Grain-oriented electrical steel sheet and method of manufacturing the same

Abstract

A method of manufacturing an oriented electrical steel sheet according to one embodiment of the present application includes a step of manufacturing a slab containing, in weight %, Si: 1.5 to 4.5 %, C: 0.70 % or less except 0 %, Mn: 1.0 % or less except 0 %, and the balance containing Fe and other inevitable impurities; a step of hot-rolling the slab to manufacture a hot-rolled sheet; a step of cold-rolling the hot-rolled sheet to manufacture a cold-rolled sheet; a step of primary recrystallization annealing the cold-rolled sheet; and a step of secondary recrystallization annealing the steel sheet after the primary recrystallization annealing. The step of secondary recrystallization annealing includes a first temperature rising step in which the steel sheet temperature is 650 °C to 900 °C, a second temperature rising step in which the steel sheet temperature exceeds 900 °C to not more than a soaking temperature, and a soaking step. After the first temperature rising step, a thickness of 10 µm range from the surface of the steel sheet to the inside of the steel sheet contains 2 to 15 weight % of forsterite, and after the second temperature rising step, contains 85 to 100 weight % of forsterite.

Description

Technical Field

[0001] One embodiment of the present invention relates to an oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to an oriented electrical steel sheet and a method for manufacturing the same, wherein the degree of oxidation is appropriately adjusted during the secondary recrystallization annealing process to reduce the deviation between the size of the magnesium olivine grains and the size of the secondary recrystallized grains in the width direction of the steel sheet, and to reduce the magnetic deviation in the width direction of the steel sheet. Background Technology

[0002] Oriented grain electrical steel is a soft magnetic material that exhibits a so-called Gaussian texture, where all grains on the steel surface are oriented with {110} planes, and the grain orientation along the rolling direction is consistent with... <001> The axes are parallel, resulting in excellent magnetic properties in the rolling direction of the steel sheet. Generally, the magnetic properties of electrical steel sheets can be represented by magnetic flux density and iron loss, and high magnetic flux density can be achieved by precisely arranging the grain orientation as {110}. <001> The orientation is used to obtain this. Electrical steel plates with high magnetic flux density not only reduce the size of the core material in electrical equipment, but also enable miniaturization and increased efficiency of electrical equipment due to reduced hysteresis losses. Iron loss refers to the electrical energy loss in the form of heat when an arbitrary alternating magnetic field is applied to a steel plate. It varies significantly with factors such as the magnetic flux density, plate thickness, amount of impurities in the steel plate, resistivity, and secondary recrystallization grain size. Higher magnetic flux density and resistivity, as well as lower plate thickness and lower impurity levels in the steel plate, result in lower iron loss, thereby improving the efficiency of electrical equipment.

[0003] On the surface of such grain-oriented electrical steel sheets, a forsterite coating formed during secondary recrystallization annealing is applied as an insulating coating agent during the final heat flattening process, thus producing the final product. This forsterite coating not only imparts surface insulation but also instills tensile stress into the steel sheet due to the difference in thermal expansion between it and the base metal, thereby improving iron loss or hysteresis characteristics. The formation state of the forsterite coating on the steel sheet surface affects not only the insulation performance and magnetic property improvement but also the operability of the core processing, product appearance, and other commercial value; therefore, it is necessary to form a uniform and stable forsterite coating.

[0004] In the manufacturing of grain-oriented electrical steel sheets, to form a forsterite coating, the cold-rolled steel sheet to its final thickness needs to undergo decarburization annealing in a humid atmosphere to form oxides mainly composed of Fe2SiO4 and SiO2. These oxides play an important role in the primary recrystallization and forsterite coating formation process. Subsequently, an annealing release agent mainly composed of MgO is coated onto the steel sheet, which is then dried, rolled into coils, and subjected to a secondary recrystallization annealing to form the forsterite coating.

[0005] During secondary recrystallization annealing, the formation of the forsterite coating involves the reaction of MgO, the main component of the annealing isolator, with SiO2, the main component of the oxides formed during primary recrystallization annealing, thus forming the coating (2MgO + SiO2 -> Mg2SiO4). When AlN is used as a depressant, spinel-structured compounds such as Al2O3, MgO, and SiO2 form near the bottom of the forsterite coating. This forsterite coating formation behavior also affects the behavior of depressants such as MnS and AlN in the steel, and therefore also influences the secondary recrystallization process, which is essential for obtaining excellent magnetic properties.

[0006] In other words, when the formation of the forsterite coating is delayed or uneven, or when the quantity and quality of the coating are unsuitable, oxygen (O) and nitrogen (N) in the annealing atmosphere can easily penetrate into the steel, leading to the decomposition and coarsening of the inhibitors in the steel, thus affecting the inhibitor strength. Furthermore, the forsterite coating formed during the secondary recrystallization annealing process plays a role in extracting and purifying the inhibitors that are no longer needed after the secondary recrystallization, thereby reducing hysteresis loss.

[0007] Therefore, the uniform formation of magnesium olivine coating and the control of its formation process are important factors affecting the quality of oriented electrical steel sheets. Summary of the Invention

[0008] (a) Technical problems to be solved One embodiment of the present invention provides an oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention provides an oriented electrical steel sheet and a method for manufacturing the same, wherein the degree of oxidation is appropriately adjusted during the secondary recrystallization annealing process to reduce the deviation between the magnesium olivine grain size and the secondary recrystallized grain size in the width direction of the steel sheet, and to reduce the magnetic deviation in the width direction of the steel sheet.

[0009] (II) Technical Solution A method for manufacturing an oriented electrical steel sheet according to an embodiment of the present invention includes: a step of manufacturing a slab, wherein the slab comprises, by weight %, Si: 1.5 to 4.5%, C: less than 0.70% and excluding 0%, Mn: less than 1.0% and excluding 0%, with the balance comprising Fe and other unavoidable impurities; a step of hot rolling the slab to manufacture a hot-rolled sheet; a step of cold rolling the hot-rolled sheet to manufacture a cold-rolled sheet; a step of performing a first recrystallization annealing on the cold-rolled sheet; and a step of performing a second recrystallization annealing on the steel sheet after the first recrystallization annealing.

[0010] The secondary recrystallization annealing step includes a first heating step with a steel plate temperature of 650°C to 900°C, a second heating step with a steel plate temperature exceeding 900°C but not exceeding the soaking temperature, and a soaking step.

[0011] After the first heating step, the steel plate contains 2 to 15% by weight of forsterite over a thickness of 10 μm from the surface to the interior of the steel plate, and after the second heating step, it contains 85 to 100% by weight of forsterite.

[0012] The slab may also contain one or more of Al: 0.015 to 0.040% by weight, N: less than 0.0055% by weight, and S: less than 0.0055% by weight.

[0013] The slab may also contain one or more of Sn: 0.03 to 0.10 wt%, Sb: 0.01 to 0.05 wt%, P: 0.01 to 0.10 wt%, Cu: 0.001% to 0.1 wt%, and Cr: 0.01% to 0.50 wt%.

[0014] After the first recrystallization annealing step and before the second recrystallization annealing step, an annealing release agent is applied. The annealing release agent may contain 100 parts by weight of MgO and 0.01 to 0.50 parts by weight of additives with a melting point below 900°C.

[0015] The additive may contain one or more of the following: hydroxides, carbonates, amide compounds, chromates, oxides, antimony compounds, chlorine compounds, chlorine oxides, sulfur compounds, nitrogen compounds, bromides, bromates, telluric acid, vanadates, borates, and phosphorus compounds.

[0016] The additive may contain one or more of the following: Li, F, Na, K, Cu, Ba, Br, Mg, Ca, Zn, Sr, Cd, B, Al, Y, Ga, In, Tl, Ti, Sn, P, Nb, Sb, Bi, S, Cr, Te, V, W, Fe, Mn, Co, and Ni.

[0017] The additive may contain one or more of the following: SrCl2, Sb2O3, FeBr2, CuCl, MnCl2, B2O3, NiSO4, CoSO4, CuBr, and SnS.

[0018] The hydration content of MgO can be 1.2% to 2.5%.

[0019] The first heating step may contain 10 to 50% by volume N2 and 50 to 90% by volume H2, the second heating step may contain less than 30% by volume N2 and more than 70% by volume H2, and the homogenization step may contain more than 99% by volume H2.

[0020] The first heating step is carried out at a heating rate of 5°C / hour (hr) to 90°C / hour, and the second heating step is carried out at a heating rate of 5°C / hour to 30°C / hour.

[0021] According to an embodiment of the present invention, the oriented electrical steel sheet comprises, by weight % (wt%), C: less than 0.005% and excluding 0%, Si: 1.5% to 4.5%, Mn: less than 1.0%, with the balance including Fe and other unavoidable impurities. One or both sides of the steel sheet matrix have a forsterite layer. The average grain size (P1) of the forsterite particles present in the forsterite layer at one end or 30% of the total width of the steel sheet from one end and the edge from 70% of the total width of the steel sheet from one end to the other end, and the ratio (P2 / P1) of the average grain size (P2) of the forsterite particles present in the forsterite layer at the center of the steel sheet from one end to more than 30% to no more than 70% of the total width of the steel sheet is 0.8 to 1.2.

[0022] Furthermore, the ratio (R2 / R1) of the average grain size (R1) of secondary recrystallization present in the edge portion to the average grain size (R2) of secondary recrystallization present in the center portion is 0.7 to 1.2.

[0023] According to one embodiment of the present invention, the oriented electrical steel sheet may further contain one or more of Al: less than 0.040 wt%, N: less than 0.0050 wt%, and S: less than 0.005 wt%.

[0024] The oriented electrical steel sheet according to one embodiment of the present invention may further contain one or more of Sn: 0.03 to 0.10 wt%, Sb: 0.01 to 0.05 wt%, P: 0.01 to 0.10 wt%, Cu: 0.001% to 0.1 wt%, and Cr: 0.01 to 0.50 wt%.

[0025] The average grain size of the forsterite particles in the edge forsterite layer can be 0.3 to 2.0 μm, and the average grain size of the forsterite particles in the central forsterite layer can be 0.3 to 2.0 μm.

[0026] The average grain size of the secondary recrystallization present in the edge portion can be 1.0 to 4.5 cm, and the average grain size of the secondary recrystallization present in the center portion can be 0.7 to 4.0 cm.

[0027] (III) Beneficial Effects According to an embodiment of the present invention, the oriented electrical steel sheet can reduce the magnetic deviation in the width direction of the steel sheet and uniformly improve the magnetism in the width direction of the steel sheet. Attached Figure Description

[0028] Figure 1 This is a schematic diagram illustrating an oriented electrical steel sheet according to an embodiment of the present invention.

[0029] Figure 2 This is a schematic diagram illustrating the coil-shaped steel sheet in the secondary recrystallization annealing step of one embodiment of the present invention. Detailed Implementation

[0030] The terms "first," "second," "third," etc., are used to describe parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, or segment from another. Therefore, without departing from the scope of the invention, the first part, component, region, layer, or segment described below can also be described as a second part, component, region, layer, or segment.

[0031] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular forms used herein are intended to include the plural forms as well. The word "comprising" as used in the specification can specifically refer to a particular feature, domain, integer, step, action, element, and / or component, but does not exclude the presence or addition of other features, domains, integers, steps, actions, elements, components, and / or groups.

[0032] When one part is described as being on top of another part, there can be other parts directly on top of the other part or in between. When one part is described as being directly on top of another part, there are no other parts in between.

[0033] Although not otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in dictionaries should be interpreted as having the same meaning as disclosed in relevant technical literature and herein, and should not be interpreted in an idealized or overly formal sense.

[0034] Furthermore, unless otherwise specified, % means by weight, and 1 ppm is 0.0001 by weight.

[0035] In one embodiment of the present invention, the inclusion of additional elements refers to the replacement of a portion of the remaining iron (Fe) by additional elements, the replacement amount being equivalent to the amount of additional elements added.

[0036] Embodiments of the present invention will be described in detail below to enable those skilled in the art to implement the invention. However, the invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0037] A method for manufacturing an oriented electrical steel sheet according to an embodiment of the present invention includes: a step of manufacturing a slab, wherein the slab comprises, by weight %, Si: 1.5 to 4.5%, C: less than 0.70% and excluding 0%, Mn: less than 1.0% and excluding 0%, with the balance comprising Fe and other unavoidable impurities; a step of hot rolling the slab to manufacture a hot-rolled sheet; a step of cold rolling the hot-rolled sheet to manufacture a cold-rolled sheet; a step of performing a first recrystallization annealing on the cold-rolled sheet; and a step of performing a second recrystallization annealing on the steel sheet after the first recrystallization annealing.

[0038] The following sections will describe each step in detail.

[0039] First, the slab is manufactured.

[0040] The slab contains, by weight percent, Si: 1.5 to 4.5%, C: less than 0.70% and excluding 0%, Mn: less than 1.0% and excluding 0%, with the balance containing Fe and other unavoidable impurities.

[0041] The reasons for limiting the amount added are described below for each element.

[0042] C: less than 0.70% by weight Carbon (C) is an element that promotes the austenite phase transformation, resulting in a uniform microstructure during hot rolling of grain-oriented electrical steel sheets. During cold rolling, it promotes the formation of Gaussian-oriented grains, making it a crucial element for manufacturing magnetically superior grain-oriented electrical steel sheets. If too much C is added, the austenite phase transformation during hot rolling leads to a finer hot-rolled microstructure. This results in finer primary recrystallized grains, which may form carbides during the coiling process after hot rolling or during cooling after annealing, and may also form Fe3C (cementite) at room temperature, easily causing microstructure inhomogeneity. Simultaneously, the time required for decarburization to below 30 ppm during the post-cold rolling decarburization process increases, leading to excessive formation of fayalite and silica on the steel sheet surface. Therefore, the C content can be below 0.70% by weight. More specifically, it can be from 0.01 to 0.50% by weight. More specifically, it can be from 0.03 to 0.10% by weight.

[0043] C is removed through decarburization during a single recrystallization annealing process, and the final oriented electrical steel sheet may contain less than 0.005% by weight. More specifically, it may contain less than 0.003% by weight. More specifically, it may contain 0.0001 to 0.0030% by weight.

[0044] Si: 1.5 to 4.5% by weight Silicon (Si) is a fundamental component of electrical steel sheets, its role being to increase the material's resistivity to reduce core loss, i.e., iron loss. If too little Si is added, the resistivity decreases, the reduction in eddy current loss is weak, and the amount of fir olivine formed during decarburization will be insufficient, potentially leading to unstable magnesium olivine coating formation. On the other hand, if too much Si is added, the steel becomes more brittle, making cold rolling difficult, and the surface quality may deteriorate due to the large amount of fir olivine formed during decarburization. Therefore, Si can be contained in the steel at 1.5 to 4.5% by weight. More specifically, it can be contained in the steel at 2.5 to 3.5% by weight.

[0045] Mn: less than 1.0% by weight Like Si, manganese (Mn) increases resistivity and reduces iron loss. However, when a large amount of Mn is added, compared with the reduction in iron loss caused by the increase in resistivity, the decrease in saturation magnetic flux density and the formation of coarse MnS precipitates weaken the grain growth inhibition force, resulting in a decrease in magnetic flux density after secondary recrystallization annealing. It also affects the composition of fir olivine and silica formed during decarburization, thus hindering the formation of a good magnesium olivine coating.

[0046] Therefore, to form a forsterite coating with excellent magnetic flux density and adhesion, the Mn content needs to be optimized. However, if too much Mn is added, it promotes the precipitation of coarse MnS. To dissolve the MnS precipitates, the slab needs to be heated to above 1150°C, which presents problems. Furthermore, it may hinder the formation of high-quality fir olivine and silica during decarburization. Therefore, the Mn content can be less than 1.0% by weight. More specifically, the Mn content can be from 0.1% to 0.5% by weight.

[0047] The slab may also contain one or more of Al: 0.015 to 0.040% by weight, N: less than 0.0055% by weight, and S: less than 0.0055% by weight.

[0048] Al: 0.015 to 0.040% by weight Aluminum (Al) combines with nitrogen to form AlN precipitates, which are typical grain growth inhibitors used to inhibit secondary recrystallization in oriented electrical steel sheets. In one embodiment of the invention, (Al,Si,Mn)N precipitates are formed by nitriding annealing after cold rolling, thereby ensuring grain growth inhibition, particularly by controlling the precipitation of precipitates in the width direction of the steel sheet to reduce magnetic deviation in the width direction. In the steelmaking process, the amount of Al added is preferably 0.015 to 0.040% by weight. If too little Al is added, the total amount of (Al,Si,Mn)N precipitates formed during primary recrystallization and nitriding annealing is very limited, which may result in insufficient inhibition of primary recrystallization grain growth. On the other hand, if too much Al is added, the precipitates will grow coarsely during slab manufacturing and hot rolling processes, resulting in coarse microstructures during nitriding annealing, which may lead to instability in the formation of secondary recrystallization during subsequent secondary recrystallization annealing. Therefore, the Al content in the slab can be 0.015 to 0.040% by weight. More specifically, it can be 0.020 to 0.035 by weight.

[0049] During the secondary recrystallization annealing process, some Al can be removed by purification annealing, and the final oriented electrical steel sheet can contain less than 0.040% by weight of Al. More specifically, it can contain 0.010 to 0.040% by weight.

[0050] N: less than 0.0055% by weight Nitrogen (N) is a key element that reacts with Al to form AlN precipitates, which inhibit grain growth. In methods for producing (Al,Si,Mn)N precipitates by nitriding after cold rolling, the steelmaking process does not require a large amount of N. However, if too little N is added, fine AlN precipitates form during slab manufacturing, resulting in smaller primary recrystallized grains and making precisely Gaussian oriented grains more susceptible to secondary recrystallization. Conversely, if too much N is added, coarse AlN precipitates form during slab manufacturing, resulting in a coarse primary recrystallized microstructure and subsequent instability in secondary recrystallization. Therefore, the range of N can be limited to below 0.0055% by weight. More specifically, N can be present from 0.0010 to 0.0050% by weight. More specifically, it can be present from 0.0030 to 0.0050% by weight.

[0051] On the other hand, in one embodiment of the present invention, nitriding may occur during the primary recrystallization annealing process, and some N can be removed by purification annealing during the subsequent secondary recrystallization annealing process, so that the final oriented electrical steel sheet may contain less than 0.0050% by weight of N. More specifically, it may contain 0.001 to 0.005% by weight.

[0052] S: less than 0.0055% by weight Sulfur (S) typically reacts with Mn and Cu to form MnS or Cu₂S precipitates, thus acting as an inhibitor of primary recrystallization grain growth. To ensure fine MnS precipitates, the added Mn and S need to be completely dissolved under slab heating conditions below 1150°C to exert an effective inhibitory effect. Therefore, it is preferable to add S within the range of Mn addition amount and reactive S content. If too much S is added, complete dissolution is difficult, potentially leading to coarse MnS precipitates. Simultaneously, S is an element prone to grain boundary or surface segregation, especially during high-temperature annealing when S diffuses to the surface of the steel sheet, causing surface segregation. This hinders the formation of the forsterite coating through the reaction of fir olivine and silica with MgO, resulting in poor adhesion of the forsterite coating. Therefore, S can be contained in amounts less than 0.0055% by weight. Specifically, it can be contained in amounts from 0.001 to 0.005% by weight. More specifically, it can be contained in amounts from 0.0020 to 0.0045% by weight. During the secondary recrystallization annealing process, some sulfur can be removed through purification annealing, and the final oriented electrical steel sheet can contain less than 0.005% by weight of sulfur. More specifically, it can contain 0.001 to 0.005% by weight.

[0053] The slab may also contain one or more of Sn: 0.03 to 0.10 wt%, Sb: 0.01 to 0.05 wt%, P: 0.01 to 0.10 wt%, Cu: 0.001% to 0.1 wt%, and Cr: 0.01% to 0.50 wt%.

[0054] Sn: 0.03 to 0.10% by weight Tin (Sn) is an auxiliary grain growth inhibitor; it segregates at grain boundaries, thus hindering grain boundary movement, with a significant effect. This compensates for the weakening effect of inhibiting grain growth as AlN particles coarsen and Si content increases. Therefore, even with a relatively high Si content, successful {110} formation can be guaranteed. <001> Secondary recrystallization texture. That is, without weakening {110} at all. <001> While maintaining the integrity of the secondary recrystallization structure, not only can the Si content be increased, but the final thickness can also be reduced. Therefore, further addition of Sn may improve magnetism. If too little Sn is added, the aforementioned effects cannot be fully obtained. On the other hand, if too much Sn is added, brittleness may increase. Therefore, when further adding Sn, 0.03 to 0.10% by weight can be added. More specifically, 0.04 to 0.07% by weight can be added.

[0055] Sb: 0.01 to 0.05% by weight Antimony (Sb) segregates at grain boundaries, thus inhibiting excessive growth of primary recrystallized grains. Therefore, further addition of Sb may improve magnetism. If too little Sb is added, the aforementioned effect cannot be achieved. On the other hand, if too much Sb is added, the size of the primary recrystallized grains becomes excessively small, the initiation temperature of secondary recrystallization decreases, leading to deterioration of magnetic properties or excessive inhibition of grain growth, potentially resulting in the failure of secondary recrystallization. Therefore, when further adding Sb, 0.01 to 0.05% by weight can be added. More specifically, 0.015 to 0.035% by weight can be added.

[0056] P: 0.01% to 0.10% by weight Phosphorus (P) promotes the growth of primary recrystallized grains, thus increasing the secondary recrystallization temperature and consequently improving the final product's {110} content. <001> The role of orientation concentration. When the primary recrystallized grains are too large, secondary recrystallization becomes unstable. However, as long as secondary recrystallization occurs, larger primary recrystallized grains are beneficial for magnetism in order to increase the secondary recrystallization temperature. On the other hand, P not only increases the {110} ion concentration in the steel sheet after primary recrystallization. <001> The number of oriented grains reduces the iron loss in the final product, and also reduces the iron loss in the primary recrystallized plate {111} <112> The highly developed texture enhances the final product's {110}. <001> The concentration of phosphorus (P) increases the magnetic flux density. Furthermore, during secondary recrystallization annealing, P segregates to the grain boundaries at temperatures up to approximately 1000°C, delaying the decomposition of the precipitates and thus enhancing the suppressive force. Therefore, further addition of P may be beneficial to magnetism. If too little P is added, the aforementioned effects cannot be fully achieved. On the other hand, if too much P is added, the size of the primary recrystallized grains decreases, making secondary recrystallization unstable and potentially increasing brittleness and impairing cold-rollability. Therefore, when further adding P, 0.01 to 0.10% by weight can be added. More specifically, 0.015 to 0.050% by weight can be added.

[0057] Cu: 0.001 to 0.1% by weight Copper (Cu) reacts with sulfur (S) to form Cu₂S precipitates, thereby acting as an inhibitor of primary recrystallization grain growth. When added together with Mn, the size of the MnS precipitates is also affected due to the formation of [MnCu]S composite precipitates. If too little Cu is added, only a small amount of Cu₂S precipitates will form, and the inhibitory effect may be low. On the other hand, if too much Cu is added, it will precipitate in the steel with S before Mn, thus failing to obtain the fine MnS precipitates desired in this invention. Therefore, the Cu content is preferably limited to the range of 0.001 to 0.100% by weight. More specifically, it may contain 0.010 to 0.070% by weight.

[0058] Cr: 0.01 to 0.50% by weight Chromium (Cr) is the first element to react with oxygen to form Cr₂O₃ on the steel plate surface. This allows carbon components in the steel to rapidly diffuse to the surface and react with oxygen in the atmosphere to form CO gas, thus promoting decarburization. If too little Cr is added, the aforementioned effect cannot be fully achieved. If too much Cr is added, it will not significantly affect the formation of the surface oxide layer. Therefore, the amount of Cr added is limited to 0.01 to 0.50% by weight. More specifically, it can contain 0.03 to 0.30% by weight.

[0059] Iron (Fe) is included as a balance. In addition, unavoidable impurities may be included. Unavoidable impurities are those that are unavoidably introduced during the steelmaking and manufacturing processes of grain-oriented electrical steel sheets. Since unavoidable impurities are well-known, specific descriptions are omitted. In one embodiment of the invention, the addition of other elements besides the aforementioned alloy composition is not excluded, and various elements may be included without affecting the technical concept of the invention. When additional elements are further included, they replace a portion of the balance Fe. For example, within the composition range of the invention, the steel may also contain at least one of Ni, Mo, Zr, Bi, Pb, As, Ge, and Ga.

[0060] Returning to the description of the manufacturing process, the slab is heated to below 1150°C. The slab can be manufactured using segmented casting, continuous casting, thin slab casting, or casting methods. When segmented casting, continuous casting, or thin slab casting are used, the slab is manufactured first, and then heated and hot rolled in subsequent processes.

[0061] Slab heating is essentially based on the manufacturing method of grain-oriented electrical steel sheets. This method ensures the formation of AlN-based precipitates, i.e., (Al,Si,Mn)N precipitates, the main crystal growth inhibitor required for secondary recrystallization of Gaussian orientation, through decarburization and nitriding annealing after cold rolling. Therefore, hot rolling can be performed after heating the slab to below 1150°C. In this slab heating and hot rolling process, in order to successfully form fine MnS as an auxiliary crystal growth inhibitor, the amount of Mn and S added is limited in the steelmaking steps so that the solution temperature of the MnS precipitates formed by the reaction of added Mn and S is below 1150°C.

[0062] If the slab is heated to excessively high temperatures, the AlN precipitates formed during the solidification process of slab manufacturing will undergo excessive dissolution during the slab heating step. These precipitates will then precipitate finely during subsequent hot rolling, leading to finer grain sizes during hot rolling and decarburization, thus hindering the secondary recrystallization of precisely Gaussian oriented grains. Within the range where the precipitated MnS can be completely dissolved, depending on the added Mn and S content, a lower slab heating temperature is better. However, considering the specific hot rolling load, heating can be performed between 1000°C and 1150°C.

[0063] Next, the slab is hot-rolled to produce hot-rolled plates.

[0064] For hot rolling, the thickness is 1.0 to 3.5 mm. Considering the rolling load, rolling can be completed at a temperature above 850°C and then cooled to a temperature below 600°C for coiling.

[0065] For hot-rolled steel sheets, the subsequent hot-rolled sheet annealing process recrystallizes the deformed structure formed during hot rolling, enabling the subsequent cold rolling process to smoothly achieve the final product thickness. Typically, for hot-rolled sheet annealing, to achieve recrystallization, it is preferable to heat to a temperature above 800°C and hold for a certain time. To control the distribution and size of precipitates, annealing at multiple temperatures can also be used. Hot-rolled sheet annealing can also be omitted if necessary.

[0066] Next, the hot-rolled sheet is cold-rolled to produce a cold-rolled sheet.

[0067] For hot-rolled sheets, the oxide layer on the steel surface is removed by pickling before cold rolling. Cold rolling is a process that reduces the thickness of the steel sheet to the final product thickness, achieved through a single cold rolling operation or multiple cold rolling operations with intermediate annealing. At this stage, the cold rolling rate increases the concentration of Gaussian orientation, thus affecting the increase in magnetic flux density after the final secondary recrystallization annealing. Therefore, cold rolling can be performed at a minimum rolling rate of 80% or higher. If the cold rolling rate is too low, the concentration of Gaussian orientation will be low, and the magnetic flux density of the final product will decrease. Therefore, the minimum cold rolling rate is 80% or higher, and for the maximum rolling rate, rolling is performed to the maximum rollable range based on the rolling capacity of the rolling equipment. Furthermore, when the plate temperature of the cold-rolled steel sheet increases by more than 50°C during cold rolling, work hardening caused by dissolved carbon will generate many secondary recrystallization nuclei with Gaussian orientation, thereby increasing the magnetic flux density of the final product. If the temperature of the cold-rolled steel sheet is too low, the formation of secondary recrystallization nuclei in the Gaussian orientation is very limited. If the temperature exceeds 300°C, the work hardening effect caused by solid solution carbon is weakened, and the formation of secondary recrystallization nuclei in the Gaussian orientation becomes less pronounced. Therefore, in the cold rolling process, the steel sheet undergoes at least one temperature range of 50 to 300°C during intermediate rolling steps. The thickness of the cold-rolled sheet can be 0.10 to 0.35 mm.

[0068] Next, the cold-rolled sheet undergoes a recrystallization annealing process.

[0069] The primary recrystallization annealing temperature can be between 800 and 950°C. If the annealing temperature of the steel sheet is too low, the time required for decarburization and nitriding is too long, making it difficult to form a proper metal oxide layer. If the annealing temperature is too high, the primary recrystallization grains will grow coarsely, the crystal growth driving force will be reduced, and stable secondary recrystallization may not be formed. The annealing time does not pose a significant problem for achieving the effects of this invention, but for productivity purposes, a time of less than 5 minutes is acceptable.

[0070] Decarburization and nitriding can be performed during a single recrystallization annealing process. Decarburization and nitriding can be performed after nitriding, after nitriding, or simultaneously.

[0071] For nitriding, a nitriding gas can be added as an atmosphere gas during a single recrystallization annealing process. This nitriding gas can contain ammonia. Introducing nitrogen ions into the steel sheet through nitriding can facilitate the precipitation of inhibitors such as (Al,Si,Mn)N and AlN.

[0072] After nitriding, the nitrogen content in the steel sheet can be from 0.0120 to 0.0280% by weight. If the nitrogen content is too low, it will be difficult to act as an inhibitor before secondary recrystallization begins. If the nitrogen content is too high, excessive nitride formation will not only hinder the formation of normal secondary recrystallization, but also, after secondary recrystallization, the N2 gas decomposed during purification may lead to coating defects such as bare spots. More specifically, the nitrogen content in the steel sheet can be from 0.0150 to 0.0250% by weight.

[0073] For nitriding gases, any gas capable of penetrating nitrogen into the steel plate can be used without restriction. Specifically, it can be ammonia or nitrogen. In an ammonia atmosphere, nitriding can be achieved through heat treatment, while in a nitrogen atmosphere, nitriding can be achieved through laser or plasma treatment, etc.

[0074] For a single recrystallization annealing step, decarburization, which removes carbon from the steel sheet, can be achieved by conducting the process in an atmosphere with an oxidation degree (PH2O / PH2) of 0.45 to 0.80. If the oxidation degree is too low, sufficient oxidation or decarburization is difficult to occur. If the oxidation degree is too high, FeO may rapidly form on the outermost layer of the oxide film, resulting in unstable oxides. More specifically, the oxidation degree can be between 0.48 and 0.75.

[0075] After a single recrystallization annealing step, an oxide layer with an average thickness of 1.6 to 3.2 μm may remain on the surface of the steel sheet. During single recrystallization annealing, an oxide layer is formed near the surface of the steel sheet due to decarburization. The oxide layer refers to the area from the surface of the steel sheet where the oxygen content changes abruptly. If the oxide layer is too thin, the magnetic inhomogeneity increases. If the oxide layer is too thick, a thicker metal oxide layer forms, the thickness of the base material is relatively reduced, and the magnetic properties may deteriorate.

[0076] After the first recrystallization annealing and before the second recrystallization annealing, a step of applying an annealing release agent may be included. In one embodiment of the invention, by using an annealing release agent containing a low-melting-point additive, the particle size of the forsterite particles can be uniformly formed. The low-melting-point additive refers to an additive with a melting point below 900°C. With such a low-melting-point additive, further oxidation and nitriding of the steel sheet are prevented during the second recrystallization annealing process, and the particle size of the forsterite particles in the width direction of the steel sheet can be uniformly formed. More specifically, the low-melting-point additive may have a melting point of 750°C.

[0077] Specifically, the additive may contain one or more of the following: hydroxides, carbonates, amide compounds, chromates, oxides, antimony compounds, chlorine compounds, chlorine oxides, sulfur compounds, nitrogen compounds, bromides, bromates, telluric acid, vanadates, borates, and phosphorus compounds.

[0078] In addition, the additive may contain one or more of the following: Li, F, Na, K, Cu, Ba, Br, Mg, Ca, Zn, Sr, Cd, B, Al, Y, Ga, In, Tl, Ti, Sn, P, Nb, Sb, Bi, S, Cr, Te, V, W, Fe, Mn, Co, and Ni.

[0079] As an example of an additive, it may contain one or more of SrCl2, Sb2O3, FeBr2, CuCl, MnCl2, B2O3, NiSO4, CoSO4, CuBr, and SnS.

[0080] The additive may contain 0.01 to 0.50 parts by weight relative to 100 parts by weight of MgO. Parts by weight refers to the relative weight ratio of each component, determined by removing all moisture from the solids. If too little low-melting-point additive is added, it will be difficult to sufficiently promote the formation of a low-melting-point vitreous layer or a forsterite coating. If too much low-melting-point additive is added, pinhole-like localized melting defects may occur. More specifically, the low-melting-point additive may contain 0.05 to 0.30 parts by weight.

[0081] The annealing release agent contains 100 parts by weight of MgO. MgO can also exist in water as Mg(OH)2. In one embodiment of the present invention, when MgO is mentioned, it should be understood as including both MgO and Mg(OH)2, and the content of MgO can be understood as the total amount of MgO and Mg(OH)2.

[0082] The hydration moisture content of MgO can be 1.2 to 2.5% by weight. This hydration moisture content, along with the aforementioned low-melting-point additives, contributes to the uniform formation of forsterite particles in the width direction of the steel plate. If the hydration moisture content is too low, insufficient moisture is used to semi-wet the atmosphere between the steel plates, resulting in a thinner forsterite coating at the center in the width direction and potentially uneven formation of forsterite particles. On the other hand, if the hydration moisture content is too high, excessive moisture content between the steel plates leads to over-oxidation at the edges, potentially increasing oxidation defects. More specifically, the hydration moisture content of MgO can be 1.5 to 2.3% by weight. The hydration moisture content of MgO refers to the total amount of residual moisture in the steel plate and the moisture remaining in the Mg(OH)2 state after the MgO powder and pure water at approximately 12°C are mixed into a slurry and coated onto the steel plate for drying. To determine the hydration level of MgO, a small amount of MgO from a dried steel plate can be weighed, and the weight of MgO after heat treatment at 1000℃ for 1 hour can also be measured. The difference between these measurements is defined as the hydration level of MgO.

[0083] In addition to MgO and low-melting-point additives, the annealing separator may further contain ceramic powders such as TiO2, SiO2, and Al2O3. When one or more of TiO2, SiO2, and Al2O3 are added, the amount may be 1 to 10 parts by weight relative to 100 parts by weight of MgO.

[0084] Next, the steel sheet after the first recrystallization annealing is subjected to a second recrystallization annealing.

[0085] During secondary recrystallization annealing, the steel sheet is rolled into a coil shape and then annealed for a long time. Figure 1 The image schematically illustrates a steel plate according to an embodiment of the present invention. Figure 2 The image schematically shows a steel sheet wound into a coil shape.

[0086] Figure 1 One end 101 corresponds to the upper end 101 of the roll plate. Figure 2 The other end 102 corresponds to the lower end 102 of the coil. The upper end 101 and lower end 102 of the coil are in direct contact with the air of the external atmosphere along with the adjacent edge portion 110, and therefore will be over-oxidized compared to the inner center portion 120, resulting in uneven particle size of the forsterite particles between the edge portion 110 and the center portion 120.

[0087] In one embodiment of the invention, the atmosphere conditions are changed according to the thermal history of the steel plate during the secondary recrystallization annealing process, thereby enabling the uniform formation of the forsterite particles between the edge portion 110 and the center portion 120. This uniformly formed forsterite particles also influences the secondary recrystallization, resulting in a uniform particle size in the secondary recrystallized material.

[0088] Specifically, the secondary recrystallization annealing step includes a first heating step with a steel plate temperature of 650°C to 900°C, a second heating step with a steel plate temperature exceeding 900°C but not exceeding the homogenization temperature, and a homogenization step, and adjusts the atmosphere conditions in each step.

[0089] The following sections will describe each step in detail.

[0090] First, the steel plate is heated in a first heating step to a temperature of 650°C to 900°C. In this first heating step, the oxide layer on the surface of the steel plate formed during the initial recrystallization annealing process is brought to a state suitable for reaction with MgO. This first heating step is carried out in an atmosphere with an oxidation state (pH₂O / pH₂) of 0.05 to 0.40. If the oxidation state is too low, the oxide layer cannot react properly with MgO in subsequent steps, and the reduction reaction of Fe-based oxides occurs, making it difficult for the forsterite particles in the central portion 120 to grow sufficiently. On the other hand, if the oxidation state is too high, the olivine and pyroxene phase oxides in the surface oxide layer of the edge portion 110 increase, which hinders the reaction with MgO, making it difficult for the forsterite particles to grow sufficiently. More specifically, the first heating step can be carried out in an atmosphere with an oxidation state (pH₂O / pH₂) of 0.10 to 0.25. The degree of oxidation may have a gradient that decreases as the temperature increases. The degree of oxidation in the first heating step refers to the average degree of oxidation over the total time of the first heating step.

[0091] The first heating step may contain 10 to 50 vol% N2 and 50 to 90 vol% H2. If there is too little N2, the inhibitor will decompose too quickly, potentially leading to a decrease in magnetic properties. If there is too much N2, it may be difficult to uniformly control the oxidation degree inside the steel plate, and the steel plate may undergo further nitriding, potentially affecting the magnesium olivine coating and magnetic properties. More specifically, the first heating step may contain 20 to 40 vol% N2 and 60 to 80 vol% H2.

[0092] The first heating step is carried out at a heating rate of 5°C / hour to 90°C / hour. If the heating rate of the first heating step is too high, the temperature deviation in the wound coil will be too large, and it will put a load on the equipment, so this should be avoided. If the heating rate of the first heating step is too low, production problems may occur. More specifically, the first heating step can be from 10°C / hour to 75°C / hour.

[0093] Following the first heating step, 2 to 15% by weight of forsterite can be contained within a 10 μm thickness extending from the steel plate surface inwards. Forsterite formation is achieved through proper control of the aforementioned oxidation degree (PH2O / PH2). If too little forsterite is present, the forsterite particles in the central 120° region will have difficulty growing sufficiently. If too much forsterite is present, the forsterite particles in the edge 110° region will have difficulty growing sufficiently. The total amount of forsterite can be analyzed and determined using an X-ray quantitative analyzer.

[0094] Next, the steel plate is heated in a second heating step, with the temperature exceeding 900°C but not exceeding the homogenization temperature. In this second heating step, the oxide layer on the steel plate surface formally begins to react with MgO, and an inhibitor removal reaction occurs. This second step is carried out in an atmosphere with an oxidation state (PH2O / PH2) of less than 0.03. If the oxidation state (PH2O / PH2) is too high, the olivine and pyroxene phase oxides in the surface oxide layer of the edge 110 increase, which hinders the reaction with MgO, making it difficult for the forsterite particles to grow sufficiently. More specifically, for the second step, the oxidation state (PH2O / PH2) can be between 0.01 and 0.03.

[0095] The second heating step may contain less than 30% by volume of N2 and more than 70% by volume of H2. If there is too much N2, it may be difficult to uniformly control the degree of oxidation inside the steel plate, and the steel plate may undergo further nitriding, which may affect the magnesium olivine coating and magnetic properties. More specifically, the second heating step may contain 10 to 30% by volume of N2 and 70 to 90% by volume of H2.

[0096] The second heating step is carried out at a rate of 5°C / hour to 30°C / hour. If the heating rate of the second heating step is too high, temperature deviations will occur in the wound coil, which will affect not only the magnetic properties but may also cause deviations in surface properties, and therefore this rate is limited. On the other hand, if the heating rate of the second heating step is too low, productivity may decrease, and this rate is also limited. More specifically, the heating rate of the second heating step can be from 8°C / hour to 25°C / hour.

[0097] Following the second heating step, 85 to 100% by weight of forsterite is incorporated over a thickness of 10 μm from the surface of the steel plate toward its interior. Forsterite is appropriately formed by properly controlling the aforementioned oxidation degree (PH2O / PH2).

[0098] Next, the secondary recrystallization annealing step includes a homogenization step of homogenizing the steel sheet at a homogenization temperature. The homogenization temperature can be above 1000°C, specifically between 1170 and 1220°C. During the homogenization step, the formation of the forsterite coating, the growth of secondary recrystallization, and the removal of inhibitors are completed. During the homogenization step, the oxidation degree (PH2O / PH2) can be maintained below 0.03. Furthermore, the removal of inhibitors and impurities is successfully achieved by using H2 containing more than 99% by volume. The homogenization step can last from 1 to 25 hours.

[0099] After secondary recrystallization annealing, unreacted annealing release agent is removed by water washing, and an insulating coating agent is applied after pickling. Subsequently, heat flattening treatment, which combines insulating coating annealing, shape correction, and stress relief annealing, can be performed.

[0100] According to one embodiment of the present invention, the oriented electrical steel sheet comprises, by weight %, less than 0.005% and excluding 0%, C, 1.5% to 4.5%, Mn, less than 1.0%, with the balance including Fe and other unavoidable impurities.

[0101] Regarding the steel composition of grain-oriented electrical steel sheets, the steel composition of the slab has already been described in the aforementioned manufacturing method of grain-oriented electrical steel sheets, so a repeat description is omitted.

[0102] As mentioned earlier, in the manufacturing method of grain-oriented electrical steel sheets, different degrees of oxidation are applied during the heating process of the secondary recrystallization annealing process, thereby reducing the deviation of the magnesium olivine particle size in the width direction of the steel sheet.

[0103] Specifically, one or both sides of the steel plate substrate have a forsterite layer, and the average grain size (P1) of the forsterite particles present in the forsterite layer at one end of the width direction of the steel plate or at the edge portion 110 from one end of the steel plate to 30% of the total width of the steel plate and from the edge portion 110 from one end of the steel plate to the other end is 0.8 to 1.2 compared with the average grain size (P2) of the forsterite particles present in the forsterite layer at the center portion 120 from one end of the steel plate to more than 30% but not more than 70% of the total width of the steel plate.

[0104] Forsterite particles refer to the crystalline oxide particles, primarily composed of Mg2SiO4, formed during the secondary recrystallization annealing process in this invention. The average particle size of the forsterite particles is determined by collecting at least 15 samples from corresponding regions along the TD direction in the edge portion 110 and the center portion 120, thereby calculating the average particle size. More specifically, after collecting the corresponding samples, the cross-section can be processed using a Carl Zeiss focused ion beam apparatus, and the forsterite coating can be measured using a JEOL transmission electron microscope. Subsequently, the forsterite particles are measured using an image analyzer from Leica. Furthermore, the method for measuring forsterite particles is not limited in this invention.

[0105] If the ratio (P2 / P1) of the average grain size (P1) of the forsterite particles present in the forsterite layer of the edge portion 110 (30% of the total width of the steel plate from one end) and the center portion 120 (more than 30% but not more than 70% of the total width of the steel plate from one end) is too small or too large, it indicates that the grain size of the forsterite particles between the edge portion 110 and the center portion 120 is not uniform. This will also affect the grain size of the secondary recrystallization below the forsterite layer, and the grain size of the secondary recrystallization will not be uniformly formed, resulting in magnetic deviation in the width direction. Specifically, the ratio (P2 / P1) of the average grain size (P1) of the forsterite particles present in the forsterite layer of the edge portion 110 at one end of the width direction of the steel plate or at 30% of the total width of the steel plate from one end to the other end of the edge portion 110 at 70% of the total width of the steel plate from one end to the other end, to the average grain size (P2) of the forsterite particles present in the forsterite layer of the central portion 120 at more than 30% to no more than 70% of the total width of the steel plate from one end of the steel plate, to the average grain size (P2) of the forsterite particles present in the forsterite layer, can be from 0.85 to 1.15.

[0106] As previously described, in one embodiment of the present invention, since the average grain size ratio (P2 / P1) of the forsterite particles is uniform, the grain size of the secondary recrystallization between the edge portion 110 and the center portion 120 is also uniformly formed. Specifically, the ratio (R2 / R1) of the average grain size (R1) of the secondary recrystallization present in the edge portion 110 at one end of the width direction of the steel plate or from one end of the steel plate to 30% of the total width of the steel plate and from one end of the steel plate to the other end of the edge portion 110 is to the average grain size (R2) of the secondary recrystallization present in the center portion 120 at more than 30% but not more than 70% of the total width of the steel plate from one end of the steel plate can be 0.7 to 1.2. More specifically, the average grain size ratio (R2 / R1) of the secondary recrystallization can be 0.80 to 1.10.

[0107] For the secondary recrystallization grain size, the sample after secondary recrystallization annealing was completely removed with hydrochloric acid to remove the insulating coating and forsterite film, and then the grain size was determined according to the American Society for Testing and Material (ASTM) grain size test method.

[0108] The average grain size of the forsterite particles present in the forsterite layer at the edge 110 is 0.3 to 2.0 μm, and the average grain size of the forsterite particles present in the forsterite layer at the center 120 is 0.3 to 2.0 μm.

[0109] Furthermore, the average grain size of the secondary recrystallization present in the edge portion 110 can be 1.0 to 4.5 cm, and the average grain size of the secondary recrystallization present in the center portion 120 can be 0.7 to 4.0 cm.

[0110] According to an embodiment of the present invention, the oriented electrical steel sheet has excellent iron loss and magnetic flux density, while the deviation of iron loss and magnetic flux density in the width direction is very small.

[0111] According to one embodiment of the present invention, the oriented electrical steel sheet has a magnetic flux density (B8) of 1.90T or higher and an iron loss (W). 17 / 50 It can be below 0.90 W / kg. At this point, the magnetic flux density B8 is the magnitude (Tesla) of the magnetic flux density produced under a magnetic field of 800 A / m, and the iron loss W... 17 / 50 This refers to the magnitude of the iron loss (W / kg) generated under conditions of 1.7 Tesla and 50 Hz. More specifically, the magnetic flux density (B8) can be from 1.91 T to 1.95 T, and the iron loss (W / kg) is... 17 / 50 The value can be 0.75 to 0.85 W / kg.

[0112] According to an embodiment of the present invention, when the width of the oriented electrical steel sheet is 1050 mm or more, the iron loss (W) between the center and the edge is...17 / 50 The ratio (center / edge) can be from 0.98 to 1.2.

[0113] Furthermore, the ratio of magnetic flux density (B8) between the center and the edge (center / edge) can be from 0.98 to 1.00. For deviations in iron loss and magnetic flux density, at least 10 samples are collected from each section, and the deviations are calculated using the average value of the samples.

[0114] Furthermore, the forsterite coating exhibits excellent adhesion. Adhesion can be determined by the minimum arc diameter at which the coating does not peel off when bent 180° onto an arc of a specific diameter. Specifically, the forsterite coating adhesion can be below 20 mmΦ.

[0115] Specific embodiments of the present invention will be described below. However, the following embodiments are merely one specific embodiment of the present invention, and the present invention is not limited to the following embodiments.

[0116] Experimental Example 1 A slab is manufactured, comprising, by weight percent, 0.060% C, 3.3% Si, 0.090% Mn, 0.028% Al, 0.04% Sb, 0.02% Cu, and 0.05% Sn, with the balance being Fe and unavoidable impurities. The slab is heated to 1150°C, then hot-rolled to a thickness of 2.3 mm, and then rapidly cooled to 600°C for coiling. The hot-rolled sheet is annealed at 1080°C and pickled, then cold-rolled once to a thickness of 0.20 mm. The cold-rolled sheet is held at 850°C in a humid atmosphere (50v% hydrogen + 50v% nitrogen) and ammonia mixture for 180 seconds, while simultaneously undergoing decarburization and nitriding annealing heat treatment to achieve a carbon content below 30 ppm and a total nitrogen content above 200 ppm. The steel plate is coated with a slurry prepared by stirring an annealing release agent in water at 8°C. The annealing release agent comprises 100 parts by weight of MgO, 5 parts by weight of TiO2, 0.15 parts by weight of SrCl2, 0.10 parts by weight of Sb2O3, and 0.05 parts by weight of FeBr2, with a hydration rate of 1.75% by weight. The coating weight per side is 6.0 g / m² after drying. 2 After drying, it is rolled into a sheet.

[0117] After the first heating step (steel plate temperature 900℃) and the second heating step, the steel plate was removed and then the magnesium olivine (Mg2SiO4) was quantitatively analyzed by XRD. The results are shown in Table 1 below.

[0118] The sample was subjected to a second recrystallization annealing process, which involved heating and homogenizing in 100% H2 at 1200°C for 6 hours. The sample was then coated with a solution mainly composed of aluminum phosphate and colloidal silica as an insulating coating on a continuous production line, followed by annealing at 850°C.

[0119] For the final manufactured grain-oriented electrical steel sheet, Epstein specimens were cut from the edge and center portions, with dimensions of [60 mm (width) × 300 mm (length)]. Twenty specimens were taken from each portion. Then, the average grain size of forsterite, the secondary recrystallization grain size, the magnetic flux density (B8), and the iron loss (W) were measured. 17 / 50 ), and are shown in Tables 2 and 3 below.

[0120] The average grain size of forsterite was determined by processing the cross-section using a Carl Zeiss focused ion beam apparatus, measuring the forsterite coating using a JEOL transmission electron microscope, and then further measuring it using a Leica image analyzer.

[0121] For the secondary recrystallization grain size, the sample after secondary recrystallization annealing was completely removed with hydrochloric acid to remove the insulating coating and forsterite film, and then the grain size was determined according to the American Society for Testing and Material (ASTM) grain size test method.

[0122] The adhesion evaluation results of the forsterite coating are shown in Table 3. Adhesion was determined by the smallest arc diameter that did not peel off when the coating was bent 180° on an arc with a diameter of 10 to 50 mm.

[0123] The deviations in iron loss and magnetic flux density are calculated based on the center / edge region.

[0124] Table 1 Table 2 Table 3 Tables 1 to 3 confirm that during the secondary recrystallization annealing process, if the atmosphere conditions are appropriately adjusted during heating and homogenization, the average grain size and secondary recrystallization grain size of magnesium olivine will be uniformly formed, resulting in excellent magnetic properties and reduced magnetic deviation in the width direction.

[0125] On the other hand, if the atmosphere is not properly regulated during heating and homogenization, the average grain size of magnesium olivine will be uneven, and the magnetic deviation in the width direction will be large.

[0126] Experiment Example 2 The implementation method is the same as in Example 1, but the annealing release agent is changed as shown in Table 4. For the finally manufactured oriented electrical steel sheet, Epstein samples were cut from the edge and center portions, with dimensions of [60 mm (width) × 300 mm (length)], and 20 samples were taken from each portion. Then, the average grain size of forsterite, the secondary recrystallization grain size, the magnetic flux density (B8), and the iron loss (W) were measured. 17 / 50 ), and are shown in Tables 5 and 6 below.

[0127] Table 4 Table 5 Table 6 Tables 4 to 6 confirm that the addition range of the low-melting-point additives proposed in this invention and the characteristics of the hydrated water in the annealing isolator have an impact on improving the uniformity of the average particle size of magnesium olivine and secondary recrystallization.

[0128] This invention can be implemented in various ways and is not limited to the embodiments and / or examples described above. Those skilled in the art will understand that the invention can be implemented in other specific ways without altering its technical concept or essential features. Therefore, it should be understood that the above embodiments and / or examples are exemplary in all respects and are not restrictive.

[0129] [Explanation of reference numerals in the attached figures] 100: Oriented grain electrical steel sheet; 101: One end 102: The other end; 110: The edge 120: Central Department

Claims

1. A method for manufacturing an oriented electrical steel sheet, comprising: The step of manufacturing a slab, in weight percent, the slab contains Si: 1.5 to 4.5%, C: less than 0.70% and excluding 0%, Mn: less than 1.0% and excluding 0%, the balance containing Fe and other unavoidable impurities; The step of hot rolling the slab to manufacture a hot-rolled plate; The step of cold rolling the hot-rolled sheet to manufacture a cold-rolled sheet; The step of performing a recrystallization annealing on the cold-rolled sheet; and The step of performing a second recrystallization anneal on a steel sheet after a first recrystallization annealing. The secondary recrystallization annealing step includes a first heating step with a steel plate temperature of 650°C to 900°C, a second heating step with a steel plate temperature exceeding 900°C but not exceeding the homogenization temperature, and a homogenization step. After the first heating step, the steel plate contains 2 to 15% by weight of forsterite in a thickness of 10 μm from the surface to the interior of the steel plate, and after the second heating step, it contains 85 to 100% by weight of forsterite.

2. The method for manufacturing oriented electrical steel sheet according to claim 1, wherein, The slab further comprises one or more of Al: 0.015 to 0.040% by weight, N: less than 0.0055% by weight, and S: less than 0.0055% by weight.

3. The method for manufacturing oriented electrical steel sheet according to claim 1, wherein, The slab further comprises one or more of Sn: 0.03 to 0.10 wt%, Sb: 0.01 to 0.05 wt%, P: 0.01 to 0.10 wt%, Cu: 0.001% to 0.1 wt%, and Cr: 0.01 to 0.50 wt%.

4. The method for manufacturing oriented electrical steel sheet according to claim 1, wherein, After the first recrystallization annealing step and before the second recrystallization annealing step, an annealing release agent is applied. The annealing release agent comprises 100 parts by weight of MgO and 0.01 to 0.50 parts by weight of additives with a melting point below 900°C.

5. The method for manufacturing oriented electrical steel sheet according to claim 4, wherein, The additive comprises one or more of the following: hydroxides, carbonates, amide compounds, chromates, oxides, antimony compounds, chlorine compounds, chlorine oxides, sulfur compounds, nitrogen compounds, bromides, bromates, telluric acid, vanadates, borates, and phosphorus compounds.

6. The method for manufacturing oriented electrical steel sheet according to claim 4, wherein, The additive contains one or more of the following: Li, F, Na, K, Cu, Ba, Br, Mg, Ca, Zn, Sr, Cd, B, Al, Y, Ga, In, Tl, Ti, Sn, P, Nb, Sb, Bi, S, Cr, Te, V, W, Fe, Mn, Co, and Ni.

7. The method for manufacturing oriented electrical steel sheet according to claim 4, wherein, The additive contains one or more of SrCl2, Sb2O3, FeBr2, CuCl, MnCl2, B2O3, NiSO4, CoSO4, CuBr, and SnS.

8. The method for manufacturing oriented electrical steel sheet according to claim 4, wherein, The hydrated water content of the MgO is 1.2 to 2.5% by weight.

9. The method for manufacturing oriented electrical steel sheet according to claim 1, wherein, The first heating step contains 10 to 50 vol% N2 and 50 to 90 vol% H2, the second heating step contains less than 30 vol% N2 and more than 70 vol% H2, and the heat equalization step contains more than 99 vol% H2.

10. The method for manufacturing the grain-oriented electrical steel sheet according to claim 1, wherein, The first heating step is carried out at a heating rate of 5°C / hour to 90°C / hour, and the second heating step is carried out at a heating rate of 5°C / hour to 30°C / hour.

11. A grain-oriented electrical steel sheet, wherein, By weight percent, the oriented electrical steel sheet contains C: less than 0.005% and excluding 0%, Si: 1.5% to 4.5%, Mn: less than 1.0%, with the balance including Fe and other unavoidable impurities. One or both sides of the steel plate substrate have a magnesium olivine layer. The ratio (P2 / P1) of the average grain size (P1) of the forsterite particles present in the forsterite layer at one end or 30% of the total width of the steel plate from one end to the other edge, and at 70% of the total width of the steel plate from one end to the other edge, to the average grain size (P2) of the forsterite particles present in the forsterite layer at the center of the steel plate, which extends from one end to more than 30% but not more than 70% of the total width of the steel plate, is 0.8 to 1.

2. The ratio (R2 / R1) of the average grain size (R1) of the secondary recrystallization present in the edge portion to the average grain size (R2) of the secondary recrystallization present in the center portion is 0.7 to 1.

2.

12. The grain-oriented electrical steel sheet according to claim 11, wherein, The oriented electrical steel sheet further comprises one or more of Al: less than 0.040 wt%, N: less than 0.0050 wt%, and S: less than 0.005 wt%.

13. The grain-oriented electrical steel sheet according to claim 11, wherein, The oriented electrical steel sheet further comprises one or more of Sn: 0.03 to 0.10 wt%, Sb: 0.01 to 0.05 wt%, P: 0.01 to 0.10 wt%, Cu: 0.001% to 0.1 wt%, and Cr: 0.01 to 0.50 wt%.

14. The grain-oriented electrical steel sheet according to claim 11, wherein, The average grain size of the forsterite particles in the forsterite layer at the edge is 0.3 to 2.0 μm, and the average grain size of the forsterite particles in the forsterite layer at the center is 0.3 to 2.0 μm.

15. The grain-oriented electrical steel sheet according to claim 11, wherein, The average grain size of the secondary recrystallization present in the edge portion is 1.0 to 4.5 cm, and the average grain size of the secondary recrystallization present in the center portion is 0.7 to 4.0 cm.

Images