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

Abstract

This grain-oriented electrical steel sheet has a base steel sheet and an insulating coating film formed on the surface of the base steel sheet, and the insulating coating film has: an intermediate layer that is formed on the base steel sheet side and contains amorphous silica, one or more of an inorganic filler and a metal oxide, and a crystalline phosphoric acid metal salt; and a tension film layer formed on the surface side of the insulating film, the average particle diameter of one or more of the amorphous silica, the inorganic filler, and the metal oxide being 10-500 nm.

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. 2023-064836 filed on April 12, 2023, the contents of which are incorporated herein by reference. Background Technology

[0003] Directional electromagnetic steel sheets are mainly used in transformers. Transformers are continuously energized during their long lifespan from installation to disposal, resulting in continuous energy loss. Therefore, the energy loss during alternating current 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] In addition, 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 final annealing process of electromagnetic steel sheets, the magnesium olivine-based coating (inorganic coating) formed by the reaction of oxides on the steel sheet surface with the annealing separating agent has excellent adhesion and is 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 mainly composed of colloidal silica and phosphate onto the surface of a steel plate to form an insulating film, is effective in reducing iron loss because it exerts a large tension on the steel plate. Therefore, retaining the magnesium olivine-based coating generated in the final annealing process and applying a phosphate-based insulating coating thereon has become a common method for manufacturing directional electromagnetic steel sheets.

[0007] However, in recent years, the requirements for miniaturization and high performance of transformers have been increasing. To achieve transformer miniaturization, directional electromagnetic steel plates are required to maintain good iron losses even under high magnetic flux density and with excellent high-magnetic-field iron losses. Meanwhile, it has been clarified in recent years that forsterite-based coatings hinder the movement of magnetic domain walls and adversely affect iron losses. In directional electromagnetic steel plates, magnetic domains change due to the movement of domain walls under an alternating magnetic field. Smooth and rapid movement of these domain walls is effective in reducing iron losses. However, it is believed that forsterite-based coatings themselves are non-magnetic, and the interface between the steel plate and the coating has an uneven structure. This uneven structure hinders the movement of magnetic domain walls, thus adversely affecting iron losses.

[0008] Therefore, as a means to improve iron loss in high magnetic fields, research is being conducted on methods to remove forsterite-based coatings (inorganic coatings) using mechanical means such as grinding or chemical means such as pickling, techniques to manufacture directional electromagnetic steel plates without forsterite-based coatings by preventing the formation of forsterite-based coatings during high-temperature final annealing, and techniques to make the steel plate surface mirror-like (in other words, techniques to magnetically smooth the steel plate surface).

[0009] As a technique to prevent the formation of forsterite-based coatings, Patent Document 2 discloses a method in which, after a typical final annealing process, surface formations are removed by pickling, and the steel plate surface is then made into a mirror finish by chemical polishing or electrolytic polishing. It has been demonstrated that by applying tension to the surface of a directional electromagnetic steel plate without forsterite-based coatings obtained using such a known method, an insulating coating can be applied, resulting in superior iron loss improvement. Furthermore, by applying an insulating coating based on tension, in addition to improving iron loss, various properties such as corrosion resistance, heat resistance, and slip resistance can also be imparted.

[0010] However, forsterite-based coatings exhibit insulating properties and act as an intermediate layer to ensure adhesion when forming tension coatings (tension-imparting insulating coatings). That is, the forsterite-based coating is formed deep within the steel sheet, resulting in excellent adhesion to the metal. Therefore, when a tension-imparting coating (tension coating) composed primarily of colloidal silica or phosphates is formed on the surface of the forsterite-based coating, the coating adhesion is excellent. On the other hand, the bonding between metals and oxides is generally difficult, making it challenging to ensure sufficient adhesion between the tension coating and the steel sheet surface in the absence of a forsterite-based coating.

[0011] Therefore, for directional electromagnetic steel sheets without forsterite-based coatings, in the case of forming tension coatings, a layer was studied to replace the function of an intermediate layer as a forsterite-based coating.

[0012] For example, Patent Document 3 discloses the following technique: annealing a directional electromagnetic steel sheet without a forsterite-based coating (inorganic coating) in a weakly reducing atmosphere, selectively thermally oxidizing the silicon inherently present in the silicon steel sheet, thereby forming a SiO2 layer on the steel sheet surface, and then forming a tension-imparting insulating coating. Furthermore, Patent Document 4 discloses the following technique: anodic electrolysis treatment of a directional electromagnetic steel sheet without a forsterite-based coating (inorganic coating) in a silicate aqueous solution, thereby forming a SiO2 layer on the steel sheet surface, and then forming a tension-imparting insulating coating.

[0013] However, for the technology disclosed in Patent Document 3, annealing in a weakly reducing atmosphere requires annealing equipment capable of atmosphere control, which presents a cost problem. Furthermore, in the technology disclosed in Patent Document 4, obtaining a SiO2 layer on the steel plate surface that maintains sufficient adhesion to the tension-imparting insulating film through anodic electrolysis in a silicate aqueous solution requires new electrolysis equipment, also presenting a cost problem.

[0014] In contrast, Patent Document 5 discloses a directional electromagnetic steel sheet having a base steel sheet and an insulating film formed on the surface of the base steel sheet. The insulating film has an intermediate layer formed on the side of the base steel sheet and containing a crystalline metal phosphate salt, and a tension film layer formed on the surface side of the insulating film. In this directional electromagnetic steel sheet, the intermediate layer can be formed by chemical conversion treatment.

[0015] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application 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

[0016] The problem that the invention aims to solve In the technology of Patent Document 5, by having an intermediate layer formed of a crystalline metal phosphate salt between the base steel sheet and the tension film, the adhesion, tension, and magnetic properties of the film can be improved. Furthermore, since the intermediate layer can be formed through a chemical conversion process, no special equipment is required. Therefore, this is a useful technology.

[0017] However, the inventors conducted research and found that in the directional electromagnetic steel sheet of Patent Document 5, improving the sealing sometimes reduces the magnetic properties of the transformer. Further research revealed that the magnetic degradation is due to the coarsening of the crystals of the phosphate metal salt precipitated through chemical conversion treatment, which reduces the duty cycle during the manufacture of actual transformers.

[0018] Therefore, the objective of this invention is to provide a directional electromagnetic steel plate on which a layer containing a metal phosphate salt is formed on the surface of a steel plate coated with a magnesium olivine-based film through chemical conversion treatment. This steel plate exhibits excellent adhesion and magnetic properties of the tension film without reducing the duty cycle of the transformer (core). This is achieved while maintaining the essential properties required by the film, such as corrosion resistance and resistance to leaching of phosphate.

[0019] Methods for solving problems The inventors have discovered that when a layer containing metal phosphate salts is provided as an intermediate layer to improve the adhesion between the base steel sheet and the tension film layer, the coarsening of metal phosphate salt crystals can be suppressed by including a substance that inhibits the crystallization of phosphate salts in the chemical conversion treatment solution.

[0020] This invention was made in view of the above-mentioned insights. The main points of this invention are as follows.

[0021] [1] One embodiment of the present invention is a directional electromagnetic steel plate comprising: a base steel plate and an insulating film formed on the surface of the base steel plate, the insulating film comprising: an intermediate layer formed on the side of the base steel plate and comprising one or more of amorphous silicon dioxide, inorganic filler and metal oxide, and crystalline metal phosphate; and a tension film layer formed on the surface side of the insulating film, wherein the average particle size of one or more of the amorphous silicon dioxide, the inorganic filler and the metal oxide is 10 to 500 nm.

[0022] [2] For the directional electromagnetic steel plate described in [1], it is also possible that the inorganic filler includes one or more of alumina, BN, AlN and kaolin.

[0023] [3] For the directional electromagnetic steel plate described in [1] or [2], it is also possible that the above-mentioned metal oxide is one or more of titanium oxide, zinc oxide, and calcium oxide.

[0024] [4] For any of the directional electromagnetic steel plates described in any of [1] to [3], it is also possible that the average crystal grain size of the above-mentioned crystalline metal phosphate salt is 1.0 to 12.0 μm.

[0025] [5] Another aspect of the present invention is a method for forming an insulating film, which is a method for forming the insulating film of the directional electromagnetic steel plate described in [1], comprising the following steps: a final annealing step, wherein an annealing separating agent containing 10 to 100% by mass of Al2O3 is coated on a steel plate, and after drying, a final annealing is performed; an annealing separating agent removal step, wherein the remaining annealing separating agent is removed from the steel plate after the final annealing step; a light pickling step, wherein the steel plate after the annealing separating agent removal step is pickled with a pickling solution containing 0.10 to 10.0% by mass of an inorganic acid selected from sulfuric acid, chloric acid, nitric acid, and phosphoric acid at a liquid temperature of 30 to 85°C for 1 to 20 seconds; and an impregnation step, wherein the steel plate after the light pickling step is impregnated with the steel plate. The steel plate is immersed in a treatment solution containing one or more of the following at a liquid temperature of 30-85°C for 5-150 seconds: 0.3-10.0% by mass of a metal phosphate salt and 0.01-10.0 g / L of colloidal silica with an average particle size of 10-500 nm, inorganic filler, and metal oxide. A drying step is then performed, in which the steel plate after the immersion step is removed from the treatment solution, the remaining treatment solution is removed, and the plate is dried. Finally, a tension film layer forming step is performed, in which a coating solution containing a metal phosphate salt and colloidal silica, with a total concentration of 10-40% by mass, is applied to the steel plate after the drying step. After drying, the plate is heated and held at a plate temperature of 700-950°C for 10-50 seconds.

[0026] Invention Effects According to the above-described solution of the present invention, a directional electromagnetic steel plate with excellent tension film sealing and magnetic properties can be provided without reducing the duty cycle of the transformer (core). Attached Figure Description

[0027] Figure 1 This is an example of a cross-sectional view of the directional electromagnetic steel plate in this embodiment. Detailed Implementation

[0028] A directional electromagnetic steel sheet according to one embodiment of the present invention (the directional electromagnetic steel sheet of this embodiment) and a manufacturing method of 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.

[0029] First, the directional electromagnetic steel plate of this embodiment will be explained.

[0030] like Figure 1As shown, the directional electromagnetic steel plate 100 of this embodiment has a base steel plate 1 and an insulating film 2 formed on the surface of the base steel plate 1. In the directional electromagnetic steel plate 100 of this embodiment, a forsterite-based film is not intentionally formed on the surface of the base steel plate 1, and the forsterite-based film is often absent, but if the film mass is 1.0 g / m 2 The following is permitted (in this case, it exists between the base steel plate 1 and the insulating film 2).

[0031] In addition, 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.

[0032] In addition, the intermediate layer 21 contains one or more of the following: crystalline metal phosphate salt, amorphous silicon dioxide with an average particle size of 10 to 500 nm, inorganic filler, and metal oxide.

[0033] The following will explain each of these.

[0034] <Base Material Steel Plate> (Chemical composition) The directional electromagnetic steel sheet 100 of this embodiment has significant features in terms of the structure of the insulating film 2 formed on the surface of the base steel sheet 1, and the chemical composition of the base steel sheet 1 in which the directional electromagnetic steel sheet 100 is provided is not limited. However, in order to obtain the characteristics generally required for directional electromagnetic steel sheets, the following components are preferably included as chemical components. In this embodiment, unless otherwise specified, the percentage of chemical components is by mass%.

[0035] C: Below 0.010% Carbon (C) is an element effective for 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 0.010% or less. The C content is more preferably 0.005% or less. The lower the C content, the better, but even if the C content is reduced to less than 0.0001%, the effect of microstructure control saturates, and the manufacturing cost increases. Therefore, the C content can be 0.0001% or more.

[0036] Si: 2.50~4.00% Silicon (Si) is an element that increases the resistivity of directional electromagnetic steel sheets and improves iron loss characteristics. When the Si content is less than 2.50%, a sufficient reduction in eddy current losses cannot be achieved. Therefore, the Si content is preferably 2.50% or more. More preferably, it is 2.70% or more, and even more preferably 3.00% or more.

[0037] 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 4.00% or less. More preferably, it is 3.80% or less, and even more preferably 3.70% or less.

[0038] Mn: 0.01~0.50% 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 is also an element that improves the hot workability of steel. When 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. More preferably, the Mn content is 0.02% or more.

[0039] 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 0.50% or less. More preferably, the Mn content is 0.20% or less, and even more preferably 0.10% or less.

[0040] N: below 0.010% 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%, the inhibitor remains excessively in the base steel sheet of the directional electromagnetic steel sheet, thus reducing the magnetic properties. Therefore, in the base steel sheet of the directional electromagnetic steel sheet of this embodiment, the N content is preferably 0.010% or less. The N content is more preferably 0.008% or less.

[0041] On the other hand, there is no specific lower limit for nitrogen content, but even if it is reduced to less than 0.001%, the manufacturing cost will increase. Therefore, the nitrogen content can be above 0.001%.

[0042] sol.Al: 0.020% or less Sol.Al (acid-soluble aluminum) 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%, the inhibitor remains excessively in the base steel sheet, reducing the magnetic properties. Therefore, in the base steel sheet of the directional electromagnetic steel sheet of this embodiment, the sol.Al content is preferably 0.020% or less. More preferably, it is 0.010% or less, and even more preferably less than 0.001%. There is no particular limit to the lower limit of the sol.Al content, but even if it is reduced to less than 0.0001%, the manufacturing cost will increase. Therefore, the sol.Al content can be 0.0001% or more.

[0043] S: below 0.010% 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 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 base steel sheet of the directional electromagnetic steel sheet is reduced to less than 0.0001%, the manufacturing cost increases. Therefore, the S content in the base steel sheet of the directional electromagnetic steel sheet can be 0.0001% or more.

[0044] Remaining components: Fe and impurities The chemical composition of the base steel plate of the directional electromagnetic steel plate of this embodiment may contain the aforementioned elements, with the remainder being Fe and impurities. However, for the purpose of improving magnetic properties, Sn, Cu, Se, and Sb may also be included within the range shown below. In addition, as other elements, even if the total content of any one or more of W, Nb, Ti, Ni, Co, V, Cr, and Mo is less than 1.0%, it will not hinder the effect of the directional electromagnetic steel plate of this embodiment.

[0045] Here, impurities refer to substances that may be introduced into the raw materials, such as ore, scrap iron, or manufacturing environment, during the industrial manufacturing of the base steel sheet. They also refer to elements that are permitted to be present in a content that does not adversely affect the function of the directional electromagnetic steel sheet of this embodiment.

[0046] Sn: 0~0.50% Sn (tin) is an element whose magnetic properties can be improved by controlling the 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.

[0047] 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 0.50% or less. More preferably, the Sn content is 0.30% or less, and even more preferably 0.10% or less.

[0048] Cu: 0~0.50% Cu (copper) is an element that contributes to increasing the occupancy 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.

[0049] 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.

[0050] Se: 0~0.020% Selenium (Se) is an element that improves magnetic properties. When Se is present, to maximize its magnetic property-improving effect, the Se content is preferably 0.001% or more. More preferably, the Se content is 0.003% or more, and even more preferably 0.006% or more.

[0051] 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.

[0052] Sb: 0~0.50% Antimony (Sb) is an element that improves magnetic properties. When containing Sb, to maximize its magnetic property improvement effect, the Sb content is preferably 0.005% or more. More preferably, the Sb content is 0.01% or more, and even more preferably 0.02% or more.

[0053] On the other hand, when the Sb content exceeds 0.50%, the adhesion of the film deteriorates significantly. Therefore, it is preferable to have an Sb content of 0.50% or less. More preferably, the Sb content is 0.30% or less, and even more preferably 0.10% or less.

[0054] As described above, this embodiment illustrates that the chemical composition of the base steel plate of the directional electromagnetic steel plate contains the aforementioned elements, with the remainder comprising Fe and impurities.

[0055] The chemical composition of the base steel sheet of the directional electromagnetic steel sheet in this embodiment can be determined using a known ICP emission spectrometry method. However, when an insulating film is formed on the surface, the film is peeled off before measurement. As a peeling method, peeling can be performed 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 performed by surface grinding.

[0056] <Insulating membrane> In this embodiment, the directional electromagnetic steel plate 100 has an insulating film 2 formed on the surface of the base steel plate 1.

[0057] In addition, 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.

[0058] (Intermediate layer) As mentioned above, directional electromagnetic steel sheets typically have a forsterite-based coating formed during the final annealing process and an insulating coating (tension insulating coating) formed thereon. However, in recent years it has been clarified that this forsterite-based coating hinders the movement of magnetic domain walls, adversely affecting iron losses. 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.

[0059] 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.

[0060] 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, as described later, when the intermediate layer is formed by immersion in a processing solution containing metal phosphate salts, it can be formed on the surface of the base steel plate 1 through a chemical reaction, thus ensuring the adhesion between the intermediate layer 21 and the base steel plate 1.

[0061] 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, preferably 90% by mass or more, and may also be 99% by mass or more. From the viewpoint of adhesion, one or more of zinc phosphate, manganese phosphate, iron phosphate, and zinc calcium phosphate are preferred as metal phosphate salts.

[0062] In the intermediate layer, as the remaining portion of the metal phosphate salt, there are sometimes oxides, elements such as Fe and Si diffused from the base steel sheet.

[0063] However, if the crystals of the crystalline metal phosphate salt in the intermediate layer become coarse, the duty cycle will decrease when manufacturing an actual transformer, resulting in a decrease in magnetic flux density per unit volume and an increase in transformer iron loss.

[0064] Therefore, in the directional electromagnetic steel sheet of this embodiment, in order to suppress the coarsening of crystals by suppressing the crystallization of crystalline metal phosphate salts, the processing solution used to form the intermediate layer includes one or more of colloidal silica, inorganic fillers, and metal oxides with an average particle size of 10 to 500 nm as additives. As a result, an intermediate layer is formed comprising crystalline metal phosphate salts, and one or more of amorphous silica, inorganic fillers, and metal oxides, wherein the average particle size of one or more of the amorphous silica, inorganic fillers, and metal oxides is 10 to 500 nm. In such an intermediate layer, the average crystal grain size of the crystalline metal phosphate salt is, for example, 1.0 to 12.0 μm.

[0065] Preferably, one or more of the following—colloidal silica, inorganic fillers, and metal oxides—with an average particle size of 10 to 500 nm are uniformly dispersed in the intermediate layer without localization. For example, it is preferable that even if secondary agglomeration occurs, the agglomerates are smaller than a few μm.

[0066] Among amorphous silica, inorganic fillers, and metal oxides added as additives and remaining in the intermediate layer, amorphous silica is preferred from the perspective of ease of acquisition. Amorphous silica differs in morphology and effect from crystalline silica produced by processes such as thermal oxidation annealing.

[0067] Furthermore, it is preferred that the inorganic filler contains 90% by mass or more of one or more of alumina, BN, AlN, and kaolin (using inorganic fillers with a purity of 90% by mass or more). Considering ease of dispersion, hexagonal BN is preferred.

[0068] Furthermore, from the viewpoint of the stability of the treatment solution, the metal oxide is preferably one or more of titanium oxide, zinc oxide, and calcium oxide.

[0069] Carbonates can also be used as an additive, but under normal baking conditions, carbonates do not remain in the intermediate layer. To obtain an intermediate layer containing carbonates, special baking conditions are required, so it is not preferred.

[0070] In addition, the content of one or more of amorphous silica, inorganic filler and metal oxide is preferably 0.01 to 1.00% by mass. When it is less than 0.01% by mass, the effect of suppressing the coarsening of phosphate metal salt crystals becomes worse, and when it exceeds 1.00% by mass, there is concern that the adhesion of the intermediate layer will deteriorate.

[0071] The intermediate layer 21 is formed at a different time than the tension film formed on it, but both the intermediate layer 21 and the tension film layer 22 function as insulating film 2.

[0072] The thickness of the intermediate layer is preferably 1.0 to 9.0 μm. When the average thickness of the intermediate layer 21 is less than 1.0 μm, the effect of improving the adhesion between the base steel plate and the insulating film through the intermediate layer cannot always be fully obtained. On the other hand, if the average thickness of the intermediate layer exceeds 9.0 μm, the magnetic properties may sometimes deteriorate.

[0073] The mass ratio and type of crystalline phosphate metal salt in the intermediate layer can be determined by measuring the cross-section along the thickness direction of the intermediate layer using a scanning electron microscope and an energy-dispersive elemental analyzer. Whether the phosphate metal salt in intermediate layer 21 is a crystalline phosphate metal salt can be determined by X-ray crystal structure analysis.

[0074] Regarding the base steel plate and the insulating film, they can be distinguished by the concentration of phosphorus (P) (if the P content is 1.0% by mass or more, it is an insulating film; if it is less than 1.0% by mass, it is a steel plate). In the insulating film 2, the intermediate layer 21 and the tension film layer 22 can be distinguished by the concentration difference of Si (if the Si content is 10% by mass or more, it is a tension film layer; if it is less than 10% by mass, it is an intermediate layer).

[0075] In addition, the average crystal grain size of crystalline metal phosphate salts can be determined by the following method.

[0076] A few millimeters square section was cut from the steel plate for easy observation. After removing microscopic shape defects such as burrs and cracks through plasma milling (CP machining), a scanning electron microscope was used to observe the sections parallel to the rolling direction and thickness direction of the steel plate, as well as sections perpendicular to the rolling direction and parallel to the thickness direction. The crystal morphology of the phosphate metal salts observable in the cross-sections was observed. The average of the major and minor axes of at least five crystals from each cross-section was measured, and these values ​​were taken as the grain size. The electron microscope was used at 1000x magnification during observation.

[0077] In addition, the content of amorphous silica, inorganic fillers, and metal oxides, as well as the average particle size, can be determined by the following methods.

[0078] Regarding the content, a few millimeters square section of steel plate was cut for easy observation. After removing microscopic shape defects such as burrs and cracks by ion milling (CP machining), sections parallel to the rolling direction and thickness direction of the steel plate, and sections perpendicular to the rolling direction and parallel to the thickness direction, were observed at 5000x magnification using a scanning electron microscope. At at least five such sections, the intermediate layer was analyzed using an energy dispersive elemental analyzer, and the content was determined accordingly.

[0079] Regarding the average particle size, for cross-sectional samples that have also undergone ion milling, after confirming the presence of amorphous silicon dioxide, inorganic fillers, and metal oxides in more than 10 locations in the intermediate layer through elemental analysis using a transmission electron microscope, the average of the major and minor axes of the particles observed at a magnification of 20,000 is used as the particle size for calculation.

[0080] The thickness of the intermediate layer can be determined using the following method.

[0081] By observing the cross-section of the sample using a scanning electron microscope and measuring the thickness at five or more points, the combined average thickness of the interlayer and the insulating film can be determined. The interlayer and the insulating film can be distinguished by the concentration difference of silicon (Si) from silica. Therefore, the thickness of the interlayer can be calculated by subtracting the thickness of the insulating film from the combined average thickness at each measurement point.

[0082] (Tension membrane layer) 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.

[0083] The tension film layer 22 is not particularly limited as long as it is used as an insulating film for directional electromagnetic steel sheets. From the viewpoint of adhesion to the intermediate layer 21 (adhesion to the base steel sheet 1 through the intermediate layer 21), it is preferably composed mainly of metal phosphate salts and silicon dioxide. More preferably, it is substantially composed of metal phosphate salts and silicon dioxide.

[0084] The tension film layer 22 preferably contains metal phosphate salt and silica (colloidal silica from the coating liquid) in a manner where the silica content is 20.0% by mass or more. On the other hand, when the silica content of the tension film layer 22 exceeds 60.0% by mass, it becomes a cause of pulverization, so it is preferably 60.0% by mass or less. Furthermore, it is preferable to contain a total of 70% by mass or more of metal phosphate salt and silica. The total amount of metal phosphate salt and silica can be 100% by mass. The remainder besides metal phosphate salt and silica sometimes includes ceramic particles such as alumina and silicon nitride. From the perspective of heat resistance, aluminum phosphate is preferred as the metal phosphate salt.

[0085] 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 above-mentioned range, the average thickness of the insulating film 2 (intermediate layer 21 + tension film layer 22) is preferably 1.0 to 20.0 μm. When the average thickness of the insulating film 2 is less than 1.0 μm, sufficient film tension cannot be obtained. In addition, the dissolution of phosphoric acid increases. At this time, it may sometimes become a cause of stickiness, reduced corrosion resistance, and film peeling. Furthermore, if the thickness of the insulating film 2 exceeds 20.0 μm, the duty cycle decreases and the magnetic properties deteriorate, or the adhesion decreases due to cracking, or the corrosion resistance decreases.

[0086] In the tension film layer 22, the mass ratio and type of phosphate metal salt can be determined in the thickness direction section using the same method as for the intermediate layer.

[0087] As mentioned above, the tension film layer and the intermediate layer can be distinguished by the Si content.

[0088] The thickness of the tension film layer can be calculated using the same method as the intermediate layer. The sum of the thickness of the tension film layer and the thickness of the intermediate layer is the thickness of the insulating film.

[0089] <Manufacturing Method> The directional electromagnetic steel sheet of this embodiment can be suitably manufactured according to the manufacturing method that meets the manufacturing conditions described below. 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.

[0090] The directional electromagnetic steel sheet of this embodiment can be manufactured by a manufacturing method including the following steps.

[0091] (I) Hot rolling process, which involves hot rolling steel billets such as slabs with a specified chemical composition to obtain hot-rolled plates; (II) Hot-rolled plate annealing process: The above-mentioned hot-rolled plate is annealed; (III) Cold rolling process: The hot-rolled plate after the above-mentioned hot-rolled plate annealing process is cold-rolled to obtain a steel plate (cold-rolled plate). (IV) Decarburization annealing process: The steel plate after the above cold rolling process is decarburized and annealed. (V) Final annealing process: The above steel plate is coated with an annealing separating agent containing 10 to 100% by mass of Al2O3, dried, and then subjected to final annealing. (VI) Annealing Separator Removal Process: For the steel plate after the final annealing process, the remaining annealing separator is removed. (VII) Light pickling process: For the steel plate after the above-mentioned annealing separating agent removal process, pickling is performed for 1 to 20 seconds using a pickling solution of 0.10 to 10.0% by mass of one inorganic acid selected from sulfuric acid, chloric acid, nitric acid, and phosphoric acid at a liquid temperature of 30 to 85°C. (VIII) Immersion process: The steel plate after the above light pickling process is immersed in a treatment solution with a liquid temperature of 30~85°C and containing 0.3~10.0% by mass of metal phosphate salt and 0.01~10.0 g / l of colloidal silica, inorganic filler and metal oxide with an average particle size of 10~500 nm for 5~150 seconds. (IX) Drying process: The steel plate after the above impregnation process is lifted from the above treatment solution, the remaining treatment solution is removed, and it is dried; and (X) Tension film formation process: A coating solution containing metal phosphate salt and colloidal silica, wherein the total concentration of the metal phosphate salt and colloidal silica is 10 to 40% by mass, is applied to the steel plate after the above drying process. After drying, the plate is heated and held at a plate temperature of 700 to 950°C for 10 to 50 seconds.

[0092] Furthermore, the method for manufacturing the directional electromagnetic steel plate of this embodiment may further include any one or both of the following steps: (XI) A nitriding process, wherein the steel plate is nitrided between the decarburizing annealing process and the final annealing process; and (XII) Magnetic domain refinement process: After the tension film formation process, the magnetic domain control of the above steel plate is performed.

[0093] In the manufacture of the directional electromagnetic steel sheet in this embodiment, the process is characterized by the (V) final annealing process to the (X) tension film layer formation process, which are mainly related to the formation of the insulating film (sometimes collectively referred to as the method of forming the insulating film), while other processes or conditions not described may use known conditions.

[0094] The following is a description of these procedures.

[0095] [Hot rolling process] 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℃. More preferably, the heating temperature is 1300℃~1400℃.

[0096] The chemical composition of the billet can be modified according to the chemical composition of the base steel plate of the desired directional electromagnetic steel plate. For example, the following chemical composition can be used: 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%, Sb: 0~0.50%, with the remainder being Fe and impurities.

[0097] There are no particular limitations on the hot rolling conditions; they can be set appropriately based on the required characteristics. For example, the thickness of the hot-rolled sheet is preferably in the range of 2.0 to 3.0 mm.

[0098] [Hot-rolled sheet annealing process] The hot-rolled sheet annealing process is a process of annealing hot-rolled sheets that have undergone the hot-rolling process. This annealing treatment causes recrystallization in the steel sheet's microstructure, resulting in good magnetic properties, and is therefore preferred.

[0099] 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 within a temperature range of 900 to 1200°C.

[0100] [Cold rolling process] 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 (excluding a series of annealing processes), or it can be a multi-stage cold rolling process with intermediate annealing interspersed, where cold rolling is interrupted before the final pass of the cold rolling process.

[0101] When performing intermediate annealing, it is preferable to hold at a temperature of 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.

[0102] Alternatively, the surface of the hot-rolled plate can be pickled before the cold rolling process.

[0103] 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> The Goss nucleus, which has a high degree of aggregation in the rolling direction, is preferred. On the other hand, when the final reduction exceeds 95%, the possibility of secondary recrystallization becoming unstable during the subsequent final annealing process increases, which is not preferred.

[0104] The final reduction rate refers to 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.

[0105] [Decarburization annealing process] In the decarburizing annealing process, the obtained steel sheet is decarburized and annealed. In decarburizing annealing, as long as the steel sheet can be recrystallized once and carbon that has an adverse effect on the magnetic properties is removed from the steel sheet, the decarburizing annealing conditions are not limited. For example, the oxidation degree (PH2O / PH2) in the annealing atmosphere (furnace atmosphere) can be set to 0.3~0.6, and the annealing temperature can be held at 800~900℃ for 10~600 seconds.

[0106] [Nitriding treatment process] Nitriding can be performed between the decarburization annealing process and the final annealing process described later.

[0107] 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 that the N content of the steel sheet after the nitriding process is 40 ppm or more. On the other hand, when the N content of the steel sheet after the nitriding process exceeds 1000 ppm, AlN remains excessively present in the steel sheet after secondary recrystallization during the final annealing. Such AlN contributes to the deterioration of iron loss. Therefore, the N content of the steel sheet after the nitriding process is preferably 1000 ppm or less.

[0108] [Final annealing process] In the final annealing process, the steel plate that has undergone decarburization annealing or further nitriding treatment (after nitriding treatment) is coated with an annealing separating agent containing 10-100% by mass of Al2O3, dried, and then subjected to final annealing.

[0109] In conventional methods for manufacturing directional electromagnetic steel sheets, a final annealing is performed by coating with an annealing release agent primarily composed of MgO, resulting in a magnesium olivine-based coating on the surface of the steel sheet (cold-rolled sheet). In contrast, in the method for manufacturing the directional electromagnetic steel sheet of this embodiment, an annealing release agent containing Al2O3 is used in a manner that almost no magnesium olivine-based coating is formed.

[0110] On the other hand, the proportion of Al2O3 can be 100% by mass, but from the viewpoint of preventing Al2O3 from adhering to the surface of the steel plate, in the manufacturing method of the directional electromagnetic steel plate of this embodiment, the annealing separating agent preferably includes MgO. MgO can also be 0%, but to obtain the above-mentioned effect, the proportion of MgO is preferably 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 90% by mass or less. The proportion of MgO is preferably 50% by mass or less. The total amount of Al2O3 and MgO, converted from solid content, should exceed 50% by mass relative to the annealing separating agent.

[0111] Furthermore, in the manufacturing method of the directional electromagnetic steel sheet of this embodiment, the annealing separating agent may also contain 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 can be 0%, but 0.5 to 10% by mass is preferred when the above-mentioned effect is obtained. Examples of effective chlorides include bismuth chloride, calcium chloride, cobalt chloride, ferric chloride, and nickel chloride.

[0112] There are no restrictions on the final annealing conditions; for example, it can be carried out at a temperature of 1150℃~1250℃ for 10~60 hours.

[0113] [Annealing Separator Removal Process] In the annealing separator removal process, the remaining annealing separator is removed from the steel sheet after the final annealing process. For example, the remaining annealing separator can be removed by washing with water.

[0114] [Light pickling process] In the light pickling process, for the steel plate after the annealing separating agent removal process, pickling is performed with 0.1-10.0% by mass of an inorganic acid selected from sulfuric acid, chloric acid, nitric acid, and phosphoric acid at a liquid temperature of 30-85℃ for 1-20 seconds. The inorganic acid is preferably selected from sulfuric acid, nitric acid, and phosphoric acid.

[0115] This results in the densification of crystalline metal phosphate salts.

[0116] Under inappropriate light pickling conditions, the adhesion of the tensile film layer or its resistance to leaching deteriorates.

[0117] [Immersion Process] [Drying Process] In the immersion process, the steel sheet after the light pickling process is immersed in the treatment solution for 5 to 150 seconds. In the drying process, the steel sheet after the immersion process is lifted out of the treatment solution, the remaining treatment solution is removed, and it is then dried. As a result, an intermediate layer is formed on the surface of the base steel sheet.

[0118] In the impregnation process, the treatment solution is adjusted to have a temperature of 30~85℃ and contains 0.3~10% by mass of metal phosphate salt and 0.01~10.0 g / l of colloidal silica with an average particle size of 10~500 nm, inorganic filler, and one or more metal oxides.

[0119] By including one or more of colloidal silica (which becomes amorphous silica in the intermediate layer), inorganic fillers, and metal oxides (sometimes called additives), the crystallization of the phosphate metal salt that forms the intermediate layer is suppressed, resulting in a smaller average crystal grain size of the crystalline phosphate metal salt in the intermediate layer.

[0120] However, when the additive content in the treatment solution is less than 0.01 g / L, sufficient effect cannot be obtained. On the other hand, if it exceeds 10.0 g / L, the treatment solution becomes unstable.

[0121] Furthermore, if the average particle size of the additive is less than 10 nm, aggregation occurs, and the treatment solution becomes unstable. Alternatively, if the average particle size exceeds 500 nm, the particles precipitate, resulting in poor dispersibility in the treatment solution.

[0122] If the temperature of the treatment solution is less than 30°C or the treatment time is less than 5 seconds, the adhesion deteriorates. On the other hand, when the temperature exceeds 85°C or the treatment time exceeds 150 seconds, the average crystal size of the crystalline metal phosphate salt becomes too large.

[0123] On the other hand, when the phosphate metal salt content in the treatment solution exceeds 10% by mass, the average crystal size of the phosphate metal salt becomes coarser, sometimes resulting in reduced adhesion. The phosphate metal salt contained in the treatment solution can be one or more of zinc phosphate, manganese phosphate, or zinc-calcium phosphate.

[0124] On the other hand, if the metal phosphate salt content in the treatment solution is less than 0.3% 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 1.0% by mass or more.

[0125] Furthermore, if the drying temperature is too high, voids may form, resulting in poor sealing. Therefore, the drying temperature is preferably below 300°C, more preferably below 200°C, and preferably above 100°C.

[0126] [Tension film layer formation process] In the tension film formation process, a coating solution containing metal phosphate salts and colloidal silica, with a total concentration of 10-40% by mass, is applied to the steel plate after the drying process. After drying, the plate is heated and held at a plate temperature of 700-950°C for 10-50 seconds, thereby forming a tension film layer on the surface of the intermediate layer.

[0127] If the plate temperature during holding is below 700°C, it becomes under low tension, and the magnetic properties deteriorate. Therefore, the plate temperature is preferably 700°C or higher. On the other hand, when the plate temperature exceeds 950°C, the rigidity of the steel plate decreases, making it prone to deformation. In this case, strain may occur in the steel plate due to handling, etc., resulting in a deterioration of the magnetic properties. Therefore, the plate temperature is preferably 950°C or lower.

[0128] Furthermore, if the holding time is less than 10 seconds, the leaching resistance deteriorates. Therefore, the holding time is set to 10 seconds or more. On the other hand, when the holding time exceeds 50 seconds, the adhesion of the tension film layer deteriorates. Therefore, the holding time is preferably 50 seconds or less.

[0129] The coating solution (insulating film solution) contains 10-40% by mass of metal phosphate salts and colloidal silica.

[0130] If the combined concentration of metal phosphate salt and colloidal silica is less than 10% by mass, the coating solution is prone to flow, leading to uneven coating. Furthermore, when it exceeds 40% by mass, the viscosity becomes excessive, causing uneven patterns and coating.

[0131] As a metal phosphate salt, 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., can be used. From the viewpoint of the stability of the treatment solution, aluminum phosphate is preferred.

[0132] The coating solution may contain vanadium, tungsten, molybdenum, zirconium, etc., as additional elements. When these elements are present, they can be added to the coating solution, for example, as oxyacids.

[0133] Colloidal silica can be of type S or type C. Type S refers to an alkaline silica solution, while type C refers to a silica particle surface treated with aluminum, 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, without precipitation concerns, but requires more processing time and is correspondingly more expensive. It is preferable to use them separately based on the stability of the prepared coating solution.

[0134] [Magnetic domain refinement process] In the manufacturing method of the directional electromagnetic steel sheet of this embodiment, a magnetic domain refinement process may also be included to refine the magnetic domains of the steel sheet after the tension film layer formation process.

[0135] By performing magnetic domain refinement, the iron loss of directional electromagnetic steel sheets can be further reduced.

[0136] As a method for refining magnetic domains, there are two methods: one is to narrow the width of 180° magnetic domains by forming linear or dot-shaped grooves extending in a direction intersecting the rolling direction at predetermined intervals along the rolling direction; the other is to narrow the width of 180° magnetic domains 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.

[0137] When forming stress-strain regions, laser beam irradiation or electron beam irradiation can be used. Furthermore, when forming grooves, mechanical groove forming methods based on gears, chemical groove forming methods based on electrolytic etching, and thermal groove forming methods based on laser irradiation can be used.

[0138] In cases where damage occurs in the insulating film due to the formation of stress-strained sections or grooves, resulting in deterioration of insulation and other properties, an insulating film can be formed again to repair the damage.

[0139] Example The casting contains, by mass percent, C: 0.08%, Si: 3.31%, sol.Al: 0.028%, N: 0.008%, Mn: 0.07%, S: less than 0.0005%, with the remainder being Fe and impurities.

[0140] The slab is heated to 1350℃ and then hot-rolled to produce a hot-rolled plate with a thickness of 2.2mm.

[0141] The hot-rolled sheet was annealed at 1100°C for 10 seconds. (Hot-rolled sheet annealing) Then, the hot-rolled sheet is cold-rolled to produce a cold-rolled sheet with a thickness of 0.22 mm.

[0142] The cold-rolled sheet was decarburized and annealed at 830°C for 90 seconds.

[0143] After decarburization annealing, an annealing separating agent containing 45% by mass of MgO, 50% by mass of Al2O3, and 5% by mass of BiCl3 as bismuth chloride is applied. After drying, a final annealing is carried out at 1200℃ for 20 hours.

[0144] After final annealing, the remaining annealing separating agent was removed by washing with water, resulting in no magnesium olivine film forming on the steel plate surface.

[0145] For this steel plate, light pickling was performed under the conditions in Table 2-1.

[0146] After light acid washing, an intermediate layer was formed using a treatment solution containing a mixture of phosphates and additives shown in Table 1. The drying temperature was set to 200°C. The resulting intermediate layer is shown in Table 2-2. The proportion of crystalline metal phosphate salts in the intermediate layer was 80% by mass or more.

[0147] Then, the insulating coating treatment solution, which is mainly composed of metal phosphate salts and colloidal silica as shown in Table 2-3, is applied and dried at 850°C for 20 seconds to form a tension coating layer on the steel plate surface.

[0148] The thicknesses of the insulating films (intermediate layer and tension film layer) are shown in Table 2-3. Furthermore, the tension film layer is essentially composed of metal phosphate salts and silicon dioxide.

[0149] Under the conditions of UA (irradiation energy density) of 2.0J and irradiation interval of 5.0mm, the obtained steel plate (directional electromagnetic steel plate) is irradiated with a laser beam to perform magnetic domain refinement treatment.

[0150] The iron loss W17 / 50 (iron loss at 50Hz at 1.7T) of the steel plate after magnetic domain refinement was determined by the Single Sheet Tester (SST) method according to JIS C2556 (2015).

[0151] In addition, the duty cycle should be determined according to the following guidelines.

[0152] [Duty Cycle] The duty cycle was determined according to 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 samples, the duty cycle was calculated by measuring the distance between the upper and lower cover plates sandwiching the laminate under a pressure of 1 MPa.

[0153] If the duty cycle is above 96.0%, it is considered that a high duty cycle has been ensured.

[0154] In addition, the coating adhesion, coating tension, corrosion resistance, and leaching resistance of the steel plate after magnetic domain refinement treatment were evaluated using the following methods. The results are shown in Table 3.

[0155] [Capsule adhesion] Regarding the adhesion of the coating, a sample with a width of 30 mm and a length of 300 mm was collected from the steel plate. The sample was subjected to stress-relieving annealing at 800°C for 2 hours in a nitrogen atmosphere. Then, it was rolled into a cylinder with a diameter of 10 mm, unwound, and evaluated based on the degree of peeling (area ratio) of the coating after the bending adhesion test.

[0156] The evaluation criteria are as follows: under conditions A or B, the film adhesion is judged to be excellent.

[0157] A: Peeling area ratio 0~0.5% B: The peeling area ratio exceeds 0.5% but is less than 5.0%. C: The stripping area ratio exceeds 5.0% but is less than 20%. D: The stripping area ratio exceeds 20% but is less than 50%. E: Peeling area ratio exceeds 50% [Capsule tension] The film tension is calculated by inversely calculating the bending condition of one side when peeling off the insulating film. A film tension of 4.0 MPa or higher is considered to have sufficient film tension.

[0158] [Corrosion Resistance] The corrosion resistance was determined according to the salt spray test of the JIS method (JIS Z2371:2015) by allowing a 5% NaCl aqueous solution to naturally decrease to the sample in an atmosphere of 35°C for 7 hours.

[0159] Then, the rusted area is evaluated on a scale of 1 to 10. The evaluation criteria are as follows. A score of 5 or higher (5~10) indicates excellent corrosion resistance.

[0160] 10: No rust 9: Very little rust (area ratio = less than 0.10%) 8: Rust area ratio = greater than 0.10% and less than 0.25% 7: The area ratio of rust is greater than 0.25% but less than 0.50%. 6: Rust area ratio = greater than 0.50% and less than 1.0% 5: Rust area ratio = greater than 1.0% and less than 2.5% 4: The area ratio of rust is greater than 2.5% but less than 5.0%. 3: The area of ​​rust exceeds 5.0% but is less than 10%. 2: The area of ​​rust = exceeding 10% but less than 25% 1: The area of ​​rust exceeds 25% but is less than 50%. [Resistance to leaching] Dissolution resistance is evaluated by whether it can inhibit the dissolution of phosphoric acid from the sample.

[0161] The method for determining the amount of phosphoric acid dissolved is as follows: The sample is boiled in boiling pure water for 10 minutes, and the amount of phosphoric acid dissolved in the pure water is measured. The amount of phosphoric acid is then divided by the area of ​​the insulating film of the directional electromagnetic steel plate being boiled. The amount of phosphoric acid dissolved in pure water is determined by cooling the pure water (solution) from which the phosphoric acid has dissolved, and then using ICP-AES to determine the phosphoric acid concentration of the sample after diluting and cooling the solution with pure water.

[0162] If the dissolution amount is less than 40 mg / m³ 2 Then it has excellent resistance to leaching.

[0163] As can be seen from Tables 1 to 3, in this invention, the sealing performance and the main characteristics of the coating are extremely excellent, and the iron loss and duty cycle are improved.

[0164] On the other hand, in the comparative example, the insulating film is not a preferred configuration, and one or more of the following are poor: the tightness of the tension film, magnetic properties, corrosion resistance, resistance to leaching of phosphoric acid, and the duty cycle of the transformer (core).

[0165] Industrial availability According to the present invention, a directional electromagnetic steel sheet can be provided that exhibits excellent adhesion and magnetic properties of the tension membrane without reducing the duty cycle of the transformer (core). Therefore, it has high industrial applicability.

[0166] Explanation of reference numerals in the attached figures 100: Directional Electromagnetic Steel Sheet 1: Base material steel plate 2: Insulating film 21: Intermediate Layer 22: Tension film layer

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 is formed on the side of the base steel plate and comprises one or more of amorphous silicon dioxide, inorganic fillers and metal oxides, and crystalline metal phosphate salts. and A tension film layer is formed on the surface side of the insulating film. The average particle size of one or more of the amorphous silicon dioxide, the inorganic filler, and the metal oxide is 10~500nm.

2. The directional electromagnetic steel plate according to claim 1, characterized in that, The inorganic filler comprises one or more of alumina, BN, AlN, and kaolin.

3. The directional electromagnetic steel plate according to claim 1 or 2, characterized in that, The metal oxide is one or more of titanium oxide, zinc oxide, and calcium oxide.

4. The directional electromagnetic steel plate according to claim 1 or 2, characterized in that, The average crystal grain size of the crystalline metal phosphate salt is 1.0~12.0 μm.

5. A method for forming an insulating film, characterized in that, It is a method for forming the insulating film of the directional electromagnetic steel plate according to claim 1, which includes the following steps: The final annealing process involves coating the steel plate with an annealing separating agent containing 10-100% by mass of Al2O3, drying it, and then performing the final annealing. Annealing separator removal process: For the steel plate after the final annealing process, remove the remaining annealing separator. In the light pickling process, the steel plate after the annealing separating agent removal process is pickled with a pickling solution containing 0.10-10.0% by mass of one inorganic acid selected from sulfuric acid, chloric acid, nitric acid, and phosphoric acid at a liquid temperature of 30-85°C for 1-20 seconds. The immersion process involves immersing the steel plate after the light pickling process in a treatment solution at a temperature of 30-85°C for 5-150 seconds in one of the following: 0.3-10.0% by mass of metal phosphate salt and 0.01-10.0 g / L of colloidal silica, inorganic filler and metal oxide with an average particle size of 10-500 nm. In the drying process, the steel plate after the impregnation process is lifted out of the treatment solution, the remaining treatment solution is removed, and the plate is dried. as well as In the tension film formation process, a coating solution containing metal phosphate salt and colloidal silica, wherein the total concentration of the metal phosphate salt and colloidal silica is 10-40% by mass, is applied to the steel plate after the drying process. After drying, the plate is heated and held at a plate temperature of 700-950°C for 10-50 seconds.

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