Grain-oriented electrical steel sheet and its manufacturing method

Abstract

A grain-oriented electrical steel sheet and a manufacturing method thereof are provided. [Solution] The method for producing grain-oriented electrical steel sheet of the present invention is characterized by including the steps of hot rolling a slab to produce a hot-rolled steel sheet, hot-rolled annealing the hot-rolled steel sheet, first cold rolling the hot-rolled steel sheet that has been annealed, first decarburization annealing the first cold-rolled steel sheet, second cold rolling the steel sheet after the first decarburization annealing, second decarburization annealing the steel sheet after the second cold rolling, a first non-oxidation annealing step of annealing the steel sheet after the second decarburization annealing at a temperature of 1000°C to 1200°C and a dew point temperature of -20°C or lower, a third cold rolling the steel sheet after the first non-oxidation annealing, and a second non-oxidation annealing step of annealing the steel sheet after the third cold rolling at a crack temperature of 800°C to 1000°C for 30 seconds to 5 minutes.

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 improved magnetic properties by undergoing multiple cold rolling and decarburization annealing steps, and a manufacturing method thereof. [Background technology] 【0002】 Grain-oriented electrical steel sheets are steel sheets with a crystal orientation of {110} <001> It is a soft magnetic material with excellent magnetic properties in the rolling direction, consisting of crystal grains with the Goss orientation. Such grain-oriented electrical steel sheets are manufactured by rolling the slab to the final thickness through hot rolling, hot-rolling, and cold rolling after heating, and then undergoing primary recrystallization annealing and high-temperature annealing for secondary recrystallization formation. 【0003】 Generally, the secondary recrystallization annealing process of grain-oriented electrical steel requires a low heating rate and long-term purification annealing at high temperature, which is a process that consumes a lot of energy. In order to manufacture grain-oriented electrical steel with excellent magnetic properties by forming secondary recrystallization through such an extreme process, the following process difficulties arise. 【0004】 First, there is a temperature difference between the outer and inner coils due to heat treatment in the coil state, and it is not possible to apply the same heat treatment pattern to each part, which results in magnetic deviation between the outer and inner coils. Second, after decarburization annealing, MgO is coated on the surface, and in the process of forming a base coating during high-temperature annealing, various surface defects occur, which reduces the yield. Third, there is a problem of reduced yield as the production process is divided into three steps, as the decarburized sheet after decarburization annealing is wound into a coil, and then after high-temperature annealing, flattening annealing is performed again and an insulating coating is applied. 【0005】 In order to overcome these process limitations, a technology has been proposed that uses normal crystal growth without relying on secondary recrystallization by adjusting the decarburization annealing and cold rolling reduction rate. However, continuous annealing is a short heat treatment time of a few minutes, so the crystal orientation is not uniform in the {110} <001> However, a large number of grains with exact Goss orientation that exactly matches the Goss orientation were not formed, and there was a limit to the improvement in iron loss. Summary of the Invention [Problem to be solved by the invention] 【0006】 An object of the present invention is to provide a grain-oriented electrical steel sheet and a manufacturing method thereof. Specifically, the present invention provides a grain-oriented electrical steel sheet and a manufacturing method thereof, in which magnetic properties are improved by undergoing multiple cold rolling and decarburization annealing steps. [Means for solving the problem] 【0007】 The method for producing a grain-oriented electrical steel sheet of the present invention includes a step of hot rolling a slab to produce a hot-rolled steel sheet, a step of hot-rolled annealing the hot-rolled steel sheet, a step of first cold rolling the hot-rolled steel sheet that has been annealed, a step of first decarburization annealing the first cold-rolled steel sheet, a step of second cold rolling the steel sheet after the first decarburization annealing, a step of second decarburization annealing the steel sheet after the second cold rolling, a first non-oxidation annealing step of annealing the steel sheet after the second decarburization annealing at a temperature of 1000°C to 1200°C and a dew point temperature of -20°C or lower, a step of third cold rolling the steel sheet after the first non-oxidation annealing, and a second non-oxidation annealing step of annealing the steel sheet after the third cold rolling at a crack temperature of 750°C to 1050°C for 30 seconds to 5 minutes. 【0008】 The slabs consist of, by weight, 1.0% to 4.0% Si, 0.1% to 0.4% C, and the balance being Fe and unavoidable impurities. The slab may further include Mn: 0.1 wt % or less and S: 0.005 wt % or less. It is preferable to include a decarburization process in the hot-rolled sheet annealing step. The hot-rolled sheet annealing step is preferably performed at a temperature of 850°C to 1000°C and a dew point temperature of 70°C or lower. 【0009】 The first decarburization annealing step can be performed at a temperature of 850°C to 1000°C and a dew point temperature of 50°C to 70°C. The first decarburization annealing step is preferably performed in an austenite single phase region or a region where a composite phase of ferrite and austenite exists. After the first decarburization annealing step, the average diameter of the crystal grains is preferably 150 to 250 μm. The first decarburization annealing step and the second cold rolling step may be repeated two or more times. The secondary decarburization annealing step is preferably performed at a temperature of 850°C to 1000°C and a dew point temperature of 50°C to 70°C. 【0010】 The second decarburization annealing step can be performed for 30 seconds to 5 minutes. The first non-oxidizing annealing step is preferably annealed for 30 seconds to 5 minutes. It is preferable that the first non-oxidizing annealing step further includes a subsequent pickling step. The second non-oxidizing annealing step can be performed in an atmosphere with a dew point temperature of -20°C or lower. 【0011】 The grain-oriented electrical steel sheet of the present invention has crystal grains whose {111} planes form an angle of 15° or less with the rolled surface of the steel sheet and are arranged in a continuous band shape, the aspect ratio of the band shape is 10 or more, and the density of the band shape is 100 mm 2 The number of pieces is 5 to 1,000 per piece. 【0012】 Grain-oriented electrical steel sheet is a steel sheet with a density of 100 mm2 or less, in which the {111} plane forms an angle of 15° or less with the rolled surface of the steel sheet. 2 The quantity is 500 to 100,000 pieces. It is preferable that the percentage of crystal grains having a crystal grain size of 10 μm to 100 μm among all the crystal grains is 20% to 99%. Gothic direction ({110} <001> It is preferable that the fraction of crystal grains forming an angle of 15° or less with respect to the crystal grains is 10 to 95%. The grain-oriented electrical steel sheet preferably contains, by weight, 1.0% to 4.0% Si, 0.005% or less (excluding 0%) C, and the balance being Fe and unavoidable impurities. The grain-oriented electrical steel sheet may further contain Mn: 0.1% by weight or less and S: 0.005% by weight or less. Effect of the Invention 【0013】 According to the present invention, the grain-oriented electrical steel sheet of the present invention utilizes normal crystal growth, and therefore has excellent magnetic properties, in particular, excellent high-frequency core loss. In addition, since AlN and MnS are not used as grain growth inhibitors, there is no need to heat the slab at high temperatures of 1,300°C or higher. In addition, there is no need to remove the precipitates N and S. This allows the purification annealing time to be relatively short, thereby improving productivity. It is also possible to provide a grain-oriented electrical steel sheet having uniform magnetic properties in the width direction. [Brief description of the drawings] 【0014】 [Figure 1] 1 is a photograph of the surface of a grain-oriented electrical steel sheet manufactured using Inventive Material 5 analyzed with an electron microscope, in which {111} / / ND crystal grains are shown in blue. [Diagram 2] 1 is a photograph of the surface of a grain-oriented electrical steel sheet manufactured using the invention material 5, analyzed by an electron microscope. <001> ) The photograph shows the crystal grains in green. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 【0015】 Terms such as first, second, and third are used to describe various parts, components, regions, layers, and / or sections, but are not limited thereto. These terms are used only to distinguish one part, component, region, layer, or section from another part, component, region, layer, or section. Thus, a first part, component, region, layer, or section described below can be referred to as a second part, component, region, layer, or section without departing from the scope of the present invention. The terminology used herein is merely for the purpose of referring to particular embodiments and is not intended to limit the present invention. As used herein, the singular form includes the plural form unless the phrase clearly indicates otherwise. As used in the specification, the term "comprising" refers to the specification of particular features, regions, integers, steps, operations, elements, and / or components, and does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components. 【0016】 When an element is referred to as being "on" or "above" another element, this can mean either directly on top of the other element, or on top of it with the other element between them. In contrast, when an element is referred to as being "directly on" another element, there is no other element between them. Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person having ordinary skill in the art to which the present invention belongs. Terms defined in commonly used dictionaries are additionally interpreted as having a meaning consistent with the relevant technical literature and the currently disclosed content, and are not interpreted as ideal or very formal meanings unless defined. Moreover, unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight. In an embodiment of the present invention, the term "additionally contain an additional element" refers to the addition of an additional amount of the additional element in place of the remaining iron (Fe). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to exemplary embodiments thereof, so that those skilled in the art will be able to easily practice the present invention. However, the present invention may be embodied in many different forms and is not limited to the embodiments set forth herein. 【0017】 A method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention includes a step of hot rolling a slab to manufacture a hot-rolled steel sheet, a step of hot-rolled annealing the hot-rolled steel sheet, a step of first cold rolling the hot-rolled steel sheet that has been annealed, a step of first decarburization annealing the first cold rolled steel sheet, a step of second cold rolling the steel sheet that has been subjected to the first decarburization annealing, a step of second decarburization annealing the steel sheet that has been subjected to the second cold rolling, a first non-oxidation annealing step of annealing the steel sheet that has been subjected to the second decarburization annealing at a temperature of 1000°C to 1200°C and a dew point temperature of -20°C or less, a step of third cold rolling the steel sheet that has been subjected to the first non-oxidation annealing, and a second non-oxidation annealing step of annealing the steel sheet that has been subjected to the third cold rolling at a crack temperature of 750°C to 1050°C for 30 seconds to 5 minutes. 【0018】 Each step will be described in detail below. First, the slab is hot rolled. The slabs consist of, by weight, 1.0% to 4.0% Si, 0.1% to 0.4% C, and the balance being Fe and unavoidable impurities. The reasons for limiting the composition are as follows. 【0019】 Silicon (Si) reduces the magnetic anisotropy of electrical steel sheet and increases resistivity to improve core loss. If the Si content is less than 1.0 wt%, the core loss is inferior, and if it exceeds 4.0 wt%, the brittleness increases. Therefore, the Si content in the slab and grain-oriented electrical steel sheet after the final annealing stage is preferably 1.0 to 4.0 wt%. More specifically, the Si content is preferably 1.5 to 3.5 wt%. 【0020】 During intermediate decarburization annealing and final decarburization annealing, the Goss crystal grains in the surface layer diffuse to the center, and a process of C in the center escaping to the surface layer is necessary, so the C content in the slab is preferably 0.1 to 0.4 wt%. More specifically, the C content in the slab is preferably 0.15 to 0.3 wt%. In addition, the carbon content in the grain-oriented electrical steel sheet finally manufactured after the continuous annealing stage where decarburization is completed is preferably 0.0050 wt% or less. More specifically, it is preferably 0.002 wt% or less. 【0021】 The slab may further include Mn: 0.1 wt % or less and S: 0.005 wt % or less. Mn and S form MnS precipitates and impede the growth of Goss crystal grains that diffuse to the center during the decarburization process. Therefore, it is preferable not to add Mn or S. However, taking into consideration the amount that is inevitably mixed in during the steelmaking process, it is preferable to control the Mn and S contents in the slab and grain-oriented electrical steel sheets after the final annealing stage to Mn: 0.1 wt% or less and S: 0.005 wt% or less, respectively. 【0022】 The balance is composed of Fe and inevitable impurities. The inevitable impurities are impurities that are mixed in during the steelmaking stage and the manufacturing process of grain-oriented electrical steel sheets, and are widely known in the art, so a detailed description will be omitted. In particular, components such as Al, N, Ti, Mg, and Ca must be suppressed as much as possible because they react with oxygen in the steel to form oxides. It is preferable to control each component to 0.005 wt% or less. 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 harm the technical idea of ​​the present invention. When an additional element is further included, it is included in place of the balance Fe. More specifically, the slab is composed of, by weight, 1.0% to 4.0% Si, 0.1% to 0.4% C, and the balance being Fe and unavoidable impurities. 【0023】 The slab can be heated before hot rolling. The slab heating temperature is preferably 1100°C to 1350°C, which is higher than the normal heating temperature. If the temperature during slab heating is high, the hot-rolled structure may become coarse, which may adversely affect the magnetic properties. However, in the method for producing grain-oriented electrical steel sheet of the present invention, the carbon content of the slab is relatively high, so that even if the slab reheating temperature is high, the hot-rolled structure does not become coarse, and reheating can be performed at a higher temperature than normal, which is more advantageous for hot rolling. 【0024】 Hot rolling can be performed to produce a hot-rolled sheet having a thickness of 1.5 to 4.0 mm by applying an appropriate rolling ratio in the final cold rolling stage so that the final product thickness can be produced. There are no particular limitations on the hot rolling temperature and cooling temperature, but as an example of a material with excellent magnetic properties, the hot rolling end temperature can be 950°C or less, and the material can be rapidly cooled with water and coiled at 600°C or less. Next, the hot-rolled steel sheet is annealed. At this time, the hot-rolled steel sheet annealing may include a decarburization process. Specifically, the hot-rolled steel sheet annealing is preferably performed at a temperature of 850°C to 1000°C and a dew point temperature of 70°C or less. After the above annealing, it is preferable to perform additional annealing at a temperature of 1000°C to 1200°C and a dew point temperature of 0°C or less. After the hot-rolled steel sheet annealing, pickling may be performed. 【0025】 Next, a first cold rolling is carried out to produce a cold-rolled steel sheet. It is known that in the manufacturing process of a typical grain-oriented electrical steel sheet, it is effective to perform cold rolling once with a high reduction rate of nearly 90%. This is to create an environment that is favorable for grain growth of only Goss crystal grains in the primary recrystallized grains. However, since the manufacturing method of grain-oriented electrical steel sheet according to one embodiment of the present invention does not utilize abnormal grain growth of Goss orientation crystal grains but causes the Goss crystal grains in the surface layer generated by decarburization annealing and cold rolling to diffuse internally, it is advantageous to form a large number of Goss orientation crystal grains distributed in the surface layer. Therefore, when cold rolling is performed at a rolling reduction of 50% to 70%, a large amount of Goss texture is formed in the surface layer portion. More specifically, the rolling reduction is preferably 55% to 65%. 【0026】 Next, the steel sheet subjected to the first cold rolling is subjected to a first decarburization annealing. At this time, the decarburization annealing step can be performed in an austenite single phase region or a region where a composite phase of ferrite and austenite exists. Specifically, it is preferable to perform annealing at a temperature of 850°C to 1000°C and a dew point temperature of 50°C to 70°C. Also, the atmosphere is preferably a mixed gas atmosphere of hydrogen and nitrogen. Also, during the decarburization annealing, the amount of decarburization is preferably 0.0300% by weight to 0.0600% by weight. After the above-mentioned annealing, it is preferable to perform additional annealing at a temperature of 1000°C to 1200°C and a dew point temperature of 0°C or less. 【0027】 During this primary decarburization annealing process, the crystal grains on the surface of the electrical steel sheet grow coarse, but the crystal grains inside the electrical steel sheet remain as fine structures. After this primary decarburization annealing, the average diameter of the crystal grains should be 150 μm to 250 μm. At this time, the crystal grains are surface ferrite crystal grains. The diameter of the crystal grains means the diameter of an imaginary circle having the same area as the crystal grain. The reference plane is a plane parallel to the rolling surface (ND plane). Next, the steel sheet that has completed the first decarburization annealing is subjected to a second cold rolling. The second cold rolling is the same as the first cold rolling, so a detailed description is omitted. 【0028】 The above-mentioned first decarburization annealing step and second cold rolling step can be repeated two or more times. By repeating the steps two or more times, a Goss texture is formed in a large amount in the surface layer. In one embodiment of the present invention, the Goss texture means a texture that forms an angle of 15° or less with the Goss direction. That is, the rolling surface (ND surface) and rolling direction (RD direction) of the steel sheet are aligned in the {110} direction of the crystal grains. <001> This means that the grains form an angle of 15° or less with the direction. 【0029】 Next, the steel plate after the second cold rolling undergoes secondary decarburization annealing. The secondary decarburization annealing stage is annealed at a temperature of 850°C to 1000°C and a dew point temperature of 50°C to 70°C. The cold-rolled sheet before the secondary annealing is in a state where the carbon content remains at 40% to 60% of the carbon weight of the slab after the decarburization annealing. Therefore, in the secondary decarburization annealing stage, the carbon is released and the crystal grains formed in the surface layer diffuse inward. In the secondary decarburization annealing stage, it is preferable to carry out decarburization so that the carbon content in the steel sheet is 0.005% by weight or less. The atmosphere is preferably a mixed atmosphere of hydrogen and nitrogen. The secondary decarburization annealing step can be performed for 30 seconds to 5 minutes. Decarburization is completed sufficiently within the above time range. 【0030】 Next, the steel sheet that has been subjected to the second decarburization annealing is subjected to a first non-oxidation annealing at a temperature of 1000°C to 1200°C and a dew point temperature of -20°C or less. If the steel sheet that has been subjected to the second decarburization annealing is additionally subjected to a third cold rolling without a non-oxidation annealing, the grains do not grow sufficiently, which may cause a problem of a low Goss fraction. In addition, not only may the rolling roll wear due to the surface oxide layer occur, but the productivity during rolling may also decrease. In one embodiment of the present invention, the Goss fraction is improved through the first non-oxidation annealing step. As a result, the third cold rolling and heat treatment can further improve the magnetic property. More specifically, it is preferable to anneal in an atmosphere of 99% or more by volume of hydrogen at a dew point temperature of -50 to -30°C. 【0031】 The first non-oxidation annealing step can be performed for 30 seconds to 5 minutes. Within the above time range, the growth of grains in which the {111} plane makes an angle of 15° or less with the rolled surface of the steel sheet ({111} / / ND) grains is sufficiently achieved. 【0032】 After the first non-oxidizing annealing step, the steel sheet may be subjected to pickling. By further including the pickling step, the oxide layer formed on the surface of the steel sheet during the first and second decarburization annealing processes may be removed. This oxide layer remains on the surface even after rolling and hinders the movement of magnetic domains, adversely affecting magnetism, so it is preferable to remove it through pickling. The pickling method is not particularly limited, but the pickling step may involve immersion in a 3.0-22.0 wt % hydrochloric acid solution for 15 to 200 seconds. At this time, the hydrochloric acid temperature is 50 to 90°C. If the hydrochloric acid concentration is too low or the immersion time is too short, the oxide layer present on the steel sheet surface may not be sufficiently removed, and if the concentration is too high or the immersion time is too long, damage to the steel sheet surface may occur beyond the removal of the oxide layer. More specifically, the pickling step may involve immersion in a 10.0-18.0 wt % hydrochloric acid solution for 20 to 100 seconds. Next, the steel sheet that has been subjected to the first non-oxidation annealing is subjected to a third cold rolling. By performing the third cold rolling, it is possible to manufacture a steel sheet with a final thickness of 20~150μm. When the third cold rolling is added, the {111} / / ND crystal grain density increases, which improves magnetic properties, especially high frequency core loss. 【0033】 Next, the steel sheet after the third cold rolling can be subjected to a second non-oxidation annealing at a cracking temperature of 750 to 1050°C for 30 seconds to 5 minutes. The purpose of the second non-oxidation annealing step is to grow the grains to a certain size or more. This increases the density of {111} / / ND grains, thereby improving magnetic properties, especially high-frequency iron loss. If the cracking temperature is too low or the time is too short, the Goss grains may not develop properly. If the cracking temperature is too high or the time is too long, the Goss grains may not remain at a fine size that is favorable for high-frequency iron loss, but may grow, resulting in a problem that the proportion of Goss grains may be reduced during the growth process. More specifically, the cracking temperature of the second non-oxidation annealing is preferably 800 to 1000°C. More specifically, it is 900 to 970°C. 【0034】 The secondary non-oxidizing annealing step can be performed at a dew point temperature of -20°C or lower. If the dew point temperature is too high, an oxide layer may be generated on the surface, which may adversely affect the magnetic properties. More specifically, it is preferable to perform annealing in an atmosphere of 99% or more by volume of hydrogen with a dew point temperature of -50 to -30°C. After the first cold rolling step, the second non-oxidation annealing step can be performed in a continuous process. A continuous process means that there is no batch process in which the steel sheet is wound into a coil and annealed. As mentioned above, the first decarburization annealing step to the second non-oxidation annealing step can be completed in a few minutes, making this a continuous process. By adding the third cold rolling step and the first and second non-oxidizing annealing steps before and after the third cold rolling step, the density of {111} / / ND crystal grains increases and the Goss fraction increases, which leads to improved magnetic properties, and in particular a dramatic improvement in high-frequency iron loss. 【0035】 The grain-oriented electrical steel sheet finally manufactured after the second non-oxidizing annealing step has a density of 500 to 100,000 grains per 100 mm2 whose {111} plane forms an angle of 15° or less with the rolled surface of the steel sheet. In one embodiment of the present invention, the grains whose {111} plane forms an angle of 15° or less with the rolled surface of the steel sheet, i.e., {111} / / ND grains, serve to reduce the size of magnetic domains and reduce high-frequency iron loss. If there are too few {111} / / ND grains, the size of the magnetic domains increases and the magnetic properties become inferior. On the other hand, if many {111} / / ND grains are formed, the grains of Goss orientation, which is advantageous for magnetic properties, decrease, which is problematic. More specifically, the number of {111} / / ND grains is preferably 1,000 to 50,000. More specifically, it is preferably 2,000 to 20,000. The reference plane is not particularly limited, and may be a plane parallel to the rolling surface (ND plane). The density of {111} / / ND grains can be formed in large numbers through the aforementioned secondary non-oxidation step. This was explained in detail in relation to the aforementioned manufacturing method for grain-oriented electrical steel sheets, so a duplicate explanation will be omitted. The number of {111} / / ND grains can be calculated by counting the grains with a grain size of 5μm or more. 【0036】 The grains whose {111} planes form an angle of 15° or less with the rolling surface of the steel plate are arranged in a continuous band shape. 2 It is preferable that the number of stripes is 5 to 1000 per 100 mm. If the number of stripes is too small, the effect of reducing the size of the magnetic domains due to the stripes is not fully realized. If the number of stripes is too large, the number of crystal grains with the Goss orientation, which is advantageous for magnetism, will decrease. More specifically, if the density of the stripes is 100 mm 2 More specifically, the density of the band shape is preferably 20 to 500 per 100 mm. 2 It is best to have 50 to 200 pieces per piece. 【0037】 The term "continuous" means that the boundaries between {111} / / ND crystal grains are adjacent to each other. The term "strip shape" means that the strips are arranged in an elongated manner with an aspect ratio of 10 or more. Specifically, the strips can be arranged with a width of 0.05mm to 1.0mm and a length of 0.5mm to 10mm. In this case, the width can be perpendicular to the rolling direction. Each strip can contain 10 to 300 {111} / / ND crystal grains. Such strip shapes serve to reduce the size of the magnetic domains and improve high frequency iron loss. The strip shapes are formed through a secondary non-oxidation heat treatment step at the positions of the grain boundaries created by rolling. This has been described in detail in relation to the manufacturing method of grain-oriented electrical steel sheet described above, so a duplicated description will be omitted. 【0038】 In one embodiment of the present invention, the fraction of crystal grains having a grain size of 10 μm to 100 μm in the entire crystal grains is preferably 20% to 99%. This is because the first and second decarburization annealing and the first and second non-oxidation annealing are performed for a short period of time in one embodiment of the present invention. When annealing is performed for a long period of time of 1 hour or more through batch annealing as in the past, the average grain size becomes larger by 5 mm or more, which is completely different from the grain size distribution of the grain oriented electrical steel sheet according to one embodiment of the present invention. More specifically, the fraction of crystal grains having a grain size of 10 μm to 100 μm in the entire crystal grains is preferably 50% or more. More specifically, the fraction of crystal grains having a grain size of 10 μm to 100 μm in the entire crystal grains is preferably 90% to 99%. Such fine crystal grains contribute to improving high frequency iron loss. The fraction of crystal grains means a volume fraction, and the area of ​​crystal grains having the corresponding grain size in any cross section of the steel sheet is calculated and regarded as the volume fraction. In the present invention, it is not necessary to consider the grain size variation in the thickness direction. The grain size of a crystal grain is calculated from the diameter of a hypothetical circle having the same area as the crystal grain. The grain-oriented electrical steel sheet of the present invention has a Goss orientation ({110} <001> ) is preferably 10-95%. The fraction of Goss grains also contributes to improving high-frequency iron loss. More specifically, the fraction of Goss grains is preferably 50-90%. In one embodiment of the present invention, the area of ​​the grains having the orientation in any cross section of the steel sheet is calculated and regarded as the volume fraction. The fraction of Goss grains does not need to vary. By forming a long and narrow {111} / / ND grain assembly around the Goss-oriented grains of the present invention, the size of the magnetic domains formed by the Goss-oriented grains can be finely divided by the strip-shaped {111} / / ND grains, thereby improving high-frequency iron loss. 【0039】 The effect of the present invention can be achieved not by the alloy components of the grain-oriented electrical steel sheet but by a specific manufacturing process and a specific microstructure generated by the manufacturing process. To further explain the alloy components of the grain-oriented electrical steel sheet, the grain-oriented electrical steel sheet according to one embodiment of the present invention may be composed of, by weight percent, 1.0% to 4.0% Si, 0.005% or less C (except 0%), and the balance being Fe and unavoidable impurities. In addition, the grain-oriented electrical steel sheet according to one embodiment of the present invention may further contain 0.1% or less by weight Mn and 0.005% or less by weight S. The description of the alloy components of the grain-oriented electrical steel sheet is the same as the description of the alloy components of the slab described above, and therefore a duplicated description will be omitted. 【0040】 In one embodiment of the present invention, the grain-oriented electrical steel sheet is excellent in magnetic properties, particularly in high-frequency core loss. 10 / 400 It is better that the power consumption is 10.00W / kg or less. 2 / 5000 It is recommended that the power consumption is 11.00W / kg or less. 0.5 / 20000 It is preferable that the power consumption is 5.00 W / kg or less. More specifically, W 10 / 400 It is recommended that the power consumption is 6.00 to 10.00 W / kg. 2 / 5000 The recommended range is 8.00 to 11.00 W / kg. 0.5 / 20000 It is preferable that the power consumption is 2.00 to 5.00 W / kg. 【0041】 Iron loss W 10 / 400 is the magnitude of the iron loss (W / kg) induced under the conditions of 1.0 Tesla and 400 Hz. Iron loss W 2 / 5000 is the magnitude of the iron loss (W / kg) induced under the conditions of 0.2 Tesla and 5000 Hz. Iron loss W 0.5 / 20000 is the magnitude of iron loss (W / kg) induced under the conditions of 0.05 Tesla and 20,000 Hz. Hereinafter, specific examples of the present invention will be described. However, the following examples are merely specific embodiments of the present invention, and the present invention is not limited to the following examples. EXAMPLES 【0042】 The slab, which contained 2.8% Si, 0.204% C by weight, with the remainder being Fe and unavoidable impurities, was heated at a temperature of 1150°C, hot rolled, and then hot-rolled at an annealing temperature of 950°C and a dew point temperature of 60°C. The steel sheet was then cooled and pickled, and subjected to a first cold rolling at a rolling reduction of 65% to produce a cold-rolled sheet with a thickness of 0.8 mm. The first cold-rolled steel sheet was then subjected to first decarburization annealing at 950°C in a wet mixed gas atmosphere of hydrogen and nitrogen (dew point temperature 60°C) for 80 seconds, and then second cold-rolled at a reduction ratio of 65% to produce a second cold-rolled sheet with a thickness of 0.28 mm. 【0043】 Then, the secondary decarburization annealing was performed for 2 minutes in a wet mixed gas atmosphere of hydrogen and nitrogen (dew point temperature 60°C) at 950°C, followed by primary non-oxidation annealing for 3 minutes in a hydrogen atmosphere (dew point temperature -40°C) at 1100°C. The oxide layer on the surface was then removed by pickling for 30 seconds in an 18.5 mass% HCl solution at 80°C. After pickling, the electrical steel sheets were tertiary cold-rolled to a thickness of 50 μm and then secondary non-oxidizing annealed for 150 seconds in a hydrogen atmosphere (dew point temperature -40°C) at the temperatures listed in Table 1 below. The Goss fraction of the crystal grains and the number of bands consisting of {111} / / ND crystal grains were determined through EBSD analysis. The iron loss distribution was determined while changing the applied frequency from 50 to 20,000 Hz, and is summarized in Table 1. Comparative material 4 is an example in which the first non-oxidizing annealing was omitted and third cold rolling was performed, and comparative material 5 is an example in which the third cold rolling and second non-oxidizing annealing were omitted and only the first non-oxidizing annealing was performed. 【0044】 [Table 1] 【0045】 As shown in Table 1, during the secondary non-oxidizing annealing process, a large number of band-shaped {111} / / ND grains and Goss grains are formed depending on the temperature, which improves the high-frequency core loss. In Comparative Materials 1 and 2, in which the temperature of the secondary non-oxidizing annealing was excessively low, recrystallization was not completed, and it was confirmed that the band shape of {111} / / ND crystal grains and Goss crystal grains were not formed in large numbers. 【0046】 It can be seen that in the comparative material 3 in which the temperature of the secondary non-oxidizing annealing was excessively high, band-shaped {111} / / ND crystal grains and many Goss crystal grains were not formed during the recrystallization growth process. In comparative material 4, a large number of band-shaped {111} / / ND crystal grains were formed, but not many Goss crystal grains were formed, resulting in poor high-frequency iron loss. In comparative material 5, a large number of Goss crystal grains were formed, but not many {111} / / ND crystal grains were formed, resulting in relatively poor high-frequency iron loss. 【0047】 Figure 1 is an electron microscope photograph of the surface of the grain-oriented electrical steel sheet manufactured with the invention material 5, in which the {111} / / ND crystal grains are shown in blue. It can be seen that the crystal grains with {111} / / ND orientation are continuously arranged in a band pattern. Figure 2 shows the grains of Goss ({110} <001> ) grains are shown in green. It can be seen that most of the Goss grains are distributed among the bands in which the {111} / / ND grains in Figure 2 are arranged. 【0048】 The present invention is not limited to the above-mentioned embodiments, and can be manufactured in various different forms, and a person having ordinary skill in the art to which the present invention pertains can understand that the present invention can be embodied in other specific forms without changing the technical concept or essential features of the present invention. Therefore, it should be understood that the above-described embodiments are illustrative in all respects and are not limiting.

Claims

[Claim 1] hot rolling the slab to produce a hot rolled steel sheet; annealing the hot-rolled steel sheet; performing a first cold rolling on the hot-rolled steel sheet that has been annealed; A step of subjecting the first cold-rolled steel sheet to a first decarburization annealing; a step of subjecting the steel sheet having undergone the first decarburization annealing to a second cold rolling; a step of subjecting the steel sheet having undergone the second cold rolling to a second decarburization annealing; A first non-oxidation annealing step in which the steel sheet after the second decarburization annealing is annealed at a temperature of 1000°C to 1200°C and a dew point temperature of -20°C or less; A third cold rolling step is performed on the steel sheet that has been subjected to the first non-oxidation annealing; and A method for manufacturing a grain-oriented electrical steel sheet, comprising: a second non-oxidation annealing step of annealing the steel sheet after the third cold rolling at a crack temperature of 750 to 1050°C for 30 seconds to 5 minutes. [Claim 2] The method for producing a grain-oriented electrical steel sheet according to claim 1, characterized in that the slab consists, by weight, of 1.0% to 4.0% Si, 0.1% to 0.4% C, and the balance being Fe and unavoidable impurities. [Claim 3] The method for producing a grain-oriented electrical steel sheet according to claim 2 , wherein the slab further contains Mn: 0.1% by weight or less and S: 0.005% by weight or less. [Claim 4] The method for producing a grain-oriented electrical steel sheet according to claim 1, wherein the step of annealing the hot-rolled sheet includes a decarburization process. [Claim 5] 2. The method of claim 1, wherein the hot-rolled sheet is annealed at a temperature of 850° C. to 1000° C. and a dew point temperature of 70° C. or less. [Claim 6] 2. The method of claim 1, wherein the first decarburization annealing is performed at a temperature of 850°C to 1000°C and a dew point temperature of 50°C to 70°C. [Claim 7] 2. The method of claim 1, wherein the first decarburization annealing is performed in an austenite single phase region or a region where a composite phase of ferrite and austenite exists. [Claim 8] The method for manufacturing a grain-oriented electrical steel sheet according to claim 1, wherein an average grain diameter after the first decarburization annealing is 150 to 250 μm. [Claim 9] The method of claim 1, wherein the first decarburization annealing and the second cold rolling are repeated two or more times. [Claim 10] 2. The method of claim 1, wherein the secondary decarburization annealing is performed at a temperature of 850°C to 1000°C and a dew point temperature of 50°C to 70°C. [Claim 11] 2. The method of claim 1, wherein the secondary decarburization annealing is performed for 30 seconds to 5 minutes. [Claim 12] 2. The method of claim 1, wherein the first non-oxidation annealing step is performed for 30 seconds to 5 minutes. [Claim 13] 2. The method of claim 1, wherein the first non-oxidation annealing step further comprises a subsequent pickling step. [Claim 14] 2. The method of claim 1, wherein the second non-oxidizing annealing step is performed in an atmosphere having a dew point temperature of −20° C. or less. [Claim 15] The grains, whose {111} planes form an angle of 15° or less with the rolling surface of the steel sheet, are continuously arranged in a band shape, the aspect ratio of the band shape is 10 or more, and the density of the band shape is 100 mm ２ The grain-oriented electrical steel sheet has 5 to 1,000 particles per one piece. [Claim 16] 16. The grain-oriented electrical steel sheet according to claim 15, wherein the density of crystal grains whose {111} planes form an angle of 15° or less with the rolled surface of the steel sheet is 500 to 100,000 grains per 100 mm2. [Claim 17] The grain-oriented electrical steel sheet according to claim 15, characterized in that the fraction of crystal grains having a grain size of 10 μm to 100 μm in all crystal grains is 20% to 99%. [Claim 18] The grain-oriented electrical steel sheet according to claim 15, characterized in that the fraction of crystal grains forming an angle of 15° or less with the Goss direction is 10 to 95%. [Claim 19] The grain-oriented electrical steel sheet according to claim 15, characterized in that the electrical steel sheet consists, by weight, of 1.0% to 4.0% Si, 0.005% or less (excluding 0%) C, and the balance being Fe and unavoidable impurities. [Claim 20] The grain-oriented electrical steel sheet according to claim 18, further comprising Mn: 0.1% by weight or less and S: 0.005% by weight or less.

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