JPH03184659A - Tundish for preventing oxidation in continuous casting and method for operating thereof - Google Patents

Abstract

PURPOSE:To prevent oxidation of molten steel caused by passing the remaining slag layer by providing weirs partitioning a molten steel receiving part from a ladle and molten steel pouring parts into molds and molten steel communicating holes at lower parts of the weirs and arranging slag communicating holes above the molten steel communicating holes. CONSTITUTION:The molten steel 12 is poured into the molten steel receiving part 16 in the weirs 4 through a short nozzle 14. The molten steel 12 is passed through the molten steel communicating holes 6 at lower part and stored into the molten steel pouring parts 18 for A strand and B strand and poured into the molds 24A, 24B through each nozzle. If the molten steel is continuously poured into the molds 24, the molten steel in the molten steel receiving part 16 and the molten steel pouring parts 18 are lowered to the same level, because there are communicated through the molten steel communicating holes 6 and the slag communicating holes 10. Further, by lowering the molten steel level, the slag 8 is caused to flow out into the molten steel pouring part 18 through the slag communicating holes 10. By this method, as the slag layer in the weirs becomes extremely thick, even if the molten metal in the second and third ladles is received this is not oxidized, and the cast slab having the target components is easily produce, and multiple sequential continuous castings can be executed.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to an oxidation-preventing tundish for continuous casting and a method of operating the same, and in particular, it does not use a long nozzle to receive molten steel from a ladle, but instead uses a short nozzle to receive molten steel. The present invention relates to an oxidation-preventing tundish for continuous casting suitable for continuous casting and a method for operating the same, and is used in the field of continuous casting of steels containing easily oxidized elements such as Ti-containing steels.

[Conventional technology]

The tundish for continuous casting is manufactured by Utility Model No. 57-56546.
As seen in Utility Model Application No. 59-25353, the molten steel receiving section from the ladle and the molten steel injection section into the mold are separated by a weir, and a molten steel communication hole is provided at the bottom of the weir, thereby making it possible to receive the molten steel from the ladle. The slag that gets mixed in at the end of the process is stored, and the operation is done to prevent slag from getting into the part where molten steel is injected into the mold.

In order to reduce the amount of slag flowing from the ladle into the tundish, it can be prevented by stopping the injection when a little more molten steel remains in the ladle, but if there is too much remaining molten steel in the ladle, there will be a large economic loss. Therefore, in pouring operations, it is desirable to keep the amount of residual steel as small as possible and the amount of slag flowing out. However, in actual operation, the flow of slag from the ladle to the tundish side cannot be avoided to some extent.

In order to avoid slag flowing from the ladle into the tundish, it is common practice to use a long nozzle and immerse its lower end in the molten steel of the tundish to avoid entraining the slag on the surface of the ladle. However, long nozzles are more expensive than short nozzles, and when inserting a long nozzle into a tundish, the ladle side cannot be raised or lowered quickly, making it difficult to handle.

Therefore, considering the purpose of installing a weir in Tanditshu, the weir can separate molten steel and slag, so if the weir function can be fully demonstrated, there will be no problem in maintaining the quality of the steel even if a short nozzle is used. It is much more advantageous in terms of cost.

The present invention relates to a tundish that can perform effective continuous casting by combining a so-called open injection method using a short nozzle and a weir, and a method for operating the same.

As described above, even with the open method, it is possible to float and separate non-metallic inclusions and slag within the tundish layer without disturbing the flow of molten steel in the tundish by providing a communicating hole at the bottom of the weir. However, conventional tundishes having only communication holes for molten steel have the following major problems.

[Problem that the invention seeks to solve]

When operating in a tundish having only communication holes for molten steel as described above, the slag that inevitably flows into the molten steel receiving part of the tundish forms a slag layer on the molten steel and floats thereon. Like the second. From the third ladle,
The molten steel injected into the molten steel receiving part of the tundish passes through the slag layer of the tundish, so if the molten steel contains elements that are easily oxidized such as Ti,
Easily oxidized elements such as Ti are oxidized by oxides such as FeO present in the slag, resulting in so-called Ti drops, which oxidize easily oxidized elements such as Ti in the molten steel from the second and third ladles. , the Ti content of the cast slabs from the second and third ladles decreases and deviates from the target content. For example, in the case of Ti-containing steel, combustion of Ti can be visually observed wA when molten steel is received from the second and third ladles.

The object of the present invention is to continuously cast m#R containing elements that are easily oxidized such as Ti, and in particular, to provide continuous casting that has an effective structure that can prevent oxidation even when continuous casting or multiple continuous casting is carried out. The present invention aims to provide an antioxidant tundish and an effective method of operating the tundish.

[Means for solving problems]

The gist of the tandish according to the present invention is as follows.

That is, it has a molten steel receiving part from the ladle, a molten steel injection part into the mold, a weir that partitions the molten steel receiving part and the injection part, and a molten steel communication hole provided at the bottom of the weir. The tundish for continuous casting is characterized in that it has a slag communication hole above the molten steel communication hole through which slag in the molten steel receiving section flows out to the molten steel injection section.

Next, the gist of the operating method using a tanditsh according to the present invention is as follows.

That is, a step of receiving the molten steel in the first ladle at the molten steel receiving section of the dandytsu, a step of causing the entire amount of slag remaining in the molten steel receiving section to flow out to the molten steel injection section through the slag communication hole, and a step of causing the molten steel receiving section to flow out. The steps of receiving molten steel from the second ladle and flowing the entire amount of slag remaining in the molten steel receiving section to the molten steel injection section through the slag communication hole are repeated, and during this period, the molten steel in the molten steel injection section is continuously fed. 2. The method of operating an oxidation-preventing tundish for continuous casting according to claim 1, characterized in that multi-continuous casting is carried out by injecting the oxidation-preventing tundish into a mold.

First, the configuration of the tandish according to the present invention is shown in FIG.
) and (B). Figure 1 is (A), (B) is A
A tundish for two strands, strand and B strand, is shown.

Two weirs 4 are provided in the center of the tanditsh 2, each of which has both ends fixed to the side wall 2A of the tanditsh 2, a bottom fixed to the bottom wall 2B of the tanditsh 2, and an open upper part made of a fireproof wall. , Molten steel communication holes 6 are provided at the bottoms of the two weirs 4, respectively.

This structure is similar to a conventional tundish, but the feature of the present invention is that a slag communication hole 10 is provided slightly above 1/2 of the height of the weir 4 to allow the slag 8 to flow out.

[For production]

The operation of the tandish with the above configuration will be explained. Molten steel 12 melted in the converter and refined by an RH vacuum degassing device or the like if necessary is stored in a ladle and transported to a continuous casting yard. Molten steel 12 containing easily oxidized elements such as Ti-containing steel, which is the object of the present invention, is injected into a molten steel receiving section 16 in salt 4 through a short nozzle 14 .

The injected molten steel 12 passes through the lower molten steel communication hole 6 and is stored in the ta injection portions 18 of the A strand and B strand, respectively, and is supplied to the tundish nozzles 2OA and 2, respectively.
0B and into respective molds 24A, 24B via submerged nozzles 22A, 22B.

The operation up to the above process is the same as that of the conventional device, but when performing continuous casting, after the injection into the molten steel receiving section 16 of the first ladle is completed, the second ladle is However, in this case, the slag 8 from the first ladle remains in the molten steel receiving section 16 in the weir 4, and when pouring the molten steel 12 from the second ladle, Since it passes through the remaining 8 layers of slag in the first ladle, as mentioned above, easily oxidizable elements such as Ti are oxidized by oxides such as FeO in the 8 layers of slag, and cannot be used as target components. Therefore, conventionally,
Unavoidably, the amount of Ti added was increased in anticipation of the oxidation ratio of Ti, etc., and the molten steel containing excess Ti was used as the molten steel in the second ladle.

In the present invention, a slag communication hole 10 is provided above the molten steel communication hole 6 of the weir 4 to prevent the above-mentioned wasteful oxidation of Ti and the like.

That is, when the molten steel 12 in the first ladle is poured into the molten steel receiving part 16 and then continuously poured into the mold 24, the molten steel level in the molten steel receiving part 16 and the molten steel injection part 18 reaches the level of the molten steel communicating hole 6 and the molten steel injecting part 18. Since the molten steel is communicated through the slag communication hole 10 and has descended to the same level, if the injection into the mold 24 is continued until the molten steel level is further lowered, the molten steel will remain in the molten steel receiving section 16 through the slag communication hole 10. The slag 8 flowing out flows into the molten steel injection section 18.

After all of the slag 8 has flowed into the molten steel injection section 18.

The molten steel from the second ladle is received in the molten steel receiving part 16 in the salt 4. By doing this, the thick layer of slag 8 remaining in the molten steel receiving section 16 is diffused over the wide surface of the molten steel injection section 18, resulting in an extremely thin slag layer, and the slag 8 remains in the molten steel receiving section 16.
Even if there is a slight slag layer at the same level as the molten steel injection part 18, it is hardly oxidized by the passage of 1fR12 of the second ladle.

The multiple casting operation method using a tundish according to the present invention will be explained with reference to FIGS. 2(A), (B), (C), and (D).

FIG. 2(A) is a schematic cross-sectional view showing a situation in which the molten steel 12 in the first ladle is being poured into the molten steel receiving portion 16 in the salt 4 through the short nozzle 4. The injected molten steel 12 passes through the lower molten steel communication hole 6 and flows out into the molten steel injection part 18, and the tundish 2 is filled with the molten steel 12 as shown in FIG. Flowing slag 8
does not flow into the molten steel injection section 18 and remains only in the upper part of the molten steel receiving section 16. When pouring into the molds 24A and 24B is started in this state, the level of molten steel in Tanditsh 2 decreases,
Finally, the slag 8 that has passed through the slag communication hole 10 and remained in the molten steel receiving section 16 flows out onto the entire surface of the molten steel injection section 18. FIG. 2(C) is a schematic sectional view showing the situation at this point. Thereafter, when new molten steel 2 is injected from the second ladle into the molten steel receiving portion 16 of the tundish 2, the slag layer 8 is extremely thin, so the new molten steel 12 passing through it will not be oxidized. Figure 2 (D) is the second
Fig. 2 (B
) and the slag situation is different.

By repeating this operation, sequentially receiving the molten steel 12 from the third and fourth ladles, and continuing to pour it into the molds 24A and 24B, a multiple casting operation can be performed.

Now, if the total surface area of the tundish 2 is So, and the area of the molten steel receiving part 16 in the salt 4 is S, then the thickness of the slag 8 on the entire molten surface of the dandish 2 according to the present invention is the same as that of the conventional S process. So, the number of multiple casts due to reassignment is So
/S hours can now be extended.

〔Example〕

C: 0.05%, Si: 0.20%, Mn: 0.50
%, Ti: 0.2%, AQ: 0.02%. Molten steel 12 with a steel composition of 0.02% is successively cast by a conventional method with slag 8 confined in the molten steel receiving part 16 in the salt 4.
According to the present invention, the slag 8 flows out from the slag communication hole 10 to the molten steel injection part 18, and the yield of Ti in the steel is compared and tested for the case where continuous casting is performed.

The amount of molten steel in the ladle used in this test was 180 tons.
, tandish capacity 20t, 2001m x 200rI
An nx611In strand continuous casting machine was used, and the casting speed was kept constant at 1.0 m/min.

The Ti yield (%) in the above comparative test was as shown in Table 1.

I was on the first table, so I stopped after 3 charges. In the case of the method of the present invention, as is clear from Table 1, the yield at the 6th charge is almost the same as that at the 3rd charge of the conventional method, and multiple continuous castings of about twice the number can be performed without rapid deterioration of the Ti yield. We were able to.

〔Effect of the invention〕

Continuous casting by providing a weir with a molten steel communication hole in the tundish is an effective method for producing slabs with perfect fa, without letting slag flow into the molten steel injection part, The molten steel in the second, third, and ladle into which the receiver is placed passes through the residual slag layer of the base circle, which has the drawback of causing oxidation of the molten steel. In particular, in the case of molten steel containing easily oxidized elements such as Ti, it is difficult to obtain slabs with the target composition, and it is necessary to prepare molten steel containing winter elements with a planned amount of oxidation reduction. In addition, in view of the conventional technology that causes variations in the elements in the slab, the tundish according to the present invention has a slag communication hole at the top of the molten steel communication hole, and every charge injection into the ladle, all the slag in the base circle is removed from the slag. Since we adopted an operating method in which the molten steel flows out to the molten steel injection section through the communication hole, we were able to achieve the following effects.

(a) Since the slag layer of the base circle becomes extremely thin, the second
Even if it receives molten steel from the third ladle, it will not be oxidized, and especially steel containing easily oxidized elements such as Ti will not be oxidized, making it easy to manufacture slabs with the target composition. .

(b) Not only continuous casting but also multiple casting in which the casting is changed several times is possible.

[Brief explanation of drawings]

FIGS. 1(A) and 1(B) show an embodiment of the oxidation-preventing tundish for continuous casting according to the present invention, and FIG. 1(A) is a front sectional view, and FIG.
B) is a plan cross-sectional view, Figures 2 (A), (B), (C), (
D) is a schematic cross-sectional view showing changes in the molten metal level and slag layer due to reassembly during multiple casting operations using the tundish of the present invention, and (A) shows the situation in the first ladle receiver. (B) shows the situation when receiving the first ladle is completed; (C) shows the situation after the slag of the carcass has flowed into the molten steel injection part through the communication hole; (D) shows the situation when receiving the second ladle is completed. . 2... Tandish 4... Weir 6... Molten steel communication hole 8... Slag 10... Slag communication hole 12... - Molten steel 14... Short nozzle 16... Molten steel receiving section 18... Molten steel injection section

Claims (2)

[Claims] (1) It has a molten steel receiving section from a ladle, a molten steel injection section into the mold, a weir that partitions the molten steel receiving section and the injection section, and a molten steel communication hole provided at the bottom of the weir. An oxidation-preventing tundish for continuous casting, characterized in that it has a slag communication hole above the molten steel communication hole through which slag in the molten steel receiving section flows out to the molten steel injection section. (2) A step of receiving the molten steel in the first ladle at the molten steel receiving section of the tundish; a step of causing the entire amount of slag remaining in the molten steel receiving section to flow out to the molten steel injection section through the slag communication hole; The steps of receiving molten steel from the second ladle into the molten steel receiving section and flowing out the entire amount of slag remaining in the molten steel receiving section to the molten steel injection section through the slag communication hole are repeated, and during this period, the molten steel in the molten steel injection section is Claim (1) characterized in that multiple continuous casting is performed by continuously injecting into a mold.
) The method of operating the oxidation-preventing tandate for continuous casting described in .