Non-directional electrical steel plate

Abstract

The invention relates to an asymmetrical electrical steel plate of a chemical composition capable of α-γ transformation, in which, where the proportion of the area of ​​the crystallinely oriented grains of the {hkl} orientation (within a tolerance of 10°) as measured by EBSD is expressed as Ahkl-uvw, A411-011 is 15.0% or more, and the asymmetrical electrical steel plate has an average grain size from 10.0µm to 40.0µm.

Description

Non-oriented electrical steel sheet

[0001] The present invention relates to a non-oriented electrical steel sheet. This application claims priority based on Japanese Patent Application No. 2021-063523 filed on April 2, 2021, the contents of which are incorporated herein by reference.

[0002] Electrical steel sheets are used as core materials for electrical equipment. Examples of electrical equipment include drive motors installed in railcars, compressor motors for air conditioners and refrigerators, and even household and industrial generators. These electrical equipment require high energy efficiency, compactness, and high output. Therefore, electrical steel sheets used as cores of electrical equipment require low core loss and high magnetic flux density. Texture control is a solution, and techniques have been proposed to develop a texture (α-fiber) that has an easy axis of magnetization within the steel sheet plane, is advantageous for improving magnetic properties, and can be relatively easily enriched by rolling processes in hot rolling and cold rolling, which are essential processes for steel sheet production. Specifically, techniques have been proposed to develop a texture in which the <110> direction is approximately parallel to the rolling direction (RD).

[0003] Patent Documents 1 to 3 all disclose methods for developing the {100}<011> orientation, and describe lowering the transformation temperature and quenching after hot rolling to refine the structure.

[0004] Specifically, Patent Document 1 describes that the steel sheet is cooled to 250°C or less at a cooling rate of 200°C / sec or more within 3 seconds after hot rolling, that no annealing is performed between hot rolling and cold rolling, and that the cumulative reduction in cold rolling is 88% or more. Patent Document 1 also describes that this enables the production of an electrical steel sheet in which grains are concentrated in the {100}<011> orientation on the steel sheet surface.

[0005] Furthermore, Patent Document 2 discloses a method for producing an electrical steel sheet containing 0.6 mass % or more and 3.0 mass % or less of Al, and describes that an electrical steel sheet in which the {100}<011> orientation is concentrated on the steel sheet surface can be produced by a process similar to that described in Patent Document 1.

[0006] On the other hand, Patent Document 3 describes that the finish rolling temperature in hot rolling is set to the Ac3 transformation point or higher, and the steel sheet temperature is cooled to 250°C within 3 seconds after hot rolling, or that the finish rolling temperature is set to the Ac3 transformation point -50°C or lower, and the steel sheet is cooled at a cooling rate faster than natural cooling. Furthermore, the manufacturing method described in Patent Document 3 involves performing two cold rollings with intermediate annealing in between, with no annealing performed between the hot rolling and the first cold rolling, and with a cumulative reduction of 5 to 15% in the second cold rolling. Patent Document 3 also describes that this enables the production of an electrical steel sheet in which grains are concentrated in the {100}<011> orientation on the steel sheet surface.

[0007] In all of the methods described in Patent Documents 1 to 3, when manufacturing an electrical steel sheet in which the {100}<011> orientation is accumulated on the steel sheet surface, if the finish rolling temperature in hot rolling is set to Ac3 point or higher, rapid cooling immediately after hot rolling is required. Rapid cooling increases the cooling load after hot rolling. In consideration of operational stability, it is preferable to be able to suppress the load on the rolling mill that performs cold rolling.

[0008] On the other hand, a technique for developing the {411} plane, which is rotated 20° from the {100} plane, has also been proposed in order to improve magnetic properties. As a method for developing the {411} plane, Patent Documents 4 to 7 all disclose techniques for developing the {411} plane, and describe optimizing the grain size in a hot-rolled sheet and strengthening the α-fiber in the texture of the hot-rolled sheet.

[0009] Specifically, Patent Document 4 describes that a hot-rolled sheet in which the density of the {211} plane is higher than that of the {411} plane is cold-rolled to a cumulative reduction ratio of 80% or more, thereby enabling the production of an electrical steel sheet in which the density of the {411} plane is accumulated on the steel sheet surface.

[0010] Furthermore, Patent Documents 5 and 6 describe a slab heating temperature of 700°C or higher and 1150°C or lower, a finish rolling starting temperature of 650°C or higher and 850°C or lower, a finish rolling ending temperature of 550°C or higher and 800°C or lower, and further a cumulative reduction rate in cold rolling of 85 to 95%. This makes it possible to produce an electrical steel sheet in which the {100} plane and {411} plane are concentrated on the steel sheet surface.

[0011] On the other hand, Patent Document 7 describes that when α-fibers are developed in the vicinity of the surface layer of a hot-rolled coil steel sheet by strip casting or the like, the {h11}<1 / h12> orientation, particularly the {100}<012> to {411}<148> orientation, is recrystallized during subsequent annealing of the hot-rolled sheet.

[0012] Japanese Patent Publication No. 2017-145462 Japanese Patent Publication No. 2017-193731 Japanese Patent Publication No. 2019-178380 Japanese Patent No. 4218077 Japanese Patent No. 5256916 Japanese Patent Publication No. 2011-111658 Japanese Patent Publication No. 2019-183185

[0013] The inventors have studied the above-mentioned techniques and found that when attempting to improve magnetic properties by strengthening the {100}<011> orientation according to Patent Documents 1 to 3, rapid cooling immediately after hot rolling is required, which poses a problem of high manufacturing load. Furthermore, they recognized that when a steel sheet strengthened in the {100}<011> orientation is used as a material for a crimped core, the core properties expected from the material may not be obtained. After studying the cause of this, they found that the {100}<011> orientation is thought to cause a large change in magnetic properties in response to stress, specifically, a large deterioration (stress sensitivity) of magnetic properties when compressive stress is applied.

[0014] Furthermore, it was found that although the techniques disclosed in Patent Documents 4 to 7 develop the {411} plane, the accumulation of the in-plane orientation in the <011> plane is weak, and the magnetic properties in the direction 45° from the steel sheet rolling direction, which is a characteristic of α-fiber, are not sufficiently improved. The in-plane orientation not being aligned with the <011> plane, i.e., the large deviation from α-fiber, is a factor that inhibits accumulation in the {411} plane as a plane orientation, and it was thought that this may be the reason why the magnetic properties are not sufficiently improved.

[0015] Furthermore, when non-oriented electrical steel sheets are used for the stator and rotor of a motor, low iron loss is particularly required for the stator, while high magnetic flux density and high strength are particularly required for the rotor. Although different characteristics are required for the stator and rotor, it is common to stamp both the stator and rotor from the same steel sheet to ensure high punching yields. Conventional techniques involve using low-temperature ACL material (tempered steel) for the rotor, which is intentionally left untreated for grain growth to reduce grain size and increase strength, and then using SRA material (tempered steel) for the stator, which is made by subjecting the tempered steel to stress relief annealing (SRA) to allow grain growth. However, this method results in high iron loss in the rotor, which causes the motor to operate at high temperatures.

[0016] In view of the above problems, an object of the present invention is to provide a non-oriented electrical steel sheet that has low core loss, high magnetic flux density, and high strength.

[0017] The present inventors have conducted extensive studies to solve the above-mentioned problems. As a result, it has been found that optimizing the chemical composition, the grain size after hot rolling, and the reduction in cold rolling is effective. Specifically, assuming a chemical composition of the α-γ transformation system, hot rolling is performed under predetermined conditions, followed by cooling under predetermined conditions to optimize the grain size, cold rolling with a predetermined reduction, controlling the temperature of intermediate annealing within a predetermined range, performing a second cold rolling (skin-pass rolling) with an appropriate reduction, and then annealing. This effectively facilitates the development of {411}<011> orientation crystal grains, which are normally difficult to develop. The present inventors have conducted further extensive studies based on this knowledge, and have conceived the following aspects of the invention.

[0018] (1) A non-oriented electrical steel sheet according to one aspect of the present invention comprises, in mass %, C: 0.0100% or less, Si: 1.5% to 4.0%, sol. Al: 0.0001% to 1.000%, S: 0.0100% or less, N: 0.0100% or less, one or more elements selected from the group consisting of Mn, Ni, and Cu: 2.5% to 5.0% in total, Co: 0.0% to 1.0%, Sn: 0.00% to 0.40%, Sb: 0.00% to 0.400%, P: 0.000% to 0.400%, and one or more elements selected from the group consisting of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd: 0.000% to 0.010% in total, A non-oriented electrical steel sheet characterized in that it satisfies the following formula (1) when the Mn content (mass%) is [Mn], the Ni content (mass%) is [Ni], the Cu content (mass%) is [Cu], the Si content (mass%) is [Si], the sol. Al content (mass%) is [sol. Al], and the P content (mass%) is [P], with the balance consisting of Fe and impurities, when the area ratio of crystal grains having a crystal orientation of {hkl}<uvw> (within a tolerance of 10°) measured by EBSD is expressed as Ahkl-uvw, A411-011 is 15.0% or more, and the average crystal grain size is 10.0 μm to 40.0 μm. (2×[Mn]+2.5×[Ni]+[Cu])-([Si]+2×[sol.Al]+4×[P])≧1.50%...(1)

[0019] (2) The non-oriented electrical steel sheet according to (1) above may have a grain orientation spread (GOS) of 0.5 to 0.8, where Gs is the number average value of the GOS measured by electron beam scattering diffraction (EBSD).

[0020] (3) The non-oriented electrical steel sheet according to (1) or (2) above may have a magnetic flux density B50 of 1.70 T or more in a direction at an angle of 45° to the rolling direction, and an iron loss W10 / 400 of 16.0 W / kg or less in a direction at an angle of 45° to the rolling direction.

[0021] According to the above aspect of the present invention, it is possible to provide a non-oriented electrical steel sheet that has low core loss, high magnetic flux density, and high strength.

[0022] Hereinafter, embodiments of the present invention will be described in detail.

[0023] First, we will explain the chemical compositions of the non-oriented electrical steel sheet according to the embodiment of the present invention, the steel material used in the manufacturing method thereof, and the cold-rolled steel sheet used in manufacturing the non-oriented electrical steel sheet. In the following description, "%," which is the unit of content of each element contained in the non-oriented electrical steel sheet or steel material, means "mass %" unless otherwise specified. Furthermore, numerical ranges expressed using "to" mean a range that includes the numerical values ​​written before and after "to" as the lower and upper limits. Numerical values ​​indicated as "less than" or "greater than" do not fall within the numerical range.

[0024] The non-oriented electrical steel sheet, cold-rolled steel sheet, and steel material according to this embodiment have a chemical composition that allows ferrite-austenite transformation (hereinafter referred to as α-γ transformation) to occur. Specifically, C: 0.0100% or less, Si: 1.5% to 4.0%, sol. The alloy has a chemical composition containing 0.0001% to 1.000% Al, 0.0100% or less S, 0.0100% or less N, 2.5% to 5.0% in total of one or more elements selected from the group consisting of Mn, Ni, and Cu, 0.0% to 1.0% Co, 0.00% to 0.40% Sn, 0.00% to 0.40% Sb, 0.000% to 0.400% P, and 0.000% to 0.010% in total of one or more elements selected from the group consisting of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd, with the balance being Fe and impurities. Furthermore, the contents of Mn, Ni, Cu, Si, sol. Al, and P satisfy the specified conditions described below. Examples of impurities include those contained in raw materials such as ores and scraps, those contained in the manufacturing process, and those that are acceptable within a range that does not adversely affect the properties of the non-oriented electrical steel sheet according to this embodiment. In this embodiment, the Ti content may be less than 0.0005% from the viewpoint of suppressing inhibition of grain growth by precipitates such as TiN.

[0025] (C: 0.0100% or less) C precipitates fine carbides, inhibiting grain growth and thereby increasing iron loss in non-oriented electrical steel sheets and causing magnetic aging. Therefore, the lower the C content, the better. This phenomenon becomes more pronounced when the C content exceeds 0.0100%. For this reason, the C content is set to 0.0100% or less. Preferably, it is 0.0050% or less, 0.0030% or less, or 0.0020% or less. The lower limit of the C content is not particularly limited, but may be 0%. However, since it may be difficult to achieve a C content of 0% in actual non-oriented electrical steel sheets due to refining technology, the C content may be set to more than 0%. In consideration of the cost of decarburization treatment during refining, the C content is preferably set to 0.0005% or more.

[0026] (Si: 1.5% to 4.0%) Si increases the electrical resistance of non-oriented electrical steel sheets, reduces eddy current loss, reduces iron loss, and increases the yield ratio, improving punching workability into iron cores. If the Si content is less than 1.5%, these effects cannot be fully achieved. Therefore, the Si content is set to 1.5% or more. Preferably, it is set to 2.0% or more, or 2.4% or more. On the other hand, if the Si content exceeds 4.0%, the magnetic flux density of the non-oriented electrical steel sheets decreases, punching workability decreases due to an excessive increase in hardness, and cold rolling becomes difficult. Therefore, the Si content is set to 4.0% or less. Preferably, it is set to 3.5% or less, or 3.0% or less.

[0027] (Sol. Al: 0.0001% to 1.000%) Sol. Al increases the electrical resistance of non-oriented electrical steel sheets, reduces eddy current loss, and reduces iron loss. Sol. Al also contributes to improving the relative magnitude of magnetic flux density B50 with respect to saturation magnetic flux density. If the sol. Al content is less than 0.0001%, these effects cannot be fully achieved. Sol. Al also has the effect of promoting desulfurization in the steelmaking process. Therefore, the sol. Al content is set to 0.0001% or more, preferably 0.001% or more, 0.005% or more. On the other hand, if the sol. Al content exceeds 1.000%, the magnetic flux density of the non-oriented electrical steel sheets decreases, the yield ratio decreases, and punching workability decreases. Therefore, the sol. Al content is set to 1.000% or less. Preferably, the sol. Al content is 0.800% or less, 0.500% or less, or 0.200% or less. Furthermore, when the sol. Al content is in the range of 0.010% to 0.100%, AlN precipitates and inhibits grain growth, resulting in a large iron loss deterioration amount, so it is preferable to avoid this content range. In this embodiment, sol. Al means acid-soluble Al, which refers to solute Al present in the steel in a solid solution state.

[0028] (S: 0.0100% or less) S is an element that may be contained in steel even if not intentionally added. S inhibits recrystallization during intermediate annealing and grain growth during final annealing by precipitating fine MnS. Therefore, the lower the S content, the better. The increase in iron loss and decrease in magnetic flux density of non-oriented electrical steel sheets caused by the inhibition of recrystallization and grain growth are significant when the S content exceeds 0.0100%. For this reason, the S content is set to 0.0100% or less. Preferably, it is 0.0050% or less, 0.0020% or less. The lower limit of the S content is not particularly limited, but may be 0%. However, taking into account the cost of desulfurization treatment during refining, it is preferably 0.0003% or more. More preferably, it is 0.0005% or more.

[0029] (N: 0.0100% or less) N deteriorates the magnetic properties of non-oriented electrical steel sheets through the formation of fine precipitates such as TiN and AlN, so the lower the N content, the better. When the N content exceeds 0.0100%, the magnetic properties of non-oriented electrical steel sheets deteriorate significantly. Therefore, the N content is set to 0.0100% or less. Preferably, it is set to 0.0050% or less, or 0.0030% or less. The lower limit of the N content is not particularly limited, but may be 0%. However, taking into account the cost of denitrification treatment during refining, the N content is preferably set to 0.0005% or more, and more preferably 0.0010% or more.

[0030] (One or more elements selected from the group consisting of Mn, Ni, and Cu: 2.5% to 5.0% in total) Mn, Ni, and Cu are elements necessary for inducing the α-γ transformation, so it is necessary to contain at least one of these elements in a total amount of 2.5% or more. It is not necessary to contain all of Mn, Ni, and Cu; only one of these elements may be contained, and its content may be 2.5% or more. The total content of Mn, Ni, and Cu is preferably 2.8% or more, 3.0% or more, or 3.7% or more. On the other hand, if the total content of these elements exceeds 5.0%, the alloy cost increases and the magnetic flux density of the non-oriented electrical steel sheet may decrease. Therefore, the total content of these elements is set to 5.0% or less, and preferably 4.0% or less.

[0031] In this embodiment, the chemical composition of the non-oriented electrical steel sheet further satisfies the following condition for the α-γ transformation to occur. That is, when the Mn content (mass%) is [Mn], the Ni content (mass%) is [Ni], the Cu content (mass%) is [Cu], the Si content (mass%) is [Si], the sol. Al content (mass%) is [sol. Al], and the P content (mass%) is [P], the following formula (1) is satisfied in mass%: (2 × [Mn] + 2.5 × [Ni] + [Cu]) - ([Si] + 2 × [sol. Al] + 4 × [P]) ≥ 1.50% (1). If the formula (1) is not satisfied, the α-γ transformation does not occur, resulting in a low magnetic flux density of the non-oriented electrical steel sheet. The left side of formula (1) is preferably 2.00% or more, 3.00% or more, or 3.40% or more. The upper limit of the left side of formula (1) is not particularly limited, but may be 10.00% or less, 6.00% or less, or 5.00% or less.

[0032] (Co: 0.0% to 1.0%) Co is an effective element for inducing the α-γ transformation, and may be contained as needed. However, excessive Co content increases alloy costs and may also reduce the magnetic flux density of the non-oriented electrical steel sheet. Therefore, the Co content is set to 1.0% or less. Preferably, it is set to 0.5% or less. The Co content may be 0.0%. However, in order to stably induce the α-γ transformation, the Co content is preferably set to 0.01% or more, and more preferably 0.1% or more.

[0033] (Sn: 0.00% to 0.40%, Sb: 0.00% to 0.40%) Sn and Sb improve the texture after cold rolling and recrystallization, thereby increasing the magnetic flux density of the non-oriented electrical steel sheet. Therefore, these elements may be added as needed, but excessive addition will embrittle the steel. Therefore, the Sn content and Sb content are both set to 0.40% or less. Preferably, both are set to 0.20% or less. Note that the Sn content and Sb content may both be 0.0%. However, when imparting the effect of improving the magnetic flux density of the non-oriented electrical steel sheet as described above, it is preferable that the Sn content or Sb content be 0.02% or more.

[0034] (P: 0.000% to 0.400%) P may be added to ensure the hardness of the non-oriented electrical steel sheet after grain growth (after finish annealing), but excessive P content will lead to embrittlement of the steel. Therefore, the P content is set to 0.400% or less. Preferably, it is set to 0.100% or less, or 0.050% or less. There is no particular lower limit for the P content, but it may be set to 0.000%, or may be set to 0.005% or more, or 0.010% or more. When further effects such as improved magnetic properties are to be imparted, the P content is preferably set to 0.020% or more.

[0035] (One or more elements selected from the group consisting of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd: 0.000% to 0.010% in total) Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd react with S in molten steel during casting to form precipitates of sulfides or oxysulfides, or both. Hereinafter, Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd may be collectively referred to as "coarse precipitate-forming elements." The particle size of precipitates formed by coarse precipitate-forming elements is about 1 μm to 2 μm, which is much larger than the particle size (about 100 nm) of fine precipitates such as MnS, TiN, and AlN. Therefore, these fine precipitates adhere to the precipitates formed by the coarse precipitate forming elements and are less likely to inhibit recrystallization and grain growth during annealing, such as intermediate annealing. As a result, the average grain size of the non-oriented electrical steel sheet can be favorably controlled, so coarse precipitate forming elements may be added as necessary. To fully achieve the above-mentioned effects, the total content of the coarse precipitate forming elements is preferably 0.0005% or more. More preferably, it is 0.001% or more, or 0.004% or more. However, if the total content of the coarse precipitate forming elements exceeds 0.010%, the total amount of sulfides, oxysulfides, or both becomes excessive, inhibiting recrystallization and grain growth during annealing, such as intermediate annealing. Therefore, the total content of the coarse precipitate forming elements is set to 0.010% or less. Preferably, it is 0.007% or less.

[0036] Next, a method for measuring the area ratio of crystal grains having a specific orientation (specific orientation grains) in the non-oriented electrical steel sheet according to this embodiment will be described. The area ratio of specific orientation grains is measured by electron backscatter diffraction (EBSD) using OMI Analysis 7.3 (manufactured by TSL) under the following measurement conditions. For example, an EBSD detector and a scanning electron microscope (SEM) are used as the measurement device. First, the target specific orientation grains are extracted from the measurement area (the tolerance is set to 10°, hereinafter referred to as "within 10° tolerance"). The area of ​​the extracted specific orientation grains is divided by the area of ​​the measurement area to obtain a percentage. This percentage is the area ratio of specific orientation grains. Hereinafter, the "area ratio of crystal grains having a crystal orientation of {hkl}<uvw> orientation (within a tolerance of 10°) relative to the measured region" and the "area ratio of crystal grains having a crystal orientation of {hkl} plane (within a tolerance of 10°) relative to the measured region" may also be simply referred to as the "{hkl}<uvw> ratio" and the "{hkl} ratio," respectively. Hereinafter, in describing the crystal orientation, it is assumed that the tolerance is within 10°.

[0037] In the non-oriented electrical steel sheet according to this embodiment, the area ratio of crystal grains having the {hkl}<uvw> orientation as measured by EBSD, expressed as Ahkl-uvw, is set to 15.0% or more, with a tolerance of 10°. If the A411-011 ({411}<011> ratio) is less than 15.0%, the non-oriented electrical steel sheet will not be able to achieve excellent magnetic properties. Therefore, the {411}<011> ratio is set to 15.0% or more. It is preferably set to 20.0% or more, and more preferably set to 25.0% or more. There is no particular upper limit, but the {411}<011> ratio may be set to 50.0% or less, 40.0% or less, or 30.0% or less.

[0038] The details of the measurement conditions for determining the area ratio of specific orientation grains are as follows: - Measurement equipment: SEM model number "JSM-6400 (manufactured by JEOL)" and EBSD detector model number "HIKARI (manufactured by TSL)" were used - Step interval: 0.3 μm (after intermediate annealing, after skin-pass rolling), or 5.0 μm (after finish annealing) - Magnification: 1000 times (after intermediate annealing, after skin-pass rolling), or 100 times (after finish annealing) - Measurement object: central layer (1 / 2 of the sheet thickness) of the Z surface (sheet surface perpendicular to the sheet thickness direction) in the center of the C direction of the steel sheet Note that it is advisable to expose 1 / 2 of the sheet thickness by reducing the thickness by polishing. - Measurement area: area of ​​1000 μm or more in the L direction and 1000 μm or more in the C direction

[0039] Furthermore, when measured by EBSD, the non-oriented electrical steel sheet according to this embodiment preferably has a maximum strength at φ1=0 to 10° within φ1=0 to 90° and φ=20°, and a maximum strength at φ=5 to 35° within φ1=0° and φ=0 to 90°. Having a maximum strength at φ1=0 to 10° within φ1=0 to 90° and φ=20° is synonymous with having a maximum strength near the {411}<011> orientation within the {411}<uvw> orientation. In other words, it is synonymous with having a high area ratio of crystal grains with a crystal orientation of the {411}<011> orientation. The {411}<011> orientation has superior 45° magnetic properties compared to orientations such as the {411}<148> orientation. It is not preferable to have the maximum intensity at φ1=20 to 30° within the range of φ1=0 to 90° and Φ=20°, because this would result in the maximum intensity being near the {411}<148> orientation. In other words, this is not preferable because the area ratio of crystal grains having a crystal orientation of the {411}<148> orientation is high and the area ratio of crystal grains having a crystal orientation of the {411}<011> orientation is low. It is more preferable to have the maximum intensity at φ1=0 to 5° within the range of φ1=0 to 90° and Φ=20°.

[0040] On the other hand, when measured by EBSD, having a maximum intensity at Φ=5 to 35° within Φ=0° and Φ=0 to 90° is synonymous with having a maximum intensity near the {411}<011> orientation among the {hkl}<011> orientations. In other words, it is synonymous with having a high area ratio of crystal grains having a crystal orientation of the {411}<011> orientation. The {411}<011> orientation has excellent magnetic properties and is less susceptible to stress than the {100}<011> orientation, so there is less degradation of magnetic properties in crimped cores, etc. Note that having a maximum intensity at Φ=0 to 3° within Φ=0° and Φ=0 to 90° is undesirable because it would have a maximum intensity near the {100}<011> orientation. That is, the area ratio of crystal grains having a crystal orientation of {100}<011> is high and the area ratio of crystal grains having a crystal orientation of {411}<011> is low, which is not preferable. It is more preferable that the maximum strength is at Φ=20 to 30° among Φ=0° and Φ=0 to 90°.

[0041] Here, a method for determining the maximum strength within a specific orientation range of a non-oriented electrical steel sheet will be described. In the EBSD measurement area, an orientation distribution function (ODF) is created under the following conditions using OMI Analysis 7.3. The created ODF data is then output, and the point where the ODF value is maximum within a specific orientation range (defined by the angles φ1 and Φ) is taken to be the maximum strength.

[0042] Next, a method for determining the ODF strength of a specific orientation in a non-oriented electrical steel sheet will be described. In the EBSD measurement area, an ODF is created under the following conditions using OMI Analysis 7.3. The created ODF data is then output, and the ODF value of the specific orientation (orientation defined by angles φ1 and Φ) is taken as the ODF strength.

[0043] The detailed conditions for creating the ODF are as follows: Series Rank [L]: 16 Gaussian Half-Width [degrees]: 5 Sample Symmetry: Triclinic (None) Bunge Euler Angles: φ1 = 0 to 90°, φ2 = 45°, φ = 0 to 90°

[0044] Furthermore, in this embodiment, the area ratio of crystal grains having a specific orientation (within a tolerance of 10°) measured by EBSD can be expressed as follows. When the area ratio of crystal grains having a crystal orientation of the {hkl}<uvw> orientation (within a tolerance of 10°) is expressed as Ahkl-uvw and the area ratio of crystal grains having a crystal orientation of the {hkl} plane (within a tolerance of 10°) is expressed as Ahkl, it is preferable that both of the following formulas (2) and (3) are satisfied. A411-011 / A411-148 ≧ 1.1 (2) A411-011 / A100-011 ≧ 2 (3)

[0045] Furthermore, magnetic properties are superior when there are many crystal grains with a {411} crystal orientation, but are inferior when there are many crystal grains with a {111} crystal orientation. Therefore, it is preferable that the {411} ratio exceeds the {111} ratio, i.e., {411} ratio / {111} ratio > 1. More preferably, the {411} ratio is at least twice the {111} ratio, i.e., {411} ratio / {111} ratio ≥ 2.

[0046] Next, the average crystal grain size of the non-oriented electrical steel sheet according to this embodiment will be described. If the crystal grains are not sufficiently coarsened and the average crystal grain size is smaller than 10.0 μm, the iron loss of the non-oriented electrical steel sheet will deteriorate. Therefore, the average crystal grain size of the non-oriented electrical steel sheet is set to 10.0 μm or more, preferably 20.0 μm or more. On the other hand, if the crystal grains are coarsened and the average crystal grain size is larger than 40.0 μm, the strength of the non-oriented electrical steel sheet will be insufficient, and not only will the workability be deteriorated, but the eddy current loss will also deteriorate. Therefore, the average crystal grain size of the non-oriented electrical steel sheet is set to 40.0 μm or less, preferably 37.0 μm or less or 35.0 μm or less. In this embodiment, the average crystal grain size is measured by a cut-off method.

[0047] Next, the thickness of the non-oriented electrical steel sheet according to this embodiment will be described. There are no particular limitations on the thickness of the non-oriented electrical steel sheet according to this embodiment. A preferred thickness of the non-oriented electrical steel sheet according to this embodiment is 0.25 to 0.5 mm. Normally, as the sheet thickness becomes thinner, the iron loss decreases, but the magnetic flux density also decreases. In light of this, if the sheet thickness is 0.25 mm or more, the iron loss becomes lower and the magnetic flux density becomes higher. Furthermore, if the sheet thickness is 0.5 mm or less, low iron loss can be maintained. A more preferred lower limit of the sheet thickness is 0.3 mm.

[0048] The non-oriented electrical steel sheet according to this embodiment preferably has the following GOS (Grain Orientation Spread) value. Here, the GOS value is the average of the orientation differences between all measurement points (pixels) within the same grain, and the GOS value is high in crystal grains with a lot of strain. If the number-average Gs of the GOS value in the non-oriented electrical steel sheet after finish annealing is high, i.e., if the non-oriented electrical steel sheet is in a high strain state, grain growth due to bulging may not occur sufficiently, and the magnetic properties of the non-oriented electrical steel sheet may deteriorate. Therefore, in the finally obtained non-oriented electrical steel sheet after finish annealing, the number-average Gs of the GOS value is preferably 0.8 or less. On the other hand, if finish annealing is performed until the number-average Gs of the GOS value is less than 0.5, grain growth may proceed too much, and the effect of reducing the grain size by annealing may not be obtained. Therefore, the number-average Gs of the GOS value after finish annealing is preferably 0.5 or more.

[0049] Here, a method for calculating the GOS value of non-oriented electrical steel sheet will be described. The EBSD data obtained when the area ratio of the specific orientation grains was measured is used to analyze the data using OIM Analysis 7.3 to determine the number-average GOS value. This gives Gs.

[0050] In the non-oriented electrical steel sheet according to this embodiment, it is preferable that the magnetic flux density B50 in the direction at 45° to the rolling direction is 1.70 T or more, and the iron loss W10 / 400 in the direction at 45° to the rolling direction is 16.0 W / kg or less. The magnetic flux density B50 in the direction at 45° to the rolling direction is more preferably 1.72 T or more. There is no particular upper limit, but it may be 1.85 T or less or 1.80 T or less. The magnetic flux density B50 averaged over the entire circumference is preferably 1.55 T or more, more preferably 1.60 T or more. The iron loss W10 / 400 in the direction at 45° to the rolling direction is 15.5 W / kg or less, more preferably 15.0 W / kg or less, or 14.0 W / kg or less. There is no particular lower limit, but it may be 12.0 W / kg or more or 13.0 W / kg or more. The iron loss deterioration rate W of the iron loss W10 / 50 under compressive stress ｘ Regarding [%], it is preferably 40.0% or less, more preferably 32.0% or less, and even more preferably 30.0% or less. Furthermore, regarding strength, it is preferable that the tensile strength is 600 MPa or more. The tensile strength is more preferably 620 MPa or more or 650 MPa or more. There is no particular upper limit, but it may be 750 MPa or less or 700 MPa or less. Here, the magnetic flux density B50 is the magnetic flux density in a magnetic field of 5000 A / m. Furthermore, the rolling direction of a non-oriented electrical steel sheet refers to the longitudinal direction of the coil. As a method for determining the rolling direction of a small sample, for example, a method can be used in which the direction parallel to the roll streaks on the surface of the non-oriented electrical steel sheet is considered to be the rolling direction.

[0051] The magnetic flux density B50 is obtained by cutting a 55 mm square sample from a non-oriented electrical steel sheet at angles such as 45° and 0° relative to the rolling direction, and measuring the magnetic flux density in a magnetic field of 5000 A / m using a single sheet magnetic measurement device. The magnetic flux density B50 in the 45° direction relative to the rolling direction is obtained by calculating the average value of the magnetic flux density in the 45° and 135° directions relative to the rolling direction. The magnetic flux density B50 averaged over the entire circumference (averaged in all directions) is obtained by calculating the average value of the magnetic flux density at 0°, 45°, 90°, and 135° relative to the rolling direction. The iron loss W10 / 400 is obtained by measuring the average energy loss (W / kg) over the entire circumference when a 400 Hz AC magnetic field is applied to a sample taken from the non-oriented electrical steel sheet using a single sheet magnetic measurement device so that the maximum magnetic flux density is 1.0 T. The iron loss deterioration rate W of the iron loss W10 / 50 under compressive stress is ｘ [%] is the iron loss deterioration rate W10 / 50 calculated by the following formula, where W10 / 50(0) is the iron loss without stress and W10 / 50(10) is the iron loss under a compressive stress of 10 MPa. ｘ The iron loss W10 / 50 can be calculated by measuring the average energy loss (W / kg) around the entire circumference when a 50 Hz AC magnetic field is applied to a sample taken at an angle of 45° to the rolling direction using a single sheet magnetic measurement device. W ｘ = {W10 / 50(10) - W10 / 50(0)} / W10 / 50(0) The tensile strength of a non-oriented electrical steel sheet is determined by taking a JIS No. 5 test piece with the longitudinal direction aligned with the rolling direction of the non-oriented electrical steel sheet and conducting a tensile test in accordance with JIS Z2241:2011.

[0052] The features of the non-oriented electrical steel sheet according to the present embodiment described above are features of the non-oriented electrical steel sheet manufactured by performing finish annealing. Hereinafter, the features of the non-oriented electrical steel sheet before performing finish annealing (and after performing skin-pass rolling) will be described.

[0053] The non-oriented electrical steel sheet after skin-pass rolling (before finish annealing) has a number-average value Gs of the GOS (Grain Orientation Spread) value described below. If the number-average value Gs of the GOS value is small, i.e., if the sheet is in a low strain state after skin-pass rolling, grain growth due to bulging is likely to occur in the subsequent finish annealing process. Therefore, it is preferable that the number-average value Gs of the GOS value after skin-pass rolling is 3.0 or less. On the other hand, if the number-average value Gs of the GOS value is less than 0.8, the amount of strain becomes too small, and the finish annealing time required for grain growth due to bulging becomes long. Therefore, it is preferable that the number-average value Gs of the GOS value after skin-pass rolling is 0.8 or more.

[0054] Furthermore, in non-oriented electrical steel sheets after skin-pass rolling (before finish annealing), the higher the α-fiber ratio, the more advantageous the magnetic properties after finish annealing. Here, a method for measuring the α-fiber ratio will be described. In this embodiment, α-fiber is defined as crystal grains having a crystal orientation of the {hkl}<011> orientation. In the EBSD measurement area, crystal grains having a crystal orientation of the {hkl}<011> orientation are extracted (within a tolerance of 10°) using OMI Analysis 7.3. The area of ​​the extracted crystal grains is divided by the area of ​​the measurement area to determine the percentage. This percentage is the α-fiber ratio.

[0055] In the non-oriented electrical steel sheet after skin-pass rolling (before finish annealing), the α-fiber ratio is preferably 20% or more, more preferably 25% or more.

[0056] Furthermore, in non-oriented electrical steel sheets after skin-pass rolling (before finish annealing), the ODF strength of the {100}<011> orientation is set to 15 or less. Here, the ODF strength of the {100}<011> orientation is the ODF value at φ1=0° and Φ=0° of the ODF created using EBSD data when measuring the area ratio of specific orientation grains. The {411}<011> orientation has excellent magnetic properties and is less susceptible to stress than the {100}<011> orientation, so magnetic deterioration in crimped cores, etc. is reduced. By setting the ODF strength of the {100}<011> orientation after skin-pass rolling (before finish annealing) to 15 or less, the {411}<011> orientation can be strengthened after the subsequent finish annealing (increasing the area ratio of crystal grains having the {411}<011> orientation).

[0057] The non-oriented electrical steel sheet according to this embodiment can be used to form a core, and is widely applicable to applications requiring magnetic properties (high magnetic flux density and low iron loss), but is particularly applicable to rotors requiring high strength. Furthermore, by allowing grain growth to occur in the non-oriented electrical steel sheet according to this embodiment, it can also be used in stators.

[0058] Next, an example of a method for manufacturing a non-oriented electrical steel sheet according to this embodiment will be described. In this embodiment, hot rolling, cold rolling, intermediate annealing, second cold rolling (skin pass rolling), and finish annealing are performed.

[0059] In the hot rolling process, a steel material satisfying the above-mentioned chemical composition is hot-rolled to produce a hot-rolled sheet. The hot rolling process includes a heating step and a rolling step.

[0060] The steel material is, for example, a slab produced by normal continuous casting, and steel material having the above-mentioned chemical composition is produced by a well-known method. For example, molten steel is produced in a converter or electric furnace. The produced molten steel is subjected to secondary refining in a degassing facility or the like to obtain molten steel having the above-mentioned chemical composition. The molten steel is cast into a slab by a continuous casting method or an ingot casting method. The cast slab may be bloomed.

[0061] In the heating step, the steel material having the above-mentioned chemical composition is preferably heated to 1000 to 1200°C. Specifically, the steel material is charged into a heating furnace or a soaking furnace and heated in the furnace. The holding time at the above-mentioned heating temperature in the heating furnace or the soaking furnace is not particularly limited, but is, for example, 30 to 200 hours.

[0062] In the rolling process, the steel material heated in the heating process is subjected to multiple passes of rolling to produce a hot-rolled sheet. Here, "pass" means that the steel sheet passes through one rolling stand having a pair of work rolls and is subjected to rolling reduction. Hot rolling may be performed, for example, by tandem rolling using a tandem rolling mill including multiple rolling stands arranged in a row (each rolling stand having a pair of work rolls), or by reverse rolling using a pair of work rolls, to perform multiple passes. From the viewpoint of productivity, it is preferable to perform multiple rolling passes using a tandem rolling mill.

[0063] Rolling in the rolling process (rough rolling and finish rolling) is performed at a temperature in the γ region (Ar1 point or higher). In other words, hot rolling is performed so that the temperature (finish rolling temperature FT (°C)) when passing through the final pass of finish rolling is Ar1 point or higher. It is also preferable to perform hot rolling so that the finish rolling temperature FT is Ac3 point or lower. By performing hot rolling so that the finish rolling temperature FT is Ac3 point or lower, strain can be preferably introduced into the crystal grains in combination with cooling, etc., as described below, and as a result, the A411-011 can be increased. If the finish rolling temperature FT is higher than the Ac3 point, strain cannot be preferably introduced into the crystal grains, and as a result, the desired A411-011 may not be obtained. The Ar1 point can be determined from the thermal expansion change of the steel sheet during cooling at an average cooling rate of 1°C / sec. The Ac3 point and the Ac1 point, which will be described later, can be determined from the thermal expansion change of the steel sheet during heating at an average heating rate of 1°C / sec.

[0064] Here, the finish rolling temperature FT means the surface temperature (°C) of the steel sheet at the exit side of the rolling stand that performs the final pass reduction in the rolling process during the hot rolling process. The finish rolling temperature FT can be measured, for example, by a thermometer installed at the exit side of the rolling stand that performs the final pass reduction. Note that the finish rolling temperature FT means, for example, the average value of the temperature measurement results of the portions excluding one section at the front end and one section at the rear end when the entire length of the steel sheet is divided into 10 equal sections in the rolling direction.

[0065] Subsequently, cooling after the rolling process transforms the austenite to ferrite, resulting in high strain and moderately fine crystal grains. The cooling conditions are such that cooling begins 0.10 seconds or more after the final pass of finish rolling, and cooling is performed so that the surface temperature of the hot-rolled sheet reaches 300°C or higher and Ar1 point or lower after 3 seconds. In this embodiment, rapid cooling immediately after hot rolling is not preferable. Rapid cooling immediately after the hot-rolled sheet (immediate rapid cooling) refers to starting water cooling within 0.10 seconds after the final pass of finish rolling, or cooling such that the surface temperature of the hot-rolled sheet reaches less than 300°C after 3 seconds. Such immediate rapid cooling can be performed by water-cooling the work rolls of the final pass of finish rolling without air-cooling after finish rolling. Since this embodiment does not perform such immediate rapid cooling, a special rapid cooling device is not required, which is advantageous in terms of manufacturing costs. Furthermore, by performing cooling that is not immediate rapid cooling as described above, a suitable crystal grain size is obtained that is not excessively refined, and by subsequently performing cold rolling, α-fibers are developed after intermediate annealing, and the {411}<011> orientation, which is usually difficult to develop, can be developed after the subsequent skin-pass rolling and finish annealing. Note that the cooling stop temperature in the cooling after the hot rolling step is not particularly limited, but is preferably set to a temperature range of 500°C or less from the viewpoint of maintaining the amount of strain.

[0066] Furthermore, it is presumed that the texture of a hot-rolled sheet becomes a structure in which non-recrystallized austenite is transformed when the sheet is immediately quenched, and becomes a structure in which partially recrystallized austenite is transformed when the sheet is cooled without immediately quenching. When the sheet is immediately quenched after finish rolling, the austenite accumulates in the {100}<011> orientation in the structure after subsequent finish annealing, while when the sheet is cooled without immediately quenching after finish rolling, the austenite accumulates in the {411}<011> orientation in the structure after subsequent finish annealing. Therefore, it is considered important to transform the partially recrystallized austenite to strengthen the {411}<011> orientation.

[0067] Here, the cooling conditions are preferably such that the average crystal grain size in the hot-rolled sheet before cold rolling is 3 to 10 μm. If the crystal grains become too coarse, it becomes difficult for α-fiber to develop after cold rolling and intermediate annealing, and the desired {411}<011> ratio may not be obtained. Moreover, if the crystal grains are made too fine, the desired {411}<011> ratio cannot be obtained. Therefore, in order to make the average crystal grain size in the hot-rolled sheet before cold rolling 3 to 10 μm, it is preferable to bring the temperature to the Ar1 point or below within 3 seconds after passing through the final pass of finish rolling. The grain size can be measured, for example, by the intercept method.

[0068] The surface temperature of the hot-rolled sheet 3 seconds after passing through the final pass of finish rolling is measured by the following method. In a hot rolling equipment line for non-oriented electrical steel sheets, a cooling device and a conveying line (e.g., conveying rollers) are arranged downstream of the hot rolling mill. A thermometer for measuring the surface temperature of the hot-rolled sheet is arranged at the exit side of the rolling stand that performs the final pass of the hot rolling mill. In addition, multiple thermometers are arranged along the conveying line on the conveying rollers arranged downstream of the rolling stand. A cooling device is arranged downstream of the rolling stand that performs the final pass. A thermometer is arranged at the entrance side of the water cooling device. The cooling device may be, for example, a well-known water cooling device or a well-known forced air cooling device. Preferably, the cooling device is a water cooling device. The coolant for the water cooling device may be water or a mixed fluid of water and air.

[0069] The surface temperature of the hot-rolled sheet is measured with a thermometer installed in the hot rolling equipment line, and the temperature is obtained 3 seconds after the final pass of finish rolling.

[0070] Thereafter, the hot-rolled sheet is coiled without being annealed, and the hot-rolled sheet is subjected to cold rolling. Note that the hot-rolled sheet annealing here refers to, for example, heat treatment performed on the hot-rolled sheet at a heating temperature in the range of 800 to 1100°C. The holding time at the heating temperature during the hot-rolled sheet annealing is, for example, 1 minute or more. If the hot-rolled sheet annealing is performed, the strain within the crystal grains cannot be controlled favorably, and as a result, the desired {411}<011> ratio cannot be obtained, which is undesirable.

[0071] The hot-rolled sheet is subjected to cold rolling without being annealed. Cold rolling may be performed, for example, by tandem rolling using a tandem rolling mill including a plurality of rolling stands arranged in a row (each rolling stand having a pair of work rolls) to perform multiple passes. Alternatively, reverse rolling may be performed using a Sendzimir rolling mill or the like having a pair of work rolls to perform single or multiple passes. From the viewpoint of productivity, it is preferable to perform multiple passes using a tandem rolling mill.

[0072] In cold rolling, cold rolling is performed without annealing treatment during the cold rolling. For example, when performing reverse rolling and performing cold rolling in multiple passes, multiple passes of cold rolling are performed without annealing treatment between the cold rolling passes. Note that cold rolling may be performed in only one pass using a reverse rolling mill. Furthermore, when performing cold rolling using a tandem rolling mill, cold rolling is performed continuously in multiple passes (passes in each rolling stand). Note that when annealing is performed during cold rolling to prevent brittle cracking, cold rolling is often performed with a small difference in reduction between before and after annealing (for example, about 10%). Therefore, the "annealing during cold rolling" referred to here and the "intermediate annealing" performed before skin-pass rolling in this embodiment can be distinguished by the difference in reduction between cold rolling before and after annealing. Furthermore, when annealing is performed between cold rolling passes by the two-pass cold rolling method or the like, cold rolling with a high reduction (for example, about 40%) is often performed after the annealing. Therefore, the "annealing between cold rolling passes" referred to here and the "intermediate annealing" performed before skin-pass rolling in this embodiment can be distinguished by the reduction of the cold rolling performed thereafter.

[0073] In this embodiment, the reduction rate RR1 (%) in cold rolling is preferably set to 75 to 95%. Here, the reduction rate RR1 is defined as follows: Reduction rate RR1 (%) = (1 - sheet thickness after the final pass in cold rolling / sheet thickness before the first pass in cold rolling) x 100

[0074] After the cold rolling is completed, intermediate annealing is performed. In this embodiment, it is preferable to control the intermediate annealing temperature T1 (°C) to the Ac1 point or lower. If the intermediate annealing temperature exceeds the Ac1 point, part of the structure of the steel sheet will transform to austenite, and the {411}<011> oriented grains in the steel sheet will decrease. Note that if the intermediate annealing temperature is too low, recrystallization will not occur, and the {411}<011> oriented grains will not grow sufficiently during the subsequent skin-pass rolling and finish annealing, which may result in an insufficient magnetic flux density of the non-oriented electrical steel sheet. Therefore, it is preferable to set the intermediate annealing temperature T1 (°C) to 600°C or higher.

[0075] Here, the intermediate annealing temperature T1 (°C) is the sheet temperature (temperature of the steel sheet surface) near the outlet of the annealing furnace. The sheet temperature in the annealing furnace can be measured by a thermometer arranged at the outlet of the annealing furnace.

[0076] The holding time at the intermediate annealing temperature T1 in the intermediate annealing step may be a time known to those skilled in the art. The holding time at the intermediate annealing temperature T1 is, for example, 5 to 60 seconds, but is not limited to this. The temperature rise rate up to the intermediate annealing temperature T1 may also be a known condition. The temperature rise rate up to the intermediate annealing temperature T1 is, for example, 10.0 to 20.0°C / second, but is not limited to this.

[0077] The atmosphere during intermediate annealing is not particularly limited, but the atmosphere during intermediate annealing may be, for example, 20% H ２ and the remainder is N ２ The cooling rate of the steel sheet after intermediate annealing is not particularly limited, and the cooling rate is, for example, 5.0 to 60.0° C. / sec.

[0078] When the intermediate annealing is completed under the above conditions, the resulting cold-rolled steel sheet has an α-fiber ratio (within a 10° tolerance) of 15% or more as measured by EBSD. In order to achieve an α-fiber ratio (within a 10° tolerance) of 15% or more before skin-pass rolling, it is effective to use a chemical composition of the α-γ transformation system (a chemical composition with high concentrations of γ-former elements Mn, Ni, and Cu) and to maintain the above-mentioned conditions from hot rolling to intermediate annealing. Controlling the cooling conditions after finish rolling is particularly effective. By transforming partially recrystallized austenite into ferrite and cold-rolling the hot-rolled sheet with an average grain size of 3 to 10 μm after hot rolling, followed by intermediate annealing, α-fibers that are likely to produce a {411}<011> orientation develop. As mentioned above, rapid cooling immediately after finish rolling results in a structure transformed from unrecrystallized austenite, and not a structure transformed from partially recrystallized austenite. The cold-rolled steel sheet produced by the above-described method is subjected to skin-pass rolling under the conditions described below, and then to finish annealing, whereby the non-oriented electrical steel sheet according to this embodiment can be obtained.

[0079] After the intermediate annealing is completed, skin pass rolling is then performed. Specifically, the cold rolled steel sheet after the intermediate annealing step is subjected to skin pass rolling (cold rolling at a light reduction) at room temperature in the atmosphere. For the skin pass rolling here, for example, a reverse rolling mill typified by the above-mentioned Sendzimir rolling mill or a tandem rolling mill is used.

[0080] In skin pass rolling, rolling is performed without performing annealing treatment in between. For example, when performing skin pass rolling in multiple passes by performing reverse rolling, multiple passes are performed without annealing treatment between passes. Note that skin pass rolling may be performed in only one pass using a reverse rolling mill. Furthermore, when performing skin pass rolling using a tandem rolling mill, rolling is performed continuously in multiple passes (passes at each rolling stand).

[0081] As described above, in this embodiment, after strain is introduced into the steel sheet by hot rolling and cold rolling, the strain introduced into the steel sheet is temporarily reduced by intermediate annealing. Then, skin-pass rolling is performed. By performing intermediate annealing while reducing the excessive strain introduced by cold rolling, preferential recrystallization of crystal grains having a {111} crystal orientation in the steel sheet surface is suppressed, and crystal grains having a {411}<011> crystal orientation are retained. Then, an appropriate amount of strain is introduced into each crystal grain in the steel sheet by skin-pass rolling, creating a state in which grain growth due to bulging is likely to occur in the subsequent finish annealing process.

[0082] In this embodiment, the reduction ratio RR2 in skin pass rolling is set to 5 to 20%. Here, the reduction ratio RR2 is defined as follows: Reduction ratio RR2 (%) = (1 - sheet thickness after rolling in the final pass in skin pass rolling / sheet thickness before rolling in the first pass in skin pass rolling) x 100

[0083] If the reduction rate RR2 is less than 5%, the amount of strain becomes too small, and the finish annealing time required for grain growth due to bulging becomes long. If the reduction rate RR2 exceeds 20%, the amount of strain becomes too large, and normal grain growth occurs instead of bulging, resulting in the growth of {411}<148> and {111}<011> during finish annealing. Therefore, the reduction rate RR2 is set to 5 to 20%.

[0084] The number of passes in the skin pass rolling may be only one pass (i.e., only one rolling), or may be multiple passes.

[0085] As described above, by recrystallizing a steel sheet having an α-γ transformation chemical composition through intermediate annealing and then performing skin pass rolling under the above conditions, the above-mentioned GOS value and α fiber ratio can be obtained.

[0086] After skin-pass rolling, finish annealing is performed under the conditions that the finish annealing temperature T2 is set to a temperature range of 800°C to 850°C and the holding time in that temperature range (finish annealing time Δt2) is set to 20 seconds to 60 seconds. If the finish annealing temperature T2 (°C) is set to less than 800°C, grain growth due to bulging does not occur sufficiently. In this case, the concentration of the {411}<011> orientation decreases. Furthermore, if the finish annealing temperature T2 exceeds 850°C, a part of the structure of the steel sheet is transformed to austenite, grain growth due to bulging does not occur, and the desired {411}<011> ratio cannot be obtained. Furthermore, if the annealing time is less than 20 seconds, even if the finish annealing temperature T2 is set to 800°C to 850°C, grain growth due to bulging does not occur sufficiently, and the concentration of the {411}<011> orientation decreases. Furthermore, if the annealing time exceeds 60 seconds, the crystal grains become coarse and the desired strength cannot be obtained.

[0087] Here, the finish annealing temperature T2 is the sheet temperature (temperature of the steel sheet surface) in the vicinity of the outlet of the annealing furnace. The furnace temperature of the annealing furnace can be measured by a thermometer arranged at the outlet of the annealing furnace.

[0088] The temperature rise rate TR2 up to the finish annealing temperature T2 in the finish annealing step may be any temperature rise rate known to those skilled in the art, and the holding time Δt2 (seconds) at the finish annealing temperature T2 may also be any time known to those skilled in the art. Here, the holding time Δt2 means the holding time after the surface temperature of the steel sheet reaches the finish annealing temperature T2.

[0089] The preferred heating rate TR2 to the finish annealing temperature T2 in the finish annealing step is 0.1°C / s or more and less than 10.0°C / s. If the heating rate TR2 is 0.1°C / s or more and less than 10.0°C / s, grain growth due to bulging occurs sufficiently. In this case, the concentration of the {411}<011> crystal orientation is further increased, and the crystal grains on the ND plane at the center of the sheet thickness are further reduced in variation.

[0090] The heating rate TR2 is determined by the following method. A thermocouple is attached to a steel sheet having the above chemical composition and obtained by carrying out the above steps from hot rolling to skin pass, to prepare a sample steel sheet. The sample steel sheet to which the thermocouple is attached is heated, and the time from the start of the heating until the temperature reaches the finish annealing temperature T2 is measured. The heating rate TR2 is determined based on the measured time.

[0091] The holding time Δt2 at the finish annealing temperature T2 in the finish annealing step is 20 to 60 seconds. If the holding time Δt2 is 20 to 60 seconds, grain growth of {411}<110> grains occurs due to bulging, and strength is increased by grain refinement strengthening. In this case, the concentration of {411}<011> crystal orientation is further increased, and the crystal grains on the ND plane at the center of the sheet thickness are further reduced in variation. The preferred lower limit of the holding time Δt2 is 25 seconds, and more preferably 30 seconds. The preferred upper limit of the holding time Δt2 is 50 seconds, and more preferably 40 seconds.

[0092] The atmosphere during the final annealing step is not particularly limited. For example, the atmosphere during the final annealing step may be 20% H ２ and the remainder is N ２ The cooling rate of the steel sheet after the finish annealing is not particularly limited. The cooling rate is, for example, 5 to 20°C / second.

[0093] As described above, the non-oriented electrical steel sheet according to this embodiment can be manufactured.

[0094] The method for manufacturing the non-oriented electrical steel sheet according to this embodiment is not limited to the manufacturing steps described above.

[0095] For example, among the above manufacturing processes, shot blasting and / or pickling may be performed after hot rolling and before cold rolling. In shot blasting, shot blasting is performed on the hot-rolled steel sheet to destroy and remove scale formed on the surface of the hot-rolled steel sheet. In pickling, pickling treatment is performed on the hot-rolled steel sheet. For example, the pickling treatment uses an aqueous hydrochloric acid solution as the pickling bath. Pickling removes scale formed on the surface of the steel sheet. Shot blasting may be performed after hot rolling and before cold rolling, and then pickling may be performed. Alternatively, pickling may be performed after hot rolling and before cold rolling, without shot blasting. Alternatively, shot blasting may be performed after hot rolling and before cold rolling, without pickling treatment. Note that shot blasting and pickling are optional processes. Therefore, it is not necessary to perform both the shot blasting process and the pickling process after hot rolling and before cold rolling.

[0096] The method for producing an electrical steel sheet according to this embodiment may further include coating after the final annealing, in which an insulating coating is formed on the surface of the steel sheet after the final annealing.

[0097] The type of insulating coating is not particularly limited. The insulating coating may be made of either an organic component or an inorganic component, and the insulating coating may contain both an organic component and an inorganic component. Examples of inorganic components include dichromate-boric acid-based, phosphoric acid-based, and silica-based resins. Examples of organic components include general acrylic, acrylic styrene-based, acrylic silicone-based, silicone-based, polyester-based, epoxy-based, and fluorine-based resins. Considering paintability, emulsion-type resins are preferred. An insulating coating that exhibits adhesive properties when heated and / or pressurized may be applied. Examples of insulating coatings with adhesive properties include acrylic, phenol-based, epoxy-based, and melamine-based resins.

[0098] The coating is an optional step, and therefore, it is not necessary to perform the coating after the final annealing.

[0099] The non-oriented electrical steel sheet according to this embodiment is not limited to the above-mentioned manufacturing method, as long as the area ratio of crystal grains having a crystal orientation of {411}<011> (within a tolerance of 10°) measured by EBSD is 15.0% or more and the average crystal grain size is 10.0 μm to 40.0 μm.

[0100] Next, the non-oriented electrical steel sheet according to the embodiment of the present invention will be specifically described with reference to examples. The examples shown below are merely examples of the non-oriented electrical steel sheet according to the embodiment of the present invention, and the non-oriented electrical steel sheet according to the present invention is not limited to the examples below.

[0101] (First Example) Molten steel was cast to produce an ingot having the composition shown in Table 1 below. Here, the left side of the formula represents the value of the left side of the above-mentioned formula (1). Furthermore, Mg, etc. represents the total of one or more elements selected from the group consisting of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn, and Cd. The produced ingot was then heated to 1150°C and hot-rolled, and finish-rolled at the finish-rolling temperature FT shown in Table 2. After passing through the final pass, the steel sheet was cooled under the cooling conditions shown in Table 2 (the time from passing through the final pass to the start of cooling, and the temperature of the steel sheet 3 seconds after passing through the final pass).

[0102] Next, the hot-rolled sheets were not subjected to hot-rolled sheet annealing, but scale was removed by pickling, and cold-rolled at a rolling reduction RR1 shown in Table 2. Then, intermediate annealing was performed in an atmosphere of 20% hydrogen and 80% nitrogen, with the intermediate annealing temperature T1 controlled to the temperature shown in Table 2, and intermediate annealing was performed for 30 seconds. Note that for No. 24, the hot-rolled sheet was subjected to hot-rolled sheet annealing by holding it at 1000°C for 1 minute.

[0103] Next, except for No. 11, the steel sheets were subjected to skin-pass rolling at a rolling reduction RR2 shown in Table 2. Then, finish annealing was performed in a 100% hydrogen atmosphere at a finish annealing temperature T2 shown in Table 2. At this time, the holding time Δt2 at the finish annealing temperature T2 was set to the time shown in Table 2.

[0104] In addition, to investigate the texture after final annealing, a portion of the non-oriented electrical steel sheet was cut out, and the cut-out test piece was reduced in thickness to 1 / 2. The {411}<011> ratio was determined by observation in the EBSD measurement area under the measurement conditions described above. Furthermore, in order to determine the number-average Gs of the GOS value, an ODF was created in the EBSD measurement area under the conditions described above using OMI Analysis 7.3, and the data of the created ODF was output to determine the number-average GOS value, which was designated as Gs. The number-average Gs of the GOS value was also determined before final annealing. The respective results are shown in Table 3.

[0105] In addition, the magnetic flux density B50 and iron loss W10 / 400 were measured to investigate the magnetic properties and tensile strength after final annealing. Furthermore, the iron loss degradation rate of iron loss W10 / 50 under compressive stress was determined as an index of stress sensitivity. Regarding the magnetic flux density B50, 55 mm square samples were collected in two directions, 0° and 45°, relative to the rolling direction. The magnetic flux density B50 of these two types of samples was measured by the above-described method. The average value of the magnetic flux densities in the 45° and 135° directions relative to the rolling direction was defined as the magnetic flux density B50 in the 45° direction, and the average value of the magnetic flux density B50 in the 0°, 45°, 90°, and 135° directions relative to the rolling direction was defined as the total circumference average. When the magnetic flux density B50 in the 45° direction was 1.70 T or more, the sheet was deemed to be a high-magnetic flux density non-oriented electrical steel sheet and was judged to be acceptable. On the other hand, if the magnetic flux density B50 in the 45° direction was less than 1.70 T, the sheet was judged to be a non-oriented electrical steel sheet with a high magnetic flux density and to have been rejected. Furthermore, if the magnetic flux density B50 in the 45° direction was 1.70 T or more and the average magnetic flux density B50 around the entire circumference was 1.55 T or more, the sheet was judged to have a higher magnetic flux density. Regarding the iron loss W10 / 400, the iron loss W10 / 400 in the 45° direction was determined by the above-mentioned method using the above samples taken at a 45° angle to the rolling direction. Furthermore, the iron loss deterioration rate W of the iron loss W10 / 50 under compressive stress was calculated. ｘ Regarding [%], when the iron loss W10 / 50 without stress is W10 / 50(0) and the iron loss W10 / 50 under a compressive stress of 10 MPa is W10 / 50(10), the iron loss deterioration rate W is calculated using the following formula: ｘ The iron loss W10 / 50 was calculated by measuring the average energy loss (W / kg) around the entire circumference when a 40 Hz AC magnetic field was applied to a sample taken at a 45° angle to the rolling direction using a single sheet magnetic measurement device, so that the maximum magnetic flux density was 1.0 T. When the iron loss W10 / 400 in the 45° direction was 16.0 W / kg or less and the iron loss degradation rate W ｘ On the other hand, when the iron loss W10 / 400 in the 45° direction was more than 16.0 W / kg or the iron loss degradation rate W ｘWhen the value of W was more than 40.0%, it was judged as not being a low-iron-loss non-oriented electrical steel sheet and was rejected. The tensile strength was measured by taking a JIS No. 5 test piece with the rolling direction of the steel sheet as the longitudinal direction and performing a tensile test in accordance with JIS Z2241:2011. When the tensile strength was 600 MPa or more, it was judged as being a high-strength non-oriented electrical steel sheet and was rejected. On the other hand, when the tensile strength was less than 600 MPa, it was judged as not being a high-strength non-oriented electrical steel sheet and was rejected. The measurement results are shown in Table 3. W ｘ = {W10 / 50(10)-W10 / 50(0)} / W10 / 50(0)

[0106]

[0107]

[0108]

[0109] The underlined values ​​in Tables 1, 2, and 3 indicate conditions outside the range of the present invention, unfavorable manufacturing conditions, or unfavorable characteristic values. Nos. 1, 4, 7, 8, and 14 to 17, which are examples of the present invention, all exhibited favorable values ​​for magnetic flux density B50, iron loss W10 / 400, iron loss deterioration rate, and tensile strength.

[0110] On the other hand, Comparative Example No. 2 was rapidly cooled after finish rolling, resulting in a small {411}<011> ratio, and the iron loss degradation rate under compressive stress was large. Furthermore, the annealing time in the finish annealing was too long, resulting in an excessively large average grain size and insufficient tensile strength. Comparative Example No. 3 contained a total of at least one element selected from the group consisting of Mn, Ni, and Cu insufficiently, and had a composition in which α-γ transformation did not occur, resulting in a small {411}<011> ratio and poor magnetic flux density B50 (45° direction), iron loss W10 / 400, and iron loss degradation rate. Since Comparative Example No. 3 had a composition in which α-γ transformation did not occur, the Ar1 point, Ac1 point, and Ac3 point are not recorded. Comparative Example No. In Comparative Example No. 5, the finish rolling temperature FT was lower than the Ar1 point, resulting in a small {411}<011> ratio, and the magnetic flux density B50 (45° direction), iron loss W10 / 400, and iron loss degradation rate were poor. In Comparative Example No. 6, the time from the final pass of finish rolling to the start of cooling was too short, and the finish annealing temperature was too high, resulting in a small {411}<011> ratio, and the magnetic flux density B50 (45° direction), iron loss W10 / 400, and iron loss degradation rate were poor.

[0111] Comparative Example No. 9 had a low Si content and the annealing time in the finish annealing was too short, resulting in a small {411}<011> ratio and an excessively small average grain size. As a result, the magnetic flux density B50 (45° direction) and iron loss W10 / 400 were poor. Comparative Example No. 10 had an excessive total content of one or more elements selected from the group consisting of Mn, Ni, and Cu, resulting in poor magnetic flux density B50 in both the 45° direction and the average magnetic flux density around the circumference. Furthermore, due to segregation, splitting into two occurred in some parts during cold rolling. Comparative Example No. 11 did not undergo skin-pass rolling, resulting in a low {411}<011> ratio and poor magnetic flux density B50 (45° direction), iron loss W10 / 400, and iron loss degradation rate. Comparative Example No. In No. 12, the reduction ratio RR2 in skin-pass rolling was too large, resulting in a small {411}<011> ratio, and the magnetic flux density B50 (45° direction) and iron loss W10 / 400 were poor. In addition, in No. 13 and No. 18 to No. 24, which are comparative examples, the desired metal structure was not obtained and the desired properties could not be obtained because the manufacturing conditions were not within the preferred range.

[0112] According to the above aspect of the present invention, it is possible to provide a non-oriented electrical steel sheet that has low core loss, high magnetic flux density, and high strength.

Claims

1. The alloy contains, by mass%, C: 0.0100% or less, Si: 1.5% to 4.0%, sol. Al: 0.0001% to 1.000%, S: 0.0100% or less, N: 0.0100% or less, one or more elements selected from the group consisting of Mn, Ni and Cu: a total of 2.5% to 5.0%, Co: 0.0% to 1.0%, Sn: 0.00% to 0.40%, Sb: 0.00% to 0.400%, P: 0.000% to 0.400%, and one or more elements selected from the group consisting of Mg, Ca, Sr, Ba, Ce, La, Nd, Pr, Zn and Cd: a total of 0.000% to 0.010%, A non-oriented electrical steel sheet characterized in that, when the Mn content (mass%) is [Mn], the Ni content (mass%) is [Ni], the Cu content (mass%) is [Cu], the Si content (mass%) is [Si], the sol.Al content (mass%) is [sol.Al], and the P content (mass%) is [P], the following formula (1) is satisfied, the balance being Fe and impurities, when the area ratio of crystal grains having a crystal orientation of {hkl}<uvw> orientation (within a tolerance of 10°) measured by EBSD is expressed as Ahkl-uvw, A411-011 is 15.0% or more, and the average crystal grain size is 10.0 μm to 40.0 μm. (2×[Mn]+2.5×[Ni]+[Cu])-([Si]+2×[sol.Al]+4×[P])≧1.50% ... (1) 2. A non-oriented electrical steel sheet according to claim 1, characterized in that, when the number average value of GOS (grain orientation spread) value measured by EBSD is taken as Gs, Gs is 0.5 to 0.

8.

3. A non-oriented electrical steel sheet as described in claim 1 or 2, characterized in that the magnetic flux density B50 in a direction at 45 degrees to the rolling direction is 1.70 T or more, and the iron loss W10 / 400 in a direction at 45 degrees to the rolling direction is 16.0 W / kg or less.