JPH0332452A - Method for continuously casting different steel kinds - Google Patents

Abstract

PURPOSE:To submerge the parting wall metal plate into molten steel in a mold while continuing pouring of the molten steel changed in a tundish through the submerged nozzle by using a parting wall metal plate cutting a part where interfered with a submerged nozzle. CONSTITUTION:At first, while using the same tundish 1, the continuous casting for different steel kinds is executed by exchanging the molten steel of the previous heat to the molten steel of the next heat having different steel kind. At this time, when the molten steel 2A of the previous heat in the tundish 1 becomes near completion of the pouring, while continuing the pouring of molten steel into the mold 5 from the submerged nozzle 4 under condition of opening a sliding nozzle 3, the parting wall metal plate 8 is carried above the mold 5, and after making the U-shaped cutting part 8B the condition being along periphery of the submerged nozzle 4, the parting wall metal plate 8 is descended and submerged into the molten metal 2A of the previous heat in the mold 5. In this result, the poured molten steel 2A is parted into upper and lower parts at the stage when the parting wall metal plate 8 is positioned below discharging holes 4A in the submerged nozzle 4.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a method for continuous casting of different steel types, and particularly to a method for continuously casting molten steel of different steel types in the next charge following the previous charge of molten steel using the same tundish. The present invention also relates to a method for continuous casting of different steel types, which can reduce cut gaps caused by mixing different steel types.

<Prior art> In continuous casting of four types of different steel, when the molten steel of the previous charge is changed to the molten steel of the different steel of the next charge and continuous casting is performed, a slab is formed by mixing the four types of different steel at the boundary between the two. Since it cannot be used for any steel type and is discarded as scrap, it is desirable to make the length of the mixed portion of different steel types as short as possible.

Conventionally, various means have been disclosed to reduce the occurrence of such mixed slabs of different steel types.For example, Japanese Patent Publication No. 57-36
Publication No. 059 discloses a step of stopping the injection of the first molten steel (pre-charge c) into the mold, settling a path material having a circular or polygonal cross section and having a guide member at a substantially central position in the mold, and forming a solidified layer around the material that is connected to the solidified shell developed from the mold wall;
A different tl including the step of injecting molten steel (next charge)
The continuous casting method of the 4 Gods is shown in JjJJ.

In this method, after the injection from the tundish containing 'fijt14 of the previous charge is completed, the tundish is replaced with the tundish for the next charge. After the material is allowed to settle, continuous cast casting is performed by injecting the next charge of different steel Il molten steel.

In this way, when continuous casting of different steel types is performed by replacing the tundish, the casting is stopped once, the tundish is raised, and the immersion nozzle is removed from the mold.
Furthermore, the tanditshu is evacuated from the casting position. Subsequently, the tundish for the next charge, which is waiting at the standby position, is moved to the casting position to replace the tundish.Then, the tundish is lowered, the immersion nozzle is set at the specified position, and the sliding nozzle is opened to insert the mold. It is necessary to carry out continuous Vt casting of different steel types by starting the casting of the next charge inside.

Replacing the tundish requires a spare tundish for the next charge, which not only increases equipment costs but also increases the cost of refractories, which is disadvantageous in terms of cost. In order to solve this problem, a method is being adopted in which continuous casting of different steel types is performed using the same tundish.

In other words, Fig. 6 shows the conventional continuous casting of different steel types using the same tundish, from the previous charge of molten steel to the next charge of different steel l! 1 When pouring molten steel, the 6th
As shown in Figure (a), the sliding nozzle 3 is closed and the mold is transferred from the tundish l through the immersion nozzle 4 with a large amount of the pre-charged molten steel 2A housed in the tundish l remaining and approximately 5 remaining. At the same time as stopping the pouring into the immersion nozzle 4,
is separated from the molten steel 2A in the mold 4.

The reason why a large amount of molten steel 142A from the previous charge remains in the tundish is that if the remaining amount is small, the molten steel 2A while pouring is stopped.
This is to prevent the solidification in the tundish nozzle 7 due to the temperature drop, resulting in nozzle clogging. Nozzle clogging is often prevented by using the inert gas 6 blown into the tundish nozzle 7 in combination.

When the partition wall hardware 8A is immersed in the molten metal 112A in the mold 5 in this state, since the partition wall hardware 8A is made of iron, it gradually settles due to the difference in specific gravity with the molten metal 112A, and becomes attached to the solidified shell 9 formed on the inner wall of the mold 5. As a result, the partition wall hardware 8A stops settling. A solidified layer of the molten steel 2A is rapidly formed around the partition wall hardware 8A which is locked to the solidified shell 9 which is being pulled out at a low speed, and the solidified layer connects with the solidified shell 9 to form a partition wall.

Subsequently, the tundish l is lowered as shown in FIG. Injection of 11 m of different molten steel 2A begins.At this point, when the sliding nozzle 3 is opened, the immersion nozzle 4 is mixed with the residual molten steel 2A from the previous charge and the molten steel 2B of a different type from the next charge. The liquid is injected upward into the partition metal fittings 8 placed in the mold 5 through the liquid.

In such a conventional continuous casting method of different steel types using the same tundish, a large amount of pre-charged molten steel remains in the tundish l, resulting in a large amount of molten steel mixed with the next charge of different steel types, resulting in the equivalent of scrap due to the mixing of different steel types. As the slab becomes longer and a large amount of broken bones are disposed of, the yield decreases. In particular, when the difference in composition between different steel types is large, there is a problem that the composition cannot be applied because there are many parts where the composition differs.

<Problems to be Solved by the Invention> As explained above, there are problems with continuous casting of different steel types, either by exchanging tundishes or by using the same tundish. It is necessary to stop the casting, raise the tundish, and evacuate the immersion nozzle from the mold, which interrupts the casting operation and reduces productivity. Particularly when the precharge is of a steel type that is highly susceptible to cracking, there is a problem in that the slab stopped in the continuous rolling machine is overcooled and surface defects such as transverse cracks are likely to occur.

The present invention solves the problems of the prior art and provides a method for continuous casting of different steel types, which can reduce equipment costs, etc., can use the same tundish without interrupting casting, and can minimize the amount of pre-charged molten steel in the tundish. The purpose is to

Means for Solving the Problems> The gist of the present invention to achieve the above object is to use the same tundish to convert continuous casting of pre-charge molten steel to continuous casting of next-charge molten steel of different steel types. In the continuous casting method, the pre-charged molten steel stored in the tundish is poured into the mold from the immersion nozzle by opening the sliding nozzle provided at the bottom of the tundish, and then near or at the end of the injection, the above-mentioned Immersing a plate-shaped bulkhead metal piece with a cutout portion interfering with the immersion nozzle in the pre-charged molten steel in the mold,
This continuous casting method for different steel types is characterized in that the next charge of molten steel of different steels received in the kundish is injected into the mold from the kundish through a submerged nozzle.

Furthermore, in the present invention, at the stage when the next charge of dissimilar steel Im molten steel is started to be received in the tundish, a plate-shaped partition metal fitting having a notched portion interfering with the immersion nozzle is immersed in the pre-charged molten steel in the mold. The plate-shaped partition wall hardware may be left immersed at a position below the immersion nozzle until the molten steel of different steel type is discharged from the immersion nozzle.

In the present invention, as described above, the plate-shaped partition wall hardware is used, with the part interfering with the immersion nozzle cut out. It can be immersed in molten steel in a mold.

Therefore, there is no need to stop pouring, raise the tundish, and evacuate the immersion nozzle from the mold, and it is possible to quickly convert from continuous casting of pre-charge molten steel to continuous casting of molten steel of different steel types for the next charge. This makes it possible to improve the operating rate of the continuous casting machine.

<Example> Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 is a perspective view showing the partition hardware used in the present invention, and FIG. 3 is a front view.

As is clear from FIGS. 2 and 3, the partition wall hardware 8 has a flat plate 8A having a notch 8B cut out in the shape of the 0-shape, for example, in accordance with the shape of the iso-ion nozzle 4, on the side opposite to the operator in the center. It consists of at least two handles 8C that protrude upward from both ends of 1i8A, and a cold metal 80 that does not protrude downward along the U-shaped notch 8B.

Since the flat plate 8A is slightly smaller than the θ measurement dimension of the mold 5, and the width of the U-shaped notch 8B is slightly larger than the outer diameter of the immersion nozzle 4, the partition metal fittings 8 do not interfere with the immersion nozzle 4. It is horizontally immersed in the pre-charge molten steel 2A ejected from the mold 4, and serves to prevent mixing with the next charge molten steel 2B of a different steel type, which is then injected.

The cooling metal 8D of the partition metal fitting 8 is made thick in order to promote solidification of the melted metal 2A existing in the vicinity of the υ-shaped notch 8B. Also, handle 8C is i! ! ! 119 or as a hanging hand during handling.

FIG. 4 is a perspective view showing another type B in which the flat plate 8A of the partition wall hardware 8 is formed into a dogleg shape with a hollow in the middle. It has the same structure as the one explained in the figure.

Next, the working procedure when the method for continuous casting of different steel types of the present invention is applied to a four-strand continuous casting machine will be explained with reference to FIG.

First, using the same tundish, and replacing the continuous casting of the pre-charge molten steel with the continuous casting of the next charge molten steel, which is different in m$1, the pre-charge molten steel 2A in the tundish 1 reaches a predetermined remaining amount, for example about IL, When the injection is about to end, as shown in FIG. 1(a), while the sliding nozzle 3 is kept open and injection into the mold 5 is continued from the submerged nozzle 4, the partition metal fittings 8 are carried above the mold 5. After the character-shaped notch 8B is aligned with the outer periphery of the immersion nozzle 8, it is lowered and the pre-charged molten steel 2A in the mold 5 is removed.
immerse in it.

In this way, as shown in FIG.
A is partitioned into upper and lower parts by partition metal fittings 8.

At this stage, as shown in Fig. 1(b), a sliding nozzle (not shown) of the ladle 10 is opened, and the next charge of molten steel 2B of different steel is supplied through the long nozzle 11 and received into the tundish l. .

In addition, if the next charge #8 steel 2B is supplied from the cancellation 10 to the tundish 1 at the stage when the partition hardware 8 is located below the discharge hole 4A of the immersion nozzle 4, the remaining amount of the previous charge molten @ 2A in the tundish 1 If the amount becomes too small, problems such as slag entrainment may occur.

In such a case, when the pre-charge molten steel 2A in the tundish l reaches a predetermined residual amount of about 11, the next charge molten steel of a different steel type is supplied from the ladle lO to the tundish l, and at the same time, the bulkhead hardware 8 is molded. The partition hardware 8 is immersed in the pre-charge molten steel 2A in the immersion nozzle 4, and the partition wall hardware 8 is kept immersed below the immersion nozzle 4 until the different steel type molten steel m2B is discharged from the discharge hole 4a of the immersion nozzle 4. You can also do it.

Since the bulkhead hardware 8 immersed in the pre-charged molten steel 2 in the mold 5 through the above procedure is made of iron, it gradually settles due to the difference in specific gravity with the molten steel 2A, and is locked in the solidified shell 9 formed on the inner wall of the mold 5. As a result, the bulkhead hardware 8 stops settling. Figure 1 (C
), the peripheral edge of the partition wall hardware 8 that is locked to the solidified shell 9 of the slab that is drawn out at low speed is solidified [! By the formation of one layer, it is connected to the solidified shell 9, and at the same time, a solidified layer is quickly formed near the chilled metal 8D, and the U-shaped notch 8B is closed, so that the pre-charged melt 112A is connected to the solidified shell 9 by the partition metal 8. Divided into upper and lower parts. Note that the handle 8C is completely dissolved at this stage.

On the other hand, between the hot water supply and the tank 1410,
(The next charged molten steel 2B of a different steel type is continuously injected into the mold 5 through the immersion nozzle 4 while being mixed with a small amount of the previous charge molten steel remaining in the Kundeitz l. Molten steel 2A in the mold 5 are partitioned by the bulkhead metal fittings 8, so the mixed molten steel of the previous charge molten steel 2A and the next charge different steel type molten steel 1i42B injected into the mold 5 is only injected above the bulkhead metal fittings 8, and is poured downward. This prevents the pre-charge molten steel 2A from penetrating into the existing pre-charge molten steel 2A.Since the pre-charge molten steel 2A remaining in the tundish l is small, the amount of mixture with the next charge different steel type 18112B will inevitably be small. , it is possible to shorten the length of the slab in the mixed part that is discarded as scrap.

It should be noted that when the partition wall hardware 8 is lowered in FIG. Sometimes, apply mold powder under the bulkhead hardware 8.
i lff1, and if there is a risk of hindering casting, use a partition wall hardware 8 with a flat plate 8a formed into a dogleg shape with a hollow in the middle, as shown in Fig. 4. Melt 11
It is preferable to remove the mold powder along the slope of the lower surface of the partition wall hardware 8 when immersing it in the water 12A.

Figure 5 shows the pre-charge t8j1 when the method of the present invention is used.
The carbon concentration 111 shift before and after changing from 4 (representative carbon 8 x 10 - %) to the next charge of different steel II molten steel (representative carbon 24 x 1 g - x %) is expressed as the distance PM (m) from the joint bordering the bulkhead hardware. It is shown by the relationship.

As is clear from FIG. 5, according to the present invention, the component mixing portion of the previous charge and the next charge is accommodated in the crop portion of the conventional method by replacing the tundish at the top of the previous charge, and the same tundish is used at the bottom of the next charge. Compared to the conventional method of 5 m, the length was significantly shorter than 2 m.

As a result, the number of component mixing parts by continuous casting of different steel types, which conventionally was an average of 14 tons/time, was reduced to 4 tons/time in the present invention.

<Effects of the Invention> As explained above, according to the present invention, using the same tundish, it is possible to replace the next charge of different molten steel without stopping casting by simply leaving a small amount of the previous charge molten steel in the tundish. As a result, an improvement in the operating rate of the continuous casting machine can be achieved. Further, since the length of the component mixing portion between the pre-charged molten steel and the next-charged molten steel of different steel types can be shortened, the yield is improved.

[Brief explanation of drawings]

Fig. 1 is a schematic explanatory diagram showing in cross section the working procedure of continuous casting of different steel types according to an embodiment of the present invention, Fig. 2 is a perspective view showing a partition wall hardware according to the present invention, and Fig. 3 is A of Fig. 2. 4 is a perspective view showing another partition wall metal fitting according to the present invention, and FIG. 5 is a front view showing the direction from arrow -A, and FIG. 5 is a different steel from the previous charge molten steel to the next charge!
l A graph showing the carbon concentration transition before and after the exchange to molten steel in relation to the distance from the joint bordering the partition wall hardware,
FIG. 6 is a schematic explanatory diagram showing, in cross section, the working procedure of continuous casting of different steel types according to a conventional example. l...Kundishu, 3...Sliding nozzle 5...Mold, 7...Tundish no.9...Solidified shell, 11...Long nozzle. 2... Molten steel, slurry, 4... Immersion nozzle, 6... Inert gas, slurry, 8... Partition hardware, 10... Ladle,

Claims (1)

[Scope of Claims] 1. In a continuous casting method of different steel types in which the same tundish is used and continuous casting of pre-charge molten steel is converted to continuous casting of next-charge molten steel of a different steel type, the pre-charge molten steel accommodated in the tundish. When the sliding nozzle provided at the bottom of the tundish is opened and the immersion nozzle continues to inject into the mold, near or at the end of the injection, a plate-shaped partition wall with a portion that interferes with the immersion nozzle is cut out. A metal article of a different steel type is immersed in the pre-charged molten steel in the mold, and then the next charge of the molten steel of a different steel type received in the tundish is injected into the mold from the tundish through an immersion nozzle. Continuous casting method. 2. At the stage when the next charge of molten steel of a different steel type has started to be received in the tundish, a plate-shaped bulkhead hardware with the part that will interfere with the immersion nozzle cut out is immersed in the previous charge molten steel in the mold, and the molten steel of the different steel type is 2. The method according to claim 1, wherein the plate-shaped partition wall hardware remains immersed at a position below the immersion nozzle until the molten steel is discharged from the immersion nozzle.