Sheet of electrical steel with an orientated grain structure and a method for forming an insulating coating

Abstract

FIELD: metallurgy.SUBSTANCE: invention relates to a sheet of electrical steel with an oriented grain structure and to a method for forming an insulating coating. An electrical steel sheet with an oriented grain structure comprises a base steel sheet and an insulating coating formed on the surface of the base steel sheet, wherein the insulating coating includes an intermediate layer formed on the side of the base steel sheet and comprising crystalline metal phosphate and one or more of amorphous silicon dioxide, an inorganic filler and a metal oxide, and a tension-imparting coating layer formed on the surface side of the insulating coating. One or more of the amorphous silica, inorganic filler and metal oxide has an average particle diameter of 10-500 nm.EFFECT: reduced iron losses.5 cl, 1 dwg, 3 tbl, 21 ex

Description

Field of technology to which the invention relates

[0001] The present invention relates to a grain-oriented electrical steel sheet and a method for forming an insulating coating. This application claims priority to Japanese Patent Application No. 2023-064836, filed on April 12, 2023, the contents of which are incorporated herein by reference.Background of the Invention

[0002] Grain-oriented electrical steel sheet is primarily used for transformers. A transformer is continuously magnetized for a long period of time, from installation to disposal, and continues to generate energy losses. Therefore, the energy loss when a transformer is magnetized by alternating current, i.e., iron loss, is the main index for determining the transformer's performance.

[0003] In order to reduce the iron loss of grain-oriented electrical steel sheet, many technologies have been developed so far in terms of (a) increasing the development of orientation {110} <001> (Goss orientation), (b) increasing the content of a solid solution element such as Si to increase the electrical resistance of the steel sheet, or (c) decreasing the sheet thickness for electrical steel sheet.

[0004] In addition, applying tension to the steel sheet is effective in reducing iron loss. This is an effective means of reducing iron loss by forming a coating made of a material with a thermal expansion coefficient lower than that of the steel sheet on the sheet surface at high temperatures. A forsterite film (an inorganic coating) with exceptional coating adhesion, formed through a reaction between the oxide on the sheet surface and an annealing separator during the final annealing of electrical steel sheets, is a coating capable of applying tension to the steel sheet.

[0005] For example, the method for forming an insulating coating by sintering a coating liquid mainly containing colloidal silica and phosphate on the surface of a sheet disclosed in Patent Document 1 is an effective method for reducing iron loss, since the method has a large effect of applying tension to the steel sheet. Therefore, a general method for producing a grain-oriented electrical steel sheet is to leave the forsterite film formed in the final annealing step and form an insulating coating mainly containing phosphate on the forsterite film.

[0006] However, in recent years, the demand for miniaturization and improved transformer performance has increased. To achieve miniaturization, grain-oriented electrical steel sheets must exhibit exceptional iron loss at high magnetic fields, so that iron loss is preferable even at high magnetic flux density. At the same time, it has been discovered in recent years that forsterite film hinders magnetic domain wall movement and has a negative impact on iron loss. In grain-oriented electrical steel sheets, the magnetic domain changes through magnetic domain wall movement under the action of an alternating magnetic field.The smooth and rapid movement of the magnetic domain wall is effective in reducing iron loss, but the forsterite film itself is a non-magnetic body and has an uneven structure at the interface between the steel sheet and the coating, and it is believed that this uneven structure makes it difficult for the magnetic domain wall to move and therefore has a negative effect on iron loss.Therefore, as a means for improving the iron loss in a high magnetic field, a technology for producing a grain-oriented electrical steel sheet without a forsterite film (inorganic coating) or a technology for making the surface of the sheet into a mirror surface state (in other words, a technology for magnetically smoothing the surface of the sheet) has been studied by removing the forsterite film by using a mechanical means such as polishing or a chemical means such as pickling; or preventing the formation of the forsterite film by high-temperature final annealing.

[0007] As a technology for preventing the formation of a fosterite film, for example, Patent Document 2 discloses a technology in which the product formed on the surface is removed by pickling after normal final annealing, and then the sheet surface is brought to a mirror surface by chemical polishing or electrolytic polishing. It was found that an improved iron loss effect can be achieved by forming a tension-type insulating coating on the surface of a grain-oriented electrical steel sheet without a forsterite film, obtained using this known method. Furthermore, the tension-type insulating coating can impart various characteristics, such as corrosion resistance, heat resistance, and slip resistance, in addition to improving iron loss.

[0008] However, when a tension-applied coating (tension-applied insulation coating) is formed, the forsterite film exhibits both insulating properties and acts as an intermediate layer to ensure adhesion. In other words, since the forsterite film is formed in a state of deep penetration into the steel sheet, the forsterite film has excellent adhesion to the steel sheet, which is a metal. Therefore, when a tension-applied coating (tension-applied coating), mainly containing colloidal silica, phosphate, and the like as the main components, is formed on the surface of the forsterite film, the coating adhesion is excellent. On the other hand, since it is generally difficult to bond metal and oxide, it is difficult to ensure sufficient adhesion between the tension-applied coating and the sheet surface without the forsterite film.Thus, in the case of forming a tension-imparting coating on a grain-oriented electrical steel sheet without a forsterite film, how to provide a layer that replaces the forsterite film as an intermediate layer was studied.

[0009] For example, Patent Document 3 discloses a technology in which a grain-oriented electrical steel sheet without a fosterite film (inorganic film) is annealed in a weakly reducing atmosphere, and the silicon inevitably contained in the electrical steel sheet is thermally oxidized selectively to form a SiO2 layer on the surface of the sheet, and then an insulating coating is formed by applying tension. Furthermore, Patent Document 4 discloses a technology in which a grain-oriented electrical steel sheet without a fosterite film (inorganic film) is subjected to anode electrolytic treatment in a silicate aqueous solution to form a SiO2 layer on the surface of the sheet, and then an insulating coating is formed by applying tension.

[0010] However, the technology disclosed in Patent Document 3 requires the preparation of an annealing apparatus capable of controlling the atmosphere to perform annealing in a weakly reducing atmosphere, and there is a problem with processing costs. The technology disclosed in Patent Document 4 requires the preparation of a new electrolytic processing apparatus to produce a SiO2 layer that maintains sufficient adhesion to the insulating coating by applying tension to the sheet surface through anodic electrolytic processing in a silicate aqueous solution, and there is a problem with processing costs.

[0011] On the other hand, Patent Document 5 discloses a grain-oriented electrical steel sheet comprising a base steel sheet and an insulating coating formed on the surface of the base steel sheet. The insulating coating is formed on the side of the base steel sheet and includes an intermediate layer containing crystalline metal phosphate and a tension-imparting coating layer formed on the surface side of the insulating coating. In this grain-oriented electrical steel sheet, the intermediate layer can be formed by chemical conversion treatment.List of ReferencesPatent Documents

[0012] Patent Document 1. Unexamined Patent Application (Japan), First Publication Number S48-039338Patent Document 2. Unexamined Patent Application (Japan), First Publication Number S49-96920Patent Document 3. Unexamined Patent Application (Japan), First Publication Number H06-184762Patent Document 4. Unexamined Patent Application (Japan), First Publication Number H11-209891Patent Document 5. International PCT Publication Number WO 2022 / 215709Summary of the InventionTechnical Problem

[0013] In the technology of Patent Document 5, an intermediate layer made of crystalline metal phosphate is provided between the base steel sheet and the tension-imparting coating, so that the coating adhesion, coating tension, and magnetic properties can be improved. Furthermore, since the intermediate layer can be formed through chemical conversion treatment, no special installation is required. Therefore, it represents a useful technology. However, as a result of research by the present inventors, it was discovered that in the grain-oriented electrical steel sheet of Patent Document 5, when adhesion is improved, the magnetic properties of the transformer may deteriorate.As a result of further investigation of this fact, it was found that the reason for the deterioration of magnetism is the coarsening of the metal phosphate crystals released during chemical conversion treatment and the decrease in the fill factor when the actual transformer is manufactured.

[0014] Therefore, the object of the present invention is to provide a grain-oriented electrical steel sheet in which a metal phosphate-containing layer is formed on the surface of the steel sheet through chemical conversion treatment, wherein the grain-oriented electrical steel sheet has excellent adhesion of a tension coating and magnetic characteristics and does not reduce the fill factor (core). At the same time, it is expected that the basic characteristics required for the coating, such as corrosion resistance and resistance to phosphoric acid dissolution, are not deteriorated. Solution to the problem

[0015] The inventors of the present invention have found that when a layer containing a metal phosphate is provided as an intermediate layer for improving the adhesion between a base steel sheet and a tension-imparting coating layer, the coarsening of metal phosphate crystals can be suppressed by including a substance for suppressing the crystallization of the phosphate in a chemical processing liquid.

[0016] The present invention has been realized taking into account the above conclusions. The essence of the present invention is as follows.

[0001] A grain-oriented electrical steel sheet according to an aspect of the present invention includes a base steel sheet; and an insulating coating formed on the surface of the base steel sheet, wherein the insulating coating includes an intermediate layer formed on the side of the base steel sheet and containing crystalline metal phosphate and one or more of amorphous silicon dioxide, an inorganic filler and a metal oxide, and a tension-imparting coating layer formed on the surface side of the insulating coating, and one or more of the amorphous silicon dioxide, the inorganic filler and the metal oxide has an average particle diameter of 10-500 nm.

[0002] In the grain-oriented electrical steel sheet according to [1], the inorganic filler may contain one or two or more of aluminum oxide, BN, AlN, and kaolin.

[0003] In the grain-oriented electrical steel sheet according to [1] or [2], the metal oxide may be one or two or more of titanium oxide, zinc oxide, and calcium oxide.

[0004] In the grain-oriented electrical steel sheet according to any one of [1] to [3], the crystalline metal phosphate may have an average grain diameter of 1.0 to 12.0 μm.

[0005] A method for forming an insulating coating according to another aspect of the present invention is a method for forming an insulating coating in a grain-oriented electrical steel sheet according to [1], wherein the method includes a final annealing step of applying an annealing separator containing 10-100 mass% of Al2O3 to the steel sheet, drying the annealing separator, and then performing final annealing; an annealing separator removing step of removing excess annealing separator from the steel sheet after the final annealing step; a light pickling step of pickling the steel sheet after the annealing separator removing step with an pickling liquid having a liquid temperature of 30-85°C and having 0.10-10.0 mass%.% of one inorganic acid selected from sulfuric acid, chloric acid, nitric acid and phosphoric acid for 1-20 seconds; an immersion step of immersing the steel sheet after the light pickling step in a treatment liquid having a liquid temperature of 30-85°C and containing 0.3-10.0 wt. % of a metal phosphate, 0.01-10.0 g / L of one or more of colloidal silicon dioxide, an inorganic filler and a metal oxide having an average particle diameter of 10-500 nm, for 5-150 seconds; a drying step of taking out the steel sheet after the immersion step from the treatment liquid, removing excess treatment liquid and then drying the steel sheet; and a step of forming a tension-imparting coating layer for application to the steel sheet after the step of drying the coating liquid containing the metal phosphate and colloidal silicon dioxide so that the total concentration of the metal phosphate and colloidal silicon dioxide is 10-40 wt.%, drying the coating liquid, then heating the steel sheet and holding the steel sheet at a sheet temperature of 700-950°C for 10-50 seconds. Advantages of the invention.

[0017] According to the above aspect of the present invention, it is possible to provide a grain-oriented electrical steel sheet that has excellent adhesion and magnetic characteristics of the tension-imparting coating and does not reduce the fill factor (core).Brief description of the drawings

[0018] Fig. 1 is an example of a cross-sectional view of a grain-oriented electrical steel sheet according to the present embodiment of the invention. Detailed Description of Embodiments of the Invention

[0019] Next, a grain-oriented electrical steel sheet according to an embodiment of the present invention (a grain-oriented electrical steel sheet according to the present embodiment) and a method for producing a grain-oriented electrical steel sheet according to the present embodiment, including a method for forming an insulating coating in the grain-oriented electrical steel sheet according to the present embodiment, will be described. First, the grain-oriented electrical steel sheet according to the present embodiment will be described.

[0020] As illustrated in Fig. 1, the grain-oriented electrical steel sheet 100 according to the present embodiment comprises a base steel sheet 1 and an insulating coating 2 formed on the surface of the base steel sheet 1. In the grain-oriented electrical steel sheet 100 according to the present embodiment, a forsterite film is not intentionally formed on the surface of the base steel sheet 1, and the forsterite film is not present in many cases. However, the presence of the forsterite film is acceptable as long as the coating weight is 1.0 g / m 2or less (in this case, a forsterite film is present between the base steel sheet 1 and the insulating coating 2). The insulating coating 2 comprises a tension coating layer 22 formed on the surface side of the insulating coating 2 (that is, on the surface side of the grain-oriented electrical steel sheet 100), and an intermediate layer 21 formed on the side of the base steel sheet 1 and containing crystalline metal phosphate. In addition, the intermediate layer 21 contains crystalline metal phosphate and one or more of amorphous silica, an inorganic filler, and a metal oxide having an average particle diameter of 10-500 nm. Each of the above is described below.

[0021] Base Steel SheetChemical CompositionThe grain-oriented electrical steel sheet 100 according to the present embodiment has a main feature in the structure of the insulating coating 2 formed on the surface of the base steel sheet 1, and the base steel sheet 1 included in the grain-oriented electrical steel sheet 100 is not limited in terms of its chemical composition. However, in order to obtain the characteristics generally required for the grain-oriented electrical steel sheet, it is preferable to include the following components as chemical components. In the present embodiment, the % related to the chemical composition is "mass%" unless otherwise specified.

[0022] C: 0.010% or lessC (carbon) is an element effective in controlling the microstructure of a steel sheet in the steps before the completion of the decarburization annealing step in the manufacturing process. However, when the C content exceeds 0.010%, the magnetic properties of the grain-oriented electrical steel sheet, which is the sheet produced, deteriorate. Therefore, in the base steel sheet for the grain-oriented electrical steel sheet according to the present embodiment, the C content is preferably 0.010% or less. The C content is more preferably 0.005% or less. The C content is preferably as low as possible, but even when the C content is reduced to less than 0.0001%, the effect of controlling the microstructure is saturated, and the manufacturing cost simply increases. Therefore, the C content can be 0.0001% or more.

[0023] Si: 2.50-4.00% Si (silicon) is an element that increases the electrical resistance of grain-oriented electrical steel sheets and improves the iron loss performance. When the Si content is less than 2.50%, a sufficient effect of reducing eddy current losses cannot be obtained. Therefore, the Si content is preferably 2.50% or more. The Si content is more preferably 2.70% or more, and even more preferably 3.00% or more. On the other hand, when the Si content exceeds 4.00%, the grain-oriented electrical steel sheets become brittle, and the rolling passability is significantly deteriorated. In addition, the machinability of the grain-oriented electrical steel sheets is deteriorated, and the steel sheet may fracture during rolling. Therefore, the Si content is preferably set to 4.00% or less.The Si content is more preferably 3.80% or less, and even more preferably 3.70% or less.

[0024] Mn: 0.01-0.50% Mn (manganese) is an element that combines with S during the manufacturing process to form MnS. This inclusion functions as an inhibitor (an inhibitor of normal grain growth) and causes secondary recrystallization in steel. Mn is also an element that improves the hot workability of steel. When the Mn content is less than 0.01%, the above-mentioned effect cannot be sufficiently obtained. Therefore, the Mn content is preferably 0.01% or more. The Mn content is more preferably 0.02% or more. On the other hand, when the Mn content exceeds 0.50%, secondary recrystallization does not occur, and the magnetic properties of the steel deteriorate. Therefore, in the base steel sheet for the grain-oriented electrical steel sheet according to the embodiment of the invention, the Mn content is preferably 0.50% or less.The Mn content is more preferably 0.20% or less, and still more preferably 0.10% or less.

[0025] N: 0.010% or lessN (nitrogen) is an element that bonds with Al during the manufacturing process to form AlN, which functions as an inhibitor. However, when the N content exceeds 0.010%, the inhibitor remains excessively in the base steel sheet for the grain-oriented electrical steel sheet, and the magnetic characteristics deteriorate. Therefore, in the base steel sheet for the grain-oriented electrical steel sheet according to the embodiment of the invention, the N content is preferably 0.010% or less. The N content is more preferably 0.008% or less. On the other hand, the lower limit of the N content is not particularly limited, but even when the N content is reduced to less than 0.001%, the manufacturing cost simply increases. Therefore, the N content can be 0.001% or more.

[0026] Soluble Al: 0.020% or lessSoluble Al (acid-soluble aluminum) is an element that combines with N during the manufacturing process of grain-oriented electrical steel sheet to form AlN, which functions as an inhibitor. However, when the soluble Al content in the base steel sheet exceeds 0.020%, the inhibitor remains excessively in the base steel sheet, so that the magnetic characteristics deteriorate. Therefore, in the base steel sheet for the grain-oriented electrical steel sheet according to the embodiment of the invention, the soluble Al content is preferably 0.020% or less. The soluble Al content is more preferably 0.010% or less, and even more preferably less than 0.001%.There is no specific lower limit for soluble Al content, but even when the content is reduced to less than 0.0001%, manufacturing costs simply increase. Therefore, soluble Al content can be 0.0001% or more.

[0027] S: 0.010% or lessS (sulfur) is an element that combines with Mn during the manufacturing process to form MnS, which functions as an inhibitor. However, when the S content exceeds 0.010%, the remaining inhibitor causes deterioration in magnetic characteristics. Therefore, in the base steel sheet for the grain-oriented electrical steel sheet according to the present embodiment, the S content is preferably 0.010% or less. The S content in the grain-oriented electrical steel sheet is more preferably as low as possible. For example, the S content is less than 0.001%. However, even if the S content in the base steel sheet for the grain-oriented electrical steel sheet is reduced to less than 0.0001%, the manufacturing cost simply increases.Therefore, the S content in the base steel sheet for the grain-oriented electrical steel sheet may be 0.0001% or more.

[0028] The rest is Fe and impuritiesThe chemical composition of the base steel sheet for the grain-oriented electrical steel sheet according to the present embodiment may contain the above-described elements, with the rest being Fe and impurities. However, the base steel sheet may further contain Sn, Cu, Se, and Sb in the following ranges for the purpose of improving magnetic characteristics and the like. In addition, for example, even when the base steel sheet contains any one or more of W, Nb, Ti, Ni, Co, V, Cr, and Mo in a total amount of 1.0% or less as elements other than these elements, the effect of the grain-oriented electrical steel sheet according to the present embodiment is not impaired.Here, the impurity is an element that is a contaminant coming from ore or scrap as a raw material, a production environment, and the like., when the base steel sheet is industrially manufactured, and means an element that can be included with a content that does not adversely affect the effect of the grain-oriented electrical steel sheet according to the embodiment of the invention.

[0029] Sn: 0-0.50%Sn (tin) is an element that contributes to improving magnetic characteristics by controlling the primary recrystallization structure. To achieve the effect of improving magnetic characteristics, the Sn content is preferably 0.01% or more. The Sn content is more preferably 0.02% or more, and even more preferably 0.03% or more. On the other hand, when the Sn content exceeds 0.50%, secondary recrystallization is unstable, and the magnetic characteristics deteriorate. Therefore, the Sn content is preferably 0.50% or less. The Sn content is more preferably 0.30% or less, and even more preferably 0.10% or less.

[0030] Cu: 0-0.50%Cu (copper) is an element that promotes an increase in the occupancy of the Goss orientation in the secondary recrystallization structure. To obtain the above-mentioned effect, the Cu content is preferably 0.01% or more. The Cu content is more preferably 0.02% or more, and even more preferably 0.03% or more. On the other hand, when the Cu content exceeds 0.50%, the steel sheet becomes brittle during hot rolling. Therefore, in the base steel sheet for the grain-oriented electrical steel sheet according to the embodiment of the invention, the Cu content is preferably 0.50% or less. The Cu content is more preferably 0.30% or less, and even more preferably 0.10% or less.

[0031] Se: 0-0.020%Selenium (Se) is an element having the effect of improving magnetic characteristics. When Se is contained, the Se content is preferably 0.001% or more, so that Se preferably exhibits the effect of improving magnetic characteristics. The Se content is more preferably 0.003% or more, and even more preferably 0.006% or more. On the other hand, when the Se content exceeds 0.020%, the coating adhesion deteriorates. Therefore, the Se content is preferably 0.020% or less. The Se content is more preferably 0.015% or less, and even more preferably 0.010% or less.

[0032] Sb: 0-0.50%Sb (antimony) is an element having the effect of improving magnetic characteristics. When Sb is contained, the Sb content is preferably 0.005% or more, so that Sb preferably exhibits the effect of improving magnetic characteristics. The Sb content is more preferably 0.01% or more, and even more preferably 0.02% or more. On the other hand, when the Sb content exceeds 0.50%, the adhesion of the coating is significantly deteriorated. Therefore, the Sb content is preferably 0.50% or less. The Sb content is more preferably 0.30% or less, and even more preferably 0.10% or less.

[0033] As described above, for example, the chemical composition of the base steel sheet for the grain-oriented electrical steel sheet according to the present embodiment of the invention contains the above-described elements, with the remainder being Fe and impurities.

[0034] The chemical composition of the base steel sheet for the grain-oriented electrical steel sheet according to the present embodiment can be measured using known ICP emission spectrometry. It should be noted that during measurement, if an insulating coating is formed on the surface, the measurement is performed after the insulating coating is removed. As a removal method, the insulating coating can be removed by immersing the base steel sheet with the insulating coating in a highly concentrated alkaline solution (for example, a 30% sodium hydroxide solution heated to 85°C) for 20 minutes or more. Whether the insulating coating peels off can be visually determined. For a small sample, the insulating coating can be removed by surface grinding.

[0035] Insulation coatingIn the grain-oriented electrical steel sheet 100 according to the present embodiment, an insulation coating 2 is formed on the surface of the base steel sheet 1. The insulation coating 2 includes an intermediate layer 21 and a tension coating layer 22 in this order from the side of the base steel sheet 1.

[0036] Intermediate LayerAs described above, grain-oriented electrical steel sheets generally have a forsterite film formed during the final annealing step and an insulating coating (tensile insulating coating) formed on it. However, in recent years, it has been discovered that the forsterite film hinders magnetic domain wall movement and has a negative impact on iron loss. Therefore, in order to further improve magnetic performance, grain-oriented electrical steel sheets without a forsterite film have been studied. However, without a forsterite film, it is difficult to ensure sufficient adhesion between the tension-inducing coating and the base steel sheet surface.

[0037] In the grain-oriented electrical steel sheet 100 according to the present embodiment, an intermediate layer 21 containing a crystalline metal phosphate is formed between the base steel sheet 1 and the tension-imparting coating in order to improve the adhesion between the base steel sheet 1 and the tension-imparting coating layer 22 through the intermediate layer 21. This is because when the intermediate layer 21 contains a crystalline metal phosphate, the adhesion between the intermediate layer and the tension-imparting coating layer is exceptional because the tension-imparting coating (which becomes the tension-imparting coating layer 22 after formation) formed on the intermediate layer 21 also contains a metal phosphate, and the affinity is high.In addition, as described below, when the intermediate layer is formed by immersion in a treatment liquid containing a metal phosphate, the intermediate layer can be formed on the surface of the base steel sheet 1 using a chemical reaction, and adhesion between the intermediate layer 21 and the base steel sheet 1 can also be ensured. When the intermediate layer 21 does not contain a crystalline metal phosphate, the above-mentioned effect cannot be obtained. The proportion of the crystalline metal phosphate in the intermediate layer is preferably 80% by mass or more, preferably 90% by mass or more, and can be 99% by mass or more. The metal phosphate is preferably one or two or more of zinc phosphate, manganese phosphate, iron phosphate, and zinc-calcium phosphate from the viewpoint of adhesion. The intermediate layer may contain, as a balance other than the metal phosphate, an oxide or an element diffusing from the base steel sheet, such as Fe or Si.

[0038] However, when the crystal of the crystalline metal phosphate in the intermediate layer coarsens, the filling factor decreases when the actual transformer is manufactured, so that the magnetic flux density per unit volume decreases and the iron loss of the transformer increases. Therefore, in the grain-oriented electrical steel sheet according to the present embodiment, in order to suppress the coarsening of the crystals by suppressing the crystallization of the crystalline metal phosphate, one or more of colloidal silica, an inorganic filler, and a metal oxide having an average particle diameter of 10-500 nm are contained as an additive in the processing liquid for forming the intermediate layer.As a result, an intermediate layer containing crystalline metal phosphate and one or more of amorphous silica, an inorganic filler, and a metal oxide, in which the average particle diameter of one or more of the amorphous silica, the inorganic filler, and the metal oxide is 10-500 nm, is formed as an intermediate layer. In such an intermediate layer, the average grain diameter of the crystalline metal phosphate, for example, is 1.0-12.0 μm. It is preferable that one or more of the colloidal silica, the inorganic filler, and the metal oxide having an average particle diameter of 10-500 nm is not localized in the intermediate layer and is uniformly dispersed. For example, it is preferable if aggregates having a size of several μm or less are formed, even when secondary aggregation occurs.

[0039] Of the amorphous silica, inorganic filler, and metal oxide added as an additive and remaining in the intermediate layer, amorphous silica is preferable in terms of availability. Amorphous silica differs in shape and effect from crystalline silicate formed through thermal-oxidative annealing, etc. In addition, the inorganic filler preferably contains 90% or more by mass of one or two or more of alumina, BN, AlN, and kaolin (elements with a purity of 90% or more by mass are used). BN preferably has a hexagonal crystal shape in view of ease of dispersion. The metal oxide is preferably one or two or more of titanium oxide, zinc oxide, and calcium oxide in view of the stability of the processing liquid.Carbonate can be used as an additive, but carbonate does not remain in the intermediate layer under normal sintering conditions, and specific sintering conditions are required to obtain an intermediate layer containing carbonate, which is not preferable. In addition, the content of one or more of amorphous silica, inorganic filler, and metal oxide is preferably 0.01 to 1.00 wt%. When the content is less than 0.01 wt%, the effect of suppressing the coarsening of metal phosphate crystals may be poor, and when the content is more than 1.00 wt%, the adhesion of the intermediate layer may be poor.

[0040] The intermediate layer 21 is formed at a time different from the time of formation of the tension-imparting coating layer thereon, but both the intermediate layer 21 and the tension-imparting coating layer 22 exhibit an effect as the insulating coating 2.

[0041] The thickness of the intermediate layer is preferably 1.0-9.0 μm. When the average thickness of the intermediate layer 21 is less than 1.0 μm, the effect of improving the adhesion between the base steel sheet and the insulation coating through the intermediate layer may not be sufficiently achieved. On the other hand, when the average thickness of the intermediate layer is more than 9.0 μm, the magnetic performance may be degraded.

[0042] The mass fraction of the crystalline metal phosphate for the metal phosphate and the type of the metal phosphate in the intermediate layer can be obtained by measuring the cross-section of the intermediate layer in the thickness direction using a scanning electron microscope and an energy-dispersive elemental analyzer. Whether the metal phosphate of the intermediate layer 21 is crystalline metal phosphate or not can be determined according to X-ray crystallography. The base steel sheet and the insulating coating can be distinguished based on the P (phosphorus) concentration (when the P content is 1.0 wt% or more, the insulating coating is determined, and when the P content is less than 1.0 wt%, the steel sheet is determined). In the insulating coating 2, the intermediate layer 21 and the tension coating layer 22 can be distinguished based on the difference in Si concentration (when the Si content is 10 wt%).% or more, a tension-imparting coating layer is defined, and when the Si content is less than 10 wt.%, an intermediate layer is defined).

[0043] The average grain diameter of crystalline metal phosphate can be determined using the following method. A steel sheet is cut into a square several millimeters in size, which is easy to observe, and subjected to ion etching (CP processing) to remove microscopic shape defects such as shear sag and cracks. A cross-section parallel to the rolling direction and the sheet thickness direction of the steel sheet, as well as a cross-section perpendicular to the rolling direction and parallel to the sheet thickness direction of the steel sheet, are then observed using a scanning electron microscope. The crystalline form of the metal phosphate observed in the cross-section is observed, and the average value of the major axis and minor axis of each crystal is measured for five or more cross-sections, and the measured value is taken as the grain diameter. The magnification of the electron microscope during observation is 1000 times.

[0044] In addition, the content of amorphous silica, inorganic filler, and metal oxide, as well as the average particle diameter, can be determined according to the following method. To obtain the content, a steel sheet is cut into a square several mm in size that is easy to observe and subjected to ion etching (CP processing) to remove micro-defects in shape, such as shear sag and cracks. Then, a section parallel to the rolling direction and the sheet thickness direction of the steel sheet, and a section perpendicular to the rolling direction and parallel to the sheet thickness direction of the steel sheet are observed using a scanning electron microscope at a magnification of 5000 times. The measurement is performed by analyzing a section of the intermediate layer using an energy-dispersive elemental analyzer in five or more cross sections.With respect to the average particle diameter, the presence of amorphous silica, inorganic filler, and metal oxide is confirmed at ten or more points in the intermediate layer by elemental analysis using a transmission electron microscope for a cross-sectional sample subjected to ion etching in an identical manner, and then the average value of the major axis and minor axis of the particle observed at a magnification of 20,000 times is calculated as the particle diameter.

[0045] The thickness of the intermediate layer can be obtained according to the following method. The total average thickness of the intermediate layer and the tension-imparting coating layer can be measured by observing a cross-section of a sample using a scanning electron microscope and measuring the thickness at five or more points. The intermediate layer and the tension-imparting coating layer may differ from each other based on the difference in the concentration of silicon (Si) extracted from silicon dioxide. Therefore, the thickness of the intermediate layer can be calculated by subtracting the thickness of the tension-imparting coating layer from the total average thickness at each measurement point.

[0046] Tension-imparting coating layerThe grain-oriented electrical steel sheet 100 according to the present embodiment has a tension-imparting coating layer 22 on the surface side of the insulating coating 2 by forming a tension-imparting coating on the surface of the intermediate layer 21.The tension-imparting coating layer 22 is not particularly limited as long as it is used as the insulating coating of the grain-oriented electrical steel sheet, but from the viewpoint of adhesion to the intermediate layer 21 (adhesion to the base steel sheet 1 through the intermediate layer 21), it is preferable that the tension-imparting coating layer 22 has a composition containing metal phosphate and silicon dioxide as the main components. It is more preferable to contain essentially metal phosphate and silicon dioxide.The tension-imparting coating layer 22 preferably contains a metal phosphate and silicon dioxide (extracted from colloidal silicon dioxide of the coating liquid) such that the silicon dioxide content is 20.0% by mass or more. On the other hand, when the silicon dioxide content of the tension-imparting coating layer 22 is more than 60.0% by mass, this causes the formation of powder, and therefore, it is preferable that the silicon dioxide content is 60.0% by mass or less. In addition, it is preferable to contain the metal phosphate and silicon dioxide in an amount of 70% by mass or more in total. The metal phosphate and silicon dioxide may constitute 100% by mass in total. As a balance other than the metal phosphate and silicon dioxide, aluminum oxide or ceramic fine particles such as silicon nitride may be contained. The metal phosphate is preferably aluminum phosphate from the viewpoint of heat resistance.The thickness of the tension-imparting coating layer 22 is not limited, but the average thickness of the insulating coating 2 (intermediate layer 21 + tension-imparting coating layer 22) is preferably set to 2.0-10.0 μm when the average thickness of the intermediate layer 21 is within the above-mentioned range. When the average thickness of the insulating coating 2 is less than 1.0 μm, sufficient coating tension cannot be obtained. In addition, the dissolution of phosphoric acid increases. In this case, this may cause viscosity and deterioration of corrosion resistance, and may cause peeling of the coating. On the other hand, when the thickness of the insulating coating 2 is more than 20.0 μm, the fill factor decreases, causing deterioration of magnetic properties, or adhesion due to cracks, etc., or corrosion resistance.

[0047] In the tension-imparting coating layer 22, the mass fraction of the metal phosphate and the type of the metal phosphate can be determined in the same manner as in the intermediate layer in the cross-section in the thickness direction. As described above, the tension-imparting coating layer and the intermediate layer can be distinguished based on the Si content.

[0048] The thickness of the tension coating layer can be determined in the same way as the intermediate layer. The sum of the tension coating layer thickness and the intermediate layer thickness constitutes the thickness of the insulating coating.

[0049] Manufacturing MethodAccording to the manufacturing method satisfying the manufacturing conditions described below, the grain-oriented electrical steel sheet according to the present embodiment can be properly manufactured. It should be noted that, as expected, the grain-oriented electrical steel sheet according to the present embodiment is not particularly limited in the manufacturing method. In other words, the grain-oriented electrical steel sheet having the above-described configuration is considered to be the grain-oriented electrical steel sheet according to the present embodiment, regardless of its manufacturing conditions.

[0050] A grain-oriented electrical steel sheet according to the present embodiment of the invention can be produced by using a manufacturing method including the following steps. (I) a hot rolling step of hot rolling a steel workpiece such as a slab having a predetermined chemical composition to obtain a hot-rolled sheet; (II) a hot-rolled sheet annealing step of annealing the hot-rolled sheet; (III) a cold rolling step of cold rolling the hot-rolled sheet after the hot-rolled sheet annealing step to obtain a steel sheet (cold-rolled sheet); (iv) a decarburization annealing step of performing decarburization annealing on the steel sheet after the cold rolling step; (V) a finish annealing step of applying an annealing separator containing 10-100 wt.% Al2O3, onto the steel sheet, drying the annealing separator, and then performing the final annealing;(VI) an annealing separator removing step for removing excess annealing separator from the steel sheet after the final annealing step;(VII) a light pickling step for pickling the steel sheet after the annealing separator removing step with an pickling liquid having a liquid temperature of 30-85°C and containing 0.10-10.0 wt.% of one inorganic acid selected from sulfuric acid, chloric acid, nitric acid, and phosphoric acid, for 1-20 seconds;(VIII) an immersion step for immersing the steel sheet after the light pickling step in a treatment liquid having a liquid temperature of 30-85°C and containing 0.3-10.0 wt.% of a metal phosphate, 0.01-10.0 g / L of one or more of colloidal silica, an inorganic filler, and a metal oxide having an average particle diameter of 10-500 nm, for 5-150 seconds; (IX) a drying step of taking out the steel sheet after the immersion step from the treatment liquid, removing excess treatment liquid, and then drying the steel sheet; and (X) a step of forming a tension coating layer for applying, on the steel sheet after the drying step, a coating liquid containing a metal phosphate and colloidal silica such that the total concentration of the colloidal silica and the metal phosphate is 10-40 mass%, drying the coating liquid, then heating the steel sheet and holding the steel sheet at a sheet temperature of 700-950°C for 10-50 seconds.In addition, the method for producing a grain-oriented electrical steel sheet according to the present embodiment of the invention may further include one or both of the following: (XI) a nitriding treatment step for subjecting the steel sheet to nitriding treatment between the decarburization annealing step and the finish annealing step, and (XII) a magnetic domain refining step for performing magnetic domain control of the steel sheet after the tension coating layer formation step.Of these, the method for producing a grain-oriented electrical steel sheet according to the present embodiment of the invention is characterized by steps from (V) a final annealing step to (X) a tension coating layer formation step (collectively referred to as an "insulation coating formation method"), mainly related to the formation of an insulation coating, and other steps or conditions that are not described can be adapted to known conditions. Hereinafter, these steps are described in this document.

[0051] Hot Rolling Stage: In the hot rolling stage, a steel blank with a predetermined chemical composition, such as a slab, is heated and then hot rolled to produce a hot-rolled sheet. The heating temperature of the steel blank is preferably in the range of 1100-1450°C. The heating temperature is more preferably 1300-1400°C. The chemical composition of the steel workpiece may vary according to the chemical composition of the base steel sheet for the grain-oriented electrical steel sheet to be finally obtained, but examples thereof include a chemical composition containing, in mass%: C: 0.01-0.20%, Si: 2.50-4.00%, soluble Al: 0.01-0.040%, Mn: 0.01-0.50%, N: 0.020% or less, S: 0.005-0.040%, Cu: 0-0.50%, Sn: 0-0.50%, Se: 0-0.020% and Sb: 0-0.50%, with the rest being Fe and impurities.Hot rolling conditions are not specifically limited and are appropriately specified according to the required characteristics. For example, the sheet thickness for hot-rolled sheet is preferably in the range of 2.0-3.0 mm.

[0052] Hot-rolled sheet annealing step. The hot-rolled sheet annealing step is the annealing of the hot-rolled sheet produced in the hot-rolling step. Through this annealing treatment, recrystallization occurs in the metallographic structure, and advantageous magnetic properties can be achieved. When annealing the hot-rolled sheet, the hot-rolled sheet produced in the hot-rolling step can be annealed according to a known method. The means for heating the hot-rolled sheet during annealing are not particularly limited, and a known heating method can be adopted. The annealing conditions are not particularly limited. For example, the hot-rolled sheet can be annealed at a temperature of 900-1200°C for 10 seconds to 5 minutes.

[0053] Cold Rolling StepIn the cold rolling step, the hot rolled sheet is subjected to cold rolling after the hot rolled sheet annealing step to obtain a steel sheet (cold rolled sheet). Cold rolling can be performed once (continuously without indirect intermediate annealing(s)). Alternatively, before the final pass in the cold rolling step, intermediate annealing can be performed at least once or two or more times by interrupting cold rolling, that is, cold rolling can be performed multiple times with indirect intermediate annealing(s). When intermediate annealing is performed, it is preferable to hold the hot rolled sheet at a temperature of 1000-1200°C for 5-180 seconds. The annealing atmosphere is not particularly limited. The number of intermediate annealings is preferably 3 or less, taking into account the manufacturing cost.In addition, before the cold rolling stage, the surface of the hot rolled sheet can be pickled.

[0054] In the cold rolling step according to the present embodiment, the hot rolled sheet after the hot rolled sheet annealing step is cold rolled according to a known method to form a steel sheet. For example, the finish rolling reduction can be in the range of 80-95%. When the finish rolling reduction is 80% or more, a Goss core in which the {110} orientation can be obtained <001> has a high degree of development in the rolling direction, which is preferable. On the other hand, when the finishing rolling reduction exceeds 95%, there is a high probability that secondary recrystallization will be unstable during the subsequent final annealing stage, which is not preferable.The finish rolling reduction is the total rolling reduction for cold rolling, and when intermediate annealing is performed, the finish rolling reduction is the total rolling reduction for cold rolling after the final intermediate annealing.

[0055] Decarburization annealing step. In the decarburization annealing step, the obtained steel sheet is subjected to decarburization annealing. During decarburization annealing, the decarburization annealing conditions are not limited, provided that the steel sheet can undergo primary recrystallization and C, which has a negative effect on magnetic properties, can be removed from the steel sheet. However, for example, the steel sheet is maintained at an annealing temperature of 800-900°C for 10-600 seconds with an oxidation state (PH2O / PH2) of 0.3-0.6 in an annealing atmosphere (furnace atmosphere).

[0056] Nitriding treatment stepNitriding treatment can be performed between the decarburization annealing step and the final annealing step, which is described below. In the nitriding treatment step, for example, the steel sheet after the decarburization annealing step is held at approximately 700-850°C in a nitriding treatment atmosphere (in an atmosphere containing a gas having a nitriding ability, such as hydrogen, nitrogen, or ammonia) to perform nitriding treatment. When AlN is used as an inhibitor, the N content of the steel sheet after the nitriding treatment step is preferably 40 ppm or more through nitriding treatment. On the other hand, when the N content of the steel sheet after the nitriding treatment step exceeds 1000 ppm, AlN is excessively present in the steel sheet even after secondary recrystallization is completed during final annealing. Such AlN causes deterioration in iron loss.Therefore, the N content of the steel sheet after the nitriding treatment step is preferably 1000 ppm or less.

[0057] Final annealing stepIn the final annealing step, an annealing separator containing 10-100 mass% Al2O3 is applied to the steel sheet that has undergone the decarburization annealing step or has further undergone nitriding treatment (after the nitriding treatment step) and dried, and then final annealing is performed. In the conventional manufacturing method of grain-oriented electrical steel sheet, a forsterite film is formed on the surface of the steel sheet (cold-rolled sheet) by applying an annealing separator mainly containing MgO and performing final annealing. On the other hand, in the method for producing a grain-oriented electrical steel sheet according to the present embodiment of the invention, an annealing separator containing Al2O3 is used, so that a forsterite film is hardly formed. On the other hand, the percentage of Al2O3 may be 100 mass.%, but in the method for producing a grain-oriented electrical steel sheet according to the present embodiment, the annealing separator preferably contains MgO from the viewpoint of preventing Al2O3 from burning onto the sheet surface. MgO may be 0%, but the percentage of MgO is preferably set to 5 mass% or more when the above-mentioned effect is to be obtained. When MgO is contained, the percentage of MgO is 90 mass% or less so as to provide 10 mass% or more of Al2O3. The percentage of MgO is preferably 50 mass% or less. Al2O3 and MgO may account for more than 50 mass% in total in terms of the solid content relative to the annealing separator. In addition, in the method for producing a grain-oriented electrical steel sheet according to the present embodiment, the annealing separator may further contain chloride.When the annealing separator contains chloride, the forsterite film is difficult to form. The chloride content is not particularly limited and can be 0%, but is preferably 0.5-10% by weight when the above-mentioned effect is to be achieved. Effective chlorides include, for example, bismuth chloride, calcium chloride, cobalt chloride, iron chloride, and nickel chloride. The final annealing conditions are not limited, but, for example, holding the steel sheet at 1150-1250°C for 10-60 hours can be used.

[0058] Annealing Separator Removal StepIn the annealing separator removal step, excess annealing separator is removed from the steel sheet after the final annealing step. For example, excess annealing separator can be removed by water rinsing.

[0059] Light pickling step. In the light pickling step, the steel sheet after the annealing step of removing the separating agent is pickled with 0.1-10.0% by weight of an inorganic acid selected from sulfuric acid, chloric acid, nitric acid, and phosphoric acid, at a liquid temperature of 30-85°C for 1-20 seconds. The inorganic acid is preferably selected from sulfuric acid, nitric acid, and phosphoric acid. As a result, the effect of compacting the crystalline metal phosphate can be achieved. If the light pickling conditions are not suitable, the adhesion of the tension coating layer becomes poor, or the dissolution resistance becomes poor.

[0060] Dipping StepDrying StepIn the dipping step, the steel sheet after the light pickling step is immersed in the treatment liquid for 5-150 seconds. In the drying step, the steel sheet after the dipping step is removed from the treatment liquid, the excess treatment liquid is removed, and then the steel sheet is dried. As a result, an intermediate layer is formed on the surface of the base steel sheet. In the dipping step, the treatment liquid is adjusted so that it contains 0.3-10 wt% of metal phosphate at a liquid temperature of 30-85°C and 0.01-10.0 g / L of one or more colloidal silica, inorganic filler, and metal oxide having an average particle diameter of 10-500 nm.By incorporating one or more of colloidal silica (which becomes amorphous silica in the intermediate layer), inorganic filler, and metal oxide (which can be referred to as an additive), the crystallization of the metal phosphate intended to constitute the intermediate layer is inhibited, resulting in a reduction in the average grain diameter of the crystalline metal phosphate in the intermediate layer. However, when the additive content in the processing liquid is less than 0.01 g / L, a sufficient effect cannot be achieved. On the other hand, when the content is more than 10.0 g / L, the processing liquid becomes unstable. When the average particle diameter of the additive is less than 10 nm, aggregation occurs, and the processing liquid becomes unstable. Alternatively, when the average particle diameter is more than 500 nm, the particles precipitate, and the dispersibility in the processing liquid becomes poor.

[0061] When the liquid temperature of the processing liquid is below 30°C or the processing time is less than 5 seconds, the adhesion is poor. On the other hand, when the liquid temperature is above 85°C or the processing time exceeds 150 seconds, the average grain diameter of the crystalline metal phosphate becomes excessively large. Furthermore, when the metal phosphate content in the processing liquid is more than 10% by mass, the average grain diameter of the metal phosphate may coarsen, resulting in decreased adhesion. The metal phosphate contained in the processing liquid may be one or more of zinc phosphate, manganese phosphate, and zinc calcium phosphate. In addition, when the metal phosphate content in the processing liquid is less than 5% by mass, the formation of the intermediate layer is slow, and the production costs are high.When the film thickness of the intermediate layer is uniform, the metal phosphate content is preferably 1.0% by mass or more. Furthermore, when the drying temperature is high, voids may form and adhesion may be poor. Therefore, the drying temperature is preferably 300°C or lower. The drying temperature is preferably 200°C or lower. The drying temperature is preferably 100°C or higher.

[0062] Step of forming a tension coating layer. In the step of forming a tension coating layer, a coating liquid containing metal phosphate and colloidal silica, having a total concentration of metal phosphate and colloidal silica of 10-40% by weight, is applied to the steel sheet after a drying step. After drying, it is heated and held for 10-50 seconds at a sheet temperature of 700-950°C to form a tension coating layer on the surface of the intermediate layer. When the sheet temperature during the holding period is below 700°C, the tension is low and the magnetic properties are poor. Therefore, the sheet temperature is preferably set to 700°C or higher. On the other hand, when the sheet temperature is above 950°C, the rigidity of the steel sheet decreases and the steel sheet is easily deformed. In this case, the steel sheet may be distorted due to transfer, etc., resulting in poor magnetic performance.Therefore, the sheet temperature is preferably set to 950°C or lower. When the holding time is less than 10 seconds, the dissolution resistance is poor. Therefore, the holding time is set to 10 seconds or more. On the other hand, when the holding time is more than 50 seconds, the adhesion of the tension coating layer is poor. Therefore, the holding time is preferably 50 seconds or less. The coating liquid (insulation coating solution) contains 10-40% by weight of metal phosphate and colloidal silica. When the total concentration of metal phosphate and colloidal silica is less than 10% by weight, the applied treatment liquid easily runs off, causing an uneven applied amount. On the other hand, when the content is more than 40% by weight, the viscosity becomes excessive, causing a pattern or uneven coating.For example, the metal phosphate may be one or a mixture of two or more of aluminum phosphate, zinc phosphate, magnesium phosphate, nickel phosphate, copper phosphate, lithium phosphate, and cobalt phosphate. Aluminum phosphate is preferred for its stability in the processing fluid.

[0063] The coating liquid may contain vanadium, tungsten, molybdenum, zirconium, and the like as additional elements. When these elements are contained, they can be added to the coating liquid, for example, as an oxyacid. As the colloidal silica, S-type or C-type colloidal silica can be used. S-type colloidal silica refers to colloidal silica in which the silica solution is alkaline, and C-type colloidal silica refers to colloidal silica in which the surface of the silica particles is treated with aluminum, and the silica solution is changed from alkaline to neutral. S-type colloidal silica is widely and commonly used and is relatively inexpensive, but care must be taken because S-type colloidal silica may aggregate and precipitate when mixed with acidic metal phosphate solution.Colloidal silica type C is stable when mixed with metal phosphate solution and is unlikely to precipitate. However, it is relatively expensive due to the number of processing steps required. It is preferable to select and use it based on the stability of the coating fluid being prepared.

[0064] Magnetic domain refining stepThe method for producing a grain-oriented electrical steel sheet according to the present embodiment of the invention may further include a magnetic domain refining step for performing magnetic domain refining of the steel sheet after the step of forming the tension coating layer. By performing the magnetic domain refining processing, the iron loss of the grain-oriented electrical steel sheet can be further reduced.A processing method for refining magnetic domains includes: a method for narrowing the width of a 180° magnetic domain (performing refining of a 180° magnetic domain) by forming linear or dotted groove sections extending in a direction intersecting the rolling direction at predetermined intervals in the rolling direction, and a method for narrowing the width of a 180° magnetic domain (performing refining of a 180° magnetic domain) by forming linear or dotted deformation sections due to mechanical stress or groove sections extending in a direction intersecting the rolling direction at predetermined intervals in the rolling direction. In the case where a deformation section due to mechanical stress is formed, laser beam irradiation, electron beam irradiation, etc. can be used.In the case where a groove section is formed, a mechanical groove formation method using a blade-shaped or similar device, a chemical groove formation method by electrolytic etching, a thermal groove formation method by laser irradiation, etc. can be used. In the case where the insulating coating is damaged due to the formation of a deformation section due to mechanical stress or a groove section, and characteristics such as insulating properties deteriorate, the insulating coating can be formed again to repair the damage. Examples.

[0065] A slab containing, in mass%: C: 0.08%, Si: 3.31%, soluble Al: 0.028%, N: 0.008%, Mn: 0.07% and S: less than 0.0005%, with the remainder being Fe and impurities, was cast. The slab was heated to 1350°C and then hot rolled to obtain a hot rolled sheet having a sheet thickness of 2.2mm. The hot rolled sheet was annealed under the condition of holding at 1100°C for 10 seconds. Annealing of hot rolled sheetAfterwards, the hot rolled sheet was cold rolled to obtain a cold rolled sheet having a sheet thickness of 0.22mm. The cold rolled sheet was subjected to decarburization annealing under the condition of holding at 830°C for 90 seconds. After decarburization annealing, an annealing separator containing 45 wt% MgO, 50 wt% Al2O3, and 5 wt% BiCl3 as bismuth chloride was applied and dried, and then final annealing was performed at 1200°C for 20 hours.After final annealing, the steel sheet was washed with water to remove excess annealing agent. As a result, no forsterite film was formed on the sheet surface. The steel sheet was subjected to light pickling under the conditions shown in Table 2-1. After light pickling, an intermediate layer was formed using a treatment liquid in which phosphate and the additive shown in Table 1 were mixed. The drying temperature was 200°C. The resulting intermediate layer was as shown in Table 2-2. The proportion of crystalline metal phosphate in the intermediate layer was 80% or more by mass.

[0066] After this, the insulating coating treatment liquid containing the metal phosphate and colloidal silica shown in Table 2-3 as the main components was applied and dried at 850°C for 20 seconds after application to form a tension-imparting coating layer on the sheet surface. The thickness of the insulating coating (intermediate layer and tension-imparting coating layer) was as shown in Table 2-3. The tension-imparting coating layer was actually composed of metal phosphate and silica.

[0067] Table 1 Intermediate layer number Immersion stage Processing fluid Processing conditions Metal phosphate Additive Temperature of processing liquid (°C) Immersion time (seconds) Type Content (wt.%) Type Average particle diameter (nm) Contained amount of colloidal particles (g / l) 1 Zinc phosphate 3,5 Colloidal silicon dioxide 20 0,5 40 20 2 Zinc phosphate 2,5 Colloidal silicon dioxide 30 1,0 30 20 3 Manganese phosphate 10,0 Colloidal silicon dioxide 45 2,0 85 10 4 Manganese phosphate 7,5 Colloidal titanium oxide 40 0,5 80 20 5 Zinc calcium phosphate 5,5 Colloidal zinc oxide particle 40 1,5 80 12 6 Zinc phosphate 1,0 Zirconium dioxide sol 200 5,0 40 5 7 Manganese phosphate 4,0 Aluminum oxide sol 40 1,5 60 5 8 Zinc phosphate 1,5 Aluminum nitride particle 50 1,0 50 120 9 Manganese phosphate 8,5 BN suspension 50 1,0 85 40 10 Zinc phosphate 1,8 A particle of kaolin 100 6,5 40 100 11 Zinc phosphate 2,0 Aluminum oxide particle 500 12,0 40 10 12 Manganese phosphate 6,5 Silicon dioxide macroparticle 2100 5,5 60 40 13 Zinc phosphate 1,5 Colloidal silicon dioxide 8 0,05 50 10 14 Zinc phosphate 1,5 Colloidal silicon dioxide 20 0,50 50 4 15 Manganese phosphate 4,0 - - - 55 150

[0068] Table 2-1 Number Light etching stage Conditions for the formation of the intermediate layer Type of acid Concentration (wt.%) Temperature (°C) Time (seconds) Intermediate layer number 1 H2SO4 2,5 85 5 1 2 H2SO4 1,0 85 10 2 3 H3PO4 1,5 65 5 3 4 H2SO4 0,5 80 20 4 5 H2SO4 3,5 80 5 5 6 H3PO4 3,0 50 10 6 7 H3PO4 2,5 60 15 7 8 H3PO4 0,8 55 20 8 9 HNO3 0,5 40 10 9 10 HNO3 0,5 35 10 10 11 H3PO4 1,0 80 10 11 12 H2SO4 0,5 60 10 12 13 H3PO4 1,0 80 10 13 14 H2SO4 0,5 60 10 14 15 H2SO4 0,5 60 10 15 16 H2SO4 0,02 80 10 1 17 H2SO4 1,5 25 10 1 18 H2SO4 0,5 94 10 1 19 H3PO4 2,5 55 0,4 3 20 H3PO4 2,5 55 60 3 21 HCl 0,5 35 20 3

[0069] Table 2-2 Number Intermediate layer Crystalline metal phosphate Thickness Amorphous silicon dioxide, inorganic filler and / or metal oxide Type Average grain diameter (µm) (µm) Type Average particle diameter (nm) Content (wt.%) 1 Zinc phosphate 4,5 6,2 Amorphous silicon dioxide 20 0,20 2 Zinc phosphate 6,8 6,8 Amorphous silicon dioxide 30 0,30 3 Manganese phosphate 8,9 7,4 Amorphous silicon dioxide 45 0,70 4 Manganese phosphate 9,4 8,4 Titanium oxide 40 0,40 5 Zinc phosphate, calcium phosphate 8,4 8,7 Zinc oxide 40 0,05 6 Zinc phosphate 3,1 3,6 Zirconium dioxide 200 0,02 7 Manganese phosphate 8,8 8,8 Aluminum oxide 40 0,40 8 Zinc phosphate 2,6 3,3 AlN 50 0,02 9 Manganese phosphate 9,7 8,9 Boron nitride 50 0,10 10 Zinc phosphate 6,7 8,3 Kaolin 100 0,50 11 Zinc phosphate 0,9 2,2 - - - 12 Zinc phosphate 14,3 21,3 (Crystalline) silicon dioxide 2100 0,20 13 Zinc phosphate 0,6 0,9 Amorphous silicon dioxide 8 0,01 14 Zinc phosphate 0,4 0,9 - - - 15 Manganese phosphate 16,3 19,2 - - - 16 Zinc phosphate 12,7 6,3 Amorphous silicon dioxide 10 0,001 17 Zinc phosphate 13,4 6,6 - - - 18 Zinc phosphate 12,4 5,8 Amorphous silicon dioxide 20 0,003 19 Manganese phosphate 15,6 6,9 - - - 20 Manganese phosphate 15,6 7,1 Amorphous silicon dioxide 40 0,001 21 Manganese phosphate 14,9 7,4 - - -

[0070] Table 2-3 Number The stage of forming a tension coating layer Tension-imparting coating layer Insulating coating Notes Covering fluid Silicon dioxide content (wt.%) Thickness (µm) Metal phosphate (100 parts by weight) Mole fraction of metallic elements Colloidal silicon dioxide Total concentration of metal phosphate and colloidal silicon dioxide (wt%) Type Type (parts by weight) 1 Aluminum phosphate - S-type 90 35 47,4 9,5 Example of invention 2 Zinc phosphate - S-type 60 36 37,5 10,1 Example of invention 3 Aluminum / zinc phosphate 0,25 C-type 140 25 58,3 10,7 Example of invention 4 Aluminum / copper phosphate 0,17 S-type 100 34 50,0 11,7 Example of invention 5 Aluminum / lithium phosphate 0,15 S-type 80 35 44,4 12,0 Example of invention 6 Aluminum / barium phosphate 0,15 C-type 75 28 42,9 6,9 Example of invention 7 Aluminum / molybdenum phosphate 0,14 C-type 100 27 50,0 12,1 Example of invention 8 Aluminum / vanadium phosphate 0,14 C-type 80 28 44,4 6,6 Example of invention 9 Aluminum / tungsten phosphate 0,17 C-type 130 26 56,5 12,2 Example of invention 10 Aluminum / zirconium phosphate 0,17 C-type 60 29 37,5 11,6 Example of invention 11 Aluminum / copper phosphate 0,17 S-type 60 36 37,5 4,7 Comparative example 12 Aluminum / copper phosphate 0,17 S-type 90 35 47,4 24,6 Comparative example 13 Aluminum / copper phosphate 0,17 S-type 60 36 37,5 20,1 Comparative example 14 Aluminum / copper phosphate 0,17 C-type 100 27 50,0 4,2 Comparative example 15 Aluminum / copper phosphate 0,17 C-type 100 27 50,0 22,5 Comparative example 16 Aluminum / vanadium phosphate 0,14 C-type 80 28 44,4 9,6 Comparative example 17 Aluminum / vanadium phosphate 0,14 C-type 80 28 44,4 9,7 Comparative example 18 Aluminum / vanadium phosphate 0,14 C-type 80 28 44,4 9,1 Comparative example 19 Aluminum / barium phosphate 0,15 C-type 75 28 42,9 7,5 Comparative example 20 Aluminum / barium phosphate 0,15 C-type 75 28 42,9 13,2 Comparative example 21 Aluminum / copper phosphate 0,17 S-type 100 34 50,0 8,2 Comparative example

[0071] The obtained steel sheet (grain-oriented electrical steel sheet) was irradiated with a laser beam under the conditions that the UA (irradiation energy density) was 2.0 J and the irradiation interval was 5.0 mm increments to perform magnetic domain refinement processing. The iron loss W17 / 50 (iron loss at 50 Hz in 1.7 T) of the steel sheet after magnetic domain refinement processing was measured using a single sheet tester (SST) according to JIS C2556 (2015). In addition, the fill factor was measured as follows.

[0072] Filling FactorThe filling factor was measured using the method specified in JIS C 2550-5 (2020). Thirty test specimens with a width of 30 mm and a length of 320 mm were used. The total mass of the specimen was measured, and then the total mass of the specimen was calculated by measuring the mass between the upper and lower contact sheets between which the laminated package was placed under a pressurized state of 1 MPa. When the filling factor was 96.0% or more, it was determined that a high filling factor was achieved.

[0073] In addition, the coating adhesion, coating tension, corrosion resistance, and dissolution resistance of the steel sheet after magnetic domain refinement treatment were evaluated according to the following methods. Table 3 shows the results.

[0074] Coating AdhesionThe coating adhesion was evaluated by the peeling rate (area fraction) of the coating after a bending adhesion strength test was performed in which a specimen having a width of 30 mm and a length of 300 mm was taken from a steel sheet, the specimen was stress-relieving annealed at 800°C for two hours in a nitrogen flow, and then wound around a cylinder by 10 mmϕ and unwound.The evaluation criteria were as follows, and in the case of A or B, it was determined that the coating adhesion was exceptional.A: Peeling area fraction of 0-0.5%B: Peeling area fraction of more than 0.5% and 5.0% or lessC: Peeling area fraction of more than 5.0% and 20% or lessD: Peeling area fraction of more than 20% and 50% or lessE: The proportion of peeling area is more than 50%

[0075] Coating Tension: The coating tension was calculated by reverse calculation from the curved state when one surface of the insulation coating was peeled off. When the resulting coating tension was 4.0 MPa or more, the coating was determined to have sufficient coating tension.

[0076] Corrosion Resistance: For corrosion resistance, a 5% NaCl aqueous solution was naturally dripped onto the sample for 7 hours in an atmosphere at 35°C according to the JIS salt spray test method (JIS Z2371:2015). Afterward, the rusting area was assessed at 10 points. The evaluation criteria were as follows. A score of 5 or more (5-10) was determined to indicate excellent corrosion resistance.10: No rust formation9: Rust was formed in an extremely small amount (area proportion was 0.10% or less)8: Rust was formed in an area proportion of more than 0.10% and 0.25% or less7: Rust was formed in an area proportion of more than 0.25% and 0.50% or less6: Rust was formed in an area proportion of more than 0.50% and 1.0% or less5: Rust was formed in an area proportion of more than 1.0% and 2.5% or less4: Rust was formed in an area proportion of more than 2.5% and 5.0% or less3: Rust was formed in an area proportion of more than 5.0% and 10% or less2: Rust was formed in an area proportion of more than 10% and 25% or less1: Rust was formed in an area proportion of more than 25% and 50% or less.

[0077] Dissolution ResistanceDissolution resistance was assessed by inhibiting the dissolution of phosphoric acid from the sample. The dissolution amount was measured by boiling the sample in boiled pure water for 10 minutes, measuring the amount of phosphoric acid eluted in the pure water, and dividing the amount of phosphoric acid by the insulation coating area of ​​the boiled grain-oriented electrical steel sheet. The amount of phosphoric acid eluted in pure water was calculated by cooling the pure water (solution) in which phosphoric acid was eluted, diluting the cooled solution with pure water, and measuring the phosphoric acid concentration of the sample using ICP-AES. When the dissolution amount was less than 40 mg / m3, 2 , it was determined that the resistance to dissolution was exceptional.

[0078] Table 3 Number Coating adhesion Coating tension (MPa) Corrosion resistance Dissolution resistance (mg / m2) Fill factor (%) Iron loss (W17 / 50), W / kg Notes 1 B 7,6 8 24 96,4 0,66 Example of invention 2 B 7,4 8 31 96,6 0,64 Example of invention 3 A 8,9 7 21 96,8 0,59 Example of invention 4 A 8,9 7 20 96,2 0,62 Example of invention 5 A 9,2 9 31 97,2 0,64 Example of invention 6 B 6,8 9 28 97,4 0,68 Example of invention 7 B 9,8 7 27 96,1 0,59 Example of invention 8 B 6,9 8 22 97,7 0,64 Example of invention 9 A 9,4 7 19 96,0 0,61 Example of invention 10 B 6,1 9 23 96,5 0,69 Example of invention 11 C 3,9 8 27 96,8 0,73 Comparative example 12 B 7,7 7 56 91,2 0,71 Comparative example 13 B 4,3 8 45 91,8 0,77 Comparative example 14 A 8,4 5 48 97,1 0,71 Comparative example 15 B 7,8 5 44 92,2 0,72 Comparative example 16 C 5,3 4 25 96,1 0,78 Comparative example 17 C 4,9 4 32 95,6 0,73 Comparative example 18 B 6,7 7 42 95,8 0,69 Comparative example 19 D 2,7 5 39 96,6 0,72 Comparative example 20 B 7,1 4 51 94,3 0,75 Comparative example 21 D 3,3 4 35 96,0 0,74 Comparative example

[0079] As can be seen from Tables 1-3, in the examples of the present invention, the main performance of the coating, including adhesion, is extremely excellent, and the iron loss and fill factor are improved. On the other hand, in the comparative examples, the insulating coating did not have the preferred composition, and the tension-imparting coating was poor in one or more of adhesion, magnetic performance, corrosion resistance, resistance to phosphoric acid dissolution, and transformer (core) fill factor. Industrial applicability

[0080] According to the present invention, it is possible to provide a grain-oriented electrical steel sheet that has excellent adhesion and magnetic properties of the tension coating and does not reduce the fill factor (core). Therefore, its industrial applicability is high. List of reference items

[0081] 100 - grain-oriented electrical steel sheet 1 - base steel sheet 2 - insulating coating 21 - intermediate layer 22 - tension coating layer

Claims

1. A sheet of grain-oriented electrical steel containing: base steel sheet; and an insulating coating formed on the surface of the base steel sheet, while The insulating coating includes: an intermediate layer formed on the side of the base steel sheet and containing a crystalline metal phosphate and one or more of amorphous silicon dioxide, an inorganic filler and a metal oxide, and a tension-imparting coating layer formed on the surface side of the insulating coating, and one or more of amorphous silicon dioxide, inorganic filler and metal oxide having an average particle diameter of 10-500 nm.

2. A grain-oriented electrical steel sheet according to claim 1, wherein the inorganic filler comprises one or two or more of aluminum oxide, BN, AlN, and kaolin.

3. A grain-oriented electrical steel sheet according to claim 1 or 2, wherein the metal oxide is one or two or more of titanium oxide, zinc oxide and calcium oxide.

4. A sheet of electrical steel with an oriented grain structure according to claim 1 or 2, in which the crystalline metal phosphate has an average grain diameter of 1.0-12.0 μm.

5. A method for forming an insulating coating in a sheet of electrical steel with an oriented grain structure according to paragraph 1, wherein the method comprises: a final annealing step in which an annealing separator containing 10-100 wt% Al2O3 is applied to the steel sheet, the annealing separator is dried, and then final annealing is performed; an annealing parting agent removal step in which excess annealing parting agent is removed from the steel sheet after the final annealing step; a light pickling step of pickling the steel sheet after the annealing separator removal step with an pickling liquid having a liquid temperature of 30-85°C and having 0.10-10.0 wt% of one inorganic acid selected from sulfuric acid, chloric acid, nitric acid and phosphoric acid for 1-20 s; an immersion step in which the steel sheet after the light etching step is immersed in a treatment liquid having a liquid temperature of 30-85°C and containing 0.3-10.0 wt.% of a metal phosphate, 0.01-10.0 g / L of one or more of colloidal silicon dioxide, an inorganic filler, and a metal oxide having an average particle diameter of 10-500 nm, for 5-150 s; a drying step in which the steel sheet after the immersion step is removed from the treatment liquid, excess treatment liquid is removed, and then the steel sheet is dried; and a step of forming a tension-imparting coating layer, in which a coating liquid containing a metal phosphate and colloidal silicon dioxide is applied to the steel sheet after the drying step in such a way that the total concentration of the metal phosphate and colloidal silicon dioxide is 10-40 wt.%, the coating liquid is dried, then the steel sheet is heated and the steel sheet is maintained at a sheet temperature of 700-950°C for 10-50 s.

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