KR100241003B1 - The manufacturing method of oriented electric steelsheet with excellent magnetic and surface quality property - Google Patents

Abstract

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet used as iron core materials for transformers, electric motors, generators and other electronic devices by low temperature slab heating, and hot rolling after treatment at low temperature reheating temperature without surface melting. By performing plate annealing to further disperse and deposit fine precipitates, and then conducting a heat transfer cycle during the final finishing annealing in a nitrogen-containing hydrogen atmosphere, the formation of a glassy insulating film by surface oxides is advantageous, resulting in excellent surface coating properties and It is an object of the present invention to provide a method for manufacturing high-strength grain-oriented electrical steel sheet with high productivity.

In the method for producing a grain-oriented electrical steel sheet by low temperature slab heating method, in weight%, C: 0.025% -0.045%, Si: 2.9-3.3%, P: 0.015% or less, dissolved Al: 0.008-0.027%, N : 0.0080 -0.012%, S: 0.007% or less, Ni and Cr alone or composite: 0.06-0.18%, Mn: 0.32% or less, Cu: 0.6% or less, slab composed of residual Fe and other unavoidable impurities 1250-1320 After reheating at ℃, hot rolling, the hot rolled sheet is annealed at a temperature of 1100-1150 ℃, first cold rolled, and the cold rolled sheet is subjected to decarbonization annealing in a wet atmosphere of 820-870 ℃, then 50% or more rolling After secondary cold rolling at a rate, recovery annealing was carried out at a temperature of 650 ° C. or lower, and then coated with a fusion inhibitor containing MgO as a main component and wound up, followed by 10-15% nitrogen-containing hydrogen at 1180-1220 ° C. A method of manufacturing a grain-oriented electrical steel sheet having excellent magnetic and surface quality characteristics by performing final finishing annealing for at least 20 hours in an atmosphere. It is decided.

Description

Manufacturing method of oriented electrical steel sheet with excellent magnetic and surface quality characteristics

The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet used for iron core materials such as transformers, electric motors, generators, and other electronic devices by low temperature slab heating, and more specifically, AlN as a secondary recrystallization inhibitor. The present invention relates to a method for manufacturing a grain-oriented electrical steel sheet having excellent magnetic and surface quality characteristics by applying a low temperature slab heating method.

Since grain-oriented electrical steel has an aggregate structure in which grains are arranged in the direction of (110) [001], it has extremely excellent magnetic properties in the rolling direction. Used as

The manufacturing process of general grain electrical steel sheet is generally melted around 2-4% of silicon and Mns and MnSe as a grain growth inhibitor, and then made slab (reheating and hot rolling)-(pre-annealing)-(middle The final product is completed through a complex process of annealing, two times cold rolling), (decarbonization annealing), (MgO fusion inhibitor table), and (final finishing annealing). But this complex process leads to the final product. However, the most difficult manufacturing process among these complicated manufacturing processes is the slab reheating process which performs heat treatment at a high temperature of about 1400 ° C.

This slab reheating process is performed to disperse the precipitates such as MnS and AlN, which are used as grain growth inhibitors, in a completely solid solution and then precipitate finely. For this purpose, it is unavoidable to maintain them for about 5 hours at a high temperature of about 1400 ° C. At this time, the surface of the hot slab becomes an oxide called Pyrite (Fe ₂ SiO ₄ ), in which oxides of Si and Fe are combined by oxidation with air, and the melting point is about 1300 ° C. so that it melts from the surface. The molten slag is designed to flow out partly, but most of it accumulates in the refractory of the upper part of the furnace, so that the completion of work and complete internal repair are inevitable. Therefore, steelworks, which are characterized by continuous operation, have enormous economic burdens such as poor workability, reduced production, and cost increase.

In order to solve this problem, the present inventors designed a component system for performing hot rolling by heating a conventional grain-oriented electrical steel sheet at around 1250-1320 ° C., which has no surface melting and a reheating temperature that is the same as that of a general steel mill. Established a new manufacturing method that can work without supplementary or new equipment in the existing manufacturing process and filed a patent with Korean Patent Application No. 93-23751. Also, additional element technologies are disclosed in Korean Patent Application No. 94-21388,21389, Patents No. 21390 and 21391.

By using the low temperature reheating method proposed above, it was possible to produce a product having a high real rate and stable magnetic properties in actual production. However, this manufacturing method usually requires high-temperature materials to be decarbonized at the intermediate thickness (typically 0.60-0.75 mmt) after the first cold rolling, unlike the manufacturing order of the thermal materials, so that the surface oxides formed in this process are usually treated at 0.30 mmt thickness. It is insufficient in quantity and quality. Therefore, the formation of the glass insulation film (Forsterite, 2MgO · SiO ₂ ) formed during the final finishing temperature annealing is uneven and unstable, so that the overall surface quality characteristics are slightly degraded. In addition, in general general aromatic products using MnS precipitates as secondary recrystallization growth suppression, the final finishing annealing is performed in a tunneled manner by annealing with 100% hydrogen single gas, which is superior to the intermittent method. However, in the newly proposed technique, the precipitate of AlN is used as a secondary recrystallization growth inhibitor, so a mixed gas containing nitrogen must be used to change the atmosphere gas, and thus an intermittent annealing treatment is inevitable.

Therefore, the present invention performs hot-rolled sheet annealing that is hot rolled after treatment at low temperature reheating temperature without surface melting, and further precipitates fine precipitates, and then conducts a heat transfer cycle in a nitrogen-containing hydrogen atmosphere during final annealing, It is an object of the present invention to provide a method for producing a grain-oriented electrical steel sheet having high surface film characteristics and excellent magnetic properties due to its favorable glassy insulating film formation with high productivity.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

The present invention is a method for producing a grain-oriented electrical steel sheet by low temperature slab heating method, by weight%, C: 0.025% -0.045%, Si: 2.9-3.3%, P: 0.015% or less, dissolved Al: 0.008-0.027 %, N: 0.0080 -0.012%, S: 0.007% or less, Ni and Cr alone or composite: 0.06-0.18%, Mn: 0.32% or less, Cu: 0.6% or less, slab composed of residual Fe and other unavoidable impurities After reheating at 1250-1320 ° C. and hot rolling, the hot rolled plate was annealed at a temperature of 1100-1150 ° C., first cold rolled, and the cold rolled plate was subjected to decarbonization annealing in a humid atmosphere of 820-870 ° C., and then 50 After secondary cold rolling at a rolling rate of at least%, after recovery annealing at a temperature of 650 ° C. or lower, and after applying and winding a fusion inhibitor containing MgO as a main component, 10-15% of the atmospheric gas at 1180-1220 ° C. The final finish annealing is carried out for 20 hours using a nitrogen-containing hydrogen atmosphere to produce oriented electrical steel sheets with excellent magnetic and surface quality characteristics. Is about the way.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

By using the low temperature reheating method proposed in Korean Patent Application No. 93-23751, which is the basis of the present invention, it was possible to produce a product having a high realization rate and stable magnetic properties during actual production. However, this manufacturing method requires decarbonization annealing at the intermediate thickness (usually 0.60-0.75mmt) after the first cold rolling, unlike the conventional materials. Therefore, the surface oxides formed in this process are 0.30mmt thick than conventional materials. Lacking and thus the formation of the glass insulation film in the final product is unstable and the surface quality characteristics are somewhat degraded. In addition, in the conventional products using MnS precipitate as the secondary recrystallization growth inhibitor, the final finishing annealing is performed by tunneling annealing according to the single gas annealing, so the productivity is excellent. However, in the newly proposed technology, the AlN precipitate is the second recrystallization growth inhibitor. As a result, the use of a mixed gas of hydrogen and nitrogen inevitably changed the atmosphere gas, resulting in an intermittent annealing treatment. Therefore, the present invention is based on the same-cycle atmosphere treatment of all cycles, which is advantageous for forming a glassy insulating film and also excellent in productivity at the time of final finishing annealing. By adjusting the concentration to 10-15%, the surface oxidation capacity (P _H20 / P _H2 ) is relatively lower with increasing hydrogen gas ratio even at the same amount of moisture, and thus SiO ₂ is easily produced under low oxidation capacity instead of FeO oxide, which is unfavorable to glass insulation film formation. Internal oxides may be produced. In addition, in order to secure the magnetic properties in the present invention, the final finishing annealing hot-rolled sheet annealing the shortage of additional AlN precipitates that may appear as a change from the normal 25% nitrogen atmosphere to a 10-15% nitrogen-containing atmosphere By adding an annealing treatment at 1100-1150 ℃ in normal annealing at the time of regeneration, the precipitated AlN in the form of a clumper can be precipitated after re-solubilization during hot-rolled precipitation, thereby replenishing the deficiency in the low nitrogen-containing atmosphere treatment. Compared to the final finishing annealing, it is easier to manage the precipitate during the hot-rolled sheet annealing.

Hereinafter, the reason for limitation of the component of this invention steel, and its range is demonstrated.

The C is required to form an appropriate rolled structure, and at least 0.025% or more because it imparts processing energy during cold rolling, and is preferably limited to 0.045% in consideration of the difficulty of the decarburization process.

The Si is a component that serves to lower the core loss or iron loss by increasing the resistivity of the material as a basic component of the electrical steel sheet, when the content is less than 2.9%, the iron loss characteristics worsen, the steel is vulnerable when the excess content is cold rolled It is desirable to limit the content of Si to 2.9-3.3% because the properties are extremely poor and the secondary recrystallization becomes unstable.

The Mn lowers the solid solution temperature of the precipitate during reheating and prevents cracks formed at both ends of the material during hot rolling. Therefore, Mn is more advantageous, but Mn oxide is formed when decarbonization is added when 0.32% or more is added. Since the adhesion of the forsterite film formed during high temperature annealing is deteriorated, the content of Mn is preferably limited to 0.32% or less.

S is a component that acts as an inhibitor by forming a precipitate in the form of Cu or Mn and an emulsion, considering that it is basically contained in the manufacturing plant, and needs to be managed as low as possible. Employment and spread of segregation becomes difficult, so de-S process should be adopted and should be restrained strongly. Therefore, the content of S is preferably limited to 0.0007% or less.

The Al component forms a precipitate of AlN together with N and is a central element to secure grain growth inhibition, and the amount of Al in the dissolved state is important, not the total amount of Al management. If the content of Al is less than 0.008%, since it does not have sufficient inhibitory force necessary for secondary recrystallization, the grain size is small and incomplete fine particles appear, resulting in low magnetic flux density and poor iron loss. Secondary recrystallization in the excellent (110) [001] orientation makes it difficult to form itself, and thus the magnetic properties are rapidly deteriorated, and thus it is a representative component that needs to be managed.

Therefore, the content of Al is preferably limited to 0.008-0.027%.

N is an essential component in secondary recrystallization because it forms a reaction precipitate with dissolved Al to act as a grain growth inhibitor of primary recrystallization. If N is less than 0.008%, formation precipitates are insufficient, and when 0.012% or more is added, the surface of steel sheet It is preferable to limit the content of N to 0.008-0.012% because a defect called an ester causes deterioration of the surface properties of the product.

The Ni and Cr may further increase the appropriate reheating temperature range by miniaturizing the primary recrystallized grains so that the precipitate dispersion effect is large. Therefore, in order to operate the reheating temperature at 1250-1300 ° C, at least 0.06% or more is required to be used alone or in combination of two kinds, and when 0.18% or more is added, the de-elasticity worsens afterwards by combining with the C component in the material. And the content of Cr is preferably limited to 0.06-0.18% alone or in combination.

The above component system uses this component system as the essential condition to lower slab reheating temperature, which is the biggest problem in the manufacture of anti-corrosion electrical steel sheet, and it has excellent magnetic properties even when the slab heating temperature is operated at 1250 ℃, which is the reheating temperature of ordinary carbon steel. It can be secured. In this case, when the reheating temperature exceeds 1320 ° C., the steel sheet slab is melted, and therefore, the steel sheet slab is preferably limited to 1250 ° C. to 1320 ° C., which is the most economical and easy reheating temperature in steel mills.

After reheating the slab to the above reheating temperature and performing hot rolling, the hot rolled sheet annealing should be performed at 1100-1150 ℃. The reason for this is that when the annealing temperature is 1100 ℃ or lower, re-use of AlN If this is impossible and the temperature is more than 1150 ° C, fine precipitation is impossible during cooling, and it is possible to grow larger precipitates than necessary.

Next, after hot-rolling the hot-rolled sheet annealed as described above, decarbonized annealing is performed in a wet atmosphere at 820-870 ° C., followed by secondary cold rolling at a rolling rate of 50% or more to adjust the final thickness. Next, recovery annealing is performed at a temperature of 650 ° C. or lower, then MgO-based fusion inhibitor is applied and wound to form a large coil, and the coil is finally finished annealed. The final annealing process is carried out in the hydrogen an atmosphere containing 10-15% nitrogen before the annealing cycle, the reason is that if the nitrogen content in the nitrogen-containing hydrogen atmosphere is less than 10%, additional AlN formation is insufficient, more than 15% This is because, under the nitrogen atmosphere, it is disadvantageous for the formation of the internal SiO ₂ oxide, which is advantageous for the formation of the glass insulating film.

The annealing temperature at the time of the final finishing annealing is preferably selected to be 1180-1220 ° C., and the annealing time is preferably set to 20 hours or more.

The present invention will be described in more detail with reference to the following Examples.

Example 1

By weight%, C: 0.032%, Si: 3.05%, P: 0.013%, dissolved Al: 0.016%, N: 0.0093%, S: 0.004%, Ni: 0.052%, Cr: 0.048%, Mn: 0.20%, Cu: 0.46% residual Fe and other unavoidable impurities are reheated at 1305 DEG C for 4 hours, followed by hot rolling, followed by hot rolling annealing from annealed to 1150 DEG C of the present invention. Was cold rolled to a thickness of 0.65 mm, then subjected to decarbonization in a wet atmosphere at 870 ° C., followed by secondary cold rolling to adjust to a final thickness of 0.30 mm. Subsequently, secondary cold rolling was performed to adjust the final thickness to 0.30 mm. Subsequently, after recovery annealing at a temperature of 550 ° C., a fusion inhibitor containing MgO as a main component was applied and wound to make a large coil, followed by final finishing annealing.

The final finishing annealing was performed at 650 ° C for the first low temperature crack, followed by an elevated temperature at a rate of 20 ° C per hour, followed by a total of 25 hours at 1200 ° C for 2 hours, and then cooled to room temperature for 30 hours. The reaction was carried out in a nitrogen atmosphere containing% nitrogen. The magnetic properties after the final finishing annealing as described above are shown in Table 1 below.

TABLE 1

* Magnetic flux density, B10 (Tesla): The magnetic flux density induced when magnetized at 1000 Amp / m

* Iron loss, W17 / 50 (W / kg): Loss of iron core when magnetized to obtain 1.7 Tesla at 50 Hz

As shown in Table 1, in the case of a conventional annealing treatment material, low magnetic flux density and high iron core loss value make it impossible to commercialize it, and the 950 ° C. treated material (comparative material (1)) also has partial magnetic properties, but also magnetic flux. It can be seen that the density value is low and the iron core loss value is high.

On the other hand, the invention (a) (b) hot-rolled annealing at 1100-1150 ℃ exhibits excellent magnetic properties with a magnetic flux density of 1.86 Tesla or more, iron core loss value of 1.20 W / Kg or less.

On the other hand, it can be seen that even in the case of the comparative material 2, the annealing temperature is higher than the range of the present invention, the magnetic properties deteriorate.

Example 2

The slab having the composition of Example 1 was reheated at 1300 ° C. for 4 hours, followed by hot rolling, followed by hot roll annealing at 1125 ° C., and then treated under the same conditions as in Example 1 to obtain a large coil. The final finishing annealing was performed at 650 ° C., the first low temperature crack, followed by an elevated temperature at a rate of 20 ° C. per hour, followed by a total of 25 hours at 1200 ° C. for 2 hours, followed by cooling at room temperature over 30 hours. In order to compare the characteristics of this method with the method performed in a 25% nitrogen-containing hydrogen atmosphere at 100 ° C and thereafter at 100% hydrogen atmosphere, and the characteristics thereof, 100% hydrogen gas, 5 After the final finish annealing treatment in%, 10%, 15% and 25% nitrogen-containing hydrogen atmosphere and compared their magnetic properties and surface quality characteristics are shown in Table 2 below.

TABLE 2

* Magnetic flux density, B10 (Tesla): The magnetic flux density induced when magnetized at 1000 Amp / m

* Iron loss, W17 / 50 (W / kg): Loss of iron core when magnetized to obtain 1.7 Tesla at 50 Hz

* Insulation property is the storage current value when the input voltage is 0.5Volt, 1.0Amp at 300psi

As shown in Table 2 above, in the case of the atmosphere change which is a normal treatment condition (normal material), the magnetic properties are relatively good, but the insulation quality is poor in the surface quality, and the surface unevenness is uniform, so as to secure the normal surface quality. You can see it's hard. On the other hand, the surface quality of 0 and 5% nitrogen-containing hydrogen atmosphere (comparative materials (3) and (4)) was secured during the same cycle of all cycles, but it was found that the product was difficult to commercialize due to inferior magnetic properties.

On the other hand, in the 10-15% nitrogen-containing hydrogen atmosphere annealing treatment according to the present invention, the magnetic flux density of [inventive material (C) and (d)] is 1.87 Tesla or more and the iron loss is 1.20 W / kg or less. In terms of surface quality, it is excellent because of low insulation properties, and it can be seen that appearance is also good. On the other hand, in the case of the comparative material (5) containing more nitrogen than the scope of the present invention, it can be seen that the magnetic properties, but the surface quality is somewhat poor.

Claims (1)

In the method for producing a grain-oriented electrical steel sheet by low temperature slab heating method, in weight%, C: 0.025% -0.045%, Si: 2.9-3.3%, P: 0.015% or less, dissolved Al: 0.008-0.027%, N : 0.0080 -0.012%, S: 0.007% or less, Ni and Cr alone or composite: 0.06-0.18%, Mn: 0.32% or less, Cu: 0.6% or less, slab composed of residual Fe and other unavoidable impurities 1250-1320 After reheating at ℃, hot rolling, the hot rolled sheet is annealed at a temperature of 1100-1150 ℃, first cold rolled, and the cold rolled sheet is subjected to decarbonization annealing in a wet atmosphere of 820-870 ℃, then 50% or more rolling After secondary cold rolling at a rate, recovery annealing was carried out at a temperature of 650 ° C. or lower, and then coated with a fusion inhibitor containing MgO as a main component and wound up, followed by 10-15% nitrogen-containing hydrogen at 1180-1220 ° C. A grain-oriented electrical steel sheet with excellent magnetic and surface quality characteristics, characterized by performing final finishing annealing for at least 20 hours in an atmosphere. Manufacturing method.