Grain-oriented electrical steel sheet and its manufacturing method

Abstract

The present invention provides a grain-oriented electrical steel sheet and a manufacturing method thereof, which can suppress magnetic deterioration even if the hot-rolled sheet annealing stage is omitted by appropriately controlling the contents of Si, C, N, Cr, Sn, etc. and appropriately adjusting the coiling temperature in the hot rolling stage. [Solution] The steel contains, by weight, 2.0-4.0% Si, 0.04-0.2% Mn, 0.010% or less (excluding 0%) N, 0.005% or less (excluding 0%) C, 0.03-0.08% Sn, and 0.01-0.2% Cr, with the balance being Fe and unavoidable impurities, and contains inclusions containing one or more of AlN, (Al, Si)N, (Al, Si, Mn)N, MnS, CuS, and Al2O3, the average grain size of the inclusions being 0.5-6.0 μm, and the medium grain size of the inclusions being 6.0 μm or less, at a density of 40-130 inclusions / mm 2 The present invention is characterized by including:

Description

[Technical field]

[0001] The present invention relates to a grain-oriented electrical steel sheet and a manufacturing method thereof. More particularly, the present invention relates to a grain-oriented electrical steel sheet in which the contents of Si, C, N, Cr, Sn, etc. are appropriately controlled and the coiling temperature is appropriately adjusted in the hot rolling stage, thereby suppressing magnetic deterioration even when the hot-rolled sheet annealing stage is omitted, and a manufacturing method thereof. [Background technology]

[0002] Grain-oriented electrical steel sheets have a {110} texture in the rolling direction. <001> It shows a Goss texture, which is a soft magnetic material with excellent magnetic properties in one direction or the rolling direction. In order to develop such a texture and improve the magnetic properties of grain-oriented electrical steel, complex processes such as component control in steelmaking, slab reheating in hot rolling, control of hot rolling process factors, hot-rolled sheet annealing heat treatment, cold rolling, primary recrystallization annealing, and secondary recrystallization annealing are required, and these processes must be managed with great precision and strictness. The hot-rolled sheet annealing process is an essential process for stably carrying out secondary recrystallization of Goss-oriented crystal grains during secondary recrystallization annealing by uniformly controlling the non-uniform microstructure and inclusions of the hot-rolled sheet after hot rolling. However, since hot-rolled sheet annealing is a factor that increases the production cost of grain-oriented electrical steel sheets, if it is possible to omit hot-rolled sheet annealing and simultaneously homogenize the microstructure and inclusions of the hot-rolled sheet, the production cost due to the hot-rolled sheet annealing process can be reduced and productivity can be improved. When heating a slab, thermal deviations inevitably occur at the skid, which results in hot-rolled inclusions and uneven microstructure. If hot-rolled annealing is omitted, the thermal deviations cannot be reduced, and if the magnetic deviation of the final grain-oriented electrical steel sheet is severe, it can lead to magnetic deterioration. Various attempts have been made to eliminate the hot strip annealing, but no technology has directly proposed a solution to reduce the thermal deviation in the skid in the heating furnace during slab heating, or to eliminate inclusions and microstructural non-uniformity. Summary of the Invention [Problem to be solved by the invention]

[0003] An object of the present invention is to provide a grain-oriented electrical steel sheet and a manufacturing method thereof, which can suppress magnetic deterioration even when the hot-rolled sheet annealing step is omitted by appropriately controlling the contents of Si, C, N, Cr, Sn, etc. and appropriately adjusting the coiling temperature in the hot rolling step. [Means for solving the problem]

[0004] The grain-oriented electrical steel sheet of the present invention contains, by weight, 2.0 to 4.0% Si, 0.04 to 0.2% Mn, 0.010% or less (excluding 0%) N, 0.005% or less (excluding 0%) C, 0.03 to 0.08% Sn, and 0.01 to 0.2% Cr, with the balance being Fe and unavoidable impurities. The grain-oriented electrical steel sheet contains inclusions consisting of one or more of AlN, (Al, Si)N, (Al, Si, Mn)N, MnS, CuS, and Al2O3, the average grain size of the inclusions being 0.5 to 6.0 μm, and the number of inclusions having a medium grain size of 6.0 μm or less is 40 to 130 inclusions / mm 2 It can include.

[0005] In the grain-oriented electrical steel sheet of the present invention, the area fraction of crystal grains having a grain size of 1 mm or less may be 10% or less. The grain-oriented electrical steel sheet of the present invention may further contain Al: 0.005 to 0.030% by weight. The composition may further contain S: 0.010% by weight or less. In addition, P: 0.0005 to 0.045% by weight may be further included. In addition, it may further contain Sb: 0.1 wt % or less, and one or more of Co: 0.1 wt % or less, Ni: 0.1 wt % or less, and Mo: 0.1 wt % or less.

[0006] A method for producing a grain-oriented electrical steel sheet of the present invention includes the steps of: hot rolling a slab which contains, by weight, 2.0-4.0% Si, 0.04-0.2% Mn, 0.010% or less (excluding 0%) N, 0.001-0.04% C, 0.03-0.08% Sn, and 0.01-0.2% Cr, with the balance being Fe and unavoidable impurities, and which satisfies the following formula 1 to produce a hot-rolled steel sheet; coiling the hot-rolled steel sheet; cooling the coiled hot-rolled steel sheet as it is and cold rolling it to produce a cold-rolled steel sheet; subjecting the cold-rolled steel sheet to primary recrystallization annealing; and subjecting the cold-rolled steel sheet which has been subjected to primary recrystallization annealing to secondary recrystallization annealing.

[0007] [Formula 1] 0.038×[Si]-0.069-[N]≦[C]≦0.038×[Si]-0.069+[N] (In formula 1, [Si], [N] and [C] respectively represent the contents (wt%) of Si, N and C in the slab.) In the winding stage, the winding temperature is 700 to 850° C., and the following formula 2 can be satisfied.

[0008] [Formula 2] 90≦(0.038×[Si]+[N]+[C])×[CT]≦130 (In formula 2, [Si], [N], and [C] respectively represent the contents (wt%) of Si, N, and C in the slab, and [CT] represents the coiling temperature (°C).) The method may further include a step of heating the slab to 1300° C. or less before the step of producing the hot rolled steel sheet. After the coiling step and before the step of producing a cold-rolled steel sheet, there is no need for a heat treatment in which heat is applied from outside the steel sheet. The step of producing the cold-rolled steel sheet can be performed by cold rolling the hot-rolled steel sheet once. The step of primary recrystallization annealing includes a decarburization step and a nitriding step, and the nitriding step may be performed after the decarburization step, or after the nitriding step, or the decarburization step and the nitriding step may be performed simultaneously. After the first recrystallization annealing step, the method may further include applying an annealing separator. The secondary recrystallization annealing step may be performed at a temperature of 900 to 1210° C. to complete the secondary recrystallization. Effect of the Invention

[0009] According to the grain-oriented electrical steel sheet of the present invention, the thermal deviation in the skid in the heating furnace during slab heating is reduced, and inclusions and uneven microstructure can be eliminated even if hot-rolled sheet annealing is omitted. Finally, the magnetic properties of the grain-oriented electrical steel sheet can be improved even if hot-rolled sheet annealing is omitted. [Brief description of the drawings]

[0010] [Figure 1] This is a photograph of an analysis of inclusions in invention material 1. [Diagram 2] 1 is a photograph showing an analysis of inclusions in comparative material 1. [Diagram 3] 1 is a photograph of the final grain-oriented electrical steel sheet manufactured using Inventive Material 7. [Figure 4] 1 is a photograph of the final grain-oriented electrical steel sheet produced using comparative material 31. [Diagram 5] 1 is a photograph of the final grain-oriented electrical steel sheet produced using comparative material 21. [Figure 6] 1 is a photograph of the final grain-oriented electrical steel sheet produced using comparative material 22. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] 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 context clearly indicates otherwise. As used herein, the term "comprising" refers to embodying 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.

[0012] When an element is referred to as being "on" or "on" another element, it may be directly on top of the other element, with other elements in between, whereas when an element is referred to as being "directly on" another element, there are no other elements in between. Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention belongs. Terms defined in commonly used dictionaries are additionally interpreted to have a meaning consistent with the relevant technical literature and the presently disclosed content, and are not interpreted in an ideal or very formal sense unless defined. Moreover, unless otherwise specified, % means % by weight, and 1 ppm is 0.0001% by weight. In one embodiment of the present invention, the term "additionally containing an additional element" refers to the inclusion of an additional amount of the additional element in place of the remaining iron (Fe).

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in detail with reference to the accompanying drawings, in which: FIG. 1 is a block diagram of a semiconductor device according to an embodiment of the present invention; The grain-oriented electrical steel sheet of the present invention contains, by weight, 2.0-4.0% Si, 0.04-0.2% Mn, 0.010% or less (excluding 0%) N, 0.005% or less (excluding 0%) C, 0.03-0.08% Sn, and 0.01-0.2% Cr, with the remainder being Fe and unavoidable impurities.

[0014] The reasons for limiting the alloy components are explained below. Si:2.0~4.0wt% Silicon (Si) is a basic component of electrical steel sheets, and it increases the resistivity of the material and reduces core loss. If the Si content is too low, the resistivity decreases, eddy current loss increases, and core loss characteristics deteriorate. During the first recrystallization annealing, phase transformation between ferrite and austenite becomes active, severely damaging the first recrystallization texture. During the second recrystallization annealing, phase transformation between ferrite and austenite occurs, making the second recrystallization unstable and severely damaging the {110} Goss texture. On the other hand, if the Si content is excessive, SiO2 and Fe2SiO4 oxide layers are formed too densely during the first recrystallization annealing, delaying the decarburization behavior, and the phase transformation between ferrite and austenite continues during the first recrystallization annealing treatment, severely damaging the first recrystallization texture. In addition, the formation of the dense oxide layer described above has the effect of retarding the decarburization behavior, which also retards the nitriding behavior (Al, Si, Mn), and nitrides such as N and AlN are not sufficiently formed, which may result in the inability to secure sufficient grain suppression force required for secondary recrystallization during high-temperature annealing. Moreover, if Si is contained in excess, the brittleness of the mechanical properties increases, the toughness decreases, the sheet breakage rate during the rolling process increases, the sheet weldability becomes inferior, and easy workability cannot be ensured. As a result, if the Si content is not controlled within the above-mentioned specified range, the secondary recrystallization becomes unstable, the magnetic properties are seriously impaired, and the workability also deteriorates. Therefore, Si can be contained in an amount of 2.0 to 4.0 wt. %. More specifically, it can be contained in an amount of 2.1 to 3.5 wt. %.

[0015] Mn:0.04~0.2wt% Manganese (Mn), like Si, has the effect of increasing resistivity and reducing eddy current loss, thereby reducing overall iron loss. It not only reacts with S in a lull state to form Mn-based sulfides, but also reacts with nitrogen introduced by nitriding together with Si to form N inclusions (Al, Si, Mn), suppressing the growth of primary recrystallized grains and causing secondary recrystallization. It is also an important element that affects the surface quality of the final product. If there is too little Mn, the surface quality of the final product may deteriorate. If there is too much Mn, the austenite phase fraction increases significantly, the Goss texture is damaged, the magnetic flux density decreases, and an oxide layer is overformed during decarburization annealing, which may hinder decarburization. Therefore, Mn may be contained in an amount of 0.04 to 0.20 wt%. More specifically, Mn may be contained in an amount of 0.07 to 0.15 wt%.

[0016] N: 0.010% by weight or less Nitrogen (N) is an important element that reacts with Al to form Al-based nitrides, and can be added to the slab at 0.010 wt% or less. If there is too much N in the slab, it can cause surface defects called blisters due to nitrogen diffusion during processes after hot rolling, and too many nitrides are formed in the slab state, making rolling difficult and subsequent processes complicated, which leads to increased manufacturing costs. More specifically, N can be contained at 0.005 wt% or less. Meanwhile, the additional N required to form nitrides such as (Al, Si, Mn)N, AlN, and (Si, Mn)N can be supplemented by nitriding the steel using ammonia gas during the annealing process after cold rolling. However, N is removed again during the secondary recrystallization annealing process, so the amount of N remaining in the final electrical steel sheet is 0.010 wt% or less.

[0017] C: 0.005% by weight or less Carbon (C) is an element that contributes to the phase transformation between ferrite and austenite, refines crystal grains, and improves the elongation rate. It is an essential element for improving the rollability of electrical steel sheets, which are brittle and have poor rollability. If C remains in the final product, it causes carbides formed by the magnetic aging effect to precipitate in the product sheet, deteriorating the magnetic properties, so it is preferable to control the content at an appropriate level. If there is too little C in the slab, the phase transformation between ferrite and austenite does not occur sufficiently, which can cause unevenness in the slab and hot-rolled microstructure. This causes inclusions to precipitate coarsely and unevenly, making the secondary recrystallization unstable and even impairing the cold rolling properties performed after hot rolling. In addition, inclusions and uneven microstructures can occur due to thermal deviations in the skid in the heating furnace during slab heating. If the slab contains too much C, the carbides become very coarse and the amount of precipitation increases excessively, so that decarburization is not performed sufficiently, the degree of integration of the Goss texture decreases, the secondary recrystallization texture is severely damaged, and further, the final product may suffer from deterioration of magnetic properties due to magnetic aging. Therefore, the C content in the slab is 0.0010 to 0.0400 wt%. More specifically, the C content in the slab may be 0.0200 to 0.0380 wt%. Meanwhile, in order to minimize the occurrence of magnetic aging during the use of the final product, i.e., the grain-oriented electrical steel sheet, the C content of the final grain-oriented electrical steel sheet product after the secondary recrystallization annealing is 0.005 wt% or less.

[0018] Sn:0.03~0.08wt% Tin (Sn) is known as a grain growth inhibitor because it is an element that hinders the movement of grains as a grain segregation element. In the Si content range of one embodiment of the present invention, the grain growth inhibition power for smooth secondary recrystallization behavior is insufficient, so Sn is necessary to hinder the movement of grains by segregating in the grains. If the amount of Sn is too small, it is difficult to properly exhibit the above-mentioned effects. On the other hand, if an excessive amount of Sn is added, the grain growth inhibition power is too strong and stable secondary recrystallization cannot be obtained unless the heating rate is adjusted or maintained for a certain time in the first recrystallization annealing section. Therefore, the Sn content may be 0.03 to 0.08 wt%. More specifically, it may be 0.03 to 0.07 wt%.

[0019] Cr:0.01~0.2wt% Chromium (Cr) promotes the formation of hard phases in hot-rolled sheets and reduces the {110} <001> By promoting the formation of Cr and promoting decarburization during the first recrystallization annealing process, the austenite transformation maintenance time is extended, and the austenite transformation maintenance time is reduced to prevent the texture from being damaged. In addition, by promoting the formation of an oxide layer on the surface formed during the first recrystallization annealing process, the drawback that the oxide layer formation is inhibited by Sn, one of the alloy elements used in the grain growth auxiliary inhibitor, can be solved. If Cr is contained in a small amount, the above-mentioned effect is difficult to be properly exhibited. On the contrary, if Cr is added in an excessive amount, it promotes the formation of a denser oxide layer than that at the time of oxide layer formation during the first recrystallization annealing process, which makes the oxide layer formation inferior and may even hinder decarburization and nitriding. Therefore, Cr may be contained in 0.01 to 0.2 wt %. More specifically, Cr may be contained in 0.03 to 0.1 wt %.

[0020] The slab of the present invention satisfies the following formula 1. [Formula 1] 0.038×[Si]-0.069-[N]≦[C]≦0.038×[Si]-0.069+[N] (In formula 1, [Si], [N] and [C] respectively represent the contents (wt%) of Si, N and C in the slab.) If the C content is controlled according to the Si and N content in the slab as shown in formula 1, the inclusions are almost or completely dissolved during the slab heating and hot rolling stages and are formed very uniformly. This reduces or prevents the adverse effects of thermal deviations in the skids in the heating furnace during slab heating even if hot-rolled sheet annealing is omitted. The average grain size of the residual inclusions that cause inferior magnetic properties after the secondary recrystallization annealing is 0.5 to 6.0 μm, which is very effective in ensuring stable magnetic properties. Meanwhile, the average grain size of the residual inclusions can be measured by removing all the oxide layer on the surface after the secondary recrystallization annealing, polishing the surface to about 50 to 100 μm, preparing a replica specimen, and performing image analysis from the photograph taken with a TEM. The measurement reference surface is a surface parallel to the rolling surface.

[0021] In the present invention, the inclusions refer to oxides such as Al-based, Mg-based, and Ca-based oxides, and various precipitates. The inclusions include precipitates, which are different from inclusions and are not oxides but nitrides and sulfides such as (Al, Si)N, (Al, Si, Mn)N, MnS, and CuS. The inclusions include one or more of AlN, (Al, Si)N, (Al, Si, Mn)N, MnS, CuS, and Al2O3. (Al, Si)N refers to a composite nitride of Al and Si, and (Al, Si, Mn)N refers to a composite nitride of Al, Si, and Mn. As described above, the thermal deviation at the skid in the heating furnace during slab heating can be reduced by the C content in the slab and formula 1. In the subsequent process, the hot-rolled sheet annealing process can be omitted to suppress the growth of inclusions due to the thermal deviation at the skid. More specifically, the average grain size of the inclusions can be 1.0 to 5.0 μm.

[0022] If the inclusions are too few, the steel sheet will be annealed after hot rolling, which is not in keeping with the object of the present invention. If the inclusions are too many, the magnetic properties may be deteriorated. The density of inclusions is 40 to 130 pieces / mm 2In this case, the standard particle size of the inclusions may be 6.0 μm or less. Inclusions exceeding 6.0 μm are not substantially generated in the present invention, so the upper limit can be limited as described above. The lower limit of the standard particle size of the inclusions is not particularly limited, but can be set to 1 nm from the viewpoint of measurement. If too few inclusions are generated, a large number of inclusions exceeding 6.0 μm are generated, which has a fatal effect on magnetic properties. If too many inclusions are present, magnetic properties may become inferior. More specifically, the density of the inclusions is 45 to 125 pieces / mm 2 It can be said that: By appropriately forming the inclusions in this way, secondary recrystallization can occur completely during the secondary recrystallization annealing process even if hot-rolled sheet annealing is omitted. Specifically, the area fraction of grains with a grain size of 1 mm or less can be 10% or less. The grain size and fraction are based on a plane parallel to the rolling surface (ND surface). The grain size is calculated using the grain size of an imaginary circle with the same area as the grain. The average grain size may be 0.1 to 5 cm.

[0023] The grain-oriented electrical steel sheet of the present invention may further contain Al: 0.005 to 0.030 wt %. As described above, when the additional element is further contained, it is added in place of Fe which is the balance. Al:0.005~0.030wt% Aluminum (Al) acts as a powerful grain growth inhibitor by forming nitrides in the form of (Al, Si, Mn)N and AlN when nitrogen ions introduced by ammonia gas in the annealing process after cold rolling are combined with Al, Si, and Mn present in the steel in a solid solution state. If the content is too low, the number and volume of the formed particles are very low, so sufficient inhibitory effect cannot be expected. On the other hand, if the content is too high, the Al-based nitrates become too coarse, reducing the grain growth inhibitory effect. In addition, Al-based nitrides are not completely dissolved during slab reheating, and after slab reheating, they are precipitated with very uneven size and distribution, making the behavior of secondary recrystallization unstable, which may cause the magnetic properties of the final product to deteriorate or increase in deviation. Therefore, if Al is further included, the content may be 0.005 to 0.030 wt%. More specifically, Al may be included in 0.015 to 0.030 wt%.

[0024] The grain-oriented electrical steel sheet of the present invention may further contain S: 0.010% by weight or less. S: 0.010% by weight or less If too much sulfur (S) is added, it segregates in the center of the slab, and sulfide inclusions such as MnS and CuS are unevenly precipitated, which leads to uneven primary recrystallization microstructure and makes secondary recrystallization unstable. Therefore, when S is further contained, its content can be 0.010 wt% or less. In addition, since it takes a huge amount of time and cost to control desulfurization to an extremely low level during steelmaking, the lower limit can be greater than 0%. In one embodiment of the present invention, no particular lower limit is set.

[0025] P:0.005~0.045wt% Phosphorus (P) segregates in the grains and hinders the grain movement, while at the same time playing a supplementary role in suppressing grain growth. <001> It has the effect of improving the texture. When P is added, if the amount added is too small, there is no effect of adding it. Conversely, if the amount added is too large, brittleness increases and rollability is significantly deteriorated. Therefore, when P is further contained, P can be further contained in an amount of 0.005 to 0.045 wt %. More specifically, P can be contained in an amount of 0.01 to 0.035 wt %.

[0026] The grain-oriented electrical steel sheet of the present invention may further contain Sb: 0.1% by weight or less. Sb: 0.1% by weight or less Antimony (Sb) has the effect of suppressing the growth of crystal grains by segregating in the crystal grain system, and has the effect of stabilizing the secondary recrystallization. However, since its melting point is low, it easily diffuses to the surface during the primary recrystallization annealing, and has the effect of preventing decarburization, oxide layer formation, and nitriding due to nitriding. Therefore, Sb can be further added as necessary. Adding an excessive amount of Sb can prevent decarburization and suppress the formation of an oxide layer that serves as the base of the base coating. Therefore, Sb can be further included at 0.1 wt% or less. More specifically, 0.01 to 0.05 wt% can be further included.

[0027] The grain-oriented electrical steel sheet of the present invention may further contain one or more of Co: 0.1% by weight or less, Ni: 0.1% by weight or less, and Mo: 0.1% by weight or less. Co: 0.1% by weight or less Cobalt (Co) is an alloying element that is effective in increasing the magnetization of iron and improving magnetic flux density, and at the same time, it is an alloying element that increases resistivity and reduces iron loss. If Co is added appropriately, the above effects can be obtained additionally. If too much Co is added, the amount of austenite phase transformation increases, which can have a negative effect on the microstructure, inclusions, and texture. Therefore, when Co is added, it can be further included in an amount of 0.1 wt% or less. More specifically, it can be further included in an amount of 0.005 to 0.05 wt%. Ni and Mo can also be added with an upper limit of 0.1% by weight. The balance is composed of iron (Fe) and unavoidable impurities. Inevitable impurities refer to impurities that are inevitably mixed in during the steelmaking and manufacturing process of grain-oriented electrical steel sheets. As unavoidable impurities are widely known, a detailed description will be omitted. The present invention does not exclude the addition of elements other than the above-mentioned alloy components, and various elements may be included within a range that does not harm the technical idea of ​​the present invention. When an additional element is further included, it is included instead of the balance Fe.

[0028] The method for producing a grain-oriented electrical steel sheet of the present invention includes the steps of hot rolling a slab to produce a hot-rolled steel sheet, coiling the hot-rolled steel sheet, cooling the coiled hot-rolled steel sheet as it is and cold rolling it to produce a cold-rolled steel sheet, subjecting the cold-rolled steel sheet to primary recrystallization annealing, and subjecting the cold-rolled steel sheet after the primary recrystallization annealing to secondary recrystallization annealing. Each step will be explained in detail below. First, the slab is hot-rolled to produce a hot-rolled steel sheet. The alloy composition of the slab has been explained in relation to the alloy composition of the grain-oriented electrical steel sheet, so a duplicate explanation will be omitted. Specifically, the slab contains, by weight, 2.0-4.0% Si, 0.04-0.2% Mn, 0.010% or less (excluding 0%) N, 0.001-0.04% C, 0.03-0.08% Sn, and 0.01-0.2% Cr, with the balance being Fe and unavoidable impurities, and can satisfy the following formula 1. [Formula 1] 0.038×[Si]-0.069-[N]≦[C]≦0.038×[Si]-0.069+[N] (In formula 1, [Si], [N] and [C] respectively represent the contents (wt%) of Si, N and C in the slab.)

[0029] Returning to the explanation of the manufacturing method, the method may further include a step of heating the slab to 1300° C. or less before the step of manufacturing the hot-rolled steel plate. The slab is then hot rolled to produce a hot rolled steel sheet, the thickness of which can be 5 mm or less. Then, the hot-rolled steel sheet is coiled. At this time, the coiling temperature can be 700 to 850°C. In the present invention, since hot-rolled sheet annealing is omitted after coiling, if the coiling temperature is too low, the size of the hot-rolled sheet inclusions becomes too small and increases, making it difficult to control the primary recrystallization microstructure, causing unstable secondary recrystallization, and causing inferior magnetic properties. If the coiling temperature is too high, the inclusions become too coarse and the amount decreases, making it difficult to control the primary recrystallization microstructure again, causing unstable secondary recrystallization, and causing inferior magnetic properties. More specifically, the coiling temperature can be 740 to 830°C. The coiling temperature means the average steel sheet temperature from the start to the completion of coiling the hot-rolled sheet after hot rolling. At this time, the following formula 2 can be satisfied. [Formula 2] 90≦(0.038×[Si]+[N]+[C])×[CT]≦130 (In formula 2, [Si], [N], and [C] respectively represent the contents (wt%) of Si, N, and C in the slab, and [CT] represents the coiling temperature (°C).) If the value of formula 2 is too low, inclusions may occur non-uniformly. If the value of formula 2 is too high, the contents of Si, N, and C will be high and inclusions may occur non-uniformly.

[0030] Next, the coiled hot-rolled steel sheet is cooled as it is and cold-rolled to produce a cold-rolled steel sheet. In the present invention, cooling directly means that there is no heat treatment in which heat is applied from the outside after coiling the hot-rolled steel sheet. That is, it means that the hot-rolled sheet annealing process is omitted. After hot rolling, pickling is performed to remove hot-rolled scale. When pickling is performed, shot blasting may or may not be performed before or after the pickling. The step of producing the cold-rolled steel sheet may include one cold rolling or two or more cold rolling steps including intermediate annealing. Specifically, the step may include one cold rolling step of the hot-rolled steel sheet. The thickness of the cold rolled steel sheet is 0.65 mm or less. Meanwhile, when cold rolling is performed, the cold rolling reduction can be 87% or more. This is because the concentration of the Goss texture increases as the cold rolling reduction increases. However, it is also possible to apply a cold rolling reduction lower than this.

[0031] Next, the cold-rolled sheet is subjected to primary recrystallization annealing. At this time, the primary recrystallization annealing step may include a decarburization step and a nitriding step. The decarburization step and the nitriding step may be performed in any order. That is, the decarburization step may be followed by the nitriding step, the decarburization step may be followed by the nitriding step, or the decarburization step and the nitriding step may be performed simultaneously. In the decarburization step, C may be decarburized to 0.005 wt% or less. More specifically, C may be decarburized to 0.003 wt% or less. In the nitriding process, N may be nitridized to 0.015 wt% or more. The crack temperature in the first recrystallization annealing step may be 840° C. to 900° C. Even if the first recrystallization annealing is performed at a temperature lower than 840° C. or higher than 900° C., there is no problem in exhibiting the function proposed by the present invention. After the first recrystallization annealing step, an annealing separator may be applied to the steel sheet. Annealing separators are widely known, so a detailed description will be omitted. For example, an annealing separator containing MgO as a main component may be used.

[0032] Next, the cold-rolled sheet that has been subjected to the primary recrystallization annealing is subjected to the secondary recrystallization annealing. The purpose of secondary recrystallization annealing is to reduce the {110} <001> These are the formation of texture, the formation of a glassy film due to the reaction between the oxide layer formed during the first recrystallization annealing and MgO to provide insulation, and the removal of impurities that impair magnetic properties. As for the method of second recrystallization annealing, a mixture of nitrogen and hydrogen gas is maintained in the temperature rise section before the second recrystallization occurs to protect the nitride, which acts as a grain growth inhibitor, allowing the second recrystallization to develop well, and after the second recrystallization is completed, at the crack stage, impurities are removed by maintaining a 100% hydrogen atmosphere for a long period of time. The secondary recrystallization annealing step may be performed at a temperature of 900 to 1210° C. to complete the secondary recrystallization.

[0033] The grain-oriented electrical steel sheet of the present invention is particularly excellent in terms of core loss and magnetic flux density properties. The grain-oriented electrical steel sheet of the present invention has a magnetic flux density (B8) of 1.87 T or more, and a core loss (W 17 / 50 ) may be 1.10 W / kg or less. In this case, 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 W 17 / 50 is the magnitude of iron loss (W / kg) induced under the conditions of 1.7 Tesla and 50 Hz. More specifically, the grain-oriented electrical steel sheet of the present invention has a magnetic flux density (B8) of 1.89 T or more and an iron loss (W 17 / 50 ) may be 1.00 W / kg or less. The thickness used as the measurement standard may be 0.30 mm.

[0034] Hereinafter, specific examples of the present invention will be described. However, the following examples are specific examples of the present invention, and the present invention is not limited to the following examples. Example 1 The steel composition was vacuum melted with the weight percentages of Si: 2.85%, Mn: 0.092%, Al: 0.025%, N: 0.0032%, S: 0.004%, Sn: 0.045%, P: 0.028%, Cr: 0.032%, and C content as shown in Table 1, with the remaining components being Fe and other unavoidable impurities, and then made into an ingot. The steel was then heated at a temperature of 1240°C, hot rolled to a thickness of 2.8 mm, and coiled at the temperature shown in Table 1. The steel was then pickled and cold rolled once to a thickness of 0.28 mm without heat treatment, and the cold-rolled sheet was subjected to simultaneous decarbonitriding annealing heat treatment at a temperature of 870°C in a wet hydrogen, nitrogen, and ammonia mixed gas atmosphere so that the carbon content was 30 ppm and the nitrogen content was 200 ppm. The steel sheets were then coated with MgO as an annealing separator and subjected to a final annealing heat treatment, which consisted of heating to 1200°C in a mixed gas atmosphere of 25 vol% nitrogen and 75 vol% hydrogen, and after reaching 1200°C, maintaining the temperature in a 100% hydrogen atmosphere for 10 hours or more, followed by furnace cooling. The measured magnetic properties according to the C content are shown in Table 1. The average grain size and density of the inclusions were measured by removing all the oxide layer on the surface after the secondary recrystallization annealing, polishing the surface to about 100μm to prepare a replica specimen, and performing image analysis on the photographs taken with a TEM. Regarding the occurrence of secondary recrystallization, when the area fraction of crystal grains with a grain size of 1 mm or less exceeded 10%, it was determined that secondary recrystallization occurred unstably or did not occur, and this was indicated by X.

[0035] [Table 1]

[0036] As shown in Table 1, the alloy composition and coiling temperature of the inventive material are within the appropriate range, and it can be confirmed that the inclusions are small and the density is low because both formulas 1 and 2 are satisfied. Finally, it can be confirmed that the secondary recrystallization is appropriately formed, and both the iron loss and magnetic flux density are excellent.

[0037] On the other hand, it can be seen that in the comparative material, the alloy components and coiling temperature were not properly adjusted, inclusions were formed non-uniformly, secondary recrystallization could not be formed properly, and the iron loss and magnetic flux density were inferior. Figures 1 and 2 are photographs showing the analysis of inclusions in the inventive material 1 and the comparative material 1. It can be seen that the inclusions in the inventive material 1 are fine and precipitate in small amounts, whereas in the comparative material 1, it can be seen that the inclusions are precipitated in large amounts. Analysis showed that the inclusions included AlN, (Al, Si, Mn)N, MnS, and CuS.

[0038] Example 2 The contents of Al: 0.022%, S: 0.003%, Sb: 0.02%, Sn: 0.06%, P: 0.02%, Cr: 0.05%, and Si, C, and N were changed as shown in Table 2 below, and the remaining components were Fe and other unavoidable impurities. The steel components were vacuum melted, and then made into ingots. The steel was then heated at a temperature of 1200°C and hot rolled to a thickness of 2.3 mm, and the coiling temperature was as shown in Table 2 below. The steel was then pickled and cold rolled once to a thickness of 0.30 mmt. The cold-rolled sheet was subjected to simultaneous decarbonitriding annealing heat treatment at a temperature of 870°C in a wet mixed gas atmosphere of hydrogen, nitrogen, and ammonia so that the carbon content was 30 ppm and the nitrogen content was 180 ppm. The steel sheets were then coated with MgO as an annealing separator and subjected to a final annealing heat treatment, which consisted of heating to 1200°C in a mixed gas atmosphere of 25v% nitrogen and 75v% hydrogen, and after reaching 1200°C, maintaining the atmosphere in 100% hydrogen for 10 hours or more, and then cooling in the furnace. After high-temperature annealing according to the content of Si, C, and N, the magnetic properties and 1mm 2 The particle size of the residual inclusions per unit area was measured and the results are shown in Table 2.

[0039] [Table 2]

[0040] As shown in Table 2, the alloy composition and coiling temperature of the inventive material are within the appropriate range, and it can be confirmed that the inclusions are small and the density is low because both formulas 1 and 2 are satisfied. Finally, it can be confirmed that the secondary recrystallization is appropriately formed, and both the iron loss and magnetic flux density are excellent. On the other hand, in the comparative material, the alloy composition and coiling temperature were not properly adjusted, so inclusions were formed unevenly and secondary recrystallization was not properly formed, resulting in inferior core loss and magnetic flux density.

[0041] Example 3 The same procedure was carried out as for Inventive Material 7, and a comparison was made between cases where hot-rolled sheet annealing was omitted or carried out after hot rolling. [Table 3]

[0042] As shown in Table 3, it can be confirmed that even when hot-rolled sheet annealing is omitted, magnetism is exhibited in a manner corresponding to the case where hot-rolled sheet annealing is performed. 3 and 4, it can be seen that the secondary recrystallization occurs perfectly in the inventive material 7 and the comparative material 31. In particular, in the case of the inventive material 7, it can be seen that the secondary recrystallization occurs perfectly even though the hot-rolled sheet annealing is omitted. On the other hand, as shown in Figures 5 and 6, in Comparative Materials 21 and 22, in which the alloy components are not appropriately controlled or the coiling temperature is low, it can be seen that secondary recrystallization does not occur completely. In other words, it can be seen that a plurality of crystal grains with a grain size of 1 mm or less are present. The present invention is not limited to the above-mentioned embodiment and / or examples, and can be manufactured in various different forms, and a person skilled in the art to which the present invention belongs can understand that the present invention can be embodied in other specific forms without changing the technical idea or essential characteristics of the present invention. Therefore, the above-described embodiment and / or examples should be understood to be illustrative in all respects and not limiting.

Claims

1. The alloy contains, by weight, 2.0 to 4.0% Si, 0.04 to 0.2% Mn, 0.010% or less (excluding 0%) N, 0.005% or less (excluding 0%) C, 0.03 to 0.08% Sn, and 0.01 to 0.2% Cr, with the balance being Fe and unavoidable impurities; AlN, (Al, Si)N, (Al, Si, Mn)N, MnS, CuS, Al ２ O ３ The inclusions include one or more of the following: The average particle size of the inclusions is 0.5 to 6.0 μm, The inclusions having a medium grain size of 6.0 μm or less are set to 40 to 130 pieces / mm ２ A directional electrical steel sheet comprising:

2. 2. The grain-oriented electrical steel sheet according to claim 1, wherein an area fraction of crystal grains having a grain size of 1 mm or less is 10% or less.

3. The grain-oriented electrical steel sheet according to claim 1 or 2, further comprising Al: 0.005 to 0.030 wt %.

4. The grain-oriented electrical steel sheet according to any one of claims 1 to 3, further comprising S: 0.010% by weight or less.

5. The grain-oriented electrical steel sheet according to any one of claims 1 to 4, further comprising P: 0.0005 to 0.045 wt.%.

6. The grain-oriented electrical steel sheet according to any one of claims 1 to 5, further comprising Sb: 0.1 wt% or less.

7. The grain-oriented electrical steel sheet according to any one of claims 1 to 6, further comprising one or more of Co: 0.1 wt % or less, Ni: 0.1 wt % or less, and Mo: 0.1 wt % or less.

8. A method for producing the grain-oriented electrical steel sheet according to any one of claims 1 to 7, comprising the steps of: A step of producing a hot-rolled steel sheet by hot rolling a slab containing, by weight, 2.0 to 4.0% Si, 0.04 to 0.2% Mn, 0.010% or less (excluding 0%) N, 0.001 to 0.04% C, 0.03 to 0.08% Sn, and 0.01 to 0.2% Cr, with the balance being Fe and unavoidable impurities, and satisfying the following formula 1: coiling the hot-rolled steel sheet; cooling the coiled hot-rolled steel sheet as it is and cold-rolling it to produce a cold-rolled steel sheet; subjecting the cold-rolled steel sheet to a primary recrystallization annealing; and The cold-rolled steel sheet that has been subjected to the first recrystallization annealing is subjected to a second recrystallization annealing, The method for producing a grain-oriented electrical steel sheet, wherein the coiling step has a coiling temperature of 700 to 850° C. and satisfies the following formula 2: [Formula 1] 0.038×[Si]-0.069-[N]≦[C]≦0.038×[Si]-0.069+[N] (In formula 1, [Si], [N] and [C] represent the contents (wt%) of Si, N and C in the slab, respectively.) [Formula 2] 90≦(0.038×[Si]+[N]+[C])×[CT]≦130 (In formula 2, [Si], [N] and [C] are the contents of Si, N and C in the slab, respectively. (% by weight), and [CT] indicates the winding temperature (°C).

9. The method of claim 8, further comprising the step of heating a slab to 1300° C. or less before the step of producing the hot-rolled steel sheet.

10. The method for producing a grain-oriented electrical steel sheet according to claim 8 or 9, wherein no heat treatment is performed by applying heat from outside the steel sheet after the coiling step and before the step of producing a cold-rolled steel sheet.

11. The method for producing a grain-oriented electrical steel sheet according to any one of claims 8 to 10, characterized in that the step of producing the cold-rolled steel sheet comprises a step of cold-rolling the hot-rolled steel sheet once.

12. The primary recrystallization annealing step includes a decarburization step and a nitriding step, The decarburization step is followed by the nitriding step, the nitriding step is followed by the decarburization step, or The method for producing a grain-oriented electrical steel sheet according to any one of claims 8 to 11, characterized in that the decarburization step and the nitriding step are carried out simultaneously.

13. The method of claim 8, further comprising the step of applying an annealing separator after the primary recrystallization annealing.

14. The method of claim 8, wherein the secondary recrystallization is completed at a temperature of 900 to 1210° C. in the secondary recrystallization annealing step.

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