KR101185226B1 - Method of desulfuration treatment of return molten steel - Google Patents

Abstract

The present invention relates to a desulfurization treatment method for a conveying steel. The present invention comprises the steps of charging a desulfurizing agent in the empty charge; Performing a first desulfurization reaction by repairing the molten iron in the charged ladle loaded with the desulfurization agent; A second desulfurization reaction by melting the molten iron with molten steel conveyed to the charged ladle; Performing a third desulfurization reaction by correcting the molten iron amount with the molten steel mixed with the molten steel with a balance measuring device; Characterizing the by-products produced in the desulfurization reactions in the charge.
According to the present invention, it is possible to prevent the temperature drop of the conveying steel by the KR desulfurization process, which is a molten iron pretreatment process, to shorten the steelmaking process time, and to prevent the impeller and the loading ladle refractory breakage generated in the KR desulfurization process. have.

Description

Method of desulfuration treatment of return molten steel}

The present invention relates to a desulfurization treatment method for a conveying steel, and more particularly, to a desulfurization treatment method for a conveying steel in which desulfurization reaction is performed by adding molten iron and molten steel to empty charging ladles containing a desulfurization agent.

The molten steel which has passed the molten iron repair, molten iron pretreatment and refining process will manufacture the slab through the continuous casting process. When continuous casting is interrupted by operation instability such as break out and nozzle clogging between continuous casting processes, the molten steel remaining in the ladle is moved to the molten iron pool for reloading the converter.

This is called conveying molten steel. The conveying molten steel is combined with a certain amount of molten iron according to the amount of molten molten iron in order to secure a converter charging requirement. The molten iron produced in the blast furnace contains impurities such as sulfur (S), phosphorus (P), and silicon (Si) in addition to carbon (C) of about 4.3 to 4.6%. Depending on the dose, sulfur concentrations range from 0.007 to 0.02%.

It is an object of the present invention to provide a desulfurization treatment method for a conveying steel for desulfurization by adding molten iron and molten steel to empty charging ladles containing a desulfurization agent.

Desulfurization treatment method of the steel for conveying according to the present invention for achieving the object as described above, the step of charging a desulfurizing agent in the empty charging ladle; Performing a first desulfurization reaction by repairing the molten iron in the charged ladle loaded with the desulfurization agent; A second desulfurization reaction by melting the molten iron with molten steel conveyed to the charged ladle; Performing a third desulfurization reaction by correcting the molten iron amount with the molten steel mixed with the molten steel with a balance measuring device; And excluding the by-products generated in the desulfurization reactions in the charging ladles.

The desulfurization agent is mixed with CaO ₂ at CaO ₂ at 5-10%, charged at 4.5-10.0 kg / ton in empty charge ladles, and the particle size of the desulfurization agent is in the range of 3-10 mm.

The molten iron is repaired 20 to 50 tonnes based on the charging ladles with a total capacity of 320 tons.

The present invention charges the desulfurization agent into the empty charging ladle, and the first desulfurization reaction by repairing the molten iron in the charging ladle loaded with the desulfurizing agent, and the second molten desulfurization by mixing with the molten steel conveyed to the repaired charging ladle After the reaction, the charged ladles are subjected to a third-desulfurization reaction by correcting the molten iron amount with a balance measuring device to remove the by-products generated in the desulfurization reactions from the charged ladles.

In this case, it is possible to prevent the temperature drop of the conveying steel by the KR desulfurization process, which is a molten iron pretreatment process, and to shorten the steelmaking process time.

In addition, it is possible to prevent the impeller and charging ladle refractory damage that may occur in the KR desulfurization process.

1 is a process chart showing a desulfurization treatment method for a steel for transportation according to the present invention.

EMBODIMENT OF THE INVENTION Hereinafter, the preferable Example of the desulfurization processing method of the steel for conveyance which concerns on this invention is described in detail.

Desulfurization treatment method of the steel for conveying according to the present invention comprises the steps of charging the desulfurization agent in the empty charging ladle, the first step of desulfurization reaction by repairing the molten iron in the charging degreased charged ladle and the charging of the molten iron Secondary desulfurization reaction by mixing with molten steel conveyed to the ladle; and tertiary desulfurization reaction by correcting the molten iron amount with a balance measurement device; and by-product ladle produced in the desulfurization reactions. Exclusion from.

Excess sulfur in the steel causes cracking, so the sulfur content is controlled up to a certain level in the secondary refining except for some special-purpose steel species. For example, for API materials and cold rolled automotive steel sheets, it is necessary to control the sulfur concentration to 0.0005% due to internal defects and surface defects.

However, it is necessary to perform desulfurization before the secondary refining because there are disadvantages such as the increase of raw materials required for desulfurization and the increase of operating time in order to secure the extreme sulfur concentration by the secondary refining alone.

As can be seen from Scheme 1, the desulfurization reaction requires a reducing atmosphere. However, in the converter process before the secondary refining, there is a limit to the desulfurization efficiency because the furnace maintains an oxidizing atmosphere.

<Reaction Scheme 1>

CaO + S = CaS + O [Desulfurization reaction]

Therefore, the oxygen potential is low and contains a large amount of carbon (C), silicon (Si), phosphorus (P), etc., which increases the activity of sulfur. Therefore, desulfurization should be performed in the molten iron phase, which is advantageous for desulfurization. do.

However, the molten steel conveyed after the continuous casting has been stopped is now formed by cooling the surface of the molten metal by a long stay in the atmosphere. Since it does not melt when combined with low temperature molten iron, mechanical stirring process using impeller (hereinafter referred to as "KR desulfurization process"), that is, mechanical stirring force by depositing the impeller to a certain depth in molten iron and rotating it at a constant speed It can lead to desulfurization reaction, but it causes impeller breakage or breakage of the refractory wall of the charging ladle. Therefore, desulfurization treatment other than the KR desulfurization process is required as the molten iron pretreatment for now-carrying molten steel.

Thus, looking at the present invention in detail, when the molten iron is generated and the molten iron is needed, 4.5 ~ 10.0 kg desulfurization agent mixed with quicklime and CaF ₂ in the ratio of 90 ~ 95: 5 ~ 10 [%] 20 to 50 ton from the molten iron carrier vessel (TLC, Torpedo Ladle Car) depending on the amount of the steel for transporting the molten iron prior to loading the molten iron and the amount of the transported steel for preheating the desulfurization agent. The primary desulfurization reaction is performed by the strong downflow generated during repair by repairing the molten iron, and the secondary desulfurization reaction is performed by the strong downflow generated by melting the molten iron with the returned molten steel. The ladle loaded with the conveying steel were surveyed by a balance measuring device to correct the molten iron to secure a target converter charging amount, followed by a third desulfurization reaction, and then the ladle ladle produced by the desulfurization reactions. By performing the step of standing excluded it can be desulfurized to be processed without separate the molten iron pretreatment step.

Here, quicklime (CaO) has a high melting point of 2,570 ℃ low desulfurization efficiency when used alone. However, quicklime has high sulfur activity and low solubility in molten iron, and can be used in combination with other additives to increase the desulfurization efficiency.

Therefore, CaF ₂ Additives are mixed and used. CaF ₂ reacts with quicklime to form low melting complex oxides. The low melting point composite oxide lowers the melting point of quicklime to improve the desulfurization efficiency.

If the ratio of quicklime and CaF ₂ is less than 95: 5 [%], the desulfurization efficiency is lowered because the effect of lowering the melting point of quicklime is insignificant. If it exceeds 90:10 [%], the refractory is eroded severely due to the effect of lowering the melting point. And shorten the lifespan of the loaded ladle.

The desulfurization agent is charged to 4.5-10.0 kg / ton. If the amount of desulfurization agent is less than 4.5 kg / ton, there is a problem in that the desulfurization reaction is lowered. When the amount of desulfurization agent is more than 10.0 kg / ton, a large number of by-products are generated due to excessive amount of desulfurization agent compared to molten iron and conveying steel and excessive slag. Due to the problem that the molten iron temperature for the desulfurization reaction falls.

The desulfurization agent mixed with quicklime and CaF ₂ is more advantageous in particle size, and is preferably in the range of 3 to 10 mm. This is because the preheated radiant heat of radiant heat prevents the dispersion of the desulfurization agent into the atmosphere, and the finer the particle size, the more the reaction interface increases, thereby increasing the desulfurization efficiency.

When the desulfurization agent is less than 3 mm in size, the desulfurization agent is dispersed in the air by radiant heat of preheated charged ladles, and when the desulfurization agent exceeds 10 mm, the desulfurization reaction is lowered.

The molten iron allows 20-50 tonnes (for charged ladles with a total capacity of 320 tonnes) to be repaired in the loading ladles containing desulfurization agent, and reacts with the desulfurizing agent by the strong flow of the molten iron in the loading ladles during the repair. First desulfurization reaction takes place. If the amount of molten iron to be repaired in the charged ladle is less than 20 tons based on the charged ladles having a total capacity of 320 tons, there is a problem in that the desulfurization effect due to the downward flow of the molten iron is insufficient. There is a problem in that dissolved oxygen and carbon in the molten iron react to generate CO gas.

In this case, the molten iron is preferably made to be repaired in the charge of the desulfurizing agent containing the desulfurizing agent before the mixing of the reaction steel and the desulfurizing agent reacts.

The reason for loading the molten iron into the loading ladles containing the desulfurization agent before loading the conveying steel is for preheating the loading ladles.

If the carrier steel is pre-loaded into the charging ladle for the conveying steel mixing, the carrier steel touches the wall of the charging ladle which is lower in temperature than the transportation steel, and now may occur on the wall of the charging ladle due to rapid cooling. The problem arises that the raw metal generated by the retention of molten steel in the air does not dissolve in the molten iron.

Although the temperature of the conveying steel is high at about 1500 ° C. but the content of C is low, the flowability is not good. The molten iron has good flowability, but the temperature is about 1300 ° C., which is lower than that of the conveying steel. For this reason, the conveying steel is now generated on the unheated charging ladle wall and is not dissolved even by charging of the molten iron.

By-products generated from the desulfurization reactions have a shape in which CaS is coated around quicklime (CaO) particles, and since the converter process is an oxidation reaction, there is a problem that duplex sulfur occurs unless the step of excluding the by-products before the converter process is performed.

The above objects, features and advantages will become more apparent from the following detailed description taken in conjunction with the accompanying drawings. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

1 is a process chart showing the desulfurization treatment method of the steel for transportation according to the present invention.

Referring to FIG. 1, when the slab is manufactured through a continuous casting process and the continuous casting process is stopped due to operation instability such as break out between nozzles and nozzle clogging, the molten steel remaining in the ladle is refurbished. It is moved to the molten iron bath for mouth, which is called conveying steel.

The conveying molten steel is combined with a certain amount of molten iron according to the conveying molten steel in order to secure a converter charging requirement. The molten steel that is mixed with the molten iron has a sulfur concentration of about 0.007% to 0.02% depending on the molten iron content.

The desulfurization treatment method of the conveying steel according to the present invention relates to a desulfurization treatment method other than the KR desulfurization process performed to secure the sulfur concentration of the slab that is finally manufactured. The molten iron is repaired according to the amount of conveying steel for preheating.

At this time, a strong downflow is generated by the repaired molten iron, and a primary desulfurization reaction occurs. After the molten iron has been repaired, they are transferred to the pool and mixed with the return steel to induce the secondary desulfurization reaction.

Charged ladles after the mixing are surveyed with a balance measurement device to secure the target converter charge amount, and then the molten iron is corrected to perform the third desulfurization reaction.

After the tertiary desulfurization reaction is completed, by carrying out the process of collecting the desulfurization formed by the desulfurization reaction, the charging of the converter can be made immediately without a separate molten iron pretreatment process, the sulfur ratio measured was less than 0.003%. Molten steel with converter charging is made into slabs through secondary refining and continuous casting processes.

Table 1 and Table 2 below show the desulfurization rate when CaO or CaO + CaF ₂ is used as the desulfurization agent.

CaO
(kg / ton) Desulfurization Rate (%) Remarks 3 58.4 Comparative example 4 56.7 Comparative example 4.5 65.4 Comparative example 5 66.1 Comparative example 6 65.9 Comparative example 7 66.7 Comparative example 8 65.0 Comparative example 9 71 Comparative example 10 75.3 Comparative example

CaO + CaF ₂ Desulfurization Rate (%) Remarks CaO
(kg / ton) CaF ₂
(kg / ton) 3 0.3 81.0 Comparative example 4 0.4 82.4 Comparative example 4.5 0.45 86.4 Inventive Example 5 0.5 86.1 Inventive Example 6 0.6 87.0 Inventive Example 7 0.7 86.9 Inventive Example 8 0.8 86.1 Inventive Example 9 0.9 91.1 Inventive Example 10 One 93.3
(By-products generated, drop in molten iron temperature) Comparative example

According to Table 1 and Table 2, when CaO + CaF ₂ is used as the desulfurization agent, the desulfurization rate was higher than that of CaO, and CaO and CaF ₂ were 90∼95: 5 ~ 10 [%]. The desulfurization rate was higher than 85% when the ratio was satisfied and charged at 4.5 kg / ton or more.

However, when the desulfurizing agent is charged in excess of 10kg / ton, the molten iron temperature is lowered, a number of by-products occur.

It can be seen that CaO ₂ is mixed with CaF _{2 at} a ratio of 90∼95: 5 ～ 10 [%] and charged at 4.5∼10.0 kg / ton to increase the desulfurization efficiency.

As a result, since the desulfurization efficiency is not increased, KR desulfurization process, which is a molten iron pretreatment process, is not required, thereby preventing the temperature drop of the conveying steel and reducing the steelmaking process time.

In addition, damage to the impeller and refractory damage of the charging ladles due to cooling of the transport steel, which may be generated by performing the KR desulfurization process, are also prevented.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the above teachings. will be.

Claims (5)

delete Charging a desulfurization agent into empty charge ladles;
Performing a first desulfurization reaction by repairing the molten iron in the charged ladle loaded with the desulfurization agent;
A second desulfurization reaction by melting the molten iron with molten steel conveyed to the charged ladle;
Performing a third desulfurization reaction by correcting the molten iron amount with the molten steel mixed with the molten steel with a balance measuring device; And
Excluding the by-products produced in the desulfurization reactions in the charging ladles,
The desulfurization agent is a desulfurization treatment method for the conveying steel, characterized in that the quicklime (CaO) and CaF ₂ is mixed at a ratio of 90 ~ 95: 5 ~ 10 [%]. The method according to claim 2,
The desulfurization agent is a desulfurization treatment method of the steel for conveying, characterized in that the charge in the empty charging ladle to 4.5 ~ 10.0 kg / ton. Charging a desulfurization agent into empty charge ladles;
Performing a first desulfurization reaction by repairing the molten iron in the charged ladle loaded with the desulfurization agent;
A second desulfurization reaction by melting the molten iron with molten steel conveyed to the charged ladle;
Performing a third desulfurization reaction by correcting the molten iron amount with the molten steel mixed with the molten steel with a balance measuring device; And
Excluding the by-products produced in the desulfurization reactions in the charging ladles,
Desulfurization treatment method of the steel for conveying, characterized in that the particle size of the desulfurization agent is in the range of 3 ~ 10 mm. Charging a desulfurization agent into empty charge ladles;
Performing a first desulfurization reaction by repairing the molten iron in the charged ladle loaded with the desulfurization agent;
A second desulfurization reaction by melting the molten iron with molten steel conveyed to the charged ladle;
Performing a third desulfurization reaction by correcting the molten iron amount with the molten steel mixed with the molten steel with a balance measuring device; And
Excluding the by-products produced in the desulfurization reactions in the charging ladles,
The molten iron is a desulfurization treatment method for a steel for conveying, characterized in that 20 to 50 tons of water on the basis of the charging ladle with a total capacity of 320 tons.

Images