JPS60152349A - Casting method of terminal billet in continuous casting - Google Patents

Abstract

PURPOSE:To suppress formation of a pipe in the terminal part of a billet and to cast the billet having high quality with high productivity by interrupting pouring to a casting mold in the end period of continuous casting and inserting a holding plate into the casting mold then pouring additionally the remaining molten steel in a tundish to the mold. CONSTITUTION:Pouring to a casting mold 5 is interrupted in the end period of casting and a holding plate 8 provided with a hook 9 and consisting preferably of an exothermic heat insulating material is inserted into the mold 5 then the remaining molten steel 6 in a tundish 2 is additionally poured to an unsolidified part 6b while formation of a solidified shell 7 is suppressed in continuous casting consisting in supplying the molten steel 6 from the tundish 2 via an immersion nozzle 4 in a bottom part 3 to the inside of the mold 5, cooling the molten steel to form successively a solidified shell 7 and drawing continuously a billet 1 while feeding the molten steel 6 to the unsolidified part 6a formed in the lower part. The pipe to be formed in the terminal part of the billet is thus thoroughly suppressed and the floating of the inclusions in the molten steel 6 is accelerated. The billet 1 having no surface defects, etc. is obtd. at a high yield with high productivity.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for casting late-stage iron pieces in continuous die making.

(Prior art) Generally, when molten steel is manufactured into slabs, billets, or other slabs using continuous casting, a pipe is generated at the end (final slab) at the end of the casting process due to solidification shrinkage of the molten steel. .

A pipe formed by the solidification and shrinkage of molten steel is formed by penetrating from the end of the casting end to the inside of the tip of the slab to a considerable depth, so the fishing piece near the end must be cut and removed. This results in a significant decrease in yield, resulting in large economic losses.

Therefore, as a method for improving the yield of slabs by reducing the pipe produced in the vicinity of the end of the chimney finishing part, for example, as disclosed in Japanese Patent Publication No. 50-29422, the metal poured into the mold is A casting method (simply referred to as heating and cooling casting method) in which the temperature of molten steel is adjusted by heating or cooling it to near the liquid phase to prevent metal adhesion, refractory wear, nozzle clogging, etc. (simply referred to as heating and cooling casting method), or casting speed. A method (simply referred to as the low-speed casting method) is being used to reduce the molten steel and quickly solidify it in the mold and immediately below the mold, thereby easily replenishing the shortage of molten steel due to solidification shrinkage and thereby suppressing the formation of pipes. .

However, these above-mentioned pipe suppression methods at the end of casting are
No matter which one is used, it is far from sufficient for the reasons described below.

The method without heating or cooling allows the molten metal in the mold to be in the vicinity of the liquid phase, so the solidification and contraction of the molten metal can be made uniform and small, which can considerably suppress pipe formation, but it has not been able to sufficiently suppress it. Moreover, it has drawbacks such as requiring a large amount of equipment costs such as a heating device. 1. The low speed casting method is able to sufficiently solidify the mold and directly below the mold to replenish the shrinkage of the molten steel due to solidification, which can considerably suppress the formation of pipes. As a result, the originally high productivity of continuous steel making is greatly hindered, and the slow speed reduction causes defects such as air bubbles on the surface of the slab.

(Objective of the Invention) The present invention has high productivity, which is the disadvantage of the conventional method as described above, and also sufficiently suppresses the formation of pipes at the ends of the slab, and obtains slabs with few surface defects. The feature is that a heat-generating heat insulating plate is inserted into the mold at the end of casting, and then the remaining molten steel in the tundish is added with hot water, which makes it extremely easy to suppress the pipe at the end of the slab. This is a method of casting slabs that allows for.

(Structure and operation of the invention) The method for casting an end slab of the present invention will be described below. In continuous casting, molten steel poured into a mold forms a solidified shell within the mold, and descends as a slab while gradually increasing its thickness. In this way, when the solidified shell grows, the molten steel contracts due to solidification, and a pipe is formed inside the slab. Further, this pipe may be enclosed (single void) or continuous by dendrites formed when molten steel solidifies. As a result of cutting and investigating various cross-sections of slabs at the final stage of casting, the inventors found that the length of a normal pipe and the penetration depth of inclusions associated with the formation of the pipe are approximately 1.5 m. In addition, the generation of the pipe is caused by insulating and insulating the vicinity of the solidified shell formed on the inner surface of the @-shaped mold from the inside and generating heat in the heat insulating plate itself, thereby suppressing the growth of the solidified shell and melting the inside. It has been discovered that if the condition is maintained, the formation of pipes and the intrusion of inclusions into the slab can be extremely effectively prevented.

In other words, for small slabs such as those produced in continuous casting, the growth of the solidified shell is directly inhibited from the inner surface, and the molten steel in the mold is maintained in a molten state to ensure sufficient flow of the molten steel to the bottom of the slab. The formation of pipes at the bottom of the slab and the inclusions at the bottom of the slab are removed by flotation. In this way, by insulating and suppressing the formation of a solidified shell by inserting a heat-generating heat insulating plate (hereinafter simply referred to as a heat insulating plate), it is possible to secure the amount of molten steel in the feeder and partially suppress the growth of the solidified shell. It is possible to prevent the formation of dendrites from inhibiting the rising of the molten steel and internal inclusions.

In addition, due to the replenishment of molten steel, the molten steel in the mold becomes insufficient and the surface of the molten steel lowers, but the amount equivalent to the shortage is equal to the amount of solidification shrinkage of the molten steel remaining in the tundish and the amount of shrinkage in the mold. However, the water is replenished from the remaining hot water.

Therefore, the present invention suppresses the growth of the solidified shell by inserting a heat insulating plate in the mold, and maintains the molten steel in the mold in a molten state. By adding hot water from the tundish, it is possible to eliminate the formation of pipes in the end slab and to float away the inclusions remaining inside. Hereinafter, a method for casting an end slab according to the present invention will be described in detail based on an embodiment of the present invention shown in the drawings. FIG. 1 shows a sectional view of an embodiment of the method for casting an end slab according to the present invention.

In the figure, the slab 1 is a molten steel 6 supplied into a mold 5 through a submerged nozzle 4 provided at the bottom 3 of a tundish 2.
is continuously cast while forming a solidified shell 7 by cooling and being pulled out by a support roll or the like (not shown) provided at the bottom of the mold 5. In this way, when one piece of slab 1 is continuously made, the solidified shell 7 grows one after another in the lower part of the mold 5 of the slab 1, and the dendrites protrude inward. Although an unsolidified portion 6a is formed up to the lower part of the mold, the formation of a pipe is suppressed due to the feeder effect caused by pouring the metal from the tundish 2 into the mold.

However, at the final stage of casting, since there is no feeder effect due to the above-mentioned pouring, an unsolidified portion 6b as shown by the dotted line is formed, and a pipe (see Fig. (not shown) occurs.

Therefore, in order to prevent the formation of this pipe, residual molten steel 6 was placed in the tundish 2 in an amount corresponding to the solidification shrinkage needle of the unsolidified portion 6a and the solidification contraction amount of the unsolidified portion 6b in the lower part of the mold 5. After stopping the casting in this state, a heat insulating plate 8 having a size slightly smaller than the inner surface of the mold 5 is inserted and fixed inside the solidified shell 7 in the mold 5 via, for example, a hanger 9. By inserting this heat insulating plate 8 between the solidified shell 7 and the molten steel 6, the growth of the solidified shell 7 is suppressed, the feeder is prevented from being inhibited by dendrites, and a sufficient amount of molten steel 6 in the feeder is ensured. Ru.

As the heat insulating plate 8 used as described above, a heat insulating material as shown in Table 1 is preferable, but it is also possible to simply use a heat insulating material. Further, when using the heat insulating plate 8, only the wide surface of the mold 5 is used, or as in the present embodiment shown in FIG. 2 (described later).

An appropriate cut inside 11 may be provided, or a heat insulating layer and a heat generating layer may be used in combination.Additionally, the effect will be further improved if a heat generating powder used in general agglomeration is added to the hot water surface.

Table 1 Next, as described above, in order to replenish the molten steel 6 in the mold 5 into the contracted part of the lower part of the slab 1 by inserting the heat insulating plate 8, the surface of the molten steel in the mold 5 is lowered. So, following this,
The remaining hot metal for the feeder left in the tundish 2 is poured into the mold 5 to complete casting.

After the casting is completed, it may be removed from the mold 5 via the hanger of the heat insulating plate 8, or it may be left as is and removed by cutting.

In addition, in the method of the present invention, in particular, when the heat insulating plate 8 is formed into a four-sided assembly and inserted into the mold 5 as shown in FIG. 2, when the solidified shell 7 on the outer periphery is appropriately formed, Since the molten steel 6 for the feeder can be poured at a higher level than the top surface of the conventional mold 5, there is also the advantage that the feeder effect can be further improved. Further, it is also possible to appropriately provide cutouts 9 in the exothermic heat insulating plate 8 to facilitate the flow of the molten steel 6.

(Example) Next, the method of casting end slabs according to the method of the present invention was carried out in a 300T continuous casting machine using the apparatus shown in Fig. 1. The results are shown in Table 2 in comparison with the conventional method. However, with this method, the cutting amount of the end slab at the final stage of casting is extremely small, and the quality of the end slab is also better than that of the conventional method.
It turns out that it is extremely good.

As mentioned above in Table 2, by using this method, the high productivity, which is a characteristic of conventional continuous casting machines, can be maintained without sacrificing the high productivity.
This is an excellent casting product that can suppress surface defects in the slab and also improve the internal quality of the end of the slab, thereby significantly improving the casting yield with the same type of slab as conventional slabs. This is the method of inclusion.

[Brief explanation of drawings]

FIG. 1 shows a sectional view of an embodiment of the method for casting end slabs according to the present invention, and FIG. 2 shows a perspective view of a heat-generating heat insulating plate used in the method for casting end slabs according to the present invention. show. l...Slab 2...Tandish 3・Bottom 4・
... Immersion nozzle 5 ... Sword-shaped 6 ... Molten steel 7 ... Solidified shell 8 ... Heat insulation plate 9 ... Hanging hand 10 ... □ cut inside 1st item 2nd quotient

Claims (1)

[Claims] In continuous casting, in which molten steel is poured into a mold through an immersion nozzle provided in the tundish, the pouring into the mold is interrupted at the end of casting, a heat insulating plate is inserted into the mold, and then the molten steel in the tundish is poured into the mold. Method for casting end UJ pieces in continuous casting characterized by adding molten steel