KR101365525B1 - Two-phase stanless steel and argon oxygen decarburization refining method of the two-phase stainless steel - Google Patents

Abstract

An aspect of the present invention is to provide a method for refining AOD of two-phase stainless steel in which the composition and temperature are adjusted to enable strip casting of two-phase stainless steel having a mixed structure of austenite and ferrite during solidification.
The AOD refining method of the two-phase stainless steel according to the embodiment of the present invention, in the AOD refining method of the two-phase stainless steel having a mixed structure of austenite and ferrite, blowing agent and decarburizing oxygen (O2) and argon (Ar) Step 1, a second step of introducing ferro alloy containing manganese (Mn), a third step of deoxidation by adding a deoxidizer, a fourth step of injecting nitrogen (N2) and tapping Including the fifth step, the two-phase stainless steel is carbon (C): 0.060 ~ 0.080wt%, silicon (Si): 0.10 ~ 0.25wt%, manganese (Mn): 7.8 ~ 8.0wt%, phosphorus (P ): 0.035 wt% or less, sulfur (S): 0.0050 wt%, chromium (Cr): 18.0-18.2 wt%, nickel (Ni): 1.85-2.10 wt%, molybdenum (Mo): 0.3 wt% or less, copper ( Cu): 2.3-2.5 wt%, balance iron (Fe) and other unavoidable impurities, nitrogen (N): 900-1100ppm.

Description

TOD O-PHASE STANLESS STEEL AND ARGON OXYGEN DECARBURIZATION REFINING METHOD OF THE TWO-PHASE STAINLESS STEEL}

The present invention relates to AOD refining method of two-phase stainless steel and two-phase stainless steel, and more particularly, to adjust the composition and temperature of the two-phase stainless steel having a mixed structure of austenite and ferrite during stripping. The present invention provides a method for refining AOD of two-phase stainless steel and two-phase stainless steel.

In general, the strip casting apparatus is a facility for supplying molten steel between a pair of rotating casting rolls to continuously manufacture sheet products having a thickness of several mm directly from the molten steel.

The thin product through the strip casting device is thin solidified as the molten steel is fed into a molten steel pool formed by a pair of casting rolls rotating while being cooled by cooling water and an edge dam sealing their sides. Cells are formed, and these coagulation cells are coalesced at the closest point to produce a continuous casting of a certain thickness.

Austenitic stainless steel produced by such a strip casting device is very important surface quality, the composition and number of high-melting point non-metallic inclusions among the factors affecting the surface defects are a big problem. That is, if inclusions remain on the surface of the product, it may damage the surface or cause cracks. However, since non-metallic inclusions inevitably occur through processes such as deoxidation of molten steel and input of ferroalloy for temperature control, the occurrence of inclusions should not be prevented, so the occurrence of inclusions should be minimized.

In general, the molten metal obtained through the electric furnace process has a high carbon content and contains a considerable amount of impurities such as silicon and sulfur, and thus has high hardness and brittleness. In order to make these molten metals stretch well and make a strong steel, it is necessary to reduce the amount of carbon and remove impurities through the refining process.

The steelmaking process is carried out through the refining process (AOD, Argon Oxygen Decarburization), the ingredient adjustment process (LT, Ladle Treatment), and the continuous casting process (C / C).

The conventional AOD refining process of stainless steel is disclosed in Korean Patent No. 10-0947434.

On the other hand, conventional austenitic stainless steels have a low strength and have a low corrosion resistance against local corrosion, and ferritic stainless steels have a low toughness defect, and as a countermeasure therefor, the austenitic stainless steel has an austenite and ferrite in an annealing state. Attention is drawn to two-phase stainless steels having a mixed structure. Therefore, there is a need for an AOD refining method for adjusting the composition and temperature to enable strip casting of two-phase stainless steel having a mixed structure of austenite and ferrite.

Patent Document 1: Republic of Korea Patent No. 10-0947434

One aspect of the present invention is to provide a method for refining AOD of two-phase stainless steel and two-phase stainless steel that adjusts the composition and temperature to enable strip casting of two-phase stainless steel having a mixed structure of austenite and ferrite during solidification. .

AOD refining method of the two-phase stainless steel according to an embodiment of the present invention, in the AOD refining method of two-phase stainless steel having a mixed structure of austenite and ferrite, the first blowing blowing and decarburization of oxygen (O2) and argon (Ar) A step, a second step of introducing ferro alloy containing manganese (Mn), a third step of deoxidizing by adding a deoxidizer, a fourth step of injecting nitrogen (N2), and a tapping step Including the fifth step, the two-phase stainless steel is carbon (C): 0.060 ~ 0.080wt%, silicon (Si): 0.10 ~ 0.25wt%, manganese (Mn): 7.8 ~ 8.0wt%, phosphorus (P) : 0.035wt% or less, sulfur (S): 0.0050wt%, chromium (Cr): 18.0 ~ 18.2wt%, nickel (Ni): 1.85 ~ 2.10wt%, molybdenum (Mo): 0.3wt% or less, copper (Cu ): 2.3-2.5wt%, balance iron (Fe) and other unavoidable impurities, nitrogen (N): 900 ~ 1100ppm.

In addition, the step of decarburizing by injecting oxygen (O2) and argon (Ar) in the first step, characterized in that the weight of carbon (C) is decarburized to 0.070wt%.

In addition, the step of decarburizing by injecting oxygen (O2) and argon (Ar) in the first step is characterized in that the decarburization is performed without inputting a raw material containing manganese (Mn).

In the third step, the deoxidation by adding the deoxidizer may include controlling silicon (Si) to 0.13 to 0.17 wt%, and adding CaO / SiO 2 to 1.8 ~ in the composition of the refinery slag by adding quicklime. The step of controlling to 2.2, characterized in that it comprises the step of adding 20 to 30% by weight of the fluorspar of the quicklime added amount.

In the two-phase stainless steel according to the embodiment of the present invention, carbon (C): 0.060 to 0.080 wt%, silicon (Si): 0.10 to 0.25 wt%, manganese (Mn): 7.8 to 8.0 wt%, phosphorus (P) : 0.035wt% or less, sulfur (S): 0.0050wt%, chromium (Cr): 18.0 ~ 18.2wt%, nickel (Ni): 1.85 ~ 2.10wt%, molybdenum (Mo): 0.3wt% or less, copper (Cu ): 2.3 ~ 2.5wt%, balance iron (Fe) and other unavoidable impurities, nitrogen (N): characterized in that it contains 900 ~ 1100ppm.

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Therefore, in the AOD refining method of two-phase stainless steel and two-phase stainless steel according to an embodiment of the present invention, the two-phase stainless steel having a mixed structure of austenite and ferrite during solidification has a very good surface quality and is subsequently cast by strip casting. There is an effect that becomes possible.

1 is a schematic cross-sectional view of an AOD refining furnace according to an embodiment of the present invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Steelmaking process according to an embodiment of the present invention is made through a refining process (AOD, Argon Oxygen Decarburization)-> ingredient adjustment process (LT, Ladle Treatment)-> continuous casting process (C / C, Continuous Casting), After (AOD) it may further comprise a vacuum decarburization (VOD) Vaccum Oxygen Decarburizatin (VOD) process.

In the refining process (AOD), desulfurization and deoxidation are performed through decarburization and slag production. That is, in the refining process AOD, argon (Ar) and oxygen (O 2) mixed gas or nitrogen (N 2) and oxygen (O 2) mixed gas are blown into the molten metal. When oxygen (O2) is supplied to the molten steel, decarburization proceeds as chromium (Cr) is oxidized first.

The vacuum decarburization process (VOD) is a vacuum decarburization method of high chromium molten steel, and the vacuum decarburization in the vacuum decarburization method generally uses molten steel preliminarily decarburized in the previous process. In the vacuum decarburization process, argon is injected into the vacuum container by argon (Ar) gas through a porous plug installed at the bottom of the ladle, and oxygen is blown from the lance installed at the top while stirring molten steel. The productivity is lower than that of the refining process (AOD), but is suitable for the production of very low carbon (C) and nitrogen (N) steels of high chromium ferrite type.

After the ingredient adjustment process (LT, Ladle Treatment) is adjusted by stirring after deoxidation.

The component adjustment process is the final process for hitting components and temperatures in molten steel. That is, when argon (Ar) and / or nitrogen (N2) is blown up in the immersion pipe in the component adjustment process, bubbles are formed in the rise pipe and rise up, and the molten steel is moved toward the down pipe due to the difference in potential energy. It comes down and circulates. As the molten steel circulates, degassing is carried out to the scattering and foam layers with the bursting of argon (Ar) and nitrogen (N2) bubbles in the ladle.

In the continuous casting process, molten steel tapped to a specific temperature is transferred to a caster column through a ladle turret and then injected into a tundish, an intermediate container. In tundish, molten steel is injected into the mold while floating the separation of molten steel.

With reference to Figure 1 looks at with respect to the refining process (AOD) of stainless steel according to an embodiment of the present invention. 1 is a schematic cross-sectional view of an AOD refining furnace according to an embodiment of the present invention.

As shown in FIG. 1, the AOD refining furnace 10 according to an embodiment of the present invention includes a furnace body 100 that receives molten steel 20 accommodated therein, a gas blown for decarburization and agitation, and an input raw material. A dust collecting hood 200 for collecting dust generated, a top lance 300 for blowing gas into the surface of molten steel from the upper surface of the furnace body 100, and a sub lance for taking a sample of molten steel and measuring temperature. 400, a raw material inlet 500 for inputting a raw material for hitting a target component, and a tuyer 600 for blowing gas into the molten steel 20 from the lower surface of the furnace 100. Can be.

After injecting the molten steel 20 into the furnace body 100 accommodating the molten steel 20, the molten steel 20 is injected by blowing oxygen (O 2) and argon (Ar) gas through the top lance 300 and the tire 600. Carbon (C) in the oxide is oxidized and decarburized, and the molten steel 20 is stirred with oxygen (O 2) and argon (Ar) gas that are stolen from the tire 600. Raw materials required for the composition adjustment are introduced through the raw material inlet 500 installed in the upper part of the furnace 100, and the dust generated at this time, the gas introduced by the top lance 300 and the tire 600, and carbon monoxide generated by decarburization. Is collected by the dust collection hood 200 is removed.

Accordingly, carbon (C) in the molten steel is removed by oxygen (O 2) and argon (Ar) gas blown from the top lance 300 and the tire 600, and the metal oxide generated in this process is a raw material inlet 500. Deoxidant such as silicon (Si) and aluminum introduced through the agonist is stirred by argon (Ar) gas that is stolen from the tire 600 and deoxidation is performed.

In the AOD refining method of two-phase stainless steel according to an embodiment of the present invention, a first step of decarburizing by injecting oxygen (O 2) and argon (Ar) gas, and adding ferro alloy to hit a target component And a second step, a third step of deoxidizing by adding a deoxidizer, a fourth step of injecting nitrogen (N2) to hit a target component, and a fifth step of tapping.

Two-phase stainless steel according to an embodiment of the present invention is carbon (C): 0.060 ~ 0.080wt% or less, silicon (Si): 0.10 ~ 0.25wt%, manganese (Mn): 7.8 ~ 8.0wt%, phosphorus (P) : 0.035wt% or less, sulfur (S): 0.0050wt% or less, chromium (Cr): 18.0-18.2wt%, nickel (Ni): 1.85-2.10wt%, molybdenum (Mo): 0.3wt% or less, copper ( Cu): 2.3 to 2.5wt%, iron (Fe), and other unavoidable impurities, and nitrogen (N): 900 to 1100ppm may be included.

Carbon (C): 0.060 ~ 0.080wt%

If the carbon (C) is lower than 0.060wt%, the strength of the two-phase stainless steel is lowered. If the carbon (C) is higher than 0.080wt%, chromium carbide precipitates and causes grain boundary corrosion.

Silicon (Si): 0.10 ~ 0.25wt%

If the silicon (Si) is lower than 0.10wt%, deoxidation may not be performed properly, and defects such as inclusions may occur. If the silicon (Si) is higher than 0.25wt%, the toughness of the two-phase stainless steel is reduced.

Manganese (Mn): 7.8-8.0 wt%, Chromium (Cr): 18.0-18.2 wt%, Nickel (Ni): 1.85-2.10 wt%,

Manganese (Mn), chromium (Cr) and nickel (Ni) are in the range of 7.8 to 8.0 wt% of manganese (Mn), 18.0 to 18.2 wt% of chromium (Cr), and 1.85 to 2.10 wt% of nickel (Ni). Must be in Manganese (Mn), chromium (Cr), and nickel (Ni) must be within the above ranges to obtain a two-phase stainless steel having a desired austenitic and ferrite mixed structure.

Phosphorus (P): 0.035 wt% or less, Sulfur (S): 0.0050 wt% or less

Phosphorus (P) and sulfur (S) act as impurities and may cause cracks when processed into products, so they should be lower than 0.035wt% and 0.0050wt%, respectively.

Molybdenum (Mo): 0.3wt% or less

Molybdenum (Mo) is added to increase the corrosion resistance, but may not be added because it is an expensive raw material.

Copper (Cu): 2.3 ~ 2.5wt%

If Cu (Cu) is lower than 2.3wt%, the effect of improving workability is low, and if it is higher than 2.5wt%, copper may cause defects due to precipitation of Cu.

Nitrogen (N): 900 ~ 1100ppm

When the nitrogen (N) is lower than 900ppm, the grain refinement is insufficient, and when higher than 1100ppm, the elongation is lowered to inhibit workability.

Hereinafter, the AOD refining method of the two-phase stainless steel according to the embodiment of the present invention will be described in detail.

(First step)

In the first step, oxygen and argon are blown to decarburize.

In the first step, decarburization is carried out only to the target carbon: 0.070wt%, and decarburization is carried out so as not to carry out a separate gasification in the subsequent process.

If carbon is decarburized at more than 0.070wt%, further decarburization is required. If carbon is decarburized at less than 0.070wt%, the temperature of molten steel is excessively increased, and a coolant for lowering the temperature in a later process is Decarburization is controlled based on carbon: 0.070wt% since additionally added and additional charcoal is required. At this time, in order to increase the efficiency of decarburization, raw materials containing manganese (Mn) are not added.

(Second step)

In the second step, ferro alloy is added to hit the target component.

Ferro Alloy including manganese (Mn) is added to hit the target component. At this time, the raw material is input after the decarburization is completed, so no further decarburization process is performed in the future.

(Third step)

In the third step, deoxidation is performed by adding a deoxidizer.

Deoxidation is performed by adding silicon (Si). At this time, the component range of silicon (Si) is 0.10 to 0.25 wt%, and preferably the component range of silicon (Si) is 0.13 to 0.17 wt%.

Refining furnace slag CaO / SiO2 (basic degree) is adjusted to 1.8 ~ 2.2 by adding quicklime, and fluorite is added at 20 ~ 30wt% of the added amount of quicklime. The reason why the refining slag CaO / SiO2 (base) is 1.8 ~ 2.2 is lower when the refining slag CaO / SiO2 (base) is lower than 1.8, and the slag CaO / SiO2 (base) is higher than 2.2 This is because the collection capacity of the deoxidation products (inclusions) generated during reduction and dehydration may be reduced.

In addition, when the fluorspar is lower than 20 wt% of the amount of quicklime added, the flowability of slag is lowered, and the trapping ability of degassing and deoxidation products (inclusions) is lowered. When the fluorspar ratio is higher than 30 wt% of the amount of quicklime added, the flowability of slag is excessively increased to refine. It is preferable to limit the amount of fluorspar added to 20 to 30% by weight of the amount of quicklime added because it accelerates refractory erosion of the furnace.

At this time, the time for stirring the molten steel is limited to 10 minutes to 15 minutes. If the stirring time is less than 10 minutes, sufficient stirring is not made and if the stirring time is 15 minutes or more, since the stirring effect is not increased compared to the secured time, the molten steel stirring time is preferably limited to 10 minutes to 15 minutes.

(Step 4)

In the fourth step, nitrogen is injected to hit the target component.

Nitrogen in molten steel is removed during oxygen and argon blowing after decarburization and ferro alloy injection, and nitrogen is injected to hit the target. At this time, since denitrification may occur in the tapping and LT process, 50 ppm higher than the target 1000 ppm is injected. The 80% real rate applies to nitrogen injection.

(Step 5)

In the fifth stage, students leave.

Although the preferred embodiment of the present invention has been described above, the technical idea of the present invention is not limited to the above-described preferred embodiment, and various strip casting 2 in the range without departing from the technical idea of the present invention specified in the claims. It can be implemented by the refining method of the upper stainless steel.

10 ... AOD refining furnace 20 ... Molten steel
100 ... body 200 ... dust collection hood
300 ... top lance 400 ... sub lance
500.Raw material input 600.Two

Claims (6)

In the AOD refining method of two-phase stainless steel having a mixed structure of austenite and ferrite,
A first step of blowing and decarburizing oxygen (O 2) and argon (Ar);
A second step of inserting ferro alloy including manganese (Mn);
A third step of performing deoxidation by adding a deoxidizer;
A fourth step of injecting nitrogen (N 2); And
Including the fifth step to leave,
The two-phase stainless steel is carbon (C): 0.060 ~ 0.080wt%, silicon (Si): 0.10 ~ 0.255%, manganese (Mn): 7.8 ~ 8.0wt%, phosphorus (P): 0.035wt% or less, sulfur (S): 0.0050 wt%, Chromium (Cr): 18.0-18.2 wt%, Nickel (Ni): 1.85-2.10 wt%, Molybdenum (Mo): 0.3 wt% or less, Copper (Cu): 2.3-2.5 wt% , AOD refining method of two-phase stainless steel containing the balance iron (Fe) and other unavoidable impurities, nitrogen (N): 900 ~ 1100ppm. The method of claim 1,
In the first step, decarburizing by injecting oxygen (O2) and argon (Ar), AOD refining method of the two-phase stainless steel, characterized in that decarburization to a weight of 0.070wt%. The method of claim 1,
Degassing by blowing oxygen (O2) and argon (Ar) in the first step, AOD refining method of a two-phase stainless steel, characterized in that the decarburization by adding a raw material containing no manganese (Mn). The method of claim 1,
In the third step, deoxidation by adding a deoxidizer may include controlling silicon (Si) to 0.13 to 0.17 wt%, and adding CaO / SiO2 to 1.8 to 2.2 in the composition of the refinery slag by adding quicklime. AOD refining method of a two-phase stainless steel, characterized in that it comprises the step of controlling, and adding a fluorite of 20 to 30% by weight of the quicklime added amount. delete Carbon (C): 0.060 ~ 0.080wt%, Silicon (Si): 0.10 ~ 0.25wt%, Manganese (Mn): 7.8 ~ 8.0wt%, Phosphorus (P): 0.035wt% or less, Sulfur (S): 0.0050wt %, Chromium (Cr): 18.0 ~ 18.2wt%, Nickel (Ni): 1.85 ~ 2.10wt%, Molybdenum (Mo): 0.3wt% or less, Copper (Cu): 2.3 ~ 2.5wt%, balance iron (Fe) And other unavoidable impurities, and comprising nitrogen (N): 900 to 1100 ppm.

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