KR970005388B1 - Refining method of low carbon steel - Google Patents

Abstract

manufacturing synthetic slag lump consisting of CaO 49-61wt.%, Al2O3 32-44wt.%, SiO2 is less than 3.0wt.%, ferric oxide is less than 2.0wt.% and impurities, and having a diameter of 3-30mm in diameter; puting the obtained synthetic slag lumps into the molten steel in a vacuum disgassing equipment, followed by removing the deoxidation product and adventitious inclusion in molten steel grown with the synthetic slags by flotation.

Description

Refining method of ultra low carbon steel using synthetic slag

The present invention has been made to solve the problems caused by the method of removing the metal inclusions in the molten steel by injecting the conventional synthetic slag body in the molten steel in view of the above situation, the synthetic slag in a lump state (lump) rather than the main body (vacuum) Ultra-low carbon steel using synthetic slag that is injected into degassing facility and refluxed with molten steel to not only raise metal inclusions floating on the upper part of molten steel but also to grow and coalesce the metal inclusions in non-injured molten steel in the aggregated slag. The purpose is to provide a refining method.

The present invention for achieving the above object is a method for refining ultra low carbon steel using synthetic slag is wt% when treating molten steel in a vacuum degassing facility by metabolizing ultra low carbon steel, CaO: 49-61%, Al ₂ O ₃ : 32-44%, SiO ₂ : 3.0% or less, Fe oxide: 2.0% or less and other impurities are prepared, and a synthetic slag lump having a particle size of 3 to 30 mm is prepared, and the synthetic slag in the lump state is prepared. Into the molten steel in the vacuum chamber in the vacuum degassing equipment as shown in Table 2, characterized in that to remove metal inclusions and foreign materials in the molten steel.

I. Composition and Function of the Invention

Injecting the synthetic slag of the present invention into the molten steel in the vacuum chamber during the treatment of ultra low carbon steel, by incorporating the deoxidation product and the requesting inclusions generated during the deoxidation of molten steel or other molten steel refining process into a low melting point, low viscosity synthetic slag The synthetic slag used in the method of the present invention has a composition of 12CaO, 7Al ₂ O ₃ , and has a melting point of 1385 ° C. as a premelted type lump. RH) It is manufactured to a size that is easy to put into the vessel (vessel) during processing.

CaO and Al ₂ O ₃ content in the composition of the synthetic slag should be prepared in a suitable ratio for the low melting point, CaO: 49 ~ 61wt%, Al ₂ O ₃ : 32 ~ 44wt% is suitable as wt%.

The reason for the numerical limitation is as follows.

If the CaO: 49 ~ 61wt%, Al ₂ O ₃ : 32 ~ 44wt% outside the range of forming a high melting point compound because it can not exist in the liquid phase in the molten steel temperature range (1550 ℃ ~ 1600 ℃) deoxidation for the purpose of adding synthetic slag It cannot play the role of adsorption of the product.

In addition, the SiO ₂ and Fe oxides are preferably suppressed as impurities as much as possible, but the synthesis slag cost increases when the synthetic slag is made of high purity CaO and Al ₂ O ₃ .

Therefore, in the present invention, it was found that SiO ₂ : 3.0% or less, Fe oxide: 2.0% or less are suitable.

SiO ₂ and Fe oxides are not necessary components and are included in the production of synthetic slag compounds, and these components need to be regulated as a reoxidation source capable of contaminating molten steel.

In addition, when the synthetic slag is introduced into the vacuum chamber, the size of the synthetic slag is less than 3mm in diameter because the size is reduced by the exhaust.

However, if the size of the synthetic slag put into the vacuum chamber is large, it takes time to dissolve and inconvenient handling, it should be less than 30mm in diameter.

Therefore, the size of the synthetic slag put into the vacuum chamber is suitable for the diameter of 3 ~ 30mm.

As described above, when the synthetic slag having the chemical composition and physical properties as shown in Table 1 is prepared and introduced into the molten steel 2 in the vessel 1 of the vacuum degassing facility as shown in FIG. 1, Al ₂ O ₃ generated during deoxidation is produced. As the synthetic slag adsorbs inclusions Al ₂ O ₃ generated during deoxidation as shown in FIG. 2, the composition moves to a region where Al ₂ O ₃ is rich, and Al ₂ O ₃ is 60% (melting point 1600 ° C.). As early as Al ₂ O ₃ is saturated, no further inclusions can be incorporated.

However, during the RH treatment (just after deoxidation), the synthetic slag is injected into the RH vessel (vacuum bath) while a certain amount is stored in the alloy coating hopper (HOPPER), one of RH's auxiliary equipment. Automatic basis weight injection is performed for the standard weight. This is the usual method.

Therefore, since the input amount of the synthetic slag should not be saturated because the synthetic slag injected through the vacuum tank absorbs the Al ₂ O ₃ inclusions, the input amount of the synthetic slag is proportional to the detalization factor, and in the present invention, the synthetic slag The input unit of is 0.6 ~ 2.0kg / TON is appropriate as shown in Table 2 below, it is possible to split input if necessary.

In Fig. 1, reference numeral 3 denotes a ladle, and 4 and 5 denote rising pipes and falling pipes, respectively.

As described above, when the synthetic slag is introduced into the molten steel through the vacuum chamber, the synthetic slag absorbs the acicular type and grows as a spherical inclusion (globular type), as shown in FIG. .

In particular, when O ₂ is blown into the vacuum chamber, since needle-like inclusions are formed more, it is preferable to add the weight of the synthetic slag within the dose standard of Table 2 above.

Next, the present invention will be described more specifically as examples.

Example

Synthetic slag in the form of agglomerate was prepared to have a chemical composition and physical properties as shown in Table 1, and the input amounts shown in Table 2 were added to molten steel through a vacuum bath at the time of adding the synthetic slag as shown in Table 3 below.

It is most suitable to input the product immediately after deoxidation, which is the point where most deoxidation products are generated during the RH refining process (see Table 3).

※ T.O: Temperature measurement and oxygen measurement, T.S.O: Temperature, specimen collection, oxygen measurement

※ OB: Oxygen blowing in vacuum chamber

In the first case, the initial synthesis slag of vacuum degassing was added, and in the second case, the synthesis slag was added immediately after deoxidation of molten steel with Al, but the effect was obtained.

That is, as shown in FIG. 3, the improvement of cleanliness in the slab had an effect of reducing inclusions (cleaning improvement) of 30% compared to the conventional method, and the incidence rate of cold rolled coils was also shown in FIG. In the present invention, when the content is 1.0, the oxide content in molten steel is 0.7, indicating that the cleanliness is improved.

1 is a schematic diagram of the input of vacuum degassing equipment and synthetic slag.

2 is an inclusion collection state of the synthetic slag particles by the method of the present invention.

3 is a graph showing the effect of improving the cleanliness of the slab according to the method of the present invention compared to the conventional method.

Figure 4 is a graph showing the effect of improving the cleanliness of the cold rolled coil according to the present invention compared with the conventional method.

* Explanation of symbols for main parts of the drawings

1: vessel 2: molten steel

3: ladle 4: riser

5: down pipe

end. Purpose of the Invention

1) the technical field to which the invention belongs and the prior art in that field

The present invention relates to a method for refining ultra low carbon steel in a vacuum degassing plant (RH-OB). The present invention relates to a method for refining ultra low carbon steel using synthetic slag that efficiently removes nonmetallic inclusions generated in the process and improves cleanliness of vacuum degassed steel.

In general, molten steel is subjected to the primary refining in a converter or an electric furnace, and the refined molten steel is subjected to the secondary refining in a refining facility such as a vacuum degassing facility, a ladle furnace, and a bap.

In the first step of the refining process including the converter and the electric furnace process, Si, P, C are refined, and the secondary refining process controls the gas components in the molten steel and the remaining trace elements in the steel.

In particular, when producing high processing materials (ultra low carbon steel) including cold rolled products, decarburization is essential in the secondary refining process, and the most commonly used equipment for decarburization and degassing is the vacuum degassing facility (RH-OB). to be.

When ultra low carbon steels are treated with vacuum degassing facilities, oxygen required for the decarburization reaction (O- = CO ↑ in molten steel in the molten steel) cannot be decarburized until decarburization is completed.

Therefore, since the molten steel must be deoxidized to Al after decarburization, carbonic acid products are generated in proportion to the amount of oxygen in the molten steel.

At this time, most of the deoxidation products generated during the reflux will float, but some of them will remain in the molten steel to reduce the cleanliness.

In particular, quality deterioration is inevitably accompanied by insufficient reflux of molten steel after deoxidation. In addition, microslag inclusions generated in the pretreatment process (converter, electric furnace) can cause poor quality in the post process if they cannot be removed during vacuum degassing.

Therefore, in order to reduce non-metallic inclusions (deoxidation products) and microslag inclusions generated in the pretreatment process when molten steel is treated in vacuum degassing process, the reflux time during vacuum degassing treatment is extended, but the reflux time is extended. Will cause a decrease in productivity.

Therefore, synthetic slag was artificially injected into molten steel to effectively remove nonmetallic inclusions in molten steel during vacuum degassing.

As such, the method of artificially injecting synthetic slag into molten steel to remove non-metallic inclusions in molten steel is a refining method that has been conventionally applied to the steelmaking process. The conventional method is to ladle low melting point and low viscosity slag to improve the refining function of the ladle slag. Most of them are used in addition to slag, and recently, a technology for blowing synthetic slag powder into molten steel has been developed and utilized. However, this is an API material that is used as a target steel material. Since the synthetic slag is sprayed into the steel in the facility, the sprayed synthetic slag exists only in the upper part of the molten steel, so that the metal inclusions floating on the upper part of the molten steel can be easily removed, but the metal inclusions in the molten steel that are not injured cannot be removed. There is a problem.

Claims (1)

When treating molten steel in a major degassing facility for ultra low carbon steel, it is wt%, CaO: 49-61%, Al ₂ O ₃ : 32-44%, SiO ₂ : 3.0% or less, Fe oxide: 2.0% or less And other impurity, producing a synthetic slag lump having a particle diameter of 3 to 30 mm, and using the automatic basis weight hopper in the molten steel in the vacuum chamber immediately after deoxidation of the synthetic slag to form a synthetic slag of 0.6 to 2.0. A method for refining ultra low carbon steel using synthetic slag, characterized in that the deoxidation product and adventitious inclusions in molten steel are coalesced into synthetic slag to remove floating flotation by adding kg / Ton-steel.