JPS59189050A - Removal of nonmetallic inclusion from molten metal - Google Patents

Abstract

PURPOSE:To provide satisfactorily the effect of adsorbing an Al2O3 inclusion for a long period of time by installing filters of lime for removing nonmetallic inclusions in a continuous casting tundish, and averting the contact of the material floating on a molten steel contg. SiO2 on the working surfaces of the filters. CONSTITUTION:Filters 7 consisting of lime refractories, for example, about 93% CaO and the balance MgO for removing nonmetallic inclusions are installed in a tundish 5, and the molten metal in a ladle is charged through a long nozzle 4 into the tundish. After the Al2O3 inclusion in the molten steel 10 is adsorbed by the filters 7, the molten steel is charged through an immersion nozzle 9 into a casting mold. A cover 11 is provided to prevent heat radiation and to obviate the use of a heat insulating material. A gate 12 for cutting slag is provided between the nozzle 4 and the filters 7 to prevent the arrival of slag 6 of SiO2 at the filters 7 and to stabilize the function for adsorbing Al2O3 for a long period of time. The effect of removing the Al2O3 inclusion by the lime refractory filter is thus satisfactorily obtd.

Description

Detailed description of the invention
This relates to a method for stably removing 06-based inclusions over a long period of time using a stone-based filter.

It is well known that nonmetallic inclusions that exist in molten steel and cannot be separated and removed at the stage of solidification have a negative impact on the workability and mechanical properties of steel, and the surface quality of finished products.

In recent years, the quality required for steel materials has become increasingly strict, and so-called clean steel with fewer impurities is now in demand. Conventional methods for removing impurities include melt washing and adding Ca to molten steel.
A method is used in which a refining agent (flux) such as O, CaF2, Na2CO3, etc. is added to perform desulfurization and dephosphorization treatment. Further, degassing of l-12, N2, etc. is carried out using vacuum degassing equipment such as RH type and DH type. Furthermore, removal of deoxidation products, that is, nonmetallic inclusions, is also an important point in cleaning molten steel. In particular, in the case of a deoxidized product, it is a deoxidized product. U205 is difficult to float and remains in the slab, which causes deterioration in product quality.

Normally, these non-metallic inclusions are floated and separated in a continuous υj ;'M 7-dish, and clean molten steel is injected into the J-type. However, there are minute nonmetallic inclusions of 100μ or less, AA, 20. Inclusions in the form of clusters are difficult to float and separate from steel, and at present no appropriate removal technology has been established.

The present inventors conducted various experiments and found that calcareous refractories that come into contact with molten steel tend to react with U205 in steel, and that AA20)
, , was found to be easier to absorb. An example of the experimental results is shown in FIG. This figure shows calcareous refractories (Cab) used in the weirs of continuous casting tanditshu.

This is the distribution of AA203 content from the refractory surface of 96 candy, balance MgO), and AA206 is 20 mm from the refractory surface.
You can see that it has penetrated to a certain degree. This is the test! j
? This is the result after casting 4 channels (400 tons) of Ayuka f''j, but the Kame no Shiro 1 fireworks are hardly eroded and the reaction products (a (CaO)b(AA
This shows that there is no contamination of 203)), and it can be seen that the reaction product itself is not the source of inclusions. From this, by bringing the calcareous refractory into contact with molten steel, the 03 in the molten metal can be separated and removed, and the first point of the present invention is to actively utilize this phenomenon. be.

Next, the second point is that in order for the calcareous refractory filter to have a cleaning effect on molten steel until the final stage of preparation, it is necessary to install an appropriate combination of, for example, a Tanditsh weir and a lid.
This is to prevent large calcareous materials from being turned into sludge by 5i02 series solos.

That is, as shown in FIG. 2, a lime-based refractory filter 7 is installed in the tundish 5, and the molten steel 2
is injected into the tundish 5 via the sliding nozzle 6 and the long nozzle 4.

After the U205-based inclusions in this molten steel are adsorbed by a lime-based refractory filter 7, the molten steel is cast into a mold through an immersion nozzle 9. An example of the filter 7 is shown in FIG.
Shown in B). Note that 8 is a presser plate.

However, at the end of pouring into the ladle or when hoisting the ladle, the surface of the molten steel 10 in the tank is downward, and the surface of the molten steel 7 is lower.
A mixture of slag and slag 6 may fall to the level of the lime-based refractory filter 7. At this time, tanditshu noro licks the surface of the lime-based refractory firku. Tanditshu slag consists of Kunditshu heat insulating material, ladle slag rolled in from the ladle, non-metallic inclusions in floated and separated molten steel, and therefore its composition is constantly changing. Usually used Tanditshu? , +1'A material is baked fir, and its components are T, C, 45-47%, 5i018-26% AA2
0324 to 60, and the ladle slag also contains 5102 at a concentration of 10 to 15%.

On the other hand, the lime-based + f + il large filter is A-A20
Its CaO content is usually 5 to increase the reactivity with 3.
It is 0w+% or more.

It is well known that C,a (') and S + 02 () have high reactivity, and CaO-8+02 (S +02
35%) has a melting point of 143 (S"C) and can be sufficiently melted at the temperature of molten steel, making it impossible to maintain its shape as a lime-based refractory filter. In addition, 5i0 on the surface of CaO
2 adheres and its composition is CaO') Sochi (Toyo 1 body), the product will remain on the surface of the refractory, and the CaO layer will not be able to come into direct contact with the molten steel, resulting in CaO in the center. Even if the i'-A203 is rich (Toyohata'), the filter no longer has the ability to adsorb i'-A203.

Therefore, when using a lime-based refractory filter, it is necessary to exclude filters containing 5i02, and
As shown in the figure, heat radiation is prevented by putting a lid 11 on the tundish (1), stopping the use of heat insulators, and installing a weir 12 for cutting slag between the long nozzle and the lime-based refractory filter. There is a method to prevent contaminants from reaching the lime-based refractory filter, and by this method, the filter effect was sufficiently obtained for molten steel cast in two pots or later in continuous casting.

In addition, as shown in Fig. 4, slotted weirs 13 are installed before and after the lime-based refractory filter. 14 is provided, and a lower region 15 is provided for the purpose of creating a short path for molten steel.
Since it is not possible to use heat insulating material between the painting stand and the painting stage, it is necessary to install a lid 16 to stop the opening 4.J. In addition, it is desirable to provide the lower part 15 to avoid a 7-yoat pass with a total of 1i:'. As an alternative to this lower part 15, bubbling with an inert gas such as Ar can be used, which can also contribute to promoting the floating of inclusions.

The specific effects of the present invention will be explained below with reference to Examples and Comparative Examples.

Example Converter discharge: After qi and j, the molten steel, which was slightly wrinkled in the RI-1 vacuum degassing table, was converted into lime-based cylindrical 11M1 as shown in Fig. 5. Place the filter loaded with large items at the position shown by 7 in Figure 3, cover it with a lid 11, do not use any heat insulating material, and receive it in a tundish equipped with a weir 12. Casting was conducted under the conditions shown in Table 1. As a result, the volume of 2 to 6 pots is the same as that of 1 pot; f <'l', (0
] = 25 ppm or less, an extremely clean steel with a maximum of 56 M2O3 inclusions/25 mm2 when observed under a microscope, and a maximum of 6 magnetic defects in the finished tin plate/100
m2, which was a very good result.

As a comparative test for the example, a filter was prepared by welding molten steel with the ingredients (shown in Table 1) using the same process as in the example, and applying a lime-based cylindrical cut material as shown in Fig. 5. the second
It was received in a tundish placed at the position shown by 7 in the figure, and cast into a cast hemorrhoid 12 using an immersion nozzle 9 under the conditions shown in Table 1. In this case, roasted fir was used as a heat insulating material, and no weir was provided. As a result, for the popular taste of one pot, T, (0) = 24 ppm, h, e
2o3 inclusions are microscopic flj6 @ 5Of solid / 2
s ma2, 2 pieces of Daigun defect Mitsusei in finished tinplate/
It was a very good result with 10D and 2, but 2 fi'
Regarding the molten steel of pots i and i to 6, the average value is 1. ', [
0340pp+n, AA20. System inclusion 135 (IB
I/25! ui2, magnetic detection defect occurrence in finished tinplate 5
A weir and a lid were installed on the tank pump to eliminate the input of 5IO2 from slag, ladle slag, etc., and the effect of the lime-based refractory filter was increased by 2. The cleanliness and product quality of the 01 piece were inferior to those of the example in which it could be obtained even after the pot.

As is clear from Table 1 and above, as well as the comparison between Examples and Comparative Examples, the method for removing inclusions according to the present invention has a stable and sufficient effect on removing Natsu 203-based inclusions using a lime-based refractory filter over a long period of time. It is something that makes a great contribution to the production of 7# Joso.

[Brief explanation of the drawing]

Figure 1 is a diagram of the surface of a large lime-based steel of Tanpuino/Yu after 1'F18 construction, and 03-containing mouth 1-hybridization. Figure 2 is a diagram showing how molten steel is supplied from a 4-y ladle using a long nozzle to a tundish equipped with an inclusion removal filter. Figure 6 shows the intervention of the present invention #5i0 to vJ removal filter
An explanatory diagram of -dll when a tundish lid and a weir are installed to prevent attacks from two sources, Figure 4 is a detailed explanatory diagram of another present invention, and Figure 5 (Al (B) is It is an explanatory diagram of installation of an inclusion removal filter made of a cylindrical refractory as an example of a refractory filter on a tongue tissue. 7. Inclusion removal filter, 12, 13. 14. Weir, 11'. 16...Heat insulation lid. Rod / Figure Lime thread refractory 1□"19T! Life (mm) Figure 3 Figure 4-7 Rod Figure 5

Claims (3)

[Claims] (1) A lime-based non-metallic inclusion removal filter is installed in the tundish for continuous GLJ construction, and AA205 inclusions can be stably maintained over a long period of time by avoiding contact of 8102-containing molten steel floats to the operating surface of the lime-based filter. A method for removing non-metallic inclusions from molten steel, characterized by adsorbing objects. (2) The patent story seeks to omit the use of preservation material by providing a lid to the kunteinongyu, and to dam the slag flowing in from the ladle by providing a dam on the inlet side of the lime-based filter. Non-gold 1, L of solution j described in range (1)
Interventional proboscis removal method. (3) Installing a weir on the outflow side of the lime-based filter 5102
A method for removing non-metallic inclusions from molten steel as set forth in claim (1), in which floating objects of molten steel are dammed up and a heat-insulating section is provided on the upper surface of the stage.