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

Description

41 GRAIN-ORIENTED ELECTRICAL STEEL SHEET AND METHOD FOR FORMING INSULATING COATING FILM TECHNICAL FIELD

[001] The present invention relates to a grain-oriented electrical steel sheet and to a method for forming an insulating coating embedded in the grain-oriented electrical steel sheet.

[002] Priority is claimed in Japanese Patent Application No. 2023-061319, filed on April 5, 2023, the contents of which are incorporated herein by reference. FUNDAMENTALS OF THE TECHNIQUE

[003] A grain-oriented electrical steel sheet is a steel sheet used primarily as an iron core of a transformer or similar. Typically, in a grain-oriented electrical steel sheet, a forsterite layer (also called a forsterite film, a glass coating, or a primer coating) is formed during high-temperature finish annealing, and an insulating coating is formed by applying a treatment liquid containing a phosphate or similar as a major component, and then baking during thermal flattening of the steel sheet.

[004] Insulating coating is necessary to impart electrical insulation properties to grain-oriented electrical steel sheet, reduce eddy current losses, and improve iron loss. The insulating coating must have several properties, such as corrosion resistance, heat resistance, slip resistance, and adhesion, in addition to insulation properties. This serves to facilitate various manufacturing processes when grain-oriented electrical steel sheet is processed into an iron core of a transformer or similar. For example, when the heat resistance, slip resistance, and adhesion of the insulating coating are poor, the insulating coating may peel off during stress-relief annealing in Petition 870250088602, dated 09 / 30 / 2025, page 12 / 55 / ​​41 manufacturing of iron core, so that the original insulation property may not be exhibited or the steel sheet may not be rolled smoothly, resulting in deterioration of workability.

[005] Furthermore, as an important feature of the insulating coating of the grain-oriented electrical steel sheet, there is an action to apply tension to the steel sheet. When tension is applied to the steel sheet, the iron loss of the grain-oriented electrical steel sheet can be improved by facilitating the movement of the domain wall. It is also possible to reduce magnetic deformation, which is one of the main causes of noise generated by a transformer manufactured with a grain-oriented electrical steel sheet as an iron core, by applying tension.

[006] In order to improve various characteristics of grain-oriented electrical steel sheet, as described above, specifically, techniques as described in the following Patent Documents 1 to 7 were researched and developed.

[007] For example, Patent Document 1 describes a technique in which an insulating coating treatment liquid containing a phosphate, a chromate, and colloidal silica with a specific composition as main components is applied to a forsterite film formed on the surface of a sheet after annealing and subsequent baking. According to the technique described in Patent Document 1, it is possible to form a high-voltage insulating coating on the surface of the sheet and reduce iron loss and magnetic deformation of the grain-oriented electrical steel sheet.

[008] Patent Document 2 describes a method in which a treatment liquid containing ultrafine colloidal silica with a grain size of 8 μm or less, a first phosphate and a chromate in a specific ratio is applied to a steel plate and then baked. According to the technique described in Patent Document 2, it is possible to maintain high voltage of Petition 870250088602, dated 09 / 30 / 2025, page 13 / 55 / ​​41 insulating coating and further improve coating lubrication.

[009] In addition, Patent Document 3 describes a technique in which a specific amount of an insulating coating containing a phosphate, a chromate and colloidal silica with a glass transition point of 950°C to 1200°C as main components is fixed to form a high-voltage insulating coating on a surface of a grain-oriented electrical steel sheet.

[0010] According to the techniques described in Patent Documents 1 to 3, it was possible to form an insulating coating with several significantly superior coating characteristics and improved coating voltage. However, in all the techniques described in Patent Documents 1 to 3, chromate, which is a chromium compound, is contained in the insulating coating. In recent years, with the increasing focus on environmental problems, it has become socially necessary to prohibit or restrict the use of compounds such as lead, chromium, and cadmium.

[0011] Thus, a technique capable of forming a good insulating coating without containing a chromium compound was studied. For example, Patent Document 4 describes a method for treating an insulating coating of a grain-oriented electrical steel sheet, in which a treatment liquid containing 20 parts by mass of colloidal silica in terms of SiO2 content, 10 to 120 parts by mass of an aluminum phosphate, 2 to 10 parts by mass of boric acid and a sulfate of one or two or more metallic elements selected from Mg, Al, Fe, Co, Ni and Zn in a total amount of 4 to 40 parts by mass is baked at 300°C or more.

[0012] Furthermore, Patent Document 5 describes a technique relating to a coating agent for forming a coating containing a mixture of boric acid and alumina sol and a water-compatible organic solvent and having a stress-applying effect on a grain-oriented electrical steel sheet. Petition 870250088602, dated 09 / 30 / 2025, page 14 / 55 / ​​41

[0013] Patent Document 6 describes a technique for adding an organic acid salt of one or two or more metallic elements selected from Ca, Mn, Fe, Zn, Co, Ni, Cu, B and Al to a surface treatment agent for a grain-oriented electrical steel sheet containing a phosphate and colloidal silica. Furthermore, in Patent Document 6, formate, acetate, oxalate, tartrate, lactate, citrate, succinate and salicylate are exemplified as organic acid salts.

[0014] Furthermore, Patent Document 7 describes a technique in which a metallic component in a phosphate is a combination of specific ratios of a divalent metallic element, a trivalent metallic element and a tetravalent metallic element or superior metallic element in an insulating coating treatment agent for a grain-oriented electrical steel sheet containing a phosphate and colloidal silica.

[0015] However, in the insulating coating described in Patent Document 4, the corrosion resistance of the steel sheet may be reduced due to sulfate ions in the sulfate. Furthermore, in the technique described in Patent Document 5, since the corrosion resistance and baking temperature of the insulating coating are very high, the steel sheet will likely be scratched. In the technique described in Patent Document 6, the surface treatment agent solution is discolored by the organic acid in the organic acid salt, and the liquid stability is low. Additionally, in the technique described in Patent Document 7, the preparation of the coating liquid is complicated, and the concentration of the coating solution cannot be increased, making uniform coating difficult.

[0016] Furthermore, the non-chromate insulating coating described in Patent Documents 4 to 7 cannot apply sufficient stress to the steel sheet and therefore it cannot be said that the iron loss of the grain-oriented electrical steel sheet can be sufficiently improved. Therefore, techniques related to the insulating coating of these electrical steel sheets Petition 870250088602, dated 09 / 30 / 2025, page 15 / 55 / ​​41 of oriented grain require further improvement. List of Citations Patent Documents

[0017] Patent Document 1: Japanese Patent Application Examined, Second Publication No. S53-28375 Patent Document 2: Japanese Patent Application No. Examined, First Publication No. S61-41778 Patent Document 3: Japanese Patent Application No. Examined, First Publication No. H11-071683 Patent Document 4: Japanese Patent Application Examined, Second Publication No. S57-9631 Patent Document 5: Unexamined Japanese Patent Application, First Publication No. H07-278828 Patent Document 6: Unexamined Japanese Patent Application, First Publication No. 2000-178760 Patent Document 7: Japanese Patent Application No. Examined, First Publication No. 2010-13692 SUMMARY OF THE INVENTION Technical Problem

[0018] As described above, there is room for improvement in the chromate-free insulating coating.

[0019] Furthermore, in the case of attempting to improve the above characteristics in an insulating coating that does not contain chromate, a method of mixing a phosphate containing a specific metallic element is conceivable, but in this case, there is a problem that the chemical stability of the coating decreases and the amount of phosphoric acid eluted from the insulating coating increases.

[0020] Therefore, an objective of the present invention is to provide a grain-oriented electrical steel sheet in which the amount of acid Petition 870250088602, dated 09 / 30 / 2025, p. 16 / 55 / 41 phosphoric eluted from an insulating coating is small (exceptional resistance to dissolution) and provide a method for forming the insulating coating (insulating coating formation method) based on a grain-oriented electrical steel sheet having an insulating coating that does not contain chromate, which has corrosion resistance, coating adhesion and coating tension equal to or greater than conventional ones. Solution to the Problem

[0021] The present inventors studied the containment of phosphoric acid dissolution from an insulating coating that does not contain chromate. As a result, the present inventors discovered that the dissolution of phosphoric acid is controlled from an insulating coating obtained by applying an insulating coating solution containing an oxoacid compound of a predetermined metallic element.

[0022] The present invention was made in view of the above verifications. The essence of the present invention is as follows.

[0023] [1] An electrically oriented grain steel sheet according to one aspect of the present invention includes a base steel sheet; a glass coating formed on a surface of the base steel sheet; and an insulating coating formed on a surface of the glass coating, wherein the base steel sheet has a sheet thickness of 0.15 to 0.35 mm, the insulating coating contains a metallic phosphate, amorphous silica and one or more oxoacid compounds of tungsten, vanadium, molybdenum and zirconium, the amorphous silica being contained in an amount of 30 to 150 parts by mass, and the oxoacid compound being contained in an amount of 1.0 to 50 parts by mass in total relative to 100 parts by mass of the metallic phosphate, and the insulating coating has a water content of 0 to 0.04% by mass.

[0024] [2] In the grain-oriented electrical steel sheet according to [1], the oxoacid compound can be a tungstate, a phosphotungstate, a silicotungstate, a vanadate, a phosphomolybdate or a zirconate. Petition 870250088602, dated 09 / 30 / 2025, page 17 / 55 / ​​41

[0025] [3] A method for forming an insulating coating according to another aspect of the present invention includes a solution preparation step for preparing an insulating coating solution containing 30 to 150 parts by mass of colloidal silica in terms of silica content and 1.0 to 50 parts by mass in total of one or more oxoacid compounds of tungsten, vanadium, molybdenum and zirconium relative to 100 parts by mass of a metallic phosphate, the insulating coating solution having a solid content concentration of 8 to 50% by mass; and a coating and drying step of applying the insulating coating solution to a steel sheet, heating the steel sheet to a temperature range of 800 to 900°C so that a heating rate between 100 and 600°C is 40 to 200°C / sec., and maintaining the insulating coating solution in the temperature range for 5 to 90 seconds.

[0026] [4] In the insulating coating formation method according to [3], in the solution preparation step, 1 to 5 parts by mass of phosphonic acid can be added to the insulating coating solution in relation to 100 parts by mass of metallic phosphate. Advantageous Effects of the Invention

[0027] According to the above aspect of the present invention, it is possible to provide a grain-oriented electrical steel sheet in which the amount of phosphoric acid eluted from an insulating coating is small, and a method for forming the insulating coating. DESCRIPTION OF THE MODALITIES

[0028] An electrically oriented grain steel sheet (an electrically oriented grain steel sheet according to the present embodiment) according to an embodiment of the present invention includes a base steel sheet, a glass coating formed on a surface of the base steel sheet and an insulating coating formed on a surface of the glass coating.

[0029] In the grain-oriented electrical steel sheet according to the Petition 870250088602, dated 09 / 30 / 2025, page 18 / 55 / ​​41, in this modality, the base steel sheet has a sheet thickness of 0.15 to 0.35 mm, the insulating coating contains a metallic phosphate, amorphous silica and one or more oxoacid compounds of tungsten, vanadium, molybdenum and zirconium, and the insulating coating has a water content of 0 to 0.04% by mass.

[0030] Each will be described below. [Base Steel Plate]

[0031] The grain-oriented electrical steel sheet according to the present embodiment has a main feature in the insulating coating, and the base steel sheet included in the grain-oriented electrical steel sheet is not limited in chemical composition, which may be within known ranges. For example, to obtain characteristics generally required for a grain-oriented electrical steel sheet, the grain-oriented electrical steel sheet preferably contains the following components. In the present embodiment, the % relative to the content of each element is % by mass, unless otherwise specified. C: 0.010% or less

[0032] C (carbon) is an effective element in controlling the microstructure of steel sheet in stages up to the completion of the decarburization annealing stage in the manufacturing process. However, when the C content exceeds 0.010%, the magnetic characteristics of the grain-oriented electrical steel sheet, which is a product sheet, deteriorate. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to the present embodiment, the C content is preferably 0.010% or less. The C content is more preferably 0.005% or less. The C content is preferably as low as possible, but even when the C content is reduced to less than 0.0001%, a microstructure control effect is saturated and the manufacturing cost is only increased. Therefore, the C content can be 0.0001% or more. Petition 870250088602, dated 09 / 30 / 2025, page 19 / 55 / ​​41 Yes: 2.00 to 6.00%

[0033] Silicon (Si) is an element that increases the electrical resistance of a grain-oriented electrical steel sheet and improves iron loss characteristics. When the Si content is less than 2.00%, it is not possible to obtain a sufficient eddy current loss reduction effect. Therefore, the Si content is preferably 2.00% or more. The Si content is more preferably 2.50% or more and even more preferably 3.00% or more.

[0034] On the other hand, when the Si content exceeds 6.00%, the grain-oriented electrical steel sheet becomes brittle and the passability deteriorates significantly. In addition, the workability of the grain-oriented electrical steel sheet deteriorates and the steel sheet may break during rolling. Therefore, the Si content is preferably set to 6.00% or less. The Si content is more preferably 5.00% or less and even more preferably 4.00% or less. Mn: 0.01 to 0.50%

[0035] Mn (manganese) is an element that binds to S in a manufacturing process to form MnS. This precipitate acts as an inhibitor (inhibitor for normal grain growth) and causes secondary recrystallization in steel. Mn is also an element that enhances the hot workability of steel. When the Mn content is less than 0.01%, the above effect cannot be sufficiently obtained. Therefore, the Mn content is preferably 0.01% or more. The Mn content is more preferably 0.02% or more.

[0036] On the other hand, when the Mn content exceeds 0.50%, secondary recrystallization does not occur and the magnetic characteristics of the steel deteriorate. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to the embodiment, the Mn content is preferably 0.50% or less. The Mn content is more preferably 0.20% or less and even more preferably 0.10% or less. Petition 870250088602, dated 09 / 30 / 2025, p. 20 / 55 / 41 N: 0.010% or less

[0037] N (nitrogen) is an element that binds to Al in the manufacturing process to form AlN, which acts as an inhibitor. However, when the N content is more than 0.010%, the magnetic characteristics deteriorate due to an excessive presence of an inhibitor in the base steel sheet. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to the embodiment, the N content is preferably 0.010% or less. The N content is more preferably 0.008% or less.

[0038] On the other hand, the lower limit value of the N content is not particularly restricted, but even when the N content is reduced to less than 0.001%, the manufacturing cost is only increased. Therefore, the N content can be 0.001% or more. Al sol.: 0.020% or less

[0039] Al (aluminum) is an element that is bonded to N in the manufacturing process of grain-oriented electrical steel sheet to form AlN, which acts as an inhibitor. However, when the content of Al sol. (acid-soluble aluminum) in the base steel sheet exceeds 0.020%, magnetic characteristics deteriorate due to an inhibitor remaining excessively in the base steel sheet. Therefore, in the base steel sheet of grain-oriented electrical steel sheet according to the embodiment, the Al sol. content is preferably 0.020% or less. The Al sol. content is more preferably 0.010% or less and even more preferably less than 0.001%. The lower limit value of the Al sol. content is not particularly restrictive, and even when the content is reduced to less than 0.0001%, the manufacturing cost is only increased. Therefore, the Al sol. content can be 0.0001% or more. S: 0.010% or less

[0040] S (sulfur) is an element that binds to Mn in the manufacturing process to form MnS, which acts as an inhibitor. However, Petition 870250088602, dated 09 / 30 / 2025, page 21 / 55 / ​​41 when the S content exceeds 0.010%, an excessive residual inhibitor causes the magnetic characteristics to deteriorate. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to the present embodiment, the S content is preferably 0.010% or less. The S content is preferably as low as possible in the grain-oriented electrical steel sheet. For example, the S content is less than 0.001%. However, even when the S content is reduced to less than 0.0001% in the grain-oriented electrical steel sheet, the manufacturing cost only increases. Therefore, the S content can be 0.0001% or more in the grain-oriented electrical steel sheet. P: 0.030% or less

[0041] P (phosphorus) is an element that degrades workability in rolling. When the P content is 0.030% or less, it is possible to prevent excessive reduction in rolling workability and prevent fracture during manufacturing. From this point of view, the P content is preferably 0.030% or less. The P content is more preferably 0.020% or less and most preferably 0.010% or less.

[0042] The lower limit of P content may include 0%; but as the detection limit of chemical analysis is 0.0001%, the actual lower limit of P content in a practical steel sheet is 0.0001%. Furthermore, P is also an element that has the effect of improving texture and enhancing magnetic characteristics. To obtain this effect, the P content may be 0.001% or more or 0.005% or more. Remaining: Iron and impurities

[0043] The chemical composition of the base steel sheet of the grain-oriented electrical steel sheet according to the present embodiment may contain the elements described above, with the remainder being Fe and impurities. However, for the purpose of improving magnetic and similar characteristics, Cu, Cr, Sn, Se, Sb, and Mo may be included in the following ranges. These elements Petition 870250088602, dated 09 / 30 / 2025, p. 22 / 55 / 41 may also be contained as impurities. The lower limit of the content is 0% because the elements may not be contained.

[0044] Furthermore, even if any one, or two or more of, for example, W, Nb, Ti, Ni, Bi, Co and V are contained as elements other than these in a total amount of 1.0% or less (regardless of whether they are intentionally added as impurities), the effect of the grain-oriented electrical steel sheet according to the present embodiment is not inhibited.

[0045] Here, an impurity is an element that is a contaminant derived from ore or scrap as a raw material, a manufacturing environment or similar when the base steel sheet is manufactured industrially, and means an element that may be included in a content that does not adversely affect the effect of the grain-oriented electrical steel sheet according to the embodiment. Cr: 0 to 0.50%

[0046] Cr (chromium) is an element that contributes to an increase in the occupancy rate of the Goss orientation in the secondary recrystallization structure to improve magnetic characteristics. To obtain the above effect, the Cr content is preferably 0.01% or more, more preferably 0.02% or more, and even more preferably set at 0.03% or more.

[0047] On the other hand, when the Cr content exceeds 0.50%, Cr oxide is formed and the magnetic characteristics deteriorate. Therefore, the Cr content is preferably 0.50% or less. The Cr content is more preferably 0.30% or less and even more preferably 0.10% or less. Sn: 0 to 0.50%

[0048] Sn (tin) is an element that contributes to the improvement of magnetic characteristics through the control of the primary recrystallization structure. In order to obtain the effect of improving magnetic characteristics, the Sn content is preferably 0.01% or more. The Sn content is more Petition 870250088602, dated 09 / 30 / 2025, p. 23 / 55 / 41 preferably 0.02% or more and even more preferably 0.03% or more.

[0049] On the other hand, when the Sn content exceeds 0.50%, secondary recrystallization is unstable and the magnetic characteristics deteriorate. Therefore, the Sn content is preferably 0.50% or less. The Sn content is more preferably 0.30% or less and even more preferably 0.10% or less. Cu: 0 to 0.50%

[0050] Cu (copper) is an element that contributes to an increase in the occupancy rate of the Goss orientation in a secondary recrystallization structure. Cu is an optional element in the base steel sheet according to the present embodiment. Therefore, the lower limit of the content is 0%. To obtain the above effect, the Cu content is preferably 0.01% or more. The Cu content is more preferably 0.02% or more and even more preferably 0.03% or more.

[0051] On the other hand, when the Cu content exceeds 0.50%, the steel sheet becomes weakened during hot rolling. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to the embodiment, the Cu content is preferably 0.50% or less. The Cu content is more preferably 0.30% or less and even more preferably 0.10% or less. If: 0 to 0.020%

[0052] Selenium is an element that has an effect of improving magnetic characteristics. Therefore, Se may be included. When Se is included, the content is preferably 0.001% or more, so that Se favorably exhibits the effect of improving magnetic characteristics. The Se content is preferably 0.003% or more and more preferably 0.006% or more.

[0053] On the other hand, when the Se content exceeds 0.020%, adhesion of the glass coating deteriorates. Therefore, the Se content is preferably 0.020% or less. The Se content is more preferably 0.015% or less and Petition 870250088602, dated 09 / 30 / 2025, p. 24 / 55 / 41, even more preferably 0.010% or less. Sb: 0 to 0.500%

[0054] Sb (antimony) is an element that has an effect of improving magnetic characteristics. Therefore, Sb may be contained. When Sb is contained, the content is preferably 0.005% or more, so that Sb favorably exhibits the effect of improving magnetic characteristics. The Sb content is more preferably 0.010% or more and even more preferably 0.020% or more.

[0055] On the other hand, when the Sb content exceeds 0.500%, the adhesion of the glass coating deteriorates significantly. Therefore, the Sb content is preferably 0.500% or less. The Sb content is more preferably 0.300% or less and even more preferably 0.100% or less. Mo: 0 to 0.10%

[0056] Molybdenum (Mo) is an element that has an effect of improving magnetic characteristics. Therefore, Mo may be included. When Mo is included, the Mo content is preferably 0.01% or more in order to favorably exhibit the effect of improving magnetic characteristics. The Mo content is more preferably 0.02% or more and even more preferably 0.03% or more.

[0057] On the other hand, when the Mo content is more than 0.10%, the cold rolling characteristics may deteriorate, leading to fracture. Therefore, the Mo content is preferably 0.10% or less. The Mo content is more preferably 0.08% or less and even more preferably 0.05% or less.

[0058] As described above, the chemical composition of the base steel sheet of the grain-oriented electrical steel sheet in the present embodiment includes the essential elements described above, and the remainder includes Fe and impurities, or includes the essential elements described above and also contains one or more of the optional elements, and the remainder includes Fe and impurities. Petition 870250088602, dated 09 / 30 / 2025, page 25 / 55 / ​​41

[0059] The chemical composition of the base steel sheet of the grain-oriented electrical steel sheet according to the present embodiment can be measured after removing the glass coating and insulating coating formed on the surface.

[0060] Specifically, the grain-oriented electrical steel sheet is immersed in an aqueous solution of sodium hydroxide containing NaOH: 10 to 20% by mass at 80 to 90°C for 7 to 10 minutes to remove the insulating coating.

[0061] The grain-oriented electrical steel sheet from which the insulating coating has been removed is washed with water and then dried with a hot air blower for just under 1 minute (e.g., 5 to 60 seconds). The grain-oriented electrical steel sheet after drying (grain-oriented electrical steel sheet not provided with insulating coating) is immersed in an aqueous solution of hydrochloric acid containing 5 to 10% by mass of HCl and at 70 to 90°C for 1 to 10 minutes to remove the glass coating.

[0062] After immersion, the base steel plate is washed with water and then dried with a hot air blower for just under 1 minute (e.g., 5 to 60 seconds).

[0063] Through the steps above, the base steel sheet can be removed from the grain-oriented electrical steel sheet.

[0064] The chemical composition of this base steel plate is obtained using a well-known component analysis method. Specifically, shavings are generated from the base steel plate using a drill, the shavings are recovered, and the recovered shavings are dissolved in an acid to obtain a solution. The solution is subjected to ICP-AES to perform elemental analysis of the chemical composition.

[0065] Here, the Si in the chemical composition of the base steel sheet is obtained using a method (quantitative silicon method) specified in Petition 870250088602, dated 09 / 30 / 2025, page 26 / 55 / 41, JIS document G1212 (1997). Specifically, when the above-described shavings are dissolved in an acid, silicon oxide is separated as a precipitate, and thus the precipitate (silicon oxide) is filtered with filter paper and the mass is measured to obtain the Si content.

[0066] The C content and S content are obtained using a well-known high-frequency combustion method (infrared absorption combustion method). Specifically, the solution described above is burned by high-frequency heating in an oxygen stream, and the carbon dioxide and sulfur dioxide generated are detected to obtain the C content and S content.

[0067] The N content is obtained using a well-known inert gas fusion thermal conductivity method. <Espessura da Chapa>

[0068] The thickness of the base steel sheet is 0.15 to 0.35 mm, considering the application of a transformer to an iron core. As the sheet thickness decreases, a reduction in eddy current loss and a preferable iron loss can be obtained. Therefore, the upper limit of the base steel sheet thickness is preferably 0.35 mm. On the other hand, manufacturing a base steel sheet with a thickness of less than 0.15 mm requires special equipment, which is undesirable in terms of production as it increases manufacturing costs. Therefore, the lower limit of the sheet thickness is industrially preferably 0.15 mm. [Glass Cladding]

[0069] In the grain-oriented electrical steel sheet according to the present embodiment, a glass coating (which may also be called a forsterite film) is formed on the surface of the base steel sheet. The glass coating can be any known coating. It is generally an inorganic coating containing magnesium silicate. Petition 870250088602, dated 09 / 30 / 2025, page 27 / 55 / ​​41 (forsterite) as the main component.

[0070] The glass coating is formed in the finishing annealing when an annealing separator including magnesia (MgO) applied to the surface of the base steel sheet reacts with a component on the surface of the base steel sheet. The glass coating has a composition derived from the annealing separator and the component of the base steel sheet, and has a microstructure including a Mg2SiO4 phase as a major phase (50% area or more) and an MgAhO4 phase. In addition to these phases, a precipitate may be included in an amount of about 1% or less.

[0071] The glass coating helps to improve the adhesion of the insulating coating. [Insulating Coating]

[0072] In the grain-oriented electrical steel sheet according to the present embodiment, the insulating coating is formed on the surface of the glass coating.

[0073] The insulating coating contains a metallic phosphate, amorphous silica and one or more oxoacid compounds of tungsten, vanadium, molybdenum and zirconium, and the ratio of metallic phosphate, amorphous silica and oxoacid compound content is 30 to 150 parts by mass of amorphous silica and 1.0 to 50 parts by mass of oxoacid compound in total relative to 100 parts by mass of metallic phosphate.

[0074] Examples of metallic phosphate include, but are not limited to, Al phosphate and Mg phosphate. However, from the point of view of moisture resistance, the ratio of Mg to metal in metallic phosphate is preferably 50% by mass or less, and more preferably 30% by mass or less (e.g., 70% by mass or more of Al phosphate and 30% by mass or less of Mg phosphate).

[0075] When the proportion of amorphous silica derived from silica Petition 870250088602, dated 09 / 30 / 2025, page 28 / 55 / ​​41. If the colloidal content in the insulating coating solution is excessive, cracks or similar defects occur in the coating, and the water content of the insulating coating increases. Furthermore, when the proportion of amorphous silica is excessively low, the proportion of phosphate becomes higher than necessary, and the water content of the insulating coating increases.

[0076] As a result of studies carried out by the present inventors, it is presumed that the reason why the amount of phosphoric acid dissolution increases when chromic acid is not present is that when an insulating coating solution that does not contain chromic acid is applied to a glass-coated steel sheet, a layer of forsterite on the steel surface reacts with the solution to generate magnesium phosphate with high moisture absorption and solubility properties.

[0077] Therefore, in the grain-oriented electrical steel sheet according to the present embodiment, a substance with higher acidity is mixed into the insulating coating to inhibit the reaction with forsterite, thus obtaining high coating voltage and inhibiting the dissolution of phosphoric acid. An oxoacid compound of a specific transition metal is used as a substance with higher acidity without causing deterioration in various coating characteristics. Specifically, a total of 1.0 to 50 parts by mass of one or more oxoacid compounds of tungsten, vanadium, molybdenum, and zirconium are contained in relation to 100 parts by mass of the metal phosphate. In the present embodiment, the transition metal oxoacid compound is a compound in which an oxygen atom is directly bonded to a transition metal element.

[0078] When the proportion of one or more oxoacid compounds of tungsten, vanadium, molybdenum, and zirconium is excessively low, the water content of the insulating coating increases and the resistance to dissolution of the insulating coating decreases. On the other hand, if the proportion is too high, the corrosion resistance may decrease or the solution may become Petition 870250088602, dated 09 / 30 / 2025, p. 29 / 55 / 41 unstable.

[0079] The oxoacid compound must be one or more oxoacids of tungsten, vanadium, molybdenum, and zirconium. Other oxoacids besides these cannot provide a sufficient effect on the resistance to dissolution of phosphoric acid.

[0080] The oxoacid compound is preferably a tungsten or vanadium oxoacid compound. For example, the oxoacid compound is tungstate, phosphotungstate, silicotungstate, vanadate, phosphomolybdate, or zirconate, and phosphotungstate and tungstate are preferred from the point of view of solution stability. More preferably, the oxoacid compound is a vanadium oxoacid compound.

[0081] Furthermore, from the point of view of miscibility with phosphate, a sodium salt, such as sodium vanadate or sodium tungstate, is preferable.

[0082] Even if tungsten, vanadium, molybdenum and / or zirconium are contained in a state other than the oxoacid compound, the intended effect cannot be obtained.

[0083] The oxoacid compound exists as a matrix (i.e., not in particle form, but in molecular form) along with the metal phosphate. For example, even in particle form, the intended effect cannot be achieved.

[0084] When the oxoacid compound is an ammonium compound, corrosion resistance may be reduced and the water content of the insulating coating may be deteriorated. Therefore, the oxoacid compound is preferably not an ammonium compound.

[0085] When boric acid or a similar substance with high moisture absorption properties is contained together with the oxoacid compound, the water content of the coating tends to increase. Therefore, the other compounds are not contained or, even if they are contained, the content of other compounds is preferably 5 parts by mass or less in relation to 100 parts by mass. Petition 870250088602, dated 09 / 30 / 2025, page 30 / 55 / ​​41 mass of metallic phosphate.

[0086] The proportion of metallic phosphate, amorphous silica and oxoacid compound in the insulating coating can be determined using the following method.

[0087] By detecting and analyzing each element in the insulating coating using an energy-dispersive X-ray analyzer, it is possible to calculate the proportions of a phosphate, silica, and oxoacid compound. Furthermore, it is possible to calculate the proportion of amorphous silica in silica using X-ray crystallography.

[0088] When each element is detected by the energy-dispersive X-ray analyzer, it is preferable to analyze about 3 points with a magnification of 1000 times to calculate an average value. Specifically, when crystallography is performed, the measurement is preferably carried out, for example, using the SmartLab manufactured by RIGAKU CORPORATION under conditions of a Cu bulb, a voltage of 40 kV, a current of 30 mA, a measurement angle (2θ) of 5 to 90°, a step of 0.02°, a scan rate of 1° / min., an incident slit of 1 / 2 degree and a light-receiving slit of 20 mm. <Teor de Água>

[0089] The water content of the insulating coating included in the grain-oriented electrical steel sheet according to the present embodiment is from 0 to 0.04% by mass.

[0090] By decreasing the water content of the insulating coating, the dissolution of phosphoric acid can be controlled. By setting the water content to 0.04% by mass or less, a noticeable effect can be obtained.

[0091] In a normal insulating coating, the water content is about 0.05 to 0.15% by mass, but the water content can be 0.04% by mass or less, setting the oxoacid compound content and baking conditions within predetermined ranges according to the compound content. Petition 870250088602, dated 09 / 30 / 2025, page 31 / 55 / ​​41 oxoacid. The water content is preferably 0.03% by mass or less, and more preferably 0.02% by mass or less.

[0092] The water content can be determined using the Karl Fischer method.

[0093] Specifically, approximately 3 g of a sample collected from a grain-oriented electrical steel sheet with an insulating coating is placed in a closed heating furnace and heated to 105°C in a nitrogen gas stream to vaporize moisture. The vaporized moisture is passed through 150 ml of an indicator solution in which a Karl Fischer reagent is dissolved, and the moisture is dissolved in the reagent solution for 30 minutes. Subsequently, quantitative analysis is performed using a Karl Fischer titration method described in JIS document K0113 (2005). <Quantidade de Adesão do Revestimento Isolante>

[0094] In the grain-oriented electrical steel sheet according to the present embodiment, the amount of adhesion of the insulating coating is not particularly limited. For example, the amount of coating of the insulating coating can be from 1 to 10 g / m2. [Manufacturing Method]

[0095] The grain-oriented electrical steel sheet according to the present embodiment can have the effect, provided it has the above composition, regardless of a manufacturing method, but it can preferably be manufactured, for example, by a manufacturing method that includes the following steps.

[0096] (i) a hot rolling step to heat a piece of steel to form a hot-rolled sheet by hot rolling; (ii) a hot-rolled sheet annealing step to perform hot-rolled sheet annealing on the hot-rolled sheet, (iii) a pickling step of the sheet Petition 870250088602, dated 09 / 30 / 2025, page 32 / 55 / ​​41 hot-rolled after the annealing stage of the hot-rolled sheet, (iv) a cold rolling stage to subject the hot-rolled sheet, after the pickling stage, to cold rolling, one or two or more times with annealing between them to form a cold-rolled sheet; (v) a decarburization annealing step to subject the cold-rolled sheet to decarburization annealing, (vi) a finishing annealing step to apply an annealing separator to the front and back surfaces of the cold-rolled sheet that is a base steel sheet after the decarburization annealing step and then performing the finishing annealing, (vii) a solution preparation step to prepare an insulating coating solution; (viii) a coating and drying step to apply the insulating coating solution to the steel sheet after the finishing annealing and heating step of the steel sheet to form an insulating coating, and (ix) a step to refine the magnetic irradiation domain of an insulating coating surface with an energy beam.

[0097] However, the conditions for steps other than (vii) the solution preparation step and (viii) the coating and drying step (collectively referred to as the insulating coating formation step) related to the formation of the insulating coating are not limited, and the steps can be performed under known manufacturing conditions of the grain-oriented electrical steel sheet. [Hot Rolling Stage]

[0098] In the hot rolling stage, a piece of steel, such as a plate, having a predetermined chemical composition (a chemical composition corresponding to the chemical composition of the base steel sheet of the plate) Petition 870250088602, dated 09 / 30 / 2025, page 33 / 55 / ​​41 of grain-oriented electrical steel according to the present embodiment) is heated and hot-rolled to form a hot-rolled sheet.

[0099] A heating temperature is, for example, from 1000 to 1400°C.

[00100] The chemical composition of the steel part to be subjected to hot rolling can be determined by considering a change in chemical composition at each stage, according to the desired chemical composition to be obtained as the grain-oriented electrical steel sheet.

[00101] There is no limit to the method for obtaining a steel part. For example, molten steel having a predetermined chemical composition can be melted down, and the steel part can be manufactured using the molten steel. The plate can be manufactured using a continuous casting method, or an ingot can be manufactured using molten steel, and the plate can be manufactured by roughing-rolling the ingot. In addition, the plate can be manufactured by other methods.

[00102] The thickness of the steel part is not particularly limited, and is, for example, 150 to 350 mm. The thickness of the steel part is preferably 220 to 280 mm. As for the steel part, a so-called thin plate having a thickness of 10 to 70 mm may be used.

[00103] A so-called hot-rolled sheet (hot-rolled steel sheet) is obtained by means of hot rolling. The thickness of the hot-rolled sheet (final sheet thickness) is not particularly limited. However, the hot-rolled sheet undergoes annealing and cold rolling after pickling, and it is known that the so-called cold rolling rate affects the magnetic characteristics of the grain-oriented electrical steel sheet, and the sheet thickness of the hot-rolled sheet is selected considering the required cold rolling rate in relation to the final sheet thickness. For example, the final sheet thickness of the hot-rolled sheet is 2.0 to 4.0 Petition 870250088602, dated 09 / 30 / 2025, page 34 / 55 / ​​41 mm. [Hot Rolled Sheet Annealing Stage]

[00104] In the annealing stage of hot-rolled sheets, the steel sheet (hot-rolled sheet) is annealed after the hot rolling stage. By performing this annealing treatment, recrystallization occurs in the metallographic structure and favorable magnetic characteristics can be obtained.

[00105] In the annealing stage of the hot-rolled sheet of the present embodiment, the hot-rolled sheet manufactured through the hot rolling stage can be annealed according to a known method. The means for heating the hot-rolled sheet at the time of annealing are not particularly limited, and a known heating method can be adopted. For example, so-called continuous annealing can be used, and discontinuous annealing can be used using a hot-rolled sheet with a coil shape. Furthermore, the annealing conditions are also not particularly limited, but, for example, the hot-rolled sheet can be annealed in 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 contain the oxidation of the steel sheet and it is preferable to carry out the oxidation in a non-oxidizing atmosphere, such as nitrogen, argon or hydrogen. [Pickling Stage]

[00106] In the pickling stage, the scale (oxide) generated on the surface of the sheet through hot rolling and annealing of the hot-rolled sheet is removed. In the pickling stage of the present embodiment, a known method is used. A known acid, such as hydrochloric acid, sulfuric acid, or nitric acid, is used as the pickling liquid. In addition, a known pickling inhibitor, pickling accelerator, or similar may be added to the liquid. Petition 870250088602, dated 09 / 30 / 2025, page 35 / 55 / 41 pickling, as needed. Furthermore, before the steel sheet comes into contact with the pickling liquid, it is also possible to perform a physical treatment, such as shot blasting on the steel sheet prior to pickling, in order to infiltrate the pickling liquid into the interface between the fouling and the steel sheet to improve pickling efficiency. [Cold Rolling Stage]

[00107] In the cold rolling stage, the steel sheet after the pickling stage is cold rolled to form a cold-rolled sheet. Cold rolling can be a single cold rolling (a series of cold rollings without intermediate annealing). Before a final pass of the cold rolling stage, cold rolling can be interrupted, at least one or more times of intermediate annealing can be performed, and a plurality of times of cold rolling can be performed with intermediate annealing interposed between them.

[00108] The conditions for cold rolling can be in accordance with a known method. The cold rolling rate on grain-oriented electrical steel sheet greatly affects its magnetic characteristics. In particular, the influence of the final rolling reduction rate is large, and the final rolling reduction rate can be set at 80 to 95%. The final rolling reduction is a cumulative cold rolling reduction, and when intermediate annealing is performed, the final rolling reduction is a cumulative cold rolling reduction after the final intermediate annealing.

[00109] In a case where intermediate annealing is performed, it is preferable to maintain the intermediate annealing at a temperature of 800 to 1200°C for 5 to 180 seconds. The annealing atmosphere is not particularly limited, but to avoid oxidation of the steel sheet, annealing is preferably carried out in a non-oxidizing atmosphere, such as nitrogen, argon, or hydrogen. Furthermore, as a method of Petition 870250088602, dated 09 / 30 / 2025, page 36 / 55 / ​​41 annealing, continuous annealing or discontinuous annealing in a coil format may be used, and other methods may be used. The number of intermediate annealing times is preferably 3 or less considering the manufacturing cost. [Decarburization Annealing Stage]

[00110] In the decarburization annealing stage, the cold-rolled sheet after the grinding stage is subjected to decarburization annealing. In this decarburization annealing, the C that negatively affects the magnetic characteristics is removed (decarburized) from the steel sheet, and the cold-rolled sheet is mainly recrystallized.

[00111] Although the conditions for decarburization annealing are not limited, annealing is carried out in an atmosphere in which the oxygen potential is increased by humidification in a mixed atmosphere of nitrogen and hydrogen for decarburization. Furthermore, as it is necessary to form a primary recrystallization texture together, the humidification temperature (dew point) is determined from the point of view of the annealing temperature required for recrystallization and the oxygen potential that can provide decarburization at the annealing temperature.

[00112] The annealing temperature is, for example, around 700 to 900°C and, as annealing is usually carried out in a continuous annealing step, the heat is equalized for about 60 seconds. [Finish annealing stage]

[00113] In the finishing annealing stage, an annealing separator is applied to the cold-rolled sheet after the decarburization annealing stage, and the finishing annealing is performed.

[00114] Because the annealing time is long, finish annealing is usually performed by rolling a steel sheet into a coil shape and performing discontinuous annealing. As the temperature of Petition 870250088602, dated 09 / 30 / 2025, page 37 / 55 / 41: When a steel sheet is heated to approximately 1200°C, an annealing separator is applied to prevent the rolled steel sheets from burning against each other. MgO is commonly used as the annealing separator. When using an annealing separator containing MgO as a primary component, a glass coating is formed on the surface of the steel sheet after the finishing annealing.

[00115] In the finishing annealing stage, the recrystallized primary grains obtained in the decarburization annealing stage are secondarily recrystallized by heating the steel sheet to obtain Goss-oriented crystal grains, and precipitates in the steel, such as nitrides (e.g., AlN) and sulfides (e.g., MnS) that have finished their functions as inhibitors, are removed (purified) by maintaining the crystal grains at an annealing temperature close to 1200°C for a predetermined time so as not to adversely affect the magnetic characteristics.

[00116] Although the conditions for final annealing are not limited, the temperature is raised in a range of 10 to 100°C / h from ambient temperature and raised by 5 to 20°C / h in a temperature range of 900 to 1000°C in which secondary recrystallization is generally caused in the Goss orientation, so that preferential growth (secondary recrystallization) is promoted in the Goss orientation and then the inhibitor that has finished its role in the vicinity of 1200°C (e.g., 1150 to 1250°C), as described above, is purified. After that, the coil is slowly cooled in a non-oxidizing atmosphere, such as hydrogen or nitrogen, and removed from the furnace. <Etapa de Preparação da Solução>

[00117] In the solution preparation stage, an insulating coating solution containing 30 to 150 parts by mass of colloidal silica in terms of silica content and 1.0 to 50 parts by mass in total of a or Petition 870250088602, dated 09 / 30 / 2025, p. 38 / 55 / 41, plus oxoacid compounds of tungsten, vanadium, molybdenum and zirconium in terms of a solid content relative to 100 parts by mass of a metallic phosphate, and having a solid content concentration of 8 to 50% by mass is prepared.

[00118] The mixing ratio of metal phosphate, colloidal silica, and oxoacid compound is a ratio for obtaining an insulating coating containing metal phosphate, amorphous silica, and oxoacid compound in the ratio described above in the insulating coating. Here, as the oxoacid compound serves as a matrix of the insulating coating, the oxoacid compound is not in an emulsion, dispersion, or suspension state, but in a hydrated state in solution.

[00119] When the solids content concentration is less than 8% by mass, the aqueous solution applied to the steel sheet becomes unstable, causing coating defects such as irregularities in the pattern and application. On the other hand, when the solids content concentration is more than 50% by mass, the service life of the aqueous solution is reduced. Furthermore, since the solids content concentration also affects the amount of oxoacid compound remaining in the insulating coating, the solids content concentration is defined taking this point into consideration.

[00120] To the insulating coating solution, it is preferable to add 1 to 5 parts by mass of phosphonic acid in relation to 100 parts by mass of metallic phosphate. In this case, the effect of improved coatingability is obtained.

[00121] On the other hand, it is preferable that the insulating coating solution does not contain boric acid or similar substances that have a high moisture absorption property, as described above. <Etapa de Revestimento e Secagem>

[00122] In the coating and drying stage, an insulating coating solution is applied to a steel sheet (a steel sheet with a glass coating formed on a surface of the base steel sheet). Petition 870250088602, dated 09 / 30 / 2025, page 39 / 55 / ​​41 after finishing annealing), heated to a temperature range of 800 to 900°C, so that a heating rate between 100 and 600°C is 40 to 200°C / sec., and maintained in this temperature range for 5 to 90 seconds to form an insulating coating (drying / baking).

[00123] When the heating rate from 100 to 600°C is less than 40°C / sec., moisture is less likely to evaporate from the surface layer of the coating, the dissolution property increases, and the water content also increases. On the other hand, when the heating rate exceeds 200°C / sec., jolts or similar events are likely to occur, and the water content also increases, which causes a decrease in corrosion resistance.

[00124] When the heating temperature is below 800°C, the polymerization of phosphate and oxoacid hardly occurs, which causes a decrease in coating tension. When the temperature exceeds 900°C, thermal deformation is generated in the steel sheet, which causes magnetodeformation to occur.

[00125] When the holding time is less than 5 seconds, phosphate and oxoacid polymerization hardly occurs, which causes a decrease in coating tension. When the holding time exceeds 90 seconds, cracking of the coating is likely to occur, which causes a decrease in corrosion resistance. <Etapa de Refinamento de Domínio Magnético>

[00126] In the magnetic domain refinement step, the surface (a surface of the insulating coating of the grain-oriented electrical steel sheet, including the base steel sheet, the glass coating and the insulating coating) of the insulating coating is irradiated with an energy beam to refine the magnetic domain by 180°.

[00127] By refining the magnetic domain, the iron loss of the grain-oriented electrical steel sheet can be further reduced.

[00128] A known method can be used as the method of Petition 870250088602, dated 09 / 30 / 2025, page 40 / 55 / ​​41, magnetic domain refinement treatment. For example, there is a method for reducing the width of the 180° magnetic domain (refining the 180° magnetic domain) by forming linear or dotted groove pieces that extend in a direction that crosses the rolling direction at predetermined intervals in the rolling direction, and a method for reducing the width of the 180° magnetic domain (refining the 180° magnetic domain) by forming linear or dotted stress-strain pieces or groove pieces that extend in a direction that crosses the rolling direction at predetermined intervals in the rolling direction.

[00129] In a case where a stress-strain part is formed, laser beam irradiation, electron beam irradiation, and similar methods can be applied. In a case where a groove part is formed, a mechanical groove forming method using a gear or similar, a chemical groove forming method by electrolytic corrosion, a thermal groove forming method by laser irradiation, and similar methods can be applied.

[00130] In a case where the insulating coating is damaged due to the formation of a stress-strain part or a grooved part and characteristics such as insulation properties are deteriorated, the insulating coating can be reformed to repair the damage. Examples

[00131] A cast steel containing 3.2% by mass of Si, 0.027% by mass of sol. Al, 0.08% by mass of Mn, 0.008% by mass of N and 0.08% by mass of C with the remainder being Fe and impurities was melted down to obtain a plate.

[00132] After heating the plate, hot rolling was carried out to obtain a steel sheet (hot-rolled sheet) with a thickness of 2.0 mm. Petition 870250088602, dated 09 / 30 / 2025, page 41 / 55 / ​​41

[00133] This steel sheet was annealed at 1100°C for 5 minutes (hot-rolled sheet annealing).

[00134] The steel sheet after annealing the hot-rolled sheet was subjected to pickling treatment and then cold rolling to obtain a steel sheet (cold-rolled sheet) having a thickness of 0.23 mm.

[00135] The steel plate was subjected to decarburization annealing, in which the steel plate was held at 850°C for 3 minutes.

[00136] After decarburization annealing, an annealing separator containing MgO as a major component (containing 90% by mass or more) was applied, and then finishing annealing was performed, in which the annealing separator was heated to 1200°C and held in a hydrogen stream at that temperature for 20 hours.

[00137] A 7 cm sample in the width direction x 30 cm in the lamination direction was cut from the steel sheet after finish annealing, and the remaining annealing separator on the surface was removed by washing with water and light pickling. However, the glass coating formed by the finish annealing was left.

[00138] Next, annealing (stress relief annealing) was performed by holding the sample at 850°C for 2 hours in a nitrogen stream to obtain a sample material.

[00139] An oxoacid compound of a metallic element shown in Table 1 was added to an insulating coating treatment liquid containing a metallic phosphate and colloidal silica as main components in a ratio shown in Table 2, and then the insulating coating treatment liquid was applied to the sample material after stress-relief annealing and dried to form an insulating coating on the surface. The amount of adhesion of the insulating coating was 5 g / m2 (in Table 2, the term “metallic phosphate type: ratio” indicates that when Al: 100%, in Petition 870250088602, dated 09 / 30 / 2025, page 42 / 55 / ​​41 metallic phosphate, the Al phosphate was 100%, and the term “Al: 75%, Mg 25%” indicates that in the metallic phosphate, the Al phosphate was 75% and the Mg phosphate was 25%). As a result, a grain-oriented electrical steel sheet was obtained, including the steel sheet (called the base steel sheet), the glass coating, and the insulating coating.

[00140] The grain-oriented electrical steel sheet thus obtained was irradiated with a laser beam to perform a magnetic domain refinement treatment. The laser irradiation was performed using a continuous laser in a direction orthogonal to the rolling direction under conditions of an irradiation step of 6 mm and an energy density of 2.0 mJ / mm2. Table 1 Symbol Compound Oxoacid Chemical Formula Notes A Sodium Vanadate NaVO3 Partially Precipitated B Ammonium Molybdate (NH4)2MoO4 Dissolved C Sodium Tungstate Na2WO4 Dissolved D Calcium Zirconate CaZrO3 Dissolved E Tungstophosphoric Acid H3PW12O40 Dissolved F Phosphomolybdic Acid H3PMoI2O40 Dissolved G Potassium Manganate K2MnO4 Disproportionate H Sodium Titanate Na2TiO3 Not Dissolved I Zinc Oxide ZnO Dissolved J Magnesium Oxide MgO Dissolved Table 2 Conditions for Forming the Insulating Coating Solution Insulating Coating Solution Coating and Drying Conditions Metal Phosphate 100 parts by mass Silica Content of Colloidal Silica Oxoacid Compound Concentration of Solid Content Other Additives Type: Ratio (% by mass) parts by mass Type parts by mass (solid content) % by mass Type parts by mass Heating Rate from 100 to 600°C (°C / sec.) Temperature (°C) Time (sec.) Example of Invention 1 Al:100 50 A 10 30 - 70 850 30 Petition 870250088602, dated 09 / 30 / 2025, p. 43 / 55 / ​​​​41 Example of Invention 2 Al:75, Mg:25 45 A 8 30 - 70 850 60 Example of Invention 3 Al:100 40 B 14 10 Phosphoric Acid 2 80 870 30 Example of Invention 4 Al:75, Mg:25 35 B 5 45 - 90 880 50 Example of Invention 5 Al:100 50 C 22 45 - 90 880 80 Example of Invention 6 Al:100 40 D 18 9 Phosphoric Acid 3 40 820 10 Example of Invention 7 Al:100 55 E 40 15 - 70 850 30 Example of Invention 8 Al:100 50 F 12 20 - 40 Comparative Example 1: Al:75, Mg:25 40 A 0.3 30 - 70 850 30 Comparative Example 2: Al:100 40 A 55 30 - 220 850 90 Comparative Example 3: Al:75, Mg:25 40 B 0.5 45 - 90 880 30 Comparative Example 4: Al:100 45 B 60 9 - 40 820 60 Comparative Example 5: Al:75, Mg:25 40 C 0.8 30 - 210 870 50 Comparative Example 6: Al:75, Mg:25 40 C 55 45 - 70 850 30 Comparative Example 7: Al:100 40 D 0.5 53 - 20 850 10 Comparative Example 8 Al:75,Mg: 25 50 D 75 20 - 40 820 80 Example Comparative 9 Al: 100 50 G 10 30 - 70 850 30 Example Comparative 10 Al: 100 50 H 10 30 - 70 850 30 Example Comparative 11 Al: 100 50 I 5 30 - 80 870 60, Petition 870250088602, dated 09 / 30 / 2025, pages 44 / 55 / 41 Comparative Example 12 Al: 100 50 J 5 30 - 95 850 40 Comparative Example 13 Al: 100 25 A 10 55 - 70 850 30 Comparative Example 14 Al: 100 170 A 10 15 - 70 850 30 Comparative Example 15 Al: 100 55 - 0.0 30 - 70 850 30 Comparative Example 16 Al: 100 50 A 10 15 - 20 850 30 Comparative Example 17 Al: 100 50 A 10 15 - 120 850 30

[00141] The chemical composition of the base steel sheet of the grain-oriented electrical steel sheet obtained contained Si: 3.2% by mass, Al sol.: 0.01% by mass, Mn: 0.07% by mass, N: less than 0.001% by mass and C: 0.001% by mass, with the remainder being Fe and impurities.

[00142] In addition, the content (parts by mass) of amorphous silica and one or more oxoacid compounds of tungsten, vanadium, molybdenum, and zirconium in the insulating coating when the amount of metal phosphate was 100 parts by mass was measured as described above using an energy-dispersive X-ray analyzer. The oxoacid compound formed a matrix of the insulating coating in a state compatible with the metal phosphate.

[00143] Table 3 shows the results.

[00144] After the formation of the insulating coating, the water content of the insulating coating of the grain-oriented electrical steel sheet was measured using the Karl Fischer method (current titration method) after 24 hours of holding at room temperature.

[00145] Specifically, approximately 3 g of a sample are placed in a closed heating oven and heated to 105°C in a stream of nitrogen gas to vaporize the moisture. The vaporized moisture undergoes 150 Petition 870250088602, dated 09 / 30 / 2025, page 45 / 55 / ​​41 ml of the indicator solution in which the Karl Fischer reagent was dissolved, and the moisture was dissolved in the reagent solution for 30 minutes and then analyzed quantitatively using the Karl Fischer titration method described in JIS document K0113 (2005).

[00146] Table 3 shows the results. Table 3 Insulating Coating Content in 100 parts. Mass of Metallic Phosphate Water Content (% by mass) Amorphous Silica (parts by mass) Oxoacid Compound Type parts by mass Example of Invention 1 50 A 10 0.01 Example of Invention 2 45 A 8 0.01 Example of Invention 3 40 B 14 0.01 Example of Invention 4 35 B 5 0.02 Example of Invention 5 50 C 22 0.02 Example of Invention 6 40 D 18 0.03 Example of Invention 7 55 E 40 0.01 Example of Invention 8 50 F 12 0.02 Comparative Example 1 40 A 0.3 0.05 Comparative Example 2 40 A 55 0.04 Comparative Example 3 40 B 0.5 0.08 Comparative Example 4 45 B 60 0.04 Example Comparative 5 40 C 0.8 0.08 Example Comparative 6 40 C 55 0.04 Example Comparative 7 40 D 0.5 0.08 Example Comparative 8 50 D 75 0.04 Example Comparative 9 50 G 10 0.05 Example Comparative 10 50 H 10 0.05 Example Comparative 11 50 I 5 0.06 Example Comparative 12 50 J 5 0.09 Example Comparative 13 25 A 10 0.05 Example Comparative 14 170 A 10 0.05 Example Comparative 15 55 - 0.0 0.Example 8 Comparative 16 50 A 10 0.05 Example Comparative 17 50 A 10 0.05,

[00147] In addition, the resulting grain-oriented electrical steel sheet was evaluated for coating tension, coating adhesion, Petition 870250088602, dated 09 / 30 / 2025, page 46 / 55 / ​​41 magnetic characteristics, corrosion resistance and dissolution resistance as follows.

[00148] In the measurement, corrosion resistance was measured after 24 hours of aging at room temperature after the formation of the insulating coating, and coating tension, coating adhesion, magnetic characteristics and resistance to dissolution were measured after 168 hours of aging at constant temperature and humidity of 50°Cx80% to measure the characteristics after moisture absorption. <Tensão de Revestimento>

[00149] The coating voltage was calculated by reverse calculation from the curved state when a surface of the insulating coating was removed.

[00150] When the obtained coating stress was 4.0 MPa or more, it was determined that the coating had sufficient coating stress. <Adesão do Revestimento>

[00151] Adhesion was evaluated by means of a flexural adhesion test using a 10 mmφ cylinder after stress relief annealing of a sample having a width of 30 mm and a length of 300 mm at 800°C for 2 hours in a nitrogen flow. The evaluation criteria were as follows according to the peel width, and when the peel width was 3 or more (3 to 5), it was determined that the coating adhesion was sufficient.

[00152] 5: No peeling 4: Almost no peeling (the peeling portion is 1 mm or less) 3: Peeling was observed with a width of more than 1 mm to less than 1 / 3. 2: Peeling was observed with a width of 1 / 3 to 1 / 2. Petition 870250088602, dated 09 / 30 / 2025, pages 47 / 55 / 41 1: Peeling width greater than 1 / 2 or across the entire width.<Características Magnéticas>

[00153] B8 (magnetic flux density at a magnetizing force of 800 A / m) and W17 / 50 (iron loss per mass at a magnetic flux density amplitude of 1.7 T and 50 Hz) were measured. These characteristic values ​​were measured using the single plate tester (SST) according to JIS C2556 (2015). <Resistência à Corrosão>

[00154] After the formation of the insulating coating, a 5% aqueous NaCl solution was naturally dripped onto the sample for 7 hours in an atmosphere at 35°C, according to the salt spray test method described in JIS document Z2371 (2015) with respect to the grain-oriented electrical steel sheet held at room temperature after a lapse of 24 hours.

[00155] The rust area was evaluated on a 10-point scale. The evaluation criteria were as follows. When the score was 5 or more (5 to 10), it was determined that the coating had sufficient corrosion resistance.

[00156] 10: No rust generation occurred. 9: Rust was generated in an extremely small quantity (the area ratio was 0.10% or less). 8: Rust was generated in an area ratio of more than 0.10% and 0.25% or less. 7: Rust was generated in an area ratio of more than 0.25% and 0.50% or less. 6: Rust was generated in an area ratio of more than 0.50% and 1.0% or less. 5: Rust was generated in an area ratio of more than 1.0% and 2.5% or less. 4: Rust was generated at an area ratio of more than Petition 870250088602, dated 09 / 30 / 2025, pages 48 / 55 / 41 2.5% and 5% or less 3: Rust was generated in an area ratio of more than 5% and 10% or less. 2: Rust was generated in an area ratio of more than 10% and 25% or less. 1: Rust was generated at an area ratio of more than 25%<Resistência à Dissolução>

[00157] The amount of phosphoric acid eluted from the sample was measured.

[00158] The sample was boiled in pure boiled water for 10 minutes, the amount of phosphorus eluted in the pure water was measured, and the amount of phosphoric acid was divided by the area of ​​the insulating coating of the boiled grain-oriented electrical steel sheet to obtain the amount of dissolution. The amount of phosphoric acid eluted in the pure water was calculated by cooling the pure water (solution) in which the phosphoric acid was eluted, diluting the cooled solution with pure water, and measuring the phosphoric acid concentration of the sample using ICP-AES.

[00159] When the amount of dissolution was less than 40 mg / m2, it was determined that the resistance to dissolution was exceptional. Table 4 Insulating Coating Characteristics Magnetic Characteristics Observations Coating Adhesion Resistance to Dissolution (mg / m2) Corrosion Resistance Coating Tensile Strength (MPa) B8 (T) W17 / 5 0 (W / kg) Treatment Liquid Stability / Surface Appearance / etc. Example of Invention 1 4 15 10 9.4 1.93 0.70 Bright / Uniform Example of Invention 2 4 12 10 9.5 1.94 0.67 Bright / Uniform Example of Invention 3 4 20 9 9.2 1.93 0.68 Bright / Uniform Example of Invention 4 4 16 9 9.1 1.94 0.69 Bright / Uniform Example of Invention 5 4 22 7 8.3 1.92 0.72 Uniform Color Tone Example of Invention 6 5 30 7 8.7 1.91 0.71 Extremely Highly Uniform Petition 870250088602, dated 09 / 30 / 2025, pages 49 / 55 / 41 Example of Invention 7 4 4 5 8.5 1.92 0.71 Uniform Color Tone Example of Invention 8 4 33 6 8.7 1.91 0.69 Uniform Color Tone Comparative Example 1 4 43 9 7.8 1.94 0.77 Whitish / Non-Uniform Comparative Example 2 3 36 3 3.7 1.91 0.81 Whitish / Non-Uniform Comparative Example 3 4 47 8 6.2 1.93 0.77 Whitish / Non-Uniform Comparative Example 4 3 33 4 3.9 1.92 0.81 Dull, but Uniform Comparative Example 5 4 51 8 8.1 1.91 0.75 Dull, but Uniform Comparative Example 6 4 37 6 3.5 1.92 0.82 White / Non-Uniform Comparative Example 7 4 54 6 6.7 1.93 0.75 White / Non-Uniform Comparative Example 8 3 44 6 2.9 1.92 0.84 Matte, but Uniform Comparative Example 9 3 42 9 4.3 1.93 0.83 Matte, but Uniform Comparative Example 10 4 49 7 3.8 1.91 0.87 White / Non-Uniform Comparative Example 11 4 46 8 7.5 1.90 0.77 White / Non-Uniform Comparative Example 12 4 53 7 7.2 1.93 0.76 White / Non-Uniform Comparative Example 13 3 46 4 6.9 1.91 0,79 White / Non-Uniform Comparative Example 14 1 36 6 5.9 1.92 0.79 White / Non-Uniform Comparative Example 15 4 55 8 7.6 1.93 0.75 Uniform Color Tone Comparative Example 16 4 41 8 6.5 1.93 0.71 Uniform Color Tone Comparative Example 17 2 30 4 7.2 1.92 0.74 Off-White / Non-Uniform

[00160] As can be seen from the results in Tables 1 to 4, in Invention Examples 1 to 8, a metallic phosphate, amorphous silica, and one or more oxoacid compounds of tungsten, vanadium, molybdenum, and zirconium were contained in a predetermined ratio, and the water content of the insulating coating was also 0.04% by mass or less. As a result, a grain-oriented electrical steel sheet having an insulating coating with corrosion resistance, coating adhesion, and voltage was obtained. Petition 870250088602, dated 09 / 30 / 2025, p. 50 / 55 / 41 sufficient coating (equal to or greater than conventional coatings) and exceptional resistance to dissolution. Furthermore, in these grain-oriented electrical steel sheets, the magnetic characteristics were also equal to or greater than those of conventional grain-oriented electrical steel sheets.

[00161] On the other hand, in Comparative Examples 1, 3, 5, 7 and 15, as the proportion of the oxoacid compound in the insulating coating was excessively low and the water content was greater than 0.04% by mass, the resistance to dissolution was poor.

[00162] In Comparative Examples 2 and 4, the amount of the oxoacid compound was excessively large, and the corrosion resistance and coating tension were poor.

[00163] In Comparative Examples 6 and 8, the amount of the oxoacid compound was excessively large and the coating tension was poor.

[00164] In Comparative Examples 9 to 12, the oxoacid compound was not one or more oxoacid compounds of tungsten, vanadium, molybdenum, and zirconium, and the water content of the insulating coating was high. As a result, the resistance to dissolution was poor.

[00165] In Comparative Example 13, the proportion of amorphous silica in the insulating coating was excessively low and the water content was high. As a result, corrosion resistance and dissolution resistance were poor.

[00166] In Comparative Example 14, the proportion of amorphous silica in the insulating coating was excessively large and the coating adhesion was poor.

[00167] In Comparative Example 16, the heating rate under the coating and drying conditions was low, and the water content of the insulating coating was high. As a result, the resistance to dissolution was poor.

[00168] In Comparative Example 17, the heating rate under the Petition 870250088602, dated 09 / 30 / 2025, page 51 / 55 / ​​41. The coating and drying conditions were poor, bumps or similar issues occurred, and the water content of the insulating coating was also high. As a result, coating adhesion and corrosion resistance were poor. INDUSTRIAL APPLICABILITY

[00169] According to the present invention, it is possible to provide a grain-oriented electrical steel sheet in which the amount of phosphoric acid eluted from an insulating coating is small, and a method for forming the insulating coating. Therefore, the industrial applicability is high. Petition 870250088602, dated 09 / 30 / 2025, pages 52 / 55

Claims

1 / 2 CLAIMS 1. Grain-oriented electrical steel sheet, characterized in that it comprises: a base steel sheet; a glass coating formed on a surface of the base steel sheet; and an insulating coating formed on a surface of the glass coating, wherein the base steel sheet has a sheet thickness of 0.15 to 0.35 mm, the insulating coating contains a metallic phosphate, amorphous silica and one or more oxoacid compounds of tungsten, vanadium, molybdenum and zirconium, the amorphous silica being contained in an amount of 30 to 150 parts by mass, and the oxoacid compound being contained in an amount of 1.0 to 50 parts by mass in total relative to 100 parts by mass of the metallic phosphate, and the insulating coating has a water content of 0 to 0.04% by mass.

2. Grain-oriented electrical steel sheet according to claim 1, characterized in that the oxoacid compound is a tungstate, a phosphotungstate, a silicotungstate, a vanadate, a phosphomolybdate or a zirconate.

3. Method for forming an insulating coating, characterized in that it comprises: a solution preparation step to prepare an insulating coating solution containing 30 to 150 parts by mass of colloidal silica in terms of silica content and 1.0 to 50 parts by mass in total of one or more oxoacid compounds of tungsten, vanadium, molybdenum and zirconium in relation to 100 parts by mass of a metallic phosphate, the insulating coating solution having a solid content concentration of 8 to 50% by mass; and a coating and drying step of applying the insulating coating solution to a steel sheet, heating the steel sheet to a temperature range of 800 to 900°C so that a heating rate between 100 and 600°C is 40 to 200°C / sec, and maintaining the steel sheet in the temperature range for 5 to 90 seconds.

4. Method for forming an insulating coating according to claim 3, characterized in that, in the solution preparation step, 1 to 5 parts by mass of phosphonic acid are added to the insulating coating solution in relation to 100 parts by mass of metallic phosphate. Petition 870250088602, dated 09 / 30 / 2025, pp. 54 / 55