Method of Production of Ultralow Carbon Cast Slab

Abstract

A method of production of an ultralow carbon cast slab characterized by adding Ti to molten steel decarburized to a carbon concentration of 0.01 mass % or less, further adding at least one of Ce, La, and Nd, and using an immersion nozzle to inject the above molten steel from a tundish to a casting mold for continuous casting while maintaining a flow rate of Ar gas blown from any location in a range from a tundish upper nozzle to discharge ports of said immersion nozzle at 3 Nl (normal liter) / min or less.

Description

TECHNICAL FIELD[0001]The present invention relates to a method of producing an ultralow carbon cast slab by continuous casting.BACKGROUND ART[0002]The dissolved oxygen in molten steel refined by a converter or vacuum treatment container is generally removed by the deoxidizing element Al. However, if deoxidizing ultralow carbon steel with a large content of dissolved oxygen by Al, alumina (Al2O3) will form. These agglomerate and merge to form large amounts of coarse clusters of hundreds of microns size or more.[0003]Part of these alumina clusters enter the immersion nozzle from the tundish at the time of continuous casting. If sticking at the inner bore of the immersion nozzle, they cause nozzle clogging and obstruct operation. Further, if the alumina clusters enter the casting mold and remain at the surface layer of the cast slab, they become causes of formation of surface flaws of thin-gauge steel sheet and have a detrimental effect on quality.[0004]As a countermeasure against this...

AI Technical Summary

Benefits of technology

[0023]The uneven distribution of the molten steel flow rate occurring due to the dropping flow of the molten steel is eased if making the secondary meniscus close to the position of the sliding nozzle. However, to obtain the effect of prevention of sticking of alumina, at least a predetermined level of Ar gas flow rate is required. Normally, the Ar gas flow rate is 5 to 20 N1 / min, but with this Ar gas flow rate, it is difficult to make the secondary meniscus close to the position of the sliding nozzle.

[0029]The present invention, in consideration of these problems, has as its object the provision of a method of production of an ultralow carbon cast slab enabling achievement of both efficiency of continuous casting and cast slab quality.

[0055]According to the present invention, in continuous casting of ultralow carbon steel, it is possible to prevent nozzle clogging and produce an ultralow carbon cast slab free of surface flaws even if worked to a thin-gauge steel sheet.

Problems solved by technology

In the technology disclosed in the above patent documents, even if using an immersion nozzle having an orifice in its inner bore, the effect of making the distribution of the flow rate uniform is hard to obtain.

This is because in the above art, there is the problem of nozzle clogging.

This reason is that at the part below the bottom end of the orifice, an eddy flow occurs and stirring is caused, so the alumina will not stick, but at the part above the top end of the orifice, no eddy flow occurs, so sticking of alumina cannot be avoided.

If a large amount of alumina-based inclusions stick here, the nozzle will clog.

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