KR100900997B1 - Refining method low carbon steel - Google Patents

Abstract

A high-tension extra-low carbon steel refining method is provided to reduce raw material cost by reducing the used amount of the manganese and quicklime. A high-tension extra-low carbon steel refining method comprises: a step for excluding residue slug; a step for determining the amount of dolomite, soft burned dolomite, and quicklime; a step for injecting dolomite, soft burned dolomite, and quicklime with converter refining; a step for injecting the manganese slug in a decarbonization section; and a step for completing converter refining operation when the concentration CO is 20~25% through exhaust gas analysis. The residue slug exclude step is performed after the residue slug coating of converter is finished. The dolomite and soft burned dolomite are injected as 4~6Ton to prevent the elution of MgO in the converter refining.

Description

Refining method low carbon steel

The present invention relates to a method for refining high-strength ultra-low carbon steel, in particular, the step of completely excluding the residual slug after the completion of the coating of the residual slug of the converter, the step of estimating subsidiary feed, the refining of the dolomite, light dolomite and quicklime Including the step of injecting, manganese slug in the decarburization section, and completing the converter refining when the CO concentration is 20 to 25% by flue gas analysis, reducing the quicklime, reducing the amount of manganese metal, and reducing the cost It is about a refining method that can reduce the cost and improve the quality.

In general, automotive steel sheet requires a different material depending on the application. High tensile ultra-low carbon steel is used as the shell material.

High tensile ultra low carbon steel as described above is subjected to the converter refining process as follows.

When the tapping work, which transfers the molten steel from the converter to the ladle, is completed, a certain amount of slug remains in the ladle, and the nitrogen dosing coating to inject high-pressure nitrogen using oxygen from the upper part is made of light dolomite and saline dolomite, Residual slug coating is performed.

When the residual slug coating is completed, charging of scrap metal and molten iron is carried out and the oxygen is blown from the top to perform the converter refining work. In the converter refining process, the plated decarburization process is carried out with the calculated basic degree of 4.0, the carbon target of 0.04%, and the phosphorus [P] component of 0.015 ~ 0.025%.

When the refining of the converter is completed, tapping, which transfers the molten steel to the ladle, is performed, in which ferropy (Fe-P) and other ferroalloys are added.

When the tapping work is completed, the ladle is transferred to vacuum degassing to carry out decarburization to adjust carbon in the carbon to 50 ppm or less and manganese and other ferroalloys. Such a series of work has the following problems.

1) In molten iron, there is phosphorus [P] called impurity. In the converter refining process, phosphorus is added to remove phosphorus below 0.015 ~ 0.025%, and then ferroferro (Fe-P) is added during tapping. This will cause a decrease in quality, such as a decrease in molten steel temperature and the occurrence of non-metallic inclusions, and a cost increase.

2) When the manganese is introduced during the tapping process after the converter refining is completed, it reacts with the oxygen in the molten steel to exist as MnO and is removed as slugs. Because of the shortage, manganese is introduced during the refining process, which causes a large temperature drop, and also causes the deterioration of molten steel quality due to the occurrence of non-metallic inclusions due to the input of ferroalloy.

3) Manganese injected from vacuum degassing should use only manganese with purity of 99% or more without impurities, causing cost increase.

The present invention is to solve the above-mentioned problems, the step of completely excluding the residual slug after the completion of the remaining slug coating of the converter, the step of calculating the input amount of the subsidiary material, the dolomite, light dolomite and quicklime at the same time as the converter refining It is an object of the present invention to provide a method for refining high-strength ultra-low carbon steel, including the step of injecting manganese slug in a decarburization section and completing the converter refining when the CO concentration is 20 to 25% by exhaust gas analysis.

In order to achieve the above object, the present invention (1) to completely exclude the residual slug after the completion of the residual slug coating of the converter, and (2) to determine the dosage of dolomite, small dolomite and quicklime when charging scrap and molten iron, The dolomite and light dolomite is determined by the amount of 8 to 10 wt% of the residual slug, the quicklime is determined by the following equation (1),

[Equation 1]

(3) injecting the dolomite, hard stone, and quicklime at the same time as refining the converter, (4) injecting manganese slug in the decarburization section, the input amount of which is based on the following equation (2),

[Equation 2]

(5) The method for refining high-tension ultra-low carbon steels comprising the step of completing the converter refining when the CO% concentration is 20-25% by flue gas analysis.

The method of the present invention described above has the effect of reducing the cost and quality by reducing the quicklime, manganese and ferropy usage.

The present invention relates to a method for refining high-strength ultra low carbon steel (S100) as described above (1) to determine the amount of residual slug removal (S110), (2) dolomite, light dolomite and quicklime (S120) (3 ) Dolomite refining and simultaneously dolomite, light dolomite, quicklime is added (S130) (4) manganese slug in the decarburizing section (S140) and (5) exhaust gas analysis by the concentration of 20 to 25% CO When the% includes the step (S150) of completing the converter refining work.

Each step will be described in detail below.

First, the residual slug exclusion step S110 will be described. As described above, it is preferable to completely exclude the residual slug after the remaining slug coating of the converter is completed. This is because the residual slug has a slug composition (wt% relative to the remaining slug) as shown in the following table, making it difficult to match the actual basicity.

Table 1

T.Fe CaO SiO2 MnO MgO P2O5 Al2O3 TiO2 13-25 35-50 5-15 2 ~ 3 7-10 2.0 ~ 3.0 2.0 ~ 3.0 2.0 ~ 3.0

After performing the step of removing the residual slug (S110), the step of calculating the input amount of dolomite, light dolomite and quicklime by using molten iron information when charging the scrap iron and molten iron (S120).

The dosing amount is preferably in the case of dolomite and light dolomite, in which the furnace body is mag carbon yeonwa, so in order to prevent MgO elution during the refining of the converter, it is preferable to set it at a level of 8 to 10 wt% of the remaining slug, and usually 4 to 6 tons. .

And quicklime can be obtained by basicity set according to the target of phosphorus (P) in molten steel. This is calculated by the following equation (1).

[Equation 1]

In this case, the basicity is 2.0 when the phosphorus (P) target in molten steel is 0.04 to 0.06wt%, the basicity is 1.5 when the phosphorus (P) target in molten steel is 0.06 to 0.08wt%.

When the dolomite, light dolomite and quicklime are determined as described above, the step of injecting the dolomite, light dolomite and quicklime is performed at the same time as starting the converter refining process (S130).

생성물이 만들어지면서 전로 슬러그화되기 때문에 상술한 백운석, 경소 돌로마이트 및 생석회를 정련 초기에 투입하는 것이 바람직하다.When dolomite, light dolomite and quicklime are added simultaneously with refining,

It is preferable to add dolomite, light dolomite and quicklime as described above at the beginning of refining, since the product is converted into converter slug.

[Scheme]

As described above, after performing the step (S130) of dolomite, hard dolomite and quicklime at the initial stage of refining, manganese slug is added in the decarburization section.

As described above, the reason for introducing manganese slug in the decarburization section is that the manganese slug is introduced to cause a passion acid action to prevent the temperature increase in molten steel by the CO reaction as described above in the decarburization section.

Injecting manganese slug reacts with oxygen and is introduced into the slug in the form of MnO. However, when the manganese content in the slug increases, the manganese phenomenon in which the manganese is returned during the refining of the converter is generated, thereby achieving an equilibrium between the molten steel and the slug.

The dose of manganese slug as described above can be determined by the following equation (2).

[Equation 2]

At this time, the said target component means the component (wt%) of manganese contained in the fixed-strength ultra low carbon steel of this invention.

In addition, the above-mentioned ingredient refers to the amount of manganese in semi-finished product state, for example, from converter refining, and refers to the amount already contained.

Therefore, when calculating the input amount of the manganese slug, it is necessary to subtract the components already contained in the target components.

Meanwhile, in the term ferroalloy content, the ferroalloy refers to the manganese slug (the name is used because manganese slug is present in the form of ferroalloy), and the ferroalloy content is included in the manganese slug. Refers to the amount of manganese present.

The ferroalloy yield refers to the ratio of manganese actually released from the ferroalloy, that is, manganese slug, and the result obtained through an experimental test method is applied at a level of 50 to 55%.

After performing the step (S140) of injecting manganese slug as described above, the converter refining process performs the step (S150) of completing the converter refining when the% concentration of CO by the exhaust gas analysis (S150).

This is because the dissolved oxygen in the molten steel is 400 to 500 ppm when the% concentration of the CO gas is 20 to 25%. At this time, the amount of reduction reduced to the molten steel in the manganese slug input is maintained at 50 to 55%.

In addition, since the dissolved oxygen is low when the% concentration of CO is higher than 25%, the dissolved oxygen necessary for decarburization cannot be obtained in the vacuum degassing process, so 20 to 25% is preferable. This is because the dissolved oxygen is reduced to 500 ~ 700ppm level and manganese slug reduction rate is 30 ~ 40%. At this time, when the dissolved oxygen increases, the content of T.Fe, that is, iron oxide in the slug increases the weight of the slug, and thus the manganese slug reduction rate is lowered because the manganese in the molten steel rises to the slug in the form of MnO.

When the step (S150) as described above can be prepared to the components of the molten steel as shown in the following table. Wherein the component has units in wt% based on the weight of the molten steel.

Table 3) Basicity Application 2, Mn Ore Input 4000kg

Component (wt%) C Si Mn P S SAL Ti 0.05-0.06 0.01 0.25-0.35 0.04-0.06 0.015 0.05 0.065

Table 4) Application of Basicity 1.5, Mn Ore Input 4000kg

Component (wt%) C Si Mn P S SAL Ti 0.05-0.06 0.01 0.25 0.06-0.08 0.015 0.05 0.065

As shown in the table above, the desired target [P] component and [Mn] component were obtained by applying the basicity and adding manganese slug.

It will be described below in contrast to the embodiment of the present invention and the prior art as shown in the following table.

Table 5

division converter ingredient RH Applied base Mn slag dosage (Kg) End point oxygen (ppm) Fe-P input amount (Kg) Target Mn (wt%) End point Mn (wt%) Target P (wt%) End point P (wt%) RH Oxygen Fe-P input amount (Kg) Manganese Metal Dose (Kg) Conventional Example 1 4 - 500 400 0.3 0.09 0.05 0.02 358 - 577.5 Conventional Example 2 2 4000 350 - 0.3 0.38 0.05 0.055 158 - - Conventional Example 3 2 4000 650 - 0.3 0.13 0.05 0.04 368 100 450 Invention 1 2 4000 410 - 0.3 0.29 0.05 0.049 258 - - Invention 2 2 4000 435 - 0.3 0.31 0.05 0.051 278 - -

In this case, the RH refers to a vacuum degassing apparatus (Rheinstaal Huttenwerke und Heraus).

In the conventional example 1, a general plate decarburization operation was carried out. In the converter, ferropy was added, and in RH, manganese metal was charged.

In the conventional example 2, the applied base degree was applied to 2, and the converter was refined in a state where the CO content (% concentration) was 25% or more. Reforms are generated and cause quality degradation.

In the conventional example 3, the basicity 2 was applied and 4000 Kg of manganese slug was added. However, the target end component could not be obtained due to high end point oxygen.

As can be seen in the present invention, the CO content (% concentration) was completed by converting the converter to 20 to 25%, and the end point oxygen was 400 to 500 ppm. It was made.

That is, in the case of the present invention, it is not necessary to add ferropy (Fe-P), thereby reducing the quality such as the molten steel temperature and the occurrence of non-metallic inclusions, it is possible to prevent the cost increase.

In addition, cost increase can be prevented because manganese is not added to vacuum degassing.

Claims (3)

As a method for refining high tensile ultra low carbon steel in the converter refining stage, (1) completely excluding the residual slug after the completion of the remaining slug coating of the converter, (2) In order to determine the dosage of dolomite, hard dolomite and quicklime at the loading of scrap iron and molten iron, the dolomite and hard dolomite are determined in an amount of 8 to 10 wt% of the residual slug, and the quicklime is represented by the following equation (1). Determining the dosage by [Equation 1]

(3) injecting the dolomite, light borosilicate and quicklime simultaneously with refining the converter; (4) Injecting the manganese slug in the decarburization section, the dosage is based on the following equation (2), [Equation 2]

(5) a high tension ultra-low carbon steel refining method comprising the step of completing the converter refining when the CO% concentration is 20 to 25% by exhaust gas analysis. The method according to claim 1, The basicity of the high-strength ultra-low carbon steel refining method, characterized in that set to 2.0 when the target value of phosphorus in the molten steel is 0.04 ~ 0.06wt%. The method according to claim 1, The basicity of the high-strength ultra-low carbon steel refining method, characterized in that set to 1.5 when the target value of phosphorus in the molten steel is 0.06 ~ 0.08wt%.