KR100900998B1 - Refining method for low carbon steel - Google Patents

Abstract

An extra-low-carbon steel refining method at a converter is provided to maintain constant basicity with reducing the amount of injected supplementary raw material like quicklime. An extra-low-carbon steel refining method at a converter comprises: a step for remaining the slug of 4~10wt% of ingot steel after completing tapping at the converter; a step for coating remained slug at the converter; a step for injecting oxidation iron(FeO) to the converter; a step for charging scrap iron and hot metal to the converter and performing dephosphorization blowing; a step for putting the slug formed through fourth step into the slug port; and a step for performing decarbonization refinement. The step for performing decarbonization refinement comprises a step for injecting siO2 having the weight of 4:1 rate to the calculated quicklime weight with quicklime.

Description

Refining method for low carbon steel

 The present invention relates to a method for refining ultra low carbon steel produced in a converter process, and more particularly, to a method for refining ultra low carbon steel in a converter capable of maintaining proper basicity while reducing the input amount of ancillary materials such as quicklime and the like.

In general, in the tapping step of transferring the molten steel refined from the converter to the ladle, the tapping is completed at the time of slug in the converter. After the tapping work is completed, the converter is tilted to the front to remove the slugs left in the converter by using the furnace. The composition table of the end slug of the converter to be excluded is as follows.

Table 1

 Slug generated from converter refining generates 150kg per ton of molten steel. When the slug is finished, the converter is established and the small dolomite and the chlorite methane having the chemical composition of Table 2 are introduced into the converter. The reason why the small dolomite and the fresh dolomite is added as described above is to raise the MgO in the slug and to lower the temperature in the slug to the temperature at which the slug coating is best.

Table 2)

 When the coating is finished, the upper part is sprayed with supersonic nitrogen and slugs are applied to the lead in the converter for about 1 to 2 minutes.When the nitrogen spray coating is completed, the converter is tilted to the charging side and the exit side of the converter. Slug coating is carried out to attach the slug to the refractory of the converter, and the slug is applied two to three times and the residual slug is disposed to facilitate the operation in the converter. Left.

When the coating is completed, the scrap metal and the molten iron are charged. The molten iron supplied from the blast furnace has the composition shown in the following table.

Table 3

Passion acid is carried out using the above-described molten iron component and molten iron temperature. Passion acid uses charge before and after. In general, to remove phosphorus from molten iron, the basicity is generally about 4.5.

Equation 1 is a formula for obtaining a general basicity.

[Equation 1]

In general, an actual basicity is obtained by using quicklime (CaO) and silica (SIO ₂ ) in the slug using a formula such as Equation 1.

However, in the actual operation, the quicklime input required for refining is calculated by the following equation.

[Equation 2]

The amount of quicklime is added by Equation 2 as described above, and the preparation is changed depending on the amount of quicklime, and in the case of the coolant, the amount of calorie remaining in the passion acid is input.

When charging of scrap metal and molten iron is completed, the operation method of general operation is explained first.

When commencement of blow in general operation, the upper part is used to remove oxygen from the molten iron by the following equation while supplying oxygen at supersonic speed using a lance.

[Equation 3]

[Equation 4]

[Equation 5]

[Equation 6]

[Equation 7]

Impurities in molten iron are removed by slugs and gases by the above formulas. In general operations, subsidiary materials (solvents and coolants) are initially added at the initial stage of refining. Changes with the progress of converter refining

The impurity in the molten iron is removed by the above equation (1).

In addition, when the amount of oxygen transferred from the lance coincides with the calculated amount of oxygen according to the amount of oxygen calculated by the passion acid, the converter refining is terminated. When the converter refining is completed, the tapping, which is a step of transferring the molten steel to be refined, is started. .

During the tap, ferroalloy is added to make the quality demanded. The tapping is completed when the molten steel in the converter is completely transferred to the ladle.

Ultra-low-lining steels such as API materials and automotive steel sheets are subjected to double slug coating.In the demineralization refining process, using the molten iron information as shown in Table 1, basic formula 2 is calculated according to the calculation formula of quicklime in [2]. It aims to inject quicklime, inject sintered semi-glow lamps, refines according to the specified blowing pattern, and finishes the decontamination converter at 15 to 30% of the total oxygen, the point at which the slug volume is the highest.

When the refining work is completed, the slugs are excluded. The amount of slugs excluded is excreted as 1.5 ~ 2% of molten iron. The composition of slugs (unit: wt%) is as follows.

Table 4

In addition, the components (wt%) of molten iron after the first refining is completed are shown in the following table.

Table 5

When slug excretion is completed, decarburization is performed. At this time, the refining process is completed according to the blowing pattern.

When refining is completed, tapping work is performed, and during the tapping work, ferroalloy is added to produce steel with the demanded properties. The molten steel is completely transferred to the ladle, that is, the slug is completed as soon as he exits the tap. The refining work as described above has the following problems.

1) In the converter refining process, excessive calcining was repeatedly performed without calculating the amount of quicklime in the residual slug when calculating the basicity.

2) In the operation of double slugs, quicklime was added with a basicity of 2.0, but the input amount was increased by adding quicklime without considering the basicity in the coating agent and slug.

3) Slug yard loads increased due to increased slug volume.

4) Molten steel production costs rose due to higher slug treatment costs.

5) The work load at the lime plant increased due to the excessive use of quicklime.

6) When dephosphorization is performed, the basicity is high and the slug volume is low, so slug is not excluded, and the amount of quicklime injected during decarburization is increased.

An object of the present invention is to provide a method for refining an ultra low carbon steel in a converter capable of maintaining an appropriate basicity while reducing the input amount of an auxiliary material such as quicklime or the like.

In order to achieve the above object, the present invention is the first step of leaving the slug corresponding to 4 ~ 10wt% of the amount of molten steel outgoing when the slug in the converter after the completion of the tapping in the converter to the slug port and And converting the remaining slug into the converter, and converting the iron oxide (FeO) having a weight ratio of quicklime (CaO) included in the remaining slug and an increase in the ratio of 1: 1 to 1: 2.5 into the converter. A third step of introducing into the furnace, a fourth step of charging scrap iron and molten iron in the converter and performing dephosphorization and a fifth step of excluding the slug prepared by the fourth step into the slug port, and decarburization refining It is characterized by an ultralow carbon steel refining method in a converter comprising a sixth step performed.

According to the present invention described above, it is possible to maintain an appropriate basicity while reducing the input amount of auxiliary raw materials such as quicklime, and the like to produce ultra low carbon steel having a concentration of phosphorus [P] in molten steel of 50 ppm or less and a concentration of phosphorus [P] in molten steel. It can be effective.

As described above, the present invention is a method for producing ultra low carbon steel having a carbon concentration of 50 ppm or less and a phosphorus [P] concentration in molten steel of 100 to 200 ppm.

That is, the method (S100) is the first step (S110) to leave the slug corresponding to 4 ~ 10wt% of the amount of molten steel out when the slug in the converter after the completion of the tapping in the converter to the slug port (S110) ), And the second step (S120) of coating the remaining slug on the converter, and iron oxide having a weight ratio of 1: 1 to 1: 2.5 and a weight of quicklime (CaO) included in the remaining slug ( A third step (S130) of introducing FeO) into the converter, a fourth step (S140) of charging scrap iron and molten iron into the converter and performing dephosphorization and a slug prepared by the fourth step (S140) It includes a fifth step (S150) for excluding the slug port, and a sixth step (S160) for performing decarburization.

The first step (S110) is 4 ~ of the amount of molten steel that can refine the slug in the converter when the slug in the converter when the tapping step, which is the step of transferring the molten steel to the ladle in the converter is completed to the slug port As a step (S110) of remaining 10wt%, by checking the basis weight installed in the slug port according to the component of the molten iron to be charged to leave the slug in the converter.

Table 6 below shows the amount of residual slug according to Si in the molten iron.

<Table 6>

Si (wt%) Residual slug wt% for molten steel 0.1 4 0.2 5 0.3 6 0.4 7 0.5 8 0.6 9 0.7 10

The second step (S120) is a step of coating the remaining slug on the converter, and as described above, when the slug excretion is completed, injecting small dolomite and fresh dolomite (S121), and slag with nitrogen from the top. Nitrogen spray coating step of spraying while cooling (S122) and the coating step (S123) to attach the slug into the furnace body by tilting the converter back and forth using the remaining slug in the converter.

That is, when the slug exclusion is completed, the converter is established, and then, the small dolomite and the raw dolomite are introduced into the converter through the sub-material hopper to lower the iron oxide concentration in the slug, and then the supersonic nitrogen is injected from the top to attach the slug to the converter refractory. Do the work.

When the nitrogen spray coating is completed, slugs are attached to the charging side and the tapping side of the converter while tilting the converter 180 degrees forward and backward.

After performing the second step S120, the third step S130 is performed.

The third step (S130) is a step of introducing iron oxide (FeO) having a weight of 1: 1 to 1: 2.5 ratio of the weight of quicklime (CaO) contained in the remaining slug and the converter.

The weight of quicklime contained in the remaining slug refers to the weight of quicklime contained in the slug after applying a coating agent including light borodolite and dopelomite to the converter, as shown in Table 7 below. Repeated experiments showed that 50 wt% to 55 wt% of the residual slug was the weight of quicklime.

<Table 7>

After calculating the weight of quicklime based on the table, iron oxide having a weight of the quicklime and a ratio of 1: 1 to 1: 2.5 is added to the converter.

After performing the third step (S130), a fourth step (S140) of charging scrap iron and molten iron in the converter and performing dephosphorization drilling is performed.

When the dephosphorization refining of the fourth step (S140) is started, refining is performed by the blowing pattern. At this time, iron oxide, silicon (Si) shown in Table 3, and residual slug react with each other. It was to promote the goods by dropping the level of the province to 1600 degrees.

At this time, when the basicity after the completion of refining is set to 2, the basicity of the residual slug is high, and it is not necessary to add quicklime. In addition, as described above, if the basicity is set to 2, the slug volume is the largest after performing the fourth step (S140) of dephosphorization, and thus, the fifth step (S150) can be easily performed. Will be.

The composition (unit: wt%) of the slug after performing the fourth step S140 is changed as shown in Table 8 below.

<Table 8>

After performing the fourth step S140 and the fifth step S150 described above, the sixth step S160, that is, decarburization and refining is performed.

In the sixth step S160, the step of calculating the quicklime weight (S161), and the step of injecting SiO2 having a weight ratio of the quicklime and 4: 1 ratio calculated by the step (S161) together with the quicklime (S162). ).

In the step of calculating the quicklime weight (S161), it can be obtained by the following Equation (8).

[Equation 8]

The weight of SiO 2 can also be calculated by the quicklime weight calculated by Equation 8, and the quicklime and SiO 2 can be added together as described above.

At this time, the basicity is set to 4 to obtain the weight of quicklime, which is advantageous for improving the quality of steel and reducing side materials.

It will be described again in contrast to the Examples and Comparative Examples of the present invention described by Table 9.

TABLE 9

Residual slug amount (Kg) Si (wt%) of molten iron Quicklime input at dephosphorization (Kg) Exclusion after dephosphorization (Kg) P (PPM) of molten steel after dephosphorization Quicklime input in decarburization (Kg) P (PPM) of molten steel after decarburization Comparative Example 1 20,000 0.2 2,300 4,000 450 5,000 120 Comparative Example 2 20,000 0.3 3,000 5,000 510 6,000 135 Comparative Example 3 20,000 0.4 4,000 4,500 480 6,000 138 Example 1 11,000 0.2 - 9,500 470 4,500 116 Example 2 14,000 0.3 - 10,000 500 5,000 127 Example 3 16,500 0.4 - 10,500 489 5,500 118 Example 4 22,000 0.5 - 9,800 493 6,400 121 Example 5 24,500 0.6 - 10,700 459 6,800 103

As described above, the present invention relates to a method for producing ultra low carbon steel having a concentration of carbon of 50 ppm or less and a concentration of phosphorus [P] in molten steel of 100 to 200 ppm.

As in Examples 1 to 5 of the present invention, the molten steel [P] level was maintained at the same level as the comparative example after dephosphorization with only residual slug without adding quicklime during dephosphorization. (See P of molten steel.)

In addition, as described above, the slug volume was also increased during the excavation work after dephosphorization and the excretion amount was more than doubled. Also, the quicklime input during decarburization was reduced compared to the molten silicon. That is, conventionally, 29 kg of quicklime was added to average molten steel to 20 to 22 kg.

Claims (6)

As a method for refining ultra low carbon steel in converters, (1) the first step of leaving the slug corresponding to 4 ~ 10wt% of the amount of molten steel out of the converter when the slug in the converter after discharging is completed to the slug port; (2) injecting light dolomite and fresh dolomite into the converter, nitrogen spray coating to cool the remaining slug by injecting nitrogen from the upper part of the converter, and tilting the converter to the residual slug. A second step of coating the converter with the remaining slug, including attaching to the converter; (3) the iron oxide (FeO) having a weight of 1: 1 to 1: 2.5 ratio of the weight of quicklime (CaO) corresponding to 50wt% to 55wt% of the remaining slug and the weight ratio of 1: 1 to 1: 2.5 after performing the second step of coating the converter The third step, (4) a fourth step of charging scrap iron and molten iron in the converter and performing dephosphorization blowing; (5) a fifth step of excluding the slug prepared by the fourth step into the slug port; (6) calculating the quicklime weight by equation (8) as a step of decarburizing and injecting SiO2 having a weight ratio of the quicklime weight and a 4: 1 ratio calculated in the step together with the quicklime Ultra-low carbon steel refining method in a converter comprising a sixth step is configured. [Equation 8]

delete delete delete The method according to claim 1, The fourth step is ultra-low carbon steel refining method of the converter, characterized in that the basicity is 2 by dephosphorization blow using only the residual slug. The method according to claim 1, In the sixth step, the basicity of [Equation 8] is calculated by 4 to calculate the quicklime weight of ultra low carbon steel in the converter, characterized in that.