JPH07124712A - Continuous casting mold - Google Patents

Abstract

PURPOSE:To halve the occurrence ratio of surface flaw on a cast slab by providing the slits flowing cooling water in the direction perpendicular to the casting direction at a meniscus position and the slits flowing the cooling water to the direction parallel to the casting direction at the downstream side from the meniscus. CONSTITUTION:A continuous casting mold is constituted of four sides of mold copper plates 1 and cooling boxes having respectively independent cooling structure. The cooling mechanism is divided into a first zone at the meniscus position and a second zone at the downstream side from the meniscus in the casting direction. Then, the slits 3 flowing the cooling water in the direction perpedicular to the casting direction are formed at the meniscus position and the slits 3 flowing the cooling water in the direction parallel to the casting direction are formed at the downstream side position. According to the casting condition, the cooling water flow rate in each slit at the down-stream side position is adjusted and each cooling degree can be controlled. By this method, the shell strength can sufficiently be secured.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a continuous casting mold.

[0002]

2. Description of the Related Art The purpose of cooling a mold in continuous casting is to reliably form an initial solidified shell and to obtain strength enough to withstand drawing in a roll band after the mold. for that reason,
Focusing on increasing the cooling strength in the mold as much as possible, a method of uniformly cooling the entire mold was devised, a technology was created to make slits on the copper plate of the mold and to plate the surface, in order to extend the service life. Was devised.

[0003]

However, in recent years, due to stricter demands on quality and demands for cost reduction by improving yield, the surface properties of cast slabs have become a problem. There has been a demand for improvement of surface defects that occur during cooling of the steel. As measures against this, the powder used for casting and the vibration of the mold have been improved, and the mold has been cooled slowly, and the effects have been improved. However, at present, these measures are not always sufficient.

As a result of investigating surface flaws, it has become clear that the steel types that are particularly prone to surface flaws are accompanied by a δ-γ phase transformation during solidification, and the surface flaws are due to strain during the phase transformation. As a countermeasure, it is effective to weaken the cooling in the mold in order to suppress the generation of strain. In addition, the cause of surface flaws in other steel types is the non-uniform formation of the shell in the mold, and if a locally thin shell thickness occurs, stress concentration occurs there and cracking may occur. found. As a countermeasure against this, gentle cooling is effective in order to achieve uniform solidification of the shell in the width direction. However, directing gentle cooling with the conventional mold cooling mechanism tends to reduce the initial shell strength, causing problems such as breakout. Therefore, the development of a mold cooling mechanism that prevents surface defects while ensuring sufficient shell strength has become an issue.

[0005]

Surface defects are formed during the early stages of shell formation. Further, in the region where the shell thickness is sufficiently developed and the strength is exhibited, the strain due to transformation is endured. Therefore, the strain during transformation is prevented by weakening only the cooling in the vicinity of the meniscus where the shell thickness / strength is insufficient, and the shell is strongly cooled in the region where it has sufficient strength so that the mold can be pulled out by subsequent rolls. It is conceivable to secure a shell thickness and strength that can withstand Here, each of the cooling water slits in the vicinity of the meniscus can adjust the amount of cooling water, the cooling is gradually weakened as the distance from the meniscus increases, and the mold copper plate surface temperature is gradually increased to the upper limit value within the allowable temperature range of the copper plate. Can be cooled. Since the molten steel surface in the mold is changed by the abrasion of the surface of the mold copper plate and the melting loss of the immersion nozzle, a mold cooling means for changing the cooling strength with respect to the casting direction was devised.

That is, the gist of the present invention is to
It has a cooling mechanism divided into a meniscus position and a position downstream from it in the casting direction.It has a slit that allows cooling water to flow perpendicularly to the casting direction at the meniscus position, and allows cooling water to flow parallel to the casting direction at the downstream side. A continuous casting mold having a slit.

Further, in the present invention, in the above-mentioned mold, the cooling water amount in each slit at the downstream side position is adjusted according to the conditions such as the type of steel to be cast, the casting speed, the molten steel level in the mold, and the like. The feature is that the cooling strength can be adjusted.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A description will be given below with reference to the drawings. FIG. 1 schematically shows the structure of a continuous casting mold for steel, and the rectangular mold is a four-sided copper plate 1 having four independent cooling structures.
And a cooling water box 2.

FIG. 2 schematically shows the cooling mechanism of the present invention. It consists of a copper plate 1 that directly removes the heat of molten steel, and a cooling water box 2 that mechanically supports it from the back surface and guides cooling water to the slits 3, and both are firmly fastened with bolts or the like. The cooling water is divided into a first zone for gently cooling the meniscus portion and a second zone for strongly cooling the shell to ensure shell strength, and each zone can be independently controlled. Further, each of the above-mentioned slits, particularly the slit at the downstream side position, can individually adjust the amount of cooling water.

FIG. 3 shows an example of processing the copper plate slit of the present invention. As shown in the figure, the slit 3 is formed so that the cooling water flows at the upstream meniscus position in a direction perpendicular to the casting direction, and the cooling water flows at the downstream side in parallel to the casting direction.

FIG. 4 is a temperature distribution on the surface of the mold copper plate according to the present invention. The temperature is high in the meniscus part, and it is being cooled slowly. In terms of strength during use and life, 350 ° C. is set as the upper limit in the examples. Further, the cooling in the vicinity of the meniscus is gradually weakened toward the downstream portion, and as a result, it is gradually cooled at a high temperature of 350 ° C. for a certain period.

The effect of applying the present invention is shown in FIG. As a result of adopting the mold according to the present invention, the rate of occurrence of slab surface flaws is 4 when the conventional value is 100 as a flaw occurrence index.
It was confirmed that it was about half that of 8.

[0013]

According to the present invention, it has become possible to reduce the occurrence rate of surface flaws in a slab to half that of the conventional one and to ensure sufficient shell strength.

[Brief description of drawings]

FIG. 1 is a schematic view of a mold assembly.

FIG. 2 is a schematic diagram of mold cooling according to the present invention.

FIG. 3 is a diagram showing an example of slitting a copper plate in a mold.

FIG. 4 is a temperature distribution diagram of a mold copper plate surface.

FIG. 5 is a diagram showing a surface flaw occurrence index when the present invention is applied, in comparison with a conventional index.

[Explanation of symbols]

 1 Mold copper plate 2 Cooling box 3 Slit

Claims (2)

[Claims] 1. A continuous casting mold has a cooling mechanism divided into a meniscus position and a position downstream thereof from the meniscus position, and has a slit for flowing cooling water perpendicularly to the casting direction at the meniscus position. The continuous casting mold is characterized in that the side has a slit for flowing cooling water parallel to the casting direction. 2. The amount of cooling water in each slit at the downstream side position can be adjusted according to the conditions such as the type of steel to be cast, the casting speed, the molten steel level in the mold, and the cooling strength of each can be adjusted. The continuous casting mold according to claim 1.