JPH0994639A - Sequentially continuous casting method for different kind of steel from ni base stainless steel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sequentially continuous casting method which can stably execute the sequentially continuous casting for different kinds of steels in a good yield even in the case of casting the molten Ni base stainless steel as the previous casting molten steel. SOLUTION: In the sequentially continuous casting method in the continuous casting of the molten Ni base stainless steel as the previous casting molten steel, the flow rate of cooling water for a mold is lowered to 1000-1200l/min just after the pouring of the previous casting molten steel 1b into the mold 2 completes and a shell fall-down preventing jig 6 is inserted into the mold 2 to prevent the fall-down of the shell. Thereafter, a partition plate 7 parting the previous casting molten steel 1a and the following casting molten steel (b) is arranged into the mold 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a continuous method for different steel types in continuous casting using Ni-based stainless molten steel as a prior molten steel.

[0002]

2. Description of the Related Art As a continuous method of different steel types in continuous casting, Japanese Patent Application Laid-Open No. 63-108949 and Japanese Patent Publication No. 3-05898.
Those described in Japanese Patent Publication No. 5-30543 and Japanese Patent Publication No. 5-30543 are known. In all of these methods, when continuously injecting molten steel of different steel types into the mold, a partition member is arranged in the mold to prevent mixing of the preceding molten steel and the following molten steel. This enables continuous casting of different steel types with stable and high yield.

[0003]

However, in such a conventional continuous steel method of different steel grades, it is a technique that can be fully utilized in general low carbon steel and ordinary steel, but Ni-based stainless molten steel became the preceding molten steel. In some cases, there are the following problems. That is, since the Ni-based stainless molten steel has a large solidification shrinkage and a large linear expansion coefficient as compared with ordinary steel grades, the shell largely falls inward in the mold due to the solidification and thermal shrinkage (see FIG. 8). Therefore, JP-A-63-
In the case of a type in which a partition plate is inserted into a mold as in Japanese Patent No. 108949 etc., the collapsed shell interferes with the insertion of the partition plate, and as a result, the molten steel is not sufficiently separated in the continuous portion of different steel types. As a result, the mixed area of different steel types becomes large, which causes a lot of loss.

Further, when the amount of collapse of the shell becomes large, a gap between the inside of the copper plate of the mold and the shell becomes large, and molten steel may flow into the gap to cause troubles such as molten metal leak. The present invention has been made in order to eliminate such inconvenience, and provides a different steel type continuous method capable of performing stable different steel type continuous casting with a good yield even when Ni-based stainless molten steel is used as the preceding molten steel. The purpose is to

[0005]

In order to achieve such an object, the method for continuously changing different grades of Ni-based stainless steel according to the present invention is a method for continuously changing different grades of Ni-based stainless steel in continuous casting using molten steel of Ni-based stainless steel as the preceding molten steel. Immediately after the injection of the preceding molten steel into the mold is completed, the mold cooling water flow rate is set to 1000 to 1
While lowering to 200 l / min, a shell fall prevention jig was inserted into the mold to prevent the shell from falling, and then a partition member for partitioning the preceding molten steel and the following molten steel was arranged in the mold. Is characterized by.

[0006]

DETAILED DESCRIPTION OF THE INVENTION An example of an embodiment of the present invention will be described below with reference to FIGS. 1 to 4 are schematic explanatory views for explaining a method for continuously joining different steel types of Ni-based stainless steel, which is an example of an embodiment of the present invention, and FIG. 5 is a mold cooling water flow rate and a mold removal at the time of stopping casting. FIG. 6 is a graph showing the relationship with the heat quantity, and FIG. 6 is a graph showing the relationship between the mold cooling water flow rate and the temperature inside the mold copper plate when the casting is stopped.
Fig. 7 shows the relationship between the amount of long-sided shell collapse and the mold cooling water flow rate when the shell collapse prevention jig is used, and the long-sided shell collapse amount and mold cooling water flow rate when the shell collapse prevention jig is not used. FIG. 8 is a graph showing a comparison with the relationship with, and FIG. 8 is an explanatory view for explaining the collapse of the shell that occurs when the Ni-based stainless molten steel stops in the mold.

First, the outline of the different steel type continuous method for Ni-based stainless steel will be described. The casting speed is decreased together with the decrease in the amount of residual steel in the tundish 5 of the Ni-based stainless molten steel (preceding molten steel) 1a (see FIG. 1). reference). Then, after the injection of the molten steel 1a in the tundish 5 into the mold 2 is completed, the casting speed is reduced in the range of 0 to 0.05 m / min,
At the same time, the tundish 5 is moved to another place to discharge the residual steel (see FIG. 2 (a)). At this point, the ladle 4 of the subsequent molten steel 1b is carried in.

During discharging of the residual steel, as shown in FIG. 2 (b) (FIG. 2 (a)
(As viewed from the direction of arrow A), a long side shell fall-in prevention jig 6 configured by arranging two substantially cylindrical members in parallel in the mold 2 is provided at a substantially central position of the long side of the mold. The axis is inserted in the thickness direction of the slab, and subsequently, the partition plates 7 which also serve as a connecting member between the preceding molten steel 1a and the following molten steel 1b are inserted on both sides of the collapse prevention jig 6 to be solidified in the mold 2. Form layer 8. Incidentally, in FIG.
Reference character a is a connecting flange formed at the upper and lower ends and the center of the partition plate 7.

Next, as shown in FIG. 3 and FIG. 4, the tundish 5 is set and the trailing molten steel 1b is poured into the tundish 5 from the ladle 4 and the casting into the mold 2 is restarted. Let In the mold 2, the solidified wall 8 of the preceding molten steel 1a is formed on one surface like ice on the water surface, so that the molten metal with the succeeding molten steel 1b is favorably prevented. The fall-down prevention jig 6 and the partition plate 7 both play the role of a chiller and must have a heat capacity enough to solidify the molten steel around them when immersed in the mold 2. In order to form the solidified layer 8 on the entire surface of the mold 2, the cross-sectional shape as close as possible to the thickness of the mold 2 is desired. In addition, the time required from the completion of the injection of the preceding molten steel 1a to the insertion of the partition plate 7 is about 3 to 5 minutes, and from the insertion of the collapse prevention jig 6 and the partition plate 7 to the start of the injection of the subsequent molten steel 1b. The time required is about 5 to 7 minutes.

By the way, as described above, in the conventional different steel type continuous method, when the Ni-based stainless molten steel having a large solidification shrinkage and a large linear expansion coefficient is used as the preceding molten steel 1a, the partition plate is formed after the injection of the preceding molten steel 1a is completed. As shown in FIG. 8, the shell 3 in the mold 2 is inserted until 7 is inserted.
Due to the solidification and heat shrinkage of the preceding molten steel 1a, the steel falls largely inward. Therefore, the partition plate 7 cannot be inserted as it is, and the preceding molten steel 1a may flow into the gap between the shells 3 from the inside of the copper plate of the mold 2 to cause leakage of molten metal.

Therefore, in this embodiment, the preceding molten steel 1
While decreasing the temperature drop of the shell 3 in the mold 2 from the end of the injection of a to the insertion of the partition plate 7,
The collapse prevention jig 6 described above is inserted into the mold 2 to prevent the shell 3 from collapse. To elaborate,
FIG. 5 is a graph showing the relationship between the mold cooling water flow rate when the casting is stopped and the amount of heat removed from the mold, and FIG. 6 is a graph showing the relationship between the mold cooling water flow rate when the casting is stopped and the temperature inside the mold copper plate. As is clear from FIG. 5, the heat removal amount of the mold decreases as the mold cooling water flow rate decreases. In this case, if the amount of heat removed from the mold is too low, the surface temperature of the copper plate of the mold 2 rises and the mold cooling water boils, so it is necessary to set the lower limit of the mold cooling water flow rate. Since the boiling temperature of the mold cooling water is 150 to 180 ° C. from the mold cooling water pressure, the lower limit value of the mold cooling water flow rate is 1 with reference to FIG.
000 l / min.

FIG. 7 is a graph showing the relationship between the amount of tilting of the long side shell 3 (dimension between the inside of the mold copper plate and the shell) C (see FIG. 8) and the mold cooling water flow rate. As is clear from FIG. 7, the collapse amount C of the long-side shell 3 decreases as the mold cooling water flow rate decreases, and is approximately 9 mm or less when the mold cooling water flow rate is 1200 l / min or less. It is generally known that the molten steel leaks when the gap between the inside of the copper plate of the mold 2 and the shell 3 is 10 mm or more on one side, and therefore the upper limit of the mold cooling water flow rate is set to 1200 l / min. In this way, by setting the mold cooling water flow rate within the range of 1000 to 1200 l / min immediately after the injection of the preceding molten steel 1a, the temperature drop of the shell 3 in the mold 2 is reduced and the collapse of the shell 3 is prevented. .

However, even if the mold cooling water flow rate is set in the range of 1000 to 1200 l / min to reduce the temperature drop of the shell 3 in the mold 2 as described above, the stop time in the mold may be reduced due to variations in working time. When extended, the mold cooling water flow rate is 1200 l / min
It is expected that the amount of collapse of the long-side shell 3 will be 10 mm or more even if it becomes the following. In this case, the upper limit of the mold cooling water flow rate may be narrowed to 1200 l / min or less, but since the lower limit value of the mold cooling water flow rate is 1000 l / min as shown in FIG. Considering this, the upper limit value is 1200 l / mi
It is difficult to narrow it to n or less.

Therefore, in this embodiment, the preceding molten steel 1
Immediately after the completion of the injection of a, the mold cooling water flow rate is set to 1000 to 1
In addition to the range of 200 l / min, the collapse prevention jig 6 of the shell is inserted into the mold 2 so that the collapse amount C of the long side shell 3 is stably secured to 9 mm or less. . Since it takes some time to insert the shell collapse prevention jig 6 into the mold 2, if the time is prolonged, the shell 3 may collapse and the insertion may not be possible. Since the collapse of the shell 3 is restricted by the adjustment of the mold cooling water flow rate, the shell 3 does not become an obstacle when the shell collapse preventing member 6 is inserted into the mold 2.

FIG. 4 shows the results when the fall-down prevention jig 6 for the shell 3 is used together with the results when not used. As is clear from this figure, in addition to setting the mold cooling water flow rate within the range of 1000 to 1200 l / min, the shell collapse prevention jig 6 is inserted into the mold 2 to stabilize the mold 2. It can be seen that the gap size between the inside of the copper plate and the shell 3 can be 9 mm or less.

After inserting the shell collapse prevention jig 6, the partition plate 7 is inserted into the mold 2,
Even when the Ni-based stainless molten steel is used as the preceding molten steel as in this embodiment, it is possible to perform continuous casting of different steel types with stable and good yield. Here, the shell collapse prevention jig 6 has a thickness of 15 mm or more than the thickness of the mold 2,
The shorter one is preferable within the range of less than mm. If the prevention jig 6 is shorter than the mold thickness by 20 mm or more, the gap between the inside of the copper plate of the mold 2 and the shell 3 is 10 mm on one side.
This is because of the above.

[0017]

[Example] Slab width 1000 to 1200 mm, thickness 19
Different steel grades were carried out with a casting size of 0 mm. Front and rear steel type, mold cooling water condition, availability of fallen jig,
Table 1 shows the in-mold stop time and the dimension of the clearance between the inside of the mold copper plate and the shell (shell collapse amount) at that time.

[0018]

[Table 1]

Comparative Example 1 is a series of different steel types (low carbon steel) having a small linear expansion coefficient that have been conventionally used, and SUS304 (Ni in the case where the present invention is not applied to Comparative Example 2).
Series stainless steel). In Comparative Example 2, since the shell collapse amount became too large and there was a danger of molten steel leakage, different steel types were interrupted. Comparative Examples 3 and 4 show different steel types of SUS304 when the mold cooling water flow rate is reduced to 1100 l / min. In Comparative Example 3, the stop time in the mold was 4 minutes, and the amount of shell collapse was small, so that different steel types could be used consecutively. However, in Comparative Example 4, the stop time in the mold was as long as 7 minutes, so the shell collapse amount was large. Since there was a danger of molten steel leaking due to too much deterioration, the different steel types were interrupted.

Examples 1 and 2 show the results when the mold cooling water flow rate was reduced to 1100 l / min and a shell collapse prevention jig was used. In Example 1, the stop time in the mold was 5 minutes, and in Example 2, the stop time in the mold was 8 minutes, but both of them were capable of stable succession of different steel types.

[0021]

As is apparent from the above description, in the present invention, the mold cooling water flow rate is reduced to 1000 to 1200 l / min immediately after the injection of the preceding molten steel into the mold is finished, and the shell is placed in the mold. Since a fall prevention tool is inserted to prevent the shell from falling, N
Even when the i-type stainless steel molten steel is used as the preceding molten steel, it is possible to perform continuous casting of different steel types with stable and good yield,
The effect that continuous casting work efficiency can be improved is obtained.

[Brief description of drawings]

FIG. 1 is an explanatory schematic diagram for explaining a method of continuously connecting different types of Ni-based stainless steel, which is an example of an embodiment of the present invention.

FIG. 2 (a) is an example of an embodiment of the present invention Ni
2B is a diagram viewed from the direction of arrow A in FIG. 2A, illustrating an explanatory schematic diagram for explaining a method for continuously joining different types of stainless steels.

FIG. 3 is an explanatory schematic diagram for explaining a method for continuously connecting different kinds of Ni-based stainless steels, which is an example of an embodiment of the present invention.

FIG. 4 is an explanatory schematic diagram for explaining a method for continuously connecting different kinds of Ni-based stainless steels, which is an example of an embodiment of the present invention.

FIG. 5 is a graph showing the relationship between the mold cooling water flow rate and the mold heat removal amount when casting is stopped.

FIG. 6 is a graph showing the relationship between the mold cooling water flow rate and the temperature inside the mold copper plate when casting is stopped.

FIG. 7 shows the relationship between the amount of long-side shell collapse and the mold cooling water flow rate when a shell collapse prevention jig is used.
FIG. 7 is a graph showing a comparison between the amount of long-side shell collapse and the mold cooling water flow rate when the shell collapse prevention jig is not used.

FIG. 8 is an explanatory diagram for explaining the collapse of the shell that occurs when the Ni-based stainless molten steel stops in the mold.

[Explanation of symbols]

 1a ... Ni-based stainless molten steel (previous molten steel) 1b ... Subsequent molten steel 2 ... Mold 3 ... Mold inner shell 4 ... Ladle 5 ... Tundish 6 ... Shell collapse prevention jig 7 ... Partition plate 8 ... Mold solidification wall C ... Amount of shell collapse in mold

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroshi Nishikawa, 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture, Kawasaki Steel Co., Ltd. Chiba Steel Works (72) Tadao Ozeki, 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Kawasaki Steel Works Co., Ltd. Chiba Works (72) Inventor Minoru Adachi 1 Kawasaki-cho, Chuo-ku, Chiba, Chiba Prefecture Kawasaki Works Chiba Works (72) Motoda Sugisawa, 1 Kawasaki-cho, Chuo-ku, Chiba Kawasaki Steel Co., Ltd. Chiba Steel Works (72) Inventor Isao Kato 1 Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba Kawasaki Steel Co., Ltd. Chiba Steel Works

Claims (1)

[Claims] 1. In a continuous casting method of different steel types in continuous casting using Ni-based stainless molten steel as the preceding molten steel, the mold cooling water flow rate is set to 1 immediately after the injection of the preceding molten steel into the mold is completed.
000 to 1200 l / min, while preventing the shell from falling by inserting a shell falling prevention jig into the mold, and then arranging a partition member for partitioning the preceding molten steel and the following molten steel into the mold. A method for continuously changing different types of Ni-based stainless steels characterized by the above.