Grain oriented electrical steel sheet and method for manufacturing same

Abstract

The method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention comprises the steps of: producing slab comprising, by weight, Si: 1.5 to 4.5%, C: 0.70 % or less (inclusive of 0%), Mn: 1.0% or less (inclusive of 0%), the balance being Fe and other inevitable impurities; hot rolling the slab to produce a hot-rolled sheet; cold rolling the hot-rolled sheet to produce a cold-rolled sheet; performing primary recrystallization annealing on the cold-rolled sheet; and performing secondary recrystallization annealing on the steel sheet subjected to the primary recrystallization annealing. The secondary recrystallization annealing step comprises: a first heating step in which the temperature of the steel sheet is 650℃ to 900℃; a second heating step in which the temperature of the steel sheet is between 900℃ (exclusive) and a cracking temperature (inclusive); and a cracking step. The first heating step is carried out in an atmosphere with an oxidizing power (PH2O / PH2) of 0.05-0.40 while the second heating step is carried out in an atmosphere with an oxidizing power(PH2O / PH2) of 0.03 or less.

Description

Grain-oriented electrical steel sheet and its manufacturing method

[0001] One embodiment of the present invention relates to a grain-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention relates to a grain-oriented electrical steel sheet and a method for manufacturing the same, wherein the variation in forsterite grain size in the width direction of the steel sheet is reduced by appropriately controlling the oxidation capacity during the secondary recrystallization annealing process, and the variation in magnetic properties in the width direction of the steel sheet is reduced.

[0002] Grain-oriented electrical steel sheets have the orientation of all crystal grains on the steel sheet surface as {110} planes and the crystal orientation in the rolling direction is <001> It is a soft magnetic material with excellent magnetic properties in the rolling direction of the steel sheet by forming a so-called Goss texture parallel to the axis. In general, the magnetic properties of electrical steel sheets can be expressed in terms of magnetic flux density and iron loss, and high magnetic flux density means that the grain orientation is {110}. <001> It can be obtained by arranging it precisely in the direction. Electrical steel sheets with high magnetic flux density can not only reduce the size of the core material of electrical devices, but also reduce the hysteresis loss, so it is possible to make the electrical devices smaller and more efficient at the same time. Iron loss is the power loss consumed as heat energy when an arbitrary alternating magnetic field is applied to the steel sheet, and it varies greatly depending on the magnetic flux density and thickness of the steel sheet, the amount of impurities in the steel sheet, resistivity, and the size of secondary recrystallized grains, and the higher the magnetic flux density and resistivity, and the lower the plate thickness and the amount of impurities in the steel sheet, the lower the iron loss, which increases the efficiency of the electrical device.

[0003] These grain-oriented electrical steel sheets have a forsterite film formed during secondary recrystallization annealing on their surface, and an insulating film is applied during the final heat flattening process to form the final product. This forsterite film not only provides surface insulation, but also improves core loss and magnetostrictive properties by imparting tensile stress to the steel sheet due to the difference in thermal expansion with the base metal. The forsterite film formed on the surface of the steel sheet not only improves insulation performance and magnetic properties depending on its formation state, but also determines the commercial value such as workability in the core processing process and the appearance of the product. Therefore, the formation of a uniform and stable quality forsterite film is required.

[0004] In order to form a forsterite film in the production of grain-oriented electrical steel sheets, steel sheets cold-rolled to the final thickness are subjected to decarburization annealing in a humid atmosphere, a process that forms oxides mainly composed of Fe2SiO4 and SiO2, which play an important role in the primary recrystallization and formation of the forsterite film. Afterwards, an annealing separator mainly composed of MgO is applied to the steel sheet, dried, coiled, and subjected to secondary recrystallization annealing, thereby forming the forsterite film.

[0005] In the secondary recrystallization annealing process, the formation reaction of the forsterite film is a film formed by the reaction between MgO, the main component of the annealing separator, and SiO2, the main component of the oxide formed in the primary recrystallization annealing (2MgO + SiO2-> Mg2SiO4). At this time, when AlN is used as an inhibitor, spinel structure compounds such as Al2O3, MgO, and SiO2 are formed near the bottom of the forsterite film. Since the forsterite film formation behavior at this time also affects the behavior of inhibitors such as MnS and AlN in the steel, it also affects the secondary recrystallization behavior, which is an essential process for having excellent magnetic properties.

[0006] That is, if the forsterite film formation reaction is delayed or progresses unevenly, or if the quantity and quality of the formed film are inadequate, O and N can easily penetrate into the steel during the annealing atmosphere, causing decomposition and coarsening of the inhibitor in the steel, which affects the inhibitor strength. Furthermore, the forsterite film formed during the secondary recrystallization annealing process has the function of drawing up and purifying the inhibitor that has become unnecessary after the secondary recrystallization is completed, thereby reducing hysteresis loss.

[0007] Therefore, the uniform formation of the forsterite film and the control process during its formation are important points that determine the quality of grain-oriented electrical steel sheets.

[0008] One embodiment of the present invention provides a grain-oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention provides a grain-oriented electrical steel sheet and a method for manufacturing the same, wherein the variation in forsterite grain size in the width direction of the steel sheet is reduced by appropriately controlling the oxidation capacity during the secondary recrystallization annealing process, and the variation in magnetic properties in the width direction of the steel sheet is reduced.

[0009] A method for manufacturing a grain-oriented electrical steel sheet according to one embodiment of the present invention comprises the steps of: manufacturing a slab containing, in wt%, Si: 1.5 to 4.5%, C: 0.70% or less (excluding 0%), Mn: 1.0% or less (excluding 0%), and the remainder including Fe and other unavoidable impurities; hot-rolling the slab to manufacture a hot-rolled sheet; cold-rolling the hot-rolled sheet to manufacture a cold-rolled sheet; first recrystallization annealing the cold-rolled sheet; and second recrystallization annealing the first recrystallization annealed steel sheet.

[0010] The secondary recrystallization annealing step includes a first temperature increasing step in which the steel sheet temperature is 650°C to 900°C, a second temperature increasing step in which the steel sheet temperature is higher than 900°C but lower than the cracking temperature, and a cracking step.

[0011] The first temperature raising step is performed in an atmosphere having an oxidation capacity (PH2O / PH2) of 0.05 to 0.40, and the second temperature raising step is performed in an atmosphere having an oxidation capacity (PH2O / PH2) of 0.03 or less.

[0012] The slab may further include at least one of Al: 0.015 to 0.040 wt%, N: 0.0055 wt% or less, and S: 0.0055 wt% or less.

[0013] The slab may further include at least one 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 separator is applied, and the annealing separator may include 100 parts by weight of MgO and 0.01 to 0.50 parts by weight of an additive having a melting point of 900°C or lower.

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

[0016] The additive may include one or more of 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 include one or more of SrCl2, Sb2O3, FeBr2, CuCl, MnCl2, B2O3, NiSO4, CoSO4, CuBr, and SnS.

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

[0019] The first heating step may include N210 to 50 vol% and H250 to 90 vol%, the second heating step may include N250 vol% or less and H250 vol% or more, and the cracking step may include H299 vol% or more.

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

[0021] After the first heating step, the steel sheet contains 2 to 15 wt% of forsterite in a thickness ranging from 10 μm from the surface of the steel sheet toward the inside of the steel sheet, and after the second heating step, the steel sheet contains 85 to 100 wt% of forsterite.

[0022]

[0023] According to one embodiment of the present invention, a grain-oriented electrical steel sheet contains, in wt%, C: 0.005% or less (excluding 0%), Si: 1.5% to 4.5%, Mn: 1.0% or less (excluding 0%), and the remainder is Fe and other unavoidable impurities, and a forsterite layer exists on one or both sides of a steel sheet substrate, and a ratio of an average grain size (P1) of forsterite particles existing in the forsterite layer in an edge portion from one end of the width direction of the steel sheet to 30% of the entire width of the steel sheet from one end of the steel sheet to the other end from 70% of the entire width of the steel sheet to the other end, and an average grain size (P2) of forsterite particles existing in the forsterite layer in a center portion from more than 30% to less than 70% of the entire width of the steel sheet from one end of the steel sheet to the other end (P2 / P1) is 0.8 to 1.2.

[0024] A directional electrical steel sheet according to one embodiment of the present invention may further include at least one of Al: 0.040 wt% or less, N: 0.0050 wt% or less, and S: 0.005 wt% or less.

[0025] The oriented electrical steel sheet according to one embodiment of the present invention may further include at least one 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%.

[0026] The average grain size of the forsterite particles present in the forsterite layer of the edge portion is 0.3 to 2.0 ㎛, and the average grain size of the forsterite particles present in the forsterite layer of the center portion is 0.3 to 2.0 ㎛.

[0027] A directional electrical steel sheet according to one embodiment of the present invention can reduce magnetic deviation in the width direction of the steel sheet and uniformly improve magnetism in the width direction of the steel sheet.

[0028] Figure 1 is a schematic diagram schematically illustrating a directional electrical steel sheet according to one embodiment of the present invention.

[0029] FIG. 2 is a schematic diagram schematically illustrating a coil-shaped steel sheet during a second recrystallization annealing step in one embodiment of the present invention.

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

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

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

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

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

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

[0036] Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily implement them. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein.

[0037]

[0038] A method for manufacturing a grain-oriented electrical steel sheet according to one embodiment of the present invention comprises the steps of: manufacturing a slab containing, in wt%, Si: 1.5 to 4.5%, C: 0.70% or less (excluding 0%), Mn: 1.0% or less (excluding 0%), and the remainder including Fe and other unavoidable impurities; hot-rolling the slab to manufacture a hot-rolled sheet; cold-rolling the hot-rolled sheet to manufacture a cold-rolled sheet; first recrystallization annealing the cold-rolled sheet; and second recrystallization annealing the first recrystallization annealed steel sheet.

[0039] Below, each step is explained in detail.

[0040] First, manufacture the slab.

[0041] The slab contains, in wt%, Si: 1.5 to 4.5%, C: 0.70% or less (excluding 0%), Mn: 1.0% or less (excluding 0%), and the remainder includes Fe and other unavoidable impurities.

[0042] Below, we explain the reasons for limiting the amount added for each element.

[0043]

[0044] C: 0.70 wt% or less

[0045] Carbon (C) is an element that promotes austenite phase transformation, making the hot-rolled structure of grain-oriented electrical steel uniform and promoting the formation of Goss-oriented grains during cold rolling, making it an important element for manufacturing grain-oriented electrical steel with excellent magnetism. If too much C is added, the primary recrystallized grains become fine due to the formation of fine hot-rolled structure due to austenite phase transformation during hot rolling. In addition, coarse carbide can be formed during the coiling process after hot rolling or the cooling process after hot-rolled sheet annealing, and Fe3C (Cementite) can easily be formed at room temperature, causing uneven structure. In addition, the time required for decarburization to 30 ppm or less during the decarburization process after cold rolling increases, which causes the problem of excessive formation of fayalite and silica on the surface of the steel sheet. Therefore, the C content may be included in an amount of 0.70 wt% or less. More specifically, it may be included in an amount of 0.01 to 0.50 wt%. More specifically, it may contain 0.03 to 0.10 wt%.

[0046] C is removed by decarburization during the primary recrystallization annealing process, and may be included in the final manufactured grain-oriented electrical steel sheet at 0.005 wt% or less. More specifically, it may be included at 0.003 wt% or less. More specifically, it may be included at 0.0001 to 0.0030 wt%.

[0047]

[0048] Si: 1.5 to 4.5 wt%

[0049] Silicon (Si) is a basic component of electrical steel sheets, and it increases the resistivity of the material, thereby reducing core loss, or iron loss. If too little Si is added, the resistivity decreases, resulting in a weak eddy current loss reduction effect. In addition, the amount of fayalite formed during the decarburization process will be absolutely insufficient, which may cause unstable forsterite film formation. Conversely, if too much Si is added, the steel becomes brittle, making cold rolling difficult. In addition, the surface quality may be deteriorated as a large amount of fayalite is formed during the decarburization process. Therefore, Si may be included in an amount of 1.5 to 4.5 wt%. More specifically, it may be included in an amount of 2.5 to 3.5 wt%.

[0050]

[0051] Mn: 1.0 wt% or less

[0052] Manganese (Mn), like Si, increases resistivity and reduces iron loss. However, adding large amounts of Mn weakens the grain growth inhibition by reducing saturation magnetic flux density and forming coarse MnS precipitates, rather than reducing iron loss through increased resistivity. This reduces the magnetic flux density after secondary recrystallization annealing. In addition, it affects the fayalite and silica components formed during the decarburization process, hindering the formation of a good forsterite film.

[0053] Therefore, in order to form a forsterite film with excellent adhesion along with excellent magnetic flux density characteristics, it is necessary to optimize the Mn content. However, if too much Mn is added, it will promote coarse MnS precipitation, and there is a problem that the slab must be heated to 1150℃ or higher to dissolve the MnS precipitates. In addition, it may interfere with the formation of good-quality Fayalite and Silica during the decarburization process. Therefore, Mn may be included in an amount of 1.0 wt% or less. More specifically, Mn may be included in an amount of 0.1 to 0.5 wt%.

[0054]

[0055] The slab may further include at least one of Al: 0.015 to 0.040 wt%, N: 0.0055 wt% or less, and S: 0.0055 wt% or less.

[0056] Al: 0.015 to 0.040 wt%

[0057] Aluminum (Al) combines with N to form AlN precipitates, and is a representative component of grain growth inhibitors for forming secondary recrystallization of grain-oriented electrical steel sheets. In one embodiment of the present invention, by forming (Al, Si, Mn) N precipitates through nitriding annealing after cold rolling, a grain growth inhibition effect is secured, and in particular, by controlling the precipitation of precipitates in the width direction of the steel, the magnetic deviation in the width direction is reduced. It is preferable to add 0.015 to 0.040 wt% of Al in the steelmaking step, but if too little Al is added, the total amount of (Al, Si, Mn) N precipitates formed during the first recrystallization and nitriding annealing processes may be small, so that the first recrystallization grain growth inhibition effect may be insufficient. Conversely, if too much Al is added, coarse precipitates may grow during the slab manufacturing and hot rolling processes, forming a coarse microstructure during nitriding annealing, which may make secondary recrystallization unstable during the subsequent secondary recrystallization annealing process. Therefore, the Al content in the slab may be 0.015 to 0.040 wt%. More specifically, it may be 0.020 to 0.035 wt%.

[0058] During the secondary recrystallization annealing process, some of the aluminum may be removed through purification annealing, and the final grain-oriented electrical steel sheet may contain 0.040 wt% or less of aluminum. More specifically, it may contain 0.010 to 0.040 wt%.

[0059] N: 0.0055 wt% or less

[0060] Nitrogen (N) is an important element that reacts with Al to form AlN precipitates that inhibit grain growth. In a manufacturing method that secures (Al, Si, Mn)N precipitates through nitriding after cold rolling, there is no need to include a lot of N in the steelmaking step. However, if too little N is added, fine AlN precipitates are formed in the slab manufacturing step, making the primary recrystallized grain size fine and facilitating secondary recrystallization of grains with exact Goss orientations. Conversely, if too much N is added, coarse AlN precipitates are formed in the slab manufacturing step, creating a coarse primary recrystallized microstructure and making secondary recrystallization unstable. Therefore, the range of N can be limited to 0.0055 wt% or less. More specifically, N can be included in the range of 0.0010 to 0.0050 wt%. More specifically, it can be included in the range of 0.0030 to 0.0050 wt%.

[0061] Meanwhile, in one embodiment of the present invention, N may be nitrided in the first recrystallization annealing process, and then, some of the N may be removed through purification annealing in the second recrystallization annealing process, and N may be included in the final grain-oriented electrical steel sheet at 0.0050 wt% or less. More specifically, it may be included at 0.001 to 0.005 wt%.

[0062] S: 0.0055 wt% or less

[0063] Sulfur (S) generally reacts with manganese (Mn) and copper (Cu) to form MnS or Cu2S precipitates, acting as an inhibitor that suppresses the growth of primary recrystallized grains. In order to secure fine MnS precipitates, the added Mn and S must be completely dissolved under slab heating conditions of 1150℃ or lower to function as an effective inhibitor. Therefore, it is desirable to add S within the range of the amount of Mn added and the content that can react. If too much S is added, complete solid solution becomes difficult, which may result in coarse MnS precipitates. In addition, S is an element that is prone to grain boundary or surface segregation. In particular, during the high-temperature annealing process, S diffuses to the surface of the steel sheet and causes surface segregation, which interferes with the forsterite film reaction formed by the reaction of fayalite, silica, and MgO, resulting in poor adhesion of the forsterite film. Therefore, S may be included in an amount of 0.0055 wt% or less. Specifically, it may be included in an amount of 0.001 to 0.005 wt%. More specifically, it may contain 0.0020 to 0.0045 wt%. Some of the S may be removed through purification annealing during the secondary recrystallization annealing process, and the S may be contained in an amount of 0.005 wt% or less in the final grain-oriented electrical steel sheet. More specifically, it may contain 0.001 to 0.005 wt%.

[0064] The slab may further include at least one 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%.

[0065] Sn: 0.03 to 0.10 wt%

[0066] Tin (Sn) is an excellent auxiliary grain growth inhibitor that segregates at grain boundaries and inhibits the movement of grain boundaries. This compensates for the weakening of the grain growth inhibitory effect as AlN particles become coarser and the Si content increases. Consequently, even with a relatively high Si content, {110} <001> Successful formation of a secondary recrystallized aggregate structure can be guaranteed, i.e. {110} <001> The Si content can be increased and the final thickness can be reduced without compromising the completeness of the secondary recrystallization structure at all. Therefore, when Sn is added further, it can have a beneficial effect on magnetism. If too little Sn is added, the aforementioned effect cannot be sufficiently obtained. Conversely, if too much Sn is added, brittleness can increase. Therefore, when Sn is added further, it can be added 0.03 to 0.10 wt% more. More specifically, it can be added 0.04 to 0.07 wt% more.

[0067] Sb: 0.01 to 0.05 wt%

[0068] Antimony (Sb) segregates at grain boundaries and acts to suppress excessive growth of primary recrystallized grains. Therefore, if more Sb is added, it can have a beneficial effect on magnetism. If too little Sb is added, the aforementioned effect cannot be sufficiently obtained. On the other hand, if too much Sb is added, the size of the primary recrystallized grains becomes excessively small, which lowers the initiation temperature of secondary recrystallization, thereby deteriorating magnetic properties, or the suppression of grain growth becomes excessively large, which may cause a problem in which secondary recrystallization is not formed. Therefore, when more Sb is added, it can be added in an amount of 0.01 to 0.05 wt%. More specifically, it can be added in an amount of 0.015 to 0.035 wt%.

[0069] P: 0.01% to 0.10 wt%

[0070] Phosphorus (P) promotes the growth of primary recrystallized grains, thereby increasing the secondary recrystallization temperature and forming {110} in the final product. <001> It plays a role in increasing the degree of integration of the direction. If the first recrystallized grains are too large, the second recrystallization becomes unstable, but as long as the second recrystallization occurs, it is advantageous for magnetism to have large first recrystallized grains to increase the second recrystallization temperature. On the other hand, P is {110} in the first recrystallized steel sheet. <001> Not only does it reduce the iron loss of the final product by increasing the number of grains with {111} orientation, but it also reduces the iron loss of the final product by increasing the number of grains with {111} orientation in the first recrystallization plate. <112> By developing a strong collective organization, the final product {110} <001> Since the degree of integration is improved, the magnetic flux density also increases. In addition, P has the function of reinforcing the suppression force by segregating at the grain boundaries up to a high temperature of about 1000℃ during the secondary recrystallization annealing and delaying the decomposition of precipitates. Therefore, if more P is added, it can have a beneficial effect on magnetism. If too little P is added, the aforementioned effect cannot be sufficiently obtained. On the other hand, if too much P is added, the size of the primary recrystallized grains is reduced, which not only makes the secondary recrystallization unstable but also increases brittleness, which can hinder the cold rolling property. Therefore, when P is added further, it can be added 0.01 to 0.10 wt% more. More specifically, it can be added 0.015 to 0.050 wt% more.

[0071] Cu: 0.001 to 0.1 wt%

[0072] Copper (Cu) reacts with S to form Cu2S precipitates, acting as an inhibitor that suppresses the growth of primary recrystallized grains. When added together with Mn, it forms [MnCu]S composite precipitates, thereby affecting the size of MnS precipitates. If too little Cu is added, the formation of Cu2S precipitates is small, which may reduce the effect as an inhibitor. Conversely, if too much Cu is added, S precipitates in the steel before Mn, making it impossible to obtain the fine MnS precipitates desired in the present invention. Therefore, the Cu content is preferably limited to the range of 0.001 to 0.100 wt%. More specifically, it may include 0.010 to 0.070 wt%.

[0073] Cr: 0.01 to 0.50 wt%

[0074] Chromium (Cr) is an element that reacts most quickly with oxygen to form Cr2O3 on the surface of the steel sheet. This allows the carbon component in the steel to rapidly diffuse to the surface of the steel sheet and react with oxygen in the ambient gas to form CO gas, thereby promoting decarburization. If too little Cr is added, the aforementioned effect cannot be sufficiently obtained. If too much Cr is added, it may not have a significant effect on the formation of a surface oxide layer. Therefore, the amount of Cr added is limited to 0.01 to 0.50 wt%. More specifically, it may include 0.03 to 0.30 wt%.

[0075] The remainder includes iron (Fe). In addition, inevitable impurities may be included. Unavoidable impurities refer to impurities that are inevitably mixed in during the manufacturing process of steelmaking and grain-oriented electrical steel sheets. Since inevitable impurities are widely known, a detailed description thereof is omitted. In one embodiment of the present invention, the addition of elements other than the alloy components described above is not excluded, and various elements may be included within a range that does not impair the technical spirit of the present invention. When additional elements are further included, they are included in place of the remainder Fe. For example, it is also possible to include at least one element among Ni, Mo, Zr, Bi, Pb, As, Ge, and Ga in the steel within the component range of the present invention.

[0076]

[0077] Returning to the manufacturing process, the slab is heated to 1150℃ or lower. Slabs can be produced using the ingot method, continuous casting, thin slab casting, or strip casting. In the case of the ingot method, continuous casting, and thin slab casting, the slab is manufactured, and subsequent processes include heating and hot rolling.

[0078] Slab heating is basically a grain-oriented electrical steel manufacturing method that secures (Al, Si, Mn) N precipitates through decarburization and nitriding annealing after cold rolling to obtain AlN precipitates, which are the main crystal growth inhibitors required for Goss orientation secondary recrystallization. Therefore, the slab can be heated to 1150℃ or lower and then hot rolled. In this slab heating and hot rolling process, in order to form fine MnS as an auxiliary crystal growth inhibitor, the amount of Mn and S added was limited in the steelmaking stage so that the solid solution temperature of the MnS precipitates formed by the reaction of the added Mn and S would be lower than 1150℃.

[0079] If the slab is heated at too high a temperature, the AlN precipitates formed during the solidification process in the slab manufacturing step will be excessively dissolved in the slab heating step and will be finely precipitated during the subsequent hot rolling process, which will make the grain size fine during the hot rolling and decarburization processes and hinder the formation of secondary recrystallization of exact Goss orientation grains. Depending on the added Mn and S contents, the lower the slab heating temperature, the better, as long as the precipitated MnS can be completely dissolved. However, specifically, considering the hot rolling load, it can be heated at 1000℃ to 1150℃.

[0080] Next, the slab is hot rolled to produce a hot-rolled plate.

[0081] Hot rolling is performed to a thickness of 1.0 to 3.5 mm, and considering the rolling load, rolling can be completed at a temperature of 850°C or higher, cooled to a temperature of 600°C or lower, and then coiled.

[0082] Hot-rolled steel sheets can be subjected to a hot-rolled sheet annealing process to recrystallize the hot-rolled deformation structure, facilitating smooth rolling to the final product thickness in the subsequent cold rolling process. Generally, it is desirable to heat the hot-rolled sheet to a temperature above 800°C for recrystallization and maintain it for a certain period of time. Annealing at multiple temperatures is also possible to control precipitate distribution and size. Hot-rolled sheet annealing can be omitted if necessary.

[0083] Next, the hot-rolled sheet is cold rolled to produce a cold-rolled sheet.

[0084] Hot-rolled steel sheets are pickled to remove the oxide layer on the steel sheet surface, and then cold-rolled. Cold rolling is a process to reduce the thickness of the steel sheet to the final product thickness. Cold rolling is performed once or more times including intermediate annealing to roll to the final product thickness. At this time, the cold rolling ratio enhances the Goss orientation density, which affects the improvement of the magnetic flux density after the final secondary recrystallization annealing, so cold rolling can be performed at a rolling ratio of at least 80%. If the cold rolling ratio is too low, the Goss orientation density is low, resulting in a decrease in the magnetic flux density of the final product. Therefore, the cold rolling ratio should be at least 80%, and the maximum rolling ratio can be rolled to the maximum rolling range depending on the rolling capacity of the rolling equipment. In addition, if the temperature of the cold-rolled steel sheet is raised to 50℃ or higher during the cold rolling process, many secondary recrystallization nuclei in the Goss orientation are generated due to work hardening by the dissolved carbon, which can improve the magnetic flux density of the final product. If the temperature of the cold-rolled steel sheet is too low, the generation of secondary recrystallization nuclei in the Goss orientation is minimal, and conversely, if it exceeds 300℃, the work hardening effect by the dissolved carbon is weakened, and the generation of secondary recrystallization nuclei in the Goss orientation is weakened. Therefore, in the cold rolling process, the steel sheet can be maintained in the temperature range of 50 to 300℃ at least once in the intermediate rolling stage. The thickness of the cold-rolled sheet after cold rolling can be 0.10 to 0.35 mm.

[0085] Next, the cold rolled sheet undergoes primary recrystallization annealing.

[0086] The primary recrystallization annealing temperature can be 800 to 950°C. If the annealing temperature of the steel sheet is too low, decarburization and nitriding will take a long time, and it will be difficult for the metal oxide layer to form properly. If the annealing temperature is too high, the primary recrystallized grains may grow coarsely, reducing the driving force for crystal growth and preventing the formation of stable secondary recrystallization. The annealing time does not significantly affect the effectiveness of the present invention, but considering productivity, it can be processed for 5 minutes or less.

[0087] Decarburization and nitriding can be performed during the primary recrystallization annealing process. Decarburization and nitriding can be performed by decarburization followed by nitriding, nitriding followed by decarburization, or nitriding and decarburization simultaneously.

[0088] Nitriding can be performed by introducing nitriding gas into the atmosphere during the primary recrystallization annealing process. The nitriding gas may include ammonia gas. Nitriding can help precipitate inhibitors such as (Al, Si, Mn)N and AlN by introducing nitrogen ions into the steel sheet.

[0089] After nitriding, the nitrogen content in the steel sheet can be 0.0120 to 0.0280 wt%. If the nitrogen content is too low, it is difficult for it to function sufficiently as an inhibitor before the secondary recrystallization begins. If the nitrogen content is too high, it not only inhibits the normal formation of secondary recrystallization by excessive formation of nitrides, but also can form film defects such as bare spots due to N2 gas decomposed during the purification process after the secondary recrystallization. More specifically, the nitrogen content in the steel sheet can be 0.0150 to 0.0250 wt%.

[0090] Any gas capable of infiltrating nitrogen into the steel plate can be used as the nitriding gas. Specifically, it can be ammonia or nitrogen. Nitriding can be achieved through heat treatment in an ammonia atmosphere, or through laser or plasma treatment in a nitrogen atmosphere.

[0091] The primary recrystallization annealing step is performed in an atmosphere with an oxidation capacity (PH2O / PH2) of 0.45 to 0.80, enabling decarburization to remove carbon from the steel sheet. If the oxidation capacity is low, sufficient oxidation or decarburization is difficult to achieve. If the oxidation capacity is too high, the outermost layer of the oxide film can become an unstable oxide, with FeO rapidly forming in the region. More specifically, the oxidation capacity can be 0.48 to 0.75.

[0092] After the first recrystallization annealing step, an oxide layer with an average thickness of 1.6 to 3.2 ㎛ may exist on the surface of the steel sheet. The oxide layer exists near the surface of the steel sheet due to decarburization during the first recrystallization annealing. The oxide layer refers to the area from the surface of the steel sheet to the part where the oxygen content changes rapidly when measuring the oxygen content. If the thickness of the oxide layer is too thin, the non-uniformity of magnetism increases. If the thickness of the oxide layer is too thick, the metal oxide layer is formed thickly, and the thickness of the base metal is relatively reduced, which may result in inferior magnetism.

[0093] After the first recrystallization annealing step and before the second recrystallization annealing step, a step of applying an annealing separator may be further included. In one embodiment of the present invention, by using an annealing separator including a low-melting-point additive, the particle size of the forsterite particles can be formed uniformly. The low-melting-point additive refers to an additive having a melting point of 900°C or lower. Such a low-melting-point additive prevents further oxidation and further nitriding of the steel sheet during the second reforming annealing process, and can allow the particle size of the forsterite particles to be formed uniformly in the width direction of the steel sheet. More specifically, the low-melting-point additive may have a melting point of 750°C.

[0094] Specifically, the additive may include one or more of hydroxides, carbonates, amide compounds, chromates, oxides, antimony compounds, chlorine compounds, chloride oxides, sulfur compounds, nitrogen compounds, bromides, bromates, telluric acid, vanadates, borates, and phosphorus compounds.

[0095] Additionally, the additive may include one or more of 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.

[0096] Examples of additives may include one or more of SrCl2, Sb2O3, FeBr2, CuCl, MnCl2, B2O3, NiSO4, CoSO4, CuBr, and SnS.

[0097] The additive may be included in an amount of 0.01 to 0.50 parts by weight per 100 parts by weight of MgO. The weight part refers to the relative weight ratio of each component, and is measured as a solid content with all moisture removed. If the amount of the low-melting-point additive added is too little, it is difficult to sufficiently obtain the effect of promoting the formation of a low-melting-point glassy layer or a forsterite film. If the amount of the low-melting-point additive added is too much, localized melting defects in the form of pinholes may occur. More specifically, the low-melting-point additive may be included in an amount of 0.05 to 0.30 parts by weight.

[0098] The annealing separator contains 100 parts by weight of MgO. MgO also exists in the form of Mg(OH)2 when present in water. In one embodiment of the present invention, MgO is interpreted to mean Mg(OH)2 together with MgO, and the content of MgO can be understood as the sum of MgO and Mg(OH)2.

[0099] The moisture content of MgO may be 1.2 to 2.5 wt%. The moisture content also helps to form the forsterite particles uniformly in the width direction of the steel sheet together with the low-melting-point additives mentioned above. If the moisture content is too low, there may be insufficient moisture to semi-wet the atmosphere between the steel sheets, resulting in a thin forsterite film in the center of the width direction and uneven formation of forsterite particles. On the other hand, if the moisture content is too high, the moisture content between the steel sheets may be excessive, resulting in excessive oxidation at the edge, which may increase oxidation defects. More specifically, the moisture content of MgO may be 1.5 to 2.3 wt%. The moisture content of MgO refers to the total amount of moisture remaining in the steel sheet and moisture remaining in the Mg(OH)2 state when MgO Powder is mixed with pure water at about 12°C or lower, a slurry is applied to the steel sheet, and then dried. The hydration moisture of MgO can be defined as the hydration moisture of MgO by measuring the weight of a small amount of MgO collected from the steel plate after drying, and then measuring the weight of MgO after heat treatment at 1000℃ for 1 hour.

[0100] The annealing separator may additionally contain ceramic powders such as TiO2, SiO2, and Al2O3 in addition to MgO and low-melting-point additives. When one or more of TiO2, SiO2, and Al2O3 is further added, it may contain 1 to 10 parts by weight per 100 parts by weight of MgO.

[0101] Next, the steel sheet that has undergone primary recrystallization annealing is subjected to secondary recrystallization annealing.

[0102] During secondary recrystallization annealing, the steel sheet is wound into a coil shape and annealed for a long period of time. Fig. 1 schematically shows a steel sheet according to an embodiment of the present invention, and Fig. 2 schematically shows a steel sheet wound into a coil shape.

[0103] One end (101) in Fig. 1 corresponds to the upper end (101) of the coil, and the other end (102) in Fig. 2 corresponds to the lower end (102) of the coil. Since the edge portion (110) adjacent to the upper end (101) and the lower end (102) of the coil comes into direct contact with the air of the external atmosphere, oxidation occurs excessively compared to the center portion (120) inside, and as a result, the particle size of the forsterite particles between the edge portion (110) and the center portion (120) becomes uneven.

[0104] In one embodiment of the present invention, by varying the atmospheric conditions according to the thermal history of the steel sheet during the secondary recrystallization annealing process, the particle size of the forsterite particles is uniformly formed between the edge portion (110) and the center portion (120).

[0105] Specifically, the second recrystallization annealing step includes a first temperature increasing step in which the steel sheet temperature is 650°C to 900°C, a second temperature increasing step in which the steel sheet temperature is higher than 900°C but lower than the cracking temperature, and a cracking step, and the atmospheric conditions at each step are controlled.

[0106] Below, each step is explained in detail.

[0107] First, the steel sheet is heated through a first temperature raising step at a temperature of 650°C to 900°C. In the first temperature raising step, the oxide layer on the surface of the steel sheet formed during the first recrystallization annealing process is prepared to a state suitable for reaction with MgO. The first temperature raising step is performed in an atmosphere having an oxidation capacity (PH2O / PH2) of 0.05 to 0.40. If the oxidation capacity is too low, the oxide layer cannot properly react with MgO in the subsequent step, and a reduction reaction of Fe-based oxides occurs, making it difficult for forsterite particles, particularly in the center portion (120), to grow sufficiently. Conversely, if the oxidation capacity is too high, olivine and pyroxene phase oxides in the surface oxide layer of the edge portion (110), increase, which hinders the reaction with MgO and makes it difficult for forsterite particles to grow sufficiently. More specifically, the first temperature raising step can be performed in an atmosphere having an oxidation capacity (PH2O / PH2) of 0.10 to 0.25. The oxidation capacity may have a slope that decreases as the temperature increases, and the oxidation capacity of the first temperature-rising step means the average oxidation capacity for the entire time of the first temperature-rising step.

[0108] The first heating step may include 10 to 50 vol% N2 and 50 to 90 vol% H2. If the N2 content is too low, the decomposition of the inhibitor may occur too quickly, which may result in a deterioration of the magnetic properties. If the N2 content is too high, it may be difficult to uniformly control the oxidation capacity within the steel sheet, and additional nitriding may occur in the steel sheet, which may affect the forsterite film and the magnetic properties. More specifically, the first heating step may include 20 to 40 vol% N2 and 60 to 80 vol% H2.

[0109] The first temperature-elevation stage operates at a temperature-elevation rate of 5°C / hr to 90°C / hr. If the temperature-elevation rate of the first temperature-elevation stage is too high, the temperature deviation within the winding coil will be excessively large, and the equipment will be overworked, so this should be avoided. If the temperature-elevation rate of the first temperature-elevation stage is too low, productivity problems may occur. More specifically, the temperature-elevation rate of the first temperature-elevation stage may be 10°C / hr to 75°C / hr.

[0110] After the first heating step, forsterite may be included in an amount of 2 to 15 wt% in a thickness ranging from 10 μm from the surface of the steel sheet toward the inside of the steel sheet. By appropriately controlling the aforementioned oxidation capacity (PH2O / PH2), forsterite is appropriately formed. If there is too little forsterite, it becomes difficult for forsterite particles in the center portion (120) to grow sufficiently. If there is too much forsterite, it becomes difficult for forsterite particles in the edge portion (110) to grow sufficiently. The total amount of forsterite can be measured by analyzing it with an X-ray quantitative analyzer.

[0111] Next, the steel sheet is heated through a second temperature increasing step in which the temperature of the steel sheet is higher than 900℃ but lower than the cracking temperature. In the second temperature increasing step, the oxide layer on the surface of the steel sheet begins to react with MgO in earnest, and an inhibitor removal reaction occurs. The second temperature increasing step is performed in an atmosphere in which the oxidation capacity (PH2O / PH2) is 0.03 or lower. If the oxidation capacity (PH2O / PH2) 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 and makes it difficult for the forsterite particles to grow sufficiently. More specifically, the oxidation capacity (PH2O / PH2) in the second temperature increasing step may be 0.01 to 0.03.

[0112] The second heating step may contain N250 vol% or less and H250 vol% or more. If there is too much N2, it may be difficult to uniformly control the oxidation ability within the steel sheet, and additional nitriding may occur in the steel sheet, which may affect the forsterite film and magnetic properties. More specifically, the second heating step may contain N230 vol% or less and H270 vol% or more. More specifically, the second heating step may contain N210 to 30 vol% and H270 to 90 vol%.

[0113] The second heating step is performed at a rate of 5°C / hr to 30°C / hr. If the heating rate of the second heating step is too high, a temperature deviation may occur within the winding coil, which may cause deviations in not only the magnetic properties but also the surface properties, and thus, the heating rate is limited. Conversely, if the heating rate of the second heating step is too low, productivity may decrease, and thus, the heating rate is limited. More specifically, the heating rate of the second heating step may be 8°C / hr to 25°C / hr.

[0114] After the second heating step, forsterite is included in an amount of 85 to 100 wt% at a thickness ranging from 10 μm from the surface of the steel sheet toward the inside of the steel sheet. By appropriately controlling the aforementioned oxidation capacity (PH2O / PH2), forsterite is appropriately formed.

[0115] Next, a cracking step is included in which the steel sheet is cracked at a cracking temperature. The cracking temperature may be 1000°C or higher, and specifically, 1170 to 1220°C. In the cracking step, the formation of a forsterite film is completed, secondary recrystallization grows, and inhibitors are removed. In the cracking step, the oxidation capacity (PH2O / PH2) can be maintained below 0.03. In addition, by including H299 vol% or more, the removal of inhibitors and impurities can be smoothly achieved. The cracking step can be performed for 1 to 25 hours.

[0116] After the secondary recrystallization annealing, the unreacted annealing separator is washed away, pickled, and an insulating film is applied. Then, heat flattening treatment, which includes annealing treatment of the insulating film, shape correction, and stress relief annealing, can be performed.

[0117] A directional electrical steel sheet according to one embodiment of the present invention contains, in wt%, C: 0.005% or less (excluding 0%), Si: 1.5% to 4.5%, Mn: 1.0% or less, and the remainder includes Fe and other unavoidable impurities.

[0118] Since the steel component of the grain-oriented electrical steel sheet has been described in the steel component of the slab in the manufacturing method of the grain-oriented electrical steel sheet mentioned above, a duplicate description will be omitted.

[0119] As described above, in the manufacturing method of oriented electrical steel sheets, by applying different oxidation capacities during the temperature-raising process in the secondary recrystallization annealing process, the deviation in the forsterite particle size in the width direction of the steel sheet is reduced.

[0120] Specifically, a forsterite layer exists on one or both sides of a steel plate substrate, and the ratio of the average grain size (P1) of the forsterite particles existing in the forsterite layer of the edge portion (110) from one end of the width direction of the steel plate to 30% of the entire width of the steel plate from one end of the steel plate to the other end and from 70% of the entire width of the steel plate to the other end, and the average grain size (P2) of the forsterite particles existing in the forsterite layer of the center portion (120) from more than 30% to less than 70% of the entire width of the steel plate from one end of the steel plate to the other end is (P2 / P1) 0.8 to 1.2.

[0121] The forsterite particles in the present invention refer to particles of a crystalline oxide mainly composed of Mg2SiO4 formed during secondary recrystallization annealing. The average particle diameter of the forsterite particles can be obtained by collecting at least 15 samples in the cross-section in the TD direction for the corresponding regions of the edge portion (110) and the center portion (120) and measuring the particle diameters of the forsterite particles in the corresponding forsterite layer. More specifically, the particle diameter of the forsterite particles can be measured by collecting the corresponding sample, processing the cross-section using a Focused Ion Beam from Carl Zeiss, and measuring the forsterite film using a Transmission Electron Microscope from JEOL. Thereafter, the forsterite particles can be measured using an Image Analyzer from Leica. In addition, the present invention does not place any restrictions on the method for measuring the forsterite particles.

[0122] If the average particle size ratio (P2 / P1) of the forsterite particles is too small or too large, it means that the particle size of the forsterite particles is not uniform between the edge portion (110) and the center portion (120), which also affects the particle size of the secondary recrystallization under the forsterite layer, and the particle size of the secondary recrystallization is not formed uniformly, and a magnetic deviation occurs in the width direction. Specifically, the average particle size ratio (P2 / P1) of the forsterite particles may be 0.85 to 1.15.

[0123] As described above, since the average grain size ratio (P2 / P1) of the forsterite particles in one embodiment of the present invention is uniform, the grain size of secondary recrystallization can also be uniformly formed between the edge portion (110) and the center portion (120). Specifically, the ratio of the average grain size (R1) of secondary recrystallization existing in the edge portion (110) from one end of the width direction of the steel sheet to 30% of the entire width of the steel sheet from one end of the steel sheet to the other end and from 70% of the entire width of the steel sheet from one end of the steel sheet to the other end, and the average grain size (R2) of secondary recrystallization existing in the center portion (120) from more than 30% to less than 70% of the entire width of the steel sheet from one end of the steel sheet, (R2 / R1) may be 0.7 to 1.2. More specifically, the average grain size ratio (R2 / R1) of secondary recrystallization may be 0.80 to 1.10.

[0124] The average grain size of the forsterite particles present in the forsterite layer of the edge portion (110) is 0.3 to 2.0 µm, and the average grain size of the forsterite particles present in the forsterite layer of the center portion (120) is 0.3 to 2.0 µm.

[0125] A oriented electrical steel sheet according to one embodiment of the present invention has excellent iron loss and magnetic flux density, while at the same time having a very small iron loss and magnetic flux density deviation in the width direction.

[0126] A directional electrical steel sheet according to one embodiment of the present invention has a magnetic flux density (B8) of 1.90 T or more and a core loss (W 17 / 50 ) may be less than 0.90 W / kg. At this time, the magnetic flux density B8 is the size (Tesla) of the magnetic flux density induced under a magnetic field of 800 A / m, and the iron loss W 17 / 50 is the magnitude of the iron loss (W / kg) induced under 1.7 Tesla and 50 Hz conditions. More specifically, when the magnetic flux density (B8) is 1.91 T to 1.95 T and the iron loss (W 17 / 50 ) can be 0.75 to 0.85 W / kg.

[0127] According to one embodiment of the present invention, a directional electrical steel sheet has a core loss (W) at the center relative to the edge at a width of 1050 mm or more. 17 / 50 ) ratio (center part / edge part) can be 0.98 to 1.2.

[0128] Additionally, the ratio of the magnetic flux density (B8) of the center to the edge (center / edge) may be 0.98 to 1.00. The deviation of the iron loss and magnetic flux density can be obtained by collecting 10 or more samples from each section and taking the average value of the samples.

[0129] Additionally, the forsterite film adhesion is excellent. Adhesion can be measured by the minimum arc diameter that does not cause film peeling when bent 180° in contact with a circular arc of a specific diameter. Specifically, the forsterite film adhesion can be 20 mmΦ or less.

[0130]

[0131] Specific examples of the present invention are described below. However, the following examples are merely specific examples of the present invention, and the present invention is not limited to the following examples.

[0132]

[0133] Experimental Example 1

[0134] A slab containing C: 0.060%, Si: 3.3%, Mn: 0.090%, Al: 0.028%, Sb: 0.04%%, Cu: 0.02%, and Sn: 0.05% by weight, with the remainder being Fe and unavoidable impurities, was prepared, and the slab was heated to a temperature of 1150°C, hot-rolled to a thickness of 2.3 mm, and then rapidly cooled to 600°C and coiled. The hot-rolled sheet was annealed at 1080°C, pickled, and then cold-rolled once to a thickness of 0.20 mm. For cold-rolled steel sheets, simultaneous decarbonitriding annealing was performed at 850℃ in a humid 50v% hydrogen and 50v% nitrogen humid atmosphere and an ammonia mixed gas atmosphere for 180 seconds so that the carbon content became 30ppm or less and the total nitrogen content became 200ppm or more. To the steel sheets, a slurry containing an annealing separator having a hydration moisture content of 1.75 wt%, 100 parts by weight of MgO, 5 parts by weight of TiO, 0.15 parts by weight of SrCl, 0.10 parts by weight of Sb2O, and 0.05 parts by weight of FeBr was stirred at a water temperature of 8℃, and applied at a rate of 6.0g / m2 per side based on the weight after drying, and then wound into a coil.

[0135] After the first heating step (steel plate temperature 900℃) and the second heating step (steel plate temperature 1200℃) were taken out, the results of quantifying forsterite (Mg2SiO4) using XRD are summarized in Table 1 below.

[0136] Afterwards, secondary recrystallization annealing was performed by heating and cracking at 1200°C in an atmosphere summarized in Table 1 below for 6 hours, and a solution containing Al phosphate and colloidal silica as main components was applied as an insulating film component in a continuous line, followed by annealing at 850°C.

[0137] For the final manufactured oriented electrical steel sheet, 20 specimens were collected by shearing them to the Epstein specimen size [60 mm (width) X 300 mm (length)] from the edge and center, respectively, and the average forsterite grain size, secondary recrystallization grain size, magnetic flux density (B8), and iron loss (W 17 / 50 ) were measured and summarized in Tables 2 and 3 below.

[0138] The average particle size of forsterite was measured by processing the cross-section using a Carl Zeiss Focused Ion Beam, measuring the forsterite film using a JEOL Transmission Electron Microscope, and then using a Leica Image Analyzer.

[0139] The secondary recrystallization grain size was measured using the ASTM (American Society for Testing and Material) grain size test method after the secondary recrystallization annealing was completed and the insulating coating and forsterite film were completely removed with hydrochloric acid.

[0140] The results of the adhesion evaluation of the forsterite film are shown in Table 3. The adhesion was measured as the minimum arc diameter without film peeling when bent 180° in contact with an arc with a diameter of 10 to 50 mm.

[0141] The deviation of iron loss and magnetic flux density was calculated at the center / edge.

[0142] First heating stageSecond heating stageOxidizing abilityNitrogenHeating rateForsterite amountOxidizing abilityNitrogenHeating rateForsterite amount(P H2O / P H2 )(vol%)(℃ / hr)(wt%)(P H2O / P H2)(vol%)(℃ / hr)(wt%)Example 10.1525155.20.02252098Example 20.1015202.80.02252094Example 30.2525207.30.02252096Example 40.0525103.40.02252088Example 50.35401512.50.02252094Comparative Example 10.0125200.10.02252081Comparative Example 20.50752522.70.02252095Comparative Example 30.20251000.10.02252083Example 60.1525755.20.01251594 Example 70.1525755.20.03251596 Example 80.1525755.20.02252589 Example 90.2525757.30.02251098 Example 100.2525757.30.02401095 Example 110.2525757.30.03502593 Comparative Example 40.1525755.20.30251590 Comparative Example 50.1525755.20.032510076 Comparative Example 60.2525757.30.03752095

[0143] Forsterite Average grain size Secondary recrystallization Average grain size Edge (P1, ㎛) Center (P2, ㎛) P2 / P1 Edge (R1, cm) Center (R2, cm) R2 / R1 Example 10.68 0.65 0.96 1.89 1.68 0.89 Example 20.58 0.53 1.09 2.18 2.02 0.93 Example 30.76 0.88 1.16 1.58 1.54 0.97 Example 40.44 0.38 0.86 2.43 2.20 91 Example 5 1.05 0.95 0.91 2.05 1.83 0.89 Comparative example 10.15 0.22 1.47 5.83 94 0.68 Comparative example 22.521.850.730.040.040.61Comparative Example 30.130.161.234.853.290.68Example 60.680.620.912.742.620.96Example 70.830.750.901.661.480.89Example 80.560.450.823.082.440.79Example 90.800.780.981.731.480.86Example 100.940.810.862.672.260.85Example 111.100.980.892.832.160.76Comparative Example 43.452.520.736.875.420.79Comparative example 50.520.270.523.021.210.40Comparative example 61.340.840.637.666.320.83

[0144] Iron loss (W17 / 50, W / kg) Magnetic flux density (B8, T) Adhesion (mm) Edge center deviation Edge center deviation Example 10.64 0.65 1.02 1.93 1.93 1.00 15 Example 20.63 0.65 1.03 1.94 1.93 0.99 18 Example 30.66 0.67 1.02 1.93 1.92 0.99 15 Example 40.63 0.65 1.03 1.94 1.93 0.99 17 Example 50.70 0.69 0.99 1.91 1.91 1.00 20 Comparative Example 10.92 0.88 0.96 1.88 1.89 1.01 45 Comparative Example 21.051.040.991.861.861.0040Comparative Example 30.920.900.981.871.871.0035Example 60.751.021.361.901.850.9745Example 70.720.821.141.921.900.9932Example 80.780.931.191.911.870.9845Example 90.640.641.001.931.931.0015Example 100.680.691.011.911.911.0020Example 110.710.700.991.911.900.9920Comparative example 40.880.911.031.891.870.9932Comparative example 50.880.850.971.881.891.0135Comparative example 60.860.871.011.871.871.0037

[0145]

[0146] As can be seen in Tables 1 to 3, when the temperature and cracking conditions are appropriately controlled during the secondary recrystallization annealing process, the average particle size of forsterite is formed uniformly, the magnetism is excellent, and the magnetic deviation in the width direction is reduced.

[0147] On the other hand, if the atmospheric conditions during heating and cracking are not properly controlled, the average particle size of forsterite is formed unevenly and the magnetic deviation in the width direction is large.

[0148]

[0149] Experimental Example 2

[0150] The same procedure as Example 1 was followed, but the annealing separator was changed as shown in Table 4. For the finally manufactured oriented electrical steel sheet, 20 specimens were collected by shearing them to the Epstein specimen size [60 mm (width) X 300 mm (length)] at the edge and center, respectively, and the forsterite average grain size, secondary recrystallization grain size, magnetic flux density (B8), and iron loss (W 17 / 50 ) were measured and summarized in Tables 5 and 6 below.

[0151] Hydration moisture (wt%) Low melting point additive (weight parts) Additive-1 Additive-2 Additive-3 Additive-4 Example 121.75 SrCl 2 0.15 Sb 2 O 3 0.10 Fe 2 0.05 - Example 131.75 Sb 2 O 3 0.15 CuCl 0.05 - Example 141.80 MnCl 2 0.05 B 2 O 3 0.05 NiSO 4 0.15 CoSO 4 0.05 Example 151.46 MnCl 2 0.10 CoSO 4 0.05 CuBr 0.15 - Example 162.31 SrCl 2 0.10 Sb 2 O 3 0.20 SnS 0.15 - Example 171.82SrCl20.10CoSO40.20NiSO40.05-Comparative Example 71.75----Comparative Example 81.91MnCl20.15B2O30.30NiSO40.25-Comparative Example 91.13SrCl20.15Sb2O30.10--Comparative Example 102.95SrCl20.15Sb2O30.10--

[0152] Forsterite Average grain size Secondary recrystallization Average grain size Edge (P1, ㎛) Center (P2, ㎛) P2 / P1 Edge (R1, cm) Center (R2, cm) R2 / R1 Example 120.660.600.912.321.800.78 Example 130.610.520.851.561.520.97 Example 140.520.581.121.281.120.88 Example 150.540.551.021.361.401.03 Example 160.650.731.122.642.080.79 Example 170.730.811.112.201.760.80 Comparative example 70.460.290.636.083.520.58Comparative example 80.580.921.595.002.680.54Comparative example 90.380.230.616.684.080.61Comparative example 101.520.990.653.645.001.37

[0153] Iron loss (W17 / 50, W / kg) Magnetic flux density (B8, T) Adhesion (mm) Edge (P1) Center (P2) Deviation (P2 / P1) Edge (P1) Center (P2) Deviation (P2 / P1) Example 120.650.671.031.931.920.9916 Example 130.670.681.021.931.920.9918 Example 140.630.651.031.941.931.0015 Example 150.650.661.021.931.920.9915 Example 160.660.691.051.921.911.0017 Example 170.650.671.031.931.931.0017Comparative example 70.800.811.011.911.880.9840Comparative example 80.751.021.361.901.850.9745Comparative example 90.720.821.141.921.900.9932Comparative example 100.780.931.191.911.870.9845

[0154] As can be seen in Tables 4 to 6, it can be confirmed that the addition range of the low-melting-point additive proposed in the present invention and the characteristics of the hydration moisture in the annealing separator have an effect on improving the uniformity of the average particle size of forsterite.

[0155]

[0156] The present invention is not limited to the above-described embodiments and / or examples, but can be manufactured in various different forms. Those skilled in the art will understand that the present invention can be implemented in other specific forms without altering the technical spirit or essential characteristics of the present invention. Therefore, the above-described embodiments and / or examples should be understood as illustrative in all respects and not restrictive.

[0157] [Explanation of symbols]

[0158] 100: Oriented electrical steel sheet, 101: Single end,

[0159] 102: other end, 110: edge,

[0160] 120: Center section

Claims

1. A step for manufacturing a slab containing, by weight%, Si: 1.5 to 4.5%, C: 0.70% or less (excluding 0%), Mn: 1.0% or less (excluding 0%), and the remainder being Fe and other unavoidable impurities; A step of manufacturing a hot-rolled plate by hot-rolling the above slab; A step of manufacturing a cold rolled sheet by cold rolling the hot rolled sheet; A step of first recrystallization annealing the above cold rolled sheet; and It includes a step of performing a second recrystallization annealing on a first recrystallization annealed steel sheet, The above second recrystallization annealing step is, It includes a first heating step in which the steel plate temperature is 650℃ to 900℃, a second heating step in which the steel plate temperature is higher than 900℃ but lower than the cracking temperature, and a cracking step. The above first temperature increase step increases the oxidation capacity (PH 2 O / PH 2 ) is performed in an atmosphere where the oxidation capacity (PH) is 0.05 to 0.40, and the second temperature increasing step 2 O / PH 2 ) A method for manufacturing a grain-oriented electrical steel sheet performed in an atmosphere having a pH of 0.03 or less.

2. In paragraph 1, A method for manufacturing a grain-oriented electrical steel sheet, wherein the above slab further includes at least one of Al: 0.015 to 0.040 wt%, N: 0.0055 wt% or less, and S: 0.0055 wt% or less.

3. In paragraph 1, A method for manufacturing a grain-oriented electrical steel sheet, wherein the above slab further contains at least one 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. In paragraph 1, After the first recrystallization annealing step, and before the second recrystallization annealing step, an annealing separator is applied. A method for manufacturing a grain-oriented electrical steel sheet, wherein the annealing separator comprises 100 parts by weight of MgO and 0.01 to 0.50 parts by weight of an additive having a melting point of 900°C or lower.

5. In paragraph 4, A method for manufacturing a grain-oriented electrical steel sheet, wherein the additive comprises at least one of a hydroxide, a carbonate, an amide compound, a chromate, an oxide, an antimony compound, a chlorine compound, a chloride oxide, a sulfur compound, a nitrogen compound, a bromide, a bromate, a telluric acid, a vanadate, a borate, and a phosphorus compound.

6. In paragraph 4, A method for manufacturing a grain-oriented electrical steel sheet, wherein the additive comprises at least one of 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. In paragraph 4, The above additive is SrCl 2 , Sb 2 O 3 , FeBr 2 , CuCl, MnCl 2 , B 2 O 3 , NiSO 4 , CoSO 4 A method for manufacturing a grain-oriented electrical steel sheet comprising at least one of CuBr and SnS.

8. In paragraph 4, A method for manufacturing a grain-oriented electrical steel sheet, wherein the hydration moisture of the above MgO is 1.2 to 2.5 wt%.

9. In paragraph 1, The above first temperature rising step is N 2 10 to 50 vol% and H 2 Containing 50 to 90 volume %, and the second heating step comprises N 2 50% by volume or less and H 2 Contains more than 50 volume%, and the cracking stage is H 2 A method for manufacturing a grain-oriented electrical steel sheet containing 99% or more by volume.

10. In paragraph 1, A method for manufacturing a grain-oriented electrical steel sheet, wherein the first heating step is performed at a heating rate of 5°C / hr to 90°C / hr, and the second heating step is performed at a heating rate of 5°C / hr to 30°C / hr.

11. In paragraph 1, A method for manufacturing a grain-oriented electrical steel sheet, which comprises 2 to 15 wt% of forsterite in a thickness ranging from 10 µm from the surface of the steel sheet toward the inside of the steel sheet after the first temperature-elevating step, and which comprises 85 to 100 wt% of forsterite in a thickness ranging from 10 µm from the surface of the steel sheet toward the inside of the steel sheet after the second temperature-elevating step.

12. Contains C: 0.005% or less (excluding 0%), Si: 1.5% to 4.5%, Mn: 1.0% or less (excluding 0%), and the remainder includes Fe and other impurities that are inevitably mixed. A forsterite layer exists on one or both sides of the steel plate substrate, The average grain size (P) of forsterite particles existing in the forsterite layer at the edge from one end of the width direction of the steel plate to 30% of the total width of the steel plate and from 70% of the total width of the steel plate to the other end 1 ) and the average grain size (P) of forsterite particles present in the center forsterite layer exceeding 30% but less than 70% of the total width of the steel plate at one end of the steel plate. 2 ) is the ratio of (P 2 / P 1 ) Grain-oriented electrical steel sheet having a molecular weight of 0.8 to 1.

2.

13. In paragraph 12, Grain-oriented electrical steel sheet further comprising at least one of Al: 0.040 wt% or less, N: 0.0050 wt% or less, and S: 0.005 wt% or less.

14. In paragraph 12, Grain-oriented electrical steel sheet further comprising at least one 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%.

15. In paragraph 12, A grain-oriented electrical steel sheet wherein the average grain size of the forsterite particles present in the forsterite layer of the edge portion is 0.3 to 2.0 ㎛, and the average grain size of the forsterite particles present in the forsterite layer of the center portion is 0.3 to 2.0 ㎛.

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