JPS59101263A - Electromagnetically stirring method of molten steel in continuous casting - Google Patents

Abstract

PURPOSE:To cast economically and stably a slab having good quality by providing an electromagnetic coil only on the one broad side of a casting slab and acting the moving magnetic field by the coil upward in parallel with the drawing direction of the slab. CONSTITUTION:An electromagnetic coil 3 is provided only on the one broad side of a slab 4 in a casting mold 1, and the moving magnetic field by the coil 3 is acted upward in parallel with the drawing direction of the slab. The stirring flow of the molten steel is thus made into single circulating flow, and the necessary stirring flow rate is assured near the surface of the mold 1 by relatively small stirring force.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for stirring I-shaped steel that can obtain high-quality scraps during continuous stirrup of slabs.

With the remarkable development of continuous casting technology, applications from plume continuous casting and billet continuous casting to slab continuous casting are being considered, and the spread is not limited to continuous casting of high-grade steels such as stainless steel and spring steel, but also to continuous casting of ordinary steel. As these issues have been studied, countermeasures against quality defects have been given up on as a serious issue.

For example, in continuous slab casting of rimmed steel and guild steel,
In order to remove the bubbles generated in rimmed steel and increase the equiaxed crystals in killed steel, electromagnetic force is applied to remove unsolidified foam during the solidification process of slab slabs (hereinafter simply referred to as "flange pieces"). Stirring the parts (hereinafter referred to as "electronic stirring") has recently become popular. There are Kusunoki's electromagnetic stirring methods that have been implemented and proposed up to now.
Due to the difference in the stirring direction, ■ The speed pect of the stirring main stream in the unsolidified part of the solidified slab shell is perpendicular to the slab drawing direction (hereinafter referred to as "lateral stirring") ■ The above speed pect is perpendicular to the slab drawing direction. It is roughly divided into those parallel to the direction (hereinafter referred to as ``vertical stirring'').

However, in the case of lateral stirring, Figures 1 (a) and (b)
) (However, as shown in (IIL) is a plan view and (b) is a front view), the molten steel level rises significantly at the corner 2.2 in the mold 1 during stirring (M in the figure). ), the molten steel surface moves significantly.As a result, the powder spread on the molten steel surface tends to get caught up, and the flow of molten steel discharged from the immersion nozzle also tends to become unstable (and also due to mold vibrations). The oscilloscope VH mark on the surface layer of the stirrup piece that occurs also tends to be disordered and tends to peel off.

On the other hand, in the case of vertical stirring, it is known that the amount of fluctuation in the molten steel level is relatively small. For example, when the dimensions of the mold are the same as that of mold 1 shown in Fig. 1, and the stirring flow velocity near the wide mold surface is constant, the fluctuation of the melt level during vertical stirring is
As shown in the figure, it is in a much smaller state than in the case of lateral stirring (see Figure 2 M'). Therefore, from the viewpoint of minimizing fluctuations in the melt level, vertical stirring is more advantageous than the above-mentioned horizontal stirring, and it is thought that vertical stirring will become the mainstream. However, the currently available vertical stirring is based on the 8th method, with the aim of actively creating a rimming action, such as that seen in the ingot making method of rimmed steel.
As shown in the figure, electromagnetic coils 8.8 are provided on both wide sides of the slab 4 that is being cast by continuous slab casting, and the moving magnetic field of the coil 8.8 is applied upward parallel to the slab drawing direction. This causes a stirring flow to form as shown by the arrow.

However, in both 1411+upward vertical stirring, the upward flow near the center of the lv steel resists the downward flow (hereinafter referred to as "
On the other hand, since the viscous resistance between the upward flow and the downward flow is relatively large, it is necessary to obtain sufficient stirring by forming a sufficient downward flow near the center of the molten steel. In this case, it is necessary to increase the stirring power just before the mold. However, this requires increasing the current, which poses a cost problem. Furthermore, even if sufficient stirring can be obtained by increasing the upward stirring force as described above, when the stirring force near the mold surface is increased too much, the passive motion of the molten metal surface will increase, causing lateral A new problem arises in that the above-mentioned interstitial point is more likely to occur during stirring, and an improvement in the vertical stirring method has been desired.

The present invention has been developed in view of these circumstances, and its purpose is to minimize the flow velocity reduction effect caused by the braking effect and viscous resistance as described above, and to make large fluctuations in the melt level even with a relatively small stirring force. The object of the present invention is to provide an electromagnetic stirring method that can form a suitable stirring flow without causing any problems.

However, the electromagnetic stirring method of this research that was able to achieve such a purpose is to install an electromagnetic coil only on one wide side of the slab that is being cast by continuous casting, and to apply the moving magnetic field of the coil to the slab. The gist of this is that the action is applied upward parallel to the drawing direction.

The configuration and effects of the present invention will be explained below based on the drawings of the embodiments. However, the following embodiments are merely representative examples and are not intended to limit the present invention. For example, design changes such as changing the size or shape of the electromagnetic coil, dividing the electromagnetic coil into a plurality of parts, etc. all belong to the technical scope of the present invention.

First, in the present invention, in order to obtain a high-quality slab, for example, a high-quality rimmed steel, it is sufficient to ensure a sound five-layer thickness of approximately 5 mm, even considering the scale loss after continuous casting. Obtained. So 80-120 ppln freedom [
When casting rimmed steel with 0], we investigated the stirring flow velocity near the mold surface that is necessary and sufficient to suppress bubble nucleation and obtain a sound rim layer on the slab surface.
If the stirring flow rate is about 0.5 m/sec or more, the suppression effect can be sufficiently obtained, and even if the stirring flow is downward at the front of the mold, the flow rate should be kept at about 0.5 mlB6.
It was found that the same effect can be obtained as long as the temperature is maintained at c3 or above. In this way, by forming a single-circulation agitation flow in which the two agitation flows on the opposing mold front surfaces are in opposite directions and each flow velocity is 6.5 m78 e c or more, freedom can be achieved.
0] was found to be able to sufficiently suppress the generation of bubble nuclei;
As shown in the figure, electromagnetic coil/L/
A unique III BM was achieved in which the moving magnetic field by the coil/I/8 acts upward.

Hereinafter, the stirring flow rate near the mold surface will be explained for each case of the present invention's upward one-sided vertical stirring (hereinafter simply referred to as "one-sided stirring") and the conventional upward double-sided vertical stirring C (hereinafter simply referred to as "both-side stirring"). Q, 5TV's e.

The stirring force and the amount of molten steel level fluctuation when the temperature is constant (constant) were calculated using the same mold size. As the stirring force, x and f obtained from the electromagnetic coil flowing in the electromagnetic coil and the frequency f (opm) are used as an index, and the stirring force in the mold is 200 to 8.
It was varied between 00 (+wa+).

The results of a comparative experiment regarding the stirring force are shown in FIG. 6, and it is clear from this figure that the stirring force in the case of one-sided stirring is less than that in the case of both-side stirring.

In addition, the results of a comparative experiment regarding molten steel level fluctuations are shown in Figure 6. This figure also shows that the amount of molten steel level fluctuations is reduced by about half in the case of one-sided stirring compared to the case of double-sided stirring. This was confirmed.

In the examples of improvement, we will mainly explain the removal of bubbles generated in rimmed steel, and it goes without saying that the structure of the present invention is also effective in increasing equiaxed crystals in killed steel. In the experiments conducted by the inventors, the stirring flow rate was 0.1.
~Q, It has been confirmed that the generation rate of hot glaze crystals reaches almost the maximum trap when 5 nl/8 e O.

The present invention is roughly constructed as described above, but the point is that the stirring flow can be made into a single circulation flow by installing a moving magnetic field on one side, so even with a relatively small stirring force, the necessary stirring flow velocity can be secured near the mold surface. As a result, it was possible to efficiently remove bubbles generated in rimmed steel or increase equiaxed crystals in killed steel. In addition, the variation in RvI4 and h-plane due to one-sided stirring is reduced to less than half compared to conventional methods, making casting operations much safer and more stable, and resulting in better performance in two-lab continuous casting.
It became possible to obtain slabs economically and stably.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the melt surface in the case of horizontal stirring, Figure (a) is its top view, Figure (b) is its front view, and Figure 2 is in the case of vertical stirring. Fig. 8 is a schematic illustration of the upward vertical stirring method on both sides, Fig. 4 is a schematic illustration of the upward vertical stirring method on one side of the present invention, and Fig. 5 is a schematic illustration of the method of the present invention and the conventional method. FIG. 6 is a graph showing the results of a comparative experiment on the amount of fluctuation in the molten metal level. l... Mold 8... Electromagnetic coil applicant Kobe Steel, Ltd.

Claims (1)

[Claims] +1+ In a method of electromagnetic stirring of molten steel in a slab slab that is being cast in a continuous casting process, an electromagnetic coil is provided only on one wide side of the slab slab, and the moving magnetic field of the coil is directed upward parallel to the direction in which the slab is pulled out. 1. A method for electromagnetic stirring of molten steel in continuous casting, characterized by causing the molten steel to act on the molten steel.