Non-oriented electrical steel sheet and method of manufacturing the same

Abstract

An electric steel sheet according to one embodiment of the present application, the steel sheet comprising, in weight %, Si: 1.5 to 4.0 %, Al: 0.7 to 2.5 %, Mn: 1 to 2 %, Cu: 0.003 to 0.02 %, and S: more than 0 % and 0.005 % or less, with the balance comprising Fe and unavoidable impurities, and satisfying the following Formula 1 and Formula 2. [Formula 1] 150 ≤ [Mn] / [Cu] ≤ 250 [Formula 2] 3 ≤ [Cu] / [S] ≤ 7 In Formula 1 and Formula 2, [Mn], [Cu], and [S] each represent the content (wt.%) of Mn, Cu, and S, respectively.

Description

[0001] This application is a divisional application of Chinese patent application No. 201980078872.0 filed on November 27, 2019, entitled “Non-oriented electrical steel sheet and manufacturing method thereof”, and claims priority to Korean application No. 10-2018-0153084. Technical Field

[0002] This invention relates to a non-oriented electrical steel sheet and its manufacturing method. Specifically, this invention relates to a non-oriented electrical steel sheet and its manufacturing method, which improves magnetic properties by appropriately controlling the distribution of sulfides through the relationship between Mn, Cu, and S. Background Technology

[0003] Non-oriented electrical steel sheets are primarily used in electric motors that convert electrical energy into mechanical energy. To achieve high efficiency during this conversion, non-oriented electrical steel sheets need to possess excellent magnetic properties. In particular, with the increasing focus on environmental protection technologies in recent years, improving the efficiency of electric motors has become crucial, as motors account for over half of all electrical energy consumption. Therefore, the demand for non-oriented electrical steel sheets with excellent magnetic properties is also increasing.

[0004] The magnetic properties of non-oriented electrical steel are mainly evaluated using iron loss and magnetic flux density. Iron loss refers to the energy loss that occurs at a specific magnetic flux density and frequency, while magnetic flux density refers to the degree of magnetization obtained under a specific magnetic field. The lower the iron loss, the more energy-efficient the electric motor can be manufactured under the same conditions. The higher the magnetic flux density, the smaller the electric motor can be or the less copper loss can be reduced. Therefore, it is important to manufacture non-oriented electrical steel sheets with low iron loss and high magnetic flux density.

[0005] Depending on the operating conditions of the electric motor, the properties of the non-oriented electrical steel sheet that need to be considered will also change. As a standard for evaluating the properties of non-oriented electrical steel sheets used in electric motors, the iron loss W of most electric motors when subjected to a 1.5T magnetic field at a commercial frequency of 50Hz is used. 15 / 50 It is considered the most important indicator. However, not all motors used for various purposes will have W. 15 / 50 Iron loss is considered the most important indicator, and it is evaluated under different frequencies or magnetic fields depending on the main operating conditions. Especially in non-oriented electrical steel sheets with a thickness of less than 0.35 mm used in drive motors for electric vehicles, magnetic properties at low magnetic fields of 1.0 T or less and high frequencies above 400 Hz are often more important. Therefore, using W... 10 / 400 The properties of non-oriented electrical steel sheets are evaluated by measuring iron loss.

[0006] To enhance the magnetic properties of non-oriented electrical steel sheets, a common method is to add alloying elements such as silicon (Si). Adding these elements increases the resistivity of the steel; as resistivity increases, eddy current losses decrease, thus reducing overall iron loss. However, increasing the amount of Si introduced leads to decreased magnetic flux density and increased brittleness. If the amount added exceeds a certain level, cold rolling becomes impossible, hindering industrial production. In particular, the thinner the electrical steel sheet, the lower the iron loss, but the decreased rollability due to brittleness becomes a fatal problem. Furthermore, to further increase the resistivity of the steel, elements such as aluminum and manganese have been explored.

[0007] In particular, the addition of manganese (Mn) can minimize the increase in steel's brittleness while increasing its resistivity. Therefore, manganese addition is actively used in the manufacturing methods of non-oriented electrical steel sheets for high-frequency applications where resistivity is critical. However, as the amount of Mn added increases, Mn can combine with sulfur, which readily bonds chemically, to form sulfides, or impurities contained in the ferroalloy can form precipitates, potentially causing magnetic degradation. Therefore, for these reasons, improving the iron loss of steel by adding Mn requires very demanding manufacturing techniques. Summary of the Invention

[0008] Technical issues This invention provides a non-oriented electrical steel sheet and a method for manufacturing the same. More specifically, this invention provides a non-oriented electrical steel sheet and a method for manufacturing the same, which improves magnetic properties by appropriately controlling the distribution of sulfides through the relationship between Mn, Cu, and S.

[0009] Technical solution According to an embodiment of the present invention, the non-oriented electrical steel sheet comprises, by weight %, Si: 1.5% to 4.0%, Al: 0.7% to 2.5%, Mn: 1% to 2%, Cu: 0.003% to 0.02% and S: greater than 0% and less than or equal to 0.005%, with the balance comprising Fe and unavoidable impurities, and satisfies the following formulas 1 and 2.

[0010] [Formula 1] 150 ≤ [Mn] / [Cu]≤ 250 [Equation 2] 3 ≤ [Cu] / [S]≤ 7 In Equations 1 and 2, [Mn], [Cu], and [S] represent the contents (by weight%) of Mn, Cu, and S, respectively.

[0011] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of C and N, the contents of which are less than or equal to 0.005 by weight.

[0012] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of Nb, Ti and V, the contents of which are less than or equal to 0.004 by weight.

[0013] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of P: less than or equal to 0.02%, B: less than or equal to 0.002%, Mg: less than or equal to 0.005%, and Zr: less than or equal to 0.005%.

[0014] The number of sulfides with a diameter of 150 nm to 300 nm can be more than twice the number of sulfides with a diameter of 20 nm to 100 nm.

[0015] The steel plate may contain sulfides with a diameter of 150 nm to 300 nm, and the area fraction of sulfides containing both Mn and Cu in the sulfides with a diameter of 150 nm to 300 nm may be greater than or equal to 70%.

[0016] The thickness of the steel plate can be from 0.1mm to 0.3mm.

[0017] The average grain diameter can range from 40 μm to 100 μm.

[0018] A method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention comprises: a step of heating a slab, wherein the slab comprises, by weight %, Si: 1.5% to 4.0%, Al: 0.7% to 2.5%, Mn: 1% to 2%, Cu: 0.003% to 0.02% and S: greater than 0% and less than or equal to 0.005%, the balance comprising Fe and unavoidable impurities, and satisfying the following formulas 1 and 2; a step of hot rolling the slab to manufacture a hot-rolled sheet; a step of cold rolling the hot-rolled sheet to manufacture a cold-rolled sheet; and a step of final annealing the cold-rolled sheet.

[0019] [Formula 1] 150 ≤ [Mn] / [Cu]≤ 250 [Equation 2] 3 ≤ [Cu] / [S]≤ 7 In Equations 1 and 2, [Mn], [Cu], and [S] represent the contents (by weight%) of Mn, Cu, and S, respectively.

[0020] The heating process for the slab can be carried out at a temperature of 1200°C or lower.

[0021] In the hot rolling process, the finishing temperature can be 750°C or higher.

[0022] Following the hot rolling step, an annealing step may be performed on the hot-rolled sheet at a temperature ranging from 850°C to 1150°C.

[0023] The cold rolling process may include one cold rolling step or two or more cold rolling steps including intermediate annealing.

[0024] The intermediate annealing temperature can be from 850℃ to 1150℃.

[0025] Invention Effects According to one embodiment of the present invention, by proposing an optimal alloy composition for non-oriented electrical steel sheets, suitable sulfide precipitates can be formed, thereby producing non-oriented electrical steel sheets with excellent magnetic properties.

[0026] Furthermore, according to one embodiment of the present invention, non-oriented electrical steel sheets with excellent magnetic properties can help improve the efficiency of electric motors and generators. Attached Figure Description

[0027] Figures 1 to 4 These are electron microscope images of sulfides containing both Mn and Cu. Detailed Implementation

[0028] The terms "first," "second," "third," etc., are used to describe parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, and / or segment from another. Therefore, without departing from the scope of the invention, the first part, component, region, layer, and / or segment described below can also be described as a second part, component, region, layer, and / or segment.

[0029] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular forms used herein are intended to include the plural forms as well. As used in the specification, "comprising" can specifically refer to a feature, field, integer, step, action, element, and / or component, but does not exclude the presence or addition of other features, fields, integers, steps, actions, elements, components, and / or groups.

[0030] If one part is described as being on top of another part, then other parts can exist directly on top of or in between the other part. When one part is described as being directly on top of another part, there are no other parts in between.

[0031] In addition, unless otherwise specified, % means weight, 1ppm is 0.0001 weight.

[0032] In one embodiment of the present invention, the inclusion of additional elements refers to the replacement of a portion of the remaining iron (Fe) by additional elements, the replacement amount being equivalent to the amount of additional elements added.

[0033] Although not otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in dictionaries should be interpreted as having the same meaning as disclosed in relevant technical literature and herein, and should not be interpreted in an idealized or overly formal sense.

[0034] Embodiments of the present invention will be described in detail below to enable those skilled in the art to implement the invention. However, the invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0035] According to an embodiment of the present invention, the non-oriented electrical steel sheet comprises, by weight %, Si: 1.5% to 4.0%, Al: 0.7% to 2.5%, Mn: 1% to 2%, Cu: 0.003% to 0.02% and S: greater than 0% and less than or equal to 0.005%, with the balance comprising Fe and unavoidable impurities, and satisfies the following formulas 1 and 2.

[0036] [Formula 1] 150 ≤ [Mn] / [Cu]≤ 250 [Equation 2] 3.00 ≤ [Cu] / [S]≤ 7.00 In Equations 1 and 2, [Mn], [Cu], and [S] represent the contents (by weight%) of Mn, Cu, and S, respectively.

[0037] The reasons for restricting the composition of non-oriented electrical steel sheets are explained below.

[0038] Si: 1.5% to 4.0% by weight Silicon (Si) is a key element added to increase the resistivity of steel and reduce eddy current losses in iron loss. Insufficient Si content leads to deterioration of iron losses. Conversely, excessive Si content significantly reduces magnetic flux density, potentially causing problems with machinability. Therefore, Si can be included within the aforementioned range. More specifically, Si can be present from 2.0 wt% to 3.9 wt%. More specifically, Si can be present from 2.5 wt% to 3.8 wt%.

[0039] Al: 0.7% to 2.5% by weight Aluminum (Al), along with silicon (Si), plays a crucial role in increasing resistivity and reducing iron loss. It also helps reduce magnetic anisotropy, minimizing magnetic deviations in the rolling direction and perpendicular to the rolling zone. If too little Al is added, the formation of fine nitrides may hinder the improvement of magnetic properties. Conversely, excessive Al addition may lead to magnetic attenuation due to the formation of too many nitrides. Therefore, Al can be included within the aforementioned range. More specifically, Al can be present from 1.0 wt% to 2.0 wt%.

[0040] Mn: 1.0 wt% to 2.0 wt% Manganese (Mn) increases the resistivity of the material, improves iron loss, and forms sulfides. If too little Mn is added, the formation of fine sulfides may cause magnetic attenuation. Conversely, if too much Mn is added, excessive Mn precipitation and the promotion of {111} textures detrimental to magnetism may cause a sharp decrease in magnetic flux density. More specifically, Mn may be present in amounts from 0.9 wt% to 1.9 wt%.

[0041] Cu: 0.003 wt% to 0.020 wt% Copper (Cu) is an element that can form metastable sulfides at high temperatures; its addition in large quantities leads to surface defects. However, when added in appropriate amounts, it increases the size of the sulfides and reduces their distribution density, thereby improving magnetism. More specifically, Cu may be present in amounts ranging from 0.005% to 0.015% by weight.

[0042] S: less than or equal to 0.005% by weight Sulfur (S) forms fine precipitates such as MnS, CuS, and (Mn, Cu)S, which deteriorate magnetic properties and hot workability, and therefore is best kept at low levels. More specifically, it may contain 0.0001 wt% to 0.005 wt%. More specifically, it may contain 0.0005 wt% to 0.0035 wt%.

[0043] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of C and N, the contents of which are less than or equal to 0.005% by weight. More specifically, it may also contain C: less than or equal to 0.005% by weight and N: less than or equal to 0.005% by weight.

[0044] C: less than or equal to 0.005% by weight Carbon (C) causes magnetic aging and combines with other impurity elements to form carbides, thereby reducing magnetic properties; therefore, the lower the carbon content, the better. When C is further included, its content can be less than or equal to 0.005% by weight. More specifically, it can also contain less than or equal to 0.003% by weight of C.

[0045] N: less than or equal to 0.005% by weight Nitrogen (N) not only forms elongated AlN precipitates within the matrix, but also combines with other impurities to form fine nitrides, thereby inhibiting grain growth and leading to deterioration of iron loss. Therefore, when N is further included, its content can be less than or equal to 0.005% by weight. More specifically, it can also contain less than or equal to 0.003% by weight of N.

[0046] According to one embodiment of the present invention, the non-oriented electrical steel sheet may further contain one or more of Nb, Ti and V, the contents of which are less than or equal to 0.004% by weight. More specifically, it may further contain less than or equal to 0.004% by weight of Nb, Ti and V respectively.

[0047] Niobium (Nb), titanium (Ti), and vanadium (V) are elements with a strong tendency to form precipitates in steel, creating fine carbides, nitrides, or sulfides within the base metal, thereby inhibiting grain growth and worsening iron loss. Therefore, when Nb, Ti, or V is further included, their respective contents can be less than or equal to 0.004% by weight. More specifically, they can each contain less than or equal to 0.002% by weight.

[0048] The non-oriented electrical steel sheet according to one embodiment of the present invention may further contain one or more of P: less than or equal to 0.02%, B: less than or equal to 0.002%, Mg: less than or equal to 0.005%, and Zr: less than or equal to 0.005%. More specifically, it may also contain P: less than or equal to 0.02%, B: less than or equal to 0.002%, Mg: less than or equal to 0.005%, and Zr: less than or equal to 0.005%.

[0049] Although these elements are trace elements, they can cause magnetic degradation due to inclusions in steel. Therefore, the concentrations can be controlled to be P: less than or equal to 0.02%, B: less than or equal to 0.002%, Mg: less than or equal to 0.005%, and Zr: less than or equal to 0.005%.

[0050] The balance includes Fe and unavoidable impurities. Unavoidable impurities are those introduced during the steelmaking process and the manufacturing process of grain-oriented electrical steel sheets; these impurities are well-known in the art and therefore specific descriptions are omitted. In one embodiment of the invention, the addition of other elements besides the aforementioned alloy composition is not excluded, and various elements may be included within the scope of the inventive concept. When additional elements are further included, they replace a portion of the Fe in the balance.

[0051] As mentioned above, in one embodiment of the present invention, the distribution of sulfides can be controlled by appropriately controlling the relationship between Mn, Cu, and S, thereby improving the magnetism.

[0052] Specifically, the number of sulfides with a diameter of 150 nm to 300 nm can be more than twice the number of sulfides with a diameter of 20 nm to 100 nm. Compared to sulfides with a diameter of 20 nm to 100 nm, sulfides with a diameter of 150 nm to 300 nm impede the movement of magnetic domain walls, thus causing less attenuation of magnetic properties. Therefore, by forming a large number of sulfides with a diameter of 150 nm to 300 nm, magnetism can be improved. Here, the diameter of the sulfide refers to the diameter when the sulfide is observed on a plane parallel to the rolled surface (ND surface). The diameter refers to the diameter of a circle with the same area as the sulfide. The ratio of the number of sulfides with a diameter of 150 nm to 300 nm to the number of sulfides with a diameter of 20 nm to 100 nm can be the ratio of the number observed on an area of ​​at least 5 μm × 5 μm. More specifically, the number of sulfides with a diameter of 150 nm to 300 nm can be 2 to 3.5 times the number of sulfides with a diameter of 20 nm to 100 nm.

[0053] Specifically, the density of sulfides with diameters ranging from 20 nm to 100 nm can be 20 per mm. 2 Up to 40 pieces / mm 2 The density of sulfides with diameters ranging from 150 nm to 300 nm can be 60 per mm. 2 Up to 100 pieces / mm 2 .

[0054] The area fraction of sulfides containing both Mn and Cu in sulfides with a diameter of 150 nm to 300 nm can be greater than or equal to 70%. Compared with sulfides containing only Mn or Cu, sulfides containing both Mn and Cu have larger sizes and fewer sulfides per unit area. Therefore, their effect on hindering magnetic domain wall movement and grain growth is significantly reduced. When the area fraction of sulfides containing both Mn and Cu is greater than or equal to 70%, the above effect is very significant, thus improving the magnetic properties of the steel plate.

[0055] The thickness of the steel plate can range from 0.1 mm to 0.3 mm. The average grain diameter can range from 40 μm to 100 μm. When the thickness and average grain diameter are appropriate, the magnetism can be improved.

[0056] As mentioned above, in one embodiment of the present invention, the distribution of sulfides can be controlled by appropriately controlling the relationship between Mn, Cu, and S, thereby improving the magnetism. Specifically, the iron loss W of the non-oriented electrical steel sheet... 15 / 50 It can be less than or equal to 1.9 W / Kg, iron loss W 10 / 400 It can be less than or equal to 9.5 W / kg, magnetic flux density B 50 It can be greater than or equal to 1.65T. Iron loss W 15 / 50 This refers to the iron loss when excited with a magnetic flux density of 1.5T at a frequency of 50Hz. Iron loss W10 / 400 This refers to the iron loss when excited with a magnetic flux density of 1.0T at a frequency of 400Hz. Magnetic flux density B 50 This refers to the magnetic flux density induced under a magnetic field of 5000 A / m. More specifically, it refers to the iron loss W of non-oriented electrical steel sheets. 15 / 50 It can be less than or equal to 1.9 W / Kg, iron loss W 10 / 400 It can be less than or equal to 9.5 W / kg, magnetic flux density B 50 It can be greater than or equal to 1.65T.

[0057] A method for manufacturing non-oriented electrical steel sheet according to an embodiment of the present invention includes the steps of heating a slab; hot rolling the slab to manufacture a hot-rolled sheet; cold rolling the hot-rolled sheet to manufacture a cold-rolled sheet; and finally annealing the cold-rolled sheet.

[0058] First, the slab is heated.

[0059] The alloy composition of the slab has already been described in the section on the alloy composition of non-oriented electrical steel sheets, so it will not be repeated here. The alloy composition does not actually change during the manufacturing process of non-oriented electrical steel sheets; therefore, the alloy composition of non-oriented electrical steel sheets is essentially the same as that of the slab.

[0060] Specifically, by weight percent, the slab contains Si: 1.5% to 4.0%, Al: 0.7% to 2.5%, Mn: 1% to 2%, Cu: 0.003% to 0.02% and S: greater than 0% and less than or equal to 0.005%, with the balance containing Fe and unavoidable impurities, and can satisfy Equations 1 and 2 below.

[0061] [Formula 1] 150 ≤ [Mn] / [Cu]≤ 250 [Equation 2] 3.00 ≤ [Cu] / [S]≤ 7.00 In Equations 1 and 2, [Mn], [Cu], and [S] represent the contents (by weight%) of Mn, Cu, and S, respectively.

[0062] For additional elements other than these, they have already been described in the section on alloy composition of non-oriented electrical steel sheets, so a repeat description is omitted.

[0063] The heating temperature of the slab is not limited, but it can be heated at 1200℃ or lower. If the heating temperature of the slab is too high, precipitates such as AlN and MnS present in the slab will be micro-precipitated during hot rolling and annealing after solution treatment, thereby inhibiting grain growth and potentially causing a decrease in magnetic properties.

[0064] Next, the slab is hot-rolled to produce a hot-rolled sheet. The thickness of the hot-rolled sheet can be less than or equal to 2.5 mm. In the process of manufacturing the hot-rolled sheet, the finishing rolling temperature can be 750°C or higher. Specifically, it can be from 750°C to 1000°C. The hot-rolled sheet can be coiled at a temperature of 700°C or lower.

[0065] Following the manufacturing process of the hot-rolled sheet, a hot-rolled sheet annealing step may be included. In this case, the annealing temperature can be between 850°C and 1150°C. If the annealing temperature is too low, the microstructure will not grow or will only show minimal growth, making it difficult to obtain a magnetically favorable texture during post-cold rolling annealing. If the annealing temperature is too high, excessive sub-grain growth will occur, potentially resulting in numerous surface defects. To increase magnetically favorable orientation, hot-rolled sheet annealing may be performed as needed, or it can be omitted. The annealed hot-rolled sheet can then be pickled.

[0066] Next, the hot-rolled sheet is cold-rolled to produce a cold-rolled sheet. For cold rolling, the final thickness is 0.1 mm to 0.3 mm. The cold rolling process may include one cold rolling step or two or more cold rolling steps including intermediate annealing. In this case, the intermediate annealing temperature may be between 850°C and 1150°C.

[0067] Next, the cold-rolled sheet undergoes final annealing. In the annealing process, the annealing temperature is generally not highly restricted, as long as it is the temperature applied to non-oriented electrical steel sheets. The iron loss of non-oriented electrical steel sheets is closely related to grain size; therefore, 900°C to 1100°C is a suitable temperature. During the final annealing process, the average grain size can be 40μm to 100μm, and all the processed microstructures formed in the previous cold rolling step (i.e., over 99%) can recrystallize.

[0068] After final annealing, an insulating film layer can be formed. The insulating film layer can be processed into an organic film layer, an inorganic film layer, or an organic-inorganic composite film layer, or it can be treated with other insulating film-forming agents.

[0069] The present invention will be described in more detail below through embodiments. However, the following embodiments are merely examples of the present invention, and the present invention is not limited to the embodiments described herein.

[0070] Example Slabs were manufactured according to the composition shown in Table 1. The slabs were heated to 1150°C and hot-rolled to a final temperature of 780°C to produce hot-rolled sheets with a thickness of 2.0 mm. The hot-rolled sheets were then annealed at 1030°C for 100 seconds, followed by pickling and cold rolling to thicknesses of 0.15 mm, 0.25 mm, 0.27 mm, and 0.30 mm, and recrystallized at 1000°C for 100 seconds.

[0071] For each sample, the following parameters are considered: thickness, [Mn] / [Cu], [Cu] / [S], ​​sulfide distribution density with diameters from 20 nm to 100 nm (a), sulfide distribution density with diameters from 150 nm to 300 nm (b), b / a, fraction of sulfides containing both Mn and Cu, and W. 15 / 50 W 10 / 400 B 50 The distribution density of sulfides with diameters of 20 nm to 100 nm and 150 nm to 300 nm was shown in Table 2. More than 20,000 TEM images of the same sample (5 μm × 5 μm × 20,000) were observed. For measurements of 0.5 μm... 2 The above-mentioned areas were used to perform EDS analysis on the precipitates found, and the diameter of the precipitates containing S was measured to represent the sulfide distribution density. The fraction of sulfides containing both Mn and Cu refers to the fraction of Mn and Cu sulfides detected simultaneously in the overall S-containing sulfide observed in the aforementioned TEM EDS observation. Figures 1 to 4 The image shows an electron microscope image of sulfides where Mn and Cu were detected simultaneously. For magnetic properties such as magnetic flux density and iron loss, five 60mm wide × 60mm long samples were cut from each specimen and measured using a single sheet tester in both the rolling direction and the direction perpendicular to the rolling. The average values ​​were used to represent the magnetic flux density and iron loss. At this point, W... 15 / 50 The iron loss, W, is the result of excitation at a frequency of 50Hz and a magnetic flux density of 1.5T. 10 / 400 The iron loss, B, is the result of excitation at a frequency of 400Hz and a magnetic flux density of 1.0T. 50 It is the magnetic flux density induced under a magnetic field of 5000 A / m.

[0072] Table 1

[0073] Table 2

[0074] As shown in Tables 1 and 2, by appropriately controlling the alloy composition of A3, A4, B3, B4, C3, C4, D3, D4, E3, and E4, the ratio of sulfides with diameters of 20 nm to 100 nm to sulfides with diameters of 150 nm to 300 nm is appropriate, thus all exhibiting excellent magnetic properties.

[0075] On the other hand, A1 and A2 have insufficient or excessive Cu content, thus increasing the number of small sulfides that are detrimental to magnetism and suppressing the formation of large sulfides, resulting in poor iron loss and magnetic flux density. B1 and B2 have excessive Mn to Cu ratios, and C1 and C2 have excessive Cu to S ratios, thus increasing the number of sulfides that are detrimental to magnetism and suppressing the formation of large complex sulfides, resulting in poor iron loss and magnetic flux density. D1 and D2 have insufficient or excessive Mn content, resulting in poor iron loss and magnetic flux density. E1 and E2 have excessive S content, thus rapidly increasing the number of small sulfides that are detrimental to magnetism, resulting in poor iron loss and magnetic flux density.

[0076] This invention can be implemented in various ways and is not limited to the embodiments described above. Those skilled in the art will understand that the invention can be implemented in other specific ways without altering its technical concept or essential features. Therefore, it should be understood that the above embodiments are exemplary in all respects and are not restrictive.

Claims

1. A non-oriented electrical steel sheet, characterized in that, The steel plate, by weight percent, comprises Si: 1.5% to 4.0%, Al: 0.7% to 2.5%, Mn: 1% to 2%, Cu: 0.003% to 0.02%, and S: greater than 0% and less than or equal to 0.005%, with the balance including Fe and unavoidable impurities, and satisfies the following formulas 1 and 2. [Formula 1] 150 ≤ [Mn] / [Cu] ≤ 250 [Equation 2] 3 ≤ [Cu] / [S] ≤ 7 In Equations 1 and 2, [Mn], [Cu], and [S] represent the contents (by weight%) of Mn, Cu, and S, respectively.

2. The non-oriented electrical steel sheet according to claim 1, characterized in that, The steel plate also contains one or more of C and N, with each content being less than or equal to 0.005 by weight.

3. The non-oriented electrical steel sheet according to claim 1, characterized in that, The steel plate also contains one or more of Nb, Ti and V, each in a content of less than or equal to 0.004 wt%.

4. The non-oriented electrical steel sheet according to claim 1, characterized in that, The steel plate also contains one or more of the following: P: less than or equal to 0.02%, B: less than or equal to 0.002%, Mg: less than or equal to 0.005%, and Zr: less than or equal to 0.005%.

5. The non-oriented electrical steel sheet according to claim 1, characterized in that, The number of sulfides with a diameter of 150 nm to 300 nm is more than twice the number of sulfides with a diameter of 20 nm to 100 nm.

6. The non-oriented electrical steel sheet according to claim 1, characterized in that, The steel plate contains sulfides with a diameter of 150 nm to 300 nm. The area fraction of the sulfides containing both Mn and Cu in the sulfides with a diameter of 150 nm to 300 nm is greater than or equal to 70%.

7. The non-oriented electrical steel sheet according to claim 1, characterized in that, The thickness of the steel plate is 0.1 mm to 0.3 mm.

8. The non-oriented electrical steel sheet according to claim 1, characterized in that, The average grain diameter is 40 μm to 100 μm.

9. A method for manufacturing a non-oriented electrical steel sheet, characterized in that, The manufacturing method includes: The step of heating the slab, by weight %, the slab contains Si: 1.5% to 4.0%, Al: 0.7% to 2.5%, Mn: 1% to 2%, Cu: 0.003% to 0.02% and S: greater than 0% and less than or equal to 0.005%, the balance containing Fe and unavoidable impurities, and satisfies the following formulas 1 and 2; The step of hot rolling the slab to manufacture a hot-rolled plate; The step of cold rolling the hot-rolled sheet to manufacture a cold-rolled sheet; as well as The final annealing step is performed on the cold-rolled sheet. [Formula 1] 150 ≤ [Mn] / [Cu] ≤ 250 [Equation 2] 3 ≤ [Cu] / [S] ≤ 7 In Equations 1 and 2, [Mn], [Cu], and [S] represent the contents (by weight%) of Mn, Cu, and S, respectively.

10. The method for manufacturing non-oriented electrical steel sheet according to claim 9, characterized in that, In the step of heating the slab, the heating is carried out at a temperature of 1200°C or lower.

11. The method for manufacturing non-oriented electrical steel sheet according to claim 9, characterized in that, The finishing temperature in the hot rolling step is 750°C or higher.

12. The method for manufacturing non-oriented electrical steel sheet according to claim 9, characterized in that, Following the hot rolling step, the process also includes an annealing step of the hot-rolled sheet at a temperature ranging from 850°C to 1150°C.

13. The method for manufacturing non-oriented electrical steel sheet according to claim 9, characterized in that, The cold rolling process includes one cold rolling step or two or more cold rolling steps including intermediate annealing.

14. The method for manufacturing non-oriented electrical steel sheet according to claim 13, characterized in that, The intermediate annealing temperature is 850°C to 1150°C.

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