JP2021169656A - Grain oriented magnetic steel sheet, analysis method and analysis system of magnetic domain structure of grain oriented magnetic steel sheet - Google Patents

Abstract

To provide a grain oriented magnetic steel sheet having improved elongation magnetostriction in a high magnetic field region.SOLUTION: A grain oriented magnetic steel sheet has the chemical composition containing, by mass%, 2.0-7.0% Si, and the balance composed of Fe with impurities, has an aggregate structure oriented in Goss orientation, and has an average diameter in the same magnetic domain angle region of 5.0 mm or more. The same magnetic domain angle region is derived as a continuous region having an angle of a 180° magnetic domain within a predetermined range on the basis of space distribution θ (n,m) of the angle of the 180°magnetic domain by cutting a plurality of partial regions xnm(k-nSk,l-mSl) corresponding to each of a plurality of positions (n, m) of a magnetic domain image G of the grain oriented magnetic steel sheet binarized by two kinds of colors from the magnetic domain image G, subjecting each of the plurality of partial regions to two-dimensional Fourier transformation, thereby determining a plurality of partial Fourier images, and performing derivation on the basis of peak positions of each spot of the plurality of partial Fourier images.SELECTED DRAWING: Figure 7

Description

The present invention relates to a method and an analysis system for analyzing magnetic domain structures of grain-oriented electrical steel sheets and grain-oriented electrical steel sheets.

The grain-oriented electrical steel sheet is a steel sheet containing 7% by mass or less of Si and having a secondary recrystallization texture in which secondary recrystallized grains are accumulated in the {110} <001> orientation (Goss orientation). The magnetic properties of grain-oriented electrical steel sheets are greatly affected by the degree of integration in the {110} <001> orientation. In the grain-oriented electrical steel sheets that have been put into practical use in recent years, the angle between the <001> direction of the crystal and the rolling direction is controlled to be within a range of about 5 °.

Electrical steel sheets are laminated and used for the iron core of transformers, etc., but in addition to the main magnetic characteristics of high magnetic flux density and low iron loss, it is required to have low magnetostriction that causes vibration and noise. .. It is known that the crystal orientation has a strong correlation with these characteristics, and for example, a precise orientation control technique as in Patent Documents 1 to 3 is disclosed.

Further, grain-oriented electrical steel sheets are used in various devices, and various methods for evaluating the magnetic domain structure of grain-oriented electrical steel sheets have been proposed in order to improve the performance of the devices. For example, Patent Document 4 and Patent Document 5 disclose a technique for improving iron loss by defining an area ratio of magnetic domains satisfying a predetermined condition.

Japanese Unexamined Patent Publication No. 2001-192785 Japanese Unexamined Patent Publication No. 2005-240079 Japanese Unexamined Patent Publication No. 2012-052229 Japanese Unexamined Patent Publication No. 2000-345306 Japanese Unexamined Patent Publication No. 2004-225154

Against the background of the demand for miniaturization of transformers, it is required to make the iron core itself smaller. To obtain the same magnetic operation, it is necessary to operate the iron core in a high magnetic field when the iron core becomes smaller. Therefore, it is required to improve the magnetic characteristics in the high magnetic field region for the grain-oriented electrical steel sheet used as the iron core material of the transformer.

Further, it is generally known that the iron loss decreases when the thickness of the grain-oriented electrical steel sheet is reduced, and the application of the grain-oriented electrical steel sheet having a thin plate thickness is expanding.

The inventors of the present application have examined in detail the characteristics of a transformer core manufactured of a thin steel plate in a high magnetic field region. As a result, it was recognized that there is room for improvement in noise reduction, even when a steel sheet whose crystal orientation is preferably controlled according to the conventional technique is used as a material.

As for the involvement of materials related to the noise of transformer cores, studies related to the magnetostriction of grain-oriented electrical steel sheets are often conducted. The inventors of the present application proceeded with the study from this point of view, but the noise in the high magnetic field region of the iron core manufactured of the thin steel plate is the noise when the material plate thickness is relatively thick and used in the low magnetic field region. However, it was found that the correlation with the magnetostriction of the material was relatively low.

Further investigation of the cause revealed that the noise in question was caused not by the vibration in the steel plate surface, which is the direction of magnetostriction of the material, that is, the magnetization direction, but by the vibration outside the steel plate surface.

A detailed observation of this phenomenon revealed the following situation. In the transformer core, the steel plates are arranged so as to form a closed magnetic path. That is, in the so-called stacked iron core, the steel plate block is assembled in a quadrangular shape, and in the so-called wound iron core, it is bent and formed so as to be substantially quadrangular. And this iron core is fixed to a copper wire coil or a case. For this reason, the material steel sheet is constrained at the end in the in-plane direction, particularly in the magnetization direction.

Considering the cause of the steel sheet vibrating outside the surface of the steel sheet in this situation, it is expected that the dimensional change such that the steel sheet stretches occurs and the steel sheet bends out of the surface of the steel sheet. In general, the magnetostriction of a steel sheet is distorted so that the dimensions of the steel sheet shrink in a region where the magnetic field is low, but it is known that the magnetostriction changes from shrinkage strain to elongation strain in a high magnetic field. Further, since noise becomes a problem when the material plate thickness is thin, the inventors of the present application conclude that the deflection outside the surface of the steel sheet due to this elongation magnetostriction is the cause of the noise to be eliminated.

Based on this conclusion, a measure to reduce the magnetostriction was examined as in the prior art, but even in the steel sheet controlled to reduce the overall magnetostriction, a remarkable reduction in the magnetostriction could not be realized. Therefore, regarding the noise caused by the out-of-plane vibration of the steel sheet, it was not possible to achieve the improvement as much as the noise when the material plate is relatively thick and used in a low magnetic field region. Moreover, although the correlation between the magnitude of the elongation magnetostriction and the noise was simply examined, the simple magnitude of the elongation magnetostriction was not sufficient as a noise reduction guideline when used in a high magnetic field region.

It is known that the magnitude and shape of the elongation magnetostriction are related to the amount of reflux magnetic domains generated in the steel sheet in the degaussed state and the magnetization rotation. Therefore, if the state of the reflux magnetic domain and the amount of magnetization rotation can be controlled, it is expected that noise when used in a high magnetic field region can be effectively suppressed. However, there were the following obstacles.

Conventionally, although there are a plurality of techniques for controlling the characteristics of grain-oriented electrical steel sheets by focusing on the magnetic domain structure, it cannot be said that the development of precise control techniques for the magnetic domain structure has been sufficiently carried out. That is, in many conventional techniques, the average spacing, area ratio, angle, etc. of the 180 ° magnetic domain, which is the main magnetic domain of the directional electromagnetic steel plate, are defined by the average information of the magnetic domain structure, and the magnetic domain structure of the directional electromagnetic steel plate. There are few things that characterize it, including the spatial distribution and non-uniformity of. In particular, it can be said that there is no quantitative evaluation method including a magnetic domain structure with high non-uniformity such as a reflux magnetic domain.

For example, Patent Document 4 and Patent Document 5 define the area ratio of magnetic domains satisfying a predetermined condition, but the dispersed state of such magnetic domains (whether it is one integrated magnetic domain or a plurality of magnetic domains). ) Is not specified, and there is no method for quantitatively obtaining them.

Based on this situation, the inventors of the present application examined the quantification of the magnetic domain structure from the following viewpoints.

The crystal structure of grain-oriented electrical steel sheets is composed of crystal grains that are relatively large and have highly aligned crystal orientations. Each crystal grain can be regarded as a single crystal, and most of its magnetic domain structure is occupied by a 180 ° magnetic domain structure, which is a simple magnetic domain structure. Under such circumstances, a reflux magnetic domain, which is a relatively complicated magnetic domain structure, tends to occur near the grain boundaries, and the amount of magnetization rotation corresponds to the angle formed by the 180 ° magnetic domain and the RD (rolling direction) axis. That is, in order to suppress the reflux magnetic domain, it is conceivable to simply increase the crystal grain size to reduce the abundance ratio of the grain boundary region, and in order to suppress the amount of magnetization rotation, the 180 ° magnetic domain and RD The axes may be parallel. However, if the crystal grain size is simply increased, the change in crystal orientation at the grain boundaries becomes large due to the continuous change in orientation due to the coil set or the like, so that the generation of recirculated magnetic domains in the region near the grain boundaries increases. On the contrary, it also increases the noise in a high magnetic field.

Upon observing the magnetic domains in more detail, it was noticed that there are grain boundaries in which reflux magnetic domains are likely to be generated and grain boundaries in which reflux magnetic domains are hardly generated. This is due to various factors such as grain boundary morphology, orientation relationship, precipitates, surface texture, strain, etc., even if there are grain boundaries, that is, even if there are discontinuous changes in crystal orientation, the magnetic domain has a morphology. It shows that it may be possible to exist continuously while maintaining it.

As a result of examining various steel sheet production conditions from this viewpoint, it was obtained that the crystal structure can be controlled so that the grain boundaries in which the formation of reflux magnetic domains is suppressed are dominant under specific production conditions. Further, the means for quantifying the magnetic domain structure was examined, and the correlation with noise in the high magnetic field region of the iron core manufactured by the thin steel plate to be controlled in the present invention is very high, which is a preferable range for reducing the noise. The analysis method and analysis system that can identify the above have been determined.

The present invention has been made in view of the above problems, and is a magnetic domain structure of a grain-oriented electrical steel sheet and a grain-oriented electrical steel sheet that enables the production of an iron core having improved noise in a high magnetic field region (magnetic field of about 1.9 T). It is an object of the present invention to provide an analysis method and an analysis system of the above.

The directional electromagnetic steel plate according to the embodiment of the present invention has a mass% of Si: 2.0 to 7.0%, Nb: 0 to 0.030%, V: 0 to 0.030%, Mo: 0 to 0. 0.030%, Ta: 0 to 0.030%, W: 0 to 0.030%, C: 0 to 0.0050%, Mn: 0 to 1.0%, S: 0 to 0.0150%, Se: 0 to 0.0150%, Al: 0 to 0.0650%, N: 0 to 0.0050%, Cu: 0 to 0.40%, Bi: 0 to 0.010%, B: 0 to 0 .080%, P: 0 to 0.50%, Ti: 0 to 0.0150%, Sn: 0 to 0.10%, Sb: 0 to 0.10%, Cr: 0 to 0.30%, Ni : 0 to 1.0%, the balance has a chemical composition of Fe and impurities, has a texture oriented in the Goss orientation, and is the average of the same magnetic region angle regions derived by a predetermined method. The diameter is 5.0 mm or more. The predetermined method for deriving the same magnetic domain angle region is a) from the magnetic domain image of the directional electromagnetic steel plate binarized by two kinds of colors or represented by three or more gradations to multiple positions in the magnetic domain image. A plurality of corresponding subregions are cut out, b) a plurality of partial Fourier images are obtained by performing a two-dimensional Fourier transformation on each of the plurality of subregions, and c) a peak of each spot of the plurality of partial Fourier images. Based on the position, the spatial distribution of the angle of the 180 ° magnetic domain of the directional electromagnetic steel plate is derived, and d) Based on the spatial distribution of the angle of the 180 ° magnetic domain, the angle of the 180 ° magnetic domain in the magnetic domain image is within a predetermined range. The continuous regions in are derived as the same magnetic domain angle region.

The method for analyzing the magnetic domain structure of the directional electromagnetic steel sheet according to the embodiment of the present invention is as follows: a) From the magnetic domain image of the directional electromagnetic steel sheet binarized by two kinds of colors or expressed in three or more gradations. A step of cutting out a plurality of subregions corresponding to a plurality of positions of a magnetic domain image, b) a step of obtaining a plurality of partial Fourier images by performing a two-dimensional Fourier transform on each of the plurality of subregions, and c). Steps to derive the spatial distribution of the 180 ° magnetic domain angle of the directional electromagnetic steel plate based on the peak position of each spot in the multiple partial Fourier images, and d) the magnetic domain image based on the spatial distribution of the 180 ° magnetic domain angle. Among them, a step of deriving a continuous region in which the angle of the 180 ° magnetic domain is within a predetermined range as the same magnetic domain angle region is provided.

The analysis system for the magnetic domain structure of a directional electromagnetic steel plate according to an embodiment of the present invention is a magnetic domain image from a magnetic domain image of a directional electromagnetic steel plate that is binarized by two kinds of colors or expressed in three or more gradations. A plurality of partial regions corresponding to a plurality of positions of the above are cut out, and a plurality of partial Fourier images are obtained by performing a two-dimensional Fourier transformation on each of the plurality of partial regions, and each spot of the plurality of partial Fourier images is obtained. Based on the peak position, the spatial distribution of the angle of the 180 ° magnetic domain of the directional electromagnetic steel plate is derived, and based on the spatial distribution of the angle of the 180 ° magnetic domain, the angle of the 180 ° magnetic domain in the magnetic domain image is within a predetermined range. It includes a calculation unit that derives a continuous region as the same magnetic domain angle region.

In the present specification, the "180 ° magnetic domain" represents a magnetic domain sandwiched between two 180 ° domain walls whose magnetization direction is the <100> orientation of the crystal and which is substantially parallel to the rolling direction.
The "angle" of the 180 ° magnetic domain represents the orientation of the 180 ° magnetic domain with respect to the reference magnetization direction. Generally, in the case of grain-oriented electrical steel sheets, the reference magnetization direction is parallel to the RD (rolling direction).

According to the present invention, by cutting out a partial region for each position from the magnetic domain image of the grain-oriented electrical steel sheet and performing a two-dimensional Fourier transform, a continuous region in which the angle of the 180 ° magnetic domain is within a predetermined range and its position can be obtained. It is possible to identify the grain-oriented electrical steel sheet by a quantitative derivation method, reduce the noise in the high magnetic field region of the transformer core, and preferably control the noise characteristics.

It is a block diagram which shows the structure of the analysis system which concerns on embodiment of this invention. It is a block diagram which shows the hardware configuration of the image acquisition apparatus of FIG. It is a block diagram which shows the hardware configuration of the analysis apparatus of FIG. It is a schematic diagram explaining the method of cutting out a plurality of partial regions from a magnetic domain image. This is an example of a plurality of partial Fourier images obtained by applying a two-dimensional Fourier transform to each of the plurality of partial regions cut out from the magnetic domain image. It is an example of an image of a nearly uniform magnetic domain without grain boundaries and an image of a non-uniform magnetic domain with grain boundaries. It is a graph which shows the spatial distribution of the angle of the 180 ° magnetic domain derived by using the short-section two-dimensional Fourier transform (ST2DFT) for each of the two magnetic domain images shown in FIG. It is a table which compares the analysis result of the magnetic domain structure by the line segment method and the analysis result of the magnetic domain structure by ST2DFT for each of the two magnetic domain images shown in FIG. It is a flow chart which illustrates the manufacturing method of the grain-oriented electrical steel sheet which concerns on this embodiment.

A preferred embodiment of the present invention will be described in detail. However, the present invention is not limited to the configuration disclosed in the present embodiment, and various modifications can be made without departing from the spirit of the present invention. In addition, the numerical limitation range described below includes a lower limit value and an upper limit value. Numerical values that indicate "greater than" or "less than" are not included in the numerical range. Further, "%" regarding the chemical composition means "mass%" unless otherwise specified.

(1) Chemical composition of grain-oriented electrical steel sheet First, the chemical composition of grain-oriented electrical steel sheet according to the present embodiment will be described. The grain-oriented electrical steel sheet of the present embodiment contains a basic element as a chemical composition, and if necessary, a selective element, and the balance is composed of Fe and impurities.

The grain-oriented electrical steel sheet according to the present embodiment contains Si (silicon): 2.00% to 7.00% as a basic element (main alloy element) in terms of mass fraction.

The content of Si is preferably 2.0 to 7.0% in order to accumulate the crystal orientation in the {110} <001> orientation.

In the present embodiment, impurities may be contained as the chemical composition. The term "impurity" refers to an element mixed from ore or scrap as a raw material, or from the manufacturing environment, etc., when steel is industrially manufactured. The upper limit of the total content of impurities may be, for example, 5%.

Further, in the present embodiment, a selective element may be contained in addition to the above-mentioned basic elements and impurities. For example, instead of a part of Fe which is the balance described above, C, Mn, S, Se, Al, N, Cu, Bi, B, P, Ti, Sn, Sb, Cr, Ni, Nb are used as selective elements. , V, Mo, Ta, W and the like may be contained.

C (carbon): 0 to 0.0050%
Mn (manganese): 0 to 1.0%
S (sulfur): 0 to 0.0150%
Se (selenium): 0 to 0.0150%
Al (acid-soluble aluminum): 0 to 0.0650%
N (nitrogen): 0 to 0.0050%
Cu (copper): 0 to 0.40%
Bi (bismuth): 0 to 0.010%
B (boron): 0 to 0.080%
P (phosphorus): 0 to 0.50%
Ti (titanium): 0 to 0.0150%
Sn (tin): 0 to 0.10%
Sb (antimony): 0 to 0.10%
Cr (chromium): 0 to 0.30%
Ni (nickel): 0 to 1.0%
Nb (niobium): 0 to 0.030%
V (vanadium): 0 to 0.030%
Mo (molybdenum): 0 to 0.030%
Ta (tantalum): 0 to 0.030%
W (tungsten): 0 to 0.030%
These selective elements may be contained according to a known purpose. It is not necessary to set the lower limit of the content of these selective elements, and the lower limit may be 0%. Further, even if these selective elements are contained as impurities, the above effect is not impaired.

In the grain-oriented electrical steel sheet, a relatively large change in chemical composition (decrease in content) occurs due to undergoing decarburization annealing and purification annealing during secondary recrystallization in the manufacturing process. Depending on the element, purification annealing may reduce the content to a level (1 ppm or less) that cannot be detected by a general analytical method. The chemical composition of the grain-oriented electrical steel sheet is the chemical composition of the final product. In general, the chemical composition of the final product of the directional electromagnetic steel plate is different from the chemical composition of the slab, which will be described later, which is the starting material, but basically the elements contained in the slab remain, and the slab composition and Adjusted according to manufacturing conditions.

The chemical composition of grain-oriented electrical steel sheets may be measured by a general method for analyzing steel. For example, the chemical composition of grain-oriented electrical steel sheets may be measured using Inductively Coupled Plasma-Atomic Emission Spectrometry (ICP-AES). Specifically, a 35 mm square test piece collected from a grain-oriented electrical steel sheet is measured with an ICPS-8100 or the like (measuring device) manufactured by Shimadzu Corporation under conditions based on a calibration curve prepared in advance to obtain a chemical composition. Be identified. C and S may be measured by using the combustion-infrared absorption method, and N may be measured by using the inert gas melting-thermal conductivity method.

The above chemical composition is a component of grain-oriented electrical steel sheets. If the grain-oriented electrical steel sheet to be the measurement sample has an intermediate layer made of oxides or the like, an insulating coating, or the like on the surface, the chemical composition is measured after removing these by the following method.

For example, as a method for removing the insulating coating, a grain-oriented electrical steel sheet having a coating may be immersed in a high-temperature alkaline solution. Specifically, NaOH: 30 to 50 _wt% + H 2 O: the 50 to 70% by weight aqueous sodium hydroxide, for 5-10 min at 80-90 ° C., after immersion, and dried by washing with water, The insulating coating can be removed from the grain-oriented electrical steel sheet. The time of immersion in the above sodium hydroxide aqueous solution may be changed according to the thickness of the insulating coating.

Further, for example, as a method for removing the intermediate layer, an electromagnetic steel sheet from which the insulating film has been removed may be immersed in high-temperature hydrochloric acid. Specifically, the concentration of hydrochloric acid preferable for removing the intermediate layer to be dissolved is examined in advance, and the mixture is immersed in hydrochloric acid having this concentration, for example, 30 to 40% by mass of hydrochloric acid at 80 to 90 ° C. for 1 to 5 minutes. The intermediate layer can be removed by washing with water and drying. Normally, an alkaline solution is used to remove the insulating film, and hydrochloric acid is used to remove the intermediate layer, so that each treatment liquid is used properly to remove each film.

(2) Magnetic domain structure of grain-oriented electrical steel sheet As described above, the magnetic domain structure defined by grain-oriented electrical steel sheet has not been sufficiently quantified so as to be able to identify a special steel sheet. Therefore, in the following, first, the magnetic domain structure quantification method used in the present embodiment will be described (see (2-1) below), and then the validity of the quantification parameters obtained by the quantification method will be described. It will be verified (see (2-2) below), and the specifications of the directional electromagnetic steel plate based on the quantification method (see (2-3) below) will be described.

(2-1) Method for Quantifying Magnetic Domain Structure of Electrical Steel Sheets Hereinafter, a method for quantifying the magnetic domain structure used in the embodiment of the present invention will be described with reference to the drawings.

<System configuration>
First, the configuration of a system that realizes the magnetic domain structure quantification method (analysis method) according to the present embodiment will be described.

FIG. 1 shows the configuration of the analysis system 100 according to the present embodiment. The analysis system 100 is a system for analyzing the magnetic domain structure of a directional electromagnetic steel plate, and as shown in FIG. 1, includes an image acquisition device 20 and an analysis device 30, and the image acquisition device 20 and the analysis device 30 have a cable. Connected via.

As shown in FIG. 2, the image acquisition device 20 includes a light source unit 21, a magneto-optical (MO) sensor 23, an image sensor 25, and a signal processing unit 27.

The light source unit 21 has a light source composed of a light emitting diode (LED), and irradiates the MO sensor 23 with light having a uniform polarization plane.

The MO sensor 23 is a device for measuring the structure of a magnetic material such as a grain-oriented electrical steel sheet, and has an observation surface on which a magnetic material sample to be measured is placed. The light emitted from the light source unit 21 passes through the inside of the MO sensor 23 and is reflected by the reflection layer, and the reflected light passes through the inside of the MO sensor 23 again and is output to the outside of the MO sensor 23. When a grain-oriented electrical steel sheet as a magnetic sample is placed on the observation surface of the MO sensor 23, a leakage magnetic field is generated inside the MO sensor 23 according to the direction of spontaneous magnetization of the grain-oriented electrical steel sheet. The leakage magnetic field rotates the plane of polarization of the reflected light.

The image sensor 25 is a Complementary Metal-Oxide-Semiconductor (CMOS) image sensor, in which the reflected light from the MO sensor 23 is imaged on the light receiving surface and photoelectrically converted, and the analog signal after the photoelectric conversion is sent to the signal processing unit 27. Output. By detecting the reflected light with the rotated polarizing surface with the image sensor 25, the spatial distribution of the leakage magnetic field can be obtained as described later, and the magnetic domain structure of the grain-oriented electrical steel sheet becomes clear.

The signal processing unit 27 includes an amplifier, an AD converter, a digital signal processor (DSP), and the like. The analog signal output from the image sensor 25 is amplified by the amplifier and converted into a digital signal by the AD converter. An image signal is generated by subjecting the digital signal to a predetermined digital process by the DSP. The image signal generated by the signal processing unit 27 is output to the analysis device 30 via the connector.

The analysis device 30 is a computer device such as a personal computer (PC), and has a calculation unit 31, a memory 33, a display unit 35, an input unit 37, and a communication I / F 39, as shown in FIG. ..

The arithmetic unit 31 has a Central Processing Unit (CPU) and executes a method of analyzing the magnetic domain structure according to a program stored in the memory 33. Details of the magnetic domain structure analysis method executed by the calculation unit 31 will be described later.

The memory 33 has a Read Only Memory (ROM) and a Random Access Memory (RAM). The ROM stores programs executed by the CPU of the arithmetic unit 31 and data necessary for executing these programs. The programs and data stored in the ROM are loaded into the RAM and executed.

The memory 33 may have a magnetic memory such as a hard disk drive (HDD) or an optical memory such as an optical disk. Alternatively, the program or data may be stored in a computer-readable recording medium that can be attached to and detached from the analysis device 30. Alternatively, the program executed by the arithmetic unit 31 may be received from the network via the communication I / F 39.

The display unit 35 has a display such as a liquid crystal display (LCD), a plasma display, or an organic electroluminescence (EL) display, displays an image based on an image signal output from the image acquisition device 20, and also displays an image. The analysis result of the magnetic zone structure by the calculation unit 31 is displayed.

The input unit 37 has an input device such as a mouse and a keyboard.
The communication I / F 39 is an interface for transmitting / receiving data to / from an external device via a network such as a Local Area Network (LAN), Wide Area Network (WAN), or the Internet.

In addition, as the arithmetic unit 31, instead of general-purpose hardware such as a CPU, dedicated hardware such as Application Specific Integrated Circuit (ASIC) or Field Programmable Gate Array (FPGA) specialized in magnetic domain structure analysis is adopted. May be good.

Further, the image acquisition device 20 and the analysis device 30 may be connected by wireless communication.
Further, although FIG. 1 shows an example in which the image acquisition device 20 and the analysis device 30 are separately provided, a system in which the image acquisition device 20 and the analysis device 30 are integrated may be adopted.

<Analysis method of magnetic domain structure>
Next, a method of analyzing the magnetic domain structure executed by the calculation unit 31 will be described.
When targeting a magnetic material having a periodic magnetic domain structure such as a grain-oriented electrical steel sheet, it is effective to evaluate the magnetic domain structure using a Fourier transform.

Therefore, first, a short-term Fourier transform (hereinafter referred to as "STFT") will be described. The FTFT is a method of analyzing while moving a window function with respect to a data string to be analyzed, and is one of the signal processing methods that have been used for a long time for time / frequency analysis of audio signals.

In the FTFT, in order to divide the discrete signal data sequence x (k) into short intervals and analyze its frequency structure, a window function Wa (k) in the range of 0 ≦ k ≦ N-1 (N is a natural number) is used. Use. As the window function Wa (k), a Hamming window, a Hanning window, a Blackman window, or the like can be applied.

ここで、ｎ（整数）はデータ列のインデックスを表し、Ｓ（整数）は窓関数のシフト量を表す。 In the FTFT, as represented by the equation (1), by shifting the window function Wa (k) by nS and multiplying it by the discrete signal data string x (k), nS ≦ k ≦ nS + N− from x (k). _{A data string x n} (knS) obtained by cutting out a section of 1.

Here, n (integer) represents the index of the data string, and S (integer) represents the shift amount of the window function.

ここで、ｆは空間周波数である。 Is defined as _{x n (n') = x n} (k-nS) against the cut out section, by performing discrete Fourier transform of Equation (2) (DFT), frequency spectrum corresponding to the data position nS Is obtained.

Here, f is a spatial frequency.

In the present embodiment, as described below, the magnetic zone structure of the directional electromagnetic steel plate is analyzed by using a short-time two-dimensional Fourier transform (hereinafter, referred to as “ST2DFT”) in which the STFT is extended to a two-dimensional region. ..

In the following, the image represented by the image signal acquired by the image acquisition device 20 (hereinafter referred to as a magnetic domain image) is referred to as x (k, l) as a data string of two-dimensional coordinates (kl coordinates). The magnetic domain image to be analyzed in the present embodiment is an image binarized by two kinds of colors such as gray scale, or an image represented by three or more gradations (multi-gradation).

In order to analyze the magnetic domain structure of the grain-oriented electrical steel sheet according to the present embodiment, the calculation unit 31 performs the following steps (A-1), (A-2), (A-3) and (A-4). Run.
(A-1) Step of cutting out a plurality of partial regions from a magnetic domain image;
(A-2) Step of performing ST2DFT;
(A-3) Step of deriving the spatial distribution of the angle of the 180 ° magnetic domain;
(A-4) Step of deriving the same magnetic domain angle region.
Hereinafter, each step will be described in detail.

(A-1) Step of cutting out a plurality of subregions from a magnetic domain image In order to cut out a plurality of subregions from a magnetic domain image and analyze each frequency structure, the range in the k direction is set to 0 ≦ k ≦ N _k -1, The window function Wa (k, l) of a rectangular window with the range in the l direction set to 0 ≦ l ≦ N _{l -1 is used (N k} and N _l are natural numbers). As the window function Wa (k, l), a Hamming window, a Hanning window, a Blackman window, or the like can be applied.

Data sequence x (k, l) of the magnetic domain image observation position in the notation the index (n, m), window function Wa (k, l) in the k direction and l directions and the shift amounts respectively S _k and S _l for Notation (n, m, _Sk , S _l are integers), as shown in equation (3), nS _k ≤ k ≤ nS _k + N _k -1, mS _l ≤ l ≤ mS _l + N _l -1 from the magnetic area image. _{The data sequence x nm} (knS _k , l-mS _l ) of the partial region obtained by cutting out the range of is obtained.

In FIG. 4, from the magnetic domain image G, the observation positions (n, m) = (1,1), (2,2), (3,3), ..., (P, Q) (P and Q are natural numbers). An example is shown in which the subregions corresponding to each are cut out.

_{In the present embodiment, N k} and N _l that define the range of the window function Wa (k, l) are parameters corresponding to the number of pixels in the k direction and the number of pixels in the l direction in the partial region, respectively.

ここで、ｆ_ｋ及びｆ_ｌは空間周波数である。空間周波数ｆ_ｋの分解能をΔｆ_ｋ、空間周波数ｆ_ｌの分解能をΔｆ_ｌと表記すると、それぞれ、式（５）及び式（６）のように定義される。

ここで、Δｋ及びΔｌは、それぞれ、磁区画像におけるｋ方向の空間分解能及びｌ方向における空間分解能である。 (A-2) Step for performing ST2DFT The data string of the partial region is defined as x _nm (n', m') = x _nm (k-nS _k , l-mS _l ), and x _nm (n', m'). _{) Is subjected to a two-dimensional Fourier transform to obtain a partial Fourier image X (f k} , f _l , n, m) corresponding to the partial region of the observation position (n, m) as shown in equation (4). Be done.

Here, f _k and f _l are spatial frequencies. Resolution Delta] f _k of the spatial frequency _{f k,} if the resolution of the spatial frequency _{f l} is expressed as Delta] f _l, respectively, is defined by the equation (5) and (6).

Here, Δk and Δl are the spatial resolution in the k direction and the spatial resolution in the l direction in the magnetic domain image, respectively.

_{For example, when a two-dimensional Fourier transform is applied to the data string x nm} (knS _k , l-mS _l ) of each subregion shown in FIG. 4, the observation position (n, m) is shown in FIG. ), A partial Fourier image X (f _k , f _l , n, m) is obtained.

(A-3) Step for deriving the spatial distribution of the angle of the 180 ° magnetic domain When the partial Fourier image X (f _k , f _l , n, m) is obtained, the partial Fourier image X (f _k , f _l , n, n,) is obtained. The coordinates of the peak position of the spot of m) (k component f _k ^max (n, m) and l component f _l ^max (n, m)) are obtained.

Then, from the resolution of the spatial frequency defined in the equations (5) and (6) and the peak position of the spot in the partial Fourier image, the spatial distribution θ (n) of the angle of the 180 ° magnetic domain is obtained as in the equation (7). , M) is derived.

(A-4) Step of Deriving the Same Magnetic Domain Angle Region Next, 180 of the magnetic domain image G is obtained based on the spatial distribution θ (n, m) of the angle of the 180 ° magnetic domain obtained in step (A-3). ° Consecutive regions where the magnetic domain angles are within a predetermined range are derived as the same magnetic domain angle region. The range of magnetic domain angles that defines the same magnetic domain angle region will be described later.

As described above, according to the method for analyzing the magnetic domain structure of the present embodiment, by using the short-section two-dimensional Fourier transform (ST2DFT), the spatial distribution of the angle of the 180 ° magnetic domain is maintained while maintaining the position information of the magnetic domain image. θ (n, m) is quantitatively derived, and the angle of the 180 ° magnetic domain in the magnetic domain image G is within a predetermined range based on the spatial distribution θ (n, m) of the angle of the 180 ° magnetic domain. A continuous region is derived as the same magnetic domain angle region. As a result, the same magnetic domain angle region and its position (n, m) can be quantitatively obtained, and can be used as a guideline for controlling the iron loss of the grain-oriented electrical steel sheet.
(2-2) Validity of quantification parameters of magnetic domain structure

Next, using the analysis system 100, the two types of magnetic domain structures (i) and (ii) of the directional electromagnetic steel plate are analyzed as follows, and the effectiveness (validity) of the quantitative derivation method by ST2DFT. Is verified in comparison with the conventional line segment method.
(I) Almost uniform magnetic domain structure without grain boundaries;
(Ii) Non-uniform magnetic domain structure with grain boundaries.

It is assumed that the size of the observation surface of the MO sensor 23 is 55.68 mm × 40.37 mm, and the spatial distribution of the leakage magnetic field in this region can be acquired at 3200pixel × 2320pixel. In this case, the spatial resolution of the magnetic domain image is Δk = Δl = 17.4 μm.

The magnetic domain image obtained by the image acquisition device 20 is 3200pixel × 2320pixel, but in the present embodiment, in order to clarify the analysis results in (i) and (ii), trimming is performed in the range of 512pixel × 512pixel. rice field.

FIG. 6 shows an example of the magnetic domain image D00 corresponding to (i) and the magnetic domain image D01 corresponding to (ii) obtained from the image acquisition device 20. In FIG. 6, “RD” represents the rolling direction of the grain-oriented electrical steel sheet. The magnetic domain image D00 has a substantially uniform magnetic domain structure, but the magnetic domain image D01 includes grain boundaries in the center of the image, so that the magnetic domain structure is significantly different between the upper part and the lower part of the image.

In the conventional method, three line segments parallel to the magnetic domain were drawn with respect to the magnetic domain structure obtained from the magnetic domain image D00, and the angle of the 95% confidence interval was obtained from the angle of the line segment by the line segment method. In addition, the width of the 180 ° magnetic domain representing the distance between adjacent domain walls (domain wall spacing) was also derived. Regarding the width of the 180 ° magnetic domain, three line segments parallel to the magnetic domain were drawn in the same manner, and the width of the 180 ° magnetic domain (average magnetic domain width) in the 95% confidence interval was derived by the line segment method. Regarding the magnetic domain structure of the magnetic domain image D01, the same measurement as in the magnetic domain image D00 was performed for each magnetic domain region, and the average magnetic domain width and angle were derived for each magnetic domain.

The average magnetic domain width and angle of the 180 ° magnetic domain derived from the magnetic domain image D00 by the line segment method were 175 μm to 189 μm and 0.13 ° to 1.5 °, respectively. Similarly, when the line segment method is used for the magnetic domain image D01, the average magnetic domain width and angle of the 180 ° magnetic domain at the upper part of the image are 131 μm to 138 μm and 10.6 ° to 12.5 °, respectively, and the lower part of the image is The average magnetic domain width and angle of the 180 ° magnetic domain were 243 μm to 249 μm and 0.63 ° to 1.7 °, respectively.

On the other hand, in ST2DFT, the parameters were set as follows:
Spatial resolution: Δk = Δl = 17.4 μm;
Size of partial area cut out from magnetic domain image: N _k = N _l = 64;
Window function shift amount: _Sk = S _l = 1.
Here, the size of the partial region to be cut out from the magnetic domain image cannot be analyzed unless the cut out partial region includes a 180 ° magnetic domain of at least one cycle or more, so N _k = N _l = 64. bottom.

FIG. 7 shows the spatial distribution θ (n, m) of the angle of the 180 ° magnetic domain for each of the magnetic domain images D00 and D01. From θ (n, m) of the magnetic domain image D01 shown in FIG. 7, it can be seen that the grain boundary portion can be clearly distinguished even in the magnetic domain including the grain boundary.

Further, as shown in FIG. 7, the relationship between the angle (deg) and the position (n, m) of the 180 ° magnetic domain can be mapped by the magnetic domain structure analysis method using ST2DFT, so that the same magnetic domain angle region can be mapped. And its position (n, m) can be easily derived.

FIG. 8 shows the result of comparing the analysis result of the magnetic domain structure by the line segment method and the analysis result of the magnetic domain structure by ST2DFT (FIG. 7).

In FIG. 8, the upper part of the magnetic domain image D01 shows a region having an m coordinate larger than 200, and the lower part of the magnetic domain image D01 shows a region having an m coordinate of 0 to 200. The analysis result by ST2DFT in FIG. 8 shows the width (denoted as “magnetic domain width” in FIG. 8) and the angle of the 180 ° magnetic domain at the observation position (n, m) = (200,200) for the magnetic domain image D00. The upper part of the magnetic domain image D01 shows the width and angle of the magnetic domain at the observation position (n, m) = (200,350), and the lower part of the magnetic domain image D01 shows the observation position (n, m) = (200,350). The magnetic domain width and angle in 100) are shown.

From FIG. 8, similar results are observed in both the line segment method and ST2DFT for the angle of the 180 ° magnetic domain, but the line segment method has higher angle resolution. This is due to the tendency that n and m assigned to the equation (7) are integers and tend to be values near the origin when calculating the angle. Assuming that the width of the 180 ° magnetic domain is 135 μm, the angular resolution is about ± 6 °, which is very coarse compared to the actual angular change of the magnetic domain. In order to solve this problem, it is effective to assume the distribution and interpolate when acquiring the peak position of the partial Fourier image, or to take the center of gravity in consideration of the intensity of the adjacent Fourier spots. it is conceivable that. Since the peak position can be continuously acquired by this method, it is possible to improve the resolution of the angle of the 180 ° magnetic domain.
Since there is a problem of resolution as described above, the derivation of the peak position in the present embodiment is performed by obtaining the spot positions (however, excluding the origin) and the intensities of 10 points having high intensities in the partial Fourier image, and determining the intensities. Derived by finding the center of gravity in consideration of the position.

As described above, the analysis result of the magnetic domain structure by ST2DFT is good as compared with the line segment method which is the conventional method, and it can be seen that the quantitative derivation method of the angle of the 180 ° magnetic domain by ST2DFT is effective.

(2-3) Definition of grain-oriented electrical steel sheet Next, the analysis result of the magnetic domain structure by ST2DFT, that is, the same magnetic domain angle region which is a continuous region in which the angle of 180 ° magnetic domain is within a predetermined range is defined. The same magnetic domain angle region is a region in which the magnetic domain angles can be regarded as substantially the same even if the regions are generally judged to be different crystal grains, and is recognized as a concept such as a "colony" regarding the crystal orientation. be able to.

The same magnetic domain angle region changes depending on how large the observation region is, how large the partial Fourier image is divided, how to determine the angles to be regarded as the same, and the like. In the present embodiment, the realistic magnetic domain size, crystal grain size, and the strength of correlation with the magnetic characteristics are taken into consideration and defined as follows.

(2-3-1) Observation area The size of the observation area to be measured in the magnetic domain image is 500 mm × 500 mm. This size is generally based on the size of the sample when the magnetic property is measured based on the single sheet tester (SST) specified in JIS C 2556: 2015. Further, the k direction is parallel to the rolling perpendicular direction (TD direction), and the l direction is parallel to the RD direction for observation.

(2-3-2) Size of Fourier image A steel plate having a size of an observation area of 500 mm × 500 mm is set so that the spatial resolution per pixel of the magnetic domain image is 25 μm or less, and is acquired in gray scale. The acquired magnetic domain image is represented by continuous 256 gradations including black and white. In the subsequent numerical processing, black is treated as a value of 0 and white is treated as a value of 255 (dimensionless quantity). If it is difficult to observe the measurement range in one measurement, the magnetic domain images measured a plurality of times may be combined and treated as one magnetic domain image. At that time, it is natural to adjust the observation position and observe so that the joints between the images do not become inconsistent.

(2-3-3) Since the magnetic domain structure of the sample to be observed is easily affected by strain, etc., the above-mentioned observation region is an region such as the end of the steel plate and the end of the observation sample, which is hardly affected by strain due to handling of the steel plate and cutting out the sample. It is natural to choose. Further, the magnetic domain image of the present embodiment shall be observed in a pre-demagnetized state by a method of exciting with a magnetic field of 1.9 T or more at 50 Hz and then gradually reducing the magnetic field. ..

(2-3-4) Size of partial Fourier image The size of the partial Fourier image is 2 mm × 2 mm. This size is large enough to include at least one 180 ° magnetic domain in the partial region. The shift amount of the window function is 25 μm or less.

(2-3-5) Magnetic domain angle regarded as the same magnetic domain angle region The magnetic domain angle obtained for a partial region is divided into three areas from 0 deg to less than 1 deg, 1 deg or more to less than 5 deg, and 5 deg or more, and adjacent partial regions are formed. When they are in the same area, it is determined that the magnetic domain angles are continuous, that is, they are in one same magnetic domain angle area. In the present embodiment, whether or not the adjacent subregions are in one same magnetic domain angle region does not depend on the difference in the magnetic domain angles from the adjacent subregions. For example, a partial region having a magnetic domain angle of 0.0 deg and a partial region having a magnetic domain angle of 0.9 deg form a continuous same magnetic domain angle region, but a partial region having a magnetic domain angle of 0.9 deg and a partial region having a magnetic domain angle of 1.1 deg are formed. Although the difference in magnetic domain angles is 0.2 deg, they are not continuous, and this boundary is the boundary of the same magnetic domain angle region.

The reason why the sections of the area are discontinuous is that the grain-oriented electrical steel sheets are highly integrated in the Goss direction, so that the orientation change is 0.5 deg in the region from 0 deg to less than 1 deg and 0 in the region of 5 deg or more. The effect of the directional change of .5 deg on the magnetic characteristics is significantly different. In particular, since the change in angle in the region from 0 deg to less than 1 deg has the greatest effect on the magnetic characteristics, the interval is shortened as it is closer to 0 deg.

It should be noted that the boundary of the same magnetic domain angle region is basically determined as described above, but in an actual steel plate, measurement due to a reflux magnetic domain generated in the 180 ° magnetic domain, scratches on the surface of the steel plate, etc. It is observed that a minute magnetic domain angle region exists inside a large magnetic domain angle region due to noise or the like at the time of measurement. The minute region observed in this way becomes a disturbance factor in the evaluation of the average diameter of the same magnetic domain angle region to be controlled in the present embodiment for the purpose of improving noise, and is found in the high magnetic field region of the present embodiment. The correlation between noise and the average diameter in the same magnetic domain angle region is significantly reduced. Therefore, in the present embodiment ^{, the region having an area of 10.0 mm 2} or less in the above operation is treated as if there is no boundary surrounding the region. That is, the ^{region observed in an area of 10.0 mm 2} or less is treated as the same magnetic domain angle region as the surrounding region, and in the derivation of the average diameter described below, "the same magnetic domain angle existing in the observation region" is used. It is not counted as "the number of regions".

(2-3-6) Average diameter of the same magnetic domain angle region The average diameter of the same magnetic domain angle region is the equivalent circle diameter of the same magnetic domain angle region in the observation region. That is, by (the area of the observation region) / (number of the same domain angular region present in the observation area) to determine the average same domain angular region area S _A, the average of the same domain angular region d to be S A ₌ πd ² The diameter. At this time, with respect to the same magnetic domain angle region tangent to the outermost boundary of the observation region, it is considered that the colonies are connected to the outside of the observation region in a mirror-symmetrical manner, and the number is calculated as "0.5".

In the present embodiment, the average diameter of the same magnetic domain angle region is 5.0 mm or more. As a result, the elongation magnetostriction in the high magnetic field region is efficiently suppressed, and the noise due to the out-of-plane vibration of the steel sheet is remarkably reduced. It is preferably 8.0 mm or more, more preferably 10.0 mm or more. The upper limit of the average diameter of the same magnetic domain angle region is not particularly limited, and from the viewpoint of exerting the effect of the present embodiment, the larger the average diameter of the same magnetic domain angle region is, the more preferable. For example, it is technically ideal that the entire steel sheet manufactured by the coil is recognized as a single magnetic domain angle region. However, in the current practical grain-oriented electrical steel sheet having a crystal grain size of only about 100 mm, it is not realistic that the entire coil having a width of several 100 mm and a length of several 100 m or more becomes a single magnetic domain angle region. It is also clear. The practical maximum diameter of the same magnetic domain angle region in the grain-oriented electrical steel sheet manufactured by the current manufacturing process is about 500 mm and further about 300 mm. In the present embodiment, the observation region is set to 500 mm × 500 mm in consideration of the realistic maximum diameter of the same magnetic domain angle region.

The reason why the noise caused by the out-of-plane vibration of the steel sheet is suppressed when the same magnetic domain angle region becomes large is not clear, but it is estimated as follows. Reflux magnetic domains are likely to occur in regions where the atomic arrangement in the crystal is disturbed. The grain boundaries, which are regions where the atomic arrangement is disturbed in the crystal structure of the directional electromagnetic steel plate, are regions where recirculation magnetic domains are likely to occur, but the frequency of occurrence is orientation change, element segregation, and strain accumulation across the crystal grain boundaries. Furthermore, it is affected by the surface texture of the steel plate. For this reason, there are crystal grain boundaries where reflux magnetic boundaries are likely to occur and crystal grain boundaries where it is difficult to occur, and even if the crystal grain size is the same (the frequency of existence of crystal grain boundaries is the same), the crystal grain boundaries where reflux magnetic boundaries are unlikely to occur If the abundance ratio is high, the abundance frequency of the recirculated magnetic group decreases. When the reflux magnetic domain is unlikely to occur at the grain boundaries, the 180 ° magnetic domain hardly changes the magnetic domain angle and occupies a continuous space across the grain boundaries. This situation is a situation in which the average diameter of the same magnetic domain angle region defined by the present embodiment is large, and the elongation magnetostriction is suppressed because the presence ratio of the reflux magnetic domain is small, and as a result, it is caused by the out-of-plane vibration of the steel sheet in the high magnetic field region. Noise is reduced. Further, the closer the angle of the 180 ° magnetic domain is to 0 deg, the less likely it is that magnetization rotation will occur when excited to a high magnetic field region. Magnetization rotation is preferably reduced because it causes harmonic components in the magnetostrictive waveform and causes an increase in noise. Therefore, it can be said that it is desirable that the area of the region of 0 to 1 deg is the maximum. Specifically, in the preferred embodiment of the present invention, the area of the region of 0 to 1 deg extends to 70% or more of the total area. In a particularly preferable form, it is as high as 90% or more. However, as mentioned above, the noise caused by the out-of-plane vibration of the steel sheet in the high magnetic field region cannot be suppressed simply by reducing the elongation magnetostriction. It is considered necessary to suppress the noise caused by the out-of-plane vibration of the steel sheet in the high magnetic field region.

The magnetic domain structure obtained by this embodiment acts independently of the coarsening of the crystal grain size. Generally, as the crystal grain size becomes coarser, the same magnetic domain angle region also becomes coarser. However, it is considered that the coarsening of the same magnetic domain angle region in the present embodiment does not necessarily contribute to the suppression of noise caused by the out-of-plane vibration of the steel sheet in the high magnetic field region when it is achieved by the coarsening of the crystal grain size. Be done. It is presumed that this is because the reduction of the reflux magnetic domain due to the difference in crystal orientation with the adjacent crystal grains is insufficient only by coarsening the same magnetic domain angle region by coarsening the crystal grain size. Therefore, coarsening of the same magnetic domain angle region in the present embodiment occurs regardless of the presence or absence of grain boundaries. Ideally, the same magnetic domain angle region exists across the grain boundaries. Therefore, in order to evaluate this ideal state, the effect is evaluated by taking the ratio of the crystal grain size Rc of the grain-oriented electrical steel sheet to the average diameter d in the same magnetic domain angle region as in the equation (8).
d / Rc ≧ 1.1… (8)
Here, Rc is the circle equivalent diameter of the average grain-oriented electrical steel sheet, an average crystal grain area S _B, the Rc of the S B ₌ πRc ² and the crystal grain size. When the above-mentioned crystal grain size Rc has a primary coating (glass coating, intermediate layer) made of an oxide or the like, an insulating coating, or the like on the surface of the mother steel plate, these are removed by a known method. Visually measure from.

Generally, when the magnetic domain angle becomes large, an adverse effect of a decrease in magnetic characteristics (increase in hysteresis loss) cannot be avoided. On the other hand, since the continuous state of the magnetic domain structure across the crystal grain boundaries, which is a feature of the present embodiment, is continuous while maintaining the magnetic domain angle, the magnetic domain angle itself does not increase even if the same magnetic domain angle region becomes coarse. Therefore, the decrease in magnetic characteristics (increase in hysteresis loss) due to the expansion of the magnetic domain angle is essentially not a problem.

As described above, the upper limit of the average diameter of the same magnetic domain angle region is not particularly limited, but an increase in the same magnetic domain angle region leads to a decrease in the frequency of existence of the reflux magnetic domain, and the steel sheet in the high magnetic field region. It is convenient for the reduction of noise caused by the out-of-plane vibration of the magnetic domain. However, the average diameter of the same magnetic domain angle region that can be achieved with a practical steel sheet is about 100 mm, which is a realistic upper limit.

Further, the magnitude of the fluctuation of the magnetic domain angle is defined as follows by the partial region determined as described above.
(2-3-7) Fluctuation of magnetic domain angle The total of the absolute values of the differences in the magnetic domain angles of the adjacent subregions in the observed region and in the l direction parallel to the RD direction is Δθl (deg), and the TD direction. The total sum of the absolute values of the differences in the magnetic domain angles of the adjacent sub-domains in the k direction parallel to is Δθk (deg), and the total sum of the areas of the sub-domains used to derive the same magnetic domain angle region is S (mm). ^{In the case of 2} ), it is preferable that the following formula (9) is satisfied.
(Δθl + Δθk) / S≤1.0degmm ^-2 ... (9)

The value of the formula (9) represents the magnitude of the magnetic domain angle variation per unit area in the l direction, that is, the rolling direction of the steel sheet, and as described above, excluding the influence of the crystal grain size, the magnetic domain structure is continuous. It is an index showing sex. The smaller this value is, the smaller the variation in the magnetic domain angle is, which corresponds to the situation where the generation of the reflux magnetic domain at the boundary of the same magnetic domain angle region is suppressed. The formula (9) is preferably 0.8 degmm ^-2 or less, more preferably 0.6 degmm ^-2 or less. The lower limit of the formula (9) is not particularly limited, and from the viewpoint of exerting the effect of the present embodiment, zero, that is, an observation region of 500 mm × 500 mm is a single same magnetic domain angle region, and further, the same magnetic domain angle. It can be said that it is an ideal state that there is no change in the magnetic domain angle even inside the region. However, it is difficult to achieve such a state in a practical grain-oriented electrical steel sheet, and even inside one crystal grain, the influence of the crystal orientation difference with the adjacent crystal grain, the grain boundary morphology, and the surface roughness It can be said that it is difficult to completely eliminate the fluctuation of the magnetic domain angle caused by the fluctuation of the shape such as the degree. As a practical lower limit value of the formula (9) in the grain ^- oriented electrical steel sheet manufactured by the current manufacturing process, 0.01 degmm-2 and further 0.005 ^degmm-2 can be mentioned.

The "high magnetic field region" in the present specification is used assuming a region of 1.9 T or more as the magnetic field in the grain-oriented electrical steel sheet. However, there is no situation where all parts of the grain-oriented electrical steel sheet used as a material in an actual iron core are 1.9 T or more. In an actual iron core, the magnetic flux is sparse and dense, and it is natural that the magnetic flux density in the portion where the magnetic flux is difficult to pass is less than 1.9 T. Even in consideration of such a situation, the noise caused by the out-of-plane vibration of the steel sheet in the high magnetic field region, which is exhibited as an effect of the present embodiment, is at least a part of the steel sheet in a situation where at least a part of the steel sheet is constrained. Is understood as vibration caused by a dimensional change of the steel sheet when magnetized with a magnetic flux density of 1.9 T or more.

(3) Plate thickness of grain-oriented electrical steel sheet It is described above that the continuous effect of the magnetic domain structure at the grain boundaries expressed in the present embodiment suppresses the deflection of the steel sheet out of the surface due to the magnetization of the steel sheet and suppresses noise. It is a street. Further, as described above, the thinner the steel plate, the easier it is for the steel plate to bend. Therefore, the effect of the present embodiment is likely to be exhibited by the thin steel plate. Strictly speaking, the effect of this embodiment is exhibited even if the plate thickness is thick. Since the noise of interest in this embodiment depends on the degree of restraint of the steel sheet in the in-plane direction including the core design and the core structure, the presence or absence of a practical noise improvement effect depends only on the thickness of the grain-oriented electrical steel sheet. Although it cannot be determined by, the thickness of the grain-oriented electrical steel sheet that exerts a sufficient effect on a general steel core is 0.35 mm or less. The effect of this embodiment is clarified for a steel plate of 0.25 mm or less, and the merit of this embodiment is remarkable for a steel plate of 0.15 mm or less.

(4) Method for manufacturing grain-oriented electrical steel sheet Next, a method for manufacturing grain-oriented electrical steel sheet according to the present embodiment will be described.

FIG. 9 is a flow chart illustrating a method for manufacturing a grain-oriented electrical steel sheet according to the present embodiment. As shown in FIG. 9, the method for manufacturing the directional electromagnetic steel plate (silicon steel plate) according to the present embodiment includes a casting step (S11), a hot rolling step (S12), and a hot rolling plate annealing step (S13). A cold rolling step (S14), a decarburization annealing step (S15), a quenching separator coating step (S16), a finish annealing step (S17), and an insulating film forming step (S21) are provided. Further, if necessary, the nitriding treatment may be performed at an arbitrary timing from the decarburization annealing step to the finish annealing step, and the magnetic domain control step (S22) is further provided at an arbitrary timing after the cold rolling step. May be good.

In order to preferably control the magnetic domain structure, which is a feature of the steel sheet of the present embodiment, it is important to control the tension in the insulating film forming step. For other manufacturing conditions, a conventionally known method for manufacturing grain-oriented electrical steel sheets can be applied. For example, there are a production method using MnS and AlN formed by high temperature slab heating as an inhibitor, and a production method using AlN formed by low temperature slab heating and subsequent nitriding treatment as an inhibitor. The switching, which is a feature of the present embodiment, can be applied to any manufacturing method, and is not limited to a specific manufacturing method. Hereinafter, a manufacturing method to which the nitriding treatment is applied will be described as an example.

(Casting process)
In the casting step (S11), a slab is prepared. An example of a slab manufacturing method is as follows. Manufacture (melt) molten steel. Manufacture slabs using molten steel. The slab may be manufactured by a continuous casting method. An ingot may be produced using molten steel, and the ingot may be lump-rolled to produce a slab. The thickness of the slab is not particularly limited. The thickness of the slab is, for example, 150-350 mm. The thickness of the slab is preferably 220 to 280 mm. As the slab, a so-called thin slab having a thickness of 10 to 70 mm may be used. When a thin slab is used, rough rolling before finish rolling can be omitted in the hot rolling step.

As the chemical composition of the slab, the chemical composition of the slab used in the production of general grain-oriented electrical steel sheets can be used. The chemical composition of the slab contains, for example, the following elements:

C: 0 to 0.0850%
Carbon (C) is an element effective in controlling the primary recrystallization structure in the manufacturing process, but if the C content of the final product is excessive, it adversely affects the magnetic properties. Therefore, the C content of the slab may be 0 to 0.0850%. The preferred upper limit of the C content is 0.0750%. C is purified in the decarburization annealing step and the finish annealing step described later, and becomes 0.0050% or less after the finish annealing step. When C is contained, the lower limit of the C content may be more than 0% or 0.0010% in consideration of productivity in industrial production.

Si: 2.0-7.0%
Silicon (Si) increases the electrical resistance of grain-oriented electrical steel sheets and reduces iron loss. If the Si content is less than 2.0%, austenite transformation occurs during finish annealing, and the crystal orientation of the grain-oriented electrical steel sheet is impaired. On the other hand, if the Si content exceeds 7.0%, the cold workability is lowered and cracks are likely to occur during cold rolling. The lower limit of the Si content is preferably 2.50%, more preferably 3.0%. The preferred upper limit of the Si content is 4.50%, more preferably 4.0%.

Mn: 0. ~ 1.0%
Manganese (Mn) binds to S or Se to produce MnS or MnSe and functions as an inhibitor. The Mn content may be 0 to 1.0%. When Mn is contained, it is preferable that the secondary recrystallization is stable when the Mn content is in the range of 0.05 to 1.0%. In this embodiment, a part of the function of the inhibitor can be carried by the nitride of the Nb group element. In this case, the strength of MnS or MnSe as a general inhibitor is controlled to be weak. Therefore, the preferable upper limit of the Mn content is 0.50%, and more preferably 0.20%.

S: 0 to 0.0350%
Se: 0-0.0350%
Sulfur (S) and selenium (Se) combine with Mn to produce MnS or MnSe, which functions as an inhibitor. The S content may be 0 to 0.0350%, and the Se content may be 0 to 0.0350%. When at least one of S and Se is contained, it is preferable that the total content of S and Se is 0.0030 to 0.0350% because secondary recrystallization is stable. In this embodiment, a part of the function of the inhibitor can be carried by the nitride of the Nb group element. In this case, the strength of MnS or MnSe as a general inhibitor is controlled to be weak. Therefore, the preferable upper limit of the total S and Se contents is 0.0250%, and more preferably 0.010%. When S and Se remain after finish annealing, they form compounds and deteriorate iron loss. Therefore, it is preferable to reduce S and Se as much as possible by purifying during finish annealing.

Here, "the total content of S and Se is 0.0030 to 0.0350%" means that the chemical composition of the slab contains only either S or Se, and either S or Se. One content may be 0.0030 to 0.0350%, the slab contains both S and Se, and the total content of S and Se is 0.0030 to 0.0350%. You may.

Al: 0-0.0650%
Aluminum (Al) binds to N and precipitates as (Al, Si) N, and functions as an inhibitor. The Al content may be 0 to 0.0650%. When Al is contained, when the Al content is in the range of 0.010 to 0.065%, AlN as an inhibitor formed by nitriding described later expands the secondary recrystallization temperature range, particularly. It is preferable because the secondary recrystallization in the high temperature range is stable. The lower limit of the Al content is preferably 0.020%, more preferably 0.0250%. From the viewpoint of stability of secondary recrystallization, the preferable upper limit of the Al content is 0.040%, more preferably 0.030%.

N: 0 to 0.0120%
Nitrogen (N) binds to Al and functions as an inhibitor. The N content may be 0 to 0.0120%. Since N can be contained by nitriding in the middle of the manufacturing process, the lower limit may be 0%. On the other hand, when N is contained, if the N content exceeds 0.0120%, blister, which is a kind of defect, is likely to occur in the steel sheet. The preferred upper limit of the N content is 0.010%, more preferably 0.0090%. N is purified in the finish annealing step and becomes 0.0050% or less after the finish annealing step.

The rest of the chemical composition of the slab consists of Fe and impurities. It should be noted that the "impurity" referred to here is unavoidably mixed from the components contained in the raw materials or the components mixed in the manufacturing process when the slab is industrially manufactured, and substantially affects the effect of the present embodiment. It means an element that does not affect.

Further, the slab may contain a known selective element instead of a part of Fe in consideration of the enhancement of the inhibitor function by compound formation and the influence on the magnetic properties in addition to solving the problems in production. .. Examples of the selection element include the following elements.

Cu: 0-0.40%
Bi: 0-0.010%
B: 0 to 0.080%
P: 0 to 0.50%
Ti: 0 to 0.0150%
Sn: 0 to 0.10%
Sb: 0 to 0.10%
Cr: 0 to 0.30%
Ni: 0-1.0%
Nb: 0 to 0.030%
V: 0 to 0.030%
Mo: 0-0.030%
Ta: 0-0.030%
W: 0 to 0.030%
These selective elements may be contained according to a known purpose. It is not necessary to set the lower limit of the content of these selective elements, and the lower limit may be 0%.

(Hot rolling process)
The hot rolling step (S12) is a step of hot rolling a slab heated to a predetermined temperature (for example, 1100 to 1400 ° C.) to obtain a hot rolled steel sheet. In the hot rolling step, for example, after rough rolling of a silicon steel material (slab) heated after the casting step, finish rolling is performed to perform hot rolling having a predetermined thickness, for example, 1.8 to 3.5 mm. Use a steel plate. After the finish rolling is completed, the hot-rolled steel sheet is wound at a predetermined temperature.

Since the MnS strength as an inhibitor is not so required, the slab heating temperature is preferably 1100 ° C. to 1280 ° C. in consideration of productivity.

(Hot rolled plate annealing process)
In the hot-rolled sheet annealing step (S13), the hot-rolled steel sheet obtained in the hot-rolled step is annealed under predetermined temperature conditions (for example, 750 to 1200 ° C. for 30 seconds to 10 minutes) to obtain a hot-rolled sheet. It is a process.

(Cold rolling process)
In the cold rolling step (S14), the hot-rolled annealed sheet obtained in the hot-rolled sheet annealing step is cold-rolled one time or a plurality of times (two or more times) through annealing (intermediate annealing). (For example, the total cold rolling ratio is 80 to 95%), for example, a step of obtaining a cold rolled steel sheet having a thickness of 0.10 to 0.50 mm.

(Decarburization annealing process)
In the decarburization annealing step (S15), the cold-rolled steel sheet obtained in the cold rolling step is decarburized and annealed (for example, at 700 to 900 ° C. for 1 to 3 minutes) to obtain a decarburized annealed steel sheet in which primary recrystallization has occurred. This is the process of obtaining. By decarburizing and annealing the cold-rolled steel sheet, C contained in the cold-rolled steel sheet is removed. The decarburization annealing is preferably performed in a moist atmosphere in order to remove "C" contained in the cold-rolled steel sheet.

(Nitriding treatment)
Nitriding is performed to adjust the strength of the inhibitor in secondary recrystallization. In the nitriding treatment, the nitrogen content of the steel sheet may be increased to about 40 to 300 ppm at an arbitrary timing from the start of the decarburization annealing described above to the start of secondary recrystallization in the finish annealing described later. As the nitriding treatment, for example, a treatment of annealing a steel sheet in an atmosphere containing a nitriding gas such as ammonia, or a decarburized annealed steel sheet coated with an annealing separator containing a powder having nitriding ability such as MnN is finished. An example is a process of annealing.

When the slab contains the Nb group element in the above numerical range, the nitride of the Nb group element formed by the nitriding treatment functions as an inhibitor in which the grain growth suppressing function disappears at a relatively low temperature, so that secondary recrystallization occurs. Starts from a lower temperature than before. It is also possible that this nitride has an advantageous effect on the selectivity of nucleation of secondary recrystallized grains and realizes a high magnetic flux density. In addition, AlN is also formed in the nitriding treatment, and this AlN functions as an inhibitor in which the grain growth suppressing function continues until a relatively high temperature. In order to obtain these effects, the amount of nitriding after the nitriding treatment is preferably 130 to 250 ppm, more preferably 150 to 200 ppm.

(Annealing separator application process)
The annealing separator coating step (S16) is a step of applying the annealing separator to the decarburized and annealed steel sheet. As the annealing separator, for example, an annealing separator containing MgO as a main component or an annealing separator containing alumina as a main component can be used.

When an annealing separator containing MgO as a main component is used, a forsterite film ( _{a film mainly composed of Mg 2} SiO ₄ ) is likely to be formed as an intermediate layer by finish annealing, and annealing containing alumina as a main component is likely to occur. When a separating agent is used, an oxide film (a film mainly composed of SiO2) is likely to be formed as an intermediate layer by finish annealing. These intermediate layers may be removed if necessary.

The decarburized annealed steel sheet after applying the annealing separating agent is subjected to finish annealing in the next finish annealing step in a coiled state.

(Finish annealing process)
The finish annealing step (S17) is a step of subjecting a decarburized annealed steel sheet coated with an annealing separator to finish annealing to cause secondary recrystallization. In this step, the {100} <001> oriented grains are preferentially grown and the magnetic flux density is dramatically improved by advancing the secondary recrystallization in a state where the growth of the primary recrystallized grains is suppressed by the inhibitor.

(Insulation film forming process)
The insulating film forming step (S21) is a step of forming an insulating film on the grain-oriented electrical steel sheet (finish-annealed steel sheet) after the finish-annealing step. For the formation of a film, which is a general main purpose, a known method is used to form an insulating film mainly composed of phosphate and colloidal silica or an insulating film mainly composed of alumina sol and boric acid on a steel sheet after finish annealing. It may be formed with.

However, this step is a step that can be used to preferably control the magnetic domain structure that is a feature of the steel sheet of the present embodiment, and is an important step in the manufacturing method described in the present specification. In order to realize the magnetic domain structure specified in the present embodiment, it is important to control the tension in this step, which is the final heat treatment in the steel sheet manufacturing. First, after controlling the maximum tension of the steel sheet before raising the temperature to 30 MPa or less, the tension at all time points in the temperature range of 750 ° C. or higher is 6.5 to 13.0 Mpa and the absolute value of the time derivative. The maximum value of is 3.0 MPa / s or less. The data for determining this tension change is a value obtained by continuously measuring the tension in the plate by a general method and averaging the tension for 10 seconds as the tension at a specific time t, going back to the time t-10 seconds. Shall be used. The reason for performing such averaging for 10 seconds is that an unintended extremely short-time stress fluctuation (hunting) may occur during plate passage, and this effect is mitigated.

By controlling the tension before the temperature rise in the final heat treatment step and in the cooling process as described above, the magnetic domain structure defined by the present embodiment becomes preferable. The cause of such changes is not clear, but the following reasons can be considered. The yield stress of the steel sheet containing 2% or more of Si, which is the target of the present embodiment, exceeds 200 MPa at room temperature, and the tension of 30 MPa, which allows the load on the steel sheet before the temperature rise, is a stress that can be judged to be within elastic deformation. Is. However, even with this level of stress, in the minute regions inside the steel plate, especially in the grain boundaries where the constituent elements and dislocations are arranged in a special structure, a slight structural change occurs due to the stress in the elastic deformation, and this continues at high temperature. It is considered that it affects the change in the heat treatment process in the region. Further, in the temperature range of 750 ° C. or higher, the movement of grain boundaries (crystal grain growth and crystal orientation change) hardly occurs, but the morphology of the grain interface and the grain are also affected by the structural change due to the tension applied before the temperature rise. Dislocation structures on the boundaries, element segregation at the grain boundaries, precipitation on the grain boundaries, etc. change, which affects the continuity of magnetic zones. The tension in this temperature range affects the effect of the present embodiment through atomic movement including dislocation formation near the grain boundaries. If the tension is too low, the above-mentioned changes in grain boundaries are unlikely to occur. If the tension is too high, it causes inadvertent growth of dislocations near the grain boundaries, which has a significant adverse effect on the continuity of the magnetic domain angles across the grain boundaries. Since atomic movement is unlikely to occur in a low temperature situation, the effect on the effect of this embodiment is small. In a high temperature situation, atomic movement becomes active and the preferable special grain boundary structure itself is eliminated, so that the effect on the effect of the present embodiment is reduced. Then, it is considered that the change further preferably enhances the change in the grain boundary characteristics by the fluctuation of the tension in an appropriate range, and as a result, enhances the continuity of the magnetic domain sandwiching the grain boundary. Basically, it is thought that the morphology of the grain boundaries will be smooth, the dislocation density will decrease, and the segregation will become uniform, but direct detection has not been possible.

The maximum tension applied to the steel sheet before the temperature rise is preferably 25 MPa or less, more preferably 20 MPa or less. It is preferable that this tension is low, but the general insulation film forming heat treatment line is "finish annealing coil delivery reel-> bridle roll-> excess annealing separator removal-> bridle roll-> inlet looper-> bridle roll-> coating material application-> annealing. It has a structure of → bridle roll → exit looper → bridle roll → take-up reel, and it is difficult to set the load tension to less than 5 MPa because the steel sheet is handled from dispensing to coating raw material application.

The fluctuation range of tension at all time points in the temperature range of 750 ° C. or higher is preferably 7.0 to 11.0 MPa, more preferably 7.5 to 10.0 MPa. The maximum value of the time derivative of tension is preferably 2.5 MPa / s or less, more preferably 2.0 MPa / s or less.

Further, the manufacturing method according to the present embodiment may further include a magnetic domain control step, if necessary.

(Magnetic domain control process)
The magnetic domain control step (S22) is a step of subdividing the magnetic domain of the grain-oriented electrical steel sheet. For example, a local fine strain or a local groove may be formed on the grain-oriented electrical steel sheet by a known method such as laser, plasma, mechanical method, or etching. Such magnetic domain subdivision processing does not impair the effect of the present embodiment.

The method for manufacturing the grain-oriented electrical steel sheet shown in FIG. 9 shows an example in which the insulating film forming step is indispensable in order to control the magnetic domain structure in the insulating film forming step. However, if the method can produce the grain-oriented electrical steel sheet having the above-mentioned magnetic domain structure, the insulating film forming step is not always necessary.

Next, the effect of this embodiment will be described in detail by way of examples. The conditions in this example are one condition example adopted for confirming the feasibility and effect of the present invention, and the present invention is not limited to this one condition example. In the present invention, various conditions can be adopted as long as the gist of the present invention is not deviated and the object of the present invention is achieved.

Using the slab having the chemical composition shown in Table 1 as a material, a grain-oriented electrical steel sheet having the chemical composition shown in Table 2 was produced. In Tables 1 and 2, "-" indicates that the content is not controlled and manufactured in consideration of the content, and the content is not measured, and the numerical value with "<" indicates the content. It is shown that the content was measured by conscious control and manufacturing, but the measured value with sufficient reliability as the content was not obtained (the measurement result is below the detection limit).

The grain-oriented electrical steel sheet was basically manufactured based on known manufacturing conditions. The slab was cast, hot-rolled, and hot-rolled and annealed.
Further, cold rolling and decarburization annealing were carried out, and in some cases, the steel sheet after decarburization annealing was subjected to nitriding treatment (nitriding annealing) in a mixed atmosphere of hydrogen-nitrogen-ammonia.

Further, an annealing separator containing MgO as a main component was applied to the steel sheet to perform finish annealing. In the final process of finish annealing, the steel sheet was held at 1200 ° C. for 20 hours (purification annealing) in a hydrogen atmosphere and naturally cooled.

A coating solution for forming an insulating film containing mainly phosphate and colloidal silica and containing chromium is applied on the primary coating (intermediate layer) formed on the surface of the manufactured directional electromagnetic steel sheet (finish-annealed steel sheet). Then, hydrogen: nitrogen was heated and held in an atmosphere of 75% by volume: 25% by volume and cooled to form an insulating film.

The manufactured grain-oriented electrical steel sheet is in contact with an intermediate layer arranged in contact with the grain-oriented electrical steel sheet (silicon steel sheet) and on the intermediate layer when viewed on a cut surface whose cutting direction is parallel to the plate thickness direction. It had an arranged insulating coating. The intermediate layer was a forsterite film having an average thickness of 2 μm, and the insulating film was an insulating film mainly composed of phosphate and colloidal silica having an average thickness of 1 μm.

(B-1) Magnetic properties of grain-oriented electrical steel sheets The magnetic properties of grain-oriented electrical steel sheets were measured based on the single sheet magnetic property test method (Single Sheet Tester: SST) specified in JIS C 2556: 2015.

As a magnetic characteristic, the magnetic flux density B8 (T) in the rolling direction of the steel sheet when excited at 800 A / m was measured.

(B-2) Magnetic domain structure of grain-oriented electrical steel sheet The magnetic domain structure of grain-oriented electrical steel sheet was quantified by the above analysis method, and the same magnetic domain angle region was measured.

(B-3) Noise characteristics of iron cores A three-phase, three-legged iron core was prepared using each steel plate as a material. The size of the iron core is an overall height of 750 mm, a width of 750 mm, a width of each of the U phase, V phase, and W phase of 150 mm, and a laminated plate thickness of 40 mm. In order to fix the iron core, both sides are surrounded by a wooden frame and fixed with clamps and bolts. The tightening torque for the clamp and bolt was adjusted so that the average tightening pressure for the iron core surface was 0.30 MPa. The iron core joint is a 6-step step wrap, and the number of simultaneous stacks is 1. Eight microphones were placed at equal intervals at positions 30 cm away from the surface of each iron core, and noise was measured.

(Measurement example 1)
When producing steel sheets having a thickness of 0.35 mm or less for steel types A, B, C, and D, four types of steel sheets each having a different average diameter d in the same magnetic domain angle region by changing the tension in the insulating film forming step (A). , B, C, D)-(1-4) were produced. At this time, in each steel type, the fluctuation of tension was controlled so as to be relatively small and almost constant. Since the condition changed only in the tension of the insulating film forming process in the manufacturing process in each steel type, the magnetic flux density, iron loss, and magnetostriction have almost the same characteristic values in each steel type. The magnetic domain structure of these steel sheets was analyzed, and the iron core was manufactured and the noise was measured. The measurement results are shown in Table 3. It can be seen that within each steel type, the change in noise has a strong correlation with d. That is, it can be seen that it is effective to control d within an appropriate range in order to reduce the noise of the iron core manufactured of a thin steel plate.

(Measurement example 2)
When manufacturing steel sheets with a thickness of 0.35 mm or less for steel types A, B, and D, four types of steel sheets with different ds by changing the tension in the insulating coating forming process, (A, B, D)-(11 to 11). 14), (B, D)-(15-18), (D19-D22) were produced. At this time, the absolute value of tension was kept constant for each steel type, and only the maximum value of the time derivative was controlled to fluctuate. Further, for the purpose of subdividing the magnetic domain, a local strain was applied or a local groove was formed in a linear or dot shape so as to extend in a direction intersecting the rolling direction under the following conditions. The pitch is the interval in the rolling direction, Ua is the energy density, the mechanical groove formation is a gear pressing method, and the chemical groove formation is an electrolytic etching method. The steel sheets B15 to B18 were magnetic domain controlled by etching, electron beam, mechanical strain, and laser, respectively. The conditions for electron beam irradiation are irradiation pitch = 4 mm and Ua = 7 mJ / mm ² , and the conditions for laser irradiation are irradiation pitch = 4 mm and Ua = 2.0 mJ / mm ^2. , Pitch = 4 mm, groove depth = 20 μm, no subgroove grains, and the conditions for chemical groove formation are pitch = 4 mm, groove depth = 20 μm. After the mechanical groove formation and the chemical groove formation, an insulating film was formed under the following conditions. For mechanical groove formation, an aluminum phosphate-based insulating film was annealed at 850 ° C. for 30 seconds. For chemical groove formation, an aluminum phosphate-based insulating film was annealed at 850 ° C. for 60 seconds.

Since the condition changed only in the tension of the insulating film forming process in the manufacturing process in each steel type, the magnetic flux density, iron loss, and magnetostriction have almost the same characteristic values in each steel type. The magnetic domain structure of these steel sheets was analyzed, and the iron core was manufactured and the noise was measured. The measurement results are shown in Table 4. It can be seen that the noise is reduced by satisfying the equation (9) in (Δθl + Δθk) / S even if d is the same in each steel type.

According to the above aspect of the present invention, the grain-oriented electrical steel sheet is identified from the magnetic domain image of the grain-oriented electrical steel sheet by a method of quantitatively deriving the region where the angle of the magnetic domain is within a predetermined range and the position thereof, and the transformer. Since it is possible to reduce the noise in the high magnetic field region of the iron core and control the noise characteristics preferably, it has high industrial utility.

20 Image acquisition device 21 Light source unit 23 MO sensor 25 Image sensor 27 Signal processing unit 30 Analysis device 31 Calculation unit 33 Memory 35 Display unit 37 Input unit 39 Communication I / F
100 analysis system

Claims (7)

By mass%
Si: 2.0-7.0%,
C: 0 to 0.0050%,
Mn: 0-1.0%,
S: 0 to 0.0150%,
Se: 0 to 0.0150%,
Al: 0-0.0650%,
N: 0-0.0050%,
Cu: 0-0.40%,
Bi: 0-0.010%,
B: 0 to 0.080%,
P: 0 to 0.50%,
Ti: 0 to 0.0150%,
Sn: 0 to 0.10%,
Sb: 0 to 0.10%,
Cr: 0 to 0.30%,
Ni: 0-1.0%,
Nb: 0 to 0.030%,
V: 0 to 0.030%,
Mo: 0-0.030%,
Ta: 0-0.030%,
W: 0 to 0.030%,
Has a chemical composition in which the balance is composed of Fe and impurities.
A grain-oriented electrical steel sheet having an texture oriented in the Goss direction and having an average diameter of the same magnetic domain angle region of 5.0 mm or more derived by a predetermined method.
The predetermined method for deriving the same magnetic domain angle region is
a) From the magnetic domain image of the grain-oriented electrical steel sheet binarized by two kinds of colors or represented by three or more gradations, a plurality of partial regions corresponding to a plurality of positions of the magnetic domain image are cut out.
b) Obtain a plurality of partial Fourier images by performing a two-dimensional Fourier transform on each of the plurality of partial regions.
c) Based on the peak position of each spot of the plurality of partial Fourier images, the spatial distribution of the angle of the 180 ° magnetic domain of the grain-oriented electrical steel sheet is derived.
d) Based on the spatial distribution of the angle of the 180 ° magnetic domain, a continuous region in the magnetic domain image in which the angle of the 180 ° magnetic domain is within a predetermined range is derived as the same magnetic domain angle region.
A grain-oriented electrical steel sheet characterized by this. Assuming that the crystal grain size of the grain-oriented electrical steel sheet is Rc and the average diameter of the same magnetic domain angle region is d.
d / Rc ≧ 1.1
The grain-oriented electrical steel sheet according to claim 1, wherein the product is satisfied. Of the magnetic domain images, a region having a predetermined size to be measured is defined as an observation region.
The magnetic domain image is represented as a data string of two-dimensional coordinates (k, l).
Of the plurality of subregions, the total of the absolute values of the differences in the magnetic domain angles of the subregions adjacent to each other in the l direction in the observation region is Δθl (deg), and the difference in the magnetic domain angles of the subregions adjacent to each other in the k direction is defined as Δθl (deg). ^{Let the total absolute value be Δθk (deg), and let S (mm 2} ) be the total area of the partial regions used to derive the same magnetic domain angle region among the plurality of partial regions.
(Δθl + Δθk) / S≤1.0degmm ^-2
The grain-oriented electrical steel sheet according to claim 1 or 2, characterized in that the condition is satisfied. The direction according to any one of claims 1 to 3, wherein in the magnetic domain image, the angle of the 180 ° magnetic domain in the same magnetic domain angle region has the highest frequency of existence in the range of 0 deg to 1 deg. Sex electromagnetic steel plate. This is a method for analyzing the magnetic domain structure of grain-oriented electrical steel sheets.
a) A step of cutting out a plurality of partial regions corresponding to a plurality of positions of the magnetic domain image from the magnetic domain image of the grain-oriented electrical steel sheet binarized by two kinds of colors or represented by three or more gradations. When,
b) A step of obtaining a plurality of partial Fourier images by performing a two-dimensional Fourier transform on each of the plurality of partial regions.
c) A step of deriving the spatial distribution of the angle of the 180 ° magnetic domain of the grain-oriented electrical steel sheet based on the peak position of each spot of the plurality of partial Fourier images.
d) A step of deriving a continuous region in the magnetic domain image in which the angle of the 180 ° magnetic domain is within a predetermined range as the same magnetic domain angle region based on the spatial distribution of the angle of the 180 ° magnetic domain.
An analysis method that comprises. The magnetic domain image is represented by a data string x (k, l) of two-dimensional coordinates (k, l).
The observation position in the magnetic domain image is (n, m).
The window function is Wa (k, l),
The shift amounts of the window function in the k direction and the l direction are set to _Sk and S _l , respectively.
The parameters corresponding to the number of pixels in the k direction and the number of pixels in the l direction of the plurality of subregions are expressed as _{N k} and N _{l, respectively.}
In step a) above,
_{By cutting out the range of nS k} ≤ k ≤ nS _k + N _k -1, mS _l ≤ l ≤ mS _l + N _l -1 from the magnetic domain image using the window function, the following is obtained for each of the plurality of subregions. Find the data sequence x _nm (knS _k , l-mS _l ) as in the formula of

In step c) above,
The spatial distribution θ (n, m) of the angle of the 180 ° magnetic domain is derived as shown in the following equation.

Delta] f _k and Delta] f _l, respectively, represent the resolution of the resolution and l directions of k direction of the spatial frequency of the magnetic domain image,
Δk and Δl represent the spatial resolution in the k direction and the spatial resolution in the l direction of the magnetic domain image, respectively.
The analysis according to claim 5, wherein f _k ^max (n, m) and f _l ^max (n, m) represent the k component and the l component of the peak position of each spot of the plurality of partial Fourier images, respectively. Method. An analysis system for the magnetic domain structure of grain-oriented electrical steel sheets.
From the magnetic domain image of the grain-oriented electrical steel sheet binarized by two kinds of colors or represented by three or more gradations, a plurality of partial regions corresponding to a plurality of positions of the magnetic domain image are cut out.
A plurality of partial Fourier images are obtained by performing a two-dimensional Fourier transform on each of the plurality of partial regions.
Based on the peak position of each spot of the plurality of partial Fourier images, the spatial distribution of the angle of the 180 ° magnetic domain of the grain-oriented electrical steel sheet is derived.
An analysis system including a calculation unit that derives a continuous region in the magnetic domain image in which the angle of the 180 ° magnetic domain is within a predetermined range as the same magnetic domain angle region based on the spatial distribution of the angle of the 180 ° magnetic domain.

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