JPS58151948A - Continuous casting method - Google Patents

Abstract

PURPOSE:To improve the quality of an ingot in continuous casting of Al-contg. molten steel by blowing inert gases from the tip of a stopper and the porous parts and slits of an immersion nozzle thereby preventing the clogging of the nozzle and enabling the continuous casting for a long period of time. CONSTITUTION:A gas purging type stopper 2 is used as a stopper for a tundish 1 in continuous casting of Al-contg. molten steel. An immersion nozzle 3 provided with porous parts 31 and slits 32 on the inside surface is used. Molten steel 10 is supplied into a mold 4 while inert gases are blown from all of the tip 21 of said stopper 2 and the porous parts 31 and slits 32 of the nozzle 3. The effect of preventing the clogging of the nozzle 3 is obtained effectively if the rates of blowing of the gases from these positions are so selected as to satisfy the conditions 0.1<=A/(B+C)<=5 and 0.1<=B/C<=5 where the rate of blowing from the tip of the stopper 21 is defined as A, the rate of blowing from the parts 31 of the nozzle 3 as B and the rate of blowing from the slits 32 as C.

Description

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

Continuous casting of steel is usually carried out by continuously transferring molten steel received in a ladle to a tundish, from where it is fed into a mold through a submerged nozzle. The immersion nozzle has the advantage of less erosion loss, so C-Al2O3
Fired crystals are preferred.

In principle, it is desirable for continuous casting to be able to continuously process molten steel in as many ladles as possible for as long as possible. There are several factors contributing to this limitation, but currently the biggest problem is blockage of the submerged nozzle. This clogging is likely to occur when the molten steel contains aluminum, particularly at a high aluminum content of 0.02% or more. This fact also supports the fact that it is known that what clogs the nozzle is the adhesion and growth of inclusions containing alumina as a main component to the tube wall.

The method is to prevent alumina from adhering to the tube wall by providing a slit or a porous section from which an inert gas such as argon or nitrogen is blown out. Retail. On the other hand, attempts have also been made to use a gas purge type stopper in which a bolus sp2 is provided at the tip of the stopper to control the flow of molten steel from the tundish to the nozzle. this is,
Part of the inert gas blown out from the tip floats up, but part of it flows down the nozzle along with the molten steel, preventing alumina from adhering to the tube wall. That's what I expected.

However, in reality, clogging of the immersion nozzle cannot be avoided by any of these measures, and conventionally, for example, in the production of special steel, it has been possible to perform continuous casting with only two charges using a typical 70-ton ladle. This limit remained unchanged even when the amount of gas blown out was increased to the maximum possible level.

As a result of many trials, the present inventors have discovered that blockage of the immersion nozzle can be effectively prevented by simultaneously blowing out inert gas from all the above-mentioned parts.
Furthermore, it has been found that the effect of preventing nozzle clogging can be enhanced by selecting the amount of gas from each part within a certain suitable range.

To explain with reference to the drawings, the continuous casting method of molten steel containing aluminum of the present invention uses a gas purge type stopper 2 as a stopper of a tundish 1, and a submerged nozzle 3 having a porous part 31 and a slit 32 on the inner surface. The molten steel 10 is supplied to the mold 4 while blowing out inert gas from the tip 21 of the stopper, the porous part 31 of the immersion nozzle, and the slit 32.

The mechanism by which such gas blowing prevents alumina from adhering to the nozzle tube wall is that first, a large number of fine air bubbles from the slits provided all over the nozzle cover the nozzle wall and prevent alumina particles from adhering. On the other hand, it is conceivable that relatively large air bubbles generated in the porous portion stir the molten steel and promote the floating of alumina particles, and that the relatively large air bubbles from the stopper tip also assist in this.

In any case, by blowing from these three places, it is far more effective at preventing blockages than when blowing from one place, such as the tip of the stopper, or from two places, such as the porous part of the immersion nozzle and the slit. The effect is great. - a certain total amount of inert gas at any one, two and three of the above locations.
It becomes clear if you compare the balloons from different places.

As mentioned above, there is a suitable effective range between the amount of inert gas blown out from each part.

That is, the amount of gas is From the tip of the stopper A From the porous part of the immersion nozzle B From the slit of the immersion nozzle C When 01≦A/(B+C)≦5, and 0.1≦C/’B≦5 As you can see from the conditions, it is a good choice.

As a guideline for actual operation, when using a submerged nozzle of a size suitable for continuous casting at a casting speed of 70 tons/hour, the suitable inert gas injection amount is A: 1 to 10 Nl/hr. It can be found in the following range: m1n B: 1-5 C: 1-5.

As shown in the following example, the present invention enables long-term continuous casting, which not only stabilizes casting operations and improves the quality of slabs, but also reduces the need for nozzle replacement and replacement of tundish refractories. Yield also improves. Therefore, an improvement in the basic unit and a channel for energy can be obtained.

Example JIS SCM 420 (case hardening) steel (AI: Q, 0
3%) was melted in an electric furnace, received in a 70-ton ladle, and continuously cast through a tundish at a rate of 70 tons/hour. Using the stopper and immersion nozzle with the structure shown in the drawing, the amount of argon gas blown out from each part (Nl
/min) was selected as follows.

In the case of Nα1, that is, only gas purge from the stopper, the nozzle was clogged after 2 charges from the ladle, and even when a slit and a porous part were provided in the immersion nozzle on floor 2 and the gas was blown from both, the nozzle was blocked after 3 charges, but according to the present invention In the case of Nα3, there were no problems even after casting 6 charges.

[Brief explanation of drawings]

The drawing is a sectional view of a submerged nozzle and its surroundings, conceptually showing a situation in which continuous casting is carried out according to the present invention. 1... Tandish 2... Stopper 3... Immersion nozzle 31... Porous part 32... Slit 4... Mold 10. ... Molten steel patent applicant Daido Steel Co., Ltd.

Claims (1)

[Claims] fl) When continuously casting molten steel containing aluminum, a gas purge type stopper is used as a tundish stopper, and an immersion nozzle having a porous part and a slit on the inner surface is used, and the tip of the stopper is immersed. A continuous casting method characterized by supplying molten steel to a mold while blowing out inert gas from all the porous parts of the nozzle and slits. (2) When the amount of inert gas blown out is A from the stopper tip, B from the porous part of the immersion nozzle, and C from the slit of the immersion nozzle, the amount of each gas is 01≦A/(B+C)≦5, and 0 .1 The continuous casting method according to claim 1, which is selectively carried out so as to satisfy the condition of ≦B/C≦5.