KR20170046216A - Apparatus for reducing inclusion in molten metal and method for manufacturing stainless steel with improved cleanness - Google Patents

Abstract

Disclosed are an apparatus for reducing an inclusion in molten steel and a method for manufacturing stainless steel with improved cleanness. According to an embodiment of the present invention, the apparatus for reducing an inclusion in molten steel receives molten steel from a ladle, discharges the molten steel to a tundish, and comprises: an outer wall to receive the molten steel; an inner wall enclosing an inner surface of the outer wall and including an inclusion; and a plurality of alumina (Al_2O_3) balls which are arranged in a space formed by the inner wall, and include alumina. Therefore, basicity (a CaO/Al_2O_3 ratio) of molten steel slag is controlled to form an inclusion which can be easily attached to alumina (Al_2O_3) in the molten steel. Subsequently, alumina (Al_2O_3) is used to reduce the inclusion in the molten steel. An immersion nozzle of the tundish is prevented from being clogged by the inclusion to improve cleanliness of stainless steel.

Description

TECHNICAL FIELD [0001] The present invention relates to an inclusive inclusion reducing device and a manufacturing method of a stainless steel having improved cleanliness. BACKGROUND OF THE INVENTION < RTI ID = 0.0 >

More particularly, the present invention relates to a method for reducing inclusions in molten steel and a method for producing stainless steel having improved cleanliness by controlling the basicity (CaO / Al ₂ O ₃ ratio) of molten steel slag to alumina (Al ₂ O ₃ ) It is possible to reduce inclusions in the molten steel by forming inclusions that are easy to adhere and removing the inclusions, thereby improving the cleanliness of the stainless steel and preventing the phenomenon that the immersion nozzle of the turnish is clogged by the inclusions To an apparatus for reducing inclusions in a molten steel and a method of manufacturing stainless steel capable of improving cleanliness.

The AOD - LT (Argon Oxygen Decarburization - Ladle Treatment) process is a series of processes consisting of a process of LT treatment after the AOD refining process. Among them, the AOD process is a process in which argon gas and oxygen gas in the ladle are blown together to remove carbon present in the molten steel.

Although the above process is used for processing various types of molten steel, it is often used in stainless steel making molten steel through an electric furnace having a weak decarburization function. A brief description of the process of manufacturing stainless steel through an electric furnace is as follows: Stainless steel is tapped in an electric furnace, and then subjected to a decarburization and reduction degassing process in AOD-LT.

The decarburization process is a process for decarburizing molten steel by blowing O ₂ gas together with Ar gas. However, since the molten steel is oxidized by the above process, the oxygen potential in the molten steel is increased, so that the high-priced metal such as Cr present in the molten steel is oxidized, and at the same time, the desulfurizing ability of the slag decreases.

Therefore, after the decarburization process, a reduction desulfurization process is performed. The reducing atmosphere increases the desulfurizing capability of the slag, and at the same time, the Cr present in the slag is reduced and recovered into the molten steel.

In the reduction process, Si is generally added to deoxidize molten steel and slag to maintain a reducing atmosphere. In order to accelerate the desulfurization reaction by CaS, CaO is added to the slag in order to improve the desulfurization performance of the slag. As a result, the slag has a composition of CaO-SiO ₂ system. Since Si is a relatively weak deoxidizing element, in the case of reduction desulfurization by Si, not only the oxidation degree of slag is high but also the oxygen potential of molten steel is relatively high.

1 shows a ladle 10 taking molten steel 1 and slag 2. From the ladle 10 molten steel 1 is fed through the tundish 20 into the immersion nozzle 21 So that continuous casting proceeds.

After the AOD process, an inert gas in the ladle 10 is blown to add molten steel while stirring the molten steel to perform fine adjustment of the components or to perform the LT process for floating the inclusions.

In general, corrosion resistance and workability are very important for stainless steel, and titanium plays an important role as a factor for inhibiting intergranular corrosion of stainless steel. Therefore, in the case of stainless steel, Ti component adjustment is generally performed in the LT step.

However, when Ti is added in the LT process, the reaction rate with SiO ₂ and dissolved oxygen in the slag and inclusions decreases and the TiO ₂ content in the inclusions increases. In this case, referring to FIG. 2, TiO ₂ And CaO-TiO _{2. When} such inclusions remain in the molten steel, the inclusion of the inclusions such as CaO-TiO ₂ in the molten steel is prevented from being formed in the inner wall of the immersion nozzle serving to supply the molten steel in the tundish to the casting mold at a constant speed, Adheres to and coalesces and grows, which causes the nozzle hole to be closed.

3 shows a sectional view of the immersion nozzle 21 under the tundish 20 in which various inclusions 22 are attached to the inner wall of the immersion nozzle 21 and the nozzle hole for advancing the molten steel 1 is narrowed And as the time passes, the inclusions grow more and the nozzle hole can be closed.

In order to prevent this, Prior Art 1 (Korean Patent Publication No. 10-2011-0071811) discloses a method of performing aluminum deoxidation and a method of controlling slag basicity. The prior art has generally the basicity (CaO / SiO ₂₎ of the control side as low as possible than 2.0 increases the fluidity of the slag increasing the trapping ability of the inclusions and lowering the activity of the aluminum and magnesium of the molten steel, MgO-Al ₂ O ₃ spinel To suppress the generation of inclusions. However, in this case, SiO ₂ in the slag is reduced by the TiO ₂ in the molten steel, thereby causing an adverse effect of increasing TiO ₂ in the slag and inclusions. In addition, in the LT regeneration step, the Ar gas is blown from the bottom of the ladle to stir the molten steel The slag having good flowability is mixed into the molten steel rather than the slag, thereby increasing the number of harmful inclusions.

In the prior art, titanium-containing inclusions are harmlessly decomposed by limiting the kind and amount of deoxidizing agent (Japanese Patent Application Laid-Open No. 2000-001718), aluminum deoxidation and slag basicity control (Japanese Patent Laid-Open No. 2006-104531) Thereby preventing the occlusion nozzle clogging and obtaining a good surface quality. However, it is impossible to remove the perfect inclusions.

Meanwhile, another conventional technique (Korean Patent Laid-open Publication No. 10-2010-0069176 and No. 10-1997-0043107) discloses a method of deoxidizing aluminum and controlling the content ratio of CaO and Al ₂ O ₃ to 1.5 to 2.0 (The content ratio of CaO and SiO ₂ is 7 or more). However, in such a case, the size tends to increase due to the incorporation of the inclusions, which may cause a large defect.

Korean Patent Publication No. 10-2011-0071811

Embodiments of the present invention are intended to provide an inclusion inclusion reducing apparatus capable of reducing inclusion in molten steel by using alumina (Al ₂ O ₃ ).

In addition, the embodiments of the present invention can be used to control the basicity (CaO / Al ₂ O ₃ ratio) of molten steel slag to form inclusions in the molten steel that are easy to adhere to alumina (Al ₂ O ₃ ) The present invention provides a method of manufacturing stainless steel which can reduce the inclusions and prevent the phenomenon that the immersion nozzle of the turnish is blocked by the inclusions, thereby improving the cleanliness of the stainless steel.

According to the inclined inclusion reducing apparatus for taking molten steel from a ladle and pouring the molten steel into a tundish according to an embodiment of the present invention, An inner wall including a surrounding refractory, and a plurality of alumina balls disposed in the space defined by the inner wall, the alumina balls including alumina (Al ₂ O ₃ ).

Also, according to an embodiment of the present invention, the slag may have a basicity (CaO / Al ₂ O ₃ ratio) of 2.5 to 3.0.

According to an embodiment of the present invention, the outer wall is made of iron and the inner wall is made of a refractory material including at least one selected from the group consisting of alumina (Al ₂ O ₂₃ ) and dolomite (CaMg (CO ₃ ) ₂ ) It can be a wall.

In addition, according to an embodiment of the present invention, a blowing nozzle disposed at a lower portion of the inclusion eliminator in the molten steel for blowing argon (Ar) gas from the outside may be included for floating the inclusion in the molten steel.

Also, according to an embodiment of the present invention, the alumina ball includes at least 99.5 wt% alumina, and the diameter of the alumina ball may be larger than the diameter of the blowing nozzle.

Further, according to the method of manufacturing stainless steel by performing Argon Oxygen Decarburization (AOD) refining and Ladle Treatment refining according to an embodiment of the present invention, followed by continuous casting through a tundish, (Cr), 0-15% nickel (Ni), 0.1% titanium (Ti), aluminum (Al) more than 200 ppm, and the balance iron (Fe) and unavoidable impurities in 10-30% Controlling the basicity (CaO / Al ₂ O ₃ ratio) of the slag of the stainless steel including 2.5 to 3.0; introducing titanium (Ti) into the stainless steel; And removing inclusions in the stainless steel by using alumina (Al ₂ O ₃ ) when the tundish is introduced.

According to an embodiment of the present invention, the inclusions removed by the alumina may be MgO-Al ₂ O ₃ inclusions.

According to an embodiment of the present invention, aluminum (Al) may be added to deoxidize the stainless steel so that the aluminum (Al) exceeds 200 ppm during the AOD refining.

Embodiments of the present invention provide a method of controlling the basicity (CaO / Al ₂ O ₃ ratio) of molten steel slag before adding titanium to molten steel to form inclusions that are easy to adhere to alumina (Al ₂ O ₃ ) Subsequently, inclusions in molten steel can be reduced by using alumina (Al ₂ O ₃ ).

In addition, the embodiments of the present invention can prevent inclusion of the inclusion nozzle of the turn-tile from being blocked by inclusions in the molten steel, thereby improving the cleanliness of the stainless steel.

1 is a cross-sectional view for explaining a conventional method of manufacturing stainless steel through LT refining and tundish.
Fig. 2 is a graph showing average inclusion inclusion composition changes observed in stainless steels generally containing titanium. Fig.
3 is a cross-sectional view of an immersion nozzle for explaining clogging of the immersion nozzle of the tundish in the conventional continuous casting process.
4 is a cross-sectional view for explaining a method of manufacturing stainless steel passing through a LT refining, inclusions reducing device, and tundish according to an embodiment of the present invention.
FIG. 5 is a graph showing the average size change of the inclusion in the molten steel according to the basicity of the molten steel slag and the holding time of the molten steel.
6 is a graph showing the change in cleanliness of the molten steel according to the basicity of the molten steel slag and the holding time of the molten steel.
7 is a graph showing changes in the content of the spinel inclusions in the molten steel due to the basicity of the molten steel slag and the holding time of the molten steel.
FIGS. 8 to 10 are graphs showing average inclusion inclusion composition changes observed in stainless steels according to the basicity of slag.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided to fully convey the spirit of the present invention to a person having ordinary skill in the art to which the present invention belongs. The present invention is not limited to the embodiments shown herein but may be embodied in other forms. For the sake of clarity, the drawings are not drawn to scale, and the size of the elements may be slightly exaggerated to facilitate understanding.

4 is a cross-sectional view for explaining a method of manufacturing stainless steel passing through a LT refining, inclusions reducing device, and tundish according to an embodiment of the present invention.

The inclusion inclusion elimination device 30 according to the embodiment of the present invention is arranged between the ladle 10 and the tundish 20 at the time of treading for continuous casting of stainless steel after LT refining of molten steel And the molten steel can go through.

The inclusion reducing device 30 includes an alumina ball 31, an outer wall 32, an inner wall 33, and a blowing nozzle 34.

The outer wall 32 takes the molten steel 1 from the ladle 10, and the outer wall 32 can be made of iron. The outer wall 32 may have a thickness of 3 mm or more.

The inner wall 33 includes a refractory surrounding the inner surface of the outer wall 32. Since the inner wall 33 directly abuts against the molten steel 1, it can be made of a material having excellent refractory performance. The inner wall 33 may have a thickness of 50 mm or more.

For example, the inner wall 33 is alumina (Al ₂ O ₃₎ and dolomite (CaMg (CO _{3) 2)} fire resistance can byeokil containing alumina (Al ₂ O ₃₎ and dolomite (CaMg (CO _{3) 2} ) may be manufactured and stacked to produce the refractory wall.

The alumina ball 31 is disposed in a space formed by the inner wall 33 and includes alumina (Al ₂ O ₃ ). The alumina ball 31 has the strongest adhesion to the MgO-Al ₂ O ₃ spinel inclusions among the inclusions in the molten steel 1. The alumina ball 31 may have a spherical shape to increase the contact area with the molten steel 1, but is not limited thereto.

And a blowing nozzle 34 disposed under the inclusion reducing device 30 to lift up and separate the inclusions in the molten steel 1 of the inclusion reducing device 30. [

The blowing nozzle 34 is disposed below the inclusion reducing device in the molten steel 1 so that argon (Ar) gas can be blown from the outside.

For example, the alumina ball 31 may comprise at least 99.5 wt% alumina (Al ₂ O ₃ ). The diameter of the alumina ball 31 is set such that the alumina ball 31 is molten by the blowing nozzle 34 and the injection nozzle into which the molten steel is injected from the ladle 10 and the tundish 20, May be formed larger than the diameters thereof in order to prevent escape to the discharge nozzle to be discharged. For example, the alumina ball 31 may have a diameter of 50 mm or more.

The molten steel 1 may have a basicity (CaO / Al ₂ O ₃ ratio) of 2.5 to 3.0 in the slag 2. The basicity of the slag 2 is a condition for reducing the inclusion in the molten steel by using the alumina ball 31. The basicity of the slag 2 may be controlled in the ladle 10 before the molten steel 1 is introduced into the inclusion reducing device 30. [

Generally, the amount of aluminum (Al) added for deoxidation after decarburization in the AOD refining furnace, the amount of calcium (Ca) introduced from titanium (Ti), slag and calcium-silicon Ca), and oxides such as magnesium (Mg) introduced from the slag and the ladle refractories form inclusions and become CaO-TiO ₂ -Al ₂ O ₃ -MgO inclusions. The inclusions of this composition are crystallized as high-melting inclusions such as CaO-TiO ₂ or MgO-Al ₂ O ₃ spinel inclusions while the temperature is lowered during the steelmaking process, and they are not well removed by floating separation and have a property of sticking to the immersion nozzle during continuous casting Lt; / RTI >

Various kinds of inclusions 22 are attached to the inner wall of the immersion nozzle 21 shown in Fig. In analyzing the composition of the inclusions in _{(22), MgO-Al 2} O 3, TiO ₂ and CaO-TiO ₂ are inclusions. At this time, it is the aluminum (Al) concentration in the molten steel that determines the composition of the deposit.

Aluminum (Al) concentration (ppm) Attachment type of immersion nozzle 50 TiO ₂ and CaO-TiO ₂ 100 TiO ₂ and CaO-TiO ₂ 150 TiO ₂ and CaO-TiO ₂ 200 TiO ₂ and CaO-TiO ₂ 300 MgO-Al ₂ O ₃ 400 MgO-Al ₂ O ₃ 500 MgO-Al ₂ O ₃ 1,000 MgO-Al ₂ O ₃

As shown in Table 1, when the Al concentration in the molten steel is 200 ppm or less, the remaining inclusions in the molten steel mainly exist as TiO ₂ and CaO-TiO _{2. When the} Al content exceeds 200 ppm, the inclusions remaining in the molten steel are mainly MgO-Al ₂ O _{3 &lt}; / RTI > All of the above three inclusions must be removed because they cause nozzle clogging.

In the present invention, in order to allow the molten steel 1 to pass through the inclusion reducing device 30 including the alumina ball 31 to allow the molten steel inclusions to adhere to the alumina balls 31 as much as possible, MgO-Al ₂ O ₃ Since the spinel inclusion adheres best to the alumina ball 31, it is preferable to control the Al concentration in the molten steel to exceed 200 ppm so that the inclusions mainly present in the molten steel become MgO-Al ₂ O ₃ .

Therefore, according to the method of manufacturing stainless steel by performing Argon Oxygen Decarburization (AOD) refining and Ladle Treatment refining according to an embodiment of the present invention, followed by continuous casting through a tundish, (Cr), 0-15% nickel (Ni), 0.1% titanium (Ti), aluminum (Al) more than 200 ppm, and the balance iron (Fe) and unavoidable impurities in 10-30% The basicity (CaO / Al ₂ O ₃ ratio) of the slag of the stainless steel included is controlled to 2.5 to 3.0. Thereafter, titanium (Ti) is added to the stainless steel to adjust the titanium component. When the stainless steel is introduced into the tundish from the ladle, the inclusions in the stainless steel are removed using alumina (Al ₂ O ₃ ) So that stainless steel having improved cleanliness can be manufactured.

The alumina for removing the inclusions in the stainless steel is the inclusions reducing apparatus 30 according to an embodiment of the present invention.

For example, the inclusions that are removed by the alumina may be an MgO-Al ₂ O ₃ inclusions.

During the AOD refining, it is preferable to control the content of aluminum (Al) in components of stainless steel taken on the ladle by adding aluminum (Al) so that the aluminum (Al) in the stainless steel exceeds 200 ppm.

The following experiment was conducted to confirm the change of the molten steel inclusion characteristics and the clogging of the immersion nozzle according to the slag basicity of molten steel.

Test Example  One

Experiments were conducted using slag prepared with stainless steel containing 18 wt% of chromium, 8 wt% of nickel, and 0.2 wt% of titanium. A vacuum induction melting furnace was used for the high temperature test, and 1 kg of stainless steel and 200 g of slag were used in each experiment. In the MgO crucible, molten steel was directly heated by the induction coil and heated to 1,700 ° C. Vacuum condition was maintained for 2 hours or more to prevent metal oxidation, and the experiment was conducted in an Ar atmosphere.

When the target temperature was reached, Al was added so that the Al concentration in the molten steel was 300 ppm. At this time, molten steel was produced by controlling the basicity of the slag (the ratio of CaO / SiO _{2 in} the slag) to 2.5. However, CaF ₂ in the slag was added in an amount of 5% by weight based on the total weight of the slag, thereby preventing the slag from being completely solidified.

Test Example  2

Molten steel was produced in the same manner as in Example 1 except that the basicity of the slag (the ratio of CaO / SiO _{2 in} the slag) was controlled at 3.0.

Test Example  3

Molten steel was produced in the same manner as in Example 1 except that the basicity of the slag (the ratio of CaO / SiO _{2 in} the slag) was controlled at 3.5.

Slag basicity Retention time after completion of basicity control Cleanliness Index Inclusion Size Index Spinel content in inclusions Test Example 1-1 2.5 30 minutes 6.4 8.0 27.0 Test Example 1-2 2.5 60 minutes 5.2 6.9 29.0 Test Example 2-1 3.0 30 minutes 4.3 5.0 29.0 Test Example 2-2 3.0 60 minutes 3.5 3.5 31.0 Test Example 3-1 3.5 30 minutes 3.6 4.6 17.0 Test Example 3-2 3.5 60 minutes 3.1 2.5 7.0

FIG. 5 is a graph showing the average size change of the inclusion in the molten steel according to the basicity of the molten steel slag and the holding time of the molten steel. 6 is a graph showing the change in cleanliness of the molten steel according to the basicity of the molten steel slag and the holding time of the molten steel. 7 is a graph showing changes in the content of the spinel inclusions in the molten steel due to the basicity of the molten steel slag and the holding time of the molten steel.

With reference to Table 2 and Figs. 5 to 7, the basicity of the molten steel slag and the influence of the inclusions will be described.

Referring to FIG. 5, the average size of inclusions in molten steel according to the basicity of the molten steel slag decreases as the basicity of the slag increases. In addition, the inclusion size of the slag decreased with the duration of the molten steel after completion of basicity control of molten steel.

When the slag basicity was 2.5, the slag inclusion index was about 6.4 after 30 minutes and decreased to about 5.2 after 60 minutes. When the slag basicity was 3.0, the inclusion index of the slag was about 4.3 after 30 minutes and decreased to about 3.4 after 60 minutes. In addition, when the slag basicity is 3.5, the inclusion size index of the slag is about 3.6 after 30 minutes and decreased to about 3.1 after 60 minutes.

Thus, it can be seen that the slag inclusion size is significantly reduced when the slag basicity is 3.0, and the slag inclusion size decreases as the molten steel retention time passes after completion of basicity control of the molten steel.

Referring to FIG. 6, the cleanliness index (the number of inclusions in the molten steel) according to the basicity of the molten steel slag decreases with an increase in the slag basicity over time. Here, the cleanliness index means the number of inclusions of 1 占 퐉 or more existing within a unit area. That is, it can be seen that as the slag basicity increases, the number of inclusions per unit area decreases. In addition, the effect of slag basicity can be confirmed from the fact that after finishing the basicity control of molten steel, the degree of purity index decreases with the holding time of molten steel.

When the slag basicity was 2.5, the purity index of slag was about 8.0 after 30 minutes and decreased to about 6.9 after 60 minutes. When the basicity of the slag was 3.0, the index of cleanliness of the slag was about 5.0 after 30 minutes and decreased to about 3.5 after 60 minutes. Also, when the basicity of slag was 3.5, the index of cleanliness of the slag was about 4.6 after 30 minutes and decreased to about 2.5 after 60 minutes.

In this way, the slag cleanliness index is significantly decreased when the slag basicity is 3.0, and the slag cleanliness index decreases as the molten steel retention time passes after completion of basicity control of the molten steel.

7, the incidence rate of MgO-Al ₂ O ₃ spinel inclusions among the inclusions according to the basicity of the molten steel slag is a percentage of the total number of inclusions in the total number of inclusions.

When the slag basicity was 2.5, the incidence of spinel inclusions was about 27.0% after 30 minutes and about 29.0% after 60 minutes. When the slag basicity is 3.0, the rate of occurrence of spinel inclusions is 29.0% after 30 minutes and 31.0% after 60 minutes. In addition, when the slag basicity was 3.5, the incidence of spinel inclusions was 17.0% after 30 minutes and decreased to 7.0% after 60 minutes.

The incidence increases as the basicity increases from 2.5 to 3.0, but decreases as the rate increases from 3.0 to 3.5. This is because, when the slag basicity is 3.0 or more, since the CaO and MgO in the slag are saturated, the spinel is not crystallized but MgO is crystallized. Inclusions with high MgO content tend to be smaller in size than spinel or other high melting point inclusions.

FIGS. 8 to 10 are graphs showing average inclusion inclusion composition changes observed in stainless steels according to the basicity of slag.

Referring to FIGS. 8 to 10, TiO ₂ or Al ₂ O ₃ inclusions at a slag basicity of 1.9 were found to have a spinelity of MgO-Al ₂ O ₃ at a slag basicity of 3.0 and a slag basicity of 3.5 to MgO.

From the above results, it can be seen that when the slag basicity is between 2.5 and 3.0, the number and size of inclusions are reduced, and the incidence of MgO-Al ₂ O ₃ spinel in inclusions is the highest.

When the slag basicity ratio of CaO and SiO ₂ is 3.5 or more, the solid phase fraction of the slag becomes too large and can not act as a slag. However, when the concentration of Al ₂ O _{3 in} the slag is more than 40% and the concentration of SiO ₂ is less than 10%, the slag becomes slag again. In this case, the slag basicity ratio of CaO to SiO ₂ is at least 5.0 and CaO-Al ₂ O ₃ system slag, it should be distinguished from the CaO-SiO ₂ system slag utilized in the present invention.

In summary, the slag basicity ratio of CaO to SiO ₂ in the present invention is limited to between 2.5 and 3.0 because the inclusions and size are reduced in this section and the incidence of MgO-Al ₂ O ₃ spinels in the inclusions is the highest, If it is more than that, the solid phase fraction of the slag is too high to be utilized as slag. When the slag basicity is 5.0 or more, CaO-Al ₂ O ₃ -based slag is formed and the generation of MgO-Al ₂ O ₃ spinel is suppressed. However, since liquid inclusions are formed, we can attach the desired inclusions to the alumina balls It is not preferable.

Hereinafter, the present invention will be described in more detail with reference to Examples.

Example  1 to 3

A titanium alloy containing 18% by weight of chromium, 8% by weight of nickel and 0.2% by weight of titanium was deoxidized in a 100-ton AOD refining furnace to aluminum and titanium was added in the component regulating (LT) stage. The basicity of the slag before the addition of titanium was adjusted to 2.5 to 3.0, and CaF ₂ in the slag composition was controlled to be 5 wt% based on the total weight of the slag. Thereafter, molten steel was passed through the inclusion reducing device of the present invention. Table 3 below shows the properties of stainless steel according to the examples.

Slag basicity Al concentration in molten steel (ppm) Cleanliness Index Inclusion Size Index Immersion nozzle clogging rate (%) Example 1 2.5 250 0.5 2.5 0 Example 2 2.7 300 0.3 2.6 0 Example 3 3.0 400 1.1 1.5 0

Referring to Table 3, the cleanliness index showed 0.5 to 1.1, the inclusion size index was 1.5 to 2.6, and the immersion nozzle was not clogged.

Comparative Example  One

Stainless steel was prepared in the same manner as in the above example except that the basicity of the slag before the addition of titanium was adjusted to 2.0 and the Al concentration in the molten steel was controlled to be 200 ppm. Table 4 below shows the properties of the stainless steel according to Comparative Example 1.

Comparative Example 1-1 in Table 4 did not use the inclusion reducing apparatus, and Comparative Example 1-2 produced stainless steel in the same manner, except that the inclusion reducing apparatus was used.

Slag basicity Al concentration in molten steel (ppm) Cleanliness Index Inclusion Size Index Immersion nozzle clogging rate (%) Comparative Example 1-1 2.0 200 6.3 12.3 70 Comparative Example 1-2 2.0 200 3.5 6.0 30

Referring to Table 4, when the inclusion reducing apparatus is not used, the cleanliness index is 6.3 and the inclusion size index is 12.3. The rate of occlusion of the immersion nozzle is 70%. When the inclusion reducing apparatus is used, Degree of indentation was 3.5, inclusion size index was 6.0, and the rate of occlusion of immersion nozzle was 30%.

Comparative Example  2

Stainless steel was prepared in the same manner as in the above example except that the basicity of the slag before the addition of titanium was adjusted to 2.0 and the Al concentration in the molten steel was controlled to be 300 ppm. Table 5 below shows the properties of the stainless steel according to Comparative Example 2.

In Comparative Example 2-1 of Table 5, no inclusion reducing device was used, and in Comparative Example 2-2, stainless steel was manufactured by the same method except that the inclusion reducing device was used.

Slag basicity Al concentration in molten steel (ppm) Cleanliness Index Inclusion Size Index Immersion nozzle clogging rate (%) Comparative Example 2-1 2.0 300 7.2 9.0 60 Comparative Example 2-2 2.0 300 2.7 4.8 20

Referring to Table 5, when the inclusion reducing apparatus was not used, the cleanliness index was 7.2 and the inclusion size index was 9.0. The rate of occlusion of the immersion nozzle was 60%. When the inclusion reducing apparatus was used, Degree of indentation was 2.7, inclusion size index was 4.8, and the rate of occlusion of immersion nozzle was 20%.

Comparative Example  3

Stainless steel was prepared in the same manner as in the above example except that the basicity of the slag before the addition of titanium was adjusted to 2.7 and the Al concentration in the molten steel was controlled to be 200 ppm. Table 6 below shows the properties of stainless steel according to Comparative Example 3.

In Comparative Example 3-1 of Table 6, no inclusion reducing device was used, and in Comparative Example 3-2, stainless steel was manufactured in the same manner, except that the inclusion reducing device was used.

Slag basicity Al concentration in molten steel (ppm) Cleanliness Index Inclusion Size Index Immersion nozzle clogging rate (%) Comparative Example 3-1 2.7 200 5.9 11.7 50 Comparative Example 3-2 2.7 200 2.5 5.0 20

Referring to Table 6, when the inclusion reducing apparatus is not used, the degree of cleanliness is 5.9, the inclusion size index is 11.7, and the rate of occlusion of the immersion nozzle is 50%. When the inclusion reducing apparatus is used, Degree of indentation was 2.5, inclusion size index was 5.0, and the rate of occlusion of immersion nozzle was 20%.

Comparative Example  4

Stainless steel was prepared in the same manner as in the above example except that the basicity of the slag before the addition of titanium was adjusted to 2.7 and the Al concentration in the molten steel was controlled to be 300 ppm. Table 7 shows the properties of stainless steel according to Comparative Example 4.

In Comparative Example 4 of Table 7 below, stainless steel was manufactured in the same manner except that the inclusion reducing apparatus was not used.

Slag basicity Al concentration in molten steel (ppm) Cleanliness Index Inclusion Size Index Immersion nozzle clogging rate (%) Comparative Example 4 2.7 300 3.1 4.5 30

Referring to Table 7, when the inclusion reducing apparatus was not used, the cleanliness index was 3.1, the inclusion size index was 4.5, and the rate of occlusion of the immersion nozzle was 30%.

Comparative Example  5

Stainless steel was prepared in the same manner as in the above example except that the basicity of the slag before the addition of titanium was adjusted to 3.5 and the Al concentration in the molten steel was controlled to be 200 ppm. Table 8 below shows the properties of stainless steel according to Comparative Example 5.

In Comparative Example 5-1 of Table 8, no inclusion reducing apparatus was used, and in Comparative Example 5-2, stainless steel was manufactured in the same manner, except that the inclusion reducing apparatus was used.

Slag basicity Al concentration in molten steel (ppm) Cleanliness Index Inclusion Size Index Immersion nozzle clogging rate (%) Comparative Example 5-1 3.5 200 2.2 3.3 30 Comparative Example 5-2 3.5 200 2.0 3.5 10

Referring to Table 8, when the inclusion reducing apparatus was not used, the cleanliness index was 2.2 and the inclusion size index was 3.3, and the rate of occluding the immersion nozzle was 30%. When the inclusion reducing apparatus was used, Index of 2.0, inclusion size index of 3.5, and the rate of occlusion of immersion nozzle was 10%.

Comparative Example  6

Stainless steel was prepared in the same manner as in the above example except that the basicity of the slag before the addition of titanium was adjusted to 3.5 and the Al concentration in the molten steel was controlled to be 300 ppm. Table 9 below shows the properties of the stainless steel according to Comparative Example 2.

Comparative Example 6-1 shown in Table 9 does not use the inclusion reducing device, and Comparative Example 6-2 uses stainless steel in the same manner except that the inclusion reducing device is used.

Slag basicity Al concentration in molten steel (ppm) Cleanliness Index Inclusion Size Index Immersion nozzle clogging rate (%) Comparative Example 6-1 3.5 300 1.8 2.8 25 Comparative Example 6-2 3.5 300 1.5 2.5 5

Referring to Table 9, when the inclusion reducing apparatus was not used, the cleanliness index was 1.8 and the inclusion size index was 2.8. The rate of occlusion of the immersion nozzle was 25%. When the inclusion reducing apparatus was used, Index of 1.5, inclusion size index of 2.5, and the rate of occlusion of immersion nozzle was 5%.

Therefore, comparing the above embodiments and comparative examples, it can be seen that, in the case of stainless steel according to the embodiments of the present invention, the degree of cleanliness decreased and the size of inclusions decreased. As a result, nozzle clogging no longer occurs.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited thereto. Those skilled in the art will readily obviate modifications and variations within the spirit and scope of the appended claims. It will be understood that various changes and modifications may be made therein without departing from the spirit and scope of the invention.

1: molten steel 2: slag
10: ladle 20: tundish
21: immersion nozzle 30: inclusion reduction device
31: alumina ball 32: outer wall
33: inner wall 34: blow nozzle

Claims (8)

1. A molten steel inclusion reducing apparatus for taking molten steel from a ladle and introducing the molten steel into a tundish,
An outer wall for taking the molten steel;
An inner wall including a refractory surrounding the inner surface of the outer wall; And
And a plurality of alumina balls disposed in the space defined by the inner wall, the alumina balls including alumina (Al ₂ O ₃ ). The method according to claim 1,
Wherein the molten steel has a slag basicity (CaO / Al ₂ O ₃ ratio) of 2.5 to 3.0. The method according to claim 1,
Wherein the outer wall is made of iron,
Wherein the inner wall is a refractory wall containing at least one selected from the group consisting of alumina (Al ₂ O ₂ ) and dolomite (CaMg (CO ₃ ) ₂ ). The method according to claim 1,
And a blowing nozzle disposed at a lower portion of the inclusion eliminator for blowing argon (Ar) gas from the outside, for lifting and separating the inclusion in the molten steel. 5. The method of claim 4,
Said alumina balls comprising at least 99.5 wt% alumina,
Wherein the diameter of the alumina ball is larger than the diameter of the blowing nozzle. A method for producing stainless steel by continuously performing AOD (Argon Oxygen Decarburization) refining and Ladle Treatment (refining) treatment through a tundish,
(Cr), 0 to 15% nickel (Ni), 0.1% titanium (Ti), more than 200 ppm aluminum (Al), and the balance iron (Fe (CaO / Al ₂ O ₃ ratio) of the slag of the stainless steel containing impurities and unavoidable impurities to 2.5 to 3.0;
Introducing titanium (Ti) into the stainless steel; And
And removing the inclusions in the stainless steel using alumina (Al ₂ O ₃ ) when the stainless steel is introduced from the ladle to the tundish. The method according to claim 6,
Inclusions that are removed by the alumina has an improved stainless steel producing method cleanliness, characterized in that Al ₂ O ₃ inclusion-MgO. The method according to claim 6,
And adding aluminum (Al) to the stainless steel so that the aluminum (Al) exceeds 200 ppm during the AOD refining, thereby deoxidizing the stainless steel.

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