Bi-directional electrical steel sheet and its manufacturing method

Abstract

The present invention provides a bi-directional electrical steel sheet that achieves secondary recrystallization of cube and {100} fiber textures using surface energy, and a method for manufacturing the same. [Solution] The bidirectional electrical steel sheet according to one embodiment of the present invention contains, by weight, Si: 2.0% or more, Al: 0.02% or less (excluding 0%), Mn: 0.02 to 0.50%, C: 0.004% or less (excluding 0%), and S: 0.0005 to 0.005%, with the remainder being Fe and other impurities, and the area fraction of crystal grains with a grain size of 2000 μm or less is 25% or less.

Description

[Technical Field]

[0001] The present invention relates to a bi-grained electrical steel sheet and a manufacturing method thereof. Specifically, one embodiment of the present invention relates to a bi-grained electrical steel sheet having excellent magnetic properties in both the rolling direction and the direction perpendicular to the rolling direction and an extremely small magnetic deviation, which is achieved by controlling the reduction rate in the secondary cold rolling and the heating rate during annealing of the cold-rolled sheet to form a small number of fine crystal grains, and a manufacturing method thereof. [Background technology]

[0002] Steel sheets made from iron have different properties depending on the direction due to their structural characteristics called BCC. Electromagnetic steel sheets used as the iron core material for motors are <100> For example, grain-oriented electrical steel sheets utilize the secondary recrystallization phenomenon of the Goss texture to maximize the properties of the product by aligning the rolling direction (RD) of the product with the direction of all the crystal grains. <100> The atoms are used in a state where they are arranged in parallel directions.

[0003] To create a texture with a specific orientation for all crystal grains, a phenomenon called secondary recrystallization is essential. Secondary recrystallization can be used to remove crystal grains with undesired orientations and allow crystal grains with the preferred orientation to grow. After secondary recrystallization is complete, only the desired crystal grain orientation remains.

[0004] However, the phenomenon of secondary recrystallization is not yet fully understood, and various theories are being debated from the perspectives of the growth of secondary crystal grains and the selection of growth orientation. The main topic of debate is the secondary recrystallization of Goss crystal grains in currently commercially available grain-oriented electrical steel sheets. Fine precipitates such as AlN must be created and used through nitriding annealing, and as AlN dissolves at high temperatures, the inhibitory force that held the grain boundaries in place is lost, allowing only Goss to grow. Of course, this phenomenon can be used to achieve both RD and TD. <001> There have been attempts to create a directional cube texture, but in the secondary recrystallization phenomenon using precipitates, only the Goss texture develops predominantly under most experimental conditions, so it is not easy to create textures other than Goss using secondary recrystallization. This patent uses the secondary recrystallization phenomenon using surface energy to manufacture bidirectional electrical steel sheets with good magnetic properties in both directions. Summary of the Invention [Problem to be solved by the invention]

[0005] One embodiment of the present invention provides a bi-directional electrical steel sheet and a manufacturing method thereof. Specifically, one embodiment of the present invention provides a bi-directional electrical steel sheet and a manufacturing method thereof that achieves secondary recrystallization of Cube and {100} fiber textures using surface energy. [Means for solving the problem]

[0006] A two-dimensional electrical steel sheet according to one embodiment of the present invention contains, by weight, 2.0% or more Si, 0.02% or less (excluding 0%) Al, 0.02 to 0.50% Mn, 0.004% or less (excluding 0%) C, and 0.0005 to 0.005% S, with the remainder being Fe and other impurities.

[0007] In a two-grained electrical steel sheet according to one embodiment of the present invention, the area fraction of crystal grains having a grain size of 2000 μm or less is 25% or less.

[0008] The bidirectional electrical steel sheet according to one embodiment of the present invention is <100> The area fraction of crystal grains whose direction is at an angle of 15° or less with respect to the normal direction of the rolled surface of the steel sheet is 75% or more. The average grain size of the crystal grains may be 1000 to 5000 μm.

[0009] The bi-directional electrical steel sheet according to one embodiment of the present invention may have a magnetic flux density (B50) of 1.82 T or more and an iron loss (W15 / 50) of 1.65 W / Kg or less.

[0010] A method for producing a bi-directional electrical steel sheet according to one embodiment of the present invention includes the steps of: hot rolling a slab containing, by weight, 2.0% or more Si, 0.02% or less (excluding 0%) Al, 0.02 to 0.50% Mn, 0.004% or less (excluding 0%) C, and 0.0005 to 0.005% S, with the balance being Fe and other impurities, to produce a hot-rolled sheet; first cold-rolling the hot-rolled sheet to produce a first cold-rolled sheet; intermediate-annealing the first cold-rolled sheet; second cold-rolling the intermediate-annealed sheet to produce a second cold-rolled sheet; and annealing the second cold-rolled sheet.

[0011] In the step of producing the second cold-rolled sheet, the rolling reduction is 55 to 85%. Before the step of annealing the second cold-rolled sheet, the method further includes a step of increasing the temperature in the range of 100 to 1000° C. at a rate of 100° C. / h or more.

[0012] After the step of producing the hot-rolled sheet, the method may further include the step of hot-rolled sheet annealing the hot-rolled sheet.

[0013] The step of producing the first cold-rolled sheet may include one cold rolling or two or more cold rollings with intermediate annealing.

[0014] The steps of producing the first cold-rolled sheet and the second cold-rolled sheet may be performed in the same direction.

[0015] The intermediate annealing step may be performed at a temperature of 700° C. or higher. The intermediate annealing may be performed in a reducing atmosphere.

[0016] After the step of preparing the second cold-rolled sheet, the method may further include the step of applying an annealing separator.

[0017] The step of annealing the second cold-rolled sheet may be performed in a reducing atmosphere. The step of annealing the second cold-rolled sheet may be performed at a temperature of 1000 to 1200° C. for 6 to 60 hours. [Effects of the Invention]

[0018] The bi-directional electrical steel sheet according to an embodiment of the present invention exhibits excellent magnetic properties such as high magnetic flux density and low core loss because the magnetic values ​​in the rolling direction and the direction perpendicular to the rolling direction are similar regardless of the direction. [Brief explanation of the drawings]

[0019] [Figure 1] 1 shows photographs of the rolled surfaces of the steel plates produced in Comparative Examples 1 to 10. [Figure 2] 1 shows photographs of the rolled surfaces of the steel plates produced in Comparative Examples 1 to 10. [Figure 3] 1 shows photographs of the rolled surfaces of the steel plates produced in Comparative Examples 1 to 10. [Figure 4] 1 shows photographs of the rolled surfaces of the steel plates produced in Comparative Examples 1 to 10. [Figure 5] 1 shows photographs of the rolled surfaces of the steel plates produced in Comparative Examples 1 to 10. [Figure 6] 1 shows photographs of the rolled surfaces of the steel plates produced in Comparative Examples 1 to 10. [Figure 7] 1 shows photographs of the rolled surfaces of the steel plates produced in Comparative Examples 1 to 10. [Figure 8] 1 shows photographs of the rolled surfaces of the steel plates produced in Comparative Examples 1 to 10. [Figure 9] 1 shows photographs of the rolled surfaces of the steel plates produced in Comparative Examples 1 to 10. [Figure 10] 1 shows photographs of the rolled surfaces of the steel plates produced in Comparative Examples 1 to 10. [Figure 11]1 shows a photograph of the rolled surface of the steel plates produced in Examples 1 and 2 (left), an Inverse Pole Figure (IPF) map photograph (middle), and an Orientation Distribution Function (ODF) map photograph (right). [Figure 12] 1 shows a photograph of the rolled surface of the steel plates produced in Examples 1 and 2 (left), an Inverse Pole Figure (IPF) map photograph (middle), and an Orientation Distribution Function (ODF) map photograph (right). DETAILED DESCRIPTION OF THE INVENTION

[0020] Terms such as "first," "second," and "third" are used to describe various portions, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one portion, component, region, layer, or section from another portion, component, region, layer, or section. Therefore, a first portion, component, region, layer, or section described below can be referred to as a second portion, component, region, layer, or section without departing from the scope of the present invention.

[0021] The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. As used in the specification, the meaning of "comprising" embodies particular features, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0022] When an element is referred to as being "on" or "above" another element, it means that it is directly on or above the other element, or there may be other elements between them. In contrast, when an element is referred to as being "directly on" another element, there are no other elements between them.

[0023] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the currently disclosed content, and are not interpreted as having an ideal or very formal meaning unless otherwise defined.

[0024] Unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight.

[0025] In one embodiment of the present invention, the inclusion of an additional element means that the remaining iron (Fe) is replaced by the additional amount of the additional element. Although the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein, the present invention will be described in detail below so that those skilled in the art can easily practice the present invention.

[0026] In one embodiment of the present invention, surface energy can be used to achieve secondary recrystallization of Cube and {100} fiber textures. It is known that the {110} plane, a close packed plane, has the lowest energy in iron with a BCC structure. However, if some impurities are present, the {100} plane also has the lowest energy. In one embodiment of the present invention, the low energy state of the {100} plane can be maintained during long-term cold-rolled sheet annealing, allowing only Cube and {100} fiber textures to grow. This secondary recrystallization phenomenon occurs through selective crystal growth using surface energy.

[0027] A two-dimensional electrical steel sheet according to one embodiment of the present invention contains, by weight, 2.0% or more Si, 0.02% or less (excluding 0%) Al, 0.02 to 0.50% Mn, 0.004% or less (excluding 0%) C, and 0.0005 to 0.005% S, with the remainder being Fe and other impurities.

[0028] The reasons for limiting the composition of bidirectional electrical steel sheets will be explained below. Si: 2.0% by weight or more Silicon (Si) increases the resistivity of steel sheets and reduces eddy current loss, ensuring that heat treatment occurs in a single ferrite phase. If the Si content is too low, partial phase transformation of ferrite to austenite may occur during heat treatment. Therefore, the lower limit of the Si content can be limited to 2.0 wt%. Furthermore, the more Si added, the more difficult coiling and cold rolling become, and if the Si content exceeds 7.0 wt%, sheet breakage may occur. Therefore, this limit can be set as necessary. That is, Si may be included in the range of 2.0 to 7.0 wt%. More specifically, to obtain steel sheets with high magnetic flux density, Si may be included in the range of 2.5 to 4.0 wt%.

[0029] Al: 0.02% by weight or less Aluminum (Al) can increase resistivity. However, when a steel sheet contains a large amount of Al, Al2O3 is formed on the steel sheet surface during heat treatment. Al2O3 can penetrate from the surface to the grain boundaries, which inhibits grain growth and hinders secondary recrystallization. Therefore, the Al content is preferably 0.02 wt% or less. More specifically, Al may be contained in an amount of 0.01 wt% or less. Even more specifically, Al may be contained in an amount of 0.005 wt% or less. Even more specifically, Al may be contained in an amount of 0.001 to 0.005 wt%.

[0030] Mn:0.02~0.50wt% Manganese (Mn) is an element that increases resistivity. However, if too much Mn is added, it may pass through the austenite region during heat treatment, causing a phase transformation. Excessive Mn also traps more sulfur than necessary, preventing the diffusion of elemental S. An appropriate amount of Mn precipitates fine MnS, weakly capturing the grain boundaries. At the appropriate temperature, the MnS melts and disappears, causing secondary recrystallization. The rate of S volatilization can also be controlled to some extent by Mn, so the inclusion of an appropriate amount of Mn can be seen to play a certain role in secondary recrystallization. More specifically, Mn can be included at 0.05 to 0.30 wt%.

[0031] C: 0.004% by weight or less Unlike the other elements mentioned above, carbon (C) is an element that does not substitute for Fe atoms but enters the interstitial sites. Due to this property, when a large amount of C is added, it inhibits the movement of electric potential and hinders the growth of crystal grains. More specifically, C can be contained in an amount of 0.003% by weight or less. More specifically, C can be contained in an amount of 0.001 to 0.003% by weight.

[0032] S:0.0005~0.0050wt% The surface energy of sulfur (S) changes depending on the amount of S segregated on the surface, and the changed surface energy can cause crystal growth of crystal grains in a specific direction. On a surface with no S, the {110} plane is stable, on a surface with weak S segregation the {100} plane is stable, and on a surface with heavy S segregation the {111} plane is stable. To weakly segregate S on the surface, the S content is adjusted to a very small amount. Mn also plays a role in further capturing S, helping to weakly segregate S on the surface. More specifically, S can be contained at 0.0010 to 0.0040 wt%.

[0033] The balance of the bidirectional electrical steel sheet of the present invention, other than the aforementioned components, is Fe and unavoidable impurities. However, this does not mean that other elements may be contained within a range that does not impair the effects of the present invention. If additional elements are contained, they may be included to replace Fe. The additional elements may be, for example, one or more of N, Ti, P, Cu, Cr, Ni, and Mo, and if additional elements are added, they may be included in an amount of 0.1 wt% or less.

[0034] In one embodiment of the present invention, the area fraction of crystal grains having a grain size of 2000 μm or less is 25% or less. In one embodiment of the present invention, the secondary cold-rolled sheet annealing is performed for a long period of time (6 hours or more). However, if fine grains do not grow further and remain, they can hinder magnetic properties. In one embodiment of the present invention, rapid heating is performed before the secondary cold-rolled sheet annealing to suppress the generation of fine grains, thereby further improving magnetic properties. More specifically, the area fraction of crystal grains having a grain size of 2000 μm or less may be 10% or less. More specifically, the area fraction of crystal grains having a grain size of 2000 μm or less may be 5% or less. In one embodiment of the present invention, the grain size of the crystal grains may be measured based on a plane parallel to the rolling surface (ND plane), and the diameter of a virtual circle having the same area as the area of ​​the crystal grain is considered to be the grain size. The area fraction of the crystal grains may also be measured based on a plane parallel to the rolling surface (ND plane). To reduce errors, the grain size is measured on a surface of at least 60 × 60 mm. 2 The area fraction can be measured from a specimen having an area. In one embodiment of the present invention, since there is no substantial variation in the grain size and area fraction across the thickness, the measurement thickness can be any thickness.

[0035] The bidirectional electrical steel sheet according to one embodiment of the present invention is <100> The area fraction of crystal grains whose direction is at an angle of 15° or less with the normal direction (ND direction) of the rolled surface of the steel sheet is 75% or more. <100> Grains whose direction is within 15° of the normal direction of the rolling surface of the steel plate, i.e., <100> / / The higher the proportion of ND crystal grains, the better the magnetic properties. <100> Based on an arbitrary plane that includes both the direction and the normal direction of the rolling surface, <100> This refers to the angle between the direction of the roll and the normal direction to the rolling surface.

[0036] In the bi-directional electrical steel sheet according to an embodiment of the present invention, the average grain size of the crystal grains may be 1000 to 5000 μm. If the average grain size of the crystal grains is excessively small, <100> The proportion of ND texture may decrease, resulting in poor magnetic properties. The grain size can be measured based on a plane parallel to the rolled surface (ND plane) of the steel sheet. More specifically, the average grain size may be 2500 μm or more. The average grain size refers to the water average grain size.

[0037] A bidirectional electrical steel sheet according to one embodiment of the present invention has excellent magnetic flux density and iron loss. The bidirectional electrical steel sheet according to one embodiment of the present invention may have a magnetic flux density (B50) of 1.82 T or more and an iron loss (W15 / 50) of 1.65 W / Kg or less. More specifically, the bidirectional electrical steel sheet according to one embodiment of the present invention may have a magnetic flux density (B50) of 1.90 T or more and an iron loss (W15 / 50) of 1.30 W / Kg or less. In one embodiment of the present invention, the magnetic flux density (B50) and iron loss (W15 / 50) refer to the average values ​​of the magnetic flux density (B50) and iron loss (W15 / 50) measured in the rolling direction (RD) and the direction perpendicular to the rolling direction (TD), respectively, and are measured based on a steel sheet thickness of 0.2 mm.

[0038] A method for manufacturing a bidirectional electrical steel sheet according to one embodiment of the present invention includes the steps of hot-rolling a slab to manufacture a hot-rolled sheet, first cold-rolling the hot-rolled sheet to manufacture a first cold-rolled sheet, intermediate-annealing the first cold-rolled sheet, second cold-rolling the intermediate-annealed sheet to manufacture a second cold-rolled sheet, and final-annealing the second cold-rolled sheet.

[0039] Each step will be explained in detail below. First, a slab is manufactured. The reasons for limiting the addition ratio of each element in the slab are the same as those for limiting the composition of the above-mentioned two-dimensional electrical steel sheet, so a repeated explanation will be omitted. Since the element contents do not substantially change during the manufacturing processes, such as hot rolling, hot-rolled sheet annealing, first cold rolling, intermediate annealing, second cold rolling, and second cold-rolled sheet annealing, the composition of the slab and the composition of the two-dimensional electrical steel sheet are substantially the same.

[0040] The slab can be produced using a thin slab method or a strip casting method. The thickness of the slab may be 200 to 300 mm. The slab can be heated as needed. The heating temperature may be 1100 to 1250°C, and the heating time may be 30 minutes or more.

[0041] The slab is then hot rolled to produce a hot rolled sheet. In the step of producing the hot-rolled sheet, the thickness of the hot-rolled sheet may be 2.0 to 3.0 mm. After the step of producing the hot-rolled sheet, the method may further include a step of annealing the hot-rolled sheet. The step of annealing the hot-rolled sheet may be annealed at a temperature of 1000 to 1150°C for 60 to 150 seconds. After the step of annealing the hot-rolled sheet, the method may further include a step of pickling.

[0042] Next, the hot-rolled sheet is subjected to the first rolling to produce a first cold-rolled sheet. The step of producing the primary cold-rolled sheet may include one cold rolling step or two or more cold rolling steps with intermediate annealing. The steps of producing the first cold-rolled sheet and the second cold-rolled sheet may be performed in the same direction.

[0043] Next, the primary cold-rolled sheet is subjected to intermediate annealing. The intermediate annealing step is sufficient to complete recrystallization, and can be performed at 700° C. or higher for 60 to 150 seconds. The intermediate annealing step may be performed in a reducing atmosphere. Since secondary cold rolling must be performed after the intermediate annealing, the annealing may be performed in an atmosphere containing a large amount of hydrogen to prevent oxidation during annealing. The remaining atmosphere may be air. More specifically, the annealing may be performed in an atmosphere containing 99% or more by volume of hydrogen.

[0044] Next, the intermediate annealed sheet is subjected to a second cold rolling to produce a second cold-rolled sheet. The reduction rate of the second cold rolling can be adjusted to 55~85%. If the reduction rate is too low, <100> / / There may be few ND grains formed. When the rolling reduction is too high, the grain size decreases after recrystallization. <001> The direction rotates, <380> It rotated even more, <250> or <120> Secondary recrystallization occurs in the following directions. More specifically, the rolling reduction may be 55 to 80%. Even more specifically, the rolling reduction may be 55 to 65%. The reduction ratio can be calculated by ([thickness of steel plate before reduction] - [thickness of steel plate after reduction]) / [thickness of steel plate before reduction]. After the second cold rolling step, an annealing separator can be applied for long-term annealing. The annealing separator can include alumina (Al2O3).

[0045] Next, the secondary cold-rolled sheet is annealed. Prior to annealing the second cold-rolled sheet, the method may further include a step of increasing the temperature at a rate of 100°C / h or more in the temperature range of 100 to 1000°C. In one embodiment of the present invention, the "heating rate" refers to the average heating rate within the temperature range. If the heating rate is too low, many fine crystal grains remain. These remain even after long annealing times in the cold-rolled sheet annealing process described below, adversely affecting magnetic properties. On the other hand, by appropriately controlling the heating rate, many fine crystal grains can be grown and minimized. The upper limit is not particularly limited, but may be 500°C / h. More specifically, the heating rate may be 100 to 300°C / h.

[0046] The second cold-rolled sheet can be annealed for 6 to 60 hours. If the annealing time is too short, <100> / / ND orientation grains may not be properly formed. If the annealing time is too long, energy may be wasted. More specifically, the final annealing step can be annealed for 12 to 48 hours.

[0047] The secondary cold-rolled sheet annealing step may be performed in a reducing atmosphere. To prevent oxidation during annealing, the annealing may be performed in an atmosphere containing a large amount of hydrogen. The remaining atmosphere may be air. More specifically, the annealing may be performed in an atmosphere containing 99% or more by volume of hydrogen.

[0048] The secondary cold-rolled sheet annealing step can be performed at a temperature of 1000~1200℃. If the annealing temperature is too low, recrystallization may not occur properly. If the annealing temperature is too high, it is difficult to improve the magnetic properties.

[0049] Preferred examples and comparative examples of the present invention will be described below. However, the following examples are merely preferred embodiments of the present invention, and the present invention is not limited to the following examples. [Example]

[0050] Experimental Example 1 Slabs containing, by weight, 3.1% Si, 0.1% Mn, 0.003% Al, 0.002% C, 0.003% S, 0.002% N, 0.001% Ti, and 0.007% P, with the remainder consisting of Fe and unavoidable impurities, were manufactured and heated at 1130°C for 2 hours before being hot-rolled to a thickness of 2.5 mm. The hot-rolled sheets were heat-treated at 1070°C for 2 minutes, pickled, and then subjected to primary cold rolling. The reduction ratio in the secondary cold rolling was varied from 50% to 90%. The final thicknesses after primary cold rolling were 2 mm (90%), 1 mm (80%), 0.67 mm (70%), and 0.50 mm (60%), respectively. After primary rolling, the specimens were heat-treated at 1050°C for approximately 2 minutes. This was done in a 100% hydrogen atmosphere. The specimens were then subjected to a second cold rolling process to a final thickness of 0.2 mm. Each specimen was cut into a 60 x 60 mm size for magnetic properties measurement using a single sheet tester (SST), and the cut specimens were heat-treated at 1200°C for 24 hours. The heating rate in the temperature range of 100 to 1000°C was changed as shown in Table 1 below.

[0051] The area fraction of fine grains was calculated by obtaining a photograph of the crystal grains through scanning and determining the area of ​​the crystal grains from the photograph. Grain orientation was measured using Laue X-ray diffraction on a 6cm x 6cm 2 The area was measured. [Table 1]

[0052] As shown in Table 1, the embodiment in which the reduction rate during the second cold rolling and the temperature rise rate during the second cold-rolled sheet annealing are appropriately adjusted is <100> / / It can be seen that ND crystal grains are properly formed, the generation of fine grains is suppressed, and magnetic properties are improved. On the other hand, if the reduction rate of the second cold rolling is too small or too large, <100> / / It can be seen that magnetic properties are inferior due to improper formation of ND crystal grains. Also, if the heating rate during secondary cold-rolled sheet annealing is not properly controlled, many fine crystal grains are formed, which can be seen to result in inferior magnetic properties.

[0053] Figures 1 to 5 are photographs of the rolled surfaces of steel sheets produced in Comparative Examples 1 to 5, respectively. It can be seen that a large amount of fine grains are formed when the heating rate is 10°C / h. Figures 6 to 10 are photographs of the rolled surfaces of steel sheets produced in Comparative Examples 6 to 10, respectively. When the heating rate is 15°C / h, secondary recrystallization begins to occur. Figures 11 and 12 are photographs of the rolled surfaces of steel sheets produced in Examples 1 and 2, respectively. It can be seen that at a heating rate of 300°C / h, secondary recrystallization occurs in over 97% of cases, with almost no fine grains present. Figures 1 to 12 are all 6cm x 6cm photographs, and the yellow lines indicate the grain boundaries between the secondary recrystallization and the fine grains.

[0054] 11 and 12 are photographs of Inverse Pole Figure (IPF) maps of the steel sheets produced in Examples 1 and 2, and FIGS. 15 and 16 are photographs of Orientation Distribution Function (ODF) maps of the steel sheets produced in Examples 1 and 2.

[0055] In the IPF maps in Figures 11 and 12, <100> / / ND is displayed in red. As shown in Figures 11 and 12, there are one or two blue areas. This is a measurement error that occurs when a large number of crystal grains are present in one measurement area due to the wide measurement interval. <111> / / It is difficult to interpret this as ND grains.

[0056] The ODF maps in Figures 11 and 12 show the case where psi2 is 45 degrees. The lattice in the ODF is spaced at 10 degrees, and it can be seen that the {100} plane is maintained while only the direction changes. Also, the contour lines of the texture intensity on the ODF are <100> / / It can be seen that it is within 15 degrees of the ND surface.

[0057] The present invention is not limited to the above-described embodiments, and can be manufactured in various different forms, and those skilled in the art will understand that the present invention can be embodied in other specific forms without changing the technical concept or essential features of the present invention. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and not limiting.

Claims

1. A bi-grained electrical steel sheet comprising, by weight percent, 2.0% or more of Si, 0.02% or less of Al (excluding 0%), 0.02 to 0.50% of Mn, 0.004% or less of C (excluding 0%), and 0.0005 to 0.005% of S, with the balance being Fe and other impurities, and the area fraction of crystal grains having a grain size of 2000 μm or less being 25% or less.

2. 2. The bi-grained electrical steel sheet according to claim 1, wherein the area fraction of crystal grains having a <100> direction at an angle of 15° or less with respect to the normal direction of the rolled surface of the steel sheet is 75% or more.

3. The bi-directional electrical steel sheet according to claim 1, characterized in that the average grain size of the crystal grains is 1000 to 5000 μm.

4. 2. The bi-directional electrical steel sheet according to claim 1, wherein the magnetic flux density (B50) is 1.82 T or more and the core loss (W15 / 50) is 1.65 W / Kg or less.

5. The method includes the steps of: hot rolling a slab containing, by weight, Si: 2.0% or more, Al: 0.02% or less (excluding 0%), Mn: 0.02 to 0.50%, C: 0.004% or less (excluding 0%), and S: 0.0005 to 0.005%, with the balance being Fe and other impurities, to produce a hot-rolled sheet; first cold rolling the hot-rolled sheet to produce a first cold-rolled sheet; intermediate annealing the first cold-rolled sheet; second cold rolling the intermediate annealed sheet to produce a second cold-rolled sheet; and annealing the second cold-rolled sheet, In the step of producing the second cold-rolled sheet, the reduction ratio is 55 to 85%, The method for producing a bi-directional electrical steel sheet further comprises, before the step of annealing the second cold-rolled sheet, a step of increasing the temperature in a temperature range of 100 to 1000° C. at a heating rate of 100° C. / h or more.

6. The method of claim 5, further comprising the step of hot-rolled sheet annealing the hot-rolled sheet after the step of producing the hot-rolled sheet.

7. The method of claim 5, wherein the step of producing the first cold rolled sheet includes one cold rolling or two or more cold rollings with intermediate annealing in between.

8. The method of claim 5, wherein the first cold-rolled sheet and the second cold-rolled sheet are rolled in the same direction.

9. The method of claim 5, wherein the intermediate annealing is performed in a reducing atmosphere.

10. The method of claim 5, further comprising the step of applying an annealing separator after the step of producing the second cold rolled sheet.

11. The method of claim 5, wherein the step of annealing the second cold rolled sheet is performed in a reducing atmosphere.

12. The method of claim 5, wherein the step of annealing the second cold rolled sheet comprises annealing the sheet at a temperature of 1000 to 1200° C. for 6 to 60 hours.

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