JPH0243315A - Method and device for reflux type degassing treatment of molten steel - Google Patents

Abstract

PURPOSE:To allow smelting of an extremely low oxygen steel and highly clean steel by blowing an inert gas from blowing devices provided to the outside of riser and downcomer immersion pipes to stir the slag on the molten steel. CONSTITUTION:The molten steel 20 in a ladle 18 is risen from the riser immer sion pipe 14A into a vacuum vessel and is subjected to a degassing treatment. The molten steel subjected to the degassing is returned by the downcomer immersion pipe 14B into the ladle 18. The inert gas is blown to the molten steel from the inert gas blowing devices 28A, 28B provided to the respective outer sides of the riser and downcomer immersion pipes 14A, 14B in such reflux type degassing treatment method for the molten steel. The slag 26 suspended on the molten steel is stirred by this blowing. The extremely low oxygen steel and the highly clean steel are smelted in this way.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a recirculation method and apparatus for degassing molten steel,
In particular, the present invention relates to a method and apparatus for producing high-purity steel by reforming slag, and is used in the field of producing high-purity steel.

[Conventional technology]

In order to further improve the quality of molten steel tapped from a refining furnace such as a converter or electric furnace, the molten steel tapped from the refining furnace is received in a ladle and subjected to secondary refining in an RH or DH degassing furnace. This is a widely practiced technique known as the ladle refining method.

Ladle refining methods include degassing treatment, powder blowing treatment, gas stirring treatment, etc., but here the improvement of the recirculation molten steel degassing treatment method and apparatus using the RI-1 degassing method is limited.

The outline of the RH degassing apparatus will be explained with reference to FIG. 5. The RH degassing tank is composed of an upper lid 2, a middle tank 4, and a lower tank 6, and the upper part is provided with a vacuum exhaust hole 8 and an alloy inlet 10, and the bottom of the lower tank 6 is equipped with holes for raising and lowering molten steel. Two reflux pipes 12 are provided, and two reflux pipes 12 for ascending and descending are further detachably connected to the two reflux pipes 12.
Installed in the wooden dip tube 14 and ladle 1.8 during the degassing process
The tip of the molten steel 20 is immersed in the molten steel 20 stored in the molten steel 20, and the molten steel 20 is raised to the lower tank 6, and the molten steel 20 that has been degassed is returned to the ladle 18 via the descending reflux pipe 12 and the immersion pipe 14. Secondary refining is carried out by repeating these operations. Furthermore, a gas blowing device 16 such as a porous plug for blowing an inert gas such as Ar is provided inside the rising immersion pipe 14A.
The melt 1120 in the ladle 18 is 0.1 to 50% in the degassing tank.
It is sucked up by the pressure difference between the Thor vacuum and atmospheric pressure,
The inert gas blown into the inside of the rising dip tube 14A causes circulation according to the principle of a gas lift pump. In addition, during the immersion v14, the ladle 18 is used during the degassing process.
Since it is immersed in the molten steel 20 inside, the reflux pipe 12 is connected to the reflux pipe 12 by bolts and nuts using a flange so that it can be easily attached and detached in order to be replaced due to melting damage.

The conventional method of RH degassing treatment with the above configuration utilizes vacuum to generate dehydrogenation, denitrification, and decarburization reactions by pre-C+○→CO reaction, and
By circulating the molten steel 20 between the lower tank 6 and the ladle 18, it is possible to promote the coalescence and levitation of non-metallic inclusions in the molten steel through strong stirring, so this method has been widely used in the melting of high-cleanliness steel. .

However, as a feature of RH degassing treatment, there is little reaction between slag and metal in the ladle 18, and as a result, although it has the advantage of high AQ addition yield and low double phosphorus, it does not reform the slag. This has the disadvantage that it is extremely inconvenient for melting higher quality steel. That is, on the surface of the molten steel 20 accommodated in the ladle 18, slag 26 from the time of tapping from the converter 1, etc. is floating, and this slag contains a large amount of oxides such as FeO and MnO. Because of this, even if the steel is cleaned by RH roasting, oxides such as FeO and MnO in the slag react with AQ in the molten steel, producing minute inclusions that remain in the steel. There is. Therefore, in order to produce steel with a higher level of cleanliness than before,
It is necessary to modify the slag itself.

In the conventional slag reforming method, as shown in FIG. 4(B), a slag reforming agent 22 is poured into molten steel 20 contained in a ladle 18, and a slag reforming agent 22 is poured into the molten steel 20 contained in a ladle 18. One method is to blow inert gas and stir the slag 26 and metal 20 to promote the reaction between the slag modifier 22 and the slag 26.

In addition, the method disclosed in JP-A-61-281809 adds modified flux to the slag on the surface of the bay steel in the ladle, heats it with a burner, and refines the molten steel in the ladle. This is a ladle refining method for molten steel in which a desulfurizing agent is added together with an inert gas into the molten steel through a lance or a bottom blowing nozzle after addition. The conventional method is to further subject the slag-modified molten steel to RH degassing treatment.

The above-mentioned conventional slag reforming method requires one step for slab reforming, so it takes a lot of time to handle the ladle and perform the RH degassing process, resulting in a significant drop in molten steel temperature. Therefore, it is necessary to raise the temperature for tapping molten steel in a converter or the like.

Increasing the tapping temperature increases the degree of erosion of refractories in refining furnaces such as converters and ladles, resulting in a problem of shortened service life.

[Problem that the invention seeks to solve]

An object of the present invention is to provide a method and apparatus for effectively reforming slag in the production of high-cleanliness steel by RH gas treatment, which eliminates the drawbacks of the prior art described above.

[Means for solving problems]

The gist of the reflux type molten steel degassing treatment according to the present invention is as follows.

That is, a step in which molten steel contained in a ladle is raised into a vacuum chamber via a rising immersion pipe to be degassed, and a step in which the degassed molten steel is returned to the ladle via a descending immersion pipe. A recirculation method for degassing molten steel comprising: blowing inert gas from inert gas blowing devices provided outside each of the rising and falling immersion pipes to stir the slab floating above the molten steel; This is a recirculation method for degassing molten steel, which is characterized by:

Next, the gist of the recirculation type molten steel gas treatment apparatus according to the present invention is as follows.

That is, a vacuum tank that vacuum-processes molten steel contained in a ladle, two reflux pipes provided at the bottom of the vacuum tank that allow the molten steel to rise and fall, respectively, and a pipe below the two reflux pipes. two immersion tubes which are detachably attached to the ladle and immersed in the molten steel in the ladle to cause the molten steel to ascend and descend into the vacuum chamber respectively; A recirculation type molten steel degassing device comprising: a gas blowing device for blowing an inert gas into a rising immersion pipe; This is a recirculation type 'eJ steel degassing equipment characterized by having an inert gas blowing device for stirring the slag floating in the slag. First, a degassing treatment apparatus according to the present invention will be explained with reference to FIGS. 1 and 5.

In addition to the gas blowing device 16 for circulating the molten steel 20 provided inside the ascending immersion pipe 14A shown in FIG. Gas blowing devices 28A and 28B are also provided outside the tube 14A and the descending dip tube 14B, respectively. The gas blowing device may have a plurality of pore tubes or porous plug blowing ports. The purpose of these gas blowing devices 28A and 28B is to blow the molten steel 2 contained in the ladle 18.
By blowing inert gas such as Ar or N2 gas into the molten steel 20, the slag 26 floating on the molten steel 20 is stirred.
Promoting the reaction between metal and slag, Fe01 in slag
The objective is to reduce M n O and reform the slag. At this time, flux for slab modification or F in slag
AQ or A as a reduction accelerator such as e01M n O
Q ash can be added.

Gas blowing devices 28A, 28 according to the invention shown in FIG.
A comparison test was conducted between the method of the present invention, which uses an RH degassing device having B, and starts blowing reformed slag gas at the same time as the start of degassing treatment, and the conventional method, which does not blow reformed slag gas. That is, the ladle component is C: 0.04-0.0
7%Si: tr Mn: 0.25~0.30% AQ: 0.06~0.08% When performing RH degassing treatment on molten steel, 0.6~0.8 kg/AQ was added onto the slag 26. Using the same molten steel as in the case of adding molten steel and reforming the slag, gas blowing device 2
FIG. 2 shows the results of measuring T and Fe% in the slag over time when degassing was performed using the conventional method without blowing inert gas from 8A and 28B. As is clear from FIG. 2, when slag reforming according to the present invention is carried out by blowing inert gas from gas blowing devices 28A and 28B, the percentages of T and Fe in the slag are significantly lower than in the conventional method. There was found. That is, it has been found that the reduction of Fe◯ in the slag is significantly promoted in the case of the present invention.

Figure 3 shows T and Fe in the slag after RH treatment in the comparative test shown in Figure 2, between the case of the present invention and the conventional method.
(%) and oxygen (ppm) in the steel after treatment. As is clear from Fig. 3, when the T and Fe (%) in the slag are low, the amount of oxygen in the steel is always low, and the present invention promotes cleaning of molten steel, making it possible to manufacture ultra-low oxygen steel. It turned out to be.

〔Example〕

230 is melted into low carbon aluminum killed steel using a bottom blowing converter and further subjected to RH degassing treatment. The amount of oxygen in steel was compared. The results are shown in Table 1.

In Table 1, in Inventive Example I, AQ was adjusted to RH during steel tapping in the converter.
It is added including the amount of slag reformed during the skin degassing treatment, and the slag is reformed at the same time as the degassing treatment, and in the example ① of the present invention, only the predetermined amount of AQ is used for deoxidizing during steel tapping in the converter. AQ is added as a slag reforming reducing agent to the slag in the ladle during the RH treatment according to the present invention.

Furthermore, in Conventional Example I, the slag was treated with the conventional RH degassing apparatus shown in FIG. 5 without performing any slag reforming. In the conventional example ■, as shown in Fig. 4 (B), when the steel is tapped from the converter, the starting run A
Q and 0.0% of Aa on the slag 26 in the ladle 1-8.
7 kg/l was added, an inert gas was blown in from the porous plug 24, the gas was stirred, the slag was reformed, and then treated with the conventional RH degassing apparatus shown in FIG.

Table 1 As is clear from Table 1, when comparing Invention Examples I and ■ with Conventional Example ■, the T and Fe in the slag are significantly reduced in the Invention Example, and the oxygen in the steel is also significantly reduced. It can be seen that it is decreasing.

Furthermore, when comparing Inventive Examples I and (2) with Conventional Example (2), the changes in molten steel temperature in each treatment process are as shown in Table 2.

As is clear from the temperatures of each step in Table 2, although the tapping temperature in the present invention example is about 20° C. lower than in the conventional example, the temperature remains the same after the RH treatment and in the continuous casting tandem. This is because the slag reforming step in the ladle is no longer necessary, and this step can be omitted. Therefore, in the case of the present invention, the output fR wetness of the converter can be reduced by about 20'C. It has been found that this can reduce melting damage to the converter and ladle, and can significantly contribute to extending the life of the converter.

Incidentally, the rising and falling immersion pipes 28A and 28B of the RH degasser used in the example of the present invention have 2II on the outer lower circumference.
10 WIlφ blow holes each, 500 fl/
Argon gas of min.

As is clear from the above Examples, it was found that high cleanliness steel could be produced by both Inventive Examples I and (2).

〔Effect of the invention〕

The present invention provides a conventional RH circulation degassing apparatus as shown in FIG. A plurality of small hole tubes or porous slugs are provided in the molten steel 20 to inject an inert gas such as Ar or N2 gas, and the slag 26 floating on the molten steel 20 is stirred by the inert gas injection to cause a reaction between the metal and the slag. Promote and Af
By adding a slag reforming reducing agent such as L or AQ ash to reform the slab floating on the molten steel in the ladle, the following effects could be achieved.

(a) By significantly reducing T and Fe in the slab, oxygen in the steel can be significantly reduced, making it possible to produce ultra-low oxygen steel and high-cleanliness steel.

(b) According to the present invention, even if ladle slag gets mixed into the continuous casting tundish, no harm will occur, so the operation of leaving molten steel in the ladle, which is conventionally carried out in high-grade steel melting, is no longer necessary. We were able to improve the molten steel yield.

(c) Since the slab reforming process that was conventionally carried out in a ladle is no longer necessary, the process can be omitted, and the processing time and temperature drop loss required for this process are eliminated, making it easier to tap steel in a refining furnace such as a converter. Since the temperature can be lowered by about 20'C than before, melting damage to the smelting furnace and ladle is reduced.
(d) The device according to the present invention requires only a simple modification of installing a gas blowing device on the outside of the ascending and descending immersion pipes, and the effect of applying the method of the present invention is extremely large. This completely changes the conventional slag reforming method.

[Brief explanation of the drawing]

Fig. 1 is a partial cross-sectional view showing the RH degassing treatment apparatus according to the present invention, and Fig. 2 shows changes in T and Fe in the slag during treatment time by RH degassing treatment comparing the method of the present invention and the conventional method. The diagram shown in Figure 3 is the RH comparing the method of the present invention and the conventional method.
Diagram showing the relationship between T and Fe (%) in the slag after degassing treatment and the amount of oxygen in the steel (ppm), Figures 4 (A) and (B)
Both are schematic diagrams showing the RH degassing process accompanied by slag reforming, (A) is the method of the present invention, (B)
is the conventional method. FIG. 5 is an overall view showing a conventional RH degassing apparatus. 6. Lower layer 12... Reflux tube 14... Immersion tube 14. A...Rising dip tube 14
B... Descending dip tube 16... Gas blowing device (conventional)
18...Ladle 20. Molten steel

Claims (3)

[Claims] (1) A step in which the molten steel contained in a ladle is raised into a vacuum chamber via an ascending immersion pipe to be degassed, and the molten steel subjected to the degassing treatment is returned to the ladle via a descending immersion pipe. In the recirculation method for degassing molten steel, the slag floating on the molten steel is stirred by blowing inert gas from inert gas blowing devices provided outside each of the rising and falling immersion pipes. A recirculation method for degassing molten steel, which is characterized by: (2) a vacuum chamber that vacuum-processes the molten steel contained in the ladle;
Two reflux pipes are provided at the bottom of the vacuum tank and allow the molten steel to rise and fall, respectively, and two reflux pipes are detachably attached below the two reflux pipes and are immersed in the molten steel in the ladle to collect the molten steel. It comprises two immersion tubes that are raised and lowered into the vacuum chamber, respectively, and a gas blowing device that blows an inert gas into the rising immersion tube through a conduit housed in the rising immersion tube. A reflux type molten steel degassing apparatus, characterized in that it has an inert gas blowing device provided outside the rising and descending immersion pipes to stir the slag floating on the molten steel accommodated in the ladle. Type molten steel degassing equipment. (3) The recirculation type molten steel degassing apparatus according to claim (2), wherein the inert gas blowing device provided outside the rising and falling immersion tubes is a plurality of small hole tubes or a porous plug.