JPH0924445A - Method for concentrating solute on surface layer of cast slab in continuous casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To modify the quality of surface layer of a cast slab by arranging a molten steel partition plate above an immersion nozzle spouting hole in a continuous casting mold and adding a desired solute element into the molten steel at the upper part from this partition plate to concentrate the added element on the surface layer of the cast slab. SOLUTION: At the time of pouring the molten steel 4 into the continuous casting mold 1 through the immersion nozzle 2, the molten steel partition plate 3 is arranged above the spouting hole of the immersion nozzle 2. At the same time, an iron wire 9 containing the element to be added is dipped and melted into the molten steel 4 at the upper part from this molten steel partition plate 3 to diffuse the added element into the molten steel in the upper zone. By this method, the mixture between the molten steel in the upper zone adding the element and the molten steel 4 in the lower zone flowed down from the immersion nozzle 2 is avoided, and the cast slab is shifted accompanied with drawing while forming the solidified shell 6 concentrated with the added element on the surface layer of the cast slab. The addition of the element into the molten steel at the upper part from the molten steel partition plate 3 can be executed by a method for mixing particles containing the element to be added into a mold flux 8.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a continuous casting method for molten steel.

[0002]

2. Description of the Related Art A slab surface layer modification that changes the solute concentration in the slab surface layer is extremely useful for controlling the material of the surface layer of a steel sheet. Conventionally, a method of adding an alloying element to the molten steel in the mold of the continuous casting machine by adding a wire is well known, but in this method, the additive element is dispersed throughout the cast piece, and the alloying element is concentrated only in the surface layer of the cast piece. It cannot be turned into

As a method of thickening the solute on the surface of the slab,
JP-A-55-70451 and JP-A-55-7045
No. 0 discloses a method of adding an alloy to molten steel between a partition wall installed parallel to the mold wall and the mold wall.
However, even with this method, the alloy elements added to the mold are mixed by the discharge flow of the immersion nozzle and dispersed inside the cast piece, and it is difficult to concentrate the alloy element only on the surface layer of the cast piece.

[0004]

As described above, there is currently no method for concentrating elements only on the surface layer of the slab by adding the element to the molten steel in the mold, and the slab is stable and at low cost. A method for concentrating a desired element on the surface layer is desired.

[0005]

Means for Solving the Problems The present invention, in continuous casting of steel, when molten steel is poured into a mold to produce a slab,
A molten steel partition plate is installed above the discharge port of the immersion nozzle in the mold, and one or more solute elements are added to the molten steel above this partition plate to add additional elements to the surface layer of the slab. It is a continuous casting method characterized by thickening.

[0006]

FIG. 1 is a schematic view of the continuous casting, in which molten steel 4 is poured into the mold 1 through the immersion nozzle 2 and the molten steel partition plate 3 is installed above the discharge hole of the immersion nozzle. . During casting, the molten steel 4 that has flowed into the mold 1 through the discharge holes of the immersion nozzle 2 flows out to a region below the molten steel partition plate 3. The molten steel 4 in the mold is solidified by heat removal from the molten steel to the mold, forming a solidified shell 6. The solidified shell is pulled downward at a certain casting speed, but with the movement of the solidified shell, part of the molten steel below the molten steel partition plate 3 flows into the upper region.

When the iron wire 9 containing the element to be added is immersed in the molten steel above the molten steel partition plate 3, the iron wire is melted and the additive element is mixed with the molten steel in the upper region. Since the molten steel containing the additive element is solidified in the mold portion above the partition plate, the solute element can be concentrated in the surface layer of the cast piece up to the thickness of the solidified shell at the position of the partition plate. The slab surface layer thickness at which the additive elements can be concentrated becomes thicker as the casting speed is slower and as the distance from the molten steel surface in the mold to the molten steel partition plate is longer. By changing these values, the thickness of the solute-enriched layer on the surface of the slab can be variously changed.

As a method of adding an element to the molten steel above the molten steel partition plate 3, in addition to the above-mentioned wire addition method, particles containing an element to be added are added to the mold flux 8
It is also possible to dissolve the additive element from the molten mold flux in contact with the molten steel surface into the molten steel, by mixing with the molten metal and pouring it into the molten steel surface in the mold.

Without the molten steel partition plate 3, the solute elements added by the wire are mixed by the molten steel flow caused by the discharge flow of the dipping nozzle and dispersed throughout the molten steel pool, so that the additive element concentration is dispersed throughout the slab. Will be done. Therefore, it is important to control the mixing of molten steel in the upper region and the lower region by partitioning the upper region to which the element is added and the lower region into which the discharge flow flows by the molten steel partition plate.

According to the present invention, due to the action of the molten steel partition plate, the mixing of the molten steel in the upper region added with the element and the molten steel in the lower region flowing from the dipping nozzle is extremely reduced, and the solute element is efficiently added to the surface layer of the slab. It is possible to thicken it.

[0011]

[Example] Bloom cast (thickness 300 mm, width 500 m
An experiment was conducted in which the alloy element was concentrated on the surface layer of m). In a continuous casting machine using a normal vibration copper mold, mold flux was used and molten steel of carbon steel containing 0.7 mass% of carbon as a main component was poured into the mold using an immersion nozzle. As for the casting conditions, the casting speed was 0.7 m / min, the degree of superheat of molten steel in the evening dish was in the range of about 10 to 30 ° C., and water spray was used for the secondary cooling of the cast pieces after the casting mold.

The molten steel partition plate has a length of 200 mm and a width of 400
mm, 50 mm thick, made of alumina graphite.
As shown in FIG. 3, the dipping nozzle was fixed to the upper part of the discharge hole and was installed so as to be dipped at a position about 400 mm below the molten steel meniscus.

Regarding the method of adding elements, a method of continuously adding iron wires containing Ti and Mn to the molten steel in the mold was tested. The Ti concentration in the molten steel to be poured is approximately 0, the Mn concentration is approximately 0.5 mass%, and the Ti concentration in the surface layer of the slab is approximately 0.1 mass% due to the addition of wire.
The amounts of Ti and Mn in the iron wire and the wire supply rate were adjusted so that the Mn concentration was increased to about 0.7 mass%. Also, experiments were carried out both with and without the use of molten steel partition plates.

Ti in the thickness direction of the slab obtained in the casting experiment
And changes in Mn concentration were analyzed. As a result, when the molten steel partition plate was not used, the concentrations of Ti and Mn in the slab were about 0.015 to 0.018 mass% and 0.035 to 0.035%, respectively.
It was 0.038 mass%, and it was found that the additive element could not be concentrated only in the surface layer of the cast piece, and the added element was dispersed in the entire cast piece.

On the other hand, when the molten steel partition plate is used, the concentrations of Ti and Mn in the surface layer portion up to about 19 mm from the surface of the cast slab are about 0.07 to 0.1 mass% and 0.65, respectively.
.About.0.70 mass%, the concentration inside the surface layer part is such that Ti is about 0.005 mass% or less, Mn is about 0.5 to 0.51 mass%, and the molten steel above the molten steel partition plate and the lower part It was found that it is possible to suppress the mixing of the molten steel of No. 1 and to concentrate the additive element on the surface layer of the cast slab.

[0016]

EFFECTS OF THE INVENTION By carrying out the present invention, it is possible to suppress the elements added in the mold from being dispersed in the entire slab, and to stably and inexpensively concentrate the additional elements on the surface layer of the slab.

[Brief description of drawings]

FIG. 1 is a schematic diagram when a molten steel partition plate is installed above a discharge hole of a dipping nozzle in continuous casting.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mold 2 Immersion nozzle 3 Molten steel partition plate 4 Molten steel 5 Flow direction of molten steel 6 Solidification shell 7 Moving direction of cast piece 8 Mold flux 9 Wire

Claims (1)

[Claims] 1. In continuous casting of steel, when molten steel is poured into a mold to produce a slab, a molten steel partition plate is installed above the discharge port of the immersion nozzle in the mold, and the partition plate A continuous casting method, characterized in that one or more solute elements are added to the molten steel at the upper part to enrich the additive elements in the surface layer of the slab.