KR101521253B1 - Grain-orinented electrical steel sheet and method for manufacturing the same - Google Patents

Abstract

A method of manufacturing a directional electrical steel sheet is disclosed. A method for producing a grain-oriented electrical steel sheet according to the present invention comprises: 2.0 to 4.0% by weight of Si, 0.02 to 0.04% by weight of Al, 0.04 to 0.07% of C, 0.04 to 0.07% : Pb: 0.01 to 0.05%, P: 0.01 to 0.05%, and the balance Fe and other unavoidable impurities, and 0.037? P + 0.5 * Sb ≤ 0.063 (where P and Sb are weight percentages of the element), producing hot rolled steel sheets by hot rolling the slabs, cold rolling the hot rolled steel sheets to obtain cold rolled steel sheets A first recrystallization annealing step of the cold-rolled steel sheet; and a final annealing step of the cold-rolled steel sheet after the primary recrystallization annealing is completed, wherein the cold-rolled steel sheet is produced by a cold rolling at a rolling reduction of 60 to 70% Holding the steel sheet having the corresponding thickness in the temperature range of 150 to 350 DEG C for 1 to 10 minutes, and then rolling to the final thickness.

Description

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

The present invention relates to a grain-oriented electrical steel sheet, and more particularly, to an iron-based steel sheet having an excellent strength improving effect by adding an appropriate amount of tin (Sn), antimony (Sb) and phosphorus (P) To a directional electric steel sheet.

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, .

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 growth of tea recrystallisations should be inhibited.

The secondary recrystallization is increased to increase the directivity so as to have a precise Goss orientation, so that it is possible to obtain an effect of increasing magnetic flux density and iron loss, which are excellent magnetic properties.

Manufacturing techniques that can effectively control secondary recrystallization can be roughly classified into three types. First, it is very important to control the inhibitor which is excellent in the inhibition of grain growth, second, control nucleation of secondary recrystallization in primary recrystallization, and formation of proper size and uniform size distribution of primary recrystallization.

In order to effectively inhibit the growth of the primary recrystallization till the first condition, the inhibitor is distributed to a sufficient amount and a proper size uniformly before the secondary recrystallization occurs, the inhibitor is thermally stable up to the high temperature at which the secondary recrystallization starts It should not be easily broken down.

The second condition, Goss Nucleation, is a good directional Goss orientation which becomes the nucleus of the secondary recrystallization to the primary recrystallization. Generally, the Goss orientation in the primary recrystallized grain of the grain-oriented electrical steel sheet occupies a very small fraction of less than 1%. When the secondary recrystallization size (about 3 cm) and the average primary recrystallization size (about 20 탆) are calculated, it is actually one of the three millions of primary recrystallized grains forming the secondary recrystallization.

It absorbs 3 million crystal grains during the secondary recrystallization process. Among these three million crystal grains, the Goss orientation is less than 10,000, one nucleus is grown by secondary recrystallization, and the remaining 9,999 are absorbed by growing secondary recrystallization grains.

Therefore, Goss Nuclear Regulation should consider two major aspects. One out of a million is making a good directional Goss which is the nucleus of the actual secondary recrystallization, and the direct degree of disappearance without the secondary recrystallization finally makes less Goss less good.

Conditions for making the Goss nuclei capable of causing such secondary recrystallization include, for example, rapid heating, hot rolling, and cold rolling rate adjustment techniques.

The third condition, primary recrystallization control, is to make the primary recrystallized grains have an appropriate size and uniform size distribution. The grain growth driving force is inversely proportional to the primary recrystallization size. The size of the primary recrystallization grain is a direct factor controlling the grain growth driving force and affects the formation of the secondary recrystallization. As mentioned above, It begins to form in a temperature range where it loses its power to inhibit the growth of the primary recrystallized grains as it grows or disappears.

This is the period during which the balance between the force that inhibits the growth of the primary recrystallized grains and the force to grow the primary recrystallized grains falls. That is, the secondary recrystallization phenomenon starts in a section where the suppressing force is gradually weakened. Therefore, the primary recrystallized grain size becomes a very important factor in the formation of secondary recrystallization.

In the formation of the secondary recrystallization, there is a proper size of the primary recrystallized grain, and likewise, the primary recrystallized grain size distribution is an important factor. Ideally, if all the grains have the same grain size, the grain growth driving force may be uniform and predictable, but the actual grain size of the polycrystalline structure will have a non-uniform distribution. As the distribution is uniform and narrow, more stable secondary recrystallization can be formed.

The method of improving the magnetic properties by making the GOS nucleus which causes the secondary recrystallization in the primary recrystallization is important for the decarburization annealing condition in which the primary recrystallization is formed. Rapid increase in temperature applied to the temperature range in which the primary recrystallization is formed is a representative example. The primary recrystallization is the energy that is accumulated in the deformed structure of the cold rolled steel sheet, and the position and frequency of the primary recrystallization are determined according to the type of the deformed structure.

Therefore, it is effective to control the process conditions at the moment of forming the primary recrystallization, but it is effective to make the above-mentioned means well implemented in the state of the cold rolling before the primary recrystallization is formed.

DISCLOSURE Technical Problem The present invention has been devised to solve the problems as described above, and it is an object of the present invention to provide a method of controlling the content of tin, antimony, and phosphorus in an appropriate range in a steel, So that the recrystallized grains having a desired size can have an appropriate size distribution.

In order to accomplish the above object, a method of manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention comprises: 2.0 to 4.0% Si, 0.02 to 0.04% of Al, 0.02 to 0.04% 0.04 to 0.07% of C, 10 to 55 ppm of N, 0.0010 to 0.0055% of S, 0.03 to 0.07% of Sn, 0.01 to 0.05% of Sb and 0.01 to 0.05% of P and balance of Fe and other unavoidable impurities 0.037 ≤ P + 0.5 * Sb ≤ 0.063 (where P and Sb represent the weight percent of the element), heating the slab to produce a hot-rolled steel sheet, A method of manufacturing a cold-rolled steel sheet, comprising the steps of: cold-rolling a hot-rolled steel sheet to produce a cold-rolled steel sheet; subjecting the cold-rolled steel sheet to primary recrystallization annealing; and finally annealing the cold- The steel sheet having a thickness corresponding to a rolling reduction of 60 to 70% at the time of rolling is maintained at a temperature range of 150 to 350 ° C for 1 to 10 minutes, It involves rolling to a thickness.

The method may further include a step of annealing the hot-rolled steel sheet by hot-rolling.

The reheating of the slab may be performed at a temperature in the range of 1,050 to 1,250 DEG C, in which the nitride is incompletely dissolved.

The primary recrystallization annealing includes a decarburization annealing and a steep annealing step,

The decarburization annealing and the steep annealing process may be performed at the same time, or the steep annealing process may be performed after the decarburization annealing process is completed.

If the decarburization annealing and the steep annealing process are simultaneously performed, the nitrogen content in the steel sheet after the decarburization annealing and the steep annealing process may be 100 to 300 ppm.

The final annealing step includes a first stage of cracking, a step of raising the temperature, and a step of secondary cracking. The initial heating rate is 18 to 75 ° C / hr in the heating step, the heating rate is 900 to 1,020 ° C Lt; RTI ID = 0.0 &gt; 15 C / hr. &Lt; / RTI &gt;

According to another preferred embodiment of the present invention, a grain-oriented electrical steel sheet is produced by hot rolling a steel slab, annealing a hot-rolled steel sheet, cold rolling, primary recrystallization annealing and final annealing, C: 0.04 to 0.07%, N: 10 to 55 ppm, S: 0.0010 to 0.0055%, Sn: 0.03 to 0.03% 0.07 ≦ P + 0.5 * Sb ≦ 0.063, where P and Sb are the weight percentages of the elements, and 0.07 to 0.07%, Sb: 0.01 to 0.05%, P: 0.01 to 0.05% and the balance Fe and other unavoidable impurities. And means that the steel sheet having a thickness corresponding to a reduction ratio of 60 to 70% during cold rolling for cold-rolled steel sheet is maintained in a temperature range of 150 to 350 ° C for 1 to 10 minutes and rolled to a final thickness .

According to the present invention, it is possible to heat the slab at a low temperature by adding an appropriate amount of tin (Sn), antimony (Sb) and phosphorus (P) to the steel, and to apply decarburization and steep annealing simultaneously and pass aging rolling It is possible to provide an electrical steel sheet excellent in magnetic properties.

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. Like reference numerals refer to like elements throughout the specification.

Hereinafter, a method for manufacturing a directional electrical steel sheet according to a preferred embodiment of the present invention will be described in detail.

A method for producing a grain-oriented electrical steel sheet according to a preferred embodiment of the present invention comprises: 2.0 to 4.0% by weight of Si, 0.02 to 0.04% of an acid soluble Al, 0.01 to 0.20% of Mn, 0.04 to 0.07% P, 0.01 to 0.05% of P, 0.01 to 0.05% of S, 0.01 to 0.05% of P, and the balance of Fe and other inevitable impurities, 0.037? P + 0.5 * Sb &lt; / = 0.063 (where P and Sb are weight percent of the element), hot rolling the slab to produce a hot rolled steel sheet, cold rolling the hot rolled steel sheet The method of manufacturing a cold-rolled steel sheet according to any one of claims 1 to 3, wherein the cold-rolled steel sheet is manufactured by a first recrystallization annealing step and a final annealing step of a cold- Holding a steel sheet having a thickness corresponding to the reduction ratio in a temperature range of 150 to 350 ° C for 1 to 10 minutes and then rolling to a final thickness It includes.

In the method for producing a grain-oriented electrical steel sheet according to the present invention, a specimen of a pass having a thickness corresponding to a reduction ratio of 60 to 70% during cold rolling is aged for 1 to 10 minutes in a temperature range of 150 to 350 ° C, Rolling is performed to give a path aging effect. The reason is as follows.

As the cold rolling progresses, the rolling progresses while reducing the thickness of each pass, and plastic deformation occurs in the steel sheet. The plastic deformation is realized by the formation and movement of dislocation tissues and the movement of dislocation tissues of the cold storage material of the present invention is performed by twelve {110} <111> slip systems of Body Centered Cubic (BCC) , 24 {123} <111>, and 12 {112} <111> are applied.

Among the low-carbon steel, C and N are interstitial elements and form a stress field. When the temperature rises, they form a cotrell atmosphere that diffuses into the space of potential and inhibits dislocation movement.

When the potential formed by the plastic deformation is suppressed by the cortel atmosphere, a new potential is formed due to the additional plastic deformation, and the operation of the slip system is varied, and the formation of the shear deformation band which increases the dislocation density of the final cold- Promote.

This effect increases the frequency of recrystallization nuclei in the formation of the primary recrystallization, thereby improving the uniformity of the size of the primary recrystallized microstructure and increasing the frequency at which Goss nucleation occurs to form the secondary recrystallization, thereby improving the final magnetic property.

More specifically, when cold rolling is performed to a reduction ratio of 60 to 70%, crystal grains existing after annealing of the hot-rolled steel sheet are compressed to a thickness of 0.3 to 0.4 times in the thickness direction and elongated to a length of 2.5 to 3.3 times in the longitudinal direction, Dislocation caused by plastic deformation is generated and moved.

Further, a shear deformation band starts to be formed within the crystal grain from a cold reduction ratio of 70% or more at which sufficient dislocation density is formed in the crystal grain. It is known that the shear deformation zone formed here serves as the nucleation site of Goss during the subsequent primary recrystallization.

Therefore, it is advantageous to increase the dislocation density and to form a large number of shear deformation zones in order to generate a large amount of Goss nuclei. It is preferable that the cold rolling shear strain zone is rolled at a rolling reduction of 60 to 70% When the cold-rolled sheet is subjected to aging at an appropriate temperature and time, it is easy to penetrate the diffusion center into the potential center of the interstitial-type elements C and N.

Since a sufficient dislocation density is formed and C and N are diffused and there are many potentials to penetrate, a Cottrell atmosphere can be easily formed at an appropriate temperature and time.

If the dislocation density is too low, the diffusion distance of C and N becomes long. Therefore, if the temperature and time are high, the effect of the cotrel atmosphere in which the potentials C and N are fixed can be expected.

In addition, by fixing the previously formed potentials in the Cottrell atmosphere before forming the shear deformation zone, the effect of promoting the formation of the new dislocation and the formation of the shear deformation zone becomes greatest.

The temperature of the pass aging is preferably in the range of 150 to 350 degrees Celsius. When the temperature is below 150 degrees Celsius, the diffusion rate of C and N is too slow to form the cotrel atmosphere. It is sufficiently fast and the thermal vibration becomes large, so that the potential fixing effect is reduced and the aging effect disappears.

The time of pass aging can be effected within a short time if the temperature is high, and long aging is required at low temperature.

For example, considering the diffusion rate of C in ferrite iron, the diffusion distance is theoretically calculated. In the case of 10 min aging at 200 ° C, C can diffuse approximately 0.78 micrometer, and 1 minute aging can spread 0.25 micrometer. have. At 150 degrees, 10 minutes of aging spread 0.22 micrometers, and at 250 degrees of 1 minute of aging, 0.68 micrometers of spread.

Therefore, it is possible to realize a path aging effect with sufficient diffusion of C through aging of 1 minute to 10 minutes or less.

The method for manufacturing a grain-oriented electrical steel sheet according to the present invention further comprises a step of annealing the hot-rolled steel sheet.

The reheating of the slab is characterized in that the temperature is in the range of 1,050 to 1,250 占 폚 at which the nitride is incompletely dissolved.

MnS or AlN contained in slabs should be reheated at a high temperature for a long time and then solidified to prepare a precipitate having a proper size and distribution in a cooling process after hot rolling so that it can be used as an inhibitor. The slab must be heated to high temperature.

Specifically, in the method using MnS as an inhibitor at 1,300 ° C and the method using MnS + AlN as an inhibitor, a high magnetic flux density can be obtained only by reheating the slab at 1,350 ° C. or more.

In the case of mass production of electrical steel sheets, the heat is reheated to a temperature of approximately 1400 ° C in order to obtain a uniform temperature distribution to the inside in consideration of the size of the slabs and the like. When the slab is heated for a long time at a high temperature for a long time, The surface portion of the heating furnace reaches the melted state and flows down, so that the maintenance cost of the heating furnace is large and the service life of the heating furnace can be shortened.

Particularly, when the columnar structure of the slab grows to a great extent by heating at a high temperature for a long time, cracks are generated in the width direction of the plate in a subsequent hot rolling process, which causes a problem of significantly reducing the water content.

Therefore, if the directional electrical steel sheet can be manufactured by lowering the reheating temperature of the slab, it can have a very beneficial effect in terms of the manufacturing cost and the error rate.

To this end, in the present invention, slab heating is performed in a temperature range in which AlN serving as an inhibitor of secondary recrystallization is partially solvated.

The primary recrystallization annealing includes a decarburization annealing and a steep annealing step, wherein the decarburization annealing and the steep annealing step are performed at the same time, or the steep annealing step is performed after the decarburization annealing step is completed.

The cold-rolled sheet undergoes decarburization and nitriding annealing in a mixed gas atmosphere of ammonia, hydrogen and nitrogen.

In the present invention, when the slab is heated only to the above-mentioned partially solution-applied temperature, there may be a large difference in the size distribution between the precipitate in the casting process and the precipitate in the hot rolling.

Therefore, the inhibitor required for the secondary recrystallization can be supplemented by nitriding the necessary inhibitor in the final thickness of the steel sheet, without depending only on the inhibitor formed in the low-temperature component. That is, the nitriding process can complement the production of the grain-oriented electrical steel sheet by the slab low-temperature heating method in which partial solution formation is performed.

For the nitriding treatment, ammonia gas may be used to form a nitrogen atmosphere in the primary recrystallization annealing step using a steel sheet rolled to the final thickness of the product. Ammonia gas has a property of decomposing into hydrogen and nitrogen at a temperature of about 500 ° C or higher. By using this property, nitrogen is supplied to nitridation.

The penetrated nitrogen reacts with the nitride-forming element in the steel sheet to form a nitride, and this nitride acts as an inhibitor. Examples of the nitride include AlN, (Al, Si) N, and the like.

On the other hand, according to the method of performing the decarburization first and then the annealing by nitriding, precipitates such as Si ₃ N ₄ and (Si, Mn) N are formed. Such precipitates are thermally unstable and are easily decomposed. As a result, It is necessary to maintain it at a high temperature for a long time in order to change into AlN or precipitates such as (Al, Si) N.

When the decarburization and the nitriding annealing are performed at the same time, there is an advantage that the AlN and (Al, Si) N are formed at the same time, so that a long processing time is not required. Therefore, a method of performing decarburization and nitriding annealing at the same time is more preferable. However, a method of performing annealing after nitriding after decarburization can still be effectively used for manufacturing a grain-oriented electrical steel sheet.

When the decarburization annealing and the steep annealing process are simultaneously performed, the nitrogen content in the steel sheet after the decarburization annealing and the steep annealing process is 100 to 300 ppm.

The final annealing step includes a first stage of cracking, a step of raising the temperature, and a step of secondary cracking. The initial heating rate is 18 to 75 ° C / hr in the heating step, the heating rate is 900 to 1,020 ° C Is 10 to 15 占 폚 / hr.

The steel sheet subjected to decarburization annealing is coated with an annealing separator containing MgO as a basic component and then wound and finally annealed for a long period of time to produce an electrical steel sheet in which crystal grains of the Goss orientation are predominantly distributed.

The detailed procedure includes a temperature raising step of raising the temperature of the first recrystallized steel sheet for secondary recrystallization after passing through a primary cracking step to remove water from the annealed separator applied to the rolled steel sheet, And a secondary cracking step to remove impurities in the steel.

The reason why the rate of increase in temperature after the primary cracking is divided into two stages is that the secondary recrystallization does not occur even when the temperature is lowered to the temperature below the melting point of the inhibitor at the time of elevated temperature, And the secondary recrystallization effect can be obtained within a short time by slowing the rate of temperature rise from the temperature at which the secondary recrystallization occurs, which is advantageous for improving the productivity.

In the present invention, the reference temperature for applying a different heating rate is set to 900 to 1,020 ° C. After the first crack, the steel sheet is heated at a rapid heating rate, and the heating rate is changed to a slow heating rate considering the secondary recrystallization in the temperature range do.

In the present invention, the temperature raising rate of the initial rapid heating speed section is set at 18 to 75 ° C / hr, and the slow heating rate considering the second recrystallization is set at 10 to 15 ° C / hr.

The grain-oriented electrical steel sheet according to another embodiment of the present invention is manufactured by hot rolling a steel slab, annealing a hot-rolled steel sheet, cold rolling, primary recrystallization annealing, and final annealing, 0.04 to 0.07% of C, 10 to 55 ppm of N, 0.0010 to 0.0055% of S, 0.03 to 0.07% of Sn and 0.01 to 0.05% of Sb in terms of an acid soluble Al: 0.02 to 0.04%, Mn: 0.01 to 0.20% 0.01 to 0.05% of P, and the balance of Fe and other unavoidable impurities, and 0.037 ≤ P + 0.5 * Sb ≤ 0.063 (where P and Sb represent the weight percent of the element) A cold rolled steel sheet having a thickness corresponding to a reduction of 60 to 70% is maintained in a temperature range of 150 to 350 DEG C for 1 to 10 minutes and rolled to a final thickness.

Hereinafter, the reason for limiting the composition ratio of the grain-oriented electrical steel sheet according to the present invention will be described. The unit is expressed in% by weight for convenience.

[Si: 2.0-4.0%]

Si lowers the magnetic anisotropy of the material of the electric steel sheet and increases the resistivity, thereby lowering the iron loss. When the Si content is less than 2.0%, the reduction of the resistivity is not so large that the iron loss is reduced. When the Si content is more than 4.0%, the brittleness is increased and the cold rolling becomes difficult.

[Al: 0.02-0.04%]

Al is a component acting as an inhibitor and forms an AlN type nitride. When the content is less than 0.02%, Al can not exhibit a sufficient effect as an inhibitor. When the content is too high, aluminum nitride precipitates and grows coarsely, It becomes scarce. Therefore, the content of Al is 0.02 ~ 0.04%.

[Mn: 0.01-0.20%]

Mn has the same effect of increasing the specific resistance as Si and reducing the iron loss. It reacts with the nitrogen introduced by the nitriding treatment together with Si to form precipitates of N (Al, Si, Mn), whereby the growth of the primary recrystallization And it is an important element for causing secondary recrystallization. However, addition of more than 0.20% by weight accelerates the austenite phase transformation during hot rolling, thereby reducing the size of the primary recrystallized grains and making secondary recrystallization unstable. Therefore, Mn should be 0.20 wt% or less. In addition, Mn is an austenite forming element and increases the austenite fraction during hot rolling reheating to increase the amount of precipitates to a large extent, so that the primary recrystallization through MnS formation is not excessively reduced. .

[Sn: 0.03 to 0.07%]

When Sn is added, iron loss can be improved by increasing the number of secondary nuclei in the {110} < 001 > orientation in order to reduce the size of the secondary crystal grains. Also, Sn plays an important role in suppressing grain growth through grain segregation in grain boundaries, which compensates for the fact that the effect of suppressing grain growth is weakened as AlN grains are coarsened and Si content increases. Consequently, even with a relatively high Si content, successful formation of the {110} < 001 > secondary recrystallized texture can be assured. That is, it is possible not only to increase the Si content but also to decrease the final thickness without completely weakening the perfection of the {110} <001> secondary recrystallization structure. The content of Sn is preferably 0.03 to 0.07% by weight within the range in which the content of other components is properly adjusted as described above. In addition, there is a problem that the brittleness is increased when the Sn content is excessive. Therefore, when the Sn content is controlled within the above range, the brittleness is also effectively improved.

[Sb: 0.01 to 0.05%]

Sb segregates at grain boundaries and has an effect of suppressing excessive growth of the primary recrystallized grains. By adding Sb to suppress the grain growth in the first recrystallization step, the non-uniformity of the primary recrystallization size along the thickness direction of the plate is eliminated, and at the same time, the secondary recrystallization is stably formed, . In particular, when the effect of Sb is contained in an amount of 0.01 to 0.05% by weight, it can be greatly improved to such an extent that it can not be predicted in the conventional literature. Sb is segregated in the grain boundaries to inhibit excessive growth of the primary recrystallized grains. When the amount of Sb is less than 0.01% by weight, the action of the primary recrystallized grains is difficult to exhibit properly. When the amount of the primary recrystallized grains is more than 0.05% The secondary recrystallization starting temperature is lowered and the magnetic properties are deteriorated or the secondary recrystallization may not be formed because the suppressing ability against grain growth becomes too large.

[P: 0.01 to 0.05%]

P promotes the growth of the primary recrystallized grains in the low-temperature directional electrical steel sheet, thus raising the secondary recrystallization temperature and increasing the degree of integration of the {110} <001> orientation in the final product. If the primary recrystallization is excessively large, secondary recrystallization becomes unstable. However, as long as secondary recrystallization occurs, a large primary recrystallization is advantageous to magnetism in order to increase the secondary recrystallization temperature. On the other hand, P not only reduces the iron loss of the final product by increasing the number of grains having a {110} <001> orientation in the primary recrystallized steel sheet, but also strongly develops the {111} <112> The {110} < 001 > density of the final product is improved and the magnetic flux density is also increased. P also segregates in the grain boundaries to a high temperature of about 1000 캜 during secondary recrystallization annealing to retard the decomposition of the precipitates and to reinforce the restraining force. When the content of P is limited to 0.01 to 0.05% by weight, a remarkable effect which can not be predicted in the prior art can be obtained. In order to exhibit the effect of P, 0.01 wt% or more is required. When P is 0.05 wt% or more, the size of the primary recrystallized grains is reduced rather than the secondary recrystallization becomes unstable as well as the brittleness is lowered to inhibit cold rolling .

[P + 0.5 * Sb: 0.0370 ~ 0.0630%] (P and S are% by weight of each element)

When the content of P + 0.5 * Sb is controlled to the above-mentioned range, the iron loss improving effect is further maximized. This is because the elements are generally added together to achieve a synergistic effect, and when the synergistic effect satisfies the expression range, it is discretely maximized as compared with other numerical ranges.

On the other hand, C is to be removed in the decarburization annealing process after cold rolling, and N and S are considered to be impurities in the constituent system of the electric steel sheet because it is desirable that the N and S are removed as much as possible through atmosphere control during the secondary crack treatment. However, since these components are present in the steel sheet due to various reasons until cold rolling, they can be included in a predetermined range in the steel slab, the hot-rolled steel sheet and the cold-rolled steel sheet (steel sheet immediately after cold rolling) It is more preferable to control it within the following range.

[C: 0.04-0.07%]

When C is included in a rolling process at a certain level or more, it promotes austenite transformation of the steel, thereby miniaturizing the hot rolled steel during hot rolling, thereby helping to form uniform microstructure. . However, if the content is excessive, coarse carbide is formed and it becomes difficult to remove it when decarburized. Therefore, it is preferable that the range is initially included.

 [N: 10-55 ppm]

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, after the cold rolling, the structure may be appropriately finely fine to assure proper primary recrystallization grain size. However, if the content is excessive, the primary recrystallization grain becomes excessively fine, The driving force that causes crystal grain growth during the secondary recrystallization increases due to the fine crystal grain, and the crystal grain can grow to an undesirable grain. Also, if the N content is excessive, it takes a long time to remove it in the final annealing process, which is not preferable. Therefore, the upper limit of the nitrogen content is set at 55 ppm. However, the lower limit of the nitrogen content is set at 10ppm considering the ratio that can be reused when reheating the slab.

 [S: 0.0010-0.0055%]

When S is contained in an amount of 0.0055% or more, the hot rolled slab is refined and finely precipitated. Therefore, the size of the primary recrystallized grains is reduced to lower the secondary recrystallization starting temperature to deteriorate the magnetic properties. In addition, since it takes a long time to remove S in the solid state in the secondary crack region of the final annealing process, the productivity of the oriented electrical steel sheet is lowered. On the other hand, when the S content is as low as 0.0055% or less, since the initial grain size before cold rolling is effective, the number of grains having {110} < 001 > orientation nucleated in the strain band in the first recrystallization step is increased. Therefore, the size of the secondary recrystallization is reduced to improve the magnetic properties of the final product, so S is set to 0.0055% or less. S forms MnS and influences the primary recrystallized grain size to some extent, and therefore, it is preferable that S contains 0.001 wt% or more. Therefore, the range of S is limited to 0.0010 to 0.0055%.

It will be understood by those skilled in the art that various components included in the grain-oriented electrical steel sheet may be included as an alloy component of the electrical steel sheet of the present invention in addition to the above-mentioned components. Combinations of known components and their application are, of course, within the scope of the present invention.

Hereinafter, a method for producing a grain-oriented electrical steel sheet according to the present invention will be described in detail with reference to examples. The following examples are illustrative of the present invention only and are not intended to limit the scope of the present invention.

<Examples>

Si: 3.27%, C: 0.055%, Mn: 0.11%, Sol. The amount of N which reused the slab of the remainder of Fe and other inevitably oriented electrical steel sheets was 0.028%, 0.028% of Al, 0.029% of P, 0.0042% of N, 0.0045% of S, 0.0045% of S, 0.0025% for 210 minutes, and hot rolled to obtain a hot-rolled steel sheet having a thickness of 2.3 mm.

The hot-rolled sheet was heated to 1,120 占 폚, held at 920 占 폚 for 90 seconds, quenched in water, and pickled. The cold rolled steel sheet was subjected to pass aging at a thickness of 0.80 mm corresponding to a reduction ratio of 65% as shown in Table 1, followed by cold rolling to a thickness of 0.30 mm.

The plate temperature for the initial decarburization annealing during the heating was passed through a dew point of 62.5 ° C (50% hydrogen + 50% nitrogen) in the range of 800 to 850 ° C. The ammonia gas was simultaneously supplied while maintaining the dew point at 68 ° C And maintained at a temperature range of 850 to 900 degrees for 180 seconds to carry out simultaneous decarburization and nitriding treatment.

In the decarburization and nitriding annealing, the size of the primary recrystallized grains was controlled to 18 to 25 占 퐉, and the nitrided steel sheet was controlled to have a nitrogen content of 180 to 220 ppm.

This 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 and the secondary cracking temperature was 1200 ° C. The temperature rise in the temperature raising range was 45 ° C per hour in the temperature range of 700 ° C to 950 ° C and 15 ° C per hour in the temperature range of 950 ° C to 1200 ° C Respectively. On the other hand, the cracking time at 1200 ° C was treated for 15 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 100% hydrogen atmosphere and then cooled. The magnetic properties measured for each condition are shown in Table 1.

Aging
Temperature
(° C) Aging
time
(sec) Magnetic flux density
(B10, Tesla) Iron loss
(W17 / 50, W / kg) division 100 60 1.922 0.973 Comparative Example 1 200 60 1.935 0.940 Inventory 1 300 60 1.944 0.930 Inventory 2 400 60 1.918 0.978 Comparative Example 2 100 600 1.924 0.965 Comparative Example 3 200 600 1.943 0.933 Inventory 3 300 600 1.942 0.935 Honorable 4 400 600 1.922 0.973 Comparative Example 4

As shown in Table 1, Examples 1 to 4, in which the aging temperature and time were controlled within the range of the present invention, are superior to those of Comparative Examples 1 to 4 in magnetic properties.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, You will understand.

Claims (7)

(% By weight), 2.0 to 4.0% of Si, 0.02 to 0.04% of Al, 0.04 to 0.07% of Mn, 0.04 to 0.07% of Mn, 10 to 55 ppm of S, 0.0010 to 0.0055% of S, 0.03 to 0.07% Sn, 0.01 to 0.05% Sb, 0.01 to 0.05% P, and the balance Fe and other unavoidable impurities,
0.037 ≤ P + 0.5 * Sb ≤ 0.063 (where P and Sb are weight percent of the element);
Hot-rolling the slab to produce a hot-rolled steel sheet;
Cold-rolling the hot-rolled steel sheet to produce a cold-rolled steel sheet;
A first recrystallization annealing step of the cold-rolled steel sheet; And
And finally annealing the cold-rolled steel sheet after the primary recrystallization annealing is completed,
Wherein the cold rolled steel sheet is manufactured by maintaining a steel sheet having a thickness corresponding to a reduction ratio of 60 to 70% in cold rolling at a temperature range of 150 to 350 ° C for 1 to 10 minutes and then rolling to a final thickness Way. The method according to claim 1,
Further comprising the step of annealing the hot-rolled steel sheet to a hot-rolled steel sheet. The method according to claim 1,
Wherein the reheating of the slab is performed at a temperature in the range of 1,050 to 1,250 ° C. at which the nitride is incompletely dissolved. The method according to claim 1,
The primary recrystallization annealing includes a decarburization annealing and a steep annealing step,
Wherein the decarburization annealing and the steep annealing step are performed simultaneously or the steep annealing step is performed after the decarburization annealing step is completed. 5. The method of claim 4,
When the decarburization annealing and the soaking annealing process are performed at the same time,
Wherein the nitrogen content in the steel sheet after the decarburization annealing and the steep annealing step is 100 to 300 ppm. The method according to claim 1,
Wherein the final annealing step comprises a primary cracking step, a heating step and a secondary cracking step,
Wherein the initial heating rate is 18 to 75 占 폚 / hr in the heating step, and the heating rate is 10 to 15 占 폚 / hr in the temperature range of 900 to 1,020 占 폚. A directional electric steel sheet produced by hot rolling a steel slab, annealing a hot-rolled steel sheet, cold rolling, primary recrystallization annealing, and final annealing,
Wherein the steel slab comprises 2.0 to 4.0% by weight Si, 0.02 to 0.04% by weight of Al, 0.0 to 0.020% by weight of Mn, 0.04 to 0.07% by weight of C, 10 to 55 ppm of N, 0.037? P + 0.5? Sb? 0.063, where P and Sb are the same as or different from each other, and the balance Fe and other unavoidable impurities are contained in an amount of 0.005 to 0.0055%, Sn is 0.03 to 0.07%, Sb is 0.01 to 0.05%, P is 0.01 to 0.05% Quot; means the weight percentage of the element)
A steel sheet having a thickness corresponding to a reduction ratio of 60 to 70% in cold rolling for cold-rolled steel sheet is held for 1 to 10 minutes in a temperature range of 150 to 350 占 폚 and then rolled to a final thickness.