JP2009541060A - Mold flux and continuous casting method using the same - Google Patents

Abstract

The present invention, CaO20～50 _wt%, SiO 2 20 to 50 _wt%, Al _{2 O} 3 20 wt% or _less, Na 2 O20 wt% or _less, Li 2 O10 _wt%, B _{2 O} 3 20 wt% or less and The present invention relates to a mold flux containing 10% by weight or less of MgO and a continuous casting method using the same. According to the present invention, the occurrence of slab surface cracks can be reduced to improve product quality, and the occurrence of breakout can be prevented to improve operational stability.

Description

  The present invention relates to a mold flux and a continuous casting method using the same, and more particularly to a continuous casting method using a molten mold flux.

  In general, the steelmaking process is performed in the order of a hot metal pretreatment process, a converter refining process, a secondary refining process, and a continuous casting process.

  In order to manufacture a slab (a collective name for slabs, billets, blooms, beam blanks, etc.) by a continuous casting process, as shown in FIG. 1, first, liquid steel in a liquid state is supplied from a ladle and supplied. The molten steel passes through the tundish 1 for storing the molten steel, the immersion nozzle 2 and the mold 3 in this order. Next, the molten steel forms a solidified shell 5 in a solid state by a cooling action in the mold 3. Further, the solidified shell 5 formed by cooling the molten steel in this way is completely solidified by the secondary cooling water sprayed from the spray nozzle while being guided by the guide roll provided at the lower part of the mold. A solid slab is produced.

  When molten steel is supplied to the mold during the continuous casting operation of such steel, mold flux as an auxiliary material is also added together. The mold flux is generally charged in a solid state such as powder or granule, and is melted by the heat from the molten steel supplied into the mold, thereby improving the lubricating ability by controlling the heat transfer between the molten steel and the mold.

  Based on FIG. 2, the function of the mold flux in the continuous casting mold 10 will be described in detail. The mold flux charged into the mold 10 in the form of powder or granules is melted on the molten steel 12 surface, and the liquid layer 21, the sintered layer 23, and the powder layer 25 (that is, molten slag) are sequentially formed from the molten metal surface. Layer 21, semi-molten layer 23 and unmelted layer 25) are formed. Since the molten slag layer 21 is almost transparent, a radiation wave having a wavelength of 500 to 4000 nm from the molten steel 12 is likely to pass therethrough. On the other hand, since the semi-molten layer 23 and the unmelted layer 25 are optically opaque, the radiation wave is blocked and the temperature of the molten metal surface is prevented from rapidly decreasing.

  However, the conventional powdered or granular mold flux is melted by the heat from the molten steel 21, and then the molten slag layer 21 flows into the gap between the mold 10 and the solidified shell 11 and solidifies on the inner wall of the mold 10. Thus, the solid phase slag film 27 is formed, and on the molten steel 12 side, the liquid slag film 21 is formed to control the heat transfer between the molten steel 12 and the mold 10 to enhance the lubricating ability.

  At this time, in the place where the dissolved slag flows into the gap between the solid phase slag film 27 and the solidified shell 11, the mold flux adhering to the mold 10 rises toward the inside of the mold 10, and this is called a slag bear 29. Is. The slag bear 29 prevents the dissolved slag from flowing into the gap between the mold flux film 27 and the solidified shell 11.

  Although the amount of mold flux consumed per unit area of the slab is limited by such a slag bear 29, generally, the amount of mold flux consumed decreases as the casting speed increases, so that the lubrication ability between the slab and the mold is reduced. As a result, the occurrence of breakout increases. Furthermore, due to the variation in the thickness of the liquid mold flux due to the slag bear 29, the shape of the solidified shell in the mold 10 varies, and surface cracks occur. This problem becomes more serious as the casting speed increases. become.

  Recently, a method has been proposed in which the mold flux is melted outside the mold and then injected into the molten metal surface. As described above, the molten mold flux is almost transparent with respect to the wavelength of 500 to 4000 nm, and as a result, the radiant wave from the molten steel easily passes and the transmission of radiant heat increases. There is an inconvenience that the molten steel surface cannot be kept warm. Thereby, when a casting process advances and predetermined time passes, the molten metal surface of a molten steel will be solidified and it will become impossible to perform a smooth continuous casting process.

  On the other hand, in the prior art, crystallization of the mold flux is promoted to achieve the initial slow cooling, but this increases the mixing of the mold flux and decreases the average heat transfer amount. There is an inconvenience of being connected.

  The present invention controls the mold flux composition and conductivity, thereby preventing solidification of the molten metal surface due to initial slow cooling, reducing the occurrence of surface cracks, and preventing the occurrence of breakout and A continuous casting method using the same is provided.

  In addition, the present invention adjusts the absorption coefficient of the mold flux during the operation of the molten mold flux, thereby increasing the heat insulation effect of the molten metal surface during casting to prevent the solidification of the molten metal surface, improving the slab quality and operating stability. The present invention provides a mold flux capable of improving the temperature and a continuous casting method using the same.

Mold flux according to one aspect of the present invention, CaO20～50 _wt%, SiO 2 20 to 50 _wt%, Al _{2 O} 3 20 wt% or _less, Na 2 O20 wt% or _less, Li 2 O10 wt% or _{less, B} 2 O ₃ 20 wt% or less and MgO 10 wt% or less.

  Preferably, the thermal conductivity of the mold flux is 1.2 W / m. k or more.

  Preferably, the mold flux has an absorption coefficient of 1000 / m or more for a wavelength of 500 to 4000 nm in a molten state.

  Further, preferably, the mold flux includes 3 parts by weight or less of transition metal oxide with respect to 100 parts by weight of the mold flux, and the basicity is 0.5 to 1.5.

In addition, the mold flux continuous casting method according to the present invention includes CaO 20 to 50% by weight, SiO ₂ 20 to 50% by weight, Al ₂ O ₃ 20% by weight or less, Na ₂ O 20% by weight or less, and Li _2. O10 wt% or less, comprising the steps of dissolving the mold flux comprising B 2 _O 3 ₂₀ wt% or less and MgO10 wt% or less, the dissolution throughout the entire process of continuous casting to control the flow rate of the dissolved mold flux Injecting the molded mold flux into the mold.

  Preferably, the thermal conductivity of the mold flux is 1.2 W / m. k or more.

  Preferably, the mold flux has an absorption coefficient of 1000 / m or more at a wavelength of 500 to 4000 nm outside the mold.

  According to the present invention, by applying the molten mold flux operation as described above, it is possible to remove the slag bear, prevent solidification of the molten metal surface due to initial slow cooling, and reduce the occurrence of surface cracks. In particular, by controlling the thermal conductivity according to the composition of the mold flux, the average heat transfer is increased to prevent the occurrence of breakout, the heat transfer between the molten steel and the mold is effectively controlled, and the lubrication ability Can be increased.

  Furthermore, by adjusting the absorption coefficient of the mold flux against the molten steel radiant heat, it is possible to increase the heat insulation effect of the hot water surface and perform stable operation over a long period of time, improving the operational stability and productivity. As well as improving the slab quality.

It is the schematic for demonstrating a normal continuous casting process. It is the schematic for demonstrating the presence form of the mold flux in a continuous casting mold. It is a schematic block diagram of the continuous casting apparatus using the molten mold flux by one Example of this invention. It is a graph which shows the absorption coefficient by the wavelength of the mold flux of a prior art. It is a graph which shows the relationship between the absorption coefficient of a molten mold flux, and the flow rate of the radiant heat in the molten metal surface. It is the photograph which image | photographed the hot_water | molten_metal surface at the time of continuous casting using the mold flux of the comparative example 4. It is the photograph which image | photographed the hot_water | molten_metal surface at the time of continuous casting using the mold flux of Example 2. FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the examples described below, and can be realized in different forms. These embodiments only complete the disclosure of the present invention and are not limited to ordinary knowledge in this technical field. It is provided in order to fully inform those who have the scope of the present invention. In the drawings, the same reference numerals indicate the same elements.

  FIG. 3 is a schematic configuration diagram of a continuous casting apparatus using a molten mold flux.

  Referring to FIG. 3, the continuous casting apparatus includes a mold 10, an immersion nozzle 30 that supplies molten steel into the mold 10, a mold cover 100 that covers the upper part of the mold 10, and a mold flux that is supplied into the mold. A mold flux melting unit 200 for melting the mold flux, and a mold flux conveying unit 300 for supplying the molten mold flux 20 melted in the mold flux melting unit 200 into the mold 10.

  Since the mold 10 and the immersion nozzle 30 are normal components applied to a conventional continuous casting apparatus, a detailed description thereof will be omitted here.

  The mold cover 100 is provided on the upper surface of the mold 10 so as to cover the entire molten metal surface, and prevents radiation waves from the molten metal surface of the molten steel 12 from leaking to the outside. For this purpose, the inner surface of the mold cover 100, that is, the surface facing the molten steel is formed of a highly reflective material such as an aluminum mirror or a gold coating mirror, and reflects the radiation wave from the molten metal surface of the molten steel 12 again. The surface of the molten mold flux 20 or the molten steel 12 is caused to absorb the radiation wave. As a result, the surface temperature of the molten steel 12 is suppressed as much as possible, and the molten mold flux 20 is prevented from re-solidifying on the wall surface of the mold 10.

  The mold flux melting unit 200 includes a mold flux supply source 205, a crucible 210 that stores a temporarily melted liquid, granular, or powder mold flux material supplied from the mold flux supply source 205, A mold flux heating means 220 such as a heat ray provided at the periphery for melting the mold flux, a discharge port 230 for discharging the molten mold flux dissolved in a desired state in the crucible 210, and the discharge port 230 And a stopper 240 that controls the amount of molten mold flux that is opened and closed and discharged. The stopper 240 controls the amount of molten mold flux discharged by adjusting the distance between the peripheral edge of the outlet 230 and the lower end of the stopper 240 while moving up and down in the upper part of the outlet 230. . At this time, the vertical movement of the stopper 240 is accurately controlled by a hydraulic or pneumatic cylinder (not shown).

  The transport unit 300 includes an injection tube 310 and an injection tube heating means 320 such as a heating coil. One end of the injection tube 310 is connected to the mold flux melting unit 200, and the other end is provided with an injection nozzle 312 that passes through the mold cover 100 and supplies the molten mold flux 20 into the mold. The injection tube heating unit 320 is provided between the mold flux melting unit 200 and the mold cover 100 so as to surround the outside of the injection tube 310. At this time, in order to maintain the molten mold flux 20 at a predetermined temperature, it is preferable that the outside of the injection tube 310 and the injection tube heating means 320 is heat-insulated with a heat insulating material.

All or part of the mold flux melting unit 200 and the conveying unit 300 can be formed of a platinum alloy material such as platinum (Pt) or platinum-rhodium (Pt-Rh). The mold flux needs to rapidly dissolve non-metallic inclusions that float on the mold surface during casting, so the viscosity is low and the rate of dissolving oxides such as Al ₂ O ₃ is high. . For this reason, the melting furnace of the refractory material used in the conventional glass industry is rapidly eroded by the molten mold flux 20. In particular, such erosion occurs in the injection pipe 310 having the discharge port 230 through which the molten mold flux 20 is discharged from the mold flux melting unit 200, the lower end of the stopper 240, and the injection nozzle 312 of the mold flux conveyance unit 300. When this occurs, it becomes impossible to accurately control the flow rate of the molten mold flux, and a stable continuous casting operation cannot be performed. Accordingly, at least the injection pipe 310 and the portion connected to the injection pipe 310, that is, the discharge port 230 through which the molten mold flux is discharged, the stopper 240, and the injection pipe 310 are manufactured from platinum or a platinum alloy material to be eroded by the mold flux. It is preferable to prevent.

  The flow rate of the molten mold flux depends on the amount of molten steel supplied into the mold per unit time, and the space between the lower end portion of the stopper 240 and the peripheral portion of the discharge port 230 is moved up and down. By controlling the flow rate, the flow rate of the molten mold flux 20 can be accurately adjusted.

  The example using the stopper to control the flow rate of the molten mold flux has been described above, but the present invention is not limited to this, and various means such as a tilting method, a siphon method using a pressure difference, or a slide gate are used. Can be used to control the flow rate of the molten mold flux.

In the continuous casting process in which the molten mold flux is injected using the above-described apparatus, the mold flux according to the embodiment of the present invention includes CaO 20 to 50 wt%, SiO ₂ for effective initial cooling and control of the heat transfer amount. 20-50 _wt%, Al _{2 O} 3 20 wt% or _less, Na 2 O20 wt% or _less, Li 2 O10 wt% or _less, B _{2 O} 3 comprises 20 wt% or less and MgO10 wt% or less, thermal conductivity 1.2 W / m. It is preferable that it is k or more.

The above CaO and SiO ₂ are components that form the basicity of the mold flux. When the CaO exceeds 50% by weight or the SiO ₂ becomes less than 20% by weight, the viscosity of the slag is remarkably reduced and the molten steel enters the molten steel. Since the inflow of slag becomes excessive, it is not preferable. On the other hand, if CaO is less than 20% by weight or SiO ₂ exceeds 50% by weight, the viscosity of the slag increases so much that it becomes difficult for the slag to flow into the molten steel. As a result, the possibility of breakout increases.

The Al ₂ O ₃ is a component that adjusts the viscosity of the mold flux. When the Al ₂ O ₃ exceeds 20% by weight, the viscosity of the mold flux increases too much and the absorption capacity of nonmetallic inclusions in the molten steel is increased. Decreases.

Like the Al ₂ O ₃ , the Na ₂ O is a component for controlling the melting point of the mold flux. When the Na ₂ O exceeds 20% by weight, the melting point of the mold flux is lowered. Since the viscosity and the surface tension are too low, the effect of suppressing the mixing of molten steel is greatly reduced. Therefore, the increase the viscosity, the it is preferable to increase the _Al 2 _{O 3} component while decreasing the Na ₂ O component, the lower the viscosity, _Al 2 _{O 3} component with increasing the Na ₂ O component Is preferably reduced.

The Li ₂ O and B ₂ O ₃ are components for controlling the melting point and viscosity of the mold flux or thermal conductivity, and the melting point and the viscosity decrease as the content of Li ₂ O and B ₂ O ₃ increases. At the same time, the thermal conductivity is increased. However, when these are added in an excessive amount, the melting point and viscosity of the mold flux are excessively lowered, and mixing into the molten steel increases. Accordingly, the Li ₂ O content is preferably 10% by weight or less, and the B ₂ O ₃ content is preferably 20% by weight or less.

  MgO has almost the same effect as CaO, but the effect per unit weight does not affect CaO. If MgO is added in an excessive amount, a high-temperature precipitate is formed to increase the viscosity of the mold flux or promote the formation of a crystalline material. Therefore, the MgO content is preferably 10% by weight or less.

  Furthermore, according to the embodiment of the present invention, by controlling the thermal conductivity of the mold flux, the amount of heat transfer required for ensuring operational stability and slab quality during continuous casting using the flux is adjusted. Can contribute. As described above, this indicates that the thermal conductivity of the mold flux according to the embodiment of the present invention is 1.2 W / m. This is because the average heat transfer amount can be increased by controlling to k or more, and the occurrence of breakout during continuous casting can be prevented.

For this reason, by optimizing the composition of the mold flux as described above, the thermal conductivity in the vitreous state is increased to 1.2 W / m. It can be controlled to k or more. In particular, when the basicity (CaO / SiO ₂ ) is decreased, the chain structure of SiO ₂ is developed, phonon transmission is facilitated, and the thermal conductivity is increased.

  According to the embodiment of the present invention, the molten mold flux operation using the mold flux described above is applied to the continuous casting process. That is, after the mold flux is completely melted outside the mold using the above-described continuous casting apparatus, the flow rate of the melted mold flux is controlled and injected into the mold periodically or continuously.

  According to the embodiment of the present invention, the slag bear can be removed by applying the molten mold flux operation, the consumption amount of the mold flux is increased, and the thickness of the mold flux film is increased. Thereby, heat transfer can be suppressed, solidification of the molten metal surface due to initial slow cooling can be prevented, and defects such as surface cracks can be reduced. As described above, by using a mold flux with improved thermal conductivity, the average heat transfer amount increases, that is, the thickness of the solidified shell can be increased to prevent the occurrence of breakout.

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

[Example]
Table 1 below shows the mold flux components of Comparative Examples 1 to 3 and the mold flux components of the examples according to the present invention.

  Comparative Examples 1 to 3 have a thermal conductivity of 1.2 W / m. k or less, Example 1 has a thermal conductivity of 1.2 W / m. k or more.

  Table 2 below shows the operation conditions and operation results of Comparative Examples 1 to 3 and Example 1. In Comparative Examples 1 to 3 and Example 1, slab casting was performed using a mold flux having the composition shown in Table 1 above and a mold having a lower end width of 1012 mm and a thickness of 140 mm. At this time, the steel type was an ultra-low carbon steel having a carbon concentration of 60 ppm.

  In Example 1 and Comparative Example 1, the mold flux was completely dissolved outside the mold, and then the molten mold flux was injected into the mold using a stopper type flow control device. At this time, the temperature of the molten mold flux at the time of injection was 1300 ° C. After the molten steel reached the target value when the molten steel was filled in the mold before the start of casting, a mold cover was provided on the mold simultaneously with the start of casting. Then, the consumption of the molten mold flux was continuously replenished with the progress of casting. The mold cover was made of an aluminum material, and its surface was polished very beautifully so that the average reflectance with respect to infrared rays in the 500 to 4000 nm region, which is the molten steel radiation region, was 85%.

In the comparative example 2 and the comparative example 3, in the same manner as the normal operation using the powder mold flux, the casting is started by introducing the powder mold flux when the molten steel is filled in the mold before the casting is started. At any time, powder mold flux was added and replenished.

  Referring to Table 2, according to Example 1, the slag bear can be removed by applying the molten mold flux operation to the continuous casting process, whereby the consumption amount of the mold flux is reduced by the powder mold flux operation. Compared with the applied comparative example 2 and comparative example 3, the friction between the mold and the solidified shell can be reduced significantly. Further, it can be seen that Example 1 achieves initial slow cooling by reducing the ratio of maximum heat transfer amount / average heat transfer amount as compared with Comparative Example 2 and Comparative Example 3. This is because by injecting the molten mold flux, the maximum heat transfer amount just below the molten metal surface is reduced as compared with the powder mold flux. That is, the ratio of the maximum heat transfer amount to the average heat transfer amount was 2.0 to 2.5 in the conventional operation in which the powder mold flux was introduced, whereas the operation according to the present invention in which the molten mold flux was introduced. In the case of carrying out, it rapidly decreases to 1.2 to 1.5.

  Furthermore, compared with the comparative example 1 which applied the same melt mold flux operation, Example 1 has thermal conductivity of 1.2 W / m. It can be seen that the average amount of heat transfer increases by controlling to k or more. That is, initial cooling is achieved by injecting molten mold flux, and the ratio of maximum heat transfer / average heat transfer is almost the same, but the thermal conductivity is 1.30 W / m. k, the thermal conductivity is 1.05 W / m. The average heat transfer amount is relatively higher than that of Comparative Example 1 that is k. Thereby, an Example can increase the thickness of a solidification shell and can prevent generation | occurrence | production of a breakout.

  Thus, the present invention has a thermal conductivity of 1.2 W / m. By using the molten mold flux controlled to be k or more, it is possible to prevent the solidification of the molten metal surface due to the initial slow cooling, reduce the occurrence of surface cracks, and improve the product quality. In addition, the occurrence of breakout can be prevented and operational stability can be improved.

  On the other hand, during continuous casting using the molten mold flux, the molten mold flux is almost transparent to the wavelength of 500 to 4000 nm, which is the molten steel radiation region, so that the radiant heat from the molten steel is easily transmitted. Will be solidified without heat insulation. For this reason, the hot water surface is kept warm using the above-described mold cover or the like.

  In addition to these, the present invention adjusts the absorption coefficient of the mold flux to increase the hot surface heat retaining effect. In order to effectively control the molten metal surface temperature during the continuous casting process in which the molten mold flux is injected, the mold flux of the present invention has an average absorption coefficient of 1000/4000 with respect to a wavelength of 500 to 4000 nm in the molten steel radiation region. It is preferable that it is m or more.

  FIG. 4 is a graph showing the absorption coefficient depending on the wavelength of the conventional mold flux. In the conventional mold flux, the absorption coefficient with respect to the wavelength of 500 to 4000 nm is distributed in the range of 100 / m to 800 / m, and 1000 / m or less. I know that there is.

  FIG. 5 is a graph showing the flow rate of radiant heat on the molten metal surface due to the reflectance of the mold cover when the thickness of the molten mold flux is 20 mm and the absorption coefficient of the mold flux with respect to a wavelength of 500 to 4000 nm is varied. Here, the heat loss increases as the flow rate of radiant heat increases, which means that the possibility of molten metal surface solidification increases.

  Referring to FIG. 5, it can be seen that the radiant heat flow rate at the molten metal surface is low as the absorption coefficient of the mold flux increases. That is, the heat loss from the molten steel is reduced, and the hot water surface warming effect can be enhanced. (A) is a calculation of the amount of heat required for temperature rise and melting when a molten mold surface heat loss in a powder mold flux operation, that is, a powdery mold flux at room temperature that is not in a molten state is introduced. B) is a calculation of the amount of heat under the condition that the surface of the molten mold flux layer does not solidify in the molten mold flux operation. It can be seen that when the absorption coefficient of the mold flux is 1000 / m or more, the condition that the surface of the molten mold flux layer does not solidify is satisfied regardless of the reflectance of the mold cover. For this reason, it is preferable that the absorption coefficient with respect to the wavelength of 500-4000 nm of a mold flux is 1000 / m or more.

  As is apparent from the figure, when the absorption coefficient of the mold flux is 1000 / m or more, the surface solidification of the molten mold flux layer can be prevented regardless of the reflectance of the mold cover provided on the upper surface of the mold. However, it is preferable to provide a mold cover because heat transfer by convection increases when there is no mold cover. Also, by adjusting the mold flux absorption coefficient to 1000 / m or more according to the present invention, the heat loss from the molten steel is suppressed as much as possible, and the mold cover surface is oxidized or the mold flux volatilization causes the reflectivity of the mold cover. Even if it falls, the hot water surface heat insulation effect can be ensured and the stable operation can be performed.

Thus, in order to adjust the absorption coefficient of the mold flux to 1000 / m or more, an appropriate amount of an oxide of a transition metal such as Fe ₂ O ₃ , TiO ₂ , NiO, Cr ₂ O ₃ is added, It is preferable to lower the basicity (CaO / SiO ₂ ) as much as possible.

  Since the transition metal element may react with Al in the molten steel, the total addition amount is preferably 3 parts by weight or less of the transition metal oxide with respect to 100 parts by weight of the mold flux. In addition, when the basicity of the mold flux is too low, the viscosity increases excessively and the lubrication function in the mold decreases, so the basicity is preferably maintained in the range of 0.5 to 1.5.

  As described above, the present invention can reduce the thickness of the slag bear by applying the molten mold flux operation and increase the consumption amount of the mold flux. Thereby, the heat transfer between the molten steel and the mold can be effectively controlled to enhance the lubricating ability. In addition, as above-mentioned, by using the mold flux which adjusted the absorption coefficient with respect to molten steel radiant heat, the hot_water | molten_metal surface heat insulation effect can be ensured, slab quality can be improved, and productivity and operation stability can be improved.

Table 3 below shows the mold flux components and absorption coefficients of Comparative Example 4 and Example 2.

  As is clear from Table 3, Comparative Example 4 has an average absorption coefficient of 470 / m for a wavelength of 0.5 to 4 μm, and Example 2 has an average absorption coefficient of 1250 / m for a wavelength of 0.5 to 4 μm. .

  Slab casting was performed using the mold flux of Comparative Example 4 and Example 2 and a mold having a lower end width of 1012 mm and a thickness of 140 mm. At this time, the steel type was an ultra-low carbon steel having a carbon concentration of 60 ppm.

  After the mold flux was completely dissolved outside the mold, the molten mold flux was injected into the mold using a stopper type flow control device. At this time, the temperature of the molten mold flux at the time of injection was 1300 ° C. After the molten steel reached the target value when the molten steel was filled into the mold before the start of casting, a mold cover was provided on the mold simultaneously with the start of casting. Then, the consumption of the molten mold flux was continuously replenished with the progress of casting. The mold cover was made of an aluminum material, and the surface was processed with 1600 sandpaper so that the average reflectance for infrared rays in the 500 to 4000 nm region, which is the molten steel radiation region, was 40%.

  6 and 7 are photographs of the molten metal surface during continuous casting using the mold fluxes of Comparative Example 4 and Example 2. FIG. Referring to FIG. 6 showing a photograph of the molten metal surface of Comparative Example 4, it can be seen that in the case of Comparative Example 4, a surface solidified layer was formed, which caused deterioration in slab quality and operational stability. Inhibits. On the other hand, referring to FIG. 7 showing a hot water surface photograph of Example 2, it can be seen that the surface solidified layer is not formed in Example 2, which is the absorption of the mold flux with respect to the wavelength of 500 to 4000 nm. This is to prevent loss of molten steel radiant heat by adjusting the coefficient. That is, the embodiment can prevent molten steel surface solidification by preventing the loss of molten steel radiant heat by the relatively high absorption coefficient of the mold flux and achieving the initial slow cooling.

  Thus, the present invention achieves initial slow cooling by using a mold flux having an absorption coefficient of 1000 / m or more at a wavelength of 500 to 4000 nm at the time of continuous casting using a molten mold flux, thereby solidifying the molten metal surface. Can be prevented. In particular, it is possible to prevent deckle which is an abnormal solidification development of the slag pool of mold flux at the early stage of casting. In addition, by ensuring the hot surface heat retaining effect, stable operation for a long time is possible at the time of molten mold flux operation. Furthermore, the F value indicating the degree to which the mold surface fluctuates can be reduced to prevent slag from being mixed, and the slab quality can be improved.

  Although the present invention has been described with reference to the drawings and embodiments, those skilled in the art will be able to make various modifications and changes without departing from the technical idea of the present invention described in the claims. It will be understood that it can be changed.

Claims (7)

In mold flux for continuous casting,
CaO20~50 _wt%, SiO 2 20 to 50 _wt%, Al _{2 O} 3 20 wt% or _less, Na 2 O20 wt% or _less, Li 2 O10 _wt%, B _{2 O} 3 20 wt% or less and MgO10 wt% or less The mold flux characterized by including.   The thermal conductivity of the mold flux is 1.2 W / m. The mold flux according to claim 1, wherein the mold flux is k or more.   The mold flux according to claim 1, wherein the mold flux has an absorption coefficient of 1000 / m or more for a wavelength of 500 to 4000 nm in a molten state.   2. The mold flux according to claim 1, wherein the mold flux includes 3 parts by weight or less of a transition metal oxide with respect to 100 parts by weight of the mold flux and has a basicity of 0.5 to 1.5. . Outside the mold, CaO20～50 _wt%, SiO 2 20 to 50 _wt%, Al _{2 O} 3 20 wt% or _less, Na 2 O20 wt% or _less, Li 2 O10 _wt%, B _{2 O} 3 20 wt% or less And dissolving a mold flux containing 10 wt% or less of MgO;
Charging the melted mold flux into the mold over the entire continuous casting process by controlling the flow rate of the melted mold flux;
A continuous casting method comprising:   The thermal conductivity of the mold flux is 1.2 W / m. The continuous casting method according to claim 5, wherein the continuous casting method is k or more.   The continuous casting method according to claim 5, wherein the mold flux has an absorption coefficient of 1000 / m or more for a wavelength of 500 to 4000 nm outside the mold.

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