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

Description

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

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

[002] Priority is claimed in Japanese Patent Application No. 2023-064826, filed on April 12, 2023, the contents of which are incorporated herein by reference. FUNDAMENTALS OF THE TECHNIQUE

[003] A grain-oriented electrical steel sheet is mainly used in a transformer. The transformer is continuously magnetized for a long period of time, from installation to disposal, and continues to generate energy loss. Therefore, the energy loss when the transformer is magnetized by alternating current, i.e., the iron loss, is a primary index for determining the transformer's performance.

[004] To reduce iron loss from grain-oriented electrical steel sheet, many techniques have been developed so far from the point of view of (a) increasing development in the orientation {110} <001> (Goss orientation), (b) increasing the amount of a solid solution element, such as Si, to increase the electrical resistance of the steel sheet, or (c) reducing the thickness of the sheet of the electrical steel sheet.

[005] In addition, applying tension to the steel sheet is effective in reducing iron loss. It is an effective means of reducing iron loss to form a coating made of a material with a coefficient of thermal expansion lower than that of the steel sheet on a sheet surface at a high temperature. A forsterite-based coating (inorganic coating) with excellent coating adhesion, generated by a reaction between an oxide on the surface of a sheet and an annealing separator in a step of Petition 870250091659, dated 07 / 10 / 2025, page 12 / 62 / 46, annealing of an electrical steel sheet, is a coating capable of applying tension to the steel sheet.

[006] For example, a method for forming an insulating coating by baking a coating liquid containing mainly colloidal silica and a phosphate onto the surface of a sheet, described in Patent Document 1, is an effective method for reducing iron loss because the method has a large stress application effect on the steel sheet. Therefore, a general method for manufacturing a grain-oriented electrical steel sheet is to leave the forsterite-based coating generated in the finishing annealing step and form an insulating coating containing mainly a phosphate onto the forsterite-based coating.

[007] However, in recent years, there has been a growing demand for miniaturization and high performance of a transformer, and to miniaturize the transformer, it is necessary that a grain-oriented electrical steel sheet have excellent iron loss in a high magnetic field, so that the iron loss is favorable even when the magnetic flux density is high. At the same time, in recent years, it has been clarified that forsterite-based coating hinders the movement of a domain wall and adversely affects iron loss. In a grain-oriented electrical steel sheet, a magnetic domain changes by the movement of a domain wall under an alternating magnetic field.The smooth and rapid movement of the domain wall is effective in reducing iron loss, but the forsterite-based coating itself is a non-magnetic body and has an irregular structure at the steel plate / coating interface, and this irregular structure hinders domain wall movement. Therefore, forsterite-based coating is considered to adversely affect iron loss.

[008] Therefore, as a means of improving iron loss in high magnetic fields, a coating removal method was studied. Petition 870250091659, dated 07 / 10 / 2025, page 13 / 62 / 46 inorganic using mechanical means, such as polishing, or chemical means, such as pickling. Furthermore, a technique for manufacturing a grain-oriented electrical steel sheet without inorganic coating, avoiding the generation of an inorganic coating in high-temperature finish annealing, and a technique for bringing the surface of a sheet to a mirror-like surface state (in other words, a technique for magnetically smoothing the surface of a sheet) were studied.

[009] As a technique for avoiding the generation of an inorganic coating, for example, Patent Document 2 describes a technique in which a product formed on the surface is removed by pickling after normal finish annealing, and then a sheet surface is brought to a mirror surface state by chemical polishing or electrolytic polishing. It has been found that a better iron loss improvement effect can be obtained by forming a voltage-applied insulating coating on the surface of a grain-oriented electrical steel sheet without an inorganic coating, obtained by a known method. Furthermore, the voltage-applied insulating coating can impart various characteristics such as corrosion resistance, heat resistance and slip resistance, in addition to improving iron loss.

[0010] However, the inorganic coating has an effect of exhibiting insulating properties and an effect of an intermediate layer to ensure adhesion when a tension coating (tension-applied insulating coating) is formed. That is, as the inorganic coating is formed in a state of deep penetration into the steel sheet, the inorganic coating has excellent adhesion to the steel sheet, which is metallic. Therefore, when a tension-applied coating (tension coating) containing colloidal silica, a phosphate or similar as a main component is formed on the surface of the inorganic coating, the adhesion of the coating is excellent. Petition 870250091659, dated 07 / 10 / 2025, page 14 / 62 / 46

[0011] On the other hand, since it is generally difficult to bond metal and oxide to each other, it is difficult to ensure sufficient adhesion between the tension coating and the surface of a steel sheet when the inorganic coating is not present.

[0012] Therefore, in a case where a tension coating is formed on a grain-oriented electrical steel sheet without inorganic coating, it was studied to form a layer that plays a role as an intermediate layer of the inorganic coating.

[0013] For example, Patent Document 3 describes a technique in which a grain-oriented electrical steel sheet, without inorganic coating, is annealed in a weakly reducing atmosphere, and the silicon inevitably contained in a silicon steel sheet is selectively thermally oxidized to form a SiO2 layer on the surface of the sheet, and then a voltage-applied type insulating coating is formed. Patent Document 4 describes a technique in which a grain-oriented electrical steel sheet without inorganic coating is subjected to an anodic electrolytic treatment in an aqueous silicate solution to form a SiO2 layer on the surface of a sheet, and then a voltage-applied type insulating coating is formed.

[0014] However, in the technique described in Patent Document 3, it is necessary to prepare an annealing plant capable of controlling an atmosphere to perform annealing in a weakly reducing atmosphere, and there is a problem with the cost of the treatment. In the technique described in Patent Document 4, it is necessary to prepare a new electrolysis treatment plant to obtain a SiO2 layer that maintains sufficient adhesion to a voltage-applied insulating coating on a sheet surface, performing an anodic electrolytic treatment in an aqueous silicate solution, and there is a problem with the cost of the treatment.

[0015] On the other hand, Patent Document 5 describes a plate Petition 870250091659, dated 07 / 10 / 2025, page 15 / 62 / 46 of grain-oriented electrical steel including: a base steel sheet; and an insulating coating formed on the surface of the base steel sheet, in which the insulating coating includes: an intermediate layer that is formed on the side of the base steel sheet and contains a crystalline metallic phosphate; and a tension coating layer formed on the surface side of the insulating coating. In grain-oriented electrical steel sheet, the intermediate layer may be formed by chemical conversion treatment.

[0016] Furthermore, Patent Document 6 describes a method for manufacturing a one-way silicon steel sheet, in which a secondary recrystallized one-way silicon steel sheet is formed with a coating containing mainly zinc phosphate in an amount of 0.1 g / m2 or more and 10 g / m2 or less per surface of the steel sheet before a voltage-transmitting insulating coating is formed. List of Citations Patent Documents

[0017] Patent Document 1: Japanese Patent Application No. Examined, First Publication No. S48-039338

[0018] Patent Document 2: Unexamined Japanese Patent Application, First Publication No. S49-96920

[0019] Patent Document 3: Unexamined Japanese Patent Application, First Publication No. H06-184762

[0020] Patent Document 4: Japanese Patent Application No. Examined, First Publication No. H11-209891

[0021] Patent Document 5: International Publication PCT No. WO 2022 / 215710

[0022] Patent Document 6: Japanese Patent Application No. Examined, First Publication No. 2005-139481 SUMMARY OF THE INVENTION Technical Problem Petition 870250091659, dated 07 / 10 / 2025, page 16 / 62 / 46

[0023] However, the present inventors studied conventional techniques, as described in Patent Documents 5 and 6, and found that when a grain-oriented electrical steel sheet obtained by a conventional technique is provided with a coating containing mainly a metallic phosphate (intermediate layer) to improve adhesion, the magnetic characteristics may deteriorate. At this point, the present inventors studied further and found that the magnetic characteristics deteriorate because, when the intermediate layer is formed, i.e., when the chemical conversion treatment is performed, the metallic phosphate crystal is precipitated and, at the same time, the surface of the base metal is etched to form an irregular structure at the interface between the base metal and the intermediate layer, so that the magnetic flux is suppressed in the base metal.

[0024] Therefore, an object of the present invention is to provide a grain-oriented electrical steel sheet that is excellent in adhesion with a coating under tension and magnetic characteristics, and does not reduce the space factor of a transformer (core), and a method for forming an insulating coating for it. Solution to the Problem

[0025] The present inventors have found that: when a layer containing a metallic phosphate is provided as an intermediate layer that intensifies the adhesion between the base steel sheet and the tension coating layer, the chemical treatment solution is adjusted to have ratios of metallic ion, phosphate ion and nitrate ion in a specific range and thus the interface between the intermediate layer and the base metal can be smoothed, so that a grain-oriented electrical steel sheet that is excellent in adhesion with a tension coating and magnetic characteristics, and does not reduce the space factor of a transformer (core) can be obtained.

[0026] The present invention was made with a view to Petition 870250091659, dated 07 / 10 / 2025, page 17 / 62 / 46 verifications above. The essence of an embodiment according to the present invention is as follows.

[0027] [1] In one embodiment of the present invention, a grain-oriented electrical steel sheet includes: a base steel sheet; and an insulating coating formed on a surface of the base steel sheet, wherein the insulating coating includes: An intermediate layer that is formed on one side of the base steel sheet and contains a crystalline metallic phosphate; and a tension coating layer formed on one side of the insulating coating surface, and when an interface between the base steel sheet and the intermediate layer is observed with a scanning electron microscope at a magnification of 5000 in a cross-section along a thickness direction of the intermediate layer, the ratio of an interface length L to a width W of the analyzed image is 100.0 to 120.0%.

[0028] [2] In the grain-oriented electrical steel sheet according to claim 1, the tension coating layer may contain a metallic phosphate and silica.

[0029] [3] In one embodiment of the present invention, a method for forming an insulating coating, which is a method for forming the insulating coating included in the grain-oriented electrical steel sheet according to [1], includes: A finishing annealing step involves applying an annealing separator containing Al2O3 in an amount of 10 to 100% by mass onto a steel sheet, drying the steel sheet, and then performing finish annealing of the steel sheet. a step to remove excess annealing separator from the steel sheet after the Petition 870250091659, dated 07 / 10 / 2025, page 18 / 62 / 46 finishing annealing stage; a pickling step to pickle the steel sheet after the annealing separator removal step with 0.1 to 5% by mass of an inorganic acid selected from the group consisting of sulfuric acid, chloric acid, nitric acid and phosphoric acid for 1 to 20 seconds; an immersion step to immerse the steel sheet after the pickling step in a treatment liquid containing a metallic phosphate, an oxidizing agent and an iron ion; A drying step to extract the steel sheet after the immersion step in the treatment liquid, remove excess treatment liquid, and then dry the steel sheet; and a tension coating layer formation step to apply a coating liquid containing a metallic phosphate and colloidal silica, the metallic phosphate and colloidal silica contained in a total concentration of 10 to 40% by mass, in terms of solid content, to the steel sheet after the drying step, dry the steel sheet and then hold the steel sheet at a sheet temperature of 700 to 950°C for 10 to 120 seconds, and the treatment liquid has: a concentration of metal ions of 1.0 to 10.0 g / L; a phosphate ion concentration of 2.0 to 25.0 g / L; a nitrate ion concentration of 2.0 to 40.0 g / L; and an iron ion concentration of 1.0 to 20.0 g / L, wherein the phosphate ion concentration is in a ratio of 1.5 to 5.0 relative to the metal ion concentration, and the nitrate ion concentration is in a ratio of 0.5 to 10.0 relative to the phosphate ion concentration.

[0030] [4] In the method for forming an insulating coating according to [3], the immersion step, the steel sheet after the pickling step can be immersed in the treatment liquid having a liquid temperature of 20 to Petition 870250091659, dated 07 / 10 / 2025, page 19 / 62 / 46 85°C for 2 to 60 seconds.

[0031] [5] In the method for forming an insulating coating according to [3], the concentration of nitrate ions can be from 2.0 to 25.0 g / L. Advantageous Effects of the Invention

[0032] According to one embodiment of the present invention, it is possible to provide a grain-oriented electrical steel sheet that is excellent in adhesion with a coating due to voltage and magnetic characteristics, and does not reduce the space factor of a transformer (core), and a method for forming an insulating coating for this purpose. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] [Figure 1] An example of a cross-sectional view of a grain-oriented electrical steel sheet according to the present embodiment.

[0034] [Figure 2] A schematic view to illustrate how to determine the irregularity index according to the modality. DESCRIPTION OF THE MODALITIES

[0035] A grain-oriented electrical steel sheet according to an embodiment of the present invention (grain-oriented electrical steel sheet according to the embodiment) and a method for manufacturing a grain-oriented electrical steel sheet according to the embodiment will be described, the method including a method for forming an insulating coating embedded in the grain-oriented electrical steel sheet according to the embodiment.

[0036] First, a grain-oriented electrical steel sheet will be described according to the embodiment.

[0037] As illustrated in figure 1, a grain-oriented electrical steel sheet 100 according to the embodiment has a base steel sheet 1 and an insulating coating 2 formed on the surface of the base steel sheet 1.

[0038] The grain-oriented electrical steel sheet 100 according to the embodiment does not have substantially any coating based on Petition 870250091659, dated 07 / 10 / 2025, page 20 / 62 / 46 forsterite on the surface of the base steel sheet 1. That is, in this embodiment, a forsterite-based coating is not intentionally formed on the surface of the base steel sheet 1. However, when the amount of forsterite-based coating is 1 g / m2 or less, its presence is permitted (in this case, in a part between the base steel sheet 1 and the insulating coating 2). That is, the oriented grain electrical steel sheet 100 according to the embodiment may have a forsterite-based coating in an amount of 0 to 1 g / m2 on the surface of the base steel sheet 1.

[0039] The insulating coating 2 includes: a tension coating layer 22 formed on the surface side of the insulating coating 2 (i.e., the surface side of the grain-oriented electrical steel sheet 100); and an intermediate layer 21 that is formed on the base steel sheet side 1 and contains a crystalline metal phosphate.

[0040] Regarding intermediate layer 21, when the interface between the base steel plate and the intermediate layer is observed with a scanning electron microscope at a magnification of 5000 in a cross-section along the thickness direction of the intermediate layer, the ratio of the interface length L to the width W of the analyzed image (roughness index) is 100 to 120%.

[0041] Next, each of the configurations of the 100 grain-oriented electrical steel sheet will be described. <Chapa de Aço Base> (Chemical Composition)

[0042] The grain-oriented electrical steel sheet 100, according to the embodiment, has a significant feature in the structure of the insulating coating 2 formed on the surface of the base steel sheet 1. The chemical composition of the base steel sheet 1 included in the grain-oriented electrical steel sheet 100 is not limited. Therefore, to obtain characteristics generally required for Petition 870250091659, dated 07 / 10 / 2025, page 21 / 62 / 46, an electrically oriented grain steel sheet, base steel sheet 1 preferably contains the following components as a chemical composition. In this embodiment, the % relating to the chemical composition is % by mass, unless otherwise specified. C: 0.010% or less

[0043] Carbon (C) is an effective element in controlling the microstructure of steel sheet in stages prior 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, are deteriorated. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to the 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%, the microstructure control effect is saturated and the manufacturing cost is only increased. Therefore, the C content can be 0.0001% or more. Yes: 2.50 to 4.00%

[0044] Si (silicon) is an element that increases the electrical resistance of grain-oriented electrical steel sheet and improves iron loss characteristics. When the Si content is less than 2.50%, it is not possible to obtain a sufficient eddy current loss reduction effect. Therefore, the Si content is preferably 2.50% or more. The Si content is more preferably 2.70% or more, and even more preferably 3.00% or more.

[0045] On the other hand, when the Si content exceeds 4.00%, 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 4.00% or less. The Si content is more Petition 870250091659, dated 07 / 10 / 2025, page 22 / 62 / 46 preferably 3.80% or less and even more preferably 3.70% or less. Mn: 0.01 to 0.50%

[0046] Mn (manganese) is an element that binds to S in the manufacturing process to form MnS. This precipitate acts as an inhibitor (normal grain growth inhibitor) 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.

[0047] On the other hand, when the Mn content exceeds 0.50%, secondary recrystallization does not occur and the magnetic characteristics of the steel are deteriorated. 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. N: 0.010% or less

[0048] 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 inhibitor remains excessively in the grain-oriented electrical steel sheet, and the magnetic characteristics are deteriorated. 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.

[0049] On the other hand, the lower limit 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. Petition 870250091659, dated 07 / 10 / 2025, page 23 / 62 / 46 Al sol.: 0.020% or less

[0050] Al sol. (acid-soluble 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 Al sol. content in the base steel sheet exceeds 0.020%, the inhibitor remains excessively in the base steel sheet, deteriorating the magnetic characteristics. Therefore, in the base steel sheet of the 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 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

[0051] Sulfur (S) is an element that binds to Mn in the manufacturing process to form MnS, which acts as an inhibitor. However, when the S content exceeds 0.010%, the remaining inhibitor deteriorates the magnetic characteristics. Therefore, in the base steel sheet of the grain-oriented electrical steel sheet according to the embodiment, the S content is preferably 0.010% or less. The S content in the grain-oriented electrical steel sheet is most preferably as low as possible. 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. Balance: Iron and impurities

[0052] The chemical composition of the base steel sheet of the grain-oriented electrical steel sheet, according to the modality, may contain the Petition 870250091659, dated 07 / 10 / 2025, page 24 / 62 / 46 elements described above, with the equilibrium being Fe and impurities. However, the base steel sheet may also contain Sn, Cu, Se and Sb in the following ranges in order to improve magnetic and similar characteristics. Furthermore, for example, even when the base steel sheet contains any one or more of W, Nb, Ti, Ni, Co, V, Cr and Mo in a total amount of 1.0% or less as elements other than these elements, the effect of the grain-oriented electrical steel sheet according to the modality is not impaired.

[0053] Here, impurities are contaminated by ore or scrap as a raw material, or from a manufacturing environment or similar when the base steel sheet is industrially manufactured. Impurities mean elements that may be included in such a content that the action of the grain-oriented electrical steel sheet according to the modality is not adversely affected. Sn: 0 to 0.50%

[0054] Tin (Sn) is an element that contributes to the improvement in magnetic characteristics through the control of the primary crystallization 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 preferably 0.02% or more and even more preferably 0.03% or more.

[0055] On the other hand, when the Sn content exceeds 0.50%, secondary recrystallization is unstable and the magnetic characteristics are deteriorated. 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%

[0056] Copper (Cu) is an element that contributes to an increase in the occupation of the Goss orientation in a secondary recrystallization structure. To obtain the above effect, the Cu content is preferably of Petition 870250091659, dated 07 / 10 / 2025, p. 25 / 62 / 46 0.01% or more. The Cu content is more preferably 0.02% or more, and even more preferably 0.03% or more.

[0057] 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%

[0058] Selenium is an element that has an effect of improving magnetic characteristics. When Se is included, the Se content is preferably 0.001% or more, so that Se favorably exhibits the effect of improving magnetic characteristics. The Se content is more preferably 0.003% or more and even more preferably 0.006% or more.

[0059] On the other hand, when the Se content exceeds 0.020%, the coating adhesion is deteriorated. Therefore, the Se content is preferably 0.020% or less. The Se content is more preferably 0.015% or less and even more preferably 0.010% or less. Sb: 0 to 0.50%

[0060] Sb (antimony) is an element that has an effect of improving magnetic characteristics. When Sb is included, the Sb content is preferably 0.005% or more, so that Sb favorably exhibits the effect of improving magnetic characteristics. The Sb content is more preferably 0.01% or more and even more preferably 0.02% or more.

[0061] On the other hand, when the Sb content exceeds 0.50%, the coating adhesion is significantly deteriorated. Therefore, the Sb content is preferably 0.50% or less. The Sb content is more preferably 0.30% or less and even more preferably 0.10% or less. Petition 870250091659, dated 07 / 10 / 2025, p. 26 / 62 / 46

[0062] As described above, for example, the chemical composition of the base steel sheet of the grain-oriented electrical steel sheet according to the embodiment contains the elements described above, with the equilibrium being Fe and impurities.

[0063] The chemical composition of the base steel sheet of the grain-oriented electrical steel sheet according to the embodiment can be measured using a known ICP emission spectrometry. Note that, at the time of measurement, in a case where an insulating coating is formed on the surface, the measurement is performed after the insulating coating has been peeled off. As a peeling method, it is possible to peel off the insulating coating by immersing the steel sheet in a high-concentration alkaline solution (e.g., a 30% sodium hydroxide solution heated to 85°C) for 20 minutes or more. It is possible to visually determine whether or not it has been peeled off. In the case of a small sample, the insulating coating can be peeled off by grinding the surface. <Revestimento Isolante>

[0064] In the grain-oriented electrical steel sheet 100 according to the embodiment, the insulating coating 2 is formed on the surface of the base steel sheet 1.

[0065] The insulating sheath 2 has a structure in which the intermediate layer 21 and the tension sheath 22 are rolled in this order from the side of the base steel sheet 1. (Intermediate layer)

[0066] As described above, in general, a grain-oriented electrical steel sheet has a forsterite-based coating generated in a finishing annealing step and an insulating coating (voltage insulating coating) formed over it. However, in recent years, it has been clarified that the forsterite-based coating hinders the movement of a domain wall and adversely affects iron loss and, Petition 870250091659, dated 07 / 10 / 2025, page 27 / 62 / 46 therefore, to further improve the magnetic characteristics, a grain-oriented electrical steel sheet without the forsterite-based coating was studied. However, when the forsterite-based coating is not present, it is difficult to ensure sufficient adhesion between the voltage-insulating coating and the surface of the base steel sheet.

[0067] In the grain-oriented electrical steel sheet 100 according to the embodiment, the intermediate layer 21 containing a crystalline metallic phosphate is formed between the base steel sheet 1 and the tension coating layer 2 to improve the adhesion between the base steel sheet 1 and the tension coating layer 22 by means of the intermediate layer 21. This occurs because when the intermediate layer 21 contains a crystalline metallic phosphate, the tension coating formed over it (after being formed, it becomes the tension coating layer 22) also contains a crystalline metallic phosphate and therefore has a high affinity for it, thus exhibiting excellent adhesion between the intermediate layer and the tension coating layer.Furthermore, as described later, when the intermediate layer 1 is formed by immersion in a treatment liquid containing a metallic phosphate, the intermediate layer 1 can be formed on the surface of the base steel sheet 1 using a chemical reaction, and adhesion between the intermediate layer 21 and the base steel sheet 1 can also be ensured.

[0068] When the intermediate layer 21 does not contain a crystalline metal phosphate, the above effect cannot be obtained. The percentage of crystalline metal phosphate in the intermediate layer 21 is preferably 80% by mass or more, and may be 100% by mass. The metal phosphate is preferably any one of zinc phosphate, manganese phosphate, calcium zinc phosphate, and manganese iron phosphate from the point of view of adhesion.

[0069] The intermediate layer 21 may contain, as the equilibrium of metallic phosphate, an oxide or an element diffused from the base steel sheet 1, Petition 870250091659, dated 07 / 10 / 2025, p. 28 / 62 / 46 as Fe or Si.

[0070] Here, the present inventors studied the adhesion and magnetic characteristics of the intermediate layer 21 using a metallic phosphate and found that when an intermediate layer containing mainly a metallic phosphate is provided to try to improve the adhesion between the base metal and the insulating coating, the grain-oriented electrical steel sheet may have deteriorated magnetic characteristics. At this point, the present inventors studied further and found that the magnetic characteristics deteriorate because when the intermediate layer is formed, i.e., when the chemical conversion treatment is carried out, the phosphate crystal is precipitated and, at the same time, the surface of the base steel sheet is etched to form an irregular structure at the interface between the base steel sheet and the intermediate layer, so that the magnetic flux flowing in the base steel sheet is suppressed.

[0071] The present inventor has studied and verified that the irregularity index also affects the space factor. The irregularity index increases as the chemical treatment solution etches the surface of the steel sheet when the intermediate layer is formed, and at the same time, the fine irregularity on the surface side of the intermediate layer 21 also increases. Therefore, the fine irregularity of the tension coating layer 22 formed above the intermediate layer 21 also increases, resulting in a reduced space factor.

[0072] Therefore, in the grain-oriented electrical steel sheet according to the embodiment, the degree of irregularity (degree of irregularity) of the interface between the base steel sheet 1 and the intermediate layer 21 is reduced so that good adhesion and spacing factor are ensured, and the deterioration of magnetic characteristics is suppressed. Specifically, in the grain-oriented electrical steel sheet according to the embodiment, when the interface between the base steel sheet 1 and the intermediate layer 21 is observed with a Petition 870250091659, dated 07 / 10 / 2025, page 29 / 62 / 46 scanning electron microscope (SEM) with a magnification of 5000 in a cross-section along the thickness direction of the intermediate layer 21, the ratio of the interface length L to the width W of the analyzed image (roughness index), L / W, is 100.0 to 120.0%.

[0073] Figure 2 is a schematic view to illustrate how to determine the L / W roughness index and is a schematic cross-sectional view along the thickness direction of the intermediate layer 21.

[0074] First, as shown in Figure 2, the cross-section is observed at a magnification of 5000 with SEM to obtain an observation image including the interface between the base steel plate 1 and the intermediate layer 21. Then, in the observation image, both ends of the interface between the base steel plate 1 and the intermediate layer 21 are connected with a straight line, and the distance between the two points is defined as the width W of the analyzed image; the actual interface path between both ends of the interface (i.e., the curved path tracing the actual interface) is defined as the interface length L; and the roughness index L / W (%) is determined. The roughness index L / W is an index of the degree of roughness of the interface. When the roughness index L / W is small, the degree of roughness is small and the interface is excellent in smoothness.Note that the degree of irregularity to be observed varies depending on the SEM magnification. Therefore, the SEM magnification is in a suitable range for observing the interface and is 5000 times in this mode.

[0075] In the cross-section of the grain-oriented electrical steel sheet, the cross-section from which an observation image to measure the L / W roughness index is obtained is selected from the flat portion where the surface of the grain-oriented electrical steel sheet does not exhibit surface defects and is not surface processed. The L / W roughness index is calculated using the average value of the values ​​measured from an image. Petition 870250091659, dated 07 / 10 / 2025, page 30 / 62 / 46, observation in three points.

[0076] The width W of the analyzed image and the interface length L can be easily determined using a “LUZEX AP” application system created by NIRECO CORPORATION or similar on a cross-sectional image obtained by an electron microscope.

[0077] In this modality, the L / W irregularity index is 100.0 to 120.0%. When the L / W irregularity index exceeds 120.0%, the degree of irregularity at the interface increases and the magnetic characteristics may deteriorate. Therefore, the irregularity index is 120.0% or less, preferably less than 120.0%, more preferably 118.0% or less, even more preferably 115.0% or less, and even more preferably 110.0% or less. The lower limit of the L / W irregularity index is 100.0%. When the L / W irregularity index is 100.0%, the width W of the analyzed image and the interface length L correspond to each other, i.e., the degree of irregularity is zero and the interface is smooth.

[0078] The thickness of the intermediate layer 21 is preferably from 1.0 to 9.0 μm. When the average thickness of the intermediate layer 21 is less than 1.0 μm, the effect of improving adhesion between the base steel sheet 1 and the insulating coating 2 by means of the intermediate layer 21 is sometimes not sufficiently achieved. On the other hand, when the average thickness of the intermediate layer 21 exceeds 9.0 μm, the magnetic characteristics may deteriorate.

[0079] The thickness of the intermediate layer 21 can be determined by the following method.

[0080] The thickness of the intermediate layer 21 can be determined by measurement using a scanning electron microscope (SEM) and an energy-dispersive element analyzer. That is, a sample containing a base steel sheet 1 and an insulating coating layer 2 is cut, and the polished cross-section is observed with a scanning electron microscope. Petition 870250091659, dated 07 / 10 / 2025, page 31 / 62 / 46 scan with a magnification of 5000, thus measuring the thickness of the insulating coating layer 2. At this point, using an energy-dispersive element analyzer, the insulating coating layer 2 can be calculated, so that the portion containing Si is the tension coating layer 22 and the portion that does not contain Si is the intermediate layer 21, to determine the thickness of the intermediate layer 21. Five or more positions are measured, and their average is defined as the thickness of the intermediate layer 21.

[0081] Although the intermediate layer 21 and the tension coating layer 22 formed over it are formed at different times, both the intermediate layer 21 and the tension coating layer 22 exhibit the effect of the insulating coating 2.

[0082] Regarding the crystalline metallic phosphate in the intermediate layer 21, the mass ratio of the metallic phosphate and the type of metallic phosphate are determined by measuring the cross-section of the intermediate layer 21 along the thickness direction with a scanning electron microscope (SEM) and an energy-dispersive element analyzer. Whether the metallic phosphate in the intermediate layer 21 is a crystalline metallic phosphate can be determined by X-ray crystallography.

[0083] The base steel sheet 1 and the insulating coating 2 can be determined by the presence or absence of phosphorus. In the insulating coating 2, the intermediate layer 21 and the tension coating layer 22 can be determined by the presence or absence of silicon. (Tension Layer Coating)

[0084] The grain-oriented electrical steel sheet 100 according to the embodiment, in which a tension coating is formed on the surface of the intermediate layer 21, has the tension coating layer 22 on the side of the insulating coating surface 2.

[0085] The 22 tension coating layer is not particularly Petition 870250091659, dated 07 / 10 / 2025, page 32 / 62 / 46 limited, provided that it is used as an insulating coating of a grain-oriented electrical steel sheet, but preferably contains a metallic phosphate from the point of view of adhesion to the intermediate layer 21 (adhesion to the base steel sheet 1 through the intermediate layer 21). In particular, it is preferable that the tension coating layer 22 mainly contains, as a composition, aluminum phosphate and silica.

[0086] The 22-tension coating layer preferably contains a metal phosphate and silica (derived from colloidal silica in the coating liquid), such that the silica content is 20.0% by mass or more. Conversely, when the silica content in the 22-tension coating layer is more than 60.0% by mass, pulverization occurs. Therefore, the silica content is preferably 60.0% by mass or less. The metal phosphate and silica are preferably contained in a total amount of 70.0% by mass or more. As a balance, in addition to the metal phosphate and silica, fine ceramic particles such as alumina or silicon nitride may be included. The metal phosphate is preferably aluminum phosphate from the point of view of heat resistance.

[0087] The thickness of the tension coating layer 22 is not limited, but the average thickness as the insulating coating 2 (intermediate layer 21 + tension coating layer 22) is preferably 2.0 to 20.0 μm when the average thickness of the intermediate layer 21 is in the above range. When the average thickness of the insulating coating 2 is less than 2.0 μm, sufficient coating tension cannot be obtained. Furthermore, the elution of phosphoric acid increases. In this case, this can cause deterioration of adhesion and corrosion resistance, and may cause peeling of the coating. When the thickness of the insulating coating 2 is more than 20.0 μm, the space factor decreases to deteriorate the magnetic characteristics, adhesion decreases due to cracking or similar, or corrosion resistance decreases. Petition 870250091659, dated 07 / 10 / 2025, page 33 / 62 / 46

[0088] In the tension coating layer 22, the mass percentage of metallic phosphate and the type of metallic phosphate can be determined in the cross section along the thickness direction in the same way as in the intermediate layer 21.

[0089] As described above, the tension coating layer 22 and the intermediate layer 21 can be determined by the difference in silica content.

[0090] The thickness of the tension coating layer 22 can be determined in the same way as for the intermediate layer 21. The total of the thickness of the tension coating layer 22 and the thickness of the intermediate layer 21 is determined as the thickness of the insulating coating 2. <Método de Fabricação da Chapa de Aço Elétrico de Grão Orientado>

[0091] According to the manufacturing method that satisfies the manufacturing conditions described below, the grain-oriented electrical steel sheet according to the embodiment can be properly manufactured. Note that, naturally, the grain-oriented electrical steel sheet according to the embodiment is not particularly limited in its manufacturing method. That is, a grain-oriented electrical steel sheet having the configurations described above is considered to be the grain-oriented electrical steel sheet according to the embodiment, regardless of its manufacturing conditions.

[0092] Grain-oriented electrical steel sheet according to the modality can be manufactured by a manufacturing method that includes the following steps: (I) a hot rolling stage for hot rolling a steel part having a predetermined chemical composition to obtain a hot band; (II) a hot band annealing step to anneal the hot band; Petition 870250091659, dated 07 / 10 / 2025, page 34 / 62 / 46 (III) a cold rolling stage of the hot strip after the annealing stage of the hot strip to obtain a steel sheet (cold strip); (IV) a decarburization annealing step to perform decarburization annealing of the steel sheet after the cold rolling step; (V) a finishing annealing step to apply an annealing separator containing Al2O3 in an amount of 10 to 100% by mass onto a steel sheet, dry the steel sheet and then perform final annealing of the steel sheet; (VII) an annealing separator removal step to remove excess annealing separator from the steel sheet after the finishing annealing step; (VIII) a pickling step to pickle the steel sheet after the annealing separator removal step with 0.1 to 5% by mass of an inorganic acid selected from the group consisting of sulfuric acid, chloric acid, nitric acid and phosphoric acid for 1 to 20 seconds; (IX) an immersion step to immerse the steel sheet after the pickling step in a treatment liquid containing a metallic phosphate, nitric acid and an iron ion, and having a liquid temperature of 20 to 85°C for 5 to 150 seconds; (X) a drying step to extract the steel sheet after the treatment liquid immersion step, remove excess treatment liquid, and then dry the steel sheet; and (XI) a tension coating layer formation step to apply a coating liquid containing a metallic phosphate and colloidal silica, the metallic phosphate and colloidal silica contained in a total concentration of 10.0 to 40.0% by mass, in terms of solid content, to Petition 870250091659, dated 07 / 10 / 2025, page 35 / 62 / 46 the steel sheet after the drying stage, dry the steel sheet and then hold the steel sheet at a sheet temperature of 700 to 950°C for 10 to 120 seconds.

[0093] In the manufacturing method of grain-oriented electrical steel sheet according to the modality, the treatment liquid satisfies the following conditions in the immersion stage: (A) concentration of metal ions: 1.0 to 10.0 g / L; (B) phosphate ion concentration: 2.0 to 25.0 g / L; (C) nitrate ion concentration: 2.0 to 40.0 g / L; (D) iron ion concentration: 1.0 to 20.0 g / L; (E) ratio between the concentration of phosphate ions and the concentration of metal ions: 1.5 to 5.0; and (F) ratio between the concentration of nitrate ions and the concentration of phosphate ions: 0.5 to 10.0.

[0094] In addition, the manufacturing method of the grain-oriented electrical steel sheet according to the embodiment may also include one or both of (XII) a nitriding treatment step to subject the steel sheet to a nitriding treatment between the decarburization annealing step and the finishing annealing step, and (XIII) a magnetic domain refinement step to perform magnetic domain control of the steel sheet after the tension coating layer formation step.

[0095] Among these steps, (V) finishing annealing step to (X) tension coating layer formation step (also collectively referred to as insulating coating formation step), which are mainly related to the formation of the insulating coating, are characteristic in the manufacture of grain-oriented electrical steel sheet according to the modality, and known conditions can be adopted for Petition 870250091659, dated 07 / 10 / 2025, page 36 / 62 / 46 other steps or conditions not described.

[0096] From here on, the respective steps will be described. [Hot Rolling Stage]

[0097] In the hot rolling stage, a piece of steel having a predetermined chemical composition, such as a plate, is heated and then hot rolled to obtain a hot strip. The heating temperature of the steel piece is preferably set in a range of 1100 to 1450°C. The heating temperature is more preferably 1300 to 1400°C.

[0098] The chemical composition of the steel part is altered according to the chemical composition of the grain-oriented electrical steel sheet to be finally obtained, but, for example, the chemical composition includes, in terms of % by mass, 0.01 to 0.20% C, 2.50 to 4.00% Si, 0.01 to 0.040% Al sol., 0.01 to 0.50% Mn, 0.020% or less N, 0.005 to 0.040% S, 0 to 0.50% Cu, 0 to 0.50% Sn, 0 to 0.020% Se, 0 to 0.50% Sb and a balance including Fe and impurities.

[0099] The hot rolling conditions are not particularly limited and can be adjusted accordingly based on the required characteristics. The sheet thickness of the hot band is preferably, for example, in a range of 2.0 mm or more and 3.0 mm or less. [Hot Band Annealing Stage]

[00100] The hot band annealing step is a step of annealing the hot band manufactured through the hot rolling step. By performing such annealing treatment, recrystallization occurs in the metallographic structure and favorable magnetic characteristics can preferably be achieved.

[00101] When hot strip annealing is performed, the hot strip manufactured through the hot rolling step is annealed according to a known method. The means for heating the hot strip in Petition 870250091659, dated 07 / 10 / 2025, page 37 / 62 / 46. The timing of the annealing is not particularly limited, and a known heating method can be adopted. The annealing conditions are not particularly limited. For example, the hot strip can be annealed in a temperature range of 900 to 1200°C for 10 seconds to 5 minutes. [Cold Rolling Step]

[00102] In the cold rolling stage, the hot strip after the hot strip annealing stage is subjected to cold rolling to obtain a steel sheet (cold strip). Cold rolling can be performed once (performed continuously without intermediate annealing intervention(s)). Alternatively, before the final pass in the cold rolling stage, intermediate annealing can be performed at least once or two or more times interrupting the cold rolling, i.e., cold rolling can be performed several times with intermediate annealing intervention(s).

[00103] When intermediate annealing is performed, it is preferable to hold the hot strip at a temperature of 1,000 to 1,200°C for 5 to 180 seconds. The annealing atmosphere is not particularly limited. The number of intermediate annealing cycles is preferably 3 or less considering the manufacturing cost.

[00104] In addition, prior to the cold rolling stage, the surface of the hot strip may be subjected to pickling.

[00105] In the cold rolling stage according to the embodiment, the hot strip after the hot strip annealing stage is cold rolled according to a known method to form a steel sheet. For example, the final rolling reduction may be in a range of 80 to 95%. When the final rolling reduction is 80% or more, a Goss core in which the orientation {110} <001> A high degree of development in one direction of lamination can be achieved, which is preferable. On the other hand, when the final lamination reduction exceeds 95%, there is a large... Petition 870250091659, dated 07 / 10 / 2025, page 38 / 62 / 46 possibility that secondary recrystallization may be unstable in the subsequent finishing annealing step, which is not preferable.

[00106] Final rolling reduction is a cumulative cold rolling reduction and, when intermediate annealing is performed, final rolling reduction is a cumulative cold rolling reduction after final intermediate annealing. [Decarburization Annealing Stage]

[00107] In the decarburization annealing stage, the resulting steel sheet is subjected to decarburization annealing. In decarburization annealing, the conditions for decarburization annealing are not limited, as long as the steel sheet can be recrystallized primarily and the C, which negatively affects the magnetic characteristics, can be removed from the steel sheet. For example, the steel sheet is held at an annealing temperature of 800 to 900°C for 10 to 600 seconds with a degree of oxidation (PH2O / PH2) of 0.3 to 0.6 in an annealing atmosphere (furnace atmosphere). [Nitriding Treatment Step]

[00108] A nitriding treatment can be performed between the decarburization annealing step and the finishing annealing step described later.

[00109] In the nitriding treatment step, for example, the steel sheet after the decarburization annealing step is maintained at approximately 700 to 850°C in a nitriding treatment atmosphere (an atmosphere containing a gas with nitriding capacity, such as hydrogen, nitrogen, or ammonia) to perform the nitriding treatment. When AlN is used as an inhibitor, the N content of the steel sheet after the nitriding treatment step is preferably 40 ppm or more. On the other hand, when the N content of the steel sheet after the nitriding treatment step exceeds 1000 ppm, AlN is excessively present in the Petition 870250091659, dated 07 / 10 / 2025, page 39 / 62 / 46 steel plate, even after the completion of secondary recrystallization in the finishing annealing. Such AlN causes iron loss deterioration. Therefore, the N content of the steel plate after nitriding treatment is preferably 1000 ppm or less. [Finish Annealing Stage]

[00110] In the finishing annealing stage, an annealing separator containing 10 to 100% by mass of Al2O3 is applied to the steel sheet that is after the decarburization annealing stage or has been subjected to nitriding treatment (after the nitriding treatment stage) and dried, and then the finishing annealing is carried out.

[00111] In a conventional manufacturing method for a grain-oriented electrical steel sheet, a forsterite-based coating is formed on the surface of a steel sheet (cold band) by applying an annealing separator containing mainly MgO and performing the finish annealing.

[00112] On the other hand, in the manufacturing method of the grain-oriented electrical steel sheet according to the embodiment, an annealing separator containing Al2O3 is used so as not to form substantially any forsterite-based coating.

[00113] On the other hand, the percentage of Al2O3 can be 100% by mass. However, in the manufacturing method of grain-oriented electrical steel sheet according to the embodiment, the annealing separator preferably contains MgO from the point of view of preventing the sheet surface from being annealed with Al2O3. The MgO can be 0%, but the percentage of MgO is preferably 5% by mass or more to obtain the above effect. When MgO is contained, the percentage of MgO is 90% by mass or less to ensure 10% by mass or more of Al2O3. The percentage of MgO is preferably 50% by mass or less.

[00114] In addition, in the manufacturing method of electrical steel sheet Petition 870250091659, dated 07 / 10 / 2025, page 40 / 62 / 46 of oriented grain according to the embodiment, the annealing separator may also contain a chloride. When the annealing separator contains a chloride, a more difficult-to-form forsterite-based coating effect can be obtained. The amount of chloride is not particularly limited and can be 0%, but is preferably 0.5 to 10% by mass when the above effect is to be obtained. As chlorides, for example, bismuth chloride, calcium chloride, cobalt chloride, iron chloride and nickel chloride are effective.

[00115] Finish annealing conditions are not limited, but, for example, a condition of holding the steel sheet at a temperature of 1150 to 1250°C for 10 to 60 hours may be adopted. [Annealing Separator Removal Stage]

[00116] In the annealing separator removal stage, excess annealing separator is removed from the steel sheet after the finishing annealing stage. For example, excess annealing separator can be removed by washing with water. [Pickling Stage]

[00117] In the pickling stage, the steel sheet, after the removal of the annealing separator, is pickled with 0.1 to 10% by mass of an inorganic acid selected from the group consisting of sulfuric acid, phosphoric acid, nitric acid, and chloric acid, for 1 to 20 seconds, with the inorganic acid heated to 30 to 85°C. Pickling under these conditions can produce an effect that allows sufficient removal of the forsterite-based coating and removal of any remaining MgO. However, so-called pickling pits are rarely formed in the pickling stage of this method. [Immersion Stage] [Drying Stage]

[00118] In the immersion stage, the steel plate, after the stage of Petition 870250091659, dated 07 / 10 / 2025, page 41 / 62 / 46 pickling, is immersed in a treatment liquid containing a metallic phosphate and nitric acid for 5 to 150 seconds. In the drying stage, the steel sheet after the immersion stage is extracted from the treatment liquid, an excess of the treatment liquid is removed, and then the steel sheet is dried. In this way, the intermediate layer is formed on the surface of the base steel sheet.

[00119] In the immersion stage, the treatment liquid is adjusted to satisfy the following conditions (A) to (F).

[00120] (A) Concentration of metal ions: 1.0 to 10.0 g / L; (B) Phosphate ion concentration: 2.0 to 25.0 g / L

[00121] The treatment liquid contains a metallic phosphate and nitric acid as an oxidizing agent. Examples of metallic phosphate include zinc phosphate, manganese phosphate, calcium zinc phosphate, and manganese iron phosphate. From the point of view of controlling the roughness index, zinc phosphate is preferable.

[00122] In the treatment liquid, the concentration of metal ions and the concentration of phosphate ions are 1.0 to 10.0 g / L and 2.0 to 25.0 g / L, respectively. When the concentration of metal ions is less than 1.0 g / L, the phosphate precipitation rate is relatively slow and the surface of the steel plate is etched, so there is a possibility that the degree of interface irregularity will increase, the L / W irregularity index will increase, and the magnetic characteristics will deteriorate. Similarly, when the concentration of phosphate ions is less than 2.0 g / L, there is a possibility that the degree of interface irregularity will increase, the L / W irregularity index will increase, and the magnetic characteristics will deteriorate. Therefore, the concentration of metal ions and the concentration of phosphate ions are preferably 1.0 g / L or more and 2.0 g / L or more, respectively.

[00123] On the other hand, when the concentration of metal ions is greater than 10.0 g / L, the pH of the treatment liquid increases and the rate of Petition 870250091659, dated 07 / 10 / 2025, p. 42 / 62 / 46. The precipitation of metallic phosphate also decreases, so there is a possibility that the degree of irregularity of the interface will increase, the L / W irregularity index will increase, and the magnetic characteristics will deteriorate. Similarly, when the concentration of phosphate ions is greater than 25.0 g / L, there is a possibility that the degree of irregularity of the interface will increase, the L / W irregularity index will increase, and the magnetic characteristics will deteriorate. Therefore, the concentration of metallic ions and the concentration of phosphate ions are preferably 10.0 g / L or less and 25.0 g / L or less, respectively.

[00124] (C) Nitrate ion concentration: 2.0 to 40.0 g / L

[00125] As described above, nitric acid is added as an oxidizing agent to the treatment liquid according to the embodiment. Nitric acid, used as an oxidizing agent, prevents the generation of hydrogen gas and efficiently forms a dense intermediate layer. However, when nitric acid is added to the treatment liquid in an excessively large quantity, the surface of the steel sheet is excessively oxidized and the phosphate precipitation rate is reduced, so there is a possibility that the degree of irregularity of the interface will increase, the L / W irregularity index will increase, and the magnetic characteristics will deteriorate. Therefore, the nitrate ion concentration is preferably 40.0 g / L or less, and more preferably 25.0 g / L or less.On the other hand, when nitric acid is added to the treatment liquid in an excessively small quantity, the generation of hydrogen gas cannot be suppressed, and a region where phosphate is precipitated in an excessively small quantity is formed in some parts, so there is a possibility that the degree of interface irregularity will increase, the L / W irregularity index will increase, and the magnetic characteristics will deteriorate. Therefore, the concentration of acid ions is preferably 2.0 g / L or more. Petition 870250091659, dated 07 / 10 / 2025, p. 43 / 62

[00126] / 46 (D) Iron ion concentration: 1.0 to 20.0 g / L; It is assumed that iron ions, contained in the treatment liquid in an appropriate quantity, have an action of suppressing the etching action of the metal phosphate treatment liquid and reducing the dissolution rate on the steel sheet surface. To obtain such action, the concentration of iron ions is preferably 1.0 g / L or more. On the other hand, when iron ions are contained in the treatment liquid in an excessively large quantity, the iron is precipitated in the intermediate layer generated to reduce adhesion. Therefore, the concentration of iron ions is preferably 20.0 g / L or less.

[00127] (E) Ratio between the concentration of phosphate ions and the concentration of metal ions: 1.5 to 5.0

[00128] From the point of view of irregularity index optimization, it is effective that the phosphoric acid concentration and the metal ion concentration are within the range described above. However, the ratio between the phosphate ion concentration and the metal ion concentration is preferably adjusted. Specifically, the ratio between the phosphate ion concentration and the metal ion concentration (phosphate ion concentration / metal ion concentration) is 1.5 to 5.0. When the ratio between the phosphate ion concentration and the metal ion concentration is excessively large, there is a possibility that the etching process will continue, making the steel sheet excessively irregular, resulting in a lower clearance factor. Therefore, the ratio between the phosphate ion concentration and the metal ion concentration is preferably 5.0 or less.On the other hand, when the ratio between the concentration of phosphate ions and the concentration of metal ions is excessively small, there is a possibility that the pH will increase and, thus, the metallic phosphate will not precipitate or will take a very long time to precipitate. Therefore, the ratio between the concentration of phosphate ions and the concentration of metal ions is preferably 1.5 or more. Petition 870250091659, dated 07 / 10 / 2025, pages 44 / 62 / 46

[00129] (F) Ratio between nitrate ion concentration and phosphate ion concentration: 0.5 to 10.0

[00130] From the point of view of the precipitation rate, the ratio between the nitrate ion concentration and the phosphate ion concentration is also adjusted. Specifically, the ratio between the nitrate ion concentration and the phosphate ion concentration (nitrate ion concentration / phosphate ion concentration) is from 0.5 to 10.0. When the ratio between the nitrate ion concentration and the phosphate ion concentration is excessively large, the steel plate may become excessively etched. Therefore, the ratio between the nitrate ion concentration and the phosphate ion concentration is preferably 10.0 or less. On the other hand, when the ratio between the nitrate ion concentration and the phosphate ion concentration is excessively small, there is a possibility that the precipitation of metallic phosphate will be suppressed, taking time to form the intermediate layer. Therefore, the ratio between the nitric acid concentration and the phosphate ion concentration is preferably 0.5 or more.

[00131] It is preferable that the temperature of the treatment liquid be between 20 and 85°C and the immersion time be between 5 and 150 seconds. When the liquid temperature is below 20°C or the immersion time is less than 5 seconds, there is a possibility that the intermediate layer will be insufficiently formed and have lower adhesion. On the other hand, when the liquid temperature is above 85°C or the process time is longer than 150 seconds, there is a possibility that the intermediate layer will have a region where the crystalline metallic phosphate is partially precipitated excessively and becomes inferior in space factor.

[00132] In the drying stage, when the drying temperature is high, there is a possibility of void formation, which leads to poor adhesion. Therefore, the drying temperature is preferably 300°C or lower, and more Petition 870250091659, dated 07 / 10 / 2025, page 45 / 62 / 46 preferably 200°C or lower. The drying temperature is preferably 100°C or higher. [Stretching Coating Layer Formation Stage]

[00133] In the tension coating layer formation stage, a coating liquid containing a metallic phosphate and colloidal silica at a concentration of 10 to 40% by mass is applied to the steel sheet after the drying stage, the steel sheet is dried and then the steel sheet is heated and held at a sheet temperature of 700 to 950°C for 10 to 50 seconds, thus forming a tension coating layer on the surface of the intermediate layer.

[00134] When the plate temperature is kept below 700°C, the voltage is low and the magnetic characteristics are poor. Therefore, the plate temperature is preferably 700°C or higher. On the other hand, when the plate temperature is above 950°C, the stiffness of the steel plate decreases and the steel plate is easily deformed. In this case, the steel plate may become distorted due to transfer or something similar, resulting in poor magnetic characteristics. Therefore, the plate temperature is preferably 950°C or lower.

[00135] When the retention time is less than 10 seconds, elution is poor. Therefore, the retention time is 10 seconds or more. On the other hand, when the retention time is more than 50 seconds, the adhesion of the tension coating layer may be poor. Therefore, the retention time is preferably 50 seconds or less.

[00136] The coating liquid (insulating coating solution) is adjusted so that the metallic phosphate and colloidal silica are contained in a total amount of 10 to 40% by mass in terms of solid content.

[00137] When the total concentration of metallic phosphate and colloidal silica is less than 10% by mass, the applied treatment liquid flows easily, which can cause uneven application. Furthermore, Petition 870250091659, dated 07 / 10 / 2025, page 46 / 62 / 46 when the total concentration of metallic phosphate and colloidal silica is more than 40% by mass, the viscosity becomes too high, which can cause a pattern or irregularity in the coating.

[00138] As a metal phosphate, for example, one or a mixture of two or more selected from aluminum phosphate, zinc phosphate, magnesium phosphate, nickel phosphate, copper phosphate, lithium phosphate and cobalt phosphate may be used. Among these, aluminum phosphate is preferred.

[00139] The coating liquid may contain vanadium, tungsten, molybdenum, zirconium and similar elements as additional elements. When these elements are present, they may be added to the coating liquid, for example, as an oxygenated acid.

[00140] Like colloidal silica, either type S or type C can be used. Type S colloidal silica is alkaline in silica solution. Type C has its silica particle surface treated with aluminum and is alkaline to neutral in silica solution. Type S colloidal silica is widely used and has a relatively low price, but care must be taken because type S colloidal silica can aggregate and precipitate when mixed with an acidic metal phosphate solution. Type C colloidal silica is stable even when mixed with a metal phosphate solution, and there is no possibility of precipitation, but type C colloidal silica is relatively expensive because the number of treatment steps is large. It is preferable to select and use them according to the stability of a coating liquid to be prepared. [Magnetic Domain Refinement Stage]

[00141] The manufacturing method for grain-oriented electrical steel sheet according to the modality may also include a magnetic domain refinement step to perform magnetic domain refinement on the steel sheet after the tension coating layer formation step. Petition 870250091659, dated 07 / 10 / 2025, page 47 / 62 / 46

[00142] By performing magnetic domain refinement treatment, the iron loss from grain-oriented electrical steel sheet can be further reduced.

[00143] The magnetic domain refinement treatment method includes: a method for narrowing the width of a 180° magnetic domain (performing 180° magnetic domain refinement) by forming linear or dotted grooved parts that extend in a direction that crosses a rolling direction at predetermined intervals in the rolling direction, and a method for narrowing the width of a 180° magnetic domain (performing 180° magnetic domain refinement) by forming linear or dotted stress-strain parts or grooved parts that extend in a direction that crosses a rolling direction at predetermined intervals in the rolling direction.

[00144] 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 grooved part is formed, a mechanical groove forming method using a gear or similar, a chemical groove forming method of forming a groove by electrolytic etching, a thermal groove forming method by laser irradiation, and similar methods can be applied.

[00145] 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

[00146] A plate was cast including, in terms of mass %, 0.08% C, 3.31% Si, 0.028% Al sol., 0.008% N, 0.07% Mn, less than 0.0005% S and an equilibrium including Fe and impurities.

[00147] This plate was heated to 1350°C and then hot-rolled. Petition 870250091659, dated 07 / 10 / 2025, pages 48 / 62 / 46 to form a hot band having a sheet thickness of 2.2 mm.

[00148] The hot strip was annealed (annealed hot strip) under holding conditions at 1100°C for 10 seconds.

[00149] Next, the hot strip was cold rolled to obtain a cold strip with a sheet thickness of 0.22 mm.

[00150] The cold band was annealed by decarburization under holding conditions at 830°C for 90 seconds.

[00151] After decarburization annealing, an annealing separator containing 95% MgO and Al2O3 and 5% BiCl3 as a bismuth chloride was applied and dried, and then the finishing annealing was carried out at 1200°C for 20 hours.

[00152] After the finishing annealing, the steel sheet was washed with water to remove excess annealing separator. As a result, a forsterite-based coating was not formed on the surface of the steel sheet.

[00153] The steel sheet was subjected to light pickling with 3% by mass sulfuric acid at 80°C for 10 seconds.

[00154] After light pickling, an intermediate layer was formed using the treatment liquid shown in Table 1. Steel wool was used as the source of iron ions, and a treatment liquid was prepared to have a concentration as shown in Table 1. The immersion conditions were as shown in Table 1. The intermediate layer obtained was shown in Table 1.

[00155] Next, an insulating coating treatment liquid containing mainly a metallic phosphate and colloidal silica shown in Table 2 was applied, and dried at 850°C for 20 seconds after application, to form a tension coating layer on the surface of the steel sheet.

[00156] In Table 2, the “Molar ratio of metallic elements” indicates the abundance ratio of metallic elements when two or more Petition 870250091659, dated 07 / 10 / 2025, page 49 / 62 / 46 metallic elements are present in metallic phosphate.

[00157] The thickness of the insulating coating (intermediate layer and tension coating layer) was shown in Table 2. The tension coating layer was substantially made of metallic phosphate and silica.

[00158] The obtained steel sheet (grain-oriented electrical steel sheet) was irradiated with a laser beam under conditions where UA (irradiation energy density) was 2.0 J and the irradiation interval was 5.0 mm pitch, thus performing magnetic domain refinement.

[00159] After refining the magnetic domain, the W17 / 50 iron loss of the steel sheet (iron loss at 50 Hz under 1.7 T) was measured by the Single Sheet Tester: SST according to JIS C2556 (2015). When the W17 / 50 iron loss was 0.68 W / kg or less, it was determined that good magnetic characteristics were guaranteed.

[00160] In addition, the space factor was measured as follows. [Space Factor]

[00161] The space factor was measured by a method in accordance with JIS C 2550-5 (2020). The specimen was 30 mm wide and 320 mm long, and 30 pieces were used. The samples were measured for total mass and then pressurized to 1 MPa, at which point the space between the top and bottom cover plates enclosing the laminate was measured to calculate the space factor.

[00162] When the space factor was 96.0% or more, it was determined that a high space factor was guaranteed.

[00163] In addition, the coating adhesion, coating tension, corrosion resistance, and elution resistance of the steel sheet after magnetic domain refinement were evaluated by the following methods. The interface irregularity index was determined by Petition 870250091659, dated 07 / 10 / 2025, page 50 / 62 / 46 following method. The results are shown in Tables 2 and 3. [Interface Irregularity Index]

[00164] First, using a scanning electron microscope, a region including the interface between the base steel plate and the intermediate layer was observed at a magnification of 5000 to obtain an observation image. Then, in the observation image, both ends of the interface between the base steel plate and the intermediate layer were connected with a straight line, and the distance between the two points was defined as the width W of the analyzed image, and the width W of the analyzed image was determined. In addition, the actual path of the interface (i.e., the curved path tracing the actual interface) was defined as the interface length L, and the interface length L was determined, and the irregularity index L / W was determined. The width W of the analyzed image and the interface length L were determined using a “LUZEX AP” application system created by NIRECO CORPORATION or similar on a cross-sectional image obtained by an electron microscope. [Coating Adhesion]

[00165] For coating adhesion, a sample with a width of 30 mm and a length of 300 mm was collected from the steel plate, and the sample was subjected to stress-relief annealing at 800°C for 2 hours in a nitrogen stream. Then, the sample was subjected to a bending and adhesion test, in which the sample was rolled and unrolled around a 10 mmφ cylinder, and then the coating was evaluated for the degree of peeling (area fraction).

[00166] The evaluation criteria were as follows, and when a sample was evaluated as ® or o, the sample was determined to have excellent coating adhesion.

[00167] ®: Peeling area fraction: 0 to 0.5% or: Peeling area fraction: more than 0.5% and 5.0% or Petition 870250091659, dated 07 / 10 / 2025, page 51 / 62 / 46 less Δ: Fraction of the peeling area: more than 5.0% [Coating Stress]

[00168] The coating stress was calculated by reverse calculation from the curved state when a surface of the insulating coating was removed. When the coating stress obtained was 4.0 MPa or more, it was determined that the coating stress was sufficient. [Corrosion resistance]

[00169] For corrosion resistance, a 5% aqueous NaCl solution was naturally added to the sample for 7 hours in an atmosphere of 35°C according to JIS: Methods of salt spray testing (JIS Z2371:2015).

[00170] Subsequently, a rust area was evaluated on a 10-point scale. Here, the evaluation criteria are as follows. For corrosion resistance, when the score was 5 or more, it was determined that the corrosion resistance was excellent.

[00171] 10: No rust generation occurred.

[00172] 9: Rust was generated in an extremely small quantity (fraction of area was 0.10% or less)

[00173] 8: Rust was generated in an area fraction of more than 0.10% and 0.25% or less

[00174] 7: Rust was generated in an area fraction of more than 0.25% and 0.50% or less

[00175] 6: Rust was generated in an area fraction of more than 0.50% and 1.0% or less

[00176] 5: Rust was generated in an area fraction of more than 1.0% and 2.5% or less

[00177] 4: Rust was generated in an area fraction greater than 2.5% and 5.0% or less

[00178] 3: Rust was generated in an area fraction greater than Petition 870250091659, dated 07 / 10 / 2025, page 52 / 62 / 46 5.0% and 10% or less

[00179] 2: Rust was generated in an area fraction of more than 10% and 25% or less

[00180] 1: Rust was generated in an area fraction of more than 25% and 50% or less [Resistance to elution]

[00181] Resistance to elution was evaluated by the possibility of suppressing the elution of phosphoric acid from the sample.

[00182] The method for measuring the amount of elution was as follows: the sample was boiled in pure boiled water for 10 minutes, the amount of phosphoric acid 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. The amount of phosphoric acid eluted in pure water was measured and calculated as follows: the pure water in which the phosphoric acid was eluted (solution) was cooled, and the cooled solution was diluted with pure water to prepare a sample, and the sample was measured for the concentration of phosphoric acid with ICP-AES.

[00183] When the elution quantity was less than 40 mg / m2, it was determined that the resistance to elution was excellent. Petition 870250091659, dated 07 / 10 / 2025, page 53 / 62 / 46 [Table 11] Petition 870250091659, dated 07 / 10 / 2025, pages 54 / 62 / 46 Comparative Example Comparative Example Comparative Example 131.4 137.3 130.8 10.8 1.6 60°C x 120 sec. 75°C x 50 sec. 75°C x 120 sec. 3.0 2.9 1.4 5.8 2.0 5.0 3.0 15.0 10.0 22.0 3.5 15.5 Zinc phosphate Zinc phosphate Zinc phosphate OI CO Tl- Observation Example of Invention Example of Invention Example of Invention Example of Invention Example of Invention Example of Invention Example of Invention Example of Invention Example of Invention Example of Invention Example of Invention Comparative Example Comparative Example Comparative Example Insulating layer (μm) 5.3 5.6 9.3 6.7 6.1 7.6 5.3 7.3 11.8 13.5 Coating layer by tension Silica content (% by mass) 38.5 40.3 37.5 29.2 37.5 37.5 50.3 31.0 42.9 38.9 28.6 28.6 28.6 Insulating coating treatment liquid Parts by weight 125 06 135 09 100 uo oo O oo O oo O oo Colloidal silica Type C Type S Type S Type S Type S Type S Type S Type S Type S Type S Type S Type C Type C Type C Molar ratio of the metallic element 0.18 OOOO 0.18 O 0.18 Phosphate (100 parts by weight) Aluminum phosphate Zinc phosphate Aluminum / zirconium phosphate Aluminum / copper phosphate Aluminum / lithium phosphate Aluminum / barium phosphate Aluminum / molybdenum phosphate Aluminum / vanadium phosphate Aluminum / tungsten phosphate Aluminum / zirconium phosphate Aluminum phosphate Aluminum phosphate Intermediate layer treatment No. 04 CO Tl- uo r- oo CO O. OO 04 CO Tl- uo r- oo O. o 04 CO, Petition 870250091659, dated 07 / 10 / 2025, pp. 55 / 62 / 46 Comparative Example Comparative Example Comparative Example C4 11.4 12.5 33.3 37.5 37.5 100 120 120 Type C Type C Type C Aluminum phosphate Aluminum phosphate Aluminum phosphate C4 CO Tf- Tf- K) Observation Example of Invention Example of Invention Example of Invention Example of Invention Example of Invention Example of Invention Example of Invention Example of Invention Example of Invention Example of Invention Example of Invention Comparative Example Comparative Example Comparative Example Comparative Example Comparative Example Comparative Example Iron Loss (W17 / 50) (W / kg) 0.65 CO 0.59 0.62 3 0.65 0.62 0.62 0.65 0.68 0.73 0.69 Ch Space Factor (%) 97.1 97.3 96.8 97.1 97.3 97.6 97 97.7 97.3 97.8 95.9 95.1 94.4 95.4 95.6 94.7 Elution Resistance (mg / m2) 27 C4 Tf- oo oo 28 O 29 23 25 m C4 44 K) 34 Corrosion resistance CF oo oo oo oo r- Ch r- r- oo r- r- Tf- Tf- Coating stress [MPa] oo 7.3 9.8 o 7.5 6.9 o 8.4 5.9 9.4 9.4 7.1 4.7 9.3 3.6 8.8 Coating adhesion o O Θ Θ OO Θ OOOOO Δ O Δ OO C4 CO Tf- MD c- oo Ch O C4 m Tf- K) Petition 870250091659, dated 07 / 10 / 2025, pages 56 / 62 / 46

[00184] As can be seen in Tables 1 to 3, the Invention Examples are extremely excellent in each property, such as coating adhesion, and are improved in iron loss and space factor.

[00185] On the other hand, the Comparative Examples are inferior in at least one of the following: coating adhesion, magnetic properties, corrosion resistance, elution resistance, and space factor of a transformer (core). LIST OF REFERENCE SIGNS

[00186] 100 Grain Oriented Electrical Steel Sheet Base steel plate Insulating coating Intermediate layer Tension coating layer INDUSTRIAL APPLICABILITY

[00187] According to the embodiment of the present invention, it is possible to provide a grain-oriented electrical steel sheet that is excellent in adhesion with a tension coating and magnetic characteristics, and does not reduce the space factor of a transformer (core). Therefore, the resulting grain-oriented electrical steel sheet can be suitably applied to an iron core material of a transformer and thus has high industrial applicability. Petition 870250091659, dated 07 / 10 / 2025, pages 57 / 62

Claims

1 / 3 CLAIMS 1. Grain-oriented electrical steel sheet, characterized in that it comprises: a base steel sheet; and an insulating coating formed on a surface of the base steel sheet, wherein the insulating coating includes: an intermediate layer that is formed on one side of the base steel sheet and contains a crystalline metallic phosphate; and a tension coating layer formed on one side of the surface of the insulating coating, and when an interface between the base steel sheet and the intermediate layer is observed with a scanning electron microscope at a magnification of 5000 in a cross-section along a thickness direction of the intermediate layer, a ratio of an interface length L to a width W of the analyzed image is 100.0 to 120.0%.

2. Grain-oriented electrical steel sheet according to claim 1, characterized in that the tension coating layer contains a metallic phosphate and silica.

3. Method for forming the insulating coating included in the grain-oriented electrical steel sheet as defined in claim 1, the method characterized in that it comprises: a finishing annealing step to apply an annealing separator containing Al2O3 in an amount of 10 to 100% by mass onto a steel sheet, drying the steel sheet and then final annealing of the steel sheet; an annealing separator removal step to remove an excess of the annealing separator from the steel sheet after the finishing annealing step; a pickling step to pickle the steel sheet after the annealing separator removal step with 0.1 to 5% by mass of Petition 870250091659, dated 07 / 10 / 2025, p. 58 / 62 2 / 3 an inorganic acid selected from the group consisting of sulfuric acid, chloric acid, nitric acid and phosphoric acid for 1 to 20 seconds;an immersion step to immerse the steel sheet after the pickling step in a treatment liquid containing a metallic phosphate, an oxidizing agent, and an iron ion; a drying step to extract the steel sheet after the immersion step from the treatment liquid, remove excess treatment liquid, and then dry the steel sheet; and a tension coating layer formation step to apply a coating liquid containing a metallic phosphate and colloidal silica, the metallic phosphate and colloidal silica contained in a total concentration of 10 to 40% by mass, in terms of solid content, to the steel sheet after the drying step, dry the steel sheet, and then hold the steel sheet at a sheet temperature of 700 to 950°C for 10 to 120 seconds, wherein the treatment liquid has: a metallic ion concentration of 1.0 to 10.0 g / L; a phosphate ion concentration of 2.0 to 25.0 g / L; a nitrate ion concentration of 2.0 to 40.0 g / L;and an iron ion concentration of 1.0 to 20.0 g / L, where the phosphate ion concentration is in a ratio of 1.5 to 5.0 to the metal ion concentration, and the nitrate ion concentration is in a ratio of 0.5 to 10.0 to the phosphate ion concentration.

4. Method for forming an insulating coating according to claim 3, characterized in that, in the immersion step, the steel sheet after the pickling step is immersed in the treatment liquid having a liquid temperature of 20 to 85°C for 2 to 60 seconds.

5. Method for forming an insulating coating according to Petition 870250091659, dated 07 / 10 / 2025, page 59 / 62 3 / 3 with claim 3, characterized in that the nitrate ion concentration is from 2.0 to 25.0 g / L. Petition 870250091659, dated 07 / 10 / 2025, page 60 / 62

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