Grain-oriented electrical steel sheet

Abstract

In a grain-oriented electrical steel sheet according to the present invention, an insulating coating does not contain a chromium compound and does contain a phosphate, and when a 31P-NMR spectrum obtained by measuring the insulating coating through a nuclear magnetic resonance method is subjected to Gaussian fitting within a range of 16 to –90 ppm, the ratio of the peak area of a Q0 structure to the total peak area is greater than 0% and no greater than 10%.

Description

grain-oriented electrical steel sheet

[0001] The present invention relates to a grain-oriented electrical steel sheet coated with a chromate-free insulating coating. In particular, the present invention relates to a grain-oriented electrical steel sheet that exhibits low phosphorus elution from the insulating coating even after long-term storage, despite not containing chromate. This application claims priority based on Japanese Patent Application No. 2024-011667, filed on January 30, 2024, the contents of which are incorporated herein by reference.

[0002] Grain-oriented electrical steel sheets are steel sheets that are primarily used as iron cores for transformers, etc. Such grain-oriented electrical steel sheets typically have two surface coating layers: a forsterite layer (also called a primary coating) formed during high-temperature finish annealing, and a phosphate coating that is formed by applying a treatment solution containing phosphate as a main component and then baking it during heat flattening of the steel sheet.

[0003] Phosphate coatings are required to provide grain-oriented electrical steel sheets with electrical insulation and reduce eddy current loss, thereby improving core loss. Phosphate coatings are also required to have various other properties in addition to insulation, such as corrosion resistance, heat resistance, slipperiness, and adhesion. This is necessary to facilitate various manufacturing processes when grain-oriented electrical steel sheets are processed into iron cores for transformers and other devices. For example, if the heat resistance, slipperiness, and adhesion of a phosphate coating are poor, the phosphate coating may peel off during stress relief annealing in core manufacturing, preventing the phosphate coating from demonstrating its inherent insulating properties or hindering smooth lamination of steel sheets, resulting in poor workability.

[0004] Furthermore, one important characteristic of the insulating coating of grain-oriented electrical steel sheets is the ability to apply tension to the steel sheets. Applying tension to steel sheets can improve the iron loss of grain-oriented electrical steel sheets by facilitating domain wall motion. Applying tension can also reduce magnetostriction (one of the main causes of noise in transformers).

[0005] In order to improve the various properties of grain-oriented electrical steel sheets as described above, specific techniques such as those disclosed in the following Patent Documents 1 to 9 have been researched and developed.

[0006] For example, Patent Document 1 discloses a method of applying an insulating coating treatment solution containing a specific composition of aluminum phosphate, chromate, and colloidal silica as main components to a forsterite coating formed on the surface of a steel sheet after finish annealing, followed by baking the solution. The technique disclosed in Patent Document 1 enables the formation of an insulating coating with high tensile strength on the surface of the steel sheet, thereby reducing the iron loss and magnetostriction of the grain-oriented electrical steel sheet.

[0007] Furthermore, Patent Document 2 discloses a method in which a treatment solution containing ultrafine colloidal silica particles with a particle size of 8 μm or less, primary phosphate, and chromate in specific proportions is applied to a steel sheet and then baked. The technology disclosed in Patent Document 2 makes it possible to maintain the high tensile strength of the insulating coating and further improve the lubricity of the coating.

[0008] Furthermore, Patent Document 3 discloses a technology for forming a high-tensile insulating coating on the surface of a grain-oriented electrical steel sheet by depositing a specific amount of an insulating coating whose main components are phosphate, chromate, and colloidal silica having a glass transition point of 950°C to 1200°C.

[0009] The techniques disclosed in Patent Documents 1 to 3 above made it possible to form insulating coatings with significantly superior coating properties and improved coating tension. However, all of the techniques disclosed in Patent Documents 1 to 3 contain chromate, a chromium compound, in the insulating coating. In recent years, with increasing attention being paid to environmental issues, there has been a social demand to prohibit or restrict the use of compounds such as lead, chromium, and cadmium.

[0010] Therefore, research has been conducted into technologies that can form good insulating coatings without containing the above-mentioned chromium compounds. However, the problem with insulating coatings that do not contain chromium compounds is that they do not impart sufficient tension to the steel sheet.

[0011] As a method for solving the above problem, for example, Patent Document 4 discloses a method for using colloidal silica in a SiO ２The present invention discloses a method for treating an insulating coating on a grain-oriented electrical steel sheet, which involves baking a treatment solution at 300°C or higher containing 20 parts by weight of ammonium nitrate, 10 to 120 parts by weight of aluminum phosphate, 2 to 10 parts by weight of boric acid, and 4 to 40 parts by weight in total of one or more sulfates of Mg, Al, Fe, Co, Ni, and Zn.

[0012] Furthermore, Patent Document 5 discloses a technology relating to a coating agent for forming a film, which contains a mixture of boric acid and alumina sol and an organic solvent that is compatible with water, and has a tension-imparting effect on grain-oriented electrical steel sheets.

[0013] Patent Document 6 discloses a surface treatment agent for grain-oriented electrical steel sheet containing primary phosphates of Al, Mg, and Ca and colloidal silica, which also contains one or more organic acid salts of Ca, Mn, Fe, Mg, Zn, Co, Ni, Cu, B, and Al. Patent Document 6 also lists formate, acetate, oxalate, tartrate, lactate, citrate, succinate, and salicylate as examples of organic acid salts.

[0014] Furthermore, Patent Document 7 discloses a technology in which, in an insulating coating treatment agent for grain-oriented electrical steel sheets containing a phosphate and colloidal silica, the metal components in the phosphate are a combination of specific proportions of divalent metal elements, trivalent metal elements, and metal elements having a valence of tetravalent or higher.

[0015] Furthermore, Patent Document 8 discloses a grain-oriented electrical steel sheet comprising a steel sheet and an insulating coating containing a first metal phosphate which is a metal phosphate of one or more metals selected from Al, Fe, Mg, Mn, Ni, and Zn, a second phosphate which is a metal phosphate of one or more metals selected from Co, Mo, V, W, and Zr, and colloidal silica.

[0016] Furthermore, Patent Document 9 discloses an aqueous composition for coating grain-oriented electrical steel, which contains aluminum cations, manganese cations, dihydrogen phosphate, hydrogen phosphate and / or phosphate anions, colloidal silicon dioxide, and optionally iron cations.

[0017] Japanese Patent Application Publication No. 48-39338 Publication of Japanese Patent Application Publication No. 61-41778 Publication of Japanese Patent Application Publication No. 11-071683 Publication of Japanese Patent Application Publication No. 54-143737 Publication of Japanese Patent Publication No. 7-27 No. 8828 Publication of Japanese Patent Publication No. 2000-178760 Publication of Japanese Patent Application Publication No. 2010-13692 Publication of International Publication No. 2017 / 057513 Publication of Japanese Special Publication No. 2022-519691

[0018] These proposals have improved various properties of insulating coatings. However, previous research by the present inventors has revealed that in the case of insulating coatings that do not contain chromium compounds, the amount of phosphorus eluted from the insulating coating increases significantly with long-term storage. After manufacturing, electrical steel sheets are loaded onto ships in coil form and transported for long periods of time under high-temperature and high-humidity conditions. Therefore, if the amount of phosphorus eluted increases significantly with long-term transportation, problems such as stickiness between coils and, in some cases, difficulty unwinding the coil may occur. None of the above techniques have yet achieved the same level of phosphorus elution after long-term storage as conventional coatings containing chromic acid, leaving room for improvement.

[0019] As described above, the insulating coating of grain-oriented electrical steel sheets must have electrical insulation properties and be capable of applying a large tension to the surface of the steel sheet. In addition, the insulating coating of grain-oriented electrical steel sheets must have good moisture absorption resistance even under high-temperature and high-humidity conditions. Furthermore, the insulating coating of grain-oriented electrical steel sheets must not increase the amount of phosphorus eluted during long-term storage.

[0020] One aspect of the present invention has been made to solve the above-mentioned problems, and aims to provide a grain-oriented electrical steel sheet that does not contain chromate, has moisture absorption resistance equivalent to or better than conventional steel sheets, and further has a low amount of phosphorus elution after long-term storage.

[0021] The gist of the present invention is as follows.

[0022] (1) A grain-oriented electrical steel sheet according to one aspect of the present invention comprises a base steel sheet and an insulating coating, wherein the insulating coating does not contain a chromium compound but contains a phosphate, and the insulating coating is subjected to a nuclear magnetic resonance (NMR) analysis under a magnetic field of a proton resonance frequency of 500 MHz, a magic angle spinning frequency of 55 kHz, and a magnetic field of ... ３１ The chemical shift of the P nucleus is based on ammonium dihydrogen phosphate (NH ４ H ２ P.O. ４ ) was set to 0.9 ppm, the observation center was set between 0 and 30 ppm, and measurements were taken under the conditions of a flip angle of 90°, a waiting time of 8 seconds, and an accumulation count of 9000. ３１ When the P-NMR spectrum was Gaussian-fitted in the range of 16 to -90 ppm, Q ０ The ratio of the peak area of ​​the structure to the total peak area is more than 0% and 10% or less.

[0023] (2) In the grain-oriented electrical steel sheet described in (1) above, the base steel sheet may contain, as a chemical composition, in mass%, C: 0.010% or less, Si: 2.00 to 4.00%, Mn: 0.05 to 1.00%, Al: 0.010 to 0.065%, N: 0.004% or less, S: 0.010% or less, Se: 0.010% or less, Cr: 0 to 0.30%, Cu: 0 to 0.40%, P: 0 to 0.50%, Ni: 0 to 1.00%, Sn: 0 to 0.30%, Sb: 0 to 0.30%, B: 0 to 0.0100%, Mo: 0 to 0.1%, Bi: 0 to 0.01%, with the balance being Fe and impurities.

[0024] According to the above aspect of the present invention, it is possible to stably obtain a grain-oriented electrical steel sheet that does not contain chromate, has excellent moisture absorption resistance, and exhibits a small amount of phosphorus elution even when stored for a long period of time in a high-temperature and high-humidity atmosphere.

[0025] FIG. 1 is a diagram showing the relationship between the amount of Na in an insulating coating treatment solution and the amount of moisture absorption of a grain-oriented electrical steel sheet coated with an insulating film. FIG. 2 is a diagram showing the relationship between the amount of Na in an insulating coating treatment solution and the amount of phosphorus eluted from a grain-oriented electrical steel sheet coated with an insulating film, for steel sheets before moisture absorption resistance evaluation. FIG. 3 is a diagram showing the relationship between the amount of Na in an insulating coating treatment solution and the amount of phosphorus eluted from a grain-oriented electrical steel sheet coated with an insulating film, for steel sheets after moisture absorption resistance evaluation. FIG. 4 is a reference diagram showing bridging oxygen in phosphate, and Q ０ , Q １ , Q ２ , Q ３ The four types of Q ｎ A reference diagram showing the structure of the insulating coating. ３１ FIG. 1 is a reference diagram showing an example of Gaussian fitting performed on a P-NMR spectrum. ３１ Q obtained by Gaussian fitting of the P-NMR spectrum ０ 1 is a diagram showing the ratio of the structure, and shows the relationship between the amount of Na in the insulating coating treatment solution and the Q ０ FIG. 1 is a diagram showing the relationship between the ratio of the structure of the insulating coating. ３１ FIG. 1 shows five peak tops whose chemical shifts fall within the range of 16 to −90 ppm in the P-NMR spectrum.

[0026] Preferred embodiments of the present invention will be described in detail below. However, the present invention is not limited to the configurations disclosed in the present embodiments, and various modifications are possible within the scope of the present invention. Furthermore, the numerical ranges shown in the present embodiments include the lower and upper limits. Numerical values ​​indicated as "greater than" or "less than" do not include the numerical range. "%" regarding the content of each element means "mass %" unless otherwise specified.

[0027] The results of the preliminary experiments that led to the production of the grain-oriented electrical steel sheet according to this embodiment will be described below.

[0028] <Experiment> A finish-annealed grain-oriented electrical steel sheet having a thickness of 0.23 mm, which was manufactured by a known method, was sheared to a width of 60 mm and a length of 300 mm, and the annealing separator adhering to the surface was removed by washing with water to prepare a base steel sheet.

[0029] Next, 250 parts by mass of an aqueous solution of aluminum phosphate dibasic with a solids content of 40% by mass, 300 parts by mass of colloidal silica with a solids content of 30% by mass, and 0 to 7 parts by mass of sodium hydroxide (solids content) were mixed to prepare 10 types of insulation coating treatment solutions, each adjusted so that the sodium (Na) content in the insulation coating treatment solution was in the range of 0.02 to 0.34 mol / kg, as shown in Table 1. Note that because sodium-stable colloidal silica was used, the Na content at the level without the addition of sodium hydroxide was 0.02 mol / kg.

[0030]

[0031] Then, the insulating coating treatment solutions were applied to the base steel sheets prepared above so that the coating adhesion amount after baking was 4.5 g / m per side. ２ The coating was then applied to both sides using a roll coater so that the coating was as follows: Then, the coating was baked at a temperature of 850° C. for 30 seconds.

[0032] As a comparative material, an insulating coating treatment solution (Na) containing 50 parts by mass of aluminum primary phosphate not containing Na, 40 parts by mass of colloidal silica (sodium stabilized type), and 10 parts by mass of chromic anhydride was used. ２ O / SiO ２ = 0.25%) was similarly applied to the base steel sheet and baked.

[0033] The moisture absorption resistance was evaluated using a steel plate prepared by applying an insulating coating solution to a base steel plate and baking it. First, the test plate was placed in a thermo-hygrostat (temperature 50°C, humidity 90%) for one week, and the weight difference before and after the temperature and humidity were quantified. The quantified weight difference was then measured on an area of ​​0.036 m on both sides of the test plate. ２ The moisture absorption amount (unit: g / m ２ The moisture absorption amount was defined as the moisture absorption amount, and the moisture absorption resistance was evaluated using this moisture absorption amount as an index. ２ If it is below this value, it can be determined that the moisture absorption resistance is excellent.

[0034] In addition, a phosphorus elution test was also conducted before and after the evaluation of moisture absorption resistance. In the phosphorus elution test, three test pieces of 40 mm x 60 mm were immersed in distilled water at 100°C for 20 minutes and boiled to eluate phosphorus from the coating surface, and the phosphorus was quantitatively analyzed. The quantitative analysis of phosphorus was conducted in accordance with JIS K 0102:2019 Industrial Wastewater Test Method 46.1.1, and the PO ４ (unit: mg / m ２ The amount of phosphorus eluted was 50 mg / m ２ If it is less than this, it can be determined that the amount of phosphorus eluted is small.

[0035] The above evaluation results were summarized in FIG. 1, showing the relationship between the amount of Na in the insulating coating treatment solution and the amount of moisture absorbed by the grain-oriented electrical steel sheet coated with the insulating coating.

[0036] As shown in FIG. 1, the moisture absorption amount of the steel sheet (comparison material) on which the chromium-containing coating was formed was 0.05 g / m ２ In contrast, the steel sheet (test material) having a coating film containing no chromium absorbed 0.2 g / m 2 in the region where the Na content was less than 0.10 mol / kg. ２ The amount is so high that sufficient moisture absorption resistance is not obtained.

[0037] In addition, in the region where the Na content is large, particularly in the region where the Na content is 0.10 mol / kg or more, the moisture absorption amount is 0.15 g / m ２ Furthermore, in the region where the Na content is 0.20 mol / kg or more, the moisture absorption amount is 0.05 g / m ２ The results show that the moisture absorption resistance is equal to or less than that of a steel sheet having a chromium-containing coating formed thereon. On the other hand, it was confirmed that when the Na content exceeds 0.30 mol / kg, the dispersibility of colloidal silica deteriorates, resulting in uneven appearance after baking.

[0038] Next, for the test specimens before evaluating moisture absorption resistance, the relationship between the amount of Na in the insulating coating treatment solution and the amount of phosphorus eluted from the grain-oriented electrical steel sheet coated with the insulating coating was analyzed and the results are shown in FIG.

[0039] As shown in Figure 2, the steel sheet coated with a chromium-free coating exhibited a small amount of phosphorus elution, similar to the steel sheet coated with a chromium-containing coating, regardless of the Na content. In other words, before maintaining constant temperature and humidity, the problem of an increase in the amount of phosphorus eluted from the insulating coating did not occur.

[0040] Furthermore, for the test specimens after the moisture absorption resistance evaluation, the relationship between the amount of Na in the insulating coating treatment solution and the amount of phosphorus eluted from the grain-oriented electrical steel sheet coated with the insulating coating was analyzed and the results are shown in FIG.

[0041] As shown in FIG. 3, the steel sheet with a chromium-free coating has a phosphorus elution amount of 50 mg / m in the region where the Na content is 0.20 mol / kg or more, similar to the steel sheet with a chromium-containing coating. ２ However, in the region where the Na content is less than 0.20 mol / kg, the amount of phosphorus eluted was 50 mg / m ２ The above results were very high, and by evaluating the moisture absorption resistance, it was confirmed that the insulating coating had deteriorated.

[0042] From the above experimental results, the mechanism by which the amount of Na in the insulating coating treatment solution affects the amount of phosphorus eluted after the constant temperature and humidity test in an insulating coating that does not contain chromium is considered as follows.

[0043] <Phosphate Structure> Phosphorus elution from the insulating coating is thought to be caused by a hydrolysis reaction in which water molecules act on the P-O-P bonds of the phosphate that makes up the insulating coating, breaking the bonds. Therefore, it is important to replace the P (phosphorus)-O (oxygen)-P (phosphorus) bond with another bond, making it P-O-M (M is a metal element).

[0044] Here, the structure of the phosphate is evaluated by a nuclear magnetic resonance (NMR) method (hereinafter, ３１ The structure of phosphate is PO, where four oxygen atoms are coordinated around the phosphorus atom. ４ The tetrahedron is used as a unit, and the oxygen atom is replaced by another PO ４ The oxygen atoms that connect the tetrahedra are called bridging oxygens, and the number of bridging oxygen atoms, n, is used as an index to determine the Qｎ As shown in Figure 4, ０ , Q １ , Q ２ , Q ３ The four types of Q ｎ They can be classified into structures.

[0045] As the number n of bridging oxygen atoms decreases, the polarity around the phosphorus atom decreases, weakening the interaction with highly polarizable water molecules, making it difficult for bonds to be broken and reducing the amount of phosphorus eluted.

[0046] <Q ０ Ratio of peak area of ​​structure to total peak area: more than 0% and not more than 10% > For steel sheets with a chromium-free coating, the ratio of the peak area of ​​various insulating coatings with different Na contents was measured before evaluating the moisture absorption resistance. ３１ P-NMR spectra were measured and Gaussian fitting was performed on these spectra in the range of 16 to -90 ppm.

[0047] Here, when performing Gaussian fitting, it is necessary to determine the peak height and line width by the Gaussian function. ３１ For the P-NMR spectrum, the six peak top positions (chemical shifts) at -49 ppm, -35 ppm, -30 ppm, -22 ppm, -8.8 ppm, and +5.9 ppm are fixed. The full width at half maximum for the -49 ppm peak is fixed at 6.291 kHz, and the full width at half maximum for the -35 ppm peak is fixed at 3.780 kHz. The initial full width at half maximum for the -30 ppm peak is set to 2.000 kHz, and the initial full width at half maximum for the -22 ppm, -8.8 ppm, and +5.9 ppm peaks is set to 3.000 kHz. After optimizing only the heights of these peaks, the optimized values ​​of the obtained heights are used as initial values, and the height and line width are used as variable parameters for −30 ppm, −22 ppm, −8.8 ppm, and +5.9 ppm, and the full width at half maximum is fixed at the above value for −49 ppm and −35 ppm, and only the height is used as a variable parameter. The Levenberg-Marquardt method is used to optimize the peaks so as to most closely approximate the experimental spectral line shape. Note that R ２For the value, R ２ In the range of 16 to -90 ppm, R ２ Optimize until the value is 0.9970 or greater.

[0048] The peak tops of the newly separated functional components in this experiment were +5.9 ppm, -8.8 ppm, -22 ppm, -30 ppm, -35 ppm, and -49 ppm. By matching these with the spectral range of the crosslinking order described in the literature, the first three components were found to be Q ０ , Q １ , Q ２ The three components after -30 ppm are determined as Q ３ (Reference: Turner, G. L., Smith, Kirkpatrick, R. J. & Oldfield, E. (1986a) J. Mag. Reason., 70, 408).

[0049] Based on the above, the insulation coating ３１ An example of Gaussian fitting performed on a P-NMR spectrum is shown in FIG.

[0050] In addition, the insulating coating ３１ Based on the results of Gaussian fitting of the P-NMR spectrum, the amount of Na in the insulating coating treatment solution and the Q ０ The relationship between the ratio of the structure and the Q ０ The proportion of the structure is Q ０ , Q １ , Q ２ , Q ３ The four types of Q ｎ Q for the total peak area obtained by summing the areas of each peak in the normal distribution curve of the structure ０ The ratio of the peak area of ​​the structure is shown. ３ The ratio of the peak area of ​​the structure was the sum of the above three components.

[0051] As shown in FIG. 6, when the amount of Na is less than 0.20 mol / kg, Q ０ The peak area ratio of the structure is 0%, whereas when the Na amount is 0.20 mol / kg or more, Q ０ The peak area ratio of the structure is more than 0%.

[0052] As shown by the above experimental results, the insulating coating does not contain chromium compounds, ３１ When the P-NMR spectrum was Gaussian-fitted in the range of 16 to -90 ppm, Q ０ By controlling the ratio of the peak area of ​​the structure (the area of ​​the peak having its top at +5.9 ppm) to the total peak area (the total area of ​​six peaks having their tops at +5.9 ppm, −8.8 ppm, −22 ppm, −30 ppm, −35 ppm, and −49 ppm) to more than 0%, it is possible to control the amount of phosphorus elution to a low level even when the sample is stored for a long period of time in a high-temperature, high-humidity atmosphere.

[0053] Q ０ The proportion of the peak area of ​​the structure is preferably more than 1%, more preferably more than 4%. ０ When the peak area ratio of the structure was over 10%, the appearance of the insulating coating was uneven. １ The proportion of the peak area of ​​the structure is preferably 9% or less.

[0054] <Q ０ The ratio of the peak area of ​​the structure to the total peak area is Q ３ In the grain-oriented electrical steel sheet according to this embodiment, the ratio of the peak area of ​​the Q structure to the total peak area is smaller than the ratio of the peak area of ​​the Q structure to the total peak area. ０ The peak area ratio of the structure is Q ３ The ratio of the peak area of ​​the structure is smaller than that of the Q ０ The above-mentioned effects are preferably obtained by controlling the ratio of the peak area of ​​the structure to more than 0% and 10% or less. However, in order to maintain the form of the insulating coating, Q ０ The peak area ratio of the structure is Q ３ The ratio of the peak area of ​​the structure is smaller than that of the peak area of ​​the structure.

[0055] Here, the insulating coating of the grain-oriented electrical steel sheet according to this embodiment ３１ A method for determining the peak area ratio from a P-NMR spectrum will be described.

[0056] ３１ ​The measurement conditions for P-NMR are described in several non-patent documents (for example, Journal of Non-Crystalline Solid, 1998, 223, pp. 32-42). ３１ It is known that the measurement conditions for P-NMR generally differ depending on the material. In this embodiment, the measurement conditions are as follows: under a magnetic field with a proton resonance frequency of 500 MHz (for example, the measurement magnetic field is 11.74 T to 11.75 T), measurement temperature: room temperature, magic angle spinning (MAS): 55 kHz, measurement method: ３１ Measurements were performed using an INOVA500 manufactured by Agilent under the following conditions: P Single Pulse Excitation (flip angle 90°), measurement wait time: 8 s, accumulation: 9000 times, standard sample (external chemical shift reference): ammonium dihydrogen phosphate 0.9 ppm, observation center set between 0 and 30 ppm. For the insulation coating, the base material of a grain-oriented electrical steel sheet was dissolved in a 10% bromine methanol solution until disappearance of the base material could be confirmed, and then filtered and recovered on a filter. The solution was washed with methanol and subjected to NMR measurement.

[0057] Insulation coating ３１ An example of peaks in the P-NMR spectrum with chemical shifts in the range of 16 to -90 ppm is shown in Figure 7. ３１ For example, five clear peaks are observed in the P-NMR spectrum. That is, from the left in FIG. 7, the peaks are located at +5.9 ppm, -8.8 ppm, -22 ppm, -30 ppm, and -35 ppm. Note that although the peak with a top at -49 ppm does not appear clearly in FIG. 7, this peak at -49 ppm may be clearly observed depending on the type of insulating coating. Also, Q ０ The peak corresponding to the structure is the peak with a peak top at +5.9 ppm in Figure 7. Q ３ The peaks corresponding to the structure are those with peak tops at −30 ppm and −35 ppm in FIG.

[0058] ３１ ​Gaussian fitting is performed on the P-NMR spectrum by the method described above, and the peak area defined as the integral value of each peak is derived. In FIG. 7, for example, the sum of the peak areas of the above five peaks is the total peak area. In FIG. 7, the area of ​​the peak whose top is at +5.9 ppm is Q ０ Similarly, in FIG. 7, the sum of the areas of the peaks whose tops are at −30 ppm and −35 ppm is Q ３ Based on these, the "Q" for the "total peak area" is calculated. ｎ Calculate the ratio of the peak area of ​​each structure.

[0059] The insulating coating of the grain-oriented electrical steel sheet according to this embodiment does not contain chromium compounds. For example, in this embodiment, when the Cr concentration in the insulating coating is less than 1 atomic %, the insulating coating is determined to contain no chromium compounds. The Cr concentration is preferably 0.8 atomic % or less, and more preferably 0.5 atomic % or less.

[0060] Furthermore, in this embodiment, the chemical composition of the insulating coating is not particularly limited, but may satisfy, for example, the following as main contained elements: P: 5 to 30 atomic %, Si: 5 to 30 atomic %, O: 30 to 80 atomic %, Al: 0.1 to 10 atomic %, Cr: less than 1 atomic %, Fe: less than 25 atomic %, Mg: 0 to 10 atomic %, Mn: 0 to 10 atomic %, Ni: 0 to 10 atomic %, Zn: 0 to 10 atomic %, V: 0 to 10 atomic %, W: 0 to 10 atomic %, Zr: 0 to 10 atomic %, Co: 0 to 10 atomic %, and Mo: 0 to 10 atomic %.

[0061] Furthermore, the insulating coating of the grain-oriented electrical steel sheet according to this embodiment means an insulating coating that is free from insufficient baking or cracking due to poor baking conditions. If the insulating coating is insufficient baking or has cracks due to poor baking conditions, it will not be able to satisfy the electrical insulation, tensioning, corrosion resistance, heat resistance, slip properties, adhesion, and other properties required of the insulating coating.

[0062] The concentrations of Cr and other elements contained in the insulating coating can be determined by performing a composition analysis of a cut surface using, for example, SEM-EDS (Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy) or TEM-EDS (Transmission Electron Microscope-Energy Dispersive X-ray Spectroscopy).

[0063] Next, the coating weight of the insulating coating of the grain-oriented electrical steel sheet according to this embodiment will be described.

[0064] In the grain-oriented electrical steel sheet according to this embodiment, the coating weight of the insulating coating is not particularly limited, but is preferably 2.0 to 7.0 g / m per side. ２ The coating weight of the insulating coating is 2.0 g / m ２ If the coating weight of the insulating coating is less than 7.0 g / m, it becomes difficult to apply high tension to the grain-oriented electrical steel sheet, and the insulating properties and corrosion resistance of the grain-oriented electrical steel sheet may also be reduced, which is not preferable. ２ If the coating weight of the insulating coating exceeds 3.0 g / m, the space factor of the grain-oriented electrical steel sheet may decrease, which may result in deterioration of the transformer characteristics, which is not preferable. ２ More preferably, 4.0 g / m ２ The coating weight of the insulating coating is more preferably 6.0 g / m ２ More preferably 5.0 g / m or less ２ The following is the result.

[0065] <Grain-oriented electrical steel sheet> Next, the base steel sheet of the grain-oriented electrical steel sheet according to this embodiment will be described. The base steel sheet of the grain-oriented electrical steel sheet is not particularly limited, but the chemical composition may contain, in mass %, C: 0.010% or less, Si: 2.00 to 4.00%, Mn: 0.05 to 1.00%, Al: 0.010 to 0.065%, N: 0.004% or less, S: 0.010% or less, with the balance being Fe and impurities. Hereinafter, the "%" related to the chemical composition refers to the mass % relative to the total mass of the base steel sheet.

[0066] C: 0.010% or less Carbon (C) is an element effective in controlling the primary recrystallization structure, but it adversely affects magnetic properties, so it is removed by decarburization annealing before final annealing. If the C concentration in the final product exceeds 0.010%, C precipitates during aging, deteriorating hysteresis loss. Therefore, the C concentration is set to 0.010% or less. The C concentration is preferably 0.007% or less, more preferably 0.005% or less. The lower limit of the C concentration includes 0%, but the C concentration may exceed 0%. However, reducing the C concentration to less than 0.0001% significantly increases manufacturing costs, so 0.0001% is the practical lower limit for practical steel sheets. In grain-oriented electrical steel sheets, the C concentration is typically reduced to approximately 0.001% or less by decarburization annealing.

[0067] Si: 2.00 to 4.00% Si (silicon) is an element that increases the electrical resistance of steel sheets and improves iron loss characteristics. If the Si concentration is less than 2.00%, γ transformation of the steel structure occurs during finish annealing, damaging the crystal orientation of the steel sheet. Therefore, the Si concentration is set to 2.00% or more. The Si concentration is preferably 2.50% or more, and more preferably 3.00% or more. On the other hand, if the Si concentration exceeds 4.00%, the workability of the grain-oriented electrical steel sheet decreases and cracks occur during rolling, so the Si concentration is set to 4.00% or less. The Si concentration is preferably 3.50% or less.

[0068] Mn: 0.05 to 1.00% Mn (manganese) is an element that prevents cracking during hot rolling and combines with S and / or Se to produce MnS and MnSe, which function as inhibitors. If the Mn concentration is less than 0.05%, the effect of adding Mn is not fully realized, so the Mn concentration is set to 0.05% or more. The Mn concentration is preferably 0.07% or more, more preferably 0.09% or more. On the other hand, if the Mn concentration exceeds 1.00%, the precipitation and dispersion of MnS and MnSe becomes non-uniform, the desired secondary recrystallization structure cannot be obtained, and the magnetic flux density decreases. Therefore, the Mn concentration is set to 1.00% or less. The Mn concentration is preferably 0.80% or less, more preferably 0.60% or less.

[0069] Al: 0.010 to 0.065% Al (aluminum) is an element that combines with N to form (Al, Si)N or AlN, which functions as an inhibitor. If the Al concentration is less than 0.010%, the effect of adding Al is not fully realized, and secondary recrystallization does not proceed sufficiently. Therefore, the Al concentration is set to 0.010% or more. The Al concentration is preferably 0.015% or more, more preferably 0.020% or more. On the other hand, if the Al concentration exceeds 0.065%, the precipitation dispersion of the inhibitor becomes nonuniform, the desired secondary recrystallization structure cannot be obtained, and the magnetic flux density decreases. Therefore, the Al concentration is set to 0.065% or less. The Al concentration is preferably 0.050% or less, more preferably 0.040% or less.

[0070] N: 0.004% or less N (nitrogen) is an element that combines with aluminum to form AlN and other elements that function as inhibitors. However, if the N concentration in the final product exceeds 0.004%, the N in the steel sheet precipitates as AlN, deteriorating hysteresis loss. Therefore, the N concentration is set to 0.004% or less. The lower limit of the N concentration includes 0%, but reducing the N concentration to less than 0.0001% significantly increases manufacturing costs, so 0.0001% is the practical lower limit for practical steel sheets. In grain-oriented electrical steel sheets, the N concentration is usually reduced to approximately 0.001% or less by finish annealing.

[0071] S: 0.010% or less S (sulfur) is an element that combines with Mn to form MnS, which functions as an inhibitor. However, if the S concentration in the final product exceeds 0.010%, the S in the steel sheet precipitates as MnS, deteriorating hysteresis loss. Therefore, the S concentration is set to 0.010% or less. The lower limit of the S concentration includes 0%, but reducing the S concentration to less than 0.0001% significantly increases production costs, so 0.0001% is the substantial lower limit for practical steel sheets. In grain-oriented electrical steel sheets, the S concentration is usually reduced to about 0.005% or less by finish annealing.

[0072] In the present embodiment, the base steel sheet may contain impurities. Note that the term "impurities" refers to substances that are mixed in from raw materials such as ore or scrap, or from the manufacturing environment, when steel is industrially manufactured.

[0073] Furthermore, in this embodiment, the base steel sheet may contain optional elements in addition to the above-described elements and impurities. For example, instead of a portion of the remaining Fe, at least one of Se, Cr, Cu, P, Ni, Sn, Sb, B, Mo, or Bi may be contained as an optional element. These optional elements may be contained according to their purpose. Therefore, there is no need to set a lower limit for these optional elements, and the lower limit may be 0%. Furthermore, even if these optional elements are contained as impurities, the above-described effects are not impaired.

[0074] For example, in this embodiment, the base steel sheet may contain one or more of the following optional additional elements without impairing its magnetic properties and enhancing other properties: Se: 0.010% or less, Cr: 0.30% or less, Cu: 0.40% or less, P: 0.50% or less, Ni: 1.00% or less, Sn: 0.30% or less, Sb: 0.30% or less, B: 0.0100% or less, Mo: 0.1% or less, and Bi: 0.01% or less.

[0075] Se: 0 to 0.010% Se (selenium) is an element that combines with Mn to produce MnSe, which functions as an inhibitor. However, if the Se concentration in the final product exceeds 0.010%, Se in the steel sheet precipitates as MnSe, deteriorating hysteresis loss. Therefore, the Se concentration is set to 0.010% or less. The lower limit of the Se concentration may be 0%, or even 0.0001%. In grain-oriented electrical steel sheets, the Se concentration is usually reduced to about 0.005% or less by finish annealing.

[0076] Cr: 0 to 0.30% Cr (chromium) is an element that improves the oxide layer during decarburization annealing and is effective in forming a glass film. Therefore, Cr may be added to the base steel sheet in a range of 0.30% or less. If the Cr concentration exceeds 0.30%, decarburization properties are significantly impaired, so the upper limit of the Cr concentration is preferably 0.30%.

[0077] Cu: 0 to 0.40% Cu (copper) is an element that is effective in increasing the resistivity of the base steel sheet and reducing iron loss. If the Cu concentration exceeds 0.40%, the iron loss reduction effect saturates and it becomes a cause of surface defects called "copper scuffs" during hot rolling, so the upper limit of the Cu concentration is preferably 0.40%.

[0078] P: 0 to 0.50% P (phosphorus) is an element that is effective in increasing the resistivity of the base steel sheet and reducing iron loss. If the P concentration exceeds 0.50%, problems arise with rollability, so the upper limit of the P concentration is preferably 0.50%.

[0079] Ni: 0 to 1.00% Ni (nickel) is an element effective in increasing the resistivity of the base steel sheet and reducing iron loss. Ni is also an element effective in controlling the steel structure of the hot-rolled sheet and improving the magnetic properties. However, if the Ni concentration exceeds 1.00%, secondary recrystallization becomes unstable, so the upper limit of the Ni concentration is preferably 1.00%.

[0080] Sn: 0 to 0.30% Sb: 0 to 0.30% Sn (tin) and Sb (antimony) are well-known grain boundary segregation elements. In this embodiment, since the base steel sheet contains Al, depending on the finish annealing conditions, Al may be oxidized by moisture released from the annealing separator, resulting in fluctuations in inhibitor strength at the coil position. As a result, magnetic properties may vary at the coil position. One solution to this problem is to prevent Al oxidation by adding these grain boundary segregation elements. For this purpose, Sn and Sb may be added to the base steel sheet at concentrations of 0.30% or less. On the other hand, if the concentrations of these elements exceed 0.30%, Si is less likely to be oxidized during decarburization annealing, resulting in insufficient glass film formation and significantly impairing decarburization annealing performance. For this reason, the upper limit of the concentrations of these elements is preferably 0.30%.

[0081] B: 0 to 0.0100% B (boron) is an element that combines with N in the base steel sheet and precipitates with MnS to form BN, which functions as an inhibitor. The lower limit of the B concentration is not particularly limited and may be 0% as described above. However, to fully exert the effect of adding B, the lower limit of the B concentration is preferably 0.0005%. The B concentration is preferably 0.001% or more, more preferably 0.0015% or more. On the other hand, if the B concentration exceeds 0.0100%, the precipitated BN becomes non-uniformly dispersed, the desired secondary recrystallization structure cannot be obtained, and the magnetic flux density decreases. Therefore, the B concentration is preferably 0.0100% or less. The B concentration is preferably 0.0080% or less, more preferably 0.0060% or less, and more preferably 0.0040% or less.

[0082] Mo: 0 to 0.1% Mo (molybdenum) is an element effective in improving surface properties during hot rolling. However, if the Mo concentration exceeds 0.1%, the effect of adding Mo becomes saturated, so the upper limit of the Mo concentration is preferably 0.1%.

[0083] Bi: 0 to 0.01% Bi (bismuth) has the effect of stabilizing precipitates such as sulfides and strengthening its inhibitory function. However, if the Bi concentration exceeds 0.01%, Bi has an adverse effect on the formation of the glass coating, so the upper limit of the Bi concentration is preferably 0.01%.

[0084] The above-mentioned chemical composition may be measured by a general analysis method for steel. For example, the chemical composition may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Al may be measured as total aluminum in accordance with JIS G1257-10-1:2013. C and S may be measured using a combustion-infrared absorption method, N may be measured using an inert gas fusion-thermal conductivity method, and, if necessary, O may be measured using an inert gas fusion-non-dispersive infrared absorption method.

[0085] The above chemical composition is that of the base steel sheet. If the grain-oriented electrical steel sheet to be measured has an insulating coating on its surface, remove the insulating coating by the following method before measuring the chemical composition.

[0086] For example, the insulating coating can be removed by immersing the grain-oriented electrical steel sheet having the coating in a high-temperature alkaline solution. ２ O: The insulating coating can be removed from the grain-oriented electrical steel sheet by immersing the sheet in a 50 to 70 mass % aqueous sodium hydroxide solution at 80 to 90°C for 5 to 10 minutes, followed by rinsing with water and drying. The immersion time in the aqueous sodium hydroxide solution can be changed depending on the thickness of the insulating coating.

[0087] <Method for manufacturing grain-oriented electrical steel sheet> Next, a method for manufacturing the grain-oriented electrical steel sheet according to this embodiment will be described. Note that the method for manufacturing the grain-oriented electrical steel sheet according to this embodiment is not limited to the method described below. The manufacturing method described below is one example for manufacturing the grain-oriented electrical steel sheet according to this embodiment.

[0088] Molten steel having a predetermined chemical composition is cast by a conventional method to produce a silicon steel slab. The chemical composition of the silicon steel slab is not limited to a specific composition as long as it can provide the magnetic and mechanical properties required for grain-oriented electrical steel sheet, but an example of the chemical composition of a silicon steel slab is as follows. For example, the silicon steel slab contains, in mass %, C: 0.085% or less, Si: 2.00 to 4.00%, Mn: 0.05 to 1.00%, Al: 0.010 to 0.065%, N: 0.004 to 0.012%, S: 0.010% or less, and B: 0.0100% or less.

[0089] C: 0.085% or less Carbon (C) is an element effective in controlling the primary recrystallization structure, but has a negative effect on magnetic properties, so it is removed by decarburization annealing before final annealing. If the C concentration exceeds 0.085%, the decarburization annealing time increases and productivity decreases, so the C concentration is set to 0.085% or less. The C concentration is preferably 0.070% or less, more preferably 0.050% or less. The lower limit of the C concentration is not particularly limited, and may be 0% or more. Considering productivity in industrial production and the magnetic properties of the product, 0.0001% is the substantial lower limit of the C concentration. In grain-oriented electrical steel sheets, the C concentration is typically reduced to approximately 0.001% or less by decarburization annealing.

[0090] Si: 2.00 to 4.00% Si (silicon) is an element that increases the electrical resistance of steel sheet and improves iron loss characteristics. If the Si concentration is less than 2.00%, γ transformation occurs during finish annealing, damaging the crystal orientation of the steel sheet, so the Si concentration is set to 2.00% or more. The Si concentration is preferably 2.50% or more, and more preferably 3.00% or more. On the other hand, if the Si concentration exceeds 4.00%, workability decreases and cracks occur during rolling, so the Si concentration is set to 4.00% or less. The Si concentration is preferably 3.50% or less.

[0091] Mn: 0.05 to 1.00% Mn (manganese) is an element that prevents cracking during hot rolling and also combines with S and / or Se to form MnS and MnSe, which function as inhibitors. If the Mn concentration is less than 0.05%, the additive effect is not fully realized, so the Mn concentration is set to 0.05% or more. The Mn concentration is preferably 0.07% or more, more preferably 0.09% or more. On the other hand, if the Mn concentration exceeds 1.00%, the precipitation and dispersion of MnS and MnSe becomes non-uniform, the desired secondary recrystallization structure cannot be obtained, and the magnetic flux density decreases. Therefore, the Mn concentration is set to 1.00% or less. The Mn concentration is preferably 0.80% or less, more preferably 0.06% or less.

[0092] Al: 0.010 to 0.065% Al (aluminum) is an element that combines with N to form (Al, Si)N or AlN, which functions as an inhibitor. If the Al concentration is less than 0.010%, the additive effect is not fully realized and secondary recrystallization does not proceed sufficiently, so the Al concentration is set to 0.010% or more. The Al concentration is preferably 0.015% or more, more preferably 0.020% or more. On the other hand, if the Al concentration exceeds 0.065%, the precipitation dispersion of (Al, Si)N and the like becomes non-uniform, the desired secondary recrystallization structure cannot be obtained, and the magnetic flux density decreases. Therefore, the Al concentration is set to 0.065% or less. The Al concentration is preferably 0.050% or less, more preferably 0.040% or less.

[0093] N: 0.004 to 0.012% N (nitrogen) is an element that combines with Al to form AlN and other compounds that function as inhibitors. However, it is also an element that forms blisters (voids) in the steel sheet during cold rolling. If the N concentration is less than 0.004%, the formation of AlN is insufficient, so the N concentration is set to 0.004% or more. The N concentration is preferably 0.006% or more, more preferably 0.007% or more. On the other hand, if the N concentration exceeds 0.012%, there is a concern that blisters (voids) may form in the steel sheet during cold rolling, so the N concentration is set to 0.012% or less. The N concentration is preferably 0.010% or less, more preferably 0.009% or less.

[0094] S: 0.010% or less S (sulfur) is an element that combines with Mn to form MnS, which functions as an inhibitor. If the S concentration exceeds 0.010%, the precipitation and dispersion of MnS becomes non-uniform after purification, the desired secondary recrystallization structure cannot be obtained, the magnetic flux density decreases, and the hysteresis loss deteriorates. Alternatively, MnS remains after purification, which deteriorates the hysteresis loss. Although there is no particular lower limit, the S concentration may be 0%, and is preferably 0.003% or more. The S concentration is more preferably 0.007% or more.

[0095] B: 0.0100% or less B (boron) is an element that bonds with N and precipitates in a composite with MnS to form BN, which functions as an inhibitor. If the B concentration exceeds 0.0100%, the precipitation dispersion of BN becomes non-uniform, the required secondary recrystallization structure cannot be obtained, and the magnetic flux density decreases. Therefore, the B concentration is set to 0.0100% or less. The B concentration is preferably 0.0060% or less, more preferably 0.0040% or less. On the other hand, the lower limit of the B concentration is not particularly limited and may be 0%.

[0096] In this embodiment, the silicon steel slab may contain impurities. The term "impurities" refers to substances that are mixed in from raw materials such as ore or scrap, or from the manufacturing environment, during industrial steel production.

[0097] In this embodiment, the silicon steel slab may contain selective elements in addition to the above-described elements and impurities. For example, instead of a portion of the remaining Fe, at least one of Se, Cr, Cu, P, Ni, Sn, Sb, Mo, and Bi may be contained as a selective element. These selective elements may be contained according to their purpose. Therefore, there is no need to set a lower limit for these selective elements, and the lower limit may be 0%. Furthermore, even if these selective elements are contained as impurities, the above-described effects are not impaired.

[0098] For example, in this embodiment, the silicon steel slab may contain one or more of Se: 0.010% or less, Cr: 0.30% or less, Cu: 0.40% or less, P: 0.50% or less, Ni: 1.00% or less, Sn: 0.30% or less, Sb: 0.30% or less, Mo: 0.1% or less, and Bi: 0.01% or less, within a range that does not impair the magnetic properties of the grain-oriented electrical steel sheet and can enhance other properties.

[0099] In the hot rolling process, a slab having the above chemical composition is hot-rolled to obtain a hot-rolled sheet. The hot-rolling conditions are not particularly limited, and ordinary conditions can be used. The hot-rolled sheet obtained by the hot-rolling process is wound into a coil.

[0100] Before the slab is subjected to hot rolling, the slab may be heated to a temperature of more than 1300°C in order to sufficiently dissolve the inhibitor components MnS and AlN. From the viewpoint of productivity and manufacturing costs, the slab may also be heated to about 1250°C on the premise that the inhibitors will be strengthened in a subsequent nitriding treatment.

[0101] In the hot-rolled sheet annealing process, the coiled hot-rolled sheet is recoiled into a strip-shaped hot-rolled sheet, and then the strip-shaped hot-rolled sheet is subjected to hot-rolled sheet annealing to obtain an annealed hot-rolled sheet. The hot-rolled sheet annealing conditions are not particularly limited, and conventional conditions can be used.

[0102] In the cold rolling process, the annealed hot-rolled sheet is subjected to one or more cold rolling processes to obtain a cold-rolled sheet having a final thickness. In this cold rolling process, the annealed hot-rolled sheet may be subjected to two or more cold rolling processes with intermediate annealing between them to obtain a cold-rolled sheet. Annealing performed before the finish (final) cold rolling homogenizes the crystalline structure. The cold rolling conditions are not particularly limited, and ordinary conditions can be used.

[0103] In the decarburization annealing process, a decarburization annealed sheet is obtained by subjecting the cold-rolled sheet to decarburization annealing. In this decarburization annealing process, the cold-rolled sheet is heat-treated in wet hydrogen to reduce the C content in the cold-rolled sheet to an amount that will not cause deterioration due to magnetic aging in the product steel sheet, and to induce primary recrystallization in the cold-rolled sheet, preparing for the subsequent secondary recrystallization. The decarburization annealing conditions are not particularly limited, and ordinary conditions can be used. The surface of the decarburization annealed sheet obtained by this decarburization annealing process has SiO ２ When a cold-rolled steel sheet is manufactured from a slab heated to about 1250°C, the decarburization-annealed steel sheet is annealed in an ammonia atmosphere after decarburization annealing, thereby generating AlN, which functions as an inhibitor, in the decarburization-annealed steel sheet.

[0104] In the method for producing a grain-oriented electrical steel sheet according to this embodiment, the steel sheet on which the insulating coating is formed may be a grain-oriented electrical steel sheet having a normal forsterite coating, or may be a grain-oriented electrical steel sheet without a forsterite coating.

[0105] In the case of grain-oriented electrical steel sheets having a normal forsterite coating, an annealing separator containing MgO as the main component is applied in the annealing separator application process, which is the process following the decarburization annealing process, in order to prevent seizure during the finish annealing process. The amount of annealing separator applied is 6.0 to 14.0 g / m per side of the decarburization annealed sheet. ２ is.

[0106] In the case of grain-oriented electrical steel sheets that do not have a forsterite coating, alumina (Al ２ O ３ The decarburized annealed sheet coated with the annealing separator is then wound into a coil after the annealing separator has dried.

[0107] In the final annealing step, the coil-shaped decarburized annealed sheet coated with the annealing separator is subjected to final annealing to obtain a base steel sheet for the final product (grain-oriented electrical steel sheet). In this final annealing step, secondary recrystallization occurs in the decarburized annealed sheet by performing final annealing at a temperature of 1100°C or higher. Note that, in order to reduce hysteresis loss in the final product, the decarburized annealed sheet after completion of secondary recrystallization may be subjected to purification annealing so that the precipitates used as inhibitors are rendered harmless.

[0108] An insulating coating is formed on the surface of the steel sheet after secondary recrystallization. The method for forming this insulating coating includes a coating step of applying an insulating coating treatment liquid to the surface of the steel sheet and a baking step of baking the insulating coating treatment liquid. The insulating coating is formed by baking.

[0109] After finish annealing, excess annealing separator is removed by rinsing, followed by pickling in a sulfuric acid bath or the like, and then rinsing. This cleans and activates the surface of the steel sheet, after which an insulating coating treatment solution is applied to the steel sheet in the coating process. There are no restrictions on the method for applying the insulating coating treatment solution to the steel sheet, but it is usually applied using a roll coater. The grain-oriented electrical steel sheet to which the insulating coating treatment solution has been applied is then subjected to a baking process under the conditions described below, whereby an insulating coating is formed on the surface.

[0110] ３１ When the P-NMR spectrum was Gaussian-fitted in the range of 16 to -90 ppm, Q ０ ​In order to make the ratio of the peak area of ​​this structure to the total peak area greater than 0% and equal to or less than 10%, it is necessary to change the P-O-P bonds of the phosphate contained in the insulating coating treatment solution to P-O-M (M is a metal element). To achieve this, the metal component contained in the insulating coating treatment solution is preferably an alkali metal element. Lithium, sodium, and potassium are preferred. Sodium and potassium are even more preferred. These alkali metal elements may be contained in an amount of 0.20 to 0.30 mol / kg relative to the insulating coating treatment solution.

[0111] Q ０ The reason why the addition of alkali metal elements such as sodium and potassium is effective in achieving a ratio of the peak area of ​​the structure to the total peak area of ​​more than 0% and less than or equal to 10% is currently unclear. However, these alkali metals are known to be modifying elements that significantly change the properties of glass, such as phosphates, and they also have small atomic radii. Therefore, it is believed that these alkali metals are easily incorporated into phosphates, resulting in a significant effect. Furthermore, the reason for the significant change in glass properties with increasing sodium content in the insulating coating is thought to be due to an increased rate of conversion from P (phosphorus)-O (oxygen)-P (phosphorus) bonds to P-O-M (M: here assumed to be Na) bonds as the sodium content increases.

[0112] Also, Q ０ In order to make the ratio of the peak area of ​​the structure to the total peak area greater than 0% and less than 10%, it is preferable that the pH of the insulating coating treatment solution is 1.7 or greater and 2.1 or less. This pH value is greater than the pH of conventional insulating coating treatment solutions. Conventional insulating coating treatment solutions usually have a pH less than 1.7. The present inventors have found that when the pH of the insulating coating treatment solution is 1.7 or greater and 2.1 or less, Q ０It has been found that the ratio of the peak area of ​​the structure to the total peak area can be preferably easily controlled to be more than 0% and not more than 10%. The reason for this is not clear at present. However, it is well known that, for example, in the hydrolysis of polyphosphate ions, hydrogen ions act as a catalyst for the cleavage of P-O-P bonds, and similarly, it is known that hydrogen ions also act as a catalyst for the cleavage of P-O-P bonds in pyrophosphate. In this embodiment, the pH of the insulating coating treatment solution is higher than that of conventional insulating coating treatment solutions, and the presence of hydrogen ions is reduced compared to conventional solutions, which is thought to be the reason for the decrease in Q in the insulating coating. ０ The pH of the insulating coating treatment solution is preferably 1.8 or higher, and more preferably 1.9 or higher.

[0113] In the baking process, the grain-oriented electrical steel sheet coated with the insulating coating treatment liquid is heated to a baking soaking temperature, held at the baking soaking temperature, and then cooled.

[0114] The baking soaking temperature (°C) refers to the sheet temperature (maximum sheet temperature) reached in the baking process, and must be 800°C or higher and 1000°C or lower. If the baking soaking temperature is lower than 800°C, the coating formation reaction of the insulating coating will not proceed sufficiently, resulting in not only a poor appearance of the coating but also in the possibility that sufficient tension cannot be imparted to the steel sheet. On the other hand, if the baking soaking temperature exceeds 1000°C, cracks may occur in the insulating coating, reducing the coating tension and insulating properties, and scratches may also occur on the steel sheet. The baking soaking temperature is more preferably 850°C or higher and 950°C or lower.

[0115] The soaking time (seconds) indicates the holding time at the baking soaking temperature. A soaking time of 10 seconds or more is required. If the soaking time is less than 10 seconds, the insulating coating may not be baked properly, resulting in a deterioration in moisture absorption resistance (an increase in the amount of moisture absorbed). A soaking time of 20 seconds or more is desirable. On the other hand, the soaking time is set to 60 seconds or less. If the soaking time exceeds 60 seconds, not only will the moisture absorption resistance remain almost unchanged, but excessive crystallization of the insulating coating may occur, leading to cracks and a decrease in coating tension. A soaking time of 45 seconds or less is more preferable, as this provides sufficient coating properties.

[0116] Also, Q ０ In order to make the ratio of the peak area of ​​the structure to the total peak area greater than 0% and less than 10%, the heating rate during heating to the baking soaking temperature in the baking step is preferably 30°C / sec or more and 100°C / sec or less. The reason for this is not clear at present. However, if the heating rate to the baking soaking temperature is too fast, the surface of the insulating coating solidifies before the interior during heating, trapping moisture inside the insulating coating. This moisture is likely to cause hole-like coating defects inside the insulating coating, and in addition, the Q in the insulating coating ０ The rate of temperature rise to the baking soaking temperature is preferably 40°C / sec or more, more preferably 60°C / sec or more. The rate of temperature rise to the baking soaking temperature is preferably 80°C / sec or less, more preferably 70°C / sec or less.

[0117] The rate of temperature rise to the baking soaking temperature means the value obtained by dividing the temperature range from the baking start temperature (e.g., room temperature) to the baking soaking temperature (a temperature of 800°C or higher and 1000°C or lower) by the time required for temperature rise.

[0118] The type of base steel sheet to be treated with the insulating coating is not particularly limited. The grain-oriented electrical steel sheet according to this embodiment is characterized primarily by the configuration of the insulating coating, and the effects of the insulating coating of the grain-oriented electrical steel sheet according to this embodiment, namely, the ability to apply large tension to the surface of the steel sheet, good adhesion and corrosion resistance, and excellent long-term stability despite not containing chromate, can be achieved regardless of the type of base steel sheet.

[0119] Preferably, the above-described insulating coating treatment may be applied to grain-oriented electrical steel sheets manufactured using the technology disclosed in, for example, Japanese Patent Laid-Open Publication No. 7-268567. In this case, the effect of further reducing iron loss can be obtained. Specifically, by applying the above-described insulating coating treatment to grain-oriented electrical steel sheets containing, by mass%, at least 0.005% or less of C and 2.5 to 7.0% of Si, and optionally containing other alloying elements (e.g., Mn: 0 to 1.0%, Al: 0 to 0.03%, N: 0.01% or less, P: 0.01% or less, and S: 0.01% or less) within ranges that do not impair the properties, with the balance being Fe and impurities, an average grain size of 1 to 10 mm, and an average angle between the (110)

[001] crystal orientation and the rolling direction of 8° or less, the effect of further reducing iron loss can be obtained.

[0120] <Insulating Coating Solution for Grain-Oriented Electrical Steel Sheet> Next, the insulating coating solution (hereinafter simply referred to as "insulating coating solution") used for the grain-orientated electrical steel sheet according to this embodiment will be described.

[0121] The insulating coating treatment solution contains colloidal silica and a metal phosphate of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W, and Zr, but does not contain chromate. The metal phosphate is preferably one or more phosphates selected from Al, Mg, Ni, V, and W, because these phosphates can provide a flat, uniform appearance under a wide range of baking conditions.

[0122] Furthermore, the insulating coating treatment solution preferably contains an alkali metal element. The alkali metals contained in the insulating coating treatment solution are preferably lithium, sodium, and potassium, with sodium and potassium being more preferred. The amount of alkali metal contained in the insulating coating treatment solution is preferably 0.20 mol / kg or more, more preferably 0.22 mol / kg or more. While the upper limit is not particularly limited, it is, for example, 0.30 mol / kg or less, preferably 0.27 mol / kg or less. If the amount of alkali metal contained is less than 0.20 mol / kg, the amount of phosphorus eluted increases during long-term storage in a high-temperature, high-humidity atmosphere. On the other hand, if the amount of alkali metal, such as Na, exceeds 0.30 mol / kg, it is undesirable because it causes uneven appearance.

[0123] In this embodiment, the amount of alkali metals such as Na in the insulation coating treatment solution can be analyzed as follows: The amount of alkali metals such as Na contained in the insulation coating treatment solution is measured by atomic absorption spectrometry and converted into an amount of substance. The amount of alkali metals such as Na is then divided by the weight of the insulation coating treatment solution to derive the amount of alkali metal.

[0124] As described above, the pH of the insulating coating treatment solution is preferably 1.7 to 2.1, more preferably 1.8 or higher, and even more preferably 1.9 or higher.

[0125] <Method for producing insulating coating solution for grain-oriented electrical steel sheet> Next, a method for producing the insulating coating solution used for the grain-oriented electrical steel sheet according to this embodiment (hereinafter simply referred to as the "method for producing the insulating coating solution") and the reasons for the limitations thereon will be described.

[0126] The method for producing the insulating coating solution includes a mixing step of a metal phosphate salt, colloidal silica, and an alkali metal salt. As long as the predetermined amount of alkali metal can be contained in the insulating coating solution, there are no particular limitations on the method for adding the alkali metal. One example is as follows.

[0127] The phosphate is based on a metal phosphate of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W, and Zr, and may further contain an alkali metal in the form of sodium phosphate or potassium phosphate.

[0128] Another possible method is to add a Na compound to the colloidal silica beforehand. However, when adding a Na compound to the colloidal silica, there is a risk that the colloidal silica will aggregate, so careful consideration is required, such as extending the stirring time.

[0129] Furthermore, after mixing the metal phosphate salt with colloidal silica, an aqueous solution of sodium hydroxide or potassium hydroxide can be added to make the insulating coating treatment solution contain an alkali metal.

[0130] The size of the colloidal silica (silica particles) used in this embodiment is not particularly limited, but the average particle size (average primary particle size) is preferably 4 to 35 nm. If the average particle size of the colloidal silica is less than 4 nm, the colloidal silica tends to aggregate, which may reduce the stability of the insulating coating treatment solution, or the insulating coating may become porous with large gaps, reducing the adhesiveness of the insulating coating. On the other hand, if the average particle size of the colloidal silica exceeds 35 nm, the reactivity of the colloidal silica may decrease, which may result in insufficient mixing of the phosphate binder with the colloidal silica, or cracks may occur in the insulating coating, reducing the adhesiveness.

[0131] Furthermore, since the smaller the particle size of the colloidal silica, the denser the coating film formed and the higher the coating tension, it is more preferable that the upper limit of the average particle size of the colloidal silica is 31 nm, 22 nm, 18 nm, or 12 nm. Furthermore, it is more preferable that the surface of the colloidal silica is chemically treated with aluminum. The average particle size (average primary particle size) of the colloidal silica can be determined, for example, by conversion from the specific surface area measured by the BET adsorption method (in accordance with JIS Z 8830:2013).

[0132] In the method for producing an insulating coating solution, the ratio of metal phosphate to colloidal silica is not particularly limited. As long as the amount of alkali metal contained in the insulating coating solution is 0.20 mol / kg or more and 0.30 mol / kg or less, the insulating coating of grain-oriented electrical steel sheet produced using this insulating coating solution will exhibit excellent properties. Preferred values ​​are shown below.

[0133] For example, the insulating coating treatment solution may be prepared by mixing an aqueous solution containing 100 parts by mass of metal phosphate, calculated as solids, 35 to 125 parts by mass of colloidal silica, calculated as solids, and an aqueous solution containing more than 0 to 7 parts by mass of sodium hydroxide, potassium hydroxide, or lithium hydroxide, calculated as solids. The insulating coating treatment solution thus prepared may contain 0.20 mol / kg or more and 0.30 mol / kg or less of lithium, sodium, or potassium as the alkali metal.

[0134] The colloidal silica content in the insulating coating treatment solution is preferably 25 to 55 mass% (solids content) relative to the total mass of the insulating coating treatment solution. A colloidal silica content of less than 25 mass% is undesirable because the insulating coating tension may be insufficient. A colloidal silica content of more than 55 mass% is undesirable because the adhesion of the insulating coating may be reduced. The colloidal silica content in the insulating coating treatment solution is more preferably 27 mass% or more, more preferably 30 mass% or more, 32 mass% or more, or 35 mass% or more, relative to the total mass of the insulating coating treatment solution, calculated as solids content. The colloidal silica content in the insulating coating treatment solution is more preferably 45 mass% or less, and even more preferably 40 mass% or less.

[0135] In the mixing step, various oxides such as titanium oxide and molybdenum oxide, boric acid, sodium borate, pigments, and inorganic compounds such as barium titanate may be further mixed into the insulating coating treatment solution.

[0136] As described above, the pH of the insulating coating treatment solution is preferably adjusted to 1.7 or higher and 2.1 or lower. For example, the pH of the insulating coating treatment solution may be adjusted by adding hydrochloric acid or an alkali metal hydroxide to the insulating coating treatment solution. The pH of the insulating coating treatment solution is preferably 1.8 or higher, and more preferably 1.9 or higher.

[0137] Next, the effects of one embodiment of the present invention will be explained in more detail using examples, but the conditions in the examples are merely examples adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to these examples. Various conditions can be adopted in the present invention as long as they do not deviate from the gist of the present invention and the object of the present invention is achieved.

[0138] As a final product, a slab whose chemical composition was adjusted so that the base steel sheet had the chemical composition shown in Table 2 was heated to 1150°C and subjected to hot rolling to obtain a hot-rolled steel sheet with a thickness of 2.6 mm. This hot-rolled steel sheet was subjected to hot-rolled sheet annealing as necessary, and then subjected to one cold rolling or multiple cold rollings with intermediate annealing in between to obtain a cold-rolled steel sheet with a final thickness of 0.23 mm. This cold-rolled steel sheet was subjected to decarburization annealing, and then to nitriding annealing in which the sheet was held in an ammonia-containing atmosphere during cooling. Note that known conditions were applied in the processes from slab heating to nitriding annealing.

[0139] The decarburization annealed steel sheet after the above-described decarburization annealing was coated with an annealing separator mainly composed of MgO and dried. The decarburization annealed steel sheet coated with the annealing separator was subjected to finish annealing at 1200°C for 20 hours.

[0140] After that, the excess annealing separator was washed away with water using a scrubber, and an insulating coating treatment solution was applied, in which the solid content ratio of colloidal silica in the insulating coating treatment solution was adjusted to 50 mass % as shown in Table 3, with the remainder being solids of phosphate, alkali metal, chromate, and inorganic compounds, as shown in Table 3. The insulating coating was then formed by baking under the conditions shown in Table 4. The Na content in the insulating coating treatment solution was adjusted by adding a 30% aqueous sodium hydroxide solution, the K content was adjusted by adding a 30% aqueous potassium hydroxide solution, and the Li content was adjusted by adding a 30% aqueous lithium hydroxide solution. The pH of the insulating coating treatment solution was adjusted to 1.6 or more and 2.2 or less, as necessary.

[0141] The chemical composition of the base steel sheet, the chemical composition of the insulating coating, the coating weight of the insulating coating, and the properties of the insulating coating were measured for the obtained grain-oriented electrical steel sheets Nos. C1 to C36 and c1 to c4. ３１ The P-NMR spectrum and other measurements were performed according to the above-mentioned method. ３１ For the P-NMR spectrum, Gaussian fitting was performed as described above to obtain the Q ０ The ratio of the peak area of ​​the structure to the total peak area (Q ０ The area ratio of the structure was calculated.

[0142] The obtained grain-oriented electrical steel sheets Nos. C1 to C36 and c1 to c4 were evaluated for moisture absorption, phosphorus elution, appearance after baking, etc., according to the following methods.

[0143] [Moisture absorption amount] The moisture absorption amount of the grain-oriented electrical steel sheet with an insulating coating was calculated by the following method. The obtained grain-oriented electrical steel sheet with an insulating coating was sheared to a length of 300 mm and a width of 60 mm, and placed in a thermo-hygrostat (temperature 50°C, humidity 90%) for one week, and the weight difference before and after the constant temperature and humidity was measured. The determined weight difference was then used to calculate the moisture absorption amount of the test piece with an area of ​​0.036 m on both sides. ２ The moisture absorption amount (unit: g / m ２ This moisture absorption amount was defined as 0.05 g / m ２ If the moisture absorption resistance was less than this, it was determined that the moisture absorption resistance was excellent.

[0144] [Phosphorus elution amount] The amount of phosphorus elution was evaluated after placing the insulating coated grain-oriented electrical steel sheet in a constant temperature and humidity chamber (temperature 50°C, humidity 90%) for one week. The amount of phosphorus elution was measured by immersing three 40 mm x 60 mm test pieces in distilled water at 100°C for 20 minutes and boiling them to eluate phosphorus from the coating surface, and then quantitatively analyzing the phosphorus. The quantitative analysis of phosphorus was performed in accordance with 46.1.1 of the industrial wastewater testing method of JIS K 0102:2019, and ４ (unit: mg / m ２ The amount of phosphorus eluted was 50 mg / m ２ If the value was less than this, the amount of phosphorus elution was judged to be small.

[0145] [Appearance] The appearance of the insulating coating after baking was also evaluated. The appearance of the insulating coating after baking was evaluated by observing the insulating coating with an SEM and judging whether or not the surface of the coating was cloudy. A cloudy area on the coating surface of less than 10% of the observed area was rated as "Very Good," 10% to 20% as "Good," and 20% or more as "Poor." If the appearance was "Very Good" or "Good," the appearance was judged to be excellent. When the surface of the sample after baking of the insulating coating was observed with an SEM, regions in which fine cracks were observed in the coating and regions in which they were not were observed. In the regions in which fine cracks were observed, diffuse reflection of light occurred, causing the sample to appear cloudy. Therefore, the area of ​​the regions in which fine cracks were observed when observed at 1000x magnification was determined, and the ratio to the total observed area was calculated. Specifically, the area ratio of the cloudy region was calculated by performing image analysis on the SEM observation image and binarizing the image into cloudy and non-cloudy regions. The threshold value for binarization was determined using discriminant analysis.

[0146] Q of grain-oriented electrical steel sheet with insulation coating ０ The evaluation results of the area ratio of the structure, the amount of moisture absorption, the amount of phosphorus eluted, and the appearance are shown in Table 5.

[0147] Although not shown in the table, the chemical composition of the insulating coating of Examples C1 to C36 of the present invention satisfied the following main elements: P: 5 to 30 atomic %, Si: 5 to 30 atomic %, O: 30 to 80 atomic %, Al: 0.1 to 10 atomic %, Cr: less than 1 atomic %, Fe: less than 25 atomic %, Mg: 0 to 10 atomic %, Mn: 0 to 10 atomic %, Ni: 0 to 10 atomic %, Zn: 0 to 10 atomic %, V: 0 to 10 atomic %, W: 0 to 10 atomic %, Zr: 0 to 10 atomic %, Co: 0 to 10 atomic %, and Mo: 0 to 10 atomic %. The coating weight of the insulating coating was 2.0 to 7.0 g / m per side. ２ was satisfied.

[0148] As can be seen from Tables 2 to 5, the inventive examples C1 to C36 had product characteristics that satisfied the ranges of the present invention, and were excellent in the amount of phosphorus elution and moisture absorption. They also had excellent appearance after baking. In contrast, the comparative examples c1 to c5 did not have product characteristics that satisfied the ranges of the present invention, and were inferior in at least one of the amount of phosphorus elution, moisture absorption, and appearance after baking. For example, comparative example c1 had a Q ０ The peak area ratio of the structure was outside the range of the present invention, and the amount of phosphorus eluted and the amount of moisture absorbed were poor. ０ The peak area ratio of the structure was outside the range of the present invention, and the appearance after baking was poor. Comparative example c3 contains chromate (chromium compound), so it is outside the range of the present invention. Comparative example c4 has a peak area ratio of Q ０ The peak area ratio of the structure was outside the range of the present invention, and the amount of phosphorus eluted, the amount of moisture absorbed, and the appearance after baking were poor. ０ The peak area ratio of the structure was outside the range of the present invention, and the amount of phosphorus eluted and the amount of moisture absorbed were poor.

[0149]

[0150]

[0151]

[0152]

[0153] According to the above aspect of the present invention, it is possible to stably obtain a grain-oriented electrical steel sheet that does not contain chromate, has excellent moisture absorption resistance, and exhibits a small amount of phosphorus elution even when stored for a long period of time in a high-temperature, high-humidity atmosphere, and therefore has high industrial applicability.

Claims

1. A grain-oriented electrical steel sheet comprising a base steel sheet and an insulating coating, wherein the insulating coating does not contain chromium compounds but contains phosphate, and the insulating coating is subjected to nuclear magnetic resonance spectroscopy under a magnetic field of 500 MHz, a proton resonance frequency, magic angle spinning of 55 kHz, and ３１ The chemical shift of the P nucleus is based on ammonium dihydrogen phosphate (NH ４ H ２ P.O. ４ ) was set to 0.9 ppm, the observation center was set between 0 and 30 ppm, and measurements were taken under the conditions of a flip angle of 90°, a waiting time of 8 seconds, and an accumulation count of 9000. ３１ When the P-NMR spectrum was Gaussian-fitted in the range of 16 to -90 ppm, Q ０ A grain-oriented electrical steel sheet, characterized in that the ratio of a peak area of a structure to a total peak area is more than 0% and 10% or less.

2. The grain-oriented electrical steel sheet according to claim 1, characterized in that the base steel sheet has a chemical composition, in mass%, of C: 0.010% or less, Si: 2.00 to 4.00%, Mn: 0.05 to 1.00%, Al: 0.010 to 0.065%, N: 0.004% or less, S: 0.010% or less, Se: 0.010% or less, Cr: 0 to 0.30%, Cu: 0 to 0.40%, P: 0 to 0.50%, Ni: 0 to 1.00%, Sn: 0 to 0.30%, Sb: 0 to 0.30%, B: 0 to 0.0100%, Mo: 0 to 0.1%, Bi: 0 to 0.01%, with the balance consisting of Fe and impurities.

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