Grain-oriented electrical steel sheet and method for producing same

Abstract

The present invention relates to a grain-oriented electrical steel sheet and a method for manufacturing the same. The grain-oriented electrical steel sheet may be a steel sheet having {110} lt; 001gt, 001gt; the size of the oriented crystal grains satisfies the following formula 1, deviation lt; 001gt, 001gt; and the area fraction of crystal grain diameters having an orientation angle within 3 DEG is 60% or more. Lt; formula 1gt; w / L < = 1.5 (In formula 1, W represents the diameter in the TD direction (the width direction of the secondary recrystallized crystal grains), and L represents the diameter in the RD direction (the length direction of the secondary recrystallized crystal grains).

Description

Technical Field

[0001] The present invention relates to grain-oriented electrical steel sheets and a method for manufacturing the same. More specifically, the present invention relates to a grain-oriented electrical steel sheet and a method for manufacturing the same, which have excellent magnetic properties through secondary recrystallization grain refinement and have less characteristic deviation in the coiled sheet. Background Art

[0002] Electrical steel sheets are products used as materials for transformers, motors, and electronic devices. Different from ordinary carbon steels that emphasize workability such as mechanical properties, electrical steel sheets are functional products that emphasize electrical properties. The electrical properties are characteristics such as iron loss, magnetic flux density, magnetic permeability, and duty ratio. For the electrical steel sheets, it is characterized by low iron loss, high magnetic flux density, magnetic permeability, and duty ratio.

[0003] The electrical steel sheets are mainly classified into grain-oriented electrical steel sheets and non-oriented electrical steel sheets. The grain-oriented electrical steel sheets utilize an abnormal grain growth phenomenon called secondary recrystallization to form a Goss texture ({110}<001> texture) throughout the steel sheet, thereby having excellent magnetic properties in the rolling direction. The non-oriented electrical steel sheets are electrical steel sheets having uniform magnetic properties in all directions of the rolled sheet.

[0004] For the grain-oriented electrical steel sheets, the grain orientations are precisely arranged in the {110}<001> orientation so as to obtain a high magnetic flux density. For electrical steel sheets with a high magnetic flux density, not only can the size of the core material of electrical equipment be reduced, but also the hysteresis loss becomes low, thereby enabling the miniaturization and high efficiency of the electrical equipment to be achieved simultaneously.

[0005] The iron loss is the power loss consumed as heat energy when an arbitrary alternating magnetic field is applied to the steel sheet. The higher the magnetic flux density and resistivity, and the lower the plate thickness and the content of impurities in the steel sheet, the lower the iron loss, thereby improving the efficiency of electrical equipment.

[0006] In addition, globally, in order to respond to the carbon neutral era, the industrial structure is transforming towards environmentally friendly and low-carbon industries, and the trend of energy conservation and high efficiency of products is continuously expanding. With the development of this trend, the demand for energy-saving and high-efficiency electrical equipment is increasing, and the social demand for grain-oriented electrical steel sheets with more excellent low iron loss characteristics is also growing.

[0007] Therefore, hitherto, in order to reduce the iron loss of grain-oriented electrical steel sheets, many research and developments have been carried out. Among them, as one of the effective methods for reducing iron loss, the technology of making secondary recrystallization grains finer has attracted attention. By adopting the technology of making secondary recrystallization grains finer, the magnetic domains in the steel sheet can be reduced, and the heat loss caused by eddy currents accompanying the movement of magnetic domains when the steel sheet is excited can be reduced.

[0008] In addition, in order to refine the secondary recrystallized grains, the Goss texture must be highly developed during the process. As a method for developing the Goss texture, a method of applying strong deformation during hot rolling can be adopted. Methods for applying strong deformation include severe plastic deformation methods such as asymmetric rolling, ECAP (equal channel angular pressing), and HPT (high pressure torsion). However, the aforementioned methods have not been realized industrially.

[0009] In addition, another method for refining the secondary recrystallized grains is to minimize the temperature deviation in the coiled sheet during the high-temperature annealing step of Goss texture growth. Generally, the high-temperature annealing is carried out in a batch annealing method. At this time, a temperature deviation of about 300 °C is generated in the coiled sheet, and the growth rate of the Goss texture changes according to the position. Specifically, a growth gradient is formed from the higher temperature side to the lower temperature side, so there will be a problem that the Goss texture becomes larger. The asymmetric growth of the Goss texture causes a deviation in magnetic properties, thereby causing an unexpected problem of deterioration of transformer characteristics. Summary of the Invention

[0010] (I) Technical Problems to be Solved

[0011] The technical problem to be solved by the present invention is to provide an oriented electrical steel sheet, which has excellent magnetic properties by refining secondary recrystallization, and at the same time has a small characteristic deviation in the coiled sheet.

[0012] Another technical problem to be solved by the present invention is to provide a method for manufacturing an oriented electrical steel sheet having the above advantages.

[0013] (II) Technical Solutions

[0014] The oriented electrical steel sheet according to an embodiment of the present invention has grains with a {110}<001> orientation, and the size thereof satisfies the following formula 1, and the area fraction of the grain diameter of grains deviating from the <001> orientation by within 3° can be 60% or more.

[0015] <Formula 1>

[0016] W / L ≤ 1.5

[0017] In the above formula 1, W represents the diameter in the TD direction (width direction of the secondary recrystallized grains), and L represents the diameter in the RD direction (length direction of the secondary recrystallized grains).

[0018] In one embodiment, the following formula 2 can be satisfied.

[0019] <Formula 2>

[0020] α × β × γ ≤ 20 °

[0021] In the above formula (2), α represents the angular difference between the {110}<001> orientation and the ND axis, β represents the angular difference between the {110}<001> orientation and the TD axis, and γ represents the angular difference between the {110}<001> orientation and the RD axis.

[0022] In one embodiment, by weight, the grain-oriented electrical steel sheet may contain Si: 2.0 to 5.0%, C: less than 0.005%, Mn: 0.03 to 0.5%, Al: 0.01 to 0.04%, and N: 0.002 to 0.005%, and further contain one or more of Sb: 0.01 to 0.05 wt%, Sn: 0.03 to 0.08 wt%, Cr: 0.01 to 0.2 wt%, S: less than 0.01 wt%, and P: 0.005 to 0.045 wt%, with the balance containing Fe and inevitable impurities.

[0023] A method for manufacturing a grain-oriented electrical steel sheet according to another embodiment of the present invention includes: a step of hot rolling a slab to manufacture a hot-rolled steel sheet; a step of pre-rolling the hot-rolled steel sheet with a reduction ratio of 10 to 40% to manufacture a pre-rolled sheet; a step of annealing the pre-rolled sheet; a step of cold rolling the annealed pre-rolled sheet to manufacture a cold-rolled steel sheet; a step of performing primary recrystallization annealing on the cold-rolled steel sheet; and a step of performing secondary recrystallization annealing on the cold-rolled steel sheet after primary recrystallization annealing. The hot rolling step includes a step of coiling the slab, and in the coiling step, the coiling temperature is 600 to 800°C. The secondary recrystallization annealing step is performed in a temperature range of 1000 to 1200°C, the secondary recrystallization heating rate is 3 to 6°C / hour (hr), and a bottom direct heating method is used. In the secondary recrystallized grains based on the secondary recrystallization annealing, the size of the grains having the {110}<001> orientation satisfies the following formula (1), and the area fraction of the grain diameter with an angle deviating from the <001> orientation within 3° can be 60% or more.

[0024] <Formula (1)>

[0025] W / L ≤ 1.5

[0026] In the above formula (1), W represents the diameter in the TD direction (the width direction of the secondary recrystallized grains), and L represents the diameter in the RD direction (the length direction of the secondary recrystallized grains).

[0027] In one embodiment, in the step of manufacturing the pre-rolled sheet, the temperature of the steel sheet before pre-rolling can be 0.4Tc to 0.6Tc °C.

[0028] The Tc represents the coiling temperature [°C].

[0029] In one embodiment, the method for manufacturing a grain-oriented electrical steel sheet may satisfy the following formula (3).

[0030] <Formula 3>

[0031] 100 ≤ T b -T a ≤ 300

[0032] In the above Formula 3, T a represents the temperature for cold rolling, and T b represents the temperature for preliminary rolling.

[0033] In one embodiment, the steps of manufacturing the hot-rolled steel sheet may include rough rolling, finish rolling, and coiling steps. In one embodiment, the thickness of the preliminary rolled sheet may be 1.5 to 3.0 mm.

[0034] In one embodiment, the step of annealing the preliminary rolled sheet may be carried out within a soaking temperature range of 700 to 1100 °C. In one embodiment, in the step of manufacturing the cold-rolled sheet, the reduction ratio may be 85 to 95%. In one embodiment, the step of manufacturing the cold-rolled steel sheet may be carried out within a temperature range of 0.2Tc to 0.4Tc °C for the temperature of the steel sheet before cold rolling.

[0035] The Tc represents the coiling temperature [°C].

[0036] (III) Beneficial Effects

[0037] For the grain-oriented electrical steel sheet according to an embodiment of the present invention, by controlling the hot rolling conditions and preliminary rolling, the secondary recrystallization can be refined, so as to provide a grain-oriented electrical steel sheet with excellent magnetic properties and small property deviations in the coiled sheet.

[0038] For the manufacturing method of the grain-oriented electrical steel sheet according to another embodiment of the present invention, a grain-oriented electrical steel sheet having the aforementioned advantages can be provided. Detailed Embodiments

[0039] If a part is described as being above another part, there may be other parts directly above or between the other parts. Conversely, when a part is described as being directly above another part, there will be no other parts therebetween.

[0040] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this invention belongs. For terms defined in a dictionary, they should be interpreted as having a meaning consistent with the relevant technical literature and the content disclosed herein, and should not be interpreted in an idealized or overly formal sense.

[0041] In addition, unless otherwise specified, % represents weight %, and 1 ppm represents 0.0001 weight %. In one embodiment of the present invention, further including additional elements means that a part of the remaining iron (Fe) is replaced by the additional elements, and the replacement amount is equivalent to the addition amount of the additional elements.

[0042] In addition, in the present invention, the Goss orientation is an orientation with Miller indices corresponding to {110}<001>.

[0043] Hereinafter, embodiments of the present invention will be described in detail so that those of ordinary skill in the art to which the present invention pertains can easily implement the present invention. However, the present invention can be implemented in various different ways and is not limited to the embodiments described herein.

[0044] The grain-oriented electrical steel sheet according to one embodiment of the present invention, in terms of weight %, contains Si: 0.1 to 6.5 weight %, Al: 0.001 to 6.5 weight %, Mn: 0.01 to 20 weight %, C: 0.0050 weight % or less, and contains one or more of N, S, and Ti, and their contents are respectively 0.0003 to 0.001 weight %, and the balance contains Fe and inevitable impurities.

[0045] The reasons for the composition limitations of the non-grain-oriented electrical steel sheet are described below.

[0046] Si: 2.0 to 5.0 weight %

[0047] Silicon (Si) plays a role in increasing the resistivity of the material to reduce iron loss and is a component as a deoxidizer in the steelmaking process. The content of the silicon can be 2.0 to 5.0 weight %. Specifically, the content of the silicon can be 3.0 to 4.5 weight %. By the content of the silicon satisfying the above range, excellent magnetic properties and productivity of the electrical steel sheet can be ensured.

[0048] If the content of the silicon is too much, the ductility and toughness in mechanical properties decrease, there is a problem that plate cracking frequently occurs during the rolling process, and in the continuous annealing for industrial production, the weldability between steel sheets decreases, resulting in a problem of deteriorated productivity. If the content of the silicon is too little, the resistivity decreases, the eddy current loss increases, and there is a problem that the iron loss characteristics deteriorate.

[0049] C: 0.005 weight % or less

[0050] Carbon (C) is an austenite stabilizing element. When added to the slab, it can refine the coarse columnar structure generated during continuous casting and can also inhibit the center segregation of sulfur (S) in the slab. In addition, during cold rolling, it promotes the work hardening of the steel sheet, thereby promoting the secondary recrystallization nucleation of the {110}<001> orientation in the steel sheet. In the slab, the content of the carbon can be 0.01 to 0.10% by weight. Specifically, the content of the carbon can be 0.03 to 0.08% by weight.

[0051] If the content of the carbon is too much, edge cracks may occur during hot rolling.

[0052] However, for the carbon, its content will decrease during the decarburization process. When a lot of the carbon remains in the finally manufactured grain-oriented electrical steel sheet, carbides formed due to the magnetic aging effect will precipitate in the steel sheet, resulting in the deterioration of magnetic properties. Therefore, after the high-temperature annealing is completed, the content of the carbon in the finally manufactured grain-oriented electrical steel sheet can be 0.005% by weight or less, specifically 0.003% by weight or less.

[0053] Mn: 0.03 to 0.50% by weight

[0054] Like Si, manganese (Mn) increases the resistivity and reduces the eddy current loss, thereby having the effect of reducing the iron loss. In addition, it reacts with sulfur (S) present in the steel to form manganese compounds or reacts with aluminum (Al) and nitrogen (N) to form nitrides in the form of (Al, Si, Mn)N, thereby playing the role of forming grain growth inhibitors. The content of the manganese can be 0.03 to 0.5% by weight. Specifically, the content of the manganese can be 0.05 to 0.3% by weight.

[0055] If the content of the manganese is too much, the growth of the Goss texture will be severely inhibited during the secondary recrystallization annealing, and the magnetic properties may drop sharply. If the content of the manganese is too little, there will be a problem that it is difficult to expect the above effects.

[0056] Al: 0.01 to 0.04% by weight

[0057] Aluminum (Al) not only combines with nitrogen ions introduced by ammonia gas as the ambient gas during nitriding in the primary recrystallization annealing process to form nitrides in the form of aluminum nitride (AlN), but also combines with silicon, manganese, and nitrogen present in the steel in a solid solution state to form nitrides in the form of (Al, Si, Mn)N, thereby playing the role of grain growth inhibitors. The content of the aluminum can be 0.01 to 0.04% by weight. Specifically, the content of the aluminum can be 0.015 to 0.035% by weight.

[0058] N: 0.002 to 0.005% by weight

[0059] Nitrogen (N) is an element that reacts with aluminum (Al) and manganese (Mn) to form compounds such as aluminum nitride (AlN) and (Al, Mn, Si)N. The content of the nitrogen can be 0.002 to 0.005% by weight. In addition, the nitrogen increases the nitrides for secondary recrystallization to form a Goss texture. The nitrides can be increased by carrying out a nitriding treatment. Ammonia gas is introduced as an ambient gas in the decarburizing annealing process so that nitrogen ions diffuse into the steel.

[0060] If the content of the nitrogen exceeds the upper limit value of the range, not only surface defects such as blisters are caused by nitrogen diffusion in the process after hot rolling, but also excessive nitrides are formed in the slab state. Therefore, there is a problem that the non-uniformity of the grain size of the subsequent hot-rolled sheet annealing and the primary recrystallized annealed sheet becomes larger. If the content of the nitrogen is less than the lower limit value of the range, the amount of aluminum compounds generated during hot rolling is too small, and there is a problem that it is difficult to control the structure of the hot-rolled annealed sheet.

[0061] Sb: 0.01 to 0.05% by weight

[0062] Antimony (Sb) segregates at grain boundaries, thus having the effect of suppressing grain growth and the effect of stabilizing secondary recrystallization. However, due to its low melting point, it is likely to diffuse to the surface during primary recrystallization annealing, which may hinder decarburization or the formation of an oxide layer and nitriding based on nitridation. The content of the antimony can be 0.01 to 0.05% by weight. Specifically, the content of the antimony can be 0.02 to 0.04% by weight.

[0063] If the content of the antimony is too much, it hinders decarburization, and there is a problem of suppressing the formation of an oxide layer as the basis of the substrate coating. If the content of the antimony is too little, there is a problem that the effect of suppressing grain growth becomes poor.

[0064] Sn: 0.03 to 0.08% by weight

[0065] As a grain boundary segregation element, tin (Sn) is an element that hinders grain boundary movement, so it acts as a grain growth inhibitor. When secondary recrystallization annealing is carried out within the content range of the aforementioned silicon, the grain growth inhibitory force for smooth secondary recrystallization behavior is insufficient. Therefore, the aforementioned tin that segregates at grain boundaries and hinders grain boundary movement can be further added.

[0066] Cr: 0.01 to 0.20% by weight

[0067] Chromium (Cr) promotes the formation of hard phases in the annealed hot-rolled steel sheet, thereby promoting the formation of {110}<001> texture during cold rolling and promoting decarburization during the primary recrystallization annealing process, so that the austenite phase transformation holding time can be shortened to prevent the texture from being damaged. In addition, the chromium promotes the formation of the surface oxide layer formed during the primary recrystallization annealing process, thereby being able to solve the drawback that antimony and tin in the alloying elements used as grain growth auxiliary inhibitors hinder the formation of the oxide layer. The content of the chromium can be 0.01 to 0.20% by weight. Specifically, the content of the chromium can be 0.02 to 0.1% by weight.

[0068] S: 0.01% by weight or less

[0069] Sulfur (S) forms fine precipitates of manganese sulfide (MnS), thereby deteriorating the magnetic properties and hot rolling workability. Therefore, it is preferably controlled to maintain a low content. The content of the sulfur can be 0.010% by weight. Specifically, the content of the sulfur can be 0.005% by weight or less. More specifically, the content of the sulfur can be 0.004% by weight or less.

[0070] If the content of the sulfur is too high, the manganese sulfide precipitates are formed in the slab, thereby inhibiting grain growth, segregating at the center of the slab during casting, and there is a problem of being difficult to control the fine structure in the subsequent process.

[0071] P: 0.005 to 0.045% by weight

[0072] Phosphorus (P) segregates at the grain boundaries to hinder the movement of the grain boundaries, and at the same time can play an auxiliary role in inhibiting grain growth, and has the effect of improving the {110}<001> texture in terms of the fine structure. The content of the phosphorus can be 0.005 to 0.045% by weight.

[0073] If the content of the phosphorus is too high, the brittleness increases and the rollability is greatly reduced. If the content of the phosphorus is too low, there is a problem that the addition effect cannot be confirmed.

[0074] The grain-oriented electrical steel sheet according to an embodiment of the present invention contains Fe and inevitable impurities as the balance. As for the inevitable impurities, they are the impurities mixed in during the steelmaking step and the manufacturing process of the grain-oriented electrical steel sheet, and these impurities are well known in the art, so the specific description is omitted. In an embodiment of the present invention, in addition to the aforementioned alloying components, the addition of other elements is not excluded, and various elements can be included within the scope not affecting the technical idea of the present invention. When further including additional elements, a part of the Fe as the balance is replaced.

[0075] The grain-oriented electrical steel sheet according to an embodiment of the present invention having the aforementioned components has the physical properties described below.

[0076] For an oriented electrical steel sheet according to an embodiment, the size of the grains having a {110}<001> orientation can satisfy the following formula 1.

[0077] <Formula 1>

[0078] W / L ≤ 1.5

[0079] In the above formula 1, W represents the diameter in the TD direction (width direction of the secondary recrystallized grains), and L represents the diameter in the RD direction (length direction of the secondary recrystallized grains).

[0080] In the above formula 1, W refers to the grain size of the secondary recrystallized grains having a Gaussian texture orientation, and the Gaussian texture orientation is the width direction of the secondary recrystallized grains, specifically the {110}<001> orientation. The secondary recrystallized grains refer to the diameter of the secondary recrystallized grains measured on the plane (ND) perpendicular to the rolling plane (RD) after the secondary recrystallization annealing step.

[0081] The size of the grains refers to the diameter of the grain size. The diameter of the grain size designates each grain (Grain) surrounded by grain boundaries in the microstructure photograph of the microscope, and the area of each grain is obtained, so that the diameter of each grain can be represented by the ECD (equivalent circular diameter) corresponding to the area. At this time, the distribution of the grain diameters is obtained using the ECD, and by taking the arithmetic mean, the average grain diameter can be calculated.

[0082] The value of the above formula 1 can be 1.5 or less. Specifically, the value of the formula 1 can be 0.7 to 1.5 or less. More specifically, the value of the formula 1 can be 0.9 to 1.5 or less. By the foregoing range satisfied by the value of the formula 1, the thermal gradient during the secondary recrystallization annealing process is reduced, thereby improving the aggregation degree of the Gaussian structure.

[0083] In one embodiment, the width direction of the secondary recrystallized grains can be in the range of 10 to 150 mm. Specifically, the width direction of the secondary recrystallized grains can be in the range of 15 to 100 mm.

[0084] If the width direction of the secondary recrystallized grains exceeds the upper limit value of the above range, there is a problem that the aggregation degree of the Gaussian structure decreases. If the width direction of the secondary recrystallized grains exceeds the lower limit value of the above range, there are also problems of decreased aggregation degree and increased eddy current loss, resulting in poor iron loss.

[0085] In one embodiment, the length direction of the secondary recrystallized grains can be in the range of 10 to 100 mm. Specifically, the length direction of the secondary recrystallized grains can be in the range of 15 to 75 mm.

[0086] If the length direction of the secondary recrystallized grains exceeds the upper limit value of the range, there is a problem of a decrease in the aggregation degree of the Goss texture. If the length direction of the secondary recrystallized grains exceeds the lower limit value of the range, there are problems of a decrease in the aggregation degree and an increase in eddy current loss, resulting in poor iron loss.

[0087] In one embodiment, the grain-oriented electrical steel sheet may satisfy the following formula 2.

[0088] <Formula 2>

[0089] α × β × γ ≤ 20 °

[0090] In the above formula 2, α represents the angular difference between the {110}<001> orientation and the ND axis, β represents the angular difference between the {110}<001> orientation and the TD axis, and γ represents the angular difference between the {110}<001> orientation and the RD axis.

[0091] For the aggregation degree of the Goss texture of the {110}<001> orientation of the secondary recrystallized grains, it can be confirmed by the deviation angle between the Goss texture orientation and the secondary recrystallized grain orientation. Specifically, the deviation angle can evaluate the aggregation degree with respect to the three rotation axes. More specifically, for the three rotation axes, the respective deviation angles of the normal direction (ND) axis of the rolling plane, the transverse direction (TD) axis, and the rolling direction (RD) axis can be used for distinction.

[0092] Based on the aforementioned deviation angle, in the above formula 2, α represents the angular difference between the Goss texture orientation and the normal direction axis of the rolling plane, β represents the angular difference between the Goss texture orientation and the transverse direction axis, and γ represents the angular difference between the Goss texture orientation and the rolling direction axis.

[0093] In one embodiment, the aforementioned α×β×γ value may be 20° or less. Specifically, the value may be 10 to 18° or less. By satisfying this value, there is an advantage of excellent aggregation degree of the Goss texture.

[0094] In one embodiment, it is important that the grain-oriented electrical steel sheet is arranged along <001> in the rolling direction, which is the easy magnetization axis, and has a feature that the area fraction of the grain size with an angle deviating from the <001> orientation within 3° is 60% or more. Specifically, it has a feature that the area fraction of the grain size with an angle deviating from the <001> orientation within 3° is 65 to 75%.

[0095] Since the area fraction of the grain size with an angle of deviation from the <001> orientation within 3° falls within the aforementioned range, the grain-oriented electrical steel sheet has the advantage of easy magnetization. If the area fraction of the grain size with an angle of deviation from the <001> orientation within 3° exceeds the aforementioned range, there is a problem of difficult magnetization.

[0096] For a method of manufacturing a grain-oriented electrical steel sheet according to another embodiment of the present invention, the method of manufacturing a grain-oriented electrical steel sheet according to another embodiment of the present invention may include: a step of hot-rolling a slab to manufacture a hot-rolled steel sheet; a step of pre-rolling the hot-rolled steel sheet to manufacture a pre-rolled sheet; a step of annealing the pre-rolled sheet; a step of cold-rolling the annealed pre-rolled sheet to manufacture a cold-rolled steel sheet; a step of performing primary recrystallization annealing on the cold-rolled steel sheet; and a step of performing secondary recrystallization annealing on the cold-rolled steel sheet after primary recrystallization annealing.

[0097] First, the slab can be hot-rolled to manufacture a hot-rolled steel sheet. Regarding the alloy components of the slab, there are relevant descriptions of the alloy components of existing grain-oriented electrical steel sheets, so repeated descriptions are omitted. Specifically, in terms of weight %, the slab contains Si: 0.1 to 6.5 wt%, Al: 0.001 to 6.5 wt%, Mn: 0.01 to 20 wt%, C: 0.0010 to 0.0150 wt%, and contains one or more of N, S, Ti, and their contents are 0.0003 to 0.001 wt% respectively, and the balance contains Fe and inevitable impurities.

[0098] Returning to the description of the manufacturing method, in one embodiment, the step of hot-rolling the slab to manufacture a hot-rolled steel sheet may include a step of heating the slab. Specifically, when heating the slab, it can be heated to below 1250 °C. Thus, according to the stoichiometric relationship of dissolved aluminum (Al) and nitrogen (N), manganese (Mn) and sulfur (S), the precipitates of aluminum nitride or manganese sulfide can be made to partially melt or completely melt.

[0099] In one embodiment, the slab can be hot-rolled to manufacture a hot-rolled steel sheet.

[0100] In one embodiment, the step of forming the slab into a hot-rolled steel sheet may include a rough rolling step, a finish rolling step, and a coiling step. Specifically, the step of forming the slab into a hot-rolled steel sheet may sequentially perform the rough rolling step, the finish rolling step, and the coiling step.

[0101] In one embodiment, for the rough rolling step, the heated slab can be rolled to a thickness of 50 to 70 mm. In one embodiment, the rough rolling step can be performed in a temperature range of 950 to 1100 °C.

[0102] In one embodiment, for the finish rolling step, the rough-rolled bar can be rolled into a thickness of 2.0 to 4.0 mm. In one embodiment, the finish rolling step can be carried out in a temperature range of 800 to 1000 °C.

[0103] In one embodiment, the hot-rolled steel sheet that has undergone the finish rolling step can be coiled. In one embodiment, the coiling step can be carried out in a temperature range of 600 to 800 °C. Specifically, the temperature range can be a temperature range of 650 to 750 °C.

[0104] If the upper limit value of the temperature range is exceeded, the fraction of Gaussian grains after annealing increases, but cracks in the side edge portion of the steel sheet increase, which may lead to poor productivity, the precipitates and the fine microstructure become coarse, and there is a problem that good and stable magnetism cannot be obtained. If the lower limit value of the temperature range is exceeded, the precipitates and the surface grain size are fine, and after the subsequent preliminary rolling step and the preliminary rolling plate annealing step, there is a problem that the effect of increasing the Gaussian texture fraction is reduced.

[0105] In one embodiment, the thickness of the hot-rolled steel sheet can be 1.0 to 4.0 mm. Specifically, the thickness of the hot-rolled steel sheet can be 1.5 to 3.0 mm.

[0106] In one embodiment, the step of subjecting the hot-rolled steel sheet to preliminary rolling to manufacture a preliminary rolling plate is a step of further rolling the hot-rolled steel sheet that has undergone the coiling step, so as to further increase the fraction of the Gaussian structure after annealing. The Gaussian structure grows in the subsequent primary recrystallization annealing and secondary recrystallization annealing steps, so that the orientation of the secondary recrystallization in the finally manufactured grain-oriented electrical steel sheet can be more precisely arranged.

[0107] In one embodiment, the preliminary rolling step can be carried out at a temperature within a range of 0.4Tc to 0.6Tc °C of the temperature of the steel sheet before preliminary rolling. The Tc represents the coiling temperature [°C]. If the upper limit value of the steel sheet temperature is exceeded, the fraction of Gaussian grains increases, but there are problems with productivity and temperature control, and if the lower limit value of the steel sheet temperature is exceeded, there is a problem that it is difficult to obtain the preliminary rolling effect. Specifically, the preliminary rolling step can be carried out at a temperature within a range of 260 to 450 °C, more specifically 300 to 400 °C, of the temperature of the steel sheet before preliminary rolling.

[0108] In one embodiment, the preliminary rolling step can be carried out at a reduction ratio of 10 to 40%. Specifically, the reduction ratio can be 15 to 35%. More specifically, the reduction ratio can be 20 to 30%.

[0109] If the reduction rate exceeds the upper limit value, the fraction of Gaussian grains after annealing increases, but cracks in the side edge portion of the steel sheet increase, resulting in a problem of deteriorated productivity. If the reduction rate exceeds the lower limit value, there is a problem that it is difficult to obtain the pre-rolling effect.

[0110] The pre-rolling step can be performed one or more times, and the thickness of the pre-rolled sheet after the pre-rolling step can be 1.5 to 3.0 mm.

[0111] In one embodiment, the step of annealing the pre-rolled sheet can be performed within a predetermined range of soaking temperature and soaking time. In one embodiment, the step of annealing the pre-rolled sheet can be performed within a soaking temperature range of 800 to 1100 °C. In one embodiment, the step of annealing the pre-rolled sheet can be performed within a soaking time range of 100 to 300 seconds.

[0112] Through the aforementioned steps of manufacturing the pre-rolled sheet and the step of annealing the pre-rolled sheet, it can be confirmed that the fraction of Gaussian grains increases. Specifically, after the step of annealing the pre-rolled sheet, among the grains of the annealed pre-rolled sheet, the volume fraction of the grains forming an angle of 15° or less with the Gaussian structure can increase by 4 to 10% within the aforementioned reduction rate range.

[0113] The step of cold-rolling the annealed pre-rolled sheet to manufacture a cold-rolled steel sheet can be performed by single cold-rolling or two or more cold-rollings including intermediate annealing. In one embodiment, the step of cold-rolling the annealed pre-rolled sheet to manufacture a cold-rolled steel sheet can be performed at a reduction rate of 85 to 95%.

[0114] If the upper limit value of the reduction rate is exceeded, the fraction of the Gaussian structure in the grains generated after single annealing decreases, and there may be a problem of deteriorated magnetic properties. If the lower limit value of the reduction rate is exceeded, an appropriate steel sheet thickness cannot be ensured, or the reduction rate needs to be increased in the hot-rolling step and the pre-rolling step, and productivity and magnetic properties may deteriorate. By performing cold-rolling within the aforementioned reduction rate range, a cold-rolled steel sheet with a thickness of 0.1 to 0.3 mm can be manufactured.

[0115] In one embodiment, the step of cold-rolling the annealed pre-rolled sheet to manufacture a cold-rolled steel sheet can roll a steel sheet with a temperature of 0.2Tc to 0.4Tc °C before rolling. The Tc represents the coiling temperature [°C]. If the upper limit of the steel sheet temperature is exceeded, the subsequent fraction of Gaussian grains decreases, and if the lower limit of the steel sheet temperature is exceeded, there is a problem that it is difficult to obtain the pre-rolling effect. Specifically, the step of cold-rolling the annealed pre-rolled sheet to manufacture a cold-rolled sheet can be performed at 130 to 300 °C, more specifically at 150 to 200 °C.

[0116] In one embodiment, the method for manufacturing an oriented electrical steel sheet may satisfy the following Formula 3.

[0117] <Formula 3>

[0118] 100 ≤ T b - T a ≤ 300

[0119] In the above Formula 3, T a represents the temperature at which cold rolling is performed, and T b represents the temperature at which preliminary rolling is performed.

[0120] In one embodiment, during the step of performing primary recrystallization annealing on the cold-rolled steel sheet, primary recrystallization with Goss grain nucleation occurs. The primary recrystallization annealing step may include a step of decarburizing and nitriding the cold-rolled steel sheet.

[0121] In one embodiment, for decarburization, the step of performing primary recrystallization annealing on the cold-rolled steel sheet may be carried out in a temperature range of 800 to 950 °C. If it exceeds the upper limit value of the temperature range, the recrystallized grains grow coarsely, the driving force for crystal growth decreases, and there is a problem that stable secondary recrystallization will not be formed.

[0122] In one embodiment, for decarburization, the step of performing primary recrystallization annealing on the cold-rolled steel sheet may be carried out at a dew point temperature of 50 to 70 °C. In one embodiment, the primary recrystallization annealing step may be carried out within 5 minutes.

[0123] In one embodiment, the step of performing primary recrystallization annealing on the cold-rolled steel sheet may include a step of decarburizing and nitriding the cold-rolled steel sheet. The decarburization step and the nitriding step may be carried out without regard to order. For example, the nitriding step may be carried out after the decarburization step or the decarburization step may be carried out after the nitriding step.

[0124] In one embodiment, it may include a step of simultaneously performing decarburization annealing and nitriding treatment on the cold-rolled steel sheet obtained by cold rolling to achieve primary recrystallization. Specifically, the decarburization step and the nitriding step may be carried out simultaneously.

[0125] In one embodiment, the decarburization step may be carried out in an environment of hydrogen, nitrogen, or a mixed gas thereof. In the decarburization step, decarburization may be carried out until C is less than 0.005 wt%. More specifically, decarburization may be carried out until C is less than 0.003 wt%.

[0126] The nitriding step is intended to nitride the steel sheet, which is a step of introducing nitrogen ions into the steel sheet and a step of precipitating precipitates such as (Al, Si, Mn)N or AlN that serve as grain growth inhibitors. Through the nitriding step, the nitrogen in the grain-oriented electrical steel sheet can be nitrided to less than 0.005%. Specifically, the nitriding step can be carried out in an environment containing ammonia gas.

[0127] In one embodiment, after the primary recrystallization annealing step, an annealing release agent can be coated on the steel sheet. For example, as the annealing release agent, an annealing release agent mainly composed of MgO or an annealing release agent mainly composed of alumina can be used. The annealing release agent is well-known, so detailed description is omitted.

[0128] In one embodiment, the step of performing secondary recrystallization annealing on the cold-rolled steel sheet after primary recrystallization annealing is to form a Goss texture through secondary recrystallization and to form a vitreous coating film through the reaction of the oxide layer formed during primary recrystallization annealing with MgO, thereby imparting insulation and removing impurities that affect magnetic properties.

[0129] In one embodiment, the secondary recrystallization annealing step can include a heating-up step and a soaking step. Specifically, the secondary recrystallization annealing step can include a heating-up step before secondary recrystallization occurs. The heating-up step can be carried out while maintaining in nitrogen gas, hydrogen gas, or a mixed gas thereof to protect the nitrides that serve as grain growth inhibitors, so that secondary recrystallization develops well.

[0130] In one embodiment, in the secondary recrystallization annealing step, the heating-up step can be carried out within a heating-up rate range of 3 to 6 °C / hour.

[0131] If it exceeds the upper limit value of the heating-up rate range, there is a problem that the effect of increasing the aggregation degree of the Goss texture and the effect of reducing the temperature deviation of the steel sheet cannot be exerted. If it exceeds the lower limit value of the heating-up rate range, there is a problem of deteriorated productivity.

[0132] In one embodiment, for the secondary recrystallization annealing step, after the secondary recrystallization is completed, it can include a soaking step. For the soaking step, for example, impurities can be removed by maintaining in a 100% hydrogen gas environment for a long time.

[0133] In one embodiment, the secondary recrystallization annealing step can be carried out by a bottom direct heating method. Specifically, for the secondary recrystallization annealing, it can include a step of applying additional heat to the bottom of the coiled sheet through a heating element, and the heating element is specifically a resistance heating element.

[0134] The heating element is disposed at the bottom of the coiled sheet. By increasing the heat flowing into the bottom of the coiled sheet, the temperature deviation of the coiled sheet during heat treatment can be reduced. The heating element can be controlled to be the same as the heat mode of the annealing furnace, or can be controlled using an independent heat mode.

[0135] The secondary recrystallization annealing step can be carried out in any one of a continuous annealing furnace or a batch annealing furnace. Specifically, the secondary recrystallization annealing step can be carried out in a batch annealing furnace.

[0136] Specific embodiments of the present invention will be described below. However, the following embodiments are only specific embodiments of the present invention, and the present invention is not limited to the following embodiments.

[0137] <Experimental Example 1>

[0138] A steel billet is prepared. By weight%, the steel billet contains Si: 3.3%, C: 0.055%, Mn: 0.08%, Al: 0.029%, N: 0.004%, Sb: 0.02%, Sn: 0.05%, Cr: 0.09% and P: 0.028%, and the balance is composed of Fe and other unavoidably mixed impurities. After heating the steel billet at 1150 °C, a hot-rolled steel sheet is manufactured by performing hot rolling and pre-rolling.

[0139] At this time, the thickness, coiling temperature, and pre-rolling conditions of the hot-rolled steel sheet are changed to different conditions as shown in Table 1 below.

[0140] The pre-rolled annealed sheet is cold-rolled to a thickness of 0.15 to 0.23 mm, and then primary recrystallization annealing is carried out under the conditions of a dew point temperature of 60 °C and a temperature of 850 °C, and secondary recrystallization annealing is carried out under the conditions of a heating rate of 3 to 6 °C / hour and a temperature of 1200 °C.

[0141] At this time, the heating rate of the secondary recrystallization annealing and the usage conditions of the bottom heating element are changed to different conditions.

[0142] Then, after removing the coating on the surface of the steel sheet using a hydrochloric acid solution, the W / L (W: diameter in the TD direction, L: diameter in the RD direction) ratio of the grains is measured, and the angle between the grains and the {110}<001> orientation is measured using an X-ray Laue analysis device.

[0143] In Table 1 below, the pre-rolling temperature refers to the temperature of the steel sheet before the pre-rolling step, and the cold-rolling temperature refers to the temperature of the steel sheet before cold-rolling.

[0144]

Table 1

[0145]

[0146] As can be confirmed from Table 1 above, by controlling the coiling temperature within the scope of the present invention, performing pre-rolling within the scope of the present invention after hot rolling, and having the heating rate during secondary recrystallization within the scope of the present invention, the use of a bottom heating element can improve the grain size distribution and the Goss orientation degree. The present invention can be implemented in various different ways and is not limited to the above-described embodiments and / or examples. Those of ordinary skill in the technical field to which the present invention pertains can understand that the present invention can be implemented in other specific ways without changing the technical idea or essential features of the present invention. Therefore, it should be understood that the above-described embodiments and / or examples are exemplary in all aspects and not restrictive.

Claims

1. An oriented electrical steel sheet, wherein the size of grains having a {110}<001> orientation satisfies the following formula 1, the area fraction of the grain diameter of grains with an angle of deviation from the <001> orientation within 3° is 60% or more, <Formula 1> W / L ≤ 1.5 In the above formula 1, W represents the diameter in the TD direction (the width direction of the secondary recrystallized grains), and L represents the diameter in the RD direction (the length direction of the secondary recrystallized grains).

2. The oriented electrical steel sheet according to claim 1, wherein the oriented electrical steel sheet satisfies the following formula 2, <Formula 2> α × β × γ ≤ 20 ° In the above formula 2, α represents the angle difference between the {110}<001> orientation and the ND axis, β represents the angle difference between the {110}<001> orientation and the TD axis, and γ represents the angle difference between the {110}<001> orientation and the RD axis.

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

4. A method for manufacturing an oriented electrical steel sheet, comprising: a step of hot rolling a slab to manufacture a hot rolled steel sheet; a step of pre-rolling the hot rolled steel sheet with a reduction ratio of 10 to 40% to manufacture a pre-rolled sheet; a step of annealing the pre-rolled sheet; a step of cold rolling the annealed pre-rolled sheet to manufacture a cold rolled steel sheet; a step of performing primary recrystallization annealing on the cold rolled steel sheet; and a step of performing secondary recrystallization annealing on the cold rolled steel sheet after primary recrystallization annealing, the hot rolling step includes a step of coiling the slab, in the coiling step, the coiling temperature is 600 to 800 °C, the secondary recrystallization annealing step is performed in a temperature range of 1000 to 1200 °C, the heating rate of secondary recrystallization is 3 to 6 °C / hour, and a bottom direct heating method is adopted, in the secondary recrystallized grains based on the secondary recrystallization annealing, the size of grains having a {110}<001> orientation satisfies the following formula 1, the area fraction of the grain diameter of grains with an angle of deviation from the <001> orientation within 3° is 60% or more, <Formula 1> W / L ≤ 1.5 In the above formula 1, W represents the diameter in the TD direction (the width direction of the secondary recrystallized grains), and L represents the diameter in the RD direction (the length direction of the secondary recrystallized grains).

5. The method for manufacturing an oriented electrical steel sheet according to claim 4, wherein in the step of manufacturing the pre-rolled sheet, the temperature of the steel sheet before pre-rolling is 0.4Tc to 0.6Tc °C, wherein Tc represents the coiling temperature [°C].

6. The method for manufacturing an oriented electrical steel sheet according to claim 4, wherein The grain-oriented electrical steel sheet satisfies the following formula (3). <Formula 3> 100 ≤ T b -T a ≤ 300 In the above formula (3), T a represents the temperature for cold rolling, and T b represents the temperature for preliminary rolling.

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

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

9. The method for manufacturing a grain-oriented electrical steel sheet according to claim 4, wherein the step of annealing the pre-rolled sheet is carried out in a soaking temperature range of 700 to 1100 °C.

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

11. The method for manufacturing a grain-oriented electrical steel sheet according to claim 4, wherein the step of manufacturing the cold-rolled steel sheet is carried out in a temperature range of 0.2Tc to 0.4Tc °C for the steel sheet before cold rolling, wherein Tc represents the coiling temperature [°C].

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