JPH0199763A - Method for controlling molten steel discharging flow in mold for continuous casting - Google Patents

Abstract

PURPOSE:To reduce enclosing quantity of non-metallic inclusion and bubbling and to improve the product quality by giving forcedly current from outside toward crossing to static magnetic field direction to form the magnetic field and adjusting flow speed of molten steel discharging flow. CONSTITUTION:Magnetic pole 4 forms the static magnetic field and the forcedly current is given at interval between the electrode 5 submerged in meniscus and foot rolls 6a just below a mold. By dependently adjusting intensity and direction for this current and the magnetic field, respectively, speed of the molten steel discharging flow 3 is accelerated and reduced to be possible to freely control the flowing pattern. Magnetic flux density in the static magnetic field is made to the range of about 2500-3500G near the center of the magnetic field 4 so as to obtain molten steel braking effect, even in case the magnetic flux density is zero of the electric conductive current. Further, the forcedly current is made to about DC 1000-2000A at one side, so that the molten steel accelerated flow speed under the above magnetic flux density becomes equal to it in the case of being no static magnetic field.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention controls the discharge flow rate of F4 steel injected into a continuous casting mold, and particularly prevents the entrainment of oxide-based nonmetallic inclusions contained in molten steel. The present invention relates to a method for controlling the discharge flow of molten steel in a continuous casting mold, which is advantageous in preventing the above problems and thereby improving the product quality of steel materials.

(Prior Art) In continuous casting of steel, it is important to prevent oxide-based nonmetallic inclusions present in molten steel from being deeply entangled within the mold. In particular, in a curved continuous casting machine, even if non-metallic inclusions that are deeply rolled up and float up, they do not come out of the meniscus and are caught on the lower surface of the solidified shell, resulting in serious defects.

As an attempt to solve such problems, for example,
Japanese Patent No. 7-17356 proposes a technique for slowing down and dispersing the flow of molten steel in a continuous casting mold using a static magnetic field.

(Problems to be Solved by the Invention) However, the above technique still has the following problems. In other words, extremely sophisticated control is required to effectively slow down the discharge flow from the immersed nozzle, but (1) the induced current that determines the magnitude of the electromagnetic force depends on the discharge flow velocity of the molten steel; cannot be controlled.

In addition, (2) a closed current circuit is created in the continuous casting mold, which accelerates the flow of molten steel locally, resulting in a uniform flow throughout (Hartmann flow), which can actually have negative effects such as inhibiting the floating of air bubbles. .

In other words, the electromotive force distribution generated in the molten steel is not uniform due to the molten steel flow distribution and magnetic flux density distribution, and the electromotive force distribution in a part of the mold cross section is large at the center of the thickness, and the electromotive force at the long side interface is Since the flow velocity is small, it becomes almost zero (see Figure 4). Therefore, considering the electric circuit made up of these electromotive forces and molten steel, the current flows in the braking direction at the center of the thickness, and vice versa near the interface.

The main feature of this invention is to propose a method of controlling a molten steel discharge flow that is advantageous in solving the above problems.

(Means for solving problems) First, the background to the elucidation of this invention will be explained.

The inventors conducted various experiments and studies regarding the control of the discharge flow of molten steel using a static magnetic field, and found that in order to freely control the flow velocity of the discharge flow of molten steel, it is necessary to We found that it is very effective to apply a forced current from the outside, as in the equation: electromagnetic force (r') oC magnetic flux density (B) x current (I).

This invention is based on the above knowledge.

That is, the present invention provides a continuous casting method in which a static magnetic field is formed within the opposing side walls of a continuous casting mold, and the flow of molten steel is controlled by electromagnetic force generated by the induced current generated by the interaction between this magnetic field and the molten steel discharge flow. , in a continuous casting mold characterized in that the flow velocity of the molten steel discharge flow is adjusted by applying a forced current from the outside in a direction crossing the direction of the static magnetic field and forming a magnetic field derived from this. This is a method of controlling molten steel discharge flow.

Hereinafter, this invention will be explained based on the drawings.

FIG. 1 shows the right half of a cross section of a continuous casting mold suitable for use in carrying out the present invention. Number 1 in the same figure
is an immersed nozzle, 2 is the short side of the mold, 3 is a flow of molten steel discharged from the immersed nozzle 1, 4 is a magnetic pole that forms a static magnetic field, and 5 is a forced current that is applied in a direction crossing the direction of the static magnetic field. 6 is a current collecting brush attached to the foot roll 6a, and 7 is a DC power source.

(Function) Now, when the molten steel discharge stream 3 discharged from the immersion nozzle 1 crosses the magnetic pole 4, an induced current is generated, and the braking force of the discharge stream 3 is normally determined by this induced current and the magnitude of the static magnetic field. However, in the conventional technology, as shown in Fig. 1 above, a closed circuit of induced current is formed in the mold, so the distribution and magnitude of the current are complicated and it is difficult to control the molten steel discharge flow 3. It was extremely difficult.

In this invention, a forced current is applied in a direction intersecting the direction of the static magnetic field, in this example, between the electrode 5 immersed in the meniscus and the foot roll 6a directly below the mold, and this current and the magnetic field By individually adjusting the magnitude and direction of each, the flow pattern can be freely controlled by accelerating or decelerating the molten steel discharge flow.

If only a static magnetic field is used as in the past, braking can only be achieved by the molten steel discharge flow velocity distribution and magnetic flux density distribution, so if the braking force is too large, the molten steel flowing around outside the range of the static magnetic field will cause inclusions and bubbles to form. Although the entrainment phenomenon may occur, in the present invention, the flow of molten steel is controlled by applying not only a braking force but also an accelerating force, so that the above-mentioned problem can be advantageously solved. In other words, it can be used as a braking device and an electromagnetic stirring device that can generate a braking effect and an accelerating effect inside the mold.

Here, the magnetic flux density in the static magnetic field is set to be in the range of about 2500 to 3500 G near the center of the magnetic pole 4, in order to obtain the molten steel braking effect even when the current is zero, and the forced current is set to the above magnetic flux density. D C10 on one side to make the accelerated flow velocity of molten steel at the bottom equal to that without a static magnetic field.
It is preferable to set it to about 00 to 200OA.

As an electrode when applying a forced current, a refractory material that has good conductivity and does not contaminate molten steel, such as molybdenum thermite, is suitable.As a current collector brush, a metallic brush that has been air purged via a foot roll is suitable. etc. are suitable. In addition, in order to prevent leakage current when using such a continuous casting mold, it is recommended to insulate the bearing part of the roll 6a with an insulating material such as drill resin to increase the insulation resistance between it and the ground. It is essential.

Next, simulation results using a small experimental facility using the continuous casting mold shown in FIG. 1 are shown in FIGS. 2(a) and 2(b) together with results using a conventional mold.

The size of the magnetic pole was set to be equivalent to 3000 G in both (a) and (b), and the forced current from the outside in (b) was set to be equivalent to 1500 A. The magnitude of the flow velocity at each part of the molten steel supplied into the mold is expressed as a vector, and if we focus on parts A and B, which correspond to the downward flow on the short side, we can see that if this invention is applied, the discharge flow of molten steel will be decelerated. In this case, the flow velocity can be reduced from the equivalent of 20 cm/s to the equivalent of 5 cm/s or less.

This fact has extremely important meaning. That is,
In conventional continuous casting, bubbles of about 0.5φllIn1 tend to accumulate near the downward flow on the short sides such as parts A and B, causing quality defects such as blisters, but in this invention, Since the downward flow on the short side can be made extremely small, it is possible for bubbles to float. In addition, in the past, in order to increase the braking force, it was necessary to make the static magnetic pole thicker, but it is now possible to obtain a large braking force with a small magnetic field by adding a forced current from the outside. Wow
It was.

In addition, in this invention, the case where a forced current is applied in the vertical direction of the continuous casting mold is shown in particular, but from the viewpoint of braking the downward flow on the short side, a case where the upward force is mainly applied to the short side part is shown. Between the two layers at the bottom of the continuous casting mold,
In other words, a forced current may be applied in the width direction of the continuously cast slab (see Fig. 3).

(Example) Operation in which the magnetic flux density of the magnetic pole (size 300 x 300 m+++) provided in the continuous casting mold of equipment capable of manufacturing continuously cast slabs with a thickness of 200 n+m and a width of 1350 to 1650 mm and external forced current were variously changed. The obtained continuously cast slabs were then finished into cold-rolled steel sheets and their surface quality was investigated.

The results are shown in Table 1 along with the magnetic flux density and forced current value during casting.

(Effects of the Invention) According to the present invention, since the molten steel discharge flow can be freely controlled, it is possible to significantly reduce the entrainment of non-metallic inclusions and air bubbles inside the continuously cast slab obtained by continuous casting, and further improve the cleanliness. Steel is obtained and helps improve product quality. Further, since the flow velocity of the discharge flow of molten steel can be accelerated, controllability of the molten steel movement in the toner field can be improved, and it is also possible to use it as an electromagnetic stirring device.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a continuous casting mold suitable for carrying out the present invention, FIGS. 2(a) and (b) are explanatory diagrams of simulation results of the present invention, and FIG. 3 is a cross-sectional view of a continuous casting mold suitable for carrying out the present invention. FIG. 4 is a schematic plan view of another continuous casting mold suitable for use in practice, and is a diagram showing the relationship among the molten steel flow distribution, magnetic flux density distribution, and electromotive force distribution. Figure 1 J

Claims (1)

[Claims] 1. A static magnetic field is formed between opposing side walls of a continuous casting mold,
In a continuous casting method in which the flow of molten steel is controlled by electromagnetic force based on the induced current generated by the interaction between this magnetic field and the molten steel discharge flow, a forced current is applied from the outside in a direction that intersects with the direction of the static magnetic field. 1. A method for controlling a molten steel discharge flow in a continuous casting mold, the method comprising: adjusting the flow velocity of the molten steel discharge flow by forming a magnetic field derived from the molten steel discharge flow. 2. The method according to claim 1, wherein the magnetic flux density of the static magnetic field is in the range of 2,500 to 3,500 Gauss, and the forced current is in the range of 1,000 to 2,000 A.