KR101707451B1 - Grain oriented electrical steel sheet and method for manufacturing the same - Google Patents

Abstract

According to the present invention, a directional grater comprises: 2.0-4.5 wt% of silicon (Si); 0.005 or less wt% of carbon (excluding 0 wt%); 0.015-0.04 wt% of aluminum (Al); 0.01-0.01 wt% of nitrogen (N); 0.01 or less wt% (excluding 0 wt%); 0.04-0.15 wt% of manganese (Mn); and the rest of ferrum (Fe) and other inevitable impurities, which meets Equation 1 below, and where a diameter of an average grain is 3 cm or less, and an area fraction of grain with 1 cm or less of diameter is 10% or less. [Equation 1] [Mn] x [S] <=0.0004 (where [Mn] and [S] represent Mn and S content (wt%), respectively).

Description

TECHNICAL FIELD [0001] The present invention relates to a grain-oriented electrical steel sheet and a method of manufacturing the same. BACKGROUND OF THE INVENTION [0002]

To a directional electric steel sheet and a manufacturing method thereof.

The grain-oriented electrical steel sheet suppresses the growth of the primary recrystallized grains and selectively grow crystal grains of {110} < 001 > orientation (hereinafter referred to as Goss orientation) in the final annealing process among the crystal grains whose growth is suppressed, So as to display the characteristic. The second recrystallization is referred to as secondary recrystallization. In order to perform the second recrystallization, fine inhibitors such as MnS and AlN are uniformly dispersed in the steel sheet before the final high-temperature annealing, so that 1 The second recrystallized grains can be grown while having an accurate Goss orientation while suppressing the growth of the secondary recrystallized grains, thereby achieving an increase in magnetic flux density and an iron loss, which are excellent magnetic properties.

In order to effectively control the secondary recrystallization, the following conditions must be met in order to effectively suppress the growth of the primary recrystallized phase until the secondary recrystallization occurs. First, the inhibitors should be uniformly distributed in a sufficient amount and in an appropriate size, and second, the inhibitor must be thermally stable to a high temperature at which the secondary recrystallization starts to take place, so that it is not easily decomposed. As these inhibitors grow or disappear, a secondary recrystallization starts to occur in a temperature range where the power to inhibit the growth of the primary recrystallized grains is lost. At this time, even secondary recrystallization occurs throughout the entire steel sheet in a relatively short time.

So far inhibitors such as AlN, MnS, MnSe and CuS have proven to be effective as grain growth inhibitors, and these inhibitors have been found to be effective under conditions that can inhibit grain growth, such as slab heating temperature, hot rolling temperature and coiling temperature, Conditions, cold rolling rate, primary recrystallization annealing, and final high-temperature annealing are known.

MnS and AlN contained in the slab are reheated at a high temperature for a long period of time in the production of a conventional directional electric steel sheet produced by steelmaking, slab manufacturing, slab heating, hot rolling, preliminary annealing, decarburization, annealing separator application, The slab should be heated to a high temperature in order to achieve this, since it is made of a precipitate having an appropriate size and distribution during the cooling process after hot rolling. When the slab is heated at a high temperature for a long time, the amount of heat to be used is increased, resulting in an increase in manufacturing cost. In addition, since the surface of the slab is melted and flows down, the maintenance cost of the heating furnace is increased and the service life of the heating furnace is shortened. Particularly, when the main phase structure of the slab grows to a great extent by heating at high temperature for a long time, cracks are generated in the width direction of the plate in a subsequent hot rolling step, thereby significantly reducing the slump failure rate.

Therefore, if a directional electric steel sheet can be manufactured by lowering the reheating temperature of the slab, it may have a very beneficial effect in terms of the manufacturing cost and the error rate. For this purpose, the slab heating is carried out in a temperature range in which the AlN serving as an inhibitor of the secondary recrystallization is partially solvated. If the slab is heated only to the temperature at which it is partially solvated, there will be a large difference in the size distribution between the precipitate in the casting process and the precipitate in the hot rolling. In order to use this method, an additional process for producing a nitride-based inhibitor is required after slab heating.

What is important in the process of manufacturing an electrical steel sheet with a low slab reheating temperature is the formation of uniform primary recrystallized microstructure. Sn, Sb and P act as intergranular segregation elements and serve as an auxiliary inhibitor to regulate grain growth in the decarburization annealing process, which helps to form an appropriate size and uniform size distribution of the primary recrystallized grains. As a method for further improving the magnetic properties of the grain - oriented electrical steel sheet, Sn, Sb and P were added in an appropriate amount range to implement such means. Segregated elements such as Sn and Sb have a strong intergranular segregation effect, which has the effect of suppressing the coarsening which increases the primary recrystallized grain size distribution during the decarburization annealing process as the component content increases.

In order to make the size distribution of the primary recrystallized grains uniform, primary recrystallization annealing conditions are important. In addition, adjustment of the grain growth restraining force due to the fine precipitates present in the pre-annealing step is an important factor. The volume fraction, size, interfacial energy and dispersion state of the fine precipitates prior to the primary recrystallization annealing can affect the grain growth inhibiting ability.

It is important to make fine and uniform precipitates before the first recrystallization since the slab is subjected to secondary recrystallization by utilizing the micro precipitates formed before the primary recrystallization in the high temperature heating method of 1200 DEG C or more. There has been proposed a method of controlling the production conditions by using AlR, which is obtained by subtracting N equivalents from acid-soluble Al (hereinafter referred to as sAl), so that fine precipitates before the first recrystallization can be uniformly and finely precipitated. In addition, a method of controlling the production conditions for AlN composite fine precipitation using Cu has been proposed.

In the slab low-temperature heating method of less than 1200 ° C, it is important to eliminate the influence of the non-uniform precipitate formed before the primary recrystallization as an inhibitor. Although these are used for the formation of primary recrystallized microstructure, the secondary recrystallization is controlled by fine precipitates formed through the primary recrystallization process or subsequent processes. The annealing conditions of hot - rolled sheets were suggested according to acid availability Al and N. In addition, when Ti is added, annealing temperature and nitriding amount of the hot-rolled sheet are specified in consideration of TiN formation.
BACKGROUND ART 1: Japanese Laid-Open Patent Publication No. 2015-196851
BACKGROUND ART 2: Japanese Patent Publication No. 5780378

One embodiment of the present invention is to provide a directional electrical steel sheet.

Yet another embodiment of the present invention is to provide a method of manufacturing a grain-oriented electrical steel sheet.

The grain-oriented electrical steel sheet according to one embodiment of the present invention comprises 2.0 to 4.5% Si, 0.005% or less (excluding 0%), 0.015 to 0.04% Al, 0.01 to 0.1% , S: not more than 0.01% (excluding 0%), Mn: 0.04 to 0.15%, and the balance Fe and other unavoidable impurities, satisfies the following formula 1 and has an average crystal grain diameter of 3 cm or less, Is 10% or less.

[Formula 1]

[Mn] x [S]? 0.0004

([Mn] and [S] in the formula 1 represent the content (% by weight) of Mn and S, respectively.)

The following expression (2) can be satisfied.

[Formula 2]

[Mn] + 14 x [S] < 0.18

([Mn] and [S] in the formula 2 represent the contents (wt%) of Mn and S, respectively).

0.01 to 0.05% of Sb, 0.03 to 0.12% of Sn, 0.02 to 0.15% of Cr and 0.01 to 0.05% of P by weight.

0.01 to 0.2% of Cu and 0.01 to 0.05% of Mo, in terms of% by weight.

A method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention includes: 2.0 to 4.5% of Si; 0.03 to 0.09% of C; 0.015 to 0.04% of Al; 0.006% (Excluding 0%), S: not more than 0.01% (excluding 0%), Mn: 0.04 to 0.15%, and the balance Fe and other unavoidable impurities. Hot rolling the slab to produce a hot rolled sheet; Annealing the hot rolled sheet to an annealing temperature (T) satisfying the following formula (3); Cold-rolling the hot-rolled sheet to produce a cold-rolled sheet; A first recrystallization annealing of the cold rolled sheet; And secondary recrystallization annealing the electric steel sheet after the primary recrystallization annealing has been completed.

[Formula 1]

[Mn] x [S]? 0.0004

([Mn] and [S] in the formula 1 represent the content (% by weight) of Mn and S, respectively.)

[Formula 3]

1100-20 x [Al] / [N] <T <1200-20 x [Al] / [N]

([Al] and [N] in the formula (3) represent the content (% by weight) of Al and N, respectively, and T represents the annealing temperature (占 폚) in the step of annealing the hot-

The slab can satisfy the following expression (2).

[Formula 2]

[Mn] + 14 x [S] < 0.18

([Mn] and [S] in the formula 2 represent the contents (wt%) of Mn and S, respectively).

The slab may further contain 0.01 to 0.05% of Sb, 0.03 to 0.12% of Sn, 0.02 to 0.15% of Cr and 0.01 to 0.05% of P, by weight.

The slab may further contain 0.01 to 0.2% of Cu and 0.01 to 0.05% of Mo in terms of% by weight.

Cooling the hot rolled plate after the step of annealing the hot rolled sheet and cooling at a cooling rate of from 10 占 폚 / sec to 300 占 sec / sec from a temperature of 700 to 850 占 폚 to 300 占 폚.

In the step of heating the slab, the slab may be heated to 1050 to 1200 ° C.

The step of annealing the hot-rolled sheet may include a step of annealing at an annealing temperature (T) satisfying the formula (3) for 5 to 100 seconds and a step of annealing at a temperature lower than the annealing temperature (T) by 10 to 100 占 폚 for 30 to 300 seconds have.

In the primary recrystallization annealing step, decarburization and sedimentation can occur simultaneously or separately.

After the primary recrystallization annealing step, the average primary recrystallized grain diameter may be 15 to 25 占 퐉.

When the microstructure is observed at 1/4 thickness of the primary recrystallization plate after the primary recrystallization annealing step, the crystal grain area fraction of 40 占 퐉 or more can be 30% or less of the total area.

The produced steel sheet has an average crystal grain diameter of 3 cm or less and an area fraction of crystal grains having a diameter of 1 cm or less may be 10% or less.

The directional electrical steel sheet according to an embodiment of the present invention allows the secondary recrystallization to uniformly grow throughout the product, so that the magnetic properties are excellent and the product characteristics are uniform.

In addition, the method for producing a grain-oriented electrical steel sheet according to an embodiment of the present invention limits the components of Mn and S according to the reheating temperature and restricts the annealing conditions of the hot-rolled steel sheet to control the non-uniformity of precipitates before the first recrystallization The formation of heterogeneous coarse grains in the microstructure of the first re-crystal plate is suppressed, and the Exact Goss orientation allows the secondary recrystallization to uniformly grow throughout the product, so that the magnetic properties are excellent, Steel sheet can be manufactured.

The terms first, second and third, etc. are used to describe various portions, components, regions, layers and / or sections, but are not limited thereto. These terms are only used to distinguish any moiety, element, region, layer or section from another moiety, moiety, region, layer or section. Thus, a first portion, component, region, layer or section described below may be referred to as a second portion, component, region, layer or section without departing from the scope of the present invention.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms as used herein include plural forms as long as the phrases do not expressly express the opposite meaning thereto. Means that a particular feature, region, integer, step, operation, element and / or component is specified and that the presence or absence of other features, regions, integers, steps, operations, elements, and / It does not exclude addition.

When referring to a portion as being "on" or "on" another portion, it may be directly on or over another portion, or may involve another portion therebetween. In contrast, when referring to a part being "directly above" another part, no other part is interposed therebetween.

Unless otherwise defined, all terms including technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Commonly used predefined terms are further interpreted as having a meaning consistent with the relevant technical literature and the present disclosure, and are not to be construed as ideal or very formal meanings unless defined otherwise.

Unless otherwise stated,% means% by weight, and 1 ppm is 0.0001% by weight.

Hereinafter, embodiments of the present invention will be described in detail so that those skilled in the art can easily carry out the present invention. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

The grain-oriented electrical steel sheet according to one embodiment of the present invention comprises 2.0 to 4.5% Si, 0.005% or less (excluding 0%), 0.015 to 0.04% Al, 0.01 to 0.1% , S: not more than 0.01% (excluding 0%), Mn: 0.04 to 0.15%, and the balance Fe and other unavoidable impurities.

First, the reason for limiting the components of the grain-oriented electrical steel sheet will be described.

[Si: 2.0 to 4.5% by weight]

Silicon (Si) plays a role in lowering the core loss, that is, the iron loss, by increasing the resistivity of the oriented electrical steel sheet material. When the Si content is less than 2.0 wt%, the resistivity decreases and the iron loss deteriorates. When the Si content exceeds 4.5 wt%, the brittleness of the steel increases, the toughness decreases, the plate fracture occurrence rate increases during the rolling process, A load is applied to the cold rolling operation, the temperature falls below the plate temperature required for pass aging during cold rolling, and the formation of the secondary recrystallization becomes unstable. Therefore, Si is limited to 2.0 to 4.5% by weight.

[C: 0.005 wt% or less]

Carbon (C) is an element which induces the formation of austenite phase, and ferrite-austenite phase transformation is activated during the hot rolling process as the C content in the slab increases, and the elongated hot rolled steel strip structure formed during the hot rolling process is increased, The ferrite grain boundary is suppressed during the hot-rolled sheet annealing process. In addition, as the C content in the slab increases, the texture of the hot rolled steel strip, which is higher in strength than that of the ferrite steel, is increased and the initial texture of the hot rolled steel sheet is further reduced. . It is considered that the effect of pass aging during cold rolling becomes large due to the residual C existing in the steel sheet after annealing the hot-rolled sheet, thereby increasing the goss fraction in the primary recrystallized grains. Therefore, the larger the C content, the longer the decarburization annealing time in the decarburized annealing anneal, and the deterioration of the productivity. If the decarburization at the initial stage of heating is insufficient, the primary recrystallization grains are unevenly distributed to unstable the secondary recrystallization. Also, since magnetic properties can be deviated due to magnetic aging phenomenon, the C content in the slab is limited to 0.03 to 0.09 wt%. The C present in the slab is removed by decarburization in the manufacturing process, and the C content in the final produced steel sheet may be 0.005 wt% or less.

[Al: 0.015 to 0.04% by weight]

Aluminum (Al) binds with N and precipitates into AlN. However, N and AlN type nitrides, which are fine precipitates (Al, Si, Mn), are formed in the annealing for decarburization and sedimentation simultaneously. More than a certain amount of solid solution Al is needed. If the content is less than 0.015% by weight, the number and the volume fraction of the precipitates to be formed are low and the effect of inhibiting the growth of grain growth is insufficient. If the content is too high, the precipitates grow coarser and the effect of inhibiting grain growth is deteriorated. Therefore, Al is added in an amount of 0.015 to 0.04% by weight.

[N: 0.001 to 0.01% by weight]

Nitrogen (N) is an element that reacts with Al or the like to refine the crystal grains. When these elements are appropriately distributed, as described above, it is possible to appropriately fine-structure the structure after cold rolling to ensure proper primary recrystallization grain size. However, if the content is excessive, the primary recrystallization grain becomes excessively fine, As a result, due to the fine crystal grains, the driving force causing crystal grain growth during the secondary recrystallization becomes large, so that it can grow to the crystal grains of an undesirable orientation. If N is contained in an amount exceeding 0.01% by weight, the secondary recrystallization starting temperature rises and the magnetic properties deteriorate. Therefore, N is set at 0.01 wt% or less. When the steeping treatment for increasing the nitrogen amount is performed between the cold rolling and the secondary recrystallization annealing, it is sufficient that the content of N in the slab is 0.006% by weight or less.

[S: not more than 0.01% by weight]

Sulfur (S) is preferably one of the inevitable impurities contained at the time of steelmaking, although it is preferable that the sulfur (S) is not contained as an element having a high solidification temperature during hot rolling and a high segregation. Also, since S forms MnS and affects the primary recrystallized grain size, the content of S is preferably limited to 0.01% by weight or less.

[Mn: 0.04 to 0.15% by weight]

Manganese (Mn) also has the effect of reducing the iron loss by increasing the resistivity as Si. It reacts with the nitrogen introduced by the nitriding treatment together with Si to form precipitates of N (Al, Si, Mn) It is an important element for suppressing the growth of sizing and causing secondary recrystallization. However, when added in an amount exceeding 0.15% by weight, a large amount of (Fe, Mn) and Mn oxide are formed on the surface of the steel sheet in addition to Fe ₂ SiO ₄ to prevent formation of a base coat formed during high temperature annealing, The size of the primary recrystallized grains becomes uneven due to the nonuniformity of the phase transformation between the ferrite and the austenite in the process, and as a result, the secondary recrystallization becomes unstable. Therefore, the content of Mn is 0.15 wt% or less.

[Sb: 0.01 to 0.05% by weight]

The antimony (Sb) has the effect of increasing the grain nuclei in the goss orientation generated during the cold rolling process and improving the fraction of the grains having the goss orientation in the primary recrystallized texture. In addition, the secondary recrystallization starting temperature of the grains having a goss aggregate structure is increased when segregating in the primary recrystallization grain boundaries and performing secondary recrystallization and high temperature annealing, so that the secondary recrystallization microstructure excellent in the degree of integration can be obtained and the magnetic flux density is increased. When Sb is further contained, if it is contained in an amount of less than 0.01% by weight, the action thereof is difficult to be exerted properly. If it exceeds 0.05% by weight, the size of the primary recrystallized grains becomes too small to lower the secondary recrystallization starting temperature, Or the inhibitory effect on the grain growth becomes too large, so that the secondary recrystallization may not be formed. Therefore, when Sb is added to the steel sheet, Sb is in the range of 0.01 to 0.05% by weight.

[Sn: 0.03 to 0.12% by weight]

Tin (Sn) is known as a crystal growth inhibitor since it is an element that interferes with the movement of grain boundaries as a grain boundary segregation element. In addition, by increasing the grain fraction of the Goss orientation in the primary recrystallized texture, the size of the secondary recrystallized microstructure is reduced because the number of the Goss bearing nuclei growing in the secondary recrystallized texture structure is decreased. As the grain size becomes smaller, The iron loss of the final product is reduced. On the other hand, Sn plays an important role in suppressing grain growth through grain segregation in grain boundaries. This not only improves the suppressing effect of suppressing the crystal growth driving force of the microcrystallized first recrystallized microstructure, (Al, Si, Mn) during the annealing process, particles causing N grain growth inhibiting effect such as N and AlN are coarsened, thereby preventing the grain growth growth inhibiting ability from being reduced. If the content of Sn is more than 0.12% by weight, the grain growth inhibiting ability is excessively increased and the grain growth driving force is increased to 1 It is necessary to perform the decarburization annealing at a low temperature because it is necessary to reduce the grain size of the recrystallized microstructure. As a result, a proper surface can not be secured because it can not be controlled by an appropriate oxide layer. In addition, in view of mechanical properties, the brittleness is increased due to excessive segregation of grain boundary segregation elements, which may cause plate break during the production process. Therefore, when Sn is added to the steel sheet, the content of Sn is preferably 0.12 wt% .

[Cr: 0.02 to 0.15% by weight]

Addition of chromium (Cr) in an amount in the range of 0.02 to 0.15 wt% as an element promoting oxidation formation suppresses the formation of a dense oxide layer in the surface layer portion and helps to form a fine oxide layer in the depth direction. With addition of Sb and Sn, addition of a Cr content in an appropriate range makes it easier to form a primary recrystallization with excellent uniformity. By adding Cr, decarburization and sedimentation due to the increase of Sb and Sn contents are delayed to overcome the phenomenon that the primary recrystallized grains are uneven, thereby forming primary recrystallized grains having excellent uniformity and enhancing the magnetic properties. According to the content of Sb and Sn, when the Cr content is added in the above range, the internal oxide layer is formed deeper and the rate of decay and decarburization is increased. Therefore, the formation of dense and thin oxide layer due to the addition of Sb and Sn leads to the formation of 1 It is possible to overcome the difficulty in controlling the size and ensuring uniformity of the tea recrystallization. When Cr is added to the steel sheet, the effect is small when the Cr content is less than the lower limit, and when the Cr content is over the upper limit value, the oxide layer is excessively formed and the effect thereof is decreased. It is not preferable.

[P: 0.01 to 0.05% by weight]

Phosphorus (P) is an element that exhibits similar effects to Sn and Sb. It can segregate in the grain boundaries and interfere with grain boundary movement, and at the same time can play an auxiliary role of suppressing grain growth. In the microstructure, {110} There is an effect of improving the organization. When P is added to the steel sheet, if the content of P is less than 0.01% by weight, there is no addition effect. If the content of P is more than 0.05% by weight, the brittleness is increased and the rolling property is greatly deteriorated. .

[Cu: 0.01 to 0.2% by weight]

Cu binds with S and precipitates as CuS. It mainly forms (Mn, Cu) S form by being mixed with MnS, and plays a role of inhibiting grain growth. In addition, as in the case of Mo, Cu causes a large amount of Goss grains having a precise orientation to be formed in the structure of the hot-rolled surface portion, thereby reducing grain size after secondary recrystallization and reducing eddy current loss, The magnetic flux density is also increased because the Goss particles of the magnetic layer grows much. When Cu is added in the steel sheet, if the content is less than 0.01% by weight, the effect is not sufficient. If the content exceeds 0.2% by weight, precipitates grow to a great extent and the effect of inhibiting grain growth is deteriorated.

[Mo: 0.01 to 0.05% by weight]

When molybdenum (Mo) is added during the hot rolling of the grain-oriented electrical steel sheet, Goss grains having a precise orientation are formed in the structure of the hot rolled surface portion, and grains remaining after the first recrystallization heat treatment are left there, . Therefore, after the secondary recrystallization, the crystal grain size decreases and the eddy current loss becomes small, so that the iron loss of the final product decreases, and the magnetic flux density also increases due to the large number of goss particles growing in the correct orientation.

In addition, Mo plays an important role in suppressing grain growth by segregating in grain boundaries as in Sn, and plays a role of controlling the secondary recrystallization so that it occurs at high temperature. Therefore, it plays a role of growing Goss particles of more accurate orientation Thereby increasing the magnetic flux density. Mo is a very effective grain growth inhibiting element because it has a relatively large size of the atom and a very high melting point of 2623 ° C, so that the diffusion rate in iron is low and the segregation effect can be maintained well to a high temperature.

When Mo is added to the steel sheet, when the content of Mo is less than 0.01% by weight, the effect of improving the magnetic property is obtained. However, the effect is insufficient and the effect of improving the degree of integration of the goss texture is small. The effect of improving the magnetic properties is insignificant because the effect of compensating the crystal grain growth inhibiting ability by the particles is small. On the other hand, when the content exceeds 0.05% by weight, the crystal grain growth inhibiting ability is excessively increased and the crystal grain size of the primary recrystallized microstructure must be decreased in order to relatively increase the crystal growth driving force. Therefore, the decarburization annealing must be performed at a low temperature, It can not be controlled by an appropriate oxide layer, so that a good surface can not be obtained. Therefore, the content of Mo is preferably 0.01 wt% to 0.05 wt%.

When the Mn content and S content are contained so as to satisfy the following formula 1, MnS is finely and uniformly precipitated to improve the uniformity of primary and secondary recrystallized grain sizes, resulting in excellent magnetic properties and uniform product characteristics.

[Formula 1]

[Mn] x [S]? 0.0004

([Mn] and [S] in the formula 1 represent the content (% by weight) of Mn and S, respectively.)

More specifically, when the Mn content and the S content are contained so as to satisfy the following formula 2, the magnetic property is excellent and the product characteristics become uniform.

[Formula 2]

[Mn] + 14 x [S] < 0.18

([Mn] and [S] in the formula 2 represent the contents (wt%) of Mn and S, respectively).

In the low temperature slab heating method, the precise Goss orientation has a grain growth advantage and is sufficiently grown during the high temperature annealing time to form a secondary recrystallized grain of 1 cm or more. The secondary recrystallized grains of 1 cm or less are mostly deviated from the exact Goss orientation.

The smaller the secondary recrystallized grain diameter (that is, the grain diameter of the steel sheet), the smaller the iron grain size and the iron loss may be. However, in the case of the grain grain size smaller than 1 cm, the grain size distribution Resulting in a magnetic variation due to an increase in deviation from the nonuniformity and the Gaussian orientation. Therefore, when the grain size fraction of 1 cm or less is 10% or less, the magnetic property and the non-uniformity are improved. Furthermore, by controlling the average crystal grain diameter to 3 cm or less, the magnetic property is excellent and the product characteristics become uniform.

Hereinafter, a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention will be described in detail.

A method of manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention includes: 2.0 to 4.5% of Si; 0.03 to 0.09% of C; 0.015 to 0.04% of Al; 0.006% , S: not more than 0.01% (excluding 0%), Mn: 0.04 to 0.15%, and the balance Fe and other unavoidable impurities; Hot rolling the slab to produce a hot rolled sheet; Annealing the hot rolled sheet to an annealing temperature (T) satisfying the following formula (3); Cold-rolling the hot-rolled sheet to produce a cold-rolled sheet; A first recrystallization annealing of the cold rolled sheet; And secondary recrystallization annealing the electric steel sheet after the primary recrystallization annealing has been completed.

[Formula 1]

[Mn] x [S]? 0.0004

([Mn] and [S] in the formula 1 represent the content (% by weight) of Mn and S, respectively.)

[Formula 3]

1100-20 x [Al] / [N] <T <1200-20 x [Al] / [N]

([Al] and [N] in the formula (3) represent the content (% by weight) of Al and N, respectively, and T represents the annealing temperature (占 폚) in the step of annealing the hot-

First heat the slab. As to the composition of the slab, the reason for limiting the components has been described in the description of the composition of the above-mentioned electric steel sheet, and thus, a duplicate description will be omitted. Specifically, the slab is heated to 1050 to 1200 占 폚. If the heating temperature of the slab is increased, the manufacturing cost of the steel sheet is increased, and the melting of the surface of the slab can repair the heating furnace and shorten the life of the heating furnace. In addition, if the slab is heated to 1200 ° C or lower, the columnar structure of the slab is prevented from being grown to a great extent, thereby preventing cracks from being generated in the width direction of the plate in the subsequent hot rolling process, thereby improving the slip rate. More specifically, the sulav may be heated to 1100 to 1150 캜.

When the heating of the slab is completed, hot rolling is performed. The hot rolling temperature and the cooling temperature are not limited. In one embodiment, hot rolling may be terminated at 950 占 폚 or lower, and the hot rolling may be performed at a temperature of 600 占 폚 or less. A hot rolled sheet having a thickness of 2.0 to 3.5 mm can be produced by hot rolling.

The hot-rolled hot-rolled sheet is subjected to hot-rolled sheet annealing. The annealing temperature (T) at the time of annealing the hot-rolled sheet is adjusted to satisfy the following formula (3).

[Formula 3]

1100-20 x [Al] / [N] <T <1200-20 x [Al] / [N]

([Al] and [N] in the formula (3) represent the content (% by weight) of Al and N, respectively, and T represents the annealing temperature (占 폚) in the step of annealing the hot-

When the above-described formula (3) is satisfied, MnS is finely and uniformly precipitated to improve the uniformity of the primary and secondary recrystallized grain sizes, resulting in excellent magnetic properties and uniform product characteristics. In one embodiment of the present invention, the non-uniformity of the precipitate before the first recrystallization is removed by determining the annealing temperature (T) according to the ratio of [Al] / [N]. The annealing time can be annealed at the annealing temperature (T) for 5 to 100 seconds.

Further, in addition to the annealing step described above, the method may further include a step of annealing at a temperature 10 to 100 deg. C lower than the annealing temperature T for 30 to 300 seconds.

The method may further include the step of cooling the hot rolled sheet after the step of annealing the hot rolled sheet. Specifically, the step of cooling may be performed at a cooling rate of 10 ° C / sec to 300 ° C / sec from a temperature of 700 ° C to 850 ° C to 300 ° C.

Thus, the precipitates are precipitated through annealing of the hot-rolled sheet, and the average diameter of the precipitates is 300 to 3000 Å.

Next, the hot-rolled sheet is cold-rolled to produce a cold-rolled sheet. Cold rolling can be carried out by using a reverse mill or a tandem mill to produce a cold rolled steel sheet having a thickness of 0.1 to 0.5 mm by a plurality of cold rolling methods including one cold rolling, multiple cold rolling or intermediate annealing have. More specifically, a cold rolled sheet having a thickness of 0.15 to 0.35 mm can be produced.

The cold-rolled steel sheet is subjected to primary recrystallization annealing. In the primary recrystallization annealing, decarburization, sedimentation, and primary recrystallization, in which nuclei of the Goss grain are generated, occur. Decarburization and sedimentation may occur at the same time, or sedimentation may occur after decarburization. The sediment can utilize ammonia gas. The carbon in the steel sheet after decarburization may be 0.005 wt% or less, and the nitrogen in the steel sheet after steepening may be 0.01 to 0.1 wt%. The primary recrystallization annealing may be to maintain the cold rolled sheet at a temperature of 800 to 900 DEG C for 30 seconds or more. If the temperature is lower than 800 ° C, sufficient energy for crystal growth may not be provided. If the temperature is lower than 30 seconds, crystal growth may be insufficient and the magnetism may be deteriorated.

The steel sheet subjected to the first recrystallization annealing is coated with an annealing separator containing MgO and subjected to secondary recrystallization annealing. The cracking temperature during the secondary recrystallization annealing may be 900 ° C to 1250 ° C. If the temperature is less than 900 ° C, the gossy crystal grains may not sufficiently grow and the magnetic properties may deteriorate. When the temperature exceeds 1250 ° C, the crystal grains may grow so large that the characteristics of the electric steel sheet may deteriorate.

The purpose of the secondary recrystallization annealing is mainly to remove the impurities that damage the magnetic properties by formation of {110} < 001 > texture by secondary recrystallization, formation of vitreous film by reaction of MgO with oxide layer formed at decarburization . As the final annealing method, the nitride is inhibited by keeping the mixed gas of nitrogen and hydrogen at the temperature rising period before the secondary recrystallization, and the secondary recrystallization is well developed. After completion of the secondary recrystallization, 100% hydrogen It is kept in the atmosphere for a long time to remove impurities.

Hereinafter, the present invention will be described in more detail with reference to examples. However, these embodiments are only for illustrating the present invention, and the present invention is not limited thereto.

Example  One

3.23% by weight of Si, 0.055% by weight of C, 0.028% by weight of P, and the contents of Mn, S and Al / N were varied as shown in Table 1 below and the balance of Fe and other inevitably contained impurities After the steel material was vacuum-melted, an ingot was formed, followed by heating at a temperature of 1200 ° C for 210 minutes, followed by hot rolling to prepare a hot-rolled steel sheet having a thickness of 2.3 mm.

The hot-rolled sheet was subjected to heat treatment at a temperature shown in Table 2 for 30 seconds, followed by further heat treatment at a temperature of 50 占 폚 for 100 seconds, followed by quenching and pickling with water, followed by hot cold rolling once to a thickness of 0.23 mm. The cold-rolled sheet was maintained at a temperature of about 860 ° C in a humid atmosphere of hydrogen and a mixed gas of nitrogen and ammonia for 180 seconds to perform simultaneous decarburization annealing and nitriding annealing so that the carbon content was 50 ppm or less and the nitrogen content was 200 ppm.

This steel sheet was coated with MgO as an annealing separator and finally annealed in a coiled state. In the final annealing, a mixed atmosphere of 25% nitrogen and 75% hydrogen was set up to 1200 ° C., and after reaching 1200 ° C., it was maintained in a 100% hydrogen atmosphere for 10 hours or more. The magnetic properties measured for each condition are shown in Table 2.

Mn (% by weight) S (% by weight) Al (% by weight) N (% by weight) The left hand side of Eq.
[Mn] x [S] The left hand side of Eq.
[Mn] + 14 x [S] division 0.12 0.005 0.021 0.0038 0.0006 0.19 Comparison 1 0.065 0.009 0.0338 0.0048 0.000585 0.191 Comparative material 2 0.055 0.004 0.0289 0.0052 0.00022 0.111 Comparative material 3 0.08 0.003 0.036 0.0075 0.00024 0.122 Comparison 4 0.05 0.005 0.039 0.004 0.00025 0.12 Comparative material 5 0.055 0.008 0.0291 0.0026 0.00044 0.167 Comparative material 6 0.1 0.004 0.025 0.0058 0.0004 0.156 Inventory 1 0.06 0.004 0.0328 0.006 0.00024 0.116 Inventory 2 0.07 0.003 0.036 0.005 0.00021 0.112 Inventory 3 0.08 0.003 0.025 0.003 0.00024 0.122 Invention 4 0.06 0.004 0.0303 0.0027 0.00024 0.116 Invention Article 5 0.1 0.002 0.0335 0.003 0.0002 0.128 Inventions 6

Al / N T (占 폚) Magnetic flux density
(B8, Tesla) Iron loss
(W17 / 50) division 5.5 1050 1.903 0.878 Comparison 1 7 1000 1.89 0.892 Comparative material 2 5.6 1120 1.89 0.93 Comparative material 3 4.8 950 1.87 0.944 Comparison 4 9.8 880 1.882 0.932 Comparative material 5 11.2 1000 1.9 0.893 Comparative material 6 4.3 1080 1.928 0.78 Inventory 1 5.5 1060 1.934 0.752 Inventory 2 7.2 1040 1.935 0.775 Inventory 3 8.3 1020 1.925 0.801 Invention 4 10.5 960 1.93 0.788 Invention Article 5 11.2 940 1.925 0.796 Inventions 6

As shown in Table 1, it can be confirmed that when the hot-rolled sheet is annealed at a temperature satisfying the formula 3 by using the composition satisfying the formula 1, the magnetic property is excellent.

Example  2

3.17% by weight of Si, 0.051% by weight of C, 0.035% by weight of P, and the contents of Mn, S and Al / N were varied as shown in the following Table 3 and the remainder of the components were mixed with Fe and other inevitably contained impurities The ingot was made by vacuum melting the steel material, followed by heating at 1180 ° C for 210 minutes and then hot rolling to produce a hot rolled steel sheet having a thickness of 2.6 mm.

The hot-rolled sheet was subjected to heat treatment at a temperature shown in Table 4 for 30 seconds, followed by further heat treatment at a temperature of 50 占 폚 for 100 seconds, followed by quenching with water and pickling, followed by hot cold rolling once to a thickness of 0.27 mm. The cold-rolled steel sheet was held at a temperature of about 860 ° C in a humid atmosphere of hydrogen and a mixed gas of nitrogen and ammonia for 180 seconds, followed by simultaneous decarburization annealing so as to have a nitrogen content of 200 ppm. As a result of measuring the microstructure of the 1/4 thickness section of the decarburized plate, it was confirmed that the average grain size of the primary recrystallization was 15 to 25 μm and the coarse grain size fraction of 40 μm or more satisfied 30% or less of the total area.

This steel sheet was coated with MgO as an annealing separator and finally annealed in a coiled state. In the final annealing, a mixed atmosphere of 25% nitrogen and 75% hydrogen was set up to 1200 ° C., and after reaching 1200 ° C., it was maintained in a 100% hydrogen atmosphere for 10 hours or more. For each condition, the specimen was etched in a solution of 50% hydrochloric acid to observe the secondary recrystallized grains, and the results are summarized in Table 4 below.

Mn (% by weight) S (% by weight) Al (% by weight) N (% by weight) The left hand side of Eq.
[Mn] x [S] The left hand side of Eq.
[Mn] + 14 x [S] division 0.12 0.008 0.0365 0.0065 0.00096 0.232 Comparison 7 0.048 0.012 0.0386 0.0053 0.000576 0.216 COMPARISON 8 0.093 0.0055 0.031 0.0072 0.000512 0.17 Comparative material 9 0.1 0.0035 0.0281 0.0033 0.00035 0.149 Comparative material 10 0.063 0.0055 0.0337 0.0037 0.000347 0.14 Invention 7 0.095 0.004 0.0275 0.0046 0.00038 0.151 Invention 8 0.09 0.004 0.0295 0.0058 0.00036 0.146 Invention 9

Al / N T (占 폚) Average grain size (cm)
Less than 1 cm Area fraction of crystal grains (%) Magnetic flux density
(B8, Tesla) Iron loss
(W17 / 50) division 5.6 1070 3.8 8 1.901 0.865 Comparison 7 7.3 990 2.7 13 1.878 0.92 COMPARISON 8 4.3 980 2.3 12 1.886 0.9 Comparative material 9 8.5 1090 3.5 9 1.893 0.883 Comparative material 10 9.1 950 2.8 8 1.933 0.777 Invention 7 6 1000 2.7 7 1.919 0.788 Invention 8 5.1 1080 2.9 9 1.938 0.763 Invention 9

As can be seen from Table 4, when the hot-rolled sheet was annealed at a temperature satisfying the formula 3 by using the composition satisfying the formula 1, it was confirmed that the grain size uniformity was improved and the magnetic property was excellent.

It will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims and their equivalents. It will be understood that the invention may be practiced. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (15)

(Excluding 0%), Al: 0.015 to 0.04%, N: 0.01 to 0.1%, S: 0.01% or less (excluding 0%), , Mn: 0.04 to 0.15%, and the balance Fe and other unavoidable impurities, and satisfying the following formula 1 and having an average crystal grain diameter of 3 cm or less and an area fraction of crystal grains having a diameter of 1 cm or less of 10% .
[Formula 1]
[Mn] x [S]? 0.0004
([Mn] and [S] in the formula 1 represent the content (% by weight) of Mn and S, respectively.) The method according to claim 1,
(2). &Lt; / RTI &gt;
[Formula 2]
[Mn] + 14 x [S] &lt; 0.18
([Mn] and [S] in the formula 2 represent the contents (wt%) of Mn and S, respectively). The method according to claim 1,
0.01 to 0.05% of Sb, 0.03 to 0.12% of Sn, 0.02 to 0.15% of Cr and 0.01 to 0.05% of P in terms of% by weight. The method according to claim 1,
By weight, further comprising 0.01 to 0.2% of Cu and 0.01 to 0.05% of Mo. (Excluding 0%), S: not more than 0.01% (excluding 0%), Si: 0.0 to 0.09%, Al: 0.015 to 0.04% 0.04 to 0.15% of Mn, and the balance Fe and other unavoidable impurities, wherein the slab satisfies the following formula (1): &quot; (1) &quot;
Hot rolling the slab to produce a hot rolled sheet;
Annealing the hot rolled sheet at an annealing temperature (T) satisfying the following formula (3) for 5 to 100 seconds and annealing at a temperature lower by 10 to 100 占 폚 than the annealing temperature (T) for 30 to 300 seconds;
Cold-rolling the hot-rolled sheet to produce a cold-rolled sheet;
Subjecting the cold-rolled sheet to primary recrystallization annealing; And
A second recrystallization annealing step of subjecting the electrical steel sheet subjected to the first recrystallization annealing to completion;
Wherein the method comprises the steps of:
[Formula 1]
[Mn] x [S]? 0.0004
([Mn] and [S] in the formula 1 represent the content (% by weight) of Mn and S, respectively.)
[Formula 3]
1100-20 x [Al] / [N] <T <1200-20 x [Al] / [N]
([Al] and [N] in the formula (3) represent the content (% by weight) of Al and N, respectively, and T represents the annealing temperature (占 폚) in the step of annealing the hot- 6. The method of claim 5,
Wherein the slab satisfies the following formula (2).
[Formula 2]
[Mn] + 14 x [S] < 0.18
([Mn] and [S] in the formula 2 represent the contents (wt%) of Mn and S, respectively). 6. The method of claim 5,
Wherein the slab contains 0.01 to 0.05% of Sb, 0.03 to 0.12% of Sn, 0.02 to 0.15% of Cr, and 0.01 to 0.05% of P in weight%. 6. The method of claim 5,
Wherein the slab further comprises 0.01 to 0.2% of Cu and 0.01 to 0.05% of Mo in weight%. 6. The method of claim 5,
Further comprising a step of cooling the hot rolled steel sheet after the step of annealing the hot rolled steel sheet and cooling the hot rolled steel sheet at a cooling rate of 10 ° C / sec to 300 ° C / sec from a temperature of 700 to 850 ° C to 300 ° C Gt; 6. The method of claim 5,
And heating the slab at 1050 to 1200 DEG C in the step of heating the slab. delete 6. The method of claim 5,
Wherein the decarburization and sedimentation occur simultaneously or separately in the primary recrystallization annealing step. 6. The method of claim 5,
After the primary recrystallization annealing step, the average primary recrystallized grain diameter is 15 to 25 占 퐉. 14. The method of claim 13,
Wherein when the microstructure is observed at a thickness of 1/4 of the primary recrystallization plate after the primary recrystallization annealing step, the crystal grain area fraction of not less than 40 mu m is not more than 30% of the total area. 6. The method of claim 5,
The produced steel sheet has an average crystal grain diameter of 3 cm or less and an area fraction of crystal grains having a diameter of 1 cm or less of 10% or less.