Grain-oriented electrical steel sheet and its manufacturing method

Abstract

To provide a grain-oriented electrical steel sheet that has excellent magnetic properties due to refined secondary recrystallization and at the same time has little variation in properties within the coil. [Solution] Grain-oriented electrical steel sheets are made of {110} <001> The size of the oriented crystal grains satisfies the following formula 1: <001> It is characterized in that the area fraction of crystal grains with angles deviating from the orientation by 3° or less is 60% or more. <Expression 1> W / L≦1.5 (In the above formula 1, W is the diameter in the TD direction (width direction of the secondary recrystallized grain), and L is the diameter in the RD direction (longitudinal direction of the secondary recrystallized grain).)

Description

[Technical Field]

[0001] The present invention relates to a grain-oriented electrical steel sheet and a manufacturing method thereof, and more particularly to a grain-oriented electrical steel sheet having excellent magnetic properties due to refinement of secondary recrystallized grains and having little variation in properties within a coil, and a manufacturing method thereof. [Background technology]

[0002] Electrical steel sheets are used in transformers, motors, and electronic devices. Unlike ordinary carbon steels, which emphasize workability as a material for machine parts, electrical steel sheets are functional products that emphasize electrical properties. These electrical properties include iron loss, magnetic flux density, magnetic permeability, and space factor. Electrical steel sheets are characterized by low iron loss and high magnetic flux density, magnetic permeability, and space factor. The electrical steel sheets are broadly divided into grain-oriented electrical steel sheets and non-oriented electrical steel sheets. The grain-oriented electrical steel sheets utilize the phenomenon of abnormal grain growth called secondary recrystallization to form a Goos texture {110} <001> The non-oriented electrical steel sheet has a texture formed throughout the entire steel sheet, and has excellent magnetic properties in the rolling direction. The non-oriented electrical steel sheet has uniform magnetic properties in all directions on the rolled sheet.

[0003] The grain orientation of the grains in the grain-oriented electrical steel sheet is {110} <001> In the case of magnetic steel sheets with high magnetic flux density, not only can the size of the iron core material of electrical equipment be reduced, but hysteresis loss can also be reduced, allowing for the miniaturization of the electrical equipment while at the same time increasing its efficiency. The iron loss is the power loss consumed as heat energy when an arbitrary AC magnetic field is applied to a steel sheet. The higher the magnetic flux density and resistivity, the lower the iron loss. The lower the sheet thickness and the impurity content in the steel sheet, the lower the iron loss, which increases the efficiency of electrical equipment. In addition, in preparation for a carbon-neutral era, industrial structures are being restructured worldwide to focus on environmentally friendly, low-carbon industries, and there is a growing trend toward energy conservation and high-efficiency product development. This trend is driving increased demand for the widespread use of highly efficient electrical equipment that uses less electrical energy, and as a result, social demand is growing for grain-oriented electrical steel sheets with superior low iron loss properties.

[0004] For this reason, much research and development has been conducted to reduce the iron loss of grain-oriented electrical steel sheets. Among these, techniques for refining secondary recrystallized grains have attracted attention as one effective method for reducing iron loss. Techniques for refining secondary recrystallized grains reduce the size of magnetic domains in steel sheets, thereby reducing heat loss due to eddy currents caused by domain wall motion when the steel sheets are magnetized. Furthermore, in order to refine the secondary recrystallized grains, a Goss structure must be strongly developed during the manufacturing process. One method for developing the Goss structure is to impart strong deformation during hot rolling. Methods for imparting strong deformation include severe plasticity processes such as asymmetric rolling, ECAP (Equal-Channel Angular Extrusion), and HPT (High Pressure Torsion). However, these methods have not yet been industrially developed.

[0005] Another method for refining the secondary recrystallized grains is to minimize the temperature deviation within the coil during the high-temperature annealing step, where the Goss structure grows. Generally, the high-temperature annealing is performed in a batch mode. During this process, a temperature deviation of approximately 300°C occurs within the coil, resulting in different growth rates of the Goss structure depending on the position. Specifically, a growth gradient is formed from high to low temperatures, which leads to the growth of the Goss structure. The asymmetric growth of the Goss structure can lead to variations in magnetic properties, resulting in unexpected degradation of transformer performance. Summary of the Invention [Problem to be solved by the invention]

[0006] The technical problem to be solved by the present invention is to provide a grain-oriented electrical steel sheet that has excellent magnetic properties due to refined secondary recrystallization and at the same time has little variation in properties within the coil. Another technical problem to be solved by the present invention is to provide a method for manufacturing a grain-oriented electrical steel sheet having the above advantages. [Means for solving the problem]

[0007] The grain-oriented electrical steel sheet of the present invention has a {110} <001> The size of the oriented crystal grains satisfies the following formula 1: <001> It is characterized in that the area fraction of crystal grains with angles deviating from the orientation by 3° or less is 60% or more. <Expression 1> W / L≦1.5 (In the above formula 1, W is the diameter in the TD direction (width direction of the secondary recrystallized grain), and L is the diameter in the RD direction (longitudinal direction of the secondary recrystallized grain).)

[0008] The steel plate can satisfy the following formula 2. <Expression 2> α×β×γ≦20° (In the above formula 2, α is {110} <001> β means the angle difference between the orientation and the ND axis, and β is {110} <001> γ means the angular difference between the orientation and the TD axis, and {110} <001> (meaning the angular difference between the azimuth and the RD axis)

[0009] The grain-oriented electrical steel sheet preferably contains, by weight, 2.0 to 5.0% Si, 0.005% or less C, 0.03 to 0.5% Mn, 0.01 to 0.04% Al, and 0.002 to 0.005% N, and further contains one or more of 0.01 to 0.05% by weight Sb, 0.03 to 0.08% by weight Sn, 0.01 to 0.2% by weight Cr, 0.01% or less S, and 0.005 to 0.045% by weight P, with the remainder consisting of Fe and unavoidable impurities.

[0010] A method for producing a grain-oriented electrical steel sheet according to the present invention includes the steps of hot-rolling a slab to produce a hot-rolled steel sheet, pre-rolling the hot-rolled steel sheet at a reduction rate of 10 to 40% to produce a pre-rolled sheet, annealing the pre-rolled sheet, cold-rolling the annealed pre-rolled sheet to produce a cold-rolled steel sheet, primary recrystallization annealing the cold-rolled steel sheet, and secondary recrystallization annealing the cold-rolled steel sheet that has been primarily recrystallized, wherein the hot-rolling step includes coiling the slab, wherein the coiling temperature is 600 to 800°C, and the secondary recrystallization annealing step is performed at a secondary recrystallization heating rate of 3 to 6°C / hr in a temperature range of 1000 to 1200°C, and a bottom direct heating method is used, and the secondary recrystallization annealing produces secondary recrystallized grains with {110} <001> The size of the oriented crystal grains satisfies the following formula 1: <001> It is characterized in that the area fraction of crystal grains with angles deviating from the orientation by 3° or less is 60% or more. <Expression 1> W / L≦1.5 (In the above formula 1, W is the diameter in the TD direction (width direction of the secondary recrystallized grain), and L is the diameter in the RD direction (longitudinal direction of the secondary recrystallized grain).)

[0011] In the step of producing the pre-rolled sheet, the temperature of the steel sheet immediately before pre-rolling may be 0.4Tc to 0.6Tc°C. (The above Tc means the coiling temperature [°C]) The method for producing the grain-oriented electrical steel sheet can satisfy the following formula 3. <Expression 3> 100≦Tb-Ta≦300 (In the above formula 3, Ta means the temperature at which cold rolling is performed, and Tb means the temperature at which pre-rolling is performed.)

[0012] The step of manufacturing the hot-rolled steel sheet may include rough rolling, finish rolling, and coiling steps. The thickness of the pre-rolled plate is preferably 1.5 to 3.0 mm. The step of annealing the pre-rolled sheet is preferably carried out at a soaking temperature range of 700 to 1,100°C. In the step of producing the cold-rolled steel sheet, the rolling reduction may be 85 to 95%. The step of producing the cold-rolled steel sheet may be carried out such that the temperature of the steel sheet immediately before cold rolling is in the range of 0.2Tc to 0.4Tc°C. (The above Tc means the coiling temperature [°C]) [Effects of the Invention]

[0013] By controlling the hot rolling conditions and applying pre-rolling, the grain-oriented electrical steel sheet of the present invention can be provided with fine secondary recrystallization, which results in excellent magnetic properties and, at the same time, small variations in properties within the coil. The method for producing a grain-oriented electrical steel sheet of the present invention can provide a grain-oriented electrical steel sheet having the above-mentioned advantages. DETAILED DESCRIPTION OF THE INVENTION

[0014] When a part is referred to as being "on top of" another part, it may be directly on top of another part, or there may be other parts between them. In contrast, when a part is referred to as being "directly on top of" another part, there are no other parts between them. Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention pertains. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal sense unless specifically defined. Furthermore, unless otherwise specified, % means % by weight, and 1 ppm is 0.0001 wt%. In one embodiment of the present invention, "additionally containing an additional element" means that the remaining iron (Fe) is substituted by the additional amount of the additional element.

[0015] In the present invention, the Goss orientation is {110} in Miller indices. <001> This is the direction equivalent to. While the present invention may be embodied in many different forms, it is to be understood that the invention is not limited to the embodiments set forth herein.

[0016] The grain-oriented electrical steel sheet of the present invention contains, by weight, 0.1 to 6.5% Si, 0.001 to 6.5% Al, 0.01 to 20% Mn, 0.0050% or less C, and 0.0003 to 0.001% each of one or more of N, S, and Ti, with the remainder consisting of Fe and unavoidable impurities. The reasons for limiting the components of the grain-oriented electrical steel sheet will be explained below.

[0017] Si:2.0~5.0wt% Silicon (Si) is a component that increases the resistivity of a material and reduces iron loss, and is used as a deoxidizer in the steelmaking process. The silicon content is preferably 2.0 to 5.0 wt %. Specifically, the silicon content is preferably 3.0 to 4.5 wt %. By ensuring that the silicon content satisfies this range, excellent magnetic properties and productivity of the electrical steel sheet can be ensured. If the silicon content is too high, there are problems such as frequent sheet breakage during rolling due to reduced ductility and toughness among mechanical properties, and reduced productivity due to reduced inter-sheet weldability during continuous annealing for commercial production.On the other hand, if the silicon content is too low, there are problems such as reduced resistivity and increased eddy current loss, resulting in degraded iron loss characteristics.

[0018] C: 0.005% by weight or less Carbon (C) is an austenite stabilizing element. It is added to the slab to refine the coarse columnar structure that occurs during the continuous casting process and suppress the segregation of sulfur (S) at the slab center. It also promotes the work hardening of the steel sheet during cold rolling and creates {110} <001> The carbon content of the slab is preferably 0.01 to 0.10% by weight, and more preferably 0.03 to 0.08% by weight. If the carbon content is too high, edge cracks may occur during hot rolling. However, the carbon content decreases during the decarburization process. If a large amount of carbon remains in the final grain-oriented electrical steel sheet, it precipitates carbides formed by the magnetic aging effect within the steel sheet, deteriorating its magnetic properties. Therefore, the carbon content of the final grain-oriented electrical steel sheet after high-temperature annealing is 0.005 wt% or less, and preferably 0.003 wt% or less.

[0019] Mn:0.03~0.50wt% Manganese (Mn), like Si, increases resistivity and reduces eddy current loss, thereby reducing iron loss. It also functions as a grain growth inhibitor by reacting with sulfur (S) present in steel to form manganese-based compounds or with aluminum (Al) and nitrogen (N) to form nitrides in the form of (Al, Si, Mn)N. The manganese content is preferably 0.03 to 0.5 wt. %. More preferably, the manganese content is 0.05 to 0.3 wt. %. If the manganese content is too high, the growth of the Goss structure during secondary recrystallization annealing may be severely suppressed, resulting in a rapid deterioration of magnetic properties, whereas if the manganese content is too low, the above effects may not be achieved.

[0020] Al:0.01~0.04wt% Aluminum (Al) acts as a grain growth inhibitor by combining with nitrogen ions introduced by ammonia gas, the atmospheric gas used in the nitriding process during primary recrystallization annealing, to form nitrides in the form of aluminum nitride (AlN), and by combining with silicon, manganese, and nitrogen present in solid solution in the steel to form nitrides in the form of (Al, Si, Mn)N. The aluminum content is preferably 0.01 to 0.04 wt. %. More preferably, the aluminum content is 0.015 to 0.035 wt. %.

[0021] N:0.002~0.005wt% Nitrogen (N) is an element that reacts with aluminum (Al) and manganese (Mn) to form compounds such as aluminum nitride (AlN) and (Al, Mn, Si)N. The nitrogen content is preferably 0.002 to 0.005 wt%. Furthermore, nitrogen reinforces nitrides for secondary recrystallization of Goss texture. Nitrogen ions can be diffused into the steel by introducing ammonia gas as an atmospheric gas during the decarburization annealing process, thereby performing nitriding and reinforcing the steel. If the nitrogen content exceeds the upper limit of the range, not only will surface defects such as blisters be caused by nitrogen diffusion during processes after hot rolling, but excessive nitrides will be formed in the slab, resulting in uneven grain sizes in the subsequent hot-rolled sheet annealing and primary recrystallization annealing.On the other hand, if the nitrogen content is below the lower limit of the range, the amount of aluminum compounds formed during hot rolling will be too small, making it difficult to control the structure of the hot-rolled annealed sheet.

[0022] Sb:0.01~0.05wt% Antimony (Sb) segregates at grain boundaries to inhibit grain growth and stabilize secondary recrystallization. However, due to its low melting point, it easily diffuses to the surface during primary recrystallization annealing, potentially interfering with decarburization, oxide layer formation, and nitriding. The antimony content is preferably 0.01 to 0.05 wt. %. More preferably, the antimony content is 0.02 to 0.04 wt. %. If the antimony content is too high, it may hinder decarburization and inhibit the formation of an oxide layer that serves as the base of the base coating, whereas if the antimony content is too low, it may reduce the grain growth inhibition effect.

[0023] Sn:0.03~0.08wt% Tin (Sn) is a grain boundary segregating element that inhibits grain boundary migration and therefore acts as a grain growth inhibitor. Since the silicon content within the aforementioned range is insufficient to inhibit grain growth for smooth secondary recrystallization during secondary recrystallization annealing, tin may be further added to inhibit grain boundary migration by segregating at the grain boundaries.

[0024] Cr:0.01~0.20wt% Chromium (Cr) promotes the formation of hard phases in the annealed sheets of hot-rolled steel sheets, and the {110} <001> Chromium promotes the formation of texture and accelerates the decarburization of carbon during the primary recrystallization annealing process, thereby preventing the loss of texture and reducing the austenite phase transformation maintenance time. Furthermore, chromium promotes the formation of a surface oxide layer during the primary recrystallization annealing process, thereby overcoming the drawback of antimony and tin, which are alloying elements used as grain growth inhibitors and inhibit the formation of the oxide layer. The chromium content is preferably 0.01 to 0.20 wt. %. More preferably, the chromium content is 0.02 to 0.1 wt. %.

[0025] S: 0.01% by weight or less Sulfur (S) forms fine precipitates of manganese sulfide (MnS), which deteriorates magnetic properties and hot workability, so it is preferable to control the sulfur content to a low level. The sulfur content is preferably 0.010 wt%. More preferably, the sulfur content is 0.005 wt% or less, and even more preferably, the sulfur content is 0.004 wt% or less. If the sulfur content is excessively high, manganese sulfide precipitates are formed in the slab, which inhibits grain growth and segregates at the center of the slab during casting, making it difficult to control the microstructure in subsequent processes.

[0026] P:0.005~0.045wt% Phosphorus (P) segregates at the grain boundaries, hindering the movement of the grain boundaries and simultaneously playing a supporting role in suppressing the growth of grains. <001> It plays a role in improving the texture. The phosphorus content is preferably 0.005 to 0.045 wt %. If the phosphorus content is too high, the brittleness may increase and the rollability may be significantly reduced, whereas if the phosphorus content is too low, the effect of adding phosphorus may not be confirmed.

[0027] The grain-oriented electrical steel sheet according to one embodiment of the present invention contains the remainder Fe and unavoidable impurities. The unavoidable impurities are impurities that are mixed in during the steelmaking stage and the manufacturing process of the grain-oriented electrical steel sheet, and are widely known in the art, so a detailed description thereof will be omitted. The present invention does not exclude the addition of elements other than the above-mentioned alloy components, and various elements may be included within a range that does not impair the technical concept of the present invention. When an additional element is further included, the additional element may be included to replace the remainder Fe.

[0028] The grain-oriented electrical steel sheet of the present invention having the above-mentioned composition has the following physical properties. Grain-oriented electrical steel sheets are {110} <001> The size of the oriented crystal grains can satisfy the following formula 1: <Expression 1> W / L≦1.5 (In the above formula 1, W is the diameter in the TD direction (width direction of the secondary recrystallized grain), and L is the diameter in the RD direction (longitudinal direction of the secondary recrystallized grain).) In the above formula 1, W is the width direction of the secondary recrystallized grain, specifically, {110} <001> The grain size of secondary recrystallized grains refers to the diameter of secondary recrystallized grains having a Goss set orientation, which is the orientation of the secondary recrystallized grains. The grain size of secondary recrystallized grains refers to the diameter of secondary recrystallized grains measured in a plane (ND) perpendicular to the rolling plane (RD) after completing the secondary recrystallization annealing step.

[0029] The grain size refers to the diameter of the grain, which can be expressed by specifying individual grains enclosed by grain boundaries in a microscopic photograph, calculating the area of ​​each grain, and expressing the diameter of each grain as an equivalent circle diameter (ECD). At this time, the distribution of grain diameters is obtained using the ECD, and the arithmetic average is calculated, allowing the average grain diameter to be calculated. The value of the above formula 1 is preferably 1.5 or less. More preferably, the value of the above formula 1 is 0.7 to 1.5 or less. Even more preferably, the value of the above formula 1 is 0.9 to 1.5 or less. When the value of the above formula 1 satisfies the above range, the thermal gradient is reduced during the secondary recrystallization annealing process, and the degree of integration of the Goss structure can be improved.

[0030] The width of the secondary recrystallized grains is preferably in the range of 10 to 150 mm, and more preferably in the range of 15 to 100 mm. If the width of the secondary recrystallized grains exceeds the upper limit of the range, there is a problem of a decrease in the density of the Goss structure, whereas if the width of the secondary recrystallized grains falls below the lower limit of the range, there is a problem of a decrease in density and an increase in eddy current loss, resulting in deterioration of iron loss. The length of the secondary recrystallized grains in the longitudinal direction is preferably in the range of 10 to 100 mm, and more preferably in the range of 15 to 75 mm.

[0031] If the longitudinal length of the secondary recrystallized grains exceeds the upper limit of the range, there is a problem of a decrease in the density of the Goss structure, whereas if the longitudinal length of the secondary recrystallized grains is below the lower limit of the range, there is a problem of a decrease in the density and an increase in eddy current loss, resulting in a deterioration in iron loss. The grain-oriented electrical steel sheet of the present invention can satisfy the following formula 2. <Expression 2> α×β×γ≦20° (In the above formula 2, α is {110} <001> β means the angle difference between the orientation and the ND axis, and β is {110} <001> γ means the angular difference between the orientation and the TD axis, and {110} <001> (meaning the angular difference between the azimuth and the RD axis)

[0032] {110} of secondary recrystallized grains <001> The degree of accumulation of Goss set orientations can be determined by the deviation angle of the secondary recrystallized grain orientation from the Goss set orientation. Specifically, the deviation angle can be used to evaluate the degree of accumulation with respect to three rotation axes. More specifically, the three rotation axes can be classified into deviation angles in the normal direction (ND) axis, the transverse direction (TD) axis, and the rolling direction (RD) axis. Based on the deviation angle, in the above formula 2, α means the angle difference between the orientation of the Goss set and the axis normal to the rolling surface, β means the angle difference between the orientation of the Goss set and the axis perpendicular to the rolling direction, and γ means the angle difference between the orientation of the Goss set and the rolling direction axis.

[0033] The value of α×β×γ is preferably 20° or less. More preferably, the value is 10 to 18° or less. By satisfying the above values, the advantage of excellent integration of the Goss structure is obtained. Grain-oriented electrical steel sheets are made with the magnetic material oriented in the rolling direction, which is the axis of easy magnetization. <001> It is important that the <001> The crystal grains are characterized by having an area fraction of 60% or more of grains that are off-axis within 3° from the orientation. <001> It is characterized in that the area fraction of crystal grains with angles deviating from the orientation by 3° or less is 65 to 75%. The aforementioned <001> When the area fraction of the crystal grains whose angle deviates from the orientation by 3° or less falls within the above range, there is an advantage that the magnetization of the grain-oriented electrical steel sheet becomes easy. <001> If the area fraction of the crystal grain size corresponding to an angle deviating from the orientation by 3° or less exceeds the above range, there is a risk that the crystal will not be easily magnetized.

[0034] The method for manufacturing a grain-oriented electrical steel sheet of the present invention includes the steps of hot-rolling a slab to manufacture a hot-rolled steel sheet, pre-rolling the hot-rolled steel sheet to manufacture a pre-rolled sheet, annealing the pre-rolled sheet, cold-rolling the annealed pre-rolled sheet to manufacture a cold-rolled steel sheet, primary recrystallization annealing the cold-rolled steel sheet, and secondary recrystallization annealing the cold-rolled steel sheet that has been primarily recrystallized. First, a slab is hot-rolled to produce a hot-rolled steel sheet. The alloy composition of the slab has been explained in relation to the alloy composition of grain-oriented electrical steel sheet, so a duplicate explanation will be omitted. Specifically, the slab contains, by weight, 0.1 to 6.5 wt% Si, 0.001 to 6.5 wt% Al, 0.01 to 20 wt% Mn, 0.0010 to 0.0150 wt% C, and 0.0003 to 0.001 wt% each of one or more of N, S, and Ti, with the remainder consisting of Fe and unavoidable impurities.

[0035] Returning to the explanation of the manufacturing method, the step of hot-rolling the slab to manufacture a hot-rolled steel sheet includes a step of heating the slab. Specifically, the slab is heated to 1250°C or less. This allows the precipitates of aluminum-based nitrides and manganese-based sulfides to be incompletely or completely dissolved according to the chemical equivalent relationships between aluminum (Al) and nitrogen (N), and manganese (Mn) and sulfur (S) that form solid solutions.

[0036] The slab is hot rolled to produce a hot rolled steel sheet. The step of manufacturing the slab into a hot-rolled steel sheet includes a rough rolling step, a finish rolling step, and a coiling step. Specifically, the step of manufacturing the slab into a hot-rolled steel sheet includes the rough rolling step, the finish rolling step, and the coiling step, which are sequentially performed.

[0037] The rough rolling step may roll the heated slab to a thickness of 50 to 70 mm, and is preferably performed at a temperature in the range of 950 to 1,100°C. The finish rolling step may roll the roughly rolled bar to a thickness of 2.0 to 4.0 mm. The finish rolling step may be performed at a temperature range of 800 to 1,000°C. The hot-rolled steel sheet that has been subjected to the finish rolling step can be coiled. The coiling step is preferably performed at a temperature in the range of 600 to 800°C, and more preferably at a temperature in the range of 650 to 750°C.

[0038] If the temperature exceeds the upper limit of the above range, the fraction of Goss grains increases after annealing, but cracks at the side edges of the steel sheet increase, which may reduce productivity, and the precipitates and microstructure become coarse, making it difficult to obtain good and stable magnetic properties.On the other hand, if the temperature is below the lower limit of the above range, the precipitates and surface crystal grain size become fine, which reduces the effect of increasing the fraction of Goss texture after the subsequent pre-rolling and pre-rolled sheet annealing steps.

[0039] The thickness of the hot-rolled steel sheet is preferably 1.0 to 4.0 mm, and more preferably 1.5 to 3.0 mm. The step of pre-rolling the hot-rolled steel sheet to manufacture a pre-rolled sheet is a step of further increasing the fraction of a Goss structure after annealing by additionally rolling the hot-rolled steel sheet that has been subjected to the coiling step. The Goss structure grows during the primary recrystallization annealing and secondary recrystallization annealing steps described below, thereby enabling the orientation of secondary recrystallization in the final grain-oriented electrical steel sheet to be more accurately aligned.

[0040] The pre-rolling step is preferably carried out at a temperature in the range of 0.4Tc to 0.6Tc°C immediately before pre-rolling, where Tc means the coiling temperature [°C]. If the steel sheet temperature exceeds the upper limit, the fraction of Goss grains increases, but there are problems with productivity and temperature control. On the other hand, if the steel sheet temperature is below the lower limit, there is a problem that it is difficult to obtain the effect of pre-rolling. Specifically, the pre-rolling step is carried out at a temperature in the range of 260 to 450°C, more preferably 300 to 400°C immediately before pre-rolling. The pre-rolling step may be carried out at a reduction of 10 to 40%, more preferably 15 to 35%, and even more preferably 20 to 30%. If the reduction ratio exceeds the upper limit, the fraction of Goss grains increases after annealing, but cracks at the side edge of the steel sheet increase, resulting in a decrease in productivity.On the other hand, if the reduction ratio is below the lower limit, it is difficult to obtain the effect of pre-rolling. The pre-rolling step may be performed once or a plurality of times, and the thickness of the pre-rolled sheet after the pre-rolling step may be 1.5 to 3.0 mm.

[0041] The step of annealing the pre-rolled sheet may be performed at a soaking temperature and for a soaking time within a predetermined range. The step of annealing the pre-rolled sheet may be performed at a soaking temperature within a range of 800 to 1,100°C. In one embodiment, the step of annealing the pre-rolled sheet may be performed for a soaking time within a range of 100 to 300 seconds. It has been confirmed that the volume fraction of Goss grains increases through the steps of producing a pre-rolled sheet and annealing the pre-rolled sheet. Specifically, after annealing the pre-rolled sheet, the volume fraction of grains in the annealed pre-rolled sheet that form an angle of 15° or less with the Goss structure can increase to 4 to 10% within the above reduction range.

[0042] The step of cold rolling the annealed pre-rolled sheet to produce a cold-rolled steel sheet may be performed in one cold rolling step or in two or more cold rolling steps including intermediate annealing. The step of cold rolling the annealed pre-rolled sheet to produce a cold-rolled steel sheet may be performed at a reduction ratio of 85 to 95%. If the reduction exceeds the upper limit, the fraction of Goss structure in the crystal grains formed after primary annealing may decrease, resulting in a problem of degraded magnetic properties. On the other hand, if the reduction falls below the lower limit, the appropriate steel sheet thickness may not be secured, or the reduction must be increased in the hot rolling and pre-rolling stages, resulting in a degradation of productivity and magnetic properties. By performing cold rolling within the above reduction range, the thickness of the cold-rolled steel sheet can be produced to 0.1 to 0.3 mm.

[0043] In the step of cold-rolling the annealed pre-rolled sheet to produce a cold-rolled steel sheet, the steel sheet may be rolled at a temperature of 0.2Tc to 0.4Tc°C immediately before rolling. Tc refers to the coiling temperature [°C]. If the steel sheet temperature exceeds the upper limit, the fraction of Goss grains thereafter decreases. Conversely, if the steel sheet temperature is below the lower limit, it is difficult to obtain the effect of pre-rolling. Specifically, the step of cold-rolling the annealed pre-rolled sheet to produce a cold-rolled sheet is preferably performed at a temperature of 130 to 300°C, more preferably 150 to 200°C. The manufacturing method of the grain-oriented electrical steel sheet can satisfy the following formula 3. <Expression 3> 100≦Tb-Ta≦300 (In the above formula 3, Ta means the temperature at which cold rolling is performed, and Tb means the temperature at which pre-rolling is performed.)

[0044] The step of subjecting the cold-rolled steel sheet to primary recrystallization annealing causes primary recrystallization in which Goss grain nuclei are generated, and the step of primary recrystallization annealing may include decarburizing and nitriding the cold-rolled steel sheet. The step of subjecting the cold-rolled steel sheet to primary recrystallization annealing is preferably performed at a temperature range of 800 to 950° C. for decarburization. If the temperature exceeds the upper limit of the temperature range, recrystallized grains grow coarsely, reducing the driving force for crystal growth and preventing stable secondary recrystallization. The step of subjecting the cold-rolled steel sheet to primary recrystallization annealing is preferably performed at a dew point temperature of 50 to 70° C. for decarburization. The step of subjecting the cold-rolled steel sheet to primary recrystallization annealing is preferably performed within 5 minutes.

[0045] The step of subjecting the cold-rolled steel sheet to primary recrystallization annealing includes the steps of decarburizing and nitriding the cold-rolled steel sheet. The decarburizing and nitriding steps can be performed in any order. For example, the decarburizing step can be followed by a nitriding step, or the nitriding step can be followed by a decarburizing step. The method includes a step of simultaneously carrying out decarburization annealing and nitriding treatment on the cold-rolled steel sheet obtained by cold rolling to cause primary recrystallization. Specifically, the decarburization step and the nitriding step can be carried out simultaneously.

[0046] The decarburization step is preferably carried out in an atmosphere of hydrogen, nitrogen, or a mixture thereof. In the decarburization step, the carbon content can be reduced to 0.005% by weight or less. More preferably, the carbon content is reduced to 0.003% by weight or less. The nitriding step is for nitriding the inside of the steel sheet and involves introducing nitrogen ions into the steel sheet. This is a step of precipitating precipitates such as (Al, Si, Mn)N or AlN, which are grain growth inhibitors. Through this nitriding step, the nitrogen content of the grain-oriented electrical steel sheet can be 0.005% or less. Specifically, the nitriding step is preferably performed in an atmosphere containing ammonia gas.

[0047] After the primary recrystallization annealing, an annealing separator may be applied to the steel sheet. For example, an annealing separator mainly composed of MgO or an annealing separator mainly composed of alumina may be used as the annealing separator. Annealing separators are widely known, and therefore, detailed description thereof will be omitted. The secondary recrystallization annealing step for cold-rolled steel sheets that have undergone primary recrystallization annealing is to form a Goss texture through secondary recrystallization, and to form a glassy film through a reaction between the oxide layer formed during primary recrystallization annealing and MgO, thereby imparting insulation properties and removing impurities that impair magnetic properties.

[0048] The secondary recrystallization annealing step may include a temperature-raising step and a soaking step. Specifically, the secondary recrystallization annealing step may include a temperature-raising step before secondary recrystallization occurs. The temperature-raising step may be performed in nitrogen, hydrogen, or a mixture thereof to protect nitrides, which act as grain growth inhibitors, and thereby promote the development of secondary recrystallization. In the secondary recrystallization annealing step, the temperature rising step may be carried out at a temperature rising rate in the range of 3 to 6° C. / hr. If the heating rate exceeds the upper limit of the range, the effect of increasing the concentration of Goss structures and the effect of reducing the temperature deviation of the steel sheet may not be achieved, whereas if the heating rate is below the lower limit of the range, the productivity may be deteriorated.

[0049] The secondary recrystallization annealing step may include a soaking step after the secondary recrystallization is completed, which may remove impurities by, for example, maintaining the steel in a 100% hydrogen atmosphere for a long period of time. The secondary recrystallization annealing step may be performed by a bottom direct heating method. Specifically, the secondary recrystallization annealing step may include applying additional heat to the bottom of the coil by a heating element, specifically, an electric resistance heating element. The heating element is disposed below the coil and increases the amount of heat flowing into the coil, thereby reducing the temperature deviation of the coil during heat treatment. The heating element can be controlled in the same manner as the heat pattern of the annealing furnace or in a separate heat pattern. The secondary recrystallization annealing step may be performed in either a continuous annealing furnace or a batch annealing furnace, and more specifically, the secondary recrystallization annealing step may be performed in a batch annealing furnace.

[0050] Hereinafter, specific examples of the present invention will be described, but the following examples are merely specific examples of the present invention and the present invention is not limited to the following examples. <Experimental Example 1> A steel slab was prepared containing, by weight, 3.3% Si, 0.055% C, 0.08% Mn, 0.029% Al, 0.004% N, 0.02% Sb, 0.05% Sn, 0.09% Cr, and 0.028% P, with the remainder consisting of Fe and other unavoidable impurities. The steel slab was heated to 1,150°C, and then hot-rolled and pre-rolled to produce a hot-rolled steel sheet. At this time, the thickness of the hot-rolled steel sheet, the coiling temperature, and the pre-rolling conditions were varied as shown in Table 1 below. The pre-rolled and annealed sheet was cold-rolled to a thickness of 0.15 to 0.23 mm, and then subjected to primary recrystallization annealing at a temperature of 850°C and a dew point temperature of 60°C, and secondary recrystallization annealing at a temperature of 1200°C and a heating rate of 3 to 6°C / hr. At this time, various conditions were changed depending on the temperature rising rate of the secondary recrystallization annealing and the conditions for using the lower heating element.

[0051] After that, the coating layer on the steel sheet surface was removed using a hydrochloric acid solution, and the W / L (W: diameter in the TD direction, L: diameter in the RD direction) ratio of the crystal grains was measured. An X-ray Laue analyzer was used to determine whether the crystal grains were {110} <001> The angle between the direction and the target was measured. In Table 1 below, the pre-rolling temperature means the temperature of the steel sheet just before the pre-rolling stage, and the cold rolling temperature means the temperature of the steel sheet just before the cold rolling stage.

[0052] [Table 1]

[0053] From Table 1, it can be seen that the grain size distribution and the degree of Goss accumulation can be improved by controlling the coiling temperature within the range of the present invention, performing pre-rolling after hot rolling within the range of the present invention, performing the heating rate during secondary recrystallization within the range of the present invention, and using a lower heating element.

[0054] The present invention is not limited to the above-described embodiments and / or examples, and can be manufactured in various different forms, and those skilled in the art will understand that the present invention can be embodied in other specific forms without changing the technical spirit or essential characteristics of the present invention. Therefore, the above-described embodiments and / or examples should be understood to be illustrative in all respects and not limiting.

Claims

1. The size of the crystal grains having the {110}<001> orientation satisfies the following formula 1: A grain-oriented electrical steel sheet characterized in that the area fraction of crystal grains that deviate from the <001> orientation by an angle of 3° or less is 60% or more. <Formula 1> W / L≦1.5 (In the above formula 1, W is the diameter in the TD direction (width direction of the secondary recrystallized grain), and L is the diameter in the RD direction (longitudinal direction of the secondary recrystallized grain).)

2. 2. The grain-oriented electrical steel sheet according to claim 1, wherein the following formula 2 is satisfied: <Formula 2> α×β×γ≦20° (In the above formula 2, α means the angular difference between the {110}<001> orientation and the ND axis, β means the angular difference between the {110}<001> orientation and the TD axis, and γ means the angular difference between the {110}<001> orientation and the RD axis.)

3. 2. The grain-oriented electrical steel sheet according to claim 1, comprising, by weight%, 2.0 to 5.0% Si, 0.005% or less C, 0.03 to 0.5% Mn, 0.01 to 0.04% Al, and 0.002 to 0.005% N, and further comprising one or more of 0.01 to 0.05% by weight Sb, 0.03 to 0.08% by weight Sn, 0.01 to 0.2% by weight Cr, 0.01% or less S, and 0.005 to 0.045% by weight P, with the balance being Fe and unavoidable impurities.

4. hot rolling the slab to produce a hot rolled steel sheet; Pre-rolling the hot-rolled steel sheet at a reduction rate of 10 to 40% to manufacture a pre-rolled sheet; annealing the pre-rolled sheet; cold rolling the annealed pre-rolled sheet to produce a cold-rolled steel sheet; subjecting the cold-rolled steel sheet to primary recrystallization annealing; and subjecting the cold-rolled steel sheet that has been subjected to primary recrystallization annealing to secondary recrystallization annealing, the hot rolling step includes coiling the slab; In the winding step, the winding temperature is 600 to 800°C, The secondary recrystallization annealing step is performed at a temperature range of 1000 to 1200 ° C. at a secondary recrystallization heating rate of 3 to 6 ° C. / hr, and employs a bottom direct heating method. In the secondary recrystallization grains obtained by the secondary recrystallization annealing, the size of crystal grains having a {110}<001> orientation satisfies the following formula 1: A method for producing a grain-oriented electrical steel sheet, characterized in that the area fraction of crystal grains that deviate from the <001> orientation by an angle of 3° or less is 60% or more. <Formula 1> W / L≦1.5 (In the above formula 1, W is the diameter in the TD direction (width direction of the secondary recrystallized grain), and L is the diameter in the RD direction (longitudinal direction of the secondary recrystallized grain).)

5. 5. The method for manufacturing a grain-oriented electrical steel sheet according to claim 4, wherein in the step of manufacturing the pre-rolled sheet, the temperature of the steel sheet immediately before pre-rolling is 0.4Tc to 0.6Tc°C. (The above Tc means the winding temperature [°C])

6. 5. The method for producing a grain-oriented electrical steel sheet according to claim 4, wherein the following formula 3 is satisfied: <Formula 3> 100≦Tb−Ta≦300 (In the above formula 3, Ta means the temperature at which cold rolling is performed, and Tb means the temperature at which pre-rolling is performed)

7. The method for manufacturing a grain-oriented electrical steel sheet according to claim 4, wherein the step of manufacturing the hot-rolled steel sheet includes rough rolling, finish rolling, and coiling.

8. The method for producing a grain-oriented electrical steel sheet according to claim 4, wherein the thickness of the pre-rolled sheet is 1.5 to 3.0 mm.

9. 5. The method of claim 4, wherein the step of annealing the pre-rolled sheet is performed at a soaking temperature range of 700 to 1,100°C.

10. The method for producing a grain-oriented electrical steel sheet according to claim 4, wherein the reduction ratio in the step of producing the cold-rolled steel sheet is 85 to 95%.

11. 5. The method of claim 4, wherein the step of producing the cold-rolled steel sheet is performed such that the temperature of the steel sheet immediately before cold rolling is in the range of 0.2Tc to 0.4Tc°C. (The above Tc means the winding temperature [°C])

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