Grain-oriented electrical steel sheet and method for forming insulating coating

Abstract

This grain-oriented electrical steel sheet comprises a base steel sheet and an insulating coating film formed on the surface of the base steel sheet, wherein the insulating coating film comprises an interlayer formed on the base steel sheet side and containing a crystalline metal phosphate and a tension coating film layer formed as a surface-side layer of the insulating coating film. The crystalline metal phosphate has a board shape and an average grain diameter of 0.5-3.0 μm.

Description

[Technical Field]

[0001] The present invention relates to a grain-oriented electrical steel sheet and a method for forming an insulating coating. This application claims priority based on Japanese Patent Application No. 2023-064840, filed on April 12, 2023, the contents of which are incorporated herein by reference. [Background technology]

[0002] Grain-oriented electrical steel sheets are primarily used in transformers. Transformers are continuously excited over a long period of time, from installation to disposal, and continue to generate energy loss. Therefore, the energy loss during magnetization with AC, i.e., core loss, is a major indicator that determines the performance of a transformer.

[0003] To reduce the iron loss of grain-oriented electrical steel sheets, (a) {110} <001> Many technologies have been developed to date, from the perspective of (a) increasing the concentration in the orientation (Goss orientation), (b) increasing the content of solid solution elements such as Si to increase the electrical resistance of the steel sheet, or (c) reducing the thickness of the electrical steel sheet.

[0004] In addition, applying tension to steel sheets is effective in reducing iron loss. Forming a coating made of a material with a smaller thermal expansion coefficient than the steel sheet at high temperatures on the steel sheet surface is an effective means of reducing iron loss. Forsterite-based coatings (inorganic coatings) with excellent coating adhesion are produced by the reaction of oxides on the steel sheet surface with annealing separators during the finish annealing process of electrical steel sheets. This coating can apply tension to steel sheets.

[0005] Furthermore, for example, the method disclosed in Patent Document 1, in which an insulating coating is formed by baking a coating liquid mainly composed of colloidal silica and phosphate onto the surface of a steel sheet, is an effective method for reducing iron loss because it is highly effective in applying tension to the steel sheet. Therefore, a common method for producing grain-oriented electrical steel sheets is to leave the forsterite-based coating formed in the final annealing process and then apply an insulating coating mainly composed of phosphate on top of it.

[0006] However, in recent years, there has been an increasing demand for smaller and higher-performance transformers. To achieve this, grain-oriented electrical steel sheets are required to have excellent high-field iron loss characteristics, i.e., good iron loss even at high magnetic flux densities. At the same time, it has become clear that forsterite-based coatings hinder domain wall movement, adversely affecting iron loss. In grain-oriented electrical steel sheets, magnetic domains change due to domain wall movement under an AC magnetic field. Smooth and rapid domain wall movement is effective in reducing iron loss. However, forsterite-based coatings are nonmagnetic and have an uneven structure at the steel sheet / coating interface. This uneven structure is thought to hinder domain wall movement and adversely affect iron loss.

[0007] Therefore, as a means for improving high magnetic field iron loss, research is being conducted on a variety of techniques, including methods for removing the forsterite-based coating by mechanical means such as polishing or chemical means such as pickling, and techniques for producing grain-oriented electrical steel sheets that do not have a forsterite-based coating by preventing the formation of a forsterite-based coating during high-temperature finish annealing, as well as techniques for making the steel sheet surface mirror-finished (in other words, techniques for magnetically smoothing the steel sheet surface).

[0008] As a technique for preventing the formation of a forsterite-based coating, for example, Patent Document 2 discloses a technique in which, after normal finish annealing, the steel sheet is pickled to remove surface deposits, and then chemically or electrolytically polished to a mirror finish. It has been found that forming a tensioned insulating coating on the surface of grain-oriented electrical steel sheet that does not have a forsterite-based coating and that has been obtained by such a known method can provide even more excellent iron loss improvement effects. Furthermore, tensioned insulating coatings can impart various properties, such as corrosion resistance, heat resistance, and slip resistance, in addition to improving iron loss.

[0009] However, in addition to exhibiting insulating properties, forsterite-based coatings also function as intermediate layers that ensure adhesion when forming tension coatings (tension-applying insulating coatings). In other words, because forsterite-based coatings are formed in a state where they penetrate deeply into the steel sheet, they have excellent adhesion to the metal steel sheet. Therefore, when a tension-applying coating (tension coating) containing colloidal silica, phosphate, or the like as a main component is formed on the surface of a forsterite-based coating, the coating exhibits excellent adhesion. However, because bonding between metals and oxides is generally difficult, it has been difficult to ensure sufficient adhesion between a tension coating and the steel sheet surface in the absence of a forsterite-based coating.

[0010] Therefore, when forming a tension coating on a grain-oriented electrical steel sheet that does not have a forsterite-based coating, it is being considered to provide a layer that takes the role of the intermediate layer of the forsterite-based coating.

[0011] For example, Patent Document 3 discloses a technique in which a grain-oriented electrical steel sheet that does not have a forsterite-based coating (inorganic coating) is annealed in a weakly reducing atmosphere to selectively thermally oxidize the silicon that is inevitably contained in the silicon steel sheet, thereby forming an SiO2 layer on the steel sheet surface, and then a tension-applying insulating coating is formed. Also, Patent Document 4 discloses a technique in which a grain-oriented electrical steel sheet that does not have a forsterite-based coating (inorganic coating) is anodically treated in a silicate aqueous solution to form an SiO2 layer on the steel sheet surface, and then a tension-applying insulating coating is formed.

[0012] However, the technology disclosed in Patent Document 3 requires the preparation of annealing equipment capable of controlling the atmosphere in order to perform annealing in a weakly reducing atmosphere, which results in a problem of processing costs. Also, in the technology disclosed in Patent Document 4, in order to perform anodic electrolysis in a silicate aqueous solution to obtain an SiO layer on the steel sheet surface that maintains sufficient adhesion with the tension-applying insulating coating, it is necessary to prepare new electrolysis equipment, which results in a problem of processing costs.

[0013] In contrast, Patent Document 5 discloses a grain-oriented electrical steel sheet having a base steel sheet and an insulating coating formed on the surface of the base steel sheet, the insulating coating being formed on the base steel sheet side, an intermediate layer containing a crystalline metal phosphate, and a tensile 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. [Prior art documents] [Patent documents]

[0014] [Patent Document 1] Japanese Unexamined Patent Publication No. 48-039338 [Patent Document 2] Japanese Patent Application Publication No. 49-96920 [Patent Document 3] Japanese Patent Application Publication No. 6-184762 [Patent Document 4] Japanese Patent Application Publication No. 11-209891 [Patent Document 5] International Publication No. 2022 / 215709 Summary of the Invention [Problem to be solved by the invention]

[0015] The technology of Patent Document 5 has an intermediate layer made of a crystalline metal phosphate between the base steel sheet and the tension coating, which can improve the coating adhesion, coating tension, and magnetic properties. In addition, since the intermediate layer can be formed by chemical conversion treatment, no special equipment is required. Therefore, it is a useful technology. On the other hand, the technology of Patent Document 5 has a problem in that further improvement of adhesion results in inferior productivity, because it takes time to precipitate the crystalline metal phosphate by chemical conversion treatment.

[0016] To address the above-mentioned issues, it is conceivable to precipitate crystalline metal phosphate by electrolytic chemical conversion treatment. However, when an attempt is made to form a crystalline metal phosphate layer on the surface of a grain-oriented electrical steel sheet without a forsterite-based coating by electrolytic chemical conversion treatment, the metal phosphate crystals may become coarse. If the metal phosphate crystals become large, the space factor will decrease when an actual transformer is manufactured.

[0017] Therefore, the present invention aims to provide a grain-oriented electrical steel sheet in which a layer containing metal phosphate is formed on the surface of a steel sheet having a forsterite-based coating by chemical conversion treatment, which has excellent adhesion and magnetic properties of a tension coating and does not reduce the space factor of a transformer (core), provided that the basic properties required of the coating, such as corrosion resistance and resistance to leaching of phosphoric acid, are not reduced. [Means for solving the problem]

[0018] The present inventors have investigated a method for obtaining grain-oriented electrical steel sheets that have excellent adhesion and magnetic properties of tension coatings and that do not reduce the space factor of transformer cores, based on the premise of forming a layer of crystalline metal phosphate on the surface of grain-oriented electrical steel sheets without a forsterite-based coating by electrolytic chemical conversion. As a result, they found that coarsening of crystalline metal phosphates can be suppressed by performing electrolytic chemical conversion at a specific current density and by setting the metal ion concentration, phosphate ion concentration, and nitrate ion concentration of the treatment solution within specific ranges. Furthermore, they found that grain-oriented electrical steel sheets having such a layer of crystalline metal phosphate exhibit excellent adhesion and magnetic properties of tension coatings and a high space factor when used as transformers.

[0019] The present invention has been made in light of the above findings. [1] A grain-oriented electrical steel sheet according to one embodiment of the present invention comprises a base steel sheet and an insulating coating formed on the surface of the base steel sheet, the insulating coating being formed on the side of the base steel sheet, an intermediate layer containing a crystalline metal phosphate, and a tensile coating layer formed on the surface side of the insulating coating, the crystalline metal phosphate being plate-shaped and having an average particle size of 0.5 to 3.0 μm. [2] In the grain-oriented electrical steel sheet according to the above [1], the crystalline metal phosphate in the intermediate layer may contain one or more of zinc phosphate, manganese phosphate, iron manganese phosphate, and zinc calcium phosphate. [3] In the grain-oriented electrical steel sheet according to the above [1], the intermediate layer may have a thickness of 0.1 to 9.0 μm. [4] A method for forming an insulating coating according to one aspect of the present invention is a method for forming the insulating coating provided on the grain-oriented electrical steel sheet according to [1], the method comprising the steps of: applying an annealing separator containing 10 to 100 mass % of Al2O3 to a steel sheet, drying the steel sheet, and then performing finish annealing; an annealing separator removal step of removing excess annealing separator from the steel sheet after the finish annealing step; and applying liquid annealing to the steel sheet after the annealing separator removal step. a light pickling step in which the steel sheet is pickled for 1 to 20 seconds using 0.1 to 10.0 mass % of one inorganic acid selected from sulfuric acid, chloric acid, nitric acid, and phosphoric acid at a temperature of 20 to 90°C; and a mixed treatment solution having a liquid temperature of 30 to 90°C, a metal ion concentration of 10 to 50 g / l, a phosphate ion concentration of 10 to 100 g / l, and a nitrate ion concentration of 20 to 80 g / l, at a current density of 1.0 to 50 A / dm 2 a drying step of removing the steel sheet after the intermediate layer forming step from the mixed treatment solution, removing excess mixed treatment solution, and then drying the steel sheet; and a tensile coating layer forming step of applying a coating solution containing a metal phosphate and colloidal silica, the total concentration of the metal phosphate and the colloidal silica being 10 to 40 mass %, to the steel sheet after the drying step, drying, and then heating the steel sheet and maintaining the sheet temperature at 700 to 950°C for 10 to 60 seconds. [Effects of the Invention]

[0020] According to the present invention, it is possible to provide a grain-oriented electrical steel sheet that has excellent adhesion of a tension coating and magnetic properties, and that does not reduce the space factor of a transformer (core). [Brief explanation of the drawings]

[0021] [Figure 1] 1 is an example of a cross-sectional view of a grain-oriented electrical steel sheet according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0022] A grain-oriented electrical steel sheet according to one embodiment of the present invention (grain-oriented electrical steel sheet according to the present embodiment) and a method for manufacturing the grain-oriented electrical steel sheet according to the present embodiment, including a method for forming an insulating coating provided on the grain-oriented electrical steel sheet according to the present embodiment, will be described. First, the grain-oriented electrical steel sheet according to this embodiment will be described.

[0023] As shown in Fig. 1, the grain-oriented electrical steel sheet 100 according to this embodiment has 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 this embodiment, a forsterite-based coating is not intentionally formed on the surface of the base steel sheet 1, and in many cases a forsterite-based coating is not present. However, the coating amount of the forsterite-based coating is 1.0 g / m 2 If it is equal to or less than this, its presence is permitted (in this case, it is present in a part between the base steel sheet 1 and the insulating coating 2).

[0024] The insulating coating 2 also has a tensile coating layer 22 formed on the surface side of the insulating coating 2 (i.e., the surface side of the directional electrical steel sheet 100), and an intermediate layer 21 formed on the base steel sheet 1 side and containing a crystalline metal phosphate.

[0025] The crystalline metal phosphate in the intermediate layer 21 is plate-shaped and has an average particle size of 0.5 to 3.0 μm. Each of these will be explained below.

[0026] <Base material steel plate> (chemical composition) The grain-oriented electrical steel sheet 100 according to this embodiment is significantly characterized by 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 properties generally required of grain-oriented electrical steel sheets, it is preferable that the chemical components contain the following: In this embodiment, % relating to the chemical components is % by mass unless otherwise specified.

[0027] C: 0.010% or less C (carbon) is an element effective for controlling the structure of steel sheets in the manufacturing process up to the completion of the decarburization annealing step. However, if the C content exceeds 0.010%, the magnetic properties of the finished grain-oriented electrical steel sheet will deteriorate. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, the C content is preferably 0.010% or less. The C content is more preferably 0.005% or less. The lower the C content, the better; however, even if the C content is reduced to less than 0.0001%, the effect of structural control will saturate and the manufacturing cost will simply increase. Therefore, the C content may be 0.0001% or more.

[0028] Si: 2.50 to 4.00% Silicon (Si) is an element that increases the electrical resistance of grain-oriented electrical steel sheets and improves their core loss characteristics. If the Si content is less than 2.50%, a sufficient eddy current loss reduction effect 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, if the Si content exceeds 4.00%, the grain-oriented electrical steel sheet becomes embrittled and the threading property deteriorates significantly. Furthermore, the workability of the grain-oriented electrical steel sheet deteriorates, and the steel sheet may break during rolling. Therefore, the Si content is preferably 4.00% or less. The Si content is more preferably 3.80% or less, and even more preferably 3.70% or less.

[0029] Mn: 0.01 to 0.50% Mn (manganese) is an element that combines with S to form MnS during the manufacturing process. This precipitate functions as an inhibitor (a suppressor of normal grain growth) and induces secondary recrystallization in steel. Mn also improves the hot workability of steel. If the Mn content is less than 0.01%, the above-mentioned effects cannot be fully 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, if 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 of the grain-oriented electrical steel sheet according to this embodiment, the Mn content is preferably 0.50% or less. The Mn content is more preferably 0.20% or less, and even more preferably 0.10% or less.

[0030] N: 0.010% or less N (nitrogen) is an element that bonds with Al during the manufacturing process to form AlN, which functions as an inhibitor. However, if the N content exceeds 0.010%, an excessive amount of inhibitor remains in the grain-oriented electrical steel sheet, resulting in a deterioration in magnetic properties. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, 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 specified, but reducing it to less than 0.001% would only increase the manufacturing cost, so the N content may be 0.001% or more.

[0031] sol.Al: 0.020% or less Sol-Al (acid-soluble aluminum) is an element that bonds with N to form AlN, which functions as an inhibitor, during the manufacturing process of grain-oriented electrical steel sheet. However, if the sol-Al content of the base steel sheet exceeds 0.020%, excessive inhibitors remain in the base steel sheet, resulting in reduced magnetic properties. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, the sol-Al content is preferably 0.020% or less. The sol-Al content is more preferably 0.010% or less, and even more preferably less than 0.001%. There is no particular restriction on the lower limit of the sol-Al content, but reducing it to less than 0.0001% simply increases manufacturing costs. Therefore, the sol-Al content may be 0.0001% or more.

[0032] S: 0.010% or less S (sulfur) is an element that combines with Mn during the manufacturing process to form MnS, which functions as an inhibitor. However, if the S content exceeds 0.010%, the magnetic properties will be reduced due to the remaining inhibitor. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, the S content is preferably 0.010% or less. It is more preferable that the S content in the grain-oriented electrical steel sheet is as low as possible, for example, less than 0.001%. However, reducing the S content in the grain-oriented electrical steel sheet to less than 0.0001% will only increase the manufacturing cost. Therefore, the S content in the grain-oriented electrical steel sheet may be 0.0001% or more.

[0033] Remainder: Fe and impurities The chemical composition of the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment may contain the above-mentioned elements, with the remainder being Fe and impurities. However, for the purpose of improving magnetic properties, etc., Sn, Cu, Se, and Sb may also be contained in the ranges shown below. Furthermore, even if other elements are contained, for example, one or more of W, Nb, Ti, Ni, Co, V, Cr, and Mo in a total amount of 1.0% or less, this does not impair the effects of the grain-oriented electrical steel sheet according to this embodiment. Here, impurities refer to elements that are mixed in from raw materials such as ore or scrap, or the manufacturing environment, when the base steel sheet is industrially manufactured, and are permissible to be contained in amounts that do not adversely affect the function of the grain-oriented electrical steel sheet according to this embodiment.

[0034] Sn: 0 to 0.50% Sn (tin) is an element that contributes to improving magnetic properties by controlling the primary recrystallization structure. To obtain the effect of improving magnetic properties, 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, if the Sn content exceeds 0.50%, secondary recrystallization becomes unstable and magnetic properties 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.

[0035] Cu: 0 to 0.50% Copper (Cu) is an element that contributes to increasing the Goss orientation occupancy rate in the secondary recrystallized structure. To achieve the above 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, if the Cu content exceeds 0.50%, the steel sheet becomes embrittled during hot rolling. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, 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.

[0036] Se: 0 to 0.020% Se (selenium) is an element that has the effect of improving magnetic properties. When Se is contained, the Se content is preferably 0.001% or more in order to effectively exhibit the effect of improving magnetic properties. The Se content is more preferably 0.003% or more, and even more preferably 0.006% or more. On the other hand, if the Se content exceeds 0.020%, the adhesion of the coating 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.

[0037] Sb: 0 to 0.50% Sb (antimony) is an element that has the effect of improving magnetic properties. When Sb is contained, the Sb content is preferably 0.005% or more in order to effectively exhibit the effect of improving magnetic properties. The Sb content is more preferably 0.01% or more, and even more preferably 0.02% or more. On the other hand, if the Sb content exceeds 0.50%, the adhesion of the coating significantly deteriorates. 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.

[0038] As described above, the chemical composition of the base steel sheet of the grain-oriented electrical steel sheet in this embodiment is, for example, one that contains the above-mentioned elements with the balance being Fe and impurities.

[0039] The chemical composition of the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment can be measured using a known ICP atomic emission spectroscopy. However, if an insulating coating is formed on the surface, it must be removed before measurement. The removal can be achieved by immersing the sample in a highly concentrated alkaline solution (e.g., a 30% sodium hydroxide solution heated to 85°C) for 20 minutes or more. Peeling can be determined visually. For small samples, removal can also be achieved by surface grinding.

[0040] <Insulating coating> In the grain-oriented electrical steel sheet 100 according to this embodiment, an insulating coating 2 is formed on the surface of a base steel sheet 1 . The insulating coating 2 is made up of an intermediate layer 21 and a tensile coating layer 22 in this order from the base steel sheet 1 side.

[0041] (middle class) As mentioned above, grain-oriented electrical steel sheets generally have a forsterite-based coating formed in the final annealing process and an insulating coating (tensile insulating coating) formed thereon. However, in recent years, it has become clear that this forsterite-based coating hinders the movement of domain walls and adversely affects iron loss. Therefore, grain-oriented electrical steel sheets without forsterite are being studied to further improve magnetic properties. However, if there is no forsterite-based coating, it is difficult to ensure sufficient adhesion between the tensile coating and the surface of the base steel sheet.

[0042] In the grain-oriented electrical steel sheet 100 of this embodiment, an intermediate layer 21 containing a crystalline metal phosphate is formed between the base steel sheet 1 and the tensile coating, thereby improving the adhesion between the base steel sheet 1 and the tensile coating layer 22 via the intermediate layer 21.

[0043] When the intermediate layer 21 contains crystalline metal phosphate, the tensile coating formed thereon (which becomes the tensile coating layer 22 after formation) also contains metal phosphate, resulting in high affinity and excellent adhesion between the intermediate layer and the tensile coating layer. Furthermore, when the intermediate layer is formed by immersion in a treatment solution containing metal phosphate, as described below, it can be formed on the surface of the base steel sheet 1 by utilizing a chemical reaction, and adhesion between the intermediate layer 21 and the base steel sheet 1 can also be ensured.

[0044] If 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 mass % or more, and may be 100 mass %. In terms of adhesion, it is preferable to use one or more of zinc phosphate, manganese phosphate, iron phosphate, and zinc calcium phosphate as the metal phosphate.

[0045] The intermediate layer may contain oxides and elements such as Fe and Si diffused from the base steel sheet as the remainder of the metal phosphate.

[0046] However, if the crystals of the crystalline metal phosphate in the intermediate layer become coarse, when an actual transformer is manufactured, the space factor decreases, which reduces the magnetic flux density per unit volume and increases the transformer iron loss.

[0047] Therefore, in the grain-oriented electrical steel sheet according to this embodiment, the crystalline metal phosphate contained in the intermediate layer is plate-shaped and has an average particle size of 0.5 to 3.0 μm. Here, plate-shaped refers to a shape in which the length of one of the three sides of the crystal is less than 1 / 5 of the length of the other two sides. In contrast, a columnar shape is defined when the length of one of the three sides of the crystal is at least 5 times the length of the other two sides, and the lengths of the other two sides are 0.5 to less than 2.0 times each other. A granular shape is defined when the length of each of the three sides of the crystal is 0.5 to less than 2.0 times each other. An acicular shape is defined when the length of one of the three sides of the crystal is at least 20 times the length of the other two sides, and the lengths of the other two sides are 0.5 to less than 2.0 times each other.

[0048] If the crystalline metal phosphate is not in a plate shape, the space factor may decrease and the adhesion may become poor.

[0049] If the average grain size is less than 0.5 μm, the crystals will be sparse and the adhesion will be poor, and if the average grain size is more than 3.0 μm, the space factor will be poor.

[0050] The intermediate layer 21 is formed at a different time from the tensile coating formed thereon, but the intermediate layer 21 and the tensile coating layer 22 together function as the insulating coating 2 .

[0051] The thickness of the intermediate layer is preferably 0.1 to 9.0 μm in order to achieve both adhesion and magnetism. If the average thickness of the intermediate layer 21 is less than 0.1 μm, the effect of improving adhesion between the base steel sheet and the insulating coating via the intermediate layer may not be sufficiently obtained. On the other hand, if the average thickness of the intermediate layer exceeds 9.0 μm, the magnetic properties may deteriorate.

[0052] The mass proportion and type of the crystalline metal phosphate in the intermediate layer can be determined by measuring a 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 in intermediate layer 21 is a crystalline metal phosphate can be determined by X-ray crystal structure analysis.

[0053] The thickness of the intermediate layer can be determined by observing the cross section of the sample with a scanning electron microscope and measuring the thickness at five or more points to determine the average thickness. The base steel sheet and the insulating coating can be distinguished by the concentration of P (phosphorus) derived from metal phosphate (if the P content is 1.0 mass% or more, it is considered to be an insulating coating, and if it is less than 1.0 mass%, it is considered to be a base steel sheet). Furthermore, the intermediate layer 21 and the tensile coating layer 22 of the insulating coating 2 can be distinguished by the presence or absence of silicon (Si) derived from silica (the tensile coating layer contains silica, as described below).

[0054] The average crystal grain size of the crystalline metal phosphate can be determined by the following method. Steel plate samples were cut into several millimeters square and subjected to ion milling (CP processing) to remove microscopic defects such as sagging and cracks. Then, cross sections of the steel plate along the rolling direction and along a direction perpendicular to the rolling direction were observed using a scanning electron microscope. If two or more crystals with one side less than one-fifth the length of the other sides were observed, it was determined that plate-like crystals had formed. The average crystal grain size was determined by measuring the long sides of five or more crystals of each observed metal phosphate crystal. The electron microscope magnification during observation was 1000x, and five observation points were observed.

[0055] (Tension coating layer) In the grain-oriented electrical steel sheet 100 according to this embodiment, a tensile coating is formed on the surface of the intermediate layer 21 , so that a tensile coating layer 22 is provided on the surface side of the insulating coating 2 .

[0056] The tensile coating layer 22 is not particularly limited as long as it is used as an insulating coating for grain-oriented electrical steel sheets, but from the viewpoint of adhesion to the intermediate layer 21 (adhesion to the base steel sheet 1 via the intermediate layer 21), it is preferable that the composition of the tensile coating layer 22 is mainly metal phosphate. It is more preferable that the composition of the tensile coating layer 22 is substantially metal phosphate and silica.

[0057] The tensile coating layer 22 preferably contains metal phosphate and silica (derived from colloidal silica in the coating liquid) so that the silica content is 20% by mass or more. On the other hand, if the silica content of the tensile coating layer 22 exceeds 60% by mass, it may cause powdering, so it is preferably 60% by mass or less. Also, it preferably contains a total of 70% by mass or more of metal phosphate and silica. The total of metal phosphate and silica may be 100% by mass. The remainder other than the metal phosphate and silica may include ceramic particles such as alumina and silicon nitride. As the metal phosphate, aluminum phosphate is preferred in terms of heat resistance.

[0058] Although the thickness of the tensile coating layer 22 is not limited, the average thickness of the insulating coating 2 (intermediate layer 21 + tensile coating layer 22) is preferably 1.0 to 20.0 μm, assuming that the average thickness of the intermediate layer 21 is within the above range. If the average thickness of the insulating coating 2 is less than 1.0 μm, sufficient coating tension cannot be obtained. Furthermore, there is a large amount of elution of phosphoric acid. This can cause stickiness and reduced corrosion resistance, and may even lead to coating peeling. Furthermore, if the thickness of the insulating coating 2 exceeds 20.0 μm, the space factor can decrease, resulting in deterioration of magnetic properties, or cracks can occur, resulting in reduced adhesion and reduced corrosion resistance.

[0059] In the tensile coating layer 22, the mass proportion of the metal phosphate and the type of the metal phosphate can be determined in a cross section in the thickness direction in the same manner as in the intermediate layer.

[0060] As mentioned above, the tension coating layer and the intermediate layer can be distinguished by their different silica contents.

[0061] The thickness of the tensile coating layer 22 can be determined in the same manner as the intermediate layer 21. The sum of the thickness of the tensile coating layer 22 and the thickness of the intermediate layer 21 is the thickness of the insulating coating 2.

[0062] <Manufacturing method> The grain-oriented electrical steel sheet according to this embodiment can be suitably manufactured by a manufacturing method that satisfies the manufacturing conditions described below. However, it goes without saying that the grain-oriented electrical steel sheet according to this embodiment is not particularly limited to a manufacturing method. In other words, a grain-oriented electrical steel sheet having the above-described configuration is considered to be the grain-oriented electrical steel sheet according to this embodiment, regardless of its manufacturing conditions.

[0063] The grain-oriented electrical steel sheet according to this embodiment can be manufactured by a manufacturing method including the following steps. (I) a hot rolling step in which a steel billet having a predetermined chemical composition is hot rolled to obtain a hot-rolled sheet; (II) a hot-rolled sheet annealing step of annealing the hot-rolled sheet; (III) a cold rolling step in which the hot-rolled sheet after the hot-rolled sheet annealing step is cold-rolled 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 to 100 mass% of Al2O3 to a steel sheet, drying the steel sheet, and then finish annealing the steel sheet; (VII) an annealing separator removing step of removing excess annealing separator from the steel sheet after the finish annealing step; (VIII) a light pickling step in which the steel sheet after the annealing separator removing step is pickled with 0.1 to 10.0 mass % of one inorganic acid selected from sulfuric acid, chloric acid, nitric acid, and phosphoric acid at a solution temperature of 20 to 90°C for 1 to 20 seconds; (IX) After the light pickling step, the steel sheet is washed with water, and then subjected to a treatment at a current density of 1.0 to 50 A / dm in a mixed treatment solution having a liquid temperature of 30 to 90°C, a metal ion concentration of 10 to 50 g / l, a phosphate ion concentration of 10 to 100 g / l, and a nitrate ion concentration of 20 to 80 g / l. 2 (X) a drying step of removing the steel sheet after the intermediate layer forming step from the mixed treatment solution, removing excess mixed treatment solution, and then drying the steel sheet; (XI) A tensile coating layer forming process, in which a coating liquid containing a metal phosphate and colloidal silica, wherein the total concentration of the metal phosphate and the colloidal silica is 10 to 40 mass %, is applied to the steel sheet after the drying process, dried, and then heated and maintained at a sheet temperature of 700 to 950°C for 10 to 60 seconds. Furthermore, the method for producing a grain-oriented electrical steel sheet according to this embodiment further includes the steps of: (XII) a nitriding treatment step of nitriding the steel sheet between the decarburization annealing step and the finish annealing step; (XIII) A magnetic domain refining step for controlling the magnetic domains of the steel sheet may be included after the tensile coating layer forming step. Of these, the manufacturing of the grain-oriented electrical steel sheet according to this embodiment is characterized by the steps (V) finish annealing step to (XI) tension coating layer forming step (these steps are sometimes collectively referred to as the method for forming the insulating coating), which are mainly related to the formation of the insulating coating, and known conditions can be used for other steps or conditions not described. These steps will be described below.

[0064] [Hot rolling process] In the hot rolling process, a steel billet such as a slab having a predetermined chemical composition is heated and then hot rolled to obtain a hot-rolled sheet. The heating temperature of the steel billet is preferably within the range of 1100 to 1450°C, and more preferably 1300 to 1400°C.

[0065] The chemical composition of the slab may be changed depending on the chemical composition of the grain-oriented electrical steel sheet that is ultimately desired to be obtained, but an example of such a chemical composition may include, in mass %, C: 0.01 to 0.20%, Si: 2.50 to 4.00%, sol. Al: 0.01 to 0.040%, Mn: 0.01 to 0.50%, N: 0.020% or less, S: 0.005 to 0.040%, Cu: 0 to 0.50%, Sn: 0 to 0.50%, Se: 0 to 0.020%, Sb: 0 to 0.50%, and the balance being Fe and impurities. The hot rolling conditions are not particularly limited and may be set appropriately based on the desired properties. The thickness of the hot rolled sheet is preferably within the range of 2.0 to 3.0 mm, for example.

[0066] [Hot-rolled sheet annealing process] The hot-rolled sheet annealing process is a process of annealing the hot-rolled sheet manufactured through the hot rolling process. By performing such an annealing treatment, recrystallization occurs in the steel sheet structure, and good magnetic properties can be achieved, which is preferable.

[0067] When hot-rolled sheet annealing is performed, the hot-rolled sheet produced through a hot rolling process may be annealed according to a known method. The means for heating the hot-rolled sheet during annealing is not particularly limited, and known heating methods can be used. The annealing conditions are also not particularly limited. For example, the hot-rolled sheet may be annealed in a temperature range of 900 to 1200°C for 10 seconds to 5 minutes.

[0068] [Cold rolling process] In the cold rolling process, the hot-rolled sheet after the hot-rolled sheet annealing process is subjected to cold rolling to obtain a steel sheet (cold-rolled sheet). The cold rolling may be a single cold rolling (a series of cold rolling without annealing in between), or may be multiple cold rolling passes with intermediate annealing between them, with the cold rolling being interrupted and at least one or two or more intermediate annealing passes being performed before the final pass of the cold rolling process.

[0069] When intermediate annealing is performed, it is preferable to hold the steel sheet at a temperature of 1000 to 1200° C. for 5 to 180 seconds. The annealing atmosphere is not particularly limited. In consideration of production costs, it is preferable to perform intermediate annealing three times or less.

[0070] Furthermore, before the cold rolling step, the surface of the hot-rolled sheet may be subjected to pickling.

[0071] In the cold rolling step according to the present embodiment, the hot-rolled sheet after the hot-rolled sheet annealing step may be cold-rolled to obtain a steel sheet according to a known method. For example, the final rolling reduction may be in the range of 80 to 95%. If the final rolling reduction is 80% or more, the {110} <001> This is preferable because it is possible to obtain Goss nuclei with a high degree of orientation accumulation in the rolling direction. On the other hand, if the final rolling reduction exceeds 95%, it is not preferable because the secondary recrystallization is likely to become unstable in the subsequent finish annealing step.

[0072] The final rolling reduction is the cumulative rolling reduction of cold rolling, and in the case where intermediate annealing is performed, it is the cumulative rolling reduction of cold rolling after final intermediate annealing.

[0073] [Decarburization annealing process] In the decarburization annealing step, the obtained steel sheet is subjected to decarburization annealing. In the decarburization annealing, the conditions for the decarburization annealing are not limited as long as the steel sheet undergoes primary recrystallization and C, which adversely affects magnetic properties, can be removed from the steel sheet. For example, the oxidation degree (PH2O / PH2) in the annealing atmosphere (furnace atmosphere) can be set to 0.3 to 0.6, and the annealing temperature can be set to 800 to 900°C, and the steel sheet can be held for 10 to 600 seconds.

[0074] [Nitriding process] Nitriding treatment may be carried out between the decarburization annealing step and the finish annealing step described below. In the nitriding process, for example, the steel sheet after the decarburization annealing process is nitrided by maintaining it at approximately 700 to 850°C in a nitriding atmosphere (an atmosphere containing hydrogen, nitrogen, and ammonia or other nitriding gases). When AlN is used as an inhibitor, it is preferable that the N content of the steel sheet after the nitriding process be 40 ppm or more by the nitriding process. On the other hand, if the N content of the steel sheet after the nitriding process exceeds 1000 ppm, excess AlN will remain in the steel sheet even after the completion of secondary recrystallization in the finish annealing. Such AlN can cause iron loss degradation. For this reason, it is preferable that the N content of the steel sheet after the nitriding process be 1000 ppm or less.

[0075] [Finishing annealing process] In the final annealing step, an annealing separator containing 10 to 100 mass% of Al2O3 is applied to the steel sheet that has been subjected to the decarburization annealing step or further nitriding treatment (nitriding treatment step), dried, and then final annealing is performed.

[0076] In conventional methods for manufacturing grain-oriented electrical steel sheets, a forsterite-based coating is formed on the surface of the steel sheet (cold-rolled sheet) by applying an annealing separator mainly composed of MgO and then performing finish annealing.

[0077] In contrast, in the method for manufacturing a grain-oriented electrical steel sheet according to this embodiment, an annealing separator containing Al2O3 is used so that a forsterite-based film is hardly formed. On the other hand, the proportion of Al2O3 may be 100% by mass, but from the viewpoint of preventing Al2O3 from seizing onto the steel sheet surface, in the method for producing a grain-oriented electrical steel sheet according to this embodiment, it is preferable that the annealing separator contains MgO. MgO may be 0%, but to obtain the above effects, the proportion of MgO is preferably 5% by mass or more. When MgO is contained, the proportion of MgO is 90% by mass or less to ensure 10% by mass or more of Al2O3. The proportion of MgO is preferably 50% by mass or less. It is sufficient that the total of Al2O3 and MgO exceeds 50% by mass in terms of solid content in the annealing separator.

[0078] Furthermore, in the method for producing a grain-oriented electrical steel sheet according to this embodiment, the annealing separator may further contain chloride. When the annealing separator contains chloride, the effect of making it more difficult for a forsterite-based coating to form is obtained. The chloride content is not particularly limited and may be 0%, but in order to obtain the above effect, a content of 0.5 to 10 mass% is preferable. Effective chlorides include, for example, bismuth chloride, calcium chloride, cobalt chloride, iron chloride, and nickel chloride.

[0079] The finish annealing conditions are not limited, but for example, conditions of holding at a temperature of 1150 to 1250° C. for 10 to 60 hours can be adopted.

[0080] [Annealing separator removal process] In the annealing separator removal step, excess annealing separator is removed from the steel sheet after the finish annealing step. For example, excess annealing separator can be removed by washing with water.

[0081] [Light pickling process] In the light pickling step, the steel sheet after the annealing separator removal step is pickled for 1 to 20 seconds with 0.1 to 10.0 mass % of one inorganic acid selected from sulfuric acid, chloric acid, nitric acid, and phosphoric acid at a solution temperature of 20 to 90°C, thereby achieving the effect of densifying the crystalline phosphate. If the light pickling conditions are not appropriate, the adhesion of the tension coating layer will be poor.

[0082] [Intermediate layer formation process] [Drying process] In the intermediate layer forming process, the steel sheet after the light pickling process is washed with water and then immersed in a treatment solution, and an electric current is passed through the treatment solution while immersed to form an intermediate layer. In the drying process, the steel sheet after the intermediate layer forming process is pulled out of the treatment solution, excess treatment solution is removed, and then the steel sheet is dried. This forms an intermediate layer on the surface of the base steel sheet.

[0083] Here, the treatment liquid is a mixed treatment liquid having a metal ion concentration of 10 to 50 g / l, a phosphate ion concentration of 10 to 100 g / l, and a nitrate ion concentration of 20 to 80 g / l.

[0084] If the metal ion concentration in the mixed treatment solution is less than 10 g / L, the formation of crystalline metal phosphate is suppressed, resulting in granular crystals and poor adhesion. On the other hand, if the concentration exceeds 50 g / L, the formation of crystalline metal phosphate tends to be uneven, resulting in the appearance of coarse crystals, which reduces the space factor and unevenly forms the intermediate layer. Furthermore, if the phosphate ion concentration in the mixed treatment solution is less than 10 g / L, the precipitation of crystalline metal phosphate takes a long time, resulting in the appearance of coarse crystals and poor space factor. On the other hand, if the concentration exceeds 100 g / L, the formation of crystalline metal phosphate tends to be uneven, resulting in the formation of coarse crystals and the etching of the steel sheet surface, which reduces the space factor and reduces corrosion resistance and coating tension. Furthermore, if the nitrate ion concentration in the mixed treatment solution is less than 20 g / L, hydrogen gas generation cannot be suppressed, making it difficult for current to flow uniformly. This results in the intermediate layer becoming too thick in areas where current flows, resulting in poor adhesion, and in areas where current does not flow, the intermediate layer becoming thin and resulting in poor coating tension. On the other hand, if it exceeds 80 g / l, the concentration of phosphate ions will decrease, which will result in a longer precipitation time for the crystalline metal phosphate salt to form coarse needle-like crystals, resulting in a poor space factor.

[0085] During immersion, the temperature of the mixed treatment solution is set to 30 to 90°C. If the temperature of the mixed treatment solution is below 30°C, it takes too long for the crystalline metal phosphate to precipitate, which is less economical. On the other hand, if the temperature is above 90°C, the mixed treatment solution becomes unstable, resulting in uneven formation of the intermediate layer.

[0086] When energizing, the current density is 1.0 to 50 A / dm 2 The current density is 1.0A / dm 2 If the amount is less than this, it takes too long for the crystalline metal phosphate to precipitate, which is economically disadvantageous.

[0087] On the other hand, when the current density is 50A / dm 2If the current is too short, the current will not flow evenly through the sample, causing uneven formation of the intermediate layer known as 'skimming'. If the current is too short, the intermediate layer will take too long to form and the adhesion will be sparse. On the other hand, if the current is too long, the intermediate layer will be formed in some places excessively, causing uneven adhesion and a non-uniform state known as 'skimming'. Therefore, it is preferable to set the current time to 3 to 30 seconds.

[0088] Furthermore, if the drying temperature is too high, voids may occur, resulting in poor adhesion, so the drying temperature is preferably 300°C or lower, more preferably 200°C or lower. The drying temperature is preferably 100°C or higher.

[0089] [Tension film layer formation process] In the tensile coating layer forming process, a coating liquid containing metal phosphate and colloidal silica, with a total concentration of the metal phosphate and colloidal silica of 10 to 40 mass %, is applied to the steel plate after the drying process, dried, and then heated and held at a plate temperature of 700 to 950°C for 10 to 60 seconds, thereby forming a tensile coating layer on the surface of the intermediate layer.

[0090] If the sheet temperature during holding is less than 700°C, the tension will be low and the magnetic properties will be poor. Therefore, it is preferable that the sheet temperature be 700°C or higher. On the other hand, if the sheet temperature is above 950°C, the rigidity of the steel sheet will decrease and it will be prone to deformation. In this case, strain may be introduced into the steel sheet due to transportation, etc., resulting in poor magnetic properties. Therefore, it is preferable that the sheet temperature be 950°C or lower.

[0091] Furthermore, if the holding time is less than 10 seconds, the resistance to elution will be poor. Therefore, the holding time is set to 10 seconds or more. On the other hand, if the holding time is more than 60 seconds, the adhesion of the tensile coating layer will be poor. Therefore, the holding time is preferably 60 seconds or less.

[0092] The coating liquid (insulating coating solution) contains a total of 10 to 40 mass % of metal phosphate and colloidal silica. If the concentration is less than 10% by mass, the applied coating liquid will tend to flow, causing unevenness in the amount of coating, while if it exceeds 40% by mass, the viscosity will be too high, causing uneven patterns and coating.

[0093] The metal phosphate may be one or a mixture of two or more selected from aluminum phosphate, zinc phosphate, magnesium phosphate, nickel phosphate, copper phosphate, lithium phosphate, cobalt phosphate, etc. Aluminum phosphate is preferred in terms of the stability of the coating liquid.

[0094] The coating liquid may contain additional elements such as vanadium, tungsten, molybdenum, zirconium, etc. When these elements are contained, they can be added to the coating liquid as, for example, an oxygen acid.

[0095] Colloidal silica can be of either type S or type C. Type S colloidal silica refers to an alkaline silica solution, while type C refers to a silica particle surface that has been aluminum-treated, resulting in an alkaline to neutral silica solution. Type S colloidal silica is widely used and relatively inexpensive, but care must be taken as it may aggregate and precipitate when mixed with an acidic metal phosphate solution. Type C colloidal silica is stable even when mixed with a metal phosphate solution and does not precipitate, but it is relatively expensive due to the large processing steps required. It is best to use the appropriate type depending on the stability of the coating solution being prepared.

[0096] [Magnetic domain refinement process] The method for manufacturing a grain-oriented electrical steel sheet according to this embodiment may further include a magnetic domain refining step of refining magnetic domains on the steel sheet after the tensile coating layer forming step. By performing magnetic domain refining treatment, it is possible to further reduce the iron loss of grain-oriented electrical steel sheets.

[0097] Methods of magnetic domain subdivision include a method of narrowing the width of 180° magnetic domains (subdividing 180° magnetic domains) by forming linear or point-like grooves extending in a direction intersecting the rolling direction at predetermined intervals along the rolling direction, and a method of narrowing the width of 180° magnetic domains (subdividing 180° magnetic domains) by forming linear or point-like stress distortion portions or grooves extending in a direction intersecting the rolling direction at predetermined intervals along the rolling direction.

[0098] When forming stress-strained portions, laser beam irradiation, electron beam irradiation, etc. can be applied. When forming grooves, mechanical groove formation methods using gears, etc., chemical groove formation methods in which grooves are formed by electrolytic etching, and thermal groove formation methods using laser irradiation can be applied.

[0099] If the insulating coating is damaged by the formation of stress-strained portions or grooves, and the insulating properties and other characteristics are deteriorated, the insulating coating may be formed again to repair the damage. [Example]

[0100] A slab containing, by mass%, C: 0.08%, Si: 3.31%, sol. Al: 0.028%, N: 0.008%, Mn: 0.07%, S: less than 0.0005%, and the balance being Fe and impurities was cast.

[0101] The slab was heated to 1350°C and then hot-rolled to a hot-rolled sheet having a thickness of 2.2 mm, which was then annealed at 1100°C for 10 seconds.

[0102] Thereafter, the hot-rolled sheet was subjected to cold rolling to obtain a cold-rolled sheet having a thickness of 0.22 mm, which was then subjected to decarburization annealing by holding at 830°C for 90 seconds.

[0103] After decarburization annealing, an annealing separator containing 45 mass% MgO, 50 mass% Al2O3, and 5 mass% BiCl3 (bismuth chloride) was applied, dried, and then finish annealed at 1200°C for 20 hours.

[0104] After the finish annealing, the steel sheet was washed with water to remove excess annealing separator, but no forsterite-based film was formed on the surface of the steel sheet. This steel sheet was subjected to light pickling under the conditions shown in Tables 2A and 2B.

[0105] After light pickling, an intermediate layer was formed by electrolysis using a treatment solution (mixed treatment solution) containing a mixture of phosphate and additives under the conditions shown in Table 1. The drying temperature was 200°C. The obtained intermediate layer was as shown in Tables 2A and 2B. The proportion of crystalline metal phosphate in the intermediate layer was 80 mass% or more.

[0106] Thereafter, an insulating coating solution consisting of metal phosphate and colloidal silica shown in Tables 2A and 2B was applied and dried at 850°C for 30 seconds to form a tensile insulating coating on the surface of the steel sheet.

[0107] The thicknesses of the insulating coatings (intermediate layer and tensile coating layer) were as shown in Tables 2A and 2B. The tensile coating layer consisted essentially of metal phosphate and silica. The shape, average particle size, and thickness were measured as described above.

[0108] [Table 1]

[0109] [Table 2A]

[0110] [Table 2B]

[0111] The obtained steel sheet (grain-oriented electrical steel sheet) was subjected to magnetic domain refining treatment by irradiating it with a laser beam under conditions of UA (irradiation energy density) of 2.0 J and irradiation intervals of 5.0 mm pitch.

[0112] The iron loss W17 / 50 (iron loss at 50 Hz at 1.7 T) of the steel sheet after magnetic domain refinement treatment was measured using a single sheet magnetic property measurement method (Single Sheet Tester: SST) in accordance with JIS C2556 (2015). If the iron loss W17 / 50 was 0.65 W / kg or less, it was determined that good magnetic properties were ensured. The space factor was measured as follows.

[0113] [Occupancy rate] The space factor was measured in accordance with JIS C 2550-5 (2020). Thirty test pieces, each 30 mm wide and 320 mm long, were used. After measuring the total mass of the sample, the distance between the upper and lower backing plates sandwiching the laminate was measured and calculated under a pressure of 1 MPa. If the space factor is 96.0% or higher, it is determined that a high space factor is ensured.

[0114] The steel sheets after the magnetic domain refining treatment were evaluated for coating adhesion, coating tension, corrosion resistance, elution resistance, and space factor using the following methods. The results are shown in Table 3.

[0115] [Coating adhesion] The adhesion of the coating was evaluated by taking a sample 30 mm wide and 300 mm long from the steel plate, annealing this sample for stress relief at 800°C for 2 hours in a nitrogen stream, then winding it around a 10 mm diameter cylinder and unwinding it, and then performing a bending adhesion test.The degree of peeling of the coating (area ratio) was measured. The evaluation criteria were as follows, and a rating of ⊚ or ◯ was judged to indicate excellent coating adhesion.

[0116] ◎: Peeling area rate 0-0.5% ○: Peeling area ratio: over 0.5% and 5.0% or less △: Peeling area rate over 5.0% and 20% or less ×: Peeling area ratio: over 20% and 50% or less ××: Peeling area rate over 50%

[0117] [Coating tension] The coating tension was calculated by back-calculating from the state of curvature when one side of the insulating coating was peeled off. If the obtained coating tension was 4.0 MPa or more, it was determined that the coating had sufficient tension.

[0118] [Corrosion resistance] Corrosion resistance was evaluated by subjecting the sample to a 5% NaCl aqueous solution that had fallen naturally onto the sample for 7 hours in a 35°C atmosphere in accordance with the JIS salt spray test (JIS Z2371:2015). Thereafter, the rusted area was evaluated on a scale of 1 to 10. The evaluation criteria were as follows: A score of 5 or more was considered to be excellent in corrosion resistance.

[0119] 10: No rust occurred 9: Very little rust (area rate 0.10% or less) 8: Area ratio of rusted surface = over 0.10% and 0.25% or less 7: Area ratio of rusted surface = over 0.25% and 0.50% or less 6: Area ratio of rusted surface = over 0.50% and 1.0% or less 5: Area ratio of rusted surface = over 1.0% to 2.5% 4: Area ratio of rusted surface = over 2.5% and 5.0% or less 3: Area ratio of rusted surface = over 5.0% and 10% or less 2: Area ratio of rusted surface = over 10% and less than 25% 1: Area ratio of rusted surface = 25% to 50%

[0120] [Elution resistance] The resistance to elution was evaluated based on whether or not the elution of phosphoric acid from the sample could be inhibited. The amount of elution was measured by boiling the sample in boiling 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 area of ​​the insulating coating of the boiled grain-oriented electrical steel sheet.The amount of phosphoric acid eluted in the pure water was measured by cooling the pure water (solution) into which the phosphoric acid had eluted, and then diluting the cooled solution with pure water to measure the phosphoric acid concentration of the sample using ICP-AES. Elution amount: 40mg / m 2 If the resistance is less than this, the resin is deemed to have excellent resistance to elution.

[0121] [Table 3]

[0122] As can be seen from Tables 1 to 3, the examples of the present invention are extremely excellent in the main properties of the coating, including adhesion, and also have improved iron loss and space factor. On the other hand, in the comparative example, the insulating coating was formed under conditions other than those preferred, and therefore the intermediate layer did not contain the specified crystalline metal phosphate, resulting in poor coating adhesion, coating tension, corrosion resistance, elution resistance, and space factor. [Explanation of symbols]

[0123] 100 grain-oriented electrical steel sheet 1 Base steel plate 2. Insulation coating 21 Middle Class 22 Tension coating layer [Industrial Applicability]

[0124] According to the above aspect of the present invention, a grain-oriented electrical steel sheet can be obtained that has excellent adhesion of a tensile coating and magnetic properties, and that does not reduce the space factor of a transformer (core). Therefore, the grain-oriented electrical steel sheet obtained can be suitably used as an iron core material for transformers, and has high industrial applicability.

Claims

1. A base steel plate; an insulating coating formed on the surface of the base steel sheet; and The insulating coating is an intermediate layer formed on the base steel sheet side and containing a crystalline metal phosphate; a tensile coating layer formed on the surface side of the insulating coating, The grain-oriented electrical steel sheet is characterized in that the crystalline metal phosphate is in the form of a plate and has an average particle size of 0.5 to 3.0 μm.

2. 2. The grain-oriented electrical steel sheet according to claim 1, wherein the crystalline metal phosphate in the intermediate layer comprises one or more of zinc phosphate, manganese phosphate, iron manganese phosphate, and zinc calcium phosphate.

3. The grain-oriented electrical steel sheet according to claim 1, wherein the thickness of the intermediate layer is 0.1 to 9.0 μm.

4. A method for forming the insulating coating provided on the grain-oriented electrical steel sheet according to claim 1, comprising: Steel plate, Al ２ O ３ a finish annealing process in which an annealing separator containing 10 to 100 mass% of the above is applied, dried, and then finish annealed; an annealing separator removing step of removing excess annealing separator from the steel sheet after the finish annealing step; a light pickling step in which the steel sheet after the annealing separator removal step is pickled with 0.1 to 10.0 mass % of one inorganic acid selected from sulfuric acid, chloric acid, nitric acid, and phosphoric acid at a liquid temperature of 20 to 90°C for 1 to 20 seconds; The steel sheet after the light pickling step is washed with water, and then treated with a mixed treatment solution having a liquid temperature of 30 to 90°C, a metal ion concentration of 10 to 50 g / l, a phosphate ion concentration of 10 to 100 g / l, and a nitrate ion concentration of 20 to 80 g / l, at a current density of 1.0 to 50 A / dm ２ an intermediate layer forming process in which current is applied for 3 to 30 seconds; a drying step of removing the steel sheet after the intermediate layer forming step from the mixed treatment solution, removing excess of the mixed treatment solution, and then drying the steel sheet; a tensile coating layer forming step of applying a coating liquid containing a metal phosphate and colloidal silica, the total concentration of the metal phosphate and the colloidal silica being 10 to 40 mass %, to the steel sheet after the drying step, drying the coating liquid, and then heating the steel sheet to maintain a sheet temperature of 700 to 950°C for 10 to 60 seconds; A method for forming an insulating coating, comprising:

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