JPH07124717A - Method for casting highly clean steel for cast slab at ladle change position - Google Patents

Abstract

PURPOSE:To improve the yield of a cast slab at a ladle change part by providing an inclusion absorbing filter in a tundish at a specific time point of a casting length. CONSTITUTION:In the continuous casting, a long nozzle 3 is used for a method for pouring molten steel from a ladle 1 to the tundish 6. Then the molten steel in the following ladle is supplied into the tundish 6 successively to the previous ladle. At this time, weirs 11 provided with the inclusion absorbing filters are dipped into the tundish from the time of having charged an amt. of molten steel equivalent to the casting length of 2m of the cast slab and the completion of pouring the molten steel in the previous ladle till the time of casting the molten steel of the length of 10m after the start of pouring the molten steel in the following ladle. By this method, the clean cast slab in the ladle change position is obtd. and the quality of a product can remarkably be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention stops air oxidation, slag flowing from a rear ladle, and molten steel after a ladle which normally occur in a tundish due to the exchange of a charge and a pot in a continuous casting slab. It relates to the technology of removing non-metallic inclusions, which increases due to re-oxidation reaction due to silica sand grains, etc., using an inclusion filter and casting without flowing out to the mold. It is a continuous technology in the steel or non-ferrous manufacturing industry. Regarding casting technology.

[0002]

2. Description of the Related Art There is a strong demand for molten steel cleaning in the steel manufacturing industry, and it is not limited to the reduction of impurity elements such as C, P and S, but also deoxidation products in converters, secondary refining processes and continuous casting processes. It is required to manufacture highly clean steel slabs by removing refining materials, refractory materials, heat insulating materials, and non-metallic inclusions caused by powders as much as possible.

Non-metallic inclusions that cause surface defects and internal defects of the product are particularly prominent due to air oxidation, outflow of ladle slag, and suspension of tundish slag, particularly in the charge and joint portions of the charge in continuous casting. It is known to increase.

In the conventional continuous casting of steel, the molten steel is poured from the ladle to the tundish as shown in FIG.
While adjusting the opening degree of the sliding nozzle 2 attached to the bottom of the nozzle, the tip of the long nozzle 3 located below the nozzle 2 is immersed in the molten steel 4 in the tundish.

However, at the final stage of pouring the molten steel in the ladle, the molten steel was poured while the ladle slag 10 was rolled up as shown in FIG.

On the other hand, after the pouring of the front pan is completed, the molten steel in the rear pan is poured using the long nozzle 3. As shown in FIG.
Silica sand 8 which is a filling material of the ladle flows out of the ladle at the end of the injection of the previous ladle, and the injection flow 9 from the long nozzle 3 together with the slag layer 5 floating on the surface of the molten steel 4 in the tundish.
Is hammered into the molten steel 4 in the tundish.

Although it depends on the tundish capacity, casting speed, etc., among the silica sand and slag that have been struck into the molten steel 4 in the tundish, large ones having a particle size of 100 μm or more are re-floated and removed. Although 1
Those having a diameter of 00 μm or less are injected into the mold together with the molten steel flow and become non-metallic inclusions in the slab, causing a significant deterioration of the quality of the slab, which is a pot replacement part, as shown in the comparative example in FIG. Was becoming.

[0008]

Therefore, as a result of the experiments and researches conducted by the present inventors, it was found that the causes of the deterioration of the quality of the slab on the front ladle side when the ladle was replaced are as follows.

1 to 2 from the time when the pan is replaced until the time when the molten steel is poured into the rear pan
Since preparation time is required, the amount of molten steel 4 in the tundish inevitably decreases if normal casting is continued.

Therefore, in order to recover the amount of molten steel 4 in the tundish, normally, the sliding nozzle shown in FIG. 6 is fully opened to perform an operation of rapidly increasing the amount of molten steel.

Therefore, the dirty molten steel in which the outflow slag of the front ladle, the tundish slag, and the silica sand grains 8 which have stopped the molten steel of the rear ladle are entrained or suspended in the tundish does not have time to float the non-metallic inclusions. , Becomes a direct flow and flows into the mold. Therefore, the quality of the slab on the front ladle deteriorates when the ladle is replaced.

On the other hand, it is well known that it is possible to reduce non-metallic inclusions suspended in molten steel by installing an inclusions filter in the tundish, for example, iron and steel, 75 (1989), P1829-1.
As described in 830, it is also effective in the steel industry.

However, it is necessary to reduce the pore size of the filter in order to increase the absorption capacity of the inclusions so that the effect can be obtained practically. Therefore, due to the increase of the passage resistance due to the clogging of the inclusions in use, However, it was difficult to use it for a long time in the steelmaking process.

However, the present inventors conducted further experiments,
As a result of continuing the research, it was possible to clean the molten steel at the pot replacement site by immersing the weir with the inclusion filter in the tundish at a specific time before and after the pot replacement, and It was found that it is possible to prevent the deterioration of quality and to prevent the passage resistance of molten steel from increasing due to the clogging of the filter.

The present invention has been made in view of the above circumstances, and a weir having an inclusion filter installed in the tundish for the molten steel in the tundish contaminated at the pot exchange site, which is the root cause of the conventional problems, is provided. The purpose is to prevent deterioration of the quality of the slab for pot replacement by cleaning by dipping.

[0016]

SUMMARY OF THE INVENTION Accordingly, the present invention provides a method for obtaining clean steel for satisfying the strict requirements for manufacturing high cleanliness steel, and the gist thereof is as follows. On the street.

In continuous casting when a long nozzle is used as a method for injecting molten steel from a ladle into a tundish, when the molten steel in the rear pot is continuously fed to the tundish in continuous casting, slab casting is performed until completion of injecting molten steel in the previous pot. 2m in length
By the time corresponding to the above, from the point of time after the start of pouring the post-pot to the point of casting 10 m in the length of the cast piece, the tundish is immersed in the weir with the inclusion absorption filter to dip the cast piece at the pot replacement site. Casting method for clean high-purity steel.

[0018]

The details of the present invention will be described below with reference to an example of an apparatus used for carrying out the present invention.

1 to 4 show an embodiment of the present invention. The converter and the RH-treated ultra low carbon steel shown in Table 1 were continuously cast for 2 charges at a casting speed of 4 t / min using a continuous casting facility.

As shown in FIG. 1, the inclusion absorption filter shown in FIG. 4, which is preheated from the time point before the completion of pouring the front ladle until the completion of pouring of the ladle, corresponds to 2 m in casting length, as shown in FIG. Weir 11 with 12 was installed.

Next, as shown in FIG. 2, the molten steel for the rear ladle is started, and the molten steel for the rear ladle is injected as shown in FIG. After the start of pouring molten steel into the rear ladle, the weir was removed at the time of casting 10 m in length of the slab.

In the case of this embodiment, the pore diameter is 5 to 7 ppi.
(Porses / inch) using an alumina filter.

FIG. 5 shows the results of the cleanliness investigation of the cast slabs after casting in comparison with the conventional material. As is clear from the figure, by using the present invention, it is possible to manufacture a slab with good cleanliness of the seam slab.

Table 2 shows a sliver of a case where the front ladle side slab of the ladle changing section when the present invention is applied and the front ladle side slab of the ladle changing section when the method of the present invention is not used are thin plate products for automobiles. The following shows the generation ratio of the degrading materials in comparison.

By using the method of the present invention, the product quality of the slab can be improved as compared with the conventional method. The example of the present invention showed the case of casting ultra-low carbon steel, but the effect of the present invention is not limited to this steel type, and is effective for all steel types of bar steel, thick plate and thin plate.

In the example of the present invention, the ceramic filter 12
Alumina is used as the material of ZrO ₂ , but ZrO ₂ may be used.
The shape of the filter is also rectangular in the present invention, but the shape is not a problem as long as the molten steel flow rate required for casting can be secured.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

By applying the present invention configured as described above, a clean slab of the pot replacement portion can be obtained, the slab yield of the pot replacement portion can be improved, and the quality of the product can be improved. Remarkably improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an embodiment of the present invention.

FIG. 3 is an explanatory diagram showing an embodiment of the present invention.

FIG. 4 is an explanatory diagram showing an embodiment of the present invention.

FIG. 5 is an explanatory diagram of an example showing the effect of the present invention.

FIG. 6 is an explanatory view showing an embodiment of a comparative example of the present invention.

FIG. 7 is an explanatory diagram showing an embodiment of a comparative example of the present invention.

FIG. 8 is an explanatory view showing an embodiment of a comparative example of the present invention.

[Explanation of symbols]

 1 Ladle 2 Sliding Nozzle 3 Long Nozzle 4 Molten Steel in Tundish 5 Slag Layer 6 Tundish 7 Metal Bare 8 Silica Grain 9 Injection Flow (from Long Nozzle) 10 Ladle Slag 11 Inclusions Weir with Filter 12 Inclusion Absorption filter

Claims (1)

[Claims] 1. In continuous casting using a long nozzle as a method of pouring molten steel from a ladle into a tundish, when the molten steel in the rear ladle is continuously fed to the tundish, casting is performed until the pouring of molten steel into the front ladle is completed. One piece casting length is 2
From the point of time corresponding to m to the point of casting 10 m after the start of the injection of the post-pot from the point of time corresponding to m, by immersing the weir with the inclusion absorption filter installed in the tundish, the slab of the pot replacement part Method for casting clean, high-purity steel.