Electrical steel sheet for electromagnetic shielding and manufacturing method thereof

Abstract

An electrical steel sheet for electromagnetic shielding according to an embodiment of the present invention comprises: a steel sheet substrate; and a film disposed on the surface of the steel sheet substrate, wherein grains in which the ratio (D2 / D1) of the outer circle diameter (D1) to the inner circle diameter (D2) is at least 0.5 account for at least 70 area% of the total area of all of the grains on the surface of the steel sheet substrate, the average grain size in a surface portion extending from the surface of the steel sheet substrate to less than 1 / 4 of the thickness of the steel sheet substrate in the thickness direction is 80-500 µm, the average grain size in a central portion extending from 1 / 4 to 1 / 2 of the thickness of the steel sheet substrate is 50 µm or less, and the film contains 100 parts by weight of a metal phosphate including at least one among Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn, and 3-150 parts by weight in total of oxides including at least two among Al, Si, Mg, and Fe.

Description

Electrical steel sheet for electromagnetic shielding and its manufacturing method

[0001] One embodiment of the present invention relates to an electromagnetic shielding electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to an electromagnetic shielding electrical steel sheet having excellent electromagnetic shielding effects and possessing insulating, oil-resistant, and chemical-resistant properties, 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 having excellent electromagnetic shielding effects and possessing insulating, oil-resistant, and chemical-resistant properties, and a method for manufacturing the same.

[0005] An electromagnetic wave shielding electrical steel sheet according to one embodiment of the present invention includes a steel sheet substrate and a film positioned on a surface of the steel sheet substrate, wherein on the surface of the steel sheet substrate, 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 account for 70% or more by area of ​​crystal grains, an average crystal grain diameter in a surface portion from the surface of the steel sheet substrate to less than 1 / 4 of the thickness of the steel sheet substrate in the thickness direction is 80 µm to 500 µm, and an average crystal grain diameter in a central portion of 1 / 4 to 1 / 2 of the thickness of the steel sheet substrate is 50 µm or less, and the film includes 100 parts by weight of a metal phosphate including at least one of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn, and 3 to 150 parts by weight of an oxide including at least two of Al, Si, Mg, and Fe.

[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] The steel plate substrate may contain, in weight %, Si: 0.3% to 7.0%, C: 0.15% or less (excluding 0%), and the remainder being Fe and unavoidable impurities.

[0009] The steel plate substrate may further include Mn: 0.1 wt% or less and S: 0.005 wt% or less.

[0010] The film may further contain 50 to 250 parts by weight of silica.

[0011] The film may further contain 2 to 10 parts by weight of chromium oxide.

[0012] 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 applying a film-forming composition comprising, as a solid content, 100 parts by weight of a metal phosphate containing at least one of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn and 3 to 150 parts by weight of an oxide containing at least two of Al, Si, Mg, and Fe, to the surface of the decarburization annealed steel sheet to form a film.

[0013] τ defined by the following equation 1 is 0.23 to 0.5.

[0014] [Formula 1]

[0015]

[0016]

[0017] (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.)

[0018] 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.

[0019] The slab may further contain Mn: up to 0.1 wt% and S: up to 0.005 wt%.

[0020] The decarburization process may be included in the annealing stage of the hot-rolled sheet.

[0021] The hot-rolled plate annealing step can be performed at a temperature of 850℃ to 1000℃ and a dew point temperature of 70℃ or lower.

[0022] 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.

[0023] The film forming composition may further comprise 50 to 250 parts by weight of silica.

[0024] The film forming composition may further comprise 2 to 10 parts by weight of chromium oxide.

[0025] According to one embodiment of the present invention, both electromagnetic wave shielding and corrosion resistance are excellent.

[0026] According to one embodiment of the present invention, an electromagnetic wave shielding steel plate having excellent workability can be provided.

[0027] Additionally, since it can be manufactured through a continuous process, the manufacturing time can be relatively shortened and productivity can be improved.

[0028] 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.

[0029] 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.

[0030] Figure 3 is a photograph showing the surface of the substrate of the electromagnetic shielding steel plate manufactured in Example 1 through EBSD analysis.

[0031] Figure 4 is a photograph of a cross-section of an electromagnetic shielding steel plate manufactured in Example 1 observed through SEM.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0037] 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.

[0038]

[0039] 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.

[0040] Fig. 1 schematically shows a cross-section of an electrical steel plate for electromagnetic shielding according to one embodiment of the present invention.

[0041] As shown in FIG. 1, an electromagnetic shielding electrical steel sheet (100) according to one embodiment of the present invention includes a steel sheet substrate (10) and a film (20) positioned on the surface of the steel sheet substrate (10), and has 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 substrate, in which an average crystal grain diameter in a surface portion (12) from the surface of the steel sheet substrate to less than 1 / 4 of the thickness of the steel sheet substrate in the thickness direction is 80 µm to 500 µm, and an average crystal grain diameter in a central portion (11) of 1 / 4 to 1 / 2 of the thickness of the steel sheet substrate is 50 µm or less.

[0042] The film (20) contains 100 parts by weight of a metal phosphate containing at least one of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn, and 3 to 150 parts by weight of an oxide containing at least two of Al, Si, Mg, and Fe.

[0043] Below, each component of an electrical steel plate for electromagnetic shielding according to one embodiment of the present invention is described in detail.

[0044] First, the steel plate substrate (10) contains, in wt%, Si: 0.3% to 7.0%, C: 0.15% or less (excluding 0%), and the remainder is Fe and unavoidable impurities.

[0045] Si: 0.3 to 7.0 wt%

[0046] 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.

[0047]

[0048] C: 0.15 wt% or less

[0049] 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.

[0050] The steel plate substrate (10) may further include Mn: 0.1 wt% or less and S: 0.005 wt% or less.

[0051] 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.

[0052] 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.

[0053] On the surface of the steel plate substrate (10), 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 among all grains may account for 70 area% or more. This is because, as described later in relation to the manufacturing process, decarburization annealing is performed for a short time. If batch annealing is performed for a long time of 1 hour 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 circle among the virtual circles surrounding the outside of the grains, and the inscribed circle refers to the largest circle among the virtual circles included in the inside of the grains. More specifically, grains having a ratio of the diameter of the circumscribed circle (D1) to the diameter of the inscribed circle (D2 / D1) of 0.5 or more among all grains may account for 75 to 95 area%. 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, and may account for 75% to 90% by area. 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, the 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 be observed on the surface (ND plane) of the base material (10) of the steel plate using an optical microscope, and the observed image may be analyzed using a computer program. When a film (20) exists on the steel plate base material (10), the film (20) may be appropriately removed, and the surface of the steel plate base material (10) may be analyzed.

[0054] In one embodiment of the present invention, the average grain size in the surface portion (12) from the surface of the steel plate substrate (10) to less than 1 / 4 of the thickness of the steel plate substrate in the thickness direction is 80 µm to 500 µm, and the average grain size in the center portion (11) of 1 / 4 to 1 / 2 of the thickness of the steel plate substrate is 50 µm or less. In this way, by forming the grain sizes of the surface portion (12) and the center portion (11) in the steel plate substrate (10) differently, the grains in the surface portion can contribute to electromagnetic wave 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 wave shielding performance. If the average grain size in the surface portion (12) is too large, the adhesion may be reduced due to a decrease in the interface contact area during coating. 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, which may result in a deterioration in electromagnetic shielding performance. More specifically, the average grain size in the surface portion (12) may be 10 ㎛ to 400 ㎛, and the average grain size in the center (11) may be 15 ㎛ to 47 ㎛. 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.

[0055] 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 wave 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.

[0056] 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 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 the low-field region. More specifically, it can be applied to the steel plate substrate. <110> / ND / <111> / ND can be 3.3 to 6.5. This can be measured using an electron backscatter diffraction pattern analyzer.

[0057]

[0058] In this way, by appropriately controlling the steel composition of the steel plate substrate (10) 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 70.0% to 85.0%.

[0059] 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.

[0060] Shielding rate (%) = (1-B 차폐적용 / B 차폐미적용 )×100

[0061] The film (20) contains 100 parts by weight of a metal phosphate containing at least one of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn, and 3 to 150 parts by weight of an oxide containing at least two of Al, Si, Mg, and Fe.

[0062] Hereinafter, each component in the film (20) will be described in detail. In one embodiment of the present invention, the weight part means a relative weight ratio based on 100 parts by weight of the metal phosphate, and is based on the solid content of each component. The solid content means the weight when each component is dried in a state free of volatile matter such as solvent. Specifically, assuming a heat treatment process when forming the film (20), it means the weight remaining after the heat treatment. When the film-forming composition is heat-treated, it can remain in the film (20) in the proportion of the solid content in the composition.

[0063] Metal phosphate acts as a binder in the film-forming composition. If the metal phosphate is not included in an appropriate amount, the adhesion of the film (20) is poor or corrosion resistance cannot be sufficiently obtained.

[0064] Metal phosphates can be manufactured through a manufacturing process in which a metal oxide is added to pure phosphoric acid (H3PO4) and reacted. To improve the adhesion of the metal phosphate, boric acid can be additionally added during the reaction process and maintained for 3 hours or more to induce a condensation reaction between the metal phosphate and boric acid. This condensation reaction product can also be used in place of the metal phosphate. In one embodiment of the present invention, the metal phosphate includes not only the metal phosphate but also the condensation reaction product of the metal phosphate and boric acid. The manufactured metal phosphate is strongly acidic.

[0065] The metal phosphate may be added to the composition using a solution having a solids content of 50 to 70 wt%. If the solids content in the solution is too low, free phosphoric acid may increase within the metal phosphate, resulting in surface moisture absorption after the metal phosphate is manufactured. If the solids content is too high, the excess solids compared to pure phosphoric acid may result in poor reaction and precipitation.

[0066] The metal phosphate and the metal oxide may include various metals without limitation. Specifically, the metal of the metal phosphate and the metal oxide may include at least one of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn. More specifically, the metal phosphate may include at least one of monobasic magnesium phosphate (Mg(H2PO4)2) and monobasic aluminum phosphate (Al(H2PO4)3). More specifically, it may include monobasic magnesium phosphate (Mg(H2PO4)2) and monobasic aluminum phosphate (Al(H2PO4)3). In this case, the metal phosphate may include 10 to 40 parts by weight of monobasic aluminum phosphate and 60 to 90 parts by weight of monobasic magnesium phosphate based on 100 parts by weight of the total metal phosphate in the film (20). If too little monobasic aluminum phosphate is included, the tensile strength improvement effect by adding monobasic aluminum phosphate may not be sufficient. When too much monobasic aluminum phosphate is added, the Al component may increase the crystallization of silica, which may cause cracks in the insulating film. Specifically, the metal phosphate may include, based on the solid content, 15 to 35 parts by weight of monobasic aluminum phosphate and 65 to 85 parts by weight of monobasic magnesium phosphate, and more specifically, 20 to 30 parts by weight of monobasic aluminum phosphate and 70 to 80 parts by weight of monobasic magnesium phosphate, per 100 parts by weight of the total.

[0067] In one embodiment of the present invention, the film (20) includes 3 to 150 parts by weight of an oxide containing two or more kinds of Al, Si, Mg, and Fe, based on 100 parts by weight of a metal phosphate. The oxide is added to improve the electromagnetic shielding and corrosion resistance of the film (20). If too little oxide is included, the electromagnetic shielding and corrosion resistance may be significantly reduced. If too much oxide is included, the solid fraction in the composition may increase, which may cause aggregation and sedimentation between oxides, and not only may pores be formed at the oxide interface after film formation, which may significantly reduce insulation and corrosion resistance. Therefore, specifically, 10 to 150 parts by weight of the oxide may be included based on 100 parts by weight of the metal phosphate. More specifically, 15 to 80 parts by weight of the oxide may be included based on 100 parts by weight of the metal phosphate.

[0068] The oxide containing two or more of Al, Si, Mg and Fe may include one or more of montmorillonite, kaolinite, illite, talc and chromite. More specifically, montmorillonite (M x (Al 4-x Mg x )Si8O 20 (OH)4). Oxides containing two or more of Al, Si, Mg, and Fe have an advantage in improving corrosion resistance compared to oxides of one type (e.g., Al2O3).

[0069] Oxides containing two or more of Al, Si, Mg and Fe having an average particle size of 10 2 nm to 10 5 It can be nm. If the average particle size of the oxide is too small, it is difficult to disperse evenly in the solution due to the electrostatic attraction of the particles themselves. If the average particle size is too large, sedimentation occurs quickly in the solution, making it difficult to achieve proper performance. The average particle size can be measured by dispersing the particles in the solution and using a laser scattering method.

[0070] The composition ratio among Al, Si, Mg, and Fe is important for oxides, and for 100% of the total weight of Al, Si, Mg, and Fe in the oxide particles, Al can be 15 to 45 wt%, Si 40 to 70 wt%, Mg 0.1 to 5 wt%, and Fe 1 to 10 wt%. The reason for limiting the main components in the oxides as above is that if there is too little Al in the oxide particles, the corrosion resistance effect cannot be seen, and if there is too much Al, the electrical conductivity increases and the film insulation deteriorates. If there is too little Si in the particles, the corrosion resistance effect cannot be seen, and if there is too much Si, the film hardness increases and the processability of the material is significantly reduced. If there is too little Mg, the affinity between water and oxides in the coating solution decreases, so the uniform dispersion of oxides in the coating solution deteriorates, and if there is too much Mg, the corrosion resistance effect cannot be seen. In addition, if Fe is too little, the heat resistance characteristics are lowered after film formation, and if Fe is too much, the specific gravity of the oxide is increased, accelerating the precipitation of the oxide, and reducing the corrosion resistance of the film. More specifically, with respect to 100% of the total weight of Al, Si, Mg, and Fe in the oxide particles, Al may be included in an amount of 20 to 40 wt%, Si in an amount of 45 to 65 wt%, Mg in an amount of 0.5 to 3 wt%, and Fe in an amount of 3 to 7 wt%. The oxide may additionally include Ca and K.

[0071] The film (20) may further contain 50 to 250 parts by weight of silica.

[0072] Silica enhances the strength and hardness of the film itself through intramolecular network reactions during film drying after coating, thereby further enhancing the corrosion resistance of the film (20). Various silicas can be used without limitation, and commercially available colloidal silica can also be used. More specifically, basic colloidal silica can be used.

[0073] Silica may be included in an amount of 50 to 250 parts by weight per 100 parts by weight of the metal phosphate. If too little silica is added, the corrosion resistance improvement effect due to the addition of silica cannot be sufficiently obtained. If too much silica is added, the amount of metal phosphate is relatively reduced, which may result in poor adhesion of the insulating film. Specifically, silica may be included in an amount of 100 to 200 parts by weight per 100 parts by weight of the metal phosphate, and more specifically, silica may be included in an amount of 125 to 175 parts by weight per 100 parts by weight of the metal phosphate. Here, "parts by weight" refers to a relative weight based on the metal phosphate.

[0074] During the drying process of the film, silica undergoes a condensation reaction through a chain reaction of silica as shown in the following reaction formula 1, and forms a network structure such as -(HO-Si-O-Si)-n.

[0075] [Reaction Formula 1]

[0076] -(HO-Si-OH-) n + -(HO-Si-OH-) n = -(HO-Si-O-Si-) n + H2O (1)

[0077] However, using only this silica creates an overly uniform network structure, which limits the film's density. Therefore, there are limitations in providing adhesion or corrosion resistance between the electrical steel base material and the insulating coating. To supplement these deficient properties, metal phosphates or metal phosphates and chromium oxides can be added.

[0078] The silica may be colloidal silica having an average particle size in the range of 7 to 20 nm. The composition may be prepared using a solution having a solid fraction of 25 to 35 wt%. If the solid fraction is too small, a problem of reduced insulation may occur. If the solid fraction is too large, a problem of reduced compatibility may occur after the film composition is prepared. More specifically, the solid fraction may be 28 to 32 wt%.

[0079] Silica is Na + The content may be 0.1 to 1.0 wt%. Na + If the content is too low, the problem of reduced film density may occur. Na + If the content is too high, the problem of inhibiting compatibility between components may occur due to an increase in cations in the coating agent. More specifically, Na + The content may be 0.3 to 0.7 wt%.

[0080] The silica solution containing silica may have a pH of 9.5 to 10.5. If the pH is too low or too high, the pH difference between the components other than silica in the coating composition may be extreme, resulting in phase separation. More specifically, the pH may be 9.5 to 10.0.

[0081] Silica may have a viscosity of 3.5 to 6.5 cp. If the viscosity is too low, the coating composition may have problems with application. If the viscosity is too high, it may thicken over time, causing aging problems. More specifically, the viscosity may be 4 to 6 cp. The viscosity can be measured using a Brookfield viscometer at 20°C based on a 30 wt% silica solution.

[0082] Silica may have a specific gravity of 1.1 to 1.3. If the specific gravity is too low, it may be difficult to control the amount of coating composition applied. If the specific gravity is too high, sedimentation problems may occur after the film composition is prepared. More specifically, the specific gravity may be 1.15 to 1.25.

[0083] Chromium oxide may be additionally added to enhance the corrosion resistance of the film (20). When chromium oxide is additionally included, it may be included in an amount of 2 to 10 parts by weight per 100 parts by weight of the metal phosphate. If too little chromium oxide is included, the corrosion resistance enhancement effect may not be sufficient, and furthermore, it may be difficult for the silica, which will be described later, to properly perform its neutralizing role. If too much chromium oxide is included, the viscosity of the film composition may rapidly increase, which may cause a problem. Specifically, chromium oxide may be included in an amount of 2 to 8 parts by weight per 100 parts by weight of the metal phosphate, and more specifically, chromium oxide may be included in an amount of 4 to 6 parts by weight per 100 parts by weight of the metal phosphate.

[0084] The film (20) does not contain a solvent as the solvent is removed during the film manufacturing process. However, the film-forming composition may further contain a solvent. The solvent facilitates application of the composition and uniformly disperses the components. The amount of the solvent is not particularly limited, but may be 100 to 1,000 parts by weight relative to 100 parts by weight of the metal phosphate.

[0085] The thickness of the film (20) may be 1 to 50 μm. If the film (20) is too thin, it is difficult to sufficiently obtain the desired corrosion resistance. Even if the film (20) is thicker, the corrosion resistance is not enhanced, and rather, cracking of the film due to excessive coating thickness may become a problem. More specifically, the thickness of the film (20) may be 3 to 30 μm.

[0086] In Fig. 2, one embodiment of the present invention shows an example of using an electrical steel plate for electromagnetic shielding. As shown in Fig. 2, an electrical steel plate for electromagnetic shielding (100) can be installed in a form in which a cylindrical shape is rolled into a tube shape and wrapped around a transmission line (200). Alternatively, in a cylindrical underground conduit wrapping a transmission line (200), an electrical steel plate for electromagnetic shielding (100) can be inserted between the transmission line and the underground conduit, or an electrical steel plate for electromagnetic shielding (100) can be installed to wrap around the underground conduit.

[0087]

[0088] 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 applying a film-forming composition comprising, as a solid content, 100 parts by weight of a metal phosphate containing at least one of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn and 3 to 150 parts by weight of an oxide containing at least two of Al, Si, Mg, and Fe, to the surface of the decarburization annealed steel sheet to form a film.

[0089] Below, each step is explained in detail.

[0090] First, the slab is hot rolled.

[0091] 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.

[0092] The slab may further contain Mn: up to 0.1 wt% and S: up to 0.005 wt%.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] Next, cold rolling is performed to manufacture cold rolled steel sheets.

[0099] 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.

[0100] 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.

[0101] 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.

[0102] [Formula 1]

[0103]

[0104]

[0105] (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.)

[0106] 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.

[0107] Next, a film-forming composition including 100 parts by weight of a metal phosphate containing at least one of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn as a solid component and 3 to 150 parts by weight of an oxide containing at least two of Al, Si, Mg, and Fe is applied to the surface of the decarburized annealed steel sheet to form a film. Since the film-forming composition is the same as that described for the components of the film (20) described above, redundant descriptions are omitted. In one embodiment of the present invention, the solid content ratio in the film-forming composition and the ratio in the film (20) may be substantially the same.

[0108] When applying the composition for film formation, the application amount is 0.5 to 6.0 g / m 2 It can be applied in a range. If the amount applied is too much, the film (20) becomes too thick and the adhesion to the steel plate may be poor. If the amount applied is too little, the corrosion resistance may not be sufficient. More specifically, the amount applied is 1.0 to 5.0 g / m 2 It could be.

[0109] After applying the composition for film formation, the film (20) can be formed by drying by heating at 550 to 900°C for 10 to 50 seconds.

[0110]

[0111] 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.

[0112]

[0113] Example

[0114] A slab containing 2.0% Si, 0.101% C by weight, and the remainder Fe and unavoidable impurities is heated at a temperature of 1270℃ and then subjected to the processes of hot rolling, hot-rolled sheet annealing, cold rolling, and decarburization annealing in that order under the manufacturing conditions in Table 1. After decarburization annealing, C was 0.005% by weight.

[0115] Manufacturing condition 11 added a step of high-temperature annealing at 1200°C for 30 minutes at a dew point of -20°C.

[0116] Afterwards, a film composition containing the solid components listed in Table 3, montmorillonite as a complex oxide, 100 parts by weight of metal phosphate, 150 parts by weight of silica, 5 parts by weight of chromium oxide, and 100 parts by weight of water was prepared at 4 g / m 2 After application, it was dried at 850℃ for 30 seconds to form a film with a thickness of 3㎛.

[0117] 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 Tables 2 and 3.

[0118] The average grain size was measured using an optical microscope.

[0119] The crystal grain morphology on the surface was measured using a backscatter electron diffraction pattern analyzer.

[0120] <110> / ND / <111> / ND was measured using a backscatter electron diffraction pattern analyzer.

[0121] The magnetic flux density was measured using Single Strip Magnetic Field Measurement.

[0122] 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.

[0123] Shielding rate (%) = (1-B 차폐적용 / B 차폐미적용 )×100

[0124] Insulation was measured by Franklin insulation, and was measured as the storage current value when an input of 0.5 V and a current of 1.0 A were passed under a pressure of 300 PSI.

[0125] Salt spray corrosion resistance was evaluated by evaluating the number of times rust began to occur in the specimen through a repeated test of 8 hours in a 5 wt%, 35°C, NaCl solution.

[0126] Soil corrosion resistance was tested under test conditions (salinity, pH control), Fog (35℃, 24hr), and test solution: NaCl 1% + Na2SO4 0.01% + Na2CO3 0.01%. The material was buried to a depth of 10 cm (moisture content control) and the time for rust occurrence was measured.

[0127] Manufacturing conditionsHot rolledHot rolled sheetCold rolledDecarburizationAnnealing parameter (τ)Finish rollingTemperature (℃)ROTCooling rate (-℃ / s)Thickness (mm)Annealing temperature (℃)Reduction ratio (%)Thickness (mm)Dew point temperature (℃)Annealing temperature (℃)1100284.0920601.60609500.2582975103.0920651.05439230.3803950132.5920700.75238730.4324925252.0920620.7658200.2435900281.5920630.56108150.3906880325.09206 11.95158950.0327911552.8920800.5608570.1088843352.7920700.81-209200.1129863302.5920800.5077450.21910965321.2920670.40558120.72911780203.8920671.25608150.102

[0128] Manufacturing conditions Average grain size (㎛) D2 / D1 0.5 or more fraction (area%) (surface / center grain size) <110> / ND / <111> / ND surface center 115346753.43.52334318810.64.53287237812.54.24263197513.63.85352259514.14.864532721.43.372319701.23.184833731.53.193532851.13.210138102721.43.111826815521.05.2

[0129] Manufacturing conditions B1 (T)B50 (T)Shielding rateShielding rate100mG (%)1G (%)10.8791.88751.272.821.3451.85366.575.631.2951.82564.074.441.2701.78161.471.251.3601.86764.275.160.5551.83530.567.870.2981.70018.361.880.6051.84631.868.790.4821.83225.267.5100.9211.70260.262.8111.4581.71072.563.5

[0130] Manufacturing conditions Film composition Insulation (mA) Corrosion resistance (salt spray, Cycle) Corrosion resistance (soil corrosion, hr) Classification Metal Phosphate Type Composite oxide Content (parts by weight) Silica average particle size (nm) 1 Mg 50 10 20 6 1400 Invention example 1 2 Mn 50 8 15 6 1450 Invention example 2 3 Al:Co = 1:1 5 0 8 12 6 1455 Invention example 3 4 Al:Mg = 1:1 5 0 20 8 6 15 40 Invention example 4 5 Al:Ca = 1:1 2 0 14 7 5 4 800 Invention example 5 6 Al:Mg = 1:1 2 0 19 11 5 3 4 80 Comparative example 1 7 Al 2 5 2 0 10 0 3 5 70 Comparative example 28 Co25141503620Comparative Example 39Mg2571203650Comparative Example 410Ca2591353625Comparative Example 511Al:Zn=1:12071113450Comparative Example 61Al:Sr=1:1207774850Invention Example 62Sr3513554825Invention Example 73Zn3514864880Invention Example 84Al:Mg=1:1-122501140Comparative Example 7

[0131] As shown in Tables 1 through 4, when process conditions are properly controlled, the steel plate substrate's aggregate structure is properly formed and its shielding ratio is excellent. Furthermore, when a film containing appropriate components is used, excellent insulation and corrosion resistance are confirmed.

[0132] On the other hand, if the process conditions are not properly controlled, it can be confirmed that the aggregate structure of the steel plate substrate is not properly formed and the shielding rate is inferior.

[0133] Even if the steel plate substrate is properly manufactured, if a complex oxide is not properly used as a film, it can be confirmed that the insulation and corrosion resistance are inferior.

[0134]

[0135] 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.

[0136] [Explanation of symbols]

[0137] 100: Electrical steel plate for electromagnetic shielding, 10: Electrical steel plate substrate,

[0138] 11: center, 12: surface,

[0139] 20: Film, 200: Transmission line

Claims

Comprising a steel plate substrate and a film positioned on the surface of the steel plate substrate, 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) among the total crystal grains (D2 / D1) is 0.5 or more, and the crystal grains account for 70% or more in area. The average grain size in the surface portion from the surface of the steel plate substrate to less than 1 / 4 of the thickness of the steel plate substrate in the thickness direction is 80 ㎛ to 500 ㎛, and the average grain size in the center portion from 1 / 4 to 1 / 2 of the thickness of the steel plate substrate is 50 ㎛ or less. An electrical steel sheet for electromagnetic shielding, wherein the film comprises 100 parts by weight of a metal phosphate containing at least one of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn, and 3 to 150 parts by weight of an oxide containing at least two of Al, Si, Mg, and Fe. In the first paragraph, Within 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, The above steel plate substrate is an electrical steel plate for electromagnetic shielding, which contains, in 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, The above steel plate substrate is an electrical steel plate for electromagnetic shielding, further containing Mn: 0.1 wt% or less and S: 0.005 wt% or less. In the first paragraph, An electrical steel sheet for electromagnetic shielding, wherein the above film further contains 50 to 250 parts by weight of silica. In the first paragraph, An electrical steel sheet for electromagnetic shielding, wherein the above film further contains 2 to 10 parts by weight of chromium oxide. 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 It comprises a step of forming a film by applying a film-forming composition including 100 parts by weight of a metal phosphate containing at least one of Al, Mg, Co, Ca, Sr, Ba, Zn, and Mn as a solid content and 3 to 150 parts by weight of an oxide containing at least two of Al, Si, Mg, and Fe, to the surface of 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 8, 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 9, 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 8, 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 8, 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 8, 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 8, A method for manufacturing an electrical steel sheet for electromagnetic shielding, wherein the film-forming composition further contains 50 to 250 parts by weight of silica. In Article 8, A method for manufacturing an electrical steel sheet for electromagnetic shielding, wherein the film-forming composition further contains 2 to 10 parts by weight of chromium oxide.

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