JP2023518735A - Tundish flux and casting method using the same - Google Patents

Abstract

A tundish flux with improved inclusion solubility and a casting method using the same are provided. Also provided is a tundish flux capable of suppressing or preventing reoxidation of molten steel and the resulting formation of inclusions, and a casting method using the same. SOLUTION: The tundish flux of the present invention contains 40% to 60% by weight of calcium oxide (CaO), 25% to 40% by weight of aluminum oxide (Al2O3), and 25% to 40% by weight of silicon oxide. It contains 5 to 10% by weight of (SiO2), 2 to 10% by weight of boron oxide (B2O3), and unavoidable impurities. Therefore, according to the flux according to the embodiment of the present invention, the solubility of inclusions or the removal efficiency of inclusions is higher than conventional ones. As a result, it is possible to manufacture a slab in which the occurrence of defects due to inclusions is suppressed or prevented as compared with the conventional method, and the quality of the slab can be improved. [Selection drawing] Fig. 1

Description

TECHNICAL FIELD 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 cast slabs and a casting method using the same.

The casting process is a process of injecting molten steel in a tundish into a mold and extracting the semi-solidified slab in the mold to produce slabs, blooms, billets, beam blanks, and other shapes of various slabs.

During such a casting process, the surface of the molten steel in the tundish is covered with flux in order to remove inclusions in the molten steel in the tundish, prevent the formation of inclusions due to reoxidation of the molten steel, and reduce the temperature of the molten steel. do.

The flux is prepared in a solid phase or powder state, and is put into a tundish containing a predetermined amount of molten steel at the beginning of casting. When the flux is put into the tundish, it is melted by the heat of the molten steel. Therefore, the molten flux, that is, the flux pool is formed on the surface of the molten steel with a predetermined thickness. That is, the molten steel surface is covered with the flux pool. If a flux pool is formed on the surface of the molten steel, inclusions in the molten steel are dissolved and absorbed by the flux pool, thereby removing the inclusions in the molten steel. In addition, since the flux pool blocks the contact between the atmosphere and the molten steel, it suppresses the reoxidation of the molten steel and the decrease in temperature.

On the other hand, the solid-phase flux supplied to the tundish is melted only after a predetermined time has elapsed. However, since the time for melting the introduced flux is insufficient at the initial stage of casting, the amount of generated flux pool is insufficient and the thickness thereof is thin. For this reason, the flux pool formed in the initial stage of casting has low solubility in inclusions, and has a weak shielding effect from the atmosphere. As a result, the removal rate of inclusions in the molten steel is low, and a large amount of inclusions are generated due to reoxidation of the molten steel, resulting in defects due to the inclusions in the molten steel on the surface or inside of the slab.

Korean Patent No. 1233836

An object of the present invention is to provide a tundish flux with improved inclusion solubility and a casting method using the same.

Another object of the present invention is to provide a tundish flux capable of suppressing or preventing the reoxidation of molten steel and the resulting formation of inclusions, and a casting method using the same.

The present invention provides a tundish flux to be put into a tundish during casting, which contains 40% to 60% by weight of calcium oxide (CaO) and 40% to 60% by weight of aluminum oxide (Al ₂ O ₃ ) of 25% 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 the remainder from unavoidable impurities. Become.

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

The tundish flux may further contain at least one of 2% to 10% by weight of sodium oxide (Na ₂ O) and 2% to 10% by weight of calcium fluoride (CaF ₂ ). good.

The tundish flux may further contain at least one of 2% to 6% by weight of sodium oxide (Na ₂ O) and 2% to 6% by weight of calcium fluoride (CaF ₂ ). good.

50% to 60% by weight of the calcium oxide (CaO), 25% to 34% by weight of the aluminum oxide (Al ₂ O ₃ ), and the silicon oxide ( SiO ₂ ) may be included in an amount of 6% to 9% by weight.

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

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

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.

The casting method of the present invention includes the steps of preparing a tundish flux, supplying molten steel to the tundish, and introducing the tundish flux into the tundish to raise the molten steel surface in the tundish. forming a flux pool thereon; and feeding molten steel in the tundish into a mold and solidifying the molten steel in the mold to cast a slab.

A ladle containing molten steel is replaced and connected to the tundish a plurality of times, and a plurality of charges are cast to continuously supply molten steel to the tundish. In the casting of the first charge in which the molten steel in the ladle is supplied to the tundish, the tundish flux is put into the tundish, and the tundish flux is injected into the tundish when casting the last charge out of the plurality of charge castings. The melting point of the flux pool is 1400° C. or less.

The tundish flux put into the tundish is completely melted within 8 minutes.

The flux pool in the tundish has a thickness of 10 mm or more when casting the first charge.

Among the plurality of charge castings, the oxygen content of the molten steel in the mold from the first charge to the last charge casting is 20 ppm or less.

According to the present invention, the solubility of inclusions or the removal efficiency of inclusions is higher than conventionally. As a result, it is possible to manufacture a slab in which the occurrence of defects due to inclusions is suppressed or prevented as compared with the conventional method, and the quality of the slab can be improved.

Moreover, since the melting point of the flux according to the embodiment is lower than that of the conventional flux, the melting speed is high. Therefore, when the flux according to the embodiment is used, a large amount of flux can be melted within a short period of time as compared with conventional methods. As a result, a sufficient amount and thickness of the flux pool is formed at the initial stage of casting, thereby more effectively preventing reoxidation and temperature drop at the initial stage of casting.

Further, since the melting point of the flux is low, even if a plurality of charges are continuously cast, the solidification of the flux can be suppressed or prevented. Therefore, it is possible to manufacture a slab in which the occurrence of defects due to inclusions is suppressed or prevented from the beginning to the end of continuous casting, and the quality of the slab can be improved.

1 shows a typical casting facility; FIG. FIG. 5 is a graph showing erosion rates of specimens during experiments using flux according to first to fifth experimental examples; FIG. It is a figure which shows an experimental apparatus. FIG. 10 is a photograph of 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 put into a tundish; FIG. The oxygen content (ppm) in the molten steel in the mold for 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. is the result of measuring When six charges of casting were continuously performed using the flux according to the first experimental example and the flux according to the third experimental example, the state of the flux in the tundish was photographed according to the order of the charges. It is a photograph shown. When casting six charges in succession using the flux according to the first experimental example and the flux according to the third experimental example, respectively, It is the result of measuring the melting point of the flux. When six charges are continuously cast using the flux according to the first experimental example and the flux according to the third experimental example, the oxygen content (ppm) in the molten steel in the mold for each charge is These are the results of measurements.

Hereinafter, embodiments of the present invention will be described in more detail based on the accompanying drawings. The present invention, however, is not intended to be limited to the embodiments disclosed below, but may be embodied in a variety of different forms and merely these embodiments should provide a complete disclosure of the invention and general knowledge. It is provided to fully inform the owner of the scope of the invention. The drawings may be exaggerated to illustrate embodiments of the present invention, wherein like reference numerals refer to like elements.

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

Before describing the tundish flux according to the embodiment of the present invention, first, a general casting method to which the tundish flux is applied will be described.

FIG. 1 shows a typical casting facility.

In the casting process, when the molten steel M received in the tundish 100 flows into the mold 300 through the submerged nozzle 400, the molten steel M begins to solidify in the mold 300 being cooled to reach a semi-solidified state as an intermediate product. It is a process in which a slab is obtained. The semi-solidified cast piece withdrawn from the mold 300 is shaped and further cooled while moving along a plurality of segments (not shown) arranged side by side in one direction below the mold 300 to complete the process. It becomes a solidified slab.

Tundish 100 is provided with molten steel from ladle 200 and feeds it into mold 300 . For this purpose, the ladle 200 is moved to the upper side of the tundish 100, and a nozzle (hereinafter referred to as a ladle nozzle 220) connected to the lower part of the ladle 200, for example, a shroud nozzle, is placed in the tundish. It should be located inside 100. Therefore, the molten steel in the ladle 200 is supplied to the tundish 100 via the ladle nozzle 220 and then to the mold 300 via the submerged nozzle 400 .

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

In addition, the tundish 100 includes an upper weir 120 disposed on the upper part of the main body 110 so as to be positioned outside the position where the ladle nozzle 220 is fitted, and the main body so as to be positioned outside the upper weir 120 . There may also be a weir 130 disposed on the bottom surface within 110 .

For example, when two molds (hereinafter referred to as first and second molds 300: 300a, 300b) are placed below the tundish 100, when the ladle 200 is positioned above the tundish 100, the ladle A nozzle 220 is positioned between the first mold 300a and the second mold 300b. Then, the upper weirs are provided in pairs, and the pair of upper weirs (hereinafter, first and second upper weirs 120: 120a, 120b) are located in the main body 110 so as to be positioned on both sides of the ladle nozzle 220. may be connected to the top of the At this time, the lower ends of the first and second upper weirs 120 a and 120 b are arranged away from the bottom surface inside the main body 110 .

In addition, the lower weirs 130 may also be provided in pairs, and the pair of lower weirs (hereinafter referred to as first and second lower weirs 130: 130a, 130b) is a submerged nozzle connecting the tundish 100 and the mold. You may arrange|position so that it may be located between weirs. That is, the first lower dam 130a is positioned between the first submerged nozzle 400a connecting the tundish 100 and the first mold 300a and the first upper dam 120a, and the tundish 100 and the second mold 300b The second lower weir 130b is positioned between the second submerged nozzle 400b and the second upper weir 120b.

Further, the vertical extension length of the upper dam 120 may be longer than the extension length of the lower dam 130 . The lower end of the upper weir 120 is positioned lower than the upper end of the lower weir 130 .

The inner space of the tundish 100 or the main body 110 is a central region 111a which is a space between the first upper dam 120a and the second upper dam 120b, and a space located outside one side of the central region 111a. It may be partitioned 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 the space between one side wall in the main body 110 and the first upper weir 120a, and the second outer region 111c is the space between the other side wall in the main body 110 and the first upper dam 120a. can be described as the space between the two upper weirs 120b. According to such a tundish 100, part of the molten steel M supplied to the central region 111a in the tundish 100 through the ladle nozzle 220 is distributed between the first upper weir 120a and the first lower weir 130a. and moves to the first outer region 111b via the passage between the second upper dam 120b and the second lower dam 130b. The molten steel moved to the first and second outer regions 111b, 111c is supplied to the first and second molds 300a, 300b through the first and second submerged nozzles 400a, 400b.

As described above, the tundish 100 is supplied with the molten steel M from the ladle 200. Hereinafter, the process of supplying the molten steel M from the ladle 200 to the tundish 100 will be briefly described. The bottom of the ladle 200 is provided with a discharge port 210 through which the molten steel M is discharged, and the discharge port 210 contains a filler containing metal oxides such as chromium oxide and silicon oxide. filled. The filler is sintered by the heat of the molten steel M contained in the ladle 200, thereby closing the outlet 210 with the sintered filler. In this state, when the gate 221 provided in the ladle nozzle 220 is opened, the filler sintered in the discharge port 210 is destroyed by the load of the molten steel M. Therefore, the discharge port 210 is naturally opened (opened) so that the molten steel M in the ladle 200 is supplied to the tundish 100 through the discharge port 210 and the ladle nozzle 220 .

On the other hand, in casting the slab, continuous casting may be performed in which the molten steel M is continuously supplied to the tundish 100 to cast the slab. 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 in the tundish 100 is emptied. For this purpose, the ladle 200 containing the molten steel M is connected to the tundish 100 multiple times. That is, before all the molten steel M in the tundish 100 is discharged, the empty ladle 200 located above the tundish 100 is replaced with another ladle 200 containing the molten steel M and connected. , do this multiple times. In general, casting a slab using the molten steel contained in one ladle 200 is called one charge. Then, the slab is cast while replacing the ladle in the order of the first (first) ladle, the second ladle, the third ladle, and so on. Name the castings 1st charge, 2nd charge, 3rd charge, and so on.

On the other hand, the molten steel M received by the ladle 200 and transferred to the tundish 100 is molten steel that has previously undergone a refining operation to remove impurities. The refining operation to remove impurities includes a preliminary de-yellowing process to remove sulfur (S) in the molten steel, and a converter to remove phosphorus (P) and carbon (C) in the molten steel by blowing oxygen into the molten steel in the converter. It includes a refining process and a deoxidizing process that removes oxygen (O) from molten steel.

A deoxidizing agent such as aluminum (Al) is added to the molten steel to deoxidize the molten steel to remove oxygen (O). However, inclusions such as metal oxides, such as aluminum oxide (Al ₂ O ₃ ), are formed in the molten steel during the deoxidizing operation, and these inclusions cause surface or internal defects in the slab. For this reason, bubbling is performed using vacuum degassing equipment such as RH (Rheinstahl-Heraus) to remove inclusions in molten steel. There is a limit to lowering below a predetermined content of

For this reason, inclusions are further removed in the casting process, and for this purpose, a tundish flux (hereinafter referred to as flux F) in which inclusions are dissolved and can be absorbed is put into the upper part of the tundish 100 . At this time, the flux F is introduced into the tundish 100 when 40% to 45% of the target amount of molten steel to be packed into the tundish is filled.

Further, in continuous casting in which a plurality of charges are continuously cast, after the flux F is introduced into the tundish 100 in the first charge, ie, the first charge, no further flux is introduced until the final charge. That is, continuous casting of a plurality of charges is performed using the flux introduced into the tundish in the first charge.

The flux F is prepared in a solid phase or 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. Therefore, a molten or liquid flux layer having a predetermined thickness is formed on the molten steel M surface. Here, the molten flux layer or liquid flux layer can be named flux pool FP. Thus, when the flux F is melted and the liquid flux pool FP is prepared, the inclusions in the molten steel M are dissolved and absorbed by the flux pool FP, thereby removing the inclusions from the molten steel. . That is, only after the solid-phase flux F is melted to form the liquid flux pool FP, inclusions in the molten steel M can be dissolved in the flux pool FP and removed.

The absorption capacity of inclusions of flux pool FP improves as the solubility of said inclusions of flux pool FP increases. Here, the solubility of inclusions in the flux pool FP means the degree to which the inclusions can be dissolved by the flux pool FP.

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, the solubility of inclusions in the flux pool FP is improved.

As described above, the flux F charged into the tundish 100 is in a solid phase or powder state, and the inclusions must be dissolved or Absorption is possible. Therefore, the earlier the solid-phase flux F that has been introduced is melted, or the faster the flux pool FP is formed, the more advantageous the removal of inclusions.

However, if the melting point of the solid-phase flux F is high, it takes a long time until the flux F is melted when it is introduced into the tundish 100 . For this reason, immediately after the flux F is introduced or in the early stage of casting, casting is performed in a state where the flux is melted or the flux pool is insufficient, so inclusions in the molten steel cannot be sufficiently removed. This may cause defects. Therefore, it is necessary to prepare a flux with a low melting point in order to melt the flux quickly.

Also, although the tundish 100 is covered by the cover member 140, it is not possible to completely block contact with the atmosphere. For this reason, the molten steel M in the tundish 100 may be oxidized (hereinafter referred to as reoxidation) by contact with the atmosphere, which may result in the formation of a large amount of inclusions in the molten steel. That is, oxygen in the atmosphere and oxidizing components in molten steel, such as aluminum (Al), may react with each other to form a large amount of inclusions such as aluminum oxide (Al ₂ O ₃ ). Such inclusions cause surface and internal defects of the slab. Further, since the tundish 100 is not provided with a separate heat source, the temperature of the molten steel contained in the tundish 100 is gradually lowered, which may cause the molten steel to solidify within the tundish 100. There is There is a risk that the submerged nozzle 400 that supplies the molten steel to the mold 300 will be blocked due to the temperature drop and solidification of the molten steel, and in such a case, the operation must be interrupted.

Therefore, flux F is introduced into the tundish 100 with the aim of suppressing or preventing reoxidation of the molten steel in the tundish 100 and a decrease in temperature. That is, by covering the surface of the molten steel M in the tundish 100 with the flux spool FP, contact between the molten steel M and the atmosphere and a decrease in the temperature of the molten steel can be suppressed or prevented.

However, if the melting point of the solid-phase flux is high, it takes a long time until the flux is melted when it is introduced into the tundish. For this reason, the flux becomes insufficient in the early stage of casting when the flux is introduced, and there is a possibility that a flux pool will not be formed in a part of the surface of the molten steel. Therefore, there is concern that part of the surface of the molten steel will be exposed to the atmosphere. Moreover, 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 becomes 10 mm or more. However, at the initial stage of casting when the flux is introduced, the thickness of the flux does not reach 10 mm or more because the flux is not sufficiently melted. For this reason, the effect of suppressing reoxidation of molten steel by the flux pool in the early stage of casting is low. Therefore, it is necessary to prepare a flux with a low melting point in order to suppress the reoxidation of the molten steel and the temperature drop.

Moreover, if the melted flux, that is, the flux pool FP has a high viscosity, the flux will not spread widely or evenly over the surface of the molten steel M. In other words, since the flux pool FP is not uniformly formed on the surface of the molten steel M and is not formed in a part of the area, there is a possibility that part of the surface of the molten steel M is exposed. In such cases, reoxidation of the molten steel occurs through the exposed molten steel surface. Therefore, it is necessary to keep the viscosity of the flux pool low in order to prevent reoxidation of the molten steel.

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

The flux F according to the embodiment of the present invention contains calcium oxide (CaO), aluminum oxide (Al ₂ O ₃ ), boron oxide (B ₂ O ₃ ) and silicon oxide (SiO ₂ ). may contain impurities. Note that the flux may further contain at least one of sodium oxide (Na ₂ O) and calcium fluoride (CaF ₂ ).

Here, silicon oxide (SiO ₂ ) is not a component that is artificially added for manufacturing the flux F. Since silicon oxide (SiO ₂ ) is contained in each of the raw material containing aluminum oxide (Al ₂ O ₃ ) and the raw material containing calcium oxide (CaO), which are mixed for the production of flux F, oxidation occurs in the flux. Silicon (SiO ₂ ) will be included.

As noted above, the flux may further include at least one of sodium oxide (Na ₂ O) and calcium fluoride (CaF ₂ ); , sodium oxide (Na ₂ O) and calcium fluoride (CaF ₂ ).

That is, the flux containing boron oxide (B ₂ O ₃ ) and not containing sodium oxide (Na ₂ O) and calcium fluoride (CaF ₂ ) is the flux according to the first embodiment, boron oxide (B ₂ O ₃ ). and a flux containing sodium oxide (Na ₂ O) and not containing calcium fluoride (CaF ₂ ), a flux according to the second embodiment, a flux containing boron oxide (B ₂ O ₃ ) and calcium fluoride (CaF ₂ ) , the flux containing no sodium oxide (Na ₂ O), the flux according to the third embodiment, the flux containing boron oxide (B ₂ O ₃ ), sodium oxide (Na ₂ O) and calcium fluoride (CaF ₂ ) The flux is named the flux according to the fourth embodiment.

To explain again based on Table 1, the flux according to the first embodiment contains 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) including. Further, 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 includes 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 melting point as low as 1310° C. or lower, more specifically 1250° C. or higher and 1310° C. or lower. The flux is completely melted within 8 minutes, more specifically within 6 to 7.5 minutes after the flux is added.

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

The flux according to the first embodiment will be described in detail below. When describing the content of the component, it is described in the form of "lower limit to upper limit", which means "more than the lower limit and less than the upper limit".

The flux F according to the first embodiment contains 40% to 60% by weight of calcium oxide (CaO) and 25% to 40% by weight of aluminum oxide (Al ₂ O ₃ ), containing 2% to 10% by weight of boron oxide (B ₂ O ₃ ) and 5% to 10% by weight of silicon oxide (SiO ₂ ). Flux F more preferably contains 50% to 60% by weight of calcium oxide (CaO), 25% to 34% by weight of aluminum oxide (Al ₂ O ₃ ), and Boron oxide (B ₂ O ₃ ) may be contained in an amount of 5% to 10% by weight, and silicon oxide (SiO ₂ ) in an amount of 6% to 9% by weight.

Calcium oxide (CaO) and aluminum oxide (Al ₂ O ₃ ) are the base materials that make up the tundish flux, and the amount of calcium oxide (CaO) is 40% to 60% by weight relative to the total weight of flux F. %, and aluminum oxide (Al ₂ O ₃ ) is contained in an amount of 25 wt % to 40 wt %. More preferably, calcium oxide (CaO) may be contained in an amount of 50-60% by weight, and aluminum oxide (Al ₂ O ₃ ) may be contained in an amount of 25-34% by weight.

On the other hand, when calcium oxide (CaO) is outside the range of 40% to 60% by weight or aluminum oxide (Al ₂ O ₃ ) is outside the range of 25% to 40% by weight, the melting point of flux F and the flux pool There is a disadvantage that the viscosity of FP is high. For this reason, the melting speed of the flux F introduced into the tundish 100 is slow, the solubility of inclusions is low, and the flux pool FP does not evenly spread over the entire surface of the molten steel, so the surface of the molten steel is exposed. There is a possibility that such an inconvenience may occur.

Silicon oxide (SiO ₂ ) is contained in the flux at 5 wt % to 10 wt %, which is the raw material for the manufacture of the flux, including aluminum oxide (Al ₂ O ₃ ) and calcium oxide (CaO ) contains silicon oxide (SiO ₂ ). 40 wt% to 60 wt% calcium oxide (CaO), 25 wt% to 40 wt% aluminum oxide (Al ₂ O ₃ ) for the production of a flux containing aluminum oxide (Al ₂ O ₃ ). By mixing the raw material and the raw material containing calcium oxide (CaO), the flux F can contain 5 to 10% by weight of silicon oxide (SiO ₂ ). As another example, _aluminum oxide (Al ₂ O ₃ By mixing a raw material containing O ₃ ) and a raw material containing calcium oxide (CaO), the flux F can contain 6 wt % to 9 wt % of silicon oxide (SiO ₂ ).

Boron oxide (B ₂ O ₃ ) is contained at 2 wt % to 10 wt % relative to the total wt % of the flux F. More preferably, boron oxide (B ₂ O ₃ ) may be included at 5 wt% to 10 wt%. Boron oxide (B ₂ O ₃ ) functions primarily 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 not so obtained. As a result, since the melting point of the flux is high, there is an inconvenience that the melting speed of the flux F introduced into 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. The lower the melting point, the faster the flux melts, which is advantageous for removing inclusions in the early stages of casting, reoxidizing molten steel, and preventing temperature drop. In general, the flux charged into the tundish has the same chemical composition regardless of the type of steel to be manufactured. However, most types of steel do not particularly limit the content of boron (B) in molten steel, but when manufacturing steel types such as thick plates, the content of boron (B) is limited to a predetermined content or less. .

For this reason, a flux containing a large amount of boron oxide (B ₂ O ₃ ) cannot be used in the manufacture of steel grades such as thick plates that require a limited boron (B) content. This is because the boron (B) in the flux is picked up by the molten steel to increase the boron (B) content in the molten steel. In addition, when the flux is prepared separately for the production of steel grades that require the content of boron (B) to be restricted, the associated cost is added.

Therefore, it is necessary to prepare a flux that can be used for general purposes regardless of the type of steel in which the content of boron (B) is not limited or the type of steel in which the content of boron (B) is limited. For this reason, in the embodiment, boron oxide (B ₂ O ₃ ) is prepared so that it is contained at 10% by weight or less with respect to the total weight of the flux. On the other hand, if the boron oxide (B ₂ O ₃ ) exceeds 10% by weight, it may become unusable for the production of steel grades requiring control of the boron (B) content, such as plate.

Such flux F is prepared in the form of powder or granules with a particle size of 10 mm or less. Preferably, it is provided to have a particle size of 0.1 mm to 10 mm, more preferably 0.1 mm to 7 mm.

On the other hand, if the particle size of the particles constituting the flux F exceeds 10 mm, the melting speed of the flux is slow, so there is a possibility that a sufficient melting speed cannot be ensured. The smaller the particle size, the higher the melting rate. may be generated in large amounts, causing difficulties in operation. Therefore, it is preferable to prepare the flux so as to have a particle size of 0.1 mm to 10 mm.

The flux F mentioned above contains 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 by no means limited to this, and the flux F may further contain sodium oxide (Na ₂ O).

That is, the flux according to the second embodiment contains 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). More specifically, flux F contains 40% to 60% by weight of calcium oxide (CaO), 25% to 40% by weight of aluminum oxide (Al ₂ O ₃ ), 2 wt% 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% to 60% by weight of calcium oxide (CaO), 25% to 34% by weight of aluminum oxide (Al ₂ O ₃ ), and 5% by weight of boron oxide (B ₂ O ₃ ). ˜10% by weight, 6% to 9% by weight of silicon oxide (SiO ₂ ), and 2% to 6% by weight of sodium oxide (Na ₂ O).

Sodium oxide (Na ₂ O) is a substance that has the effect of lowering the melting point and viscosity, and is 2 wt% to 10 wt%, more preferably 2 wt% to 6 wt%, based on the total weight of the flux. included. However, if sodium oxide (Na ₂ O) is less than 2% by weight, the addition of sodium oxide (Na ₂ O) may not have the effect of lowering the melting point and viscosity.

On the other hand, sodium oxide (Na ₂ O) can react with aluminum oxide (Al ₂ O ₃ ) in the flux to produce a refractory crystal phase in the form of Na ₂ O—Al ₂ O ₃ . The melting point of the flux F increases as the high-melting-point crystal phase is generated or the amount of the generated phase increases. Also, 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, the content of sodium oxide (Na ₂ O) is adjusted to 10% by weight or less in order to suppress the formation of a high melting point crystal phase due to sodium oxide (Na ₂ O).

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, resulting in a large amount of high-melting crystal phase. There is a risk that it will be generated. As a result, 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 )including. However, the present invention is by no means limited to this, and flux F does not contain sodium oxide (Na ₂ O) and further contains calcium fluoride (CaF ₂ ).

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

Calcium fluoride (CaF ₂ ) is a substance that has the effect of lowering the melting point and viscosity, and is 2 wt% to 10 wt%, more preferably 2 wt% to 6 wt%, based on the total weight of the flux. included. However, if the content of calcium fluoride (CaF ₂ ) is less than 2% by weight, the addition of calcium fluoride (CaF ₂ ) may not have the effect of lowering the melting point and viscosity.

On the other hand, calcium fluoride (CaF ₂ ) may react with aluminum oxide (Al ₂ O ₃ ) to produce a high melting point crystal phase in the form of CaO—Al ₂ O ₃ , and this high melting point crystal phase is It is a factor that increases the melting point of the flux and the viscosity of the flux pool. Therefore, the content of calcium fluoride (CaF ₂ ) is adjusted to 10% by weight or less in order to suppress the formation of a high melting point crystal phase due to calcium fluoride (CaF ₂ ).

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, resulting in a large amount of high-melting crystal phase. There is a risk of generation. As a result, 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 contains either one of sodium oxide (Na ₂ O) and calcium fluoride (CaF ₂ ). However, the present invention is by no means limited to this, and the flux F may contain both sodium oxide (Na ₂ O) and calcium fluoride (CaF ₂ ).

That is, the flux F according to the fourth embodiment contains calcium oxide (CaO), aluminum oxide (Al ₂ O ₃ ), boron oxide (B ₂ O ₃ ) and silicon oxide (SiO ₂ ), and contains sodium oxide (Na ₂ O) and calcium fluoride (CaF ₂ ). More specifically, flux F contains 40% to 60% by weight of calcium oxide (CaO), 25% to 40% by weight of aluminum oxide (Al ₂ O ₃ ), 2 wt% 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% by weight calcium fluoride (CaF ₂ ). More preferably, the flux contains 50% to 60% by weight of calcium oxide (CaO), 25% to 34% by weight of aluminum oxide (Al ₂ O ₃ ), and 5% by weight of boron oxide (B ₂ O ₃ ). ˜10 wt %, 6 wt % to 9 wt % silicon oxide (SiO ₂ ), 2 wt % to 6 wt % sodium oxide (Na ₂ O), 2 wt % to 6 wt % calcium fluoride (CaF ₂ ). % 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, since the solubility of the inclusions is higher than that of the conventional flux, the absorption or removal rate of the inclusions is high.

Table 1 shows the component composition, melting point, viscosity and corrosion rate of the flux according to the first to fifth experimental examples. FIG. 2 is a graph showing the erosion rate of the test piece during the experiment using the flux according to the first to fifth experimental examples. FIG. 3 is a diagram showing an experimental apparatus.

The first experimental example is a conventional flux containing calcium oxide (CaO), aluminum oxide (Al ₂ O ₃ ) and silicon oxide (SiO ₂ ), boron oxide (B ₂ O ₃ ), sodium oxide ( Na ₂ O) and calcium fluoride (CaF ₂ ). Fluxes according to the second to fifth experimental examples contain calcium oxide (CaO), aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO ₂ ) and boron oxide (B ₂ O ₃ ). Note that the fluxes according to the third to fifth experimental examples further contain at least one of sodium oxide (Na ₂ O) and calcium fluoride (CaF ₂ ).

In the first to fifth experimental examples, calcium oxide (CaO) is 40% to 60% by weight, aluminum oxide (Al ₂ O ₃ ) is 25% to 40% by weight, and silicon oxide (SiO ₂ ) is It is contained at 5% to 10% by weight. In the second to fifth experimental examples, boron oxide (B ₂ O ₃ ) is contained at 2 wt % to 10 wt %. In addition, the third and fifth experimental examples contained sodium oxide (Na ₂ O) at 2% to 10% by weight, and the fourth and fifth experimental examples contained calcium fluoride (CaF ₂ ). It is contained at 2% to 10% by weight.

Therefore, 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 flux according to the third embodiment. can be described as the flux according to the fourth embodiment.

The viscosity was measured by heating each of the fluxes according to the first to fifth experimental examples to a temperature of 1400°C and using a viscosity measuring instrument at a temperature of 1400°C. The erosion rate is the result of an experiment using the experimental apparatus shown in FIG. First, based on FIG. 3, the experimental device will be described.

Referring to FIG. 3, the experimental apparatus 10 includes a tube 11 having an inner space, a crucible 12 disposed inside the tube 11 and capable of accommodating a flux F, a heater 13 for heating the crucible 12, and a specimen S The lower part of the crucible 12 supports the sample S so that it can be inserted into the crucible 12 , and has a rotatable rotor 14 and a thermometer 15 capable of measuring the temperature of the crucible 12 .

Tube 11 may be made from a material including quartz. The heater 13 may be arranged outside the tube 11 so as to surround the outer peripheral surface of the tube 11 . Here, the heater 13 may be means having a heating wire that is heated by a resistance heating method. The temperature gauge 15 may be arranged so that at least a part of it is positioned inside the tube 11 so as to be positioned below the crucible. Such a thermometer 15 may be, for example, a thermo couple.

The specimen S is made of the same composition as inclusions in 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. For this purpose, a flux pool FP is provided inside the crucible. After the flux pool FP is formed, the rotor 14 is lowered to deposit the lower portion of the sample S on the flux pool FP. Then, the rotating body 14 is used to rotate the sample S for a predetermined time.

Such experiments are separately performed using each of the fluxes according to the first to fifth experimental examples. The amount of flux charged into the crucible 12, the depth of depositing the sample S in the flux pool FP, the depositing time, the rotation time, and the rotation speed were all the same for each experiment. In addition, the specimen S used for each experiment has the same composition, size and mass.

The erosion rate is calculated using the difference between the weight of the specimen S before being deposited in the flux pool FP (the initial weight of the specimen) and the weight of the specimen S after the experiment is over. be able to. More specifically, the weight of the specimen S (initial weight of the specimen) is measured before starting the experiment, and the weight of the specimen S is measured after the experiment is over. Then, the difference between the initial weight of the specimen S and the S weight of the specimen after the end of the experiment is calculated. Here, the calculated weight is the weight that has been reduced by being dissolved in the flux pool FP (hereinafter referred to as reduced weight).

Then, by dividing the reduced weight by the initial weight of the specimen S (weight reduced/initial weight of the specimen), the weight reduction rate is calculated. Alternatively, the calculated weight reduction rate can be multiplied by 100% to calculate the weight reduction rate (%) in % units. Then, dividing the calculated weight loss rate (%) by the total time (min) that the specimen S was deposited in the flux pool FP gives the weight loss rate per hour, e.g., per minute (min) ( %/min) is calculated and defined as the erosion rate (%/min).

Referring to Table 1, the melting points of the second to fifth experimental examples containing boron oxide (B ₂ O ₃ ) are lower than those of the first experimental example not containing boron oxide (B ₂ O ₃ ). and low viscosity, high erosion rate. 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 higher. On the other hand, in the second to fifth experimental examples, the melting point is as low as 1310° C. or lower and the viscosity is as low as 7 poise or lower.

Further, when the corrosion rate is compared, it is as low as 0.6 or less in the first experimental example, but as high as 0.8 or higher in the second to fifth experimental examples.

Here, the specimen S is made of the same material as the inclusions, and since the weight of the specimen S is reduced by being melted by the flux pool FP in the crucible, the calculated erosion rate is It can be interpreted that the higher the flux pool, the higher the solubility of the inclusions or the higher the removal efficiency of the inclusions. Therefore, it can be seen that the flux pools generated by the fluxes according to the second to fifth experimental examples have higher inclusion solubility and inclusion removal efficiency than the first experimental example.

FIG. 2 shows the rate of weight loss of the coupons with time immersed in the flux, as described above. That is, the reduced weight of the test piece is cumulatively calculated with the passage of time when the flux is deposited, and is divided by the initial weight of the test piece and expressed as a ratio, as shown in FIG.

Referring to FIG. 2, taking the first experimental example as an example, when the sample was deposited in the flux for 10 minutes, the initial weight of the sample decreased by about 6%. Also, when the time the coupon was deposited in the flux was 20 minutes, the coupon lost about 9% of its initial weight. Then, the change in the weight reduction rate over time can be used to know the weight reduction rate. Here, the weight reduction of the specimen occurs when the specimen melts into the flux pool, that is, it is eroded, so the weight reduction rate in FIG. 2 can be interpreted as the erosion rate of the specimen. can be done.

Referring to FIG. 2, the erosion speed of the second to fifth experimental examples is faster than that of the first experimental example. This means that the inclusion dissolution rate is faster in the flux pools formed by the fluxes according to the second to fifth experimental examples than in the first experimental example.

Thus, the fluxes according to the second to fifth experimental examples have lower viscosities and higher erosion rates and erosion speeds than those of the first experimental example. Therefore, compared to the first experimental example, when casting using the fluxes according to the second to fifth experimental examples, the efficiency of removing inclusions by dissolving inclusions in 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.

Also, the melting points of the fluxes according to the second to fifth experimental examples are lower than those of the first experimental example. Therefore, the melting speed of the flux in the second to fifth experimental examples is faster than that in the first experimental example. Therefore, when using the flux according to the second to fifth experimental examples, it is possible to generate a relatively large amount or a thick flux pool within a short time compared to the first experimental example. Therefore, by forming a sufficient amount and thickness of the flux pool FP at the initial stage of casting, it is possible to more effectively prevent reoxidation and temperature drop at the initial stage of casting.

Returning to Table 1 and FIG. 2 and comparing the second to fifth experimental examples, the erosion rate of the third and fifth experimental examples is 1.4 or more, and the second and fourth experimental examples (1 below), and the erosion rates of the third and fifth experimental examples are higher than those of the second and fourth experimental examples. From this, it can be seen that the flux pools formed by the fluxes according to the third and fifth experimental examples have higher inclusion solubility or inclusion removal efficiency than the second and fourth experimental examples.

To explain this in another way, among boron oxide (B ₂ O ₃ ), sodium oxide (Na ₂ O) and calcium fluoride (CaF ₂ ), flux containing boron oxide (B ₂ O ₃ ) (No. 2 Experimental Example), boron oxide (B ₂ O ₃ ) and sodium oxide (B 2 O 3 ) compared with the flux containing boron oxide (B ₂ O ₃ ) and calcium fluoride (CaF ₂ ) (fourth Experimental Example). Flux containing (Na ₂ O) (third experimental example), flux containing boron oxide (B ₂ O ₃ ), sodium oxide (Na ₂ O) and calcium fluoride (CaF ₂ ) (fifth experimental example) Example) improves the removal efficiency of inclusions in molten steel.

Further, when comparing the third experimental example and the fifth experimental example, compared to the case of using the flux containing boron oxide (B ₂ O ₃ ) and sodium oxide (Na ₂ O) (third experimental example), , boron oxide (B ₂ O ₃ ), sodium oxide (Na ₂ O) and calcium fluoride (CaF ₂ ) when using a flux (fifth experimental example), inclusion removal efficiency in molten steel is found to improve.

FIG. 4 is a photograph of the melting state of the flux over time when the flux according to the first experimental example and the flux according to the third experimental example in Table 1 are put into a tundish. FIG. 5 shows the oxygen content in the molten steel in the mold for 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. (ppm) is the result of measurement.

For the experiments, fluxes according to the first and third experimental examples were introduced into the tundish 100 of an actual casting facility as shown in FIG. That is, 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.

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

Since the inside of the tundish 100 is defined by the first and second upper weirs 120a and 120b, the flux introduced into the central region 111a and the first and second outer regions 111b and 111c are mutually not mixed.

After the introduction of the flux into the tundish 100 is completed, the upper side of the first outer region 111b into which the flux according to the first experimental example is introduced and the second outer region 111c into which the flux according to the third experimental example is introduced. Photographs were taken at each of the upper sides of the . More specifically, the image was taken using a hole provided in the cover member 140 for sampling. At this time, photographs were taken with the passage of time, and the photographs are collectively shown in FIG.

Further, 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. , the oxygen content (ppm) in the molten steel in the mold 300 was measured for each charge. That is, each of the molten steel M in the first mold 300a and the molten steel M in the second mold 300b was sampled at each charge to measure the oxygen content, and the results are summarized as shown in FIG. .

Here, the molten steel in the first mold 300a is the molten steel covered by the flux in the tundish 100 according to the first experimental example, and the molten steel in the second mold 300b is the molten steel in the tundish 100. 3 is the molten steel covered by the flux according to Experimental Example 3.

Referring to FIG. 4, the flux introduced into the first outer region 111b (first experimental example) was completely melted about 14 minutes after being introduced. On the other hand, it can be seen that the flux introduced into the second outer region 111c (third experimental example) was completely melted in about 6.9 minutes after being introduced. From this, it can be seen that the flux according to the third experimental example has a lower melting point than the flux according to the first experimental example, and the melting speed is about twice as fast.

Furthermore, referring to FIG. 5, the content of oxygen (O) in the molten steel tends to decrease as the order of charging increases. ) content is low.

On the other hand, since inclusions in molten steel exist in the form of metal oxides, it is possible to relatively know the content of inclusions in molten steel using the content of oxygen (O) in molten steel. That is, it can be interpreted that when the oxygen (O) content in the molten steel is low, the content of inclusions in the molten steel is relatively low compared to when the oxygen (O) content is high. Therefore, it can be seen from FIG. 5 that the removal efficiency of inclusions in molten steel is higher when using the flux according to the third experimental example than in the first experimental example.

FIG. 6 shows the state of the flux in the tundish when six charge castings are continuously performed using the flux according to the first experimental example and the flux according to the third experimental example. It is a photograph taken and shown as it progresses. FIG. 7 shows the 2nd, 4th, and 6th charges when six charges are continuously cast using the flux according to the first experimental example and the flux according to the third experimental example, respectively. This is the result of sometimes measuring the melting point of the flux in the tundish. FIG. 8 shows the oxygen content ( ppm) is measured.

For the experiment, flux was introduced into the tundish 100 of an actual casting facility as shown in FIG. 1 and six charges were cast in succession. At this time, the flux according to the first experimental example was applied to all of the central region 111a and the first and second outer regions 111b and 111c of the tundish 100, and six charges were continuously cast. Similarly, the flux according to the third experimental example was applied to all of the central region 111a and the first and second outer regions 111b and 111c of the tundish, and six charges were continuously cast.

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

Also, when casting a plurality of charges in succession in the actual casting operation, ashed rice husks are thrown in to keep the molten steel M in the tundish warm. For this reason, during the experiment, the incinerated rice husks were put into the tundish 100 each time the ladle 200 was replaced or each time a new charge was started.

Six charges are continuously cast using the fluxes of the first and third experimental examples thus introduced. At this time, photographs were taken from the upper side of the central region 111a of the tundish 100 for each charge from the second charge to the sixth charge, and the photographs are collectively shown in FIG.

In addition, while continuous casting was performed for six charges, the flux in the tundish was sampled at the second, fourth, and sixth charges, and the melting point was measured. .

In addition, while performing continuous casting of six charges, the oxygen content (ppm) in the molten steel in the mold was measured for each charge from the second charge to the sixth charge, and the results were summarized. is shown in FIG.

Looking at the photograph of the third charge of the first experimental example in FIG. 6, there is a relatively highly saturated or dark portion, and this portion is the portion where the flux pool is solidified. In addition, compared to the third charge, the fourth charge, the fifth charge, and the sixth charge are generally higher in saturation or darker. This is because the solidified area of the flux pool is wider (or increased) in the fourth charge, the fifth charge, and the sixth charge than in the third charge.

Further, the solidification of the flux can be known not only by the saturation or brightness as described above, but also by grasping the roughness of the surface visually, not by photographing. Taking the third charging of the first experimental example as an example, the surface of the partially solidified area is as rough as stone, but the rest of the area is not. Therefore, the presence or absence of solidification of the flux pool or the solidified area can be known by visually grasping the surface roughness.

In the case of the first experimental example, the phenomenon of flux solidification begins to occur in the third charge. From the fourth charge onwards, the solidified area increases. The solidification of the flux is due to the fact that the melting point of the flux in the tundish rises due to the addition of ladle filler and ashed rice husks each time the ladle is replaced.

On the other hand, in the case of the third experimental example, solidification did not occur until the sixth charge. This is because the melting point of the flux according to the third experimental example is lower than that of the first experimental example, so that the phenomenon of solidification is alleviated compared to the first experimental example. Therefore, the flux according to the third experimental example either begins to solidify later than the flux according to the first experimental example, or does not solidify. Therefore, it is possible to increase the number of times the flux is used and charged or the usage time.

The presence or absence of solidification and the solidified area in each of the first and third experimental examples as described above can be grasped by the saturation or brightness on the photograph of FIG. It was a decision made on a whim.

As the flux is solidified or the amount of solidified increases, the melting point of the flux charged into the tundish rises. Referring to FIG. 7, the melting point of the first experimental example exceeds 1400° C. at the time of the fourth charge, whereas the melting point of the third experimental example exceeds 1350° C. even after the sixth charge (last charge). not exceeding and 1400° C. or less.

From this, even if the same amount of ladle filler and ashed rice husks are added each time the ladle is replaced, compared to the first embodiment using the flux according to the third embodiment, It can be seen that the melting point of the flux in the tundish can be kept low.

Also, referring to FIG. 8, comparing the content (ppm) of oxygen (O) in the molten steel in the mold according to each charge, the third experimental example is lower than the first experimental example. Further, in the case of the third experimental example, the oxygen content of the molten steel in the mold from the first charge to the last charge is 20 ppm or less. From this, it can be seen that the removal efficiency of inclusions is higher when using the flux according to the third experimental example than in the first experimental example.

The flux according to the embodiment of the present invention or the flux pool formed by the flux has higher inclusion solubility or inclusion removal efficiency than conventional ones. As a result, it is possible to manufacture a slab in which the occurrence of defects due to inclusions is suppressed or prevented as compared with the conventional method, and the quality of the slab can be improved.

Moreover, since the melting point of the flux according to the embodiment is lower than that of the conventional flux, the melting speed is high. Therefore, when the flux according to the embodiment is used, a large amount of flux can be melted within a short period of time as compared with conventional methods. As a result, a sufficient amount and thickness of the flux pool is formed at the initial stage of casting, thereby more effectively preventing reoxidation and temperature drop at the initial stage of casting.

Furthermore, since the melting point of the flux is low, solidification of the flux can be suppressed or prevented even if multiple charges are cast in succession. Therefore, it is possible to manufacture a slab in which the occurrence of defects due to inclusions is suppressed or prevented from the beginning to the end of continuous casting, and the quality of the slab can be improved.

According to the flux according to the embodiment of the present invention, the solubility of inclusions or the removal efficiency of inclusions is higher than conventional ones. As a result, it is possible to manufacture a slab in which the occurrence of defects due to inclusions is suppressed or prevented as compared with the conventional method, and the quality of the slab can be improved.

Moreover, since the melting point of the flux according to the embodiment is lower than that of the conventional flux, the melting speed is high. Therefore, when the flux according to the embodiment is used, a large amount of flux can be melted within a short period of time as compared with conventional methods. As a result, a sufficient amount and thickness of the flux pool is formed at the initial stage of casting, thereby more effectively preventing reoxidation and temperature drop at the initial stage of casting.

Claims (14)

A tundish flux that is put into the tundish during casting,
Calcium oxide (CaO) is 40% to 60% by weight, aluminum oxide (Al ₂ O ₃ ) is 25% to 40% by weight, and silicon oxide (SiO ₂ ) is 5% to 5% by weight, relative to the total weight%. A tundish flux comprising 10% by weight, 2% to 10% by weight of boron oxide (B ₂ O ₃ ), and the remainder consisting of unavoidable impurities. 2. The tundish flux according to claim 1, wherein said boron oxide (B ₂ O ₃ ) is contained in an amount of 5% to 10% by weight with respect to the total weight of said tundish flux. The tundish flux further includes at least one of sodium oxide (Na ₂ O) of 2 wt % to 10 wt % and calcium fluoride (CaF ₂ ) of 2 wt % to 10 wt %. The tundish flux according to claim 1, wherein The tundish flux further includes at least one of sodium oxide (Na ₂ O) of 2 wt % to 6 wt % and calcium fluoride (CaF ₂ ) of 2 wt % to 6 wt %. The tundish flux according to claim 2, wherein 50% to 60% by weight of the calcium oxide (CaO), 25% to 34% by weight of the aluminum oxide (Al ₂ O ₃ ), and the silicon oxide ( SiO ₂ ) in an amount of 6% to 9% by weight. The tundish flux according to any one of claims 1 to 5, wherein the tundish flux has a melting point of 1310°C or less. 7. The tundish flux according to claim 6, wherein the tundish flux has a melting point of 1280[deg.] C. or lower. The tundish flux according to any one of claims 1 to 5, wherein the tundish flux has a viscosity of 7 poise or less at 1400°C. The tundish flux according to claim 8, wherein the tundish flux has a viscosity of 2 poise or more and 4 poise or less at 1400°C. A step of providing a tundish flux according to any one of claims 1 to 5;
a process of supplying molten steel to a tundish;
a step of charging the tundish flux into the tundish to form a flux pool on the surface of the molten steel in the tundish;
a step of 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 ladle containing molten steel is replaced and connected to the tundish multiple times to cast a plurality of charges that continuously supply molten steel to the tundish,
In the casting of the first charge of supplying the molten steel in the first ladle to the tundish among the plurality of charge castings, the tundish flux is introduced into the tundish,
11. The casting method according to claim 10, wherein the melting point of the flux pool in the tundish is 1400[deg.] C. or lower during the casting of the last charge among the casting of the plurality of charges. 12. The casting method according to claim 11, wherein all of the tundish flux charged into the tundish is melted within 8 minutes. 12. The casting method according to claim 11, wherein the thickness of the flux pool in the tundish is 10 mm or more when casting the first charge. 12. The casting method according to claim 11, wherein the oxygen content of the molten steel in the mold is 20 ppm or less from the first charge to the last charge casting among the plurality of charge castings.

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