Directional electromagnetic steel sheet

Abstract

This grain-oriented electrical steel sheet is the average value aveφ of the angle deviation φ measured at at least 1,000 measurement points spaced 1 mm apart along the rolling direction L. L is 4.0° or less, and the grain size D measured along the rolling direction L L Arrange them in descending order and determine the particle size D that is 10% of the largest. L 10 is (100-15×aveφ L ) mm or less.

Description

[Technical field]

[0001] The present invention relates to a grain-oriented electrical steel sheet. This application claims priority based on Japanese Patent Application No. 2023-106556, filed on June 29, 2023, the contents of which are incorporated herein by reference. [Background technology]

[0002] Grain-oriented electrical steel sheets contain silicon and have grains with a Goss orientation (cubic {110} <001> ) near the easy axis of magnetization. <001> The orientation is almost aligned in the rolling direction during the steel sheet manufacturing process. Such grain-oriented electrical steel sheets are excellent materials for the iron cores of transformers, etc. Among the magnetic properties of grain-oriented electrical steel sheets, the most important are magnetic flux density and core loss.

[0003] The magnetic flux density of grain-oriented electrical steel sheets when a certain magnetizing force is applied tends to be higher as the degree to which the magnetization easy axis of the crystal grains is aligned in the rolling direction of the steel sheet, i.e., the orientation of the crystal orientation, increases. Magnetic flux density B8 is generally used as an index of magnetic flux density. Magnetic flux density B8 is the value of the magnetic flux density of a magnetized grain-oriented electrical steel sheet when a magnetizing force of 800A / m is applied in the rolling direction. In other words, grain-oriented electrical steel sheets with a higher magnetic flux density B8 value are more easily magnetized with a certain magnetizing force and have a higher magnetic flux density, making them more suitable for small, highly efficient transformers.

[0004] In addition, the iron loss W 17 / 50 is used. Iron loss W 17 / 50 is the iron loss when grain-oriented electrical steel sheet is excited with AC current under the conditions of maximum magnetic flux density of 1.7T and frequency of 50Hz. Iron loss W 17 / 50 The smaller the value of the grain-oriented electrical steel sheet, the lower the energy loss and the more suitable it is for transformers.

[0005] There are several methods to reduce iron loss, including increasing electrical resistance by adding Si, which is effective in reducing eddy current loss, reducing the thickness of the steel sheet, reducing the crystal grain size, and aligning the crystal grain orientation, which is effective in reducing hysteresis loss. That is, the higher the magnetic flux density B8, the more the crystal orientation is aligned to the Goss orientation, and the lower the hysteresis loss. Therefore, the higher the magnetic flux density B8, the lower the iron loss W 17 / 50 On the other hand, when the development of Goss oriented grains is promoted in order to improve the degree of integration of the crystal orientation, the crystal grain size tends to become larger, which increases eddy current loss, and there is a trade-off between the fact that even if the B8 value is high, if the crystal grains become too large, the iron loss deteriorates.

[0006] In recent years, methods have been developed to artificially divide the magnetic domain width by introducing distortion through irradiation with laser light or plasma jet, or by forming grooves mechanically or by etching, to control the magnetic domains. By using such methods, in steel sheets in which the degree of integration of crystal orientation is increased and the magnetic flux density is increased, eddy current loss can be reduced and iron loss can be sufficiently reduced even if the secondary recrystallized grain size is large. However, when distortion is introduced into steel sheets, magnetostriction (λ P-P ) increases. Furthermore, if heat treatment is performed at a temperature of about 800°C after magnetic domain refinement, the iron loss reduction effect disappears, so the material cannot be used in applications that require stress relief annealing at 800°C or higher after irradiation. On the other hand, the magnetic domain control method using grooves has the problem of a decrease in magnetic flux density B8.

[0007] Generally, grain-oriented electrical steel sheets are manufactured as follows. A steel sheet material (slab) containing a specified amount of Si is hot-rolled, annealed, and cold-rolled to obtain a steel sheet of the desired thickness. The cold-rolled steel sheet is then annealed (also called primary annealing or decarburization annealing). This annealing causes primary recrystallization, and the primary recrystallized grains contain {110} lattice grains with their easy magnetization axis aligned in the rolling direction. <001> The crystal grains (hereinafter referred to as Goss-oriented grains) are formed with a crystal orientation that is offset by 10° or less from the strict Goss orientation described in the above. This annealing also serves as decarburization annealing. After that, an annealing separator mainly composed of MgO is applied to the surface of the steel sheet on which primary recrystallization has occurred. Next, the steel sheet on which the annealing separator has been applied is wound up to produce a steel sheet coil, and this steel sheet coil is subjected to batch processing annealing (also called secondary recrystallization annealing or finish annealing). This annealing causes the Goss-oriented grains to eat away at other grains, causing secondary recrystallization and forming a so-called glass coating on the surface of the steel sheet. During secondary recrystallization, the Goss-oriented grains grow preferentially due to the influence of inhibitors contained in the steel sheet, and the grain size of the larger grains may be 100 mm or more. Next, while unwinding the steel sheet coil, annealing is performed to flatten the steel sheet on which secondary recrystallization has occurred, and an insulating coating is formed.

[0008] As mentioned above, grain-oriented electrical steel undergoes secondary recrystallization during final annealing, resulting in the formation of {110} <001> The desired magnetic properties are obtained by obtaining a crystal structure consisting of Goss-oriented grains accumulated in the direction. In order to obtain this crystal structure, it is effective to increase the frequency of minor Goss-oriented grains after the primary annealing, or to increase the frequency of grains that have good matching with the Goss-oriented grains in the crystal lattice. For example, <001> The orientation and crystal lattice are highly consistent and have a corresponding orientation relationship of Σ9 with the Goss orientation {778} <447> (≒{111} <112> Direction) and {411} <148> The grains of the Goss orientation (called the corresponding orientation grains) are easily encroached by the Goss orientation grains, and it is effective to include many of them in the primary recrystallized texture. However, when controlling the crystal orientation of the grains generated by the above-mentioned primary annealing, it is difficult to simultaneously increase the frequency of the Goss orientation grains and the frequency of the grains having the corresponding orientation relationship. For example, in the region where the cold rolling reduction is 85% or more, the frequency of the corresponding orientation grains, which are easily encroached by the Goss orientation grains, increases with an increase in the cold rolling reduction, whereas the frequency of the Goss orientation grains decreases with an increase in the cold rolling reduction. In addition, the frequency of the Goss orientation grains, which are the minor orientation in the primary recrystallized texture, increases as the heating rate of the primary annealing is increased, whereas the frequency of the {111} grains, which are the major orientation in the primary recrystallized texture, decreases as the heating rate of the primary annealing is increased. <112> Conversely, the frequency of corresponding orientation grains with orientation decreases as the heating rate of the primary annealing increases. That is, under conventional process control conditions, it has not been possible to independently control the frequency of existence of Goss-oriented grains and the frequency of existence of grains of a corresponding orientation that are easily encroached upon by the Goss-oriented grains.

[0009] Here, the ideal {110} crystal orientation observed in grain-oriented electrical steel sheets is <001> The deviation angle from the orientation is the deviation angle α, and the ideal {110} <001> The deviation angle from the orientation is the deviation angle β, and the ideal {110} <001> The deviation angle from the orientation is defined as deviation angle γ. The angle deviation θ is the ideal {110} <001> Define the angular deviation θ from the azimuth. θ = (α 2 +β 2 +γ 2 ) 1 / 2 (Formula A)

[0010] As mentioned above, the Goss orientation grains are not crystal grains that have a Goss orientation (ideal Goss orientation) in the strict sense (called ideal Goss orientation grains). <001> ) does not necessarily coincide completely with the rolling direction, and there is an angle deviation θ between the easy axis of magnetization and the rolling direction. Crystal grains for which the angle deviation θ from the ideal Goss orientation based on (Equation A) is 10° or less are called Goss-oriented grains (practical Goss-oriented grains). When the angle deviation θ of practical Goss-oriented grains increases, the alignment of the crystal orientation decreases, and the magnetic flux density B8 decreases.

[0011] Generally, the Goss-oriented grains contained in the steel sheet after primary recrystallization include grains with a large angle deviation θ. However, when the grains grow by secondary recrystallization, excluding the effect of the size advantage of the grain size at the beginning of secondary recrystallization, the smaller the angle deviation θ among the Goss-oriented grains, the greater the driving force for grain growth and the more they continue to grow preferentially until secondary recrystallization is completed. Therefore, the smaller the angle deviation θ of the Goss-oriented grains, the larger the grain size after secondary recrystallization tends to be. In other words, in a manufacturing method that highly orients secondary recrystallized grains in the Goss orientation, specific grains are preferentially grown, so the grain size is inevitably likely to increase.

[0012] In addition, during secondary recrystallization, the steel sheet is not flat but curved due to being wound in a coil, but the crystal grains grow while maintaining the linearity of the crystal orientation. Therefore, when the coiled steel sheet is unwound and flattened after secondary recrystallization, some parts of the crystal grains are not parallel to the surface of the grain-oriented electrical steel sheet. This coil unwinding mainly increases the value of the deviation angle β and also increases the angle deviation θ. The increase in the angle deviation θ due to coil unwinding is more noticeable the larger the crystal grain size. In other words, Goss-oriented grains with a small angle deviation θ tend to grow preferentially during secondary recrystallization, but if the secondary recrystallized grain size becomes coarse, the angle deviation θ increases due to coil unwinding.

[0013] Patent Document 1 discloses a technique in which an etching process is performed on the surface of a steel sheet after final cold rolling to form linear grooves that satisfy predetermined conditions, and then in the primary annealing, the heating rate in the steel sheet temperature range of 500°C to 750°C is made faster in the linear groove parts than in parts other than the linear grooves. Patent Document 1 artificially creates parts with a fast heating rate and parts with a slow heating rate, thereby intentionally arranging parts (linear groove parts) where the frequency of (110)

[0001] orientation grains is increased, and parts (parts other than the linear grooves) where the frequency of (111)

[0112] orientation grains is increased.

[0014] Patent Document 2 discloses a technique in which a laser beam is irradiated multiple times at a predetermined interval PL in the rolling direction toward the surface of a silicon steel sheet between cold rolling and finish annealing. When secondary recrystallization is caused in this silicon steel sheet by finish annealing, the positions along the trajectory of the laser beam become grain boundaries that penetrate the front and back of the silicon steel sheet. In Patent Document 2, after finish annealing, the length of the crystal grains in the rolling direction is at most about 30 mm, which corresponds to the irradiation interval PL, and the direction of the easy axis of magnetization (cubic crystal {110} <001> The angle deviation β between the rolling direction and the rolling direction is within a range of 0° to 6°.

[0015] Patent Document 3 discloses a method for manufacturing a grain-oriented electrical steel sheet that has a high magnetic flux density and a small difference in the degree of orientation concentration in the Goss orientation between the inner and outer periphery of a coil with different curvatures, based on a high-temperature slab heating process. In Patent Document 3, a cold-rolled steel sheet is locally heated in a linear manner, and this linearly heated portion acts as a barrier to the growth of secondary recrystallized grains, suppressing the growth of secondary recrystallized grains. [Prior art documents] [Patent documents]

[0016] [Patent Document 1] Japanese Patent Application Publication No. 2007-169762 [Patent Document 2] International Publication No. WO2012 / 014290 [Patent Document 3] Japanese Patent Application Publication No. 2022-161269 Summary of the Invention [Problem to be solved by the invention]

[0017] As described above, attempts have been made to improve the magnetic properties of grain-oriented electrical steel sheets, but the improvements in magnetic properties achieved by conventional techniques are not sufficient.

[0018] The present invention has been made in view of the above problems, and has an object to provide a grain-oriented electrical steel sheet that is excellent in both magnetic flux density and core loss. [Means for solving the problem]

[0019] That is, the gist of the present invention is as follows.

[0020] [1] A grain-oriented electrical steel sheet according to one aspect of the present invention is The deviation angle from the ideal Goss orientation with the normal direction Z of the rolling surface as the rotation axis is defined as α, The deviation angle from the ideal Goss orientation with the rolling direction C as the rotation axis is defined as β. The deviation angle from the ideal Goss orientation with the rolling direction L as the rotation axis is defined as γ. The deviation angle of the crystal orientation measured at one measurement point on the plate surface is expressed as (α β γ), The angle deviation at the one measurement point is φ = (α 2 +β 2 ) 1 / 2 Define it as: The average value of the angle deviation φ obtained at at least 1,000 measurement points spaced 1 mm apart along the rolling direction L is aveφ L When we define The above aveφ L But, aveφ L ≦4.0° is satisfied, The deviation angles of the crystal orientation measured at two adjacent measurement points on the plate surface, spaced 1 mm apart, are represented as (α1β1γ1) and (α2β2γ2), [(α2-α1) 2 +(β2-β1) 2 +(γ2-γ1) 2 ] 1 / 2 The midpoint between the two measurement points that satisfy ≧1.0° is defined as the grain boundary GB. The grain size in the rolling direction L determined based on the grain boundary GB is expressed in mm as D L Define it as: Grain size D along the rolling direction L L Arrange them in ascending order and determine the particle size that is 10% of the largest by number in mm. L When defined as 10, D L 10 is D L 10≦100-15×abeφ L Meet the following. Effect of the Invention

[0021] According to the above aspect of the present invention, it is possible to provide a grain-oriented electrical steel sheet that is excellent in both magnetic flux density and core loss.

[0022] Specifically, according to the above-described aspect of the present invention, it is possible to provide a grain-oriented electrical steel sheet that has excellent magnetic flux density because the angle deviation in the rolling direction is controlled to be small, and that has excellent iron loss even without magnetic domain control (magnetic domain refining treatment) because the grain size in the rolling direction is controlled to be small.

[0023] According to the above-mentioned aspect of the present invention, it is possible to reduce the adverse effects of conventional magnetic domain control (e.g., deterioration of transformer noise due to laser magnetic domain control, reduction in magnetic flux density due to the introduction of grooves, etc.), and to provide a grain-oriented electrical steel sheet that is excellent in both magnetic flux density and iron loss. [Brief description of the drawings]

[0024] [Figure 1] FIG. 2 is a schematic diagram showing crystal orientation measurement points spaced 1 mm apart along the rolling direction on a steel sheet. [Diagram 2] FIG. 1 is a diagram showing the influence of the average value of the angle deviation in the rolling direction and the crystal grain size on the magnetic properties of the grain-oriented electrical steel sheet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] A preferred embodiment of the present invention will be described in detail. However, the present invention is not limited to the configuration disclosed in this embodiment, and various modifications are possible within the scope of the present invention. In addition, the lower and upper limits of the numerical ranges described below are included in the ranges. Numerical values ​​indicated as "greater than" or "less than" are not included in the numerical ranges. In addition, "%" in relation to chemical composition means "mass %" unless otherwise specified.

[0026] As mentioned above, the ideal Goss orientation is {110} <001> The frequency of practical Goss oriented grains, which have small angular deviations θ and φ with respect to the orientation, increases as the heating rate of the primary annealing (decarburization annealing) increases. <447> (≒{111} <112> ) direction and {411} <148> The frequency of crystal grains that are easily encroached upon by Goss orientation grains (called corresponding orientation grains) decreases as the heating rate of the primary annealing increases. Therefore, it has been difficult to increase the ratio of practical Goss orientation grains while also increasing the ratio of corresponding orientation grains in the primary annealing.

[0027] The technique described in Patent Document 1 forms linear grooves on the surface of a steel sheet by etching, and increases the heating rate of the linear grooves during primary annealing to arrange a portion with a high ratio of Goss-oriented grains (linear groove portion) and a portion with a high ratio of corresponding-oriented grains (portion other than the linear grooves). However, with this method, it is difficult to increase the difference in heating rate during primary annealing between the linear groove portion and other portions, and the effect obtained is limited. Specifically, the difference in heating rate between the linear groove portion and the portion other than the linear grooves is not so large. For example, even if the entire steel sheet is heated at 100°C / sec, the degree to which the sheet thickness of this portion is thinned by the formation of the grooves does not exceed about 10% of the original sheet thickness (because the normal groove depth is about 20 μm or less, which is about 10% or less of the sheet thickness), and considering the thermal conductivity of the steel sheet, the heating rate ratio is less than the sheet thickness ratio for the same heat input, so the ratio of Goss-oriented grains in the linear groove portion is difficult to increase compared to the portion other than the linear grooves. In addition, in this method, since the heating rate of the linear groove portion is increased during the primary annealing, the grain size of the Goss oriented grains formed in the linear groove portion after the primary annealing does not increase in size compared to the overall average primary recrystallized grain size, but remains the same or fine.

[0028] In addition, the technology described in Patent Document 2 irradiates a laser beam toward the steel sheet surface before finish annealing. However, this method only controls the laser beam irradiation area to the grain boundary of secondary recrystallization, and does not control the orientation of Goss orientation grains generated by primary recrystallization. In addition, the area heated by laser irradiation is only the area near the surface where the laser is irradiated, and heat diffusion to the surrounding area is significant, so it is usually not possible to ensure a thermal history that recrystallizes the steel sheet.

[0029] In addition, the technology described in Patent Document 3 irradiates a laser beam toward the surface of the steel sheet after cold rolling. However, in this method, as in the above, the laser beam irradiation portion is only controlled to the grain boundary of the secondary recrystallization, and the heating rate is not controlled, so the orientation of the Goss orientation grains generated by the primary recrystallization is not controlled. In Patent Document 3, the laser beam irradiation portion acts as a barrier to the growth of the secondary recrystallized grains, thereby only reducing the grain size in the rolling direction of the secondary recrystallized grains, and the grain growth temperature range in the local heating region that is effective for increasing the diameter of the Goss orientation grains in the local heating region is not secured. This method may be able to reduce the difference in the orientation accumulation degree to the Goss orientation at the inner and outer periphery of the coil with different curvatures, but it does not obtain Goss orientation grains whose crystal orientation is close to the ideal Goss orientation. In other words, this method suppresses the decrease in magnetic flux density due to the increase in the grain size in the rolling direction of the secondary recrystallized grains, but does not aim to fundamentally increase the orientation of the Goss orientation grains.

[0030] In this embodiment, it has been discovered for the first time that a grain-oriented electrical steel sheet having excellent quality can be obtained by locally and rapidly heating the steel sheet to form a locally heated region prior to the primary annealing (decarburization annealing). The locally heated region formed prior to the primary annealing is arranged locally with respect to the surface of the steel sheet. The crystalline structure of this locally heated region is composed of one or both of a recrystallized structure and a recovered structure at the end of the localized rapid heating. The crystalline structure of the non-locally heated region of the steel sheet surface other than the locally heated region remains as it is cold-rolled and is therefore composed of a cold-worked structure.

[0031] The heating rate of the local heating region is preferably 500°C / sec or more, preferably 2000°C / sec or more, more preferably 5000°C / sec or more, and even more preferably 10000°C / sec or more. In this way, it was found that when a local heating region is formed on the surface of a steel sheet before primary annealing and then the steel sheet is subjected to primary annealing, a large number of crystal grains having a practical Goss orientation are formed in the local heating region. It was also found that, among the practical Goss orientation crystals formed, the ratio of Goss orientation grains having smaller angle deviations θ and φ from the ideal Goss orientation increases, and the grain size of the Goss orientation grains increases.

[0032] The frequency of Goss-oriented grains in the locally heated region is higher than that in the non-locally heated region. This characteristic is due to the fact that the non-locally heated region retains the processed structure. Specifically, when local rapid heating is performed, recovery and recrystallization occur in the locally heated region, resulting in the generation of practical Goss-oriented grains and facilitating grain growth, but recovery and recrystallization do not occur in the non-locally heated region.

[0033] The locally heated regions having the above characteristics are scattered on the steel sheet surface by localized rapid heating before the primary annealing, and then the primary annealing and secondary annealing are performed. The Goss oriented grains formed in the locally heated regions grow preferentially during the secondary annealing after the primary annealing. The Goss oriented grains formed in the locally heated regions include Goss oriented grains with large crystal grain size that are close to the ideal Goss orientation with particularly small angle deviation θ and angle deviation φ, and such Goss oriented grains grow preferentially in the secondary recrystallization.

[0034] Since the Goss-oriented grains that become the nuclei of secondary recrystallization are supplied to the locally heated region, it is not necessary to form Goss-oriented grains in the matrix portion other than the locally heated region, i.e., the non-locally heated region other than the locally heated region, by primary annealing. Therefore, the heat treatment conditions for the primary annealing are set to be slow heating conditions with a slow heating rate, and the {111} <112> Directions and <148> It is also possible to adopt primary annealing conditions that will form many corresponding orientation grains in the non-locally heated region. For example, by setting the heating rate in the primary annealing to 300°C / sec or less, many Goss orientation grains with large crystal grain size close to the ideal Goss orientation will be formed in the locally heated region, while few Goss orientation grains will be formed in the non-locally heated region, and many corresponding orientation grains will be formed.

[0035] As described above, in the locally heated region of a steel sheet (decarburized annealed steel sheet) that has been subjected to localized rapid heating and primary annealing, many Goss-oriented grains that are close to the ideal Goss orientation and have large grain sizes are present. On the other hand, in the matrix portion (non-locally heated region), there are almost no large-sized Goss-oriented grains, and many corresponding-oriented grains that are easily eroded can be present. When such a steel sheet is subjected to secondary annealing, the Goss-oriented grains that are present in the locally heated region, that are close to the ideal Goss orientation and have large grain sizes, start to grow preferentially and grow toward the non-locally heated region.

[0036] In addition, when the locally heated regions are scattered on the steel sheet surface by the localized rapid heating before the primary annealing, the size, shape, and arrangement of the crystal grains after the secondary annealing can be controlled by appropriately arranging the localized rapid heating on the steel sheet surface. For example, if the grain growth of Goss-oriented grains starting from one locally heated region is stopped by collision with another Goss-oriented grain starting from an adjacent locally heated region, the grain size of the Goss-oriented grains at the end of the secondary annealing becomes small, and the steel sheet can have excellent iron loss. In particular, as described above, in the early stage of the secondary annealing, the Goss-oriented grains that grow preferentially from the locally heated affected region have a crystal orientation close to the ideal Goss orientation, so that a good magnetic flux density can be obtained despite the small secondary recrystallized grain size.

[0037] The grain-oriented electrical steel sheet according to the present embodiment has been obtained based on the above technical concept. The characteristics of the grain-oriented electrical steel sheet according to the present embodiment will be specifically described.

[0038] The grain-oriented electrical steel sheet (base steel sheet) according to this embodiment is The deviation angle from the ideal Goss orientation with the normal direction Z of the rolling surface as the rotation axis is defined as α, The deviation angle from the ideal Goss orientation with the rolling direction C as the rotation axis is defined as β. The deviation angle from the ideal Goss orientation with the rolling direction L as the rotation axis is defined as γ. The deviation angle of the crystal orientation measured at one measurement point on the plate surface is expressed as (α β γ), The angle deviation at the one measurement point is φ=(α 2 +β 2 ) 1 / 2 Define it as: The average value of the angle deviation φ obtained at at least 1,000 measurement points spaced 1 mm apart along the rolling direction L is aveφ L When we define Above aveφ L But, aveφ L ≦4.0°.

[0039] In addition, the grain-oriented electrical steel sheet (base steel sheet) according to this embodiment has The deviation angles of the crystal orientations measured at two adjacent measurement points on the plate surface, spaced 1 mm apart, are represented as (α1β1γ1) and (α2β2γ2), [(α2-α1) 2 +(β2-β1) 2 +(γ2-γ1) 2 ] 1 / 2 The midpoint between the two measurement points that satisfy ≧1.0° is defined as the grain boundary GB. The grain size in the rolling direction L calculated based on the above grain boundary GB is expressed in mm as D L Define it as: Grain size D measured along the rolling direction L L Arrange them in ascending order and determine the particle size that is 10% of the largest by number in mm. L When defined as 10, Above D L 10 is D L10≦100-15×abeφ L Meet the following.

[0040] In the grain-oriented electrical steel sheet according to this embodiment, when all of the above conditions are satisfied simultaneously, it is possible to reduce the adverse effects of conventional magnetic domain control (e.g., deterioration of transformer noise due to laser magnetic domain control, reduction in magnetic flux density due to the introduction of grooves, etc.), and to improve both the magnetic flux density and the iron loss characteristics.

[0041] In this embodiment, the angle deviation φ is defined by the deviation angles α and β. In general, the angle deviation θ is often evaluated by three components, the deviation angles α, β, and γ. However, in this embodiment, the angle deviation φ is defined by two components, the deviation angles α and β, excluding the deviation angle γ, which has little effect on the magnetic flux density and iron loss characteristics. If the above conditions are satisfied using this angle deviation φ, the above effects can be obtained. On the other hand, the grain boundaries and grain sizes may be determined based on the three components, the deviation angles α, β, and γ.

[0042] Above aveφ L A mean angle deviation φ of 4.0° or less means that the average angular deviation φ is small at each measurement point along the rolling direction L. In other words, this means that the angular deviation between the rolling direction L and the direction of the easy axis of magnetization is small. As a result, the magnetic properties, particularly the magnetic flux density, are favorably improved. aveφ L is preferably 3.5°, more preferably 3.2° or less, more preferably 3.0° or less, and even more preferably 2.7° or less. L Since the smaller the value, the better, the lower limit is not particularly limited. L It is not easy to make aveφ zero. L It is sufficient that the angle is 0.5° or more, and 1.0° or more.

[0043] Above D L 10 is (100-15×aveφ L) mm or less means that the crystal grains do not grow coarsely in the rolling direction L. If the crystal grains do not grow coarsely in the rolling direction L, it is possible to suppress an increase in the above-mentioned misalignment angles, particularly the misalignment angle β. If the increase in the misalignment angle β is suppressed, a decrease in magnetic flux density is suppressed. In addition, if the crystal grains do not grow coarsely in the rolling direction L, the magnetic domains are subdivided without the application of conventional magnetic domain control technology. If the magnetic domains are subdivided, an increase in iron loss is suppressed. D L When 10 satisfies the above conditions, the magnetic flux density and core loss characteristics are favorably improved. L 10 is (90-15×aveφ L ) mm or less, and (80-15×aveφ L ) mm or less is more preferable. L Since the smaller the value, the more preferable it is, the lower limit is not particularly limited. For example, D L The number 10 may be 5 mm or more, or 10 mm or more.

[0044] The above-mentioned deviation angles α, β, γ, etc. can be measured by setting a measurement line including at least 1000 measurement points at 1 mm intervals on the rolled surface to measure the crystal orientation. For example, the crystal orientation can be measured by the X-ray diffraction method (Laue method). The Laue method is a method in which an X-ray beam is irradiated onto a steel sheet and the transmitted or reflected diffraction spots are analyzed. By analyzing the diffraction spots, the crystal orientation at the location where the X-ray beam is irradiated can be identified. By changing the irradiation position and analyzing the diffraction spots at multiple locations, the crystal orientation distribution at each irradiation position can be measured. The Laue method is a method suitable for measuring the crystal orientation of a metal structure having coarse crystal grains.

[0045] It is sufficient that the number of measurement points for the crystal orientation is at least 1000, but it is preferable to appropriately increase the number of measurement points depending on the size of the secondary recrystallized grains. For example, if the number of measurement points for measuring the crystal orientation is 1000 and the number of secondary recrystallized grains included in the measurement line is less than 20, it is preferable to extend the measurement line by increasing the measurement points at 1 mm intervals so that the measurement line includes 20 or more secondary recrystallized grains. In addition, if it is difficult to set 1000 measurement points on one measurement line, multiple measurement lines may be set to measure the crystal orientation at a total of 1000 or more measurement points.

[0046] The crystal orientation is measured at 1 mm intervals on the rolled surface, and the above-mentioned deviation angles α, β, γ, etc. are determined for each measurement point. Based on the deviation angles at each measurement point, the angle deviations φ, aveφ L , grain boundary GB, grain size D L , D L We just need to find 10. L 10 is the particle size D L Then, arrange the crystal grains with a diameter of 2 mm or more in order of size, and find the grain size that is 10% by number from the largest. In addition, if the irradiation area of ​​the X-ray beam at the measurement point of the crystal orientation by the Laue method straddles two crystal grains, and it is impossible to determine which crystal grain the X-ray diffraction results come from, then add 0.5 mm to the grain sizes of the two crystal grains.

[0047] The grain-oriented electrical steel sheet according to this embodiment has the above-mentioned technical features, which may be expressed as follows: The features of the grain-oriented electrical steel sheet according to this embodiment will be explained again.

[0048] The grain-oriented electrical steel sheet according to this embodiment is φ defined below m ≦4.0° is satisfied, The D10 defined below is f(φ m ) or less. In the rolling direction (RD), n points (at least 1000 points) are set at 1 mm pitch to measure the crystal orientation, and the ideal {110} around ND, TD, and RD at measurement point i (i = 1 to n) is <001> Deviation angle from azimuth α i , β i , γ i Measure and calculate φ using the following formula (1). i After determining the average angle deviation φ m Request. φ i =(α i 2 +β i 2 ) 1 / 2 (1) φ m =[Σ i=1 n φ i ] / n=[Σ i=1 n (α i 2 +β i 2 ) 1 / 2 ] / n (2) f(φ m )=100-15·φ m (3) In addition, in the row of crystal orientation measurement positions in the rolling direction (RD) measured above, [(α i -α i=1 ) 2 +(β i -β i=1 ) 2 +(γ i -γ i=1 ) 2 ] 1 / 2 If the value of D10 differs by 1° or more, it is determined that a grain boundary exists between the adjacent measurement positions, and the distance between adjacent grain boundaries is the grain size D in the rolling direction (RD) of one grain. When the grains are arranged in order of increasing grain size D, the grain size of the grain that is 10% from the largest grain size D among all the grains is determined to be D10.

[0049] Regarding the angle deviation φ, the average angle deviation φ of the steel plate in the rolling direction (RD) m Define. As shown in Figure 1, n points (at least 1000 points) are set at 1 mm pitch in the rolling direction (RD) to measure the crystal orientation, forming a measurement point sequence. The crystal orientation can be measured using an X-ray diffraction device using the Laue method. At measurement point i, the ideal {110} <001> Deviation angle from azimuth α i , β i , γ i Measure and calculate φ in the above formula (1). i Then, the average angle deviation φ is calculated using the above formula (2). m is obtained. In addition, for the transverse direction (TD), one row of measurement points may be set at any position, or multiple rows of measurement points may be set in the transverse direction (TD) to be used as measurement positions. In particular, when there is variation in the magnetic properties in the transverse direction (TD), multiple rows of measurement points must be set in the coil (steel strip) width direction (transverse direction (TD)) to obtain information on the crystal orientation that characterizes the average magnetic properties in the transverse direction (TD) of the magnetic properties. When multiple rows of measurement points are set in the transverse direction (TD) for measurement, the value of n is the number of all measurement points.

[0050] Next, when the crystal grains are arranged in order of size, the grain size (D10) of the crystal grain that is 10% from the largest among all the crystal grains is defined. As described above, the crystal orientation was measured at each measurement position, and then the [(α i -α i=1 ) 2 +(β i -β i=1 ) 2 +(γ i -γ i=1 ) 2 ] 1 / 2 If the value of is shifted by 1° or more, it is determined that a grain boundary exists between the adjacent measurement positions, and if the value between the adjacent measurement positions is less than 1°, it is determined that a grain boundary does not exist between the adjacent measurement positions. In the example shown in Figure 1, the φ of the measurement position located in the center in the rolling direction (RD) is φ i Then, φ i-1 and φ i-2 Between [(αi=1 -α i-2 ) 2 +(β i=1 -β i-2 ) 2 +(γ i=1 -γ i-2 ) 2 ] 1 / 2 The value of exceeds 1°, the grain boundary a exists between these measurement points, and φ i+1 and φ i+2 Between [(α i+2 -α i+1 ) 2 +(β i+2 -β i+1 ) 2 +(γ i+2 -γ i+1 ) 2 ] 1 / 2 exceeds 1°, and grain boundary b exists between these measurement points. The grain size D in the rolling direction (RD) formed by grain boundary a and grain boundary b is defined as 1 mm × [(i+2)-(i-1)] = 3 mm.

[0051] Furthermore, the grain size D obtained by such a procedure is 1 mm or more, but when determining D10, a grain size D of 2 mm or more is used. As described above, the grain boundaries and grain size D are determined within the range measured in the rolling direction (RD), and the grains with D values ​​of 2 mm or more are arranged in order of increasing D value. The grain size of the grains that are 10% from the largest among all the grains is defined as D10. In addition, there are cases where the X-ray irradiation area at the measurement point straddles two crystal grains, making it impossible to determine which crystal grain it is. In such cases, the crystal grain size of the two straddling crystal grains is assigned 0.5 mm each.

[0052] The investigations conducted by the present inventors will be specifically described below.

[0053] As one aspect of the localized rapid heating, a case where spot current heating by electric resistance heating is used will be described. In the spot current heating, spot electrodes are pressed against both sides of a steel sheet so as to face each other, and an electric current is passed between the spot electrodes to spot current heating the electrode holding portion of the steel sheet. A steel having the composition shown in Table 1 was used, and a cold-rolled steel sheet having a sheet thickness of 0.22 mm was obtained by hot rolling and cold rolling. This steel sheet was subjected to spot current heating. The spot current heating was performed using a copper electrode having a diameter of 3 mm under the following conditions: a current of 5.0 kA or less, which is a range in which the steel sheet surface does not melt, a current time of 20 milliseconds to 80 milliseconds, an electrode pressure of 50 kgf to 150 kgf, and an electrode holding time after current of 0.1 to 0.5 seconds.

[0054] [Table 1]

[0055] This cold-rolled steel sheet was subjected to decarburization annealing (primary annealing). In the decarburization annealing, the cold-rolled steel sheet was heated at a heating rate of 20°C / sec and held at 830°C for 90 seconds. After further nitriding, an annealing separator mainly composed of MgO was applied, and then secondary annealing was performed. The secondary annealing conditions were a hydrogen-nitrogen atmosphere, a heating rate of 15°C / hr (°C / hr), and holding at 1200°C for 20 hr (hr).

[0056] For the grain-oriented electrical steel sheets manufactured by the above method (without domain control), m (aveφ L ) and D10(D L 10) and evaluated the magnetic properties. Figure 2 shows the effect of the average value of the angular deviation in the rolling direction and the grain size on the magnetic properties of the grain-oriented electrical steel sheet. In Figure 2, the horizontal axis is φ m (aveφ L ), and the vertical axis is D10(D L 10) In addition, in Fig. 2, B8 ≥ 1.93T and W 17 / 50 If the value satisfies ≦0.79W / kg, mark it with a circle, and mark it with B8 or W 17 / 50 Cases where at least one of the above conditions is not met are indicated with a black circle.

[0057] From Figure 2, φ m (aveφ L ) is 4.0° or less, and D10 is f(φ m ) or less (D L 10 is (100-15×aveφ L ) or less), good magnetic properties can be obtained, specifically, both the magnetic flux density and the core loss are excellent even without domain control.

[0058] The current-carrying electrode used in the spot current heating has a circular shape, and its diameter, in terms of the circle equivalent diameter, is preferably 0.5 mmφ to 10 mmφ, and more preferably 1 mmφ to 5 mmφ. Note that, although a circular current-carrying electrode was used in the above, it is sufficient to locally increase the heating rate of the cold-rolled steel sheet, form Goss-oriented grains in this region, and cause the grains to grow, and the electrode shape may be other shapes, for example, elliptical or linear.

[0059] A preferred chemical composition of the grain-oriented electrical steel sheet according to this embodiment will be described.

[0060] The grain-oriented electrical steel sheet according to this embodiment may have a chemical composition that contains, by mass fraction, 2.0% to 7.0% Si, with the remainder being Fe and impurities. The above chemical composition has a crystal orientation of {110} <001> This is a preferred chemical composition for controlling the orientation of the particles.

[0061] Furthermore, this grain-oriented electrical steel sheet may contain known optional elements in place of a portion of Fe in order to improve the magnetic properties. There is no need to set a lower limit for the optional elements, and the lower limit may be 0%. Furthermore, the upper limit for the optional elements may be set to a range in which no significant decrease in magnetic flux density or iron loss occurs. The upper limit values ​​serving as a guide for each optional element are listed below.

[0062] Specifically, the grain-oriented electrical steel sheet (base steel sheet) according to this embodiment has a chemical composition, in mass%, of: Si: 2.0-7.0%, C: 0 to 0.0050%, Mn: 0-1.0%, S and Se: 0 to 0.0150% in total, Al: 0 to 0.0650%, N: 0 to 0.0050% Nb, V, Mo, Ta, and W: 0 to 0.050% in total, Cu: 0-0.40%, Bi: 0 to 0.010%, B: 0~0.080%, P: 0-0.50%, Ti: 0 to 0.0150%, Sn: 0-0.10%, Sb: 0 to 0.10%, Cr: 0~0.30%, Ni: 0-1.0% and the remainder being Fe and impurities.

[0063] Si: 2.0-7.0% Si (silicon) is a basic element for base steel sheet. If the Si content is less than 2.0%, eddy current loss cannot be sufficiently reduced, and good magnetic properties cannot be obtained. Therefore, the Si content of the base steel sheet is set to 2.0% or more. The Si content is preferably 2.50% or more, and more preferably 3.0% or more. On the other hand, if the Si content exceeds 7.0%, the steel sheet becomes embrittled and the sheet passing property during production is significantly deteriorated, so the Si content of the base steel sheet is set to 7.0% or less. The Si content is preferably 4.50% or less, and more preferably 4.0% or less.

[0064] C: 0 to 0.0050% C (carbon) is a selective element for the base steel sheet. C is contained in the steel slab, but if excessive C remains in the base steel sheet after finish annealing, good core loss characteristics may not be obtained. Therefore, the C content of the base steel sheet may be 0.0050% or less. The C content is preferably 0.0040% or less, more preferably 0.0030% or less. On the other hand, the lower limit of the C content of the base steel sheet is not particularly limited and may be 0%. However, since it is not industrially easy to make the C content 0%, the C content may be more than 0% or may be 0.00010% or more.

[0065] Mn: 0-1.0% Mn (manganese) is an optional element for the base steel sheet. Mn is contained in the steel slab, but if it is contained in excess, the steel undergoes a phase transformation during secondary recrystallization annealing, secondary recrystallization does not proceed sufficiently, and good magnetic properties may not be obtained. Therefore, the Mn content of the base steel sheet may be 1.0% or less. The Mn content is preferably 0.50% or less, more preferably 0.20% or less. On the other hand, the lower limit of the Mn content of the base steel sheet is not particularly limited and may be 0%. However, since Mn forms MnS and MnSe and has the effect of acting as an inhibitor during secondary recrystallization, the Mn content may be more than 0% or may be 0.00010% or more.

[0066] Sum of S and Se: 0 to 0.0150% S (sulfur) and Se (selenium) are optional elements for the base steel sheet. S and Se are contained in a steel slab, but if S and Se remain in excess in the base steel sheet after final annealing, they may adversely affect the magnetic properties. Therefore, the total content of S and Se in the base steel sheet may be 0.0150% or less. The total content of S and Se is preferably 0.010% or less, more preferably 0.0050% or less. On the other hand, the lower limit of the total content of S and Se in the base steel sheet is not particularly limited and may be 0%. However, since S and Se form MnS and MnSe and have the effect of acting as an inhibitor during secondary recrystallization, the total content of S and Se may be more than 0% or may be 0.00010% or more.

[0067] Al: 0 to 0.0650% Al (aluminum) is a selective element for the base steel sheet. Al is contained in the steel slab, but if excessive Al remains in the base steel sheet after finish annealing, it may adversely affect the magnetic properties. Therefore, the Al content of the base steel sheet may be 0.0650% or less. The Al content is preferably 0.040% or less, more preferably 0.035% or less. On the other hand, the lower limit of the Al content of the base steel sheet is not particularly limited and may be 0%. However, since Al forms AlN and has the effect of acting as an inhibitor during secondary recrystallization, the Al content may be more than 0% or may be 0.00010% or more. The above Al content is acid-soluble Al (sol.Al).

[0068] N: 0 to 0.0050% N (nitrogen) is a selective element for the base steel sheet. N is contained in the steel slab, but if excessive N remains in the base steel sheet after finish annealing, it may adversely affect the magnetic properties. Therefore, the N content of the base steel sheet may be 0.0050% or less. The N content is preferably 0.0040% or less, more preferably 0.0030% or less. On the other hand, the lower limit of the N content of the base steel sheet is not particularly limited and may be 0%. However, since N forms AlN and has the effect of acting as an inhibitor during secondary recrystallization, the N content may be more than 0% or may be 0.00010% or more.

[0069] Total of Nb, V, Mo, Ta, and W: 0 to 0.050% Nb (niobium), V (vanadium), Mo (molybdenum), Ta (tantalum), and W (tungsten) are optional elements for the base steel sheet. If an excessive amount of Nb group elements (one or more of Nb, V, Mo, Ta, and W) remains in the base steel sheet, it may adversely affect the magnetic properties. Therefore, the total content of Nb, V, Mo, Ta, and W in the base steel sheet may be 0.050% or less. The Nb group elements are preferably 0.030% or less, preferably 0.020% or less, and more preferably 0.010% or less. On the other hand, the total content of Nb, V, Mo, Ta, and W in the base steel sheet is not particularly limited and may be 0%. However, since Nb, V, Mo, Ta, or W forms carbides, nitrides, or carbonitrides and has the effect of acting as an inhibitor during secondary recrystallization, the total content of Nb, V, Mo, Ta, and W may be more than 0% or may be 0.003% or more.

[0070] Cu: 0-0.40% Cu (copper) is an optional element for the base steel sheet. If the Cu content exceeds 0.40%, the steel sheet may become embrittled during hot rolling. Therefore, the Cu content of the base steel sheet may be 0.40% or less. The Cu content is preferably 0.30% or less, more preferably 0.10% or less. On the other hand, the lower limit of the Cu content is not particularly limited and may be 0%. However, since Cu has the effect of increasing the concentration of Goss orientation and improving magnetic properties, the Cu content may be more than 0% or may be 0.010% or more.

[0071] Bi: 0 to 0.010% Bi (bismuth) is an optional element for the base steel sheet. If the Bi content exceeds 0.010%, the coating adhesion may decrease. Also, if the purification during the final annealing is insufficient and Bi remains in excess, it may have an adverse effect on the magnetic properties. Therefore, the Bi content of the base steel sheet may be 0.010% or less. The Bi content is preferably 0.0050% or less, more preferably 0.0020% or less, and more preferably 0.0010% or less. On the other hand, the lower limit of the Bi content is not particularly limited and may be 0%. However, since Bi has an effect of improving the magnetic flux density, the Bi content may be more than 0% or may be 0.00050% or more.

[0072] B: 0~0.080% B (boron) is an optional element for the base steel sheet. If the B content exceeds 0.080%, the variation (standard deviation) of the magnetic flux density may become large. Therefore, the B content may be 0.080% or less. The Bi content is preferably 0.070% or less, more preferably 0.060% or less. On the other hand, the lower limit of the B content is not particularly limited and may be 0%. However, since B forms nitrides and has the effect of acting as an inhibitor during secondary recrystallization, the B content may be more than 0% or may be 0.00050% or more.

[0073] P: 0~0.50% P (phosphorus) is an optional element for the base steel sheet. If the P content exceeds 0.50%, the workability of the steel sheet may be significantly reduced. Therefore, the P content of the base steel sheet may be 0.50% or less. The P content is preferably 0.30% or less, and more preferably 0.10% or less. On the other hand, the lower limit of the P content is not particularly limited and may be 0%. However, since P has the effect of improving the texture and improving the magnetic properties of the steel sheet, the P content may be more than 0% or may be 0.0020% or more.

[0074] Ti: 0 to 0.0150% Ti (titanium) is an optional element for the base steel sheet. If the Ti content exceeds 0.0150%, the magnetic properties may be significantly reduced. Therefore, the Ti content of the base steel sheet may be 0.0150% or less. The Ti content is preferably 0.0130% or less, more preferably 0.010% or less. On the other hand, the lower limit of the Ti content is not particularly limited and may be 0%. However, since Ti forms carbides, nitrides, and carbonitrides and has the effect of acting as an inhibitor during secondary recrystallization, the Ti content may be more than 0% or may be 0.0020% or more.

[0075] Sn: 0 to 0.10% Sn (tin) is an optional element for the base steel sheet. If the Sn content exceeds 0.10%, the secondary recrystallization becomes unstable, which may adversely affect the magnetic properties. Therefore, the Sn content of the base steel sheet may be 0.10% or less. The Sn content is preferably 0.090% or less, more preferably 0.080% or less. On the other hand, the lower limit of the Sn content is not particularly limited, and may be 0%. However, since Sn has the effect of increasing the concentration of Goss orientation and improving the magnetic properties, the Sn content may be more than 0% or may be 0.0050% or more.

[0076] Sb: 0 to 0.10% Sb (antimony) is an optional element for the base steel sheet. If the Sb content exceeds 0.10%, it may have an adverse effect on the magnetic properties. Therefore, the Sb content of the base steel sheet may be 0.10% or less. The Sb content is preferably 0.090% or less, more preferably 0.080% or less. On the other hand, the lower limit of the Sb content is not particularly limited and may be 0%. However, since Sb functions as an inhibitor and has the effect of stabilizing secondary recrystallization, the Sb content may be more than 0% or may be 0.010% or more.

[0077] Cr: 0~0.30% Cr (chromium) is an optional element for the base steel sheet. If the Cr content exceeds 0.30%, Cr oxides are formed, which may adversely affect the magnetic properties. Therefore, the Cr content of the base steel sheet may be 0.30% or less. The Cr content is preferably 0.20% or less, and more preferably 0.10% or less. On the other hand, the lower limit of the Cr content is not particularly limited and may be 0%. However, since Cr has the effect of increasing the concentration of Goss orientation and improving the magnetic properties, the Cr content may be more than 0% or may be 0.010% or more.

[0078] Ni: 0-1.0% Ni (nickel) is an optional element for the base steel sheet. If the Ni content exceeds 1.0%, secondary recrystallization may become unstable. Therefore, the Ni content of the base steel sheet may be 1.0% or less. The Ni content is preferably 0.20% or less, and more preferably 0.10% or less. On the other hand, the lower limit of the Ni content is not particularly limited and may be 0%. However, since Ni has the effect of increasing electrical resistance and reducing iron loss, the Ni content may be more than 0% or may be 0.010% or more.

[0079] The base steel sheet of the grain-oriented electrical steel sheet according to the present embodiment may contain impurities. Note that the term "impurities" refers to substances that are mixed in from raw materials such as ores and scraps, or from the manufacturing environment, during industrial production of steel.

[0080] The chemical composition of the above-mentioned base steel sheet may be measured by a general analytical method. For example, it may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Acid-soluble Al may be measured by ICP-AES using the filtrate obtained by thermally decomposing a sample with acid. C and S may be measured using the combustion-infrared absorption method, N may be measured using the inert gas fusion-thermal conductivity method, and O may be measured using the inert gas fusion-non-dispersive infrared absorption method.

[0081] The above chemical composition is that of the base steel sheet. If the grain-oriented electrical steel sheet to be used as the measurement sample has an insulating coating on its surface, the coating is removed by the following method before measuring the chemical composition.

[0082] For example, the insulating coating can be removed by immersing the grain-oriented electrical steel sheet having the coating in a high-temperature alkaline solution. Specifically, the insulating coating can be removed from the grain-oriented electrical steel sheet by immersing the sheet in an aqueous sodium hydroxide solution of 30-50% by mass of NaOH and 50-70% by mass of H2O at 80-90°C for 5-10 minutes, followed by rinsing with water and drying. The time for immersion in the aqueous sodium hydroxide solution can be changed depending on the thickness of the insulating coating.

[0083] Furthermore, a method for removing the forsterite coating (glass coating) can be achieved by immersing the electrical steel sheet from which the insulating coating has been removed by the above method in hot hydrochloric acid. Specifically, the concentration of hydrochloric acid suitable for removing the forsterite coating to be dissolved is determined in advance, and the forsterite coating can be removed by immersing the sheet in hydrochloric acid of this concentration (e.g., 30-40 mass% hydrochloric acid) at 80-90°C for 1-5 minutes, followed by rinsing with water and drying. Typically, different treatment solutions are used to remove each coating, such as an alkaline solution being used to remove the insulating coating and hydrochloric acid being used to remove the forsterite coating.

[0084] Next, a preferred method for producing the grain-oriented electrical steel sheet according to this embodiment will be described.

[0085] The method for producing the grain-oriented electrical steel sheet according to the present embodiment is not limited to the method described below. The method described below is one example for producing the grain-oriented electrical steel sheet according to the present embodiment.

[0086] The steps and quantitative conditions for each step shown below are examples adopted to demonstrate the feasibility of the present embodiment, and the present embodiment is not limited to these steps and quantitative values. The method for producing a grain-oriented electrical steel sheet according to the present embodiment may adopt various conditions as long as the object of the present embodiment is achieved without departing from the gist of the present embodiment.

[0087] The manufacturing method of the grain-oriented electrical steel sheet according to the present embodiment can apply a conventional known manufacturing method of grain-oriented electrical steel sheet as a basic process. For example, examples of the conventional manufacturing method of grain-oriented electrical steel sheet include a manufacturing method in which inhibitors such as MnS and AlN are formed by high-temperature slab heating, and a manufacturing method in which AlN inhibitors are formed by low-temperature slab heating and nitriding treatment. The manufacturing method of the grain-oriented electrical steel sheet according to the present embodiment is not limited to a specific manufacturing method. Below, a method of applying nitriding treatment as a low-temperature slab heating process will be described.

[0088] (Casting process) In the casting process, a slab is prepared. An example of a method for producing a slab is as follows. Molten steel is produced (smelted). A slab is produced using the molten steel. The slab may be produced by a continuous casting method. An ingot may be produced using the molten steel, and the ingot may be bloomed to produce a slab. The thickness of the slab is not particularly limited. The thickness of the slab is, for example, 150 to 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 process.

[0089] For example, the above slab may contain the following elements as its chemical composition:

[0090] C: 0.085% or less, Carbon (C) is an effective element for controlling the primary recrystallization structure in the manufacturing process, but if the content in the final product is excessive, it adversely affects the magnetic properties. Therefore, the C content is 0.085% or less. The preferred upper limit of the C content is 0.075%. C is purified in the decarburization annealing process and the finish annealing process, and becomes 0.005% or less. When C is contained, the lower limit of the C content may be more than 0%, or may be 0.001%, taking into account the productivity in industrial production.

[0091] 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%, γ transformation occurs during finish annealing, damaging the crystal orientation of the grain-oriented electrical steel sheets. On the other hand, if the Si content exceeds 7.0%, cold workability decreases and cracks tend to occur during cold rolling. The lower limit of the Si content is preferably 2.5%, more preferably 3.0%. The upper limit of the Si content is preferably 4.5%, more preferably 4.0%.

[0092] Mn: 0.05 to 1.00% Manganese (Mn) combines with S or Se to produce MnS or MnSe, which functions as an inhibitor. When Mn is contained, secondary recrystallization is stable when the Mn content is within the range of 0.05 to 1.00%. It is possible for a part of the inhibitor function to be borne by a nitride of an Nb group element. In this case, the strength of MnS or MnSe as a general inhibitor is controlled to be weak. For this reason, the upper limit of the Mn content is preferably 0.50%, more preferably 0.20%.

[0093] At least one of S and Se: 0.003 to 0.035% in total Sulfur (S) and selenium (Se) combine with Mn to produce MnS or MnSe, which functions as an inhibitor. When at least one of S and Se is contained, if the total content of S and Se is 0.003 to 0.035%, the secondary recrystallization is stable. It is possible for a part of the inhibitor function to be borne by a nitride of an Nb group element. In this case, the strength of MnS or MnSe as a general inhibitor is controlled to be weak. For this reason, the preferred upper limit of the total content of S and Se is 0.025%, more preferably 0.010%. If S and Se remain after final annealing, they form compounds and deteriorate the iron loss. Therefore, it is preferable to reduce S and Se as much as possible by purification during final annealing.

[0094] Here, the total content of S and Se means that at least one of S and Se is included, and the total content thereof is the total content.

[0095] Al: 0.010 to 0.065% Aluminum (Al) combines with N to precipitate as (Al,Si)N, and functions as an inhibitor. When Al is contained, AlN formed as an inhibitor by nitriding, which will be described later, expands the secondary recrystallization temperature range when the Al content is within the range of 0.010 to 0.065%, and secondary recrystallization is particularly stable in the high temperature range. Therefore, the Al content is 0.010 to 0.065%. The preferred lower limit of the Al content is 0.020%, and more preferably 0.025%. From the viewpoint of the stability of secondary recrystallization, the preferred upper limit of the Al content is 0.040%, and more preferably 0.035%.

[0096] N: 0.012% or less Nitrogen (N) combines with Al to function as an inhibitor. Since N can be incorporated by nitriding during the manufacturing process, no lower limit is specified. For example, the lower limit of the N content may be more than 0%, or may be 0.001%. On the other hand, when N is incorporated, if the N content exceeds 0.012%, blisters, a type of defect, tend to occur in the steel sheet. The preferred upper limit of the N content is 0.010%, and more preferably 0.009%. N is purified in the final annealing process, and is 0.005% or less after the final annealing process.

[0097] The balance of the above chemical composition is composed of Fe and impurities. The term "impurities" refers to elements that are mixed in from raw materials such as ores and scraps, or from the manufacturing environment, during industrial production of steel. The upper limit of the total content of impurities may be, for example, 5%.

[0098] The above-mentioned chemical composition may contain a known optional element instead of a part of Fe, taking into consideration not only solving the problems in production but also strengthening the inhibitor function by compound formation and the effect on magnetic properties. The optional element contained in place of a part of Fe may, for example, be the following elements.

[0099] Nb group elements: 0.050% or less The total content of Nb group elements (one or more of Nb, V, Mo, Ta, and W) may be 0.050% or less. When using Nb group elements as a part of the inhibitor, it is preferable that the total content of Nb group elements is 0.030% or less, since secondary recrystallization is started at an appropriate timing. In addition, the orientation of the secondary recrystallized grains generated becomes very favorable, and the structure can be controlled to be favorable for the final magnetic properties. In particular, Nb and Ta have a strong effect and are preferable. There is no need to set a lower limit for the total content of Nb group elements, and the lower limit may be 0%. This lower limit is preferably 0.003%.

[0100] The total content of the Nb group elements is more preferably 0.004 to 0.020%, and further preferably 0.005 to 0.010%.

[0101] Here, the total content of Nb group elements means that at least one of Nb, V, Mo, Ta, and W is included and the total content thereof.

[0102] The slab also contains, as optional elements, in mass %: Cu: 0.40% or less, Bi: 0.010% or less, B: 0.080% or less, P: 0.50% or less, Ti: 0.015% or less, Sn: 0.10% or less, Sb: 0.10% or less, Cr: 0.30% or less, Ni: 1.00% or less It may contain at least one of the following. Since these optional elements may be contained according to known purposes, there is no need to set a lower limit for the content of the optional elements, and the lower limit may be 0%.

[0103] The chemical composition of the slab may be measured by the above-mentioned analytical method, like the chemical composition of the grain-oriented electrical steel sheet as the final product.

[0104] (Hot rolling process) The hot rolling process is a process in which a slab heated to a predetermined temperature (e.g., 1100 to 1400°C) is hot-rolled to obtain a hot-rolled steel sheet. In the hot rolling process, for example, the silicon steel material (slab) heated in the heating process is roughly rolled, and then finish-rolled to obtain a hot-rolled steel sheet with a predetermined thickness, for example, 1.8 to 3.5 mm. After the finish rolling is completed, the hot-rolled steel sheet is coiled at a predetermined temperature.

[0105] In the case of a process including a nitriding step during or after decarburization annealing, the strength of MnS as an inhibitor is not so necessary, so that the slab heating temperature may be set to 1100°C to 1280°C in consideration of productivity.

[0106] (Hot-rolled sheet annealing process) The hot-rolled sheet annealing process is a process in which the hot-rolled steel sheet obtained in the hot rolling process is annealed under a predetermined temperature condition (for example, at 750 to 1200 ° C for 30 seconds to 10 minutes) to obtain an annealed steel sheet. The hot-rolled sheet annealing is generally performed to control the steel sheet structure such as the recrystallization rate, residual strain, and crystal grain size, and to preferably adjust the precipitate form in the steel by annealing the hot-rolled steel sheet after the hot rolling process. For example, in the high-temperature slab heating process, it is a process for finally controlling the form of precipitates such as AlN, and the conditions are adjusted so that they precipitate uniformly and finely. In the hot-rolled sheet annealing, for example, the steel sheet is heated to 1050 ° C to 1150 ° C, and then slowly cooled to an intermediate temperature (850 ° C to 950 ° C) over 50 to 150 seconds in order to properly precipitate AlN, etc., and then water-cooled.

[0107] (Cold rolling process) The cold rolling process is a process in which the annealed steel sheet obtained in the hot-rolled sheet annealing process is subjected to one cold rolling or multiple (two or more) cold rolling (e.g., total cold rolling rate of 80 to 95%) via annealing (intermediate annealing) to obtain a cold-rolled steel sheet having a thickness of, for example, 0.10 to 0.50 mm. In order to improve the magnetic properties, for example, the interpass temperature in the cold rolling may be set to about 100°C to 300°C.

[0108] The total cold rolling reduction is defined as follows. Total cold rolling rate (%) = (1 - thickness of steel plate after cold rolling / thickness of steel plate before cold rolling) x 100

[0109] (Localized rapid heating process) In this embodiment, localized rapid heating is performed on the cold-rolled steel sheet after the cold rolling process to form a localized heating region. The rapid heating method is not particularly limited as long as it can locally heat the steel sheet. For example, a method of heating by contacting a spot electrode with the front and back surfaces of the steel sheet and passing an electric current through the steel sheet, a method of heating by irradiating the surface of the steel sheet with laser light or an electron beam, a method of locally heating by induction heating, a method of heating by contacting a hot piece, etc. can be adopted. The size of each localized heating region can be a dot-like region with a diameter of about 10 μm to 10 mm, or a linear region with a width of about 10 μm to 10 mm. In addition, the electrode used for current heating may be a circular electrode as described above, or a linear electrode.

[0110] Regarding the size of the locally heated region, the minimum diameter and width depend on the shape of the spot electrode and the technology for reducing the focused diameter of the laser light or electron beam. In principle, it is possible to further reduce the size of the locally heated region, but considering that the current size of the nuclei of recrystallized grains is about 1 μm, it is considered that the effect can be obtained if the size of the locally heated region is 1 μm or more. In industry, the above minimum diameter and minimum width should be 10 μm or more. Regarding the size of the locally heated region, if the maximum diameter and maximum width exceed 10 mm, the area ratio of Goss orientation grains with relatively large angle deviation θ and angle deviation φ that cannot grow outside the locally heated region increases. In this case, it becomes difficult to obtain the effect of local rapid heating.

[0111] In the localized rapid heating, the heating rate may be 500°C / sec or more in the center of the locally heated region as viewed in the thickness direction and at 1 / 5 of the thickness of the steel plate. If the heating rate in the above region is 500°C / sec or more, the structure of the locally heated region can be preferably controlled to a recovered structure or a recrystallized structure. The above heating rate is preferably 2000°C / sec or more, and more preferably 10000°C / sec or more. On the other hand, the upper limit of the above heating rate is not particularly limited, and may be, for example, 1000000°C / sec.

[0112] In addition, the above heating rate is preferably controlled in conjunction with the heating rate during decarburization annealing, which will be described later. For example, if the heating rate during decarburization annealing is faster than the heating rate during local rapid heating, it is difficult to obtain the intended effect. Therefore, although it depends on the value of the heating rate, it is preferable to set the heating rate during local rapid heating to be equal to or higher than the heating rate during decarburization annealing.

[0113] The above-mentioned 1 / 5 part of the plate thickness of the steel plate means a depth equivalent to 1 / 5 of the plate thickness of the steel plate from the surface of the steel plate in the plate thickness direction.

[0114] In addition, in the localized rapid heating, it is sufficient that the maximum temperature reached is 700°C or higher in the center of the locally heated region as viewed from the plate thickness direction and at 1 / 5 of the plate thickness of the steel plate. If the maximum temperature reached is 700°C or higher in the above region, the structure of the locally heated region can be preferably controlled to a recovered structure or a recrystallized structure. The above maximum temperature reached is preferably 800°C or higher, and more preferably 900°C or higher. On the other hand, the above maximum temperature reached may be lower than the melting point of the steel plate, for example, 1400°C or lower.

[0115] In addition, in the localized rapid heating, the holding time from reaching the maximum temperature to cooling to 700°C at the center of the locally heated region as viewed from the thickness direction and at 1 / 5 of the thickness of the steel plate may be 0.1 seconds or more. If the holding time is 0.1 seconds or more in the above region, the structure of the locally heated region can be preferably controlled to a recovered structure or a recrystallized structure. The holding time is preferably 0.2 seconds or more, more preferably 0.3 seconds or more, and even more preferably 0.4 seconds or more. On the other hand, the upper limit of the holding time is not particularly limited, and may be, for example, 10 seconds or less. The holding time from reaching the maximum temperature to cooling to 700°C has an essential effect on the formation of coarse Goss orientation grains close to the ideal Goss orientation.

[0116] In localized rapid heating, it is important to control the above-mentioned heating rate and maximum temperature, as well as the above-mentioned holding time. During this holding time, subgrain structures and recrystallization nuclei that are advantageous for the formation of coarse Goss-oriented grains in the locally heated region can be formed. By controlling the subgrain structure in the locally heated region by the holding time, favorable structural control can be performed in the subsequent process.

[0117] As described above, the method of local rapid heating is not particularly limited. For example, local rapid heating may be performed by spot current heating, laser irradiation, or electron beam irradiation. Regardless of the method of local rapid heating, it is sufficient to control the heating rate, maximum temperature, and holding time as described above. A person skilled in the art can combine the conditions of the local rapid heating method to control the desired heating rate, maximum temperature, and holding time.

[0118] For example, a person skilled in the art can perform a heat conduction analysis using the finite element method to control the heating rate and the maximum temperature reached at the center of the local heating region as viewed from the thickness direction and at 1 / 5 of the thickness of the steel plate. In addition, a person skilled in the art can control the above-mentioned holding time by adjusting the heat extraction conditions after the maximum temperature is reached. For example, in the case of spot current heating, the electrode holding time after current application can be controlled, or the shape of the spot electrode can be changed to a shape suitable for heat extraction. In addition, in the case of laser irradiation or electron beam irradiation, the irradiation speed can be adjusted, or the shape of the irradiation region can be changed to an ellipse or the like to gradient the irradiation energy from the center to the outer edge of the irradiation region.

[0119] Generally, when heating by laser irradiation, only the vicinity of the irradiated steel sheet surface is heated preferentially, and the inside of the steel sheet is not easily heated. In addition, since heating by laser irradiation is non-contact heating, heat is quickly removed after heating and the temperature is not easily maintained. Therefore, when performing laser irradiation heating as localized rapid heating, in order to recover or recrystallize the cold-worked structure in the laser irradiated area, it is necessary to control the conditions so that not only the surface of the steel sheet but also the inside of the steel sheet is heated, and the cooling rate is slowed down to relatively coarsen the subgrain structure in the laser irradiated area. The laser irradiation conditions for localized rapid heating are completely different from the laser irradiation conditions for magnetic domain refinement. For example, the laser irradiation conditions for magnetic domain refinement (usually 0.5 to 50 mJ / mm 2 ) is applied to this embodiment, the structure of the locally heated region is not controlled favorably, and coarse Goss oriented grains close to the ideal Goss orientation are not formed in the steel sheet after the decarburization annealing process. The same applies to electron beam irradiation as to laser irradiation. Even if the electron beam irradiation conditions for magnetic domain refinement are applied to this embodiment, the structure of the locally heated region is not controlled favorably, and coarse Goss oriented grains close to the ideal Goss orientation are not formed in the steel sheet after the decarburization annealing process.

[0120] It is difficult to form coarse Goss oriented grains close to the ideal Goss orientation even if the input power of laser irradiation or electron beam irradiation is simply increased. For example, when rapid heating is performed by laser irradiation or electron beam irradiation, it is preferable to make the beam shape elliptical or adjust the scan speed, etc., so that a temperature range for grain growth of the crystal grains in the region after rapid heating can be secured.

[0121] Conventionally, in electrical steel sheets, laser irradiation or electron beam irradiation has been performed to reduce iron loss by controlling magnetic domains on steel sheets after secondary recrystallization. Under these laser irradiation or electron beam irradiation conditions, about 20 μm from the surface of the steel sheet is heated, so heat is removed quickly after heating. Therefore, under conventional conditions, it is difficult to ensure the holding time from reaching the maximum temperature to cooling to 700 ° C. as described above. That is, under conventional laser irradiation or electron beam irradiation conditions, it may be possible to make the irradiated part act as a barrier to the growth of secondary recrystallized grains, but it is difficult to form coarse Goss-oriented grains having an orientation close to the ideal Goss orientation as in this embodiment. In order to form coarse Goss-oriented grains close to the ideal Goss orientation by laser irradiation or electron beam irradiation, it is necessary to consider the conditions of laser irradiation or electron beam irradiation as described above.

[0122] In addition, when locally heated regions are scattered on the steel sheet surface by localized rapid heating, the size, shape, and arrangement of crystal grains after secondary annealing can be controlled by appropriately arranging the locally heated regions on the steel sheet surface. For example, if the locally heated regions are arranged on the steel sheet surface so that a Goss oriented grain that starts growing from one locally heated region collides with another Goss oriented grain that starts growing from an adjacent locally heated region, the grain size of the Goss oriented grains in any direction at the end of secondary annealing can be controlled to be small.

[0123] (Decarburization annealing process) In the decarburization annealing process, the cold-rolled steel sheet after the local rapid heating process is subjected to decarburization annealing (primary annealing). This decarburization annealing increases the frequency of Goss-oriented grains formed in the local heating region, increases the grain size of the Goss-oriented grains, and favorably grows coarse Goss-oriented grains having an orientation close to the ideal Goss orientation. The decarburization annealing conditions may be, for example, an annealing temperature of 700 to 900°C and an annealing time of 1 to 3 minutes. By subjecting the cold-rolled steel sheet to decarburization annealing, C contained in the cold-rolled steel sheet is removed. Decarburization annealing is preferably performed in a moist atmosphere in order to remove "C" contained in the cold-rolled steel sheet.

[0124] In addition, it is effective to reduce the primary recrystallized grain size by controlling the conditions of the above-mentioned hot rolling and hot-rolled sheet annealing, or by lowering the decarburization annealing temperature as necessary. The primary recrystallized grain size is not particularly limited, but is preferably 8 to 30 μm.

[0125] In this embodiment, coarse Goss-oriented grains with an orientation close to the ideal Goss orientation are formed in the locally heated region. Therefore, it is not necessary to form Goss-oriented grains again by decarburization annealing. The heating rate of the decarburization annealing may be 10,000°C / sec or less. However, by setting the heating rate of the decarburization annealing to a slow rate, it is possible to prevent the {111} <112> Oriented grains and {411} <148> For example, the heating rate of the decarburization annealing is preferably 300° C. / sec or less, more preferably 200° C. / sec or less, and even more preferably 100° C. / sec or less.

[0126] In addition, the amount of decarbonation and the state of the surface oxide layer affect the formation of the glass film, so in decarburization annealing, the degree of oxidation (PH2O / PH2) in the annealing atmosphere (furnace atmosphere) may be appropriately adjusted.

[0127] (nitriding) Nitriding is an effective treatment in a low-temperature slab heating process in which the slab heating temperature is 1280°C or less, and is an important process for adjusting the strength of the inhibitor in secondary recrystallization. Nitriding increases the nitrogen content of the steel sheet by about 40 to 200 ppm from the start of the decarburization treatment to the start of secondary recrystallization in finish annealing. Examples of nitriding include annealing in an atmosphere containing a nitriding gas such as ammonia, and finish annealing of a decarburized annealed steel sheet coated with an annealing separator containing a powder having nitriding ability such as MnN. The amount of nitride after nitriding is preferably 130 to 350 ppm, more preferably 150 to 250 ppm.

[0128] (Annealing separator application process) The annealing separator application process is a process of applying an annealing separator to the decarburized annealed steel sheet. As the annealing separator, for example, an annealing separator mainly composed of MgO or an annealing separator mainly composed of Al2O3 can be used. After the annealing separator is applied, the decarburized annealed steel sheet is wound into a coil and finish-annealed in the next finish-annealing process.

[0129] (finish annealing process) The final annealing process is a process in which the decarburized annealed steel sheet coated with the annealing separator is subjected to final annealing (secondary annealing) to cause secondary recrystallization. In this process, the growth of the primary recrystallized grains is suppressed by the inhibitor, and secondary recrystallization is allowed to proceed, resulting in the formation of {100} <001> Oriented grains are preferentially grown, dramatically improving magnetic flux density.

[0130] The heating rate in the heating process of the final annealing step is not particularly limited. For example, the temperature may be raised at a heating rate of 3 to 20 ° C. / hour. In addition, slow heating may be performed in the temperature range of 1000 ° C. to 1200 ° C. during heating. For example, the heating rate in the temperature range of 1000 ° C. to 1200 ° C. during heating is preferably 3 to 12 ° C. / hour, more preferably 3 to 9 ° C. / hour, and more preferably 3 to 7 ° C. / hour. Alternatively, the temperature may be stopped once during the heating process of the final annealing step and held at that temperature so that the precipitates pinning the primary recrystallized grains do not decompose suddenly. For example, the temperature may be stopped once in the temperature range of 1050 ° C. to 1100 ° C. during heating, and held for 5 hours to 15 hours. For example, adjusting the heating rate in the secondary recrystallization temperature range affects the decomposition rate of the inhibitor and can improve the magnetic flux density.

[0131] After the heating process in the final annealing step, a holding process (purification annealing) may be performed by holding the steel sheet for 10 hours to 60 hours in a temperature range of 1000° C. to 1300° C. The atmosphere during the final annealing may be, for example, a nitrogen atmosphere or a mixed atmosphere of nitrogen and hydrogen.

[0132] (Insulating film formation process) If necessary, a coating solution containing phosphoric acid or a phosphate, chromic anhydride or a chromate, and colloidal silica may be applied to the steel sheet after the finish annealing and baked (for example, at 350°C to 1150°C for 5 to 300 seconds) to form an insulating coating.

[0133] (others) If necessary, the grain-oriented electrical steel sheet may be subjected to a magnetic domain refinement treatment for forming localized micro-distortion regions or grooves by a known method such as laser, plasma, mechanical method, etching, etc. However, the grain-oriented electrical steel sheet according to the present embodiment has excellent magnetic flux density, but since coarsening of the secondary recrystallized grain size is suppressed, the magnetic domains are refined even without the magnetic domain refinement treatment.

[0134] In addition, when a magnetic domain refinement process is performed, the micro-distorted regions and grooves caused by the magnetic domain refinement process may become abnormal points in the measurement of crystal orientation and grain size. Therefore, when measuring crystal orientation, it is preferable that the measurement point does not overlap with the micro-distorted regions and grooves. EXAMPLES

[0135] Next, the effects of the present invention will be specifically described in detail using examples. The conditions in the examples are one example of conditions adopted to confirm the feasibility and effects of the present invention, and the present invention is not limited to this one example of conditions. The present invention can adopt various conditions as long as they do not deviate from the gist of the present invention and achieve the object of the present invention.

[0136] Using the slabs with adjusted chemical composition as the raw material, cold-rolled steel sheets were manufactured with the chemical compositions shown in Table 2. These chemical compositions were measured based on the above-mentioned method. In Table 2, "-" indicates that the content was not measured because the content was not controlled or measured.

[0137] When producing the above cold-rolled steel sheets, the slabs were heated to 1150°C and subjected to hot rolling to obtain hot-rolled steel sheets having a thickness of 2.6 mm. The hot-rolled steel sheets were heated to 1100°C and subsequently subjected to hot-rolled sheet annealing by annealing at 900°C, and then pickled to remove scale formed on the surface. These steel sheets were subjected to one cold rolling or multiple cold rolling with intermediate annealing in between to obtain cold-rolled steel sheets having a final thickness of 0.22 mm.

[0138] The above cold-rolled steel sheet was subjected to local rapid heating under the conditions shown in Tables 3 to 6. In the spot current heating, a copper electrode with a diameter of 3 mm was used in the contact portion with the steel sheet, and the electrode shape, electrode pressure, current, current time, and electrode holding time after current were changed in a composite manner to control the heating rate, maximum temperature, and holding time from reaching the maximum temperature to cooling to 700°C (holding time of 700°C or more). In the laser heating, a fiber laser was used, and the focusing spot diameter of the laser light in the rolling direction (i.e., the diameter including 86% of the laser output) was set to 30 μm (except for Tests No. 62 and No. 63), and the laser irradiation energy density, laser scanning speed, and shape of the laser irradiation area were changed in a composite manner to control the heating rate, maximum temperature, and holding time of 700°C or more. Those skilled in the art can combine the conditions of the local rapid heating method to control the desired heating rate, maximum temperature, and holding time of 700°C or more.

[0139] In Test No. 60, the laser beam was elongated in the scanning direction, and the holding time from reaching the maximum temperature until cooling to 700°C during localized rapid heating was controlled to 0.2 seconds, so that coarse Goss-oriented grains with an orientation close to the ideal Goss orientation were formed in the locally heated area. In Test No. 61, general laser irradiation conditions for magnetic domain refinement were applied. In Test No. 62, the focused spot diameter was set to 0.5 mm, and the laser irradiation energy density was set to 2.0 J / mm. 2 In test No. 63, the focal spot diameter was set to 0.5 mm, and the laser irradiation energy density was set to 30.0 J / mm. 2 The laser beam was controlled so that the laser beam irradiated area was finally located on the grain boundary of the secondary recrystallized grains.

[0140] In the table, "No treatment" for the heating method of localized rapid heating indicates that localized rapid heating was not performed. The local heating conditions "Linear or spotted" indicate the shape of the localized heated area on the surface of the cold-rolled steel sheet, and the local heating conditions "Rolling direction spacing" and "Width direction spacing" indicate the spacing in the rolling direction and transverse direction at which the localized heated areas are arranged on the surface of the cold-rolled steel sheet. The localized heated areas are evenly spaced at equal intervals in the rolling direction and transverse direction. When providing localized heated areas on the surface of the cold-rolled steel sheet, they are arranged so that the distribution of the localized heated areas is not uneven.

[0141] The produced cold-rolled steel sheets were subjected to decarburization annealing under the conditions shown in Tables 3 to 6. In the decarburization annealing, the degree of oxidation (PH2O / PH2) in the annealing atmosphere (furnace atmosphere) was set to 0.13.

[0142] The decarburized annealed steel sheets produced were nitrided at 750°C in a nitrogen-hydrogen-ammonia atmosphere to set the nitrogen content of the steel sheets to 220 ppm. In addition, an annealing separator mainly composed of MgO was applied, and finish annealing was performed. In the finish annealing, the steel sheets were heated to 1000°C (1070°C in the "Step" below) at a heating rate of 15°C / hour in a mixed atmosphere of hydrogen and nitrogen, and then heated to 1200°C under one of the following conditions, and held at 1200°C for 20 hours in a hydrogen atmosphere. Normal: 1000℃~1200℃ at 15℃ / hour Gradual heating 1: 1000℃~1200℃ at 10℃ / hour Gradual heating: 1000℃~1200℃ at 7.5℃ / hour Gradual heating 2: 1000℃~1200℃ at 5.0℃ / hour Step: 1070℃ x 10 hours

[0143] After the finish annealing, the steel sheet was coated with a coating solution for an insulating film, which was mainly composed of colloidal silica and phosphate, and optionally contained chromic anhydride, and baked to form an insulating film.

[0144] For the obtained grain-oriented electrical steel sheets, the chemical composition of the base steel sheet, aveφ L (φm ), 100-15×aveφ L The value of (f(φ m )), D L 10 (D10) was measured according to the method described above. The results are shown in Tables 7 to 11. In Table 11, "-" indicates that no control or production was carried out with the content in mind, and the content was not measured.

[0145] The crystal orientation was measured by setting a measurement line including 1,000 measurement points at 1 mm intervals in the rolling direction (RD), and setting 10 of these measurement lines at 50 mm intervals in the direction perpendicular to the rolling direction (TD).

[0146] The grain-oriented electrical steel sheets thus obtained were evaluated for various properties. The evaluation results are shown in Tables 7 to 11.

[0147] The magnetic properties of the grain-oriented electrical steel sheets were measured based on the single sheet magnetic property test method (SST: Single Sheet Tester) specified in JIS C 2556:2015.

[0148] From the obtained grain-oriented electrical steel sheets, 20 samples for single sheet magnetic measurement of 100 mm x 500 mm size were prepared, and single sheet magnetic measurement was performed. As a magnetic property, the magnetic flux density B8 (T) in the rolling direction of the steel sheet when excited at 800 A / m was measured. The magnetic flux density B8 was judged to pass or fail based on the Si content of the steel sheet. For example, it is known that the lower the Si content of the steel sheet, the higher the saturation magnetic flux density, and the higher the saturation magnetic flux density, the higher the B8. Therefore, for steels A to Z with a Si content of 3.3 to 3.5%, it was judged to pass if B8 was 1.930 T or more, for steel AA with a Si content of 2.5%, it was judged to pass if B8 was 1.960 T or more, and for steel AB with a Si content of 4.1%, it was judged to pass if B8 was 1.890 T or more.

[0149] In addition, as magnetic properties, the iron loss W, defined as the power loss per unit weight (1 kg) of the steel plate under the conditions of AC frequency: 50 Hz, excitation magnetic flux density: 1.7 T, is 17 / 50(W / kg) was measured. 17 / 50 Regarding this, a rating of 0.79 W / kg or less was deemed to be acceptable.

[0150] Among Nos. 1 to 66, the grain-oriented electrical steel sheets according to the present invention have an aveφ L ≦4.0°, and D L 10≦100-15×abeφ L In all of these examples of the present invention, as grain-oriented electrical steel sheets, the angle deviation in the rolling direction was controlled to be small, so that they had excellent magnetic flux density, and the grain size in the rolling direction was controlled to be small, so that they had excellent iron loss without domain control (domain refinement treatment). Therefore, in these examples of the present invention, it is possible to reduce the adverse effects of conventional domain control (for example, deterioration of transformer noise due to laser domain control, and reduction in magnetic flux density due to the introduction of grooves).

[0151] On the other hand, among Nos. 1 to 66, the grain-oriented electrical steel sheets, which are comparative examples, had an aveφ L ≦4.0°, or D L 10≦100-15×abeφ L In these comparative examples, preferable magnetic flux density and core loss were not obtained as grain-oriented electrical steel sheets.

[0152] [Table 2]

[0153] [Table 3]

[0154] [Table 4]

[0155] [Table 5]

[0156] [Table 6]

[0157] [Table 7]

[0158] [Table 8]

[0159] [Table 9]

[0160] [Table 10]

[0161] [Table 11] [Industrial Applicability]

[0162] According to the above-mentioned aspect of the present invention, it is possible to provide a grain-oriented electrical steel sheet that is excellent in both magnetic flux density and core loss while reducing the adverse effects of conventional magnetic domain control (e.g., deterioration of transformer noise due to laser magnetic domain control, reduction in magnetic flux density due to the introduction of grooves, etc.), and thus has high industrial applicability. [Explanation of symbols]

[0163] 1 steel plate 2. Crystal orientation measurement points

Claims

[Claim 1] A grain-oriented electrical steel sheet, The deviation angle from the ideal Goss orientation with the normal direction Z of the rolling surface as the rotation axis is defined as α, The deviation angle from the ideal Goss orientation with the direction perpendicular to the rolling direction C as the rotation axis is defined as β, The deviation angle from the ideal Goss orientation with the rolling direction L as the rotation axis is defined as γ, The deviation angle of the crystal orientation measured at one measurement point on the plate surface is represented as (α β γ), The angular deviation at one measurement point is φ = (α ２ +β ２ ) １／２ Define it as: The average value of the angle deviation φ obtained at at least 1,000 measurement points spaced 1 mm apart along the rolling direction L is aveφ. Ｌ When we define The above aveφ Ｌ But, aveφ Ｌ ≦4.0° is satisfied, The deviation angle of the crystal orientation measured at two adjacent measurement points on the plate surface, spaced 1 mm apart, is defined as (α １ β １ Gamma １ ) and (α ２ β ２ Gamma ２ ) and [(α ２ -α １ ) ２ + (β ２ -β １ ) ２ + (γ ２ -γ １ ) ２ ] １／２ The midpoint between the two measurement points that satisfy ≧1.0° is defined as the grain boundary (GB), The grain size in the rolling direction L determined based on the grain boundary GB is expressed in mm as D Ｌ Define it as: Grain size D measured along the rolling direction L Ｌ Arrange them in ascending order and determine the particle size that is 10% of the largest in number, in mm. Ｌ When defined as 10, The above D Ｌ 10 is D Ｌ 10≦100-15×aveφ Ｌ Fulfill A directional electrical steel sheet.