Cold-rolled steel sheet

Abstract

In a cold rolled steel sheet for a grain oriented electrical steel sheet, when a region of 100 mm × 100 mm on the sheet surface is defined as a divided domain and when it is confirmed whether the Goss-oriented grain is included in the divided domain in at least 100 divided domains, an area fraction of divided domains including at least one Goss-oriented grain having a grain size of 5 µm or more is 30% or more as compared with all divided domains.

Description

TECHNICAL FIELD

[0001] The present invention relates to a cold rolled steel sheet for a grain oriented electrical steel sheet.

[0002] Priority is claimed on Japanese Patent Application No. 2023-106555, filed June 29, 2023, the content of which is incorporated herein by reference.BACKGROUND ART

[0003] A grain oriented electrical steel sheet includes Si, the crystal orientation of the grains thereof closely aligns in the Goss orientation (cubic crystal {110}<001>), and the <001> orientation, which is a magnetization easy axis, is substantially aligned in the rolling direction in the steel sheet manufacturing process. Such a grain oriented electrical steel sheet is very desirable as a material for an iron core and the like of a transformer. Among the magnetic characteristics of the grain oriented electrical steel sheet, magnetic flux density and iron loss are particularly important.

[0004] The magnetic flux density of the grain oriented electrical steel sheet when a predetermined magnetizing force is applied tends to increase as the degree to which the magnetization easy axes of the grains are aligned in the rolling direction of the steel sheet, that is, the orientation of the grains is higher. A magnetic flux density B 8 is generally used as an index representing the magnetic flux density. The magnetic flux density B 8 is a value of the magnetic flux density of the grain oriented electrical steel sheet excited at a magnetizing force of 800 A / m in the rolling direction. That is, the grain oriented electrical steel sheet having a larger value of the magnetic flux density B 8 is more easily magnetized with a certain magnetizing force, the magnetic flux density becomes high, and thus it is suitable for a small-sized and highly efficient transformer.

[0005] In addition, an iron loss W 17 / 50 is generally used as an index representing the iron loss. The iron loss W 17 / 50 is an iron loss when the grain oriented electrical steel sheet is excited by alternating current so as to be a maximum magnetic flux density of 1.7 T under the condition of a frequency of 50 Hz. The grain oriented electrical steel sheet having a smaller value of the iron loss W 17 / 50 has a lower energy loss and is suitable for a transformer.

[0006] The methods for reducing the iron loss include a method of increasing the electric resistance by containing Si, a method of reducing the thickness of the steel sheet, and a method of decreasing the grain size, which are effective for reducing the eddy-current loss, and a method of aligning the orientation of the grains which is effective for reducing the hysteresis loss. That is, when the value of the magnetic flux density B 8 becomes higher, the crystal orientation is aligned with the Goss orientation, and the hysteresis loss is reduced. Thus, when the value of the magnetic flux density B 8 becomes higher, the value of the iron loss W 17 / 50 tends to be lower. On the other hand, when the growth of Goss-oriented grains is promoted in order to improve the alignment degree of the crystal orientation, the grain size tends to coarsen, and the eddy-current loss increases. Thus, when the grains are excessively coarse even when the value of B 8 is high, the iron loss tends to deteriorate. As explained above, there is an antinomy.

[0007] In recent years, in order to purposely refine a width of magnetic domain, a method of controlling the magnetic domain by applying strain by irradiation with laser beam, plasma jet, and the like, or by forming grooves by mechanical processing, etching, and the like has been developed. By using such a method, in the steel sheet in which the alignment degree of the crystal orientation is increased and the magnetic flux density is increased, the eddy-current loss can be reduced, and the iron loss can be sufficiently reduced even when the secondary recrystallized grain size coarsens. However, when the strain is applied into the steel sheet, magnetostriction (λ P-P ) increases due to the strain. In addition, when heat treatment is performed at a temperature of approximately 800°C after the magnetic domain refinement, the effect of reducing the iron loss disappears, and therefore the above steel sheet cannot be used for utilization requiring strain relief annealing at 800°C or higher after irradiation. On the other hand, in the magnetic domain refinement using the grooves, there is a problem in that the magnetic flux density B 8 decreases.

[0008] In general, the grain oriented electrical steel sheet is manufactured as described below. A steel sheet material (slab) including a predetermined amount of Si is subjected to hot rolling, annealing, and cold rolling to obtain a steel sheet having a desired thickness. Then, the steel sheet after cold rolling is annealed (this is also referred to as primary annealing or decarburization annealing). By this annealing, primary recrystallization occurs, and grains having a crystal orientation in which the magnetization easy axes are aligned in the rolling direction and a deviation angle from an ideal Goss orientation expressed by {110}<001> is 10° or less (hereinafter, referred to as Goss-oriented grains) are formed in the primary recrystallized grains. This annealing is also performed as decarburization annealing. Thereafter, an annealing separator including MgO as a main component is applied to the surface of the steel sheet in which primary recrystallization has occurred. Subsequently, the steel sheet to which the annealing separator has been applied is coiled to prepare a steel sheet coil, and this steel sheet coil is subjected to batch treatment annealing (also referred to as secondary recrystallization annealing or final annealing). By this annealing, the Goss-oriented grains encroach on other grains, secondary recrystallization occurs, and a so-called glass film is formed on the surface of the steel sheet. At the time of secondary recrystallization, due to the effect of an inhibitor included in the steel sheet, the Goss-oriented grains preferentially grow, and the grain size may be 100 mm or more in coarse grains. Next, uncoiling the steel sheet coil, annealing for flattening the steel sheet in which the secondary recrystallization has occurred, forming an insulating coating, and the like are performed.

[0009] As described above, the grain oriented electrical steel sheet obtains the desired magnetic properties by inducing the secondary recrystallization during final annealing to obtain a crystal structure including Goss-oriented grains aligned in the {110}<001> orientation. In order to obtain this crystal structure, it is effective to increase an existence frequency of Goss-oriented grains which are minor or increase the existence frequency of grains having higher lattice matching with the Goss-oriented grains by the primary annealing. For instance, grains of the {778} <447> (≈ {111}<112>) orientation and the {411}<148> orientation which have higher lattice matching with the {110}<001> orientation and a Σ9 coincidence site lattice relationship with a Goss orientation (referred to as CSL oriented grains) are the grains easily encroached by Goss-oriented grains, and thus, it is effective to include a large amount of the above grains in the primary recrystallized structure. However, when the crystal orientation of the grains formed by the primary annealing is controlled, it is difficult to simultaneously improve the existence frequency of the Goss-oriented grains and the existence frequency of the grains having the coincidence site lattice relationship. For instance, in a case where the cold rolling reduction is 85% or more, the existence frequency of the CSL oriented grains which are easily encroached by the Goss-oriented grains increases as the cold rolling reduction increases, whereas the existence frequency of the Goss-oriented grains decreases as the cold rolling reduction increases. In addition, the existence frequency of the Goss-oriented grains which are minor in the primary recrystallization texture increases as the heating rate of the primary annealing increases, whereas the existence frequency of the CSL oriented grains having the {111}<112> orientation which are major in the primary recrystallization texture conversely decreases as the heating rate of the primary annealing increases.

[0010] That is, under conventional process control conditions, the existence frequency of the Goss-oriented grains and the existence frequency of the CSL oriented grains that are easily encroached by the Goss-oriented grains cannot be controlled independently.

[0011] Here, in regard to the crystal orientation which is identified in the grain oriented electrical steel sheet, a deviation angle from the ideal {110}<001> orientation around the normal direction Z (ND) is referred to as a deviation angle α, a deviation angle from the ideal {110}<001> orientation around the transverse direction C (TD) is referred to as a deviation angle β, and a deviation angle from the ideal {110}<001> orientation around the rolling direction L (RD) is referred to as a deviation angle γ. Then, an angular deviation θ is defined as the angular deviation from the ideal {110}<001> orientation obtained by the following (Formula 1) using the deviation angles α, β, and γ around the ND, TD, and RD of the crystal orientation identified in the grain oriented electrical steel sheet. θ = α 2 + β 2 + γ 2 1 / 2

[0012] As described above, the Goss-oriented grains are not grains having a Goss orientation (ideal Goss orientation) (referred to as ideal Goss-oriented grains) in a strict sense. A direction of the magnetization easy axis (cubic crystal {110}<001>) of each grain and the rolling direction do not always completely coincide with each other, and the angular deviation θ exists between the direction of the magnetization easy axis and the rolling direction. On the basis of (Formula 1), a grain in which the angular deviation θ from the ideal Goss orientation is 10° or less is referred to as the Goss-oriented grain (practical Goss-oriented grain). When the angular deviation θ of the practical Goss-oriented grain increases, the orientation of the grains decreases, and the magnetic flux density B 8 decreases.

[0013] In general, grains having large angular deviation θ are also mixed in the Goss-oriented grains included in the steel sheet after primary recrystallization. However, when grains grow by secondary recrystallization, except for the effect of size advantage of grain at an initial stage of secondary recrystallization, the grains having small angular deviation θ among the Goss-oriented grains have a larger driving force of grain growth and continue to grow preferentially until the secondary recrystallization is completed. Therefore, when the angular deviation θ of the Goss-oriented grains is smaller, the grain size after secondary recrystallization tends to be larger. That is, in a manufacturing method in which secondary recrystallized grains are highly made to align in the Goss orientation, specific grains are preferentially grown, and thus, the grains size necessarily tends to coarsen.

[0014] In addition, at the time of secondary recrystallization, the steel sheet is not flat but curved since it is coiled in a coil shape, but the grains grow while maintaining the linearity of the crystal orientation. Therefore, when the coiled steel sheet is uncoiled and made to be flat after secondary recrystallization, a region in which the direction of the magnetization easy axis is not parallel to the surface of the grain oriented electrical steel sheet arises in the grains. Due to uncoiling explained above, the value of the deviation angle β mainly increases, and the angular deviation θ also increases. The increase in the angular deviation θ due to uncoiling becomes excessive as the grain size increases. That is, the Goss-oriented grains having small angular deviation θ tend to preferentially grow during secondary recrystallization, but when the secondary recrystallized grain size is coarse, the angular deviation θ increases due to uncoiling.

[0015] Patent Document 1 discloses a technique in which linear grooves satisfying a predetermined condition are formed by performing an etching treatment on the surface of steel sheet after final cold rolling, and a heating rate in a temperature range where a steel sheet temperature is 500°C or more and 750°C or less is increased in a region of the linear grooves as compared with a region other than the linear grooves by subsequent primary annealing. In Patent Document 1, by purposely separating a region where the heating rate is high and a region where the heating rate is low, a region (region of the linear grooves) where the existence frequency of (110)

[001] oriented grains is increased and a region (region other than the linear groove) where the existence frequency of (111)

[112] oriented grains is increased are purposely arranged.

[0016] Patent Document 2 discloses a technique of irradiating the surface of a silicon steel sheet with a laser beam plural times at predetermined spacing PL in a rolling direction between cold rolling and final annealing. When the silicon steel sheet is made to be secondary recrystallized by final annealing, a trace line along the laser beam becomes a grain boundary which reaches from one surface to the other surface of the silicon steel sheet. In Patent Document 2, after the final annealing, the length of the grains in the rolling direction is maximally 30 mm which corresponds to the spacing PL of the irradiation, and the angular deviation between the direction of the magnetization easy axis (cubic crystal { 110}<001>) and the rolling direction is in the range of 0° to 6°.

[0017] Patent Document 3 discloses a method for manufacturing a grain oriented electrical steel sheet that has a small difference in alignment degree to a Goss orientation in the inner and outer circumferences of coils having different curvatures and has a high magnetic flux density on the premise of a high temperature slab heating process. In Patent Document 3, by performing linear local heating on a cold-rolled steel sheet, the linear heated region acts as a barrier for growth of secondary recrystallized grains, and thereby the growth of secondary recrystallized grains is suppressed.Citation ListPatent Document

[0018] Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2007-169762 Patent Document 2: PCT International Publication No. WO 2012 / 014290 Patent Document 3: Japanese Unexamined Patent Application, First Publication No. 2022-161269 SUMMARY OF INVENTIONTechnical Problem

[0019] As described above, the magnetic characteristics of the grain oriented electrical steel sheet have been tried to be improved until today. However, it is insufficient to improve of the magnetic characteristics by the conventional techniques.

[0020] The present invention has been made in consideration of the above-mentioned situations. An object of the present invention is to provide a cold rolled steel sheet for a grain oriented electrical steel sheet capable of increasing a magnetic flux density. Specifically, an object is to provide a cold rolled steel sheet for a grain oriented electrical steel sheet capable of increasing a magnetic flux density while suppressing coarsening of a secondary recrystallized grain size.Solution to Problem

[0021] An aspect of the present invention employs the following. [1] A cold rolled steel sheet for a grain oriented electrical steel sheet according to an aspect of the present invention, wherein when a deviation angle from an ideal Goss orientation based on a rotation axis parallel to a normal direction is defined as α, when a deviation angle from the ideal Goss orientation based on a rotation axis parallel to a transverse direction is defined as β, when a deviation angle of a crystal orientation measured at a measurement point on a sheet surface is represented as (α β), when an angular deviation at the measurement point is defined as ϕ = (α 2< + β 2< ) 1 / 2< , when a grain having the angular deviation ϕ of 10° or less is defined as a Goss-oriented grain, when a region of 100 mm × 100 mm on the sheet surface is defined as a divided domain, and when it is confirmed whether the Goss-oriented grain is included in the divided domain in at least 100 divided domains, an area fraction of divided domains including at least one Goss-oriented grain having a grain size of 5 µm or more is 30% or more as compared with all divided domains. Advantageous Effects of Invention

[0022] According to the above aspects of the present invention, it is possible to provide a cold rolled steel sheet for a grain oriented electrical steel sheet capable of increasing a magnetic flux density. Specifically, it is possible to provide the cold rolled steel sheet for the grain oriented electrical steel sheet capable of increasing the magnetic flux density while suppressing coarsening of the secondary recrystallized grain size.

[0023] For instance, local rapid heating is performed for the material sheet for the grain oriented electrical steel sheet before primary annealing for manufacturing the grain oriented electrical steel sheet, Goss-oriented grains of 5 µm or more are formed in the cold rolled steel sheet, and thereby, the magnetic flux density can be improved as the grain oriented electrical steel sheet. Moreover, regions where the local rapid heating is performed are preferably and dispersedly arranged in the steel sheet, and thereby, the magnetic flux density can be improved as the grain oriented electrical steel sheet while suppressing coarsening of the secondary recrystallized grain size.BRIEF DESCRIPTION OF DRAWINGS

[0024] [FIG. 1] A schema illustrating an instance of using spot electric heating as a local rapid heating method and illustrating an instance of arrangement of a locally heated region in a cold rolled steel sheet for a grain oriented electrical steel sheet according to the present embodiment. [FIG. 2] A schema illustrating a distribution of Goss-oriented grains of a cold rolled steel sheet for a grain oriented electrical steel sheet according to an embodiment of the present invention. DESCRIPTION OF EMBODIMENTS

[0025] Hereinafter, a preferred embodiment of the present invention is described in detail. However, the present invention is not limited only to the configuration which is disclosed in the present embodiment, and various modifications are possible without departing from the aspect of the present invention. In addition, the limitation range as described below includes a lower limit and an upper limit thereof. However, the value represented by "more than" or "less than" does not include in the limitation range. Unless otherwise noted, "%" of the chemical composition represents "mass%".

[0026] As described above, the existence frequency of practical Goss-oriented grains having small angular deviation θ and small angular deviation ϕ from the {110}<001> orientation which is the ideal Goss orientation increases as the heating rate of the primary annealing (decarburization annealing) increases. On the other hand, for the grains of the {778}<447> (≈{111}<112>) orientation, the {411}<148> orientation, and the like which have a Σ9 coincidence site lattice relationship with the Goss orientation and tend to be encroached by Goss-oriented grains (referred to as CSL oriented grains), the existence frequency conversely decreases as the heating rate of the primary annealing increases. Therefore, it was difficult to increase the fraction of the CSL oriented grains while increasing the fraction of the practical Goss-oriented grains by the primary annealing.

[0027] In the technique described in Patent Document 1, linear grooves are formed on a surface of a steel sheet by etching treatment, a heating rate near the region of the linear grooves is to be increased during primary annealing, and thereby, the region (region of the linear grooves) having a large fraction of Goss-oriented grains and a region (region other than the linear groove) having a large fraction of CSL oriented grains are arranged. However, in this method, it is difficult to increase the difference in the heating rate during primary annealing between the region of the linear grooves and the other region, and the obtained effect is limited. Specifically, the difference between the heating rate in the region of the linear grooves and the heating rate in the region other than the linear grooves is not so large. For instance, even when the entire steel sheet is heated at 100 °C / sec, since the reduction of the thickness at the region by forming the grooves is only 10% or less as compared with the original thickness (since the depth of the grooves is 20 µm or less in general and is approximately 10% or less of the sheet thickness), the ratio between the heating rates is equal to or less than the ratio between the thicknesses for the same heat input when considering the thermal conduction of the steel sheet, and thus, the ratio between the fraction of the Goss-oriented grains in the region of the linear grooves and that in the region other than the linear grooves is less likely to increase as compared with the ration between the thickness in the region of the linear grooves and that in the region other than the linear grooves. In addition, in this method, the heating rate near the region of the linear grooves is increased during primary annealing, and thus, the grain size of the Goss-oriented grains formed in the region of the linear grooves after the primary annealing is not increased but is almost the same or fine as compared with the grain size of the primary recrystallized grains as an overall average.

[0028] In addition, in the technique described in Patent Document 2, the surface of the steel sheet is irradiated with a laser beam before final annealing. However, in this method, the laser beam irradiated region is only controlled to be the grain boundary of the secondary recrystallization, and the orientation of the Goss-oriented grains formed by the primary recrystallization is not controlled. In addition, the region heated by the laser irradiation is only the vicinity of the surface irradiated with the laser, the thermal diffusion to the peripheral region is remarkable, and thus, it is difficult to secure a thermal history that make the steel sheet recrystallize.

[0029] In addition, in the technique described in Patent Document 3, the sheet surface after cold rolling is irradiated with a laser beam. However, in this method, similarly to the above, the laser beam irradiated region is only controlled to be the grain boundary of the secondary recrystallization, the heating rate is not controlled, and the orientation of the Goss-oriented grains formed by the primary recrystallization is not controlled. In Patent Document 3, only the grain size of the secondary recrystallized grains in the rolling direction is reduced by making the laser beam irradiated region act as a barrier for the growth of the secondary recrystallized grains, and the temperature range of the grain growth in the locally heated region effective for increasing the size of the Goss-oriented grains in the locally heated region is not secured. Thus, in this method, the difference in the alignment degree to the Goss orientation in the inner and outer circumferences of the coil having different curvatures may be reduced, but the Goss-oriented grains having the crystal orientation close to the ideal Goss orientation cannot be obtained. That is, in this method, a decrease in the magnetic flux density is suppressed by coarsening the grain size of the secondary recrystallized grains in the rolling direction, but the orientation of the Goss-oriented grains is not fundamentally improved.

[0030] In the present embodiment, it has been found for the first time that a grain oriented electrical steel sheet having exceptional quality is obtained by performing local rapid heating on a steel sheet to form a locally heated region before performing primary annealing (decarburization annealing). The locally heated region that forms before the primary annealing is arranged locally on the surface of the steel sheet. The crystal structure of the locally heated region includes one or both of the recrystallized structure and the recovered structure at the end of the local rapid heating. The crystal structure of a non-locally heated region other than the locally heated region on the sheet surface consists of a cold-deformed structure which is as-cold rolled.

[0031] In the locally heated region, the heating rate is preferably 500 °C / sec or more, preferably 2000 °C / sec or more, preferably 5000 °C / sec or more, and more preferably 10000 °C / sec or more. As described above, it has been found that, when the locally heated region is formed on the surface of the steel sheet before the primary annealing, the grains having the practical Goss orientation are formed in the locally heated region. In addition, it has become clear that, among the Goss-oriented grains to be formed, the fraction of the Goss-oriented grains having small angular deviation θ and small angular deviation ϕ from the ideal Goss orientation is increased, and the grain size of the Goss-oriented grains is increased.

[0032] The frequency of Goss-oriented grains included in the locally heated region is higher than the frequency of Goss-oriented grains included in the non-locally heated region. This feature is derived from the deformed structure of the non-locally heated region. Specifically, it is derived from the fact that in a case where the local rapid heating is performed, recovery and recrystallization occur in the locally heated region and then the practical Goss-oriented grains tend to be formed and growth, but the recovery and recrystallization do not occur in the non-locally heated region.

[0033] The locally heated region having the above feature is dispersedly arranged on the surface of the steel sheet by the local rapid heating before primary annealing, and then the primary annealing and secondary annealing are further performed. The Goss-oriented grains formed in the locally heated region preferentially grow during secondary annealing after the primary annealing. Although Goss-oriented grains are formed in the locally heated region, and among them, the Goss-oriented grains that are close to the ideal Goss orientation, have particularly small angular deviation θ and small angular deviation ϕ, and have a large grain size are included. In the secondary recrystallization, the above Goss-oriented grains among the grains grow preferentially.

[0034] Since the Goss-oriented grains which act as the nucleus of the secondary recrystallization are arranged in the locally heated region, it is not necessary to form the Goss-oriented grains by the primary annealing in a matrix region other than the locally heated region, that is, the non-locally heated region other than the locally heated region. Accordingly, as the heat treatment condition of the primary annealing, a mild heating condition with a low heating rate may be employed, and a primary annealing condition may be employed in which a large number of CSL oriented grains having the {111}<112> orientation and the {411}<148> orientation, which are easily encroached, are formed in the non-locally heated region. For instance, by controlling the heating rate of the primary annealing to 300 °C / sec or less, a large number of Goss-oriented grains close to the ideal Goss orientation and having large grain size are formed in the locally heated region, while Goss-oriented grains are hardly formed in the non-locally heated region, and conversely, a large number of CSL oriented grains are formed.

[0035] As described above, in the locally heated region of the steel sheet (decarburization-annealed steel sheet) in which the local rapid heating and the primary annealing have been completed, a large number of Goss-oriented grains close to the ideal Goss orientation and having large grain size are included. On the other hand, in the matrix region (non-locally heated region), the Goss-oriented grains having large size are hardly included, whereas a large number of CSL oriented grains that are easily encroached may be included.

[0036] As an aspect of local rapid heating, a case where spot electric heating by electric resistance heating is used will be described. In the spot electric heating, spot electrodes are arranged and contacted so as to be opposite to each other on both surfaces of the steel sheet, and a current flows between the spot electrodes to perform the spot electric heating on a region where the electrodes are held on the steel sheet. Steel having the composition indicated in Table 1 was used, and hot rolling and cold rolling were performed to obtain a cold-rolled steel sheet having a thickness of 0.22 mm. The steel sheet was subjected to the spot electric heating. The spot electric heating was performed using copper electrodes having a diameter of 3 mmϕ under the conditions of a flowing current of 5.0 kA or less which was a range where the sheet surface was not melted, a time of current flow of 20 to 80 milliseconds, an electrode force of 50 to 150 kgf, and an electrode retention time after current flow of 0.2 seconds. On the surface of the cold-rolled steel sheet, the spot electric heating was performed in a grid pattern at a pitch of 30 mm in the rolling direction and a pitch of 30 mm in the width direction (transverse direction) to form the locally heated region.

[0037] FIG.1 illustrate an instance of arrangment of the locally heated region in the cold rolled steel for the grain oriented electrical steel sheet according to the present embodiment. In FIG. 1, the steel sheet 1, the locally heated regions 2, the rolling deirection 21, and the width direction (transverse direction) 22 are schematically illustrated. [Table 1]CHEMICAL COMPOSITION (mass%)CSiMnSAlN0.063.40.100.0060.0260.008

[0038] In order to prepare an observed section for Electron Back Scattering Diffraction pattern (EBSD) from the surface of a cold rolled steel sheet (cold rolled steel sheet after local rapid heating and before primary annealing), a surface was smoothed by mechanical polishing, and electrolytic polishing was performed to remove added strain of the surface. Thereafter, an image quality (IQ) value and a crystal orientation in a region including the locally heated region were measured by the EBSD under condition of a step of 0.5 µm. FIG. 2 is a schema illustrating a distribution of the Goss-oriented grains of the cold rolled steel sheet for the grain oriented electrical steel sheet according to the present embodiment.

[0039] In FIG. 2, an observed area including the locally heated region 2 and the non-locally heated region 3 (matrix region) are illustrated. The non-locally heated region 3 has the cold-deformed structure. Thus, when the IQ value is measured by EBSD after performing the above pretreatment on the surface of steel sheet, the non-locally heated region 3 shows the IQ value as the cold-deformed structure. The locally heated region 2 has a recovered structure and a recrystallized structure, and thus, the IQ value becomes higher than that of the cold-deformed structure. By the comparison of these IQ values, it is possible to identify the locally heated region 2 and the non-locally heated region 3 and to confirm the locally heated region 2, the non-locally heated region 3, and boundaries (locally heated region boundary 4). When it is not easy to identify the locally heated region boundary 4 by microstructure observation, the region including the Goss-oriented grains having the grain size of 5 µm or more can be regarded as the locally heated region 2.

[0040] An electrode used for spot electric heating has a circular shape, and the diameter thereof is preferably 0.5 to 10 mmϕ, and more preferably 1 to 5 mmϕ in an equivalent circle diameter. Note that, in the above description, the electrode having the circular shape is used, but in so far as the heating rate of the cold-rolled steel sheet is locally increased and Goss-oriented grains are formed and grown in this region, the electrode shape may be another shape, for instance, an elliptical shape or a linear shape.

[0041] In FIG. 2, based on the definition of the angular deviation ϕ = (α 2< + β 2< ) 1 / 2< , grains having the angular deviation ϕ of 10° or less from the ideal Goss orientation (Goss-oriented grains 14) are indicated by "∘". Further, among the grains having the angular deviation ϕ of 10° or less, grains having the grain size of 5 µm or more (coarse Goss-oriented grains 15) are indicated by "⊙".

[0042] As illustrated in FIG. 2, the cold rolled steel sheet (steel sheet 1) for the grain oriented electrical steel sheet according to the present embodiment includes the Goss-oriented grains 14 and also includes the coarse Goss-oriented grains 15. In particular, the region including the coarse Goss-oriented grains 15 corresponds to the locally heated region 2. Note that, the Goss-oriented grains are hardly observed in the matrix region 3 (non-locally heated region 3) where the local heating is not performed.

[0043] The above cold rolled steel sheet was subjected to the primary annealing (decarburization annealing). In the primary annealing, the cold rolled steel sheet was heated at a heating rate of 100 °C / sec and held at 830°C for 90 seconds. In a decarburization-annealed steel sheet after primary annealing, a large number of Goss-oriented grains were included in the locally heated region, and the grains were grown coarsely. On the other hand, the Goss-oriented grains were hardly observed in the matrix region (non-locally heated region).

[0044] The decarburization-annealed steel sheet was further subjected to nitridation, applying an annealing separator including MgO as a main component, and then secondary annealing. The secondary annealing conditions are a hydrogen-nitrogen atmosphere, a heating rate of 15 °C / hour, and holding at 1200°C for 20 hour. The obtained steel sheet was subjected to macroetching to reveal grain boundaries. When a region corresponding to the locally heated region was observed in the steel sheet after the macroetching, it was observed that plural secondary recrystallized grains grew from the region corresponding to the locally heated region or that the secondary recrystallized grain grew from the center of the region corresponding to the locally heated region. In addition, in the region corresponding to the locally heated region, fine grains of 2 mm or less may or may not be observed as a vestige of the locally heated region. Although the secondary recrystallized macrostructure may slightly change depending on the condition of the local heating, the alignment degree of the Goss orientation can be increased as compared with the case where the local heat treatment is not performed, and as a result, the magnetic flux density B 8 of the steel sheet is improved. It was confirmed for the crystal orientation of the obtained secondary recrystallized grains that the deviation from the ideal Goss orientation was extremely small (B 8 was improved from 1.911 T to 1.943 T in this steel sheet). As described above, the cold rolled steel sheet according to the present embodiment includes the coarse Goss-oriented grains 15 in addition to the Goss-oriented grains 14. It is considered that the coarse Goss-oriented grains 15 which are close to the ideal Goss orientation and which have the size advantage are formed, and thereby, the crystal orientation of the secondary recrystallized grains is improved.

[0045] The features of the cold rolled steel sheet for the grain oriented electrical steel sheet according to the present embodiment will be described in detail. The above cold rolled steel sheet shown in FIG. 2 satisfies the following features.

[0046] A cold rolled steel sheet for a grain oriented electrical steel sheet according to the present embodiment, wherein when a deviation angle from an ideal Goss orientation based on a rotation axis parallel to a normal direction is defined as α, when a deviation angle from the ideal Goss orientation based on a rotation axis parallel to a transverse direction is defined as β, when a deviation angle of a crystal orientation measured at a measurement point on a sheet surface is represented as (α β), when an angular deviation at the measurement point is defined as ϕ = (α 2< + β 2< ) 1 / 2< , when a grain having the angular deviation ϕ of 10° or less is defined as a Goss-oriented grain, when a region of 100 mm × 100 mm on the sheet surface is defined as a divided domain, and when it is confirmed whether the Goss-oriented grain is included in the divided domain in at least 100 divided domains, an area fraction of divided domains including at least one Goss-oriented grain having a grain size of 5 µm or more is 30% or more as compared with all divided domains.

[0047] For instance, the above domains are divided using the cold rolled steel sheet with 1000 mm in a longitudinal direction, a total area of the divided domains including at least one Goss-oriented grain having a grain size of 5 µm or more (coarse Goss-oriented grain) are measured, and then, the fraction as compared with an area of all divided domains may be calculated.

[0048] Herein, in the present embodiment, the above grain size is determined by identifying the grain boundaries where the disorientation from the adjacent measurement point is 1° or more. In addition, the above grain size indicates an equivalent circle diameter.

[0049] In addition, in the present embodiment, the angular deviation ϕ is defined using the deviation angle α and the deviation angle β. The general angular deviation θ is often evaluated using three components: the deviation angle α, the deviation angle β, and the deviation angle γ. However, since the present embodiment is particularly directed to improvement in magnetic flux density, the angular deviation ϕ is defined using two components: the deviation angle α and the deviation angle β except for the deviation angle γ which does not significantly influence the magnetic flux density.

[0050] In addition, the above coarse Goss-oriented grain is defined as the Goss-oriented grain having the grain size of 5 µm or more, but an upper limit of the grain size is not particularly limited. For instance, the upper limit of the grain size of the coarse Goss-oriented grain may be 100 µm.

[0051] In the cold rolled steel sheet according to the present embodiment, when at least one coarse Goss-oriented grain (coarse Goss-oriented grain close to ideal Goss orientation) is included in the divided domain of 100 mm × 100 mm on the cold rolled steel sheet and when the total area of the divided domains including the above coarse Goss-oriented grain is 30% or more as compared with all divided domains, the Goss-oriented grains grow in a preferable form in the secondary recrystallization, and thereby, it is possible to obtain the grain oriented electrical steel sheet having excellent magnetic characteristics.

[0052] In order to form the coarse Goss-oriented grain in the cold rolled steel sheet as explained above, it is necessary to promote the formation of Goss-oriented grain by increasing the heating rate in the locally heated region and to secure the time in which the recrystallized grain formed in the locally heated region is stayed in a temperature range where the grain can be grown after recrystallization. The above phenomenon (recrystallization and grain growth of Goss-oriented grain) does not occur under conditions such as laser irradiation and electron beam irradiation used in general magnetic domain control. In particular, in order to remain the coarse Goss-oriented grain in the locally heated region after primary recrystallization, it is effective to prolong the time from reaching the maximum temperature until cooling to 700°C during local rapid heating. For instance, it is effective that the holding time from reaching the maximum temperature until cooling to 700°C is 0.1 second or more. The holding time is preferably 0.2 second or more, and more preferably 0.3 second or more. For instance, by suppressing heat dissipation from the steel sheet using heated spot electrodes during local rapid heating, it is possible to promote the grain growth of formed Goss-oriented grain and to promote the formation of the Goss-oriented grain having the size effective in favorable secondary recrystallization and having the crystal orientation close to the ideal Goss orientation. As explained above, when a diameter of an electrode is 0.5 to 10 mmϕ in an equivalent circle diameter, it is possible to preferably secure the holding time from reaching the maximum temperature until cooling to 700°C. Under the general conditions of laser irradiation and electron beam irradiation, it is difficult to secure the holding time from reaching the maximum temperature until cooling to 700°C as described above.

[0053] It is preferable that the divided domains including at least one coarse Goss-oriented grain exist uniformly over the entire cold rolled steel sheet. However, the above condition may not be satisfied over the entire sheet surface of the cold rolled steel sheet. For instance, even when the divided domains including at least one coarse Goss-oriented grain are unevenly arranged in a part of the cold rolled steel sheet, when an area fraction of the divided domains is 30% or more as compared with all divided domains, the grain oriented electrical steel sheet having excellent magnetic characteristics can be finally obtained.

[0054] As explained above, when the local rapid heating is performed for the steel sheet after finishing the cold rolling, the coarse Goss-oriented grain 15 is formed in the locally heated region 2 as shown in FIG. 2. On the other hand, the coarse Goss-oriented grain is not formed in the non-locally heated region 3. Thus, by performing the local rapid heating so that the locally heated regions 2 are dispersedly arranged on the surface of cold rolled steel sheet, it is possible to control the distribution of the coarse Goss-oriented grains 15 on the surface of steel sheet.

[0055] The area fraction of divided domains including at least one coarse Goss-oriented grain (the Goss-oriented grain having the grain size of 5 µm or more) is preferably 50% or more, more preferably 70% or more, and more preferably 90% or more as compared with all divided domains.

[0056] In a case where a heat cycle is properly controlled during conventional secondary recrystallization annealing, the Goss-oriented grain having favorable orientation grows until approximately 100 mm. However, since an existence frequency of the Goss-oriented grains having favorable orientation is small in the primary recrystallized grains, the magnetic flux density B 8 increases only to approximately 1.911 T in the conventional technique. On the other hand, in the present embodiment, by performing the local heating for the divided domains of 30 area% or more as compared with all divided domains as explained above, the area fraction of divided domains including at least one coarse Goss-oriented grain is 30% or more as compared with all divided domains. Thus, in the present embodiment, the Goss-oriented grain having favorable orientation grows preferentially, and thus, the magnetic flux density is improved as compared with the conventional technique. Of course, when the area fraction of divided domains including at least one coarse Goss-oriented grain is 100% as compared with all divided domains, the magnetic flux density is further improved.

[0057] Moreover, when at least one locally heated region is included in each divided domain, the magnetic flux density B 8 is improved. However, the grain size after secondary recrystallization increases with a decrease in a number of the locally heated regions in the divided domain. In the steel sheet having the above feature, although the magnetic flux density is improved, the iron loss tends not to be improved without applying the magnetic domain control technique such as laser irradiation, linear grooves forming, and the like. Thus, for instance, in average, the formed locally heated regions are preferably 3 regions or more, more preferably 5 regions or more, and more preferably 9 regions or more in each divided domain of 100 mm × 100 mm.

[0058] When the cold rolled steel sheet according to the present embodiment is used, the coarse Goss-oriented grains close to the ideal Goss orientation are preferentially grown among Goss-oriented grains in the locally heated region during secondary recrystallization. Therefore, it is possible to obtain the steel sheet occupied by the secondary recrystallized grains close to the ideal Goss orientation without coarsening the secondary recrystallized grains. For instance, at the time when the locally heated regions are discretely arranged on the sheet surface, if the locally heated regions are appropriately arranged on the sheet surface, it is possible to control the size, shape, and arrangement of the grains after the secondary annealing. For instance, the Goss-oriented grain initiates to grow from one locally heated region, the grain growth stops when the grain encounters with another Goss-oriented grain which initiates to grow from an adjacent locally heated region, and thereby, the grain size of the Goss-oriented grains after secondary recrystallization becomes small. In the case, it is possible to obtain the steel sheet excellent in iron loss. In particular, as described above, in the initial stage of the secondary annealing, the Goss-oriented grains preferentially grown from the locally heated region have the crystal orientation close to the ideal Goss orientation, and as a result, excellent magnetic characteristics can be obtained even though the secondary recrystallized grain size is small.

[0059] That is, when the cold rolled steel sheet according to the present embodiment is used, it is possible to improve the magnetic flux density while suppressing coarsening of the secondary recrystallized grain size, and thus, it is possible to omit or reduce the refinement of the width of magnetic domain by applying the strain or forming the grooves. Specifically, since the effect of the magnetic domain refinement can be preferably obtained by the grain boundaries that increase as a result of the refinement of the secondary recrystallized grain size, the magnetic domain is refined without applying the conventional magnetic domain control technique. Therefore, it is not necessary to apply the strain into the steel sheet contrary to the conventional magnetic domain control technique, and thus, it is possible to suppress an increase in the magnetostriction (λ P-P ). In addition, it is not necessary to form the grooves on the steel sheet contrary to the conventional magnetic domain control technique, and thus, it is possible to suppress a decrease in the magnetic flux density B 8 . In addition, it is possible to use the grain oriented electrical steel sheet using the cold rolled steel sheet according to the present embodiment for utilization requiring the strain relief annealing at 800°C or higher.

[0060] Moreover, as explained above, in the cold rolled steel sheet according to the present embodiment, the coarse Goss-oriented grain included in the divided domain may have the grain size of 5 µm or more. In order to make the ideal Goss-oriented grain with size advantage further grow preferentially, the coarse Goss-oriented grain included in the divided domain may have preferably the grain size of 8 µm or more. Specifically, it is preferable that an area fraction of divided domains including at least one Goss-oriented grain having a grain size of 8 µm or more is 30% or more as compared with all divided domains. The area fraction of the divided domains is preferably 50% or more, more preferably 70% or more, and more preferably 90% or more as compared with all divided domains.

[0061] Herein, the above grain size of the Goss-oriented grains and the like may be measured by the EBSD. When the region to be measured is larger than the region that can be measured by the EBSD, the region to be measured may be divided and EBSD measurement may be performed plural times. For instance, in the EBSD measurement, the step size may be 0.5 µm.

[0062] Next, a preferred chemical composition of the cold rolled steel sheet according to the present embodiment will be described.

[0063] First, the chemical composition of the grain oriented electrical steel sheet as a final product manufactured using the cold rolled steel sheet according to the present embodiment will be described.

[0064] The grain oriented electrical steel sheet as the final product may contain, as a chemical composition, Si: 2.0% to 7.0% in mass percentage and the balance consisting of Fe and impurities.

[0065] In addition, this grain oriented electrical steel sheet may contain a known optional element as substitution for part of Fe for improving the magnetic characteristics. A lower limit of the optional element does not need to be limited, and the lower limit may be 0%. Moreover, an upper limit of the optional element may be a value in which the magnetic flux density or the iron loss does not significantly deteriorate. For instance, the upper limit of each optional element is described below.

[0066] The grain oriented electrical steel sheet (base steel sheet) as the final product may contain, as a chemical composition, by mass%, at least one of: C: 0.005% or less, Si: 2.0 to 7.0%, Mn: 1.00% or less, S and Se: 0.015% or less in total, Al: 0.065% or less, N: 0.005% or less, Nb, V, Mo, Ta, and W: 0.050% or less in total, Cu: 0.40% or less, Bi: 0.010% or less, B: 0.080% or less, P: 0.50% or less, Ti: 0.015% or less, Sn: 0.10% or less, Sb: 0.10% or less, Cr: 0.30% or less, and Ni: 1.00% or less.

[0067] The optional elements may be contained according to a known purpose, a lower limit of the optional elements does not need to be limited, and the lower limit may be 0%. Note that, the total amount of S and Se represents that at least one of S and Se is included and the amount thereof corresponds to the above total amount. Similarly, the total amount of one or more of Nb, V, Mo, Ta, and W represents that at least one of Nb, V, Mo, Ta, and W is included and the amount thereof corresponds to the above total amount.

[0068] In the grain oriented electrical steel sheet, the chemical composition changes relatively drastically (the amount of alloying element decreases) through the decarburization annealing and through the purification annealing during secondary recrystallization. Depending on the element, the content may be decreased to 50 ppm or less or may reach to an undetectable level (1 ppm or less) using the typical analytical methods if the purification annealing is sufficiently performed.

[0069] In addition, even if the above optional elements are contained as impurities, the effects of the present embodiment are not impaired. The impurities correspond to elements which are contaminated during industrial production of steel sheet from ores and scrap that are used as a raw material of steel, or from environment of a manufacturing process. For instance, an upper limit of the impurities may be 5% in total.

[0070] The chemical composition as described above may be measured by typical analytical methods for the steel. For instance, the chemical composition may be measured by using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometer: inductively coupled plasma emission spectroscopy spectrometry). Specifically, it is possible to obtain the chemical composition by conducting the measurement by ICP-AES (measurement device) under the condition based on calibration curve prepared in advance using samples with 35mm square taken from the steel sheet. In addition, C and S may be measured by the infrared absorption method after combustion, and N may be measured by the thermal conductometric method after fusion in a current of inert gas.

[0071] The chemical composition of the cold rolled steel sheet according to the present embodiment contains, for instance, the elements described below.

[0072] The cold rolled steel sheet according to the present embodiment may contain, as a chemical composition, by mass%: C: 0 to 0.0850%, Si: 2.0 to 7.0%, Mn: 0.05 to 1.0%, S and Se: 0.003 to 0.035% in total, Al: 0.010 to 0.0650%, N: 0 to 0.012%, Nb, V, Mo, Ta, and W: 0 to 0.050% in total, Cu: 0 to 0.40%, Bi: 0 to 0.010%, B: 0 to 0.080%, P: 0 to 0.50%, Ti: 0 to 0.0150%, Sn: 0 to 0.10%, Sb: 0 to 0.10%, Cr: 0 to 0.30%, Ni: 0 to 1.0%, and the balance consisting of Fe and impurities. C: 0 to 0.0850%

[0073] Carbon (C) is an element effective in controlling the primary recrystallized structure in the manufacturing process. Thus, the C content is 0.085% or less. A preferable upper limit of the C content is 0.075%. C is decarburized and purified in the decarburization annealing process explained below, and the content may be controlled to 0.0050% or less in order to suppress an occurrence of magnetic aging after final annealing process. In order to favorably suppress the magnetic aging, the C content is preferably 0.003% or less and more preferably 0.002% or less. The lower limit of the C content may be more than 0% from the productivity standpoint in the industrial production when C is included. However, since the C content depends on a decarburization annealing time, the lower limit may be 0.0001% in consideration of an annealing cost. Moreover, the lower limit may be 0.0005% in consideration of a manufacturing cost.Si: 2.0 to 7.0%

[0074] Silicon (Si) is an element which increases the electric resistance of the grain oriented electrical steel sheet and thereby decreases the iron loss. When the Si content is less than 2.0%, γ transformation occurs during the final annealing and the crystal orientation of the grain oriented electrical steel sheet is impaired. On the other hand, when the Si content is more than 7.0%, the cold workability deteriorates and the cracks tend to occur during cold rolling. The lower limit of the Si content is preferably 2.5%, and is more preferably 3.0%. The upper limit of the Si content is preferably 4.5%, and is more preferably 4.0%.Mn: 0.05 to 1.0%

[0075] Manganese (Mn) forms MnS and / or MnSe by bonding to S and / or Se, which act as the inhibitor. When Mn is included and the Mn content is 0.05 to 1.0%, the secondary recrystallization becomes stable. The nitride of the Nb group element (Nb, V, Mo, Ta, and W) can bear part of the function of the inhibitor. In the case, the inhibitor intensity as MnS and / or MnSe in general is controlled weakly. Thus, the upper limit of the Mn content is preferably 0.50%, and is more preferably 0.20%.S and Se: 0.003 to 0.035% in total

[0076] Sulfur (S) and Selenium (Se) form MnS and / or MnSe by bonding to Mn, which act as the inhibitor. When at least one of S and Se is included, and when the total amount of S and Se is 0.003 to 0.035%, the secondary recrystallization becomes stable. The nitride of the Nb group element can bear part of the function of the inhibitor. In the case, the inhibitor intensity as MnS and / or MnSe in general is controlled weakly. Thus, in a case of a low temperature slab heating process as the manufacturing method, the upper limit of the total amount of S and Se is preferably 0.025%, and is more preferably 0.010%. When S and / or Se remain in the steel after the final annealing, the compound is formed, and thereby, the iron loss is deteriorated. Thus, it is preferable to reduce S and Se as much as possible by the purification during the final annealing.

[0077] Here, the total amount of S and Se represents that at least one of S and Se is included and the amount thereof corresponds to the above total amount.Al: 0.010 to 0.0650%

[0078] Aluminum (Al) forms (Al, Si)N by bonding to N, which acts as the inhibitor. When Al is included and the Al content is 0.010 to 0.0650%, the inhibitor AlN formed by the nitridation mentioned below expands the temperature range of the secondary recrystallization, and the secondary recrystallization becomes stable especially in higher temperature range. Therefore, the Al content is 0.010 to 0.0650%. The lower limit of the Al content is preferably 0.020%, and is more preferably 0.025%. The upper limit of the Al content is preferably 0.040%, and is more preferably 0.035% from the stability standpoint in the secondary recrystallization.N: 0 to 0.012%

[0079] Nitrogen (N) bonds to Al and acts as the inhibitor. The lower limit thereof is not limited because it is possible to include N by the nitridation in midstream of the manufacturing process. For instance, the lower limit of the N content may be more than 0% or may be 0.001%. When N is included and the N content is more than 0.012%, the blister which is a kind of defect tends to be formed in the steel sheet. The upper limit of the N content is preferably 0.010%, and is more preferably 0.009%. N is purified in the final annealing process, and then, the N content becomes 0.005% or less after the final annealing process.

[0080] The balance of the chemical composition consists of Fe and impurities. The impurities correspond to elements which are contaminated during industrial production of steel from ores and scrap that are used as a raw material of steel, or from environment of a manufacturing process. For instance, an upper limit of the impurities may be 5% in total.Total of Nb, V, Mo, Ta, and W: 0 to 0.050%

[0081] The total amount of niobium (Nb), vanadium (V), molybdenum (Mo), tantalum (Ta), and tungsten (W) may be 0.050% or less. When the Nb group element (at least one of Nb, V, Mo, Ta, and W) is utilized as part of the inhibitor, the effect of improving B 8 is obtained. On the other hand, when the Nb group element remains excessively in the base steel sheet, the magnetic characteristics may be adversely affected. Therefore, the total amount of Nb, V, Mo, Ta, and W may be 0.050% or less. Further, when the total amount of the Nb group elements is 0.030% or less (preferably 0.003% or more and 0.030% or less), the secondary recrystallization starts at appropriate timing, which is preferable. Moreover, the orientation of the formed secondary recrystallized grain becomes very favorable, and the microstructure is finally controlled to be favorable for the magnetization characteristics. In particular, Nb and Ta prominently shows the above effects, which is preferable. The lower limit of the total amount of the Nb group elements does not need to be limited, and the lower limit may be 0%. The lower limit is preferably 0.003%.

[0082] The total amount of the Nb group elements is more preferably 0.004 to 0.020%. The total amount is more preferably 0.005 to 0.010%.

[0083] Here, the total amount of the Nb group elements represents that at least one of Nb, V, Mo, Ta, and W is included and the amount thereof corresponds to the above total amount.

[0084] In addition, the cold rolled steel sheet according to the present embodiment may contain, as the optional element, by mass%, at least one of: 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%, and Ni: 0 to 1.0%.

[0085] The optional elements may be contained according to a known purpose, a lower limit of the optional elements does not need to be limited, and the lower limit may be 0%.

[0086] The chemical composition of the cold rolled steel sheet according to the present embodiment may be measured by the above analytical methods, as with the chemical composition of the grain oriented electrical steel sheet as the final product.

[0087] Next, an aspect of a preferred method for manufacturing the cold rolled steel sheet for the grain oriented electrical steel sheet according to the present embodiment will be described.

[0088] The method for manufacturing the cold rolled steel sheet according to the present embodiment is not limited to the following method. The following manufacturing method is an instance for manufacturing the cold rolled steel sheet according to the present embodiment.

[0089] Moreover, the processes and the quantitative conditions in each process described below are an instance employed to confirm the operability of the present embodiment, so that the present embodiment is not limited to the processes and the quantitative values. The method for manufacturing the cold rolled steel sheet according to the present embodiment can employ various types of conditions as long as the conditions do not depart from the scope of the present embodiment and can achieve the object of the present embodiment.

[0090] In the method for manufacturing the cold rolled steel sheet according to the present embodiment, it is possible to apply a conventional known method for manufacturing the grain oriented electrical steel sheet as fundamental processes. For instance, the conventional method for manufacturing the grain oriented electrical steel sheet includes a manufacturing method utilizing MnS and AlN as inhibitor which are formed by high temperature slab heating, a manufacturing method utilizing AlN as inhibitor which is formed by low temperature slab heating and subsequent nitridation, and the like. The method for manufacturing the cold rolled steel sheet according to the present embodiment is not limited to a specific manufacturing method. Hereinafter, the method which employs the low temperature slab heating with the nitridation is explained for instance.(Casting Process)

[0091] In the casting process, a slab is made. For instance, a method for making the slab is as follow. A molten steel is made (a steel is melted). The slab is made by using the molten steel. The slab may be made by continuous casting. An ingot may be made by using the molten steel, and then, the slab may be made by blooming the ingot. A thickness of the slab is not particularly limited. The thickness of the slab may be 150 to 350 mm for instance. The thickness of the slab is preferably 220 to 280 mm. The slab with the thickness of 10 to 70 mm which is a so-called thin slab may be used. When using the thin slab, it is possible to omit a rough rolling before final rolling in the hot rolling process.

[0092] For instance, as the chemical composition, the above slab may include the following elements.C: 0.085% or less

[0093] Carbon (C) is an element effective in controlling the primary recrystallized structure in the manufacturing process. However, when the content in the final product is excessive, the magnetic characteristics are negatively affected. Thus, the C content may be 0.085% or less. The upper limit of the C content is preferably 0.075%. C is decarburized and purified in the decarburization annealing process and the final annealing process, and then, the content becomes 0.005% or less. When C is included, the lower limit of the C content may be more than 0%, and may be 0.001% from the productivity standpoint in the industrial production.Si: 2.0 to 7.0%

[0094] Silicon (Si) is an element which increases the electric resistance of the grain oriented electrical steel sheet and thereby decreases the iron loss. When the Si content is less than 2.0%, an austenite transformation occurs during the final annealing and the crystal orientation of the grain oriented electrical steel sheet is impaired. On the other hand, when the Si content is more than 7.0%, the cold workability deteriorates and the cracks tend to occur during cold rolling. The lower limit of the Si content is preferably 2.5%, and is more preferably 3.0%. The upper limit of the Si content is preferably 4.5%, and is more preferably 4.0%.Mn: 0.05 to 1.00%

[0095] Manganese (Mn) forms MnS and / or MnSe by bonding to S and / or Se, which act as the inhibitor. When Mn is included and the Mn content is 0.05 to 1.00%, the secondary recrystallization becomes stable. The nitride of the Nb group element can bear part of the function of the inhibitor. In the case, the inhibitor intensity as MnS and / or MnSe in general is controlled weakly. Thus, the upper limit of the Mn content is preferably 0.50%, and is more preferably 0.20%.At least one of S and Se: 0.003 to 0.035% in total

[0096] Sulfur (S) and Selenium (Se) form MnS and / or MnSe by bonding to Mn, which act as the inhibitor. When at least one of S and Se is included, and when the total amount of S and Se is 0.003 to 0.035%, the secondary recrystallization becomes stable. The nitride of the Nb group element can bear part of the function of the inhibitor. In the case, the inhibitor intensity as MnS and / or MnSe in general is controlled weakly. Thus, the upper limit of the total amount of S and Se is preferably 0.025%, and is more preferably 0.010%. When S and / or Se remain in the steel after the final annealing, the compound is formed, and thereby, the iron loss is deteriorated. Thus, it is preferable to reduce S and Se as much as possible by the purification during the final annealing.

[0097] Here, the total amount of S and Se represents that at least one of S and Se is included and the amount thereof corresponds to the above total amount.Al: 0.010 to 0.065%

[0098] Aluminum (Al) forms (Al, Si)N by bonding to N, which acts as the inhibitor. When Al is included and the Al content is 0.010 to 0.065%, the inhibitor AlN formed by the nitridation mentioned below expands the temperature range of the secondary recrystallization, and the secondary recrystallization becomes stable especially in higher temperature range. Therefore, the Al content is 0.010 to 0.065%. The lower limit of the Al content is preferably 0.020%, and is more preferably 0.025%. The upper limit of the Al content is preferably 0.040%, and is more preferably 0.035% from the stability standpoint in the secondary recrystallization.N: 0.012% or less

[0099] Nitrogen (N) bonds to Al and acts as the inhibitor. The lower limit thereof is not limited because it is possible to include N by the nitridation in midstream of the manufacturing process. For instance, the lower limit of the N content may be more than 0% or may be 0.001%. When N is included and the N content is more than 0.012%, the blister which is a kind of defect tends to be formed in the steel sheet. The upper limit of the N content is preferably 0.010%, and is more preferably 0.009%. N is purified in the final annealing process, and then, the N content becomes 0.005% or less after the final annealing process.

[0100] The balance of the chemical composition consists of Fe and impurities. The impurities correspond to elements which are contaminated during industrial production of steel from ores and scrap that are used as a raw material of steel, or from environment of a manufacturing process. For instance, an upper limit of the impurities may be 5% in total.

[0101] In addition to solving manufacturing problems, in consideration of the influence on the magnetic characteristics and the improvement of the inhibitors function by forming compounds, the above chemical composition may include the known optional elements as substitution for part of Fe. For instance, the optional elements as substitution for part of Fe may be the following elements.Nb group element: 0.050% or less

[0102] The total amount of the Nb group element (at least one of Nb, V, Mo, Ta, and W) may be 0.050% or less. When the Nb group element (at least one of Nb, V, Mo, Ta, and W) is utilized as part of the inhibitor, and when the total amount of the Nb group element is 0.030% or less, the secondary recrystallization starts at appropriate timing, which is preferable. Moreover, the orientation of the formed secondary recrystallized grain becomes very favorable, and the microstructure is finally controlled to be favorable for the magnetization characteristics. In particular, Nb and Ta prominently shows the above effects, which is preferable. The lower limit of the total amount of the Nb group elements does not need to be limited, and the lower limit may be 0%. The lower limit is preferably 0.003%.

[0103] The total amount of the Nb group elements is more preferably 0.004 to 0.020%. The total amount is more preferably 0.005 to 0.010%.

[0104] Here, the total amount of the Nb group elements represents that at least one of Nb, V, Mo, Ta, and W is included and the amount thereof corresponds to the above total amount.

[0105] In addition, the slab may contain, as the optional element, by mass%, at least one of: Cu: 0.40% or less, Bi: 0.010% or less, B: 0.080% or less, P: 0.50% or less, Ti: 0.015% or less, Sn: 0.10% or less, Sb: 0.10% or less, Cr: 0.30% or less, and Ni: 1.00% or less.

[0106] The optional elements may be contained according to a known purpose, a lower limit of the optional elements does not need to be limited, and the lower limit may be 0%.

[0107] The chemical composition of the slab may be measured by the above analytical methods, as with the chemical composition of the grain oriented electrical steel sheet as the final product.(Hot Rolling Process)

[0108] In the hot rolling process, the slab is heated to a predetermined temperature (for instance, 1100 to 1400°C), and then, is subjected to hot rolling in order to obtain a hot rolled steel sheet. In the hot rolling process, for instance, the silicon steel material (slab) is heated in heating stage, is rough-rolled, and then, is final-rolled in order to obtain the hot rolled steel sheet with a predetermined thickness, for instance, 1.8 to 3.5 mm. After finishing the final rolling, the hot rolled steel sheet is coiled at a predetermined temperature.

[0109] In a case where of a process including the nitridation during decarburization annealing or after decarburization annealing, the inhibitor intensity as MnS is not necessarily needed, it is preferable that the slab heating temperature is 1100 to 1280°C from the productivity standpoint.(Hot-Band Annealing Process)

[0110] In the hot band annealing process, the hot rolled steel sheet after the hot rolling process is annealed under predetermined conditions (for instance, 750 to 1200°C for 30 seconds to 10 minutes) in order to obtain a hot band annealed sheet. The hot-band annealing is generally performed to control the microstructure of the steel sheet such as the recrystallization fraction, the residual strain, and the grain size by annealing the hotrolled steel sheet after the hot rolling process and to preferably control the morphology of precipitates in the steel. For instance, in high temperature slab heating process, the above process is to finally control the morphology of precipitates such as AlN, and the conditions are controlled so that the precipitates are uniformly and finely precipitated. For instance, as the hot band annealing, the steel sheet may be heated to 1050°C to 1150°C, may be slow-cooled to an intermediate temperature (850°C to 950°C) for 50 to 150 seconds in order to appropriately precipitates AlN and the like, and thereafter, may be water-cooled.(Cold Rolling Process)

[0111] In the cold rolling process, the hot band annealed sheet after the hot band annealing process is cold-rolled once or is cold-rolled plural times (two times or more) with an annealing (intermediate annealing) (for instance, 80 to 95% of total cold reduction) in order to obtain a cold rolled steel sheet with a thickness, for instance, 0.10 to 0.50 mm. In order to improve the magnetic characteristics, for instance, an interpass temperature of the cold rolling may be approximately 100°C to 300°C.

[0112] The total cold reduction of cold rolling is defined as follows. (Local Rapid Heating Process)

[0113] In the present embodiment, local rapid heating for forming the locally heated region is performed on the cold-rolled steel sheet after the cold rolling process. The rapid heating method is not particularly limited as long as the steel sheet can be locally heated. For instance, it is possible to adopt a method in which spot electrodes are arranged and contacted on both surfaces of the steel sheet and the steel sheet is heated by flowing a current in the steel sheet, a method in which the steel sheet is heated by irradiating the surface thereof with laser beam, electron beam, and the like, a method in which the steel sheet is locally heated by induction heating, a method in which the steel sheet is heated by contacting a heated piece, and the like. The size of each locally heated region may be a dotted region having a diameter of approximately 10 µm to 10 mm or a linear region having a width of approximately 10 µm to 10 mm. In addition, the electrode used for electric heating may be a circular electrode or a linear electrode as described above.

[0114] Note that regarding the size of the locally heated region, the minimum diameter and the minimum width depend on the shape of the spot electrode and the technique of reducing the focusing diameter of the laser beam or the electron beam. Although it is possible in principle to further reduce the size of the locally heated region, it is considered that the effect can be obtained when the size of the locally heated region is 1 µm or more in consideration of the fact that the nucleus of the recrystallized grain has a size of approximately 1 µm under the present conditions. However, in the present embodiment, in order to form the Goss-oriented grain having the grain size of 5 µm or more, the minimum diameter and the minimum width may be 10 µm or more. In addition, with respect to the size of the locally heated region, when the maximum diameter or the maximum width exceeds 10 mm, the area fraction of the Goss-oriented grains having relatively large angular deviation θ or angular deviation ϕ that cannot grow out of the locally heated region increases. In this case, it is difficult to obtain the effect of performing local rapid heating.

[0115] In the local rapid heating, the heating rate may be 500 °C / sec or more at a central position of the locally heated region as viewed in the thickness direction and at a thickness 1 / 5 position of the steel sheet. When the heating rate is 500 °C / sec or more at the above region, the microstructure of the locally heated region can be preferably controlled to a recovered structure or a recrystallized structure. The heating rate is preferably 2000 °C / sec or more, and more preferably 10000 °C / sec or more. On the other hand, the upper limit of the heating rate is not particularly limited, and the upper limit may be, for instance, 1000000 °C / sec.

[0116] In addition, it is preferable that the heating rate is controlled with the heating rate during decarburization annealing described below. For instance, it is difficult to obtain the intended effect when the heating rate during decarburization annealing is faster than the heating rate during local rapid heating. Therefore, although depending on the degree of the value of the heating rate, the heating rate during local rapid heating is preferably equal to or more than the heating rate during decarburization annealing.

[0117] Herein, the thickness 1 / 5 position of the steel sheet indicates a depth corresponding to 1 / 5 of the thickness of the steel sheet from the surface of the steel sheet along the thickness direction.

[0118] In addition, in the local rapid heating, the maximum attained temperature may be 700°C or more at the central position of the locally heated region as viewed in the thickness direction and at the thickness 1 / 5 position of the steel sheet. When the maximum attained temperature is 700°C or more in the above region, the microstructure of the locally heated region can be preferably controlled to the recovered structure or the recrystallized structure. The maximum attained temperature is preferably 800°C or higher, and more preferably 900°C or higher. On the other hand, the maximum attained temperature may be equal to or lower than the melting point of the steel sheet, and may be, for instance, 1400°C or lower.

[0119] In addition, in the local rapid heating, the holding time from reaching the maximum temperature until cooling to 700°C may be 0.1 seconds or more at the central position of the locally heated region as viewed in the thickness direction and at the thickness 1 / 5 position of the steel sheet. When the holding time is 0.1 seconds or more in the above region, the microstructure of the locally heated region can be preferably controlled to the recovered structure or the recrystallized structure. The holding time is preferably 0.2 seconds or more, more preferably 0.3 seconds or more, and still more preferably 0.4 seconds or more. On the other hand, the upper limit of the holding time is not particularly limited, and the upper limit may be, for instance, 10 seconds or less. The holding time from reaching the maximum temperature until cooling to 700°C has essentially affected the formation of the coarse Goss-oriented grains close to the ideal Goss orientation.

[0120] In the local rapid heating, it is important to control the above holding time in addition to the heating rate and the maximum attained temperature described above. During this holding time, it is possible to form a sub-grain structure or a recrystallized nucleus, which is advantageous for the formation of the coarse Goss-oriented grains in the locally heated region. As a result, it is possible to form the Goss-oriented grain having the grain size of 5 µm or more in the locally heated region after the local rapid heating. By the control described above through the holding time in the locally heated region, it is possible to preferably control the microstructure in the subsequent process.

[0121] As described above, the method of local rapid heating is not particularly limited. For instance, local rapid heating may be performed by spot electric heating, laser irradiation, or electron beam irradiation. Any local rapid heating method may be controlled so as to satisfy the heating rate, the maximum attained temperature, and the holding time described above. A person skilled in the art can combine the conditions of the local rapid heating, and thereby, can control the heating rate, maximum attained temperature, and holding time according to the purpose.

[0122] For instance, a person skilled in the art can control the heating rate and the maximum attained temperature at the central position of the locally heated region as viewed in the thickness direction and at the thickness 1 / 5 position of the steel sheet by performing thermal conductivity analysis using finite element method. Additionally, a person skilled in the art can control the above holding time by controlling conditions of heat dissipation after reaching the maximum temperature. For instance, in the case of spot electric heating, the electrode retention time after current flow may be controlled, or the shape of the spot electrode may be changed to a shape suitable for heat dissipation. In addition, in the case of laser irradiation or electron beam irradiation, the irradiation speed may be adjusted, or the shape of irradiated region may be changed to an ellipse and the like to add a gradient to the irradiation energy from the central region toward the outer edge region in irradiated region.

[0123] In general, in heating by laser irradiation, only the vicinity of the irradiated sheet surface is preferentially heated, and the inside of the steel sheet is hardly heated. In addition, since heating by laser irradiation is non-contact heating, heat dissipation after heating is fast, and it is difficult to hold the temperature. Therefore, when heating by laser irradiation is performed as the local rapid heating, in order to recover or recrystallize the cold-deformed structure in the laser-irradiated region, it is necessary to perform heating under a condition of heating not only the sheet surface but also the inside of the steel sheet and under a condition of relatively coarsening the sub-grain structure in the laser-irradiated region by slowing the cooling rate. The condition of laser irradiation for performing the local rapid heating is quite different from the condition of laser irradiation for performing the magnetic domain refinement. For instance, even if the condition of laser irradiation for performing magnetic domain refinement (usually 0.5 to 50 mJ / mm 2< ) is applied to the present embodiment, the microstructure of the locally heated region cannot be controlled in a preferable one, and the coarse Goss-oriented grains close to the ideal Goss orientation are not formed in the cold rolled steel sheet. In addition, the situation with electron beam irradiation is the same as with laser irradiation. Even if the condition of electron beam irradiation for performing magnetic domain refinement is applied to the present embodiment, the microstructure of the locally heated region cannot be controlled in a preferable one, and the coarse Goss-oriented grains close to the ideal Goss orientation are not formed in the cold rolled steel sheet.

[0124] Note that, even when the input power of laser irradiation or electron beam irradiation is simply increased, it is difficult to form the coarse Goss-oriented grains close to the ideal Goss orientation. For instance, when the rapid heating is performed by laser irradiation or electron beam irradiation, it is preferable to make the beam shape elliptical or control the scan speed and the like in order to secure a temperature range where the grains in the region grow after the rapid heating.

[0125] Conventionally, in an electrical steel sheet, laser irradiation and electron beam irradiation have been performed to reduce the iron loss by performing magnetic domain control on the steel sheet after secondary recrystallization. Under conditions of these laser irradiation and electron beam irradiation, since approximately 20 µm from the surface of the steel sheet is heated, heat dissipation after heating is fast. Therefore, under the conventional conditions, it is difficult to secure the holding time from reaching the maximum temperature until cooling to 700°C as described above. That is, under the conditions of conventional laser irradiation and electron beam irradiation, it may be possible to make the irradiated region act as a barrier for the growth of the secondary recrystallized grains, but it is difficult to form the coarse Goss-oriented grains having the orientation close to the ideal Goss orientation as in the present embodiment. In order to form the coarse Goss-oriented grains close to the ideal Goss orientation by laser irradiation or electron beam irradiation, it is necessary to investigate conditions of laser irradiation or electron beam irradiation as described above.

[0126] Through the above processes, the cold rolled steel sheet for the grain oriented electrical steel sheet according to the present embodiment can be manufactured. In the cold rolled steel sheet according to the present embodiment manufactured comprehensively and inseparably by controlling each condition of each process, the coarse Goss-oriented grains are formed in a preferable form in the steel sheet.

[0127] Hereinafter, a method for manufacturing the grain oriented electrical steel sheet using the cold rolled steel sheet according to the present embodiment will be described.(Decarburization Annealing Process)

[0128] 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 existence frequency of the Goss-oriented grains formed in the locally heated region is increased, the grain size of the Goss-oriented grains is increased, and the coarse Goss-oriented grains having the orientation close to the ideal Goss orientation are preferably grown. As conditions of the decarburization annealing, for instance, the annealing temperature may be 700 to 900°C, and the annealing time may be 1 to 3 minutes. By performing decarburization annealing on the cold-rolled steel sheet, C included in the cold-rolled steel sheet is removed. In order to remove "C" included in the cold rolled steel sheet, it is preferable that the decarburization annealing is conducted in moist atmosphere.

[0129] In addition, it is effective to reduce the primary recrystallized grain size by controlling the conditions of the hot rolling and hot-band annealing described above and by decreasing the decarburization annealing temperature as necessary. The primary recrystallized grain size is not particularly limited but is preferably 8 to 30 µm.

[0130] In addition, in the present embodiment, the coarse Goss-oriented grains having the orientation close to the ideal Goss orientation are formed in the locally heated region. Therefore, it is not necessary to form the Goss-oriented grains again by decarburization annealing. Thus, the heating rate of the decarburization annealing does not need to be increased. On the other hand, it is preferable to decrease the heating rate of the decarburization annealing in order to form {111}<112> oriented grains or {411}<148> oriented grains that are easily encroached in the matrix region (non-locally heated region).

[0131] In addition, the amount of oxidation caused by the decarburization annealing and the state of surface oxidized layer affect the formation of the glass film. Therefore, in the decarburization annealing, the oxidation degree (PH 2 O / PH 2 ) in the annealing atmosphere (furnace atmosphere) may be controlled as necessary.(Nitridation)

[0132] Nitridation 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 controlling the inhibitor intensity in secondary recrystallization. In the nitridation, the nitrogen content of the steel sheet is made to increase to 40 to 200 ppm from starting the decarburization annealing to starting the secondary recrystallization in the final annealing. For instance, the nitridation may be a treatment of annealing the steel sheet in an atmosphere containing a gas having a nitriding ability such as ammonia, a treatment of final-annealing the decarburization annealed steel sheet being applied an annealing separator containing a powder having a nitriding ability such as MnN and the like. The nitrogen content after the nitridation is preferably 130 to 350 ppm, and more preferably 150 to 250 ppm.(Annealing Separator Applying Process)

[0133] In the annealing separator applying process, the decarburization-annealed steel sheet is applied an annealing separator to. For instance, as the annealing separator, it is possible to use an annealing separator mainly including MgO. The decarburization-annealed steel sheet after applying the annealing separator is coiled and is final-annealed in the subsequent final annealing process.(Final Annealing Process)

[0134] In the final annealing process, the decarburization annealed steel sheet after applying the annealing separator is final-annealed so that the secondary recrystallization (secondary annealing) occurs. In the process, the secondary recrystallization proceeds under conditions such that the grain growth of the primary recrystallized grain is suppressed by the inhibitor. Thereby, the grain having the {110}<001> orientation is preferentially grown, and the magnetic flux density is drastically improved.

[0135] The heating rate in the heating stage of the final annealing process is not particularly limited. For instance, the heating may be performed at a heating rate of 3 to 20 °C / hour. Moreover, slow heating may be performed in a temperature range of 1000 to 1200°C during heating. For instance, the heating rate in the temperature range of 1000 to 1200°C during heating is preferably 3 to 12 °C / hour, more preferably 3 to 9 °C / hour, and preferably 3 to 7 °C / hour. Otherwise, holding may be performed by stopping heating once in the heating stage of the final annealing process. For instance, the heating may be stopped once in a temperature range of 1050 to 1100°C during heating, and the holding may be performed for 5 hours or more and 15 hours or less. For instance, the adjustment of the heating rate in the temperature range of secondary recrystallization influences a decomposition rate of the inhibitor, and thus, it is possible to improve the magnetic flux density.

[0136] After the heating stage of the final annealing process, as a holding stage (purification annealing), holding may be performed for 10 hours or more and 60 hours or less in a temperature range of 1000°C or more and 1300°C or less. The atmosphere during final annealing may be, for instance, a nitrogen atmosphere or a mixed atmosphere of nitrogen and hydrogen.(Insulating Coating Forming Process)

[0137] A coating solution including phosphoric acid or phosphate, chromic anhydride or chromate, and colloidal silica is applied to the steel sheet, and is baked (for instance, 350 to 1150°C for 5 to 300 seconds) to form the insulation coating.(Others)

[0138] The grain oriented electrical steel sheet may be subjected to magnetic domain refinement for forming local minute strain or grooves by a known method such as laser, plasma, a mechanical method, or etching as necessary. However, in the grain oriented electrical steel sheet manufactured using the cold rolled steel sheet according to the present embodiment, coarsening of the secondary recrystallized grain size is suppressed even though the magnetic flux density is excellent, and thus, the magnetic domains are refined without performing magnetic domain refinement treatment.Example 1

[0139] Hereinafter, the effects of the present invention are described in detail with reference to the following examples. However, the condition in the examples is an example condition employed to confirm the operability and the effects of the present invention, so that the present invention is not limited to the example condition. The present invention can employ various types of conditions as long as the conditions do not depart from the scope of the present invention and can achieve the object of the present invention.

[0140] Using slabs having adjusted chemical composition as materials, cold rolled steel sheets with chemical composition shown in Table 2A were manufactured. The chemical composition was measured by the above-mentioned methods. In Table 2, "-" indicates that the control and manufacturing conscious of content did not perform and thus, the content was not measured.

[0141] When the cold rolled steel sheets were manufactured, the slabs were heated to 1150°C, and then hot-rolled to obtain the hot rolled steel sheets having the thickness of 2.6 mm. The hot rolled steel sheets were subjected to the hot band annealing in which the annealing was conducted at 1100°C and then at 900°C, and then were pickled in order to remove the surface scale. The steel sheets were cold-rolled once or cold-rolled plural times with the intermediate annealing to obtain the cold rolled steel sheets having the final thickness of 0.22 mm.

[0142] The cold-rolled steel sheets were subjected to local rapid heating under conditions shown in Tables 3 to 7. For spot electric heating, copper electrodes having a diameter of 3 mm which corresponds to contact area with the steel sheet were used, and then, the heating rate, the maximum attained temperature, the holding time from reaching the maximum temperature until cooling to 700°C (holding time above 700°C) were respectively controlled by comprehensively adjusting the electrode shape other than the contact area with the steel sheet, the electrode force, the flowing current, the time of current flow, the electrode retention time after current flow, and the like. For laser heating, fiber laser was used, focusing spot diameter of laser beam in the rolling direction (specifically, diameter including 86% of laser output) was to be 30 µm (except for Test Nos. 85 and 86), and then, the heating rate, the maximum attained temperature, the holding time above 700°C were respectively controlled by comprehensively adjusting the energy density of laser irradiation, the laser scanning speed, the shape of laser irradiated region, and the like. A person skilled in the art can combine the conditions of the local rapid heating, and thereby, can control the heating rate, the maximum attained temperature, and the holding time above 700°C according to the purpose.

[0143] Note that, in Test No. 83, the laser beam was elongated along scanning direction, and thereby, the holding time from reaching the maximum temperature until cooling to 700°C was controlled to 0.2 seconds in the local rapid heating, in order to form the coarse Goss-oriented grains having the orientation close to the ideal Goss orientation in the locally heated region. In Test No. 84, the general condition of laser irradiation for performing the magnetic domain refinement was applied. In Test No. 85, the focusing spot diameter was 0.5mm, and the energy density of laser irradiation was 2.0 J / mm 2< , in order to control the irradiated region of laser beam to be finally the grain boundary of the secondary recrystallization. In Test No. 86, the focusing spot diameter was 0.5mm, and the energy density of laser irradiation was 30.0 J / mm 2< , in order to control the irradiated region of laser beam to be finally the grain boundary of the secondary recrystallization.

[0144] For the manufactured cold rolled steel sheets, the divided domains including at least one Goss-oriented grain having the grain size of 5 µm or more were measured by the above-mentioned methods. The results are indicated in Tables 8 to 12. Herein, the measurement on EBSD was performed on a surface of which was parallel to the surface of steel sheet and was at 20 µm toward the thickness direction. From the IQ value of EBSD, it was confirmed that the crystal structure of the locally heated region was the recrystallized structure and the recovered structure, and the crystal structure of the non-locally heated region other than the locally heated region was the deformed structure.

[0145] In the tables, "Not performed" of heating method of local rapid heating indicates that the local rapid heating was not performed. "Linear or Dotted" of local heating condition indicates the shape of the locally heated region on the surface of the cold-rolled steel sheet, and "Spacing in rolling direction" and "Spacing in width direction" of local heating condition indicates the spacing in the rolling direction and the transverse direction in which the locally heated regions were arranged on the surface of the cold-rolled steel sheet. The locally heated regions were uniformly arranged at even spacing in the rolling direction and the transverse direction. For instance, when both "Spacing in rolling direction" and "Spacing in width direction" are 100 mm or less, the locally heated regions were arranged in all the divided domains. On the other hand, when either "Spacing in rolling direction" or "Spacing in width direction" is more than 100 mm, the divided domain where the locally heated region was not arranged existed. Herein, among all the divided domains, the divided domains where the locally heated region was arranged were arranged so that the distribution was not uneven.

[0146] Moreover, in the tables, "Fraction of locally heated domains" of local heating condition indicates an area fraction of divided domains including the locally heated region on the surface of the steel sheet. Specifically, when a region of 100 mm × 100 mm on the sheet surface is defined as a divided domain, and when it is confirmed in at least 100 divided domains whether the locally heated region is included in the divided domain, "Fraction of locally heated domains" corresponds to the value obtained by dividing the total area of divided domains including the locally heated region by the area of all divided domains, and the value is showed as 100 percent in the tables.

[0147] In the same way, in the tables, "Area fraction of divided domains including the Goss-oriented grain having the grain size of 5 µm or more" of the manufacturing results indicates an area fraction of divided domains including the coarse Goss-oriented grain on the surface of the cold rolled steel sheet. Specifically, when a region of 100 mm × 100 mm on the sheet surface is defined as a divided domain, and when it is confirmed in at least 100 divided domains whether the Goss-oriented grain (coarse Goss-oriented grain) having the equivalent circle diameter of 5 µm or more for the grains which is determined under conditions such that the angular deviation ϕ = (α 2< + β 2< ) 1 / 2< is 10° or less and that the grain boundaries are identified as the boundary where the disorientation is 1° or more is included in the divided domain, "Area fraction of divided domains including the Goss-oriented grain having the grain size of 5 µm or more" corresponds to the value obtained by dividing the total area of divided domains including the coarse Goss-oriented grain by the area of all divided domains, and the value is showed as 100 percent in the tables. Herein, the Goss-oriented grain having the grain size of 5 µm or more was hardly observed in the matrix region (non-locally heated region) other than the locally heated region.

[0148] The manufactured cold-rolled steel sheets were subjected to decarburization annealing under the conditions shown in Tables 8 to 12. Herein, in the decarburization annealing, the oxidation degree (PH 2 O / PH 2 ) in the annealing atmosphere (furnace atmosphere) was 0.13.

[0149] The manufactured decarburization-annealed steel sheet was subjected to nitridation at 750°C in nitrogen-hydrogen-ammonia atmosphere, and the nitrogen content of the steel sheet was to be 220 ppm. Thereafter, the annealing separator including MgO as a main component was applied and the final annealing was performed. In the final annealing, the steel sheet was heated to 1000°C (or heated to 1070°C in a case of the following "step", ) at the heating rate of 15 °C / hour in a mixed atmosphere of hydrogen and nitrogen, and thereafter, heated to 1200°C under one of the following conditions. And then, the steel sheets were held at 1200°C - 20hour in a hydrogen atmosphere. Normal: heated at 15 °C / hour from 1000°C to 1200°C. Slow Heating 1: heated at 10 °C / hour from 1000°C to 1200°C. Slow Heating: heated at 7.5 °C / hour from 1000°C to 1200°C. Slow Heating 2: heated at 5.0 °C / hour from 1000°C to 1200°C. Step: held for 10 hours at 1070°C.

[0150] For the steel sheet after the final annealing, the coating solution for forming insulation coating which mainly included the phosphate and the colloidal silica and which included the chromic anhydride as necessary was applied and baked to form the insulating coating.

[0151] Various features of the obtained grain oriented electrical steel sheet were evaluated. The evaluation results are shown in Tables 8 to 12.

[0152] The magnetic characteristics of the grain oriented electrical steel sheet were measured based on the single sheet tester (SST) method regulated by JIS C 2556: 2015.

[0153] The samples of 20 sheets with a size of 100 mm × 500 mm for the single sheet tester were taken from the obtained grain oriented electrical steel sheets, and then, the single sheet test was performed. As the magnetic characteristics, the magnetic flux density B 8 (T) in the rolling direction of the steel sheet was measured under the condition such that the steel sheet was excited at 800 A / m. The magnetic flux density B 8 was judged to as acceptable or not based on the Si content of the steel sheet and the conditions of final annealing. Specifically, the steel sheets were classified as the steel A to Z where the Si content was 3.3 to 3.5%, the steel AA where the Si content was 2.5%, and the steel AB where the Si content was 4.1%, and then, the steel sheets were compared under the same conditions of final annealing. When the difference of the magnetic flux density B 8 as compared with B 8 of the steel sheet in which the local rapid heating did not performed was 0.010T or more in the same conditions, it was judged to as acceptable. For instance, since the magnetic flux density B 8 of the test No. 1 in which the steel type was "steel A", the condition of final annealing was "Normal", and the local rapid heating was "Not performed" was 1.911T, it was judged to as acceptable for the steel sheet in which the steel type was "steel A" and the condition of final annealing was "Normal" when the magnetic flux density B 8 became 1.921T or more by the local rapid heating.

[0154] Moreover, for reference, as the magnetic characteristics, the iron loss W 17 / 50 (W / kg) which was defined as the power loss per unit weight (1 kg) of the steel sheet was measured under the conditions of 50 Hz of AC frequency and 1.7 T of excited magnetic flux density.

[0155] In the cold rolled steel sheets which were the inventive examples among Nos. 1 to 89, the "Area fraction of divided domains including the Goss-oriented grain having the grain size of 5 µm or more" was favorably controlled. These inventive examples showed excellent magnetic flux density even though coarsening of the secondary recrystallized grain size was suppressed as the grain oriented electrical steel sheet. In addition, since coarsening of the secondary recrystallized grain size was suppressed, these inventive examples also showed excellent iron loss.

[0156] In addition, although not shown in the tables, in the cold rolled steel sheets which were the inventive examples among Nos. 1 to 89, the value of the area fraction of divided domains including at least one Goss-oriented grain having the grain size of 8 µm or more was the same as that of the area fraction of divided domains including at least one Goss-oriented grain having the grain size of 5 µm or more.

[0157] On the other hand, in the cold rolled steel sheets which were the comparative examples among Nos. 1 to 89, the "Area fraction of divided domains including the Goss-oriented grain having the grain size of 5 µm or more" was not favorably controlled. In these comparative examples, excellent magnetic flux density was not obtained as the grain oriented electrical steel sheet. [Table 3]No.STEEL TYPEMANUFACTURING CONDITIONSTOTAL COLD REDUCTION OF COLD ROLLINGLOCAL RAPID HEATINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONLINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONFRACTION OF LOCALLY HEATED DOMAINS%°C / sec°Csecmmmm%1A91.5NOT PERFORMED------02A91.5SPOT ELECTRIC50009000.3DOTTED300300113A91.5SPOT ELECTRIC50009000.3DOTTED200200254A91.5SPOT ELECTRIC50009000.3DOTTED150150445A91.5SPOT ELECTRIC50009000.3DOTTED120120696A91.5SPOT ELECTRIC50009000.3DOTTED1001001007A91.5SPOT ELECTRIC50009000.3DOTTED16030638A91.5SPOT ELECTRIC50009000.3DOTTED12030839A91.5SPOT ELECTRIC50009000.3DOTTED803010010A91.5SPOT ELECTRIC50009000.3DOTTED603010011A91.5SPOT ELECTRIC50009000.3DOTTED503010012A91.5SPOT ELECTRIC50009000.3DOTTED303010013A91.5SPOT ELECTRIC50009000.3DOTTED153010014A91.5NOT PERFORMED------015A91.5SPOT ELECTRIC50009000.3DOTTED160306316A91.5SPOT ELECTRIC50009000.3DOTTED120308317A91.5SPOT ELECTRIC50009000.3DOTTED803010018A91.5SPOT ELECTRIC50009000.3DOTTED6030100 [Table 4] No.STEEL TYPEMANUFACTURING CONDITIONSTOTAL COLD REDUCTION OF COLD ROLLINGLOCAL RAPID HEATINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONLINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONFRACTION OF LOCALLY HEATED DOMAINS%°C / sec°Csecmmmm%19A91.5SPOT ELECTRIC50009000.3DOTTED503010020A91.5SPOT ELECTRIC50009000.3DOTTED303010021A91.5SPOT ELECTRIC50009000.3DOTTED153010022A91.5NOT PERFORMED------023A91.5SPOT ELECTRIC50009000.3DOTTED160306324A91.5SPOT ELECTRIC50009000.3DOTTED120308325A91.5SPOT ELECTRIC50009000.3DOTTED803010026A91.5SPOT ELECTRIC50009000.3DOTTED603010027A91.5SPOT ELECTRIC50009000.3DOTTED503010028A91.5SPOT ELECTRIC50009000.3DOTTED505010029A91.5SPOT ELECTRIC50009000.3DOTTED3010010030A91.5SPOT ELECTRIC50009000.3DOTTED1003010031A91.5SPOT ELECTRIC50009000.3DOTTED10010010032A91.5SPOT ELECTRIC50009000.3DOTTED303010033A91.5SPOT ELECTRIC50009000.3DOTTED153010034A91.5NOT PERFORMED------035A91.5NOT PERFORMED------036AA92.1NOT PERFORMED------0 [Table 5] No.STEEL TYPEMANUFACTURING CONDITIONSTOTAL COLD REDUCTION OF COLD ROLLINGLOCAL RAPID HEATINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONLINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONFRACTION OF LOCALLY HEATED DOMAINS%°C / sec°Csecmmmm%37AB89.0NOT PERFORMED------038A91.5SPOT ELECTRIC50009000.3DOTTED303010039AA92.1SPOT ELECTRIC50009000.3DOTTED303010040AB89.0SPOT ELECTRIC50009000.3DOTTED303010041A90.4NOT PERFORMED------042A90.4SPOT ELECTRIC50009000.3DOTTED202010043B90.4SPOT ELECTRIC50009000.3DOTTED202010044C90.4SPOT ELECTRIC50009000.3DOTTED202010045D90.4SPOT ELECTRIC50009000.3DOTTED202010046E90.4SPOT ELECTRIC50009000.3DOTTED202010047F90.4SPOT ELECTRIC50009000.3DOTTED202010048G90.4SPOT ELECTRIC50009000.3DOTTED202010049H90.4SPOT ELECTRIC50009000.3DOTTED202010050I90.4SPOT ELECTRIC50009000.3DOTTED202010051J90.4SPOT ELECTRIC50009000.3DOTTED202010052K90.4SPOT ELECTRIC50009000.3DOTTED202010053L90.4SPOT ELECTRIC50009000.3DOTTED202010054M90.4SPOT ELECTRIC50009000.3DOTTED2020100 [Table 6] No.STEEL TYPEMANUFACTURING CONDITIONSTOTAL COLD REDUCTION OF COLD ROLLINGLOCAL RAPID HEATINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONLINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONFRACTION OF LOCALLY HEATED DOMAINS%°C / sec°Csecmmmm%55N90.4SPOT ELECTRIC50009000.3DOTTED202010056O90.4SPOT ELECTRIC50009000.3DOTTED202010057P90.4SPOT ELECTRIC50009000.3DOTTED202010058Q90.4SPOT ELECTRIC50009000.3DOTTED202010059R90.4SPOT ELECTRIC50009000.3DOTTED202010060S90.4SPOT ELECTRIC50009000.3DOTTED202010061T90.4SPOT ELECTRIC50009000.3DOTTED202010062U90.4SPOT ELECTRIC50009000.3DOTTED202010063V90.4SPOT ELECTRIC50009000.3DOTTED202010064W90.4SPOT ELECTRIC50009000.3DOTTED202010065X90.4SPOT ELECTRIC50009000.3DOTTED202010066Y90.4SPOT ELECTRIC50009000.3DOTTED202010067Z90.4SPOT ELECTRIC50009000.3DOTTED202010068A90.4NOT PERFORMED------069A90.4SPOT ELECTRIC50009000.3DOTTED30301070A90.4SPOT ELECTRIC50009000.3DOTTED30302071A90.4SPOT ELECTRIC50009000.3DOTTED30303072A90.4SPOT ELECTRIC50009000.3DOTTED303040 [Tbale 7] No.STEEL TYPEMANUFACTURING CONDITIONSTOTAL COLD REDUCTION OF COLD ROLLINGLOCAL RAPID HEATINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONLINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONFRACTION OF LOCALLY HEATED DOMAINS%°C / sec°Csecmmmm%73A90.4SPOT ELECTRIC50009000.3DOTTED30305074A90.4SPOT ELECTRIC50009000.3DOTTED30306075A90.4SPOT ELECTRIC50009000.3DOTTED30307076A90.4SPOT ELECTRIC50009000.3DOTTED30308077A90.4SPOT ELECTRIC50009000.3DOTTED30309078A90.4SPOT ELECTRIC50009000.3DOTTED303010079A91.5SPOT ELECTRIC50009000.3DOTTED10010010080A91.5SPOT ELECTRIC50009000.2DOTTED10010010081A91.5SPOT ELECTRIC50009000.1DOTTED10010010082A91.5SPOT ELECTRIC50009000.03DOTTED10010010083A90.4LASER20008000.2LINEAR10-10084A90.4LASER< 2000< 200< 0.03LINEAR10-10085A90.4LASER5000800< 0.03LINEAR10-10086A90.4LASER7000800< 0.03LINEAR10-10087A91.5SPOT ELECTRIC5009000.3DOTTED10010010088A91.5SPOT ELECTRIC20009000.3DOTTED10010010089A91.5SPOT ELECTRIC100009000.3DOTTED100100100 [Table 8] No.STEEL TYPEMANUFACTURING CONDITIONSMANUFACTURING RESULTSEVALUATION RESULTSNOTEDECARBURIZATION ANNEALINGFINAL ANNEALINGAREA FRACTION OF DIVIDED DOMAINS INCLUDING THE GOSS-ORIENTED GRAIN HAVING THE GRAIN SIZE OF 5 µm OR MOREMAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50HEATING RATEANNEALING TEMPERATUREANNEALING TIMEANNEALING PROCEDUREHEATING RATE TO 1000°CHEATING RATE TO 1200°C°C / sec°Csec°C / hr°C / hr%TW / kg1A100850100NORMAL151501.9110.839COMPARATIVE EXAMPLE2A100850100NORMAL1515111.9120.835COMPARATIVE EXAMPLE3A100850100NORMAL1515251.9150.830COMPARATIVE EXAMPLE4A100850100NORMAL1515441.9250.814INVENTIVE EXAMPLE5A100850100NORMAL1515691.9300.807INVENTIVE EXAMPLE6A100850100NORMAL15151001.9330.804INVENTIVE EXAMPLE7A100850100NORMAL1515631.9260.833INVENTIVE EXAMPLE8A100850100NORMAL1515831.9290.820INVENTIVE EXAMPLE9A100850100NORMAL15151001.9350.797INVENTIVE EXAMPLE10A100850100NORMAL15151001.9370.789INVENTIVE EXAMPLE11A100850100NORMAL15151001.9380.784INVENTIVE EXAMPLE12A100850100NORMAL15151001.9400.755INVENTIVE EXAMPLE13A100850100NORMAL15151001.9430.729INVENTIVE EXAMPLE14A100850100SLOW HEATING157.501.9220.828COMPARATIVE EXAMPLE15A100850100SLOW HEATING157.5631.9370.811INVENTIVE EXAMPLE16A100850100SLOW HEATING157.5831.9400.798INVENTIVE EXAMPLE17A100850100SLOW HEATING157.51001.9460.775INVENTIVE EXAMPLE18A100850100SLOW HEATING157.51001.9480.767INVENTIVE EXAMPLE [Table 9] No.STEEL TYPEMANUFACTURING CONDITIONSMANUFACTURING RESULTSEVALUATION RESULTSNOTEDECARBURIZATION ANNEALINGFINAL ANNEALINGAREA FRACTION OF DIVIDED DOMAINS INCLUDING THE GOSS-ORIENTED GRAIN HAVING THE GRAIN SIZE OF 5 µm OR MOREMAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50HEATING RATEANNEALING TEMPERATUREANNEALING TIMEANNEALING PROCEDUREHEATING RATE TO 1000°CHEATING RATE TO 1200°C°C / sec°Csec°C / hr°C / hr%TW / kg19A100850100SLOW HEATING157.51001.9490.762INVENTIVE EXAMPLE20A100850100SLOW HEATING157.51001.9510.733INVENTIVE EXAMPLE21A100850100SLOW HEATING157.51001.9540.707INVENTIVE EXAMPLE22A100850100Step151501.9410.814COMPARATIVE EXAMPLE23A100850100Step1515631.9580.834INVENTIVE EXAMPLE24A100850100Step1515831.9640.807INVENTIVE EXAMPLE25A100850100Step15151001.9690.761INVENTIVE EXAMPLE26A100850100Step15151001.9710.728INVENTIVE EXAMPLE27A100850100Step15151001.9720.712INVENTIVE EXAMPLE28A100850100Step15151001.9700.753INVENTIVE EXAMPLE29A100850100Step15151001.9680.751INVENTIVE EXAMPLE30A100850100Step15151001.9670.786INVENTIVE EXAMPLE31A100850100Step15151001.9630.802INVENTIVE EXAMPLE32A100850100Step15151001.9730.679INVENTIVE EXAMPLE33A100850100Step15151001.9740.648INVENTIVE EXAMPLE34A100850100NORMAL151501.9110.839COMPARATIVE EXAMPLE35A100850100SLOW HEATING 215501.9300.816COMPARATIVE EXAMPLE36AA100850100SLOW HEATING 215501.9530.887COMPARATIVE EXAMPLE [Table 10] No.STEEL TYPEMANUFACTURING CONDITIONSMANUFACTURING RESULTSEVALUATION RESULTSNOTEDECARBURIZATION ANNEALINGFINAL ANNEALINGAREA FRACTION OF DIVIDED DOMAINS INCLUDING THE GOSS-ORIENTED GRAIN HAVING THE GRAIN SIZE OF 5 µm OR MOREMAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50HEATING RATEANNEALING TEMPERATUREANNEALING TIMEANNEALING PROCEDUREHEATING RATE TO 1000°CHEATING RATE TO 1200°C°C / sec°Csec°C / hr°C / hr%TW / kg37AB100850100SLOW HEATING 215501.8750.798COMPARATIVE EXAMPLE38A100850100SLOW HEATING 21551001.9590.697INVENTIVE EXAMPLE39AA100850100SLOW HEATING 21551001.9770.765INVENTIVE EXAMPLE40AB100850100SLOW HEATING 21551001.9250.662INVENTIVE EXAMPLE41A100850100SLOW HEATING 1151001.9130.826COMPARATIVE EXAMPLE42A100850100SLOW HEATING 115101001.9460.693INVENTIVE EXAMPLE43B100850100SLOW HEATING 115101001.9690.651INVENTIVE EXAMPLE44C100850100SLOW HEATING 115101001.9500.680INVENTIVE EXAMPLE45D100850100SLOW HEATING 115101001.9480.685INVENTIVE EXAMPLE46E100850100SLOW HEATING 115101001.9460.696INVENTIVE EXAMPLE47F100850100SLOW HEATING 115101001.9570.674INVENTIVE EXAMPLE48G100850100SLOW HEATING 115101001.9660.657INVENTIVE EXAMPLE49H100850100SLOW HEATING 115101001.9630.675INVENTIVE EXAMPLE50I100850100SLOW HEATING 115101001.9560.688INVENTIVE EXAMPLE51J100850100SLOW HEATING 115101001.9500.698INVENTIVE EXAMPLE52K100850100SLOW HEATING 115101001.9670.654INVENTIVE EXAMPLE53L100850100SLOW HEATING 115101001.9580.675INVENTIVE EXAMPLE54M100850100SLOW HEATING 115101001.9610.687INVENTIVE EXAMPLE [Table 11] No.STEEL TYPEMANUFACTURING CONDITIONSMANUFACTURING RESULTSEVALUATION RESULTSNOTEDECARBURIZATION ANNEALINGFINAL ANNEALINGAREA FRACTION OF DIVIDED DOMAINS INCLUDING THE GOSS-ORIENTED GRAIN HAVING THE GRAIN SIZE OF 5 µm OR MOREMAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50HEATING RATEANNEALING TEMPERATUREANNEALING TIMEANNEALING PROCEDUREHEATING RATE TO 1000°CHEATING RATE TO 1200°C°C / sec°Csec°C / hr°C / hr%TW / kg55N100850100SLOW HEATING 115101001.9680.656INVENTIVE EXAMPLE56O100850100SLOW HEATING 115101001.9530.678INVENTIVE EXAMPLE57P100850100SLOW HEATING 115101001.9500.685INVENTIVE EXAMPLE58Q100850100SLOW HEATING 115101001.9480.687INVENTIVE EXAMPLE59R100850100SLOW HEATING 115101001.9460.702INVENTIVE EXAMPLE60S100850100SLOW HEATING 115101001.9590.671INVENTIVE EXAMPLE61T100850100SLOW HEATING 115101001.9490.683INVENTIVE EXAMPLE62U100850100SLOW HEATING 115101001.9460.697INVENTIVE EXAMPLE63V100850100SLOW HEATING 115101001.9470.690INVENTIVE EXAMPLE64W100850100SLOW HEATING 115101001.9480.686INVENTIVE EXAMPLE65X100850100SLOW HEATING 115101001.9490.684INVENTIVE EXAMPLE66Y100850100SLOW HEATING 115101001.9620.631INVENTIVE EXAMPLE67Z100850100SLOW HEATING 115101001.9410.677INVENTIVE EXAMPLE68A100850100Step151501.9410.814COMPARATIVE EXAMPLE69A100850100Step1515101.9420.814COMPARATIVE EXAMPLE70A100850100Step1515201.9430.812COMPARATIVE EXAMPLE71A100850100Step1515301.9530.783INVENTIVE EXAMPLE72A100850100Step1515401.9540.751INVENTIVE EXAMPLE [Table 12] No.STEEL TYPEMANUFACTURING CONDITIONSMANUFACTURING RESULTSEVALUATION RESULTSNOTEDECARBURIZATION ANNEALINGFINAL ANNEALINGAREA FRACTION OF DIVIDED DOMAINS INCLUDING THE GOSS-ORIENTED GRAIN HAVING THE GRAIN SIZE OF 5 µm OR MOREMAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50HEATING RATEANNEALING TEMPERATUREANNEALING TIMEANNEALING PROCEDUREHEATING RATE TO 1000°CHEATING RATE TO 1200°C°C / sec°Csec°C / hr°C / hr%TW / kg73A100850100Step1515501.9580.739INVENTIVE EXAMPLE74A100850100Step1515601.9620.727INVENTIVE EXAMPLE75A100850100Step1515701.9650.715INVENTIVE EXAMPLE76A100850100Step1515801.9670.703INVENTIVE EXAMPLE77A100850100Step1515901.9700.691INVENTIVE EXAMPLE78A100850100Step15151001.9730.679INVENTIVE EXAMPLE79A100850100NORMAL15151001.9330.804INVENTIVE EXAMPLE80A100850100NORMAL15151001.9310.808INVENTIVE EXAMPLE81A100850100NORMAL15151001.9290.810INVENTIVE EXAMPLE82A100850100NORMAL1515201.9140.835COMPARATIVE EXAMPLE83A30083090SLOW HEATING 115101001.9380.674INVENTIVE EXAMPLE84A30083090SLOW HEATING 1151001.9090.841COMPARATIVE EXAMPLE85A30083090SLOW HEATING 11510101.9110.822COMPARATIVE EXAMPLE86A30083090SLOW HEATING 11510151.9100.814COMPARATIVE EXAMPLE87A10083090SLOW HEATING 115101001.9280.817INVENTIVE EXAMPLE88A10083090SLOW HEATING 115101001.9320.809INVENTIVE EXAMPLE89A10083090SLOW HEATING 115101001.9400.776INVENTIVE EXAMPLE INDUSTRIAL APPLICABILITY

[0158] According to the above aspects of the present invention, it is possible to provide a cold rolled steel sheet for a grain oriented electrical steel sheet. Specifically, it is possible to provide the cold rolled steel sheet for the grain oriented electrical steel sheet capable of increasing the magnetic flux density while suppressing coarsening of the secondary recrystallized grain size. Accordingly, the present invention has significant industrial applicability.REFERENCE SIGNS LIST

[0159] 1Steel sheet 2Locally heated region 3Non-locally heated region (matrix region) 4Locally heated region boundary 14Goss-oriented grain 15Coarse Goss-oriented grain (Goss-oriented grain having grain size of 5 µm or more) 21Rolling direction 22Width direction (transverse direction)

Examples

example 1

[0139]Hereinafter, the effects of the present invention are described in detail with reference to the following examples. However, the condition in the examples is an example condition employed to confirm the operability and the effects of the present invention, so that the present invention is not limited to the example condition. The present invention can employ various types of conditions as long as the conditions do not depart from the scope of the present invention and can achieve the object of the present invention.

[0140]Using slabs having adjusted chemical composition as materials, cold rolled steel sheets with chemical composition shown in Table 2A were manufactured. The chemical composition was measured by the above-mentioned methods. In Table 2, "-" indicates that the control and manufacturing conscious of content did not perform and thus, the content was not measured.

[0141]When the cold rolled steel sheets were manufactured, the slabs were heated to 1150°C, and then hot-r...

TECHNICAL FIELD

[0001] The present invention relates to a cold rolled steel sheet for a grain oriented electrical steel sheet.

[0002] Priority is claimed on Japanese Patent Application No. 2023-106555, filed June 29, 2023, the content of which is incorporated herein by reference.BACKGROUND ART

[0003] A grain oriented electrical steel sheet includes Si, the crystal orientation of the grains thereof closely aligns in the Goss orientation (cubic crystal {110}<001>), and the <001> orientation, which is a magnetization easy axis, is substantially aligned in the rolling direction in the steel sheet manufacturing process. Such a grain oriented electrical steel sheet is very desirable as a material for an iron core and the like of a transformer. Among the magnetic characteristics of the grain oriented electrical steel sheet, magnetic flux density and iron loss are particularly important.

[0004] The magnetic flux density of the grain oriented electrical steel sheet when a predetermined magnetizing force is applied tends to increase as the degree to which the magnetization easy axes of the grains are aligned in the rolling direction of the steel sheet, that is, the orientation of the grains is higher. A magnetic flux density B 8 is generally used as an index representing the magnetic flux density. The magnetic flux density B 8 is a value of the magnetic flux density of the grain oriented electrical steel sheet excited at a magnetizing force of 800 A / m in the rolling direction. That is, the grain oriented electrical steel sheet having a larger value of the magnetic flux density B 8 is more easily magnetized with a certain magnetizing force, the magnetic flux density becomes high, and thus it is suitable for a small-sized and highly efficient transformer.

[0005] In addition, an iron loss W 17 / 50 is generally used as an index representing the iron loss. The iron loss W 17 / 50 is an iron loss when the grain oriented electrical steel sheet is excited by alternating current so as to be a maximum magnetic flux density of 1.7 T under the condition of a frequency of 50 Hz. The grain oriented electrical steel sheet having a smaller value of the iron loss W 17 / 50 has a lower energy loss and is suitable for a transformer.

[0006] The methods for reducing the iron loss include a method of increasing the electric resistance by containing Si, a method of reducing the thickness of the steel sheet, and a method of decreasing the grain size, which are effective for reducing the eddy-current loss, and a method of aligning the orientation of the grains which is effective for reducing the hysteresis loss. That is, when the value of the magnetic flux density B 8 becomes higher, the crystal orientation is aligned with the Goss orientation, and the hysteresis loss is reduced. Thus, when the value of the magnetic flux density B 8 becomes higher, the value of the iron loss W 17 / 50 tends to be lower. On the other hand, when the growth of Goss-oriented grains is promoted in order to improve the alignment degree of the crystal orientation, the grain size tends to coarsen, and the eddy-current loss increases. Thus, when the grains are excessively coarse even when the value of B 8 is high, the iron loss tends to deteriorate. As explained above, there is an antinomy.

[0007] In recent years, in order to purposely refine a width of magnetic domain, a method of controlling the magnetic domain by applying strain by irradiation with laser beam, plasma jet, and the like, or by forming grooves by mechanical processing, etching, and the like has been developed. By using such a method, in the steel sheet in which the alignment degree of the crystal orientation is increased and the magnetic flux density is increased, the eddy-current loss can be reduced, and the iron loss can be sufficiently reduced even when the secondary recrystallized grain size coarsens. However, when the strain is applied into the steel sheet, magnetostriction (λ P-P ) increases due to the strain. In addition, when heat treatment is performed at a temperature of approximately 800°C after the magnetic domain refinement, the effect of reducing the iron loss disappears, and therefore the above steel sheet cannot be used for utilization requiring strain relief annealing at 800°C or higher after irradiation. On the other hand, in the magnetic domain refinement using the grooves, there is a problem in that the magnetic flux density B 8 decreases.

[0008] In general, the grain oriented electrical steel sheet is manufactured as described below. A steel sheet material (slab) including a predetermined amount of Si is subjected to hot rolling, annealing, and cold rolling to obtain a steel sheet having a desired thickness. Then, the steel sheet after cold rolling is annealed (this is also referred to as primary annealing or decarburization annealing). By this annealing, primary recrystallization occurs, and grains having a crystal orientation in which the magnetization easy axes are aligned in the rolling direction and a deviation angle from an ideal Goss orientation expressed by {110}<001> is 10° or less (hereinafter, referred to as Goss-oriented grains) are formed in the primary recrystallized grains. This annealing is also performed as decarburization annealing. Thereafter, an annealing separator including MgO as a main component is applied to the surface of the steel sheet in which primary recrystallization has occurred. Subsequently, the steel sheet to which the annealing separator has been applied is coiled to prepare a steel sheet coil, and this steel sheet coil is subjected to batch treatment annealing (also referred to as secondary recrystallization annealing or final annealing). By this annealing, the Goss-oriented grains encroach on other grains, secondary recrystallization occurs, and a so-called glass film is formed on the surface of the steel sheet. At the time of secondary recrystallization, due to the effect of an inhibitor included in the steel sheet, the Goss-oriented grains preferentially grow, and the grain size may be 100 mm or more in coarse grains. Next, uncoiling the steel sheet coil, annealing for flattening the steel sheet in which the secondary recrystallization has occurred, forming an insulating coating, and the like are performed.

[0009] As described above, the grain oriented electrical steel sheet obtains the desired magnetic properties by inducing the secondary recrystallization during final annealing to obtain a crystal structure including Goss-oriented grains aligned in the {110}<001> orientation. In order to obtain this crystal structure, it is effective to increase an existence frequency of Goss-oriented grains which are minor or increase the existence frequency of grains having higher lattice matching with the Goss-oriented grains by the primary annealing. For instance, grains of the {778} <447> (≈ {111}<112>) orientation and the {411}<148> orientation which have higher lattice matching with the {110}<001> orientation and a Σ9 coincidence site lattice relationship with a Goss orientation (referred to as CSL oriented grains) are the grains easily encroached by Goss-oriented grains, and thus, it is effective to include a large amount of the above grains in the primary recrystallized structure. However, when the crystal orientation of the grains formed by the primary annealing is controlled, it is difficult to simultaneously improve the existence frequency of the Goss-oriented grains and the existence frequency of the grains having the coincidence site lattice relationship. For instance, in a case where the cold rolling reduction is 85% or more, the existence frequency of the CSL oriented grains which are easily encroached by the Goss-oriented grains increases as the cold rolling reduction increases, whereas the existence frequency of the Goss-oriented grains decreases as the cold rolling reduction increases. In addition, the existence frequency of the Goss-oriented grains which are minor in the primary recrystallization texture increases as the heating rate of the primary annealing increases, whereas the existence frequency of the CSL oriented grains having the {111}<112> orientation which are major in the primary recrystallization texture conversely decreases as the heating rate of the primary annealing increases.

[0010] That is, under conventional process control conditions, the existence frequency of the Goss-oriented grains and the existence frequency of the CSL oriented grains that are easily encroached by the Goss-oriented grains cannot be controlled independently.

[0011] Here, in regard to the crystal orientation which is identified in the grain oriented electrical steel sheet, a deviation angle from the ideal {110}<001> orientation around the normal direction Z (ND) is referred to as a deviation angle α, a deviation angle from the ideal {110}<001> orientation around the transverse direction C (TD) is referred to as a deviation angle β, and a deviation angle from the ideal {110}<001> orientation around the rolling direction L (RD) is referred to as a deviation angle γ. Then, an angular deviation θ is defined as the angular deviation from the ideal {110}<001> orientation obtained by the following (Formula 1) using the deviation angles α, β, and γ around the ND, TD, and RD of the crystal orientation identified in the grain oriented electrical steel sheet. θ = α 2 + β 2 + γ 2 1 / 2

[0012] As described above, the Goss-oriented grains are not grains having a Goss orientation (ideal Goss orientation) (referred to as ideal Goss-oriented grains) in a strict sense. A direction of the magnetization easy axis (cubic crystal {110}<001>) of each grain and the rolling direction do not always completely coincide with each other, and the angular deviation θ exists between the direction of the magnetization easy axis and the rolling direction. On the basis of (Formula 1), a grain in which the angular deviation θ from the ideal Goss orientation is 10° or less is referred to as the Goss-oriented grain (practical Goss-oriented grain). When the angular deviation θ of the practical Goss-oriented grain increases, the orientation of the grains decreases, and the magnetic flux density B 8 decreases.

[0013] In general, grains having large angular deviation θ are also mixed in the Goss-oriented grains included in the steel sheet after primary recrystallization. However, when grains grow by secondary recrystallization, except for the effect of size advantage of grain at an initial stage of secondary recrystallization, the grains having small angular deviation θ among the Goss-oriented grains have a larger driving force of grain growth and continue to grow preferentially until the secondary recrystallization is completed. Therefore, when the angular deviation θ of the Goss-oriented grains is smaller, the grain size after secondary recrystallization tends to be larger. That is, in a manufacturing method in which secondary recrystallized grains are highly made to align in the Goss orientation, specific grains are preferentially grown, and thus, the grains size necessarily tends to coarsen.

[0014] In addition, at the time of secondary recrystallization, the steel sheet is not flat but curved since it is coiled in a coil shape, but the grains grow while maintaining the linearity of the crystal orientation. Therefore, when the coiled steel sheet is uncoiled and made to be flat after secondary recrystallization, a region in which the direction of the magnetization easy axis is not parallel to the surface of the grain oriented electrical steel sheet arises in the grains. Due to uncoiling explained above, the value of the deviation angle β mainly increases, and the angular deviation θ also increases. The increase in the angular deviation θ due to uncoiling becomes excessive as the grain size increases. That is, the Goss-oriented grains having small angular deviation θ tend to preferentially grow during secondary recrystallization, but when the secondary recrystallized grain size is coarse, the angular deviation θ increases due to uncoiling.

[0015] Patent Document 1 discloses a technique in which linear grooves satisfying a predetermined condition are formed by performing an etching treatment on the surface of steel sheet after final cold rolling, and a heating rate in a temperature range where a steel sheet temperature is 500°C or more and 750°C or less is increased in a region of the linear grooves as compared with a region other than the linear grooves by subsequent primary annealing. In Patent Document 1, by purposely separating a region where the heating rate is high and a region where the heating rate is low, a region (region of the linear grooves) where the existence frequency of (110)

[001] oriented grains is increased and a region (region other than the linear groove) where the existence frequency of (111)

[112] oriented grains is increased are purposely arranged.

[0016] Patent Document 2 discloses a technique of irradiating the surface of a silicon steel sheet with a laser beam plural times at predetermined spacing PL in a rolling direction between cold rolling and final annealing. When the silicon steel sheet is made to be secondary recrystallized by final annealing, a trace line along the laser beam becomes a grain boundary which reaches from one surface to the other surface of the silicon steel sheet. In Patent Document 2, after the final annealing, the length of the grains in the rolling direction is maximally 30 mm which corresponds to the spacing PL of the irradiation, and the angular deviation between the direction of the magnetization easy axis (cubic crystal { 110}<001>) and the rolling direction is in the range of 0° to 6°.

[0017] Patent Document 3 discloses a method for manufacturing a grain oriented electrical steel sheet that has a small difference in alignment degree to a Goss orientation in the inner and outer circumferences of coils having different curvatures and has a high magnetic flux density on the premise of a high temperature slab heating process. In Patent Document 3, by performing linear local heating on a cold-rolled steel sheet, the linear heated region acts as a barrier for growth of secondary recrystallized grains, and thereby the growth of secondary recrystallized grains is suppressed.Citation ListPatent Document

[0018] Patent Document 1: Japanese Unexamined Patent Application, First Publication No. 2007-169762 Patent Document 2: PCT International Publication No. WO 2012 / 014290 Patent Document 3: Japanese Unexamined Patent Application, First Publication No. 2022-161269 SUMMARY OF INVENTIONTechnical Problem

[0019] As described above, the magnetic characteristics of the grain oriented electrical steel sheet have been tried to be improved until today. However, it is insufficient to improve of the magnetic characteristics by the conventional techniques.

[0020] The present invention has been made in consideration of the above-mentioned situations. An object of the present invention is to provide a cold rolled steel sheet for a grain oriented electrical steel sheet capable of increasing a magnetic flux density. Specifically, an object is to provide a cold rolled steel sheet for a grain oriented electrical steel sheet capable of increasing a magnetic flux density while suppressing coarsening of a secondary recrystallized grain size.Solution to Problem

[0021] An aspect of the present invention employs the following. [1] A cold rolled steel sheet for a grain oriented electrical steel sheet according to an aspect of the present invention, wherein when a deviation angle from an ideal Goss orientation based on a rotation axis parallel to a normal direction is defined as α, when a deviation angle from the ideal Goss orientation based on a rotation axis parallel to a transverse direction is defined as β, when a deviation angle of a crystal orientation measured at a measurement point on a sheet surface is represented as (α β), when an angular deviation at the measurement point is defined as ϕ = (α 2< + β 2< ) 1 / 2< , when a grain having the angular deviation ϕ of 10° or less is defined as a Goss-oriented grain, when a region of 100 mm × 100 mm on the sheet surface is defined as a divided domain, and when it is confirmed whether the Goss-oriented grain is included in the divided domain in at least 100 divided domains, an area fraction of divided domains including at least one Goss-oriented grain having a grain size of 5 µm or more is 30% or more as compared with all divided domains. Advantageous Effects of Invention

[0022] According to the above aspects of the present invention, it is possible to provide a cold rolled steel sheet for a grain oriented electrical steel sheet capable of increasing a magnetic flux density. Specifically, it is possible to provide the cold rolled steel sheet for the grain oriented electrical steel sheet capable of increasing the magnetic flux density while suppressing coarsening of the secondary recrystallized grain size.

[0023] For instance, local rapid heating is performed for the material sheet for the grain oriented electrical steel sheet before primary annealing for manufacturing the grain oriented electrical steel sheet, Goss-oriented grains of 5 µm or more are formed in the cold rolled steel sheet, and thereby, the magnetic flux density can be improved as the grain oriented electrical steel sheet. Moreover, regions where the local rapid heating is performed are preferably and dispersedly arranged in the steel sheet, and thereby, the magnetic flux density can be improved as the grain oriented electrical steel sheet while suppressing coarsening of the secondary recrystallized grain size.BRIEF DESCRIPTION OF DRAWINGS

[0024] [FIG. 1] A schema illustrating an instance of using spot electric heating as a local rapid heating method and illustrating an instance of arrangement of a locally heated region in a cold rolled steel sheet for a grain oriented electrical steel sheet according to the present embodiment. [FIG. 2] A schema illustrating a distribution of Goss-oriented grains of a cold rolled steel sheet for a grain oriented electrical steel sheet according to an embodiment of the present invention. DESCRIPTION OF EMBODIMENTS

[0025] Hereinafter, a preferred embodiment of the present invention is described in detail. However, the present invention is not limited only to the configuration which is disclosed in the present embodiment, and various modifications are possible without departing from the aspect of the present invention. In addition, the limitation range as described below includes a lower limit and an upper limit thereof. However, the value represented by "more than" or "less than" does not include in the limitation range. Unless otherwise noted, "%" of the chemical composition represents "mass%".

[0026] As described above, the existence frequency of practical Goss-oriented grains having small angular deviation θ and small angular deviation ϕ from the {110}<001> orientation which is the ideal Goss orientation increases as the heating rate of the primary annealing (decarburization annealing) increases. On the other hand, for the grains of the {778}<447> (≈{111}<112>) orientation, the {411}<148> orientation, and the like which have a Σ9 coincidence site lattice relationship with the Goss orientation and tend to be encroached by Goss-oriented grains (referred to as CSL oriented grains), the existence frequency conversely decreases as the heating rate of the primary annealing increases. Therefore, it was difficult to increase the fraction of the CSL oriented grains while increasing the fraction of the practical Goss-oriented grains by the primary annealing.

[0027] In the technique described in Patent Document 1, linear grooves are formed on a surface of a steel sheet by etching treatment, a heating rate near the region of the linear grooves is to be increased during primary annealing, and thereby, the region (region of the linear grooves) having a large fraction of Goss-oriented grains and a region (region other than the linear groove) having a large fraction of CSL oriented grains are arranged. However, in this method, it is difficult to increase the difference in the heating rate during primary annealing between the region of the linear grooves and the other region, and the obtained effect is limited. Specifically, the difference between the heating rate in the region of the linear grooves and the heating rate in the region other than the linear grooves is not so large. For instance, even when the entire steel sheet is heated at 100 °C / sec, since the reduction of the thickness at the region by forming the grooves is only 10% or less as compared with the original thickness (since the depth of the grooves is 20 µm or less in general and is approximately 10% or less of the sheet thickness), the ratio between the heating rates is equal to or less than the ratio between the thicknesses for the same heat input when considering the thermal conduction of the steel sheet, and thus, the ratio between the fraction of the Goss-oriented grains in the region of the linear grooves and that in the region other than the linear grooves is less likely to increase as compared with the ration between the thickness in the region of the linear grooves and that in the region other than the linear grooves. In addition, in this method, the heating rate near the region of the linear grooves is increased during primary annealing, and thus, the grain size of the Goss-oriented grains formed in the region of the linear grooves after the primary annealing is not increased but is almost the same or fine as compared with the grain size of the primary recrystallized grains as an overall average.

[0028] In addition, in the technique described in Patent Document 2, the surface of the steel sheet is irradiated with a laser beam before final annealing. However, in this method, the laser beam irradiated region is only controlled to be the grain boundary of the secondary recrystallization, and the orientation of the Goss-oriented grains formed by the primary recrystallization is not controlled. In addition, the region heated by the laser irradiation is only the vicinity of the surface irradiated with the laser, the thermal diffusion to the peripheral region is remarkable, and thus, it is difficult to secure a thermal history that make the steel sheet recrystallize.

[0029] In addition, in the technique described in Patent Document 3, the sheet surface after cold rolling is irradiated with a laser beam. However, in this method, similarly to the above, the laser beam irradiated region is only controlled to be the grain boundary of the secondary recrystallization, the heating rate is not controlled, and the orientation of the Goss-oriented grains formed by the primary recrystallization is not controlled. In Patent Document 3, only the grain size of the secondary recrystallized grains in the rolling direction is reduced by making the laser beam irradiated region act as a barrier for the growth of the secondary recrystallized grains, and the temperature range of the grain growth in the locally heated region effective for increasing the size of the Goss-oriented grains in the locally heated region is not secured. Thus, in this method, the difference in the alignment degree to the Goss orientation in the inner and outer circumferences of the coil having different curvatures may be reduced, but the Goss-oriented grains having the crystal orientation close to the ideal Goss orientation cannot be obtained. That is, in this method, a decrease in the magnetic flux density is suppressed by coarsening the grain size of the secondary recrystallized grains in the rolling direction, but the orientation of the Goss-oriented grains is not fundamentally improved.

[0030] In the present embodiment, it has been found for the first time that a grain oriented electrical steel sheet having exceptional quality is obtained by performing local rapid heating on a steel sheet to form a locally heated region before performing primary annealing (decarburization annealing). The locally heated region that forms before the primary annealing is arranged locally on the surface of the steel sheet. The crystal structure of the locally heated region includes one or both of the recrystallized structure and the recovered structure at the end of the local rapid heating. The crystal structure of a non-locally heated region other than the locally heated region on the sheet surface consists of a cold-deformed structure which is as-cold rolled.

[0031] In the locally heated region, the heating rate is preferably 500 °C / sec or more, preferably 2000 °C / sec or more, preferably 5000 °C / sec or more, and more preferably 10000 °C / sec or more. As described above, it has been found that, when the locally heated region is formed on the surface of the steel sheet before the primary annealing, the grains having the practical Goss orientation are formed in the locally heated region. In addition, it has become clear that, among the Goss-oriented grains to be formed, the fraction of the Goss-oriented grains having small angular deviation θ and small angular deviation ϕ from the ideal Goss orientation is increased, and the grain size of the Goss-oriented grains is increased.

[0032] The frequency of Goss-oriented grains included in the locally heated region is higher than the frequency of Goss-oriented grains included in the non-locally heated region. This feature is derived from the deformed structure of the non-locally heated region. Specifically, it is derived from the fact that in a case where the local rapid heating is performed, recovery and recrystallization occur in the locally heated region and then the practical Goss-oriented grains tend to be formed and growth, but the recovery and recrystallization do not occur in the non-locally heated region.

[0033] The locally heated region having the above feature is dispersedly arranged on the surface of the steel sheet by the local rapid heating before primary annealing, and then the primary annealing and secondary annealing are further performed. The Goss-oriented grains formed in the locally heated region preferentially grow during secondary annealing after the primary annealing. Although Goss-oriented grains are formed in the locally heated region, and among them, the Goss-oriented grains that are close to the ideal Goss orientation, have particularly small angular deviation θ and small angular deviation ϕ, and have a large grain size are included. In the secondary recrystallization, the above Goss-oriented grains among the grains grow preferentially.

[0034] Since the Goss-oriented grains which act as the nucleus of the secondary recrystallization are arranged in the locally heated region, it is not necessary to form the Goss-oriented grains by the primary annealing in a matrix region other than the locally heated region, that is, the non-locally heated region other than the locally heated region. Accordingly, as the heat treatment condition of the primary annealing, a mild heating condition with a low heating rate may be employed, and a primary annealing condition may be employed in which a large number of CSL oriented grains having the {111}<112> orientation and the {411}<148> orientation, which are easily encroached, are formed in the non-locally heated region. For instance, by controlling the heating rate of the primary annealing to 300 °C / sec or less, a large number of Goss-oriented grains close to the ideal Goss orientation and having large grain size are formed in the locally heated region, while Goss-oriented grains are hardly formed in the non-locally heated region, and conversely, a large number of CSL oriented grains are formed.

[0035] As described above, in the locally heated region of the steel sheet (decarburization-annealed steel sheet) in which the local rapid heating and the primary annealing have been completed, a large number of Goss-oriented grains close to the ideal Goss orientation and having large grain size are included. On the other hand, in the matrix region (non-locally heated region), the Goss-oriented grains having large size are hardly included, whereas a large number of CSL oriented grains that are easily encroached may be included.

[0036] As an aspect of local rapid heating, a case where spot electric heating by electric resistance heating is used will be described. In the spot electric heating, spot electrodes are arranged and contacted so as to be opposite to each other on both surfaces of the steel sheet, and a current flows between the spot electrodes to perform the spot electric heating on a region where the electrodes are held on the steel sheet. Steel having the composition indicated in Table 1 was used, and hot rolling and cold rolling were performed to obtain a cold-rolled steel sheet having a thickness of 0.22 mm. The steel sheet was subjected to the spot electric heating. The spot electric heating was performed using copper electrodes having a diameter of 3 mmϕ under the conditions of a flowing current of 5.0 kA or less which was a range where the sheet surface was not melted, a time of current flow of 20 to 80 milliseconds, an electrode force of 50 to 150 kgf, and an electrode retention time after current flow of 0.2 seconds. On the surface of the cold-rolled steel sheet, the spot electric heating was performed in a grid pattern at a pitch of 30 mm in the rolling direction and a pitch of 30 mm in the width direction (transverse direction) to form the locally heated region.

[0037] FIG.1 illustrate an instance of arrangment of the locally heated region in the cold rolled steel for the grain oriented electrical steel sheet according to the present embodiment. In FIG. 1, the steel sheet 1, the locally heated regions 2, the rolling deirection 21, and the width direction (transverse direction) 22 are schematically illustrated. [Table 1]CHEMICAL COMPOSITION (mass%)CSiMnSAlN0.063.40.100.0060.0260.008

[0038] In order to prepare an observed section for Electron Back Scattering Diffraction pattern (EBSD) from the surface of a cold rolled steel sheet (cold rolled steel sheet after local rapid heating and before primary annealing), a surface was smoothed by mechanical polishing, and electrolytic polishing was performed to remove added strain of the surface. Thereafter, an image quality (IQ) value and a crystal orientation in a region including the locally heated region were measured by the EBSD under condition of a step of 0.5 µm. FIG. 2 is a schema illustrating a distribution of the Goss-oriented grains of the cold rolled steel sheet for the grain oriented electrical steel sheet according to the present embodiment.

[0039] In FIG. 2, an observed area including the locally heated region 2 and the non-locally heated region 3 (matrix region) are illustrated. The non-locally heated region 3 has the cold-deformed structure. Thus, when the IQ value is measured by EBSD after performing the above pretreatment on the surface of steel sheet, the non-locally heated region 3 shows the IQ value as the cold-deformed structure. The locally heated region 2 has a recovered structure and a recrystallized structure, and thus, the IQ value becomes higher than that of the cold-deformed structure. By the comparison of these IQ values, it is possible to identify the locally heated region 2 and the non-locally heated region 3 and to confirm the locally heated region 2, the non-locally heated region 3, and boundaries (locally heated region boundary 4). When it is not easy to identify the locally heated region boundary 4 by microstructure observation, the region including the Goss-oriented grains having the grain size of 5 µm or more can be regarded as the locally heated region 2.

[0040] An electrode used for spot electric heating has a circular shape, and the diameter thereof is preferably 0.5 to 10 mmϕ, and more preferably 1 to 5 mmϕ in an equivalent circle diameter. Note that, in the above description, the electrode having the circular shape is used, but in so far as the heating rate of the cold-rolled steel sheet is locally increased and Goss-oriented grains are formed and grown in this region, the electrode shape may be another shape, for instance, an elliptical shape or a linear shape.

[0041] In FIG. 2, based on the definition of the angular deviation ϕ = (α 2< + β 2< ) 1 / 2< , grains having the angular deviation ϕ of 10° or less from the ideal Goss orientation (Goss-oriented grains 14) are indicated by "∘". Further, among the grains having the angular deviation ϕ of 10° or less, grains having the grain size of 5 µm or more (coarse Goss-oriented grains 15) are indicated by "⊙".

[0042] As illustrated in FIG. 2, the cold rolled steel sheet (steel sheet 1) for the grain oriented electrical steel sheet according to the present embodiment includes the Goss-oriented grains 14 and also includes the coarse Goss-oriented grains 15. In particular, the region including the coarse Goss-oriented grains 15 corresponds to the locally heated region 2. Note that, the Goss-oriented grains are hardly observed in the matrix region 3 (non-locally heated region 3) where the local heating is not performed.

[0043] The above cold rolled steel sheet was subjected to the primary annealing (decarburization annealing). In the primary annealing, the cold rolled steel sheet was heated at a heating rate of 100 °C / sec and held at 830°C for 90 seconds. In a decarburization-annealed steel sheet after primary annealing, a large number of Goss-oriented grains were included in the locally heated region, and the grains were grown coarsely. On the other hand, the Goss-oriented grains were hardly observed in the matrix region (non-locally heated region).

[0044] The decarburization-annealed steel sheet was further subjected to nitridation, applying an annealing separator including MgO as a main component, and then secondary annealing. The secondary annealing conditions are a hydrogen-nitrogen atmosphere, a heating rate of 15 °C / hour, and holding at 1200°C for 20 hour. The obtained steel sheet was subjected to macroetching to reveal grain boundaries. When a region corresponding to the locally heated region was observed in the steel sheet after the macroetching, it was observed that plural secondary recrystallized grains grew from the region corresponding to the locally heated region or that the secondary recrystallized grain grew from the center of the region corresponding to the locally heated region. In addition, in the region corresponding to the locally heated region, fine grains of 2 mm or less may or may not be observed as a vestige of the locally heated region. Although the secondary recrystallized macrostructure may slightly change depending on the condition of the local heating, the alignment degree of the Goss orientation can be increased as compared with the case where the local heat treatment is not performed, and as a result, the magnetic flux density B 8 of the steel sheet is improved. It was confirmed for the crystal orientation of the obtained secondary recrystallized grains that the deviation from the ideal Goss orientation was extremely small (B 8 was improved from 1.911 T to 1.943 T in this steel sheet). As described above, the cold rolled steel sheet according to the present embodiment includes the coarse Goss-oriented grains 15 in addition to the Goss-oriented grains 14. It is considered that the coarse Goss-oriented grains 15 which are close to the ideal Goss orientation and which have the size advantage are formed, and thereby, the crystal orientation of the secondary recrystallized grains is improved.

[0045] The features of the cold rolled steel sheet for the grain oriented electrical steel sheet according to the present embodiment will be described in detail. The above cold rolled steel sheet shown in FIG. 2 satisfies the following features.

[0046] A cold rolled steel sheet for a grain oriented electrical steel sheet according to the present embodiment, wherein when a deviation angle from an ideal Goss orientation based on a rotation axis parallel to a normal direction is defined as α, when a deviation angle from the ideal Goss orientation based on a rotation axis parallel to a transverse direction is defined as β, when a deviation angle of a crystal orientation measured at a measurement point on a sheet surface is represented as (α β), when an angular deviation at the measurement point is defined as ϕ = (α 2< + β 2< ) 1 / 2< , when a grain having the angular deviation ϕ of 10° or less is defined as a Goss-oriented grain, when a region of 100 mm × 100 mm on the sheet surface is defined as a divided domain, and when it is confirmed whether the Goss-oriented grain is included in the divided domain in at least 100 divided domains, an area fraction of divided domains including at least one Goss-oriented grain having a grain size of 5 µm or more is 30% or more as compared with all divided domains.

[0047] For instance, the above domains are divided using the cold rolled steel sheet with 1000 mm in a longitudinal direction, a total area of the divided domains including at least one Goss-oriented grain having a grain size of 5 µm or more (coarse Goss-oriented grain) are measured, and then, the fraction as compared with an area of all divided domains may be calculated.

[0048] Herein, in the present embodiment, the above grain size is determined by identifying the grain boundaries where the disorientation from the adjacent measurement point is 1° or more. In addition, the above grain size indicates an equivalent circle diameter.

[0049] In addition, in the present embodiment, the angular deviation ϕ is defined using the deviation angle α and the deviation angle β. The general angular deviation θ is often evaluated using three components: the deviation angle α, the deviation angle β, and the deviation angle γ. However, since the present embodiment is particularly directed to improvement in magnetic flux density, the angular deviation ϕ is defined using two components: the deviation angle α and the deviation angle β except for the deviation angle γ which does not significantly influence the magnetic flux density.

[0050] In addition, the above coarse Goss-oriented grain is defined as the Goss-oriented grain having the grain size of 5 µm or more, but an upper limit of the grain size is not particularly limited. For instance, the upper limit of the grain size of the coarse Goss-oriented grain may be 100 µm.

[0051] In the cold rolled steel sheet according to the present embodiment, when at least one coarse Goss-oriented grain (coarse Goss-oriented grain close to ideal Goss orientation) is included in the divided domain of 100 mm × 100 mm on the cold rolled steel sheet and when the total area of the divided domains including the above coarse Goss-oriented grain is 30% or more as compared with all divided domains, the Goss-oriented grains grow in a preferable form in the secondary recrystallization, and thereby, it is possible to obtain the grain oriented electrical steel sheet having excellent magnetic characteristics.

[0052] In order to form the coarse Goss-oriented grain in the cold rolled steel sheet as explained above, it is necessary to promote the formation of Goss-oriented grain by increasing the heating rate in the locally heated region and to secure the time in which the recrystallized grain formed in the locally heated region is stayed in a temperature range where the grain can be grown after recrystallization. The above phenomenon (recrystallization and grain growth of Goss-oriented grain) does not occur under conditions such as laser irradiation and electron beam irradiation used in general magnetic domain control. In particular, in order to remain the coarse Goss-oriented grain in the locally heated region after primary recrystallization, it is effective to prolong the time from reaching the maximum temperature until cooling to 700°C during local rapid heating. For instance, it is effective that the holding time from reaching the maximum temperature until cooling to 700°C is 0.1 second or more. The holding time is preferably 0.2 second or more, and more preferably 0.3 second or more. For instance, by suppressing heat dissipation from the steel sheet using heated spot electrodes during local rapid heating, it is possible to promote the grain growth of formed Goss-oriented grain and to promote the formation of the Goss-oriented grain having the size effective in favorable secondary recrystallization and having the crystal orientation close to the ideal Goss orientation. As explained above, when a diameter of an electrode is 0.5 to 10 mmϕ in an equivalent circle diameter, it is possible to preferably secure the holding time from reaching the maximum temperature until cooling to 700°C. Under the general conditions of laser irradiation and electron beam irradiation, it is difficult to secure the holding time from reaching the maximum temperature until cooling to 700°C as described above.

[0053] It is preferable that the divided domains including at least one coarse Goss-oriented grain exist uniformly over the entire cold rolled steel sheet. However, the above condition may not be satisfied over the entire sheet surface of the cold rolled steel sheet. For instance, even when the divided domains including at least one coarse Goss-oriented grain are unevenly arranged in a part of the cold rolled steel sheet, when an area fraction of the divided domains is 30% or more as compared with all divided domains, the grain oriented electrical steel sheet having excellent magnetic characteristics can be finally obtained.

[0054] As explained above, when the local rapid heating is performed for the steel sheet after finishing the cold rolling, the coarse Goss-oriented grain 15 is formed in the locally heated region 2 as shown in FIG. 2. On the other hand, the coarse Goss-oriented grain is not formed in the non-locally heated region 3. Thus, by performing the local rapid heating so that the locally heated regions 2 are dispersedly arranged on the surface of cold rolled steel sheet, it is possible to control the distribution of the coarse Goss-oriented grains 15 on the surface of steel sheet.

[0055] The area fraction of divided domains including at least one coarse Goss-oriented grain (the Goss-oriented grain having the grain size of 5 µm or more) is preferably 50% or more, more preferably 70% or more, and more preferably 90% or more as compared with all divided domains.

[0056] In a case where a heat cycle is properly controlled during conventional secondary recrystallization annealing, the Goss-oriented grain having favorable orientation grows until approximately 100 mm. However, since an existence frequency of the Goss-oriented grains having favorable orientation is small in the primary recrystallized grains, the magnetic flux density B 8 increases only to approximately 1.911 T in the conventional technique. On the other hand, in the present embodiment, by performing the local heating for the divided domains of 30 area% or more as compared with all divided domains as explained above, the area fraction of divided domains including at least one coarse Goss-oriented grain is 30% or more as compared with all divided domains. Thus, in the present embodiment, the Goss-oriented grain having favorable orientation grows preferentially, and thus, the magnetic flux density is improved as compared with the conventional technique. Of course, when the area fraction of divided domains including at least one coarse Goss-oriented grain is 100% as compared with all divided domains, the magnetic flux density is further improved.

[0057] Moreover, when at least one locally heated region is included in each divided domain, the magnetic flux density B 8 is improved. However, the grain size after secondary recrystallization increases with a decrease in a number of the locally heated regions in the divided domain. In the steel sheet having the above feature, although the magnetic flux density is improved, the iron loss tends not to be improved without applying the magnetic domain control technique such as laser irradiation, linear grooves forming, and the like. Thus, for instance, in average, the formed locally heated regions are preferably 3 regions or more, more preferably 5 regions or more, and more preferably 9 regions or more in each divided domain of 100 mm × 100 mm.

[0058] When the cold rolled steel sheet according to the present embodiment is used, the coarse Goss-oriented grains close to the ideal Goss orientation are preferentially grown among Goss-oriented grains in the locally heated region during secondary recrystallization. Therefore, it is possible to obtain the steel sheet occupied by the secondary recrystallized grains close to the ideal Goss orientation without coarsening the secondary recrystallized grains. For instance, at the time when the locally heated regions are discretely arranged on the sheet surface, if the locally heated regions are appropriately arranged on the sheet surface, it is possible to control the size, shape, and arrangement of the grains after the secondary annealing. For instance, the Goss-oriented grain initiates to grow from one locally heated region, the grain growth stops when the grain encounters with another Goss-oriented grain which initiates to grow from an adjacent locally heated region, and thereby, the grain size of the Goss-oriented grains after secondary recrystallization becomes small. In the case, it is possible to obtain the steel sheet excellent in iron loss. In particular, as described above, in the initial stage of the secondary annealing, the Goss-oriented grains preferentially grown from the locally heated region have the crystal orientation close to the ideal Goss orientation, and as a result, excellent magnetic characteristics can be obtained even though the secondary recrystallized grain size is small.

[0059] That is, when the cold rolled steel sheet according to the present embodiment is used, it is possible to improve the magnetic flux density while suppressing coarsening of the secondary recrystallized grain size, and thus, it is possible to omit or reduce the refinement of the width of magnetic domain by applying the strain or forming the grooves. Specifically, since the effect of the magnetic domain refinement can be preferably obtained by the grain boundaries that increase as a result of the refinement of the secondary recrystallized grain size, the magnetic domain is refined without applying the conventional magnetic domain control technique. Therefore, it is not necessary to apply the strain into the steel sheet contrary to the conventional magnetic domain control technique, and thus, it is possible to suppress an increase in the magnetostriction (λ P-P ). In addition, it is not necessary to form the grooves on the steel sheet contrary to the conventional magnetic domain control technique, and thus, it is possible to suppress a decrease in the magnetic flux density B 8 . In addition, it is possible to use the grain oriented electrical steel sheet using the cold rolled steel sheet according to the present embodiment for utilization requiring the strain relief annealing at 800°C or higher.

[0060] Moreover, as explained above, in the cold rolled steel sheet according to the present embodiment, the coarse Goss-oriented grain included in the divided domain may have the grain size of 5 µm or more. In order to make the ideal Goss-oriented grain with size advantage further grow preferentially, the coarse Goss-oriented grain included in the divided domain may have preferably the grain size of 8 µm or more. Specifically, it is preferable that an area fraction of divided domains including at least one Goss-oriented grain having a grain size of 8 µm or more is 30% or more as compared with all divided domains. The area fraction of the divided domains is preferably 50% or more, more preferably 70% or more, and more preferably 90% or more as compared with all divided domains.

[0061] Herein, the above grain size of the Goss-oriented grains and the like may be measured by the EBSD. When the region to be measured is larger than the region that can be measured by the EBSD, the region to be measured may be divided and EBSD measurement may be performed plural times. For instance, in the EBSD measurement, the step size may be 0.5 µm.

[0062] Next, a preferred chemical composition of the cold rolled steel sheet according to the present embodiment will be described.

[0063] First, the chemical composition of the grain oriented electrical steel sheet as a final product manufactured using the cold rolled steel sheet according to the present embodiment will be described.

[0064] The grain oriented electrical steel sheet as the final product may contain, as a chemical composition, Si: 2.0% to 7.0% in mass percentage and the balance consisting of Fe and impurities.

[0065] In addition, this grain oriented electrical steel sheet may contain a known optional element as substitution for part of Fe for improving the magnetic characteristics. A lower limit of the optional element does not need to be limited, and the lower limit may be 0%. Moreover, an upper limit of the optional element may be a value in which the magnetic flux density or the iron loss does not significantly deteriorate. For instance, the upper limit of each optional element is described below.

[0066] The grain oriented electrical steel sheet (base steel sheet) as the final product may contain, as a chemical composition, by mass%, at least one of: C: 0.005% or less, Si: 2.0 to 7.0%, Mn: 1.00% or less, S and Se: 0.015% or less in total, Al: 0.065% or less, N: 0.005% or less, Nb, V, Mo, Ta, and W: 0.050% or less in total, Cu: 0.40% or less, Bi: 0.010% or less, B: 0.080% or less, P: 0.50% or less, Ti: 0.015% or less, Sn: 0.10% or less, Sb: 0.10% or less, Cr: 0.30% or less, and Ni: 1.00% or less.

[0067] The optional elements may be contained according to a known purpose, a lower limit of the optional elements does not need to be limited, and the lower limit may be 0%. Note that, the total amount of S and Se represents that at least one of S and Se is included and the amount thereof corresponds to the above total amount. Similarly, the total amount of one or more of Nb, V, Mo, Ta, and W represents that at least one of Nb, V, Mo, Ta, and W is included and the amount thereof corresponds to the above total amount.

[0068] In the grain oriented electrical steel sheet, the chemical composition changes relatively drastically (the amount of alloying element decreases) through the decarburization annealing and through the purification annealing during secondary recrystallization. Depending on the element, the content may be decreased to 50 ppm or less or may reach to an undetectable level (1 ppm or less) using the typical analytical methods if the purification annealing is sufficiently performed.

[0069] In addition, even if the above optional elements are contained as impurities, the effects of the present embodiment are not impaired. The impurities correspond to elements which are contaminated during industrial production of steel sheet from ores and scrap that are used as a raw material of steel, or from environment of a manufacturing process. For instance, an upper limit of the impurities may be 5% in total.

[0070] The chemical composition as described above may be measured by typical analytical methods for the steel. For instance, the chemical composition may be measured by using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometer: inductively coupled plasma emission spectroscopy spectrometry). Specifically, it is possible to obtain the chemical composition by conducting the measurement by ICP-AES (measurement device) under the condition based on calibration curve prepared in advance using samples with 35mm square taken from the steel sheet. In addition, C and S may be measured by the infrared absorption method after combustion, and N may be measured by the thermal conductometric method after fusion in a current of inert gas.

[0071] The chemical composition of the cold rolled steel sheet according to the present embodiment contains, for instance, the elements described below.

[0072] The cold rolled steel sheet according to the present embodiment may contain, as a chemical composition, by mass%: C: 0 to 0.0850%, Si: 2.0 to 7.0%, Mn: 0.05 to 1.0%, S and Se: 0.003 to 0.035% in total, Al: 0.010 to 0.0650%, N: 0 to 0.012%, Nb, V, Mo, Ta, and W: 0 to 0.050% in total, Cu: 0 to 0.40%, Bi: 0 to 0.010%, B: 0 to 0.080%, P: 0 to 0.50%, Ti: 0 to 0.0150%, Sn: 0 to 0.10%, Sb: 0 to 0.10%, Cr: 0 to 0.30%, Ni: 0 to 1.0%, and the balance consisting of Fe and impurities. C: 0 to 0.0850%

[0073] Carbon (C) is an element effective in controlling the primary recrystallized structure in the manufacturing process. Thus, the C content is 0.085% or less. A preferable upper limit of the C content is 0.075%. C is decarburized and purified in the decarburization annealing process explained below, and the content may be controlled to 0.0050% or less in order to suppress an occurrence of magnetic aging after final annealing process. In order to favorably suppress the magnetic aging, the C content is preferably 0.003% or less and more preferably 0.002% or less. The lower limit of the C content may be more than 0% from the productivity standpoint in the industrial production when C is included. However, since the C content depends on a decarburization annealing time, the lower limit may be 0.0001% in consideration of an annealing cost. Moreover, the lower limit may be 0.0005% in consideration of a manufacturing cost.Si: 2.0 to 7.0%

[0074] Silicon (Si) is an element which increases the electric resistance of the grain oriented electrical steel sheet and thereby decreases the iron loss. When the Si content is less than 2.0%, γ transformation occurs during the final annealing and the crystal orientation of the grain oriented electrical steel sheet is impaired. On the other hand, when the Si content is more than 7.0%, the cold workability deteriorates and the cracks tend to occur during cold rolling. The lower limit of the Si content is preferably 2.5%, and is more preferably 3.0%. The upper limit of the Si content is preferably 4.5%, and is more preferably 4.0%.Mn: 0.05 to 1.0%

[0075] Manganese (Mn) forms MnS and / or MnSe by bonding to S and / or Se, which act as the inhibitor. When Mn is included and the Mn content is 0.05 to 1.0%, the secondary recrystallization becomes stable. The nitride of the Nb group element (Nb, V, Mo, Ta, and W) can bear part of the function of the inhibitor. In the case, the inhibitor intensity as MnS and / or MnSe in general is controlled weakly. Thus, the upper limit of the Mn content is preferably 0.50%, and is more preferably 0.20%.S and Se: 0.003 to 0.035% in total

[0076] Sulfur (S) and Selenium (Se) form MnS and / or MnSe by bonding to Mn, which act as the inhibitor. When at least one of S and Se is included, and when the total amount of S and Se is 0.003 to 0.035%, the secondary recrystallization becomes stable. The nitride of the Nb group element can bear part of the function of the inhibitor. In the case, the inhibitor intensity as MnS and / or MnSe in general is controlled weakly. Thus, in a case of a low temperature slab heating process as the manufacturing method, the upper limit of the total amount of S and Se is preferably 0.025%, and is more preferably 0.010%. When S and / or Se remain in the steel after the final annealing, the compound is formed, and thereby, the iron loss is deteriorated. Thus, it is preferable to reduce S and Se as much as possible by the purification during the final annealing.

[0077] Here, the total amount of S and Se represents that at least one of S and Se is included and the amount thereof corresponds to the above total amount.Al: 0.010 to 0.0650%

[0078] Aluminum (Al) forms (Al, Si)N by bonding to N, which acts as the inhibitor. When Al is included and the Al content is 0.010 to 0.0650%, the inhibitor AlN formed by the nitridation mentioned below expands the temperature range of the secondary recrystallization, and the secondary recrystallization becomes stable especially in higher temperature range. Therefore, the Al content is 0.010 to 0.0650%. The lower limit of the Al content is preferably 0.020%, and is more preferably 0.025%. The upper limit of the Al content is preferably 0.040%, and is more preferably 0.035% from the stability standpoint in the secondary recrystallization.N: 0 to 0.012%

[0079] Nitrogen (N) bonds to Al and acts as the inhibitor. The lower limit thereof is not limited because it is possible to include N by the nitridation in midstream of the manufacturing process. For instance, the lower limit of the N content may be more than 0% or may be 0.001%. When N is included and the N content is more than 0.012%, the blister which is a kind of defect tends to be formed in the steel sheet. The upper limit of the N content is preferably 0.010%, and is more preferably 0.009%. N is purified in the final annealing process, and then, the N content becomes 0.005% or less after the final annealing process.

[0080] The balance of the chemical composition consists of Fe and impurities. The impurities correspond to elements which are contaminated during industrial production of steel from ores and scrap that are used as a raw material of steel, or from environment of a manufacturing process. For instance, an upper limit of the impurities may be 5% in total.Total of Nb, V, Mo, Ta, and W: 0 to 0.050%

[0081] The total amount of niobium (Nb), vanadium (V), molybdenum (Mo), tantalum (Ta), and tungsten (W) may be 0.050% or less. When the Nb group element (at least one of Nb, V, Mo, Ta, and W) is utilized as part of the inhibitor, the effect of improving B 8 is obtained. On the other hand, when the Nb group element remains excessively in the base steel sheet, the magnetic characteristics may be adversely affected. Therefore, the total amount of Nb, V, Mo, Ta, and W may be 0.050% or less. Further, when the total amount of the Nb group elements is 0.030% or less (preferably 0.003% or more and 0.030% or less), the secondary recrystallization starts at appropriate timing, which is preferable. Moreover, the orientation of the formed secondary recrystallized grain becomes very favorable, and the microstructure is finally controlled to be favorable for the magnetization characteristics. In particular, Nb and Ta prominently shows the above effects, which is preferable. The lower limit of the total amount of the Nb group elements does not need to be limited, and the lower limit may be 0%. The lower limit is preferably 0.003%.

[0082] The total amount of the Nb group elements is more preferably 0.004 to 0.020%. The total amount is more preferably 0.005 to 0.010%.

[0083] Here, the total amount of the Nb group elements represents that at least one of Nb, V, Mo, Ta, and W is included and the amount thereof corresponds to the above total amount.

[0084] In addition, the cold rolled steel sheet according to the present embodiment may contain, as the optional element, by mass%, at least one of: 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%, and Ni: 0 to 1.0%.

[0085] The optional elements may be contained according to a known purpose, a lower limit of the optional elements does not need to be limited, and the lower limit may be 0%.

[0086] The chemical composition of the cold rolled steel sheet according to the present embodiment may be measured by the above analytical methods, as with the chemical composition of the grain oriented electrical steel sheet as the final product.

[0087] Next, an aspect of a preferred method for manufacturing the cold rolled steel sheet for the grain oriented electrical steel sheet according to the present embodiment will be described.

[0088] The method for manufacturing the cold rolled steel sheet according to the present embodiment is not limited to the following method. The following manufacturing method is an instance for manufacturing the cold rolled steel sheet according to the present embodiment.

[0089] Moreover, the processes and the quantitative conditions in each process described below are an instance employed to confirm the operability of the present embodiment, so that the present embodiment is not limited to the processes and the quantitative values. The method for manufacturing the cold rolled steel sheet according to the present embodiment can employ various types of conditions as long as the conditions do not depart from the scope of the present embodiment and can achieve the object of the present embodiment.

[0090] In the method for manufacturing the cold rolled steel sheet according to the present embodiment, it is possible to apply a conventional known method for manufacturing the grain oriented electrical steel sheet as fundamental processes. For instance, the conventional method for manufacturing the grain oriented electrical steel sheet includes a manufacturing method utilizing MnS and AlN as inhibitor which are formed by high temperature slab heating, a manufacturing method utilizing AlN as inhibitor which is formed by low temperature slab heating and subsequent nitridation, and the like. The method for manufacturing the cold rolled steel sheet according to the present embodiment is not limited to a specific manufacturing method. Hereinafter, the method which employs the low temperature slab heating with the nitridation is explained for instance.(Casting Process)

[0091] In the casting process, a slab is made. For instance, a method for making the slab is as follow. A molten steel is made (a steel is melted). The slab is made by using the molten steel. The slab may be made by continuous casting. An ingot may be made by using the molten steel, and then, the slab may be made by blooming the ingot. A thickness of the slab is not particularly limited. The thickness of the slab may be 150 to 350 mm for instance. The thickness of the slab is preferably 220 to 280 mm. The slab with the thickness of 10 to 70 mm which is a so-called thin slab may be used. When using the thin slab, it is possible to omit a rough rolling before final rolling in the hot rolling process.

[0092] For instance, as the chemical composition, the above slab may include the following elements.C: 0.085% or less

[0093] Carbon (C) is an element effective in controlling the primary recrystallized structure in the manufacturing process. However, when the content in the final product is excessive, the magnetic characteristics are negatively affected. Thus, the C content may be 0.085% or less. The upper limit of the C content is preferably 0.075%. C is decarburized and purified in the decarburization annealing process and the final annealing process, and then, the content becomes 0.005% or less. When C is included, the lower limit of the C content may be more than 0%, and may be 0.001% from the productivity standpoint in the industrial production.Si: 2.0 to 7.0%

[0094] Silicon (Si) is an element which increases the electric resistance of the grain oriented electrical steel sheet and thereby decreases the iron loss. When the Si content is less than 2.0%, an austenite transformation occurs during the final annealing and the crystal orientation of the grain oriented electrical steel sheet is impaired. On the other hand, when the Si content is more than 7.0%, the cold workability deteriorates and the cracks tend to occur during cold rolling. The lower limit of the Si content is preferably 2.5%, and is more preferably 3.0%. The upper limit of the Si content is preferably 4.5%, and is more preferably 4.0%.Mn: 0.05 to 1.00%

[0095] Manganese (Mn) forms MnS and / or MnSe by bonding to S and / or Se, which act as the inhibitor. When Mn is included and the Mn content is 0.05 to 1.00%, the secondary recrystallization becomes stable. The nitride of the Nb group element can bear part of the function of the inhibitor. In the case, the inhibitor intensity as MnS and / or MnSe in general is controlled weakly. Thus, the upper limit of the Mn content is preferably 0.50%, and is more preferably 0.20%.At least one of S and Se: 0.003 to 0.035% in total

[0096] Sulfur (S) and Selenium (Se) form MnS and / or MnSe by bonding to Mn, which act as the inhibitor. When at least one of S and Se is included, and when the total amount of S and Se is 0.003 to 0.035%, the secondary recrystallization becomes stable. The nitride of the Nb group element can bear part of the function of the inhibitor. In the case, the inhibitor intensity as MnS and / or MnSe in general is controlled weakly. Thus, the upper limit of the total amount of S and Se is preferably 0.025%, and is more preferably 0.010%. When S and / or Se remain in the steel after the final annealing, the compound is formed, and thereby, the iron loss is deteriorated. Thus, it is preferable to reduce S and Se as much as possible by the purification during the final annealing.

[0097] Here, the total amount of S and Se represents that at least one of S and Se is included and the amount thereof corresponds to the above total amount.Al: 0.010 to 0.065%

[0098] Aluminum (Al) forms (Al, Si)N by bonding to N, which acts as the inhibitor. When Al is included and the Al content is 0.010 to 0.065%, the inhibitor AlN formed by the nitridation mentioned below expands the temperature range of the secondary recrystallization, and the secondary recrystallization becomes stable especially in higher temperature range. Therefore, the Al content is 0.010 to 0.065%. The lower limit of the Al content is preferably 0.020%, and is more preferably 0.025%. The upper limit of the Al content is preferably 0.040%, and is more preferably 0.035% from the stability standpoint in the secondary recrystallization.N: 0.012% or less

[0099] Nitrogen (N) bonds to Al and acts as the inhibitor. The lower limit thereof is not limited because it is possible to include N by the nitridation in midstream of the manufacturing process. For instance, the lower limit of the N content may be more than 0% or may be 0.001%. When N is included and the N content is more than 0.012%, the blister which is a kind of defect tends to be formed in the steel sheet. The upper limit of the N content is preferably 0.010%, and is more preferably 0.009%. N is purified in the final annealing process, and then, the N content becomes 0.005% or less after the final annealing process.

[0100] The balance of the chemical composition consists of Fe and impurities. The impurities correspond to elements which are contaminated during industrial production of steel from ores and scrap that are used as a raw material of steel, or from environment of a manufacturing process. For instance, an upper limit of the impurities may be 5% in total.

[0101] In addition to solving manufacturing problems, in consideration of the influence on the magnetic characteristics and the improvement of the inhibitors function by forming compounds, the above chemical composition may include the known optional elements as substitution for part of Fe. For instance, the optional elements as substitution for part of Fe may be the following elements.Nb group element: 0.050% or less

[0102] The total amount of the Nb group element (at least one of Nb, V, Mo, Ta, and W) may be 0.050% or less. When the Nb group element (at least one of Nb, V, Mo, Ta, and W) is utilized as part of the inhibitor, and when the total amount of the Nb group element is 0.030% or less, the secondary recrystallization starts at appropriate timing, which is preferable. Moreover, the orientation of the formed secondary recrystallized grain becomes very favorable, and the microstructure is finally controlled to be favorable for the magnetization characteristics. In particular, Nb and Ta prominently shows the above effects, which is preferable. The lower limit of the total amount of the Nb group elements does not need to be limited, and the lower limit may be 0%. The lower limit is preferably 0.003%.

[0103] The total amount of the Nb group elements is more preferably 0.004 to 0.020%. The total amount is more preferably 0.005 to 0.010%.

[0104] Here, the total amount of the Nb group elements represents that at least one of Nb, V, Mo, Ta, and W is included and the amount thereof corresponds to the above total amount.

[0105] In addition, the slab may contain, as the optional element, by mass%, at least one of: Cu: 0.40% or less, Bi: 0.010% or less, B: 0.080% or less, P: 0.50% or less, Ti: 0.015% or less, Sn: 0.10% or less, Sb: 0.10% or less, Cr: 0.30% or less, and Ni: 1.00% or less.

[0106] The optional elements may be contained according to a known purpose, a lower limit of the optional elements does not need to be limited, and the lower limit may be 0%.

[0107] The chemical composition of the slab may be measured by the above analytical methods, as with the chemical composition of the grain oriented electrical steel sheet as the final product.(Hot Rolling Process)

[0108] In the hot rolling process, the slab is heated to a predetermined temperature (for instance, 1100 to 1400°C), and then, is subjected to hot rolling in order to obtain a hot rolled steel sheet. In the hot rolling process, for instance, the silicon steel material (slab) is heated in heating stage, is rough-rolled, and then, is final-rolled in order to obtain the hot rolled steel sheet with a predetermined thickness, for instance, 1.8 to 3.5 mm. After finishing the final rolling, the hot rolled steel sheet is coiled at a predetermined temperature.

[0109] In a case where of a process including the nitridation during decarburization annealing or after decarburization annealing, the inhibitor intensity as MnS is not necessarily needed, it is preferable that the slab heating temperature is 1100 to 1280°C from the productivity standpoint.(Hot-Band Annealing Process)

[0110] In the hot band annealing process, the hot rolled steel sheet after the hot rolling process is annealed under predetermined conditions (for instance, 750 to 1200°C for 30 seconds to 10 minutes) in order to obtain a hot band annealed sheet. The hot-band annealing is generally performed to control the microstructure of the steel sheet such as the recrystallization fraction, the residual strain, and the grain size by annealing the hotrolled steel sheet after the hot rolling process and to preferably control the morphology of precipitates in the steel. For instance, in high temperature slab heating process, the above process is to finally control the morphology of precipitates such as AlN, and the conditions are controlled so that the precipitates are uniformly and finely precipitated. For instance, as the hot band annealing, the steel sheet may be heated to 1050°C to 1150°C, may be slow-cooled to an intermediate temperature (850°C to 950°C) for 50 to 150 seconds in order to appropriately precipitates AlN and the like, and thereafter, may be water-cooled.(Cold Rolling Process)

[0111] In the cold rolling process, the hot band annealed sheet after the hot band annealing process is cold-rolled once or is cold-rolled plural times (two times or more) with an annealing (intermediate annealing) (for instance, 80 to 95% of total cold reduction) in order to obtain a cold rolled steel sheet with a thickness, for instance, 0.10 to 0.50 mm. In order to improve the magnetic characteristics, for instance, an interpass temperature of the cold rolling may be approximately 100°C to 300°C.

[0112] The total cold reduction of cold rolling is defined as follows. (Local Rapid Heating Process)

[0113] In the present embodiment, local rapid heating for forming the locally heated region is performed on the cold-rolled steel sheet after the cold rolling process. The rapid heating method is not particularly limited as long as the steel sheet can be locally heated. For instance, it is possible to adopt a method in which spot electrodes are arranged and contacted on both surfaces of the steel sheet and the steel sheet is heated by flowing a current in the steel sheet, a method in which the steel sheet is heated by irradiating the surface thereof with laser beam, electron beam, and the like, a method in which the steel sheet is locally heated by induction heating, a method in which the steel sheet is heated by contacting a heated piece, and the like. The size of each locally heated region may be a dotted region having a diameter of approximately 10 µm to 10 mm or a linear region having a width of approximately 10 µm to 10 mm. In addition, the electrode used for electric heating may be a circular electrode or a linear electrode as described above.

[0114] Note that regarding the size of the locally heated region, the minimum diameter and the minimum width depend on the shape of the spot electrode and the technique of reducing the focusing diameter of the laser beam or the electron beam. Although it is possible in principle to further reduce the size of the locally heated region, it is considered that the effect can be obtained when the size of the locally heated region is 1 µm or more in consideration of the fact that the nucleus of the recrystallized grain has a size of approximately 1 µm under the present conditions. However, in the present embodiment, in order to form the Goss-oriented grain having the grain size of 5 µm or more, the minimum diameter and the minimum width may be 10 µm or more. In addition, with respect to the size of the locally heated region, when the maximum diameter or the maximum width exceeds 10 mm, the area fraction of the Goss-oriented grains having relatively large angular deviation θ or angular deviation ϕ that cannot grow out of the locally heated region increases. In this case, it is difficult to obtain the effect of performing local rapid heating.

[0115] In the local rapid heating, the heating rate may be 500 °C / sec or more at a central position of the locally heated region as viewed in the thickness direction and at a thickness 1 / 5 position of the steel sheet. When the heating rate is 500 °C / sec or more at the above region, the microstructure of the locally heated region can be preferably controlled to a recovered structure or a recrystallized structure. The heating rate is preferably 2000 °C / sec or more, and more preferably 10000 °C / sec or more. On the other hand, the upper limit of the heating rate is not particularly limited, and the upper limit may be, for instance, 1000000 °C / sec.

[0116] In addition, it is preferable that the heating rate is controlled with the heating rate during decarburization annealing described below. For instance, it is difficult to obtain the intended effect when the heating rate during decarburization annealing is faster than the heating rate during local rapid heating. Therefore, although depending on the degree of the value of the heating rate, the heating rate during local rapid heating is preferably equal to or more than the heating rate during decarburization annealing.

[0117] Herein, the thickness 1 / 5 position of the steel sheet indicates a depth corresponding to 1 / 5 of the thickness of the steel sheet from the surface of the steel sheet along the thickness direction.

[0118] In addition, in the local rapid heating, the maximum attained temperature may be 700°C or more at the central position of the locally heated region as viewed in the thickness direction and at the thickness 1 / 5 position of the steel sheet. When the maximum attained temperature is 700°C or more in the above region, the microstructure of the locally heated region can be preferably controlled to the recovered structure or the recrystallized structure. The maximum attained temperature is preferably 800°C or higher, and more preferably 900°C or higher. On the other hand, the maximum attained temperature may be equal to or lower than the melting point of the steel sheet, and may be, for instance, 1400°C or lower.

[0119] In addition, in the local rapid heating, the holding time from reaching the maximum temperature until cooling to 700°C may be 0.1 seconds or more at the central position of the locally heated region as viewed in the thickness direction and at the thickness 1 / 5 position of the steel sheet. When the holding time is 0.1 seconds or more in the above region, the microstructure of the locally heated region can be preferably controlled to the recovered structure or the recrystallized structure. The holding time is preferably 0.2 seconds or more, more preferably 0.3 seconds or more, and still more preferably 0.4 seconds or more. On the other hand, the upper limit of the holding time is not particularly limited, and the upper limit may be, for instance, 10 seconds or less. The holding time from reaching the maximum temperature until cooling to 700°C has essentially affected the formation of the coarse Goss-oriented grains close to the ideal Goss orientation.

[0120] In the local rapid heating, it is important to control the above holding time in addition to the heating rate and the maximum attained temperature described above. During this holding time, it is possible to form a sub-grain structure or a recrystallized nucleus, which is advantageous for the formation of the coarse Goss-oriented grains in the locally heated region. As a result, it is possible to form the Goss-oriented grain having the grain size of 5 µm or more in the locally heated region after the local rapid heating. By the control described above through the holding time in the locally heated region, it is possible to preferably control the microstructure in the subsequent process.

[0121] As described above, the method of local rapid heating is not particularly limited. For instance, local rapid heating may be performed by spot electric heating, laser irradiation, or electron beam irradiation. Any local rapid heating method may be controlled so as to satisfy the heating rate, the maximum attained temperature, and the holding time described above. A person skilled in the art can combine the conditions of the local rapid heating, and thereby, can control the heating rate, maximum attained temperature, and holding time according to the purpose.

[0122] For instance, a person skilled in the art can control the heating rate and the maximum attained temperature at the central position of the locally heated region as viewed in the thickness direction and at the thickness 1 / 5 position of the steel sheet by performing thermal conductivity analysis using finite element method. Additionally, a person skilled in the art can control the above holding time by controlling conditions of heat dissipation after reaching the maximum temperature. For instance, in the case of spot electric heating, the electrode retention time after current flow may be controlled, or the shape of the spot electrode may be changed to a shape suitable for heat dissipation. In addition, in the case of laser irradiation or electron beam irradiation, the irradiation speed may be adjusted, or the shape of irradiated region may be changed to an ellipse and the like to add a gradient to the irradiation energy from the central region toward the outer edge region in irradiated region.

[0123] In general, in heating by laser irradiation, only the vicinity of the irradiated sheet surface is preferentially heated, and the inside of the steel sheet is hardly heated. In addition, since heating by laser irradiation is non-contact heating, heat dissipation after heating is fast, and it is difficult to hold the temperature. Therefore, when heating by laser irradiation is performed as the local rapid heating, in order to recover or recrystallize the cold-deformed structure in the laser-irradiated region, it is necessary to perform heating under a condition of heating not only the sheet surface but also the inside of the steel sheet and under a condition of relatively coarsening the sub-grain structure in the laser-irradiated region by slowing the cooling rate. The condition of laser irradiation for performing the local rapid heating is quite different from the condition of laser irradiation for performing the magnetic domain refinement. For instance, even if the condition of laser irradiation for performing magnetic domain refinement (usually 0.5 to 50 mJ / mm 2< ) is applied to the present embodiment, the microstructure of the locally heated region cannot be controlled in a preferable one, and the coarse Goss-oriented grains close to the ideal Goss orientation are not formed in the cold rolled steel sheet. In addition, the situation with electron beam irradiation is the same as with laser irradiation. Even if the condition of electron beam irradiation for performing magnetic domain refinement is applied to the present embodiment, the microstructure of the locally heated region cannot be controlled in a preferable one, and the coarse Goss-oriented grains close to the ideal Goss orientation are not formed in the cold rolled steel sheet.

[0124] Note that, even when the input power of laser irradiation or electron beam irradiation is simply increased, it is difficult to form the coarse Goss-oriented grains close to the ideal Goss orientation. For instance, when the rapid heating is performed by laser irradiation or electron beam irradiation, it is preferable to make the beam shape elliptical or control the scan speed and the like in order to secure a temperature range where the grains in the region grow after the rapid heating.

[0125] Conventionally, in an electrical steel sheet, laser irradiation and electron beam irradiation have been performed to reduce the iron loss by performing magnetic domain control on the steel sheet after secondary recrystallization. Under conditions of these laser irradiation and electron beam irradiation, since approximately 20 µm from the surface of the steel sheet is heated, heat dissipation after heating is fast. Therefore, under the conventional conditions, it is difficult to secure the holding time from reaching the maximum temperature until cooling to 700°C as described above. That is, under the conditions of conventional laser irradiation and electron beam irradiation, it may be possible to make the irradiated region act as a barrier for the growth of the secondary recrystallized grains, but it is difficult to form the coarse Goss-oriented grains having the orientation close to the ideal Goss orientation as in the present embodiment. In order to form the coarse Goss-oriented grains close to the ideal Goss orientation by laser irradiation or electron beam irradiation, it is necessary to investigate conditions of laser irradiation or electron beam irradiation as described above.

[0126] Through the above processes, the cold rolled steel sheet for the grain oriented electrical steel sheet according to the present embodiment can be manufactured. In the cold rolled steel sheet according to the present embodiment manufactured comprehensively and inseparably by controlling each condition of each process, the coarse Goss-oriented grains are formed in a preferable form in the steel sheet.

[0127] Hereinafter, a method for manufacturing the grain oriented electrical steel sheet using the cold rolled steel sheet according to the present embodiment will be described.(Decarburization Annealing Process)

[0128] 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 existence frequency of the Goss-oriented grains formed in the locally heated region is increased, the grain size of the Goss-oriented grains is increased, and the coarse Goss-oriented grains having the orientation close to the ideal Goss orientation are preferably grown. As conditions of the decarburization annealing, for instance, the annealing temperature may be 700 to 900°C, and the annealing time may be 1 to 3 minutes. By performing decarburization annealing on the cold-rolled steel sheet, C included in the cold-rolled steel sheet is removed. In order to remove "C" included in the cold rolled steel sheet, it is preferable that the decarburization annealing is conducted in moist atmosphere.

[0129] In addition, it is effective to reduce the primary recrystallized grain size by controlling the conditions of the hot rolling and hot-band annealing described above and by decreasing the decarburization annealing temperature as necessary. The primary recrystallized grain size is not particularly limited but is preferably 8 to 30 µm.

[0130] In addition, in the present embodiment, the coarse Goss-oriented grains having the orientation close to the ideal Goss orientation are formed in the locally heated region. Therefore, it is not necessary to form the Goss-oriented grains again by decarburization annealing. Thus, the heating rate of the decarburization annealing does not need to be increased. On the other hand, it is preferable to decrease the heating rate of the decarburization annealing in order to form {111}<112> oriented grains or {411}<148> oriented grains that are easily encroached in the matrix region (non-locally heated region).

[0131] In addition, the amount of oxidation caused by the decarburization annealing and the state of surface oxidized layer affect the formation of the glass film. Therefore, in the decarburization annealing, the oxidation degree (PH 2 O / PH 2 ) in the annealing atmosphere (furnace atmosphere) may be controlled as necessary.(Nitridation)

[0132] Nitridation 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 controlling the inhibitor intensity in secondary recrystallization. In the nitridation, the nitrogen content of the steel sheet is made to increase to 40 to 200 ppm from starting the decarburization annealing to starting the secondary recrystallization in the final annealing. For instance, the nitridation may be a treatment of annealing the steel sheet in an atmosphere containing a gas having a nitriding ability such as ammonia, a treatment of final-annealing the decarburization annealed steel sheet being applied an annealing separator containing a powder having a nitriding ability such as MnN and the like. The nitrogen content after the nitridation is preferably 130 to 350 ppm, and more preferably 150 to 250 ppm.(Annealing Separator Applying Process)

[0133] In the annealing separator applying process, the decarburization-annealed steel sheet is applied an annealing separator to. For instance, as the annealing separator, it is possible to use an annealing separator mainly including MgO. The decarburization-annealed steel sheet after applying the annealing separator is coiled and is final-annealed in the subsequent final annealing process.(Final Annealing Process)

[0134] In the final annealing process, the decarburization annealed steel sheet after applying the annealing separator is final-annealed so that the secondary recrystallization (secondary annealing) occurs. In the process, the secondary recrystallization proceeds under conditions such that the grain growth of the primary recrystallized grain is suppressed by the inhibitor. Thereby, the grain having the {110}<001> orientation is preferentially grown, and the magnetic flux density is drastically improved.

[0135] The heating rate in the heating stage of the final annealing process is not particularly limited. For instance, the heating may be performed at a heating rate of 3 to 20 °C / hour. Moreover, slow heating may be performed in a temperature range of 1000 to 1200°C during heating. For instance, the heating rate in the temperature range of 1000 to 1200°C during heating is preferably 3 to 12 °C / hour, more preferably 3 to 9 °C / hour, and preferably 3 to 7 °C / hour. Otherwise, holding may be performed by stopping heating once in the heating stage of the final annealing process. For instance, the heating may be stopped once in a temperature range of 1050 to 1100°C during heating, and the holding may be performed for 5 hours or more and 15 hours or less. For instance, the adjustment of the heating rate in the temperature range of secondary recrystallization influences a decomposition rate of the inhibitor, and thus, it is possible to improve the magnetic flux density.

[0136] After the heating stage of the final annealing process, as a holding stage (purification annealing), holding may be performed for 10 hours or more and 60 hours or less in a temperature range of 1000°C or more and 1300°C or less. The atmosphere during final annealing may be, for instance, a nitrogen atmosphere or a mixed atmosphere of nitrogen and hydrogen.(Insulating Coating Forming Process)

[0137] A coating solution including phosphoric acid or phosphate, chromic anhydride or chromate, and colloidal silica is applied to the steel sheet, and is baked (for instance, 350 to 1150°C for 5 to 300 seconds) to form the insulation coating.(Others)

[0138] The grain oriented electrical steel sheet may be subjected to magnetic domain refinement for forming local minute strain or grooves by a known method such as laser, plasma, a mechanical method, or etching as necessary. However, in the grain oriented electrical steel sheet manufactured using the cold rolled steel sheet according to the present embodiment, coarsening of the secondary recrystallized grain size is suppressed even though the magnetic flux density is excellent, and thus, the magnetic domains are refined without performing magnetic domain refinement treatment.Example 1

[0139] Hereinafter, the effects of the present invention are described in detail with reference to the following examples. However, the condition in the examples is an example condition employed to confirm the operability and the effects of the present invention, so that the present invention is not limited to the example condition. The present invention can employ various types of conditions as long as the conditions do not depart from the scope of the present invention and can achieve the object of the present invention.

[0140] Using slabs having adjusted chemical composition as materials, cold rolled steel sheets with chemical composition shown in Table 2A were manufactured. The chemical composition was measured by the above-mentioned methods. In Table 2, "-" indicates that the control and manufacturing conscious of content did not perform and thus, the content was not measured.

[0141] When the cold rolled steel sheets were manufactured, the slabs were heated to 1150°C, and then hot-rolled to obtain the hot rolled steel sheets having the thickness of 2.6 mm. The hot rolled steel sheets were subjected to the hot band annealing in which the annealing was conducted at 1100°C and then at 900°C, and then were pickled in order to remove the surface scale. The steel sheets were cold-rolled once or cold-rolled plural times with the intermediate annealing to obtain the cold rolled steel sheets having the final thickness of 0.22 mm.

[0142] The cold-rolled steel sheets were subjected to local rapid heating under conditions shown in Tables 3 to 7. For spot electric heating, copper electrodes having a diameter of 3 mm which corresponds to contact area with the steel sheet were used, and then, the heating rate, the maximum attained temperature, the holding time from reaching the maximum temperature until cooling to 700°C (holding time above 700°C) were respectively controlled by comprehensively adjusting the electrode shape other than the contact area with the steel sheet, the electrode force, the flowing current, the time of current flow, the electrode retention time after current flow, and the like. For laser heating, fiber laser was used, focusing spot diameter of laser beam in the rolling direction (specifically, diameter including 86% of laser output) was to be 30 µm (except for Test Nos. 85 and 86), and then, the heating rate, the maximum attained temperature, the holding time above 700°C were respectively controlled by comprehensively adjusting the energy density of laser irradiation, the laser scanning speed, the shape of laser irradiated region, and the like. A person skilled in the art can combine the conditions of the local rapid heating, and thereby, can control the heating rate, the maximum attained temperature, and the holding time above 700°C according to the purpose.

[0143] Note that, in Test No. 83, the laser beam was elongated along scanning direction, and thereby, the holding time from reaching the maximum temperature until cooling to 700°C was controlled to 0.2 seconds in the local rapid heating, in order to form the coarse Goss-oriented grains having the orientation close to the ideal Goss orientation in the locally heated region. In Test No. 84, the general condition of laser irradiation for performing the magnetic domain refinement was applied. In Test No. 85, the focusing spot diameter was 0.5mm, and the energy density of laser irradiation was 2.0 J / mm 2< , in order to control the irradiated region of laser beam to be finally the grain boundary of the secondary recrystallization. In Test No. 86, the focusing spot diameter was 0.5mm, and the energy density of laser irradiation was 30.0 J / mm 2< , in order to control the irradiated region of laser beam to be finally the grain boundary of the secondary recrystallization.

[0144] For the manufactured cold rolled steel sheets, the divided domains including at least one Goss-oriented grain having the grain size of 5 µm or more were measured by the above-mentioned methods. The results are indicated in Tables 8 to 12. Herein, the measurement on EBSD was performed on a surface of which was parallel to the surface of steel sheet and was at 20 µm toward the thickness direction. From the IQ value of EBSD, it was confirmed that the crystal structure of the locally heated region was the recrystallized structure and the recovered structure, and the crystal structure of the non-locally heated region other than the locally heated region was the deformed structure.

[0145] In the tables, "Not performed" of heating method of local rapid heating indicates that the local rapid heating was not performed. "Linear or Dotted" of local heating condition indicates the shape of the locally heated region on the surface of the cold-rolled steel sheet, and "Spacing in rolling direction" and "Spacing in width direction" of local heating condition indicates the spacing in the rolling direction and the transverse direction in which the locally heated regions were arranged on the surface of the cold-rolled steel sheet. The locally heated regions were uniformly arranged at even spacing in the rolling direction and the transverse direction. For instance, when both "Spacing in rolling direction" and "Spacing in width direction" are 100 mm or less, the locally heated regions were arranged in all the divided domains. On the other hand, when either "Spacing in rolling direction" or "Spacing in width direction" is more than 100 mm, the divided domain where the locally heated region was not arranged existed. Herein, among all the divided domains, the divided domains where the locally heated region was arranged were arranged so that the distribution was not uneven.

[0146] Moreover, in the tables, "Fraction of locally heated domains" of local heating condition indicates an area fraction of divided domains including the locally heated region on the surface of the steel sheet. Specifically, when a region of 100 mm × 100 mm on the sheet surface is defined as a divided domain, and when it is confirmed in at least 100 divided domains whether the locally heated region is included in the divided domain, "Fraction of locally heated domains" corresponds to the value obtained by dividing the total area of divided domains including the locally heated region by the area of all divided domains, and the value is showed as 100 percent in the tables.

[0147] In the same way, in the tables, "Area fraction of divided domains including the Goss-oriented grain having the grain size of 5 µm or more" of the manufacturing results indicates an area fraction of divided domains including the coarse Goss-oriented grain on the surface of the cold rolled steel sheet. Specifically, when a region of 100 mm × 100 mm on the sheet surface is defined as a divided domain, and when it is confirmed in at least 100 divided domains whether the Goss-oriented grain (coarse Goss-oriented grain) having the equivalent circle diameter of 5 µm or more for the grains which is determined under conditions such that the angular deviation ϕ = (α 2< + β 2< ) 1 / 2< is 10° or less and that the grain boundaries are identified as the boundary where the disorientation is 1° or more is included in the divided domain, "Area fraction of divided domains including the Goss-oriented grain having the grain size of 5 µm or more" corresponds to the value obtained by dividing the total area of divided domains including the coarse Goss-oriented grain by the area of all divided domains, and the value is showed as 100 percent in the tables. Herein, the Goss-oriented grain having the grain size of 5 µm or more was hardly observed in the matrix region (non-locally heated region) other than the locally heated region.

[0148] The manufactured cold-rolled steel sheets were subjected to decarburization annealing under the conditions shown in Tables 8 to 12. Herein, in the decarburization annealing, the oxidation degree (PH 2 O / PH 2 ) in the annealing atmosphere (furnace atmosphere) was 0.13.

[0149] The manufactured decarburization-annealed steel sheet was subjected to nitridation at 750°C in nitrogen-hydrogen-ammonia atmosphere, and the nitrogen content of the steel sheet was to be 220 ppm. Thereafter, the annealing separator including MgO as a main component was applied and the final annealing was performed. In the final annealing, the steel sheet was heated to 1000°C (or heated to 1070°C in a case of the following "step", ) at the heating rate of 15 °C / hour in a mixed atmosphere of hydrogen and nitrogen, and thereafter, heated to 1200°C under one of the following conditions. And then, the steel sheets were held at 1200°C - 20hour in a hydrogen atmosphere. Normal: heated at 15 °C / hour from 1000°C to 1200°C. Slow Heating 1: heated at 10 °C / hour from 1000°C to 1200°C. Slow Heating: heated at 7.5 °C / hour from 1000°C to 1200°C. Slow Heating 2: heated at 5.0 °C / hour from 1000°C to 1200°C. Step: held for 10 hours at 1070°C.

[0150] For the steel sheet after the final annealing, the coating solution for forming insulation coating which mainly included the phosphate and the colloidal silica and which included the chromic anhydride as necessary was applied and baked to form the insulating coating.

[0151] Various features of the obtained grain oriented electrical steel sheet were evaluated. The evaluation results are shown in Tables 8 to 12.

[0152] The magnetic characteristics of the grain oriented electrical steel sheet were measured based on the single sheet tester (SST) method regulated by JIS C 2556: 2015.

[0153] The samples of 20 sheets with a size of 100 mm × 500 mm for the single sheet tester were taken from the obtained grain oriented electrical steel sheets, and then, the single sheet test was performed. As the magnetic characteristics, the magnetic flux density B 8 (T) in the rolling direction of the steel sheet was measured under the condition such that the steel sheet was excited at 800 A / m. The magnetic flux density B 8 was judged to as acceptable or not based on the Si content of the steel sheet and the conditions of final annealing. Specifically, the steel sheets were classified as the steel A to Z where the Si content was 3.3 to 3.5%, the steel AA where the Si content was 2.5%, and the steel AB where the Si content was 4.1%, and then, the steel sheets were compared under the same conditions of final annealing. When the difference of the magnetic flux density B 8 as compared with B 8 of the steel sheet in which the local rapid heating did not performed was 0.010T or more in the same conditions, it was judged to as acceptable. For instance, since the magnetic flux density B 8 of the test No. 1 in which the steel type was "steel A", the condition of final annealing was "Normal", and the local rapid heating was "Not performed" was 1.911T, it was judged to as acceptable for the steel sheet in which the steel type was "steel A" and the condition of final annealing was "Normal" when the magnetic flux density B 8 became 1.921T or more by the local rapid heating.

[0154] Moreover, for reference, as the magnetic characteristics, the iron loss W 17 / 50 (W / kg) which was defined as the power loss per unit weight (1 kg) of the steel sheet was measured under the conditions of 50 Hz of AC frequency and 1.7 T of excited magnetic flux density.

[0155] In the cold rolled steel sheets which were the inventive examples among Nos. 1 to 89, the "Area fraction of divided domains including the Goss-oriented grain having the grain size of 5 µm or more" was favorably controlled. These inventive examples showed excellent magnetic flux density even though coarsening of the secondary recrystallized grain size was suppressed as the grain oriented electrical steel sheet. In addition, since coarsening of the secondary recrystallized grain size was suppressed, these inventive examples also showed excellent iron loss.

[0156] In addition, although not shown in the tables, in the cold rolled steel sheets which were the inventive examples among Nos. 1 to 89, the value of the area fraction of divided domains including at least one Goss-oriented grain having the grain size of 8 µm or more was the same as that of the area fraction of divided domains including at least one Goss-oriented grain having the grain size of 5 µm or more.

[0157] On the other hand, in the cold rolled steel sheets which were the comparative examples among Nos. 1 to 89, the "Area fraction of divided domains including the Goss-oriented grain having the grain size of 5 µm or more" was not favorably controlled. In these comparative examples, excellent magnetic flux density was not obtained as the grain oriented electrical steel sheet. [Table 3]No.STEEL TYPEMANUFACTURING CONDITIONSTOTAL COLD REDUCTION OF COLD ROLLINGLOCAL RAPID HEATINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONLINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONFRACTION OF LOCALLY HEATED DOMAINS%°C / sec°Csecmmmm%1A91.5NOT PERFORMED------02A91.5SPOT ELECTRIC50009000.3DOTTED300300113A91.5SPOT ELECTRIC50009000.3DOTTED200200254A91.5SPOT ELECTRIC50009000.3DOTTED150150445A91.5SPOT ELECTRIC50009000.3DOTTED120120696A91.5SPOT ELECTRIC50009000.3DOTTED1001001007A91.5SPOT ELECTRIC50009000.3DOTTED16030638A91.5SPOT ELECTRIC50009000.3DOTTED12030839A91.5SPOT ELECTRIC50009000.3DOTTED803010010A91.5SPOT ELECTRIC50009000.3DOTTED603010011A91.5SPOT ELECTRIC50009000.3DOTTED503010012A91.5SPOT ELECTRIC50009000.3DOTTED303010013A91.5SPOT ELECTRIC50009000.3DOTTED153010014A91.5NOT PERFORMED------015A91.5SPOT ELECTRIC50009000.3DOTTED160306316A91.5SPOT ELECTRIC50009000.3DOTTED120308317A91.5SPOT ELECTRIC50009000.3DOTTED803010018A91.5SPOT ELECTRIC50009000.3DOTTED6030100 [Table 4] No.STEEL TYPEMANUFACTURING CONDITIONSTOTAL COLD REDUCTION OF COLD ROLLINGLOCAL RAPID HEATINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONLINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONFRACTION OF LOCALLY HEATED DOMAINS%°C / sec°Csecmmmm%19A91.5SPOT ELECTRIC50009000.3DOTTED503010020A91.5SPOT ELECTRIC50009000.3DOTTED303010021A91.5SPOT ELECTRIC50009000.3DOTTED153010022A91.5NOT PERFORMED------023A91.5SPOT ELECTRIC50009000.3DOTTED160306324A91.5SPOT ELECTRIC50009000.3DOTTED120308325A91.5SPOT ELECTRIC50009000.3DOTTED803010026A91.5SPOT ELECTRIC50009000.3DOTTED603010027A91.5SPOT ELECTRIC50009000.3DOTTED503010028A91.5SPOT ELECTRIC50009000.3DOTTED505010029A91.5SPOT ELECTRIC50009000.3DOTTED3010010030A91.5SPOT ELECTRIC50009000.3DOTTED1003010031A91.5SPOT ELECTRIC50009000.3DOTTED10010010032A91.5SPOT ELECTRIC50009000.3DOTTED303010033A91.5SPOT ELECTRIC50009000.3DOTTED153010034A91.5NOT PERFORMED------035A91.5NOT PERFORMED------036AA92.1NOT PERFORMED------0 [Table 5] No.STEEL TYPEMANUFACTURING CONDITIONSTOTAL COLD REDUCTION OF COLD ROLLINGLOCAL RAPID HEATINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONLINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONFRACTION OF LOCALLY HEATED DOMAINS%°C / sec°Csecmmmm%37AB89.0NOT PERFORMED------038A91.5SPOT ELECTRIC50009000.3DOTTED303010039AA92.1SPOT ELECTRIC50009000.3DOTTED303010040AB89.0SPOT ELECTRIC50009000.3DOTTED303010041A90.4NOT PERFORMED------042A90.4SPOT ELECTRIC50009000.3DOTTED202010043B90.4SPOT ELECTRIC50009000.3DOTTED202010044C90.4SPOT ELECTRIC50009000.3DOTTED202010045D90.4SPOT ELECTRIC50009000.3DOTTED202010046E90.4SPOT ELECTRIC50009000.3DOTTED202010047F90.4SPOT ELECTRIC50009000.3DOTTED202010048G90.4SPOT ELECTRIC50009000.3DOTTED202010049H90.4SPOT ELECTRIC50009000.3DOTTED202010050I90.4SPOT ELECTRIC50009000.3DOTTED202010051J90.4SPOT ELECTRIC50009000.3DOTTED202010052K90.4SPOT ELECTRIC50009000.3DOTTED202010053L90.4SPOT ELECTRIC50009000.3DOTTED202010054M90.4SPOT ELECTRIC50009000.3DOTTED2020100 [Table 6] No.STEEL TYPEMANUFACTURING CONDITIONSTOTAL COLD REDUCTION OF COLD ROLLINGLOCAL RAPID HEATINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONLINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONFRACTION OF LOCALLY HEATED DOMAINS%°C / sec°Csecmmmm%55N90.4SPOT ELECTRIC50009000.3DOTTED202010056O90.4SPOT ELECTRIC50009000.3DOTTED202010057P90.4SPOT ELECTRIC50009000.3DOTTED202010058Q90.4SPOT ELECTRIC50009000.3DOTTED202010059R90.4SPOT ELECTRIC50009000.3DOTTED202010060S90.4SPOT ELECTRIC50009000.3DOTTED202010061T90.4SPOT ELECTRIC50009000.3DOTTED202010062U90.4SPOT ELECTRIC50009000.3DOTTED202010063V90.4SPOT ELECTRIC50009000.3DOTTED202010064W90.4SPOT ELECTRIC50009000.3DOTTED202010065X90.4SPOT ELECTRIC50009000.3DOTTED202010066Y90.4SPOT ELECTRIC50009000.3DOTTED202010067Z90.4SPOT ELECTRIC50009000.3DOTTED202010068A90.4NOT PERFORMED------069A90.4SPOT ELECTRIC50009000.3DOTTED30301070A90.4SPOT ELECTRIC50009000.3DOTTED30302071A90.4SPOT ELECTRIC50009000.3DOTTED30303072A90.4SPOT ELECTRIC50009000.3DOTTED303040 [Tbale 7] No.STEEL TYPEMANUFACTURING CONDITIONSTOTAL COLD REDUCTION OF COLD ROLLINGLOCAL RAPID HEATINGHEATING METHODHEATING RATEMAXIMUM ATTAINED TEMPERATUREHOLDING TIME ABOVE 700°CLOCAL HEATING CONDITIONLINEAR OR DOTTEDSPACING IN ROLLING DIRECTIONSPACING IN WIDTH DIRECTIONFRACTION OF LOCALLY HEATED DOMAINS%°C / sec°Csecmmmm%73A90.4SPOT ELECTRIC50009000.3DOTTED30305074A90.4SPOT ELECTRIC50009000.3DOTTED30306075A90.4SPOT ELECTRIC50009000.3DOTTED30307076A90.4SPOT ELECTRIC50009000.3DOTTED30308077A90.4SPOT ELECTRIC50009000.3DOTTED30309078A90.4SPOT ELECTRIC50009000.3DOTTED303010079A91.5SPOT ELECTRIC50009000.3DOTTED10010010080A91.5SPOT ELECTRIC50009000.2DOTTED10010010081A91.5SPOT ELECTRIC50009000.1DOTTED10010010082A91.5SPOT ELECTRIC50009000.03DOTTED10010010083A90.4LASER20008000.2LINEAR10-10084A90.4LASER< 2000< 200< 0.03LINEAR10-10085A90.4LASER5000800< 0.03LINEAR10-10086A90.4LASER7000800< 0.03LINEAR10-10087A91.5SPOT ELECTRIC5009000.3DOTTED10010010088A91.5SPOT ELECTRIC20009000.3DOTTED10010010089A91.5SPOT ELECTRIC100009000.3DOTTED100100100 [Table 8] No.STEEL TYPEMANUFACTURING CONDITIONSMANUFACTURING RESULTSEVALUATION RESULTSNOTEDECARBURIZATION ANNEALINGFINAL ANNEALINGAREA FRACTION OF DIVIDED DOMAINS INCLUDING THE GOSS-ORIENTED GRAIN HAVING THE GRAIN SIZE OF 5 µm OR MOREMAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50HEATING RATEANNEALING TEMPERATUREANNEALING TIMEANNEALING PROCEDUREHEATING RATE TO 1000°CHEATING RATE TO 1200°C°C / sec°Csec°C / hr°C / hr%TW / kg1A100850100NORMAL151501.9110.839COMPARATIVE EXAMPLE2A100850100NORMAL1515111.9120.835COMPARATIVE EXAMPLE3A100850100NORMAL1515251.9150.830COMPARATIVE EXAMPLE4A100850100NORMAL1515441.9250.814INVENTIVE EXAMPLE5A100850100NORMAL1515691.9300.807INVENTIVE EXAMPLE6A100850100NORMAL15151001.9330.804INVENTIVE EXAMPLE7A100850100NORMAL1515631.9260.833INVENTIVE EXAMPLE8A100850100NORMAL1515831.9290.820INVENTIVE EXAMPLE9A100850100NORMAL15151001.9350.797INVENTIVE EXAMPLE10A100850100NORMAL15151001.9370.789INVENTIVE EXAMPLE11A100850100NORMAL15151001.9380.784INVENTIVE EXAMPLE12A100850100NORMAL15151001.9400.755INVENTIVE EXAMPLE13A100850100NORMAL15151001.9430.729INVENTIVE EXAMPLE14A100850100SLOW HEATING157.501.9220.828COMPARATIVE EXAMPLE15A100850100SLOW HEATING157.5631.9370.811INVENTIVE EXAMPLE16A100850100SLOW HEATING157.5831.9400.798INVENTIVE EXAMPLE17A100850100SLOW HEATING157.51001.9460.775INVENTIVE EXAMPLE18A100850100SLOW HEATING157.51001.9480.767INVENTIVE EXAMPLE [Table 9] No.STEEL TYPEMANUFACTURING CONDITIONSMANUFACTURING RESULTSEVALUATION RESULTSNOTEDECARBURIZATION ANNEALINGFINAL ANNEALINGAREA FRACTION OF DIVIDED DOMAINS INCLUDING THE GOSS-ORIENTED GRAIN HAVING THE GRAIN SIZE OF 5 µm OR MOREMAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50HEATING RATEANNEALING TEMPERATUREANNEALING TIMEANNEALING PROCEDUREHEATING RATE TO 1000°CHEATING RATE TO 1200°C°C / sec°Csec°C / hr°C / hr%TW / kg19A100850100SLOW HEATING157.51001.9490.762INVENTIVE EXAMPLE20A100850100SLOW HEATING157.51001.9510.733INVENTIVE EXAMPLE21A100850100SLOW HEATING157.51001.9540.707INVENTIVE EXAMPLE22A100850100Step151501.9410.814COMPARATIVE EXAMPLE23A100850100Step1515631.9580.834INVENTIVE EXAMPLE24A100850100Step1515831.9640.807INVENTIVE EXAMPLE25A100850100Step15151001.9690.761INVENTIVE EXAMPLE26A100850100Step15151001.9710.728INVENTIVE EXAMPLE27A100850100Step15151001.9720.712INVENTIVE EXAMPLE28A100850100Step15151001.9700.753INVENTIVE EXAMPLE29A100850100Step15151001.9680.751INVENTIVE EXAMPLE30A100850100Step15151001.9670.786INVENTIVE EXAMPLE31A100850100Step15151001.9630.802INVENTIVE EXAMPLE32A100850100Step15151001.9730.679INVENTIVE EXAMPLE33A100850100Step15151001.9740.648INVENTIVE EXAMPLE34A100850100NORMAL151501.9110.839COMPARATIVE EXAMPLE35A100850100SLOW HEATING 215501.9300.816COMPARATIVE EXAMPLE36AA100850100SLOW HEATING 215501.9530.887COMPARATIVE EXAMPLE [Table 10] No.STEEL TYPEMANUFACTURING CONDITIONSMANUFACTURING RESULTSEVALUATION RESULTSNOTEDECARBURIZATION ANNEALINGFINAL ANNEALINGAREA FRACTION OF DIVIDED DOMAINS INCLUDING THE GOSS-ORIENTED GRAIN HAVING THE GRAIN SIZE OF 5 µm OR MOREMAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50HEATING RATEANNEALING TEMPERATUREANNEALING TIMEANNEALING PROCEDUREHEATING RATE TO 1000°CHEATING RATE TO 1200°C°C / sec°Csec°C / hr°C / hr%TW / kg37AB100850100SLOW HEATING 215501.8750.798COMPARATIVE EXAMPLE38A100850100SLOW HEATING 21551001.9590.697INVENTIVE EXAMPLE39AA100850100SLOW HEATING 21551001.9770.765INVENTIVE EXAMPLE40AB100850100SLOW HEATING 21551001.9250.662INVENTIVE EXAMPLE41A100850100SLOW HEATING 1151001.9130.826COMPARATIVE EXAMPLE42A100850100SLOW HEATING 115101001.9460.693INVENTIVE EXAMPLE43B100850100SLOW HEATING 115101001.9690.651INVENTIVE EXAMPLE44C100850100SLOW HEATING 115101001.9500.680INVENTIVE EXAMPLE45D100850100SLOW HEATING 115101001.9480.685INVENTIVE EXAMPLE46E100850100SLOW HEATING 115101001.9460.696INVENTIVE EXAMPLE47F100850100SLOW HEATING 115101001.9570.674INVENTIVE EXAMPLE48G100850100SLOW HEATING 115101001.9660.657INVENTIVE EXAMPLE49H100850100SLOW HEATING 115101001.9630.675INVENTIVE EXAMPLE50I100850100SLOW HEATING 115101001.9560.688INVENTIVE EXAMPLE51J100850100SLOW HEATING 115101001.9500.698INVENTIVE EXAMPLE52K100850100SLOW HEATING 115101001.9670.654INVENTIVE EXAMPLE53L100850100SLOW HEATING 115101001.9580.675INVENTIVE EXAMPLE54M100850100SLOW HEATING 115101001.9610.687INVENTIVE EXAMPLE [Table 11] No.STEEL TYPEMANUFACTURING CONDITIONSMANUFACTURING RESULTSEVALUATION RESULTSNOTEDECARBURIZATION ANNEALINGFINAL ANNEALINGAREA FRACTION OF DIVIDED DOMAINS INCLUDING THE GOSS-ORIENTED GRAIN HAVING THE GRAIN SIZE OF 5 µm OR MOREMAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50HEATING RATEANNEALING TEMPERATUREANNEALING TIMEANNEALING PROCEDUREHEATING RATE TO 1000°CHEATING RATE TO 1200°C°C / sec°Csec°C / hr°C / hr%TW / kg55N100850100SLOW HEATING 115101001.9680.656INVENTIVE EXAMPLE56O100850100SLOW HEATING 115101001.9530.678INVENTIVE EXAMPLE57P100850100SLOW HEATING 115101001.9500.685INVENTIVE EXAMPLE58Q100850100SLOW HEATING 115101001.9480.687INVENTIVE EXAMPLE59R100850100SLOW HEATING 115101001.9460.702INVENTIVE EXAMPLE60S100850100SLOW HEATING 115101001.9590.671INVENTIVE EXAMPLE61T100850100SLOW HEATING 115101001.9490.683INVENTIVE EXAMPLE62U100850100SLOW HEATING 115101001.9460.697INVENTIVE EXAMPLE63V100850100SLOW HEATING 115101001.9470.690INVENTIVE EXAMPLE64W100850100SLOW HEATING 115101001.9480.686INVENTIVE EXAMPLE65X100850100SLOW HEATING 115101001.9490.684INVENTIVE EXAMPLE66Y100850100SLOW HEATING 115101001.9620.631INVENTIVE EXAMPLE67Z100850100SLOW HEATING 115101001.9410.677INVENTIVE EXAMPLE68A100850100Step151501.9410.814COMPARATIVE EXAMPLE69A100850100Step1515101.9420.814COMPARATIVE EXAMPLE70A100850100Step1515201.9430.812COMPARATIVE EXAMPLE71A100850100Step1515301.9530.783INVENTIVE EXAMPLE72A100850100Step1515401.9540.751INVENTIVE EXAMPLE [Table 12] No.STEEL TYPEMANUFACTURING CONDITIONSMANUFACTURING RESULTSEVALUATION RESULTSNOTEDECARBURIZATION ANNEALINGFINAL ANNEALINGAREA FRACTION OF DIVIDED DOMAINS INCLUDING THE GOSS-ORIENTED GRAIN HAVING THE GRAIN SIZE OF 5 µm OR MOREMAGNETIC FLUX DENSITY B 8 IRON LOSS W17 / 50HEATING RATEANNEALING TEMPERATUREANNEALING TIMEANNEALING PROCEDUREHEATING RATE TO 1000°CHEATING RATE TO 1200°C°C / sec°Csec°C / hr°C / hr%TW / kg73A100850100Step1515501.9580.739INVENTIVE EXAMPLE74A100850100Step1515601.9620.727INVENTIVE EXAMPLE75A100850100Step1515701.9650.715INVENTIVE EXAMPLE76A100850100Step1515801.9670.703INVENTIVE EXAMPLE77A100850100Step1515901.9700.691INVENTIVE EXAMPLE78A100850100Step15151001.9730.679INVENTIVE EXAMPLE79A100850100NORMAL15151001.9330.804INVENTIVE EXAMPLE80A100850100NORMAL15151001.9310.808INVENTIVE EXAMPLE81A100850100NORMAL15151001.9290.810INVENTIVE EXAMPLE82A100850100NORMAL1515201.9140.835COMPARATIVE EXAMPLE83A30083090SLOW HEATING 115101001.9380.674INVENTIVE EXAMPLE84A30083090SLOW HEATING 1151001.9090.841COMPARATIVE EXAMPLE85A30083090SLOW HEATING 11510101.9110.822COMPARATIVE EXAMPLE86A30083090SLOW HEATING 11510151.9100.814COMPARATIVE EXAMPLE87A10083090SLOW HEATING 115101001.9280.817INVENTIVE EXAMPLE88A10083090SLOW HEATING 115101001.9320.809INVENTIVE EXAMPLE89A10083090SLOW HEATING 115101001.9400.776INVENTIVE EXAMPLE INDUSTRIAL APPLICABILITY

[0158] According to the above aspects of the present invention, it is possible to provide a cold rolled steel sheet for a grain oriented electrical steel sheet. Specifically, it is possible to provide the cold rolled steel sheet for the grain oriented electrical steel sheet capable of increasing the magnetic flux density while suppressing coarsening of the secondary recrystallized grain size. Accordingly, the present invention has significant industrial applicability.REFERENCE SIGNS LIST

[0159] 1Steel sheet 2Locally heated region 3Non-locally heated region (matrix region) 4Locally heated region boundary 14Goss-oriented grain 15Coarse Goss-oriented grain (Goss-oriented grain having grain size of 5 µm or more) 21Rolling direction 22Width direction (transverse direction)

Examples

example 1

[0139]Hereinafter, the effects of the present invention are described in detail with reference to the following examples. However, the condition in the examples is an example condition employed to confirm the operability and the effects of the present invention, so that the present invention is not limited to the example condition. The present invention can employ various types of conditions as long as the conditions do not depart from the scope of the present invention and can achieve the object of the present invention.

[0140]Using slabs having adjusted chemical composition as materials, cold rolled steel sheets with chemical composition shown in Table 2A were manufactured. The chemical composition was measured by the above-mentioned methods. In Table 2, "-" indicates that the control and manufacturing conscious of content did not perform and thus, the content was not measured.

[0141]When the cold rolled steel sheets were manufactured, the slabs were heated to 1150°C, and then hot-r...

Claims

1. A cold rolled steel sheet for a grain oriented electrical steel sheet, wherein when a deviation angle from an ideal Goss orientation based on a rotation axis parallel to a normal direction is defined as α, when a deviation angle from the ideal Goss orientation based on a rotation axis parallel to a transverse direction is defined as β, when a deviation angle of a crystal orientation measured at a measurement point on a sheet surface is represented as (α β), when an angular deviation at the measurement point is defined as ϕ = (α2 + β2)1 / 2, when a grain having the angular deviation ϕ of 10° or less is defined as a Goss-oriented grain, when a region of 100 mm × 100 mm on the sheet surface is defined as a divided domain, and when it is confirmed whether the Goss-oriented grain is included in the divided domain in at least 100 divided domains, an area fraction of divided domains including at least one Goss-oriented grain having a grain size of 5 µm or more is 30% or more as compared with all divided domains.

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