Grain-oriented electrical steel sheet

Abstract

The insulating coating of the grain-oriented magnetic steel sheet contains no chromium compound but contains a phosphate, and the content of the phosphate is 0.5% or more and less than 2.0% as measured by the nuclear magnetic resonance method 31 The P-NMR spectrum was subjected to Gaussian fitting in the range of 16 to -90 ppm, and the proportion of the peak area of the structure to the total peak area was more than 0% and 10% or less. 0 The P-NMR spectrum was subjected to Gaussian fitting in the range of 16 to -90 ppm, and the proportion of the peak area of the structure to the total peak area was more than 0% and 10% or less.

Description

Technical Field

[0001] This invention relates to directional electromagnetic steel sheets coated with an insulating film that does not contain chromate. In particular, this invention relates to directional electromagnetic steel sheets that, despite not containing chromate, exhibit low phosphorus leaching from the insulating film, even under long-term storage conditions.

[0002] 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. Background Technology

[0003] Directional electromagnetic steel sheets are steel sheets mainly used as cores for transformers, etc. Typically, two surface coatings are formed on such directional electromagnetic steel sheets: a magnesium olivine layer (also known as a primary coating) formed during high-temperature finished product annealing; and a phosphate coating formed by baking during hot straightening of the steel sheet after coating with a treatment solution with phosphates as the main component.

[0004] Phosphate coating is essential for improving iron losses by imparting electrical insulation to directional electromagnetic steel sheets and reducing eddy current losses. In addition to insulation, phosphate coatings are required to possess various properties such as corrosion resistance, heat resistance, smoothness, and adhesion. This is to ensure smooth manufacturing processes when processing directional electromagnetic steel sheets to produce transformer cores, etc. For example, if the heat resistance, smoothness, and adhesion of the phosphate coating are poor, the coating may peel off during stress-relief annealing in core manufacturing, potentially preventing the phosphate coating from achieving its original insulating properties, hindering the successful stacking of steel sheets, and deteriorating workability.

[0005] Furthermore, as an important characteristic of the insulating film of directional electromagnetic steel sheets, applying tension to the steel sheet can be cited. Applying tension to the steel sheet facilitates the movement of magnetic domain walls, thereby improving the iron loss of the directional electromagnetic steel sheet. Applying tension also reduces magnetostriction (one of the main causes of noise in transformers).

[0006] In order to improve the various properties of the aforementioned directional electromagnetic steel sheet, specifically, the technology disclosed in the following patent documents 1 to 9 has been researched and developed.

[0007] For example, Patent Document 1 discloses the following: after annealing the finished product, an insulating coating treatment solution with aluminum phosphate, chromate, and colloidal silica as the main components is applied to a magnesium olivine coating formed on the surface of the steel plate, followed by baking. According to the technology disclosed in Patent Document 1, a high-tensile insulating coating can be formed on the surface of the steel plate, thereby reducing the iron loss and magnetostriction of the directional electromagnetic steel plate.

[0008] Furthermore, Patent Document 2 discloses a method in which a treatment solution containing colloidal silica with a particle size of less than 8 μm, dihydrogen phosphate, and chromate in a specific ratio is coated onto a steel plate and then baked. According to the technology disclosed in Patent Document 2, the high tension of the insulating film can be maintained, further improving the lubricity of the film.

[0009] Furthermore, Patent Document 3 discloses a technology that forms a high-tensile insulating film on the surface of a directional electromagnetic steel plate by attaching a specific amount of an insulating film mainly composed of phosphate, chromate and colloidal silica with a glass transition point of 950°C to 1200°C.

[0010] According to the technologies disclosed in Patent Documents 1 to 3, it is possible to form insulating films with exceptionally superior film properties and increased film tension. However, the technologies disclosed in Patent Documents 1 to 3 all involve the inclusion of chromate compounds, such as chromium compounds, in the insulating film. In recent years, with increasing attention to environmental issues, there have been calls to ban or restrict the use of compounds such as lead, chromium, and cadmium.

[0011] Therefore, research has been conducted on techniques that can form good insulating films even without the aforementioned chromium compounds. However, insufficient tension imparted to the steel sheet remains a problem when using insulating films that do not contain chromium compounds.

[0012] As a method to solve the above problems, for example, Patent Document 4 discloses an insulating film treatment method for directional electromagnetic steel plates, which involves baking a treatment solution containing 20 parts by weight of colloidal silicon dioxide, 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 of sulfates selected from Mg, Al, Fe, Co, Ni and Zn at a temperature of 300°C or higher.

[0013] In addition, Patent Document 5 discloses a technology involving a coating agent for forming a film, which comprises a mixture of boric acid and alumina sol and an organic solvent that is compatible with water, and has the effect of imparting tension to directional electromagnetic steel sheets.

[0014] Furthermore, Patent Document 6 discloses a technique in which a surface treatment agent for directional electromagnetic steel sheets containing dihydrogen phosphate and colloidal silica contains one or more organic acid salts of Ca, Mn, Fe, Mg, Zn, Co, Ni, Cu, B, and Al. In addition, Patent Document 6 exemplifies formate, acetate, oxalate, tartrate, lactate, citrate, succinate, and salicylate as organic acid salts.

[0015] In addition, Patent Document 7 discloses a technology in which the metal components in the phosphate are set to a specific combination of divalent, trivalent and quadrivalent metal elements in an insulating coating treatment agent for directional electromagnetic steel plates containing phosphate and colloidal silica.

[0016] In addition, Patent Document 8 discloses a directional electromagnetic steel plate comprising an insulating film and a steel plate, the insulating film containing: a metal phosphate salt selected from one or more metals selected from Al, Fe, Mg, Mn, Ni and Zn, namely a first metal phosphate salt; a metal phosphate salt selected from one or more metals selected from Co, Mo, V, W and Zr, namely a second phosphate salt; and colloidal silicon dioxide.

[0017] In addition, Patent Document 9 discloses an aqueous composition for coating directional electromagnets, which comprises aluminum cations, manganese cations, dihydrogen phosphate, hydrogen phosphate and / or anions of phosphate, colloidal silica and optional iron cations.

[0018] Existing technical documents Patent documents Patent Document 1: Japanese Patent Application Publication No. 48-39338 Patent Document 2: Japanese Patent Application Publication No. 61-41778 Patent Document 3: Japanese Patent Application Publication No. 11-071683 Patent Document 4: Japanese Patent Application Publication No. 54-143737 Patent Document 5: Japanese Patent Application Publication No. 7-278828 Patent Document 6: Japanese Patent Application 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: Japanese Patent Publication No. 2022-519691 Summary of the Invention

[0019] The problem that the invention aims to solve These proposals have improved various properties of the insulating film. However, according to the inventors' research to date, it is known that in the case of insulating films without chromium compounds, the leaching of phosphorus from the insulating film increases significantly with long-term storage. Electromagnetic steel sheets may be transported on ships in coil form after manufacturing, under high temperature and humidity conditions for extended periods. Therefore, with the significant increase in phosphorus leaching due to long-term transportation, adhesion between coils may occur, potentially leading to coils becoming unremovable. Regardless of the technology used, the phosphorus leaching after long-term storage has not reached the same level as conventional coatings containing chromic acid, leaving room for improvement.

[0020] As mentioned above, the insulating film of directional electromagnetic steel sheets must possess electrical insulation properties and be able to impart high tensile strength to the surface of the steel sheet. Furthermore, the insulating film of directional electromagnetic steel sheets is required to exhibit good moisture resistance even under high temperature and humidity conditions. Moreover, the insulating film of directional electromagnetic steel sheets is also required to prevent an increase in phosphorus leaching during long-term storage.

[0021] One aspect of the present invention is to solve the aforementioned problems. The objective of one aspect of the present invention is to provide a directional electromagnetic steel sheet that, without containing chromates, exhibits moisture resistance and other properties comparable to or better than conventional steels, and thus results in low phosphorus leaching after long-term storage.

[0022] Methods for solving problems The main points of this invention are as follows.

[0023] (1) One embodiment of the present invention provides a directional electromagnetic steel plate comprising a base steel plate and an insulating film. The insulating film contains phosphates but not chromium compounds. Using nuclear magnetic resonance (NMR), under a magnetic field with a proton resonance frequency of 500 MHz, the magic angle rotation was set to 55 kHz. 31 The chemical shift reference for the P-core was set at 0.9 ppm in ammonium dihydrogen phosphate (NH4H2PO4). The observation center was set between 0 and 30 ppm, the flip angle was 90°, the waiting time was 8 seconds, and the cumulative number of scans (also known as the number of scans) was 9000. The obtained results... 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 greater than 0% and less than 10%.

[0024] (2) In the directional electromagnetic steel sheet described in (1) above, the base steel sheet, as a chemical composition, may also contain, by mass%,: C: Below 0.010% Si: 2.00~4.00% Mn: 0.05~1.00%, Al: 0.010~0.065% N: below 0.004% S: Below 0.010% Se: below 0.010% Cr: 0~0.30% Cu: 0–0.40% P: 0–0.50%, Ni: 0~1.00%, Sn: 0~0.30% Sb: 0~0.30%, B: 0~0.0100% Mo: 0–0.1% Bi: 0~0.01%, The remaining portion contains Fe and impurities.

[0025] Invention Effects According to the above-described scheme of the present invention, it is possible to stably obtain directional electromagnetic steel sheets that have excellent moisture resistance and other properties without containing chromates, and that have low phosphorus leaching even after long-term storage in a high-temperature and high-humidity atmosphere. Attached Figure Description

[0026] Figure 1 This is a graph showing the relationship between the amount of Na in the insulating film treatment solution and the moisture absorption of the directional electromagnetic steel plate covered with the insulating film.

[0027] Figure 2 This is a graph showing the relationship between the amount of Na in the insulating coating treatment solution and the amount of phosphorus leached from the directional electromagnetic steel sheet coated with the insulating coating, for the steel sheet before the moisture absorption resistance evaluation.

[0028] Figure 3 This is a graph showing the relationship between the amount of Na in the insulating film treatment solution and the amount of phosphorus leached from the directional electromagnetic steel sheet coated with the insulating film, for steel sheets after moisture absorption resistance evaluation.

[0029] Figure 4 This is a reference diagram representing the cross-linking oxygen of phosphate, and it represents Q. 0 Q 1 Q 2 Q 3 These 4 types of Q n Reference diagram of the structure.

[0030] Figure 5 It indicates the insulating film. 31 A reference figure for an example of Gaussian fitting of the P-NMR spectrum.

[0031] Figure 6 It indicates the insulating film. 31 Q is obtained by Gaussian fitting of the P-NMR spectrum. 0 The diagram showing the proportions of the structures represents the ratio of Na in the insulating film treatment solution to Q in the insulating film. 0 A diagram showing the proportional relationships of the structures.

[0032] Figure 7 It refers to an insulating film. 31 The chemical shifts in the P-NMR spectrum are contained in five peaks within the range of 16 to -90 ppm. Detailed Implementation

[0033] The preferred embodiments of the present invention will now be described in detail. However, the present invention is not limited to the configuration disclosed in this embodiment, and various modifications can be made without departing from the spirit of the invention. Furthermore, in the numerical ranges shown in this embodiment, the lower and upper limits are included within the range. Values ​​expressed as "more than" or "less than" are not included in the numerical range. The percentage of each element's content, unless otherwise specified, refers to "mass %".

[0034] The following describes the results of preliminary experiments leading to the directional electromagnetic steel sheet of this embodiment.

[0035] <Experiment> A finished annealed directional electromagnetic steel sheet with a thickness of 0.23 mm, manufactured using a known method, is cut into sheets with a width of 60 mm and a length of 300 mm. The annealing release agent adhering to the surface is removed by washing with water, and such steel sheets are prepared as base steel sheets.

[0036] Next, 250 parts by weight of an aqueous solution of 40% aluminum dihydrogen phosphate (solid component), 300 parts by weight of colloidal silica (solid component), and 0–7 parts by weight of sodium hydroxide (solid component) were mixed, as shown in Table 1, and adjusted to a sodium (Na) content in the insulating film treatment solution ranging from 0.02 to 0.34 mol / kg, thus preparing 10 such insulating film treatment solutions. It should be noted that, because sodium-stabilized colloidal silica was used, the Na content without added sodium hydroxide was 0.02 mol / kg.

[0037] [Table 1] Then, using a roller coater, the above-mentioned insulating film treatment solution is applied to each sheet of pre-prepared base steel plate at a coating thickness of 4.5 g / m² after baking. 2 The coating is applied to both sides using a specific method. Then, it is baked at 850°C for 30 seconds.

[0038] In addition, as a comparative material, an insulating coating treatment solution (Na2O / SiO2=0.25%) containing 50 parts by mass of sodium-free aluminum dihydrogen phosphate, 40 parts by mass of colloidal silica (sodium-stabilized type) and 10 parts by mass of chromic anhydride was similarly coated onto the base steel plate and baked.

[0039] The steel sheet coated with an insulating film treatment solution and then baked was used as a test piece for evaluating its moisture absorption resistance. First, the test piece was placed in a constant temperature and humidity bath (50℃, 90% humidity) for one week, and the weight difference before and after the constant temperature and humidity period was quantified. Then, the quantified weight difference was divided by the area of ​​the two sides of the test piece, 0.036 m². 2 The obtained value is defined as moisture absorption (unit: g / m³). 2 The moisture absorption capacity is used as an indicator to evaluate moisture resistance. If the moisture absorption capacity is 0.05 g / m³... 2 The following can be judged as having excellent moisture resistance.

[0040] In addition, phosphorus leaching tests were conducted before and after the hygroscopic resistance evaluation. The phosphorus leaching test involved immersing three 40mm × 60mm test pieces in distilled water at 100℃ for 20 minutes and then boiling them, causing phosphorus to dissolve from the coating surface. Quantitative analysis of the phosphorus was then performed. The quantitative analysis of phosphorus was based on JIS K 0102:2019 Factory Wastewater Test Method 46.1.1, expressed as PO4 (unit: mg / m³). 2 Quantification is performed. If the phosphorus leaching amount is 50 mg / m³, then... 2 The following can be used to determine that the amount of phosphorus leached out is low.

[0041] The results, which summarize the relationship between the Na content in the insulating film treatment solution and the moisture absorption of the directional electromagnetic steel plate coated with the insulating film, are shown below. Figure 1 middle.

[0042] like Figure 1 As shown, for the steel sheet with the chromium-containing coating (comparative material), the moisture absorption is 0.05 g / m³. 2 Below this, there is almost no moisture absorption. In contrast, for steel plates (test material) with a chromium-free coating, moisture absorption in areas with Na content below 0.10 mol / kg can exceed 0.2 g / m³. 2 It cannot achieve sufficient moisture resistance.

[0043] Furthermore, in areas with high Na content, especially those with Na content exceeding 0.10 mol / kg, the moisture absorption rate is 0.15 g / m³. 2 Furthermore, in regions where the Na content is 0.20 mol / kg or higher, the moisture absorption is 0.05 g / m³. 2 The following results showed that the moisture resistance was equivalent to that of steel plates with a chromium-containing coating. On the other hand, it was confirmed that if the Na content exceeded 0.30 mol / kg, the dispersibility of colloidal silica deteriorated, resulting in unevenness in the appearance after baking.

[0044] Next, the results showing the relationship between the amount of Na in the insulating film treatment solution and the amount of phosphorus leached from the directional electromagnetic steel plate coated with the insulating film, based on the test pieces before the moisture absorption resistance evaluation, are presented. Figure 2 middle.

[0045] like Figure 2 As shown, even steel sheets with a chromium-free coating exhibit low phosphorus leaching, regardless of the amount of sodium, just like steel sheets with a chromium-containing coating. That is, no problem of increased phosphorus leaching from the insulating coating arises before maintaining constant temperature and humidity.

[0046] Furthermore, the results of analyzing the relationship between the amount of Na in the insulating film treatment solution and the amount of phosphorus leached from the directional electromagnetic steel plate coated with the insulating film, based on the test pieces after moisture absorption resistance evaluation, are presented below. Figure 3 middle.

[0047] like Figure 3 As shown, in regions where the Na content is 0.20 mol / kg or higher, the phosphorus leaching amount of steel plates with chromium-free coatings is 50 mg / m³, similar to that of steel plates with chromium-containing coatings. 2 Below. However, in regions where the Na molar ratio is below 0.20 mol / kg, the phosphorus leaching amount is 50 mg / m³. 2 The above, a great many, confirmed the deterioration of the insulating film through moisture absorption resistance evaluation.

[0048] Based on the above experimental results, the mechanism by which the amount of Na in the insulating film treatment solution affects the amount of phosphorus leaching after the constant temperature and humidity test in an insulating film without chromium is considered as follows.

[0049] <Structure of phosphate> It is believed that the leaching of phosphorus from the insulating film is caused by a hydrolysis reaction in which water molecules act on the POP bond of the phosphate forming the insulating film, resulting in the breakage of the bond. Therefore, it is important to set the P(phosphorus)-O(oxygen)-P(phosphorus) bond to be replaced by a POM (where M is a metal element) with other bonds.

[0050] Here, the structural evaluation of phosphates is generally performed using nuclear magnetic resonance (NMR) (hereinafter referred to as...). 31 (P-NMR). The structure of phosphate is based on a PO4 tetrahedron with four oxygen atoms coordinated around a phosphorus atom as the unit unit. A three-dimensional structure is formed by sharing oxygen atoms at the vertices with other PO4 tetrahedra. The oxygen atoms that connect the tetrahedra to each other are called cross-linked oxygens, and Q is an indicator of the number of cross-linked oxygens, n. n Such a counting method, such as Figure 4 As shown, it can be classified as Q 0 Q 1 Q 2 Q 3 These 4 types of Q n structure.

[0051] The smaller the number n of cross-linked oxygen atoms, the less polarity the phosphorus atoms become, and the weaker their interaction with highly polarized water molecules. As a result, the bonds become less likely to be broken, and the amount of phosphorus dissolved decreases.

[0052] 0 The ratio of peak area of ​​the structure to the total peak area: greater than 0% and less than 10% For steel sheets with a chromium-free coating, the sodium content of various insulating coatings was measured before evaluating moisture resistance. 31 For the P-NMR spectra, Gaussian fitting was performed in the range of 16 to -90 ppm.

[0053] Here, when performing Gaussian fitting, it is necessary to determine the peak height and linewidth based on the Gaussian function. In this embodiment, for the insulating film... 31 ​The p-NMR spectra were used to fix the peak positions (chemical shifts) of six peaks: -49 ppm, -35 ppm, -30 ppm, -22 ppm, -8.8 ppm, and +5.9 ppm. Based on this, the full width at half maximum (FWHM) of the -49 ppm peak was fixed at 6.291 kHz, and the FWHM of the -35 ppm peak was fixed at 3.780 kHz. Furthermore, the initial FWHM of the -30 ppm peak was set to 2.000 kHz, and the initial FWHMs of the -22 ppm, -8.8 ppm, and +5.9 ppm peaks were set to 3.000 kHz. After optimizing only the heights of these peaks, the optimized height values ​​were used as initial values. Then, for -30ppm, -22ppm, -8.8ppm, and +5.9ppm, both height and linewidth were used as variable parameters. For -49ppm and -35ppm, the above values ​​were used to fix the full width at half maximum (WWHM) while only the height was used as a variable parameter. Optimization was performed using the Levenberg-Marquardt method in a manner that best approximates the experimental spectral lineshape. It should be noted that R represents the goodness of optimization. 2 The value is optimized to R in the overall spectrum. 2 The value becomes above 0.9600, optimized to R in the range of 16 to -90 ppm. 2 The value becomes 0.9970 or higher.

[0054] It should be noted that the peak values ​​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 correlating these values ​​with the spectral ranges corresponding to the number of crosslinking events recorded in the literature, the initial three components were sequentially identified as Q. 0 Q 1 Q 2 The three components after -30ppm were identified as Q. 3 (References: Turner, GL, Smith, Kirkpatrick, RJ. & Oldfield, E. (1986a) J. Mag. Reason., 70, 408).

[0055] Based on the above, the insulating film will be... 31 An example of Gaussian fitting of the P-NMR spectrum is shown below. Figure 5 middle.

[0056] In addition, based on the insulating film 31 The results of Gaussian fitting of P-NMR spectra were used to summarize the relationship between the Na content in the insulating film treatment solution and the Q content in the insulating film. 0 The results of the proportional relationship of the structure are shown in Figure 6 In the middle. It should be noted that, Figure 6 Q in 0 The proportion of the structure represents Q 0 The peak area of ​​the structure relative to Q 0 Q 1 Q 2 Q 3 These 4 types of Q n The proportion of the total peak area obtained by summing the peak areas of the normal distribution curve of the structure. It should be noted that Q... 3 The proportion of peak area of ​​the structure is the sum of the values ​​of the three components mentioned above.

[0057] like Figure 6 As shown, when the amount of Na is less than 0.20 mol / kg, Q 0 The peak area ratio of the structure is 0%, while Q is higher when the Na content is above 0.20 mol / kg. 0 The proportion of peak area in the structure becomes more than 0%.

[0058] As shown in the experimental results above, the insulating film does not contain chromium compounds, and 31 When the P-NMR spectrum was Gaussian fitted in the range of 16 to -90 ppm, by using Q 0 The ratio of the peak area of ​​the structure (the area of ​​the peak with a peak of +5.9 ppm) to the total peak area (the combined area of ​​the six peaks with peaks of +5.9 ppm, -8.8 ppm, -22 ppm, -30 ppm, -35 ppm and -49 ppm) is controlled to be more than 0%, so that even under long-term storage in a high temperature and high humidity atmosphere, the amount of phosphorus leaching can be kept to a low level.

[0059] Q 0 The proportion of peak area in the structure is preferably greater than 1%, and more preferably greater than 4%. On the other hand, in Q... 0 When the peak area ratio of the structure exceeds 10%, unevenness exists in the appearance of the insulating film. Q 1 The peak area ratio of the structure is preferably below 9%.

[0060] 0 The ratio of the peak area of ​​the structure to the total peak area is less than Q. 3 The ratio of peak area to total peak area of ​​the structure > In the directional electromagnetic steel plate of this embodiment, Q 0 The proportion of peak area in the structure is less than Q. 3 The proportion of peak areas in the structure. By Q 0 ​The peak area ratio of the structure is controlled to be greater than 0% and less than 10% to preferably achieve the above-mentioned effect. However, in order to maintain the morphology of the insulating film, Q 0 The proportion of peak area in the structure becomes smaller than Q. 3 The proportion of peak area in the structure.

[0061] Here, the insulating film of the directional electromagnetic steel plate of this embodiment... 31 This paper explains the method of determining the peak area ratio using P-NMR spectroscopy.

[0062] 31 The measurement conditions for p-NMR are described in some non-patent literature (e.g., Journal of Non-Crystalline Solid, 1998, 223, pp. 32-42). However, it is known that... 31 The measurement conditions for P-NMR generally vary depending on the material. In this embodiment, the conditions are set as follows: a magnetic field with a proton resonance frequency of 500 MHz (e.g., a measurement magnetic field of 11.74 T to 11.75 T), measurement temperature: room temperature, magic angle rotation (MAS): 55 kHz, and measurement method: 31 P-single pulse excitation ( 31 The measurements were performed using a single-pulse excitation (flip angle 90°), with a measurement waiting time of 8 seconds, a cumulative total of 9000 measurements, and a standard sample (external chemical shift reference): ammonium dihydrogen phosphate at 0.9 ppm. The observation center range was 0–30 ppm. Measurements were conducted using an Agilent INOVA 500. Regarding the insulating film, the base material of the directional electromagnetic steel sheet was dissolved in a 10% bromomethanol solution until its disappearance was confirmed. The solution was then filtered, and the material recovered onto the filter was washed with methanol for NMR analysis.

[0063] Insulating film 31 An example of a chemical shift in a p-NMR spectrum containing peaks in the range of 16 to -90 ppm is shown below. Figure 7 In. Figure 7 In 31 Five distinct peaks were identified, for example, in the p-NMR spectrum. That is, from... Figure 7 From left to right, the peaks are located at +5.9 ppm, -8.8 ppm, -22 ppm, -30 ppm, and -35 ppm, respectively. It should be noted that... Figure 7 A peak with a peak of -49 ppm is not explicitly observed, but this -49 ppm peak can sometimes be clearly identified depending on the type of insulating film. Additionally, the equivalent of Q... 0 The peak of the structure is Figure 7 The peak in the middle is +5.9 ppm. This is equivalent to Q.3 The peak of the structure is Figure 7 The peaks were -30ppm and -35ppm.

[0064] for 31 P-NMR spectra, using the method described above, are fitted with Gaussian to derive the peak areas, which are defined as the integral values ​​of each peak. Figure 7 For example, the sum of the peak areas of the five peaks mentioned above constitutes the total peak area. Furthermore, in... Figure 7 In the middle, the area of ​​the peak with a apex of +5.9 ppm becomes Q. 0 Peak area of ​​the structure. Similarly, in Figure 7 In the middle, the sum of the areas of the peaks with apexes of -30ppm and -35ppm is Q. 3 The peak area of ​​the structure. Based on these, calculate "Q". n The ratio of the "peak area of ​​the structure" to the "total peak area".

[0065] It should be noted that the insulating film of the directional electromagnetic steel plate in this embodiment does not contain chromium compounds. For example, in this embodiment, when the Cr concentration in the insulating film is less than 1 atomic%, it is determined that the insulating film does not contain chromium compounds. The Cr concentration is preferably 0.8 atomic% or less, and more preferably 0.5 atomic% or less.

[0066] Furthermore, in this embodiment, the chemical composition of the insulating film is not particularly limited, but for example, the main constituent elements only need to satisfy the following: P: 5-30 atomic%, Si: 5-30 atomic%, O: 30-80 atomic%, Al: 0.1-10 atomic%, Cr: less than 1 atomic%, Fe: less than 25 atomic%, Mg: 0-10 atomic%, Mn: 0-10 atomic%, Ni: 0-10 atomic%, Zn: 0-10 atomic%, V: 0-10 atomic%, W: 0-10 atomic%, Zr: 0-10 atomic%, Co: 0-10 atomic%, Mo: 0-10 atomic%.

[0067] Furthermore, the insulating film of the directional electromagnetic steel plate in this embodiment refers to an insulating film that is free from insufficient baking or cracking caused by poor baking conditions. If the insulating film contains insufficient baking or cracking due to poor baking conditions, it cannot meet the required electrical insulation, tensile strength, corrosion resistance, heat resistance, sliding properties, and sealing properties.

[0068] The concentrations of Cr and other elements contained in the insulating film can be analyzed by examining the cross-section using SEM-EDS (Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy) or TEM-EDS (Transmission Electron Microscope-Energy Dispersive X-ray Spectroscopy).

[0069] Next, the amount of insulating film attached to the directional electromagnetic steel plate in this embodiment will be explained.

[0070] In the directional electromagnetic steel plate of this embodiment, the amount of insulating film attached is not particularly limited, but it is 2.0 to 7.0 g / m² per single side. 2 This is appropriate. The coating thickness of the insulating film is less than 2.0 g / m². 2 In some cases, it may become difficult to impart high tension to the directional electromagnetic steel sheet, and the insulation and corrosion resistance of the directional electromagnetic steel sheet may also decrease, making it undesirable. On the other hand, when the coating weight of the insulating film exceeds 7.0 g / m²... 2 In such cases, the duty cycle of the directional electromagnetic steel plate may decrease, leading to a deterioration in transformer characteristics, which is therefore undesirable. A more preferable coating weight for the insulating film is 3.0 g / m². 2 The above is further preferred to be 4.0 g / m 2 The above. More preferably, the coating weight of the insulating film is 6.0 g / m². 2 The following is a further preferred value: 5.0 g / m 2 the following.

[0071] <Directional Electromagnetic Steel Sheet> Next, the base steel plate of the directional electromagnetic steel sheet of this embodiment will be described. The base steel plate of the directional electromagnetic steel sheet is not particularly limited, but its chemical composition, by mass%, should contain: 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, with the remainder being Fe and impurities. Hereinafter, the "%" in the chemical composition refers to mass percentage relative to the total mass of the base steel plate.

[0072] C: Below 0.010% Carbon (C) is an element effective in controlling the primary recrystallization structure, but it is removed by decarburization annealing before the finished product is annealed because it adversely affects magnetic properties. If the C concentration in the final product exceeds 0.010%, C will precipitate due to aging, and hysteresis loss will deteriorate. Therefore, the C concentration is set to be below 0.010%. The C concentration is preferably below 0.007%, and more preferably below 0.005%. The lower limit of C concentration includes 0%, but the C concentration can also exceed 0%. However, if the C concentration is to be reduced to below 0.0001%, the manufacturing cost will increase significantly. Therefore, 0.0001% is a substantial lower limit for practical steel sheets. It should be noted that in directional electromagnetic steel sheets, the C concentration is usually reduced to around 0.001% or less by decarburization annealing.

[0073] Si: 2.00~4.00% Silicon (Si) is an element that increases the resistivity of steel sheets and improves iron loss characteristics. When the Si concentration is below 2.00%, a γ-phase transformation occurs in the steel structure during finished product annealing, damaging the crystal orientation of the steel sheet. Therefore, the Si concentration is set to 2.00% or higher. The Si concentration is preferably 2.50% or higher, and more preferably 3.00% or higher. On the other hand, if the Si concentration exceeds 4.00%, the processability of the directional electromagnetic steel sheet decreases, and cracking occurs during rolling. Therefore, the Si concentration is set to 4.00% or lower. The Si concentration is preferably 3.50% or lower.

[0074] Mn: 0.05~1.00% Manganese (Mn) is an element that prevents cracking during hot rolling and combines with sulfur (S) and / or selenium (Se) to form MnS and MnSe, which function as inhibitors. When the Mn concentration is below 0.05%, the effect of adding Mn is not sufficiently observed; therefore, 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 become uneven, the desired secondary recrystallization structure is not 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.

[0075] Al: 0.010~0.065% Al (aluminum) is an element that combines with nitrogen to form (Al, Si)N or AlN, which function as an inhibitor. When the Al concentration is below 0.010%, the effect of adding Al is not fully manifested, and secondary recrystallization is not fully carried out. 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 become uneven, the desired secondary recrystallization structure is not 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.

[0076] N: below 0.004% Nitrogen (N) is an element that combines with Al to form AlN and other compounds that function as inhibitors. However, if the N concentration in the final product exceeds 0.004%, N in the steel sheet will precipitate as AlN, deteriorating hysteresis losses. Therefore, the N concentration is set below 0.004%. The lower limit for N concentration includes 0%, but if the N concentration is to be reduced to below 0.0001%, the manufacturing cost increases significantly. Therefore, 0.0001% is a practical lower limit for practical steel sheets. It should be noted that in directional electromagnetic steel sheets, the N concentration is usually reduced to around 0.001% or less through finished product annealing.

[0077] S: below 0.010% Sulfur (S) combines with manganese (Mn) to form MnS, which functions as an inhibitor. However, in the final product, if the S concentration exceeds 0.010%, S in the steel sheet will precipitate as MnS, deteriorating hysteresis losses. Therefore, the S concentration is set below 0.010%. The lower limit of S concentration includes 0%, but if the S concentration is to be reduced to below 0.0001%, the manufacturing cost increases significantly. Therefore, 0.0001% is a practical lower limit for practical steel sheets. It should be noted that in directional electromagnetic steel sheets, the S concentration is usually reduced to around 0.005% or less through finished product annealing.

[0078] In this embodiment, the base steel plate may also contain impurities. It should be noted that "impurities" refer to substances that are mixed in from the ore, waste, or manufacturing environment used as raw materials during the industrial manufacturing of steel.

[0079] In addition to the elements and impurities described above, the base steel plate may also contain optional elements. For example, as optional elements, at least one of Se, Cr, Cu, P, Ni, Sn, Sb, B, Mo, or Bi may be included to replace the remaining Fe. These optional elements can be included as needed for their intended purpose. Therefore, it is not necessary to limit the lower limit value of these optional elements; the lower limit value can also be 0%. Furthermore, even if these optional elements are included as impurities, the above-mentioned effects will not be impaired.

[0080] For example, in this embodiment, the base steel plate may be made of one or more of the following additive elements, namely Se: less than 0.010%, Cr: less than 0.30%, Cu: less than 0.40%, P: less than 0.50%, Ni: less than 1.00%, Sn: less than 0.30%, Sb: less than 0.30%, B: less than 0.0100%, Mo: less than 0.1%, and Bi: less than 0.01%, to improve other properties without hindering its magnetic properties.

[0081] Se: 0~0.010% Selenium (Se) combines with Mn to form MnSe, which functions as an inhibitor. However, in the final product, if the Se concentration exceeds 0.010%, Se in the steel sheet will precipitate as MnSe, deteriorating hysteresis losses. Therefore, the Se concentration is set below 0.010%. The lower limit of Se concentration can be 0%, or even 0.0001%. It should be noted that in directional electromagnetic steel sheets, the Se concentration is usually reduced to around 0.005% or less through finished product annealing.

[0082] Cr: 0~0.30% Chromium (Cr) is an effective element for improving the oxide layer in decarburized annealing and for forming glass films. Therefore, Cr can be added to the base steel sheet in the range of 0.30% or less. If the Cr concentration exceeds 0.30%, it significantly hinders decarburization, so the upper limit of the Cr concentration is preferably 0.30%.

[0083] Cu: 0~0.40% Cu (copper) is an effective element for reducing iron loss by increasing the resistivity of the base steel sheet. If the Cu concentration exceeds 0.40%, the iron loss reduction effect saturates and it becomes a cause of surface defects such as "copper scale folds" during hot rolling. Therefore, the upper limit of Cu concentration is preferably 0.40%.

[0084] P: 0–0.50% Phosphorus (P) is an effective element for increasing the resistivity of the base steel sheet, thereby reducing iron loss. If the P concentration exceeds 0.50%, rollability problems arise; therefore, the upper limit of the P concentration is preferably 0.50%.

[0085] Ni: 0~1.00% Ni (Ni) is an effective element for reducing iron loss by increasing the resistivity of the base steel sheet. Additionally, Ni is effective in improving the magnetic properties of hot-rolled steel sheets by controlling the steel microstructure. However, if the Ni concentration exceeds 1.00%, secondary recrystallization becomes unstable; therefore, an upper limit of 1.00% for the Ni concentration is preferred.

[0086] Sn: 0~0.30% Sb: 0~0.30% Sn (tin) and Sb (antimony) are well-known grain boundary segregating elements. In this embodiment, since the base steel sheet contains Al, the Al may be oxidized by moisture released from the annealing separator depending on the annealing conditions, causing variations in the inhibitor strength at the coil location. As a result, the magnetic properties may change depending on the coil location. One countermeasure is to prevent Al oxidation by adding these grain boundary segregating elements; therefore, Sn and Sb can be added to the base steel sheet at concentrations of 0.30% or less. On the other hand, if the concentration of these elements exceeds 0.30%, Si is difficult to oxidize during decarburization annealing, resulting in insufficient glass film formation and significantly hindering decarburization annealing. Therefore, the upper limit of the concentration of these elements is preferably 0.30%.

[0087] B: 0~0.0100% Boron (B) is an element that combines with nitrogen (N) in the base steel sheet and precipitates in combination with MnS to form boron nanotubes (BN), which function as an inhibitor. There is no particular limitation on the lower limit of the B concentration; it can be 0% as described above. However, to fully utilize 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 precipitation and dispersion of BN become uneven, 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 even more preferably 0.0040% or less.

[0088] Mo: 0–0.1% Mo (molybdenum) is an effective element for improving surface properties during hot rolling. However, if the Mo concentration exceeds 0.1%, the effect of Mo addition becomes saturated, so the upper limit of Mo concentration is preferably 0.1%.

[0089] Bi: 0~0.01% Bismuth (Bi) has the effect of stabilizing precipitates such as sulfides, thus enhancing its function as an inhibitor. However, if the Bi concentration exceeds 0.01%, Bi will adversely affect the formation of the glass coating; therefore, the upper limit of the Bi concentration is preferably 0.01%.

[0090] The aforementioned chemical composition can be determined using general analytical methods for steel. For example, the chemical composition can be determined using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). It should be noted that Al, as total aluminum, can be determined according to JIS G1257-10-1:2013. Furthermore, C and S can be determined using the combustion-infrared absorption method, N can be determined using the inert gas melting-thermal conductivity method, and O can be determined using the inert gas melting-non-dispersive infrared absorption method if necessary.

[0091] It should be noted that the above chemical composition refers to the composition of the base steel plate. When the directional electromagnetic steel plate used as the test sample has an insulating film on its surface, the insulating film is removed using the method described below before the chemical composition is determined.

[0092] For example, as a method for removing the insulating film, the directional electromagnet plate with the film can be simply immersed in a high-temperature alkaline solution. Specifically, the insulating film can be removed from the directional electromagnet plate by immersing it in a sodium hydroxide aqueous solution of NaOH (30-50% by mass) + H₂O (50-70% by mass) at 80-90°C for 5-10 minutes, followed by washing with water and drying. It should be noted that the immersion time in the sodium hydroxide aqueous solution can be adjusted according to the thickness of the insulating film.

[0093] <Manufacturing Method of Directional Electromagnetic Steel Sheets> Next, the method for manufacturing the directional electromagnetic steel sheet of this embodiment will be described. It should be noted that the method for manufacturing the directional electromagnetic steel sheet of this embodiment is not limited to the method described below. The following manufacturing method is an example for manufacturing the directional electromagnetic steel sheet of this embodiment.

[0094] Silicon steel slabs are produced by casting molten steel with a specified chemical composition using conventional methods. The chemical composition of the silicon steel slab is not limited to a specific composition, as long as it produces the magnetic and mechanical properties required for directional electromagnetic steel sheets. However, an example of the chemical composition of a silicon steel slab is given below. For instance, the chemical composition of a silicon steel slab, by mass%, contains: C: less than 0.085%, Si: 2.00–4.00%, Mn: 0.05–1.00%, Al: 0.010–0.065%, N: 0.004–0.012%, S: less than 0.010%, and B: less than 0.0100%.

[0095] C: Below 0.085% Carbon (C) is an element effective in controlling the primary recrystallization structure, but because it adversely affects magnetic properties, it is removed by decarburization annealing before finished product annealing. If the C concentration exceeds 0.085%, the decarburization annealing time becomes longer, reducing productivity; therefore, the C concentration is set to below 0.085%. The preferred C concentration is below 0.070%, more preferably below 0.050%. There is no particular limitation on the lower limit of the C concentration; 0% is acceptable, but it can also exceed 0%. Considering productivity in industrial production and the magnetic properties of the product, 0.0001% is a substantially acceptable lower limit for the C concentration. It should be noted that in directional electromagnetic steel sheets, the C concentration is typically reduced to around 0.001% or less during decarburization annealing.

[0096] Si: 2.00~4.00% Silicon (Si) is an element that increases the resistivity of steel sheets and improves iron loss characteristics. When the Si concentration is below 2.00%, a γ-phase transformation occurs during finished product annealing, damaging the crystal orientation of the steel sheet. Therefore, the Si concentration is set to 2.00% or higher. The Si concentration is preferably 2.50% or higher, and more preferably 3.00% or higher. On the other hand, if the Si concentration exceeds 4.00%, processability decreases, and cracking occurs during rolling. Therefore, the Si concentration is set to 4.00% or lower. The Si concentration is preferably 3.50% or lower.

[0097] Mn: 0.05~1.00% 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. When the Mn concentration is below 0.05%, the additive effect is not sufficiently observed; therefore, 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 become uneven, the desired secondary recrystallization structure is not 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.

[0098] Al: 0.010~0.065% Al (aluminum) is an element that combines with N to form (Al, Si)N or AlN, which function as an inhibitor. When the Al concentration is below 0.010%, the additive effect is not sufficiently observed, and secondary recrystallization is not sufficiently achieved. 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 (Al, Si)N, etc., become uneven, the desired secondary recrystallization structure is not 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.

[0099] N: 0.004~0.012% Nitrogen (N) is an element that combines with Al to form AlN and other structures that function as inhibitors. However, it is also an element that can form pores (voids) in steel sheets during cold rolling. When the N concentration is below 0.004%, AlN formation becomes insufficient; therefore, the N concentration is set to 0.004% or higher. The N concentration is preferably 0.006% or higher, and more preferably 0.007% or higher. On the other hand, if the N concentration exceeds 0.012%, pores (voids) may form in the steel sheet during cold rolling; therefore, the N concentration is set to 0.012% or lower. The N concentration is preferably 0.010% or lower, and more preferably 0.009% or lower.

[0100] S: below 0.010% Sulfur (S) 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 after purification becomes uneven, the desired secondary recrystallization structure cannot be obtained, the magnetic flux density decreases, the hysteresis loss deteriorates, or MnS remains after purification, further deteriorating the hysteresis loss. No specific lower limit is set, but the S concentration can also be 0%, preferably 0.003% or higher. A more preferred S concentration is 0.007% or higher.

[0101] B: Below 0.0100% Boron (B) is an element that combines with nitrogen (N) and recombines with MnS to form boron nanoparticles (BN), which function as an inhibitor. If the B concentration exceeds 0.0100%, the BN precipitation dispersion becomes uneven, the desired 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 can also be 0%.

[0102] In this embodiment, the silicon steel slab may also contain impurities. It should be noted that "impurities" refer to substances that are mixed in from the ore, waste, or manufacturing environment used as raw materials during the industrial manufacturing of steel.

[0103] In addition to the elements and impurities described above, the silicon steel slab may also contain optional elements. For example, as optional elements, at least one of Se, Cr, Cu, P, Ni, Sn, Sb, Mo, or Bi may be included to replace the Fe that constitutes the remaining portion. These optional elements can be included as long as they are intended to be included. Therefore, it is not necessary to limit the lower limit value of these optional elements, and the lower limit value may be 0%. Furthermore, even if these optional elements are included as impurities, the above-mentioned effects will not be impaired.

[0104] For example, in this embodiment, the silicon steel slab may contain one or more of the following components within a range that does not impede the magnetic properties of the directional electromagnetic steel sheet and can improve 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, Mo: 0.1% or less, and Bi: 0.01% or less.

[0105] In the hot rolling process, a hot-rolled sheet is obtained by hot rolling a slab having the above-mentioned chemical composition. 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 then coiled into a sheet shape.

[0106] Before hot rolling, the slab can be heated to a temperature exceeding 1300°C to fully dissolve the inhibitory components of MnS and AlN. Alternatively, from the perspective of productivity and manufacturing cost, the slab can be heated to around 1250°C, provided that the inhibitors are enhanced in the subsequent nitriding process.

[0107] In the hot-rolled sheet annealing process, a hot-rolled sheet in coil form is unrolled into a strip, and then the strip is annealed to obtain an annealed hot-rolled sheet. There are no particular limitations on the annealing conditions for hot-rolled sheets; standard conditions can be used.

[0108] In the cold rolling process, a cold-rolled sheet with a final thickness is obtained by performing one or more cold rolling passes on an annealed hot-rolled sheet. Alternatively, a cold-rolled sheet can be obtained by performing two or more cold rolling passes with intermediate annealing on an annealed hot-rolled sheet. The annealing performed before the final cold rolling process homogenizes the crystal structure. There are no particular limitations on the cold rolling conditions; standard conditions can be used.

[0109] In the decarburization annealing process, decarburized annealed sheets are obtained by decarburizing cold-rolled sheets. In this process, the carbon content in the cold-rolled sheet is reduced to a level that will not deteriorate due to magnetic aging when used as finished steel by heat treatment in wet hydrogen. This process also induces primary recrystallization in the cold-rolled sheet, preparing it for subsequent secondary recrystallization. The decarburization annealing conditions are not particularly limited and can be performed under standard conditions. A SiO2 oxide film is formed on the surface of the decarburized annealed sheet obtained through this process. It should be noted that when cold-rolled sheets are manufactured from slabs heated to approximately 1250°C, after decarburization annealing, the decarburized annealed sheet is annealed in an ammonia atmosphere, thereby generating AlN, which functions as an inhibitor, within the decarburized annealed sheet.

[0110] In the manufacturing method of the directional electromagnetic steel sheet of this embodiment, the steel sheet with the insulating coating can be a typical directional electromagnetic steel sheet with a magnesium olivine coating, or a directional electromagnetic steel sheet without a magnesium olivine coating.

[0111] In the case of typical directional electromagnetic steel sheets with a forsterite coating, in the annealing release agent coating process, which is the next step after the decarburization annealing process, an annealing release agent with MgO as the main component is applied to prevent burning and sticking during the finished annealing process. The coating amount of the annealing release agent is 6.0 to 14.0 g / m² per single side of the decarburized annealed sheet. 2 .

[0112] In the case of directional electromagnetic steel sheets without a magnesium olivine coating, an annealing release agent with alumina (Al2O3) as the main component is applied during the annealing release agent coating process. After the annealing release agent is dried, the decarburized annealed sheet coated with the annealing release agent is rolled into a roll.

[0113] In the finished product annealing process, a decarburized annealed sheet coated with an annealing separating agent is annealed to obtain the base steel sheet for the final product (directional electromagnetic steel sheet). In this finished product annealing process, secondary recrystallization occurs in the decarburized annealed sheet by annealing at a temperature above 1100°C. It should be noted that, in order to reduce the hysteresis loss of the final product, the decarburized annealed sheet after secondary recrystallization can also be purified by annealing in a manner that renders the precipitates used as inhibitors harmless.

[0114] An insulating film is formed on the surface of a steel sheet that has undergone secondary recrystallization. The method for forming this insulating film includes: a coating step of applying an insulating film treatment solution to the surface of the steel sheet; and a baking step of baking the insulating film treatment solution. The insulating film is formed by baking.

[0115] After the finished product is annealed, and the remaining annealing separating agent is removed by washing with water, it undergoes pickling treatment using a sulfuric acid bath and water washing treatment. This cleans and activates the steel plate surface. Then, in the coating process, an insulating film treatment solution is applied to the steel plate. There are no restrictions on the method of applying the insulating film treatment solution to the steel plate, but a roller coater is typically used. The directional electromagnetic steel plate coated with the insulating film treatment solution is then subjected to a baking process under the conditions described later, thereby forming an insulating film on the surface.

[0116] In 31 When the P-NMR spectrum was Gaussian fitted in the range of 16 to -90 ppm, in order to Q 0 The ratio of the peak area of ​​the structure to the total peak area is set to be greater than 0% and less than 10%, which requires changing the POP bond of the phosphate contained in the insulating film treatment solution to POM (where M is a metal element). Therefore, the metal component contained in the insulating film treatment solution is preferably an alkali metal element. Lithium, sodium, and potassium are preferred. Sodium and potassium are more preferred. Containing 0.20 to 0.30 mol / kg of these alkali metal elements relative to the insulating film treatment solution is sufficient.

[0117] For Q 0 Setting the ratio of peak area to total peak area to be greater than 0% and less than 10% is effective for using alkali metals such as sodium and potassium, although the reason for this is currently unclear. However, these alkali metals are well-known as modifiers that significantly alter the properties of glasses such as phosphates, and they have small atomic radii. Therefore, it is believed that these alkali metals are readily absorbed into phosphates, resulting in significant effects. Furthermore, the reason for the significant change in glass properties with increasing sodium content in the insulating film, as mentioned above, is believed to be due to the increased proportion of the change from P(phosphorus)-O(oxygen)-P(phosphorus) bonds to POM (M: assumed to be Na in this case) bonds with increasing sodium content.

[0118] In addition, in order to Q 0 The ratio of the peak area of ​​the structure to the total peak area is set to be greater than 0% and less than 10%, and the pH of the insulating coating treatment solution is preferably 1.7 to 2.1. This pH value is higher than that of conventional insulating coating treatment solutions, which typically have a pH below 1.7. The inventors of this invention have discovered that when the pH of the insulating coating treatment solution is 1.7 to 2.1, it is easier to... 0 The ratio of the peak area of ​​the structure to the total peak area is preferably controlled to be greater than 0% and less than 10%. The reason for this is currently unclear. However, for example, in the hydrolysis of polyphosphate ions, hydrogen ions are known to act as catalysts for the breaking of POP bonds; similarly, hydrogen ions are known to act as catalysts for the breaking of POP bonds in pyrophosphate. It is believed that in this embodiment, the pH of the insulating film treatment solution is higher than that of conventional insulating film treatment solutions, and the presence of hydrogen ions is lower than before, which has an impact on the Q in the insulating film. 0 The proportions of the structure have an impact. The pH of the insulating film treatment solution is preferably 1.8 or higher, and more preferably 1.9 or higher.

[0119] In the baking process, the directional electromagnetic steel plate coated with insulating film treatment liquid is heated to the baking uniform temperature, maintained at the baking uniform temperature, and then cooled.

[0120] The baking uniform temperature (°C) represents the maximum plate temperature reached during the baking process, which needs to be between 800°C and 1000°C. If the baking uniform temperature is below 800°C, the insulating film will not undergo sufficient film formation reaction, resulting in a poor appearance and potentially failing to impart sufficient tension to the steel plate. On the other hand, if the baking uniform temperature exceeds 1000°C, cracks may occur in the insulating film, reducing film tension or insulation properties, and defects may also be generated in the steel plate. A baking uniform temperature of 850°C to 950°C is more preferable.

[0121] The heat soaking time (in seconds) represents the holding time at the baking heat soaking temperature. The heat soaking time needs to be 10 seconds or more. If the heat soaking time is less than 10 seconds, the insulating film may be underbaked, leading to a deterioration in moisture resistance (increased moisture absorption). Preferably, it is 20 seconds or more. On the other hand, the heat soaking time is set to 60 seconds or less. If the heat soaking time exceeds 60 seconds, not only will the moisture resistance hardly change, but excessive crystallization of the insulating film may also cause cracking, resulting in reduced film tension. A more preferable heat soaking time is 45 seconds or less, which allows for obtaining the necessary and sufficient properties of the film.

[0122] In addition, in order to Q 0The ratio of the peak area of ​​the structure to the total peak area is set to be greater than 0% and less than 10%, preferably with a heating rate of 30°C / second to 100°C / second when heating to the uniform baking temperature during the baking process. The rationale for this is currently unclear. However, it is believed that if the heating rate up to the uniform baking temperature is too fast, the surface of the insulating film will solidify before the interior during heating, and moisture will be trapped inside the insulating film. This moisture will make the interior of the insulating film more prone to porous defects, and will also negatively impact the Q content of the insulating film. 0 The proportions of the structure have an impact. The heating rate up to the uniform baking temperature is preferably 40°C / second or more, and more preferably 60°C / second or more. In addition, the heating rate up to the uniform baking temperature is preferably 80°C / second or less, and more preferably 70°C / second or less.

[0123] It should be noted that the heating rate mentioned above up to the uniform baking temperature refers to the value obtained by dividing the temperature range from the baking start temperature (e.g., room temperature) to the uniform baking temperature (800℃~1000℃) by the time required for heating.

[0124] It should be noted that there is no particular limitation on the type of base steel sheet for which the above-described insulating film treatment is performed. This is because the main feature of the directional electromagnetic steel sheet of this embodiment lies in the composition of the insulating film. The insulating film of the directional electromagnetic steel sheet of this embodiment has the effect of imparting high tension to the surface of the steel sheet, good adhesion, corrosion resistance, and excellent long-term stability even though it does not contain chromates. Such effects are achieved regardless of the type of base steel sheet.

[0125] Preferably, the above-described insulating film treatment can be applied to a directional electromagnetic steel sheet manufactured using the technology disclosed in Japanese Patent Application Publication No. 7-268567. In this case, the effect of further reducing iron loss can be obtained. Specifically, by applying the above-described insulating film treatment to the following directional electromagnetic steel sheet, the effect of further reducing iron loss can be obtained. The directional electromagnetic steel sheet contains at least 0.005% or less of C and 2.5 to 7.0% of Si by mass, and may further contain 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 a range that does not impair the properties. The remainder contains Fe and impurities, the average crystal grain size is 1 to 10 mm, and the average angle between the crystal orientation of (110)

[001] and the rolling direction is 8° or less.

[0126] <Insulating Coating Treatment Solution for Directional Electromagnetic Steel Sheets> Next, the insulating film treatment liquid (hereinafter also referred to as "insulating film treatment liquid") used in the directional electromagnetic steel plate of this embodiment will be described.

[0127] The insulating coating treatment solution contains metal phosphate salts selected from one or more metals chosen from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W, and Zr, as well as colloidal silica, and does not contain chromates. The metal phosphate salts are preferably selected from one or more phosphates chosen from Al, Mg, Ni, V, and W. This is because selecting these phosphates allows for a flat and uniform appearance under a wide range of baking conditions.

[0128] Furthermore, the insulating film treatment solution preferably contains an alkali metal element. The alkali metals contained in the insulating film treatment solution are preferably lithium, sodium, and potassium, more preferably sodium and potassium. The amount of alkali metal contained in the insulating film treatment solution is preferably 0.20 mol / kg or more, more preferably 0.22 mol / kg or more. On the other hand, there is no particular upper limit, but it is, for example, 0.30 mol / kg or less, preferably 0.27 mol / kg or less. When the amount of alkali metal contained is less than 0.20 mol / kg, the amount of phosphorus leached increases under long-term storage in a high-temperature and high-humidity atmosphere. On the other hand, if the amount of alkali metals such as sodium exceeds 0.30 mol / kg, unevenness occurs in the appearance, which is therefore undesirable.

[0129] In this embodiment, the amount of alkali metals such as Na in the insulating film treatment solution can be analyzed as follows. The amount of alkali metals such as Na in the insulating film treatment solution is determined by atomic absorption spectrophotometry and converted into a molar amount. Then, the amount of alkali metals such as Na can be derived by dividing the amount of alkali metals such as Na by the weight of the insulating film treatment solution.

[0130] Furthermore, as described above, the pH of the insulating film treatment solution is preferably 1.7 to 2.1. The pH of the insulating film treatment solution is preferably 1.8 or higher, and more preferably 1.9 or higher.

[0131] <Manufacturing Method of Insulating Coating Treatment Liquid for Directional Electromagnetic Steel Sheets> Next, the method for manufacturing the insulating film treatment liquid used in the directional electromagnetic steel plate of this embodiment (hereinafter referred to as "the method for manufacturing the insulating film treatment liquid") and the reasons for its limitation will be described.

[0132] The manufacturing method of the insulating film treatment solution includes a mixing step of metal phosphate salt, colloidal silica, and alkali metal salt. The method of containing the alkali metal is not particularly limited, as long as it is sufficient to ensure that the insulating film treatment solution contains a specified amount of alkali metal; however, an example is given below.

[0133] Phosphates may be based on metal phosphates of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W and Zr, and may contain alkali metals in the form of sodium phosphate or potassium phosphate.

[0134] Alternatively, a method of pre-adding a sodium compound to colloidal silica has been considered. However, when a sodium compound is added to colloidal silica, there is a risk that the colloidal silica will agglomerate, so the extension of stirring time, etc., needs to be carefully studied.

[0135] Alternatively, an alkali metal can be added to the insulating film treatment solution by mixing metal phosphate salts and colloidal silica and then adding aqueous solutions of sodium hydroxide and potassium hydroxide.

[0136] The size of the colloidal silica (silica particles) used in this embodiment is not particularly limited, but an average particle size (average primary particle size) of 4 to 35 nm is preferred. If the average particle size of the colloidal silica is less than 4 nm, the colloidal silica may easily aggregate, resulting in poor stability of the insulating film treatment solution, or the insulating film may become a porous film with large gaps, reducing the adhesion of the insulating film, which is therefore undesirable. On the other hand, if the average particle size of the colloidal silica exceeds 35 nm, the reactivity of the colloidal silica may become insufficient, the mixing of the phosphate as a binder with the colloidal silica may become inadequate, or cracks may occur in the insulating film, resulting in reduced adhesion, which is also undesirable.

[0137] Furthermore, the smaller the particle size of colloidal silica, the denser the film formed, and the higher the film tension. Therefore, the upper limit of the average particle size of colloidal silica is further preferably set to 31 nm, 22 nm, 18 nm, or 12 nm. Moreover, it is further preferred that the surface of the colloidal silica be chemically treated with aluminum. It should be noted that the average particle size (average primary particle size) of the colloidal silica can be calculated, for example, by conversion from the specific surface area measured using the BET adsorption method (according to JIS Z 8830:2013).

[0138] In the manufacturing method of the insulating film treatment solution, the ratio of metal phosphate salt to colloidal silica is not particularly limited. As long as the amount of alkali metal contained in the insulating film treatment solution is 0.20 mol / kg to 0.30 mol / kg, the insulating film of the directional electromagnetic steel plate using this insulating film treatment solution exhibits excellent properties. It should be noted that preferred values ​​are shown below.

[0139] For example, the insulating film treatment solution can be prepared by mixing an aqueous solution containing 100 parts by mass of a metal phosphate salt (based on solid content), 35 to 125 parts by mass of colloidal silica (based on solid content), and an aqueous solution containing more than 0 parts by mass and less than 7 parts by mass of sodium hydroxide, potassium hydroxide, or lithium hydroxide (based on solid content). The insulating film treatment solution prepared in this way only needs to contain 0.20 mol / kg to 0.30 mol / kg of lithium, sodium, or potassium as an alkali metal.

[0140] Furthermore, the content of colloidal silica in the insulating film treatment solution is preferably set to 25-55% by mass relative to the total mass of the insulating film treatment solution, calculated as solids. If the content of colloidal silica in the insulating film treatment solution is less than 25% by mass, the film tension of the insulating film may become insufficient, which is undesirable. If the content of colloidal silica in the insulating film treatment solution exceeds 55% by mass, the adhesion of the insulating film may decrease, which is also undesirable. More preferably, the content of colloidal silica in the insulating film treatment solution is 27% by mass or more relative to the total mass of the insulating film treatment solution, calculated as solids, and even more preferably 30% by mass or more, 32% by mass or more, or 35% by mass or more. More preferably, the content of colloidal silica in the insulating film treatment solution is 45% by mass or less, and even more preferably 40% by mass or less.

[0141] In the above mixing process, various oxides such as titanium oxide and molybdenum oxide, boric acid, sodium borate, pigments, and inorganic compounds such as barium titanate can also be further mixed into the insulating film treatment solution.

[0142] Furthermore, as described above, it is preferable to adjust the pH of the insulating film treatment solution to 1.7 to 2.1. For example, the pH of the insulating film treatment solution can also be adjusted by adding hydrochloric acid or an alkali metal hydroxide to the insulating film treatment solution. The pH of the insulating film treatment solution is preferably 1.8 or higher, and more preferably 1.9 or higher.

[0143] Example Next, the effects of one aspect of the present invention will be described in more detail through embodiments. However, the conditions in the embodiments are examples adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to these one example. Various conditions can be adopted as long as they do not depart from the spirit of the present invention and achieve the purpose of the present invention.

[0144] A slab, whose chemical composition was adjusted to the composition shown in Table 2 according to the chemical composition of the base steel sheet, was heated to 1150°C and hot-rolled to produce a hot-rolled steel sheet with a thickness of 2.6 mm. This hot-rolled steel sheet was then subjected to hot-rolled annealing as needed, followed by a single cold rolling or multiple cold rolling processes with intermediate annealing, to produce a cold-rolled steel sheet with a final thickness of 0.23 mm. This cold-rolled steel sheet underwent decarburization annealing, followed by nitriding annealing while maintaining a temperature in an ammonia-containing atmosphere during the cooling process. It should be noted that known conditions were used in the processes from slab heating to nitriding annealing.

[0145] The decarburized annealed plates described above were coated with an annealing separating agent mainly composed of MgO and then dried. The decarburized annealed plates coated with the annealing separating agent were then subjected to finished product annealing at 1200℃ for 20 hours.

[0146] Afterwards, the remaining annealing separating agent was washed away with water using a scrubber. As shown in Table 3, the insulating film coating solution, with a solid content of 50% by mass of colloidal silica and the remainder adjusted to consist of solids of phosphates, alkali metals, chromates, and inorganic compounds, was baked under the conditions shown in Table 4 to form an insulating film. It should be noted that the Na content in the insulating film coating solution was adjusted by adding a 30% sodium hydroxide aqueous solution, the K content by adding a 30% potassium hydroxide aqueous solution, and the Li content by adding a 30% lithium hydroxide aqueous solution. Furthermore, the pH of the insulating film coating solution was adjusted as needed, setting it to 1.6–2.2.

[0147] For the obtained directional electromagnetic steel plates No. C1~C36 and c1~c4, the chemical composition of the base steel plate, the chemical composition of the insulating film, the film adhesion amount of the insulating film, and the insulating film were determined based on the above method. 31 P-NMR spectroscopy, etc. Additionally, for the measured insulating film... 31 The P-NMR spectrum was subjected to Gaussian fitting using the method described above to obtain Q. 0 The ratio of the peak area of ​​the structure to the total peak area (Q) 0 (Structure area ratio).

[0148] In addition, for the obtained directional electromagnetic steel sheets No. C1 to C36 and c1 to c4, the moisture absorption, phosphorus leaching, and appearance after baking were evaluated based on the following methods.

[0149] [moisture absorption] The moisture absorption of a directional electromagnetic steel sheet with an insulating coating was derived using the following method. The resulting directional electromagnetic steel sheet with the insulating coating was cut into lengths of 300 mm and widths of 60 mm, and placed in a constant temperature and humidity bath (temperature 50℃, humidity 90%) for one week. The weight difference before and after the constant temperature and humidity period was measured. Then, the quantified weight difference was divided by the area of ​​the two sides of the test piece, 0.036 m². 2 The obtained value is defined as moisture absorption (unit: g / m³). 2 If the moisture absorption is 0.05 g / m³ 2 The following are judged to have excellent moisture resistance.

[0150] [Phosphorus leaching amount] The phosphorus leaching amount was evaluated after immersing the directional electromagnetic steel plate with an insulating coating in a constant temperature and humidity bath (temperature 50℃, humidity 90%) for one week. The phosphorus leaching amount was determined by immersing three 40mm × 60mm test pieces in distilled water at 100℃ for 20 minutes and then boiling them, thereby leaching phosphorus from the coating surface, followed by quantitative analysis. The quantitative analysis of phosphorus was performed according to JIS K 0102:2019, Factory Wastewater Test Method 46.1.1, expressed as PO4 (unit: mg / m³). 2 Quantification is performed. If the phosphorus leaching amount is 50 mg / m³, then... 2 The following indicates that the amount of phosphorus leaching is low.

[0151] [Appearance] In addition, the appearance of the insulating film after baking was evaluated. The appearance of the insulating film after baking was evaluated using SEM, and the presence or absence of white opacity on the observed film surface was used for judgment. A white opacity area of ​​less than 10% of the observed area was judged as "very good," more than 10% but less than 20% as "good," and more than 20% as "poor." If the appearance was "very good" or "good," it was judged as excellent.

[0152] It should be noted that when using SEM to observe the surface of a baked sample with an insulating film, areas where fine cracks can be identified and areas where they cannot be identified will be observed within the film. Diffuse reflection of light occurs in these areas where fine cracks are identified, resulting in a cloudy appearance of the sample. Therefore, the area of ​​the region where fine cracks can be identified at 1000x magnification is calculated, and its ratio relative to the total observed area is derived. Specifically, this ratio of the cloudy area is derived by image analysis and binarization of the SEM image into cloudy and non-cloudy regions. Discriminant analysis was used for the binarization threshold.

[0153] The Q-type directional electromagnetic steel plate with an insulating film 0 The evaluation results of the area ratio, moisture absorption, phosphorus leaching, and appearance of the structure are shown in Table 5.

[0154] It should be noted that, although not shown in the table, the chemical composition of the insulating films C1 to C36 used as examples of the present invention, as the main constituent elements, satisfies the following conditions: P: 5-30 atomic%, Si: 5-30 atomic%, O: 30-80 atomic%, Al: 0.1-10 atomic%, Cr: less than 1 atomic%, Fe: less than 25 atomic%, Mg: 0-10 atomic%, Mn: 0-10 atomic%, Ni: 0-10 atomic%, Zn: 0-10 atomic%, V: 0-10 atomic%, W: 0-10 atomic%, Zr: 0-10 atomic%, Co: 0-10 atomic%, Mo: 0-10 atomic%. Furthermore, the coating weight of the insulating film satisfies 2.0-7.0 g / m² per single side. 2 .

[0155] As shown in Tables 2-5, the products of C1-C36, which are examples of the present invention, meet the characteristics of the present invention, and have excellent phosphorus leaching and moisture absorption. In addition, their appearance after baking is also excellent.

[0156] In contrast, the product characteristics of comparative examples c1 to c5 do not meet the scope of the present invention, and at least one of phosphorus leaching, moisture absorption, and appearance after baking is inferior. For example, Q of comparative example c1 is inferior. 0 The peak area ratio of the structure is outside the scope of this invention, and the phosphorus dissolution and hygroscopicity are inferior. As a comparative example, c2 has Q... 0 The peak area ratio of the structure is outside the scope of this invention, resulting in a poor appearance after baking. Comparative example c3, because it contains chromate (chromium compound), is therefore outside the scope of this invention. Comparative example c4, Q... 0 The peak area ratio of the structure is outside the scope of this invention, and the phosphorus dissolution, moisture absorption, and appearance after baking are inferior. As a comparative example, c5 has Q... 0 The peak area ratio of the structure is outside the scope of this invention, and the phosphorus dissolution and hygroscopicity are poor.

[0157] [Table 2] [Table 3] [Table 4] [Table 5] Industrial availability According to the above-described scheme of the present invention, directional electromagnetic steel sheets with excellent moisture resistance without the presence of chromates and low phosphorus leaching even after long-term storage in a high-temperature and high-humidity atmosphere can be stably obtained. Therefore, it has high industrial applicability.

Claims

1. A directional electromagnetic steel plate, characterized in that, It has a base steel plate and an insulating film. The insulating film contains phosphates but not chromium compounds. Using nuclear magnetic resonance (NMR), under a magnetic field with a proton resonance frequency of 500 MHz, the magic angle rotation was set to 55 kHz. 31 The chemical shift reference for the P-core was set at 0.9 ppm (ammonium dihydrogen phosphate, NH4H2PO4). The observation center was set between 0 and 30 ppm, the flip angle was 90°, the waiting time was 8 seconds, and the cumulative measurement was 9000 times. The obtained results... 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 greater than 0% and less than 10%.

2. The directional electromagnetic steel plate according to claim 1, characterized in that, The base steel plate, in terms of chemical composition, contains, by mass%,: C: Below 0.010% Si: 2.00~4.00% Mn: 0.05~1.00%, Al：0.010～0.065%、 N: below 0.004% S: Below 0.010% Se: below 0.010% Cr：0～0.30%、 Cu: 0–0.40% P：0～0.50%、 Ni: 0~1.00%, Sn: 0~0.30% Sb: 0~0.30%, B：0～0.0100%、 Mo: 0–0.1% Bi: 0~0.01%, The remaining portion contains Fe and impurities.

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