JPH0211246A - Horizontal continuous casting method for steel - Google Patents

Abstract

PURPOSE:To prevent bubbling on molten steel surface in a tundish and to prevent secondary oxidation of the molten steel and enclosure of slag into a mold by blowing the specific rate of inert gas through gas blowing holes arranged at least two positions at bottom part of the tundish. CONSTITUTION:In horizontal continuous casting method for steel, at least two gas blowing holes 20 are arranged at the bottom part of the tundish 2 and the inert gas of Ar, etc., is blown from the gas blowing holes 20. In this result, as the molten steel 4 at the blowing position is risen up accompanied by gas bubbling, slag on the molten steel surface at the blowing position is temporarily come together to the opposite side, but even at the time of changing the blowing position of the inert gas accompanied by changing of oscillating direction, splash is not developed and only the molten steel and the slag are shifted, and the enclosure of slag into the molten steel 4 can be eliminated. Then, in order to prevent the oxidation of molten steel 4 and restrain the development of splash, the blowing rate of inert gas is limited to <=10l/min.ton of the molten steel.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for horizontal continuous casting of steel, and in particular to a method for preventing ripples on the surface of a tundish bath in bidirectional drawing type horizontal continuous casting and producing slabs of excellent quality. This invention relates to a horizontal continuous casting method that can be manufactured.

[Conventional technology]

In recent years, in the field of continuous casting, instead of the conventional vertical or curved continuous casting method, molten steel is injected into the mold from the bottom of the tundish, and the slab produced in the mold is continuously pulled out in two opposite horizontal directions. A bidirectional pultrusion type horizontal continuous casting method has been proposed and put into practical use.

JP-A-58-13 as a conventional bidirectional drawing type horizontal continuous casting method
8544 is disclosed. This method will be explained with reference to FIG. That is, the molten steel 4 stored in the tundish 2 is injected into the mold 8 through the feed nozzle 6. A break ring 10 is set at a portion of the feed nozzle 6 that connects to the mold 8, and the mold 8 is provided with a water-cooled copper plate 12 inside. The mold 8 is vibrated from side to side in the horizontal direction by an oscillation device 14 while pinch rolls 16 pull out the solidified shell, that is, the slab 18 in two opposite horizontal directions.

The vibration caused by the above oscillation device M14 is usually 120
times/win, the amplitude of the oscillation is approximately 6 m, and the mold 8 and the tundish 2 have an integral structure, so
As the mold 8 vibrates, the tundish 2 also vibrates. As a result, ripples occur on the surface of the molten steel 4 accommodated in the tanditshu 2.

Due to the splash of molten steel 4 associated with this, the molten steel 4
In addition to the secondary oxidation of the molten steel 4, there is a problem that the powder thrown onto the surface of the molten steel 4 gets caught up in the molten steel 4 during casting, resulting in deterioration of the quality of the slab 18.

This phenomenon is caused by the fact that the tundish 2 generally used for horizontal continuous casting has a small capacity of about 50 ml, so when Franks powder etc. is involved, there is no time for it to float and it gets mixed into the mold 8. One of the reasons is that

Conventional techniques for solving this problem include JP-A-58-163551 and JP-A-58-187240. In the former method, before pouring molten steel into the mold, a slag inflow prevention member made of graphite or other refractory material is fitted to the entrance of the mold, and then molten steel is poured into the tundish, after which the dummy bar is removed and the molten steel is poured into the mold. In this method, the fitting of the slab inflow prevention member is released prior to this, the slag is floated to the surface of the tundish, and the slab is pulled out while only molten steel is injected into the mold. However, in this method, even after the slag drift prevention member is released, the tundish is still vibrating, so there is a possibility that the slag may be caught below the surface of the hot water, and this alone is not sufficient.

In the latter method, an inert gas is blown into the molten steel near the entrance of the mold, and the bubbling of the gas creates an upward flow for casting, causing the slag to float to the surface of the tundish. However, this method of simply blowing inert gas is undesirable because it lowers the temperature of the molten steel and increases costs.

[Problem that the invention seeks to solve]

The purpose of the present invention is to solve the above-mentioned problems of the prior art in horizontally continuous VT#4 steel construction, to prevent the surface of the tundish containing molten steel from undulating, to prevent secondary oxidation of the molten steel, and to prevent the slab from entering the mold. To provide a horizontal continuous casting method capable of preventing entrainment and producing slabs of excellent quality.

[Means and operations for solving the problems] The gist of the present invention is as follows.

In other words, molten steel is continuously supplied into the mold through a feed nozzle from a tundish that is installed on the top of the vibrating mold and vibrates together with the mold, and continuously in two opposite directions of the mold. In a horizontal continuous casting method for steel in which slabs are drawn, gas blowing holes are provided at least at two locations at the bottom of the tundish containing molten steel, and the molten steel is inertly injected through the gas blowing holes to an inertness of at least 10Q/■in. This is a horizontal continuous casting method for steel characterized by blowing gas.

The horizontal continuous casting method according to the present invention is compared with the conventional method in Figure 1 (A
), (B) and FIGS. 2(A) and (B).

As mentioned above, the mold 8 and tundish 2 are usually vibrated 120 times/+*in by the oscillation device 14.
, with an amplitude of about 6IIIl, as shown in FIG. 1(A).

As shown in the conventional example in (B), when the oscillation direction oscillates to the right in the drawing as shown in FIG. When the vibration becomes high and vibrates to the left as shown in Fig. 1 (B), on the contrary, the scene on the right becomes high, and when the vibration changes, molten steel splash occurs, which not only causes secondary oxidation of the molten steel. This will involve the slag generated by the flags powder thrown into the scene.

Therefore, in the present invention, as shown in FIGS. 2(A) and (B),
At least two gas inlet holes 2 at the bottom of the tundish 2
0 is provided, and an inert gas such as Ar is blown through the gas blowing hole 20. The gas blowing hole 20 is normally arranged as shown in Fig. 3 (A
), as shown in (B).

It is preferable to use porous bricks with a large number of pores, and either one on each side in the oscillation direction, or two symmetrically on the left and right and front and rear with the center in the oscillation direction in between.

Alternatively, it is preferable to use three pieces at a time.

In this way, by blowing inert gas such as Ar through the gas blowing hole 20, which is a tuyere, the molten steel 4 at the blowing position is blown with gas bubbles, as shown in FIGS. 2(A) and (B). As a result, the slag on the surface of the molten steel at the injection position temporarily gathers in the opposite direction, but even when the inert gas injection position is changed due to the change of the vibration direction, the molten steel and slag remain silent without splashing. By simply moving, it is possible to almost completely eliminate slag from being caught in the molten steel 4.

The amount of inert gas such as Ar is blown into the molten steel at 10Q/l1.
It should be limited to in or more. The reason is 10Q/si
If it is less than n, the effect of preventing oxidation of molten steel and suppressing the occurrence of splash will be small, and the object of the present invention will not be achieved. However, if the amount exceeds 15 Q/win, it will slightly roughen the molten metal surface and cause oxidation of the molten steel.
A range of 15 Ω/l1in is most desirable.

〔Example〕

The present invention is applied to bi-directional drawing type horizontal continuous casting of a billet of 150 x 150+w+ using a tundish with a capacity of A comparative test was conducted to compare the effects of the present invention by carrying out the conventional method without injecting molten steel under the same conditions and measuring the changes in the oxygen concentration of both molten steels.

The molten steel components (weight %) used in the test are as follows.

C: 0.04% Si: 0.02% Mn: 0.45% AQ: 0.040% Figure 4 shows the transition of the oxygen concentration of molten steel from the start to the end of casting, and the A curve shows the transition of 100 Q/+*
This is an example of the present invention in which in-bottom blowing was performed, and curve 8 is a conventional example in which Ar bottom blowing was not performed at all. As is clear from Figure 4, even if the same concentration of molten steel is used in the ladle, the
When the conventional method was used, the oxygen concentration increased by about 20 ppm after a few minutes had elapsed, and although it decreased somewhat after that,
At the end of casting, more than 10 pp■ of oxidation contamination was observed compared to when the ladle was finished.

On the other hand, in the case of the present invention, the oxygen concentration increases slightly immediately after the start of casting, but gradually decreases, and by the end of casting, the oxygen concentration is almost the same as that in the ladle, and there is no oxidation contamination.
It was found that the oxygen concentration was about 15 ppm lower than in the conventional method.

Next, the amount of Ar injected from the bottom of the tanditshu is 5 to 20.
The influence of the amount of blown Ar on the change in molten steel oxygen concentration was investigated using molten steel of the same composition by varying Q/rain and t. The results are shown in FIG. As is clear from Fig. 5, the Ar injection amount is 10 Q/min,
Since it is not possible to suppress the increase in the molten steel oxygen concentration when it is less than Therefore, in the present invention, as already described, <Ar
The blowing rate of inert gas such as at least 10 Q/min,
It was limited to t. However, if it exceeds 10L/sin/t, the molten metal surface becomes rough and there is a slight tendency for molten steel to oxidize. However, in the above comparative test, there were cases in which there was almost no oxidation contamination of the molten steel by injecting Ar at 100fi/11in, t, so the negative effects of excessive injection are not that great. Should be 10-15 Q
The range of /*in, t is most desirable.

It goes without saying that the present invention can also be applied to a one-sided pultrusion type continuous casting method, which has mainly been described with reference to the two-way pultrusion type horizontal continuous casting method.

〔Effect of the invention〕

In the bidirectional drawing type horizontal continuous casting method, the mold is vibrated back and forth in the drawing direction of the #4 piece, but the mold and the tundish located above it have an integral structure, so that the #4 piece is housed in the tundish. The present invention has been able to solve the problem of molten steel shaking and rippling, causing oxidation contamination of the molten steel, and ultimately deteriorating the quality of the slab. That is, by providing gas blowing holes in at least two places symmetrically in the oscillation direction at the bottom of the tundish, and blowing an inert gas such as Ar through the gas blowing holes at a rate of 10 Q/sin or more per molten steel, the above problem can be solved. The results were effective in resolving the issues. That is, the effects of the present invention are as follows, as shown in the above embodiments.

(b) By suppressing the ripples caused by the vibration switching of the molten steel housed in the tundish and making it a quiet oscillation, it was possible to prevent molten steel splash and slag entrainment.

As a result of (b) and (a), it was possible to produce slabs of excellent quality without any oxidation contamination of molten steel or inclusion of slag.

(c) According to the present invention, the Ar injection amount is 10 to 1 per molten steel.
Since it only requires about 5 Q/win, the temperature of molten steel does not decrease as in the conventional technology which takes the same measures, and moreover, it is possible to achieve great effects at low cost.

[Brief explanation of the drawing]

Fig. 1 (A), (B) and Fig. 2 (A), (B) are schematic cross-sectional views comparing the oscillation of molten steel due to the oscillation of the tundish in the bidirectional drawing type horizontal continuous casting method. Figures 1 (A) and (B) are the conventional example, and Figure 2 (
A) and (B) are examples of the present invention, in which (A) the oscillation direction is in the right direction, and (B) in both cases the oscillation direction is in the left direction. 3(A) and 3(B) are both plan views showing an embodiment of the arrangement position of the gas blowing holes in the bottom of the tundish according to the present invention, and FIG. 4 is a plan view showing the embodiment of the present invention from the start to the end of casting. Figure 5 shows the influence of changes in the amount of Ar injection from the bottom of the tundish on the amount of oxygen rise based on ladle oxygen during the experimental process for obtaining the present invention. FIG. 6 is a schematic sectional view showing the state of slab production using a conventional bidirectional drawing type horizontal continuous casting machine. 2... Tandish 4... Molten steel 6... Feed nozzle 8... Mold 14... Oscillation device 18... Solidified shell (slab) 20... Gas blowing hole

Claims (1)

[Claims] (1) Continuously supplies molten steel into the mold through a feed nozzle from a tundish that is installed on the top of the vibrating mold and vibrates together with the mold, continuously in two opposite directions of the mold. In a horizontal continuous casting method for steel in which slabs are drawn, gas blowing holes are provided at at least two locations at the bottom of the tundish containing molten steel, and at least 10 l/min of inert gas per ton of molten steel is supplied through the gas blowing holes. A horizontal continuous casting method for steel characterized by blowing.