Non-oriented electrical steel sheet and method for producing same

Abstract

The present invention provides a method for manufacturing a non-oriented electrical steel sheet, comprising the steps of: hot-rolling a slab, the slab includes 0 (excluding 0) to 0.005 wt% (including 0.005) of carbon (C), 2.0 to 4.0 wt% (including 2.0 and 4.0) of silicon (Si), 0.1 to 0.5 wt% (including 0.1 and 0.5) of manganese (Mn), 0.9 to 1.5 wt% (including 0.9 and 1.5) of aluminum (Al), 0 (excluding 0) to 0.015 wt% (including 0.015) of phosphorus (P), 0 (excluding 0) to 0.005 wt% (including 0.005) of sulfur (S), 0 (excluding 0) to 0.005 wt% (including 0.005) of nitrogen (N), 0 (excluding 0) to 0.005 wt% (including 0.005) of titanium (Ti), and the balance of iron and unavoidable impurities. The balance of iron (Fe) and unavoidable impurities; carrying out primary annealing on the hot-rolled plate; performing cold rolling on the hot rolled plate subjected to primary annealing; and performing cold annealing on the cold-rolled sheet; the cold annealing step comprises a first heating stage in which the cold-rolled sheet is heated from a starting temperature to a recrystallization temperature at a first average heating rate, a second heating stage in which the cold-rolled sheet is heated at a second average heating rate, and a soaking stage in which the cold-rolled sheet is heated at a second average heating rate. And heating the cold-rolled sheet from the recrystallization temperature to the target temperature in a second heating stage at a second average heating rate that is faster than the first average heating rate.

Description

Technical Field

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

[0002] In recent years, the demand for environmental protection and improvement of energy efficiency has been increasing. In particular, the transition from internal combustion engine vehicles to electric vehicles or hybrid vehicles has been accelerating.

[0003] Non-oriented electrical steel sheets are materials with uniform magnetic properties in all directions regardless of the rolling direction, and are used to reduce iron loss and increase magnetic flux density to improve energy efficiency.

[0004] The manufacturing process of non-oriented electrical steel sheets varies with the silicon (Si) content. Therefore, when the silicon (Si) content exceeds 2.0 wt%, brittleness may increase and fracture may occur during cold rolling. Therefore, an annealing and pickling line (APL) process must be performed before final cold rolling.

[0005] Related technologies include Korean Patent Publication No. 10-2021-0094027 (titled “Method of Manufacturing Non-Oriented Electrical Steel Sheet”). Summary of the invention

[0006] Technical issues

[0007] The embodiment of the present invention can manufacture a non-oriented electrical steel sheet having improved magnetic properties by controlling a heating rate in a cold annealing step.

[0008] Solution

[0009] An embodiment of the present invention provides a method for manufacturing a non-oriented electrical steel sheet, the method comprising hot rolling a slab, the slab comprising greater than 0 wt % to 0.005 wt % or less carbon (C), 2.0 wt % or more to 4.0 wt % or less silicon (Si), 0.1 wt % or more to 0.5 wt % or less manganese (Mn), 0.9 wt % or more to 1.5 wt % or less aluminum (Al), greater than 0 wt % to 0.015 wt % or less phosphorus (P), greater than 0 wt % to 0.005 wt % or less sulfur (S), greater than 0 wt % to 0.005 wt % or less less nitrogen (N), greater than 0 wt % to 0.005 wt % or less titanium (Ti), the balance iron (Fe) and inevitable impurities; preliminary annealing the hot-rolled plate; cold rolling the preliminary annealed hot-rolled plate; and cold annealing the cold-rolled plate; wherein the cold annealing includes a first heating stage, a second heating stage and a soaking stage, in which the cold-rolled plate is heated from a starting temperature to a recrystallization temperature at a first average heating rate in the first heating stage, and in the second heating stage, the cold-rolled plate is heated from the recrystallization temperature to a target temperature at a second average heating rate faster than the first average heating rate.

[0010] In this embodiment, the first average heating rate may be greater than 5° C. / s and less than 20° C. / s.

[0011] In the present embodiment, the second average heating rate may be 15° C. / s or more and 30° C. / s or less.

[0012] In the present embodiment, the recrystallization temperature may be 750°C to 800°C.

[0013] In this embodiment, the target temperature may be 850°C to 1,050°C.

[0014] In the present embodiment, the cold annealing may further include a cooling stage, in which the cold-rolled annealed sheet may be cooled at a cooling rate of 30° C. / s or more.

[0015] In this embodiment, the texture of the non-oriented electrical steel sheet <111> / / ND orientation fraction may be 30% or less.

[0016] In this embodiment, the texture of the non-oriented electrical steel sheet <100> / / ND orientation fraction may be 20% or more.

[0017] In the present embodiment, the average grain size of the non-oriented electrical steel sheet may be 100 micrometers or more and 130 micrometers or less.

[0018] Another embodiment of the present invention provides a nonoriented electrical steel sheet comprising more than 0 wt % to 0.005 wt % or less of carbon (C), 2.0 wt % or more to 4.0 wt % or less of silicon (Si), 0.1 wt % or more to 0.5 wt % or less of manganese (Mn), 0.9 wt % or more to 1.5 wt % or less of aluminum (Al), more than 0 wt % to 0.015 wt % or less of phosphorus (P), more than 0 wt % to 0.005 wt % or less of sulfur (S), more than 0 wt % to 0.005 wt % or less of nitrogen (N), more than 0 wt % to 0.005 wt % or less of titanium (Ti), the balance of iron (Fe) and inevitable impurities, wherein the texture <111> / / ND orientation fraction is 30% or less, texture <100> / / ND orientation fraction is 20% or more.

[0019] In the present embodiment, the nonoriented electrical steel sheet may have an iron loss of 13.0 W / kg or less (regarding W10 / 400) and a magnetic flux density of 1.68 T or more (regarding B50).

[0020] In the present embodiment, the non-oriented electrical steel sheet may have a yield strength (YP) of 400 MPa or more, and a tensile strength (TS) of 500 MPa or more.

[0021] Other aspects, features, and advantages of the present invention will become more fully apparent from the detailed description, claims, and accompanying drawings which are intended to enable the invention to be implemented.

[0022] Advantageous Effects of the Invention

[0023] According to the embodiments of the present invention as described above, a non-oriented electrical steel sheet having improved magnetic properties can be manufactured by controlling the heating rate in the cold annealing step. The scope of the present invention is not limited by these effects. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0025] Figure 2 is a diagram showing phases according to silicon (Si) composition.

[0026] Figure 3 is a graph showing texture magnetization velocity according to orientation.

[0027] Figure 4 It is shown in <100> Orientation and <111> Plot of the hysteresis loop on orientation.

[0028] Figure 5 is a graph showing magnetic flux density according to texture orientation.

[0029] Figure 6a to Figure 6g This is a photograph obtained by observing the microstructure according to the heat treatment temperature using electron backscatter diffraction (EBSD). DETAILED DESCRIPTION

[0030] Mode for Carrying Out the Invention

[0031] Since the present invention allows various changes and a large number of embodiments, certain embodiments will be shown in the drawings and described in the detailed description. The effects and features of the present invention and methods for achieving them will become clear with reference to the embodiments described in detail below in conjunction with the drawings. However, the present invention is not limited to the following embodiments, but can be implemented in various forms.

[0032] Although the terms "first", "second", etc. may be used to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another.

[0033] As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0034] It will be further understood that the terms “comprise” or “comprising” used herein indicate the presence of stated features or components, but do not preclude the presence or addition of one or more other features or components.

[0035] It will be further understood that when a layer, region or component is referred to as being “on” another layer, region or component, it can be directly on another layer, region or component, or can be indirectly on another layer, region or component with intervening layers, regions or components.

[0036] For the convenience of explanation, the size of the components in the drawings may be enlarged or reduced. For example, the size and thickness of the components in the drawings are arbitrarily shown for the convenience of explanation, and the present invention is not limited thereto.

[0037] "A and / or B" is used herein to select only A, only B, or both A and B. In addition, "at least one of A and B" is used herein to select only A, only B, or both A and B.

[0038] In the following embodiments, the meaning of the wiring "extending in the first direction or the second direction" includes not only extending in a straight line along the first direction or the second direction, but also extending in a zigzag or curved shape along the first direction or the second direction.

[0039] In the following embodiments, a "plan view of an object" means a "view of an object seen from above", and a "cross-sectional view of an object" means a "view of an object cut vertically and seen from the side". In the following embodiments, when an element "overlaps", it may mean that the element overlaps in both the "plan view" and the "cross-sectional view".

[0040] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings, wherein the same or corresponding elements are identified by the same reference numerals throughout.

[0041] Figure 1 is a flow chart schematically illustrating a method of manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention.

[0042] Reference Figure 1 , a method of manufacturing a non-oriented electrical steel sheet according to one embodiment may include a hot rolling step (S100), a preliminary annealing step (S200), a cold rolling step (S300), a cold annealing step (S400), and a coating step (S500).

[0043] In the method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention, the semi-finished product to be hot-rolled may be a slab. After a molten steel of a certain composition is obtained through a steelmaking process, a slab in a semi-finished state may be obtained through a continuous casting process.

[0044] In one embodiment, the slab may contain greater than 0 wt% to 0.005 wt% or less carbon (C), 2.0 wt% or more to 4.0 wt% or less silicon (Si), 0.1 wt% or more to 0.5 wt% or less manganese (Mn), 0.9 wt% or more to 1.5 wt% or less aluminum (Al), greater than 0 wt% to 0.015 wt% or less phosphorus (P), greater than 0 wt% to 0.005 wt% or less sulfur (S), greater than 0 wt% to 0.005 wt% or less nitrogen (N), greater than 0 wt% to 0.005 wt% or less titanium (Ti), balance iron (Fe) and unavoidable impurities.

[0045] Carbon (C) is a component that increases iron loss by forming carbides such as TiC or NbC. In one embodiment, the content of carbon (C) may be greater than 0 wt% to 0.005 wt% or less relative to the total weight of the slab. When the content of carbon (C) is greater than 0.005 wt% relative to the total weight of the slab, the magnetic properties of the manufactured non-oriented electrical steel sheet may deteriorate due to magnetic aging. When the content of carbon (C) is greater than 0 wt% to 0.005 wt% or less relative to the total weight of the slab, the magnetic aging phenomenon may be suppressed.

[0046] Figure 2 is a diagram showing phases according to the composition of silicon (Si).

[0047] like Figure 2 As shown, when the content of silicon (Si) is 2.0 wt% or more, a ferrite single phase may exist in all regions without phase transformation. On the other hand, when the content of silicon (Si) is less than 2.0 wt%, an austenite phase exists in some regions, and thus a phase transformation occurs during heat treatment at a target temperature of about 950° C. as described below. At this time, when a phase transformation occurs during the heat treatment process, the texture orientation distribution changes, and therefore it is preferable to limit the content of silicon (Si) to a composition range where a phase transformation does not occur.

[0048] Silicon (Si) is a component that reduces eddy current loss by increasing resistivity. In one embodiment, the content of silicon (Si) can be 2.0% or more to 4.0% or less relative to the total weight of the slab. When the content of silicon (Si) is less than 2.0% relative to the total weight of the slab, it will be difficult to obtain a low iron loss value. On the other hand, as the content of silicon (Si) contained in the slab increases, the investment rate and the magnetic flux density decrease. In addition, when the content of silicon (Si) is greater than 4.0% relative to the total weight of the slab, the brittleness increases and the cold rolling performance decreases, which reduces productivity.

[0049] Manganese (Mn) is a component that increases resistivity and improves texture together with silicon (Si). In one embodiment, the content of manganese (Mn) can be 0.1 wt% or more to 0.5 wt% or less relative to the total weight of the slab. When the content of manganese (Mn) is less than 0.1% by weight relative to the total weight of the slab, fine MnS precipitates are formed to inhibit grain growth. On the other hand, when the content of manganese (Mn) is greater than 0.5% by weight relative to the total weight of the slab, coarse MnS precipitates are formed, thereby deteriorating magnetic properties, such as reducing magnetic flux density. When the content of manganese (Mn) is 0.1 wt% or more to 0.5 wt% or less relative to the total weight of the slab, the microstructure and texture in the slab (or non-oriented electrical steel sheet) can be controlled.

[0050] Aluminum (Al) is a component that increases resistivity and reduces eddy current loss together with silicon (Si). In addition, aluminum (Al) can reduce magnetic anisotropy, thereby reducing magnetic deviation. In one embodiment, the content of aluminum (Al) can be 0.9 weight % or more to 1.5 weight % or less relative to the total weight of the slab. When the content of aluminum (Al) is less than 0.9% relative to the total weight of the slab, it will be difficult to obtain a low iron loss value. In addition, the magnetic property deviation can be increased by forming fine nitrides. On the other hand, when the content of aluminum (Al) is greater than 1.5% relative to the total weight of the slab, the cold rolling performance will be reduced, and nitrides will be excessively formed to reduce the magnetic flux density, which will reduce the magnetic properties.

[0051] Phosphorus (P), as a grain boundary segregation element, is a component for developing texture. In one embodiment, the content of phosphorus (P) may be greater than 0 wt% to 0.015 wt% or less relative to the total weight of the slab. When the content of phosphorus (P) is greater than 0.015 wt% relative to the total weight of the slab, grain growth may be inhibited, magnetic properties may be reduced, and cold rolling performance may be reduced due to the segregation effect.

[0052] Sulfur (S) may increase iron loss and inhibit grain growth by forming precipitates such as MnS and CuS. In one embodiment, the content of sulfur (S) may be greater than 0 wt% to 0.005 wt% or less relative to the total weight of the slab. When the content of sulfur (S) is greater than 0.005% relative to the total weight of the slab, precipitates such as MnS and CuS are formed, which increase iron loss and inhibit grain growth.

[0053] Nitrogen (N) may increase iron loss and inhibit grain growth by forming precipitates such as AlN, TiN, or NbN. In one embodiment, the content of nitrogen (N) may be greater than 0 wt% to 0.005 wt% or less relative to the total weight of the slab. When the content of nitrogen (N) is greater than 0.005% relative to the total weight of the slab, precipitates such as AlN, TiN, or NbN are formed, which increases iron loss and inhibits grain growth.

[0054] Titanium (Ti) can inhibit grain growth by forming precipitates such as TiC and TiN. In one embodiment, the content of titanium (Ti) can be greater than 0 wt% to 0.005 wt% or less relative to the total weight of the slab. When the content of titanium (Ti) is greater than 0.005% relative to the total weight of the slab, precipitates such as TiC and TiN may be formed, which may deteriorate magnetic properties.

[0055] In the hot rolling step (S100), a hot rolled plate can be obtained by reheating the slab and then hot rolling the reheated slab. First, in the hot rolling step (S100), the slab can be reheated. When the slab heating temperature is too high, precipitates such as C, S or N in the slab are reused in subsequent rolling and annealing steps to form fine precipitates, which inhibits grain growth and deteriorates magnetic properties. On the other hand, when the slab heating temperature is too low, the rolling load during hot rolling increases, which reduces the rolling performance. In one embodiment, the slab reheating temperature in the hot rolling step (S100) can be about 1,000°C to about 1,200°C.

[0056] In addition, in the hot rolling step (S100), the reheated slab may be rolled at a specific finishing outlet temperature (FDT). In one embodiment, the FDT of the hot rolling stage (S100) may be about 860°C to about 900°C.

[0057] In addition, in the hot rolling step (S100), the hot rolled sheet may be cooled to a specific coiling temperature (CT) and coiled. In one embodiment, the CT may be about 550°C to about 650°C.

[0058] In one embodiment, the thickness of the hot rolled sheet after hot rolling may be about 1.8 mm to about 2.6 mm. At this time, when the thickness of the hot rolled sheet exceeds about 2.6 mm, the cold rolling reduction rate increases, which may deteriorate the texture.

[0059] The preliminary annealing step (S200) may be performed after the hot rolling step (S100). In the preliminary annealing step (S200), the hot rolled sheet that has been coiled and cooled may be subjected to preliminary annealing. At this time, the hot rolled sheet that has undergone preliminary annealing may be referred to as a hot rolled annealed sheet. The preliminary annealing step (S200) may ensure uniformity of the microstructure and cold rolling performance of the hot rolled sheet.

[0060] The preliminary annealing step (S200) may be performed at an annealing temperature of about 950°C to about 1,100°C, a holding time of about 30 seconds to about 120 seconds, and a heating rate of about 20°C / s or more. At this time, when the annealing temperature of the preliminary annealing step (S200) is too low, fine inclusions such as carbides and nitrides are formed from the surface layer, and the inclusions cannot grow sufficiently, which may deteriorate the magnetic properties of the final product. On the other hand, when the annealing temperature of the preliminary annealing step (S200) is too high, not only are the inclusions distributed excessively, but also the grains grow excessively, resulting in a large grain size deviation and a large amount of oxidation, which may adversely affect the final product.

[0061] In the preliminary annealing step (S200), the hot-rolled annealed sheet may be cooled at a cooling rate of about 30° C. / s. At this time, the hot-rolled annealed sheet may be cooled to about 200° C. to about 250° C. In addition, after the preliminary annealing step (S200), an oxide layer formed on the surface of the hot-rolled annealed sheet may be removed using an acid cleaning solution.

[0062] The cold rolling step (S300) may be performed after the preliminary annealing step (S200). In the cold rolling step (S300), the hot-rolled annealed sheet may be cold rolled. At this time, the hot-rolled annealed sheet that has been cold rolled may be referred to as a cold-rolled sheet. In the cold rolling step (S300), the hot-rolled annealed sheet that has been pickled may be cold rolled to a thickness of about 0.35 mm or less. At this time, hot rolling may be performed by raising the sheet temperature (e.g., the temperature of the hot-rolled annealed sheet) to about 150°C to about 200°C to provide rolling performance. The final reduction rate in the cold rolling step (S300) may be about 80% to about 85%.

[0063] Figure 3 is a graph showing the texture magnetization velocity according to orientation. Specifically, Figure 3 It is shown <100> orientation, <110> Orientation and <111> Plot of magnetization velocity over orientation.

[0064] Reference Figure 3 , it can be seen that <100> The magnetization velocity of the orientation is <100> orientation, <110> Orientation and <111> is the fastest among the orientations. That is, it can be seen that <100> The magnetization orientation <100> orientation, <110> Orientation and <111> It is easiest to find the orientation. Therefore, it can be seen that <100> Orientation and <111> In orientation, <100> Orientation and <111> Orientation is beneficial to the magnetic properties.

[0065] Figure 4 It is shown <100> Orientation and <111> Plot of the hysteresis loop on orientation.

[0066] exist Figure 4 In the equation, the area enclosed by the hysteresis loop represents the energy loss per unit volume. That is, the larger the area enclosed by the hysteresis loop, the greater the energy loss per unit volume.

[0067] Reference Figure 4 , it can be seen that <100> The area of ​​the hysteresis loop in the orientation is less than <111> The area of ​​the hysteresis loop in the orientation. That is, it can be seen that <100> Orientation ratio <111> orientation has lower iron loss and higher magnetic flux density.

[0068] Figure 5 is a graph showing magnetic flux density according to the orientation of texture.

[0069] Reference Figure 5 , it can be seen that <111> The average magnetic flux density of the orientation is the lowest, while <100> The average magnetic flux density of the orientation is the highest. <100> As the orientation increases, the magnetic flux density of the non-oriented electrical steel sheet containing the same increases.

[0070] In general, when a cold rolled sheet that has been cold rolled is heat treated, the microstructure of the cold rolled annealed sheet (or final annealed sheet) can be formed through recovery, recrystallization and growth processes. In addition, during the heat treatment near the recrystallization temperature, nucleation and growth for recovery and recrystallization occur. In the heat treatment process, the heating rate affects the recovery / nucleation / recrystallization process.

[0071] Since the accumulated deformation energy at each position is different, when the heating rate is fast, recrystallization and growth will occur first in the area with high deformation energy, forming a large amount of <111> / / ND orientation, while in the growth stage, the regions with low deformation energy will be relatively delayed and dissipated.

[0072] The texture after the final cold rolling may include two orientations, α fiber and γ fiber, and during the heat treatment process of the cold annealing step (S400), when passing through the recrystallization temperature stage, nucleation and recrystallization may first occur at the γ fiber position with relatively high deformation energy. At this time, a negative magnetic property is formed at this position. <111> / / ND oriented grains, and first formed <111> / / ND oriented texture tries to grow first in the growth stage after recrystallization. Therefore, in the texture of the final cold rolled annealed sheet, <111> / / ND orientation appears strongly, which leads to poor iron loss and flux density.

[0073] On the other hand, when the heating rate is reduced, recovery and recrystallization can occur uniformly in all regions, and as a result, <100> / / ND Orientation and <111> / / ND orientation will compete and grow.

[0074] Therefore, the orientation of the texture can be controlled by determining the time to complete recrystallization and controlling the heating rate before reaching the recrystallization temperature.

[0075] Figure 6a to Figure 6g This is a photograph obtained by observing the microstructure according to the heat treatment temperature using electron backscatter diffraction (EBSD). Specifically, Figure 6a This is a photo of the microstructure observed using EBSD when the heat treatment temperature was 600°C. Figure 6b This is a photo of the microstructure observed using EBSD when the heat treatment temperature was 650°C. Figure 6c This is a photo of the microstructure observed using EBSD when the heat treatment temperature was 700°C. Figure 6d This is a photo of the microstructure observed using EBSD when the heat treatment temperature was 750°C. Figure 6e This is a photo of the microstructure observed using EBSD when the heat treatment temperature was 800°C. Figure 6f This is a photo of the microstructure observed using EBSD when the heat treatment temperature was 850°C. Figure 6g This is a photograph of the microstructure observed using EBSD when the heat treatment temperature was 950°C.

[0076] See also Figure 6a to Figure 6g , when the cold-rolled sheet is heat-treated after cold rolling, it can be seen that recrystallization is completed at about 800°C.

[0077] Therefore, the orientation of the texture can be controlled by controlling the heating rate to about 800°C or less.

[0078] After the cold rolling step (S300), a cold annealing step (S400) may be performed. In the cold annealing step (S400), the cold rolled sheet may be annealed. At this time, the annealed cold rolled sheet may be referred to as an annealed cold rolled sheet.

[0079] In one embodiment, the cold annealing step (S400) may include a heating stage, a soaking stage, and a cooling stage. In addition, the heating stage may include a first heating stage and a second heating stage. That is, the cold annealing step (S400) may include a first heating stage, a second heating stage, a soaking stage, and a cooling stage. At this time, the heating stage refers to a stage in which the cold-rolled sheet is heated to increase the temperature of the cold-rolled sheet, the soaking stage refers to a stage in which the cold-rolled sheet is soaked and heated to a target temperature, and the cooling stage refers to a stage in which the soaked and heated cold-rolled sheet is cooled.

[0080] In one embodiment, the cold rolled sheet may be heated in the heating stage of the cold annealing step (S400). At this time, the heating stage may include a first heating stage and a second heating stage. That is, the heating stage may be divided into a first heating stage and a second heating stage. The first heating stage and the second heating stage may have different average heating rates.

[0081] In one embodiment, the cold rolled sheet may be heated (or heated) from a starting temperature to a recrystallization temperature at a first average heating rate in a first heating stage. The starting temperature may be room temperature. For example, the starting temperature may be from about 15°C to about 25°C. The recrystallization temperature is the temperature at which the recrystallization of the texture in the cold rolled sheet is completed. For example, the recrystallization temperature may be from about 750°C to about 800°C. However, the present invention is not limited thereto.

[0082] Moreover, the first average heating rate may be greater than about 5°C / s and less than about 20°C / s. More preferably, the first average heating rate may be greater than about 10°C / s and less than about 15°C / s. When the first average heating rate is about 5°C / s or less, the grains may grow excessively due to the low heating rate, which may increase eddy current losses and result in insignificant improvement in magnetic properties. In addition, as the heat treatment time increases, productivity and process costs may increase. On the other hand, when the first average heating rate is about 20°C / s or more, the heating rate to reach the recrystallization temperature is too high (e.g., too fast), the primary recrystallization is formed finely, and <111> / / ND-oriented texture is formed and grows first, thus increasing <111> / / ND parts, resulting in increased iron loss and reduced flux density.

[0083] Therefore, when the first average heating rate is greater than about 5°C / s and less than about 20°C / s (or, 5°C / s to 20°C / s), a non-oriented electrical steel sheet having excellent magnetic properties can be manufactured. Specifically, below the temperature at which the microstructure completes recrystallization, the heating rate is greater than about 5°C / s and less than about 20°C / s, so that <100> / / ND Orientation and <111> / / ND orientation can compete for growth, thereby increasing the texture <100> / / The number of portions of ND orientation, and thus the non-oriented electrical steel sheet manufactured thereby can have low iron loss and high magnetic flux density.

[0084] In one embodiment, the cold rolled sheet heated (or heated) by the first heating stage can be heated (or heated) from the recrystallization temperature to the target temperature at a second average heating rate in the second heating stage. As described above, the recrystallization temperature is the temperature at which the recrystallization of the texture in the cold rolled sheet is completed. For example, the recrystallization temperature can be about 750°C to about 800°C. However, the present invention is not limited thereto.

[0085] In one embodiment, the target temperature (i.e., the temperature at which the heated (or temperature-raising) cold-rolled sheet is soaked and heated (or annealed)) may be about 850° C. to about 1,050° C. When the target temperature in the cold annealing step (S400) is too low, the grain size is fine, which increases the hysteresis loss. On the other hand, when the target temperature in the cold annealing step (S400) is too high, the grain size increases too much, which increases the eddy current loss.

[0086] In one embodiment, the second average heating rate may be greater than the first average heating rate. That is, the average heating rate of the second heating stage may be faster than the average heating rate of the first heating stage. The second average heating rate may be about 15°C / s to about 30°C / s. More preferably, the second average heating rate may exceed the first average heating rate, but may be about 30°C / s or less. When the second average heating rate is equal to or less than the first average heating rate, productivity and process costs may increase as the heat treatment time increases. On the other hand, when the second average heating rate exceeds about 30°C / s, <111> / / ND fraction will increase, and as a result, iron loss will increase and magnetic flux density will decrease. This will be described in more detail below.

[0087] Therefore, when the second average heating rate is 15° C. / s or more and about 30° C. / s or less, a non-oriented electrical steel sheet having excellent magnetic properties can be manufactured.

[0088] In one embodiment, the target temperature maintenance time can be about 40 seconds to about 200 seconds. However, the present invention is not limited thereto. For example, the total time for performing the cold annealing step (S400) can be about 40 seconds to about 200 seconds.

[0089] Thereafter, in a cooling stage, the cold rolled annealed sheet may be cooled at a cooling rate of about 30°C / s or more. At this time, the cold rolled annealed sheet may be cooled to about 200°C to about 250°C.

[0090] In one embodiment, the cold annealing step (S400) can be performed under a mixed atmosphere of nitrogen and hydrogen. Specifically, the cold annealing step (S400) can be performed in an atmosphere containing about 5 volume % to about 40 volume % of hydrogen and the balance of nitrogen.

[0091] After the cold annealing step (S400), a coating step (S500) may be performed. In the coating step (S500), a coating layer may be formed on the cold-rolled annealed sheet. The coating layer is formed through the coating stage (S500), so that the stamping performance can be improved and the insulation performance can be ensured.

[0092] The non-oriented electrical steel sheet manufactured by the method for manufacturing a non-oriented electrical steel sheet according to an embodiment of the present invention may have an average grain size of about 100 micrometers to about 130 micrometers. The manufactured non-oriented electrical steel sheet may have an iron loss of about 13.0 W / kg or less (about W10 / 400) and a magnetic flux density of about 1.68 T or more (about B50). In addition, the manufactured non-oriented electrical steel sheet may have a yield strength (YP) of about 400 MPa or more and a tensile strength (TS) of about 500 MPa or more.

[0093] <Experimental Example>

[0094] The present invention will be described in more detail below by experimental examples. However, the following experimental examples are intended to explain the present invention in more detail, and the scope of the present invention is not limited to the following experimental examples. Those skilled in the art can make appropriate modifications and changes to the following experimental examples within the scope of the present invention.

[0095] [Table 1]

[0096]

[0097] [Table 2]

[0098]

[0099] Table 1 is a slab composition table including main components and impurities. Embodiment 1, Embodiment 2, Comparative Example 1, Comparative Example 2 and Comparative Example 3 are all manufactured using the slabs in Table 1.

[0100] Referring to Tables 1 and 2, a slab including the component composition shown in Table 1 was heated at about 1150°C and hot rolled at an FDT of about 890°C and a CT of about 610°C, thereby manufacturing a hot rolled plate having a thickness of about 2.0 mm. Thereafter, the hot rolled plate was preliminarily annealed at 1050°C for 60 seconds and then pickled. Then, the hot rolled annealed plate was cold rolled to form a cold rolled plate having a thickness of about 0.25 mm, and cold annealed at the first average heating rate, the second average heating rate, and the target temperature shown in Table 2. At this time, the target temperature holding time was about 30 seconds, the cooling rate was 30°C / s, and the cold annealing was performed in a mixed atmosphere of 30% hydrogen and 70% nitrogen.

[0101] [Table 3]

[0102]

[0103]

[0104] Table 3 shows the grain sizes of Embodiment 1, Embodiment 2, and Comparative Examples 1 to 3. <111> / / ND orientation fraction (area %), <100> / / Table of ND orientation fraction (area %), iron loss, and magnetic flux density measurement results. EBSD can be used to measure grain size, <111> / / ND orientation copies and <100> / / ND orientation fractions, and the measurement data can be obtained using TSLOIM analysis software. However, the present invention is not limited thereto. For magnetic measurement, the average values ​​of the iron loss value and the magnetic flux density value are calculated after measuring in the L direction and the C direction by a single-piece tester (SST). In Table 3, B50 is the magnetic flux density at 5000A / m, and W10 / 400 is the iron loss at a frequency of 400Hz and a magnetic flux density of 1.0 Tesla.

[0105] Referring to Table 2 and Table 3, it can be seen that the slower the first average heating rate in the first heating stage of the cold annealing step S400, <111> / / Orientation shares decrease and <100> / / ND orientation fraction increases. However, when the first average heating rate in the first heating stage of the cold annealing step (S400) is too small, grains may overgrow and heat treatment time may increase due to the low heating rate, which may reduce productivity and increase process costs.

[0106] In addition, in the case of Embodiment 1 and Embodiment 2, it can be seen that the grain sizes are 123 μm and 117 μm, respectively, which satisfy about 100 μm or more and about 130 μm or less. In the case of Embodiment 1 and Embodiment 2, it can be seen that the texture <111> / / ND orientation fraction is 30% or less, and the texture <100> / / ND orientation fraction is 20% or more. In addition, in the case of Embodiment 1 and Embodiment 2, it can be seen that the iron loss is 13.0 W / kg or less and the magnetic flux density is 1.68 T or more.

[0107] When the first average heating rate is greater than 5℃ / s and less than 20℃ / s, it can be seen that the grain size and texture <111> / / ND orientation fraction, texture <100> / / ND orientation fraction, iron loss and magnetic flux density meet the expected conditions.

[0108] Specifically, when the first average heating rate satisfies the range of greater than 5°C / s and less than 20°C / s, the grain size may satisfy the range of about 100 micrometers or more and about 130 micrometers or less, and the texture <111> / / ND orientation fraction will decrease and texture <100> / / ND orientation fraction will increase. As mentioned above, due to the texture <100> / / ND Orientation Ratio <111> / / ND orientation is excellent. When the first average heating rate is greater than 5℃ / s and less than 20℃ / s, the texture <111> / / ND orientation decreases, texture <100> / / As the ND orientation fraction increases, the iron loss of the manufactured non-oriented electrical steel sheet can be reduced and its magnetic flux density can be increased.

[0109] However, in the case of Comparative Example 1, the first average heating rate is performed at 5° C. / s, so grains may grow excessively due to the low heating rate and the heat treatment time may increase due to the low heating rate, which may reduce productivity and increase process costs.

[0110] In addition, in the case of Comparative Example 2 and Comparative Example 3, it can be seen that the first average heating rate is greater than 20°C / s, <111> / / ND orientation has a large proportion, texture <100> / / ND orientation fraction is low, iron loss is high, and magnetic flux density is low.

[0111] Therefore, when the first average heating rate in the first heating stage of the cold annealing step (S400) satisfies the range of greater than about 5°C / s and less than about 20°C / s, more preferably greater than about 10°C / s and less than about 15°C / s, the manufactured non-oriented electrical steel sheet may have an iron loss of about 13.0 W / kg or less (regarding W10 / 400) and a magnetic flux density of about 1.68 T or more (regarding B50). That is, when the first average heating rate in the first heating stage of the cold annealing step (S400) satisfies the range of greater than about 5°C / s and less than about 20°C / s, a non-oriented electrical steel sheet having excellent magnetic properties may be manufactured.

[0112] Although the present invention has been specifically shown and described with reference to the embodiments of the present invention, they are provided for illustrative purposes, and it will be appreciated by those skilled in the art that various modifications and other equivalent embodiments may be made according to the present invention. Therefore, the true technical scope of the present invention is limited by the technical spirit of the appended claims.

Claims

1. A method for manufacturing a non-oriented electrical steel sheet, the method comprising: hot rolling a slab comprising more than 0 wt % to 0.005 wt % or less carbon (C), 2.0 wt % or more to 4.0 wt % or less silicon (Si), 0.1 wt % or more to 0.5 wt % or less manganese (Mn), 0.9 wt % or more to 1.5 wt % or less aluminum (Al), more than 0 wt % to 0.015 wt % or less phosphorus (P), more than 0 wt % to 0.005 wt % or less sulfur (S), more than 0 wt % to 0.005 wt % or less nitrogen (N), more than 0 wt % to 0.005 wt % or less titanium (Ti), and the balance of iron (Fe) and unavoidable impurities; Performing preliminary annealing on the hot-rolled plate; cold rolling the preliminarily annealed hot-rolled sheet; and cold annealing the cold rolled plate; Among them, cold annealing includes a first heating stage, a second heating stage and a soaking stage. heating the cold rolled sheet from a starting temperature to a recrystallization temperature at a first average heating rate in a first heating stage, and In the second heating stage, the cold-rolled sheet is heated from the recrystallization temperature to the target temperature at a second average heating rate that is faster than the first average heating rate.

2. The method according to claim 1, wherein: The first average heating rate is greater than 5° C. / s and less than 20° C. / s.

3. The method according to claim 2, wherein: The second average heating rate is 15° C. / s or more and 30° C. / s or less.

4. The method according to claim 1, wherein: The recrystallization temperature is 750°C to 800°C.

5. The method according to claim 1, wherein: The target temperature is 850°C to 1,050°C.

6. The method according to claim 1, wherein: Cold annealing also includes a cooling phase, and The cold-rolled annealed sheet is cooled at a cooling rate of 30° C. / s or more in the cooling stage.

7. The method according to claim 1, wherein: The texture of the non-oriented electrical steel sheet <111> / / ND orientation fraction is 30% or less.

8. The method according to claim 1, wherein: The texture of the non-oriented electrical steel sheet <100> / / ND orientation fraction is 20% or more.

9. The method according to claim 1, wherein: The non-oriented electrical steel sheet has an average grain size of 100 micrometers or more and 130 micrometers or less.

10. A non-oriented electrical steel sheet, comprising: more than 0 wt% to 0.005 wt% or less of carbon (C), 2.0 wt% or more to 4.0 wt% or less of silicon (Si), 0.1 wt% or more to 0.5 wt% or less of manganese (Mn), 0.9 wt% or more to 1.5 wt% or less of aluminum (Al), more than 0 wt% to 0.015 wt% or less of phosphorus (P), more than 0 wt% to 0.005 wt% or less of sulfur (S), more than 0 wt% to 0.005 wt% or less of nitrogen (N), more than 0 wt% to 0.005 wt% or less of titanium (Ti), the balance of iron (Fe) and unavoidable impurities, in, Textured <111> / / ND orientation fraction is 30% or less, and the texture <100> / / ND orientation fraction is 20% or more.

11. The non-oriented electrical steel sheet according to claim 10, wherein: The non-oriented electrical steel sheet has an iron loss (regarding W10 / 400) of 13.0 W / kg or less, and a magnetic flux density (regarding B50) of 1.68 T or more.

12. The non-oriented electrical steel sheet according to claim 10, wherein: The non-oriented electrical steel sheet has a yield strength (YP) of 400 MPa or more and a tensile strength (TS) of 500 MPa or more.

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