JP2969579B2 - Steel continuous casting method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for minimizing a mixed area of components in a slab between steel types having different components when continuously casting a plurality of steel types having different molten steel components. is there.

[0002]

2. Description of the Related Art In continuous casting of steel, a method of continuously casting molten steel in a plurality of molten steel pots in one mold in order to improve productivity and reduce manufacturing cost, so-called continuous casting, is widely used. Is being done.

[0003] As a further expanded method,
2. Description of the Related Art Continuous casting of a plurality of steel types having different molten steel components, so-called continuous casting of different steel types, is performed.

[0004] However, when continuously casting different types of steel,
When exchanging the molten steel ladle, components are mixed in the cast part (seam part), and as a result, slabs whose components do not meet the purpose of production are produced, so the slab of the seam part is degraded, scrapped, or seamed. Since the rolling of the slabs before and after the part is suspended until the result of the component determination is obtained, these obstacles have been a major problem in successive casting of different steel types.

[0005] In order to reduce the mixing of the components at the joints generated during the continuous casting of different types of steel, the molten steel in the rear pan is poured after the remaining hot water in the front pan in the tundish is reduced as much as possible. Method to prevent the mixing of components in the tundish by temporarily reducing the casting speed when starting the casting of molten steel in the back pan, and the depth at which the discharge flow from the pouring nozzle penetrates into the molten steel in the mold Method to prevent mixing in the mold by making it shallow, to temporarily stop casting at the joint, and to prevent mixing in the mold by inserting an iron plate as a shielding plate in the mold, and to apply a static magnetic field directly under the mold Forming and casting while suppressing the circulating flow at the seam
No. 459) has been proposed.

[0006]

However, in the prior art as described above, since the casting speed is reduced at each joint, not only the productivity of continuous casting itself is impaired, but also the temperature of the cast slab is partially reduced. Mechanical load on the caster in bending and straightening of the cast slab, etc., which shortens the equipment life, impedes the schedule of hot direct rolling, and places the iron plate in the mold. In addition, it is not possible to say that the mixed area of the joints at the time of continuous casting of different types of steels is not necessarily reduced to a satisfactory degree, and that it is not necessarily satisfactory. It is difficult to determine the length of the degraded portion or the length of the scraped portion in the cast slab.

Therefore, as a method of compensating for this, a component check is performed on the cast pieces before and after the joint.

Therefore, there is a problem that not only the rolling schedule is disturbed, but also the inventory (surplus material) temporarily increases.

[0009] This means that, as described above, it is not sufficient to only perform casting while suppressing the circulating flow in the presence of a magnetic field, and it is necessary to make a state in which there is no flow (plug flow). The present invention aims to solve this problem.

[0010]

Means for Solving the Problems The present inventors have conducted various studies to solve the above problems, and as a result, have found the following means.

That is, when continuously casting steels having different molten steel components, the steels are cast in order from a steel type having a high molten steel density to a steel type having a low molten steel density.

In particular, using a mold having a pair of magnets disposed on the opposite wide surface in the mold or behind the same, a direct current magnetic flux is applied across the wide surface in the direction crossing the thickness of the slab, and the casting in the mold is performed. This is a continuous casting method for steel in which a static magnetic field zone is formed in the direction by the DC magnetic flux, molten steel is poured into a casting space above the casting, and steel is cast in ascending order of molten steel density.

[0013]

The following is a detailed description of the present invention along with the operation.

In order to solve the above-mentioned problems in the prior art, the present inventors have studied the effect of the difference in density between two types of molten steel and the static magnetic field imparted to the slab on the mixing of components during successive casting of different steel types. Was studied in detail.

FIG. 1 shows the relationship between the difference in density between the molten steel in the front ladle and the molten steel in the rear lane and the length in the casting direction of the component mixing region, ie, the depth of molten steel penetration, during continuous casting.

From this figure, when the density of the molten steel in the front ladle is higher than the density of the molten steel in the rear ladle, ie, the density difference Δρ between the two types of molten steel
Is negative, it can be seen that the length of the component mixing region becomes shorter.

This is probably because the mixing of molten steel based on the density difference in the strand pool was suppressed. Thus, when performing continuous casting, it is important to consider the physical property value, that is, the density, of the molten steel.

Next, the effect of reducing the length of the component mixed region when a static magnetic field is applied to the slab is shown in FIG. 2 for the normalized concentration. It can be seen that the application of the static magnetic field significantly reduces the component mixing region. In addition, the influence on the molten steel in the front ladle is reduced to a length from the meniscus position, which is almost a joint, to the center position of the static magnetic field zone.

This is because a brake effect (Lorentz force) acts on the discharge flow due to the static magnetic field, so that the velocity distribution in the cross section of the slab is made uniform (rectified), and the penetration depth of the discharge flow into the strand pool is reduced. Because it became shallow. In particular, the effect of suppressing the mixing of molten steel is remarkable when the density of the molten steel in the front ladle is higher than the density of the molten steel in the rear ladle.

This is because when the density of the molten steel in the front ladle is smaller than the density of the molten steel in the rear ladle, even if the discharge flow is once rectified by the static magnetic field, it is based on the density difference after the seam passes through the static magnetic field zone. If the density of the molten steel in the front ladle is higher than the density of the molten steel in the rear lane while the convection mixing occurs, this does not occur and the rectified state is maintained.

As described above, it has been found that the component mixing region of the joint portion can be reduced by taking into account the difference in the density of the molten steel between the steel types in the continuous casting of different steel types, and by further combining this with the application of a static magnetic field. .

[0022]

EXAMPLE Continuous casting of different types of steel was performed using a continuous casting apparatus having a mold in which a pair of electromagnets were disposed behind opposing wide surfaces in a mold as shown in FIG.

The shape of the mold is 245 mm (thickness) x 1500 m
m (width) and the casting speed was 1.0 m / min. The position of the static magnetic field zone is 450 mm to 700 from the meniscus in the mold.
mm, and the intensity of the DC magnetic flux was 0.35 Tesla. Molten steel was injected into the upper casting space of the static magnetic field.

The solute concentration distribution in the slab obtained after casting was investigated, and the length of the component mixed region, that is, the molten steel penetration depth was determined. Table 1 shows the relationship between the casting conditions and the length of the component mixture region when continuous casting was performed. It can be seen that in each of the examples of the present invention, a remarkable effect of reducing the component mixed region can be obtained as compared with the comparative example.

[0025]

[Table 1]

[0026]

As described above, according to the present invention, it is possible to reduce the component mixing region of the joint at the time of continuous casting of different steel types without impairing productivity, and to reduce the manufacturing cost. The effect brought about is great.

[Brief description of the drawings]

FIG. 1 is a graph showing the effect of the present invention, showing the relationship between the density difference and the length of a component mixed region.

FIG. 2 is a diagram showing the effect of the present invention, showing the effect on the length of a component mixing region when a static magnetic field is applied.

FIG. 3 is a schematic view of a continuous casting apparatus mold portion used in carrying out the present invention, (a) is a sketch drawing thereof, and (b) is a cross-sectional view in a slab width direction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Immersion nozzle 2 Static magnetic field zone 3 Mold long side 4 Mold 5 Rectification

──────────────────────────────────────────────────続 き Continued on the front page (72) Shozo Mizoguchi, Inventor 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technology Development Division (56) References JP-A-58-1868464 (JP, A) JP-A Sho 61-1459 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) B22D 11/00 B22D 11/10

Claims (2)

(57) [Claims] 1. A continuous casting method for steel, characterized in that, when continuously casting steels having different molten steel components, steels having a higher molten steel density are cast in order from a steel type having a smaller molten steel density. 2. A casting mold in which a pair of magnets are disposed on the opposite wide surface in the mold or at the rear thereof, and a direct current magnetic flux is applied across the entire width of the wide surface in a direction crossing the thickness of the slab. 2. The continuous casting method for steel according to claim 1, wherein a static magnetic field zone is formed by the DC magnetic flux, and molten steel is poured into a casting space above the casting and casting is performed in order from a steel type having a higher molten steel density.