KR101431026B1 - Vacuum oxygen decarbrization method for ferritic stainless steel - Google Patents

Abstract

A method for vacuum degassing a molten steel of stainless steel, comprising the steps of: adjusting the carbon concentration of the molten steel to 0.15 to 0.25 [wt%];
A decarburization step of reducing argon gas in the molten steel to maintain a degree of vacuum of 10 [mbar] or less while removing oxygen to make the carbon concentration of the molten steel 0.015 [wt]% or less;
A micro-decarburization step of reducing argon gas in the molten steel while maintaining a vacuum of 250 to 350 [mbar];
And a deoxidizing step of adding a deoxidizing agent to the molten steel while maintaining the vacuum degree at 250 to 350 [mbar].

Description

[0001] The present invention relates to a vacuum decarburization method for ferritic stainless steel,

More particularly, the present invention relates to a method of vacuum decarburization of a ferritic stainless steel so as to have a carbon concentration of 0.015 [wt]% or less and a nitrogen concentration of 0.015 to 0.030 [wt]% .

In order to produce stainless steel, chrome alloy iron, nickel alloy iron and scrap are charged into an electric furnace and dissolved in an arc and a burner. At this time, the molten steel which has been subjected to the electric furnace process has a high carbon content and a considerable amount of impurities such as silicon and sulfur, which is high in hardness and weak in properties. In order to make such molten steel as well as strong steel, it is necessary to reduce carbon amount and remove impurities through refining process. This process is called steelmaking.

The steelmaking process consists of AOD, Argon Oxygen Decarburization (VOD), Vaccum Oxygen Decarburization (VOD) and Ladle Treatment (LT). At this time, the vacuum decarburization process is a process for lowering the carbon concentration and nitrogen concentration to 0.010 [wt]% or less, and a ferritic stainless steel is used so as to have a carbon concentration of 0.015 [wt]% or less and a nitrogen concentration of 0.015 to 0.030 [ There is a problem that it is difficult to perform vacuum decarburization.

Korean Patent No. 10-0922060 (October 16, 2009)

A problem to be solved by the present invention is to provide a vacuum decarburization method of a waste light stainless steel in which a ferritic stainless steel is vacuum decarburized so as to have a carbon concentration of 0.015 [wt]% or less and a nitrogen concentration of 0.015 to 0.030 [wt] .

According to an aspect of the present invention, there is provided a method of vacuum degassing a molten steel of stainless steel, comprising the steps of: adjusting carbon concentration of molten steel to 0.15 to 0.25 wt%;

A decarburization step of reducing argon gas in the molten steel to maintain a degree of vacuum of 10 [mbar] or less while removing oxygen to make the carbon concentration of the molten steel 0.015 [wt]% or less;

A micro-decarburization step of reducing argon gas in the molten steel while maintaining a vacuum of 250 to 350 [mbar];

And a reduction degassing step of adding a deoxidizing agent to the molten steel while maintaining the vacuum degree at 250 to 350 [mbar]. The present invention also provides a vacuum decarburization method for a waste light system stainless steel.

Here, in the decarburization step, the argon gas may be reduced to 300 to 400 [l / min].

In the micro-decarburization step, the argon gas can be reduced to 400 to 600 [m / l].

When the nitrogen concentration of the sample is in the range of 0.010 to 0.015 [wt%], the nitrogen gas may be supplied at a rate of 400 to 600 [l / min] in the reduction desulfurization step, min, the molten steel is stirred for 15 minutes, and when the nitrogen concentration of the sample exceeds 0.015 [wt]%, the molten steel is refluxed at 400 to 600 [l / min] Lt; / RTI >

The ferritic stainless steel refining method according to the present invention has the effect of producing a ferritic stainless steel having a carbon concentration of 0.015 [wt%] or less and a nitrogen concentration of 0.015 to 0.030 [wt%].

1 is a block diagram of a vacuum degassing apparatus.
2 is a flowchart of a vacuum decarburization method of a ferritic stainless steel according to an embodiment of the present invention.

1 is a configuration diagram of a vacuum decarburization facility. 1, the vacuum decarburization facility includes a ladle 20 having a porous plug 40 for receiving molten steel and blowing an inert gas to the lower end thereof, a vacuum cover 12 for enclosing and sealing the ladle 20, A tank 10, and a top lance 30 for blowing oxygen into the vacuum tank 10.

In the vacuum decarburization process (VOD), 500 to 900 [Nm³] of oxygen and 25 to 50 [Nm³] of argon were blown into the molten steel at a degree of vacuum of 10 mbar to produce 0.015 [wt] ]% Or less of nitrogen. In this case, after decarburization, deoxidation is performed with aluminum (Al) or silicon (Si) to prevent clogging of the performance nozzle, and ferritic stainless steel is produced by adding additional raw materials as necessary.

However, in order to produce molten steel having 0.015 wt% or less of carbon and 0.015 to 0.030 wt% of nitrogen, the degree of vacuum must be controlled. If the degree of vacuum is maintained at 10 mbar or more, Is 10 [mbar] or less, the nitrogen concentration becomes 0.010 [wt%] or less, and additional holding time is required. In the vacuum decarburization process (VOD) and the component adjustment process (LT), the production time is excessively long, and the production of molten steel having 0.015 wt% or less of carbon and 0.015 to 0.030 wt% impossible.

On the other hand, when the carbon concentration is lowered to 0.015 [wt%] or less in the refining process and then the vacuum degree is higher than 100 [mbar] in the vacuum decarburization process (VOD), denitrification does not occur and production becomes possible. However, in this case, decarburization of 0.010 [wt%] or less in the refining process (AOD) causes excessive oxygen in the molten steel and affects the lifetime of the AOD furnace body. Also, when the vacuum degree is 100 [mbar] or more in VOD, the agitation force is weaker than 10 [mbar], so that the molten steel is produced for the heat of cleanliness.

In order to solve the above-mentioned problems, an embodiment of a vacuum degassing method of a ferritic stainless steel according to the present invention will be described with reference to the accompanying drawings. 1 and 2, a method of vacuum decarburization of a ferritic stainless steel according to an embodiment of the present invention will be described.

Generally, stainless steel refining process consists of AOD (Argon Oxygen Decarburization) - VOC, Vaccum Oxygen Decarburizatin - LT (Ladle Treatment) - Continuous Casting process (C / C, Continuous Casting) Lt; / RTI > In the refining process (AOD), desulfurization and deoxidation are performed through decarburization and slag production. That is, in the refining process (AOD), a mixed gas of argon (Ar) and oxygen (O 2) or a mixed gas of nitrogen (N 2) and oxygen (O 2) is blown into molten steel. At this time, oxygen (O 2) is supplied to the molten steel, and the chromium (Cr) is oxidized first, and the decarburization reaction proceeds.

In this refining process (AOD), the steel produces 0.15 to 0.25 wt% of carbon, 0.035 to 0.45 wt% of nitrogen, and 0.010 wt% or less of sulfur through decarburization, denitrification and desulfurization. Specifically, in the refining process (AOD), 75 to 85 [ton] of molten steel is charged into a refining furnace and 1000 to 1500 [Nm³] of oxygen is introduced through a top lance, and 1000 ~ 1500 [Nm³] of oxygen and 1000 ~ 2000 [Nm³] of argon are blown to produce the regulated steel.

Vacuum decarburization process (VOD) is a vacuum decarburization method for molten steel of ferritic stainless steel, and molten steel subjected to preliminary decarburization treatment in the refining process (AOD) is used. 1, a ladle 20 is placed in a vacuum tank 10 and an argon (Ar) gas is supplied through a porous plug 40 provided on the floor of the ladle 20. In the vacuum decarburization process (VOD) And oxygen (O2) is blown from the top lance 30 installed in the upper part while molten steel is stirred to perform decarburization treatment.

A vacuum decarburization method of a waste light system stainless steel according to an embodiment of the present invention includes a preparation step, a decarburization step, a micro decarburization step and a reduction desulfurization step.

In the preparation step, the slag of the molten steel produced in the refining process (AOD) is removed, and if necessary, the raw material containing carbon is introduced to make the carbon concentration of the molten steel to 0.15 to 0.25 [wt%] (S10) . The reason for making the carbon concentration of the molten steel at 0.15 to 0.25 [wt%] at this time is that when the carbon content exceeds 0.25 wt%, the working time becomes unnecessarily long. When the carbon content is less than 0.15 wt% This is because the work time becomes unnecessarily long due to the degradation of performance.

In this preparation step, the nitrogen concentration is controlled so that denitrification of 0.010 [wt%] or more occurs even if excessive denitrification occurs by lecturing at a concentration of 0.035 to 0.045 [wt%] in the AOD process for nitrogen. If denitrification is performed at 0.035 [wt]% or less, it takes a long time for molten steel having 0.01 [wt%] or less of nitrogen to be produced, and production becomes impossible due to a decrease in molten steel temperature. Also, in case of molten steel of 0.045 [wt]% or more of nitrogen, the target component, 0.03 [wt]% or less, will not be satisfied if denitrification is not possible.

In the decarburization step, argon (Ar) gas is blown at 300-400 [l / min] from the plug 40 installed at the bottom of the ladle, and the degree of vacuum of 300 [mbar] is reduced to a degree of vacuum of 10 [mbar] This is maintained, oxygen is blown from the top lance, and decarburization and denitrification are performed (S20). At this time, it is preferable that the top lance is installed at a distance of 1200 to 1500 [mm] from the molten steel surface, and the decarburization step is performed until the carbon concentration of the molten steel of the stainless steel becomes 0.015 [wt]% or less.

In the micro decarburization step, the oxygen blowing is stopped and the degree of vacuum is increased to 200 to 350 [mbar] and argon (Ar) gas is blown from the plug at the bottom of the ladle into 400 to 600 [m / Thereby promoting the micro-decarbonization reaction according to the reaction of carbon (S30). At this time, in the micro-decarburization step, component analysis through sampling of molten steel can be performed. In addition, inclusion of an additive in the micro-decarburization step may cause inclusion of inclusions due to slag.

In the reduction desulfurization step, a deoxidizing agent and a subsidiary raw material are introduced to allow desulfurization and deoxidization to occur (S40). In this case, when the concentration of nitrogen measured in the micro-decarburization step is 0.010 to 0.015 [wt]%, when the concentration of nitrogen measured in the micro-decarburization step exceeds 0.015 [wt]%, The molten steel is stirred at 400 to 600 [l / min] for 15 minutes.

By doing so, it becomes possible to perform vacuum decarburization so that the ferritic stainless steel contains 0.015 [wt]% or less of carbon and 0.015 to 0.030 [wt%] of nitrogen.

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

(Example)

In the present embodiment, the nitrogen concentration and the carbon concentration contained in the waste light stainless steel were measured when the ferritic stainless steel was vacuum decarburized while changing the nitrogen concentration, the carbon concentration and the degree of vacuum in the decarburization step, The results are shown in Table 1 below.

division step Start [C]
[wt]% Exit [C]
[wt]% Start [N]
[wt]% End [N]
[wt]% Vacuum degree
[mbar] Nitrogen 0.015 to 0.030 [wt]%
Whether Carbon 0.015 [wt]%
Below Honor Decarburization step 0.164 0.0042 0.0385 0.0158 6 O O Micro-decarburization + Reduction degreasing 0.0042 0.006 0.0158 0.0182 207 O O Comparative Example 1 Decarburization step 0.21 0.0067 0.0395 0.0092 One X O Micro-decarburization + Reduction degreasing 0.0067 0.0078 0.0092 0.0129 0 X O Comparative Example 2 Decarburization step 0.0497 0.0473 0.0217 0.0201 122 O X (no decarburization) Micro-decarburization + Reduction degreasing 0.0473 0.0442 0.0201 0.0195 333 O X

C] is 0.015 [wt]% or less in the state where the beginning [C] of the decarburization step is 0.15 to 0.25 [wt%] and the degree of vacuum is not more than 10 [mbar] By weight of carbon and 0.015 to 0.030% by weight of nitrogen by maintaining the degree of vacuum at 200 to 350 [mbar] in the micro-decarburization + It can be seen that the ferritic stainless steel is refined.

On the contrary, in the comparative example (1-2) which does not satisfy the vacuum decarburization condition of the present invention, the ferrite stainless steel containing 0.015 [wt%] or less of carbon and 0.015 to 0.030 [wt% Able to know.

LT (Ladle Treatment) is a process in which coolant is injected so that the temperature becomes suitable for casting after releasing vacuum, and ferroalloy is injected so that it becomes a suitable component for casting.

The continuous casting process (C / C, Continuous Casting) is a process of solidifying molten steel. It injects molten steel into a continuous casting mold and continuously strips the semi-solidified pieces from the bottom of the mold to produce products such as billets and slabs to be.

It will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims and their equivalents. Of course, such modifications are within the scope of the claims.

10: Vacuum tank 12: Vacuum cover
20: Ladle 30: Top lance
40: Plug

Claims (4)

A method of vacuum decarburizing molten steel of stainless steel,
A preparation step of adjusting the carbon concentration of the molten steel to 0.15 to 0.25 [wt%];
A decarburization step of reducing argon gas in the molten steel to maintain the degree of vacuum at 10 mbar or less and oxygen concentration to 0.015 wt% or less;
A micro-decarburization step of reducing argon gas in the molten steel while maintaining the degree of vacuum at 250 to 350 [mbar]; and
And a reduction desulfurization step of adding a deoxidizing agent to the molten steel while maintaining the vacuum degree at 250 to 350 [mbar]
In the micro-decarburization step, the component analysis is performed through the sampling of the molten steel,
The reduction desulfurization step
Nitrogen gas is supplied at a rate of 400 to 600 l / min when the nitrogen concentration of the sample is 0.010 to 0.015 wt%, and argon gas is supplied at a rate of 400 to 600 l / min when the nitrogen concentration of the sample exceeds 0.015 wt% wherein the molten steel is agitated for a predetermined period of time. The method according to claim 1,
Wherein the argon gas is reduced to 300 to 400 l / min in the decarburization step. The method according to claim 1,
Wherein the argon gas is reduced to 400 to 600 [m / l] in the micro-decarburization step. The method according to claim 1,
Wherein the preset time is 15 minutes. ≪ RTI ID = 0.0 > 18. < / RTI >

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