JPH04367358A - Method for supplying adding wire in continuous casting - Google Patents

Abstract

PURPOSE:To prevent crack and double skin in a cast slab by passing a wire through a semi-immersion nozzle and supplying this into molten steel while dipping into the molten steel and heating by conducting electric power after preheating the semi-immersion nozzle composed of refractory material. CONSTITUTION:Before dipping the semi-immersion nozzle 4 composed of the refractory material, such as refractory, ceramic, this is preheated in order to prevent stickness of the metal. After dipping the semi-immersion nozzle 4 into the molten steel 7, the electric power is charged to this nozzle 4 through an electrode 14 from a power source 13 to heat the semi-immersion nozzle 4. By this method, lowering of temp. of the molten steel 7 is prevented. Under this condition, while supplying the adding wire 2 through pinch rolls 1 and a guide pipe 3, casting is executed. As the semi-immersion nozzle 4 is heated, the molten steel 7 at the part, in where the adding wire 2 is supplied, is not solidified. Therefore, the adding wire 2 can be smoothly supplied.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for supplying additive wire to molten steel in a mold in continuous casting, and more particularly to a method for smoothly supplying additive wire and producing slabs with good surface properties.

0002

BACKGROUND OF THE INVENTION In continuous casting, a method is known in which an additive wire is supplied to molten steel in a mold in order to prevent or reduce center segregation and center porosity in the manufactured slab.

However, the conventional method of supplying additive wire to the molten steel in the mold involves rolling in mold powder or slag produced by melting it onto the surface of the molten steel in the mold, thereby improving the cleanliness of the manufactured slab. It has the disadvantage of being harmful.

As a method for preventing such problems, a method for supplying additives into a continuous casting mold is known, for example, as disclosed in Japanese Patent Application Laid-open No. 110130/1983.

[0005] This method will be explained with reference to FIG. 1. An additive wire 2 supplied by a pinch roll 1 is guided by a guide pipe 3 and supplied to molten steel 7 in a mold 9.

Powder 6 and slag 5 are present on the surface of molten steel.
However, by immersing the semi-immersion nozzle 4, it is possible to prevent the wire 2 from coming into contact with the powder 6 and the slag 5, and to prevent the wire 2 from entraining the powder and slag.

In this case, inert gas or reducing gas 11 is injected into the molten steel 7 through a nozzle 10 installed inside the semi-immersion nozzle 4, since metal adhesion occurs in the semi-immersion nozzle 4 due to the temperature drop of the molten steel. By stirring the molten steel 7 by ejecting it, a drop in temperature is prevented.

However, when the semi-immersion nozzle 4 is immersed in the molten steel 7, the molten steel 7 is cooled by the semi-immersion nozzle and the molten steel 7 in the semi-immersion nozzle 4 solidifies, making it impossible to supply the additive wire 2. There are cases.

Furthermore, when a bottomed immersion nozzle is used, the molten steel flow from the immersion nozzle collides with the semi-immersion nozzle, making the molten steel flow non-uniform in the mold, causing cracks and double strands in the manufactured slab. Skin may form, and the molten metal level in the mold may fluctuate due to uneven molten steel flow, which may cause slag to be rolled in and deteriorate the cleanliness of the slab.

0010

SUMMARY OF THE INVENTION The present invention immerses a semi-immersion nozzle in molten steel in a continuous casting mold, and prevents the molten steel in the semi-immersion nozzle from solidifying when feeding a wire through the semi-immersion nozzle. The purpose of this method is to prevent cracks and double skin in slabs caused by unevenness caused by the molten steel flow from the immersion nozzle discharge hole colliding with the semi-immersion nozzle.

[0011]

[Means for Solving the Problems] The present invention has been made to solve the above-mentioned problems, and its gist is that when casting while supplying additive wire to molten steel in a continuous casting mold, The method is characterized in that a semi-immersion nozzle made of a refractory material is preheated and then immersed in the molten steel, and the wire is supplied to the molten steel through the semi-immersion nozzle while being heated with electricity.

FIG. 2 shows an example of an apparatus in which a semi-immersion nozzle according to the present invention is immersed in molten steel in a mold and is cast while supplying wire.

Semi-immersion nozzle 4 in the present invention
is made of a refractory material such as a refractory or ceramics, and before the semi-immersion nozzle 4 is immersed in the molten steel 7, it is preheated to prevent base metal from adhering.

[0014] Preheating temperature is preferably 900°C or higher. After the semi-immersion nozzle 4 is immersed in the molten steel, power is applied to the nozzle from the power source 13 through the electrode 14 to heat the semi-immersion nozzle 4. The heating temperature is preferably 1200°C or higher.

[0015] This prevents the temperature of the molten steel 7 from decreasing. In this state, casting is performed while supplying the additive wire 2 via the pinch roll 1 and the guide pipe 3.

The molten steel in the portion to which the additive wire 2 is supplied does not cool and solidify because the semi-immersion nozzle 4 is heated.

[0017] Therefore, troubles such as impossibility of supplying the additive wire can be avoided, and smooth supply can be achieved.

[0018] Since the inside of the semi-immersion nozzle 4 is in the state of bare hot water without the presence of mold powder 6 and slag 5, the molten steel comes into contact with the atmosphere and oxidizes.

In order to prevent this, an inert gas 11 is supplied into the semi-immersion nozzle 4 from the gas introduction pipe 15.

In the wire feeding method in continuous casting, when a bottomed immersion nozzle is used as the immersion nozzle, the molten steel flow from the immersion nozzle discharge hole collides with the semi-immersion nozzle, making the molten steel flow non-uniform. Cracks and double skin occur in slabs.

The gist according to claim 2 of the present invention is that when molten steel is injected into a continuous casting mold through a bottomed immersion nozzle, the immersion depth of the semi-immersion nozzle satisfies the following formula (1). It is characterized by maintaining the state of

[0022]X≦Z-Y・tanθ...(1
)X: Immersion depth of semi-immersion nozzle (mm) Z:
Immersion depth of the immersion nozzle (mm) Y: Distance from the upper end of the immersion nozzle discharge hole to the outer edge of the semi-immersion nozzle (mm) θ: Immersion nozzle discharge hole angle (deg)

In FIG. 3, the bottomed immersion nozzle discharge hole 12
The upward discharge angle of the molten steel flow from A is determined by the angle θ of the discharge hole.

Further, the immersion depth of the semi-immersion nozzle 4 is X, the distance from the upper end of the immersion nozzle discharge hole 12A to the outer edge of the semi-immersion nozzle is Y, and the distance from the lower end of the semi-immersion nozzle to the upper end of the immersion nozzle discharge hole at this time is When the distance to is W, the range H directly influenced by the molten steel flow from the immersion nozzle discharge hole 12A is expressed as H=Y·tanθ.

Therefore, if the distance W from the lower end of the semi-immersion nozzle to the upper end of the immersion nozzle discharge hole is larger than the range H directly affected by the molten steel flow from the immersion nozzle discharge hole, that is, W=Z−X≧H=Y・If tan θ, the molten steel flow will not collide with the semi-immersion nozzle. From this, equation (1) is obtained.

[0026]

[Example 1] As an example of the present invention, the apparatus shown in Fig. 2 was used to cast SUS304 class stainless molten steel, in which the superheating temperature of the molten steel in the tundish was 40°C, into a mold with cross-sectional dimensions of 143 mm x 1575 mm. After preheating a semi-immersion nozzle using alumina graphite refractory to 1000°C with a gas burner, it was immersed in the molten steel in the mold to prevent mold powder and slag from being drawn in, and a current of 200°C was applied through the electrode.
0A was supplied to the semi-immersion nozzle.

After the semi-immersion nozzle is heated to 1400° C. by starting the supply of electric current, an additive wire of 7.0φmm is added into the molten steel at a rate of 0.87 kg per ton of molten steel via a pinch roll and a guide pipe. Cast while feeding.

The distance (Y) from the immersion nozzle discharge hole to the outer end of the semi-immersion nozzle is 300 mm, the immersion nozzle discharge hole angle (θ) is 15°, and the immersion depth of the immersion nozzle (Z).
) is 120 mm, and the right side of equation (1) is 40 mm, so the immersion depth (X) of the semi-immersion nozzle is set to 3.
It was set to 5 mm.

As a result, there is no turbulence in the flow of molten steel in the mold, and there is no base metal adhering to the additive wire due to the cooling solidification of the molten steel in the semi-immersion nozzle, making it possible to supply the additive wire to the molten steel in the mold extremely smoothly. It was possible to produce slabs with good surface properties.

As a comparative example, when casting SUS304 class stainless steel, in which the superheating temperature of the molten steel in the tundish is 40°C, into a mold with cross-sectional dimensions of 143 mm x 1575 mm, the apparatus shown in Fig. 2 was used to cast alumina graphite refractory steel. After immersing the semi-immersion nozzle into the molten steel in the mold to prevent mold powder and slag from being rolled into the molten steel in the mold without preheating, a 7.0φmm additive wire was passed through the pinch rolls and guide pipe. Casting was carried out while supplying molten steel at a rate of 0.87 kg per ton of molten steel.

The distance (Y) from the immersion nozzle discharge hole to the outer end of the semi-immersion nozzle is 300 mm, the immersion nozzle discharge hole angle (θ) is 15°, and the immersion depth of the immersion nozzle (Z).
) is 120 mm, and the right side of equation (1) is 40 mm.

On the other hand, the immersion depth (X) of the semi-immersion nozzle was set to 60 mm.

As a result, the molten steel flow from the immersion nozzle collides with the semi-immersion nozzle, making the molten steel flow non-uniform.
Cracks and double skin occurred in the slab.

Furthermore, the molten steel in the semi-immersion nozzle cooled and solidified during immersion in the semi-immersion nozzle, and the supply of the additive wire was discontinued.

[0035]

Effects of the Invention The present invention is a method of casting while supplying additive wire to molten steel in a continuous casting mold through a semi-immersion nozzle. By immersing the semi-immersion nozzle in molten steel and casting the semi-immersion nozzle while heating it with electricity, it is possible to prevent the molten steel in the semi-immersion nozzle from cooling and solidifying. Therefore, the additive wire can be supplied smoothly.

Furthermore, by setting the semi-immersion nozzle or the bottomed type immersion nozzle to the conditions determined by equation (1), the molten steel flow from the immersion nozzle discharge hole collides with the semi-immersion nozzle, causing the molten steel flow to be uneven. It is possible to prevent cracking and double skin of the slab that would otherwise occur.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing a conventional method of inserting additive wire into a continuous casting mold.

FIG. 2 is a cross-sectional view showing a method of heating a semi-immersion nozzle and a method of inserting an additive wire into molten steel according to the present invention.

FIG. 3 is a cross-sectional view showing the arrangement of a semi-immersion nozzle and a bottomed immersion nozzle according to the present invention.

[Explanation of symbols]

1 Pinch roll 2 Additive wire 3 Guide pipe 4 Semi-immersion nozzle 5 Slag 6 Powder 7 Molten steel 8 Solidified shell 9 Continuous casting mold 10 Nozzle 11 Inert (reducing) gas 12 Immersion nozzle 12A Immersion nozzle discharge hole 13 Power supply 14 Electrode 15 Gas introduction pipe

Claims (2)

[Claims] 1. When casting while supplying additive wire to molten steel in a continuous casting mold, a semi-immersion nozzle made of a refractory material is preheated, and then immersed in the molten steel and heated while heating the semi-immersion wire. A method for supplying wire in continuous casting, characterized in that the wire is supplied to the molten steel through an immersion nozzle. 2. In the method according to claim 1, when molten steel is injected into the continuous casting mold through a bottomed immersion nozzle, the immersion depth of the semi-immersion nozzle is as follows (1).
A method characterized by maintaining a state that satisfies Eq. X≦Z-Y・tanθ... (1) Distance (mm) θ: Immersion nozzle discharge hole angle (deg)