KR100925594B1 - A method for refining the molten steel of non-oriented electrical steel sheet having low iron loss - Google Patents

Abstract

The present invention relates to a method for refining molten steel for producing non-oriented electrical steel sheet used in materials such as generators, motors, transformers and magnetic switches.

In the present invention, the slag deoxidizer of 35-50 wt% of metallic aluminum (Al) is added to the slag layer of the ladle 3 immediately after tapping the molten steel after the refining in the converter 1 with the ladle 3. Lowering (T.Fe + MnO) to 5-10% by weight of slag; Transferring the ladle (3) to a vacuum degassing apparatus (5) to perform decarburization to lower carbon (C) to 30 ppm or less; Adding silicon (Si) in the vacuum degassing apparatus (5) to adjust the silicon (Si) component to 0.3 to 0.7% by weight; After the decarburization reaction and the addition of Si, the slag oxidizer is added to the slag layer to lower the (T.Fe + MnO) in the slag to 1.5 wt% or less and at the same time the (% CaO) / (% Al ₂ O ₃ ) ratio of the slag. Adjusting the range to 1.3 to 1.7; And transferring the ladle to a facility capable of upper bubbling, and depositing the upper lance from the top to stir the interface layer between the slag and the molten steel.

Iron loss, non-oriented electrical steel sheet, converter, vacuum degasser, slag deoxidizer, top lance

Description

A method for refining molten steel for reducing iron loss non-oriented electrical steel sheet {A METHOD FOR REFINING THE MOLTEN STEEL OF NON-ORIENTED ELECTRICAL STEEL SHEET HAVING LOW IRON LOSS}

1 is a schematic diagram showing a refining process to which the method of the present invention is applied.

      Explanation of symbols on the main parts of the drawings

1 ...... converter 3 ...... ladle

5 ...... Vacuum degasser 6 ...... Floating lance

The present invention relates to a method for refining molten steel for manufacturing non-oriented electrical steel sheet used as a material for generators, motors, transformers and magnetic switches, more specifically 30 ppm or less of carbon (C) in the steelmaking process, (Si) 0.3 ~ 0.7% by weight, less than 30ppm nitrogen (N), less than 50ppm sulfur (S) and less than 50ppm aluminum (Al) refined to easily manufacture non-oriented electrical steel sheet with reduced fracture To a method of refining.

In general, non-oriented electrical steel sheets used as materials for generators, motors, transformers, and magnetic switches have a low iron loss (hereinafter, iron loss) when current is applied to the material, so energy loss due to heat and noise is generally low. Requires material characteristics of low iron loss.

In order to reduce the iron loss of such an non-oriented electrical steel sheet, it is usually necessary to add a large amount of Si in steel and to control C, N, S, etc. which exist as impurities as low as possible. Therefore, among the various kinds of non-oriented electrical steel sheet, the material used for the small motor requires a chemical composition of 0.3 to 0.7 wt% of Si, 30 ppm or less of C, 30 ppm or less of N, 50 ppm or less of Al, and 50 ppm or less of Al.

Here, Si adds ferro silicon (Fe-Si) ferroalloy directly to molten steel during refining, so the component control is relatively easy, and in the case of C and N, the pick-up factor is removed at the molten steel stage and RH, etc. It can be controlled easily by performing a vacuum process using a vacuum degassing apparatus.

On the other hand, there are various problems in keeping S below 50 ppm while keeping Al below 50 ppm. That is, the S content of the molten steel withdrawn from the converter is 60 ~ 80ppm, in order to lower these S to 50ppm or less, reducing oxygen, that is, less than 3ppm dissolved oxygen is required, while Al is 50ppm or less, dissolved oxygen 20 ~ 50ppm It is an oxidizing atmosphere present. Therefore, many separate refining methods are required to remove S to 50 ppm or less in an oxidizing atmosphere in which 20 to 50 ppm of dissolved oxygen is present.

Accordingly, proposals related to the non-oriented electrical steel refining method include Japanese Patent Application Laid-Open Nos. 98-310850, 97-316535, and 96-333658, and the above proposals are for decarburization and deoxidation in a vacuum degassing apparatus. And adding a molten steel desulfurization agent to further lower the content of sulfur (S).

The above proposals are more than 0.02% by weight of Al in the molten steel, that is, a state in which an appropriate reducing atmosphere is maintained, while further desulfurization reaction is possible.

In another method, Korean Patent Application No. 2000-51450 has been proposed, which adjusts the slag composition to 60-65% by weight of CaO, 30-35% by weight of Al ₂ O ₃ and SiO ₂ while maintaining Al at 0.2-1.5% by weight. It is characterized by.

However, if Al is maintained in the range of 0.2 to 1.5% by weight as described above, it is possible to reduce the S content to 10 ppm or less since it is a very strong reducing atmosphere. It is difficult to remove S because an oxidizing atmosphere of 20 to 50 ppm is formed.

Therefore, the present invention has been proposed in order to solve the conventional problems as described above, the object of which is to produce a non-oriented electrical steel sheet by adding a slag deoxidizer after the converter tapping step and degassing treatment, by controlling the slag composition, Al The present invention is to provide a method for refining molten steel for non-oriented electrical steel sheet, which can produce non-oriented electrical steel sheet having low iron loss by reducing S to 50 ppm or less in an oxidizing atmosphere of 50 ppm or less.

As a technical configuration for achieving the above object, the present invention,

Non-oriented electricity containing 30 ppm or less of carbon (C), 0.3-0.7 wt% of silicon (Si), 30 ppm or less of nitrogen (N), 50 ppm or less of sulfur (S), 50 ppm or less of aluminum (Al), balance Fe and other unavoidable impurities In the method of refining molten steel to cast steel sheet,

Immediately after refining molten steel in the converter into a ladle, a slag deoxidizer of 35-50% by weight of metal aluminum (Al) was added to the slag layer of the ladle to obtain (T.Fe + MnO) in the slag. Lowering to weight percent;

Transferring the teaming ladle to a vacuum degassing apparatus to perform decarburization to lower carbon (C) to 30 ppm or less;

Adding silicon (Si) in the vacuum degassing apparatus to adjust the silicon (Si) component to 0.3 to 0.7% by weight;

After the decarburization reaction and the addition of Si, the slag oxidizer is added to the slag layer to lower the slag weight (T.Fe + MnO) to 1.5 wt% or less and at the same time the slag (% CaO) / (% Al ₂ O ₃ ) ratio. Adjusting the range to 1.3 to 1.7; And

The ladle is transferred to a facility capable of upper bubbling, and the upper layer lance is deposited to agitate the interface layer between the slag and the molten steel, thereby providing a molten steel refining method for reducing iron loss-free non-oriented electrical steel sheet. By

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

The non-oriented electrical steel sheet according to the present invention is a general material of iron loss of about 5.5 ~ 7.0W / kg, the required chemical composition is C 30ppm or less, Si 0.3 ~ 0.7% by weight, N 30ppm or less, S 50ppm or less and Al 50ppm It is a steel including the following.

1 is a schematic diagram showing a refining process to which the method of the present invention is applied, as shown in FIG. 1, a molten iron of C 4.0 to 4.5 wt% and S 30 to 60 ppm is charged into the converter 1, and oxygen is removed from the oxygen blowing lance. Is sprayed at supersonic speed, the chemical composition of the molten steel at which the blowdown of the converter (1) is completed is 1650 ~ 1700 ℃ temperature, dissolved oxygen (hereinafter referred to as [O]) 400 ~ 800ppm, carbon (C) 0.02 ~ 0.05 % By weight, sulfur (S) 60-80ppm.

And, the slag generated in the converter (1) refining process will contain 40 to 50% by weight of CaO, 5 to 10% by weight of SiO ₂ , 15 to 25% by weight (T.Fe + MnO), etc. In the process of tapping the molten steel after the refining in the ladle 3) slag having the above chemical composition is mixed into the ladle (3) together with the molten steel by 4 ~ 6kg per ton of molten steel.

Since the slag is a strongly oxidizing slag containing 15 to 25% by weight of (T.Fe + MnO), the present invention adds a slag deoxidizer to the slag layer formed on the top of the teaming ladle 3 immediately after finishing tapping. Lower the (T.Fe + MnO) component in the slag to 5-10 wt%.

Here, the added slag deoxidizer is a commercially supplied slag deoxidizer composed of 35 to 50% by weight of metal aluminum, 40 to 60% by weight of CaCO ₃ and 5% by weight or less of impurities, wherein (T The amount of slag deoxidizer added to adjust .Fe + MnO) to 5 to 10% by weight is sufficient to be 0.6 to 1.5 kg per ton of molten steel.

As described above, when molten steel slag deoxidizer is added into the ladle 3 from which the molten steel is pulled out from the converter 1, (T.Fe + MnO) in the components contained in the slag is reduced by the reaction of Formula 1 below. Here, (T.Fe) is a mixture of (FeO) and (Fe2O3) in slag, (MnO) is MnO in slag, and m.Al means metal Al in slag deoxidizer.

(T.Fe), (MnO) + m.Al = (Al ₂ O) + Fe, Mn

In the present invention, the reason for controlling the (T.Fe + MnO) component in the range of 5 to 10% by weight is less than 5%, which is advantageous for the desulfurization reaction of molten steel, but due to the addition of slag deoxidizer This is because a large amount of (O) is reduced and it is difficult to control C to 30 ppm or less in the vacuum degassing apparatus 5 which is a post process.

On the other hand, according to the experiments of the present inventors, when the (T.Fe + MnO) component contained in the slag exceeds 10% by weight, even after adding a large amount of slag deoxidizer after the decarburization reaction (T.Fe + MnO) was difficult to obtain.

m.Al + [O] = Al ₂ O ₃

Subsequently, after the addition of the slag deoxidizer is finished to the molten steel withdrawn from the converter into the ladle 3, the molten steel of the ladle 3 is transferred to the vacuum degassing apparatus 5, where the vacuum degassing is performed. The apparatus 1 is irrelevant to any of RH, VTD, and VOD, and any apparatus capable of decarburizing while maintaining a vacuum of 1 torr or less is sufficient.

That is, when the timing ladle 3 is transferred to the vacuum degassing apparatus 5 and the vacuum degree of the vacuum vessel is maintained at 1 torr or less while stirring the molten steel, the molten steel may be [C] and The reaction of [O] leads to a decrease in the carbon content.

For example, in the RH vacuum degassing apparatus, when the initial carbon [C] is 0.02 to 0.05% by weight and oxygen [O] is 300 to 500 ppm, the stirring gas is 120 to 150 Nm ³ / hr and the vacuum degree is 30 ppm or less if it is maintained for 13 to 17 minutes under 1 torr. [C] concentration can be obtained.

[C] + [O] = CO (g)

When the decarburization reaction in the vacuum degassing apparatus 1 is finished, silicon is added to control the [Si] component of the molten steel to 0.3 to 0.7 wt%. In the case of the [Si] component, it can be adjusted to the target range by the addition of ferro silicon (Fe-Si) during the tapping from the converter (1), in which case [O] is reduced by the reaction of the following formula (4) In addition to preventing the decarburization reaction in the vacuum degassing apparatus 5 proceeding at, the produced (SiO ₂ ) inhibits molten steel desulfurization reaction.

Si + 2 [O] = SiO ₂

On the other hand, after the decarburization reaction in the vacuum degassing apparatus (5), it is possible to use Si alloys such as Fe-Si, Si-Mn in order to increase the [Si] concentration, but if they are added to the carbon contained therein Since the [C] component of molten steel increases because of (C) component, it is preferable to add metal Si as much as possible. For example, in order to obtain [Si] concentration of 0.3 to 0.7 wt% in a 300 ton RH vacuum degassing apparatus, it is sufficient to add 3.3 to 8.0 kg of metal Si per ton of molten steel. In this case, the concentration of [O] is 20 to 50 ppm and [S] ] The concentration reaches 60 ~ 80ppm, [N] 15 ~ 250ppm.

Subsequently, when the decarburization reaction and the Si addition reaction in the vacuum degassing apparatus 5 are completed, the same slag deoxidizer is added to reduce the (T.Fe + MnO) concentration in the slag to 1.5% by weight or less.

According to the experiments of the present inventors, when the [O] concentration in the molten steel (T.Fe + MnO) concentration exceeds 1.5% by weight in 20 ~ 50ppm conditions, it was found that the desulfurization reaction of the molten steel does not proceed. This is because the desulfurization reaction of molten steel should proceed to the reaction of Chemical Formula 5, but since 20-50 ppm [O] is present on the right side, the forward reaction, that is, the reaction to the right side is suppressed.

CaO (s) + [S] = CaS (s) + [O]

Meanwhile, according to the present invention, a slag deoxidizer is added to the molten steel in which the decarburization reaction and the Si addition reaction in the vacuum degassing apparatus 5 are completed, thereby lowering the (T.Fe + MnO) component to 1.5% by weight or less and simultaneously slag. In the case of adjusting the medium (% CaO) / (% Al ₂ O ₃ ) ratio in the range of 1.3 to 1.7, it was confirmed that a range of molten steel desulfurization proceeded, and the reason was locally in the interface of slag and molten steel. It is judged to be the phenomenon which progresses to reaction of 6.

2m.Al + 3 [S] + 3CaO (s) = 3CaS (s) + (Al ₂ O ₃ )

In Formula 6, m.Al is a metal Al in the slag deoxidizer, and CaCO ₃ added with CaO as the slag deoxidizer is produced by decomposition of CaO + CO ₂ .

For example, according to the experiments of the present inventors, in order to adjust the (T.Fe + MnO) component of 1.5 wt% or less and the (% CaO) / (% Al ₂ O ₃ ) ratio in the range of 1.3 to 1.7 in a 300 ton teaming ladle. It was sufficient to add 0.7 ~ 1.3kg of slag deoxidizer per ton of molten steel.

As described above, if the slag deoxidizer is added to molten steel to control the ratio of (T.Fe + MnO) component and (% CaO) / (% Al ₂ O ₃ ) and maintain sufficient time, desulfurization of Chemical Formula 6 may be expected. However, in the steelmaking process, the time management is very important, so to obtain the desulfurization effect in a short time, the teaming ladle is transferred to a facility capable of bubbling.

Subsequently, the upper lance 6 capable of blowing argon (Ar) from the top is dipped in molten steel to stir the interface layer between slag and molten steel. Here, the upper lance (6) is located at 1/5 to 1/2 of the total height of the molten steel in the teaming ladle from the tap surface, the Ar flow is controlled in the range 0.3 ~ 1.0 Nm ³ / min the slag It is preferable to stir the interface layer of and molten steel.

Here, when the height of the upper lance 6 is less than 1/5, there is a disadvantage that there is no slag on the hot water surface, that is, the hot water is generated so that nitrogen is introduced from the atmosphere to increase the [N] concentration of the molten steel, 1/2 In the case of exceeding, the inflow of [O] into the molten steel interface was excessive, and thus it was difficult to obtain the desired desulfurization effect.

In addition, when the Ar flow rate of the upper lance 6 is less than 0.3 Nm ³ / min, it is difficult to obtain a desired desulfurization effect in a short time, and when it exceeds 1.0 Nm ³ / min, ground sugar is generated [N]. It has been found that there is a disadvantage that the concentration is excessively increased.

When the [S] concentration is about 60 to 80 ppm before the desulfurization of the molten steel, in order to obtain the [S] concentration of 50 ppm or less, the Ar blowing time through the upper lance 6 is preferably maintained for 3 to 10 minutes. .

Hereinafter, the present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples.

EXAMPLE

After finishing the refining in the 300 ton converter, it was confirmed that the molten steel temperature is in the range of 1650 ~ 1700 ℃, the dissolved oxygen [O] was measured, the molten steel sample was collected and analyzed the major impurities such as C, N, S.

Subsequently, immediately after the tapping of the molten steel of the converter is completed with the ladle ₃ , the hot water slag layer of the molten steel stored in the ladle _{3 with} a CaCO ₃ -based slag oxidizing agent containing a main component of CaCO ₃ and containing metal Al 41.2%. [O] was measured again, and slag samples were taken to analyze main components such as (CaO), (SiO ₂ ), (Al ₂ O ₃ ), (T.Fe), and (MnO).

Subsequently, the molten steel is transferred to the RH vacuum degassing apparatus 5 and the decarburization reaction of the molten steel is performed while stirring the molten steel with Ar 150 Nm ³ / hr as the reflux gas while maintaining the vacuum degree of 1torr or less, and the vacuum degassing apparatus ( At the end of the decarburization reaction using 5), 3.3 to 8.0 kg of metal Si was added per ton of molten steel to adjust the concentration of [Si] to 0.3 to 0.7 wt%.

In addition, a molten steel sample is collected at the end of the molten steel refining using the RH degassing apparatus 5, the main impurities such as C, N, S, etc. are analyzed, and the slag deoxidizer described above is once again immediately after the refining is finished. (T.Fe + MnO) concentration and (% CaO) / (% Al ₂ O ₃ ) in the slag were added at the same time.

Then, the molten steel in which the slag preparation is finished is transferred to an apparatus capable of bubbling bubbling, and the upper lance 6 composed of refractory is lowered from above, and the tip portion thereof is 1/3 of the total melt height from the water surface. In the positioned state, the interface layer of slag and molten steel was stirred for 4 to 8 minutes while blowing Ar. After the agitation was completed, a molten steel sample was taken for component analysis.

Table 1 summarizes the experimental conditions and results of the comparative material and the present invention performed in the Examples.                     

Comparative Material 1 Comparative Material 2 Invention 1 Invention 2 Invention 3 Comparative Material 3 Comparative Material 4 Electric furnace (ppm) C (ppm) 350 330 340 360 350 370 290 O (ppm) 570 600 580 580 600 560 690 S (ppm) 65 75 70 79 75 78 75 N (ppm) 17 19 17 18 20 16 23 Tapping slag salt (kg / t-s) 0.6 1.0 1.0 0.8 1.3 0.3 1.7 Dissolved Oxygen (O) (ppm) 370 340 330 350 310 410 240 (T.Fe + MnO), wt% 11.5 9.1 8.5 9.5 7.4 13.5 5.3 RH decarburization time (min) 14 15 15 14 16 14 19 RH end point C (ppm) 27 25 25 23 23 25 32 S (ppm) 64 73 71 78 76 80 75 N (ppm) 16 17 16 18 19 16 21 Slagtalizer (kg / t-s) 1.9 1.1 0.8 1.3 1.1 2.2 0.7 (T.Fe + MnO), wt% 3.6 1.5 1.3 1.1 1.2 4.7 1.3 (% CaO) / (Al ₂ O ₃ ) 1.2 1.5 1.6 1.4 1.5 1.8 1.7 Upper stirring Ar (Nma ³ / hr) 0.5 1.2 0.3 0.8 1.0 0.3 0.5 Time (min) 10 4 8 5 4 8 5 S (ppm) 63 45 40 36 43 77 45 N (ppm) 18 34 19 23 23 19 23

As can be seen in Table 1, in the case of the present invention 1, 2 and 3, after the tapping by adding 0.8 ~ 1.3kg of slag deoxidizer per ton of molten steel in the upper part of the slag during tapping as described above. 350 ppm and (T.Fe + MnO) 7.4 to 9.5 ppm can be obtained.

In addition, 14 to 16 minutes of decarburization was performed in an RH vacuum degassing apparatus, and the level of [C] 23 to 25 ppm was obtained, and [S] and [N] were 71 to 76 ppm, respectively, which were not significantly different from the end of the converter. And 16 to 19 ppm.

At the end of the RH vacuum degassing operation, 0.8 to 1.3 kg of slag deoxidizer was added per ton of molten steel to make 1.1 to 1.3% of (T.Fe + MnO), (% CaO) / (% Al ₂ O ₃ ) ratio. 1.4 to 1.6, and by argon performing upper bubbling for 4 to 8 minutes at a flow rate of 0.3 to 1.0 Nm ³ / hr, [S] 40, 36 and 43 ppm, [N] 19, 23 and 23 ppm were obtained. The chemical composition required in the non-oriented electrical steel sheet in the range of 5.5 ~ 7.0W / kg, that is, C 30ppm or less, N 30ppm or less, S 50ppm or less can be obtained stably.

On the other hand, the analysis of the molten steel sample collected at the time of the top bubbling (Top bubbling) was confirmed, it was confirmed that the Si concentration of the present invention is 0.23 ~ 0.28% by weight, Al is 23 ~ 41ppm range. Here, it is determined that Al is introduced by reducing (Al ₂ O ₃ ) in the slag.

On the other hand, in the case of Comparative Material 1, the chemical composition is similar to the present invention at the end of the converter refining, but by adding a slag deoxidizer less than 0.6kg / ts in the present invention, [O] concentration is 370ppm decarburization reaction While sufficient for, it can be seen that (T.Fe + MnO) is as high as 11.5 wt%.

In this case, even if the slag deoxidizer is added 1.9 kg per ton of molten steel than the present invention after finishing the decarburization operation in the vacuum degassing apparatus, the (T.Fe + MnO) component reaches 3.6% by weight, thereby providing sufficient upper bubbling (Top Even when bubbling), it can be seen that [S] is 63 ppm and exceeds the target range (50 ppm or less). In this case, it is difficult to obtain the desired iron loss in the non-oriented electrical steel sheet.

In the case of Comparative Material 2, the chemical composition was similar to the present invention at the end of converter refining, and when the slag deoxidizer was added, 0.8 kg / ts similar to the present invention was added, and the [O] concentration was 340 ppm, which was sufficient for the decarburization reaction (( T.Fe + MnO) component also can be seen that the appropriate level at 9.1% by weight. In addition, after the decarburization reaction of the vacuum degassing apparatus 5 was added, 1.1 kg / ts of slag deoxidizer was added, and 1.5 wt% of (T.Fe + MnO) and 1.5 (% CaO) / (% Al ₂ O ₃ ) were added. The ratio was sufficient, and the flow rate of 1.3Nm ³ / min at the top bubbling resulted in a stable [S] concentration (34 ppm), while the [N] concentration was greatly increased from 17 ppm to 34 ppm. It can be seen that it is out of the target range (30 ppm or less). Even in this case, it is difficult to obtain a desired iron loss due to the concentration of [N].

In the case of Comparative Material 3, as in Comparative Material 1, the slag deoxidizer amount was 0.3 kg / ts when the converter was pulled down, so that the (T.Fe + MnO) content was 13.5%, so that the decarburization of vacuum degassing was easy, Even after the decarburization of the vacuum degassing reaction, an excessive amount of slag deoxidizer (2.2 kg / ts) is added, it is difficult to obtain a concentration of (T.Fe + MnO) of less than 1.5%, and then appropriate top bubbling is performed. It was difficult to obtain the desired [S] concentration even if carried out.

In the case of Comparative Material 4, when the converter refining was completed, it was confirmed that [O] was 690 ppm, and 1.7 kg / ts of slag deoxidizer was added, and the (T.Fe + MnO) component was excellent in 5.1 wt%, compared to [O]. It was confirmed that the low as 240ppm. It is thought that the added slag deoxidizer excessively reduced [O]. The molten steel was transferred to the vacuum degassing apparatus 5 for decarburization for 19 minutes, but the concentration of [C] was 33 ppm. (30 ppm or less) exceeded and exceeded. Thereafter, 0.7 kg / ts of slag deoxidizer was added to the molten steel to obtain 1.3 wt% of (T.Fe + MnO) component and (% CaO) / (% Al ₂ O ₃ ) ratio of 0.5 to [S] and within the target range. [N] concentration was obtained, but the desired iron loss is difficult to be obtained due to the [C] concentration above the target range.

According to the present invention as described above, it is easy to control the concentration of [C], [Si], [S], [N] and [Al] contained in molten steel during refining of molten steel for producing non-oriented electrical steel sheet, By using refined molten steel, it is possible to cast non-oriented electrical steel sheet in the range of iron loss of 5.5 ~ 7.0W / kg, and it is possible to produce small motors of excellent quality made of non-oriented electrical steel sheet with reduced iron loss. Lose.

While the invention has been shown and described with respect to specific embodiments thereof, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit or scope of the invention as set forth in the claims below. I would like to clarify that knowledge is easy to know.

Claims (7)

Non-oriented electricity containing 30 ppm or less of carbon (C), 0.3-0.7 wt% of silicon (Si), 30 ppm or less of nitrogen (N), 50 ppm or less of sulfur (S), 50 ppm or less of aluminum (Al), balance Fe and other unavoidable impurities In the method of refining molten steel to cast steel sheet, The slag deoxidizer of 35-50 wt% of metallic aluminum (Al) is added to the slag layer of the ladle 3 immediately after tapping the molten steel after refining in the converter 1 into the ladle 3 ( Lowering T.Fe + MnO) to 5-10 wt%; Transferring the ladle (3) to a vacuum degassing apparatus (5) to perform decarburization to lower carbon (C) to 30 ppm or less; Adjusting the silicon (Si) component to 0.3 to 0.7% by weight by adding silicon (Si) in the vacuum degassing apparatus (5); After the decarburization reaction and the addition of Si, the slag oxidizer is added to the slag layer to lower the slag weight (T.Fe + MnO) to 1.5 wt% or less and at the same time the slag (% CaO) / (% Al ₂ O ₃ ) ratio. Adjusting the range to 1.3 to 1.7; And Transferring the ladle (3) to a facility capable of upper bubbling, and depositing the upper lance (6) from the top to stir the interface layer between slag and molten steel; iron loss reduction type non-directional Molten steel refining method for electrical steel sheet. The method of claim 1, The slag oxidizer added to the ladle 3 when the converter 1 is pulled out is composed of 35 to 50% by weight of Al, 40 to 60% by weight of CaCO ₃ and 5% by weight or less of impurities, and 0.6 to 1 ton of molten steel. Molten steel refining method for iron loss reduction non-oriented electrical steel sheet, characterized in that added 1.5kg. The method of claim 1, The decarburization reaction for lowering the carbon (C) concentration to 30 ppm or less in the vacuum degassing apparatus (5) is performed for 13 to 17 minutes while maintaining the vacuum degree below 1 torr. The method of claim 1, After the decarburization reaction in the vacuum degassing apparatus (5), the step of controlling Si is iron loss reduction type characterized in that to control the [Si] concentration by adding 3.3 ~ 8.0kg of silicon (Si) per ton molten steel Molten steel refining method for non-oriented electrical steel sheet. The method of claim 1, The slag deoxidizer added at the end of the vacuum degassing operation is composed of 35 to 50% by weight of Al, 40 to 60% by weight of CaCO ₃ and 5% by weight or less of impurities, and 0.7 to 1.3 kg per ton of molten steel is added. A method for refining molten steel for reducing iron loss non-oriented electrical steel sheet. The method of claim 1, In the stirring step, the Ar flow rate supplied from the upper lance 6 is controlled in the range of 0.3 to 1.0 Nm 3 / min, and the iron loss reduction type non-directional electricity is characterized in that the stirring of the interface layer of slag and molten steel for 3 to 10 minutes. Method of refining molten steel for steel sheet. The method according to claim 1 or 6, The tip portion of the upper lance (6) is molten steel refining method for iron loss reduction non-oriented electrical steel sheet, characterized in that located between 1/5 ~ 1/2 of the total height of the molten steel in the ladle (3).

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