Grain-oriented electrical steel sheet

Abstract

This grain-oriented electrical steel sheet has an insulating coating that does not contain chromium compounds but contains phosphates, and the insulating coating was measured using a nuclear magnetic resonance method. 31 When P-NMR spectra were fitted with Gaussian waves in the range of 16 to -90 ppm, Q 1 The ratio of the peak area of ​​the structure to the total peak area is more than 3% and 18% or less, and Q 1 The proportion of the structure is Q 3 Smaller than the proportion of the structure.

Description

[Technical Field]

[0001] The present invention relates to a grain-oriented electrical steel sheet coated with a chromate-free insulating coating, and in particular 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. 2024-011678, filed on January 30, 2024, the contents of which are incorporated herein by reference. [Background technology]

[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) that is formed during high-temperature finish annealing, and a phosphate coating that is formed by applying a treatment solution containing phosphate as the 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, an 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 facilitates domain wall motion, thereby improving the iron loss of grain-oriented electrical steel sheets. 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 that an insulating coating treatment solution containing a specific composition of aluminum phosphate, chromate, and colloidal silica as its main components is applied to a forsterite coating formed on the surface of a steel sheet after finish annealing, and then baked. The technology disclosed in Patent Document 1 allows an insulating coating with high tensile strength to be formed on the surface of the steel sheet, thereby reducing the iron loss and magnetostriction of the grain-oriented electrical steel sheet.

[0007] 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 applying a specific amount of insulating coating whose main components are phosphate, chromate, and colloidal silica with 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-mentioned problems, for example, Patent Document 4 discloses a method for treating an insulating coating on a grain-oriented electrical steel sheet, which involves baking at 300°C or higher a treatment solution containing 20 parts by weight of colloidal silica (SiO2 content), 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 selected from the group consisting of 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 that contains a mixture of boric acid and alumina sol and an organic solvent that is compatible with water, and that has the effect of imparting tension to grain-oriented electrical steel sheets.

[0013] Patent Document 6 discloses a technology in which a surface treatment agent for grain-oriented electrical steel sheet contains primary phosphates of Al, Mg, and Ca and colloidal silica, and further 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 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 with 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. [Prior art documents] [Patent documents]

[0017] [Patent Document 1] Japanese Patent Publication No. 48-39338 [Patent Document 2] Japanese Patent Publication No. 61-41778 [Patent Document 3] Japanese Patent Application Publication No. 11-071683 [Patent Document 4] Japanese Patent Publication No. 54-143737 [Patent Document 5] Japanese Patent Application Publication No. 7-278828 [Patent Document 6] Japanese Patent Publication No. 2000-178760 [Patent Document 7] Japanese Patent Application Publication No. 2010-13692 [Patent Document 8] International Publication No. 2017 / 057513 [Patent Document 9] Japan Special Publication No. 2022-519691 Summary of the Invention [Problem to be solved by the invention]

[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. [Means for solving the problem]

[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 is A steel plate base material and an insulating coating are provided. the insulating coating does not contain a chromium compound but contains a phosphate; The insulating coating was subjected to nuclear magnetic resonance spectroscopy under a magnetic field with a proton resonance frequency of 500 MHz, magic angle spinning at 55 kHz, 31The chemical shift reference for the P nucleus was set to 0.9 ppm using ammonium dihydrogen phosphate (NH4H2PO4), and the observation center was set between 0 and 30 ppm. Measurements were performed under the conditions of a flip angle of 90°, a waiting time of 8 seconds, and 9000 accumulations. 31 When P-NMR spectrum was fitted with Gaussian in the range of 16 to -90 ppm, Q 1 The ratio of the peak area of ​​the structure to the total peak area is more than 3% and not more than 18%; and Q 1 The proportion of structures is Q 3 It is smaller than the ratio of the peak area of ​​the structure to the total peak area.

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

[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. [Brief explanation of the drawings]

[0025] [Figure 1] FIG. 1 is a graph showing the relationship between the amount of Na in an insulating coating treatment solution and the amount of moisture absorbed by a grain-oriented electrical steel sheet coated with an insulating coating. [Figure 2] FIG. 10 is a graph 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 coating, for steel sheets before evaluation of moisture absorption resistance. [Figure 3] FIG. 10 is a graph showing 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, for the steel sheet after the moisture absorption resistance evaluation. [Figure 4] This is a reference diagram showing the bridging oxygen of phosphate, and also shows four types of Qn structures: Q0, Q1, Q2, and Q3. [Figure 5] FIG. 10 is a reference diagram showing an example of Gaussian fitting performed on the 31P-NMR spectrum of an insulating coating. [Figure 6] FIG. 10 is a graph showing the proportion of Q1 structure determined by Gaussian fitting of the 31P-NMR spectrum of the insulating coating, and is a graph showing the relationship between the amount of Na in the insulating coating treatment solution and the proportion of Q1 structure in the insulating coating. [Figure 7] FIG. 1 is a diagram showing five peak tops in the chemical shift range of 16 to −90 ppm in the 31P-NMR spectrum of an insulating coating. DETAILED DESCRIPTION OF THE INVENTION

[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, 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 rinsing with water to prepare a base steel sheet.

[0029] Next, 250 parts by mass of an aqueous solution of aluminum phosphate dibasic with a solid content of 40% by mass, 300 parts by mass of colloidal silica with a solid content of 30% by mass, and 0 to 7 parts by mass of sodium hydroxide (solid content) were mixed to prepare 10 types of insulation coating treatment solutions, each adjusted so that the amount of sodium (Na) 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 amount of Na at the level without the addition of sodium hydroxide was 0.02 mol / kg.

[0030] [Table 1]

[0031] Then, the insulating coating treatment liquids 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 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 (Na2O / SiO2 = 0.25%) consisting of 50 parts by mass of sodium-free aluminum phosphate, 40 parts by mass of colloidal silica (sodium stabilized), and 10 parts by mass of chromic anhydride was similarly applied to a 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 piece was placed in a constant temperature and humidity chamber (temperature 50°C, humidity 90%) for one week, and the weight difference before and after the constant temperature and humidity was quantified. The quantified weight difference was then measured on an area of ​​0.036 m on both sides of the test piece. 2 The moisture absorption amount (unit: g / m 2 ) and 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] Phosphorus elution tests were also conducted before and after the moisture absorption resistance evaluation. For the phosphorus elution test, three 40mm x 60mm test pieces were immersed in distilled water at 100°C for 20 minutes and boiled to elute phosphorus from the coating surface, and the phosphorus was then quantitatively analyzed. The quantitative analysis of phosphorus was conducted in accordance with JIS K 0102:2019 Industrial Wastewater Testing Method 46.1.1, and the PO4 (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] Based on the above evaluation results, 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 was summarized and shown in Figure 1.

[0036] As shown in Figure 1, the moisture absorption amount of the steel sheet with a chromium-containing coating (comparison material) was 0.05 g / m 2 In contrast, the steel sheet (test material) with a coating that does not contain 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 areas where the Na content is large, especially in areas 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 2The moisture absorption resistance was found to be equal to or less than that of a steel sheet coated with a chromium-containing coating. On the other hand, it was confirmed that when the Na content exceeded 0.30 mol / kg, the dispersibility of the colloidal silica deteriorated, 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 Figure 2.

[0039] As shown in Figure 2, steel sheets coated with a chromium-free coating exhibited a small amount of phosphorus elution, similar to steel sheets coated with a chromium-containing coating, regardless of the sodium content. In other words, before maintaining constant temperature and humidity, the problem of increased phosphorus elution 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 Figure 3.

[0041] As shown in Figure 3, the steel sheet with a chromium-free coating has a phosphorus elution rate 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] Based on the above experimental results, the mechanism by which the amount of sodium 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> The elution of phosphorus from the insulating coating is thought to be caused by a hydrolysis reaction in which water molecules act on the POP bonds in the phosphate that makes up the insulating coating, breaking the bonds. Therefore, it is important to replace the P (phosphorus)-O (oxygen)-P (phosphorus) bonds with other bonds to create POM (where M is a metal element).

[0044] Here, the structure of phosphate is evaluated using the Nuclear Magnetic Resonance (NMR) method (hereinafter referred to as 31 The structure of phosphates is a PO4 tetrahedron, where four oxygen atoms are coordinated around a phosphorus atom, forming a three-dimensional structure by sharing an oxygen atom with another PO4 tetrahedron at the vertex. The oxygen atoms connecting the tetrahedra are called bridging oxygens, and the number of these bridging oxygens, n, is used as an index to measure the Q n As shown in Figure 4, Q 0 , Q 1 , Q 2 , Q 3 The four types of Q n They can be classified into structures.

[0045] As the number of bridging oxygen atoms, n, decreases, the polarity around the phosphorus atom decreases, weakening the interaction with highly polarizable water molecules, making the bond less likely to break. For example, in an insulating coating, 0 The higher the proportion of the structure, the less likely phosphorus is to be eluted from the insulating coating.

[0046] On the other hand, as the number n of bridging oxygen atoms decreases, the number of bridging oxygen atoms connecting the PO4 tetrahedra decreases, and the insulating coating ability tends to decrease. Therefore, in the grain-oriented electrical steel sheet according to this embodiment, the Q 0 , Q 1 , Q 2 , Q 3 The four types of Q n Among the structures, especially Q 1 Focus on structure.

[0047] 1 ​Ratio of peak area of ​​structure to total peak area: More than 3% and less than 18% Before evaluating the moisture absorption resistance of steel sheets coated with a chromium-free coating, the properties of various insulating coatings with different Na contents were evaluated. 31 P-NMR spectra were measured and Gaussian fitting was performed on these spectra in the range of 16 to -90 ppm.

[0048] 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 (FWHM) of the -49 ppm peak is fixed at 6.291 kHz, and the full width at half maximum (FWHM) of the -35 ppm peak is fixed at 3.780 kHz. The initial FWHM of the -30 ppm peak is set to 2.000 kHz, and the initial FWHM of 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 height values ​​obtained are used as the 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. These are then optimized by the Levenberg-Marquardt method to best approximate the experimental spectral line shape. Note that the R 2 For the value, R 2 In the range of 16 to -90 ppm, R 2 Optimize until the value is 0.9970 or greater.

[0049] 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 Q0 , Q 1 , Q 2 The three components after -30 ppm are determined as Q 3 (References: Turner, GL, Smith, Kirkpatrick, RJ. & Oldfield, E. (1986a) J. Mag. Reason., 70, 408).

[0050] Based on the above, the insulation coating 31 An example of Gaussian fitting for a P-NMR spectrum is shown in Figure 5.

[0051] 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 1 The relationship between the ratio of the structure and the Q 1 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 1 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.

[0052] As shown in Figure 6, when the amount of Na is less than 0.20 mol / kg, Q 1 The peak area ratio of the structure is 3% or less, whereas when the Na content is 0.20 mol / kg or more, Q 1 The proportion of the peak area of ​​the structure is more than 3%.

[0053] As shown by the above experimental results, the insulating coating does not contain chromium compounds, 31 When P-NMR spectra were fitted with Gaussian waves in the range of 16 to -90 ppm, Q 1By controlling the ratio of the peak area of ​​the structure (the area of ​​the peak with a peak top at -8.8 ppm) to the total peak area (the total area of ​​six peaks with peak tops at +5.9 ppm, -8.8 ppm, -22 ppm, -30 ppm, -35 ppm, and -49 ppm) to more than 3%, it is possible to keep the amount of phosphorus eluted low even when stored for a long period of time in a high-temperature, high-humidity atmosphere. In addition, there is no problem with a decrease in the ability to form an insulating coating.

[0054] Q 1 The proportion of the peak area of ​​the structure is preferably more than 4%, more preferably more than 8%. 1 When the ratio of the peak area of ​​the structure exceeds 10%, it is preferable because the film-forming ability is particularly excellent. 1 When the peak area ratio of the structure was over 18%, the appearance of the insulating coating was uneven. 1 The proportion of the peak area of ​​the structure is preferably 16% or less.

[0055] 1 The ratio of the peak area of ​​a structure to the total peak area is Q 3 The ratio of the peak area of ​​the structure to the total peak area is smaller than In the grain-oriented electrical steel sheet according to this embodiment, Q 1 The peak area ratio of the structure is Q 3 Q is smaller than the peak area ratio of the structure. 1 The above-mentioned effect can be preferably obtained by controlling the peak area ratio of the structure to be more than 3% and not more than 18%. However, in order to maintain the morphology of the insulating coating, Q 1 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.

[0056] Here, the insulating coating of the grain-oriented electrical steel sheet according to this embodiment 31 This section explains how to calculate the peak area ratio from a P-NMR spectrum.

[0057] 31 ​The measurement conditions for P-NMR are described in several non-patent documents (e.g., 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 Agilent INOVA500 under the following conditions: P Single Pulse Excitation (flip angle 90°), measurement wait time: 8 s, accumulation: 9000 times, standard sample (external chemical shift standard): ammonium dihydrogen phosphate 0.9 ppm, observation center set between 0 and 30 ppm. For the insulation coating, the base material of grain-oriented electrical steel sheet was dissolved in a 10% bromine-methanol solution until the disappearance of the base material could be confirmed, then filtered and collected on the filter. The material was washed with methanol and subjected to NMR measurement.

[0058] 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 the peak with a top at -49 ppm is not clearly visible in FIG. 7, but this peak at -49 ppm may be clearly visible depending on the type of insulating coating. Also, Q 1 The peak corresponding to the structure is the peak with a peak top at -8.8 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.

[0059] 31For the P-NMR spectrum, Gaussian fitting is performed as described above to derive the peak area defined as the integral value of each peak. In Figure 7, for example, the sum of the peak areas of the above five peaks is the total peak area. In Figure 7, the area of ​​the peak whose top is -8.8 ppm is Q 1 Similarly, in Figure 7, the sum of the areas of the peaks with peak tops 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.

[0060] 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.

[0061] 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 %.

[0062] 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.

[0063] The concentrations of Cr and other elements contained in the insulating coating can be determined by performing 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).

[0064] Next, the coating weight of the insulating coating of the grain-oriented electrical steel sheet according to this embodiment will be described.

[0065] 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 undesirable. 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 or less, more preferably 5.0 g / m 2 The following is the result.

[0066] <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, % relating to the chemical composition means mass% with respect to the total mass of the base steel sheet.

[0067] 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, and 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 usually reduced to approximately 0.001% or less by decarburization annealing.

[0068] Si: 2.00 to 4.00% Silicon (Si) 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.

[0069] Mn: 0.05 to 1.00% Manganese (Mn) is an element that prevents cracking during hot rolling and 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 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, and 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, and more preferably 0.60% or less.

[0070] 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, and more preferably 0.020% or more. On the other hand, if the Al concentration exceeds 0.065%, the precipitation and dispersion of the inhibitor 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, and more preferably 0.040% or less.

[0071] 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, degrading hysteresis loss, so the N concentration must be 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 around 0.001% or less by finish annealing.

[0072] 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, degrading hysteresis loss, so the S concentration must be 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 manufacturing costs, so 0.0001% is the practical lower limit for practical steel sheets. In grain-oriented electrical steel sheets, the S concentration is usually reduced to approximately 0.005% or less by finish annealing.

[0073] 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.

[0074] 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 the 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.

[0075] For example, in this embodiment, the base steel sheet may contain one or more of the following optional elements added thereto without impairing its magnetic properties and for the purpose of 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.

[0076] Se: 0 to 0.010% Se (selenium) is an element that combines with Mn to form MnSe, which functions as an inhibitor. However, if the Se concentration in the final product exceeds 0.010%, the Se in the steel sheet precipitates as MnSe, deteriorating hysteresis loss. Therefore, the Se concentration must be 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 approximately 0.005% or less by finish annealing.

[0077] 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 is significantly impaired, so the upper limit of the Cr concentration is preferably 0.30%.

[0078] Cu: 0 to 0.40% Copper (Cu) 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. Therefore, the upper limit of the Cu concentration is preferably 0.40%.

[0079] 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 in the rollability, so the upper limit of the P concentration is preferably 0.50%.

[0080] Ni: 0 to 1.00% Ni (nickel) is an element that is effective in increasing the resistivity of the base steel sheet and reducing iron loss. Ni is also an element that is 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%.

[0081] 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 conditions of the final annealing, 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 add these grain boundary segregation elements to prevent Al oxidation. For this purpose, Sn and Sb may be added to the base steel sheet at a concentration of 0.30% or less. On the other hand, if the concentration of these elements exceeds 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 concentration of these elements is preferably 0.30%.

[0082] B: 0 to 0.0100% Boron (B) is an element that combines with N in the base steel sheet and precipitates together 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 recrystallized 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.

[0083] Mo: 0 to 0.1% Mo (molybdenum) is an element that is 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%.

[0084] 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 a negative effect on glass film formation, so the upper limit of the Bi concentration is preferably 0.01%.

[0085] The above-mentioned chemical composition may be measured by a general analytical 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 the combustion-infrared absorption method, N may be measured using the inert gas fusion-thermal conductivity method, and, if necessary, O may be measured using the inert gas fusion-non-dispersive infrared absorption method.

[0086] 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.

[0087] 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. Specifically, the insulating coating can be removed from the grain-oriented electrical steel sheet by immersing the sheet in a sodium hydroxide solution containing 30-50% by mass of NaOH and 50-70% by mass of HO at 80-90°C for 5-10 minutes, followed by rinsing with water and drying. The time for immersion in the sodium hydroxide solution can be adjusted depending on the thickness of the insulating coating.

[0088] <Method of manufacturing grain-oriented electrical steel sheets> 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.

[0089] 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 sheets. 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.

[0090] C: 0.085% or less Carbon (C) is an element effective in controlling the primary recrystallization structure, but it 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 becomes longer and productivity decreases, so the C concentration is set to 0.085% or less. The C concentration is preferably 0.070% or less, and more preferably 0.050% or less. There is no particular restriction on the lower limit of the C concentration, and it may be 0% or more. When considering productivity in industrial production and the magnetic properties of the product, 0.0001% is the practical lower limit of the C concentration. In grain-oriented electrical steel sheets, the C concentration is usually reduced to approximately 0.001% or less by decarburization annealing.

[0091] Si: 2.00 to 4.00% Silicon (Si) is an element that increases the electrical resistance of steel sheets and improves their 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. 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%, 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.

[0092] Mn: 0.05 to 1.00% Manganese (Mn) 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 effect of the addition is not fully realized, so the Mn concentration is set to 0.05% or more. The Mn concentration is preferably 0.07% or more, and 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, and more preferably 0.06% or less.

[0093] 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, so 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.

[0094] 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, but it is also an element that forms blisters (voids) in steel sheets during cold rolling. If the N concentration is less than 0.004%, the formation of AlN will be 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) will form in the steel sheets 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.

[0095] 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 hysteresis loss deteriorates. Alternatively, MnS remains after purification, deteriorating 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.

[0096] B: 0.0100% or less B (boron) is an element that bonds with N and precipitates together with MnS to form BN, which functions as an inhibitor. If the B concentration exceeds 0.0100%, the precipitated BN will not be dispersed uniformly, the required secondary recrystallized structure will not be obtained, and the magnetic flux density will decrease. Therefore, the B concentration is set to 0.0100% or less. The B concentration is preferably 0.0060% or less, and 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%.

[0097] 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.

[0098] 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, or Bi may be contained as a selective element. These selective elements may be contained according to their intended 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.

[0099] 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.

[0100] 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.

[0101] Before the slab is subjected to hot rolling, it may be heated to a temperature exceeding 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 by a nitriding treatment in a subsequent process.

[0102] 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.

[0103] In the cold rolling process, the annealed hot-rolled sheet is subjected to cold rolling once or twice or more times to obtain a cold-rolled sheet having a final thickness. In this cold rolling process, the annealed hot-rolled sheet may be subjected to cold rolling twice or more times with intermediate annealing in between to obtain a cold-rolled sheet. Annealing performed before the finish (final) cold rolling homogenizes the crystal structure. The cold rolling conditions are not particularly limited, and ordinary conditions can be used.

[0104] 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 carbon content in the cold-rolled sheet to an amount that will not cause deterioration due to magnetic aging in the product steel sheet, and primary recrystallization occurs in the cold-rolled sheet, preparing it for the subsequent secondary recrystallization. The decarburization annealing conditions are not particularly limited, and conventional conditions can be used. An SiO2 oxide film is formed on the surface of the decarburization annealed sheet obtained by this decarburization annealing process. When a cold-rolled sheet is produced from a slab heated to approximately 1250°C, the decarburization annealed sheet is annealed in an ammonia atmosphere after decarburization annealing to produce AlN, which functions as an inhibitor, in the decarburization annealed sheet.

[0105] 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.

[0106] In the case of grain-oriented electrical steel sheets with 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, 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.

[0107] In the case of grain-oriented electrical steel sheets that do not have a forsterite coating, an annealing separator whose main component is alumina (Al2O3) is applied during the annealing separator application process. The decarburized annealed sheet to which the annealing separator has been applied is then wound into a coil after the annealing separator has dried.

[0108] In the final annealing process, the coil-shaped decarburized annealed sheet coated with the annealing separator is subjected to final annealing to obtain the base steel sheet for the final product (grain-oriented electrical steel sheet). In this final annealing process, 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.

[0109] 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.

[0110] 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.

[0111] 31 When P-NMR spectra were fitted with Gaussian waves in the range of 16 to -90 ppm, Q 1 To make the ratio of the peak area of ​​the structure to the total peak area greater than 3% and equal to or less than 18%, it is necessary to convert the POP bonds of the phosphates contained in the insulation coating treatment solution to POM (M is a metal element). To achieve this, the metal component contained in the insulation 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 insulation coating treatment solution.

[0112] Q 1The reason why the addition of alkali metal elements such as sodium and potassium is effective in achieving a ratio of the structural peak area to the total peak area of ​​more than 3% and less than 18% is unclear at present. However, these alkali metals are known to be modifying elements that significantly change the properties of glasses such as phosphates, and in addition, they have small atomic radii. Therefore, it is thought 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 POM (M: assumed here to be Na) bonds as the sodium content increases.

[0113] Also, Q 1 In order to make the ratio of the peak area of ​​the structure to the total peak area more than 3% and not more than 18%, it is preferable that the pH of the insulating coating treatment solution is 1.7 or more and 2.1 or less. This pH value is higher than the pH of conventional insulating coating treatment solutions. Conventional insulating coating treatment solutions usually have a pH of less than 1.7. The present inventors have found that when the pH of the insulating coating treatment solution is 1.7 or more and 2.1 or less, Q 1 It has been found that the ratio of the peak area of ​​the structure to the total peak area can be preferably controlled to be more than 3% and not more than 18%. The reason for this is not clear at present. However, for example, it is well known that in the hydrolysis of polyphosphate ions, hydrogen ions act as a catalyst for the cleavage of POP bonds, and similarly, it is known that hydrogen ions also act as a catalyst for the cleavage of POP bonds in pyrophosphates. 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 Q in the insulating coating. 1 It is believed that this influences the proportion of the structure. The pH of the insulating coating treatment solution is preferably 1.8 or higher, and more preferably 1.9 or higher.

[0114] 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.

[0115] The baking soaking temperature (°C) refers to the sheet temperature (maximum sheet temperature) reached during 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 a poor coating appearance and insufficient tension being imparted to the steel sheet. On the other hand, if the baking soaking temperature is higher than 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.

[0116] The soaking time (seconds) indicates the time required to maintain the temperature at the baking 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 (increased moisture absorption). A soaking time of 20 seconds or more is desirable. On the other hand, the soaking time should be 60 seconds or less. If the soaking time exceeds 60 seconds, not only will there be almost no change in moisture absorption resistance, 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.

[0117] Also, Q 1 In order to make the ratio of the peak area of ​​the structure to the total peak area more than 3% and not more than 18%, it is preferable that the heating rate when heating to the baking soaking temperature in the baking process is 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 pore-like coating defects inside the insulating coating, and in addition, the Q in the insulating coating 1The 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.

[0118] The rate of temperature rise to the baking soaking temperature means the temperature range from the baking start temperature (room temperature) to the baking soaking temperature (temperature of 800°C or higher and 1000°C or lower) divided by the time required for temperature rise.

[0119] 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.

[0120] Preferably, the above-mentioned insulating coating treatment is 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-mentioned 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., 0 to 1.0% of Mn, 0 to 0.03% of Al, 0.01% or less of N, 0.01% or less of P, and 0.01% or less of S) 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)

[0001] crystal orientation and the rolling direction of 8° or less, the effect of further reducing iron loss can be obtained.

[0121] <Insulating coating treatment solution for grain-oriented electrical steel sheets> Next, the insulating coating treatment liquid (hereinafter simply referred to as "insulating coating treatment liquid") used for the grain-oriented electrical steel sheet according to this embodiment will be described.

[0122] 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 provide a flat, uniform appearance over a wide range of baking conditions.

[0123] 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 there is no particular upper limit, 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.

[0124] 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 obtain the desired value.

[0125] As described above, the pH of the insulating coating treatment solution is preferably 1.7 or more and 2.1 or less, more preferably 1.8 or more, and even more preferably 1.9 or more.

[0126] <Method of manufacturing an insulating coating treatment solution for grain-oriented electrical steel sheets> 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.

[0127] 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.

[0128] 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.

[0129] Another possible method is to add a sodium compound to the colloidal silica beforehand. However, when adding a sodium compound to colloidal silica, there is a risk that the colloidal silica will aggregate, so careful consideration is required, such as extending the stirring time.

[0130] 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.

[0131] 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.

[0132] Furthermore, since the smaller the particle size of the colloidal silica, the denser the coating film formed and the higher the coating tension, the upper limit of the average particle size of the colloidal silica is more preferably 31 nm, 22 nm, 18 nm, or 12 nm. Furthermore, it is even 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).

[0133] 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 listed below.

[0134] For example, the insulating coating treatment solution may be prepared by mixing an aqueous solution containing 100 parts by mass of metal phosphate (solids content), 35 to 125 parts by mass of colloidal silica (solids content), and an aqueous solution containing more than 0 to 7 parts by mass of sodium hydroxide, potassium hydroxide, or lithium hydroxide (solids content).The insulating coating treatment solution prepared in this manner may contain 0.20 mol / kg or more and 0.30 mol / kg or less of lithium, sodium, or potassium as the alkali metal.

[0135] The colloidal silica content in the insulating coating treatment solution is preferably 25 to 55 mass% in terms of 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 may not have sufficient coating tension, while a colloidal silica content of more than 55 mass% is undesirable because the adhesiveness 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, in terms of solids content relative to the total mass of the insulating coating treatment solution. 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.

[0136] 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.

[0137] 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. [Example]

[0138] 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.

[0139] 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 hot-rolled 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 to one cold rolling or multiple cold rolling steps 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.

[0140] After the decarburization annealing described above, the decarburization annealed sheet was coated with an annealing separator mainly composed of MgO and dried. The decarburization annealed sheet coated with the annealing separator was then subjected to finish annealing at 1200°C for 20 hours.

[0141] After that, the excess annealing separator was washed away with water using a scrubber, and an insulation coating treatment solution was applied, in which the solid content of colloidal silica in the insulation 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 insulation coating was then formed by baking under the conditions shown in Table 4. The amount of Na in the insulation coating treatment solution was adjusted by adding a 30% aqueous solution of sodium hydroxide, the amount of K by adding a 30% aqueous solution of potassium hydroxide, and the amount of Li by adding a 30% aqueous solution of lithium hydroxide. The pH of the insulation coating treatment solution was adjusted to between 1.6 and 2.2, as needed.

[0142] 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 investigated for the obtained grain-oriented electrical steel sheets Nos. C1 to C36 and c1 to c4. 31P-NMR spectra and other measurements were performed based on the above method. 31 For the P-NMR spectrum, Gaussian fitting was performed as described above to obtain the Q 1 The ratio of the peak area of ​​a structure to the total peak area (Q 1 The area ratio of the structure was calculated.

[0143] 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, and the like, according to the following methods.

[0144] [Moisture absorption amount] The moisture absorption amount of the grain-oriented electrical steel sheet with an insulating coating was calculated using 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 constant temperature and humidity chamber (temperature 50°C, humidity 90%) for one week, and the weight difference before and after 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 ) was defined as the moisture absorption amount of 0.05 g / m 2 If the moisture absorption resistance was less than this, it was determined that the moisture absorption resistance was excellent.

[0145] [Phosphorus elution amount] The amount of phosphorus elution was evaluated after placing the grain-oriented electrical steel sheets with the insulating coating 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 40mm x 60mm test pieces in distilled water at 100°C for 20 minutes and boiling them to elute 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 JIS K 0102:2019 industrial wastewater testing method, using PO4 (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.

[0146] [exterior] 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 coating surface was cloudy. If the cloudy area of ​​the coating surface was less than 10% of the observed area, it was judged as "Very Good", if it was 10% or more but less than 20%, it was judged as "Good", and if it was 20% or more, it was judged as "Poor". If the appearance was "Very Good" or "Good", it was judged to have excellent appearance. When the surface of a sample after baking of the insulating coating is observed using an SEM, areas where fine cracks are found in the coating and areas where they are not are observed. In the areas where these fine cracks are found, diffuse reflection of light occurs, causing the sample to appear cloudy. Therefore, the area of ​​the areas where fine cracks were found when observed at 1000x magnification was calculated and the ratio to the total observed area was calculated. Specifically, the area ratio of these cloudy areas was calculated by performing image analysis on the SEM observation image and binarizing it into cloudy and non-cloudy areas. The threshold for binarization was determined using discriminant analysis.

[0147] Q of grain-oriented electrical steel sheet with insulation coating 1 Table 5 shows the evaluation results for the area ratio of the structure, moisture absorption amount, phosphorus elution amount, and appearance.

[0148] 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.

[0149] As can be seen from Tables 2 to 5, the product characteristics of the inventive examples C1 to C36 satisfied the ranges of the inventive invention, and were excellent in the amount of phosphorus elution and moisture absorption. In addition, the appearance after baking was also excellent. Furthermore, although not shown in the tables, there was no problem with the decrease in the ability to form an insulating coating. In particular, Q 1 When the peak area ratio of the structure was more than 10%, the film forming ability was particularly excellent and a dense insulating film was formed. In contrast, the comparative examples c1 to c5 did not satisfy the product characteristics within the scope of the present invention, and were inferior in at least one of the amount of phosphorus elution, the amount of moisture absorption, and the appearance after baking. 1 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. 1 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 1 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. 1 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.

[0150] [Table 2]

[0151] [Table 3]

[0152] [Table 4]

[0153] [Table 5] [Industrial Applicability]

[0154] 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, the insulating coating does not contain a chromium compound but contains a phosphate; The insulating coating was subjected to nuclear magnetic resonance spectroscopy under a magnetic field of proton resonance frequency 500 MHz, magic angle spinning 55 kHz, 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 １ The ratio of the peak area of ​​the structure to the total peak area is more than 3% and 18% or less; and Q １ The proportion of the structure is Q ３ The ratio of the peak area of ​​the structure to the total peak area is smaller than Grain-oriented electrical steel sheet characterized by:

2. The base steel plate has a chemical composition, in mass%, of C: 0.010% or less, Si: 2.00-4.00%, Mn: 0.05-1.00%, Al: 0.010-0.065%, 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: 0-0.50%, Ni: 0 to 1.00%, Sn: 0 to 0.30%, Sb: 0 to 0.30%, B: 0 to 0.0100%, Mo: 0-0.1%, Contains Bi: 0 to 0.01%; The balance is Fe and impurities. The grain-oriented electrical steel sheet according to claim 1 .

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