JP5962677B2 - Evaluation method for adhesion of insulating coating on the surface of grain-oriented electrical steel sheet - Google Patents

Description

  The present invention relates to a method for evaluating an insulating coating on the surface of a grain-oriented electrical steel sheet.

  Oriented electrical steel sheets are mainly used as iron core materials for transformers and other electrical equipment. For this reason, a grain-oriented electrical steel sheet having excellent magnetization characteristics, particularly a grain-oriented electrical steel sheet with low iron loss is desired.

Such grain oriented electrical steel sheet is hot-rolled steel slab containing an inhibitor necessary for secondary recrystallization, such as MnS, MnSe, AlN, etc., and then hot-rolled sheet annealed as necessary. Then, after the final sheet thickness is obtained by one or two or more cold rolling sandwiching intermediate annealing, decarburization annealing is performed. Next, after applying an annealing separator such as MgO to the surface of the steel sheet, the final finishing annealing is performed. Note that a forsterite (Mg ₂ SiO ₄ ) -like insulating coating (also referred to as a forsterite layer) is formed on the surface of the grain-oriented electrical steel sheet, except for special cases.

  This forsterite layer effectively contributes to reducing the eddy current by electrically insulating the layers when the steel plates are laminated. However, if the forsterite layer on the surface of the steel sheet is not uniform or the forsterite layer is peeled off during the production of the wound iron core, the commercial value is lowered. In addition, the space factor is reduced, and further, the insulation is lowered due to tightening at the time of assembling the iron core to cause local heat generation, leading to an accident in the transformer.

  In addition, this forsterite layer is not only used for the purpose of electrical insulation, but it can apply tensile stress to the steel sheet by utilizing its low thermal expansion property, contributing to improvement of iron loss and further magnetostriction. doing. Furthermore, this forsterite layer contributes to the improvement of magnetic properties by sucking up the inhibitor component that is no longer necessary after the completion of secondary recrystallization into the layer and purifying the steel sheet. Therefore, obtaining a uniform and smooth forsterite layer is one of the important points affecting the product quality of grain-oriented electrical steel sheets.

  In addition, generally, when the amount of the forsterite layer formed is too large, a point defect in which the forsterite layer is locally peeled easily occurs. On the other hand, if the amount of forsterite layer formed is too small, the adhesion to a steel plate or the like is poor. Therefore, conventionally, the formation amount of a forsterite layer (hereinafter sometimes referred to as “forsterite amount”) and distribution form are important, and it is necessary to control these in the production of grain-oriented electrical steel sheets.

  Conventional techniques for investigating the amount of forsterite and its distribution include the following.

  There is a method of measuring the amount of forsterite by oxygen analysis of the steel sheet surface. Specifically, since a tension coating layer for improving magnetic properties is usually provided on the forsterite layer, this is first removed, and iron is dissolved, and then oxygen is measured by a combustion infrared method. .

  As a method for confirming the distribution of the forsterite layer, there is a method of observing the surface from which the tension coating layer has been removed with a scanning electron microscope (SEM). At this time, characteristic X-rays may be detected and elemental analysis may be performed.

  Further, as a method for viewing the distribution from the cross section, there is a method in which the cross section of the steel sheet is prepared by polishing or the like, and the cross section is similarly observed by SEM (for example, Patent Document 1).

  On the other hand, in order to further reduce the iron loss, there is a method of performing magnetic domain refinement on the grain-oriented electrical steel sheet. For this method, it is effective to apply a residual stress to the steel sheet by providing grooves or by irradiating with an electron beam or a laser beam. However, when electron beam irradiation or laser beam irradiation is performed, the forsterite layer is peeled off depending on the irradiation conditions, and the corrosion resistance of the grain-oriented electrical steel sheet is lowered. As a countermeasure, for example, there is a method of coating again for the purpose of covering the peeled portion. However, this method increases the manufacturing cost of the grain-oriented electrical steel sheet.

  For this reason, it is important to minimize the peeling of the forsterite layer, and the grain-oriented electrical steel sheet (with the tension coating on the forsterite layer) before the magnetic domain subdivision is resistant to peeling. In other words, there is a demand for high insulation film adhesion, and there is a demand for accurate evaluation of insulation film adhesion.

JP 2012-36447 A

  In the method described in Patent Document 1, sample preparation takes time. Further, in the method of observing the surface from which the tension coating layer has been removed with the scanning electron microscope (SEM) as described above, the measurement area is small, so that the representativeness as data is lacking. In addition, if the measurement area satisfying the representativeness as data is taken, it takes a lot of time and there is a problem that it is not very efficient. Further, regarding the adhesion evaluation of the insulating coating, conventionally, the bending diameter (unit: cm) at which peeling occurs is used as an index of adhesion, and the quantitativeness is lacking.

  The present invention has been made to solve the above-mentioned problems, and its purpose is to provide a method for easily and accurately evaluating the adhesion of the forsterite layer of the insulating coating on the surface of the grain-oriented electrical steel sheet in a short time. It is to provide.

As a result of persistently examining the method for evaluating the forsterite layer, the inventors have reported in Japanese Patent Application No. 2013-068403 that emission of light from the forsterite layer occurs when the surface of the grain-oriented electrical steel sheet is irradiated with an electron beam. Yes. This light is electron beam excitation light, that is, cathodoluminescence (hereinafter abbreviated as CL). The inventors attach a light evaluation part (light evaluation part composed of a light detection part) to the SEM, irradiate the surface and cross section of the grain-oriented electrical steel sheet with an electron beam, and create an image with the generated optical signal of the light. CL images are observed to clarify the following.
(1) Based on CL generated from the forsterite layer, the presence of the forsterite layer in the sample can be visualized and confirmed (evaluated).
(2) In the observation from the surface of the grain-oriented electrical steel sheet, a CL image of the forsterite layer can be obtained even if the tension coating layer remains attached.
(3) The CL signal amount (signal intensity and brightness) obtained from the electron beam excitation light in the forsterite layer has a high correlation with the forsterite layer.
(4) The distribution of the forsterite layer of the grain-oriented electrical steel sheet can be derived based on the CL image obtained from the electron beam excitation light by the forsterite layer.
(5) Rather than directly detecting the light intensity of the electron beam excitation light in the forsterite layer, the CL image is first acquired and the brightness of the CL image is quantified to quantify the distribution of the forsterite layer. Can be evaluated easily and easily.

The present invention has been further studied and the inventors have quantified the brightness of the CL image obtained from the forsterite layer on the surface of the grain-oriented electrical steel sheet, thereby improving the adhesion of the forsterite layer. It was found that it can be evaluated. In addition, the inventors quantified the brightness of the CL image obtained from the forsterite layer after being irradiated with an electron beam or a laser beam for the purpose of magnetic domain subdivision, so that It was found that the adhesion of the forsterite layer can be evaluated. The summary is described below.
[1] Obtained by irradiating the surface of a directional electrical steel sheet having a tension coating layer, a forsterite layer, and a directional electrical steel sheet in this order from the surface side, and detecting light generated by excitation by the electron beam. A method for evaluating the adhesion of an insulating coating on a surface of a grain-oriented electrical steel sheet, wherein the adhesion of a forsterite layer, which is an insulating coating on the surface of the grain-oriented electrical steel sheet, is evaluated based on the obtained image.
[2] The adhesiveness of the forsterite layer is evaluated by binarizing the brightness of the image into a bright part and a dark part, and determining the ratio of the area of the bright part or the dark part [1] The evaluation method of the adhesiveness of the insulating film of the grain-oriented electrical steel sheet surface described in 1.
[3] The evaluation according to [1] or [2], wherein the adhesion of the forsterite layer on the surface of the grain-oriented electrical steel sheet after being subjected to magnetic domain subdivision by irradiation with an electron beam or a laser beam is evaluated. Evaluation method of adhesion of insulating coating on surface of grain-oriented electrical steel sheet.

  ADVANTAGE OF THE INVENTION According to this invention, the adhesiveness of the insulating film on a grain-oriented electrical steel sheet surface can be evaluated easily and correctly in a short time.

It is a figure which shows typically an example of the evaluation apparatus of a forsterite layer. It is a figure which shows typically the light evaluation part with which the forsterite layer evaluation apparatus shown in FIG. 1 is provided. It is a figure which shows the CL image of a forsterite layer, and the brightness | luminance histogram after giving a magnetic domain subdivision (after the electron beam irradiation for magnetic domain subdivision) about the directionality electrical steel sheet from which an adhesiveness index differs. It is a figure which shows the relationship between an adhesion parameter | index and the peeling area rate after giving a magnetic domain subdivision (after the electron beam irradiation for magnetic domain subdivision). Fig. 5 is a CL image of a forsterite layer after irradiating an electron beam after magnetic domain subdivision (after irradiating an electron beam for magnetic domain subdivision) for grain oriented electrical steel sheets having different forsterite layer formation conditions. is there. (A) is a figure which shows the relationship between an adhesion parameter | index and the peeling area rate after giving magnetic domain subdivision (after the electron beam irradiation for magnetic domain subdivision), (b) is a damage generation electric current and magnetic domain subdivision. It is a figure which shows the relationship with the peeling area rate after giving (after the electron beam irradiation for magnetic domain subdivision).

  Hereinafter, embodiments of the present invention will be described. In addition, this invention is not limited to the following embodiment.

  First, in the present invention, as a grain-oriented electrical steel sheet for evaluating the adhesion of an insulating coating, a laminate having a tension coating layer, a forsterite layer (insulating coating), and a grain-oriented electrical steel sheet in this order from the surface of the grain-oriented electrical steel sheet. The grain-oriented electrical steel sheet which consists of a structure is mentioned. Or, irradiate an electron beam or a laser beam to a directional electrical steel sheet having a laminated structure having a tension coating layer, a forsterite layer (insulating coating), and a directional electrical steel sheet in this order from the surface side of the directional electrical steel sheet. The grain-oriented electrical steel sheet after magnetic domain subdivision is mentioned. In addition, the conditions at the time of irradiating the electron beam or laser beam for the purpose of magnetic domain subdivision will be described later.

Examples of the method for forming the forsterite layer on the grain-oriented electrical steel sheet include the following methods. First, decarburization annealing (also used for recrystallization annealing) is performed on a grain oriented electrical steel sheet containing an appropriate amount of Si finished to a final thickness. Next, an annealing separator (preferably containing MgO as a main component) is applied, and then wound around a coil and subjected to final finishing annealing for the purpose of secondary recrystallization and forsterite layer formation. Here, in the decarburization annealing, an oxide film (subscale) containing SiO ₂ as a main component is generated on the steel plate surface, and this oxide film and MgO in the annealing separator are reacted during the final finish annealing. Thus, a forsterite layer (Mg ₂ SiO ₄ ) is formed on the grain-oriented electrical steel sheet.

  Examples of the method of forming the tension coating layer include a method of forming a tension coating layer on the forsterite layer by a ceramic coating by inorganic coating, physical vapor deposition, chemical vapor deposition, or the like after final finish annealing. . If a tension coating layer is formed, iron loss can be reduced.

Next, a forsterite evaluation apparatus capable of implementing the evaluation method of the present invention will be described. FIG. 1 is a diagram schematically illustrating an example of a forsterite evaluation apparatus. FIG. 2 is a diagram schematically illustrating a light evaluation unit included in the forsterite evaluation apparatus illustrated in FIG. 1. As shown in FIG. 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, a sample stage 10, an electron beam irradiation unit 11, a light evaluation unit 12, and a wavelength cut filter 14 are accommodated in a vacuum chamber 13. Here, the vacuum that can be realized by the vacuum chamber is a degree of vacuum capable of operating the SEM, and is usually 10 ⁻² Pa. However, this is not the case with devices having differential exhaust. For example, a degree of vacuum up to about 200 Pa is possible.

  The forsterite evaluation apparatus 1 of the present embodiment includes the wavelength cut filter 14, but even without the wavelength cut filter 14, the target information such as the amount of forsterite can be confirmed based on the light information. Can do. Therefore, the wavelength cut filter 14 may not be provided.

  The forsterite evaluation apparatus 1 can irradiate the sample 2 held on the sample stage 10 with an electron beam from an electron beam irradiation unit 11 (for example, an electron beam generation unit and an electron optical system that performs an aperture scanning of the electron beam) ( The electron beam is indicated by a dotted arrow). When the sample 2 irradiated with the electron beam has forsterite, the sample 2 emits light by excitation with the electron beam. By evaluating this light emission by the light evaluation unit 12, the presence of forsterite, the position where the forsterite exists, the amount of forsterite, and the distribution of the amount of forsterite can be confirmed. The forsterite evaluation apparatus 1 has a wavelength cut filter 14. When the wavelength cut filter 14 is used, the light evaluation unit 12 can evaluate light having a wavelength in a specific range from the electron beam excitation light. As described later, the accuracy of confirmation is increased by using light having a wavelength of 560 nm or more. Among the evaluation apparatuses for carrying out the confirmation method of the present invention, the evaluation apparatus having the wavelength cut filter 14 corresponds to the evaluation apparatus of the present invention.

  As illustrated in FIG. 2, the light evaluation unit 12 includes a light measurement unit 120, a quantitative analysis unit 121, and a correlation storage unit 122. The light evaluation unit 12 is a general photodetector that detects light and measures the signal intensity and brightness of light, a correlation storage unit 122 that stores a specific correlation, and a light detection based on the above correlation. This is a combination of a quantitative analysis unit 121 that performs quantitative analysis by applying information from a vessel. Therefore, for example, a combination of a computer that stores the above-described correlation and has a normal quantitative analysis function and a general photodetector provides a light evaluation unit 12 that is preferable in the present invention.

  The light measurement unit 120 is not particularly limited as long as it can detect visible light, and may detect light using a photomultiplier tube (PMT) or the like. The light measurement unit 120 has a function of converting detected light information into information such as signal intensity and brightness. Therefore, when the sample is irradiated with an electron beam from the electron beam irradiation unit 11, light emitted by excitation by the electron beam is detected, and information on this light is converted into information such as signal intensity and brightness. . As described above, the presence of the forsterite layer can be confirmed by confirming the detection of light from the light measurement unit 120.

  The light measurement unit 120 can detect light emitted by excitation with an electron beam for each region when the surface of the sample is divided into a plurality of regions. For this reason, by confirming the detection of light from the light measurement unit 120, the position (region) where the forsterite is present can also be confirmed. The area of the region is not particularly limited, and may be adjusted as appropriate according to the required accuracy of confirmation.

  In this way, the presence and position of forsterite can be confirmed. The method for confirming the information of the light detected by the light measurement unit 120 is not particularly limited, but can be confirmed by using the light evaluation unit 12 in combination with the SEM.

  As described above, the light measurement unit 120 can measure the signal intensity or brightness of light. This signal intensity or brightness is sent to the quantitative analysis unit 121, and the quantitative analysis unit 121 irradiates the sample having forsterite with an electron beam and the correlation stored in the correlation storage unit 122. Sometimes, the distribution of the amount of forsterite and the amount of forsterite in the sample is derived based on the signal intensity of light emitted by excitation with an electron beam or the correlation between the brightness and the amount of forsterite. More specifically, the forsterite amount in a predetermined area is derived from the correlation between the signal intensity and the brightness, and the forsterite amount distribution is derived by combining the information on the amount of forsterite in a plurality of areas. Is done. Note that the brightness refers to the brightness in the CL image derived based on the signal intensity of the electron beam excitation light, and can be expressed using, for example, luminance.

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

  Therefore, in the present invention, it is possible to visualize only the forsterite layer by acquiring a CL image for the grain-oriented electrical steel sheet surface on which the forsterite layer that is an insulating film is formed. A missing part, that is, a covered part or a peeled part can be specified. Therefore, it is possible to know the form and degree of forsterite layer peeling from this visualization information.

  In addition, in the CL image, since a signal is not obtained in a portion where the forsterite layer is not present, that is, a peeled portion, it can be easily binarized. Therefore, the CL image can be binarized with an appropriate threshold value and divided into a bright part and a dark part. By calculating the area ratio of the bright part or the dark part with respect to the sum of the bright part and the dark part, the forsterite layer coverage or the forsterite layer peeling ratio can be obtained. This value is an adhesion index of the forsterite layer. That is, the higher the coverage of the forsterite layer, the higher the forsterite layer adhesion.

  In the evaluation method of the present invention, as described above, as described above, a directional electrical steel sheet having a laminated structure in which a forsterite layer and a tension coating layer are laminated in this order on a directional electrical steel sheet. Therefore, in this invention, the adhesiveness of the insulating coating (forsterite layer) on the grain-oriented electrical steel sheet surface can be evaluated easily and easily in a short time. Furthermore, in the case of such a measurement sample, the adhesion of the insulating coating (forsterite layer) on the surface of the grain-oriented electrical steel sheet can be evaluated without destroying the measurement sample. For this reason, the state of the forsterite layer in the formation process of the forsterite layer can be confirmed. By using the present invention, it is possible to easily determine conditions for forming a forsterite layer in a desired range with respect to the amount and distribution of forsterite.

  Further, in the present invention, as described above, magnetic domain subdivision is performed by irradiating the surface of a grain oriented electrical steel sheet having a laminated structure in which a forsterite layer and a tension coating layer are laminated in this order from the surface side. The grain-oriented electrical steel sheet after having been subjected to the conversion can also be used as a measurement object. The magnetic domain subdivision is performed by electron beam irradiation or laser beam irradiation. For this reason, in the present invention, by evaluating the adhesion of the forsterite layer on the surface of the grain-oriented electrical steel sheet after being irradiated with an electron beam or a laser beam, the insulating coating (forsterite layer) on the grain-oriented electrical steel sheet surface is evaluated. The influence of magnetic domain subdivision can be investigated, and the adhesion of the insulating coating (forsterite layer) on the grain-oriented electrical steel sheet surface after magnetic domain subdivision can be evaluated. In the present invention, since the adhesion of the insulating coating (forsterite layer) on the grain-oriented electrical steel sheet after the magnetic domain subdivision can be evaluated, the present invention can be used to determine the amount and distribution of forsterite. The formation conditions of the forsterite layer in which the forsterite layer does not peel off even when the treatment is performed can be easily determined.

  Here, an example of a method for preparing a measurement sample in the case of evaluating the adhesion of the insulating coating (forsterite layer) on the surface of the grain-oriented electrical steel sheet after magnetic domain subdivision will be described. First, for the purpose of magnetic domain fragmentation, the forsterite layer on the surface of the grain-oriented electrical steel sheet to be evaluated is peeled off. In order to peel the forsterite layer on the surface of the grain-oriented electrical steel sheet, electron beam irradiation or laser beam irradiation may be performed.

In the electron beam irradiation for the purpose of magnetic domain subdivision, the acceleration voltage E (kV), beam current I (mA), and beam scanning speed V (m / s) are preferably performed under the following conditions.
40 ≦ E ≦ 150
6 ≦ I ≦ 12
V ≦ 40
The beam diameter of the electron beam is preferably 0.4 mm or less. Irradiation may be performed once or a plurality of times.

In laser beam irradiation for the purpose of magnetic domain subdivision, the average laser output P (W), beam scanning speed V (m / s), and beam diameter d (mm) are preferably performed under the following conditions.
10 ≦ P / V ≦ 35
V ≦ 30
d ≧ 0.20
The upper limit of d is preferably about 0.85 mm.

  Next, a method for evaluating the adhesion of the forsterite layer on the above-mentioned grain-oriented electrical steel sheet will be described.

  When a sample is irradiated with an electron beam and light emitted at that time is detected, CL intensity (intensity of electron beam excitation light) can be obtained. Further, a CL image is obtained by measuring the CL intensity in synchronization with the position where the focused electron beam is scanned on the sample surface. Here, when the sample is used, the acceleration voltage of incident electrons is preferably selected in the range of 0.1 kV to 100 kV.

  Usually, when a tension coating layer is formed on a forsterite layer, it is considered difficult to evaluate the state of the forsterite layer nondestructively. However, according to the evaluation method of the present invention, the state of the forsterite layer can be evaluated without removing the tension coating layer. This is because when the electron beam is irradiated, the accelerated electrons penetrate through the upper tension coating layer and reach the forsterite layer. Therefore, when evaluating the forsterite layer existing below the tension coating layer as in this embodiment, it is necessary to adjust the acceleration voltage, which is the electron beam irradiation condition. The required acceleration voltage varies depending on the type and thickness of the tension coating layer, but when the thickness of the phosphate-based tension coating layer is 1 to 2 μm, the acceleration voltage may be appropriately set from the range of 10 to 60 kV. Specifically, the higher the acceleration voltage, the more light that can be excited, which is advantageous for detection in that the amount of information is large. However, the higher the accelerating voltage, the more the electron beam spreads within the measurement object, so the spatial resolution decreases. Moreover, since the energy of the electron beam is high, the emission intensity is reduced. The acceleration voltage may be adjusted according to these guidelines and the thickness of the tension coating layer.

  Next, the obtained CL image is binarized. In the binarized CL image, by calculating the area ratio of the bright part (or dark part) with respect to the sum of the bright part and the dark part, the proportion of the forsterite layer covered (deficient) is derived. be able to. It can be said that the higher the proportion of the forsterite layer is coated, the higher the adhesion of the forsterite layer. The threshold for binarizing the obtained CL image can be, for example, the frequency distribution (histogram) of the CL image, and the frequency between the peak of the bright part and the dark part can be used as the threshold value.

  In addition, what is necessary is just to calculate the ratio of the area of a bright part or a dark part with respect to the whole area for an area ratio. As for the entire area, a sufficiently wide area including the peeled portion of the forsterite layer may be selected as appropriate, and it is desirable to use an area obtained by averaging the areas obtained from a plurality of fields of view.

  The accuracy of confirming the presence of the forsterite layer is improved by detecting light in a specific wavelength range from the electron beam excitation light. Since the CL spectrum obtained at the acceleration voltage of 25 kV from the surface of the grain-oriented electrical steel sheet has broad peaks of 400 nm and 650 nm, for example, the amount of forsterite can be confirmed more accurately by using a wavelength cut filter. That is, the accuracy of confirmation is increased by using light in a range of 560 nm or more as an evaluation target under a condition that does not include a peak near 400 nm.

  In addition to the binarization, the obtained CL image may be derived by ternarization or quaternarization to derive the coverage ratio of the forsterite layer.

  As described above, according to the evaluation method of the present invention, the adhesiveness of the insulating coating on the surface of the grain-oriented electrical steel sheet can be easily and accurately evaluated in a short time.

  For four types of grain-oriented electrical steel sheets (No. 1 to No. 4) having different adhesion properties, CL images were obtained with a forsterite layer evaluation apparatus and binarized. Specifically, with respect to 3 fields of 2.3 mm × 1.7 mm square of these grain-oriented electrical steel sheets, an electron beam was scanned and irradiated at an acceleration voltage of 30 kV (electron beam diameter: 300 μm, current value: 16 mA), A CL image was obtained under the same conditions using the light evaluation unit 12 composed of a light guide and a PMT. The obtained CL image was evaluated with an average luminance of 256 gradations using existing image processing software (Photoshop CS6), and binarized by confirming the histogram.

  For the four types of grain-oriented electrical steel sheets, grain-oriented electrical steel sheets having a forsterite layer and a phosphate-based tension coating layer in this order on the steel sheet surface were used.

  In addition, regarding the adhesion of the four types of grain-oriented electrical steel sheets, a bending test (the minimum bending diameter (diameter) at which the peeling of the coating does not occur when the electromagnetic steel sheets are wound around cylindrical rods having various diameters) is previously determined. The test which evaluates the adhesiveness of a film is calculated | required.) It evaluated in five steps from the value of the curvature diameter R when it peeled, and it was set as the adhesiveness index. In addition, adhesiveness is so bad that the numerical value of an adhesiveness index is large.

  Next, from the binarized value, the area ratio of the dark part with respect to the sum of the bright part and the dark part was calculated to obtain the peeled area ratio (%) of the forsterite layer. In the calculation of the peeled area ratio, the average value of the peeled area ratios of the three fields of view was calculated for each measurement sample.

  As a result of investigating the relationship between the adhesion index and the peeled area ratio by the above evaluation method, the directional electrical steel sheet judged to have poor adhesion by a bending test, that is, the directional electrical steel sheet having a large value of the adhesion index is It was also found that the value of the peeled area ratio was increased. Therefore, the grain-oriented electrical steel sheet having poor adhesion by a bending test has a large amount of peeling of the forsterite layer, and the adhesion can be easily evaluated from the value of the peeling area ratio of the forsterite layer. Further, when the time required for the conventional adhesion evaluation method and the evaluation method of the present invention was examined, it was confirmed that the evaluation method of the present invention required less time than the conventional adhesion evaluation method. . As mentioned above, it can evaluate simply in a short time by using the evaluation method of this invention.

  Next, the forsterite of the grain-oriented electrical steel sheet after being irradiated with the electron beam for magnetic domain fragmentation for the four types of grain-oriented electrical steel sheets (No. 1 to No. 4) having the same adhesion as in Example 1. The peel rate of the layer was determined. About the grain-oriented electrical steel sheet after electron beam irradiation, the CL image was acquired with the forsterite layer evaluation apparatus, and it binarized. The coverage of the forsterite layer was derived from the binarized value. The electron beam irradiation for magnetic domain subdivision was performed once. A region having a length of about 2.3 mm (dotted line portion in the figure) was irradiated, and the electron beam diameter was about 300 μm, the current value was 12 mA, the scanning speed was 32 m / s, and the acceleration voltage was 60 kV. The binarization and the forsterite layer peeling rate were determined in the same manner as in Example 1.

  FIG. 3 is an example of CL images and luminance histograms obtained on the surface of the four types of grain-oriented electrical steel sheets after one electron beam irradiation. FIG. 4 is a graph in which the horizontal axis represents the adhesion index and the vertical axis represents the peeled area ratio of the forsterite layer. From FIG. 1 shows that there are many dark parts and there is much peeling amount of a forsterite layer. On the other hand, no. 4 shows that there are few dark parts and there is little peeling amount of a forsterite layer.

  Further, from FIG. 4, the grain-oriented electrical steel sheet determined to have poor adhesion by a bending test, that is, the grain-oriented electrical steel sheet having a large adhesion index value also has a large peel area ratio. Therefore, even in the case of grain-oriented electrical steel sheets that have been subjected to electron domain irradiation and subjected to magnetic domain fragmentation, grain-oriented electrical steel sheets with poor adhesion by a bending test have a large amount of forsterite layer peeling. The adhesiveness can be easily evaluated from the value of the peeled area ratio. Further, when the time required for the conventional adhesion evaluation method and the evaluation method of the present invention was examined, the electron beam irradiation process for the purpose of magnetic domain fragmentation was performed as in Example 1 compared with the conventional adhesion evaluation method. It was found that the time required for the evaluation method of the present invention is shorter even when there is a problem. From the above, even with a grain-oriented electrical steel sheet after magnetic domain subdivision, the adhesion can be easily evaluated in a short time by using the evaluation method of the present invention.

  For seven grain-oriented electrical steel sheets (No. 3-1 to No. 3-7) having different forsterite layer formation conditions, the adhesion index was determined under the same conditions as in Example 1. The forsterite layer was formed by appropriately changing the composition of the annealing separator.

  For the seven grain-oriented electrical steel sheets, no. 3-1. For No. 3-2, the adhesion index is 2, No. 3-2. 3-3 No. For 3-5, the adhesion index was 3 and no difference in adhesion index was observed. Therefore, the forsterite layer formation conditions could not be found from the conventional adhesion evaluation results.

  Next, electron beam irradiation for the purpose of magnetic domain fragmentation was performed. The electron beam irradiation conditions were the same as in Example 2. For the grain-oriented electrical steel sheet after irradiation with an electron beam for magnetic domain subdivision, the CL value was obtained and the luminance was binarized in the same manner as in Examples 1 and 2, and the peeled area ratio was obtained. On the other hand, the current value (damage generation current) at which peeling of the forsterite layer occurred in electron beam irradiation for magnetic domain subdivision was determined. The occurrence of peeling of the forsterite layer was confirmed visually.

  FIG. 5 is a CL image obtained for each measurement sample after electron beam irradiation for magnetic domain subdivision. In FIG. 3-1. 3-2 is an adhesion index of 2 (numerical values in parentheses in FIG. 5). 3-3 No. 3-5 has an adhesion index of 3 and No. 3-5. 3-6 has an adhesion index of 5, No. 3-6. 3-7 has an adhesion index of 4. From FIG. 5, No. with the same adhesion index. 3-1. 3-2, no. 3-3 No. As for 3-5, it can be seen that the area of the dark part is different although the adhesion index is the same.

  FIG. 6A is a graph showing the relationship between the adhesion index and the peeled area ratio, and FIG. 6B is a graph showing the relationship between the damage generation current and the peeled area ratio. From FIG. 6 (a), No. with the same adhesion index. 3-1. 3-2, no. 3-3 No. About 3-5, a peeling area rate differs. Therefore, the threshold value of the forsterite layer forming condition can be appropriately determined from the peeled area ratio. As for the damage generation current, the damage generation current is the same. 3-3 and no. 3-5-No. About 3-7, it turns out that a peeling area rate differs. From the above, it is difficult to find the threshold value of the forsterite layer formation condition in conventional adhesion evaluation (adhesion index) and damage occurrence current. On the other hand, by using the evaluation method (peeling area ratio) of the present invention, the threshold value of the forsterite layer forming condition can be determined as appropriate.

DESCRIPTION OF SYMBOLS 1 Evaluation apparatus of forsterite layer 10 Sample stand 11 Electron beam irradiation part 12 Light evaluation part 120 Light measurement part 121 Quantitative analysis part 122 Correlation memory | storage part 13 Vacuum chamber 14 Wavelength cut filter 2 Sample (oriented electrical steel sheet)

Claims (3)

  From the image obtained by irradiating the surface of the grain-oriented electrical steel sheet having the tension coating layer, the forsterite layer, and the grain-oriented electrical steel sheet in this order from the surface side, and detecting the light generated by excitation by the electron beam A method for evaluating the adhesion of an insulating coating on the surface of a grain-oriented electrical steel sheet, comprising evaluating the adhesion of a forsterite layer which is an insulating coating on the surface of the grain-oriented electrical steel sheet.   The brightness of the image is binarized into a bright part and a dark part, and the adhesion of the forsterite layer is evaluated by calculating the ratio of the area of the bright part or the dark part. Evaluation method of adhesion of insulating coating on surface of grain-oriented electrical steel sheet.   3. The grain-oriented electrical steel sheet surface according to claim 1 or 2, wherein the adhesion of the forsterite layer on the grain-oriented electrical steel sheet surface after magnetic domain subdivision by irradiation with an electron beam or a laser beam is evaluated. Evaluation method of adhesiveness of insulating coatings.