Non-oriented electrical steel sheet, motor core and motor

Abstract

This non-oriented electrical steel sheet has a composition that may undergo an α-γ transformation. The composition contains 0.3% to 0.7% of sol. Al and 0.0005% to 0.0020% of Ti, with the contents of Si, Mn and sol. Al satisfying a specific relationship. When the surface of the steel sheet is measured using a scanning electronic microscope with electron backscattered diffraction (SEM-EBSD), if the area ratio of crystal grains in a \{hkl\}<uvw> orientation (with a tolerance within 10°) with respect to the entire field of view is represented by Ahkl-uvw, A411-011 is 15% or more, and the number density of precipitates is 0.0001 per μm2 to 0.3000 per μm2.

Description

Non-oriented electrical steel sheets, motor cores and motors

[0001] This application claims priority to Japanese Patent Application No. 2023-023379, filed on February 17, 2023, 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 automobiles, 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) with an easy axis of magnetization within the steel sheet plane, which is advantageous for improving magnetic properties and can be relatively easily enriched by hot rolling and cold rolling, which are essential processes in steel sheet manufacturing. Specifically, a texture is formed 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. This makes it possible to produce 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 setting the finish rolling temperature in hot rolling to the Ac3 transformation point or higher and cooling the steel sheet temperature to 250°C within 3 seconds after hot rolling, or setting the finish rolling temperature to the Ac3 transformation point -50°C or lower and cooling 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. This is said to enable the manufacture 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} orientation, which is rotated 20° from the {100} orientation, has also been proposed in order to improve magnetic properties. As a method for developing the {411} orientation, Patent Documents 4 to 7 all disclose techniques for developing the {411} orientation, and describe optimizing the grain size in a hot-rolled sheet or strengthening α-fibers in the texture of the hot-rolled sheet.

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

[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} and {411} orientations are integrated 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] 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 increase the change in magnetic properties in response to stress, specifically, the deterioration of magnetic properties (stress sensitivity) when compressive stress is applied.

[0013] Furthermore, it was found that although the techniques disclosed in Patent Documents 4 to 7 develop the {411} orientation, the concentration of the in-plane orientation in the <011> orientation 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> orientation, i.e., the large deviation from α-fiber, is a factor that inhibits the concentration of the {411} orientation as a plane orientation, and it is thought that this may be the reason why the magnetic properties are not sufficiently improved.

[0014] Furthermore, in non-oriented electrical steel sheets for automobiles, there is a strong demand not only for higher magnetic flux density but also for reduced iron loss, which has been achieved by reducing the thickness of the sheets. However, reducing the thickness of the sheets leads to a decrease in motor production efficiency, so a method is needed to reduce iron loss while maintaining the thickness.

[0015] 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

[0016] In view of the above problems, an object of the present invention is to provide a non-oriented electrical steel sheet that does not increase the manufacturing load, does not require thinning of the sheet thickness, and achieves both low iron loss and high magnetic flux density.

[0017] The present inventors have conducted extensive research to solve the above-mentioned problems. As a result, it has become clear that it is important to optimize the chemical composition, the grain size after hot rolling, and the reduction in cold rolling. Specifically, it is important to optimize the grain size by cooling under predetermined conditions after hot rolling, controlling the intermediate annealing temperature within a predetermined range, and performing a second cold rolling with an appropriate reduction followed by annealing, thereby facilitating the development of {411}<011> oriented crystal grains, which are normally difficult to develop. Based on this knowledge, the present inventors have conducted further extensive research and have conceived the following aspects of the invention.

[0018] (1) In mass%, C: 0.010% or less, Si: 1.50% to 4.00%, sol. Al: 0.3% to 0.7%, S: 0.010% or less, N: 0.010% or less, Ti: 0.0005% to 0.0020%, one or more selected from the group consisting of Mn, Ni, and Cu: 2.50% to 5.00% in total, Co: 0.000% to 1.000%, Sn: 0.000% to 0.400%, Sb: 0.000% to 0.400%, and P: 0.000% to 0.400%, wherein the Mn content (mass%) is [Mn], the Ni content (mass%) is [Ni], the Cu content (mass%) is [Cu], the Si content (mass%) is [Si], and the sol. Al content (mass%) is [sol. The steel sheet has a chemical composition in which the content of [Al] and the content of P (mass%) are [P], and the balance is Fe and impurities, and when the area ratio of crystal grains having {hkl}<uvw> orientation (within a tolerance of 10°) to the entire field of view measured by a scanning electron microscope with electron backscatter diffraction (SEM-EBSD) is expressed as Ahkl-uvw, A411-011 is 15% or more, and the number density of precipitates is 0.0001 particles / μm ２ ~0.3000 pieces / μm ２ (2×[Mn]+2.5×[Ni]+[Cu])-([Si]+2×[sol. Al]+4×[P])≧3.0% (1) 10.5≦([Si]+[Mn])÷[sol. Al]≦12.5 (2) A motor core comprising laminated non-oriented electrical steel sheets according to (1) above. (3) A motor having the motor core according to (2) above.

[0019] According to the present invention, it is possible to provide a non-oriented electrical steel sheet, a motor core, and a motor that achieve both low iron loss and high magnetic flux density without increasing the manufacturing load and eliminating the need to reduce the sheet thickness.

[0020] Hereinafter, embodiments of the present invention will be described in detail.

[0021] 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 explanation, "%," 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.

[0022] The non-oriented electrical steel sheet, cold-rolled steel sheet, and steel material according to this embodiment have a chemical composition in which ferrite-austenite transformation (hereinafter, α-γ transformation) can occur, and contain the following: C: 0.010% or less, Si: 1.50% to 4.00%, sol. Al: 0.3% to 0.7%, S: 0.010% or less, N: 0.010% or less, Ti: 0.0005% to 0.0020%, one or more elements selected from the group consisting of Mn, Ni, and Cu: 2.50% to 5.00% in total, Co: 0.000% to 1.000%, Sn: 0.000% to 0.400%, Sb: 0.000% to 0.400%, and P: 0.000% to 0.400%, with the balance being Fe and impurities. Furthermore, the contents of Mn, Ni, Cu, Si, sol. Al, and P satisfy the predetermined conditions described below. Examples of impurities include those contained in raw materials such as ore and scrap, and those contained in the manufacturing process.

[0023] (C: 0.010% or less) C precipitates fine carbides and inhibits grain growth, thereby increasing iron loss and causing magnetic aging. Therefore, the lower the C content, the better. This phenomenon becomes more pronounced when the C content exceeds 0.010%. For this reason, the C content is set to 0.010% or less. There is no particular lower limit for the C content, but it is preferably set to 0.0005% or more in consideration of the cost of decarburization treatment during refining.

[0024] (Si: 1.50% to 4.00%) Si increases electrical resistance, decreases eddy current loss, reduces iron loss, and increases the yield ratio, improving punching workability into iron cores. If the Si content is less than 1.50%, these effects cannot be fully obtained. Therefore, the Si content is set to 1.50% or more. On the other hand, if the Si content exceeds 4.00%, the magnetic flux density decreases, punching workability decreases due to an excessive increase in hardness, and cold rolling becomes difficult. Therefore, the Si content is set to 4.00% or less.

[0025] (Sol. Al: 0.3% to 0.7%) Sol. Al increases electrical resistance, 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. Here, magnetic flux density B50 is the magnetic flux density in a magnetic field of 5000 A / m. In addition, in order to reduce TiN, which is a fine precipitate that inhibits the grain growth of {411}<110> grains due to bulging, it is necessary to facilitate the precipitation of AlN, which is relatively coarse compared to TiN, thereby reducing the number density of precipitates. If the sol. Al content is less than 0.3%, these effects cannot be fully obtained. In addition, sol. Al also has the effect of promoting desulfurization in steelmaking. Therefore, the sol. Al content is set to 0.3% or more. On the other hand, If the Al content exceeds 1.0%, the magnetic flux density decreases, the yield ratio decreases, and punching workability decreases. Therefore, the sol. Al content is set to 0.7% or less. Preferably, the sol. Al content is 0.5% to 0.6%.

[0026] (S: 0.010% or less) S is not an essential element and is contained in steel, for example, as an impurity. S inhibits recrystallization and grain growth during annealing by precipitating fine MnS. Therefore, the lower the S content, the better. Such an increase in iron loss and a decrease in magnetic flux density due to the inhibition of recrystallization and grain growth are significant when the S content exceeds 0.010%. For this reason, the S content is set to 0.010% or less. Note that there is no particular lower limit for the S content, but it is preferably set to 0.0003% or more in consideration of the cost of desulfurization treatment during refining.

[0027] (N: 0.010% or less) N deteriorates magnetic properties through the formation of fine precipitates such as TiN, so the lower the N content, the better. Therefore, the N content is set to 0.010% or less. There is no particular lower limit for the N content, but in consideration of the cost of denitrification treatment during refining, the N content is preferably set to 0.001% or more.

[0028] (Ti: 0.0005% to 0.0020%) Ti is an element that is normally contained in molten steel at the steelmaking stage, and from the viewpoint of refining costs, the Ti content is set to 0.0005% or more. Furthermore, if the Ti content exceeds 0.0020%, a large amount of TiN, which is a fine precipitate, is formed, which deteriorates the magnetic properties. Therefore, the Ti content is set to 0.0020% or less. Preferably, the Ti content is 0.0010% to 0.0015%.

[0029] (One or more elements selected from the group consisting of Mn, Ni, and Cu: 2.50% to 5.00% in total) These elements are necessary for causing the α-γ transformation, and furthermore, as described below, they are elements that contribute to the formation of AlN, so it is necessary to contain at least one of these elements in a total amount of 2.50% or more. On the other hand, if the total amount exceeds 5.00%, the cost will increase and the magnetic flux density may decrease. Therefore, the total amount of at least one of these elements is set to 5.00% or less.

[0030] Furthermore, the following condition must be satisfied 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) must be satisfied in mass%: (2×[Mn]+2.5×[Ni]+[Cu])-([Si]+2×[sol. Al]+4×[P])≧3.0% (1) If the formula (1) is not satisfied, the α-γ transformation will not occur, or even if the α-γ transformation does occur, it will be impossible to perform rolling at a temperature in the γ region or the γ-α mixed region (Ar1 point or higher) in the rolling step described below, resulting in a low magnetic flux density.

[0031] Furthermore, it was found that adjusting the balance of components in specific components in order to reduce the number density of fine precipitates such as TiN makes it easier for AlN, which is relatively coarse compared to TiN, to be generated, thereby making it possible to reduce the number density of fine precipitates.

[0032] Increasing the Si concentration stabilizes the α phase during the slab heating process, thereby reducing MnS derived from S, which is easily dissolved in the α phase, and increasing AlN derived from N, which is easily dissolved in the γ phase. On the other hand, increasing the Si concentration reduces the amount of dissolved C in the steel during cold rolling, making TiC more likely to form. Furthermore, increasing the Mn concentration makes MnS more likely to form, while increasing the Al concentration makes AlN more likely to form. The inventors conducted various studies focusing on the balance of the formation of these precipitates and found a correlation between the Si content, Mn content, and Al content to reduce the number density of fine precipitates. Specifically, the relationship between the Si content, sol. Al content, and Mn content satisfies the following formula (2): 10.5≦([Si] + [Mn]) ÷ [sol. Al] ≦ 12.5 (2)

[0033] The upper and lower limits of formula (2) are set at 10.5 and 12.5, respectively. Outside these ranges, it becomes difficult to control the formation of AlN. In formula (2), if ([Si] + [Mn]) ÷ [sol. Al] is less than 10.5, AlN is formed in excess, inhibiting grain growth. On the other hand, if ([Si] + [Mn]) ÷ [sol. Al] exceeds 12.5, AlN is not formed in sufficient quantity, and precipitates such as TiC and MnS increase, making it impossible to reduce the number density of fine precipitates.

[0034] (Co: 0.000% to 1.000%) Co is an element effective in causing the α-γ transformation, so it may be contained as needed, but excessive Co content increases costs and may also reduce magnetic flux density. Therefore, the Co content is set to 1.000% or less.

[0035] (Sn: 0.000% to 0.400%, Sb: 0.000% to 0.400%) Sn and Sb improve the texture after cold rolling and recrystallization, and increase the magnetic flux density. Therefore, these elements may be contained as needed, but excessive content will embrittle the steel. Therefore, the Sn content and Sb content are both set to 0.400% or less. In order to impart further effects such as magnetic properties as described above, it is preferable to contain one or more elements selected from the group consisting of 0.020% to 0.400% Sn and 0.020% to 0.400% Sb.

[0036] (P: 0.000% to 0.400%) P may be added to ensure the hardness of the steel sheet after recrystallization, but excessive P content can lead to embrittlement of the steel. Therefore, the P content is set to 0.400% or less. To impart further effects such as magnetic properties, it is preferable to add 0.020% to 0.400% P.

[0037] Next, a method for measuring the area ratio of specific orientation grains in a non-oriented electrical steel sheet according to this embodiment will be described. The area ratio of specific orientation grains is measured by extracting the specific orientation of interest from a measurement area observed under the following measurement conditions using a scanning electron microscope (SEM) equipped with electron backscattering diffraction (EBSD) using OMI Analysis 7.3 (manufactured by TSL). The tolerance is set to 10°, hereinafter referred to as "within 10° tolerance"). The extracted area is divided by the area of ​​the measurement area to determine a percentage. This percentage is the area ratio of specific orientation grains. Hereinafter, the terms "area ratio of crystal grains having a crystal orientation of {hkl}<uvw> orientation (within 10° tolerance) relative to the measurement area" and "area ratio of crystal grains having a crystal orientation of {hkl} orientation (within 10° tolerance) relative to the measurement area" may also be simply referred to as "{hkl}<uvw> ratio" and "{hkl} ratio," respectively. Hereinafter, the crystal orientation will be described with a tolerance of 10° or less.

[0038] In the non-oriented electrical steel sheet according to this embodiment, the {411}<011> ratio is set to 15% or more when the steel sheet surface is measured by SEM-EBSD. If the {411}<011> ratio is less than 15%, excellent magnetic properties cannot be obtained. Therefore, the {411}<011> ratio is set to 15% or more, preferably 25% or more.

[0039] The details of the measurement conditions for determining the area ratio of each orientation grain 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 (cut surface of the steel sheet in the sheet thickness direction) in the center of the C direction of the steel sheet - Measurement area: area of ​​1000 μm or more in the L direction and 1000 μm or more in the C direction

[0040] Furthermore, when the steel sheet surface is measured by SEM-EBSD, it is preferable that the maximum strength is at φ1=0 to 10° within φ1=0 to 90° and φ=20°, and that the maximum strength is at φ=5 to 35° within φ1=0° and φ=0 to 90°. Having the maximum strength at φ1=0 to 10° within φ1=0 to 90° and φ=20° is synonymous with having the maximum strength near the {411}<011> orientation within the {411}<uvw> orientation. The {411}<011> orientation has superior 45° magnetic properties compared to {411}<148> and the like. It is more preferable that the maximum strength is at φ1=0 to 5° within φ1=0 to 90° and φ=20°.

[0041] On the other hand, when measuring the steel sheet surface with SEM-EBSD, having maximum strength at Φ=5 to 35° among Φ=0° and Φ=0 to 90° is synonymous with having maximum strength near the {411}<011> orientation among the {hkl}<011> orientations. 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 less. It is more preferable to have maximum strength at Φ=20 to 30° among Φ=0° and Φ=0 to 90°.

[0042] Here, we will explain how to determine the maximum strength within a specific orientation range in a steel sheet. In the area measured by SEM-EBSD, 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 angles φ1 and Φ) is taken to be the maximum strength.

[0043] Next, we will explain how to determine the ODF strength of a specific orientation in a steel sheet. In the measurement area using SEM-EBSD, an ODF is created using OMI Analysis 7.3 under the following conditions. Then, the created ODF data is output, and the ODF value of a specific orientation (orientation specified by angles φ1 and Φ) is taken as the ODF strength.

[0044] 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°

[0045] Furthermore, the area ratio of crystal grains having a specific orientation (within a tolerance of 10°) relative to the entire field of view measured by SEM-EBSD is expressed as follows: When the area ratio of crystal grains having a crystal orientation of {hkl}<uvw> orientation (within a tolerance of 10°) relative to the entire field of view is expressed as Ahkl-uvw, and the area ratio of crystal grains having a crystal orientation of {hkl} orientation (within a tolerance of 10°) relative to the entire field of view is expressed as Ahkl, it satisfies both the following formulas (3) and (4): A411-011 / A411-148 ≧ 1.1 (3) A411-011 / A100-011 ≧ 2 (4)

[0046] Furthermore, the 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, and more preferably, the {411} ratio is at least twice the {111} ratio.

[0047] Next, the number density of precipitates in the non-oriented electrical steel sheet according to this embodiment will be described. The precipitates are mainly fine precipitates such as TiN, but also include fine precipitates such as AlN and MnS. Since the chemical composition contains Ti and Al, the number density of these precipitates is substantially 0.0001 precipitates / μm. ２ On the other hand, the number of precipitates increases, and the number density of precipitates becomes 0.3000 particles / μm. ２ If the density is larger than 0.0001 particles / μm, the precipitates of TiN (or AlN) become excessive, resulting in deterioration of magnetic properties. ２ ~0.3000 pieces / μm ２ Let's say.

[0048] The number density of precipitates is measured, for example, by observing a sample using a transmission electron microscope (TEM) by the extraction replica method and calculating the number density. Specifically, the surface at a depth of 1 / 2 the sheet thickness t from the surface of the steel sheet is observed by the extraction replica method using a transmission electron microscope, and the number of fine precipitates with a circle-equivalent diameter of 20 to 500 nm in a 5 μm × 5 μm field of view is counted for the same sample. However, during observation, coarse precipitates (circle-equivalent diameter of 1 μm or more) that are not included in the calculation of the number density are not included in the field of view. Then, the number of precipitates is counted in 10 or more fields of view for the same sample, and the average value is calculated as the number density of the precipitates. Note that image analysis software may be used to count the number of precipitates.

[0049] 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 0.50 mm. Normally, as the thickness decreases, the iron loss decreases, but the magnetic flux density also decreases. Taking this into consideration, if the thickness is 0.25 mm or more, the iron loss becomes lower and the magnetic flux density becomes higher. Furthermore, if the thickness is 0.50 mm or less, low iron loss can be maintained. A more preferred lower limit of the thickness is 0.30 mm.

[0050] Furthermore, the non-oriented electrical steel sheet according to this embodiment preferably has excellent magnetic properties such as a magnetic flux density B50 in a direction at 45° to the rolling direction of 1.70 T or more and an iron loss W10 / 400 in a direction at 45° to the rolling direction of 14 W / kg or less. Furthermore, with regard to strength, the tensile strength is preferably 600 MPa or more.

[0051] The tensile strength is determined by taking a JIS No. 5 test piece with the rolling direction of the non-oriented electrical steel sheet as the longitudinal direction and conducting a tensile test in accordance with JIS Z2241:2011.

[0052] The above-mentioned non-oriented electrical steel sheet is characterized by the non-oriented electrical steel sheet manufactured by performing finish annealing. Hereinafter, the characteristics of the non-oriented electrical steel sheet before performing finish annealing (after performing skin-pass rolling) will be described.

[0053] The non-oriented electrical steel sheet according to this embodiment after skin-pass rolling (before finish annealing) has the following GOS (Grain Orientation Spread) value (Gs). 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 GOS value Gs is small after skin-pass rolling, i.e., in a low-strain state, grain growth due to bulging is likely to occur in the subsequent finish annealing process. Therefore, the upper limit of the GOS value Gs after skin-pass rolling is set to 3.0. On the other hand, if the GOS value Gs 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, the GOS value Gs after skin-pass rolling is set to 0.8 or more and 3.0 or less.

[0054] Here, we will explain how to calculate Gs in steel sheets. Using the SEM-EBSD data obtained when the crystal orientation was specified above, the number average value of the GOS value was determined by analysis using OIM Analysis 7.3, and this was taken as Gs.

[0055] 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 explained. In this embodiment, the α-fiber has the {hkl}<011> orientation. In the measurement area using SEM-EBSD, the {hkl}<011> orientation is extracted (within a tolerance of 10°) using OMI Analysis 7.3. The extracted area is divided by the area of ​​the measurement area to determine the percentage. This percentage is the α-fiber ratio.

[0056] In the non-oriented electrical steel sheet after skin pass rolling (before finish annealing), the α-fiber ratio is 20% or more, and preferably 25% or more.

[0057] 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 SEM-EBSD data when the above crystal orientations were specified. The {411}<011> orientation has excellent magnetic properties and is less susceptible to stress than the {100}<011> orientation, resulting in less magnetic degradation in crimped cores, etc. 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.

[0058] The non-oriented electrical steel sheet according to this embodiment can be widely applied to applications requiring magnetic properties (high magnetic flux density and low iron loss) by forming a core, but can also be applied to applications requiring particularly high strength, such as rotors. Specifically, the non-oriented electrical steel sheet according to this embodiment can be laminated to form a motor core, and can be widely applied to applications such as motors that include this motor core, but can also be applied to the rotor that constitutes the motor.

[0059] 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 soft reduction cold rolling (hereinafter referred to as skin pass rolling), and finish annealing are performed.

[0060] 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.

[0061] The steel material is, for example, a slab produced by normal continuous casting, and steel material having the above-mentioned 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.

[0062] In the heating step, in order to prevent Ti from forming a solid solution and precipitating as TiN, it is preferable to heat the steel material having the above-mentioned chemical composition to 1000 to 1080°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 heating temperature in the heating furnace or soaking furnace is not particularly limited, but is, for example, 30 to 200 hours. Furthermore, when heating the slab, in order to prevent Ti from forming a solid solution, the temperature rise rate from 600°C to the heating temperature is set to 0.02°C / second or less.

[0063] 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.

[0064] The rolling in the rolling process (rough rolling and finish rolling) is performed at a temperature in the γ region or the γ-α mixed 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.

[0065] 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.

[0066] Subsequently, cooling after the rolling process transforms austenite to ferrite, resulting in high strain and moderately fine crystal grains. The cooling conditions are such that cooling begins 0.1 seconds or more after the final pass of finish rolling, and immediate rapid cooling is avoided so that the surface temperature of the hot-rolled sheet is 300°C or higher and Ar1 point or lower after 3 seconds. Avoiding immediate rapid cooling in this way eliminates the need for a special rapid cooling device, which is also advantageous in terms of production (cost). When cold rolling is then performed in a suitable crystal grain size that is not excessively refined, α-fibers develop after intermediate annealing, and the {411}<011> orientation, which is usually difficult to develop, can be developed after the subsequent skin pass and finish annealing.

[0067] Furthermore, it is presumed that the texture of a hot-rolled sheet is a structure in which non-recrystallized austenite is transformed when the sheet is immediately quenched, and a structure in which partially recrystallized austenite is transformed when the immediately quenching is omitted. When the sheet is immediately quenched after finish rolling, the austenite concentrates in the {100}<011> orientation in the structure after the subsequent finish annealing, whereas when the immediately quenching is omitted after finish rolling, the austenite concentrates in the {411}<011> orientation in the structure after the subsequent finish annealing. Therefore, it is considered important to transform the partially recrystallized austenite to strengthen the {411}<011> orientation.

[0068] 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, the temperature must be brought to the Ar1 point or below within 3 seconds after passing the final pass of finish rolling. The grain size can be measured, for example, by the intercept method.

[0069] 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 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.

[0070] The temperature of the hot-rolled sheet is measured by a thermometer installed in the hot rolling equipment line, and the temperature is measured 3 seconds after the final pass of the finish rolling.

[0071] The hot-rolled sheet is then coiled without being annealed, and the hot-rolled sheet is then cold-rolled. Note that the hot-rolled sheet annealing referred to here means, for example, heat treatment in which the temperature rises to the Ac1 point or lower and is 300°C or higher.

[0072] 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.

[0073] In cold rolling, cold rolling is performed without performing 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 at each rolling stand).

[0074] 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

[0075] 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 less. If the intermediate annealing temperature exceeds the Ac1 point, part of the structure of the steel sheet will be transformed into austenite, and the strain in the steel sheet will be excessively reduced. 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. Therefore, it is preferable to set the intermediate annealing temperature T1 (°C) to 600°C or higher.

[0076] 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.

[0077] 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.

[0078] 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.

[0079] 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 SEM-EBSD. In order to achieve an α-fiber ratio (within a 10° tolerance) of 15% or more before skin-pass rolling, it is necessary to use an α-γ transformation system composition (high concentrations of γ-former elements such as Mn, Ni, and Cu, hereinafter referred to as "high Mn") and to maintain the above-mentioned conditions from hot rolling to intermediate annealing. The cooling conditions after finish rolling are particularly important. Alpha fibers, which are prone to forming {411}<011> orientation, are developed by transforming partially recrystallized austenite into ferrite, cold-rolling a hot-rolled sheet with an average grain size of 3 to 10 μm after hot rolling, and then intermediate annealing. As mentioned above, rapid cooling immediately after hot-rolling results in a structure transformed from unrecrystallized austenite, rather than a structure transformed from partially recrystallized austenite. The cold-rolled steel sheet produced in this manner is subjected to skin-pass rolling under the conditions described below, and then to finish annealing, to obtain the non-oriented electrical steel sheet of the present invention.

[0080] After the intermediate annealing is completed, skin pass rolling is then performed. Specifically, the cold rolled steel sheet after the intermediate annealing step is rolled (cold rolling) 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.

[0081] 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).

[0082] 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 {111} grains is suppressed in the steel sheet surface, and {411}<011> crystal orientation grains 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.

[0083] 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

[0084] 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%.

[0085] The number of passes in the skin pass rolling may be only one pass (i.e., only one rolling), or may be multiple passes.

[0086] As described above, the GOS value and α-fiber ratio can be obtained by recrystallizing a steel sheet having an α-γ transformation system composition (high Mn, etc.) through intermediate annealing and then skin-pass rolling under the above-described conditions.

[0087] After skin-pass rolling, finish annealing is performed at 750°C or higher and Ac1 point or lower for 2 hours or more. If the finish annealing temperature T2 (°C) is set to less than 750°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 the Ac1 point, 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 2 hours, even if the finish annealing temperature T2 is 750°C or higher and Ac1 point or lower, grain growth due to bulging does not occur sufficiently, and the concentration of the {411}<011> orientation decreases. Note that the upper limit of the annealing time for finish annealing is not particularly limited, but the effect saturates even if the annealing time exceeds 10 hours, so the preferred upper limit is 10 hours.

[0088] Here, the finish annealing temperature T2 is the sheet temperature (temperature of the steel sheet surface) near 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.

[0089] 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.

[0090] 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.

[0091] 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.

[0092] The holding time Δt2 at the finish annealing temperature T2 in the finish annealing step is 2 hours or more. If the holding time Δt2 is 2 hours or more, 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 lower limit of the holding time Δt2 is 2 hours, preferably 3 hours. As mentioned above, the preferred upper limit of the holding time Δt2 is 10 hours, more preferably 5 hours.

[0093] 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.

[0094] It is also possible to ship the skin-pass rolled non-oriented electrical steel sheet without performing finish annealing. For example, the processes up to skin-pass rolling may be performed by a steel sheet manufacturing company, and the non-oriented electrical steel sheet may be punched or laminated at a core manufacturing company to which the steel sheet is shipped, and then stress relief annealing may be performed instead of finish annealing at an annealing temperature of 750°C or higher and Ac1 point or lower for an annealing time of 2 hours or longer.

[0095] As described above, the non-oriented electrical steel sheet according to this embodiment can be manufactured.

[0096] The method for manufacturing the non-oriented electrical steel sheet according to this embodiment is not limited to the manufacturing steps described above.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] The coating is an optional step, and therefore, it is not necessary to perform the coating after the final annealing.

[0101] The non-oriented electrical steel sheet according to this embodiment is not limited to the above-mentioned manufacturing method. It is also possible to manufacture a non-oriented electrical steel sheet having the above-mentioned composition range, and further, when the steel sheet surface is measured by electron backscatter diffraction (EBSD), the area ratio of crystal grains having the {411}<011> orientation (within a tolerance of 10°) to the entire field of view is 15% or more, and the number density of precipitates is 0.0001 particles / μm ２ ~0.3000 pieces / μm ２ If so, the manufacturing method is not limited to the above.

[0102] 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.

[0103] (First Example) Molten steel was cast to produce ingots having the chemical compositions shown in Table 1 below. Here, "Formula (1)" in Table 1 represents the value of the left side of the aforementioned formula (1), and "Formula (2)" in Table 1 represents the value of ([Si] + [Mn]) ÷ [sol. Al] in the aforementioned formula (2). The produced ingots were then heated to a slab heating temperature ST shown in Table 2 and hot rolled, and then finish rolled at a finish rolling temperature FT shown in Table 2. The heating rate from 600°C to the slab heating temperature ST is also shown in Table 2. Then, 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).

[0104] Next, the hot-rolled steel sheets were not subjected to hot-rolled sheet annealing, but scale was removed by pickling, and cold rolling was performed at a rolling reduction RR1 shown in Table 2. Then, intermediate annealing was performed in an atmosphere of 20% hydrogen and 80% nitrogen, and intermediate annealing temperature T1 was controlled to the temperature shown in Table 2, and intermediate annealing was performed for 30 seconds.

[0105] Next, all steel sheets except for No. 9 and No. 10 were subjected to skin-pass rolling at a rolling reduction RR2 shown in Table 2. Then, all steel sheets except for No. 9 were subjected to finish annealing 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. Before the finish annealing, the GOS value Gs was calculated under the measurement conditions described above.

[0106] Furthermore, to investigate the texture after finish annealing, a portion of the steel sheet was excised and the excised test piece was reduced in thickness to half. The {411}<011> ratio was determined by observing the measurement area using SEM-EBSD under the measurement conditions described above. The number density of precipitates was determined by observing precipitates with an equivalent circle diameter of 20 to 500 nm using a transmission electron microscope at an acceleration voltage of 200 kV and the extraction replica method under the measurement conditions described above. The results are shown in Table 3.

[0107] In addition, to investigate the magnetic properties and tensile strength after final annealing, the magnetic flux density B50 and iron loss W10 / 400 were measured, and the iron loss deterioration rate of the iron loss W10 / 50 under compressive stress was calculated as an index of stress sensitivity. For the magnetic flux density B50, 55 mm square samples were taken in two directions, 0° and 45°, from the rolling direction. These two types of samples were measured, and the value in the 45° direction relative to the rolling direction was taken as the magnetic flux density B50 in the 45° direction, and the average value at 0°, 45°, 90°, and 135° relative to the rolling direction was taken as the overall average of the magnetic flux density B50. For the iron loss W10 / 400, the above measurement samples taken in the 45° direction relative to the rolling direction were used to calculate the average value in the 45° 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 Wx was calculated using the following formula. The measurement results are shown in Table 3. W ｘ = {W10 / 50(10)-W10 / 50(0)} / W10 / 50(0)

[0108]

[0109]

[0110]

[0111] The underlined values ​​in Tables 1 and 3 indicate conditions outside the scope of the present invention. Inventive examples No. 1, No. 4, No. 7, and No. 13 all had good values ​​for magnetic flux density B50, iron loss W10 / 400, iron loss deterioration rate, and tensile strength.

[0112] On the other hand, Comparative Example No. 2 had a sol. Al deficiency exceeding the upper limit of formula (2), resulting in a lack of AlN as fine precipitates. Furthermore, the high heating rate during slab heating resulted in Ti solid solution, resulting in the precipitation of a large amount of finer TiN. Furthermore, rapid cooling after finish rolling resulted in a small {411}<110> fraction, and poor iron loss W10 / 400 and iron loss degradation rate. Comparative Example No. 3 had a deficiency in the total amount of one or more elements selected from the group consisting of Mn, Ni, and Cu, and had a composition that did not cause α-γ transformation. This resulted in a small {411}<011> fraction, and poor magnetic flux density B50 (45° direction), iron loss W10 / 400, and iron loss degradation rate. Comparative Example No. 5 exceeded the upper limit of formula (2), resulting in insufficient AlN formation, resulting in the precipitation of a large amount of fine TiN. As a result, the number density of precipitates increased, and the iron loss W10 / 400 and iron loss deterioration rate were poor. In Comparative Example No. 6, the value was below the lower limit of formula (2), so excessive AlN was generated, which increased the number density of precipitates. As a result, the iron loss W10 / 400 and iron loss deterioration rate were poor.

[0113] Comparative Example No. 8 exceeded the upper limit of formula (2) and contained excessive Ti. Furthermore, the heating rate during slab heating was high, resulting in the formation of a large amount of TiN, resulting in a high number density, and furthermore, due to a lack of Si, the iron loss W10 / 400 was poor. Comparative Example No. 9 contained an excessive total amount of one or more elements selected from the group consisting of Mn, Ni, and Cu, which led to segregation and the resulting lamination during cold rolling, after which production was discontinued. Comparative Example No. 10 did not undergo skin-pass rolling, resulting in a small {411}<011> ratio, and therefore poor magnetic flux density B50 (45° direction), iron loss W10 / 400, and iron loss degradation rate. Comparative Example No. In the case of No. 11, the rolling reduction rate RR2 in the 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 the case of No. 12, which is a comparative example, the slab heating temperature ST was too high, resulting in the precipitation of a large amount of fine TiN, which increased the number density. As a result, the iron loss W10 / 400 was poor.

[0114] According to the present invention, it is possible to provide a non-oriented electrical steel sheet, a motor core, and a motor that achieve both low iron loss and high magnetic flux density without increasing the manufacturing load and eliminating the need to reduce the sheet thickness, and thus has great industrial value.

Claims

1. C: 0.010% or less, Si: 1.50% to 4.00%, sol. Al: 0.3% to 0.7%, S: 0.010% or less, N: 0.010% or less, Ti: 0.0005% to 0.0020%, one or more selected from the group consisting of Mn, Ni, and Cu: 2.50% to 5.00% in total, Co: 0.000% to 1.000%, Sn: 0.000% to 0.400%, Sb: 0.000% to 0.400%, and P: 0.000% to 0.400%, where the Mn content (mass%) is [Mn], the Ni content (mass%) is [Ni], the Cu content (mass%) is [Cu], the Si content (mass%) is [Si], and the sol. The steel sheet has a chemical composition in which the balance consists of Fe and impurities, and the area ratio of crystal grains having {hkl}<uvw> orientation (within a tolerance of 10°) to the entire field of view when the steel sheet surface is measured with a scanning electron microscope with electron backscatter diffraction (SEM-EBSD) is expressed as Ahkl-uvw, A411-011 is 15% or more, and the number density of precipitates is 0.0001 particles / μm ２ ~0.3000 pieces / μm ２ (2×[Mn]+2.5×[Ni]+[Cu])−([Si]+2×[sol.Al]+4×[P])≧3.0% (1) 10.5≦([Si]+[Mn])÷[sol.Al]≦12.5 (2) 2. A motor core comprising the non-oriented electrical steel sheets according to claim 1 laminated together.

3. A motor comprising the motor core according to claim 2.