KR20140060714A - Oriented electrical steel sheets and method for manufacturing the same - Google Patents

Abstract

The present invention relates to an oriented electrical steel sheet and a method for manufacturing the same comprising: a step for manufacturing a steel slab including 2.0-4.0% of Si, 0.04-0.07% of C, 0.02-0.04% of acid soluble Al, 0.01-0.20% of Mn, 0.001-0.0055% of N, 0.001-0.0055% of S, 0.03-0.07% of Sn, 0.01-0.05% of Sb, and 0.01-0.05% of P by wt%, while the P and Sb are satisfied with P+0.5Sb: 0.0370-0.0630% by wt%, and the residues including Fe and other impurities; a step for reheating the steel slab in the range of 1050-1250°C; a step for coiling the steel slab after hot rolling the reheated steel slab; a step for cold rolling the steel sheet after hot band annealing the coiled steel sheet; a step for decarburization annealing and nitrification annealing the cold rolled steel sheet; and a step for finally high temperature annealing the decarburization annealed and nitrification annealed steel sheet. According to the present invention, the coiling temperature (CT) after hot rolling is satisfied with the below equation (1) and (2). 7750 X carbon content + 93.75 <= CT <= 7750 X carbon content + 213.75 -----(1)500 <= CT <= 650------------------------(2) In the above equation (1) and (2), the unit of the equation is Celsius temperature (°C), the carbon content is the content of the low carbon, and the unit of the carbon content is the weight percentage (wt%).

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a directional electric steel sheet,

The present invention relates to a directional electric steel sheet and a method of manufacturing the same, and more particularly, to a directional electric steel sheet having improved magnetic properties by controlling the coiling temperature in accordance with the carbon content in the steel bar during hot rolling.

Generally, 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 grains whose growth is suppressed, And exhibits excellent magnetic properties.

In order to induce secondary recrystallization, fine inhibitors such as MnS and AlN are uniformly dispersed in the steel sheet before the final high-temperature annealing, so that the Goss orientation It is possible to obtain excellent magnetic properties, that is, high magnetic flux density and low iron loss by increasing the degree of integration so that the secondary recrystallization grains have a precise goss orientation by suppressing the growth of primary recrystallized grains having other orientations.

As means for effectively controlling the secondary recrystallization and improving the magnetic properties, it is possible to control the inhibitor excellent in the effect of inhibiting the growth of grains, the proper size and homogeneous size of the nucleation control and primary recrystallization forming the secondary recrystallization in the primary recrystallization Distribution formation is important. Korean Patent Laid-Open Publication No. 2009-0072116 discloses a method for further improving the magnetic properties of the grain-oriented electrical steel sheet, and Sn, Sb and P are added in an appropriate amount range to implement such means.

However, in order to obtain the optimum magnetic improvement effect in the production of the grain-oriented electrical steel sheet by controlling the coiling temperature of the electric steel sheet in which the content of Sn, Sb and P is adjusted and the hot rolling step, the improvement of the magnetic property due to the coiling temperature after hot rolling is maximized It is necessary to establish conditions that can be applied.

In order to solve the above problems, the present invention provides a directional electric steel sheet having improved magnetic properties by controlling the coiling temperature according to the amount of carbon steel after hot rolling, thereby maximizing the effect of interpassing treatment in the cold rolling process, and a manufacturing method thereof I want to.

In one or more embodiments of the present invention, it is preferable to use a steel sheet comprising 2.0 to 4.0% of Si, 0.04 to 0.07% of C, 0.02 to 0.04% of an acid soluble Al, 0.01 to 0.20% of Mn, 0.01 to 0.20% 0.001 to 0.0055% of S, 0.001 to 0.0055% of Sn, 0.03 to 0.07% of Sn, 0.01 to 0.05% of Sb and 0.01 to 0.05% of P, and P and Sb are P + 0.5Sb: 0.0370 To 0.0630%, the remainder consisting of Fe and other inevitably added impurities; Reheating the steel slab in a range of 1050 to 1250 占 폚; Hot rolling and reeling the reheated steel slab; Rolling the rolled steel sheet by annealing the hot rolled steel sheet; Subjecting the cold-rolled steel sheet to decarburization annealing and nitriding annealing; And a final high-temperature annealing of the steel sheet subjected to the decarburization annealing and nitriding annealing; , And the coiling temperature after hot rolling (CT) satisfies the following formulas (1) and (2).

7750 X Carbon content + 93.75? CT? 7750 X Carbon content + 213.75 ----- (1)

                       500? CT? 650 - (2)

In the above formulas (1) and (2), the unit of the formula is the Celsius temperature (占 폚), and the carbon content is the content of the carbon black and the unit is the weight percentage (wt%).

Characterized in that the size of the primary recrystallized grains after the decarburization annealing and nitriding annealing is 18.0 to 23.0 占 퐉 and the residual nitrogen amount in the steel sheet after decarburization annealing and nitriding annealing is 100 to 300 ppm.

The final high-temperature annealing step includes a primary cracking step, a temperature raising step and a secondary cracking step, wherein the raising step raises the temperature at a rate of 18 to 75 ° C / hr at 700 to 900 ° C, And the temperature is raised at a rate of 10 to 15 ° C / hr at 1020 ° C.

Wherein the step of performing the decarburization annealing and nitriding annealing is performed at a temperature in the range of 800 to 900 ° C, the secondary cracking step is performed at a temperature in the range of 1020 to 1200 ° C, and the cold rolling is one cold rolling step .

Further, in the embodiment according to the present invention, a directional electrical steel sheet produced by the above method can be provided.

According to the embodiment of the present invention, it is possible to manufacture a grain-oriented electrical steel sheet having improved magnetic properties by controlling the coiling temperature after hot rolling so that the fine carbonized material can be easily reused when the hot-rolled steel sheet is annealed.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. However, it is to be understood that the present invention is not limited to the disclosed embodiments, but may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. It is intended that the disclosure of the present invention be limited only by the terms of the appended claims.

The embodiment according to the present invention is characterized in that it comprises 0.03 to 0.07% by weight of Sn, 0.01 to 0.05% of Sb, 2.0 to 4.0% of Si, 0.020 to 0.040% of acid soluble Al, 0.01 to 0.20% of Mn, 0.004 to 0.07% of C, 0.0010 to 0.0055% of C, 0.0010 to 0.0055% of S and 0.01 to 0.05% of P, P + 0.5Sb of 0.037 to 0.063%, and the balance of Fe and And other impurities, and a method for producing the same.

In the production of the grain-oriented electrical steel sheet according to the embodiment of the present invention, the steel slab having the above composition is reheated at a temperature in the range of 1050 to 1250 ° C, hot rolled, rolled, annealed to the hot rolled steel sheet, . After the cold rolling, decarburization annealing and nitriding annealing are simultaneously or sequentially carried out in a temperature range of 800 to 900 ° C to perform secondary recrystallization annealing, and the coiling temperature (CT) It is performed in a temperature range that satisfies both conditions simultaneously. The unit in the following formula is the temperature in degrees Celsius, and the carbon content is the content of carbon black, and the unit is the weight percentage (wt%).

7750 X Carbon content + 93.75? CT? 7750 X Carbon content + 213.75 ----- (1)

500? CT? 650 ----------------------- (2)

Hereinafter, the reason for limiting the numerical values of the components in the embodiment according to the present invention will be described.

Si: 2.0 to 4.0 wt%

Si is a basic composition of an electric steel sheet and plays a role of lowering the core loss by increasing the resistivity of the material. When the Si content is less than 2.0% by weight, the resistivity is decreased, the eddy current loss is increased to deteriorate the iron loss characteristic, and the decarburization annealing causes active transformation between the ferrite and the austenite, so that the primary recrystallization texture is severely damaged. In addition, phase transformation between ferrite and austenite occurs at high temperature annealing, so that secondary recrystallization becomes unstable as well as gross aggregate structure is severely damaged. On the other hand, when the Si content is more than 4.0% by weight, the SiO2 and Fe2SiO4 oxide layers are excessively densely formed during the decarburization annealing, thereby delaying the decarburization behavior so that the phase transformation between the ferrite and the austenite continuously occurs during the decarburization annealing And the primary recrystallization texture is severely damaged. Further, since the nitriding behavior is delayed by the decarburization behavior delay effect due to the formation of the dense oxide layer described above, nitrides such as (Al, Si, Mn) N and AlN are not sufficiently formed and sufficient crystal grain restraining force required for secondary recrystallization It can not be ensured.

If the Si content exceeds 4.0% by weight, the mechanical properties of the electrical steel sheet increase in brittleness and the toughness decreases, so that the occurrence rate of the plate fracture during the rolling process becomes worsened and the weldability of the plate weld becomes poor, I will not. As a result, if the Si content is not controlled within the predetermined range, the formation of the secondary recrystallization becomes unstable, the magnetic properties are severely damaged, and the workability is also deteriorated. Therefore, Si in the embodiment of the present invention is limited to 2.0 to 4.0% by weight.

C: 0.04 to 0.07 wt%

C is an element that causes phase transformation between ferrite and austenite and is an essential element for improving the rolling property of an electric steel sheet having a strong brittleness and poor rolling property, but a carbide formed by a magnetic aging effect when remaining in a final product Since it is an element that deteriorates magnetic properties, it should be controlled to an appropriate amount. If the content of C is less than 0.04% by weight in the range of the Si content described above, the phase transformation between the ferrite and the austenite does not occur properly, resulting in nonuniformity of the slab and hot rolled microstructure. In addition, when the phase transformation between ferrite and austenite is excessively large during annealing of the hot-rolled sheet, re-heating of the slab causes coarse precipitates to precipitate, resulting in non-uniform primary recrystallization microstructure, The recrystallization behavior of the tea becomes unstable. Therefore, the minimum content of C is preferably 0.04 wt% or more.

On the other hand, by increasing the shear deformation zone by increasing the stiffness of the potential during cold rolling by the residual carbon in the steel sheet after annealing of the hot-rolled sheet, the Goss grain fraction of the primary recrystallized microstructure is increased, Therefore, if C is contained in an amount of more than 0.07% by weight in the range of the above-described Si content, coarse carbide is formed, and it is not easy to decarbonize sufficiently in a normal decarburization annealing process. not. Furthermore, if the decarburization is not sufficient, magnetic properties of magnetic products due to magnetic aging may be deteriorated when the final product is applied to electric power equipment. Therefore, in the examples according to the present invention, C is limited to 0.04 to 0.07% by weight.

Sb: 0.01 to 0.05 wt%

Sb is a grain boundary segregation element and has an effect of suppressing grain growth growth and also has an effect of improving core loss. However, since Sb has a low melting point, diffusion behavior toward the surface during the primary recrystallization annealing is generated to suppress the formation of the surface oxide layer. Therefore, the excessive addition of Sb causes the surface oxidation layer formed during the primary recrystallization annealing, And the crystal grain growth inhibiting ability is excessively increased to grow to other texture tissues which are not correlated with the Goss texture, thereby deteriorating the secondary recrystallization texture and damaging the magnetic properties. If Sb is added in an amount of 0.01 wt% or more, the effect of suppressing grain growth is exhibited. If the amount of Sb is more than 0.05 wt%, the effect of suppressing crystal grain growth is excessively high and stable secondary recrystallized microstructure can not be obtained. Base coating can not be obtained. Therefore, Sb is limited to 0.01 to 0.05 wt% in the examples of the present invention.

P: 0.01 to 0.05 wt%

P is segregated in grain boundaries, and can interfere with grain boundary movement and at the same time can play an auxiliary role of suppressing grain growth, and has an effect of improving {110} < 001 > If the content of P is less than 0.01% by weight in the Si content range of the present invention, there is no addition effect. If the content of P is more than 0.05% by weight, the brittleness is drastically increased and the rolling property is greatly deteriorated. In the examples, the content of P is limited to 0.01 to 0.05% by weight.

Al: 0.02 to 0.04 wt%

In addition to AlN fine precipitated at the time of hot rolling and annealing of hot-rolled steel sheet, Al also has nitrogen ions introduced by ammonia gas in the annealing step after cold rolling combined with Al, Si, and Mn, Si, &lt; / RTI &gt; Mn) N and AlN type nitride to form a strong grain growth inhibitor. If the content of Al is 0.02% by weight or less, a sufficient effect as an inhibitor can not be expected because the number and volume to be formed are considerably low, and when the Al content exceeds 0.010% by weight, a coarse nitride is formed, The deterrent is reduced. Therefore, in the embodiment of the present invention, the content of Al is limited to 0.02 to 0.040% by weight.

Mn: 0.01 to 0.20 wt%

Mn has an effect of reducing the total iron loss by decreasing the eddy current loss by increasing the resistivity as Si, and reacting with 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 primary recrystallization and causing secondary recrystallization. In order to exhibit such an effect, 0.01 wt% or more is required. However, when it is added in an amount exceeding 0.20% by weight, a large amount of (Fe, Mn) and Mn oxide are formed on the surface of the steel sheet in addition to Fe2SiO4 to prevent formation of a base coat formed during high temperature annealing, , The ferrite and austenite phase transformation is induced, so that the aggregate structure is seriously damaged and the magnetic properties are greatly deteriorated. Therefore, in the embodiment of the present invention, Mn is limited to 0.01 to 0.20% by weight.

Sn: 0.03 to 0.07 wt%

Sn has an effect of suppressing crystal grain growth as a grain boundary segregation element like Sb and has an effect of improving iron loss. However, since Sn has a low melting point, diffusion behavior toward the surface occurs during the primary recrystallization annealing to suppress the formation of the surface oxide layer. Therefore, the excessive addition of Sn causes the surface oxide layer formed during the primary recrystallization annealing And the crystal grain growth inhibiting ability is excessively increased to grow to other aggregate tissues which are not correlated with the Goss aggregate structure, thereby destroying the secondary recrystallized aggregate structure, thereby hindering the magnetic properties. When Sn is added in an amount of 0.03% by weight or more, the effect of inhibiting grain growth is exhibited. When the amount of Sn is more than 0.07% by weight, the effect of suppressing grain growth is excessively excessive, so that a stable secondary recrystallized microstructure can not be obtained. A stable base coating can not be obtained. Therefore, in the embodiment of the present invention, Sn is limited to 0.03 to 0.07% by weight.

N: 0.001 to 0.0055 wt%

N is an important element that reacts with Al to form AlN, and is preferably added in an amount of 0.001 wt% or more in the steelmaking step. However, if it is added excessively, a surface defect called a blister due to nitrogen diffusion will occur in the process after the hot rolling process, and since too much nitride is formed in the slab state, rolling becomes difficult and the subsequent process becomes complicated, It is controlled to 0.0055% by weight or less. Therefore, in the embodiment of the present invention, N is limited to 0.001 to 0.0055% by weight.

On the other hand, N, which is further required to form nitrides such as (Al, Si, Mn) N and AlN, can be reinforced by nitriding steel using ammonia gas in the annealing process after cold rolling.

S: 0.001 to 0.0055 wt%

As with N, S is an important element forming the precipitate MnS, and it is preferable that S is added in an amount of 0.001 wt% or more. However, if it exceeds 0.0055% by weight, precipitates of MnS are formed in the slab to inhibit grain growth, and it is difficult to control the microstructure in the subsequent process due to segregation at the center of the slab during casting. Further, since MnS is not used as a main inhibitor of grain growth in the present invention, it is not preferable that S is added in an amount inevitably added to precipitate. Therefore, the content of S in the examples according to the present invention is limited to 0.001 to 0.0055% by weight.

Hereinafter, a method of manufacturing an electrical steel sheet according to an embodiment of the present invention will be described.

In the embodiment according to the present invention, when the slab is reheated before the hot rolling, N and S which are solved are carried out at a predetermined temperature range in which the solution is incompletely solution-formed. If N and S are completely dissolved, a large amount of nitride or sulfide is formed after annealing of the hot-rolled steel sheet, which makes it impossible to perform hot rolling once, which is a subsequent process, and thus an additional process is required. And the size of the primary recrystallized grains becomes considerably small, so that it may become impossible to develop appropriate secondary recrystallization.

When the slab is heated to 1250 ° C or higher, the surface of the steel sheet melts due to the formation of fayalite, which is a compound of iron having a low melting point and iron as a base metal, on the steel sheet, so that hot workability becomes difficult, The amount of maintenance work is increased.

However, if the slab heating temperature is less than 1050 ° C, it is difficult to perform the hot rolling. Therefore, the slab heating temperature in the embodiment of the present invention is limited to 1050 to 1250 ° C.

In the hot rolling process, the coiling temperature (CT) is performed in a temperature range that simultaneously satisfies the following two conditions.

7750 X Carbon content + 93.75? CT? 7750 X Carbon content + 213.75 --- (1)

                       500? CT? 650 ---------------------- (2)

The unit of the above formula is the temperature in degrees Celsius, and the carbon content means the weight percent (wt%) by the content of carbon black.

The small carbon means the carbon in the steel before the heat treatment or the hot rolling. When the carbon content is high, excellent magnetic properties can be obtained even at a high coiling temperature because the carbon content contributing to the inter-pass aging treatment in the cold rolling process is increased.

When the coiling temperature is lower than 500 ° C, it is difficult to wind the hot-rolled coil at high speed, and the brittleness becomes so strong that it is difficult to handle the coils. However, when the coiling temperature is 650 ° C or more, It is not easily re-used in a short time even after the annealing process of the hot-rolled sheet, so that the amount of the used carbon that contributes to the improvement of the magnetic property in the subsequent cold rolling process is reduced, and as a result, the magnetic property of the final product is deteriorated.

Therefore, in the embodiment of the present invention, the hot rolling is performed at a temperature of 500 to 650 ° C.

Inter-pass aging is used to cold-roll the grain-oriented electrical steel sheet. This treatment increases the frequency of recrystallization nuclei in the formation of the first recrystallization after cold rolling, thereby improving the uniformity of the first recrystallization microstructure size. And there is an increase in the frequency at which Goss nucleation, which forms secondary recrystallization, may occur, and ultimately has the effect of improving the magnetic properties.

When the inter-pass aging treatment is performed, the carbon atoms existing in the solid state exist in the interstitial-type element with the interstitial elements to form the stress field. When the temperature rises, the seeds diffuse near the dislocation and inhibit the dislocation. ) Atmosphere.

When the dislocations formed by the plastic deformation are inhibited from moving by the cotlen atmosphere, a new potential is formed by the additional plastic deformation, and the operation of the slip system is varied, thereby promoting the formation of the shear deformation band. In the shear deformation band, in the formation of the first recrystallization, goss nucleation acting as the nucleus of the secondary recrystallization is generated, so that the magnetization of the secondary recrystallized grains is ultimately improved.

On the other hand, the amount of carbon present in a solid state in the cold rolling process is directly related to the coiling temperature of the hot rolling process. After the hot rolling is completed, the carbon is mostly present in a carbide state. Thereafter, the fine carbonized material is reused in the annealing process of the hot-rolled steel sheet, so that the hot-rolled steel sheet is in an employment state after the annealing process.

However, when the hot carbon is present as a crude carbide after the completion of the hot rolling process, the amount of carbon present in the solid carbon is small because the carbide is difficult to be solidified in the hot-rolled sheet annealing process.

Therefore, the effect of improving the magnetic property by the inter-pass aging treatment depends on the amount of carbon present in the solid carbon before cold rolling, and the amount of carbon present in the solid carbon before cold rolling is related to the amount of low carbon, Is the same, it depends on the coiling temperature of the hot-rolled steel sheet.

The hot rolled coiling temperature is preferably controlled in a low range so that the carbide formed in the hot rolling process can be reused in the hot rolled coiling process. It is easier to re-use.

In the embodiment according to the present invention, cold rolling is performed after annealing the hot-rolled steel sheet, as in a general steel sheet manufacturing process, while using a reverse rolling mill or a tandem rolling mill so that the inter- . At this time, one-time cold rolling is preferred, in which the intermediate structure is rolled from the initial hot-rolled thickness to the final product thickness without annealing heat treatment of the deformed structure.

With one strong cold rolling, orientations with low degrees of integration in the {110} < 001 > orientation are rotated in the direction of the deformation, and only the gothese grains best aligned with the {110} < 001 > orientation are present in the cold rolled plate. Therefore, in the two or more rolling methods, orientations having a low degree of integration are also present in the cold-rolled steel sheet, and secondary recrystallization is similarly performed at the time of the final high-temperature annealing to obtain low magnetic flux density and iron loss.

Therefore, in the embodiment according to the present invention, the cold rolling is performed by cold rolling at one time of cold rolling to a cold rolling rate of 87% or more.

Thereafter, the cold-rolled steel sheet is subjected to a decarburization annealing process, recrystallization of the deformed structure, and nitriding treatment using ammonia gas. At this time, in order to form nitrides such as (Al, Si, Mn) N and AlN, which are precipitates, by introducing nitrogen ions into the steel sheet using ammonia gas, the nitrides are sequentially nitrided using ammonia gas after decarburization and recrystallization , And a method of using ammonia gas at the same time so that decarburization and nitriding can be performed at the same time.

The decarburization annealing and the nitriding annealing in the embodiment according to the present invention are performed at 800 to 900 占 폚. If the temperature is lower than 800 占 폚, the magnetism becomes poor. When the temperature exceeds 900 占 폚, the secondary recrystallization does not occur well, The temperature during decarburization annealing and nitriding annealing is limited to 800 to 900 占 폚.

If the residual nitrogen amount is less than 100 ppm, the nitrogen may not form the inhibitor properly, and when the amount of residual nitrogen is more than 300 ppm It may take an excessive amount of time to remove nitrogen in the final annealing process.

In the embodiment of the present invention, the size of the primary recrystallization is controlled to be 18.0-23.0 탆. If the size of the primary recrystallization is smaller than 18.0 탆, the temperature at which the crystal growth driving force is large and the secondary recrystallization starts The primary recrystallization is suppressed while the selective growth period in which only the secondary recrystallization grows becomes narrower.

In this case, the conditions for the growth of a good secondary recrystallized structure are not well established, so that the degree of secondary recrystallization is poor and the secondary recrystallized grain size becomes large.

On the other hand, if the size of the primary recrystallized grains is larger than 23.0 탆, the crystal growth driving force is low and the temperature at which the secondary recrystallization starts is increased, the inhibitor suddenly loses its force and the primary recrystallization is suppressed, In the region where the secondary recrystallization does not grow during the secondary recrystallization forming section, the size of the primary recrystallized grains becomes larger and the specimen passes through in the thickness direction. So that a secondary recrystallization fine grain is formed.

The {110} plane of the steel sheet is parallel to the rolling surface, and the <001> plane of the steel sheet is parallel to the rolling plane by applying an annealing separator based on MgO to the steel sheet during the production of the oriented electrical steel sheet, 110} < 001 > texture structure parallel to the rolling direction to produce a grain oriented electrical steel sheet excellent in magnetic properties.

The final annealing is to remove the impurities which impair the magnetic properties by imparting the insulating property by the formation of the {110} < 001 > texture by secondary recrystallization, the formation of a vitreous film by the reaction between the oxide layer and MgO formed during decarburization.

The final annealing step in the embodiment according to the present invention comprises a primary cracking step, a heating step and a secondary cracking step, and the step of raising the temperature is performed at a temperature of from 700 to 900 DEG C at a rate of from 18 to 75 DEG C / hr And the temperature is raised at a rate of 10 to 15 ° C / hr at 900 to 1020 ° C. At this time, the secondary cracking step for the secondary recrystallization is performed in the range of 1020 to 1200 ° C.

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, so that the secondary recrystallization can be well developed, and after the secondary recrystallization is completed It is kept in a 100% hydrogen atmosphere for a long time to remove impurities.

Hereinafter, embodiments according to the present invention will be described in more detail.

[Example 1]

3.25% Si, 0.050% C, 0.12% Mn, Sol. 0.028% of Al, 0.032% of P, 0.0045% of N, 0.0041% of S, 0.035% of Sb and the remaining slabs of Fe and other inevitably oriented electrical steel sheets were heated at 1180 ° C for 210 minutes, Rolled to obtain a hot-rolled sheet having a thickness of 2.5 mm.

The coiling temperature during hot rolling was varied as shown in Table 1 below. The hot-rolled sheet was heated to 1120 占 폚, held at 930 占 폚 for 90 seconds, quenched in water, and pickled. After the pickling, the steel sheet was cold-rolled to a final thickness of 0.30 mm.

The cold-rolled sheet was simultaneously supplied with ammonia gas at a dew point of 65 占 폚 (50% hydrogen + 50% nitrogen) and held at 865 占 폚 for 180 seconds to simultaneously perform decarburization and nitriding. The nitrogen content of the steel sheet was controlled in the range of 180 to 220 ppm by decarburization annealing and nitriding annealing.

Then, the steel sheet subjected to decarburization annealing and nitriding annealing was coated with MgO as an annealing separator and finally annealed in a coiled state. During the final annealing, the primary cracking temperature was 700 ° C and the secondary cracking temperature was 1200 ° C. The rate of temperature rise in the temperature rise stage was 45 ° C / hr in the temperature range of 700-950 ° C, 15 Lt; 0 &gt; C / hr. On the other hand, the cracking time at 1200 캜 was 20 hours. The atmosphere at the final annealing was a mixed atmosphere of 25% nitrogen + 75% hydrogen up to 1200 ° C. After reaching 1200 ° C, it was kept in a 100% hydrogen atmosphere and then cooled. The magnetic properties measured for each condition are shown in Table 1.

Coiling temperature
(° C) Magnetic flux density
(B8, Tesla) Iron loss
(W17 / 50, W / kg) division 510 1.942 0.921 Inventory 1 550 1.931 0.939 Inventory 2 580 1.923 0.945 Inventory 3 635 1.908 0.986 Comparative Example 1

As shown in the results of Table 1, the inventive example satisfying all the ranges of the coiling temperature according to the embodiment of the present invention has a higher magnetic flux density and lower iron loss than the comparative example. The coiling temperature of the comparative example 1 satisfies the formula (2) but does not satisfy the formula (1) and is classified as a comparative example.

[Example 2]

0.032%, P: 0.029%, N: 0.0041%, S: 0.0048%, Sb: 0.038% Then, the slabs of Fe and other inevitably oriented electrical steel sheets were heated at 1180 ° C for 210 minutes and then hot rolled to obtain a hot rolled steel sheet having a thickness of 2.7 mm. The coiling temperature during hot rolling was varied as shown in Table 2 below. The hot-rolled sheet was heated to 1120 占 폚, held at 930 占 폚 for 90 seconds, quenched in water, and pickled. After the pickling, the steel sheet was cold-rolled to a final thickness of 0.30 mm.

The cold-rolled plate was subjected to simultaneous decarburization and nitridation treatment by simultaneously supplying a mixed gas of a dew point of 65 占 폚 (50% hydrogen + 50% nitrogen) and ammonia gas at a temperature of 860 占 폚 for 180 seconds. The amount of residual nitrogen in the steel sheet after the decarburization and nitriding treatment was in the range of 180 to 220 ppm.

Thereafter, the decarburized and nitrided steel sheet was coated with MgO as an annealing separator and finally annealed in a coiled state. During the final annealing, the primary cracking temperature was 700 ° C, the secondary cracking temperature was 1200 ° C, and the temperature raising rate was 15 ° C / hr.

On the other hand, the cracking time at 1200 캜 was 20 hours. The atmosphere at the final annealing was a mixed atmosphere of 25% nitrogen + 75% hydrogen up to 1200 ° C. After reaching 1200 ° C, it was kept in a 100% hydrogen atmosphere and then cooled. The magnetic properties measured for each condition are shown in Table 2.

Carbon steel
(wt.%) Coiling temperature
(° C) Magnetic flux density
(B8, Tesla) Iron loss
(W17 / 50, W / kg) division 0.045 520 1.931 0.935 Honorable 4 545 1.926 0.944 Inventory 5 590 1.912 0.975 Comparative Example 2 625 1.903 0.984 Comparative Example 3 0.063 540 1.915 0.971 Comparative Example 4 590 1.951 0.917 Inventory 6 630 1.940 0.925 Honorable 7 675 1.895 1.023 Comparative Example 5

As shown in the results of Table 2, the inventive example satisfying all of the winding temperature range of the embodiment according to the present invention is not only high in magnetic flux density but also low in iron loss as compared with the comparative example.

The electrical steel sheet excellent in magnetic properties of the embodiment of the present invention was prepared by appropriately adding Sn, Sb and P and simultaneously applying low temperature slab annealing, simultaneous decarburization annealing, steep annealing, and hot rolling coiling temperature control.

The secondary recrystallization is stabilized by controlling the primary recrystallized grains having a large size of secondary recrystallization nuclei having {110} < 001 > orientations to have a desired size and uniform size distribution by working in the winding temperature range of the hot- So that a grain-oriented electrical steel sheet having low iron loss and high magnetic flux density can be produced.

While the present invention has been described in connection with certain exemplary embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined by the appended claims.

It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive. The scope of the present invention is defined by the appended claims rather than the detailed description, and all changes or modifications derived from the meaning and scope of the claims and their equivalents should be interpreted as being included in the scope of the present invention .

Claims (8)

(% By weight), Si: 2.0-4.0%, C: 0.04-0.07%, acid-soluble Al: 0.02-0.04%, Mn: 0.01-0.20%, N: 0.001-0.0055%, S: 0.001-0.0055 0.01 to 0.05% of Sn, 0.03 to 0.07% of Sn, 0.01 to 0.05% of Sb and 0.01 to 0.05% of P, wherein P and Sb satisfy P + 0.5Sb: 0.0370 to 0.0630% by weight, And other inevitably added impurities in the steel slab;
Reheating the steel slab in a range of 1050 to 1250 占 폚;
Hot rolling and reeling the reheated steel slab;
Subjecting the wound steel sheet to hot rolling annealing followed by cold rolling;
Subjecting the cold-rolled steel sheet to decarburization annealing and nitriding annealing; And
Subjecting the steel sheet subjected to decarburization annealing and nitriding annealing to final high-temperature annealing;
, &Lt; / RTI &
Wherein the coiling temperature after hot rolling (CT) satisfies the following formulas (1) and (2).
7750 X Carbon content + 93.75? CT? 7750 X Carbon content + 213.75 ----- (1)
500? CT? 650 - (2)
In the above formulas (1) and (2), the unit of the formula is the Celsius temperature (占 폚), and the carbon content is the content of the carbon black and the unit is the weight percentage (wt%). The method according to claim 1,
Wherein the size of the primary recrystallized grains after decarburization annealing and annealing after nitriding is 18.0 to 23.0 占 퐉. 3. The method of claim 2,
Wherein the amount of residual nitrogen in the steel sheet after the decarburization annealing and annealing is 100 to 300 ppm. The method according to claim 1,
The final high-temperature annealing may include:
Wherein the step of raising the temperature includes raising the temperature at a rate of 18 to 75 ° C / hr at 700 to 900 ° C, raising the temperature to 10 to 15 ° C at a temperature of 900 to 1020 ° C / hr. &lt; / RTI &gt; The method of claim 3,
Wherein the step of decarburization annealing and nitriding annealing is performed in a temperature range of 800 to 900 占 폚. 5. The method of claim 4,
Wherein the secondary cracking step is performed at a temperature in the range of 1020 to 1200 占 폚. The method according to claim 5 or 6,
Wherein the cold rolling is one step of cold rolling. A directional electrical steel sheet produced by any one of claims 1 to 7.