Non-oriented electrical steel sheet, motor core, and motor

Abstract

Provided is a non-oriented electrical steel sheet, wherein: the chemical composition of a base material contains, in mass%, 0.0050% or less of C, more than 3.50% but not more than 4.50% of Si, less than 0.60% of Mn, 0.30-0.90% of Al, 0.030% or less of P, 0.0020% or less of S, 0.0040% or less of N, less than 0.0040% of Ti, less than 0.0040% of Nb, less than 0.0040% of Zr, less than 0.0040% of V, less than 0.200% of Cu, less than 0.500% of Ni, 0.010-0.060% of the total of one or two of Sn and Sb, with the remainder comprising Fe and impurities; the chemical composition of the base material satisfies [4.2≤Si+Al+0.5×Mn≤4.9]; the average crystal grain size of the base material is more than 40 μm but not more than 140 μm; the texture of the base material satisfies [{100}+{411}] / [{111}+{211}]≥0.35; and the plate thickness is 0.10-0.30 mm.

Description

Non-oriented electrical steel sheets, motor cores and motors

[0001] The present invention relates to a non-oriented electrical steel sheet, a motor core, and a motor.

[0002] In recent years, global environmental issues have been attracting attention, and the demand for energy conservation efforts has been increasing. In particular, there is a strong demand for higher efficiency in electrical equipment. Therefore, there is an increasing demand for improved magnetic properties in non-oriented electrical steel sheets, which are widely used as iron core materials for motors, generators, and the like. This trend is particularly evident in drive motors for electric and hybrid vehicles and air conditioner compressor motors. Furthermore, there is a growing demand for drive motors and compressor motors with higher output, which is effective in miniaturizing the equipment.

[0003] To achieve high motor efficiency, it is important to reduce iron loss and copper loss, which are the main causes of loss. Reducing iron loss in the electromagnetic steel sheets used in motor cores is effective for reducing iron loss, while increasing the magnetic flux density of the electromagnetic steel sheets is effective for reducing copper loss. On the other hand, to achieve high motor output, it is important to increase torque and speed. Increasing the magnetic flux density of electromagnetic steel sheets is effective for increasing torque, while increasing the strength of electromagnetic steel sheets is effective for increasing speed. Therefore, to achieve high motor efficiency and high output, electromagnetic steel sheets with low iron loss, high magnetic flux density, and high strength are required.

[0004] The motor cores of the various motors described above are composed of a stator, which is the fixed part, and a rotor, which is the rotating part. The characteristics required for the stator and rotor that make up the motor core are not the same. While the stator is required to have excellent magnetic properties (low iron loss and high magnetic flux density), the rotor is required to have low iron loss and excellent mechanical properties (high strength).

[0005] Because the required characteristics of the stator and rotor are different, the desired characteristics can be achieved by producing different non-oriented electrical steel sheets for the stator and the rotor. However, preparing two types of non-oriented electrical steel sheets complicates the core manufacturing process and reduces yield. Therefore, in order to achieve the low iron loss and high strength required for the rotor while also achieving the low iron loss and high magnetic flux density required for the stator, non-oriented electrical steel sheets with excellent magnetic properties and strength have been studied.

[0006] For example, Patent Documents 1 to 4 attempt to achieve excellent magnetic properties and high strength.

[0007] International Publication No. 2019 / 017426 International Publication No. 2020 / 091039 International Publication No. 2020 / 091043 Japanese Patent Application Laid-Open No. 2010-90474

[0008] However, in order to realize a non-oriented electrical steel sheet that combines low iron loss and high strength, it is necessary to contain a large amount of alloying elements, as disclosed in Patent Documents 1 to 4, which has the problem of reducing toughness and making the sheet more susceptible to fracture during cold rolling.

[0009] The present invention has been made to solve these problems, and has an object to stably provide a non-oriented electrical steel sheet having excellent magnetic properties and high strength.

[0010] The present invention relates to the following non-oriented electrical steel sheet, motor core, and motor.

[0011] (1) The chemical composition of the base material is, in mass%, C: 0.0050% or less, Si: more than 3.50% and less than 4.50%, Mn: less than 0.60%, Al: 0.30 to 0.90%, P: 0.030% or less, S: 0.0020% or less, N: 0.0040% or less, Ti: less than 0.0040%, Nb: less than 0.0040%, Zr: less than 0.0040%, V: less than 0.0040%, Cu: less than 0.200%, Ni: less than 0.500%, Sn and Sb in total: 0.010 to 0.060%, and the balance: Fe and impurities, and the following formula (i) is satisfied: The average crystal grain size of the base material is more than 40 μm and less than 140 μm, A non-oriented electrical steel sheet having a thickness of 0.10 to 0.30 mm, wherein the texture of the base material satisfies the following formula (ii): 4.2≦Si+Al+0.5×Mn≦4.9 (i), where the element symbols in the formula indicate the content (mass%) of each element: [{100}+{411}] / [{111}+{211}]≧0.35 (ii), where {100}, {411}, {111}, and {211} in the formula are the X-ray integrated intensity ratios of the {100} orientation, {411} orientation, {111} orientation, and {211} orientation in an inverse pole figure at a position 1 / 4 of the sheet thickness from the surface of the base material, respectively.

[0012] (2) The non-oriented electrical steel sheet according to (1) above, having a 0.2% yield strength of 450 MPa or more.

[0013] (3) The non-oriented electrical steel sheet according to (1) or (2) above, wherein an insulating coating is provided on the surface of the base material.

[0014] (4) A motor core in which the non-oriented electrical steel sheets according to any one of (1) to (3) above are laminated.

[0015] (5) A motor including the motor core described in (4) above.

[0016] According to the present invention, a non-oriented electrical steel sheet having excellent magnetic properties and high strength can be obtained.

[0017] As a result of extensive research conducted by the present inventors to solve the above problems, the present inventors have come to the following findings.

[0018] In order to obtain a non-oriented electrical steel sheet that has low iron loss, high magnetic flux density, and high strength while ensuring toughness during cold rolling, it is necessary to optimize the contents of the main alloying elements Si, Mn, and Al.

[0019] Specifically, the Si content is set to more than 3.50% and not more than 4.50%, which has the highest solid solution strengthening ability and contributes most to increasing electrical resistance. Additionally, to obtain good grain growth properties, the Al content is set to 0.30% or more. On the other hand, to suppress deterioration of toughness, the Al content is set to 0.90% or less.

[0020] Furthermore, Mn has the lowest solid solution strengthening ability of the three elements, but it contributes to increasing electrical resistance with little deterioration in toughness. However, as a result of extensive research by the inventors, it was found that if Mn, which has a lower solid solution strengthening ability than Si and Al, is contained in excess, the magnetic flux density decreases significantly compared to the increase in strength. Therefore, the Mn content is set to less than 0.60%.

[0021] In the manufacturing process of non-oriented electrical steel sheets, hot-rolled sheet annealing is generally performed before cold rolling. In order to suppress problems such as sheet breakage and edge cracking during cold rolling, it is desirable to lower the soaking temperature in hot-rolled sheet annealing. However, it is known that the higher the soaking temperature in hot-rolled sheet annealing, the higher the magnetic flux density, and lowering the soaking temperature results in a decrease in magnetic flux density.

[0022] Therefore, the present inventors investigated a method for improving magnetic flux density while lowering the soaking temperature during annealing of a hot-rolled sheet. As a result, they found that by using a continuous annealing furnace for annealing the hot-rolled sheet, setting the soaking temperature to 800 to 880°C and the soaking time to 70 to 300 seconds, it is possible to suppress the development of the {111} and {211} orientations, which are detrimental to magnetic properties, and promote the development of the {100} and {411} orientations, which are advantageous to magnetic properties.

[0023] The present invention was made based on the above findings. Each of the features of the present invention will be described in detail below.

[0024] 1. Overall Configuration The non-oriented electrical steel sheet according to one embodiment of the present invention has excellent magnetic properties and high strength, making it suitable for both stators and rotors. Furthermore, the non-oriented electrical steel sheet according to this embodiment preferably has an insulating coating on the surface of the base material, as described below.

[0025] 2. Chemical composition of the base material The reasons for limiting the content of each element are as follows: In the following description, "%" for the content means "% by mass."

[0026] C: 0.0050% or less C (carbon) is an element that causes iron loss degradation in non-oriented electrical steel sheets. If the C content exceeds 0.0050%, the iron loss of the non-oriented electrical steel sheet deteriorates, making it impossible to obtain good magnetic properties. Therefore, the C content is set to 0.0050% or less. The C content is preferably 0.0040% or less, and more preferably 0.0035% or less. There is no need to set a lower limit for the C content; it may be 0%. However, since C contributes to increasing the strength of non-oriented electrical steel sheets, if this effect is desired, the C content is preferably more than 0%, more preferably 0.0005% or more, and even more preferably 0.0010% or more.

[0027] Si: More than 3.50% and Not More than 4.50% Si (silicon) is an element that increases the electrical resistance of steel, reduces eddy current loss, and improves the iron loss of non-oriented electrical steel sheets. Si also has a high solid-solution strengthening ability, making it an effective element for increasing the strength of non-oriented electrical steel sheets. To achieve these effects, the Si content is set to more than 3.50%. The Si content is preferably 3.60% or more, more preferably 3.70% or more, and even more preferably 3.80% or more. On the other hand, excessive Si content significantly deteriorates workability, making cold rolling difficult. Therefore, the Si content is set to 4.50% or less. The Si content is preferably 4.40% or less, more preferably 4.30% or less.

[0028] Mn: Less than 0.60% Mn (manganese) is an element that increases the electrical resistance of steel, reduces eddy current loss, and is effective in improving the iron loss of non-oriented electrical steel sheets. However, since Mn has a poorer solid solution strengthening ability than Si and Al, a large amount of Mn is required to achieve high strength, which significantly reduces magnetic flux density. Therefore, the Mn content is set to less than 0.60%. The Mn content is preferably 0.55% or less, more preferably 0.50% or less. There is no need to set a lower limit for the Mn content; it may be 0%. However, to achieve the above effects, the Mn content is preferably more than 0%, more preferably 0.10% or more, and even more preferably 0.20% or more.

[0029] Al: 0.30 to 0.90% Al (aluminum) is an element that increases the electrical resistance of steel, thereby reducing eddy current loss and improving iron loss in non-oriented electrical steel sheets. Furthermore, Al contributes to increasing the strength of non-oriented electrical steel sheets through solid-solution strengthening, although to a lesser extent than Si. Furthermore, adding an appropriate amount of Al suppresses the refinement of AlN, which forms when combined with N in the steel, and improves grain growth during finish annealing. To achieve these effects, the Al content is set to 0.30% or more. The Al content is preferably 0.40% or more, and more preferably 0.50% or more. On the other hand, excessive Al content can deteriorate toughness and lead to fracture during cold rolling. Furthermore, Al easily forms internal oxides that deteriorate pickling properties during production. In particular, Al-containing oxides are hard, which can cause uneven roll wear during cold rolling, destabilizing the cold rolling and further increasing the likelihood of fracture. Therefore, the Al content is set to 0.90% or less. The Al content is preferably 0.80% or less, and more preferably 0.70% or less.

[0030] In this embodiment, the electrical resistance of the steel is ensured by appropriately controlling the contents of Si, Al, and Mn. Furthermore, from the viewpoint of ensuring strength, it is also necessary to appropriately control the contents of Si, Al, and Mn. On the other hand, from the viewpoint of ensuring magnetic flux density and toughness, upper limits are also necessary. Therefore, in addition to the contents of Si, Al, and Mn being within the respective ranges, the following formula (i) must also be satisfied. When prioritizing strength, the value of the middle part of the following formula (i) is preferably 4.3 or more, more preferably 4.4 or more, and even more preferably 4.5 or more. On the other hand, when prioritizing magnetic flux density and toughness, it is preferably 4.8 or less, more preferably 4.7 or less, and even more preferably 4.5 or less.

[0031] 4.2≦Si+Al+0.5×Mn≦4.9 (i) where the element symbols in the above formula indicate the content (mass %) of each element.

[0032] P: 0.030% or less P (phosphorus) is contained in steel as an impurity, and if its content is excessive, the toughness of the non-oriented electrical steel sheet is significantly reduced. Therefore, the P content is set to 0.030% or less. The P content is preferably 0.025% or less, and more preferably 0.020% or less. There is no need to set a lower limit for the P content; it may be 0%. However, since an extreme reduction in the P content may increase manufacturing costs, the P content is preferably more than 0%, more preferably 0.001% or more, more preferably 0.003% or more, and even more preferably 0.005% or more.

[0033] S: 0.0020% or less S (sulfur) is an element that increases iron loss by forming fine precipitates of MnS, thereby degrading the magnetic properties of non-oriented electrical steel sheets. Therefore, the S content is set to 0.0020% or less. The S content is preferably 0.0018% or less, and more preferably 0.0016% or less. There is no need to set a lower limit for the S content; it may be 0%. However, since an extreme reduction in the S content may increase manufacturing costs, the S content is preferably more than 0%, more preferably 0.0001% or more, even more preferably 0.0003% or more, and even more preferably 0.0005% or more.

[0034] N: 0.0040% or less N (nitrogen) is an element that is inevitably mixed into steel and forms nitrides, increasing iron loss and degrading the magnetic properties of non-oriented electrical steel sheets. Therefore, the N content is set to 0.0040% or less. The N content is preferably 0.0030% or less, and more preferably 0.0020% or less. There is no need to set a lower limit for the N content; it may be 0%. However, since an extreme reduction in the N content may increase manufacturing costs, the N content is preferably more than 0%, more preferably 0.0001% or more, even more preferably 0.0003% or more, and even more preferably 0.0005% or more.

[0035] Ti: Less than 0.0040% Ti (titanium) is an element that is inevitably mixed into steel and can combine with carbon or nitrogen to form precipitates (carbides and nitrides). When carbides or nitrides are formed, these precipitates themselves degrade the magnetic properties of non-oriented electrical steel sheets. Furthermore, they inhibit grain growth during finish annealing, degrading the magnetic properties of non-oriented electrical steel sheets. Therefore, the Ti content is set to less than 0.0040%. The Ti content is preferably 0.0030% or less, more preferably 0.0025% or less. There is no need to set a lower limit for the Ti content; it may be 0%. However, since an extreme reduction in the Ti content may increase manufacturing costs, the Ti content is preferably more than 0%, more preferably 0.0001% or more, even more preferably 0.0003% or more, and even more preferably 0.0005% or more.

[0036] Nb: Less than 0.0040% Nb (niobium) is an element that contributes to high strength by combining with carbon or nitrogen to form precipitates (carbides, nitrides), but these precipitates themselves degrade the magnetic properties of non-oriented electrical steel sheets. Therefore, the Nb content is less than 0.0040%. The Nb content is preferably 0.0030% or less, more preferably 0.0025% or less, and even more preferably 0.0020% or less. There is no need to set a lower limit for the Nb content; it may be 0%. However, since an extreme reduction in the Nb content may increase manufacturing costs, the Nb content is preferably more than 0%, more preferably 0.0001% or more, even more preferably 0.0003% or more, and even more preferably 0.0005% or more.

[0037] Zr: Less than 0.0040% Zr (zirconium) is an element that contributes to high strength by combining with carbon or nitrogen to form precipitates (carbides and nitrides), but these precipitates themselves degrade the magnetic properties of non-oriented electrical steel sheets. Therefore, the Zr content is set to less than 0.0040%. The Zr content is preferably 0.0030% or less, more preferably 0.0025% or less, and even more preferably 0.0020% or less. There is no need to set a lower limit for the Zr content; it may be 0%. However, since an extreme reduction in the Zr content may increase manufacturing costs, the Zr content is preferably more than 0%, more preferably 0.0001% or more, even more preferably 0.0003% or more, and even more preferably 0.0005% or more.

[0038] V: Less than 0.0040% V (vanadium) is an element that contributes to high strength by combining with carbon or nitrogen to form precipitates (carbides and nitrides), but these precipitates themselves degrade the magnetic properties of non-oriented electrical steel sheets. Therefore, the V content is set to less than 0.0040%. The V content is preferably 0.0030% or less, more preferably 0.0025% or less, and even more preferably 0.0020% or less. There is no need to set a lower limit for the V content; it may be 0%. However, since an extreme reduction in the V content may increase manufacturing costs, the V content is preferably more than 0%, more preferably 0.0001% or more, even more preferably 0.0003% or more, and even more preferably 0.0005% or more.

[0039] Cu: Less than 0.200% Cu (copper) is an element that is inevitably mixed into steel. Intentional inclusion of Cu increases the manufacturing cost of non-oriented electrical steel sheets. Therefore, in this embodiment, Cu does not need to be actively added; it is sufficient to add Cu at an impurity level. The Cu content is less than 0.200%, which is the maximum value that can be unavoidably mixed in during the manufacturing process. The Cu content is preferably 0.150% or less, more preferably 0.100% or less. The lower limit of the Cu content is not particularly limited and may be 0%. However, excessive reduction of the Cu content may increase manufacturing costs. Therefore, the Cu content is preferably more than 0%, more preferably 0.001% or more, even more preferably 0.003% or more, and even more preferably 0.005% or more.

[0040] Ni: Less than 0.500% Ni (nickel) is an element that is inevitably mixed into steel. However, since Ni also improves the strength of non-oriented electrical steel sheets, it may be intentionally added. However, because Ni is expensive, the Ni content is set to less than 0.500%. The Ni content is preferably 0.400% or less, more preferably 0.300% or less. The lower limit of the Ni content is not particularly limited and may be 0%. However, an extreme reduction in the Ni content may result in an increase in manufacturing costs. Therefore, the Ni content is preferably more than 0%, more preferably 0.001% or more, even more preferably 0.003% or more, and even more preferably 0.005% or more. Furthermore, when Ni is intentionally added, the Ni content is preferably 0.200% or more.

[0041] Sum of one or both of Sn and Sb: 0.010 to 0.060% Sn (tin) and Sb (antimony) have the effect of improving the texture and increasing the magnetic flux density of non-oriented electrical steel sheets. They are also useful elements for ensuring low iron loss in non-oriented electrical steel sheets by segregating to the surface of the base material and suppressing oxidation and nitriding during annealing. To achieve these effects, the total content of one or both of Sn and Sb is set to 0.010% or more. This total content is preferably 0.015% or more, and more preferably 0.020% or more. On the other hand, if the total content of Sn and Sb is excessive, the toughness of the steel decreases, making cold rolling difficult. Therefore, the total content of one or both of Sn and Sb is set to 0.060% or less. This total content is preferably 0.050% or less, and more preferably 0.040% or less.

[0042] The chemical composition of the base material of the non-oriented electrical steel sheet of the present invention is made up of the balance Fe and impurities, where "impurities" refer to components that are mixed in during industrial steel production due to various factors in raw materials such as ores and scraps, and in the manufacturing process, and are acceptable within a range that does not adversely affect the present invention.

[0043] The contents of Cr and Mo as impurity elements are not particularly specified. In the non-oriented electrical steel sheet according to this embodiment, even if these elements are contained in a range of 0.5% or less, there is no particular effect on the properties of the non-oriented electrical steel sheet according to this embodiment. Furthermore, even if Ca and Mg are contained in a range of 0.002% or less, there is no particular effect on the properties of the non-oriented electrical steel sheet according to this embodiment. Even if rare earth elements (REM) are contained in a range of 0.004% or less, there is no particular effect on the properties of the non-oriented electrical steel sheet according to this embodiment. In this embodiment, REM refers to a total of 17 elements consisting of Sc, Y, and lanthanoids, and the REM content refers to the total content of these elements.

[0044] Although O is also an impurity element, even if it is contained in a range of 0.035% or less, it does not affect the properties of the non-oriented electrical steel sheet according to this embodiment. Because O may be mixed into steel during the annealing process, even if it is contained in a range of 0.010% or less in the slab stage (i.e., ladle value), it does not particularly affect the properties of the non-oriented electrical steel sheet according to this embodiment.

[0045] In addition to the above elements, elements such as Zn, Pb, Bi, As, B, and Se may be contained as impurity elements. However, as long as the content of each of these elements is in the range of 0.0050% or less, the properties of the non-oriented electrical steel sheet according to this embodiment are not impaired.

[0046] The chemical composition of the base material of the non-oriented electrical steel sheet according to this embodiment can be measured by combining various known measurement methods. In the present invention, the chemical composition is measured using inductively coupled plasma (ICP) atomic emission spectroscopy (ICP-AES) and inductively coupled plasma (ICP) mass spectrometry (ICP-MS) depending on the element content. Furthermore, C and S are measured using the combustion-infrared absorption method, N is measured using the inert gas combustion-thermal conductivity method, and O is measured using the inert gas fusion-non-dispersive infrared absorption method.

[0047] 3. Grain size In this embodiment, the average grain size of the base material is set to be more than 40 μm and not more than 140 μm. By setting the average grain size of the base material to be more than 40 μm, it is possible to suppress deterioration of hysteresis loss and improve magnetic properties. On the other hand, by setting the average grain size to be not more than 140 μm, it is possible to obtain the effect of improving the strength of the steel and suppress deterioration of iron loss due to increased eddy current loss. The average grain size is preferably not less than 50 μm, and more preferably not less than 60 μm. Furthermore, the average grain size is preferably not more than 130 μm, and more preferably not more than 120 μm.

[0048] In the present invention, the average grain size of the base material is determined in accordance with JIS G 0551:2013 "Steel - Microscopic test method for grain size".

[0049] 4. Texture In this embodiment, the development of a texture that is unfavorable to magnetic properties is suppressed, while the development of a texture that is favorable to magnetic properties is promoted. Specifically, the texture of the base material is controlled to satisfy the following formula (ii). The value of the left side of formula (ii) is preferably 0.40 or more, more preferably 0.45 or more. There is no need to set an upper limit to the value of the left side of formula (ii), but it is preferably 1.00 or less. [{100} + {411}] / [{111} + {211}] ≥ 0.35 (ii) where {100}, {411}, {111}, and {211} are the X-ray integrated intensity ratios of the {100} orientation, {411} orientation, {111} orientation, and {211} orientation in the inverse pole figure at a position ¼ of the plate thickness from the surface of the base material, respectively.

[0050] The X-ray integrated intensity ratios of the {100}, {411}, {111}, and {211} orientations are measured using an X-ray diffractometer. The X-ray integrated intensity ratio is a value obtained by measuring the X-ray intensity of a standard sample without accumulation in a specific orientation and the test material using X-ray diffraction under the same conditions, and dividing the resulting X-ray intensity of the test material by the X-ray intensity of the standard sample. The specific measurement method is as follows. A test piece with a diameter of 26 mm is punched out from the base material of the non-oriented electrical steel sheet used as the test material, and the test piece is polished by chemical polishing to a depth of 1 / 4 of the sheet thickness from one side of the surface. From the viewpoint of achieving both measurement accuracy and test efficiency, the number of test pieces used for the measurement is 10. The X-ray integrated intensity ratios of the {100} orientation, the {411} orientation, the {111} orientation, and the {211} orientation are defined as the values ​​obtained by calculating the integrated intensity of diffraction of each crystal plane from the X-ray diffraction profile measured by an X-ray diffractometer and dividing the calculated value by the integrated intensity of a standard sample, respectively.

[0051] <Measurement Method> A 26 mm diameter test piece is placed in the sample magazine. A standard sample provided by the manufacturer that does not have a specific orientation is also placed at the same time. The measurement conditions for inverse X-ray analysis are: measurement axis 2θ / θ, measurement method FT, and counting unit CPS. The step width is 0.010°, counting time is 0.6 s, voltage is 50 kV, current is 200 mA, divergence / scattering slit is 1°, divergence vertical slit is 10 mm, and receiving slit is 0.15 mm. The measurement ranges are: (110): 2θ = 18.000-21.500°, (200): 2θ = 27.750-29.500°, and (222): 2θ = 49.750-52.000°.

[0052] <Analysis method> Analysis software called "Invpole.cnd" is used for analysis. Since it is necessary to select standard results for analysis, it is set to refer to the data of the standard sample measured together with the test piece. Smoothing processing, peak correction, and background removal are not performed in the analysis. For intensity calculation, "integrated intensity" is selected, and as the crystal system, cubic (α axis: 2.866 Å) is selected.

[0053] 5. Magnetic Properties In the non-oriented electrical steel sheet according to this embodiment, excellent magnetic properties are defined as iron loss W １０／４００ is low, and the magnetic flux density B ５０ means that is high.

[0054] Here, the magnetic properties (iron loss W １０／４００ and magnetic flux density B ５０ ) is measured in accordance with the Epstein test method specified in JIS C 2550-1:2011. １０／４００ means the iron loss that occurs under the condition that the maximum magnetic flux density is 1.0 T and the frequency is 400 Hz, and the magnetic flux density B ５０ means the magnetic flux density in a magnetic field of 5000 A / m.

[0055] The density of the steel sheet during measurement is a value calculated by [7.865 - 0.065 x (Si + 1.7 x Al)], where Si and Al in the formula are the respective contents (mass%) in the steel sheet. When measuring iron loss in accordance with the Epstein test method, the excitation directions are two directions: a direction parallel to the rolling direction (hereinafter referred to as the L direction) and a direction perpendicular to the rolling direction (hereinafter referred to as the C direction), and measurements are performed using half of each test piece excited in the L direction and the C direction.

[0056] In the non-oriented electrical steel sheet according to this embodiment, iron loss W １０／４００ Low means that the magnetic flux density B is 14.5 W / kg or less for a plate thickness of 0.26 mm or more, 12.5 W / kg or less for a plate thickness of 0.21 to 0.25 mm, and 11.5 W / kg or less for a plate thickness of 0.20 mm or less. ５０ High means that the strength is 1.64T or more when the plate thickness is 0.26mm or more, 1.63T or more when the plate thickness is 0.21 to 0.25mm, and 1.62T or more when the plate thickness is 0.20mm or less.

[0057] Next, a method for measuring the magnetic properties of a motor core will be described. It is not possible to obtain large test pieces such as Epstein test pieces from a motor core. Therefore, when evaluating the magnetic properties of a motor core, magnetic measurements are performed using the following procedure. First, the laminated motor core is separated into steel plates, and small test pieces for single-plate magnetic measurements are prepared by electrical discharge machining, with dimensions that can be obtained according to the size of the separated steel plates. Then, iron loss W is measured using a small single-plate tester that is compatible with the small test pieces. １０／４００ and magnetic flux density B ５０ The measurement principle follows the Single Sheet Tester (SST) method defined in JIS C 2556:2015. When measuring iron loss using the Single Sheet Tester, the excitation directions are the L direction and the C direction, and the average of the values ​​measured in each direction is calculated as the magnetic property value of the material.

[0058] In addition, the above-mentioned Epstein test pieces and small test pieces were taken from several kinds of non-oriented electrical steel sheets in advance, and the iron loss W was measured by the Epstein method and the single sheet magnetic property measurement method.１０／４００ and magnetic flux density B ５０ The values ​​measured by the veneer tester are then corrected using the conversion formula to be equivalent to the values ​​measured by the Epstein method.

[0059] 6. Mechanical Properties The non-oriented electrical steel sheet according to this embodiment has high strength. The 0.2% yield strength does not need to be particularly limited, but it is preferably 450 MPa or more. The 0.2% yield strength is more preferably 460 MPa or more, and even more preferably 470 MPa or more. Here, the 0.2% yield strength is measured by the offset method by conducting a tensile test in accordance with JIS Z 2241:2011.

[0060] Test specimens are taken with the rolling direction as the longitudinal direction while keeping the plate thickness as it is, and then processed into the shape of a JIS No. 5 test specimen. Note that if it is difficult to take a JIS No. 5 test specimen due to the size of the steel plate, a tensile test may be carried out using a reduced-scale shape.

[0061] 7. Sheet Thickness In the non-oriented electrical steel sheet according to this embodiment, the sheet thickness of the base material is set to 0.10 mm or more from the viewpoint of manufacturing costs of cold rolling and finish annealing. On the other hand, from the viewpoint of reducing iron loss, the sheet thickness of the base material is set to 0.30 mm or less. Therefore, the sheet thickness of the non-oriented electrical steel sheet according to this embodiment is 0.10 to 0.30 mm. The sheet thickness of the base material is preferably 0.15 to 0.27 mm.

[0062] 8. Insulating Coating In the non-oriented electrical steel sheet according to this embodiment, it is preferable that an insulating coating be provided on the surface of the base material. Since the non-oriented electrical steel sheet is used after being punched into a core blank and then laminated, providing an insulating coating on the surface of the base material can reduce eddy currents between the sheets, thereby making it possible to reduce eddy current loss in the core.

[0063] The type of insulating coating is not particularly limited, and known insulating coatings used for non-oriented electrical steel sheets can be used. Examples of such insulating coatings include composite insulating coatings primarily composed of inorganic materials and further containing organic materials. Here, a composite insulating coating is an insulating coating primarily composed of at least one inorganic material, such as a metal chromate salt, a metal phosphate salt, colloidal silica, a Zr compound, or a Ti compound, with fine organic resin particles dispersed therein. In particular, from the perspective of reducing the environmental impact during manufacturing, which has become increasingly important in recent years, insulating coatings using metal phosphate salts, Zr or Ti coupling agents, or Zr or Ti carbonates or ammonium salts as starting materials are preferably used.

[0064] The amount of the insulating coating is not particularly limited, but for example, it is 200 to 3000 mg / m per side. ２ The coating amount is preferably about 300 to 2500 mg / m per side. ２ It is more preferable to set the range as follows. By forming the insulating coating so that the coating weight falls within the above range, it is possible to maintain excellent uniformity. When measuring the coating weight of the insulating coating afterward, various known measurement methods can be used. For example, a method of measuring the difference in mass before and after immersion in a sodium hydroxide aqueous solution, or a fluorescent X-ray method using a calibration curve method may be used as appropriate.

[0065] 9. Motor Core and Motor A motor core according to one embodiment of the present invention is formed by laminating the above-described non-oriented electromagnetic steel sheets. The motor core is obtained by laminating a plurality of non-oriented electromagnetic steel sheets that have been punched into a predetermined shape. Some or all of the plurality of laminated non-oriented electromagnetic steel sheets may be the above-described non-oriented electromagnetic steel sheets. A motor according to one embodiment of the present invention includes the above-described motor core.

[0066] 10. Manufacturing Method The manufacturing method of the non-oriented electrical steel sheet according to this embodiment is not particularly limited, but it can be manufactured by sequentially carrying out a hot rolling step, a hot-rolled sheet annealing step, a descaling step, a cold rolling step, and a finish annealing step on a steel ingot having the above-described chemical composition under the conditions shown below, for example. Furthermore, if an insulating coating is formed on the surface of the base material, an insulating coating formation step is carried out after the finish annealing step. Each step will be described in detail below.

[0067] <Hot Rolling Step> A steel ingot (slab) having the above chemical composition is heated and hot-rolled to obtain a hot-rolled sheet. The heating temperature of the steel ingot when subjected to hot rolling is not particularly specified, but is preferably, for example, 1050 to 1250°C. The thickness of the hot-rolled sheet after hot rolling is also not particularly specified, but is preferably, for example, about 1.5 to 3.0 mm, taking into account the final thickness of the base material.

[0068] <Hot-rolled sheet annealing process> Thereafter, hot-rolled sheet annealing is performed for the purpose of reducing iron loss of the steel sheet. For hot-rolled sheet annealing, a continuous annealing furnace is used, which has higher productivity than batch annealing and produces a highly homogeneous metal structure after annealing. Furthermore, in this embodiment, the magnetic flux density can be improved by lowering the soaking temperature during hot-rolled sheet annealing while extending the soaking time. Specifically, hot-rolled sheet annealing is performed under conditions of a soaking temperature of 800 to 880°C and a soaking time of 70 to 300 seconds. As described above, by lowering the temperature and extending the time of hot-rolled sheet annealing, it is possible to suppress the development of texture that is unfavorable to magnetic properties and promote the development of texture that is advantageous to magnetic properties.

[0069] <Descaling Process> The steel sheet after the hot-rolled sheet annealing is subjected to pickling to remove the scale layer formed on the surface of the base material. The pickling conditions, such as the concentration of the acid used in pickling, the concentration of the accelerator used in pickling, and the temperature of the pickling solution, are not particularly limited and can be any known pickling conditions. Non-oriented electrical steel sheets, which contain a large amount of Si and Al, which are more easily oxidized than the base iron, may form a scale layer containing an internal oxide layer of Si and Al in addition to the iron-based scale, making it difficult to obtain good pickling properties. In particular, if a large amount of Al-based internal oxide remains, it can cause uneven wear of the rolling rolls during subsequent cold rolling, so sufficient removal is necessary. To improve descaling properties, including the internal oxide layer, it is preferable to add a shot blast treatment after hot-rolled sheet annealing and before pickling.

[0070] <Cold Rolling Step> The steel sheet after the descaling is subjected to cold rolling at a reduction ratio such that the final thickness of the base material is 0.10 to 0.30 mm.

[0071] <Finish annealing step> Finish annealing is carried out after the cold rolling. In the method for producing a non-oriented electrical steel sheet according to this embodiment, a continuous annealing furnace is used for the finish annealing. The finish annealing is carried out under conditions of a soaking temperature of 880 to 1050°C and a soaking time of 1 to 300 seconds. ２ The ratio of H is 1 to 100% by volume. ２ and N ２ A mixed atmosphere of H ２ +N ２ = 100% by volume), and the dew point of the atmosphere is preferably set to −50 to +10° C. By setting the dew point of the atmosphere to +10° C. or less, it is possible to suppress the occurrence of internal oxidation that leads to deterioration of iron loss.

[0072] If the soaking temperature is less than 880°C, the grain size becomes small and the core loss deteriorates, which is not preferable, whereas if the soaking temperature exceeds 1050°C, the strength becomes insufficient, which is not preferable. Also, if the soaking time is less than 1 second, the grains cannot grow sufficiently. On the other hand, if the soaking time exceeds 300 seconds, the manufacturing cost increases.

[0073] <Insulating Coating Forming Step> After the above-mentioned finish annealing, an insulating coating forming step is carried out as necessary. Here, the method for forming the insulating coating is not particularly limited, and a known insulating coating forming treatment liquid such as that described below may be used, and the treatment liquid may be applied and dried by a known method. An example of a known insulating coating is a composite insulating coating that is mainly made of an inorganic material and further contains an organic material.

[0074] The composite insulating coating is an insulating coating that is primarily composed of at least one of a metal salt such as a metal chromate salt or a metal phosphate salt, or an inorganic substance such as colloidal silica, a Zr compound, or a Ti compound, with fine organic resin particles dispersed therein. In particular, from the perspective of reducing the environmental impact during production, which has become increasingly necessary in recent years, insulating coatings that use a metal phosphate salt, a Zr or Ti coupling agent as a starting material, or an insulating coating that uses a carbonate or ammonium salt of a Zr or Ti coupling agent as a starting material are preferably used.

[0075] Before applying the treatment liquid, the surface of the base material on which the insulating coating is to be formed may be subjected to any pretreatment, such as degreasing treatment with an alkali or pickling treatment with hydrochloric acid, sulfuric acid, phosphoric acid, etc. The treatment liquid may also be applied to the surface of the base material as is after finish annealing without applying these pretreatments.

[0076] The non-oriented electrical steel sheet of the present invention obtained as described above has excellent properties such as low iron loss, high magnetic flux density and high strength, and is therefore suitable as a material for both rotors and stators.

[0077] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0078] A slab having the chemical composition shown in Table 1 was heated to 1150°C, then hot-rolled at a finishing temperature of 850°C to a finishing thickness of 1.8 mm, and coiled at 600°C to obtain a hot-rolled steel sheet. The obtained hot-rolled steel sheet was subjected to hot-rolled sheet annealing in a continuous annealing furnace under the conditions shown in Table 2. The steel sheet thus obtained was descaled by shot blasting and pickling, and then cold-rolled to obtain a cold-rolled steel sheet having a thickness of 0.25 mm.

[0079] Furthermore, H ２ : 20%, N ２ The steel sheets were subjected to finish annealing in a mixed atmosphere of 80% CO₂ and a dew point of −30°C under the conditions shown in Table 2. After the finish annealing, an insulating coating made of aluminum phosphate and an acrylic-styrene copolymer resin emulsion with a particle size of 0.2 μm was applied to the steel sheets, and baked at 350°C in the atmosphere.

[0080]

[0081]

[0082] For each test material obtained, the average grain size of the base material was measured in accordance with JIS G 0551:2013 "Steel - Microscopic test method for grain size." In addition, Epstein test pieces were taken from each test material in the rolling direction and width direction, and the iron loss W was measured by an Epstein test in accordance with JIS C 2550-1:2011. １０／４００ and magnetic flux density B ５０ The density of the steel sheet was calculated as [7.865-0.065×(Si+1.7×Al)], and magnetic measurements were carried out.

[0083] The base material of each test material was chemically polished to remove the surface from one side to a depth of 1 / 4 of the plate thickness, and the X-ray integrated intensity ratios of the {100} orientation, {411} orientation, {111} orientation, and {211} orientation on the polished surface were measured using an X-ray diffractometer (Rigaku Corporation: RINT-2500). Next, JIS No. 5 tensile test specimens were taken from each test material in accordance with JIS Z 2241:2022, with the longitudinal direction coinciding with the rolling direction of the steel plate. Then, using the test specimens, a tensile test was performed in accordance with JIS Z 2241:2022, and the 0.2% proof stress was measured.

[0084] The above results are also shown in Table 2.

[0085] In Test Nos. 2, 3, 4, 6, 9, 12, 14, 18, 20, 22 and 23, which satisfy the provisions of the present invention, the iron loss W １０／４００ is low, and the magnetic flux density B ５０In contrast, in Test Nos. 1, 5, 7, 8, 10, 11, 13, 15 to 17, 19, 21, and 24 to 26, which are comparative examples, the iron loss W １０／４００ is inferior, or magnetic flux density B ５０ The strength was poor, the 0.2% yield strength was poor, or the toughness was significantly deteriorated, making manufacturing difficult.

[0086] Specifically, in Test Nos. 1 and 25, the soaking time in the hot-rolled sheet annealing was short, and {(111) + (411)} / {(111) + (211)} was lower than the specified range, resulting in poor magnetic flux density. In Test No. 5, the S content was higher than the specified range, resulting in a large amount of MnS precipitation and poor iron loss.

[0087] In Test No. 7, the total content of Sn and Sb was lower than the specified range, so {(111) + (411)} / {(111) + (211)} was lower than the specified range, resulting in poor magnetic flux density. In Test No. 8, the total content of Sn and Sb was higher than the specified range, so toughness was deteriorated and the specimen fractured during cold rolling, making it impossible to measure 0.2% proof stress and magnetic properties. In Test No. 10, the Mn content was higher than the specified range, resulting in poor magnetic flux density.

[0088] In Test No. 11, the Si+Al+0.5×Mn content was lower than the specified range, resulting in poor 0.2% yield strength. In Test No. 13, the Si+Al+0.5×Mn content was higher than the specified range, resulting in poor toughness and fracture during cold rolling, making it impossible to measure 0.2% yield strength and magnetic properties. In Test No. 15, the Si content was lower than the specified range, resulting in poor 0.2% yield strength.

[0089] In Test No. 16, the Si content was higher than the specified range, which resulted in poor toughness and fracture during cold rolling, making it impossible to measure 0.2% yield strength and magnetic properties. In Test No. 17, the Al content was lower than the specified range, resulting in an average grain size smaller than the specified range and poor iron loss. In Test No. 19, the Al content was higher than the specified range, which resulted in poor toughness and fracture during cold rolling, making it impossible to measure 0.2% yield strength and magnetic properties.

[0090] In Test No. 21, the soaking temperature during finish annealing was low, resulting in an average crystal grain size smaller than the specified range and poor iron loss. In Test No. 24, the soaking temperature during finish annealing was high, resulting in an average crystal grain size larger than the specified range and poor 0.2% yield strength. In Test No. 26, the soaking temperature during hot-rolled sheet annealing was high, resulting in poor toughness and fracture during cold rolling, making it impossible to measure 0.2% yield strength and magnetic properties.

[0091] As described above, according to the present invention, a non-oriented electrical steel sheet having excellent magnetic properties and high strength can be obtained.

Claims

1. The chemical composition of the base material is, in mass%, C: 0.0050% or less, Si: more than 3.50% and less than 4.50%, Mn: less than 0.60%, Al: 0.30 to 0.90%, P: 0.030% or less, S: 0.0020% or less, N: 0.0040% or less, Ti: less than 0.0040%, Nb: less than 0.0040%, Zr: less than 0.0040%, V: less than 0.0040%, Cu: less than 0.200%, Ni: less than 0.500%, Sn and / or Sb: 0.010 to 0.060% in total, and the balance: Fe and impurities; and the following formula (i) is satisfied; the average crystal grain size of the base material is more than 40 μm and less than 140 μm; A non-oriented electrical steel sheet having a thickness of 0.10 to 0.30 mm, wherein the texture of the base material satisfies the following formula (ii): 4.2≦Si+Al+0.5×Mn≦4.9 (i), where the element symbols in the formula indicate the content (mass%) of each element: [{100}+{411}] / [{111}+{211}]≧0.35 (ii), where {100}, {411}, {111}, and {211} in the formula are the X-ray integrated intensity ratios of the {100} orientation, {411} orientation, {111} orientation, and {211} orientation in an inverse pole figure at a position 1 / 4 of the sheet thickness from the surface of the base material, respectively.

2. The non-oriented electrical steel sheet according to claim 1, having a 0.2% yield strength of 450 MPa or more.

3. The non-oriented electrical steel sheet according to claim 1 or 2, wherein an insulating coating is provided on the surface of the base material.

4. A motor core in which the non-oriented electrical steel sheets according to any one of claims 1 to 3 are laminated.

5. A motor comprising the motor core according to claim 4.

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