JPS6325862B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous casting method, and its main purpose is to reduce the air oxidation of the injection flow and the molten metal surface of the tundish when starting to pour molten metal from a ladle into a tundish. The purpose is to prevent the slag floating above from penetrating into the bath and to avoid contamination of the molten metal by the slag, thereby obtaining a high quality slab at the initial stage of casting.

In continuous casting, molten metal is first injected from a ladle to a predetermined level in a tundish, and then, while maintaining this level, it is injected from the tundish into a mold to start continuous casting. Also, when changing the ladle for so-called continuous casting, in which several charges of molten metal are continuously cast while changing the ladle, the level of the molten metal in the tundish is maintained until the next ladle starts pouring the molten metal. The level decreases to a lower permissible limit set below the predetermined level.

While the molten metal in the tundish bath is maintained at a predetermined level, that is, during the middle period of steady casting, the pouring part of the ladle and the inside of the tundish bath are connected through a long nozzle, which prevents air oxidation of the molten metal injection flow. However, when starting the injection of molten metal during the initial stage of continuous casting and when changing the ladle in continuous casting, it is possible to prevent the injection of molten metal from flowing down between the lower end of the long nozzle and the surface of the molten metal below a predetermined level. When the flow comes into contact with the atmosphere, it is exposed to air oxidation and slag floating on the surface of the molten metal is thrown in, resulting in significant contamination of the molten metal. Continuously cast slabs from this period have more non-metallic inclusions than slabs from other periods. It also contains a large amount of oxidized inclusions, which has a large adverse effect on quality and is a major cause of a decrease in yield.

For this reason, attempts have been made to use large-scale equipment to replace the air in the tundish with inert gas, but this approach deteriorates work efficiency and cannot prevent the slag from being rolled in. was strongly requested.

The present invention provides an excellent method that solves these problems all at once in a simple manner.The present invention is characterized by the use of a durable long nozzle connected to the molten metal pouring part of the ladle. The lower end of the long nozzle is positioned in advance at a predetermined level below the melt surface of the tundish, and a soluble nozzle mainly composed of a composition with a melting point lower than the temperature of the molten metal is connected to the lower end of the long nozzle, and its lower end is positioned at the bottom of the tundish. A continuous casting method characterized by starting the injection of molten steel from a pot into a tundish. There is a continuous casting method in which pouring of molten metal into a tundish from the ladle is started.

That is, the present invention includes a soluble nozzle having a composition that melts at a temperature lower than the molten metal temperature at the lower end of a durable long nozzle that is usually attached to the pouring part of the ladle with a length that reaches below the predetermined melt level of the tundish from the ladle. The lower end of the soluble nozzle is connected to the tundish where the molten metal is empty, or the lower end of the soluble nozzle is immersed in the surface of the tundish in which the molten metal has fallen below a predetermined level. By injecting the molten metal from the ladle, it is possible to reliably prevent air oxidation of the molten metal injection flow, and also to maintain the molten metal surface level while preventing the slag floating on the molten metal surface from being knocked into the molten metal surface. As the molten metal rises, the immersed part of the soluble nozzle melts, and the discharge position at the lower end of the soluble nozzle rises.Finally, when the molten metal level rises to a predetermined level, it is immersed below the molten metal surface at a predetermined level. The long durability nozzle completely disappears down to the lower end, allowing a smooth transition to continuous casting that maintains a predetermined level.

This prevents contamination of the molten metal in the tundish during the initial stage of casting or when changing the ladle during successive castings, making it possible to cast slabs of good quality at a high yield.

FIG. 1 shows one embodiment of the method of the present invention, in which 1 is a ladle, 2 is an empty tundish, 3 is a mold, and 4 is a slide nozzle at the spouting part of the ladle 1 supported by a holder 6. It is a durable alumina graphite long nozzle with a length of 900 mm, an outer diameter of 170 mm, and an inner diameter of 100 mm, which is connected to the lower end of the SN by pressure welding.
It is located at the bottom (1200mm from the bottom of the tray). 5 is threadedly connected to the lower end of the durable long nozzle 4 (other fittings, joining via adhesive, etc.) is connected, length 750 mm, inner diameter 164 mm, outer diameter 204 mm
mm, mainly composed of Al ₂ O ₃ : 55%, SiO ₂ : 45%,
Melting temperature 1430 with 5% composition of other binders etc.
℃, bulk specific gravity of about 0.38 g/cm ³ (mixed with other substances such as CaO to improve molten metal contamination at the initial stage of injection), and its lower end was positioned 200 mm above the bottom of the tundish 2. It is something.

From this state, open the slide nozzle SN,
Injection of the 1580° C. molten steel in the ladle 1 into the tundish 2 was started, and the molten metal level L in the tundish was raised to the target predetermined level 1. During this time, the slag on the surface of the molten metal does not knock in, and the soluble nozzle 5 begins to self-fuse from the inside due to the molten metal injection flow and from the outside due to immersion as the molten metal level rises. By the time it reached that point, all of the nozzles had disappeared, leaving only the durable long nozzle with its tip submerged below the hot water surface. As a result, air oxidation of the molten metal injection stream and slag intrusion are prevented, and the pick-up of N, for example, is significantly improved compared to an example in which the soluble nozzle is not used, as shown in Fig. 2, which shows the difference △Nppm from the mid-stage casting level. The molten metal could be injected into the tundish in a small amount, and as shown in FIG. 3, a clean slab of good quality with very few inclusions was obtained.

[Brief explanation of the drawing]

FIG. 1 is a side explanatory view showing one embodiment of the present invention;
FIG. 2 is a graph showing the cleanliness of the molten metal in the tundish contained by the molten metal injection method of the present invention together with a comparative example, and FIG. 3 is a graph showing the amount of inclusions in slabs obtained with the above molten metal together with a comparative example. . In the figure, 1...Ladle, 2...Tundaishu, 3
...Mold, 4...Durable long nozzle, 5...Soluble nozzle.

Claims (1)

[Claims] 1. The lower end of a durable long nozzle connected to the molten metal pouring part of the ladle is positioned in advance at a predetermined level below the molten metal surface of the tundish, and the lower end of this long nozzle is injected with a composition mainly containing a melting point composition lower than the molten metal temperature. A continuous casting method, characterized in that a soluble nozzle is connected, its lower end is positioned at the bottom of a tundish, and injection of molten steel from the ladle into the tundish is started.