Grain-oriented electrical steel sheet and its manufacturing method

Abstract

The present invention provides a manufacturing method for grain-oriented electrical steel sheet that improves magnetic properties by controlling the tension applied to the steel sheet during the insulating coating layer formation process, adjusting the stress applied to each layer, and suppressing the formation of subgrain boundaries. [Solution] The magnetic steel sheet includes an electrical steel sheet substrate containing 2.0 to 7.0% by weight of Si and 0.01 to 0.07% by weight of Sb, with the remainder being Fe and other unavoidable impurities, a fine-grained interface layer located from the surface of the electrical steel sheet substrate toward the inside of the electrical steel sheet substrate, a base coating layer located on the fine-grained interface layer, and an insulating coating layer located on the base coating layer, and satisfies the following formula 1. [Formula 1] ([P]×[PS]+[F]×[FS]+[C]×[CS]) / -([S] / 2)≧13.0MPa (In formula 1, [P] is the thickness of the insulating coating layer (μm), [PS] is the residual stress of the insulating coating layer (MPa), [F] is the thickness of the base coating layer (μm), [FS] is the residual stress of the base coating layer (MPa), [C] is the thickness of the fine grain interface layer (μm), [CS] is the residual stress of the fine grain interface layer (MPa), and [S] is the thickness of the electrical steel sheet substrate (μm).)

Description

[Technical Field]

[0001] The present invention relates to a grain-oriented electrical steel sheet and a manufacturing method thereof, and more particularly to a grain-oriented electrical steel sheet and a manufacturing method thereof, in which the tension applied to the steel sheet during the process of forming an insulating coating layer is controlled, the stress applied to each layer is adjusted, and the formation of subgrain boundaries is suppressed, thereby improving magnetic properties. [Background technology]

[0002] Generally, grain-oriented electrical steel sheets are steel sheets containing silicon, and the grain orientation is {110} <001> This refers to electrical steel sheets that have a texture aligned in the {110} direction and have extremely excellent magnetic properties in the rolling direction. <001> Obtaining a texture is possible through a combination of various manufacturing processes, and in particular, the composition of the steel slab, as well as the series of processes including heating, hot rolling, hot-rolled sheet annealing, primary recrystallization annealing, and secondary recrystallization annealing must be very strictly controlled. Specifically, grain-oriented electrical steels suppress the growth of primary recrystallized grains, and within the suppressed grains, {110} <001> The secondary recrystallized structure obtained by selectively growing grains with the {110} orientation is what gives the alloy its excellent magnetic properties, so the growth inhibitors for the primary recrystallized grains are even more important. <001> One of the key issues in grain-oriented electrical steel manufacturing technology is to enable preferential growth of grains with a specific orientation texture. Primary grain growth inhibitors that meet the above conditions and are currently widely used industrially include MnS, AlN, and MnSe.

[0003] Specifically, MnS, AlN, MnSe, etc. contained in a steel slab are reheated at high temperatures for a long time to form a solid solution, and then hot-rolled. During the subsequent cooling process, the elements are formed as precipitates with the appropriate size and distribution, which are used as the growth inhibitors. However, this method has the problem of necessarily heating the steel slab at high temperatures. In recent years, efforts have been made to improve the magnetic properties of grain-oriented electrical steel sheets by heating steel slabs at low temperatures. To this end, a method of adding antimony (Sb) to grain-oriented electrical steel sheets has been proposed, but this method has been criticized for causing uneven and coarse grain size after final high-temperature annealing, resulting in poor noise quality in transformers.

[0004] To minimize power loss in grain-oriented electrical steel sheets, an insulating coating (or tensile coating layer) is typically formed on the surface. This insulating coating must have high electrical insulation, excellent adhesion to the substrate, and a uniform color without external defects. In addition, due to recent tightening of international standards for transformer noise and intensifying competition in the related industry, research into magnetic deformation (magnetostriction) phenomena is needed to reduce noise from the insulating coating of grain-oriented electrical steel sheets. Specifically, when a magnetic field is applied to the electrical steel sheet used as the iron core of a transformer, it repeatedly contracts and expands, inducing vibrations. These vibrations cause vibration and noise in the transformer. Conventional grain-oriented electrical steel sheets form an insulating coating on the steel sheet and a forsterite-based coating. The difference in the thermal expansion coefficients of the insulating coating applies tensile stress to the steel sheet, improving core loss and reducing noise caused by magnetic deformation. However, this approach has limitations in meeting the noise levels currently required for high-quality grain-oriented electrical steel sheets.

[0005] Meanwhile, wet coating is a known method for reducing 90° magnetic domains in grain-oriented electrical steel sheets. Here, 90° magnetic domains refer to regions with magnetization perpendicular to the direction of the applied magnetic field. The fewer the 90° magnetic domains, the smaller the magnetic deformation. However, the conventional wet coating method lacks the noise reduction effect of applying tensile stress, and requires a thick coating, which can reduce the space factor and efficiency of transformers. Other known methods for imparting high tensile strength to the surface of grain-oriented electrical steel sheets include vacuum deposition coating methods such as physical vapor deposition (PVD) and chemical vapor deposition (CVD). However, these coating methods are difficult to commercialize, and grain-oriented electrical steel sheets manufactured using these methods have the disadvantage of poor insulation properties. Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a method for manufacturing a grain-oriented electrical steel sheet, specifically, a method for manufacturing a grain-oriented electrical steel sheet that improves magnetic properties by controlling the tension applied to the steel sheet during the insulating coating layer formation process, adjusting the stress applied to each layer, and suppressing the formation of subgrain boundaries. [Means for solving the problem]

[0007] The grain-oriented electrical steel sheet of the present invention comprises an electrical steel sheet substrate containing 2.0 to 7.0 wt. % Si and 0.01 to 0.07 wt. % Sb, with the remainder being Fe and other unavoidable impurities, a fine-grained interface layer located from the surface of the electrical steel sheet substrate toward the interior of the electrical steel sheet substrate, a base coating layer located on the fine-grained interface layer, and an insulating coating layer located on the base coating layer. The grain-oriented electrical steel sheet of the present invention satisfies the following formula 1. [Formula 1] ([P]×[PS]+[F]×[FS]+[C]×[CS]) / -([S] / 2)≧13.0MPa (In Equation 1, [P] is the thickness of the insulating coating layer (μm), [PS] is the residual stress of the insulating coating layer (MPa), [F] is the thickness of the base coating layer (μm), [FS] is the residual stress of the base coating layer (MPa), [C] is the thickness of the fine-grained interface layer (μm), [CS] is the residual stress of the fine-grained interface layer (MPa), and [S] is the thickness of the electrical steel sheet substrate (μm).)

[0008] The fine grain interface layer may have an average crystal grain size of 0.1 to 5 μm. The residual stress in the RD direction of the base coating layer may be −50 to −1500 MPa. The residual stress in the RD direction of the insulating coating layer may be −10 to −1000 MPa. The electrical steel sheet substrate may have a residual stress in the RD direction of 1 to 50 MPa. The fine grain interface layer may have a residual stress in the RD direction of -10 to -1000 MPa. The thickness of the fine grained interface layer can be 0.1 to 5 μm. The thickness of the base coating layer can be from 0.1 to 15 μm. The thickness of the insulating coating layer may be 0.1 to 15 μm. The insulating coating layer contains pores with a diameter of 10 nm or more, and the electrical steel sheet substrate has sub-grains in a region (A) within 1500 μm from the center of the pore in the RD direction, and in a region (B) 50 to 100 μm from the surface of the electrical steel sheet substrate toward the interior of the electrical steel sheet substrate, and the sub-grains have a crystal orientation of {110} <001> The angle is 1° to 15° from the center, and the area fraction of the subgrains in the ND cross section is 5% or less. The ratio (y / z) of the length of the sub-grain in the TD direction (y) to the length of the sub-grain in the ND direction (z) may be 1.5 or less. The crystal orientation is {110} in the region (B) extending from the surface of the electrical steel sheet substrate to the interior of the electrical steel sheet substrate at a depth of 50 to 100 μm. <001> The Goss grains are less than 1° from the ND plane, and the average grain size of the Goss grains (L G ) to the average grain size of the subgrains (L S ) ratio (L S / L G ) may be 0.20 or less. There can be 1 to 300 pores with a diameter of 10 nm or more per mm in the RD direction.

[0009] The method for producing a grain-oriented electrical steel sheet of the present invention includes the steps of producing a grain-oriented electrical steel sheet substrate containing 2.0 to 7.0 wt. % Si and 0.01 to 0.07 wt. % Sb, with the remainder being Fe and other unavoidable impurities, applying an insulating coating layer-forming composition onto the grain-oriented electrical steel sheet substrate, and heat-treating the grain-oriented electrical steel sheet substrate to form an insulating coating layer on the grain-oriented electrical steel sheet substrate, wherein a tension of 0.2 to 0.7 kgf / mm is applied to the steel sheet in the step of forming the insulating coating layer. 2 and the maximum value (MA) and minimum value (MI) of the tension with respect to the entire length of the steel plate satisfy the following formula 2. [Formula 2] [MI] ≥ 0.5 × [MA] The step of forming the insulating coating layer may be performed by heat treatment at a temperature of 550 to 1100°C. [Effects of the Invention]

[0010] According to the present invention, the grain-oriented electrical steel sheet can improve the magnetic properties by suppressing the sub-grains that adversely affect the magnetic properties. Furthermore, the residual stress in the base coating layer, the insulating coating layer and the fine grain interface layer increases, thereby improving the magnetic properties. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram of a TD cross section of a steel plate according to the present invention. [Figure 2] 1 is an electron backscatter diffraction (EBSD) photograph of the steel sheet produced in Example 1. [Figure 3] 1 is a diagram showing a method for calculating coating tension using a radius of curvature. [Figure 4] 1 is a diagram showing the slope in the measurement of residual stress. DETAILED DESCRIPTION OF THE INVENTION

[0012] Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited to these. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Thus, a first part, component, region, layer, or section described below can be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention. The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular forms "a," "an," and "the" include the plural forms unless the context clearly dictates otherwise. As used in the specification, the term "comprising" embodies certain properties, regions, integers, steps, operations, elements, and / or components and does not exclude the presence or addition of other properties, regions, integers, steps, operations, elements, and / or components. When we refer to an element as being "on" or "above" another element, this includes being on top of the other element, even if there are other elements between them. In contrast, when we refer to an element as being "directly on top of" another element, there are no other elements between them.

[0013] Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal sense unless otherwise defined. Unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight. In one embodiment of the present invention, the additional element means that the remaining iron (Fe) is replaced by the additional amount of the additional element.

[0014] While the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, the present invention will be described in detail below so that those skilled in the art can easily practice the present invention.

[0015] FIG. 1 is a schematic diagram showing a TD cross section of a grain-oriented electrical steel sheet according to the present invention. As shown in FIG. 1 , the grain-oriented electrical steel sheet 100 of the present invention includes an electrical steel sheet substrate 10, a fine-grained interface layer 12 located on the electrical steel sheet substrate 10, a base coating layer 20 located on the fine-grained interface layer 12, and an insulating coating layer 30 located on the base coating layer 20.

[0016] Each of the components of the present invention will be described in detail below. The electrical steel sheet substrate 10 refers to a portion of the grain-oriented electrical steel sheet 100 excluding the base coating layer 20 and the insulating coating layer 30 . In the present invention, this is expressed by the pores 31 in the insulating coating layer 30 and the sub-grains 11 in the electromagnetic steel sheet substrate 10, regardless of the alloy composition of the electromagnetic steel sheet substrate 10. Next, the alloy composition of the electromagnetic steel sheet substrate 10 will be explained. The electrical steel sheet substrate 10 contains 2.0 to 7.0 wt % Si, 0.01 to 0.10 wt % Sn, 0.01 to 0.07 wt % Sb, 0.020 to 0.040 wt % Al, 0.01 to 0.20 wt % Mn, 0.01 wt % or less C, 0.005 wt % or less N, and 0.005 wt % or less S, with the remainder being Fe and other unavoidable impurities.

[0017] Si:2.0~7.0wt% Silicon (Si) increases the resistivity of steel and reduces iron loss. However, if the Si content is too low, the resistivity of the steel decreases, deteriorating iron loss characteristics. Furthermore, a phase transformation interval may exist during secondary recrystallization annealing, making the secondary recrystallization unstable. If the Si content is too high, the steel may become brittle, making cold rolling difficult. Therefore, the Si content can be adjusted within the aforementioned range. More specifically, the Si content is 2.5 to 5.0 wt.%.

[0018] Sn:0.01~0.10wt% Tin (Sn) is a grain segregation element that hinders the movement of grains, and therefore acts as a grain growth inhibitor, and is used in the {110} <001> It is an important element in strengthening the grain growth suppression force, as it promotes the generation of Goss crystal grains with the right orientation and allows secondary recrystallization to develop well. If the Sn content is too low, the effect is reduced, and if the Sn content is too high, grain segregation becomes severe, the brittleness of the steel sheet increases, and the sheet breaks during rolling. Therefore, the Sn content can be adjusted within the above range. More specifically, Sn is contained in an amount of 0.02 to 0.08 wt%.

[0019] Sb:0.01~0.05wt% Antimony (Sb) is {110} <001> Sb is an element that promotes the formation of Goss crystal grains in the desired orientation. If the Sb content is too low, it will not be effective as a Goss crystal grain formation promoter. If the Sb content is too high, it will segregate on the surface, suppressing the formation of an oxide layer and causing surface defects. Therefore, the Sb content can be adjusted within the above-mentioned range. More specifically, Sb is contained in an amount of 0.02 to 0.04 wt%.

[0020] Al:0.020~0.040wt% Aluminum (Al) is an element that ultimately becomes nitrides in the form of AlN, (Al, Si)N, and (Al, Si, Mn)N and acts as an inhibitor. If the Al content is too low, sufficient inhibitor effect cannot be expected. On the other hand, if the Al content is too high, Al-based nitrides precipitate and grow very coarsely, resulting in insufficient inhibitor effect. Therefore, the Al content can be adjusted within the aforementioned range. More specifically, Al is contained in an amount of 0.020 to 0.030 wt%.

[0021] Mn:0.01~0.20wt% Manganese (Mn), like Si, increases resistivity and reduces iron loss. It also reacts with Si to form (Al, Si, Mn)N precipitates, inhibiting the growth of primary recrystallized grains and inducing secondary recrystallization. However, excessive Mn content promotes austenite phase transformation during hot rolling, reducing the size of primary recrystallized grains and destabilizing secondary recrystallization. Furthermore, too little Mn can be insufficient as an austenite-forming element, increasing the austenite fraction during hot-rolling reheating and increasing the amount of precipitates dissolved therein. This can lead to refinement of precipitates and the prevention of excessive primary recrystallization grain size due to the formation of MnS. Therefore, the Mn content can be adjusted within the aforementioned range.

[0022] C: 0.010% by weight or less In the present embodiment, carbon (C) is an element that is not particularly useful for improving the magnetic properties of grain-oriented electrical steel sheets, so it is preferable to eliminate it as much as possible. However, if present at a certain level or above, it has the beneficial effect of accelerating the austenite transformation of steel during rolling and refining the hot-rolled structure during hot rolling, thereby forming a uniform fine structure. The C content in the slab is preferably 0.04 wt% or more. However, if the C content is too high, coarse carbides are formed that are difficult to remove during decarburization, so it can be set to 0.07 wt% or less. Decarburization is performed during the primary recrystallization annealing process, and after decarburization, the final grain-oriented electrical steel sheet substrate contains 0.005 wt% or less.

[0023] N: 0.005% by weight or less Nitrogen (N) is an element that reacts with Al and other elements to refine crystal grains. When these elements are appropriately distributed, they are useful for appropriately refining the structure after cold rolling, as described above, and ensuring an appropriate primary recrystallization grain size. However, excessive N content can result in excessive refinement of the primary recrystallization grains. As a result, the driving force for grain growth during secondary recrystallization increases due to the fine grains, which can lead to the growth of grains with undesirable orientations. Furthermore, excessive N content is undesirable because it takes a long time to remove it during the final annealing process. Therefore, the upper limit of the nitrogen content can be set to 0.005 wt.%. The amount of nitrogen can increase due to nitriding during the primary recrystallization process. This is then removed again during the secondary recrystallization annealing process, resulting in the same amount of nitrogen in the slab and the final grain-oriented electrical steel sheet substrate 10.

[0024] S: 0.005% by weight or less If the sulfur (S) content exceeds 0.005% by weight, it redissolves and precipitates finely during heating of the hot-rolled slab, reducing the size of the primary recrystallized grains and lowering the secondary recrystallization start temperature, resulting in a deterioration of magnetic properties. Furthermore, it takes a long time to remove the dissolved S in the secondary crack zone during the final annealing process, reducing the productivity of grain-oriented electrical steel sheets. On the other hand, if the S content is low, at 0.005% or less, it has the effect of coarsening the size of the initial crystal grains before cold rolling, resulting in the {110} deformation bands nucleating during the primary recrystallization process. <001> The number of oriented crystal grains increases. Therefore, in order to reduce the size of secondary recrystallized grains and improve the magnetic properties of the final product, the S content is preferably 0.005 wt % or less.

[0025] The remainder consists of Fe and unavoidable impurities. Affected elements are elements that are inevitably added during the steelmaking and grain-oriented electrical steel sheet manufacturing processes, and as they are widely known, further explanation is omitted. The present invention does not exclude the addition of elements other than the aforementioned alloy components, but includes various elements within a range that does not impair the technical spirit of the present invention. When additional elements are further included, they are included to replace the remaining Fe.

[0026] The electrical steel sheet substrate 10 may have a residual stress in the RD direction of 1 to 50 MPa. The reason for the presence of residual stress in this range is the presence of the base coating layer 20 and insulating coating layer 30 on top of the electrical steel sheet substrate 10. The presence of residual stress in the above range imparts coating tension to the base iron, improving magnetic properties. Specifically, the electrical steel sheet substrate 10 may have a residual stress in the RD direction of 16.0 to 30.0 MPa. The residual stress of the electrical steel sheet substrate 10 can be determined by taking the sum of the residual stresses of the fine-grained interface layer 12, the base coating layer 20, and the insulating coating layer 30, which will be described later, as zero. TIFF0007801347000001.tif15128t i : thickness of each layer σ i : Residual stress in each layer i: Base coating layer / fine grain interface layer / base steel plate

[0027] As shown in Figure 1, a fine grain interface layer 12 may be present from the surface of the electrical steel sheet substrate 10 toward the interior of the electrical steel sheet substrate. This fine grain interface layer 12 may have an average crystal grain size of 0.1 to 5 µm. The fine grain interface layer 12 is formed due to the influence of non-uniform surface energy.

[0028] The thickness of the fine grain interface layer 12 may be 0.1 to 5 μm. If the fine grain crystal layer 12 is too thick, the magnetic properties will be deteriorated, so it is advantageous to make the thickness thin. More specifically, the thickness of the fine grain interface layer 12 may be 0.5 to 3 μm. The fine-grained interface layer 12 may have a residual stress in the RD direction of -10 to -1000 MPa. In this case, the negative sign indicates the stress imparted by the fine-grained interface layer 12 to the electrical steel sheet substrate 10. More specifically, the fine-grained interface layer 12 may have a residual stress in the RD direction of -100 to -500 MPa. Even more specifically, the fine-grained interface layer 12 may have a residual stress in the RD direction of -400 to -500 MPa.

[0029] As shown in FIG. 1 , the grain-oriented electrical steel sheet 100 of the present invention may include a base coating layer 20 located between the electrical steel sheet substrate 10 and the insulating coating layer 30 .

[0030] The base coating layer 20 is formed when an oxide layer formed during the primary recrystallization process reacts with components in the annealing separator. The base coating layer 20 improves adhesion between the insulating coating layer 30 and the electrical steel sheet substrate 10, and, together with the insulating coating layer 30, provides insulation to the grain-oriented electrical steel sheet 100. The components of the base coating layer 20 are not particularly limited, but when the annealing separator component contains MgO, it may contain forsterite (Mg2SiO4).

[0031] The thickness of the base coating layer 20 may be 0.1 to 15 μm. If the thickness of the base coating layer 20 is too thin, it will not be able to adequately perform the aforementioned functions of insulation and improving adhesion with the insulating coating layer 30. If the base coating layer 20 is too thick, the space factor will be low and adhesion with the insulating coating layer 30 may be reduced. More specifically, the thickness of the base coating layer 20 may be 0.5 to 3 μm. The residual stress in the RD direction of the base coating layer 20 may be −50 to −1500 MPa, more specifically −500 to −1000 MPa, and even more specifically −760 to −1000 MPa.

[0032] As shown in Fig. 1, the insulating coating layer 30 is located on the base coating layer 20. The insulating coating layer 30 provides insulation to the grain-oriented electrical steel sheet 100 and also serves to improve iron loss by applying tension to the electrical steel sheet substrate 10. The insulating coating layer 30 may be made of a material that can provide insulating properties to the surface of the electrical steel sheet 100. Specifically, it may contain phosphate (H3PO4). The insulating coating layer 30 is formed by applying an insulating coating layer-forming composition containing a solvent onto a steel sheet and then heat-treating it. At this time, as the solvent evaporates at high temperature, pores 31 are inevitably formed in the insulating coating layer 30. The pores 31 refer to empty spaces, i.e., the absence of anything in a given area.

[0033] Pores with a diameter of 10 nm or more may exist at 1 to 300 per mm in the RD direction. More specifically, 1 to 30 per mm may exist. In this case, the diameter of the pores may be measured based on the ND or TD plane. The number of pores may be measured based on the TD plane. There are 1 to 30 sub-crystal grains per pore with a grain size of 10 nm or more. As mentioned above, there may be no sub-crystal grains 11 in the lower regions (A, B) of the pore 31, or there may be two or more sub-crystal grains 11. However, there may be cases where sub-crystal grains 11 do not exist in any regions other than the lower regions (A, B) of the pore 31.

[0034] The thickness of the insulating coating layer 30 may be 0.1 to 15 μm. If the insulating coating layer 30 is too thin, it will not be able to adequately perform the insulating function described above. If the insulating coating layer 30 is too thick, the space factor will be low and the adhesion to the steel sheet substrate 10 may be reduced. More specifically, the thickness of the insulating coating layer 30 may be 1.0 to 5.0 μm. The residual stress in the RD direction of the insulating coating layer 30 may be −10 to −1000 MPa, more specifically, −70 to −500 MPa.

[0035] The grain-oriented electrical steel sheet of the present invention satisfies the following formula 1. [Formula 1] ([P]×[PS]+[F]×[FS]+[C]×[CS]) / -([S] / 2)≧13.0MPa (In Equation 1, [P] is the thickness of the insulating coating layer (μm), [PS] is the residual stress of the insulating coating layer (MPa), [F] is the thickness of the base coating layer (μm), [FS] is the residual stress of the base coating layer (MPa), [C] is the thickness of the fine-grained interface layer (μm), [CS] is the residual stress of the fine-grained interface layer (MPa), and [S] is the thickness of the electrical steel sheet substrate (μm).) Equation 1 represents the tensile stress in the rolling direction of the grain-oriented electrical steel sheet. For example, if the left side of Equation 1 is too small, problems such as inferior magnetic properties may occur. More specifically, the left side of Equation 1 may be 14.0 to 21.0.

[0036] The insulating coating layer 30 is formed by applying an insulating coating layer-forming composition containing a solvent onto a steel sheet and then heat-treating the sheet. At this time, as the solvent evaporates at high temperature, pores 31 are inevitably formed in the insulating coating layer 30. When the pores 31 become larger than 10 nm, the stress applied to the steel sheet is concentrated at the bottom of the pores 31, forming sub-grains 11. This has a detrimental effect on magnetic properties compared to Goss grains, which are the main grains in grain-oriented electrical steel sheets, and it is therefore preferable to suppress this as much as possible. In the present invention, the correlation between the positions of the pores 31 and the sub-grains 11 and the cause of the formation of the sub-grains 11 are analyzed, and the formation of the sub-grains 11 is suppressed as much as possible.

[0037] In FIG. 1, the pores 31 and the sub-grains 11 are shown schematically. As shown in Fig. 1, sub-grains 11 are present below pores 31. All sub-grains 11 in the steel sheet substrate 10 are present in a specific region below the pores 31. However, not all pores 31 have sub-grains 11 below them, and there may be pores 31 that do not have sub-grains 11 below them. As shown in FIG. 1, sub-grains 11 exist within an electrical steel sheet substrate 10. The sub-grains 11 have a crystal orientation of {110} <001> The Goss grains are distinguished from the remaining Goss grains excluding the subgrains at the point where the angle between the subgrains and the crystal orientation is 1° to 15°. <001> The crystal orientation is expressed by the Miller index.

[0038] In the present invention, the sub-grains 11 are located below the pores 31. Specifically, the sub-grains 11 exist in a region (A) within 1500 μm from the center of the pore in the RD direction and in a region (B) 50 to 100 μm from the surface of the electrical steel sheet substrate toward the interior of the electrical steel sheet substrate. In FIG. 1, the positions defined by regions A and B are indicated by dotted rectangles. Specifically, all regions of the sub-grains 11 are included in the positions defined by regions A and B. In the present invention, the sub-grains 11 exist only in the aforementioned regions, and no sub-grains 11 exist in other parts. In the present invention, the magnetic properties can be improved by suppressing such sub-crystal grains 11. Specifically, the area fraction of the sub-crystal grains in the ND cross section can be 5% or less. If the area fraction of the sub-crystal grains 11 is too large, the magnetic properties will be deteriorated. More specifically, the area fraction of the sub-crystal grains in the ND cross section can be 0.1 to 5%. Even more specifically, it can be 1 to 3%. The ND cross section means a plane perpendicular to the ND direction.

[0039] The grain size of the sub-grains 11 is 1 to 500 nm, and they can be distinguished from the remaining Goss grains by their grain size. Specifically, the average grain size of the Goss grains excluding the sub-grains can be 5 to 100 mm. This is the grain size in the ND cross section of the grains. More specifically, the grain size of the sub-grains 11 is 10 to 250 nm, and the average grain size of the Goss grains excluding the sub-grains can be 10 to 50 mm. The average grain size of Goss grains in the ND cross section (L G ) to the average grain size of the subgrains (L S ) ratio (L S / L G) may be 0.20 or less. More specifically, it may be 0.10 or less. In the present invention, the particle size means the diameter of an imaginary circle having the same area as the area of ​​the particle size.

[0040] A method for manufacturing a grain-oriented electrical steel sheet according to the present invention includes the steps of: preparing a grain-oriented electrical steel sheet substrate; applying an insulating coating layer-forming composition onto the grain-oriented electrical steel sheet substrate; and heat-treating the grain-oriented electrical steel sheet substrate to form the insulating coating layer-forming composition on the grain-oriented electrical steel sheet. Each step will be explained in detail below. First, a grain-oriented electrical steel sheet substrate is manufactured. At this time, the grain-oriented electrical steel sheet substrate 10 having the base coating layer 20 formed thereon may be used. The present invention has a technical feature in that the tension applied to the steel sheet is adjusted in the step of forming the insulating coating layer, and various known methods can be used to manufacture the grain-oriented electrical steel sheet.

[0041] Hereinafter, an example of a method for manufacturing a grain-oriented electrical steel sheet substrate before forming an insulating coating layer will be described. The method for manufacturing a grain-oriented electrical steel sheet substrate may further include the steps of hot-rolling a slab to manufacture a hot-rolled sheet, cold-rolling the hot-rolled sheet to manufacture a cold-rolled sheet, performing primary recrystallization annealing on the cold-rolled sheet, and performing secondary recrystallization annealing on the cold-rolled sheet after the primary recrystallization annealing. The slab contains 2.0 to 7.0 wt% Si, 0.01 to 0.10 wt% Sn, 0.01 to 0.07 wt% Sb, 0.020 to 0.040 wt% Al, 0.01 to 0.20 wt% Mn, 0.04 to 0.07 wt% C, 10 to 50 wt ppm N, and 0.001 to 0.005 wt% S, with the remainder consisting of Fe and other unavoidable impurities.

[0042] First, a slab is hot rolled to produce a hot-rolled sheet. Hereinafter, the alloy components of the slab are the same as those of the magnetic steel sheet substrate 10 except for the C content, so duplicated explanations will be omitted. Prior to the step of producing a hot-rolled sheet, a step of heating the slab to 1230°C or less can be further included. This step allows precipitates to be partially dissolved. Furthermore, this prevents the columnar crystal structure of the slab from growing coarsely, thereby preventing cracks from occurring in the width direction of the sheet during the subsequent hot rolling process, thereby improving yield. If the slab heating temperature is too high, the surface of the slab may melt, requiring repairs to the heating furnace and shortening the furnace's lifespan. More specifically, the slab can be heated at 1130 to 1200°C. It is also possible to hot-roll the continuously cast slab directly without heating it.

[0043] In the step of producing a hot-rolled sheet, a hot-rolled sheet having a thickness of 1.8 to 2.3 mm can be produced by hot rolling.

[0044] After preparing the hot-rolled sheet, the method may further include annealing the hot-rolled sheet, which may be performed by heating the hot-rolled sheet to a temperature of 950 to 1,100°C, annealing the hot-rolled sheet at a temperature of 850 to 1,000°C, and then cooling the hot-rolled sheet.

[0045] Next, the hot-rolled sheet is cold-rolled to produce a cold-rolled sheet. Cold rolling is performed through a single cold rolling process, but can be performed through multiple passes. During rolling, warm rolling is performed at least once at a temperature of 200-300°C to impart a pass aging effect, allowing for production with a final thickness of 0.14-0.25mm. The cold-rolled sheet undergoes decarburization and recrystallization of the deformed structure during the primary recrystallization annealing process, and nitriding treatment using nitriding gas.

[0046] Next, the rolled sheet is subjected to primary recrystallization annealing. It can be decarburized or nitrided during the primary recrystallization annealing process. The primary recrystallization annealing stage can be performed at a temperature of 800 to 900°C. If the temperature is too low, the primary recrystallization does not occur and nitriding may not proceed smoothly. If the temperature is too high, the primary recrystallization grows too large, causing a deterioration in magnetic properties. Decarburization can be performed in an atmosphere with an oxidation power (PH2O / PH2) of 0.5 to 0.7. By decarburizing, the steel sheet can contain carbon at 0.005 wt% or less, more specifically, 0.003 wt% or less.

[0047] Next, an annealing separator is applied to the cold-rolled steel sheet after the first recrystallization annealing, followed by the second recrystallization annealing. Various separators can be used as the annealing separator. For example, an annealing separator mainly composed of MgO can be applied. At this time, after the second recrystallization annealing, a base coating layer 20 containing forsterite is formed.

[0048] The purpose of secondary recrystallization annealing is to remove the {110} <001> The purpose of secondary recrystallization annealing is to remove impurities that impair texture formation and magnetic properties. The method of secondary recrystallization annealing is to maintain a mixed gas of nitrogen and hydrogen in the temperature rising section before secondary recrystallization occurs, protecting the nitrides that act as grain growth inhibitors and allowing secondary recrystallization to develop smoothly, and after secondary recrystallization is complete, the material can be maintained in a 100% hydrogen atmosphere for a long period of time to remove impurities.

[0049] A secondary recrystallization annealing step and a flattening annealing step may be included. Returning to the explanation of the manufacturing process of the grain-oriented electrical steel sheet according to the present invention, an insulating coating layer-forming composition is applied onto the grain-oriented electrical steel sheet substrate and the base coating layer. In the present invention, various insulating coating layer-forming compositions can be used and are not particularly limited. For example, an insulating coating layer-forming composition containing phosphate can be used.

[0050] Next, the grain-oriented electrical steel sheet substrate is heat-treated to form an insulating coating layer on the grain-oriented electrical steel sheet substrate and the base coating layer 20 . During this heat treatment, the solvent evaporates at high temperatures, inevitably forming pores 31 in the insulating coating layer 30. At this time, stress applied to the steel sheet is concentrated below the pores 31, forming sub-grains 11. In the present invention, the formation of sub-grains 11 is suppressed as much as possible by adjusting the tension applied to the steel sheet during the process of forming the insulating coating layer. Specifically, in the step of forming the insulating coating layer, the tension applied to the steel sheet is 0.20 to 0.70 kgf / mm 2 is. If the tension applied to the steel sheet is too small, scratches may occur on the surface, resulting in poor corrosion resistance and other problems. If the tension applied to the steel sheet is too large, a large number of sub-grains 11 may be formed, which may have an adverse effect on magnetic properties. More specifically, the tension is set to 0.20 to 0.50 kgf / mm. 2 More specifically, it can be 0.3 to 0.47 kgf / mm 2 In this case, the tension is the average tension in the longitudinal direction of the steel sheet measured at the exit side of the heat treatment process.

[0051] In the step of forming the insulating coating layer, the tension applied may vary depending on the longitudinal direction (RD) of the steel sheet. In the present invention, the difference between the maximum tension (MA) and the minimum tension (MI) over the entire length of the steel sheet is minimized to appropriately control the residual stress applied to each layer, thereby suppressing the formation of sub-grains 11. Specifically, the maximum value (MA) and minimum value (MI) of the tension over the entire length of the steel plate satisfy the following formula 2. [Formula 2] [MI] ≥ 0.5 × [MA] If Equation 2 is not satisfied and there is a large deviation in tension in the longitudinal direction (RD) of the steel plate, localized non-uniformity increases, residual stress cannot be properly adjusted, and a large amount of sub-grains 11 are formed.

[0052] In conventional processes, the line speed varies widely during the flattening annealing process, resulting in significant tension deviations along the steel sheet's length (RD), increasing localized non-uniformity. Specifically, laser welding is performed at the minimum line speed to join the tail of the preceding coil and the top of the following coil at the flattening annealing entry point. After welding is complete, the line speed is increased to improve productivity, resulting in significant tension deviations. More specifically, line speed variations increase in the bridle roll and hearth roll speeds due to line speed changes. The high temperatures inevitably associated with flattening annealing lead to significant tension deviations along the steel sheet's length (RD), increasing localized non-uniformity and preventing proper adjustment of residual stress. As a result, the minimum tension (MI) was limited to less than 0.5 × [MA].

[0053] There are several methods for reducing the difference between the maximum and minimum tensions (MA and MI). In the present invention, for example, bridle roll control and hearth roll speed control can be used. Bridle roll control is a method of feedback tension control that follows tension meter values. More specifically, it is a method of controlling the bridle roll speed to reduce the difference between the maximum and minimum tensions. Furthermore, hearth roll control is a method of feedforward tension control that follows the bridle roll speed. More specifically, to reduce the difference between the maximum and minimum tensions, the hearth roll speed can be increased while the tension is controlled to be lower. In the present invention, even if the line speed fluctuates during the flattening annealing process, the tension can be controlled within a specific range while simultaneously reducing the difference between the maximum and minimum tensions (MA and MI).

[0054] In the step of forming the insulating coating layer, the heat treatment temperature may be 550 to 1100° C. At the above temperature, the number of pores 31 is reduced and the residual stress of the insulating coating layer 30 is appropriately provided.

[0055] Preferred examples and comparative examples of the present invention will be described below. However, the following examples are merely preferred examples of the present invention, and the present invention is not limited to these examples.

[0056] Example The steel contained 3.4 wt% Si, 0.05 wt% Sn, 0.02 wt% Sb, 0.02 wt% Al, 0.10 wt% Mn, 0.05 wt% C, 0.002 wt% N, and 0.001 wt% S, with the remainder being Fe and other unavoidable impurities. The steel was vacuum melted to produce an ingot, which was then heated at 1150°C for 210 minutes and hot-rolled to produce a 2.0 mm thick hot-rolled sheet. After pickling, the sheet was cold-rolled to a thickness of 0.220 mm.

[0057] The cold-rolled sheet was subjected to decarburization and nitriding annealing heat treatment at a temperature of approximately 800-900°C in a humid atmosphere of 50v% hydrogen and 50v% nitrogen and ammonia mixed gas atmosphere so that the carbon content was increased to 30ppm or less and the total nitrogen content to 130ppm or more.

[0058] The steel sheet was coated with an annealing separator, MgO, and then coiled and final annealed. The final annealing was performed in a mixed atmosphere of 25v% nitrogen and 75v% hydrogen up to 1200°C. After reaching 1200°C, the atmosphere was maintained at 100% hydrogen for 10 hours or more, followed by furnace cooling.

[0059] An insulating coating layer-forming composition containing phosphate and silica was applied to this steel sheet, and the steel sheet was heat-treated at a temperature of about 820° C. for 2 hours to form an insulating coating layer.

[0060] When forming the insulating coating layer, the average tension on the exit side was adjusted as shown in Table 1 below. The pores, subgrains, and other grain characteristics of the manufactured grain-oriented electrical steel sheets are summarized in Table 1, and the properties and core loss of the interface layer, base coating layer, and insulating coating layer are summarized in Table 2.

[0061] It was confirmed that the subgrains were located only in specific regions below the pores. The number of pores was measured only for pores with a diameter of 10 nm or more. The subgrain fraction was measured by electron backscatter diffraction (EBSD) with respect to the volume per unit area.

[0062] Iron loss (W17 / 50) and magnetic flux density (B8) were measured immediately after the formation of the insulating coating layer and after heat treatment at 820°C for two hours, which simulates stress relief annealing. Iron loss was measured using the single sheet measurement method at 1.7 Tesla and 50 Hz. Magnetic flux density induced in a magnetic field of 800 A / m was also measured. Residual stress in the insulating coating layer was measured using a 3D curvature measurement device (ATOS core 45). The insulating coating layer on one side was removed and the amount of bending of the steel plate was measured.

[0063] The insulation properties were measured on the top of the coating using a Franklin measuring instrument based on the ASTM A717 international standard. Corrosion resistance is measured based on the JIS Z2371 international standard, which indicates the area of ​​rust formed on the surface after 8 hours at 35°C and 5% NaCl. The following formula is a method for calculating coating tension using the radius of curvature (reference: M. Bielawski et al., Surf. & Coat. Techno., 200 (2006) 2987). Coating tension can be calculated from images measured using dedicated software for 3D scanners. The R value can be measured for specimens before (R2) and after (R1) removal of the phosphate coating layer.

[0064] TIFF0007801347000002.tif321321.σ f : Film tension 2. Es : Young's modulus of the base layer (electrical steel plate: 176,900 MPa) 3. U s : Poisson's ratio of base layer (electrical steel sheet: 0.3) 4.t f : Coating thickness (mm) 5.t s : Base specimen thickness (mm) 6. R2: Radius of curvature of base layer after coating (mm) 7. R1: Radius of curvature of base layer before coating (mm)

[0065] Residual stress in the base coating layer and the fine-grained interface layer was measured using a synchrotron XRD device. X-ray residual stress measurement uses a strain gauge to measure the distance between lattice planes of crystal grains. When a sample is under stress, the distance between lattice planes changes depending on the relative angle between the stress direction and the crystal planes. Due to the Poisson effect, the distance between lattice planes parallel to the tensile direction, i.e., ψ = 0°, is smaller than when the stress is zero, while the distance between lattice planes with a ψ angle tilted toward the tensile direction is larger than when the stress is zero. X-ray residual stress is measured by measuring the peak shift according to the tilting angle Ψ. Therefore, X-ray residual stress calculations can be expressed as follows using the sin2Ψ method: TIFF0007801347000003.tif38147d ψ : d-spacing of the lattice plane oriented in the ψ direction d z : d-spacing of the lattice plane when the lattice plane direction is perpendicular to the sample surface d o : d-spacing of stress-free lattice plane

[0066] [Table 1]

[0067] [Table 2]

[0068] [Table 3]

[0069] As shown in Tables 1 to 3, when the tension is properly controlled during the insulating coating layer formation process, the value of Equation 1 exceeds 7.0 MPa, sub-grains are suppressed, and residual stress in the fine grain interface layer, base coating layer, and insulating coating layer increases, improving magnetic properties, insulating properties, and corrosion resistance. On the other hand, when the tension is not properly controlled during the insulating coating layer formation process, residual stress is not properly applied, a large number of sub-grains are formed, and magnetic properties, insulating properties, and corrosion resistance are inferior.

[0070] The present invention is not limited to the above-described embodiments, and can be manufactured in various different forms, and a person skilled in the art to which the present invention pertains will understand that the present invention can be embodied in other specific forms without changing the technical concept or essential characteristics of the present invention. Therefore, the above-described embodiments should be understood to be illustrative in all respects and not limiting. [Explanation of symbols]

[0071] 100 grain-oriented electrical steel sheet, 10 Electromagnetic steel sheet base material, 11 subgrains, 12 fine grain interface layer, 20 base coating layer, 30 insulating coating layer, 31 Stomata

Claims

1. an electrical steel sheet substrate containing 2.0 to 7.0 wt % Si, 0.01 to 0.10 wt % Sn, 0.01 to 0.07 wt % Sb, 0.020 to 0.040 wt % Al, 0.01 to 0.20 wt % Mn, 0.01 wt % or less C, 0.005 wt % or less N, and 0.005 wt % or less S, with the balance being Fe and other unavoidable impurities; a fine-grained interface layer located from the surface of the electrical steel sheet substrate toward the interior of the electrical steel sheet substrate; a base coating layer located on the fine-grained interfacial layer; and The insulating coating layer is located on the base coating layer, and satisfies the following formula 1, and the fine grain interface layer has an average crystal grain size of 0.1 to 5 μm, the insulating coating layer contains pores with a diameter of 10 nm or more; the electromagnetic steel sheet substrate has sub-grains in a region (A) within 1500 μm from the center of the pore in the RD direction and in a region (B) from the surface of the electromagnetic steel sheet substrate toward the interior of the electromagnetic steel sheet substrate, The subgrains have a crystal orientation at an angle of 1° to 15° from {110}<001>; A grain-oriented electrical steel sheet characterized in that the area fraction of subgrains in an ND cross section is 5% or less. [Formula 1] ([P]×[PS]+[F]×[FS]+[C]×[CS]) / -([S] / 2)≧13.0MPa (In Equation 1, [P] represents the thickness (μm) of the insulating coating layer, [PS] represents the residual stress (MPa) in the RD direction of the insulating coating layer, [F] represents the thickness (μm) of the base coating layer, [FS] represents the residual stress (MPa) in the RD direction of the base coating layer, [C] represents the thickness (μm) of the fine-grained interface layer, [CS] represents the residual stress (MPa) in the RD direction of the fine-grained interface layer, and [S] represents the thickness (μm) of the electrical steel sheet substrate.)

2. 2. The grain-oriented electrical steel sheet according to claim 1, wherein the residual stress in the RD direction of the base coating layer is −50 to −1500 MPa.

3. 3. The grain-oriented electrical steel sheet according to claim 1, wherein the insulating coating layer has a residual stress in the RD direction of −10 to −1000 MPa.

4. The grain-oriented electrical steel sheet according to any one of claims 1 to 3, characterized in that the electrical steel sheet substrate has a residual stress in the RD direction of 1 to 50 MPa.

5. The grain-oriented electrical steel sheet according to any one of claims 1 to 4, wherein the fine grain interface layer has a residual stress in the RD direction of -10 to -1000 MPa.

6. The grain-oriented electrical steel sheet according to any one of claims 1 to 5, wherein the fine grain interface layer has a thickness of 0.1 to 5 µm.

7. The grain-oriented electrical steel sheet according to any one of claims 1 to 6, wherein the base coating layer has a thickness of 0.1 to 15 µm.

8. The grain-oriented electrical steel sheet according to any one of claims 1 to 7, wherein the insulating coating layer has a thickness of 0.1 to 15 µm.

9. manufacturing a grain-oriented electrical steel sheet substrate containing 2.0 to 7.0 wt % Si, 0.01 to 0.10 wt % Sn, 0.01 to 0.07 wt % Sb, 0.020 to 0.040 wt % Al, 0.01 to 0.20 wt % Mn, 0.01 wt % or less C, 0.005 wt % or less N, and 0.005 wt % or less S, with the balance being Fe and other unavoidable impurities; applying an insulating coating layer-forming composition onto the grain-oriented electrical steel sheet substrate; and heat-treating the grain-oriented electrical steel sheet substrate to form an insulating coating layer on the grain-oriented electrical steel sheet substrate, In the step of forming the insulating coating layer, the tension applied to the steel sheet is 0.2 to 0.70 kgf / mm ２ and The method for producing a grain-oriented electrical steel sheet according to any one of claims 1 to 8, characterized in that the maximum (MA) and minimum (MI) tension values ​​with respect to the entire length of the steel sheet satisfy the following formula 2: [Formula 2] [MI]≧0.5×[MA]

10. 10. The method of claim 9, wherein the insulating coating layer is formed by heat treatment at a temperature of 550 to 1100°C.

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