KR20050009783A - Process for excluding phosphate of ingot steel - Google Patents

Abstract

PURPOSE: To provide a method for retreating molten steel containing phosphate exceeding an upper limit by dealuminizing molten steel in vacuum degassing process, securing dissolved oxygen in molten steel, injecting quicklime and fluorite into molten steel and performing top bubbling to promote dephosphorization in molten steel, thereby preventing recharging of molten steel into a converter. CONSTITUTION: The method comprises a step of deoxidizing molten steel by injecting ferroalloy into molten steel in a tapping process of transferring molten steel to a ladle in the state that converter refining is completed; a step of checking phosphorus in molten steel by sampling molten steel to check components of molten steel that completed tapping at a molten steel pretreatment(bubbling aluminum powder) station; a step of treating molten steel in a vacuum degassing process if phosphorus in molten steel is deviated from an upper limit; a step of checking components in molten steel in the vacuum degassing process; a step of oxidizing aluminum in molten steel using oxygen in the vacuum degassing process if content of phosphorus is deviated from an allowable range; a step of blowing oxygen into molten steel, thereby maintaining molten steel in the non-deoxidized state so that molten steel contains 200 to 300 ppm of dissolved oxygen; a step of injecting quicklime and fluorite into a ladle after transferring the ladle to the molten steel pretreatment station again; a step of refining phosphorus in the ladle while performing bubbling in a rate of 0.8 to 1.2 Nm¬3 for 3 to 6 minutes by transferring a top-lance of the molten steel pretreatment station; and a step of retreating molten steel in the vacuum degassing process.

Description

Process for excluding phosphate of ingot steel

The present invention relates to a method to be carried out when the phosphorus component in the molten steel in the converter out of the upper limit than the limited range in the converter refining process, more specifically, to transfer the molten steel into the ladle after the converter refining is completed. When molten steel arrives at the post-process vacuum degassing and ladle furnace (LF) in a state where the molten steel is completely deoxidized in the process and the phosphorus in the molten steel is performing to the upper limit than the component limit range, the molten steel is transferred to the converter process again and reloaded. It relates to a reprocessing method in the event of extrapersonality to prevent.

In general, in the converter refining process, in order to produce low phosphorus steel, steels of less than 0.02% by weight are produced by using various refining methods such as blowing patterns, subsidiary material input patterns, and lance heights. It is regulated to less than 0.010. Phosphorus in molten steel is segregated during slab manufacture and adversely affects hot rolled and cold rolled products.

The steelmaking process transfers the molten iron from the blast furnace to the preliminary molten iron by Torpedo Ladle Car, removes sulfur in the molten iron, prepares the molten iron in the molten iron preparation building, and then prepares the molten iron in the converter. The molten iron is charged, the impurities in the molten iron are removed using pure oxygen, refined into molten steel, and then alloyed iron is added to meet the components of the quality demanded during the tapping operation for transporting the molten steel to the ladle. When the tapping operation is completed, the molten steel temperature measurement and sampling is performed in Bubbling Aluminum Powder (BAP).

When the temperature measurement and sampling work is completed in the molten steel pretreatment plant, ladles are transferred and refined in vacuum degassing and ladle furnaces.

The refining operation refers to the components analyzed as samples in the molten steel pretreatment plant, and finely adjusts the components and separates and floats the impurities to further improve the quality of the molten steel, followed by casting in the casting process.

The conventional process of the steelmaking process as described above is to take a sample in the molten steel pretreatment plant as shown in Figure 1 (step 10) and if the phosphorus occurs in the sample to the upper limit of the component range of the molten steel (step 20) vacuum degassing or In the ladle furnace treatment step (step 30), the sample is taken again to check the components of the molten steel, and if the phosphorus is not higher than the upper limit of the component range (step 40), the process is completed (step 50), and then the casting process (step 100) is performed. Done.

If the composition range of the molten steel is the upper limit, check the production control to determine if the steel grade can be changed (step 60). If possible, change the steel grade if the steel grade can be changed (step 70). 100).

If it is impossible to change the steel type (step 60), if casting is possible after the other steel type (step 80), casting (step 100) is performed.

However, if other steel type matching is impossible after casting (step 80), it is returned (step 200).

When the return (step 200) occurs as described above, as shown in Figure 2, the deoxidation of the molten steel is completely confirmed (step 210), and if it is not completely deoxidized, the deoxidation (step 280) is performed again. After complete deoxidation, the ladle transfer trolley is used to arrive at the charter preparation stage (step 220), and the surface of the molten steel is hardened (step 230).

After recharging molten steel with high phosphorus into the converter (step 240), the molten iron mixture is charged (step 250) and the converter is refined (step 260), followed by the out-of-furnace refining process (step 270), followed by casting (step 100). Done.

If the return (step 200) is performed as described above, the following problems occur.

Firstly, when the recirculation occurs as described above, it is transferred back to the molten iron preparation unit, and the processing time of the revolving molten steel becomes longer while checking the surface state of the molten steel, reloading the molten steel into the converter, and charging the molten metal. In addition, there is a problem of lowering productivity, such as affecting other converters during charging molten steel.

Secondly, in the slewing molten steel, nitrogen is absorbed in the converter refining process and the nitrogen in the molten steel is re-refined in the converter, so that the nitrogen rises in the molten steel, which causes extraneous nitrogen separation, so the nitrogen is matched to the steel grade of 60PPM or more. There was a difficulty in adjusting the production schedule in the control.

Third, since only the iron source can be dehydrated in the molten steel, the loss of the iron source, which is a valuable metal, increases in order to increase the temperature of the molten steel, thereby increasing the manufacturing cost of the molten steel.

Fourthly, the iron source, which is a valuable metal, reacts with oxygen in molten steel while the oxygen source in molten steel reacts with MgO in the converter refractory and burns out the refractory refractory, thereby raising the unit of refractory.

An object of the present invention was devised to solve the above problems, in order to prevent the return caused when the phosphor is in the upper limit than the component range during the converter refining process and other steel type matching after casting does not match It reduces the waiting time generated when the molten steel is generated, improves productivity, prevents difficulty in adjusting the production schedule to match the molten steel, prevents the loss of iron source, a valuable metal, prevents the loss of cost, and reduces the unit of refractory. To provide a reprocessing method.

1 is a flow diagram showing a prior art reprocessing flow

2 is a flow chart showing a processing flow at the time of the occurrence of the return;

3 is a flow diagram illustrating a reprocessing flow of the present invention.

Figure 4 is a table and a graph showing the relationship between the caustic at the time of top-bubbling after the quicklime, fluorspar input of the present invention

5 is a table summarized by the experimental analysis of the embodiment of the present invention

6 is a graph showing phosphorus in molten steel before and after reprocessing of the present invention;

<Description of the symbols for the main parts of the drawings>

10: sampling step 20: phosphorus component identification step

40: upper bound of the scope 50: post-processing stage

100: casting step 200: return step

Hereinafter, the present invention will be described in more detail.

In the process of reprocessing the case of the character of the present invention, the step of deoxidation in the process of injecting ferroalloy into the tapping process to transfer the molten steel to the ladle in the converter refining state, and to check the components of the molten steel is completed in the molten steel pretreatment plant Sampling to confirm the composition of phosphorus in the molten steel; if the phosphorus component deviates from the upper limit of the composition, treating it in a vacuum degassing process without a ladle furnace (LF) treatment; Identifying the component, and if the phosphorus component is out of the component range, the step of oxidizing aluminum in the molten steel using oxygen in the vacuum degassing process, blowing oxygen into the molten steel using oxygen to de-oxidize the molten steel to about 200 ~ 300PPM And the ladles are transferred to the molten steel pretreatment plant to remove quicklime and fluorspar in the ladles. Refining phosphorus in ladle while bubbling at 0.8 ~ 1.2N㎥ by transferring Top-Lance of molten steel pretreatment plant after inputting quicklime and fluorspar. And refining the phosphorus in the ladle and then in a vacuum degassing process.

Hereinafter will be described in detail with respect to the reprocessing process of the personality of the present invention.

Figure 3 shows a reprocessing flow of the present invention, the reprocessing method of the present invention is the step of deoxidizing in the process of putting the ferroalloy in the tapping process for transferring the molten steel in the state where the converter refining is completed (step 300) and In order to check the composition of the molten steel completed tapping in the molten steel pretreatment plant, sampling (step 310) to check the component of phosphorus in the molten steel, and if the phosphorus component is out of the upper limit of the component range (step 320) ladle furnace (LF The step of processing in a vacuum degassing process (step 330), the step of checking the components in the molten steel in the vacuum degassing process (step 340), and when the phosphorus component is out of the component range, the molten steel in the vacuum degassing process Oxidation of the aluminum in the oxygen step (step 350), and oxygen is blown into the molten steel using oxygen to make the molten steel in the de-oxidized state to about 200 ~ 300PPM Giving step (step 360), transferring the ladle back to the molten steel pretreatment stage (step 370), and injecting the quicklime and fluorspar into the ladle (step 380); Top-Lance) to purify phosphorus in ladle (bubbling) for 3-6 minutes at 0.8 ~ 1.2N㎥ (Step 390) and vacuum degassing process after refining phosphorus in ladle Reprocessing is done in step (400).

In the step of deoxidation (step 300) in the process of injecting ferroalloy into the tapping process for transferring molten steel to the ladle in the state in which the converter refining is completed, the ferroalloy is added while deoxidizing to make a component required by the demand.

In the step (310) of checking the components of phosphorus in the molten steel by sampling to check the components of the molten steel completed tapping in the molten steel pretreatment plant, after confirming the various components in the molten steel in the converter refining process, vacuum degassing And the ladle furnace (Ladle Furnace) was sampled to check the components in the molten steel so as to make fine adjustments during the processing.

In the case where the component range of the phosphorus component is out of the upper limit (step 320), the ladle furnace (LF) treatment is performed when the phosphorus in the molten steel is high in the step (step 330) without the ladle furnace (LF) treatment. In order to prevent this, phosphorus in the slag on the upper part of the slag is coated in the molten steel so that the treatment is carried out by vacuum degassing.

When the phosphorus component is out of the component range in the step of identifying the component in the molten steel in the vacuum degassing process (step 340), the aluminum in the molten steel is oxidized using oxygen in the vacuum degassing process (step 350).

If the phosphorus component does not exceed the upper limit range is cast after vacuum degassing as in the prior art, if the phosphorus component exceeds the upper limit range, if the steel type change is possible, vacuum degassing and casting after the steel type change.

In the dealuminum step (step 350), since aluminum in molten steel must be burned to raise oxygen potential in molten steel later, oxygen was supplied to molten steel to raise aluminum into slag by the following reaction formula.

[Scheme 1]

2Al + 3O = Al2O3

In the step (360) of blowing molten steel into oxygen by using oxygen to make the molten steel into an undeoxidized state at about 200 to 300 PPM, oxygen must be present in molten steel to refine phosphorus in molten steel in a ladle at a molten steel pretreatment plant. Oxygen is blown into the molten steel to increase the dissolved oxygen in the molten steel by the following equation.

[Scheme 2]

Fe + O = FeO

Oxygen potential of dissolved oxygen in molten steel is increased by the above reaction formula, and oxygen in molten steel is increased by the following equation.

[Equation 1]

X = K * P

X: amount of oxygen to be supplied in molten steel (N㎥)

K: Constant value (0.35)

P: Target dissolved oxygen in molten steel (PPM)

In the step of injecting quicklime and fluorspar from the molten steel pretreatment plant (step 380), Al 2 O 3, which is a non-metallic inclusion generated while burning aluminum in molten steel in a vacuum degassing process, is collected in the slag, which is collected by the following equation.

Scheme 3

12CaO + 7Al2O3 = 12CaO.7Al2O3

In addition, the purpose of adding quicklime to increase the basicity in slag, fluorite is to lower the melting point of the quicklime to 2500 ℃ ℃. In order to reduce phosphorus in molten steel to 0.02% or less, quicklime is added based on the table of FIG.

4 shows a table and a graph showing the relationship between caustic at the time of top-bubbling after the quicklime and fluorite input of the present invention.

Injecting quicklime and fluorspar to transfer the Top-Lance of the molten steel pretreatment plant to refine the phosphorus in the ladle while bubbling at 0.8 ~ 1.2N㎥ for 3-6 minutes (step 390) ), Top bubbling is carried out at 1.0 Nm3 / min using the lance of the molten steel pretreatment plant to recycle quicklime and fluorspar. By something like

1) The oxygen concentration in the slag increases the basicity

2) P2O5 activity and temperature should be lowered.

3) Increased contact area with slag (increased stirring force)

4) Increased mass transfer speed (slag viscosity drop)

By the above reaction, phosphorus in the molten steel is moved into the slag, and nonmetallic inclusions and impurities in the molten steel are moved into the slag, thereby improving the quality of the molten steel.

In the dephosphorization operation as described above, as shown in FIG. 4, Top Bubbling is suitable for about 3 to 6 minutes.

After refining the phosphorus in the ladle and reprocessing in the vacuum degassing process (step 400), the deoxidation work is performed again in the vacuum degassing process, finely adjusting the components in the molten steel, followed by sufficient reflux and vacuum degassing refining. After the work is completed, casting is performed.

The following describes the present invention in detail by way of examples.

Example

After arriving at the molten steel pretreatment plant, the arrival phosphorus [P] resulted in 0.025% or more in the vacuum degassing process, and the arrival phosphorus [P] also achieved 0.025% or more in the vacuum degassing process. After making dissolved oxygen in molten steel to 300PPM by 1, and moving the ladle to the molten steel pretreatment plant, to adjust the quicklime and fluorite to 0.02% or less in the molten steel based on FIG. After inputting 120 Kg of fluorspar, top bubbling was performed at 1.0 Nm 3 / min for 3 minutes, followed by vacuum degassing, and casting.

BAP (%) Vacuum degassing (%) Re-BAP (%) Re-vacuum degassing (%) play(%) Remarks Conventional Example 1 0.027 0.027 Return Conventional Example 2) 0.026 0.026 0.026 Conventional Example 3) 0.028 0.028 Return Conventional Example 4) 0.026 0.027 Return Conventional Example 5) 0.027 0.027 Return Conventional Example 6) 0.028 0.028 Return Conventional Example 7 0.029 0.028 Return Conventional Example 8 0.029 0.029 Return Conventional Example 9) 0.028 0.029 Return Conventional Example 10) 0.027 0.028 Return Example 1 0.028 0.028 0.019 0.019 0.019 Example 2 0.027 0.027 0.018 0.018 0.018 Example 3 0.028 0.028 0.019 0.019 0.019 Example 4 0.027 0.027 0.017 0.017 0.017 Example 5 0.029 0.028 0.019 0.020 0.020 Example 6 0.028 0.029 0.019 0.019 0.019 Example 7 0.027 0.027 0.018 0.018 0.018 Example 8 0.028 0.028 0.019 0.019 0.019 Example 9 0.028 0.028 0.019 0.019 0.019 Example 10 0.029 0.029 0.019 0.020 0.020

As can be seen from the examples as described above, it can be seen that the production of low phosphorus steel of 0.02% or less was easy, as can be seen from the result after top bubbling after adding quicklime and fluorspar in the molten steel pretreatment plant.

5 shows a table summarizing the embodiments of the present invention by experimental analysis.

Referring to the table of Figure 5, the dephosphorization operation according to the quicklime, fluorspar input amount and the top bubbling time was facilitated.

6 is a graph showing phosphorus in molten steel before and after reprocessing of the present invention.

Referring to Figure 6, it can be seen that the low-phosphorous steel production of 0.02% by weight or less can be achieved by the re-edgering method of the present invention.

According to the above-described method for reprocessing the phosphorus case, the phosphorus, which is high in the converter refining process, is dealuminized in a vacuum degassing process to secure dissolved oxygen in molten steel, and quicklime and fluorspar are added to the slab. After maintaining it in a high base, the top bubbling is carried out to increase the stirring power to promote the reaction between the slag and the metal to promote the dephosphorization in the molten steel, thereby facilitating the production of low tough steel. It is possible to obtain the practical effect of reducing the production cost of molten steel by securing quality, refractory protection, productivity improvement, and preventing the reloading of molten steel into the converter.

Claims (1)

Deoxidation in the process of injecting ferroalloy into the tapping process to transfer the molten steel to the ladle in the state where the converter refining is completed; Checking the composition of phosphorus in the molten steel by sampling in order to confirm the composition of the molten steel in the molten steel pretreatment (BAP) field; If the phosphorus component is out of the upper limit of the ingredient range is treated in a vacuum degassing process, Identifying the components in the molten steel in a vacuum degassing process; When the phosphorus component is out of the component range, the step of oxidizing aluminum in the molten steel using oxygen in a vacuum degassing process, Blowing oxygen into the molten steel by using oxygen to make molten steel into an undeoxidized state at about 200 ~ 300PPM, Transferring the ladle to a molten steel pretreatment (BAP) site to introduce quicklime and fluorspar into the ladle; The step of refining phosphorus in ladle while feeding quick-lime and fluorspar and transferring the Top-Lance of molten steel pretreatment (BAP) to bubbling at 0.8 ~ 1.2N㎥ for 3-6 minutes. And, After refining the phosphorus in the ladle and reprocessing in a vacuum degassing process.