KR101239537B1 - Method for deceasing a depression of strip surface by optimization a deposition depth in submerged entry nozzle - Google Patents

Abstract

The present invention relates to a method for reducing flaw surface defects by optimizing the deposition depth of an immersion nozzle capable of stabilizing a mold level when the strand EMS (Electro Magnetic Stirrer) is operated to improve isotropic crystals during continuous casting of wastelite-based stainless steel. . In the continuous casting of the ferritic stainless steel according to the present invention, the optimum deposition depth of the immersion nozzle according to the casting speed, the slab width and the EMS current value is controlled by the following equation.

d (mm) = a1 + a2 * V (m / min) + a3 * I (A) + a4 * w (mm)

(d = depth of immersion nozzle, V = casting speed, I = EMS current value, w = cast width,

a1, a2, a3 and a4 are parameters that can be changed according to the equipment, respectively)

By such a configuration, by controlling the deposition depth of the immersion nozzle to stabilize the mold level, it is possible to reduce the defective rate of the cast produced by continuous casting to improve productivity.

Immersion nozzle, depth of deposition, mold level, continuous casting, EMS

Description

Method for deceasing a depression of strip surface by optimization a deposition depth in submerged entry nozzle}

1 is a schematic cross-sectional view showing a situation in a mold in which a conventional continuous casting process is in progress.

Figure 2 is a cross-sectional view showing a continuous casting machine according to an embodiment of the present invention.

Figure 3 is a graph showing the mold level variation index during the depth control of the immersion nozzle according to an embodiment of the present invention.

♣ Explanation of symbols for the main parts of the drawing ♣

33: sliding gate nozzle 34: tundish

35: immersion nozzle 36: mold

37: discharge port 38: EMS

The present invention relates to a method for reducing the surface defect of cast steel by optimizing the deposition depth of the immersion nozzle, and more particularly, when the strand EMS (Electro Magnetic Stirrer) is operated to improve the equiaxed axis during continuous casting of wastelite-based stainless steel, The present invention relates to a method for reducing slab surface defects by optimizing the deposition depth of an immersion nozzle capable of controlling the deposition depth of the immersion nozzle to stabilize the mold level.

In general, the steelmaking process for the production of steel products is produced in the blast furnace or electric furnace, and after securing the target composition and temperature of the molten steel in the refining furnace, the molten steel is transferred to the continuous casting process in the ladle. The moved molten steel is supplied to a mold which is cooled by a continuous casting process, that is, a tundish, thereby solidifying and continuously producing cast steel.

Hereinafter, a mold in progress of the conventional continuous casting process will be described in detail with reference to the accompanying drawings.

1 is a schematic cross-sectional view showing a situation in a mold in which a conventional continuous casting process is in progress.

Referring to FIG. 1, molten steel 14 is supplied from a tundish (not shown) to the mold 13 through an immersion nozzle 11. Since the mold 13 is cooled by the cooling water flowing therein, the molten steel 14 solidifies from the wall of the mold 13 to form a solidification cell 16. The molten steel 14 surface of the mold 13 at the time of continuous casting is normally called a mold level. On the other hand, the molten steel 14 exited from the immersion nozzle 11 is controlled in real time by a sliding gate or stopper between the tundish and the immersion nozzle 11, thereby causing a slight variation.

Generally, in the continuous casting process of ferritic stainless steel, EMS (Electro Magnetic Stirrer) 15 is operated to secure equiaxed crystals. The biggest problem that occurs during continuous casting of ferritic stainless steel in the cast steel thus produced is mold level instability that occurs during EMS 15 operation.

In general, the molten steel 14 supplied from the tundish through the immersion nozzle 11 exits the mold through the discharge port and flows strongly to both sides of the mold 13, one to the top of the mold 13 and the other to the mold. It flows to the lower part of (13). Flow chart by the stirring force of the EMS (15) installed directly under the mold 13 is moved to the bottom and the other to the top to cause a change in the mold level.

Therefore, if the agitation force of the EMS is high, the mold level fluctuates severely (when the fluctuation width is larger than the thickness of the mold slag), and the inflow of the mold slag is momentarily interrupted and the heat transfer from the coagulation cell to the mold is severely uneven. Done. When the instability of the mold level is severe, there is a problem that causes a defect in the cap due to the mixing of the mold slag.

Therefore, the present invention is designed to solve the above-mentioned conventional problems, an object of the present invention is to increase the mold level when operating the strand EMS (Electro Magnetic Stirrer) to improve the equiaxed crystal during continuous casting of the waste-light stainless steel The present invention provides a method for reducing the surface defect of cast steel by optimizing the deposition depth of the immersion nozzle which can be stabilized.

In order to achieve the above object, in the continuous casting of ferritic stainless steel according to the present invention, it is characterized by controlling the optimum deposition depth of the immersion nozzle according to the casting speed, slab width and EMS current value by the following equation. .

d (mm) = a1 + a2 * V (m / min) + a3 * I (A) + a4 * w (mm)

Here, d = depth of immersion nozzle, V = casting speed, I = EMS current value, w = slab width, a1, a2, a3 and a4 are parameters that can be changed according to the equipment, respectively.

Hereinafter, with reference to the drawings showing an embodiment of the present invention will be described in detail the slab surface defect reduction method by optimizing the deposition depth of the immersion nozzle according to the present invention.

2 is a cross-sectional view showing a continuous casting machine according to an embodiment of the present invention.

Referring to Figure 2, the continuous casting machine, generally, continuous casting is a method of extracting continuously while solidifying the molten steel 31 in the bottomless mold 36, square, rectangular, circular, such as a simple cross-section It is used for the manufacture of long products and slabs, blooms, billets, etc., which are mainly materials for rolling.

Casting by the continuous casting method is made in a continuous casting machine consisting of a tundish 34, a mold 36, a secondary cooling stand 39, a pinch roll, a cutter.

A shrouding nozzle 32 is installed between the ladle 30 and the tundish 34 containing the molten steel 31 that has been refined in the steelmaking process, and between the tundish 34 and the mold 36. An immersion nozzle 35 is installed, and a hydraulic or electric sliding gate nozzle 33 for adjusting the flow rate of the molten steel 31 is mounted on the nozzles 32 and 33, and the immersion nozzle 35 ) Forms a discharge port 37 in the lower portion, and since the molten steel 31 is introduced into the mold 36 through the discharge hole 37, the shape, material and installation method of the immersion nozzle 35 is cast workability and It will greatly affect the quality of cast steel. In addition, EMS (Electro magnetic stirrer) is operated to ensure equiaxed crystal during continuous casting of ferritic stainless steel.

The tundish 34 is a container for receiving the molten steel 31 from the ladle 30 and supplying the molten steel 31 to the mold 36. The tundish 34 of the molten steel 31 is supplied from the tundish 34 to the mold 36. Speed control, distribution and storage of molten steel 31 supplied to each mold 36, and separation of slag and non-metallic inclusions (impurities contained in molten steel) are made. At this time, the flow of the molten steel 31 in the mold 36 has a great influence on the quality of the cast steel, and in order to prevent the oxidation and nitriding of the molten steel 31, the molten steel 31 should not be exposed to air.

Therefore, an immersion nozzle 35 is installed at the exit of the tundish 34, the end is inserted into the molten steel 31 in the mold 36, and the flow of the molten steel 31 in the mold 36 is controlled, and the molten steel 31 is provided. ) Can be prevented from being exposed to air.

That is, the immersion nozzle 35 used for casting of the molten steel 31 is installed between the tundish 34 and the mold 36 during continuous casting of the steel to prevent oxidation and nitriding of the molten steel 31, and the molten steel 31 By controlling the flow in the mold 36 of the) to serve to improve the quality of the cast cast.

In addition, the flow of molten steel 31 in the mold 36 of the continuous casting machine is affected by the prevention of mixing of the mold due to the stability of the water surface behavior, ensuring the uniform cooling capacity of the cast quality, and the prevention of breakout due to the inflow of the mold. . Therefore, in order to ensure stable operation during continuous casting, it is essential to strictly secure the flow form of the mold level. For this purpose, the depth of the immersion nozzle 35 is controlled through the following Equation 1 in the present invention.

According to the present invention, EMS (38) is a technology that can improve the integrity of the casting structure, such as crystal grain refinement, segregation reduction, improved equiaxed crystallization by applying a strong electric field stirring during continuous casting, imparting flow without contacting the molten steel 31 can do. There are two types of continuous stirring methods, vertical and horizontal, which are widely used for melting or casting metals.

Flow by EMS 38 results in a uniform chemical composition or temperature of molten steel 31. As a result, the time required for alloying is shortened in the melting process, and in the case of the upper and lower stirring devices, the temperature variation is reduced, and ultimately, the energy required for melting is reduced.

In the present invention, in the continuous casting of ferritic stainless steel, the casting speed is changed to 0.8 and 1.2, and the EMS current is changed to 700A and 900A for each casting speed, and the test is performed under the following equation (1). The critical deposition depth of is obtained.

d (mm) = 10 + 62.1 * V (m / min) + 0.043I (A) + 0.032w (mm)

Here, d, V, I, w represent the depth of deposition of the immersion nozzle 35, casting speed, EMS current value, slab width, respectively.

According to Equation 1, the deposition depth of the optimal immersion nozzle 35 to stabilize the mold level should be increased according to the casting speed, EMS current value, and slab width, where the number and location of the EMS 38 equipment The stirring force generated by the method is not used for generalization because the stirring force is different, but the optimum deposition depth relationship can be obtained by the relationship of Equation (1).

Hereinafter, specific effects will be described through examples of the present invention.

≪ Example 1 >

3 is a graph showing a mold level variation index when controlling the depth of immersion nozzle according to an embodiment of the present invention.

Referring to Figure 3, it can be seen the variation in the mold level applied to the above-described casting speed and EMS current value during continuous casting of 430 stainless steel. As a result of comparing the deposition depth derived from the conventional method and the present invention, the mold level variation index of the conventional material was about 0.75, while the mold level variation index of the invention material was about 0.37. That is, it can be seen that the mold level variation index is reduced by about 51% compared to the conventional art.

By controlling the depth of deposition, the mold level is stabilized, thereby making the width direction heat transfer inside the mold uniform, and forming a constant solidification cell.

Although the technical spirit of the present invention has been described in detail according to the above-described preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of 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.

As described above, according to the present invention, when the strand EMS (Electro Magnetic Stirrer) is operated to improve the equiaxed crystal during continuous casting of waste light-based stainless steel, by controlling the deposition depth of the immersion nozzle to stabilize the mold level, Productivity can be improved by reducing the defective rate of cast steel produced by continuous casting.

Claims (1)

In continuous casting of ferritic stainless steel, A method for reducing the surface defect of cast iron by optimizing the deposition depth of the immersion nozzle, characterized in that the optimum deposition depth of the immersion nozzle according to the casting speed, cast width and the current value of the EMS installed directly below the mold outlet. d (mm) = 10 + 62.1 * V (m / min) + 0.043I (A) + 0.032w (mm) (d = depth of immersion nozzle, V = casting speed, I = EMS current value, w = cast width)

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