Grain-oriented electrical steel sheet

Abstract

In this grain-oriented electrical steel sheet, the average value aveφL of an angle deviation φ determined at 1,000 measurement points or less at 1 mm intervals along the rolling direction L is 4.0° or less; and particle sizes DL10 representing 10% of particle sizes DL determined along the rolling direction L, which have been arranged in descending order, in terms of the count from large to small are (100–15×aveφL) mm or less.

Description

grain-oriented electrical steel sheet

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

[0002] Grain-oriented electrical steel sheets contain silicon, and the crystal orientation of the silicon grains is concentrated near the Goss orientation (cubic {110}<001>), with the <001> orientation, which is the axis of easy magnetization, being nearly aligned with the rolling direction during the steel sheet manufacturing process. Such grain-oriented electrical steel sheets are excellent materials for transformer cores, etc. Among the magnetic properties of grain-oriented electrical steel sheets, the magnetic flux density and core loss are particularly important.

[0003] The magnetic flux density of a grain-oriented electrical steel sheet when a predetermined magnetizing force is applied tends to increase 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. ８ is used. Magnetic flux density B ８ is the value of the magnetic flux density of the magnetized grain-oriented electrical steel sheet when a magnetizing force of 800 A / m is applied in the rolling direction. That is, the magnetic flux density B ８ The larger the value of σ, the easier it is to magnetize with a certain magnetizing force and the greater the magnetic flux density, making it suitable for small, highly efficient transformers.

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

[0005] There are several methods for reducing 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 grain size, and aligning the grain orientation, which is effective in reducing hysteresis loss. ８The larger the value of B, the more the crystal orientation is aligned with the Goss orientation, and the lower the hysteresis loss. ８ The larger the value of W, the greater the iron loss １７／５０ On the other hand, when the development of Goss oriented grains is promoted to improve the degree of integration of the crystal orientation, the grain size tends to become larger, which increases the eddy current loss and decreases the B ８ Even if the value of is high, if the grains become too large, there is a trade-off in that the core loss deteriorates.

[0006] In recent years, methods have been developed to artificially subdivide the magnetic domain width by introducing strain 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 when the secondary recrystallized grain size is large. However, when strain 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 this method cannot be used in applications that require stress relief annealing at 800°C or higher after irradiation. On the other hand, in the magnetic domain control method using grooves, the magnetic flux density B ８ There is a problem of a decrease in

[0007] Generally, grain-oriented electrical steel sheets are manufactured as follows. A steel sheet material (slab) containing a predetermined 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 referred to as primary annealing or decarburization annealing). This annealing causes primary recrystallization, and crystal grains with a crystal orientation whose easy axis of magnetization is aligned in the rolling direction and whose deviation angle from the strict Goss orientation described by {110}<001> is 10° or less (hereinafter referred to as Goss-oriented grains) are formed within the primary recrystallized grains. This annealing also serves as decarburization annealing. Then, an annealing separator mainly composed of MgO is applied to the surface of the steel sheet where primary recrystallization has occurred. Next, the steel sheet coated with the annealing separator is wound up to produce a steel sheet coil, and this steel sheet coil is subjected to batch annealing (also called secondary recrystallization annealing or finish annealing). This annealing causes Goss-oriented grains to encroach on other crystal grains, resulting in secondary recrystallization and the formation of a so-called glass coating on the surface of the steel sheet. During secondary recrystallization, Goss-oriented grains grow preferentially due to the influence of inhibitors contained in the steel sheet, and in some cases, the grain size can reach 100 mm or more. Next, while the steel sheet coil is unwound, annealing is performed to flatten the steel sheet where secondary recrystallization has occurred, and an insulating coating is formed.

[0008] As described above, grain-oriented electrical steel sheets achieve desired magnetic properties by undergoing secondary recrystallization during final annealing to obtain a crystalline structure consisting of Goss-oriented grains concentrated in the {110}<001> orientation. To obtain this crystalline structure, it is effective to increase the frequency of minor Goss-oriented grains after primary annealing or to increase the frequency of grains that have good lattice matching with the Goss-oriented grains. For example, {778}<447> (≒{111}<112> orientation) and {411}<148> orientation grains (called "matching orientation grains"), which have high lattice matching with the {110}<001> orientation and a Σ9 matching orientation relationship with the Goss orientation, are easily encroached upon by Goss-oriented grains. Therefore, it is effective to include many of them in the primary recrystallized structure. However, when controlling the crystal orientation of the crystal grains generated by the primary annealing, it is difficult to simultaneously increase the frequency of Goss-oriented grains and the frequency of grains having a corresponding orientation relationship. For example, in the region where the cold-rolling reduction is 85% or more, the frequency of corresponding-oriented grains, which are easily encroached upon by Goss-oriented grains, increases with increasing cold-rolling reduction, while the frequency of Goss-oriented grains decreases with increasing cold-rolling reduction. Furthermore, the frequency of Goss-oriented grains, which are the minor orientation in the primary recrystallization texture, increases with increasing heating rate during primary annealing, while the frequency of corresponding-oriented grains, which have the {111}<112> orientation, which is the major orientation in the primary recrystallization texture, decreases with increasing heating rate during primary annealing. In other words, conventional process control conditions have not been able to independently control the frequency of Goss-oriented grains and the frequency of corresponding-oriented grains, which are easily encroached upon by Goss-oriented grains.

[0009] Here, the deviation angle of the crystal orientation observed in the grain-oriented electrical steel sheet from the ideal {110}<001> orientation around the normal direction Z (ND) to the rolling surface is defined as deviation angle α, the deviation angle from the ideal {110}<001> orientation around the direction perpendicular to the rolling direction C (TD) is defined as deviation angle β, and the deviation angle from the ideal {110}<001> orientation around the rolling direction L (RD) is defined as deviation angle γ. The angular deviation θ of the crystal orientation observed in the grain-oriented electrical steel sheet from the ideal {110}<001> orientation is defined as the angular deviation θ obtained from the deviation angles α, β, and γ around the ND, TD, and RD by the following formula A: θ=(α２ +β ２ +γ ２ ) １／２ (Formula A)

[0010] As mentioned above, Goss-oriented grains are not crystal grains (called ideal Goss-oriented grains) that have a Goss orientation (ideal Goss orientation) in the strict sense. The easy axis direction of magnetization (cubic {110}<001>) of each crystal grain does not necessarily coincide perfectly with the rolling direction, and there is an angular deviation θ between the easy axis direction of magnetization and the rolling direction. Crystal grains whose angular 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 angular deviation θ of practical Goss-oriented grains increases, the orientation of the crystal orientation decreases, and the magnetic flux density B ８ decreases.

[0011] Generally, the Goss-oriented grains contained in steel sheets after primary recrystallization include grains with a large angular deviation θ. However, when grains grow due to secondary recrystallization, excluding the effect of the grain size advantage in the early stages of secondary recrystallization, the smaller the angular deviation θ among the Goss-oriented grains, the stronger the driving force for grain growth and the more likely they are to grow preferentially until secondary recrystallization is complete. Therefore, the smaller the angular deviation θ, the more likely the grain size after secondary recrystallization is to become large. In other words, in manufacturing methods that highly orient secondary recrystallized grains in the Goss orientation, specific grains are preferentially grown, which inevitably leads to an increase in grain size.

[0012] Furthermore, during secondary recrystallization, the steel sheet is not flat but curved due to being wound into a coil, but the crystal grains grow while maintaining the linearity of their crystal orientation. Therefore, when the coiled steel sheet is unwound and flattened after secondary recrystallization, portions of the crystal grains will have an orientation where the axis of easy magnetization is not parallel to the surface of the grain-oriented electrical steel sheet. This coil unwinding mainly increases the value of the misalignment angle β, and also increases the angle deviation θ. The increase in the angle deviation θ due to coil unwinding becomes more pronounced as the crystal grain size increases. 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 treatment 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 subsequent primary annealing, the heating rate in the linear groove portions is made faster than in portions other than the linear grooves in a temperature range in which the steel sheet temperature is 500° C. or higher and 750° C. In Patent Document 1, by artificially creating portions with a fast heating rate and portions with a slow heating rate, portions (linear groove portions) where the frequency of (110)

[001] oriented grains is increased and portions (portions other than the linear grooves) where the frequency of (111)

[112] oriented grains is increased are arranged.

[0014] Patent Document 2 discloses a technique in which, between cold rolling and finish annealing, a laser beam is irradiated onto the surface of a silicon steel sheet multiple times at a predetermined interval PL in the rolling direction. When secondary recrystallization occurs 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 angle deviation β between the magnetization easy axis direction (cubic {110}<001>) and the rolling direction is within the range of 0° to 6°.

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

[0016] Japanese Patent Publication No. 2007-169762 International Publication No. WO2012 / 014290 Japanese Patent Publication No. 2022-161269

[0017] As mentioned 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 have not been sufficient.

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

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

[0020] [1] In a grain-oriented electrical steel sheet according to one aspect of the present invention, the deviation angle from the ideal Goss orientation when the normal direction Z to the rolling surface is the rotation axis is defined as α, the deviation angle from the ideal Goss orientation when the direction perpendicular to the rolling direction C is the rotation axis is defined as β, and the deviation angle from the ideal Goss orientation when the rolling direction L is the rotation axis is defined as γ, the deviation angle of the crystal orientation measured at one measurement point on the sheet surface is expressed as (α β γ), and the angular deviation at the one measurement point is expressed as φ = (α ２ +β ２ ) １／２ 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 defined as aveφ. Ｌ When the above-mentioned aveφ is defined as Ｌ But, aveφ Ｌ ≦4.0°, and the deviation angle of the crystal orientation measured at two adjacent measurement points on the plate surface that are spaced apart by 1 mm 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 satisfying the relation ≧1.0° is defined as the grain boundary GB, and the grain size in the rolling direction L calculated based on the grain boundary GB is expressed as D in mm. Ｌ The grain size D obtained along the rolling direction L is defined as Ｌ Arrange them in descending order and determine the particle size that is 10% of the largest by number in mm. Ｌ When defined as 10, the D Ｌ 10 is D Ｌ 10≦100−15×aveφ Ｌ Meet the following.

[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-described aspects 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.

[0024] 1 is a schematic diagram showing measurement points of the crystal orientation on a steel sheet at intervals of 1 mm along the rolling direction, and FIG. 2 is a diagram showing the influence of the average value of the angular deviation in the rolling direction and the crystal grain size on the magnetic properties of the grain-oriented electrical steel sheet.

[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. Furthermore, the numerical ranges described below include the lower and upper limits. Numerical values ​​indicated as "greater than" or "less than" are not included in the numerical range. Furthermore, "%" in relation to chemical composition means "mass %" unless otherwise specified.

[0026] As mentioned above, the frequency of practical Goss orientation grains, which have small angular deviations θ and φ from the ideal Goss orientation {110}<001>, increases as the heating rate of the primary annealing (decarburization annealing) increases. In contrast, crystal grains that are easily encroached upon by Goss orientation grains, such as those with {778}<447> (≒{111}<112>) and {411}<148> orientations, which have a Σ9 correspondence orientation relationship with the Goss orientation, (referred to as "corresponding orientation grains"), decrease as the heating rate of the primary annealing increases. Therefore, it has been difficult to increase the proportion of practical Goss orientation grains while also increasing the proportion of corresponding orientation grains during the primary annealing.

[0027] The technology described in Patent Document 1 forms linear grooves on the surface of a steel sheet by etching, and then increases the heating rate of the linear grooves during primary annealing to create a region with a high proportion of Goss-oriented grains (the linear grooves) and a region with a high proportion of correspondingly oriented grains (the regions 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 grooves and other regions, and the resulting effect is limited. Specifically, the difference in heating rate between the linear grooves and the regions other than the linear grooves is not significant. For example, even if the entire steel sheet is heated at 100°C / s, the thickness reduction in this region due to the groove formation does not exceed about 10% of the original thickness (because a typical groove depth is about 20 μm or less, or about 10% of the thickness). Therefore, considering the thermal conductivity of the steel sheet, the heating rate ratio is less than the thickness ratio for the same heat input, and therefore the ratio of Goss-oriented grains in the linear grooves is unlikely to increase compared to the regions other than the linear grooves. Furthermore, in this method, the heating rate of the linear groove portion is increased during the primary annealing, so that the grain size of the Goss-oriented grains formed in the linear groove portion after the primary annealing does not increase compared to the overall average primary recrystallization grain size, but remains the same or finer.

[0028] In addition, the technology described in Patent Document 2 irradiates a laser beam onto the surface of a steel sheet 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-oriented grains generated by primary recrystallization. Furthermore, the area heated by laser irradiation is limited to 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 sufficient to recrystallize the steel sheet.

[0029] In addition, the technology described in Patent Document 3 irradiates a laser beam onto the surface of a steel sheet after cold rolling. However, as with the above, this method only controls the laser beam irradiation area to the grain boundaries of secondary recrystallization, but does not control the heating rate or the orientation of Goss-oriented grains generated by primary recrystallization. Patent Document 3 only reduces the grain size of secondary recrystallized grains in the rolling direction by using the laser beam irradiation area as a barrier to the growth of secondary recrystallized grains. It does not ensure a grain growth temperature range in the locally heated region that is effective for increasing the diameter of Goss-oriented grains in the locally heated region. While this method may be able to reduce the difference in the degree of orientation concentration of Goss orientation at the inner and outer peripheries of a coil with different curvatures, it does not produce Goss-oriented grains with a crystal orientation 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 of secondary recrystallized grains in the rolling direction, but does not aim to fundamentally improve the orientation of Goss-oriented grains.

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

[0031] The heating rate of the locally heated 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. Thus, it has been found that when a locally heated region is formed on the surface of a steel sheet before primary annealing and then primary annealing is performed on this steel sheet, a large number of crystal grains having the practical Goss orientation are formed in the locally heated region. It has also been found that, among the practical Goss orientation crystals formed, the proportion of Goss orientation grains with smaller angular deviations θ and φ from the ideal Goss orientation increases, and the grain size of the Goss orientation grains also 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 formation of practical Goss-oriented grains and facilitating grain growth, but recovery and recrystallization do not occur in the non-locally heated region.

[0033] Prior to primary annealing, localized rapid heating is performed to scatter locally heated regions having the above characteristics on the steel sheet surface, followed by primary annealing and then secondary annealing. The Goss-oriented grains formed in the locally heated regions grow preferentially during the secondary annealing after the primary annealing. Among the Goss-oriented grains formed in the locally heated regions are those with particularly small angular deviations θ and φ, which are close to the ideal Goss orientation, and have large crystal grain sizes. These Goss-oriented grains grow preferentially during secondary recrystallization.

[0034] Because Goss-oriented grains, which serve as nuclei for secondary recrystallization, are supplied to the locally heated region, there is no need 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, during primary annealing. Therefore, the heat treatment conditions for the primary annealing may be a slow heating condition with a low heating rate, which allows for the formation of many corresponding-oriented grains with the {111}<112> and {411}<148> orientations, which are susceptible to corrosion, in the non-locally heated region. For example, by setting the heating rate for the primary annealing to 300°C / sec or less, many Goss-oriented grains with large grain sizes and close to the ideal Goss orientation are formed in the locally heated region, while almost no Goss-oriented grains are formed in the non-locally heated region, allowing for the formation of many corresponding-oriented grains.

[0035] As described above, in a steel sheet (decarburized annealed steel sheet) that has undergone localized rapid heating and primary annealing, many Goss-oriented grains with a grain size close to the ideal Goss orientation are present in the locally heated region. On the other hand, the matrix portion (non-locally heated region) contains almost no large-sized Goss-oriented grains, and many correspondingly oriented grains that are susceptible to erosion can be present. When such a steel sheet is subjected to secondary annealing, the Goss-oriented grains with a grain size close to the ideal Goss orientation that are present in the locally heated region begin to grow preferentially, growing toward the non-locally heated region.

[0036] In addition, when localized rapid heating is performed before primary annealing to scatter locally heated regions on the steel sheet surface, the size, shape, and arrangement of crystal grains after secondary annealing can be controlled by appropriately arranging the localized rapid heating on the steel sheet surface. For example, if Goss-oriented grains that start growing from one locally heated region collide with other Goss-oriented grains that start growing from an adjacent locally heated region and their grain growth stops, the grain size of the Goss-oriented grains at the end of secondary annealing will be small, resulting in a steel sheet with excellent core loss. In particular, as described above, Goss-oriented grains that preferentially grow from the localized heat-affected regions in the early stages of secondary annealing have a crystal orientation close to the ideal Goss orientation, so that good magnetic flux density can be obtained despite the small secondary recrystallized grain size.

[0037] The grain-oriented electrical steel sheet according to this embodiment was obtained based on the above technical concept. The characteristics of the grain-oriented electrical steel sheet according to this embodiment will now be described in detail.

[0038] The grain-oriented electrical steel sheet (base steel sheet) according to this embodiment defines the deviation angle from the ideal Goss orientation with the normal direction Z of the rolling surface as the rotation axis as α, the deviation angle from the ideal Goss orientation with the direction perpendicular to the rolling C as the rotation axis as β, the deviation angle from the ideal Goss orientation with the rolling direction L as the rotation axis as γ, the deviation angle of the crystal orientation measured at one measurement point on the sheet surface as (α β γ), and the angular deviation at the one measurement point as φ = (α ２ +β ２ ) １／２ 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 defined as aveφ. ＬWhen defined as above, the above aveφ Ｌ But, aveφ Ｌ ≦4.0°.

[0039] In addition, the grain-oriented electrical steel sheet (base steel sheet) according to this embodiment is characterized in that the deviation angle of the crystal orientation measured at two adjacent measurement points on the sheet surface that are spaced apart by 1 mm (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 satisfying the relation ≧1.0° is defined as the grain boundary GB, and the grain size in the rolling direction L calculated based on the grain boundary GB is expressed as D in mm. Ｌ The grain size D obtained along the rolling direction L is defined as Ｌ Arrange them in descending order and determine the particle size that is 10% of the largest by number in mm. Ｌ When defined as 10, the above D Ｌ 10 is D Ｌ 10≦100−15×aveφ 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 also to improve both the magnetic flux density and the iron loss characteristics.

[0041] In this embodiment, the angular deviation φ is defined by the deviation angles α and β. The general angular deviation θ is often evaluated by three components: the deviation angles α, β, and γ. However, in this embodiment, the angular 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. The above-mentioned effects can be obtained by using this angular deviation φ to satisfy the above conditions. Meanwhile, 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 value of 4.0° or less means that the angular deviation φ is small on average 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°, is preferably 3.2° or less, is more preferably 3.0° or less, and is even more preferably 2.7° or less. Ｌ Since a smaller value is more preferable, 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 x aveφ Ｌ ) mm or less means that the crystal grains have not grown 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 applying conventional magnetic domain control technology. If the magnetic domains are subdivided, an increase in iron loss is suppressed. D Ｌ When the above conditions are satisfied, the magnetic flux density and core loss characteristics are improved. Ｌ 10 is (90-15 x aveφ Ｌ) mm or less, and (80-15 × ave φ Ｌ ) mm or less. Ｌ Since the smaller the value of D10, the more preferable it is, the lower limit is not particularly limited. 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 1,000 measurement points at 1 mm intervals on the rolled surface to measure the crystal orientation. For example, the crystal orientation can be measured by X-ray diffraction (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 technique suitable for measuring the crystal orientation of a metal structure with coarse crystal grains.

[0045] It is sufficient that the number of measurement points for the crystal orientation is at least 1,000, but it is preferable to increase the number of measurement points appropriately depending on the size of the secondary recrystallized grains. For example, if the number of measurement points for measuring the crystal orientation is 1,000 and the number of secondary recrystallized grains included within a measurement line is less than 20, it is preferable to extend the measurement line by increasing the number of measurement points at 1 mm intervals so that the measurement line includes 20 or more secondary recrystallized grains. Furthermore, if it is difficult to set 1,000 measurement points on a single measurement line, it is sufficient to set multiple measurement lines and measure the crystal orientation at a total of 1,000 or more measurement points.

[0046] The crystal orientation is measured at 1 mm intervals on the rolled surface, and then the 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, etc. are calculated. Ｌ , grain boundary GB, grain size D Ｌ , D Ｌ 10. Ｌ 10 is the particle size D ＬThe grain size of the crystal grains having a diameter of 2 mm or more can be determined by arranging the crystal grains in descending order of size and finding the grain size that accounts for 10% of the largest grains by number. In addition, if the irradiation area of ​​the X-ray beam at the point of measurement of crystal orientation by the Laue method straddles two crystal grains and it is not possible to determine which crystal grain the X-ray diffraction result comes from, 0.5 mm can be added to each of 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 now be described again.

[0048] The grain-oriented electrical steel sheet according to this embodiment has a φ defined as follows: ｍ ≦4.0°, and D10 defined below satisfies f(φ ｍ However, n points (at least 1000 points) are determined at 1 mm pitch in the rolling direction (RD) to measure the crystal orientation, and the deviation angle α from the ideal {110}<001> orientation around ND, TD, and RD at measurement point i (i = 1 to n) is ｉ , β ｉ , γ ｉ is measured and calculated using the following formula (1): ｉ After determining the average angle deviation φ ｍ 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 is deviated 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 of one grain in the rolling direction (RD). When the grains are arranged in descending order of grain size D, the grain size of the grain that is 10% from the largest grain size D among all the grains is defined as D10.

[0049] Regarding the angle deviation φ, the average angle deviation φ of the steel plate in the rolling direction (RD) ｍ 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 diffractometer using the Laue method. The deviation angle α from the ideal {110}<001> orientation at measurement point i in the normal direction (ND), transverse direction (TD), and rolling direction (RD) is ｉ , β ｉ , γ ｉ Measure and use the above formula (1) to calculate φ ｉ Then, the average angle deviation φ is calculated using the above formula (2). ｍ is calculated. Note that, for the transverse direction (TD), one measurement point row may be set at any position, or multiple measurement point rows may be set in the transverse direction (TD) as measurement positions. In particular, when there is variation in magnetic properties in the transverse direction (TD), multiple measurement point rows 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 measurement point rows 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 descending order, the grain size (D10) of the crystal grain at the position of the largest 10% of all the crystal grains is defined. As described above, after measuring the crystal orientation at each measurement position, the difference [(α ｉ -α ｉ＝１ ) ２ + (β ｉ -β ｉ＝１ ) ２ + (γ ｉ -γ ｉ＝１ ) ２ ] １／２ When the value of is shifted by 1° or more, it is determined that a grain boundary exists between the adjacent measurement positions, and when 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, φ at the measurement position located in the center in the rolling direction (RD) is φ ｉ When this is the case, φ ｉ－１ and φ ｉ－２ Between [(α ｉ＝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°, a 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 The value of exceeds 1°, and a grain boundary b exists between these measurement points. The grain size D in the rolling direction (RD) formed by the grain boundaries a and b is defined as 1 mm × [(i+2)-(i-1)] = 3 mm.

[0051] Furthermore, the grain size D obtained by this procedure is 1 mm or more, but when determining D10, grain sizes with a grain size D of 2 mm or more are used. After determining the grain boundaries and grain size D within the range measured in the rolling direction (RD) as described above, and arranging the grains with a D value of 2 mm or more in descending order of D value, the grain size of the grains at the position of the largest 10% of all grains is taken as D10. In addition, there are cases where the X-ray irradiation area at the measurement point straddles two grains, making it impossible to determine which grain it is. In such cases, 0.5 mm is assigned to the grain sizes of the two straddling grains.

[0052] The details of the investigations carried out by the present inventors will be specifically described below.

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

[0054]

[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 magnetic domain control), ｍ (aveφ Ｌ ) and D10 (DＬ 10) and evaluated the magnetic properties. Figure 2 shows the influence of the average value of the angular deviation in the rolling direction and the grain size on the magnetic properties of grain-oriented electrical steel sheets. In Figure 2, the horizontal axis is φ ｍ (aveφ Ｌ ), the vertical axis is D10 (D Ｌ 10). In addition, in Figure 2, B ８ ≧1.93T and W １７／５０ ≦0.79 W / kg is indicated by ○, and B ８ or W １７／５０ Cases where at least one of the above conditions is not met are indicated by a black circle.

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

[0058] The current-carrying electrode used in spot resistance heating is circular, and its diameter, in terms of circle equivalent diameter, is preferably 0.5 mmφ to 10 mmφ, 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 containing, by mass fraction, 2.0% to 7.0% Si, with the remainder being Fe and impurities. The above chemical composition is preferable for controlling the crystal orientation so that it is concentrated in the {110}<001> orientation.

[0061] Furthermore, this grain-oriented electrical steel sheet may contain known optional elements in place of a portion of Fe for the purpose of improving 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 within a range in which a significant decrease in magnetic flux density or iron loss does not occur. 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 to 7.0%, C: 0 to 0.0050%, Mn: 0 to 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 to 0.40%, Bi: 0 to 0.010%, B: 0 to 0.080%, P: 0 to 0.50%, Ti: 0 to 0.0150%, Sn: 0 to 0.10%, Sb: 0 to 0.10%, Cr: 0 to 0.30%, Ni: 0 to 1.0%. and the remainder may be Fe and impurities.

[0063] Si: 2.0 to 7.0% Si (silicon) is a basic element for the 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 threadability during production deteriorates significantly, 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 an optional element for the base steel sheet. C is contained in the steel billet (slab), but if excessive C remains in the base steel sheet after finish annealing, good iron 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 achieve a C content of 0%, the C content may be more than 0% or may be 0.00010% or more.

[0065] Mn: 0 to 1.0% Mn (manganese) is an optional element for the base steel sheet. Although Mn is contained in steel slabs, excessive Mn can cause phase transformation of the steel during secondary recrystallization annealing, preventing secondary recrystallization from progressing sufficiently and resulting in poor magnetic properties. 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 acts as an inhibitor during secondary recrystallization, the Mn content may be greater 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 steel slabs, but if excessive S and Se remain in the base steel sheet after finish annealing, it 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 inhibitors 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 an optional element for the base steel sheet. Al is contained in steel slabs, but if excessive Al remains in the base steel sheet after finish annealing, it may adversely affect 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 greater 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 an optional element for the base steel sheet. N is contained in the steel billet (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 to 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%, coating adhesion may decrease. Furthermore, if purification during finish annealing is insufficient and excessive Bi remains, it may adversely affect 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 the effect of improving magnetic flux density, the Bi content may be more than 0% or may be 0.00050% or more.

[0072] B: 0 to 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 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 to 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 deteriorate. Therefore, the Ti content of the base steel sheet may be 0.0150% or less. The Ti content is preferably 0.0130% or less, and 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%, 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 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 to 0.30% Cr (chromium) is an optional element for the base steel sheet. If the Cr content exceeds 0.30%, Cr oxides may be 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 to 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, 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 this embodiment may contain impurities. Here, "impurities" refer to substances that are mixed in from raw materials such as ore or scrap, or from the manufacturing environment, when steel is industrially produced.

[0080] The chemical composition of the base steel sheet may be measured by a common 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 a combustion-infrared absorption method, N may be measured using an inert gas fusion-thermal conductivity method, and O may be measured using an 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 measured 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. ２ O: The insulating coating can be removed from the grain-oriented electrical steel sheet by immersing the sheet in a 50 to 70 mass % aqueous sodium hydroxide solution at 80 to 90°C for 5 to 10 minutes, followed by rinsing with water and drying. The immersion time in the aqueous sodium hydroxide solution can be changed depending on the thickness of the insulating coating.

[0083] Furthermore, a method for removing a 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 high-temperature hydrochloric acid. Specifically, the concentration of hydrochloric acid preferred 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 to 40 mass % hydrochloric acid) at 80 to 90°C for 1 to 5 minutes, followed by rinsing with water and drying. Typically, different treatment solutions are used to remove each coating, such as using an alkaline solution to remove the insulating coating and hydrochloric acid to remove the forsterite coating.

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

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

[0086] Furthermore, the steps and quantitative conditions for each step shown below are examples adopted to demonstrate the feasibility of this embodiment, and this embodiment is not limited to these steps and quantitative values. The method for manufacturing a grain-oriented electrical steel sheet according to this embodiment can adopt various conditions as long as they do not deviate from the gist of this embodiment and achieve the object of this embodiment.

[0087] The method for manufacturing the grain-oriented electrical steel sheet according to the present embodiment can apply, as a basic step, conventional methods for manufacturing grain-oriented electrical steel sheets. For example, conventional methods for manufacturing grain-oriented electrical steel sheets include a method for forming inhibitors such as MnS or AlN by high-temperature slab heating, and a method for forming AlN inhibitors by low-temperature slab heating and nitriding. The method for manufacturing the grain-oriented electrical steel sheet according to the present embodiment is not limited to a specific manufacturing method. Below, a method for applying nitriding as the 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 continuous casting. The molten steel may be used to produce an ingot, 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. A so-called thin slab having a thickness of 10 to 70 mm may be used as the slab. 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 during the manufacturing process, but excessive C content in the final product 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, resulting in a C content of 0.005% or less. When C is contained, taking into account productivity in industrial production, the lower limit of the C content may be more than 0%, or even 0.001%.

[0091] Si: 2.0 to 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, making cracks more likely to occur during cold rolling. The preferred lower limit of the Si content is 2.5%, more preferably 3.0%. The preferred upper limit of the Si content is 4.5%, more preferably 4.0%.

[0092] Mn: 0.05 to 1.00% Manganese (Mn) combines with S or Se to form MnS or MnSe, which functions as an inhibitor. When Mn is contained, secondary recrystallization is stabilized when the Mn content is within the range of 0.05 to 1.00%. Note that part of the inhibitor function can be performed by nitrides of Nb group elements. 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 Mn content is 0.50%, and 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 form MnS or MnSe, functioning as an inhibitor. When at least one of S and Se is contained, secondary recrystallization is stabilized if the total content of S and Se is 0.003 to 0.035%. It is possible for part of the inhibitor function to be performed by nitrides of Nb group elements. 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 S and Se content is 0.025%, more preferably 0.010%. If S and Se remain after final annealing, they form compounds that deteriorate iron loss. Therefore, it is preferable to reduce S and Se as much as possible through 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 included.

[0095] Al: 0.010 to 0.065% Aluminum (Al) combines with N to precipitate as (Al, Si)N, functioning as an inhibitor. When Al is contained, if the Al content is within the range of 0.010 to 0.065%, AlN, which acts as an inhibitor formed by nitriding (described later), expands the secondary recrystallization temperature range, stabilizing secondary recrystallization particularly 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 secondary recrystallization stability, 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 and functions 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 greater than 0%, or even 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%, more preferably 0.009%. N is purified in the final annealing process, and the N content 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 ore or scrap, 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 known optional elements in place of a portion of Fe, taking into consideration not only solving problems in production but also strengthening the inhibitor function by compound formation and the influence on magnetic properties. Examples of optional elements that can be contained in place of a portion of Fe include 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 Nb group elements are used as part of the inhibitor, a total content of Nb group elements of 0.030% or less is preferable because it initiates secondary recrystallization at an appropriate timing. In addition, the orientation of the secondary recrystallized grains that occur becomes very favorable, and ultimately, it is possible to control the structure to be favorable for 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; the lower limit may be 0%. This lower limit is preferably 0.003%.

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

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

[0102] The slab may also contain, as optional elements, at least one of the following 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, and Ni: 1.00% or less. These optional elements may be contained according to known purposes, so 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, in the same manner as 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 (for example, 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 rough-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 that includes a nitriding step during or after decarburization annealing, the strength of MnS as an inhibitor is not so necessary, so in consideration of productivity, the slab heating temperature should be set to 1100°C to 1280°C.

[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 predetermined temperature conditions (e.g., at 750 to 1200°C for 30 seconds to 10 minutes) to obtain an annealed steel sheet. Hot-rolled sheet annealing is generally performed to control the steel sheet structure, such as the recrystallization rate, residual strain, and crystal grain size, by annealing the hot-rolled steel sheet after the hot-rolling process, and to favorably adjust the precipitate morphology in the steel. For example, in a high-temperature slab heating process, this is a process that ultimately controls the morphology of precipitates such as AlN, and conditions are adjusted to precipitate uniformly and finely. In 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 to properly precipitate AlN, etc., followed by water cooling.

[0107] (Cold Rolling Step) The cold rolling step is a step in which the annealed steel sheet obtained in the hot-rolled sheet annealing step is subjected to a single cold rolling or multiple (two or more) cold rolling steps (e.g., a 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 reduction (%) = (1 - thickness of steel sheet after cold rolling / thickness of steel sheet 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 locally heated region. The rapid heating method is not particularly limited as long as it can locally heat the steel sheet. For example, a method in which spot electrodes are brought into contact with the front and back surfaces of the steel sheet and an electric current is passed through the steel sheet to heat it, a method in which laser light or an electron beam is irradiated onto the surface of the steel sheet to heat it, a method in which localized heating is performed by induction heating, or a method in which a hot piece is brought into contact with the steel sheet to heat it can be used. The size of each locally heated 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. The electrodes used for electrical heating may be circular electrodes as described above, or linear electrodes.

[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. While it is theoretically possible to further reduce the size of the locally heated region, considering that the current size of recrystallized grain nuclei is approximately 1 μm, it is believed that a locally heated region of 1 μm or greater will be effective. Industrially, the minimum diameter and width should be 10 μm or greater. Regarding the size of the locally heated region, if the maximum diameter or width exceeds 10 mm, the area proportion of Goss-oriented grains with relatively large angular deviations θ and φ that cannot grow outside the locally heated region increases. In this case, the effect of local rapid heating is less likely to be achieved.

[0111] In localized rapid heating, the heating rate should be 500°C / s or more at 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 / s or more, the structure of the locally heated region can be preferably controlled to a recovered structure or a recrystallized structure. The heating rate is preferably 2000°C / s or more, and more preferably 10000°C / s or more. On the other hand, the upper limit of the heating rate is not particularly limited, and may be, for example, 1000000°C / s.

[0112] Furthermore, it is preferable to control the heating rate in accordance 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 desired effect. Therefore, although it depends on the magnitude 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 corresponding to 1 / 5 of the plate thickness of the steel plate from the surface of the steel plate in the plate thickness direction.

[0114] Furthermore, in 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 thickness direction and at 1 / 5 of the thickness of the steel plate. If the maximum temperature reached in the above region is 700°C or higher, 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] Furthermore, 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 in the thickness direction and at 1 / 5 of the thickness of the steel plate is 0.1 seconds or more. If the holding time in the above region is 0.1 seconds or more, 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, there is no particular limitation on the upper limit of the holding time, and it may be, for example, 10 seconds or less. The holding time from reaching the maximum temperature to cooling to 700°C has a fundamental effect on the formation of coarse Goss-oriented grains close to the ideal Goss orientation.

[0116] In localized rapid heating, it is important to control the heating rate and maximum temperature, as well as the 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. Controlling the subgrain structure in the locally heated region by the holding time allows for favorable microstructural control in subsequent processes.

[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 local rapid heating method, 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 heat conduction analysis using the finite element method to control the heating rate and the maximum temperature reached 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. Additionally, a person skilled in the art can control the above-mentioned holding time by adjusting the heat removal conditions after the maximum temperature is reached. For example, in the case of spot current heating, this can be achieved by controlling the electrode holding time after current application or by changing the shape of the spot electrode to a shape suitable for heat removal. Furthermore, 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] In general, heating by laser irradiation preferentially heats only the vicinity of the irradiated steel sheet surface, and the interior of the steel sheet is less likely to be heated. Furthermore, since heating by laser irradiation is non-contact heating, heat is removed quickly after heating and the temperature is difficult to maintain. Therefore, when laser irradiation heating is performed 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 interior of the steel sheet is heated, and the cooling rate is slowed 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] However, simply increasing the input power of laser or electron beam irradiation makes it difficult to form coarse Goss-oriented grains close to the ideal Goss orientation. For example, when rapid heating is performed by laser or electron beam irradiation, it is preferable to make the beam shape elliptical or adjust the scan speed, etc., so as to ensure a temperature range in which the crystal grains in that region can grow after rapid heating.

[0121] Conventionally, laser irradiation or electron beam irradiation has been performed on electrical steel sheets to control magnetic domains after secondary recrystallization and reduce iron loss. Under these laser or electron beam irradiation conditions, the steel sheet is heated to a depth of approximately 20 μm from the surface, resulting in rapid heat dissipation after heating. Therefore, under conventional conditions, it is difficult to ensure the required holding time from reaching the maximum temperature to cooling to 700°C. In other words, under conventional laser or electron beam irradiation conditions, although the irradiated area may be able to act as a barrier to the growth of secondary recrystallized grains, it is difficult to form coarse Goss-oriented grains with an orientation close to the ideal Goss orientation, as in the present embodiment. To form coarse Goss-oriented grains close to the ideal Goss orientation by laser or electron beam irradiation, the conditions for laser or electron beam irradiation must be considered as described above.

[0122] Furthermore, when locally heated regions are scattered on the steel sheet surface by local rapid heating, the size, shape, and arrangement of crystal grains after secondary annealing can be controlled by appropriately arranging the locally rapid heating on the steel sheet surface. For example, by arranging the locally heated regions on the steel sheet surface so that Goss-oriented grains that start growing from one locally heated region collide with other Goss-oriented grains that start growing from an adjacent locally heated region, the grain size of 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 locally heated 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. 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 humid atmosphere to remove "C" contained in the cold-rolled steel sheet.

[0124] It is also effective to reduce the primary recrystallized grain size by controlling the conditions of the hot rolling and hot-rolled sheet annealing described above, 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] Furthermore, in this embodiment, coarse Goss-oriented grains with an orientation close to the ideal Goss orientation are formed in the locally heated region. Therefore, there is no need to form Goss-oriented grains by decarburization annealing. The heating rate of decarburization annealing may be 10,000°C / s or less. However, it is preferable to use a slower heating rate in decarburization annealing to form {111}<112>-oriented grains and {411}<148>-oriented grains that are easily eroded into the matrix portion (non-locally heated region). For example, the heating rate of decarburization annealing is preferably 300°C / s or less, more preferably 200°C / s or less, and even more preferably 100°C / s or less.

[0126] The amount of decarbonation and the state of the surface oxide layer affect the formation of the glass film. Therefore, in decarburization annealing, the degree of oxidation (PH) in the annealing atmosphere (furnace atmosphere) is important. ２ O / PH ２ ) may be adjusted appropriately.

[0127] (Nitriding) Nitriding is an effective treatment in low-temperature slab heating processes where the slab heating temperature is 1280°C or less, and is an important step for adjusting the strength of the inhibitor in secondary recrystallization. Nitriding increases the nitrogen content of the steel sheet by approximately 40 to 200 ppm between the start of decarburization and 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 nitriding powder such as MnN. The amount of nitride after nitriding is preferably 130 to 350 ppm, and more preferably 150 to 250 ppm.

[0128] (Annealing separator application step) The annealing separator application step is a step of applying an annealing separator to a decarburized annealed steel sheet. Examples of the annealing separator include an annealing separator containing MgO as a main component and an annealing separator containing Al. ２ O３ The decarburized annealed steel sheet after being coated with the annealing separator is wound into a coil and then finish-annealed in the subsequent finish-annealing step.

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

[0130] The heating rate during the heating process in the final annealing step is not particularly limited. For example, the temperature may be increased at a heating rate of 3 to 20°C / hour. Furthermore, slow heating may be performed within a temperature range of 1000°C to 1200°C during the temperature increase. For example, the heating rate within the temperature range of 1000°C to 1200°C during the temperature increase is preferably 3 to 12°C / hour, more preferably 3 to 9°C / hour, and even more preferably 3 to 7°C / hour. Alternatively, the temperature increase may be stopped and held during the heating process in the final annealing step to prevent the precipitates pinning the primary recrystallized grains from suddenly decomposing. For example, the temperature increase may be stopped once within a temperature range of 1050°C to 1100°C during the temperature increase, and the temperature may be held for 5 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 step in the final annealing step, a holding step (purification annealing) may be performed by holding the steel sheet in a temperature range of 1000° C. to 1300° C. for 10 hours to 60 hours. The atmosphere during the final annealing may be, for example, a nitrogen atmosphere or a mixed atmosphere of nitrogen and hydrogen.

[0132] (Insulating Coating Forming Step) If necessary, an insulating coating may be formed on the steel sheet after the finish annealing by applying a coating solution containing phosphoric acid or a phosphate, chromic anhydride or a chromate, and colloidal silica, and baking the coating (for example, at 350°C to 1150°C for 5 to 300 seconds).

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

[0134] When magnetic domain refinement is performed, the micro-distortion 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 to avoid the measurement point overlapping with the micro-distortion regions and grooves.

[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 the object of the present invention is achieved.

[0136] Using the slabs with adjusted chemical compositions as raw materials, cold-rolled steel sheets having the chemical compositions shown in Table 2 were manufactured. These chemical compositions were measured based on the above-mentioned method. In Table 2, "-" indicates that the content was not measured, and that control and manufacturing were not carried out with the content in mind.

[0137] When producing the above cold-rolled steel sheets, slabs were heated to 1150°C and subjected to hot rolling to obtain hot-rolled steel sheets with a thickness of 2.6 mm. The hot-rolled steel sheets were then heated to 1100°C and subsequently annealed at 900°C (hot-rolled sheet annealing), after which pickling was performed to remove scale formed on the surface. These steel sheets were subjected to a single cold rolling or multiple cold rollings with intermediate annealing in between to obtain cold-rolled steel sheets with a final thickness of 0.22 mm.

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

[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 local 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 region. 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 laser beam was focused at a spot diameter of 0.5 mm and a laser irradiation energy density of 30.0 J / mm. ２ The laser beam was controlled so that the laser beam irradiated area would ultimately be the grain boundary of the secondary recrystallized grains.

[0140] In the table, "No treatment" for the localized rapid heating method indicates that localized rapid heating was not performed. The localized heating conditions "Linear or spotted" represent the shape of the localized heated area on the surface of the cold-rolled steel sheet, and the localized heating conditions "Rolling direction spacing" and "Width direction spacing" represent 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 (PH) in the annealing atmosphere (furnace atmosphere) was measured. ２ O / PH ２ ) was set to 0.13.

[0142] The produced decarburized annealed steel sheets were nitrided at 750°C in a nitrogen-hydrogen-ammonia atmosphere to adjust the nitrogen content of the steel sheets to 220 ppm. Furthermore, 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°C to 1200°C at 15°C / hour Gradual heating 1: 1000°C to 1200°C at 10°C / hour Gradual heating: 1000°C to 1200°C at 7.5°C / hour Gradual heating 2: 1000°C to 1200°C at 5.0°C / hour Step: 1070°C x 10 hours hold

[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, with chromic anhydride added as needed, and baked to form an insulating film.

[0144] For the obtained grain-oriented electrical steel sheet, the chemical composition of the base steel sheet, aveφ Ｌ (φ ｍ ), 100-15 × aveφ Ｌ The value of (f(φ ｍ )) D Ｌ10 (D10) was measured according to the method described above. The results are shown in Tables 7 to 11. In Table 11, "-" indicates that the content was not measured because the control and production were not carried out with the content in mind.

[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 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, and 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, each measuring 100 mm x 500 mm, were prepared, and single sheet magnetic measurement was carried out. As the magnetic properties, the magnetic flux density B ８ (T) was measured. ８ The pass / fail judgment was made based on the Si content of the steel sheet. For example, the lower the Si content of the steel sheet, the higher the saturation magnetic flux density. ８ Therefore, for steels A to Z with a Si content of 3.3 to 3.5%, ８ The steel AA having a Si content of 2.5% was judged to be acceptable when the value of B was 1.930T or more. ８ The steel AB having a Si content of 4.1% was judged to be acceptable when the value of the steel AB was 1.960T or more. ８ When the value was 1.890T or more, it was judged to be acceptable.

[0149] In addition, as magnetic properties, the iron loss W defined as the power loss per unit weight (1 kg) of the steel sheet 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 the resistance, a value of 0.79 W / kg or less was judged to be acceptable.

[0150] Among Nos. 1 to 66, the grain-oriented electrical steel sheets according to the present invention have aveφ Ｌ ≦4.0°, and D Ｌ 10≦100−15×aveφ Ｌ In all of these examples of the present invention, the angular deviation in the rolling direction was controlled to be small, so that the grain size in the rolling direction was controlled to be small, and therefore the iron loss was excellent without the need for magnetic domain control (magnetic domain refining treatment). Therefore, these examples of the present invention can reduce the adverse effects of conventional magnetic domain control (for example, the deterioration of transformer noise due to laser magnetic domain control, and the reduction of 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 used as comparative examples had aveφ Ｌ ≦4.0°, or D Ｌ 10≦100−15×aveφ Ｌ In these comparative examples, desirable magnetic flux density and iron loss were not obtained as grain-oriented electrical steel sheets.

[0152]

[0153]

[0154]

[0155]

[0156]

[0157]

[0158]

[0159]

[0160]

[0161]

[0162] According to the above-described aspects 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, and therefore has high industrial applicability.

[0163] 1 Steel plate 2 Crystal orientation measurement point

Claims

1. A grain-oriented electrical steel sheet, wherein 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, and 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 sheet surface is expressed as (α β γ), and the angular deviation at the one measurement point is expressed as φ = (α ２ +β ２ ) １／２ 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 defined as aveφ. Ｌ When the above-mentioned aveφ is defined as Ｌ But, aveφ Ｌ ≦4.0°, and the deviation angle of the crystal orientation measured at two adjacent measurement points on the plate surface that are spaced apart by 1 mm 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 the relation ≧1.0° is defined as the grain boundary GB, and the grain size in the rolling direction L calculated based on the grain boundary GB is expressed as D in mm. Ｌ The grain size D measured along the rolling direction L is defined as 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 D Ｌ 10 is D Ｌ 10≦100-15×aveφ Ｌ The grain-oriented electrical steel sheet satisfies the above.

Images