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 an oxide of at least one of Mg, Al, and Si; and an insulating coating layer formed on the surface of the oxide layer, in which one or more oxides of Mg, Al, and Si having an equivalent circle diameter of 0.1-3.0 [mu] m are present at a density of 0.010-0.200 / [mu] m2 within a range of 10 [mu] m in the 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 the thickness of the insulating coating layer is 10 [mu] m. The average thickness of the flat crystal grains in the direction perpendicular to the surface is 0.5-5.0 [mu] m, the aspect ratio, which is the ratio of the crystal grain width in the direction parallel to the surface to the average thickness, is 1.5 or more, and the deviation between the crystal orientation and the Gaussian orientation is 10 DEG or more, and in the cross section in the plate thickness direction, the average thickness of the flat crystal grains is 0.5-5.0 [mu] m. The length of the grain boundary of the flat crystal grains in the length of the interface between the silicon steel sheet and the oxide layer is 70% or more.

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. 2022-186165 filed on November 22, 2022, and incorporates its content herein. Background Art

[0003] The grain-oriented electrical steel sheet is a soft magnetic material and is mainly used as a core material for transformers. The grain-oriented electrical steel sheet is, for example, a steel sheet containing 2.00 to 6.00% of Si and having the crystal orientation of the product highly concentrated in the {110}<001> orientation. As its magnetic properties, high magnetic flux density represented by the B8 value and 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 been increasing, and the requirement for reducing the iron loss of grain-oriented electrical steel sheets has been increasing.

[0004] In response to this requirement, as a means for reducing the iron loss of grain-oriented electrical steel sheets, a so-called magnetic domain refinement technique for reducing the magnetic domain width existing in the steel sheet has been developed. Hereinafter, such a technique, that is, the magnetic domain refinement technique may sometimes be referred to as a "magnetic domain control technique", and the effect brought about by the magnetic domain control technique may also be referred to as a "magnetic domain control effect".

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

[0006] Most of the wound cores mainly used for medium and small transformers are manufactured by a core manufacturing method using mechanical bending processing. In this manufacturing method, in order to eliminate the increase in iron loss caused by the processing strain introduced into the steel sheet by bending processing, after forming the core shape by mechanical processing, stress relief annealing is generally performed (for example, at 800°C for about 2 to 4 hours). By such stress relief annealing, although the strain caused by mechanical processing introduced into the core is reduced and disappears, the thermal strain introduced into the steel sheet for magnetic domain refinement by laser irradiation disappears. Therefore, a grain-oriented electrical steel sheet whose magnetic domains are refined by introducing thermal strain typified by laser irradiation is generally considered inapplicable to wound cores.

[0007] As a magnetic domain control technique that does not lose the magnetic domain control effect even when stress relief annealing as described above is performed, a "groove introduction type magnetic domain control technique" in which linear grooves are periodically formed in a direction crossing the rolling direction is widely known. As such a groove introduction type magnetic domain control technique, a groove formation technique using machining, a groove formation technique using etching, a groove formation technique using laser irradiation, etc. are known. For example, a groove formation technique using laser irradiation is disclosed in Patent Document 2. However, only by these groove formation methods, it is not possible to sufficiently meet the requirements for reducing iron loss that have been gradually increasing in recent years.

[0008] In addition, as a technique for reducing iron loss by other methods, a technique is disclosed in Patent Document 3, in which sharp and fine irregularities are formed on the surface of a steel sheet before decarburization annealing to activate the surface, and an oxide layer rich in silicon dioxide is formed at the time after decarburization annealing.

[0009] In addition, a technique is disclosed in Patent Document 4, in order to improve film characteristics and magnetic characteristics, an annealing film made of an oxide mainly composed of Mg, Si, and Al is provided on the surface, and in the steel sheet portion within 3 μm from the boundary between the film and the steel sheet, or in the crystal orientation distribution of the steel sheet grains in the mixed existence region of the film and the steel sheet grains, the proportion of crystal orientation grains with a deviation angle of 10 degrees or less from the Goss orientation is set to 50% or less.

[0010] However, these methods also cannot sufficiently meet the requirements for reducing iron loss that have been gradually increasing in recent years.

[0011] Prior art documents

[0012] Patent documents

[0013] Patent Document 1: Japanese Patent Laid-Open No. 56-51522

[0014] Patent Document 2: Japanese Patent Laid-Open No. 2005-59014

[0015] Patent Document 3: Japanese Patent Laid-Open No. 62-151522

[0016] Patent Document 4: Japanese Patent Laid-Open No. 2003-27194 Summary of the invention

[0017] Problems to be solved by the invention

[0018] As described above, studies have been made on the improvement of the magnetic flux density obtained and the reduction effect of iron loss commensurate with the increased amount. However, it cannot be said to be sufficient for the increasing requirements in recent years. In particular, with respect to the grain-oriented electrical steel sheet (GO) that is suitably applied to the wound core manufactured by performing stress-relieving annealing during core processing, it is not possible to sufficiently obtain the improvement of the magnetic flux density and the reduction effect of iron loss commensurate with the increased amount.

[0019] Therefore, the subject of the present invention is to provide a grain-oriented electrical steel sheet having excellent magnetic properties (high magnetic flux density and low iron loss commensurate with the magnetic flux density) and a method for manufacturing the same. The subject is to provide a grain-oriented electrical steel sheet and a method for manufacturing the same. The grain-oriented electrical steel sheet is preferably contemplated for use in cores such as wound cores that are subjected to stress-relieving annealing, and is manufactured without using non-heat-resistant magnetic domain control (the above-described magnetic domain control achieved by introducing thermal strain into the steel sheet by laser irradiation on the surface of the steel sheet), and has excellent magnetic properties (high magnetic flux density and low iron loss commensurate with the magnetic flux density).

[0020] Means for Solving the Subject

[0021] The inventors of the present invention have studied the improvement of the magnetic properties of the grain-oriented electrical steel sheet suitably applied to the wound core, that is, the increase in the magnetic flux density and the reduction of iron loss. As a result, it has been found that by having one or more oxides of Mg, Al, and Si present at a prescribed density near the surface of the silicon steel sheet (base material steel sheet) included in the grain-oriented electrical steel sheet, and further forming flat grains on the surface side of the silicon steel sheet with a deviation angle of 10° or more from the Goss orientation ({110}<001> orientation), it is possible to control the 180° magnetic domain width to a small state in terms of energy. As a result, it is possible to reduce the eddy current loss and the iron loss.

[0022] In addition, the inventors of the present invention have studied the influence of the manufacturing conditions. As a result, insights have been obtained regarding the following aspects.

[0023] That is, in the final annealing process of the manufacturing process of a grain-oriented electrical steel sheet, the Gaussian orientation that exhibits high magnetic properties causes precipitates such as AlN and MnS, which are called inhibitors, to exist at the crystal grain boundaries. By utilizing the abnormal grain growth phenomenon called "secondary recrystallization" brought about by the pinning effect of these precipitates, the grains are highly aggregated. After the aggregation of the Gaussian orientation in the steel sheet is completed, that is, when the steel sheet surface is almost covered with Gaussian-oriented grains, the completed inhibitor is decomposed and oxidized by the temperature increase in the latter half of the final annealing process and removed from the steel sheet. That is, it is not preferable for the decomposition / oxidation of the inhibitor to occur before the Gaussian orientation in the steel sheet is sufficiently aggregated. Furthermore, for the inhibitor, by suppressing the decomposition / oxidation to a higher temperature, the Gaussian orientation can be aggregated more highly, that is, crystals closer to the ideal Gaussian orientation can be aggregated. Therefore, a method of improving the heat resistance of the precipitates that play the role of the inhibitor is used.

[0024] The inventors of the present invention found that as a method of improving the heat resistance of the inhibitor, it is effective to make oxides that can suppress the decomposition / oxidation of the inhibitor during the final annealing exist on the steel sheet surface in the decarburizing annealing process that is usually carried out in the manufacture of grain-oriented electrical steel sheets. Furthermore, it was found that by using the decarburizing annealing process before the final annealing to make the above-mentioned oxides that can suppress the decomposition / oxidation of the inhibitor exist on the steel sheet surface, flat grains with a crystal orientation deviation of 10° or more from the Gaussian orientation can be generated near the interface between the oxide on the steel sheet surface and the steel sheet, and these flat grains contribute to the improvement of magnetic properties.

[0025] In addition, the inventors of the present invention found that in order to generate flat grains that are more preferable for the improvement of magnetic properties, it is effective to form oxide particles more densely, thicker, and uniformly on the surface side of the cold-rolled sheet that is the base steel sheet in the decarburizing annealing process; in order to form the oxide particles densely, thickly, and uniformly, it is effective to grind the cold-rolled sheet under specified conditions before the decarburizing annealing process to remove the reactants with the steel sheet surface that hinder the uniform oxidation of the steel sheet surface during decarburizing annealing.

[0026] In addition, it was found that by combining the above-mentioned steel sheet with the groove-introduced magnetic domain control technology under specified conditions, a further reduction in iron loss can be achieved.

[0027] The present invention has been completed in view of the above insights. The gist of the present invention is as follows.

[0028] [1] A directionally oriented electromagnetic steel sheet according to one embodiment of the present invention has: 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 film layer formed on the surface of the oxide layer. Within a range of 10 μm in the plate thickness direction from the interface between the silicon steel sheet and the oxide layer of the silicon steel sheet, 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 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 that account for the length of the interface between the silicon steel sheet and the oxide layer is 70% or more.

[0029] [2] In the directionally oriented electromagnetic steel sheet according to [1], the average of the average thickness of the flat grains may also exceed 2.0 μm and be 5.0 μm or less.

[0030] [3] In the directionally oriented electromagnetic 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 also be 50% or more.

[0031] [4] In the directionally oriented electromagnetic steel sheet according to [1] or [2], there may also be a plurality of grooves on the silicon steel sheet with a depth of 10 to 30 μm and extending in a direction at 80 to 100° with respect to the rolling direction. The interval between adjacent grooves in the rolling direction is 1.0 to 20.0 mm.

[0032] [5] In the directionally oriented electromagnetic steel sheet according to [3], there may also be a plurality of grooves on the silicon steel sheet with a depth of 10 to 30 μm and extending in a direction at 80 to 100° with respect to the rolling direction. The interval between adjacent grooves in the rolling direction is 1.0 to 20.0 mm.

[0033] [6] The directionally oriented electromagnetic steel sheet according to [4] may also have flat grains in the groove on the surface side of the silicon steel sheet. The average grain diameter of the flat grains in the groove in the direction perpendicular to the surface of the groove 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 grain diameter, is 2.0 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 perpendicular to the extending direction of the groove, the length of the grain boundaries of the flat grains in the groove accounts for 70% or more of the length of the inner surface of the groove.

[0034] [7] The directionally oriented electromagnetic steel sheet according to [5] may also have flat grains in the groove on the surface side of the silicon steel sheet. The average grain diameter of the flat grains in the groove in the direction perpendicular to the surface of the groove 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 grain diameter, is 2.0 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 perpendicular to the extending direction of the groove, the length of the grain boundaries of the flat grains in the groove accounts for 70% or more of the length of the inner surface of the groove.

[0035] [8] In the directionally oriented electromagnetic steel sheet according to [6], the average of the average grain diameter of the flat grains in the groove may also exceed 2.0 μm and be 5.0 μm or less.

[0036] [9] In the directionally oriented electromagnetic steel sheet according to [7], the average of the average grain diameter of the flat grains in the groove may also exceed 2.0 μm and be 5.0 μm or less.

[0037]

[10] A method for manufacturing a grain-oriented electromagnetic steel sheet according to another aspect of the present invention includes the following steps: 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 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 liquid phase 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 finish annealing step of applying an annealing release agent to the cold rolled sheet after the decarburizing annealing step and performing finish 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 becomes the base material steel sheet; and an insulating film forming step of forming an insulating film layer on the surface of the oxide layer after the finish annealing step. In the grinding step, abrasive grains having a Knoop hardness of 1000 or more, a maximum particle size exceeding 50 μm and 500 μm or less, or sandpaper, a roll, or a brush fixed with the abrasive grains are used, and grinding is performed at a reduction amount of 1.0 to 5.0 mm and a grinding speed of 500 mpm or more, and the grinding amount of the cold rolled sheet is set to 0.10 to 10.0 g / m on at least one surface. 2 .

[0038]

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

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

[0039]

[12] The method for manufacturing a grain-oriented electromagnetic steel sheet according to

[11] may also form the groove in the groove forming step by irradiating the surface of the cold rolled sheet with a laser to melt a part of the steel sheet surface and removing the melt from the surface.

[0040] Advantages of the Invention

[0041] According to the above aspect of the present invention, it is possible to provide a grain-oriented electromagnetic steel sheet having excellent magnetic properties and a method for manufacturing the same. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 is a schematic cross-sectional view of the grain-oriented electromagnetic steel sheet of the present embodiment.

[0043] Figure 2It is a schematic cross-section of the grain-oriented electrical steel sheet of the present embodiment in the case of forming grooves.

[0044] Figure 3 It is a diagram for explaining a method of measuring the average thickness and aspect ratio of crystal grains.

[0045] Figure 4 It is a diagram for explaining a method of measuring the coverage rate of the oxide layer at flat crystal grains. Detailed Embodiment

[0046] Hereinafter, a grain-oriented electrical steel sheet (the grain-oriented electrical steel sheet of the present embodiment) of an embodiment of the present invention and a method for manufacturing the same will be described.

[0047] <Grain-Oriented Electrical Steel Sheet>

[0048] As Figure 1 shown, the grain-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 film layer 31 formed on the surface of the oxide layer 21.

[0049] The oxide layer 21 and the insulating film layer 31 may be formed only on one side of the steel sheet, but are preferably formed on both sides from the viewpoint of insulation and the like.

[0050] Each will be described below.

[0051] [Silicon Steel Sheet]

[0052] (Within a range of 10 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 )

[0053] In the grain-oriented electrical steel sheet, by suppressing the decomposition and oxidation of inhibitors (precipitates such as AlN present at crystal grain boundaries) during finish annealing so that they exist up to a high temperature, it becomes possible to highly aggregate Goss orientations during secondary recrystallization, that is, it becomes possible to aggregate crystals closer to the ideal Goss orientation, and the magnetic flux density can be increased, so that a reduction in iron loss can be achieved.

[0054] The size of the precipitate that becomes an inhibitor is very small, on the order of several 10 nm to about 100 nm in terms of equivalent circle diameter. Additionally, there is a size distribution. When there is a size distribution, the inhibitor with a small size decomposes / oxidizes at a low temperature, and its effect as an inhibitor is deactivated. In this case, it becomes difficult to achieve secondary recrystallization with a Gaussian orientation closer to the ideal Gaussian orientation, and it is difficult to increase the magnetic flux density. On the other hand, if the size distribution of the inhibitor (in a manner where the difference in size becomes smaller) is controlled to be constant, the above problem is eliminated, but it is extremely difficult industrially.

[0055] In contrast, even in a state where a size distribution of the inhibitor is present, if decomposition / oxidation can be suppressed by some method so that the inhibitor remains until a high temperature, secondary recrystallization of grains closer to the ideal Gaussian orientation can occur. Additionally, as a method for suppressing the decomposition / oxidation of the inhibitor, there is a method of using an inhibitor with high heat resistance. On the other hand, as a method that can be achieved without changing the composition, etc. of the inhibitor, it is known that oxide particles of Si (hereinafter sometimes referred to as Si-based pre-oxides) formed on the surface of the steel sheet or in the surface layer part (in the steel) during the decarburizing annealing process play a role. The mechanism is speculative, but it is thought that the oxidation of the inhibitor is caused by trace amounts of oxygen contained in the final annealing atmosphere oxidizing AlN, etc. on the surface of the steel sheet, but the above Si-based pre-oxides prevent / mitigate this oxidation.

[0056] However, the formation state of the Si-based pre-oxides on the surface of the silicon steel sheet easily becomes non-uniform at each part. If the formation state is non-uniform, the effect of suppressing the decomposition / oxidation of the inhibitor varies depending on the position within the steel sheet surface, and the target effect cannot be fully obtained.

[0057] The inventors of the present invention investigated the reason why the formation state of the oxide layer after final annealing becomes non-uniform 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 the oily agent or extreme pressure additive contained in the rolling oil used during cold rolling, etc. with the surface metal of the steel sheet are unevenly present on the steel sheet surface, and these Fe-based oxides and reactants hinder the dense, thick, and uniform formation of the Si-based pre-oxides in a certain thickness region from the surface during decarburizing annealing.

[0058] Since it was difficult for the inventors of the present invention to make the above-mentioned 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, it was found that, as described later, by using abrasive grains, or sandpaper, rolls, or brushes fixed with abrasive grains to perform certain grinding on the surface (at least one surface) of the cold-rolled sheet before the decarburizing annealing process to expose a clean metal surface, and then immediately contacting it with an aqueous liquid phase, it is possible to remove the Fe-based oxides and reactants that are the factors hindering the formation of Si-based pre-oxides from the surface of the steel sheet, and Si-based pre-oxides can be formed in a region at a certain thickness from the surface of the steel sheet with a specified number density after the decarburizing annealing process.

[0059] Based on these insights, in the grain-oriented electrical steel sheet of the present embodiment, as Figure 1 shown in, within a range of 10 μm in the plate thickness direction from the interface between the steel sheet (silicon steel sheet) 11 and the oxide layer 21, oxides 101 (oxide particles) of one or more of Mg, Al, and Si, which are oxides that change through oxidation by an inhibitor or solid-phase reaction with an annealing release agent during processes such as finish annealing, and have an equivalent circle diameter of 0.1 to 3.0 μm, exist at a density of 0.010 to 0.200 pieces / μm 2 . The oxide 101 only needs to be an oxide (including composite oxides) of one or more of Mg, Al, and Si, but under the premise of the manufacturing conditions described later, it is mostly an oxide containing Mg, Al, and Si such as spinel (MgAl2O4), alumina (Al2O3), and mullite (2SiO2·3Al2O3).

[0060] If the number density of the oxide 101 is too small, the adhesion of the oxide layer 21 to the steel sheet becomes poor, and the formation of the flattened grains 102 described later becomes uneven. On the other hand, if the number density of the oxide 101 is too large, the proportion of the metal part of the steel sheet 11 becomes smaller, so the magnetic flux density decreases. In addition, the proportion of the flattened grains 102 also becomes relatively smaller, so it is difficult to obtain the effect of reducing iron loss.

[0061] By uniformly forming the oxide 101 in a specified region, the unevenness of each part in the inhibitory effect on the decomposition / oxidation of the inhibitor during finish annealing is reduced, and in the grain-oriented electrical steel sheet 1, the magnetic flux density is increased. In addition, by appropriately forming the flattened grains 102, the 180° magnetic domain width becomes smaller, and the effect of reducing iron loss corresponding to the magnetic flux density can be obtained.

[0062] Considering the formation process, the above-mentioned oxide 101 mostly exists in the flattened grains 102 described later.

[0063] (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.)

[0064] (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 70% or more.)

[0065] As described above, in the grain-oriented electrical steel sheet of the present embodiment, by mainly forming a Si-based pre-oxide uniformly in the surface layer portion (the range within 10 μm from the surface) of the silicon steel sheet (base material steel sheet) using a decarburizing annealing process or the like, decomposition and oxidation of the inhibitor are suppressed during finish annealing, and it exists up to a high temperature. In this case, it becomes possible to highly aggregate the Goss orientation, that is, to aggregate crystals closer to the ideal Goss orientation. As a result, the magnetic flux density is increased. That is, a reduction in iron loss can be achieved.

[0066] 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. In this case, the number of Goss orientation grains that undergo secondary recrystallization becomes smaller, so the number of Goss orientation grains per unit area of the steel sheet becomes smaller. That is, the crystal grain size of each Goss orientation grain becomes larger.

[0067] The iron loss required for a grain-oriented electrical steel sheet is classified into hysteresis loss and eddy current loss as its details. The hysteresis loss is reduced by an increase in the magnetic flux density. On the other hand, the eddy current loss has a classical eddy current loss that is reduced by a decrease in the plate thickness and an increase in the resistivity of the steel sheet, and an anomalous eddy current loss that is reduced by a decrease in the magnetic domain width formed within the Goss orientation grains. The reduction in the plate thickness and the increase in the resistivity of the steel sheet in the reduction of the above-mentioned classical eddy current loss mostly affect the productivity. Therefore, it is important to reduce the anomalous 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. Generally, the magnetic domain width of the so-called 180° magnetic domains generated in the grain-oriented electrical steel sheet due to the reduction of the crystal grain size also becomes smaller accordingly.

[0068] That is, although the magnetic flux density is increased by the above-mentioned control of the oxide, the anomalous eddy current loss increases due to the coarsening of the crystal grain size, and it may not be possible to obtain an iron loss reduction effect commensurate with the increase in the magnetic flux density.

[0069] Therefore, the inventors of the present invention have studied a method for reducing iron loss commensurate with an increase in magnetic flux density, that is, a method for reducing the magnetic domain width to solve the coarsening of crystal grain size that secondarily occurs, based on the existence frequency of ideal Goss-oriented grains. As a result, it has been found that: as described above, secondary recrystallization occurs at a higher temperature, and only grains closer to the ideal Goss orientation undergo secondary recrystallization. Even when their crystal grain size is large, by having flat grains (flat grains) with a deviation angle of 10° or more from the Goss orientation on the surface of the steel sheet, the 180° magnetic domain width can be controlled to a small state in terms of energy, and an increase in eddy current loss can be suppressed.

[0070] Specifically, as Figure 1 shown in [reference], it is known that when flat grains 102 exist on the surface side of the base steel sheet 11, the average thickness of the flat grains 102 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 (deviation angle) of the crystal orientation from the Goss orientation is 10° or more (the flat grains 102 exist as the grains constituting the outermost layer of the silicon steel sheet 11), the eddy current loss is reduced.

[0071] For grains with an average thickness less than 0.5 μm, an aspect ratio less than 1.5, or a deviation from the Goss orientation less than 10°, the effect of reducing the magnetic domain width cannot be obtained sufficiently, and the iron loss cannot be reduced sufficiently.

[0072] On the other hand, since there is a deviation from the Goss orientation in these grains, if the average thickness of the grains exceeds 5.0 μm, the overall magnetic properties deteriorate, that is, the magnetic flux density decreases and the iron loss increases.

[0073] From the aspect of sufficiently obtaining the effect of reducing the magnetic domain width, the average of the average thickness of each flat grain is preferably more than 2.0 μm and 5.0 μm or less.

[0074] In addition, in order to sufficiently obtain the above-mentioned magnetic domain refinement 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 sheet and the oxide layer is 70% or more.

[0075] If the proportion of the flat grains constituting the interface is small, the effect of reducing the magnetic domain width is insufficient, and thus a sufficient effect on reducing the iron loss cannot be obtained.

[0076] In the method for manufacturing a grain-oriented electrical steel sheet, during finish annealing, minute Goss-oriented grains located inside the steel sheet in the thickness direction grow while consuming the surrounding grains having orientations other than the Goss orientation. As a result, from the inside to the surface in the thickness direction, the proportion of 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.

[0077] It is considered that in the grain-oriented electrical steel sheet of the present embodiment, since oxides are discretely present (at a prescribed number density) in the surface layer portion of the silicon steel sheet as described above, when the Goss-oriented grains existing inside the sheet thickness grow, minute flat grains in the surface layer portion of the steel sheet remain without being consumed by the Goss-oriented grains, and as a result, "flat grains" which are confirmed to be flat grains are formed.

[0078] The average thickness, aspect ratio, and deviation of crystal orientation of the grains present on the surface side can be measured by the following method.

[0079] From the steel sheet, a specimen of about 20 mm square is cut out, for example, in such a manner that a plane parallel to the rolling direction (RD direction) becomes a cross section, and is polished so that its cross section becomes a mirror surface. In addition, since it becomes difficult to measure the crystal orientation in a state where strain caused by polishing is imparted to the steel sheet, a polishing specimen is produced using a polishing material such as colloidal silica in the final polishing step so as not to generate strain. The cross-sectional shape is observed by FE-SEM using this polishing 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 listed as an example. The range including the base steel sheet, the oxide layer, and the insulating film layer is observed at a magnification of 500 times by FE-SEM for the cross section to obtain an electron microscope image. The interfaces between the insulating film layer and the oxide layer and between the oxide layer and the steel sheet described later are determined from the difference in electron density in the electron microscope image. When an elemental analysis device (EDS) is attached to the FE-SEM, the interfaces can be determined more precisely from the difference in the types of elements contained in the insulating film layer, the oxide layer, and the silicon steel sheet, such as P, B, O, and Fe.

[0080] Next, for cross-sections with the same field of view, the crystal orientation of the steel plate is measured by EBSD. Specifically, in a 500-fold field of view assuming more than 100 flat grains, as the cross-section length, a region with a length of 200 μm in the rolling direction and a thickness of 70 μm in the plate thickness direction is taken as the object, and the crystal orientation is measured every 0.25 μm as the measurement point spacing. The boundary with a crystal orientation difference of 15° or more is taken as the crystal grain boundary, and the range surrounded by this crystal grain boundary is taken as the grain. When the number of grains in the field of view is less than 100, additional fields of view are measured.

[0081] Regarding this grain, as Figure 3 shown in, the average thickness of the grain is obtained by the methods shown in a) to d).

[0082] a) Draw a hypothetical line (1) that determines the two ends of the grain in the plate thickness direction (normal direction) of the steel plate.

[0083] b) With respect to the distance L between the two ends, draw hypothetical lines in the plate thickness direction at 2.5% of the distance from the two ends of the grain respectively (the line representing the 95% width of the grain between them) (2).

[0084] c) For the part between the hypothetical lines drawn in b) above (the 95% width part of the grain), draw an average line (3) 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).

[0085] d) Obtain the distance between the two average lines drawn in c) above as the thickness t (4) (average the total of 5 points: the two ends, the center, and the midpoints between the two ends and the center).

[0086] In addition, the range of the two ends of the grain drawn in a) above is taken as the width of the grain, and the aspect ratio is calculated.

[0087] For all grains with an average thickness of 0.5 to 5.0 μm and an aspect ratio of 1.5 or more among the above grains, the crystal orientation of the ferrite phase of Fe is measured. Based on the crystal orientation measured here, a crystal orientation map called an IPF map is made, and a map showing the crystal orientation with respect to the rolling direction (RD direction) and the steel plate surface normal direction (ND direction) is obtained. Calculate the average of the orientation differences of each 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 set as a flat grain.

[0088] The average (simple average) of the average thickness of the flat grains is obtained by dividing the sum of the average thicknesses of the flat grains obtained above by the number of flat grains.

[0089] Since flat grains are flat in the rolling direction (length direction) and width direction, if it is a cross-section in the plate thickness direction, it can be observed by any method. However, for the above steel plate, a method of obtaining a plane parallel to the rolling direction (RD direction) as a cross-section and using EBSD to obtain a crystal orientation map to confirm the existence of "flat grains" has high precision, so it is preferred. In addition, as a method of simply confirming the existence of "flat grains", there is also a method of confirming by obtaining a smooth cross-section by grinding a plane parallel to the rolling direction (RD direction) and then using the so-called Nital method (nitric acid ethanol method, described in JIS-G-0553(2019), etc.) to reveal the crystal grain boundaries. However, in this method, the crystal orientation cannot be determined, and it is necessary to measure the crystal orientation separately by EBSD, etc. Therefore, in this embodiment, the above-mentioned FE-SEM and EBSD methods are adopted and used together.

[0090] In addition, the proportion of the length of the grain boundaries of flat grains in the length of the interface between the base steel plate and the oxide layer can be obtained by the following method.

[0091] For example, in a field of view observed at a magnification of 500 times, for the interface between the silicon steel plate and the oxide layer, which is the cross-section length in the rolling direction, a region of 200 μm is used as the object, and SEM observation and EBSD measurement are carried out. Five such regions, that is, with a total interface length of 1000 μm, are subjected to SEM observation and EBSD measurement. 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 Gaussian orientation of 10° or more in the length of the interface between the silicon steel plate and the oxide layer (1000 μm) is measured. The identification of the insulating film layer, oxide layer, interface of the silicon steel plate, flat grains, etc. can be carried out in the same manner as above.

[0092] During the measurement, by setting the length of the oxide layer formed on the surface of the silicon steel plate in the measurement range B as B' (if the oxide layer is formed in the entire measurement range, then B = B'), where flat grains are formed on the outermost surface of the silicon steel plate, and the interface between the silicon steel plate and the oxide layer is the length of the part of the crystal grain boundaries of the flat grains set as b1, b2... bi (i = 3 in the figure), and dividing the sum of the lengths of b1 to bi (Σbi) by the length B' of the oxide layer formed on the surface of the silicon steel plate (Σbi / B'), the proportion of the length of the grain boundaries of flat grains in the length of the interface between the base steel plate and the oxide layer is measured.

[0093] (Groove)

[0094] Magnetic domain control can be carried out by periodically forming linear grooves in a direction crossing the rolling direction. In the directionally electromagnetic steel sheet of the present embodiment, in order to obtain this effect, as Figure 2 shown in, it is preferable to form grooves G on the surface of the base steel sheet 11. Specifically, it is preferable that there are a plurality of grooves G on the silicon steel sheet (base steel sheet) 11 with a depth (in the plate thickness direction) of 10 to 30 μm and extending in a direction of 80 to 100° with respect to the rolling direction, and the interval in the rolling direction between adjacent grooves G is 1.0 to 20.0 mm. The interval in the rolling direction between adjacent grooves G is more preferably 2.0 to 10.0 mm.

[0095] If the size and interval of the grooves are not within the above ranges, sufficient effects cannot be obtained. The interval of the grooves refers to the distance from the center of the width of one groove to the center of the width of the adjacent groove.

[0096] The shape of the grooves is not limited. For example, the cross section is substantially rectangular or substantially triangular. In addition, the cross section can also be an arcuate shape that is part of a circle. The width of the grooves is preferably about 0.5 times to 3.0 times the depth of the grooves. When the width of the grooves is less than 0.5 times the depth of the grooves, sufficient magnetic domain control effects cannot be obtained, and it is also difficult to form the grooves themselves. On the other hand, when the width of the grooves is greater than 3.0 times the depth of the grooves, the occupancy rate of the grooves on the steel sheet surface becomes large, and as a result, the magnetic flux density decreases. On the other hand, the magnetic domain control effect saturates, so the iron loss reduction effect cannot be obtained, and on the contrary, an increase in iron loss may occur.

[0097] The effect of reducing abnormal eddy current loss brought about by the above-mentioned flattened grains is also effective for the magnetic domain control material formed by the grooves.

[0098] That is, when the inner surface (bottom surface, side surface) of the grooves is the surface of the base steel sheet, as Figure 2 shown in, if there are flattened grains (flattened grains in the grooves) G102 on the surface side of the grooves of the base steel sheet, the average grain diameter of the flattened grains (flattened grains in the grooves) G102 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 grain diameter, is 2.0 or more, and the deviation of the crystal orientation from the Goss orientation is 10° or more (the flattened grains in the grooves G102 exist as the outermost layer grains constituting the grooves of the silicon steel sheet), and in the cross section in the plate thickness direction perpendicular to the extending direction, the length of the grain boundaries of the flattened grains in the grooves G102 in the length of the inner surface of the grooves G accounts for 70% or more, then not only the magnetic domain refinement effect brought about by the formation of the grooves can be obtained, but also the eddy current loss reduction effect brought about by the flattened grains in the grooves G102 can be obtained, so it is more preferable.

[0099] The average grain size of the flat grains G102 in the groove is more preferably more than 2.0 μm and 5.0 μm or less on average.

[0100] Regarding the presence or absence of flat grains in the groove, and their average grain size, aspect ratio, and the deviation of the crystal orientation from the Goss orientation, they can be obtained in the same manner as the flat grains on the surface of the base steel plate described above.

[0101] However, when the groove provided on the surface of the steel plate is not a straight line but a curve, for example, a cross-section perpendicular to the tangent of the curve at the observation target part is shown. In this case, the deviation angle of this cross-section with respect to the rolling direction (RD direction) is measured and obtained, and correction is performed during the measurement of the crystal orientation of the flat grains.

[0102] In addition, the length of the grain boundaries of the flat grains in the groove in the length of the inner surface of the groove can be obtained by performing EBSD measurement of the cross-section in the plate thickness direction perpendicular to the extending direction of the groove in the same manner as the measurement of the flat grains on the surface side of the silicon steel plate.

[0103] (Chemical composition)

[0104] The chemical composition of the silicon steel plate is not limited as long as it is equivalent to the base steel plate of a known grain-oriented electrical steel plate. For example, the compositions within the ranges described below can be cited.

[0105] The chemical composition of the silicon steel plate contains Si: 2.00 to 6.00% by mass. This is to control the Goss texture in which the crystal orientation is concentrated in the {110}<001> orientation and ensure good magnetic properties.

[0106] For other elements, there is no particular limitation, and it is allowed to contain known elements within a known range to replace Fe. In addition, the balance is Fe and impurities.

[0107] The representative content ranges (mass%) of representative elements other than Si are as follows.

[0108] C: 0 to 0.0050%,

[0109] Mn: 0 to 1.0%,

[0110] S: 0 to 0.0150%,

[0111] Se: 0 to 0.0150%,

[0112] Al: 0 to 0.0650%,

[0113] N: 0 to 0.0050%,

[0114] Cu: 0 to 0.40%,

[0115] Bi: 0 to 0.010%,

[0116] B: 0 to 0.080%,

[0117] P: 0 to 0.50%,

[0118] Ti: 0 to 0.0150%,

[0119] Sn: 0 to 0.10%,

[0120] Sb: 0 to 0.10%,

[0121] Cr: 0 to 0.30%,

[0122] Ni: 0 to 1.0%,

[0123] Nb: 0 to 0.030%,

[0124] V: 0 to 0.030%,

[0125] Mo: 0 to 0.030%,

[0126] Ta: 0 to 0.030%,

[0127] W: 0 to 0.030%,

[0128] These optional elements may be contained according to their purposes, so there is no need to limit the lower limit value, and they may not be substantially contained. In addition, even if these optional elements are contained as impurities, the effects of the present invention will not be impaired. Impurities refer to elements that are not intentionally contained, and are elements that are mixed in from ores, waste materials, or manufacturing environments, etc. as raw materials during the industrial manufacture of the base metal steel sheet.

[0129] The chemical composition of the silicon steel sheet is determined by the following method.

[0130] A solution is prepared by acid-decomposing the silicon steel sheet with hydrochloric acid or the like. On this basis, a calibration curve for each element solution with a pre-known concentration is determined by ICP (inductively coupled plasma) analysis. On this basis, the obtained solution is analyzed to quantify the contained elements.

[0131] When an oxide layer and / or an insulating film layer is formed on the surface of the silicon steel sheet (in the case of a grain-oriented electrical steel sheet including a silicon steel sheet, an oxide layer, and an insulating film layer), the measurement can be performed after removing the oxide layer and the insulating film layer.

[0132] Specifically, in the case of forming an insulating film layer, the grain-oriented electrical steel sheet with the insulating film layer is immersed in an aqueous sodium hydroxide solution at 80 - 90 °C containing 30 - 50% by mass of NaOH and 50 - 70% by mass of H2O for 7 - 10 minutes to remove the insulating film layer. The grain-oriented electrical steel sheet from which the insulating film layer has been removed is washed with water, and after washing, it is dried with a warm air blower for slightly less than 1 minute.

[0133] In the case of forming an oxide layer, the grain-oriented electrical steel sheet with the oxide layer is immersed in an aqueous hydrochloric acid solution containing 10% by mass of HCl at 80 - 90 °C for 1 - 10 minutes to remove the oxide layer. The base metal steel sheet after immersion is washed with water, and after washing, it is dried with a warm air blower for slightly less than 1 minute.

[0134] Through the above processes, the silicon steel sheet as the base metal steel sheet can be obtained from the grain-oriented electrical steel sheet formed with an oxide layer and / or an insulating film layer.

[0135] (Thickness of the sheet)

[0136] The thickness of the silicon steel sheet of the grain-oriented electrical steel sheet in this embodiment is not limited, but is preferably 0.15 - 0.35 mm. If it exceeds 0.35 mm, the sheet 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 sheet thickness is less than 0.15 mm, the rolling efficiency decreases, which is disadvantageous in terms of productivity and cost.

[0137] [Oxide layer]

[0138] In the grain-oriented electrical steel sheet of this embodiment, an oxide layer containing one or more of Mg, Al, and Si is formed on the surface of the base metal steel sheet.

[0139] This oxide layer is formed by a solid-phase reaction between Mg and / or Al contained in the annealing parting agent during finish annealing and the Si-based pre-oxide formed on the steel sheet surface. For example, in the case of using an annealing parting agent containing MgO, a layer mainly forming a forsterite (Mg2SiO4) 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 silicon steel sheet in the latter half of finish annealing. Along with this, spinel (MgAl2O4), alumina (Al2O3), or mullite (2SiO2·3Al2O3) is generated on the surface of the silicon steel sheet. However, in the case of using an annealing parting agent with MgO as the main component, it is almost generated as spinel (MgAl2O4).

[0140] By covering the surface of the flat grains with this oxide layer, an effect of improving the adhesion to the insulating film layer applied thereon can be obtained. When sufficient effect is to be obtained, the coverage rate of the oxide layer at the flat grains is preferably 50% or more.

[0141] The coverage rate can be obtained by the following method.

[0142] That is, in accordance with the above-mentioned procedure, the presence of flat grains is determined by EBSD. 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 based on the FE-SEM image. Measure the length of the oxide layer containing one or more of Mg, Al, and Si in the projection part in the direction inside the steel sheet from between the insulating film layer and the flat grain or from the surface side of the flat grain at the flat grain. As the interface length between the oxide layer or the insulating film layer and the flat grain, obtain the length rate of the presence of the oxide layer as a percentage for 1000 μm.

[0143] For example, if it is Figure 4 such a state, the coverage rate (%) can be obtained by (A1 + A2 + A3) / (a1 + a2 + a3)×100.

[0144] [Insulating film layer]

[0145] In the grain-oriented electrical steel sheet of the present embodiment, an insulating film layer is formed on the surface of the oxide layer (as the upper layer). This insulating film layer is essential when using the grain-oriented electrical steel sheet as a transformer. When the grain-oriented electrical steel sheet is used as a transformer, it is laminated and used. If a short circuit occurs between the laminated steel sheets (silicon steel sheets), eddy currents are generated in the transformer core, which becomes a cause of an increase in core loss. Therefore, a layer of insulating film is formed on the steel sheet surface to reduce the core loss of the transformer by imparting electrical insulation. In addition, by applying tension to the steel sheet in the insulating film of the grain-oriented electrical steel sheet, the magnetic domain width can be reduced, and a reduction in abnormal eddy current loss and even core loss can be achieved.

[0146] In addition, regarding the insulating film 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 film type mainly composed of phosphate and colloidal silica is used as the insulating film. In addition, for the purpose of applying greater tension to the steel sheet, a film mainly composed of aluminum borate or a film containing aluminum borate and silica may be used. Any film can be a well-known film formed by coating a coating solution obtained by dissolving or dispersing the components contained therein on the surface of the oxide layer and baking it.

[0147] <Manufacturing method>

[0148] The grain-oriented electrical steel sheet of the present embodiment is not dependent on the manufacturing method, and as long as it has the above characteristics, its effects can be obtained. However, if it is a manufacturing method including the following processes, it can be stably manufactured, and thus is preferred.

[0149] (I) A hot rolling process of heating a slab and performing hot rolling to form a hot rolled sheet;

[0150] (II) A hot rolled sheet annealing process of annealing the hot rolled sheet after the above hot rolling process;

[0151] (III) A pickling process of pickling the hot rolled sheet after the above hot rolled sheet annealing process;

[0152] (IV) A cold rolling process of cold rolling the hot rolled sheet after the above pickling process to form a cold rolled sheet;

[0153] (V) A grinding process of grinding the surface of the cold rolled sheet after the above cold rolling process;

[0154] (VI) A contact process of bringing the cold rolled sheet after the above grinding process into contact with an aqueous liquid phase having a pH of 4.0 to 10.0;

[0155] (VII) A decarburizing annealing process of decarburizing and annealing the cold rolled sheet after the above contact process;

[0156] (VIII) A final annealing process of coating an annealing release agent on the cold rolled sheet after the above decarburizing annealing process, performing final annealing, and forming 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; and

[0157] (IX) An insulating film forming process of forming an insulating film layer on the surface of the oxide layer after the above final annealing process.

[0158] In addition, the manufacturing method of the grain-oriented electrical steel sheet of the present embodiment may further have any one or more of the following processes.

[0159] (X) A groove forming process of further forming a plurality of grooves having a depth of 10 to 30 μm extending in a direction at an angle of 80 to 100° with respect to the rolling direction on the cold rolled sheet at intervals of 1.0 to 20.0 mm in the rolling direction before the above grinding process;

[0160] (XI) A nitriding treatment process of increasing the nitrogen content of the cold rolled sheet.

[0161] The manufacturing method of the directionally-oriented electromagnetic steel sheet of the present embodiment among them is characterized by a grinding process, a contact process, and a groove forming process. On the other hand, for the hot rolling process, the hot rolled sheet annealing process, the cold rolling process, the decarburizing annealing process, the nitriding process, the finish annealing process, and the insulating film forming process, they can be carried out under known conditions.

[0162] Hereinafter, the preferred conditions will be described. For the conditions not described, they can also be carried out under known conditions.

[0163] [Hot rolling process]

[0164] In the hot rolling process, a slab having a specified chemical composition (a chemical composition corresponding to the chemical composition of the silicon steel sheet of the directionally-oriented electromagnetic steel sheet of the present embodiment) is heated and hot rolled to produce a hot rolled sheet.

[0165] The slab heating temperature is, for example, 1000 to 1400 °C.

[0166] The chemical composition of the slab to be hot rolled only needs to be determined according to the chemical composition desired to be obtained as a directionally-oriented electromagnetic steel sheet, taking into account the changes in chemical composition in each process.

[0167] In the case of obtaining the chemical composition of the silicon steel sheet of the above-mentioned preferred directionally-oriented electromagnetic steel sheet of the present embodiment, in the hot rolling stage, the following chemical composition is exemplified: by mass%, containing C: 0.040 to 0.100%, Si: 2.00 to 6.00%, in addition, as inhibitors, in a specified range to form AlN, MnS, MnSe, BN, containing Al, Mn, Se, S, B, N, etc., and further containing elements such as Cu, Sn, Cr, Ni, Mo, Nb, Bi, Sb, P, Ti, V, Ta, W, etc. as required.

[0168] The method of obtaining the slab is not limited. For example, molten steel having a specified chemical composition is melted, and the molten steel can be used to manufacture it. The slab can also be manufactured by the continuous casting method, or a steel ingot can be manufactured using molten steel, and the steel ingot can be bloomed to manufacture the slab. In addition, the slab can also be manufactured by other methods.

[0169] The thickness of the slab is not particularly limited, but for example, it is 150 to 350 mm. The thickness of the slab is preferably 220 to 280 mm. As the slab, so-called thin slabs with a thickness of 10 to 70 mm can also be used.

[0170] The so-called hot-rolled sheet (hot-rolled steel sheet) is obtained by hot rolling. The sheet thickness (final sheet thickness) of the hot-rolled sheet is not particularly limited. However, it is known that annealing the hot-rolled sheet and then performing cold rolling after pickling, but the so-called cold rolling rate affects the magnetic properties of the grain-oriented electrical steel sheet, and the sheet thickness of the hot-rolled sheet is selected in the form of adding the necessary cold rolling rate to the final sheet thickness. For example, when the final sheet thickness is 0.20 to 0.30 mm, the final sheet thickness of the hot-rolled sheet is preferably in the range of 2.0 to 4.0 mm.

[0171] [Hot-rolled sheet annealing process]

[0172] In the hot-rolled sheet annealing process, the above-mentioned hot-rolled sheet after the hot rolling process is annealed. By performing such annealing treatment, recrystallization is generated in the steel sheet structure, and good magnetic properties can be achieved.

[0173] In the hot-rolled sheet annealing process of the present embodiment, the hot-rolled sheet manufactured through the hot rolling process may be annealed according to a known method. There is no particular limitation on the means of heating the hot-rolled sheet during annealing, and a known heating method can be adopted. For example, it can be so-called continuous annealing, or the hot-rolled sheet can be made into a coil shape and set for batch annealing. In addition, there is no particular limitation on the annealing conditions either. 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 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.

[0174] [Pickling process]

[0175] In the pickling process, the scale (oxide) generated on the surface of the steel sheet is removed by hot rolling and hot-rolled sheet annealing. In the pickling process of the present embodiment, a known method is used. As the pickling solution, known acids such as hydrochloric acid, sulfuric acid, and nitric acid can be used. In addition, 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 made to penetrate to the interface between the scale and the steel sheet, and for the purpose of improving the pickling efficiency, physical treatments such as shot peening of the steel sheet can also be performed before pickling.

[0176] [Cold rolling process]

[0177] In the cold rolling process, the pickled steel sheet is cold rolled to form a cold-rolled sheet. The cold rolling can be single-pass (a series without intermediate annealing) cold rolling, or before the final pass of the cold rolling process, the cold rolling can be interrupted to perform at least one or two or more intermediate annealings, and multiple cold rollings with intermediate annealing can be performed.

[0178] The conditions for cold rolling 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 ratio is large, and the final reduction ratio can be set to 80 to 95%. The final reduction ratio refers to the cumulative reduction ratio of cold rolling. In the case of performing intermediate annealing, it is the cumulative reduction ratio of cold rolling after the final intermediate annealing.

[0179] In the case of 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, but in order to prevent oxidation of the steel sheet, it is preferably carried out in a non-oxidizing atmosphere such as nitrogen, argon, hydrogen, etc. In addition, as the annealing method, either so-called continuous annealing or batch annealing in the form of a coil can be used, and other methods can also be used. Considering the manufacturing cost, the number of intermediate annealings is preferably within 3 times.

[0180] [Groove forming process]

[0181] In the groove forming process, grooves with a depth of 10 to 30 μm extending in a direction at an angle of 80 to 100° with respect to the rolling direction are formed on the cold-rolled sheet before the grinding process. A plurality of such grooves are formed such that the intervals in the rolling direction are each 1.0 to 20.0 mm. The interval in the rolling direction is more preferably 2.0 to 10.0 mm.

[0182] By forming the above-mentioned grooves on the surface of the cold-rolled sheet (base metal steel sheet), when recrystallization of the Goss orientation is carried out, the magnetic domains are refined by the effect of the grooves, and the magnetic properties are improved. Specifically, the abnormal eddy current loss is reduced, thereby reducing the iron loss. If the direction, interval, shape, etc. of the grooves are outside the above ranges, sufficient effects cannot be obtained.

[0183] As the method for forming the grooves, there is no particular limitation, and well-known methods as shown below can be used. For example, methods using physical contact (methods such as damaging the surface of the steel sheet with a blade, etc., and methods of roll-transfer printing and pressing using a die with a blade), methods not relying on physical contact (methods such as locally melting a part of the surface of the steel sheet using a laser, electron beam, plasma, etc. and removing the melt outside the system), and chemical methods (methods of masking the surface of the steel sheet with a resin, etc., removing a part of the mask in accordance with the shaped groove shape, bringing an acid, etc. into contact with the mask-removed part, and melting and damaging a part of the steel sheet by etching to form grooves) can be cited.

[0184] Among them, the method not relying on the above physical contact has advantages over the physical contact method and the chemical method in the following aspects.

[0185] The method using physical contact involves bringing the blade and die into contact with the steel plate, thereby imparting strain to the steel plate and causing deterioration of magnetic properties. In addition, since the grooves are introduced into the steel plate at intervals of 1.0 to 20.0 mm with respect to the rolling direction, in order to impart grooves to a steel plate coil reaching several thousand meters, the wear of the blade and die becomes significant. Therefore, frequent replacement is required, resulting in the disadvantage of low productivity.

[0186] In addition, regarding the chemical method, as described above, it requires multiple processes such as resin masking the surface of the steel plate and then removing part of the mask and performing etching. This mainly has problems in terms of productivity. Furthermore, etching mostly uses strongly acidic liquids with a pH of around 1 such as hydrochloric acid, and the costs for removing Fe dissolved in the strongly acidic liquid and treating the waste liquid of the strongly acidic liquid are also high.

[0187] For a method that does not rely on physical contact, as one method, there is the following method: By irradiating the surface of the cold-rolled plate with a laser, a part of the surface of the steel plate is melted, and the melt is removed from the surface to form grooves. This method uses a high-energy source with high collimation such as a laser, so that grooves can be accurately formed at a position where the height control of the irradiation position on the steel plate surface can be performed and at a determined part, which is a great advantage. In addition, the melt generated from the steel plate during irradiation can be removed to the outside of the system by providing a suction channel at the laser irradiation part, and this has no influence on the laser irradiation control. In addition, it is preferable that the melt is removed as much as possible without adhering to the surface of the steel plate, but even if the melt adheres to the surface of the steel plate by chance, it can be removed from the surface of the steel plate before the decarburizing annealing process in the grinding process, and the surface of the steel plate can be kept clean.

[0188] When irradiating the laser, for example, high-output lasers generally used in industry such as fiber lasers, YAG lasers, semiconductor lasers, or CO2 lasers can be used. In addition, the output form can be pulsed laser or continuous-wave laser. In order to form grooves of a specified shape, preferably, the laser output power is set to 200 to 3000 W, the diameter of the focused laser spot in the rolling direction of the laser (the diameter including 86% of the laser output power) is set to 10 to 1000 μm, the diameter of the focused laser spot in the plate width direction is set to 10 to 1000 μm, and the laser scanning speed is set in the range of 5 to 100 m / s. In addition, as a method for removing the melt from the surface, blowing of auxiliary gas, etc. can be cited. For example, by blowing air, CO2, argon, etc. to the irradiation part simultaneously with the laser irradiation, and on the other hand, providing a suction part near it, the reattachment of the melt on the surface of the steel plate can be reduced.

[0189] The groove forming process is not essential and can be omitted.

[0190] [Grinding process]

[0191] In the grinding process, the surface of the cold-rolled sheet after the cold-rolling process (or the cold-rolled sheet after the groove-forming process if the groove-forming process has been performed) is ground. At this time, grinding is performed using abrasive grains having a Knoop hardness of 1000 or more, a maximum particle size exceeding 50 μm and 500 μm or less, or a sandpaper, roll, or brush to which the above abrasive grains are fixed. When grinding a coil-shaped cold-rolled sheet, it is preferable in terms of productivity and quality to perform grinding continuously using a through-feed line. In this case, generally, abrasive grains fixed in a brush are mainly used. Of course, a plate-shaped cold-rolled sheet can also be used, and in this case, grinding can also be performed using sandpaper or the like.

[0192] As described above, by allowing the inhibitor (precipitates such as AlN present at the crystal grain boundaries) to exist up to a high temperature during finish annealing, only the grains having a crystal orientation closer to the ideal Gaussian orientation grow, and the magnetic flux density is increased.

[0193] However, although the size of the inhibitor is very small, being several 10 nm 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 Gaussian orientation (ideal Gaussian 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 be constant within the preferred size range (in such a way that the difference in size becomes smaller).

[0194] In contrast, by suppressing the decomposition / oxidation of the inhibitor, as long as the inhibitor can be made to exist up to a high temperature, the secondary recrystallization of only the grains closer to the Gaussian orientation can be achieved. In addition, it is known that the above-mentioned Si-based pre-oxide formed in the base steel sheet (the cold-rolled sheet that becomes the base steel sheet) in the decarburizing annealing process contributes to the suppression of the decomposition / oxidation of the inhibitor.

[0195] However, this Si-based pre-oxide is easily affected by the process preceding the decarburizing annealing process, and the formation state on each part of the steel sheet surface easily becomes uneven. If its formation state is uneven, the suppression effect of the decomposition / oxidation of the inhibitor varies depending on the part within the steel sheet surface, and the target effect cannot be obtained.

[0196] Therefore, in the method for manufacturing a grain-oriented electrical steel sheet of the present embodiment, in order to make the formation state of the oxide layer after finish annealing as uniform as possible in a certain thickness region of the steel sheet surface, along with the implementation of cold rolling or the like that hinders the uniform formation of these oxide layers, the reactants on the steel sheet surface such as Fe-based oxides, oil-based agents, or extreme pressure additives that are unevenly formed on the steel sheet surface are removed from the steel sheet surface together with the grinding of the steel sheet surface before decarburizing annealing.

[0197] Specifically, by using abrasive grains having a Knoop hardness of 1000 or more, a maximum particle size exceeding 50 μm and being 500 μm or less, or sandpaper, a roll, or a brush to which the above abrasive grains are fixed, at least one surface of the steel plate is ground, thereby removing the Fe-based oxide film and the reaction product from the surface of the steel plate.

[0198] If the Knoop hardness is less than 1000, the hardness of the abrasive grains is insufficient with respect to the steel plate, so that grinding becomes difficult. Or the grinding efficiency decreases. In addition, if the maximum particle size of the abrasive grains is 50 μm or less, the particle size of the abrasive grains becomes relatively small with respect to the surface roughness of the steel plate, so that grinding becomes difficult. Or the grinding efficiency decreases. On the other hand, if the maximum particle size exceeds 500 μm, the particle size of the abrasive grains becomes relatively excessively large with respect to the surface roughness of the steel plate, so that surface defects are likely to be conspicuous during grinding, and the appearance quality of the product decreases. The upper limit of the Knoop hardness is not limited, but hard abrasive grains are liable to be brittle and liable to cause obstacles such as poor grinding during continuous use of sandpaper, rolls, brushes, etc. containing the abrasive grains. Therefore, 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.

[0199] Specifically, taking the process of grinding cold-rolled steel sheets as an example, the case of using a brush roll equipped with abrasive grains will be described. The brush roll has a resin lining on the surface of a metal roll, and abrasive grains embedded in fibers made of acrylic resin or the like are implanted in a hairy form on the surface of the resin layer of the roll. If 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 approximately in the range of 20 to 200 mpm (meters per minute; m / min), while moving the steel sheet, the brush roll rotating in a direction opposite to the sheet passing direction of the steel sheet is brought into contact with the steel sheet at the position where the steel sheet and the brush roll are in contact 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 (path line). The amount of press-down at this time is set to 1.0 to 5.0 mm. If the amount of press-down is small, the grinding amount becomes small. On the other hand, if the amount of press-down is increased to increase the grinding amount, since the brush roll is opposite to the sheet passing direction of the steel sheet, so-called "flutter" is likely to occur in which the steel sheet cannot pass smoothly due to the frictional force between the steel sheet and the brush roll and slight movement occurs. "Flutter" is an extremely undesirable event that should be avoided because the grinding on the surface of the steel sheet becomes uneven. The diameter of the brush roll is usually a roll of about 200 to 500 mm. This is because: if it is too small, the wear of the brush and the abrasive grains is fast, and if it is too large, the metal roll becomes excessively large and the equipment becomes large-scale. The brush rotates in a direction opposite to the sheet passing direction of the steel sheet as described above to perform 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 grinding speed (if it is a brush roll, it corresponds to the rotational speed) is set to 500 mpm or more. If the grinding speed (if it is a brush roll, it is the rotational speed) is small, the grinding amount becomes insufficient, the Si-based pre-oxide is not sufficiently formed, and the formation of flat grains becomes insufficient.

[0200] On the other hand, in the case of a brush roll, if the rotational speed becomes greater than 2000 mpm, the frictional force between the brush roll and the steel sheet becomes excessively large, not only causing the above-mentioned "flutter", but also overloading the motor driving the brush roll. Therefore, the rotational speed of the brush roll is preferably 2000 mpm or less.

[0201] 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 in at least one surface 2 or more. On the other hand, if the grinding amount exceeds 10.0 g / m 2 , the 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 the generation of sludge during grinding becomes significant. This treatment takes time and becomes a cause of defects on the surface of the steel sheet due to pressing in or the like. Therefore, the grinding amount is 10.0 g / m2 As follows.

[0202] The grinding amount can be confirmed based on the weight difference of the steel plate before and after grinding. The grinding amount is the grinding amount per single side. In the case where grinding is performed on both sides, it is obtained as the grinding amount per two sides. For convenience, from the viewpoint of removing the Fe-based oxide film and reactants before and after from the entire surface of the steel plate by setting its value to half, the preferable range of the grinding amount is 0.30 g / m 2 ~3.0 g / m 2 .

[0203] As described later, when forming a groove in the cold-rolled plate before the grinding process, the preferable depth of the groove is 10 to 30 μm. The surface of the steel plate inside the groove is also ground, so the effect of grinding is also effective on the inner surface of the groove formed on the surface of the cold-rolled plate. Therefore, flat grains (flat grains in the groove) are also formed on the surface side inside the groove of the base steel plate that has undergone decarburizing annealing and finish annealing.

[0204] [Contact process]

[0205] In the contact process, after the grinding process and before the decarburizing annealing process, the surface of the cold-rolled plate is brought into contact with an aqueous liquid phase having a pH of 4.0 to 10.0. Thereby, abrasive grains attached to the steel plate surface during grinding and steel sludge generated during grinding are removed. As the aqueous liquid, it can be ion-exchanged water, or it can contain minerals such as Ca and Mg in them, and can also contain carbonic acid and silicic acid as counter ions. In addition, a solution obtained by adding an acid selected from sulfuric acid, nitric acid, phosphoric acid, carbonic acid, carboxylic acid, phosphonic acid, etc. at about 0.01% by weight and adjusting the pH with an alkali metal, alkaline earth metal, etc. can also be used. Especially regarding carboxylic acid and phosphonic acid, the effect of removing abrasive grains and sludge from the steel plate is high. In the case of ion-exchanged water, from the viewpoint of preventing melting loss, its conductivity is preferably 0.1 to 10 μS / cm.

[0206] If the pH is lower than 4.0, melting loss of the steel plate occurs due to etching of the steel plate surface by the acidic aqueous liquid. If the pH exceeds 10.0, oxidation of the metal surface after grinding is promoted by the action of the alkaline aqueous liquid. Therefore, although the Fe-based oxide unevenly formed on the steel plate surface is removed during the grinding process, its effect is reduced. In this case, the initial target effect of uniformly forming the oxide layer and oxide particles after finish annealing cannot be obtained sufficiently.

[0207] For the above purposes, the contact time is preferably 0.1 to 60 seconds, more preferably 1 to 60 seconds, and further preferably 5 to 60 seconds. The flow rate of the aqueous liquid is preferably 1 to 100 L / min.

[0208] In addition, by performing the contacting step, abrasive grains and sludge can be removed from the surface of the steel sheet, and factors that hinder the uniform formation of the oxide layer and oxide particles after finish annealing can be avoided.

[0209] In the grinding step, the surface of the cold-rolled sheet can also be brought into contact with an aqueous liquid phase. However, if the contacting step is not performed after the grinding step, the above-described effects cannot be obtained.

[0210] [Decarburizing annealing step]

[0211] In the decarburizing annealing step, the cold-rolled sheet after the grinding step 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.

[0212] The decarburizing annealing conditions are not limited. However, as a nitrogen-hydrogen mixed atmosphere for decarburization, annealing is performed in an atmosphere in which the oxygen potential is increased by humidification. In addition, since it is necessary to form a primary recrystallized structure at the same time, the humidification temperature (dew point) is determined from the viewpoints of the annealing temperature required for recrystallization and the oxygen potential at which decarburization can be performed at this annealing temperature.

[0213] The annealing temperature is about 700 to 900 °C. Generally, annealing is performed in a continuous annealing step, and thus soaking is performed for about 60 seconds. As described above, it is known that annealing is performed in a humidified atmosphere with a high oxygen potential for decarburization. Therefore, Si contained in the steel forms a layered oxide on the surface of the steel sheet and oxide particles inside the steel sheet (hereinafter, referred to as the same Si-based pre-oxide).

[0214] [Nitriding treatment step]

[0215] In the nitriding treatment step, 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 finish annealing step. In the nitriding treatment step, it is preferable to set the nitrogen content of the steel sheet after the nitriding treatment to 0.015 to 0.050 mass%. The method of nitriding treatment is not limited and may be a known method.

[0216] The nitriding treatment step is not essential and may be omitted. When the nitriding treatment is performed, it is preferably performed between the decarburizing annealing step and the finish annealing step.

[0217] [Finish annealing step]

[0218] In the finish annealing step, an annealing release agent is applied to the cold-rolled sheet after the decarburizing annealing step (after the nitriding treatment step if the nitriding treatment is performed), and finish annealing is performed 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).

[0219] Final annealing is usually carried out by coiling the steel sheet into a coil shape and performing intermittent annealing because of the long annealing time. In order to raise the temperature of the steel sheet to about 1200 °C, an annealing parting agent is applied in such a way that the coiled steel sheet is not baked. Generally, MgO is mainly used as the annealing parting agent. By performing final annealing after applying such an annealing parting agent, a solid-phase reaction occurs between Mg contained in the annealing parting agent and the Si-based pre-oxide formed on the surface of the steel sheet in the decarburizing annealing process, and an oxide layer containing one or more of Mg and Si is formed on the surface of the cold-rolled sheet. For example, in the case of using an annealing parting agent containing MgO, a layer of forsterite (Mg2SiO4) film is mainly 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, but at this time, it is formed as spinel (MgAl2O4), alumina (Al2O3), or mullite (2SiO2·3Al2O3). In the case of using an annealing parting agent substantially containing only MgO, it is almost generated as spinel (MgAl2O4).

[0220] In addition, in the final annealing process, the primary recrystallized grains obtained in the decarburizing annealing process are subjected to secondary recrystallization by heating the steel sheet, grains with a Goss orientation are obtained, and the steel sheet is held at a specified time at an annealing temperature close to 1200 °C, whereby precipitates in the steel such as nitrides (e.g., AlN) and sulfides (e.g., MnS) that have completed their role as inhibitors are removed (purified) in such a way as not to have an adverse effect on magnetic properties.

[0221] In the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment, in the cold-rolled sheet subjected to final annealing, the size of the inhibitor is larger than usual and is uniformly controlled. Therefore, secondary recrystallization occurs only for grains close to the Goss orientation (grains having an orientation close to the Goss orientation).

[0222] The conditions for final annealing are not limited, but for example, the temperature is raised in the range from room temperature to 10 - 100 °C / h, and then raised at 5 - 20 °C / h in the temperature range of 900 - 1000 °C generally considered to cause secondary recrystallization to the Goss orientation to promote the preferential growth (secondary recrystallization) to the Goss orientation. After that, purification of the inhibitor that has completed its role is carried out near 1200 °C (e.g., 1150 - 1250 °C) as described above. Then, slow cooling is carried out in a non-oxidizing atmosphere such as hydrogen or nitrogen, and the coil is taken out of the furnace.

[0223] [Insulating film forming process]

[0224] In the insulating film forming process, an insulating film layer is formed on the surface of the above-mentioned oxide layer after the final annealing process.

[0225] For example, the insulating film layer can be formed in the following manner: A coating solution containing phosphoric acid or phosphate, colloidal silica, and chromic anhydride or chromate is coated on a cold-rolled plate (base steel plate + oxide layer) after finish annealing, and then baked and dried at 300 to 950 °C for 10 seconds or more. The atmosphere during baking is not particularly limited, but it is preferably non-oxidizing to inhibit oxidation of the steel plate, and it is preferably carried out in a non-oxidizing atmosphere such as nitrogen, argon, or hydrogen. As the film type, a coating solution with boric acid and alumina sol as the main components, or a coating solution with boric acid and aluminosilicate (such as kaolin minerals) as the main components can be used instead of the above-mentioned phosphate to form an insulating film with aluminum borate as the main component. By applying aluminum borate, a large tension can be imparted to the steel plate, thus reducing iron loss.

[0226] In this process, it also functions to flatten the steel plate that becomes in a coil shape during the batch annealing in the above-mentioned finish annealing by continuous annealing. That is, the baking of the insulating film and the continuous annealing of the steel plate in a coil shape are carried out at about 800 °C while applying a certain tension to obtain a flat steel plate. Therefore, it is sometimes also called the flattening annealing process.

[0227] Through these processes, a grain-oriented electrical steel sheet having a silicon steel sheet (base steel plate), an oxide layer, and an insulating film layer can be obtained.

[0228] Examples

[0229] (Example 1)

[0230] A steel melt containing Si: 3.25 mass%, Mn: 0.13 mass%, S: 0.006 mass%, C: 0.050 mass%, acid-soluble Al: 0.025 mass%, and N: 0.007 mass% is continuously cast to obtain a slab with a thickness of 300 mm.

[0231] After the slab is heated in an electric furnace adjusted to a nitrogen atmosphere at 1150 °C for 60 minutes, it is rough hot-rolled to obtain a steel plate with a thickness of 40 mm, and then further finish-rolled to obtain a hot-rolled plate with a thickness of 2.3 mm.

[0232] After that, hot-rolled plate annealing is carried out by heating in a continuous annealing furnace adjusted to a nitrogen atmosphere at 1100 °C for 60 seconds and then cooling.

[0233] The obtained steel plate (hot-rolled plate) is pickled with 10% hydrochloric acid to remove the scale on the steel plate.

[0234] After that, cold rolling is carried out to obtain a cold-rolled plate with a thickness of 0.22 mm.

[0235] The obtained cold-rolled sheet is ground on the surface while flowing ion-exchanged water with a pH of 2.5 to 12.0 using various abrasive brushes described in Table 1. Additionally, after grinding, the ion-exchanged water with a pH of 2.5 to 12.0 is brought into contact with the surface. However, as shown in Table 1, for some steel sheets, as a comparison, it is set as a steel sheet that is not ground and not brought into contact with ion-exchanged water after grinding. During contact, the contact time is 5 seconds, and the flow rate of the aqueous liquid is set to 10 L / min.

[0236] For the steel sheets that have been ground and brought into contact with the aqueous liquid (in the case where neither is performed, it is the cold-rolled sheet after cold rolling, or in the case where contact with the aqueous liquid is not performed, it is the cold-rolled sheet after the grinding process), a 1000 mm × 1000 mm specimen is collected and the appearance is evaluated by visual observation.

[0237] The judgment criteria are set as follows.

[0238] 5: Very beautiful

[0239] 4: Beautiful

[0240] 3: Partially has stripe defects

[0241] 2: Has attachment unevenness

[0242] 1: The entire surface has stripe defects

[0243] In the case where the appearance evaluation is 1, as it fails to meet the general appearance requirements, subsequent evaluations are not carried out.

[0244] Additionally, for the steel sheets that have been ground and brought into contact with the aqueous liquid (in the case where neither is performed, it is the cold-rolled sheet after cold rolling, or in the case where contact with the aqueous liquid is not performed, it is the cold-rolled sheet after the grinding process), decarburizing annealing is carried out. The annealing atmosphere is set as a nitrogen 50% + hydrogen 50% atmosphere, and the oxygen potential (P H2O / P H2 ) is set to 0.33. The oxygen potential is adjusted by humidifying the atmosphere before introducing it into the furnace to adjust the moisture content. In this atmosphere, decarburizing annealing is carried out by soaking at 850 °C for 60 seconds.

[0245] After that, nitriding treatment is carried out by soaking at 750 °C for 30 seconds in a nitrogen-hydrogen-ammonia atmosphere. At this time, the ammonia concentration is adjusted so that the nitrogen content after nitriding treatment becomes 0.020 mass%.

[0246] After that, the aqueous slurry of the annealing separating agent mainly composed of MgO is adjusted so that the dried adhesion amount per single side becomes 6 g / m 2The annealing release agent is coated on both sides of the steel sheet in such a way that the steel sheet is dried. At this time, as the composition of the annealing release agent, with respect to 100 parts by mass of MgO, TiO2 is set to 5 parts by weight, and FeCl2 is set to 0.020% by mass in terms of Cl.

[0247] After that, as finish annealing, the specimen is placed in an intermittent annealing furnace and heated at an average heating rate of 20 °C / h in an atmosphere of 50% nitrogen + 50% hydrogen. After heating to 1200 °C, the atmosphere is switched to 100% hydrogen and held for 20 h for soaking, and then cooled to room temperature.

[0248] After the finish annealing is completed, the steel sheet is taken out of the furnace and washed with water to remove the annealing release agent. At this time, a glass film containing forsterite is formed on the surface of the steel sheet (silicon steel sheet), and an oxide layer containing granular spinel (MgAl2O4), alumina (Al2O3) and / or mullite is formed between the glass film and the steel sheet.

[0249] By coating a liquid medicine containing an insulating film composition including aluminum phosphate, colloidal silica, and chromic anhydride on this steel sheet (a steel sheet with an oxide layer, i.e., a glass film, formed on the surface of the silicon steel sheet as the base material steel sheet), heating to 800 °C in a nitrogen atmosphere and holding for 30 seconds, baking is carried out to form an insulating film layer. The coating amount of the insulating film layer is 4.8 g / m per single side 2 。

[0250] In addition, in the obtained silicon steel sheet (having a silicon steel sheet, a glass film (oxide layer) and an insulating film layer), the evaluation of oxides and flat grains in the range of 10 μm in the thickness direction from the interface with the oxide layer is carried out by the above method. The results are shown in Table 2.

[0251] In this embodiment, as shown in the table, the oxides of one or more of Mg, Al, and Si with an equivalent circle diameter of 0.1 - 3.0 μm in the range of 10 μm in the 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.

[0252] From the obtained grain-oriented electrical steel sheet (having a silicon steel sheet, a glass film (oxide layer) and an insulating film layer), 36 specimens with a plate width direction of 30 mm × a rolling direction of 280 mm are collected by shearing, and stress relief annealing is carried out on these specimens at 800 °C for 2 h in a nitrogen atmosphere.

[0253] Thereafter, using the magnetic property measurement method specified by the Epstein method described in JIS-C-2550-1:2011, the magnetic flux density (hereinafter referred to as B8) at an excitation magnetic force of 800 A / m and the iron loss (hereinafter referred to as W17 / 50) at an excitation of an excitation frequency of 50 Hz and a magnetic flux density of 1.7 T were measured.

[0254] If B8 is 1.90 T or more and W17 / 50 is 0.85 W / kg or less, it is judged to have excellent magnetic properties. The results are shown in Table 2.

[0255] In addition, from the obtained grain-oriented electrical steel sheet, a specimen with a size of 300 mm in the rolling direction and 300 mm in the width direction was collected, and the specimen was wound around a SUS304 round bar with a diameter of 20 mm After unwinding, the insulating film on the concave part on the inner side of the wound part was observed to evaluate the adhesion of the insulating film.

[0256] The judgment criteria are set as follows.

[0257] G (good): No film peeling

[0258] P (poor): Part of the film peeling

[0259] B (bad): The entire surface film peeling

[0260] The results are shown in Table 2.

[0261] [Table 1]

[0262]

[0263] [Table 2]

[0264]

[0265] According to the results shown in Table 1 and Table 2, for the examples of grinding the surface of the steel sheet and contacting with the aqueous liquid under the conditions of the present invention, within a range of 10 μm in the plate thickness direction from the interface between the silicon steel sheet and the above oxide layer, one or more oxides of Mg, Al, and Si with an equivalent circle diameter of 0.1 to 3.0 μm exist at a density of 0.010 to 0.200 per μm 2 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 70% or more. In addition, as a result, for these examples, the magnetic properties are excellent.

[0266] On the other hand, in the case of non-contact with the aqueous liquid as specified or examples where the grinding conditions are not preferable, the appearance that does not meet the usual requirements, or the oxide in the surface layer is not sufficiently formed or the flat grains are not sufficiently formed. Additionally, as a result, the magnetic properties are inferior (a part with poor appearance is not evaluated).

[0267] (Example 2)

[0268] Using the same molten steel and slab as those used in Example 1, hot rolling, hot rolled sheet annealing, pickling, and cold rolling were performed in the same manner as in Example 1 to obtain a cold rolled sheet with a thickness of 0.22 mm.

[0269] On one side of the obtained cold rolled sheet, a commercially available fiber laser was used to perform laser irradiation under the conditions of the laser output power, condensing spot diameter (in the transverse direction TD and rolling direction RD of the sheet width), and scanning speed shown in the table. During laser irradiation, argon was blown as an assist gas in such a way that the melt generated from the steel sheet no longer adhered to the steel sheet. A suction channel was provided at a position opposite to the assist gas ejection port to recover the dust caused by the melt generated by laser irradiation. Through this laser irradiation, linear grooves with a cross-sectional projection shape of approximately triangular in width and depth shown in the table were formed on its surface. The grooves extend in the direction shown in the table, and the grooves are periodically formed parallel to the rolling direction and at intervals shown in the table in the rolling direction.

[0270] Next, while flowing ion-exchanged water with pH = 4.0 - 6.0, the surface of the cold rolled sheet with grooves was ground under the conditions shown in Table 2. Further, after grinding, it was brought into contact with ion-exchanged water with pH = 4.0 - 6.0. During contact, the contact time was 5 seconds, and the flow rate of the aqueous liquid was set to 10 L / min.

[0271] After that, decarburization annealing, nitriding treatment, coating with an annealing separating agent mainly composed of MgO, and finish annealing were performed under the same conditions as in Example 1.

[0272] After finish annealing, the annealing separating agent was removed by water washing, and as a result, a glass film (oxide layer) was formed on the surface of the steel sheet.

[0273] By coating a liquid medicine containing an insulating film component including aluminum phosphate, colloidal silica, and chromic anhydride on the silicon steel sheet having this glass film, heating to 800 °C in a nitrogen atmosphere and holding for 30 seconds, the insulating film was baked. At this time, the coating amount of the insulating film layer was 5.0 g / m per one side 2 .

[0274] In the obtained silicon steel sheet (having a silicon steel sheet, a glass film (oxide layer), and an insulating film layer), the evaluation of the oxide and flat grains in the range of 10 μm in the plate thickness direction from the interface with the oxide layer was performed in the same manner as in Example 1. In addition, in this example, the flat grains in the slot were also evaluated.

[0275] From the obtained grain-oriented electrical steel sheet (having a silicon steel sheet, a glass film (oxide layer), and an insulating film layer), 36 specimens with a plate width direction of 30 mm and a rolling direction of 280 mm were collected by shearing, and these specimens were stress-relieved annealed at 800 °C for 2 h in a nitrogen atmosphere.

[0276] After that, using the magnetic property measurement method specified by the Epstein method described in JIS-C-2550-1:2011, the magnetic flux density (hereinafter referred to as B8) at an excitation magnetic force of 800 A / m and the iron loss (hereinafter referred to as W17 / 50) at an excitation of an excitation frequency of 50 Hz and a magnetic flux density of 1.7 T were measured.

[0277] In addition, by collecting a specimen with a rolling direction of 300 mm and a width direction of 300 mm from the obtained grain-oriented electrical steel sheet, the specimen was wound around a SUS304 round bar with a diameter of 20 mm After unwinding, the insulating film on the inner concave part of the wound part was observed to evaluate the adhesion of the insulating film.

[0278] The judgment criteria were set as follows.

[0279] G (good; GOOD): No film peeling

[0280] P (poor; POOR): Part of the film peeling

[0281] B (bad; BAD): The entire surface film peeling

[0282] [Table 3]

[0283]

[0284] [Table 4]

[0285]

[0286] [Table 5]

[0287]

[0288] As can be seen from Tables 3 to 5, sufficient film adhesion can be obtained in any case, and a low iron loss of 0.85 W / kg or less is achieved. However, in the case of forming the slot under preferred conditions, the iron loss is further reduced to 0.76 W / Kg or less.

[0289] Industrial Applicability

[0290] According to the present invention, a grain-oriented electrical steel sheet having excellent magnetic properties and a method for manufacturing the same can be provided. Therefore, the industrial applicability is high.

[0291] Symbol Explanation

[0292] 1 Grain-oriented electrical steel sheet

[0293] 11 Silicon steel sheet

[0294] 21 Oxide layer

[0295] 31 Insulating film layer

[0296] 101 Oxide (oxide particles)

[0297] 102 Elongated grain

[0298] G Groove

[0299] t Thickness

[0300] 102 Elongated grain in the groove

Claims

1. A directional 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 10 μm in the plate thickness direction from the interface between the silicon steel sheet and the oxide layer of the silicon steel sheet, oxides of one or more of Mg, Al, and Si with an equivalent circle diameter of 0.1 to 3.0 μm exist at a density of 0.010 to 0.200 per μm 2 ​ 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 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 70% or more.

2. The grain-oriented electromagnetic steel sheet according to claim 1, wherein the average of the average thickness of the flat grains exceeds 2.0 μm and is 5.0 μm or less.

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

4. The grain-oriented electromagnetic steel sheet according to claim 1 or 2, wherein a plurality of grooves with a depth of 10 to 30 μm and extending in a direction at 80 to 100° with respect to the rolling direction exist on the silicon steel sheet, the interval in the rolling direction between adjacent grooves is 1.0 to 20.0 mm.

5. The grain-oriented electromagnetic steel sheet according to claim 3, wherein a plurality of grooves with a depth of 10 to 30 μm and extending in a direction at 80 to 100° with respect to the rolling direction exist on the silicon steel sheet, the interval in the rolling direction between adjacent grooves is 1.0 to 20.0 mm.

6. The grain-oriented electromagnetic steel sheet according to claim 4, wherein intra-groove flat grains exist on the surface side of the grooves of the silicon steel sheet, the average particle size of the intra-groove flat grains in the direction perpendicular to the surface of the grooves 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 particle size, is 2.0 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 perpendicular to the extending direction of the grooves, the length of the grain boundaries of the intra-groove flat grains in the length of the inner surface of the grooves is 70% or more.

7. The grain-oriented electromagnetic steel sheet according to claim 5, wherein intra-groove flat grains exist on the surface side of the grooves of the silicon steel sheet, the average particle size of the intra-groove flat grains in the direction perpendicular to the surface of the grooves 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 particle size, is 2.0 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 perpendicular to the extending direction of the grooves, the length of the grain boundaries of the intra-groove flat grains in the length of the inner surface of the grooves is 70% or more.

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

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

10. A method for manufacturing a directional electromagnetic steel sheet, characterized in that, The following steps are included: 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 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 liquid phase 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 finish annealing step of coating a finish annealing release agent on the cold rolled sheet after the decarburizing annealing step, performing finish annealing, and forming an oxide layer containing one or more of Mg, Al, and Si on the surface of the cold rolled sheet that becomes the base metal steel sheet; and An insulating film forming step of forming an insulating film layer on the surface of the oxide layer after the finish annealing step, In the grinding process, grinding is performed at a depth of cut of 1.0 to 5.0 mm and a grinding speed of 500 mpm or more using abrasive grains having a Knoop hardness of 1000 or more, a maximum particle size exceeding 50 μm and 500 μm or less, or a sandpaper, roll, or brush to which the abrasive grains are fixed, and the grinding amount of the cold-rolled sheet is set to 0.10 to 10.0 g / m in at least one surface. 2 .

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

12. The method for manufacturing a grain-oriented electrical steel sheet according to claim 11, characterized in that in the groove forming step, the groove is formed by irradiating the surface of the cold rolled sheet with a laser to melt a part of the steel sheet surface and removing the melt from the surface.

Images