WO2021187749A1 - Tundish flux and casting method using same - Google Patents

Abstract

Tundish flux according to embodiments of the present invention comprises, with respect to the total weight %, 40% to 60% by weight of calcium oxide (CaO), 25% to 40% by weight of aluminum oxide (Al₂O₃), 5% to 10% by weight of silicon oxide (SiO₂), 2% to 10% by weight of boron oxide (B₂O₃), and unavoidable impurities. Therefore, according to the flux of the embodiments of the present invention, solubility of inclusions or efficiency of removing inclusions is higher than in the prior art. Thus, it is possible to manufacture a slab in which, compared to the prior art, the occurrence of defects due to inclusions is suppressed or prevented, and the quality of the slab can be improved.

Description

Tundish flux and casting method using same

The present invention relates to a tundish flux and a casting method using the same, and more particularly, to a tundish flux capable of improving the quality and productivity of a slab and a casting method using the same.

The casting process is a process of manufacturing slabs of various shapes such as slabs, blooms, billets, beam blanks, etc. by injecting molten steel in a tundish into a mold, and drawing out the reacted and solidified slabs in the mold.

During this casting process, the molten steel molten steel surface in the tundish is covered with flux to remove inclusions from the molten steel in the tundish, to suppress the occurrence of inclusions due to re-oxidation of the molten steel and the temperature drop of the molten steel.

The flux is provided in a solid state or a powder state, and the flux is introduced into a tundish in which a predetermined amount of molten steel is accommodated at the initial stage of casting. When flux is introduced into the tundish, it is melted by the heat of molten steel. Accordingly, a molten flux, that is, a flux pool, is formed to a predetermined thickness on the molten steel molten steel surface. That is, the molten steel bath surface is covered by the flux pool. When a flux pool is formed on the surface of the molten steel, inclusions in the molten steel are dissolved and absorbed into the flux pool, thereby removing the inclusions in the molten steel. In addition, since the flux pool blocks contact between the atmosphere and the molten steel, reoxidation of the molten steel and temperature drop are suppressed.

On the other hand, the solid flux supplied to the tundish is melted after a predetermined time has elapsed. However, in the initial stage of casting, there is not enough time for the injected flux to melt, so the amount of flux pool generated is insufficient, and the thickness thereof is thin. Accordingly, the flux pool formed at the initial stage of casting has low solubility for inclusions and has a weak blocking effect with the atmosphere. For this reason, the removal rate of inclusions in the molten steel is low, and as a large amount of inclusions are generated due to reoxidation of the molten steel, defects due to inclusions in the molten steel occur on the surface or inside of the cast steel.

(Prior art literature)

(Patent Document 1) Korean Patent KR1233836

The present invention provides a tundish flux having improved solubility of inclusions and a casting method using the same.

The present invention provides a tundish flux capable of suppressing or preventing the reoxidation of molten steel and the occurrence of inclusions thereby, and a casting method using the same.

Examples of the present invention are tundish fluxes that are added to the tundish during casting, and based on the total weight%, calcium oxide (CaO) is 40 to 60 wt%, and aluminum oxide (Al ₂ O ₃ ) is 25 wt% % to 40% by weight, 5% to 10% by weight of _{silicon oxide (SiO 2 ), 2% to 10% by weight of boron oxide (B 2} O ₃ ) and unavoidable impurities.

Based on the total weight % of the tundish flux, the boron oxide (B ₂ O ₃ ) may be included in an amount of 5 wt% to 10 wt%.

The tundish flux may further include at least one of 2 wt% to 10 wt% sodium oxide (Na ₂ O) and 2 wt% to 10 wt% calcium fluoride (CaF _{2 ).}

The tundish flux may further include at least one of 2 wt% to 6 wt% sodium oxide (Na ₂ O) and 2 wt% to 6 wt% calcium fluoride (CaF _{2 ).}

Based on the total weight % of the tundish flux, the calcium oxide (CaO) is 50% to 60% by weight, the aluminum oxide (Al ₂ O ₃ ) is 25% to 34% by weight, the silicon oxide (SiO ₂ ) 6 wt% to 9 wt% may be included.

The melting point of the tundish flux is 1310° C. or less.

The melting point of the tundish flux may be 1280° C. or less.

The tundish flux has a viscosity of 7 poise or less at 1400°C.

The tundish flux may have a viscosity of 2 poise or more and 4 poise or less at 1400°C.

A casting method according to an embodiment of the present invention comprises the steps of providing a tundish flux; The process of supplying molten steel to the tundish; inputting the tundish flux into the tundish to form a flux pool on the molten steel molten steel surface in the tundish; and supplying the molten steel of the tundish to a mold, and solidifying the molten steel in the mold to cast a slab.

The ladle in which the molten steel is accommodated is alternately connected to the tundish a plurality of times to perform casting of multiple charges in which molten steel is continuously supplied to the tundish, and during the casting of the multiple charges, the molten steel of the first ladle is supplied to the tundish The tundish flux is introduced into the tundish in the first charge casting to be performed, and the melting point of the flux pool in the tundish is 1400° C. or less during the last charge casting during the multi-charge casting.

The tundish flux injected into the tundish is all melted within 8 minutes.

The thickness of the flux pool in the tundish at the time of the first charge casting is 10 mm or more.

During the multi-charge casting, from the first charge to the last charge casting, the molten steel oxygen content in the mold is 20 ppm or less.

According to the flux according to the embodiments of the present invention, solubility of inclusions or efficiency of removing inclusions is higher than in the related art. Accordingly, compared to the prior art, it is possible to manufacture a cast slab in which the occurrence of defects due to inclusions is suppressed or prevented, and the quality of the slab can be improved.

In addition, since the melting point of the flux according to the embodiments is lower than that of the prior art, the melting rate is high. Accordingly, when using the flux according to the embodiments, it is possible to melt a large amount of flux within a shorter time than in the related art. Due to this, as a sufficient amount and thickness of the flux pool is formed in the initial stage of casting, reoxidation and temperature drop in the initial stage of casting can be more effectively prevented.

In addition, since the melting point of the flux is low, it is possible to suppress or prevent the solidification of the flux even when casting of a plurality of charges is continuously performed. Therefore, it is possible to manufacture a slab in which the occurrence of defects due to inclusions is suppressed or prevented from the initial stage to the end of continuous casting, and the quality of the slab can be improved.

1 is a view showing a general casting equipment.

2 is a graph showing the erosion rate of a specimen during an experiment using the flux according to Experimental Examples 1 to 5;

3 is a diagram illustrating an experimental apparatus.

4 is a photograph showing the molten state of the flux over time when the flux according to the first experimental example and the flux according to the third experimental example are introduced into the tundish.

5 is a diagram illustrating the measurement of oxygen content (ppm) in the molten steel in the mold at each charge when casting is continuously performed seven times using the flux according to the first experimental example and the flux according to the third experimental example, respectively; is a result

6 is a view showing the state of the flux in the tundish in the order of the charge when casting the charge six times continuously using the flux according to the first experimental example and the flux according to the third experimental example, respectively. It's a photo.

7 shows a tundish at the second, fourth, and sixth charges when casting of the sixth charge is continuously performed using the flux according to the first experimental example and the flux according to the third experimental example, respectively; This is the result of measuring the melting point of my flux.

8 shows the results of measuring the oxygen content (ppm) in the molten steel in the mold at each charge when the casting of six charges is continuously performed using the flux according to the first experimental example and the flux according to the third experimental example, respectively; am.

Hereinafter, embodiments of the present invention will be described in more detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, and only these embodiments allow the disclosure of the present invention to be complete, and the scope of the invention to those of ordinary skill in the art will be completely It is provided to inform you. The drawings may be exaggerated in order to explain the embodiments of the present invention, and like reference numerals in the drawings refer to like elements.

The present invention relates to a tundish flux having improved inclusion solubility or inclusion removal efficiency. Further, the present invention relates to a tundish flux capable of suppressing or preventing reoxidation and temperature drop of molten steel. Here, the solubility of inclusions means the degree to which inclusions are dissolved by the flux.

Prior to the description of the tundish flux according to the embodiments of the present invention, a general casting method to which the tundish flux is applied will be described.

1 is a view showing a general casting equipment.

In the casting process, when the molten steel M received in the tundish 100 flows into the mold 300 through the immersion nozzle 400, the solidification of the molten steel M starts in the cooled mold 300, This is a process in which cast steel in a solid state, which is an intermediate product, is obtained. The reaction solid slab drawn from the mold 300 is molded and further cooled while moving along a plurality of segments (not shown) arranged in one direction from the lower side of the mold 300 to become a fully solidified slab.

The tundish 100 receives the molten steel from the ladle 200 and supplies it to the mold 300 . To this end, the ladle 200 is moved to the upper side of the tundish 100, and the nozzle connected to the lower part of the ladle 200 (hereinafter, the ladle nozzle 220), for example, the lower part of the shroud nozzle is turned. to be located inside the dish 100 . Accordingly, the molten steel in the ladle 200 is supplied to the tundish 100 through the ladle nozzle 220 , and then is supplied to the mold 300 through the immersion nozzle 400 .

The tundish 100 includes a body 110 having an internal space and a cover member 140 covering an upper side of the body 110 . A hole into which the ladle nozzle 220 is inserted and a hole for sampling may be provided in the cover member 140 .

In addition, the tundish 100 is located outside the upper weir 120 and the upper weir 120 installed in the upper portion of the main body 110 so as to be located outside the position where the ladle nozzle 220 is inserted. (110) It may further include a lower weir (weir) 130 installed on the bottom.

For example, when two molds (hereinafter, first and second molds 300: 300a, 300b) are disposed on the lower side of the tundish 100, the ladle 200 is located on the upper side of the tundish 100 When done, the ladle nozzle 220 is arranged to be positioned between the first mold 300a and the second mold 300b. And, the upper weirs are provided as a pair, and the pair of upper weirs (hereinafter, first and second upper weirs 120: 120a, 120b) are located on both sides with the ladle nozzle 220 as the center. It may be connected to an upper portion of the body 110 . At this time, the lower ends of the first and second upper weirs 120a and 120b are installed to be spaced apart from the bottom surface of the main body 110 .

In addition, the lower weir 130 may also be provided as a pair, and a pair of lower weirs (hereinafter, first and second lower weirs 130: 130a, 130b) connects the tundish 100 and the mold. It may be installed so as to be located between the submerged nozzle and the upper weir. That is, the first lower weir 130a is positioned between the first submerged nozzle 400a and the first upper weir 120a connecting the tundish 100 and the first mold 300a, and the tundish 100 A second lower weir 130b is positioned between the second submerged nozzle 400b and the second upper weir 120b connecting the and the second mold 300b.

In addition, the vertical extension length of the upper weir 120 may be formed longer than the extension length of the lower weir 130 . In addition, the lower end of the upper weir 120 is provided to be positioned lower than the upper end of the lower weir 130 .

The inner space of the tundish 100 or the main body 110 is located outside the central area 111a, which is a space between the first upper weir 120a and the second upper weir 120b, one side of the central area 111a. The space may be divided into a first outer region 111b and a second outer region 111c, which is a space located outside the other side of the central region 111a. Here, the first outer region 111b is a space between one sidewall and the first upper weir 120a in the main body 110 , and the second outer region 111c is the other sidewall and the second upper weir in the main body 110 . It can be described as the space between (120b). According to the tundish 100, a portion of the molten steel M passed through the ladle nozzle 220 and supplied to the central region 111a in the tundish 100 is a first upper weir 120a and a first lower weir ( 130a), it moves to the first outer region 111b, and moves to the first outer region 111b through the passage between the second upper weir 120b and the second lower weir 130b. The molten steel moved to the first and second outer regions 111b and 111c is supplied to the first and second molds 300a and 300b through the first and second immersion nozzles 400a and 400b.

The tundish 100 receives the molten steel M from the ladle 200 as described above. Hereinafter, a process in which the molten steel M of the ladle 200 is supplied to the tundish 100 will be briefly described. At the bottom of the ladle 200, an outlet 210, which is a passage through which the molten steel M is discharged, is provided, and a filler including a metal oxide such as chromium oxide and silicon oxide is filled in the outlet 210. The filler is sintered by the heat of the molten steel M accommodated in the ladle 200, and thus the outlet 210 is closed by the sintered filler. When the gate 221 provided in the ladle nozzle 220 is opened in this state, the filler sintered in the outlet 210 is destroyed by the load of the molten steel M. Accordingly, as the outlet 210 is naturally opened (opened), the molten steel M in the ladle 200 is supplied to the tundish 100 through the outlet 210 and the ladle nozzle 220 .

On the other hand, in casting the slab, continuous casting in which the slab is cast by continuously supplying the molten steel M to the tundish 100 may be performed. That is, the molten steel is supplied to the tundish 100 before the molten steel M in the tundish 100 is completely discharged into the mold 300 or before the molten steel is emptied in the tundish 100 . For this, the ladle 200 in which the molten steel M is accommodated is connected to the tundish 100 a plurality of times. That is, before all the molten steel (M) in the tundish 100 is discharged, the empty ladle 200 located on the upper side of the tundish 100 is replaced with another ladle 200 in which the molten steel M is accommodated and connected. and do this multiple times. In general, casting a slab by using the molten steel accommodated in one ladle 200 is called one charge (charge). And, the first (first) ladle, the second ladle, the third ladle, … The cast is cast while replacing the ladle in this order, and the casting is made according to the order of the ladle or the order to be replaced: 1st charge, 2nd charge, 3rd charge, ... named as

On the other hand, the molten steel M that is taken by the ladle 200 and moved to the tundish 100 is molten steel after a refining operation to remove impurities before that. The refining operation to remove impurities is a preliminary desulfurization process to remove sulfur (S) from molten steel, a converter refining process to remove phosphorus (P) and carbon (C) from molten steel by blowing oxygen into the molten steel in the converter, and oxygen ( O) including deoxidation process.

In performing deoxidation to remove oxygen (O) in molten steel, a deoxidizing agent, for example, aluminum (Al) is introduced into the molten steel. However, in the deoxidation operation, inclusions such as metal oxides, for example, aluminum oxide (Al ₂ O ₃ ) in molten steel are generated, and these inclusions are a factor of surface or internal defects of the cast steel. Accordingly, in order to remove inclusions in the molten steel, bubbling is performed using a vacuum degassing facility, for example, RH (Rheinstahl-Heraus), but there is a limit to lowering the inclusions in the molten steel below a desired predetermined content in this step. .

Accordingly, the inclusions are additionally removed in the casting process, and for this purpose, the tundish flux (hereinafter, flux F) in which the inclusions can be dissolved and absorbed is added to the upper portion of the tundish 100 . At this time, the flux F is injected into the tundish 100 when the molten steel of 40% to 45% of the target amount of molten steel to be filled in the tundish is filled.

In addition, during continuous casting in which a plurality of charges are continuously performed, the flux F is added to the tundish 100 from the first charge, that is, the first charge, and then the flux is not added until the last charge. In other words, continuous casting of multiple charges is performed using the flux injected from the first charge into the tundish.

The flux F is provided in a solid state or a powder state, and when the flux F is introduced into the molten steel M in the tundish 100, the flux F is melted by the heat of the molten steel. Accordingly, a molten flux layer or a liquid flux layer having a predetermined thickness is formed on the molten steel M. Here, the molten flux layer or the liquid flux layer may be referred to as a flux pool (FP). In this way, when the flux F is melted to prepare the liquid flux pool FP, the inclusions in the molten steel M are dissolved and absorbed into the flux pool FP, thereby removing the inclusions from the molten steel. That is, when the solid flux F is melted to form a liquid flux pool FP, inclusions in the molten steel M can be dissolved into the flux pool FP and removed.

The inclusion absorption capacity of the flux pool FP is improved as solubility of inclusions of the flux pool FP increases. Here, the solubility of inclusions in the flux pool FP means the degree to which the flux pool FP can dissolve inclusions.

In order for the flux pool FP to have sufficient inclusion solubility, it is necessary to ensure a low viscosity of the flux pool FP. That is, when the viscosity of the flux pool FP is sufficiently low, solubility of inclusions in the flux pool FP is improved.

As described above, the flux F input to the tundish 100 is in a solid or powder state, and the flux F input into the molten steel M in the tundish 100 must be melted to dissolve or absorb inclusions. do. It is advantageous to remove inclusions as the injected solid flux F melts faster or the flux pool FP is formed faster.

However, if the melting point of the solid flux (F) is high, a long time is required until the flux (F) is melted when the flux (F) is introduced into the tundish (100). Accordingly, immediately after the flux F is added or at the beginning of casting, as casting is performed in a state in which the flux is melted or the flux pool is insufficient, the inclusions in the molten steel cannot be sufficiently removed, which may cause defects. Therefore, for rapid melting of the flux, it is necessary to provide a flux having a low melting point.

In addition, although the tundish 100 is covered with the cover member 140 , contact with the atmosphere cannot be completely blocked. Accordingly, the molten steel M in the tundish 100 may be oxidized (hereinafter, re-oxidized) by contact with the atmosphere, and thus a large amount of inclusions may be generated in the molten steel. That is, oxygen in the atmosphere and an oxidizing component in molten steel, for example, aluminum (Al) react, so that a large amount of inclusions such as _{aluminum oxide (Al 2} O _{3 ) may be generated.} These inclusions become a factor causing surface and internal defects of the cast steel. And, since a separate heat source is not provided to the tundish 100 , the temperature of the molten steel accommodated in the tundish 100 is gradually decreased, and thus the molten steel may be solidified in the tundish 100 . And, the immersion nozzle 400 for supplying the molten steel to the mold 300 may be blocked by the temperature drop and solidification of the molten steel, and in this case, the operation should be stopped.

Accordingly, the flux F is also introduced into the tundish 100 for the purpose of suppressing or preventing the reoxidation and temperature drop of the molten steel in the tundish 100 . That is, as the flux pool FP covers the molten steel M in the tundish 100, contact between the molten steel M and the atmosphere and the temperature drop of the molten steel can be suppressed or prevented.

However, if the melting point of the solid flux is high, a long time is required until the flux is melted when the flux is introduced into the tundish. Accordingly, the flux of the flux becomes insufficient at the initial stage of casting in which the flux is added, and thus the flux pool may not be formed in some areas of the molten steel molten steel. Accordingly, a portion of the molten steel molten steel surface may be exposed to the atmosphere. In addition, the direct contact between the atmosphere and the molten steel can be suppressed only when the flux is sufficiently melted and the thickness of the flux pool is 10 mm or more. However, since the flux of the flux is insufficient at the initial stage of casting in which the flux is added, the thickness of the flux cannot be 10 mm or more. Accordingly, the effect of inhibiting the reoxidation of the molten steel by the flux pool at the initial stage of casting is low. Therefore, it is necessary to provide a flux having a low melting point in order to inhibit the reoxidation of molten steel and decrease in temperature.

In addition, when the viscosity of the molten flux, that is, the flux pool FP is high, the flux is not spread widely or evenly on the molten steel M molten steel surface. In other words, since the flux pool FP is not evenly formed on the molten steel M, and is not formed in some areas, a portion of the molten steel M may be exposed. In this case, the molten steel is reoxidized through the exposed hot water surface. Therefore, it is necessary to ensure a low viscosity of the plus pool in order to prevent reoxidation of the molten steel.

Hereinafter, the components of the flux according to the embodiments of the present invention will be described in detail.

Flux F according to embodiments of the present invention includes calcium oxide (CaO), aluminum oxide (Al ₂ O ₃ ), boron oxide (B ₂ O ₃ ), and silicon oxide (SiO ₂ ), and other unavoidable impurities. may be included. In addition, the flux may further include at least one of _{sodium oxide (Na 2} O) and calcium fluoride (CaF _{2 ).}

Here, silicon oxide (SiO ₂ ) is not an artificially added component to prepare the flux (F). _{A raw material containing aluminum oxide (Al 2} O ₃ ) and a raw material containing calcium oxide (CaO), which are mixed for the production of the flux (F), _{each contain silicon oxide (SiO 2} ), so that silicon oxide (SiO 2 ) is contained in the flux ₂ ) will be included.

As described above, the flux may _{further include at least one of sodium oxide (Na 2} O) and calcium fluoride (CaF ₂ ). Hereinafter, for convenience of description, sodium oxide (Na ₂ O) and calcium fluoride ( CaF ₂ ) is divided into different fluxes depending on whether each is included or not.

That is, the flux according to the first embodiment containing _{boron oxide (B 2} O ₃ ) and not including sodium oxide (Na ₂ O) and calcium fluoride (CaF _{2 ), boron oxide (B 2} O ₃ ) And sodium oxide (Na ₂ O), including the _{flux not containing calcium fluoride (CaF 2} ), the flux according to the second embodiment, boron oxide (B ₂ O ₃ ) and calcium fluoride (CaF ₂ ) and , the flux containing no sodium oxide (Na ₂ O), the flux according to the third embodiment, boron oxide (B ₂ O ₃ ), sodium oxide (Na ₂ O), and the flux containing all of _{calcium fluoride (CaF 2 )} is called the flux according to the fourth embodiment.

division	CaO	Al 2 O 3	SiO 2	B 2 O 3	Na 2 O	CaF 2
first embodiment	○	○	○	○	X	X
second embodiment	○	○	○	○	○	X
third embodiment	○	○	○	○	X	○
4th embodiment	○	○	○	○	○	○

Referring back to Table 1, the flux according to the first embodiment includes calcium oxide (CaO), aluminum oxide (Al ₂ O ₃ ), boron oxide (B ₂ O ₃ ) and silicon oxide (SiO ₂ ). , the flux according to the second embodiment includes calcium oxide (CaO), aluminum oxide (Al ₂ O ₃ ), boron oxide (B ₂ O ₃ ), silicon oxide (SiO ₂ ), and sodium oxide (Na ₂ O). . In addition, the flux according to the third embodiment includes calcium oxide (CaO), aluminum oxide (Al ₂ O ₃ ), boron oxide (B ₂ O ₃ ), silicon oxide (SiO ₂ ) and calcium fluoride (CaF ₂ ), and , The flux according to the fourth embodiment is calcium oxide (CaO), aluminum oxide (Al ₂ O ₃ ), boron oxide (B ₂ O ₃ ), silicon oxide (SiO ₂ ), sodium oxide (Na ₂ O), and calcium fluoride (CaF ₂ ). The flux according to these embodiments has a low melting point of 1310° C. or less, more specifically 1250° C. or more, and 1310° C. or less. And, it is completely melted within 8 minutes, more specifically, within 6 minutes to 7.5 minutes after adding the flux.

In addition, the melting point of the flux may be 1250°C or higher and 1280°C or lower. And, the viscosity at 1400 ℃ is as low as 7 poise or less, more specifically 2 poise or more, and 7 poise or less. Also, the viscosity of the flux may be 2 poise or more and 4 poise or less. In addition, solubility or removal efficiency of inclusions of such a flux pool is higher than that of the related art.

Hereinafter, the flux according to the first embodiment will be described in detail. In describing the component content, it is described in the form of 'from the lower limit to the upper limit', which means 'above the lower limit and below the upper limit'.

The flux (F) according to the first embodiment comprises 40 wt% to 60 wt% of calcium oxide (CaO) and 25 wt% to 40 wt% of aluminum oxide (Al ₂ O) based on the total weight of the flux (F). ₃ ), 2 wt% to 10 wt% boron oxide (B ₂ O ₃ ) and 5 wt% to 10 wt% silicon oxide (SiO ₂ ). The flux (F) is, more preferably, 50 wt% to 60 wt% of calcium oxide (CaO), and 25 wt% to 34 wt% of _{aluminum oxide (Al 2} O _{3 ), based on the total weight% of the flux (F).} , boron oxide (B ₂ O ₃ ) 5 wt% to 10 wt%, silicon oxide (SiO ₂ ) 6 wt% to 9 wt% may be included.

Calcium oxide (CaO) and aluminum oxide (Al ₂ O ₃ ) are base materials constituting the tundish flux, and 40 to 60 wt% of calcium oxide (CaO) is included with respect to the total weight% of the flux (F), Aluminum oxide (Al ₂ O ₃ ) is included in an amount of 25 wt% to 40 wt%. More preferably, calcium oxide (CaO) may be included in an amount of 50 wt% to 60 wt%, and aluminum oxide (Al ₂ O ₃ ) may be included in an amount of 25 wt% to 34 wt%.

On the other hand, when calcium oxide (CaO) is out of the range of 40 wt% to 60 wt%, or aluminum oxide (Al ₂ O ₃ ) is out of the range of 25 wt% to 40 wt%, the melting point of the flux (F) and the flux pool ( There is a problem that the viscosity of FP) is high. Accordingly, the melting rate of the flux F injected into the tundish 100 is slow, the solubility of inclusions is low, and the flux pool FP is not uniformly spread over the entire molten steel slab surface, which may cause a problem that the molten steel surface is exposed. .

Silicon oxide (SiO ₂ ) is contained in the flux in an amount of 5 wt% to 10 wt%, which _{is oxidized in each of a raw material containing aluminum oxide (Al 2} O ₃ ) and a raw material containing calcium oxide (CaO) for producing the flux. This is because silicon (SiO ₂ ) is included. That is, 40 wt% to 60 wt% of calcium oxide (CaO), 25 wt% to 40 wt% of aluminum oxide (Al ₂ O ₃ ) For producing a flux containing aluminum oxide (Al ₂ O ₃ ) containing When the raw material and the raw material including calcium oxide (CaO) are mixed, 5 wt% to 10 wt% of silicon oxide (SiO ₂ ) may be included in the flux (F). _{In another example, aluminum oxide (Al 2} O ₃ ) is included to prepare a flux comprising 50% to 60% by weight of calcium oxide (CaO), 25% to 34% by weight of aluminum _{oxide (Al 2} O ₃ ) When the raw material and the raw material containing calcium oxide (CaO) are mixed, 6 wt% to 9 wt% of silicon oxide (SiO ₂ ) may be included in the flux (F).

Boron oxide (B ₂ O ₃ ) is included in an amount of 2 wt% to 10 wt% based on the total wt% of the flux (F). More preferably, boron oxide (B ₂ O ₃ ) may be included in an amount of 5 wt% to 10 wt%. Boron oxide (B ₂ O ₃ ) mainly functions to lower the melting point. However, when boron oxide (B ₂ O ₃ ) is less than 2% by weight, the effect of lowering the melting point is insignificant. Accordingly, there is a problem in that the melting point of the flux is high, and the melting rate of the flux F input to the tundish 100 is slow.

On the other hand, as _{the content of boron oxide (B 2} O ₃ ) increases, the melting point of the flux tends to decrease. And, since the flux melts faster as the melting point is lower, it is advantageous to remove inclusions in the initial stage of casting, re-oxidize the molten steel, and prevent temperature drop. And, in general, the flux input to the tundish uses the same component composition regardless of the steel type to be manufactured. However, most steel types do not specifically limit the content of boron (B) in molten steel, but when a steel type such as a thick plate is manufactured, the content of boron (B) is limited to a predetermined content or less.

Therefore, a flux containing a large amount of boron oxide (B ₂ O ₃ ) cannot be used in the manufacture of steel grades that require limited boron (B) content, such as a heavy plate. This is because boron (B) in the flux is picked up into the molten steel to increase the boron (B) content in the molten steel. In addition, when a flux is separately provided for the production of a steel type requiring boron (B) content limitation, a corresponding cost is added.

Therefore, it is necessary to provide a flux that can be used universally regardless of a steel type having no limited boron (B) content and a steel type having a limited boron (B) content. Accordingly, in the embodiment, the amount of boron oxide (B ₂ O ₃ ) is prepared to be included in an amount of 10% by weight or less based on the total weight% of the flux. On the other hand, if the boron oxide (B ₂ O ₃ ) exceeds 10% by weight, it may not be used in the manufacture of steel grades that require control of the boron (B) content, for example, a thick plate.

This flux F is provided in a powder or granular state, and the particle diameter thereof is provided to be 10 mm or less. Preferably it is provided to have a particle diameter of 0.1mm to 10mm, more preferably 0.1mm to 7mm.

On the other hand, when the particle diameter of the particles constituting the flux F exceeds 10 mm, the melting rate of the flux is slow, it may not be possible to secure a sufficient melting rate. In addition, the smaller the particle size, the higher the melting rate. However, when the particle size is too small, when the flux F is introduced into the tundish 100 or the prepared flux F is transferred, a large amount of dust is generated and is difficult to operate. difficulties may arise. Therefore, it is preferable to provide the flux to have a particle diameter of 0.1 mm to 10 mm.

The above-described flux (F) includes calcium oxide (CaO), aluminum oxide (Al ₂ O ₃ ), boron oxide (B ₂ O ₃ ), and silicon oxide (SiO ₂ ). However, the present invention is not limited thereto, and the flux F may _{further include sodium oxide (Na 2} O).

That is, the flux according to the second embodiment includes calcium oxide (CaO), aluminum oxide (Al ₂ O ₃ ), boron oxide (B ₂ O ₃ ), and silicon oxide (SiO ₂ ), and sodium oxide (Na ₂ O). ) is further included. More specifically, the flux (F) comprises 40 wt% to 60 wt% of calcium oxide (CaO), 25 wt% to 40 wt% of aluminum oxide (Al ₂ O ₃ ), and 2 wt% based on the total weight of the flux. to 10 wt% boron oxide (B ₂ O ₃ ), 5 wt% to 10 wt% silicon oxide (SiO ₂ ) and 2 wt% to 10 wt% sodium oxide (Na ₂ O). More preferably, the flux contains 50 wt% to 60 wt% of calcium oxide (CaO), 25 wt% to 34 wt% of _{aluminum oxide (Al 2} O ₃ ), and 5 wt% to 5 wt% of _{boron oxide (B 2} O _{3 )} 10 wt%, silicon oxide (SiO ₂ ) 6 wt% to 9 wt%, sodium oxide (Na ₂ O) 2 wt% to 6 wt% may be included.

Sodium oxide (Na ₂ O) is a material having an effect of lowering the melting point and viscosity, and is included in an amount of 2 wt% to 10 wt%, more preferably 2 wt% to 6 wt%, based on the total weight of the flux. However, when sodium oxide (Na ₂ O) is less than 2% by weight, the effect of lowering the melting point and viscosity by the addition of _{sodium oxide (Na 2 O) may be insignificant.}

Meanwhile, sodium oxide (Na ₂ O) may react with aluminum oxide (Al ₂ O ₃ ) in the flux to generate a high melting point crystalline phase in the form of _{Na 2} O-Al ₂ O _{3 .} In addition, the melting point of the flux F increases as the high-melting-point crystalline phase is generated or the amount thereof is increased. In addition, the higher the content of the high melting point crystal phase in the flux (F), the higher the viscosity of the flux pool (FP). Therefore, in order to suppress the high-melting crystalline phase generated by the sodium (Na ₂ O) oxidation, to adjust the content of sodium (Na ₂ O) oxidation to less than 10% by weight.

On the other hand, when sodium oxide (Na ₂ O) exceeds 10% by weight _{, the amount of reaction between sodium oxide (Na 2} O) and aluminum oxide (Al ₂ O ₃ ) is large, and a large amount of high melting point crystalline phase may be generated. And due to this, the melting point of the flux may increase, and the viscosity may increase.

The flux (F) according to the second embodiment described above includes calcium oxide (CaO), aluminum oxide (Al ₂ O ₃ ), boron oxide (B ₂ O ₃ ), silicon oxide (SiO ₂ ), and sodium oxide (Na ₂ O). ) is included. However, the present invention is not limited thereto, and the flux F _{does not include sodium oxide (Na 2} O) and further includes calcium fluoride (CaF _{2 ).}

That is, the flux F according to the third embodiment includes calcium oxide (CaO), aluminum oxide (Al ₂ O ₃ ), boron oxide (B ₂ O ₃ ) and silicon oxide (SiO ₂ ), and calcium fluoride ( CaF ₂ ) may be further included. More specifically, the flux (F) comprises 40% to 60% by weight of calcium oxide (CaO), 25% to 40% by weight of aluminum oxide (Al ₂ O ₃ ), 2% by weight, based on the total weight of the flux. to 10 wt% boron oxide (B ₂ O ₃ ), 5 wt% to 10 wt% silicon oxide (SiO ₂ ) and 2 wt% to 10 wt% calcium fluoride (CaF ₂ ). More preferably, the flux contains 50 wt% to 60 wt% of calcium oxide (CaO), 25 wt% to 34 wt% of _{aluminum oxide (Al 2} O ₃ ), and 5 wt% to 5 wt% of _{boron oxide (B 2} O _{3 )} 10 wt%, silicon oxide (SiO ₂ ) 6 wt% to 9 wt%, calcium fluoride (CaF ₂ ) 2 wt% to 6 wt% may be included.

Calcium fluoride (CaF ₂ ) is a material having an effect of lowering the melting point and viscosity, and is included in an amount of 2 wt% to 10 wt%, more preferably 2 wt% to 6 wt%, based on the total weight of the flux. However, when calcium fluoride (CaF ₂ ) is less than 2% by weight, the effect of reducing the melting point and viscosity by adding _{calcium fluoride (CaF 2 ) may be insignificant.}

On the other hand, calcium fluoride (CaF ₂ ) may react with aluminum oxide (Al ₂ O ₃ ) to generate a high melting point crystalline phase in the form of CaO-Al ₂ O ₃ , which is the melting point of the flux and the viscosity of the flux pool. is a factor that increases Therefore, in order to suppress the high-melting crystalline phase generated by a calcium fluoride (CaF _2), to adjust the content of calcium fluoride (CaF ₂₎ to below 10% by weight.

However, when calcium fluoride (CaF ₂ ) exceeds 10% by weight _{, the amount of reaction between calcium fluoride (CaF 2} ) and aluminum oxide (Al ₂ O ₃ ) is large, and a large amount of high-melting-point crystal phases may be generated. And due to this, the melting point of the flux may increase, and the viscosity may increase.

The flux F according to the second and third embodiments described above includes any one of _{sodium oxide (Na 2} O) and calcium fluoride (CaF _{2 ).} However, the present invention is not limited thereto, and the flux F may include both sodium oxide (Na ₂ O) and calcium fluoride (CaF ₂ ).

That is, the flux (F) according to the fourth embodiment includes calcium oxide (CaO), aluminum oxide (Al ₂ O ₃ ), boron oxide (B ₂ O ₃ ) and silicon oxide (SiO ₂ ), and sodium oxide ( Na ₂ O) and calcium fluoride (CaF ₂ ). More specifically, the flux (F) comprises 40 wt% to 60 wt% of calcium oxide (CaO), 25 wt% to 40 wt% of aluminum oxide (Al ₂ O ₃ ), and 2 wt% based on the total weight of the flux. to 10 wt% boron oxide (B ₂ O ₃ ), 5 wt% to 10 wt% silicon oxide (SiO ₂ ), 2 wt% to 10 wt% sodium oxide (Na ₂ O) and 2 wt% to 10 wt% % by weight of calcium fluoride (CaF ₂ ). More preferably, the flux contains 50 wt% to 60 wt% of calcium oxide (CaO), 25 wt% to 34 wt% of _{aluminum oxide (Al 2} O ₃ ), and 5 wt% to 5 wt% of _{boron oxide (B 2} O _{3 )} 10 wt%, silicon oxide (SiO ₂ ) 6 wt% to 9 wt%, sodium oxide (Na ₂ O) 2 wt% to 6 wt%, calcium fluoride (CaF ₂ ) 2 wt% to 6 wt% may be included .

The flux according to the first to fourth embodiments as described above has a low melting point of 1310° C. or less, and a viscosity at 1400° C. of 7 poise or less. In addition, the solubility of inclusions is high compared to conventional fluxes, and the absorption or removal rate of inclusions is high.

Table 1 is a table showing the component composition, melting point, viscosity, and erosion rate of the fluxes according to Experimental Examples 1 to 5. 2 is a graph showing the erosion rate of a specimen during an experiment using the flux according to Experimental Examples 1 to 5; 3 is a diagram illustrating an experimental apparatus.

The first experimental example includes calcium oxide (CaO), aluminum oxide (Al ₂ O ₃ ) and silicon oxide (SiO ₂ ) as a conventional flux, boron oxide (B ₂ O ₃ ), sodium oxide (Na ₂ O) and calcium fluoride (CaF ₂ ). And the fluxes according to the second to fifth experimental examples include calcium oxide (CaO), aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO ₂ ), and boron oxide (B ₂ O ₃ ). In addition, the fluxes according to Experimental Examples 3 to 5 further include at least one of _{sodium oxide (Na 2} O) and calcium fluoride (CaF _{2 ).}

All of the first to fifth experimental examples include 40% to 60% by weight of calcium oxide (CaO), 25% to 40% by weight of _{aluminum oxide (Al 2} O ₃ ), and 5% by weight of _{silicon oxide (SiO 2 )} to 10% by weight. And, all of the second to fifth experimental examples contain boron oxide (B ₂ O ₃ ) in an amount of 2 wt% to 10 wt%. In addition, in Experimental Examples 3 and 5, sodium oxide (Na ₂ O) is contained in an amount of 2 wt% to 10 wt%, and in Experimental Examples 4 and 5, calcium fluoride (CaF ₂ ) is contained in an amount of 2 wt% to 10 wt% included in %.

Accordingly, the second experimental example is the flux according to the first embodiment, the third experimental example is the flux according to the second embodiment, the fourth experimental example is the flux according to the third embodiment, and the fifth experimental example is the fourth embodiment. It can be described as a flux according to

division	CaO (weight%)	Al 2 O 3 (weight%)	SiO 2 (weight%)	Na 2 O (weight%)	B 2 O 3 (weight%)	CaF 2 (weight%)	Melting point (℃)	viscosity (@1400℃)	erosion rate (%/m min)
Experiment 1	56.87	37.60	5.31	0	0	0	1371	23.7	0.536
2nd Experimental Example	60.00	29.51	5.32	0	5.09	0	1271	3.01	0.918
3rd Experimental Example	55.54	31.64	5.10	2.59	5.12	0	1303	3.5	1.457
4th embodiment	57.18	26.62	5.06	0	5.43	5.71	1279	6.43	0.868
Experiment 5	53.77	28.24	5.35	2.11	5.37	5.15	1283	2.19	1.563

Viscosity is measured by heating each of the fluxes according to Experimental Examples 1 to 5 to a temperature of 1400°C, and measuring the flux at a temperature of 1400°C with a viscometer. And, the erosion rate is a result obtained by an experiment using the experimental apparatus shown in FIG. 3 . First, an experimental apparatus will be described with reference to FIG. 3 .

Referring to FIG. 3 , the experimental apparatus 10 is a tube 11 having an internal space, a crucible 12 that is installed inside the tube 11 and the flux F can be accommodated, and the crucible 12 is heated. The heater 13, supporting the specimen S so that the lower part of the specimen S can be inserted into the crucible 12, and measuring the temperature of the rotatable rotating body 14 and the crucible 12 It includes a thermometer (15).

The tube 11 may be made of a material including quartz. The heater 13 may be installed to surround the outer circumferential surface of the tube 11 from the outside of the tube 11 . Here, the heater 13 may be a means including a heating wire heated by a resistance heating method. The thermometer 15 may be installed such that at least a part thereof is positioned inside the tube 11 so as to be positioned at the lower part of the crucible. Such a thermometer 15 may be, for example, a thermocouple.

The specimen (S) is prepared with the same components as the inclusions in the molten steel, and the specimen (S) used for this experiment is made of aluminum oxide (Al ₂ O ₃ ).

For the experiment, the flux F is charged into the crucible 12 and the heater is operated to melt the flux. Accordingly, the flux pool FP is provided in the crucible. When the flux pool FP is formed, the rotating body 14 is lowered to deposit the lower portion of the specimen S with the flux pool FP. Then, the specimen S is rotated for a predetermined time using the rotating body 14 .

These experiments were conducted separately using each of the fluxes according to Experimental Examples 1 to 5. In addition, the amount of flux injected into the crucible 12 for each experiment, the depth at which the specimen S is immersed into the flux pool FP, immersion time, rotation time, and rotation speed were all the same. And, the specimen S used for each experiment has the same composition, size, and mass.

The erosion rate can be calculated through the difference between the weight of the specimen (S) before immersion into the flux pool (FP) (the initial weight of the specimen) and the weight of the specimen (S) after the experiment is finished. More specifically,

Measure the weight of the specimen (S) before the start of the experiment (the initial weight of the specimen), and measure the weight of the specimen (S) after the experiment is finished. Then, the difference between the initial weight of the specimen (S) and the weight of the specimen (S) after the end of the experiment is calculated. Here, the calculated weight is a weight reduced by dissolving into the flux pool FP (hereinafter, reduced weight).

Then, when the reduced weight is divided by the initial weight of the specimen (S) (reduced weight / initial weight of the specimen), the weight reduction ratio is calculated. Also, by multiplying the calculated weight reduction ratio by 100%, a weight reduction ratio (%) in % may be calculated. Then, if the calculated weight reduction ratio (%) is divided by the total time (min) that the specimen (S) is immersed in the flux pool (FP), the weight reduction ratio per hour, for example, per minute (min) (%/min) is It is calculated, and it is defined as the erosion rate (%/min).

Referring to Table 1, the oxide of boron (B ₂ O ₃₎ The second to fifth experiment example of the oxidation of boron (B ₂ O ₃₎ a low melting point and viscosity as compared to the first experimental example that does not contain include, erosion rates two high. That is, in the first experimental example, the melting point is as high as 1360° C. or higher, and the viscosity is as high as 23 poise or more. In contrast, in Experimental Examples 2 to 5, the melting point was as low as 1310° C. or less, and the viscosity was as low as 7 poise or less.

In addition, when the erosion rate is compared, the first experimental example is as low as 0.6 or less, but the second to fifth experimental examples are as high as 0.8 or more.

Here, the specimen (S) is made of the same material as the inclusions, and since the specimen (S) is melted into the flux pool (FP) in the crucible and the weight of the specimen is reduced, the higher the calculated erosion rate, the more the flux pool is attached to the inclusions. It can be interpreted as having high solubility or inclusion removal efficiency. Accordingly, it can be seen that the flux pools generated by the fluxes according to Experimental Examples 2 to 5 have higher inclusion solubility and inclusion removal efficiency than in Experimental Example 1, respectively.

2 is a graph showing the weight reduction ratio of the specimen according to the time immersed in the flux, as described above. That is, it is shown in FIG. 2 by accumulatively calculating the reduced weight of the specimen with the lapse of time immersed in the flux, dividing it by the initial weight of the specimen and displaying the ratio.

Referring to the first experimental example in FIG. 2 as an example, when the time that the specimen is immersed in the flux is 10 minutes, about 6% of the initial weight of the specimen is reduced. In addition, when the specimen was immersed in the flux for 20 minutes, about 9% of the initial weight of the specimen was reduced. And through this change in the weight reduction ratio over time, the weight reduction rate can be known. Here, since the weight reduction of the specimen is caused by dissolution, that is, erosion of the specimen into the flux pool, the weight reduction rate in FIG. 2 can be interpreted as the erosion rate of the specimen.

Referring to FIG. 2 , the erosion rate of Experimental Examples 2 to 5 is faster than that of Experimental Example 1 . This means that in the flux pool formed by the flux according to Experimental Examples 2 to 5, the dissolution rate of inclusions is faster than that of Experimental Example 1.

As such, the fluxes according to Experimental Examples 2 to 5 have lower viscosity and higher erosion rate and erosion rate than those of Experimental Example 1, respectively. Therefore, compared to the first experimental example, when casting using the flux according to the second to fifth experimental examples, the efficiency of removing the inclusions by dissolving and removing the inclusions of the molten steel is improved. Therefore, it is possible to manufacture a slab in which the occurrence of defects due to inclusions is suppressed or prevented, and the quality of the slab can be improved.

In addition, the melting points of the fluxes according to Experimental Examples 2 to 5 are lower than those of Experimental Example 1. Therefore, the melting rate of the fluxes according to Experimental Examples 2 to 5 is higher than that of Experimental Example 1 . Accordingly, when using the fluxes according to Experimental Examples 2 to 5 compared to Experiment 1, it is possible to generate a relatively large amount or thick flux pool within a short time. Therefore, as the flux pool FP of a sufficient amount and thickness is formed in the initial stage of casting, reoxidation and temperature drop in the initial stage of casting can be more effectively prevented.

Returning to Table 1 and FIG. 2 and comparing the second to fifth experimental examples, the erosion rates of the third and fifth experimental examples are 1.4 or more, which is higher than that of the second and fourth experimental examples (1 or less), and the third and fourth experimental examples The erosion rate of Experiment 5 was faster than that of Experiments 2 and 4. From this, it can be seen that the flux pool formed by the flux according to Experimental Examples 3 and 5 has higher inclusion solubility or inclusion removal efficiency than in Experimental Examples 2 and 4.

In other words, boron oxide (B ₂ O ₃ ), sodium oxide (Na ₂ O) and calcium fluoride (CaF ₂ ), a flux including boron oxide (B ₂ O ₃ ) (Experiment 2), Compared to the case of using a flux containing boron oxide (B ₂ O ₃ ) and calcium fluoride (CaF ₂ ) (Experiment 4), flux containing boron oxide (B ₂ O ₃ ) and sodium oxide (Na ₂ O) (Experiment 3), boron oxide (B ₂ O ₃ ), sodium oxide (Na ₂ O) and calcium fluoride (CaF ₂ ) when using a flux (Example 5) including all inclusions removal efficiency in molten steel It can be seen that this is improved.

In addition, the third Comparing the experimental examples in the fifth experimental example, oxide of boron (B ₂ O ₃₎ oxide and boron compared to using a flux (third experimental example) containing sodium (Na ₂ O) oxide (B ₂ O ₃ ), sodium oxide (Na ₂ O), and calcium fluoride (CaF ₂ ) It can be seen that when a flux containing all of (Experiment 5) is used, the efficiency of removing inclusions in molten steel is improved.

4 is a photograph showing the molten state of the flux over time when the flux according to Experimental Example 1 and the flux according to Experimental Example 3 of Table 1 were introduced into a tundish. 5 is a diagram illustrating the measurement of oxygen content (ppm) in the molten steel in the mold at each charge when casting is continuously performed seven times using the flux according to the first experimental example and the flux according to the third experimental example, respectively; is a result

For the experiment, the fluxes according to the first and third experimental examples were introduced into the tundish 100 of the actual casting facility as shown in FIG. 1 . That is, the flux according to the first experimental example is input to the central region 111a and the first outer region 111b of the tundish 100, and the flux according to the third experimental example is input to the second outer region 111c. did.

A total of 70 tons of molten steel is supplied into the tundish 100, and the fluxes according to the first and third experimental examples were added at the time when the molten steel reached 30 tons in the tundish. At this time, the amount of flux injected into the central region 111a, the first outer region 111b, and the second outer region 111c was equal to 130 kg.

Since the inside of the tundish 100 is separated by the first and second upper weirs 120a and 120b, the flux injected into the central region 111a and the first and second outer regions 111b and 111c, respectively, is mutually exclusive. do not mix

After the input of the flux into the tundish 100 is completed, the upper side of the first outer region 111b to which the flux according to the first experimental example is input and the upper side of the second outer region 111c to which the flux according to the third experimental example is input, respectively photo was taken in More specifically, a photograph was taken using a hole provided for sampling in the cover member 140 . At this time, pictures were taken over time, and they are summarized as shown in FIG. 4 .

In addition, as described above, the flux according to the first experimental example was applied to the central region 111a and the first outer region 111b of the tundish 100 and the flux according to the third experimental example was applied to the second outer region 111c. When the casting was continuously carried out seven times by input, the oxygen content (ppm) in the molten steel in the mold 300 was measured at each charge time. That is, the oxygen content was measured by sampling each of the molten steel M in the first mold 300a and the molten steel M in the second mold 300b at each charge time, and it is summarized as shown in FIG. 5 .

Here, the molten steel in the first mold 300a is the molten steel covered by the flux according to the first experimental example in the tundish 100, and the molten steel in the second mold 300b is in the tundish 100. The molten steel was covered by the flux according to the third experimental example.

Referring to FIG. 4 , the flux (Example 1) injected into the first outer region 111b was completely melted at about 14 minutes after being injected. On the other hand, it can be seen that the flux injected into the second outer region 111c (the third experimental example) is completely melted in about 6.9 minutes after being injected. From this, it can be seen that the flux according to Experimental Example 3 has a lower melting point and a melting rate of about twice that of the flux according to Experimental Example 1, respectively.

In addition, referring to FIG. 5 , as the charge order increases, the oxygen (O) content in the molten steel tends to decrease, and it can be seen that the third experimental example has a lower oxygen (O) content than the first experimental example. .

Meanwhile, since the inclusions in the molten steel exist in the form of metal oxides, the content of inclusions in the molten steel can be relatively known through the oxygen (O) content in the molten steel. That is, when the oxygen (O) content in the molten steel is low, it can be interpreted that the inclusion content in the molten steel is relatively low compared to when it is high. Accordingly, it can be seen from FIG. 5 that the efficiency of removing inclusions in the molten steel is higher when the flux according to the third experimental example is used compared to the first experimental example.

6 is a photograph showing the state of the flux in the tundish according to the charge when casting the charge six times continuously using the flux according to the first experimental example and the flux according to the third experimental example, respectively; am. 7 shows a tundish at the second, fourth, and sixth charges when casting of the sixth charge is continuously performed using the flux according to the first experimental example and the flux according to the third experimental example, respectively; This is the result of measuring the melting point of my flux. 8 is a result of measuring the oxygen content (ppm) in the molten steel in the mold for each charge when the casting of six charges is continuously performed using the flux according to the first experimental example and the flux according to the third experimental example, respectively.

For the experiment, the flux was introduced into the tundish 100 of the actual casting facility as shown in FIG. 1 , and casting was continuously performed six times. At this time, the flux according to the first experimental example was injected into all of the central region 111a and the first and second outer regions 111b and 111c of the tundish 100, and six charge castings were continuously performed. Also, in the same manner, the flux according to the third experimental example was injected into all of the central region 111a and the first and second outer regions 111b and 111c of the tundish, and casting of the charge six times was continuously performed.

A total of 70 tons of molten steel was supplied into the tundish, and flux was added when the molten steel reached 30 tons in the tundish. And, the input amount of the flux according to the first and third experimental examples was the same as 130 kg.

In addition, when the casting of a plurality of charges is continuously performed during the actual casting operation, the chaff is input to keep the molten steel (M) in the tundish. Accordingly, even during the experiment, each time the ladle 200 is replaced or a new charge is started, the rice husk was put into the tundish 100 .

Casting of the charge six times is continuously performed using the fluxes according to the first and third experimental examples thus added. At this time, a photo was taken from the upper side of the central area 111a of the tundish 100 at each charge from the second to the sixth charge, and it is summarized as shown in FIG. 6 .

And, while continuous casting of the sixth charge was performed, the flux in the tundish was sampled at the second, fourth, and sixth charges to measure the melting point, and FIG. 7 is a summary of these.

In addition, during continuous casting of six charges, the oxygen content (ppm) in the molten steel in the mold was measured at each charge from the second charge to the sixth charge, and FIG. 8 shows the results.

Referring to the photo of the third charge in the first experimental example of FIG. 6 , there is a relatively high saturation or dark portion, which is a portion where the flux pool is solidified. Also, compared to the third charge, the overall saturation is higher or darker in the fourth, fifth, and sixth charges. This is because the solidified area of the flux pool in the fourth, fifth, and sixth charges is enlarged (or increased) compared to the third charge.

In addition, the solidification of the flux can be known by not only the chroma or contrast as described above, but also grasping the roughness of the surface with the naked eye rather than a photograph. When explaining the third charge of the first experimental example as an example, the partially solidified part has a rough surface like a stone, but the rest of the region is not. Accordingly, by visually grasping the surface roughness, it is possible to know whether the slag pool is solidified or the solidified area.

In the case of the first experimental example, the solidification phenomenon of the flux starts to occur at the third charge. And from the fourth charge, the solidified area increases. The solidification of the flux is because the filler and the rice husks of the ladle are added every time the ladle is replaced, and the melting point of the flux in the tundish is increased.

On the other hand, in the case of the third experimental example, solidification did not occur even at the sixth charge. This is because the flux according to the third experimental example has a lower melting point than that of the first experimental example, and thus the solidification phenomenon is alleviated compared to that of the first experimental example. Therefore, the flux according to Experimental Example 3 starts to solidify later or does not solidify compared to Experimental Example 1. Accordingly, it is possible to increase the number of charges used or the duration of use of the flux.

The solidification and solidification area of each of the first and third experimental examples as described above are determined by chroma or contrast in the photo of FIG. 6 , or by an operator visually grasping the surface roughness.

When the flux solidifies or the amount of solidification increases, the melting point of the flux injected into the tundish increases. Referring to FIG. 7 , the melting point of the first experimental example exceeds 1400° C. during the fourth charge, while the third experimental example does not exceed 1350° C.

From this, it can be seen that even if the same amount of ladle filler and rice husk are added every time the ladle is replaced, the melting point of the flux in the tundish can be maintained lower than in the first embodiment using the flux according to the third embodiment.

In addition, when comparing the oxygen (O) content (ppm) in the molten steel in the mold according to each charge with reference to FIG. 8 , the third experimental example is lower than the first experimental example. And, in the third experimental example, the oxygen content of the molten steel in the mold from the first charge to the casting of the last charge is 20 ppm or less. Through this, it can be seen that the inclusion removal efficiency is higher when the flux according to the third experimental example is used compared to the first experimental example.

In the flux or the flux pool formed by the flux according to the embodiments of the present invention, solubility of inclusions or inclusion removal efficiency is higher than in the related art. Accordingly, compared to the prior art, it is possible to manufacture a cast slab in which the occurrence of defects due to inclusions is suppressed or prevented, and the quality of the slab can be improved.

In addition, since the melting point of the flux according to the embodiments is lower than that of the prior art, the melting rate is high. Accordingly, when using the flux according to the embodiments, it is possible to melt a large amount of flux within a shorter time than in the related art. Due to this, as a sufficient amount and thickness of the flux pool is formed in the initial stage of casting, reoxidation and temperature drop in the initial stage of casting can be more effectively prevented.

In addition, since the melting point of the flux is low, it is possible to suppress or prevent the solidification of the flux even when casting of a plurality of charges is continuously performed. Therefore, it is possible to manufacture a slab in which the occurrence of defects due to inclusions is suppressed or prevented from the initial stage to the end of continuous casting, and the quality of the slab can be improved.

According to the flux according to the embodiments of the present invention, solubility of inclusions or efficiency of removing inclusions is higher than in the related art. Accordingly, compared to the prior art, it is possible to manufacture a cast slab in which the occurrence of defects due to inclusions is suppressed or prevented, and the quality of the slab can be improved.

In addition, since the melting point of the flux according to the embodiments is lower than that of the prior art, the melting rate is high. Accordingly, when using the flux according to the embodiments, it is possible to melt a large amount of flux within a shorter time than in the related art. Due to this, as a sufficient amount and thickness of the flux pool is formed in the initial stage of casting, reoxidation and temperature drop in the initial stage of casting can be more effectively prevented.

Claims (14)

1. As a tundish flux injected into a tundish at the time of casting,

   Based on the total weight%, calcium oxide (CaO) 40% to 60% by weight, aluminum oxide (Al ₂ O ₃ ) 25% to 40% by weight, silicon oxide (SiO ₂ ) 5% to 10% by weight %, boron oxide (B ₂ O ₃ ) Tundish flux containing 2% to 10% by weight and unavoidable impurities.
2. The method according to claim 1,

   The tundish flux comprising 5 to 10 wt% of the _{boron oxide (B 2} O ₃ ) based on the total weight of the tundish flux.
3. The method according to claim 1,

   The tundish flux further comprises at least one of 2 wt% to 10 wt% sodium oxide (Na ₂ O) and 2 wt% to 10 wt% calcium fluoride (CaF _{2 ).}
4. 3. The method according to claim 2,

   The tundish flux further comprises at least one of 2 wt% to 6 wt% sodium oxide (Na ₂ O) and 2 wt% to 6 wt% calcium fluoride (CaF _{2 ).}
5. 5. The method according to claim 4,

   Based on the total weight % of the tundish flux, the calcium oxide (CaO) is 50% to 60% by weight, the aluminum oxide (Al ₂ O ₃ ) is 25% to 34% by weight, the silicon oxide (SiO ₂ ) A tundish flux containing 6% to 9% by weight of
6. 6. The method according to any one of claims 1 to 5,

   The melting point of the tundish flux is 1310 ℃ or less tundish flux.
7. 7. The method of claim 6,

   The melting point of the tundish flux is 1280 ℃ or less tundish flux.
8. 6. The method according to any one of claims 1 to 5,

   The tundish flux is a tundish flux having a viscosity of 7 poise or less at 1400°C.
9. 9. The method of claim 8,

   The tundish flux is a tundish flux having a viscosity of 2 poise or more and 4 poise or less at 1400°C.
10. The process of preparing the tundish flux according to any one of claims 1 to 5;

    The process of supplying molten steel to the tundish;

    inputting the tundish flux into the tundish to form a flux pool on the molten steel molten steel surface in the tundish; and

    supplying the molten steel of the tundish to a mold, and solidifying the molten steel in the mold to cast a slab;

    A casting method comprising a.
11. 11. The method of claim 10,

    By replacing and connecting the ladle in which the molten steel is accommodated to the tundish a plurality of times, casting of multiple charges is performed to continuously supply the molten steel to the tundish,

    During the casting of the plurality of charges, the tundish flux is injected into the tundish in the first charge casting for supplying the molten steel of the first ladle to the tundish,

    A casting method wherein the melting point of the flux pool in the tundish is 1400° C. or less during the last charge casting among the multiple-charge casting.
12. 12. The method of claim 11,

    A casting method in which all of the tundish flux injected into the tundish is melted within 8 minutes.
13. 12. The method of claim 11,

    A casting method in which the thickness of the flux pool in the tundish is 10 mm or more at the time of the first charge casting.
14. 12. The method of claim 11,

    A casting method wherein the molten steel oxygen content in the mold is 20 ppm or less from the first charge to the last charge casting during the multi-charge casting.

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