KR101122127B1 - Method of refining and oriented electrcal steel sheet - Google Patents

Abstract

The present invention relates to a refining method and a grain-oriented electrical steel sheet produced by the present invention, embodiments of the present invention after the ferro-silicon is added to the ladle after tapping the molten steel to ladle, and after the molten steel tapping completion Bubbling and degassing are carried out. In addition, after the bubbling component analysis to calculate the additional input of the aluminum, or in the first reflux during the degassing treatment with reference to the component after bubbling can be calculated the additional input of aluminum.

Directivity, Electrical Steel, Molten Steel, Aluminum, Input, Bubbling, Degassing, Cleanliness

Description

Refining method and oriented electrical steel sheet produced thereby

The present invention relates to a refining method and a grain-oriented electrical steel sheet produced thereby, and more particularly, to a refining method and a grain-oriented electrical steel sheet produced thereby, which can minimize aluminum inclusions and improve molten steel cleanliness.

A transformer is a device that receives AC power from one circuit and changes its characteristics by electromagnetic induction to supply it to another circuit. For efficient operation of the transformer, oriented electrical steel sheet is used as the iron core. A grain-oriented electrical steel sheet exhibits the best magnetic properties when magnetized in its rolling direction. Therefore, when used in a transformer, it is used to match the magnetization direction <100> direction and the rolling direction as much as possible.

Iron loss is one of the major influences on transformer losses in the properties of electrical steel sheets. In order to reduce iron loss, it is necessary to grow a proper grain orientation, and for this purpose, improvement of cleanliness and narrow control of aluminum and nitrogen components are very important. However, when the micro inclusions are present, the grain growth is suppressed, thereby lowering the magnetic properties. Therefore, in order to manufacture high-performance electrical steel sheet, it is required to concentrate on improving the quality of materials through securing cleanliness of component management and inclusions in steelmaking / casting.

In general, molten steel dissolved in the converter contains 600 ~ 800ppm of oxygen, so it must be deoxidized at the time of tapping. At this time, the deoxidation treatment is performed by adding a deoxidizer such as aluminum and ferrosilicon, some of which remain in molten steel to serve as an alloying element. In addition, aluminum added as a deoxidizer reacts with oxygen in the molten steel to form alumina inclusions and floats on the molten steel surface to form slag, but also exists as an inclusion in the steel.

The deoxidizer is added when molten steel taps into the ladle from the converter, and aluminum is used by dissolving the amount of aluminum calculated according to the end point dissolved oxygen in the tapping flow and dissolving it in the molten steel at a half time point during the tapping time.

However, since the difference in the amount of aluminum input fluctuates greatly depending on the end point oxygen and there is a limit in accurately predicting the tapping time, the timing of aluminum injection is different according to the contractor, causing variation in aluminum components. It remains in the molten steel. In addition, after finishing tapping for the purpose of slag deoxidation, a large amount of crude agent is added. Accordingly, there is a problem in that steel production costs increase and impurities such as titanium in the crude agent flow into molten steel.

Thus, the alumina inclusions generated in molten steel may interfere with the movement of magnetic domains in the grain-oriented electrical steel sheet and degrade the performance and efficiency of the product, resulting in quality complaints. In addition, there is a significant difficulty in controlling the aluminum narrowly, which plays an important role in controlling the primary recrystallized grains to an appropriate size in the rolling annealing process using AlN precipitates. On the other hand, the deoxidation method of adding both calcium carbide and aluminum deoxidizer before the tapping proceeds 30% in aluminum deoxidized steel, but there is a problem that does not provide appropriate measures for the steel deoxidation method for oriented electrical steel sheet.

The present invention provides a refining method for stably narrowing aluminum components so that the grain-oriented electrical steel sheet has stable magnetic properties, and the grain-oriented electrical steel sheet produced thereby.

The present invention provides a refining method capable of narrowly controlling aluminum components stably by minimizing the formation of alumina inclusions, improving molten steel cleanliness and suppressing reoxidation, and a grain-oriented electrical steel sheet produced thereby.

Refining method according to an embodiment of the present invention comprises the steps of providing a molten steel in the converter; Injecting ferrosilicon into the ladle; Tapping the molten steel from the converter to the ladle; And injecting aluminum into the molten steel when the tapping of the molten steel is completed.

Bubbling and degassing the molten steel in which the aluminum is added further.

After the bubbling further comprises the step of adding the aluminum, the aluminum is further added according to the following equation (1).

Equation  One

Aluminum input (kg) = 288.578-1208.1 × aluminum soluble in molten steel after bubbling + 124817 × (solid soluble aluminum in molten steel after bubbling) ²

And further adding aluminum during the degassing treatment, wherein the additional amount of aluminum is calculated by referring to the component after the bubbling, and when the aluminum component is close to a target upper limit, the aluminum is added according to equation (2). If the input amount is calculated, and the aluminum component is close to the lower limit of the width table, the added amount of aluminum is calculated according to the equation (3).

Equation  2

Input Al (kg) = 76.2-2615 × solid solution aluminum contained in molten steel after bubbling + solid solution aluminum contained in molten steel after primary RH

Equation  3

Input Al (kg) = 68.5-1956 × solid solution aluminum contained in molten steel after bubbling + 258 × solid solution aluminum contained in molten steel after primary RH

The grain-oriented electrical steel sheet according to another embodiment of the present invention is a grain-oriented electrical steel sheet manufactured by the above-described refining method, C: 0.04 to 0.07% by weight, Si: 2.8 to 3.6%, P: 0.02 to 0.075%, S : 0.006% or less, Mn: 0.2% or less, Al: 0.02-0.04%, N: 0.003-0.0075%, Ti: 0.005% or less, and consist of residual Fe and other unavoidable impurities.

Embodiments of the present invention after the ferro-silicon is added to the ladle and the molten steel is pulled out to the ladle, and the aluminum is added to the molten steel tapping time and then bubbling and degassing treatment. In addition, after the bubbling component analysis to calculate the additional input of aluminum, the additional input of aluminum can be calculated by referring to the component after bubbling at the first reflux during the degassing treatment.

According to embodiments of the present invention, by deoxidation with ferrosilicon to secure oxygen of the molten steel to a predetermined level or less, and when the deoxidation by adding aluminum at the time of finishing tapping can minimize the effect of the end point oxygen. In addition, when aluminum is put on the slag and the top bubbling is strongly performed at the bubbling station, the slag may be deoxidized without additional preparation. Therefore, the deoxidation efficiency can be improved, the preparation agent can be omitted, and steel excellent in cleanliness can be manufactured. In addition, it is possible to reduce the molten steel manufacturing cost by reducing the aluminum input amount for deoxidation purposes.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention; However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms, and only the embodiments are intended to complete the disclosure of the present invention and to those skilled in the art. It is provided for complete information.

First, the grain-oriented electrical steel sheet according to an embodiment of the present invention has a target composition of% by weight of C: 0.04 to 0.07%, Si: 2.8 to 3.6%, P: 0.02 to 0.075%, S: 0.006% or less, and Mn: 0.2 % Or less, Al: 0.02 to 0.04%, N: 0.003 to 0.0075%, Ti: 0.005% or less, and consist of residual Fe and other inevitable impurities.

C is a component added to refine the hot rolled structure, and after functioning during hot rolling, it becomes an impurity and adversely affects its magnetic properties and should be removed. If the content of C is too high, coarse carbides precipitate and carbon removal becomes difficult during decarbonization annealing. Therefore, it is 0.1% or less, Preferably it is 0.07% or less.

Si is a component added to increase the electrical resistance of the steel sheet to lower the iron loss. If the content is 4.8% or more, cold rolling is impossible, and when it is 1.0% or less, the addition effect is almost insignificant. Therefore, the content of Si is made 1.0 to 4.8%, preferably 2.8 to 3.6%.

P increases the secondary recrystallization temperature by promoting the growth of primary recrystallized grains in the grain-oriented electrical steel sheet to improve the degree of integration of the {110} <001> orientation in the final product. If the primary recrystallization is too large, the secondary recrystallization becomes unstable, but as long as the secondary recrystallization occurs, it is advantageous for the magnet to have a large primary recrystallized grain to increase the secondary recrystallization temperature. On the other hand, P not only lowers the iron loss of the final product by increasing the number of grains having the {110} <001> orientation in the primary recrystallized steel sheet, but also strongly develops the {111} <112> texture in the primary recrystallized sheet. This increases the density of the {110} <001> of the final product, thus increasing the magnetic flux density. In addition, P has a function of reinforcing the suppression force by segregating at the grain boundary to a high temperature of about 1000 ° C. during secondary recrystallization annealing, to delay decomposition of the precipitate. If the P content is limited to 0.02 to 0.075%, significant effects can be obtained. In order for P to be fully effective, 0.02% or more is required, and when P is more than 0.075%, the size of the primary recrystallized grains is rather decreased, which not only makes the secondary recrystallization unstable, but also increases the brittleness and impairs cold rolling. .

S is preferably an element which has high solubility temperature and high segregation during hot rolling so as not to be contained as much as possible. However, S is an unavoidable impurity contained in steelmaking. Even so, the content of S is preferably limited to 0.01% or less, preferably 0.006% or less.

Mn is a component having an effect of lowering iron loss by increasing electrical resistance, and when the content is too large, Mn causes a decrease in magnetic flux density. Therefore, the content of Mn is 0.2% or less, preferably 0.05 to 2.0%.

Al is a component that finally acts as an inhibitor by forming nitrides of AlN, (Al, Si) N and (Al, Si, Mn) N forms. If the Al content is 0.01% or less, a sufficient effect as an inhibitor cannot be expected. If the Al content is too high, nitride of the Al system grows coarsely and the inhibitor's ability is lowered. Therefore, the Al content is set to 0.01 to 0.05%, preferably 0.02 to 0.04%.

Since N is reinforced during the high temperature annealing process, an amount of impurities entering the impurity at the time of melting is sufficient. No adverse effects from the addition of nitrogen have been found, but hot rolling is difficult when exceeding 0.0075%. Therefore, the content of N is to be 0.003 ~ 0.0075%.

Next, the present invention will be described using the process flowchart of FIG. 1 for explaining a method for refining a grain-oriented electrical steel sheet according to an embodiment of the present invention.

Referring to FIG. 1, in the method for refining a grain-oriented electrical steel sheet according to an embodiment of the present disclosure, after injecting ferrosilicon into the ladle, tapping the molten steel into the ladle (S110) and aluminum at the completion of the tapping of the molten steel It includes the step (S120), bubbling the molten steel (S130), and the step (S140) for degassing in the degassing apparatus, each step will be described in detail as follows.

S110: First, the deoxidizer is added when tapping the molten steel after the converter refining, and the ferrosilicon is added before the aluminum. In other words, the ferrous silicon is put into the ladle, and the molten steel is tapped into the ladle. The reason why the ferrosilicon is added first is the oriented electrical steel sheet, which is a silicon alloy steel with a large amount of silicon, and the ferrosilicon is added to the ladle first because the total amount of ferrosilicon cannot be added during the tapping time considering the input time of ferroalloy from the hopper. You are going to Ladle. Ferrosilicon is first introduced and deoxidized to secure oxygen in the molten steel below a certain level.

S120: After molten steel taps into the ladle, aluminum is put into the ladle. At this time, the aluminum input amount is calculated and added, and factors affecting the aluminum input amount are as follows. 1) Aluminum amount for deoxidizing molten steel oxygen, 2) Aluminum amount for deoxidizing slag flowing out during tapping, 3) Aluminum amount reacting with oxygen in the atmosphere as aluminum enters during tapping, and 4) For adjusting components The total amount of aluminum is calculated by considering at least one of the amount of aluminum to be added. By the way, when the overcharging occurs during the drilling, the end point molten oxygen increases, and when the lower oxide such as the total amount of Fe + Mn0 (T.Fe + Mn0) in the slag increases, fine inclusions due to molten steel reoxidation increase. Therefore, in consideration of this, the amount of aluminum input should also be increased, so it is desirable to induce the target operation to 700 ppm or less of the end point oxygen.

On the other hand, as a method of adding aluminum, conventionally, a method of dissolving aluminum in the molten steel by hitting the tapping flow at a half time of tapping time was used. However, the tapping time may vary depending on the amount of molten steel. Deviation occurs depending on the number of times there is a problem that the operator is difficult to predict accurately. However, in the present invention, after deoxidizing molten steel oxygen with ferrosilicon, aluminum can be added at the time of tapping to minimize the effect of the end point oxygen, and the variation due to the difference in aluminum addition time can be eliminated, and a separate preparation agent is added. The slag can be deoxidized without.

S130: In the oriented electrical steel sheet, since aluminum narrow control is the most important influence on the magnetic properties, transfer the molten steel with ladle to the bubbling station, and for example, argon for 4 minutes to make the molten steel uniform. Bubbling is done.

S140: Subsequently, degassing and fine component adjustment are performed in a vacuum degassing apparatus. The vacuum degassing apparatus may use any one of Ruhrstahl Herause (RH), VTD, and VOD. When using RH, the reflux gas may use at least one of nitrogen or argon. In addition, the RH reflux pattern (Pattern) may increase the water content of ferroalloy raw materials in the summer and increase hydrogen in the steel in the summer, so the time to maintain 2 Torr is increased from 15 to 18 minutes to help dehydrogenation. Internal cracks can be reduced.

As described above, in the method for manufacturing molten steel of the grain-oriented electrical steel sheet according to an embodiment of the present invention, the ferrosilicon is first introduced into the ladle, and then the molten steel is pulled out to the ladle, and the aluminum is input by calculating the aluminum input amount at the completion of the tapping. Done. Therefore, by deoxidizing molten steel oxygen with ferrosilicon and adding aluminum at the time of tapping completion, the effect of the end point oxygen can be minimized, and the variation due to the difference of aluminum addition time can be eliminated, and slag can be removed without additional preparation agent. Can be deoxidized.

Meanwhile, although aluminum is added to the ladle at the time when the molten steel is completed, aluminum may be additionally added at at least one portion after bubbling and degassing. And described with reference to Figure 3 as follows.

2 is a process flowchart illustrating a molten steel manufacturing method of a grain-oriented electrical steel sheet according to another embodiment of the present invention.

Referring to FIG. 2, in the molten steel manufacturing method of the grain-oriented electrical steel sheet according to another embodiment of the present invention, after the ferrosilicon is injected into the ladle, the molten steel is pulled out to the ladle (S110), and the tapping completion time of the molten steel is obtained. Injecting aluminum into (S120), Bubbling molten steel (S130), Analyzing molten steel components to further inject aluminum (S135), and degassing in the degassing apparatus (S140) Include.

S110: After the ferrosilicon is injected into the ladle, the molten steel after the converter refining is finished.

S120: At the time of completion of tapping of molten steel, aluminum is injected into the ladle. At this time, 1) aluminum amount for deoxidizing molten steel oxygen, 2) aluminum amount for deoxidizing slag flowing out during tapping, 3) aluminum amount reacted with oxygen in the air while aluminum is in tapping, and 4) component adjustment The total amount of aluminum is calculated in consideration of at least one of the amount of aluminum to be added for the purpose.

S130: The molten steel stepped out of the ladle is transferred to a bubbling station, and bubbling with argon, for example, for 4 minutes to make the molten steel component uniform.

S135: Then, component analysis of the bubbled molten steel is performed. At this time, the molten steel sample for analyzing the component should be analyzed within 7 minutes to minimize the deviation between the actual molten steel component and the analysis result value. The aluminum component is finely controlled according to the aluminum heavy component included in the analyzed molten steel, that is, the soluble aluminum value. At this time, in order to improve the target component hit ratio, and to minimize the deviation between operators is added aluminum in accordance with the correlation equation as shown in [Equation 1]. Here, the following [Equation 1] is obtained by the graph of FIG. 3 is a graph of the relationship between the soluble aluminum (X-axis) and the amount of aluminum input (Y-axis) included in molten steel after primary bubbling. The aluminum input amount is obtained, and [Equation 1] is derived by calculating the equation based on the statistical values thus obtained.

Input aluminum (kg) = 288.578-1208.1 × aluminum that can be dissolved in molten steel after bubbling + 124817 × (soluble aluminum in molten steel after bubbling) ²

S145: Subsequently, degassing and fine component adjustment are performed in a vacuum degassing apparatus. The vacuum degassing apparatus may use any one of Ruhrstahl Herause (RH), VTD, and VOD. However, in order to match the target aluminum component value when the primary reflux is performed in the RH apparatus, the aluminum input amount may be calculated by referring to the component after bubbling and the component of the primary RH in the bubbling station. Here, when the aluminum component is close to the target upper limit, the aluminum addition amount can be calculated based on [Equation 2], and when the aluminum component is close to the lower limit, the addition amount is calculated and added based on [Equation 3], and the hit ratio Can increase. By the way, the following [Equation 2] and [Equation 3] is obtained by the graph of FIG. 4 is a graph showing the relationship between the soluble aluminum (X-axis) included in molten steel after primary RH in degassing and the amount of aluminum input (Y-axis) accordingly, and shows the additional amount of aluminum added after bubbling at the bubbling station. For reference, a plurality of experiments and experiences can be used to obtain the aluminum available and the amount of aluminum input, and based on the statistical values thus obtained, Equations 2 and 3 are derived. Meanwhile, in order to minimize the difference between the component analysis result and the actual molten steel component, the analysis result should be derived within 7 minutes to minimize the component deviation when further component adjustments are made.

Input Al (kg) = 76.2-2615 × solid solution aluminum contained in molten steel after bubbling + solid solution aluminum contained in molten steel after primary RH

Input Al (kg) = 68.5-1956 × solid solution aluminum contained in molten steel after bubbling + 258 × solid solution aluminum contained in molten steel after primary RH

Meanwhile, another embodiment of the present invention has been described as additionally adding aluminum at the first reflux after the bubbling and degassing, but may be additionally added to the aluminum at the first reflux or after the bubbling. . That is, aluminum may be further added after at least one portion of the primary reflux after bubbling.

Example

The molten iron from the blast furnace is charged to the converter through the deflow reaction in the molten iron preliminary treatment, and when the iron is transferred, the impurities of molten iron, Si, C, Mn, and P, react with oxygen and are removed as slag, and the dissolved oxygen content during tapping is 700 ppm. The drilling ends with the following objective. The deoxidizer is added when the ladle is pulled from the converter, and the grain-oriented electrical steel sheet has a silicon content of about 3% and adds 13 tons of ferrosilicon ferroalloy for deoxidation and composition adjustment. Considering the ferroalloy input time from the ferroalloy hopper, it is impossible to put the whole amount during the tapping time, so ferrosilicon is first introduced into the ladle, and the molten steel is pulled out to the ladle and deoxidized to ferrosilicon. When the converter slag was analyzed when the end point of molten steel oxygen was completed with the target of 700ppm or less, the slag oxidation (T.Fe + MnO) was 16.8% ~ 20.0% and the slag discharged during tapping was considered. It is possible to calculate the aluminum input amount to deoxidize.

By deoxidation with ferrosilicon ferroalloy to secure oxygen of molten steel below a certain level, and deoxidation by adding aluminum at the completion of tapping, the effect of end point oxygen can be minimized, and aluminum is put on slag and bubbling station If top bubbling is strong for 4 minutes, slag can be deoxidized without additional preparation. Therefore, it was possible to omit the preparation and to reduce the amount of aluminum input for total deoxidation purposes.

Table 1 below shows the analysis results of aluminum and total oxygen in the product according to the molten steel deoxidation method of the conventional example and the present invention example. In Comparative Examples 1 to 5, aluminum was added according to the end point oxygen during tapping and 300 kg of crude agent was added after the tapping was completed. In Comparative Examples 6 to 8, aluminum was added according to the end point oxygen during tapping, but the preparation was omitted. It is the result of the test, and the invention examples 1-5 showed the result which aluminum was added and the preparation agent was omitted after completion of tapping.

division
Terminal oxygen
ppm Preparation
kg Al input amount
kg After bubbling
[Al],% Product [TO]
ppm Comparative Example 1 902 300 341 0.0238 9 Comparative Example 2 686 300 301 0.0161 9 Comparative Example 3 708 300 350 0.0253 9 Comparative Example 4 505 300 301 0.0260 8 Comparative Example 5 817 300 334 0.0245 - Comparative Example 6 710 - 329 0.0195 8 Comparative Example 7 536 - 286 0.0193 10 Comparative Example 8 620 - 291 0.0283 10 Inventive Example 1 766 - 270 0.0337 7 Inventive Example 2 833 - 272 0.0286 6 Inventive Example 3 684 - 278 0.0336 7 Inventive Example 4 797 - 275 0.0281 7 Inventive Example 5 551 - 272 0.0231 7

Test result In the invention example, it was confirmed that the deoxidation efficiency was improved by obtaining an aluminum real ratio of 10-30% higher than that of aluminum in the end point molten steel oxygen equivalent to the comparative example, and the total oxygen measured in the product hot rolled coil It was reduced by about 3ppm, indicating that molten steel cleanliness was improved. As described above, it was found that the complex deoxidation method, which deoxidizes with ferrosilic acid of the present invention and deoxidizes with aluminum, not only has higher deoxidation efficiency than conventional deoxidation method but also significantly improves cleanliness.

In addition, the following Table 2 shows the aluminum addition standard of the comparative example and the aluminum addition standard of the invention example according to the end point oxygen. The invention example is equivalent to the conventional example even if the amount of aluminum addition is reduced without adding the preparation agent at the equivalent end point oxygen reference. The above aluminum real error rate was obtained.

division
End point oxygen (ppm) Preparation agent (kg)
500 600 700 800 900 Comparative Example 9 280 300 320 340 360 300 Comparative Example 10 360 380 420 440 460 - Inventive Example 280 290 300 310 320 -

On the other hand, although the technical spirit of the present invention has been described in detail according to the above embodiment, it should be noted that the above embodiment is for the purpose of explanation and not for the limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

1 is a process flow chart illustrating a molten steel manufacturing method of a grain-oriented electrical steel sheet according to an embodiment of the present invention.

2 is a process flow chart for explaining a molten steel manufacturing method of a grain-oriented electrical steel sheet according to another embodiment of the present invention.

Figure 3 is a graph of the relationship between the amount of aluminum can be dissolved and the additional amount of aluminum after bubbling to derive Equation 1 according to the present invention.

Figure 4 is a graph of the relationship between the amount of aluminum to be dissolved and the amount of additional aluminum input after reflux to derive Equations 2 and 3 according to the present invention.

Claims (8)

Providing molten steel in the converter; Injecting ferrosilicon into the ladle; Tapping the molten steel from the converter to the ladle; Injecting aluminum into the molten steel at the time of finishing tapping of the molten steel; And Bubbling and degassing the molten steel into which the aluminum is injected; After the bubbling further comprises the step of adding the aluminum according to the following equation (1). Equation 1 Input aluminum (kg) = 288.578-1208.1 × aluminum that can be dissolved in molten steel after bubbling + 124817 × (soluble aluminum in molten steel after bubbling) ² delete delete delete The refining method of claim 1, further comprising adding aluminum during the degassing treatment. The refining method according to claim 5, wherein the additional dose of aluminum is calculated by referring to the component after the bubbling. The refining of claim 6, wherein when the aluminum component is close to the target upper limit, the additional aluminum dose is calculated according to Equation 2; and when the aluminum component is close to the lower limit of the width table, the additional aluminum dose is calculated according to Equation 3. Way. Equation  2 Input Al (kg) = 76.2-2615 × solid solution aluminum contained in molten steel after bubbling + solid solution aluminum contained in molten steel after primary RH Equation  3 Input Al (kg) = 68.5-1956 × solid solution aluminum contained in molten steel after bubbling + 258 × solid solution aluminum contained in molten steel after primary RH The grain-oriented electrical steel sheet manufactured according to at least one of claims 1 and 5 to 7, wherein the weight percent C: 0.04 to 0.07%, Si: 2.8 to 3.6%, P: 0.02 to 0.075%, S: A grain-oriented electrical steel sheet comprising 0.006% or less, Mn: 0.2% or less, Al: 0.02 to 0.04%, N: 0.003 to 0.0075%, Ti: 0.005% or less, and residual Fe and other unavoidable impurities.

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