Grain-oriented electrical steel sheet

Abstract

In this grain-oriented electrical steel sheet, the average value ave [phi] L of the angular deviation [phi] determined at measurement points of at least 1000 points at an interval of 1 mm in the rolling direction L is 4.0 DEG or less, and the particle diameter DL10, which is obtained by arranging the particle diameters DL determined in the rolling direction L in the order from large to small, and which is 10% of the particle diameters DL10 from the large particle diameter DL10 on the basis of the number thereof, is (100-15 * ave [phi] L) mm or less.

Description

TECHNICAL FIELD

[0001] The present application relates to a grain-oriented magnetic steel sheet.

[0002] This application claims priority based on Japanese Patent Application No. 2023-106556 filed on June 29, 2023, and the contents thereof are hereby incorporated by reference. BACKGROUND

[0003] A grain-oriented magnetic steel sheet contains Si, the crystal orientation of the crystal grains thereof is concentrated around a Goss orientation (cubic crystal {110} <001>), and the <001> orientation as an easy magnetization axis is substantially aligned in the rolling direction in a steel sheet manufacturing process. Such a grain-oriented magnetic steel sheet is very excellent as a material for a core of a transformer or the like. Particularly important among the magnetic properties of the grain-oriented magnetic steel sheet are the magnetic flux density and the iron loss.

[0004] The magnetic flux density of the grain-oriented magnetic steel sheet when a prescribed magnetization force is applied has the tendency that the higher the degree of alignment of the easy magnetization axis of the crystal grains in the rolling direction of the steel sheet, that is, the higher the orientation of the crystal orientation, the larger the magnetic flux density becomes. As an index indicating the magnetic flux density, the magnetic flux density B8 is generally used. The magnetic flux density B8 is the value of the magnetic flux density of the grain-oriented magnetic steel sheet that is magnetized when a magnetization force of 800 A / m is applied in the rolling direction. That is, it can be said that the more the value of the magnetic flux density B8 of the grain-oriented magnetic steel sheet, the more easily the grain-oriented magnetic steel sheet is magnetized with a certain magnetization force, the larger the magnetic flux density becomes, and thus the grain-oriented magnetic steel sheet is suitable for a transformer that is small and excellent in efficiency.

[0005] In addition, as an index indicating the iron loss, the iron loss W 17 / 50 is generally used. The iron loss W 17 / 50 is the iron loss when the grain-oriented magnetic steel sheet is ac-excited under the conditions that the maximum magnetic flux density is 1.7 T and the frequency is 50 Hz. It can be said that the more the value of the iron loss W 17 / 50 of the grain-oriented magnetic steel sheet, the lower the energy loss and the more suitable the grain-oriented magnetic steel sheet is for a transformer.

[0006] As a method of reducing the iron loss, there are a method of containing Si effective for reduction of eddy current loss to increase the electric resistance, a method of thinning the steel sheet thickness, a method of reducing the crystal grain size, and a method of aligning the orientation of the crystal grains effective for reduction of hysteresis loss, and the like. That is, the larger the value of the magnetic flux density B8, the more the crystal orientation is aligned with the Goss orientation, and the hysteresis loss is reduced, and thus there is a tendency that the larger the value of the magnetic flux density B8, the smaller the value of the iron loss W 17 / 50 becomes. On the other hand, if the development of the Goss orientation grains is promoted in order to increase the concentration degree of the crystal orientation, there is a tendency that the crystal grain size becomes large, and thus the eddy current loss becomes large, and in the case where the crystal grains excessively become large even though the value of B8 is high, there is a paradox that the iron loss deteriorates.

[0007] In recent years, in order to artificially refine the domain width, a method of controlling the domain by introducing strain by irradiation of laser, plasma jet, or the like, or by forming a groove by mechanical or etching, or the like, has been developed. In the case of a steel sheet in which the degree of aggregation of crystal orientation is improved by using such a method to thereby improve the magnetic flux density, even in the case where the secondary recrystallized grain diameter becomes large, the eddy current loss can be reduced, and the iron loss can be sufficiently reduced. However, if strain is introduced into the steel sheet, magnetostriction (λ P-P ) increases due to the strain. In addition, if heat treatment is performed at a temperature of about 800°C after the domain refinement, the iron loss reduction effect disappears, and thus the method cannot be used for applications in which strain relief annealing at 800°C or higher is required after irradiation. On the other hand, in the case of the domain control method using a groove, there is a problem in that the magnetic flux density B8 decreases.

[0008] Generally, a directionally electromagnetic steel sheet is manufactured by the following operations. A raw material (slab) of a steel sheet containing a prescribed amount of Si is subjected to hot rolling, annealing, and cold rolling to obtain a steel sheet of a desired thickness. Next, the steel sheet after the cold rolling is subjected to annealing (also referred to as primary annealing, decarburization annealing). By this annealing, primary recrystallization is generated, and in the primary recrystallized grains, grains having a crystal orientation in which the easy magnetization axis is aligned in the rolling direction with a deviation angle of 10° or less from the strict Goss orientation described by {110} <001> (hereinafter referred to as Goss-oriented grains) are formed. This annealing also serves as decarburization annealing. Thereafter, on the surface of the steel sheet in which primary recrystallization has been generated, an annealing release agent having MgO as a main component is applied. Next, the steel sheet to which the annealing release agent has been applied is coiled to produce a steel sheet coil, and the steel sheet coil is subjected to batch processing annealing (also referred to as secondary recrystallization annealing, finish annealing). By this annealing, the Goss-oriented grains encroach on other grains, secondary recrystallization is generated, and a so-called glass film is formed on the surface of the steel sheet. At the time of the secondary recrystallization, due to the influence of inhibitors contained in the steel sheet, it is possible that the Goss-oriented grains grow preferentially, and the crystal grain diameter of the large grains becomes 100 mm or more. Next, while the steel sheet coil is uncoiled, annealing to flatten the steel sheet after the secondary recrystallization, formation of an insulating film, and the like are performed.

[0009] The grain structure containing the Goss-oriented grains aggregated in the {110} <001> orientation is obtained by causing secondary recrystallization in the final annealing, and thus the prescribed magnetic characteristics are obtained. In order to obtain this grain structure, it is effective to increase the frequency of occurrence of the secondary Goss-oriented grains and to increase the frequency of occurrence of the grains having a good matching property with the crystal lattice after the primary annealing. For example, the grains having the {778} <447> (≈ {111} <112> orientation) and {411} <148> orientations, which have a high {110} <001> orientation and a Σ9 coincidence site lattice orientation relationship with the Goss orientation, are grains that are easily eaten away by the Goss-oriented grains, and it is effective to contain a large number of these grains in the primary recrystallized structure. However, in controlling the crystal orientation of the grains generated by the primary annealing described above, it is difficult to simultaneously increase the frequency of occurrence of the Goss-oriented grains and the frequency of occurrence of the grains having the coincidence site lattice orientation relationship. For example, in a region where the cold-rolling reduction is 85% or more, the coincidence site lattice-oriented grains that are easily eaten away by the Goss-oriented grains increase in frequency of occurrence as the cold-rolling reduction increases, whereas, in contrast, the Goss-oriented grains decrease in frequency of occurrence as the cold-rolling reduction increases. In addition, the Goss-oriented grains, which are the secondary orientation in the primary recrystallized structure, increase in frequency of occurrence as the heating rate of the primary annealing is increased, whereas, in contrast, the coincidence site lattice-oriented grains having the {111} <112> orientation, which are the primary orientation in the primary recrystallized structure, decrease in frequency of occurrence as the heating rate of the primary annealing is increased.

[0010] That is, under the conventional process control conditions, it is not possible to independently control the frequency of occurrence of the Goss-oriented grains and the frequency of occurrence of the coincidence site lattice-oriented grains that are easily eaten away by the Goss-oriented grains.

[0011] Here, the deviation angle of the crystal orientation observed in the grain-oriented magnetic steel sheet from the ideal {110} <001> orientation around the rolling surface normal direction Z (ND) is set as the deviation angle α, the deviation angle of the crystal orientation from the ideal {110} <001> orientation around the rolling right-angle direction C (TD) is set as the deviation angle β, and the deviation angle of the crystal orientation from the ideal {110} <001> orientation around the rolling direction L (RD) is set as the deviation angle γ. Then, as the angle deviation θ, the angle deviation θ from the ideal {110} <001> orientation obtained by the deviation angles α, β, γ of the crystal orientation observed in the grain-oriented magnetic steel sheet around the above-described ND, TD, RD by the following (Formula A) is defined.

[0012] θ = (α 2 + β 2 + γ 2 ) 1 / 2 (Formula A) As described above, the Goss-oriented grain is not a grain having a strict Goss orientation (ideal Goss orientation) (referred to as an ideal Goss-oriented grain). The direction of the easy magnetization axis (cubic crystal {110} <001>) of each grain does not necessarily coincide with the rolling direction, and there is an angle deviation θ between the direction of the easy magnetization axis and the rolling direction. A grain in which the angle deviation θ from the ideal Goss orientation is 10° or less is referred to as a Goss-oriented grain (practical Goss-oriented grain) based on (Formula A). If the angle deviation θ of the practical Goss-oriented grain increases, the orientation of the crystal orientation decreases, and the magnetic flux density B8 decreases.

[0013] Generally, in a steel sheet after primary recrystallization, there are also mixed grains having a large angle deviation θ among the Goss-oriented grains. However, when the grains are grown by secondary recrystallization, if the effect of the size advantage of the crystal grain size at the initial stage of the secondary recrystallization is excluded, the more the angle deviation θ of the grain is small in the Goss-oriented grain, the greater the driving force for the grain growth, and the more the grain is preferentially grown until the secondary recrystallization is completed. Therefore, the more the angle deviation θ of the Goss-oriented grain is small, the more the crystal grain size after the secondary recrystallization is easily increased in diameter. That is, in a manufacturing method in which the secondary recrystallization grains are oriented to the Goss orientation, since a specific grain is preferentially grown, the crystal grain size is necessarily easily increased.

[0014] In addition, at the time of the secondary recrystallization, the steel sheet is not flat but is bent to be in a coiled shape, but the grains grow while maintaining the linearity of the crystal orientation. Therefore, if the steel sheet in the coiled shape is uncoiled and flattened after the secondary recrystallization, a portion in which the direction of the easy magnetization axis becomes non-parallel to the surface of the directionally magnetic steel sheet is generated in the grain. Due to the uncoiling of the coil, mainly the value of the deviation angle β is increased, and the angle deviation θ is also increased. The more the crystal grain size is large, the more the increase in the angle deviation θ due to the uncoiling of the coil becomes significant. That is, the Goss-oriented grain having a small angle deviation θ is preferentially grown at the time of the secondary recrystallization, but if the secondary recrystallization grain size becomes large, the angle deviation θ is increased due to the uncoiling of the coil.

[0015] In Patent Document 1, a technique is disclosed in which etching treatment is performed on the surface of a steel sheet after final cold rolling to form linear grooves satisfying a prescribed condition, and in the subsequent primary annealing, the heating rate of the steel sheet is accelerated in the linear groove portion compared to the portion other than the linear groove portion in the temperature region of 500°C to 750°C. In Patent Document 1, by artificially making the portion having a fast heating rate and the portion having a slow heating rate, the portion in which the frequency of occurrence of the (110)

[001] oriented grain is increased (linear groove portion) and the portion in which the frequency of occurrence of the (111)

[112] oriented grain is increased (portion other than the linear groove portion) are actively arranged.

[0016] A technique is disclosed in Patent Literature 2, which irradiates a laser beam toward a surface of a silicon steel sheet at a prescribed interval PL with respect to a rolling direction multiple times between cold rolling and finish annealing. If the silicon steel sheet is subjected to secondary recrystallization by finish annealing, a position along a trace of the laser beam becomes a crystal grain boundary that penetrates a surface and a back of the silicon steel sheet. In Patent Literature 2, after finish annealing, a length of a rolling direction of a crystal grain becomes about 30 mm, which corresponds to the interval PL of irradiation, even at a maximum, and an angle deviation β of an easy magnetization axis direction (cubic crystal {110} <001>) from the rolling direction is in a range of 0° to 6°.

[0017] A manufacturing method of a grain-oriented electromagnetic steel sheet is disclosed in Patent Literature 3, which takes a high-temperature slab heating process as a premise, and a difference in orientation concentration of a high-Gauss orientation between inner and outer peripheries of a coil having different curvatures is small, and has a high magnetic flux density. In Patent Literature 3, by performing linear local heating on a cold-rolled steel sheet, the linear heated portion functions as a growth barrier of secondary recrystallized grains, and growth of the secondary recrystallized grains is suppressed.

[0018] Prior Art Documents Patent Literature Patent Literature 1: Japanese Patent Application Publication No. 2007-169762 Patent Literature 2: International Publication No. WO2012 / 014290 Patent Literature 3: Japanese Patent Application Publication No. 2022-161269 SUMMARY

[0019] Problems to be Solved by the Invention As described above, improvement of magnetic properties of a grain-oriented electromagnetic steel sheet has been attempted since the past. However, the improvement of magnetic properties brought about by the conventional techniques cannot be said to be sufficient.

[0020] The present invention has been achieved in view of the above-described problems. An object of the present invention is to provide a grain-oriented electromagnetic steel sheet that is excellent in both magnetic flux density and iron loss.

[0021] Means for Solving the Problems That is, the gist of the present invention is as follows.

[0022] A grain-oriented electromagnetic steel sheet according to one aspect of the present invention defines a deviation angle from an ideal high-Gauss orientation with a rolling face normal direction Z as a rotation axis as a, defines a deviation angle from the ideal high-Gauss orientation with a rolling right-angle direction C as a rotation axis as β, defines a deviation angle from the ideal high-Gauss orientation with a rolling direction L as a rotation axis as γ, expresses a deviation angle of a crystal orientation measured at one measurement point on a sheet face as (a, β, γ), and defines an angle deviation of the one measurement point as φ = (a 2 + β 2 ).1 / 2 The average value of the angle deviation φ calculated from at least 1000 measurement points spaced 1 mm apart along the rolling direction L is defined as aveφ L When aveφ L Satisfies aveφ L ≤ 4.0°, The deviation angle of the crystal orientation measured at 2 measurement points adjacent and spaced 1 mm apart on the plate surface is expressed as (α1, β1, γ1) and (α2, β2, γ2), and the middle point of the 2 measurement points satisfying [ (α2-α1) 2 + (β2-β1) 2 + (γ2-γ1) 2 ] 1 / 2 ≥ 1.0° is defined as a grain boundary GB, and the particle size of the rolling direction L calculated based on the grain boundary GB is defined as D L The particle size D L calculated along the rolling direction L is arranged in descending order and the particle size of 10% from the largest is defined as D L 10 in mm. L When D L 10 satisfies D L 10 ≤ 100 - 15 x aveφ

[0023] Inventive Effects According to the above-described aspect of the present application, a grain-oriented magnetic steel sheet excellent in both magnetic flux density and iron loss can be provided.

[0024] Specifically, according to the above-described aspect of the present application, a grain-oriented magnetic steel sheet in which the angle deviation of the rolling direction is controlled to be small, and thus the magnetic flux density is excellent, and the particle size of the rolling direction is controlled to be small, and thus the iron loss is excellent even without implementing magnetic domain control (magnetic domain refinement treatment) can be provided.

[0025] According to the above-described aspect of the present application, a grain-oriented magnetic steel sheet in which the drawbacks caused by magnetic domain control in the past (for example, deterioration of transformer noise caused by laser magnetic domain control, decrease in magnetic flux density caused by slot introduction, etc.) can be alleviated, and on this basis, both the magnetic flux density and the iron loss are excellent. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 is a schematic view showing measurement points of crystal orientation spaced 1 mm apart along the rolling direction on a steel sheet.

[0027] Figure 2 is a graph showing the effects of the average value of the angle deviation of the rolling direction and the crystal particle size on the magnetic properties as a grain-oriented magnetic steel sheet. DETAILED DESCRIPTION

[0028] A preferred embodiment of the present application will be described in detail. However, the present application is not limited to the configuration disclosed in the present embodiment, and various modifications can be made without departing from the spirit of the present application. In addition, for the numerical limit range described below, the lower limit value and the upper limit value are included in the range. As for the numerical value expressed as "more than" or "less than", the value is not included in the numerical range. In addition, as for the "%" of the chemical composition, unless otherwise specified, it means "mass%".

[0029] As described above, the practical Goss-oriented grains having a small angle deviation θ, an angle deviation φ from the {110} <001> orientation which is the ideal Goss orientation increase in frequency as the heating rate of the primary annealing (decarburization annealing) is accelerated. On the contrary, the grains (referred to as the superlattice-oriented grains) such as the {778} <447> (≈{111} <112>) orientation, the {411} <148> orientation, etc. which have a superlattice orientation relationship with the Goss orientation decrease in frequency if the heating rate of the primary annealing is accelerated. Therefore, in the primary annealing, it is difficult to increase the ratio of the superlattice-oriented grains while increasing the ratio of the practical Goss-oriented grains.

[0030] The technique described in Patent Literature 1 forms linear grooves on the surface of a steel sheet by etching treatment, accelerates the heating rate of the portion of the linear grooves at the time of primary annealing, and arranges a portion in which the ratio of the Goss-oriented grains is high (the linear groove portion) and a portion in which the ratio of the superlattice-oriented grains is high (the portion other than the linear groove). However, in this method, it is difficult to increase the difference in the heating rate of the primary annealing between the linear groove portion and the portion other than the linear groove, and the effect obtained is limited. Specifically, the difference in the heating rate between the linear groove portion and the portion other than the linear groove does not become so large. For example, even if the entire steel sheet is heated at 100°C / sec, the degree of thinning of the sheet thickness of the portion by the formation of the grooves does not exceed about 10% or so with respect to the original sheet thickness (for the reason that: the usual groove depth is about 20 μm or less, which is about 10% or less of the sheet thickness), and therefore if the heat conduction of the steel sheet is also considered, the heating rate ratio becomes less than the sheet thickness ratio with respect to the same heat input, and therefore the ratio of the Goss-oriented grains in the linear groove portion is difficult to increase compared to the portion other than the linear groove. In addition, in this method, since the heating rate of the linear groove portion is accelerated at the time of the primary annealing, the grain size of the Goss-oriented grains formed in the linear groove portion after the primary annealing does not become large compared to the primary recrystallized grain size which is the average as a whole, and becomes equivalent or fine.

[0031] In addition, the technology described in Patent Literature 2 is to irradiate a laser beam toward the surface of a steel sheet before product annealing. However, in this method, only the laser beam irradiation portion is controlled to be a crystal grain boundary of secondary recrystallization, and the orientation of the Goss-oriented grains generated by primary recrystallization is not controlled. In addition, the region heated by laser irradiation is only the surface layer portion irradiated with the laser, and heat diffusion to the surrounding portion is significant, and thus it is generally not possible to secure a thermal history that recrystallizes the steel sheet.

[0032] In addition, the technology described in Patent Literature 3 is to irradiate a laser beam toward the surface of a steel sheet after cold rolling. However, in this method, as in the above, only the laser beam irradiation portion is controlled to be a crystal grain boundary of secondary recrystallization, and the heating rate is not controlled, and the orientation of the Goss-oriented grains generated by primary recrystallization is not controlled. In Patent Literature 3, only the laser beam irradiation portion is made to function as a growth barrier for secondary recrystallization grains to reduce the particle diameter of the secondary recrystallization grains in the rolling direction, and a grain growth temperature region in the local heating region that is effective for the enlargement of the Goss-oriented grains in the local heating region is not secured, and in this method, it is possible to reduce the difference in the orientation concentration toward the Goss orientation between the inner and outer circumferences of the coil having different curvatures, but it is not possible to obtain Goss-oriented grains having a crystal orientation close to the ideal Goss orientation. That is, this method suppresses the decrease in the magnetic flux density by increasing the particle diameter of the secondary recrystallization grains in the rolling direction, but does not aim to fundamentally improve the orientation of the Goss-oriented grains.

[0033] In the present embodiment, it was first found that by locally and rapidly heating a steel sheet at a stage before primary annealing (decarburization annealing) to form a local heating region, it is possible to obtain a grain-oriented electrical steel sheet having excellent quality. The local heating region formed before primary annealing is locally arranged with respect to the surface of the steel sheet. The crystal structure of the local heating region is made of one or both of a recrystallized structure and a recovered structure at the time of completion of the local and rapid heating. The crystal structure of a non-local heating region outside the local heating region in the surface of the steel sheet is made of a cold worked structure because it is in a cold-rolled state.

[0034] The local heating region described above is preferably heated at a rate of 500°C / sec or more, more preferably 2000°C / sec or more, further more preferably 5000°C / sec or more, and further more preferably 10000°C / sec or more. In this way, it was found that if a local heating region is formed on the surface of a steel sheet before primary annealing and primary annealing is then performed on the steel sheet, a large number of grains having a practically Goss orientation can be formed in the local heating region. In addition, it was found that the ratio of Goss-oriented grains having a smaller angle deviation θ and a smaller angle deviation φ from the ideal Goss orientation is higher in the practically Goss-oriented grains formed, and the particle diameter of the Goss-oriented grains is increased.

[0035] The frequency of the Goss-oriented grains contained in the local heating region becomes larger than the frequency of the Goss-oriented grains contained in the non-local heating region. This feature results from the fact that the non-local heating region is a worked structure. Specifically, this results from the fact that, in the case where local rapid heating is performed, recovery and recrystallization occur in the local heating region to generate practical Goss-oriented grains, and grain growth is easily performed, but recovery and recrystallization do not occur in the non-local heating region.

[0036] On the basis of the fact that the local heating region having the above-described feature is dispersed on the surface of the steel sheet by the local rapid heating before the primary annealing, the primary annealing is performed, and further, the secondary annealing is performed. The Goss-oriented grains formed in the local heating region grow preferentially at the time of the secondary annealing via the primary annealing. Although the Goss-oriented grains are formed in the local heating region, the Goss-oriented grains having a large crystal grain diameter and a small angle deviation θ, a small angle deviation φ, and a near-ideal Goss orientation are preferentially grown in the secondary recrystallization.

[0037] The Goss-oriented grains that become the nuclei of the secondary recrystallization are supplied to the local heating region, and thus it is not necessary to form Goss-oriented grains in the matrix portion other than the local heating region, that is, the non-local heating region other than the local heating region, by the primary annealing. Therefore, as the heat treatment conditions of the primary annealing, it is also possible to adopt a primary annealing condition in which a slow heating condition in which the heating rate is set to be low is set, and the heavy point lattice-oriented grains having {111} <112> orientation, {411} <148> orientation that are easily eaten away are formed in large amounts in the non-local heating region. For example, by setting the heating rate of the primary annealing to be 300°C / sec or less, the Goss-oriented grains having a large crystal grain diameter and a near-ideal Goss orientation can be formed in large amounts in the local heating region, and on the other hand, the Goss-oriented grains are hardly formed in the non-local heating region, and instead, the heavy point lattice-oriented grains that are easily eaten away can be formed in large amounts.

[0038] As described above, in the local heating region of the steel sheet (decarburized annealed steel sheet) after the local rapid heating and the primary annealing, the Goss-oriented grains having a large crystal grain diameter and a near-ideal Goss orientation are present in large amounts. On the other hand, in the matrix portion (non-local heating region), the Goss-oriented grains having a large diameter are hardly present, and the heavy point lattice-oriented grains that are easily eaten away can be present in large amounts. If such a steel sheet is subjected to the secondary annealing, the Goss-oriented grains having a large crystal grain diameter and a near-ideal Goss orientation present in the local heating region start to grow preferentially, and grow toward the non-local heating region.

[0039] Further, when the local rapid heating before the once annealing causes the local heating regions to spread on the steel sheet surface, by appropriately disposing the local rapid heating at the steel sheet surface, the size, shape, disposition of the grains after the secondary annealing can be controlled. For example, if the growth of the grains is stopped by the collision of the grains grown from one local heating region with other grains grown from the adjacent local heating region, the grain diameter of the grains at the end of the secondary annealing becomes small, and a steel sheet with excellent iron loss can be produced. In particular, as described above, at the initial stage of the secondary annealing, the grains grown preferentially from the local heating affected regions have a crystal orientation close to the ideal Goss orientation, and thus, a good magnetic flux density can be obtained despite the small secondary recrystallized grain diameter.

[0040] The grain-oriented electromagnetic steel sheet of the present embodiment is obtained based on the above-described technical idea. The features of the grain-oriented electromagnetic steel sheet of the present embodiment are described in detail.

[0041] The grain-oriented electromagnetic steel sheet (base steel sheet) of the present embodiment is such that, when an angle of deviation of a crystal orientation measured at one measurement point on a sheet surface is defined as (α, β, γ), and an angle deviation of the above one measurement point is defined as φ = (α 2 + β 2 ) 1 / 2 , and an average value of the angle deviations φ calculated from at least 1000 points spaced by 1 mm along the rolling direction L is defined as aveφ L , the above aveφ L satisfies aveφ L ≤ 4.0°.

[0042] Further, the grain-oriented electromagnetic steel sheet (base steel sheet) of the present embodiment is such that, when angles of deviation of crystal orientations measured at two measurement points adjacent to each other and spaced by 1 mm on the above sheet surface are defined as (α1, β1, γ1) and (α2, β2, γ2), and a middle point of the two measurement points satisfying [(α2-α1) 2 + (β2-β1) 2 + (γ2-γ1) 2 ] 1 / 2 ≥ 1.0° is defined as a grain boundary GB, and a grain diameter in the rolling direction L calculated based on the above grain boundary GB is defined as D L in mm. LThe particle diameter of 10% in terms of number is defined as D L 10, the above D L 10 satisfies D L 10≤100-15x aveφ L .

[0043] In the case where the above all conditions are satisfied, the directional electromagnetic steel sheet of the present embodiment becomes capable of reducing the drawbacks due to magnetic domain control in the past (for example, deterioration of transformer noise due to laser magnetic domain control, reduction of magnetic flux density due to slot introduction, and the like), and on this basis, both of the magnetic flux density and the iron loss characteristics can be improved.

[0044] Note that in the present embodiment, the angle deviation φ is defined by the deviation angle α and the deviation angle β. Generally, the angle deviation θ is evaluated by three components of the deviation angle α, the deviation angle β, and the deviation angle γ. However, in the present embodiment, the deviation angle γ, which has a small influence on the magnetic flux density and the iron loss characteristics, is excluded, and the angle deviation φ is defined by two components of the deviation angle α and the deviation angle β. If the above conditions are satisfied using this angle deviation φ, the above effects can be obtained. On the other hand, the crystal grain boundary and the crystal grain diameter can be determined based on the three components of the deviation angle α, the deviation angle β, and the deviation angle γ.

[0045] The above aveφ L 4.0° or less means that the angle deviation φ is small on average at each measurement point along the rolling direction L. That is, it means that the angle deviation between the rolling direction L and the easy magnetization axis direction is small. As a result, the magnetic characteristics, particularly the magnetic flux density, are preferably improved. The aveφ L 3.5°, preferably 3.2° or less, more preferably 3.0° or less, and more preferably 2.7° or less. On the other hand, the aveφ L The smaller the value of the aveφ L It is not easy to set the aveφ L 0.5° or more, and 1.0° or more.

[0046] The above D L 10 is (100-15x aveφ Lmm or less means that the crystal grains do not grow thickly with respect to the rolling direction L. If the crystal grains do not grow thickly with respect to the rolling direction L, the increase in the misorientation angles, particularly the misorientation angle β, described above can be suppressed. If the increase in the misorientation angle β is suppressed, the decrease in the magnetic flux density can be suppressed. Furthermore, if the crystal grains do not grow thickly with respect to the rolling direction L, the magnetic domains are refined even without applying the conventional magnetic domain control technique. If the magnetic domains are refined, the increase in the iron loss can be suppressed. In D L 10 When the above condition is satisfied, the magnetic flux density and the iron loss characteristics are preferably improved. D L 10 More preferably, (90 - 15 x aveφ L ) mm or less, more preferably (80 - 15 x aveφ L ) mm or less. On the other hand, D L 10 is smaller, the more preferable, and thus the lower limit is not particularly limited. For example, D L 10 can be 5 mm or more, or 10 mm or more.

[0047] Note that the above misorientation angle α, misorientation angle β, misorientation angle γ, and the like can be measured by setting a measurement line of measurement points containing at least 1000 points at 1 mm intervals on the rolling surface to measure the crystal orientation. For example, the crystal orientation can be measured by an X-ray diffraction method (Laue method). The Laue method refers to a method of irradiating an X-ray beam on a steel sheet and analyzing the transmitted or reflected diffraction spots. By analyzing the diffraction spots, the crystal orientation of the portion irradiated with the X-ray beam can be identified. If the irradiation position is changed and the diffraction spots are analyzed at a plurality of portions, the crystal orientation distribution of each irradiation position can be measured. The Laue method is a method suitable for measuring the crystal orientation of a metal structure having thick crystal grains.

[0048] Note that the measurement points of the crystal orientation can be at least 1000 points, but it is preferable to appropriately increase the measurement points depending on the size of the secondary recrystallized grains. For example, when the secondary recrystallized grains contained in the measurement line in which the measurement points for measuring the crystal orientation are set to 1000 points become less than 20 in number, it is preferable to increase the measurement points at 1 mm intervals so as to extend the above measurement line in a manner that 20 or more secondary recrystallized grains are contained in the measurement line. In addition, in a case where it is difficult to set 1000 points of measurement points with one measurement line, a plurality of measurement lines can be set and the crystal orientation can be measured with measurement points totaling 1000 points or more.

[0049] The crystal orientation is measured at 1 mm intervals on the rolling surface, and on this basis, the above misorientation angle α, misorientation angle β, misorientation angle γ, and the like are determined with respect to each measurement point. Based on the misorientation angles at each measurement point determined, the angle deviation φ, aveφ L , the grain boundary GB, and the particle diameter DL D L 10 is sufficient. It should be noted that regarding D... L 10. Calculate the particle size D. L Grains larger than 2 mm should be arranged in descending order of size, and the largest grains should be counted as 10% of the total grain size. Additionally, if the X-ray beam irradiation area spans two grains at the measurement point for crystal orientation based on the Laue method, and it is impossible to determine which grain the X-ray diffraction result originates from, the grain size of each of the two grains should be increased by 0.5 mm.

[0050] The directional electromagnetic steel sheet of this embodiment has the above-described technical features, but these features can also be expressed as follows. The features of the directional electromagnetic steel sheet of this embodiment will be described again.

[0051] The directional electromagnetic steel plate in this embodiment can also be as follows: φ that satisfies the following definition m ≤4.0° D10, as defined below, is f(φ) as specified by equation (3) below. m )the following.

[0052] In the rolling direction (RD), the crystal orientation measurement positions of n points (at least 1000 points) are specified at 1 mm intervals, and the crystal orientation around ND, TD, and RD at measurement point i (i=1~n) is measured to be in line with the ideal {110}. <001> Orientation deviation angle α i β i γ i φ is defined by the following equation (1). i Then, the average angular deviation φ is calculated using the following equation (2). m .

[0053] 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) Furthermore, in the crystal orientation measurement position list of the above-mentioned rolling direction (RD), between adjacent measurement positions [(α i -α i=1 ) 2 +(β) i -β i=1 ) 2 +(γ) i -γ i=1 ) 2 ] 1 / 2 If the value deviates by more than 1°, it is set that there is a crystal boundary between adjacent measurement positions. The interval between adjacent crystal boundaries is set to the crystal grain size D in the rolling direction (RD) of a grain. When the grains are arranged in order so that the crystal grain size D is from largest to smallest, the grain size of the grains at the position where the crystal grain size D is 10% from the largest in the whole grain is set to D10.

[0054] Regarding the angular deviation φ, the average angular deviation φ of the steel plate along the rolling direction (RD) is defined. m .

[0055] like Figure 1 As shown, the crystal orientation is determined at n points (at least 1000 points) with a spacing of 1 mm along the rolling direction (RD), forming a measurement point array. The crystal orientation is determined using an X-ray diffraction apparatus based on the Laue method. The measurements at measurement point i are taken along the normal direction (ND) of the rolling surface, the rolling perpendicular direction (TD), and the rolling direction (RD), with respect to the ideal {110}. <001> Orientation deviation angle α i β i γ i φ is defined by the above equation (1). i Based on this, the average angular deviation φ is calculated using the above equation (2). m It should be noted that for the rolling right-angle direction (TD), a single column of measurement points can be set at any location, or multiple columns of measurement points can be set along the rolling right-angle direction (TD) as measurement locations. In particular, when there is magnetic inhomogeneity along the rolling right-angle direction, in order to obtain information on the crystal orientation of the average magnetic properties along the rolling right-angle direction characterizing the magnetic properties, multiple columns of measurement points need to be set along the width direction of the coil (steel strip) (rolling right-angle direction (TD)). When multiple columns of measurement points are set along the rolling right-angle direction (TD) for measurement, the value of n becomes the total number of measurement points.

[0056] Next, with the grains arranged in descending order, the grain size (D10) of the grains at the position representing 10% of the largest grains in the whole grain structure is defined.

[0057] As described above, based on the determination of crystal orientation at each measurement location, between adjacent measurement locations in the rolling direction (RD) [(α i -α i=1 ) 2 +(β) i -β i=1 ) 2 +(γ) i -γ i=1 ) 2 ] 1 / 2 When the value deviates by more than 1°, it is set that a crystal boundary exists between the adjacent measurement positions; when the value is less than 1° between adjacent measurement positions, it is set that no crystal boundary exists between the adjacent measurement positions. Figure 1 In the example shown, φ is set to φ at the measurement position located at the center of the rolling direction (RD). i At φ i-1 With 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 Values ​​exceeding 1° indicate the presence of crystal boundaries a between these measurement points, and at φ i+1 With 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 exceeds 1°, and there is a crystal boundary b between these measurement points. The grain size D of the crystal in the rolling direction (RD) formed by the crystal boundaries a and b is defined as 1 mm × [(i+2) - (i-1)] = 3 mm.

[0058] In addition, the crystal grain size D obtained in this process is 1 mm or more, but when D10 is determined, a crystal grain size D of 2 mm or more is adopted.

[0059] When the crystal grain boundaries and the crystal grain diameters D are defined in the range of the measurement in the rolling direction (RD) as above, in the case where the crystal grains whose values of D are 2 mm or more are arranged in order from large to small when the values of D, the grain diameters of the crystal grains at positions from which 10% of the whole crystal grains are large are set to D10.

[0060] In addition, it is possible that the X-ray irradiation region at the measurement point straddles two crystal grains and it is not possible to determine which crystal grain, but in this case, the crystal grain diameters of the two crystal grains straddled are each allocated 0.5 mm.

[0061] Hereinafter, the research contents by the inventors of the present application will be specifically described.

[0062] As one of the above-described local rapid heating, a case where point passage current heating based on resistance heating is used will be described. With regard to the point passage current heating, a point electrode is press-bonded to the steel sheet in opposition to both surfaces of the steel sheet, and the electrode holding portion of the steel sheet is subjected to point passage current heating by causing a current to flow between the point electrodes. A steel having the composition shown in Table 1 was used, and a cold-rolled steel sheet having a sheet thickness of 0.22 mm was produced by hot rolling and cold rolling. The steel sheet was subjected to point passage current heating. The point passage current heating was performed using a copper electrode having a diameter of 3 mm, under conditions where the passage current was 5.0 kA or less at which the surface of the steel sheet was not melted, the passage current time was 20 milliseconds to 80 milliseconds, the electrode pressing force was 50 kgf to 150 kgf, and the electrode holding time after the passage of the current was 0.1 to 0.5 seconds.

[0063] [Table 1] The 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 treatment, the steel sheet was coated with an annealing separator having MgO as a main component, and then subjected to secondary annealing. The secondary annealing conditions were a hydrogen-nitrogen atmosphere, a heating rate of 15°C / hr, and a holding time of 1200°C-20 hours.

[0064] For the grain-oriented magnetic steel sheet produced by the above-described method (in which the magnetic domain control was not performed), φ m (aveφ L ) and D10 (D L 10) were measured, and the magnetic characteristics were evaluated. The effects of the average value of the angle deviation in the rolling direction and the crystal grain diameter on the magnetic characteristics of the grain-oriented magnetic steel sheet are shown in Figure 2 . In Figure 2 , the horizontal axis is φ m (aveφ L ), and the vertical axis is D10 (DL 10). Additionally, in Figure 2 In the diagram, ○ represents the condition that B8 ≥ 1.93T and W 17 / 50 For values ​​≤0.79W / kg, use ● to indicate that B8 or W is not satisfied. 17 / 50 At least one of the following cases.

[0065] Depend on Figure 2 It can be seen that: at φ m (aveφ) L ) becomes the region below 4.0°, and D10 becomes f(φ) m The area below (D) L 10 becomes (100-15×aveφ) L In the region below, good magnetic properties can be obtained. Specifically, even without magnetic domain control, both magnetic flux density and iron loss are excellent.

[0066] The energized electrode used for point-current heating is circular, and its diameter is preferably 0.5 mmφ to 10 mmφ, more preferably 1 mmφ to 5 mmφ, in terms of equivalent circle diameter. It should be noted that although a circular energized electrode is used in the above description, as long as the heating rate of the cold-rolled steel sheet is locally accelerated to form Gaussian-oriented grains and promote grain growth in that region, the electrode shape can also be other shapes, such as elliptical or linear.

[0067] The preferred composition of the directional electromagnetic steel sheet of this embodiment will be described.

[0068] The directional electromagnetic steel sheet of this embodiment has a chemical composition containing 2.0% to 7.0% Si by mass fraction, with the remainder containing Fe and impurities.

[0069] The above chemical composition is intended to cause the crystals to align and aggregate in {110}. <001> The chemical composition is optimized by controlling the orientation.

[0070] Furthermore, to improve the magnetic properties, this directional electromagnetic steel sheet may contain known optional elements to replace a portion of the Fe. There is no need to set a lower limit for these optional elements; the lower limit can be 0%. The upper limit for these optional elements should be the range where a decrease in magnetic flux density and a significant decrease in iron loss do not occur. The target upper limits for each optional element are listed below.

[0071] Specifically, the directional electromagnetic steel sheet (base steel sheet) of this embodiment, in terms of chemical composition, contains, by mass%, only the following: Si: 2.0–7.0% C: 0~0.0050% Mn: 0~1.0%, S and Se: total 0 to 0.0150%, Al: 0 to 0.0650%, N: 0 to 0.0050% Nb, V, Mo, Ta and W: total 0 to 0.050%, Cu: 0 to 0.40%, Bi: 0 to 0.010%, B: 0 to 0.080%, P: 0 to 0.50%, Ti: 0 to 0.0150%, Sn: 0 to 0.10%, Sb: 0 to 0.10%, Cr: 0 to 0.30%, Ni: 0 to 1.0%, The remainder includes Fe and impurities.

[0072] Si: 2.0 to 7.0% Si (silicon) is an essential element for the base material steel sheet. If the Si content is less than 2.0%, the eddy current loss cannot be sufficiently reduced, and thus good magnetic properties cannot be obtained. Therefore, the Si content of the base material 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 is embrittled, and the through-plate property is significantly deteriorated at the time of manufacture, and thus the Si content of the base material 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.

[0073] C: 0 to 0.0050% C (carbon) is a selective element for the base material steel sheet. C is contained in a steel billet (slab), but if C is excessively remained in the base material steel sheet after annealing of a finished product, it can be possible that good iron loss properties cannot be obtained. Therefore, the C content of the base material steel sheet is 0.0050% or less. The C content is preferably 0.0040% or less, and more preferably 0.0030% or less. On the other hand, the lower limit value of the C content of the base material steel sheet is not particularly limited, and is 0% or more. However, it is not easy to set the C content to 0% in industry, and thus it is also possible to set the C content to more than 0%, and it is also possible to set to 0.00010% or more.

[0074] Mn: 0 to 1.0% Mn (manganese) is a selection element for the base material steel sheet. Mn is contained in the steel billet (slab), but if it is contained in excess, the steel undergoes phase transformation at the time of secondary recrystallization annealing, the secondary recrystallization does not sufficiently proceed, and there is a possibility that good magnetic properties cannot be obtained. Therefore, the Mn content of the base material steel sheet can be 1.0% or less. The Mn content is preferably 0.50% or less, and more preferably 0.20% or less. On the other hand, the lower limit value of the Mn content of the base material steel sheet is not particularly limited, and can be 0%. However, Mn has an effect as an inhibitor at the time of secondary recrystallization because it forms MnS and MnSe, and therefore the Mn content can be set to more than 0%, and can be set to 0.00010% or more.

[0075] Total of S and Se: 0 to 0.0150% S (sulfur) and Se (selenium) are selection elements for the base material steel sheet. S and Se are contained in the steel billet (slab), but if S and Se remain in excess in the base material steel sheet after the finish annealing, there is a possibility that adverse effects on the magnetic properties are caused. Therefore, the total content of S and Se of the base material steel sheet can be 0.0150% or less. The total content of S and Se is preferably 0.010% or less, and more preferably 0.0050% or less. On the other hand, the lower limit value of the total content of S and Se of the base material steel sheet is not particularly limited, and can be 0%. However, S and Se have an effect as an inhibitor at the time of secondary recrystallization because they form MnS and MnSe, and therefore the total content of S and Se can be set to more than 0%, and can be set to 0.00010% or more.

[0076] Al: 0 to 0.0650% Al (aluminum) is a selection element for the base material steel sheet. Al is contained in the steel billet (slab), but if Al remains in excess in the base material steel sheet after the finish annealing, there is a possibility that adverse effects on the magnetic properties are caused. Therefore, the Al content of the base material steel sheet can be 0.0650% or less. The Al content is preferably 0.040% or less, and more preferably 0.035% or less. On the other hand, the lower limit value of the Al content of the base material steel sheet is not particularly limited, and can be 0%. However, Al has an effect as an inhibitor at the time of secondary recrystallization because it forms AlN, and therefore the Al content can be set to more than 0%, and can be set to 0.00010% or more. Note that the above Al content is acid-soluble Al (sol. Al).

[0077] N: 0 to 0.0050% N (nitrogen) is a selection element for the base steel sheet. N is contained in a steel billet (slab), but if N is excessively contained in the base steel sheet after annealing as a finished product, it can adversely affect the magnetic properties. Therefore, the N content of the base steel sheet is 0.0050% or less. The N content is preferably 0.0040% or less, and 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 can be 0%. However, N has an effect as an inhibitor at the time of secondary recrystallization because of the formation of AlN, and thus the N content can be set to more than 0%, and can be set to 0.00010% or more.

[0078] Nb, V, Mo, Ta, and W: 0 to 0.050% Nb (niobium), V (vanadium), Mo (molybdenum), Ta (tantalum), and W (tungsten) are selection elements for the base steel sheet. If the Nb group elements (one or more of Nb, V, Mo, Ta, and W) are excessively contained in the base steel sheet, it can adversely affect the magnetic properties. Therefore, the total content of Nb, V, Mo, Ta, and W of the base steel sheet is 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 of the base steel sheet is not particularly limited, and can be 0%. However, Nb, V, Mo, Ta, or W has an effect as an inhibitor at the time of secondary recrystallization because of the formation of carbides, nitrides, and carbonitrides, and thus the total content of Nb, V, Mo, Ta, and W can be set to more than 0%, and can be set to 0.003% or more.

[0079] Cu: 0 to 0.40% Cu (copper) is a selection element for the base steel sheet. If the Cu content exceeds 0.40%, the steel sheet can be embrittled in hot rolling. Therefore, the Cu content of the base steel sheet is 0.40% or less. The Cu content is preferably 0.30% or less, and more preferably 0.10% or less. On the other hand, the lower limit of the Cu content is not particularly limited, and can be 0%. However, Cu has an effect of improving the degree of Goss orientation and improving the magnetic properties, and thus the Cu content can be set to more than 0%, and can be set to 0.010% or more.

[0080] Bi: 0 to 0.010% Bi (bismuth) is a selective element for the base steel sheet. If the Bi content exceeds 0.010%, there is a possibility that the adhesion of the coating film is reduced. In addition, if the purification at the time of the annealing of the finished product is insufficient and Bi is excessively left, there is a possibility that the magnetic characteristics are adversely affected. Therefore, the Bi content of the base steel sheet is 0.010% or less. The Bi content is preferably 0.0050% or less, more preferably 0.0020% or less, and still more preferably 0.0010% or less. On the other hand, the lower limit value of the Bi content is not particularly limited and is 0% or more. However, Bi has an effect of increasing the magnetic flux density, and therefore the Bi content can be set to more than 0% and can be set to 0.00050% or more.

[0081] B: 0 to 0.080% B (boron) is a selective element for the base steel sheet. If the B content exceeds 0.080%, there is a possibility that the unevenness (standard deviation) of the magnetic flux density becomes large. Therefore, the B content is 0.080% or less. The B content is preferably 0.070% or less, and more preferably 0.060% or less. On the other hand, the lower limit value of the B content is not particularly limited and is 0% or more. However, B has an effect of being an inhibitor at the time of secondary recrystallization by forming a nitride, and therefore the B content can be set to more than 0% and can be set to 0.00050% or more.

[0082] P: 0 to 0.50% P (phosphorus) is a selective element for the base steel sheet. If the P content exceeds 0.50%, there is a possibility that the workability of the steel sheet is significantly reduced. Therefore, the P content of the base steel sheet is 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 value of the P content is not particularly limited and is 0% or more. However, P has an effect of improving the texture and improving the magnetic characteristics of the steel sheet, and therefore the P content can be set to more than 0% and can be set to 0.0020% or more.

[0083] Ti: 0 to 0.0150% Ti (titanium) is a selective element for the base steel sheet. If the Ti content exceeds 0.0150%, there is a possibility that the magnetic characteristics are reduced. Therefore, the Ti content of the base steel sheet is 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 value of the Ti content is not particularly limited and is 0% or more. However, Ti has an effect of being an inhibitor at the time of secondary recrystallization by forming a carbide, a nitride, and a carbonitride, and therefore the Ti content can be set to more than 0% and can be set to 0.0020% or more.

[0084] Sn: 0 to 0.10% Sn (tin) is a selective element for the base steel sheet. If the Sn content exceeds 0.10%, the secondary recrystallization becomes unstable, and it is possible to adversely affect the magnetic properties. Therefore, the Sn content of the base steel sheet can be 0.10% or less. The Sn content is preferably 0.090% or less, and more preferably 0.080% or less. On the other hand, the lower limit value of the Sn content is not particularly limited, and can be 0%. However, Sn has an effect of improving the degree of aggregation of the Goss orientation and improving the magnetic properties, and therefore the Sn content can be set to more than 0%, and can be set to 0.0050% or more.

[0085] Sb: 0 to 0.10% Sb (antimony) is a selective element for the base steel sheet. If the Sb content exceeds 0.10%, it is possible to adversely affect the magnetic properties. Therefore, the Sb content of the base steel sheet can be 0.10% or less. The Sb content is preferably 0.090% or less, and more preferably 0.080% or less. On the other hand, the lower limit value of the Sb content is not particularly limited, and can be 0%. However, Sb has an effect of stabilizing the secondary recrystallization by functioning as an inhibitor, and therefore the Sb content can be set to more than 0%, and can be set to 0.010% or more.

[0086] Cr: 0 to 0.30% Cr (chromium) is a selective element for the base steel sheet. If the Cr content exceeds 0.30%, it is possible to form Cr oxides, and adversely affect the magnetic properties. Therefore, the Cr content of the base steel sheet can 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 value of the Cr content is not particularly limited, and can be 0%. However, Cr has an effect of improving the degree of aggregation of the Goss orientation and improving the magnetic properties, and therefore the Cr content can be set to more than 0%, and can be set to 0.010% or more.

[0087] Ni: 0 to 1.0% Ni (nickel) is a selective element for the base steel sheet. If the Ni content exceeds 1.0%, it is possible that the secondary recrystallization becomes unstable. Therefore, the Ni content of the base steel sheet can be 1.0% or less. The Ni content is preferably 0.20% or less, and more preferably 0.10% or less. On the other hand, the lower limit value of the Ni content is not particularly limited, and can be 0%. However, Ni has an effect of increasing the electrical resistance and reducing the iron loss, and therefore the Ni content can be set to more than 0%, and can be set to 0.010% or more.

[0088] The base steel sheet of the grain-oriented electromagnetic steel sheet of the present embodiment can contain impurities. Note that "impurities" refer to substances that are mixed from ores, waste materials, or manufacturing environments, etc. as raw materials when steel is manufactured industrially.

[0089] The chemical composition of the base steel sheet described above can be measured by a general analysis method. For example, it can be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Note that the acid-soluble Al can be measured using a filtrate obtained by heating and decomposing a sample with an acid and by ICP-AES. In addition, C and S can be measured using a combustion-infrared absorption method, N can be measured using an inert gas fusion-thermal conductivity method, and O can be measured using an inert gas fusion-non-dispersive infrared absorption method.

[0090] Note that the chemical composition described above is a component of the base steel sheet. In the case where the grain-oriented magnetic steel sheet to be a measurement sample has an insulating coating film or the like on the surface, the coating film or the like is removed by the following method before measuring the chemical composition.

[0091] For example, as a method for removing the insulating coating film, it is only necessary to immerse the grain-oriented magnetic steel sheet having the coating film in a high-temperature alkali solution. Specifically, by immersing in a sodium hydroxide aqueous solution of NaOH: 30 to 50 mass% + H2O: 50 to 70 mass% at 80 to 90°C for 5 to 10 minutes, and then performing water washing and drying, the insulating coating film can be removed from the grain-oriented magnetic steel sheet. Note that the immersion time in the sodium hydroxide aqueous solution described above can be changed according to the thickness of the insulating coating film.

[0092] In addition, as a method for removing the forsterite coating film (glass coating film), it is only necessary to immerse the grain-oriented magnetic steel sheet from which the insulating coating film has been removed by the method described above in a high-temperature hydrochloric acid. Specifically, by preliminarily investigating the concentration of hydrochloric acid that is preferred for removing the forsterite coating film to be dissolved, and then immersing in the hydrochloric acid (for example, 30 to 40 mass% hydrochloric acid) at 80 to 90°C for 1 to 5 minutes, and then performing water washing and drying, the forsterite coating film can be removed. Generally, in the same manner as using an alkali solution in the removal of the insulating coating film and using hydrochloric acid in the removal of the forsterite coating film, the respective coating films are removed using treatment liquids separately.

[0093] Next, a preferred manufacturing method of the grain-oriented magnetic steel sheet of the present embodiment will be described.

[0094] Note that the method for manufacturing the grain-oriented magnetic steel sheet of the present embodiment is not limited to the method described below. The manufacturing method described below is one example for manufacturing the grain-oriented magnetic steel sheet of the present embodiment.

[0095] In addition, the processes and the quantitative conditions in each process shown below are one example adopted in order to show the implementability of the present embodiment, and the present embodiment is not limited to these processes and quantitative values. The manufacturing method of the grain-oriented electromagnetic steel sheet of the present embodiment can adopt various conditions as long as the gist of the present embodiment is not deviated from and the object of the present embodiment is achieved.

[0096] The manufacturing method of the grain-oriented electromagnetic steel sheet of the present embodiment can apply the conventional known manufacturing method of the grain-oriented electromagnetic steel sheet as a basic process. For example, as the conventional manufacturing method of the grain-oriented electromagnetic steel sheet, a manufacturing method of forming an inhibitor such as MnS, AlN by high-temperature slab heating, a manufacturing method of forming an AlN inhibitor by low-temperature slab heating and nitriding treatment, and the like can be exemplified. The manufacturing method of the grain-oriented electromagnetic steel sheet of the present embodiment is not limited to a specific manufacturing method. Hereinafter, a method of applying nitriding treatment as a low-temperature slab heating process will be described.

[0097] (Casting process) A slab is prepared in the casting process. One example of the manufacturing method of the slab is described below. A molten steel is manufactured (smelted). The slab is manufactured using the molten steel. The slab can also be manufactured by a continuous casting method. A steel ingot can also be manufactured using the molten steel, and the slab can be manufactured by blooming the steel ingot. The thickness of the slab is not particularly limited. The thickness of the slab is, for example, 150 to 350 mm. The thickness of the slab is preferably 220 to 280 mm. As the slab, a so-called thin slab having a thickness of 10 to 70 mm can also be used. In the case of using the thin slab, in the hot rolling process, the rough rolling before the finish rolling can be omitted.

[0098] For example, the slab described above contains, as a chemical composition, only the following elements.

[0099] C: 0.085% or less, Carbon (C) is an element effective for the control of primary recrystallized structure in the manufacturing process, but if the content in the final product is excessive, it adversely affects the magnetic characteristics. Therefore, the C content is 0.085% or less. The preferable upper limit of the C content is 0.075%. C is purified to be 0.005% or less in the decarburization annealing process and the finish annealing process. In the case of containing C, if the productivity in industrial production is considered, the lower limit of the C content can also exceed 0%, and can be 0.001%.

[0100] Si: 2.0 to 7.0% Silicon (Si) increases the electrical resistance of the grain-oriented magnetic steel sheet and reduces the iron loss. If the Si content is less than 2.0%, a γ phase transformation occurs at the time of the product annealing, and the crystal orientation of the grain-oriented magnetic steel sheet is damaged. On the other hand, if the Si content exceeds 7.0%, the cold workability is reduced, and it becomes easy to generate cracks at the time of cold rolling. The preferable lower limit of the Si content is 2.5%, and further preferably 3.0%. The preferable upper limit of the Si content is 4.5%, and further preferably 4.0%.

[0101] Mn: 0.05 to 1.00% Manganese (Mn) combines with S or Se to form MnS or MnSe, and functions as an inhibitor. In the case where Mn is contained, the Mn content is in the range of 0.05 to 1.00% in order to stabilize the secondary recrystallization. Note that a part of the function of the inhibitor can be assumed by the nitride of the Nb group element. In this case, the strength control of MnS or MnSe as a general inhibitor is weak. Therefore, the preferable upper limit of the Mn content is 0.50%, and further preferably 0.20%.

[0102] At least one of S and Se: total 0.003 to 0.035% Sulfur (S) and selenium (Se) combine with Mn to form MnS or MnSe, and function as an inhibitor. In the case where at least one of S and Se is contained, if the content of S and Se is a total of 0.003 to 0.035%, the secondary recrystallization is stabilized. Note that a part of the function of the inhibitor can be assumed by the nitride of the Nb group element. In this case, the strength control of MnS or MnSe as a general inhibitor is weak. Therefore, the preferable upper limit of the total of the contents of S and Se is 0.025%, and further preferably 0.010%. If S and Se remain after the product annealing, compounds are formed, and the iron loss is deteriorated. Therefore, it is preferable to reduce S and Se as much as possible by purification in the product annealing.

[0103] Here, the total content of S and Se means the total content including at least one of S and Se.

[0104] Al: 0.010 to 0.065% Al combines with N to precipitate as (Al, Si)N, and functions as an inhibitor. In the case where Al is contained, the AlN formed as an inhibitor by nitriding described later expands the secondary recrystallization temperature region, and particularly, the secondary recrystallization is stabilized in the high temperature region, in the case where the Al content is in the range of 0.010 to 0.065%. Therefore, the Al content is 0.010 to 0.065%. The preferable lower limit of the Al content is 0.020%, and further preferably, 0.025%. From the viewpoint of the stability of the secondary recrystallization, the preferable upper limit of the Al content is 0.040%, and further preferably, 0.035%.

[0105] N: 0.012% or less N combines with Al to function as an inhibitor. N is not regulated to have a lower limit because it can be contained by nitriding in the middle of the manufacturing process. For example, the lower limit of the N content can exceed 0%, and can be 0.001%. On the other hand, in the case where N is contained, if the N content exceeds 0.012%, it becomes easy to generate a blister, which is one kind of defects, in the steel sheet. The preferable upper limit of the N content is 0.010%, and further preferably, 0.009%. N is purified in the finish annealing process, and becomes 0.005% or less after the finish annealing process.

[0106] The remaining portion of the above-described chemical composition contains Fe and impurities. Note that "impurities" means elements mixed from ores, waste materials, or manufacturing environments, etc. as raw materials when steel is manufactured industrially. The upper limit of the total content of impurities can be, for example, 5% or less.

[0107] The above-described chemical composition can contain a known optional element instead of a part of Fe in order to consider the strengthening of the inhibitor function due to the formation of a compound, and the influence on the magnetic characteristics, in addition to considering the solution of the manufacturing problems. As the optional element contained instead of a part of Fe, for example, the following elements can be listed.

[0108] Nb group element: 0.050% or less The total content of the Nb group elements (one or more of Nb, V, Mo, Ta, and W) can be 0.050% or less. In the case where the Nb group elements are used as a part of the inhibitor, if the total content of the Nb group elements is 0.030% or less, the secondary recrystallization is started at an appropriate timing, and therefore, is preferable. In addition, the orientation of the secondary recrystallization grains generated becomes very preferable, and finally, it is possible to control the structure which is preferable for the magnetic characteristics. Particularly, the effects of Nb and Ta are strongly preferable. The total content of the Nb group elements does not necessarily have a lower limit, and the lower limit can be 0%. The lower limit is preferably 0.003%.

[0109] The total content of the Nb group elements is more preferably 0.004 to 0.020%. It is further preferably 0.005 to 0.010%.

[0110] Here, the total content of the Nb group elements means the total content of at least one of Nb, V, Mo, Ta, and W.

[0111] In addition, the slab described above can also contain, as optional elements, at least one of the following elements in mass%: Cu: 0.40% or less, Bi: 0.010% or less, B: 0.080% or less, P: 0.50% or less, Ti: 0.015% or less, Sn: 0.10% or less, Sb: 0.10% or less, Cr: 0.30% or less, Ni: 1.00% or less.

[0112] These optional elements are contained according to the known purposes, and thus it is not necessary to set a lower limit value of the content of the optional elements, and the lower limit value can be 0%.

[0113] The chemical composition of the slab described above is measured in the same manner as the chemical composition of the grain-oriented magnetic steel sheet as a final product by the analysis method described above.

[0114] (Hot rolling step) The hot rolling step is a step of performing hot rolling of a slab heated to a prescribed temperature (for example, 1100 to 1400°C) to obtain a hot-rolled steel sheet. In the hot rolling step, for example, after rough rolling of a silicon steel raw material (slab) heated by the heating step is performed, finish rolling is performed to produce a hot-rolled steel sheet of a prescribed thickness, for example, 1.8 to 3.5 mm. After the finish rolling is completed, the hot-rolled steel sheet is coiled at a prescribed temperature.

[0115] When the process including the nitriding step at or after the decarburization annealing, the strength of MnS as an inhibitor is not so required, and thus the slab heating temperature can be set to 1100 to 1280°C in consideration of productivity.

[0116] (Hot-rolled sheet annealing step) The hot-rolled plate annealing process is a process in which the hot-rolled steel plate obtained in the hot-rolling process is annealed under prescribed temperature conditions (for example, at 750 to 1200°C for 30 seconds to 10 minutes) to obtain an annealed steel plate. The hot-rolled plate annealing is generally performed to control the recrystallization rate, residual strain, crystal grain size, and the like of the steel plate by annealing the hot-rolled steel plate after the hot-rolling process, and is also performed in order to optimally adjust the precipitate form in the steel. For example, in the high-temperature slab heating process, it is a process in which the form of precipitates such as AlN is finally controlled, and the conditions are adjusted in such a manner that the precipitates are uniformly and finely precipitated. As the hot-rolled plate annealing, for example, in order to appropriately precipitate AlN and the like after heating the steel plate to 1050°C to 1150°C, it is also possible to slowly cool to an intermediate temperature (850°C to 950°C) for 50 to 150 seconds and then perform water cooling.

[0117] (Cold-rolling process) The cold-rolling process is a process in which the annealed steel plate obtained in the hot-rolled plate annealing process is cold-rolled once or a plurality of times (2 or more times) via annealing (intermediate annealing) (for example, at a total cold-rolling rate of 80 to 95%) to obtain a cold-rolled steel plate having a thickness of, for example, 0.10 to 0.50 mm. In order to improve the magnetic properties, for example, the inter-pass temperature of the cold-rolling can be set to about 100°C to 300°C.

[0118] Note that the total cold-rolling rate of the cold-rolling is defined as follows.

[0119] Total cold-rolling rate (%) = (1 - plate thickness of steel plate after cold-rolling / plate thickness of steel plate before cold-rolling) x 100 (Local rapid heating process) In the present embodiment, the cold-rolled steel plate after the cold-rolling process is subjected to local rapid heating for forming local heating regions. As the rapid heating method, there is no particular limitation as long as the steel plate can be locally heated. For example, a method in which a point electrode is brought into contact with the front and back surfaces of the steel plate to pass an electric current through the steel plate to heat the steel plate, a method in which a laser or an electron beam or the like is irradiated onto the surface of the steel plate to heat the steel plate, a method in which local heating is performed by induction heating, a method in which a contact heat sheet is used to heat the steel plate, and the like can be employed. The size of each local heating region can be set to a dot-shaped region having a diameter of about 10 μm to 10 mm or a linear region having a width of about 10 μm to 10 mm. In addition, the electrode for the passage heating can be set to a circular electrode as described above, or can be set to a linear electrode.

[0120] Note that the minimum diameter, the minimum width in terms of the size of the local heating region depend on the shape of the point electrode, the technique of reducing the condensing diameter of the laser or electron beam. It is possible in principle to further reduce the size of the local heating region, but if the present recrystallized grains have a nucleus of about 1 μm in size, it is considered that an effect is obtained if the size of the local heating region is 1 μm or more. In industry, it is sufficient to set the minimum diameter, the minimum width described above to 10 μm or more. In addition, in terms of the size of the local heating region, if the maximum diameter, the maximum width exceeds 10 mm, the area ratio of the high-Goss orientation grains having a relatively large angle deviation Θ, angle deviation φ grown outside the local heating region becomes large. In this case, it becomes difficult to obtain the effect of performing local rapid heating.

[0121] In the local rapid heating, at the center portion observed from the plate thickness direction of the local heating region and the 1 / 5 portion of the plate thickness of the steel sheet, the heating rate becomes 500°C / sec or more. If the heating rate is 500°C / sec or more in the region described above, it is possible to preferably control the structure of the local heating region to be a recovered structure or a recrystallized structure. The heating rate described above is preferably 2000°C / sec or more, further preferably 10000°C / sec or more. On the other hand, the upper limit of the heating rate described above is not particularly limited, and for example, it is sufficient to set to 1000000°C / sec.

[0122] In addition, the heating rate described above is preferably controlled in combination with the heating rate at the time of decarburization annealing described later. For example, in the case where the heating rate at the time of decarburization annealing is faster than the heating rate at the time of local rapid heating, it is difficult to obtain the target effect. Therefore, although depending on the magnitude of the value of the heating rate, the heating rate at the time of local rapid heating is preferably set to be equal to or more than the heating rate at the time of decarburization annealing.

[0123] Note that the 1 / 5 portion of the plate thickness of the steel sheet described above means a depth corresponding to 1 / 5 of the plate thickness of the steel sheet from the surface of the steel sheet toward the plate thickness direction.

[0124] In addition, in the local rapid heating, at the center portion observed from the plate thickness direction of the local heating region and the 1 / 5 portion of the plate thickness of the steel sheet, the maximum attained temperature becomes 700°C or more. If the maximum attained temperature is 700°C or more in the region described above, it is possible to preferably control the structure of the local heating region to be a recovered structure or a recrystallized structure. The maximum attained temperature described above is preferably 800°C or more, further preferably 900°C or more. On the other hand, the maximum attained temperature described above is sufficient to be below the melting point of the steel sheet, and for example, it is sufficient to be 1400°C or less.

[0125] In addition, in the local rapid heating, the holding time from the time when the maximum temperature is reached until the temperature is cooled to 7000C at the center portion observed from the local heating region in the plate thickness direction and at the 1 / 5 portion of the plate thickness of the steel sheet is 0.1 second or more. If the holding time is 0.1 second or more in the above-mentioned region, the structure of the local heating region can be preferably controlled to be a recovered structure or a recrystallized structure. The holding time is preferably 0.2 second or more, further preferably 0.3 second or more, and further preferably 0.4 second or more. On the other hand, the upper limit of the holding time is not particularly limited, and for example, can be 10 seconds or less. This holding time from the time when the maximum temperature is reached until the temperature is cooled to 7000C has a substantial influence on the formation of coarse Goss-oriented grains close to ideal Goss orientation.

[0126] In the local rapid heating, it is important to control not only the heating rate and the maximum temperature reached as described above, but also the holding time as described above. In the holding time, a subgrain structure and a recrystallization nucleus that are advantageous for the formation of coarse Goss-oriented grains in the local heating region can be formed. By controlling the subgrain structure of the local heating region with the holding time, the structure control can be preferably performed in the subsequent process.

[0127] As described above, the method of the local rapid heating is not particularly limited. For example, the local rapid heating can be performed by spot welding, laser irradiation, or electron beam irradiation. Regardless of the method of the local rapid heating, as long as the control is performed in a manner that satisfies the heating rate, the maximum temperature reached, and the holding time as described above, the conditions of the local rapid heating method can be combined to control the heating rate, the maximum temperature reached, and the holding time as targets.

[0128] For example, as long as the person skilled in the art, the heating rate and the maximum temperature reached at the center portion observed from the local heating region in the plate thickness direction and at the 1 / 5 portion of the plate thickness of the steel sheet can be controlled by performing a heat conduction analysis using a finite element method. In addition, as long as the person skilled in the art, the holding time as described above can be controlled by adjusting the heat dissipation conditions after the maximum temperature is reached. For example, in the case of spot welding, as long as the electrode holding time after the welding is controlled, or the shape of the spot electrode is changed to a shape suitable for heat dissipation, the holding time can be controlled. In addition, in the case of laser irradiation or electron beam irradiation, as long as the irradiation rate is adjusted, or the shape of the irradiation region is changed to an ellipse or the like so that the irradiation energy is gradient from the center portion to the outer portion of the irradiation region, the holding time can be controlled.

[0129] Note that, in general, with heating by laser irradiation, only the vicinity of the irradiated surface of the steel sheet is preferentially heated, and the inside of the steel sheet is difficult to heat. Also, with heating by laser irradiation, since it is non-contact heating, the heat dissipation after heating is fast, and it is difficult to maintain the temperature. Therefore, when performing laser irradiation heating as local rapid heating, in order to cause the cold worked structure of the laser irradiation region to recover or recrystallize, it is necessary to control the conditions so as to heat not only the surface of the steel sheet but also the inside of the steel sheet, and to slow the cooling rate so as to make the subgrain structure of the laser irradiation region relatively coarse. The laser irradiation conditions for performing local rapid heating are completely different from the laser irradiation conditions for performing magnetic domain refinement. For example, even if the laser irradiation conditions for performing magnetic domain refinement (generally 0.5 to 50 mJ / mm 2 ) are applied to the present embodiment, the structure of the local heating region will not be optimally controlled, and coarse Goss-oriented grains close to ideal Goss orientation will not be formed in the steel sheet after the decarburization annealing process. Also, the same applies to electron beam irradiation. Even if the electron beam irradiation conditions for performing magnetic domain refinement are applied to the present embodiment, the structure of the local heating region will not be optimally controlled, and coarse Goss-oriented grains close to ideal Goss orientation will not be formed in the steel sheet after the decarburization annealing process.

[0130] Note that, even if the input power of the laser irradiation, electron beam irradiation is simply increased, it is difficult to form coarse Goss-oriented grains close to ideal Goss orientation. For example, in the case of performing rapid heating by laser irradiation, electron beam irradiation, in order to be able to secure a temperature region in which the grains of the region after rapid heating are used for grain growth, it is preferable to set the beam shape to be elliptical, or to adjust the scanning speed, etc.

[0131] In the past, in electromagnetic steel sheets, in order to perform magnetic domain control on steel sheets after secondary recrystallization to reduce iron loss, laser irradiation, electron beam irradiation was performed. Under these laser irradiation, electron beam irradiation conditions, the heating is performed to a depth of about 20 μm from the surface of the steel sheet, and therefore the heat dissipation after heating is fast. Therefore, under the past conditions, it is difficult to secure the above-mentioned holding time from reaching the maximum temperature to cooling to 700°C. That is, under the past laser irradiation, electron beam irradiation conditions, it is possible to cause the irradiated portion to function as a growth barrier for secondary recrystallized grains, but it is difficult to form Goss-oriented grains having orientation close to ideal Goss orientation and being coarse as in the present embodiment. In order to form coarse Goss-oriented grains close to ideal Goss orientation by laser irradiation, electron beam irradiation, it is necessary to research the conditions of the laser irradiation, electron beam irradiation as described above.

[0132] In addition, when the local rapid heating region is spread over the steel sheet surface by the local rapid heating, the size, shape, and arrangement of the grains after the secondary annealing can be controlled by appropriately arranging the local rapid heating on the steel sheet surface. For example, if the local rapid heating regions are arranged on the steel sheet surface in a manner that the Gaussian-oriented grains growing from one local rapid heating region collide with other Gaussian-oriented grains growing from an adjacent local rapid heating region, the grain size of the Gaussian-oriented grains in any direction at the end of the secondary annealing can be controlled to be small.

[0133] (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). By this decarburization annealing, the frequency of occurrence of the Gaussian-oriented grains formed in the local heating region is increased, the grain size of the Gaussian-oriented grains is increased, and coarse Gaussian-oriented grains having an orientation close to an ideal Gaussian orientation preferably grow. As the decarburization annealing conditions, for example, annealing at an annealing temperature of 700 to 900°C and an annealing time of 1 to 3 minutes is sufficient. By decarburization annealing of the cold-rolled steel sheet, C contained in the cold-rolled steel sheet is removed. In order to remove "C" contained in the cold-rolled steel sheet, the decarburization annealing is preferably performed in a humid atmosphere.

[0134] In addition, it is effective to reduce the primary recrystallized grain size by controlling the conditions of the hot rolling and the hot-rolled sheet annealing described above or, as necessary, by lowering the decarburization annealing temperature. The primary recrystallized grain size is not particularly limited, but is preferably 8 to 30 μm.

[0135] In addition, in the present embodiment, coarse Gaussian-oriented grains having an orientation close to an ideal Gaussian orientation are formed in the local heating region. Therefore, it is not necessary to reform the Gaussian-oriented grains in the decarburization annealing. The heating rate of the decarburization annealing can be 10,000°C / sec or less, but it is preferable to set the heating rate of the decarburization annealing to be low, and to form {111} <112> oriented grains and {411} <148> oriented grains which are easily eroded by the matrix portion (non-local heating region). For example, the heating rate of the decarburization annealing is preferably 300°C / sec or less, further preferably 200°C / sec or less, and further preferably 100°C / sec or less.

[0136] In addition, the decarburization oxidation amount and the state of the surface oxidation layer affect the formation of the glass film. Therefore, in the decarburization annealing, the oxidation degree (PH2O / PH2) in the annealing atmosphere (furnace atmosphere) can be appropriately adjusted.

[0137] (Nitriding treatment) The nitriding treatment is a treatment effective in the low-temperature slab heating process in which the slab heating temperature is 1280°C or lower, and is an important process for adjusting the strength of the inhibitors in the secondary recrystallization. The nitriding treatment increases the nitrogen content of the steel sheet by about 40 to 200 ppm during the period from the start of the decarburization treatment to the start of the secondary recrystallization in the finish annealing. As the nitriding treatment, for example, there can be mentioned a treatment in which annealing is performed in an atmosphere containing a gas having a nitriding ability such as ammonia, a treatment in which a decarburization annealed steel sheet to which an annealing separator containing a powder having a nitriding ability such as MnN is applied is subjected to finish annealing, and the like. The nitriding amount after the nitriding treatment is preferably set to 130 to 350 ppm, and further preferably set to 150 to 250 ppm.

[0138] (Annealing separator application step) The annealing separator application step is a step in which an annealing separator is applied to the decarburization annealed steel sheet. As the annealing separator, for example, an annealing separator in which MgO is the main component, an annealing separator in which Al2O3 is the main component can be used. The decarburization annealed steel sheet to which the annealing separator is applied is subjected to finish annealing in the next finish annealing step in a state in which it is coiled into a coiled material.

[0139] (Finish annealing step) The finish annealing step is a step in which finish annealing (secondary annealing) is performed on the decarburization annealed steel sheet to which the annealing separator is applied, and secondary recrystallization is generated. This step allows the {100} <001> oriented grains to grow preferentially by causing the secondary recrystallization to proceed in a state in which the growth of the primary recrystallized grains is inhibited by the inhibitors, and allows the magnetic flux density to be dramatically increased.

[0140] The heating rate in the heating process of the finish annealing step is not particularly limited. For example, the temperature can be increased at a heating rate of 3 to 20°C / hour. In addition, slow heating can be performed in the temperature range of 1000°C to 1200°C at the time of temperature increase. For example, the heating rate in the temperature range of 1000°C to 1200°C at the time of temperature increase is preferably set to 3 to 12°C / hour, more preferably set to 3 to 9°C / hour, and further more preferably set to 3 to 7°C / hour. Alternatively, in order not to cause the precipitates that pin the primary recrystallized grains to be rapidly decomposed, the temperature increase can be temporarily stopped and holding can be performed in the heating process of the finish annealing step. For example, the temperature increase can be temporarily stopped in the temperature range of 1050°C to 1100°C at the time of temperature increase, and holding of 5 to 15 hours can be performed. For example, adjusting the heating rate in the secondary recrystallization temperature region has an effect on the decomposition rate of the inhibitors, and allows the magnetic flux density to be increased.

[0141] After the heating process of the finish annealing process, as a holding process (purification annealing), holding at a temperature region of 1000°C to 1300°C for 10 hours to 60 hours is sufficient. The atmosphere at the finish annealing can be set to, for example, a nitrogen atmosphere or a mixed atmosphere of nitrogen and hydrogen.

[0142] (insulating film forming process) On the steel sheet after the finish annealing, as needed, a coating solution containing phosphoric acid or a phosphoric acid salt, chromic anhydride or a chromic acid salt, and colloidal silica can be applied and baked (for example, at 350°C to 1150°C for 5 to 300 seconds) to form an insulating film.

[0143] (other) For the grain-oriented electromagnetic steel sheet, as needed, a magnetic domain refinement process of forming a local minute strain region or a groove can be performed by a known method such as laser, plasma, a mechanical method, etching, and the like. However, the grain-oriented electromagnetic steel sheet of the present embodiment, although having an excellent magnetic flux density, suppresses the coarsening of the secondary recrystallized grain diameter, and thus the magnetic domains are refined even without performing the magnetic domain refinement process.

[0144] Note that in the case where the magnetic domain refinement process is performed, the minute strain region and the groove resulting from the magnetic domain refinement process can possibly become abnormal points in the measurement of the crystal orientation and the grain diameter. Therefore, in the measurement of the crystal orientation, it is preferable to make the measurement points not overlap the minute strain region and the groove.

[0145] [Example 1] Next, the effects of the present application are specifically explained in detail by examples. The conditions in the examples are one condition example adopted in order to confirm the implementability and effects of the present application, and the present application is not limited to this one condition example. Various conditions can be adopted as long as the present application does not depart from the gist of the present application and achieves the object of the present application.

[0146] A slab having a chemical composition adjusted was used as a raw material to produce a cold-rolled steel sheet having a chemical composition shown in Table 2. Note that these chemical compositions were measured based on the above-described method. In Table 2, "-" indicates that the control and production considering the content were not performed and the measurement of the content was not performed.

[0147] In producing the above-described cold-rolled steel sheet, the slab was heated to 1150°C to be subjected to hot-rolling to produce a hot-rolled steel sheet having a sheet thickness of 2.6 mm. The hot-rolled steel sheet was heated to 1100°C, and then subjected to a hot-rolled sheet annealing of annealing at 900°C, and then subjected to pickling to remove the oxide scale generated on the surface. These steel sheets were subjected to cold-rolling once or cold-rolling a plurality of times with interposed annealing to produce a cold-rolled steel sheet having a final sheet thickness of 0.22 mm.

[0148] The cold-rolled steel sheets described above were subjected to local rapid heating under the conditions shown in Tables 3 to 6. Note that, in the case of spot electric heating, a copper electrode having a diameter of 3 mm was used as the portion in contact with the steel sheet, and on the basis of this, the electrode shape other than the portion in contact with the steel sheet, the electrode pressure, the electric current, the electric current time, the electrode holding time after electric current, and the like were varied in combination to control the heating rate, the maximum temperature reached, and the holding time from the time of reaching the maximum temperature to the time of cooling to 700°C (the holding time at 700°C or higher). In the case of laser heating, a fiber laser was used, the rolling direction condensing spot diameter of the laser (i.e., the diameter including 86% of the laser output power) was set to 30 μm (except for Test Nos. 62 and 63), and on the basis of this, the laser irradiation energy density, the laser scanning speed, the shape of the laser irradiation region, and the like were varied in combination to control the heating rate, the maximum temperature reached, and the holding time at 700°C or higher. As long as a person skilled in the art, the conditions of the local rapid heating method can be combined to control the heating rate, the maximum temperature reached, and the holding time at 700°C or higher as targets.

[0149] Note that, in the case of Test No. 60, by elongating the laser beam in the scanning direction, the holding time from the time of reaching the maximum temperature to the time of cooling to 700°C was controlled to 0.2 seconds at the time of local rapid heating, and a coarse Goss-oriented grain having an orientation close to an ideal Goss orientation was formed in the local heating region. In the case of Test No. 61, a general laser irradiation condition for performing magnetic domain refinement was applied. In the case of Test No. 62, the condensing spot diameter was set to 0.5 mm, the laser irradiation energy density was set to 2.0 J / mm 2 , and control was performed in such a manner that the crystal grain boundary of the laser beam irradiation portion eventually becomes a secondary recrystallized grain. In the case of Test No. 63, the condensing spot diameter was set to 0.5 mm, the laser irradiation energy density was set to 30.0 J / mm 2 , and control was performed in such a manner that the crystal grain boundary of the laser beam irradiation portion eventually becomes a secondary recrystallized grain.

[0150] In the table, "no treatment" of the heating method of local rapid heating indicates that no local rapid heating was performed. "Linear or dot-like" of the local heating condition indicates the shape of the local heating region on the surface of the cold-rolled steel sheet, and "rolling direction interval" and "width direction interval" of the local heating condition indicate the intervals in the rolling direction and the direction at right angles to the rolling direction in which the local heating regions are arranged on the surface of the cold-rolled steel sheet. The local heating regions are arranged at equal intervals in the rolling direction and the direction at right angles to the rolling direction. Note that, when the local heating regions are arranged on the surface of the cold-rolled steel sheet, the arrangement is performed in such a manner that the distribution of the local heating regions does not become uneven.

[0151] For the manufactured cold-rolled steel sheet, decarburization annealing under the conditions shown in Tables 3 to 6 was performed. Note that in the decarburization annealing, the degree of oxidation (PH2O / PH2) in the annealing atmosphere (furnace atmosphere) was set to 0.13.

[0152] For the manufactured decarburization annealed steel sheet, nitriding treatment was performed at 750°C in a nitrogen-hydrogen-ammonia atmosphere, and the nitrogen content of the steel sheet was set to 220 ppm. Further, product annealing was performed by applying an annealing separator in which MgO was the main component. In the product annealing, the steel sheet was heated to 1000°C (the "Step" described below is 1070°C) at a heating rate of 15°C / hour in a mixed atmosphere of hydrogen and nitrogen, and then heated to 1200°C under either of the following conditions, and held at 1200°C for 20 hours in a hydrogen atmosphere.

[0153] General: heating from 1000°C to 1200°C at 15°C / hour Slow heating 1: heating from 1000°C to 1200°C at 10°C / hour Slow heating: heating from 1000°C to 1200°C at 7.5°C / hour Slow heating 2: heating from 1000°C to 1200°C at 5.0°C / hour Step: holding at 1070°C for 10 hours On the steel sheet after the product annealing, an insulating coating solution in which colloidal silica and phosphate were the main components, and chromic anhydride was added as necessary, was applied and baked to form an insulating coating.

[0154] For the obtained grain-oriented electromagnetic steel sheet, the chemical composition of the base steel sheet, aveφ L (φ m ), the value (f(φ L )) of 100-15 x aveφ m ), D L 10 (D10) were measured based on the above-described methods. The results are shown in Tables 7 to 11. In Table 11, "-" indicates that control and manufacture taking the content into consideration were not performed, and measurement of the content was not performed.

[0155] Note that regarding the crystal orientation, a measurement line in which measurement points containing 1000 points at 1 mm intervals were set was set in the rolling direction (RD), and 10 such measurement lines were set at 50 mm intervals in the rolling right angle direction (TD), and the crystal orientation was measured using these 10 lines.

[0156] In addition, for the obtained grain-oriented electromagnetic steel sheet, various characteristics were evaluated. The evaluation results are shown in Tables 7 to 11.

[0157] The magnetic properties of the directional electromagnetic steel sheet were determined based on the Single Sheet Tester (SST) method specified in JIS C 2556:2015.

[0158] From the obtained directional electromagnetic steel plates, 20 single-plate magnetic samples of 100mm × 500mm size were prepared for magnetic measurement. Single-plate magnetic measurements were performed. As a magnetic characteristic, the magnetic flux density B8(T) in the rolling direction of the steel plate was measured when energized at 800 A / m. The magnetic flux density B8 was determined based on the Si content of the steel plate. For example, it is known that the lower the Si content of the steel plate, the higher the saturation magnetic flux density, and the higher the saturation magnetic flux density, the higher B8. Therefore, for steels A to Z with a Si content of 3.3–3.5%, a B8 of 1.930T or higher is considered acceptable; for steel AA with a Si content of 2.5%, a B8 of 1.960T or higher is considered acceptable; and for steel AB with a Si content of 4.1%, a B8 of 1.890T or higher is considered acceptable.

[0159] In addition, as a magnetic characteristic, the iron loss W, defined as the electrical loss per unit weight (1 kg) of steel plate, was measured under the conditions of AC frequency of 50 Hz and excitation magnetic flux density of 1.7 T. 17 / 50 (W / kg). Regarding W 17 / 50 The condition below 0.79 W / kg is considered qualified.

[0160] The directional electromagnetic steel plates in Nos. 1 to 66, which are examples of the present invention, satisfy aveφ. L ≤4.0° and D L 10≤100-15×aveφ L In these examples of the present invention, the angular deviation in the rolling direction of directional electromagnetic steel sheets is controlled to be small, resulting in excellent magnetic flux density. Furthermore, the grain size in the rolling direction is controlled to be small, thus ensuring excellent iron loss even without domain control (domain refinement treatment). Therefore, in these examples of the present invention, the drawbacks caused by conventional domain control (such as the deterioration of transformer noise caused by laser domain control and the reduction in magnetic flux density caused by slot introduction) can be mitigated.

[0161] On the other hand, the directional electromagnetic steel plates used as comparative examples in Nos. 1 to 66 do not satisfy aveφ. L ≤4.0° or D L 10≤100-15×aveφ L At least one of them. These comparative examples, as directional electromagnetic steel sheets, did not achieve preferred magnetic flux density and iron loss.

[0162] [Table 2] [Table 3] [Table 4] [Table 5] [Table 6] [Table 7] [Table 8] [Table 9] [Table 10] [Table 11] Industrial applicability According to the above-described aspect of the present application, it is possible to provide a directionality electromagnetic steel sheet which can reduce the drawbacks caused by magnetic domain control in the past (for example, deterioration of transformer noise caused by laser magnetic domain control, reduction of magnetic flux density caused by slot introduction, etc.), on the basis of which both the magnetic flux density and the iron loss are excellent. Therefore, the industrial applicability is high.

[0163] Explanation of symbols 1 Steel sheet 2 Measuring point of crystal orientation

Claims

1. A grain-oriented electrical steel sheet characterized by comprising: (1) a non-oriented electrical steel sheet having a composition containing, in mass %: (2 In the case where an angle of deviation from an ideal Gaussian orientation with a rolling face normal direction Z as a rotation axis is defined as α, an angle of deviation from an ideal Gaussian orientation with a rolling right angle direction C as a rotation axis is defined as β, an angle of deviation from an ideal Gaussian orientation with a rolling direction L as a rotation axis is defined as γ, an angle of deviation of a crystal orientation measured at one measurement point on a sheet surface is expressed as (α, β, γ), an angle deviation of the one measurement point is defined as φ = (α 2 + β 2 ) 1 / 2 , and an average value of angle deviations φ calculated from measurement points of at least 1000 points spaced by 1 mm along the rolling direction L is defined as aveφ L , the aveφ L satisfies aveφ L ≤ 4.0°, The deviation angles of the crystal orientation measured at two adjacent measurement points with a spacing of 1 mm on the plate are denoted as (α1, β1, γ1) and (α2, β2, γ2), which satisfy [(α2-α1)]. 2 +(β2-β1) 2 +(γ2-γ1) 2 ] 1 / 2 The midpoint between two measurement points with an angle ≥1.0° is defined as the grain boundary GB. The grain size in the rolling direction L, calculated based on the grain boundary GB, is defined as D in mm. L The particle size D is obtained along the rolling direction L. L Arranged in descending order, and counting the largest particles by their number as the basis, the 10% of the particle size is defined as D in mm. L At 10 o'clock, the D L 10 satisfies D L 10≤100-15×aveφ L .

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