JP2003266162A - Highly clean steel manufacturing method by continuous casting - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for preventing degradation of cleanability of steel caused by inclusions in a tundish in changing a ladle during the continuous casting. <P>SOLUTION: In the highly clean steel manufacturing method by the continuous casting, Hkeep satisfies inequality of Hkeep≥Hmin+Hdown, where Hkeep is the required height from a tundish bottom part 6 of the molten steel level 7 in the tundish 1 when the molten steel is regularly fed from the ladle before changing the ladle so as to set the height of the molten steel level 4 in the tundish to be in a specified range, Hdown is the reduction of the height of the molten steel level 7 in the tundish caused by stopping the feed of the molten steel when the ladle is changed, and Hmin is the minimum height of the molten steel level 7 in the tundish 1 in which inclusions 9 afloat on the molten steel 4 in the tundish are not involved in the flow of the molten steel 4 in the tundish 1. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing high-cleanliness steel by continuous casting. In particular, it relates to molten steel in a tundish.

[0002]

2. Description of the Related Art Conventionally, in continuous casting, particularly continuous casting of high-cleanliness steel, the supply of molten steel from the ladle to the tundish is interrupted when the ladle is replaced at the time of charge connection. It is inevitable that the height of molten steel in the dish will decrease.

When the height of the molten steel in the tundish decreases, the molten steel flows in the tundish near the upper surface of the molten steel in the tundish, so that the inclusions temporarily floating on the molten steel in the tundish are generated. , Caught in the flow of molten steel in the tundish.

On the other hand, if the height of the molten steel in the tundish is sufficiently high, the inclusions entrained in the molten steel flow in the tundish will re-float in the tundish, but the height of the molten steel in the tundish will increase. When is low, inclusions and the like caught in the flow of molten steel in the tundish cannot re-float in the tundish and remain as inclusions in the steel to deteriorate cleanliness. In the conventional method, the cleanliness of the bloom obtained when the amount of molten steel in the tundish is reduced is worse than that obtained in the steady state, and inclusions having a ground defect size of 50 to several thousand μm may appear. In some cases, the required quality cannot be satisfied for the intended use.

[0005]

SUMMARY OF THE INVENTION The problem to be solved by the present invention is to prevent the inclusion of inclusions in the tundish during continuous casting, especially when changing the ladle during charge connection in continuous casting. It is to provide a means for preventing deterioration of cleanliness.

[0006]

According to the invention of claim 1, in the continuous casting method, the height of the molten steel surface in the tundish is controlled within a specific range. It is a method for producing a high-cleanliness steel by continuous casting, which is characterized by maintaining the temperature for a long time.

In the second aspect of the invention, the specific range to be controlled and maintained is Hkeep, which is the required height of the molten steel surface in the tundish from the bottom of the tundish during constant supply of molten steel from the ladle before replacement of the ladle. , Hdo decrease of the height of the molten steel surface in the tundish due to interruption of molten steel supply when replacing the ladle
Let wn be the minimum height of the molten steel surface in the tundish, where the floating inclusions floating above the molten steel in the tundish are not caught in the flow of the molten steel in the tundish.
The method for producing a high cleanliness steel by continuous casting according to claim 1, characterized in that when it is in, Hkeep represented by the formula (1) is used.

[0008]

## EQU00002 ## Hkeep.gtoreq.Hmin + Hdown (1) Needless to say, Hkeep is lower than the tundish height.

With the above means, in continuous casting, particularly continuous casting, inclusions floating on the molten steel in the tundish are prevented from being entrained in the flow of the molten steel in the tundish and mixed in the molten steel. The inclusions involved can be easily re-surfaced.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described with reference to the drawings. FIG. 1A shows a state of the tundish 1 at the time of steady supply of molten steel from the ladle before the ladle is replaced. In the tundish 1, the slag caught in the pouring water 3 from the ladle is floated and separated by the weir 2, and the molten steel 4 flows into the tundish 1 from the lower portion of the weir 2 as a molten steel flow 8. The height of the molten steel surface 7 is maintained at the height Hkeep from the tundish bottom portion 6, and the inclusions float on the molten steel surface 7 and are separated as floating inclusions 9. On the other hand, the molten steel 4 from which inclusions are separated is supplied from the nozzle 5 of the tundish bottom 6 to the continuous casting mold.

FIG. 1 (b) shows a tundish 1 due to interruption of molten steel supply when a ladle is exchanged when a continuous casting charge is connected.
Indicates the state of. In the tundish 1, the molten steel 4 continues to be supplied to the mold from the tapping nozzle 5 of the tundish bottom portion 6, so that the height of the molten steel surface 7 decreases. When the amount of decrease in height of the molten steel surface 7 in the tundish 1, that is, the decreased height is indicated by Hdown, this Hdown differs depending on the continuous casting equipment, casting conditions and ladle replacement work, and is different for each continuous casting equipment. Hdown is determined by a water model or the like. FIG. 2 shows the relationship between the stop period of the molten steel supply from the ladle and the Hdown of the amount of decrease in the height of the molten steel surface 7 in the tundish 1. It should be noted that FIG. 2 shows the case of continuous casting of 130 tons per hour, for example.

Further, in FIG. 1 (c), the molten steel surface 7 is lowered in the tundish 1 when the molten steel supply is interrupted, and the floating inclusions 9 and the like floating on the molten steel in the tundish 1 are in the tundish 1. Shows the state in the tundish 1 when the molten steel surface 7 that is not involved in the flow of the molten steel 4 is lowered to the lowest, and the arrow 10 indicates inclusions that are caught in the molten steel when the molten steel surface 7 is further lowered. . When the minimum height from the tundish bottom 6 of the molten steel 4 in the state of (c) is indicated by Hmin, this Hmin differs depending on the continuous casting equipment and the casting conditions similarly to the above, and is different for each continuous casting equipment. In the same way, Hmi
Determine n. When the height of the molten steel surface 7 in the tundish 1 becomes lower than the Hmin of (c), the inclusions involved in the molten steel flow flow into the mold together with the molten steel 4, and a part of the inclusions is cast slab. It will be captured inside.

Therefore, the height of the molten steel surface 7 from the tundish bottom 6 which is the required height of the molten steel in the tundish 1 at the time of steady supply of molten steel from the ladle before replacement of the ladle is Hkee.
When p is set, in this embodiment, the height of the molten steel surface 7 in the tundish 1 is controlled and maintained in a specific range in the continuous casting method.
Secure at least n + Hdown and maintain it. By maintaining the height of the molten steel surface 7 in the tundish 1 in this manner, the molten steel in the tundish 1 can be replaced even when the ladle is replaced, where the height of the molten steel surface 7 in the tundish 1 is the lowest. Four
It is possible to prevent the floating inclusions 9 floating above from being caught in the flow of the molten steel 4 in the tundish 1.

[0014]

Example: In the tundish used for continuous casting of 130 tons per hour described above, Hdown of the height decrease of the molten steel surface 7 in the tundish 1 at the time of ladle exchange was 200 mm (determined by a water model). Molten steel 5t equivalent)
And the minimum height H of the molten steel surface 7 in the tundish
min is 320 mm (equivalent to 6 t of molten steel). Therefore, the required height of molten steel in the tundish before replacing the ladle is Hkeep.
Was 520 mm (equivalent to 11 t of molten steel).

Therefore, the Hheep of the required height of the molten steel surface 7 in the tundish 1 before the ladle is replaced is 840 mm (corresponding to 20 t of molten steel), and the minimum molten steel surface 7 when the ladle is replaced.
Actual height Hmin of 660mm (equivalent to 15t of molten steel)
Met. By taking this into consideration the value determined by the above water model and extending the interval of ladle replacement, the molten steel minimum height Hmin in the tundish 1 at the time of ladle replacement can be set in the tundish 1 of the above embodiment. The floating inclusions 9 and the like that have floated above the molten steel are not caught in the flow of the molten steel in the tundish 1 Minimum height of molten steel in the tundish 1 Hmin
It was possible to control up to 320 mm (corresponding to 6 t of molten steel).

By this method, deterioration of cleanliness due to inclusion of inclusions in the tundish when the ladle was exchanged could be properly prevented.

[0017]

As described above, according to the present invention, in continuous casting, by controlling and maintaining the height of the molten steel surface in the tundish within a specific range, the present invention occurs when the ladle is replaced at the time of charge connection. It is possible to accurately prevent deterioration of the cleanliness of steel due to inclusion of inclusions in the tundish.
The present invention has an excellent effect that has never been obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a state of molten steel in a tundish,
(A) shows the state of the tundish at the time of steady supply of molten steel from the ladle before the ladle is exchanged, and (b) shows the state of the tundish due to interruption of the molten steel supply at the time of ladle exchange at the time of charge connection. 3C shows the state when the floating inclusions are not caught in the flow of the molten steel in the tundish when the supply of the molten steel is interrupted and the molten steel surface is at the lowest position.

FIG. 2 is a graph showing a relationship between a stop period of molten steel supply from a ladle and a reduction amount Hdown of a height of a molten steel surface in a tundish.

[Explanation of symbols]

1 tundish 2 weirs 3 pouring 4 Molten steel 5 Steel tap nozzle 6 Tundish bottom 7 Molten steel surface 8 Molten steel flow 9 Levitating inclusions 10 Inclusions involved

Claims (2)

[Claims] 1. A method for producing high-cleanliness steel by continuous casting, characterized in that the height of the molten steel surface in the tundish is controlled and maintained in a specific range in the continuous casting method. 2. The specific range to be controlled and maintained is Hkeep, which is the required height of the molten steel surface in the tundish from the bottom of the tundish at the time of steady supply of molten steel from the ladle before the ladle is changed. The amount of decrease in the height of the molten steel surface in the tundish due to the interruption of the molten steel supply is Hdown, and the floating inclusions floating on the molten steel in the tundish do not get caught in the flow of the molten steel in the tundish. When the minimum height of the molten steel surface inside is Hmin,
The method for producing a high cleanliness steel by continuous casting according to claim 1, wherein the Hkeep is represented by the formula (1). ## EQU00001 ## Hkeep.gtoreq.Hmin + Hdown (1)