Non-oriented electrical steel sheet and method for producing same

Abstract

A non-oriented electromagnetic steel sheet in which a base material has a chemical composition, in mass%, of 0.0040% or less of C, more than 3.50% and 4.50% or less of Si, less than 0.60% of Mn, 0.30-0.90% of Al, 0.030% or less of P, 0.0018% or less of S, 0.0040% or less of N, less than 0.0040% of Ti, less than 0.0050% of Nb, less than 0.0050% of Zr, less than 0.0050% of V, less than 0.200% of Cu, less than 0.500% of Ni, 0.005-0.060% of one or both of Sn and Sb, and the balance being Fe and impurities, and satisfies [4.2 < = Si + Al + 0.5 * Mn < = 4.9]; the average crystal grain size of the base material is more than 40 [mu] m and 140 [mu] m or less; the degree of aggregation of {111} orientation is 4.0 or less; the plate thickness of the base material ranges from 0.10 mm to 0.30 mm.

Description

Technical Field

[0001] The present invention relates to a non-oriented electromagnetic steel sheet and a manufacturing method thereof. Background Art

[0002] In recent years, global environmental issues have attracted considerable attention, and the demand for energy conservation has further increased. In particular, there is a strong desire for higher efficiency in electronic equipment. Consequently, the demand for improved magnetic properties in non-oriented electromagnetic steel sheets, which are widely used as core materials for motors and generators, is also intensifying. This trend is particularly pronounced in drive motors for electric and hybrid vehicles, as well as in compressor motors for air conditioners. Furthermore, the desire for higher output in drive motors and compressor motors, which effectively minimizes the size of the equipment, is also growing.

[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 is effective in reducing the iron loss of the electromagnetic steel sheets used as the motor's core, while increasing the magnetic flux density of the electromagnetic steel sheets is effective in reducing copper loss. On the other hand, achieving high motor output requires increasing torque and high rotation speeds. Increasing the magnetic flux density of the electromagnetic steel sheets is effective for achieving high torque, while increasing the strength of the electromagnetic steel sheets is effective for achieving high rotation speeds. Therefore, to promote 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 core of each of the aforementioned motors consists of a stator (stationary component) and a rotor (rotating component). The stator and rotor that make up the motor core require different properties. While the stator requires excellent magnetic properties (low iron loss and high magnetic flux density), the rotor requires low iron loss and excellent mechanical properties (high strength).

[0005] Because the stator and rotor require different properties, the desired properties can be achieved by manufacturing separate non-oriented electromagnetic steel sheets for the stator and rotor. However, preparing two types of non-oriented electromagnetic steel sheets complicates the core manufacturing process and reduces yield. Therefore, to achieve the low iron loss and high strength required for the rotor, and the low iron loss and high magnetic flux density required for the stator, research has been ongoing to develop non-oriented electromagnetic steel sheets with both excellent magnetic properties and strength.

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

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: International Publication No. 2019 / 017426

[0010] Patent Document 2: International Publication No. 2020 / 091039

[0011] Patent Document 3: International Publication No. 2020 / 091043

[0012] Patent Document 4: Japanese Patent Application Publication No. 2010-90474 Summary of the Invention

[0013] Technical problem to be solved by the invention

[0014] However, in order to realize a non-oriented electrical steel sheet having both low iron loss and high strength, as disclosed in Patent Documents 1 to 4, a large amount of alloying elements must be contained, which leads to a problem that toughness is reduced and fracture is easily caused during cold rolling.

[0015] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to stably provide a non-oriented electrical steel sheet having excellent magnetic properties and high strength.

[0016] Technical means for solving technical problems

[0017] The present invention is directed to the following non-oriented electrical steel sheet and a method for producing the same.

[0018] (1) A non-oriented electromagnetic steel sheet, wherein the chemical composition of the base material is expressed in mass %,

[0019] C: 0.0040% or less,

[0020] Si: more than 3.50% and 4.50% or less,

[0021] Mn: less than 0.60%,

[0022] Al: 0.30~0.90%,

[0023] P: 0.030% or less,

[0024] S: 0.0018% or less,

[0025] N: 0.0040% or less,

[0026] Ti: less than 0.0040%,

[0027] Nb: less than 0.0050%,

[0028] Zr: less than 0.0050%,

[0029] V: less than 0.0050%,

[0030] Cu: less than 0.200%,

[0031] Ni: less than 0.500%,

[0032] The total of one or two of Sn and Sb: 0.005 to 0.060%,

[0033] The rest: Fe and impurities,

[0034] And satisfy the following formula (i),

[0035] 4.2≤Si+Al+0.5×Mn≤4.9···(i)

[0036] The element symbols in the above formula are the content of each element (mass %),

[0037] The average crystal grain size of the base material exceeds 40 μm and is less than 140 μm;

[0038] The degree of concentration of the {111} orientation at a position 1 / 4 of the plate thickness from the surface of the base material is 4.0 or less;

[0039] The thickness of the base material is 0.10 to 0.30 mm.

[0040] (2) The non-oriented electromagnetic steel sheet according to (1) above, wherein

[0041] The tensile strength is 580 MPa or more.

[0042] (3) The non-oriented electromagnetic steel sheet according to (1) or (2) above, wherein:

[0043] An insulating film is provided on the surface of the base material.

[0044] (4) A method for producing a non-oriented electromagnetic steel sheet, which is to produce the non-oriented electromagnetic steel sheet as described in (1) to

[0045] (3) The method for forming a non-oriented electrical steel sheet according to any one of the above,

[0046] The steel ingots are sequentially subjected to the following steps: a hot rolling process; a hot-rolled plate annealing process with a soaking temperature of 800 to 920°C and a soaking time of 1 second to 10 minutes; a descaling process of pickling after shot blasting; a cold rolling process of reducing the plate to a thickness of 0.10 to 0.30 mm; and a final annealing process with a soaking temperature of 900 to 1050°C and a soaking time of 1 second to 10 minutes after heating to a temperature of 850°C or higher at a heating rate of 400°C / s or higher in a temperature range of 500 to 850°C.

[0047] The steel ingot has the following chemical composition: in mass %,

[0048] C: 0.0040% or less,

[0049] Si: more than 3.50% and 4.50% or less,

[0050] Mn: less than 0.60%,

[0051] Al: 0.30~0.90%,

[0052] P: 0.030% or less,

[0053] S: 0.0018% or less,

[0054] N: 0.0040% or less,

[0055] Ti: less than 0.0040%,

[0056] Nb: less than 0.0050%,

[0057] Zr: less than 0.0050%,

[0058] V: less than 0.0050%,

[0059] Cu: less than 0.200%,

[0060] Ni: less than 0.500%,

[0061] The total of one or two of Sn and Sb: 0.005 to 0.060%,

[0062] The rest: Fe and impurities,

[0063] And satisfy the following formula (i),

[0064] 4.2≤Si+Al+0.5×Mn≤4.9···(i)

[0065] The element symbols in the above formulas represent the content (mass %) of each element.

[0066] Effects of the Invention

[0067] According to the present invention, a non-oriented electrical steel sheet having excellent magnetic properties and high strength can be stably obtained. DETAILED DESCRIPTION

[0068] The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have obtained the following findings.

[0069] In order to obtain a non-oriented electrical steel sheet having low iron loss, high magnetic flux density and high strength while ensuring toughness during cold rolling, it is necessary to optimize the contents of Si, Mn and Al, which are main alloying elements.

[0070] Specifically, the Si content, which has the highest solid solution strengthening ability and contributes most to increasing electrical resistance, is set to exceed 3.50% and be below 4.50%. Furthermore, to improve grain growth and consistently achieve excellent magnetic properties, the Al content is set to 0.30% or above. Meanwhile, to suppress degradation of toughness, the Al content is set to 0.90% or below.

[0071] Furthermore, Mn has the lowest solid solution strengthening ability of the three elements, but it contributes to a smaller deterioration in toughness and thus contributes to an increase in electrical resistance. However, the present inventors have conducted repeated studies and have found that excessive inclusion of Mn, which has a lower solid solution strengthening ability than Si and Al, significantly reduces magnetic flux density compared to the increase in strength. High Mn contents make it difficult to stably improve magnetic properties. Therefore, the Mn content is set to less than 0.60%.

[0072] In the production process of non-oriented electrical steel sheets, hot-rolled sheet annealing is generally performed before cold rolling. However, when the Si content in the steel sheet is high and the sheet thickness needs to be reduced to reduce iron loss, it is preferable to lower the soaking temperature during hot-rolled sheet annealing to prevent problems such as sheet breakage and edge cracking during cold rolling. On the other hand, it is known that higher soaking temperatures during hot-rolled sheet annealing increase the magnetic flux density, and lowering the soaking temperature results in a decrease in magnetic flux density.

[0073] Therefore, the present inventors investigated methods for simultaneously lowering the soaking temperature during hot-rolled sheet annealing while also increasing the magnetic flux density. They discovered that rapid heating during the final annealing after cold rolling can suppress the development of textures detrimental to magnetic properties, and thus, even at low soaking temperatures during hot-rolled sheet annealing, suppress the reduction in magnetic flux density.

[0074] In addition, the inventors conducted experiments on rapid heating to various reaching temperatures and found that even if rapid heating was performed, the magnetic properties could not be improved when the reaching temperature was low. However, the magnetic properties would be improved by rapid heating to a temperature above 850°C.

[0075] The present invention has been accomplished based on the above findings. Hereinafter, each element of the present invention will be described in detail.

[0076] 1. Overall composition

[0077] The non-oriented electrical steel sheet according to one embodiment of the present invention has excellent magnetic properties and high strength, and is therefore suitable for both stators and rotors. Furthermore, the non-oriented electrical steel sheet according to this embodiment preferably includes an insulating coating on the surface of a base material described below.

[0078] 2. Chemical composition of the base material

[0079] The reasons for limiting the content of each element are as follows. In the following description, "%" for the content means "mass %".

[0080] C: 0.0040% or less

[0081] Carbon (C) is an element that degrades the iron loss of non-oriented electrical steel sheets. If the C content exceeds 0.0040%, the iron loss of the non-oriented electrical steel sheet deteriorates, and good magnetic properties cannot be achieved. Therefore, the C content is set to 0.0040% or less. Preferably, the C content is 0.0035% or less, and more preferably, 0.0030% or less. Furthermore, C contributes to the high strength of the non-oriented electrical steel sheet. To achieve this effect, the C content is preferably 0.0005% or more, and more preferably 0.0010% or more.

[0082] Si: more than 3.50% and less than 4.50%

[0083] Si (silicon) is an element that increases the electrical resistance of steel and reduces eddy current loss, thereby improving the iron loss of non-oriented electromagnetic steel sheets. In addition, Si has a large solid solution strengthening ability, so it is also an element effective in increasing the strength of non-oriented electromagnetic steel sheets. In order to achieve these effects, the Si content is set to more than 3.50%. Preferably, the Si content is 3.60% or more, more preferably 3.70% or more, and even more preferably 3.80% or more. On the other hand, when the Si content is excessive, the workability will be significantly deteriorated, making cold rolling difficult. Therefore, the Si content is set to 4.50% or less. Preferably, the Si content is 4.40% or less, and more preferably 4.30% or less.

[0084] Mn: less than 0.60%

[0085] Mn (manganese) is an element effective in increasing the electrical resistance of steel, reducing eddy current loss, and improving the iron loss of non-oriented electrical steel sheets. However, because Mn has a lower solid solution strengthening ability than Si and Al, a large amount of Mn must be included to achieve high strength, which significantly reduces magnetic flux density. Therefore, the Mn content is set to less than 0.60%. Preferably, the Mn content is 0.55% or less, and more preferably, 0.50% or less. There is no need to set a lower limit for the Mn content, but to achieve the above-mentioned effects, the Mn content is preferably set to 0.10% or more, and more preferably, 0.20% or more.

[0086] Al: 0.30~0.90%

[0087] Al (aluminum) is an element that has the effect of reducing eddy current loss by increasing the electrical resistance of steel, thereby improving the iron loss of non-oriented electromagnetic steel sheets. Although Al is not as effective as Si, it contributes to the high strength of non-oriented electromagnetic steel sheets due to solid solution strengthening. Furthermore, the addition of an appropriate amount of Al has the effect of suppressing the refinement of AlN formed by combining with N in the steel and improving the grain growth during final annealing. To achieve these effects, the Al content is set to 0.30% or more. Preferably, the Al content is 0.40% or more, more preferably, it exceeds 0.45%, and even more preferably, it is 0.50% or more. On the other hand, when the Al content is excessive, the toughness deteriorates and the risk of fracture during cold rolling increases. Therefore, the Al content is set to 0.90% or less. Preferably, the Al content is 0.80% or less, and more preferably, it is 0.70% or less.

[0088] In this embodiment, the electrical resistance of the steel is ensured by appropriately controlling the contents of Si, Al, and Mn. In addition, from the perspective of ensuring strength, it is also necessary to appropriately control the contents of Si, Al, and Mn. On the other hand, from the perspective of ensuring magnetic flux density and toughness, an upper limit is also required. Therefore, the contents of Si, Al, and Mn are respectively within the above-mentioned ranges, and furthermore, the following formula (i) needs to be satisfied. Regarding the middle value of the following formula (i), it is preferably 4.3 or more, more preferably 4.4 or more, preferably 4.8 or less, and more preferably 4.7 or less.

[0089] 4.2≤Si+Al+0.5×Mn≤4.9···(i)

[0090] The element symbols in the above formulas represent the content (mass %) of each element.

[0091] P: 0.030% or less

[0092] Phosphorus (P) is contained in steel as an impurity. Excessive P content significantly reduces the toughness of non-oriented electrical steel sheets. Therefore, the P content is set to 0.030% or less. Preferably, the P content is 0.025% or less, and more preferably, 0.020% or less. Furthermore, extreme reductions in the P content may increase manufacturing costs. Therefore, the P content is preferably 0.003% or more, and more preferably 0.005% or more.

[0093] S: 0.0018% or less

[0094] S (sulfur) is an element that forms fine MnS precipitates, increasing iron loss and degrading the magnetic properties of non-oriented electrical steel sheets. Therefore, the S content is set to 0.0018% or less. Preferably, the S content is 0.0016% or less, and more preferably, 0.0014% or less. Furthermore, an extreme reduction in the S content may increase manufacturing costs. Therefore, the S content is preferably 0.0001% or more, more preferably 0.0003% or more, and even more preferably 0.0005% or more.

[0095] N: 0.0040% or less

[0096] N (nitrogen) is an element that inevitably incorporates into steel. It 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. Preferably, the N content is 0.0030% or less, and more preferably, 0.0020% or less. Furthermore, extreme reductions in the N content may increase manufacturing costs, so the N content is preferably set to 0.0005% or more.

[0097] Ti: less than 0.0040%

[0098] Ti (titanium) is an element that inevitably incorporates into steel and can combine with carbon or nitrogen to form precipitates (carbides, nitrides). When carbides or nitrides form, these precipitates themselves degrade the magnetic properties of the non-oriented electrical steel sheet. Furthermore, they hinder grain growth during final annealing, degrading the magnetic properties of the non-oriented electrical steel sheet. Therefore, the Ti content is set to less than 0.0040%. Preferably, the Ti content is 0.0030% or less, and more preferably, 0.0025% or less. Furthermore, extreme reductions in the Ti content may increase manufacturing costs, so the Ti content is preferably set to 0.0005% or more.

[0099] Nb: less than 0.0050%

[0100] Nb (niobium) is an element that contributes to high strength by combining with carbon or nitrogen to form precipitates (carbides and nitrides). However, these precipitates themselves degrade the magnetic properties of non-oriented electrical steel sheets. Therefore, the Nb content is set to less than 0.0050%. Preferably, the Nb content is 0.0040% or less, more preferably 0.0030% or less, and even more preferably 0.0020% or less. Furthermore, extreme reductions in the Nb content may increase manufacturing costs, so the Nb content is preferably set to 0.0001% or more.

[0101] Zr: less than 0.0050%

[0102] Zr (zirconium) is an element that contributes to high strength by combining with carbon or nitrogen to form precipitates (carbides and nitrides). However, these precipitates themselves degrade the magnetic properties of non-oriented electrical steel sheets. Therefore, the Zr content is set to less than 0.0050%. Preferably, the Zr content is 0.0040% or less, more preferably 0.0030% or less, and even more preferably 0.0020% or less. Furthermore, extreme reductions in the Zr content may increase manufacturing costs, so the Zr content is preferably set to 0.0001% or more.

[0103] V: less than 0.0050%

[0104] V (vanadium) is an element that contributes to high strength by combining with carbon or nitrogen to form precipitates (carbides and nitrides). However, these precipitates themselves degrade the magnetic properties of non-oriented electrical steel sheets. Therefore, the V content is set to less than 0.0050%. Preferably, the V content is 0.0040% or less, more preferably 0.0030% or less, and even more preferably 0.0020% or less. Furthermore, extreme reductions in the V content may increase manufacturing costs, so the V content is preferably set to 0.0001% or more.

[0105] Cu: less than 0.200%

[0106] Cu (copper) is an element that is inevitably mixed into steel. When Cu is intentionally contained, the manufacturing cost of the non-oriented electrical steel sheet increases. Therefore, in this embodiment, there is no need to actively contain Cu; the impurity level is sufficient. The Cu content is set to be less than the maximum value that can be inevitably mixed in during the manufacturing process, that is, 0.200%. Preferably, the Cu content is 0.150% or less, and more preferably, 0.100% or less. In addition, the lower limit of the Cu content is not particularly limited, but an extreme reduction in the Cu content may lead to an increase in manufacturing costs. Therefore, the Cu content is preferably 0.001% or more, more preferably 0.003% or more, and even more preferably 0.005% or more.

[0107] Ni: less than 0.500%

[0108] Nickel (Ni) is an element that inevitably mixes into steel. However, Ni also increases the strength of non-oriented electrical steel sheets and can be intentionally contained. However, Ni is expensive, so the Ni content is set to less than 0.500%. Preferably, the Ni content is 0.400% or less, and more preferably, 0.300% or less. The lower limit of the Ni content is not specifically defined, but an extreme reduction in the Ni content may increase manufacturing costs. Therefore, the Ni content is preferably 0.001% or more, more preferably 0.003% or more, and even more preferably 0.005% or more. Furthermore, when intentionally contained, the Ni content is preferably 0.200% or more.

[0109] Total of one or both of Sn and Sb: 0.005 to 0.060%

[0110] Sn (tin) and Sb (antimony) have the effect of improving the texture and increasing the magnetic flux density of the non-oriented electromagnetic steel sheet. In addition, they are also useful elements for ensuring low iron loss in the non-oriented electromagnetic steel sheet by segregating on the surface of the base material and suppressing oxidation and nitridation during annealing. In order to achieve these effects, the total content of one or both of Sn and Sb is set to 0.005% or more. Preferably, the above total content is 0.010% or more, and more preferably, it is 0.015% or more. On the other hand, when the total content of Sn and Sb is excessive, the toughness of the steel decreases and cold rolling becomes difficult. Therefore, the total content of one or both of Sn and Sb is set to 0.060% or less. Preferably, the above total content is 0.050% or less, and more preferably, it is 0.040% or less.

[0111] In the chemical composition of the base material of the non-oriented electrical steel sheet of the present invention, the remainder is Fe and impurities. Here, "impurities" refer to components that may be introduced during industrial steel production due to various factors, such as raw materials such as ore and scrap, or during the manufacturing process. These components are permissible within a range that does not adversely affect the present invention.

[0112] The contents of Cr and Mo as impurity elements are not specifically specified. In the non-oriented electrical steel sheet of this embodiment, even if these elements are contained within a range of 0.5% or less, there is no particular effect on the properties of the non-oriented electrical steel sheet of this embodiment. Furthermore, even if Ca and Mg are contained within a range of 0.002% or less, there is no particular effect on the properties of the non-oriented electrical steel sheet of this embodiment. Even if rare earth elements (REM) are contained within a range of 0.004% or less, there is no particular effect on the properties of the non-oriented electrical steel sheet of this embodiment. In this embodiment, REM refers to a total of 17 elements consisting of Sc, Y, and lanthanoids, and the REM content mentioned above refers to the total content of these elements.

[0113] O is also an impurity element, but even if it is contained within a range of 0.035% or less, it will not affect the properties of the non-oriented electrical steel sheet of this embodiment. O may also be mixed into the steel during the annealing process. Therefore, even if it is contained within a range of 0.010% or less in the slab stage (i.e., ladle value), it will not have a particular effect on the properties of the non-oriented electrical steel sheet of this embodiment.

[0114] Furthermore, in addition to the above elements, Zn, Pb, Bi, As, B, Se and other elements may be contained as impurity elements. However, when the content of each is within the range of 0.0050% or less, the characteristics of the non-oriented electrical steel sheet of this embodiment are not impaired.

[0115] The chemical composition of the base material of the non-oriented electrical steel sheet of this embodiment can be determined using various known measurement methods. For example, it can be determined using ICP emission spectrometry, gravimetric analysis, or spark discharge emission spectrometry. Furthermore, C and S can be determined using the combustion-infrared absorption method, N using the inert gas combustion-heat conduction method, and O using the inert gas fusion-non-dispersive infrared absorption method.

[0116] 3. Crystal size

[0117] In this embodiment, the average crystal grain size of the base material is set to be greater than 40 μm and less than 140 μm. By setting the average crystal grain size of the base material to be greater than 40 μm, the deterioration of hysteresis loss can be suppressed and the magnetic properties can be improved. On the other hand, by setting the average crystal grain size to be less than 140 μm, the strength of the steel can be improved and the deterioration of the iron loss caused by the increase in eddy current loss can be suppressed. Preferably, the average crystal grain size is greater than 50 μm, more preferably, greater than 60 μm. In addition, preferably, the average crystal grain size is less than 130 μm, more preferably, less than 120 μm.

[0118] In the present invention, the average crystal grain size of the base material is determined in accordance with JIS G 0551:2013 “Steel—Microscopic testing method for grain size”.

[0119] 4. Texture

[0120] In this embodiment, the development of texture that degrades magnetic properties is suppressed. Specifically, the degree of concentration of the {111} orientation is set to 4.0 or less. By suppressing the development of the {111} orientation, the magnetic properties can be improved. Preferably, the degree of concentration of the {111} orientation is 3.8 or less, and more preferably, 3.6 or less. There is no need to set a lower limit for the degree of concentration of the {111} orientation, but 1.0 is a practical lower limit.

[0121] The degree of aggregation of the {111} orientation is measured by an X-ray diffraction device. In addition, the so-called aggregation degree refers to the value obtained by measuring the X-ray intensity of a standard sample and a test material that do not have aggregation in a specific orientation by the X-ray diffraction method under the same conditions, and dividing the obtained X-ray intensity of the test material by the X-ray intensity of the standard sample. The specific measurement method is as follows. The measurement is carried out on the polished surface after the base material of the non-oriented electromagnetic steel plate of the test material is removed from the single-side surface to a depth of 1 / 4 of the plate thickness by chemical polishing. The degree of aggregation of the {111} orientation is based on the extreme point diagram of the {200} plane, {110} plane, {310} plane, and {211} plane of the α-Fe phase measured by the X-ray diffraction device, and is calculated according to the crystal orientation distribution function ODF (Orientation Distribution Functions) representing the three-dimensional texture calculated by the series expansion method. Displayed in the ODF The cross section has Φ = 55°, The average value of the aggregation degree is defined as the aggregation degree of {111} orientation. The degree of aggregation was measured at 5° intervals, and the average value of 19 degrees of aggregation from 0° to 90° was used.

[0122] In addition, the {111} orientation is sometimes classified into {111}<011> orientation and {111}<112> orientation. However, the degree of aggregation of the {111}<011> orientation is not shown in the ODF. The cross section of Φ=55°, only The aggregation value of the {111}<112> orientation is shown in the ODF. The cross section of Φ=55°, only Therefore, they are consistent with the values ​​of the degree of aggregation shown in the ODF of this application. The cross section is Φ=55°, The average value of the degree of aggregation, representing the degree of aggregation of the {111} orientation, was determined by different methods.

[0123] 5.Magnetic properties

[0124] In the non-oriented electrical steel sheet of this embodiment, the excellent magnetic properties mean that the iron loss W 10 / 400 Lower, magnetic flux density B 50 Higher.

[0125] Here, the magnetic properties (iron loss W 10 / 400 and magnetic flux density B 50 ) was measured according to the Epstein test method specified in JIS C 2550-1:2011. In addition, at this time, the density of the steel plate was set to 7.65 g / cm 3 To carry out magnetic measurement. In addition, the iron loss W 10 / 400 This means the iron loss generated under the conditions of maximum magnetic flux density of 1.0T and frequency of 400Hz, magnetic flux density B 50 This means the magnetic flux density in a magnetic field of 5000 A / m.

[0126] In the non-oriented electromagnetic steel sheet of this embodiment, the iron loss W 10 / 400 Low means that when the plate thickness is 0.26mm or more, it is 14.5W / kg or less, when the plate thickness is 0.21-0.25mm, it is 12.5W / kg or less, and when the plate thickness is 0.20mm or less, it is 11.2W / kg or less. 50 Higher means that when the plate thickness is 0.26 mm or more, it is 1.64 T or more, when the plate thickness is 0.21 to 0.25 mm, it is 1.63 T or more, and when the plate thickness is 0.20 mm or less, it is 1.62 T or more.

[0127] 6. Mechanical characteristics

[0128] The non-oriented electrical steel sheet of this embodiment has high strength. While the tensile strength is not particularly limited, it is preferably 580 MPa or higher. More preferably, it is 590 MPa or higher, and even more preferably, 600 MPa or higher. The tensile strength is measured by a tensile test in accordance with JIS Z 2241:2011.

[0129] 7.Plate thickness

[0130] In the non-oriented electrical steel sheet of this embodiment, the base material thickness is set to 0.10 mm or greater from the perspective of manufacturing costs during cold rolling and final annealing. On the other hand, from the perspective of reducing iron loss, the base material thickness is set to 0.30 mm or less. Therefore, the base material thickness of the non-oriented electrical steel sheet of this embodiment is 0.10 to 0.30 mm. The base material thickness is preferably 0.15 to 0.27 mm.

[0131] 8. Insulation film

[0132] In the non-oriented electrical steel sheet of this embodiment, it is preferable to have an insulating coating on the surface of the base material. Since the non-oriented electrical steel sheets are used after punching out the core blanks and then stacking them, providing the insulating coating on the surface of the base material can reduce eddy currents between the sheets and reduce eddy current losses in the core.

[0133] There are no particular limitations on the type of insulating coating, and any known insulating coating used as an insulating coating for non-oriented electrical steel sheets can be used. Examples of such insulating coatings include composite insulating coatings primarily composed of inorganic substances and also containing organic substances. A composite insulating coating herein refers to an insulating coating primarily composed of at least one of an inorganic substance such as a metal chromate, a metal phosphate, colloidal silica, a Zr compound, or a Ti compound, in which fine organic resin particles are dispersed. In particular, from the perspective of reducing the environmental burden during manufacturing, which has been in high demand in recent years, insulating coatings using metal phosphates, Zr or Ti coupling agents, or their carbonates or ammonium salts as starting materials are preferred.

[0134] The amount of the insulating film applied is not particularly limited, but is preferably 200 to 3000 mg / m2 per side. 2 More preferably, it is set to 300 to 2500 mg / m per side. 2 By forming the insulating film so that the adhesion amount falls within the above range, excellent uniformity can be maintained. Furthermore, when measuring the adhesion amount of the insulating film afterwards, various known measurement methods can be used, such as a method of measuring the mass difference before and after immersion in a sodium hydroxide aqueous solution, or a fluorescent X-ray method using a calibration curve method.

[0135] 9. Manufacturing method

[0136] The non-oriented electrical steel sheet of this embodiment is not particularly limited in its manufacturing method. However, it can be manufactured by, for example, sequentially performing a hot rolling step, a hot-rolled sheet annealing step, a descaling step, a cold rolling step, and a final annealing step under the conditions shown below using a steel ingot having the above-described chemical composition. Furthermore, when an insulating film is formed on the surface of the base material, the insulating film forming step is performed after the final annealing step. Each step is described in detail below.

[0137] Hot rolling process

[0138] The steel ingot (slab) having the above chemical composition is heated and hot-rolled to obtain a hot-rolled plate. The heating temperature of the steel ingot during hot rolling is not particularly specified, but is preferably set to 1050-1250°C, for example. The thickness of the hot-rolled plate after hot rolling is not particularly specified, but is preferably set to approximately 1.5-3.0 mm, for example, taking into account the final thickness of the base material.

[0139] Hot-rolled sheet annealing process

[0140] Then, hot-rolled plate annealing is performed for the purpose of reducing the iron loss of the steel plate. For hot-rolled plate annealing, it is preferable to use a continuous annealing furnace, which has higher productivity and higher homogeneity of the metal structure after annealing compared to batch annealing. In addition, as mentioned above, when the Si content in the steel plate is high and the plate thickness needs to be reduced in order to reduce the iron loss, it is preferable to lower the soaking temperature in the hot-rolled plate annealing. Therefore, the hot-rolled plate annealing is carried out under the conditions of a soaking temperature of 800 to 920°C and a soaking time of 1 second to 10 minutes. In order to obtain good magnetic properties, it is preferably above 820°C. In order to obtain good toughness, it is preferably below 900°C.

[0141] Descaling process

[0142] After the hot-rolled steel sheet is annealed, it is shot peened and then pickled to remove the scale layer formed on the surface of the base material. Since the scale layer develops during the hot-rolled steel sheet annealing, shot peening before pickling facilitates descaling during the subsequent pickling. The pickling conditions, such as the concentration of the pickling acid, the concentration of the pickling accelerator, and the temperature of the pickling solution, are not particularly limited and can be conventional pickling conditions.

[0143] Cold rolling process

[0144] The descaled steel sheet is then cold-rolled at a reduction ratio such that the final thickness of the base material becomes 0.10 to 0.30 mm.

[0145] <Final annealing process>

[0146] After the cold rolling, final annealing is performed. In the method for producing a non-oriented electrical steel sheet according to this embodiment, a continuous annealing furnace is preferably used for the final annealing. The final annealing is performed at a soaking temperature of 900-1050°C and a soaking time of 1 second to 10 minutes. The atmosphere is preferably a mixed atmosphere of H2 and N2 with an H2 ratio of 1-100% by volume (i.e., H2+N2=100% by volume), with a dew point of -50-+10°C.

[0147] A soaking temperature below 900°C results in a smaller grain size and reduced iron loss, which is not preferred. A soaking temperature exceeding 1050°C also results in insufficient strength and reduced iron loss, which is also not preferred. Furthermore, soaking times of less than 1 second prevent sufficient grain growth. On the other hand, soaking times exceeding 10 minutes increase manufacturing costs.

[0148] In this embodiment, rapid heating is performed in the final annealing step to suppress the development of a texture that is detrimental to magnetic properties. Therefore, in the final annealing step, heating is performed to a temperature of 850°C or higher, with a heating rate of 400°C / s or higher in the temperature range of 500-850°C.

[0149] By setting the heating rate to 400°C / s or more, the development of textures that are detrimental to magnetic properties can be suppressed. The heating rate is preferably 800°C / s or more, more preferably 1000°C or more. The faster the heating rate, the better, so there is no need to set an upper limit in particular, but considering the constraints on the equipment, it is preferred that the heating rate be 2000°C / s or less. In addition, as described above, the magnetic properties can be improved by rapidly heating to a temperature of 850°C or more. In addition, it is also possible to set the average heating rate to 1 to 2000°C / s in the temperature range of less than 500°C and in the entire heating process including the soaking temperature.

[0150] Furthermore, rapid heating under the above conditions is difficult with conventional direct heating using gas combustion, radiant tubes, electric heaters, etc. Therefore, in this embodiment, it is preferable to use electric heating, induction heating, etc.

[0151] <Insulation film forming process>

[0152] After the final annealing, an insulating film forming step is performed as needed. The insulating film forming method is not particularly limited; a known insulating film forming treatment solution, such as the one described below, can be used, and the treatment solution can be applied and dried using known methods. Examples of known insulating films include composite insulating films primarily composed of inorganic substances and also containing organic substances.

[0153] A composite insulation coating refers to an insulation film primarily composed of at least one of a metal salt such as a metal chromate or metal phosphate, or an inorganic substance such as colloidal silica, a Zr compound, or a Ti compound, dispersed with fine organic resin particles. In particular, from the perspective of reducing the environmental burden during manufacturing, which has been in high demand in recent years, insulation coatings using metal phosphates, Zr, or Ti coupling agents as starting materials, or using metal phosphates, Zr, or Ti coupling agents as carbonates or ammonium salts as starting materials, are preferred.

[0154] The surface of the base material on which the insulating coating is to be formed may be subjected to any pretreatment, such as degreasing with alkali or the like, or pickling with hydrochloric acid, sulfuric acid, phosphoric acid, or the like, before the treatment liquid is applied. Alternatively, the treatment liquid may be applied to the surface of the base material after final annealing without performing any of these pretreatments.

[0155] The non-oriented electromagnetic 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 either a rotor core or a stator.

[0156] Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

[0157] Example

[0158] After heating a billet having the chemical composition shown in Table 1 to 1150°C, hot rolling was performed at a final temperature of 850°C and a final thickness of 2.0 mm, followed by coiling at 600°C to produce hot-rolled steel sheets. The resulting hot-rolled steel sheets were annealed in a continuous annealing furnace under the conditions shown in Table 2. The resulting steel sheets were descaled by shot peening and pickling, and then cold rolled to produce cold-rolled steel sheets having the thickness shown in Table 2.

[0159] Furthermore, final annealing was performed under the conditions shown in Table 2 in a mixed atmosphere of 20% H2, 80% N2, and a dew point of -30°C. Induction heating was used for temperature increase during final annealing, with rapid heating to the target temperature shown in Table 2. Radiant tube heating was used for the temperature increase and soaking steps from the target temperature to the soaking temperature. The rate of temperature increase from the target temperature to the soaking temperature was approximately 5°C / s. The steel sheets after final annealing were coated with an insulating coating composed of aluminum phosphate and an acrylic-styrene copolymer resin emulsion with a particle size of 0.2μm, and then fired in air at 350°C.

[0160] [Table 1]

[0161]

[0162] [Table 2]

[0163]

[0164] Underlined elements are outside the scope of the present invention.

[0165] The #1 heating rate indicates the heating rate in the temperature range of 500 to 850°C.

[0166] #2 indicates the temperature reached during rapid heating.

[0167] For each test material obtained, the average crystal grain size of the base material was measured according to JIS G 0551:2013 "Steel - Microscopic testing methods for grain size". In addition, Epstein test pieces were taken from the rolling direction and width direction of each test material, and the iron loss W was measured by the Epstein test based on JIS C 2550-1:2011. 10 / 400 and magnetic flux density B 50 The density of the steel plate was set to 7.65 g / cm 3 Magnetic measurements were performed.

[0168] In the polished surface of each test material, after the base material was removed from one side surface to a depth of 1 / 4 of the plate thickness by chemical polishing, the concentration of the {111} orientation was determined based on the extreme point diagram of the {200}, {110}, {310}, and {211} planes of the α-Fe phase measured by an X-ray diffractometer, and from the crystal orientation distribution function (ODF) representing the three-dimensional texture calculated using the series expansion method.

[0169] Next, JIS No. 5 tensile test pieces were taken from each test material in accordance with JIS Z 2241: 2011, with the longitudinal direction aligned with the rolling direction of the steel plate. Tensile tests were then conducted using these test pieces in accordance with JIS Z 2241: 2011, and the tensile strength was measured.

[0170] The above results are shown in Table 2.

[0171] In Test Nos. 2, 3, 5, 6, 9, 12, 15, 17, 22, 25, 27, and 28, which satisfy the requirements of the present invention, it can be seen that the iron loss W 10 / 400 Lower, magnetic flux density B 50 It is relatively high and has a high tensile strength of more than 580 MPa.

[0172] On the other hand, in the comparative examples Test Nos. 1, 4, 7, 8, 10, 11, 13, 14, 16, 18 to 21, 23, 24, 26, and 29, the iron loss W 10 / 400 Poor or magnetic flux density B 50 Poor or poor tensile strength, significantly deteriorated toughness, and more difficult to manufacture.

[0173] Specifically, in Test No. 1, the heating rate during the final annealing was lower than the specified range, resulting in a concentration of the {111} orientation exceeding the specified range and poor magnetic flux density. In Test No. 4, the peak temperature during the rapid heating during the final annealing was lower than the specified range, resulting in a concentration of the {111} orientation exceeding the specified range and poor magnetic flux density.

[0174] In Test No. 7, the plate thickness exceeded the specified range, resulting in poor iron loss. In Test No. 8, the S content exceeded the specified range, resulting in increased MnS precipitation and poor iron loss. In Test No. 10, the combined Sn and Sb content was lower than the specified range, resulting in a concentration of {111} orientation exceeding the specified range and poor magnetic flux density. In Test No. 11, the combined Sn and Sb content exceeded the specified range, resulting in poor toughness and fracture during cold rolling, making it impossible to measure tensile strength and magnetic properties.

[0175] In Test No. 13, the Mn content exceeded the specified range, resulting in poor magnetic flux density. In Test No. 14, the Si+Al+0.5×Mn content was below the specified range, resulting in poor iron loss and tensile strength. In Test No. 16, the Si+Al+0.5×Mn content exceeded the specified range, resulting in poor toughness and fracture during cold rolling, making it impossible to measure tensile strength and magnetic properties.

[0176] In Test No. 18, the Si content was lower than the specified range, resulting in poor tensile strength. In Test No. 19, the Si content was higher than the specified range, resulting in poor toughness and fracture during cold rolling, making it impossible to measure tensile strength and magnetic properties. In Test No. 20, the Al content was lower than the specified range, resulting in a smaller average grain size after final annealing than the specified range, resulting in poor iron loss.

[0177] In Test No. 21, the soaking temperature during hot-rolled sheet annealing was lower than the specified range, resulting in a concentration of the {111} orientation exceeding the specified range and poor magnetic flux density. In Test No. 23, the soaking temperature during hot-rolled sheet annealing was higher than the specified range, leading to deterioration in toughness and fracture during cold rolling, making it impossible to measure tensile strength and magnetic properties. In Test No. 24, the Al content was higher than the specified range, leading to deterioration in toughness and fracture during cold rolling, making it impossible to measure tensile strength and magnetic properties.

[0178] In Test No. 26, the soaking temperature during the final annealing was lower than the specified range, the average grain size was smaller than the specified range, and the iron loss was poor. In Test No. 29, the soaking temperature during the final annealing was higher than the specified range, the average grain size was larger than the specified range, and the tensile strength was poor.

[0179] Industrial Availability

[0180] As described above, according to the present invention, a non-oriented electrical steel sheet having excellent magnetic properties and high strength can be obtained stably at low cost.

Claims

1. A non-oriented electromagnetic steel sheet, wherein the chemical composition of the base material is expressed in mass %, C: 0.0040% or less, Si: more than 3.50% and 4.50% or less, Mn: less than 0.60%, Al：0.30～0.90％， P: 0.030% or less, S: 0.0018% or less, N: 0.0040% or less, Ti: less than 0.0040%, Nb: less than 0.0050%, Zr: less than 0.0050%, V: less than 0.0050%, Cu: less than 0.200%, Ni: less than 0.500%, The total of one or two of Sn and Sb: 0.005 to 0.060%, The rest: Fe and impurities, And satisfy the following formula (i): 4.2≤Si+Al+0.5×Mn≤4.9···(i) in, The element symbols in the above formula are the content of each element (mass %), The average crystal grain size of the base material exceeds 40 μm and is less than 140 μm; The degree of concentration of the {111} orientation at a position 1 / 4 of the plate thickness from the surface of the base material is 4.0 or less; The thickness of the base material is 0.10 to 0.30 mm.

2. The non-oriented electrical steel sheet according to claim 1, wherein: The tensile strength is 580 MPa or more.

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

4. A method for producing a non-oriented electrical steel sheet, comprising: producing the non-oriented electrical steel sheet according to any one of claims 1 to 3; The steel ingots are sequentially subjected to the following steps: a hot rolling step; a hot rolled plate annealing step at a soaking temperature of 800-920°C and a soaking time of 1 second to 10 minutes; a descaling step of pickling after shot blasting; a cold rolling step of reducing the plate to a thickness of 0.10-0.30 mm; and a final annealing step of heating to a temperature of 850°C or higher at a heating rate of 400-2000°C / s within a temperature range of 500-850°C, followed by a soaking temperature of 900-1050°C and a soaking time of 1 second to 10 minutes. The steel ingot has the following chemical composition: in mass %, C: 0.0040% or less, Si: more than 3.50% and 4.50% or less, Mn: less than 0.60%, Al：0.30～0.90％， P: 0.030% or less, S: 0.0018% or less, N: 0.0040% or less, Ti: less than 0.0040%, Nb: less than 0.0050%, Zr: less than 0.0050%, V: less than 0.0050%, Cu: less than 0.200%, Ni: less than 0.500%, The total of one or two of Sn and Sb: 0.005 to 0.060%, The rest: Fe and impurities, And satisfy the following formula (i), 4.2≤Si+Al+0.5×Mn≤4.9· · · (i) in, The element symbols in the above formulas represent the content (mass %) of each element.

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