JP4289476B2 - High cleanliness steel casting method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
In the present invention, in continuously casting steel, when the molten steel is taken out from the bottom steel outlet of the ladle filled with molten steel, the slag in the ladle is entrained by the vortex generated along with the outflow of the molten steel. The present invention relates to a continuous casting method for producing a steel slab having high cleanliness by preventing slag from flowing out together with molten steel and flowing into a tundish.
[0002]
[Prior art]
In continuous casting of steel, the molten steel in the refined ladle is poured into the tundish while controlling the flow rate of the molten steel through the opening and closing controller provided at the bottom of the ladle, and the molten steel is cast from the tundish as a mold. The slab is manufactured by continuous casting. In this manufacturing process, in order to melt high cleanliness steel, when pouring the molten steel in the ladle into the tundish, it is to prevent the slag floating on the molten steel in the ladle from flowing out. . By the way, the outflow of slag from the ladle into the tundish was caused by the vortex of the molten steel generated near the top of the tap opening provided at the bottom of the ladle as the amount of molten steel in the ladle decreased. The eddy current is caused by the floating slag on the molten steel in the ladle and flowing out with the molten steel.
[0003]
Therefore, as a method for preventing slag outflow, the slag outflow prevention method disclosed in Japanese Patent Application Laid-Open No. Sho 62-203667 was adjusted for specific gravity when the level of molten steel in the ladle was lowered and eddy current was generated. The floating valve is positioned at the slag-molten steel interface immediately above the outlet of the steel outlet to prevent eddy currents from occurring and prevent the slag from entraining. Is to prevent.
[0004]
In this method, it is necessary to particularly arrange a stopper, a lifting device or the like for preventing the vortex flow in the ladle and closing the steel outlet. However, since the inside of the ladle or its periphery is very high temperature, the cost concerning an installation becomes great.
[0005]
Furthermore, in the molten steel pouring method of the tundish for continuous casting disclosed in JP-A-8-1295, the molten steel pouring amount is decreased until the molten steel vortex generation can be prevented at the end of the pouring of molten steel from the ladle, and cannot be detected. This prevents the small amount of slag from entering the molten steel, and then detects the slag at the position of the molten steel injection nozzle in the ladle as the slag layer in the ladle descends, and closes the molten steel injection nozzle based on this result. . However, with this method, slag detection is performed at the nozzle position, and slag has already flowed into the tundish at the time of detection, and is not suitable for melting steel with high cleanliness.
[0006]
[Problems to be solved by the invention]
Highly clean by preventing the outflow of slag from the ladle to the tundish without arranging a stopper or the like in the ladle while efficiently adjusting the amount of molten steel remaining in the ladle. It is to provide a method for continuously casting steel.
[0007]
[Means for Solving the Problems]
In the invention of claim 1, the means for solving the above-mentioned problem is that , in the molten steel injected into the tundish from the ladle and continuously cast, This is a high cleanliness steel casting method characterized in that the molten steel injection nozzle is closed at the remaining steel height h in the ladle shown in the following formula (1), which can prevent the generation of molten steel vortex .
[0008]
[Expression 2]
h> 0.48Q ^2/5 ... (1) Formula However,
h: Remaining steel height in the ladle (m)
Q: Injection flow rate from ladle to tundish (m ³ / s)
[0009]
(Reason for setting conditions)
The inventor quantitatively investigated the effects of the residual steel height in the ladle 1 and the molten steel injection flow rate on the vortex generation at the end of the ladle injection using a water model. As a result, as shown in FIG. 2, it was found that the height (m) of the vortex generating region 9 where vortices are generated is proportional to the 2 / 5th power of the molten steel injection flow rate (m ³ / s). Therefore, as shown in FIG. 2, by closing the molten steel injection nozzle 6 at a height higher than the vortex generation line 8, the ladle 1 can be moved into the tundish 4 with an appropriate amount of remaining steel without generating vortices. It was found that slag spillage could be prevented.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the invention are illustrated by the following examples.
[0011]
【Example】
In FIG. 1, C: 0.35%, Si: 0.3%, Mn in mass% having a slag layer 2 in the upper portion in a frustoconical ladle 1 having a bottom diameter of 3150 mm, a top diameter of 3550 mm, and a height of 3400 mm : 0.8%, P: 0.01%, S: 0.003%, Cr: 1.0%, Mo: 0.15%, steel consisting of the remaining Fe and other inevitable impurities, 1550 ° C molten steel 3 Fill and set this on the tundish 4. Next, the molten steel 3 is introduced into the tundish 4 from the injection nozzle 6 having a circular steel outlet 5 of φ100 mm installed at the bottom of the ladle (equivalent to 4.6 × 10 ⁻³ m ³ / s). Inject with. Thereafter, molten steel 7 is poured into a mold (380 mm × 490 mm) installed at the bottom of the tundish 4 and continuously cast at a speed of 0.5 m / min. At this time, immediately after the molten steel 3 at the end of pouring from the ladle 1 is in the range of the remaining steel height h in the ladle according to the present invention 3.1 t (h = 0.56 m), the pouring nozzle 6 is moved. The injection into the tundish 4 is terminated. When cast in this manner, there was no slag in the tundish 4, and the inclusion index in the φ167 steel slab after hot rolling after casting showed a good value of 47. Further, as a comparative example, 2 t / min (equivalent to 4.655 × 10 ⁻³ m ³ / s) is injected into the tundish 4 and injected into the tundish 4 immediately before the remaining steel 2t (equivalent to h = 0.036 m). , The inclusion index of the billet deteriorated to 58.
[0012]
The remaining steel height h in the ladle can be replaced by a molten steel weight calculated from the shape of the ladle and the specific gravity of the molten steel. Further, as the injection flow rate Q from the ladle 1 to the tundish 4, a value calculated from the relationship between the molten steel amount in the tundish 4 and the casting speed can be used.
[0013]
【The invention's effect】
As described above, the method of the present invention can surely prevent the outflow of slag from the ladle to the tundish, and can be cast with an appropriate amount of remaining steel, so that high purity steel can be produced with a high yield. I can do it. In addition, since the present invention does not require significant capital investment, it is possible to expect an excellent effect at low cost.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view of a ladle and a tundish according to an embodiment of the present invention.
FIG. 2 is a graph showing a vortex generation region in the present invention.
[Explanation of symbols]
1 Ladle 2 Slag layer 3 Molten steel 4 Tundish 5 Steel outlet 6 Injection nozzle 7 Molten steel 8 Vortex generation line 9 Vortex generation area

Claims (1)

When ladle is poured from the ladle into the tundish for continuous casting, the ladle shown in the following formula (1) can prevent the molten steel vortex from occurring in the ladle at the end of the molten steel injection from the ladle to the tundish A casting method for high cleanliness steel, characterized in that the molten steel injection nozzle is closed at the inner residual steel height h .
[Expression 1]
h> 0.48Q ^2/5 ... (1) Formula However,
h: Remaining steel height in the ladle (m)
Q: Injection flow rate from ladle to tundish (m ³ / s)

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