Non-oriented electrical steel sheet and its manufacturing method

Abstract

Provided is a non-oriented electrical steel sheet, wherein: the chemical composition of a base material contains, in mass%, 0.0040% or less of C, greater than 3.50%-4.50% of Si (exclusive of 3.50%), 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 the total of one or two among Sn and Sb, with the remainder comprising Fe and impurities; the chemical composition satisfies [4.2≤Si+Al+0.5×Mn≤4.9]; the average crystal particle diameter of the base material is greater than 40 μm but less than or equal to 140 μm; the integration degree in the ｛111｝-orientation is 4.0 or less; and the plate thickness of the base material is 0.10-0.30 mm.

Description

[Technical Field]

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

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

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

[0004] The motor cores of the various motors mentioned above are made up of a stator, which is the stationary 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 (low iron loss and high magnetic flux density), 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 separate non-oriented electrical steel sheets for the stator and rotor. However, preparing two types of non-oriented electrical steel sheets complicates the core manufacturing process and reduces yield. Therefore, non-oriented electrical steel sheets with excellent magnetic properties and strength have been studied to achieve the low iron loss and high strength required for the rotor while also achieving the low iron loss and high magnetic flux density required for the stator.

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

[0007] [Patent Document 1] International Publication No. 2019 / 017426 [Patent Document 2] International Publication No. 2020 / 091039 [Patent Document 3] International Publication No. 2020 / 091043 [Patent Document 4] Japanese Patent Application Laid-Open No. 2010-90474 Summary of the Invention [Problem to be solved by the invention]

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

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

[0010] The present invention relates to the following non-oriented electrical steel sheet and a method for producing the same.

[0011] (1) The chemical composition of the base material is, in mass%, C: 0.0040% or less, Si: more than 3.50% and less than 4.50%, 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% Sn and Sb: 0.005 to 0.060% The balance is Fe and impurities. 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, The degree of accumulation of the {111} orientation at a position of 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. Non-oriented electrical steel sheet. 4.2≦Si+Al+0.5×Mn≦4.9 (i) In the above formula, the element symbols indicate the content (mass %) of each element.

[0012] (2) Tensile strength is 580 MPa or more; The non-oriented electrical steel sheet according to (1) above.

[0013] (3) The base material has an insulating coating on its surface. The non-oriented electrical steel sheet according to (1) or (2) above.

[0014] (4) A method for producing a non-oriented electrical steel sheet according to any one of (1) to (3) above, In mass%, C: 0.0040% or less, Si: more than 3.50% and less than 4.50%, 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% Sn and Sb: 0.005 to 0.060% The balance is Fe and impurities. For a steel ingot having a chemical composition that satisfies the following formula (i), The hot rolling process, the hot-rolled sheet annealing process in which the soaking temperature is 800 to 920°C and the soaking time is 1 second to 10 minutes, the descaling process in which the sheet is shot blasted and then pickled, the cold rolling process in which the sheet is reduced to a thickness of 0.10 to 0.30 mm, and the final annealing process in which the sheet is heated to a temperature of 850°C or higher at a heating rate of 400°C / s or higher in the temperature range of 500 to 850°C, and then the soaking temperature is 900 to 1050°C and the soaking time is 1 second to 10 minutes are carried out in this order. Manufacturing method for non-oriented electrical steel sheets. 4.2≦Si+Al+0.5×Mn≦4.9 (i) However, the element symbols in the above formula indicate the content (mass %) of each element. [Effects of the Invention]

[0015] According to the present invention, it is possible to stably obtain non-oriented electrical steel sheets having excellent magnetic properties and high strength. DETAILED DESCRIPTION OF THE INVENTION

[0016] 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.

[0017] To obtain non-oriented electrical steel sheets with low core loss, high magnetic flux density, and high strength while maintaining toughness during cold rolling, it is necessary to optimize the contents of the main alloying elements Si, Mn, and Al.

[0018] Specifically, the Si content is set to more than 3.50% and not more than 4.50%, as Si has the highest solid solution strengthening ability and contributes most to increasing electrical resistance. Additionally, to improve grain growth and obtain consistently excellent magnetic properties, the Al content is set to 0.30% or more. On the other hand, to prevent deterioration of toughness, the Al content is set to 0.90% or less.

[0019] Furthermore, Mn has the lowest solid solution strengthening ability of the three elements, but it contributes to increasing electrical resistance with little deterioration in toughness. However, as a result of extensive research, the inventors have found that if Mn, which has a lower solid solution strengthening ability than Si and Al, is included in excess, the magnetic flux density decreases significantly compared to the increase in strength, and if the Mn content is high, it becomes difficult to stably improve the magnetic properties. Therefore, the Mn content is set to less than 0.60%.

[0020] In the manufacturing 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 desirable to lower the soaking temperature in the hot-rolled sheet annealing in order to suppress problems such as sheet breakage and edge cracking during cold rolling. On the other hand, it is known that the magnetic flux density increases as the soaking temperature in the hot-rolled sheet annealing increases, and lowering the soaking temperature results in a decrease in magnetic flux density.

[0021] Therefore, the present inventors have investigated a method for improving magnetic flux density while lowering the soaking temperature during annealing of a hot-rolled sheet. As a result, they have found that rapid heating during finish annealing after cold rolling makes it possible to suppress the development of texture that is detrimental to magnetic properties, and that even when the soaking temperature during annealing of a hot-rolled sheet is low, a decrease in magnetic flux density can be suppressed.

[0022] Furthermore, the inventors conducted experiments in which rapid heating was performed to various ultimate temperatures, and found that rapid heating did not have any effect on improving the magnetic properties when the ultimate temperature was low, but that rapid heating to a temperature of 850°C or higher improved the magnetic properties.

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

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

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

[0026] C: 0.0040% or less C (carbon) is an element that causes deterioration of iron loss in 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 obtained. Therefore, the C content is set to 0.0040% or less. The C content is preferably 0.0035% or less, and more preferably 0.0030% or less. Note that C contributes to increasing the strength of non-oriented electrical steel sheets, so if this effect is desired, the C content is preferably 0.0005% or more, and more preferably 0.0010% or more.

[0027] Si: more than 3.50% and less than 4.50% Silicon (Si) 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, and more preferably 4.30% or less.

[0028] Mn: Less than 0.60% Manganese (Mn) is an element that increases the electrical resistance of steel, reduces eddy current loss, and is effective in improving the iron loss of non-oriented electrical steel sheets. However, since Mn has a poorer solid-solution strengthening ability than Si and Al, a large amount of Mn is required to achieve high strength, which significantly reduces magnetic flux density. Therefore, the Mn content is set to less than 0.60%. The Mn content is preferably 0.55% or less, 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 effects, the Mn content is preferably 0.10% or more, and more preferably 0.20% or more.

[0029] Al: 0.30 to 0.90% Aluminum (Al) 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 inhibits 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 0.30% or more. The Al content is preferably 0.40% or more, more preferably more than 0.45%, and even more preferably 0.50% or more. On the other hand, excessive Al content reduces toughness and increases the risk of fracture during cold rolling. Therefore, the Al content is set to 0.90% or less. The Al content is preferably 0.80% or less, and more preferably 0.70% or less.

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

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

[0032] P:0.030% or less P (phosphorus) is contained in steel as an impurity, and excessive P content significantly reduces the toughness of non-oriented electrical steel sheet. 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. However, since an extreme reduction in the P content may increase manufacturing costs, the P content is preferably 0.003% or more, and more preferably 0.005% or more.

[0033] S: 0.0018% 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 0.0018% or less. The S content is preferably 0.0016% or less, and more preferably 0.0014% or less. However, since an excessive reduction in the S content may increase manufacturing costs, the S content is preferably 0.0001% or more, more preferably 0.0003% or more, and even more preferably 0.0005% or more.

[0034] N: 0.0040% or less N (nitrogen) is an element that is inevitably mixed into steel and forms nitrides, increasing iron loss and degrading the magnetic properties of non-oriented electrical steel sheets. Therefore, the N content is set to 0.0040% or less. The N content is preferably 0.0030% or less, and more preferably 0.0020% or less. However, since an extreme reduction in the N content may increase manufacturing costs, the N content is preferably 0.0005% or more.

[0035] Ti: less than 0.0040% Titanium (Ti) 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, and more preferably 0.0025% or less. Because excessively low Ti content can increase manufacturing costs, the Ti content is preferably 0.0005% or more.

[0036] Nb: less than 0.0050% Nb (niobium) 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 Nb content is set to less than 0.0050%. The Nb content is preferably 0.0040% or less, more preferably 0.0030% or less, and even more preferably 0.0020% or less. However, because an excessive reduction in the Nb content can increase manufacturing costs, the Nb content is preferably 0.0001% or more.

[0037] Zr: Less than 0.0050% 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 0.0050%. The Zr content is preferably 0.0040% or less, more preferably 0.0030% or less, and even more preferably 0.0020% or less. However, because an excessively low Zr content can increase manufacturing costs, the Zr content is preferably 0.0001% or more.

[0038] V: Less than 0.0050% Vanadium (V) 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 0.0050%. The V content is preferably 0.0040% or less, more preferably 0.0030% or less, and even more preferably 0.0020% or less. However, because an excessive reduction in the V content can increase manufacturing costs, the V content is preferably 0.0001% or more.

[0039] Cu: Less than 0.200% Cu (copper) is an element that is inevitably mixed into steel. Intentional inclusion of Cu increases the manufacturing cost of the non-oriented electrical steel sheet. Therefore, in this embodiment, it is not necessary to actively include Cu; it is sufficient to include 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, and more preferably 0.100% or less. Note that the lower limit of the Cu content is not particularly limited, but an extreme reduction in the Cu content may increase 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.

[0040] Ni: Less than 0.500% Ni (nickel) is an element that is inevitably mixed into steel. However, since Ni also improves the strength of non-oriented electrical steel sheets, it may be intentionally added. However, because Ni is expensive, the Ni content is set to less than 0.500%. The Ni content is preferably 0.400% or less, and more preferably 0.300% or less. There is no particular lower limit for the Ni content, but an extreme reduction in the Ni content may result in an increase in 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, if Ni is intentionally added, the Ni content is preferably 0.200% or more.

[0041] Sn and Sb: 0.005 to 0.060% Sn (tin) and Sb (antimony) have the effect of improving the texture and increasing the magnetic flux density of non-oriented electrical steel sheets. They are also useful elements for ensuring low iron loss in non-oriented electrical steel sheets by segregating to the surface of the base material and suppressing oxidation and nitriding during annealing. To achieve these effects, the total content of one or both of Sn and Sb is set to 0.005% or more. The total content is preferably 0.010% or more, and more preferably 0.015% or more. On the other hand, if the total content of Sn and Sb is excessive, the toughness of the steel decreases, making cold rolling difficult. Therefore, the total content of one or both of Sn and Sb is set to 0.060% or less. The total content is preferably 0.050% or less, and more preferably 0.040% or less.

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

[0043] Note that 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 each, 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 each, 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. Note that in this embodiment, REM refers to a total of 17 elements consisting of Sc, Y, and lanthanoids, and the above REM content refers to the total content of these elements.

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

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

[0046] The chemical composition of the base material of the non-oriented electrical steel sheet according to this embodiment can be measured using various known methods. For example, it can be measured using ICP optical emission spectrometry, gravimetry, or spark discharge optical emission spectrometry. Furthermore, C and S can be measured using a combustion-infrared absorption method, N can be measured using an inert gas combustion-thermal conductivity method, and O can be measured using an inert gas fusion-non-dispersive infrared absorption method.

[0047] 3.Crystal grain size In this embodiment, the average crystal grain size of the base material is set to be more than 40 μm and not more than 140 μm. By setting the average crystal grain size of the base material to be more than 40 μm, it is possible to suppress deterioration of hysteresis loss and improve magnetic properties. On the other hand, by setting the average crystal 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 crystal grain size is preferably not less than 50 μm, and more preferably not less than 60 μm. Furthermore, the average crystal grain size is preferably not more than 130 μm, and more preferably not more than 120 μm.

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

[0049] 4. Collective organization In this embodiment, the development of texture that deteriorates magnetic properties is suppressed. Specifically, the degree of orientation of {111} is set to 4.0 or less. By suppressing the development of the {111} orientation, it is possible to improve magnetic properties. The degree of orientation of {111} is preferably 3.8 or less, and more preferably 3.6 or less. There is no need to set a lower limit for the degree of orientation of {111}, but 1.0 is a substantial lower limit.

[0050] The {111} orientation density was measured using an X-ray diffractometer. The density was calculated by measuring the X-ray intensity of a standard specimen without orientation density under the same conditions as the test specimen, and dividing the X-ray intensity of the test specimen by that of the standard specimen. The specific measurement method is as follows. The test specimen was a non-oriented electrical steel sheet, and the base material was polished by chemical polishing to remove a quarter of the sheet thickness from one side of the surface. The density of the {111} orientation was calculated from the orientation distribution functions (ODFs), which represent the three-dimensional texture, calculated using the series expansion method based on the pole figures of the {200}, {110}, {310}, and {211} planes of the α-Fe phase measured using an X-ray diffractometer. The average value of the density of φ1 = 0 to 90° at Φ = 55° on the φ2 = 45° cross section of the ODF display was defined as the density of the {111} orientation. The density of φ1 = 0 to 90° was measured at 5° intervals, and the average density of 19 samples from 0 to 90° was used.

[0051] The {111} direction is further divided into {111} <011> Orientation and <112> However, <011> The orientation accumulation is the numerical value of only the accumulation at φ1=0° at φ=55° in the φ2=45° cross section of the ODF display, and is the {111} <112> The orientation density is a numerical value for the density at Φ=55° and Φ1=30° on the Φ2=45° cross section in ODF display, and is therefore measured using a different method from the density of the {111} orientation, which is shown as the average density at Φ=55° and Φ1=0 to 90° on the Φ2=45° cross section in ODF display in the present application.

[0052] 5.Magnetic properties In the non-oriented electrical steel sheet according to this embodiment, excellent magnetic properties are obtained by reducing the iron loss W 10 / 400 is low, and the magnetic flux density B 50 means that is high.

[0053] Here, the magnetic properties (iron loss W 10 / 400 and magnetic flux density B 50) shall be measured in accordance with the Epstein test method specified in JIS C 2550-1:2011. In this case, the density of the steel plate shall be 7.65 g / cm 3 The magnetic measurement is carried out as follows. 10 / 400 means the iron loss that occurs under the condition that the maximum magnetic flux density is 1.0 T and the frequency is 400 Hz, and the magnetic flux density B 50 means the magnetic flux density in a magnetic field of 5000 A / m.

[0054] In the non-oriented electrical steel sheet according to this embodiment, iron loss W 10 / 400 Low means that the magnetic flux density B is 14.5 W / kg or less for thicknesses of 0.26 mm or more, 12.5 W / kg or less for thicknesses of 0.21 to 0.25 mm, and 11.2 W / kg or less for thicknesses of 0.20 mm or less. 50 High means that the strength is 1.64T or more for a plate thickness of 0.26mm or more, 1.63T or more for a plate thickness of 0.21 to 0.25mm, and 1.62T or more for a plate thickness of 0.20mm or less.

[0055] 6. Mechanical properties The non-oriented electrical steel sheet according to this embodiment has high strength. The tensile strength does not need to be particularly limited, but it is preferably 580 MPa or more. The tensile strength is more preferably 590 MPa or more, and even more preferably 600 MPa or more. Here, the tensile strength is measured by conducting a tensile test in accordance with JIS Z 2241:2011.

[0056] 7. Plate Thickness In the non-oriented electrical steel sheet according to this embodiment, the 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, the thickness of the base material is set to 0.30 mm or less from the viewpoint of reducing iron loss. Therefore, the thickness of the base material of the non-oriented electrical steel sheet according to this embodiment is 0.10 to 0.30 mm. The thickness of the base material is preferably 0.15 to 0.27 mm.

[0057] 8.Insulating coating In the non-oriented electrical steel sheet according to this embodiment, it is preferable that an insulating coating is 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.

[0058] The type of insulating coating is not particularly limited, and known insulating coatings used for insulating 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 their carbonates or ammonium salts as starting materials are preferred.

[0059] 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.

[0060] 9. Manufacturing method The non-oriented electrical steel sheet according to this embodiment is not particularly limited in terms of the manufacturing method, but can be manufactured by, for example, sequentially carrying out a hot rolling process, a hot-rolled sheet annealing process, a descaling process, a cold rolling process, and a finish annealing process on a steel ingot having the above-described chemical composition under the conditions shown below. Furthermore, if an insulating coating is formed on the surface of the base material, an insulating coating formation process is carried out after the finish annealing process. Each process will be described in detail below.

[0061] <Hot rolling process> 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 limited, but is preferably, for example, 1050 to 1250°C. The thickness of the hot-rolled sheet after hot rolling is also not particularly limited, but is preferably, for example, about 1.5 to 3.0 mm, taking into account the final thickness of the base material.

[0062] <Hot-rolled sheet annealing process> Thereafter, hot-rolled sheet annealing is carried out for the purpose of reducing 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 produces a highly homogeneous metal structure after annealing. Furthermore, as mentioned above, when the Si content in the steel sheet is high and it is necessary to reduce the sheet thickness to reduce iron loss, it is desirable to lower the soaking temperature in hot-rolled sheet annealing. Therefore, hot-rolled sheet annealing is carried out under conditions where the soaking temperature is 800 to 920°C and the soaking time is 1 second to 10 minutes. To obtain good magnetic properties, a soaking temperature of 820°C or higher is preferable. To obtain good toughness, a soaking temperature of 900°C or lower is preferable.

[0063] <Descaling process> The steel sheet after the hot-rolled sheet annealing is subjected to shot blasting and then pickling to remove the scale layer formed on the surface of the base material. Since a scale layer develops during the hot-rolled sheet annealing, shot blasting before pickling facilitates descaling by the subsequent pickling. Here, the pickling conditions, such as the concentration of the acid used in pickling, the concentration of the accelerator used in pickling, and the temperature of the pickling solution, are not particularly limited and can be any known pickling conditions.

[0064] <Cold rolling process> The descaled steel sheet is then cold rolled at a reduction ratio such that the final thickness of the base material is 0.10 to 0.30 mm.

[0065] <Finishing annealing process> After the cold rolling, finish annealing is carried out. 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 finish annealing. Finish annealing is carried out under conditions of a soaking temperature of 900 to 1050°C and a soaking time of 1 second to 10 minutes. The atmosphere is preferably a mixed atmosphere of H2 and N2 with a H2 ratio of 1 to 100% by volume (i.e., H2 + N2 = 100% by volume), and the dew point of the atmosphere is preferably -50 to +10°C.

[0066] If the soaking temperature is less than 900°C, the grain size becomes small and the core loss deteriorates, which is undesirable. If the soaking temperature exceeds 1050°C, the strength becomes insufficient and the core loss deteriorates, which is undesirable. Also, if the soaking time is less than 1 second, the grains cannot grow sufficiently. On the other hand, if the soaking time exceeds 10 minutes, the manufacturing cost increases.

[0067] In this embodiment, rapid heating is performed in the final annealing step to suppress the development of texture that is detrimental to magnetic properties. Therefore, in the final annealing step, heating is performed to a temperature of 850°C or higher at a heating rate of 400°C / s or higher in the temperature range of 500 to 850°C.

[0068] By setting the heating rate at 400°C / s or higher, it is possible to suppress the development of texture that is detrimental to magnetic properties. The heating rate is preferably 800°C / s or higher, and more preferably 1000°C or higher. The faster the heating rate, the better, so there is no need to set an upper limit. However, considering equipment constraints, the heating rate is preferably 2000°C / s or lower. Furthermore, as mentioned above, rapid heating to a temperature of 850°C or higher can improve magnetic properties. Note that the average heating rate may be 1 to 2000°C / s throughout the entire heating process, including the temperature range below 500°C and the soaking temperature.

[0069] It is difficult to achieve rapid heating under the above conditions using ordinary direct heating by gas combustion, radiant tubes, electric heaters, etc. Therefore, in this embodiment, it is desirable to use electrical heating, induction heating, etc.

[0070] <Insulating film formation process> After the above-mentioned finish annealing, an insulating coating formation 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.

[0071] A composite insulating coating is an insulating coating that is primarily composed of at least one of a metal salt such as a metal chromate salt or a metal phosphate salt, or an inorganic substance such as colloidal silica, a Zr compound, or a Ti compound, with fine organic resin particles dispersed therein. In particular, from the perspective of reducing the environmental impact during production, which has become increasingly necessary in recent years, insulating coatings that use a metal phosphate salt, a Zr or Ti coupling agent as a starting material, or an insulating coating that uses a carbonate or ammonium salt of a metal phosphate salt, a Zr or Ti coupling agent as a starting material are preferred.

[0072] 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.

[0073] The non-oriented electrical steel sheet of the present invention obtained as described above has excellent properties such as low iron loss, high magnetic flux density, and high strength, and is therefore suitable as a material for both rotor cores and stators.

[0074] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples. [Example]

[0075] 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 the thickness shown in Table 2.

[0076] Furthermore, the steel sheets were subjected to finish annealing under the conditions shown in Table 2 in a mixed atmosphere of 20% H2, 80% N2, with a dew point of -30°C. During finish annealing, induction heating was used to rapidly heat the steel sheets to the target temperature shown in Table 2. Radiant tube heating was used for the temperature rise process from the target temperature to the soaking temperature and the soaking process. The heating rate from the target temperature to the soaking temperature was approximately 5°C / s. After finish annealing, an insulating coating consisting 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 the coating was baked in air at 350°C.

[0077] [Table 1]

[0078] [Table 2]

[0079] For each test material obtained, the average grain size of the base material was measured in accordance with JIS G 0551:2013 "Steel - Microscopic test method for grain size." In addition, Epstein test pieces were taken from each test material in the rolling direction and width direction, and the iron loss W was measured by an Epstein test in accordance with JIS C 2550-1:2011. 10 / 400 and magnetic flux density B 50 The density of the steel sheet was 7.65 g / cm 3 Magnetic measurements were carried out.

[0080] The base material of each test material was removed from one surface to a depth of 1 / 4 of the plate thickness by chemical polishing. On the polished surface, the degree of accumulation of the {111} orientation was determined from the crystal orientation distribution function (ODF), which represents the three-dimensional texture, calculated by the series expansion method based on the pole figures of the {200}, {110}, {310}, and {211} planes of the α-Fe phase measured by an X-ray diffractometer.

[0081] Next, JIS No. 5 tensile test pieces were taken from each test material so that the longitudinal direction coincided with the rolling direction of the steel plate in accordance with JIS Z 2241: 2011. Then, a tensile test was performed using the test pieces in accordance with JIS Z 2241: 2011 to measure the tensile strength.

[0082] The above results are also shown in Table 2.

[0083] In Test Nos. 2, 3, 5, 6, 9, 12, 15, 17, 22, 25, 27 and 28, which satisfy the provisions of the present invention, the iron loss W 10 / 400 is low, and the magnetic flux density B 50 It was found that the tensile strength was high, exceeding 580 MPa.

[0084] In contrast, in Test Nos. 1, 4, 7, 8, 10, 11, 13, 14, 16, 18 to 21, 23, 24, 26 and 29, which are comparative examples, the iron loss W 10 / 400 is inferior or magnetic flux density B 50 The material had poor mechanical strength, poor tensile strength, or significantly deteriorated toughness, making manufacturing difficult.

[0085] Specifically, in Test No. 1, the heating rate during final annealing was lower than the specified range, resulting in a concentration of {111} orientation exceeding the specified range and a poor magnetic flux density.In Test No. 4, the temperature reached by rapid heating during final annealing was lower than the specified range, resulting in a concentration of {111} orientation exceeding the specified range and a poor magnetic flux density.

[0086] In Test No. 7, the sheet thickness was greater than the specified range, resulting in poor iron loss. In Test No. 8, the S content was higher than the specified range, resulting in a large amount of MnS precipitation and poor iron loss. In Test No. 10, the total Sn and Sb content was lower than the specified range, resulting in the concentration of {111} orientation exceeding the specified range and poor magnetic flux density. In Test No. 11, the total Sn and Sb 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.

[0087] In Test No. 13, the Mn content was higher than the specified range, resulting in poor magnetic flux density. In Test No. 14, the Si+Al+0.5×Mn content was lower than the specified range, resulting in poor core loss and tensile strength. In Test No. 16, the Si+Al+0.5×Mn content was higher than the specified range, resulting in poor toughness and fracture during cold rolling, making it impossible to measure tensile strength and magnetic properties.

[0088] 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 the average crystal grain size after finish annealing being smaller than the specified range and poor iron loss.

[0089] In Test No. 21, the soaking temperature during hot-rolled sheet annealing 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. 23, the soaking temperature during hot-rolled sheet annealing 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. 24, the Al 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.

[0090] In Test No. 26, the soaking temperature during final annealing was lower than the specified range, resulting in a smaller average grain size than the specified range and poor iron loss.In Test No. 29, the soaking temperature during final annealing was higher than the specified range, resulting in a larger average grain size than the specified range and poor tensile strength. [Industrial Applicability]

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

Claims

1. The chemical composition of the base material is, in mass%, C: 0.0040% or less, Si: more than 3.50% and less than 4.30%, 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% Sn and Sb: 0.005 to 0.060% in total, The balance is Fe and impurities. 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, The degree of accumulation of the {111} orientation at a position of 1 / 4 of the plate thickness from the surface of the base material is 3.6 or less, The thickness of the base material is 0.10 to 0.30 mm. Non-oriented electrical steel sheet. 4.2≦Si+Al+0.5×Mn≦4.9...(i) In the above formula, the element symbols indicate the content (mass %) of each element.

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

3. The base material has an insulating coating on its surface. The non-oriented electrical steel sheet according to claim 1.

4. A method for producing the non-oriented electrical steel sheet according to any one of claims 1 to 3, comprising: In mass%, C: 0.0040% or less, Si: more than 3.50% and less than 4.30%, 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% Sn and Sb: 0.005 to 0.060% in total, The balance is Fe and impurities. For a steel ingot having a chemical composition that satisfies the following formula (i), The process includes a hot rolling process, a hot-rolled sheet annealing process in which the soaking temperature is 800 to 920°C and the soaking time is 1 second to 10 minutes, a descaling process in which the sheet is shot blasted and then pickled, 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 sheet is heated to a temperature of 850°C or higher so that the heating rate in the temperature range of 500 to 850°C is 400 to 2000°C / s, and then the soaking temperature is 900 to 1050°C and the soaking time is 1 second to 10 minutes. Manufacturing method for non-oriented electrical steel sheets. 4.2≦Si+Al+0.5×Mn≦4.9...(i) In the above formula, the element symbols indicate the content (mass %) of each element.

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