JPH0871717A - Continuous casting equipment and continuous casting method - Google Patents

Abstract

PURPOSE: To produce a cast slab excellent in quality by positioning the setting position of an iron core between a molten steel surface corresponding level in a mold and an immersion nozzle dipping corresponding level of the molten steel in the mold to disperse the molten steel flow onto the whole moltin steel surface in the mold. CONSTITUTION: At the time of pouring the molten steel 3 into the mold 1 from the immersion nozzle 2, the molten steel is diverted to ascending flows in the molten steel surface direction and desceding flows to the lower part of the mold by impinging against the mold short side walls 1a side. The ascending flows are dispersed in the molten steel surface direction by receiving the braking force with static magnetic field generated with the iron core 5 of an electromagnet. That is, the static magnetic field is impressed near the molten metal surface, and in the case of fixing the deliverly rate of the molten steel from the immersion nozzle, the ascending flow is dispersed on the whole molten steel surface by impinging against the mold short side wall sides by the braking force. The flowing speed of the ascending flow is decreased and the rising up of the molten steel surface is decreased to suppress the variation of the molten steel surface. Further, the stagnant area of molten steel flow is cancelled to eliminate the low temp. area of the molten steel surface, and the lowering of the molten steel surface temp. is prevented and the temp. and viscosity are uniformized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous casting apparatus and a casting method capable of homogenizing the flow of molten steel in the continuous casting mold in the vicinity of the surface of the molten steel and improving the quality of the slab.

[0002]

2. Description of the Related Art In order to improve the quality of a slab in continuous casting of steel, the flow of molten steel in a mold is appropriately suppressed, the occurrence of entrainment of powder for continuous casting in molten steel, and the formation of an initial solidified shell. It is necessary to prevent the trapping of inclusions and to make the thickness of the solidified shell uniform.

The powder for continuous casting is used as a lubricant between the mold and the slab, but when the powder is caught in the molten steel due to excessive molten steel flow, slag chewing flaws and the like occur, and the slab Deteriorate the quality of. Further, the fluctuation of the molten metal level locally changes the amount of powder flowing between the mold and the slab as a lubricant, which causes nonuniformity of the solidified shell thickness.

On the other hand, when stagnation occurs in the molten steel flow in the mold, the molten steel temperature at that portion lowers, the solidified shell grows locally rapidly, and the shell thickness becomes uneven. As a result, the stress acting on the slab becomes different, causing vertical cracks and the like.

It will be explained in more detail that such a defect of the cast piece is closely related to the flow phenomenon of the molten steel in the mold.
That is, a refractory nozzle immersed in the molten steel is used to inject the molten steel into the mold, but due to the discharge flow from the immersion nozzle, the molten steel flow in the mold becomes irregular and the flow velocity is not constant. For this reason, the molten steel surface (hereinafter referred to as the molten metal surface) fluctuates and fluctuates up and down, so that the molten metal surface temperature becomes uneven in the mold, and the thickness of part of the molten powder layer present on the molten metal surface Becomes smaller, or there is a portion where the molten powder layer itself disappears.

As a result, the unmelted powder existing on the molten powder layer comes into contact with the molten steel, is caught in the molten steel, and is more often caught, resulting in slag bite flaws. In addition, when the molten metal level changes, the amount of molten powder that flows between the slab and the mold locally changes, and the amount of heat transferred from the molten steel to the mold is not uniform. It causes cracks and flaws.

The situation in the case of the conventional continuous casting as described above will be described with reference to FIG.

FIG. 3 is a longitudinal sectional view schematically showing the flow of molten steel in a mold in conventional continuous casting. When the molten steel 3 is injected into the mold 1 from the dipping nozzle 2, the molten steel flow colliding with the mold short side wall 1a side of the mold 1 becomes an upward flow toward the molten metal surface and a downward flow toward the lower side of the mold 1. Divide. The ascending flow raises the level of the molten metal near the short side wall 1a of the mold as shown in the figure, and causes fluctuations in the molten metal surface. Therefore, the thickness of the molten powder layer 9 becomes smaller at the rising position of the molten metal surface and becomes larger at the lowered position of the molten metal surface as shown in the figure. When the casting speed is increased to improve the productivity, the discharge flow rate from the immersion nozzle 2 is increased and the upflow rate of the molten steel 3 is also increased. For this reason, the amount of swelling on the surface of the molten metal increases, and the ripples on the surface of the molten metal and the fluctuations in the vertical direction also increase. Due to such a phenomenon, unmelted powder is entrained in molten steel, and the thickness of the solidified shell 4 is varied or uneven, which causes a problem in quality of the slab such as biting or vertical cracking. It becomes.

As a method for improving the quality of a slab, Japanese Unexamined Patent Publication (Kokai) No. 5-55220 discloses a continuous casting method using a static magnetic field and its mold. This method generates a static magnetic field between each pair of upper and lower magnetic poles provided on each back surface of the opposite side wall of the mold, the strength of the static magnetic field generated between one magnetic pole is smaller or larger than that of the other, This is to add damping to the molten steel flow supplied from the immersion nozzle into the mold. With this, it is possible to apply braking to the ascending flow and the descending flow generated when the discharge flow from the immersion nozzle collides with the short side wall of the mold, and the inclusion of deep inclusions in the molten steel or the molten metal due to the descending flow. As a result of suppressing surface fluctuations and temperature non-uniformity, melting of the powder for continuous casting is not hindered, and it is said that a slab of good quality can be manufactured with high efficiency.

[0010]

However, the method of the above invention has the following problems. That is, when a static magnetic field is applied to the molten steel flow in the mold, a force acts in the direction opposite to the direction of the molten steel flow, so the molten steel flow velocity in the static magnetic field application region decreases,
Since the braking force does not act on the molten steel flowing in the direction of the static magnetic field application area outside the static magnetic field application area, the molten steel flow tries to turn in the direction without the static magnetic field, and the discharge flow from the immersion nozzle moves up and down the mold. Is narrowed by the static magnetic field due to the magnetic poles installed in
During this period, the molten steel flow becomes stagnant.

When the casting speed is constant, the discharge flow from the dipping nozzle is also constant, so that the discharge flow enters the stagnant region of the molten steel flow sandwiched by the static magnetic field, and the molten steel flow in this region fluctuates greatly. , Becomes extremely unstable. Therefore, due to the discharge flow from the immersion nozzle, inclusions are entrained in the molten steel and captured by the solidified shell, or the molten metal surface fluctuates drastically, and powder is entrained in the molten steel.
A slab defect occurs.

The present invention has been made to solve the above problems, and an object of the present invention is to disperse a molten steel flow over the entire molten metal surface in a mold, and to prevent fluctuations in the molten steel flow without causing a stagnant zone. It is intended to provide a continuous casting apparatus and a casting method capable of suppressing the above-mentioned problems and manufacturing a slab with excellent quality.

[0013]

The summary of the present invention is as follows.
It is in the continuous casting apparatus of (1) and the method of using this apparatus of (2).

(1) A continuous casting apparatus in which one electromagnet is opposed to the outside of both long side walls of a continuous casting mold having a rectangular horizontal section, and the electromagnet surrounds a plurality of iron cores. It consists of one coil, and the intervals between multiple iron cores and the outer surface of the mold wall can be adjusted independently for each iron core. The installation positions of the multiple iron cores are equivalent to the molten steel surface level in the mold and the immersion nozzle. The continuous casting apparatus is characterized in that it is between the level equivalent to the immersion depth in the molten steel in the mold.

(2) Using the apparatus of (1) above, by increasing the distance between the iron core at the center of the mold long side wall and the outer surface of the mold wall, the magnetic field strength in the mold at the center of the mold long side wall is increased. A continuous casting method, characterized in that casting is performed with a small size.

[0016]

The continuous casting apparatus of the present invention will be described with reference to FIGS. FIG. 1 is a partial side view and a partial vertical cross-sectional view schematically showing the side surface viewed from the long side wall of the mold, and FIG. 2 is a plan view of the side surface viewed from above.

The immersion nozzle 2 is fixed to the center of the continuous casting mold 1 so as to have a constant immersion depth, and the molten steel 3 is injected into the mold 1 from the immersion nozzle 2. The solidified shell 4 grows from within the mold 1. Powder (not shown) is put on the surface of the molten steel 3, that is, on the molten metal surface.

Both long side walls 1b of the mold 1 shown in FIG.
On the outer side of the side, within the range of the level equivalent to the molten metal surface in the mold and the level equivalent to the immersion depth of the immersion nozzle 2 as shown in FIG. 1, the width direction outside the long side wall 1b of the mold as shown in FIG. Further, a pair of electromagnets including a plurality of iron cores 5 and a coil 6 surrounding the plurality of iron cores are provided so as to face each other.

Each iron core 5 of the electromagnet has a mechanism capable of independently changing the distance d between the iron core 5 and the outer surface of the long side wall 1b. As this mechanism, for example, the following method may be used.

A hydraulic cylinder 7 is connected to each iron core 5 of the electromagnet, and the main body of the hydraulic cylinder 7 is fixed to a frame 8 supporting the mold 1. By adjusting the hydraulic pressure and independently changing the length of each hydraulic cylinder rod, the distance d between the iron core 5 and the outer surface of the long side wall 1b of the mold can be changed for each iron core 5. Although the example in which the hydraulic cylinder 7 is used is shown here, an air cylinder, a motor drive, a manual worm gear, or the like may be used as a control mechanism of the interval d instead.

With such a mechanism, even if the current flowing through the coil 6 is constant, the magnetic field strength generated in the mold 1 is locally controlled according to the number of the iron cores 5 by appropriately controlling the intervals d. Can be changed to.

As shown in FIG. 1, the molten steel 3 is immersed in the immersion nozzle 2
When injected into the mold 1 from the above, it collides with the mold short side wall 1a side, and is divided into an upward flow in the direction of the molten metal surface and a downward flow in the downward direction of the mold. A braking force is applied to the ascending flow by the static magnetic field generated in the iron core 5 of the electromagnet, and the upward flow is dispersed in the molten metal surface direction. That is, when a static magnetic field is applied in the vicinity of the molten metal surface and the amount of molten steel discharged from the immersion nozzle is kept constant, the above-mentioned braking force causes the upward flow due to the collision on the mold short side wall 1a side over the molten metal surface. Distributed. When the ascending flow is dispersed over the molten metal surface in this way, the flow velocity of the ascending flow is reduced, the amount of rise of the molten metal surface is also reduced, fluctuations in the molten metal surface are suppressed, and the stagnant region of the molten steel flow is eliminated. The low temperature region on the surface of the molten metal disappears, and the prevention of lowering of the surface of the molten metal and the uniformization of temperature and viscosity are achieved.

The position of the iron core 5 in the height direction with respect to the mold 1 is limited between the level corresponding to the molten metal surface in the mold and the level equivalent to the immersion depth of the immersion nozzle 2 for the following reason.

That is, when a static magnetic field is applied to the molten steel flow, the molten steel flow moves in the direction in which there is no static magnetic field due to the action of the braking force that acts in the opposite direction to the molten steel flow. For this reason, it is necessary to avoid directly applying the static magnetic field to the discharge flow from the immersion nozzle 2.

At this time, if the distance d between the iron core 5 and the outer surface of the long side wall 1b is increased in the central portion of the long side wall 1b of the mold near the dipping nozzle 2, the magnetic field strength is reduced in this portion. As described above, the distribution of the magnetic field strength can be provided in the mold long side wall 1b, that is, in the width direction of the slab. The "central portion of the mold long side wall 1b in the vicinity of the dipping nozzle 2" referred to here is, for example, five iron cores 5 provided in FIG.
The position corresponds to the center position of, and corresponds to the vicinity of the position of the immersion nozzle 2. A desirable "mold central portion" is in the range of 10 to 30% with respect to the inner length of the long side wall 1b of the mold.

As a result, it is possible to suppress the reduction of the molten steel flow velocity in the vicinity of the molten metal surface in the center of the mold, and to make the molten steel flow velocity in the vicinity of the immersion nozzle uniform. This makes it possible to easily eliminate the low temperature region that tends to occur in the center of the mold.

With the continuous casting apparatus of the present invention, the following effects can be further obtained when the casting speed is increased. That is, the discharge speed of the molten steel from the immersion nozzle increases as the casting speed increases, so that the speed of the upward flow generated by collision with the short side of the mold also increases, and the flow velocity in the direction of the immersion nozzle also increases. Since the molten steel flow velocity near the molten metal surface changes depending on the casting speed as described above, it is necessary to more strongly control the molten steel flow by changing the magnetic field strength generated by the electromagnet according to the increase of the casting speed. Even in the case where there is such a need, an electromagnet having a plurality of iron cores and one coil is provided opposite to each other at appropriate height direction positions outside both long side walls of the mold, and the iron core and the mold length are provided. Distance d from the outside of the side wall
Can be changed arbitrarily and easily to obtain the desired control of the molten steel flow, thereby making it possible to manufacture a slab with excellent quality.

In FIGS. 1 and 2, the number of iron cores 5 is 5 on one side, but a desirable number range is 3 to 7 on one side. The desirable magnetic field strength range for each of the iron cores 5 is 500 to 3000 Gauss, and the desirable range of the variable distance d is 10 to 300 mm. When changing the magnetic field strength, the magnetic field strength at the center is 20 when the strength at both ends is 100.
It is desirable that the range is about 70%, and the magnetic field strength of the iron core between both ends and the center is a value between them.

[0029]

EXAMPLE A continuous casting test of medium carbon steel slabs was conducted under the conditions shown in Tables 1 and 2 using the apparatus having the structure shown in FIG. The incidence was investigated.

[0030]

[Table 1]

[0031]

[Table 2]

Casting conditions other than those shown were as follows.

Continuous casting model, number of strands: 1 Mold width (long side inside length): 1250 mm Mold thickness (short side inside length): 250 mm Tundish molten steel superheat: 10-40 ° C Immersion nozzle immersion depth Size: 300 mm Coil current: 3000 A Surface defects are evaluated by visual observation to find the total crack length per unit length, and internal defects are evaluated by cutting the slab in a direction perpendicular to the casting direction and visually observing unit length. Measurement of the total length of the
1.0 was set as the standard value. The survey results are also shown in Table 1.

As shown in Table 1, with respect to the occurrence rate of any defect, when the uniform static magnetic field was applied, the magnetic field strength became weaker toward the center of the mold in the width direction than in the comparative example in which the static magnetic field was not applied. It was found that the results were good in the order of the cases, and in particular, the present invention example 3 in which the static magnetic field strength reduction ratio was increased toward the central iron core No. 3 was the most excellent.

[0035]

According to the present invention, a continuously cast slab with few external and internal defects can be obtained.

[Brief description of drawings]

FIG. 1 is a partial side view and a partial vertical cross-sectional view schematically showing a side surface of a continuous casting device of the present invention as viewed from a long side wall side of a mold.

FIG. 2 is a plan view of FIG. 1 seen from above.

FIG. 3 is a vertical cross-sectional view schematically showing molten steel flow in a mold in conventional continuous casting.

[Explanation of symbols]

1: Mold 1a: Short side wall of mold 1b: Long side wall of mold 2:
Immersion nozzle, 3: molten steel, 4: solidified shell, 5: iron core,
6: coil, 7: hydraulic cylinder,
8: Frame, 9: Molten powder layer

Claims (2)

[Claims] 1. A continuous casting apparatus in which one electromagnet is opposed to the outer sides of both long side walls of a continuous casting mold having a rectangular horizontal cross section, and the electromagnet includes a plurality of iron cores and surroundings thereof.
It consists of individual coils, and the spacing between multiple iron cores and the outer surface of the mold wall can be adjusted independently for each iron core, and the installation positions of the multiple iron cores are equivalent to the molten steel surface level in the mold and the immersion nozzle. A continuous casting device, characterized in that it is between a level equivalent to the immersion depth in the molten steel in the mold. 2. The magnetic field strength in the mold at the center of the long side wall of the mold is increased by increasing the distance between the iron core at the center of the long side wall of the mold and the outer surface of the mold wall using the apparatus according to claim 1. A continuous casting method, characterized in that the casting is performed in a small size.