KR100256342B1 - The manufacturing method for oriented electric steel sheet with magnetic and decarburing property - Google Patents

Abstract

PURPOSE: A method for manufacturing an oriented electrical steel sheet having superior magnetism and decarburization is provided to improve magnetism by containing carbon content in an amount of 0.025 wt.% or less during the steel making process, thereby improving decarburization in the subsequent processes, and increasing a second cold rolling ratio, thereby obtaining strong processing energy. CONSTITUTION: The method comprises the processes of hot rolling after reheating a slab comprising 2.9 to 3.3 wt.% of Si, 0.015 wt.% or less of P, 0.011 to 0.027 wt.% of sol-Al, 0.0080 to 0.012 wt.% of N, 0.007 wt.% or less of S, 0.06 to 0.18 wt.% of Ni and/or Cr, 0.32 wt.% or less of Mn, 0.6 wt.% or less of Cu, 0.010 to 0.025 wt.% wt.% of C and a balance of Fe and other inevitable impurities to a temperature of 1250 to 1320 deg.C; annealing the hot rolled steel slab at a temperature of 1000 deg.C or less; controlling a final thickness of the steel slab with a second cold rolling ratio of 58 to 65% by carrying out two times of cold rollings including the decarburization annealing performed under wet atmosphere (H) of a temperature ranging from 820 to 870 deg.C; coating a fusion preventing agent having a main constituent of MgO on the steel sheet and winding the steel sheet after performing a recovering annealing on the cold rolled steel sheet at a temperature of 600 deg.C or less; final finish annealing passing through a heat cycle in which the steel sheet is soaked for more than 20 hours and cooled; and cooling the resulting steel sheet.

Description

Manufacturing method of oriented electrical steel sheet excellent in magnetic and decarburization

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 electric equipments by low temperature slab heating, wherein AIN is a secondary recrystallization inhibitor and low temperature slab heating. It relates to a method for producing a grain-oriented electrical steel sheet having excellent magnetic and decarburization properties.

A grain-oriented electrical steel has an aggregate structure in which the grain orientation is aligned in the direction of (110) [001], and this product has extremely good magnetic properties in the rolling direction. It is used as iron core material for equipment.

The manufacturing process of the grain-oriented electrical steel sheet is generally 2-4% of silicon and grain growth inhibitors, and most of them contain MnS or MnSe, and after making slabs, (reheating and hot rolling)-(pre-annealing)-( One time cold rolling with intermediate annealing)-(Decarburization annealing)-(Adhesion prevention agent)-(Final finishing high temperature annealing) is completed to the final product. An existing process is a slab reheating step of performing heat treatment at a high temperature. This slab reheating process focuses on having to completely disperse the precipitates such as MnS and AIN, which are used as grain growth inhibitors, and then deposit them finely. Done. At this time, on the surface of the hot slab, an oxide called Pyrite (Fe ₂ SiO ₄ ) in which oxides of Si and Fe components are combined by an oxidation reaction with air is melted from the surface with a melting point as low as 1300 ° C. At this time, the molten slag is designed to flow outward, but most of it accumulates in the refractory of the upper part of the furnace. Therefore, steelworks, which are characterized by continuous work, have enormous economic burdens such as poor workability, reduced productivity, and higher costs.

Efforts to lower the slab reheating temperature are proceeding with full attention from leading manufacturers and various methods are being proposed. As a method, the reheating is performed on the basis of adjusting the degree at a temperature of about 1300 ° C. or less at which the slab does not melt, and in addition to this ingredient adjustment, improvement in the method of managing the precipitate during the manufacturing process has been proposed. Known technologies up to now include Korean Patent Publication Nos. 89-8334, 89-13200, 92-702728, 92-9999, 92-14941 and Publication No. 89-8892, which have been mainly studied in Japan and have disclosed the technology to Korea. have. These were all targeted for high magnetic flux density oriented electrical steel sheets, and the actual reheating temperature was usually in the range of 1150-1200 ° C, and decarbonized annealing was used to supplement the N component, which is one of the grain growth inhibitor components, in order to secure the magnetic flux density value. After the process, a nitriding treatment process in which nitrogen is impregnated into the material is essentially added. Therefore, as these technologies are managed at a temperature lower than the reheating temperature of 1250-1280 ℃ of general steel in steelworks, there is mutual work interference, and it is inevitable to install additional equipment for achievement reaction, which incurs cost burden, especially securing growth control. As the process control becomes extremely difficult with one-time rolling treatment, the magnetic variation per lot is severe, resulting in low error rate.

The present inventors designed a component system for performing hot rolling by heat treating a conventional grain-oriented electrical steel sheet near 1250-1300 ° C., which is a reheating temperature almost the same as that of general steelworks, and supplementing or not installing a facility in an existing manufacturing process. Established a new manufacturing method that can be operated without a patent application in Korea Patent Application No. 93-23751, and additional element technologies in Korea Patent Application No. 94-21388, 21389, 21390 and 21391.

By using the proposed low temperature reheating method, it was possible to produce a product having high real rate and excellent magnetic properties in actual production. However, according to this manufacturing method, decarbonization annealing must be carried out at the intermediate thickness after the first cold rolling, unlike the manufacturing procedure of ordinary materials. In some cases, it may inevitably lead to a decrease in the usage characteristics of the demand because it may inevitably exceed the limit of 25 ppm, which is the limit of residual carbon in the final product. Therefore, in order to reduce the process load at the production plant and to proceed smoothly, if the carbon content can be managed within 25ppm within a short time in the middle thickness of the decarbonization process, the process proceeds smoothly. The production cost can be shortened. Therefore, the inventors of the present invention have optimized the amount of carbon in the initial steel sheet in consideration of the amount of carbon removed by the decarburization reaction occurring at the same time during the formation of the natural loss during the process and the oxide of the material surface necessary for forming a glass film (base coating). In the steelmaking, the carbon content was found to be 0.025% or less, and the present invention was proposed by establishing a method of securing stable magnetism using such a low carbon component system. It is intended to provide a method of manufacturing a grain-oriented electrical steel sheet that can improve the magnetism by containing less than% to improve the decarburization in the subsequent process and increase the secondary cold rolling rate to have a strong processing energy.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated.

According to the present invention, Si: 2.9-3.3%, P: 0.015% or less, dissolved Al: 0.011-0.027%, N: 0.0080-0.012%, S: 0.007% or less, Ni or Cr alone or in combination: Reheating the slab composed of 0.06-0.18%, Mn: 0.32% or less, Cu: 0.6% or less, C: 0.010-0.025% and other unavoidable impurities to 1250-1320 ° C, followed by hot rolling, followed by 1000 ° C or less After annealing the hot rolled sheet at the temperature, adjust the final thickness by two cold rolling including decarbonization annealing in a humidified hydrogen atmosphere at 820-870 ° C, and then set the secondary cold rolling rate to 58-65%. After recovery and annealing, MgO-based fusion inhibitor is applied and wound up. Then, the temperature is raised to 1180-1220 ° C at room temperature, and the atmosphere gas in the temperature rising zone is 20-25% nitrogen-containing hydrogen atmosphere. Cooling after cracking for more than 20 hours using 100% hydrogen atmosphere of atmospheric gas at the highest crack temperature range of 1220 ℃ After performing a final finishing annealing through a thermal cycle, there is provided a method for producing a grain-oriented electrical steel sheet having excellent cooling magnetic properties and decarburization.

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

Determination of the magnetic properties in the final product allows the precipitates, which are grain growth inhibitors, to play an optimal role in the production of secondary recrystallization. The component system of the present invention is an AIN center component system which strongly suppresses the amount of S. During the hot rolling process, the AIN precipitates in an extremely fine form effective in forming secondary recrystallized particles having excellent magnetic properties, thereby precipitating the precipitate by hot-rolled sheet annealing. Control is not necessary in the component system of the present invention and is then cold rolled. In addition, a feature of the present invention is to decarbonize an intermediate thickness to further form a precipitate of Si ₃ N ₄ . In addition, secondary cold rolling is performed under low carbon after decarbonization, so that processing energy is relatively low, thereby making secondary recrystallization easier. The primary recrystallization is performed at the low temperature portion during the final annealing, and the first and second recrystallizations in which the secondary recrystallization is terminated during the subsequent elevated temperature can be caused during the final annealing, thereby shortening the production process without the secondary annealing process. Particularly, during the final annealing, perfect primary recrystallization over a long period of time, the secondary recrystallized grains formed thereafter may have a more aligned aggregate structure in the (110) [001] direction, which is the easy magnetization direction, so that it is extremely more than general general orientation. It is a feature of the present invention that it is possible to secure excellent magnetic properties.

The breakthrough advances in manufacturing technology have been made by the new low temperature reheating method, but there is a desire to establish a manufacturing process more easily.

Deterioration of the magnetic properties of electrical steel materials before use occurs over time when processing aromatic products at demand. This is called magnetic aging. For example, the temperature of the transformer itself increases when it is processed and assembled into a transformer, and the carbon content inside the material is grains of carbide such as Fe ₃ C. Precipitation mainly occurs in the grain boundary, and the presence of nitrogen and sulfur also causes the magnetic domains to deteriorate due to the formation of nitrides or sulfides, respectively, which interfere with the movement of the magnetic domains. At this time, since the most severe component of self-aging is carbon, manufacturing technicians pay particular attention to the management of carbon components, and the self-management range in the factory is kept below 25 ppm. This is because the self aging phenomenon with time is very weak at the residual carbon amount. However, in the manufacturing method of Korean Patent Application No. 93-23751, which is generally applied as a basic manufacturing method, it requires a long annealing of 7-8 minutes in the management of residual carbon in the intermediate decarbonization annealing process, which enormously hinders the progress of the process. When annealing at, the residual carbon content can exceed 25ppm, so deterioration of characteristics is inevitable when using a consumer. Therefore, the present inventors have optimized the amount of carbon in the initial steel sheet in consideration of the amount of carbon removed by the decarburization reaction occurring at the same time during the formation of the natural loss during the process and the oxide of the material surface required for forming the glass film (base coating). The amount of carbon in steel is 0.025% or less, so that it is adjusted to 0.025% or less in steelmaking. Afterwards, changes in the aggregate structure due to the decrease in the amount of carbon steel in the manufacturing process are strictly managed under the given basic conditions. It can be supplemented, and in particular, by increasing the secondary cold rolling rate to 58% or more compared to ordinary materials, it is possible to increase the processing energy of the material during cold rolling, thereby stabilizing the first and second recrystallizations formed during final annealing. It can contribute to orientation in the (110) [001] orientation which is more favorable for magnetic enhancement.

EMBODIMENT OF THE INVENTION Hereinafter, the reason for resin limitation of this invention is demonstrated.

Part C should be present because it forms an appropriate rolled structure and imparts processing energy during cold rolling. However, in consideration of the difficulty of the decarburization process, C is removed at the minimum decarburization time necessary for the formation of natural loss and oxide layer during the process. It is limited to 0.025% or less, which is a value considering the amount of carbon. Preferably, the carbon amount is 0.010% or more, which is an amount inevitably added.

The Si serves to lower the core loss, that is, iron loss by increasing the resistivity of the material as a basic component of the electrical steel sheet. It is preferable to limit the content of Si to 2.9-3.3% because the iron loss property is poor at 2.9% or less, the steel becomes brittle when excessively contained, the cold rolling property is extremely poor and the secondary recrystallization is unstable.

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

S is a component that acts as an inhibitor by forming precipitates in the form of emulsions with Cu or Mn, considering that it is basically contained in the manufacturing plant up to 0.005%, and the minimum limit management is necessary, if more than 0.007% is contained in hot rolling Since low temperature reheating makes it difficult to employ and spread the central segregation, it should be strongly restrained by adopting a desorption process. Therefore, the content of S is preferably limited to 0.007% or less.

The Al component forms a precipitate of AIN together with N and is a central element to secure grain growth inhibitory power, and the amount of Al in the dissolved state is important, not the total amount of Al management. When the Al content is 0.01% or less, 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. Above 0.027%, the restraining force is too strong to make the secondary recrystallization itself in the (110) [001] orientation which is excellent in magnetism, and the magnetic properties deteriorate rapidly.

Therefore, the Al content is preferably limited to 0.011-0.027%.

N is an essential component in secondary recrystallization since it forms a reaction precipitate with dissolved Al to act as a grain growth inhibitor of primary recrystallization. If N is not more than 0.008%, the precipitate formed is insufficient, and when added to 0.012% or more, 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.

Cu is combined with S, which is an impurity component, to form a precipitate of Cu ₂ S, which is a solid solution at the lowest temperature of the precipitate. In the present invention, the S component should be suppressed to form MnS as much as possible. If the oxide is more than 0.60%, the oxides formed during decarbonization do not only adversely affect the formation of the insulating film, but the secondary recrystallized grains have a large magnetic flux density, but the iron loss can be deteriorated, so the total amount of Cu is limited to 0.6% or less. It is desirable to.

Since the Cr of Ni is finer in the primary recrystallized grains, the precipitate dispersion effect is greater, so that the optimum reheating temperature range can be further increased. Therefore, in order to operate the reheating temperature basically at 1250-1300 ° C., a minimum of 0.06 is used alone or in combination. Since addition of more than% is required, since debonding becomes worse after combining with C component in the material when adding more than 0.18%, the content of Ni and Cr is preferably limited to 0.06-0.18% alone or in combination.

The above component system is an essential condition for lowering slab reheating temperature, which is the biggest problem in producing oriented electrical steel sheet. When the slab composition is formed as described above, the slab heating temperature is generally excellent even when the slab heating temperature is performed at 1250 ° C, which is the reheating temperature of ordinary carbon steel. It is possible to secure enemy characteristics, so the economic effect is great. In this case, since the reheating temperature exceeds 1320 ° C., the steel sheet slab is melted, and therefore, it is preferable to limit the reheating temperature from 1250 ° C. to 1320 ° C., which is the most economical and easy reheating temperature in re-iron.

After that, the manufacturing process is performed by hot-rolled sheet annealing at 1000 ° C. or lower, followed by primary cold rolling, and then adjusted to the final thickness by secondary cold rolling including a wet atmosphere decarbonized annealing at 820-870 ° C. in the middle. In this case, in order to stabilize the magnetic properties under low carbon of the present invention, it is necessary to secure higher processing energy during cold rolling, so that the secondary cold reduction rate must be at least 58% or more to secure excellent magnetic properties in the low carbon component system of the present invention. At this time, the secondary recrystallization itself is impossible at 58% or less, the magnetism is sharply lowered, decarburization may deteriorate at 65% or more, so in the present invention, limiting the secondary cold reduction rate to 58% or more and 65% or less. desirable.

The material adjusted to the final thickness is subjected to an intermediate recovery annealing at 600 ° C. or lower, followed by application of an annealing separator containing MgO as a main component, followed by winding into a large coil, followed by a final finishing annealing process. In particular, during the final temperature of annealing up to 1200 ± 20 ℃, the atmosphere gas is subjected to 20-25% nitrogen-containing hydrogen atmosphere and cracks in 100% hydrogen atmosphere at the highest crack temperature range of 1200 ± 20 ℃ for a total of 20 hours. By carrying out the finishing high temperature annealing through the heat cycle to cool after the abnormal treatment, a grain-oriented electrical steel sheet excellent in decarburization and magnetic properties is produced.

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

Example 1

C by weight based on Si: 3.18%, Mn: 0.205%, S: 0.005%, N: 0.005%, dissolved Al: 0.017%, Cu: 0.493%, Cr: 0.047% and Ni: 0.049% The amounts were changed to 0.019, 0.022, 0.033, 0.041 and 0.052%, and the five component systems including the remaining Fe and other unavoidable impurities were dissolved, and then a 230 mm thick slab was prepared. These slabs were hot-rolled after 4.5 hours of reheating at a low temperature of 1300 ° C. without surface melting to form a 2.3 mm thick hot rolled sheet. Next, hot-rolled sheet annealing was carried out at 960 ° C. and after primary pickling, cold rolling was performed to adjust the thickness to 0.75 mm. The intermediate annealing plate was subjected to final cold rolling to a thickness of 0.30 mm through decarbonization annealing in a 850 ° C. wet atmosphere. Subsequently, after recovery annealing and application of MgO at 560 ° C., the coils were wound in a coil state to give a final high temperature annealing. The final finishing annealing was performed at 600 ° C. for the first low temperature crack, followed by an elevated temperature at a rate of 20 ° C. per hour, and then cooled to room temperature for 30 hours after the secondary high temperature cracking for more than 20 hours at 1200 ° C. for a total of 20 hours. The temperature was increased in a 25% nitrogen-containing hydrogen atmosphere and thereafter in a 100% hydrogen atmosphere to secure magnetic properties. At this time, the amount of residual carbon of the material after decarbonization annealing was measured, and the magnetism after the final finishing annealing was measured and shown in Table 1 below.

As shown in Table 1, in the case of the inventive materials (a) and (b) having a material carbon amount of 0.019 and 0.023%, the residual carbon content after decarbonization annealing satisfies the management criteria of 25 ppm or less. The magnetic properties also show that the magnetic flux density is higher than 1.876 Tesla and the core loss characteristics (iron loss) are lower than 1.19 W / Kg, thus ensuring excellent magnetic properties. However, in the comparative material material carbon of 0.032% or more, the magnetic properties are relatively good, but it can be seen that the material residual carbon far exceeds the management standard value, and this is excluded from the scope of the present invention because the use characteristics at the demand price may be sharply worsened.

Example 2

By weight ratio, C: 0.013%, Si: 3.18%, Mn: 0.205%, S: 0.005%, N: 0.0095%, dissolved Al: 0.017%, Cu: 0.493%, Cr: 0.047% and Ni: 0.049% balance Fe And a component system composed of other unavoidable impurities to prepare a slab having a thickness of 230 mm. These slabs were hot-rolled after 4 hours of reheating at a low temperature of 1310 ° C. without slab surface melting to form a 2.3 mm thick hot rolled sheet. Then, hot-rolled sheet annealing at 950 ℃ and after the pickling, the primary cold rolling was adjusted by adjusting the thickness so that the final secondary cold rolling rate is 50-62.5%. After the intermediate annealing plate was subjected to decarbonization annealing for 3 minutes on a crack basis in a humid atmosphere at 870 ° C., all the specimens were finally cold rolled to a thickness of 0.30 mm. Subsequently, after recovery annealing and application of MgO at 560 ° C., the coils were wound in a coil state, and final finishing high temperature annealing was performed. The final finishing annealing was performed at 600 ° C. for the first low temperature crack, followed by an elevated temperature at a rate of 20 ° C. per hour, and then cooled to room temperature for 30 hours after the secondary high temperature crack at 20 ° C. for a total of 20 hours or more. At elevated temperatures, the magnetic properties were ensured in a 25% nitrogen-containing hydrogen atmosphere and thereafter in a 100% hydrogen atmosphere. In this case, the residual carbon content of the material after decarbonization annealing and the magnetism after the final finishing annealing according to the secondary cold rolling rate were measured and shown in Table 2 below.

As shown in Table 2, in the comparative materials (4) and (5) where the secondary cold rolling rate is 50-54%, which corresponds to the normal cold rolling rate, almost no secondary recrystallization is formed, so that magnetism is not secured and 57%. In the case of the comparative material 6, which is a case of the magnetism is somewhat unstable, in the case of the comparative material (7) it can be seen that the residual carbon exceeds the management standard 30ppm. However, when the rolling ratio in accordance with the present invention is 58% or more, the invention material (ce) has a high magnetic flux density, low iron core loss, excellent magnetic properties, and low residual carbon in the material. .

Claims (1)

Si: 2.9-3.3%, P: 0.015% or less, dissolved Al: 0.011-0.027%, N: 0.0080-0.012%, S: 0.007% or less, Ni or Cr alone or in combination: 0.06-0.18%, Mn: 0.32% or less, Cu: 0.6% or less, C: 0.010-0.025%, remainder Fe and other unavoidable slabs are reheated to 1250-1320 ° C, followed by hot rolling, followed by a temperature of 1000 ° C or less. After performing hot-rolled sheet annealing, adjust the final thickness by two cold rolling including decarbonization annealing in a humidified hydrogen atmosphere at 820-870 ℃, and recover the temperature of secondary cold rolling to 58-65% and below 600 ℃. After annealing, the film is wound by applying a fusion inhibitor containing MgO as its main ingredient, and then the temperature is raised to 1180-1220 ° C at room temperature, and the atmosphere gas in the heating zone is 20-25% nitrogen-containing hydrogen atmosphere and the highest is 1180-1220 ° C. Atmospheric gas at the cracking temperature range is 100% hydrogen atmosphere and heat is cooled after cracking for more than 20 hours After carrying out finishing annealing method for producing a magnetic cooling and de-oriented electrical steel sheet excellent in elasticity undergoes.