Grain-oriented electrical steel sheet

Abstract

This grain-oriented electrical steel sheet is the average value aveφ of the angle deviation φ measured at multiple measurement points spaced 1 mm apart along the rolling direction L. L is 3.5° or less, and the grain size D measured along the rolling direction L L Arrange them in descending order and determine the particle size D that is 10% of the largest. L 10 is (100-15×aveφ L ) mm or less and the grain size D measured along the direction perpendicular to the rolling direction C C Average value of aveD C is 50mm or more.

Description

[Technical field]

[0001] The present invention relates to a grain-oriented electrical steel sheet. This application claims priority based on Japanese Patent Application No. 2023-106860, filed on June 29, 2023, the contents of which are incorporated herein by reference. [Background technology]

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

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

[0004] So far, methods have been proposed for obtaining steel sheets with high magnetic flux density by controlling the growth of crystal grains in secondary recrystallization. For example, Patent Documents 1 and 2 disclose a method for advancing secondary recrystallization while applying a temperature gradient to the steel sheet in the tip region of the secondary recrystallized grains which are encroaching on the primary recrystallized grains in the finish annealing process.

[0005] When secondary recrystallized grains are grown using a temperature gradient, secondary recrystallized grains with an orientation close to the ideal Goss orientation are generated in the parts of the steel sheet that reach the secondary recrystallization start state early, and these secondary recrystallized grains grow preferentially due to the temperature gradient. As a result, the concentration of grains in the Goss orientation increases, and the magnetic flux density B8 improves.

[0006] However, when secondary recrystallized grains are grown using a temperature gradient, the grains with orientations close to the ideal Goss orientation grow preferentially, but the secondary recrystallized grains tend to become excessively large. If the secondary recrystallized grains grow excessively large, the leading edge region of the secondary recrystallized grains will deviate significantly from the ideal Goss orientation, which may hinder the effect of improving magnetic flux density.

[0007] For example, secondary recrystallization progresses when the steel sheet is wound into a coil. In other words, the secondary recrystallized grains grow while the steel sheet has a curvature. However, the secondary recrystallized grains grow while maintaining the linearity of the crystal orientation. Therefore, the larger the secondary recrystallized grains grow, the greater the deviation from the ideal Goss orientation at the leading edge region of the secondary recrystallized grains due to the curvature of the coil.

[0008] The deviation between the actual crystal orientation and the ideal Goss orientation can be expressed by the deviation angle α, deviation angle β, and deviation angle γ. The deviation angle α is the deviation angle of the crystal projected onto the rolling surface when viewed from the normal direction Z of the rolling surface. <001> The misalignment angle β is the angle between the rolling direction L and the rolling direction L. The misalignment angle β is the angle between the rolling direction C (sheet width direction) and the rolling direction L. <001> The deviation angle γ is the angle between the rolling direction L and the rolling direction L. The deviation angle γ is the angle between the rolling direction L and the rolling direction L. <110> The angle between the direction and the normal direction Z of the rolling surface.

[0009] Of these deviation angles α, β, and γ, it is known that the deviation angles α and β affect the magnetic flux density. The smaller the deviation angles α and β are, the higher the magnetic flux density B8 is.

[0010] In addition, it is known that the misalignment angle β, among the misalignment angles α, β, and γ, affects magnetostriction. The smaller the misalignment angle β, the better the magnetostriction properties. Magnetostriction is a phenomenon in which a magnetic body changes shape when a magnetic field is applied. In grain-oriented electrical steel sheets used in transformers, etc., magnetostriction is a cause of vibration and noise, so small magnetostriction is required. For example, Patent Documents 3 to 5 disclose controlling the misalignment angle β. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 57-002839 [Patent Document 2] Japanese Patent Publication No. 61-190017 [Patent Document 3] Japanese Patent Publication No. 2001-294996 [Patent Document 4] Japanese Patent Application Publication No. 2005-240102 [Patent Document 5] Japanese Patent Application Publication No. 2015-206114 Summary of the Invention [Problem to be solved by the invention]

[0012] As described above, attempts have been made to increase the magnetic flux density of grain-oriented electrical steel sheets, for example by increasing the concentration of grains in the Goss orientation by promoting secondary recrystallization while applying a temperature gradient to the steel sheet, thereby improving the magnetic flux density.

[0013] However, when the secondary recrystallized grains are grown using a temperature gradient, the secondary recrystallized grains inevitably become excessively large and deviate from the ideal Goss orientation, which can hinder the improvement of the magnetic flux density and can also deteriorate the magnetostriction characteristics.

[0014] The present invention has been made in view of the above problems. An object of the present invention is to provide a grain-oriented electrical steel sheet excellent in magnetic flux density and magnetostriction characteristics. Specifically, an object of the present invention is to provide a grain-oriented electrical steel sheet excellent in both magnetic flux density and magnetostriction characteristics even when a technology of applying a temperature gradient to the steel sheet during secondary recrystallization is applied. [Means for solving the problem]

[0015] That is, the gist of the present invention is as follows.

[0016] [1] A grain-oriented electrical steel sheet according to one aspect of the present invention is The deviation angle from the ideal Goss orientation with the normal direction Z of the rolling surface as the rotation axis is defined as α, The deviation angle from the ideal Goss orientation with the rolling direction C as the rotation axis is defined as β. The deviation angle from the ideal Goss orientation with the rolling direction L as the rotation axis is defined as γ. The deviation angle of the crystal orientation measured at one measurement point on the plate surface is expressed as (α β γ), The angle deviation at the one measurement point is φ = (α 2 +β 2 ) 1 / 2 Define it as: The average value of the angle deviation φ measured at multiple measurement points spaced 1 mm apart along the rolling direction L is aveφ L When we define The above aveφ L But, aveφ L ≦3.5° is satisfied, The deviation angles of the crystal orientation measured at two adjacent measurement points on the plate surface, spaced 1 mm apart, are represented as (α1β1γ1) and (α2β2γ2), [(α2-α1) 2 +(β2-β1) 2 +(γ2-γ1) 2 ] 1 / 2 The midpoint between the two measurement points that satisfy ≧1.0° is defined as the grain boundary GB. The grain size in the rolling direction L determined based on the grain boundary GB is expressed in mm as D L Define it as: Grain size D along the rolling direction L LArrange them in ascending order and determine the particle size that is 10% of the largest by number in mm. L When defined as 10, D L 10 is D L 10≦100-15×abeφ L Fulfilling The grain size in the direction perpendicular to the rolling direction C calculated based on the grain boundary GB is expressed in mm as D C Define it as: Grain size D measured along the direction perpendicular to the rolling direction C C The average value of C When we define aveD C But, aveD C Satisfy ≧50. Effect of the Invention

[0017] According to the above-mentioned aspects of the present invention, it is possible to provide a grain-oriented electrical steel sheet excellent in magnetic flux density and magnetostriction characteristics. Specifically, it is possible to provide a grain-oriented electrical steel sheet excellent in both magnetic flux density and magnetostriction characteristics even when a technology of applying a temperature gradient to the steel sheet during secondary recrystallization is applied. [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is a diagram showing an example of using spot current heating as a local rapid heating method, and is a schematic diagram showing an example of the arrangement of local heat affected regions in a decarburized annealed steel sheet. [Diagram 2] FIG. 2 is a schematic diagram showing the distribution of Goss-oriented grains in a decarburized annealed steel sheet. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] A preferred embodiment of the present invention will be described in detail. However, the present invention is not limited to the configuration disclosed in this embodiment, and various modifications are possible within the scope of the present invention. In addition, the lower and upper limits of the numerical ranges described below are included in the ranges. Numerical values ​​indicated as "greater than" or "less than" are not included in the numerical ranges. In addition, "%" in relation to chemical composition means "mass %" unless otherwise specified.

[0020] The grain-oriented electrical steel sheet (base steel sheet) according to this embodiment is The deviation angle from the ideal Goss orientation with the normal direction Z of the rolling surface as the rotation axis is defined as α, The deviation angle from the ideal Goss orientation with the rolling direction C as the rotation axis is defined as β. The deviation angle from the ideal Goss orientation with the rolling direction L as the rotation axis is defined as γ. The deviation angle of the crystal orientation measured at one measurement point on the plate surface is expressed as (α β γ), The angle deviation at the one measurement point is φ=(α 2 +β 2 ) 1 / 2 Define it as: The average value of the angle deviation φ measured at multiple measurement points spaced 1 mm apart along the rolling direction L is aveφ L When we define Above aveφ L But, aveφ L ≦3.5°.

[0021] In addition, the grain-oriented electrical steel sheet (base steel sheet) according to this embodiment has The deviation angles of the crystal orientations measured at two adjacent measurement points spaced 1 mm apart on the plate surface are represented as (α1β1γ1) and (α2β2γ2), [(α2-α1) 2 +(β2-β1) 2 +(γ2-γ1) 2 ] 1 / 2 The midpoint between the two measurement points that satisfy ≧1.0° is defined as the grain boundary GB. The grain size in the rolling direction L determined based on the grain boundary GB is expressed in mm as D L Define it as: Grain size D measured along the rolling direction LL Arrange them in ascending order and determine the particle size that is 10% of the largest by number in mm. L When defined as 10, Above D L 10 is D L 10≦100-15×abeφ L Meet the following.

[0022] In addition, the grain-oriented electrical steel sheet (base steel sheet) according to this embodiment has The grain size in the direction perpendicular to the rolling direction C calculated based on the grain boundary GB is expressed in mm as D C Define it as: Grain size D measured along the direction perpendicular to the rolling direction C C The average value of C When we define Above aveD C But, aveD C Satisfy ≧50.

[0023] In the grain-oriented electrical steel sheet according to this embodiment, when all of the above conditions are satisfied simultaneously, it is possible to improve both the magnetic flux density and the magnetostriction characteristics even when a technique for applying a temperature gradient to the steel sheet during secondary recrystallization is applied.

[0024] In this embodiment, the angle deviation φ is defined by the deviation angles α and β. In general, the angle deviation θ is often evaluated by three components, the deviation angles α, β, and γ. However, in this embodiment, the angle deviation φ is defined by two components, the deviation angles α and β, excluding the deviation angle γ, which has little effect on the magnetic flux density and magnetostriction characteristics. If the above conditions are satisfied using this angle deviation φ, the above effects can be obtained. On the other hand, the grain boundaries and grain sizes may be determined based on the three components, the deviation angles α, β, and γ.

[0025] Above aveφ LA mean angle deviation φ of 3.5° or less means that the average angular deviation φ is small at each measurement point along the rolling direction L. In other words, this means that the angular deviation between the rolling direction L and the direction of the easy axis of magnetization is small. As a result, the magnetic properties, particularly the magnetic flux density, are favorably improved. aveφ L is preferably 3.2° or less, more preferably 3.0° or less, and even more preferably 2.7° or less. L Since the smaller the value, the better, the lower limit is not particularly limited. L It is not easy to make aveφ zero. L It is sufficient that the angle is 0.5° or more, and 1.0° or more.

[0026] Above D L 10 is (100-15×aveφ L ) mm or less means that the crystal grains do not grow coarsely in the rolling direction L. If the crystal grains do not grow coarsely in the rolling direction L, it is possible to suppress the increase in the above-mentioned misalignment angles, particularly the misalignment angle β. If the increase in the misalignment angle β is suppressed, the decrease in magnetic flux density is suppressed, and the increase in magnetostriction is also suppressed. L When the above conditions are satisfied, the magnetic flux density and magnetostriction characteristics are preferably improved. L 10 is (90-15×aveφ L ) mm or less, and (80-15×aveφ L ) mm or less is more preferable. L Since the smaller the value, the more preferable it is, the lower limit is not particularly limited. For example, D L The number 10 may be 5 mm or more, or 10 mm or more.

[0027] aveD CA mean diameter of 50 mm or more indicates that the shape of the crystal grains extends in the direction C perpendicular to the rolling direction. The grain-oriented electrical steel sheet according to this embodiment is based on the premise that a technology for applying a temperature gradient to the steel sheet during secondary recrystallization is applied. Therefore, the secondary recrystallized grains tend to grow coarse. However, in this embodiment, as described above, the grains are suppressed from growing coarsely in the rolling direction L. On the other hand, in this embodiment, the grains are permitted to grow coarsely in the direction C perpendicular to the rolling direction. The grain-oriented electrical steel sheet according to this embodiment is based on the premise that a technology for applying a temperature gradient to the steel sheet during secondary recrystallization is applied. Therefore, the secondary recrystallized grains tend to grow coarse, and the aveD C is 50mm or more. aveD C is preferably 80 mm or more, more preferably 100 mm or more, and even more preferably 200 mm or more. C There is no particular upper limit to the above. For example, the grain size of the crystal grains in the direction perpendicular to the rolling direction C may be the coil width (for example, width 1000 mm). C It is sufficient if the distance is 800 mm or less, or 500 mm or less.

[0028] The above-mentioned deviation angles α, β, γ, etc. can be measured by setting a measurement line including at least 500 measurement points at 1 mm intervals on the rolled surface to measure the crystal orientation. For example, the crystal orientation can be measured by the X-ray diffraction method (Laue method). The Laue method is a method in which an X-ray beam is irradiated onto a steel sheet and the transmitted or reflected diffraction spots are analyzed. By analyzing the diffraction spots, the crystal orientation at the location where the X-ray beam is irradiated can be identified. By changing the irradiation position and analyzing the diffraction spots at multiple locations, the crystal orientation distribution at each irradiation position can be measured. The Laue method is a method suitable for measuring the crystal orientation of a metal structure having coarse crystal grains.

[0029] It is sufficient that the number of measurement points for the crystal orientation is at least 500, but it is preferable to appropriately increase the number of measurement points depending on the size of the secondary recrystallized grains. For example, if the number of measurement points for measuring the crystal orientation is 500 and the number of secondary recrystallized grains included within the measurement line is less than 10, it is preferable to extend the measurement line by increasing the number of measurement points at 1 mm intervals so that the measurement line includes 10 or more secondary recrystallized grains. In addition, if it is difficult to set 500 measurement points on one measurement line, multiple measurement lines may be set to measure the crystal orientation at a total of 500 or more measurement points.

[0030] The crystal orientation is measured at 1 mm intervals on the rolled surface, and the above-mentioned deviation angles α, β, γ, etc. are determined for each measurement point. Based on the deviation angles at each measurement point, the angle deviations φ, aveφ L , grain boundary GB, grain size D L , D L 10, particle size D C , aveD C It is sufficient to find D L 10 is the particle size D L The grains with a diameter of 2 mm or more are arranged in order of size, and the grain size that makes up 10% of the largest grains is found. C is the particle size D C The average grain size can be calculated based on the grains with a diameter of 2 mm or more. In addition, when the irradiation area of ​​the X-ray beam at the measurement point of the crystal orientation by the Laue method spans two grains, and it is impossible to determine which grain the X-ray diffraction result comes from, 0.5 mm can be added to the grain sizes of the two grains.

[0031] Moreover, the grain-oriented electrical steel sheet according to this embodiment may have the following chemical composition.

[0032] The grain-oriented electrical steel sheet according to this embodiment may have a chemical composition that contains, by mass fraction, 2.0% to 7.0% Si, with the remainder being Fe and impurities.

[0033] Furthermore, this grain-oriented electrical steel sheet may contain known optional elements in place of a portion of Fe in order to improve the magnetic properties. There is no need to set a lower limit for the optional elements, and the lower limit may be 0%. Furthermore, the upper limit for the optional elements may be set to a range in which no significant decrease in magnetic flux density or iron loss occurs. The upper limit values ​​serving as a guide for each optional element are listed below.

[0034] Specifically, the grain-oriented electrical steel sheet (base steel sheet) according to this embodiment has a chemical composition, in mass%, of: Si: 2.0-7.0%, C: 0 to 0.0050%, Mn: 0-1.0%, S and Se: 0 to 0.0150% in total, Al: 0 to 0.0650%, N: 0 to 0.0050%, Nb, V, Mo, Ta, and W: 0 to 0.050% in total, Cu: 0-0.40%, Bi: 0 to 0.010%, B: 0~0.080%, P: 0-0.50%, Ti: 0 to 0.0150%, Sn: 0~0.10%, Sb: 0 to 0.10%, Cr: 0~0.30%, Ni: 0-1.0%, and the remainder being Fe and impurities.

[0035] Si: 2.0-7.0% Si (silicon) is a basic element for base steel sheet. If the Si content is less than 2.0%, eddy current loss cannot be sufficiently reduced, and good magnetic properties cannot be obtained. Therefore, the Si content of the base steel sheet is set to 2.0% or more. The Si content is preferably 2.50% or more, and more preferably 3.0% or more. On the other hand, if the Si content exceeds 7.0%, the steel sheet becomes embrittled and the sheet passing property during production is significantly deteriorated, so the Si content of the base steel sheet is set to 7.0% or less. The Si content is preferably 4.50% or less, and more preferably 4.0% or less.

[0036] C: 0 to 0.0050% C (carbon) is a selective element for the base steel sheet. C is contained in the steel slab, but if excessive C remains in the base steel sheet after finish annealing, good core loss characteristics may not be obtained. Therefore, the C content of the base steel sheet may be 0.0050% or less. The C content is preferably 0.0040% or less, more preferably 0.0030% or less. On the other hand, the lower limit of the C content of the base steel sheet is not particularly limited and may be 0%. However, since it is not industrially easy to make the C content 0%, the C content may be more than 0% or may be 0.00010% or more.

[0037] Mn: 0-1.0% Mn (manganese) is an optional element for the base steel sheet. Mn is contained in the steel slab, but if it is contained in excess, the steel undergoes a phase transformation during secondary recrystallization annealing, secondary recrystallization does not proceed sufficiently, and good magnetic properties may not be obtained. Therefore, the Mn content of the base steel sheet may be 1.0% or less. The Mn content is preferably 0.50% or less, more preferably 0.20% or less. On the other hand, the lower limit of the Mn content of the base steel sheet is not particularly limited and may be 0%. However, since Mn forms MnS and MnSe and has the effect of acting as an inhibitor during secondary recrystallization, the Mn content may be more than 0% or may be 0.00010% or more.

[0038] Sum of S and Se: 0 to 0.0150% S (sulfur) and Se (selenium) are optional elements for the base steel sheet. S and Se are contained in a steel slab, but if S and Se remain in excess in the base steel sheet after final annealing, they may adversely affect the magnetic properties. Therefore, the total content of S and Se in the base steel sheet may be 0.0150% or less. The total content of S and Se is preferably 0.010% or less, more preferably 0.0050% or less. On the other hand, the lower limit of the total content of S and Se in the base steel sheet is not particularly limited and may be 0%. However, since S and Se form MnS and MnSe and have the effect of acting as an inhibitor during secondary recrystallization, the total content of S and Se may be more than 0% or may be 0.00010% or more.

[0039] Al: 0 to 0.0650% Al (aluminum) is a selective element for the base steel sheet. Al is contained in the steel slab, but if excessive Al remains in the base steel sheet after finish annealing, it may adversely affect the magnetic properties. Therefore, the Al content of the base steel sheet may be 0.0650% or less. The Al content is preferably 0.040% or less, more preferably 0.035% or less. On the other hand, the lower limit of the Al content of the base steel sheet is not particularly limited and may be 0%. However, since Al forms AlN and has the effect of acting as an inhibitor during secondary recrystallization, the Al content may be more than 0% or may be 0.00010% or more. The above Al content is acid-soluble Al (sol.Al).

[0040] N: 0 to 0.0050% N (nitrogen) is a selective element for the base steel sheet. N is contained in the steel slab, but if excessive N remains in the base steel sheet after finish annealing, it may adversely affect the magnetic properties. Therefore, the N content of the base steel sheet may be 0.0050% or less. The N content is preferably 0.0040% or less, more preferably 0.0030% or less. On the other hand, the lower limit of the N content of the base steel sheet is not particularly limited and may be 0%. However, since N forms AlN and has the effect of acting as an inhibitor during secondary recrystallization, the N content may be more than 0% or may be 0.00010% or more.

[0041] Total of Nb, V, Mo, Ta, and W: 0 to 0.050% Nb (niobium), V (vanadium), Mo (molybdenum), Ta (tantalum), and W (tungsten) are optional elements for the base steel sheet. If an excessive amount of Nb group elements (one or more of Nb, V, Mo, Ta, and W) remains in the base steel sheet, it may adversely affect the magnetic properties. Therefore, the total content of Nb, V, Mo, Ta, and W in the base steel sheet may be 0.050% or less. The Nb group elements are preferably 0.030% or less, preferably 0.020% or less, and more preferably 0.010% or less. On the other hand, the total content of Nb, V, Mo, Ta, and W in the base steel sheet is not particularly limited and may be 0%. However, since Nb, V, Mo, Ta, or W forms carbides, nitrides, or carbonitrides and has the effect of acting as an inhibitor during secondary recrystallization, the total content of Nb, V, Mo, Ta, and W may be more than 0% or may be 0.003% or more.

[0042] Cu: 0-0.40% Cu (copper) is an optional element for the base steel sheet. If the Cu content exceeds 0.40%, the steel sheet may become embrittled during hot rolling. Therefore, the Cu content of the base steel sheet may be 0.40% or less. The Cu content is preferably 0.30% or less, more preferably 0.10% or less. On the other hand, the lower limit of the Cu content is not particularly limited and may be 0%. However, since Cu has the effect of increasing the concentration of Goss orientation and improving magnetic properties, the Cu content may be more than 0% or may be 0.010% or more.

[0043] Bi: 0 to 0.010% Bi (bismuth) is an optional element for the base steel sheet. If the Bi content exceeds 0.010%, the coating adhesion may decrease. Also, if the purification during the final annealing is insufficient and Bi remains in excess, it may have an adverse effect on the magnetic properties. Therefore, the Bi content of the base steel sheet may be 0.010% or less. The Bi content is preferably 0.0050% or less, more preferably 0.0020% or less, and more preferably 0.0010% or less. On the other hand, the lower limit of the Bi content is not particularly limited and may be 0%. However, since Bi has an effect of improving the magnetic flux density, the Bi content may be more than 0% or may be 0.00050% or more.

[0044] B: 0~0.080% B (boron) is an optional element for the base steel sheet. If the B content exceeds 0.080%, the variation (standard deviation) of the magnetic flux density may become large. Therefore, the B content may be 0.080% or less. The Bi content is preferably 0.070% or less, more preferably 0.060% or less. On the other hand, the lower limit of the B content is not particularly limited and may be 0%. However, since B forms nitrides and has the effect of acting as an inhibitor during secondary recrystallization, the B content may be more than 0% or may be 0.00050% or more.

[0045] P: 0~0.50% P (phosphorus) is an optional element for the base steel sheet. If the P content exceeds 0.50%, the workability of the steel sheet may be significantly reduced. Therefore, the P content of the base steel sheet may be 0.50% or less. The P content is preferably 0.30% or less, and more preferably 0.10% or less. On the other hand, the lower limit of the P content is not particularly limited and may be 0%. However, since P has the effect of improving the texture and improving the magnetic properties of the steel sheet, the P content may be more than 0% or may be 0.0020% or more.

[0046] Ti: 0 to 0.0150% Ti (titanium) is an optional element for the base steel sheet. If the Ti content exceeds 0.0150%, the magnetic properties may be significantly reduced. Therefore, the Ti content of the base steel sheet may be 0.0150% or less. The Ti content is preferably 0.0130% or less, more preferably 0.010% or less. On the other hand, the lower limit of the Ti content is not particularly limited and may be 0%. However, since Ti forms carbides, nitrides, and carbonitrides and has the effect of acting as an inhibitor during secondary recrystallization, the Ti content may be more than 0% or may be 0.0020% or more.

[0047] Sn: 0 to 0.10% Sn (tin) is an optional element for the base steel sheet. If the Sn content exceeds 0.10%, the secondary recrystallization becomes unstable, which may adversely affect the magnetic properties. Therefore, the Sn content of the base steel sheet may be 0.10% or less. The Sn content is preferably 0.090% or less, more preferably 0.080% or less. On the other hand, the lower limit of the Sn content is not particularly limited, and may be 0%. However, since Sn has the effect of increasing the concentration of Goss orientation and improving the magnetic properties, the Sn content may be more than 0% or may be 0.0050% or more.

[0048] Sb: 0 to 0.10% Sb (antimony) is an optional element for the base steel sheet. If the Sb content exceeds 0.10%, it may have an adverse effect on the magnetic properties. Therefore, the Sb content of the base steel sheet may be 0.10% or less. The Sb content is preferably 0.090% or less, more preferably 0.080% or less. On the other hand, the lower limit of the Sb content is not particularly limited and may be 0%. However, since Sb functions as an inhibitor and has the effect of stabilizing secondary recrystallization, the Sb content may be more than 0% or may be 0.010% or more.

[0049] Cr: 0~0.30% Cr (chromium) is an optional element for the base steel sheet. If the Cr content exceeds 0.30%, Cr oxides are formed, which may adversely affect the magnetic properties. Therefore, the Cr content of the base steel sheet may be 0.30% or less. The Cr content is preferably 0.20% or less, and more preferably 0.10% or less. On the other hand, the lower limit of the Cr content is not particularly limited and may be 0%. However, since Cr has the effect of increasing the concentration of Goss orientation and improving the magnetic properties, the Cr content may be more than 0% or may be 0.010% or more.

[0050] Ni: 0-1.0% Ni (nickel) is an optional element for the base steel sheet. If the Ni content exceeds 1.0%, secondary recrystallization may become unstable. Therefore, the Ni content of the base steel sheet may be 1.0% or less. The Ni content is preferably 0.20% or less, and more preferably 0.10% or less. On the other hand, the lower limit of the Ni content is not particularly limited and may be 0%. However, since Ni has the effect of increasing electrical resistance and reducing iron loss, the Ni content may be more than 0% or may be 0.010% or more.

[0051] The base steel sheet of the grain-oriented electrical steel sheet according to the present embodiment may contain impurities. Note that the term "impurities" refers to substances that are mixed in from raw materials such as ores and scraps, or from the manufacturing environment, during industrial production of steel.

[0052] The chemical composition of the above-mentioned base steel sheet may be measured by a general analytical method. For example, it may be measured using ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectrometry). Acid-soluble Al may be measured by ICP-AES using the filtrate obtained by thermally decomposing a sample with acid. C and S may be measured using the combustion-infrared absorption method, N may be measured using the inert gas fusion-thermal conductivity method, and O may be measured using the inert gas fusion-non-dispersive infrared absorption method.

[0053] The above chemical composition is that of the base steel sheet. If the grain-oriented electrical steel sheet to be used as the measurement sample has an insulating coating or the like on its surface, the coating or the like is removed by the method described below before measuring the chemical composition.

[0054] For example, the insulating coating can be removed by immersing the grain-oriented electrical steel sheet having the coating in a high-temperature alkaline solution. Specifically, the insulating coating can be removed from the grain-oriented electrical steel sheet by immersing the sheet in an aqueous sodium hydroxide solution of 30-50% by mass of NaOH and 50-70% by mass of H2O at 80-90°C for 5-10 minutes, followed by rinsing with water and drying. The time for immersion in the aqueous sodium hydroxide solution can be changed depending on the thickness of the insulating coating.

[0055] Furthermore, a method for removing the forsterite coating (glass coating) can be achieved by immersing the electrical steel sheet from which the insulating coating has been removed by the above method in hot hydrochloric acid. Specifically, the concentration of hydrochloric acid suitable for removing the forsterite coating to be dissolved is determined in advance, and the forsterite coating can be removed by immersing the sheet in hydrochloric acid of this concentration (e.g., 30-40 mass% hydrochloric acid) at 80-90°C for 1-5 minutes, followed by rinsing with water and drying. Typically, different treatment solutions are used to remove each coating, such as an alkaline solution being used to remove the insulating coating and hydrochloric acid being used to remove the forsterite coating.

[0056] The process by which the grain-oriented electrical steel sheet according to this embodiment was obtained will be described below.

[0057] Ideal Goss orientation {110} <001> The frequency of practical Goss oriented grains, which have small angular deviations θ and φ with respect to the orientation, increases as the heating rate of the primary annealing (decarburization annealing) increases. <447> (≒{111} <112> ) direction and {411} <148> The frequency of crystal grains that are easily encroached upon by Goss orientation grains (called corresponding orientation grains) decreases as the heating rate of the primary annealing increases. Therefore, it has been difficult to increase the ratio of practical Goss orientation grains while also increasing the ratio of corresponding orientation grains in the primary annealing.

[0058] In this embodiment, it has been discovered for the first time that a grain-oriented electrical steel sheet having excellent quality can be obtained by forming a locally heated region by locally rapid heating a cold-rolled steel sheet, controlling the annealing conditions of the primary annealing (decarburization annealing), and controlling the annealing conditions of the secondary annealing (finish annealing).

[0059] The locally heated region formed before the primary annealing is arranged locally on the surface of the steel sheet. The crystalline structure of this locally heated region is composed of one or both of a recrystallized structure and a recovered structure at the time of completion of the local rapid heating. The crystalline structure of the non-rapidly heated portion of the steel sheet surface other than the locally heated region is composed of a cold worked structure that is as it is cold rolled.

[0060] The local rapid heating is preferably performed at a heating rate of 500°C / sec or more, preferably 2000°C / sec or more, and more preferably 10000°C / sec or more. Thus, it has been found that when a local heating region is formed on the surface of a steel sheet before the primary annealing and then the steel sheet is subjected to the primary annealing, a large number of crystal grains having a practical Goss orientation are formed in the region (local heat-affected region) that has been thermally affected by the local rapid heating. It has also been found that, among the Goss-oriented grains that are formed, the ratio of Goss-oriented grains having smaller angular deviations θ and φ from the ideal Goss orientation increases, and the grain size of the Goss-oriented grains after the primary annealing increases.

[0061] The frequency of coarse Goss-oriented grains in the local heat affected zone is higher than that obtained by normal rapid heating of the entire sheet. This characteristic is considered to be due to the fact that the peripheral area of ​​the locally heated zone is a processed structure that retains a lot of strain. Specifically, when local rapid heating is performed, the practical Goss-oriented grains generated in the locally heated zone preferentially encroach on the peripheral unrecrystallized area that retains a lot of strain during primary annealing, and increase in diameter. However, when the entire steel sheet is heated, the generation and growth of recrystallized grains occurs uniformly in the steel sheet, and it is considered that such increase in diameter does not occur.

[0062] After the local heat affected zones having the above characteristics are scattered on the surface of the steel sheet by the primary annealing, secondary annealing is further performed. In the secondary annealing, secondary recrystallization is promoted while applying a temperature gradient to the steel sheet. At this time, the Goss oriented grains formed in the local heat affected zone grow preferentially during the secondary annealing. A large number of Goss oriented grains are formed in the local heat affected zone, and among them are Goss oriented grains that are close to the ideal Goss orientation with particularly small angle deviation θ and angle deviation φ and have large crystal grain size after the primary annealing, and such Goss oriented grains grow preferentially in the secondary recrystallization.

[0063] Since the Goss-oriented grains that become the nuclei of secondary recrystallization are supplied to the local heat-affected zone, it is not necessary to form Goss-oriented grains in the matrix part other than the local heat-affected zone, i.e., the local heat-unaffected zone, by primary annealing. Therefore, the heat treatment conditions for the primary annealing are set to be slow heating conditions with a slow heating rate, and the {111} <112> Directions and <148> It is also possible to adopt primary annealing conditions that will form many corresponding orientation grains in the region not affected by the local heating. For example, by setting the heating rate in the primary annealing to 300°C / sec or less, many Goss orientation grains that are close to the ideal Goss orientation and have large crystal grain sizes will be formed in the region affected by the local heating, while almost no Goss orientation grains will be formed in the region not affected by the local heating, and conversely, many corresponding orientation grains will be formed.

[0064] As described above, in the local heat affected region of a steel sheet (decarburized annealed steel sheet) that has been subjected to local rapid heating and primary annealing, there are many Goss oriented grains that are close to the ideal Goss orientation and have a large grain size. On the other hand, in the matrix portion (region not affected by local heating), there are almost no large Goss oriented grains, and it is possible to have many corresponding oriented grains that are easily eroded.

[0065] When such a steel sheet (decarburization annealed steel sheet) is subjected to secondary annealing, the Goss oriented grains that are present in the local heat affected zone, are close to the ideal Goss orientation, and have a large grain size, start to grow preferentially and grow toward the zone not affected by the local heat.

[0066] In addition, in this embodiment, secondary recrystallization is advanced by applying a temperature gradient to the steel sheet in the tip region of the secondary recrystallized grain that is eating away at the primary recrystallized grain during secondary annealing. When the secondary recrystallized grain is grown using a temperature gradient, secondary recrystallized grains having an orientation close to the ideal Goss orientation are generated from the portion of the steel sheet that reaches the secondary recrystallization start state early, and these secondary recrystallized grains grow preferentially due to the temperature gradient. As a result, the degree of accumulation in the Goss orientation is preferably increased. The direction in which the above temperature gradient is applied may be the direction C perpendicular to the rolling direction.

[0067] Conventionally, when secondary recrystallized grains are grown using a temperature gradient, the secondary recrystallized grains become excessively large, and it is unavoidable to worsen the misalignment angle β due to coil setting. Specifically, for example, when the temperature gradient during secondary annealing is set in the rolling perpendicular direction C, secondary recrystallized Goss orientation grains tend to grow on the low temperature side of the steel sheet (rolling perpendicular direction C), but at that time, secondary recrystallized grains also grow in the rolling direction L. Therefore, the grain size D in the rolling direction L In other words, in the conventional technology, the higher the magnetic flux density is, the larger the grain size D in the rolling direction becomes. L However, in this embodiment, the frequency of secondary recrystallized grains close to the ideal Goss orientation can be increased by the local rapid heating described above, so that the grain size D in the rolling direction can be increased. LThis can suppress an increase in the slip angle β, and can suppress the deterioration of the slip angle β due to coil setting. In this way, in this embodiment, by suppressing the deterioration of the slip angle β, a steel sheet having better magnetic flux density and magnetostriction characteristics than the conventional steel sheet can be obtained. In addition, in this embodiment, secondary recrystallized grains having an orientation close to the ideal Goss orientation are preferentially generated, so that the deterioration of the slip angle α can also be suppressed. Therefore, a steel sheet having better magnetic flux density than the conventional steel sheet can be obtained.

[0068] The investigations conducted by the present inventors will be specifically described below.

[0069] As one aspect of the localized rapid heating, a case where spot current heating by electric resistance heating is used will be described. In the spot current heating, spot electrodes are pressed against both sides of a steel sheet so as to face each other, and a current is passed between the spot electrodes to spot current heating the electrode holding portion of the steel sheet. A steel having the composition shown in Table 1 was used, and a cold-rolled steel sheet having a sheet thickness of 0.22 mm was obtained by hot rolling and cold rolling. This steel sheet was subjected to spot current heating. The spot current heating was performed using a copper electrode having a diameter of 3 mm under the conditions of a current of 5.0 kA or less, which is a range in which the steel sheet surface does not melt, a current time of 20 milliseconds to 80 milliseconds, an electrode pressure of 50 kgf to 150 kgf, and an electrode holding time after current application of 0.2 seconds. Spot current heating was performed on the surface of the cold-rolled steel sheet at a position 10 mm from the end of the cold-rolled steel sheet in the rolling perpendicular direction at a pitch of 20 mm in the rolling direction to form a locally heated region. This cold-rolled steel sheet was subjected to decarburization annealing (primary annealing), in which the cold-rolled steel sheet was heated at a heating rate of 20° C. / sec and held at 830° C. for 90 seconds.

[0070] An example of the arrangement of the local heat affected zone in a decarburized annealed steel sheet produced under the above conditions is shown in Figure 1. In Figure 1, a decarburized annealed steel sheet 1, a local heat affected zone 2, a rolling direction 21, and a width direction (direction perpendicular to the rolling direction) 22 are shown.

[0071] [Table 1]

[0072] To prepare the surface of the decarburized annealed steel sheet (steel sheet after localized rapid heating and primary annealing) for observation by EBSD (Electron Back Scattering Diffraction pattern), a smooth surface was created by mechanical polishing, electrolytic polishing was performed to remove processing distortion on the surface, and the IQ (Image Quality) value and crystal orientation were measured in 0.5 μm steps by EBSD for the area including the locally heated area. Figure 2 is a schematic diagram showing the distribution of Goss orientation grains in the decarburized annealed steel sheet manufactured under the above conditions.

[0073] The current-carrying electrode used in the spot current heating has a circular shape, and its diameter, in terms of the circle equivalent diameter, is preferably 0.5 mmφ to 10 mmφ, and more preferably 1 mmφ to 5 mmφ. Note that, although a circular current-carrying electrode was used in the above, it is sufficient to locally increase the heating rate of the cold-rolled steel sheet, form Goss-oriented grains in this region, and cause the grains to grow, and the electrode shape may be other shapes, for example, elliptical or linear.

[0074] In Figure 2, the angle deviation φ = (α 2 +β 2 ) 1 / 2 Based on the definition, crystal grains (Goss oriented grains 14) with an angle deviation φ of 10° or less from the ideal Goss orientation were displayed with a "○". Furthermore, among the crystal grains with an angle deviation φ of 10° or less, crystal grains with a coarse crystal grain size (coarse Goss oriented grains 15) were displayed with a "◎". Note that coarse Goss oriented grains 15 refer to Goss oriented grains with a grain size three times or more larger than the average grain size.

[0075] As shown in Fig. 2, the decarburized annealed steel sheet 1 produced under the above conditions contains Goss oriented grains 14 and coarse Goss oriented grains 15. In particular, the region containing the coarse Goss oriented grains 15 corresponds to the local heat affected region 2. Note that Fig. 2 shows a schematic diagram of the local heat affected region boundary 4 and the local heat affected region boundary 5, but it is not easy to distinguish these boundaries by observing the structure. However, the region containing the coarse Goss oriented grains 15 can be regarded as the local heat affected region 2.

[0076] The above decarburized annealed steel sheet was further subjected to nitriding treatment, and then an annealing separator mainly composed of MgO was applied, followed by secondary annealing. The secondary annealing conditions were a hydrogen-nitrogen atmosphere, a heating rate of 15°C / hr (°C / hour), and holding at 1200°C for 20 hr (hours). In addition, during heating for secondary annealing, a temperature gradient of 5°C / cm was applied in the direction perpendicular to the rolling direction at the boundary between the primary recrystallized region and the secondary recrystallized region in the steel sheet.

[0077] The obtained steel sheet was subjected to macro-etching to reveal the grain boundaries. When the steel sheet after macro-etching was observed at the location corresponding to the local heat affected zone, it was found that multiple secondary recrystallized grains had grown from the location corresponding to the local heat affected zone, and that secondary recrystallized grains had spread from the center of the location corresponding to the local heat affected zone. In addition, in the location corresponding to the local heat affected zone, minute grains of 2 mm or less were sometimes observed as traces of the local heat affected zone, but not in other cases. Although the secondary recrystallized macrostructure may change slightly depending on the local heating conditions, the degree of accumulation in the Goss orientation was increased compared to the case without local heat treatment.

[0078] In addition, the crystal orientation of the obtained steel sheet was measured by the Laue method described above. L is less than 3.5°, and D L 10 is (100-15×aveφ L ) mm or less and aveD C As a result, the obtained steel sheet was excellent in both magnetic flux density and magnetostriction, even though a temperature gradient was applied to the steel sheet during secondary recrystallization.

[0079] As described above, it was confirmed that the obtained grain-oriented electrical steel sheet had an extremely small deviation between the crystal orientation of the secondary recrystallized grains and the ideal Goss orientation, and that the angle deviation φ was small on average at each measurement point along the rolling direction L, the crystal grains did not grow coarsely with respect to the rolling direction L, and the shape of the crystal grains tended to be elongated in the direction perpendicular to the rolling C and flattened in the rolling direction L.

[0080] Considering the above results, it is believed that the reason for the good secondary recrystallization orientation is that the decarburized annealed steel sheet has coarse Goss orientation grains close to the ideal Goss orientation with a size advantage. In addition, it is believed that the reason for the improvement in both magnetic flux density and magnetostriction is that the local heating region is preferably arranged before the primary annealing, the annealing conditions during the primary annealing are preferably controlled, and the annealing conditions during the secondary annealing are preferably controlled.

[0081] For example, when the above-mentioned decarburized annealed steel sheet is used, during secondary recrystallization, among the many Goss-oriented grains in the local heat affected zone, the coarse Goss-oriented grains (Goss-oriented grains with large crystal grain size) close to the ideal Goss orientation grow preferentially. Therefore, even if the secondary recrystallized grains are not allowed to grow large, it is possible to obtain a steel sheet dominated by secondary recrystallized grains close to the ideal Goss orientation. For example, when scattering the local heat affected zones on the steel sheet surface, the size, shape, and arrangement of the crystal grains after secondary annealing can be controlled by appropriately arranging the local heat affected zones on the steel sheet surface. For example, if a Goss-oriented grain that starts to grow from one local heat affected zone collides with another Goss-oriented grain that starts to grow from an adjacent local heat affected zone and the grain growth stops, the grain size of the Goss-oriented grains at the end of secondary annealing (especially the grain size D in the rolling direction) can be controlled. L ) can be made into a steel sheet with a small magnetic flux density. In particular, as described above, in the early stage of secondary annealing, the Goss orientation grains that grow preferentially from the local heat affected region have a crystal orientation close to the ideal Goss orientation, so that good magnetic flux density can be obtained despite the small secondary recrystallized grain size. In addition, since the crystal grains are prevented from growing coarsely in the rolling direction L, the deterioration of the misalignment angle β due to coil setting can be suppressed, and good magnetostriction characteristics can be obtained.

[0082] In other words, the grain size of the above-mentioned grain-oriented electrical steel sheet is secondary recrystallized (particularly the grain size in the rolling direction D L) can be suppressed from becoming coarse while increasing the degree of accumulation in the Goss orientation, so that it is not necessary to introduce strain or form grooves to refine the magnetic domain width, or this can be reduced. Specifically, the magnetic domain refinement effect can be obtained favorably by the grain boundaries that increase with the refinement of the secondary recrystallized grain size, so that the magnetic domains are refined without applying the conventional magnetic domain control technology. Therefore, unlike the conventional magnetic domain control technology, it is not necessary to introduce strain into the steel sheet, or this can be reduced, so that an increase in magnetostriction can be prevented. In addition, unlike the conventional magnetic domain control technology, it is not necessary to form grooves in the steel sheet, or this can be reduced in depth, so that a decrease in magnetic flux density B8 can be prevented. In addition, the above-mentioned grain-oriented electrical steel sheet can be used for applications requiring strain relief annealing at 800°C or higher.

[0083] As described above, the grain-oriented electrical steel sheet according to the present embodiment has a secondary recrystallized grain size (particularly the grain size in the rolling direction D L ) is finer, the number of grain boundaries increases, which can provide a favorable magnetic domain refinement effect, resulting in excellent core loss characteristics.

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

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

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

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

[0088] (Casting process) In the casting process, a slab is prepared. An example of a method for producing a slab is as follows. Molten steel is produced (smelted). A slab is produced using the molten steel. The slab may be produced by a continuous casting method. An ingot may be produced using the molten steel, and the ingot may be bloomed to produce a slab. The thickness of the slab is not particularly limited. The thickness of the slab is, for example, 150 to 350 mm. The thickness of the slab is preferably 220 to 280 mm. As the slab, a so-called thin slab having a thickness of 10 to 70 mm may be used. When a thin slab is used, rough rolling before finish rolling can be omitted in the hot rolling process.

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

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

[0091] Si: 2.0-7.0% Silicon (Si) increases the electrical resistance of grain-oriented electrical steel sheets and reduces iron loss. If the Si content is less than 2.0%, γ transformation occurs during finish annealing, damaging the crystal orientation of the grain-oriented electrical steel sheets. On the other hand, if the Si content exceeds 7.0%, cold workability decreases and cracks tend to occur during cold rolling. The lower limit of the Si content is preferably 2.5%, more preferably 3.0%. The upper limit of the Si content is preferably 4.5%, more preferably 4.0%.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

[0108] (Localized rapid heating process) In this embodiment, local rapid heating is performed on the cold-rolled steel sheet after the cold rolling process to form a local heating region. The rapid heating method is not particularly limited as long as it can locally heat the steel sheet. For example, a method of heating by contacting a spot electrode with the front and back surfaces of the steel sheet and passing an electric current through the steel sheet, a method of heating by irradiating the surface of the steel sheet with laser light or an electron beam, a method of locally heating by induction heating, a method of heating by contacting a hot piece, etc. can be adopted. The size of each local heating region can be a dot-like region with a diameter of about 10 μm to 10 mm, or a linear region with a width of about 10 μm to 10 mm. In addition, the electrode used for electric heating may be a circular electrode as described above, or a linear electrode.

[0109] Regarding the size of the locally heated region, the minimum diameter and width depend on the shape of the spot electrode and the technology for reducing the focused diameter of the laser light or electron beam. In principle, it is possible to further reduce the size of the locally heated region, but considering that the current size of the nuclei of recrystallized grains is about 1 μm, it is considered that the effect can be obtained if the size of the locally heated region is 1 μm or more. In industry, the above minimum diameter and minimum width should be 10 μm or more. Regarding the size of the locally heated region, if the maximum diameter and maximum width exceed 10 mm, the area ratio of Goss orientation grains with relatively large angle deviation θ and angle deviation φ that cannot grow outside the locally heated region increases. In this case, it becomes difficult to obtain the effect of local rapid heating.

[0110] In the localized rapid heating, the heating rate may be 500°C / sec or more in the center of the locally heated region as viewed in the thickness direction and at 1 / 5 of the thickness of the steel plate. If the heating rate in the above region is 500°C / sec or more, the structure of the locally heated region can be preferably controlled to a recovered structure or a recrystallized structure. The above heating rate is preferably 2000°C / sec or more, and more preferably 10000°C / sec or more. On the other hand, the upper limit of the above heating rate is not particularly limited, and may be, for example, 1000000°C / sec.

[0111] In addition, it is preferable to control the above heating rate in combination with and inseparably with the heating rate during decarburization annealing, which will be described later. For example, in this embodiment, the aim is to have coarse Goss oriented grains in the local heat affected zone after decarburization annealing, but if the heating rate during decarburization annealing is faster than the heating rate during local rapid heating, the above objective is difficult to achieve. Therefore, although it depends on the magnitude of the heating rate, it is preferable to set the heating rate during local rapid heating to be equal to or higher than the heating rate during decarburization annealing. If a person skilled in the art understands the objective of having coarse Goss oriented grains in the local heat affected zone after decarburization annealing, he or she can preferably control the heating rate during local rapid heating and the heating rate during decarburization annealing.

[0112] The above-mentioned 1 / 5 part of the plate thickness of the steel plate means a depth equivalent to 1 / 5 of the plate thickness of the steel plate from the surface of the steel plate in the plate thickness direction.

[0113] In addition, in the localized rapid heating, it is sufficient that the maximum temperature reached is 700°C or higher in the center of the locally heated region as viewed from the plate thickness direction and at 1 / 5 of the plate thickness of the steel plate. If the maximum temperature reached is 700°C or higher in the above region, the structure of the locally heated region can be preferably controlled to a recovered structure or a recrystallized structure. The above maximum temperature reached is preferably 800°C or higher, and more preferably 900°C or higher. On the other hand, the above maximum temperature reached may be lower than the melting point of the steel plate, for example, 1400°C or lower.

[0114] In addition, in the localized rapid heating, the holding time from reaching the maximum temperature to cooling to 700°C at the center of the locally heated region as viewed from the thickness direction and at 1 / 5 of the thickness of the steel plate may be 0.1 seconds or more. If the holding time is 0.1 seconds or more in the above region, the structure of the locally heated region can be preferably controlled to a recovered structure or a recrystallized structure. The holding time is preferably 0.2 seconds or more, more preferably 0.3 seconds or more, and even more preferably 0.4 seconds or more. On the other hand, the upper limit of the holding time is not particularly limited, and may be, for example, 10 seconds or less. The holding time from reaching the maximum temperature to cooling to 700°C has an essential effect on the formation of coarse Goss orientation grains close to the ideal Goss orientation.

[0115] In localized rapid heating, it is important to control the above-mentioned heating rate and maximum temperature, as well as the above-mentioned holding time. During this holding time, subgrain structures and recrystallization nuclei that are advantageous for the formation of coarse Goss-oriented grains in the locally heated region can be formed. By controlling the subgrain structure in the locally heated region by the holding time, favorable structural control can be performed in the subsequent process.

[0116] As described above, the method of local rapid heating is not particularly limited. For example, local rapid heating may be performed by spot current heating, laser irradiation, or electron beam irradiation. Regardless of the method of local rapid heating, it is sufficient to control the heating rate, maximum temperature, and holding time as described above. A person skilled in the art can combine the conditions of the local rapid heating method to control the desired heating rate, maximum temperature, and holding time.

[0117] For example, a person skilled in the art can perform a heat conduction analysis using the finite element method to control the heating rate and the maximum temperature reached at the center of the local heating region as viewed from the thickness direction and at 1 / 5 of the thickness of the steel plate. In addition, a person skilled in the art can control the above-mentioned holding time by adjusting the heat extraction conditions after the maximum temperature is reached. For example, in the case of spot current heating, the electrode holding time after current application can be controlled, or the shape of the spot electrode can be changed to a shape suitable for heat extraction. In addition, in the case of laser irradiation or electron beam irradiation, the irradiation speed can be adjusted, or the shape of the irradiation region can be changed to an ellipse or the like to gradient the irradiation energy from the center to the outer edge of the irradiation region.

[0118] Generally, when heating by laser irradiation, only the vicinity of the irradiated steel sheet surface is heated preferentially, and the inside of the steel sheet is not easily heated. In addition, since heating by laser irradiation is non-contact heating, heat is quickly removed after heating and the temperature is not easily maintained. Therefore, when performing laser irradiation heating as localized rapid heating, in order to recover or recrystallize the cold-worked structure in the laser irradiated area, it is necessary to control the conditions so that not only the surface of the steel sheet but also the inside of the steel sheet is heated, and the cooling rate is slowed down to relatively coarsen the subgrain structure in the laser irradiated area. The laser irradiation conditions for localized rapid heating are completely different from the laser irradiation conditions for magnetic domain refinement. For example, the laser irradiation conditions for magnetic domain refinement (usually 0.5 to 50 mJ / mm 2 ) is applied to this embodiment, the structure of the locally heated region is not controlled favorably, and coarse Goss oriented grains close to the ideal Goss orientation are not formed in the steel sheet after the decarburization annealing process. The same applies to electron beam irradiation as to laser irradiation. Even if the electron beam irradiation conditions for magnetic domain refinement are applied to this embodiment, the structure of the locally heated region is not controlled favorably, and coarse Goss oriented grains close to the ideal Goss orientation are not formed in the steel sheet after the decarburization annealing process.

[0119] It is difficult to form coarse Goss oriented grains close to the ideal Goss orientation even if the input power of laser irradiation or electron beam irradiation is simply increased. For example, when rapid heating is performed by laser irradiation or electron beam irradiation, it is preferable to make the beam shape elliptical or adjust the scan speed, etc., so that a temperature range for grain growth of the crystal grains in the region after rapid heating can be secured.

[0120] Conventionally, in electrical steel sheets, laser irradiation or electron beam irradiation has been performed to reduce iron loss by controlling magnetic domains on steel sheets after secondary recrystallization. Under these laser irradiation or electron beam irradiation conditions, about 20 μm from the surface of the steel sheet is heated, so heat is removed quickly after heating. Therefore, under conventional conditions, it is difficult to ensure the holding time from reaching the maximum temperature to cooling to 700 ° C. as described above. That is, under conventional laser irradiation or electron beam irradiation conditions, it may be possible to make the irradiated part act as a barrier to the growth of secondary recrystallized grains, but it is difficult to form coarse Goss-oriented grains having an orientation close to the ideal Goss orientation as in this embodiment. In order to form coarse Goss-oriented grains close to the ideal Goss orientation by laser irradiation or electron beam irradiation, it is necessary to consider the conditions of laser irradiation or electron beam irradiation as described above.

[0121] In addition, the local heat affected regions on the steel sheet surface may be appropriately arranged according to the purpose. In the manufacturing method of the grain-oriented electrical steel sheet according to the present embodiment, the shape of the secondary recrystallized grains may be controlled so that they have a tendency to be flattened by extending in the direction perpendicular to the rolling direction C and being crushed in the rolling direction L. For example, the larger the interval between the local heat affected regions in the rolling direction L, the more likely the secondary recrystallized grain size will be coarse in the rolling direction L. Similarly, the larger the interval between the local heat affected regions in the direction perpendicular to the rolling direction C, the more likely the secondary recrystallized grain size will be coarse in the direction perpendicular to the rolling direction C. The arrangement of these local heat affected regions in the rolling direction L and the direction perpendicular to the rolling direction C influence each other. For example, if the interval in the rolling direction L is large, even if the interval in the direction perpendicular to the rolling direction C is small, the secondary recrystallized grain size may be coarse in the direction perpendicular to the rolling direction C. In addition, the chemical composition of the steel and the temperature gradient in the heating process of the finish annealing described later also affect the grain growth of the secondary recrystallized grains. Therefore, these conditions may be controlled in a composite manner to control the above-mentioned flat shape. Those skilled in the art can control the secondary recrystallized grains to have the above-mentioned flat shape by appropriately adjusting the arrangement of the local heat affected zones and other conditions.

[0122] (Decarburization annealing process) In the decarburization annealing process, the cold-rolled steel sheet after the local rapid heating process is subjected to decarburization annealing (primary annealing). This decarburization annealing increases the frequency of Goss-oriented grains formed in the local heat affected region, increases the grain size of the Goss-oriented grains, and preferably forms coarse Goss-oriented grains having an orientation close to the ideal Goss orientation. The decarburization annealing conditions may be a heating rate of 10 to 10,000°C / sec, an annealing temperature of 700 to 900°C, and an annealing time of 10 to 600 seconds. In addition, by subjecting the cold-rolled steel sheet to decarburization annealing, C contained in the cold-rolled steel sheet is removed. The decarburization annealing is preferably performed in a moist atmosphere in order to remove "C" contained in the cold-rolled steel sheet.

[0123] In addition, it is effective to reduce the primary recrystallized grain size by controlling the conditions of the above-mentioned hot rolling and hot-rolled sheet annealing, or by lowering the decarburization annealing temperature as necessary. The primary recrystallized grain size is not particularly limited, but is preferably 8 to 30 μm.

[0124] In this embodiment, a large number of coarse Goss-oriented grains with an orientation close to the ideal Goss orientation are formed in the local heat-affected region. Therefore, it is not necessary to form Goss-oriented grains again by decarburization annealing. As described above, the heating rate of the decarburization annealing should be 10,000°C / sec or less. However, by slowing down the heating rate of the decarburization annealing, it is possible to prevent the {111} grains from being easily eaten away by the matrix portion (region not affected by local heat). <112> Oriented grains and {411} <148> For example, the heating rate of the decarburization annealing is preferably 300° C. / sec or less, more preferably 200° C. / sec or less, and even more preferably 100° C. / sec or less.

[0125] In addition, the amount of decarbonation and the state of the surface oxide layer affect the formation of the glass film. Therefore, in decarburization annealing, the degree of oxidation (PH2O / PH2) in the annealing atmosphere (furnace atmosphere) may be set to 0.01 to 0.15. The degree of oxidation PH2O / PH2 can be defined as the ratio of the water vapor partial pressure PH2O to the hydrogen partial pressure PH2 in the atmosphere.

[0126] (nitriding) Nitriding is an effective treatment in a low-temperature slab heating process in which the slab heating temperature is 1280°C or less, and is an important process for adjusting the strength of the inhibitor in secondary recrystallization. Nitriding increases the nitrogen content of the steel sheet by about 40 to 200 ppm from the start of the decarburization treatment to the start of secondary recrystallization in finish annealing. Examples of nitriding include annealing in an atmosphere containing a nitriding gas such as ammonia, and finish annealing of a decarburized annealed steel sheet coated with an annealing separator containing a powder having nitriding ability such as MnN. The amount of nitride after nitriding is preferably 130 to 350 ppm, more preferably 150 to 250 ppm.

[0127] (Annealing separator application process) The annealing separator application process is a process of applying an annealing separator to the decarburized annealed steel sheet. As the annealing separator, for example, an annealing separator mainly composed of MgO or an annealing separator mainly composed of Al2O3 can be used. After the annealing separator is applied, the decarburized annealed steel sheet is wound into a coil and finish-annealed in the next finish-annealing process.

[0128] (finish annealing process) The final annealing process is a process in which the decarburized annealed steel sheet coated with the annealing separator is subjected to final annealing (secondary annealing) to cause secondary recrystallization. In this process, the growth of the primary recrystallized grains is suppressed by the inhibitor, and secondary recrystallization is allowed to proceed, resulting in the formation of {100} <001> Oriented grains are preferentially grown, dramatically improving magnetic flux density.

[0129] In the final annealing, the decarburized annealed steel sheet that has been coated with an annealing separator and dried may be held for 10 to 60 hours in a temperature range of 1000° C. to 1300° C. The atmosphere during the final annealing may be, for example, a nitrogen atmosphere or a mixed atmosphere of nitrogen and hydrogen.

[0130] In this embodiment, secondary recrystallization may be caused by applying a temperature gradient of more than 0.5°C / cm to the boundary between the primary recrystallized region and the secondary recrystallized region in the steel sheet during the heating process of the final annealing, preferably by applying a temperature gradient of 1.0°C / cm or more. For example, the above temperature gradient may be applied to the steel sheet during the growth of secondary recrystallized grains in a temperature range of 800°C or more during the heating process of the final annealing. The direction in which the above temperature gradient is applied may be the direction perpendicular to the rolling direction C. The above temperature gradient may be appropriately changed depending on the chemical composition of the steel. For example, if the chemical composition is such that secondary recrystallized grains tend to grow preferentially, the temperature gradient may be more than 0.5°C / cm (preferably 1.0°C / cm or more), while if the chemical composition is such that secondary recrystallized grains tend not to grow preferentially, the temperature gradient is preferably more than 1.0°C / cm.

[0131] The method of providing the temperature gradient is not particularly limited, and a known method may be applied. For example, when a box-shaped annealing furnace is used and a coiled steel sheet is placed in the furnace and heated, the position and arrangement of the heating device and the temperature distribution in the annealing furnace may be controlled so that a sufficient temperature difference occurs from the top to the bottom of the coil or from the outside to the inside. Alternatively, a temperature distribution may be formed in the coil to be annealed by actively heating only a part of the coil by arranging an induction heating device, a high-frequency heating device, an electric current heating device, or the like.

[0132] If a temperature gradient is applied to the steel sheet during the heating process of the final annealing, secondary recrystallized grains with a sharp orientation are generated from the part of the coil that has reached the secondary recrystallization start state early, and these secondary recrystallized grains grow preferentially due to the temperature gradient. For example, the secondary recrystallized grains can be made to grow throughout the entire coil.

[0133] (Insulating film formation process) A coating solution containing phosphoric acid or a phosphate, chromic anhydride or a chromate, and colloidal silica is applied to the steel sheet after final annealing and baked (for example, at 350°C to 1150°C for 5 to 300 seconds) to form an insulating coating.

[0134] The grain-oriented electrical steel sheet according to the present embodiment can be manufactured by the above steps. The grain-oriented electrical steel sheet according to the present embodiment, which is manufactured by controlling the conditions of each step in a composite and inseparable manner, has an extremely small deviation between the crystal orientation of the secondary recrystallized grains and the ideal Goss orientation, an average small angle deviation φ at each measurement point along the rolling direction L, the crystal grains do not grow coarse with respect to the rolling direction L, and the shape of the crystal grains tends to be elongated in the direction perpendicular to the rolling C and flattened in the rolling direction L. Therefore, despite the temperature gradient being applied to the steel sheet during secondary recrystallization, it is excellent in both magnetic flux density and magnetostriction. EXAMPLES

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

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

[0137] When producing the above decarburized annealed steel sheet, a slab was heated to 1150°C and subjected to hot rolling to obtain a hot rolled steel sheet having a thickness of 2.6 mm. The hot rolled steel sheet was heated to 1100°C and then subjected to hot rolled sheet annealing by annealing at 900°C, and then subjected to pickling to remove scale formed on the surface. The steel sheet was subjected to one cold rolling or multiple cold rolling with intermediate annealing therebetween to obtain a cold rolled steel sheet having a final thickness of 0.22 mm.

[0138] The above cold-rolled steel sheet was subjected to local rapid heating under the conditions shown in Tables 3 to 7. In the spot current heating, a copper electrode with a diameter of 1 mm was used in the contact portion with the steel sheet, and the electrode shape, electrode pressure, current, current time, and electrode holding time after current were changed in a composite manner other than the contact portion with the steel sheet to control the heating rate, maximum temperature, and holding time from reaching the maximum temperature to cooling to 700°C (holding time of 700°C or more). In the laser heating, a fiber laser was used, and the focusing spot diameter of the laser light in the rolling direction (i.e., the diameter including 86% of the laser output) was set to 30 μm (excluding Test No. 71 and No. 72), and the laser irradiation energy density, laser scanning speed, and shape of the laser irradiation area were changed in a composite manner to control the heating rate, maximum temperature, and holding time of 700°C or more. Those skilled in the art can combine the conditions of the local rapid heating method to control the desired heating rate, maximum temperature, and holding time of 700°C or more.

[0139] In Test No. 69, the laser beam was elongated in the scanning direction, and the holding time from reaching the maximum temperature until cooling to 700°C during localized rapid heating was controlled to 0.2 seconds, so that coarse Goss-oriented grains with an orientation close to the ideal Goss orientation were formed in the locally heated area. In Test No. 70, general laser irradiation conditions for magnetic domain refinement were applied. In Test No. 71, the focused spot diameter was set to 0.5 mm, and the laser irradiation energy density was set to 2.0 J / mm. 2 In test No. 72, the focal spot diameter was set to 0.5 mm, and the laser irradiation energy density was set to 30.0 J / mm. 2 The laser beam was controlled so that the laser beam irradiated area was finally located on the grain boundary of the secondary recrystallized grains.

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

[0141] In addition, in the table, the width direction interval "end 10" in the local heating condition of localized rapid heating indicates that a locally heated region was formed only at a position 10 mm from the end of the steel plate in the direction perpendicular to the rolling direction.

[0142] The cold-rolled steel sheets after localized rapid heating were subjected to decarburization annealing under the conditions shown in Tables 3 to 7. In the decarburization annealing, the degree of oxidation (PH2O / PH2) in the annealing atmosphere (furnace atmosphere) was set to 0.13.

[0143] The manufactured decarburized annealed steel sheets were subjected to nitriding treatment at 750°C in a nitrogen-hydrogen-ammonia atmosphere to adjust the nitrogen content of the steel sheets to 220 ppm. Furthermore, an annealing separator mainly composed of MgO was applied, and finish annealing was performed.

[0144] In the heating process of the final annealing, the steel sheet was heated to 1000°C at a rate of 15°C / hr (°C / hour) in a mixed atmosphere of hydrogen and nitrogen, and then heated to 1200°C at the heating rate shown in Tables 3 to 7. In addition, in the heating process of the final annealing, in the temperature range of 800°C or higher, a temperature gradient shown in Tables 3 to 7 was applied in the direction perpendicular to the rolling direction C to the boundary portion between the primary recrystallization region and the secondary recrystallization region in the steel sheet. In Tables 3 to 7, a temperature gradient of "<1.0" in the heating process of the final annealing indicates that the temperature gradient in the heating process was not substantially controlled. After the heating process of the final annealing, the steel sheet was held at 1200°C for 20 hr (hours) in a hydrogen atmosphere.

[0145] After the finish annealing, the steel sheet was coated with a coating solution for an insulating film, which was mainly composed of colloidal silica and phosphate, and optionally contained chromic anhydride, and baked to form an insulating film.

[0146] For the grain-oriented electrical steel sheets produced, the chemical composition of the base steel sheet and the average value of the angle deviation φ aveφ L , particle size D L Number standard 10% particle size D L 10, and particle size D C Average value of aveD C was measured according to the method described above. The results are shown in Tables 7 to 13. In Table 13, "-" indicates that control and production were not performed with consideration given to the content, and that the content was not measured. In addition, various characteristics were evaluated for the produced grain-oriented electrical steel sheets. The evaluation results are shown in Tables 7 to 12.

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

[0148] From the obtained grain-oriented electrical steel sheets, 20 samples for single sheet magnetic measurement measuring 100 mm x 500 mm were prepared and single sheet magnetic measurement was carried out. As magnetic properties, the magnetic flux density B8 (T) in the rolling direction of the steel sheet when excited at 800 A / m was measured. A magnetic flux density B8 of 1.945 T or more was judged to be acceptable. For reference, the iron loss W, defined as the power loss per unit weight (1 kg) of the steel sheet under the conditions of AC frequency: 50 Hz, excitation magnetic flux density: 1.7 T, was also measured. 17 / 50 (W / kg) was measured.

[0149] Furthermore, as magnetic properties, the magnetostriction λp-p@1.7T (the difference between the minimum and maximum values ​​of magnetostriction at 1.7T) generated in the steel sheet under the conditions of an AC frequency of 50Hz and an excitation magnetic flux density of 1.7T was measured. Specifically, the maximum length L max and the minimum length L min , and using the length L0 of the test piece at magnetic flux density 0T, λp-p@1.7T=(L max -Lmin )÷L0.

[0150] Based on the above magnetic property values, the magnetostriction rate level at 1.7 T was obtained. The magnetostriction rate level Lva (unit: dB) was calculated by Fourier transforming the magnetostriction waveform of 2 or more periods, obtained at a sampling frequency of 6.4 kHz, and using the magnetostriction amount λ(fi) (0 Hz to 3.2 kHz) for each frequency obtained, according to the following formula 1. The magnetostriction rate level Lva was examined for the 200 Hz component.

[0151] Lva=20×log 10 [{ρc×{Σ(2 1 / 2 π×fi×λ(fi)×α(fi)) 2} 1 / 2} / P0] ···(Formula 1)

[0152] Where: ρ: air density (kg / m 3 ) c: Speed ​​of sound (m / sec) P0: The minimum pressure (Pa) at which a 1 kHz sound can be heard by humans. fi: frequency (Hz) λ(fi): Magnetostriction amount per frequency obtained by Fourier transformation α(fi): A characteristic of frequency fi π: Pi

[0153] In calculating Lva@1.7T, the following values ​​were substituted: ρ = 1.185 (kg / m 3 ) c=346.3(m / sec) P0 = 2 × 10 -5 (Pa)

[0154] When the magnetic flux density B8 was 1.945 T or more and the magnetostriction rate level Lva@1.7 T was 41 dB or less, it was determined that both the magnetic flux density and the magnetostriction characteristics were good.

[0155] Among Nos. 1 to 98, the grain-oriented electrical steel sheets according to the present invention have an aveφ L , DL 10, and aveD C All of these examples of the present invention were excellent in magnetic flux density and magnetostriction characteristics, and also in core loss.

[0156] On the other hand, among Nos. 1 to 98, the grain-oriented electrical steel sheets, which are comparative examples, have an aveφ L , D L 10, or aveD C In these comparative examples, preferred magnetic flux density or magnetostriction characteristics were not obtained as grain-oriented electrical steel sheets.

[0157] [Table 2]

[0158] [Table 3]

[0159] [Table 4]

[0160] [Table 5]

[0161] [Table 6]

[0162] [Table 7]

[0163] [Table 8]

[0164] [Table 9]

[0165] [Table 10]

[0166] [Table 11]

[0167] [Table 12]

[0168] [Table 13] [Industrial Applicability]

[0169] According to the above-mentioned aspect of the present invention, even if a technology of applying a temperature gradient to the steel sheet during secondary recrystallization is applied, it is possible to provide a grain-oriented electrical steel sheet that is excellent in both magnetic flux density and magnetostriction characteristics, and therefore the present invention has high industrial applicability. [Explanation of symbols]

[0170] 1. Decarburized annealed steel sheet 2 Localized heat affected area 3. Area not affected by local heating (matrix part) 4 Local heating region boundary 5 Local heat affected area boundary 14 Goss Grain 15 Coarse Goss grains 21 Rolling direction 22 Width direction (perpendicular to rolling direction)

Claims

[Claim 1] A grain-oriented electrical steel sheet, The deviation angle from the ideal Goss orientation with the normal direction Z of the rolling surface as the rotation axis is defined as α, The deviation angle from the ideal Goss orientation with the direction perpendicular to the rolling direction C as the rotation axis is defined as β, The deviation angle from the ideal Goss orientation with the rolling direction L as the rotation axis is defined as γ, The deviation angle of the crystal orientation measured at one measurement point on the plate surface is represented as (α β γ), The angular deviation at one measurement point is φ = (α ２ +β ２ ) １／２ Define it as: The average value of the angle deviation φ obtained at multiple measurement points spaced 1 mm apart along the rolling direction L is aveφ Ｌ When we define The above aveφ Ｌ But, aveφ Ｌ ≦3.5° is satisfied, The deviation angle of the crystal orientation measured at two adjacent measurement points on the plate surface, spaced 1 mm apart, is defined as (α １ β １ Gamma １ ) and (α ２ β ２ Gamma ２ ) and [(α ２ -α １ ) ２ + (β ２ -β １ ) ２ + (γ ２ -γ １ ) ２ ] １／２ The midpoint between the two measurement points that satisfy ≧1.0° is defined as the grain boundary (GB), The grain size in the rolling direction L determined based on the grain boundary GB is expressed in mm as D Ｌ Define it as: Grain size D measured along the rolling direction L Ｌ Arrange them in ascending order and determine the particle size that is 10% of the largest in number, in mm. Ｌ When defined as 10, The above D Ｌ 10 is D Ｌ 10≦100-15×aveφ Ｌ Fulfilling The grain size in the direction perpendicular to the rolling direction C calculated based on the grain boundary GB is expressed in mm as D Ｃ Define it as: Grain diameter D measured along the direction perpendicular to the rolling direction C Ｃ The average value of aveD Ｃ When we define The above aveD Ｃ But, aveD Ｃ Meet ≧50 A directional electrical steel sheet.