Grain-oriented electrical steel sheet and method for forming an insulating film

Abstract

The present application relates to a grain-oriented magnetic steel sheet having a base steel sheet and an insulating coating film formed on the surface of the base steel sheet, the insulating coating film having an intermediate layer containing a crystalline metal phosphate formed on the side of the base steel sheet, and a tension coating layer formed on the surface side of the insulating coating film, the average thickness of the intermediate layer being 0.3 to 10.0 μm, the average thickness of the insulating coating film being 2.0 to 10.0 μm, the crystalline metal phosphate of the intermediate layer being one or two or more of zinc phosphate, manganese phosphate, iron phosphate, and calcium zinc phosphate, the tension coating layer containing a metal phosphate and silicon dioxide, the content of the silicon dioxide in the tension coating layer being 20 to 60 mass%.

Description

Technical Field

[0001] This invention relates to a method for forming directional electromagnetic steel sheets and insulating films.

[0002] This application claims priority based on Japanese Patent Application No. 2021-064964, filed on April 6, 2021, the contents of which are incorporated herein by reference. Background Technology

[0003] Directional electromagnetic steel plates are mainly used in transformers. Transformers are continuously energized for a long period of time from installation to disposal, resulting in continuous energy loss. Therefore, the energy loss during alternating magnetization, i.e., iron loss, becomes the main indicator determining the performance of a transformer.

[0004] To reduce the iron loss of directional electromagnetic steel sheets, from (a) increasing the directional {110} <001> Based on the ideas of (a) increasing the concentration of Gaussian orientation, (b) increasing the content of solid solution elements such as Si to improve the resistance of steel plates, or (c) reducing the thickness of electromagnetic steel plates, many technologies have been developed to date.

[0005] Furthermore, applying tension to the steel sheet is effective in reducing iron loss. Forming a coating on the steel sheet surface at high temperatures with a material having a lower coefficient of thermal expansion than the steel sheet is an effective means of reducing iron loss. In the finished annealing process of electromagnetic steel sheets, the magnesium olivine-based coating (inorganic coating) with excellent adhesion, formed by the reaction of oxides on the steel sheet surface with the annealing separating agent, is a coating capable of applying tension to the steel sheet.

[0006] Furthermore, for example, the method disclosed in Patent Document 1, which involves baking a coating liquid primarily composed of colloidal silica and phosphate onto the surface of a steel sheet to form an insulating film, is effective in reducing iron loss due to its strong effect of applying tension to the steel sheet. Therefore, retaining the forsterite-based coating generated in the finished product annealing process and applying a phosphate-based insulating coating to it has become a common manufacturing method for directional electromagnetic steel sheets.

[0007] However, in recent years, the requirements for miniaturization and high performance of transformers have increased. To achieve transformer miniaturization, directional electromagnetic steel plates are required to exhibit excellent iron losses even under high magnetic flux density, such as high magnetic field iron loss. Simultaneously, it has become clear that forsterite-based coatings hinder the movement of magnetic domain walls and negatively impact iron losses. In directional electromagnetic steel plates, magnetic domains change due to the movement of domain walls under an alternating magnetic field. While the smooth and rapid movement of these domain walls is effective in reducing iron losses, it is believed that forsterite-based coatings, being non-magnetic and possessing an uneven structure at the steel plate / coating interface, hinder the movement of magnetic domain walls, thus negatively affecting iron losses.

[0008] Therefore, as a means to improve iron loss in high magnetic fields, the following technologies have been studied: methods to remove inorganic coatings by mechanical means such as grinding or chemical means such as pickling; technologies to manufacture directional electromagnetic steel plates without inorganic coatings by preventing the formation of inorganic coatings during high-temperature annealing of finished products; and technologies to make the surface of the steel plate into a mirror state (in other words, technologies to smooth the surface of the steel plate with magnetic gas).

[0009] As a technique to prevent the formation of inorganic coatings, for example, Patent Document 2 discloses a method in which, after routine annealing of the finished product, surface formations are removed by pickling, and the surface of the steel plate is made into a mirror state by chemical polishing or electrolytic polishing. It has been found that for the surface of a directional electromagnetic steel plate without an inorganic coating obtained by such a known method, a superior iron loss improvement effect can be obtained by forming an insulating coating through tension. Furthermore, if an insulating coating is formed using tension, various properties such as corrosion resistance, heat resistance, and slip resistance can be imparted in addition to iron loss improvement.

[0010] However, inorganic coatings exhibit insulating properties and serve as an intermediate layer to ensure adhesion when forming tension coatings (tension-imparting insulating coatings). Specifically, inorganic coatings, formed by penetrating deeply into the steel sheet, exhibit excellent adhesion to the metal. Therefore, when a tension-imparting coating (tension coating) with colloidal silica or phosphate as its main components is formed on the surface of an inorganic coating, the coating adhesion is excellent. On the other hand, since the bonding between metals and oxides is generally difficult, it is difficult to ensure sufficient adhesion between the tension coating and the steel sheet surface in the absence of an inorganic coating.

[0011] Therefore, a layer was studied to replace the inorganic coating as an intermediate layer when a tension coating is formed on a directional electromagnetic steel sheet without an inorganic coating.

[0012] For example, Patent Document 3 discloses a technique in which a tension-imparting insulating film is formed by annealing a directional electromagnetic steel sheet without an inorganic coating in a weakly reducing atmosphere, thereby selectively thermally oxidizing the silicon inherently present in the silicon steel sheet, and forming a SiO2 layer on the steel sheet surface. Furthermore, Patent Document 4 discloses a technique in which a tension-imparting insulating film is formed by anodic electrolysis of a directional electromagnetic steel sheet without an inorganic coating in a silicate aqueous solution, thereby forming a SiO2 layer on the steel sheet surface.

[0013] Furthermore, Patent Document 5 discloses a technique in which the adhesion of the tension-imparting insulating film is ensured by pre-applying a coating that serves as an intermediate layer during the formation of the tension-imparting coating.

[0014] Furthermore, Patent Document 6 discloses a directional electromagnetic steel plate, which is a directional electromagnetic steel plate having a base steel plate and a tension-imparting insulating film, wherein the tension-imparting insulating film exists on the surface of the directional electromagnetic steel plate, and an iron oxide layer with a thickness of 100 to 500 nm exists between the base steel plate and the tension-imparting insulating film.

[0015] Existing technical documents

[0016] Patent documents

[0017] Patent Document 1: Japanese Patent Application Publication No. 48-039338

[0018] Patent Document 2: Japanese Patent Application Publication No. 49-96920

[0019] Patent Document 3: Japanese Patent Application Publication No. 6-184762

[0020] Patent Document 4: Japanese Patent Application Publication No. 11-209891

[0021] Patent Document 5: Japanese Patent Application Publication No. 5-279747

[0022] Patent Document 6: Japanese Patent Application Publication No. 2020-111814 Summary of the Invention

[0023] The problem that the invention aims to solve

[0024] However, the technology disclosed in Patent Document 3 requires annealing equipment with a controllable atmosphere to perform annealing in a weakly reducing atmosphere, which presents a cost problem. Furthermore, the technology disclosed in Patent Document 4 requires new electrolytic treatment equipment to obtain a SiO2 layer on the steel plate surface that maintains sufficient adhesion to the tension-imparting insulating film by performing anodic electrolysis treatment in a silicate aqueous solution, which also presents a cost problem.

[0025] Furthermore, regarding the technology disclosed in Patent Document 5, there is a problem that the insulating film cannot maintain a good seal with high tension.

[0026] Furthermore, in the technology disclosed in Patent Document 6, in order to form an iron-based oxide layer, the surface-treated directional electromagnetic steel sheet is heated at a steel sheet temperature of 700-900°C for 5-60 seconds in an atmosphere with an oxygen concentration of 1-21% by volume and a dew point of -20-30°C. Therefore, when manufacturing steel sheets with inorganic coatings using the same production line, it is necessary to change the atmosphere of the annealing furnace, resulting in poor workability.

[0027] As mentioned above, it is difficult to provide directional electromagnetic steel sheets that do not have inorganic coatings, excellent coating adhesion, high coating tension, and excellent magnetic properties, provided that the method does not restrict equipment or degrade workability.

[0028] Therefore, the objective of this invention is to provide a directional electromagnetic steel sheet that does not have an inorganic coating, exhibits excellent coating adhesion, excellent coating tension, and excellent magnetic properties. Furthermore, the objective of this invention is to provide a method for forming an insulating coating on such a directional electromagnetic steel sheet.

[0029] Methods for solving problems

[0030] The inventors have studied the aforementioned issues. Their findings indicate that, in directional electromagnetic steel sheets without a magnesium olivine-based coating, the coating adhesion, coating tension, and magnetic properties can be improved by having an intermediate layer formed of a crystalline metal phosphate salt between the base steel sheet and the tension coating.

[0031] This invention is based on the above-mentioned insights. The main points of this invention are as follows.

[0032] [1] One aspect of the present invention is a directional electromagnetic steel plate having a base steel plate and an insulating film formed on the surface of the base steel plate. The insulating film has an intermediate layer formed on the side of the base steel plate and containing a crystalline metal phosphate salt, and a tension film layer formed on the surface side of the insulating film. The average thickness of the intermediate layer is 0.3 to 10.0 μm, and the average thickness of the insulating film is 2.0 to 10.0 μm. The crystalline metal phosphate salt of the intermediate layer is one or more of zinc phosphate, manganese phosphate, iron phosphate, and zinc calcium phosphate. The tension film layer contains a metal phosphate salt and silicon dioxide, and the content of silicon dioxide in the tension film layer is 20 to 60% by mass.

[0033] [2] Another aspect of the present invention is a method for forming the insulating film of the directional electromagnetic steel plate described above [1], comprising the following steps: coating a steel plate with an annealing separating agent containing 10 to 100% by mass of Al2O3 and drying it, followed by a finished product annealing process; removing the remaining annealing separating agent from the steel plate after the finished product annealing process; and annealing the steel plate after the annealing separating agent removal process in a liquid at a temperature of 40 to 85°C and containing 5 to 50% by mass of Al2O3. The process includes: an immersion process in a treatment solution containing % metal phosphate for 5 to 150 seconds; a drying process after which the steel plate is pulled out of the treatment solution and the remaining treatment solution is removed; and a tension film formation process after which a coating solution containing metal phosphate and colloidal silica is applied to the steel plate after the drying process, wherein the colloidal silica comprises 30 to 150 parts by mass relative to 100 parts by mass of metal phosphate and 30 to 150 parts by mass of colloidal silica, and the plate is dried, and then held at a plate temperature of 700 to 950°C for 10 to 120 seconds.

[0034] [3] According to the method for forming the insulating film described in [2] above, the annealing separating agent may further include one or two of MgO: 5 to 90% by mass and chloride: 0.5 to 10.0% by mass.

[0035] Invention Effects

[0036] According to the above-described solution of the present invention, a directional electromagnetic steel sheet with excellent film adhesion, excellent film tension, and excellent magnetic properties can be provided. Furthermore, according to the above-described solution of the present invention, a method for forming an insulating film in a directional electromagnetic steel sheet with excellent film adhesion and excellent magnetic properties can be provided. Attached Figure Description

[0037] Figure 1 This is an example of a cross-sectional view of the directional electromagnetic steel plate in this embodiment. Detailed Implementation

[0038] A directional electromagnetic steel sheet according to an embodiment of the present invention (the directional electromagnetic steel sheet of this embodiment) and a method for manufacturing the directional electromagnetic steel sheet of this embodiment, including a method for forming an insulating film provided with the directional electromagnetic steel sheet of this embodiment, will be described.

[0039] First, the directional electromagnetic steel plate of this embodiment will be explained.

[0040] The directional electromagnetic steel plate 100 in this embodiment is as follows: Figure 1As shown, it has a base steel plate 1 and an insulating film 2 formed on the surface of the base steel plate 1, but the surface of the base steel plate 1 does not have a magnesium olivine-based film.

[0041] Furthermore, the insulating film 2 has a tension film layer 22 formed on the surface side of the insulating film 2 (i.e., the surface side of the directional electromagnetic steel plate 100) and an intermediate layer 21 formed on the side of the base steel plate 1 and containing crystalline metal phosphate salts.

[0042] <Base Material Steel Plate>

[0043] (Chemical composition)

[0044] The directional electromagnetic steel sheet 100 of this embodiment has significant features in the structure of the insulating film 2 formed on the surface of the base steel sheet 1. The chemical composition of the base steel sheet 1 used in the directional electromagnetic steel sheet 100 is not limited and is preferably within a known range. To obtain the characteristics generally required for a directional electromagnetic steel sheet, the following components are preferably included as the chemical composition. In this embodiment, unless otherwise specified, the percentages related to the chemical composition are by mass%.

[0045] C: Below 0.010%

[0046] Carbon (C) is an element effective in controlling the microstructure of steel sheets during the manufacturing process up to the completion of the decarburization annealing process. However, if the C content exceeds 0.010%, the magnetic properties of the directional electromagnetic steel sheet used as the finished product decrease. Therefore, in the base steel sheet of the directional electromagnetic steel sheet of this embodiment, the C content is preferably set to 0.010% or less. The C content is more preferably 0.005% or less. The lower the C content, the more preferred, but even if the C content is reduced to less than 0.0001%, the effect of microstructure control saturates, resulting only in increased manufacturing costs. Therefore, the C content can also be set to 0.0001% or more.

[0047] Si: 2.50–4.00%

[0048] Silicon (Si) is an element that increases the resistance of directional electromagnetic steel sheets and improves iron loss characteristics. When the Si content is below 2.50%, a sufficient reduction in eddy current losses cannot be obtained. Therefore, the Si content is preferably set to 2.50% or more. More preferably, the Si content is 2.70% or more, and even more preferably 3.00% or more.

[0049] On the other hand, if the Si content exceeds 4.00%, the directional electromagnetic steel sheet becomes brittle, and its through-sheet properties deteriorate significantly. Furthermore, the machinability of the directional electromagnetic steel sheet decreases, and the sheet may break during rolling. Therefore, the Si content is preferably set to 4.00% or less. More preferably, the Si content is 3.80% or less, and even more preferably 3.70% or less.

[0050] Mn: 0.01~0.50%

[0051] Manganese (Mn) is an element that combines with sulfur (S) during the manufacturing process to form MnS. This precipitate functions as an inhibitor (an inhibitor of normal grain growth) and exhibits secondary recrystallization in steel. Mn also improves the hot workability of steel. When the Mn content is below 0.01%, the aforementioned effects cannot be sufficiently obtained. Therefore, the Mn content is preferably set to 0.01% or more. More preferably, it is 0.02% or more.

[0052] On the other hand, if the Mn content exceeds 0.50%, secondary recrystallization will not occur, and the magnetic properties of the steel will decrease. Therefore, in the base steel sheet of the directional electromagnetic steel sheet of this embodiment, the Mn content is preferably set to 0.50% or less. More preferably, the Mn content is 0.20% or less, and even more preferably 0.10% or less.

[0053] N: below 0.010%

[0054] Nitrogen (N) is an element that combines with Al during the manufacturing process to form AlN, which functions as an inhibitor. However, if the N content exceeds 0.010%, excessive inhibitors remain in the directional electromagnetic steel sheet, reducing its magnetic properties. Therefore, in the base steel sheet of the directional electromagnetic steel sheet of this embodiment, the N content is preferably set to 0.010% or less. More preferably, the N content is 0.008% or less.

[0055] On the other hand, there is no specific lower limit for nitrogen content, but even if it is reduced to below 0.001%, it only increases manufacturing costs. Therefore, the nitrogen content can also be set above 0.001%.

[0056] sol.Al: 0.020% or less

[0057] Sodium aluminum (sol.Al) is an element that combines with nitrogen (N) during the manufacturing process of directional electromagnetic steel sheets to form AlN, which functions as an inhibitor. However, if the sol.Al content of the base steel sheet exceeds 0.020%, excessive inhibitors remain in the base steel sheet, reducing magnetic properties. Therefore, in the base steel sheet of the directional electromagnetic steel sheet of this embodiment, the sol.Al content is preferably set to 0.020% or less. More preferably, it is 0.010% or less, and even more preferably less than 0.001%. The lower limit of the sol.Al content is not particularly specified, but even if it is reduced to less than 0.0001%, only the manufacturing cost increases. Therefore, the sol.Al content can also be set to 0.0001% or more.

[0058] S: below 0.010%

[0059] Sulfur (S) 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 magnetic properties decrease due to the residual inhibitor. Therefore, in the base steel sheet of the directional electromagnetic steel sheet of this embodiment, the S content is preferably set to 0.010% or less. The S content in the directional electromagnetic steel sheet is more preferably as low as possible, for example, less than 0.001%. However, even if the S content in the directional electromagnetic steel sheet is reduced to less than 0.0001%, only the manufacturing cost increases. Therefore, the S content in the directional electromagnetic steel sheet can also be 0.0001% or more.

[0060] Remaining components: Fe and impurities

[0061] The chemical composition of the base steel plate of the directional electromagnetic steel plate of this embodiment may also contain the elements (basic elements) described above, with the remainder being Fe and impurities. However, for the purpose of improving magnetic properties, etc., one or more of Sn, Cu, Se, and Sb may be further included within the range shown below. In addition, as other elements, even if one or more of W, Nb, Ti, Ni, Co, V, Cr, and Mo are contained in a total of 1.0% or less (whether intentionally added or contained as impurities is not a problem), it will not hinder the effect of the directional electromagnetic steel plate of this embodiment.

[0062] Here, impurities refer to elements that are mixed in from the raw materials such as ore, waste, or the manufacturing environment during the industrial manufacturing of the base steel plate. These are elements that are allowed to be present in a content that does not adversely affect the function of the directional electromagnetic steel plate of this embodiment.

[0063] Sn: 0-0.50%

[0064] Sn (tin) is an element whose magnetic properties are improved by controlling the primary recrystallization structure. To achieve the effect of improved magnetic properties, it is preferable to set the Sn content to 0.01% or more. More preferably, the Sn content is 0.02% or more, and even more preferably 0.03% or more.

[0065] On the other hand, when the Sn content exceeds 0.50%, secondary recrystallization becomes unstable, and the magnetic properties deteriorate. Therefore, the Sn content is preferably set to 0.50% or less. The Sn content is more preferably 0.30% or less, and even more preferably 0.10% or less.

[0066] Cu: 0–0.50%

[0067] Cu (copper) is an element that contributes to increasing the proportion of Goss orientation in secondary recrystallization structures. To achieve the above effect, it is preferable to set the Cu content to 0.01% or more. More preferably, the Cu content is 0.02% or more, and even more preferably 0.03% or more.

[0068] 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 of the directional electromagnetic steel sheet of this embodiment, it is preferable to set the Cu content to 0.50% or less. More preferably, the Cu content is 0.30% or less, and even more preferably 0.10% or less.

[0069] Se: 0~0.020%

[0070] Selenium (Se) is an element that improves magnetic properties. When Se is present, to maximize its magnetic property improvement effect, it is preferable to set the Se content to 0.001% or more. More preferably, the Se content is 0.003% or more, and even more preferably 0.006% or more.

[0071] On the other hand, if the Se content exceeds 0.020%, the adhesion of the film deteriorates. Therefore, it is preferable to set the Se content to 0.020% or less. More preferably, the Se content is 0.015% or less, and even more preferably 0.010% or less.

[0072] Sb: 0~0.50%

[0073] Antimony (Sb) is an element that improves magnetic properties. In the presence of Sb, to maximize its magnetic property improvement effect, it is preferable to set the Sb content to 0.005% or more. More preferably, the Sb content is 0.01% or more, and even more preferably 0.02% or more.

[0074] On the other hand, if the Sb content exceeds 0.50%, the adhesion of the film is significantly deteriorated. Therefore, it is preferable to set the Sb content to 0.50% or less. More preferably, the Sb content is 0.30% or less, and even more preferably 0.10% or less.

[0075] As described above, the chemical composition of the base steel plate of the directional electromagnetic steel plate shown in this embodiment contains the aforementioned basic elements and the remaining portion contains Fe and impurities, or contains the basic elements, further contains one or more other optional elements, and the remaining portion contains Fe and impurities.

[0076] The chemical composition of the base steel plate of the directional electromagnetic steel sheet in this embodiment can be determined using the well-known ICP-based spectral analysis method. Regarding Si, it can be determined using the method specified in JIS G 1212 (1997) (quantitative method for silicon). Specifically, if the above-mentioned shavings are dissolved in acid, silicon oxide precipitates out as a precipitate. This precipitate (silicon oxide) is then filtered through filter paper, its mass is measured, and the Si content is determined.

[0077] The C and S contents are determined using the well-known high-frequency combustion method (combustion-infrared absorption method). Specifically, the solution is burned in an oxygen stream by high-frequency heating, and the produced carbon dioxide and sulfur dioxide are measured to determine the C and S contents.

[0078] The nitrogen content is determined using the well-known inert gas melting-thermal conductivity method.

[0079] However, during testing, if an insulating film has formed on the surface, it is peeled off before measurement. As a peeling method, it can be achieved by immersing the sample in a high-concentration alkaline solution (e.g., a 30% sodium hydroxide solution heated to 85°C) for at least 20 minutes. Whether peeling has occurred can be determined visually. In the case of small samples, peeling can also be achieved by surface grinding.

[0080] <Insulating membrane>

[0081] The directional electromagnetic steel plate 100 of this embodiment has an insulating film 2 formed on the surface of the base steel plate 1. In this embodiment, the directional electromagnetic steel plate 100 does not have a magnesium olivine-based film. Furthermore, it does not have a SiO2 layer as shown in Patent Documents 3 and 4. Therefore, the insulating film 2 is formed in direct contact with the base steel plate 1.

[0082] Furthermore, the insulating film 2 includes an intermediate layer 21 and a tension film layer 22 sequentially from the side of the base steel plate 1.

[0083] (Middle layer)

[0084] The intermediate layer 21 contains a crystalline metal phosphate salt and is a layer (film) with a thickness of 0.3 to 10.0 μm.

[0085] As mentioned above, directional electromagnetic steel sheets generally have a forsterite-based coating formed during the finished product annealing process and an insulating coating (tension insulating coating) formed thereon. However, in recent years, it has become clear that this forsterite-based coating hinders the movement of magnetic domain walls and adversely affects iron loss. Therefore, in order to further improve magnetic properties, directional electromagnetic steel sheets without a forsterite-based coating have been studied. However, in the absence of a forsterite-based coating, it is difficult to ensure sufficient adhesion between the tension coating and the surface of the base steel sheet.

[0086] In the directional electromagnetic steel plate 100 of this embodiment, by forming an intermediate layer 21 containing a crystalline metal phosphate salt between the base steel plate 1 and the tension film, the adhesion between the base steel plate 1 and the tension film layer 22 is improved via the intermediate layer 21.

[0087] This is because if the intermediate layer 21 contains crystalline metal phosphate salts, the tension film formed thereon (which becomes tension film layer 22 after formation) also contains metal phosphate salts, resulting in high affinity and excellent adhesion between the intermediate layer and the tension film layer. Furthermore, when the intermediate layer 21 is formed by immersion in a processing solution containing metal phosphate salts as described later, it can be formed on the surface of the base steel plate 1 through a chemical reaction, ensuring the adhesion between the intermediate layer 21 and the base steel plate 1.

[0088] The above-mentioned effect cannot be obtained if the intermediate layer 21 does not contain crystalline metal phosphate salts. The proportion of crystalline metal phosphate salts in the intermediate layer is preferably 80% by mass or more, more preferably 90% by mass or more, and may also be 100% by mass. As metal phosphate salts, from the perspective of adhesion, one or more of zinc phosphate, manganese phosphate, iron phosphate, and zinc calcium phosphate are selected.

[0089] From the perspective of adhesion to the base steel plate, in the phosphate metal salt, the total amount (mol) of metal (M) and Fe is preferably 2.0 times or more, and more preferably 3.0 times or more, relative to the amount (mol) of P.

[0090] If the metal phosphate salt is a hydrate, its corrosion resistance decreases; therefore, it is preferable that it is not a hydrate. Generally, the total amount (mol) of the metal (M) and Fe mentioned above is 1.5 times or less relative to the amount (mol) of P. In the case of the directional electromagnetic steel sheet of this embodiment, there are also cases where hydrates inevitably formed during the formation of the intermediate layer eventually remain, but they are in small amounts (usually less than 5.0% by mass of the entire insulating film 2).

[0091] Furthermore, from the viewpoint of adhesion, the processing solution is made free of colloidal silica during the formation of the intermediate layer. The remaining portion of the metal phosphate salt in the intermediate layer sometimes contains oxides or elements such as Fe and Si diffused from the base steel sheet, but since silica is not intentionally present as described above, the Si content is, for example, less than 1.0% by mass.

[0092] The intermediate layer 21 is formed at a different time than the tension film formed thereon, but both the intermediate layer 21 and the tension film layer 22 function as insulating film 2.

[0093] The amounts of metal (M), Fe (Fe), and P (P) in the phosphate metal salt were determined by EDS (energy-dispersive X-ray spectrophotometry) analysis on cross-sections along the thickness direction of the insulating film. Measurements were performed at approximately three locations, and the average value was taken as the amount (mol) for each.

[0094] In addition, the amount of hydrate can be roughly determined by measuring the water content using a thermobalance method.

[0095] The average thickness of the intermediate layer 21 is 0.3–10.0 μm.

[0096] When the average thickness of the intermediate layer 21 is less than 0.3 μm, the effect of improving the adhesion between the base steel plate and the insulating film through the intermediate layer is insufficient. On the other hand, if the average thickness of the intermediate layer exceeds 10.0 μm, the deterioration of the magnetic properties becomes significant.

[0097] (Tension membrane layer)

[0098] In the directional electromagnetic steel plate 100 of this embodiment, a tension film layer 22 is formed on the surface of the insulating film 2 by forming a tension film on the surface of the intermediate layer 21.

[0099] The tension film layer 22 is not particularly limited as long as it is used as an insulating film for directional electromagnetic steel sheets. However, from the viewpoint of good adhesion to the intermediate layer 21 (adhesion between the intermediate layer 21 and the base steel sheet 1), it contains metal phosphate salts and silica (colloidal silica derived from the coating liquid) in a manner that ensures the silica content is 20% by mass or more. On the other hand, if the silica content of the tension film layer exceeds 60% by mass, it will cause pulverization, so it is set to 60% by mass or less.

[0100] The tension film layer 22 preferably comprises a total of 70% by mass or more of a metal phosphate salt and silicon dioxide. The remainder, in addition to the metal phosphate salt and silicon dioxide, sometimes contains ceramic microparticles such as alumina and silicon nitride.

[0101] The thickness of the tension film layer 22 is not limited, but when the average thickness of the intermediate layer 21 is set within the aforementioned range, the average thickness of the insulating film 2 (intermediate layer 21 + tension film layer 22) is set to 2.0–10.0 μm. When the average thickness of the insulating film 2 is less than 2.0 μm, sufficient film tension cannot be obtained. Furthermore, the dissolution of phosphoric acid increases. In this case, it leads to reduced adhesion and corrosion resistance, and sometimes even film peeling. Moreover, when the thickness of the insulating film 2 exceeds 10.0 μm, the fill power decreases and magnetic properties deteriorate, or the adhesion decreases due to cracks, or corrosion resistance decreases.

[0102] The thickness of the insulating film 2 is determined by the following method.

[0103] The average thickness can be determined by observing the cross-section of the sample with a scanning electron microscope and measuring the thickness at more than 5 points. The intermediate layer 21 and the tension film layer 22 in the insulating film 2 can be distinguished by the content of silicon (Si) derived from silicon dioxide (as described above, the tension film layer contains silicon dioxide).

[0104] Furthermore, by summing the average thickness of the intermediate layer 21 and the average thickness of the tension film layer 22, the average thickness of the insulating film 2 can be obtained.

[0105] In the intermediate layer 21 and the tension film layer 22, the mass ratio and type of phosphate metal salt can be determined by the following method.

[0106] Similarly, the mass ratio and type of phosphate metal salt can be determined by using a scanning electron microscope and an energy dispersive elemental analyzer, as with the method for measuring the thickness of the intermediate layer 21 and the tension film layer 22.

[0107] Furthermore, whether the phosphate metal salt in the intermediate layer 21 is a crystalline phosphate metal salt can be determined by X-ray crystal structure analysis.

[0108] Furthermore, the silica content of the tension film layer 22 can be determined using a scanning electron microscope and an energy dispersive elemental analyzer.

[0109] <Manufacturing Method>

[0110] If a manufacturing method that meets the manufacturing conditions described below is used, the directional electromagnetic steel sheet of this embodiment can preferably be manufactured. However, the directional electromagnetic steel sheet of this embodiment is not particularly limited to the manufacturing method. That is, a directional electromagnetic steel sheet having the above-described configuration is considered to be the directional electromagnetic steel sheet of this embodiment regardless of its manufacturing conditions.

[0111] The directional electromagnetic steel plate of this embodiment can be manufactured by a manufacturing method including the following steps:

[0112] (I) A hot rolling process in which a steel billet having a specified chemical composition is hot rolled to obtain a hot-rolled plate;

[0113] (II) Annealing process of hot-rolled plate for annealing the above-mentioned hot-rolled plate;

[0114] (III) A cold rolling process in which the hot-rolled plate after the above-mentioned annealing process is cold rolled to obtain a steel plate (cold-rolled plate);

[0115] (IV) A decarburizing annealing process for the steel sheet after the above cold rolling process;

[0116] (V) A finished product annealing process in which an annealing separating agent containing 10 to 100% by mass of Al2O3 is applied to the steel plate after the above decarburization annealing process and dried, and then finished product annealing is carried out.

[0117] (VI) Annealing separator removal process for removing the remaining annealing separator from the steel plate after the above-mentioned finished product annealing process;

[0118] (VII) An immersion process in a treatment solution containing 5 to 50% by mass of metal phosphate salt at a liquid temperature of 40 to 85°C for 5 to 150 seconds after the above-mentioned annealing separating agent removal process is performed.

[0119] (VIII) A drying process in which the steel plate after the above impregnation process is pulled out of the above treatment liquid and the remaining above treatment liquid is removed, and then dried.

[0120] (IX) After the above drying process, a coating solution containing metal phosphate and colloidal silica is applied to the above steel plate in such a way that the colloidal silica is 30 to 150 parts by mass relative to 100 parts by mass of metal phosphate and the coating solution is applied to the plate and dried. Then, a tension film is formed at a plate temperature of 700 to 950°C for 10 to 120 seconds.

[0121] Furthermore, the method for manufacturing the directional electromagnetic steel plate of this embodiment may further include one or both of the following steps:

[0122] (X) A nitriding process in which the steel plate is nitrided between the above-mentioned decarburization annealing process and the above-mentioned finished product annealing process.

[0123] (XI) After the tension film formation process, the magnetic domain subdivision process of the above-mentioned steel plate magnetic domain control is performed.

[0124] Furthermore, the method for manufacturing the directional electromagnetic steel sheet of this embodiment may further include, between the above-mentioned annealing separating agent removal step and the above-mentioned impregnation step:

[0125] (XII) Surface conditioning process for controlling the reactivity of the surface of the above-mentioned steel plate.

[0126] In the manufacturing of the directional electromagnetic steel sheet in this embodiment, the characteristic steps are the (V) finished product annealing process to the (IX) tension film layer formation process, which are mainly related to the formation of the insulating film. Other processes or conditions not described can use known conditions.

[0127] The following is a description of these procedures.

[0128] <Hot Rolling Process>

[0129] In the hot rolling process, steel billets, such as slabs, with a specified chemical composition are heated and then hot rolled to obtain hot-rolled plates. The heating temperature of the steel billets is preferably set within the range of 1100–1450°C. More preferably, the heating temperature is 1300–1400°C.

[0130] The chemical composition of the billet can be changed according to the desired chemical composition of the directional electromagnetic steel sheet. For example, a chemical composition can be shown as follows (by mass%): C: 0.01-0.20%, Si: 2.50-4.00%, sol.Al: 0.01-0.040%, Mn: 0.01-0.50%, N: less than 0.020%, S: 0.005-0.040%, Cu: 0-0.50%, Sn: 0-0.50%, Se: 0-0.020%, and Sb: 0-0.50%, with the remainder being Fe and impurities.

[0131] There are no particular limitations on the hot rolling conditions; they can be appropriately set based on the required characteristics. The thickness of the hot-rolled sheet is preferably in the range of 2.0 mm or more and 3.0 mm or less.

[0132] <Hot-rolled sheet annealing process>

[0133] The hot-rolled sheet annealing process is a process of annealing hot-rolled sheets manufactured through the hot rolling process. By performing such annealing treatment, recrystallization can occur in the steel sheet structure, resulting in good magnetic properties, and therefore it is preferred.

[0134] When annealing hot-rolled steel sheets, it is sufficient to anneal the hot-rolled sheets manufactured through the hot-rolling process according to known methods. There are no particular limitations on the method of heating the hot-rolled sheet during annealing; known heating methods can be used. Furthermore, there are no particular limitations on the annealing conditions. For example, the hot-rolled sheet can be annealed for 10 seconds to 5 minutes in a temperature range of 900–1200°C.

[0135] <Cold rolling process>

[0136] In the cold rolling process, the hot-rolled sheet after the annealing process is cold-rolled to obtain a steel sheet (cold-rolled sheet). Cold rolling can be a single cold rolling (a series of cold rollings without intermediate annealing), or it can be a multiple cold rolling process with intermediate annealing interspersed before the final pass of the cold rolling process, where the cold rolling is interrupted and at least one or two intermediate annealings are performed.

[0137] When performing intermediate annealing, it is preferable to hold the temperature at 1000–1200°C for 5–180 seconds. The annealing atmosphere is not particularly limited. Considering manufacturing costs, the number of intermediate annealing cycles is preferably no more than 3.

[0138] In addition, the surface of the hot-rolled plate can be pickled before the cold rolling process.

[0139] In the cold rolling process of this embodiment, the hot-rolled sheet after the annealing process is cold-rolled according to a known method to produce a steel sheet. For example, the final reduction rate can be set in the range of 80% to 95%. If the final reduction rate is 80% or more, {110} can be obtained. <001> Goss nuclei with high aggregation in the rolling direction are preferred. On the other hand, when the final reduction exceeds 95%, the possibility of secondary recrystallization becoming unstable during the subsequent finished product annealing process increases, which is not preferred.

[0140] The final reduction rate is the cumulative reduction rate of cold rolling. In the case of intermediate annealing, it is the cumulative reduction rate of cold rolling after final intermediate annealing.

[0141] <Decarburization Annealing Process>

[0142] In the decarburizing annealing process, the obtained steel sheet is decarburized and annealed. As for decarburizing annealing, there are no restrictions on the decarburizing annealing conditions as long as it can cause recrystallization of the steel sheet in one step and remove carbon that has an adverse effect on the magnetic properties from the steel sheet. However, for example, it can be illustrated by setting the oxidation degree (PH2O / PH2) in the annealing atmosphere (furnace atmosphere) to 0.3 to 0.6 and holding it at an annealing temperature of 800 to 900°C for 10 to 600 seconds.

[0143] <Nitriding treatment process>

[0144] Nitriding can also be performed between the decarburization annealing process and the finished product annealing process described later.

[0145] In the nitriding process, for example, the steel sheet after the decarburization annealing process is nitrided at approximately 700–850°C in a nitriding atmosphere (an atmosphere containing nitriding gases such as hydrogen, nitrogen, and ammonia). When AlN is used as an inhibitor, it is preferable to set the N content of the steel sheet after the nitriding process to 40 ppm or more. On the other hand, if the N content of the steel sheet after the nitriding process exceeds 1000 ppm, excessive AlN will remain in the steel sheet even after secondary recrystallization during finished product annealing. Such AlN will contribute to the deterioration of iron loss. Therefore, it is preferable to set the N content of the steel sheet after the nitriding process to 1000 ppm or less.

[0146] <Finished product annealing process>

[0147] In the finished product annealing process, steel plates that have undergone decarburization annealing or further nitriding treatment (after nitriding treatment) are coated with an annealing separating agent containing 10-100% by mass of Al2O3 and dried before finished product annealing.

[0148] In conventional methods for manufacturing directional electromagnetic steel sheets, the finished product is annealed by coating with an annealing release agent primarily composed of MgO, thereby forming a magnesium olivine-based coating on the surface of the steel sheet (cold-rolled sheet). In contrast, in the method for manufacturing directional electromagnetic steel sheets of this embodiment, an annealing release agent containing Al2O3 is used to prevent the formation of a magnesium olivine-based coating.

[0149] On the other hand, the proportion of Al2O3 can also be 100% by mass, but from the viewpoint of preventing Al2O3 from being baked onto the surface of the steel plate, in the manufacturing method of the directional electromagnetic steel plate of this embodiment, it is preferable to include MgO in the annealing separating agent. MgO can also be 0%, but to achieve the above-mentioned effect, the proportion of MgO is preferably set to 5% by mass or more. When MgO is included, in order to ensure 10% by mass or more of Al2O3, the proportion of MgO is set to 90% by mass or less. The proportion of MgO is preferably 50% by mass or less.

[0150] Furthermore, in the manufacturing method of the directional electromagnetic steel sheet of this embodiment, the annealing separating agent may be further enriched with chlorides. By including chlorides in the annealing separating agent, it is possible to obtain an effect where it is less likely to form a magnesium olivine-based coating. The chloride content is not particularly limited and may be 0%, but when the above-mentioned effect is obtained, 0.5% to 10% by mass is preferred. As chlorides, bismuth chloride, calcium chloride, cobalt chloride, ferric chloride, nickel chloride, etc. are effective.

[0151] There are no restrictions on the annealing conditions for the finished product, but for example, it can be carried out at a temperature of 1150 to 1250°C for 10 to 60 hours.

[0152] <Removal of annealing separating agent process>

[0153] For steel sheets after the annealing process, remove any remaining annealing separating agent. This can be done, for example, by washing with water.

[0154] <Surface conditioning process>

[0155] A surface conditioning process to control the reactivity of the steel sheet surface can also be performed between the annealing separator removal process and the impregnation process.

[0156] There are no restrictions on the conditions for the surface conditioning process, but examples can be given of immersing the steel sheet after the annealing separator removal process in a commercially available surface conditioning agent for 30 seconds to 1 minute.

[0157] <Immersion Process>

[0158] <Drying Process>

[0159] After the annealing separating agent removal process (or after a further surface conditioning process if necessary), the steel sheet is immersed in a treatment solution at a temperature of 40–85°C containing 5–50% by mass of a specified metal phosphate salt for 5–150 seconds (immersion process). Afterward, it is pulled out of the treatment solution, the remaining treatment solution is removed, and it is dried (drying process). This forms an intermediate layer containing crystalline metal phosphate salts on the surface of the steel sheet (base steel sheet).

[0160] If the liquid temperature is below 40°C or the immersion time is less than 5 seconds, a sufficiently thick intermediate layer cannot be obtained. On the other hand, if the liquid temperature exceeds 85°C or the immersion time exceeds 150 seconds, the thickness of the intermediate layer becomes excessive.

[0161] Furthermore, if the metal phosphate salt content in the treatment solution is less than 5% by mass, the formation of the intermediate layer is slow, leading to higher industrial costs. To ensure uniform film thickness in the intermediate layer, the metal phosphate salt content is preferably 10% by mass or more.

[0162] On the other hand, if the metal phosphate salt exceeds 50% by mass, the crystal grains may become coarse, leading to reduced adhesion. The metal phosphate salt included in the treatment solution can be one or more of zinc phosphate, manganese phosphate, or zinc-calcium phosphate.

[0163] Furthermore, if the drying temperature is too high, voids may form, resulting in poor sealing. Therefore, the drying temperature is preferably set to 300°C or below. More preferably, it is 200°C or below. The drying temperature is preferably 100°C or above.

[0164] <Tension film formation process>

[0165] In the tension film layer formation process, a coating solution containing metal phosphate salts and colloidal silica is applied to a steel sheet (a steel sheet with an intermediate layer formed on a base steel sheet) after the drying process, and then dried. The sheet is then held at a temperature of 700–950°C for 10–120 seconds to form a tension film. The layer containing this tension film (tension film layer 22) and the intermediate layer 21 together form the insulating film 2.

[0166] If the plate temperature during holding is below 700°C, the tensile strength becomes low and the magnetic properties deteriorate. Therefore, the plate temperature is preferably set to 700°C or higher. On the other hand, if the plate temperature exceeds 950°C, the rigidity of the steel plate becomes easily reduced, leading to deformation. In this case, strain may sometimes form in the steel plate through processes such as transfer, resulting in deteriorated magnetic properties. Therefore, the plate temperature is preferably set to 950°C or lower.

[0167] Furthermore, if the holding time is less than 10 seconds, the dissolution becomes poor. Therefore, the holding time is set to 10 seconds or more. On the other hand, if the holding time exceeds 120 seconds, the productivity becomes poor. Therefore, the holding time is preferably less than 120 seconds.

[0168] The coating solution comprises metal phosphate and colloidal silica in such a manner that the colloidal silica is 30 to 150 parts by mass relative to 100 parts by mass of metal phosphate. As the metal phosphate, 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., may be used.

[0169] Vanadium, tungsten, molybdenum, zirconium, etc., may also be included as additional elements in the coating solution. When these elements are present, they can be added to the coating solution, for example, as oxyacids.

[0170] Colloidal silica can be of type S or type C. Type S refers to colloidal silica with an alkaline silica solution, while type C refers to colloidal silica with an aluminum-treated surface, resulting in an alkaline to neutral silica solution. Type S colloidal silica is widely used and relatively inexpensive, but it may coagulate and precipitate when mixed with acidic metal phosphate solutions, requiring caution. Type C colloidal silica is stable even when mixed with metal phosphate solutions and does not precipitate, but it requires more processing time and is more expensive. It is preferable to use them separately based on the stability of the prepared coating solution.

[0171] <Magnetic domain subdivision process>

[0172] In the manufacturing method of the directional electromagnetic steel sheet of this embodiment, a magnetic domain subdivision process may be further included to subdivide the magnetic domains of the steel sheet after the tension film layer formation process.

[0173] By performing magnetic domain subdivision processing, the iron loss of directional electromagnetic steel sheets can be further reduced.

[0174] As a method for magnetic domain subdivision processing, there are two methods: one is to narrow the width of a 180° magnetic domain by forming linear or dot-shaped grooves extending in a direction intersecting the rolling direction at predetermined intervals along the rolling direction (subdivision of 180° magnetic domains); the other is to narrow the width of a 180° magnetic domain by forming linear or dot-shaped stress-strain portions or grooves extending in a direction intersecting the rolling direction at predetermined intervals along the rolling direction (subdivision of 180° magnetic domains).

[0175] When forming stress-strain regions, laser beam irradiation, electron beam irradiation, etc., can be applied. In addition, when forming grooves, mechanical groove forming methods using gears or the like, chemical groove forming methods using electrolytic etching, and thermal groove forming methods using laser irradiation, etc., can be applied.

[0176] In cases where damage occurs in the insulating film due to the formation of stress-strained sections or grooves, resulting in deterioration of insulation properties, the insulating film can be reformed to repair the damage.

[0177] Example

[0178] The casting contains, by mass percent, C: 0.08%, Si: 3.29%, sol.Al: 0.028%, N: 0.008%, Mn: 0.15%, S: 0.007%, with the remainder being Fe and impurities.

[0179] The slab is heated to 1350℃ and then hot-rolled to produce a hot-rolled plate with a thickness of 2.2mm.

[0180] After annealing the hot-rolled sheet at 1100℃ for 10 seconds (hot-rolled sheet annealing), it is cold-rolled until the sheet thickness is 0.22mm to obtain a steel sheet (cold-rolled sheet).

[0181] The steel plate was decarburized and annealed at 830°C for 90 seconds in an atmosphere with a pH of 0.4 (pH2O / pH2).

[0182] Subsequently, except for No. 127, an annealing separating agent containing 48% by mass Al2O3, 48% by mass MgO, and 4% by mass bismuth chloride was applied to the steel plate and dried, followed by final annealing at 1200°C for 20 hours. For No. 127, an annealing separating agent containing only Al2O3 (100% by mass) was applied to the steel plate and dried, followed by final annealing at 1200°C for 20 hours.

[0183] For steel plates after the annealing process, the remaining annealing separating agent is removed by washing with water, resulting in no magnesium olivine film forming on the surface of the steel plate.

[0184] The steel plate is immersed in the treatment solution shown in Table 1, then heated to 100–150°C and dried to form an intermediate layer (any one of intermediate layers No. 1–10). The average thickness of the intermediate layer is as shown in Table 1.

[0185] The X-ray crystal structure analysis results show that the phosphate salts in the intermediate layers No. 1 to No. 9 are all crystalline phosphate salts. In these crystalline phosphate salts, the ratio of the total stoichiometry (mol) of metal (M) to Fe to the total stoichiometry (mol) of P is approximately 2:1 or 3:1. The phosphate salt No. 10 (magnesium phosphate) is not a crystalline phosphate salt.

[0186]

[0187] Steel plates (No. 101-127) with various intermediate layers are cut into multiple pieces as needed. For each steel plate, a coating solution containing the metal phosphate salts and colloidal silica shown in Table 2 is applied. The plates are then baked in a drying oven for the time specified in Table 2, according to the plate temperature in Table 2, to form a tension film on the surface. When the coating solution contains vanadium, tungsten, molybdenum, or zirconium, these are added in the form of oxyacids (V₂O₄, WO₃, MoO₃, ZrO₂) at the molar ratios shown in Table 2. During formation, the thickness of the tension film layer is varied by changing the amount of coating solution applied. A portion of the coating solution contains, as a remainder, alumina or silicon nitride.

[0188] This led to the manufacture of steel plates (directional electromagnetic steel plates).

[0189] For the obtained steel plates (No. 101~127), the content of silica and metal phosphate salts in the tension film layer and the average thickness of the insulating film are determined by the above method.

[0190] The results are shown in Table 2.

[0191] In addition, the chemical composition of the base steel plate was investigated, and the results showed that it contained Si: 3.28%, C: 0.001%, sol.Al: less than 0.001%, N: 0.001%, Mn: 0.07%, S: less than 0.0005%, and the remainder was Fe and impurities.

[0192]

[0193] Furthermore, for these steel plates, the adhesion, film tension, corrosion resistance, leaching properties, and magnetic properties of the insulating film were determined using methods described later. The results are shown in Table 3.

[0194] [Seamlessness]

[0195] The adhesion of the coating is evaluated by the degree of peeling (area ratio) of the coating after the following bending adhesion test: a sample with a width of 30 mm and a length of 300 mm is taken from a steel plate, and the sample is subjected to stress relief annealing at 800°C for 2 hours in a nitrogen atmosphere. After that, it is wound onto a 10 mm φ cylinder and unwound.

[0196] The evaluation criteria are set as follows: under conditions A or B, the film adhesion is judged to be excellent.

[0197] A: Peeling area ratio 0-0.5%

[0198] B: Peeling area ratio exceeding 0.5% but below 5.0%

[0199] C: The stripping area ratio exceeds 5.0% but is less than 20%.

[0200] D: Peeling area ratio exceeding 20% ​​but below 50%

[0201] E: Peeling area ratio exceeds 50%

[0202] [Capsule tension]

[0203] The film tension is calculated by taking a sample from a steel plate and reciprocally calculating the bending condition when peeling off the insulating film from one side of the sample.

[0204] If the obtained film tension is above 4.0 MPa, it is judged to be of excellent film tension.

[0205] [Corrosion Resistance]

[0206] According to the salt spray test of JIS Z2371:2015, the sample was allowed to fall naturally with a 5% NaCl aqueous solution for 7 hours in an atmosphere of 35°C.

[0207] The area of ​​rust is then evaluated using a 10-point scale.

[0208] The evaluation criteria are set as follows: a score of 5 or above (5-10) is considered to be excellent corrosion resistance.

[0209] 10: No rust was produced.

[0210] 9. Rust formation is extremely minor (area rate less than 0.1%).

[0211] 8: The area of ​​rust formation = exceeding 0.1% but less than 0.25%

[0212] 7: The area of ​​rust formation is greater than 0.25% but less than 0.50%.

[0213] 6: The area of ​​rust formation = exceeding 0.50% but less than 1%.

[0214] 5: The area of ​​rust formation = exceeding 1% but less than 2.5%

[0215] 4: The area of ​​rust formation = exceeding 2.5% but less than 5%

[0216] 3: The area of ​​rust formation is greater than 5% but less than 10%.

[0217] 2: The area of ​​rust formation is greater than 10% but less than 25%.

[0218] 1: The area of ​​rust formation is greater than 25% but less than 50%.

[0219] [Solubility]

[0220] Samples were collected from the obtained steel plates and boiled in boiling pure water for 10 minutes. The amount of phosphoric acid dissolved into the pure water was measured. The solubility (mg / m²) was evaluated by dividing the amount of dissolved phosphoric acid by the area of ​​the insulating film of the boiled directional electromagnetic steel plate. 2 ).

[0221] The amount of phosphoric acid dissolved in pure water is determined by cooling the pure water (solution) containing dissolved phosphoric acid, and then using ICP-AES to determine the phosphoric acid concentration of the sample after diluting the cooled solution with pure water, and thus calculating the phosphoric acid concentration.

[0222] If the dissolution rate per unit area is less than 140 mg / m² 2 If it is, then it is judged to have excellent solubility.

[0223] [Magnetic properties]

[0224] As a magnetic property, iron loss is evaluated. Specifically, for the obtained steel plate, with UA (irradiation energy density) of 2.0 mJ / mm², the iron loss is evaluated. 2 The magnetic domain subdivision process was performed by irradiating a laser beam under certain conditions, and the iron loss after the magnetic domain subdivision process (iron loss W17 / 50 at 50Hz at 1.7T) was measured.

[0225] If the iron loss is below 0.70 W / kg, it is judged to have excellent magnetic properties.

[0226] [Table 3]

[0227]

[0228] As shown in Tables 1 to 3, Nos. 101 to 115 and 127, which are examples of the present invention, exhibit excellent film adhesion, excellent film tension, and excellent magnetic properties. Furthermore, their corrosion resistance and dissolution are also satisfactory. In contrast, Nos. 116 to 126 exhibit at least one inferior aspect in terms of film adhesion, film tension, and magnetic properties. Additionally, their corrosion resistance and dissolution are also inferior.

[0229] Explanation of symbols

[0230] 1. Base material steel plate

[0231] 2 Insulating film

[0232] 21 Intermediate Layer

[0233] 22 Tension film layer

[0234] 100 directional electromagnetic steel sheet

Claims

1. A directional electromagnetic steel plate, characterized in that, It has the following characteristics: Base material steel plate, and An insulating film formed on the surface of the base steel plate. The insulating film has the following characteristics: An intermediate layer formed on the side of the base steel plate, comprising crystalline metal phosphate salts and having a Si content of less than 1.0% by mass, and Tension film layer formed on the surface side of the insulating film, The average thickness of the intermediate layer is 0.3–10.0 μm. The average thickness of the insulating film is 2.0–10.0 μm. The crystalline metal phosphate salt in the intermediate layer is one or more of zinc phosphate, manganese phosphate, iron phosphate, and zinc calcium phosphate, and is not a hydrate. In the crystalline metal phosphate salt, the total amount of metal (M) and Fe relative to the amount of P is more than 2.0 times, expressed in moles. The tension film layer comprises a metal phosphate salt and silicon dioxide, wherein the content of silicon dioxide in the tension film layer is 20-60% by mass.

2. A method for forming an insulating film, characterized in that, The method for forming the insulating film of the directional electromagnetic steel plate according to claim 1 includes the following steps: The finished product annealing process involves coating a steel plate with an annealing separating agent containing 10-100% by mass of Al2O3, drying it, and then annealing the finished product. The annealing separator removal process is for removing the remaining annealing separator from the steel plate after the finished annealing process; The steel plate after the annealing separating agent removal process is immersed in a treatment solution with a liquid temperature of 40-85°C and containing 5-50% by mass of metal phosphate salt for 5-150 seconds. A drying process is performed after the steel plate following the impregnation process is pulled out of the treatment solution and the remaining treatment solution is removed, and then the plate is dried. After the drying process, a coating solution containing metal phosphate and colloidal silica is applied to the steel plate in such a way that 30 to 150 parts by mass of colloidal silica are relative to 100 parts by mass of metal phosphate. After drying, the plate is then subjected to a tension film formation process at a plate temperature of 700 to 950°C for 10 to 120 seconds.

3. The method for forming an insulating film according to claim 2, characterized in that, The annealing separating agent further comprises one or two of the following: MgO: 5-90% by mass, chloride: 0.5-10.0% by mass.

Images