KR19990042920A - High efficiency slag deoxidizer with low molten steel deoxidation - Google Patents

Abstract

The present invention relates to a slag deoxidizer for deoxidizing slag from a steel ladle after tapping in a converter or an electric furnace during steelmaking process, and more particularly, to prevent direct contact between metal aluminum and molten steel to improve deoxidation efficiency of slag and to make ultra low carbon. The present invention relates to a high efficiency slag deoxidizer with low molten steel deoxidation that prevents deterioration of steel quality.

The slag deoxidizer of the present invention is composed of 35-60 wt% of CaO and 40-65 wt% of Al ₂ O _{3 so} that the inside (1) is composed of metal aluminum and the outside (2) inhibits deoxidation reaction with molten steel. The composition is characterized by being coated with a molten oxide.

Description

High efficiency slag deoxidizer with low molten steel deoxidation

The present invention relates to a slag deoxidizer for deoxidizing slag from a steel ladle after tapping in a converter or an electric furnace during steelmaking process, and more particularly, to prevent direct contact between metal aluminum and molten steel to improve deoxidation efficiency of slag and to make ultra low carbon. The present invention relates to a high efficiency slag deoxidizer with low molten steel deoxidation that prevents deterioration of steel quality.

When the 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 a steel ladle for secondary refining. At this time, the slag containing a large amount of iron oxide from the converter or the electric furnace flows into the steel ladle to reduce the error rate of the ferroalloy used in the 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. To this end, there are attempts to prevent the slag from being mixed into the converter ladles, or to inject a large amount of subsidiary material into the spilled slag, to dilute it, or to remove the slag and to form the slag again. It is not large and has disadvantages of economic disadvantage.

Therefore, generally, a method of reducing iron oxide of a steel ladle using a slag deoxidizer containing metal aluminum is widely used. Slag deoxidizers include aluminum dross, which is a by-product of aluminum production, or briquette type deoxidizers formed by mixing CaO or CaCO ₃ with powder or aluminum dross to increase reaction efficiency. .

Aluminum dross contains some metallic aluminum in its composition, mixed with other aluminum oxides and nitrides, extremely uneven particle size, and contains a large amount of fine powder, which makes it difficult to inject it using a hopper. The molten steel is deoxidized. Briquette-type deoxidizer has the advantage that can be added because it is a molded body, but also has a problem that the molten steel is deoxidized by the exposed aluminum because it is configured in the form of a mixture.

In particular, in the case of producing ultra low carbon steel, it is impossible to obtain the desired carbon concentration in the converter. Therefore, it is necessary to perform decarburization by vacuum treatment using oxygen remaining in the steel.

However, if a large amount of oxygen in the steel is deoxidized during slag deoxidation as described above, oxygen is forced into the steel for decarburization, resulting in deterioration of quality, thereby additionally requiring aluminum, which is used as a deoxidizer, and the life of the refractory. It causes many problems such as adversely affecting.

The present invention has been made to solve the problems of the prior art described above, by providing a slag deoxidizer that can prevent direct contact between metal aluminum and molten steel to improve the slag deoxidation efficiency and prevent the degradation of the ultra-low carbon steel quality The purpose is to provide a high efficiency slag deoxidizer with low deoxidation.

1 is a cross-sectional view showing a slag deoxidizer of the present invention,

2 is a graph showing the relationship between the type of deoxidizer and oxygen reduction in molten steel;

3 is a diagram showing the relationship between the type of deoxidizer and the amount of FeO reduction in slag.

<Explanation of symbols for main parts of drawing>

1: metal aluminum 2: oxide film

In order to achieve the above object, the slag deoxidizer of the present invention comprises 35-60 wt% of CaO and 40-65 wt% of Al ₂ O _{3 so} that the inside is composed of metal aluminum and the outside inhibits deoxidation reaction with molten steel. The composition is characterized by being coated with a molten oxide.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings showing preferred embodiments.

When slag deoxidizer is injected (both manually or hopper), it is floated into slag because the specific gravity is light after penetrating into molten steel by the falling energy. However, when penetrated into molten steel, a general deoxidizer reacts with oxygen in molten steel by aluminum exposed to the surface, and a large part of aluminum is used to deoxidize molten steel, and the ratio actually contributes to slag is very low.

The present inventors thus prepared a slag deoxidizer coated with metal aluminum oxide.

Since the deoxidizer has an oxide layer on the surface even when it comes into contact with molten steel during injection, when the oxide on the surface melts with the slag when it floats as a slag layer, it does not react with the molten steel. Reacts with iron oxides. Therefore, the reaction with oxygen in the molten steel hardly occurs, but only with the iron oxide in the slag.

At this time, the oxide on the surface of the metal aluminum is appropriate to control the composition range to be melted at 1600 ℃ or less of the molten steel temperature of the steel ladle. This is because if the melting point is higher than the ionicity, the molten metal is not melted in the slag layer and thus it is difficult to expect the exposure of the metal aluminum. In addition, considering the speed of goods, the premelting type is more preferable.

On the other hand, the composition of the oxide layer on the surface is appropriate to the composition of the ladle slag, which is to minimize the variation of the ladle slag composition to prevent the change in refining capacity.

Therefore, as the slag deoxidizer that satisfies the above conditions, as shown in FIG. 1, the inner melting of the CaO-Al ₂ O ₃ system is similar to that of the ladle slag composition having a melting point of 1600 ° C. or less. By using the slag deoxidizer composed of the oxide coating 2 thus obtained, deoxidation of molten steel does not occur and only slag deoxidation is possible.

The present invention will be described in more detail with reference to the following Examples.

Example 1

CaO-Al ₂ O ₃ -based oxides, similar in composition to ladle slag to cover the surface of metal aluminum, are preferably melted below 1600 ° C., the molten steel temperature in the steel ladle, in order to improve the reactivity of the deoxidizer. Therefore, it is necessary to investigate the melting point according to these component ratios.

Melting temperature is defined as when mixing by using reagent with the component ratio shown in Table 1 and then forming 2mm in diameter and 4mm in height and melting it to 2/3 of the initial sample height while raising the temperature on the platinum plate and raising the temperature. Was taken with a high temperature camera to measure the melting temperature.

Number Chemical composition (wt%) Melting temperature (℃) CaO Al ₂ O ₃ One 65 35 1770 2 62 38 1670 3 60 40 1600 4 56 44 1530 5 50 50 1410 6 42 58 1575 7 35 64 1597 8 30 70 1700 9 25 75 1765

The measurement results are shown in Table 1, and as can be seen, the composition range of melting temperature of 1600 ° C or less shows that the composition of the oxide is in the range of 35-60 wt% of Ca0 and 40-65 wt% of Al ₂ O ₃ . .

Based on this measurement result, the graphite crucible was mounted inside the induction furnace, and the composition 3-7 of Table 1 was added thereto, and the temperature was maintained at 1650 ° C. to melt the mixture therein. An aluminum sphere having a diameter of about 2 cm was added thereto, the surface was coated with molten oxide, and then taken out and cooled to obtain a slag deoxidizer as shown in FIG. 1.

Example 2

In order to investigate the deoxidation capacity of the slag deoxidizer obtained in Example 1, 60 kg of steel ingot was added to a 100 kg air induction melting furnace and heated up to 1650 ° C. to melt, and 1 kg of converter slag having the chemical composition shown in Table 2 was added thereto. Oxygen change in molten steel before and after the addition was maintained by adding the conventional deoxidizer (Comparative Examples 1, 2) and the slag deoxidizer of the present invention coated with the oxide of composition 5 of Example 1 It was measured using a sensor and the FeO concentration in the slag was investigated by chemical analysis by collecting the slag before and after the injection.

Meanwhile, the FeO concentration in the slag after the injection was adjusted to 6% so that the total amount of metal aluminum added to all three kinds of deoxidizer was 60 g.

(weight%) CaO SiO ₂ MgO FeO MnO Al ₂ O ₃ TiO ₂ P ₂ O ₅ 43.3 9.8 7.2 30.1 3.3 2.15 1.11 3.04

(weight%) division Metal aluminum Aluminum Oxide + Nitride CaCO ₃ Remarks Comparative Example 1 45 55 - Al-Dross Comparative Example 2 50 40 10 Briquette

The deoxidizer having the oxide film of composition 5 prepared in Example 1 was calculated based on the amount of aluminum added and the weight obtained after coating, and the metal aluminum content was 57%.

Therefore, the experiment was performed by calculating the total input amount using the aluminum content of Comparative Examples 1 and 2 of Table 3 and the aluminum content of the deoxidizer prepared according to the present invention. Oxygen and slag sampling time in the steel was added to the deoxidizer so that the deoxidant reacts sufficiently, and the oxygen was measured 3 minutes after the slag was collected.

Figure 2 shows the results of the oxygen reduction amount in the molten steel before and after each slag deoxidizer is added, it can be seen that the molten steel deoxidation hardly occurs by the CaO-Al ₂ O ₃ oxide film coated on the surface of the slag deoxidizer obtained by the present invention have. As a result, the slag deoxidation efficiency is also increased, and as shown in FIG. 4, the amount of FeO reduction in the slag is also significantly higher than that of Comparative Examples 1 and 2.

According to the slag deoxidizer which hardly deoxidizes molten steel of the present invention as described above, since the total amount of aluminum injected into the slag deoxidation efficiency is reduced, the cost can be reduced and the oxygen concentration in the molten steel can be ensured. Reduced forced oxygen injection operation can prevent operation stability and prevent deterioration of the quality of molten steel and improve the life of the refractory.

Claims (1)

Molten steel deoxidation, characterized in that the inside is made of metal aluminum, the outside is coated with a molten oxide consisting of 35 to 60% by weight of CaO and 40 to 65% by weight of Al ₂ O _{3 so} as to suppress the deoxidation reaction with molten steel. Less high efficiency slag deoxidizer.