Grain-oriented electromagnetic steel strip, stacked iron core, and method for manufacturing grain-oriented electromagnetic steel strip

Abstract

A grain-oriented electrical steel strip in which magnetic domains are refined by linearly introducing strain on at least one surface so as to intersect with the rolling direction, and the ratio of a region within the sheet thickness where the maximum inter-wall distance of closure domains is 10 μm or more as measured with an X-ray magnetic circularly polarized light emission microscope to the total length of the grain-oriented electrical steel strip in the rolling direction is 50% or more.

Description

[Technical Field]

[0001] The present invention relates to grain-oriented electrical steel strip, a stacked iron core, and a method for manufacturing grain-oriented electrical steel strip. [Background technology]

[0002] Transformers that use grain-oriented electrical steel sheets are required to have low iron loss and low noise. Reducing the iron loss of grain-oriented electrical steel sheets themselves is an effective way to reduce iron loss in transformers, and one technology for doing so is to subdivide magnetic domains by irradiating the steel sheet surface with high-energy beams such as laser beams, plasma beams, and electron beams. This technology not only subdivides the main magnetic domains but also forms a new magnetic domain structure called a closure domain within the steel sheet, thereby achieving low iron loss.

[0003] FIG. 1 is a schematic diagram showing the magnetic domain structure of a grain-oriented electrical steel sheet that has been subjected to the magnetic domain refining treatment, observed from a direction perpendicular to the surface of the steel sheet. The grain-oriented electrical steel sheet has alternating main magnetic domains 10a-10h with different magnetization directions, each extending in the rolling direction (RD). Linear regions (strain-introduced portions 20) where strain has been introduced by irradiation with a high-energy beam are formed so as to cross the rolling direction, and closure domains 21a-21d are formed in the strain-introduced portions 20. Like the main magnetic domains, the closure domains also have alternating closure domains 21a-21d with different magnetization directions. The boundary between adjacent magnetic domains is called a domain wall, and the distance between the domain walls is called the domain wall distance (or domain width). As shown in this figure, by introducing strain across the main magnetic domain, the main magnetic domain can be subdivided, that is, the magnetic domain width of the main magnetic domain can be reduced. As a result, the iron loss of the grain-oriented electrical steel sheet can be reduced. Note that Figure 1 is merely a schematic representation of the structure of an extremely narrow region of a grain-oriented electrical steel sheet, and the number and dimensional ratios of the magnetic domains shown in the figure do not correspond to the actual structure.

[0004] As described above, progress has been made in improving the iron loss of grain-oriented electrical steel sheets, but even if a transformer is manufactured using grain-oriented electrical steel sheets with low iron loss in its core, the iron loss of the resulting transformer (transformer iron loss) is not necessarily low. This is because, while the excitation magnetic flux used to evaluate the iron loss of grain-oriented electrical steel sheets themselves has only a component in the rolling direction, when the steel sheet is actually used as a transformer core, the excitation magnetic flux has a component in both the rolling direction and a component perpendicular to the rolling direction.

[0005] The building factor (BF), defined as the ratio of the transformer's iron loss to the iron loss of the base steel sheet, is commonly used as an indicator of the difference in iron loss between the base steel sheet itself and the transformer manufactured using that steel sheet. A BF greater than 1 means that the transformer's iron loss is greater than the iron loss of the base steel sheet. Grain-oriented electrical steel sheet is a material whose iron loss is lowest when magnetized in the rolling direction. Therefore, when it is incorporated into a transformer that is magnetized in a direction other than the rolling direction, the iron loss increases and the BF becomes greater than 1. To improve the energy efficiency of a transformer, it is necessary not only to reduce the iron loss of the base steel sheet, but also to make this BF as low as possible, i.e., to approach 1.

[0006] For example, Patent Document 1 discloses a method for improving BF by optimizing the total tension applied to a steel sheet by a forsterite film and a tension coating, even when the coating is deteriorated by laser irradiation or electron beam irradiation.

[0007] Furthermore, Patent Document 2 discloses a technique for obtaining good iron loss in a transformer by optimizing the intervals between points of an electron beam irradiated in a point sequence.

[0008] On the other hand, a technique has been proposed that focuses on closure domains formed during magnetic domain refinement using laser irradiation, and reduces iron loss by optimizing their shape and dimensions (Patent Documents 3 and 4). [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-031498 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-036450 [Patent Document 3] Japanese Patent Application Publication No. 11-279645 [Patent Document 4] Patent No. 2002-012918 Summary of the Invention [Problem to be solved by the invention]

[0010] By applying the techniques described above, it is possible to improve BF to some extent. However, it is still far from achieving a BF of 1, and further improvement in BF is currently desired.

[0011] The present invention has been made in view of the above circumstances, and has an object to provide a grain-oriented electrical steel strip and a stacked core that can further reduce BF. [Means for solving the problem]

[0012] The inventors have conducted extensive research to solve the above-mentioned problems. In particular, they have focused on the fact that BF may differ even when the iron loss of grain-oriented electrical steel strips used as raw materials (hereinafter referred to as "raw material iron loss") is the same, and have investigated the cause of this. As a result, they have obtained the following findings. (1) The maximum domain wall distance (domain width) of the closure domains measured by an X-ray magnetic circularly polarized emission microscope within the thickness of the sheet significantly affects the BF. (2) In the conventional general magnetic domain refining method, the distance between the magnetic domain walls varies greatly in the rolling direction of a single steel strip, resulting in a deterioration of the BF. (3) When performing magnetic domain refining by irradiating a high-energy beam, the distance between magnetic domain walls can be appropriately controlled by introducing strain while dynamically controlling the focus of the high-energy beam, thereby effectively improving the BF.

[0013] The main results of the experiments conducted to obtain the above findings will be described below.

[0014] - Deterioration of BF over a long period of time Magnetic domain refinement treatment of grain-oriented electrical steel strips is typically performed by irradiating the surface of the steel strip with a high-energy beam while continuously transporting the steel strip after finish annealing in the rolling direction of the steel strip. Although the time required for magnetic domain refinement treatment of one steel strip is not particularly long, such magnetic domain refinement treatment is performed continuously on a large number of steel strips. Therefore, magnetic domain refinement treatment equipment in actual plants is used continuously for long periods of time, such as several months or more.

[0015] To investigate the effect of such continuous long-term magnetic domain refinement treatment on BF, magnetic domain refinement was carried out continuously for a period of more than six months using a single magnetic domain refinement treatment facility. During this period, magnetic domain refinement treatment was carried out by electron beam irradiation under the same conditions on steel strips after finish annealing, which were produced under the same conditions every other month. The resulting magnetic domain refined steel strips (grain-oriented electrical steel strips) are designated steel strips A to G in order of the timing of the magnetic domain refinement treatment, starting with the strips that were subjected to the treatment earliest.

[0016] Samples (single plate samples) for evaluating material iron loss were cut out from each of the steel strips A to G. 17 / 50 The results are shown in Figure 2A.

[0017] Furthermore, a transformer core was fabricated by stacking grain-oriented electromagnetic steel sheets cut from the grain-oriented electromagnetic steel strip. The core was a three-phase, three-legged stacked core, with a rectangular shape of 500 mm on each side, made of 100 mm-wide steel sheets. The grain-oriented electromagnetic steel sheets were bevel-cut so that the longitudinal direction was the rolling direction, and the sheets were stacked to a thickness of approximately 15 mm and a core weight of approximately 20 kg. The stacking method was a five-stage step-lap stack of two sheets. The core was stacked flat on a flat surface and further clamped and fixed between Bakelite pressure plates under a load of approximately 0.1 MPa.

[0018] Next, the transformer iron loss of the fabricated stacked core was measured. The excitation conditions for the measurement were a phase difference of 120°, a maximum magnetic flux density of 1.7 T, and a frequency of 50 Hz. From the obtained transformer iron loss and the material iron loss calculated earlier, BF was calculated using the following formula. The results are shown in Figure 2B. BF = transformer iron loss / material iron loss

[0019] As can be seen from the results shown in Figures 2A and 2B, the material iron loss remained at roughly the same level over a long period of time, whereas BF gradually increased.

[0020] Correlation between the maximum domain wall distance and BF obtained using different measurement methods and measurement positions The inventors suspected that the deterioration in BF was due to differences in the closure domains introduced by the domain refinement process, and so observed the closure domains of each of the steel strips A to G and measured the average inter-domain wall distance of the closure domains. The "inter-domain wall distance" refers to the distance between adjacent domain walls and is also called the "domain width." In Figure 1, d denotes the inter-domain wall distance between individual closure domains, and this "inter-domain wall distance (domain width) d" is different from the overall width of the region (strain-introduced portion 20) where the closure domains are formed.

[0021] Observation of the closure domains was carried out using the following three methods, of which (2) and (3) were carried out at two locations: on the surface of the steel sheet and inside the steel sheet. Note that the method using a domain viewer can only be applied to the surface of the steel sheet. (1) Observation using Domain Viewer (2) Observation using a Kerr effect microscope (3) Observation using X-ray magnetic circularly polarized light emission microscope

[0022] For the observation using the domain viewer (1) above, a CMOS-Magview manufactured by Matesy GmbH was used. For the observation using the Kerr effect microscope (2) above, a Kerr effect microscope BH-786V-JS manufactured by NeoArc was used. For the observation using the X-ray magnetic circularly polarized emission microscope (3) above, synchrotron radiation was used. The specific observation method was as described in "Observation of transverse domains in grain-oriented electrical steel by means of X-ray magnetic circularly polarized emission microscopy" in the 46th Annual Conference on Magnetics in Japan, 2022, p. 58. For the observation using the X-ray magnetic circularly polarized emission microscope, the incident position of the synchrotron radiation was changed to observe magnetic domains on the surface and inside of the steel strip.

[0023] The average domain wall distance on the steel strip surface was measured as follows. First, the steel strip to be measured was divided into 50 equal parts in the rolling direction (longitudinal direction), and 50 samples were taken. Next, each sample was further divided into 10 parts in the strip width direction, and a 30 mm × 30 mm observation sample was taken from the center of each divided area. The closure domains on the surface of the observation sample were then observed in a 1 mm × 1 mm field of view randomly selected from within the 30 mm × 30 mm area, and the domain wall distance of the closure domains was measured. The average value of the domain wall distances for the 10 observation samples divided into 10 parts in the strip width direction was taken as the average domain wall distance in the strip width direction. Similar measurements were performed on 50 samples divided into 50 parts in the rolling direction, and the average value of the obtained average domain wall distances in the strip width direction was taken as the "average domain wall distance on the steel strip surface."

[0024] For the observation of the interior of the steel sheet, the steel strip was further divided into sections at 5 μm intervals in the depth direction (thickness direction), and the average inter-domain wall distance at each depth was determined using the procedure described above. The maximum value of the average inter-domain wall distances obtained at each depth was then defined as the "maximum inter-domain wall distance within the thickness direction" of the steel strip.

[0025] The above measurements were performed on each of steel strips A to G, and the "average magnetic domain wall distance on the steel strip surface" and the "maximum magnetic domain wall distance within the strip thickness" were obtained. The correlation between the obtained "average magnetic domain wall distance on the steel strip surface" or "maximum magnetic domain wall distance within the strip thickness" and BF is shown in Figures 3 to 5. Each figure corresponds to the following observation results. Figure 3: Measurement results of steel strip surface using Domain Viewer Figure 4A: Measurement results of the steel strip surface using a Kerr effect microscope Figure 4B: Measurement results for the inside of the plate using a Kerr effect microscope Figure 5A: Measurement results of steel strip surface using X-ray magnetic circularly polarized light emission microscope Figure 5B: Measurement results for the inside of the plate using an X-ray magnetic circularly polarized light emission microscope

[0026] As shown in Figure 5B, there was a correlation between the "maximum inter-domain wall distance within the thickness of the sheet" observed using an X-ray magnetic circularly polarized light emission microscope and BF. In contrast, no correlation was observed between the "maximum inter-domain wall distance within the thickness of the sheet" measured using a Kerr effect microscope and BF. Furthermore, there was no correlation observed with the "average inter-domain wall distance on the steel strip surface" using either measurement method.

[0027] The reason for the differences due to the measurement method and measurement position is not clear, but is thought to be as follows.

[0028] (i) Cross-sectional observation using a Kerr effect microscope requires processing the steel strip to expose the observation surface. This processing releases the constraints inside the steel strip and changes the internal strain distribution. As a result, it is not possible to observe the magnetic domains as they would be in an actual iron core.

[0029] (ii) In contrast, X-ray magnetic circularly polarized light emission microscopes allow non-destructive observation of the inside of steel strips, making it possible to observe magnetic domains as they are used in actual iron cores.

[0030] (iii) Because closure domains have magnetization components other than those in the rolling direction, their presence is advantageous in reducing BF. Furthermore, because closure domains repeatedly appear and disappear during the magnetization process, the larger the domain wall distance (i.e., the wider the domain width), the less likely the closure domains are to disappear, which is advantageous in reducing BF.

[0031] (iv) Because the strain caused by high-energy beam irradiation is introduced from the surface layer of the steel strip, the thermal energy that causes the strain is sufficiently large in the surface layer of the steel sheet. Therefore, the influence of fluctuations in the conditions during the magnetic domain refinement treatment on the magnetic domain wall distance is relatively small. As a result, no significant correlation was found between the "average magnetic domain wall distance on the steel strip surface" and BF.

[0032] (v) On the other hand, the thermal energy introduced by high-energy beam irradiation decays as it propagates into the steel strip. In this decayed state, the influence of fluctuations in the conditions during the magnetic domain refinement process on the inter-wall distance is relatively large. As a result, a correlation was found between the "maximum inter-wall distance within the strip thickness" and BF.

[0033] -Focus condition fluctuations As shown in Figure 5B above, we investigated the fluctuation of the "maximum inter-domain wall distance within the thickness of the plate" due to the fluctuation of the focus conditions during high-energy beam irradiation.

[0034] During magnetic domain refinement processing by electron beam irradiation, the focus of the electron beam can be adjusted by controlling the convergence current. In the magnetic domain refinement processing of the steel strips A to G described above, the initially set convergence current value I0 was used without any change.

[0035] At that time, a beam profiler was used to measure the convergence current I that becomes the JUST focus during the processing of each steel strip A to G (every month). A ~I G Here, JUST focus refers to the state where the beam profile intensity on the processing surface (steel strip surface) is at its maximum (beam diameter is at its minimum). The obtained focusing current I A ~I G The difference between each of these and the initially set convergence current value I0 is taken as the convergence current deviation ΔI. Figure 6 shows the correlation between the obtained convergence current deviation ΔI and BF.

[0036] As can be seen from Figure 6, a correlation was found between the focus current deviation ΔI and BF. This indicates that when magnetic domain refinement is performed continuously over a long period of time, the focus current that results in JUST focus gradually deviates from the initially set focus current value I0, resulting in an increase in BF.

[0037] We believe that this focus shift occurs for the following reasons. In the case of electron beams, continuous use of an electron beam source reduces the electron generation efficiency due to wear on the cathode. As a result, to extract the same number of electrons, the electron generation area must be increased. This change in electron generation area fluctuates the initial beam diameter, which is thought to change the convergence current that results in just focus. In addition to changes over time, electron generation efficiency is also thought to change due to individual differences in the cathode, variations in the cathode heating temperature, and variations in the vacuum level in the electron gun chamber, which in turn causes just focus to fluctuate.

[0038] As mentioned above, the steel strips A to G have almost the same material iron loss. Therefore, even if the above-mentioned fluctuations in the focus conditions occur, if product performance is evaluated based only on the material iron loss, all of them will be at an acceptable level. In that sense, the fluctuations in the focus conditions are a minor issue. However, in order to improve BF, it is considered important to perform focus adjustment with higher precision in order to reduce the influence of such fluctuations in the focus conditions.

[0039] Control based on bias voltage As mentioned above, fluctuations in focus conditions can be caused by a variety of factors. It is difficult to grasp and control all of these factors. Therefore, we attempted to estimate fluctuations in focus conditions by monitoring the bias voltage, which reflects the ease of electron extraction from the cathode, and to control the focusing current value based on the results.

[0040] First, the electron generation efficiency was changed by changing the cathode heating temperature. This change in electron generation efficiency resulted in a change in the bias voltage. Therefore, we investigated the relationship between the bias voltage and the focusing current that results in a JUST focus. As a result, as shown in Figure 7, it was found that the focusing current that results in a JUST focus decreases as the bias voltage decreases.

[0041] Next, in order to confirm the effect of controlling the convergence current, the magnetic domain refining process was carried out at one-month intervals under the following three conditions, similar to the above-mentioned experiment.

[0042] Condition 1: No convergence current adjustment Under condition 1, the convergence current was not adjusted. That is, after the convergence current was set when the first steel strip was subjected to the magnetic domain refinement treatment, the treatment was continued with the same convergence current.

[0043] Condition 2: Adjustment by steel strip Under Condition 2, when the magnetic domain refinement process was performed at monthly intervals as described above, the convergence current was adjusted based on the bias voltage at the start of processing each steel strip. That is, when performing the magnetic domain refinement process at each timing (every month), the bias voltage was checked, and the deviation in the convergence current was predicted from the difference between the bias voltage when the focus was set and the current bias voltage. The convergence current was adjusted to achieve JUST focus, and then the magnetic domain refinement process was performed.

[0044] Condition 3: Dynamic control Under condition 3, the focusing current was adjusted based on the bias voltage while performing the magnetic domain refinement process on a single steel strip. Under these conditions, the focus was dynamically controlled while the magnetic domain refinement process was continuously performed on a single steel strip while it was being transported, so irradiation was always performed in a focused state.

[0045] The obtained steel strips (grain-oriented electromagnetic steel strips) that have been subjected to the magnetic domain refinement treatment are designated as steel strips H to P in order of the timing of the magnetic domain refinement treatment.

[0046] When the iron loss of the steel strips obtained in the above experiment was measured, the iron loss W 17 / 50 The magnetic field strength was approximately 0.68 W / kg, which was very good.

[0047] Meanwhile, when stacked cores were made from each steel strip using the same procedure as in the previous experiment and the BF was measured, the results shown in Figure 8 were obtained. That is, under condition 1, where no control was performed, the BF deteriorated over time, similar to the results shown in Figure 2B above. On the other hand, under condition 2, where the focus was adjusted on a steel strip basis, the deterioration of BF was suppressed compared to condition 1, but was not completely suppressed. In contrast, under condition 3, where the focus was dynamically controlled, the deterioration of BF was significantly suppressed, even compared to condition 2.

[0048] These results demonstrate that when performing magnetic domain refinement by irradiating a high-energy beam, it is important to dynamically control the focus of the high-energy beam to introduce strain. This indicates that fluctuations in the focus conditions occur not only over long time spans such as one month, but also over extremely short time scales such as the time it takes to perform magnetic domain refinement on a single steel strip.

[0049] Next, the "maximum inter-domain wall distance within the thickness direction" of steel strip H obtained under each of conditions 1 to 3 was measured using an X-ray magnetic circular polarization luminescence microscope. Figure 9 is a graph in which the measured "maximum inter-domain wall distance within the thickness direction" is plotted against the position in the rolling direction (longitudinal direction) of the steel strip. Note that the distance of zero on the horizontal axis of Figure 9 indicates the leading edge of the steel strip, i.e., the position where the magnetic domain refinement treatment was first performed.

[0050] These results show that under conditions 1 and 2, where no dynamic control was performed during the processing of a single steel strip, the maximum domain wall distance varied significantly depending on the position in the rolling direction of the steel strip. This variation is believed to be due to the variation in the focus conditions, as described above. Under condition 2, the focus current was adjusted at the start of the magnetic domain refinement process for that steel strip, resulting in an overall increase in the maximum domain wall distance compared to condition 1. However, the slopes of the plots under conditions 2 and 1 were similar. This indicates that simply adjusting the focus current at the start of the magnetic domain refinement process cannot prevent subsequent variations in the focus conditions. In contrast, under condition 3, where the focus was dynamically controlled, the variation in the maximum domain wall distance depending on the position in the rolling direction of the steel strip was significantly suppressed.

[0051] Maximum closure domain width As described above, we found that the fluctuation of the maximum closure domain width can be suppressed by introducing strain while dynamically controlling the focus when irradiating a high-energy beam to perform magnetic domain refinement. Therefore, we next investigated what range of the maximum closure domain width is necessary to suppress the increase in BF.

[0052] Specifically, we produced steel strips with various inter-domain wall distances by subjecting steel strips obtained under the same conditions after finish annealing to magnetic domain refinement treatment under different focus conditions. In the magnetic domain refinement treatment, the focus was dynamically controlled during the treatment of one steel strip to maintain a constant focus state over the entire length in the rolling direction. The focus state was varied from upper focus to under focus for each steel strip.

[0053] Next, the "maximum inter-wall distance within the thickness direction" and BF of each of the obtained steel strips were measured using the method described above. Note that for all steel strips, the "maximum inter-wall distance within the thickness direction" was constant and did not vary in the rolling direction.

[0054] Figure 10 is a graph plotting the measured BF against the "maximum domain wall distance within the thickness of the sheet." This result shows that if the maximum domain wall distance of the closure domains measured with an X-ray magnetic circular polarization luminescence microscope is 10 μm or more, the BF can be maintained in a good condition.

[0055] Orifice temperature-based control In the magnetic domain refining process using electron beam irradiation, focus control is possible not only by the bias voltage but also by monitoring the orifice temperature. The orifice is installed so as to cut off some of the electrons in the beam path. The orifice is installed between the cathode and the focusing coil.

[0056] When the ease of electron extraction from the cathode changes, the area within the cathode that emits electrons changes. When electrons are easy to extract, the emission area is small, and when electrons are difficult to extract, the emission area is large. The beam diameter up to the focusing coil changes depending on the emission area, and the focusing current value that achieves just focus on the steel sheet surface changes depending on the beam diameter when it reaches the focusing coil. When the beam diameter changes, the number of electrons cut by the orifice changes. The number of electrons cut is reflected in the orifice temperature, so fluctuations in beam diameter can be determined by monitoring the orifice temperature. Specifically, if the orifice temperature increases, the beam diameter increases, and conversely, if the orifice temperature decreases, the beam diameter decreases.

[0057] Therefore, if the relationship between the orifice temperature and the focusing current is known in advance, it is possible to dynamically control the focus based on the change in the orifice temperature during the magnetic domain refining process.

[0058] The position at which the orifice temperature is measured is not particularly limited, and it can be measured at any one point on the orifice. However, from the perspective of grasping beam changes in more detail, it is preferable to measure the temperature at multiple positions on the orifice. For example, in a substantially circular orifice, the temperature can be measured at multiple positions equally spaced in the angular direction (circumferential direction). When measuring at 120° intervals, the number of measurement points is three, and when measuring at 90° intervals, the number of measurement points is four. Measuring the temperature at multiple positions in this way also makes it possible to determine in which direction the beam has changed. In focus control, the average value of the temperatures measured at multiple positions on the orifice may be used as the orifice temperature.

[0059] All of the above experiments used magnetic domain refinement processing by electron beam irradiation. However, we found that similar fluctuations in focus conditions also occur when magnetic domain refinement processing is performed by laser irradiation. In laser irradiation, the thermally induced optical distortion generated in the focusing lens changes depending on the output power of the irradiated beam. This thermally induced optical distortion changes the focal length of the lens, and is therefore the main cause of focus fluctuations. Although it is difficult to monitor the amount of distortion, if the relationship between laser output and focal length fluctuations is understood in advance, it is possible to dynamically control the focus based on the laser beam output during magnetic domain refinement processing. Note that laser output not only changes over time, but also changes with irradiation conditions (such as temperature and humidity). Therefore, it is highly likely that the conditions for achieving just focus will fluctuate even immediately after focus adjustment.

[0060] Dynamic focus control in laser irradiation can be performed based on the orifice temperature, as in electron beam irradiation. The orifice is installed so that a portion of the laser beam is cut off in the beam path. When the laser output is higher than the set value, the beam energy cut off by the orifice increases, resulting in a higher orifice temperature. Conversely, when the output is lower than the set value, the beam energy cut off decreases, resulting in a lower orifice temperature. Therefore, based on the previously determined relationship between the orifice temperature and focal length, the position of the focusing lens of the laser beam can be adjusted in accordance with the measured orifice temperature.

[0061] Effect on stacked core Next, when manufacturing a stacked core by stacking multiple grain-oriented electrical steel sheets, we investigated the effect of the maximum inter-domain wall distance within the thickness of the grain-oriented electrical steel sheets on the BF. Specifically, grain-oriented electrical steel sheets were cut from grain-oriented electrical steel strips manufactured under various conditions, and these sheets were combined to manufacture stacked cores with various BFs.

[0062] Figure 11 is a graph plotting BF against the "weight percentage of regions where the maximum inter-wall distance is 10 μm or greater." Note that the "weight percentage of regions where the maximum inter-wall distance is 10 μm or greater" on the horizontal axis refers to the "percentage of the region within the thickness of the grain-oriented electrical steel sheet where the maximum inter-wall distance of the closure domains, as measured with an X-ray magnetic circular polarization luminescence microscope, is 10 μm or greater relative to the total weight of the multiple grain-oriented electrical steel sheets that make up the stacked core."

[0063] 11, the BF improved when the "weight ratio of the region where the maximum inter-domain wall distance is 10 μm or more" was 50% or more. Furthermore, the BF improved further when the "weight ratio of the region where the maximum inter-domain wall distance is 10 μm or more" was 80% or more, and the BF was lowest when it was 100%.

[0064] Furthermore, if the grain-oriented electrical steel strips used as the raw material for stacked cores also contain regions where BF increase can be suppressed at a similar rate, stacked cores with good BF can be obtained even if the steel strips used are selected arbitrarily without strict management of the grain-oriented electrical steel strips. Therefore, in grain-oriented electrical steel strips, it is desirable that the ratio of regions within the sheet thickness where the maximum inter-wall distance of closure domains is 10 μm or more as measured with an X-ray magnetic circularly polarized light emission microscope to the total length of the grain-oriented electrical steel strip in the rolling direction is 50% or more.

[0065] The present invention has been completed based on the above findings, and the gist and configuration of the present invention are as follows.

[0066] 1. A grain-oriented electrical steel strip in which magnetic domains are refined by linearly introducing strain on at least one surface so as to intersect with the rolling direction, A grain-oriented electrical steel strip in which the ratio of the area within the thickness of the sheet where the maximum inter-wall distance of closure domains is 10 μm or more as measured using an X-ray magnetic circular polarization luminescence microscope to the total length of the grain-oriented electrical steel strip in the rolling direction is 50% or more.

[0067] 2. A stacked core made of multiple grain-oriented electromagnetic steel sheets, A stacked core, wherein the proportion of a region within the thickness of the grain-oriented electrical steel sheets in which the maximum inter-wall distance of closure domains as measured with an X-ray magnetic circularly polarized light emission microscope is 10 μm or more to the total weight of the plurality of grain-oriented electrical steel sheets is 50% or more.

[0068] 3. A method for producing the grain-oriented electrical steel strip described in 1 above, and subjecting the surface of the steel strip after the finish annealing to a magnetic domain refinement treatment by irradiating the surface of the steel strip with a high-energy beam while continuously transporting the steel strip in the rolling direction of the steel strip, A method for manufacturing grain-oriented electrical steel strip, wherein, during irradiation of the high-energy beam, strain is introduced while dynamically controlling the focus of the high-energy beam, thereby making the ratio 50% or more.

[0069] 4. A method for producing a grain-oriented electrical steel strip according to the above item 3, the high-energy beam is an electron beam; In the dynamic focus control, Measure the bias voltage, A method for manufacturing a grain-oriented electrical steel strip, comprising adjusting the focusing current of the electron beam in accordance with the measured bias voltage based on a previously determined relationship between the bias voltage and the focusing current.

[0070] 5. A method for producing a grain-oriented electrical steel strip according to the above item 3, the high-energy beam is an electron beam; an orifice is installed in a beam path of the electron beam so as to cut off a part of the electron beam; In the dynamic focus control, measuring the temperature of the orifice; A method for manufacturing a grain-oriented electromagnetic steel strip, comprising adjusting the focusing current of the electron beam in accordance with the measured temperature of the orifice based on a previously determined relationship between the orifice temperature and the focusing current.

[0071] 6. A method for producing a grain-oriented electrical steel strip according to the above item 3, the high-energy beam is a laser beam; an orifice is installed in the beam path of the laser beam so as to cut off a part of the laser beam; In the dynamic focus control, measuring the temperature of the orifice; A method for manufacturing a grain-oriented electromagnetic steel strip, comprising adjusting the position of the focusing lens of the laser beam in accordance with the measured temperature of the orifice based on a previously determined relationship between the orifice temperature and the focal length. [Effects of the Invention]

[0072] According to the present invention, the BF can be reduced. [Brief explanation of the drawings]

[0073] [Figure 1]FIG. 2 is a schematic diagram showing the magnetic domain structure of a grain-oriented electrical steel sheet that has been subjected to a magnetic domain refinement treatment, observed from a direction perpendicular to the surface of the steel sheet. [Figure 2A] 1 is a graph showing the change in material iron loss when grain-oriented electrical steel strips are produced at one-month intervals. [Figure 2B] 1 is a graph showing changes in BF when grain-oriented electrical steel strips are produced at one-month intervals. [Figure 3] This is a graph showing the correlation between the "average magnetic domain wall distance on the steel strip surface" measured using a domain viewer and BF. [Figure 4A] 1 is a graph showing the correlation between the "average magnetic domain wall distance on the steel strip surface" measured using a Kerr effect microscope and BF. [Figure 4B] 1 is a graph showing the correlation between the "maximum inter-domain wall distance within the thickness of the plate" measured using a Kerr effect microscope and BF. [Figure 5A] 1 is a graph showing the correlation between the "average magnetic domain wall distance on the steel strip surface" measured using an X-ray magnetic circularly polarized light emission microscope and BF. [Figure 5B] 1 is a graph showing the correlation between the "maximum distance between magnetic domain walls within the thickness of the plate" measured using an X-ray magnetic circularly polarized light emission microscope and BF. [Figure 6] 10 is a graph showing the correlation between the convergence current deviation ΔI and BF. [Figure 7] 10 is a graph showing an example of the relationship between a bias voltage and a focusing current that provides a just focus. [Figure 8] 1 is a graph showing changes in BF when grain-oriented electrical steel strips are produced at one-month intervals. [Figure 9] 1 is a graph in which the "maximum inter-domain wall distance within the sheet thickness" is plotted against the position in the rolling direction (longitudinal direction) of the steel strip. [Figure 10] 1 is a graph showing the relationship between the "maximum distance between magnetic domain walls within the plate thickness" and BF. [Figure 11] 1 is a graph plotting BF against the "weight ratio of regions where the maximum inter-domain wall distance is 10 μm or more." [Figure 12]10 is a graph showing an example of the relationship between the orifice temperature and the focusing current that results in a JUST focus. [Figure 13] 10 is a graph showing an example of the relationship between the orifice temperature and the focal length at which the image is in just focus. DETAILED DESCRIPTION OF THE INVENTION

[0074] The present invention will be described in detail below. Note that the following description is of preferred embodiments of the present invention, and the present invention is not limited to the embodiments described below.

[0075] [Grain-oriented electromagnetic steel strip] In one embodiment of the present invention, the grain-oriented electrical steel strip is a grain-oriented electrical steel strip in which magnetic domains are refined by linearly introducing strain on at least one surface so as to intersect with the rolling direction, and the ratio of a region within the sheet thickness where the maximum inter-domain wall distance of closure domains as measured with an X-ray magnetic circularly polarized light emission microscope is 10 μm or more to the total length of the grain-oriented electrical steel strip in the rolling direction is 50% or more. In the following description, the "maximum inter-domain wall distance of closure domains as measured with an X-ray magnetic circularly polarized light emission microscope within the sheet thickness" may be simply referred to as the "maximum inter-domain wall distance."

[0076] As the experimental results above show, to obtain a good BF, the area where the "maximum inter-domain wall distance" is 10 μm or more must account for 50% or more of the total length of the grain-oriented electrical steel strip in the rolling direction. The larger the maximum average inter-domain wall distance within the sheet thickness, the later the timing at which the closure domains completely disappear when used as a transformer core, thereby suppressing the increase in BF. While there is no particular upper limit for the maximum inter-domain wall distance, it is approximately 100 μm because the width of the strain-introducing region is the practical upper limit.

[0077] From the viewpoint of further improving BF, the ratio of the region where the maximum inter-domain distance is 10 μm or more to the total length of the grain-oriented electrical steel strip in the rolling direction is preferably 75% or more, more preferably 90% or more. On the other hand, the upper limit of this ratio is not particularly limited and may be 100%. Most preferably, this ratio is 100%.

[0078] The ratio of the area where the maximum inter-domain distance is 10 μm or more to the total length of the grain-oriented electrical steel strip in the rolling direction can be determined by the following procedure.

[0079] First, the steel strip is divided into 50 equal parts in the rolling direction (longitudinal direction), 10 parts in the width direction, and a 5 μm pitch in the depth direction (thickness direction). Each divided part is observed using an X-ray magnetic circular polarization luminescence microscope, and the distance between the domain walls of the closure domains is measured. Next, the measured domain wall distances are averaged at 10 points in the width direction to determine the "average domain wall distance in the width direction" for each depth. The maximum value of the "average domain wall distance in the width direction" obtained at each depth is defined as the "maximum domain wall distance." This gives the "maximum domain wall distance" for each of the 50 parts divided in the rolling direction. Then, the percentage of the 50 regions divided in the rolling direction where the maximum domain wall distance is 10 μm or more is calculated.

[0080] The distance between the closure domain walls in each divided region was measured using the method described above. Specifically, a 30 mm × 30 mm observation sample was taken from the center of each divided region. The closure domains on the surface of the observation sample were then observed in a 1 mm × 1 mm field of view randomly selected from within the 30 mm × 30 mm region, and the distance between the closure domain walls was measured.

[0081] From the viewpoint of reducing the variation in properties within the steel strip and further improving the BF, the difference Δd between the maximum and minimum values ​​of the maximum magnetic domain wall distance over the entire longitudinal direction of the steel strip is preferably 10 μm or less, and more preferably 5 μm or less. On the other hand, from the viewpoint of further reducing the BF, the smaller Δd, the better. Therefore, the lower limit of Δd is not particularly limited and may be 0 μm.

[0082] [Stacked core] In one embodiment of the present invention, the stacked core is a stacked core formed by stacking a plurality of grain-oriented electrical steel sheets, and the proportion of the region within the thickness of the grain-oriented electrical steel sheets where the maximum inter-wall distance of closure domains as measured with an X-ray magnetic circular polarization luminescence microscope is 10 μm or more to the total weight of the plurality of grain-oriented electrical steel sheets is 50% or more.

[0083] As shown by the above experimental results, if the weight ratio is 50% or more, the BF can be improved. Furthermore, the weight ratio is preferably 80% or more, and more preferably 90% or more. On the other hand, the upper limit of the weight ratio is not particularly limited and may be 100%. The weight ratio is most preferably 100%.

[0084] Note that stacked cores that satisfy the above conditions can be manufactured by using grain-oriented electrical steel sheets with known weight ratios. Furthermore, when evaluating the weight ratios of existing stacked cores, the lamination direction can be used as the reference instead of the rolling direction. For example, each part in a stacked core can be divided evenly into 50 parts in the lamination direction, and 50 samples can be taken. Then, a 30 mm x 30 mm observation sample can be taken from the center of each sample and measured.

[0085] In the stacked core of the present invention, the desired effects can be achieved by using grain-oriented electrical steel sheets that satisfy certain conditions as described above. Therefore, the type of stacked core is not particularly limited. For example, the stacked core may be either a single-phase or three-phase core, and may be either a shell-type or a core-type core. Furthermore, the stacked core may have any number of legs, for example, either a three-legged core or a five-legged core.

[0086] [Manufacturing method of grain-oriented electromagnetic steel strips] Next, a method for producing a grain-oriented electrical steel strip according to one embodiment of the present invention will be described. The method for producing a grain-oriented electrical steel strip according to one embodiment of the present invention includes irradiating a high-energy beam onto the surface of a steel strip after finish annealing while continuously transporting the steel strip in the rolling direction of the steel strip to perform a magnetic domain refinement treatment. During the irradiation of the high-energy beam, strain is introduced while dynamically controlling the focus of the high-energy beam, thereby setting the ratio at 50% or more.

[0087] The dynamic control method is not particularly limited. The focus control may be performed continuously or intermittently. Examples of suitable control methods are described below. Note that the control method is not limited to the methods described below.

[0088] In the case of electron beam irradiation When performing magnetic domain refinement processing by electron beam irradiation, the bias voltage can be monitored (measured) during processing and the focus can be controlled accordingly. The bias voltage can be measured continuously or intermittently. The focus can be adjusted by changing the current (focus current) in the focus coil. To perform this control, it is necessary to determine in advance the relationship between the bias voltage and the focus current that results in just focus at that bias voltage. When determining this relationship, the bias voltage can be changed by adjusting the heater current.

[0089] When performing magnetic domain refining processing by electron beam irradiation, it is possible to monitor not only the bias voltage but also the orifice temperature and control the focus accordingly. The orifice temperature can be measured continuously or intermittently. The focus can be adjusted by changing the current (focus current) in the focus coil. To perform this control, it is necessary to determine in advance the relationship between the orifice temperature and the focus current that results in just focus at that orifice temperature. When determining this relationship, the orifice temperature can be changed by adjusting the heater current.

[0090] In the case of laser irradiation On the other hand, in the case of laser irradiation, the main cause of focus changes is thermal distortion of the lens due to output fluctuations. Therefore, when performing magnetic domain refining processing by laser irradiation, an orifice is installed in the beam path and a portion of the laser beam is cut off by the orifice. In this case, the temperature of the orifice changes due to the cut laser energy. Therefore, it is sufficient to monitor (measure) the orifice temperature during processing and control the focus accordingly.

[0091] The orifice temperature can be measured continuously or intermittently. The focus can be adjusted by changing the position of the condenser lens. To perform this control, the relationship between the orifice temperature and the focal length that results in just focus at that orifice temperature is determined in advance, and the position of the condenser lens is changed so that the distance between the condenser lens and the object becomes the focal length that corresponds to that orifice temperature. When determining this relationship, the orifice temperature can be changed by intentionally changing the beam output setting.

[0092] As described above, in the present invention, it is important to dynamically control the focus during the magnetic domain refining process. Therefore, other magnetic domain refining process conditions are not limited, and general conditions can be applied.

[0093] For example, when irradiating a high-energy beam, the scanning direction of the beam may be a direction intersecting the rolling direction of the steel strip. In other words, the scanning direction may be greater than 0° and less than 90° relative to the rolling direction (RD) of the steel strip. By irradiating the steel strip while scanning the beam in a direction intersecting the rolling direction of the steel strip, linear strain can be introduced into the surface of the steel strip so as to intersect with the rolling direction. In other words, the angle of the linearly introduced strain is the same as the scanning direction. The 90° direction corresponds to the transverse direction (TD). The scanning direction is preferably 60 to 90° relative to the rolling direction (RD) of the steel strip.

[0094] The output of the high-energy beam to be irradiated is not particularly limited, and may be adjusted so as to introduce the desired strain. Typically, the output can be 50 W to 5 kW in both the electron beam irradiation and the laser irradiation. From the viewpoint of productivity, the deflection speed (scanning speed) is preferably 10 m / s or higher. Meanwhile, there is no upper limit to the deflection speed. However, if the deflection speed is excessively high, larger equipment will be required to ensure the energy density required for magnetic domain refinement. Therefore, the deflection speed is preferably 400 m / s or lower, and more preferably 200 m / s or lower.

[0095] In the magnetic domain refinement treatment, the high-energy beam is repeatedly irradiated at intervals in the rolling direction (longitudinal direction) of the steel strip. This interval is generally referred to as the "irradiation line interval" or simply the "line interval." The line interval is not particularly limited, but from the viewpoint of further reducing the iron loss of the grain-oriented electrical steel sheet, it is preferably more than 3.0 mm and less than 8.0 mm.

[0096] The line spacing is equal to the spacing in the rolling direction of the linear strain introduced into the grain-oriented electrical steel strip. Therefore, in one embodiment of the grain-oriented electrical steel strip, the spacing in the rolling direction of the linear strain is preferably more than 3.0 mm and less than 8.0 mm.

[0097] Furthermore, from the viewpoint of further reducing iron loss, it is preferable that the beam diameter be 0.20 mm or less. On the other hand, although there is no particular lower limit for the beam diameter, it is industrially preferable that the beam diameter be 0.010 mm or more. Note that the beam diameter here refers to the diameter of the irradiated energy beam when it reaches the surface of the steel strip.

[0098] The steel strip to be subjected to the magnetic domain refinement treatment is not particularly limited and can be produced by a general method. An example of a method for producing a steel strip to be subjected to the magnetic domain refinement treatment will be described below.

[0099] Typical manufacturing processes for grain oriented electrical steel strips are as follows: A hot rolling process in which steel material (steel slab) is hot rolled into hot rolled steel strip; a cold rolling step of cold rolling the hot rolled steel strip to obtain a cold rolled steel strip; a primary recrystallization annealing step of subjecting the cold-rolled steel strip to primary recrystallization annealing and decarburization; a coating step of coating an annealing separator on the surface of the steel strip after the primary recrystallization annealing step; and a finish annealing step in which the steel strip after the coating step is subjected to secondary recrystallization annealing and purification. The magnetic domain refinement treatment can be performed after this finish annealing step. Furthermore, a hot-rolled sheet annealing step can be optionally included after the hot rolling step and before the cold rolling step. Furthermore, the cold rolling step can also include two or more cold rolling steps with intermediate annealing between them.

[0100] ·Ingredient composition The steel strip to be subjected to the magnetic domain refinement treatment can be produced, for example, by subjecting a steel material (steel slab) to treatments such as rolling and annealing. Therefore, we will first explain examples of the chemical composition of a steel material (steel slab) that can be suitably used. However, the present invention is not limited to the content described below. In the explanation of the chemical composition, the units of content "%" and "ppm" refer to "% by mass" and "ppm by mass," respectively, unless otherwise specified.

[0101] First, the component composition of the steel material (steel slab) used can contain C, Si, and Mn as basic components in the following contents.

[0102] C: 0.08% or less C is an element added to improve the hot-rolled sheet structure. However, since residual C can cause magnetic aging, decarburization is generally performed during the manufacturing process of an electrical steel strip to reduce the C content in the steel to 50 ppm or less, at which point magnetic aging does not occur. However, if the initial C content (C content of the steel material) exceeds 0.08%, it becomes difficult to reduce the C content to 50 ppm or less even by decarburization. Therefore, it is preferable that the C content of the steel material be 0.08% or less. On the other hand, because secondary recrystallization is possible even when the steel material does not contain C, the lower limit of the C content is not particularly limited and may be 0%. However, from the perspective of improving the hot-rolled sheet structure, it is preferable that the C content be 0.01% or more.

[0103] Si: 2.0 to 8.0% Si is an element that has the effect of increasing the electrical resistance of steel and improving iron loss. To fully obtain this effect, the Si content is preferably 2.0% or more. On the other hand, if the Si content exceeds 8.0%, not only will workability decrease, but the magnetic flux density will also decrease. Therefore, the Si content is preferably 8.0% or less, and more preferably 4.0% or less.

[0104] Mn: 0.005 to 1.0% Mn is an element that has the effect of improving hot workability. To enhance this effect, the Mn content is preferably 0.005% or more, and more preferably 0.01% or more. On the other hand, if the Mn content exceeds 1.0%, the magnetic flux density of the finally obtained grain-oriented electrical steel strip decreases. Therefore, the Mn content is preferably 1.0% or less, and more preferably 0.1% or less.

[0105] Furthermore, in order to further improve the magnetic properties, the composition of the steel material may optionally contain at least one component selected from the group listed below in addition to the above basic components. Ni: 0.03 to 1.50% Sn: 0.01 to 1.50% Sb: 0.005 to 1.50% Cu: 0.03 to 3.0% P: 0.03 to 0.50% Mo: 0.005 to 0.10% Cr: 0.03 to 1.50%

[0106] Ni is an element that has the effect of improving the hot-rolled sheet structure and further enhancing magnetic properties, and can be added as desired. To enhance this effect, the Ni content is preferably 0.03% or more. On the other hand, if the Ni content exceeds 1.50%, secondary recrystallization becomes unstable, which may result in deterioration of magnetic properties. Therefore, the Ni content is preferably 1.50% or less.

[0107] Furthermore, Sn, Sb, Cu, P, Mo, and Cr are elements that further improve magnetic properties and can be added arbitrarily. When adding at least one of these elements, it is preferable to set the content of the element to the aforementioned lower limit or higher in order to enhance the effect. On the other hand, excessive addition inhibits the development of secondary recrystallized grains. Therefore, when adding at least one of these elements, it is preferable to set the content of the element to the aforementioned upper limit or lower.

[0108] Furthermore, the composition of the steel material may further contain an inhibitor element, which is preferably at least one selected from the following group: Al: 0.01 to 0.065% N: 0.005 to 0.012% S: 0.005 to 0.03% Se: 0.005 to 0.03%

[0109] For example, when using an AlN-based inhibitor, Al and N can be added. When using an MnS-based or MnSe-based inhibitor, Mn can be added in addition to either or both Se and S. Multiple inhibitors can also be used in combination.

[0110] Conversely, in the present invention, grain-oriented electrical steel strip can also be produced without using an inhibitor. When an inhibitor is not used, it is preferable to control the contents of Al, N, S, and Se in the composition of the steel material to the following ranges, respectively. On the other hand, the lower limits of the contents of Al, N, S, and Se are not particularly limited and may be 0 ppm. Al: 100ppm or less N:50ppm or less S: 50ppm or less Se: 50ppm or less

[0111] The balance other than the above components is unavoidable impurities and Fe. The unavoidable impurities may include, for example, elements that are mixed in as impurities during the manufacturing process.

[0112] On the other hand, in the manufacturing process of grain-oriented electrical steel strip, primary recrystallization annealing is performed after rolling. During this primary recrystallization annealing, the steel strip undergoes decarburization, reducing the C content. Furthermore, during final annealing, the steel strip undergoes purification, resulting in reductions in Al, N, S, Se, and other elements. As a result, the contents of C, Al, N, S, and Se in the final grain-oriented electrical steel strip are reduced to impurity levels. Therefore, in the chemical composition of grain-oriented electrical steel strip, Al, N, S, and Se can be considered unavoidable impurities. Typically, the Al content is 0.01% or less, and the contents of C, N, S, and Se are each 0.005% or less.

[0113] It should be noted that the variations in the contents of elements other than those mentioned above that are reduced by decarburization and purification are negligible during the manufacturing process, and therefore the contents of other elements contained in the composition of the final grain-oriented electrical steel strip are the same as the composition of the steel material described above. [Example]

[0114] Next, the present invention will be described in more detail based on examples. The following examples are examples of preferred embodiments of the present invention, and the present invention is not limited to these examples. The embodiments of the present invention can be appropriately modified within the scope of the invention, and all such modifications are included in the technical scope of the present invention.

[0115] First, several 0.23 mm thick, finish-annealed steel strips with the same magnetic flux density (B8 = 1.92 T) were prepared. The steel strips were subjected to magnetic domain refinement treatment over the entire longitudinal direction to obtain grain-oriented electrical steel strips. The magnetic domain refinement treatment was carried out under the conditions shown in Table 1 while the steel strips were continuously transported.

[0116] When performing the above-mentioned magnetic domain refinement process, in some examples, distortion was introduced while dynamically controlling the focus of a high-energy beam (electron beam or laser). In examples using electron beam irradiation, the dynamic control was performed based on the previously determined relationship between the bias voltage and the focusing current that results in just focus (Figure 7) or the relationship between the orifice temperature and the focusing current (Figure 12). In examples using laser irradiation, the dynamic control was performed based on the previously determined relationship between the orifice temperature and the focal length that results in just focus (Figure 13). The focusing current that results in just focus is the focusing current that maximizes the beam profile intensity (minimum beam diameter) on the treatment surface (steel strip surface), and was determined by changing the focusing current value and measuring the beam profile intensity using a known beam profiler.

[0117] For comparison, in some cases the magnetic domain refining process was carried out without dynamic focus control.

[0118] Next, for each of the obtained grain-oriented electrical steel strips, the material iron loss W 17 / 50The distance between the closure domain walls of the grain-oriented electrical steel strips within the thickness direction was measured using an X-ray magnetic circularly polarized light emission microscope, and the maximum distance between the domain walls and the difference Δd between the maximum and minimum values ​​of the maximum distance between the domain walls over the entire longitudinal direction of the steel strip were determined. The measurement results are shown in Table 1.

[0119] Next, a three-phase stacked core was fabricated using the obtained grain-oriented electromagnetic steel strips. The stacked core had an overall width of 890 mm, a depth of 800 mm, a lamination thickness of 250 mm, a core mass of approximately 1.0 t, and a capacity of 2000 kVA. The joining method was the step-lap method.

[0120] The resulting loss of the stacked core W 17 / 50 The BF was calculated by comparing it with the iron loss of the material. The results are shown in Table 1.

[0121] As can be seen from the results shown in Table 1, even without dynamic focus control, if other irradiation conditions were the same, material iron loss was obtained that was equivalent to that obtained with dynamic control. However, in the inventive example in which dynamic focus control was performed, fluctuations in the magnetic domain wall distance in the longitudinal direction of the steel strip were suppressed, and a grain-oriented electrical steel strip that met the conditions of the present invention was obtained. Furthermore, the stacked core manufactured using this grain-oriented electrical steel strip met the conditions of the present invention and had an improved BF compared to the comparative example.

[0122] [Table 1] [Explanation of symbols]

[0123] 10a~10h Main magnetic domain 20 Distortion introduction 21a~21d closure domains RD rolling direction

Claims

1. A grain-oriented electrical steel strip in which magnetic domains are refined by linearly introducing strain on at least one surface so as to intersect with the rolling direction, A grain-oriented electrical steel strip, wherein the ratio of the area within the thickness of the sheet where the maximum inter-wall distance of closure domains is 10 μm or more as measured by an X-ray magnetic circular polarization luminescence microscope to the total length of the grain-oriented electrical steel strip in the rolling direction is 50% or more.

2. A stacked core made of multiple grain-oriented electromagnetic steel sheets, a region within the thickness of the grain-oriented electrical steel sheets, in which the maximum inter-wall distance of closure domains as measured with an X-ray magnetic circular polarization luminescence microscope is 10 μm or more, accounts for 50% or more of the total weight of the plurality of grain-oriented electrical steel sheets.

3. A method for producing a grain-oriented electrical steel strip according to claim 1, and subjecting the surface of the steel strip after the finish annealing to a magnetic domain refinement treatment by irradiating the surface of the steel strip with a high-energy beam while continuously transporting the steel strip in the rolling direction of the steel strip, A method for manufacturing a grain-oriented electrical steel strip, wherein, during irradiation of the high-energy beam, strain is introduced while dynamically controlling the focus of the high-energy beam, thereby making the ratio 50% or more.

4. The method for producing a grain-oriented electrical steel strip according to claim 3, the high-energy beam is an electron beam; In the dynamic focus control, Measure the bias voltage, A method for manufacturing a grain-oriented electrical steel strip, comprising adjusting the focusing current of the electron beam in accordance with the measured bias voltage based on a previously determined relationship between the bias voltage and the focusing current.

5. The method for producing a grain-oriented electrical steel strip according to claim 3, the high-energy beam is an electron beam; an orifice is installed in a beam path of the electron beam so as to cut off a part of the electron beam; In the dynamic focus control, measuring the temperature of the orifice; A method for manufacturing a grain-oriented electromagnetic steel strip, comprising adjusting the focusing current of the electron beam in accordance with the measured temperature of the orifice based on a previously determined relationship between the orifice temperature and the focusing current.

6. The method for producing a grain-oriented electrical steel strip according to claim 3, the high-energy beam is a laser beam; an orifice is installed in the beam path of the laser beam so as to cut off a part of the laser beam; In the dynamic focus control, measuring the temperature of the orifice; A method for manufacturing a grain-oriented electromagnetic steel strip, comprising adjusting the position of the focusing lens of the laser beam in accordance with the measured temperature of the orifice based on a previously determined relationship between the orifice temperature and the focal length.

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