KR20130014907A - Mold for continuous casting - Google Patents

Abstract

PURPOSE: A mold for continuous casting is provided to omit a grinding process by suppressing growth of a slag bear resulting in excellent surface quality by decreasing black line crack defects generated by carburizing of carbon in the superficial layer of a slab. CONSTITUTION: In a mold for continuous casting, a dummy member(8) is installed in the inner wall of the mold and at least some part of the dummy member is located to contact with the mold powder(4). The dummy member is protruded toward inside of the mold in a hemisphere shape. The maximum protruded height of the dummy member is in the range of 10-40 mm. The dummy member is being gradually protruded toward inside of the mold with reaching the upper part of the mold powder from the boundary between the molten steel and the mold powder. The dummy member includes a fixing unit being fixed to the mold and a contact unit(8a) being contacted with the inner wall of the mold. The fixing unit of the dummy member is detachably formed in the mold. The mold powder is distributed to be gradually decreasing from the center of the mold to the inner wall of the mold.

Description

Mold for continuous casting {Mold for continuous casting}

The present invention relates to a continuous casting mold, and more particularly, to a continuous casting mold provided with a dummy member capable of producing casts with reduced surface defects.

Mold powder is used in the continuous casting process of general stainless steel. The mold powder is a kind of lubrication that enables the casting operation to prevent the solidification shell and the mold from fusion when the molten steel in the mold solidifies in the continuous casting process.

More specifically, such mold powder is in powder form before heating, and is injected into the molten steel surface in the mold in a continuous casting process. At this time, lubrication is performed between the mold and the solidification shell in the molten state through the sintered state at a relatively low melting point on the molten steel surface over 1500 ℃.

In addition to lubrication, mold powder plays a very important role in continuous casting such as absorption removal of non-metallic inclusions in molten steel, insulation of molten steel and heat transfer to the mold.

Such a mold powder is composed of various components, among which carbon may be contained. However, when the carbon content in the mold powder is excessively high or the depth of the molten pool of the mold powder is shallow, the carbon is carburized in the molten steel. As a result, black bands are generated in the final cast pieces, and appear on the surface of the cast pieces as black bands.

Therefore, there is a need for a solution for solving the black band defect generated on the surface of the cast steel.

It is an object of the present invention to provide a continuous casting mold capable of reducing carbon carburization on the surface of a slab by minimizing the growth of slag bear when the mold powder is injected in the continuous casting process.

In the continuous casting mold in which the mold powder is put on the molten steel according to the present invention, a dummy member is installed on the inner wall of the mold, and at least a part of the dummy member is positioned in contact with the mold powder.

The dummy member may protrude in a hemispherical shape toward the inside of the mold.

The maximum protruding height of the dummy member may be 10 mm to 40 mm.

The dummy member may be formed to gradually protrude toward the inside of the mold toward the upper side of the mold powder from the interface between the molten steel and the mold powder.

The dummy member may include a fixing part fixed to the mold and a contact part contacting the mold inner wall.

The fixing part of the dummy member may be formed to be detachable from the mold.

The mold powder may be distributed to be lower from the center of the mold toward the inner wall of the mold.

According to the present invention, by suppressing the growth of the slag bear to a minimum, black band defects caused by carbon carburization on the surface of the slab are reduced, so that the surface quality is good and the grinding process can be omitted, thereby reducing the cost. Can be.

1 is a view showing a continuous casting device for producing a typical stainless steel.
Figure 2 is a photograph showing a defect occurred on the surface of the stainless steel produced using a mold powder containing carbon during continuous casting.
3 is a cross-sectional view showing a state of a mold powder supplied to a general mold.
4 is an enlarged view illustrating a portion A of FIG. 3.
5 is a cross-sectional view showing a layer generated when the mold powder is injected into the mold during continuous casting.
6 is a cross-sectional view showing a state of a mold powder when the dummy member according to the present invention is used in a mold.
7 is an enlarged view illustrating a portion B of FIG. 6.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to embodiments of the present invention and other details necessary for those skilled in the art to understand the present invention with reference to the accompanying drawings. However, the present invention may be embodied in various different forms within the scope of the claims, and thus the embodiments described below are merely exemplary, regardless of expression.

In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear. It should be noted that the same components in the drawings are denoted by the same reference numerals and signs as possible even if they are shown in different drawings. In addition, the thickness and size of each layer in the drawings may be exaggerated for convenience and clarity, and may differ from actual layer thicknesses and sizes.

1 is a view showing a continuous casting device for producing a general stainless steel.

Referring to FIG. 1, molten steel produced through an electric furnace and a refining furnace is cast in a ladle 1 to start casting in a continuous casting process. The molten steel 9 of the ladle 1 is transferred to the tundish 2 and again injected into the mold 5 through the immersion nozzle 3. On top of the mold 5, a mold powder 4, which serves as a lubrication between the mold 5 and the solidification shell 15 (see FIG. 5), is continuously introduced.

As such, the molten steel 9 is introduced into the copper plate mold 5 for water cooling, and discharged out of the mold 5 when solidification is started. Subsequently, the molten steel 9 is cut into a predetermined size after solidification is completed by the secondary cooling stand 6 and is produced as a slab 9a.

Figure 2 is a photograph showing a defect that occurred on the surface of the stainless steel produced using a mold powder containing carbon during continuous casting.

Referring to FIG. 2, when carbon is included in the mold powder injected during the continuous casting process, black band defects may occur on the surface of the cast steel produced after the continuous casting process. However, in the composition of the mold powder, carbon is the most important factor in determining the performance of all mold powders. The main role of carbon is to control the melt rate of the injection mold powder and to suppress the reoxidation caused by the reaction of molten steel with the atmosphere to ensure a stable casting environment and sound cast quality.

Accordingly, in order to solve the black band defect generated on the surface of the cast steel using a mold powder containing carbon, the produced cast steel was ground to remove surface layer defects. However, in this case, expensive cast loss (about 2 mm loss in one grinding) occurs. In addition, the cost of grinding the cast steel is high.

In the present invention, the dummy member is provided on the inner wall of the mold during continuous casting, thereby minimizing the growth of the slag bear during the injection of the mold powder, thereby having a good cast quality without black band defects.

3 is a cross-sectional view illustrating a state of a mold powder supplied to a general mold, and FIG. 4 is an enlarged view illustrating part A of FIG. 3.

3 and 4, after injecting molten steel 9 into the mold 5, a mold powder acting as a lubrication between the mold 5 and the solidification shell 15 (see FIG. 5) on the molten steel 9. Input (4). In addition to the lubrication function, the mold powder 4 plays a very important role in continuous casting such as absorption removal of non-metallic inclusions in the molten steel 9, thermal insulation of the molten steel 9, and heat transfer control to the mold 5.

This mold powder 4 can be sprayed directly by the operator directly into the mold or automatically supplied to the mold powder supply 7. At this time, the slag bear 4a is grown on the edge of the mold 5 through the following steps.

First, the mold powder 4 is introduced into the mold 5 (S11). Then, the inner wall of the mold 5 in which the mold 5 and the mold powder 4 abut due to uneven melting by the immersion nozzle 3. In the mold powder 4 is stacked the highest (S12).

In this state, when the mold 5 oscillates, a gap is generated between the mold 5 and the mold powder 4, and the slag bear 4a and the molten slag layer 12 (see FIG. 5) are brought into the atmosphere. Exposed. As a result, uneven carbon grows in the slag bear 4a due to uneven heat dissipation (S13).

5 is a cross-sectional view showing a layer generated when the mold powder is introduced into a mold during continuous casting.

Referring to FIG. 5, when the mold powder 4 (see FIG. 3) is introduced into the molten steel 9, the powder layer 10, the sintered layer 11, and the molten slag layer 12 may be caused by radiant heat of the molten steel 9. ) Is formed, and a slag bear 4a is generated near the water-cooled mold 5. Among them, the molten slag layer 12 flows between the solidification shell 15 and the copper plate mold 5 and lubricates, thereby enabling continuous casting.

The slag bear 4a is generated when carbon contained in the mold powder 4 is burned by heat. Over time, the slag bear 13 grows larger and larger at the edge of the mold 5. The slag bare 4a forms a carbon accumulation portion 14 in which carbon is integrated in the lower slag layer.

When the distance between the slag bear 4a and the initial solidification shell 15 is short, the supply of the molten slag layer 12 is not smooth, and the carbon accumulation portion 14 of the lower layer of the slag bear 4a is carburized in the slab. To form. As a result, black band defects are generated in the coil after annealing of the cast steel. Therefore, in the present invention, it is possible to reduce the growth of the slag bare 4a so that the carbon accumulation portion 14 generated in the slag lower layer portion does not react with the slab. To this end, a dummy member 8 (see FIG. 6) capable of controlling the distribution of the mold powder 4 may be installed on the inner wall of the mold 5 to reduce black band defects.

6 is a cross-sectional view showing a state of a mold powder when the dummy member according to the present invention is used in a mold, and FIG. 7 is an enlarged view showing part B of FIG.

6 and 7, a dummy member 8 is installed on the inner wall of the continuous casting mold 4 into which the mold powder 4 is placed on the molten steel 9 according to the present invention. At least a part of this dummy member 8 is positioned to be in contact with the mold powder 4. The dummy member 8 may include a fixing part 8b fixed to the mold 5 and a contact part 8a contacting the inner wall of the mold 5.

At this time, the fixing part 8b of the dummy member 8 may be detachably formed on the mold 5. For example, the fixing part 8b of the dummy member 8 may be formed in a hook shape.

In addition, the contact portion 8a of the dummy member 8 may protrude in a hemispherical shape toward the inside of the mold 5. At this time, the protruding height of the contact portion 8a of the dummy member 8 may be 10 mm to 40 mm. When the protruding height of the dummy member 8 contact portion 8a exceeds 40 mm, a bridge phenomenon in which the immersion nozzle and the dummy member 8 are connected is generated, resulting in breakout. When the protruding height of the contact portion 8a of the dummy member 8 is less than 10 mm, the variation of the surface defects is very large, and there is a problem that the size of the slag bear 4a is not reduced.

When the dummy member 8 of the mold powder 4 is formed in a hemispherical shape, the mold member 4 gradually goes toward the inside of the mold 5 from the interface between the molten steel 9 and the mold powder 4 toward the upper side of the mold powder 4. Protruding portions may be located.

By installing the dummy member 8 for controlling the distribution of the mold powder 4 of the present invention in the inner star of the mold 5 and supplying the mold powder 4, the mold powder 4 is formed on the inner wall of the mold 5 in the following steps. It is possible to suppress the growth of the slag bear 4a.

First, a dummy member 8 capable of controlling the distribution of the mold powder 4 is provided on the inner wall of the mold 5 (S21). After that, the mold powder 4 is formed by the temperature of the molten steel 9. It is melted and formed of a powder layer, a sintered layer, and a molten slab layer. Then, the mold powder 4 is homogenized and heat flux uniformed (S22). At this time, since the dummy member 8 is provided at the position where the mold powder 4 contacts the inner wall of the mold 5, the slag bare Growth of (4a) is suppressed. Here, the mold powder 4 may be distributed by the dummy member 8 so as to be lowered toward the inner wall of the mold 5 from the center of the mold 5 (S23).

Hereinafter, the present invention will be described in more detail with reference to Examples.

The description of these examples is only intended to illustrate the practice of the invention, and the invention is not limited by the description of these examples.

(Example)

In the continuous casting of ferritic stainless steel, the test result of the height of the protrusion of the dummy member 8 for controlling the distribution of the mold powder 4 is controlled.

division Protruding height (mm) of dummy member for distribution control of mold powder Slag Bear Size (mm) % Defective Conventional material none 42 9.33 Comparison 1 45 5 Breakout occurs Comparative material 2 5 35 4.2 Inventory 1 10 24 1.33 Inventory 2 15 22 1.04 Inventory 3 20 10 0.30 Invention 4 25 5 Not occurring Invention Article 5 30 5 Not occurring Inventions 6 35 6 Not occurring Invention 7 40 4 Not occurring

As shown in Table 1, in the case of the mold 5 without the mold powder 4 dummy member 8 for distribution control, the growth of the slag bear 4a was excessively 42 mm, resulting in a 9.33% black band defect incidence rate. It was.

In the case of Inventive Material 1 to Inventive Material 6, the size of the slag bear 4a decreased as the protrusion height of the mold member 4 distribution control dummy member 8 increased in the range of 10 mm to 40 mm. And the defect incidence rate generated only 1.33% (invention material 1) at most, and the defect was not generate | occur | produced in invention material 4-7.

For example, in the case of Inventive Material 1, the protruding height of the dummy member 8 was set to be 10 mm, whereby the size of the slag bear was reduced to 24 mm, and the defect occurrence rate was also reduced to 1.33%. Further, Inventive Materials 4 to 7 were installed so that the protruding height of the dummy member 8 was 25 mm to 40 mm, in which the sizes of the slag bear 4a were 5 mm, 5 mm, 6 mm, and 4 mm, respectively. Was reduced. Moreover, it turns out that no defect generate | occur | produced on the surface of a cast steel.

However, as in Comparative Material 1, when the protruding height of the dummy member 8 was 45 mm, the size of the slag bear 4a was 5 mm, similar to that of the slag bear 4a according to the present invention. However, there is a problem in that a bridge phenomenon in which the immersion nozzle 3 and the dummy member 4a are connected and breakout occurs.

In addition, as in Comparative Material 2, when the projecting height of the dummy member 8 was 5 mm, the size of the slag bear 4a was 35 mm, which was not reduced at all compared with the conventional material. And although the defect generation rate was 4.2%, there existed a problem that the deviation of defect generation was very large.

As a result, in the case of continuous casting using the mold 5 having the dummy member 8 according to the present invention, the surface defect of the slab due to carburization of carbon can be remarkably improved by reducing the size of the slag bear 4a. Can be.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. It will be apparent to those skilled in the art that various modifications may be made without departing from the scope of the present invention.

The scope of the above-described invention is defined in the following claims, which are not bound by the description of the specification, and all modifications and variations belonging to the equivalent scope of the claims will belong to the scope of the present invention.

1: ladle 2: tundish
3: immersion nozzle 4: mold powder
5: mold 6: secondary cooling stand
7: mold powder supply unit 8: dummy member
8a: contacting part 8b: fixing part
9: molten steel 9a: cast steel
10 mold powder layer 11 sintered layer
12: molten slag layer 13: slag bear
14: carbon integrated part 15: coagulation cell

Claims (7)

In the continuous casting mold in which the mold powder is put on the molten steel,
A dummy member is installed on the inner wall of the mold, and at least a part of the dummy member is positioned to be in contact with the mold powder. The method of claim 1,
The dummy member is a mold for continuous casting, characterized in that protruding in a hemisphere shape toward the inside of the mold. The method of claim 2,
Continuous casting mold, characterized in that the maximum protruding height of the dummy member is formed from 10mm to 40mm. The method of claim 1,
The dummy member is a continuous casting mold, characterized in that to protrude gradually toward the inside of the mold toward the mold powder from the interface between the molten steel and the mold powder. The method of claim 1,
The dummy member includes a fixing part fixed to the mold and a contact part in contact with the inner wall of the mold. The method of claim 5,
The fixed part of the dummy member is a mold for continuous casting, characterized in that formed on the mold detachable. The method of claim 1,
And the mold powder is distributed to be lowered toward the inner wall of the mold from the center of the mold.

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