KR101277594B1 - Slag deoxidizer - Google Patents

Abstract

The present invention relates to a slag deoxidizer introduced into slag before tapping of the converter in the steelmaking process, Al-Mg intermetallic compound containing 3 to 10% by weight of magnesium and 90 to 97% by weight of aluminum, and the Al-Mg It provides limestone (CaCO ₃ ) coated on the surface of the intermetallic compound.

Description

Slag deoxidizer {SLAG DEOXIDIZER}

The present invention relates to a deoxidizer, and more particularly, to a slag deoxidizer input into slag before tapping of a converter in a steelmaking process.

When molten steel is produced in the steelmaking process, the molten iron or scrap is first refined in a converter or an electric furnace, and then the molten steel is transferred to the steel bars to be refined secondly. At this time, the slag containing a large amount of iron oxide from the converter or the electric furnace flows into the steel bars to lower the error rate of the ferroalloy used for deoxidation and to promote the oxidation of the alloying elements in the molten steel to generate non-metallic inclusions in the molten steel.

Therefore, it is desirable to lower the iron oxide in the slag of the steel ladle as much as possible. For this purpose, the slag deoxidizer composed of Al or Si is used for the purpose of reducing T.Fe in the slag in the converter or the electric furnace, but the slag deoxidizer mentioned above not only reduces the T.Fe but also reduces the oxygen concentration in the molten steel with a strong oxidation-affinity component. It also has its drawbacks.

Related prior art is Korean Patent Publication No. 1997-043126 (published date; July 26, 1997).

An object of the present invention is to provide a slag deoxidizer capable of reducing T.Fe in slag without reducing the oxygen concentration of molten steel by preventing direct contact between aluminum deoxidizer and molten steel.

The technical problems to be achieved by the present invention are not limited to the technical problems mentioned above.

The slag deoxidizer of the present invention for achieving the above object is Al-Mg intermetallic compound in which 3 to 10% by weight of magnesium and 90 to 97% by weight of aluminum; And limestone (CaCO ₃ ) coated on the surface of the Al-Mg intermetallic compound.

The limestone may be coated with a thickness of 1 mm to 3 mm on the surface of the Al-Mg intermetallic compound.

As described above, according to the present invention, when the slag deoxidizer of the Al-Mg intermetallic compound coated with CaCO ₃ is introduced into the converter, CaCO ₃ is decomposed into CaO and CO ₂ at approximately 900 ° C. or higher, and thus the produced CaO has a slag basicity. Used for conditioning, CO ₂ will affect the increase in stirring power in the molten steel. And when CaCO ₃ is decomposed, the brittle deoxidizer of Al-Mg component may rise as slag in slag or molten steel and react with Fe oxide in slag to reduce T.Fe in slag.

Accordingly, when the slag carbonate is added, the oxygen concentration in the molten steel is not reduced, and the Fe oxide in the slag can be reduced.

1 is a schematic cross-sectional view showing a converter for explaining slag deoxidation of the present invention.
2 is a view showing a slag deoxidizer according to the present invention.
3 and 4 are diagrams for explaining the molten steel and the slag reaction of the slag deoxidizer.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. Like elements in the figures are denoted by the same reference numerals wherever possible. In the following description, well-known functions or constructions are not described in detail since they would obscure the invention in unnecessary detail.

1 is a schematic cross-sectional view showing a converter for explaining slag deoxidation of the present invention.

First, the primary refining in the converter 10 or the electric furnace is a process of removing a large amount of oxygen to remove impurities in molten iron or scrap metal, and oxygen dissolved in the molten steel 11 at the end of refining, that is, dissolved Oxygen (free oxygen) is 600 ~ 1000ppm, carbon content is 0.03 ~ 0.08% by weight.

The slag layer 15 formed at the top of the molten steel 11 at the time of tapping the converter 10 may include materials such as FeO, SiO ₂ , CaO, P ₂ O ₅ , MnO, and the like in the molten steel 11. Metal materials containing a large amount of Fe and oxygen (O), nitrogen (N), carbon (C) and the like may be included.

For example, in the case of manufacturing ultra low carbon steel, a certain amount of oxygen gas must remain in the molten steel 11 that has been refined and exited from the converter 10. The reason for this is that a certain amount of oxygen gas in the molten steel 11 is advantageous in the decarburization process for producing ultra-low carbon steel when performing a reflux vacuum degassing process (RH process).

In the converter 10, a deoxidizer composed of Al or Si is generally used just before the tapping of the converter 10 for the purpose of reducing the total Fe in the slag (hereinafter referred to as T.Fe). Aluminum-based slag deoxidizers are widely used because they are relatively inexpensive among commercially available metals and possess excellent deoxidizing power. However, the slag deoxidizer may reduce the oxygen concentration in the molten steel 11 with a strong oxidation affinity component as well as T.Fe reduction. As described above, it is not preferable that the oxygen concentration of the molten steel 11 is reduced more than necessary. The process of reducing the T.Fe component means that Fe components such as FeO and Fe ₂ O ₃ in the slag layer 15 are lowered to increase the Fe recovery rate.

The slag deoxidizer 50 according to the present invention is preferably made of a component capable of reducing T.Fe in the slag without reducing the oxygen concentration in the molten steel 11. Slag deoxidizer 50 according to the present invention can be formed as shown in FIG.

That is, the slag deoxidizer 50 is composed of Al-Mg intermetallic compound 51 (Mg ₂ Al ₃ ) to solve not only the reduction of T.Fe in the slag but also the decrease in oxygen concentration in the molten steel 11. The Al-Mg intermetallic compound 51 has a brittle property and can be easily crushed in the slag layer 15 to serve as an efficient slag deoxidizer 50. However, when the highly brittle slag deoxidizer 50 is introduced into the molten steel 11 without being crushed in the slag layer 15, the oxygen concentration in the molten steel 11 is expected to be inevitable. The surface of the _trivalent Al-Mg intermetallic compound 51 may be coated.

Here, since the specific gravity of magnesium (about 1.71g / cm ³⁾ of (Mg) is an aluminum (Al) ratio of approximately 63% (approximately 2.7g / cm ³⁾ level, when introduced into the molten steel 11 is lighter than conventional deoxidizer It is easily floated to the slag layer 15. The magnesium component will be more efficient in terms of recycling if the Mg scrap is used as a shielding material for electromagnetic waves. Since Mg scrap contains more than 90% high purity Mg component, it is expected that it will not be a big problem in terms of deoxidizer component. However, since magnesium is an oxidation-friendly element like aluminum, strong heat of oxidization is generated when reacting with oxygen, and thus the risk of explosion cannot be excluded, so it is preferably used at 10% by weight or less. However, when the amount of magnesium is too small, there is no big difference in terms of specific gravity from the existing aluminum deoxidizer, and it is preferable that magnesium is added in an amount of 3 to 10% by weight and 90 to 97% by weight of aluminum. That is, the slag deoxidizer 50 according to the present invention is mixed and pressed with aluminum dross or aluminum chips at a predetermined ratio with magnesium scrap, and molded into briquette or pelletizing. Of course, the aluminum dross or the aluminum chips may be mixed and melted with magnesium scrap in a set ratio to form the slag deoxidizer 50.

The limestone 55 (CaCO ₃ ) coated on the surface of the Al-Mg intermetallic compound 51 may be coated with a thickness of 1 mm to 3 mm, and the maximum inner diameter of the Al-Mg intermetallic compound 51 may be 30 mm or more. It can be about 60mm. Here, when the thickness of the limestone 55 is thinner than 1 mm, the Al-Mg intermetallic compound 51 is molten steel before the limestone reacts with the molten steel so that the slag deoxidizer 50 floats into the slag layer 15. 11), and when the thickness of the limestone 55 is greater than 3 mm, the limestone 55 continues to react with the molten steel 11 so that the Al-Mg intermetallic compound 51 is slag layer 15. Reaction with Fe oxide may be delayed.

When the slag deoxidizer 50 configured as described above is introduced into the converter 10 immediately before the tapping, the slag deoxidizer 50 may penetrate into the molten steel 11 through the slag layer 15 as shown in FIG. 3. At this time, the limestone 55 (CaCO ₃ ) coated on the surface of the slag deoxidizer 50 is decomposed as shown in Scheme 1 below at 900 ° C. or more in the molten steel 11. Limestone 55 is decomposed at 900 ° C or more to generate calcium oxide (CaO) and carbon dioxide (CO ₂ ), the molten steel 11 may be promoted by itself by the CO ₂ gas stirring.

Scheme 1

CaCO ₃ → CaO + CO ₂ ↑ (920 ℃)

Calcium oxide (CaO) produced by Scheme 1 is used to control the basicity of the slag (15), the stirring itself is promoted by the carbon dioxide (CO ₂ ) gas generated during the decomposition of the limestone 55, deoxidizer (Al-Mg ) And the slag 15 can be promoted. Of course, the limestone 55 also serves to slow down the time when the Al-Mg intermetallic compound 51 is in direct contact with the molten steel 11 when the slag deoxidizer 50 is introduced into the converter 10.

When the limestone 55 coated on the surface of the slag deoxidizer 50 is decomposed, the brittle deoxidizer of the Al-Mg component floats into the slag layer 15 and the Al-Mg intermetallic compound (51) floated into the slag layer 15 (51). ) Are brittle and separated from each other. Here, since the melting point of aluminum is about 660 ° C. and the melting point of magnesium is about 650 ° C., the Al-Mg intermetallic compound 51 may be directly in a liquid state when exposed to molten steel 11 of about 1500 ° C. or more. Of course, the temperature of the slag layer 15 is lower than that of the molten steel 11 but is maintained at a high temperature of about 1000 ° C. or higher, so that the limestone 55 is decomposed and the brittle reaction of the Al-Mg intermetallic compound 51 is performed. .

As shown in FIG. 4, the brittle and separated aluminum and magnesium have higher oxygen affinity than iron, thereby binding to oxygen of Fe oxide in slag. That is, the brittle aluminum has stronger oxygen affinity than Fe, so it is bonded with O (oxygen) of Fe oxide such as FeO in the slag layer 15. The reaction described above is shown in Scheme 2 below.

Scheme 2

2Al + 3FeO (slag) = Al ₂ O ₃ + 3Fe

As shown in Scheme 2, aluminum reacts with the Fe oxide to produce alumina (Al ₂ O ₃ ), and the separated iron is recovered back to the molten steel 11 to increase the iron recovery rate in the molten steel 11.

On the other hand, magnesium separated from aluminum has a stronger oxygen affinity than Fe, so it is combined with O of Fe oxide such as FeO in the slag layer 15. The reaction described above is shown in Scheme 3 below.

Scheme 3

Mg + FeO (slag) = MgO + Fe

Here, magnesium may be exploded when combined with oxygen of Fe oxide, and thus may be dangerous when 10% by weight or more of the deoxidizer is contained. Therefore, it is preferably used at 10% by weight or less.

As described above, in the present invention, when CaCO ₃ (55) is coated on the Al-Mg intermetallic compound (51), CaCO ₃ is decomposed into CaO and CO ₂ at approximately 927 ° C., and thus the produced CaO is used for slag basicity control. ₂ affects the stirring force increase in the molten steel 11. When CaCO ₃ is decomposed, the brittle deoxidizer 50 of the Al-Mg component may rise as slag upon inflow of slag or molten steel 11 and react with Fe oxide in slag to reduce T.Fe in slag.

In the present invention, by recycling the resources such as aluminum dross, aluminum chips, and magnesium scrap to produce a slag deoxidizer, it is environmentally friendly, it is possible to lower the manufacturing cost when manufacturing molten steel.

Such slag deoxidizer is not limited to the configuration of the embodiments described above. The above embodiments may be configured such that various modifications may be made by selectively combining all or part of the embodiments.

10: converter 11: molten steel
15: slag 50: slag deoxidizer
51: Al + Mg intermetallic compound 55: CaCO ₃

Claims (3)

delete Al-Mg intermetallic compound combining 3-10 wt% magnesium and 90-97 wt% aluminum; And
It includes; limestone (CaCO ₃ ) coated on the surface of the Al-Mg intermetallic compound,
The limestone is a slag deoxidizer is coated with a thickness of 1mm to 3mm on the surface of the Al-Mg intermetallic compound.
The method according to claim 2,
The slag deoxidizer is a slag deoxidizer is injected into the converter just before the tapping.

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