JP7420963B2 - Tundish flux and casting method using the same - Google Patents

Description

The present invention relates to a tundish flux and a casting method using the same, and more particularly to a tundish flux that can improve the quality and productivity of slabs and a casting method using the same.

The casting process is a process in which molten steel in a tundish is poured into a mold, and semi-solidified slabs are pulled out from within the mold to produce slabs of various shapes such as slabs, blooms, billets, and beam blanks.

During this type of casting process, the surface of the molten steel in the tundish is covered with flux in order to remove inclusions from the molten steel in the tundish, suppress the generation 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 or powder state, and at the beginning of casting, the flux is poured into a tundish containing a predetermined amount of molten steel. When flux is introduced into the tundish, it is melted by the heat of the molten steel. Therefore, a molten flux, that is, a flux pool, is formed to a predetermined thickness on the surface of the molten steel. That is, the surface of the molten steel is covered by the flux pool. When a flux pool is formed on the surface of the molten steel, the inclusions in the molten steel are dissolved and absorbed by the flux pool, and therefore the inclusions in the molten steel are removed. In addition, since the flux pool blocks contact between the atmosphere and the molten steel, re-oxidation of the molten steel and a decrease in temperature are suppressed.

On the other hand, the solid phase flux supplied to the tundish is melted only after a predetermined period of time has elapsed. However, at the beginning 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 of the flux pool is thin. Therefore, 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 caused by the inclusions in the molten steel on the surface or inside of the slab.

Korean Registered Patent No. 1233836

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

Another object of the present invention is to provide a tundish flux that can suppress or prevent reoxidation of molten steel and the generation of inclusions thereby, and a casting method using the same.

The present invention is a tundish flux that is put into a tundish during casting, and contains 40% to 60% by weight of calcium oxide (CaO) and aluminum oxide (Al ₂ O ₃ ), 5% to 10% by weight of silicon oxide (SiO ₂ ), 2% to 10% by weight of boron oxide (B ₂ O ₃ ), and the rest from unavoidable impurities. Become.

The boron oxide (B ₂ O ₃ ) may be included in an amount of 5% to 10% by weight 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.

With respect to 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, and the silicon oxide (Al 2 O 3 ) is 25% to 34% by weight. 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 a process of preparing tundish flux, a process of supplying molten steel to the tundish, and charging the tundish flux into the tundish to raise the level of the molten steel in the tundish. and a step of supplying the molten steel in the tundish to 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 to cast a plurality of charges that continuously supply molten steel to the tundish, and the first of the plurality of charges is cast. In the first charge casting in which the molten steel in the ladle is supplied to the tundish, the tundish flux is introduced into the tundish, and when the last charge is cast among the plurality of charges, the tundish flux is poured into the tundish. The melting point of the flux spool is 1400°C or less.

The tundish flux added to the tundish is completely melted within 8 minutes.

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

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

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

Further, since the melting point of the flux according to the embodiment is lower than that of the conventional flux, the melting speed is fast. Therefore, when using the flux according to the embodiment, a larger amount of flux can be melted in a shorter time than conventionally. As a result, a flux pool having a sufficient amount and thickness is formed in the early stage of casting, thereby making it possible to more effectively prevent re-oxidation and temperature drop in the early stage of casting.

Since the flux has a low melting point, solidification of the flux can be suppressed or prevented even if a plurality of charges are continuously cast. Therefore, it is possible to produce 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.

It is a figure showing normal casting equipment. FIG. 7 is a graph showing the erosion rate of the specimen during experiments using fluxes according to the first to fifth experimental examples. FIG. FIG. 2 is a diagram showing an experimental apparatus. It is a photograph taken 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 were put into a tundish. When performing casting in which seven consecutive charges are performed using each of 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 This is the result of measuring. When casting six charges in succession 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 charging. This is a photo 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, the inside of the tundish was charged during the second, fourth, and sixth charging. This is the result of measuring the melting point of the flux. When casting six charges in succession using each of 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 was determined for each charge. These are the measured results.

Embodiments of the present invention will be described in more detail below based on the accompanying drawings. However, the present invention is in no way limited to the embodiments disclosed below, but may be embodied in a variety of different forms, and these embodiments do not constitute a complete disclosure of the present invention and are beyond the ordinary skill in the art. This information is provided to fully convey the scope of the invention to those skilled in the art. The drawings may be exaggerated to illustrate embodiments of the invention, and like numbers refer to like elements throughout the figures.

The present invention relates to a tundish flux with improved inclusion solubility or inclusion removal efficiency. The present invention relates to a tundish flux that can suppress or prevent reoxidation of molten steel and a decrease in temperature. Here, the solubility of inclusions means the degree to which inclusions are dissolved in flux.

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

FIG. 1 is a diagram showing a typical 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 molten steel M begins to solidify in the cooled mold 300 and becomes an intermediate product in a semi-solid state. This is a process that yields a slab of . The semi-solid slab pulled out from the mold 300 is shaped and further cooled while moving along a plurality of segments (not shown) arranged in one direction under the mold 300, and is then completely cooled. It becomes a solidified slab.

The tundish 100 is provided with molten steel from the ladle 200 and supplies it to the mold 300. To this end, the ladle 200 is moved above 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 connected to the tundish. 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 immersion 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 inserted and a hole for sampling.

In addition, the tundish 100 has an upper weir 120 disposed at the upper part of the main body 110 so as to be located outside the position where the ladle nozzle 220 is inserted, and a main body so as to be located outside the upper weir 120. It may further include 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 arranged below the tundish 100, when the ladle 200 is located above the tundish 100, the ladle Nozzle 220 is arranged between first mold 300a and second mold 300b. A pair of upper weirs are provided, and the pair of upper weirs (hereinafter referred to as first and second upper weirs 120: 120a, 120b) are located inside the main body 110 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 120a and 120b are arranged away from the bottom surface within the main body 110.

Further, the lower weirs 130 may also be provided in a pair, and the pair of lower weirs (hereinafter referred to as first and second lower weirs 130: 130a, 130b) connects the immersion nozzle and the upper weir that connect the tundish 100 and the mold. It may be arranged so as to be located between the weir and the weir. That is, the first lower dam 130a is located between the first immersion nozzle 400a and the first upper dam 120a that connect the tundish 100 and the first mold 300a, and the first lower dam 130a connects the tundish 100 and the first mold 300b. The second lower weir 130b is located between the second immersion nozzle 400b and the second upper weir 120b.

The vertical extension length of the upper weir 120 may be longer than the extension length of the lower weir 130. Note that the lower end of the upper weir 120 is located lower than the upper end of the lower weir 130.

The internal space of the tundish 100 or the main body 110 is a central region 111a, which is a space between the first upper weir 120a and the second upper weir 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 a space between one side wall in the main body 110 and the first upper weir 120a, and the second outer region 111c is a space between the other side wall in the main body 110 and the first upper weir 120a. It can be explained that it is the space between the two upper weirs 120b. According to such a tundish 100, a part of the molten steel M passed through the ladle nozzle 220 and supplied to the central region 111a in the tundish 100 is transferred to 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. Note that the molten steel that has moved to the first and second outer regions 111b and 111c is supplied to the first and second molds 300a and 300b via the first and second immersion nozzles 400a and 400b.

As described above, the tundish 100 is supplied with the molten steel M from the ladle 200. Hereinafter, a process in which the molten steel M from the ladle 200 is supplied to the tundish 100 will be briefly described. A discharge port 210, which is a passage through which the molten steel M is discharged, is provided at the bottom of the ladle 200, and a filler containing metal oxides such as chromium oxide and silicon oxide is inside the discharge port 210. Filled. The filler is sintered by the heat of the molten steel M contained in the ladle 200, so that the discharge port 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 discharge port 210 is destroyed by the load of the molten steel M. Therefore, by naturally opening (opening) the discharge port 210, the molten steel M in the ladle 200 passes through the discharge port 210 and the ladle nozzle 220 and is supplied to the tundish 100.

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 M in the tundish 100 becomes empty. 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 and connected to another ladle 200 containing molten steel M. , do this multiple times. Generally, casting a slab using molten steel contained in one ladle 200 is referred to as one charge. Then, the slab is cast while changing the ladles in the order of the first (first) ladle, second ladle, third ladle, etc. Depending on the order of the ladles or the order in which they are replaced, Name the castings as 1st charge, 2nd charge, 3rd charge, etc.

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

When performing deoxidation to remove oxygen (O) from molten steel, a deoxidizing agent such as aluminum (Al) is added to the molten steel. However, inclusions such as metal oxides such as aluminum oxide (Al ₂ O ₃ ) are generated in the molten steel during the deoxidation operation, and these inclusions become a cause of 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 the content below a certain level.

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

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, that is, the first charge, no further flux is introduced until the last charge. That is, continuous casting of a plurality of charges is performed using the flux charged 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 poured into the molten steel M in the tundish 100, the flux F is melted by the heat of the molten steel. Therefore, a molten flux layer or a liquid flux layer with a predetermined thickness is formed on the surface of the molten steel M. Here, the molten flux layer or liquid flux layer can be named 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 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 can the inclusions in the molten steel M be dissolved into the flux pool FP and removed.

The ability of the flux pool FP to absorb inclusions increases as the solubility of the inclusions in the flux pool FP increases. Here, the solubility of inclusions in the flux spool FP means the degree to which the flux spool FP can dissolve inclusions.

In order for the flux pool FP to have sufficient inclusion solubility, it is necessary to ensure that the viscosity of the flux pool FP is low. 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 introduced into the tundish 100 is in a solid or powder state, and only when the flux F introduced into the molten steel M in the tundish 100 is melted can the inclusions be dissolved or Absorption is possible. Therefore, the faster the introduced solid phase flux F is melted or the faster the flux pool FP is formed, the more advantageous it is to remove inclusions.

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

Further, although the tundish 100 is covered by the cover member 140, contact with the atmosphere cannot be completely blocked. Therefore, there is a possibility that the molten steel M in the tundish 100 will be oxidized (hereinafter referred to as re-oxidation) due to contact with the atmosphere, and as a result, there is a possibility that a large amount of inclusions will be generated in the molten steel. That is, there is a possibility that oxygen in the atmosphere reacts with an oxidizing component in the molten steel, such as aluminum (Al), and a large amount of inclusions such as aluminum oxide (Al ₂ O ₃ ) are generated. Such inclusions cause surface and internal defects in the slab. Since the tundish 100 is not provided with a separate heat source, the temperature of the molten steel accommodated in the tundish 100 gradually decreases, which may cause the molten steel to solidify within the tundish 100. There is. Note that there is a risk that the immersion nozzle 400 that supplies the molten steel to the mold 300 may become clogged due to the temperature drop and solidification of the molten steel, and in such a case, the operation must be interrupted.

For this reason, flux F is introduced into the tundish 100 with the aim of suppressing or preventing re-oxidation 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 pool 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 solid phase flux has a high melting point, it will take a long time to melt when the flux is introduced into the tundish. For this reason, the flux may not be sufficiently melted at the beginning of casting when the flux is introduced, and as a result, there is a possibility that a flux pool may not be formed in a part of the surface of the molten steel. Therefore, there is a concern that a portion of the molten steel surface may be exposed to the atmosphere. Further, 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 beginning of casting when the flux is added, the thickness of the flux does not reach 10 mm or more because the flux is not sufficiently melted. Therefore, the effect of suppressing reoxidation of molten steel by the flux pool is low in the early stage of casting. Therefore, it is necessary to prepare a flux with a low melting point in order to suppress reoxidation of molten steel and decrease in temperature.

Moreover, if the viscosity of the molten flux, that is, the flux pool FP, is high, the flux will not spread widely or uniformly on 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 some areas, there is a possibility that a part of the surface of the molten steel M may be exposed. In such a case, reoxidation of the molten steel occurs via the exposed molten metal surface. Therefore, it is necessary to ensure that the viscosity of the flux pool is low to prevent re-oxidation of molten steel.

Below, the components of the flux according to the embodiment of the present invention will be explained 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 ), and in addition to these, unavoidable 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 artificially added for producing flux F. Since silicon oxide (SiO ₂ ) is contained in the raw materials containing aluminum oxide (Al ₂ O ₃ ) and the raw materials containing calcium oxide (CaO) that are mixed for the production of flux F, oxidation occurs in the flux. Silicon (SiO ₂ ) will be included.

As mentioned above, the flux may further include at least one of sodium oxide (Na ₂ O) and calcium fluoride (CaF ₂ ), but in the following, for ease of explanation, , sodium oxide (Na ₂ O), and calcium fluoride (CaF ₂ ).

That is _, the flux according to the first embodiment contains boron oxide (B ₂ O ₃ ) and does not contain sodium oxide (Na ₂ O) and calcium fluoride (CaF _{2 )} . The flux according to the second embodiment contains boron oxide ( _{B 2 O 3} ) and calcium fluoride (CaF _{2 )} . , the flux according to the third embodiment does not contain sodium oxide (Na ₂ O), and the flux contains boron oxide (B ₂ O ₃ ), sodium oxide (Na ₂ O), and calcium fluoride (CaF ₂ ). The flux is named 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 contains 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 ). The flux according to the fourth embodiment contains 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. It should be noted that the flux is completely melted within 8 minutes, more specifically within 6 to 7.5 minutes after the flux is introduced.

Further, the melting point of the flux may be 1250°C or more and 1280°C or less. 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. Note that the solubility or removal efficiency of inclusions in such a flux pool is higher than in the past.

Hereinafter, the flux according to the first embodiment will be explained in detail. When explaining the content of a component, it is explained in the form of "lower limit value to upper limit value", which means "not less than the lower limit value and not more than the upper limit value".

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 ), based on the total weight% of flux F. Boron oxide (B ₂ O ₃ ) may be contained in an amount of 5% to 10% by weight, and silicon oxide (SiO ₂ ) may be contained in an amount of 6% to 9% by weight.

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

On the other hand, if 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 spool There is a disadvantage that the FP has a high viscosity. For this reason, the melting speed of the flux F charged into the tundish 100 is slow, the solubility of inclusions is low, and the flux pool FP is not evenly distributed over the entire surface of the molten steel, resulting in the surface being exposed. There is a possibility that this inconvenience may occur.

Silicon oxide (SiO ₂ ) is contained in the flux at 5% to 10% by weight, which is the same as raw materials containing aluminum oxide (Al ₂ O ₃ ) and calcium oxide (CaO ) contains silicon oxide (SiO ₂ ). That is, aluminum oxide (Al ₂ O ₃ ) is used to produce a flux containing 40% to 60% by weight of calcium oxide (CaO) and 25% to 40% by weight of aluminum oxide (Al ₂ O ₃ ). By mixing the raw material and the raw material containing calcium oxide (CaO), it becomes possible for the flux F to 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% to 9% by weight of silicon oxide (SiO ₂ ).

Boron oxide (B ₂ O ₃ ) is contained in an amount of 2% to 10% by weight based on the total weight% of flux F. More preferably, boron oxide (B ₂ O ₃ ) may be included in an amount of 5% to 10% by weight. Boron oxide (B ₂ O ₃ ) primarily 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 not so great. Thereby, since the melting point of the flux is high, there is a disadvantage that the melting speed of the flux F put 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 is melted, which is advantageous for removing inclusions at the initial stage of casting, preventing re-oxidation of molten steel, and lowering the temperature. Note that, in general, the flux to be charged into the tundish has the same composition regardless of the type of steel being manufactured. However, for most steel types, the content of boron (B) in molten steel is not particularly limited, but when producing steel types such as thick plates, the content of boron (B) is limited to below a predetermined content. .

For this reason, a flux containing a large amount of boron oxide (B ₂ O ₃ ) cannot be used in the production of steel types such as thick plates where the content of boron (B) needs to be limited. This is because boron (B) in the flux is picked up by the molten steel and increases the boron (B) content in the molten steel. Note that when flux is separately prepared for manufacturing a steel type that requires a restriction on the boron (B) content, the accompanying cost is added.

Therefore, it is necessary to prepare a flux that can be used for general purposes, regardless of whether the boron (B) content is not limited or whether the boron (B) content is limited. Therefore, in the embodiment, boron oxide (B ₂ O ₃ ) is prepared so as to be contained in an amount of 10% by weight or less based on the total weight% of the flux. On the other hand, if boron oxide (B ₂ O ₃ ) exceeds 10% by weight, it may not be usable for manufacturing steel types that require control of the boron (B) content, such as thick plates.

Such flux F is prepared in the form of powder or granules, and the particle size is prepared to be 10 mm or less. Preferably, the particles are prepared to have a particle size of 0.1 mm to 10 mm, more preferably 0.1 mm to 7 mm.

On the other hand, when the particle size of the particles constituting the flux F exceeds 10 mm, the melting speed of the flux is slow, and there is a possibility that a sufficient melting speed cannot be ensured. Note that the smaller the particle size, the higher the melting rate; however, if the particle size is too small, dust may be generated when the flux F is introduced into the tundish 100 or when the manufactured flux F is transported. There is a risk that a large amount of water will be generated, causing difficulties in operation. Therefore, it is preferable to prepare the flux 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 not limited thereto, 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 contains sodium oxide (Na ₂ O) 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 ), based on the total weight of the flux. It contains 2% to 10% by weight of boron oxide (B ₂ O ₃ ), 5% to 10% by weight of silicon oxide (SiO ₂ ), and 2% to 10% by weight of 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, silicon oxide (SiO ₂ ) from 6% to 9% by weight, and sodium oxide (Na ₂ O) from 2% to 6% by weight.

Sodium oxide (Na ₂ O) is a substance that has the effect of lowering the melting point and viscosity, and is present in an amount of 2% to 10% by weight, more preferably 2% to 6% by weight based on the total weight% of the flux. included. However, if the amount of sodium oxide (Na ₂ O) is less than 2% by weight, the addition of sodium oxide (Na ₂ O) may not be very effective in 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 high melting point crystalline phase in the form of Na ₂ O--Al ₂ O ₃ . The more the high melting point crystalline phase is generated or the larger the amount of the high melting point crystal phase generated, the higher the melting point of the flux F increases. Moreover, the higher the content of the high melting point crystalline phase in the flux F, the higher the viscosity of the flux pool FP. Therefore, in order to suppress the formation of a high melting point crystalline phase due to sodium oxide (Na ₂ O), the content of sodium oxide (Na ₂ O) is adjusted to 10% by weight or less.

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 point crystal phase. There is a possibility that it will be generated. This may raise the melting point of the flux and increase its viscosity.

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 not limited thereto, 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 ), based on the total weight of the flux. It contains 2% to 10% by weight of boron oxide (B ₂ O ₃ ), 5% to 10% by weight of silicon oxide (SiO ₂ ), and 2% to 10% by weight of 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, silicon oxide (SiO ₂ ) from 6% to 9% by weight, and calcium fluoride (CaF ₂ ) from 2% to 6% by weight.

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

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 . This is a factor that increases the melting point of the flux and the viscosity of the flux pool. Therefore, in order to suppress the formation of a high melting point crystal phase due to calcium fluoride (CaF ₂ ), the content of calcium fluoride (CaF ₂ ) is adjusted to 10% by weight or less.

However, when calcium fluoride (CaF ₂ ) exceeds 10% by weight, a large amount of high melting point crystal phase forms due to the large amount of reaction between calcium fluoride (CaF ₂ ) and aluminum oxide (Al ₂ O ₃ ). There is a risk of generation. This may raise the melting point of the flux and increase its viscosity.

The flux F according to the second and third embodiments described above contains either sodium oxide (Na ₂ O) or calcium fluoride (CaF ₂ ). However, the present invention is not limited thereto, 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 ), based on the total weight of the flux. 2% to 10% by weight boron oxide (B ₂ O ₃ ), 5% to 10% by weight silicon oxide (SiO ₂ ), 2% to 10% by weight sodium oxide (Na ₂ O), and 2% by weight % to 10% by weight of 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 ), 2% to 6% by weight of sodium oxide (Na ₂ O), 2% to 6% by weight of calcium fluoride (CaF ₂ ) % may be included.

The fluxes according to the first to fourth embodiments as described above have a low melting point of 1310°C or less and a low viscosity of 7 poise or less at 1400°C. Note that since the solubility of inclusions is higher than that of conventional fluxes, the absorption rate or removal rate of inclusions is high.

Table 1 is a table showing the component composition, melting point, viscosity, and erosion rate of fluxes according to the first to fifth experimental examples. FIG. 2 is a graph showing the erosion rate of the specimen during experiments using fluxes according to the first to fifth experimental examples. FIG. 3 is a diagram showing the 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 ( Contains no Na ₂ O) and calcium fluoride (CaF ₂ ). 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 ). 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) was 40% to 60% by weight, aluminum oxide (Al ₂ O ₃ ) was 25% to 40% by weight, and silicon oxide (SiO ₂ ) was It is contained in an amount of 5% to 10% by weight. In the second to fifth experimental examples, boron oxide (B ₂ O ₃ ) is contained in an amount of 2% to 10% by weight. Further, in the third and fifth experimental examples, sodium oxide (Na ₂ O) was contained at 2% to 10% by weight, and in the fourth and fifth experimental examples, calcium fluoride (CaF ₂ ) was contained. It is contained in an amount of 2% to 10% by weight.

Therefore, the second experimental example uses the flux according to the first embodiment, the third experimental example uses the flux according to the second embodiment, the fourth experimental example uses the flux according to the third embodiment, and the fifth experimental example uses the flux according to the third embodiment. The experimental example 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 device at a temperature of 1400°C. Note that the erosion rate is the result obtained through an experiment using the experimental apparatus shown in FIG. First, the experimental apparatus will be explained based on FIG. 3.

Referring to FIG. 3, the experimental apparatus 10 includes a tube 11 having an internal 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 specimen S is supported so that the lower part thereof can be fitted into the inside of the crucible 12, and includes a rotatable rotating body 14 and a temperature measuring device 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 a means provided with a heating wire that is heated by a resistance heating method. The temperature measuring device 15 may be arranged so that at least a portion thereof is located inside the tube 11 so as to be located at the lower part of the crucible. Such a temperature measuring device 15 may be, for example, a thermocouple.

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

For the experiment, flux F is charged into the crucible 12 and the heater is operated to melt the flux. For this reason, a flux spool FP is prepared within the crucible. Once the flux pool FP is formed, the rotating body 14 is lowered to deposit the lower part of the specimen S in the flux pool FP. Then, the sample S is rotated using the rotating body 14 for a predetermined period of time.

Such experiments are conducted separately using each of the fluxes according to the first to fifth experimental examples. The amount of flux injected into the crucible 12, the depth at which the sample S is deposited in the flux pool FP, the time for depositing, the rotation time, and the rotation speed were all the same for each experiment. Note that the sample 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 it is deposited in the flux pool FP (initial weight of the specimen) and the weight of the specimen S after the experiment is finished. be able to. To be more specific, the weight of the sample S (initial weight of the sample) is measured before starting the experiment, and the weight of the sample S is measured after the experiment is finished. 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 reduced by being dissolved in the flux spool FP (hereinafter referred to as reduced weight).

Then, by dividing the reduced weight by the initial weight of the specimen S (reduced weight/initial weight of the specimen), the weight reduction rate is calculated. Moreover, the weight reduction rate (%) in % units can also be calculated by multiplying the calculated weight reduction rate by 100%. Next, by dividing the calculated weight reduction rate (%) by the entire time (min) in which the specimen S was deposited in the flux pool FP, the weight reduction rate (%) per hour, for example, per minute (min) is obtained. %/min) is calculated, and this is defined as the erosion rate (%/min).

Referring to Table 1, the melting points of the second to fifth experimental examples that contain boron oxide (B ₂ O ₃ ) are lower than that of the first experimental example that does not contain boron oxide (B ₂ O ₃ ). and low viscosity and high erosion rate. That is, the first experimental example has a high melting point of 1360° C. or higher and a high viscosity of 23 poise or higher. On the other hand, in the second to fifth experimental examples, the melting point was as low as 1310° C. or less, and the viscosity was as low as 7 poise or less.

Further, when comparing the erosion rates, the first experimental example is low at 0.6 or less, but the second to fifth experimental examples are high at 0.8 or more.

Here, the specimen S is made of the same material as the inclusion, and the weight of the specimen S is reduced by being melted into the flux pool FP in the crucible, so the calculated erosion rate is The higher it is, the more it can be interpreted that the flux pool is more soluble in inclusions or more efficient in removing 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 specimen over the time it was deposited in the flux, as described above. In other words, the weight loss of the specimen as time elapses after it has been deposited in the flux is cumulatively calculated, and this is divided by the initial weight of the specimen to form a ratio, as shown in Figure 2.

Referring to FIG. 2, taking the first experimental example as an example, when the sample was deposited in the flux for 10 minutes, about 6% of the initial weight of the sample was reduced. Furthermore, when the time for which the specimen was deposited in the flux reached 20 minutes, about 9% of the initial weight of the specimen had decreased. Then, by using the change in the weight reduction rate over time in this way, the weight reduction rate can be determined. Here, the weight reduction of the specimen occurs when the specimen is dissolved in the flux pool, that is, eroded, so the weight reduction rate in Figure 2 can be interpreted as the erosion rate of the specimen. I can do it.

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

As described above, the fluxes according to the second to fifth experimental examples have lower viscosity and higher erosion rate and erosion rate than those in the first experimental example. Therefore, compared to the first experimental example, when casting is performed using the fluxes according to the second to fifth experimental examples, the inclusion removal efficiency of melting and removing the inclusions of molten steel is improved. Therefore, it is possible to produce a slab in which the occurrence of defects due to inclusions is suppressed or prevented, and the quality of the slab can be improved.

Further, the melting points of the fluxes according to the second to fifth experimental examples are lower than those in the first experimental example. Therefore, compared to the first experimental example, the flux melting speed in the second to fifth experimental examples is faster. Therefore, when using the fluxes according to the second to fifth experimental examples compared to the first experimental example, a relatively larger amount or thicker flux pool can be generated within a short time. Therefore, by forming a sufficient amount and thickness of the flux pool FP at the beginning of casting, it is possible to more effectively prevent re-oxidation and temperature drop at the beginning of casting.

Returning to Table 1 and FIG. 2, when comparing the second to fifth experimental examples, the erosion rates of the third and fifth experimental examples are 1.4 or more, and the erosion rates of 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 a higher inclusion solubility or inclusion removal efficiency than the second and fourth experimental examples.

To explain this in another way, flux containing boron oxide (B ₂ O ₃ ) among boron oxide (B ₂ O ₃ ), sodium oxide (Na ₂ O) and calcium fluoride (CaF ₂ ) 2), a flux containing boron oxide (B ₂ O ₃ ) and calcium fluoride (CaF ₂ ) (4th experimental example), boron oxide (B ₂ O ₃ ) and sodium oxide (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 experiment); It can be seen that when using Example), the removal efficiency of inclusions in molten steel is improved.

Also, when comparing the third experimental example and the fifth experimental example, it is found that compared to using a flux (third experimental example) containing boron oxide (B ₂ O ₃ ) and sodium oxide (Na ₂ O), , when using a flux (fifth experimental example) containing boron oxide (B ₂ O ₃ ), sodium oxide (Na ₂ O), and calcium fluoride (CaF ₂ ), the removal efficiency of inclusions in molten steel It can be seen that this improves.

FIG. 4 is a photograph showing 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 shown in Table 1 were put into a tundish. Figure 5 shows the oxygen content in the molten steel in the mold for each charge when casting is performed using the flux according to the first experimental example and the flux according to the third experimental example. (ppm).

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

A total of 70 tons (tons) of molten steel was supplied into the tundish 100, and when the molten steel reached 30 tons (tons) in the tundish, the fluxes according to the first and third experimental examples were introduced. 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 set to be the same as 130 kg.

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

After the addition of flux to 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 introduced and the second outer region 111c to which the flux according to the third experimental example is introduced Photographs were taken on each of the upper sides. More specifically, the photograph was taken using a hole provided in the cover member 140 for sampling. At this time, photographs were taken over time, and the photographs are collectively shown in Figure 4.

In addition, as described above, the flux according to the first experimental example was applied to the central area 111a and the first outer area 111b of the tundish 100, and the flux according to the third experimental example was applied to the second outer area 111c, and the flux was applied seven times. When casting continuous charges, the oxygen content (ppm) in the molten steel in the mold 300 was measured for each charge. That is, at each charging time, each of the molten steel M in the first mold 300a and the molten steel M in the second mold 300b was sampled and the oxygen content was measured, and this was summarized as shown in FIG. .

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

Referring to FIG. 4, the flux (first experimental example) injected into the first outer region 111b was completely melted about 14 minutes after being injected. On the other hand, it can be seen that the flux (third experimental example) introduced into the second outer region 111c 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 and about twice the melting rate than the flux according to the first experimental example.

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

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

FIG. 6 shows the state of the flux in the tundish when the charge is cast six times using each of the flux according to the first experimental example and the flux according to the third experimental example. These are photos taken as we progress. FIG. 7 shows the results of the second, fourth, and sixth charges when six charges are sequentially cast using the flux according to the first experimental example and the flux according to the third experimental example. This is the result of measuring the melting point of the flux inside the tundish. FIG. 8 shows the oxygen content ( These are the results of measuring ppm).

For the purpose of the experiment, flux was poured into the tundish 100 of an actual casting facility as shown in FIG. 1, and six charges were cast continuously. At this time, the flux according to the first experimental example was poured into 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 poured into 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 (ton) of molten steel was supplied into the tundish, and flux was added when the molten steel reached 30 tons (ton) in the tundish. Note that the amount of flux input in the first and third experimental examples was the same as 130 kg.

Further, when a plurality of charges are continuously cast during an actual casting operation, incinerated rice husks are added to keep the molten steel M in the tundish warm. For this reason, in the experiment, incinerated rice husks were added to the tundish 100 each time the ladle 200 was replaced or each time a new charge was started.

Using the fluxes according to the first and third experimental examples thus introduced, six charges are continuously cast. At this time, a photograph was taken from above 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. 6.

In addition, while performing continuous casting for six charges, the melting point was measured by sampling the flux in the tundish during the second, fourth, and sixth charges, and the results are summarized in Figure 7. .

In addition, while continuous casting was performed for 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 are 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 part, and this part is the part where the flux pool has solidified. Note that, compared to the third charge, the saturation is higher or darker overall in the fourth charge, fifth charge, and sixth charge. This is because the solidified area of the flux pool becomes wider (or increases) in the fourth charge, fifth charge, and sixth charge compared to the third charge.

Further, the solidification of the flux can be determined not only by the saturation or brightness as described above, but also by visual observation other than photography to determine the roughness of the surface. 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 remaining area is not. Therefore, it is possible to visually check the surface roughness and know whether or not the flux pool is solidified or the solidified area.

In the case of the first experimental example, the phenomenon of flux solidification begins to occur during the third charge. From the fourth charge, the solidified area increases. The solidification of the flux is caused by the fact that filler and ashed rice husk are added to the ladle each time the ladle is replaced, increasing the melting point of the flux in the tundish.

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

The presence or absence of solidification and the solidified area in each of the first and third experimental examples as described above can be determined by checking the saturation or brightness on the photograph in Figure 6, or by visually checking the surface roughness by an operator. It was determined based on the following.

As the flux solidifies or the amount of solidified flux increases, the melting point of the flux charged into the tundish increases. Referring to FIG. 7, in the first experimental example, the melting point exceeds 1400°C at the fourth charge, whereas in the third experimental example, the melting point exceeds 1350°C even at the sixth charge (last charge). 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.

Further, with reference to FIG. 8, when 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. In the case of the third experimental example, the oxygen content of the molten steel in the mold is 20 ppm or less from the first charging to the final charging casting. From this, it can be seen that inclusion removal efficiency is higher when the flux according to the third experimental example is used compared to the first experimental example.

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

Further, since the melting point of the flux according to the embodiment is lower than that of the conventional flux, the melting speed is fast. Therefore, when using the flux according to the embodiment, a larger amount of flux can be melted in a shorter time than conventionally. As a result, a flux pool having a sufficient amount and thickness is formed in the early stage of casting, thereby making it possible to more effectively prevent re-oxidation and temperature drop in the early stage of casting.

Furthermore, since the flux has a low melting point, solidification of the flux can be suppressed or prevented even if a plurality of charges are continuously cast. Therefore, it is possible to produce 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 that of conventional fluxes. As a result, it is possible to produce a slab in which the occurrence of defects due to inclusions is suppressed or prevented compared to the conventional method, and the quality of the slab can be improved.

Further, since the melting point of the flux according to the embodiment is lower than that of the conventional flux, the melting speed is fast. Therefore, when using the flux according to the embodiment, a larger amount of flux can be melted in a shorter time than conventionally. As a result, a flux pool having a sufficient amount and thickness is formed in the early stage of casting, thereby making it possible to more effectively prevent re-oxidation and temperature drop in the early stage of casting.

Claims (13)

Tundish flux that is put into the tundish during casting,
Based on the total weight%, 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. 10% by weight, 2% to 10% by weight of boron oxide (B ₂ O ₃ ), and the rest consists of unavoidable impurities,
The tundish flux has a viscosity of 7 poise or less at 1400°C . The tundish flux according to claim 1, wherein the boron oxide (B ₂ O ₃ ) is contained in an amount of 5% to 10% by weight based on the total weight of the tundish flux. The tundish flux contains 2% to 10% by weight of sodium oxide (Na ₂ O) and 2% to 10% by weight of calcium fluoride (CaF ₂ ) based on the total weight of the tundish flux. The tundish flux according to claim 1, further comprising at least one of the following. The tundish flux contains 2% to 6% by weight of sodium oxide (Na ₂ O) and 2% to 6% by weight of calcium fluoride (CaF ₂ ) based on the total weight of the tundish flux. The tundish flux according to claim 2, further comprising at least one of the following. With respect to 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, and the silicon oxide (Al 2 O 3 ) is 25% to 34% by weight. The tundish flux according to claim 4, characterized in that the tundish flux contains 6% by weight to 9% by weight of SiO ₂ ). The tundish flux according to any one of claims 1 to 5, wherein the tundish flux has a melting point of 1310°C or lower. The tundish flux according to claim 6, wherein the melting point of the tundish flux is 1280°C or lower. The tundish flux according to any one of claims 1 to 5 , wherein the tundish flux has a viscosity of 2 poise or more and 4 poise or less at 1400°C. A step of preparing the tundish flux according to any one of claims 1 to 5;
The process of supplying molten steel to the tundish;
A step of charging the tundish flux into the tundish to form a flux pool above the surface of the molten steel in the tundish;
supplying the molten steel in the tundish to a mold, solidifying the molten steel in the mold to cast a slab;
A casting method characterized by comprising: Casting a plurality of charges that continuously supply molten steel to the tundish by replacing and connecting a ladle containing molten steel to the tundish a plurality of times,
Among the casting of the plurality of charges, in the casting of the first charge in which molten steel in the first ladle is supplied to the tundish, the tundish flux is introduced into the tundish,
10. The casting method according to claim 9 , wherein the melting point of the flux spool in the tundish is 1400° C. or lower when casting the last charge among the plurality of charges. The casting method according to claim 10 , wherein the tundish flux charged into the tundish is completely melted within 8 minutes. 11. The casting method according to claim 10 , wherein the thickness of the flux pool in the tundish is 10 mm or more during the first charge casting. 11. The casting method according to claim 10 , wherein the oxygen content of the molten steel in the mold from the first charge to the last charge among the plurality of charge castings is 20 ppm or less.

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