阅读说明：本技术 方向性电磁钢板、方向性电磁钢板的制造方法及铁心 (Grain-oriented electromagnetic steel sheet, method for producing grain-oriented electromagnetic steel sheet, and iron core ) 是由 名越正泰 松岛朋裕 渡边诚 高城重宏 高宫俊人 上坂正宪 寺岛敬 于 2015-09-11 设计创作，主要内容包括：一种方向性电磁钢板,在钢板上具有镁橄榄石覆膜,并且进行了磁畴细化处理,该方向性电磁钢板的特征在于,具有从表面看散布于镁橄榄石覆膜的、宽度为20μm以下的条状的缺损部和直径为5μm～50μm的点状的缺损部中的至少一种缺损部,相对于镁橄榄石层的表面积,该缺损部的总面积率为0.1％以上且不足1.5％。(A grain-oriented electrical steel sheet having a forsterite coating on a steel sheet and having a magnetic domain refining treatment, characterized by having at least one type of defect portions of stripe-shaped defect portions having a width of 20 [ mu ] m or less and dot-shaped defect portions having a diameter of 5 [ mu ] m to 50 [ mu ] m scattered in the forsterite coating when viewed from the surface, and the total area ratio of the defect portions is 0.1% or more and less than 1.5% with respect to the surface area of a forsterite layer.)

1. A grain-oriented electrical steel sheet having a forsterite coating film on a steel sheet and having magnetic domain refining treatment thereon,

the forsterite coating has at least one of stripe-shaped defects having a width of 20 [ mu ] m or less and dot-shaped defects having a diameter of 5 [ mu ] m to 50 [ mu ] m, which are scattered in the forsterite coating when viewed from the surface, and the total area ratio of the defects is 0.1% or more and less than 1.5% with respect to the surface area of the forsterite layer.

2. The grain-oriented electrical steel sheet according to claim 1,

at least a part of the defect portion is striped.

3. A core comprising the grain-oriented electrical steel sheet according to claim 1 or 2 laminated thereon.

4. A method for producing a grain-oriented electrical steel sheet,

the method comprises a step of determining whether or not to refine the magnetic domain, wherein the step of determining whether or not to refine the magnetic domain comprises irradiating the grain-oriented electrical steel sheet with an electron beam, and determining whether or not to refine the magnetic domain of the grain-oriented electrical steel sheet having a tensile coating film or a forsterite coating film on the steel sheet surface based on whether or not the total area ratio of strip-shaped defective portions having a width of 20 [ mu ] m or less and/or dot-shaped defective portions having a diameter of 5 [ mu ] m to 50 [ mu ] m, which are scattered in the forsterite coating film, is in a range of 0.1% or more and less than 1.5% when viewed from the surface.

5. The method of manufacturing a grain-oriented electrical steel sheet according to claim 4,

the step of determining whether or not to refine the magnetic domain may further include a magnetic domain refining step of performing a magnetic domain refining process on the surface of the grain-oriented electrical steel sheet determined as yes.

Technical Field

The present invention relates to a grain-oriented electrical steel sheet (grain-oriented electrical steel sheet), a method for producing the grain-oriented electrical steel sheet, a method for evaluating the grain-oriented electrical steel sheet, and an iron core.

Background

Grain-oriented electrical steel sheets are mainly used as iron core materials for transformers, motors of electrical equipment, and the like. Therefore, from the viewpoint of energy saving, there is a need for a grain-oriented electrical steel sheet having excellent magnetization characteristics, particularly a grain-oriented electrical steel sheet having low iron loss.

Such grain-oriented electrical steel sheet is produced by hot rolling a slab including an inhibitor required for secondary recrystallization, for example, elements for forming MnS, MnSe, AlN, and the like (for example, Mn and S in the case of MnS), hot rolling, annealing the hot rolled sheet as necessary, then cold rolling twice or more times with intermediate annealing added thereto once or in between to obtain a final sheet thickness, decarburizing annealing, then coating an annealing separator such as MgO on the surface of the steel sheet, and finally finish annealing.

In the process of passing throughThe surface of the grain-oriented electrical steel sheet produced by the method is formed with what is called forsterite (Mg) except for special cases₂SiO₄) (forsterite) ceramic-based insulating coating film (also called forsterite coating film). ). Generally, a tension coating (stretching coating) is applied to the upper layer for the purpose of improving insulation and imparting tension to the steel sheet.

When a grain-oriented electrical steel sheet is laminated and used as an iron core, the forsterite coating film and the tensile coating film electrically insulate the steel sheets from each other, and contribute to reduction of eddy current (eddy current). The laminated core includes a laminated core obtained by cutting and punching a flat plate to stack a plurality of sheets (for example, see patent document 1) and a wound core obtained by winding the flat plate into a roll and laminating the sheets (for example, see patent document 2). If the adhesion of the forsterite film is low at the punched end portion of the stacked core and the bent portion of the wound core, the forsterite film is easily peeled from the surface of the steel sheet. If the forsterite coating peels off, the electrical insulation between the steel plates is reduced due to the compression during the assembly of the core. If the electrical insulation is reduced, when the laminated core is used in a transformer or a motor, local heat generation occurs, which may reduce the performance of the electrical equipment and may cause an accident such as dielectric breakdown. Further, if the adhesion between the surface of the steel sheet and the forsterite film is low, the forsterite film may be peeled off not only when the steel sheet is deformed but also by collision with foreign matter. This peeling usually occurs at the interface between the steel sheet and the forsterite film. There is a possibility that the steel sheet corrodes due to peeling of the forsterite coating film from after the manufacture to during the assembly of the core. Corrosion of steel sheets also causes a reduction in the commercial value of grain-oriented electrical steel sheets.

However, in order to further reduce the iron loss in grain-oriented electrical steel sheets, a method of refining magnetic domains (magnetic domain refining) has been proposed and put to practical use. This method is a method of imparting defects such as grooves (grooves) to the surface of the steel sheet after the final cold rolling, or introducing strain locally to the surface of the steel sheet by electron beam (electron beam) irradiation or laser beam irradiation after the secondary recrystallization annealing, thereby refining magnetic domains. Among these magnetic domain refining techniques, a technique of locally introducing strain is performed after the formation of a forsterite film. However, if the adhesion property of the forsterite coating film is low, the forsterite coating film and thus the tension coat layer may be peeled off together from the steel sheet depending on the conditions of electron beam irradiation or laser beam irradiation. If they are peeled from the steel sheet, the insulation and corrosion resistance of the grain-oriented electrical steel sheet are significantly reduced. As a countermeasure, if plating is performed again for the purpose of covering the peeled portion, not only the production cost of the grain-oriented electrical steel sheet increases, but also the effect of refining the magnetic domain is significantly reduced because local strain is relieved by the plating treatment of the tensile coating.

It is very important to improve the adhesion between the steel sheet and the forsterite coating film and to minimize the peeling. In particular, a high-grade grain-oriented electrical steel sheet subjected to magnetic domain refining treatment is required to have high peeling resistance, that is, to have high adhesion between a forsterite film and the surface of the steel sheet.

In addition, the forsterite coating also exerts a tensile stress on the surface of the steel sheet to improve the magnetic properties. Therefore, it is desired to form a coating film having excellent film adhesion and high ability to apply tensile stress to the surface of the steel sheet. The film adhesion indicates the adhesion between the forsterite film and the surface of the steel sheet.

Disclosure of Invention

Technical problem to be solved by the invention

However, it is not easy to form a forsterite coating film having high adhesion to the surface of the steel sheet. This is because the factor of the adhesion of the left and right forsterite films cannot be sufficiently grasped. For example, the adhesion of a forsterite film has been conventionally evaluated by an adhesion test (or peeling test), but the adhesion of a forsterite film irradiated with an electron beam tends to be different from the results of a bending peeling test that is usually performed.

A first object of the present invention is to provide a grain-oriented electrical steel sheet having excellent adhesion between a forsterite coating and a steel sheet surface, an iron core produced using the grain-oriented electrical steel sheet, and a method for producing the grain-oriented electrical steel sheet.

A second object of the present invention is to provide an evaluation method capable of evaluating the adhesion between a forsterite film and the surface of a steel sheet, a second object of the present invention is to provide an evaluation method capable of evaluating the adhesion and the amount of forsterite, a third object of the present invention is to provide a method for producing a grain-oriented electrical steel sheet having a step of evaluation by the evaluation method, and a fourth object of the present invention is to provide a grain-oriented electrical steel sheet obtained by screening by the evaluation method and an iron core produced using the grain-oriented electrical steel sheet.

Technical solution for solving technical problem

The present inventors have found a method capable of easily performing non-destructive evaluation of the distribution of a forsterite film from the surface of the forsterite film or the surface of a tensile coating layer formed on the forsterite film.

This method is a method of irradiating a grain-oriented electrical steel sheet with an electron beam and detecting electron-beam excitation light (electron-beam-excitation light), i.e., electroluminescence (hereinafter, abbreviated as CL), emitted from a forsterite film as a signal. That is, the present inventors have found that the distribution of the forsterite film in the grain-oriented electrical steel sheet can be derived by attaching a light evaluation unit (light evaluation unit including a light detection unit or the like) to an electron scanning microscope (hereinafter abbreviated as SEM), scanning and irradiating the surface and cross section of the grain-oriented electrical steel sheet with an electron beam, and observing a CL image generated by a signal of electron beam excitation light emitted from the forsterite film.

The present inventors have also found that a grain-oriented electrical steel sheet having high film adhesion can be obtained by evaluating the relationship between the distribution of the forsterite film and the film adhesion (adhesion between the surface of the steel sheet and the forsterite film) by this method and controlling the coating rate of the forsterite film to a certain range, and have completed the invention for solving the first problem.

The present inventors have also measured CL spectra of various grain-oriented electrical steel sheets having a forsterite coating film and studied the correlation with the properties of the forsterite coating film in detail. As a result, the presence of light emission centered around a wavelength of 410nm (referred to as emission peak a), light emission existing around a wavelength of 500nm (referred to as emission peak B), and light emission centered around a wavelength of 640nm (referred to as emission peak C) was confirmed. Further, it was found that the emission peak wavelength of each grain-oriented electrical steel sheet was greatly different from that of each grain-oriented electrical steel sheet, but the emission intensity of each peak was greatly changed. This is closely related to properties such as adhesion between the forsterite film and the surface of the steel sheet and the amount of formed forsterite (forsterite amount), and the properties of the forsterite film can be quantitatively evaluated by using the peak intensity or the peak intensity ratio. Further, by utilizing the relationship between the emission peak intensity ratio and the forsterite amount, an appropriate range of properties of the forsterite film can be specified. The present inventors have completed the invention for solving the second problem based on these findings.

The present invention has been made based on the above findings, and the gist thereof is as follows.

[1] A grain-oriented electrical steel sheet having a forsterite coating on a steel sheet and having a magnetic domain refining treatment, characterized by having at least one type of defect portions of stripe-shaped defect portions having a width of 20 [ mu ] m or less and dot-shaped defect portions having a diameter of 5 [ mu ] m to 50 [ mu ] m scattered in the forsterite coating when viewed from the surface, and the total area ratio of the defect portions is 0.1% or more and less than 1.5% with respect to the surface area of a forsterite layer.

[2] The grain-oriented electrical steel sheet according to [1], wherein at least a part of the defective portion is in a stripe shape.

[3] An iron core comprising the grain-oriented electrical steel sheet according to [1] or [2] laminated thereon.

[4] A method for manufacturing a grain-oriented electrical steel sheet, characterized by comprising a step for determining whether or not to refine a magnetic domain, wherein the step for determining whether or not to refine a magnetic domain comprises irradiating the grain-oriented electrical steel sheet with an electron beam, and determining whether or not to refine a magnetic domain of a grain-oriented electrical steel sheet having a tensile coating film or a forsterite coating film on the steel sheet surface, based on whether or not the total area ratio of linear defects having a width of 20 [ mu ] m or less and/or a dot-like defect having a diameter of 5 [ mu ] m to 50 [ mu ] m, which are scattered in the forsterite coating film, is in the range of 0.1% or more and less than 1.5% when viewed from the surface.

[5] The method of manufacturing a grain-oriented electrical steel sheet according to [4], further comprising a magnetic domain refining step of performing a magnetic domain refining process on the surface of the grain-oriented electrical steel sheet determined as yes in the step of determining whether or not to refine the magnetic domain.

[6] A method for manufacturing a grain-oriented electrical steel sheet, characterized by comprising a step of selecting the quality of a grain-oriented electrical steel sheet having a forsterite coating on the steel sheet based on whether or not the total area percentage of defects scattered in the forsterite coating is within a predetermined range when viewed from the surface.

[7] The method of manufacturing a grain-oriented electrical steel sheet according to [6], further comprising a magnetic domain refining step of performing a magnetic domain refining process on a surface of the grain-oriented electrical steel sheet selected as superior in the step of selecting superior or inferior.

[8] A method of evaluating the adhesion between a forsterite coating and the surface of a grain-oriented electrical steel sheet having the forsterite coating thereon, characterized in that the adhesion between the forsterite coating and the surface of the steel sheet is evaluated by irradiating the surface of the grain-oriented electrical steel sheet with an electron beam to split the spectrum of the generated light, and by using at least one of the intensity of a light emission peak A and/or a light emission peak B appearing in the wavelength range of 380 to 600nm and the following intensity ratio,

(intensity ratio)

The intensity ratio of any one of Ia/Ic, Ib/Ic and (Ia + Ib)/Ic,

wherein Ia represents the intensity of the emission peak A, Ib represents the intensity of the emission peak B located on the higher wavelength side than the emission peak A, and Ic represents the intensity of the emission peak C appearing in the wavelength range of 600 to 665 nm.

[9] A method of evaluating a grain-oriented electrical steel sheet having a forsterite coating on the steel sheet, wherein the adhesion between the forsterite coating and the steel sheet surface and the amount of forsterite are evaluated, characterized in that the adhesion between the forsterite coating and the steel sheet surface is evaluated by irradiating the surface of the grain-oriented electrical steel sheet with an electron beam, dispersing the spectrum of the generated light, and using at least one of the intensity of a light emission peak A and/or a light emission peak B appearing in a wavelength range of 380 to 600nm and the following intensity ratio,

the amount of forsterite in the forsterite coating film was evaluated by using the intensity of the emission peak C appearing in the wavelength range of 600 to 665nm,

(intensity ratio)

Any intensity ratio of Ia/Ic, Ib/Ic and (Ia + Ib)/Ic,

here, Ia represents the intensity of the emission peak a, Ib represents the intensity of the emission peak B located on the higher wavelength side than the emission peak a, and Ic represents the intensity of the emission peak C.

[10] The method for evaluating a grain-oriented electrical steel sheet according to [8] or [9], wherein the evaluation is performed using the intensity of the emission peak A and/or Ia/Ic appearing in a range of 380 to 450 nm.

[11] A method for producing a grain-oriented electrical steel sheet having a forsterite coating film on a steel sheet, characterized in that,

the method comprises a quality screening step for screening the quality of a grain-oriented electrical steel sheet by irradiating the surface with an electron beam after the formation of the forsterite coating, dispersing the spectrum of the generated light, and evaluating the adhesion between the forsterite coating and the surface of the steel sheet by using at least one of the intensity of a light emission peak A and/or a light emission peak B appearing in a wavelength range of 380 to 600nm and the following intensity ratio,

(intensity ratio)

Any intensity ratio of Ia/Ic, Ib/Ic and (Ia + Ib)/Ic,

wherein Ia represents the intensity of the emission peak A, Ib represents the intensity of the emission peak B located on the higher wavelength side than the emission peak A, and Ic represents the intensity of the emission peak C appearing in the wavelength range of 600 to 665 nm.

[12] A method for producing a grain-oriented electrical steel sheet having a forsterite coating film on a steel sheet, characterized in that,

the method comprises a quality screening step of screening the quality of an oriented electrical steel sheet by irradiating the surface with an electron beam after the formation of the forsterite coating, dispersing the spectrum of the generated light, evaluating the adhesion between the forsterite coating and the surface of the steel sheet by using at least one of the intensity of an emission peak A and/or an emission peak B appearing in the wavelength range of 380 to 600nm and the following intensity ratio, and evaluating the forsterite amount of the forsterite coating by using the intensity of an emission peak C appearing in the wavelength range of 600 to 665nm,

(intensity ratio)

Any intensity ratio of Ia/Ic, Ib/Ic and (Ia + Ib)/Ic,

here, Ia represents the intensity of the emission peak a, Ib represents the intensity of the emission peak B located on the higher wavelength side than the emission peak a, and Ic represents the intensity of the emission peak C.

[13] The method for producing a grain-oriented electrical steel sheet according to [11] or [12], wherein the evaluation is performed in the step of screening for superiority and inferiority by using the intensity of the emission peak A and/or Ia/Ic appearing in a range of 380 to 450 nm.

[14]A grain-oriented electromagnetic steel sheet having a magnesium olive on a steel sheetA grain-oriented electrical steel sheet characterized in that the surface is irradiated with an electron beam to split the spectrum of the generated light, the intensity ratio Ia/Ic of the peak intensity Ia of the emission peak A appearing in the wavelength range of 380 to 450nm to the intensity Ic of the emission peak C appearing in the wavelength range of 600 to 665nm is 0.4 or more, and the oxygen adhesion amount of the forsterite film is 2.6g/m²The above.

[15] The grain-oriented electrical steel sheet according to [14], characterized in that the magnetic domain refining treatment is performed.

[16] An iron core comprising the grain-oriented electrical steel sheet according to [14] or [15] laminated thereon.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a grain-oriented electrical steel sheet having a forsterite coating film with high adhesion to the surface of the steel sheet can be provided. Further, according to the present invention, it is possible to provide a grain-oriented electrical steel sheet having a forsterite coating film with high adhesion to the surface of the steel sheet even if the magnetic domain refining treatment is performed.

Further, according to the present invention, a grain-oriented electrical steel sheet having a high-performance forsterite coating (a forsterite coating having high adhesion to the surface of a steel sheet) can be evaluated, manufactured, and provided.

Drawings

FIG. 1-1 is a diagram illustrating a first embodiment, and schematically shows an example of a forsterite evaluation device.

FIG. 1-2 is a view for explaining the first embodiment, and schematically shows a light evaluation unit provided in the forsterite evaluation device shown in FIG. 1-1.

Fig. 1 to 3(a) and (b) are views explaining the first embodiment, and show an example of the results of examining the distribution of the forsterite coating film.

Fig. 1-4(a) and (b) are views for explaining the first embodiment, and show binary images obtained by separating defective parts (defective parts) and film existing parts at appropriate thresholds from the CL images shown in fig. 1-3.

Fig. 1 to 5 are views for explaining the first embodiment, and show the relationship between the area ratio of the defect portion before the domain refining treatment by the electron beam and the area ratio of the peeled film after the domain refining treatment by the electron beam.

FIG. 2-1 is a view schematically showing an example of a forsterite evaluation device.

FIG. 2-2 is a view schematically showing a light evaluation unit provided in the forsterite evaluation device shown in FIG. 2-1.

Fig. 2 to 3 show an example of CL spectrum of a grain-oriented electrical steel sheet having a tensile coating layer and a forsterite film in this order from the front surface side.

FIGS. 2 to 4 are graphs showing examples of luminescence spectra obtained by measuring forsterite powder synthesized from the reagent under the same conditions as in FIGS. 2 to 3.

FIGS. 2 to 5 are graphs showing CL spectra obtained when the electron acceleration voltage was set to 5kV, 15kV, and 25 kV.

Fig. 2 to 6 are graphs showing examples in which the peak height is used as the intensity of the emission peak.

FIGS. 2 to 7 are graphs showing the relationship between the height intensity ratio of the emission peak A to the emission peak C and the amount of oxygen attached in examples.

Detailed Description

Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the following embodiments.

< first embodiment >

The following description relates to the invention of the first embodiment. In the present invention, the grain-oriented electrical steel sheet preferably has a forsterite coating on the steel sheet, and preferably has a tensile coating, a forsterite coating, and a steel sheet in this order from the front side.

The steel sheet is a conventionally known grain-oriented electrical steel sheet, and can be preferably used regardless of whether or not an inhibitor component is used, for example. In the present specification, for convenience of explanation, a grain-oriented electrical steel sheet having a forsterite coating film on a steel sheet, a grain-oriented electrical steel sheet having a tensile coating film and a forsterite coating film are referred to as a grain-oriented electrical steel sheet, and a grain-oriented electrical steel sheet before the tensile coating film and the forsterite coating film are formed is referred to as a steel sheet.

Here, as a method of forming a forsterite coating on a steel sheet, for example, the following methods can be exemplified. First, the steel sheet is finished to a final sheet thickness, and decarburization annealing which also includes recrystallization annealing is performed on the steel sheet containing an appropriate amount of Si. Next, an annealing separator (preferably, MgO as a main component) is applied, and final finish annealing (final finishing annealing) is performed for the purpose of secondary recrystallization and formation of a forsterite film.

SiO is formed in advance on the surface of the steel sheet in the decarburization annealing₂An oxide film (sub-surface oxidation) as a main component, and in the final finish annealing, the oxide film is reacted with MgO in the annealing separating agent to form a forsterite film (Mg) on the steel sheet₂SiO₄)。

As a method for forming the tensile coat, a known method is possible, but for example, a method for forming a tensile coat on a forsterite coating film by performing ceramic plating by an inorganic plating method, a physical vapor deposition method, a chemical vapor deposition method, or the like after final finish annealing can be cited. If the tensile coating is formed, the iron loss can be reduced.

Next, a preferred embodiment of the grain-oriented electrical steel sheet of the present invention will be described. The total area ratio (in some cases, simply referred to as "area ratio") of the defective region (defective portion ") of the forsterite coating was less than 1.5%. Hereinafter, a method of specifying the area ratio of the defective portion will be described.

First, a forsterite evaluation device necessary for the above specification will be described.

FIG. 1-1 is a view schematically showing an example of a forsterite evaluation device. FIG. 1-2 is a view schematically showing a light evaluation unit provided in the forsterite evaluation device shown in FIG. 1-1. As shown in FIG. 1-1, the forsterite evaluation apparatus 1 includes a sample stage 10, an electron beam irradiation unit 11, a light evaluation unit 12, a vacuum chamber 13, and a wavelength cut filter 14. As shown in FIG. 1-1, a sample stage 10, an electron beam irradiation unit 11, a light evaluation unit 12, and a wavelength evaluation unit are accommodated in a vacuum chamber 13A cut-off filter 14. The vacuum that can be achieved by the vacuum chamber is a vacuum level that enables SEM to operate, and is typically 10 degrees f^-2Pa. However, the present invention is not limited to this in a system provided with a differential pumping (differential elevation). For example, the vacuum degree may be about 200Pa or less.

The forsterite evaluation device 1 shown in fig. 1-1 includes a wavelength cut filter 14. However, even if the wavelength cut filter 14 is not provided, information for the purpose of, for example, the presence or absence of forsterite can be confirmed based on the information of light. Therefore, the wavelength cut filter 14 may not be provided.

In the forsterite evaluation apparatus 1, an electron beam can be irradiated from an electron beam irradiation unit 11 (for example, an electron beam generation unit and an electron optical system that focuses and scans an electron beam) onto a sample 2 (a sample that is a grain-oriented electrical steel sheet) held on a sample stage 10 (the electron beam is shown by a broken-line arrow in fig. 1-1). In the case where sample 2 irradiated with the electron beam has forsterite, sample 2 emits light due to excitation of the electron beam. By evaluating the light emission by the light evaluation unit 12, the presence or absence of forsterite, the position of the forsterite, the amount of forsterite, and the distribution of the amount of forsterite can be confirmed based on the region in which light is emitted and the region in which light is not emitted.

As shown in fig. 1-2, the light evaluation unit 12 has a light measurement unit 120, a quantitative analysis unit 121, and a correlation storage unit 122. The light evaluation unit 12 is a device in which a correlation storage unit 122 that stores a specific correlation and a quantitative analysis unit 121 that performs quantitative analysis by substituting information from a photodetector into the correlation are combined with a general photodetector (corresponding to the light measurement unit 120) that detects light and measures the signal intensity and luminance of light. The optical measurement unit 120, the quantitative analysis unit 121, and the correlation storage unit 122 are connected by a signal cable or the like, but need not necessarily be integrated, and for example, the optical measurement unit 120 may be independent, and the quantitative analysis unit 121 and the correlation storage unit 122 may be located in a computer separate from the apparatus. Therefore, for example, a computer having a normal quantitative analysis function and storing the correlation is combined with a general photodetector, thereby forming the light evaluation unit 12 preferable in the present invention.

The light measurement unit 120 is not particularly limited as long as it can detect visible light, and light can be detected using a photomultiplier tube (PMT) or the like. The light measurement unit 120 has a function of converting information of the detected light into information such as signal intensity or brightness. Therefore, when the electron beam irradiation unit 11 irradiates the sample 2 with the electron beam, light emitted by excitation of the electron beam is detected, and information on the light is converted into information such as signal intensity or brightness (brightness).

The light measuring unit 120 can detect light emitted by excitation of the electron beam for each of the plurality of regions when the surface of the sample is divided into the plurality of regions. Therefore, by checking the detection of light from the light measuring unit 120, the area of the light emitting region and the area of the non-light emitting region can also be checked. The area of the region (area per unit) is not particularly limited, and may be appropriately adjusted according to the required confirmation accuracy or the like.

The method of confirming the information of the light detected by the light measurement unit 120 is not particularly limited, and confirmation can be performed by using the light evaluation unit 12 in combination with the SEM. For example, the light measurement unit 120 can be attached to the SEM, and the signal thereof can be imaged in accordance with the scanning position of the electron beam.

As described above, the light measurement unit 120 can measure the signal intensity or brightness of light. The signal intensity or brightness is transmitted to the quantitative analysis unit 121, and the quantitative analysis unit 121 can derive the forsterite amount and the distribution of the forsterite amount in the sample based on the correlation (correlation between the signal intensity or brightness of light emitted by excitation of the electron beam and the forsterite amount when the sample having forsterite is irradiated with the electron beam) stored in the correlation storage unit 122. More specifically, the forsterite amount in a predetermined region is derived from the signal intensity, brightness, and correlation, and the distribution of the forsterite amount is derived from the information on the forsterite amount in a plurality of regions. In the quantitative analysis unit 121, it is assumed that forsterite is present when the signal intensity or brightness is equal to or higher than a predetermined threshold, and that forsterite is not present when the signal intensity or brightness is lower than the threshold, and the area ratio of the defective region is derived from the binary distribution. The luminance refers to the luminance in the CL image derived based on the signal intensity of the electron beam excitation light, and can be expressed by, for example, luminance (luminance). The threshold value may be set as appropriate in accordance with the brightness in the CL image or the like.

The method of deriving the correlation stored in the correlation storage unit 122 is not particularly limited. For example, the amount of forsterite in a sample can be determined by using a plurality of samples having different amounts of forsterite, irradiating each sample with an electron beam, and measuring the signal intensity or brightness of electron beam excitation light.

The present inventors used the above forsterite evaluation apparatus to observe the state of production of a forsterite film nondestructively from above a tensile coat layer, with the aim of clarifying the difference in the state of production of the forsterite film, with respect to a grain-oriented electrical steel sheet having excellent film adhesion (adhesion between the steel sheet surface and the forsterite layer) and a grain-oriented electrical steel sheet having poor film adhesion. Fig. 1 to 3 show an example of the results of examining the distribution of the forsterite coating film. The CL image shown in fig. 1 to 3 was observed in a region of about 1.7mm × 2.1mm at a magnification of 50 times that of the jewel (registered trademark) photograph. In the CL images shown in fig. 1 to 3, the signal of the excitation light is not substantially obtained in the region where the forsterite film is not present, and therefore, the dark contrast is obtained. Such regions are shown in fig. 1-3 as dark contrasts illustrated by arrows in the CL images. This region will be referred to as a forsterite coating defect portion (or simply referred to as a defect portion) hereinafter.

Fig. 1 to 3(a) show CL images of grain-oriented electrical steel sheets having excellent film adhesion, and fig. 1 to 3(b) show CL images of grain-oriented electrical steel sheets having poor film adhesion. As is clear from comparison of the two, the CL image of the grain oriented electrical steel sheet having excellent film adhesion occupies a small area in the defect portion of the surface of the forsterite film. The width of the defect portion is about 20 μm or less, and in most cases, the defect portion extends in one direction by a length of 50 μm or more and is distributed in a stripe shape, but there are also portions in which some portions are connected in a dot shape.

As described above, the defect portion is constituted by dots having a diameter of 5 to 50 μm. As shown in fig. 1-3, the dots are distributed discretely. The defect portion does not include a size which can be visually confirmed, for example, a coating defect which corresponds to a circle having a diameter of more than 200 μm, an ellipse, or an irregular shape close thereto and which exists at a low frequency (for example, a frequency lower than the frequency of the presence of one defect in a field of view of 10mm × 10mm (the probability of the presence of one defect in the field of view is less than 50%)). Therefore, these defects are excluded from the evaluation target of the coating defect of the present invention.

Fig. 1 to 4 show binary images obtained by separating the CL image shown in fig. 1 to 3 from the defective portion and the film-existing portion with an appropriate threshold. The binary image of fig. 1-4(a) corresponds to the CL image of fig. 1-3(a), and the binary image of fig. 1-4(b) corresponds to the CL image of fig. 1-3 (b). As shown in fig. 1 to 4, the area ratio of the defective portion of the coating can be quantified by calculating the area ratio of the dark portion to the sum of the areas of the light portion (coating existing portion) and the dark portion (defective portion). Since the defective portions are substantially uniformly distributed on the surface of the forsterite film, the area ratio can be evaluated as the area ratio of the defective portions on the surface of the forsterite film by calculating the area ratio in a partial region.

The inventors of the present invention examined the relationship between the area ratio of the defective portion of the forsterite film and the film adhesion after the magnetic domain refining treatment, for grain-oriented electrical steel sheets having different film adhesion. Specifically, the electron beam used for the domain refining treatment was intentionally set to a constant strong irradiation condition (16mA), and the forsterite film was forcibly peeled off by irradiation from the tensile coating layer, and the film adhesion was evaluated at the area ratio of the defective portion at that time. If the area ratio of the peeled film is less than 10%, it is judged that the film has good adhesion, and if it is 10 to 15%, it is judged that the film is in the allowable range. The area ratio of the forsterite film defect portion and the film peeling area ratio were obtained from the binary image of the CL image.

Fig. 1 to 5 show the relationship between the area ratio of the defective portion before the domain refining treatment by the electron beam (the area ratio of the defective portion of the film on the horizontal axis) and the area ratio of the peeled film after the domain refining treatment by the electron beam (the area ratio of the peeled film by the electron beam irradiation on the vertical axis). From this, it is found that when the area ratio of the defect portion before the treatment is 1.5% or more, the peeled area ratio of the coating after the treatment exceeds 15%, and the adhesion is deteriorated. Further, as is clear from FIGS. 1 to 5, when the area ratio of the defective portion of the forsterite film is less than 0.1%, the adhesion is also deteriorated to some extent.

Therefore, only when the area ratio of the defect portion is less than 1.5%, the film adhesion after the electron beam treatment is high, and thus the film adhesion can be said to be extremely high. As described above, the area ratio of the defective portion is preferably 0.1% or more.

The defective portions are scattered on the surface of the forsterite coating film, and at least a part of the defective portions are formed in a stripe shape. The striped defect portion includes not only a case where the striped defect portion is long but also a case where the striped defect portion is connected in a dot shape and the whole striped defect portion. These defective portions can be confirmed from the CL image. Further, the present inventors have found that a striped defect portion (including a case where the defect portion is connected in a dot shape and the entire defect portion is striped) may be a starting point of peeling of the coating film by examining the distribution pattern of the forsterite coating before and after irradiation with the magnetic domain refining beam. Therefore, as described later, although it is preferable that the defective portion in a stripe shape or the like is present at a certain amount or more, it is possible to sufficiently secure adhesion in practical use by making the area ratio of the defective portion less than 1.5%.

As described above, from the viewpoint of the film adhesion property by the electron beam irradiation for domain refinement, a film having a defective portion in a stripe shape or the like in an area ratio of 0.1% or more and less than 1.5% is preferable as compared with a film having no defective portion in a stripe shape or the like. This is presumed to be because the defective portions such as stripes have an effect of preventing peeling propagation of the coating, and the distribution of the defective portions of the coating appropriately imparts flexibility to the coating with respect to an external force. In addition, it is industrially advantageous to have an appropriate defective portion. That is, it is not necessary to completely cover the surface of the steel sheet with forsterite, and for example, it is not necessary to form a large amount of oxides.

The method for forming the defective portion can be, for example, the method described in the examples. In addition, when forming the striped defective portion, a defective portion extending along the rolling direction of the grain-oriented electrical steel sheet is selected, but the striped defective portion is preferable because it is easy to form.

As described above, the area ratio of the defective portion of the forsterite film can be evaluated by obtaining a CL image so as not to break or peel off the tensile coating. In the manufactured product, the film adhesion can be evaluated in advance by whether or not the area ratio of the defective portion falls within the above range.

The above-described evaluation method of a forsterite film may be performed by using the above-described forsterite evaluation apparatus. As described above, for example, a device can be used in which a detector (corresponding to the light measurement unit 120) capable of detecting light is attached to the SEM and an image is formed by associating the signal with the scanning position of the electron beam. Preferably the image is taken as an electronic signal. The detector is not particularly limited as long as it can detect visible light, and light can be detected using a photomultiplier tube (PMT) or the like.

In order to evaluate the forsterite film present under the tensile coating layer, it is necessary to adjust the acceleration voltage, which is the irradiation condition of the excitation electron beam. The required acceleration voltage differs depending on the type and thickness of the tensile coat, and an acceleration voltage that is as small as possible not affected by the surface shape and that enables observation of the distribution of the forsterite coating film may be selected by comparing the CL image with a normal secondary electron image. This is because the CL image and the secondary electron image can be observed by changing the acceleration voltage, and thus excessive trial and error can be avoided. By way of example, when the thickness of the phosphate based tension coating (phosphate based coating) is 1 to 2 μm, a preferable range of the acceleration voltage is 20 to 40 kV. The magnification of the image can be arbitrarily determined, and a low magnification is preferable for observing the coating distribution in a wide field of view. For example, in the example of fig. 1 to 3, an image with a magnification of 50 times that of a photograph of peleli (registered trademark) is observed in an area of about 1.7mm × 2.1 mm. For evaluation of the area ratio of the defective portion of the forsterite film, CL images at the magnification of three or more fields of view are obtained, and the CL images are binarized and averaged. The threshold value for the binarization depends on the brightness or contrast when the CL image is obtained, but as shown in fig. 1 to 4, it is sufficient to select a condition that a coating defect such as a streak is extracted while observing the image and that the dot-like dark contrast is reduced as much as possible.

Next, a method for producing a grain-oriented electrical steel sheet according to the present invention will be described.

After hot rolling the heated slab, the grain-oriented electrical steel sheet is cold-rolled once or twice with intermediate annealing to have a final thickness, and then subjected to decarburization annealing. Subsequently, an annealing separator such as MgO is applied to the surface of the steel sheet, and then finish annealing is performed, thereby forming a forsterite coating as described above. The formation of the streaky forsterite film defect portion on the surface can be performed by adjusting the cold rolling conditions and providing a convex portion mainly in the rolling direction on the surface of the steel sheet before decarburization annealing. When the annealing separator is applied, it is difficult to apply the annealing separator to the convex portion of the steel sheet, and a streaky forsterite film defect portion is formed in the final finish annealing. Alternatively, the annealing separator may be applied by forming a streak-like annealing separator defect portion with a brush or the like. In addition, the number of the portions with defective rolled scale is too large, and the decarburization annealing conditions may be changed to reduce the number of the portions. Specifically, for example, when a large number of defects are formed due to insufficient subcutaneous oxidation, the atmospheric oxidation (P (H) at the time of decarburization annealing is increased₂O)/P(H₂) Thick subcutaneous oxidation is formed). In this case, the annealing separator defect portion becomes a streaky forsterite film defect portion at the time of the final finish annealing. As described above, the stripe-shaped defective portion of the forsterite coating is preferably formed along the longitudinal direction (rolling direction) of the steel coil because continuous processing is possible, and the ease and efficiency of manufacturing are excellent. The amount of the forsterite film formed is not particularly limited, butWhen the amount of forsterite is evaluated using the oxygen content in the coating film, the oxygen content is preferably 2.4g/m²The above. This is because if the film formation amount (forsterite amount) is less than this, there is a case where sufficient film adhesion cannot be obtained even if the forsterite film defect portion is adjusted within the scope of the present invention.

Although there is no particular limitation on a specific method for performing the domain refining treatment on the grain-oriented electrical steel sheet of the present invention, since the forsterite film hardly peels off in the steel sheet in which the domain is refined by the electron beam irradiation (unlike the electron beam for obtaining a CL image), it is not necessary to recoat (recoat) the peeled portion in order to ensure corrosion resistance. Therefore, a grain-oriented electrical steel sheet having low iron loss and corrosion resistance can be obtained at low cost. Here, as a preferable range of the electron beam irradiation conditions for domain refinement, the acceleration voltage e (kv), the electron beam current i (ma), and the scanning speed V (m/s) of the electron beam are preferably performed under the following conditions.

40≤E≤150

6≤I≤12

V≤40

The diameter of the electron beam is preferably 0.4mm or less. In addition, the irradiation may be performed one or more times. In this range, conditions that do not cause film peeling may be selected, but the grain-oriented electrical steel sheet of the present invention is less likely to cause film peeling when irradiated under conditions of higher current. The "higher current condition" is 8mA or more. The upper limit is not particularly limited, and may be set as appropriate within the range in which the forsterite film does not peel off.

As described above, the grain-oriented electrical steel sheet according to the present invention has a total area percentage of the defective portions scattered in the forsterite film of less than 1.5% with respect to the surface area of the forsterite layer, and therefore the film adhesion of the forsterite film is high.

In addition, one of the characteristics of the grain-oriented electrical steel sheet of the present invention is that the film adhesion can be improved when electron beam treatment is performed.

By applying the present invention to a production line and feeding back the obtained results for adjustment of the production conditions, a grain-oriented electrical steel sheet coil can be produced in which the film properties are ensured over the entire length.

As described above, the present invention provides a grain-oriented electrical steel sheet having excellent film adhesion, and an excellent core can be obtained if the sheet is used to manufacture a core. The core assumed in the present invention is a core for a motor, and examples thereof include a wound core and a stacked core.

Further, by adopting a manufacturing method having a good-and-bad screening step for screening the good and bad of the grain-oriented electrical steel sheet based on the total area percentage of the defect portions scattered in the forsterite coating as seen from the surface, and a manufacturing method having a magnetic domain refining step for performing magnetic domain refining on the steel sheet that is screened as good, it is possible to efficiently manufacture an excellent grain-oriented electrical steel sheet. Further, the steel sheet which is not selected by the screening can be used for applications which are not high in the required property grade.

< second embodiment >

The following description relates to the invention of the second embodiment.

First, a grain-oriented electrical steel sheet having a tensile coating layer, a forsterite coating layer, and a steel sheet in this order from the front side will be described. The steel sheet may be a conventionally known grain-oriented electrical steel sheet, and for example, can be preferably used regardless of whether or not an inhibitor component is used. In the present specification, for convenience of explanation, a grain-oriented electrical steel sheet having a forsterite coating film, a grain-oriented electrical steel sheet having a tensile coating film and a forsterite coating film are referred to as a grain-oriented electrical steel sheet, and a grain-oriented electrical steel sheet before the tensile coating film and the forsterite coating film are formed is referred to as a steel sheet.

The method for forming the forsterite coating film and the method for forming the tensile coat layer are not particularly limited, and examples thereof include the following methods.

Here, as a method of forming a forsterite coating on a steel sheet, for example, the following methods can be cited. First, the steel sheet is finished to a final sheet thickness, and decarburization annealing which also includes recrystallization annealing is performed on the steel sheet containing an appropriate amount of Si. Next, an annealing separating agent (preferably, MgO as a main component) is applied, and finish annealing is performed for the purpose of secondary recrystallization and formation of a forsterite film.

SiO is formed on the surface of the steel sheet in the decarburization annealing₂An oxide film (sub-surface oxidation) as a main component, and in the final finish annealing, the oxide film is reacted with MgO in the annealing separating agent to form a forsterite film (Mg) on the steel sheet₂SiO₄)。

As a method for forming the tensile coat, a known method is possible, but for example, a method for forming a tensile coat on a forsterite coating film by performing ceramic plating by an inorganic plating method, a physical vapor deposition method, a chemical vapor deposition method, or the like after final finish annealing can be cited. If the tensile coating is formed, the iron loss can be reduced.

Next, a method for evaluating the adhesion between the forsterite film and the surface of the steel sheet will be described.

FIG. 2-1 is a view schematically showing an example of a forsterite evaluation device. FIG. 2-2 is a view schematically showing a light evaluation unit provided in the forsterite evaluation device shown in FIG. 2-1. As shown in FIG. 2-1, the forsterite evaluation apparatus 1 includes a sample stage 10, an electron beam irradiation unit 11, a light evaluation unit 12, a vacuum chamber 13, and a wavelength cut filter 14. As shown in fig. 2-1, a sample stage 10, an electron beam irradiation unit 11, a light evaluation unit 12, and a wavelength cut filter 14 are housed in a vacuum chamber 13. The vacuum that can be achieved by the vacuum chamber is a vacuum level that enables SEM to operate, and is typically 10 degrees f^-2Pa. However, the present invention is not limited to this in a system provided with a differential pumping (differential elevation). For example, the vacuum degree may be about 200Pa or less.

The forsterite evaluation device 1 shown in fig. 2-1 includes a wavelength cut filter 14. However, even without the wavelength cut filter 14, the properties of the forsterite film can be confirmed based on the information of light. Therefore, the wavelength cut filter 14 may not be provided.

In the forsterite evaluation apparatus 1, an electron beam (indicated by a broken line arrow) can be irradiated from an electron beam irradiation unit 11 (for example, an electron beam generation unit and an electron optical system that focuses and scans an electron beam) onto a sample 2 (a sample that is a grain-oriented electrical steel sheet) held on a sample stage 10. In the case where sample 2 irradiated with the electron beam has forsterite, sample 2 emits light due to excitation of the electron beam. By evaluating the luminescence by the light evaluation unit 12, the properties of the forsterite coating such as coating adhesion, forsterite amount, magnetic properties, strain, and impurities can be confirmed. The adhesion of the coating can be confirmed by using at least one of the intensity of the emission peak a and/or the emission peak B (see fig. 2 to 3) appearing in the wavelength range of 380 to 600nm and the following intensity ratio. The forsterite content can be confirmed by using the intensity of the emission peak C (see FIGS. 2 to 3) appearing in the wavelength range of 600 to 665 nm. The magnetic properties can be confirmed using the intensity of the emission peak a and/or the emission peak B. The impurities can be confirmed using the intensities of the emission peaks a to D (see fig. 2 to 3).

As shown in fig. 2-2, the light evaluation unit 12 has a light measurement unit 120, a quantitative analysis unit 121, and a correlation storage unit 122. The light evaluation unit 12 is a device having a function of measuring the CL spectrum (how to measure the CL spectrum will be described later), and is a device in which a correlation storage unit 122 for storing a specific correlation in combination with a general photodetector (corresponding to the light measurement unit 120) for detecting light and measuring the signal intensity and luminance of light of a specific wavelength in the CL spectrum, and a quantitative analysis unit 121 for performing quantitative analysis by substituting information from the photodetector into the correlation are provided. Therefore, for example, a computer having a normal quantitative analysis function and storing the correlation is combined with a general photodetector, thereby forming the light evaluation unit 12 preferable in the present invention.

The light measurement unit 120 is not particularly limited as long as it can detect visible light, and light can be detected using a photomultiplier tube (PMT) or the like. The light measurement unit 120 has a function of converting information of the detected light into information such as signal intensity or brightness. Therefore, when the electron beam irradiation unit 11 irradiates the sample 2 with the electron beam, light emitted by excitation of the electron beam is detected, and information of light having a specific wavelength in the CL spectrum is converted into information such as signal intensity or brightness.

The light measuring unit 120 can detect light emitted by excitation of the electron beam for each of the regions obtained by dividing the surface of the sample into a plurality of regions, in addition to detecting light emitted by excitation of the electron beam for each of the regions obtained by capturing the surface of the sample as one region. When the film is divided into a plurality of regions, the properties of the forsterite film can be evaluated for each region. The area of the region is not particularly limited, and can be appropriately adjusted according to the required confirmation accuracy and the like.

The method of confirming the information of the light detected by the light measurement unit 120 is not particularly limited, and confirmation can be performed by using the light evaluation unit 12 in combination with the SEM. For example, the light measurement unit 120 can be attached to the SEM, and the signal thereof can be imaged in accordance with the scanning position of the electron beam.

As described above, the light measurement unit 120 can measure the signal intensity or brightness of light having a specific wavelength in the CL spectrum. The signal intensity or brightness is transmitted to the quantitative analysis unit 121, and the quantitative analysis unit 121 can derive the film adhesion and the forsterite amount based on the correlation (correlation between the intensity or intensity ratio of the specific light emission peak and the film adhesion, correlation between the intensity or intensity ratio of the specific light emission peak and the forsterite amount, correlation between the intensity or intensity ratio of the specific light emission peak and the magnetic properties, and the like) stored in the correlation storage unit 122 and the information of the light. The brightness is the brightness in the CL image derived from the signal intensity of the electron beam excitation light, and can be expressed by, for example, the luminance.

The method of deriving the correlation stored in the correlation storage unit 122 is not particularly limited. For example, the amount of forsterite or the film adhesion in the sample is known, and a plurality of samples having different amounts of forsterite or film adhesion are used, and each sample is irradiated with an electron beam, and the signal intensity or the brightness of a specific emission peak is measured.

The present invention is characterized by utilizing the correlation between a specific emission peak and the properties of a forsterite film. The "correlation between a specific emission peak and the properties of the forsterite film" refers to, for example, a correlation between a specific emission peak and the film adhesion, a correlation between a specific emission peak and the amount of forsterite, and a correlation between a specific emission peak and the magnetic properties. Then, the correlation will be specifically described below.

Fig. 2 to 3 show an example of CL spectrum of a grain-oriented electrical steel sheet having a tensile coating layer, a forsterite coating film, and a steel sheet in this order from the front surface side. In the CL spectrum, there are a light-emitting group (referred to as a light-emitting peak A) of 380 to 450nm centered around 410nm, a light-emitting group (referred to as a light-emitting peak B) of 450 to 600nm also centered around 500nm, and a light-emitting group (referred to as a light-emitting peak C) of 600 to 665nm also centered around 640 nm. Further, a light-emitting group having a wavelength of about 680nm (referred to as an emission peak D) was also observed.

The luminescence spectrum of forsterite powder synthesized from the reagent is measured under the same conditions as in FIGS. 2 to 3, for example

Shown in FIGS. 2-4 (denoted as synthetic forsterite). The light-emitting group having a peak wavelength of about 615nm (considered as a light-emitting peak C as compared with the light-emitting group) was strong. The reason why the emission peak C from the synthetic forsterite is different from the emission peak C from the forsterite coating film shown in fig. 2 to 3 will be described later. Fig. 2 to 4 show CL spectra (referred to as forsterite coating extracts) obtained by dissolving forsterite coating powders extracted from a tensile coating layer of a grain oriented electrical steel sheet and a steel sheet, which have the tensile coating layer, the forsterite coating, the steel sheet, and the steel sheet in this order from the surface side, and only the emission peak C appears strong in the same manner.

The intensity axis of the CL spectrum of the amplified synthetic forsterite has a very weak emission peak a at the same position as the CL spectrum of the grain-oriented electrical steel sheet. For the addition of Al during the synthesis of forsterite₂O₃And various oxides such as CaO, and the like. Depending on the oxide added, the intensity of peak a increases slightly, but peaks C are both dominant, e.g.None of the emission peaks A, B showed a strong characteristic as in the CL spectrum of the grain-oriented electrical steel sheet shown in fig. 2 to 3. Considering that only forsterite emits light in the sample when the results of fig. 2 to 3 are obtained, it can be said that the emission peaks a and B (emission peak (a + B)) are caused by characteristic light emission of a forsterite coating film formed on a grain-oriented electrical steel sheet.

Since changes in the depth direction of the CL spectrum of a grain-oriented electrical steel sheet having a tensile coating layer with a thickness of 2 μm were examined, the CL spectrum was measured while setting the incident electron acceleration voltage to 5kV, 15kV, and 25kV, respectively. The results are shown in FIGS. 2 to 5. Note that the intensity of the CL spectrum is scaled by the current of the incident electrons. The intensity of the CL spectrum increases with an increase in the acceleration voltage of the incident electrons. This is considered to be because the number of pairs of electrons and holes to be light-emitting sources increases due to the increase in acceleration voltage. It is to be noted that the light emission peak a and the light emission peak B increase relatively with respect to the light emission peak C with an increase in the acceleration voltage. This indicates that the emission peak a and the emission peak B are signals from positions relatively deeper than the sample surface, that is, in the vicinity of the steel plate.

Based on the above results, the assignment of each emission peak was examined.

The emission peak a and the emission peak B are derived from lattice defects of forsterite crystals, and the intensity is increased slightly due to coexistence of solid solution elements such as Al and Ti, and the strength is particularly increased by strongly binding the forsterite film to the steel sheet, that is, by strengthening the adhesion between the surface of the steel sheet and the forsterite film. For example, it is considered that the emission intensity is increased by stress generated in the interface bonding between the forsterite coating film and the steel sheet surface.

On the other hand, since a strong emission peak C is observed in all of the grain-oriented electrical steel sheet, the forsterite coating extracted from the grain-oriented electrical steel sheet, and the synthesized forsterite, it is considered to be derived from the inherent emission of forsterite. The intensity of the emission peak increases due to the presence of Mn, but is hardly affected by other elements. The wavelength of the emission peak of the grain-oriented electrical steel sheet is slightly longer than the wavelength of the emission peak of the extracted forsterite coating and the synthesized forsterite. It is estimated that this occurs because the peak position of the emission peak C occurs due to contact with the steel sheet. Although the wavelength of the emission peak C was shifted, no clear change in the emission peak intensity was observed. The emission peak D is considered to be a peak occurring due to the presence of Al or Cr.

In summary of the above-described studies, it is considered that the intensity of the emission peak A, B reflects the magnitude of the effect of the forsterite film due to the bonding with the steel sheet surface, and therefore can be used as an index of the adhesion between the forsterite film and the steel sheet surface. On the other hand, the intensity of the emission peak C hardly changes depending on the form of the forsterite, and thus can be used as an index of the amount of forsterite. Based on such findings, a method of evaluating the properties of the forsterite coating of the grain-oriented electrical steel sheet by the intensity and intensity ratio of the emission peak of the CL spectrum is considered.

Next, the evaluation method will be specifically described. As described above, the following correlation is considered to exist.

(1) The intensity Ia of the emission peak a and/or the intensity Ib of the peak B serves as an index of the adhesion between the forsterite coating and the steel sheet surface.

(2) The intensity Ic of the emission peak C becomes an index of the forsterite amount.

The CL spectrum is measured under the same measurement conditions as usual, or a conversion equation for adjusting the measurement conditions is previously obtained, and the adhesion between the forsterite film and the steel sheet and the amount of forsterite can be evaluated by performing the measurement under different conditions. In the forsterite amount, if a detection line is generated between the intensity Ic of the online emission peak C and a value proportional to the forsterite amount, for example, the oxygen attachment amount, the forsterite amount can be quantified from the intensity Ic of the emission peak C. Since the above-mentioned adhesion and the forsterite amount have an influence on the magnetic properties, the tendency of the magnetic properties can be confirmed by using the intensities of the emission peaks A, B and C and the above-mentioned intensity ratio.

Note that the intensity of the emission peak may use a peak area or a peak height. An example of the latter is shown in fig. 2-6. As is clear from fig. 2 to 3 and 2 to 6, the emission peak B partially overlaps with the emission peak a and the emission peak C, and therefore, it is preferable to use only the emission peak a that is less susceptible to the influence of other peaks as an index of the adhesion between the forsterite film and the steel sheet surface.

As an index of the adhesiveness between the surface of the steel sheet and the forsterite film in (1), the intensity ratio Ia/Ic of the emission peak a to the emission peak C, the intensity ratio Ib/Ic of the emission peak B to the emission peak C, or the intensity ratio (Ia + Ib)/Ic of the emission peaks a and B to the emission peak C can be used. The method using a plurality of emission peaks as described above has a first advantage in that external disturbances such as fluctuations in measurement conditions can be mitigated by using the peak intensity ratio. The second advantage is that the change is more significant as an index of the adhesiveness of the coating film. In general, if the amount of the forsterite film formed is too large, it is known that a point defect in which the forsterite film is peeled off is likely to occur locally. When the intensity ratio is used, it is more preferable to use Ia/Ic of the emission peak a which is less likely to be affected by other peaks.

Next, measurement conditions of the CL spectrum will be described. A device basically having an electron beam irradiation device, a spectrometer capable of splitting visible light, a vacuum holding or pressure reduction for holding them, or a chamber capable of replacing light-weight gas (for example, the device shown in fig. 2-1) can be used. For example, a spectrometer may be attached to the SEM. The acceleration voltage of the incident electrons can be 5kV to 150 kV. When SEM is used, the voltage is preferably in the range of 10 to 40kV, more preferably in the range of 20 to 30 kV. If the acceleration voltage is lower than this, it is difficult to obtain a signal in a region close to the steel plate. In addition, if the acceleration voltage above this is used in the SEM, not only the device becomes a special specification, but also the effect is deteriorated. The other conditions are not particularly limited as long as a CL spectrum capable of evaluating the emission peak intensity is obtained.

The evaluation method of a forsterite film of the present invention is developed at a manufacturing site by providing a device having an electron source, a spectrometer, and a chamber capable of inserting steel sheets in batches or continuously passing steel sheets and realizing vacuum or pressure reduction or light gas replacement on a steel strip conveying path. When a chamber is provided through which the steel strip continuously passes after the final finish annealing step, the film properties can be evaluated on the production line. A plurality of measuring devices having a spectrometer for scanning an electron beam in the width direction can be provided in the width direction. Thus, the entire length and width of the steel strip can be evaluated. The measurement in the production line may be provided with a dedicated measurement system, but may be performed by electron beam irradiation in a production line having a magnetic domain refining step as described later.

By applying the present invention to a production line and feeding back the obtained results for adjustment of the production conditions, a grain-oriented electrical steel sheet coil can be produced in which the film properties are ensured over the entire length.

Based on the above evaluation methods, CL spectra of various grain-oriented electrical steel sheets composed of a tensile coating, a forsterite film, and a steel sheet were measured using an incident electron beam having an acceleration voltage of 25kV, and the adhesiveness of the films was compared. As a result, the intensity ratio Ia/Ic of the intensity (height) Ia of the emission peak A to the intensity (height) Ic of the emission peak C was 0.4 or more, and the oxygen deposition amount of the forsterite film was 2.6g/m²As described above, a grain-oriented electrical steel sheet having excellent film adhesion can be obtained.

However, it is known that the grain-oriented electrical steel sheet can be practically applied by improving the iron loss by performing a domain refining treatment. The grain-oriented electrical steel sheet having a high film adhesion in the present invention can be irradiated with, for example, an electron beam to refine the magnetic domain without causing damage such as film peeling. As a result, a magnetic domain-refined grain-oriented electrical steel sheet having high corrosion resistance and magnetic properties can be obtained without performing secondary plating.

As described above, when the domain refining process is performed by electron beam irradiation, the evaluation of the properties of the forsterite film can be performed nondestructively on the production line by measuring the emission spectrum accompanying the electron beam irradiation.

As described above, according to the present invention, a grain-oriented electrical steel sheet excellent in coating adhesion and the like can be obtained, and therefore, if a core is produced using the grain-oriented electrical steel sheet, an excellent core can be obtained. The core assumed in the present invention is a core used for a motor, a transformer, or the like, and examples thereof include a wound core, a stacked core, and the like.

Further, by adopting a manufacturing method having a quality screening step for screening the quality of the grain-oriented electrical steel sheet based on the emission peak, and further adopting a manufacturing method having a domain refining step, it is possible to efficiently manufacture an excellent grain-oriented electrical steel sheet. Further, the steel sheets that are selected as no can be used for applications where the required property level is not high.