KR20000042706A - Method for producing oriented electric steel plate by heating slab at low temperature - Google Patents

Abstract

PURPOSE: A method is provided to stably produce an oriented electric steel plate without loosing a benefit of a low slab heating and with a reduced process than an existing technique at the same time. CONSTITUTION: A cold rolled plate is produced by heating, hot-rolling, a cold-rolling and preliminarily annealing a silicon steel slab. A separating agent of annealing is spread after decarbonization-annealing the cold rolled plate. An oriented electric steel plate is produced by an annealing of high temperature. The silicon steel slab is composed of C of 0.03-0.08wt%, Si of 2.90-3.30wt%, Mn of 0.05-0.30wt%, S under 0.007wt%, a soluble Al of 0.010-0.040wt%, N of 0.03-0.010wt%, P of 0.01-0.04wt%, Cr of 0.05-0.20wt%, Fe and other impurities. A heating temperature of the silicon steel slab is at 1100-1250°C. The preliminary annealing process is performed through heat treating cycle to crack for 5seconds-1minute at first to solidify a coarsening nitrated extract formed at the hot rolling, to cool to 700-800°C to re-extract and to control the extract in an appropriate size and to cool to a normal temperature.

Description

Method for manufacturing oriented electrical steel sheet by slab low temperature heating

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet used as iron core materials for transformers, generators, and other electrical equipment, and more particularly, adding a specific component controlled to enable low-temperature slab heating and undergoing a second recrystallization stabilization process. The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet capable of shortening a process as compared with the related art.

A grain-oriented electrical steel sheet is a steel sheet having an aggregate structure in which grain orientations are aligned in the (110) [001] direction and has excellent magnetic properties in the cold rolling direction.

The magnetic properties of oriented electrical steel are mainly represented by magnetic flux density and iron loss. The magnetic flux density is the magnetic flux density (B10) that is induced in the iron core by the magnetic field of 1000A / m, and the iron loss is 1.7 Tesla by the alternating frequency of 50Hz. When the magnetic flux density is obtained, it is evaluated as energy loss (W17 / 50) that is wasted by heat in the iron core.

The use of materials with high magnetic flux density enables the manufacture of small, high-performance electrical devices. The smaller the iron loss, the greater the loss of electrical energy.

The (110) [001] texture is obtained by using a secondary recrystallization phenomenon. Secondary recrystallization is a crystal grain of a specific orientation among fine grains produced by ordinary primary recrystallization, called a Goss orientation ( 110) [001] The grains (usually referred to as the nucleus of the secondary recrystallization) are abnormally grown throughout the specimen, and the magnetic flux density is excellent when the secondary recrystallization occurs completely and its orientation is excellent. It is known to be done.

In order to stabilize the secondary recrystallization, the primary recrystallized grains are uniform in size, and the orientation of the primary recrystallized grains (hereinafter referred to as the primary recrystallized aggregate) is not only eroded into the nucleus of the secondary recrystallization but also the secondary recrystallization. It is known that secondary recrystallization adheres to the ideal [001] direction during the growth process, that is, it should be advantageous to develop secondary recrystallized grains having excellent directionality.

To achieve these objectives, it is necessary to form the appropriate primary recrystallization aggregate structure with proper alloy design and appropriate process control. For example, by forming an appropriate amount of hard particles such as fine carbide before rolling to the final thickness and performing cold rolling, {111} [112], etc., which is advantageous for secondary recrystallization, can be the main component of the primary recrystallization texture. have.

This is known because the cold rolling texture changes when dislocations are stuck by hard particles during rolling.

Equally important, it is necessary to restrain the growth of primary recrystallized grains before secondary recrystallization occurs. As a grain growth inhibitor for this, precipitates such as MnS, MnSe, AlN, Cu ₂ S, and the like are known, and in general, the stronger the grain growth inhibition by the precipitates, the more the secondary recrystallization is stabilized.

However, in order to obtain strong grain growth inhibition, the amount, size, and distribution of the precipitates must be well controlled. It is known that the grain growth inhibitory force is increased when the fine precipitates of several hundred to 2000 microns are uniformly distributed as much as possible. .

In the case of conventional grain-oriented electrical steel sheet manufacturing for proper control of the precipitate distribution, an appropriate amount of precipitate forming element is added in the steelmaking step, and the coarse precipitate formed in the slab after continuous casting is completely dissolved by slab heating, followed by a hot rolling process. The emphasis is on controlling the precipitates to be finely and uniformly distributed.

To this end, in the conventional process, the slab heating should be performed at about 1200 ° C. for about 5 hours. At this time, an oxide called faylite is formed on the surface of the hot slab by the oxidation reaction with air. The oxide has a low melting point, so that even when the slab surface temperature is about 1330 ° C, the molten metal melts from the surface.

At this time, the molten slag is designed to flow outward, but some of it accumulates in the support in the furnace and requires internal repair to remove the solidification scale at the end of the work. There is a significant cost burden such as poor quality, reduced productivity, and higher costs.

Therefore, if it is possible to heat the slab at a temperature of 1320 ° C. or less, at which the slab does not melt, very large profits can be expected.

Efforts to lower the slab heating temperature are intensively driven by leading manufacturers, mainly by adjusting the basic component system, namely selecting grain growth inhibitors that enable the employment of precipitates even at low temperature slab heating, slab heating and hot rolling. Techniques are known which carry out additional precipitate management in subsequent processes without controlling the precipitates in the rolling process.

These methods do not form precipitates that are inhibitors based solely on the elements contained in the cast steel, but rather in the appropriate steps of a series of manufacturing processes.

As such a method, a nitriding treatment method is known, as shown in Japanese Patent Application Laid-Open No. 1-283324, which is a nitriding treatment of a steel sheet in a gas atmosphere having nitriding ability after cracking in a decarburization process.

However, since these inventions require additional nitrogen enrichment (or sedimentation) annealing after decarbonization annealing, additional cost is required such as additional equipment or two annealing (if using an existing annealing furnace).

In order to solve the above problems, the present inventors have conducted numerous experiments such as changing the steel composition and changing the conditions of pre-annealing (hot-rolled sheet annealing). As a result, an appropriate amount of Cr is added in the steelmaking step, and according to the content of Cr, When pre-annealed, nitride precipitates such as AlN and Al (Si) N having appropriate sizes and distributions can be obtained, and primary recrystallized textures advantageous for secondary recrystallization can be obtained by formation of hard particles such as fine carbides. As a result, it was found that the secondary recrystallization can be stably performed without annealing, and thus, a grain-oriented electrical steel sheet can be manufactured by low temperature slab heating.

The present invention is characterized in that an appropriate amount of Cr is added to properly form the nitride precipitate and hard particles during pre-annealing, and pre-annealed with a cycle of an appropriate condition according to the content of Cr, thereby losing the advantages of low-temperature slab heating. At the same time, the object of the present invention is to provide a method for stably producing a grain-oriented electrical steel sheet by a shorter manufacturing process compared to the known art.

In the method for producing a grain-oriented electrical steel sheet of the present invention for achieving the above object, after the silicon steel slab is heated and hot rolled, then pre-annealed, by cold rolling once to make a cold rolled plate of the final thickness, the cold rolling In the method for producing a grain-oriented electrical steel sheet comprising the step of decarbonizing the plate, applying an annealing separator, and then finishing high temperature annealing, the silicon steel slab is in weight%, C: 0.03 to 0.08%, Si: 2.90 to 3.30%, Mn: 0.05 to 0.30%, S≤0.007%, acid soluble Al: 0.010 to 0.040%, N: 0.03 to 0.10%, P: 0.01 to 0.04%, Cr: 0.05 to 0.20% and the balance Fe and Other inevitably contained impurities; The heating temperature of the silicon steel slab is 1100 to 1250 ° C; In addition, the pre-annealing step is used to regenerate the coarse nitride precipitate formed during hot rolling, T ₁ = 1000 + (1400 / Cr) ^1/2 ± 5 (° C.) [where T ₁ : proper primary crack temperature, Cr : First crack at 5 seconds to 1 minute at a temperature satisfying the [Cr content (%)], and second crack at 30 minutes to 10 minutes at 850 to 950 ° C. to reprecipitate and control the precipitate to an appropriate size. In order to form fine hard particles, the cooling rate satisfies V _C = 15 (Cr / 0.0014) ^1/2 ± 1 (° C / sec) [V _C : proper cooling rate, Cr: Cr content (%)]. After cooling to 700-800 degreeC, it is comprised by the heat processing cycle which water-cools to normal temperature.

Hereinafter, the present invention will be described in detail with reference to preferred embodiments.

The present invention is characterized by producing a grain-oriented electrical steel sheet by low-temperature slab heating method by optimizing the pre-annealing conditions according to the Cr content, which will be described below.

Generally, AlN nitride precipitates in oriented electrical steel sheets are reusable or coarsened at a temperature of about 1100 ° C. At this time, reclaimed precipitates are known to have a very small size and coarse precipitates have a large size. .

Therefore, when coarse AlN-based precipitates are formed during hot rolling as in the case of the present invention, there is a need for a method capable of increasing the solubility of the coarse precipitates during pre-annealing of a conventional method.

In order to solve this problem, the present inventors conducted experiments to investigate the effect of adding various components, and when preannealed under appropriate heat treatment conditions according to the appropriate amount of Cr, the inventors of the coarse precipitates could be innovatively increased, thereby increasing the stock size of the precipitates. It was found that the distribution was obtained, and the present invention was proposed based on this.

However, the suitability in terms of grain growth suppression force of the precipitate distribution obtained at this time is somewhat insufficient compared to the case of the conventional high-temperature slab heating method or the known technology such as decarburization after decarburization, it is necessary to devise a method to compensate for this. Do. That is, from the viewpoint of forming a primary recrystallized texture structure advantageous for secondary recrystallization, a method of forming an appropriate amount of hard particles such as fine carbide or martensite phase during pre-annealing may be considered.

However, in the case of the grain-oriented electrical steel sheet of the component system, it is difficult to form the hard particles, which requires quenching of about 15 ° C./sec or more at a temperature range of about 1750 ° C. to about 750 ° C., which is difficult to implement due to the equipment conditions. This is because

On the other hand, the present inventors have found that addition of Cr and cooling at a controlled cooling rate in accordance with the amount of Cr can sufficiently form hard particles even by slow cooling of the degree of cooling in the temperature section.

This phenomenon is presumed to be related to the improvement of the hardenability of the steel, that is, Cr inhibits the coarsening of carbides and increases the solubility.

The inventors have found that sufficient cooling of the hard particles to 700-800 ° C., the maximum solidus temperature range of carbides, at a suitable cooling rate, depending on the Cr content, results in the formation of an adequate primary recrystallized texture. Based on this, the method of manufacturing a grain-oriented electrical steel sheet of low-temperature slab heating method, which can achieve stabilization of secondary recrystallization by supplementing the rather poor precipitate distribution (inadequate grain growth suppression) by forming an optimal primary recrystallized texture. Was proposed.

The components and manufacturing conditions of the silicon steel slab used in the present invention must satisfy the following conditions.

C is an element that forms austenite in the slab to facilitate the solid solution of AlN. If it is added less than 0.03%, the amount of austenite is too low, and if it is more than 0.08%, it takes a long time for decarbonization annealing. .

If Si is less than 2.90%, excellent iron loss characteristics are not obtained, and if it is more than 3.30%, cold rolling property is deteriorated, which is not preferable.

Mn is an element that forms austenite in the slab to facilitate the solid solution of AlN, and when it is added below 0.05%, the amount of austenite formation is too low, and when it exceeds 0.30%, the roll force during rolling is high. It is not good because it increases too much and the plate shape becomes uneven.

When S is excessively added, S segregation in the center of the slab becomes severe, and in order to homogenize the slab, the slab needs to be heated to a temperature higher than the range of the invention, so that the S content is preferably 0.007% or less.

Acid Soluble Al and N are elements necessary for the formation of AlN precipitates. If the acid-soluble Al is less than 0.010%, the orientation of the secondary recrystallization deteriorates and the magnetic flux density is lowered. If the acid-soluble Al exceeds 0.040%, the development of the secondary recrystallization becomes unstable. On the other hand, N is less than the amount of AlN is less than 0.03%, if it exceeds 0.10% Blister (Blister) -type defects are likely to occur in the product is not preferable.

P is a grain boundary segregation element that reinforces the grain growth suppression force. If the content is less than 0.01%, the grain growth inhibiting ability is insufficient and the secondary recrystallization becomes unstable, and if it is more than 0.04%, it is not preferable because it may cause plate break during cold rolling.

Cr, the main additive element of the present invention, promotes the re-use of coarse nitride precipitates during pre-annealing and facilitates the formation of hard particles such as fine carbides, and is an element necessary for stabilization of secondary recrystallization. If the added amount is less than 0.05%, the secondary recrystallization stabilization effect is not exhibited, which is not preferable. In addition, when the content exceeds 0.20%, the secondary recrystallization stabilization effect is not increased by an increase in the Cr content, which is not preferable because it causes a cost increase due to alloy addition.

The steel component of this invention is as above and consists of remainder Fe. In addition, the present invention steel may contain a small amount (less than 80ppm) of the unavoidable elements (B, Ti, Nb, V, etc.) mixed from the raw materials during steelmaking.

Subsequently, when the heating temperature of the silicon steel slab composed of the above-described steel components is less than 1100 ° C., the roll force becomes excessive during hot rolling, which makes it difficult to control the plate shape, and at the temperature exceeding 1250 ° C., the steel surface is not preferable. It is not preferable because the amount of oxide scale increases.

If the thickness of the slab is too thin, hot rolling productivity is lowered, and if the slab is too thick, the slab heating time should be long, so it is preferable to control the slab to 150 to 350 mm.

After the usual hot rolling in consideration of the final final cold rolling thickness is usually produced by hot rolled steel sheet having a thickness of 1.5 ~ 2.6mm.

One of the features of the present invention is a pre-annealing process is a primary cracking treatment to re-use the coarse nitride precipitate formed during hot rolling, the second cracking treatment to re-precipitate and grow the solid solution to a suitable size and then hard particles such as fine carbide After cooling to an appropriate cooling rate to form a heat treatment cycle consisting of water cooling to room temperature.

At this time, in the annealing atmosphere, it is preferable to use a nitrogen atmosphere to prevent the loss of nitride.

The temperature at the first crack is less than T ₁ = 1000 + (1400 / Cr) ^1/2 ± 5 (° C.) [where T ₁ : the appropriate primary crack temperature, Cr: Cr content (%)] or the crack time is If it is less than 5 seconds, the availability of coarse precipitates is insufficient. As a result, the distribution of precipitates of the appropriate size is not obtained during subsequent cracks, and as a result, the secondary recrystallization becomes unstable, and thus excellent magnetic properties cannot be obtained. When the T exceeds ₁ or the crack time exceeds 1 minute, a high capacity increase of the nitride precipitate can be expected, but it is not preferable because the grain thickness of the steel sheet surface layer grows so coarsely that the secondary recrystallization becomes unstable.

If the temperature during the second crack is less than 850 ° C. or the crack time is less than 30 seconds, the nitride precipitates do not grow to the extent that they can exert grain growth suppression, so that the secondary recrystallization becomes unstable, and the secondary crack temperature is increased. If the temperature exceeds 950 ° C or the crack time exceeds 10 minutes, the size of the nitride precipitates is too coarse, which is not preferable in terms of secondary recrystallization.

When the cooling rate after the second cracking is less than V _C = 15-(Cr / 0.0014) ^1/2 ± 1 (° C / sec) [where V _C : proper cooling rate, Cr: Cr content (%)] Is not preferable because coarse carbides such as grain boundary carbides are formed rather than fine carbides, and the secondary recrystallization becomes unstable.In addition, when V _C is exceeded, it is not disadvantageous in terms of improving the solid solubility of carbides. It is not preferable from the viewpoint of practical use.

When the temperature reached during cooling after the secondary cracking is less than 700 ° C. and when it exceeds 800 ° C., the solid solution of carbides becomes insufficient so that hard particles such as fine carbides or martensite cannot be formed sufficiently during subsequent water cooling. It is not preferable because primary recrystallization texture which is advantageous for stabilization of recrystallization cannot be obtained.

Since the cooling to room temperature is faster, it is advantageous to the formation of hard particles, but water cooling is preferable in terms of industrial equipment.

The preannealed steel sheet is cold rolled once to make 0.23-0.35 mm thick. If the thickness of the final cold rolled sheet is less than 0.23mm, secondary recrystallization is not well developed, and if the thickness of the final cold rolled plate is more than 0.35mm, the vortex iron loss characteristics are deteriorated.

Subsequently, in order to lower the residual carbon amount of the cold rolled sheet to 30 ppm or less, decarbonization is performed using a mixed gas atmosphere of wet hydrogen + nitrogen having a dew point of 30 to 70 ° C for 30 seconds to 10 minutes at a temperature of 700 to 950 ° C. .

At this time, limiting the allowable value of residual carbon amount to 30ppm or less, if it exceeds this, the direction of secondary recrystallization formed during subsequent high temperature annealing is deteriorated, so that excellent magnetic flux density is not obtained and magnetic in use as a product such as transformer. This is because aging causes deterioration of iron loss characteristics.

When annealing annealing temperature is less than 700 ℃ or less than 30 seconds, decarburization is insufficient, and at temperatures exceeding 950 ℃, the primary recrystallization structure becomes too coarse and the secondary recrystallization becomes unstable, so the excellent magnetic flux density is achieved. It is not preferable to not obtain, and an annealing time of more than 10 minutes is uneconomical.

In addition, the atmosphere gas during decarbonization annealing may be used in any mixed atmosphere that enables simultaneous decarburization and nitrogen enrichment within the scope of the present invention, but is preferably a mixed gas atmosphere of wet hydrogen + nitrogen in which industrial decarburization is easily controlled. It is good to use

However, if the dew point of the atmosphere gas is too low, it is not good because the annealing time should be increased due to the decrease in decarburization performance. If the dew point of the atmosphere gas is too low, the glass oxide film formed during the subsequent high temperature annealing is poorly formed because the surface oxide layer is unevenly formed. Therefore, it is preferable to limit it to the range of 30-70 degreeC.

The temperature increase rate during finishing high temperature annealing should completely control the secondary recrystallization, and should be controlled in the range of 10 to 50 ° C./hr to improve its directivity. As an atmospheric gas for high temperature annealing, it is preferable to use dry hydrogen or a mixed gas of hydrogen and nitrogen to remove residual impurities such as N and S after the formation of the glass film and the completion of the secondary recrystallization.

If the temperature of finishing high temperature annealing is less than 1150 ° C or the cracking time is less than 1 hour, it is difficult to form a good glass film and remove impurities, and it is not preferable for the temperature above 1250 ° C or more than 30 hours because it is uneconomical. not.

The surface of the steel sheet in which the inorganic glass coating is formed by the high temperature annealing may be subjected to a tension coating after the high temperature annealing for the purpose of improving insulation and improving iron loss by miniaturization of magnetic domains.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example 1

By weight, C: 0.055%, Si: 3.10%, Mn: 0.11%, S: 0.005%, Acid Soluble Al: 0.025%, N: 0.077%, P: 0.025% and Cr were added as shown in Table 1 below. A 210 mm thick slab made of different and rest Fe was prepared. This was hot rolled after slab heating at 1200 ° C. for 4 hours to prepare a hot rolled plate having a thickness of 2.3 mm.

Then, after pre-annealing and pickling under different conditions as shown in Table 1 in a nitrogen gas atmosphere, a final cold rolled steel sheet having a thickness of 0.285 mm was prepared by one rolling. Thereafter, decarburization and decarbonization to form primary recrystallized structures were performed using a wet 25% H ₂ + 75% N ₂ mixed gas atmosphere having a dew point of 45 ° C. at 850 ° C. for 3 minutes.

Subsequently, an annealing separator containing MgO as a main component was applied to the surface of the steel sheet, followed by finishing high temperature annealing. At this time, the high temperature annealing the second was raised at a heating rate of 20 ℃ / hr to generate the re-crystallization from 1200 ℃ and line cycle thermal treatment for cooling After 15 hours cracking, atmosphere gas of elevated temperature is _{25% N 2 + 75% H} 2 After the temperature was raised to 1200 ° C., pure hydrogen gas was used. As described above, the secondary recrystallization rate and magnetic properties of the specimens in which Cr addition amount and preannealing conditions were changed are shown in Table 1 below.

The secondary recrystallization rate was measured by observing the macrostructure exposed by corrosion of the surface of the finished hot-annealed steel sheet with 20% hydrochloric acid solution at about 80 ℃, and the magnetic properties of B10 and W17 / 50 were measured by single plate magnetometer. It was.

TABLE 1

division Cr amount (%) Proper pre-annealing conditions according to Cr content Pre Annealing Condition Secondary Recrystallization Development Rate (%) Magnetic flux density Iron loss 1st crack temperature Ti (℃) Cooling rate Vc (℃ / sec) after 2nd crack Primary crack temperature (℃) 1st crack time (sec) Second crack temperature (℃) Second crack time (minutes) Cooling rate after 2nd crack (℃ / sec) Reach temperature after secondary crack B10 (Tesla) W17 / 50 (W / Kg) Comparative Material 1 0.02 * - - 1172 10 900 2 8 750 75 * 1.68 * 2.06 * Invention 1 0.05 1167 ± 5 9.0 ± 1 1172 10 900 2 8 750 100 1.89 1.05 Invention 2 0.10 1118 ± 5 6.6 ± 1 1113 10 900 2 5.6 750 100 1.90 1.03 Invention 3 0.15 1097 ± 5 4.7 ± 1 1092 10 900 2 3.7 750 100 1.90 1.03 Invention 4 0.20 1084 ± 5 3.1 ± 1 1079 10 900 2 2.1 750 100 1.90 1.03 Comparative Material 2 0.05 1167 ± 5 9.0 ± 1 1150 * 10 900 2 8 750 95 * 1.83 * 1.53 * Comparative Material 3 0.10 1118 ± 5 6.6 ± 1 1100 * 10 900 2 5.6 750 95 * 1.82 * 1.55 * Comparative Material 4 0.15 1097 ± 5 4.7 ± 1 1080 * 10 900 2 3.7 750 95 * 1.82 * 1.55 * Comparative Material 5 0.20 1084 ± 5 3.1 ± 1 1070 * 10 900 2 2.1 750 95 * 1.81 * 1.57 * Comparative Material 6 0.05 1167 ± 5 9.0 ± 1 1180 * 10 900 2 8 750 97 * 1.84 * 1.41 * Comparative Material7 0.10 1118 ± 5 6.6 ± 1 1130 * 10 900 2 5.6 750 97 * 1.85 * 1.39 * Comparative Material 8 0.15 1097 ± 5 4.7 ± 1 1120 * 10 900 2 3.7 750 97 * 1.86 * 1.38 * Comparative Material 9 0.20 1084 ± 5 3.1 ± 1 1100 * 10 900 2 2.1 750 97 * 1.85 * 1.39 * Comparative Material 10 0.05 1167 ± 5 9.0 ± 1 1172 10 900 2 7 * 750 97 * 1.85 * 1.40 * Comparative Material 11 0.10 1118 ± 5 6.6 ± 1 1113 10 900 2 5 * 750 97 * 1.87 * 1.35 * Comparative Material 12 0.15 1097 ± 5 4.7 ± 1 1092 10 900 2 3 * 750 97 * 1.86 * 1.38 * Comparative Material 13 0.20 1084 ± 5 3.1 ± 1 1079 10 900 2 One* 750 97 * 1.86 * 1.38 * Comparative Material14 0.15 1097 ± 5 4.7 ± 1 1100 3 900 2 5 750 95 * 1.82 * 1.56 * Comparative Material 15 0.15 1097 ± 5 4.7 ± 1 1100 70 * 900 2 5 750 97 * 1.85 * 1.39 * Comparative Material 16 0.15 1097 ± 5 4.7 ± 1 1100 10 830 * 2 5 750 95 * 1.82 * 1.55 * Comparative Material17 0.15 1097 ± 5 4.7 ± 1 1100 10 970 * 2 5 750 95 * 1.83 * 1.53 * Comparative Material 18 0.15 1097 ± 5 4.7 ± 1 1100 10 900 20 seconds * 5 750 95 * 1.81 * 1.61 * Comparative Material 19 0.15 1097 ± 5 4.7 ± 1 1100 10 900 11 * 5 750 95 * 1.82 * 1.56 * Comparative Material 20 0.15 1097 ± 5 4.7 ± 1 1100 10 900 2 5 670 * 97 * 1.85 * 1.39 * Comparative Material21 0.15 1097 ± 5 4.7 ± 1 1100 10 900 2 5 830 * 97 * 1.84 * 1.42 *

* Indicates that the results do not meet the conditions of the present invention.

As shown in Table 1, in the case where the amount of Cr added is less than the scope of the present invention (Comparative Material 1), the secondary recrystallization is very unstable, resulting in inferior magnetic properties, while adding an appropriate amount of Cr and preliminary annealing. In the case of controlling each condition within the scope of the present invention (invention material 1-4), an appropriate grain growth suppression force and a primary recrystallization texture were obtained to stabilize the secondary recrystallization, thereby obtaining excellent magnetic properties.

On the other hand, even if an appropriate amount of Cr is added, the primary cracking temperature at pre-annealing is T ₁ = 1000 + (1400 / Cr) ^1/2 ± 5 (℃) [wherein T ₁ : the appropriate primary cracking temperature and Cr: Cr content (%)] Less than (Comparative Materials 2-5), or when the crack time is less than 5 seconds (Comparative Material 14), insufficient reusability of the coarse precipitates results in the inability to obtain adequately sized precipitates during secondary cracking. As the secondary recrystallization becomes unstable, excellent magnetic properties could not be obtained.

In addition, when the primary cracking temperature exceeded T ₁ (Comparative Material 6-9) or the crack time exceeded 1 minute (Comparative Material 15), the secondary recrystallization became unstable, resulting in inferior magnetic properties.

Furthermore, if the cooling rate after the second crack is less than V _C = 15- (Cr / 0.0014) ^1/2 ± 1 (° C / sec) [where V _{C is the} appropriate cooling rate and Cr: Cr content (%)] Comparative material 10-13) could not obtain excellent magnetic properties as a result of unstable secondary recrystallization because no proper primary recrystallization texture was formed.

On the other hand, if the secondary cracking temperature is less than 850 ° C. (Comparative Material 16) or the cracking time is less than 30 seconds (Comparative Material 18) during pre-annealing, the secondary recrystallization becomes unstable due to the lack of grain growth inhibition. In the case where the crack temperature exceeds 950 ° C. (Comparative Material 17) or the crack time exceeds 10 minutes (Comparative Material 19), the magnetic properties deteriorate due to unstable development of the secondary recrystallization.

In addition, when the temperature reached by controlled cooling after the secondary crack is less than 700 ° C. (comparative material 20) and when it exceeds 800 ° C. (comparative material 20), the solid solution of carbides is insufficient to stabilize the secondary recrystallization. It was not possible to obtain an advantageous primary recrystallized texture, resulting in low magnetic flux density.

Therefore, according to the present invention as described above, when an appropriate amount of Cr is added in the steelmaking step, and pre-annealed with an appropriate cycle according to the content of Cr, nitrides such as AlN and Al (Si) N having an appropriate size and distribution By forming hard particles such as fine carbides, it is possible to obtain a primary recrystallized texture structure that is advantageous for secondary recrystallization, and to produce secondary recrystallization stably without sedimentation annealing. It is possible to do, after the decarbonization annealing does not need to additionally perform nitrogen enrichment (or sedimentation) annealing can shorten the process, reducing the manufacturing cost.

Claims (3)

After the silicon steel slab is heated and hot rolled, and after pre-annealing, a cold rolled sheet having a final thickness is produced by cold rolling once, after the cold rolled sheet is decarbonized, and then annealing separator is applied, followed by finishing hot annealing. In the method for producing a grain-oriented electrical steel sheet comprising a step, The silicon steel slab is, by weight, C: 0.03 to 0.08%, Si: 2.90 to 3.30%, Mn: 0.05 to 0.30%, S≤0.007%, acid soluble Al: 0.010 to 0.040%, N: 0.03 to 0.10 %, P: 0.01 to 0.04%, Cr: 0.05 to 0.20% and the balance Fe and other unavoidably contained impurities; The heating temperature of the silicon steel slab is 1100 to 1250 ° C; And, the pre-annealing step, T ₁ = 1000 + (1400 / Cr) ^1/2 ± 5 (° C.) in order to re-employ the coarse nitride precipitate formed during hot rolling [where, T ₁ : appropriate primary crack temperature, Cr: Cr content (%)] is first cracked for 5 seconds to 1 minute at a temperature that satisfies, and second cracked at 30 to 10 minutes at 850 to 950 ℃ to reprecipitate and control the precipitate to an appropriate size, Subsequently, V _C = 15 (Cr / 0.0014) ^1/2 ± 1 (° C / sec) (where V _C : proper cooling rate and Cr: Cr content (%)) to form fine hard particles. A method of manufacturing a grain-oriented electrical steel sheet by low temperature heating of a slab, characterized in that the cooling is performed to a temperature of 700 to 800 ° C. at a satisfactory cooling rate, followed by a heat treatment cycle of cooling to room temperature. 2. The method of claim 1, wherein the slab is subjected to a tension coating after hot annealing to improve iron loss. The method of claim 1, wherein the atmosphere of the pre-annealing step is a nitrogen atmosphere, the method for producing a grain-oriented electrical steel sheet by low temperature heating slab.