KR100435479B1 - A method for manufacturing low temperature slab reheating grain-oriented electrical steel sheet with superior film property - Google Patents

Abstract

The present invention relates to a method for manufacturing low-temperature slab heating oriented electrical steel sheet, by lowering the reduction ratio of secondary cold rolling and adjusting the atmosphere during intermediate annealing, thereby improving the characteristics of the glass coating and at the same time preventing directional degradation of the secondary recrystallization. To produce a low-temperature slab heating oriented electrical steel sheet having excellent coating properties, the purpose is.

According to the present invention, after the silicon steel slab is heated and hot rolled, the hot rolled sheet is annealed and the cold rolled sheet is finally made by two cold rolling including intermediate annealing, and the second cold annealed sheet is annealed and annealing separator. In the manufacturing method of the grain-oriented electrical steel sheet comprising the step of applying a high temperature annealing finish

The silicon steel slab is by weight, C: 0.02 to 0.08%, Si: 2.90 to 3.30%, Mn: 0.10 to 0.40%, S≤0.006%, acid soluble Al: 0.005 to 0.030%, N: 0.005 to 0.012% , Cu: 0.30 to 0.70%, Cr: 0.03 to 0.07% and the balance Fe and other inevitably contained impurities;

The intermediate annealing is carried out in a temperature range of 850 ~ 950 ℃;

Controlling the secondary cold rolling rate during the cold rolling to 25 to 45% so that the thickness of the final cold rolled sheet is 0.26 to 0.35 mm;

The secondary annealing is carried out for 30 seconds to 10 minutes at 800 to 900 ° C. under humid hydrogen and nitrogen atmosphere;

The finishing high temperature annealing is carried out by heating up to a temperature range of 1150 to 1200 ℃ at a temperature rising rate of 10 to 50 ℃ / hr, and cracking at that temperature for 5 hours or more. The manufacturing method of an electrical steel sheet shall be the technical summary.

Description

A method for manufacturing low-temperature slab heating oriented electrical steel with excellent film characteristics {A METHOD FOR MANUFACTURING LOW TEMPERATURE SLAB REHEATING GRAIN-ORIENTED ELECTRICAL STEEL SHEET WITH SUPERIOR FILM PROPERTY}

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 electronic devices, and more particularly, by adding a specific component and lowering the secondary cold rolling rate, thereby providing an oxide layer suitable for the final cold rolled sheet. The present invention relates to a method for producing a grain-oriented electrical steel sheet which can improve the directionality of secondary recrystallization and obtain stable glassy film characteristics and excellent magnetic properties at the same time.

The grain-oriented electrical steel sheet has an aggregate structure in which the orientations of the grains are aligned in the (110) [001] direction, and thus have 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 a magnetic flux density (B ₁₀ ) that is induced in the iron core by a magnetic field of 1000 A / m, and the iron loss is alternating at a constant frequency, for example, 50 Hz. When the magnetic flux density of 1.7 Tesla is obtained, it is estimated to be W _17/50 , that is, energy loss wasted due to heat in the iron core.

The use of materials with high magnetic flux density makes it possible to manufacture small, high-performance electrical devices. The less iron loss, the greater the loss of electrical energy.

Since the manufacturing method was invented by N.P.Goss, the oriented electrical steel sheet having the above characteristics has been improved and many improvements have been made. The history of research on oriented electrical steel sheets is not an exaggeration to say that it is a history of iron loss reduction efforts. Major improvements include thinning the product, varying the number of additives in the components, or minimizing the domains by irradiating the product with a laser. All of these methods increase manufacturing costs and require a lot of labor.

However, in recent years, as the demands of the demanders are diversified, there is a movement to select a material economically for the purpose of the final product, but the products are not subdivided enough to satisfy these various needs. For example, in addition to the demand for iron core products of low iron loss electronic devices, there are demands for low-cost supply of oriented electrical steel sheets for iron cores of small, high-performance devices with low processing costs.

In order to satisfy these needs, there is a need for a technology capable of manufacturing a thick high magnetic flux density oriented electrical steel sheet by a low temperature slab heating method. In addition, the iron loss of such a product would be desirable if the energy loss is not so great that the thickness of the steel sheet is thick, even considering the thickness.

Therefore, if the oriented electrical steel sheet can be manufactured as a thick material, in terms of demand, it is advantageous to save time and expense of punching the electrical steel sheet with iron core, and also from the producer side, it is manufactured by continuous rolling and continuous annealing. In this case, there is also an advantage that productivity is increased compared to conventional thin oriented electrical steel sheet.

On the other hand, the (110) [001] texture is obtained by using a secondary recrystallization phenomenon. Secondary recrystallization is a grain of a specific orientation, which is called a Goss orientation, among the fine grains produced by ordinary primary recrystallization. Abnormal growth of crystal grains (nuclei of secondary recrystallization) with an orientation of (110) [001] is called, and the magnetic properties are improved when such secondary recrystallization occurs completely and its orientation is excellent. It is known.

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

To achieve this goal, proper alloy design and appropriate process control are required. Equally important, it is necessary to suppress the growth of the primary recrystallized grains before the secondary recrystallization occurs.

As the 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 stable the second recrystallization. However, in order to obtain strong grain growth inhibition, it is necessary to control the amount, size, and distribution of precipitates well, and it is known that the grain growth inhibitory force increases correspondingly if the fine precipitates of several hundred to 2000 microns are uniformly distributed as much as possible. have.

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 1400 ° C. for about 5 hours. At this time, the surface of the hot slab has an oxide called Payalite, in which Si and Fe are combined by oxidation with air. The oxide has a low melting point, and even though 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 workability, reduced productivity, and higher costs. Therefore, if it is possible to heat the slab at a temperature of 1320 ° C. or less, which is a temperature at which the slab does not melt, very large profits can be expected.

Thus, the present inventor has proposed a method of manufacturing a grain-oriented electrical steel sheet by low temperature slab heating method in Korean Patent Publication No. 96-6026. This technique adds the appropriate steel component, first cold rolls to 0.60-0.75mm, then performs intermediate decarbonization annealing in a wet atmosphere at a temperature of 820-840 ℃, then completes second cold rolling to the final product thickness. It is characterized in that the secondary annealing in a dry atmosphere at a temperature of 500-600 ℃ where primary recrystallization does not occur.

However, in this case, since the secondary annealing has to be performed at a low temperature in a dry atmosphere, it is difficult not only to form an appropriate amount of oxide layer on the surface of the steel sheet during the second annealing, but also to form a plate such as a center wave formed during the secondary cold rolling. There is a problem that it is difficult to correct the shape defect. This makes it difficult to form an excellent glassy film on the surface of the product after the subsequent finishing high temperature annealing, and the surface flatness is deteriorated, thereby lowering the error rate of the product.

This problem can be solved when the wet atmosphere is heat-treated at a temperature of 800 ° C. or higher during the second annealing, but at this time, fine primary recrystallization having an average particle size of about 13 μm or less is formed so that the secondary recrystallization is 100 ° C. compared with the known technology. As a result of the low temperature around 950 DEG C, it was observed that the problem of deterioration in the orientation of the secondary recrystallization was caused by the problem that excellent magnetic properties were not obtained. This is because small particle size of primary recrystallization increases the driving force for secondary recrystallization, reducing the possibility of selective growth of the so-called Goss orientation.

On the other hand, the primary recrystallized grain size may be considered a method of performing secondary annealing at a high temperature, but since grains such as AlN are already formed in the grain-oriented silicon steel, grain growth is suppressed, so that the grain size increases until the secondary recrystallization occurs. There will be almost no.

Thus, the present inventors have repeatedly conducted research and experiments to solve the above problems and propose the present invention based on the results, and the present invention lowers the reduction rate of the secondary cold rolling and the second after the second cold rolling. The purpose of the present invention is to manufacture low-temperature slab heating oriented electrical steel sheets having excellent coating properties that can improve the characteristics of glassy coatings and prevent directional deterioration of secondary recrystallization by adjusting the differential annealing atmosphere and temperature.

According to the present invention, after the silicon steel slab is heated and hot rolled, the hot rolled sheet is annealed and the cold rolled sheet is finally made by two cold rolling including intermediate annealing, and the second cold annealed sheet is annealed and annealing separator. In the manufacturing method of the grain-oriented electrical steel sheet comprising the step of applying a high temperature annealing finish

The silicon steel slab is by weight, C: 0.02 to 0.08%, Si: 2.90 to 3.30%, Mn: 0.10 to 0.40%, S≤0.006%, acid soluble Al: 0.005 to 0.030%, N: 0.005 to 0.012% Cu: 0.30 to 0.70%, Cr: 0.03 to 0.07% and the balance Fe and other inevitable impurities; the intermediate annealing is performed at a temperature range of 850 to 950 ° C;

Controlling the secondary cold rolling rate during the cold rolling to 25 to 45% so that the thickness of the final cold rolled sheet is 0.26 to 0.35 mm;

Secondary annealing of the cold rolled sheet is carried out for 30 seconds to 10 minutes at 800 ~ 900 ℃ under a mixed atmosphere of wet hydrogen and nitrogen; The finishing high temperature annealing is 1150 ~ 1200 ℃ at a temperature rising rate of 10 ~ 50 ℃ / hr It relates to a method for producing a low-temperature slab heating oriented electrical steel sheet having excellent coating properties, characterized in that the temperature is raised to a temperature range and cracked at that temperature for at least 5 hours.

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

In order to simultaneously solve the above-mentioned problems of the prior art, the present inventors have conducted a number of experiments varying manufacturing process conditions. As a result, when the secondary cold rolling reduction rate is reduced to 25-45%, the wet atmosphere is higher than 800 ° C. Even when secondary annealing is carried out, primary recrystallization of about 20 μm or more is formed, and similarly to the above known technique, secondary recrystallization is started at around 1050 ° C. and its orientation is not degraded after completion of secondary recrystallization. there was. This may be because the decrease in the cold reduction rate decreases the number of nucleation sites of primary recrystallization such as dislocation.

That is, the present invention is a method of manufacturing a grain-oriented electrical steel sheet that enables low-temperature slab heating by adding a specific steel component, by greatly reducing the reduction rate during the secondary cold rolling compared to the known technique to form an appropriate amount of oxide layer and Even if the secondary annealing is performed in a wet atmosphere at about 800 ° C or above, which is easy to correct the plate shape, the primary recrystallized grain size is obtained. The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet of low temperature slab heating method having a magnetic property comparable to the conventional method.

Hereinafter, the component of the silicon steel slab of this invention is demonstrated.

When the content of C is less than 0.02%, the grains grow coarsely during slab heating, and the development of secondary recrystallization becomes unstable at the time of final high temperature annealing. It is preferable to set it to 0.08%.

If the content of Si is less than 2.90%, excellent iron loss characteristics are not obtained. If the content of Si is more than 3.30%, the cold rolling property is deteriorated, the content thereof is preferably set to 2.90 to 3.30%.

The Mn is an element that forms austenite in the slab to facilitate the solid solution of AlN. If the content is less than 0.10%, the amount of austenite is too small. If the content exceeds 0.40%, the rolling force is increased. Since it increases too much and the plate shape becomes nonuniform, it is preferable to set the content to 0.10 to 0.40%.

When the S is excessively added, the S segregation in the center of the slab becomes severe, so that the slab needs to be heated to a temperature above the range of the present invention to homogenize it, so that the S content is preferably 0.006% or less.

The acid soluble Al and N are elements necessary for the formation of AlN precipitates. If the content of acid-soluble Al is less than 0.005%, the direction of secondary recrystallization deteriorates and the magnetic flux density is lowered. If it exceeds 0.030%, the development of secondary recrystallization becomes unstable, so the content is set to 0.005 to 0.030%. It is preferable.

When the content of N is less than 0.005%, the amount of AlN formation is insufficient, so that secondary recrystallization becomes unstable, and when the content exceeds 0.012%, a blister defect occurs in the steel sheet, so that the content is 0.005 to 0.012%. It is preferable to set to.

Cu and Cr are important components added not only to make the hot rolled sheet microstructure homogeneous but also to homogenize the first recrystallized microstructure after the second annealing, and the addition amounts thereof are selected as 0.3 to 0.7% and 0.03 to 0.07%, respectively. It is desirable to.

When any one of the above components is added below the lower limit of the added amount, the microstructure of the primary recrystallization becomes nonuniform, and the secondary recrystallization becomes unstable and the magnetic properties deteriorate. In addition, when the upper limit of each component range is exceeded, the effect of addition is not large. Rather, it is not preferable because the annealing time should be increased to lower the amount of carbon remaining in the steel sheet below the allowable value (about 30 ppm or less) after the second annealing, making it difficult to decarburize. not.

In addition to the above components, the steel slab of the present invention may contain an unavoidable element (B, Ti, Nb, V) mixed from raw materials during steelmaking in a trace amount (below 80 ppm).

Hereinafter, the process of manufacturing a grain-oriented electrical steel sheet using the silicon steel slab comprised as mentioned above is demonstrated.

The silicon steel slab is preferably reheated at a temperature range of 1200 to 1320 ° C. The reason for this is that when the heating temperature is less than 1200 ° C, it is difficult to work during hot rolling, and when the temperature is higher than 1320 ° C, the magnetic properties are greatly affected. Nonetheless, the benefits from low-temperature heating of slabs are greatly reduced. In addition, the slab heating time is set to 1 to 10 hours in consideration of cracking and economical efficiency to the inside of the slab.

The slabs heated as described above are hot rolled in a conventional manner, and the hot rolled sheet thickness is preferably limited to 1.5 to 3 mm in consideration of the subsequent final cold rolled thickness.

Thereafter, hot-rolled sheet annealing (pre-annealing) is performed. The pre-annealing is preferably carried out at 850 to 1000 ° C. for 30 seconds to 10 minutes to improve pickling properties of the steel sheet and to obtain precipitates such as AlN having an appropriate size.

The pre-annealed hot rolled sheet as described above is produced to the final thickness by two cold rolling including the intermediate annealing. At this time, the intermediate annealing is preferably carried out for 30 seconds to 10 minutes at 850 ~ 950 ℃ in a mixed gas atmosphere of dry nitrogen and hydrogen in order to form an appropriate primary recrystallized texture and further formation of the precipitate.

The secondary cold reduction ratio during the cold rolling is preferably selected to be 25 to 45%, because if less than 25%, the primary recrystallization average particle size is too coarse and the secondary recrystallization becomes unstable and exceeds 45%. This is because the directivity of the secondary recrystallization deteriorates.

In addition, the thickness of the final cold rolled sheet is preferably selected to be 0.26 ~ 0.35mm thickness, because the second recrystallization is not well developed when the thickness of the final cold rolled sheet is less than 0.26mm, if it exceeds 0.35mm This is because the vortex iron loss property is deteriorated, which is not preferable.

Cold rolled sheet as described above is wet nitrogen and hydrogen having a dew point of 30 to 70 ℃ for 30 seconds to 10 minutes at a temperature of 800 ~ 900 ℃ to correct the poor plate shape formed during decarburization, the formation of an appropriate amount of oxide layer and cold rolling Is annealed under a mixed gas atmosphere of. When the annealing temperature is less than 800 ° C. or less than 30 seconds, decarburization and plate shape correction are insufficient, and when the annealing temperature is more than 900 ° C. or the time is more than 10 minutes, the texture of the primary recrystallization deteriorates. This is not preferable because excellent magnetic flux density cannot be obtained as a result of not obtaining excellent aromatic secondary recrystallization. In this case, when the dew point of the atmosphere gas is too low, the annealing time should be increased due to the decrease in decarburization ability. If the dew point is too high, the glass film formed during the subsequent high temperature annealing may be formed unevenly. ) Is poorly formed, it is preferable to select in the range of 30 to 70 ℃.

At this time, the wet hydrogen and nitrogen atmosphere can use the atmosphere commonly used during secondary annealing of the grain-oriented electrical steel sheet, a typical example is the hydrogen: 10 ~ 50%, the atmosphere consisting of the remaining nitrogen. Considering the precipitate produced in the component system of, the average particle size of a suitable primary recrystallization is about 20 to 30 μm.

After secondary annealing as described above, an annealing separator containing MgO as a main component is applied to the surface of the steel sheet, followed by finishing high temperature annealing.

Specifically, the finish high temperature annealing consists of a temperature rising section for developing a secondary recrystallized structure and a high temperature cracking section for forming a glassy film and removing impurities. At this time, if the rate of temperature increase is too fast, the secondary recrystallization becomes unstable. On the other hand, if the rate of temperature rise is too slow, the annealing time is long and uneconomical, and thus the rate of temperature increase of 10 to 50 ° C / hr is preferable. After heating up to 1150-1200 degreeC by the said temperature increase rate, it is preferable to crack-process at least 5 hours for formation and purification of a glassy film. At this time, as the atmospheric gas during high temperature annealing, both pure gas or a mixed gas of nitrogen and hydrogen can be used.

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 coating after the high temperature annealing for the purpose of improving the insulation and improving the iron loss due to finer microstructure.

Hereinafter, the present invention will be described in detail through examples.

(Example)

Composition by weight: C: 0.35%, Si: 3.15%, Mn: 0.17%, S: 0.006%, acid soluble Al: 0.016%, N: 0.009%, Cu: 0.5%, Cr: 0.05% and the balance Fe A slab of 210 mm thickness was prepared. The slab was heated at 1300 ° C. for 5 hours and hot rolled to make a 2.0 mm thick hot rolled coil. Then, pre-annealed and pickled at 930 ° C. for 2 minutes, followed by two cold rolling including intermediate annealing to adjust to a final thickness of 0.29 mm. At this time, the primary cold rolling was changed to the thickness of the primary cold rolling plate in order to change the reduction rate during the secondary cold as shown in Table 1, the intermediate annealing is 900 in a dry 25% H ₂ + 75% N ₂ atmosphere It carried out for 3 minutes and 30 seconds at ° C.

Thereafter, the final thickness of the rolled sheet was subjected to secondary annealing at 850 ° C. for 3 minutes and 30 seconds in a 25% H ₂ + 75% N ₂ atmosphere having a dew point of 50 ° C., followed by 5% TiO ₂ and the remaining MgO in weight%. The annealing separator consisting of a coating on the surface of the steel sheet and then finished high temperature annealing. At this time, the temperature was raised to 1200 ° C. at a temperature rising rate of 20 ° C./hr to cause secondary recrystallization, and after cooling at 10 ° C. for 10 hours to form a glassy film and to remove impurities, it was cooled by 25% H ₂ as an atmosphere gas during temperature rising. + 75% N ₂ was used and pure hydrogen gas was used in the crack section at 1200 ° C.

The primary recrystallization average particle size was measured after the secondary annealing on the specimens with the secondary cold reduction rate as described above, and the secondary recrystallization development rate and the magnetic properties were measured after the finishing high temperature annealing. The state and plate shape were visually observed, and the results are shown in Table 1 below. Here, the average particle size of primary recrystallization was measured by Image Analyzer after etching the end face of secondary annealing plate with 2% nitric acid solution, and the secondary recrystallization development rate was corroded with 20% hydrochloric acid solution at about 80 ℃ after high temperature annealing. The secondary recrystallization area ratio was observed by observing the exposed macrostructure. The magnetic properties were measured by measuring B ₁₀ and W _17/50 with a single-plate magnetometer.

division Primary cold rolled thickness (mm) Secondary cold reduction rate (%) Primary recrystallization average particle size (μm) Secondary Recrystallization Rate (%) Vitreous coating appearance Product plate shape Magnetic flux density Iron loss B ₁₀ (Tesla) W _17/50 (W / Kg) Comparative Material 1 0.36 20 33 40 Good Good 1.67 2.01 Invention 1 0.39 25 30 100 Good Good 1.85 1.18 Invention 2 0.41 30 26 100 Good Good 1.86 1.15 Invention 3 0.53 45 20 100 Good Good 1.85 1.16 Comparative Material 2 0.58 50 17 100 Good Good 1.80 1.35 Comparative Material 2 0.73 60 13 100 Good Good 1.79 1.39

As shown in Table 1, the comparative material (1) having a secondary cold reduction ratio of less than the scope of the present invention, the primary recrystallization grain size is too coarse, the secondary recrystallization unstable, resulting in inferior magnetic properties, while Comparing materials (2) and (3) whose reduction ratios exceed the scope of the present invention, secondary recrystallization occurs completely, but the orientation is deteriorated, and the magnetic properties are inferior.

However, the inventive materials (1) to (3) in which the secondary cold reduction rate was controlled in the present invention range were able to obtain a good glassy film and excellent magnetic properties at the same time.

As described above, the present invention has the effect of improving the glass coating properties and at the same time providing excellent magnetic properties by adjusting the cold reduction rate and appropriately controlling the secondary annealing conditions.

Claims (5)

After the silicon steel slab is heated and hot rolled, hot rolled sheet is annealed and cold rolled sheet of final thickness is made by two cold rolling including intermediate annealing, and then the cold rolled sheet is annealed secondly and coated with annealing separator. In the manufacturing method of the grain-oriented electrical steel sheet comprising the step of finishing high temperature annealing, The silicon steel slab is by weight, C: 0.02 to 0.08%, Si: 2.90 to 3.30%, Mn: 0.10 to 0.40%, S≤0.006%, acid soluble Al: 0.005 to 0.030%, N: 0.005 to 0.012% , Cu: 0.30 to 0.70%, Cr: 0.03 to 0.07% and the balance Fe and other inevitably contained impurities; The intermediate annealing is carried out in a temperature range of 850 ~ 950 ℃; Controlling the secondary cold rolling rate during the cold rolling to 25 to 45% so that the thickness of the final cold rolled sheet is 0.26 to 0.35 mm; The secondary annealing is carried out for 30 seconds to 10 minutes at 800 to 900 ° C. under humid hydrogen and nitrogen atmosphere; The finishing high temperature annealing is carried out by heating up to a temperature range of 1150 to 1200 ℃ at a temperature rising rate of 10 to 50 ℃ / hr, and cracking at that temperature for 5 hours or more. Method of manufacturing electrical steel sheet. The method of claim 1, wherein the cold rolled sheet after the primary cold rolling has a thickness of 1.5 to 3.0 mm. delete The method for manufacturing a low-temperature slab heated oriented electrical steel sheet having excellent coating properties according to claim 1 or 2, wherein the average particle size of the primary recrystallization after the second annealing is 20 to 30 µm. delete