Non-oriented electrical steel sheet and method for producing same

Abstract

A non-oriented electrical steel sheet wherein: the chemical composition of a base material contains, in terms of mass%, not more than 0.0050% C, more than 3.50% but not more than 4.50% Si, less than 0.60% Mn, 0.25-0.65% Al, not more than 0.030% P, not more than 0.0020% S, not more than 0.0040% N, less than 0.0040% Ti, less than 0.0040% Nb, less than 0.0040% Zr, less than 0.0040% V, less than 0.200% Cu, less than 0.500% Ni, and Sn and / or Sb in a total amount of not more than 0.030%, with the remainder being Fe and impurities; [4.3≤Si+Al+0.5×Mn≤5.0] is satisfied; the average crystal grain size of the base material is more than 40 μm but not more than 140 μm, the degree of integration of the {111} direction is not less than 3.0, the degree of integration of the {110} direction is not more than 0.15; and the sheet thickness is 0.10-0.30 mm.

Description

Non-oriented electrical steel sheet and its manufacturing method

[0001] The present invention relates to a non-oriented electrical steel sheet and a method for manufacturing the same.

[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 sources 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 sheets is effective for reducing copper loss. Meanwhile, achieving high motor output requires increasing torque and speed. Increasing the magnetic flux density of the sheets is effective for increasing torque, while increasing the strength of the sheets is effective for increasing speed. Furthermore, increasing speed requires increasing frequency, which increases iron loss, necessitating the need for low-iron-loss electromagnetic steel sheets. Therefore, to achieve high motor efficiency and output, electromagnetic steel sheets with low iron loss, high magnetic flux density, and high strength are required. Of these three characteristics, low iron loss is the most effective means of achieving both high efficiency and high output, and high strength is the next most important, given the recent trend toward higher speeds.

[0004] The motor cores of the various motors mentioned 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. The stator is required to have excellent magnetic properties (especially low iron loss), while 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 manufacturing process of the iron core 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 required for the stator, non-oriented electrical steel sheets with low iron loss and high strength have been studied.

[0006] On the other hand, the dimensional accuracy of the iron core, which is manufactured by punching, is also important for improving the practical performance of the motor.It is known that the dimensional accuracy of the iron core is affected by the anisotropy of the mechanical properties of the electromagnetic steel sheet, and methods for improving dimensional accuracy have been investigated.

[0007] For example, Patent Documents 1 to 4 attempt to achieve excellent magnetic properties and high strength. Patent Document 5 proposes adjusting the dimensions of a mold in accordance with the anisotropy of the mechanical properties of the electrical steel sheet.

[0008] International Publication No. 2019 / 017426 International Publication No. 2020 / 091039 International Publication No. 2020 / 091043 JP 2010-90474 A International Publication No. 2022 / 210867

[0009] However, to realize a non-oriented electrical steel sheet that combines low iron loss and high strength, it is necessary to include a large amount of alloying elements, as disclosed in Patent Documents 1 to 4, which poses the problem of reduced toughness and increased susceptibility to fracture during cold rolling. Also, to improve the dimensional accuracy during punching of the iron core, as disclosed in Patent Document 5, there is a problem in that an extremely cumbersome method is required, in which the dimensions of the die are adjusted each time in accordance with the anisotropy of the mechanical properties of the electrical steel sheet.

[0010] The present invention has been made to solve these problems, and has an object to stably provide a non-oriented electrical steel sheet that has low iron loss, high strength, and excellent dimensional accuracy during punching.

[0011] The present invention relates to the following non-oriented electrical steel sheet and a method for producing the same.

[0012] (1) The chemical composition of the base material is, in mass%, C: 0.0050% or less, Si: more than 3.50% and 4.50% or less, Mn: less than 0.60%, Al: 0.25 to 0.65%, 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%, the sum of one or both of Sn and Sb: 0.030% or less, 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 140 μm or less, A non-oriented electrical steel sheet, wherein the degree of integration of the {111} orientation is 3.0 or more and the degree of integration of the {110} orientation is 0.15 or less at a position 1 / 4 of the sheet thickness from the surface of the base material, and the sheet thickness is 0.10 to 0.30 mm, 4.3≦Si+Al+0.5×Mn≦5.0 (i), where the element symbols in the above formula represent the content (mass%) of each element.

[0013] (2) The non-oriented electrical steel sheet according to (1) above, having a 0.2% yield strength of 450 MPa or more.

[0014] (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.

[0015] (4) A method for producing a non-oriented electrical steel sheet according to any one of (1) to (3) above, comprising the steps of: (i) adding, to a steel ingot having a chemical composition, in mass%, of C: 0.0050% or less, Si: more than 3.50% and 4.50% or less, Mn: less than 0.60%, Al: 0.25 to 0.65%, 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: 0.030% or less in total, and the balance: Fe and impurities, A method for manufacturing a non-oriented electrical steel sheet, comprising the steps of: a hot rolling process; a hot-rolled sheet annealing process in which the soaking temperature is 760 to 880°C and the soaking time is 5 to 100 seconds; a descaling process by pickling; a cold rolling process in which the sheet is reduced to a thickness of 0.10 to 0.30 mm; and a finish annealing process in which the soaking temperature is 850 to 1050°C and the soaking time is 1 to 300 seconds after heating to a temperature of 850°C or higher at a heating rate of 100°C / s or less in the temperature range of 500 to 850°C. 4.3≦Si+Al+0.5×Mn≦5.0 (i) where the element symbols in the above formula represent the content (mass%) of each element.

[0016] According to the present invention, it is possible to obtain a non-oriented electrical steel sheet that has excellent magnetic properties and high strength, and also has excellent dimensional accuracy during punching.

[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 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 0.25% or more. On the other hand, to suppress deterioration of toughness and form a texture that provides good dimensional accuracy, the Al content is set to 0.65% or less.

[0020] Furthermore, Mn has the lowest solid solution strengthening ability of the three elements, but contributes to increasing electrical resistance with little deterioration in toughness. It also fixes S as MnS, thereby mitigating the adverse effects of S on magnetic properties and surface properties. However, after extensive research, the inventors have found that excessive inclusion of Mn, which has a lower solid solution strengthening ability than Si and Al, results in a significant increase in alloy cost compared to the increase in strength, and the effect of mitigating the adverse effects of S also saturates. Therefore, the Mn content is set to less than 0.60%.

[0021] As described above, reducing the anisotropy of the mechanical properties of electrical steel sheets is effective in obtaining excellent dimensional accuracy. The present inventors further investigated methods for reducing the anisotropy of the mechanical properties. As a result, they found that the anisotropy of the mechanical properties can be reduced by controlling the texture.

[0022] In order to develop a texture that is advantageous for dimensional accuracy, it is effective to reduce the contents of Al, Sn, and Sb and to lower the soaking temperature in the annealing of the hot-rolled sheet.

[0023] However, the texture that is advantageous for dimensional accuracy is also unfavorable for magnetic properties. Therefore, a certain degree of decrease in magnetic flux density is unavoidable. However, after detailed investigations, the inventors found that the effect on iron loss is negligible.

[0024] The present invention was made based on the above findings. Each of the features of the present invention will be described in detail below.

[0025] 1. Overall Configuration The non-oriented electrical steel sheet according to one embodiment of the present invention has low iron loss, high strength, and excellent dimensional accuracy during punching, 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.

[0026] 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."

[0027] 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.

[0028] 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.

[0029] Mn: Less than 0.60% Mn (manganese) is an element effective in increasing the electrical resistance of steel, reducing eddy current loss, and improving iron loss in non-oriented electrical steel sheets. It also fixes S as MnS, thereby mitigating the adverse effects of S on magnetic properties and surface texture. However, Mn has poorer solid-solution strengthening ability than Si and Al, so a large amount is required to achieve high strength, which significantly reduces magnetic flux density and increases alloy costs. Furthermore, excessive Mn content saturates the effect of mitigating the adverse effects of S. 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.

[0030] Al: 0.25 to 0.65% Al (aluminum) is an element that increases the electrical resistance of steel, thereby reducing eddy current loss and improving the iron loss of non-oriented electrical steel sheets. Furthermore, Al contributes to increasing the strength of non-oriented electrical steel sheets through solid-solution strengthening, although not as much as Si. Furthermore, adding an appropriate amount of Al suppresses the refinement of AlN, which occurs when Al combines with N in the steel, and improves grain growth during finish annealing. To achieve these effects, the Al content is set to 0.25% or more. The Al content is preferably 0.30% or more, and more preferably 0.35% or more. On the other hand, excessive Al content reduces the concentration of the {111} orientation and increases the concentration of the {110} orientation, adversely affecting the dimensional accuracy of the iron core during punching. Therefore, the Al content is set to 0.65% or less. The Al content is preferably 0.60% or less, and more preferably 0.55% or less.

[0031] 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 toughness, an upper limit is also necessary. Therefore, in addition to the contents of Si, Al, and Mn being within the respective ranges described above, it is also necessary to satisfy the following formula (i). The value of the middle part of the following formula (i) is preferably 4.4 or more, more preferably 4.5 or more, and preferably 4.9 or less, more preferably 4.8 or less.

[0032] 4.3≦Si+Al+0.5×Mn≦5.0 (i) In the above formula, the element symbols represent the content (mass %) of each element.

[0033] 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, even more preferably 0.003% or more, and even more preferably 0.005% or more.

[0034] 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.

[0035] 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 0.0035% or less, and more preferably 0.0030% 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] Sum of one or both of Sn and Sb: 0.030% or less While Sn (tin) and Sb (antimony) have the effect of increasing the magnetic flux density of non-oriented electrical steel sheets, they also have the effect of inhibiting the development of texture, which is advantageous for dimensional accuracy. Furthermore, 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 0.030% or less. The total content of Sn and Sb is preferably 0.025% or less, more preferably 0.020% or less. The contents of Sn and Sb are each preferably 0.025% or less, more preferably 0.020% or less, and even more preferably 0.015% or less.

[0043] It should be noted that there is no need to set a lower limit for the Sn and Sb contents, and both may be 0%. On the other hand, Sn and Sb are elements useful 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 obtain this effect, the total content of one or both of Sn and Sb is preferably more than 0%, more preferably 0.001% or more, even more preferably 0.005% or more, even more preferably 0.010% or more, and even more preferably 0.015% or more.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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 iron loss. 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.

[0050] 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".

[0051] 4. Texture In this embodiment, in order to improve the dimensional accuracy during punching, the {111} orientation is developed while the development of the {110} orientation is suppressed. Specifically, the density of the {111} orientation, which is advantageous for dimensional accuracy, is set to 3.0 or more, and the density of the {110} orientation, which is disadvantageous for dimensional accuracy, is set to 0.15 or less. The density of the {111} orientation is preferably 3.5 or more, more preferably more than 4.0. Furthermore, the density of the {110} orientation is preferably 0.12 or less, more preferably 0.10 or less. There is no need to set an upper limit to the density of the {111} orientation, but considering manufacturability, the substantial upper limit is 7.0. There is also no need to set a lower limit to the density of the {110} orientation, and it may be 0. On the other hand, the iron loss W １０／４００ In order to sufficiently reduce the degree of concentration of the {110} orientation, it is preferable that the degree of concentration is 0.01 or more, and more preferably 0.02 or more.

[0052] The degree of accumulation of the {111} and {110} orientations is measured using an X-ray diffractometer. The degree of accumulation is calculated 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 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 remove the surface from one side to a depth of 1 / 4 of the sheet thickness. From the viewpoint of achieving both measurement accuracy and test efficiency, the number of test pieces used for the measurement is 10. The degree of integration of the {111} orientation and the {110} orientation is defined as the value 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 it by the integrated intensity of a standard sample.

[0053] <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°.

[0054] <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.

[0055] 5. Magnetic Properties In the non-oriented electrical steel sheet according to this embodiment, excellent magnetic properties are defined as iron loss W １０／４００means that is low.

[0056] Here, iron loss W １０／４００ The iron loss W 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 conditions of a maximum magnetic flux density of 1.0 T and a frequency of 400 Hz.

[0057] 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.

[0058] It is not possible to extract large test pieces such as Epstein test pieces from a motor core. To evaluate the iron loss of a motor core, the laminated core is separated into steel plates, and small test pieces for single-sheet magnetic measurement are fabricated by electrical discharge machining to match the size of the separated steel plates. The iron loss value is then measured using a small single-sheet tester compatible with the small test pieces. The measurement principle follows the Single Sheet Tester (SST) method specified in JIS C 2556:2015. When measuring iron loss using the single-sheet magnetic property measurement method, the excitation direction is set to two directions, 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.

[0059] In addition, the above-mentioned Epstein test pieces and small test pieces are taken in advance from several types of non-oriented electrical steel sheets, and the iron loss values ​​are measured by the Epstein method and the single sheet magnetic property measurement method, and a conversion formula is derived from the relationship between the two measurements.The iron loss value measured by the single sheet tester is then corrected using the conversion formula so that it is equivalent to the iron loss value measured by the Epstein method.

[0060] In the non-oriented electrical steel sheet according to this embodiment, iron loss W １０／４００Low means that the iron loss W 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 11.2 W / kg or less for a plate thickness of 0.20 mm or less. １０／４００ is preferably 14.3 W / kg or less for a plate thickness of 0.26 mm or more, 12.3 W / kg or less for a plate thickness of 0.21 to 0.25 mm, and 11.0 W / kg or less for a plate thickness of 0.20 mm or less.

[0061] 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 470 MPa or more, and even more preferably 490 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.

[0062] 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.

[0063] 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 base material 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.

[0064] 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.

[0065] 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.

[0066] The amount of the insulating coating is not particularly limited, but is, for example, 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.

[0067] 9. 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.

[0068] <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.

[0069] <Hot-rolled sheet annealing process> Thereafter, hot-rolled sheet annealing is carried out for the purpose of reducing the iron loss of the steel sheet. For hot-rolled sheet annealing, it is preferable to use a continuous annealing furnace, which has higher productivity than batch annealing and has a high homogeneity of the metal structure after annealing. Hot-rolled sheet annealing is carried out under conditions of a soaking temperature of 760 to 880°C and a soaking time of 5 seconds or more and 100 seconds or less. As mentioned above, by lowering the soaking temperature, it becomes possible to develop a texture that is advantageous for dimensional accuracy. On the other hand, low iron loss W １０／４００ In order to ensure this, the soaking temperature is set to 760°C or higher. The lower the Si content of the base material, the higher the soaking temperature is desired. Specifically, when the Si content is 4.40% or less, the soaking temperature is preferably set to 770°C or higher, and when the Si content is 4.30% or less, the soaking temperature is preferably set to 780°C or higher.

[0070] <Descaling step> 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 the pickling, the concentration of the accelerator used in the pickling, and the temperature of the pickling solution, are not particularly limited, and known pickling conditions can be used. Note that, in order to improve descaling properties, it is preferable to add a shot blast treatment after the hot-rolled sheet annealing and before the pickling.

[0071] <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.

[0072] <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, it is preferable to use a continuous annealing furnace for the finish annealing. Finish annealing is carried out by heating the sheet to a temperature of 850°C or higher so that the temperature rise rate in the temperature range of 500 to 850°C is 100°C / s or less, and then by soaking the sheet at a temperature of 850 to 1050°C for 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 -50 to +10°C.

[0073] By setting the heating rate in the temperature range of 500 to 850°C to 100°C / s or less, it is possible to develop a texture that is advantageous for dimensional accuracy. If the heating rate exceeds 100°C / s, the degree of accumulation of the {111} orientation may be less than 3.0. Note that the average heating rate may be set to 1 to 100°C / s throughout the entire heating process, including the temperature range below 500°C and the soaking temperature.

[0074] Furthermore, if the soaking temperature is less than 850°C, the grain size becomes small and the core loss deteriorates, which is undesirable, while if the soaking temperature exceeds 1050°C, the strength becomes insufficient and the core loss deteriorates, which is undesirable. Furthermore, 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.

[0075] <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.

[0076] 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 metal phosphate salt, a Zr or Ti carbonate salt, or an ammonium salt as a starting material are preferably used.

[0077] Before applying the treatment liquid to the surface of the base material on which the insulating coating is to be formed, any pretreatment may be performed, such as degreasing with an alkali or pickling 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 performing these pretreatments.

[0078] The non-oriented electrical steel sheet of the present invention obtained as described above has the properties of low iron loss, high strength, and excellent dimensional accuracy during punching, and is therefore suitable as a material for both rotors and stators.

[0079] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0080] 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 2.0 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.

[0081] 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.

[0082]

[0083]

[0084] 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 was evaluated.

[0085] The base material of each test material was chemically polished to remove a quarter of the sheet thickness from one surface, and the degree of integration of the {111} and {110} orientations on the polished surface was measured using an X-ray diffractometer (Rigaku Corporation: RINT-2500). Subsequently, JIS No. 5 tensile test specimens were taken from each test material in accordance with JIS Z 2241:2011, with the longitudinal direction coinciding with the rolling direction of the steel sheet. Then, a tensile test was performed using the test specimens in accordance with JIS Z 2241:2011, and the 0.2% proof stress was measured.

[0086] Furthermore, in this example, in order to evaluate the dimensional accuracy during punching, a disk having a diameter of 50 mm was punched, and the roundness of the punched steel plate was measured. The indication of roundness in this invention conforms to the description in JIS B0621 (1984), which states, "When a circular shape is sandwiched between two concentric geometric circles, the roundness is expressed as the radius difference at the smallest distance between the two concentric circles, and is expressed as roundness_mm or roundness_μm." In this example, a roundness of 30 μm or less was determined to be excellent in dimensional accuracy during punching.

[0087] The above results are also shown in Table 2.

[0088] In Test Nos. 1, 4, and 5, which satisfy the provisions of the present invention, the iron loss W １０／４００ It was found that the iron loss W １０／４００ The 0.2% proof stress was equivalent to that of the inventive example, but the roundness was inferior.

[0089] Specifically, in Test No. 2, the Sn content was higher than the specified range, so the concentration of the {110} orientation exceeded the specified range, resulting in poor circularity. In Test No. 3, the Sn content was higher than the specified range, and the soaking temperature for hot-rolled sheet annealing exceeded the specified range, so the concentration of the {111} orientation was below the specified range and the concentration of the {110} orientation was higher than the specified range, resulting in poor circularity.

[0090] In Test No. 6, the temperature rise rate in the finish annealing was higher than the specified range, so the concentration of the {111} orientation was lower than the specified range, resulting in poor circularity. As described above, it was revealed that when the concentration of the {111} orientation was lower than the specified range, the concentration of the {110} orientation was higher than the specified range, or when the concentration of both orientations was outside the specified range at the same time, the circularity was poor.

[0091] A slab having the chemical composition shown in Table 3 was heated to 1150°C, then hot-rolled at a finishing temperature of 850°C to a finishing thickness of 2.0 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 4. 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.

[0092] Furthermore, H ２ : 20%, N ２ The steel sheets were subjected to finish annealing in a mixed atmosphere of 80% CO₂ and 80°C dew point, under the conditions shown in Table 4. 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.

[0093]

[0094]

[0095] For each of the obtained test materials, the average grain size of the base material and the iron loss W were measured in the same manner as in Example 1. １０／４００ The degree of orientation of {111} and {110}, and the 0.2% yield strength were measured. The results are shown in Table 4.

[0096] In Test Nos. 7, 9, 11, 13, 14, and 16, which satisfy the provisions of the present invention, the iron loss W １０／４００ In contrast, in Test Nos. 8, 10, 12, 15, 17, and 18, which are comparative examples, the iron loss W １０／４００ However, the 0.2% proof stress or texture was poor, and the specimens broke during cold rolling, making it impossible to evaluate their properties.

[0097] Specifically, in Test No. 8, the Si content was higher than the specified range, resulting in fracture during cold rolling. In Test No. 10, the Si content was lower than the specified range, resulting in poor 0.2% yield strength. In Test No. 12, the Al content was higher than the specified range, resulting in a lower concentration of {111} orientation than the specified range and a higher concentration of {110} orientation than the specified range.

[0098] In Test No. 15, the S content was higher than the specified range, resulting in a grain size lower than the specified range and poor iron loss. In Test No. 17, the Al content was lower than the specified range, resulting in a grain size lower than the specified range and poor iron loss. In Test No. 18, the Si+Al+0.5×Mn content was higher than the specified range, resulting in fracture during cold rolling and making it impossible to evaluate the properties.

[0099] As described above, according to the present invention, it is possible to obtain a non-oriented electrical steel sheet that has excellent magnetic properties and high strength, and also has excellent dimensional accuracy during punching.

Claims

1. The chemical composition of the base material is, in mass%, C: 0.0050% or less, Si: over 3.50% and 4.50% or less, Mn: less than 0.60%, Al: 0.25 to 0.65%, 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%, the sum of one or both of Sn and Sb: 0.030% or less, the balance: Fe and impurities, and the following formula (i) is satisfied; the average crystal grain size of the base material is over 40 μm and 140 μm or less, A non-oriented electrical steel sheet, wherein the concentration of {111} orientation is 3.0 or more and the concentration of {110} orientation is 0.15 or less at a position 1 / 4 of the sheet thickness from the surface of the base material, and the sheet thickness is 0.10 to 0.30 mm. 4.3≦Si+Al+0.5×Mn≦5.0 (i) where the element symbols in the above formula indicate the content (mass%) of each element.

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, having an insulating coating on the surface of the base material.

4. A method for producing a non-oriented electrical steel sheet according to any one of claims 1 to 3, comprising the steps of: (mass%) C: 0.0050% or less, Si: over 3.50% and 4.50% or less, Mn: less than 0.60%, Al: 0.25 to 0.65%, 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%, the sum of one or both of Sn and Sb: 0.030% or less, balance: Fe and impurities, for a steel ingot having a chemical composition that satisfies the following formula (i): A method for manufacturing a non-oriented electrical steel sheet, comprising the steps of a hot rolling process, a hot-rolled sheet annealing process in which the soaking temperature is 760 to 880°C and the soaking time is 5 to 100 seconds, a descaling process by pickling, a cold rolling process in which the sheet is reduced to a thickness of 0.10 to 0.30 mm, and a finish annealing process in which the soaking temperature is 850 to 1050°C and the soaking time is 1 to 300 seconds after heating to a temperature of 850°C or higher so that the heating rate in the temperature range of 500 to 850°C is 100°C / s or less. 4.3≦Si+Al+0.5×Mn≦5.0 ...(i) where the element symbols in the above formula indicate the content (mass%) of each element.

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