JPH09141402A - Method for removing non-metallic inclusions in molten steel - Google Patents

Abstract

(57) 【Abstract】 PROBLEM TO BE SOLVED: To efficiently remove non-metallic inclusions in molten steel and improve the quality of a cast slab. A method of removing non-metallic inclusions in molten steel, wherein particles, which are easily adsorbed by non-metallic inclusions, are suspended in the molten steel flowing through a nozzle for injecting molten steel into a tundish or a mold. Since it is a method of adsorbing to particles, it does not become clogged like a filter using porous bricks, it can be used for a long time and high removal efficiency becomes possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention, in the field of steelmaking, which is a manufacturing process of steel, efficiently removes non-metallic inclusions generated in molten steel and reduces defects caused by non-metallic inclusions. The present invention relates to a method for removing non-metallic inclusions capable of improving the quality of a slab.

[0002]

2. Description of the Related Art For the purpose of removing non-metallic inclusions in molten steel,
Many methods have been proposed (for example, JP-A-60-2).
21158). Although these have some differences, they generally have a configuration as shown in FIG. Molten steel 2 is passed through a substance 1 having a gap, such as a porous brick, and nonmetallic inclusions 3 are captured in the gap to remove the nonmetallic inclusions from the molten steel.

[0003]

However, in the conventional method described above, when the size of the gap is small (FIG. 4 (a)), the non-metallic inclusions are well captured in the gap and high removal efficiency can be obtained. However, the non-metallic inclusions 3 close the gap, and the passage of the molten steel 2 is also hindered.
Cannot be used for a long time.

If the size of the gap is large (see FIG. 4)
In (b), the nonmetallic inclusions 3 pass through the gap, and the removal efficiency of the nonmetallic inclusions 3 is low. In any case, the conventional method cannot remove non-metallic inclusions with high efficiency over a long period of time.

The present invention provides a conventional method for removing non-metallic inclusions in molten steel, which has a high removal efficiency without obstructing the passage of molten steel.

[0006]

As shown in FIG. 1, in the removing method of the present invention, nonmetallic inclusions are adsorbed in the molten steel flowing in the nozzle 4 for injecting molten steel into the tundish or mold. It is characterized in that the easy particles 5 are suspended and the non-metallic inclusions 3 are adsorbed to the particles 5 to remove the inclusions.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION As shown in FIG. 1, the present invention is a system in which non-metallic inclusions 3 are adsorbed by the particles 5 floating in molten steel. Since it is not a method of trapping in the gaps of the porous body, non-metallic inclusions cannot block the gaps and hinder the passage of molten steel. Furthermore, since the molten steel flow velocity in the nozzle 4 for injecting the molten steel into the tundish or the mold is high and the flow pattern is complicatedly disturbed, the collision probability of the particles 5 and the non-metallic inclusions 3 is high, and the non-metallic inclusions are high. The effect of removing is great.

The particles 5 are made of a material that does not react with the molten steel and does not melt at the molten steel temperature. Specifically, it is desirable to use a ceramic ball made by spherically firing a raw material of alumina, zirconia, magnesia or lime. .

When the particles 5 flow out from the nozzle 4, the particles 5 may be mixed in the slab and cause defects.
In order to prevent the particles 5 from flowing out, the particles 5 in the molten steel
It is necessary to increase the ascent rate. The particle levitation speed up in the stationary fluid is up = (ρFe−ρP) d2g / (18μ) where u: molten steel descending flow velocity in the nozzle ρFe: molten steel density ρP: density of the particles g: gravity constant d: diameter μ of the particles It is represented by the viscosity coefficient of molten steel, and if the floating speed is higher than the molten steel descending flow velocity, the particles 5 do not flow out from the nozzle 4. That is, it is desirable that the diameter and the specific gravity of the particles satisfy u <(ρFe−ρP) d2g / (18μ).

Further, inside the nozzle, a pseudo meniscus 6 is formed in the vicinity of the molten steel surface 8 due to incomplete sealing at the nozzle upper joint. In reality, it is considered that the particles 5 float in the range from the pseudo meniscus 6 to the nozzle lower end 7 due to the molten steel descending flow. If the ratio of the total volume of the particles to the volume inside the nozzle 4 from the nozzle lower end 7 to the molten steel surface 8 (hereinafter referred to as the solid fraction) is extremely increased,
When the particles 5 adsorb the non-metallic inclusions 3 and become huge,
There is a possibility that the gap between the particles 5 becomes narrow and the passage of the molten steel 2 may be hindered. Further, if the solid fraction is extremely low, the frequency of collision between the non-metal inclusions 3 and the particles 5 decreases, and the non-metal inclusion removal efficiency decreases. For these reasons, the solid fraction is 0.
002 or more and 0.2 or less are desirable. By using the present invention described above, it is possible to obtain a high nonmetal removal efficiency for a long time without clogging by nonmetal inclusions.

[0011]

EXAMPLE A method of the present invention was carried out in which particles having a diameter of 1.5 cm and made of alumina were suspended in molten steel flowing in a tundish injection nozzle. At this time (see FIG. 2 hereafter),
The inner diameter of the nozzle is 100 mm in the narrow part and 20 in the wide hem.
A portion of 0 mm and 250 mm from the lower end of the nozzle was immersed in molten steel. The alumina particles were suspended in the nozzle in an amount such that the ratio (solid phase ratio) of the total volume of the alumina particles to the volume of the immersed nozzle was 0.1. On the other hand, as a comparative example, a conventional method in which porous bricks having gap sizes of 1 mm and 5 mm were fixed in a tundish injection nozzle having the same specifications was also carried out at the same time. The material of the porous brick was alumina, and it was installed within a range of 50 mm below the molten steel surface level.
In both cases of the present invention method and the conventional method, the molten steel passing average velocity is 70 at the portion where the nozzle diameter is large.
The condition is cm / s, and in each case, the T.S. The O value (total oxygen amount) was investigated.

The results are shown in Table 1. Compared with the conventional method, the method of the present invention does not block the T.T. It was confirmed that the range of decrease in O value was increased and the alumina-based inclusions were efficiently removed.

[0013]

[Table 1]

[0014]

According to the method for removing non-metallic inclusions in molten steel of the present invention described above, the removal efficiency of non-metallic inclusions can be increased without closing the nozzle.

[Brief description of the drawings]

FIG. 1 is a sectional view illustrating a method for removing non-metallic inclusions according to the present invention.

FIG. 2 is a sectional view illustrating a nozzle of the present invention.

FIG. 3 is a sectional view illustrating a conventional method for removing non-metallic inclusions.

FIG. 4 is a cross-sectional view illustrating a conventional method for removing non-metallic inclusions, where (a) shows a case where the size of the gap is small, and (b) shows a case where the size of the gap is large.

[Explanation of symbols]

1 Porous Brick 2 Molten Steel 3 Non-Metallic Inclusions 4 Injection Nozzle 5 Particles That Non-Metallic Inclusions Are Easily Adsorbed 6 Pseudo Meniscus 7 Nozzle Bottom 8 Molten Steel Molten Surface

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B01J 20/28 B01J 20/28 A C21C 7/00 C21C 7/00 H

Claims (5)

[Claims] 1. A method for removing non-metallic inclusions in molten steel, wherein particles, which are easily adsorbed by non-metallic inclusions, are suspended in the molten steel flowing through a nozzle for injecting molten steel into a tundish. 2. A method for removing non-metallic inclusions in molten steel, characterized in that particles, which are easily adsorbed by non-metallic inclusions, are suspended in the molten steel flowing in a nozzle for injecting molten steel into a mold. 3. The method for removing non-metallic inclusions in molten steel according to claim 1, wherein a raw material of alumina, zirconia, magnesia, or lime is fired into a spherical shape and used as the particles. 4. The method for removing non-metallic inclusions in molten steel according to claim 1, wherein the diameter and the density of the particles satisfy the following relational expression. u <(ρFe−ρP) d2g / (18μ) u: Downflow velocity of molten steel in nozzle ρFe: Density of molten steel ρP: Density of particles g: Gravitational constant d: Diameter of particles μ: Viscosity coefficient of molten steel 5. The ratio of the total volume of the particles to the volume inside the nozzle from the lower end of the nozzle to the position of the molten metal is 0.002.
5. The method for removing non-metallic inclusions in molten steel according to claim 1, wherein the content is not less than 0.2 and not more than 0.2.