Grain-oriented electrical steel sheet and method for manufacturing the same

Abstract

This grain-oriented electrical steel sheet has: a base material steel sheet; and an insulating coating that is formed on the surface of the base material steel sheet and contains a metal phosphate, wherein the base material steel sheet has an oxide layer that includes an oxide of Si in a region in contact with the interface between the base material steel sheet and the insulating coating, and the average thickness of the oxide layer from the interface is 0.5-2.5 μm.

Description

Technical Field

[0001] The present invention relates to a grain-oriented electrical steel sheet and a method for manufacturing the same. This application claims priority based on Japanese Patent Application No. 2024-018850 filed in Japan on February 9, 2024, and incorporates the content herein by reference.

Background Art

[0002] Grain-oriented electrical steel sheets are mainly used in transformers. Transformers are continuously excited over a long period from installation to disposal and continue to generate energy losses. Therefore, the energy loss during magnetization with alternating current, that is, the iron loss, becomes a major index determining the performance of transformers.

[0003] To reduce the iron loss of grain-oriented electrical steel sheets, many techniques have been developed so far from the viewpoints of (a) increasing the aggregation in the {110}<001> orientation (Goss orientation), (b) increasing the content of solid solution elements such as Si to increase the electrical resistance of the steel sheet, or (c) reducing the thickness of the electrical steel sheet. <​​​​​​​​​However, in recent years, there has been a growing demand for smaller and more powerful transformers. To achieve this miniaturization, grain-oriented electrical steel sheets are required to exhibit excellent high-field iron loss performance, meaning that iron loss is good even at high magnetic flux densities. At the same time, it has recently become clear that forsterite coatings hinder the movement of magnetic domain walls and adversely affect iron loss. In grain-oriented electrical steel sheets, magnetic domains change as magnetic domain walls move under an alternating magnetic field. Smooth and rapid movement of these magnetic domain walls is effective in reducing iron loss, but forsterite coatings (also called glass coatings or primary coatings) are themselves nonmagnetic and have an uneven structure at the interface between the steel sheet and the coating. This uneven structure is thought to hinder the movement of magnetic domain walls and thus adversely affect iron loss. Therefore, as a means of improving high-field iron loss, research is being conducted on techniques to manufacture grain-oriented electrical steel sheets without forsterite coatings by removing forsterite coatings using mechanical means such as polishing or chemical means such as pickling, or by preventing the formation of forsterite coatings during high-temperature finish annealing, as well as techniques to make the steel sheet surface mirror-like (in other words, techniques to magnetically smooth the steel sheet surface).

[0007] As a technique for preventing the formation of forsterite-based coatings, for example, Patent Document 2 discloses a technique in which, after normal finish annealing, surface deposits are removed by pickling, and then the steel sheet surface is polished to a mirror finish by chemical polishing or electrolytic polishing. It has been found that by forming a tension-imparting insulating coating on the surface of grain-oriented electrical steel sheets that do not have forsterite-based coatings, obtained by such known methods, an even better iron loss improvement effect can be obtained. In addition, the tension-imparting insulating coating can impart various properties other than iron loss improvement, such as corrosion resistance, heat resistance, and slipperiness.

[0008] However, forsterite-based coatings not only exhibit insulating properties but also act as an intermediate layer to ensure adhesion when forming tension coatings (tension-imparting insulating coatings). In other words, because forsterite-based coatings are formed deeply embedded in the steel sheet, they exhibit excellent adhesion to the steel sheet, which is a metal. Therefore, when a tension-imparting coating (tension coating) mainly composed of colloidal silica or phosphate is formed on the surface of a forsterite-based coating, the coating adhesion is excellent. On the other hand, since bonding between metals and oxides is generally difficult, it was difficult to ensure sufficient adhesion between the tension coating and the steel sheet surface when a forsterite-based coating was not present. Therefore, when forming a tension coating on grain-oriented electrical steel sheets that do not have a forsterite coating, it is being considered to provide a layer that replaces the role of the forsterite coating as an intermediate layer.

[0009] Patent Document 3 discloses a technique for ensuring the adhesion of a tension-imparting insulating film by applying an intermediate coating beforehand when forming the tension-imparting coating. However, the technology disclosed in Patent Document 3 has the problem that it is not possible to maintain good adhesion of a tension-applying insulating coating that has high tension.

[0010] Furthermore, for example, Patent Document 4 discloses a grain-oriented electrical steel sheet having a base steel sheet and an insulating coating formed on the surface of the base steel sheet, wherein the insulating coating is formed on the base steel sheet side and has an intermediate layer containing a crystalline metal phosphate salt and a tension coating layer formed on the surface side of the insulating coating. Patent Document 4 shows that the grain-oriented electrical steel sheet does not have a forsterite-based coating, has excellent coating adhesion, excellent coating tension, and excellent magnetic properties.

[0011] However, depending on the application, grain-oriented electrical steel sheets may be subjected to stress-relieving annealing after being processed into a predetermined shape. As a result of the inventors' investigation, it was found that stress-relieving annealing was not anticipated for grain-oriented electrical steel sheets to which the technology of Patent Document 4 was applied, and that if stress-relieving annealing is performed, the adhesion of the coating may decrease. [Prior art documents] [Patent Documents]

[0012] [Patent Document 1] Japanese Patent Publication No. 48-39338 [Patent Document 2] Japanese Patent Publication No. 49-96920 [Patent Document 3] Japanese Patent Application Publication No. 5-279747 [Patent Document 4] International Publication No. 2022 / 215709 [Overview of the Initiative] [Problems that the invention aims to solve]

[0013] As described above, Patent Documents 1 to 4 did not disclose a grain-oriented electrical steel sheet that does not have a forsterite-based coating and that can obtain excellent coating adhesion even after strain-relieving annealing (after strain-relieving annealing). Therefore, the present invention aims to provide a grain-oriented electrical steel sheet that does not have a forsterite-based coating, while ensuring that the coating tension, corrosion resistance, phosphorus leaching resistance from the coating, packing ratio when used as a core, and iron loss are equal to or better than those of conventional materials, and that can be obtained even after stress-relieving annealing, as well as a method for manufacturing the same. [Means for solving the problem]

[0014] The inventors investigated the effect of strain-relieving annealing on the adhesion of insulating coatings. As a result, we found that by forming an intermediate layer and a phosphate coating that serves as an insulating film on the surface of a grain-oriented electrical steel sheet without a forsterite coating by chemical conversion treatment, fusing the intermediate layer and the insulating film during stress-relieving annealing, and forming a layer containing Si oxide (oxide layer) directly beneath the resulting insulating film, it is possible to suppress the decrease in adhesion of the insulating film without degrading magnetic properties or other film properties.

[0015] This invention was made in view of the above findings. The gist of this invention is as follows: [1] A grain-oriented electrical steel sheet according to one aspect of the present invention is a grain-oriented electrical steel sheet having a base steel sheet and an insulating film containing a metal phosphate salt formed on the surface of the base steel sheet, wherein the base steel sheet has an oxide layer containing Si oxide in a region in contact with the interface between the base steel sheet and the insulating film, and the average thickness of the oxide layer from the interface is 0.5 to 2.5 μm. The grain-oriented electrical steel sheet described in [2][1] may have a ratio of 30% or more of the length of the interface between the oxide layer and the insulating coating to the length of the interface between the base steel sheet and the insulating coating. The grain-oriented electrical steel sheet described in [3] [1] or [2] may have a void area ratio of 30% or less in the insulating coating. [4] The manufacturing method of the grain-oriented electromagnetic steel sheet according to another aspect of the present invention includes a finish annealing step of applying an annealing separator containing 10 to 100% by mass of Al2O3 to a steel sheet, drying it, and then performing finish annealing, an annealing separator removing step of removing the excess annealing separator from the steel sheet after the finish annealing step, a light pickling step of pickling the steel sheet after the annealing separator removing step with an inorganic acid of 0.1 to 5.0% by mass for 10 to 60 seconds, a water washing step of washing and drying the steel sheet after the light pickling step, a first insulating film forming step of dipping the steel sheet after the water washing step in a treatment liquid with a liquid temperature of 30 to 85°C and a metal phosphate concentration of 1.0 to 10.0% by mass for 5 to 150 seconds, washing and removing the treatment liquid, and then drying the steel sheet, and a second insulating film forming step of applying a coating liquid containing a metal phosphate and colloidal silica to the steel sheet after the first insulating film forming step, with the content of the colloidal silica being 30 to 150 parts by mass with respect to 100 parts by mass of the metal phosphate and a solid content concentration of 10 to 40% by mass, drying it, and then holding it at a plate temperature of 700 to 950°C for 10 to 90 seconds, and a heat treatment step of heating the steel sheet after the second insulating film forming step to a temperature range of 700 to 900°C in an atmosphere with a dew point of 0 to 30°C, a nitrogen content of 50 to 100% by volume, and a hydrogen content of 0 to 50% by volume, and holding it in the temperature range for 10 to 180 minutes. [5] The manufacturing method of the grain-oriented electromagnetic steel sheet according to [4] may further include one or two of MgO: 5 to 90% by mass and chloride: 0.5 to 10.0% by mass in the annealing separator.

Effects of the Invention

[0016] According to the above aspect of the present invention, it is possible to provide a grain-oriented electromagnetic steel sheet having excellent film adhesion even after stress relief annealing and a manufacturing method thereof.

Brief Description of the Drawings

[0017] [Figure 1] This is an example of a photograph of a cross section including an insulating film and a base steel sheet of the grain-oriented electromagnetic steel sheet according to this embodiment.

Embodiments for Carrying Out the Invention

[0018] A grain-oriented electrical steel sheet according to an embodiment of the present invention (the grain-oriented electrical steel sheet according to this embodiment) and a method for manufacturing the same will be described.

[0019] [Grain-oriented electrical steel sheet] As shown in FIG. 1, the grain-oriented electrical steel sheet according to this embodiment has a base steel sheet 11 and an insulating film 21 containing a metal phosphate formed on the surface of the base steel sheet 11. Hereinafter, each will be described.

[0020] [Base steel sheet] As shown in FIG. 1, the base steel sheet 11 has an oxide layer 12 containing an oxide of Si in a region in contact with the interface IF between the base steel sheet 11 and the insulating film 21. The portion other than the oxide layer 12 is made of a steel sheet.

[0021] (Oxide layer) In the grain-oriented electrical steel sheet according to this embodiment, an oxide layer containing an oxide of Si is formed in a region of the base steel sheet in contact with the interface between the base steel sheet and the insulating film. This oxide layer contributes to improving the adhesion between the base steel sheet and the insulating film. If the oxide layer is not formed, sufficient adhesion cannot be ensured. When obtaining a high adhesion improvement effect and magnetic properties, the average thickness of the oxide layer from the interface between the base steel sheet and the insulating film is 0.5 to 2.5 μm. If the average thickness is less than 0.5 μm, the effect of improving adhesion becomes small. On the other hand, if the average thickness exceeds 2.5 μm, the magnetic properties become inferior.

[0022] Also, since the oxide layer exists in the region in contact with the interface between the base steel sheet and the insulating film, that is, by constituting the interface with the insulating film, the adhesion (adhesion of the film) is improved. When obtaining a higher adhesion improvement effect, it is preferable that the ratio (coverage rate) of the length of the interface between the oxide layer and the insulating film to the length of the interface between the base steel sheet and the insulating film is 30% or more. The ratio of the length may be 100%. <​​The oxide layer mainly contains silicon oxide, but the silicon content in the silicon oxide layer is preferably 60-70% by mass. The silicon oxide includes composite oxides containing silicon, such as SiO2 and FeSiO4. In addition to silicon oxide, iron oxide, aluminum oxide, chromium oxide, etc., may also be included. Furthermore, the phosphorus content of the oxide layer is 1.0% by mass or less, making it clearly distinguishable from the insulating film. Furthermore, the oxide layer of the grain-oriented electrical steel sheet according to this embodiment is formed as part of the base steel sheet, resulting in extremely high adhesion to the base steel sheet.

[0024] Whether an oxide layer is formed, the average thickness of the oxide layer, and the proportion of the interface covered (coverage rate) can each be determined by the following methods. A transmission electron microscope (TEM) is used to magnify the cross-section of the steel plate, including the surface layer, to 30,000 times, and images are taken of the vicinity along interfaces with a length of 10 μm or more. The captured images allow for differentiation between the base steel plate and the insulating coating. This is because the base material is composed almost entirely of iron atoms, while the insulating coating contains phosphates, aggregated colloidal silica, and voids. Furthermore, the base steel sheet has an oxide layer as an internal oxide layer, but it is composed almost entirely of silica with a low P content, and since it is located inside the base material, the difference from the insulating coating which is mainly composed of phosphate can be confirmed by elemental analysis. If the image resolution is low and a clear image cannot be obtained, it is possible to clarify it using an image processing device such as Luzex. Alternatively, the interface between the insulating coating and the base material may be defined as the point where the distribution of element P decreases sharply from the insulating coating side. This is because element P exists in the insulating coating in the form of phosphoric acid or phosphorus oxide and hardly diffuses into the steel. Similarly, the interface between the insulating film and the base material may be defined as a point where Al, Mg, Mn, Zn, Ca, Cu, Co, and Li, which are presumed to exist as cations in the insulating film, decrease sharply. Based on the three or more TEM images obtained as described above, the average thickness of the oxide layer is calculated by averaging the thickness of the oxide layer measured at three locations within each image (i.e., a total of nine or more locations). The proportion of the oxide layer at the interface is obtained by measuring the length of the interface between the oxide layer and the insulating film at three locations within each of the three or more TEM images, within a range of 10 μm in width, calculating the proportion, and averaging the results.

[0025] The Si content of the oxide layer is obtained by performing elemental analysis at three or more locations in each of three fields of view using an energy-dispersive X-ray analyzer attached to a transmission electron microscope, and then averaging the measurement results.

[0026] (chemical composition) The chemical composition of the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, excluding the oxide layer (steel sheet portion), may be within the range known for grain-oriented electrical steel sheets, in order to obtain the properties generally required for grain-oriented electrical steel sheets. For example, the following are preferably included as chemical components constituting the chemical composition. In this embodiment, percentages for chemical components are mass percentages unless otherwise specified.

[0027] C: 0.010% or less Carbon (C) is an effective element 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 grain-oriented electrical steel sheet, which is the finished product, deteriorate. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, the C content is preferably 0.010% or less. More preferably, the C content is 0.005% or less. While a lower C content is preferable, reducing the C content to less than 0.0001% will saturate the effect of microstructure control, only increasing manufacturing costs. Therefore, the C content may be 0.0001% or more.

[0028] Si: 2.50~4.00% Silicon (Si) is an element that increases the electrical resistance of grain-oriented electrical steel sheets and improves iron loss characteristics. If the Si content is less than 2.50%, a sufficient eddy current loss reduction effect cannot be obtained. Therefore, it is preferable that the Si content be 2.50% or more. More preferably, the Si content is 2.70% or more, and even more preferably 3.00% or more. On the other hand, if the Si content exceeds 4.00%, the grain-oriented electrical steel sheet becomes brittle, and its treadability deteriorates significantly. In addition, the workability of the grain-oriented electrical steel sheet decreases, and the sheet may break during rolling. For this reason, it is preferable to keep the Si content at 4.00% or less. More preferably, the Si content is 3.80% or less, and even more preferably 3.70% or less.

[0029] 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 agent that suppresses normal grain growth) and causes secondary recrystallization in steel. Furthermore, Mn is an element that also improves the hot workability of steel. If the Mn content is less than 0.01%, the above effects cannot be fully obtained. Therefore, it is preferable that the Mn content be 0.01% or more. More preferably, the Mn content is 0.02% or more. On the other hand, if the Mn content exceeds 0.50%, secondary recrystallization does not occur, and the magnetic properties of the steel deteriorate. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, the Mn content is preferably 0.50% or less. More preferably, the Mn content is 0.20% or less, and even more preferably 0.10% or less.

[0030] N: 0.010% or less Nitrogen (N) is an element that combines with Al during the manufacturing process to form AlN, which functions as an inhibitor. However, if an excess of inhibitor remains in the grain-oriented electrical steel sheet and the N content exceeds 0.010%, the magnetic properties will deteriorate. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, the N content is preferably 0.010% or less. More preferably, the N content is 0.008% or less. On the other hand, there is no specific lower limit for the N content, but reducing it to less than 0.001% would only increase manufacturing costs. Therefore, the N content may be 0.001% or higher.

[0031] sol.Al: 0.020% or less sol.Al (acid-soluble aluminum) is an element that, in the manufacturing process of grain-oriented electrical steel sheets, combines with N to form AlN, which functions as an inhibitor. However, if an excess of the inhibitor remains in the base steel sheet and the sol.Al content exceeds 0.020%, the magnetic properties deteriorate. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, the sol.Al content is preferably 0.020% or less. More preferably, the sol.Al content is 0.010% or less, and even more preferably less than 0.001%. There is no particular lower limit for the sol.Al content, but reducing it to less than 0.0001% would only increase manufacturing costs. Therefore, the sol.Al content may be 0.0001% or more.

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

[0033] Remainder: Fe and impurities The chemical composition of the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment contains the elements described above, with the remainder being Fe and impurities. However, for the purpose of improving magnetic properties, etc., Sn, Cu, Se, and Sb may be further included in the ranges shown below. Furthermore, even if one or more of the following elements, such as W, Nb, Ti, Ni, Co, V, Cr, and Mo, are included in a total amount of 1.0% or less, it will not impair the effects of the grain-oriented electrical steel sheet according to this embodiment. Here, "impurities" refers to elements that are mixed in during the industrial manufacturing of the base steel sheet from raw materials such as ore, scrap, or the manufacturing environment, and which are permitted to be present in amounts that do not adversely affect the function of the grain-oriented electrical steel sheet according to this embodiment.

[0034] Sn: 0~0.50% Tin (Sn) is an element that contributes to improving magnetic properties through the control of the primary recrystallization structure. To obtain the effect of improving magnetic properties, it is preferable to have a Sn content of 0.01% or more. More preferably, the Sn content is 0.02% or more, and even more preferably 0.03% or more. On the other hand, if the Sn content exceeds 0.50%, secondary recrystallization becomes unstable, and the magnetic properties deteriorate. Therefore, it is preferable to keep the Sn content at 0.50% or less. More preferably, the Sn content is 0.30% or less, and even more preferably 0.10% or less.

[0035] Cu: 0~0.50% Copper (Cu) is an element that contributes to increasing the Goss orientation occupancy in the secondary recrystallized structure. To obtain the above effect, it is preferable to have a Cu content of 0.01% or more. More preferably, the Cu content is 0.02% or more, and even more preferably 0.03% or more. On the other hand, if the Cu content exceeds 0.50%, the steel sheet becomes brittle during hot rolling. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment, it is preferable to have a Cu content of 0.50% or less. The Cu content is more preferably 0.30% or less, and even more preferably 0.10% or less.

[0036] Se: 0~0.020% Se (selenium) is an element that has the effect of improving magnetic properties. When Se is included, it is preferable to have a Se content of 0.001% or more in order to exhibit a good effect of improving magnetic properties. The Se content is more preferably 0.003% or more, and even more preferably 0.006% or more. On the other hand, if the Se content exceeds 0.020%, the adhesion of the coating deteriorates. Therefore, it is preferable to keep the Se content at 0.020% or less. More preferably, the Se content is 0.015% or less, and even more preferably 0.010% or less.

[0037] Sb: 0~0.50% Antimony (Sb) is an element that improves magnetic properties. When Sb is included, it is preferable to have an Sb content of 0.005% or more in order to exhibit a good magnetic property improvement effect. More preferably, the Sb content is 0.01% or more, and even more preferably 0.02% or more. On the other hand, if the Sb content exceeds 0.50%, the adhesion of the coating deteriorates significantly. Therefore, it is preferable to keep the Sb content at 0.50% or less. More preferably, the Sb content is 0.30% or less, and even more preferably 0.10% or less.

[0038] As described above, in this embodiment, the chemical composition of the base steel sheet of the grain-oriented electrical steel sheet is exemplified as containing the above-mentioned elements, with the remainder being Fe and impurities.

[0039] The chemical composition of the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment can be measured using a known ICP emission spectrometry method. However, if an insulating film is formed on the surface, it must be removed before measurement. The film can be removed by immersing the sheet in a high-concentration alkaline solution (for example, a 30% sodium hydroxide solution heated to 85°C) for 20 minutes or more. Whether the film has been removed can be determined visually. For small samples, the film may also be removed by surface grinding.

[0040] (plate thickness) The thickness of the base steel plate is not limited, but it is preferably 0.15 to 0.35 mm in terms of iron loss.

[0041] [Insulating coating] In the grain-oriented electrical steel sheet according to this embodiment, an insulating coating is formed on the base steel sheet. That is, since no forsterite-based coating is formed, the insulating coating is formed in direct contact with the base steel sheet. As described later, the insulating coating included in the grain-oriented electrical steel sheet according to this embodiment is a single layer formed by the fusion of a first insulating coating and a second insulating coating through heat treatment. This insulating coating contains metal phosphate salts. Examples of metal phosphate salts include aluminum phosphate, magnesium phosphate, manganese phosphate, zinc phosphate, calcium phosphate, iron phosphate, copper phosphate, copper phosphate, and lithium phosphate. Furthermore, this insulating coating contains Si derived from colloidal silica. In the insulating coating, it is preferable that the metal phosphate salt content is 90 to 50% by mass and the Si content is 10 to 40% by mass.

[0042] The proportion of metal phosphate salts and Si content in the insulating coating can be measured by SEM-EDS, as described later.

[0043] (Void) In insulating coatings, the void area ratio is preferably 30% or less. Reducing the void area ratio results in improved coating tension.

[0044] The area ratio of voids in the insulating coating is determined by the following method. The cross-section of the steel plate, including the surface layer, is captured using a transmission electron microscope (TEM) and magnified 30,000 times. Images of lengths of 10 μm or more are used to identify the phosphate-based insulating coating and voids by elemental analysis, and the void area is determined. The void area percentage (%) is defined as the ratio of the void area to the total area of ​​the observation field. If the image resolution is low and a clear image cannot be obtained, it is possible to clarify the image using an image processing device such as a Luzex.

[0045] (Thickness) In the grain-oriented electrical steel sheet according to this embodiment, the thickness of the insulating coating 21 is preferably 1.0 to 10.0 μm in terms of the packing factor.

[0046] The thickness of the insulating coating is determined by the following method. In the flat section, a sample measuring 10 mm square (10 mm in the rolling direction and 10 mm perpendicular to the rolling direction) is taken, and the cross-section of the sample perpendicular to the rolling direction is observed with a scanning electron microscope. The thickness is measured at five or more points, and the average of these measurements is taken as the thickness of the insulating coating. In this process, the P content is measured using an energy-dispersive elemental analyzer, and the point where the distribution of element P decreases sharply from the insulating coating side (surface side) is defined as the interface between the insulating coating and the base steel sheet. Alternatively, the interface between the insulating coating and the base material may be defined as the point where Al, Mg, Mn, Zn, Ca, Cu, Co, and Li, which are presumed to exist as cations in the insulating coating, decrease sharply.

[0047] Furthermore, the mass percentage and type of metal phosphate salt are identified using a scanning electron microscope and an energy-dispersive elemental analyzer. The Si content can also be measured using the scanning electron microscope and energy-dispersive elemental analyzer. The mass percentage and Si content of the metal phosphate salt are measured at three locations, and the average value is used.

[0048] <Manufacturing method> The grain-oriented electrical steel sheet according to this embodiment can achieve the above-described effects regardless of the manufacturing method, but it can be preferably manufactured by a manufacturing method that includes, for example, the following steps. (i) A hot rolling process in which the steel billet is heated and the steel billet is made into a hot-rolled sheet by hot rolling, (ii) A hot-rolled sheet annealing step, in which the hot-rolled sheet is subjected to hot-rolled sheet annealing, (iii) Pickling step of pickling the hot-rolled sheet after the hot-rolled sheet annealing step, (iv) A cold rolling process in which the hot-rolled sheet after the pickling process is cold-rolled to form a steel sheet (cold-rolled sheet), (v) Decarburization annealing process, which involves subjecting the steel plate to decarburization annealing. (vi) A finish annealing step in which an annealing release agent containing 10 to 100% by mass of Al2O3 is applied to the steel sheet after decarburization annealing, and after drying, finish annealing is performed. (vii) An annealing separating agent removal step in which excess annealing separating agent is removed from the steel plate after the finish annealing step, (viii) A light pickling step in which the steel plate after the annealing separating agent removal step is pickled with 0.1 to 5.0% by mass of inorganic acid for 10 to 60 seconds. (ix) A water washing step in which the steel plate after the light pickling step is washed with water and dried, (x) The steel sheet after the water washing step is immersed in a treatment solution having a liquid temperature of 30 to 85°C and a metal phosphate salt concentration of 1.0 to 10.0% by mass for 5 to 150 seconds, the treatment solution is washed off with water, and the steel sheet is dried to form a first insulating film, a first insulating film forming step. (xi) A second insulating film formation step, wherein a coating solution containing a metal phosphate salt and colloidal silica, wherein the colloidal silica content is 30 to 150 parts by mass per 100 parts by mass of the metal phosphate salt and the solid content concentration is 10 to 40% by mass, is applied to the steel sheet after the first insulating film formation step, and after drying, the sheet is held at a temperature of 700 to 950°C for 10 to 90 seconds to form a second insulating film, and (xii) A heat treatment step in which the steel sheet after the second insulating film formation step is heated to a temperature range of 700 to 900°C in an atmosphere having a dew point of 0 to 30°C, a nitrogen content of 50 to 100% by volume, and a hydrogen content of 0 to 50% by volume, and held in the said temperature range for 10 to 180 minutes, thereby fusing the first insulating film and the second insulating film to form an insulating film and forming an oxide layer in the steel sheet. The manufacturing method for grain-oriented electrical steel sheets according to this embodiment is characterized by (vi) the finish annealing process to (xii) the heat treatment process, and (i) the hot rolling process to (v) the decarburization annealing process is not particularly limited and known conditions can be applied.

[0049] [Hot rolling process] In the hot rolling process, a steel billet, such as a slab having a predetermined chemical composition, is heated and then hot-rolled to obtain a hot-rolled sheet. The heating temperature of the steel billet is preferably in the range of 1100 to 1450°C. More preferably, the heating temperature is 1300 to 1400°C. The chemical composition of the steel billet can be changed according to the chemical composition of the base steel sheet of the grain-oriented electrical steel sheet to be obtained in the end. For example, a chemical composition can be exemplified by containing, in mass%, C: 0.01~0.20%, Si: 2.50~4.00%, sol.Al: 0.01~0.040%, Mn: 0.01~0.50%, N: 0.020% or less, S: 0.005~0.040%, Cu: 0~0.50%, Sn: 0~0.50%, Se: 0~0.020%, Sb: 0~0.50%, with the remainder being Fe and impurities. The hot rolling conditions are not particularly limited and should be set appropriately based on the desired characteristics. The thickness of the hot-rolled sheet is preferably in the range of 2.0 mm to 3.0 mm.

[0050] [Hot-rolled sheet annealing process] In the hot-rolled sheet annealing process, the steel sheet (hot-rolled sheet) is annealed after the hot-rolling process. This annealing treatment causes recrystallization in the steel sheet's structure, making it possible to achieve good magnetic properties. In the hot-rolled sheet annealing process of this embodiment, the hot-rolled sheet manufactured through the hot-rolling process can be annealed according to a known method. The means for heating the hot-rolled sheet during annealing are not particularly limited, and any known heating method can be used. For example, so-called continuous annealing may be used, or the hot-rolled sheet may be coiled and annealed in batches. The annealing conditions are also not particularly limited, but for example, the hot-rolled sheet can be annealed at a temperature range of 900 to 1200°C for 10 seconds to 5 minutes. The atmosphere is not particularly limited, but it is preferable to suppress oxidation of the steel sheet, and it is preferable to carry out the annealing in a non-oxidizing atmosphere such as nitrogen, argon, or hydrogen.

[0051] [Pickling process] In the pickling process, scale (oxides) formed on the surface of the steel sheet during hot rolling and hot-rolled sheet annealing is removed. In the pickling process of this embodiment, known methods are used. Known acids such as hydrochloric acid, sulfuric acid, and nitric acid are used as the pickling solution. In addition, known pickling inhibitors and pickling accelerators may be added to the pickling solution as needed. Furthermore, before contacting the steel sheet with the pickling solution, it is also possible to perform physical treatment on the steel sheet, such as shot blasting, in order to penetrate the pickling solution into the interface between the scale and the steel sheet and improve the pickling efficiency.

[0052] [Cold rolling process] In the cold rolling process, the steel sheet after the pickling process is cold-rolled to produce a cold-rolled sheet (a steel sheet having the same thickness as the base steel sheet of the grain-oriented electrical steel sheet). Cold rolling may be performed in a single cold rolling (series of cold rolling without intermediate annealing) or multiple cold rollings with intermediate annealing may be performed by interrupting the cold rolling before the final pass of the cold rolling process and performing at least one or more intermediate annealings. The cold rolling conditions should follow known methods. The cold rolling ratio in grain-oriented electrical steel sheets greatly affects their magnetic properties. The final reduction ratio has a particularly significant effect, and it can be set to 80-95%. The final reduction ratio is the cumulative reduction ratio of cold rolling, and if intermediate annealing is performed, it is the cumulative reduction ratio of cold rolling after the final intermediate annealing. When performing intermediate annealing, for example, the material is held at a temperature of 800-1200°C for 5-180 seconds. The annealing atmosphere is not particularly limited, but it is preferable to use a non-oxidizing atmosphere such as nitrogen, argon, or hydrogen to prevent oxidation of the steel sheet. The annealing method can be continuous annealing, batch annealing in coil form, or any other method. Considering the manufacturing cost, it is preferable to perform intermediate annealing three times or less.

[0053] [Decarburization annealing process] In the decarburization annealing process, the cold-rolled sheet is subjected to decarburization annealing after the grinding process. In this decarburization annealing, carbon, which adversely affects the magnetic properties of the steel sheet, is removed (decarburized), and the cold-rolled sheet undergoes primary recrystallization. While there are no restrictions on the decarburization annealing conditions, annealing is performed in a nitrogen-hydrogen mixed atmosphere with increased oxygen potential due to humidification. Furthermore, since it is necessary to form a primary recrystallized structure, the humidification temperature (dew point) is determined in terms of the annealing temperature required for recrystallization and the oxygen potential at which decarburization is possible at that annealing temperature. The annealing temperature is typically around 700-900°C, and since annealing is generally carried out in a continuous annealing process, soaking is performed for 30-90 seconds.

[0054] [Nitriding process] Nitriding may be performed between the decarburization annealing process and the finish annealing process described later. In the nitriding process, for example, a decarburized annealed steel sheet is subjected to nitriding treatment by maintaining it at approximately 700-850°C in a nitriding atmosphere (an atmosphere containing gases with nitriding ability such as hydrogen, nitrogen, and ammonia). When using AlN as an inhibitor, it is preferable to raise the nitrogen concentration of the steel sheet to 40 ppm (0.0040 mass%) or higher through nitriding. On the other hand, if the nitrogen concentration of the steel sheet exceeds 1000 ppm (0.1000 mass%), excess AlN will remain in the steel sheet even after secondary recrystallization is completed in finish annealing. Such AlN can cause iron loss degradation. Therefore, it is preferable to keep the nitrogen concentration of the steel sheet after the nitriding process below 1000 ppm.

[0055] [Finishing annealing process] In the finish annealing process, an annealing release agent containing 10-100% by mass of Al2O3 is applied to the steel sheet after the decarburization annealing process (or nitriding process), and after drying, finish annealing is performed. Conventional methods for manufacturing grain-oriented electrical steel sheets involve applying an annealing separation agent mainly composed of MgO and performing finish annealing to form a forsterite-based coating on the surface of the steel sheet (cold-rolled sheet). In contrast, the method for manufacturing grain-oriented electrical steel sheets according to this embodiment uses an annealing separation agent containing 10% by mass or more of Al2O3 to prevent the formation of a forsterite-based coating. The Al2O3 content is preferably 40% by mass or more. On the other hand, while the proportion of Al2O3 may be 100% by mass, in order to prevent Al2O3 from burning onto the surface of the steel sheet, it is preferable that the annealing separating agent in the manufacturing method of grain-oriented electrical steel sheet according to this embodiment contains MgO. The amount of MgO may be 0%, but in order to obtain the above effect, it is preferable that the proportion of MgO be 5% by mass or more. When MgO is included, the proportion of MgO should be 90% by mass or less in order to ensure that 10% by mass or more of Al2O3 is secured. Preferably, the proportion of MgO is 50% by mass or less. The total of Al2O3 and MgO relative to the annealing separating agent should be more than 50% by mass in terms of solid content. Furthermore, in the method for manufacturing grain-oriented electrical steel sheets according to this embodiment, the annealing separating agent may further contain chlorides. Including chlorides in the annealing separating agent has the effect of making it more difficult for forsterite-based coatings to form. The chloride content is not particularly limited and may be 0%, but to obtain the above effect, 0.5 to 10.0% by mass is preferred. Examples of effective chlorides include bismuth chloride, calcium chloride, cobalt chloride, iron chloride, nickel chloride, etc. The finish annealing conditions are not limited, but for example, conditions such as holding at a temperature of 1150-1250°C for 10-60 hours can be used.

[0056] [Annealing Separating Agent Removal Process] In the annealing release agent removal process, excess annealing release agent is removed from the steel sheet after the finish annealing process. For example, excess annealing release agent can be removed by washing with water.

[0057] [Light pickling process] In the light pickling process, the steel sheet after the annealing separating agent removal process is pickled with 0.1 to 5.0% by mass of inorganic acid for 10 to 60 seconds. If the conditions for light pickling are unfavorable, excess annealing separating agent may remain on the steel sheet surface, increasing surface roughness and reducing the packing density. Alternatively, if the acid is too strong, the steel sheet surface may be etched, leading to a decrease in magnetic properties.

[0058] [Water washing process] In the water washing process, the steel plates that have undergone the light pickling process are washed with water and dried. This removes the pickling solution, making it possible to suppress rust formation. There are no restrictions on the conditions for washing and drying.

[0059] [First insulation film formation process] In the first insulating film formation step, the steel sheet after the water washing step is immersed for 5 to 150 seconds in a treatment solution with a liquid temperature of 30 to 85°C and a metal phosphate salt concentration of 1.0 to 10.0% by mass. After the treatment solution is washed off with water, the steel sheet is dried to form a first insulating film on the surface of the steel sheet. If the processing solution temperature is below 30°C, the amount of the first insulating film formed is insufficient, resulting in a partial decrease in the adhesion of the insulating film. On the other hand, if the solution temperature exceeds 85°C, the first insulating film becomes excessively thick in certain areas, ultimately resulting in increased surface roughness and a decrease in the packing density. Furthermore, if the concentration of the metal phosphate salt is less than 1.0 mass%, the formation of the first insulating film takes too long, resulting in a cost disadvantage. On the other hand, if the concentration of the metal phosphate salt is greater than 10.0 mass%, the formation of the first insulating film becomes partially thick, ultimately resulting in an uneven insulating film. Furthermore, if the processing time is less than 5 seconds, the amount of the first insulating film formed is insufficient, resulting in a partial decrease in the adhesion of the insulating film. On the other hand, if it exceeds 150 seconds, it takes too long and becomes costly.

[0060] [Second insulation film formation process] In the second insulating film formation step, a coating liquid (insulating film forming liquid) containing a metal phosphate salt and colloidal silica, wherein the colloidal silica content is 30 to 150 parts by mass per 100 parts by mass of the metal phosphate salt and the solid content concentration is 10 to 40% by mass, is applied to the steel sheet after the first insulating film formation step, and after drying, the sheet is held at a temperature of 700 to 950°C for 10 to 90 seconds to form a second insulating film on top of the first insulating film. If the plate temperature is below 700°C, the tension will be low and the magnetic properties will be inferior. Therefore, it is preferable to keep the plate temperature at 700°C or higher. On the other hand, if the plate temperature exceeds 950°C, the rigidity of the steel plate decreases and it becomes more susceptible to deformation. In this case, the steel plate may become distorted due to transportation, etc., and the magnetic properties may be inferior. Therefore, it is preferable to keep the plate temperature at 950°C or lower. Furthermore, if the holding time is less than 10 seconds, the elution resistance will be inferior. Therefore, the holding time should be 10 seconds or more. On the other hand, if the holding time exceeds 90 seconds, the adhesion will decrease, or productivity will be reduced if efforts are made to avoid the decrease in adhesion. Therefore, a holding time of 90 seconds or less is preferable. The coating solution contains a metal phosphate salt and colloidal silica, with a ratio of 30 to 150 parts by mass of colloidal silica per 100 parts by mass of metal phosphate salt. The solid content concentration of the coating solution is 10 to 40% by mass, and it is preferable that the total amount of metal phosphate salt and colloidal silica in terms of solid content exceeds 50% by mass relative to the coating solution. As the metal phosphate salt, one or more selected from aluminum phosphate, zinc phosphate, magnesium phosphate, nickel phosphate, copper phosphate, lithium phosphate, cobalt phosphate, etc., can be used. The coating solution may also contain additional elements such as vanadium, tungsten, molybdenum, and zirconium. Colloidal silica can be of either S-type or C-type. S-type colloidal silica refers to silica solutions that are alkaline, while C-type colloidal silica refers to silica particles treated with aluminum, resulting in a silica solution that is alkaline to neutral. S-type colloidal silica is widely used and relatively inexpensive, but caution is needed as it may aggregate and precipitate when mixed with acidic metal phosphate solutions. C-type colloidal silica is stable even when mixed with metal phosphate solutions and does not precipitate, but it is relatively more expensive due to the increased processing steps. It is preferable to choose the type based on the stability of the coating solution being prepared.

[0061] [Magnetic domain refining process] In the magnetic domain subdivision process, energy rays may be irradiated onto the surface of the insulating coating (the surface of the insulating coating in a grain-oriented electrical steel sheet comprising a base steel sheet and an insulating coating) to subdivide the 180° magnetic domains. By subdividing the magnetic domains, the iron loss of the grain-oriented electrical steel sheet can be further reduced. A known method can be used for the magnetic domain subdivision process. For example, one method involves narrowing the width of the 180° magnetic domain (subdividing the 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. When forming grooves, mechanical groove formation methods using gears, chemical groove formation methods using electrolytic etching, and thermal groove formation methods using laser irradiation can be applied. If the insulating coating is damaged due to the formation of stress-strained areas or grooves, and its properties such as insulation deteriorate, the insulating coating may be reapplied to repair the damage.

[0062] [Heat treatment process] In the heat treatment process, the steel sheet after the second insulating film formation process is heated to a temperature range of 700 to 900°C in an atmosphere with a dew point of 0 to 30°C, a nitrogen content of 50 to 100% by volume, and a hydrogen content of 0 to 50% by volume. By holding it in this temperature range for 10 to 180 minutes, the first insulating film and the second insulating film are fused to form an insulating film, and an oxide layer is formed in the steel sheet. Furthermore, this heat treatment process can also serve as a stress-relieving annealing process. When the heat treatment process also serves as a stress-relieving annealing process, processing may be performed before the heat treatment process to change the shape of the steel sheet to a predetermined shape (for example, an iron core shape). If the dew point is below 0°C, the oxide layer will not form sufficiently. On the other hand, if the dew point is above 30°C, the average thickness of the oxide layer will be excessive. If the hydrogen content in the atmosphere exceeds 50% by volume, there is a risk that the oxide layer may not form sufficiently. If the heat treatment temperature is below 700°C, the oxide layer formation rate is slow, and the oxide does not form sufficiently. On the other hand, if the temperature exceeds 900°C, the oxide formation rate becomes too fast, resulting in large variations and an excessive thickness of the oxide layer. Furthermore, if the holding time is less than 10 minutes, oxide formation is insufficient and variability increases, resulting in an excessively thick oxide layer. On the other hand, if the holding time exceeds 180 minutes, the amount of oxidation becomes excessive, resulting in an excessively thick oxide layer. In this application, additional annealing may be performed in conjunction with the formation of the oxide layer. For example, heating may be performed for 10 minutes in an atmosphere with a dew point of 20°C, followed by annealing for 120 minutes in an atmosphere of 100% nitrogen with a dew point of -20°C. [Examples]

[0063] A slab containing, by mass%, C:0.08%, Si:3.31%, Mn:0.07%, sol.Al:0.028%, and N:0.008%, with the remainder being Fe and impurities, was cast. After heating the slab, it was hot-rolled to produce a 2.2 mm thick hot-rolled sheet. This hot-rolled sheet was annealed by holding it at 1100°C for 10 seconds. Subsequently, after pickling under known conditions, the material was cold-rolled to 0.22 mm by continuous cold rolling without intermediate annealing to obtain a steel sheet (cold-rolled sheet). This steel plate was subjected to decarburization annealing, held at 830°C for 3 minutes. After decarburization annealing, an annealing separation agent containing MgO: 48% by mass, Al2O3: 48% by mass, and BiCl3: 4% by mass was applied, dried, and then heated to 1200°C and held for 20 hours for finish annealing. After the final annealing, the steel sheet was rinsed with water to remove excess annealing separator, and no forsterite-based coating was found on the surface. This steel plate was subjected to light pickling under the conditions shown in Table 1. Afterward, the steel plates were washed with water and dried. The steel plate was immersed in a treatment solution containing a mixture of metal phosphate salts and additives such as preservatives and viscosity modifiers, as shown in Table 1. After rinsing off the treatment solution with water, the steel plate was dried to form a first insulating coating. Subsequently, a coating solution containing the metal phosphate salt and colloidal silica shown in Table 2 in the proportions shown in Table 2 was applied and dried to form a second insulating film. Subsequently, grooves with a depth of 20 μm and a width of 50 μm were formed on the steel plate surface at 6 mm intervals, in a direction inclined 80° from the rolling direction, using a tooth profile. Subsequently, heat treatment was performed under the conditions shown in Table 3 to obtain grain-oriented electrical steel sheets.

[0064] For the obtained grain-oriented electrical steel sheets, the presence or absence of an oxide layer, the average thickness of the oxide layer, and the coverage rate of the oxide layer were measured. Furthermore, the composition and thickness of the insulating coating were measured. The results are shown in Table 4.

[0065] Although not shown in the table, the chemical composition of the base steel sheet (excluding the oxide layer) was Si: 3.30 mass%, C: 0.0018 mass%, Mn: 0.06 mass%, sol.Al: 0.002 mass%, with the remainder being Fe and impurities.

[0066] Furthermore, the following parameters were measured for the obtained grain-oriented electrical steel sheets: coating adhesion, coating tension, corrosion resistance, elution resistance, packing ratio, and iron loss. The results are shown in Table 5.

[0067] [Coating adhesion] The adhesion of the coating was evaluated by measuring the degree of delamination (area ratio) of the coating after performing a bending adhesion test by taking a sample of 30 mm wide and 300 mm long from a steel plate, wrapping this sample around a 10 mm diameter cylinder, and unwrapping it. The evaluation criteria were as follows, and in the cases of Ex, G, and F, it was determined that the coating adhesion was excellent. Example: Peeling area ratio 0-0.5% G: Peeling area rate more than 0.5%, less than 5.0% F: Peeling area ratio more than 5.0%, less than 20% P: Peeling area ratio more than 20%, less than 50% B: Peeling area ratio over 50%

[0068] [Coating tension] The coating tension was calculated by working backward from the curvature of the insulating coating after peeling off one side. A coating tension of 4.0 MPa or higher was considered sufficient.

[0069] [Corrosion resistance] Corrosion resistance was tested according to the JIS salt spray test (JIS Z2371:2015), by allowing a 5% NaCl aqueous solution to naturally fall onto the sample in a 35°C atmosphere for 7 hours. Subsequently, the rusted area was evaluated on a 10-point scale. The evaluation criteria were as follows: A score of 5 or higher was considered to indicate excellent corrosion resistance. 10: No rust occurred. 9: Very little rust formation (area ratio: 0.10% or less) 8. Percentage of rusted area = over 0.10% and under 0.25% 7. Percentage of rusted area = over 0.25% and under 0.50% 6. Percentage of rusted area = over 0.50% and under 1.0% 5. Percentage of rusted area = over 1.0% and 2.5% or less 4. Percentage of rusted area = Over 2.5% to 5.0% or less 3: Area percentage where rust occurred = more than 5.0% but less than or equal to 10% 2: Percentage of rusted area = over 10% and 25% or less 1: Area percentage where rust has occurred = more than 25% but less than or equal to 50%

[0070] [Elution resistance] Dissolution resistance was evaluated by whether the reagent could suppress the elution of phosphate from the sample. The amount of eluted phosphoric acid was measured by boiling the sample in boiling pure water for 10 minutes, measuring the amount of phosphoric acid dissolved in the pure water, and dividing the amount of phosphoric acid by the area of ​​the insulating coating on the boiled grain-oriented electrical steel sheet. The amount of phosphoric acid dissolved in the pure water was calculated by cooling the pure water (solution) in which the phosphoric acid had dissolved, and then measuring the phosphoric acid concentration of the sample obtained by diluting the cooled solution with pure water using ICP-AES. The amount of elution is 40 mg / m². 2 If the value is less than this, it is considered to have excellent elution resistance.

[0071] [Occupancy rate] The packing factor was measured according to the method compliant with JIS C 2550-5 (2020). Thirty test specimens, each 30 mm wide and 320 mm long, were used. After measuring the total mass of the sample, the packing factor was calculated by measuring the distance between the upper and lower backing plates sandwiching the laminate while under a pressure of 1 MPa. If the occupancy rate is 96.0% or higher, it is judged that a high occupancy rate has been secured.

[0072] [Iron loss] The obtained steel sheet (grain-oriented electrical steel sheet) was subjected to measurements of B8 (magnetic flux density at a magnetization force of 800 A / m) and W17 / 50 (iron loss per unit mass at a magnetic flux density amplitude of 1.7 T and 50 Hz). These characteristic values ​​were measured using the Single Sheet Tester (SST) method in accordance with JIS C2556 (2015). If the iron loss is 0.74 W / kg or less, it is judged to have excellent magnetic properties.

[0073] [Table 1]

[0074] [Table 2]

[0075] [Table 3]

[0076] [Table 4]

[0077] [Table 5]

[0078] As can be seen from Tables 1 to 5, the grain-oriented electrical steel sheet corresponding to the inventive example, obtained by the preferred manufacturing method, has a base steel sheet and an insulating coating containing a metal phosphate salt formed on the surface of the base steel sheet. The base steel sheet has an oxide layer containing Si oxide in the region in contact with the interface between the base steel sheet and the insulating coating, and the average thickness of the oxide layer from the interface is 0.5 to 2.5 μm, resulting in excellent coating adhesion, coating tension, corrosion resistance, elution resistance, packing factor, and iron loss. In contrast, in the comparative example of grain-oriented electrical steel sheet, one or more conditions in the first coating formation process, the second coating formation process, or the heat treatment process fell outside the scope of the present invention, resulting in the failure to form the predetermined oxide layer, and one or more of the following properties—coating adhesion, coating tension, corrosion resistance, elution resistance, space factor, and iron loss—falling below the target. [Explanation of Symbols]

[0079] 11 Base steel plate 12. Oxide layer 21 Insulating coating

Claims

1. Base material steel plate, An insulating coating containing a metal phosphate salt is formed on the surface of the base steel plate, A grain-oriented electrical steel sheet having, The base steel sheet has an oxide layer containing Si oxide in the region in contact with the interface between the base steel sheet and the insulating coating. The average thickness of the oxide layer from the interface is 0.5 to 2.5 μm. The area ratio of voids in the aforementioned insulating coating is 5% or more. A grain-oriented electrical steel sheet characterized by the following features.

2. The ratio of the length of the interface between the oxide layer and the insulating coating to the length of the interface between the base steel plate and the insulating coating is 30% or more. The grain-oriented electrical steel sheet according to claim 1, characterized in that

3. In the insulating coating, the area ratio of the voids is 5 to 30%. A grain-oriented electrical steel sheet according to claim 1 or 2, characterized in that...

4. On the steel plate, Al ２ O ３ A finish annealing step involves applying an annealing release agent containing 10 to 100% by mass of [the substance], drying it, and then performing finish annealing. An annealing separating agent removal step is performed on the steel plate after the finish annealing step to remove any excess annealing separating agent, A light pickling step is performed in which the steel plate after the annealing separating agent removal step is pickled with 0.1 to 5.0% by mass of inorganic acid for 10 to 60 seconds. The steel plate after the light pickling process is washed with water and dried in a washing process, The first insulating coating formation step involves immersing the steel plate, after the water washing step, in a treatment solution with a liquid temperature of 30 to 85°C and a metal phosphate salt concentration of 1.0 to 10.0% by mass for 5 to 150 seconds, then washing off the treatment solution with water, and finally drying the steel plate. A second insulating film formation step is performed, in which a coating solution containing a metal phosphate salt and colloidal silica is applied to the steel sheet after the first insulating film formation step, the colloidal silica content being 30 to 150 parts by mass per 100 parts by mass of the metal phosphate salt, and the solid content concentration being 10 to 40% by mass, and after drying, the sheet is held at a temperature of 700 to 950°C for 10 to 90 seconds. A heat treatment step is performed in which the steel sheet after the second insulating film formation step is heated to a temperature range of 700 to 900°C in an atmosphere having a dew point of 0 to 30°C, a nitrogen content of 50 to 100% by volume, and a hydrogen content of 0 to 50% by volume, and held at that temperature range for 10 to 180 minutes. including, A method for manufacturing grain-oriented electrical steel sheets, characterized by the following features.

5. The annealing separating agent further comprises one or two of the following: MgO: 5 to 90% by mass, and chloride: 0.5 to 10.0% by mass. A method for manufacturing grain-oriented electrical steel sheets according to claim 4, characterized in that

Images