JPH0671402A - Controller for fluid of molten steel in continuous casting mold - Google Patents

Abstract

PURPOSE:To provide a controller for the fluid of a molten steel in a continuous casting mold, by which a cast slab having excellent surface property is obtd. by controlling flowing speed at the front surface of the solidification in the mold with a shifting magnetic field and a static magnetic field. CONSTITUTION:In the controller for the fluid of the molten steel in the continuous casting mold, two or more sets of the electromagnetic coils 7-1, 7-2 are arranged in the transverse direction of the continuous casting mold so that the center of the electromagnetic coils in the casting direction positions in the vicinity of the meniscus and a control part 10 which can synchronously control the shifting magnetic field in the reverse direction with the faced coils in the thickness direction of the mold and the static magnetic field in the thickness direction are connected with the coils. Thus, the meniscus flowing speed of the molten steel in the mold is controlled and the lowering flow is also controlled at the same time, and the entrapment of the inclusion into the solidified shell is prevented and the cast slab having excellent surface property can be obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow control device for molten steel in a continuous casting mold.

[0002]

2. Description of the Related Art In continuous casting, the flow of molten steel in a continuous casting mold is an important factor that affects the quality of the slab. Therefore, it is generally practiced to electromagnetically stir the unsolidified portion of the slab to reduce segregation inside the slab and obtain a good slab.

For example, in Japanese Examined Patent Publication No. 64-10305, two electromagnetic stirrers are installed facing each other near the meniscus on the long side of at least one of the molds, and the electromagnetic stirrer installed on the long side is used to mold the mold. It is disclosed that a flow toward the center in the width direction is applied to the inner molten steel so that the depth of penetration of the molten steel flow from the immersion nozzle into the molten steel in the mold is made shallow to produce a slab of good quality.

In Japanese Patent Laid-Open No. 64-2771, a moving magnetic field is applied according to the strength of the molten steel discharge flow from the left and right discharge ports of the immersion nozzle to realize an appropriate level fluctuation of the molten metal surface. It is disclosed to prevent surface defects due to mold powder entrainment and surface cracking of a slab due to abnormal fluctuations in the molten metal surface.

[0005]

The present invention further provides a molten steel flow control device in a continuous casting mold for controlling a solidification front flow velocity in the mold to obtain a slab having excellent surface properties.

[0006]

According to the present invention, one or more electromagnetic coils are provided in the width direction of a continuous casting mold so that the center of the electromagnetic coil in the casting direction is located near the meniscus, and both AC current and DC current are applied. The flow of molten steel in a continuous casting mold characterized by connecting to the coil a control unit that can simultaneously control the moving magnetic field in the opposite direction with the coil facing the mold thickness direction, and the static magnetic field in the thickness direction. It is a control device.

[0007]

The operation of the present invention will be described in detail below. FIG. 2 is a perspective view showing a main part of a mold for continuous casting according to the present invention with a part thereof cut away.

The mold is composed of long-side mold copper plates 1-1 and 1-2 and short-side mold copper plates 1-3 and 1-4, and the lower part of the immersion nozzle 2 attached to the tundish provided above is inserted. There is. The discharge holes provided in the lower portion of the immersion nozzle 2 are open one by one on both sides of the immersion nozzle 2 so as to face each other in the direction of the shorter side of the mold, but are not particularly limited.

Molten steel 3 is injected from the tundish into the mold through the immersion nozzle 2. The discharge flow 5 discharged from the immersion nozzle 2 is directed toward the short side mold copper plate 1-3 and hits the short side. , The molten steel flow that splits downward and goes upward becomes a discharge reversal flow 8 and forms a solidification front flow 6. On the other hand, the molten steel flow directed downward becomes the downflow 7.

According to the present invention, as shown in FIG. 1, 2 in the width direction of the mold is provided outside the long side surfaces 1-1 and 1-2 of the mold which face each other.
The electromagnetic coils 7-1 and 7-2 divided into more than the divided parts are provided. Further, the coil has a three-phase structure of U, V and W, and by applying alternating current and direct current simultaneously as a power source, a moving magnetic field can be applied in the mold width direction and a static magnetic field can be applied in the thickness direction at the same time. The controller 10 controls the switching current in the magnetic field direction.

According to the experiments conducted by the present inventors, the immersion nozzle 2
It is extremely effective in improving the surface quality of the slab to secure the collision strength of the molten steel 3 poured from above and control the flow rate of the solidification front surface formed by the discharge flow 5 within a certain range while suppressing the downward flow 7. We have found that it is effective. That is, in the present invention, the centers of the electromagnetic coils 7-1 and 7-2 in the casting direction are provided so as to be located near the meniscus.

In order to wash away the surface layer of the solidified shell 4 and remove inclusions and segregation, a certain molten steel discharge flow rate is necessary. Further, in order to remove inclusions and the like that are discharged together with the discharge flow 5 and flow downward with the downward flow 7, it is also necessary to suppress the downward flow 7. Furthermore, in order to prevent inclusions from being trapped by the meniscus, it is necessary to control the solidification front flow 6.

The inventors of the present invention have set the solidification front flow velocity to 10 cm /
It was found that the surface defects of the slab are reduced by setting the time to sec-60 cm / sec. However, it has been found that even with this, it is not possible to suppress defects caused by inclusions and the like on the downflow 7. Therefore, the inventors of the present invention have made intensive studies, and have simultaneously controlled the downflow velocity such as the downflow 7a together with the solidification front velocity.

The solidification front flow velocity is measured by, for example, inserting a thermorey cylinder into the molten steel flow and measuring the resistance force F due to the flow with a strain gauge. The strain and resistance can be determined by a regression equation by drawing a calibration curve using a weight in advance.

The control unit 10 shown in FIG. 1A can simultaneously control the direction and strength of the moving magnetic field and the static magnetic field for each of the electromagnetic coils 7-1, 7-2. The action of each coil is shown in FIG.

[0016]

[Examples] Under the mold conditions and electromagnetic stirring conditions shown in Table 1, continuous casting was performed using the stirring pattern shown in FIG. 3, and the occurrence rate of surface defects was investigated. Table 2 shows the coil specifications and capabilities in this case.

FIGS. 3 (a) and 3 (b) show a mode of a stirring pattern of molten steel, showing a pattern of stirring a discharge reversal upflow and suppressing a downflow.

[0018]

[Table 1]

[0019]

[Table 2]

FIG. 4A shows the surface defect occurrence rate of the conventional example when only electromagnetic stirring is performed. 10-60 cm / s
Although the maximum ec is about 5%, it is not yet perfect. According to the example of the present invention, as shown in FIG. 4B, the surface defect occurrence rate was 1% or less within the range of the solidification front flow velocity of 10 to 60 cm / sec. Further, the downward flow suppressing effect of the present invention is
This is as shown in 7a of FIG.

[0021]

According to the molten steel flow control device of the present invention, both an alternating current and a direct current are applied to an electromagnetic coil provided in the vicinity of a meniscus, and a moving magnetic field and a static magnetic field are applied simultaneously in the thickness direction of the mold for continuous operation. By controlling the solidification front flow velocity of the molten steel in the casting mold for casting and preventing inclusions from being included in the solidification shell due to the downward flow, it is possible to obtain a slab having excellent surface properties.

[Brief description of drawings]

1A and 1B show a main part of the present invention, FIG. 1A is a perspective view showing the arrangement of electromagnetic coils, and FIG. 1B is a drawing showing the action of each coil.

FIG. 2 is a partially cutaway perspective view of a main part of a mold for continuous casting according to the present invention.

3 (a) and 3 (b) are drawings showing a stirring pattern of molten steel according to an embodiment of the present invention.

4A and 4B show the relationship between the solidification front flow velocity and the surface defect occurrence rate, FIG. 4A is a conventional example, and FIG. 4B is a drawing showing the present invention example.

[Explanation of symbols]

 1-1, 1-2 Long-sided mold copper plate 1-3, 1-4 Short-sided mold copper plate 2 Immersion nozzle 3 Molten metal (molten steel) 4 Solidification shell 5 Molten metal discharge flow 6 Solidification front flow 7 Downflow (conventional example) 7a Descent Flow (Example of the present invention) 8 Upflow 7-1, 7-2 Stirring coil 10 Control unit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jun Fukuda 1 Kimitsu, Kimitsu-shi, Chiba Nippon Steel Corporation Kimitsu Works

Claims (1)

[Claims] 1. A continuous casting mold is provided with one or more electromagnetic coils so that the center of the electromagnetic coil in the casting direction is located near the meniscus, and by applying both an alternating current and a direct current to the casting thickness direction. A flow control device for molten steel in a continuous casting mold, characterized in that a control unit capable of simultaneously controlling a moving magnetic field in the opposite direction and a static magnetic field in the thickness direction is connected to the coils facing each other.