JPS5948696B2 - Method for producing clean steel in continuous casting - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing clean steel that reduces non-metallic inclusions in continuously cast slabs.

In conventional continuous casting of steel, molten steel is poured from a ladle into a trough by adjusting the opening of a sliding nozzle 2 attached to the bottom of a ladle 1, as shown in FIG. The tip of the long nozzle 3 located at the bottom of the tundish is immersed in the molten steel 4 in the tundish.

However, when replacing the ladle, as shown in Figs.
When injection of molten steel from the rear ladle is started while the steel is immersed, the base metal 7 and slag 5 will adhere to the surface of the molten steel in the tundish of the nozzle 3, or the silica sand grains 8 that have stopped the molten steel in the rear ladle may fall and adhere. As a result, the tip of the nozzle 3 is blocked, and the molten steel injection flow 9 from the rear pan is filled with deposits 5. 7. Due to the resistance of the sliding nozzle 2 and the long nozzle 3, the long nozzle 3 is rapidly filled without entering the container 6, causing the problem that it is blown out from the joint between the sliding nozzle 2 and the long nozzle 3.

Therefore, as a safety measure, a method is adopted in which the molten steel surface is lowered only when pouring into the rear ladle is started and the tip of the long nozzle 3 is exposed to the atmosphere.

By this method, it is possible to prevent the metal 7, slag 5, etc. from adhering to the long nozzle 3, and the silica sand grains 8 are washed away by the injection flow 9. On the other hand, the slag layer 5 that flows out from the pot at the end of the front wheel injection and is floating on the surface of the molten steel 4 in the tundish is blown out by the injection flow 9 from the long nozzle 3. Of the slag thrown into the inside of the molten steel 4 in the tundish, although it varies depending on the tundish capacity, casting speed, etc.
Those with a particle size of 100μ or more will resurface, but
If it is less than 100 μm, it will be injected into the mold together with the molten steel flow and become non-metallic inclusions in the slab, causing a significant deterioration in the quality of the slab.

In order to solve the above-mentioned problems, several methods have been tried in the past.

That is, there is a method (1) of removing the slag layer directly below the long nozzle by blowing gas from gas injection pipes provided on both sides of the long nozzle.

With this method, there is a limit to the thickness of the slag layer that can be blown away, making it extremely difficult to control the slag thickness.
Since a large amount of gas is blown, there are problems such as splash and dust generation.

Another method is to install a weir inside the tank to make it easier for the slag to float, but with this method, it is difficult to completely float the slag.

Furthermore, there is a method to remove slag by inserting a tube inside the tanditshu, but this method does not require a tube.

Or, since the weight is attached to the pipe body, it becomes very heavy, resulting in poor workability and impractical.

As mentioned above, the conventional methods cannot sufficiently achieve the effects expected by the applicant.

Therefore, the present invention provides a method for obtaining clean steel as expressed by grade A in Table 1, and its feature is that in continuous casting of molten steel, the next time the molten steel in the ladle continues from the previous time in the ladle, A slag breaker is installed in the long nozzle to supply the
A method for manufacturing clean steel in continuous casting, characterized in that the lower end of the cylinder of the slag breaker is immersed in the molten metal so that it is located at least 20 mm below the surface of the tundish molten metal.

Hereinafter, the present invention will be described based on an example of an apparatus used for carrying out the present invention.

FIG. 3 shows an example of the invention.

The tube 10 used in the present invention needs to have an inner diameter of 600 mmφ from the long nozzle outer diameter.

This is determined by the diameter that can store sand in the filling of the ladle SH and the diameter that can overcome the levitation required to immerse the thin iron plate 11 in the molten steel in the initial state in which the thin iron plate 11 is attached to the tube 10.

Further, the tube 10 must not melt for at least one minute until the tundish hot water level 12 is immersed in the lower end of the long sozzle after the start of pouring, and for example, asbestos or the like must be selected.

In addition, the thickness is 0.3 to 2.0 mm to prevent the slag 5 from penetrating into the tube 10 when the lower end of the tube 10 is immersed in molten steel. It is necessary to attach a thin iron plate 11 of 0 mm.

Furthermore, in order to immerse the cylinder 10 with the thin iron plate 11 attached thereto at least 20 mm below the hot water surface 12 using a long nozzle (Fig. 3), and to prevent the cylinder 10 from floating up, a shelf 13 is installed.
need to be installed.

Hereinafter, one embodiment for carrying out the present invention will be described in detail, and its effects will be described.

As shown in one embodiment in FIG. 3, 3 is a long nozzle, and 10 is a cylinder made of, for example, asbestos.

A shelf 13 is made of, for example, round steel (6 mmφ) and locks the cylinder 10 thereon.

5 represents floating slag, and 12 represents the tanditsu hot water surface.

11 is a thin iron plate having a thickness of 0.7 mm, for example.

Examples of dimensions are as follows. L, 750mm
1.350 mm It can be seen that inclusions in the slab can be significantly reduced.

By applying the present invention configured as described above, problems such as the molten steel blowing out from the joint between the sliding nozzle and the long nozzle, and the increase in inclusions in the slab due to inclusions being thrown in by the molten steel flow can be solved, and the ladle can be replaced. It is possible to significantly improve the yield of slabs immediately after this process.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing how molten steel is poured into a tundish in conventional continuous casting. Fig. 2 is a partially enlarged view of Fig. 1, showing how troubles occur during injection of molten steel, Fig. 3 is an example of equipment used to carry out the present invention, and Fig. 4 shows the immersion depth of the cylinder. FIG. 5 shows the relationship between the slag cutting index and the nozzle immersion depth.

Claims (1)

[Claims] 1. In continuous casting of molten steel, when supplying the next molten steel in the ladle to the tundish following the previous ladle, a slag breaker is attached to the long nozzle, and the lower end of the cylinder of the slag breaker is at least 20 mm below the tundish hot water level. A method for manufacturing clean steel in continuous casting, characterized in that the injection is performed by immersing the steel so as to be positioned in the molten metal.