Electrical steel sheet for electromagnetic wave shielding, and manufacturing method therefor

Abstract

In an electrical steel sheet for electromagnetic wave shielding, according to one embodiment of the present invention, grains having a ratio (D2 / D1) of the diameter (D1) of a circumscribed circle to the diameter (D2) of an inscribed circle of 0.5 or more account for 70 area% or more among all grains on the surface of the steel sheet, the average grain diameter in a surface portion from the surface of the steel sheet to less than 2 / 5 of the thickness of the steel sheet in the thickness direction is 100 μm to 500 μm, and the average grain diameter in a central portion corresponding to 2 / 5 to 3 / 5 of the thickness of the steel sheet is 55 μm to 90 μm.

Description

Electrical steel sheet for electromagnetic shielding and its manufacturing method

[0001] One embodiment of the present invention relates to an electromagnetic wave shielding electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to an electromagnetic wave shielding electrical steel sheet with excellent electromagnetic wave shielding effects and a method for manufacturing the same.

[0002] Burying transmission towers underground, either by directly burying high-voltage power lines or constructing underground tunnels like power lines, can improve the cityscape and prevent accidents caused by natural disasters. These underground power lines generate electromagnetic fields that can affect the human body, and aluminum is used to shield them. While aluminum is corrosion-resistant and offers long-term durability, it requires a thick layer to achieve adequate shielding. This thick aluminum material complicates construction and increases the cost of shielding underground lines due to its high material usage.

[0003] To address the above issues, the use of steel, which is relatively inexpensive compared to aluminum, has been proposed. To ensure excellent magnetic shielding properties in steel, the content of interstitial and precipitate-forming elements is limited. This is because the strain generated by interstitial elements and the precipitates formed significantly reduce magnetic permeability, so a method to limit these factors was proposed. Furthermore, by limiting the composition of the elements and minimizing the size of the precipitates, an attempt was made to achieve excellent magnetic flux density. However, when shielding electromagnetic waves generated in low fields, both the influence of the constituent elements and grain size control must be applied simultaneously to ensure excellent shielding properties, necessitating additional microstructural control. Furthermore, because electromagnetic shielding steels are often installed underground, exposed to soil corrosion, and required to ensure electromagnetic shielding properties around transmission and distribution lines, high processability and constructability are required. Therefore, the steel for electromagnetic shielding requires a surface treatment that is highly corrosion-resistant in environments such as soil, and excellent processability of the material is required. However, there is no shielding material that meets this requirement.

[0004] One embodiment of the present invention provides an electromagnetic shielding electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention provides an electromagnetic shielding electrical steel sheet with excellent electromagnetic shielding effects and a method for manufacturing the same.

[0005] An electrical steel sheet for electromagnetic shielding according to one embodiment of the present invention has 70 area% or more of crystal grains having a ratio (D2 / D1) of a diameter of a circumscribed circle (D1) to a diameter of an inscribed circle (D2) of 0.5 or more among all crystal grains on the surface of the steel sheet, an average crystal grain diameter within a surface portion from the surface of the steel sheet to less than 2 / 5 of the thickness of the steel sheet in the thickness direction is 100 µm to 500 µm, and an average crystal grain diameter within a central portion of 2 / 5 to 3 / 5 of the thickness of the steel sheet is 55 µm to 90 µm.

[0006] Inside the steel plate <111> The area fraction of grains whose direction is parallel to the rolling direction of the steel plate within 15° <110> The ratio of the area fraction of grains whose direction is parallel to the rolling direction of the steel plate and is within 15° may be 3 or more.

[0007] The ratio of the average grain size within the surface to the average grain size within the center (surface / center) may be 2.0 or greater.

[0008] An electrical steel sheet for electromagnetic shielding according to one embodiment of the present invention may include, in weight %, Si: 0.3% to 7.0%, C: 0.15% or less (excluding 0%), and the remainder being Fe and unavoidable impurities.

[0009] An electrical steel sheet for electromagnetic shielding according to one embodiment of the present invention may further include Mn: 0.1 wt% or less and S: 0.005 wt% or less.

[0010] A method for manufacturing an electrical steel sheet for electromagnetic shielding according to one embodiment of the present invention comprises the steps of: hot-rolling a slab to manufacture a hot-rolled steel sheet; hot-rolling the hot-rolled steel sheet; cold-rolling the hot-rolled steel sheet annealed; decarburization annealing the cold-rolled steel sheet; and non-oxidation annealing the decarburization annealed steel sheet.

[0011] τ defined by the following equation 1 is 0.23 to 0.5.

[0012] [Formula 1]

[0013]

[0014]

[0015] (In Equation 1, the finishing rolling temperature is the hot rolling finishing rolling temperature (℃), the ROT cooling rate is the cooling rate (-℃ / s) in the ROT section before the coil is coiled after the hot rolling finishing rolling, the hot rolled sheet thickness is the thickness of the hot rolled sheet (mm), the dew point temperature is the dew point temperature (℃) of the atmosphere in the decarburization annealing stage, the annealing temperature is the annealing temperature (℃) in the decarburization annealing stage, and the cold rolled sheet thickness means the steel sheet thickness (mm) after the first cold rolling.)

[0016] The slab may contain, by weight %, Si: 0.3% to 7.0%, C: 0.01% to 0.4%, and the remainder being Fe and unavoidable impurities.

[0017] The slab may further contain Mn: up to 0.1 wt% and S: up to 0.005 wt%.

[0018] The decarburization process may be included in the annealing stage of hot-rolled steel.

[0019] The step of annealing the hot-rolled plate can be performed at a temperature of 850℃ to 1000℃ and a dew point temperature of 70℃ or lower.

[0020] The decarburization annealing step can be performed at a temperature of 600°C to 1000°C and a dew point temperature of 0°C to 70°C.

[0021] The non-oxidizing annealing step can be performed at a soaking temperature of 750 to 1050°C for 30 seconds to 5 minutes.

[0022] The non-oxidizing annealing step can be performed in an atmosphere with a dew point temperature of -20℃ or lower.

[0023] According to one embodiment of the present invention, electromagnetic wave shielding properties are excellent.

[0024] According to one embodiment of the present invention, an electromagnetic wave shielding steel plate having excellent workability can be provided.

[0025] Additionally, since it can be manufactured through a continuous process, the manufacturing time can be relatively shortened and productivity can be improved.

[0026] Figure 1 is a schematic diagram schematically showing a cross-section of a steel plate for electromagnetic wave shielding according to one embodiment of the present invention.

[0027] Figure 2 is a schematic diagram schematically showing one example of use of an electromagnetic wave shielding steel plate according to one embodiment of the present invention.

[0028] Figure 3 is a photograph showing the surface of the electromagnetic shielding steel plate manufactured in Example 1 through EBSD analysis.

[0029] Figure 4 is a photograph of a cross-section of an electromagnetic shielding steel plate manufactured in Example 1 observed through an optical microscope.

[0030] The terms first, second, and third, etc., are used to describe, but are not limited to, various parts, components, regions, layers, and / or sections. These terms are used solely to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Accordingly, a first part, component, region, layer, or section described below may be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention.

[0031] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising," as used herein, specifies particular features, regions, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0032] When a part is referred to as being "on" or "over" another part, it can be directly on or over the other part, or there may be other parts intervening. Conversely, when a part is referred to as being "directly on" another part, there are no other parts intervening.

[0033] Although not defined otherwise, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention pertains. Terms defined in commonly used dictionaries are further interpreted to have meanings consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or overly formal unless otherwise defined.

[0034] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0035] In one embodiment of the present invention, the inclusion of additional elements means including the remaining iron (Fe) in an amount equivalent to the additional amount of the additional elements.

[0036]

[0037] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0038] Fig. 1 schematically shows a cross-section of an electrical steel plate for electromagnetic shielding according to one embodiment of the present invention.

[0039] As shown in Fig. 1, an electrical steel plate (100) for electromagnetic shielding according to one embodiment of the present invention has 70 area% or more of crystal grains having a ratio (D2 / D1) of a diameter of a circumscribed circle (D1) to a diameter of an inscribed circle (D2) of 0.5 or more among all crystal grains on the surface of the steel plate, and an average crystal grain diameter in a surface portion (12) from the surface of the steel plate to less than 2 / 5 of the thickness of the steel plate in the thickness direction is 100 µm to 500 µm, and an average crystal grain diameter in a central portion (11) of 2 / 5 to 3 / 5 of the thickness of the steel plate is 55 to 90 µm.

[0040] Below, each component of an electrical steel plate for electromagnetic shielding according to one embodiment of the present invention is described in detail.

[0041] First, an electrical steel plate (100) for electromagnetic shielding according to one embodiment of the present invention contains, in wt%, Si: 0.3% to 7.0%, C: 0.15% or less (excluding 0%), and the remainder being Fe and unavoidable impurities.

[0042] Si: 0.3 to 7.0 wt%

[0043] Silicon (Si) improves the electromagnetic shielding performance of a material in low-field regions. If the Si content is too low, the material's ability to absorb external magnetic fields in low-field regions may be compromised. If the Si content is too high, the material's impurity content increases, which can lead to a decrease in saturation magnetic flux density, thereby reducing shielding performance. More specifically, the material may contain 0.5 to 4.0 wt% Si.

[0044] C: 0.15 wt% or less

[0045] Carbon (C) content in the slab may be 0.010 to 0.400 wt% because the Goss crystal grains in the surface layer need to diffuse to the center during the intermediate decarburization annealing and final decarburization annealing, and the C in the center needs to escape to the surface layer. More specifically, the C content in the slab may be 0.100 to 0.300 wt%. In addition, the carbon content in the steel sheet after the decarburization annealing step in which manufacturing is completed may be 0.150 wt% or less. More specifically, it may be 0.100 wt% or less. More specifically, it may be 0.050 wt% or less.

[0046] An electrical steel sheet for electromagnetic shielding according to one embodiment of the present invention may further include Mn: 0.1 wt% or less and S: 0.005 wt% or less.

[0047] Mn and S form MnS precipitates, which inhibit the growth of Goss grains that diffuse toward the center during the decarburization process. Therefore, it is preferable not to add Mn or S. However, considering the amount that is inevitably mixed during the steelmaking process, the Mn and S in the slab and steel sheet after the non-oxidizing annealing step can be controlled to Mn: 0.1 wt% or less and S: 0.005 wt% or less, respectively.

[0048] The remainder includes Fe and unavoidable impurities. Unavoidable impurities are impurities mixed in during the steelmaking stage and the manufacturing process of electrical steel sheets, and since this is widely known in the field, a detailed description is omitted. Specifically, components such as Al, N, Ti, Mg, and Ca react with oxygen in steel to form oxides, and therefore, strong suppression is required, and therefore, each component can be managed to 0.005 wt% or less. In one embodiment of the present invention, the addition of elements other than the alloy components described above is not excluded, and various elements may be included within a range that does not impair the technical spirit of the present invention. When additional elements are further included, they are included in place of the remainder Fe.

[0049] On the surface of the steel sheet, grains having a ratio of the diameter of the circumscribed circle (D1) to the diameter of the inscribed circle (D2) (D2 / D1) of 0.5 or more may account for 70 area% or more of all grains. This is because, as described later in relation to the manufacturing process, decarburization annealing and non-oxidation annealing are performed for a short time. If batch annealing is performed for a long time of 30 minutes or more after decarburization annealing, the diameter of the circumscribed circle (D1) becomes significantly larger than the inscribed circle (D2), so that the ratio cannot be 0.5 or more. Here, the circumscribed circle refers to the smallest virtual circle surrounding the outside of the grain, and the inscribed circle refers to the largest virtual circle included in the inside of the grain. More specifically, grains having a ratio of the diameter of the circumscribed circle (D1) to the diameter of the inscribed circle (D2) of 0.5 or more (D2 / D1) may account for 75 area% or more of all grains. More specifically, among the entire crystal grains, the ratio of the diameter of the circumscribed circle (D1) to the diameter of the inscribed circle (D2) (D2 / D1) may be 0.5 or more, accounting for 75 to 97 area% of the crystal grains. Crystal grains of this shape react to an external magnetic field, especially in a low-field region, and contribute to electromagnetic shielding by having the material absorb the magnetic field. Among the entire crystal grains, crystal grains having a ratio of the diameter of the circumscribed circle (D1) to the diameter of the inscribed circle (D2) (D2 / D1) of 0.5 or more can be observed on the surface (ND plane) of the steel plate with an optical microscope, and the observed images can be analyzed using a computer program.

[0050] In one embodiment of the present invention, the average grain size in the surface portion (12) from the surface of the steel sheet to less than 2 / 5 of the steel sheet thickness in the thickness direction is 100 µm to 500 µm, and the average grain size in the center portion (11) of 2 / 5 to 3 / 5 of the steel sheet thickness is 55 to 90 µm. In this way, by forming the grain sizes of the surface portion (12) and the center portion (11) differently, the surface grains can contribute to electromagnetic shielding by causing the material to react and absorb an external magnetic field. If the average grain size in the surface portion (12) is too small, the ability of the material to absorb an external magnetic field may be reduced, which may lower the electromagnetic shielding performance. If the average grain size in the surface portion (12) is too large, the ductility of the material may be greatly reduced, which may cause problems such as material breakage during cold rolling or plate breakage in a continuous line. If the average grain size of the center (11) is too large, the ability of the material to react and absorb an external magnetic field may decrease, resulting in a deterioration in electromagnetic shielding performance. More specifically, the average grain size in the surface portion (12) may be 150 μm to 450 μm, and the average grain size in the center (11) may be 58 to 88 μm. The average grain size can be obtained by measuring the number of grains per measurement area for a cross-section including the steel sheet thickness direction, dividing the measurement area by the number of grains, and obtaining the average grain area. The grain size can be obtained as the diameter of a circle having the same area.

[0051] The ratio of the average grain size within the surface to the average grain size within the center (surface / center) may be 2.0 or greater. If this ratio is too small, the ability of the material to respond to an external magnetic field may be reduced, resulting in poor electromagnetic shielding properties. More specifically, the ratio of the average grain size within the surface to the average grain size within the center (surface / center) may be 3.0 to 20.0.

[0052] <111> The area fraction of grains whose direction is parallel to the rolling direction of the steel plate within 15° <110> The ratio of the area fraction of grains whose direction is parallel to the rolling direction of the steel plate within 15° ( <110> / ND / <111> / ND) can be 3.0 or higher. If this ratio is high, it can contribute to electromagnetic shielding by increasing the investment rate in low-field situations. More specifically, <110> / ND / <111> / ND can be 3.3 to 6.5. This can be measured using backscatter electron diffraction pattern analyzer (EBSD).

[0053] In this way, by appropriately controlling the steel composition of the steel plate and appropriately forming the aggregate structure, the electromagnetic shielding performance is excellent. Specifically, the shielding rate in a 60 Hz, 100 mG magnetic field may be 50% or more, and the shielding rate in a 60 Hz, 1 G magnetic field may be 65% or more. More specifically, the shielding rate in a 60 Hz, 100 mG magnetic field may be 50.0% to 75.0%, and the shielding rate in a 60 Hz, 1 G magnetic field may be 65.0% to 85.0%.

[0054] At this time, the shielding rate can be measured by generating a magnetic field of less than 1G using the Helmholtz coil method and installing a pickup coil capable of measuring the magnetic field at the center of the generated magnetic field. The shielding rate is calculated by shielding the pickup coil with a shielding material, obtaining the strength of the magnetic field measured before and after shielding, and calculating it as follows. The pickup coil shielding is done by wrapping the coil in a cylindrical shape or shielding all four sides in a box shape.

[0055] Shielding rate (%) = (1-B 차폐적용 / B 차폐미적용 )×100

[0056] Although omitted in Fig. 1, a film positioned on the surface of the electrical steel plate (100) for electromagnetic shielding may be additionally included.

[0057]

[0058] In Fig. 2, one embodiment of the present invention illustrates an example of using an electromagnetic shielding electrical steel plate. As shown in Fig. 2, the electromagnetic shielding electrical steel plate (100) may be installed to wrap around an underground conduit (power pipe), or may be used by inserting the electromagnetic shielding electrical steel plate (100) between a transmission line and an underground conduit (power pipe). Alternatively, the electromagnetic shielding electrical steel plate (100) may be rolled into a cylindrical tube shape and installed to wrap around a transmission line (200).

[0059]

[0060] A method for manufacturing an electrical steel sheet for electromagnetic shielding according to one embodiment of the present invention comprises the steps of: hot-rolling a slab to manufacture a hot-rolled steel sheet; hot-rolling the hot-rolled steel sheet; cold-rolling the hot-rolled steel sheet annealed; decarburization annealing the cold-rolled steel sheet; and non-oxidation annealing the decarburization annealed steel sheet.

[0061] Below, each step is explained in detail.

[0062] First, the slab is hot rolled.

[0063] The slab may contain, by weight %, Si: 0.3% to 7.0%, C: 0.01% to 0.4%, and the remainder being Fe and unavoidable impurities.

[0064] The slab may further contain Mn: up to 0.1 wt% and S: up to 0.005 wt%.

[0065] The description of the steel composition of the slab is the same as that of the electrical steel plate for electromagnetic shielding mentioned above, so any duplicate description will be omitted. Except for C, the steel composition of the steel plate can be substantially the same as that of the slab.

[0066] The slab can be heated before hot rolling. The slab heating temperature can be 1050℃ to 1350℃, which is higher than the usual heating temperature. When the temperature is high during slab reheating, there is a problem that the hot-rolled structure becomes coarser, which adversely affects magnetism. However, in the method for manufacturing an electrical steel sheet according to an embodiment of the present invention, since the carbon content is higher than in the past, even if the slab reheating temperature is high, the hot-rolled structure does not become coarser, and by reheating at a higher temperature than in the usual case, it is advantageous during hot rolling. However, when the reheating temperature is high, the solid solubility of precipitates such as TiN and AlN increases, so that a large number of fine precipitates are distributed during cooling, which acts to hinder the growth of crystal grains on the surface.

[0067] Hot rolling can be used to manufacture hot-rolled sheets with a thickness of 1.3 to 4.3 mm by applying an appropriate rolling ratio in the final cold rolling stage so that the final product thickness can be manufactured. More specifically, it can be manufactured with a thickness of 1.5 to 4.0 mm.

[0068] The hot rolling finish rolling temperature may be 750°C to 1050°C. If the hot rolling finish rolling temperature is too high, surface defects may occur, lowering the quality. In addition, if the finish rolling temperature is too low, the rolling load increases, which reduces the rollability and productivity. More specifically, it may be 800 to 1030°C. In one embodiment of the present invention, the cooling rate in the ROT section after the hot rolling finish rolling and before the coil is wound can be controlled. More specifically, the cooling rate in the ROT section can be controlled to -50 to -5°C / s. If the cooling rate is too high, the growth of surface grains is suppressed, making it difficult to obtain coarse grains. More specifically, the cooling rate can be controlled to -30 to -7°C / s.

[0069] After hot rolling, the hot-rolled steel sheet is subjected to hot-rolled sheet annealing. This hot-rolled sheet annealing may include a decarburization process. Specifically, the hot-rolled sheet annealing may be performed at a temperature of 850°C to 1000°C and a dew point temperature of 70°C or lower. More specifically, the annealing may be performed at a dew point temperature of -70°C to 70°C. After the aforementioned annealing, further annealing may be performed at a temperature of 1000°C to 1200°C and a dew point temperature of 0°C or lower. After the hot-rolled sheet annealing, pickling may be performed.

[0070] Next, cold rolling is performed to manufacture cold rolled steel sheets.

[0071] Therefore, cold rolling can be performed at a reduction ratio of 50% to 80%. More specifically, it can be 55% to 75%. Through this, cold rolled steel sheets with a final thickness of 0.3 to 2.0 mm can be manufactured.

[0072] Next, the cold-rolled steel sheet is decarburized and annealed. The decarburization annealing step can be performed in the austenite single-phase region or in a region where ferrite and austenite exist in a composite phase. Specifically, the annealing can be performed at a temperature of 800°C to 970°C and a dew point temperature of 3°C to 65°C. Furthermore, the atmosphere can be a mixed gas atmosphere of hydrogen and nitrogen. Furthermore, after decarburization annealing, the carbon content in the steel sheet can be 0.15 wt% or less.

[0073]

[0074] In a method for manufacturing an electrical steel sheet for electromagnetic shielding according to one embodiment of the present invention, τ defined by the following equation 1 is 0.230 to 0.500.

[0075] [Formula 1]

[0076]

[0077]

[0078] (In Equation 1, the finishing rolling temperature is the hot rolling finishing rolling temperature (℃), the ROT cooling rate is the cooling rate (-℃ / s) in the ROT section before the coil is coiled after the hot rolling finishing rolling, the hot rolled sheet thickness is the thickness of the hot rolled sheet (mm), the dew point temperature is the dew point temperature (℃) of the atmosphere in the decarburization annealing stage, the annealing temperature is the annealing temperature (℃) in the decarburization annealing stage, and the cold rolled sheet thickness means the steel sheet thickness (mm) after the first cold rolling.)

[0079] If τ is too small, grain growth at the surface (12) may not be sufficient. If τ is too large, grain growth at the center (11) may occur significantly, which may adversely affect electromagnetic shielding performance. More specifically, τ may be 0.240 to 0.450.

[0080] After decarburization annealing, a second cold rolling step may be further included. Through this, a cold rolled steel sheet having a final thickness of 0.1 to 1.0 mm can be manufactured.

[0081] Next, the decarburized annealed steel plate is subjected to non-oxidation annealing.

[0082] The non-oxidative annealing step can be performed at a soaking temperature of 750 to 1050°C for 30 seconds to 5 minutes.

[0083] The purpose of the non-oxidizing annealing step is to grow the crystal grains of the surface (12) and the center (11) to a certain size or larger. This allows the crystal grains of the surface to grow, thereby further improving the electromagnetic shielding performance in a low-field region. If the soaking temperature is too low or the time is too short, the crystal grain growth of the surface (12) and the center (11) may not be sufficient, and the electromagnetic shielding performance may not be sufficiently improved. If the soaking temperature is too high or the time is too long, the crystal grain sizes of the surface and the interior become uniform, making it impossible to obtain excellent shielding rates at the same time in magnetic fields of 100 mG and 1 G. More specifically, the soaking temperature of the non-oxidizing annealing may be 800 to 1000°C. More specifically, it may be 900 to 970°C.

[0084] The secondary non-oxidizing annealing step can be performed at a dew point temperature of -20°C or lower. If the dew point temperature is too high, an oxide layer may form on the surface, adversely affecting magnetism. More specifically, annealing can be performed in an atmosphere containing at least 99% hydrogen by volume and with a dew point temperature of -50°C to -30°C.

[0085] After the cold rolling step, the non-oxidizing annealing step can be performed as a continuous process. A continuous process means that there is no need for batch processes, such as coiling the steel sheet and annealing it. As mentioned above, the decarburization annealing step and the non-oxidizing annealing step can be completed in less than a few minutes, making a continuous process possible.

[0086] Specific examples of the present invention are described below. However, the following examples are merely specific examples of the present invention, and the present invention is not limited to the following examples.

[0087]

[0088] Example

[0089] A slab containing 2.0% Si, 0.101% C, and the remainder Fe and unavoidable impurities was heated to 1270°C and then subjected to hot rolling, hot-rolled sheet annealing, cold rolling, decarburization annealing, and non-oxidation annealing in that order under the manufacturing conditions shown in Table 1. After decarburization annealing, C was 0.05% by weight or less. Non-oxidation annealing was performed for 30 seconds at the temperatures shown in Table 1 and a dew point temperature of -20°C.

[0090] Manufacturing condition 11 was then subjected to non-oxidative annealing for 30 minutes.

[0091] The manufactured specimens were measured for their surface and center average grain size, magnetic flux density, and electromagnetic shielding ratio, and these are shown in Table 2.

[0092] The average grain size was measured using an optical microscope.

[0093] The grain morphology on the surface was measured using an electron backscatter diffraction pattern analyzer (EBSD).

[0094] <110> / ND / <111> / ND was measured using an backscatter electron diffraction pattern analyzer (EBSD).

[0095] The magnetic flux density was measured by Single Strip Magnetic Field Measurement, and the average value of the magnetic flux density measured in the rolling direction and the direction perpendicular to the rolling direction is shown in Table 3. The magnetic flux density measured at 50 Hz, 100 A / m was denoted as B1, and the magnetic flux density measured at 50 Hz, 5000 A / m was denoted as B50.

[0096] The electromagnetic shielding rate was measured by generating a magnetic field of less than 1 G using the Helmholtz coil method and installing a cylindrical pickup coil capable of measuring the magnetic field at the center of the generated magnetic field. The pickup coil was shielded with a gingham plate, and the magnetic field strength measured before and after shielding was obtained, and the shielding rate was calculated as follows.

[0097] Shielding rate (%) = (1-B차폐적용 / B 차폐미적용 )×100

[0098] Manufacturing conditionsHot rolledHot rolled plateCold rolledDecarburizationAnnealingParameter (τ)Non-oxidizing annealingFinish rollingTemperature (℃)ROTCooling rate (-℃ / s)Thickness (mm)Annealing temperature (℃)Reduction ratio (%)Thickness (mm)Dew point temperature (℃)Annealing temperature (℃)Annealing temperature (℃)1100284.0920601.60609500.2589852975103.0920651.05439230.3809703950132.5920700.75238730.4329474925252.0920620.7658200.2439455900281.5920630.56108150.3909206880325.0920611. 95158950.03210327911552.8920800.5608570.1089528843352.7920700.81-209200.1129129863302.5920800.5077450.21987510965321.2920670.40558120.72990211780203.8920671.25608150.1021200

[0099] Classification Manufacturing Conditions Average grain size (㎛) D2 / D1 0.5 or more fraction (area%) (surface / center grain size) <110> / ND / <111> / ND surface center invention example 1118487822.13.8 invention example 2240159926.84.8 invention example 3334464815.44.4 invention example 4431666784.84.2 invention example 5542268966.25.0 comparison example 165448771.13.4 comparison example 272829761.03.2 comparison example 385850781.23.3 comparison example 494248860.93.3 comparison example 510166102741.53.5 comparison example 61111021095631.06.2

[0100] Manufacturing conditions B1 (T)B50 (T)Shielding rateShielding rate classification100mG (%)1G (%)11.0211.81261.373.2Invention example121.3851.80367.272.3Invention example231.3401.78466.071.0Invention example341.3011.71164.167.4Invention example451.4101.70569.866.0Invention example560.6231.815 33.574.0Comparative Example 170.3071.83021.275.5Comparative Example 280.6421.81138.173.1Comparative Example 390.5111.81930.474.2Comparative Example 4100.9861.69262.259.8Comparative Example 5111.5021.61388.757.5Comparative Example 6

[0101] As shown in Tables 1 to 3, when the process conditions are properly controlled, it can be confirmed that the aggregate structure of the steel plate is properly formed and the shielding rate is excellent.

[0102] On the other hand, if the process conditions are not properly controlled, it can be confirmed that the aggregate structure of the steel plate is not properly formed and the shielding rate is inferior.

[0103] In particular, for Manufacturing Condition 11, annealing for a long period of 30 minutes reduces the size difference between surface and internal grains, resulting in uniform grains. This results in excellent shielding at 100 mG, but poor shielding at 1 G, confirming that not all characteristics resulting from the differences in surface and internal grains are achieved.

[0104]

[0105] The present invention is not limited to the above-described embodiments and / or examples, but can be manufactured in various different forms. Those skilled in the art will understand that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the above-described embodiments and / or examples should be understood as illustrative in all respects and not restrictive.

[0106] [Explanation of symbols]

[0107] 100: Electrical steel plate for electromagnetic shielding, 11: Center,

[0108] 12: Surface area, 200: Transmission line

Claims

On the surface of the steel plate, the ratio of the diameter of the outer circle (D1) to the diameter of the inner circle (D2) (D2 / D1) of the entire grains is 0.5 or more, and 70% or more of the area of ​​the grains is An electrical steel sheet for electromagnetic shielding, wherein the average grain size within a surface portion from the surface of the steel sheet to less than 2 / 5 of the steel sheet thickness in the thickness direction is 100 ㎛ to 500 ㎛, and the average grain size within a central portion from 2 / 5 to 3 / 5 of the steel sheet thickness is 55 to 90 ㎛. In the first paragraph, In the above steel plate <111> The area fraction of grains whose direction is parallel to the rolling direction of the steel plate within 15° <110> Electrical steel sheet for electromagnetic shielding, having an area fraction ratio of crystal grains whose direction is parallel to the rolling direction of the steel sheet within 15° of 3 or more. In the first paragraph, An electrical steel sheet for electromagnetic shielding, wherein the ratio of the average grain size in the surface portion to the average grain size in the center portion is 2.0 or more. In the first paragraph, An electrical steel sheet for electromagnetic shielding containing, by weight, Si: 0.3% to 7.0%, C: 0.15% or less (excluding 0%), and the remainder being Fe and unavoidable impurities. In the first paragraph, Electrical steel sheet for electromagnetic shielding further containing Mn: 0.1 wt% or less and S: 0.005 wt% or less. A step of manufacturing hot rolled steel sheets by hot rolling a slab; A step of annealing the hot-rolled steel plate; A step of cold rolling a hot-rolled steel sheet that has been annealed; Step of decarburizing and annealing a cold rolled steel sheet; and Comprising a step of non-oxidation annealing a decarburized steel sheet, A method for manufacturing an electrical steel sheet for electromagnetic shielding, wherein τ defined by the following equation 1 is 0.23 to 0.

5. [Formula 1] (In Equation 1, the finishing rolling temperature is the hot rolling finishing rolling temperature (℃), the ROT cooling rate is the cooling rate (-℃ / s) in the ROT section before the coil is coiled after the hot rolling finishing rolling, the hot rolled sheet thickness is the thickness of the hot rolled sheet (mm), the dew point temperature is the dew point temperature (℃) of the atmosphere at the decarburization annealing stage, the annealing temperature is the annealing temperature (℃) at the decarburization annealing stage, and the cold rolled sheet thickness means the steel sheet thickness (mm) after cold rolling.) In Article 6, A method for manufacturing an electrical steel sheet for electromagnetic shielding, wherein the above slab contains, in weight %, Si: 0.3% to 7.0%, C: 0.01% to 0.4%, and the remainder being Fe and unavoidable impurities. In Article 7, A method for manufacturing an electrical steel sheet for electromagnetic shielding, wherein the above slab further contains Mn: 0.1 wt% or less and S: 0.005 wt% or less. In Article 6, A method for manufacturing an electrical steel sheet for electromagnetic shielding, the method including a decarburization process in the step of annealing the hot-rolled sheet. In Article 6, A method for manufacturing an electrical steel sheet for electromagnetic shielding, wherein the step of annealing the hot-rolled sheet is performed at a temperature of 850°C to 1000°C and a dew point temperature of 70°C or lower. In Article 6, A method for manufacturing an electrical steel sheet for electromagnetic shielding, wherein the above decarburization annealing step is performed at a temperature of 600°C to 1000°C and a dew point temperature of 0°C to 70°C. In Article 6, A method for manufacturing an electrical steel sheet for electromagnetic shielding, wherein the non-oxidizing annealing step is performed at a soaking temperature of 750 to 1050°C for 30 seconds to 5 minutes. In Article 6, A method for manufacturing an electrical steel sheet for electromagnetic shielding, wherein the non-oxidizing annealing step is performed in an atmosphere having a dew point temperature of -20℃ or lower.

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