Non-oriented electrical steel sheet and method for manufacturing same

Abstract

Provided is a non-oriented electrical steel sheet which has a base material having a chemical composition that contains, in mass%, not more than 0.0050% of C, 2.80-4.50% of Si, 0.10-2.00% of Mn, 0.10-2.00% of Al, not more than 0.030% of P, not more than 0.0050% of S, not more than 0.0050% of N, and more than 0% but not more than 0.06% of Sn, the remainder comprising Fe and impurities. Plane orientation intensities I(110), I(200), and I(222), which are respectively derived from (110), (200), and (222), satisfy [0.10 ≤ I(110) ≤ 0.40], [1.00 ≤ I(200) ≤ 3.00], and [2.00 ≤ I(222) ≤ 7.00] as determined using X-ray diffraction.

Description

Non-oriented electrical steel sheet and its manufacturing method

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

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

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

[0004] For example, Patent Document 1 discloses a non-oriented electrical steel sheet having excellent magnetic properties and a method for manufacturing the same.

[0005] Japanese Patent Application Laid-Open No. 2022-74677

[0006] However, as a result of extensive investigations, the present inventors have found that there is room for further improvement in the magnetic properties.

[0007] The present invention has been made to solve these problems, and has an object to provide a non-oriented electrical steel sheet having excellent magnetic properties.

[0008] The present invention relates to the following non-oriented electrical steel sheet and a method for producing the same.

[0009] (1) The chemical composition of the base material is, in mass%, C: 0.0050% or less, Si: 2.80 to 4.50%, Mn: 0.10 to 2.00%, Al: 0.10 to 2.00%, P: 0.030% or less, S: 0.0050% or less, N: 0.0050% or less, Sn: more than 0.06% or less, and the balance: Fe and impurities. The plane orientation intensities I derived from each of (110), (200), and (222) planes using X-ray diffraction are （１１０） , I （２００） , and I （２２２） A non-oriented electrical steel sheet that satisfies the following formulas (i) to (iii): 0.10≦I （１１０） ≦0.40...(i) 1.00≦I （２００） ≦3.00...(ii) 2.00≦I （２２２） ≦7.00...(iii)

[0010] (2) The non-oriented electrical steel sheet according to (1), wherein the base material has a chemical composition that contains, in place of a portion of Fe, one or more elements selected from Ca: 0.0050% or less, Zn: 0.0050% or less, Mg: 0.0050% or less, Ti: 0.015% or less, Cr: 0.20% or less, Sb: 0.20% or less, Mo: 0.015% or less, Nb: 0.015% or less, and Cu: 0.20% or less.

[0011] (3) A steel slab having a chemical composition, in mass%, of C: 0.0050% or less, Si: 2.80 to 4.50%, Mn: 0.10 to 2.00%, Al: 0.10 to 2.00%, P: 0.030% or less, S: 0.0050% or less, N: 0.0050% or less, Sn: more than 0% and 0.06% or less, and the balance: Fe and impurities, is subjected to a hot rolling process, a pickling process, a cold rolling process, and a finish annealing process in this order; the finish annealing step involves heating from room temperature to 350 to 450°C so that the heating rate from 100°C to 350°C is 10 to 500°C / s, followed by retention in the temperature range of 350 to 450°C for 0.1 to 100 seconds, and subsequently heating from the temperature range of 350 to 450°C to an ultimate temperature within a temperature range of 600°C to 840 to 950°C so that the heating rate to the ultimate temperature is 700°C / s or more.

[0012] (4) The method for producing a non-oriented electrical steel sheet according to (3), wherein the chemical composition of the steel slab contains, in place of a portion of Fe, one or more elements selected from Ca: 0.0050% or less, Zn: 0.0050% or less, Mg: 0.0050% or less, Ti: 0.015% or less, Cr: 0.20% or less, Sb: 0.20% or less, Mo: 0.015% or less, Nb: 0.015% or less, and Cu: 0.20% or less.

[0013] According to the present invention, a non-oriented electrical steel sheet having excellent magnetic properties can be obtained.

[0014] 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.

[0015] When a predetermined amount or more of Sn is contained, Sn segregates at the interfaces between crystal grains crushed by cold rolling. It was discovered that by performing rapid heating in the finish annealing after cold rolling in a state where Sn is sufficiently segregated at the grain boundaries, it is possible to suppress the development of a texture that is unfavorable to the magnetic properties and to develop a highly symmetric texture that is favorable to the magnetic properties, thereby improving the magnetic flux density.

[0016] On the other hand, since Sn is an element that reduces cold rolling property, it is desirable to reduce its content. However, even when the Sn content is reduced, it is possible to promote grain boundary segregation of Sn by performing the temperature increase in two stages in the finish annealing and maintaining the temperature in a predetermined temperature range between the first and second stages.

[0017] Furthermore, the inventors conducted experiments in which rapid heating was performed to various ultimate temperatures, and found that even if rapid heating was performed, no improvement in magnetic properties was observed when the ultimate temperature was low, but that the magnetic properties were improved by performing rapid heating to a temperature of 840°C or higher.

[0018] The present invention was made based on the above findings. Each of the features of the present invention will be described in detail below.

[0019] 1. Overall Configuration The non-oriented electrical steel sheet according to one embodiment of the present invention has excellent magnetic properties. In addition, 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.

[0020] 2. Chemical composition of the base material The reasons for limiting the content of each element are as follows: In the following description, "%" for the content means "mass %."

[0021] C: 0.0050% or less C (carbon) is an element that causes iron loss degradation in non-oriented electrical steel sheets. If the C content exceeds 0.0050%, the iron loss of the non-oriented electrical steel sheet deteriorates, making it impossible to obtain good magnetic properties. Therefore, the C content is set to 0.0050% or less. The C content is preferably 0.0040% or less, and more preferably 0.0030% or less. Note that, since a lower C content is preferable, there is no need to set a lower limit; it may be 0%. However, an extreme reduction in the C content may result in an increase in manufacturing costs. Furthermore, C contributes to increasing the strength of non-oriented electrical steel sheets. Therefore, the C content is preferably greater than 0%, more preferably 0.0005% or more, and even more preferably 0.0010% or more.

[0022] Si: 2.80 to 4.50% Si (silicon) is an element that increases the electrical resistance of steel, reduces eddy current loss, and improves the iron loss of non-oriented electrical steel sheets. Si also has a high solid-solution strengthening ability, making it an effective element for increasing the strength of non-oriented electrical steel sheets. To achieve these effects, the Si content is set to 2.80% or more. The Si content is preferably 3.00% or more, and more preferably 3.20% 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 4.00% or less, and more preferably 3.70% or less.

[0023] Mn: 0.10 to 2.00% Mn (manganese) is an element that effectively increases the electrical resistance of steel, reduces eddy current loss, and improves iron loss in non-oriented electrical steel sheets without degrading workability. Although Mn has a lower solid solution strengthening ability than Si, it is an element that can contribute to high strength without degrading workability. To achieve these effects, the Mn content is set to 0.10% or more. The Mn content is preferably 0.20% or more, and more preferably 0.40% or more. On the other hand, excessive Mn content not only significantly reduces magnetic flux density, but also significantly degrades workability, making cold rolling difficult. Therefore, the Mn content is set to 2.00% or less. The Mn content is preferably 1.50% or less, and more preferably 1.00% or less.

[0024] Al: 0.10 to 2.00% Al (aluminum) is an element that increases the electrical resistance of steel, thereby reducing eddy current loss and improving the iron loss of non-oriented electrical steel sheets. Furthermore, Al contributes to increasing the strength of non-oriented electrical steel sheets through solid solution strengthening, although not as much as Si. Furthermore, adding an appropriate amount of Al suppresses the refinement of AlN, which occurs when Al combines with N in the steel, and improves grain growth during finish annealing. To achieve these effects, the Al content is set to 0.10% or more. The Al content is preferably 0.20% or more, and more preferably 0.40% or more. On the other hand, excessive Al content deteriorates toughness, making cold rolling difficult. Therefore, the Al content is set to 2.00% or less. The Al content is preferably 1.50% or less, and more preferably 1.00% or less.

[0025] 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 sheets. Therefore, the P content is set to 0.030% or less. The P content is preferably 0.025% or less, more preferably 0.020% or less, and even more preferably 0.010% or less. Note that since the lower the P content, the better, there is no need to set a lower limit; it may be 0%. However, since an extreme reduction in the P content may increase manufacturing costs, the P content is preferably more than 0%, and more preferably 0.001% or more.

[0026] S: 0.0050% 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 0.0050% or less. The S content is preferably 0.0040% or less, and more preferably 0.0030% or less. Note that, since the lower the S content, the better, there is no need to set a lower limit; it may be 0%. However, since an extreme reduction in the S content may increase manufacturing costs, the S content is preferably more than 0%, more preferably 0.0001% or more, even more preferably 0.0003% or more, and even more preferably 0.0005% or more.

[0027] N: 0.0050% 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 0.0050% or less. The N content is preferably 0.0040% or less, and more preferably 0.0030% or less. There is no need to set a lower limit for the N content; it may be 0%. However, since an extreme reduction in the N content may increase manufacturing costs, the N content is preferably more than 0%, more preferably 0.0001% or more, even more preferably 0.0003% or more, and even more preferably 0.0005% or more.

[0028] Sn: More than 0% and 0.06% or less Sn (tin) segregates to grain boundaries during finish annealing, thereby suppressing the development of texture that is unfavorable to magnetic properties, and also develops a highly symmetric texture that is favorable to magnetic properties, thereby increasing the magnetic flux density of non-oriented electrical steel sheets. To achieve these effects, the Sn content is set to more than 0%. The Sn content is preferably 0.01% or more. On the other hand, reducing the Sn content makes it possible to suppress a decrease in the toughness of the steel and improve its cold rolling properties. Therefore, the Sn content is set to 0.06% or less. The Sn content is preferably 0.03% or less.

[0029] Ca: 0.0050% or less Ca (calcium) is an element that forms sulfides to fix S and contributes to reducing iron loss, so it may be contained as needed. However, excessive inclusion of Ca may result in poor economic efficiency, so the Ca content is set to 0.0050% or less. The Ca content is preferably 0.0040% or less, and more preferably 0.0030% or less. The lower limit of the Ca content is not particularly limited and may be 0%. However, when the above-mentioned effects are desired, the Ca content is preferably more than 0%, and more preferably 0.0003% or more.

[0030] Zn: 0.0050% or less Zn (zinc), like Ca, forms sulfides to fix S and contributes to reducing iron loss, so it may be contained as needed. However, excessive inclusion of Zn may result in poor economic efficiency, so the Zn content is set to 0.0050% or less. The Zn content is preferably 0.0040% or less, and more preferably 0.0030% or less. The lower limit of the Zn content is not particularly limited and may be 0%. However, when the above-mentioned effects are desired, the Zn content is preferably more than 0%, and more preferably 0.0003% or more.

[0031] Mg: 0.0050% or less Like Ca and Zn, Mg (magnesium) is an element that forms sulfides to fix S and contributes to reducing iron loss, and therefore may be contained as needed. However, excessive inclusion of Mg may result in poor economic efficiency, so the Mg content is set to 0.0050% or less. The Mg content is preferably 0.0040% or less, and more preferably 0.0030% or less. The lower limit of the Mg content is not particularly limited and may be 0%. However, if the above-mentioned effects are desired, the Mg content is preferably more than 0%, and more preferably 0.0003% or more.

[0032] Ti: 0.015% or less Like Ca, Zn, and Mg, Ti (titanium) is an element that forms sulfides to fix S and contributes to reducing iron loss, and therefore may be contained as needed. However, excessive inclusion of Ti may result in poor economic efficiency, so the Ti content is set to 0.015% or less. The Ti content is preferably 0.010% or less, and more preferably 0.005% or less. The lower limit of the Ti content is not particularly limited and may be 0%. However, when the above-mentioned effects are desired, the Ti content is preferably more than 0%, and more preferably 0.001% or more.

[0033] Cr: 0.20% or less Cr (chromium) is an element that can be mixed in as an impurity. However, since Cr is also an element that improves magnetic properties, it may be intentionally added. However, excessive addition may result in poor economic efficiency, so the Cr content when intentionally added is set to 0.20% or less. The Cr content is preferably 0.15% or less, more preferably 0.10% or less. The lower limit of the Cr content is not particularly limited and may be 0%. However, to achieve the above effects, the Cr content is preferably more than 0%, more preferably 0.01% or more.

[0034] Sb: 0.20% or less Sb (antimony) is an element that can be mixed in as an impurity. However, since Sb is also an element that improves magnetic properties, it may be intentionally added. However, excessive Sb content may result in poor economic efficiency, so the Sb content when intentionally added is set to 0.20% or less. The Sb content is preferably 0.15% or less, more preferably 0.10% or less. The lower limit of the Sb content is not particularly limited and may be 0%. However, if the above-mentioned effects are desired, the Sb content is preferably more than 0%, more preferably 0.01% or more.

[0035] Mo: 0.015% or less Mo (molybdenum) is an element that contributes to high strength by combining with carbon or nitrogen to form precipitates (carbides, nitrides), and therefore may be contained as needed. However, excessive inclusion of Mo may result in poor economic efficiency, so the Mo content is set to 0.015% or less. The Mo content is preferably 0.010% or less, and more preferably 0.005% or less. The lower limit of the Mo content is not particularly limited and may be 0%. However, if the above-mentioned effects are desired, the Mo content is preferably more than 0%, and more preferably 0.001% or more.

[0036] Nb: 0.015% or less Nb (niobium) is an element that contributes to high strength by bonding with carbon or nitrogen to form precipitates (carbides, nitrides), and may therefore be contained as necessary. However, excessive Nb content may result in poor economic efficiency, so the Nb content is set to 0.015% or less. The Nb content is preferably 0.010% or less, and more preferably 0.005% or less. The lower limit of the Nb content is not particularly limited and may be 0%. However, when the above-mentioned effects are desired, the Nb content is preferably more than 0%, and more preferably 0.001% or more.

[0037] Cu: 0.20% or less Cu (copper) is an element that can be mixed in as an impurity. However, because Cu also improves magnetic properties, it may be intentionally added. However, excessive Cu content may result in poor economic efficiency, so the Cu content when intentionally added is set to 0.20% or less. The Cu content is preferably 0.15% or less, more preferably 0.10% or less. The lower limit of the Cu content is not particularly limited and may be 0%. However, to achieve the above effects, the Cu content is preferably more than 0%, more preferably 0.01% or more.

[0038] The chemical composition of the base material of the non-oriented electrical steel sheet of the present invention is made up of the balance Fe and impurities, where "impurities" refer to components that are mixed in during industrial steel production due to various factors in raw materials such as ores and scraps, and in the manufacturing process, and are acceptable within a range that does not adversely affect the present invention.

[0039] 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. In the present invention, the chemical composition is measured using inductively coupled plasma (ICP) atomic emission spectroscopy (ICP-AES) and inductively coupled plasma (ICP) mass spectrometry (ICP-MS) depending on the content of each element. Furthermore, carbon and sulfur are measured using a combustion-infrared absorption method, nitrogen is measured using an inert gas combustion-thermal conductivity method, and oxygen is measured using an inert gas fusion-non-dispersive infrared absorption method.

[0040] 3. Grain size In this embodiment, there is no particular restriction on the average grain size of the base material. However, if it is desired to achieve both excellent magnetic properties and high strength, the average grain size of the base material is preferably 50 to 150 μm. By setting the average grain size of the base material to 50 μm or more, it is possible to suppress deterioration of hysteresis loss and improve iron loss. On the other hand, by setting the average grain size to 150 μm or less, it is possible to obtain the effect of improving the strength of the steel and suppress deterioration of iron loss due to increased eddy current loss. The average grain size is preferably 55 μm or more, more preferably 60 μm or more. Furthermore, the average grain size is preferably 140 μm or less, more preferably 130 μm or less.

[0041] 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".

[0042] 4. Texture In this embodiment, the development of a texture that is unfavorable to magnetic properties is suppressed, and a highly symmetric texture that is favorable to magnetic properties is developed. From this viewpoint, in the non-oriented electrical steel sheet according to this embodiment, the plane orientation intensities I derived from (110), (200), and (222) planes using X-ray diffraction are （１１０） , I （２００） , and I （２２２）The following formulas (i) to (iii) are satisfied: 0.10≦I （１１０） ≦0.40...(i) 1.00≦I （２００） ≦3.00...(ii) 2.00≦I （２２２） ≦7.00...(iii)

[0043] I （１１０） is the plane orientation strength derived from (110). The (110) orientation has a relatively good symmetry, so it is necessary to develop it to improve the magnetic properties. （１１０） is 0.10 or more. （１１０） is preferably 0.13 or more, and more preferably greater than 0.15. （１１０） The higher the value, the more preferable it is, but the upper limit that can be industrially produced is 0.40.

[0044] I （２００） is the plane orientation strength derived from (200). The (200) orientation has excellent symmetry, so it is necessary to develop it to improve the magnetic properties. （２００） As described above, by performing rapid heating in the finish annealing after cold rolling in a state where Sn is sufficiently segregated at grain boundaries, I （２００） It is possible to increase the （２００） is preferably 1.50 or more, and more preferably 2.00 or more. （２００） The higher the value, the more preferable it is, but the upper limit that can be industrially produced is 3.00.

[0045] I （２２２） is the plane orientation strength derived from (222). The (222) orientation is a texture that is unfavorable to magnetic properties, so it is necessary to suppress its development in order to improve magnetic properties. （２２２） is 7.00 or less. （２２２） is preferably 6.00 or less, more preferably 5.00 or less, and even more preferably 4.00 or less. （２２２） The lower the value, the more preferable it is, but the lower limit at which industrial production is possible is 2.00.

[0046] The plane orientation intensity is measured by inverse X-ray analysis using an X-ray diffractometer. The plane orientation intensity is the integrated value of the X-ray peak intensity in each orientation. The specific measurement method is as follows: First, a test piece with a diameter of 26 mm is punched out from the non-oriented electrical steel sheet as the test material. From the viewpoint of achieving both measurement accuracy and test efficiency, the number of test pieces used for the measurement is 10. The measurement is performed on the surface of the base material. If an insulating coating is applied to the surface of the base material, the insulating coating is removed using an existing method. For example, the insulating coating can be removed by immersing the base material in a 20% NaOH aqueous solution heated to 80°C for 5 minutes.

[0047] <Measurement Method> A 26 mm diameter test piece is placed in the sample magazine. A standard sample provided by the manufacturer that does not have a specific orientation is also placed at the same time. The measurement conditions for inverse X-ray analysis are: measurement axis 2θ / θ, measurement method FT, and counting unit CPS. The step width is 0.010°, counting time is 0.6 s, voltage is 50 kV, current is 200 mA, divergence / scattering slit is 1°, divergence vertical slit is 10 mm, and receiving slit is 0.15 mm. The measurement ranges are: (110): 2θ = 18.000-21.500°, (200): 2θ = 27.750-29.500°, and (222): 2θ = 49.750-52.000°.

[0048] <Analysis method> Analysis software called "Invpole.cnd" is used for analysis. Since it is necessary to select standard results for analysis, it is set to refer to the data of the standard sample measured together with the test piece. Smoothing processing, peak correction, and background removal are not performed in the analysis. For intensity calculation, "integrated intensity" is selected, and as the crystal system, cubic (α axis: 2.866 Å) is selected.

[0049] 5. Magnetic Properties In the non-oriented electrical steel sheet according to this embodiment, excellent magnetic properties are defined as iron loss W １０／４００ is low, and the magnetic flux density B ５０ means that is high.

[0050] Here, the magnetic properties (iron loss W １０／４００ and magnetic flux density B ５０) are measured by the following method. First, a small test piece of 55 mm × 55 mm is prepared from a non-oriented electrical steel sheet. Then, iron loss and magnetic flux density are measured using a small single sheet tester that corresponds to the small test piece. In this case, the measurement principle follows the single sheet magnetic property measurement method (Single Sheet Tester: SST) specified in JIS C 2556:2015.

[0051] When measuring the iron loss and magnetic flux density, the excitation direction is set to two directions, a direction parallel to the rolling direction (hereinafter referred to as L direction) and a direction perpendicular to the rolling direction (hereinafter referred to as C direction), and the average value of the values ​​measured in each direction is calculated as the magnetic property value of the material. The number of small test pieces of 55 mm x 55 mm is set to 10 from the viewpoint of achieving both measurement accuracy and test efficiency. 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.

[0052] The magnetic property values ​​obtained by SST are obtained using correction factors. Specifically, Epstein test pieces and the above-mentioned small test pieces are taken in advance from several types of non-oriented electrical steel sheets, and the magnetic property values ​​are measured by the Epstein method specified in JIS C 2550-1:2011 and the above-mentioned SST, and a conversion formula is derived from the relationship between the two measured values. Then, the magnetic property values ​​measured by the single sheet tester are corrected using the above-mentioned conversion formula so that they are equivalent to the magnetic property values ​​measured by the Epstein method.

[0053] The density of the steel sheet when measured by the Epstein method is a value calculated by [7.865 - 0.065 x (Si + 1.7 x Al)], where Si and Al in the formula are the respective contents (mass%) in the steel sheet. When measuring magnetic property values ​​in accordance with the Epstein test method, the excitation directions are two directions, the L direction and the C direction, and measurements are performed using half of each test piece excited in the L direction and the C direction.

[0054] In the non-oriented electrical steel sheet according to this embodiment, iron loss W １０／４００Low means that the magnetic flux density B is 14.5 W / kg or less for a plate thickness of 0.26 mm or more, 12.5 W / kg or less for a plate thickness of 0.21 to 0.25 mm, and 11.2 W / kg or less for a plate thickness of 0.20 mm or less. ５０ High means that the strength is 1.63T or more when the plate thickness is 0.26 mm or more, 1.62T or more when the plate thickness is 0.21 to 0.25 mm, and 1.61T or more when the plate thickness is 0.20 mm or less.

[0055] 6. Mechanical Properties In this embodiment, there is no particular limitation on the strength. However, the tensile strength is preferably 340 MPa or more, more preferably 400 MPa or more, and even more preferably 430 MPa or more. Here, the tensile strength is measured by a tensile test (by the offset method) in accordance with JIS Z 2241:2022.

[0056] Test specimens are taken with the rolling direction as the longitudinal direction while keeping the plate thickness as it is, and then processed into the shape of a JIS No. 5 test specimen. Note that if it is difficult to take a JIS No. 5 test specimen due to the size of the steel plate, a tensile test may be carried out using a reduced-scale shape.

[0057] 7. Sheet Thickness There is no particular limitation on the sheet thickness of the non-oriented electrical steel sheet according to this embodiment. However, from the viewpoint of the manufacturing costs of cold rolling and finish annealing, the sheet thickness of the base material is preferably 0.10 mm or more. On the other hand, from the viewpoint of reducing iron loss, the sheet thickness of the base material is preferably 0.30 mm or less. The sheet thickness is more preferably 0.15 mm or more, even more preferably 0.20 mm or more, and even more preferably 0.25 mm or less.

[0058] 8. Insulating Coating In the non-oriented electrical steel sheet according to this embodiment, it is preferable that an insulating coating be provided on the surface of the base material. Since the non-oriented electrical steel sheet is used after being punched into a core blank and then laminated, providing an insulating coating on the surface of the base material can reduce eddy currents between the sheets, thereby making it possible to reduce eddy current loss in the core.

[0059] The type of insulating coating is not particularly limited, and known insulating coatings used for non-oriented electrical steel sheets can be used. Examples of such insulating coatings include composite insulating coatings primarily composed of inorganic materials and further containing organic materials. Here, a composite insulating coating is an insulating coating primarily composed of at least one inorganic material, such as a metal chromate salt, a metal phosphate salt, colloidal silica, a Zr compound, or a Ti compound, with fine organic resin particles dispersed therein. In particular, from the perspective of reducing the environmental impact during manufacturing, which has become increasingly important in recent years, insulating coatings using metal phosphate salts, Zr or Ti coupling agents, or Zr or Ti carbonates or ammonium salts as starting materials are preferably used.

[0060] The amount of the insulating coating is not particularly limited, but for example, it is 200 to 1500 mg / m per side. ２ The coating amount is preferably about 300 to 1200 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.

[0061] 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 sequentially performing a hot rolling step, a pickling step, a cold rolling step, and a finish annealing step on a steel billet having the above-described chemical composition under the conditions shown below, for example. A hot-rolled sheet annealing step may be performed between the hot rolling step and the pickling step, or between the pickling step and the cold rolling step. Furthermore, when an insulating coating is formed on the surface of the base material, an insulating coating formation step is performed after the finish annealing step. Each step will be described in detail below.

[0062] <Hot Rolling Step> A slab having the above chemical composition is heated and hot-rolled to obtain a hot-rolled sheet. The heating temperature of the slab when subjected to hot rolling is not particularly specified, but is preferably, for example, 1050 to 1250°C. The thickness of the hot-rolled sheet after hot rolling is also not particularly specified, but is preferably, for example, about 1.0 to 3.0 mm, taking into account the final thickness of the base material. The hot-rolling step is preferably completed while the temperature of the steel sheet is in the range of 700 to 1000°C.

[0063] <Hot-rolled sheet annealing process> Thereafter, hot-rolled sheet annealing is performed as necessary for the purpose of reducing iron loss of the steel sheet. In the case of continuous annealing, the hot-rolled sheet may be annealed, for example, by soaking at 750 to 1200°C for 10 seconds to 10 minutes. In the case of box annealing, the hot-rolled steel sheet may be annealed, for example, by soaking at 650 to 950°C for 30 minutes to 24 hours. Note that although the magnetic properties will be inferior compared to when the hot-rolled sheet annealing process is performed, in order to reduce costs, the hot-rolled sheet may be subjected to self-annealing or the hot-rolled sheet annealing process may be omitted.

[0064] <Pickling step> The steel sheet after the hot rolling or after the hot-rolled sheet annealing is subjected to pickling to remove the scale layer formed on the surface of the base material. When the hot-rolled sheet annealing is box annealing, the pickling step is preferably performed before the hot-rolled sheet annealing from the viewpoint of descaling properties. Here, the pickling conditions, such as the concentration of the acid used in the pickling, the concentration of the accelerator used in the pickling, and the temperature of the pickling solution, are not particularly limited, and known pickling conditions can be used.

[0065] <Cold Rolling Step> The steel sheet after the descaling is subjected to cold rolling, for example, at a reduction ratio such that the final thickness of the base material is 0.10 to 0.30 mm.

[0066] <Finish annealing step> Finish annealing is performed after the cold rolling. In the manufacturing method of the non-oriented electrical steel sheet according to this embodiment, it is preferable to use a continuous annealing furnace for the finish annealing. The finish annealing is composed of at least three steps: a first heating step, a second heating step, and a soaking step. The first heating step promotes Sn segregation, and the second heating step reduces the {111} orientation, which is disadvantageous for magnetic properties. Both steps are controls for creating recrystallization orientation nuclei that are favorable for magnetic properties. The subsequent soaking step controls the coarsening of recrystallization orientation nuclei that are favorable for magnetic properties, i.e., controls grain growth.

[0067] <First Heating Step> First, in the first heating step of the finish annealing, the steel sheet is heated from room temperature to 350 to 450°C so that the heating rate from 100°C to 350°C is 10 to 500°C / s. If the heating rate in the first stage is less than 10°C / s, the manufacturing cost increases. On the other hand, if the heating rate exceeds 500°C / s, the grain boundary segregation of Sn cannot be sufficiently promoted.

[0068] Next, a residence time of 0.1 to 100 seconds is ensured within a temperature range of 400±50°C. This is because it is believed that grain boundary segregation of Sn is likely to be promoted within this temperature range. By maintaining the temperature within this range for a predetermined time, it becomes possible to sufficiently segregate Sn at the grain boundaries.

[0069] <Second Heating Step> In the second heating step of the finish annealing, the steel sheet is heated to an ultimate temperature within a temperature range of 840 to 950° C. At this time, rapid heating is performed so that the heating rate from 600° C. to the ultimate temperature is 700° C. / s or more.

[0070] If the ultimate temperature is less than 840°C, the crystal grain size becomes small and the iron loss deteriorates, which is not preferable, and if the ultimate temperature exceeds 950°C, the strength becomes insufficient and the magnetism deteriorates, which is not preferable. In order to further reduce the iron loss, the ultimate temperature is preferably 870 to 930°C.

[0071] In addition, by performing rapid heating under the above conditions, I （２２２） and I （１１０）In addition, by performing rapid heating in a state where Sn is sufficiently segregated at grain boundaries, I （２００） Therefore, the temperature rise rate is set to 700°C / s or more. The temperature rise rate is preferably 1000°C / s or more. The temperature rise rate in the second temperature rise step is preferably as fast as possible, and therefore there is no need to set an upper limit. However, in consideration of equipment constraints, the temperature rise rate is preferably 2000°C / s or less, and more preferably 1600°C / s or less.

[0072] It is difficult to achieve rapid heating under the conditions of the second heating step using direct heating by ordinary gas combustion, radiant tubes, electric heaters, etc. Therefore, in this embodiment, it is desirable to use electrical heating, induction heating, etc. for the second heating step.

[0073] <Soaking Step> In the soaking step of the finish annealing, the temperature is held within a temperature range of 840 to 1200°C for 1 to 150 seconds. The final temperature and the soaking temperature do not necessarily have to be the same. In this case, any heat cycle from the final temperature to the soaking temperature may be used. For example, a cycle in which the material is cooled to room temperature once, reheated, and then heated to the soaking temperature at a rate of 10 to 50°C / s may be used. However, because this method imposes a high production load, it is preferable that the heating rate from the final temperature to the soaking temperature be controlled within a range of -100°C to +100°C.

[0074] Furthermore, in the final annealing, it is preferable that the atmospheric dew point during the temperature rise from 600°C be -50 to 10°C. By controlling the atmospheric dew point low, it is possible to suppress the internal oxidation of Si and to suppress the deterioration of magnetic properties. In addition, from the viewpoint of suppressing internal oxidation, it is preferable that the atmosphere during the final annealing is H ２ The ratio of H is 1 to 100% by volume. ２ and N ２ A mixed atmosphere of H ２ +N ２ = 100% by volume.

[0075] <Insulating Coating Forming Step> After the above-mentioned finish annealing, an insulating coating forming step is carried out as necessary. Here, the method for forming the insulating coating is not particularly limited, and a known insulating coating forming treatment liquid such as that described below may be used, and the treatment liquid may be applied and dried by a known method. An example of a known insulating coating is a composite insulating coating that is mainly made of an inorganic material and further contains an organic material.

[0076] The composite insulating coating is an insulating coating that is primarily composed of at least one of a metal salt such as a metal chromate salt or a metal phosphate salt, or an inorganic substance such as colloidal silica, a Zr compound, or a Ti compound, with fine organic resin particles dispersed therein. In particular, from the perspective of reducing the environmental impact during production, which has become increasingly necessary in recent years, insulating coatings that use a metal phosphate salt, a Zr or Ti coupling agent as a starting material, or an insulating coating that uses a carbonate or ammonium salt of a Zr or Ti coupling agent as a starting material are preferably used.

[0077] Before applying the treatment liquid to the surface of the base material on which the insulating coating is to be formed, any pretreatment may be performed, such as degreasing with an alkali or pickling with hydrochloric acid, sulfuric acid, phosphoric acid, etc. The treatment liquid may also be applied to the surface of the base material as is after finish annealing without performing these pretreatments.

[0078] The non-oriented electrical steel sheet according to this embodiment obtained as described above has excellent properties such as low iron loss and high magnetic flux density, and can therefore be suitably used as a material for rotor cores and stators.

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

[0080] A slab having the chemical composition shown in Table 1 was heated to 1150°C, then hot-rolled at a finishing temperature of 850°C and 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 descaled by pickling and then hot-rolled annealed at 750°C for 20 hours in a box annealing furnace. The steel sheet thus obtained was cold-rolled to obtain a cold-rolled steel sheet having a thickness of 0.25 mm.

[0081] Furthermore, following the first and second temperature-raising steps under the conditions described below, H ２ : 20%, N ２ The steel sheets were subjected to a soaking step of holding at 1100°C for 30 seconds in a mixed atmosphere of 80% RH and a dew point of -30°C, followed by finish annealing. The heating steps were all performed in a nitrogen atmosphere. In the first heating step, the steel sheets were heated in the temperature range from 100°C to 350°C at a heating rate of 100°C / s, and then held at a temperature range of 350 to 450°C for 1 second. In the second heating step, the steel sheets were rapidly heated from 600°C to a final temperature of 880°C at a heating rate of 1400°C / s. An insulating coating was applied to the steel sheets after the finish annealing, and the steel sheets were baked in air at 350°C.

[0082]

[0083] For each of the obtained test materials, the plane orientation strength was measured by inverse X-ray analysis using an X-ray diffractometer (Rigaku Corporation: RINT-2500). The specific measurement and analysis methods are as described above. Next, small test pieces of 55 mm x 55 mm were prepared from each test material, and the iron loss W １０／４００ and magnetic flux density B ５０ Furthermore, the average grain size and tensile strength were measured according to the procedures described above.

[0084] The results are shown in Table 2.

[0085]

[0086] As shown in Table 2, Test Nos. 1 to 24, which satisfied the requirements of the present invention, resulted in excellent magnetic properties. In contrast, Test Nos. 25 to 34, which had chemical compositions that did not comply with the requirements of the present invention, either could not be manufactured due to difficulties in cold rolling, or resulted in poor magnetic flux density or iron loss.

[0087] Specifically, in Test No. 25, the C content was excessive, and in Test No. 26, the Si content was insufficient, resulting in high iron loss. In Test No. 27, the Si content was excessive, making cold rolling difficult and production impossible. In Test No. 28, the Mn content was insufficient, resulting in high iron loss. In Test No. 29, the Mn content was excessive, making cold rolling difficult and production impossible.

[0088] In Test No. 30, the S content was excessive, and in Test No. 31, the Al content was insufficient, resulting in high iron loss. In Test No. 32, the Al content was excessive, making cold rolling difficult and unmanufacturable. In Test No. 33, the N content was excessive, resulting in high iron loss. In Test No. 34, the P content was excessive, making cold rolling difficult and unmanufacturable.

[0089] A portion of the slabs having the chemical compositions shown in Table 1 was heated to 1150°C, hot-rolled at a finishing temperature of 850°C and a finishing thickness of 2.0 mm, and then coiled at 600°C to obtain hot-rolled steel sheets. The obtained hot-rolled steel sheets were subjected to hot-rolled sheet annealing under the conditions shown in Table 3. Note that, when performing hot-rolled sheet annealing, a continuous annealing furnace was used for Test Nos. 35 to 41 and 49, and a box annealing furnace was used for Test Nos. 42 to 48. Test Nos. 35 to 41 and 49 were subjected to descaling treatment by pickling and shot blasting after annealing, while Test Nos. 42 to 48 were subjected to descaling treatment by pickling before annealing. The steel sheets thus obtained were cold-rolled to obtain cold-rolled steel sheets having a thickness of 0.25 mm.

[0090] Furthermore, H ２ : 3%, N ２Finish annealing was performed in a mixed atmosphere of 97% RH and -30°C dew point under the conditions shown in Table 3. The heating rate in the first heating step was the heating rate in the temperature range from 100°C to 350°C, and the residence time was the residence time in the temperature range of 350 to 450°C, while the heating rate in the second heating step was the heating rate in the temperature range from 600°C to the final temperature. An insulating coating was applied to the steel sheet after finish annealing, and the steel sheet was baked at 350°C in air. Note that in Test No. 49, the "-" in the "Attained Temperature" and "Residence Time" columns in the first heating step means that the steel sheet was heated continuously from room temperature to the final temperature in the second heating step.

[0091] The average grain size, plane orientation strength, tensile strength, iron loss W of each test material obtained were measured by the same method as in Example 1. １０／４００ and magnetic flux density B ５０ Measurements were carried out.

[0092] The above results are also shown in Table 3.

[0093]

[0094] As shown in Table 3, Test Nos. 35 to 38 and 42 to 45, which satisfied the requirements of the present invention, showed excellent magnetic properties. In contrast, Test Nos. 39 to 41 and 46 to 49, in which the heating rate or ultimate temperature in the second heating step during finish annealing did not comply with the requirements of the present invention, failed to develop a highly symmetrical texture, resulting in a decrease in magnetic flux density and an increase in iron loss.

[0095] As described above, according to the present invention, a non-oriented electrical steel sheet having excellent magnetic properties can be obtained.

Claims

1. The chemical composition of the base material is, in mass%, C: 0.0050% or less, Si: 2.80 to 4.50%, Mn: 0.10 to 2.00%, Al: 0.10 to 2.00%, P: 0.030% or less, S: 0.0050% or less, N: 0.0050% or less, Sn: more than 0.06% or less, balance: Fe and impurities, and the plane orientation intensity I derived from each of (110), (200), and (222) using X-ray diffraction is （１１０） , I （２００） , and I （２２２） A non-oriented electrical steel sheet that satisfies the following formulas (i) to (iii): 0.10≦I （１１０） ≦0.40...(i) 1.00≦I （２００） ≦3.00...(ii) 2.00≦I （２２２） ≦7.00...(iii) 2. The non-oriented electrical steel sheet according to claim 1, wherein the chemical composition of the base material contains, in place of a portion of Fe, one or more elements selected from the group consisting of Ca: 0.0050% or less, Zn: 0.0050% or less, Mg: 0.0050% or less, Ti: 0.015% or less, Cr: 0.20% or less, Sb: 0.20% or less, Mo: 0.015% or less, Nb: 0.015% or less, and Cu: 0.20% or less.

3. A steel slab having a chemical composition, in mass%, of C: 0.0050% or less, Si: 2.80 to 4.50%, Mn: 0.10 to 2.00%, Al: 0.10 to 2.00%, P: 0.030% or less, S: 0.0050% or less, N: 0.0050% or less, Sn: more than 0% and 0.06% or less, the balance being Fe and impurities, is subjected to a hot rolling process, a pickling process, a cold rolling process, and a finish annealing process in that order; the finish annealing step involves heating from room temperature to 350 to 450°C so that the heating rate from 100°C to 350°C is 10 to 500°C / s, followed by retention in the temperature range of 350 to 450°C for 0.1 to 100 seconds, and subsequently heating from the temperature range of 350 to 450°C to an ultimate temperature within a temperature range of 600°C to 840 to 950°C so that the heating rate to the ultimate temperature is 700°C / s or more.

4. The method for producing a non-oriented electrical steel sheet according to claim 3, wherein the chemical composition of the steel slab contains, in place of a portion of Fe, one or more elements selected from the group consisting of Ca: 0.0050% or less, Zn: 0.0050% or less, Mg: 0.0050% or less, Ti: 0.015% or less, Cr: 0.20% or less, Sb: 0.20% or less, Mo: 0.015% or less, Nb: 0.015% or less, and Cu: 0.20% or less.

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