JPH0740009A - Continuous casting method by constant immersed depth of nozzle - Google Patents

Abstract

PURPOSE:To provide a continuous casting method, by which a nozzle is immersed into molten steel while keeping good slagging condition without entrapping protecting agent for molten steel surface. CONSTITUTION:The molten steel is poured into a mold through a straight immersion nozzle arranging a discharging hole at the tip part from a tundish to execute the continuous casting. The immersion nozzle 2 forming an easy-to-erode material with the molten steel in the tip part 2a and a difficult-to-erode material with the molten steel in the other parts 2b, 2c. The eroded quantity of the tip part 2a of the immersion nozzle with the molten steel with the lapse of time is beforehand measured, and the tun-dish is descended with the lapse of casting time based on the measured result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for continuously casting molten metal such as steel and stainless steel.

[0002]

2. Description of the Related Art Generally, in continuous casting of molten steel, when casting molten steel in a ladle into a mold through a tundish, an injection flow is oxidized to ambient air and a product generated by the oxidation is a slab. In many cases, it adheres to and adheres to the steel, resulting in a marked deterioration of steel quality.

In order to prevent this air oxidation, it is necessary to interrupt the contact between molten steel and air. As shown in FIG. 1, a single hole straight immersion nozzle 2 is provided between a tundish (not shown) and the mold 1. (Hereinafter, simply referred to as a dipping nozzle) is arranged, and further, the powder surface protective material 3 for continuous casting is provided on the surface of the mold.
The method of floating (hereinafter referred to as CC powder) is widely adopted in continuous casting.

However, CC used as a surface protection material
The powder is usually CaO, SiO ₂A whose main component is
Low basicity, low melting material blended with Lucari fluoride carbon
And Al as a deoxidation product₂O₃Easy to melt
The composition is such that it can be caulked, and it is added to molten steel.
After melting, it melts due to the temperature of the molten steel, becomes a molten state, and floats on the molten metal surface.
I'm thinking. As mentioned above, CC powder is Al₂O₃
Since it has the effect of easily melting the
It easily reacts with the alumina component of and dissolves.

Therefore, Japanese Unexamined Patent Publication No. 50-55539.
Japanese Unexamined Patent Publication (Kokai) No. 57-32858 proposes an immersion nozzle having high powder resistance.

[0006]

By the way, the depth of immersion of the nozzle in the molten steel affects the entrainment / slagging of the CC powder. As shown in FIG. 5, when the immersion depth of the nozzle into the molten steel becomes shallow, the heat supply to the molten metal surface becomes large and the slag formation of the CC powder becomes good. Further, when the depth of immersion of the nozzle in the molten steel becomes shallow, CC powder is entrained along the wall surface of the nozzle, which causes a problem that the quality of steel deteriorates.
Therefore, it is necessary to control the immersion depth of the nozzle into the molten steel in consideration of the inclusion and slag formation of the CC powder.

However, the immersion nozzles proposed in the above-mentioned JP-A-50-55539 and JP-A-57-32858 have a high powder resistance and thus have a long use time, but the nozzle is If it is not moved, melting damage will locally progress at the contact portion with the CC powder and the nozzle will eventually be cut. Therefore, even when these immersion nozzles are used, as shown in FIG. , The immersion depth of the nozzle into the molten steel must be changed according to the casting time. That is, in continuous casting using these immersion nozzles, it is not possible to carry out operations in consideration of slagging and entrainment of CC powder.

[0008] Therefore, an object of the present invention is to provide a continuous casting method in which a nozzle is immersed in molten steel while maintaining a good state of slag formation without the inclusion of CC powder.

[0009]

In order to achieve the above object, the present invention is a method for continuously casting molten steel from a tundish into a mold through an immersion nozzle having a discharge hole at its tip. Therefore, use an immersion nozzle whose tip is made of a material that is more susceptible to corrosion than molten steel and the other part is made of a material that is less susceptible to corrosion than molten steel. It is measured, and based on the measured result, the tundish is lowered as the casting time elapses.

[0010]

The present invention is a method for continuously casting molten steel into a mold from a tundish through a dipping nozzle provided with a discharge hole at its tip, which is a material which is more easily eroded than molten steel at its tip. Using other parts of the immersion nozzle formed of a material that is more resistant to corrosion than molten steel, the amount of corrosion of the tip of this immersion nozzle with molten steel is measured in advance over time, and based on the results of the measurement, the casting time Since the tundish is lowered with the lapse of time, casting can be performed while always keeping the immersion depth of the nozzle in the molten steel constant.

[0011]

An embodiment of the present invention will be described below with reference to the accompanying drawings. FIG. 2 is a diagram showing the structure of an immersion nozzle used in the method of the present invention.

In FIG. 2, reference numeral 2 is an immersion nozzle used in the present invention, and the tip portion 2a is made of a material such as SiO _{2 which} is easily melted in the molten steel in the mold, and the end surface is formed into an inclined shape. The portion 2c is made of Al ₂ O ₃ -C quality, and the protector portion 2b located in the CC powder during operation is made of ZrO ₂ -C quality material which is difficult to melt into CC powder.

The present invention is carried out by using the nozzle having the above-mentioned structure, and the melting rate of the SiO ₂ substance forming the tip portion 2a of the nozzle 2 is measured in advance, and the tip portion 2a of the tip portion 2a is measured. The tundish is lowered with the lapse of time according to the melting rate.

At this time, since the tip portion 2a of the nozzle 2 immersed in the molten steel has an inclined end surface, the CC powder dissolved in the molten steel causes the melting to proceed, but the shape changes. The length of the nozzle 2 changes without doing so. Since the tundish is lowered according to the speed at which the tip 2a of the nozzle 2 melts, the length of the nozzle 2 immersed in the molten steel is always kept constant.

As described above, since the length of the nozzle immersed in the molten steel is always kept constant, it is possible to maintain a good state of slag formation without the inclusion of CC powder. Figure 3
FIG. 4 shows the casting time and the molten metal surface temperature in the casting by the method of the present invention and the casting by the conventional method, and FIG. 4 shows the defect occurrence rate due to the inclusion of slag in the casting by the method of the present invention and the casting by the conventional method.

From FIGS. 3 and 4, it is clear that when the continuous casting method of the present invention is used, the molten metal surface temperature is kept stable at a high temperature and the defect occurrence rate due to the inclusion of slag is reduced as compared with the conventional method. is there.

[0017]

As described above, according to the method of the present invention, the length of the nozzle immersed in the molten steel is always kept constant, and CC powder is not entrained in the molten steel in a good state of slag formation. Since casting can be performed, the quality of steel is stable and the occurrence of defects is reduced.

[Brief description of drawings]

FIG. 1 is a view showing a situation in which an immersion nozzle is arranged between a tundish and a mold.

FIG. 2 is a diagram showing a configuration of an immersion nozzle used in the method of the present invention.

FIG. 3 is a diagram showing a casting time and a molten metal surface temperature in casting by the method of the present invention and casting by the conventional method.

FIG. 4 is a diagram showing a defect occurrence rate due to mixing of slag in casting by the method of the present invention and casting by the conventional method.

FIG. 5 (a) is a diagram showing the relationship between the immersion depth of a nozzle into molten steel and the inclusion of CC powder, and FIG. 5 (b) is a relationship between the immersion depth of a nozzle into molten steel and the formation of CC powder. It is a figure.

FIG. 6 is a diagram showing the relationship between the casting time and the immersion depth of the nozzle into the molten steel in the conventional method.

[Explanation of symbols]

 1 Mold 2 Immersion Nozzle 2a Tip 2b Protector 2c Base Metal 3 Powder casting surface protection material for continuous casting

Claims (1)

[Claims] 1. A method for continuous casting by injecting molten steel into a mold from a tundish through a single-hole straight immersion nozzle having a discharge hole at its tip, which is made of a material that is more likely to corrode than molten steel at its tip. , The other portion is formed of a material that is more resistant to corrosion than molten steel, the amount of corrosion of the tip of this immersion nozzle due to molten steel is measured in advance over time, and the casting time is based on the measured result. The continuous casting method with a constant nozzle immersion depth, characterized in that the tundish is lowered with the passage of.