KR100554735B1 - Method for strip casting with superior productivity by controlling surface tension of slag - Google Patents

Abstract

The present invention relates to a sheet casting method for directly casting a final product from molten metal, the purpose of which is to lower the surface tension of the slag of the molten steel surface to improve the contact between the molten steel and the roll in the initial stage between the solidification angle and the roll By minimizing the gas gap of the heat extraction amount is increased to provide a sheet casting method that can improve the productivity.

In order to achieve the above object, the present invention provides a method of casting a thin plate by supplying molten steel between a pair of casting rolls by an immersion nozzle, wherein the sheet tension is maintained while maintaining the surface tension of the molten steel upper slag at 450 dyne / cm or less. The technical gist of the sheet casting method having excellent productivity by slag surface tension control, including

Sheet Metal Casting, Surface Tension, NaO, Slag

Description

Method for strip casting with superior productivity by controlling surface tension of slag}             

1 is a schematic diagram of a thin plate casting process.

2 shows the degree of contact between the roll and the molten steel in the sheet casting process,

Figure 2 (a) is the case where the contact between the roll and the slag is poor

2 (b) is a case where the contact between the roll and the slag is good

3 is a graph showing the change of the surface tension of slag with the addition of oxide.

4 is a schematic view showing a method of adding an oxide.

* Explanation of symbols for main parts of the drawings

1 ..... Casting Roll 2 ..... Molten Steel

3 ..... Immersion nozzle 4 ..... Cast

5 ..... molten steel surface slag 6, 6 '..... gas gap

7 ..... Added Oxide 8 ..... Added Oxide Feeding Nozzle

9 ..... Addition oxide coated on immersion nozzle

The present invention relates to a thin plate casting method for directly casting a final product from molten metal, and more particularly, to improve productivity by lowering the surface tension of the upper slag of molten steel to increase the degree of contact between the casting roll and the solidified shell to increase the amount of heat extraction. The present invention relates to a thin sheet casting method.

In general, the thin plate casting process is a process that directly casts the final product from molten metal to omit the intermediate process (hot rolling process), and it is a lightweight facility that can significantly reduce the production cost as compared with the conventional steel process. It also enables the production of difficult processable products that are difficult to manufacture.

In the thin sheet casting process, as shown in FIG. 1, molten steel is supplied between casting rolls 1 by an immersion nozzle 3 while rotating a pair of casting rolls 1 to be cooled in water to form a molten steel pool 2. While casting the sheet. The molten steel is solidified on the surface of the casting roll 1 so that the two solidification shells are combined to form a thin plate. Therefore, as shown in FIG. 2, the amount of heat extraction varies depending on the degree of contact between the casting roll 1 and the solidification shell 5, that is, the degree of gas gap. Since the contact between the casting roll and the solidification shell is very good and there is almost no gas gap, the heat extraction becomes large, so that the solidification rate is increased and the peripheral speed is increased, thereby improving productivity.

As a method for increasing the contact degree between the casting roll and the solidification shell, a technique of increasing productivity by reducing the gas gap between the molten stainless steel and the roll by using the atmospheric gas as nitrogen during the stainless steel sheet casting is known. However, this technique can be used in steel grades with high nitrogen solubility because Cr is present in molten steel such as stainless steel, and it is difficult to use in steel grades without Cr in molten steel. In addition, it is difficult to use for steel grades that need to suppress nitride in the produced thin plate.

As another method, a method of increasing the amount of heat extraction by adding Bi, Te, Sn, etc., which decreases the surface tension of molten steel to a molten steel of 0.01% or less (iron and steel 1989, pp 1308-1315) is known. However, since a thin oxide slag film such as MnO and SiO ₂ exists on the surface of the molten steel surface, addition of a substance that reduces the surface tension of molten steel such as Bi, Te, Sn, and the like does not produce a great effect.

In the present invention, by lowering the surface tension of the slag of the molten steel surface to improve the contact when the molten steel initially contacts the roll, by minimizing the gas gap between the solidification angle and the roll, the amount of heat extraction is increased to improve productivity To provide a casting method, the purpose is.

In the thin plate casting method of the present invention for achieving the above object, in the method for producing a thin plate by supplying molten steel between a pair of casting rolls by a needle nozzle, the surface tension of the upper slag of the molten steel to 450 dyne / cm or less It is configured to include sheet casting while maintaining.

Hereinafter, the present invention will be described in detail.

The present inventors paid attention to the surface tension of the slag by focusing on the fact that slag exists on the molten steel surface, thereby lowering the surface tension of the molten steel can increase the contact between the solidified shell and the casting roll rather than lowering the surface tension of the molten steel.

2 is a schematic view showing a shape at the time of contact between a roll and molten steel. When the roll 1 and the molten steel 2 are in contact, the actual contact does not occur in the roll and the molten steel, but the thin oxide film formed on the molten steel surface, that is, the slag is in contact with the roll. When the surface tension of the slag film is high, as shown in FIG. 2 (a), the contact between the roll and the slag film is worse, the gas gap is increased, the heat transfer resistance is increased, the amount of heat extraction is reduced, the solidification rate is decreased, and the productivity is lowered. On the other hand, when the surface tension of the slag film is low, as shown in FIG. 2 (b), the contact between the roll and the slag film is good, so that the gas gap is small and the heat transfer resistance is low, so that the amount of heat extraction is increased and the solidification rate is increased, thereby increasing productivity.

Therefore, the present inventors have studied the surface tension of slag to secure the contact between the cast roll and molten steel in the sheet casting process, when the surface tension of the slag is maintained below 450 dyne / cm gas between the solidification angle and the roll By minimizing the gap, the heat extraction amount was increased to confirm that the productivity was improved.

In the case of stainless steel, the surface tension of MnO generated on the surface of the steel is high at 635 dyne / cm. Therefore, it is necessary to change the composition of slag to lower the surface tension. The inventors have found that the surface tension of the slag is lowered as a result of injecting an oxide to lower the surface tension of the slag. As a result of adding various oxides to the FeO oxide as shown in Figure 3, when a small amount of Na ₂ O, P ₂ O _{5 It} can be seen that the surface tension is sharply reduced. In the case of FeO alone oxide, 580 dyne / cm, but when 8 mol% Na ₂ O is added, 410 dyne / cm or P ₂ O ₅ is reduced to 420 dyne / cm. Therefore, it can be seen that when Na ₂ O or P ₂ O ₅ is added to the surface slag (oxide), the surface tension of the slag decreases and the contact between the roll and the slag becomes very good.

In the case of P ₂ O ₅ , it is an acidic oxide, and when a large amount is added, the viscosity of the slag increases, the thickness of the slag increases, and a tendency to agglomeration occurs, so it is necessary to add a small amount. On the other hand, Na ₂ O is a basic oxide, and as the addition amount is increased, the viscosity of the slag decreases, so that the increase in the slag thickness is small even if a large amount is added compared to P ₂ O ₅ . Since the heat resistance increases as the thickness of the slag increases, the heat resistance may increase if the amount of the added slag increases, so it should not be added much. Therefore, 10 mol% or less for Na ₂ O and 5 mol% or less for P ₂ O ₅ are appropriate. This amount is up to 8.5 wt% for Na ₂ O and up to 9.5 wt% for P ₂ O ₅ .

According to the present invention, the composition of the slag is changed by the oxide to lower the surface tension, and there are two methods of adding the oxide.

First, as shown in (a) of FIG. 4, the oxide is directly sprayed on the tap surface through a feeding nozzle or fed into the tap surface. This method melts when the additive oxide comes in contact with molten steel and reacts with the existing hot water surface slag to produce a low surface tension oxide containing Na ₂ O, P ₂ O ₅ .

The second method is to coat the oxide on the surface of the immersion nozzle as shown in Figure 4 (b), to immerse in the hot water surface. Alternatively, an oxide may be coated on another ceramic block to be immersed.

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

EXAMPLE

In the sheet casting process of FIG. At this time, when slag (oxide) was added to the molten surface of Na ₂ O to 7 mol% (that is, 6wt%) to produce a slab of 3.56mm thickness, the circumferential speed was lowered to 45mpm.

According to the present invention, when Na ₂ O was added to the molten surface to 7 mol% (ie, 6 wt%), it was confirmed that the surface tension of the molten rice slag was reduced to increase the amount of heat extraction, resulting in a productivity increase of about 10%. . As the surface tension of the slag was lowered, an increase in productivity occurred. However, in order to lower the surface tension of the slag, it is necessary to increase the amount of Na ₂ O or P ₂ O _5, etc. In this case, disadvantages such as increasing the slag thickness appeared. Therefore, it is preferable to limit the amount of Na ₂ O or P ₂ O ₅ , and the like, and according to the present invention, when the surface tension of the surface of the slag is 450 dyne / cm or less, a significant increase in productivity occurs.

As described above, according to the present invention, the heat extraction amount is increased by lowering the surface tension of the molten steel surface slag, thereby increasing the solidification rate and increasing the peripheral speed, thereby improving productivity.

Claims (3)

A method of casting a thin plate by supplying molten steel between a pair of casting rolls by an immersion nozzle, wherein the slag is cast while maintaining the surface tension of the upper slag of the molten steel at 450 dyne / cm or less. Thin plate casting method with high productivity by surface tension control. The method of claim 1, wherein the surface tension of the slag is adjusted by adding an oxide of Na ₂ O: 8.5wt% or P ₂ O ₅ : 9.5wt% to the slag excellent productivity by the slag surface tension control Sheet metal casting method. The method of claim 1 or 2, wherein the addition of the oxide is a nozzle Furnace oxide powder is injected into the molten steel or coating the oxide to the immersion nozzle, the coating oxide is characterized in that the coated oxide is dissolved and added in the molten steel.

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