JPH07214252A - Method for continuous casting of clean steel - Google Patents

Abstract

PURPOSE:To prevent the entrapment and beating in of slag from occurring ordinarily caused in a tundish accompanied with ladle change between the preceding charge and the following charge in the continuous casting for cast slab, and to cast without flowing non-metallic inclusion into a mold. CONSTITUTION:In the continuous casting method using a long nozzle as the method for pouring molten steel 4 into a tundish from a ladle 1, at the time of supplying the molten steel in the following ladle in succession to the molten steel in the preceding ladle into the tundish, the dipping depth of the long nozzle 3 is made to be >=50mm and the pouring velocity from the long nozzle is made to <=2.5 times of the stationary condition at the pouring starting of the following ladle. By this method, the yield can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention prevents slag entrapment and tapping, which normally occur in a tundish, when a charge in a continuously cast slab and a pan for the charge are exchanged, and a non-metallic inclusion is molded. It relates to a technique for casting without spillage.

[0002]

2. Description of the Related Art There is a strong demand for molten steel cleaning in the steel manufacturing industry, and it is not limited to the reduction of impurity elements such as C, P and S, but also deoxidation products in converters, secondary refining processes and continuous casting processes. It is required to manufacture highly clean steel slabs by removing refining materials, refractory materials, heat insulating materials, and non-metallic inclusions caused by powders as much as possible.

It is known that non-metallic inclusions which cause surface defects and internal defects of products are remarkably increased due to suspension of tundish slag, particularly at the charge and the joint portion of the charge in continuous casting. .

In the conventional continuous casting of steel, the molten steel is poured from the ladle to the tundish by adjusting the opening of the sliding nozzle 2 mounted on the bottom of the ladle 1 as shown in FIG. Long nozzle 3 located at the bottom
It is performed in a state in which the tip portion of is immersed in the molten steel 4 in the tundish.

However, after the pouring of the front ladle is finished, the molten steel of the rear ladle is poured using the long nozzle 3, but at the start of the pouring of the rear ladle, the slag layer 5 floating on the surface of the molten steel 4 in the tundish is Injected into the molten steel 4 in the tundish by the injection flow 9 from the long nozzle 3, or
It is knocked in.

Although it depends on the tundish capacity, casting speed, etc., among the slags poured into the molten steel 4 in the tundish, the large slags having a grain size of approximately 100 μm or more re-float, but 100 μm or less. The molten steel was poured into the mold together with the molten steel flow and became non-metallic inclusions in the cast, causing the remarkable deterioration of the quality of the pot replacement part (seam part) cast.

[0007]

Then, as a result of the experiments and researches conducted by the present inventors, it was found that the cause of the deterioration of the quality of the slab at the seam at the time of pan replacement is as follows.

1 to 2 from the time the pan is changed until the time when the molten steel is poured into the rear pan
Since preparation time is required, the amount of molten steel 4 in the tundish inevitably decreases if normal casting is continued.

Therefore, when the sliding nozzle of the rear pan is fully opened and the molten steel is supplied to the tundish through the long nozzle, the slag floating on the tundish molten steel is generated in the molten steel by the molten steel flow discharged from the long nozzle. Dirty molten steel that has been knocked in or thrown in and is suspended flows into the mold. This deteriorates the quality of the slab for pot replacement.

Therefore, hitherto, the seam slab cannot be applied to a strict quality machine, and the yield is deteriorated by scrapping.

However, as a result of the experiments and researches conducted by the present inventors, it was possible to clean the molten steel at the seam by defining the immersion depth and the pouring speed of the long nozzle at the start of pouring the pan. It was found that the quality deterioration of the slab can be prevented.

[0012]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a method for obtaining clean steel for satisfying the strict requirements for manufacturing high cleanliness steel, and the gist thereof is as follows. On the street.

As a method for injecting molten steel from a ladle into a tundish, in a continuous casting method in which a long nozzle is used, a long nozzle at the start of injecting a rear ladle is used to supply molten steel to the tundish after the front ladle. The continuous casting method for clean steel is characterized in that the immersion depth is 50 mm or more, and the injection speed from the long nozzle is 2.5 times or less than that in a steady state.

The details of the present invention will be described below based on examples.

FIG. 2 shows the effect of the long nozzle immersion depth on the seam inclusions at the start of the pan.

The horizontal axis represents the long nozzle immersion depth, and the vertical axis represents the number of inclusions within 3 m before and after the seam position at the start of the pan. Here, the injection rate is 10 t / min.

As shown in FIG. 2, as the long nozzle immersion depth increases, the number of inclusions decreases. This is because the inclusion of slag in the tundish is prevented, and when the immersion depth is 50 mm or more. The inclusion level was comparable to that of a middle slab.

As a result, the long nozzle immersion depth required for cleaning the seam is 50 mm or more.

FIG. 3 shows the effect of the pot pouring speed on the seam inclusions. The horizontal axis is the casting length based on the position of the mold surface at the start of the pan, the vertical axis is the number of inclusions, ◯ is the pot pouring speed of 16 t / min, and ● is the pot pouring speed of 10 t / min. In both cases, the long nozzle immersion depth is fixed to 50 mm.

As shown in FIG. 3, the smaller the pouring speed of the pan, the smaller the number of inclusions. This is because the discharge flow of the long nozzle was suppressed and the inclusion of slag in the tundish was prevented.

Even when the injection rate was 4 t / min, the level of inclusions at the time of injection was 10 t / min, or a better result was obtained.

From the above, the pot pouring speed required for cleaning the seam is 10 t / min or less.

[0023]

As described above, by applying the present invention, the level of inclusions in the seam slab at the time of pan replacement is improved to the level of a middle slab, and it is possible to apply it to a planned standard without scrapping. It became possible and it was possible to contribute to the improvement of the yield.

[Brief description of drawings]

FIG. 1 is a diagram showing a state in which molten steel is being supplied to a tundish through a long nozzle.

FIG. 2 is a diagram showing the influence of the immersion depth of a long nozzle on the level of inclusions.

FIG. 3 is a diagram showing the effect of the injection rate of molten steel from a long nozzle on the level of inclusions.

[Explanation of symbols]

 1 Ladle 2 Sliding nozzle 3 Long nozzle 4 Molten steel 5 Slag layer 9 Injection flow

Claims (1)

[Claims] 1. A method for injecting molten steel from a ladle into a tundish, in a continuous casting method using a long nozzle, in order to continuously supply molten metal to the tundish in a front ladle after starting the pouring of a rear ladle. A continuous casting method for clean steel, characterized in that the immersion depth of the long nozzle is 50 mm or more, and the injection speed from the long nozzle is 2.5 times or less than that in a steady state.