KR100922058B1 - Method for refining the ferrit stainless hot metal having high Cr - Google Patents

Abstract

The present invention relates to a method for refining molten steel of high chromium ferritic stainless steel, the method for refining molten steel of high chromium ferritic stainless steel of the present invention to inject oxygen and argon gas into the refinery to refine carbon and nitrogen in the molten steel. step; Gradually reducing the oxygen gas to stop the blowing of the oxygen gas blown into the refinery; Stirring the molten steel; And re-blowing oxygen gas into the refinery in which the argon gas is blown.

Denitrification, Deoxidation, Pulse Steps, High Chromium Ferritic Stainless Steels

Description

Method for refining the ferrit stainless hot metal having high Cr}

The present invention relates to a method for refining high chromium ferritic stainless steel molten steel, and more particularly, to a method for refining a high chromium ferritic stainless steel molten steel which can simplify the refining step by changing the method of refining stainless steel.

In general, the refining of the high chromium ferritic stainless steel is continuously cast through an electric furnace-refining furnace (AOD)-true process furnace (VOD) -rattle (LT). Argon Oxigen Decarburization (AOD) blows inert gases such as oxygen (0), argon (Ar) and nitrogen (N ₂ ) to decarburize, denitrify and reduce, desulfurize and deoxidize molten steel. VOD (Vaccum Oxigen Decarburization) blows oxygen and an inert gas into the vacuum refinery in a vacuum atmosphere, and decarburizes it, reducing, dehydrating and deoxidizing it. In addition, in the lattice (LT), inert gas is blown and molten steel is stirred to adjust the temperature of molten steel, uniformity of components, separation of inclusions, and component adjustment.

On the other hand, in ferritic stainless steel, carbon (C) and nitrogen (N) are important factors for determining properties such as corrosion resistance and workability. In order to improve the workability and corrosion resistance of ferritic stainless steel, the carbon and nitrogen in the ferritic stainless steel should be reduced to an extremely low state. However, as shown in FIG. 2, chromium (Cr) in the ferritic stainless steel has a strong affinity with carbon, so that the higher the content of chromium in the stainless steel, the more decarbonized it is. The steel disclosed in FIG. 2 is an STS439 steel containing 18% of chromium, and decarbonized carbon to an extremely low region using a vacuum refining furnace lowering Pco (CO partial pressure) to lower carbon and nitrogen to an extremely low region. Or by improving the stirring force by the inert gas to reduce the blowing ratio (O ₂ / Ar) of oxygen and low odor inert gas (Ar) to improve the efficiency of decarburization.

As described above, in order to deoxidize the carbon of the ferritic stainless steel, the carbon of the stainless steel is roughly decarburized to 0.2 to 0.3% in the refining furnace, and then decarburized to the target level using the vacuum refining furnace. Then, after adjusting the alloying components in the rattle process and finishes the continuous casting of molten steel.

In addition, the nitrogen of the ferritic stainless steel also becomes more difficult to refine as chromium increases. As shown in FIG. 3, nitrogen in molten steel is collected and refined by an inert gas such as carbon gas (CO) and argon (Ar) generated in the decarburization process. Therefore, the ferritic stainless steel is denitrified simultaneously with the decarburization process, and the denitrification process is affected by the stirring force by the amount of CO generated during the decarburization process and the inert gas (Ar).

As described above, the high chromium ferritic stainless steel is subjected to the decarburization and denitrification operations for lowering carbon and nitrogen concentrations below a certain level in the refining furnace, and finally decarburization and denitrification operations are performed in the vacuum refining furnace. do. This has been disclosed in Japanese Patent 2000-160229, 2000-160230 and 2001-049322.

As described above, in order to refine carbon and nitrogen of the high chromium ferritic stainless steel, deoxidation and denitrification are performed through a refining furnace and a vacuum refining furnace, thereby increasing an idle step and increasing process time.

Therefore, the present invention is an invention derived to solve the above-mentioned problems, the present invention is to form a concentration of carbon and nitrogen of the ferritic stainless steel aimed at the deoxidation and denitrification operation of the high chromium ferritic stainless steel through a refining furnace To provide a method for refining chromium ferritic stainless steel.

According to an aspect of the present invention for achieving the above object, the high chromium ferrite stainless steel molten steel refining method of the present invention comprises the steps of blowing oxygen and argon gas into the refinery to refine carbon and nitrogen in the molten steel ; Gradually reducing the oxygen gas to stop the blowing of the oxygen gas blown into the refinery; Stirring the molten steel; And re-blowing oxygen gas into the refinery in which the argon gas is blown.

In this case, the molten steel is accommodated in the refining furnace, and the upper surface of the refining furnace is provided with a top blowing for blowing gas into the surface of the molten steel, and the lower surface of the refining furnace for blowing gas into the molten steel. Low odor can be installed. In addition, the oxygen gas is blown into the refinery through the upper and lower odor, the ratio of the oxygen gas blown into the upper and lower odor may be 55:45. In addition, in the step of re-blowing the oxygen gas in the refinery in which the argon gas is blown, the flow rate of the argon gas may be at least 6 times or more than the flow rate of the oxygen gas.

The present invention can reduce the concentration of carbon and nitrogen of the target ferritic stainless steel through the refining furnace only through the deoxidation and denitrification operation of the high chromium ferritic stainless steel through only the refining furnace and the vacuum refining furnace. Accordingly, the refining process step can be simplified, and the refining time can be reduced.

In addition, as carbon and nitrogen of the ferritic stainless steel are lowered to an extremely low state, workability and corrosion resistance of the stainless steel may be improved.

Hereinafter, with reference to the drawings showing an embodiment of the present invention, the present invention will be described in more detail.

Figure 4 is a step diagram showing the manufacturing process of high chromium ferritic stainless steel according to the present invention.

Referring to FIG. 4, high chromium ferritic stainless steel is continuously cast through an electric furnace-refining furnace (AOD) -rattle (LT). That is, in the present invention, the deoxidation and denitrification of the high chromium ferritic stainless steel may be performed only in the smelting furnace without passing through the smelting furnace and the vacuum smelting furnace, thereby reducing process steps and processing time.

5 is a schematic cross-sectional view of a refining furnace according to the present invention.

Referring to FIG. 5, the molten steel 110 is accommodated in the refining furnace 100. A top lance 120 is installed on the upper surface of the refining furnace 100 to inject gas into the surface of the molten steel 110, and the gas is injected into the molten steel 110 on the lower surface of the refining furnace 100. Tuyere 130 is installed to make. In order to refine carbon and nitrogen in the molten steel 110, oxygen and argon gas are blown into the refining furnace 100. At this time, the oxygen gas is blown into the surface of the molten steel 110 and the inside of the molten steel 110 through the upper odor 120 and the lower odor 130, the argon gas is blown into the interior of the molten steel 110 through the low odor 130. do. In addition, the oxygen gas blown through the upper and lower odors 120 and 130 is injected at 70 and 60 at the lower odor 130. This is in comparison with the oxygen gas 100 blown in the upper uptake and the oxygen gas 30 blown in the low uptake, the oxygen gas blown up in the uptake is reduced and the oxygen gas blown up in the low uptake is increased by 30 or more.

That is, while the ratio of the oxygen gas blown into the conventional upper odor 120 and the lower odor 130 is 75:25 while the present invention is set to 55:45, by raising the ratio of the oxygen gas blown from the low odor 130 Enhance the ability to remove nitrogen by carbon gas in molten steel. As shown in FIG. 6, the nitrogen concentration of the conventional material is 73 ppm, and the ash of the present invention is 64 ppm, and the nitrogen concentration in the steel is significantly lowered as the oxygen gas ratio is changed from 75:25 to 55:45. It can be seen that.

In addition, Figure 7 is a graph showing that the carbon ratio of the X-axis is gradually lowered as the ratio of oxygen in the ratio of argon and oxygen is gradually lowered to improve the decarburization efficiency. For example, when carbon is 0.2 mass%, decarburization efficiency is most effective when the ratio of 0 ₂ : Ar is 1: 2.

That is, in the case of the vacuum refining furnace (VOD), the O ₂ : Ar ratio is generally small, which is advantageous for decarburization, and in the refining furnace, the ratio of O ₂ : Ar is generally high, which is disadvantageous for decarburization. Accordingly, in the present invention, a pulsing step having a small O ₂ : Ar ratio in the refinery is added to improve decarburization efficiency of the refinery.

Thereafter, the blowing of the oxygen gas is gradually reduced to stop the supply of the oxygen gas blown into the refining furnace 100. Accordingly, only argon gas is blown into the refining furnace 100. In addition, when only argon gas is blown into the refining furnace 100, the molten steel 110 is stirred.

As such, the step of injecting oxygen and argon gas into the refining furnace 100, gradually reducing the amount of oxygen gas blown and blowing only the argon gas into the refining furnace 100, followed by a rinsing step. It is called.

In addition, in order to lower the concentration of carbon and nitrogen in the molten steel 110 which has undergone the rinsing step to an extremely low state, oxygen gas is reinjected into the refining furnace 100 into which argon gas is blown. That is, in the present invention, in order to lower the carbon and nitrogen of the molten steel 110 subjected to the rinsing step to an extremely low state, a pulsing step of re-injecting oxygen gas into the refining furnace 100 is further added. At this time, the flow rate of argon gas is set at least 6 times higher than oxygen gas.

As such, the present invention may add a pulsing step of re-injecting oxygen gas into the refining furnace 100 to lower carbon and nitrogen in the molten steel to an extremely low state without using a vacuum refining furnace. In addition, the stainless steel derived by the above-described method, based on the weight of 100%, contains 17 to 19% chromium, 0.015% or less carbon, 0.015% or less nitrogen.

EXAMPLE

Example was selected STS439 steel, the composition of the steel is shown in Table 1.

C Si Cr Ti N ingredient ≤0.030 ≤1.00 17.00-19.00 0.20 + 4X (C + N) ~ 1.10 0.030≤

Hereinafter, the molten steel having a composition as shown in Table 1 will be compared with the carbon / nitrogen concentrations of the conventional material and the present invention which have been subjected only to a refinery furnace, a vacuum refinery furnace, and a refinery furnace.

First, the STS439 steel, which is roughly refined with a refining furnace, sets the amount of oxygen in the upper and lower odors to 70:60, blows into the refining furnace, injects argon gas from the low odor after stirring the oxygen, and stirs the steel, Oxygen gas is blown into the refining furnace with a high flow rate of argon gas through a low odor. After that, the carbon and nitrogen components before the tapping of the refining furnace through the final reduction and degassing process were measured and compared with the concentrations of carbon and nitrogen in the molten steel which passed through the conventional refining and vacuum refining furnaces.

8 is a graph showing the concentrations of carbon and nitrogen in the ash (stainless steel) of the prior art and the present invention. The nitrogen concentration of the conventional material is 82 ppm and the nitrogen concentration of the present invention is 59 ppm. In addition, the carbon concentration of the conventional material is 76 ppm and the carbon concentration of the present invention is 69 ppm.

That is, the ash of the present invention can be seen that the concentration of nitrogen and carbon is significantly lower than the conventional material. In addition, in the case of refining carbon and nitrogen of stainless steel according to the above-described method, stainless steel skips the vacuum refining (VOD) process to prevent melting of the ladle refractory material by operation and argon agitation under high temperature in the vacuum refining furnace. have. Accordingly, the life of the ladle can be improved. That is, in the case of a vacuum refining furnace, the work is performed in the ladle, and the ladle refractory is damaged by the strong stirring force, which shortens the life of the ladle refractory. However, the present invention can improve the life of the ladle refractory by omitting the vacuum refining process.

As described above, the preferred embodiment of the present invention has been disclosed through the detailed description and the drawings. The terms are used only for the purpose of describing the present invention and are not used to limit the scope of the present invention as defined in the meaning or claims. Therefore, those skilled in the art will understand that various modifications and equivalent other embodiments are possible from this. Therefore, the true technical protection scope of the present invention will be defined by the technical spirit of the appended claims.

1 is a step flowchart illustrating a manufacturing process of high chromium ferritic stainless steel.

2 is a graph comparing the concentration of carbon in equilibrium according to carbon monoxide partial pressure (Pco) according to chromium content.

3 is a flow chart of a mechanism for denitrification in molten steel.

4 is a flowchart illustrating a manufacturing process of a high chromium ferritic stainless steel according to the present invention.

5 is a schematic cross-sectional view of a refining furnace according to the present invention.

6 is a graph showing the nitrogen concentration at the top of the refinery furnace according to the amount of oxygen in the upper and lower odors.

Figure 7 is a graph showing the efficiency of the stripping according to the oxygen and argon blowing ratio.

8 is a graph showing the concentrations of carbon and nitrogen after refining the existing material and the present invention.

 ♣ Explanation of symbols for the main parts of the drawing ♣

  100: refinery 110: molten steel

  120: odor 130: odor

Claims (4)

In the refining method of high chrome ferritic stainless steel molten steel continuously cast through an electric furnace-refining furnace (AOD) -rattle (LT), Blowing oxygen and argon gas into the refinery to refine carbon and nitrogen in the molten steel; Gradually reducing the oxygen gas to stop the blowing of the oxygen gas blown into the refinery; Stirring the molten steel; And Re-injecting oxygen gas into the refinery in which the argon gas is blown; The molten steel is accommodated in the refining furnace, and the upper surface of the refining furnace is provided with a top blowing for blowing gas into the surface of the molten steel, and a low odor for blowing gas into the molten steel in the lower surface of the refining furnace. Installed, The oxygen gas is blown into the refining furnace through the upper and lower odor, the ratio of the oxygen gas blown into the upper and lower odor is a 55:45 refining method of the high chromium ferritic stainless steel molten steel. delete delete According to claim 1, In the step of re-blowing oxygen gas in the refinery in which the argon gas is blown, The flow rate of the argon gas is at least six times or more than the flow rate of the oxygen gas refining method of high chrome ferritic stainless molten steel.

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