KR100925598B1 - Method for Refining Return Molten Steel - Google Patents

Abstract

The present invention relates to a method for refining refractory steel generated in a steelmaking process of a steelworks.

According to the present invention, there is provided a method of manufacturing a semiconductor device,

Feeding the transformed refined molten steel into the molten state as described above; And

Degreasing the molten steel introduced in the microlitic state as described above in a vacuum degassing process under the conditions of a vacuum degree of 0.5 to 0 Torr and an Ar blowing amount of 0.4 to 0.6 Nm ³ / molten steel-ton for 20 to 30 minutes A refining method of refractory steel is provided.

According to the present invention, it is possible to manufacture various kinds of steels by manufacturing refined low-nitrogen steels having nitrogen of 60 PPM or less by appropriately refining the steels generated in the steelmaking process, thereby improving productivity.

Conveying steel, refining, low nitrogen, mineral acid, vacuum degassing, denitrification

Description

[0001] The present invention relates to a method for refining molten steel,

1 is a process diagram showing a process for refining refractory steel according to a conventional method

Fig. 2 is a schematic diagram showing that external air is sucked in the case of deoxidization according to the conventional method during feeding and lapping of molten steel passed through a transformer

Fig. 3 is a graph showing the change in nitrogen content in the molten steel after the refining of the refractory steel and the deoxidization /

4 is a flow chart showing a process of refining refractory steel according to the present invention

Fig. 5 is a schematic view showing that air present in the ladle is pushed out of the ladle when the molten steel passed through the ladle is laden during the ladle operation according to the present invention when the molten steel is refined.

6 is a graph showing the change in mass transfer coefficient of the adsorption reaction depending on the content of oxygen and sulfur

7 is a graph showing changes in nitrogen content in molten steel after refinement and refinement of the refractory steel according to the present invention

8 is a graph showing the change in denitration rate constant according to oxygen and sulfur content

Description of the Related Art [0002]

1 ... converter 2 ... ladle 3 ... creep 4 ... slag < RTI ID = 0.0 >

5 ... molten steel

The present invention relates to a method for refining refractory steel generated in a steelmaking process, and more particularly, to refining refractory steel for refractory steel capable of producing refractory steel having a nitrogen content of 60 PPM or less.

Generally speaking, refinement steel refers to that it is difficult to match with other machines after the lapping operation after the lapping operation in the converter, or the refinement work is performed by re-charging the lapping furnace with the post-process temperature low temperature and the component nap.

Since the molten steel has already been introduced in the converter, there is already about 20 PPM in the molten steel and about 50 PPM in the molten steel.

When the electrolytic refining is performed in the state where the dissolved nitrogen is about 20 to 50 PPM in the molten steel, the amount of air sucked during the refining operation is increased because of the presence of 0.007 to 0.2 wt% of [C] in the returning steel. [N] of the molten steel is 60 to 80 PPM or more.

When the returning steel is generated as described above, it is matched with the quality control steel as shown in FIG. 1, recharged to the converter, charging the charcoal, and then conducting the refinement work.

When the converter refining operation is completed, the molten steel is led to the ladle, and in order to match the steel component required by the demand during the ladle operation, deoxidizing operation is performed at the stage of inputting the ferroalloy, and the ladle operation is completed.                         

When the lecture is completed, the post-processing is performed.

In the above operation method. The reason for charging the molten steel after charging the molten steel is to prevent the air from being sucked into the molten steel due to the generation of CO gas during the refining operation by inducing the reaction formula (1) during the refining operation of the molten steel.

C + O = CO ↑

However, since there is usually a large amount of molten steel, the amount of molten metal to be charged after charging the molten steel is less than that of molten steel

For example, the molten steel is 270 Tons or more, and the amount of charged glass is about 20 to 30 Tons.

On the other hand, oxygen for supplying the molten steel is required to make the molten steel easy to work in the post-processing.

For example, the amount of oxygen to be supplied from the operation for which the molten steel is 270 Ton or more and the charged dose is about 20 to 30 Ton is 3000 Nm ³ .

The content of [C] contained in the molten iron is 4.5% but the amount of molten iron charged is small, so that the amount of [C] as a whole is small, and the reaction of the above reaction formula (1) is completed in the middle of refining the molten steel.

Therefore, Fe in the molten steel increases the temperature of the molten steel while increasing the dissolved oxygen in the molten steel while increasing the [N] value of the molten steel while reacting with oxygen supplied to regulate the tempering temperature, as in the following reaction formula (2) Increases nitrogen.

Fe + O = FeO

Also, in the case of deoxidizing molten steel during the ladle operation, as shown in FIG. 2, the external air is sucked in during the ladle operation and the adsorption occurs, which is also proved in FIG.

That is, as shown in FIG. 3, it can be seen that the amount of nitrogen is increased by about 20 to 30 PPM during the feeding.

2, reference numeral 1 denotes a converter, reference numeral 2 denotes ladle, reference numeral 3 denotes a lubrication flow, reference numeral 4 denotes slag, and reference numeral 5 denotes molten steel.

Also, even if the work is carried out in the degassing process during the post-process operation, the denitrification reaction does not easily occur because there is no oxygen in the molten steel.

In particular, in recent years, it is difficult to match the quality of recycled molten steel to the quality control steel due to the increase in the ratio of high grade steel.

Further, when the molten steel is matched to the nitrogen-regulated steel, there arises a problem such that component nuisance is caused by the upper limit of nitrogen.

Therefore, there is a demand for a technique for refining refractory steel to produce molten steel having a nitrogen content sufficient to satisfy the standard of nitrogen-regulated steel.

The present invention has been proposed in order to meet the above-mentioned demands. In the vacuum degassing process after the refining, the molten steel is denitrified under suitable conditions to produce a low-nitrogen molten steel having a low nitrogen content And to provide a refining method of refractory molten steel which can be used for refining molten steel.

Hereinafter, the present invention will be described.

The present invention relates to a method for manufacturing a semiconductor device,

Feeding the transformed refined molten steel into the molten state as described above; And

Degreasing the molten steel introduced in the microlitic state as described above in a vacuum degassing process under the conditions of a vacuum degree of 0.5 to 0 Torr and an Ar blowing amount of 0.4 to 0.6 Nm ³ / molten steel-ton for 20 to 30 minutes The present invention relates to a refining method for refractory steel.

Hereinafter, the present invention will be described in detail.

In the case where the machine is difficult to match with the performance process after the lapping operation in the converter, or the postprocessing temperature is low or the component is out of order, returning steel is generated.

Since the molten steel has already been excavated in the converter, nitrogen is already present in the molten steel in the amount of about 20 PPM or more and about 50 PPM in the molten steel.

When the electrolytic refining is performed in the state where the dissolved nitrogen is about 20 to 50 PPM in the molten steel, the amount of air sucked during the refining operation is increased because of the presence of 0.007 to 0.2 wt% of [C] in the returning steel. [N] of the molten steel is 60 to 80 PPM or more.

The present invention relates to a method for refining refractory steel produced as described above into molten steel containing low nitrogen.

According to the present invention, in order to refine the refractory steel into molten steel containing low nitrogen, as shown in Fig. 4, the refractory steel is first charged into the converter according to a conventional method, and the molten iron is charged.                     

Usually, the conversion ratio of 85 ~ 92% is used in the general refining process. However, when the returning steel is generated, the ratio of the dose to the total amount of the reactor is 3 ~ 5% Is used.

Next, pure oxygen is blown through the lance at the top to refine the molten steel.

In the present invention, the ladle should be ladled in the faded state after refining is completed.

In the present invention, the refined molten steel is to be liquefied in the flesh state.

First, according to the present invention, when molten steel is introduced into the molten state, CO bubbles are generated in the molten steel by the exothermic reaction while [C] and dissolved oxygen present in the molten steel react with the reaction formula (1) , The air existing in the ladle 2 is pushed out of the ladder and the pressure in the ladle is kept higher than the atmospheric pressure and the volume of the CaO introduced during the ladle is kept high, Thereby preventing the incoming air from reacting with the molten steel 5 and preventing the adsorption.

In addition, since oxygen, which is a surface active element, is small around the CO bubbles, the nitrogen moves to the CO bubble interface, and the effect of the denitrification reaction is generated so that the nitrogen is removed while being discharged to the surface together with the CO bubbles.

Second, during the lubrication operation, the molten steel is lowered by the fluctuation of the molten steel due to the lubrication flow and the molten iron is injected, and the absorption reaction is decreased because dissolved oxygen exists in the molten steel.                     

This is because as shown in FIG. 6, the adsorption reaction decreases as the temperature is lower and the concentration of oxygen and sulfur is higher.

Oxygen and sulfur are adsorbed on the interface as a typical interfacial activation element, which reduces the adsorption effect because of increased resistance to mass transfer through the interface.

Third, the denitrification in the post-process vaginal desorbing gas process is more difficult than in the metic acid condition after deoxidization because the Ar gas is generated as bubbles in the process of treating molten steel by decompression in the vacuum degassing process, The effect of denitrification occurs because nitrogen existing together with oxygen is elevated upward.

As shown in FIG. 7, when nitrogen is excited in the above-mentioned micronic state, there is almost no rise of nitrogen during the ladle.

Mittal acid conditions as degree of vacuum, and per hour 0.4~0.6Nm ³ / 0.5~0Torr molten steel of the tapped molten steel in a vacuum degassing step and transferred to a vacuum degassing process, as described above with - under the conditions of Ar blown amount of 20-30 tons bun The denitrification process is performed to obtain a low-nitrogen-containing molten steel.

The denitrification process in the degassing vacuum process step is carried out through the following process.

One). The solute atoms move from the inside of the bath to the vicinity of the surface

2). Diffusion in the surface boundary layer

3). Creation of molecules at the surface and migration to the atmosphere

4). The diffusion of the surface boundary layer

The denitrification proceeds through the above process and the denitration reaction rate is represented by the following reaction formula (3).                     

{N ₂ } = [N]

Log K _N2 (Log a [N] / (P _N2 ) ^1/2 = -518 / T -1.063

As shown in FIG. 8, it can be seen that the higher the oxygen concentration in the molten steel, the faster the denitrification rate is, and the lower the oxygen concentration in the molten steel, the slower the denitrification rate is.

In the present invention, when the degree of vacuum during the denitrification process in the vacuum degassing process is too low, the molten steel can not be sufficiently refluxed in the vacuum degassing apparatus, so that sufficient denitrification can not be ensured and it is difficult to manufacture a low- The refluxing rate of the molten steel is too fast to sufficiently obtain the effect of the denitration reaction, so that the degree of vacuum during the denitration treatment is preferably limited to 0.5 to 0 Torr.

If the amount of the Ar gas introduced in the denitrification process in the vacuum degassing process is too small, the discharge amount of nitrogen to the outside of the molten steel due to the Ar gas is small and the denitrification efficiency is deteriorated. It is preferable to limit the blowing amount of the Ar gas to 0.4 to 0.6 Nm ³ / molten steel-ton per hour.

When the treatment time in the vacuum degassing treatment step is too short, sufficient denitrification effect can not be obtained. When the treatment time is too long, the denitrification effect can be sufficiently secured. However, Therefore, it is preferable to limit the denitration treatment time to 20 to 30 minutes.

On the other hand, when the nitrogen concentration before the vacuum treatment is high, the denitrification effect of about 25% can be obtained, and in the low concentration region where the nitrogen concentration is 40 PPM or less, it is difficult to expect the denitrification effect by the vacuum treatment.

Therefore, in the present invention, the content of nitrogen in the molten steel before denitrification in the vacuum degassing step is preferably applied to molten steel higher than the reference value of the nitrogen-regulated steel.

Hereinafter, the present invention will be described more specifically by way of examples.

(Example)

(Conventional example)

The refractory steel was charged into a converter according to the conventional method and converted into molten steel having the concentration of the end point [N] shown in the following Table 1, followed by degassing while deoxidizing in the furnace and then degassing the furnace, [N] concentration after degassing treatment was analyzed, and the results are shown in Table 1 below.

Example No. 2. End point [N] (PPM) After [N] (PPM) After degassing [N] (PPM) Conventional Example 1) 63 79 78 Conventional Example 2) 74 91 90 Conventional Example 3) 59 75 74 Conventional Example 4) 71 83 82

As shown in Table 1, the prior art (1-4), in which reflow steel was refined according to the conventional method,

The nitrogen content in the molten steel after degassing treatment is about 78 to 90 PPM, which means that the nitrogen content is not satisfied.

(Honorable Mention)

Conveying molten steel 270Ton and molten iron 25Ton were charged into the converter to perform the converter refining operation. Then, the transformed refined molten steel was finished in the molten state and then denitrified in the vacuum degassing step. Then, the nitrogen content in the molten steel was investigated , And the results are shown in Table 2 below.

The nitrogen content in the molten steel after completion of the refining of the converter and after completion of the excavation was examined, and the results are also shown in Table 2 below.

Example No. 2. Concentration [N] concentration (PPM) after refining Conditions for denitration treatment in vacuum degassing process [N] concentration after denitrification (PPM) Processing time (min) Vacuum degree (Torr) The amount of Ar injected per hour (Nm ³ / molten steel-tone) Inventory 1 63 21 0.4 0.4 43 Inventory 2 62 20 0.4 0.4 52 Inventory 3 72 25 0.4 0.4 59 Honorable 4 71 27 0.4 0.4 58 Inventory 5 69 25 0.4 0.4 49 Inventory 6 57 23 0.5 0.5 48 Honorable 7 81 22 0.5 0.5 56 Honors 8 74 29 0.5 0.5 43 Proposition 9 68 30 0.5 0.5 56 Inventory 10 63 22 0.5 0.5 53 Exhibit 11 82 25 0.5 0.5 58 Inventory 12 72 26 0 0.5 56 Inventory 13 76 24 0 0.6 57 Inventory 14 75 25 0 0.6 56 Honorable Mention 15 68 26 0.3 0.6 48 Inventory 16 67 27 0.3 0.6 46 Inventory 17 59 25 0.3 0.6 44 Inventory 18 73 22 0.2 0.6 52 Evidence 19 76 26 0.2 0.6 55 Inventory 20 72 25 0.1 0.6 56 Inventory 21 63 22 0.1 0.6 49 Inventory 22 66 23 0.1 0.6 53 Inventory 23 68 22 0 0.6 53 Honors 24 65 23 0 0.6 44 Honors 25 83 28 0 0.6 59 Evidence 26 74 29 0 0.6 58 Comparative Example 1 85 18 0.7 0.3 75 Comparative Example 2 73 17 0.7 0.3 63 Comparative Example 3 63 33 -1.0 0.8 44 Comparative Example 4 78 32 -1.0 0.7 58 Comparative Example 5 68 35 -1.0 0.8 49

As shown in Table 2, in the case of denitrification treatment of the mineral ladle steel under the denitration treatment conditions in the vacuum degassing process according to the present invention (Examples 1-26), low nitrogen feed steels having a nitrogen concentration of 60 PPM or less were produced It can be seen that

It can be seen that the molten steel having a nitrogen concentration of 60 PPM or more is produced when denitrification treatment of the molten steel is performed under the condition that the denitration treatment condition of the present invention is out of the range of the present invention (Comparative Example 1-2).

On the other hand, low denitrifying steels having a nitrogen concentration of 60 PPM or less could be produced in the case of denitrification under the conditions of the denitration treatment conditions of the present invention (Comparative Example 3-5). However, Burnout of the deposit tube was detected.

INDUSTRIAL APPLICABILITY As described above, the present invention can produce various kinds of steels by properly refining refractory steels generated in a steelmaking process to produce low nitrogen steels having nitrogen of 60 PPM or less, thereby improving productivity.

Claims (1)

Charging refractory steel and molten iron into a converter to refine the converter; Feeding the transformed refined molten steel into the molten state as described above; And Degreasing the molten steel introduced in the microlitic state as described above in a vacuum degassing process under the conditions of a vacuum degree of 0.5 to 0 Torr and an Ar blowing amount of 0.4 to 0.6 Nm ³ / molten steel-ton for 20 to 30 minutes Refining method of refractory steel constituted by

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