EP4790169A1

EP4790169A1 - Grain-oriented electrical steel sheet

Info

Publication number: EP4790169A1
Application number: EP25748718.1A
Authority: EP
Inventors: Keiko Goto; Shinsuke TAKATANI; Kazutoshi Takeda
Original assignee: Nippon Steel Corp
Current assignee: Nippon Steel Corp
Priority date: 2024-01-30
Filing date: 2025-01-30
Publication date: 2026-08-12
Also published as: JP7755224B1; KR20260070294A; WO2025164715A1; JPWO2025164715A1; CN122228361A

Abstract

A grain-oriented electrical steel sheet includes an insulation coating which is free of a chromium compound and contains a phosphate, and when the insulation coating is measured by a nuclear magnetic resonance and when an obtained 31P-NMR spectrum is subjected to a Gaussian fitting in a range from 16 to -90 ppm, a ratio of a peak area of a Q1 structure to a total peak area is more than 3% and 18% or less and the ratio of the Q1 structure is smaller than a ratio of a peak area of a Q3 structure.

Description

TECHNICAL FIELD

The present invention relates to a grain-oriented electrical steel sheet coated with an insulation coating free of chromium compounds. In particular, the present invention relates to a grain-oriented electrical steel sheet in which the amount of phosphorus elution from the insulation coating is small even when being stored for a long term although the chromate is not included.
Priority is claimed on Japanese Patent Application No. 2024-011678, filed January 30, 2024 , the content of which is incorporated herein by reference.

BACKGROUND ART

The grain-oriented electrical steel sheet is a steel sheet mainly used as an iron core of a transformer or the like. In general, on the grain-oriented electrical steel sheet, a two-layer surface coating including a forsterite layer (also referred to as a primary coating) formed during high-temperature final annealing, and a phosphate coating formed by applying a treatment solution containing a phosphate and the like as a main component and baking the treatment solution during heat flattening of the steel sheet is formed.
The phosphate coating is required to apply electrical insulation properties to the grain-oriented electrical steel sheet and to improve the iron loss by reducing eddy-current loss. In addition, the phosphate coating is required to have various characteristics such as corrosion resistance, heat resistance, slipperiness, and adhesion in addition to the insulation properties. This is to facilitate various manufacturing processes when the grain-oriented electrical steel sheet is processed into an iron core of a transformer or the like. For instance, when the phosphate coating is poor in heat resistance, slipperiness, and adhesion, the phosphate coating is detached during the stress relief annealing of iron core manufacturing. As a result, the insulation properties of the phosphate coating cannot be properly exhibited, of the steel sheets cannot be smoothly stacked resulting in deterioration of the operational efficiency.
Further, an important characteristic of the insulation coating of the grain-oriented electrical steel sheet is that it applies tension to the steel sheet. When the tension is applied to the steel sheet, the movement of magnetic domain wall is made to occur easily, thereby it is possible to improve the iron loss of the grain-oriented electrical steel sheet. Also, by applying the tension, it is possible to reduce the magnetostriction (one of the main causes of noise in the transformer).
In order to improve various characteristics of the grain-oriented electrical steel sheet as described above, specifically, techniques as disclosed in the following Patent Documents 1 to 9 have been researched and developed.
For instance, Patent Document 1 discloses a technique of applying an insulation coating treatment solution containing, as main components, an aluminum phosphate having a specific composition, a chromate, and colloidal silica onto a forsterite film formed on the sheet surface after final annealing, and baking the insulation coating treatment solution. According to the technique disclosed in Patent Document 1, it is possible to form an insulation coating having high tension on the sheet surface and to reduce the iron loss and magnetostriction of the grain-oriented electrical steel sheet.
Patent Document 2 discloses a method of applying a treatment solution containing ultrafine colloidal silica having a particle size of 8 µm or less, a primary phosphate, and a chromate at a specific ratio to a steel sheet, and then baking the treatment solution. According to the technique disclosed in Patent Document 2, it is possible to maintain high tension of the insulation coating and further improve lubricity of the coating.
Further, Patent Document 3 discloses a technique of forming a high tension insulation coating on the surface of a grain-oriented electrical steel sheet by attaching a specific amount of an insulation coating containing a phosphate, a chromate, and colloidal silica having a glass transition point of from 950°C to 1200°C as main components to the steel sheet.
According to the techniques disclosed in Patent Documents 1 to 3, it has been possible to form an insulation coating having remarkably excellent various characteristics and improved coating tension. However, in all the techniques disclosed in Patent Documents 1 to 3, the insulation coating contains the chromate which is a chromium compound. In recent years, with the growing focus on environmental problems, it is socially required to prohibit or restrict the use of compounds such as lead, chromium, and cadmium.
Therefore, a technique capable of forming a good insulation coating without containing the chromium compound has been studied. However, the insulation coating free of the chromium compound has had a problem that the tension being applied to the steel sheet is insufficient.
As a method for solving the above problem, for instance, Patent Document 4 discloses a method for treating an insulation coating of a grain-oriented electrical steel sheet by baking a treatment solution containing 20 parts by weight of colloidal silica in terms of SiO₂ content, 10 to 120 parts by weight of aluminum phosphate, 2 to 10 parts by weight of boric acid, and 4 to 40 parts by weight in total of one or two or more selected from sulfates of Mg, Al, Fe, Co, Ni, and Zn at 300°C or higher.
In addition, Patent Document 5 discloses a technique related to a coating agent for forming a coating, including a mixture of boric acid and alumina sol and an organic solvent compatible with water, and having an effect of applying tension on a grain-oriented electrical steel sheet.
In addition, Patent Document 6 discloses a technique of including one or more organic acid salts of Ca, Mn, Fe, Mg, Zn, Co, Ni, Cu, B, and Al in a surface treatment agent for a grain-oriented electrical steel sheet, containing a primary phosphate of Al, Mg, or Ca, and colloidal silica. In addition, Patent Document 6 exemplifies formate, acetate, oxalate, tartrate, lactate, citrate, succinate, and salicylate as the organic acid salt.
Further, Patent Document 7 discloses a technique of, in an insulation coating treatment agent for a grain-oriented electrical steel sheet containing a phosphate and colloidal silica, using, as a metal component in a phosphate, a combination of a divalent metal element, a trivalent metal element, and a metal element having a valence of tetravalent or more at a specific ratio.
Further, Patent Document 8 discloses a grain-oriented electrical steel sheet including: an insulation coating containing a first metal phosphate which is a metal phosphate of one or more metals selected from Al, Fe, Mg, Mn, Ni, and Zn, a second metal phosphate which is a metal phosphate of one or more metals selected from Co, Mo, V, W, and Zr, and colloidal silica; and a steel sheet.
Also, Patent Document 9 discloses an aqueous composition for coating grain-oriented electrical steel containing aluminum cations, manganese cations, dihydrogen phosphate, hydrogen phosphate and/or phosphate anions, colloidal silicon dioxide and optionally iron cations.

Citation List

Patent Documents

Patent Document 1: Japanese Unexamined Patent Application, First Publication No. S48-39338
Patent Document 2: Japanese Unexamined Patent Application, First Publication No. S61-41778
Patent Document 3: Japanese Unexamined Patent Application, First Publication No. H11-071683
Patent Document 4: Japanese Unexamined Patent Application, First Publication No. S54-143737
Patent Document 5: Japanese Unexamined Patent Application, First Publication No. H07-278828
Patent Document 6: Japanese Unexamined Patent Application, First Publication No. 2000-178760
Patent Document 7: Japanese Unexamined Patent Application, First Publication No. 2010-13692
Patent Document 8: PCT International Publication No. WO 2017/057513
Patent Document 9: Published Japanese Translation No. 2022-519691 of the PCT International Publication

SUMMARY OF INVENTION

Technical Problem

These proposals have improved various characteristics of insulation coating. However, the present inventors have found from studies that in the case of the insulation coating free of the chromium compound, the amount of phosphorus elution from the insulation coating greatly increases with long-term storage. The electrical steel sheet is placed on a ship in a state of a coil after manufacturing, and is transported under a high-temperature and high-humidity atmosphere for a long term in some cases. Therefore, when the amount of phosphorus elution greatly increases with long-term transportation, a trouble may occur such that stickiness between the coils increases or the coil cannot be uncoiled. Even by using any of the above techniques, the amount of phosphorus elution after long-term storage has not reached the same level as that of the conventional coating containing chromic acid, and there is room for improvement.
As described above, the insulation coating of the grain-oriented electrical steel sheet must have the electrical insulation properties and be able to apply the sufficient tension to the surface of the steel sheet. In addition, the insulation coating of the grain-oriented electrical steel sheet is also required to have good moisture absorption resistance even under high-temperature and high-humidity conditions. Further, the insulation coating of the grain-oriented electrical steel sheet is required not to increase the amount of phosphorus elution with long-term storage.
An aspect of the present invention has been made to solve the above problems. An object of an aspect of the present invention is to provide a grain-oriented electrical steel sheet in which the amount of phosphorus elution after long-term storage is small, on the premise that the chromate is not included and moisture absorption resistance and the like are equal to or higher than conventional grain-oriented electrical steel sheets.

Solution to Problem

An aspect of the present invention employs the following.

(1) A grain-oriented electrical steel sheet according to an aspect of the present invention includes: a base steel sheet; and an insulation coating, wherein
- the insulation coating is free of a chromium compound and contains a phosphate, and
- when the insulation coating is measured by a nuclear magnetic resonance under the conditions such that: a magnetic field of a proton resonance frequency is 500 MHz; a magic angle spinning rate is 55 kHz; a chemical shift of a ³¹P nucleus is referenced to 0.9 ppm using an ammonium dihydrogen phosphate (NH₄H₂PO₄); an observation offset is set between 0 and 30 ppm; a flip angle is 90°; a waiting time is 8 seconds; and a number of scans is 9000 times, and when an obtained ³¹P-NMR spectrum is subjected to a Gaussian fitting in a range from 16 to -90 ppm,
- a ratio of a peak area of a Q¹ structure to a total peak area is more than 3% and 18% or less, and
- the ratio of the Q¹ structure is smaller than a ratio of a peak area of a Q³ structure to the total peak area.
(2) In the grain-oriented electrical steel sheet according to (1), the base steel sheet may contain, as a chemical composition, in terms of mass%,
- 0.010% or less of C,
- 2.00 to 4.00% of Si,
- 0.05 to 1.00% of Mn,
- 0.010 to 0.065% of Al,
- 0.004% or less of N,
- 0.010% or less of S,
- 0.010% or less of Se,
- 0 to 0.30% of Cr,
- 0 to 0.40% of Cu,
- 0 to 0.50% of P,
- 0 to 1.00% of Ni,
- 0 to 0.30% of Sn,
- 0 to 0.30% of Sb,
- 0 to 0.0100% of B,
- 0 to 0.1% of Mo,
- 0 to 0.01% of Bi, and
- a balance consisting of Fe and impurities.

Advantageous Effects of Invention

According to the above-described aspect of the present invention, it is possible to stably obtain a grain-oriented electrical steel sheet in which the chromate is not included, the moisture absorption resistance and the like are excellent, and the amount of phosphorus elution is small even when being stored for a long term in a high-temperature and high-humidity atmosphere.

BRIEF DESCRIPTION OF DRAWINGS

[FIG. 1] A graph showing a relationship between a Na content in an insulation coating treatment solution and an amount of moisture absorption in a grain-oriented electrical steel sheet coated with an insulation coating.
[FIG. 2] A graph showing a relationship between a Na content in an insulation coating treatment solution and an amount of phosphorus elution from a grain-oriented electrical steel sheet coated with an insulation coating for a steel sheet before evaluation of moisture absorption resistance.
[FIG. 3] A graph showing a relationship between a Na content in an insulation coating treatment solution and an amount of phosphorus elution from a grain-oriented electrical steel sheet coated with an insulation coating for a steel sheet after evaluation of moisture absorption resistance.
[FIG. 4] A reference illustration showing bridging oxygen of phosphate, and showing four types of Qⁿ structures of Q⁰, Q¹, Q², and Q³.
[FIG. 5] A reference graph showing an instance in which Gaussian fitting is performed on a ³¹P-NMR spectrum of an insulation coating.
[FIG. 6] A graph showing a ratio of a Q¹ structure obtained by performing Gaussian fitting on a ³¹P-NMR spectrum of an insulation coating, and is a graph showing a relationship between a Na content in an insulation coating treatment solution and a ratio of a Q¹ structure in an insulation coating.
[FIG. 7] A graph showing five peak tops which are included in the range of chemical shifts from 16 to -90 ppm in a ³¹P-NMR spectrum of an insulation coating.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a preferable embodiment of the present invention is described in detail. However, the present invention is not limited only to the configuration which is disclosed in the embodiment, and various modifications are possible without departing from the aspect of the present invention. In addition, the limitation range as described below includes a lower limit and an upper limit thereof. However, the value expressed by "more than" or "less than" does not include in the limitation range. Unless otherwise noted, "%" of the amount of respective elements expresses "mass%".
Hereinafter, a result of a preliminary experiment for obtaining the grain-oriented electrical steel sheet according to the present embodiment will be described.

A final-annealed grain-oriented electrical steel sheet having a sheet thickness of 0.23 mm and manufactured by a known method was cut 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 to prepare a base steel sheet.

Next, 250 parts by mass of an aqueous solution containing 40 mass% of an aluminum primary phosphate in solid equivalent, 300 parts by mass of a solution containing 30 mass% of colloidal silica in solid equivalent, and 0 to 7 parts by mass of sodium hydroxide (in solid equivalent) were mixed to prepare 10 types of insulation coating treatment solutions adjusted so that the sodium (Na) content in the insulation coating treatment solution was in a range of 0.02 to 0.34 mol/kg as shown in Table 1. Since sodium-stabilized colloidal silica was applied, the Na content in the solution to which sodium hydroxide was not added was 0.02 mol/kg.

[Table 1]

Treatment Solution No.	Na [ mol/kg ]	Amount of Moisture Absorption [ g/m² ]
1	0.02	0.295
2	0.11	0.133
3	0.13	0.089
4	0.16	0.066
5	0.18	0.051
6	0.20	0.026
7	0.22	0.023
8	0.25	0.019
9	0.29	0.031
10	0.34	0.034
Reference Material (containing Cr)	0.02	0.03

Then, each of the insulation coating treatment solutions was applied to both surfaces of the base steel sheet prepared in advance by a roll coater such that the amount of coating after baking was 4.5 g/m² per one surface. Thereafter, baking was performed at a temperature of 850°C for 30 seconds.
In addition, as a reference material, an insulation coating treatment solution (Na₂O/SiO₂ = 0.25%) composed of 50 parts by mass of aluminum primary phosphate which did not include Na, 40 parts by mass of colloidal silica (sodium-stabilized), and 10 parts by mass of chromic anhydride was similarly applied to the base steel sheet and baked.
Moisture absorption resistance was evaluated using, as a test piece, a steel sheet obtained by applying an insulation coating treatment solution to a base steel sheet and performing baking. First, the test piece was placed in a thermo-hygrostat (temperature: 50°C, humidity: 90%) for one week, and the weight difference before and after being held at the constant temperature and constant humidity was quantified. Then, a value obtained by dividing the quantified weight difference by 0.036 m² which was the total area of both surfaces of the test piece was defined as an amount of moisture absorption (unit: g/m²). The moisture absorption resistance was evaluated by using this amount of moisture absorption as an index. When the amount of moisture absorption is 0.05 g/m² or less, it can be determined that the moisture absorption resistance is excellent.
In addition, a test of phosphorus elution before and after evaluation of moisture absorption resistance was also performed. In the test of phosphorus elution, three test pieces with 40 mm × 60 mm were immersed in distilled water and boiled at 100°C for 20 minutes to elute phosphorus from the surface of the coating, and the phosphorus was quantitatively analyzed. Quantitative analysis of phosphorus was performed as PO₄ (unit: mg/m²) in accordance with JIS K 0102: 2019 Testing methods for industrial wastewater 46.1.1. When the amount of phosphorus elution is 50 mg/m² or less, it can be determined that the amount of phosphorus elution is small.
FIG. 1 shows the organized result of the relationship between the Na content in the insulation coating treatment solution and the amount of moisture absorption of the grain-oriented electrical steel sheet coated with the insulation coating for the above evaluation results.
As shown in FIG. 1, in the steel sheet (reference material) on which a chromium-containing coating is formed, the amount of moisture absorption is 0.05 g/m² or less, and little moisture is absorbed. On the other hand, in the steel sheet (test material) on which a chromium-free coating is formed, the amount of moisture absorption is more than 0.2 g/m² in the region where the Na content is less than 0.10 mol/kg, indicating that sufficient moisture absorption resistance is not obtained.
In a region where the Na content is high, particularly in a region where the Na content is 0.10 mol/kg or more, the amount of moisture absorption is 0.15 g/m² or less. Further, in a region where the Na content is 0.20 mol/kg or more, the amount of moisture absorption is 0.05 g/m² or less, indicating that moisture absorption resistance equivalent to that of the steel sheet on which the chromium-containing coating is formed is obtained. On the other hand, it was confirmed that when the Na content was more than 0.30 mol/kg, dispersibility of the colloidal silica deteriorated, and unevenness occurred in external appearance after baking.
Next, FIG. 2 shows the organized result of the relationship between the Na content in the insulation coating treatment solution and the amount of phosphorus elution from the grain-oriented electrical steel sheet coated with the insulation coating for the test piece before evaluation of the moisture absorption resistance.
As shown in FIG. 2, even in the steel sheet on which the chromium-free coating is formed, the amount of phosphorus elution is small regardless of the Na content, similarly to the steel sheet on which the chromium-containing coating is formed. That is, there is no problem that the amount of phosphorus elution from the insulation coating increases before being held at the constant temperature and constant humidity.
Further, FIG. 3 shows the organized result of the relationship between the Na content in the insulation coating treatment solution and the amount of phosphorus elution from the grain-oriented electrical steel sheet coated with the insulation coating for the test piece after evaluation of the moisture absorption resistance.
As shown in FIG. 3, in the steel sheet on which the chromium-free coating was formed, the amount of phosphorus elution was 50 mg/m² or less in a region where the Na content was 0.20 mol/kg or more, similarly to the steel sheet on which the chromium-containing coating was formed. However, in a region where the Na content was less than 0.20 mol/kg, the amount of phosphorus elution was 50 mg/m² or more, which is very large, confirming that the insulation coating deteriorated by performing evaluation of the moisture absorption resistance.
From the above experimental results, the mechanism in which the Na content in the insulation coating treatment solution affects the amount of phosphorus elution after the constant temperature and humidity test in the chromium-free insulation coating is considered as follows.

It is considered that the elution of phosphorus from the insulation coating is caused by a hydrolysis reaction in which water molecules act on the P-O-P bond portion of the phosphate forming the insulation coating to break the bond. Therefore, it is important to use P-O-M (M is a metal element) in which a P (phosphorus)-O (oxygen)-P (phosphorus) bond is replaced with another bond.
Here, the structure of phosphate is commonly evaluated using a nuclear magnetic resonance (hereinafter, referred to as ³¹P-NMR). The structural unit of phosphate is a PO₄ tetrahedron in which four oxygen atoms are coordinated around a phosphorus atom, and oxygen atoms are shared at the apex with another PO₄ tetrahedron to form a three-dimensional structure. The oxygen atom connecting the tetrahedrons is called a bridging oxygen, and the notation of Qⁿ using the number n of bridging oxygen as an index is used. As shown in FIG. 4, it can be classified into four types of Qⁿ structures of Q⁰, Q¹, Q², and Q³.
As the number n of bridging oxygens decreases, the polarity around the phosphorus atom decreases, and the interaction with water molecules having high polarity is weakened, so that the bond is less likely to be broken. For instance, as the ratio of the Q⁰ structure in the insulation coating increases, phosphorus is less likely to be eluted from the insulation coating.
Meanwhile, as the number n of the bridging oxygens decreases, the number of the bridging oxygens connecting the PO₄ tetrahedrons decreases, and thus the forming ability of the insulation coating tends to decrease. Therefore, in the grain-oriented electrical steel sheet according to the present embodiment, in consideration of both the amount of phosphorus elution and the coating-forming ability, attention is particularly paid to the Q¹ structure among the four types of Qⁿ structures of Q⁰, Q¹, Q², and Q³.

For the steel sheet on which the chromium-free coating was formed, ³¹P-NMR spectra of various insulation coatings having different Na contents were measured before evaluation of the moisture absorption resistance, and then Gaussian fitting was performed on these spectra in a range from 16 to -90 ppm.
Here, when Gaussian fitting is performed, it is necessary to determine a peak height and a line width of a Gaussian function. In the present embodiment, six peak top positions (chemical shifts) of -49 ppm, -35 ppm, -30 ppm, -22 ppm, -8.8 ppm, and +5.9 ppm are fixed for the ³¹P-NMR spectrum of the insulation coating. Then, the full width at half maximum is fixed at 6.291 kHz for the peak of -49 ppm, and the full width at half maximum is fixed at 3.780 kHz for the peak of -35 ppm. In addition, the initial value of the full width at half maximum of the peak of -30 ppm is set to 2.000 kHz, and the initial values of the full widths at half maximum of the peaks of -22 ppm, -8.8 ppm, and +5.9 ppm are set to 3.000 kHz. Only the heights of these peaks are optimized, and then the obtained optimized values of the heights are used as initial values. Further, the height and the line width are used as variable parameters for -30 ppm, -22 ppm, -8.8 ppm, and +5.9 ppm, and the full width at half maximum is fixed with the above values and only the height is used as a variable parameter for -49 ppm and -35 ppm. Optimization is performed by the Levenberg-Marquardt method so as to most closely approximate the experimental spectrum. Note that optimization is performed until the R² value which indicates the quality of optimization reaches 0.9600 or more in the entire spectrum, and until the R² value reaches 0.9970 or more in a range from 16 to -90 ppm.
The peak tops of the function components newly separated in this experiment were +5.9 ppm, -8.8 ppm, -22 ppm, -30 ppm, -35 ppm, and -49 ppm. By comparing these peak tops with the spectral ranges of the bridging orders described in the literature values, the first three components of +5.9 ppm, -8.8 ppm, and -22 ppm were respectively determined as Q⁰, Q¹, and Q², and the three components after -30 ppm were determined as Q³ (reference: Turner, G.L., Smith, Kirkpatrick, RJ. & Oldfield, E. (1986a) J. Mag. Reason., vol. 70, p. 408).
FIG. 5 shows an instance in which Gaussian fitting was performed on the ³¹P-NMR spectrum of the insulation coating based on the above.
FIG. 6 shows the organized result of the relationship between the Na content in the insulation coating treatment solution and the ratio of the Q¹ structure in the insulation coating based on the result of performing Gaussian fitting on the ³¹P-NMR spectrum of the insulation coating. The ratio of the Q¹ structure in FIG. 6 indicates the ratio of the peak area of the Q¹ structure to the total peak area obtained by summing the peak areas of the normal distribution curves of the four types of Qⁿ structures Q⁰, Q¹, Q², and Q³. The sum of the peak areas of the above three components was used for the ratio of the peak area of the Q³ structure.
As shown in FIG. 6, when the Na content is less than 0.20 mol/kg, the ratio of the peak area of the Q¹ structure is 3% or less, whereas when the Na content is 0.20 mol/kg or more, the ratio of the peak area of the Q¹ structure is more than 3%.
As shown in the above experimental results, it is possible to control the amount of phosphorus elution to be small even in the case of storing in a high-temperature and high-humidity atmosphere for a long term, by controlling the ratio of the peak area of the Q¹ structure (area of the peak having a peak top at -8.8 ppm) to the total peak area (total area of six peaks having peak tops at +5.9 ppm, -8.8 ppm, -22 ppm, -30 ppm, -35 ppm, and -49 ppm) to more than 3% when a ³¹P-NMR spectrum of the insulation coating free of the chromium compound is subjected to Gaussian fitting in a range from 16 to -90 ppm. In addition, the problem that the forming ability of the insulation coating deteriorates does not occur.
The ratio of the peak area of the Q¹ structure is preferably more than 4%, and more preferably more than 8%. When the ratio of the peak area of the Q¹ structure is more than 10%, it is preferable because the coating-forming ability is particularly excellent. On the other hand, under the condition that the ratio of the peak area of the Q¹ structure was more than 18%, there was unevenness in the external appearance of the insulation coating. The ratio of the peak area of the Q¹ structure is preferably 16% or less.

In the grain-oriented electrical steel sheet according to the present embodiment, the ratio of the peak area of the Q¹ structure is smaller than the ratio of the peak area of the Q³ structure. The above-described effect can be preferably obtained by controlling the ratio of the peak area of the Q¹ structure to more than 3% and 18% or less, but in order to maintain the form as an insulation coating, the ratio of the peak area of the Q¹ structure is smaller than the ratio of the peak area of the Q³ structure.
Here, a method for obtaining the ratio of the peak area from the ³¹P-NMR spectrum of the insulation coating of the grain-oriented electrical steel sheet according to the present embodiment will be described.
Measurement conditions of ³¹P-NMR are described in some non-patent documents (for instance, Journal of Non-Crystalline Solid, 1998, vol. 223, p. 32 to 42.). However, it is known that the measurement conditions of ³¹P-NMR are generally different for each material. In the present embodiment, measurement was performed by INOVA500 manufactured by Agilent Technologies, Inc. under the conditions such that: the magnetic field of the proton resonance frequency is 500 MHz (for instance, the measurement magnetic field is 11.74T to 11.75T); the measurement temperature is room temperature; the magic angle spinning (MAS) rate is 55 kHz; the measurement method is ³¹P Single Pulse Excitation (flip angle 90°); the measurement waiting time is 8 s; the number of scans is 9000 times; the standard sample (chemical shift external standard) is ammonium dihydrogen phosphate at 0.9 ppm; and the observation offset is set between 0 and 30 ppm. The base metal of the grain-oriented electrical steel sheet was dissolved in a 10% bromine methanol solution until disappearance of the base metal was confirmed. Then, the resultant was filtered to collect the residue on a filter, and the residue was washed with methanol and subjected to NMR measurement for the insulation coating.
As an instance, FIG. 7 shows peaks which are included in the range of chemical shifts from 16 to -90 ppm in a ³¹P-NMR spectrum of an insulation coating. In FIG. 7, for instance, five clear peaks are confirmed in the ³¹P-NMR spectrum. That is, the five peaks are peaks having peak tops located at +5.9 ppm, -8.8 ppm, -22 ppm, -30 ppm, and - 35 ppm in order from the left side of FIG. 7. Although a peak having a peak top at -49 ppm does not clearly appear in FIG. 7, this peak of -49 ppm may be clearly confirmed depending on the type of the insulation coating. The peak corresponding to the Q¹ structure is a peak having a peak top at -8.8 ppm in FIG. 7. The peaks corresponding to the Q³ structure are peaks having peak tops at -30 ppm and -35 ppm in FIG. 7.
Gaussian fitting is performed on the ³¹P-NMR spectrum by the above-described method to derive a peak area defined as an integral value of each peak. In FIG. 7, for instance, the total peak area of the five peaks is the total peak area. In FIG. 7, the area of the peak having a peak top at -8.8 ppm is the peak area of the Q¹ structure. Similarly, in FIG. 7, the sum of the areas of the peaks having peak tops at -30 ppm and -35 ppm is the peak area of the Q³ structure. Based on these, the ratio of the "peak area of the Qⁿ structure" to the "total peak area" is determined.
The insulation coating of the grain-oriented electrical steel sheet according to the present embodiment is free of the chromium compound. For instance, in the present embodiment, when the concentration of Cr contained in the insulation coating is less than 1 atom%, it is determined that the insulation coating is free of the chromium compound. The Cr concentration is preferably 0.8 atom% or less, and more preferably 0.5 atom% or less.
In the present embodiment, the chemical composition of the insulation coating is not particularly limited, but may satisfy, for instance, as main elements to be contained, P: 5 to 30 atom%, Si: 5 to 30 atom%, O: 30 to 80 atom%, Al: 0.1 to 10 atom%, Cr: less than 1 atom%, Fe: less than 25 atom%, Mg: 0 to 10 atom%, Mn: 0 to 10 atom%, Ni: 0 to 10 atom%, Zn: 0 to 10 atom%, V: 0 to 10 atom%, W: 0 to 10 atom%, Zr: 0 to 10 atom%, Co: 0 to 10 atom%, and Mo: 0 to 10 atom%.
The insulation coating included in the grain-oriented electrical steel sheet according to the present embodiment indicates an insulation coating without insufficient baking or crack propagation due to poor baking conditions of the insulation coating. When the insulation coating has insufficient baking, crack propagation, or the like due to poor baking conditions, it is not possible to satisfy electrical insulation properties, tension application, corrosion resistance, heat resistance, slipperiness, adhesion, and the like which are required for the insulation coating.
The concentration of Cr and other elements contained in the insulation coating can be determined by, for instance, analyzing the composition of the cross section by Scanning Electron Microscope-Energy Dispersive X-ray Spectroscopy (SEM-EDS) or Transmission Electron Microscope-Energy Dispersive X-ray Spectroscopy (TEM-EDS).
Next, the amount of insulation coating of the grain-oriented electrical steel sheet according to the present embodiment will be described.
In the grain-oriented electrical steel sheet according to the present embodiment, the amount of insulation coating is not particularly limited, but is appropriately 2.0 to 7.0 g/m² per one surface. When the amount of insulation coating is less than 2.0 g/m², it is difficult to apply high tension to the grain-oriented electrical steel sheet, and the insulation properties, corrosion resistance and the like of the grain-oriented electrical steel sheet may deteriorate, which is not preferable. On the other hand, when the amount of insulation coating is more than 7.0 g/m², there is a possibility that the space factor of the grain-oriented electrical steel sheet decreases to deteriorate the transformer characteristics, which is not preferable. The amount of insulation coating is more preferably 3.0 g/m² or more, and still more preferably 4.0 g/m² or more. The amount of insulation coating is more preferably 6.0 g/m² or less, and still more preferably 5.0 g/m² or less.

<Grain-Oriented Electrical Steel Sheet>

Next, the base steel sheet of the grain-oriented electrical steel sheet according to the present embodiment will be described. The base steel sheet of the grain-oriented electrical steel sheet is not particularly limited, and may contain, as a chemical composition, in terms of mass%, 0.010% or less of C, 2.00 to 4.00% of Si, 0.05 to 1.00% of Mn, 0.010 to 0.065% of Al, 0.004% or less of N, and 0.010% or less of S, and a balance consisting of Fe and impurities. Hereinafter, % relating to the chemical composition indicates mass% with respect to the total mass of the base steel sheet.

C: 0.010% or less

C (carbon) is an element effective for controlling the primary recrystallization structure, but is an element to be removed by decarburization annealing before final annealing because it adversely affects magnetic characteristics. When the C concentration exceeds 0.010% in the final product, C precipitates during aging, deteriorating hysteresis loss. Thus, the C concentration is set to 0.010% or less. The C concentration is preferably 0.007% or less, and more preferably 0.005% or less. The lower limit of the C concentration includes 0%, but the C concentration may be more than 0%. However, when the C concentration is reduced to less than 0.0001%, the manufacturing cost is greatly increased. Thus, 0.0001% is a substantial lower limit on the practical steel sheet. In the grain-oriented electrical steel sheet, the C concentration is usually reduced to about 0.001 % or less by decarburization annealing.

Si: 2.00 to 4.00%

Si (silicon) is an element that increases the electric resistance of the steel sheet to improve iron loss characteristics. When the Si concentration is less than 2.00%, γ transformation of the steel structure occurs during the final annealing, and the crystal orientation of the steel sheet is impaired. Thus, the Si concentration is set to 2.00% or more. The Si concentration is preferably 2.50% or more, and more preferably 3.00% or more. On the other hand, when the Si concentration exceeds 4.00%, the deformability of the grain-oriented electrical steel sheet deteriorates, and cracks occur during rolling. Thus, the Si concentration is set to 4.00% or less. The Si concentration is preferably 3.50% or less.

Mn: 0.05 to 1.00%

Mn (manganese) is an element that prevents cracking during hot rolling, and bonds to S and/or Se to form MnS or MnSe that functions as an inhibitor. When the Mn concentration is less than 0.05%, the addition effect of Mn is not sufficiently exhibited. Thus, 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, when the Mn concentration exceeds 1.00%, precipitation and dispersion of MnS and MnSe become non-uniform, and a desired secondary recrystallization structure cannot be obtained, leading to a decrease in magnetic flux density. Thus, 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.

Al: 0.010 to 0.065%

Al (aluminum) is an element that bonds to N to form (Al, Si)N or AlN that functions as an inhibitor. When the Al concentration is less than 0.010%, the addition effect of Al is not sufficiently exhibited, and secondary recrystallization does not sufficiently proceed. Thus, 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, when the Al concentration exceeds 0.065%, precipitation and dispersion of the inhibitor become non-uniform, and a desired secondary recrystallization structure cannot be obtained, leading to a decrease in magnetic flux density. Thus, 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.

N: 0.004% or less

N (nitrogen) is an element that bonds to Al to form AlN or the like that functions as an inhibitor. However, when the N concentration exceeds 0.004% in the final product, N in the steel sheet precipitates as AlN, deteriorating hysteresis loss. Thus, the N concentration is set to 0.004% or less. The lower limit of the N concentration includes 0%, but when the N concentration is reduced to less than 0.0001%, the manufacturing cost is greatly increased. Thus, 0.0001% is a substantial lower limit on a practical steel sheet. In the grain-oriented electrical steel sheet, the N concentration is usually reduced to about 0.001% or less by final annealing.

S: 0.010% or less

S (sulfur) is an element that bonds to Mn to form MnS that functions as an inhibitor. However, when the S concentration exceeds 0.010% as a final product, S in the steel sheet precipitates as MnS, deteriorating hysteresis loss. Thus, the S concentration is set to 0.010% or less. The lower limit of the S concentration includes 0%, but when the S concentration is reduced to less than 0.0001%, the manufacturing cost greatly increases. Thus, 0.0001% is a substantial lower limit on the practical steel sheet. In the grain-oriented electrical steel sheet, the S concentration is usually reduced to about 0.005% or less by final annealing.
In the present embodiment, the base steel sheet may contain impurities. The impurities correspond to elements which are contaminated during industrial production of steel from ores and scrap that are used as a raw material of steel, or from environment of a production process.
In the present embodiment, the base steel sheet may contain an optional element in addition to the above-described elements and impurities. For instance, as substitution for a part of Fe which is the balance, the base steel sheet may contain at least one of Se, Cr, Cu, P, Ni, Sn, Sb, B, Mo, or Bi as an optional element. The optional elements may be included as necessary. Thus, a lower limit of the respective optional elements does not need to be limited, and the lower limit may be 0%. Moreover, even if the optional elements may be included as impurities, the above mentioned effects are not affected.
For instance, in the present embodiment, one or two or more of 0.010% or less of Se, 0.30% or less of Cr, 0.40% or less of Cu, 0.50% or less of P, 1.00% or less of Ni, 0.30% or less of Sn, 0.30% or less of Sb, 0.0100% or less of B, 0.1% or less of Mo, and 0.01% or less of Bi may be added as an optional additive element to the base steel sheet, for the purpose of not inhibiting the magnetic characteristics of the base steel sheet and improving other characteristics.

Se: 0 to 0.010%

Se (selenium) is an element that bonds to Mn to form MnSe that functions as an inhibitor. However, when the Se concentration exceeds 0.010% as a final product, Se in the steel sheet precipitates as MnSe, deteriorating hysteresis loss. Thus, the Se concentration is set to 0.010% or less. The lower limit of the Se concentration may be 0% or may be 0.0001%. In the grain-oriented electrical steel sheet, the Se concentration is usually reduced to about 0.005% or less by final annealing.

Cr: 0 to 0.30%

Cr (chromium) is an element that improves the oxide layer of decarburization annealing and thus is effective for forming a glass film. Therefore, Cr may be added to the base steel sheet in a range of 0.30% or less. When the Cr concentration exceeds 0.30%, the decarburization properties are significantly inhibited. Thus, the upper limit of the Cr concentration is preferably 0.30%.

Cu: 0 to 0.40%

Cu (copper) is an element effective for increasing the specific electrical resistance of the base steel sheet to reduce the iron loss. When the Cu concentration exceeds 0.40%, the iron loss reduction effect is saturated, and a surface defect called "copper scab" is caused during hot rolling. Thus, the upper limit of the Cu concentration is preferably 0.40%.

P: 0 to 0.50%

P (phosphorus) is an element effective for increasing the specific electrical resistance of the base steel sheet to reduce the iron loss. When the P concentration exceeds 0.50%, there is a problem in rolling performance. Thus, the upper limit of the P concentration is preferably 0.50%.

Ni: 0 to 1.00%

Ni (nickel) is an element effective for increasing the specific electrical resistance of the base steel sheet to reduce the iron loss. Ni is also an element effective for controlling the steel structure of the hot-rolled steel sheet to improve magnetic characteristics. However, when the Ni concentration exceeds 1.00%, secondary recrystallization becomes unstable. Thus, the upper limit of the Ni concentration is preferably 1.00%.

Sn: 0 to 0.30%

Sb: 0 to 0.30%

Sn (tin) and Sb (antimony) are well-known elements segregating at grain boundaries. In the present embodiment, since the base steel sheet contains Al, Al may be oxidized by the moisture released from the annealing separator depending on the final annealing conditions, and the inhibitor strength may fluctuate at the coil position. As a result, the magnetic characteristics may fluctuate at the coil position. As one of the countermeasures, there is a method of preventing the oxidation of Al by adding these elements segregating at grain boundaries, and for this purpose, Sn and Sb may be added to the base steel sheet at a concentration of 0.30% or less, respectively. On the other hand, when the concentration of these elements exceeds 0.30%, Si is less likely to be oxidized during the decarburization annealing, the formation of the glass film becomes insufficient, and the decarburization annealing properties are significantly impaired. Thus, the upper limit of the concentration of these elements is preferably 0.30%.

B: 0 to 0.0100%

B (boron) is an element that bonds to N in the base steel sheet, and complexly precipitates with MnS to form BN that functions as an inhibitor. The lower limit of the B concentration is not particularly limited, and may be 0% as described above. However, in order to sufficiently exhibit the addition effect of B, the lower limit of the B concentration is preferably 0.0005%. The B concentration is preferably 0.001% or more, and more preferably 0.0015% or more. On the other hand, when the B concentration exceeds 0.0100%, precipitation and dispersion of BN become non-uniform, and a desired secondary recrystallization structure cannot be obtained, leading to a decrease in magnetic flux density. Thus, the B concentration is preferably 0.0100% or less. The B concentration is preferably 0.0080% or less, more preferably 0.0060% or less, and more preferably 0.0040% or less.

Mo: 0 to 0.1%

Mo (molybdenum) is an element effective for improving the surface properties during hot rolling. However, when the Mo concentration exceeds 0.1%, the Mo addition effect is saturated. Thus, the upper limit of the Mo concentration is preferably 0.1%.

Bi: 0 to 0.01%

Bi (bismuth) has an effect of stabilizing a precipitate such as sulfide to enhance the function as an inhibitor. However, when the Bi concentration exceeds 0.01%, Bi adversely affects the formation of the glass film. Thus, the upper limit of the Bi concentration is preferably 0.01%.
The above-described chemical composition may be measured by a general analysis method for steel. For instance, it is sufficient if the chemical composition is measured using Inductively Coupled Plasma-Atomic Emission Spectrometer (ICP-AES). Al may be measured in accordance with JIS G1257-10-1:2013 as total aluminum. In addition, C and S may be measured by the infrared absorption method after combustion, N may be measured by the thermal conductometric method after fusion in a current of inert gas, and O may be measured by, as necessary, the non-dispersive infrared absorption method after fusion in a current of inert gas.
Herein, the chemical composition is a component of the base steel sheet. When the grain-oriented electrical steel sheet, which is a measurement sample, includes an insulation coating or the like on the surface, the chemical composition is measured after removing the coating or the like by the method described below.
For instance, as a method for removing the insulation coating, the grain-oriented electrical steel sheet with the coating may be immersed in hot alkaline solution. Specifically, it is possible to remove the insulation coating from the grain-oriented electrical steel sheet by immersing the steel sheet in sodium hydroxide aqueous solution which includes 30 to 50 mass% of NaOH and 50 to 70 mass% of H₂O at 80 to 90°C for 5 to 10 minutes, washing it with water, and then, drying it. Moreover, the immersing time in sodium hydroxide aqueous solution may be adjusted depending on the thickness of the insulation coating.

Next, a method for manufacturing the grain-oriented electrical steel sheet according to the present embodiment will be described. The method for manufacturing the grain-oriented electrical steel sheet according to the present embodiment is not limited to the following method. The following manufacturing method is an instance for manufacturing the grain-oriented electrical steel sheet according to the present embodiment.
Molten steel having a predetermined chemical composition is cast by an ordinary 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 magnetic characteristics and mechanical characteristics required for the grain-oriented electrical steel sheet can be obtained, but an instance of the chemical composition of the silicon steel slab is as follows. For instance, the silicon steel slab contains, as a chemical composition, in terms of mass%, 0.085% or less of C, 2.00 to 4.00% of Si, 0.05 to 1.00% of Mn, 0.010 to 0.065% of Al, 0.004 to 0.012% of N, 0.010% or less of S, and 0.0100% or less of B.

C: 0.085% or less

C (carbon) is an element effective for controlling the primary recrystallization structure, but is an element to be removed by decarburization annealing before final annealing because it adversely affects magnetic characteristics. When the C concentration exceeds 0.085%, the decarburization annealing time becomes long, and the productivity deteriorates. Thus, the C concentration is set to 0.085% or less. The C concentration is preferably 0.070% or less, and more preferably 0.050% or less. The lower limit of the C concentration is not particularly limited, and may be 0% or more than 0%. Considering productivity in industrial production and magnetic characteristics of products, the lower limit of the substantial C concentration is 0.0001%. In the grain-oriented electrical steel sheet, the C concentration is usually reduced to about 0.001% or less by decarburization annealing.

Si: 2.00 to 4.00%

Si (silicon) is an element that increases the electric resistance of the steel sheet to improve iron loss characteristics. When the Si concentration is less than 2.00%, γ transformation occurs during the final annealing, and the crystal orientation of the steel sheet is impaired. Thus, the Si concentration is set to 2.00% or more. The Si concentration is preferably 2.50% or more, and more preferably 3.00% or more. On the other hand, when the Si concentration exceeds 4.00%, deformability deteriorates, and cracking occurs during rolling. Thus, the Si concentration is set to 4.00% or less. The Si concentration is preferably 3.50% or less.

Mn: 0.05 to 1.00%

Mn (manganese) is an element that prevents cracking during hot rolling, and bonds to S and/or Se to form MnS or MnSe that functions as an inhibitor. When the Mn concentration is less than 0.05%, the addition effect is not sufficiently exhibited. Thus, 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, when the Mn concentration exceeds 1.00%, precipitation and dispersion of MnS and MnSe become non-uniform, and a desired secondary recrystallization structure cannot be obtained, leading to a decrease in magnetic flux density. Thus, the Mn concentration is set to 1.00% or less. The Mn concentration is preferably 0.80% or less, and more preferably 0.06% or less.

Al: 0.010 to 0.065%

Al (aluminum) is an element that bonds to N to form (Al, Si)N or AlN that functions as an inhibitor. When the Al concentration is less than 0.010%, the addition effect is not sufficiently exhibited, and secondary recrystallization does not sufficiently proceed. Thus, 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, when the Al concentration exceeds 0.065%, precipitation and dispersion of (Al, Si)N and the like become non-uniform, and a desired secondary recrystallization structure cannot be obtained, leading to a decrease in magnetic flux density. Thus, 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.

N: 0.004 to 0.012%

N (nitrogen) is an element that bonds to Al to form AlN or the like that functions as an inhibitor, but is also an element that forms blisters (pores) in the steel sheet during cold rolling. When the N concentration is less than 0.004%, the formation of AlN becomes insufficient. Thus, the N concentration is set to 0.004% or more. The N concentration is preferably 0.006% or more, and more preferably 0.007% or more. On the other hand, when the N concentration exceeds 0.012%, blisters (pores) may be formed in the steel sheet during cold rolling. Thus, the N concentration is set to 0.012% or less. The N concentration is preferably 0.010% or less, and more preferably 0.009% or less.

S: 0.010% or less

S (sulfur) is an element that bonds to Mn to form MnS that functions as an inhibitor. When the S concentration exceeds 0.010%, precipitation and dispersion of MnS become non-uniform after purification, and a desired secondary recrystallization structure cannot be obtained. As a result, the magnetic flux density decreases to deteriorate hysteresis loss, and MnS remains after purification to deteriorate hysteresis loss. The lower limit is not particularly provided, but the S concentration may be 0%, and is preferably 0.003% or more. The S concentration is more preferably 0.007% or more.

B: 0.0100% or less

B (boron) is an element that bonds to N and is complexly precipitated with MnS to form BN that functions as an inhibitor. When the B concentration exceeds 0.0100%, precipitation and dispersion of BN become non-uniform, and a required secondary recrystallization structure cannot be obtained, leading to a decrease in magnetic flux density. Thus, the B concentration is set to 0.0100% or less. The B concentration is preferably 0.0060% or less, and more preferably 0.0040% or less. On the other hand, the lower limit of the B concentration is not particularly limited, and may be 0%.
In the present embodiment, the silicon steel slab may contain impurities. The impurities correspond to elements which are contaminated during industrial production of steel from ores and scrap that are used as a raw material of steel, or from environment of a production process.
In the present embodiment, the silicon steel slab may contain an optional element in addition to the above-described elements and impurities. For instance, as substitution for a part of Fe which is the balance, the base steel sheet may contain at least one of Se, Cr, Cu, P, Ni, Sn, Sb, Mo, or Bi as an optional element. The optional elements may be included as necessary. Thus, a lower limit of the respective optional elements does not need to be limited, and the lower limit may be 0%. Moreover, even if the optional elements may be included as impurities, the above mentioned effects are not affected.
For instance, in the present embodiment, the silicon steel slab may contain one or two or more of 0.010% or less of Se, 0.30% or less of Cr, 0.40% or less of Cu, 0.50% or less of P, 1.00% or less of Ni, 0.30% or less of Sn, 0.30% or less of Sb, 0.1% or less of Mo, and 0.01% or less of Bi within a range in which the magnetic characteristics of the grain-oriented electrical steel sheet are not inhibited and other characteristics can be enhanced.
In the hot rolling process, a slab having the above-described chemical composition is subjected to hot rolling to obtain a hot-rolled steel sheet. The hot rolling conditions are not particularly limited, and general conditions can be used. The hot-rolled steel sheet obtained by the hot rolling process is coiled into a coil shape.
Before the slab is subjected to hot rolling, the slab may be heated to a temperature higher than 1300°C in order to sufficiently solutionize the inhibitor components of MnS and AlN. In addition, from the viewpoint of productivity and manufacturing cost, the slab may be heated to about 1250°C on the premise that the inhibitor is enhanced by the nitriding treatment in the subsequent process.
In the hot-rolled steel sheet annealing process, a coil-shaped hot-rolled steel sheet is uncoiled into a band-shaped hot-rolled steel sheet, and then the band-shaped hot-rolled steel sheet is subjected to hot-rolled steel sheet annealing to obtain an annealed hot-rolled steel sheet. The hot-rolled steel sheet annealing conditions are not particularly limited, and general conditions can be used.
In the cold rolling process, the annealed hot-rolled steel sheet is subjected to cold rolling once or twice or more to obtain a cold-rolled steel sheet having a final sheet thickness. In this cold rolling process, the annealed hot-rolled steel sheet may be subjected to two or more times of cold rolling including intermediate annealing to obtain a cold-rolled steel sheet. In the annealing performed before the finish (final) cold rolling, the crystal structure is homogenized. The cold rolling conditions are not particularly limited, and general conditions can be used.
In the decarburization annealing process, the cold-rolled steel sheet is subjected to decarburization annealing to obtain a decarburization-annealed steel sheet. In this decarburization annealing process, the C content in the cold-rolled steel sheet is reduced to an amount such that deterioration due to magnetic aging as a manufactured steel sheet does not occur by heat-treating the cold-rolled steel sheet in wet hydrogen, and primary recrystallization is caused in the cold-rolled steel sheet to prepare the next secondary recrystallization. The decarburization annealing conditions are not particularly limited, and general conditions can be used. An oxide film of SiO₂ is formed on the surface of the decarburization-annealed steel sheet obtained by the decarburization annealing process. When a cold-rolled steel sheet is manufactured from a slab heated to about 1250°C, after decarburization annealing, the decarburization-annealed steel sheet is annealed in an ammonia atmosphere to form AlN functioning as an inhibitor in the decarburization-annealed steel sheet.
In the method for manufacturing the grain-oriented electrical steel sheet according to the present embodiment, the steel sheet on which the insulation coating is formed may be a grain-oriented electrical steel sheet having a general forsterite film or a grain-oriented electrical steel sheet having no forsterite film.
In the case of a grain-oriented electrical steel sheet having a general forsterite film, an annealing separator containing MgO as a main component is applied in an annealing separator applying process, which is a process subsequent to the decarburization annealing process, for the purpose of preventing baking in the final annealing process. The amount of the annealing separator applied is 6.0 to 14.0 g/m² per one surface of the decarburization-annealed steel sheet.
In the case of a grain-oriented electrical steel sheet having no forsterite film, an annealing separator containing alumina (Al₂O₃) as a main component is applied in the annealing separator applying process. The decarburization-annealed steel sheet coated with the annealing separator is coiled into a coil shape after the annealing separator is dried.
In the final annealing process, the coil-shaped decarburization-annealed steel sheet coated with the annealing separator is subjected to final annealing to obtain a base steel sheet of a final product (grain-oriented electrical steel sheet). In this final annealing process, secondary recrystallization is caused in the decarburization-annealed steel sheet by performing final annealing at a temperature of 1100°C or higher. In order to reduce the hysteresis loss of the final product, the decarburization-annealed steel sheet after completion of the secondary recrystallization may be subjected to purification annealing so that the precipitate used as the inhibitor is detoxified.
An insulation coating is formed on the surface of the steel sheet in which secondary recrystallization has been completed. The method for forming an insulation coating includes an application process of applying an insulation coating treatment solution to a surface of a steel sheet, and a baking process of baking the insulation coating treatment solution. An insulation coating is formed by baking.
After the final annealing, the excess annealing separator is washed with water and removed, and then a pickling treatment with a sulfuric acid bath or the like and a water washing treatment are performed. As a result, the surface of the steel sheet is cleaned and activated, and then the insulation coating treatment solution is applied to the steel sheet in the application process. The method for applying the insulation coating treatment solution to the steel sheet is not limited, but the insulation coating treatment solution is usually applied by a roll coater. The grain-oriented electrical steel sheet to which the insulation coating treatment solution has been applied is subjected to a baking process under the conditions described later, thereby forming an insulation coating on the surface.
In order to control the ratio of the peak area of the Q¹ structure to the total peak area to more than 3% and 18% or less when Gaussian fitting is performed on the ³¹P-NMR spectrum in a range from 16 to -90 ppm, it is necessary to change the P-O-P bond portion of the phosphate contained in the insulation coating treatment solution to P-O-M (M is a metal element). For this purpose, the metal component contained in the insulation coating treatment solution is preferably an alkali metal element. The metal component is preferably lithium, sodium, and potassium. The metal component is more preferably sodium and potassium. These alkali metal elements may be contained in an amount of 0.20 to 0.30 mol/kg with respect to the insulation coating treatment solution.
The reason why the application of an alkali metal element such as sodium or potassium is effective in order to set the ratio of the peak area of the Q¹ structure to the total peak area to more than 3% and 18% or less is not clear at present. However, these alkali metals are known as modifying elements that significantly change the properties of glass in glasses such as phosphates, and have a small atomic radius. Therefore, it is considered that these alkali metals were easily incorporated into a phosphate, and as a result, had a great influence on the phosphate. In addition, as described above, the reason why the properties of glass significantly changed with the increase in the sodium content in the insulation coating is considered to be that the ratio of the change from a P (phosphorus)-O (oxygen)-P (phosphorus) bond to a P-O-M (M: here, Na is assumed) bond increased with the increase in the sodium content.
In addition, in order to set the ratio of the peak area of the Q¹ structure to the total peak area to more than 3% and 18% or less, the pH of the insulation coating treatment solution is preferably 1.7 or more and 2.1 or less. This pH value is larger than the pH of the conventional insulation coating treatment solution. The conventional insulation coating treatment solution usually has a pH of less than 1.7. The present inventors have found that when the pH of the insulation coating treatment solution is 1.7 or more and 2.1 or less, it is easy to preferably control the ratio of the peak area of the Q¹ structure to the total peak area to more than 3% and 18% or less. The reason for this is not clear at present. However, for instance, it is well known that, in the hydrolysis of a polyphosphate ion, a hydrogen ion acts as a catalyst on the cleavage of a P-O-P bond. Similarly, it is also known that a hydrogen ion acts as a catalyst on the cleavage of a P-OP bond in pyrophosphate. In the present embodiment, the pH of the insulation coating treatment solution becomes larger than that of the conventional insulation coating treatment solution, and the presence of hydrogen ions becomes smaller than that of the conventional insulation coating treatment solution, which is considered to affect the ratio of the Q¹ structure in the insulation coating. The pH of the insulation coating treatment solution is preferably 1.8 or more, and more preferably 1.9 or more.
In the baking process, the grain-oriented electrical steel sheet coated with the insulation coating treatment solution is heated to a baking temperature, held at the baking temperature, and then cooled.
The baking temperature (°C) represents an achieving sheet temperature (maximum sheet temperature) in the baking process, and needs to be 800°C or higher and 1000°C or lower. When the baking temperature is lower than 800°C, the reaction for formation of the coating does not sufficiently proceed in the insulation coating. As a result, not only the external appearance of the coating becomes poor, but also a sufficient tension cannot be applied to the steel sheet in some cases. On the other hand, when the baking temperature is higher than 1000°C, cracks may be initiated in the insulation coating, which may deteriorate the coating tension or the insulation properties and the like, and defects may be formed in the steel sheet. The baking temperature is more preferably 850°C or higher and 950°C or lower.
The holding time (sec) indicates a holding time at baking temperature. The holding time is required to be 10 seconds or more. When the holding time is less than 10 seconds, baking of the insulation coating is insufficient, and moisture absorption resistance may deteriorate (amount of moisture absorption may increase). The holding time is desirably 20 seconds or more. On the other hand, the holding time is 60 seconds or less. When the holding time is more than 60 seconds, not only moisture absorption resistance hardly changes, but also excessive crystallization of the insulation coating may cause cracks, leading to deterioration of coating tension. The holding time is more preferably 45 seconds or less at which various characteristics of the coating that are necessary and sufficient are obtained.
In addition, in order to set the ratio of the peak area of the Q¹ structure to the total peak area to more than 3% and 18% or less, the heating rate when heating to the baking temperature in the baking process is preferably 30°C/sec or more and 100°C/sec or less. The reason for this is not clear at present. However, when the heating rate to the baking temperature is too fast, the surface of the insulation coating is solidified earlier than the inside of the insulation coating during heating, and as a result, moisture is confined in the insulation coating. The confined moisture tends to cause a porous coating defect in the insulation coating, which is considered to affect the ratio of the Q¹ structure in the insulation coating. The heating rate to the baking temperature is preferably 40°C/sec or more, and more preferably 60°C/sec or more. The heating rate to the baking temperature is preferably 80°C/sec or less, and more preferably 70°C/sec or less.
The heating rate to the baking temperature indicates a value obtained by dividing a temperature range from the baking start temperature (room temperature) to the baking temperature (temperature of 800°C or higher and 1000°C or lower) by a time required for raising the temperature.
The type of the base steel sheet subjected to the insulation coating treatment is not particularly limited. This is because the main feature of the grain-oriented electrical steel sheet according to the present embodiment lies in the configuration of the insulation coating, and the effects of the insulation coating of the grain-oriented electrical steel sheet according to the present embodiment, that is, the effects that a large tension can be applied to the surface of the steel sheet, the adhesion and corrosion resistance are good, and the long-term stability is excellent even though the insulation coating is free of chromate are exhibited regardless of the type of base steel sheet.
Preferably, for instance, the above-described insulation coating treatment may be applied to a grain-oriented electrical steel sheet manufactured using the technique disclosed in Patent Document: Japanese Unexamined Patent Application, First Publication No. H07-268567 . At this time, the effect of further reducing the iron loss can be obtained. Specifically, the effect of further reducing the iron loss can be obtained by performing the above-described insulation coating treatment on a grain-oriented electrical steel sheet containing in terms of mass%, C in an amount of 0.005% or less and Si in an amount of 2.5 to 7.0% at least, other alloying elements (for instance, 0 to 1.0% of Mn, 0 to 0.03% of Al, 0.01% or less of N, 0.01% or less of P, and 0.01% or less of S) which can be optionally contained within a range in which characteristics are not impaired, and the balance including Fe and impurities, wherein the average grain size is 1 to 10 mm, and the angle formed by the (110)[001] crystal orientation and the rolling direction is 8° or less on average.

Next, an insulation coating treatment solution used for the grain-oriented electrical steel sheet according to the present embodiment (hereinafter, also simply referred to as "insulation coating treatment solution") will be described.
The insulation coating treatment solution contains a metal phosphate of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W, and Zr, and colloidal silica, and is free of a chromate. The metal phosphate is preferably a phosphate of one or more selected from Al, Mg, Ni, V, and W. This is because when these phosphates are selected, a flat and uniform external appearance can be obtained under a wide range of baking conditions.
The insulation coating treatment solution preferably contains an alkali metal element. The alkali metal contained in the insulation coating treatment solution is preferably lithium, sodium, and potassium, and more preferably sodium and potassium. The amount of alkali metal contained in the insulation coating treatment solution is preferably 0.20 mol/kg or more, and more preferably 0.22 mol/kg or more. On the other hand, the upper limit is not particularly limited, and is preferably 0.30 mol/kg or less and preferably 0.27 mol/kg or less, for instance. When the amount of alkali metal to be contained is less than 0.20 mol/kg, the amount of phosphorus elution increases in the case of storing in a high-temperature and high-humidity atmosphere for a long term. On the other hand, when the amount of alkali metal such as Na exceeds 0.30 mol/kg, unevenness occurs in external appearance, which is not preferable.
In the present embodiment, the amount of alkali metal such as Na in the insulation coating treatment solution can be analyzed as follows. The amount of alkali metal such as Na contained in the insulation coating treatment solution is measured by atomic absorption spectrometry and converted into the amount of substance. Then, the amount of alkali metal such as Na in the insulation coating treatment solution can be derived by dividing the amount of alkali metal such as Na by the weight of the insulation coating treatment solution.
As described above, the pH of the insulation coating treatment solution is preferably 1.7 or more and 2.1 or less. The pH of the insulation coating treatment solution is preferably 1.8 or more, and more preferably 1.9 or more.

Next, a method for manufacturing the insulation coating treatment solution used for the grain-oriented electrical steel sheet according to the present embodiment (hereinafter, simply referred to as "method for manufacturing insulation coating treatment solution") and reasons for limitation will be described.
The method for manufacturing the insulation coating treatment solution includes a mixing process of mixing a metal phosphate, colloidal silica, and an alkali metal salt. As long as a predetermined amount of alkali metal can be contained in the insulation coating treatment solution, a method for containing them is not particularly limited, and an instance is as follows.
The phosphate contains a metal phosphate of one or more metals selected from Al, Fe, Mg, Mn, Ni, Zn, Co, Mo, V, W, and Zr, as a base, and can further contain an alkali metal as sodium phosphate or potassium phosphate.
In addition, a method of adding a Na compound to the colloidal silica in advance is also conceivable. However, when a Na compound is added to the colloidal silica, there is a risk that the colloidal silica is aggregated, and therefore it is necessary to carefully consider prolongation of stirring time and the like.
Further, it is also possible to add an alkali metal in the insulation coating treatment solution by mixing a metal phosphate with colloidal silica and then by adding a sodium hydroxide or potassium hydroxide aqueous solution.
The size of the colloidal silica (silica particles) used in the present embodiment is not particularly limited, but the average particle size (average primary particle size) thereof is preferably 4 to 35 nm. When the average particle size of the colloidal silica is less than 4 nm, there is a case where the colloidal silica is likely to aggregate to deteriorate the stability of the insulation coating treatment solution, or a case where the insulation coating becomes a porous coating with a large gap to deteriorate the adhesion of the insulation coating, which is not preferable. On the other hand, when the average particle size of the colloidal silica is more than 35 nm, there is a case where the reactivity of the colloidal silica becomes poor, resulting in insufficient mixing of the phosphate as a binder and the colloidal silica, or a case where cracks are initiated on the insulation coating to deteriorate the adhesion, which is not preferable.
In addition, as the particle size of the colloidal silica is smaller, a denser coating is formed, and the coating tension can be increased. Thus, the upper limit of the average particle size of the colloidal silica is more preferably 31 nm, 22 nm, 18 nm, or 12 nm. Further, it is more preferable that the surface of the colloidal silica is chemically treated with aluminum. The average particle size (average primary particle size) of the colloidal silica can be determined, for instance, by conversion from a specific surface area measurement value (according to JIS Z 8830: 2013) by a BET adsorption method.
In the method for manufacturing the insulation coating treatment solution, the ratio between the metal phosphate and the colloidal silica is not particularly limited. As long as the amount of alkali metal contained in the insulation coating treatment solution is 0.20 mol/kg or more and 0.30 mol/kg or less, the insulation coating of the grain-oriented electrical steel sheet using this insulation coating treatment solution exhibits excellent characteristics. Preferable values are exemplified below.
For instance, the insulation coating treatment solution may be prepared by mixing an aqueous solution containing 100 parts by mass of a metal phosphate in solid equivalent, 35 to 125 parts by mass of colloidal silica in solid equivalent, and an aqueous solution containing more than 0 to 7 parts by mass of sodium hydroxide, potassium hydroxide, or lithium hydroxide in solid equivalent. The insulation coating treatment solution prepared as described above 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.
In addition, the amount of the colloidal silica in the insulation coating treatment solution is preferably 25 to 55 mass% in solid equivalent with respect to the total mass of the insulation coating treatment solution. When the amount of the colloidal silica in the insulation coating treatment solution is less than 25 mass%, the coating tension of the insulation coating may be insufficient, which is not preferable. When the amount of the colloidal silica in the insulation coating treatment solution is more than 55 mass%, the adhesion of the insulation coating may deteriorate, which is not preferable. The amount of the colloidal silica in the insulation coating treatment solution is more preferably 27 mass% or more, still more preferably 30 mass% or more, 32 mass% or more, or 35 mass% or more in solid equivalent with respect to the total mass of the insulation coating treatment solution. The amount of the colloidal silica in the insulation coating treatment solution is more preferably 45 mass% or less, and still more preferably 40 mass% or less.
In the mixing process, various oxides such as titanium oxide and molybdenum oxide, and inorganic compounds such as boric acid, sodium borate, a pigment, and barium titanate may be further mixed with the insulation coating treatment solution.
As described above, the pH of the insulation coating treatment solution is preferably adjusted to 1.7 or more and 2.1 or less. For instance, the pH of the insulation coating treatment solution may be adjusted by adding hydrochloric acid or alkali metal hydroxide to the insulation coating treatment solution. The pH of the insulation coating treatment solution is preferably 1.8 or more, and more preferably 1.9 or more. Examples
Hereinafter, the effects of an aspect of the present invention are described in detail with reference to the following examples. However, the condition in the examples is an example condition employed to confirm the operability and the effects of the present invention, so that the present invention is not limited to the example condition. The present invention can employ various types of conditions as long as the conditions do not depart from the scope of the present invention and can achieve the object of the present invention.
Each of the slabs having chemical compositions adjusted so that the chemical compositions of the base steel sheets as final products were as shown in Table 2 was heated to 1150°C and subjected to hot rolling to obtain a hot-rolled steel sheet having a sheet thickness of 2.6 mm. The hot-rolled steel sheet was subjected to hot-rolled steel sheet annealing as necessary, and then subjected to one time cold rolling or a plurality of times of cold rolling including intermediate annealing to obtain a cold-rolled steel sheet having a final sheet thickness of 0.23 mm. The cold-rolled steel sheet was subjected to decarburization annealing, and the decarburization-annealed steel sheet was held in an atmosphere containing ammonia during cooling to perform nitriding annealing. In the processes from slab heating to nitriding annealing, known conditions were applied.
The decarburization-annealed steel sheet after the decarburization annealing described above was coated with an annealing separator mainly composed of MgO, followed by drying. The decarburization-annealed steel sheet coated with the annealing separator was subjected to final annealing at 1200°C for 20 hours.
Thereafter, the excess annealing separator was washed with water and removed using a scrubber. Then, as shown in Table 3, each insulation coating treatment solution in which the colloidal silica in the insulation coating treatment solution was 50 mass% in solid equivalent and the balance in solid equivalent was adjusted to a phosphate, an alkali metal, a chromate, and an inorganic compound was applied and baked under the conditions shown in Table 4 to form an insulation coating. The Na content in the insulation coating treatment solution was adjusted by adding a 30% sodium hydroxide aqueous solution, the K content was adjusted by adding a 30% potassium hydroxide aqueous solution, and the Li content was adjusted by adding a 30% lithium hydroxide aqueous solution. In addition, the pH of the insulation coating treatment solution was adjusted as necessary to 1.6 or more and 2.2 or less.
The chemical composition of the base steel sheet, the chemical composition of the insulation coating, the amount of insulation coating, the ³¹P-NMR spectrum of the insulation coating, and the like were measured for the obtained grain-oriented electrical steel sheets Nos. C1 to C36 and c1 to c4 based on the above-described methods. Gaussian fitting was performed on the measured ³¹P-NMR spectrum of the insulation coating by the above-described method to determine the ratio of the peak area of the Q¹ structure to the total peak area (area fraction of the Q¹ structure).
The amount of moisture absorption, the amount of phosphorus elution, the external appearance after baking, and the like were evaluated for the obtained grain-oriented electrical steel sheets Nos. C1 to C36 and c1 to c4 based on the following methods.

[Amount of Moisture Absorption]

The amount of moisture absorption of the grain-oriented electrical steel sheet with an insulation coating was derived by the following method. The obtained grain-oriented electrical steel sheet with an insulation coating was cut to a length of 300 mm and a width of 60 mm and placed in a thermo-hygrostat (temperature: 50°C, humidity: 90%) for one week, and a weight difference before and after being held at the constant temperature and constant humidity was measured. Then, a value obtained by dividing the quantified weight difference by 0.036 m² which is the total area of both surfaces of the test piece was defined as an amount of moisture absorption (unit: g/m²). When the amount of moisture absorption was 0.05 g/m² or less, it was determined that the moisture absorption resistance was excellent.

[Amount of Phosphorus Elution]

The amount of phosphorus elution was evaluated after the grain-oriented electrical steel sheet with an insulation coating was placed in a thermo-hygrostat (temperature: 50°C, humidity: 90%) for one week. The amount of phosphorus elution was determined by immersing three test pieces with 40 mm × 60 mm in distilled water at 100°C for 20 minutes, boiling the test pieces to elute phosphorus from the surface of the coating, and quantitatively analyzing the phosphorus. Quantitative analysis of phosphorus was performed as PO₄ (unit: mg/m²) in accordance with Testing methods for industrial wastewater 46.1.1 of JIS K 0102: 2019. When the amount of phosphorus elution was 50 mg/m² or less, it was determined that the amount of phosphorus elution was small.

[External Appearance]

In addition, the external appearance of the insulation coating after baking was evaluated. The external appearance of the insulation coating after baking was evaluated by observing the insulation coating with a SEM, and was judged based on the presence or absence of opaqueness of the observed coating surface. A case in which the proportion of the area where the coating surface was opaque was less than 10% of the observed area was evaluated as "Very Good", 10% or more and less than 20% was evaluated as "Good", and 20% or more was evaluated as "Poor". When this external appearance was "Very Good" or "Good", it was determined that the external appearance was excellent.
When the surface of the sample after baking of the insulation coating is observed using a SEM, a region where fine cracks are observed and a region where no fine cracks are observed are observed in the coating. In the region where fine cracks are observed, diffuse reflection of light occurs, and the sample is observed to be opaque. Thus, the area of the region where fine cracks were observed at a magnification of 1000 was determined, and the proportion of the area in the entire observed area was derived. Specifically, the area proportion of the opaque region was derived by performing image analysis on the SEM observation image, and binarizing the image into an opaque region and a non-opaque region. The threshold value of binarization was determined using a discriminant analysis method.
The evaluation results of the ratio of the peak area of the Q¹ structure, the amount of moisture absorption, the amount of phosphorus elution, and the external appearance of the grain-oriented electrical steel sheet with an insulation coating are shown in Table 5.
Although not shown in the table, in C1 to C36 according to Inventive Examples, the chemical composition of the insulation coating satisfied, as main elements to be contained, P: 5 to 30 atom%, Si: 5 to 30 atom%, O: 30 to 80 atom%, Al: 0.1 to 10 atom%, Cr: less than 1 atom%, Fe: less than 25 atom%, Mg: 0 to 10 atom%, Mn: 0 to 10 atom%, Ni: 0 to 10 atom%, Zn: 0 to 10 atom%, V: 0 to 10 atom%, W: 0 to 10 atom%, Zr: 0 to 10 atom%, Co: 0 to 10 atom%, and Mo: 0 to 10 atom%. In addition, the amount of insulation coating satisfied 2.0 to 7.0 g/m² per one surface.
As can be seen from Tables 2 to 5, in C1 to C36 according to Inventive Examples, the product features satisfied the scope of the present invention, and the amount of phosphorus elution and the amount of moisture absorption were excellent. The external appearance after baking was also excellent. In addition, although not shown in the tables, deterioration of the forming ability of the insulation coating was not a problem. In particular, when the ratio of the peak area of the Q¹ structure was more than 10%, a dense insulation coating having particularly excellent coating-forming ability was formed.

On the other hand, in c1 to c5 according to Comparative Examples, the product features did not satisfy the scope of the present invention, and at least one of the amount of phosphorus elution, the amount of moisture absorption, and the external appearance after baking was poor. For instance, in c1 according to Comparative Examples, the ratio of the peak area of the Q¹ structure was out of the range of the present invention, and the amount of phosphorus elution and the amount of moisture absorption were poor. In c2 according to Comparative Examples, the ratio of the peak area of the Q¹ structure was out of the range of the present invention, and the external appearance after baking was poor. c3 according to Comparative Examples contains a chromate (chromium compound), and thus is out of the scope of the present invention. In c4 according to Comparative Examples, the ratio of the peak area of the Q¹ structure was out of the range of the present invention, and the amount of phosphorus elution, the amount of moisture absorption, and the external appearance after baking were poor. In c5 according to Comparative Examples, the ratio of the peak area of the Q¹ structure was out of the range of the present invention, and the amount of phosphorus elution and the amount of moisture absorption were poor.

[Table 2]

Steel No.	Manufacturing Results
	Chemical Composition of Base Steel Sheet (In Units of mass%, Balance: Fe And Impurities)
	Si	Mn	Cr	Cu	P	Sn	Sb	Ni
Steel A	3.3	0.1	0.1	-	0.03	0.05	-	-
Steel B	2.7	0.2	-	-	-	-	-	-
Steel C	3.8	0.1	0.1	0.2	0.02	0.08	-	-
Steel D	3.3	0.5	0.1	-	-	-	-	-
Steel E	3.3	0.1	0.2	-	-	-	-	-
Steel F	3.3	0.1	0.1	0.3	-	-	-	-
Steel G	3.3	0.1	0.1	-	0.2	-	-	-
Steel H	3.3	0.1	0.1	-	-	0.1	0.1	-
Steel I	3.4	0.1	0.1	-	-	-	-	0.3
Steel J	3.3	0.1	0.1	-	-	-	-	-
Steel K	3.3	0.1	0.1	-	-	-	-	-
Steel L	3.3	0.1	0.1	-	-	-	-	-

"-" in the table indicates that the alloying element was not added intentionally.

[Table 2] (Continued)

Steel No.	Manufacturing Results
	Chemical Composition of Base Steel Sheet (In Units of mass%, Balance: Fe And Impurities)
	B	Mo	Bi	Al	C	N	S	Se
Steel A	-	-	-	0.026	0.001	0.001	0.001	-
Steel B	-	-	-	0.026	0.001	0.001	0.001	-
Steel C	-	-	-	0.026	0.001	0.001	0.001	0.001
Steel D	-	-	-	0.026	0.001	0.001	0.001	-
Steel E	-	-	-	0.026	0.001	0.001	0.001	-
Steel F	-	-	-	0.026	0.001	0.001	0.001	-
Steel G	-	-	-	0.026	0.001	0.001	0.001	-
Steel H	-	-	-	0.026	0.001	0.001	0.001	-
Steel I	-	-	-	0.026	0.001	0.001	0.001	-
Steel J	0.001	-	-	0.026	0.001	0.001	0.001	-
Steel K	-	0.05	-	0.026	0.001	0.001	0.001	-
Steel L	-	-	0.001	0.026	0.001	0.001	0.001	-

[Table 3]

Treatment Solution No.	Insulation Coating Treatment Solution
	Metal Phosphate		Alkali Metal
	Metal	Metal Content Ratio molar ratio	Element	Amount Thereof mol/kg
A1	Al	100	Na	0.20
A2	Al	100	K	0.20
A3	Al	100	Li	0.20
A4	Al	100	Na	0.22
A5	Al	100	K	0.22
A6	Al	100	Li	0.22
A7	Al	100	Na	0.25
A8	Al	100	K	0.25
A9	Al	100	Li	0.25
A10	Al	100	Na	0.27
A11	Al	100	K	0.27
A12	Al	100	Li	0.27
A13	Al	100	Na	0.30
A14	Al	100	K	0.30
A15	Al	100	Li	0.30
A16	Al	100	Na	0.25
A17	Al	100	Na	0.25
A18	Al	100	Na	0.25
A19	Al	100	Na	0.25
A20	Al	100	Na	0.25
A21	Al	100	Na	0.25
A22	Al/Fe	80/20	Na	0.25
A23	Al/Mg	80/20	Na	0.25
A24	Al/Mn	80/20	Na	0.25
A25	Al/Ni	80/20	Na	0.25
A26	Al/Zn	80/20	Na	0.25
A27	Al/Co	80/20	Na	0.25
A28	Al/Mo	80/20	Na	0.25
A29	Al/V	80/20	Na	0.25
A30	Al/W	80/20	Na	0.25
A31	Al/Zr	80/20	Na	0.25
a1	Al	100	Na	0.10
a2	Al	100	Na	0.40
a3	Al	100	Na	0.20
a4	Al	100	Na	0.20

[Table 3] (Continued)

Treatment Solution No.	Insulation Coating Treatment Solution
Treatment Solution No.	Amount of Colloidal Silica mass%	Chromate	Inorganic Compounds	pH
A1	50	-	-	1.7
A2	50	-	-	1.7
A3	50	-	-	1.7
A4	50	-	-	1.8
A5	50	-	-	1.8
A6	50	-	-	1.8
A7	50	-	-	1.9
A8	50	-	-	1.9
A9	50	-	-	1.9
A10	50	-	-	2.0
A11	50	-	-	2.0
A12	50	-	-	2.0
A13	50	-	-	2.1
A14	50	-	-	2.1
A15	50	-	-	2.1
A16	50	-	Titanium Oxide	1.9
A17	50	-	Molybdenum Oxide	1.9
A18	50	-	Boric Acid	1.9
Al9	50	-	Sodium Borate	1.9
A20	50	-	Pigment (Talc)	1.9
A21	50	-	Barium Titanate	1.9
A22	50	-	-	1.9
A23	50	-	-	1.9
A24	50	-	-	1.9
A25	50	-	-	1.9
A26	50	-	-	1.9
A27	50	-	-	1.9
A28	50	-	-	1.9
A29	50	-	-	1.9
A30	50	-	-	1.9
A31	50	-	-	1.9
a1	50	-	-	1.7
a2	50	-	-	2.1
a3	50	Contained	-	1.7
a4	50	-	-	1.6

[Table 4]

Manufacturing Method No.	Baking Process
Manufacturing Method No.	Heating Rate °C /sec.	Baking Temperature °C	Holding Time sec.
B1	100	800	30
B2	30	1000	30
B3	50	850	10
B4	60	850	60
B5	60	850	30
B6	65	950	30
b1	60	750	30

[Table 5]

Test No.	Treat ment Soluti on No.	Manu factur ing Meth od No.	Steel No.	Manufacturing & Evaluation Results					Note
Test No.	Treat ment Soluti on No.	Manu factur ing Meth od No.	Steel No.	Ratio of Peak Area of Q ¹ Structure %	Ratio of Peak Area of Q³ Structure %	Amount of Phosphor us Elution mg/m²	Amount of Moisture Absorpti on g/m²	External Appearan ce after Baking	Note
C1	A1	B5	Steel A	4.0	78.5	44	0.026	Very good	Inventive Example
C2	A2	B5	Steel A	4.1	77.8	43	0.024	Very good	Inventive Example
C3	A3	B5	Steel A	3.6	79.2	46	0.028	Very good	Inventive Example
C4	A4	B5	Steel A	8.7	53.8	41	0.023	Very good	Inventive Example
C5	A5	B5	Steel A	9.2	52.4	40	0.022	Very good	Inventive Example
C6	A6	B5	Steel A	8.1	56.7	44	0.026	Very good	Inventive Example
C7	A7	B5	Steel A	12.2	37.9	38	0.019	Very good	Inventive Example
C8	A8	B5	Steel A	12.1	37.2	36	0.018	Very good	Inventive Example
C9	A9	B5	Steel A	11.8	39.3	40	0.022	Very good	Inventive Example
C10	A10	B5	Steel A	12.7	35.0	34	0.023	Good	Inventive Example
C11	A11	B5	Steel A	13.1	33.5	32	0.022	Good	Inventive Example
C12	A12	B5	Steel A	11.8	37.9	36	0.024	Good	Inventive Example
C13	A13	B5	Steel A	15.3	21.9	25	0.032	Good	Inventive Example
C14	A14	B5	Steel A	15.5	20.5	22	0.031	Good	Inventive Example
C15	A15	B5	Steel A	14.6	24.1	28	0.034	Good	Inventive Example
C16	A16	B5	Steel A	11.9	37.2	42	0.020	Very good	Inventive Example
C17	A17	B5	Steel B	12.8	35.0	43	0.021	Very good	Inventive Example
C18	A18	B5	Steel C	12.1	37.9	44	0.019	Very good	Inventive Example
C19	A19	B5	Steel D	11.8	38.6	47	0.020	Very good	Inventive Example
C20	A20	B5	Steel E	11.6	40.1	46	0.021	Very good	Inventive Example
C21	A21	B5	Steel F	11.6	40.1	47	0.021	Very good	Inventive Example
C22	A22	B5	Steel G	12.2	37.9	46	0.020	Very good	Inventive Example
C23	A23	B5	Steel H	12.1	37.2	44	0.022	Very good	Inventive Example
C24	A24	B5	Steel I	12.2	37.9	47	0.021	Very good	Inventive Example
C25	A25	B5	Steel J	12.2	37.2	45	0.019	Very good	Inventive Example
C26	A26	B5	Steel K	12.0	38.6	47	0.020	Very good	Inventive Example
C27	A27	B5	Steel L	11.9	39.3	46	0.021	Very good	Inventive Example
C28	A28	B5	Steel A	11.9	38.6	42	0.020	Very good	Inventive Example
C29	A29	B5	Steel B	12.4	35.7	43	0.018	Very good	Inventive Example
C30	A30	B5	Steel C	12.1	36.4	44	0.019	Very good	Inventive Example
C31	A31	B5	Steel D	12.0	37.9	48	0.022	Very good	Inventive Example
C32	A7	B 1	Steel E	11.4	40.8	49	0.028	Very good	Inventive Example
C33	A7	B2	Steel F	11.8	37.9	40	0.019	Good	Inventive Example
C34	A7	B3	Steel G	11.5	40.1	48	0.031	Very good	Inventive Example
C35	A7	B4	Steel H	12.0	37.9	43	0.018	Good	Inventive Example
C36	A7	B6	Steel I	12.0	37.2	41	0.017	Good	Inventive Example
c1	a1	B5	Steel A	2.1	87.2	85	0.180	Very good	Comparative Example
c2	a2	B5	Steel A	18.1	16.1	25	0.046	Poor	Comparative Example
c3	a3	B5	Steel A	9.6	50.2	45	0.008	Very good	Comparative Example
c4	A7	b1	Steel A	2.3	87.2	182	0.320	Poor	Comparative Example
c5	a4	B5	Steel A	2.2	87.2	82	0.130	Good	Comparative Example

INDUSTRIAL APPLICABILITY

Claims

A grain-oriented electrical steel sheet comprising: a base steel sheet; and an insulation coating, wherein
the insulation coating is free of a chromium compound and contains a phosphate, and

when the insulation coating is measured by a nuclear magnetic resonance under conditions such that: a magnetic field of a proton resonance frequency is 500 MHz; a magic angle spinning rate is 55 kHz; a chemical shift of a ³¹P nucleus is referenced to 0.9 ppm using an ammonium dihydrogen phosphate (NH₄H₂PO₄); an observation offset is set between 0 and 30 ppm; a flip angle is 90°; a waiting time is 8 seconds; and a number of scans is 9000 times, and when an obtained ³¹P-NMR spectrum is subjected to a Gaussian fitting in a range from 16 to -90 ppm,

a ratio of a peak area of a Q¹ structure to a total peak area is more than 3% and 18% or less, and

the ratio of the Q¹ structure is smaller than a ratio of a peak area of a Q³ structure to the total peak area.
The grain-oriented electrical steel sheet according to claim 1, wherein
the base steel sheet contains, as a chemical composition, in terms of mass%,

0.010% or less of C,

2.00 to 4.00% of Si,

0.05 to 1.00% of Mn,

0.010 to 0.065% of Al,

0.004% or less of N,

0.010% or less of S,

0.010% or less of Se,

0 to 0.30% of Cr,

0 to 0.40% of Cu,

0 to 0.50% of P,

0 to 1.00% of Ni,

0 to 0.30% of Sn,

0 to 0.30% of Sb,

0 to 0.0100% of B,

0 to 0.1% of Mo,

0 to 0.01% of Bi, and

a balance consisting of Fe and impurities.