KR20000038157A - Method for producing oriented electric steel plate of high magnetic flux density by slab heating method at low temperature - Google Patents

Abstract

PURPOSE: A method for producing an aromatic electric steel plate is provided to have the excellent characteristic of magnetic flux density in a larger range by adding a specific component controlled to be able to heat a slab of low temperature and by stabilizing a secondary recrystalline. CONSTITUTION: A silicon steel slab composed of 0.020-0.045% of a C, 2.90-3.30% of a Si, 0.05-0.30% of a Mn, 0.001-0.012% of a B, 0.005-0.019% of an Al, 0.003-0.008% of a N, a S under 0.007%, 0.030-0.70% of a Cu, 0.03-0.07% of a Ni, 0.03-0.07% of a Cr, a P under 0.020%, a Fe and other impurities. The silicon steel slab is re-heated at a temperature within 1050-1250°C and a cold rolled sheet of 0.23-0.7mm is made by cold-rolling at first after a hot rolling and an annealing of hot rolled sheet. The cold rolled sheet is annealed to be a remained carbon amount under 30ppm and a whole nitrogen amount of 125-82.9(1+(Cu%+10(Ni%+Cr%)))ppm and to generate a decarbonization and a nitrification for 30seconds-10minutes at 850-950°C under a gas atmosphere contained a nitrogen having a dew point of 30-70°C at the same time. Thereby an aromatic electronic steel plate of high magnetic flux density is produced by spreading a separating agent of annealing and by annealing at a high temperature.

Description

Manufacturing method of high magnetic flux density oriented electrical steel sheet by low temperature slab heating method

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 controlled to enable low-temperature slab heating and stabilizing secondary recrystallization. The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet having excellent magnetic flux density characteristics in a wide range of steel sheet thicknesses through conventional processes.

The grain-oriented electrical steel sheet has an aggregate structure in which the grain orientation is aligned in the (110) [001] direction, and the product 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 a magnetic flux density, B ₁₀ , induced in the iron core by a magnetic field of 1000 A / m. By using the magnetic flux density of 1.7 Tesla, it is estimated to be W _17/50 . The use of materials with high magnetic flux density enables the manufacture of small, high-performance electrical devices. The less iron loss, the greater the loss of electrical energy.

Since the invention of producing a grain-oriented electrical steel sheet by cold rolling by N.P.Goss, many improvements have been made. It is no exaggeration to say that the history of research on oriented electrical steel sheet is the history of efforts to reduce iron loss. Major improvements include thinning the product, varying the amount of added elements in the components, or minimizing magnetic domains by irradiating the laser with the product. All of these methods increase manufacturing costs and require a lot of labor.

However, in recent years, as the demands of 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 thin products of low iron electronics, there are many 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 low temperature slab heating. In addition, iron loss of such a product may be desirable if the energy loss is not so great that the steel sheet thickness is large, even in view of thickness. If the oriented electrical steel sheet can be manufactured as a thick material, there is an advantage in that it can save time and cost of punching the electrical steel sheet in terms of demand, and in the case of the producer, it can be manufactured by continuous rolling and continuous annealing. There is also an advantage of increased productivity compared to conventional thin oriented electrical steel sheet.

On the other hand, the inventors of the Republic of Korea patent for a technology that enables low-temperature slab heating through additional precipitate management in the subsequent process to improve the problem of conventional oriented electrical steel sheet that is heated slab at high temperature for the employment of precipitates (eg AlN) It has been proposed in the applications 97-28305 and 97-37247 (hereinafter referred to as "prior art").

The prior art proposed in No. 97-28305 is based on a method of simultaneously performing decarburization and nitrogen enrichment under appropriate conditions after the completion of rolling a silicon steel slab containing an appropriate amount of Cu, Ni and Cr to the final product thickness. It is a method of manufacturing a grain-oriented electrical steel sheet of low temperature slab heating method that can secure high grain density by securing grain growth suppression force and making the primary recrystallized microstructure uniform.

In addition, the prior art proposed in No. 97-37247 is a method of manufacturing a high magnetic flux density oriented electrical steel sheet capable of low-temperature slab heating by forming a primary recrystallization growth inhibitor after cold rolling to the final product thickness to be. Specifically, this method is to reduce the content of C, to make the final thickness of the silicon steel slab containing an appropriate amount of B, and to nitriding under the appropriate conditions to form a BN precipitate, allowing the slab to be heated at low temperatures, and to change the existing equipment. It is a method that can produce electrical steel sheet without.

The above-mentioned prior arts are a remarkable technology that can be used for low temperature slab heating and stably produce high magnetic flux density oriented electrical steel sheet by using nitriding treatment while using existing equipment as it is. By the way, these methods are effective when manufacturing the steel sheet to 0.35mm or less, but there is a disadvantage in that excellent magnetic flux density cannot be obtained when producing a thicker than 0.4mm. The reason is that the prior art supplements the problem that the primary recrystallization structure becomes nonuniform in the thickness direction of the steel sheet in the process of simultaneously performing decarburization and nitrogen enrichment, but the effect is weak at a thickness above the threshold.

The present inventors have conducted in-depth studies to solve the above problems. As a result, primary recrystallization is carried out by decarburizing and nitriding under controlled conditions while using BN having excellent effects as an inhibitor by adding Cu, Ni, Cr and B in combination. Further experiments confirm that the uniformity of the tissue results in the development of secondary recrystallization to obtain high magnetic flux density characteristics stably even when the steel sheet thickness is not less than 0.4 mm as well as the usual steel sheet thickness of 0.23-0.35 mm, On the basis of this experimental result, the present invention was proposed.

The present invention provides a method for producing a high magnetic flux density oriented electrical steel sheet by low temperature slab heating, which can stably obtain excellent magnetic properties not only in thin materials but also in thick materials by nitriding treatment in a decarbonization annealing process.

The present invention for achieving the above object, in weight%, C: 0.020-0.045%, Si: 2.90-3.30%, Mn: 0.05-0.30%, B: 0.001-0.012%, Al: 0.005-0.019%, N : 0.003-0.008%, S: 0.007% or less, Cu: 0.30-0.70%, Ni: 0.03-0.07%, Cr: 0.03-0.07%, P: 0.020% or less, remaining Fe and other inevitable impurities The silicon steel slab is reheated at a temperature of 1050-1250 ° C, followed by hot rolling and annealing of the sheet, followed by cold rolling once to form a cold rolled sheet of 0.23 to 0.7 mm. 30 seconds to 10 seconds at a temperature of 850 to 950 ° C. under a nitrogen gas atmosphere with a dew point of 30 to 70 ° C. such that the total nitrogen amount is 125 to 82.9 (1 + [Cu% + 10 (Ni% + Cr%)] ² ) ppm. Annealing is performed to simultaneously decarburize and nitride for several minutes, and then apply annealing separator and finish hot annealing.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

In the present invention, the term 'museum' specifically refers to a cold rolled steel sheet of about 0.23-0.4mm, and the term 'thickness' specifically refers to a cold rolled steel sheet of about 0.4-07mm, through the cold rolling process of the present invention. The thickness of the cold rolled sheet to be produced includes a material and a thick material. In the present invention, the annealing step of simultaneously performing decarburization and nitriding treatment is also referred to as 'simultaneous decarburization annealing'.

The present invention, through the simultaneous decarbonation annealing to secure a stable secondary recrystallization not only in the museum but also in the thick material to increase the magnetism compared to the prior art, it is characterized by, compared to the prior art as follows.

In the case of simultaneous decarbonation annealing according to the above-mentioned prior art, in particular, the primary recrystallization structure becomes non-uniform in the thickness of the thick material, and even though the grain growth inhibitory force is given to the appropriate amount of nitrogen enrichment, the secondary recrystallization becomes unstable and thus high magnetic flux density is achieved. The problem of not being able to obtain characteristics appeared.

The present inventors conducted numerous experiments to prevent the non-uniform distribution of the primary recrystallization in the thickness of the thick, as a result of adding the appropriate amount of Cu, Ni, Cr and B during steelmaking, the appropriate amount according to the addition amount of Cu, Ni and Cr When nitrogen was enriched and BN was used as an inhibitor by simultaneous decarbonation annealing, it was found that a uniform primary recrystallized structure was obtained even at a wide range of steel sheet thickness, especially in thick material. To this end, the present invention properly controls the manufacturing conditions with the steel component management, hereinafter will be described separately.

[The composition of silicon steel slab]

In the case of containing less than 0.02% of C in the steel slab, the grains grow coarsely upon heating the slab, which is not preferable because the development of secondary recrystallization becomes unstable during the final high temperature annealing, and when the content exceeds 0.045%, simultaneous decarbonation is performed. Since decarburization takes a long time in the annealing process, it is not preferable, so the content of C is preferably selected from 0.02-0.045%.

The Si is a component that serves to lower the iron loss by increasing the resistivity of the material as a basic component of the electrical steel sheet, but the iron loss characteristics are bad when the content is less than 2.90%, cold rolling properties when the content exceeds 3.30% It is preferable to select Si content of 2.90-3.30% because of deterioration.

The Mn is a component having an effect of lowering iron loss by increasing electrical resistance, but when the content is too large, the magnetic flux density is lowered, so the Mn content is preferably selected to 0.05-0.30%.

The B exists in solid solution in the steel and is cold-rolled to the final thickness, and then combined with nitrogen introduced into the steel from the annealing atmosphere in the simultaneous decarbonation annealing process to form BN precipitates, thereby forming a uniform primary recrystallized structure. It is effective to distribute, which is explained as follows. In the case of Al having a slow diffusion coefficient compared to B, AlN formed during simultaneous decarbonation annealing is mainly formed in the grain boundary of the steel sheet surface to suppress grain growth, resulting in nonuniform primary recrystallization, resulting in lower magnetic flux density of the final product. On the other hand, in the case of B, since the diffusion rate is high, BN is formed relatively uniformly not only at the surface layer of the steel sheet but also at the grain boundary of the central part, so that a uniform primary recrystallization structure can be obtained after simultaneous decarbonation annealing. It can be raised. Therefore, the present invention is added in the range of 0.001-0.012% in consideration of the role of B. It is confirmed that when the content of B is less than 0.001%, the amount of the inhibitor is insufficient to obtain a stable secondary recrystallized tissue, and when it exceeds 0.012%, the secondary recrystallized tissue can be obtained but the magnetic flux density decreases. Because

Al is a nitride of the AlN and (Al, Si) N form, unlike the conventional component system to act as an inhibitor, in the present invention is not significant from the viewpoint of the inhibitor. However, Al, like Si, is an element that increases resistivity, so adding up to 0.019% is advantageous to magnetic properties. However, when Al or more is added, the workability of hot rolling decreases. Therefore, the content of Al is preferably selected from 0.005-0.019% in terms of specific resistance and workability of hot rolling. In the conventional manufacturing method, although AlN should be used as an inhibitor even if the workability of the hot rolling is reduced, it is added up to 0.05%. However, this is not necessary in the present invention.

Since N is used by reinforcing in the simultaneous decarbonation annealing process, an amount sufficient to enter impurities during dissolution is sufficient. However, when the amount of N is less than 0.003%, it is not preferable because it causes a cost increase during steelmaking, whereas when the amount of N exceeds 0.008%, coarse precipitate of AlN reacts with Al contained in the steel. The amount of N is preferably selected to be 0.003-0.008%, since the first recrystallization nonuniformity is caused and the magnetic properties deteriorate.

When the S is excessively added, the S segregation of the center of the slab becomes severe, and in order to homogenize the slab, the slab needs to be heated to a temperature of the range of the present invention.

Since P may cause plate breakage during cold rolling in more cases than usual, P is preferably limited to 0.020% or less, which can be controlled without causing cost increase in steelmaking.

The Cu, Ni, and Cr are important components added not only to homogenize the hot rolled sheet microstructure according to carbon reduction, but also to homogenize the primary recrystallized microstructure of the simultaneous decarbonation annealing plate, the addition amount of which is 0.3- It is preferable to select 0.7%, 0.03-0.07% and 0.03-0.07%. When any one of the above components is added below the lower limit of the added amount, the microstructure homogenization effect of the primary recrystallization after simultaneous decarbonation annealing becomes weak, and the secondary recrystallization becomes unstable and the magnetic properties deteriorate. In addition, when the upper limit of each component range is exceeded, its addition effect is not large, and in the case of Cu and Cr, it is rather difficult to decarburize, and in the case of Ni, it is not preferable because cost increases due to the addition of expensive alloys.

In the above-described steel slab, in addition to the above components, unavoidable elements (Ti, Nb, V) mixed from raw materials during steelmaking may be contained in a small amount (80 ppm or less). The molten steel as described above can also be used as a raw material of the present invention even when manufactured using any conventional melting method, ingot method, performance method, or the like.

[Manufacturing Conditions of Silicon Steel Slabs]

If the thickness of the silicon steel slab composition as described above is too thin, the productivity of hot rolling is reduced, if the thickness is too thick, the slab heating time should be long, it is preferable to control to 150-350mm.

Preferably, the heating temperature of the silicon steel slab is selected to be 1050-1250 ° C. The reason is that when the heating temperature is 1050 ° C or less, it is difficult to work during hot rolling, and when the temperature is higher than 1250 ° C, the magnetic properties are not significantly affected. This is because the benefits from low-temperature heating of slabs are greatly reduced. In the conventional reheating process, hot slab heating is inevitable because AlN or MnS must be dissolved and re-precipitated during hot rolling to control the size and distribution. However, the present invention adopts a method of forming an inhibitor after cold rolling to the final product thickness, so that hot slab heating to control the precipitate is not necessary. Therefore, the heating temperature of the slab is preferably selected in the range of 1050-1250 ° C. in consideration of hot rolling workability and economical efficiency as described above. In the present invention, the heating time of the slab may be selected from 1 to 10 hours in consideration of cracking and economical efficiency to the inside of the slab.

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

The hot rolled sheet annealing (pre-annealed) is performed after hot rolling as described above, and the hot rolled sheet annealing is followed by simultaneous decarburization annealing to form a primary recrystallized structure of appropriate particle size and part of the nitride precipitates such as AlN formed during hot rolling. In consideration of the anti-coarsening aspect, it is preferably carried out at 900-1150 ° C. for 30 seconds to 10 minutes, and in this case, it is preferable to use a nitrogen atmosphere to suppress the loss of the precipitate. In case of pre-annealing at a temperature lower than the pre-annealing temperature or for a shorter time than the pre-annealing time, the primary recrystallization grain size becomes fine and secondary recrystallization cannot be developed at a high temperature, so excellent magnetic flux density cannot be obtained. In the case of pre-annealing at a temperature exceeding the pre-annealing temperature or for a longer time than the pre-annealing time, the secondary recrystallization becomes unstable due to coarsening of precipitates, which is not preferable.

The pre-annealed hot rolled sheet as described above is cold rolled once, and the thickness of the cold rolled sheet is preferably selected to be 0.23-0.7mm thick, because the second cold rolled sheet is less than 0.23mm thick. This is because the recrystallization is not well developed, and if it exceeds 0.7 mm, the vortex iron loss characteristics are deteriorated, which is not preferable. The cold rolling reduction rate is preferably selected to 70-90%.

The cold rolled cold rolled plate as described above is preferably subjected to simultaneous decarbonation annealing under a mixed gas atmosphere of nitrogen containing a dew point of 30-70 ° C. for 30 seconds to 10 minutes at a temperature of 850-950 ° C. The reason is that when the annealing temperature is less than 850 ° C. or less than 30 seconds, decarburization and nitrogen enrichment are insufficient, and when the annealing temperature is higher than 950 ° C., the primary recrystallization structure becomes too coarse and the secondary recrystallization becomes unstable. This is because when the magnetic flux density cannot be obtained and when the annealing time exceeds 10 minutes, the annealing time is long and it is uneconomical.

As the annealing atmosphere, any nitrogen gas atmosphere may be used for decarburization and nitrogen enrichment. However, it is preferable to use a mixed gas atmosphere of ammonia + hydrogen + nitrogen in which industrial control of decarburization and nitrogen enrichment is easy. Do.

At this time, when the dew point of the atmosphere gas is too low, it is not preferable because the annealing time should be increased due to the decrease in decarburization ability, and if it is too high, the glass oxide film is formed during the subsequent high temperature annealing due to the non-uniformity of the steel sheet surface oxide layer. Since it is poorly formed, it is preferable to select it in the range of 30-70 degreeC.

In the case of using the mixed gas atmosphere of ammonia + hydrogen + nitrogen during the simultaneous decarburization annealing, the amount of nitrogen that enters the inside of the steel sheet is affected by the annealing temperature, the annealing time, and the ammonia fraction in the atmosphere and is appropriate according to the steel composition. It is controlled by the amount of nitrogen, and the amount of ammonia which has the greatest influence among these variables is preferably adjusted in the range of 0.1-1.0% in consideration of the sedimentation effect and the safety of gas leakage.

In addition, the carbon of the steel sheet is removed under the annealing conditions, wherein the decarburization capacity is determined by the hydrogen partial pressure and the vapor pressure. When performing simultaneous decarbonation annealing as described above, it is necessary to lower the residual carbon amount to 30 ppm or less. In other words, if the amount of residual carbon exceeds 30 ppm, the secondary recrystallization formed during subsequent high temperature annealing deteriorates, so that excellent magnetic flux density cannot be obtained, and magnetic aging occurs during use as a product such as a transformer, resulting in deterioration of iron loss characteristics. to be.

As described above, nitrogen enriched by simultaneous decarbonation annealing reacts with excess B, acid-soluble Al, Cu, Mn, Si, etc. in the steel in the low temperature region during subsequent high temperature annealing to form additional precipitates. The grain growth inhibitory force obtained varies depending on the distribution state such as amount and size. Therefore, in order to secure appropriate grain growth inhibiting force, it is preferable to select the total nitrogen content in the steel sheet in the range of 125 to 82.9 x {1 + [Cu% + 10 x (Ni% + Cr%)] ² } ppm. That is, if the total nitrogen is less than 125ppm is not desirable because the minimum precipitate is not formed, the grain growth inhibitory power is insufficient and the secondary recrystallization becomes unstable. In addition, when the total nitrogen content exceeds 82.9 x {1 + [Cu% + 10 x (Ni% + Cr%)] ² } ppm, not only the primary recrystallized structure is formed non-uniformly, but also the precipitate The secondary recrystallization development becomes unstable because the dialogue is advanced and the grain growth suppression force is not maintained up to a high temperature, which is not preferable because excellent magnetic flux density is not obtained. At this time, the upper limit of the total nitrogen amount is determined in relation to the contents of Cu, Ni and Cr, since Cu, Ni and Cr act to uniformly distribute the primary recrystallized structure. In addition, the lower limit of the total nitrogen amount depends on the presence or absence of B, which is presumed to be due to the strong inhibitory power of BN in the precipitates formed after simultaneous decarbonation annealing, whereby the minimum required amount of nitrogen is lower than when B is not added. .

On the other hand, the particle size of the primary recrystallization is determined by the size and distribution of the precipitate formed after nitriding. The grain size suitable for the precipitate produced in the component system of the present invention is about 20-35 μm.

After simultaneous decarbonation 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 high temperature annealing is composed of a temperature rising section for developing a secondary recrystallized structure and a pure annealing section for removing impurities. At this time, the temperature increase rate is important because the rearrangement of the precipitate occurs, the second recrystallization is unstable if the temperature rise rate is too fast, while the annealing time is too economical if the temperature rise rate is too slow. Therefore, the preferable temperature increase rate is 10-40 degreeC / hr. After the temperature is raised to a temperature of 1150-1250 ° C at the same temperature rate, it is preferable to crack for 1-30 hours to purify. At this time, it is preferable to maintain the atmosphere containing nitrogen in order to prevent the loss of the nitride used as an inhibitor during the temperature rising process, and as an atmosphere of pure annealing, N, S and the like remain after the formation of the glassy film and the completion of the secondary recrystallization. It is preferable to use dry hydrogen or a mixed gas of hydrogen and nitrogen to remove impurities.

The surface of the steel sheet on 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 more detail with reference to Examples.

Example 1

By weight, C: 0.025%, Si: 3.15%, Mn: 0.23%, S: 0.004%, acid soluble Al: 0.018%, N: 0.0055%, B: 0.0035%, P: 0.015% and Cu, Ni, Cr was added to vary the amount as shown in Table 1, to prepare a slab of 210mm thickness consisting of the remaining Fe. The slab was heated at a temperature of 1200 ° C. for 2 hours and 30 minutes and then hot rolled to form a 2.3 mm thick hot rolled sheet. Subsequently, after annealing in a nitrogen gas atmosphere at 900 ° C. for 3 minutes, pickling was performed, and a final cold rolled plate having a thickness of 0.30 mm was made by one rolling. Subsequently, simultaneous decarbonation annealing for decarburization, nitrogen enrichment, and primary recrystallization was carried out using a wet ammonia (NH ₃ ) + hydrogen + nitrogen mixed gas atmosphere having a dew point of 45 ° C. at 870 ° C. for 3 minutes.

At this time, in order to change the total nitrogen of the steel sheet as shown in Table 1, the atmosphere gas is a volume%, ammonia with a different concentration in the range of 0.05-10% and hydrogen and the remaining nitrogen with a different concentration in the range of 5-80% A mixed gas consisting of was used. 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 finishing high temperature annealing was performed by a heat treatment cycle to increase the temperature to 1200 ℃ at a temperature rising rate of 20 ℃ / hr and crack for 15 hours to cool the secondary recrystallization, 25% N ₂ + 75% After using H ₂ and raising the temperature to 1200 ° C., pure hydrogen gas was used.

Residual carbon content, total nitrogen amount, uniformity of primary recrystallized microstructure after simultaneous decarbonation annealing, secondary recrystallization rate, and the like for the specimens in which the addition amount of Cu, Ni, Cr and total nitrogen were changed as described above. , Magnetic flux density was investigated, and the results are shown in Table 1 below.

Here, the uniformity of the primary recrystallized microstructure was determined by polishing the cross section of the specimen subjected to simultaneous decarbonation annealing and etching with 3% nital and observing with an optical microscope. The determination method at this time was to compare the distribution area of the grains grown in the thickness direction with the grains of isotropic crystals per 1 mm ² of the specimen, so that the area of the grains of the isotropic crystals was large and uniform, if not uniform. The secondary recrystallization rate was measured by observing the macrostructure in which the surface of the finished hot-annealed steel sheet was corroded with 20% hydrochloric acid solution at about 80 ° C. and exposed. The magnetic flux density is a value obtained by measuring B ₁₀ (magnetic flux density induced at an excitation force of 1000 A / m) with a single plate magnetic measuring device.

division Alloy addition amount (% by weight) Proper Total Nitrogen Range (ppm) Atmosphere gas fraction (% by volume) Total Nitrogen Content after Simultaneous Decarbonation Nitride (ppm) Residual carbon (ppm) Primary recrystallization uniformity Secondary Recrystallization Development Rate (%) Magnetic flux density B ₁₀ (Tesla) NH ₃ H ₂ Cu Ni Cr Comparative Material 1 0.5 0.05 0.05 125-269 0.05 5 122 ^* 26 Uniformity 95 ^* 1.88 ^* Invention 1 0.5 0.05 0.05 125-269 0.5 25 220 24 Uniformity 100 1.95 Invention 2 0.5 0.05 0.05 125-269 0.7 25 265 22 Uniformity 100 1.95 Invention 3 0.5 0.05 0.06 125-269 0.6 25 233 19 Uniformity 100 1.96 Comparative Material 2 0.5 0.05 0.05 125-269 0.08 5 280 ^* 14 Non-uniformity ^* 80 ^* 1.77 ^* Invention 4 0.4 0.06 0.07 125-322 1.0 10 311 17 Uniformity 100 1.94 Invention 5 0.6 0.03 0.04 125-223 0.5 35 204 21 Uniformity 100 1.95 Invention 6 0.5 0.04 0.04 125-223 0.5 25 220 25 Uniformity 100 1.97 Comparative material 3 0.3 0.03 0.03 125-150 0.07 25 120 ^* 26 Uniformity 75 ^* 1.78 ^* Invention Material 7 0.3 0.03 0.03 125-150 0.1 50 148 24 Uniformity 100 1.94 Comparative material 4 0.3 0.03 0.03 125-150 0.09 25 160 ^* 22 Non-uniformity ^* 95 ^* 1.88 ^* Comparative material 5 0.7 0.07 0.07 125-449 0.07 20 123 ^* 28 Uniformity 70 ^* 1.75 ^* Invention Material 8 0.7 0.07 0.07 125-449 1.0 5 430 14 Uniformity 100 1.97 Comparative Material 6 0.7 0.07 0.07 125-449 10 80 460 ^* 13 Non-uniformity ^* 90 ^* 1.88 ^* Comparative material 7 0.2 ^* 0.07 0.07 125-295 0.08 5 280 23 Non-uniformity ^* 85 ^* 1.82 ^* Comparative Material 8 0.5 0.02 ^* 0.05 125-202 1.5 80 190 20 Non-uniformity ^* 85 ^* 1.83 ^* Comparative material 9 0.5 0.06 0.02 ^* 125-223 2 80 210 19 Non-uniformity ^* 90 ^* 1.87 ^* Comparative Material 10 Not added ^* Not added ^* 0.05 - 2 80 220 16 Non-uniformity ^* 90 ^* 1.88 ^* Comparative Material 11 0.8 ^* 0.04 0.04 125-295 5 80 290 45 ^* Uniformity 100 1.86 ^* Comparative Material 12 0.5 0.04 0.08 ^* 125-322 5 70 308 46 ^* Uniformity 100 1.84 ^* * Indicates that the result does not meet the conditions of the present invention

As shown in Table 1, the addition amount of Cu, Ni, Cr is added within the scope of the present invention, and the total nitrogen amount after simultaneous decarburization annealing is 125-82.9 (1 + [Cu% + 10 (Ni% + Cr%) )] ² ) In the case of the invention material (1-8) controlled in the range of ppm, the precipitates of BN and AlN distributed in uniform primary recrystallization structure and controlled size and amount are obtained, and secondary recrystallization takes place completely. In addition, the directionality was also improved to show an excellent magnetic flux density value.

On the other hand, in the case of the comparative material (1,3,5) having a total nitrogen content of less than 125 ppm after the simultaneous decarbonation annealing, the secondary growth of the second recrystallization was unstable because an adequate amount of growth inhibition was not obtained. In addition, in the case of the comparative material (2, 4, 6) in which the total nitrogen exceeds the scope of the present invention, not only the primary recrystallized structure is not uniformly formed, but also the coarsening of the precipitates during the high temperature annealing is rapidly progressed, thereby making it easy to suppress grain growth. Because of the loss, secondary recrystallization development is unstable, and excellent magnetic flux density was not obtained.

In addition, even when the total nitrogen amount is controlled within the scope of the present invention, the comparative material (7-10) added to any one of the three elements of Cu, Ni, and Cr less than the scope of the present invention has a non-uniform primary recrystallized structure 2 As a result of unstable car recrystallization, low magnetic flux density was shown.

In the comparative materials 11 and 12 in which the addition amount of Cu and Cr exceeds the scope of the present invention, secondary recrystallization takes place completely, but decarburization deteriorates (more than 30 ppm of residual carbon), and its orientation deteriorates, thereby providing excellent magnetic flux density. Couldn't get it.

Example 2

By weight%, C: 0.025%, Si: 3.15%, Mn: 0.23%, S: 0.004%, acid soluble Al: 0.019%, N: 0.0060%, P: 0.015% and B, Cu, Ni, Cr By varying the addition amount as shown in Table 2, to prepare a slab of 210mm thickness consisting of the remaining Fe. The slab was heated at a temperature of 1160 ° C. for 3 hours 30 minutes and then hot rolled to form a 2.3 mm thick hot rolled sheet. Subsequently, after pre-annealing in a nitrogen gas atmosphere at 950 ° C. for 3 minutes, pickling was performed, and a final cold rolled sheet having a different steel sheet thickness was obtained by rolling once. Thereafter, decarburization, nitrogen enrichment, and simultaneous decarbonation annealing were performed to form primary recrystallized structure using a wet ammonia (NH ₃ ) + hydrogen + nitrogen mixed gas atmosphere having a dew point of 60 ° C. at 900 ° C. for 3 minutes.

At this time, in order to control the total nitrogen of the steel sheet in the range of 125 ~ 82.9 (1 + [1 + (Cu% + 10 (Ni% + Cr%)] ² ) ppm after the simultaneous decarbonation annealing in volume% as the atmosphere gas, A mixed gas consisting of 0.5% ammonia, 25% hydrogen and the remaining nitrogen was used, and then the process conditions were the same as in Example 1, and the addition of Cu, Ni, Cr, and B as described above and the thickness of the steel sheet were used. The residual carbon content, total nitrogen amount, uniformity of primary recrystallized microstructure, secondary recrystallization rate, and magnetic flux density after co-denitrification annealing were investigated, and the results are shown in Table 2 below.

division Alloy addition amount (% by weight) Steel plate thickness (mm) Total nitrogen (ppm) Residual carbon (ppm) Primary recrystallization uniformity Secondary Recrystallization Development Rate (%) Magnetic flux density B ₁₀ (Tesla) _Iron loss W _17/50 (W / kg) B Cu Ni Cr Comparative Material 13 0.004 Not added ^* Not added ^* Not added ^* 0.35 215 11 Uniformity 100 1.94 1.06 Comparative Material14 Not added ^* 0.5 0.05 0.05 0.35 210 12 Uniformity 100 1.94 1.06 Comparative Material 15 0.004 Not added ^* Not added ^* Not added ^* 0.40 200 15 Non-uniformity ^* 90 ^* 1.86 ^* 1.70 ^* Comparative Material 16 Not added ^* 0.5 0.05 0.05 0.40 200 15 Non-uniformity ^* 90 ^* 1.87 ^* 1.65 ^* Comparative Material17 0.004 0.5 0.05 0.05 0.20 ^* 255 10 Uniformity 95 ^* 1.88 ^* 1.25 ^* Invention Material 9 0.004 0.5 0.05 0.05 0.23 235 10 Uniformity 100 1.95 1.00 Invention 10 0.004 0.5 0.05 0.05 0.27 220 11 Uniformity 100 1.95 1.02 Invention 11 0.004 0.5 0.05 0.05 0.30 210 12 Uniformity 100 1.95 1.04 Invention Material12 0.004 0.5 0.05 0.05 0.34 205 14 Uniformity 100 1.95 1.08 Invention Material 13 0.004 0.5 0.06 0.05 0.40 200 16 Uniformity 100 1.94 1.12 Invention 14 0.004 0.5 0.06 0.05 0.50 190 18 Uniformity 100 1.94 1.18 Invention Material 15 0.004 0.5 0.05 0.05 0.60 190 20 Uniformity 100 1.94 1.24 Invention Material 16 0.004 0.5 0.05 0.05 0.70 180 23 Uniformity 100 1.94 1.27 Comparative Material 18 0.004 0.5 0.05 0.05 0.08 ^* 175 26 Uniformity 100 1.93 1.36 ^* * Indicates that the result of implementation does not meet the conditions example of the present invention.

As shown in Table 2 above, in the case of using only B and not adding Cu, Ni, or Cr, or in the case of the known technology using only Cu, Ni, and Cr, in contrast, it is relatively excellent at a thickness of 0.35 mm, which is the upper limit of the conventional thickness. In the case of 0.40mm thickness (Comparative Materials 15 and 16), the non-uniform primary recrystallization structure is distributed on the steel plate after simultaneous decarbonation annealing, resulting in instability of secondary recrystallization. Magnetic flux density values are shown.

On the other hand, when the addition amount of B, Cu, Ni, and Cr is added within the scope of the present invention, the uniform primary recrystallization structure is not only in the thickness of 0.23-0.35mm, but also in the thick material of 0.40-0.70mm thicker than this. And precipitates such as BN and AlN distributed in appropriate sizes and amounts were obtained, not only secondary recrystallization completely occurred, but also the orientation thereof was improved to obtain high magnetic flux density characteristics (Invention 9-16). Therefore, it can be seen that the present invention is effective in comparison with the above known techniques not only in the usual thickness, but especially in the production of thick high magnetic flux oriented electrical steel sheets.

However, even if the steel sheet thickness is too thin (Comparative Material 17) in the present invention, the component and content are inferior in magnetic flux density due to incomplete secondary recrystallization, and when the steel sheet thickness is too thick (Comparative Material 18), High magnetic flux density characteristics are obtained by the development of good secondary recrystallization, but iron loss is so bad that it is excluded from the scope of the present invention.

As described above, the present invention can provide a method for manufacturing a thick grain-oriented electrical steel sheet having excellent magnetic properties by a low-temperature slab reheating method, and the thick grain-oriented electrical steel sheet punches the electrical steel sheet in terms of demand. There is an advantage to save time and money, and also from the producer's point of view, when manufactured by continuous rolling and continuous annealing, there is an advantage that the productivity is increased compared to the conventional thin oriented electrical steel sheet.

Claims (3)

By weight, C: 0.020-0.045%, Si: 2.90-3.30%, Mn: 0.05-0.30%, B: 0.001-0.012%, Al: 0.005-0.019%, N: 0.003-0.008%, S: 0.007% Below, the temperature of 1050-1250 degreeC is the silicon steel slab which consists of Cu: 0.30-0.70%, Ni: 0.03-0.07%, Cr: 0.03-0.07%, P: 0.020% or less, and remaining Fe and other unavoidable impurities. After reheating, followed by hot rolling and annealing, annealing, and then cold rolling once to form a cold rolled sheet of 0.23 to 0.7 mm. The cold rolled sheet is then 30 ppm or less in residual carbon and 125 to 82.9 (1 + [ Cu% + 10 (Ni% + Cr%)] ² ) Annealing so that decarburization and nitriding occur simultaneously for 30 seconds to 10 minutes at a temperature of 850 to 950 ° C. under a nitrogen gas atmosphere with a dew point of 30 to 70 ° C. Then, the method for producing a high magnetic flux density oriented electrical steel sheet of a low temperature slab heating method comprising applying an annealing separator and finishing high temperature annealing. The method of claim 1, wherein the hot-rolled sheet annealing is performed for 30 seconds to 10 minutes at a temperature of 900 to 1150 ℃ in a nitrogen atmosphere. The method according to claim 1, wherein the nitrogen gas is a mixed gas of ammonia + hydrogen + nitrogen, and the concentration of the ammonia is 0.1 to 1.0% by volume fraction.