio, which is the ratio of the grain width in the direction parallel to the surface to the average thickness, is 1.5 or more, and the deviation of the crystal orientation from the Goss orientation is 10° or more. In a cross section in the plate thickness direction, the length of the grain boundaries of the flat grains in the length of the interface between the silicon steel sheet and the oxide layer is 50% or more. A plurality of linear thermal strains extending in a direction at an angle of 80 to 100° with respect to the rolling direction are formed on the surface of the silicon steel sheet at intervals of 1.0 to 20.0 mm with respect to the rolling direction.

[0033] [2] In the grain-oriented electrical steel sheet according to [1], the average of the average thickness of the flat grains may be 0.5 to 2.0 μm.

[0034] [3] In the grain-oriented electrical steel sheet according to [1] or [2], the coverage rate of the oxide layer on the surface of the flat grains constituting the interface may be 50% or more.

[0035] [4]Another method for manufacturing an oriented electromagnetic steel sheet according to the present invention includes: a hot rolling step of heating a slab and performing hot rolling to produce a hot rolled sheet; a hot rolled sheet annealing step of annealing the hot rolled sheet after the above 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 produce a cold rolled sheet; a grinding step of grinding the 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 having a pH of 4.0 to 10.0; a decarburizing annealing step of performing decarburizing annealing on the cold rolled sheet after the contact step; a final annealing step of applying an annealing release agent to the cold rolled sheet after the decarburizing annealing step and then performing final annealing to form an oxide layer containing one or more of Mg, Al, and Si on the surface of the cold rolled sheet that becomes the base material steel sheet; an insulating coating forming step of forming an insulating coating layer on the surface of the oxide layer after the final annealing step to obtain an oriented electromagnetic steel sheet having the above silicon steel sheet, the oxide layer, and the insulating coating layer; and a magnetic domain control step of irradiating the surface of the oriented electromagnetic steel sheet after the insulating coating forming step with a laser, an electron beam, or a plasma to form a plurality of linear thermal strains extending in a direction at an angle of 80 to 100° with respect to the rolling direction at intervals of 1.0 to 20.0 mm in the rolling direction on the surface of the silicon steel sheet. In the grinding step, an abrasive grain having a Knoop hardness of 1000 or more or abrasive paper, a roll, or a brush fixed with the abrasive grain is used so that the grinding amount of the cold rolled sheet reaches 0.10 to 3.00 g / m on at least one surface. 2 Grind in such a manner.

[0036] Advantages of the Invention

[0037] According to the above aspect of the present invention, an oriented electromagnetic steel sheet having excellent magnetic properties and a method for manufacturing the same can be provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 is a schematic cross-sectional view of the oriented electromagnetic steel sheet of the present embodiment.

[0039] Figure 2 is a diagram for explaining a method of measuring the average thickness and aspect ratio of crystal grains.

[0040] Figure 3 is a diagram for explaining a method of measuring the coverage rate of the oxide layer in flat crystal grains. DETAILED DESCRIPTION OF THE INVENTION

[0041] Hereinafter, an oriented electromagnetic steel sheet (the oriented electromagnetic steel sheet of the present embodiment) and a method for manufacturing the same according to an embodiment of the present invention will be described.

[0042] <Oriented electrical steel sheet>

[0043] As Figure 1 shown, the oriented electrical steel sheet 1 of the present embodiment has a silicon steel sheet 11 (hereinafter sometimes referred to as a base steel sheet or simply as a steel sheet), an oxide layer 21 containing one or more oxides of Mg, Al, and Si formed on the surface of the silicon steel sheet 11, and an insulating coating layer 31 formed on the surface of the oxide layer 21.

[0044] The oxide layer 21 and the insulating coating layer 31 may be formed only on one side of the steel sheet, but are preferably formed on both sides from the viewpoints of insulation and the like. Explanation will be given separately below.

[0045] [Silicon steel sheet]

[0046] (In the range of 5 μm in the plate thickness direction from the interface between the silicon steel sheet and the oxide layer, one or more oxides 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 per μm 2 )

[0047] In the oriented electrical steel sheet, by suppressing the decomposition and oxidation of the inhibitor (precipitates present in the crystal grain boundaries such as AlN) during the final annealing so that it exists up to a high temperature, Goss orientation can be highly aggregated during secondary recrystallization, that is, crystals closer to the ideal Goss orientation can be aggregated, the magnetic flux density is increased, and thus a reduction in iron loss can be achieved.

[0048] The size of the precipitate as the inhibitor is very small, with an equivalent circle diameter of several 10 nm to about 100 nm. In addition, its size has a distribution. In the case where there is a size distribution, the small-sized inhibitor decomposes and oxidizes at a low temperature and the effect as an inhibitor is inactivated. In this case, it becomes difficult to perform secondary recrystallization of Goss orientation closer to the ideal Goss orientation, and it is difficult to increase the magnetic flux density. On the other hand, if the size distribution of the inhibitor is controlled to be constant (the difference in size is made smaller), the above problems are eliminated, but it is extremely difficult industrially.

[0049] In contrast, even in a state where the size distribution of the inhibitor is generated, as long as the decomposition and oxidation can be suppressed by some method so that the inhibitor exists up to a high temperature, secondary recrystallization of grains closer to the ideal Goss orientation can be generated. In addition, there is a method of suppressing the decomposition and oxidation of the inhibitor by using an inhibitor with high heat resistance. On the other hand, as a method of achieving this without changing the composition of the inhibitor, etc., it is known that oxide particles of Si in steel (hereinafter referred to as Si-based pre-oxides) formed on the surface or near the surface of the steel sheet in the decarburizing annealing process play a role. The mechanism is speculated, but it is considered that the oxidation of the inhibitor is caused by oxidizing AlN, etc. with trace amounts of oxygen contained in the final annealing atmosphere on the steel sheet surface, but the above Si-based pre-oxides prevent and reduce this oxidation.

[0050] However, the formation state of the Si-based pre-oxides on the surface of the silicon steel sheet tends to become uneven at each part. If the formation state is uneven, the suppression effect of the decomposition and oxidation of the inhibitor will deviate depending on the position within the steel sheet surface, and the target effect cannot be fully obtained.

[0051] The inventors of the present invention investigated the reason why the formation state of the oxide layer after final annealing becomes uneven at each part of the surface. As a result, it was found that on the surface of the silicon steel sheet (cold-rolled sheet) before decarburizing annealing, Fe-based oxides, reactants of oily agents or extreme pressure additives contained in the rolling oil used during cold rolling, etc., exist unevenly on the steel sheet surface, and these Fe-based oxides and reactants hinder the Si-based pre-oxides on the steel sheet surface from forming densely, thickly, and uniformly in a constant thickness region from the surface during decarburizing annealing.

[0052] Since it is difficult for the inventors of the present invention to make the above Fe-based oxide film and reactants uniform during cold rolling, they conducted research on rendering harmless the factors that hinder the formation of these Si-based pre-oxides. As a result, as described later, it was found that by using abrasive grains or abrasive paper, rolls or brushes fixed with abrasive grains to grind the surface (at least one surface) of the cold-rolled sheet before the decarburizing annealing process to a constant level, exposing a clean metal surface, and then immediately contacting it with an aqueous liquid, the Fe-based oxides and reactants that are the factors hindering the formation of Si-based pre-oxides can be removed from the surface of the steel sheet, and after the decarburizing annealing process, the Si-based pre-oxides can be uniformly formed in a region of a constant thickness from the surface of the steel sheet. Therefore, based on these insights, its optimization was carried out in magnetic domain control materials based on irradiation such as lasers, electron beams, and plasmas.

[0053] Based on the above insights, in the oriented electrical steel sheet 1 of the present embodiment, within a range of 5 μm in the plate thickness direction from the interface between the silicon steel sheet 11 and the oxide layer 21, at 0.010 to 0.200 pieces / μm 2The density has one or more oxides (oxide particles 101) of Mg, Al, and Si with an equivalent circle diameter of 0.1 to 3.0 μm. The oxide may be any one or more oxides (including composite oxides) of Mg, Al, and Si, but under the premise of the manufacturing conditions described below, it is mostly spinel (MgAl2O4), alumina (Al2O3), mullite (2SiO2·3Al2O3), etc., which are oxides containing Mg, Al, and Si.

[0054] If the number density of the oxides is too small, the adhesion of the oxide layer to the steel sheet becomes poor, and the formation of the flat grains described below becomes uneven. On the other hand, if the number density is too large, the proportion of the metal part of the steel sheet becomes smaller, so the magnetic flux density decreases. In addition, the proportion of flat grains also becomes relatively smaller, so it is difficult to obtain the effect of reducing iron loss.

[0055] By uniformly forming a Si-based pre-oxide in a specified area after decarburizing annealing, the deviation of the inhibitory effect of the inhibitor decomposition and oxidation in the final annealing is reduced in the steel sheet surface, and the magnetic flux density is increased in the grain-oriented electrical steel sheet. In addition, by appropriately forming flat grains, the 180° magnetic domain width is reduced, and even when used as a magnetic domain control material, the iron loss reduction effect can be obtained corresponding to a high magnetic flux density.

[0056] (There are flat grains on the surface side of the silicon steel sheet. The average thickness of the flat grains in the direction perpendicular to the surface is 0.5 to 5.0 μm, the aspect ratio, which is the ratio of the grain width in the direction parallel to the surface to the average thickness, is 1.5 or more, and the deviation of the crystal orientation from the Goss orientation is 10° or more).

[0057] (In the cross-section in the plate thickness direction, the length of the grain boundaries of the flat grains in the length of the interface between the silicon steel sheet and the oxide layer is 50% or more)

[0058] As described above, in the grain-oriented electrical steel sheet of the present embodiment, a Si-based pre-oxide is mainly formed uniformly in the surface layer portion (the range within 5 μm from the surface) of the silicon steel sheet (base material steel sheet) by using a decarburizing annealing process, etc., so that the decomposition and oxidation of the inhibitor are suppressed during the final annealing and it exists up to a high temperature. In this case, the Goss orientation can be highly aggregated, that is, crystals closer to the ideal Goss orientation can be aggregated, and as a result, the magnetic flux density is increased. That is, the reduction of iron loss can be achieved.

[0059] On the other hand, the occurrence of secondary recrystallization at a higher temperature means that only grains closer to the ideal Goss orientation undergo secondary recrystallization. At this time, the number of Goss-oriented grains in secondary recrystallization becomes smaller, so the number of Goss-oriented grains per unit area of the steel sheet becomes smaller. That is, the grain diameter of each Goss-oriented grain becomes larger.

[0060] The iron loss required for the grain-oriented electrical steel sheet is classified into hysteresis loss and eddy current loss as its details. The hysteresis loss decreases as the magnetic flux density increases. On the other hand, the eddy current loss has a classical eddy current loss that decreases due to the reduction of the plate thickness and the increase in the resistivity of the steel sheet, and an abnormal eddy current loss that decreases due to the reduction of the magnetic domain width formed within the Goss-oriented grains. In many cases, the reduction of the plate thickness and the increase in the resistivity of the steel sheet in the reduction of the classical eddy current loss affect the productivity. Therefore, it is important to reduce the abnormal eddy current loss, that is, to reduce the magnetic domain width. The magnetic domain width generally has a correlation with the crystal grain size of the Goss orientation. Usually, the magnetic domain width of the so-called 180° magnetic domain generated in the grain-oriented electrical steel sheet due to the reduction of the crystal grain size also becomes smaller accordingly.

[0061] That is, although the magnetic flux density is increased by the control of the above-mentioned oxide, due to the coarsening of the crystal grain size, the abnormal eddy current loss increases, and it is possible that the effect of reducing the iron loss commensurate with the increase in the magnetic flux density cannot be obtained. The same applies to the magnetic domain control materials produced by irradiation with laser, electron beam, plasma, etc.

[0062] Therefore, the present inventors have studied a method for reducing the iron loss commensurate with the increase in the magnetic flux density, that is, a method for reducing the abnormal eddy current loss on the premise of improving the existence frequency of ideal Goss-oriented grains and magnetic domain control, that is, a method for reducing the magnetic domain width. As a result, as described above, secondary recrystallization occurs at a higher temperature, and only grains closer to the ideal Goss orientation undergo secondary recrystallization. Even when the crystal grain size is large, by the presence of flat grains (flat grains) on the surface of the steel sheet with a deviation angle of 10° or more with respect to the Goss orientation, the 180° magnetic domain width can be controlled to a small state in terms of energy, and the increase in eddy current loss can be suppressed. This effect also works in the magnetic domain control materials produced by irradiation with laser, electron beam, plasma, etc. Specifically, as Figure 1 shown, on the surface side of the base steel sheet (silicon steel sheet) 11, when there are flat grains 102 with an average thickness in the direction perpendicular to the surface of 0.5 to 5.0 μm, an aspect ratio (the ratio of the grain width in the direction parallel to the surface to the average thickness) of 1.5 or more, and a deviation of the crystal orientation from the Goss orientation of 10° or more (the flat grains exist as the outermost layer grains constituting the silicon steel sheet), the eddy current loss is reduced even before magnetic domain control, and this effect can be enjoyed even after magnetic domain control.

[0063] In grains with an average thickness of less than 0.5 μm, an aspect ratio of less than 1.5, or a deviation from the Goss orientation of less than 10°, the effect of reducing the magnetic domain width cannot be obtained sufficiently, and the iron loss cannot be reduced sufficiently.

[0064] On the other hand, the grains have a deviation from the Goss orientation. Therefore, if the average thickness of the grains exceeds 5.0 μm, the overall magnetic properties deteriorate, i.e., the magnetic flux density decreases and the iron loss increases.

[0065] Regarding the average of the average thickness of the flat grains, from the aspect of being able to sufficiently obtain the effect of reducing the magnetic domain width under the thermal strain imparted by laser, electron beam, plasma irradiation, etc. that can originally reduce the magnetic domain width, it is preferably 0.5 to 2.0 μm.

[0066] In addition, in order to sufficiently obtain the above-mentioned magnetic domain subdivision effect, in the cross-section in the plate thickness direction, the length of the grain boundaries of the flat grains in the length of the interface between the base steel plate and the oxide layer is 50% or more.

[0067] If the proportion of the flat grains constituting the interface is small, the effect of reducing the magnetic domain width is insufficient, and thus the effect of sufficiently reducing the iron loss cannot be obtained.

[0068] In the manufacturing method of the grain-oriented electrical steel sheet, during the final annealing, the minute Goss-oriented grains located inside the steel sheet in the plate thickness direction grow while consuming the grains with orientations other than the surrounding Goss orientation. As a result, from the inside to the surface of the plate thickness, the proportion of the Goss-oriented grains (grains with the <100> direction in the length direction of the silicon steel sheet and the <110> direction in the plane direction) further increases with respect to the rolling direction and the width direction.

[0069] It is considered that in the grain-oriented electrical steel sheet of the present embodiment, by the discrete presence of oxides in the surface layer portion of the steel sheet, when the grain growth of the Goss-oriented grains existing inside the plate thickness occurs, the minute flat-shaped grains in the surface layer portion of the steel sheet are not consumed by the Goss-oriented grains and remain. As a result, "flat grains" that are recognized as flat-shaped grains are formed.

[0070] The average thickness, aspect ratio, and deviation of the crystal orientation of the grains existing in the surface layer portion (range within 5 μm from the interface) of the silicon steel sheet can be measured by the following method.

[0071] A specimen of about 20 mm square is cut out from the steel plate so that the surface parallel to the rolling direction (RD direction) is used as the cross-section, and it is polished until the cross-section becomes a mirror surface. In addition, in the state where strain caused by polishing is imparted to the steel plate, it becomes difficult to measure the crystal orientation. Therefore, in the final polishing process, a polishing material such as colloidal silica is used to produce a polished specimen without generating strain. The cross-sectional shape is observed by FE-SEM using this polished specimen, and then the crystal orientation is measured by EBSD measurement. As an example of FE-SEM, "SU-70" (manufactured by Hitachi High-Tech Corporation) is used, and as an example of EBSD measurement, "Digiview" manufactured by TSL Solutions is used. As a specific method, the following is given as an example. The range including the base steel plate, the oxide layer, and the insulating coating layer is observed by FE-SEM at a magnification of 500 times the cross-section to obtain an electron microscope image. The interfaces between the insulating coating layer and the oxide layer and between the oxide layer and the steel plate are specified from the difference in electron density in the electron microscope image. When specifying the above interfaces, in the case of an FE-SEM equipped with an energy-dispersive spectrometer (EDS), the interfaces can be specified more precisely according to the different types of elements contained in the insulating coating layer, the oxide layer, and the silicon steel plate, such as P, B, O, and Fe.

[0072] Next, for the cross-section of the same field of view, the crystal orientation of the steel plate is measured by EBSD. Specifically, in a field of view of 500 times that is assumed to contain 100 or more flat grains, as the cross-section length, an area with a length of 200 μm in the rolling direction and a thickness of 70 μm in the plate thickness direction is targeted, and the crystal orientation is measured at intervals of 0.25 μm as the measurement point spacing. The boundary with a crystal orientation difference of 15° or more is defined as the crystal grain boundary, and the range surrounded by this crystal grain boundary is defined as the grain. When the number of grains in the field of view is less than 100, the measurement is performed on an additional field of view.

[0073] Regarding this grain, as Figure 2 shown, the average thickness of the grain is obtained by the methods shown in a) to d).

[0074] a) Imaginary lines (1) that determine the two ends of the grain are drawn in the plate thickness direction (normal direction) of the steel plate.

[0075] b) With respect to the distance L between the two ends, imaginary lines (the lines representing 95% of the width of the grain) (2) in the plate thickness direction are drawn from the two ends of the grain to 2.5% of L.

[0076] c) For the part between the imaginary lines drawn in b) (95% width part of the grain), an average line (3) is drawn for the envelope lines of the interface between the grain and the oxide layer and the lower side of the grain (the crystal grain boundary on the opposite side of the oxide layer).

[0077] d) Obtain the distance between the two average lines derived in c) above as the thickness t(4) (average at a total of 5 points including both ends and the center, and the midpoint between both ends and the center).

[0078] In addition, take the range at both ends of the crystal grains derived in a) above as the width of the crystal grains, and calculate the aspect ratio.

[0079] For all crystal grains with an average thickness of 0.5 to 5.0 μm and an aspect ratio of 1.5 or more in the above crystal grains, measure the crystal orientation of the ferrite phase of Fe. Take the crystal orientation measured thereon as a crystal orientation map called an IPF map, and obtain a map showing the crystal orientation with respect to the rolling direction (RD direction) and the normal direction of the steel plate surface (ND direction). Calculate the average of the orientation differences of each crystal grain from the Goss orientation as the deviation from the Goss orientation. If the deviation from the Goss orientation is 10° or more, it is a flat crystal grain.

[0080] The average of the average thicknesses of flat crystal grains (simple average) is obtained by dividing the sum of the average thicknesses of each flat crystal grain obtained above by the number of flat crystal grains.

[0081] Flat crystal grains are flat in the rolling direction (length direction) and the width direction. Therefore, as long as it is a cross-section in the plate thickness direction, it can be observed by any method. However, the method of obtaining the above steel plate with a plane parallel to the rolling direction (RD direction) as the cross-section and using EBSD to obtain a crystal orientation map to confirm the existence of "flat crystal grains" has high accuracy, so it is preferred. In addition, as a method of simply confirming the existence of "flat crystal grains", there is a method of confirming by a method that shows crystal grain boundaries such as the so-called nitric acid ethanol method (described in Nitric Acid Ethanol Method, JIS-G-0553(2019), etc.) after grinding a plane parallel to the rolling direction (RD direction) to obtain a smooth cross-section. However, in this method, the crystal orientation cannot be specified, and in addition, crystal orientation measurement needs to be performed by EBSD, etc. Therefore, in this embodiment, it is most suitable to use the above-mentioned FE-SEM and EBSD methods in combination.

[0082] In addition, the ratio of the length of the grain boundaries of flat crystal grains in the length of the interface between the base metal steel plate and the oxide layer can be obtained by the following method.

[0083] For example, in the field of view observed at a magnification of 500 times, for the interface between the silicon steel sheet and the oxide layer, which is the cross-sectional length in the rolling direction, a region of 200 μm is taken as the object, and SEM observation and EBSD measurement are carried out. For five places of it, that is, for a quantity of 1000 μm, which is the interface length, SEM observation and EBSD measurement are carried out. Measure the proportion (percentage) of the grain boundaries of flat grains with an average thickness of 0.5 to 5.0 μm, an aspect ratio of 1.5 or more, and an orientation difference from the Goss orientation of 10° or more in the length of the interface (1000 μm) between the silicon steel sheet and the oxide layer.

[0084] The identification of the interface between the insulating coating layer, the oxide layer, and the silicon steel sheet, and flat grains can be carried out in the same manner as described above.

[0085] During the measurement, the length of the oxide layer formed on the surface of the silicon steel sheet in the measurement range B is set as B' (if the oxide layer is formed over the entire measurement range, then B = B'). Among them, flat grains are formed on the outermost layer of the silicon steel sheet. The interface between the silicon steel sheet and the oxide layer is such that the partial lengths of the crystal grain boundaries of the flat grains are set as b1, b2... bi (i = 3 in the figure), and the sum of the lengths of b1 to bi (Σbi) is divided by the length B' of the oxide layer formed on the surface of the silicon steel sheet (Σbi / B'), thereby measuring the proportion of the length of the grain boundaries of the flat grains in the length of the interface between the base metal steel sheet and the oxide layer.

[0086] (Thermal strain)

[0087] Magnetic domain control can be carried out by periodically forming linear thermal strains extending in a direction crossing the rolling direction in the rolling direction. In the oriented electrical steel sheet of the present embodiment, during the manufacture of the oriented electrical steel sheet, thermal strain is imparted to the steel sheet after the insulating coating formation process.

[0088] Specifically, after coating a coating liquid containing an insulating coating component having a tension imparting function on the steel sheet after final annealing, annealing is carried out which combines the baking of the coating and the flattening of the steel sheet. After the annealing for this baking and flattening, thermal strain is imparted to the steel sheet.

[0089] The thermal strain is set as a linear thermal strain extending in a direction of 80 to 100° with respect to the rolling direction of the oriented electrical steel sheet. A plurality of such thermal strains exist periodically in the rolling direction, and the interval in the rolling direction between adjacent thermal strain imparting regions is 1.0 to 20.0 mm. It is preferable that the thermal strains are substantially parallel to each other and the intervals in their rolling directions are equally spaced. The interval of the thermal strain application regions is the distance from the center of the thermal strain application region to the center of the adjacent thermal strain application region. The thermal strain can be imparted by laser, electron beam, or plasma irradiation as described later.

[0090] The effect of reducing abnormal eddy current loss brought about by the above-mentioned flat grains is exerted even when magnetic domain control is performed by forming a region given thermal strain. Furthermore, it has a secondary effect in the following thermal strain-imparting type of magnetic domain control.

[0091] That is, oxides are formed as uniformly as possible from the surface in a constant thickness region over the entire in-plane region of the steel sheet, making the tone distribution on the surface more uniform. In addition, the oxides generated on the surface layer and the surface of the steel sheet are formed in a constant thickness direction, increasing the emissivity over the entire in-plane region of the steel sheet and making it uniform. That is, when thermal strain is imparted, energy is easily and uniformly absorbed by laser or electron beam irradiation, thereby reducing iron loss and deviation. As a result, the magnetic domain width can be reduced at each part of the steel sheet, and the iron loss can be reduced.

[0092] In other words, in a steel sheet in which flat grains are controlled, by performing magnetic domain control based on the imparting of thermal strain, a higher effect can be obtained through a synergistic effect compared to the case of performing each individually.

[0093] The chemical composition of the base steel sheet (silicon steel sheet) is not limited as long as it is equivalent to the base steel sheet of a known grain-oriented electrical steel sheet. For example, the compositions within the ranges described below can be cited.

[0094] The chemical composition of the base steel sheet contains Si: 2.00 to 6.00% by mass, and the balance contains Fe and impurities. This chemical composition is for controlling the crystal orientation to a Goss texture formed by the aggregation of {110}<001> orientations, ensuring good magnetic properties. For other elements, there is no particular limitation, and they can be replaced with Fe and contain known elements within a known range. The representative content ranges (by mass) of representative elements other than Si are as follows.

[0095] C: 0 to 0.0050%

[0096] Mn: 0 to 1.0%

[0097] S: 0 to 0.0150%

[0098] Se: 0 to 0.0150%

[0099] Al: 0 to 0.0650%

[0100] N: 0 to 0.0050%

[0101] Cu: 0 to 0.40%

[0102] Bi: 0 to 0.010%

[0103] B: 0 to 0.080%

[0104] P: 0 to 0.50%

[0105] Ti: 0 to 0.0150%

[0106] Sn: 0 to 0.10%

[0107] Sb: 0 to 0.10%

[0108] Cr: 0 to 0.30%

[0109] Ni: 0 to 1.0%

[0110] Nb: 0 to 0.030%

[0111] V: 0 to 0.030%

[0112] Mo: 0 to 0.030%

[0113] Ta: 0 to 0.030%

[0114] W: 0 to 0.030%

[0115] These selected elements may be contained according to their purpose, so there is no need to limit the lower limit value, and they may also be substantially not contained. In addition, even if these selected elements are contained as impurities, the effects of the present invention will not be impaired. Impurities refer to elements inadvertently contained. In the industrial production of the base metal steel sheet, they refer to elements mixed in from ores, waste materials, or manufacturing environments as raw materials.

[0116] The chemical composition of the silicon steel sheet is a solution obtained by acid-decomposing the base metal steel sheet with hydrochloric acid or the like. A standard curve of a solution of each element with a known concentration is previously obtained by ICP (inductively coupled plasma) analysis thereon, and the solution obtained above is analyzed thereon to quantitatively determine the contained elements.

[0117] In the case of an oriented electrical steel sheet having an oxide layer and an insulating coating layer formed on the surface of the base metal steel sheet (silicon steel sheet), the measurement is performed after removing the oxide layer and the insulating coating layer.

[0118] The insulating coating layer can be removed by immersing the oriented electrical steel sheet containing 30 to 50% by mass of NaOH and 50 to 70% by mass of H2O in an aqueous sodium hydroxide solution at 80 to 90 °C for 7 to 10 minutes.

[0119] In addition, the oriented electrical steel sheet from which the insulating coating layer has been removed is washed with water, and after washing, it is dried with a warm air blower for less than 1 minute. The oxide layer can be removed by immersing the dried oriented electrical steel sheet (oriented electrical steel sheet without an insulating coating layer) in an aqueous hydrochloric acid solution containing 10% by mass of HCl at 80 to 90 °C for 1 to 10 minutes.

[0120] The impregnated base metal steel plate is washed with water. After washing, it is dried with a warm air blower for less than 1 minute, whereby the base metal steel plate (silicon steel plate) can be taken out from the grain-oriented electrical steel sheet having an oxide layer and an insulating coating layer.

[0121] (Plate thickness)

[0122] The plate thickness of the silicon steel plate (base metal steel plate) of the grain-oriented electrical steel sheet of the present embodiment is not limited, but in consideration of its iron loss value, it is preferably 0.15 to 0.35 mm. If it exceeds 0.35 mm, the plate thickness is large, so the above-mentioned classical eddy current loss becomes large and the iron loss becomes large. On the other hand, if the plate thickness is less than 0.15 mm, the rolling efficiency decreases, which is disadvantageous in terms of productivity and cost.

[0123] [Oxide layer]

[0124] In the grain-oriented electrical steel sheet of the present embodiment, an oxide layer containing one or more of Mg, Al, and Si is formed on the surface of the silicon steel plate (base metal steel plate).

[0125] This oxide layer is formed by a solid-phase reaction between Mg and / or Al contained in the annealing separator and the Si-based pre-oxide formed on the steel plate surface during final annealing. For example, when using an annealing separator containing MgO, as the oxide layer, a layer mainly forming a forsterite (Mg2SiO4) coating is formed. In addition, AlN contained as an inhibitor in the steel is oxidized by oxygen in the annealing atmosphere on the surface of the silicon steel plate in the latter half of final annealing. Along with this, spinel (MgAl2O4) or alumina (Al2O3) or mullite (2SiO2·3Al2O3) is generated. When using an annealing separator substantially containing only MgO, substantially spinel (MgAl2O4) is generated.

[0126] By covering the surface of the flat grains with this oxide layer, the effect of improving the adhesion to the insulating coating layer applied thereon can be obtained. In the case of obtaining a sufficient effect, the coverage rate of the oxide layer in the flat grains is preferably 50% or more.

[0127] The coverage rate can be obtained by the following method. That is, the existence of flat grains is specified by EBSD according to the above-mentioned procedure. On this basis, focus on the FE-SEM image of each flat grain or the elemental analysis image obtained by elemental analysis such as EDS with FE-SEM. Measure the length of the oxide layer containing one or more of Mg, Al, and Si in the projection part from the interface between the insulating coating layer and the flat grain or from the surface side of the flat grain to the inside of the steel plate in the flat grain. As the interface length between the oxide layer or the insulating coating layer and the flat grain, for a quantity of 1000 μm, the length rate of the existence of the oxide layer is obtained as a percentage.

[0128] For example, if it is in the Figure 3 state as such, the coverage rate (%) can be obtained by (A1 + A2 + A3) / (a1 + a2 + a3)×100.

[0129] [Insulating coating layer]

[0130] In the grain-oriented electrical steel sheet of the present embodiment, an insulating coating layer is formed on the surface of the oxide layer (as the upper layer). This insulating coating layer is essential when using the grain-oriented electrical steel sheet as a transformer. The grain-oriented electrical steel sheet is used in a laminated manner when used as a transformer. If the laminated steel sheets (silicon steel sheets) are short-circuited, eddy currents will be generated in the transformer core, which is the main cause of the increase in core iron loss. Therefore, a layer of insulating coating is formed on the surface of the steel sheet to reduce the core iron loss of the transformer by imparting electrical insulation. 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, the abnormal eddy current loss can be reduced, and further the iron loss can be reduced.

[0131] In addition, regarding the insulating coating of the grain-oriented electrical steel sheet, in addition to the electrical insulation as described above, various characteristics required during core manufacturing such as corrosion resistance, heat resistance, and slidability are also required. Based on these requirements, for example, a coating type mainly composed of phosphate and colloidal silica is used as the insulating coating. In addition, for the purpose of applying a large tension to the steel sheet, a coating mainly composed of aluminum borate or a coating containing aluminum borate and silica may also be used. Any coating can be a well-known coating formed by coating a coating liquid in which the components contained therein are dissolved or dispersed on the surface of the oxide layer and baking.

[0132] <Manufacturing method>

[0133] As long as the grain-oriented electrical steel sheet of the present embodiment has the above characteristics regardless of the manufacturing method, its effects can be obtained. However, as long as it is a manufacturing method including the following processes, it can be stably manufactured, so it is preferred.

[0134] (I) A hot rolling process in which a slab is heated and hot rolled to form a hot rolled sheet;

[0135] (II) A hot rolled sheet annealing process in which the hot rolled sheet after the above hot rolling process is annealed;

[0136] (III) A pickling process in which the hot rolled sheet after the above hot rolled sheet annealing process is pickled;

[0137] (IV) A cold rolling process in which the hot rolled sheet after the above pickling process is cold rolled to form a cold rolled sheet;

[0138] (V) A grinding process for grinding the surface of the cold-rolled sheet after the above-mentioned cold-rolling process;

[0139] (VI) A contacting process for bringing the cold-rolled sheet after the above-mentioned grinding process into contact with an aqueous solution having a pH of 4.0 to 10.0;

[0140] (VII) A decarburizing annealing process for performing decarburizing annealing on the cold-rolled sheet after the above-mentioned contacting process;

[0141] (VIII) After applying an annealing parting agent to the cold-rolled sheet after the above-mentioned decarburizing annealing process, performing final annealing to form an oxide layer containing one or more oxides of Mg, Al, and Si on the surface of the cold-rolled sheet that has become a silicon steel sheet (base material steel sheet), the final annealing process;

[0142] (IX) Forming an insulating coating layer on the surface of the oxide layer after the above-mentioned final annealing process to obtain an insulating coating formation process for an oriented electrical steel sheet having the above-mentioned silicon steel sheet, the above-mentioned oxide layer, and the above-mentioned insulating coating layer; and

[0143] (X) Irradiating the surface of the oriented electrical steel sheet after the above-mentioned insulating coating formation process with a laser, an electron beam, or a plasma to form a plurality of linear thermal strains extending in a direction at an angle of 80 to 100° with respect to the rolling direction at intervals of 1.0 to 20.0 mm in the rolling direction on the surface of the silicon steel sheet, the magnetic domain control process.

[0144] In addition, the method for manufacturing an oriented electrical steel sheet according to the present embodiment may further include any one or more of the following processes.

[0145] (XI) A nitriding treatment process for increasing the nitrogen content of the cold-rolled sheet.

[0146] Among them, the method for manufacturing an oriented electrical steel sheet according to the present embodiment is characterized by the grinding process, the contacting process, and the magnetic domain control process. On the other hand, the hot-rolling process, the hot-rolled sheet annealing process, the cold-rolling process, the decarburizing annealing process, the nitriding treatment process, the final annealing process, and the insulating coating formation process can be carried out under known conditions.

[0147] Hereinafter, preferred conditions will be described. For conditions not described, they can also be carried out under known conditions.

[0148] [Hot-rolling process]

[0149] In the hot-rolling process, a slab having a predetermined chemical composition (the chemical composition corresponding to the chemical composition of the silicon steel sheet of the oriented electrical steel sheet according to the present embodiment) is heated and hot-rolled to produce a hot-rolled sheet.

[0150] The conditions are not limited, but the slab heating temperature is, for example, 1000 to 1400 °C.

[0151] The chemical composition of the slab for hot rolling may be determined according to the chemical composition desired to obtain a grain-oriented electrical steel sheet, taking into account the changes in the chemical composition in each process.

[0152] In the case of obtaining the chemical composition of the silicon steel sheet of the grain-oriented electrical steel sheet of the above preferred embodiment, for example, a slab having the following chemical composition is preferably used.

[0153] By mass%, it contains C: 0.040 to 0.100%, Si: 2.00 to 4.00%. In addition, as inhibitors, Al, Mn, Se, S, B, N, etc. are contained within a specified range so as to form AlN, MnS, MnSe, BN. Furthermore, a chemical composition containing elements such as Cu, Sn, Cr, Ni, Mo, Nb, Bi, Sb, etc. is exemplified as needed.

[0154] The method for obtaining the slab is not limited. For example, molten steel having a specified chemical composition is melted and used to manufacture it. The slab can be manufactured by continuous casting, or an ingot can be manufactured using molten steel and the ingot can be subjected to blooming rolling to manufacture the slab. In addition, the slab can also be manufactured by other methods.

[0155] The thickness of the slab is not particularly limited, for example, it is 150 to 350 mm. The thickness of the slab is preferably 220 to 280 mm. As the slab, a so-called thin slab having a thickness of 10 to 70 mm can also be used.

[0156] A so-called hot-rolled sheet (hot-rolled steel sheet) is obtained by hot rolling. The sheet thickness (finished sheet thickness) of the hot-rolled sheet is not particularly limited. However, it is known that annealing the hot-rolled sheet and pickling it followed by cold rolling, and the so-called cold rolling ratio affects the magnetic properties of the grain-oriented electrical steel sheet. The sheet thickness of the hot-rolled sheet is selected in the form of adding the necessary cold rolling ratio to 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 the range of 2.0 to 4.0 mm.

[0157] [Hot-rolled sheet annealing process]

[0158] In the hot-rolled sheet annealing process, the hot-rolled sheet after the hot rolling process is annealed. By performing such an annealing treatment, recrystallization occurs in the steel sheet structure, and good magnetic properties can be achieved.

[0159] In the annealing process of the hot-rolled sheet in this embodiment, the hot-rolled sheet manufactured through the hot-rolling process can be annealed according to a well-known method. The method of heating the hot-rolled sheet during annealing is not particularly limited, and a well-known heating method can be adopted. For example, it can be so-called continuous annealing, or the hot-rolled sheet can be batch-annealed in the form of a coil. In addition, the annealing conditions are not particularly limited. 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, but it is preferred to suppress the oxidation of the steel sheet, and it is preferably carried out in a non-oxidizing atmosphere such as nitrogen, argon, or hydrogen.

[0160] [Pickling process]

[0161] In the pickling process, the hot-rolled sheet after the hot-rolled sheet annealing process is pickled to remove the scale (oxide) generated on the surface through hot rolling and hot-rolled sheet annealing. In the pickling process of this embodiment, a well-known method is used. As the pickling solution, well-known acids such as hydrochloric acid, sulfuric acid, and nitric acid can be used. In addition, well-known pickling inhibitors, pickling accelerators, etc. can also be added to the pickling solution as needed. Furthermore, before bringing the steel sheet into contact with the pickling solution, the pickling solution is allowed to penetrate into the interface between the scale and the steel sheet. For the purpose of improving the pickling efficiency, physical treatments such as shot peening of the steel sheet can also be carried out before pickling.

[0162] [Cold rolling process]

[0163] In the cold rolling process, the hot-rolled sheet after the hot-rolled sheet annealing process is pickled and cold-rolled to produce a cold-rolled sheet. The cold rolling can be single-pass (a series without intermediate annealing) cold rolling, or intermediate annealing can be interrupted before the final pass of the cold rolling process, and at least one or two or more intermediate annealings can be carried out to perform multi-pass cold rolling with intermediate annealing in between.

[0164] The cold rolling conditions can be in accordance with well-known methods. The cold rolling rate in the grain-oriented electrical steel sheet has a great influence on its magnetic properties. In particular, the influence of the final reduction rate is large, and the final reduction rate can be in the range of 80 to 95%. The final reduction rate is the cumulative reduction rate of cold rolling. In the case of performing intermediate annealing, it is the cumulative reduction rate of cold rolling after the final intermediate annealing.

[0165] When performing intermediate annealing, for example, it is held at a temperature of 800 to 1200 °C for 5 to 180 seconds. The annealing atmosphere is not particularly limited. In order to prevent the oxidation of the steel sheet, it is preferably carried out in a non-oxidizing atmosphere such as nitrogen, argon, or hydrogen. In addition, as the annealing method, either so-called continuous annealing or batch annealing in the form of a coil can be used, or other methods can also be used. Considering the manufacturing cost, the number of intermediate annealings is preferably within 3 times.

[0166] [Grinding process]

[0167] In the grinding process, the surface of the cold-rolled sheet after the cold rolling process is ground. At this time, grinding is performed using abrasive grains having a Knoop hardness of 1000 or more, or abrasive paper, a roll, or a brush to which the abrasive grains are fixed. In the case of grinding a rolled cold-rolled sheet, it is preferable to perform grinding continuously using a through-feed line in terms of productivity and quality. In this case, abrasive grains fixed in a brush are generally mainly used. Of course, a plate-shaped cold-rolled sheet may be used instead of a coil, and in this case, grinding may also be performed using abrasive paper or the like.

[0168] As described above, by allowing the inhibitor (precipitates present at the crystal grain boundaries of crystals such as AlN) to exist up to a high temperature as much as possible during final annealing, only the crystal grains having a crystal orientation closer to the ideal Goss orientation grow, and the magnetic flux density is increased.

[0169] However, although the size of the inhibitor is very small, such as several tens to about 100 nm, there is a size distribution. In the case where there is a size distribution, the small-sized inhibitor starts to decompose at a low temperature. In this case, the secondary recrystallization of only the grains close to the Goss orientation (ideal Goss orientation) becomes difficult, and it is difficult to increase the magnetic flux density. On the other hand, it is extremely difficult industrially to control the size of the inhibitor to a constant preferred size (reduce the size difference).

[0170] On the contrary, by suppressing the decomposition and oxidation of the inhibitor, if the inhibitor can be made to exist up to a high temperature, secondary recrystallization of only the grains closer to the Goss orientation can occur. In addition, it is known that the aforementioned Si-based pre-oxide formed on the base steel plate (cold-rolled sheet that becomes the base steel plate) in the decarburizing annealing process helps to suppress the decomposition and oxidation of the inhibitor.

[0171] However, this Si-based pre-oxide is easily affected by the previous process of the decarburizing annealing process, and the formation state on each part of the steel plate surface tends to become uneven. If the formation state is uneven, the suppression effect of the decomposition and oxidation of the inhibitor varies depending on the part within the steel plate surface, and the target effect cannot be obtained.

[0172] Therefore, in the method for manufacturing an oriented electrical steel sheet according to the present embodiment, in order to make the formation state of the oxide layer after final annealing as uniform as possible in a constant thickness region on the surface of the steel plate, Fe-based oxides, oily agents, extreme pressure additives, etc., which are reactants with the steel plate surface and are unevenly formed on the steel plate surface along with the implementation of cold rolling or the like that hinders the uniform formation of these oxide layers, are removed from the steel plate surface by grinding the steel plate surface before decarburizing annealing.

[0173] Specifically, at least one surface of a steel sheet is ground using abrasive grains having a Knoop hardness of 1000 or more, or abrasive paper, a roll, or a brush on which the abrasive grains are fixed, and accordingly, an Fe-based oxide film and reaction products are removed from the surface of the steel sheet. When the Knoop hardness is less than 1000, the hardness of the abrasive grains is insufficient with respect to the steel sheet, so that grinding is difficult. Or the grinding efficiency is reduced. In addition, if the maximum particle size of the abrasive grains is less than 30 μm, the particle size of the abrasive grains is relatively small with respect to the surface roughness of the steel sheet, so that grinding is difficult, or the grinding efficiency is reduced, and thus it is not preferred. On the other hand, if the maximum particle size exceeds 300 μm, the particle size of the abrasive grains is relatively too large with respect to the surface roughness of the steel sheet, so that surface scratches are likely to be conspicuous during grinding, and the appearance quality of the product is reduced, and thus it is not preferred. The upper limit of the Knoop hardness is not limited, but hard abrasive grains are liable to become brittle and liable to cause obstacles such as poor grinding due to continuous use of abrasive paper, rolls, brushes, etc. containing the abrasive grains, and thus it is preferably 8000 or less, more preferably 5000 or less. As the abrasive grains, alumina (Knoop hardness of about 2000), silicon carbide (Knoop hardness of about 2500), boron nitride (Knoop hardness of about 5000), diamond (Knoop hardness of about 7000), etc. are mainly used.

[0174] Specifically, taking the case of using a brush roll equipped with abrasive grains as an example, the process of grinding cold-rolled steel sheets will be described. The brush roll has a resin lining on the surface of a metal roll, and a roll in which the above-mentioned abrasive grains are embedded in fibers made of acrylic resin or the like is implanted in a hairy form on the surface of the resin layer on the roll surface. If it is described by taking the application in a continuous sheet passing line as an example, when grinding a steel sheet with a brush roll, the sheet passing speed of the steel sheet is in the range of about 20 to 200 meters per minute (mpm). While moving the steel sheet, at the position where the steel sheet contacts the brush roll, the brush roll rotating in the direction opposite to the sheet passing direction of the steel sheet contacts the steel sheet to grind the steel sheet. When grinding the steel sheet with a brush roll, the steel sheet is clamped by the brush roll and an idler roll, and further, the brush roll is pressed and pressed into grinding toward the idler roll side with respect to the sheet passing line (pass line). The amount of press-down at this time is preferably about 1.0 to 5.0 mm. The brush roll diameter generally uses a roll of about 200 to 500 mm. This is because if it is too small, the brush or abrasive grains will wear quickly, and if it is too large, the metal roll will become too large and the equipment scale will become large. The brush rotates in the direction opposite to the sheet passing direction of the steel sheet as described above for grinding. The sheet passing speed of the steel sheet is in the range of 20 to 200 mpm as described above, but in this case, the rotational speed of the brush is approximately 500 to 2000 mpm, so it is suitable to make the grinding amount within a specified range. If the rotational speed is small, the grinding amount will decrease. If the amount of press-down is increased to increase the grinding amount, the brush roll will be opposed to the sheet passing of the steel sheet, so it is easy to generate a so-called "chatter" in which the steel sheet cannot pass smoothly due to the frictional force between the steel sheet and the brush roll and the steel sheet jerks. "Chatter" makes the grinding on the surface of the steel sheet uneven, so it is a phenomenon that should be avoided extremely unfavorably. In addition, if the rotational speed of the brush roll is greater than 2000 mpm, the frictional force between the brush roll and the sheet passing of the steel sheet will become too large, not only generating the above-mentioned "chatter", but also overloading the motor driving the brush roll, so it is not preferable.

[0175] In addition, in order to sufficiently remove the Fe-based oxide film and reactants unevenly formed on the surface of the cold-rolled steel sheet, the grinding amount is 0.10 g / m on at least one surface 2 or more. The above-mentioned Fe-based oxide film and reactants are sufficiently removed from the surface of the steel sheet. On the other hand, the service life of the abrasive grains becomes short, and residues are significantly generated during grinding. This treatment takes time and becomes the cause of defects on the surface of the steel sheet caused by press-in or the like. Therefore, the grinding amount is 3.00 g / m 2 or less.

[0176] The grinding amount can be confirmed based on the weight difference of the steel sheet before and after grinding. The grinding amount is the grinding amount per single side. In the case of grinding both sides, it is obtained as the grinding amount per two sides, and for convenience, this value is obtained as half. From the viewpoint of removing the Fe-based oxide film and reactants from the entire surface of the steel sheet, the preferable range of the grinding amount is 0.30 g / m2 3.00 g / m or more 2 and below.

[0177] [Contact process]

[0178] In the contact process, after the grinding process and before the decarburizing annealing process, the surface of the cold-rolled sheet is brought into contact with an aqueous solution having a pH of 4.0 to 10.0. Thereby, abrasive grains attached to the surface of the steel sheet and steel residues generated during grinding are removed. As the above aqueous solution, ion-exchanged water may also be used. In addition, they may contain minerals such as Ca and Mg, and may also contain carbonic acid and silicic acid as counter ions. In addition, a substance obtained by adjusting the pH with an alkali metal, an alkaline earth metal, etc. by adding an acid selected from sulfuric acid, nitric acid, phosphoric acid, carbonic acid, carboxylic acid, phosphonic acid, etc. at about 0.01 wt% may also be used. In particular, carboxylic acid and phosphonic acid have a high effect of removing abrasive grains and residues from the steel sheet. In the case of ion-exchanged water, from the viewpoint of preventing melting loss, its conductivity is preferably 0.1 to 10 μS / cm.

[0179] If the pH is less than 4.0, melting loss of the steel sheet occurs due to etching of the steel sheet surface by the acidic aqueous solution. If the pH exceeds 10.0, oxidation of the metal surface after grinding is promoted by the action of the alkaline aqueous solution. Therefore, although the Fe-based oxide unevenly formed on the steel sheet surface is removed in the grinding process, its effect is reduced. In this case, the initial target effect of uniformly forming the oxide layer and oxide particles after final annealing cannot be sufficiently obtained.

[0180] For the above purposes, the contact time is preferably 0.1 to 60 seconds, more preferably 1 to 60 seconds. Even more preferably 5 to 60 seconds. The flow rate of the aqueous solution is preferably 1 to 100 L / minute.

[0181] In addition, by performing the contact process, abrasive grains and residues can be removed from the steel sheet surface, and factors that hinder the uniform formation of the oxide layer and oxide particles after final annealing can be avoided.

[0182] In the case of performing the contact process, in view of the above purposes, it is performed after the grinding process.

[0183] In the grinding process, the surface of the cold-rolled sheet may also be brought into contact with an aqueous solution. However, if the contact process is not performed after the grinding process, the above effects cannot be obtained.

[0184] [Decarburizing annealing process]

[0185] In the decarburizing annealing process, the cold-rolled sheet after the grinding process is subjected to decarburizing annealing. In this decarburizing annealing, C that has an adverse effect on magnetic properties is removed (decarburized) from the steel sheet, and the cold-rolled sheet undergoes primary recrystallization.

[0186] The decarburizing annealing conditions are not limited. However, as a nitrogen-hydrogen mixed atmosphere for decarburization, annealing is carried out in an atmosphere with an increased oxygen potential by humidification. In addition, it is necessary to form a primary recrystallized structure at the same time. Therefore, from the viewpoints of the annealing temperature required for recrystallization and the oxygen potential at which decarburization can occur at this annealing temperature, the humidification temperature (dew point) is determined. The annealing temperature is about 700 to 900 °C, and annealing is usually carried out in a continuous annealing process, so soaking is carried out for about 60 seconds. As described above, annealing is carried out in a humidified atmosphere with a high oxygen potential for decarburization. Therefore, it is known that Si contained in steel forms layered oxides on the surface of the steel sheet and oxide particles are formed inside the steel sheet (hereinafter referred to as the same Si-based pre-oxides).

[0187] [Nitriding treatment process]

[0188] In the nitriding treatment process, the amount of nitride is increased by increasing the nitrogen content of the steel sheet, thereby promoting the secondary recrystallization of grains closer to the Goss orientation in the final annealing process. In the nitriding treatment process, it is preferable that the nitrogen content of the steel sheet after nitriding treatment is 0.015 to 0.050 mass%. The method of nitriding treatment is not limited and may be a known method.

[0189] The nitriding treatment process is not essential and may be omitted. When nitriding treatment is carried out, it is preferably carried out between the decarburizing annealing process and the final annealing process.

[0190] [Final annealing process]

[0191] In the final annealing process, an annealing release agent is coated on the cold-rolled sheet after the decarburizing annealing process (after the nitriding treatment process when nitriding treatment is carried out), and final annealing is carried out to form an oxide layer containing one or more of Mg, Al, and Si on the surface of the cold-rolled sheet that becomes the base steel sheet (silicon steel sheet).

[0192] Final annealing is usually carried out by batch annealing with the steel sheet coiled, due to the long annealing time. In order to raise the temperature of the steel sheet to about 1200 °C, an annealing separating agent is coated in a way that the coiled steel sheet is not baked. MgO is usually mainly used as the annealing separating agent. After coating such an annealing separating agent and then carrying out final annealing, a solid-phase reaction occurs between Mg contained in the annealing separating agent and the Si-based pre-oxide formed on the surface of the steel sheet in the decarburizing annealing process, forming an oxide layer containing one or more of Mg and Si on the surface of the cold-rolled sheet. For example, in the case of using an annealing separating agent containing MgO, a layer mainly forming a forsterite (Mg2SiO4) coating film is formed as the oxide layer. In addition, AlN contained as an inhibitor in the steel is oxidized by oxygen in the annealing atmosphere on the surface of the steel sheet in the latter half of the final annealing, and at this time, it forms as spinel (MgAl2O4) or alumina (Al2O3) or mullite (2SiO2·3Al2O3). In the case of using an annealing separating agent substantially containing only MgO, approximately spinel (MgAl2O4) is generated.

[0193] In addition, in the final annealing process, the primary recrystallized grains obtained in the decarburizing annealing process by heating the steel sheet are subjected to secondary recrystallization to obtain grains with a Goss orientation, and are held at a specified time at an annealing temperature close to 1200 °C, thereby removing (purifying) precipitates in the steel such as nitrides (e.g., AlN) and sulfides (e.g., MnS) that have ended their role as inhibitors in a manner that does not adversely affect the magnetic properties.

[0194] In the method for manufacturing an oriented electrical steel sheet of the present embodiment, in the cold-rolled sheet supplied for final annealing, the size of the inhibitor is larger than usual and is uniformly controlled. Therefore, only secondary recrystallization of grains with a Goss orientation (grains having an orientation close to the Goss orientation) occurs.

[0195] The conditions for final annealing are not limited. For example, the temperature is raised in the range from room temperature to 10 - 100 °C / hour, and usually in the temperature range of 900 - 1000 °C where secondary recrystallization of the Goss orientation occurs, the temperature is raised at 5 - 20 °C / hour to promote the preferential growth (secondary recrystallization) of the Goss orientation. Then, as described above, the purification of the inhibitor that has ended its role is carried out near 1200 °C (e.g., 1150 - 1250 °C). Then, it is slowly cooled in a non-oxidizing atmosphere such as hydrogen or nitrogen, and the coil is taken out of the furnace.

[0196] [Insulating coating film forming process]

[0197] In a coil after the final annealing process, an insulating coating layer is formed on the surface portion that becomes the steel sheet during the subsequent insulating coating formation process. In a grain-oriented electrical steel sheet, it is laminated for use in transformer manufacturing. However, if there is a short circuit between the laminations when the transformer is operating, the iron loss increases, and sometimes the transformer may burn out. Therefore, the insulating coating formation process is an important process. The annealing release agent on the coil after the final annealing process is removed by water washing and pickling, and an insulating coating layer is formed on the surface of the oxide layer formed on the steel sheet surface.

[0198] For example, the insulating coating layer can be formed by coating a coating solution containing phosphoric acid or phosphate, colloidal silica, and chromic anhydride or chromate on the cold-rolled sheet (base steel sheet + oxide layer) after final annealing, and baking and drying at 300 - 950 °C for 10 seconds or more. The atmosphere during baking is not particularly limited, but it is preferably to inhibit the oxidation of the steel sheet, and it is preferably carried out in a non-oxidizing atmosphere such as nitrogen, argon, or hydrogen. In addition, as the coating type, a coating solution mainly composed of boric acid and alumina sol or a coating solution mainly composed of boric acid and aluminosilicate (such as kaolin minerals) other than the above phosphates can also be used to form an insulating coating mainly composed of aluminum borate. By applying aluminum borate, a large tension can be imparted to the steel sheet, so the iron loss can be reduced. In addition, in this process, it also plays a role in flattening the steel sheet that was in the coil shape during the batch annealing in the above final annealing through continuous annealing. That is, the baking of the insulating coating and the continuous annealing of the steel sheet in the coil shape are carried out while applying a constant tension at about 800 °C to obtain a flat steel sheet. Therefore, it is sometimes also called the flattening annealing process.

[0199] Through these processes, a grain-oriented electrical steel sheet with a base steel sheet (silicon steel sheet), an oxide layer, and an insulating coating layer can be obtained.

[0200] [Magnetic domain control process]

[0201] In the magnetic domain control process, a laser, electron beam, or plasma is irradiated onto the grain-oriented electrical steel sheet after the insulating coating formation process, and a plurality of linear thermal strains extending in a direction at an angle of 80 - 100° with respect to the rolling direction are formed on the surface of the base steel sheet at intervals of 1.0 - 20.0 mm in the rolling direction.

[0202] By forming the above-mentioned thermal strain imparting regions on the surface of the grain-oriented electrical steel sheet, the magnetic domains are subdivided and the iron loss is reduced. When the direction, interval, etc. of the thermal strain are outside the above range, sufficient effects cannot be obtained.

[0203] Thermal strain can be imparted by irradiating a base metal steel plate with a laser, an electron beam, a plasma, etc. under the condition that the base metal steel plate does not melt. The conditions are not limited. For example, if laser irradiation is used, continuous wave laser or pulsed laser is used as the laser for irradiation. For example, as described in Patent Document 1, it is preferable to control the average energy density within the range of 0.8 to 2.0 mJ / mm 2 range.

[0204] Examples

[0205] (Example 1)

[0206] A steel slab containing Si: 3.25% by mass, Mn: 0.13% by mass, S: 0.006% by mass, C: 0.050% by mass, acid-soluble Al: 0.025% by mass, and N: 0.007% by mass was continuously cast to obtain a slab with a thickness of 300 mm.

[0207] After heating the slab in an electric furnace adjusted to a nitrogen atmosphere at 1150°C for 60 minutes, a rough hot-rolled steel plate with a thickness of 40 mm was obtained, and then further hot-rolled to obtain a hot-rolled plate with a thickness of 2.3 mm.

[0208] Then, it was heated in a continuous annealing furnace adjusted to a nitrogen atmosphere at 1100°C for 60 seconds and then cooled to perform hot-rolled plate annealing.

[0209] The obtained steel plate (hot-rolled plate) was pickled with 10% hydrochloric acid to remove the scale on the steel plate.

[0210] Then, cold rolling was performed to obtain a cold-rolled plate with a thickness of 0.22 mm.

[0211] The surface of the obtained cold-rolled plate was ground using various abrasive brushes described in Table 1. After grinding, ion-exchanged water with a pH of 2.5 to 12.0 was brought into contact with the surface. Among them, for comparison, some steel plates were steel plates without grinding and steel plates not in contact with ion-exchanged water after grinding. During contact, the contact time was 5 seconds, and the flow rate of the aqueous liquid was 10 L / minute.

[0212] For the steel plates that had been ground and brought into contact with the aqueous liquid (in the case where neither was performed, it was the cold-rolled plate after cold rolling, or in the case where contact with the aqueous liquid was not performed, it was the cold-rolled plate after the grinding process), samples with a width of 1.0 m and a length of 1.0 m were taken, and the appearance of both sides was evaluated.

[0213] The judgment criteria are as follows:

[0214] 5: Very beautiful (completely no stripe scratches in the through-plate direction)

[0215] 4: Beautiful (several stripe scratches in the through-plate direction)

[0216] 3: There are partial stripe scratches (less than 20 stripe scratches in the through-plate direction)

[0217] 1: The entire surface has stripe scratches or attachments with unevenness

[0218] Regarding examples of poor appearance (evaluation: 1), subsequent evaluations are not conducted except for some cases.

[0219] In addition, for steel plates that have been ground and contacted with aqueous liquid (in the case where neither has been performed, it is the cold-rolled plate after cold rolling, or in the case where there is no contact with aqueous liquid, it is the cold-rolled plate after the grinding process), decarburizing annealing is performed under the following conditions. The annealing atmosphere is set to a nitrogen 50% + hydrogen 50% atmosphere, and the oxygen potential is set to PH2O / PH2 = 0.30. The oxygen potential is humidified before introducing the atmosphere into the furnace to adjust the moisture content. In this atmosphere, soaking is carried out at 850 °C for 60 seconds to perform decarburizing annealing.

[0220] Then, nitriding treatment is carried out by soaking at 750 °C for 30 seconds in a nitrogen-hydrogen-ammonia atmosphere. The ammonia concentration is adjusted so that the nitrogen content of the steel plate after nitriding treatment becomes N: 0.020 mass%.

[0221] Then, the aqueous slurry of the annealing parting agent mainly composed of MgO is adjusted, and the annealing parting agent is coated on both sides of the steel plate so that the dried adhesion amount per single side becomes 6 g / m 2 and dried. At this time, as the composition of the annealing parting agent, TiO2: 5 mass parts is added relative to 100 mass parts of MgO, and FeCl2 is added in such a way that when it is Cl, it becomes 0.020 mass%.

[0222] Then, as the final annealing, the specimen is placed in a batch annealing furnace, and the temperature is raised at an average heating rate of 20 °C / hour in a nitrogen 50% + hydrogen 50% atmosphere. After raising the temperature to 1200 °C, the atmosphere is switched to hydrogen 100%, soaking is carried out for 20 hours, and then the temperature is lowered.

[0223] After the final annealing is completed, the steel plate is taken out of the furnace and washed with water to remove the annealing parting agent. At this time, a glass coating film in which secondary recrystallization is completed and contains forsterite, and an oxide layer containing granular spinel (MgAl2O4), alumina (Al2O3) and / or mullite formed between the glass coating film and the steel plate are formed on the surface of the steel plate (silicon steel plate).

[0224] Next, on this steel plate (a steel plate in which a glass coating film as an oxide layer is formed on the surface of the silicon steel plate as the base material steel plate), a liquid medicine containing an insulating coating film component is coated. The insulating coating film component contains aluminum phosphate, colloidal silica and chromic anhydride, and is heated to 800 °C and held for 30 seconds in a nitrogen atmosphere to perform baking. At this time, the adhesion amount of the insulating coating film layer per single side is 4.8 g / m 2Thus, an oriented electromagnetic steel sheet is obtained.

[0225] The surface of the obtained oriented electromagnetic steel sheet (having a silicon steel sheet, a glass coating film (oxide layer), and an insulating coating film layer) is irradiated with a laser. At this time, a fiber laser with a laser output of 200 W is used, the laser irradiation diameter is adjusted to φ0.2 mm, and the irradiation energy density is adjusted to 1.5 mJ / mm 2 . In addition, the scanning direction is a direction 88° with respect to the steel sheet rolling direction, and the irradiation pitch (interval in the rolling direction of thermal strain) is 4.0 mm.

[0226] By the above method, the number density of one or more oxides of Mg, Al, Si with an equivalent circle diameter of 0.1 to 3.0 μm in the range of 5 μm in the plate thickness direction from the interface between the silicon steel sheet of the obtained oriented electromagnetic steel sheet and the oxide layer, the coverage rate of the oxide layer, and the evaluation of flat grains are carried out.

[0227] In this embodiment, one or more oxides of Mg, Al, Si with an equivalent circle diameter of 0.1 to 3.0 μm in the range of 5 μm in the plate thickness direction from the interface between the oxide layer are spinel (MgAl2O4), alumina (Al2O3), and mullite (2SiO2·3Al2O3), that is, oxides containing Mg, Al, and Si.

[0228] <Magnetic property measurement>

[0229] In addition, 10 sheets are taken from the obtained oriented electromagnetic steel sheet in the size of 500 × 500 mm in the plate width direction and the rolling direction, and the magnetic flux density (hereinafter referred to as B8) when excited with a magnetizing force of 800 A / m by the single-sheet magnetic property measurement method described in JIS-C-2556:2015 and the iron loss (hereinafter referred to as W17 / 50) at an excitation frequency of 50 Hz and an excitation magnetic flux density of 1.7 T are measured.

[0230] If B8 is 1.90 T or more and W17 / 50 is 0.73 W / kg or less, it is judged to have excellent magnetic properties.

[0231] <Adhesion>

[0232] In addition, a specimen of 300 mm in the rolling direction and 300 mm in the width direction is selected, the specimen is wound around a SUS304-made round bar with a diameter of 20 mm (φ20 mm), and after unwinding, the insulating coating film on the concave part on the inner side of the winding is observed, thereby evaluating the adhesion of the insulating coating film.

[0233] The judgment criteria are as follows.

[0234] G (GOOD): No film peeling

[0235] P (POOR): Partial film peeling

[0236] B (BAD): Whole-surface film peeling

[0237]

[0238]

[0239] Table 3

[0240]

[0241] As can be seen from Tables 1 to 3, in the examples of grinding the surface of the steel sheet and contacting it with the aqueous liquid under the conditions of the present invention, within a range of 5 μm in the plate thickness direction from the interface between the silicon steel sheet and the above oxide layer, there are oxides of one or more of Mg, Al, and Si with an equivalent circle diameter of 0.1 to 3.0 μm at a density of 0.010 to 0.200 per μm 2 The length of the grain boundaries of the flattened grains in the length of the interface between the silicon steel sheet and the oxide layer in the cross-section in the plate thickness direction is 50% or more. In addition, as a result, in these examples, the magnetic properties are excellent.

[0242] On the other hand, in the examples where contact with the specified aqueous liquid is not carried out or the grinding conditions are not preferable, the appearance that does not meet the usual requirements, or the oxides in the surface layer are not sufficiently formed or the flattened grains are not sufficiently formed. In addition, as a result, the magnetic properties are poor (the parts with poor appearance are not evaluated).

[0243] (Example 2)

[0244] Steel water and slab with the same composition as the steel used in Example 1 were used, and hot rolling, hot rolled sheet annealing, pickling, and cold rolling were carried out in the same manner as in Example 1 to produce a cold rolled sheet with a thickness of 0.22 mm.

[0245] The surface of the steel sheet was ground using a brush containing various abrasive grains described in Table 4, and then contacted with ion-exchanged water with a pH of 6.0. During contact, the contact time was 5 seconds and the flow rate of the aqueous liquid was 10 L / minute. Then, in the same manner as in Example 1, decarburization annealing, nitriding treatment, annealing release agent coating, final annealing were carried out, and after washing with water to remove the annealing release agent, an insulating film layer was formed to obtain an oriented electrical steel sheet.

[0246] The surface of the obtained oriented electrical steel sheet (having a silicon steel sheet, a glass film (oxide layer), and an insulating film layer) was irradiated with a laser. At this time, a fiber laser with a laser output of 200 W was used, the laser irradiation diameter φ was adjusted to 0.2 mm, and the irradiation energy density was adjusted to 1.8 mJ / mm 2In addition, the scanning direction is set to a direction of 75 to 105° with respect to the rolling direction of the steel plate, and the irradiation pitch (the pitch in the rolling direction of the thermal strain) is changed in the range of 0.5 to 25.0 mm.

[0247] Using the same method as in Example 1, evaluation was performed on the number density of one or more oxides of Mg, Al, and Si having an equivalent circle diameter in the range of 0.1 to 3.0 μm within 5 μm in the plate thickness direction from the interface with the oxide layer, the coverage rate of the oxide layer, and the flat grains in the silicon steel sheet of the obtained grain-oriented electrical steel sheet.

[0248] In this example, one or more oxides of Mg, Al, and Si having an equivalent circle diameter in the range of 0.1 to 3.0 μm within 5 μm in the plate thickness direction from the interface with the oxide layer are spinel (MgAl2O4), alumina (Al2O3), and mullite (2SiO2·3Al2O3), that is, oxides containing Mg, Al, and Si.

[0249] <Magnetic property measurement>

[0250] Evaluation was performed by the same method as in Example 1.

[0251] <Adhesion>

[0252] Measurement was performed by the same method as in Example 1.

[0253]

[0254]

[0255] Table 6

[0256]

[0257] As can be seen from Tables 4 to 6, when the laser irradiation conditions are outside the scope of the present invention, sufficiently low iron loss cannot be obtained.

[0258] Industrial applicability

[0259] According to the present invention, it is possible to provide a grain-oriented electrical steel sheet having excellent magnetic properties and a method for manufacturing the same. Therefore, the industrial utilization possibility is high.

[0260] Explanation of reference numerals

[0261] 1 Grain-oriented electrical steel sheet

[0262] 11 Silicon steel sheet

[0263] 21 Oxide layer

[0264] 31 Insulating coating layer

[0265] 101 oxide particles

[0266] 102 flat grains

Claims

1. An oriented electromagnetic steel sheet, characterized in that, comprising: a silicon steel sheet; an oxide layer formed on the surface of the silicon steel sheet and containing one or more oxides of Mg, Al, and Si; and an insulating coating layer formed on the surface of the oxide layer, Within a range of 5 μm in the thickness direction from the interface between the silicon steel sheet and the oxide layer in the silicon steel sheet, there is one or more oxides of Mg, Al, and Si with an equivalent circle diameter of 0.1 to 3.0 μm at a density of 0.010 to 0.200 per μm 2 and the density of the oxides is 0.010 to 0.200 per μm flat grains exist on the surface side of the silicon steel sheet, the average thickness of the flat grains in the direction perpendicular to the surface is 0.5 to 5.0 μm, the aspect ratio, which is the ratio of the grain width in the direction parallel to the surface to the average thickness, is 1.5 or more, and the deviation of the crystal orientation from the Goss orientation is 10° or more, in the cross-section in the plate thickness direction, the length of the grain boundaries of the flat grains in the length of the interface between the silicon steel sheet and the oxide layer is 50% or more, a plurality of linear thermal strains extending in a direction at an angle of 80 to 100° with respect to the rolling direction are formed on the surface of the silicon steel sheet at intervals of 1.0 to 20.0 mm with respect to the rolling direction.

2. The grain-oriented electrical steel sheet according to claim 1, wherein The average of the average thickness of the flat grains is 0.5 to 2.0 μm.

3. The oriented electromagnetic steel sheet according to claim 1 or 2, wherein On the surface of the flat grains constituting the interface, the coverage rate of the oxide layer is 50% or more.

4. A method for manufacturing an oriented electromagnetic steel sheet, characterized in that, comprising: a hot rolling process of heating a slab and performing hot rolling to produce a hot rolled sheet; a hot rolled sheet annealing process of annealing the hot rolled sheet after the hot rolling process; a pickling process of pickling the hot rolled sheet after the hot rolled sheet annealing process; a cold rolling process of cold rolling the hot rolled sheet after the pickling process to produce a cold rolled sheet; a grinding process of grinding the surface of the cold rolled sheet after the cold rolling process; a contact process of bringing the cold rolled sheet after the grinding process into contact with an aqueous solution having a pH of 4.0 to 10.0; a decarburizing annealing process of performing decarburizing annealing on the cold rolled sheet after the contact process; a final annealing process of applying an annealing release agent to the cold rolled sheet after the decarburizing annealing process and then performing final annealing to form an oxide layer containing one or more of Mg, Al, and Si on the surface of the cold rolled sheet that becomes the base material steel sheet; an insulating coating forming process of forming an insulating coating layer on the surface of the oxide layer after the final annealing process to obtain an oriented electromagnetic steel sheet having the silicon steel sheet, the oxide layer, and the insulating coating layer; and a magnetic domain control process of irradiating the surface of the oriented electromagnetic steel sheet after the insulating coating forming process with a laser, an electron beam, or a plasma to form a plurality of linear thermal strains extending in a direction at an angle of 80 to 100° with respect to the rolling direction at intervals of 1.0 to 20.0 mm in the rolling direction on the surface of the silicon steel sheet, In the grinding process, abrasive grains with a Knoop hardness of 1000 or more, or abrasive papers, rolls, or brushes fixed with the abrasive grains are used to grind the cold-rolled sheet so that the grinding amount reaches 0.10 to 3.00 g / m on at least one surface. 2 Grinding is performed in such a manner.

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