KR20060035274A - Method for manufacturing molten steel for galvanized steel plate - Google Patents

Abstract

The method for producing molten steel for galvanized steel sheet according to the present invention is to prevent the forced oxidation of the molten steel due to the lack of dissolved oxygen in the vacuum degassing process by pursuing proper dissolved oxygen in the converter refining operation, and by the excessive input of the deoxidizer when the dissolved oxygen is excessive. Minimizes the occurrence of nonmetallic inclusions, and removes the lower oxides in the ladle slag manufactured during the tapping stage by using a silicon-based slag deoxidizer to maintain the basicity of the ladle slag properly and improve the absorption ability of the nonmetallic inclusions in the cold rolling process. There is an advantage that can reduce the steelmaking defects in the production of plated steel sheet.

Converter, refining, galvanized steel, aluminum, silicon, deoxidation

Description

Method for manufacturing molten steel for galvanized steel sheet {Method for manufacturing molten steel for galvanized steel plate}

1 is a process flow diagram showing the progress of a conventional operation.

Figure 2 is a process flow chart showing the manufacturing process of the molten steel for galvanized steel sheet of the present invention.

The present invention relates to a method for manufacturing molten steel, and more particularly, to a method for manufacturing molten steel for performing steel sheet galvanizing in the cold rolling process of the steel produced in the converter.

In general, converters produce hundreds of steel grades. In particular, the converter refining method for steel grades that are subjected to annealing after galvanizing in the cold rolling process is difficult to secure proper dissolved oxygen because tapping is performed at high temperatures. It is also difficult to control the alumina ratio for lower oxides and quicklime in slag.

Referring to Figure 1 is a method of manufacturing a molten steel for a general galvanized steel sheet as follows.

Before starting the refining work, the worker checks the conditions of the main raw materials, checks the various conditions of the fermentation acid in the converter, and compares the conditions before and after. At this time, if the sensible heat generated in the furnace and the generated heat are small, the negative heat is mixed and the dissolved oxygen rapidly increases after the converter refining is completed. On the other hand, when the sensible heat and the generated heat is large, it is determined to add a coolant, and then the scrap iron and molten iron are charged into the converter. Then, the high pressure oxygen gas is blown to start the blowing operation, and a coolant, a preparation agent, a solvent, and the like are introduced during the blowing operation, and these are added according to the amount calculated in the passion acid operation. When 80% of the blowing process proceeds, that is, when the decarburization reaction reaches the rate step, the temperature of the molten steel in the converter and the carbon content in the molten steel are measured, and the final oxygen content is reached according to the measured temperature and carbon content. When you complete the drill. When the blow is completed, the temperature and oxygen are measured. If the measured value is near the target value, tapping is performed. During tapping work, quicklime is added to prepare slag in the ladle, and fluorspar is added to promote the quicklime's goods. When tapping is completed, slag deoxidation is performed using an aluminum slag deoxidizer to remove lower oxides in the ladle slag.

Table 1 below shows the ladle slag composition after the tapping is completed.

Here, T.Fe is an iron oxide formed by oxidizing iron due to oxygen injected into the converter, and consists of various complex oxides such as FeO, Fe ₂ O ₃ , Fe ₃ O ₄ , and 10 to 13% in the ladle slag after tapping. Included.

When slag deoxidation is performed on the ladle slag by using the aluminum-based slag deoxidizer, it has the following composition.

As can be seen in Table 2, due to the deoxidation of the ladle slag, lower oxides T.Fe, MnO, P ₂ O ₅ and the like in the slag can be reduced. At this time, the amount of the aluminum-based slag deoxidizer added to the ladle slag is changed according to the amount of dissolved oxygen in the molten steel.

The deoxidation of the ladle slag in this way can reduce the lower oxides in the slag, and the ladle slag must maintain an appropriate ratio of quicklime to alumina for absorption of nonmetallic inclusions. However, conventionally, by using all of the slag deoxidizer based on alumina, the ratio of alumina is very large compared to the quicklime content, so that the proper ratio cannot be adjusted. Thus, ladle slag lacks the ability to absorb nonmetallic inclusions and molten steel contains a large amount of nonmetallic inclusions. When the galvanized steel sheet is manufactured using such molten steel, steelmaking defects occur during the cold rolling process, and defects occur during galvanizing, which causes quality deterioration.

In addition, in the case of the enthusiastic acid step performed before the converter refining operation, the sensible heat that enters the converter and the heat generated during the converter refining operation becomes negative passion acid. When the flow rate of oxygen blown into the converter increases, there is a problem of increasing the converter refining time and thereby lowering the productivity.

In addition, the final oxygen flow rate was accurately calculated by measuring the temperature of the molten steel and the carbon content of the molten steel at 80% of the time of the smelting operation, but calculating the standard of dissolved oxygen required in the post process, that is, the vacuum degassing process. There was no suitable way to do this, and generally tapping was performed with dissolved oxygen of 450 to 1000 ppm. However, this method has a problem in that non-metallic inclusions increase due to forced oxidation of molten steel due to lack of dissolved oxygen or excessive input of deoxidizer due to excess of dissolved oxygen.

The present invention is to solve the above problems, to prevent the forced oxidation of molten steel due to the lack of dissolved oxygen in the vacuum degassing process by pursuing the appropriate dissolved oxygen in the converter refining operation, and the excessive input of deoxidizer when excess dissolved oxygen It provides a method of manufacturing molten steel for galvanized steel sheet to minimize the occurrence of non-metallic inclusions due to the improvement, improve the quality of slag deoxidation to improve the absorption of the non-metallic inclusions when removing the lower oxide of the ladle slag manufactured in the tapping step. It aims to do it.

In order to achieve the above object, the method for manufacturing molten steel for galvanized steel sheet according to the present invention includes the step of performing a passion acid, and in the case of lacking the heat source calculated in the passion acid step, injecting ferrosilicone into the converter to correct the heat source and injecting quicklime. Correcting the basicity, charging the scrap iron and molten iron into the converter, performing the drilling operation, predicting the end oxygen amount in the molten steel during the drilling process, correcting the oxygen flow rate, and transferring the molten steel to the ladle after completing the drilling operation step. Tapping and generating a ladle slag and deoxidizing the ladle slag.

The step of correcting the oxygen flow rate during the blowing operation and the blowing operation, by measuring the temperature and carbon at the 75 to 85% time point of the blowing progress

That is, oxygen flow rate = (oxygen flow rate at the time of measurement) + (corrected oxygen amount)

              = Oxygen flow rate at the time of measurement

                + [1220+ (1928 X carbon content) + (1.06 X end oxygen amount)]

As described above, the blown oxygen flow rate is again determined and blown. The end point oxygen amount is characterized in that 550 to 650 ppm.

In addition, the deoxidation step of the ladle slag, the first slag deoxidation step of deoxidizing the slag by adding a silicon-based slag deoxidizer and a secondary slag deoxidation step of deoxidizing the slag by adding an aluminum-based slag deoxidizer.

The primary slag deoxidation step is characterized in that the basicity of the ladle slag is adjusted to 5.5 to 6.0, the silicon-based slag deoxidizer is characterized in that it comprises 35 to 40wt% CaCO ₃ , 40 to 42wt% Si.

Hereinafter, a method of manufacturing molten steel for galvanized steel sheet according to the present invention will be described in detail with reference to the accompanying drawings.

Figure 2 shows the process progress of the manufacturing method of molten steel for galvanized steel sheet according to the present invention.

First, before performing the converter refining operation, ferrosilicone is added to correct the heat source when it becomes negative passion acid by referring to the sensible heat entering the converter and the heat generated during the converter refining in the step of conducting the passion acid. In addition, quicklime is added to correct the basicity (CaO / SiO ₂ ) that changes according to the introduction of the ferrosilicon. As described above, changes in the molten steel temperature due to the addition of ferrosilicon and the quicklime for correcting the basicity are added as follows.

As shown in Table 3, the ferrosilicon (Fe-Si) for correcting the heat source increases the temperature of the molten steel by 8.7 ° C. when the 100 kg is added. .

Table 4 shows the temperature change according to the dose of ferrosilicon and quicklime as described above.                     

Using Table 4, when the heat source is insufficient, ferrosilicon is added to correct the heat source, and quicklime is added to correct the basicity.

Thus, charging work is started in which the scrap iron and the molten iron are charged into the converter and the high pressure oxygen gas is blown to remove impurities. At this time, a coolant, a preparation, a solvent, and the like are added according to the amount calculated by the passion acid. Then, the temperature and carbon content in the furnace are measured at 75 to 85% of the time of blowing, and the oxygen flow rate is determined again using the measured values. The present invention predicts the end point oxygen, that is, the dissolved oxygen at the time of completion of blowing, in order to adjust the proper end point oxygen to keep the vacuum degassing arrival oxygen constant and determines the blown oxygen flow rate by the following equation.

Corrected oxygen amount = 1220 + (1928 × carbon content) + (1.06 × end point oxygen)

Oxygen flow rate = Oxygen flow rate at the time of measurement + Corrected oxygen amount

In the above formula, the end point oxygen is dissolved oxygen in the molten steel at the completion of blowing, and the present invention is based on 550 to 650 ppm.

For example, the temperature and carbon content of the molten steel were measured at an oxygen flow rate of 10300 Nm ³ at 80% of the time of blowing, and the temperature of the molten steel was 1612 ° C and the carbon content was 0.56%. At this time, when the dissolved oxygen at the end point is set to 550 ppm, the oxygen flow rate can be determined again by calculating the corrected oxygen amount using the above equation.

Corrected oxygen amount = 1220+ (1928 × 0.56) + (1.06 × 550)

= 2882.68 Nm ³

Oxygen flow rate = 10300 Nm ³ + 2882.68 Nm ³

= 13182.68 Nm ³

In this way, when the blowing operation is performed by blowing at the oxygen flow rate corrected using the above equation, the end point oxygen is appropriately adjusted to maintain a constant amount of oxygen arriving at the vacuum degassing process, thereby It is possible to prevent forced oxidation of molten steel due to lack and to minimize the occurrence of non-metallic inclusions due to excessive input of deoxidizer when excess dissolved oxygen is present.

After tapping the appropriate dissolved oxygen by the above-described blowing method, the tapping work for transferring the molten steel in the converter to the ladle is performed. During tapping work, quicklime is added to generate ladle slag and fluorite is added to promote the quicklime's goods. When the tapping operation is completed, slag deoxidation is performed to remove lower oxides in the ladle slag. The present invention deoxidizes slag by using a first slag deoxidation step of deoxidizing slag using a silicon-based slag deoxidizer and an aluminum slag deoxidizer. Proceeds to the second slag deoxidation step.

The silicon-based slag deoxidizer used in the first slag deoxidation step is composed of a composition containing CaCO ₃ 35 to 40wt%, Si 40 to 42wt% or other impurities, and when the silicon-based slag deoxidizer is added to ladle slag, the following reaction This happens.

2 FeO + Si = Fe + SiO ₂

MnO + Si = Mn + SiO ₂

The lower oxide in the ladle slag can be removed by adding a silicon-based slag deoxidizer as in Scheme 1 and Scheme 2.

In the first slag deoxidation step, the basicity of the ladle slag is adjusted to 5.5 to 6.0 using a silicon-based slag deoxidizer. This is because when the basicity is 5.5 or less, a problem of phosphorus (P) component in the slag caused by the lowering of the basicity occurs, whereas when the basicity is 6.0 or more, the ability to absorb non-metallic inclusions is greatly reduced.

In order to obtain the input amount of the silicon-based slag deoxidizer introduced in the first slag deoxidation step, the amount of ladle slag is first calculated by using quicklime and fluorite introduced as a slag modifier, and slag generally flowing into the ladle as follows.

Ladle slag amount = slag outflow into quicklime + fluorspar + ladle

As described above, in order to adjust the basicity of the ladle slag to 5.5 to 6.0, the required SiO ₂ content is obtained by the following equation using the amount of the ladle slag obtained in the above formula, and the amount of the silicon-based deoxidizer is calculated.

Required SiO ₂ wt% = (quick lime (wt%) / target basicity in ladle slag)

SiO ₂ (wt%) in the ladle slag

Silicon-based deoxidizer input = (ladle slag amount × required SiO ₂ wt% × (Si / SiO ₂ ))

                     / (Silicone content x silicon real rate in silicon-based deoxidizer)

The above formula can be used to calculate the amount of silicon-based deoxidizer to adjust the basicity in the ladle slag to 5.5 to 6.0.                     

For example, when the SiO ₂ content of 4.5%, CaO content of 43%, and other unnecessary impurities are included in a 3000 kg ladle slag component, a silicon-based deoxidizer input amount is used as follows to adjust the basicity to 6.0. Calculate

Required SiO ₂ wt% = (quick lime (wt%) / target basicity in ladle slag)

SiO ₂ (wt%) in the ladle slag

             = (43/6)-4.5

             = 2.26 (%)

Silicon-based deoxidizer input = (ladle slag amount × required SiO ₂ wt% × (Si / SiO ₂ ))

                     / (Silicone content x silicon real rate in silicon-based deoxidizer)

                       = (3000 × 2.26 × 0.46) / (0.4 × 0.3)

                       = 259.9 (kg)

When the first slag deoxidation step is completed, a second slag deoxidation step using an aluminum-based slag deoxidizer is performed to deoxidize the remaining lower oxide. When the aluminum slag deoxidizer is added to the ladle slag, the following reaction occurs.

(T.Fe) + Al = Fe + Al ₂ O ₃

As shown in Scheme 3, the lower oxide in the ladle slag may be removed by adding an aluminum slag deoxidizer.

In the second slag deoxidation step, the input amount of the aluminum-based slag deoxidizer is calculated by using a lower oxide in the ladle slag after the first slag deoxidation. The following table shows the ladle slag composition after the first slag deoxidation step.

The input amount of the aluminum-based slag deoxidizer is calculated using the ladle slag composition after finishing the primary slag deoxidation as shown in Table 5.

Aluminum Deoxidizer Input = Ladle Slag

× (T.Fe (wt%)-target T.Fe (wt%) in slag) × (Al / Al ₂ O ₃ )

               / (Aluminum content in aluminum deoxidizer × aluminum real rate)

Lower oxides such as T.Fe can be reduced by injecting aluminum slag deoxidizer of the input amount calculated using the above equation into the ladle slag and performing deoxidation.

For example, the goal is to adjust the T.Fe content to 8.0 wt% of the 3000 kg ladle slag components after the first slag deoxidation step and 3.0 wt% after the secondary slag deoxidation. The real ratio of aluminum is based on 30%, and the composition of the aluminum slag deoxidizer is 35 to 40% of CaCO ₃ , 38 to 42% of Al, and contains other unnecessary elements.

Aluminum Deoxidizer Input = Ladle Slag                     

× (T.Fe (wt%)-target T.Fe (wt%) in slag) × (Al / Al ₂ O ₃ )

               / (Aluminum content in aluminum deoxidizer × aluminum real rate)

                         = 3000 × (8-3) × (27/102) / (0.4 × 0.3)

                         = 330.88 (kg)

As described above, the present invention removes the lower oxide by deoxidizing the ladle slag by using the silicon-based slag deoxidizer and the aluminum-based slag deoxidizer, and adjusts the basicity of the ladle slag to 5.5 to 6.0 to facilitate the collection of non-metallic inclusions. Stiffness defects can be reduced.

Hereinafter, the present invention will be described in more detail with reference to Examples.

As can be seen from Table 6, Examples 1 to 9 can be suitably adjusted within 1.2 to 1.6, the alumina ratio for quicklime in the vacuum degassing process using a silicon-based slag deoxidizer is excellent in the absorption capacity of the non-metallic inclusions. . In addition, the end point oxygen can be controlled to 550 to 650 ppm, and T.Fe in the ladle slag, which is a lower oxide, is also reduced to 3 to 4, so that the collection of nonmetallic inclusions is easy. In addition, the amount of oxygen arriving at the vacuum degassing process is also suitable, thereby preventing forced oxidation as in Comparative Examples 1 and 2, and the amount of aluminum used to deoxidize molten steel is also constant.

The method of manufacturing molten steel for galvanized steel sheet according to the present invention prevents the rapid increase of dissolved oxygen by adding ferrosilicon and quicklime when the heat source is insufficient in converter refining operation, and measures the molten steel temperature measured at 75 to 85% of the progress of the drilling. The amount of non-metallic inclusions is corrected by using the carbon content to correct the oxygen flow blown and to control the end point oxygen so that the dissolved oxygen is kept constant during the vacuum degassing process to prevent forced oxidation of the molten steel in the vacuum degassing process or to reduce the input of deoxidizer By minimizing the use of silicon-based slag deoxidizer, it is possible to maintain the basicity of the ladle slag properly and improve the absorption ability of the non-metallic inclusions of the ladle slag, thereby reducing the steelmaking defects in manufacturing the galvanized steel sheet in the cold rolling process.

Claims (6)

Conducting a passion mountain; Correcting the heat source by injecting ferrosilicon into the converter when the heat source calculated in the passion acid step is insufficient and correcting the basicity by adding quicklime; Charging scrap metal and molten iron in the converter; Correcting the oxygen flow rate by performing the blowing operation and predicting the amount of the end point oxygen in the molten steel during the drilling process; Performing a tapping operation for transferring the molten steel to the ladle after completing the blowing operation step and generating a ladle slag; And Method of producing a molten steel for galvanized steel sheet comprising the step of deoxidizing the ladle slag. The method of claim 1, Performing the blowing operation and correcting the oxygen flow rate during the blowing process, The temperature and carbon were measured at 75 to 85% of the time of blowing and the following formula That is, oxygen flow rate = (oxygen flow rate at the time of measurement) + (corrected oxygen amount)               = Oxygen flow rate at the time of measurement                 + [1220+ (1928 X carbon content) + (1.06 X end oxygen amount)] The method for producing molten steel for galvanized steel sheet, characterized in that the blowing oxygen flow rate is again determined and blown. The method of claim 2, The end point oxygen amount is a manufacturing method of molten steel for galvanized steel sheet, characterized in that 550 to 650ppm. The method according to any one of claims 1 to 3, The deoxidation step of the ladle slag, A first slag deoxidation step of deoxidizing slag by adding a silicon-based slag deoxidizer; And A method of manufacturing molten steel for galvanized steel sheet comprising a secondary slag deoxidation step of deoxidizing slag by adding an aluminum slag deoxidizer. The method of claim 4, wherein The primary slag deoxidation step is a method of manufacturing molten steel for galvanized steel sheet, characterized in that the basicity of the ladle slag is adjusted to 5.5 to 6.0. The method of claim 4, wherein The silicon-based slag deoxidizer is a method for producing molten steel for galvanized steel sheet, characterized in that it comprises 35 to 40wt% CaCO ₃ , 40 to 42wt% Si.

Images