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

Abstract

The present invention provides a non-oriented electrical steel sheet containing silicon (Si): 2.8 to 3.8% by weight, manganese (Mn): 0.2 to 0.5% by weight, aluminum (Al): 0.5 to 1.2% by weight, carbon (C): more than 0 and 0.002% by weight or less, phosphorus (P): more than 0 and 0.015% by weight or less, sulfur (S): more than 0 and 0.002% by weight or less, nitrogen (N): more than 0 and 0.002% by weight or less, titanium (Ti): more than 0 and 0.002% by weight or less, and the balance of iron (Fe) and other inevitable impurities. In the final microstructure, the crystal grains having the {111} / / ND orientation have a volume fraction of 30% or less and an average misorientation angle of 23° or more, and the crystal grains having the {001} / / ND orientation have a volume fraction of 15% or more and an average misorientation angle of 48° or more.

Description

[Technical Field]

[0001] The present invention relates to non-oriented electrical steel sheets and methods for manufacturing the same, and more particularly to high-efficiency non-oriented electrical steel sheets and methods for manufacturing the same. [Background technology]

[0002] Electrical steel sheets can be classified into grain-oriented and non-oriented types based on their magnetic properties. Grain-oriented electrical steel sheets are manufactured to be easily magnetized in the rolling direction of the steel sheet, and have particularly excellent magnetic properties in the rolling direction. Therefore, they are mainly used as core materials for large, medium, and small transformers where low iron loss and high permeability are required. In contrast, non-oriented electrical steel sheets have uniform magnetic properties regardless of the orientation of the steel sheet, and are therefore widely used as core materials for small electric motors, small power transformers, ballasts, and other devices.

[0003] A relevant prior art document is Korean Published Patent No. 10-2015-0001467. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] The technical problem that this invention aims to solve is to provide a non-oriented electrical steel sheet with excellent high-frequency iron loss and uniform magnetic properties, as well as a method for manufacturing the same.

[0005] However, these challenges are illustrative and do not limit the scope of the present invention. [Means for solving the problem]

[0006] A non-oriented electrical steel sheet according to one aspect of the present invention for solving the above problems is a non-oriented electrical steel sheet containing silicon (Si): 2.8~3.8 wt%, manganese (Mn): 0.2~0.5 wt%, aluminum (Al): 0.5~1.2 wt%, carbon (C): greater than 0 and 0.002 wt% or less, phosphorus (P): greater than 0 and 0.015 wt% or less, sulfur (S): greater than 0 and 0.002 wt% or less, nitrogen (N): greater than 0 and 0.002 wt% or less, titanium (Ti): greater than 0 and 0.002 wt% or less, and the remaining iron (Fe) and other unavoidable impurities. In the final microstructure, the volume fraction of crystal grains having the {111} / / ND orientation is 30% or less, and the average misorientation angle is 23° or more, and the volume fraction of crystal grains having the {001} / / ND orientation is 15% or more, and the average misorientation angle is 48° or more.

[0007] In the aforementioned non-oriented electrical steel sheet, the iron loss (W) is 13.5 W / kg or less. 10 / 400 ) may have a standard deviation of 0.725 W / kg or less for iron loss.

[0008] In the aforementioned non-oriented electrical steel sheet, the average grain size may be 80 to 150 μm.

[0009] A method for manufacturing non-oriented electrical steel sheets according to one aspect of the present invention to solve the above problems is to provide a steel material containing silicon (Si): 2.8~3.8 wt%, manganese (Mn): 0.2~0.5 wt%, aluminum (Al): 0.5~1.2 wt%, carbon (C): greater than 0.002 wt% or less, phosphorus (P): greater than 0.015 wt% or less, sulfur (S): greater than 0.002 wt% or less, nitrogen (N): greater than 0.002 wt% or less, titanium (Ti): greater than 0.002 wt% or less, and the remaining iron (Fe) and other unavoidable impurities; hot rolling the steel material; first annealing heat treatment of the hot-rolled steel material; and The process includes the steps of: cold rolling; and second annealing heat treatment of the cold-rolled steel material, wherein the hot rolling step is performed under the conditions of a reheating temperature of 1100-1200°C, a finish rolling temperature of 800-1000°C, and a coiling temperature of 560-600°C; the first annealing heat treatment step is performed under the conditions of a heating rate of 10°C / s or more, an annealing start temperature of 900-1050°C, an annealing duration of 30-90 seconds, and a cooling rate of 20°C / s or more; and the second annealing heat treatment step is performed under the conditions of a heating rate of 10°C / s or more, an annealing start temperature of 900-1100°C, an annealing duration of 30-90 seconds, and a cooling rate of 30°C / s or more.

[0010] In the method for manufacturing the non-oriented electrical steel sheet, after the first annealing heat treatment, the average grain size is 140 to 250 μm, and in the central layer <110> / / The volume fraction of crystal grains having an RD orientation may be 20% or less.

[0011] In the method for manufacturing the non-oriented electrical steel sheet, the cold rolling step may be performed under conditions of a reduction ratio of 81-92%.

[0012] In the method for manufacturing the non-oriented electrical steel sheet, the thickness of the steel material after hot rolling may be 1.6 to 2.6 mm, and the thickness of the steel material after cold rolling may be 0.1 to 0.3 mm. [Effects of the Invention]

[0013] According to embodiments of the present invention, it is possible to provide non-oriented electrical steel sheets with excellent high-frequency iron loss and uniform magnetic properties, as well as a method for manufacturing the same. For example, by adjusting the pre-annealing conditions after hot rolling, it is possible to provide non-oriented electrical steel sheets with low average iron loss and standard deviation. By limiting the temperature and grain size during pre-annealing, it is possible to suppress increases in production costs. By manufacturing non-oriented electrical steel sheets with uniform microstructure and texture, uniform magnetic properties can be ensured.

[0014] Of course, the scope of the present invention is not limited by such effects. [Brief explanation of the drawing]

[0015] [Figure 1] This flowchart shows a method for manufacturing a non-oriented electrical steel sheet according to one embodiment of the present invention. [Figure 2] This is a photograph of the texture (IPF MAP) observed through EBSD analysis on a non-oriented electrical steel sheet according to Example 1 of the experimental examples of the present invention. [Figure 3] This is a photograph of the texture (IPF MAP) observed through EBSD analysis on a non-oriented electrical steel sheet according to Comparative Example 2 of the experimental examples of the present invention. [Modes for carrying out the invention]

[0016] A method for manufacturing non-oriented electrical steel sheets according to one embodiment of the present invention will be described in detail. The terms described below are terms that have been appropriately selected considering the function in the present invention, and the definitions of such terms must be based on the content throughout this specification.

[0017] Generally, electrical steel sheets are classified into grain-oriented electrical steel sheets and non-grain-oriented electrical steel sheets. Grain-oriented electrical steel sheets are mainly used in stationary devices such as transformers, while non-grain-oriented electrical steel sheets are mainly used in rotating rotating equipment such as motors and generators. Recently, in response to global environmental issues, technology has been rapidly shifting from existing internal combustion engines to alternative hybrid vehicles (HEV), electric vehicles (EV), hydrogen vehicles, and the like.

[0018] Non-grain-oriented electrical steel sheet used as a core material for motors plays the role of converting electrical energy into mechanical energy in rotating equipment. For energy saving, it is important that the steel sheet has good magnetic properties, that is, low core loss and high magnetic flux density. Core loss is the energy loss generated during the magnetization process, and magnetic flux density refers to the force that generates power. Magnetic flux density is represented by B 50 , and for core loss, W 15 / 50 is generally used as the main evaluation index. However, when high-frequency characteristics are required, such as for electric vehicles, W 10 / 400 is used to evaluate core loss. B 50 indicates the magnetic flux density at 5000 A / m, W 15 / 50 indicates the core loss at 50 Hz and 1.5 T, and W 10 / 400 indicates the core loss at 400 Hz and 1.0 T.

[0019] In order to satisfy these required properties, it is necessary to appropriately control the Si content, product thickness, crystal grain size, texture, precipitates, and other parameters. Increasing the Si content and reducing product thickness is effective for reducing core loss, but has the disadvantage of lowering magnetic flux density. To compensate for this, control of crystal grain size, texture and precipitates is very important in the manufacturing process of non-grain-oriented electrical steel sheets. Magnetic properties (core loss and magnetic flux density) change very sensitively depending on crystal grain size, texture and precipitates, so variations in the manufacturing process will lead to variations in magnetic properties.

[0020] A motor core has a structure formed by laminating dozens to hundreds of non-oriented electrical steel sheets. When non-oriented electrical steel sheets with large variations in magnetic properties are applied to the manufacturing of such a motor core, problems may occur in the operation of the motor.

[0021] In order to achieve low iron loss and high magnetic flux density, the non-oriented electrical steel sheet for automobile drive motors according to the present invention is subjected to pre-annealing after hot rolling and before cold rolling. Said pre-annealing is different from the final annealing performed after cold rolling.

[0022] According to related research, after pre-annealing, a method of performing cold rolling and final annealing with the grain size set to 400µm or above has been proposed, but this may cause the problem of variation in magnetic properties due to non-uniform microstructure and texture. According to other research, after pre-annealing, a technology of controlling the grain size to 150µm or above and improving the texture through ensuring productivity has been proposed, but it does not set a limit on the grain size after pre-annealing and does not take into account the variation in magnetic properties caused by the subsequent non-uniform microstructure / texture.

[0023] In the present invention, by controlling the appropriate grain size and texture after pre-annealing, a non-oriented electrical steel sheet having uniform microstructure and texture after cold rolling and final annealing and a manufacturing method therefor are provided.

[0024] Figure 1 is a flowchart illustrating a method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0025] Referring to Figure 1, the method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention comprises: providing a steel material containing silicon (Si), manganese (Mn) and aluminum (Al) (step S10); hot-rolling said steel material (step S20); subjecting said hot-rolled steel material to a first annealing heat treatment (step S30); cold-rolling said first annealing heat-treated steel material (step S40); and subjecting said cold-rolled steel material to a second annealing heat treatment (step S50).

[0026] Steel material supply step (S10)

[0027] The steel material fed into the hot rolling process is steel material for manufacturing non-oriented electrical steel sheets, and includes, for example, silicon (Si): 2.8-3.8% by weight, manganese (Mn): 0.2-0.5% by weight, aluminum (Al): 0.5-1.2% by weight, carbon (C): greater than 0% or less than 0.002% by weight, phosphorus (P): greater than 0% or less than 0.015% by weight, sulfur (S): greater than 0% or less than 0.002% by weight, nitrogen (N): greater than 0% or less than 0.002% by weight, titanium (Ti): greater than 0% or less than 0.002% by weight, and the remainder being iron (Fe) and other unavoidable impurities.

[0028] The following describes the roles and contents of exemplary compositional components to which the method for manufacturing non-oriented electrical steel sheets according to the technical concept of the present invention can be applied.

[0029] Silicon (Si): 2.8-3.8% by weight

[0030] Silicon (Si) is a major additive element that increases resistivity and reduces iron loss (eddy current loss). When the amount of silicon added is low, less than 2.8% by weight, it becomes difficult to obtain the desired high-frequency low iron loss value, and as the amount of silicon added increases, the permeability and magnetic flux density decrease. Furthermore, when the amount of silicon added exceeds 3.8% by weight, brittleness increases, making cold rolling difficult and reducing productivity.

[0031] Manganese (Mn): 0.2-0.5% by weight

[0032] Manganese (Mn), along with silicon, increases resistivity and improves texture. Adding more than 0.5% by weight of manganese degrades magnetic properties, such as the formation of coarse MnS precipitates and a decrease in magnetic flux density. Furthermore, when the manganese content exceeds 0.5% by weight, while the reduction in iron loss is small compared to the amount added, a significant decrease in cold rolling properties occurs. Moreover, when the manganese content is less than 0.2% by weight, it can form fine MnS precipitates and suppress grain growth; therefore, the manganese composition can be adjusted to a range of 0.2-0.5% by weight.

[0033] Aluminum (Al): 0.5-1.2% by weight

[0034] Aluminum (Al), along with silicon, is a major additive element that increases resistivity and reduces iron loss (eddy current loss). Aluminum also plays a role in reducing magnetic anisotropy and decreasing magnetic variability. Aluminum combines with nitrogen to induce the precipitation of AlN. If the aluminum content is less than 0.5% by weight, the above effects are unlikely to be achieved, and fine nitrides may form, increasing the variability of magnetic properties. If the aluminum content exceeds 1.2% by weight, cold rolling properties decrease, excess nitrides are formed, the magnetic flux density decreases, and the magnetic properties deteriorate.

[0035] Carbon (C): More than 0 and 0.002% by weight or less

[0036] Carbon (C) is an element that increases iron loss by forming carbides such as TiC and NbC, and it is preferable to have less of it, limiting it to 0.002% by weight or less. If the carbon content exceeds 0.002% by weight, magnetic aging occurs and the magnetic properties decrease, and if it is 0.002% by weight or less, the magnetic aging phenomenon is suppressed.

[0037] Phosphorus (P): More than 0 and 0.015% by weight or less

[0038] Phosphorus (P) is a grain boundary segregating element that promotes the development of texture. When the phosphorus content exceeds 0.015% by weight, the segregation effect inhibits grain growth, degrades magnetic properties, and reduces cold rolling properties.

[0039] Sulfur (S): More than 0 and 0.002% by weight or less

[0040] Sulfur (S) forms precipitates such as MnS and CuS, increasing iron loss and inhibiting grain growth. Therefore, its addition should be kept as low as possible, limiting it to 0.002% by weight or less. If the sulfur content exceeds 0.002% by weight, the problem of increased iron loss will occur.

[0041] Nitrogen (N): Greater than 0% by weight and less than or equal to 0.002% by weight

[0042] Nitrogen (N) forms precipitates such as AlN, Tin, and NbN, increasing iron loss and inhibiting grain growth. Therefore, its addition should be kept as low as possible, limited to 0.002% by weight or less. If the nitrogen content exceeds 0.002% by weight, the problem of increased iron loss will occur.

[0043] Titanium (Ti): Less than 0% by weight

[0044] Titanium (Ti) inhibits grain growth by forming fine precipitates such as TiC and TiN. Since the magnetic properties deteriorate as titanium is added, it should be added as little as possible, limiting it to 0.002% by weight or less. If the titanium content exceeds 0.002% by weight, problems arise with the deterioration of magnetic properties.

[0045] Hot rolling step (S20)

[0046] The steel material having the above-described composition undergoes a hot rolling process. The hot rolling step (S20) of the steel material may be carried out under the following conditions: reheating temperature: 1100~1200°C, finish rolling temperature: 800~1000°C, and coiling temperature: 560~600°C.

[0047] If the slab reheating temperature exceeds 1200°C, precipitates such as C, S, and N in the slab may redissolve, leading to the formation of fine precipitates in subsequent rolling and annealing processes, suppressing grain growth and potentially degrading magnetism. If the slab reheating temperature is below 1100°C, the rolling load increases, which can result in high iron loss in the final product.

[0048] After performing the step of hot rolling the steel material (S20), the thickness of the hot-rolled sheet may be, for example, 1.6 to 2.6 mm. As the thickness of the hot-rolled sheet increases, the reduction ratio of the cold rolling increases, and the texture becomes inferior, so it is preferable to control the thickness to 2.6 mm or less.

[0049] The hot-rolled steel material may be wound at a winding temperature (CT) of 560 to 600°C. If the winding temperature is below 560°C, there is no annealing effect on the steel material, and therefore no grain growth occurs. If the winding temperature exceeds 600°C, oxidation may increase during cooling, which may result in poor pickling properties.

[0050] First annealing heat treatment step (S30)

[0051] The hot-rolled steel material can be subjected to a first annealing heat treatment (S30). The first annealing heat treatment is an APL (Annealing and Pickling Line) step in which the hot-rolled sheet is annealed and pickled, and can be understood as a pre-annealing treatment or a hot-rolling annealing treatment.

[0052] The first annealing heat treatment step (S30) includes an annealing process in which the temperature is raised at a heating rate of 10°C / s or more, followed by initiating annealing at a temperature of 900 to 1050°C and maintaining it for 30 to 90 seconds. After annealing, the steel material can be cooled at a cooling rate of 20°C / s or more. After cooling, the step of pickling may be further included.

[0053] After hot rolling, the hot-rolled sheet is annealed to ensure uniformity of the microstructure and cold-rollability. The first annealing temperature is adjusted to 900-1050°C to form a uniform microstructure from which the stretched cast structure has been removed. If the first annealing temperature is too low (below 900°C), the stretched cast structure remaining after hot rolling will persist, inducing microstructure non-uniformity, resulting in smaller grain sizes, which can hinder cold rolling. On the other hand, if the first annealing temperature is too high (above 1050°C), it can induce variations in the texture of the final product, leading to anisotropy in its properties.

[0054] After the first annealing heat treatment, the average grain size was 140-250 μm, and in the central layer <110> / / The volume fraction of crystal grains having an RD orientation may be greater than 0% and less than or equal to 20%. Here, RD means Rolling Direction, and the central layer means the central region (thickness 1 / 4 to 3 / 4) obtained by removing t / 4 of the thickness (t) of the steel material from the surface portion of the steel material to the top and bottom.

[0055] Cold rolling step (S40)

[0056] The steel material that has undergone the first annealing heat treatment is subjected to the cold rolling step (S40). The reduction ratio of the cold rolling is 81-92%, and the thickness of the steel material after cold rolling may be 0.1-0.3 mm. In order to impart rollability, the plate temperature can be raised to 100-200°C and warm rolling can be performed.

[0057] Second annealing heat treatment step (S50)

[0058] The cold-rolled steel material can be subjected to a second annealing heat treatment. The second annealing heat treatment is an ACL (Annealing and Coating Line) step in which the cold-rolled sheet is final annealed, and can be understood as a cold-rolling annealing treatment. The second annealing heat treatment step (S50) may include a step of annealing under the conditions of heating rate: 10°C / s or more, annealing temperature: 900~1100°C, and holding time: 30~90 seconds, and a step of cooling under the conditions of cooling rate: 30°C / s or more.

[0059] The second annealing heat treatment is performed on the cold-rolled sheet obtained after cold rolling. The temperature is applied to derive the optimal grain size, taking into consideration the improvement of iron loss and mechanical properties. To prevent surface oxidation and nitriding during cold rolling annealing, heating is performed under mixed atmosphere conditions. The surface is further smoothed by passing it through a mixed atmosphere of nitrogen and hydrogen. If the cold rolling annealing temperature is below 900°C, the grain size is fine, which may increase hysteresis loss, and if the cold rolling annealing temperature exceeds 1100°C, the grain size becomes coarse, and eddy current loss increases.

[0060] On the other hand, after the final cold rolling and annealing, a coating process can be performed to form an insulating coating layer. By forming an insulating coating layer, improved punchability and insulation properties can be ensured. The thickness of the insulating coating layers formed on the upper and lower parts of the cold-rolled material may be approximately 1 to 2 μm.

[0061] The non-oriented electrical steel sheet produced by the manufacturing method described above is a non-oriented electrical steel sheet containing silicon (Si): 2.8-3.8 wt%, manganese (Mn): 0.2-0.5 wt%, aluminum (Al): 0.5-1.2 wt%, carbon (C): greater than 0 and less than 0.002 wt%, phosphorus (P): greater than 0 and less than 0.015 wt%, sulfur (S): greater than 0 and less than 0.002 wt%, nitrogen (N): greater than 0 and less than 0.002 wt%, titanium (Ti): greater than 0 and less than 0.002 wt%, and the remaining iron (Fe) and other unavoidable impurities. In the final microstructure, the volume fraction of crystal grains having the {111} / / ND orientation is greater than 0 and less than 30%, and the average orientation difference angle (misorientation) is greater than 0 and less than 30%. The angle is 23° or greater (for example, 23° to 40°), the volume fraction of crystal grains having the {001} / / ND orientation is 15% or greater (for example, 15% to 50%), and the average misorientation angle is 48° or greater (for example, 48° to 60°).

[0062] Here, the ND direction is perpendicular to the rolling direction (RD) and perpendicular to the upper surface of the steel sheet. The crystal grains having the {111} / / ND orientation include crystal grains in which the specimen face and the {111} plane are parallel, and the crystal grains having the {001} / / ND orientation include crystal grains in which the specimen face and the {001} plane are parallel.

[0063] Steel materials are composed of numerous crystal grains, each with a different orientation. This distribution of orientations is called texture. Adjacent crystal grains each have their own orientation. The difference in orientation angle between adjacent crystal grains is called the misorientation angle.

[0064] A larger average misorientation angle indicates fewer crystal grains of similar orientation in the surrounding area, resulting in a more uniform microstructure. Conversely, a smaller average misorientation angle indicates more crystal grains of similar orientation in the surrounding area, resulting in a more heterogeneous microstructure. The misorientation angle differs for each orientation and for each material.

[0065] In the final microstructure described above, the average grain size may be 80 to 150 μm. The final non-oriented electrical steel sheet exhibits an iron loss (W) of 13.5 W / kg or less. 10 / 400 ) has the following properties, and the standard deviation of iron loss may be 0.725 W / kg or less.

[0066] The non-oriented electrical steel sheet and its manufacturing method according to the embodiment of the present invention make it possible to provide a non-oriented electrical steel sheet with low average iron loss and standard deviation by adjusting the pre-annealing conditions after hot rolling. By limiting the temperature and grain size during pre-annealing, the increase in production costs can be suppressed. By manufacturing a non-oriented electrical steel sheet with a uniform microstructure and texture, uniform magnetic properties can be ensured.

[0067] Experimental example

[0068] The following are preferred experimental examples to aid in understanding the present invention. However, these experimental examples are merely for the purpose of aiding in understanding the present invention, and the present invention is not limited to these experimental examples.

[0069] 1. Composition of the test specimen

[0070] In this experimental example, test pieces having the compositions (unit: wt%) of alloy elements shown in Table 1 are provided.

[0071]

Table 1

[0072] Referring to Table 1, the composition of the non-oriented electrical steel sheet according to the present experimental example satisfies: silicon (Si): 2.8 to 3.8 wt%, manganese (Mn): 0.2 to 0.5 wt%, aluminum (Al): 0.5 to 1.2 wt%, carbon (C): more than 0 and 0.002 wt% or less, phosphorus (P): more than 0 and 0.015 wt% or less, sulfur (S): more than 0 and 0.002 wt% or less, nitrogen (N): more than 0 and 0.002 wt% or less, titanium (Ti): more than 0 and 0.002 wt% or less, with the balance being iron (Fe). A slab having said composition was reheated to 1130°C, and hot rolling was carried out under the condition that the finish rolling temperature (FDT) was 850°C, after which a hot-rolled sheet having a thickness of 2.0 mm was produced. A first annealing heat treatment (preliminary annealing) was performed on the hot-rolled sheet under the conditions of a heating rate: 15°C / s, an annealing holding time: 50 seconds, and a cooling rate: 30°C / s. After cold rolling, a second annealing heat treatment (final annealing) was performed under the conditions of a heating rate: 20°C / s, an annealing starting temperature: 1000°C, an annealing holding time: 50 seconds, and a cooling rate: 30°C / s. Thereafter, a final product was produced through a coating process. The final annealing atmosphere was a mixed atmosphere of 30% hydrogen and 70% nitrogen.

[0073] 2. Evaluation of process conditions and physical properties

[0074] Table 2 shows the process conditions (preliminary annealing temperature) of the present experimental example and the results of physical property evaluation obtained thereby. In the experimental examples in Table 2, a condition of 975°C was applied for all final annealing temperatures. Iron loss was measured on 3000 mm at mutually different positions 2 Measurements were performed 10 or more times using test pieces having the above area.

[0075] On the other hand, Figure 2 is a photograph of the texture (IPF MAP) observed through EBSD analysis on a non-oriented electrical steel sheet according to Example 1 of the experimental examples of the present invention, and Figure 3 is a photograph of the texture (IPF MAP) observed through EBSD analysis on a non-oriented electrical steel sheet according to Comparative Example 2 of the experimental examples of the present invention. In Figures 2 and 3, (a) is a photograph of the texture after pre-annealing (first annealing heat treatment), and (b) is a photograph of the texture after final annealing (second annealing heat treatment).

[0076] [Table 2]

[0077] Referring to Table 2, Examples 1 to 3 underwent the first annealing heat treatment under the following conditions: heating rate: 10°C / s or higher, annealing start temperature: 900 to 1050°C, annealing duration: 30 to 90 seconds, and cooling rate: 20°C / s or higher. After the first annealing heat treatment, the average crystal grain size was 140 to 250 μm, and in the central layer... <110> The volume fraction of grains with the / / RD orientation is 20% or less, satisfying the range. Furthermore, after the final annealing (second annealing heat treatment), in the final microstructure, the volume fraction of grains with the {111} / / ND orientation is 30% or less, and the average misorientation angle is 23° or more, and the volume fraction of grains with the {001} / / ND orientation is 15% or more, and the average misorientation angle is 48° or more, satisfying the range, and the iron loss (W) is 13.5 W / kg or less. 10 / 400 ) is present, and it can be confirmed that the standard deviation of iron loss is 0.725 W / kg or less. Examples 1 to 3 embody a texture favorable to magnetism and have a small average iron loss value, but a uniform microstructure / texture develops and the standard deviation can be controlled to 0.725 W / kg or less. Referring to Figure 2, it can be confirmed that a uniform microstructure / texture develops.

[0078] In contrast, Comparative Example 1 fails to meet the requirements as the annealing start temperature falls below the range of 900-1050°C during pre-annealing (first annealing heat treatment). As a result, after the first annealing heat treatment, the average grain size falls below the range of 140-250 μm, failing to meet the requirements, and the central layer... <110> / / The volume fraction of grains with RD orientation exceeds the range of 20% or less and does not satisfy the requirement. After the final annealing (second annealing heat treatment), in the final microstructure, the volume fraction of grains with {111} / / ND orientation exceeds the range of 30% or less and does not satisfy the requirement. The volume fraction of grains with {001} / / ND orientation falls below the range of 15% or more and does not satisfy the requirement. Iron loss (W) is 13.5 W / kg or less. 10 / 400の It does not satisfy the range of ).

[0079] Comparative Example 2 fails to meet the requirements because, in the pre-annealing (first annealing heat treatment), the annealing start temperature exceeds the range of 900-1050°C. As a result, after the first annealing heat treatment, the average grain size exceeds the range of 140-250 μm, failing to meet the requirements. After the final annealing (second annealing heat treatment), the final microstructure fails to meet the requirements because the average misorientation angle for grains with {111} / / ND orientation falls below the range of 23° or more, failing to meet the requirements. The average misorientation angle for grains with {001} / / ND orientation falls below the range of 48° or more, failing to meet the requirements. Iron loss is 13.5 W / kg or less (W 10 / 400 While the first condition is satisfied, it can be confirmed that the standard deviation of iron loss does not meet the requirement of being 0.725 W / kg or less. In comparative example 2, although the average iron loss value is small due to the presence of a texture favorable to magnetism, a heterogeneous microstructure / texture developed, causing the standard deviation to exceed 0.725 W / kg. Referring to Figure 3, it can be confirmed that a heterogeneous microstructure / texture developed.

[0080] Comparative Example 3 fails to meet the requirements because the annealing start temperature in the pre-annealing (first annealing heat treatment) falls below the range of 900-1050°C. As a result, after the first annealing heat treatment, the average grain size falls below the range of 140-250 μm, failing to meet the requirements, and the central layer... <110> / / The volume fraction of grains with RD orientation exceeds the range of 20% or less and does not satisfy the requirement. After the final annealing (second annealing heat treatment), in the final microstructure, the volume fraction of grains with {111} / / ND orientation exceeds the range of 30% or less and does not satisfy the requirement. The volume fraction of grains with {001} / / ND orientation falls below the range of 15% or more and does not satisfy the requirement. Iron loss (W) is 13.5 W / kg or less. 10 / 400 It does not satisfy the range of ).

[0081] Comparative Example 4 fails to meet the requirements because, in the pre-annealing (first annealing heat treatment), the annealing start temperature exceeds the range of 900-1050°C. As a result, after the first annealing heat treatment, the average grain size exceeds the range of 140-250 μm, failing to meet the requirements. Furthermore, after the final annealing (second annealing heat treatment), the final microstructure fails to meet the requirements because the average misorientation angle for grains with {001} / / ND orientation falls below the range of 48° or more, failing to meet the requirements. The iron loss is less than 13.5 W / kg (W). 10 / 400 Although the condition is satisfied, it can be confirmed that the standard deviation of iron loss does not satisfy the range of 0.725 W / kg or less. Comparative Example 4 exhibits a texture favorable to magnetism and has a small average iron loss value, but a non-uniform microstructure / texture has developed and the standard deviation exceeds 0.725 W / kg.

[0082] The above description has focused on embodiments of the present invention, but various modifications and variations can be made at the level of those skilled in the art. Such modifications and variations can be said to fall within the scope of the present invention as long as they do not depart from the scope of the present invention. Therefore, the scope of the rights of the present invention must be determined by the appended claims.

Claims

1. This is a non-oriented electrical steel sheet consisting of silicon (Si): 2.8-3.8 wt%, manganese (Mn): 0.2-0.5 wt%, aluminum (Al): 0.5-1.2 wt%, carbon (C): greater than 0 and 0.002 wt%, phosphorus (P): greater than 0 and 0.015 wt%, sulfur (S): greater than 0 and 0.002 wt%, nitrogen (N): greater than 0 and 0.002 wt%, titanium (Ti): greater than 0 and 0.002 wt%, and the remaining iron (Fe) and other unavoidable impurities. In the final microstructure, grains with the {111} / / ND orientation have a volume fraction of 30% or less and an average misorientation angle of 23° or more, and grains with the {001} / / ND orientation have a volume fraction of 15% or more and an average misorientation angle of 48° or more. A non-oriented electrical steel sheet characterized by having an iron loss of 13.5 W / kg or less (W 10 / 400) and a standard deviation of iron loss of 0.725 W / kg or less.

2. The non-oriented electrical steel sheet according to claim 1, characterized in that the average grain size is 80 to 150 μm.

3. A step of providing a steel material comprising: silicon (Si): 2.8 to 3.8 wt%, manganese (Mn): 0.2 to 0.5 wt%, aluminum (Al): 0.5 to 1.2 wt%, carbon (C): greater than 0 and less than 0.002 wt%, phosphorus (P): greater than 0 and less than 0.015 wt%, sulfur (S): greater than 0 and less than 0.002 wt%, nitrogen (N): greater than 0 and less than 0.002 wt%, titanium (Ti): greater than 0 and less than 0.002 wt%, and the remaining iron (Fe) and other unavoidable impurities; The steps include: hot rolling the aforementioned steel material; The steps include: performing a first annealing heat treatment on the hot-rolled steel material; The first step of cold rolling the annealed steel material, The step includes a second annealing heat treatment of the cold-rolled steel material, The hot rolling step is performed under the following conditions: reheating temperature: 1100-1200°C, finish rolling temperature: 800-1000°C, and winding temperature: 560-600°C. The first annealing heat treatment step is carried out under the following conditions: heating rate: 10°C / s or more, annealing start temperature: 900 to 1050°C, annealing duration: 30 to 90 seconds, cooling rate: 20°C / s or more. The second annealing heat treatment step is carried out under the following conditions: heating rate: 10°C / s or more, annealing start temperature: 900 to 1100°C, annealing duration: 30 to 90 seconds, cooling rate: 30°C / s or more. Regarding the non-oriented electrical steel sheets to be manufactured, in the final microstructure, the volume fraction of crystal grains having the {111} / / ND orientation is 30% or less, and the average misorientation angle is 23° or more, and the volume fraction of crystal grains having the {001} / / ND orientation is 15% or more, and the average misorientation angle is 48° or more. A method for manufacturing non-oriented electrical steel sheets, wherein the manufactured non-oriented electrical steel sheet has an iron loss of 13.5 W / kg or less (W 10 / 400) and a standard deviation of iron loss of 0.725 W / kg or less.

4. The method for manufacturing a non-oriented electrical steel sheet according to claim 3, wherein, after the first annealing heat treatment, the average grain size is 140 to 250 μm, and the volume fraction of grains having the <110> / / RD orientation in the central layer is 20% or less.

5. The method for manufacturing a non-oriented electrical steel sheet according to claim 3, wherein the cold rolling step is performed under the condition of a reduction ratio of 81 to 92%.

6. The thickness of the steel material after hot rolling is 1.6 to 2.6 mm. The method for manufacturing a non-oriented electrical steel sheet according to claim 3, wherein the thickness of the steel material after cold rolling is 0.1 to 0.3 mm.

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