Grain-oriented electrical steel sheet

Abstract

In this grain-oriented electrical steel sheet, the average value aveφL of an angle deviation φ determined at a plurality of measurement points at 1 mm intervals along the rolling direction L is 3.5° or less; particle sizes DL10 representing 10% of particle sizes DL determined along the rolling direction L, which have been arranged in descending order, in terms of the count from large to small are (100–15×aveφL) mm or less; and the average value aveDC of particle sizes DC determined along a direction C orthogonal to the rolling direction is 50 mm or more.

Description

grain-oriented electrical steel sheet

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

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

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

[0004] So far, methods have been proposed for obtaining a steel sheet with a 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 promoting secondary recrystallization in a finish annealing step while applying a temperature gradient to the steel sheet in the tip region of the secondary recrystallized grains that are encroaching on the primary recrystallized grains.

[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 area 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 concentration of the Goss orientation increases, and the magnetic flux density B ８ will improve.

[0006] However, when secondary recrystallized grains are grown using a temperature gradient, 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 deviation from the ideal Goss orientation at the tip of the secondary recrystallized grain growth becomes significant, which can hinder the improvement of magnetic flux density.

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

[0008] The deviations between the actual crystal orientation and the ideal Goss orientation can be expressed by deviation angles α, β, and γ. The deviation angle α is the angle between the <001> direction of the crystal projected onto the rolling surface when viewed from the normal direction Z of the rolling surface and the rolling direction L. The deviation angle β is the angle between the <001> direction of the crystal projected onto the L cross section (cross section having the normal line in the rolling direction) when viewed from the direction C perpendicular to the rolling (sheet width direction) and the rolling direction L. The deviation angle γ is the angle between the <110> direction of the crystal projected onto the C cross section (cross section having the normal line in the rolling direction) when viewed from the rolling direction L 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, the lower the magnetic flux density B ８ will improve.

[0010] In addition, it is known that, among the misalignment angles α, β, and γ, the misalignment angle β affects magnetostriction. The smaller the misalignment angle β, the better the magnetostriction characteristics. Magnetostriction is a phenomenon in which a magnetic material changes shape when a magnetic field is applied. Grain-oriented electrical steel sheets used in transformers and the like are required to have low magnetostriction because magnetostriction causes vibration and noise. For example, Patent Documents 3 to 5 disclose controlling the misalignment angle β.

[0011] Japanese Patent Publication No. 57-002839 Japanese Patent Publication No. 61-190017 Japanese Patent Publication No. 2001-294996 Japanese Patent Publication No. 2005-240102 Japanese Patent Publication No. 2015-206114

[0012] As mentioned 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.

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

[0014] The present invention has been made in view of the above-mentioned problems. An object of the present invention is to provide a grain-oriented electrical steel sheet that is excellent in both magnetic flux density and magnetostriction characteristics. Specifically, an object of the present invention is to provide a grain-oriented electrical steel sheet that is 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.

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

[0016] [1] In a grain-oriented electrical steel sheet according to one aspect of the present invention, the deviation angle from the ideal Goss orientation when the normal direction Z to the rolling surface is the rotation axis is defined as α, the deviation angle from the ideal Goss orientation when the direction perpendicular to the rolling direction C is the rotation axis is defined as β, and the deviation angle from the ideal Goss orientation when the rolling direction L is the rotation axis is defined as γ, the deviation angle of the crystal orientation measured at one measurement point on the sheet surface is expressed as (α β γ), and the angular deviation at the one measurement point is expressed as φ = (α ２ +β ２ ) １／２ The average value of the angle deviation φ obtained at a plurality of measurement points spaced 1 mm apart along the rolling direction L is defined as aveφ. Ｌ When the above-mentioned aveφ is defined as Ｌ But, aveφ Ｌ≦3.5°, and the deviation angle of the crystal orientation measured at two adjacent measurement points on the plate surface that are spaced apart by 1 mm is defined as (α １ β １ gamma １ ) and (α ２ β ２ gamma ２ ) and [(α ２ -α １ ) ２ + (β ２ -β １ ) ２ + (γ ２ -γ １ ) ２ ] １／２ The midpoint between the two measurement points satisfying the relation ≧1.0° is defined as the grain boundary GB, and the grain size in the rolling direction L calculated based on the grain boundary GB is expressed as D in mm. Ｌ The grain size D obtained along the rolling direction L is defined as Ｌ Arrange them in descending order and determine the particle size that is 10% of the largest by number in mm. Ｌ When defined as 10, the D Ｌ 10 is D Ｌ 10≦100−15×aveφ Ｌ The grain size in the direction perpendicular to the rolling direction C determined based on the grain boundary GB is expressed in mm as D Ｃ The grain size D measured along the direction perpendicular to the rolling direction C is defined as Ｃ The average value of aveD Ｃ When the above-mentioned aveD is defined as Ｃ But, aveD Ｃ ≧50.

[0017] According to the above aspects of the present invention, it is possible to provide a grain-oriented electrical steel sheet that is excellent in both magnetic flux density and magnetostriction characteristics. Specifically, it is possible to provide a grain-oriented electrical steel sheet that is 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.

[0018] 1 is a diagram showing an example of spot current heating as a local rapid heating method, and is a schematic diagram showing an example of the arrangement of local heat affected zones in a decarburization annealed steel sheet. FIG. 2 is a schematic diagram showing the distribution of Goss oriented grains in a decarburization annealed steel sheet.

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

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

[0021] In addition, the grain-oriented electrical steel sheet (base steel sheet) according to this embodiment is characterized in that the deviation angle of the crystal orientation measured at two adjacent measurement points on the sheet surface that are spaced apart by 1 mm (α １ β １ gamma １ ) and (α ２ β ２ gamma ２ ) and [(α ２ -α １ ) ２ + (β ２ -β １ ) ２ + (γ ２ -γ １ ) ２ ] １／２ The midpoint between the two measurement points satisfying the relation ≧1.0° is defined as the grain boundary GB, and the grain size in the rolling direction L calculated based on the grain boundary GB is expressed as D in mm. ＬThe grain size D obtained along the rolling direction L is defined as Ｌ Arrange them in descending order and determine the particle size that is 10% of the largest by number in mm. Ｌ When defined as 10, the above D Ｌ 10 is D Ｌ 10≦100−15×aveφ Ｌ Meet the following.

[0022] In addition, in the grain-oriented electrical steel sheet (base steel sheet) according to this embodiment, the grain diameter in the direction perpendicular to the rolling direction C calculated based on the grain boundary GB is expressed in mm as D Ｃ The grain diameter D measured along the direction C perpendicular to the rolling direction is defined as Ｃ The average value of aveD Ｃ When defined as above, the above aveD Ｃ But, aveD Ｃ ≧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 technology for applying a temperature gradient to the steel sheet during secondary recrystallization is applied.

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

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

[0026] Above D Ｌ 10 is (100-15 x aveφ Ｌ ) mm or less means that the crystal grains do not grow coarsely in the rolling direction L. If the crystal grains do not grow coarsely in the rolling direction L, it is possible to suppress an increase in the above-mentioned misalignment angles, particularly the misalignment angle β. If the increase in the misalignment angle β is suppressed, a decrease in magnetic flux density is suppressed, and an increase in magnetostriction is also suppressed. Ｌ When the above conditions are satisfied, the magnetic flux density and magnetostriction characteristics are improved. Ｌ 10 is (90-15 x aveφ Ｌ ) mm or less, and (80-15 × ave φ Ｌ ) mm or less. Ｌ Since the smaller the value of D10, the more preferable it is, the lower limit is not particularly limited. Ｌ The number 10 may be 5 mm or more, or 10 mm or more.

[0027] aveD Ｃ is 50 mm or more indicates that the shape of the crystal grains is elongated in the direction C transverse to the rolling direction. The grain-oriented electrical steel sheet according to this embodiment is based on the premise that a technology of applying a temperature gradient to the steel sheet is applied during secondary recrystallization. Therefore, the secondary recrystallized grains tend to grow coarse. However, in this embodiment, as described above, the coarse growth of the crystal grains in the rolling direction L is suppressed. On the other hand, in this embodiment, the coarse growth of the crystal grains in the direction C transverse to the rolling direction is permitted. The grain-oriented electrical steel sheet according to this embodiment is based on the premise that a technology of applying a temperature gradient to the steel sheet is applied during secondary recrystallization, so the secondary recrystallized grains tend to grow coarse, and the aveD Ｃ is 50 mm or more.Ｃ is preferably 80 mm or more, more preferably 100 mm or more, and even more preferably 200 mm or more. Ｃ For example, the grain size of the crystal grains in the direction C perpendicular to the rolling direction may be the coil width (for example, a width of 1000 mm). Ｃ It is sufficient if it 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 X-ray diffraction (Laue method). The Laue method is a method in which an X-ray beam is irradiated onto a steel sheet and the transmitted or reflected diffraction spots are analyzed. By analyzing the diffraction spots, the crystal orientation at the location where the X-ray beam is irradiated can be identified. By changing the irradiation position and analyzing the diffraction spots at multiple locations, the crystal orientation distribution at each irradiation position can be measured. The Laue method is a technique suitable for measuring the crystal orientation of a metal structure with coarse crystal grains.

[0029] It is sufficient that the number of measurement points for the crystal orientation is at least 500, but it is preferable to increase the number of measurement points appropriately depending on the size of the secondary recrystallized grains. For example, if the number of measurement points for measuring the crystal orientation is 500 and the number of secondary recrystallized grains included within a 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. Furthermore, if it is difficult to set 500 measurement points on a single measurement line, it is sufficient to set multiple measurement lines and 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 then the deviation angles α, β, γ, etc. are determined for each measurement point. Based on the deviation angles at each measurement point, the angle deviations φ, aveφ, etc. are calculated. Ｌ , grain boundary GB, grain size D Ｌ , D Ｌ 10. Particle size D Ｃ , aveD Ｃ It is sufficient to find DＬ 10 is the particle size D Ｌ The crystal grains with a diameter of 2 mm or more are arranged in descending order, and the grain size that accounts for 10% of the largest grains is found. Ｃ is the particle size D Ｃ In addition, when the X-ray beam irradiation area at the measurement point of the crystal orientation by the Laue method straddles two crystal grains and it is not possible to determine which crystal grain the X-ray diffraction result comes from, 0.5 mm can be added to the crystal grain sizes of the two crystal grains.

[0031] 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 contain, as a chemical composition, 2.0% to 7.0% Si by mass fraction, 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 for the purpose of improving magnetic properties. There is no need to set a lower limit for the optional elements, and the lower limit may be 0%. Furthermore, the upper limit for the optional elements may be set within a range in which a significant decrease in magnetic flux density or iron loss does not occur. The upper limit values ​​serving as a guide for each optional element are listed below.

[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 to 7.0%, C: 0 to 0.0050%, Mn: 0 to 1.0%, S and Se: 0 to 0.0150% in total, Al: 0 to 0.0650%, N: 0 to 0.0050%, Nb, V, Mo, Ta, and W: 0 to 0.050% in total, Cu: 0 to 0.40%, Bi: 0 to 0.010%, B: 0 to 0.080%, P: 0 to 0.50%, Ti: 0 to 0.0150%, Sn: 0 to 0.10%, Sb: 0 to 0.10%, Cr: 0 to 0.30%, Ni: 0 to 1.0%, and the remainder may be Fe and impurities.

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

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

[0037] Mn: 0 to 1.0% Mn (manganese) is an optional element for the base steel sheet. Although Mn is contained in steel slabs, excessive Mn can cause phase transformation of the steel during secondary recrystallization annealing, preventing secondary recrystallization from progressing sufficiently and resulting in poor magnetic properties. Therefore, the Mn content of the base steel sheet may be 1.0% or less. The Mn content is preferably 0.50% or less, more preferably 0.20% or less. On the other hand, the lower limit of the Mn content of the base steel sheet is not particularly limited, and may be 0%. However, since Mn forms MnS and MnSe and acts as an inhibitor during secondary recrystallization, the Mn content may be greater than 0% or may be 0.00010% or more.

[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 steel slabs, but if excessive S and Se remain in the base steel sheet after finish annealing, it may adversely affect the magnetic properties. Therefore, the total content of S and Se in the base steel sheet may be 0.0150% or less. The total content of S and Se is preferably 0.010% or less, more preferably 0.0050% or less. On the other hand, the lower limit of the total content of S and Se in the base steel sheet is not particularly limited and may be 0%. However, since S and Se form MnS and MnSe and have the effect of acting as inhibitors during secondary recrystallization, the total content of S and Se may be more than 0% or may be 0.00010% or more.

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

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

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

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

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

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

[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 deteriorate. Therefore, the Ti content of the base steel sheet may be 0.0150% or less. The Ti content is preferably 0.0130% or less, and more preferably 0.010% or less. On the other hand, the lower limit of the Ti content is not particularly limited, and may be 0%. However, since Ti forms carbides, nitrides, and carbonitrides and has the effect of acting as an inhibitor during secondary recrystallization, the Ti content may be more than 0% or may be 0.0020% or more.

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

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

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

[0051] The base steel sheet of the grain-oriented electrical steel sheet according to this embodiment may contain impurities. Here, "impurities" refer to substances that are mixed in from raw materials such as ore or scrap, or from the manufacturing environment, when steel is industrially produced.

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

[0053] The above chemical composition is that of the base steel sheet. If the grain-oriented electrical steel sheet to be measured has an insulating coating on its surface, the coating is removed by the following method before measuring the chemical composition.

[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. ２ O: The insulating coating can be removed from the grain-oriented electrical steel sheet by immersing the sheet in a 50 to 70 mass % aqueous sodium hydroxide solution at 80 to 90°C for 5 to 10 minutes, followed by rinsing with water and drying. The immersion time in the aqueous sodium hydroxide solution can be changed depending on the thickness of the insulating coating.

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

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

[0057] The frequency of practical Goss orientation grains, which have small angular deviations θ and φ from the ideal Goss orientation, increases as the heating rate of the primary annealing (decarburization annealing) increases. In contrast, crystal grains that are easily encroached upon by Goss orientation grains, such as those with {778}<447> (≒{111}<112>) and {411}<148> orientations, which have a Σ9 correspondence orientation relationship with the Goss orientation, (called "corresponding orientation grains"), decrease as the heating rate of the primary annealing increases. Therefore, it has been difficult to increase the proportion of practical Goss orientation grains while also increasing the proportion of corresponding orientation grains during the primary annealing.

[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 locally rapid heating a cold-rolled steel sheet to form a locally heated region, 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 located locally on the surface of the steel sheet. The crystalline structure of this locally heated region consists of one or both of a recrystallized structure and a recovered structure at the end of the local rapid heating. The crystalline structure of the non-rapidly heated portion of the steel sheet surface other than the locally heated region consists of a cold-worked structure that remains as it was cold-rolled.

[0060] The localized rapid heating is preferably performed at a heating rate of 500°C / s or more, preferably 2000°C / s or more, and more preferably 10000°C / s or more. Thus, it has been found that when a locally heated region is formed on the surface of a steel sheet before primary annealing and then primary annealing is performed on this steel sheet, many crystal grains having the practical Goss orientation are formed in the region heat-affected by the localized rapid heating (localized heat-affected region). It has also been found that, among the formed Goss-oriented grains, the proportion 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 primary annealing also increases.

[0061] The frequency of coarse Goss-oriented grains in the local heat-affected zone is higher than that obtained by conventional rapid heating of the entire sheet. This characteristic is thought to be due to the fact that the peripheral area of ​​the locally heated zone has a deformed 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 region, which retains a lot of strain, during primary annealing, thereby increasing in diameter. However, when the entire steel sheet is heated, the formation and growth of recrystallized grains occurs uniformly within the steel sheet, so the above-mentioned enlargement of grain diameter is thought to be prevented.

[0062] After the primary annealing has scattered local heat-affected zones with the above characteristics on the surface of the steel sheet, secondary annealing is then performed. During secondary annealing, secondary recrystallization is promoted while applying a temperature gradient to the steel sheet. During this process, Goss-oriented grains formed in the local heat-affected zone grow preferentially during secondary annealing. Many Goss-oriented grains are formed in the local heat-affected zone, and among these grains are Goss-oriented grains with particularly small angular deviations θ and φ, which are close to the ideal Goss orientation and have large crystal grain sizes after the primary annealing. These Goss-oriented grains grow preferentially during secondary recrystallization.

[0063] Since Goss-oriented grains, which serve as nuclei for secondary recrystallization, are supplied to the local heat-affected zone, there is no need to form Goss-oriented grains in the matrix portion other than the local heat-affected zone, i.e., the local heat-unaffected zone, during primary annealing. Therefore, the primary annealing conditions may be slow heating conditions with a low heating rate, which allows for the formation of many corresponding-oriented grains with the {111}<112> and {411}<148> orientations, which are susceptible to corrosion, in the local heat-unaffected zone. For example, by setting the heating rate of the primary annealing to 300°C / sec or less, many Goss-oriented grains with large grain sizes and close to the ideal Goss orientation are formed in the local heat-affected zone, while almost no Goss-oriented grains are formed in the local heat-unaffected zone, resulting in the formation of many corresponding-oriented grains.

[0064] As described above, in the local heat affected zone of a steel sheet (decarburized annealed steel sheet) that has undergone local rapid heating and primary annealing, many Goss-oriented grains with large grain sizes and close to the ideal Goss orientation are present. On the other hand, in the matrix portion (zone not affected by local heating), there are almost no large-sized Goss-oriented grains, and many corresponding-orientation grains that are susceptible to erosion can be present.

[0065] When such a steel sheet (decarburization annealed steel sheet) is subjected to secondary annealing, Goss-oriented grains that are present in the local heat-affected zone, have a close-to-ideal Goss orientation, and are large in grain size, begin to grow preferentially toward the local heat-unaffected zone.

[0066] In addition, in this embodiment, secondary recrystallization is promoted by applying a temperature gradient to the steel sheet in the tip region of the secondary recrystallized grains that are encroaching on the primary recrystallized grains during secondary annealing. When secondary recrystallized grains are grown using a temperature gradient, secondary recrystallized grains with an orientation close to the ideal Goss orientation are generated from the portion of the steel sheet that reaches the secondary recrystallization initiation 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 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 slip 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 That is, in the prior art, 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, and therefore the grain size D in the rolling direction can be increased. Ｌ This can suppress an increase in the slip angle β, thereby suppressing 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, it is possible to obtain a steel sheet that is superior to conventional steel sheets in magnetic flux density and magnetostriction characteristics. In addition, in this embodiment, secondary recrystallized grains having an orientation close to the ideal Goss orientation are preferentially formed, so that the deterioration of the slip angle α can also be suppressed. Therefore, it is possible to obtain a steel sheet that is superior to conventional steel sheets in magnetic flux density.

[0068] The details of the investigations carried out by the present inventors will be specifically described below.

[0069] As one embodiment of the localized rapid heating described above, a case where spot resistance heating by electrical resistance heating is used will be described. In spot resistance heating, spot electrodes are pressure-bonded to both sides of a steel sheet so as to face each other, and an electric current is passed between the spot electrodes to spot-heat the electrode-holding portion of the steel sheet. A steel having the chemical composition shown in Table 1 was hot-rolled and cold-rolled to obtain a cold-rolled steel sheet having a thickness of 0.22 mm. This steel sheet was subjected to spot resistance heating. The spot resistance heating was performed using copper electrodes with a diameter of 3 mm under the following conditions: a current of 5.0 kA or less, which is within a range in which the steel sheet surface does not melt; a current time of 20 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 resistance 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 direction perpendicular to the rolling direction, at a 20 mm pitch 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 decarburization-annealed steel sheet produced under the above conditions is shown in Figure 1. The decarburization-annealed steel sheet 1, the local heat affected zone 2, the rolling direction 21, and the width direction (direction perpendicular to the rolling direction) 22 are schematically shown in Figure 1.

[0071]

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

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

[0074] In FIG. 2, the angle deviation φ=(α ２ +β ２ ) １／２ Based on the definition of "Goss orientation," crystal grains (Goss-oriented grains 14) with an angular deviation φ of 10° or less from the ideal Goss orientation were marked with a "○." Furthermore, from among the crystal grains with an angular deviation φ of 10° or less, crystal grains with coarse grain sizes (coarse Goss-oriented grains 15) were marked 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 Figure 2, the decarburization annealed steel sheet 1 produced under the above conditions contains Goss-oriented grains 14 as well as coarse Goss-oriented grains 15. In particular, the region containing the coarse Goss-oriented grains 15 corresponds to the local heat-affected zone 2. Note that although Figure 2 schematically illustrates the local heat-affected zone boundary 4 and the local heat-affected zone boundary 5, it is not easy to distinguish these boundaries by observing the structure. However, the region containing the coarse Goss-oriented grains 15 can be considered the local heat-affected zone 2.

[0076] The decarburized annealed steel sheet was further subjected to nitriding, and then an annealing separator containing MgO as the main component was applied, followed by secondary annealing. The secondary annealing conditions were a hydrogen-nitrogen atmosphere, a temperature increase rate of 15°C / hr (°C / hr), and a holding time of 1200°C for 20 hr (hr). 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 resulting steel sheets were subjected to macro-etching to reveal the grain boundaries. Observation of the areas corresponding to the local heat-affected zones on the steel sheets after macro-etching revealed that multiple secondary recrystallized grains had grown from the areas corresponding to the local heat-affected zones, and that secondary recrystallized grains had spread from the center of the areas corresponding to the local heat-affected zones. Furthermore, in areas corresponding to the local heat-affected zones, small grains of 2 mm or less were sometimes observed as traces of the local heat-affected zones, but not in other cases. Although the secondary recrystallized macrostructure may change slightly depending on the local heating conditions, the degree of integration in the Goss orientation was increased compared to when local heat treatment was not performed.

[0078] In addition, the crystal orientation of the obtained steel sheet was measured by the Laue method described above. Ｌ is 3.5° or less, and D Ｌ 10 is (100-15 x aveφ Ｌ ) mm or less, and aveD Ｃ As a result, the obtained steel sheet was excellent in both magnetic flux density and magnetostriction, despite the temperature gradient 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 angular deviation φ was small on average at each measurement point along the rolling direction L, that the crystal grains did not grow coarsely with respect to the rolling direction L, and that the shape of the crystal grains tended to be elongated in the direction C perpendicular to the rolling direction and flattened in the rolling direction L.

[0080] Considering the above results, it is believed that the formation of coarse Goss-oriented grains close to the ideal Goss orientation with a size advantage in the decarburized annealed steel sheet is the cause of the favorable secondary recrystallization orientation. In addition, it is believed that the favorable placement of the localized heating region before the primary annealing, the favorable control of the annealing conditions during the primary annealing, and the favorable control of the annealing conditions during the secondary annealing are the causes of the improvement in both magnetic flux density and magnetostriction.

[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, coarse Goss-oriented grains (Goss-oriented grains with large grain size) close to the ideal Goss orientation grow preferentially. Therefore, even if the secondary recrystallized grains are not allowed to grow large, a steel sheet can be obtained in which secondary recrystallized grains close to the ideal Goss orientation are dominated. For example, when scattering the local heat-affected zones on the steel sheet surface, the size, shape, and arrangement of the 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 started growing from one local heat-affected zone collides with another Goss-oriented grain that started growing 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 (particularly the grain size D in the rolling direction) can be controlled. Ｌ ) can be obtained as a steel sheet with a small value. In particular, as described above, in the early stage of secondary annealing, the Goss-oriented grains that grow preferentially from the local heat-affected zone 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 slip angle β due to coil setting can be suppressed, and good magnetostriction characteristics can be obtained.

[0082] That is, the grain-oriented electrical steel sheet has a secondary recrystallized grain size (particularly, the grain size in the rolling direction D Ｌ Since the degree of accumulation in the Goss orientation can be increased while suppressing the coarsening of grains, the magnetic domain width refinement by introducing strain or forming grooves can be eliminated or reduced. Specifically, the magnetic domain refinement effect can be favorably obtained by the grain boundaries that increase with the refinement of the secondary recrystallized grain size, so that magnetic domains are refined without applying conventional magnetic domain control techniques. Therefore, unlike conventional magnetic domain control techniques, the introduction of strain into the steel sheet can be eliminated or reduced, and an increase in magnetostriction can be prevented. Furthermore, unlike conventional magnetic domain control techniques, the formation of grooves in the steel sheet can be eliminated or the groove depth can be reduced, and therefore the magnetic flux density B ８ The grain-oriented electrical steel sheet can be used in applications requiring stress relief annealing at 800°C or higher.

[0083] As described above, the grain-oriented electrical steel sheet according to this embodiment has a secondary recrystallized grain size (particularly, the grain size in the rolling direction D Ｌ The increased number of grain boundaries due to the miniaturization of the grains allows for favorable magnetic domain refinement, resulting in excellent core loss characteristics.

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

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

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

[0087] The method for manufacturing the grain-oriented electrical steel sheet according to the present embodiment can apply, as a basic step, conventional methods for manufacturing grain-oriented electrical steel sheets. For example, conventional methods for manufacturing grain-oriented electrical steel sheets include a method for forming inhibitors such as MnS or AlN by high-temperature slab heating, and a method for forming AlN inhibitors by low-temperature slab heating and nitriding. The method for manufacturing the grain-oriented electrical steel sheet according to the present embodiment is not limited to a specific manufacturing method. Below, a method for applying nitriding as the low-temperature slab heating process will be described.

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

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

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

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

[0092] Mn: 0.05 to 1.00% Manganese (Mn) combines with S or Se to form MnS or MnSe, which functions as an inhibitor. When Mn is contained, secondary recrystallization is stabilized when the Mn content is within the range of 0.05 to 1.00%. Note that part of the inhibitor function can be performed by nitrides of Nb group elements. In this case, the strength of MnS or MnSe as a general inhibitor is controlled to be weak. For this reason, the preferred upper limit of the Mn content is 0.50%, and more preferably 0.20%.

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

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

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

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

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

[0098] The above-mentioned chemical composition may contain known optional elements in place of a portion of Fe, taking into consideration not only solving problems in production but also strengthening the inhibitor function by compound formation and the influence on magnetic properties. Examples of optional elements that can be contained in place of a portion of Fe include the following elements.

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

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

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

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

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

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

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

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

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

[0108] (Localized Rapid Heating Process) In this embodiment, localized rapid heating is performed on the cold-rolled steel sheet after the cold rolling process to form a locally heated region. The rapid heating method is not particularly limited as long as it can locally heat the steel sheet. For example, a method of heating by contacting spot electrodes to 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 steel sheet surface with laser light or an electron beam, a method of locally heating by induction heating, or a method of heating by contacting a hot piece can be used. The size of each locally heated region can be a dot-like region with a diameter of about 10 μm to 10 mm, or a linear region with a width of about 10 μm to 10 mm. Furthermore, the electrodes used for electrical heating may be circular electrodes as described above, or linear electrodes.

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

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

[0111] Furthermore, 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. However, if the heating rate during decarburization annealing is faster than the heating rate during local rapid heating, it is difficult to achieve the above objective. 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 greater than the heating rate during decarburization annealing. Those skilled in the art will be able to preferably control the heating rates during local rapid heating and decarburization annealing if they understand the aim of having coarse Goss-oriented grains in the local heat-affected zone after decarburization annealing.

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

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

[0114] Furthermore, in the localized rapid heating, the holding time from reaching the maximum temperature to cooling to 700°C at the center of the locally heated region as viewed in the thickness direction and at 1 / 5 of the thickness of the steel plate is 0.1 seconds or more. If the holding time in the above region is 0.1 seconds or more, the structure of the locally heated region can be preferably controlled to a recovered structure or a recrystallized structure. The holding time is preferably 0.2 seconds or more, more preferably 0.3 seconds or more, and even more preferably 0.4 seconds or more. On the other hand, there is no particular limitation on the upper limit of the holding time, and it may be, for example, 10 seconds or less. The holding time from reaching the maximum temperature to cooling to 700°C has a fundamental effect on the formation of coarse Goss-oriented grains close to the ideal Goss orientation.

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

[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 local rapid heating method, it is sufficient to control the heating rate, maximum temperature, and holding time as described above. A person skilled in the art can combine the conditions of the local rapid heating method to control the desired heating rate, maximum temperature, and holding time.

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

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

[0119] However, simply increasing the input power of laser or electron beam irradiation makes it difficult to form coarse Goss-oriented grains close to the ideal Goss orientation. For example, when rapid heating is performed by laser or electron beam irradiation, it is preferable to make the beam shape elliptical or adjust the scan speed, etc., so as to ensure a temperature range in which the crystal grains in that region can grow after rapid heating.

[0120] Conventionally, laser irradiation or electron beam irradiation has been performed on electrical steel sheets to control magnetic domains after secondary recrystallization and reduce iron loss. Under these laser or electron beam irradiation conditions, the steel sheet is heated to a depth of approximately 20 μm from the surface, resulting in rapid heat dissipation after heating. Therefore, under conventional conditions, it is difficult to ensure the required holding time from reaching the maximum temperature to cooling to 700°C. In other words, under conventional laser or electron beam irradiation conditions, although the irradiated area may be able to act as a barrier to the growth of secondary recrystallized grains, it is difficult to form coarse Goss-oriented grains with an orientation close to the ideal Goss orientation, as in the present embodiment. To form coarse Goss-oriented grains close to the ideal Goss orientation by laser or electron beam irradiation, the conditions for laser or electron beam irradiation must be considered as described above.

[0121] Furthermore, the local heat-affected zones on the steel sheet surface may be appropriately positioned depending on the purpose. In the manufacturing method of a grain-oriented electrical steel sheet according to this embodiment, the shape of the secondary recrystallized grains may be controlled so that they tend to be elongated in the transverse direction C and flattened in the transverse direction L. For example, the larger the spacing between the local heat-affected zones in the rolling direction L, the more likely the secondary recrystallized grain size will coarsen in the rolling direction L. Similarly, the larger the spacing between the local heat-affected zones in the transverse direction C, the more likely the secondary recrystallized grain size will coarsen in the transverse direction C. The positions of these local heat-affected zones in the rolling direction L and the transverse direction C affect each other. For example, if the spacing in the rolling direction L is large, the secondary recrystallized grain size may coarsen in the transverse direction C even if the spacing in the transverse direction C is small. In addition, the chemical composition of the steel and the temperature gradient during the heating process of the finish annealing, which will be described later, also affect the grain growth of the secondary recrystallized grains. Therefore, the above-mentioned flat shape may be controlled by controlling these conditions in a composite manner. Those skilled in the art can control the flat shape of secondary recrystallized grains by appropriately adjusting the arrangement of the local heat affected zone 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 zone, increases the grain size of the Goss-oriented grains, and preferably forms coarse Goss-oriented grains with an orientation close to the ideal Goss orientation. The decarburization annealing conditions may be a heating rate of 10 to 10,000°C / s, an annealing temperature of 700 to 900°C, and an annealing time of 10 to 600 seconds. Furthermore, by subjecting the cold-rolled steel sheet to decarburization annealing, C contained in the cold-rolled steel sheet is removed. Decarburization annealing is preferably performed in a humid atmosphere to remove "C" contained in the cold-rolled steel sheet.

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

[0124] Furthermore, in this embodiment, many coarse Goss-oriented grains with orientations close to the ideal Goss orientation are formed in the local heat-affected zone. Therefore, there is no need to form Goss-oriented grains by decarburization annealing. As described above, the heating rate for decarburization annealing may be 10,000°C / s or less. However, it is preferable to use a slower heating rate for decarburization annealing to form {111}<112>-oriented grains and {411}<148>-oriented grains that are easily eroded into the matrix portion (local heat-unaffected zone). For example, the heating rate for decarburization annealing is preferably 300°C / s or less, more preferably 200°C / s or less, and even more preferably 100°C / s or less.

[0125] The amount of decarbonation and the state of the surface oxide layer affect the formation of the glass film. Therefore, in decarburization annealing, the degree of oxidation (PH) in the annealing atmosphere (furnace atmosphere) is important. ２ O / PH ２ ) may be set to 0.01 to 0.15. ２ O / PH ２ is the partial pressure of water vapor in the atmosphere, PH ２ O and hydrogen partial pressure PH ２ It can be defined as the ratio of

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

[0127] (Annealing separator application step) The annealing separator application step is a step of applying an annealing separator to a decarburized annealed steel sheet. Examples of the annealing separator include an annealing separator containing MgO as a main component and an annealing separator containing Al. ２ O ３ The decarburized annealed steel sheet after being coated with the annealing separator is wound into a coil and then finish-annealed in the subsequent finish-annealing step.

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

[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 hours to 60 hours in a temperature range of 1000° C. to 1300° C. The atmosphere during the final annealing may be, for example, a nitrogen atmosphere or a mixed atmosphere of nitrogen and hydrogen.

[0130] In this embodiment, secondary recrystallization may be induced by applying a temperature gradient of more than 0.5°C / cm, preferably 1.0°C / cm or more, to the boundary between the primary recrystallized region and the secondary recrystallized region in the steel sheet during the heating process of finish annealing. 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 higher during the heating process of finish annealing. The direction in which the temperature gradient is applied may be the direction perpendicular to the rolling direction C. The temperature gradient may be appropriately changed depending on the chemical composition of the steel. For example, if the chemical composition favors preferential growth of secondary recrystallized grains, the temperature gradient may be more than 0.5°C / cm (preferably 1.0°C / cm or more). On the other hand, if the chemical composition favors preferential growth of secondary recrystallized grains, the temperature gradient may be more than 1.0°C / cm.

[0131] The method for providing a temperature gradient is not particularly limited, and any known method may be applied. For example, when a box-type 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 is generated 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 portion of the coil using an induction heating, high-frequency heating, or electric current heating device.

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

[0133] (Insulating Coating Forming Step) A coating solution containing phosphoric acid or a phosphate, chromic anhydride or a chromate, and colloidal silica is applied to the steel sheet after the 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 this embodiment can be manufactured by the above-described steps. The grain-oriented electrical steel sheet according to this embodiment, 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 angular deviation φ at each measurement point along the rolling direction L, no crystal grains growing coarsely with respect to the rolling direction L, and a tendency for the shape of the crystal grains to be elongated in the direction transverse to the rolling direction C and flattened in the rolling direction L. Therefore, despite the temperature gradient applied to the steel sheet during secondary recrystallization, the steel sheet is excellent in both magnetic flux density and magnetostriction.

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

[0136] Using the slabs with adjusted chemical compositions as raw materials, 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 control and manufacturing were not carried out with the content in mind.

[0137] When producing the above-mentioned 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. This hot-rolled steel sheet was then subjected to hot-rolled sheet annealing by heating to 1100°C and subsequently annealing at 900°C, and then subjected to pickling to remove scale formed on the surface. These steel sheets were subjected to a single cold rolling or multiple cold rollings with intermediate annealing in between to obtain a cold-rolled steel sheet having a final thickness of 0.22 mm.

[0138] The above cold-rolled steel sheets were subjected to localized rapid heating under the conditions shown in Tables 3 to 7. In spot current heating, a copper electrode with a diameter of 1 mm was used in contact with the steel sheet. The electrode shape, electrode pressure, current, current application time, and electrode holding time after current application were varied in a composite manner to control the heating rate, maximum temperature, and holding time from reaching the maximum temperature until cooling to 700°C (holding time above 700°C). In laser heating, a fiber laser was used, and the focused spot diameter of the laser beam in the rolling direction (i.e., the diameter containing 86% of the laser output) was set to 30 μm (except for Tests No. 71 and 72). The laser irradiation energy density, laser scanning speed, and shape of the laser irradiation region were varied in a composite manner to control the heating rate, maximum temperature, and holding time above 700°C. Those skilled in the art can combine the conditions of the localized rapid heating method to control the desired heating rate, maximum temperature, and holding time above 700°C.

[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 local rapid heating was controlled to 0.2 seconds, so that coarse Goss-oriented grains with an orientation close to the ideal Goss orientation were formed in the locally heated region. In Test No. 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 laser beam was focused at a spot diameter of 0.5 mm and a laser irradiation energy density of 30.0 J / mm. ２ The laser beam was controlled so that the laser beam irradiated area would ultimately be the grain boundary of the secondary recrystallized grains.

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

[0141] In the table, the widthwise spacing "End 10" in the local heating conditions of localized rapid heating indicates that a localized heating region was formed only at a position 10 mm from the end of the steel sheet 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 (PH) in the annealing atmosphere (furnace atmosphere) was ２ O / PH ２ ) was set to 0.13.

[0143] The produced 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 containing MgO as the main component was applied, and finish annealing was performed.

[0144] In the heating process for finish annealing, the steel sheet was heated to 1000°C at a rate of 15°C / hr (°C / hr) 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 for finish annealing, a temperature gradient shown in Tables 3 to 7 was applied in the direction perpendicular to the rolling direction C to the boundary region between the primary recrystallization region and the secondary recrystallization region in the steel sheet in the temperature range of 800°C or higher. In Tables 3 to 7, a temperature gradient of "<1.0" in the heating process for finish annealing indicates that the temperature gradient in the heating process was not substantially controlled. After the heating process for finish annealing, the steel sheet was held at 1200°C for 20 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, with chromic anhydride added as needed, and baked to form an insulating film.

[0146] For the manufactured grain-oriented electrical steel sheets, the chemical composition of the base steel sheet, the average value of the angle deviation φ (aveφ) Ｌ , particle size D Ｌ Number-based 10% particle size D Ｌ 10, and particle size D Ｃ Average value aveD Ｃ were measured according to the above-mentioned method. The results are shown in Tables 7 to 13. In Table 13, "-" indicates that the content was not measured, and control and manufacturing were not carried out with the content in mind. In addition, various properties were evaluated for the manufactured 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, each measuring 100 mm x 500 mm, were prepared, and single sheet magnetic measurement was carried out. As the magnetic properties, the magnetic flux density B ８ (T) was measured. ８ 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 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 50 Hz and an excitation magnetic flux density of 1.7T was measured. Specifically, the maximum length L of the test piece (steel sheet) under the above excitation conditions was ｍａｘ and the minimum length L ｍｉｎ , and the length L of the test piece at magnetic flux density 0 T ０ Using this, λp-p@1.7T=(L ｍａｘ -Lｍｉｎ ) ÷ L ０ It was calculated by:

[0150] Based on the above magnetic characteristic values, the magnetostriction rate level at 1.7 T was determined. The magnetostriction rate level Lva (unit: dB) was calculated using the following formula 1, by Fourier transforming a magnetostriction waveform of two or more periods, acquired at a sampling frequency of 6.4 kHz, and using the magnetostriction amount λ(fi) (0 Hz to 3.2 kHz) obtained for each frequency. 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} / P ０ ] ...(Formula 1)

[0152] Where, ρ: air density (kg / m ３ ) c: Speed ​​of sound (m / sec) P ０ : The minimum pressure (Pa) at which a 1 kHz sound can be heard by humans, fi: Frequency (Hz), λ(fi): Magnetostriction amount for each frequency obtained by Fourier transformation, α(fi): A-weighting of frequency fi, π: Circular constant

[0153] In calculating Lva@1.7T, the following values ​​were substituted: ρ=1.185 (kg / m ３ ) c=346.3 (m / sec) P ０ = 2 x 10 －５ (Pa)

[0154] Magnetic flux density B ８ When the magnetic flux density 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 aveφ Ｌ , D Ｌ 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 used as comparative examples had aveφ Ｌ , D Ｌ 10, or aveD Ｃ In these comparative examples, desirable magnetic flux density or magnetostriction characteristics were not obtained as grain-oriented electrical steel sheets.

[0157]

[0158]

[0159]

[0160]

[0161]

[0162]

[0163]

[0164]

[0165]

[0166]

[0167]

[0168]

[0169] According to the above-described aspects of the present invention, it is possible to provide a grain-oriented electrical steel sheet that is 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, and therefore the present invention has high industrial applicability.

[0170] REFERENCE SIGNS LIST 1 Decarburization annealed steel sheet 2 Local heat affected zone 3 Local heat unaffected zone (matrix part) 4 Local heat affected zone boundary 5 Local heat affected zone boundary 14 Goss oriented grain 15 Coarse Goss oriented grain 21 Rolling direction 22 Width direction (direction perpendicular to rolling)

Claims

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

Images