Grain-oriented electrical steel sheets

Abstract

This oriented electrical steel sheet has an insulating film that does not contain chromium compounds and contains phosphates, and when the 31P-NMR spectrum obtained by measuring the insulating film by nuclear magnetic resonance is Gaussian fitted in the range of 16 to -90 ppm, the ratio of the peak area of ​​the Q0 structure to the total peak area is greater than 0% and less than or equal to 10%.

Description

Technology Field

[0001] The present invention relates to a oriented electrical steel sheet coated with an insulating film that does not contain chromate. In particular, the present invention relates to a oriented electrical steel sheet that has a low amount of phosphorus leaching from the insulating film even after long-term storage, despite not containing chromate.

[0002] The present application claims priority based on patent application No. 2024-011667 filed in Japan on January 30, 2024, and incorporates the contents thereof herein by reference. Background Technology

[0003] Grain-oriented electrical steel sheets are steel sheets primarily used as cores for transformers, etc. Typically, these grain-oriented electrical steel sheets have two surface films formed: a forsterite layer (also called a primary film) formed during high-temperature finish annealing, and a phosphate film formed during heat flattening of the steel sheet after applying a treatment solution mainly composed of phosphates.

[0004] Phosphate coatings are necessary to impart electrical insulation to grain-oriented electrical steel sheets and to improve iron loss by reducing eddy current losses. In addition to insulation, phosphate coatings require various properties such as corrosion resistance, heat resistance, slipperiness, and adhesion. This is to facilitate various manufacturing processes when grain-oriented electrical steel sheets are processed into iron cores for transformers, etc. For example, if the heat resistance, slipperiness, and adhesion of the phosphate coating are poor, the phosphate coating may peel off during stress relief annealing for iron core manufacturing, which may result in the phosphate coating's original insulation properties not being exhibited or the steel sheets not being laminated smoothly, thereby worsening workability.

[0005] In addition, applying tension to the steel sheet can be cited as an important characteristic of the insulating film of the oriented electrical steel sheet. When tension is applied to the steel sheet, the iron loss of the oriented electrical steel sheet can be improved by facilitating the movement of the magnetic domain walls. By applying tension, it is also possible to reduce magnetic deformation (one of the main causes of noise in transformers).

[0006] In order to improve various properties of the oriented electrical steel sheet as described above, specifically, technology as disclosed in the following patent documents 1 to 9 has been researched and developed.

[0007] For example, Patent Document 1 discloses that an insulating film treatment solution, mainly composed of aluminum phosphate, chromate, and colloidal silica of a specific composition, is applied to a forsterite film formed on the surface of a steel sheet after finishing annealing, and then baked. According to the technology disclosed in Patent Document 1, an insulating film having high tensile strength is formed on the surface of a steel sheet, and the iron loss and magnetostriction of the oriented electrical steel sheet can be reduced.

[0008] In addition, Patent Document 2 discloses a method of applying a treatment solution containing ultrafine colloidal silica particles with a particle size of 8 μm or less, a primary phosphate, and a chromate in specific proportions to a steel plate, and then baking it. According to the technology disclosed in Patent Document 2, the high strength of the insulating film can be maintained, and the lubricity of the film can also be improved.

[0009] In addition, Patent Document 3 discloses a technique for forming a high-strength insulating film on the surface of a oriented electrical steel sheet by attaching a specific amount of an insulating film composed mainly of phosphate, chromate, and colloidal silica having a glass transition point of 950°C to 1200°C.

[0010] According to the technology disclosed in the above patent documents 1 to 3, it was possible to form an insulating film with significantly superior various film properties and improved film tension. However, the technology disclosed in patent documents 1 to 3 all contain chromate, which is a chromium compound, in the insulating film. Recently, as environmental issues have come into focus, there is a social demand to prohibit or restrict the use of compounds such as lead, chromium, and cadmium.

[0011] Therefore, technology capable of forming a good insulating film without containing the aforementioned chromium compound is being investigated. However, in the case of insulating films that do not contain chromium compounds, insufficient tensioning of the steel sheet has been a challenge.

[0012] As a method for solving the above-mentioned problem, for example, Patent Document 4 discloses a method for treating an insulating film on a oriented electrical steel sheet by baking at 300°C or higher, wherein the treatment solution contains 20 parts by weight of colloidal silica with an SiO2 content, 10 to 120 parts by weight of aluminum phosphate, 2 to 10 parts by weight of boric acid, and a total of 4 to 40 parts by weight of one or more selected from sulfates of Mg, Al, Fe, Co, Ni, and Zn.

[0013] In addition, Patent Document 5 discloses a coating agent for forming a film that comprises a mixture of boric acid and alumina sol and an organic solvent compatible with water, and has a tension-improving effect on oriented electrical steel sheets.

[0014] In addition, Patent Document 6 discloses a surface treatment agent for oriented electrical steel sheets containing a primary phosphate of Al, Mg, and Ca and colloidal silica, wherein the agent contains one or more organic acid salts of Ca, Mn, Fe, Mg, Zn, Co, Ni, Cu, B, and Al. Furthermore, 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 for an insulating film treatment agent for oriented electrical steel sheets containing phosphate and colloidal silica, wherein the metal component in the phosphate is a combination of a specific ratio of a divalent metal element, a trivalent metal element, and a metal element having a valence of tetravalent or higher.

[0016] In addition, Patent Document 8 discloses a oriented electrical steel sheet comprising an insulating film containing colloidal silica and a steel sheet, a first metal phosphate salt which is a metal phosphate salt of one or more metals selected from Al, Fe, Mg, Mn, Ni, and Zn, a second phosphate salt which is a metal phosphate salt of one or more metals selected from Co, Mo, V, W, and Zr.

[0017] In addition, Patent Document 9 discloses an aqueous composition for coating a directional electron steel comprising an aluminum cation, a manganese cation, dihydrogen phosphate, hydrogen phosphate and / or an anion of phosphate, colloidal silicon dioxide, and optionally an iron cation. Prior art literature

[0018] Japanese Patent Publication No. Sho 48-39338 Japanese Patent Publication No. Sho 61-41778 Japanese Patent Publication No. Hei 11-071683 Japanese Patent Publication No. Sho 54-143737 Japanese Patent Publication No. Hei 7-278828 Japanese Patent Publication No. 2000-178760 Japanese Patent Publication No. 2010-13692 International Publication No. 2017 / 057513 Japanese Patent Publication No. 2022-519691 The problem to be solved

[0019] Various properties of insulating films have been improved through these proposals. However, through the inventors' research to date, it has been found that in the case of insulating films that do not contain chromium compounds, the amount of phosphorus leaching from the insulating film increases significantly during long-term storage. Electrical steel sheets are sometimes loaded onto ships in the form of coils after manufacturing and transported over long periods under high temperature and high humidity conditions. Consequently, if the amount of phosphorus leaching increases significantly during long-term transport, there is a possibility of problems occurring, such as sticking between coils or, in some cases, the coils failing to unwind. Regardless of the aforementioned techniques, the amount of 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 the grain-oriented electrical steel sheet must possess electrical insulation properties and be capable of applying high tensile strength to the surface of the steel sheet. Furthermore, the insulating film of the grain-oriented electrical steel sheet is required to have good moisture resistance even under high temperature and high humidity conditions. Moreover, the insulating film of the grain-oriented electrical steel sheet is required not to increase the amount of phosphorus leaching associated with long-term storage.

[0021] One embodiment of the present invention has been made to solve the above-mentioned problem. One embodiment of the present invention aims to provide a directional electrical steel sheet that does not contain chromate and, on the premise that its moisture resistance, etc., is equivalent to or better than that of the conventional material, additionally has a low amount of phosphorus leaching after long-term storage. means of solving the problem

[0022] The gist of the present invention is as follows.

[0023] (1) A directional electrical steel sheet according to one aspect of the present invention is,

[0024] A base steel plate and an insulating film are provided,

[0025] The above insulating film does not contain a chromium compound and contains a phosphate, and

[0026] The above insulating film, by nuclear magnetic resonance, under a magnetic field with a proton resonance frequency of 500 MHz, magic angle rotation of 55 kHz, 31 The chemical shift reference of the P nucleus was set to 0.9 ppm using ammonium dihydrogen phosphate (NH4H2PO4), the observation center was set between 0 and 30 ppm, and measurements were taken under conditions of a flip angle of 90°, a waiting time of 8 seconds, and an accumulation of 9,000 cycles, and the obtained 31 When the P-NMR spectrum is Gaussian-fitted to the range of 16 to -90 ppm,

[0027] Q 0 The ratio of the peak area of ​​the structure to the total peak area is greater than 0% and less than or equal to 10%.

[0028] (2) In the oriented electrical steel sheet described in (1) above,

[0029] The above base steel plate, as a chemical composition, in mass%,

[0030] C: 0.010% or less,

[0031] Si: 2.00 to 4.00%,

[0032] Mn: 0.05 to 1.00%,

[0033] Al: 0.010 to 0.065%,

[0034] N: 0.004% or less,

[0035] S: 0.010% or less,

[0036] Se: 0.010% or less,

[0037] Cr: 0 to 0.30%,

[0038] Cu: 0 to 0.40%,

[0039] P: 0 to 0.50%,

[0040] Ni: 0 to 1.00%,

[0041] Sn: 0 to 0.30%,

[0042] Sb: 0 to 0.30%,

[0043] B: 0 to 0.0100%,

[0044] Mo: 0 to 0.1%,

[0045] Bi: Contains 0 to 0.01%,

[0046] The remainder may consist of Fe and impurities. Effects of the invention

[0047] According to the above embodiment of the present invention, a directional electrical steel sheet that does not contain chromate, has excellent moisture resistance, and has a low phosphorus leaching amount even when stored for a long time in a high-temperature and high-humidity atmosphere can be stably obtained. Brief explanation of the drawing

[0048] Figure 1 is a diagram illustrating the relationship between the amount of Na in the insulating film treatment solution and the amount of moisture absorbed by the oriented electrical steel sheet coated with the insulating film. Figure 2 is a diagram illustrating the relationship between the amount of Na in the insulating film treatment solution and the amount of phosphorus leached from the oriented electrical steel sheet coated with an insulating film, for a steel sheet before moisture resistance evaluation. Figure 3 is a diagram illustrating the relationship between the amount of Na in the insulating film treatment solution and the amount of phosphorus leached from the oriented electrical steel sheet coated with an insulating film, for a steel sheet after hygroscopicity evaluation. Figure 4 is a reference diagram illustrating the cross-linking oxygen of phosphate, and Q 0 , Q 1 , Q 2 , Q 3 4 types of Q n This is a reference diagram illustrating the structure. Figure 5 shows the insulating film. 31 This is a reference diagram illustrating an example of Gaussian fitting performed on a P-NMR spectrum. Figure 6 shows an insulating film. 31 Q obtained by performing a Gaussian fitting on the P-NMR spectrum 0 It is a drawing illustrating the ratio of the structure, and the amount of Na in the insulating film treatment solution and Q in the insulating film 0 It is a drawing that illustrates the relationship between the ratios of the structure. Figure 7 shows the insulating film 31 This is a diagram showing five peak tops in which the chemical shift in the P-NMR spectrum is included in the range of 16 to -90 ppm. Specific details for implementing the invention

[0049] Preferred embodiments of the present invention are 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 that does not deviate from the spirit of the present invention. Furthermore, the numerical limit ranges shown in the present embodiments include lower and upper limits. Numerical values ​​indicated as "greater than" or "less than" are not included in the numerical range. Unless otherwise specified, "%" regarding the content of each element means "mass%".

[0050] Below, the results of preliminary experiments leading to obtaining a directional electrical steel sheet according to the present embodiment are described.

[0051] Experiment

[0052] A oriented electrical steel sheet with a thickness of 0.23 mm and finished annealing, manufactured by a known method, was sheared to a width of 60 mm and a length of 300 mm, and the annealing separator attached to the surface was removed by washing with water, and this was prepared as a base steel sheet.

[0053] Next, 250 parts by mass of a first aluminum phosphate aqueous solution with a solid content of 40 mass%, 300 parts by mass of colloidal silica with a solid content of 30 mass%, and 0 to 7 parts by mass of sodium hydroxide (solid content) were mixed to produce 10 types of insulating film treatment solutions, adjusted so that the amount of sodium (Na) in the insulating film treatment solution ranged from 0.02 to 0.34 mol / kg, as shown in Table 1. In addition, since sodium-stable colloidal silica was used, the amount of Na at the level without adding sodium hydroxide was 0.02 mol / kg.

[0054]

[0055] Then, the above insulating film treatment solution was applied to each of the base steel plates prepared first using a roll coater on both sides such that the amount of film adhered after baking was 4.5 g / m² per side. After that, it was baked at a temperature of 850°C for 30 seconds.

[0056] In addition, as a comparative material, an insulating film treatment solution (Na2O / SiO2=0.25%) consisting of 50 parts by mass of aluminum phosphate that does not contain Na, 40 parts by mass of colloidal silica (sodium-stable type), and 10 parts by mass of anhydrous chromic acid was similarly applied to a base steel plate and baked.

[0057] Moisture resistance was evaluated using a steel plate as a test specimen, which had been baked after applying an insulating coating solution to a base steel plate. First, the test specimen was placed in a constant temperature and humidity chamber (temperature 50°C, humidity 90%) for one week, and the weight difference before and after maintaining the constant temperature and humidity was quantified. Then, the quantified weight difference was divided by the surface area of ​​both sides of the test specimen (0.036 m²) to define the moisture absorption amount (unit: g / m²), and moisture resistance was evaluated using this moisture absorption amount as an indicator. If this moisture absorption amount is 0.05 g / m² or less, it can be judged that the moisture resistance is excellent.

[0058] In addition, a phosphorus leaching test was conducted before and after the hygroscopicity evaluation. For the phosphorus leaching test, three test specimens measuring 40 mm × 60 mm were immersed in distilled water at 100°C for 20 minutes and boiled to leach phosphorus from the surface of the film, and the phosphorus was quantitatively analyzed. The quantitative analysis of phosphorus was performed in accordance with JIS K 0102:2019 Plant Wastewater Test Method 46.1.1, and was quantified as PO4 (unit mg / m²). If the amount of phosphorus leached is 50 mg / m² or less, it can be determined that the amount of phosphorus leached is low.

[0059] Figure 1 illustrates the results of summarizing the relationship between the amount of Na in the insulating film treatment solution and the amount of moisture absorbed by the oriented electrical steel sheet coated with the insulating film, based on the above evaluation results.

[0060] As shown in Figure 1, in the steel plate with a chromium-containing coating (comparative material), the moisture absorption was 0.05 g / m² or less and hardly absorbed moisture. In contrast, in the steel plate with a non-chromium-containing coating (test material), the moisture absorption was high, exceeding 0.2 g / m² in the region where the Na content was less than 0.10 mol / kg, and sufficient moisture resistance was not obtained.

[0061] In addition, in regions where the amount of Na is high, particularly in regions where the amount of Na is 0.10 mol / kg or higher, the amount of moisture absorbed is 0.15 g / m² or less. Also, in regions where the amount of Na is 0.20 mol / kg or higher, the amount of moisture absorbed is 0.05 g / m² or less, and moisture resistance equivalent to that of a steel plate with a chromium-containing coating is obtained. On the other hand, it was confirmed that when the amount of Na exceeds 0.30 mol / kg, the dispersibility of colloidal silica deteriorates, and non-uniformity occurs in the appearance after baking.

[0062] Next, for the test specimen prior to the hygroscopicity evaluation, the results of summarizing the relationship between the amount of Na in the insulating film treatment solution and the amount of phosphorus leached from the oriented electrical steel sheet coated with the insulating film are shown in Figure 2.

[0063] As shown in FIG. 2, even in steel plates with a coating that does not contain chromium, the amount of phosphorus leaching is low regardless of the amount of Na, just like in steel plates with a coating that contains chromium. In other words, the problem of increased phosphorus leaching from the insulating coating does not occur before maintaining constant temperature and humidity.

[0064] In addition, for the test specimen after the moisture resistance evaluation, the results of summarizing the relationship between the amount of Na in the insulating film treatment solution and the amount of phosphorus leached from the oriented electrical steel sheet coated with the insulating film are shown in Figure 3.

[0065] As shown in Fig. 3, in the region where the Na content is 0.20 mol / kg or more, the phosphorus leaching amount of the steel plate with a chromium-containing film was 50 mg / m² or less, similar to the steel plate with a chromium-containing film. However, in the region where the Na content is less than 0.20 mol / kg, the phosphorus leaching amount was very high, exceeding 50 mg / m², and it was confirmed that the insulating film was deteriorated by evaluating the moisture resistance.

[0066] Based on the above experimental results, regarding 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 a chromium-free insulating film, the following is considered.

[0067] Structure of Phosphate

[0068] The leaching of phosphorus from the insulating film is thought to be due to a hydrolysis reaction in which water molecules act on the POP bonds of the phosphate forming the insulating film, causing the bonds to break. Therefore, it is important to use POM (where M is a metal element) in which the P(phosphorus)-O(oxygen)-P(phosphorus) bond is substituted with another bond.

[0069] Here, for the structural evaluation of phosphates, the Nuclear Magnetic Resonance (NMR) method (hereinafter, 31 It is common to use (referred to as P-NMR). The structure of phosphate consists of a PO4 tetrahedron as the unit unit, in which four oxygen atoms are coordinated around a phosphorus atom, and forms a three-dimensional structure by sharing oxygen atoms at the vertices with separate PO4 tetrahedra. The oxygen atoms connecting the tetrahedra are called bridging oxygens, and Q is an index based on the number n of these bridging oxygens. n The notation is used, and as shown in FIG. 4, Q 0 , Q 1 , Q 2 , Q 3 4 types of Q n It can be classified by structure.

[0070] As the number of these cross-linking oxygen atoms n decreases, the polarity surrounding the phosphorus atom decreases, and since the interaction with highly polar water molecules weakens, the bond becomes difficult to break, and the amount of phosphorus leached decreases.

[0071] 0 Ratio of the peak area of ​​the structure to the total peak area: Greater than 0% and less than or equal to 10%

[0072] ​For steel sheets with a chromium-free coating, prior to evaluating moisture resistance, various insulating coatings with different Na contents 31 P-NMR spectra were measured, and Gaussian fitting was performed on the spectra in the range of 16 to -90 ppm.

[0073] Here, when performing Gaussian fitting, it is necessary to determine the peak height and linewidth using a Gaussian function. In this embodiment, the insulating film 31 For the P-NMR spectrum, six peak top positions (chemical shifts) of -49 ppm, -35 ppm, -30 ppm, -22 ppm, -8.8 ppm, and +5.9 ppm are fixed. Then, the full width at half for the -49 ppm peak is fixed at 6.291 kHz, and the full width at half for the -35 ppm peak is fixed at 3.780 kHz. In addition, the initial value of the full width at half for the -30 ppm peak is set to 2.000 kHz, and the initial value of the full width at half for the -22 ppm, -8.8 ppm, and +5.9 ppm peaks is set to 3.000 kHz. After optimizing only the heights of these peaks, the obtained optimized height values ​​are used as initial values. Additionally, for -30 ppm, -22 ppm, -8.8 ppm, and +5.9 ppm, the Levenberg-Marquardt method is used to optimize the results to most closely approximate the experimental spectral linearity, with height and linewidth as variable parameters; for -49 ppm and -35 ppm, the half-width is fixed at the aforementioned values ​​and only the height is used as a variable parameter. Furthermore, R, which indicates the quality of the optimization, 2 Regarding the value, R across the entire spectrum 2 R in the range of 16 to -90 ppm until the value becomes 0.9600 or higher 2 Optimize until the value becomes 0.9970 or higher.

[0074] In addition, the peak tops of the newly isolated functional components in this experiment are +5.9 ppm, -8.8 ppm, -22 ppm, -30 ppm, -35 ppm, and -49 ppm, and by correlating them with the spectral ranges of the crosslinking order described in the literature, the first three components are Q in order. 0 , Q 1 , Q 2 Determined as such, and the three components after -30ppm are Q 3 It was determined as follows (Reference: Turner, GL, Smith, Kirkpatrick, RJ. & Oldfield, E.(1986a) J. Mag. Reason., 70, 408).

[0075] Based on the above, the insulating film 31 An example of Gaussian fitting performed on a P-NMR spectrum is shown in Fig. 5.

[0076] In addition, of the insulating film 31 Based on the results of Gaussian fitting to the P-NMR spectrum, the amount of Na in the insulating coating solution and Q in the insulating film 0 The results summarizing the relationship of the structural ratios are shown in Fig. 6. In addition, Q in Fig. 6 0 The ratio of the structure is Q 0 , Q 1 , Q 2 , Q 3 4 types of Q n Q for the total peak area, which is the sum of the peak areas of the normal distribution curve of the structure 0 It represents the ratio of the peak areas of the structure. In addition, the ratio of the peak areas of the Q3 structure used the value of the sum of the three components above.

[0077] As shown in Fig. 6, when the amount of Na is less than 0.20 mol / kg, Q 0 While the ratio of the peak area of ​​the structure is 0%, when the amount of Na is 0.20 mol / kg or more, Q 0 The ratio of the peak area of ​​the structure becomes greater than 0%.

[0078] As shown in the experimental results above, the insulating film does not contain chromium compounds, 31 When the P-NMR spectrum is Gaussian-fitted in the range of 16 to -90 ppm, Q 0 By controlling the ratio of the peak area of ​​the structure (the area of ​​the peak with a peak top of +5.9 ppm) to the total peak area (the sum of the areas of the six peaks with peak tops of +5.9 ppm, -8.8 ppm, -22 ppm, -30 ppm, -35 ppm, and -49 ppm) to be greater than 0%, it is possible to control the amount of phosphorus leaching to be low even when stored for a long time in a high temperature and humid atmosphere.

[0079] Q 0 The ratio of the peak area of ​​the structure is preferably greater than 1%, more preferably greater than 4%. Meanwhile, Q 0 Under conditions where the ratio of the peak area of ​​the structure exceeds 10%, there was non-uniformity in the appearance of the insulating film. The ratio of the peak area of ​​the Q1 structure is preferably 9% or less.

[0080] 0 The ratio of the peak area of ​​the structure to the total peak area is Q 3 It is smaller than the ratio of the peak area of ​​the structure to the total peak area.

[0081] In the oriented electrical steel sheet according to the present embodiment, Q 0 The ratio of the peak area of ​​the structure is Q 3 It is smaller than the ratio of the peak area of ​​the structure. Q 0 Although the above-mentioned effect is preferably obtained by controlling the ratio of the peak area of ​​the structure to be greater than 0% and less than or equal to 10%, in order to maintain the form as an insulating film, Q 0 The ratio of the peak area of ​​the structure is Q 3 It becomes smaller than the ratio of the peak area of ​​the structure.

[0082] Herein, the insulating film of the directional electrical steel sheet according to the present embodiment 31 ​Explains how to determine the ratio of peak areas from a P-NMR spectrum.

[0083] 31 The measurement conditions for P-NMR are described in several non-patent literatures (e.g., Journal of Non-Crystalline Solid, 1998, 223, pp. 32-42). However, 31 It is known that the measurement conditions for P-NMR generally vary depending on the material. In the present embodiment, under a magnetic field with a proton resonance frequency of 500 MHz (e.g., the measurement magnetic field becomes 11.74 T to 11.75 T), the measurement temperature is room temperature, the MAS rotation is 55 kHz, and the measurement method is: 31 P Single Pulse Excitation (flipping angle 90°), measurement waiting time: 8s, integration: 9000 times, standard sample (chemical shift external reference): ammonium dihydrogen phosphate 0.9 ppm, observation center between 0 and 30 ppm, and measurements were performed using an Agilent INOVA500. For the insulating film, the base material of the oriented electrical steel sheet was dissolved in a 10% bromide methanol solution until the disappearance of the base material was confirmed, filtered, and the recovered material was washed with methanol and provided for NMR measurement.

[0084] insulating film 31 Figure 7 illustrates an example of a peak in which the chemical shift in the P-NMR spectrum falls within the range of 16 to -90 ppm. In Figure 7, 31 In the P-NMR spectrum, for example, five distinct peaks are identified. That is, starting from the left side of Fig. 7, the peaks are located at +5.9 ppm, -8.8 ppm, -22 ppm, -30 ppm, and -35 ppm. Additionally, although the peak with a peak top of -49 ppm is not clearly visible in Fig. 7, this -49 ppm peak may be clearly identified depending on the type of insulating film. Also, Q 0The peak corresponding to the structure is the peak with a peak top of +5.9 ppm in Fig. 7. Q 3 The peaks corresponding to the structure are the peaks with peak tops of -30 ppm and -35 ppm in Fig. 7.

[0085] 31 For the P-NMR spectrum, Gaussian fitting is performed using the method described above, and the peak area defined as the integral value of each peak is derived. In FIG. 7, for example, the sum of the peak areas of the five peaks becomes the total peak area. In FIG. 7, the area of ​​the peak with a peak top of +5.9 ppm is Q 0 It becomes the peak area of ​​the structure. Similarly, in Fig. 7, the sum of the peak areas where the peak tops are at -30 ppm and -35 ppm is Q 3 It becomes the peak area of ​​the structure. Based on these, "Q" for the "total peak area" n Calculate the ratio of the "peak area of ​​the structure".

[0086] In addition, the insulating film of the oriented electrical steel sheet according to the present embodiment does not contain chromium compounds. For example, in the present embodiment, it is determined that the insulating film does not contain chromium compounds when the Cr concentration included in the insulating film is less than 1 atomic percent. The Cr concentration is preferably 0.8 atomic percent or less, and more preferably 0.5 atomic percent or less.

[0087] In addition, in the present embodiment, the chemical composition of the insulating film is not particularly limited, but, for example, as the main contained elements, it is sufficient to satisfy 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%.

[0088] Furthermore, the insulating film provided by the oriented electrical steel sheet according to the present embodiment refers to an insulating film that is free from insufficient baking or cracking caused by poor baking conditions of the insulating film. If the insulating film has insufficient baking or cracking caused by poor baking conditions, it cannot satisfy the electrical insulation, tensile strength, corrosion resistance, heat resistance, slipperiness, adhesion, etc. required for the insulating film.

[0089] The concentration of Cr or other elements contained in the insulating film can be analyzed by analyzing the composition of the cross-section using, for example, SEM-EDS (Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy) or TEM-EDS (Transmission Electron Microscope-Energy Dispersive X-ray Spectroscopy).

[0090] Next, the amount of insulating film applied to the oriented electrical steel sheet according to the present embodiment will be explained.

[0091] In the oriented electrical steel sheet according to the present embodiment, the amount of insulating film applied is not particularly limited, but 2.0 to 7.0 g / m² per side is suitable. If the amount of insulating film applied is less than 2.0 g / m², it becomes difficult to impart high strength to the oriented electrical steel sheet, and the insulation and corrosion resistance of the oriented electrical steel sheet may also deteriorate, so this is undesirable. On the other hand, if the amount of insulating film applied exceeds 7.0 g / m², the packing density of the oriented electrical steel sheet decreases, and there is a possibility that the transformer characteristics may deteriorate, so this is undesirable. More preferably, the amount of insulating film applied is 3.0 g / m² or more, and even more preferably 4.0 g / m² or more. More preferably, the amount of insulating film applied is 6.0 g / m² or less, and even more preferably 5.0 g / m² or less.

[0092] Grain-oriented electrical steel sheets

[0093] Next, the base steel sheet of the oriented electrical steel sheet according to the present embodiment will be described. The base steel sheet of the oriented electrical steel sheet is not particularly limited, but as a chemical composition, it 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, and the remainder may consist of Fe and impurities. Hereinafter, % regarding the chemical composition refers to the mass% relative to the total mass of the base steel sheet.

[0094] C: 0.010% or less

[0095] Carbon (C) is an element effective for controlling the primary recrystallization structure, but since it has an adverse effect on magnetic properties, it is an element that is removed by decarburization annealing before final annealing. If the C concentration in the final product exceeds 0.010%, C precipitates during aging, causing the hysteresis loss to deteriorate; therefore, the C concentration is kept below 0.010%. 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, if the C concentration is reduced to less than 0.0001%, manufacturing costs increase significantly; therefore, for practical steel sheets, 0.0001% is the practical lower limit. Furthermore, in grain-oriented electrical steel sheets, the C concentration is typically reduced to about 0.001% or less by decarburization annealing.

[0096] Si: 2.00 to 4.00%

[0097] Silicon (Si) is an element that improves iron loss characteristics by increasing the electrical resistance of steel sheets. If the Si concentration is less than 2.00%, γ-transformation of the steel structure occurs during finish annealing, causing damage to 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 workability of the oriented electrical steel sheet deteriorates, and cracks occur during rolling; therefore, the Si concentration is set to 4.00% or lower. The Si concentration is preferably 3.50% or lower.

[0098] Mn: 0.05 to 1.00%

[0099] Manganese (Mn) is an element that prevents cracking during hot rolling and, in addition, combines with S and / or Se to form MnS or MnSe, which function as inhibitors. Since the effect of adding Mn is not sufficiently expressed if the Mn concentration is less than 0.05%, the Mn concentration is set to 0.05% or higher. The Mn concentration is preferably 0.07% or higher, and more preferably 0.09% or higher. On the other hand, if the Mn concentration exceeds 1.00%, the precipitation dispersion of MnS or MnSe becomes non-uniform, the desired secondary recrystallization structure is not obtained, and the magnetic flux density decreases; therefore, the Mn concentration is set to 1.00% or lower. The Mn concentration is preferably 0.80% or lower, and more preferably 0.60% or lower.

[0100] Al: 0.010 to 0.065%

[0101] Al (aluminum) is an element that combines with N to form (Al, Si)N or AlN, which function as inhibitors. If the Al concentration is less than 0.010%, the effect of Al addition is not sufficiently expressed and secondary recrystallization does not proceed sufficiently; therefore, the Al concentration is set to 0.010% or higher. The Al concentration is preferably 0.015% or higher, and more preferably 0.020% or higher. On the other hand, if the Al concentration exceeds 0.065%, the precipitation dispersion of the inhibitor becomes non-uniform, the desired secondary recrystallization structure is not obtained, and the magnetic flux density decreases; therefore, the Al concentration is set to 0.065% or lower. The Al concentration is preferably 0.050% or lower, and more preferably 0.040% or lower.

[0102] N: 0.004% or less

[0103] N (nitrogen) is an element that combines with Al to form AlN, which functions as an inhibitor. However, if the N concentration in the final product exceeds 0.004%, N in the steel sheet precipitates as AlN, degrading hysteresis loss; therefore, the N concentration is kept below 0.004%. Although the lower limit for N concentration includes 0%, reducing the N concentration to less than 0.0001% significantly increases manufacturing costs; thus, for practical steel sheets, 0.0001% is the practical lower limit. Furthermore, in grain-oriented electrical steel sheets, the N concentration is typically reduced to about 0.001% or less through finish annealing.

[0104] S: 0.010% or less

[0105] Sulfur (S) 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, which degrades hysteresis loss; therefore, the S concentration is kept below 0.010%. Although the lower limit of the S concentration includes 0%, if the S concentration is reduced to less than 0.0001%, manufacturing costs increase significantly; thus, for practical steel sheets, 0.0001% is the practical lower limit. Furthermore, in grain-oriented electrical steel sheets, the S concentration is typically reduced to about 0.005% or less through finish annealing.

[0106] In this embodiment, the base steel sheet may contain impurities. In addition, "impurities" refers to substances that are introduced from raw materials such as ore or scrap, or from the manufacturing environment, when steel is manufactured industrially.

[0107] In addition, in the present embodiment, the base steel sheet may contain a selective element in addition to the elements and impurities mentioned above. For example, instead of a portion of the remainder of Fe mentioned above, at least one of Se, Cr, Cu, P, Ni, Sn, Sb, B, Mo, or Bi may be contained as a selective element. These selective elements may be included according to the purpose. Accordingly, there is no need to limit the lower limit of these selective elements, and the lower limit may be 0%. Furthermore, even if these selective elements are contained as impurities, the above effect is not impaired.

[0108] For example, in the present embodiment, the base steel sheet may have one or more optional additive elements added, such as 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, for the purpose of improving other properties without impairing its magnetic properties.

[0109] Se: 0 to 0.010%

[0110] 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%, Se in the steel sheet precipitates as MnSe and degrades hysteresis loss; therefore, the Se concentration must be 0.010% or less. The lower limit of the Se concentration should be 0%, and 0.0001% is acceptable. Furthermore, in grain-oriented electrical steel sheets, the Se concentration is typically reduced to about 0.005% or less by finish annealing.

[0111] Cr: 0 to 0.30%

[0112] Cr (chromium) is an element effective for improving the oxide layer of decarburization annealing and forming a glass film. For this reason, Cr may be added to the base steel sheet in a range of 0.30% or less. Since decarburization is significantly inhibited if the Cr concentration exceeds 0.30%, it is desirable that the upper limit of the Cr concentration be 0.30%.

[0113] Cu: 0 to 0.40%

[0114] Copper (Cu) is an element effective in reducing iron loss by increasing the resistivity of the base steel sheet. If the Cu concentration exceeds 0.40%, the effect of reducing iron loss becomes saturated, and it causes surface scratches called "copper hege" during hot rolling, so it is desirable that the upper limit of the Cu concentration be 0.40%.

[0115] P: 0 to 0.50%

[0116] Phosphorus is an element effective in reducing iron loss by increasing the resistivity of the base steel sheet. Since problems with rollingability occur when the P concentration exceeds 0.50%, it is desirable that the upper limit of the P concentration be 0.50%.

[0117] Ni: 0 to 1.00%

[0118] Nickel (Ni) is an element effective in reducing iron loss by increasing the resistivity of the base steel sheet. In addition, Ni is also an element effective in improving magnetic properties by controlling the steel structure of the hot-rolled sheet. However, since secondary recrystallization becomes unstable when the Ni concentration exceeds 1.00%, it is desirable that the upper limit of the Ni concentration be 1.00%.

[0119] Sn: 0 to 0.30%

[0120] Sb: 0 to 0.30%

[0121] 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 finishing annealing conditions, Al may be oxidized by moisture released from the annealing separator, causing the inhibitor strength at the coil position to fluctuate. As a result, magnetic properties may fluctuate at the coil position. As one countermeasure to this, there is a method to prevent the oxidation of Al by adding these grain boundary segregation elements, and thus Sn and Sb may be added to the base steel sheet at a concentration of 0.30% or less each. On the other hand, if the concentration of these elements exceeds 0.30%, it becomes difficult for Si to oxidize during decarburization annealing, resulting in insufficient formation of the glass film and significantly hindering decarburization annealing performance. Therefore, it is preferable that the upper limit of the concentration of these elements be 0.30%.

[0122] B: 0 to 0.0100%

[0123] Boron (B) is an element that combines with N in the base steel sheet and precipitates complexly with MnS to form BN, which functions as an inhibitor. The lower limit of the B concentration is not particularly restricted and may be 0% as described above. However, to fully exhibit the effect of adding B, it is preferable that the lower limit of the B concentration be 0.0005%. The B concentration is preferably 0.001% or more, and more preferably 0.0015% or more. On the other hand, if the B concentration exceeds 0.0100%, the precipitation dispersion of BN becomes non-uniform, the desired secondary recrystallization structure is not obtained, and the magnetic flux density decreases. For this reason, it is preferable that the B concentration be 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.

[0124] Mo: 0 to 0.1%

[0125] Mo (molybdenum) is an element effective for improving surface properties during hot rolling. However, if the Mo concentration exceeds 0.1%, the effect of adding Mo becomes saturated, so it is desirable that the upper limit of the Mo concentration be 0.1%.

[0126] Bi: 0 to 0.01%

[0127] Bi (bismuth) has the effect of stabilizing precipitates such as sulfides and enhancing their function as an inhibitor. However, if the Bi concentration exceeds 0.01%, Bi has an adverse effect on the formation of the glass film, so it is desirable that the upper limit of the Bi concentration be 0.01%.

[0128] The chemical composition described above can be measured by general analytical methods for steel. For example, the chemical composition can be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Additionally, Al can be measured as total aluminum in accordance with JIS G 1257-10-1:2013. Furthermore, C and S can be measured using the combustion-infrared absorption method, N using the inert gas melt-thermal conductivity method, and, if necessary, O using the inert gas melt-non-dispersive infrared absorption method.

[0129] In addition, the above-mentioned chemical composition is the component of the base steel sheet. If the oriented electrical steel sheet used as the measurement sample has an insulating film on its surface, the chemical composition is measured after removing this insulating film by the following method.

[0130] For example, as a method for removing an insulating film, a grain-oriented electrical steel sheet having a film can be immersed in a high-temperature alkaline solution. Specifically, the insulating film can be removed from the grain-oriented electrical steel sheet by immersing it in an aqueous sodium hydroxide solution of NaOH: 30 to 50 mass% + H2O: 50 to 70 mass% at 80 to 90°C for 5 to 10 minutes, and then washing and drying it. In addition, the immersion time in the above-mentioned aqueous sodium hydroxide solution can be varied depending on the thickness of the insulating film.

[0131] Method for manufacturing grain-oriented electrical steel sheets

[0132] Next, a method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment is described. Furthermore, the method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment is not limited to the following method. The following manufacturing method is one example for manufacturing a grain-oriented electrical steel sheet according to the present embodiment.

[0133] Molten steel having a predetermined chemical composition is cast by a conventional method to form a silicon steel slab. The chemical composition of the silicon steel slab is not limited to a specific composition as long as it can obtain the magnetic and mechanical properties required for oriented electrical steel sheets, but an example of the chemical composition of the 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 as a chemical composition.

[0134] C: 0.085% or less

[0135] Carbon (C) is an element effective for controlling the primary recrystallization structure, but since it has an adverse effect on magnetic properties, it is an element that is removed by decarburization annealing before final annealing. If the C concentration exceeds 0.085%, the decarburization annealing time becomes longer, which lowers productivity; therefore, the C concentration is kept below 0.085%. The C concentration is preferably below 0.070%, and more preferably below 0.050%. The lower limit of the C concentration is not specifically limited; it can be 0% or above 0%. When considering productivity in industrial production and the magnetic properties of the product, 0.0001% is the practical lower limit of the C concentration. Furthermore, in grain-oriented electrical steel sheets, the C concentration is typically reduced to about 0.001% or less through decarburization annealing.

[0136] Si: 2.00 to 4.00%

[0137] Silicon (Si) is an element that improves iron loss characteristics by increasing the electrical resistance of the steel sheet. 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 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%, workability is reduced and cracks occur during rolling; therefore, the Si concentration is set to 4.00% or lower. The Si concentration is preferably 3.50% or lower.

[0138] Mn: 0.05 to 1.00%

[0139] Manganese (Mn) is an element that prevents cracking during hot rolling and, in addition, combines with S and / or Se to form MnS or MnSe, which function as inhibitors. Since the additive effect is not sufficiently expressed if the Mn concentration is less than 0.05%, the Mn concentration is set to 0.05% or higher. The Mn concentration is preferably 0.07% or higher, and more preferably 0.09% or higher. On the other hand, if the Mn concentration exceeds 1.00%, the precipitation dispersion of MnS or MnSe becomes non-uniform, the desired secondary recrystallization structure is not obtained, and the magnetic flux density decreases; therefore, the Mn concentration is set to 1.00% or lower. The Mn concentration is preferably 0.80% or lower, and more preferably 0.06% or lower.

[0140] Al: 0.010 to 0.065%

[0141] Al (aluminum) is an element that combines with N to form (Al,Si)N or AlN, which function as inhibitors. If the Al concentration is less than 0.010%, the addition effect is not sufficiently expressed and secondary recrystallization does not proceed sufficiently; therefore, the Al concentration is set to 0.010% or higher. The Al concentration is preferably 0.015% or higher, and more preferably 0.020% or higher. On the other hand, if the Al concentration exceeds 0.065%, the precipitation dispersion of (Al,Si)N, etc. becomes non-uniform, the desired secondary recrystallization structure is not obtained, and the magnetic flux density decreases; therefore, the Al concentration is set to 0.065% or lower. The Al concentration is preferably 0.050% or lower, and more preferably 0.040% or lower.

[0142] N: 0.004 to 0.012%

[0143] Nitrogen (N) is an element that combines with Al to form AlN, which functions as an inhibitor, but it is also an element that forms blisters (voids) in the steel sheet during cold rolling. Since the formation of AlN becomes insufficient if the N concentration is less than 0.004%, 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, since there is a risk that blisters (voids) will be generated in the steel sheet during cold rolling if the N concentration exceeds 0.012%, 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.

[0144] S: 0.010% or less

[0145] 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 dispersion of MnS after purification becomes non-uniform, the desired secondary recrystallization structure is not obtained, the magnetic flux density decreases, and the hysteresis loss deteriorates, or MnS remains after purification, and the hysteresis loss deteriorates. Although no lower limit is specifically provided, the S concentration may be 0%, and preferably 0.003% or higher. More preferably, the S concentration is 0.007% or higher.

[0146] B: 0.0100% or less

[0147] B (Boron) is an element that combines with N and precipitates complexly with MnS to form BN, which functions as an inhibitor. If the B concentration exceeds 0.0100%, the precipitation dispersion of BN becomes non-uniform, the necessary secondary recrystallization structure is not 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, and more preferably 0.0040% or less. Meanwhile, the lower limit of the B concentration is not particularly limited and may be 0%.

[0148] In this embodiment, the silicon steel slab may contain impurities. In addition, "impurities" refer to substances that are introduced from raw materials such as ore or scrap, or from the manufacturing environment, when steel is manufactured industrially.

[0149] In addition, in the present embodiment, the silicon steel slab may contain a selective element in addition to the elements and impurities mentioned above. For example, instead of a portion of the Fe remaining above, 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 included according to the purpose. Accordingly, there is no need to limit the lower limit of these selective elements, and the lower limit may be 0%. Furthermore, even if these selective elements are contained as impurities, the above effect is not impaired.

[0150] For example, in the present embodiment, the silicon steel slab may contain one or more of the following elements within a range that can enhance other properties without impairing the magnetic properties of the oriented electrical steel sheet: 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.

[0151] In the hot rolling process, a hot-rolled plate is obtained by performing hot rolling on a slab having the chemical composition described above. The hot rolling conditions are not particularly limited, and ordinary conditions may be used. The hot-rolled plate obtained by the hot rolling process is wound into a coil shape.

[0152] Before providing the slab for hot rolling, the slab may be heated to a temperature of over 1300°C to sufficiently solidify the inhibitor components of MnS or AlN. Additionally, for the sake of productivity and manufacturing costs, the slab may be heated to about 1250°C on the premise that the inhibitors will be increased by subsequent nitriding treatment.

[0153] In the hot-rolled sheet annealing process, a coil-shaped hot-rolled sheet is unwound into a strip-shaped hot-rolled sheet, and then annealed hot-rolled sheet is obtained by performing hot-rolled sheet annealing on the strip-shaped hot-rolled sheet. The hot-rolled sheet annealing conditions are not particularly limited, and normal conditions can be used.

[0154] In the cold rolling process, a cold-rolled sheet having a final thickness is obtained by performing one or two or more cold rollings on an annealed hot-rolled sheet. In this cold rolling process, a cold-rolled sheet may also be obtained by performing two or more cold rollings on an annealed hot-rolled sheet with intermediate annealing in between. In the annealing performed before the finishing (final) cold rolling, homogenization of the crystal structure is performed. The cold rolling conditions are not particularly limited, and normal conditions may be used.

[0155] In the decarburization annealing process, a decarburized annealed plate is obtained by performing decarburization annealing on a cold-rolled plate. In this decarburization annealing process, the cold-rolled plate is heat-treated in damp hydrogen to reduce the carbon content in the cold-rolled plate to a level that does not deteriorate due to self-aging as a product steel plate, while simultaneously inducing primary recrystallization in the cold-rolled plate and preparing for subsequent secondary recrystallization. The decarburization annealing conditions are not particularly limited, and ordinary conditions may be used. An oxide film of SiO2 is formed on the surface of the decarburized annealed plate obtained by this decarburization annealing process. Furthermore, when a cold-rolled plate is manufactured from a slab heated to approximately 1250°C, after decarburization annealing, the decarburized annealed plate is annealed in an ammonia atmosphere to generate AlN, which functions as an inhibitor, within the decarburized annealed plate.

[0156] In the method for manufacturing a oriented electrical steel sheet according to the present embodiment, the steel sheet on which the insulating film is formed may be a oriented electrical steel sheet having a conventional forsterite film, or a oriented electrical steel sheet not having a forsterite film.

[0157] In the case of a oriented electrical steel sheet having a conventional forsterite film, an annealing separator, which is the next process after the decarburization annealing process, is applied to prevent baking during the finishing annealing process. The amount of annealing separator applied is 6.0 to 14.0 g / m² per side of the decarburization annealing sheet.

[0158] In the case of oriented electrical steel sheets that do not have a forsterite film, an annealing separator with alumina (Al2O3) as the main component is applied during the annealing separator application process. The decarburized annealed sheet coated with the annealing separator is wound into a coil shape after drying the annealing separator.

[0159] In the finishing annealing process, a base steel sheet of the final product (oriented electrical steel sheet) is obtained by performing finishing annealing on a coil-shaped decarburized annealed plate coated with an annealing separator. In this finishing annealing process, secondary recrystallization is induced on the decarburized annealed plate by performing finishing annealing at a temperature of 1100°C or higher. In addition, to reduce hysteresis loss of the final product, a harmonizing annealing may be performed on the decarburized annealed plate after the completion of secondary recrystallization so that the precipitate used as an inhibitor becomes harmless.

[0160] An insulating film is formed on the surface of a steel plate after secondary recrystallization is completed. The method for forming this insulating film includes a coating process of applying an insulating film treatment solution to the surface of the steel plate and a baking process of baking the insulating film treatment solution. An insulating film is formed by baking.

[0161] After the final annealing, the excess annealing separator is washed away, and then pickling and washing treatments are performed using a sulfuric acid bath or the like. Through this, the surface of the steel sheet is cleaned and activated, and subsequently, in the coating process, an insulating film treatment solution is applied to the steel sheet. There are no restrictions on the method of applying the insulating film treatment solution to the steel sheet, but it is typically applied by a roll coater. An insulating film is formed on the surface of the oriented electrical steel sheet to which the insulating film treatment solution has been applied by performing a baking process under the conditions described below.

[0162] 31 When the P-NMR spectrum is Gaussian-fitted in the range of 16 to -90 ppm, Q 0 In order to make the ratio of the peak area of ​​the structure to the total peak area greater than 0% and less than or equal to 10%, it is necessary to change the POP bonds of the phosphate contained in the insulating film treatment solution into POM (where M is a metal element). To this end, it is preferable that the metal component contained in the insulating film treatment solution be an alkali metal element. Preferably, it is lithium, sodium, and potassium. More preferably, it is sodium and potassium. These alkali metal elements should be contained in the insulating film treatment solution at a concentration of 0.20 to 0.30 mol / kg.

[0163] Q 0It is not clear at present why the application of alkali metal elements such as sodium or potassium is effective in making the ratio of the peak area of ​​the structure to the total peak area greater than 0% and less than or equal to 10%. However, these alkali metals are known as modifying elements that significantly alter the properties of glass in phosphates, and furthermore, they have small atomic radii. Therefore, it is thought that these alkali metals are easily introduced into phosphates and have had a significant effect as a result. In addition, as mentioned above, the reason why the properties of the glass changed significantly with an increase in the sodium content in the insulating film is thought to be due to the increase in the ratio of changes from P(phosphorus)-O(oxygen)-P(phosphorus) bonds to POM(M: here assuming Na) bonds with an increase in sodium content.

[0164] Also, Q 0 In order to make the ratio of the peak area of ​​the structure to the total peak area greater than 0% and less than or equal to 10%, it is preferable that the pH of the insulating film treatment solution be 1.7 or higher and 2.1 or lower. This pH value is greater than the pH of conventional insulating film treatment solutions. Conventional insulating film treatment solutions typically have a pH of less than 1.7. The inventors have determined that when the pH of the insulating film treatment solution is 1.7 or higher and 2.1 or lower, Q 0 It was found that the ratio of the peak area of ​​the structure to the total peak area is preferably easy to control to greater than 0% and less than or equal to 10%. The reason for this is not clear at this point in time. However, for example, it is well known that hydrogen ions act as catalysts for the cleavage of POP bonds in the hydrolysis of polyphosphate ions, and similarly, it is known that hydrogen ions act as catalysts for the cleavage of POP bonds in pyrophosphates. In the present 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 becomes lower than in the conventional case, which in turn affects Q in the insulating film. 0It is thought to affect the ratio of the structure. The pH of the insulating film treatment solution is preferably 1.8 or higher, and more preferably 1.9 or higher.

[0165] In the baking process, an oriented electrical steel sheet coated with an insulating film treatment solution is heated to the baking crack temperature, maintained at the baking crack temperature, and then cooled.

[0166] The baking crack temperature (°C) refers to the plate temperature reached during the baking process (maximum plate temperature), and it is required to be 800°C or higher and 1000°C or lower. If the baking crack temperature is less than 800°C, the film formation reaction of the insulating film does not proceed sufficiently, so not only is the appearance of the film defective, but there may also be cases where sufficient tension cannot be applied to the steel plate. On the other hand, if the baking crack temperature exceeds 1000°C, cracks may occur in the insulating film, which may result in a decrease in film tension or insulation performance, and may also cause scratches on the steel plate. More preferably, the baking crack temperature is 850°C or higher and 950°C or lower.

[0167] The crack holding time (seconds) indicates the holding time at the baking crack temperature. A crack holding time of at least 10 seconds is required. If the crack holding time is less than 10 seconds, the baking of the insulating film is insufficient, and there is a possibility that the moisture resistance will deteriorate (the amount of moisture absorbed will increase). Preferably, it is at least 20 seconds. On the other hand, the crack holding time should be 60 seconds or less. If the crack holding time exceeds 60 seconds, not only is the moisture resistance hardly changed, but excessive crystallization of the insulating film may occur, causing cracks to form and reducing film tension. A crack holding time of 45 seconds or less is more preferable to obtain the necessary and sufficient various film properties.

[0168] Also, Q 0In order to keep the ratio of the peak area of ​​the structure to the total peak area greater than 0% and less than or equal to 10%, it is desirable that the heating rate when heating to the baking crack temperature during the baking process be between 30°C / second and 100°C / second. The reason for this is not clear at this point. However, if the heating rate to the baking crack temperature is excessively fast, the surface of the insulating film solidifies inwardly before the interior during heating, and moisture becomes trapped inside the insulating film. Consequently, due to this moisture, hole-shaped film defects are prone to occur inside the insulating film, and furthermore, Q within the insulating film 0 It is thought to affect the ratio of the structure. The heating rate to the baking crack temperature is preferably 40°C / second or higher, and more preferably 60°C / second or higher. In addition, the heating rate to the baking crack temperature is preferably 80°C / second or lower, and more preferably 70°C / second or lower.

[0169] In addition, the heating rate to the baking crack temperature mentioned above refers to the value obtained by dividing the temperature range from the baking start temperature (e.g., room temperature) to the baking crack temperature (a temperature of 800°C or higher and 1000°C or lower) by the time taken to heat up.

[0170] Furthermore, the type of base steel sheet on which the above-mentioned insulating film treatment is performed is not particularly limited. The main feature of the oriented electrical steel sheet according to the present embodiment lies in the composition of the insulating film, and the effects of the insulating film of the oriented electrical steel sheet according to the present embodiment—namely, the ability to apply high tension to the surface of the steel sheet, good adhesion and corrosion resistance, and excellent long-term stability despite not containing chromate—are exhibited regardless of the type of base steel sheet.

[0171] Preferably, the above-described insulating film treatment may be performed on a oriented electrical steel sheet, such as one manufactured using the technology disclosed in, for example, Japanese Patent Publication No. Hei 7-268567. At this time, an additional effect of reducing iron loss can be obtained. Specifically, by performing the above-described insulating film treatment on a oriented electrical steel sheet containing at least 0.005% or less of C and 2.5 to 7.0% of Si in mass%, optionally containing additional 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 properties, with the remainder being Fe and impurities, having an average crystal grain size of 1 to 10 mm, and having an average angle of 8° or less between the crystal orientation of (110)

[0001] and the rolling direction, an additional effect of reducing iron loss can be obtained.

[0172] Insulating coating solution for grain-oriented electrical steel sheets

[0173] Next, an insulating film treatment solution used in the oriented electrical steel sheet according to the present embodiment (hereinafter also simply referred to as the "insulating film treatment solution") will be described.

[0174] The insulating film treatment solution contains a metal phosphate salt of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W, and Zr, and colloidal silica, and does not contain chromates. It is preferable that the metal phosphate salt be one or more phosphates selected from Al, Mg, Ni, V, and W. This is because, when these phosphates are selected, a flat and uniform appearance is obtained under a wide range of baking conditions.

[0175] In addition, it is desirable for the insulating film treatment solution to contain alkali metal elements. The alkali metals contained in the insulating film treatment solution are preferably lithium, sodium, and potassium, and sodium and potassium are more desirable. The amount of alkali metal contained in the insulating film treatment solution is preferably 0.20 mol / kg or more, and also preferably 0.22 mol / kg or more. Meanwhile, although the upper limit is not specifically limited, for example, it is preferably 0.30 mol / kg or less and 0.27 mol / kg or less. If the amount of alkali metal contained is less than 0.20 mol / kg, the amount of phosphorus leaching increases when stored for a long period under a high temperature and high humidity atmosphere. On the other hand, if the amount of alkali metal such as Na exceeds 0.30 mol / kg, non-uniformity occurs in the appearance, which is undesirable.

[0176] 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 contained in the insulating film treatment solution is measured by atomic absorption spectrophotometry and converted into a substance amount. Subsequently, the amount of alkali metals such as Na can be derived by dividing the amount by the weight of the insulating film treatment solution.

[0177] In addition, as mentioned above, it is preferable that the pH of the insulating film treatment solution be 1.7 or higher and 2.1 or lower. It is preferable that the pH of the insulating film treatment solution be 1.8 or higher, and more preferable that it be 1.9 or higher.

[0178] Method for manufacturing an insulating film treatment solution for grain-oriented electrical steel sheets

[0179] Next, a method for manufacturing an insulating film treatment solution used in oriented electrical steel sheets according to the present embodiment (hereinafter simply referred to as the "method for manufacturing an insulating film treatment solution") and the reasons for the limitation thereof will be described.

[0180] The method for manufacturing the insulating film treatment solution comprises a mixing process of a metal phosphate salt, colloidal silica, and an alkali metal salt. As long as a predetermined amount of alkali metal can be contained in the insulating film treatment solution, the method of inclusion is not particularly limited, but an example is as follows.

[0181] 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 additionally contain an alkali metal as sodium phosphate or potassium phosphate.

[0182] In addition, a method of adding a Na compound to the colloidal silica in advance is also considered. However, since adding a Na compound to the colloidal silica carries a risk of aggregation, careful consideration is required, such as extending the stirring time.

[0183] In addition, it is also possible to incorporate alkali metals into the insulating film treatment solution by adding an aqueous solution of sodium hydroxide or potassium hydroxide after mixing metal phosphate salts and colloidal silica.

[0184] The size of the colloidal silica (silica particles) used in the present embodiment is not particularly limited, but it is preferable that the average particle size (average primary particle size) is 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 is undesirable because the stability of the insulating film treatment solution may deteriorate, or the insulating film may become a porous film with large gaps, which may reduce the adhesion of the insulating film. On the other hand, if the average particle size of the colloidal silica exceeds 35 nm, the reactivity of the colloidal silica becomes insufficient, which may result in insufficient mixing of the binder phosphate and the colloidal silica, or cracks may occur in the insulating film, which may reduce adhesion.

[0185] In addition, as the particle size of the colloidal silica becomes smaller, a denser film is formed, which can increase film tension; therefore, it is more preferable to set the upper limit of the average particle size of the colloidal silica to 31 nm, 22 nm, 18 nm, or 12 nm. In addition, it is more preferable that the surface of the colloidal silica be chemically treated with aluminum. In addition, the average particle size (average primary particle size) of the colloidal silica can be obtained, for example, by conversion from the specific surface area measurement value by the BET adsorption method (based on JIS Z 8830:2013).

[0186] In the method for manufacturing the insulating film treatment solution, the ratio of metal phosphate salt and 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 or more and 0.30 mol / kg or less, the insulating film of a grain-oriented electrical steel sheet using this insulating film treatment solution exhibits excellent properties. In addition, preferred values ​​are exemplified below.

[0187] For example, an insulating film treatment solution may be prepared by mixing an aqueous solution containing 100 parts by mass of a metal phosphate salt in terms of solid content, 35 to 125 parts by mass of colloidal silica in terms of solid content, and an aqueous solution containing more than 0 to 7 parts by mass of sodium hydroxide, potassium hydroxide, or lithium hydroxide in terms of solid content. The insulating film treatment solution prepared in this way may contain lithium, sodium, or potassium as an alkali metal in an amount of 0.20 mol / kg or more and 0.30 mol / kg or less.

[0188] In addition, it is preferable that the content of colloidal silica in the insulating film treatment solution be 25 to 55 mass% in terms of solid content relative to the total mass of the insulating film treatment solution. If the content of colloidal silica in the insulating film treatment solution is less than 25 mass%, it is undesirable because the film tension of the insulating film may not be sufficient; and if the content of colloidal silica in the insulating film treatment solution exceeds 55 mass%, it is undesirable because the adhesion of the insulating film may be reduced. Furthermore, the content of colloidal silica in the insulating film 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 solid content relative to the total mass of the insulating film treatment solution. The content of colloidal silica in the insulating film treatment solution is more preferably 45 mass% or less, and even more preferably 40 mass% or less.

[0189] In the above-described mixing process, various oxides such as titanium oxide and molybdenum oxide, boric acid, sodium borate, pigments, and inorganic compounds such as barium titanate may be additionally mixed into the insulating film treatment solution.

[0190] In addition, as mentioned above, it is desirable to adjust the pH of the insulating film treatment solution to 1.7 or higher and 2.1 or lower. For example, the pH of the insulating film treatment solution may be adjusted by adding hydrochloric acid or an alkali metal hydroxide to the insulating film treatment solution. It is desirable that the pH of the insulating film treatment solution be 1.8 or higher, and more desirable that it be 1.9 or higher.

[0191] Examples

[0192] Next, the effects of one embodiment of the present invention will be explained in more detail through examples; however, the conditions in the examples are examples of conditions adopted to verify the feasibility and effects of the present invention, and the present invention is not limited to these examples of conditions. The present invention may adopt various conditions as long as the objectives of the present invention are achieved without departing from the gist of the present invention.

[0193] As a final product, a slab with a chemical composition adjusted so that the chemical composition of the base steel sheet is as shown in Table 2 was heated to 1150°C and provided for hot rolling to produce a hot-rolled steel sheet with a thickness of 2.6 mm. After performing hot-rolled annealing on this hot-rolled steel sheet as necessary, multiple cold-rolling steps were performed with one cold rolling step or intermediate annealing in between to produce a cold-rolled steel sheet with a final thickness of 0.23 mm. Decarburization annealing was performed on this cold-rolled steel sheet, and nitriding annealing was performed by maintaining it in an atmosphere containing ammonia during cooling. In addition, known conditions were applied to the process from heating the slab to nitriding annealing.

[0194] A decarburized annealed plate after the decarburized annealing described above was coated with an annealing separator mainly composed of MgO and dried. On the decarburized annealed plate coated with the annealing separator, a finishing annealing was performed at 1200°C for 20 hours.

[0195] Subsequently, after removing excess annealing separator by washing with water using a scrubber, an insulating film treatment solution was applied in which the solid content ratio of colloidal silica in the insulating film treatment solution was 50 mass% as shown in Table 3, and the remainder was adjusted to solids of phosphates, alkali metals, chromates, and inorganic compounds, and an insulating film was formed by baking under the conditions shown in Table 4. In addition, the amount of Na in the insulating film treatment solution was adjusted by adding a 30% aqueous sodium hydroxide solution, the amount of K was adjusted by adding a 30% aqueous potassium hydroxide solution, and the amount of Li was adjusted by adding a 30% aqueous lithium hydroxide solution. Furthermore, the insulating film treatment solution was adjusted as necessary to set the pH to between 1.6 and 2.2.

[0196] With respect to the obtained oriented electrical steel sheets No. C1 to C36 and C1 to C4, the chemical composition of the base steel sheet, the chemical composition of the insulating film, the amount of insulating film applied, and the insulating film 31 P-NMR spectra, etc., were measured based on the above method. In addition, the measured insulating film 31 For the P-NMR spectrum, a Gaussian fitting is performed using the method described above, and Q 0 Ratio of the peak area of ​​the structure to the total peak area (Q 0 The area ratio of the structure was calculated.

[0197] In addition, for the obtained oriented electrical steel sheets No. C1 to C36 and c1 to c4, the moisture absorption, phosphorus leaching amount, appearance after baking, etc. were evaluated based on the following method.

[0198] [Moisture absorption]

[0199] The moisture absorption amount of a oriented electrical steel sheet equipped with an insulating film was determined by the following method. The obtained oriented electrical steel sheet equipped with an insulating film was cut to a length of 300 mm and a width of 60 mm, 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 measured. The quantified weight difference was then divided by the area of ​​both sides of the test specimen, 0.036 m², to define the moisture absorption amount (unit: g / m²). If this moisture absorption amount was 0.05 g / m² or less, it was determined that the moisture resistance was excellent.

[0200] [Phosphorus leaching amount]

[0201] The amount of phosphorus leaching was evaluated after placing the oriented electrical steel sheet equipped with an insulating film in a constant temperature and humidity bath (temperature 50°C, humidity 90%) for one week. The phosphorus leaching was performed by immersing three test specimens of 40 mm × 60 mm in distilled water at 100°C for 20 minutes and boiling them to leach phosphorus from the surface of the film, and then quantitatively analyzing the phosphorus. The quantitative analysis of phosphorus was performed in accordance with Section 46.1.1 of the factory wastewater test method of JIS K 0102:2019, and was quantified as PO4 (unit mg / m²). If the amount of phosphorus leaching was 50 mg / m² or less, it was determined that the amount of phosphorus leaching was low.

[0202] [appearance]

[0203] In addition, the appearance of the insulating film after baking was evaluated. The appearance of the insulating film after baking was evaluated by observing the insulating film with an SEM and determining the presence or absence of cloudiness on the observed film surface. The area of ​​cloudiness on the film surface was judged as "Very Good" if it was less than 10% of the observed area, "Good" if it was 10% or more but less than 20%, and "Poor" if it was 20% or more. If the appearance was "Very Good" or "Good," the appearance was judged to be excellent.

[0204] In addition, when observing the surface of the sample after baking the insulating film using SEM, areas with visible fine cracks and areas without are observed in the film. In these areas where fine cracks are visible, diffuse reflection of light occurs, causing the sample to appear cloudy. Therefore, the area of ​​the region where fine cracks are visible was calculated when observed at a magnification of 1000x, and the ratio to the total observed area was derived. Specifically, the ratio of the area of ​​this cloudy region was derived by analyzing the SEM observation images and binarizing them into cloudy and non-cloudy regions. Discriminant analysis was used for the threshold value of the binarization.

[0205] Q of oriented electrical steel sheets equipped with an insulating film 0 The evaluation results of the structural area ratio, moisture absorption, phosphorus leaching amount, and appearance are shown in Table 5.

[0206] In addition, although not shown in the table, the chemical composition of the insulating film of the present invention examples C1 to C36 satisfies the following as major 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%. In addition, the amount of insulating film applied satisfied 2.0 to 7.0 g / m² per side.

[0207] As can be seen from Tables 2 to 5, the examples of the present invention C1 to C36 have product characteristics that satisfy the scope of the present invention, and the phosphorus leaching amount and moisture absorption amount were excellent. In addition, the appearance after baking was also excellent.

[0208] In contrast, comparative examples c1 to c5 did not satisfy the scope of the present invention in terms of product characteristics, and at least one of the phosphorus leaching amount, moisture absorption amount, and appearance after baking was inferior. For example, comparative example c1 is Q 0 The ratio of the peak areas of the structure was outside the scope of the present invention, and the phosphorus leaching and hygroscopic amounts were inferior. Comparative example c2 is Q 0 The ratio of the peak areas of the structure was outside the scope of the present invention, and the appearance after baking was inferior. Comparative example c3 is outside the scope of the present invention because it contains chromate (chromium compound). Comparative example c4 is Q 0 The ratio of the peak area of ​​the structure was outside the scope of the present invention, and the phosphorus elution amount, hygroscopicity, and appearance after baking were inferior. Comparative example c5 is Q 0 The ratio of the peak area of ​​the structure was outside the scope of the present invention, and the phosphorus leaching amount and hygroscopicity were inferior.

[0209]

[0210]

[0211]

[0212] Industrial applicability

[0213] According to the above embodiment of the present invention, it is possible to stably obtain a oriented electrical steel sheet that does not contain chromate, has excellent moisture resistance, and has a low phosphorus leaching amount even when stored for a long period in a high-temperature, high-humidity atmosphere. Therefore, it has high potential for industrial application.

Claims

Claim 1 A oriented electrical steel sheet comprising a base steel sheet and an insulating film, wherein the insulating film does not contain a chromium compound and contains a phosphate, and the insulating film, by nuclear magnetic resonance, under a magnetic field of a proton resonance frequency of 500 MHz, a magic angle rotation of 55 kHz, 31 The chemical shift reference of the P nucleus was set to 0.9 ppm using ammonium dihydrogen phosphate (NH4H2PO4), the observation center was set between 0 and 30 ppm, and measurements were taken under conditions of a flip angle of 90°, a waiting time of 8 seconds, and an accumulation of 9,000 cycles, and the obtained 31 When the P-NMR spectrum is Gaussian-fitted in the range of 16 to -90 ppm, Q 0 A oriented electrical steel sheet characterized by the ratio of the peak area of ​​the structure to the total peak area being greater than 0% and less than or equal to 10%. Claim 2 The oriented electrical steel sheet according to claim 1, wherein the base steel sheet contains, in mass% as a chemical composition, C: 0.010% or less, Si: 2.00 to 4.00%, Mn: 0.05 to 1.00%, Al: 0.010 to 0.065%, N: 0.004% or less, S: 0.010% or less, Se: 0.010% or less, Cr: 0 to 0.30%, Cu: 0 to 0.40%, P: 0 to 0.50%, Ni: 0 to 1.00%, Sn: 0 to 0.30%, Sb: 0 to 0.30%, B: 0 to 0.0100%, Mo: 0 to 0.1%, Bi: 0 to 0.01%, and the remainder being Fe and impurities.

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