JPH11197807A - Immersion nozzle for multilayer slab casting and method for manufacturing multilayer slab - Google Patents

Abstract

(57) [Abstract] [Problem] To provide a production technique by continuous casting of a multilayer slab which is easy and economically advantageous in controlling the flow rate of molten steel and does not induce powder entrainment. SOLUTION: Injecting molten steel from a tundish 4 into a casting mold 1 in accordance with a continuous casting method of steel in which a static magnetic field is applied in one or more stages in a casting direction to perform casting. Outlets 2c and 2d, a molten steel channel which communicates with each of the discharge ports and is separated from each other by a partition wall 2f, and an auxiliary material addition port 2a and / or 2 which communicates with only one of the molten steel channels.
The molten steels 5 and 6 in the respective molten steel channels are made to have different compositions from each other by adding a sub-material through the sub-material addition port using the immersion nozzle 2 for multilayer slab casting comprising Are separately injected above and below the static magnetic field.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an immersion nozzle for casting a multi-layer slab and a method for producing a multi-layer slab, which can be produced with high quality and economically by continuous casting.

[0002]

2. Description of the Related Art Continuous casting of a multilayer slab having a composition different from the surface layer portion (outer peripheral portion) and the inner portion of a slab is required.
This is important because it leads to significant cost reductions and further expansion of the market is expected. For this reason, various studies and studies have been made on the continuous casting method of multilayer slabs.
Development is progressing, and some of them have reached the level of practical use.

For example, JP-A-5-208244, JP-A-4-270032, JP-A-4-313447, and JP-A-4
No. 313448, Japanese Patent Application Laid-Open No. 4-313449, etc., as disclosed as a series of techniques, molten steel of different composition is injected into a mold using a plurality of nozzles, and the injected molten steel is further subjected to a magnetic field. There is known a technique of separating by means of a filter. They are,
This is a clever method of manufacturing a multilayer slab by individually controlling the flow rate of molten steel of different composition (hereinafter, appropriately referred to as different types of molten steel) and performing casting while preventing mutual mixing with a magnetic field. However, it is difficult to control the flow rate of the molten steel and control the temperature during casting, and it is necessary to prepare at least twice as many devices as a ladle, a nozzle, a tundish, and the like, which is not economically advantageous.

On the other hand, Japanese Patent Application Laid-Open Nos.
As disclosed in JP-A-122833 or the like, a method is also known in which an alloy element is added from the upper part of a mold using powder or powder + wire. This method is more economically advantageous than the method using a plurality of nozzles. Here, the problem of non-uniformity of the component concentration in the molten steel caused only by addition from the wire or powder is addressed by stirring in the mold, so that the component concentration in the upper part of the mold is well uniformed. ing. Further, it is completely separated from the molten steel in the lower part of the mold by a static magnetic field. However, these methods have a serious disadvantage that powder stirring is induced due to stirring in the mold in order to make the component concentrations uniform, resulting in deterioration of slab quality. In addition, when added from a wire, there is a fear that powder entrainment is further promoted by introducing the wire into molten steel. In addition, the addition of powder also sacrifices the inherent lubricating function of the powder, so that lubrication is not sufficiently performed, and breakout due to seizure is liable to occur.

[0005]

As described above, in the method of injecting different types of molten steel into the mold from separate nozzles, it is difficult to control the flow rate of molten steel and the like, and it is economically disadvantageous because the number of devices is increased. In addition, in the method of adding an alloy component from a wire or powder, stirring in a mold is required, so that there is a problem in that the slab quality is deteriorated due to induction of powder entrainment.

SUMMARY OF THE INVENTION An object of the present invention is to overcome the problems of the prior art, to easily control the flow rate of molten steel, to be economically advantageous, and to produce a multi-layer slab by continuous casting which does not induce powder entrainment. Is to provide.

[0007]

SUMMARY OF THE INVENTION The present invention relates to an immersion nozzle for use in continuous casting, which supplies molten steel from a tundish into a mold, and has a multistage discharge port in a vertical direction, which communicates with each of the discharge ports. A multi-layer slab casting characterized by having a molten steel channel separated from each other by partition walls, and further having at least one auxiliary material addition port communicating with only one of the molten steel channels. Immersion nozzle.

The present invention also relates to a method for casting molten steel from a tundish into a mold in accordance with a continuous casting method of steel in which a static magnetic field is applied in one or more stages in a casting direction. The molten steel in each molten steel channel is made to have a different composition from each other by adding the auxiliary material from the auxiliary material addition port using a slab casting immersion nozzle, and the molten steel having the different composition is separately injected above and below the static magnetic field. A method for producing a multilayer cast slab.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The gist of the present invention will be described with reference to FIG. 1A is a structural explanatory view of the periphery of the nozzle as viewed from the short side of the mold, and FIG. In the present invention, as a nozzle (immersion nozzle) 2 for supplying molten steel from the tundish 4 into the mold 1, the nozzle 2 has multiple outlets 2 c and 2 d in the vertical direction (two stages are illustrated in FIG. 1). 2
The molten steel flow path communicating with each of c and 2d is separated from each other by a partition wall 2f, and has a multi-layer slab casting having an auxiliary material addition port 2a and / or 2b communicating with only one of the molten steel flow paths. Immersion nozzle 2 is used. In FIG. 1,
Reference numeral 7 denotes a powder (mold powder).

Then, a tundish is applied in accordance with a continuous casting method of steel in which a static magnetic field is applied by a static magnetic field generator 3 (one step is illustrated in FIG. 1) provided in one or more stages in the casting direction. Injecting molten steel into mold 2 from nozzle 4
By adding an auxiliary material from the auxiliary material addition ports 2a and / or 2b, the molten steels in the respective molten steel flow paths have different compositions, and the molten steels having different compositions are separately injected above and below the static magnetic field.

According to this configuration, the auxiliary raw material is added to one or more of the molten steel passages in one dipping nozzle 2 and completely separated by the partition wall 2f. (Molten steel) 5, 6 can be easily produced independently of each other without mixing, and the component concentrations can be made uniform without stirring in the mold, so that powder entrainment is not induced. The molten steels 5 and 6 from the discharge ports 2 c and 2 d are respectively separated and discharged in the upper and lower portions of the mold 2, and are forcibly moved above and below the static magnetic field by the static magnetic field applied by the static magnetic field generator 3. Since they are separated, mixing in the mold 2 is also prevented. As a result, the molten steel 5
The solidified shell 51 of the molten steel 6 is provided on the inner side.
However, each of them grows without being mixed in composition, and a sound multilayer slab can be obtained.

The immersion nozzle 2 having such a plurality of molten steel channels can be easily manufactured. And since only one such immersion nozzle 2 is required, it is not necessary to prepare a nozzle and other devices for each different type of molten steel as in the prior art, and it is economically advantageous because it is possible to avoid upsizing of equipment. When a plurality of molten steel flow paths are partitioned by the partition wall 2f, the flow path cross-sectional area ratio in the nozzle is designed in accordance with the ratio of different types of molten steel to be solidified as a multilayer cast slab. When the ratio becomes too small, the cross-sectional area ratio is not adjusted by changing the thickness of the partition wall 2f. For example, as shown in FIG. It is better to adjust by changing the size.

[0013]

(Example 1) 0.5% of Cr, 0.3% of Cu and 0.3% of Ni are present on the outer periphery (10mm in thickness) of a slab 260 mm thick x 1600 mm wide.
A casting experiment was conducted to produce a low carbon steel multi-layer cast slab 1%, each of which was enriched, according to the present invention. As a mold (mold), a water-cooled Cu mold is used. As shown in FIG. 2, a DC magnetic field (3) is formed by using static magnetic field generators 3 and 3 arranged in two steps in the casting direction (casting direction) on the long side of the mold. A static magnetic field) is applied, and the nozzle 2 has an auxiliary material addition port 2a which communicates only with the discharge port 2c opened in the upper part of the mold. It was made to be. The casting speed was 1.2 m / s. The auxiliary materials were added while sealing with Ar gas.

In order to confirm the separation effect by applying a static magnetic field, casting was performed while changing the strength of the magnetic field at four levels of 0.1T, 0.3T, 0.5T, and 0.7T, and the component concentration distribution in the cross section of the slab after casting. Was measured. FIG. 3 illustrates the relationship between the strength of the magnetic field and the component concentration distribution in the cross section of the slab. In FIG. 3, the component is Cr, and the concentration is an index value normalized by setting the chemical analysis value at each site to 100 at the outermost periphery. As illustrated in FIG. 3, a layer separation state in which components are switched in a stepwise manner from the height of the outer peripheral portion to the inner lower portion at the interface between the outer peripheral portion and the inner portion by applying a static magnetic field having a strength of 0.3 T or more is good (clear). It has been found that a multilayer slab (having a natural interface) can be obtained. Further, in Example 1, no slab defect due to entrainment of mold powder was observed.

(Example 2) The composition of an outer peripheral portion (thickness 10 mm) of a cast slab having a thickness of 260 mm and a width of 1200 mm was 0.04% for C and Si for Trace.
, Mn: 0.3%, P: 0.02% or less, S: 0.01% or less, and the internal composition is C: 0.14%, Si: 0.28%, Mn: 1.3%,
Example 2 A casting experiment was conducted to produce a multilayer slab having a surface layer softening in which P: 0.02% or less and S: 0.01% or less according to the present invention.
And As the mold, a water-cooled Cu mold is used. As shown in FIG. 2, a DC magnetic field (static magnetic field) is generated by using static magnetic field generators 3, 3 arranged in two stages in the casting direction (casting direction) on the long side of the mold.
Is applied, and the nozzle 2 has a discharge port 2d opening at the lower part in the mold.
A material having an auxiliary material addition port 2b that communicates only with the raw material was used, and the auxiliary material was added from there to concentrate the components in the slab. The casting speed was 1.0 m / s. The auxiliary materials were added while sealing with Ar gas.

In order to confirm the separation effect by applying a static magnetic field, the strength of the magnetic field was set to 0.1T, 0.3T, 0.5T,
Casting was performed while changing the four levels of 0.7T, and the component concentration distribution in the cross section of the slab after casting was measured. As a result, although not shown, a layer separation state in which the component concentration switches stepwise from low in the outer portion to high in the inner portion at the interface between the outer portion and the inner portion by applying a static magnetic field having a strength of 0.3 T or more is good. It was found that a multilayer slab (having a clear interface as in Example 1) was obtained.
Then, as in Example 1, no slab defect due to entrainment of the mold powder was observed in Example 2.

As described above, according to the present invention, it is apparent that the composition can be easily changed in both the outer peripheral portion and the inner portion of the multilayer slab, and that the slab quality is not deteriorated.

[0018]

As described above, according to the present invention, it is possible to produce a multilayer slab having a high quality and a clear interface at a low cost, and to add an auxiliary material to both the outer peripheral portion and the inner portion of the slab. Thus, a remarkable effect is obtained that the composition can be freely changed.

[Brief description of the drawings]

FIG. 1A is a structural explanatory view of the vicinity of a nozzle as viewed from the short side of a mold, and FIG.

FIG. 2 is a structural explanatory view around a nozzle as viewed from a long side of a mold according to an embodiment.

FIG. 3 is a graph showing an example of a relationship between a magnetic field strength and a component concentration distribution in a cross section of a slab.

[Description of Signs] 1 Mold 2 Nozzle (immersion nozzle, immersion nozzle for multilayer slab casting) 2a, 2b Sub-material addition port 2c, 2d Discharge port 2f Partition wall 2g Flow rate controller 3 Static magnetic field generator 4 Tan Dish 5, 6 Molten steel (different molten steel) 7 Powder (mold powder) 51 Solidified shell of molten steel 5 61 Solidified shell of molten steel 6

Claims (2)

[Claims] 1. An immersion nozzle for use in continuous casting, for supplying molten steel from a tundish into a mold, wherein the molten steel is provided with a plurality of discharge ports in an up-down direction and each of the discharge ports is partitioned by a partition wall. And at least one auxiliary material addition port that communicates with only one of the molten steel channels.
An immersion nozzle for casting a multilayer slab, comprising: 2. The method according to claim 1, wherein the molten steel is poured into the mold from a tundish in accordance with a continuous casting method of steel in which a static magnetic field is applied in one or more stages in the casting direction. The molten steel in each molten steel channel is made to have a different composition from each other by adding the auxiliary material from the auxiliary material addition port using a slab casting immersion nozzle, and the molten steel having the different composition is separately injected above and below the static magnetic field. A method for producing a multilayer slab.