KR20140058938A - Grain-oriented electrical steel sheet and manufacturing method for the same - Google Patents

Abstract

Disclosed are an oriented electrical steel plate and a manufacturing method for the same. According to the present invention, a method for manufacturing the oriented electrical steel plate comprises a step of: 1) reheating a slab consisting of 2.0 ~4.5 wt% of Si; 0.005 ~ 0.040 wt% of Al; less than 0.20 wt% of Mn; less than 0.010 wt% of N; less than 0.010 wt% of S; 0.005 ~ 0,05 wt% of P; 0.04 ~ 0.07 wt% of C; 0.08 ~ 0.10 wt% of Sn, residual Fe and other impurities; 2) cooling the slab with one of the air cooling, water cooling, and oil cooling methods at the cooling speed of 20°C/s after hot-rolling the slab; 3) annealing the cooled hot-rolled steel plate; 4) strongly cold-rolling the annealed hot-rolled steel plate; 5) first annealing the cold-rolled steel plate for recrystallization; and 6) finally annealing the annealed and recrystallized steel plate. The hot-rolled steel plate consists of martensite, bainite, or cementite made up of segmented carbides inside.

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]

More particularly, the present invention relates to a directional electric steel sheet and a method of manufacturing the same, and more particularly, to a method of manufacturing a directional electric steel sheet and a method of manufacturing the same, Shaped magnetic steel sheet having improved magnetic properties and a method for producing the same.

Directional electrical steel sheet is a soft magnetic material with excellent magnetic properties in one direction or rolling direction because it shows a goss texture with a texture of {110} < 001 > In order to manifest such aggregate structure, complicated processes such as component control in steelmaking, slab reheating in hot rolling and hot rolling process control, hot-rolled sheet annealing, primary recrystallization annealing, and final annealing (secondary recrystallization annealing) And these processes must also be very precise and strictly controlled.

On the other hand, it is very important to control phosphorus as one of the factors expressing Goss aggregation breakfast because it inhibits indiscreet growth of primary recrystallization and allows only goss cluster tissue to grow when secondary recrystallization occurs. In order to obtain Goss texture in the final annealing, the growth of all the primary recrystallized grains must be suppressed until immediately before the secondary recrystallization. To obtain sufficient restraining force, the amount of inhibitor should be sufficiently large and the distribution should be uniform .

On the other hand, in order to cause secondary recrystallization during the final annealing process at a high temperature, the phosphorous should have excellent thermal stability so as not to be easily decomposed. The secondary recrystallization is a phenomenon that occurs when the inhibitor that inhibits the growth of the primary recrystallized grains during the final annealing dissolves or loses its restraining ability in the proper temperature range. In this case, the specific grains such as relatively GOS grains grow rapidly in a relatively short time do.

 Generally, the quality of the grain-oriented electrical steel sheet can be evaluated by the magnetic flux density and iron loss, which are representative magnetic characteristics, and the higher the precision of the Goss texture, the better the magnetic properties. In addition, the directional electric steel sheet having high quality can manufacture high-efficiency electric power equipment due to the re-characteristics, thereby achieving miniaturization of electric power equipment and high efficiency.

Research and development for lowering the iron loss of a directional electric steel sheet have been carried out first from research and development to increase magnetic flux density. The initial oriented electrical steel sheet was prepared by cold rolling two times using MnS as a grain growth inhibitor proposed by M. F. Littman (Special Issue 30-3651). The secondary recrystallization was formed stably, but the magnetic flux density was not so high and the iron loss was high. Japanese Unexamined Patent Publication (Kokai) No. 40-15644 discloses a method for producing a grain-oriented density and low iron loss directional electrical steel sheet by simultaneously using AlN and MnS precipitates, and cold rolling the cold rolling rate by 80% or more once. By increasing the {110} < 001 > orientation orientation in the rolling direction by a strong grain growth inhibitor and steel cold rolling, it was possible to obtain the high magnetic flux density and the hysteresis loss was greatly improved, .

On the other hand, by increasing the silicon content of the electric steel sheet, the resistivity of the steel sheet is increased, the eddy current flowing in the steel sheet is suppressed to improve the iron loss, and the secondary recrystallization is followed by the refining annealing to remove unnecessary impurities in the steel sheet, Method was also devised and a method of reducing core loss by controlling the size of the secondary recrystallized grains to an appropriate size was also studied.

Silicon is an element with a very high resistivity, and its iron loss is greatly improved when added. However, as the content increases, the brittleness increases greatly and the workability is very poor. In the decarburization annealing, the SiO ₂ oxide layer is densely formed and the formation of base coating becomes very difficult. In order to remove impurities, 100% hydrogen gas is used for the calcination annealing at 1200 ° C. for 10 hours or more. Increasing the annealing temperature to further reduce the impurity content at present may increase the burden of the manufacturing cost. The effect of iron loss improvement through proper secondary recrystallization size control is a very complicated process to control the formation of secondary recrystallization through control of grain growth inhibitor, cold rolling and primary recrystallization. Respectively.

On the other hand, researches have been carried out to significantly improve the iron loss through a method of making the magnetic domains of the secondary recrystallized grains formed, and considerable technological progress has been made. There are two methods of making the magnetic domains finer: a method of irradiating a laser on the surface of the steel sheet to impart a temporary stress to the surface of the steel sheet to refine the magnetic domains of the {110} <001> orientation, and a method of applying a certain deformation to the surface of the steel sheet, There is a method of miniaturizing the magnetic domain by inducing a structural change. This method of magnetic domain refinement has a burden of raising the manufacturing cost since the final product is further subjected to a process of finely finishing the magnetic domain after the final secondary recrystallization annealing is completed.

Generally, a method of reducing eddy current loss, which is one of the typical components of iron loss, by reducing the thickness of a steel sheet can be obtained by adding strain during cold rolling. In this case, the crystal growth driving force is increased. As the original crystal growth inhibitor, The secondary recrystallization is unstable. In order to reduce the thickness while balancing the crystal growth and the crystal growth inhibiting ability, it is necessary to roll at a proper cold rolling rate in the final cold rolling. The proper cold rolling rate depends on the suppressing power of the crystal growth inhibitor. Previously, when the AlN and MnS complex precipitates proposed by Taguchi are used as a crystal growth inhibitor, the appropriate cold rolling rate is about 87%, and in the case of the precipitates of MnS suggested by Littman, a cold rolling rate of 50 to 70% is appropriate. Another reason is that the secondary recrystallization is unevenly formed, and the other is that since the width of the magnetic domain increases as the thickness decreases in terms of the magnetostrictive energy, it is difficult to move the magnetic domain when applying an arbitrary magnetic field.

Japanese Unexamined Patent Publication No. 5-302122 proposes to preliminarily cold-melt 10 to 50% of hot-rolled steel sheets in order to solve the problem of the restriction of the hot-rolled steel sheet thickness and the final rolling ratio in the manufacture of the high- And then performing hot-rolled sheet annealing and hot-cold rolling. However, in this case, there is a burden of increase in manufacturing cost due to cold rolling twice and annealing twice for recrystallization.

On the other hand, in order to suppress the enlarged crystal growth driving force due to steel cold rolling, in addition to the alloy component adjustment and the multi-stage cold rolling patent for manufacturing a grain-oriented electrical steel sheet having a steel sheet thickness of 0.23 mm or less and a low iron loss and high specific gravity density, distribution of fine AlN and MnS precipitates A hot-rolled sheet annealing method capable of forming a hot-rolled annealed sheet is proposed in Japanese Patent Laid-Open Nos. 2-259019 and 5-125446.

However, as in Japanese Patent Application Laid-Open No. 4-329830, the slab heating temperature is 1200 ° C. or less, and the hot-rolled sheet heating temperature must be controlled according to the acid-soluble aluminum content.

In addition, Patent No. 4-014940 for a method of electrostatically applying MgO, which is an annealing separator, and Patent No. 4-002526, which proposes 3 times cold rolling and 3 times vacuum annealing, as a patent for a method of producing a directional electric steel sheet of 0.23 mm or less, A method of manufacturing a polar material by changing the diameter of the work roll according to the rolling thickness is proposed in Korean Patent Publication 2002-0033021. These patents have a disadvantage that they are economically incompatible with quality, which is a very difficult technology to accumulate additional facility investment and operation know-how in preparation for the currently commercialized manufacturing technology.

To summarize the conventional techniques that have been discussed so far, development of a crystal growth inhibitor for ensuring the high magnetic flux density characteristics and purification of the impurities such as refining of the impurities, annealing for removing the impurities for improving the cleanliness of the steel sheet, In the development of ultra-low iron loss directional electric steel sheet through reduction of thickness, it was necessary to derive the appropriate cold rolling rate according to the reduction of thickness and to perform multi-stage cold rolling, In addition to the addition of B and Ti and the combined addition of Sn and Cr to reinforce the inhibitor, a strict slab heating temperature and a hot-rolled annealing method have been proposed. However, the actual conditions presented are strict production conditions, .

In order to further improve the magnetic properties of the grain-oriented electrical steel sheet, an alloy element capable of obtaining a suppression effect similar to that of the precipitate, unlike the technique of suppressing the growth of crystal grains due to precipitates, is added to obtain secondary recrystallization high- In the first recrystallization annealing process, the proportion of the goss texture in the primary recrystallization texture is increased to increase the secondary recrystallization microstructure fraction of the goss texture after the secondary recrystallization and high temperature annealing And a technology for uniformly distributing the size of the primary recrystallized grains so as to prevent the aggregate structure that does not contribute to the improvement of the magnetic properties due to the nonuniformity of the primary recrystallized microstructure.

In order to implement various means for improving the magnetic characteristics of the grain-oriented electrical steel sheet, the conventional method includes adding an alloy component to the steel sheet.

In Japanese Patent Laid-Open No. 1-283324, it is proposed to add B and Ti in order to reinforce the weakening of crystal growth suppression ability by one-time cold rolling. However, in case of B, Also, it is easy to form coarse BN in the steel after the addition, and Ti is also present after secondary recrystallization due to formation of TIN or TiC having a heating temperature of 1300 ° C or higher, which is a factor for increasing iron loss rather.

Another method for improving the grain growth inhibiting ability is to produce a grain oriented electrical steel sheet using MnSe and Sb as grain growth inhibitors. A representative known technique is described in Japanese Patent Laid-Open Publication No. 51-13469, which is briefly as follows. The method includes the steps of hot slab heating, hot rolling, hot rolling annealing, primary cold rolling, intermediate annealing, secondary cold rolling, decarburization annealing, and final annealing. This method has a high magnetic flux density However, since the material itself becomes considerably small, cold rolling can not be performed once, and cold rolling is carried out twice through intermediate annealing to increase the manufacturing cost. In addition, since toxic and expensive Sb and Se are used, there is a disadvantage that separate facilities for handling toxic substances are necessary, the preparation is bad, and the manufacturing cost is also high.

Another proposal for improving the grain growth inhibiting power is to add a mixture of Sn and Cr, heat-treat the slab at a temperature of 1200 ° C or less, perform hot rolling, intermediate annealing, cold rolling once or twice, decarburization annealing, And a nitriding treatment is carried out. The typical known technique is Japanese Patent Laid-Open No. 3-281072. However, the above-mentioned prior art strictly controls the annealing temperature of the hot-rolled sheet in accordance with a very stringent production standard for producing low-loss-loss, high-magnetic-strength, grain-oriented electrical steel sheets, that is, Since Cr is added to Sn in combination with the Sn, the production cost is increased, and the oxide layer formed in the decarburization annealing process due to Cr having a strong oxygen affinity is formed in a considerably dense manner, so that decarburization is difficult and nitriding is difficult.

On the other hand, when elements such as Sb, P, Sn and the like are added to the steel sheet, the magnetic properties of the steel sheet can be greatly improved.

That is, 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, Sb is segregated in the primary recrystallization grain boundaries to increase the secondary recrystallization starting temperature of the grains having a goss texture when the secondary recrystallization annealing is performed at a high temperature to obtain a secondary recrystallized microstructure excellent in the degree of integration. However, when Sb is added above a certain level, the crystal grain growth inhibiting power is too strong, so that the secondary recrystallization of the goss texture does not occur properly, and the oxidation reaction on the surface during decarburization annealing is inhibited, Has a disadvantage in that the base coating is deteriorated after secondary recrystallization annealing at a high temperature.

In addition, P has been reported to have an effect of improving aggregate texture during primary recrystallization. That is, it has the effect of increasing the fraction of the grains having the Goss orientation during the primary recrystallization. However, P tends to be segregated at the grain boundary, and if the control is not properly performed at a predetermined weight in the low-temperature state, plate breakage frequently occurs during the rolling process.

Examples of patents for adding Sb, P, Sn, or the like to the grain-oriented electrical steel sheet as described above include Japanese Patent Application Laid-Open Nos. 2006-241503, 2-294428, 2007-254829, Open Publication No. 2007-051338, and Japanese Patent Laid-Open No. 11-335794.

Among them, the Japanese Patent Application Laid-Open No. 2006-241503 discloses that one or two selected from the group consisting of 0.015 to 0.07 wt% of P and 0.005 to 0.2 wt% of Sb and 0.01 to 0.5 wt% of Sn, A further production method is disclosed in which a species is further added to have stable magnetic properties.

Japanese Unexamined Patent Publication (KOKAI) No. 2-294428 discloses a high magnetic flux density directional electric steel sheet to which P: 0.0007 to 0.045 wt% is added.

On the other hand, a technique of adding Sb, P, or Sn alone or in combination is proposed, which is well known from Japanese Patent Laid-Open Publication No. 2007-254829. That is, a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties containing at least one of Sn, Sb and P in an amount of 0.02 to 0.30 wt% is disclosed. Also, in Japanese Patent Application Laid-Open No. 2007-051338, P is added to the steel in an amount of 0.2 wt% or less and, if necessary, further contains at least one element selected from 0.001 to 0.02 wt% of Sb and 0.002 to 0.1 wt% of Sn A method of manufacturing a directional electrical steel sheet is disclosed in which the magnetic properties are excellent in the direction of 45 ° in the rolling direction.

 Japanese Patent Application Laid-Open No. 11-335794 discloses an electric steel sheet in which 0.0005 to 2.0 wt% of at least one element selected from elements such as Sb, P, Sn, B, Bi, Mo, Te, A manufacturing method is disclosed.

As described above, the known techniques describe a rough configuration of technologies for producing a grain-oriented electrical steel sheet by adding alloying elements such as Ti, B, Se, Sb, P, and Sn. However, And the description of the effect of each of the alloying elements is not only insignificant, but also includes only two or more kinds of alloying elements, most of which is not the sole effect. That is, according to the known techniques to date, only the extent to which the magnetic property can be improved by the addition of Ti, B, Se, Sb, P, Sn or the like is described, , There is no description of the synergistic effect caused by elemental interactions. In other words, no remedy for the effect of the above-mentioned alloying elements is provided, and even if it is presented, the cause and relationship between the elements are insufficient.

Also, although the primary recrystallization and the secondary recrystallization behavior of the directional electrical steel sheets added with the alloying elements described in the above-mentioned known technologies are different from the directional electrical steel sheets proposed by the prior art, the known technologies do not provide any solution .

Directional electrical steel sheet is a soft magnetic material with excellent magnetic properties in one direction or rolling direction because it shows a goss texture with a texture of {110} < 001 > In order to manifest such aggregate structure, complicated processes such as component control in steelmaking, slab reheating in hot rolling and hot rolling process control, hot-rolled sheet annealing, primary recrystallization annealing, and final annealing (secondary recrystallization annealing) And these processes must also be very precise and strictly controlled.

On the other hand, it is very important to control phosphorus as one of the factors expressing Goss aggregation breakfast because it inhibits indiscreet growth of primary recrystallization and allows only goss cluster tissue to grow when secondary recrystallization occurs. In order to obtain Goss texture in the final annealing, the growth of all the primary recrystallized grains must be suppressed until immediately before the secondary recrystallization. To obtain sufficient restraining force, the amount of inhibitor should be sufficiently large and the distribution should be uniform .

On the other hand, in order to cause secondary recrystallization during the final annealing process at a high temperature, the phosphorous should have excellent thermal stability so as not to be easily decomposed. The secondary recrystallization is a phenomenon that occurs when the inhibitor that inhibits the growth of the primary recrystallized grains during the final annealing dissolves or loses its restraining ability in the proper temperature range. In this case, the specific grains such as relatively GOS grains grow rapidly in a relatively short time do.

 Generally, the quality of the grain-oriented electrical steel sheet can be evaluated by the magnetic flux density and iron loss, which are representative magnetic characteristics, and the higher the precision of the Goss texture, the better the magnetic properties. In addition, the directional electric steel sheet having high quality can manufacture high-efficiency electric power equipment due to the re-characteristics, thereby achieving miniaturization of electric power equipment and high efficiency.

Research and development for lowering the iron loss of a directional electric steel sheet have been carried out first from research and development to increase magnetic flux density. The initial oriented electrical steel sheet was prepared by cold rolling two times using MnS as a grain growth inhibitor proposed by M. F. Littman (Special Issue 30-3651). The secondary recrystallization was formed stably, but the magnetic flux density was not so high and the iron loss was high. Japanese Unexamined Patent Publication (Kokai) No. 40-15644 discloses a method for producing a grain-oriented density and low iron loss directional electrical steel sheet by simultaneously using AlN and MnS precipitates, and cold rolling the cold rolling rate by 80% or more once. By increasing the {110} < 001 > orientation orientation in the rolling direction by a strong grain growth inhibitor and steel cold rolling, it was possible to obtain the high magnetic flux density and the hysteresis loss was greatly improved, .

On the other hand, by increasing the silicon content of the electric steel sheet, the resistivity of the steel sheet is increased, the eddy current flowing in the steel sheet is suppressed to improve the iron loss, and the secondary recrystallization is followed by the refining annealing to remove unnecessary impurities in the steel sheet, Method was also devised and a method of reducing core loss by controlling the size of the secondary recrystallized grains to an appropriate size was also studied.

Silicon is an element with a very high resistivity, and its iron loss is greatly improved when added. However, as the content increases, the brittleness increases greatly and the workability is very poor. In the decarburization annealing, the SiO ₂ oxide layer is densely formed and the formation of base coating becomes very difficult. In order to remove impurities, 100% hydrogen gas is used for the calcination annealing at 1200 ° C. for 10 hours or more. Increasing the annealing temperature to further reduce the impurity content at present may increase the burden of the manufacturing cost. The effect of iron loss improvement through proper secondary recrystallization size control is a very complicated process to control the formation of secondary recrystallization through control of grain growth inhibitor, cold rolling and primary recrystallization. Respectively.

On the other hand, researches have been carried out to significantly improve the iron loss through a method of making the magnetic domains of the secondary recrystallized grains formed, and considerable technological progress has been made. There are two methods of making the magnetic domains finer: a method of irradiating a laser on the surface of the steel sheet to impart a temporary stress to the surface of the steel sheet to refine the magnetic domains of the {110} <001> orientation, and a method of applying a certain deformation to the surface of the steel sheet, There is a method of miniaturizing the magnetic domain by inducing a structural change. This method of magnetic domain refinement has a burden of raising the manufacturing cost since the final product is further subjected to a process of finely finishing the magnetic domain after the final secondary recrystallization annealing is completed.

Generally, a method of reducing eddy current loss, which is one of the typical components of iron loss, by reducing the thickness of a steel sheet can be obtained by adding strain during cold rolling. In this case, the crystal growth driving force is increased. As the original crystal growth inhibitor, The secondary recrystallization is unstable. In order to reduce the thickness while balancing the crystal growth and the crystal growth inhibiting ability, it is necessary to roll at a proper cold rolling rate in the final cold rolling. The proper cold rolling rate depends on the suppressing power of the crystal growth inhibitor. Previously, when the AlN and MnS complex precipitates proposed by Taguchi are used as a crystal growth inhibitor, the appropriate cold rolling rate is about 87%, and in the case of the precipitates of MnS suggested by Littman, a cold rolling rate of 50 to 70% is appropriate. Another reason is that the secondary recrystallization is unevenly formed, and the other is that since the width of the magnetic domain increases as the thickness decreases in terms of the magnetostrictive energy, it is difficult to move the magnetic domain when applying an arbitrary magnetic field.

Japanese Unexamined Patent Publication No. 5-302122 proposes to preliminarily cold-melt 10 to 50% of hot-rolled steel sheets in order to solve the problem of the restriction of the hot-rolled steel sheet thickness and the final rolling ratio in the manufacture of the high- And then performing hot-rolled sheet annealing and hot-cold rolling. However, in this case, there is a burden of increase in manufacturing cost due to cold rolling twice and annealing twice for recrystallization.

On the other hand, in order to suppress the enlarged crystal growth driving force due to steel cold rolling, in addition to the alloy component adjustment and the multi-stage cold rolling patent for manufacturing a grain-oriented electrical steel sheet having a steel sheet thickness of 0.23 mm or less and a low iron loss and high specific gravity density, distribution of fine AlN and MnS precipitates A hot-rolled sheet annealing method capable of forming a hot-rolled annealed sheet is proposed in Japanese Patent Laid-Open Nos. 2-259019 and 5-125446.

However, as in Japanese Patent Application Laid-Open No. 4-329830, the slab heating temperature is 1200 ° C. or less, and the hot-rolled sheet heating temperature must be controlled according to the acid-soluble aluminum content.

In addition, Patent No. 4-014940 for a method of electrostatically applying MgO, which is an annealing separator, and Patent No. 4-002526, which proposes 3 times cold rolling and 3 times vacuum annealing, as a patent for a method of producing a directional electric steel sheet of 0.23 mm or less, A method of manufacturing a polar material by changing the diameter of the work roll according to the rolling thickness is proposed in Korean Patent Publication 2002-0033021. These patents have a disadvantage that they are economically incompatible with quality, which is a very difficult technology to accumulate additional facility investment and operation know-how in preparation for the currently commercialized manufacturing technology.

To summarize the conventional techniques that have been discussed so far, development of a crystal growth inhibitor for ensuring the high magnetic flux density characteristics and purification of the impurities such as refining of the impurities, annealing for removing the impurities for improving the cleanliness of the steel sheet, In the development of ultra-low iron loss directional electric steel sheet through reduction of thickness, it was necessary to derive the appropriate cold rolling rate according to the reduction of thickness and to perform multi-stage cold rolling, In addition to the addition of B and Ti and the combined addition of Sn and Cr to reinforce the inhibitor, a strict slab heating temperature and a hot-rolled annealing method have been proposed. However, the actual conditions presented are strict production conditions, .

In order to further improve the magnetic properties of the grain-oriented electrical steel sheet, an alloy element capable of obtaining a suppression effect similar to that of the precipitate, unlike the technique of suppressing the growth of crystal grains due to precipitates, is added to obtain secondary recrystallization high- In the first recrystallization annealing process, the proportion of the goss texture in the primary recrystallization texture is increased to increase the secondary recrystallization microstructure fraction of the goss texture after the secondary recrystallization and high temperature annealing And a technology for uniformly distributing the size of the primary recrystallized grains so as to prevent the aggregate structure that does not contribute to the improvement of the magnetic properties due to the nonuniformity of the primary recrystallized microstructure.

In order to implement various means for improving the magnetic characteristics of the grain-oriented electrical steel sheet, the conventional method includes adding an alloy component to the steel sheet.

In Japanese Patent Laid-Open No. 1-283324, it is proposed to add B and Ti in order to reinforce the weakening of crystal growth suppression ability by one-time cold rolling. However, in case of B, Also, it is easy to form coarse BN in the steel after the addition, and Ti is also present after secondary recrystallization due to formation of TIN or TiC having a heating temperature of 1300 ° C or higher, which is a factor for increasing iron loss rather.

Another method for improving the grain growth inhibiting ability is to produce a grain oriented electrical steel sheet using MnSe and Sb as grain growth inhibitors. A representative known technique is described in Japanese Patent Laid-Open Publication No. 51-13469, which is briefly as follows. The method includes the steps of hot slab heating, hot rolling, hot rolling annealing, primary cold rolling, intermediate annealing, secondary cold rolling, decarburization annealing, and final annealing. This method has a high magnetic flux density However, since the material itself becomes considerably small, cold rolling can not be performed once, and cold rolling is carried out twice through intermediate annealing to increase the manufacturing cost. In addition, since toxic and expensive Sb and Se are used, there is a disadvantage that separate facilities for handling toxic substances are necessary, the preparation is bad, and the manufacturing cost is also high.

Another proposal for improving the grain growth inhibiting power is to add a mixture of Sn and Cr, heat-treat the slab at a temperature of 1200 ° C or less, perform hot rolling, intermediate annealing, cold rolling once or twice, decarburization annealing, And a nitriding treatment is carried out. The typical known technique is Japanese Patent Laid-Open No. 3-281072. However, the above-mentioned prior art strictly controls the annealing temperature of the hot-rolled sheet in accordance with a very stringent production standard for producing low-loss-loss, high-magnetic-strength, grain-oriented electrical steel sheets, that is, Since Cr is added to Sn in combination with the Sn, the production cost is increased, and the oxide layer formed in the decarburization annealing process due to Cr having a strong oxygen affinity is formed in a considerably dense manner, so that decarburization is difficult and nitriding is difficult.

On the other hand, when elements such as Sb, P, Sn and the like are added to the steel sheet, the magnetic properties of the steel sheet can be greatly improved.

That is, 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, Sb is segregated in the primary recrystallization grain boundaries to increase the secondary recrystallization starting temperature of the grains having a goss texture when the secondary recrystallization annealing is performed at a high temperature to obtain a secondary recrystallized microstructure excellent in the degree of integration. However, when Sb is added above a certain level, the crystal grain growth inhibiting power is too strong, so that the secondary recrystallization of the goss texture does not occur properly, and the oxidation reaction on the surface during decarburization annealing is inhibited, Has a disadvantage in that the base coating is deteriorated after secondary recrystallization annealing at a high temperature.

In addition, P has been reported to have an effect of improving aggregate texture during primary recrystallization. That is, it has the effect of increasing the fraction of the grains having the Goss orientation during the primary recrystallization. However, P tends to be segregated at the grain boundary, and if the control is not properly performed at a predetermined weight in the low-temperature state, plate breakage frequently occurs during the rolling process.

Examples of patents for adding Sb, P, Sn, or the like to the grain-oriented electrical steel sheet as described above include Japanese Patent Application Laid-Open Nos. 2006-241503, 2-294428, 2007-254829, Open Publication No. 2007-051338, and Japanese Patent Laid-Open No. 11-335794.

Among them, the Japanese Patent Application Laid-Open No. 2006-241503 discloses that one or two selected from the group consisting of 0.015 to 0.07 wt% of P and 0.005 to 0.2 wt% of Sb and 0.01 to 0.5 wt% of Sn, A further production method is disclosed in which a species is further added to have stable magnetic properties.

Japanese Unexamined Patent Publication (KOKAI) No. 2-294428 discloses a high magnetic flux density directional electric steel sheet to which P: 0.0007 to 0.045 wt% is added.

On the other hand, a technique of adding Sb, P, or Sn alone or in combination is proposed, which is well known from Japanese Patent Laid-Open Publication No. 2007-254829. That is, a method for producing a grain-oriented electrical steel sheet having excellent magnetic properties containing at least one of Sn, Sb and P in an amount of 0.02 to 0.30 wt% is disclosed. Also, in Japanese Patent Application Laid-Open No. 2007-051338, P is added to the steel in an amount of 0.2 wt% or less and, if necessary, further contains at least one element selected from 0.001 to 0.02 wt% of Sb and 0.002 to 0.1 wt% of Sn A method of manufacturing a directional electrical steel sheet is disclosed in which the magnetic properties are excellent in the direction of 45 ° in the rolling direction.

 Japanese Patent Application Laid-Open No. 11-335794 discloses an electric steel sheet in which 0.0005 to 2.0 wt% of at least one element selected from elements such as Sb, P, Sn, B, Bi, Mo, Te, A manufacturing method is disclosed.

As described above, the known techniques describe a rough configuration of technologies for producing a grain-oriented electrical steel sheet by adding alloying elements such as Ti, B, Se, Sb, P, and Sn. However, And the description of the effect of each of the alloying elements is not only insignificant, but also includes only two or more kinds of alloying elements, most of which is not the sole effect. That is, according to the known techniques to date, only the extent to which the magnetic property can be improved by the addition of Ti, B, Se, Sb, P, Sn or the like is described, , There is no description of the synergistic effect caused by elemental interactions. In other words, no remedy for the effect of the above-mentioned alloying elements is provided, and even if it is presented, the cause and relationship between the elements are insufficient.

Also, although the primary recrystallization and the secondary recrystallization behavior of the directional electrical steel sheets added with the alloying elements described in the above-mentioned known technologies are different from the directional electrical steel sheets proposed by the prior art, the known technologies do not provide any solution .

In order to achieve the above object, a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention comprises: 2.0 to 4.5% of Si, 0.005 to 0.040% of Al, 0.20% : 0.010% or less, S: not more than 0.010%, P: 0.005 to 0.05%, C: 0.04 to 0.07%, Sn: 0.08 to 0.10% and remainder Fe and other inevitably incorporated impurities , Cooling the slab by hot rolling, cooling at least one cooling method selected from air cooling, water cooling and oil cooling, and a cooling rate of 20 ° C / s or more, annealing the cooled hot- A step of hot-rolling the hot-rolled steel sheet, a step of annealing the cold-rolled steel sheet by primary recrystallization; And final annealing the primary recrystallized annealed steel sheet, wherein cementite in which martensite, bainite or carbide is separated is present in the hot-rolled sheet by the cooling.

The temperature of the slab reheating step may be 1,050 to 1,250 ° C.

The N content reused in the steel sheet in the slab reheating step may be 20 to 50 ppm.

The temperature of the hot-rolled sheet annealing step may be 900 to 1,200 ° C.

The primary recrystallization annealing step may be a decarburization annealing and a nitriding annealing at 800 to 950 ° C.

The size of the primary recrystallized grains by the primary recrystallization annealing may be 18 to 25 mu m.

The method for manufacturing a grain-oriented electrical steel sheet according to the present invention has the following effects.

It is possible to further improve the crystal grain growth inhibiting ability of the nitride and sulfide, which are the crystal grain growth inhibitors of the conventional grain oriented electrical steel sheet, as the grain growth inhibitor because it is an element which interferes with the movement of grain boundaries as the Sn grain boundary segregation element as the core element.

Particularly, in the primary recrystallized texture, since the number of Goss bearing nuclei growing in the secondary recrystallized texture is increased by increasing the grain fraction of the Goss orientation, the size of the secondary recrystallized microstructure is smaller than that obtained in the conventional directional electric steel sheet . As a result, the smaller the grain size in the final product, the smaller the eddy current loss, so that the improved magnetic characteristics can be obtained.

1 is a process diagram of a method for manufacturing a grain-oriented electrical steel sheet according to an embodiment of the present invention.

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 grain-oriented electrical steel sheet according to a preferred embodiment of the present invention will be described.

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; 0.005 to 0.040% of Al; 0.20% or less of Mn; 0.010% or less of N; : 0.010% or less, P: 0.005 to 0.05%, C: 0.04 to 0.07%, Sn: 0.08 to 0.10%, and remainder of Fe and other inevitably incorporated impurities. The slab is subjected to hot rolling Cooling the hot rolled steel sheet by at least one cooling method selected from the group consisting of air cooling, water cooling and oil cooling, and a cooling rate of 20 DEG C / s or more; annealing the cooled hot rolled steel sheet by hot rolling; A first recrystallization annealing step of the cold-rolled steel sheet; And final annealing the primary recrystallized annealed steel sheet, wherein cementite in which martensite, bainite or carbide is separated is present in the hot-rolled sheet by the cooling.

The reason for limiting the slab component used in the reheating step S10 of the slab is as follows.

Si: 2.0 to 4.5 wt%

Silicon (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 wt%, the resistivity is decreased, and the eddy current loss is increased to deteriorate the iron loss characteristic. When the annealing is performed at high temperature, the ferrite and the austenite phase transformation are generated and the secondary recrystallization becomes unstable. do. On the other hand, when the Si content exceeds 4.5 wt%, the mechanical properties of the electrical steel sheet increase in brittleness and the toughness decreases, so that the plate rupture incidence during the rolling process becomes intense and the formation of the secondary recrystallization becomes unstable. Therefore, Si is limited to a range of 2.0 to 4.5 wt%.

Al: 0.005 to 0.04 wt%

In addition to AlN precipitated at the time of hot rolling and hot-rolled annealing, aluminum (Al) is combined with Al, Si, and Mn in which nitrogen ions introduced by ammonia gas exist in a solid state in steel during annealing after cold rolling (Al, Si, Mn) N and AlN type nitrides to serve as strong grain growth inhibitors. When the content of Al is less than 0.005 wt%, sufficient effect as an inhibitor can not be expected because the number and volume of AlN to be formed are considerably low, and when it exceeds 0.04 wt%, coarse nitride is formed to deteriorate the crystal growth inhibiting ability. Therefore, the content of Al is limited to 0.005 to 0.040 wt%.

Mn: not more than 0.20 wt%

Manganese (Mn) is a component that reduces the total iron loss by reducing the eddy current loss by increasing the resistivity as Si. (Al, Si, Mn) by reacting with nitrogen introduced by the nitriding treatment together with Si to form a precipitate of N, which is an important element for suppressing the growth of the primary recrystallized grains and causing secondary recrystallization. However, when the content of Mn is more than 0.20 wt%, 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 , which hinders formation of a base coat formed during high temperature annealing, Since the phase transformation between ferrite and austenite is caused in the high temperature annealing process, the aggregate structure is seriously damaged and the magnetic properties are greatly deteriorated. Therefore, Mn is limited to 0.20 wt% or less.

N: 0.010 wt% or less

Nitrogen (N) is an important element that reacts with Al to form AlN, and is preferably added in an amount of 0.01 wt% or less in the steelmaking step. When the content of N exceeds 0.01 wt%, surface defects called blisters due to nitrogen diffusion are caused in the step after hot rolling, and since too much nitride is formed in the slab state, rolling becomes difficult and the subsequent steps become complicated Which may cause the manufacturing cost to rise. Therefore, the content of N is limited to 0.010 wt% or less.

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.

C: 0.04 to 0.07 wt%

Carbon (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 poor brittleness and poor rolling property. However, when it remains in the final product, Is an element that deteriorates the magnetic properties, it is necessary to control the content to an appropriate level. When the content of C is less than 0.04 wt% in the range of the above Si content, heterogeneity of slab and hot rolled microstructure is caused because the phase transformation between ferrite and austenite does not work properly.

On the other hand, after the annealing of the hot-rolled steel sheet, the residual carbon in the steel sheet activates the dislocation of the potential during cold rolling to increase the shear strain band to increase the generation site of the Goss nucleus, thereby increasing the fraction of the GOS grains in the primary recrystallized microstructure If the content of C is more than 0.07 wt% in the range of the Si content described above, it is not possible to obtain sufficient decarburization in the decarburization annealing process unless a separate process or equipment is added, The secondary recrystallization texture is severely damaged due to the phase transformation phenomenon, and furthermore, when the final product is applied to the electric power machine, magnetic properties due to magnetic aging are deteriorated. Therefore, the content of C is limited to 0.04 to 0.07 wt%.

S: not more than 0.010 wt%

When the content of sulfur (S) is more than 0.01 wt%, 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 grain growth inhibitor in the present invention, it is not preferable that S is added in an amount inevitably added to precipitate. Therefore, the content of S is limited to 0.010 wt% or less.

Sn: 0.08 to 0.10 wt%

Tin (Sn) is a core alloy element in one embodiment of the present invention and 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, the effect of suppressing the grain growth inhibiting ability by coarsening the particles causing the grain growth inhibiting effect of N and AlN, and the effect of reducing the grain growth Thereby preventing the grain growth growth inhibiting ability from being weakened.

Consequently, even at low Si content and high Si content, the successful expression of secondary recrystallized texture is ensured. In addition, when the thickness of the final product is reduced, that is, when the rolling is carried out to increase the rolling rate, the thermal instability of the grain, which is pointed out as a problem of the grain oriented grain- Can compensate for its successful growth.

As a result, the addition of Sn increases the fraction of goss texture in the primary recrystallized texture and increases the grain growth inhibiting ability. Therefore, the better texture, stable grain growth inhibition, In other words, it is possible to secure a secondary recrystallized texture structure composed of a gaseous crystal grain having a high degree of integration.

When the content of Sn is less than 0.08 wt%, the effect of improving the magnetic properties is small, but the effect is not sufficient. Also, the effect of improving the degree of integration of the goss texture is small and the effect of compensating the grain growth inhibiting ability The magnetic properties can not be improved.

On the other hand, when the content exceeds 0.10 wt%, the crystal grain growth inhibiting ability is excessively increased, so that the grain size of the primary recrystallized microstructure must be decreased in order to relatively increase the grain 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. In addition, from the viewpoint of mechanical properties, brittleness increases due to excessive segregation of grain boundary segregation elements, which may cause sheet breakage during manufacturing. Therefore, the content of Sn is limited to 0.08 to 0.10 wt%.

P: 0.005 to 0.05 wt%

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 the content of P is 0.005 wt% or less, the addition effect is not effective. When the content of P is 0.05 wt% or more, the brittleness is increased and the rolling property is greatly deteriorated. Therefore, the content of P is limited to 0.005 to 0.05 wt%.

The slab of the above composition is reheated to a predetermined temperature. (S10) At this time, the temperature range may be a temperature at which N and S to be solved are incompletely dissolved. 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 difficult to carry out a subsequent cold rolling step. Lt; / RTI &gt; In addition, since the size of the primary recrystallized grains becomes considerably small, it may become impossible to develop appropriate secondary recrystallization.

In one embodiment of the present invention, it is more important to control the amount of N contained in the lobster. That is, the reusable N determines the size and amount of the additional AlN to be formed in the decarburization annealing process, and the size and amount of the AlN are determined. When the size of the AlN is the same, if the amount is too large, It is not possible to obtain a suitable secondary recrystallized microstructure composed of goss texture. On the contrary, if the amount is too small, the crystal growth driving force of the primary recrystallized microstructure is increased, so that an appropriate secondary recrystallized microstructure can not be obtained similarly to the above-mentioned phenomenon.

The content of N reused in the steel through the slab reheating is preferably 20 to 50 ppm. The amount of reused N should be considered in consideration of the content of Al contained in the liquefied natural gas, because the nitrides used as the grain growth inhibitors are (Al, Si, Mn) N and AlN.

The correlation equation for the employment of Al and N in the pure 3% silicon steel sheet was proposed by Iwayama and is shown in Equation 1 below.

[Formula 1]

Assuming that the acid soluble aluminum is 0.028 wt% and N is 0.0050 wt%, the theoretical heating temperature by the Iwayama formula is 1258 캜, and the slab of such an electric steel sheet must be heated to 1300 캜.

However, if the slab is heated to 1280 ° C or higher, the surface of the steel sheet is melted due to the generation 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 rolling workability becomes very difficult, Resulting in an increase in maintenance.

Therefore, it is desirable to limit the temperature range of the slab reheating to 1,050 ~ 1,250 ° C for incomplete solution formation that enables proper control of the heating furnace repair, cold rolling and primary recrystallization texture.

(S20) The cooling rate at the time of quenching may be 20 ° C / s or more. The cooling method may be at least one of air cooling, water cooling and oil cooling.

The austenite phase present during hot rolling is transformed into a hard bainite or martensite phase having a very high strength in the quenching process. During annealing of the hot-rolled sheet after hot rolling, the bainat or martensite phase provides a nucleation site of the austenite phase and is present as a fine osetitite phase, promoting recrystallization in the subsequent heat treatment and cold rolling, Can help to form.

Therefore, if the hard martensite, bainite, or carbide is present in the form of cementite in a substantially segmented state by controlling the cooling rate after hot rolling to not less than 20 ° C / s, and then annealing of the hot-rolled sheet is performed, Is more uniformly controlled, and the AlN is more uniformly dissolved due to the fine and uniform base structure before cold rolling.

(S30) In the hot-rolled steel sheet, there is a deformed structure stretched in the rolling direction due to the stress, and AlN and MnS are precipitated in the hot-rolled steel sheet during the hot rolling. . Therefore, in order to obtain uniform recrystallized microstructure and fine precipitate distribution of AlN before cold rolling, the hot rolled sheet is heated again to the temperature below the slab heating temperature to recrystallize the deformed structure, and sufficient austenite phase is secured, It is important to promote employment of the grain growth inhibitor.

Therefore, it is preferable that the annealing temperature of the hot-rolled sheet be heated to 900 to 1200 ° C to maximize the austenite fraction, followed by heat-cracking and cooling. The average size of the precipitate in the strip after annealing the hot-rolled sheet may be about 200 to 3000 Å.

(S40) Cold rolling is carried out at a thickness of 0.23 mm or less by using a reverse mill or a tandem mill, and the annealed hot rolled sheet is subjected to cold rolling One-time cold rolling, which does not heat-treat and rolls from the initial hot-rolled thickness to the final product thickness, is most preferred. This is because with one strong cold rolling, orientations with a low degree of integration in {110} < 001 > orientation will rotate in the direction of deformation and only Goss grains best aligned with the {110} < 001 & . 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, it is most preferable that the cold rolling is performed at a cold rolling rate of at least 87% by one-time cold rolling.

The cold-rolled steel sheet is subjected to primary recrystallization annealing. (S50) Primary recrystallization annealing is performed by decarburization, recrystallization of the deformed structure, and nitriding treatment using ammonia gas. 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, nitriding is performed using ammonia gas after decarburization and recrystallization, And ammonia gas may be simultaneously used so that nitriding treatment can be performed at the same time.

On the other hand, in the case of adding Sn, the balance between the crystal growth inhibiting ability and the crystal growth driving force is different from that of the conventional component system, so it is necessary to strictly consider this. In other words, when the component is controlled to the above-described composition range, not only the size of the primary recrystallized grains becomes finer but also the secondary recrystallization does not occur well under the condition of the same primary recrystallization. Secondary recrystallization is effective when the size of the primary recrystallized grains becomes finer. However, since these elements have an effect of strengthening the grain growth inhibition by segregating in the grain boundaries, the secondary recrystallization in the same grain size category having the above- It is necessary to clarify the decarburization annealing temperature condition by carefully examining which factors of grain growth driving force and grain growth inhibiting power act more dominantly.

In the embodiment of the present invention, the increasing factor of the crystal grain growth driving force acts more strongly than the increasing factor of the crystal grain growth restraining force, and the secondary recrystallization tends to occur quickly. When the above-mentioned grain boundary segregation element is added, the crystal grain growth inhibiting effect is affected during the formation of the primary recrystallized microstructure, and when the annealing heat treatment is performed in a normal temperature range, the grain size becomes finer than that of a microstructure obtained by a general component system. That is, since the grain growth driving force may be stronger than in a general component system, it is necessary to stabilize the primary recrystallized microstructure at a temperature slightly higher than a normal temperature range. Therefore, in the present invention, it is necessary to set the decarburization annealing temperature range to at least about 10 DEG C or more and at most about 30 DEG C or more, and more preferably about 800 to 950 DEG C, as compared with the usual case.

When the primary recrystallization annealing temperature of the steel sheet is less than 800 ° C, the crystal grain size becomes too small as compared with a conventional component system, and the crystal growth driving force is increased, and it takes a long time due to annealing annealing at a low temperature for decarburization. And the Fe ₂ SiO ₄ is formed on the surface of the steel sheet to a considerable degree. As a result, decarburization and formation of the internal oxide layer are delayed, and the SiO ₂ oxide layer is densely formed in a narrow region, resulting in base coating defects. If the primary recrystallization annealing temperature is higher than 950 DEG C, recrystallized grains and nitrides grow to a great extent and the crystal growth driving force is lowered, so that stable secondary recrystallization is not formed.

In the component system of one embodiment of the present invention, the size of the primary recrystallized grain which can appropriately balance the grain growth driving force and the grain growth restraining force is preferably about 18 to 25 μm. The annealing time is not a problem for exerting the effect of the present invention, but it is preferable that the annealing is performed within 5 minutes in consideration of productivity.

Finally, the steel sheet subjected to the first recrystallization annealing is subjected to final annealing. (S70) Normally, an annealing separator based on MgO is applied to the steel sheet during the production of the grain-oriented electrical steel sheet, and then the final annealing is performed for a long time to cause secondary recrystallization A {110} < 001 > aggregate structure in which the {110} planes of the steel sheet are parallel to the rolled surface and the < 001 > direction is parallel to the rolling direction is formed, whereby a grain oriented electrical steel sheet having excellent magnetic properties can be manufactured.

The objective of the final annealing is largely the formation of {110} < 001 > texture by secondary recrystallization, the formation of a vitreous film by the reaction of the oxide layer and MgO formed during decarburization, and the removal of impurities which impair magnetic properties. 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 The impurities can be removed by keeping it in a 100% hydrogen atmosphere for a long time.

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

Si: 3.25%, C: 0.055%, Mn: 0.099%, S: 0.0045%, N: 0.0043%, Sol. 0.028% of Al, 0.028% of P, 0.08% of Sn, and the balance Fe and other inevitably incorporated impurities were vacuum-melted to prepare an ingot. Subsequently, the steel sheet was heated to a temperature of 1200 캜, hot-rolled to a thickness of 2.3 mm, and cooled to a predetermined cooling rate as shown in Table 1.

The hot-rolled hot-rolled sheet was heated at a temperature of 1050 占 폚 and maintained at 950 占 폚 for 180 seconds. The hot rolled annealed sheet was pickled and then subjected to one-time cold rolling to a thickness of 0.23 mm. The cold rolled sheet was maintained at a temperature of 870 ° C in a humid atmosphere of hydrogen and a mixture of nitrogen and ammonia for 180 seconds so that the nitrogen content was 200 ppm Simultaneous decarburization and nitriding annealing. This steel sheet was coated with MgO as an annealing separator and finally annealed in a coiling manner. In the final annealing, a mixed atmosphere of 25% nitrogen and 75% hydrogen was set to 1200 ° C., and after reaching 1200 ° C., it was maintained in a 100% hydrogen atmosphere for 10 hours or more and then cooled. The cooling rate and the magnetic properties after hot rolling were measured and are shown in Table 1 below.

Cooling rate (° C / s) Iron loss (W17 / 50, W / kg) Magnetic flux density (B10, Tesla) division 0.5 0.904 1.894 Comparative Example 1 2 0.915 1.896 Comparative Example 2 5 0.902 1.896 Comparative Example 3 10 0.874 1.904 Comparative Example 4 15 0.857 1.919 Comparative Example 5 20 0.815 1.913 Inventory 1 22 0.804 1.915 Inventory 2 25 0.802 1.911 Inventory 3 30 0.802 1.901 Honorable 4 34 0.814 1.910 Inventory 5 40 0.801 1.901 Inventory 6

As can be seen in Table 1, it was found that the iron loss and magnetic flux density of the inventors whose cooling rate after hot rolling was controlled to 20 ° C / s or higher were superior to the comparative materials.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the exemplary embodiments or constructions. It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. will be.

It is therefore to be understood that the above-described embodiments are illustrative and non-restrictive in every respect. 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 (7)

The steel sheet according to any one of claims 1 to 3, wherein the steel sheet contains, by weight percent (wt%), 2.0-4.5% Si, 0.005-0.040% Al, To 0.07%, Sn: 0.08 to 0.10%, and the balance of Fe and other inevitably incorporated impurities;
Cooling the slab by hot rolling followed by cooling at least one cooling method selected from the group consisting of air cooling, water cooling and oil cooling and a cooling rate of 20 ° C / s or more;
Annealing the cooled hot-rolled sheet by hot-rolled sheet annealing;
Hot-rolling the annealed hot-rolled sheet;
A first recrystallization annealing step of a cold-rolled steel sheet; And
A step of final annealing the primary recrystallized annealed steel sheet
/ RTI &gt;
Wherein the cementite having martensite, bainite, or carbide segments is present in the hot-rolled sheet by the cooling. The method of claim 1,
Wherein the temperature of the slab reheating step is 1,050 to 1,250 ° C. 3. The method of claim 2,
Wherein the content of N reused in the steel sheet in the slab reheating step is 20 to 50 ppm. The method of claim 1,
Wherein the temperature of the hot-rolled sheet annealing step is 900 to 1,200 ° C. The method of claim 1,
Wherein the primary recrystallization annealing step comprises decarburization annealing and nitriding annealing at 800 to 950 占 폚. The method of claim 5,
Wherein the size of the primary recrystallized grains by the primary recrystallization annealing is 18 to 25 占 퐉. A directional electrical steel sheet produced by any one of claims 1 to 6.

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