JP5195609B2 - Hot reuse of tundish - Google Patents

Description

  The present invention can suppress oxidation of the remaining steel remaining in the tundish when continuously using the tundish in continuous casting of steel, and can reduce contamination of molten steel at the start of casting of the next heat. It is about the method.

  When tundish is continuously used in continuous casting, the remaining steel remaining in the tundish at the end of continuous casting is oxidized to iron oxide. This iron oxide reacts with Al in the molten steel at the time of casting of the next heat to produce alumina, which causes inclusion defects in the final product and causes quality deterioration.

In order to solve the above problems, various techniques have been disclosed.
For example, Patent Document 1 discloses a technique for suppressing the oxidation of the remaining steel by flowing an inert gas equal to or greater than the residual steel discharge amount into the tundish immediately after the end of casting and immediately before starting the tundish tilt. It is disclosed.

  However, the technique disclosed in Patent Document 1 does not flow an inert gas from the end of casting to the start of tilting, and the tundish is not a completely sealed structure. May be mixed. In addition, the inert gas may leak from the tundish and the inflow amount of the inert gas necessary for preventing oxidation may be insufficient.

  Patent Document 2 discloses a method of blowing an inert gas of 20 liters / min or more, preferably 100 to 200 liters / min from a sliding nozzle plate provided at the bottom of a tundish when molten steel is stored in the tundish. Is disclosed.

  However, since the technique disclosed in Patent Document 2 is expected to reduce the defective opening of the sliding nozzle in the initial casting stage, the flow rate of the inert gas is insufficient for use as a measure against bullion oxidation. is there.

JP-A-7-284890 JP-A-8-257708

  The problem to be solved by the present invention is that, in the prior art, during continuous use of the tundish in continuous casting of steel, the remaining steel remaining in the tundish is suppressed from being oxidized, and at the start of casting of the next heat. It is a point that a molten steel contamination cannot be reduced effectively.

The hot reuse method of the tundish of the present invention is as follows.
To suppress oxidation of the remaining steel remaining in the tundish during continuous use of the tundish in continuous casting of steel, in order to effectively reduce molten steel contamination at the start of casting of the next heat,
After the pouring of molten steel from the ladle being cast into the tundish is completed, at least after the molten steel is poured into the tundish from the ladle for casting of the next heat, the tundish is poured into the tundish through the immersion nozzle. Until the start of pouring molten steel into the mold,
At a gas flow rate that satisfies the following formula (a):
After the pouring of the molten steel from the ladle being cast into the tundish is completed, nitrogen gas or inert gas is blown from a purge seal gas pipe disposed near the upper lid of the tundish,
After the casting of molten steel from the ladle for the next heat into the tundish is completed, the above-mentioned purge seal gas pipe arranged near the upper lid of the tundish , and the sliding upper nozzle or immersion nozzle arranged at the bottom of the tundish The main feature is that nitrogen gas or inert gas is blown into the tundish from the upper plate of the slide gate.
Q / V ≧ 0.5 (a)
Here, Q: gas flow rate to be introduced (liter / min), V: tundish internal volume (liter).

  According to the present invention, oxidation of the remaining steel remaining in the tundish can be effectively suppressed, so that the amount of T. [O] pickup during casting of the next heat can be reduced. Furthermore, if it is possible to switch between nitrogen gas and inert gas depending on the steel type, the cost can be rationalized.

It is sectional drawing which showed the purge method in a tundish from the casting last stage to the casting start of the next heat. It is the figure which showed the T. [O] pick-up amount by the presence or absence of the purge in a tundish from the end of casting to the start of casting of the next heat. It is the figure which showed the relationship between Q / V and T. [O] pick-up amount at the time of performing nitrogen gas purge only from the upper part of a tundish. It is the figure which showed the relationship between Q / V and T. [O] pick-up amount by the presence or absence of the purge in a tundish from the end of casting to the start of casting of the next heat, and the kind of purge.

  In the present invention, for the purpose of suppressing the oxidation of the remaining steel remaining in the tundish, after the start of injection of molten steel into the tundish of the next heat, until the start of injection of molten steel in the tundish into the mold, This was realized by introducing nitrogen gas or inert gas into the tundish.

Hereafter, the hot reuse method of the tundish of this invention is demonstrated using FIG.
FIG. 1 is a cross-sectional view showing a tundish purge method from the end of casting to the start of casting of the next heat.

  The present invention intends to reduce air contamination into the tundish 1 after the injection of molten steel from the ladle being cast into the tundish 1 is finished.

  More specifically, after the molten steel injection is completed, the molten steel in the tundish 1 is injected into the mold through the immersion nozzle 2 after the start of the molten steel injection into the tundish 1 from the ladle for casting of the next heat. In order to reduce air contamination until the start, it is carried out as follows.

  First, after pouring molten steel from the ladle being cast into the tundish 1, nitrogen gas or inert gas is introduced into the tundish 1 from the purge gas pipe 3 disposed at the top of the tundish 1. Infuse.

  After casting of molten steel into the tundish 1 from the ladle for casting of the next heat, nitrogen gas or inert from the upper plate 2a of the slide gate of the immersion nozzle 2 provided on each strand at the bottom of the tundish 1 Inject gas.

  The state of purging the tundish 1 from the top and bottom of the tundish 1 at the same time is continued from the tundish tilt to the start of casting of the next heat, and the inside of the tundish 1 is always filled with nitrogen gas or inert gas. Let

  By doing so, it becomes possible to reduce the influence of atmospheric oxidation, which has been a problem in the past, to the limit. In the present invention, the gas blown into the tundish is preferably Ar gas in the case of extremely low [S] steel that requires a low [N] component standard, and nitrogen gas is preferably used in other steel types. . In addition, 4 in FIG. 1 is the remaining steel remaining in the tundish 1.

  Hereinafter, in order to confirm the effect of the method of the present invention, when casting low-carbon steel and medium-carbon steel round slabs with a continuous casting machine capable of producing round slabs with outer diameters of 225 mm and 310 mm, the capacity L is The result of reusing 8000 liters of tundish hot will be described.

  After the pouring of the molten steel from the ladle being cast into the tundish was completed, 4500 liters of nitrogen gas was blown into the tundish from the upper part of the tundish through a seal gas pipe.

  And after casting of the molten steel into the tundish from the ladle for casting of the next heat was completed, 1800 liters of nitrogen gas was blown from the upper plate of the immersion nozzle provided in each strand at the bottom of the tundish. .

  When casting 80 tons of the next heat, slab samples are taken at the top and middle of the casting for multiple steel types, the T. [O] value is analyzed, and the inside of the tundish is purged with nitrogen gas The cleanliness was evaluated when the purge with nitrogen gas was not performed.

  The result is shown in FIG. The black circle in FIG. 2 indicates the T. [O] value of the casting top portion, and the range indicated by the solid line in the vertical axis direction indicates the difference in T. [O] value between the casting top portion and the middle portion. is there.

  From FIG. 2, it can be seen that by performing the purge in the tundish with nitrogen gas, the amount of T. [O] pickup at the casting top portion can be suppressed as compared with the case where the inert gas purge is not performed.

  FIG. 3 shows casting when nitrogen gas is purged by changing the gas flow rate only from the upper part of the tundish when casting the middle carbon steel using the same continuous casting machine and tundish as in FIG. The difference in T. [O] value between the top part and the middle part is shown.

  The effect of purging nitrogen gas only from the upper part of the tundish is increased according to the nitrogen gas flow rate Q (liter / min), and especially when Q / V is 0.5 or more, T. [O] The pickup amount has become smaller.

  This confirms that the nitrogen gas is not sufficiently distributed in the tundish when the nitrogen gas flow rate is small because the nitrogen gas leaks from the gap between the tundish.

  FIG. 4 is a view similar to FIG. 3 when purging nitrogen gas from only the top of the tundish, only from the bottom of the tundish, and from the top and bottom of the tundish.

  When purging nitrogen gas only from the top of the tundish, the T. [O] pickup amount is small when Q / V is 0.5 or more (see FIG. 3), but in the case of the same Q / V The amount of T. [O] pick-up was further reduced by flowing nitrogen gas simultaneously from the upper bottom of the tundish (see FIG. 4).

  This is presumably because when nitrogen gas is flowed only from the upper part of the tundish, the nitrogen gas drifts due to thermal convection in the tundish, so that the effect is not sufficient.

The present invention is not limited to the above embodiment, if the scope of the technical spirit as set forth in 請 Motomeko, it may of course be changed as appropriate embodiment.

  For example, the position where the gas is blown from the bottom of the tundish may be not only from the upper plate of the slide gate of the immersion nozzle but also from the sliding upper nozzle.

1 Tundish 2 Immersion pipe 2a Upper plate 3 Seal gas pipe

Claims (1)

A method for hot reuse of tundish,
After the pouring of molten steel from the ladle being cast into the tundish is completed, at least after the molten steel is poured into the tundish from the ladle for casting of the next heat, the tundish is poured into the tundish through the immersion nozzle. Until the start of pouring molten steel into the mold,
At a gas flow rate that satisfies the following formula (a):
After the pouring of the molten steel from the ladle being cast into the tundish is completed, nitrogen gas or inert gas is blown from a purge seal gas pipe disposed near the upper lid of the tundish,
After the casting of molten steel from the ladle for the next heat into the tundish is completed, the above-mentioned purge seal gas pipe arranged near the upper lid of the tundish , and the sliding upper nozzle or immersion nozzle arranged at the bottom of the tundish A method for hot reuse of tundish, characterized in that nitrogen gas or inert gas is blown into the tundish from the upper plate of the slide gate.
Q / V ≧ 0.5 (a)
Here, Q: gas flow rate to be introduced (liter / min), V: tundish internal volume (liter).

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