JPS58100952A - Continuous casting method - Google Patents

Abstract

PURPOSE:To prevent the closing of an immersion nozzle and to permit the continuous casting of a larger number of ladles of molten metal in the stage of casting molten steel continuously by using the molten steel of which the content of Mg is reduced to specific or lower values in the stage of transferring the same from ladles. CONSTITUTION:In a method for continuous casting of molten steel, more particularly molten stainless steel or high alloy steel subjected to an AOD (argon- oxygen decarburization), the molten steel of which the content of Mg is reduced to 0.0005% in the stage of transferring the same from a ladle into a tundish is used. Then, the molten steel can be cast continuously for a long time while the closing of an immersion nozzle is prevented in the case of casting the molten steel continuously from the tundish through the immersion nozzle into the mold. In this case, the content of Mg in the molten steel is controlled by selecting the compsn. of slag adequately.

Description

[Detailed description of the invention] The present invention relates to improvements in continuous steel casting methods.

Continuous casting of steel is performed by continuously transferring the controlled temperature received in a ladle to a tundish, and then feeding it into a mold by casting a submerged nozzle. As for the material of the immersion nozzle, C-A is used when it is necessary to avoid melting damage.
I, z, 03 It is normal to select baked crystals.

However, the immersion nozzle of the tundish may become clogged during use, forcing the interruption of continuous casting.
Nozzle blockage is especially caused by AOD (argon-oxygen decarburization)
This is more likely to occur on treated steel types. Moreover, it is noticeable in ultra-low sulfur steels with an S content of 0.002% or less, such as header materials.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for preventing immersion nozzle clogging in continuous casting of steel, thereby enabling continuous casting of a larger number of ladle molten metal.

In order to achieve this objective, the present inventors first investigated the cause of nozzle blockage and analyzed the blockage, and discovered that it contained a large amount of MO.

This MO is thought to have been eluted from the refractory bricks (semi-ribboned maguro bricks are usually used) in the furnace or ladle used for melting and refining steel. When performing AOD treatment, the bricks are in contact with high-temperature molten steel for a long time, so the amount of Mg eluted is correspondingly large.

However, at present, it is not practical to use refractories that do not contain MO for various furnaces and ladle materials, especially for ADD furnaces, in terms of furnace lifespan and cost.
It is impossible to prevent M(l) from entering during refining.

Therefore, the inventors of the present invention repeatedly attempted to prevent nozzle clogging by reducing the amount of Mg in the molten steel to be cast, and found that the criticality was found to be near Mg: 0.0005%, or 5 ppm. It has been found that if the M(+ content is less than this), nozzle clogging will not be a problem.

Therefore, the continuous #S manufacturing method of the present invention is suitable for molten steel, especially AOD
-3- In a method of continuously producing molten steel of treated stainless steel or high alloy steel, it is recommended to reduce the MCI content to 0.0005% or less and use 1C molten steel when transferring from the ladle. This feature enables continuous casting over a long period of time while preventing the immersion nozzle from clogging.

As known to those skilled in the art, the M content in molten steel can be controlled by appropriately selecting the slag composition. In the case of stainless steel,
Furthermore, by selecting the composition of the slag material to be added after slag removal (after Or reduction), (Ca O + MQ O) / (Si 0
2. +A12,03) basicity defined as 1.
The amount of M(I) can be reduced by forming a slab with a basicity of 7 or less, which is not very high.

Regarding the criticality of MO content, the present inventors have not yet clarified the mechanism, but M9 in molten steel
If the content of eel is below the above limit, it is considered that there is almost no chance that M(+ will form a precipitate on the inner wall of the nozzle).

-4= The continuous casting method of the present invention can be applied to various molten steels, but as can be understood from the above explanation, molten steels that have been subjected to AOD treatment, especially Ni-containing steels such as 5US304.5US316.
The significance is significant when dealing with stainless steels such as stainless steels and Or series stainless steels such as 5US410.5US430. Of course, it is also useful for other high alloy steels.

As shown in the example below, the present invention enables continuous casting over long periods of time, which not only stabilizes casting operations and improves the quality of slabs, but also reduces the need for nozzle replacement and replacement of refractories, and improves casting efficiency. Improved yield improves unit consumption and saves energy.

11 5 US304 steel material is melted in an electric furnace, transferred to an AOD vessel and subjected to AOD treatment, the slag of decarburization and chromium reduction is removed, and then a slag-forming agent is added to reduce the basicity of the slab. MO removal is carried out by keeping F within the range of 1.5 to 1.7.
After deoxidizing, the melt was poured into a 20-ton ladle and continuously cast through a 3-5-ton capacity tundish.

When a sample was taken from the top of the ladle and the amount of Mil contained was measured by emission spectrometry, it was found to be 4 ppm, or 0.
．． It was 0004%.

Even when this 8-charge dowel was continuously cast, the immersion nozzle of the tundish did not become clogged.

For comparison, the above Mg removal was incomplete and Mg: 0.0
006% molten metal and IjRM (without performing l, M
Continuous casting was also carried out under the same conditions for g:Q, 0012%.

The former experienced nozzle clogging trouble during the second charge, and the latter as early as the first charge.

Patent applicant: Daido Steel Co., Ltd. Agent: Patent Attorney Souo Suga −6=

Claims (3)

[Claims] (1) A method for continuously casting molten steel, characterized in that molten steel whose M content is reduced to 0.0005% or less is used when pouring from a ladle. (2) The continuous casting method according to claim 1, wherein the molten steel is stainless steel or high alloy steel subjected to AOD (argon-oxygen decarburization) treatment. (3) Stainless steel is 5US304.5US316
Ni-based stainless steel such as 5US410, S U
The continuous casting method according to claim 2, wherein the continuous casting method is Cr-based stainless steel such as S430. 4) The continuous casting method according to any one of claims 1 to 3, wherein the molten steel is ultra-low sulfur steel with an S content of 0.002% or less. -1-