Grain-oriented electrical steel sheet and method of manufacturing same

Abstract

The grain-oriented electrical steel sheet according to one embodiment of the present invention includes, by wt%, 2.0 to 5.0% of Si, 0.005 to 0.04% of Al, and 0.01 to 0.20% of Mn, and the balance Fe and inevitable impurities, wherein the fraction of grains in which the <110> direction forms an angle of 5° or less with respect to ND is 60 area% or greater.

Description

Grain-oriented electrical steel sheet and its manufacturing method

[0001] One embodiment of the present invention relates to a oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention provides a method for stably forming a Goss {110} steel sheet by appropriately controlling conditions during hot rolling. <001> The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet having excellent magnetic properties by forming secondary recrystallization toward the direction of the magnetic field.

[0002] Grain-oriented electrical steel sheets utilize an abnormal grain growth phenomenon called secondary recrystallization to produce a Goss texture ({110} <001> It is a soft magnetic material that forms a grain structure (grain texture) throughout the steel sheet and has excellent magnetic properties in the rolling direction and is used as a core for electronic devices such as transformers that require excellent one-way magnetic properties. In general, magnetic properties can be expressed in terms of magnetic flux density and iron loss, and high magnetic flux density causes the grain orientation to be {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 that the electrical devices can be miniaturized and have high efficiency 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] Secondary recrystallization of grain-oriented electrical steel sheets, unlike conventional grain growth, occurs when the normal grain growth is inhibited by the movement of grain boundaries due to precipitates, inclusions, or elements that are dissolved or segregated at grain boundaries. Furthermore, in order to grow grains with a high degree of integration along the Goss orientation, complex processes such as component control during steelmaking, slab reheating and hot rolling process parameter control during hot rolling, hot-rolled sheet annealing, primary recrystallization annealing, and secondary recrystallization annealing are required, and these processes must be managed very precisely and strictly. Precipitates and inclusions that inhibit grain growth in this way are specifically called grain growth inhibitors, and research on grain-oriented electrical steel sheet manufacturing technology through secondary recrystallization along the Goss orientation has focused on securing excellent magnetic properties by forming secondary recrystallization with a high degree of integration along the Goss orientation using powerful grain growth inhibitors.

[0004] Initially developed grain-oriented electrical steel sheets used MnS as a grain growth inhibitor and were manufactured through a two-pass cold rolling process. This resulted in stable secondary recrystallization, but the magnetic flux density was not very high and the core loss was also high. Later, a method was proposed to manufacture grain-oriented electrical steel sheets using a composite of AlN and MnS precipitates and a single cold rolling process with a cold rolling ratio of 80% or higher. Recently, a method has been proposed to manufacture grain-oriented electrical steel sheets without using MnS. This method involves performing a single cold rolling process without decarburization, followed by a separate nitriding process using ammonia gas to supply nitrogen into the steel sheet, thereby inducing secondary recrystallization by Al-based nitrides that exert a strong grain growth inhibitory effect.

[0005] Until now, almost all steel companies producing grain-oriented electrical steel have employed a manufacturing method that primarily utilizes precipitates such as AlN and MnS[Se] as grain-growth inhibitors, thereby inducing secondary recrystallization. While this manufacturing method offers the advantage of stably inducing secondary recrystallization, to achieve a strong grain-growth inhibition effect, the precipitates must be distributed very finely and uniformly throughout the steel sheet. To achieve this uniform distribution of fine precipitates, the slab must be heated at a high temperature for an extended period of time before hot rolling to dissolve any coarse precipitates present in the steel. Hot rolling must then be performed very quickly to ensure that no precipitation occurs. This requires large-scale slab heating equipment. Furthermore, the hot rolling and coiling processes must be strictly controlled to minimize precipitation, and the subsequent hot-rolled sheet annealing process must ensure that the dissolved precipitates are finely dispersed. In addition, when the slab is heated at a high temperature, slab washing occurs as Fe2SiO4 with a low melting point is formed, which reduces the yield.

[0006] Recently developed technology for manufacturing grain-oriented electrical steel sheets by slab low-temperature heating method, which forms secondary recrystallization through Al-based nitrides after decarburization annealing following cold rolling and nitriding treatment, has improved many problems such as difficulties in operating slab heating equipment and low yield in the hot rolling stage by relatively lowering the slab heating temperature. However, in order to use this method, a process for additionally generating nitride-based inhibitors is essential during the annealing process after slab heating. For this purpose, nitriding treatment is performed using ammonia gas during the primary recrystallization annealing process. Ammonia gas has the property of decomposing into hydrogen and nitrogen at temperatures above approximately 500℃. Nitriding is performed using this, and the infiltrating nitrogen reacts with the nitride-forming elements in the steel sheet to form nitrides such as AlN and (Al,Si)N, which act as inhibitors.

[0007] As transformer efficiency regulations tighten worldwide, demand for thin grain-oriented electrical steel is increasing. Typically, as thickness decreases, precipitates lose their grain-growth inhibition relatively quickly during secondary recrystallization annealing. This leads to unstable secondary recrystallization behavior, resulting in poor Goss orientation integration and increased hysteresis loss, which in turn offsets the eddy current loss reduction associated with reduced thickness. To address this issue, technologies are being developed to enhance grain-growth inhibition using precipitates other than Al-based nitrides. However, these technologies face the challenge of achieving complete purification annealing.

[0008] In one embodiment of the present invention, a method for manufacturing a oriented electrical steel sheet is provided. Specifically, in one embodiment of the present invention, by appropriately controlling conditions during hot rolling, a Goss {110} steel sheet can be stably manufactured. <001> A method for manufacturing a grain-oriented electrical steel sheet having excellent magnetic properties is provided by forming secondary recrystallization toward the direction of the magnetic field.

[0009] A directional electrical steel sheet according to one embodiment of the present invention comprises Si: 2.0 to 5.0% by weight, Al: 0.005 to 0.04%, and Mn: 0.01 to 0.20%, with the remainder being Fe and unavoidable impurities. <110> The fraction of crystals whose direction forms an angle with ND of 5° or less is 60% or more by area.

[0010] Directional electrical steel sheet according to one embodiment of the present invention <001> The fraction of crystals whose direction forms an angle of 5° or less with respect to ND may be 70% or more by area.

[0011] A directional electrical steel sheet according to one embodiment of the present invention may further include at least one of C: 0.005 wt% or less, N: 0.01 wt% or less, and S: 0.01 wt% or less.

[0012] The oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of P: 0.0005% to 0.045 wt%, Sn: 0.03 to 0.08 wt%, and Cr; 0.01 to 0.20 wt%.

[0013] A method for manufacturing a grain-oriented electrical steel sheet according to one embodiment of the present invention comprises the steps of: hot-rolling a slab containing, in wt%, C: 0.03 to 0.07%, Si: 2.0 to 5.0%, Al: 0.005 to 0.04%, and Mn: 0.01 to 0.20%, with the remainder being Fe and unavoidable impurities, to manufacture a hot-rolled sheet; pre-rolling the hot-rolled sheet to manufacture a pre-rolled sheet; a hot-rolled sheet annealing step of annealing the pre-rolled sheet; cold-rolling the annealed pre-rolled sheet to manufacture a cold-rolled sheet; a step of first recrystallization annealing the cold-rolled sheet; and a step of second recrystallization annealing the steel sheet subjected to the first recrystallization annealing.

[0014] The step of manufacturing a hot-rolled plate includes a step of manufacturing a bar by rough rolling a slab and a step of manufacturing a hot-rolled plate by slit rolling the bar, and the step of manufacturing the bar has an average of A values ​​calculated by the following equation 1 of 1.35 to 1.65.

[0015] [Formula 1]

[0016] A = 2 × (work roll diameter × (thickness before rolling - thickness after rolling)) 0.5 / (Thickness before rolling + thickness after rolling)

[0017] (In Equation 1, the units of the work roll diameter, thickness before rolling, and thickness after rolling are all mm.)

[0018] The slab may further contain one or more of N: 0.01 wt% or less and S: 0.01 wt% or less.

[0019] The slab may further comprise at least one of P: 0.0005 to 0.045 wt%, Sn: 0.03 to 0.08 wt%, and Cr; 0.01 to 0.20 wt%.

[0020] The bar manufacturing process can take anywhere from 3 to 8 passes.

[0021] In the stage of manufacturing the pre-rolled plate, the reduction ratio may be 20 to 50%.

[0022] After the hot-rolled sheet annealing step, when analyzing the ODF of the steel sheet, the strength in the direction of φ1=90°, Φ=65°, and φ2=45° may be 2.0 or more.

[0023] The oriented electrical steel sheet and the method for manufacturing the same according to one embodiment of the present invention have excellent magnetism by stably growing crystal grains with a very high degree of integration in the Goss direction.

[0024] 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.

[0025] 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 "a," "an," and "the" include plural forms as well, unless the context clearly dictates otherwise. The word "comprising," as used herein, specifies particular features, regions, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of other features, regions, integers, steps, operations, elements, and / or components.

[0026] 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.

[0027] 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.

[0028] Also, unless otherwise stated, % means weight%, and 1 ppm is 0.0001 weight%.

[0029] 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.

[0030] 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.

[0031]

[0032] A directional electrical steel sheet according to one embodiment of the present invention comprises Si: 2.0 to 5.0% by weight, Al: 0.005 to 0.04%, and Mn: 0.01 to 0.20%, with the remainder being Fe and unavoidable impurities. <110> The fraction of crystals whose direction forms an angle with ND of 5° or less is 60% or more by area.

[0033] Below, the reasons for limiting the alloy composition of steel plates are explained.

[0034]

[0035] Si: 2.0 to 5.0 wt%

[0036] Silicon (Si) is a basic component of electrical steel, increasing its resistivity and reducing core loss. Excessive Si content can lead to decreased resistivity and deteriorated core loss characteristics. Furthermore, decarburization annealing can promote phase transformation between ferrite and austenite, severely damaging the primary recrystallization texture. Furthermore, secondary recrystallization annealing can also cause phase transformation between ferrite and austenite, leading to unstable secondary recrystallization and severe damage to the Goss texture. Excessive Si addition to the slab can lead to the formation of excessive and dense SiO2 and Fe2SiO4 oxide layers during decarburization annealing, delaying decarburization. Furthermore, the mechanical properties of electrical steel, such as brittleness and toughness, can increase, leading to a higher incidence of sheet fracture during rolling. Consequently, weldability between sheets can be poor, making it difficult to ensure easy workability. Therefore, in one embodiment of the present invention, Si may be included in an amount of 2.0 to 5.0 wt%. More specifically, it may be included in an amount of 2.5 to 4.5 wt%. More specifically, it may be included in an amount of 3.0 to 3.5 wt%.

[0037] Al: 0.005 to 0.040 wt%

[0038] Aluminum (Al) acts as a powerful grain growth inhibitor by forming nitrides in the form of (Al,Si,Mn)N, (Al,Si)N, and AlN when nitrogen ions introduced by ammonia gas during the annealing process after cold rolling combine with Al, Si, and Mn present in a solid solution state in the steel, in addition to the finely precipitated AlN during hot rolling and hot-rolled sheet annealing. If too little Al is included, it is difficult to expect a sufficient effect as an inhibitor because the number and volume formed are quite low. If too much Al is included, the grain growth inhibition ability may be reduced by forming coarse nitrides. More specifically, Al may be included in an amount of 0.010 to 0.030 wt%.

[0039] Mn: 0.01 to 0.20 wt%

[0040] Manganese (Mn), like Si, also has the effect of reducing iron loss by increasing resistivity, and it is an important element for inducing secondary recrystallization by reacting with nitrogen introduced through nitriding together with Si to form (Al, Si, Mn)N precipitates, thereby inhibiting the growth of primary recrystallized grains. If the Mn content is too low, the number and volume formed will be low, making it difficult to expect a sufficient effect as an inhibitor. If the content is too high, in addition to Fe2SiO4, a large amount of (Fe, Mn) and Mn oxides are formed on the surface of the steel sheet, which interferes with the formation of a base coating formed during secondary recrystallization annealing, lowering the surface quality. In addition, since it causes non-uniformity in the phase transformation between ferrite and austenite during the primary recrystallization annealing process, the size of the primary recrystallized grains becomes non-uniform, resulting in unstable secondary recrystallization. Therefore, the Mn content may be included in an amount of 0.01 to 0.20 wt%. It may contain 0.05 to 0.15 wt%.

[0041] A directional electrical steel sheet according to one embodiment of the present invention may further include at least one of C: 0.005 wt% or less, N: 0.01 wt% or less, and S: 0.01 wt% or less.

[0042] C: 0.005 wt% or less

[0043] Carbon (C) is an element that contributes to grain refinement and improved elongation by inducing a phase transformation between ferrite and austenite. C is essential for improving the rollability of electrical steel sheets, which are brittle and therefore poorly rollable. However, if C remains in the final product, it can precipitate carbides formed during magnetic aging, thereby deteriorating magnetic properties. Therefore, its content must be controlled to an appropriate level.

[0044] If the C content in the slab is too low within the aforementioned Si content range, austenite phase transformation will not occur sufficiently, resulting in non-uniformity of the slab and hot-rolled microstructure. This will also impair cold-rollability.

[0045] If the C content is too high within the aforementioned Si content range, sufficient decarburization cannot be achieved during the decarburization annealing process. The resulting phase transformation severely damages the secondary recrystallization texture. Furthermore, when the final product is applied to power devices, it can result in deterioration of magnetic properties due to magnetic aging.

[0046] Therefore, the content of C in the slab may be comprised between 0.03 and 0.07 wt%. More specifically, it may be comprised between 0.050 and 0.065 wt%.

[0047] In one embodiment of the present invention, decarburization annealing is performed during the manufacturing process, and the C content in the final grain-oriented electrical steel sheet manufactured after decarburization annealing may be 0.005 wt% or less. More specifically, it may be 0.003 wt% or less. More specifically, it may contain 0.0001 to 0.0030 wt%.

[0048] N: 0.0100 wt% or less

[0049] Nitrogen (N) is an important element that reacts with Al to form AlN precipitates. If too much N is added, it can cause surface defects called blisters due to nitrogen diffusion in the process after hot rolling, and because too many nitrides are formed in the slab state, rolling becomes difficult, which complicates the subsequent process and increases the manufacturing cost. On the other hand, N, which is additionally required to form nitrides such as (Al,Si,Mn)N, (Al, Si)N, AlN, (B,Si,Mn)N, (Al,B)N, and BN, can be reinforced by nitriding the steel using ammonia gas in the annealing process after cold rolling. Some of the N is removed during the secondary recrystallization annealing process, and the final grain-oriented electrical steel sheet can contain 0.0100 wt% or less of N. More specifically, it can contain 0.0001 to 0.0070 wt% of N. More specifically, it may contain 0.001 to 0.005 wt%.

[0050] S: 0.010 wt% or less

[0051] Sulfur (S) is an element that has a high solidification temperature and severe segregation during hot rolling, so it is desirable to minimize its inclusion as much as possible. It is an unavoidable impurity contained during steelmaking. In addition, S forms MnS and affects the primary recrystallized grain size, so the S content can be limited to 0.01 wt% or less. More specifically, S can be included in an amount of 0.0001 to 0.0070 wt%. More specifically, it can be included in an amount of 0.001 to 0.005 wt%.

[0052] The oriented electrical steel sheet according to one embodiment of the present invention may further include at least one of P: 0.0005% to 0.045 wt%, Sn: 0.03 to 0.08 wt%, and Cr; 0.01 to 0.20 wt%.

[0053] P: 0.0005 to 0.0450 wt%

[0054] Phosphorus (P) can play an auxiliary role by segregating at grain boundaries, thereby inhibiting grain boundary movement and simultaneously suppressing grain growth, and in terms of microstructure, it is {110} <001> It has the effect of improving the aggregate structure. If the content of P is too low, the addition effect may not be sufficient. If too much P is included, brittleness may increase, which may significantly deteriorate the rollability. Therefore, when P is included more, it may be included in an amount of 0.0005 to 0.0450 wt%. More specifically, it may be included in an amount of 0.0010 to 0.0400 wt%. More specifically, it may be included in an amount of 0.0100 to 0.0300 wt%.

[0055] Sn: 0.03 to 0.08 wt%

[0056] Tin (Sn), like P, is known as a grain growth inhibitor because it is a grain boundary segregation element that inhibits the movement of grain boundaries. In the Si content range suggested in one embodiment of the present invention, the grain growth inhibition power for smooth secondary recrystallization behavior during secondary recrystallization annealing is insufficient, so Sn, which inhibits the movement of grain boundaries by segregating at grain boundaries, can be further added to reinforce it. When more Sn is added, if too little Sn is added, the effect may not be sufficient. If too much Sn is added, the growth inhibition power may be too strong, making it difficult to obtain stable secondary recrystallization. Therefore, when more Sn is added, the Sn content may be added in an amount of 0.03 to 0.08 wt%. More specifically, Sn may be included in an amount of 0.05 to 0.07 wt%.

[0057] Cr: 0.01 to 0.20 wt%

[0058] Chromium (Cr) promotes the formation of a hard phase in hot-rolled and annealed sheets, thereby promoting the formation of the Goss texture during cold rolling. It also promotes the decarburization of C during the decarburization annealing process, thereby preventing the phenomenon of the austenite phase transformation retention time becoming longer and the texture being damaged, which is a disadvantage when the C content is high, and reducing the austenite phase transformation retention time. In addition, it can solve the disadvantage of inhibiting the formation of the oxide layer due to Sn, an alloying element used as an inhibitor of grain growth, by promoting the formation of an oxide layer on the surface formed during the decarburization annealing process, so it can be added additionally. If too little Cr is added, the effect of adding it may not be sufficient. If too much Cr is included, the formation of a denser oxide layer during the decarburization process of the first recrystallization annealing may be promoted, which may actually hinder the formation of the oxide layer and even decarburization and nitriding. Therefore, when Cr is included further, the Cr content may be 0.01 to 0.20 wt%. More specifically, it may further contain 0.05 to 0.15 wt% of Cr.

[0059] In addition to the above-mentioned components, alloying elements that are advantageous for the formation of Goss aggregate structure may be added as needed. For example, one or more of Cu: 0.001 to 0.050 wt%, Se: 0.001 to 0.050 wt%, Sb: 0.01 to 0.08 wt%, and Ni: 0.02 to 0.5 wt% may be further included.

[0060] The remainder includes Fe and unavoidable impurities. Unavoidable impurities are impurities mixed in during the steelmaking step and the manufacturing process of grain-oriented electrical steel sheets, and since this is widely known in the field, a detailed description is omitted. Specifically, components such as Ti, Mg, and Ca react with oxygen in steel to form oxides, and therefore, strong suppression is required, and therefore, each component can be managed to 0.005 wt% or less. 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.

[0061]

[0062] Directional electrical steel sheet according to one embodiment of the present invention <110> The fraction of crystals having an angle of 5.000° or less with respect to the ND is 60% or more in area. In one embodiment of the present invention, <110> It is possible to produce a large number of crystal grains more precisely arranged at an angle of 5,000° or less with respect to the ND direction, thereby improving magnetism. More specifically, <110> The fraction of crystals having an angle of 5.000° or less with respect to the ND may be 75 to 90 area%.

[0063] Directional electrical steel sheet according to one embodiment of the present invention <001> The fraction of crystals whose direction forms an angle of 5° or less with respect to ND may be 70% or more by area. In one embodiment of the present invention, <001> It is possible to produce a large number of crystal grains more precisely arranged at an angle of 5° or less with respect to the ND direction, thereby improving magnetism. If the fraction of crystal grains is small, it is difficult to obtain sufficient magnetic improvement. More specifically, <001> The fraction of crystals having an angle of 5° or less with respect to the ND may be 72 to 90 area% or more. <001> The fraction of crystals whose direction forms an angle with ND of 5° or less can be measured using the X-ray Laue method.

[0064]

[0065] The grain-oriented electrical steel sheet according to one embodiment of the present invention has excellent magnetic flux density and iron loss characteristics at the same time. The grain-oriented electrical steel sheet according to one embodiment of the present invention may have a magnetic flux density (B8) of 1.91 T or more. Here, the magnetic flux density B8 is the size (Tesla) of the magnetic flux density induced under a magnetic field of 800 A / m. More specifically, the grain-oriented electrical steel sheet according to one embodiment of the present invention has a magnetic flux density (B 10 ) may be 1.91 to 2.00 T. In addition, the oriented electrical steel sheet according to one embodiment of the present invention has a core loss (W 17 / 50 ) can be less than 0.67 W / kg. The iron loss W17 / 50 is the iron loss until it is magnetized to 1.7 Tesla at 50 Hz. More specifically, the iron loss (W 17 / 50 ) can be 0.50 to 0.65 W / kg. At this time, the thickness of the steel plate can be 0.20 mm.

[0066]

[0067] A method for manufacturing a grain-oriented electrical steel sheet according to one embodiment of the present invention comprises the steps of: hot-rolling a slab containing, in wt%, C: 0.03 to 0.07%, Si: 2.0 to 5.0%, Al: 0.005 to 0.04%, and Mn: 0.01 to 0.20%, with the remainder being Fe and unavoidable impurities, to manufacture a hot-rolled sheet; pre-rolling the hot-rolled sheet to manufacture a pre-rolled sheet; a hot-rolled sheet annealing step of annealing the pre-rolled sheet; cold-rolling the annealed pre-rolled sheet to manufacture a cold-rolled sheet; a step of first recrystallization annealing the cold-rolled sheet; and a step of second recrystallization annealing the steel sheet subjected to the first recrystallization annealing.

[0068] First, the slab is hot-rolled to produce hot-rolled steel sheets. The steel composition of the slab has been described in the previously mentioned grain-oriented electrical steel sheet, so a detailed explanation will be omitted. Except for C, the components may be substantially the same.

[0069] An additional step of heating the slab prior to hot rolling the slab may be included.

[0070] The slab can be heated to a temperature range of 1000 to 1250°C, which is the temperature range where N and S are incompletely dissolved. If N and S are completely dissolved, a large amount of fine nitrides or sulfides are precipitated after hot-rolled sheet annealing, making the subsequent single-stage cold rolling impossible. In addition, the primary recrystallized grain size is formed to be quite fine, making it impossible to form appropriate secondary recrystallization. More specifically, the slab heating temperature can be 1050 to 1200°C.

[0071] In one embodiment of the present invention, the step of manufacturing a hot-rolled plate includes the step of rough rolling a slab to manufacture a bar and the step of finishing rolling the bar to manufacture a hot-rolled plate. The rough rolling is a step of rolling a slab to manufacture a bar having a thickness of 40 mm to 70 mm. If the rough rolling thickness is too thick, the latent heat of the steel plate surface is large, and the rolling speed is slowed, which increases the growth of scale during rolling, which is disadvantageous for the descaling of the hot-rolled coil. On the other hand, if the rough rolling thickness is too thin, the cooling of the steel material is accelerated, which may reduce the rollability. More specifically, the thickness may be 45 mm to 65 mm. The finishing rolling is a step of rolling a bar to manufacture a hot-rolled steel plate. The method may further include a coiling step of coiling the steel plate manufactured after the finishing rolling.

[0072] In one embodiment of the present invention, the step of manufacturing a bar is such that the average of the A values ​​calculated by the following equation 1 is 1.35 to 1.65.

[0073] [Formula 1]

[0074] A = 2 × (work roll diameter × (thickness before rolling - thickness after rolling)) 0.5 / (Thickness before rolling + thickness after rolling)

[0075] (In Equation 1, the units of the work roll diameter, thickness before rolling, and thickness after rolling are all mm.)

[0076] The average A value is the average of the sum of the A values ​​for each pass divided by the number of passes when the bar manufacturing process consists of multiple passes. A pass refers to the number of times the work roll passes.

[0077] A very small average A value means that the number of passes is large, resulting in a small reduction ratio per pass, or that the reduction ratio per pass is low in the front end of the roughing mill and high in the back end. In the former case, the reduction ratio per pass decreases, which reduces the shear strain imparted to the steel sheet, and thus reduces the Goss fraction in the hot-rolled sheet. In the latter case, the rolling load at the back end of the roughing mill is excessively high, which causes production difficulties. A very large average A value means that the number of passes is small, resulting in an excessively high reduction ratio per pass, or that the total reduction ratio of the roughing mill is high. In both the former and the latter cases, the rolling load is excessively high, which causes production difficulties, and in the latter case in particular, the total reduction ratio of the finishing mill decreases, which causes the Goss fraction in the hot-rolled sheet to decrease. More specifically, the average A value may be 1.35 to 1.60.

[0078] The total reduction ratio of the roughing process can be greater than 70%. The bar manufacturing process can have three to eight total passes.

[0079] The hot rolled sheet thickness can be manufactured in a thickness of 1.5 to 5.0 mm so that pre-rolling and final cold rolling can be applied.

[0080] There are no special restrictions on the hot rolling temperature or cooling temperature, but for example, if the magnetism is excellent, the hot rolling end temperature can be set to 950℃ or lower, and the cooling can be done rapidly with water so that the coiling can be done at 600℃ or lower.

[0081] A hot rolled sheet is pre-rolled to manufacture a pre-rolled sheet. If necessary, the pre-rolled sheet can be pickled. By adding the step of manufacturing a pre-rolled sheet, the thickness of the grain-oriented electrical steel sheet to be finally manufactured can be further reduced without adding a load in the cold rolling described later. The reduction ratio during the pre-rolling can be 20.0 to 50.0%. If the reduction ratio is too small, the effect of improving the texture by the pre-rolling is small, and if the reduction ratio is too large, the thickness of the hot rolled sheet becomes excessively thick, and edge cracks, etc. may occur. More specifically, the reduction ratio during the pre-rolling can be 20.0 to 45.0%. The reduction ratio can be obtained by (thickness before rolling - thickness after rolling) / (thickness before rolling) × 100.

[0082] Next, in the hot-rolled sheet annealing step, the pre-rolled sheet is annealed. Hot-rolled sheet annealing is performed to control the microstructure and precipitates, and can be performed by heating to a temperature of 1,000 to 1,250°C and then lowering the soaking temperature to 950°C or lower.

[0083] If hot rolling and pre-rolling are properly controlled, the strength of the orientation of ODF φ1=90°, Φ=65°, φ2=45° in hot-rolled sheet annealing develops to 2.0 or more. This orientation is formed by the rotation of Goss crystal grains formed in hot rolling during pre-rolling, and is quickly {111} during cold rolling. <112> In cold rolling, the friction between the thickness direction surface and the rolling roll is small, so unlike hot rolling, shear deformation hardly acts, and only plane deformation that reduces the thickness of the steel sheet and increases the length is applied. As a result, Goss grains, which are a stable organization in shear deformation, are formed in {111} during cold rolling. <112> It rotates and disappears, {111} <112> It is formed in small quantities by shear deformation of the shear band within the deformation structure. When hot rolling and pre-rolling are properly controlled, {111} <112> Not only does the strain structure fraction increase, but Goss grains formed within the shear band also increase because they are formed quickly during cold rolling. More specifically, the strength in the orientation of ODF φ1=90°, Φ=65°, φ2=45° can be 2.3 to 3.5. ODF analysis can be measured by EBSD so that the full thickness is included in either the plane perpendicular to TD (TD plane) or the plane perpendicular to RD (RD plane). The scan size can be measured so that it is "full thickness" x "3 mm or more".

[0084] Next, the hot-rolled sheet is cold-rolled to produce a cold-rolled sheet.

[0085] Cold rolling is performed using a reverse rolling mill or a tandem rolling mill, either through a single cold rolling process or two or more cold rolling processes including intermediate annealing, to produce a cold-rolled sheet having the final product thickness. Furthermore, warm rolling, which maintains the temperature of the steel sheet above 100°C during cold rolling, is advantageous in improving magnetism. Through cold rolling, a final thickness of 0.10 to 0.50 mm, or more specifically, 0.15 to 0.35 mm, can be produced.

[0086] Next, the cold-rolled sheet is subjected to primary recrystallization annealing. During this process, decarburization, nitriding, and primary recrystallization occur. The steel sheet can be heat-treated at an annealing temperature ranging from 800 to 950°C. If the annealing temperature is low, decarburization takes a long time, and if the annealing temperature is too high, the recrystallized grains grow coarsely, reducing the driving force for crystal growth and preventing stable secondary recrystallization from forming. The annealing time does not significantly affect the effectiveness of the present invention, but can be processed within 5 minutes.

[0087] Decarburization and nitriding can be done by using ammonia gas after decarburization and recrystallization, or by using a method that uses ammonia gas simultaneously so that decarburization and nitriding can be done at the same time.

[0088] Next, the cold-rolled steel sheet that has undergone the first recrystallization annealing is subjected to the second recrystallization annealing. The first recrystallized steel sheet is subjected to the second recrystallization annealing after applying an annealing separator, so that the {110} plane is parallel to the rolling surface. <001> Goss {110} with direction parallel to the rolling direction <001> It allows the formation of a cohesive structure. The annealing separator is not particularly limited, and an annealing separator containing MgO as its main component can be used. Since annealing separators are widely known, a detailed description is omitted.

[0089] Secondary recrystallization high temperature annealing is performed by increasing the temperature at an appropriate rate to {110} <001> Secondary recrystallization of the Goss orientation is induced, followed by purification annealing, a process for removing impurities, and then cooling. During this process, the annealing atmosphere gas is used as a mixture of hydrogen and nitrogen during the temperature increase process as in the usual case, and during the purification annealing process, 100% hydrogen gas is used and maintained for a long period of time to remove impurities.

[0090] Next, after removing unreacted MgO from the grain-oriented electrical steel sheet that has undergone secondary recrystallization annealing, additional insulation coating and flattening annealing can be performed. Flattening annealing is performed to remove residual stress generated during secondary recrystallization annealing and to correct the shape, and can be performed at temperatures above 800°C.

[0091] In order to improve iron loss through domain refinement on the surface of oriented electrical steel sheets subjected to flattening annealing and tension coating, a continuous wave mode CO2 laser (TEM) was used. 00 ) may further include a step of irradiating the beam. The optical system is configured so that the laser beam has an oval shape with a width and a length of 0.05 to 0.20 mm and 5 to 15 mm, respectively, and the laser is irradiated so that the longitudinal direction of the oval is the width direction of the steel plate. The laser irradiation interval is irradiated at an interval of 3 to 7 mm in the longitudinal direction, and the rotation speed of the polygon mirror is controlled in conjunction with the steel plate speed so that the laser can be irradiated at a constant interval to the entire steel plate. The laser output intensity can be adjusted to an appropriate range that provides a good iron loss improvement rate while not excessively damaging the coating layer on the surface of the steel plate.

[0092]

[0093] Specific examples of the present invention are described below. However, the following examples are only specific examples of the present invention, and the present invention is not limited to the following examples.

[0094]

[0095] Example 1

[0096] Grain-oriented electrical steel sheets composed of Si: 3.47%, Sol-Al: 0.029%, Mn: 0.097%, N: 0.005%, S: 0.005%, P: 0.028%, Sn: 0.063%, Cr: 0.11%, C: 0.063%, the remainder Fe, and other unavoidable impurities in wt% were vacuum melted to make ingots, and then heated to a temperature of 1150°C and hot-rolled under the conditions shown in Table 1 below, and then pickled with a hydrochloric acid solution and pre-rolled at the reduction ratio shown in Table 1 below. Next, the hot-rolled sheet was heated to a temperature of 1100℃, maintained at a soaking temperature of 900℃ for 80 seconds, and quenched in water to perform hot-rolled sheet annealing. Subsequently, the hot-rolled annealed sheet was pickled and cold-rolled to the thickness shown in Table 1 below. The cold-rolled sheet was simultaneously decarbonitriding annealed at a temperature of 850℃ for 180 seconds in a humid hydrogen, nitrogen, and ammonia mixed gas atmosphere so that the nitrogen content became 200 ppm and the carbon content became 30 ppm. After applying MgO as an annealing separator to the steel sheet, the final annealing was performed. The final annealing was performed in a mixed gas atmosphere of 25 vol% nitrogen and 75 vol% hydrogen up to 1200℃, and after reaching 1200℃, it was maintained in a 100% hydrogen gas atmosphere for more than 10 hours and then furnace-cooled. After removing unreacted MgO, an insulating coating composition containing phosphate and silica as main components was applied, followed by heat treatment to form an insulating film and flattening annealing. To temporarily refine the surface of the grain-oriented electrical steel sheet on which the insulating coating was completed, a continuous mode CO2 laser (TEM) was used. 00 ) beam was investigated. The laser beam was oval-shaped with a width and length of 0.1 mm and 10 mm, respectively, and the longitudinal direction of the oval was in the width direction of the steel plate, and the beam was irradiated at intervals of 5.0 mm. The crystal of the grain-oriented electrical steel plate according to each condition <110> Direction and <001> The angle formed by the direction with respect to ND and the magnetic properties are as shown in Table 1.

[0097] After hot-rolled sheet annealing, the strength of ODF φ1=90°, Φ=65°, φ2=45° was measured using EBSD on the full thickness x 3 mm in the plane perpendicular to TD (TD plane).

[0098] Decision of <110> and <001> The angle formed by the direction with the ND was measured using the X-ray Laue method, and the specimen whose magnetic properties were measured was scanned at regular intervals, and the crystals were compared with the entire point. <110> and <001> The ratio of points whose direction forms an angle of 5° or less with respect to ND was calculated.

[0099] The magnetic flux density and iron loss were measured using the single sheet measurement method. The magnetic flux density B8 is the magnitude (Tesla) of the magnetic flux density induced under a magnetic field of 800 A / m, and the iron loss W17 / 50 is the loss (W / kg) when a magnetic flux density of 1.7 Tesla is induced at a frequency of 50 Hz.

[0100]

[0101] Steel No. Number of rough rolling passes A value Average pre-rolling reduction ratio (%) Strength of ODF φ1=90°, Φ=65°, φ2=45° direction after hot-rolled sheet annealing Thickness of cold-rolled sheet (mm) 161.44 0.01.40.23 261.44 9.81.60.23 361.44 20.72.60.23 461.44 28.13.00.23 561.44 0.01.30.20 661.44 13.01.80.20 761.44 21.62.50.20 861.44 31.03.20.20 961.44 37.53.30.20 1061.44 10.01.60.18 11 61.4421.72.60.181261.4429.43.10.181361.4437.93.20.181461.4443.82.90.181561.350.00.80.201661.3521.62.00.201761.400.01.00.201861.4021.62.30.201971.3221.61.80.202051.5621.62.80.20

[0102] River No. <110> Fraction (area %) of which the angle formed by the direction with the ND is 5° or less <001> The angle formed by the direction with the ND is less than 5° Fraction (area %) Magnetic flux density (B8, Tesla) Iron loss (W17 / 50, W / kg) Classification 153681.900.75 Comparative example 1256691.900.75 Comparative example 2376761.920.68 Invention example 1484821.930.66 Invention example 2545661.890.70 Comparative example 3658691.900.69 Comparative example 4777761.920.62 Invention example 3887821.930.60 Invention example 4986831.930.60 Invention example 51048671.890.65 Comparative example 511 76781.920.58 Invention Example 61283821.930.55 Invention Example 71384811.930.56 Invention Example 81478791.920.56 Invention Example 91532621.880.73 Comparative Example 61663721.910.65 Invention Example 101745651.890.71 Comparative Example 71873751.920.63 Invention Example 111955681.900.69 Comparative Example 82081801.930.61 Invention Example 12

[0103] As can be seen in Tables 1 and 2, the invention examples, where process conditions were appropriately controlled, demonstrated adequate formation of aggregate structure, resulting in both excellent magnetic flux density and iron loss. Conversely, the comparative examples, where process conditions were not appropriately controlled, demonstrated inadequate development of aggregate structure, resulting in inferior magnetic flux density and iron loss.

[0104]

[0105] 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.

Claims

Containing Si: 2.0 to 5.0% by weight, Al: 0.005 to 0.04%, and Mn: 0.01 to 0.20%, with the remainder being Fe and inevitable impurities; <110> Grain-oriented electrical steel sheet having a fraction of crystals having an angle of 5° or less with respect to ND of 60 area% or more. In the first paragraph, <001> Grain-oriented electrical steel sheet having a fraction of crystals whose angle formed by the ND direction is 5° or less of 70% or more by area. In the first paragraph, Grain-oriented electrical steel sheet further comprising at least one of C: 0.005 wt% or less, N: 0.01 wt% or less, and S: 0.01 wt% or less. In the first paragraph, Grain-oriented electrical steel sheet further comprising at least one of P: 0.0005 wt% to 0.045 wt%, Sn: 0.03 to 0.08 wt%, and Cr; 0.01 to 0.20 wt%. A step of manufacturing a hot-rolled sheet by hot-rolling a slab containing C: 0.03 to 0.07% by weight, Si: 2.0 to 5.0%, Al: 0.005 to 0.04%, and Mn: 0.01 to 0.20%, with the remainder being Fe and unavoidable impurities; A step of manufacturing a pre-rolled plate by pre-rolling the hot-rolled plate; A hot-rolled plate annealing step for annealing the above-mentioned pre-rolled plate; A step of manufacturing a cold rolled sheet by cold rolling the annealed pre-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 step of manufacturing the above hot-rolled plate includes the step of manufacturing a bar by rough rolling a slab and the step of manufacturing a hot-rolled plate by slit rolling the bar. A method for manufacturing a grain-oriented electrical steel sheet, wherein the step of manufacturing the above bar is performed by calculating an average of A values ​​of 1.35 to 1.65 by the following Equation 1. [Formula 1] A = 2× (work roll diameter × (thickness before rolling - thickness after rolling)) 0.5 / (Thickness before rolling + Thickness after rolling) (In Equation 1, the units of the work roll diameter, thickness before rolling, and thickness after rolling are all mm.) In paragraph 5, A method for manufacturing a grain-oriented electrical steel sheet, wherein the above slab further includes at least one of N: 0.01 wt% or less and S: 0.01 wt% or less. In paragraph 5, A method for manufacturing a grain-oriented electrical steel sheet, wherein the above slab further contains at least one of P: 0.0005 to 0.045 wt%, Sn: 0.03 to 0.08 wt%, and Cr; 0.01 to 0.20 wt%. In paragraph 5, A method for manufacturing a grain-oriented electrical steel sheet, wherein the step of manufacturing the above bar comprises 3 to 8 total passes. In paragraph 5, A method for manufacturing a grain-oriented electrical steel sheet having a reduction ratio of 20 to 50% in the step of manufacturing the above-mentioned preliminary rolled sheet. In the first paragraph, A method for manufacturing grain-oriented electrical steel sheets having a strength of 2.0 or more in the direction of φ1=90°, Φ=65°, and φ2=45° when analyzing the ODF of the steel sheet after the above hot-rolled sheet annealing step.