Grain-oriented electrical steel sheet and method of manufacturing the same

Abstract

An oriented electrical steel sheet according to one embodiment of the present application, the oriented electrical steel sheet comprising, in terms of weight %, Si: 2.0 to 4.0 %, Mn: 0.04 to 0.2 %, N: 0.010 % or less (except 0 %), C: 0.005 % or less (except 0 %), Sn: 0.03 to 0.08 %, Cr: 0.01 to 0.2 %, and the balance of Fe and inevitable impurities, inclusions comprising at least one of AlN, (Al, Si)N, (Al, Si, Mn)N, MnS, CuS, Al2O3, the average particle diameter of the inclusions being 0.5 to 6.0 µm, the inclusions having a particle diameter of 6.0 µm or less being 40 to 130 pieces / mm2 2 .

Description

Technical Field

[0001] One embodiment of the present invention relates to an oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention provides an oriented electrical steel sheet and a method for manufacturing the same, which suppresses magnetic degradation even if the annealing process of the hot-rolled sheet is omitted by appropriately controlling the contents of Si, C, N, Cr, Sn, etc., and appropriately adjusting the coiling temperature during the hot rolling process. Background Technology

[0002] Oriented grain electrical steel sheet is a soft magnetic material with a steel sheet texture of {110} relative to the rolling direction. <001> The Goss texture of grain-oriented electrical steel results in excellent magnetic properties in one direction or the rolling direction. To improve the magnetic properties of grain-oriented electrical steel sheets by characterizing this texture, complex processes are required, including composition control in steelmaking, slab reheating and hot rolling process parameter control, hot-rolled plate annealing heat treatment, cold rolling, primary recrystallization annealing, and secondary recrystallization annealing. These processes must be managed with great precision and strictness.

[0003] In the aforementioned process, the hot-rolled sheet annealing process is a necessary step to stably achieve the secondary recrystallization of Gaussian-oriented grains during the secondary recrystallization annealing process by uniformly controlling the non-uniform microstructure and precipitates of the hot-rolled sheet. However, since hot-rolled sheet annealing increases the production cost of grain-oriented electrical steel sheets, if the microstructure and precipitates of the hot-rolled sheet can be made uniform while omitting the hot-rolled sheet annealing process, the manufacturing cost generated by the hot-rolled sheet annealing process can be reduced, and productivity can be improved.

[0004] Thermal deviations inevitably occur on the skid during slab heating, resulting in uneven precipitates and microstructure in the hot-rolled sheet. If annealing of the hot-rolled sheet is omitted, the aforementioned thermal deviations cannot be reduced, ultimately leading to increased magnetic deviations in the final manufactured grain-oriented electrical steel sheet, and in severe cases, magnetic attenuation.

[0005] Various attempts have been made to eliminate the need for annealing of hot-rolled plates, but no technology has yet directly proposed a solution for reducing thermal deviations on the skids in the heating furnace during slab heating, or for addressing precipitates and uneven microstructure. Summary of the Invention

[0006] (a) Technical problems to be solved

[0007] One embodiment of the present invention relates to an oriented electrical steel sheet and a method for manufacturing the same. Specifically, one embodiment of the present invention provides an oriented electrical steel sheet and a method for manufacturing the same, which suppresses magnetic degradation even if the annealing process of the hot-rolled sheet is omitted by appropriately controlling the contents of Si, C, N, Cr, Sn, etc., and appropriately adjusting the coiling temperature during the hot rolling process.

[0008] (II) Technical Solution

[0009] According to one embodiment of the present invention, the grain-oriented electrical steel sheet comprises, by weight percent, 2.0 to 4.0% Si, 0.04 to 0.2% Mn, less than 0.010% N (excluding 0%), less than 0.005% C (excluding 0%), 0.03 to 0.08% Sn, 0.01 to 0.2% Cr, and the balance Fe and unavoidable impurities.

[0010] The inclusions contain at least one of AlN, (Al,Si)N, (Al,Si,Mn)N, MnS, CuS, and Al2O3, wherein the average particle size of the inclusions is 0.5 to 6.0 μm, and the number of inclusions with a particle size of less than 6.0 μm is 40 to 130 per mm. 2 .

[0011] According to one embodiment of the present invention, the area fraction of grains with a grain size of 1 mm or less in the oriented electrical steel sheet is 10% or less.

[0012] The grain-oriented electrical steel sheet according to one embodiment of the present invention may further contain Al: 0.005 to 0.030% by weight.

[0013] According to one embodiment of the present invention, the oriented electrical steel sheet may further contain S: less than 0.010% by weight.

[0014] According to one embodiment of the present invention, the grain-oriented electrical steel sheet may further contain P: 0.0005 to 0.045% by weight.

[0015] According to one embodiment of the present invention, the oriented electrical steel sheet may further contain Sb: less than 0.1% by weight.

[0016] According to one embodiment of the present invention, the oriented electrical steel sheet may further contain one or more of Co: less than 0.1 wt%, Ni: less than 0.1 wt%, and Mo: less than 0.1 wt%.

[0017] A method for manufacturing an oriented electrical steel sheet according to an embodiment of the present invention comprises: a step of hot-rolling a slab to manufacture a hot-rolled steel sheet, wherein the slab, by weight percent, comprises Si: 2.0 to 4.0%, Mn: 0.04 to 0.2%, N: less than 0.010% (excluding 0%), C: 0.001 to 0.04%, Sn: 0.03 to 0.08%, Cr: 0.01 to 0.2%, and the balance Fe and unavoidable impurities, the slab satisfying Formula 1 below; a step of coiling the hot-rolled steel sheet; a step of directly cooling the coiled hot-rolled steel sheet and then cold-rolling it to manufacture a cold-rolled steel sheet; a step of performing a first recrystallization annealing on the cold-rolled steel sheet; and a step of performing a second recrystallization annealing on the cold-rolled steel sheet after the first recrystallization annealing.

[0018] [Formula 1]

[0019] 0.038×[Si]-0.069–[N]≤[C]≤0.038×[Si]-0.069+[N]

[0020] In Equation 1, [Si], [N] and [C] represent the contents (wt%) of Si, N and C in the slab, respectively.

[0021] In the winding step, the winding temperature is 700 to 850°C, satisfying the following equation 2.

[0022] [Equation 2]

[0023] 90≤(0.038×[Si]+[N]+[C])×[CT]≤130

[0024] In Equation 2, [Si], [N], and [C] represent the contents (wt%) of Si, N, and C in the slab, respectively, and [CT] represents the winding temperature (°C).

[0025] Prior to the step of manufacturing the hot-rolled steel sheet, the process further includes a step of heating the slab to below 1300°C.

[0026] No heat treatment involving external heating is performed after the coiling step and before the step of manufacturing the cold-rolled steel sheet.

[0027] The process of manufacturing cold-rolled steel sheet is completed by performing a cold rolling process on the hot-rolled steel sheet.

[0028] The primary recrystallization annealing step includes a decarburization step and a nitriding step. The nitriding step is performed after the decarburization step, or after the nitriding step, or both the decarburization step and the nitriding step are performed simultaneously.

[0029] Following the recrystallization annealing step, a step of applying an annealing release agent is also included.

[0030] The secondary recrystallization annealing step is performed at a temperature of 900°C to 1210°C.

[0031] (III) Beneficial Effects

[0032] According to an embodiment of the present invention, the oriented electrical steel sheet can reduce the thermal deviation on the skid in the heating furnace during slab heating, and can solve the problems of uneven precipitates and microstructure even if the hot-rolled plate annealing is omitted.

[0033] Ultimately, even omitting the annealing of hot-rolled steel sheets can improve the magnetic properties of grain-oriented electrical steel sheets. Attached Figure Description

[0034] Figure 1 It is a photograph of the inclusions in Invention Material 1.

[0035] Figure 2 These are photographs of the inclusions in Material 1.

[0036] Figure 3 This is a photograph of the final orientation electrical steel sheet manufactured from Inventive Material 7.

[0037] Figure 4 This is a photograph of the final orientation electrical steel sheet manufactured from comparative material 31.

[0038] Figure 5 This is a photograph of the final orientation electrical steel sheet manufactured from comparative material 21.

[0039] Figure 6 This is a photograph of the final orientation electrical steel sheet manufactured from comparative material 22. Detailed Implementation

[0040] In this document, the terms "first," "second," "third," etc., are used to describe parts, components, regions, layers, and / or segments, but these parts, components, regions, layers, and / or segments should not be limited by these terms. These terms are only used to distinguish one part, component, region, layer, and / or segment from another. Therefore, without departing from the scope of this invention, the first part, component, region, layer, and / or segment described below can also be described as a second part, component, region, layer, and / or segment.

[0041] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. Unless the context clearly indicates otherwise, the singular forms used herein are intended to include the plural forms as well. The word "comprising" as used in the specification can specifically refer to a particular feature, field, integer, step, action, element, and / or component, but does not exclude the presence or addition of other features, fields, integers, steps, actions, elements, components, and / or groups.

[0042] If one part is described as being on top of another part, then other parts can exist directly on top of or in between the other part. When one part is described as being directly on top of another part, there are no other parts in between.

[0043] Although not otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in dictionaries should be interpreted as having the same meaning as disclosed in relevant technical literature and herein, and should not be interpreted in an idealized or overly formal sense.

[0044] Additionally, unless otherwise specified, % indicates weight, and 1 ppm is 0.0001 wt%.

[0045] In one embodiment of the present invention, the inclusion of additional elements refers to the replacement of a portion of the remaining iron (Fe) by additional elements, the replacement amount being equivalent to the amount of additional elements added.

[0046] The embodiments of the present invention are described in detail below to enable those skilled in the art to implement the invention. However, the present invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0047] According to one embodiment of the present invention, the oriented electrical steel sheet comprises, by weight %, 2.0 to 4.0% Si, 0.04 to 0.2% Mn, less than 0.010% N (excluding 0%), less than 0.005% C (excluding 0%), 0.03 to 0.08% Sn, 0.01 to 0.2% Cr and the balance Fe and unavoidable impurities.

[0048] The reasons for limiting the alloy composition will be described below.

[0049] Si: 2.0 to 4.0% by weight

[0050] Silicon (Si) is a fundamental component of electrical steel sheets, its role being to increase the material's resistivity and reduce core loss. If the Si content is too low, the resistivity decreases, leading to increased eddy current losses and a decline in core loss characteristics. Furthermore, during primary recrystallization annealing, the phase transformation between ferrite and austenite becomes more active, severely damaging the primary recrystallization texture. In addition, during secondary recrystallization annealing, a phase transformation occurs between ferrite and austenite, making secondary recrystallization unstable and severely damaging the {110} Gaussian texture. On the other hand, when the Si content is too high, an excessively dense SiO2 and Fe2SiO4 oxide layer forms during primary recrystallization annealing, delaying decarburization. The phase transformation between ferrite and austenite continues during primary recrystallization annealing, potentially severely damaging the primary recrystallization texture. Furthermore, due to the delayed decarburization effect caused by the formation of a dense oxide layer, the nitriding behavior is also delayed, and nitrides such as (Al, Si, Mn)N and AlN cannot be fully formed, thus failing to ensure sufficient grain suppression force required for secondary recrystallization during high-temperature annealing.

[0051] Furthermore, excessive Si content increases brittleness as a mechanical property while decreasing toughness, leading to an increased rate of plate cracking during rolling, poor weldability between steel plates, and potentially compromising workability. In summary, if the Si content is not controlled within the predetermined range, secondary recrystallization becomes unstable, magnetic properties are severely impaired, and workability deteriorates. Therefore, Si can be contained at 2.0 to 4.0% by weight. More specifically, it can be contained at 2.1 to 3.5% by weight.

[0052] Mn: 0.04 to 0.2% by weight

[0053] Like Si, manganese (Mn) reduces eddy current losses by increasing resistivity, thus reducing overall iron loss. In the steelmaking state, Mn reacts with S to form Mn-based sulfides. It also reacts with nitrogen introduced during nitriding treatment, along with Si, to form (Al,Si,Mn)N precipitates, thereby inhibiting the growth of primary recrystallized grains and inducing secondary recrystallization. Furthermore, manganese is a crucial element affecting the surface quality of the final product. Insufficient Mn content may result in poor surface quality, while excessive Mn content significantly increases the austenite fraction, leading to impaired Gaussian texture, reduced magnetic flux density, and excessive oxide layer formation during decarburization annealing, potentially hindering decarburization. Therefore, Mn content can range from 0.04 to 0.20% by weight. More specifically, Mn content can range from 0.07 to 0.15% by weight.

[0054] N: less than 0.010% by weight

[0055] Nitrogen (N) is an important element that reacts with Al to form Al-based nitrides, and can be added to slabs at levels below 0.010 wt%. Excessive N in the slab causes surface defects called blistering due to nitrogen diffusion during hot rolling. The excessive formation of nitrides in the slab state makes rolling difficult, complicates subsequent processes, and increases manufacturing costs. More specifically, N can be contained at levels below 0.005 wt%. On the other hand, additional N required for the formation of nitrides such as (Al,Si,Mn)N, AlN, and (Si,Mn)N is supplemented by nitriding the steel with ammonia during the annealing process after cold rolling. However, since N is removed again during the secondary recrystallization annealing process, the residual N in the final electrical steel sheet can be below 0.010 wt%.

[0056] C: less than 0.05% by weight

[0057] Carbon (C) is an element that induces a phase transformation between ferrite and austenite, refining the grain size and thus contributing to increased elongation. It is also essential for improving the rollability of electrical steel sheets, which are often brittle and have poor rollability. When these C elements remain in the final product, carbides formed due to magnetic aging precipitate within the steel sheet, leading to deterioration of magnetic properties. Therefore, it is preferable to control the C content to an appropriate level. If the C content in the slab is too low, the phase transformation between ferrite and austenite will not occur sufficiently, resulting in inhomogeneity in the slab and the hot-rolled microstructure. Consequently, precipitates will be coarse and unevenly distributed, not only making secondary recrystallization unstable but also impairing cold rollability after hot rolling. Furthermore, thermal deviations on the skid in the heating furnace during slab heating can also contribute to inhomogeneity in precipitates and microstructure. If the slab contains excessive carbon (C), the carbides become too coarse and the precipitation increases excessively, preventing sufficient decarburization. This leads to a decrease in the aggregation of the Gaussian texture and severe damage to the secondary recrystallization texture, potentially causing magnetic property degradation in the final product due to magnetic aging. Therefore, the C content in the slab can be from 0.0010 to 0.0400% by weight. More specifically, the C content in the slab can be from 0.0200 to 0.0380% by weight. On the other hand, to minimize magnetic aging during the use of the final product (i.e., grain-oriented electrical steel sheet), the C content of the final grain-oriented electrical steel sheet product after secondary recrystallization annealing is below 0.005% by weight.

[0058] Sn: 0.03 to 0.08% by weight

[0059] Tin (Sn), as a grain boundary segregation element, hinders grain boundary movement and thus acts as a grain growth inhibitor. Within the Si content range of one embodiment of the present invention, the grain growth inhibition force for facilitating secondary recrystallization is insufficient; therefore, Sn, which inhibits grain boundary movement due to grain boundary segregation, is essential. If the Sn content is too low, the aforementioned effect cannot be adequately achieved. On the other hand, if too much Sn is added, and the heating rate is not adjusted or maintained for a certain time in the primary recrystallization annealing zone, stable secondary recrystallization cannot be obtained due to the excessively strong grain growth inhibition force. Therefore, Sn can be contained in 0.03 to 0.08% by weight. More specifically, it can be contained in 0.03 to 0.07% by weight.

[0060] Cr: 0.01 to 0.2% by weight

[0061] Chromium (Cr) promotes the formation of a hard phase within hot-rolled sheets, which in turn promotes the formation of a Gaussian texture in {110} during cold rolling. <001> Furthermore, it promotes decarburization during primary recrystallization annealing, thereby reducing the austenite transformation retention time and preventing texture damage caused by prolonged austenite transformation retention time. Additionally, it promotes the formation of a surface oxide layer during primary recrystallization annealing, thus overcoming the drawback of Sn and Sb, alloying elements used as grain growth inhibitors, hindering oxide layer formation. If the Cr content is low, the aforementioned effects are difficult to achieve adequately. On the other hand, if the Cr content is excessive, it promotes the formation of a denser oxide layer during primary recrystallization annealing, resulting in poor oxide layer formation and potentially hindering decarburization and nitriding. Therefore, Cr can be contained in 0.01 to 0.2% by weight. More specifically, it can be contained in 0.03 to 0.1% by weight.

[0062] According to an embodiment of the present invention, the slab satisfies the following formula 1.

[0063] [Formula 1]

[0064] 0.038×[Si]-0.069–[N]≤[C]≤0.038×[Si]-0.069+[N]

[0065] When the C content is controlled according to the Si and N content in the slab as shown in Equation 1, the precipitates formed during the slab heating and hot rolling steps are almost or completely dissolved and precipitated very uniformly. Even if the hot-rolled annealing is omitted, the adverse effects caused by thermal deviations on the skid in the heating furnace during slab heating can be reduced or prevented. Moreover, after secondary recrystallization annealing, the average particle size of the residual inclusions that lead to deterioration of magnetic properties becomes 0.5 to 6.0 μm, which is very effective in ensuring stable magnetic properties. On the other hand, after secondary recrystallization annealing, the oxide layer on the surface is completely removed, and then the surface is ground to 50 to 100 μm to create a replica sample. Image analysis of the photographs taken by TEM allows the average particle size of the residual precipitates to be measured. The measurement reference surface is a surface parallel to the rolling surface.

[0066] In one embodiment of the present invention, inclusions refer to Al-based, Mg-based, and Ca-based oxides and various precipitates. Inclusions include precipitates, which, unlike inclusions, refer to non-oxide nitrides and sulfides such as (Al,Si)N, (Al,Si,Mn)N, MnS, and CuS. 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.

[0067] As described above, by adjusting the carbon content in the slab and using Formula 1, the thermal deviation of the slab on the furnace slide during heating can be reduced. In subsequent processes, the growth of inclusions due to thermal deviation in the slide can be suppressed by omitting the hot-rolled annealing process. More specifically, the average particle size of the inclusions can be 1.0 to 5.0 μm.

[0068] Inclusions that are too small are present during the annealing of hot-rolled steel sheets, which does not meet the purpose of one embodiment of the present invention. If the inclusions are too large, the magnetic properties may deteriorate.

[0069] Inclusion density can be 40 to 130 inclusions / mm 2 In this case, the standard particle size of the inclusions can be below 6.0 μm. Since inclusions larger than 6.0 μm are substantially not generated in one embodiment of the invention, the upper limit can be limited as described above. There is no particular limitation on the lower limit of the standard particle size of the inclusions, but from a measurement point of view, it can be 1 nm. Too few inclusions are a case of a large number of inclusions larger than 6.0 μm being generated, which has a fatal effect on magnetism. If too many inclusions are present, the magnetic properties may deteriorate. More specifically, it can be 45 to 125 inclusions / mm².

[0070] Thus, by appropriately forming inclusions, secondary recrystallization can be fully initiated during the secondary recrystallization annealing process, even without omitting the hot-rolled plate annealing. Specifically, the area fraction of grains with a diameter 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 plane). For the average grain size, assuming a virtual circle with the same area as the grain, the average grain size is calculated from the diameter of that circle.

[0071] The average grain size can be 0.1 to 5 cm.

[0072] The oriented electrical steel sheet according to one embodiment of the present invention may further contain Al: 0.005 to 0.030% by weight. As previously mentioned, when additional elements are further included, a portion of the balance Fe is replaced.

[0073] Al: 0.005 to 0.030% by weight

[0074] In addition to forming Al-based nitrides precipitated during hot rolling, aluminum (Al) also acts as a strong grain growth inhibitor during the annealing process following cold rolling. Nitrogen ions introduced by ammonia combine with Al, Si, and Mn, which are in solid solution in the steel, to form (Al,Si,Mn)N and AlN nitrides. If the Al content is too low, the quantity and volume of the nitrides formed are too small to be considered sufficiently effective as an inhibitor. On the other hand, if the Al content is too high, the Al-based nitrides become too coarse, reducing the grain growth inhibition. Furthermore, since the Al-based nitrides do not completely dissolve during slab reheating, the precipitates after reheating are highly uneven in size and distribution, leading to unstable secondary recrystallization behavior and potentially worsening or increasing the deviation in the magnetic properties of the final product. Therefore, when further containing Al, the Al content can be from 0.005 to 0.030% by weight. More specifically, the Al content can be from 0.015 to 0.030% by weight.

[0075] The oriented electrical steel sheet according to one embodiment of the present invention may further contain S: less than 0.010% by weight.

[0076] S: less than 0.010% by weight

[0077] When excessive sulfur (S) is added, it segregates in the center of the slab, resulting in the uneven precipitation of sulfides such as MnS and CuS. This induces an uneven primary recrystallization microstructure, leading to instability in secondary recrystallization. Therefore, when further sulfur is added, its content can be below 0.010% by weight. Furthermore, since controlling desulfurization at very low levels during steelmaking requires significant time and money, the lower limit can exceed 0%. In one embodiment of the invention, no specific lower limit is set.

[0078] P: 0.005 to 0.045% by weight

[0079] Phosphorus (P) segregation at grain boundaries hinders grain boundary movement and can also play an auxiliary role in inhibiting grain growth, while improving the microstructure {110}. <001> The effect on texture. When P is added, if the amount added is too small, there is no effect. On the other hand, if the amount added is too large, brittleness increases and rollability is greatly reduced. Therefore, when further including P, P can be contained in amounts from 0.005 to 0.045% by weight. More specifically, it can be contained in amounts from 0.01 to 0.035% by weight.

[0080] The oriented electrical steel sheet according to one embodiment of the present invention may further contain Sb: less than 0.1% by weight.

[0081] Sb: less than 0.1% by weight

[0082] Antimony (Sb) has the effect of inhibiting grain growth by segregating at grain boundaries and also has the effect of stabilizing secondary recrystallization. However, due to its low melting point, it easily diffuses to the surface during primary recrystallization annealing, thus hindering decarburization or the formation of an oxide layer and nitriding based on nitriding. Therefore, Sb can be further added as needed. If too much Sb is added, it hinders decarburization and may inhibit the formation of an oxide layer as the basis for the base coating. Therefore, Sb can be contained in amounts of 0.1% by weight or less. More specifically, it can be contained in amounts of 0.01 to 0.05% by weight.

[0083] According to an embodiment of the present invention, the oriented electrical steel sheet may further contain one or more of Co: less than 0.1 wt%, Ni: less than 0.1 wt%, and Mo: less than 0.1 wt%.

[0084] Co: less than 0.1% by weight

[0085] Cobalt (Co) is an effective alloying element for increasing the magnetization of iron and improving magnetic flux density, while also increasing resistivity and reducing iron loss. These effects can be further achieved when Co is added appropriately. However, excessive Co addition increases the austenite phase change, which may adversely affect the microstructure, precipitates, and texture. Therefore, when Co is added, it can be contained at a concentration of less than 0.1% by weight. More specifically, it can be contained from 0.005% to 0.05% by weight.

[0086] Ni and Mo can also have their upper limit limited to 0.1% by weight.

[0087] The balance includes iron (Fe). Additionally, unavoidable impurities may be included. Unavoidable impurities are those that are unavoidably introduced during the steelmaking and manufacturing processes of grain-oriented electrical steel sheets. These unavoidable impurities are well-known and therefore specific descriptions are omitted. In one embodiment of the invention, the addition of other elements besides the aforementioned alloy composition is not excluded, and various elements may be included without affecting the technical concept of the invention. When additional elements are further included, they replace a portion of the Fe in the balance.

[0088] A method for manufacturing an oriented electrical steel sheet according to an embodiment of the present invention includes: hot rolling a slab to manufacture a hot-rolled steel sheet; coiling the hot-rolled steel sheet; directly cooling the coiled hot-rolled steel sheet and cold rolling it to produce a cold-rolled steel sheet; performing a first recrystallization annealing on the cold-rolled steel sheet; and performing a second recrystallization annealing on the cold-rolled steel sheet after the first recrystallization annealing.

[0089] The following is a detailed description of each step.

[0090] First, the slab is hot-rolled to produce a hot-rolled steel sheet. Regarding the alloy composition of the slab, since the alloy composition of grain-oriented electrical steel sheets has already been described, a repetition is omitted. Specifically, in weight percent, the grain-oriented electrical steel sheet comprises Si: 2.0 to 4.0%, Mn: 0.04 to 0.2%, N: less than 0.010% (excluding 0%), C: less than 0.005% (excluding 0%), Sn: 0.03 to 0.08%, Cr: 0.01 to 0.2%, and the balance Fe and unavoidable impurities, and may satisfy the following formula 1.

[0091] [Formula 1]

[0092] 0.038×[Si]-0.069–[N]≤[C]≤0.038×[Si]-0.069+[N]

[0093] In Equation 1, [Si], [N] and [C] represent the contents (by weight%) of Si, N and C in the slab, respectively.

[0094] Returning to the description of the manufacturing method, before the step of manufacturing hot-rolled steel sheet, a step of heating the slab to below 1300°C may also be included.

[0095] Next, the slab is hot-rolled to produce hot-rolled steel sheets. The thickness of hot-rolled steel sheets can be less than 5 mm.

[0096] Then, the hot-rolled steel sheet is coiled.

[0097] At this point, the coiling temperature can be between 700 and 850°C. In one embodiment of the present invention, since the annealing of the hot-rolled plate is omitted after coiling, if the coiling temperature is too low, the inclusions in the hot-rolled plate are too small and numerous, making it difficult to control the fine structure of the primary recrystallization, resulting in unstable secondary recrystallization and deterioration of magnetic properties. If the coiling temperature is too high, the inclusions become too large and few, making it difficult to control the fine structure of the primary recrystallization, and the secondary recrystallization may also be unstable, resulting in deterioration of magnetic properties. More specifically, the coiling temperature can be between 740°C and 830°C. The coiling temperature refers to the average steel plate temperature from the start of coiling to the end of coiling after hot rolling.

[0098] At this point, Equation 2 can be satisfied.

[0099] [Equation 2]

[0100] 90≤(0.038×[Si]+[N]+[C])×[CT]≤130

[0101] In Equation 2, [Si], [N], and [C] represent the contents (wt%) of Si, N, and C in the slab, respectively, and [CT] represents the winding temperature (°C).

[0102] If the value of Equation 2 is too low, inhomogeneous inclusions may form. If the value of Equation 2 is too high, the content of Si, N and C will be high, and inhomogeneous inclusions may also form.

[0103] Next, the hot-rolled steel sheet is cooled directly and then cold-rolled to produce cold-rolled steel sheet.

[0104] In one embodiment of the invention, direct cooling refers to heat treatment without external heating after the hot-rolled steel sheet is coiled. That is, the annealing process for the hot-rolled sheet is omitted. After hot rolling, pickling is performed to remove the hot-rolled oxide scale. When performing pickling, shot blasting can be performed before or after pickling, or it can be omitted.

[0105] The manufacturing process of cold-rolled steel sheets can involve a single cold rolling operation or two or more cold rolling operations, including intermediate annealing. Specifically, it can be accomplished by a single cold rolling operation on hot-rolled steel sheets.

[0106] The thickness of cold-rolled steel sheets is 0.65 mm or less. On the other hand, when cold rolling is performed, the cold rolling reduction rate can be 87% or more. This is because the aggregation of the Gaussian texture increases with the increase of the cold rolling reduction rate. However, a cold rolling reduction rate lower than the above can also be used.

[0107] Next, the cold-rolled sheet undergoes a recrystallization annealing process. This recrystallization annealing step can include both decarburization and nitriding. The decarburization and nitriding steps are not sequential. That is, nitriding can be performed after decarburization, after nitriding, or simultaneously. In the decarburization step, the carbon content can be reduced to less than 0.005% by weight. More specifically, it can be reduced to less than 0.003% by weight. During nitriding, the nitrogen content can be increased to more than 0.015% by weight.

[0108] The homogenization temperature for the first recrystallization annealing step can be between 840°C and 900°C. Even if the first recrystallization annealing is performed at a temperature below 840°C or above 900°C, there is no problem in achieving the functions proposed in this invention.

[0109] After a recrystallization annealing step, an annealing release agent can be applied to the steel sheet. Annealing release agents are well-known, so a detailed description is omitted. As an example, an annealing release agent with MgO as the main component can be used.

[0110] Next, the cold-rolled sheet after the first recrystallization annealing is subjected to a second recrystallization annealing.

[0111] The purpose of secondary recrystallization annealing is roughly to form {110} through secondary recrystallization. <001> The texture and the reaction between the oxide layer formed during the first recrystallization annealing and MgO form a glassy film layer, which imparts insulation and removes impurities detrimental to magnetic properties. In the second recrystallization annealing method, the temperature rise stage before the second recrystallization occurs is maintained with a mixture of nitrogen and hydrogen to protect the nitrides, which act as grain growth inhibitors, allowing the second recrystallization to proceed smoothly. After the second recrystallization is completed, the homogenization step is maintained for an extended period in a 100% hydrogen atmosphere to remove impurities.

[0112] The secondary recrystallization annealing step can be completed at a temperature of 900°C to 1210°C.

[0113] The grain-oriented electrical steel sheet according to one embodiment of the present invention exhibits particularly excellent iron loss and magnetic flux density characteristics. The grain-oriented electrical steel sheet according to one embodiment of the present invention has a magnetic flux density (B8) of 1.85 T or higher and an iron loss (W17 / 50) of 1.10 W / kg or lower. Here, the magnetic flux density B8 is the magnitude (Tesla) of the induced magnetic flux density under a magnetic field of 800 A / m, and the iron loss W17 / 50 is the magnitude (W / kg) of the iron loss induced under conditions of 1.7 Tesla and 50 Hz. More specifically, the grain-oriented electrical steel sheet according to one embodiment of the present invention has a magnetic flux density (B8) of 1.89 T or higher and an iron loss (W17 / 50) of 1.00 W / kg or lower.

[0114] The thickness used as a measurement standard can be 0.30 mm.

[0115] Specific embodiments of the present invention will be described below. However, the following embodiments are merely one specific embodiment of the present invention, and the present invention is not limited to the following embodiments.

[0116] Example 1

[0117] The steel components were vacuum melted to form steel ingots. By weight, the steel components comprised 2.85% Si, 0.092% Mn, 0.025% Al, 0.0032% N, 0.004% S, 0.045% Sn, 0.028% P, 0.032% Cr, and C with varying contents as shown in Table 1. The remaining components included the balance Fe and other unavoidable impurities. The ingots were then heated to 1240°C and hot-rolled to a thickness of 2.8 mm, followed by coiling under the conditions shown in Table 1. After pickling, the ingots were cold-rolled to a thickness of 0.28 mm without heat treatment. The cold-rolled sheet was then subjected to decarburization and nitriding annealing heat treatment at 870°C in a humid mixed gas environment of hydrogen, nitrogen, and ammonia to achieve a carbon content of 30 ppm and a nitrogen content of 200 ppm. Next, the steel plate was coated with an annealing release agent MgO and then subjected to a final annealing heat treatment. The final annealing heat treatment was carried out by heating to 1200°C in a mixed gas environment of 25 vol% nitrogen and 75 vol% hydrogen. After reaching 1200°C, it was held in a 100% hydrogen environment for more than 10 hours before furnace cooling. The measured values ​​of magnetic properties based on C content are shown in Table 1.

[0118] After secondary recrystallization annealing, the oxide layer on the surface is completely removed, and then the surface is ground to about 100 μm to make a replica sample. Image analysis is performed on the photographs taken by TEM, so that the average particle size and density of the inclusions can be measured.

[0119] Regarding whether secondary recrystallization occurs, if the area fraction of grains with a grain size of less than 1 mm is greater than 10%, it is judged that secondary recrystallization has occurred unstablely or has not occurred, and is indicated as X.

[0120] Table 1

[0121]

[0122] As shown in Table 1, it can be confirmed that the alloy composition and winding temperature of the material of the present invention fall within an appropriate range and satisfy Formulas 1 and 2, thus resulting in small and low-density inclusions. Finally, it can be confirmed that proper secondary recrystallization leads to excellent iron loss and magnetic flux density.

[0123] Conversely, in the comparative materials, the alloy composition and winding temperature were not properly controlled, the formation of inclusions was uneven, and secondary recrystallization was not properly formed, which confirmed poor iron loss and magnetic flux density.

[0124] Figure 1 and 2 These are photographs of inclusions analyzed in Inventive Material 1 and Comparative Material 1. In Inventive Material 1, it can be confirmed that the inclusions are fine and precipitated in small quantities, while in contrast, Comparative Material 1, it can be confirmed that the inclusions are large and precipitated in large quantities.

[0125] The analysis results showed that the inclusions contained AlN, (Al, Si, Mn)N, MnS, and CuS.

[0126] Example 2

[0127] The steel components are vacuum melted to form steel ingots. By weight, the steel components comprise Al: 0.022%, S: 0.003%, Sb: 0.02%, Sn: 0.06%, P: 0.02%, Cr: 0.05%, and Si, C, and N with varying contents as shown in Table 2. The remaining components include the balance Fe and other unavoidable impurities. The ingots are then heated to 1200°C and hot-rolled to a thickness of 2.3 mm. They are then coiled at the temperatures shown in Table 2. After pickling, the ingots are cold-rolled once to a thickness of 0.30 mm. The cold-rolled sheet is then subjected to decarburization and nitriding annealing heat treatment at 870°C in a humid mixed gas environment of hydrogen, nitrogen, and ammonia to achieve a carbon content of 30 ppm and a nitrogen content of 180 ppm. Next, the steel plate was coated with an annealing release agent MgO and then subjected to a final annealing heat treatment. The final annealing heat treatment was carried out by heating to 1200°C in a mixed gas environment of 25 vol% nitrogen and 75 vol% hydrogen. After reaching 1200°C, it was held in a 100% hydrogen environment for more than 10 hours before furnace cooling. The magnetic properties after high-temperature annealing based on Si, C, and N content, as well as the measured values ​​of the average particle size of residual precipitates per square millimeter, are shown in Table 2.

[0128] Table 2

[0129]

[0130] As shown in Table 2, it can be confirmed that the alloy composition and winding temperature of the invented material are within an appropriate range and satisfy Equations 1 and 2, thus resulting in small and low-density inclusions. Finally, it can be confirmed that proper secondary recrystallization is achieved, resulting in excellent iron loss and magnetic flux density.

[0131] Conversely, in the comparative materials, the alloy composition and winding temperature were not properly controlled, the formation of inclusions was uneven, secondary recrystallization was not properly formed, and the iron loss and magnetic flux density were poor.

[0132] Example 3

[0133] The implementation method is the same as that of Invention Material 7, and the cases in which annealing of the hot-rolled plate is omitted or performed are compared.

[0134]

[0135] As shown in Table 3, it can be confirmed that even if hot-rolled plate annealing is omitted, the same magnetic properties will be exhibited as if hot-rolled plate annealing were performed.

[0136] like Figure 3 and Figure 4 As shown, it can be confirmed that both the inventive material 7 and the comparative material 31 undergo complete secondary recrystallization. In particular, in the case of the inventive material 7, it can be confirmed that secondary recrystallization occurs completely even if the hot-rolled plate annealing is omitted.

[0137] On the other hand, such as Figure 5 and Figure 6 As shown, it can be confirmed that secondary recrystallization did not occur completely in comparative materials 21 and 22, where the alloy composition was not properly controlled. That is, it can be confirmed that a large number of grains with a diameter of less than 1 mm are present.

[0138] This invention can be implemented in various ways and is not limited to the embodiments described above. Those skilled in the art will understand that the invention can be implemented in other specific ways without altering its technical concept or essential features. Therefore, it should be understood that the above embodiments are exemplary in all respects and are not restrictive.

Claims

1. A type of oriented electrical steel sheet, wherein, By weight percent, the oriented electrical steel sheet comprises Si: 2.0 to 4.0%, Mn: 0.04 to 0.2%, N: less than 0.010% and excluding 0%, C: less than 0.005% and excluding 0%, Sn: 0.03 to 0.08%, Cr: 0.01 to 0.2%, and the balance Fe and unavoidable impurities. Inclusions containing at least one of AlN, (Al,Si)N, (Al,Si,Mn)N, MnS, CuS, and Al2O3. The average particle size of the inclusions is 0.5 to 6.0 μm. The inclusions with a particle size of less than 6.0 μm consist of 40 to 130 inclusions per mm. 2 ,and The area fraction of grains with a grain size of less than 1 mm is less than 10%.

2. The grain-oriented electrical steel sheet according to claim 1, wherein, Further contains Al: 0.005 to 0.030 by weight.

3. The grain-oriented electrical steel sheet according to claim 1, wherein, Further includes S: less than 0.010% by weight.

4. The grain-oriented electrical steel sheet according to claim 1, wherein, Further contains P: 0.0005 to 0.045 by weight.

5. The grain-oriented electrical steel sheet according to claim 1, wherein, Further contains Sb: less than 0.1% by weight.

6. The grain-oriented electrical steel sheet according to claim 1, wherein, It further comprises one or more of Co: less than 0.1 wt%, Ni: less than 0.1 wt%, and Mo: less than 0.1 wt%.

7. A method for manufacturing an oriented electrical steel sheet, comprising: The step of hot-rolling a slab to produce a hot-rolled steel sheet, wherein the slab, by weight percent, comprises Si: 2.0 to 4.0%, Mn: 0.04 to 0.2%, N: less than 0.010% and excluding 0%, C: 0.001 to 0.04%, Sn: 0.03 to 0.08%, Cr: 0.01 to 0.2%, and the balance Fe and unavoidable impurities, wherein the slab satisfies the following formula 1; The step of coiling the hot-rolled steel sheet; The step of directly cooling the coiled hot-rolled steel sheet and then cold-rolling the coiled hot-rolled steel sheet to manufacture cold-rolled steel sheet; The step of performing a recrystallization annealing on the cold-rolled steel sheet; and The step of performing a second recrystallization anneal on the cold-rolled steel sheet after the first recrystallization annealing. In the winding step, the winding temperature is 740 to 830°C, satisfying the following equation 2. The oriented electrical steel sheet contains inclusions of at least one of AlN, (Al,Si)N, (Al,Si,Mn)N, MnS, CuS, and Al2O3. The inclusions have an average particle size of 0.5 to 6.0 μm, and the number of inclusions with a particle size of less than 6.0 μm is 40 to 130 per mm. 2 , The area fraction of grains with a grain size of less than 1 mm is less than 10%. [Formula 1] 0.038 × [Si] - 0.069 – [N] ≤ [C] ≤ 0.038 × [Si] - 0.069 + [N] In Equation 1, [Si], [N], and [C] represent the weight percentage of Si, N, and C in the slab, respectively. [Equation 2] 90 ≤ (0.038 × [Si] + [N] + [C]) × [CT] ≤ 130 In Equation 2, [Si], [N], and [C] represent the weight % content of Si, N, and C in the slab, respectively, and [CT] represents the winding temperature in °C.

8. The method for manufacturing oriented electrical steel sheet according to claim 7, wherein, Prior to the step of manufacturing the hot-rolled steel sheet, the process further includes a step of heating the slab to below 1300°C.

9. The method for manufacturing oriented electrical steel sheet according to claim 7, wherein, No heat treatment involving external heating is performed after the coiling step and before the step of manufacturing the cold-rolled steel sheet.

10. The method for manufacturing the grain-oriented electrical steel sheet according to claim 7, wherein, The process of manufacturing cold-rolled steel sheet is completed by performing a cold rolling process on the hot-rolled steel sheet.

11. The method for manufacturing oriented electrical steel sheet according to claim 7, wherein, The primary recrystallization annealing step includes a decarburization step and a nitriding step. The nitriding step is performed after the decarburization step, or The decarburization step is performed after the nitriding step, or The decarburization step and the nitriding step are performed simultaneously.

12. The method for manufacturing oriented electrical steel sheet according to claim 7, wherein, Following the recrystallization annealing step, a step of applying an annealing release agent is also included.

13. The method for manufacturing oriented electrical steel sheet according to claim 7, wherein, The secondary recrystallization annealing step is performed at a temperature of 900°C to 1210°C.

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