JP4881203B2 - Powder for continuous casting - Google Patents

Description

  The present invention relates to a powder for continuous casting added to a mold in continuous casting of molten metal.

  In continuous casting of molten metal, powder for continuous casting (hereinafter also simply referred to as “powder”) is added to the surface of the molten metal injected into the mold. The powder for continuous casting added to the mold is heated and melted by the high-temperature molten metal and flows between the mold and the solidified shell. Continuous casting powder is mainly used for heat insulation and oxidation prevention on the surface of the molten metal in the mold, absorption of non-metallic inclusions floating in the molten metal, lubrication by the powder film flowing between the mold and the shell, Exhibits the function of controlling heat removal. In addition, if the molten powder is caught in the molten metal, it may cause a quality defect. Therefore, it is necessary to perform continuous casting with less powder entrainment.

  The lubrication characteristics between the mold and the solidified shell are regarded as the most important, and many powder varieties with adjusted melt properties according to casting varieties and continuous casting conditions have been produced. Among the powder melt properties, the viscosity at 1300 ° C. is an important index for controlling the lubricity, and the lower the viscosity, the larger the amount of inflow between the mold and the solidified shell, and the higher the lubrication effect can be expected. On the other hand, an immersion nozzle is used to supply molten metal into the mold. The molten metal in the mold is stirred by the molten metal flow discharged from the immersion nozzle, and the meniscus portion of the molten metal is also affected by the stirring. When low-viscosity powder is used as the powder for continuous casting, there is a property that the molten powder is easily caught in the molten metal due to the stirring of the molten metal in the meniscus part and the vortex generated near the immersion nozzle. It remains inside the slab and becomes an inclusion defect. For this reason, powder for ultra-low carbon steel, which is often used for strict applications against internal defects in slabs, has been tried to increase the viscosity within a range that does not interfere with lubrication and minimize powder entrainment. Yes.

Patent Document 1 discloses a powder having a viscosity at 1300 ° C. of 10 poise to 150 poise and defining a relationship between a solid phase ratio and a temperature at the time of solidification. Thereby, the defect at the time of the process resulting from inclusion and the entrainment of powder can be prevented, preventing the trouble by powder inflow failure. In Patent Document 2, there is a powder in which CaO / SiO ₂ is in the range of 0.3 to 0.8, the viscosity at 1300 ° C. is more than 10 poise and 50 poise or less, and the solidification temperature and the crystallization rate after cooling are defined. It is disclosed. As a result, it is possible to manufacture a steel material with less powder entrainment and excellent surface properties while ensuring inflow properties.

The powders described in Patent Documents 1 and ₂ have a high content of SiO _{2 in} the powder and a low content of CaO as a means for making the viscosity at 1300 ° C. a high viscosity of 10 poise or more. The value of CaO / SiO ₂ is lowered.

The ultra-low carbon steel having a carbon concentration of 0.01% by mass or less contains Al and Ti for the purpose of deoxidation and the like. At the meniscus in the mold, the molten steel is in contact with the molten powder. At this interface, Al and Ti in the molten steel react with SiO ₂ in the molten powder, and the following reaction is generated.
4 [Al] +3 (SiO ₂ ) → 2 (Al ₂ O ₃ ) +3 [Si] (1)
[Ti] + (SiO ₂ ) → (TiO ₂ ) + [Si] (2)
Here, [] means a component in molten steel, and () means a component in molten slag.

When the SiO ₂ content in the molten powder is reduced by the reaction of the above formulas (1) and (2), the viscosity of the molten powder at 1300 ° C. is reduced as a result. Therefore, the property of the high viscosity that the powder originally had is lost, and the entrainment of the powder cannot be sufficiently prevented.

In order to prevent the reaction of the above formulas (1) and (2) at the interface between the molten steel and the molten powder, it is effective to lower the SiO ₂ activity in the molten powder. Therefore, attempts have been made to reduce the SiO ₂ content in the powder. For example, Patent Document 3 proposes a powder for continuous casting having a viscosity at 1300 ° C. of 3 to 8 poise and a basicity (CaO / SiO ₂ ) of 1.3 or more and less than 3.0 as a highly basic powder having a high viscosity. However, the viscosity is 8 poise or less, and it cannot be said that the viscosity is high.

In Patent Document 4, Al ₂ O ₃ or the like is effective for increasing the viscosity of the high basicity powder. However, when Al ₂ O ₃ or the like is simply added to the high basicity powder, crystals formed in the powder film are formed. It is said that the precipitation becomes unstable. And in this document, Akerumanaito, precipitated as main crystals composition when melted slag solidifying the Gehlenite like, CaO / SiO ₂ is _{1.0~1.5, Al 2 O 3, MgO} , Na 2 O, Li 2 A powder having a component range such as O and a solidification temperature and a viscosity at 1300 ° C. of 0.2 to 1.3 poise is disclosed. The powder described in this document cannot be said to have a sufficiently high viscosity.

In Patent Document 5, by reducing the activity of SiO ₂ in the powder, the reaction between the powder and the molten steel is suppressed, the decrease in the interfacial tension between the molten steel and the powder is suppressed, and the decrease in the viscosity is also suppressed. It is said that it is possible to prevent entrainment of powder in molten steel. Then, the CaO / SiO ₂ in the powder 0.6-1.2, the SiO ₂ content is 10 to 35% and reduce the SiO ₂ activity of the powder. According to the Example, the example whose viscosity in 1300 degreeC is 8-20 poise is shown.

The one described in Patent Document 6 is an invention in which the powder viscosity at 1300 ° C. is 12 poise or less, and the content of SiO _{2 and the} content of Na ₂ O or the like in the powder is lower than a constant value determined from the powder viscosity. . Thereby, the reactivity of the powder melt and aluminum in the molten steel is reduced, and the entrainment of powder in the molten steel at the time of bubble breakage on the molten metal surface of argon gas is significantly reduced.

  It has been practiced to predict the occurrence of a constraining breakout (hereinafter referred to as “BO”) by embedding a thermocouple in a continuous casting mold and monitoring fluctuations in the mold temperature during casting. The mold temperature below the meniscus portion is monitored, and when the mold temperature at this portion rises unsteadily, it is recognized that the fracture portion of the shell due to restraint has fallen to this portion, and the casting speed is rapidly reduced. Thereby, the fracture | rupture part of a shell can be repaired and restraint BO generation | occurrence | production can be prevented. The frequency of occurrence of the restrictive BO prediction signal differs depending on the type of powder, and powder having a lower frequency of occurrence is more stable and preferable. In addition, when the time variation of the temperature of the thermocouple in the mold is large, it can be recognized that the inflow state of the powder is unstable.

JP 2003-290888 A JP 2004-167527 A Japanese Patent No. 2991057 Japanese Patent Laid-Open No. 2005-40835 JP 2006-175472 A JP 2006-192440 A

Those described in Patent Documents 3 and 4, although reducing the reaction between Al and the like of the SiO ₂ in the component and the molten steel in powder by using a high basicity powder, that never high viscosity viscosity at 1300 ° C. I can't.

Those described in Patent Document 5, to lower the SiO ₂ activity of the powder suppresses the reaction between the powder and the molten steel has a viscosity at 1300 ° C. simultaneously achieves high viscosity and 8～20Poise. Patent Document 6 discloses a powder having a viscosity at 1300 ° C. of 12 poise or less and low reactivity with molten steel components. However, it has been found that when high-viscosity powders described in Patent Documents 5 and 6 are used for continuous casting, fluctuations in the mold temperature measured by a thermocouple embedded in the mold increase.

  The present invention has a sufficiently high powder viscosity that can reduce the entrainment of powder, prevent the reaction between the powder and molten steel components to prevent the powder viscosity from being lowered during casting, and the thermoelectric embedded in the mold during casting. An object of the present invention is to provide a powder for continuous casting which can reduce the temperature fluctuation of the pair.

That is, the gist of the present invention is as follows.
(1) By mass%, SiO ₂ : 5.0 to 35.0%, Al ₂ O ₃ : 5.0 to 35.0%, T.I. CaO: 40.0% or less, Na ₂ O: 3.0 to 15.0%, F: 2.0 to 10.0%, MgO is regulated to 1.5% or less, and other component contents Is 20% or less. A powder for continuous casting, wherein CaO / SiO ₂ is 0.15 to 1.05, the viscosity at 1300 ° C. is 10 to 20 poise, and the solidification temperature is 1260 ° C. or less.

However, T.W. CaO is the CaO content calculated assuming that all Ca in the powder is CaO.
(2) further continuous casting powder according to (1), characterized in that it comprises 1.0 to 10 wt% including the ZrO _2.
(3) further continuous casting powder according to (1) or (2) and having containing 0.4 to 5.0% of C.
(4) The powder for continuous casting according to any one of (1) to (3), wherein SrO is further regulated to 5.0% or less.

The present invention prevents the entrainment of powder by increasing the viscosity at 1300 ° C. to 6 poise or higher, and prevents the reaction between the powder and molten steel by setting the SiO ₂ content to 35.0% or less. By reducing the MgO content to 2.5% or less and at the same time the basicity to 1.05 or less, temperature fluctuations of the thermocouple embedded in the mold during casting can be reduced, and extremely low carbon Powder entrainment can be stably reduced during steel casting.

  The powder for continuous casting of the present invention has a viscosity at 1300 ° C. of 6 to 30 poise. When the viscosity is less than 6 poise, the entrainment of powder cannot be sufficiently reduced in the casting of ultra-low carbon steel. On the other hand, if the viscosity exceeds 30 poise, the in-mold lubricating function by the powder film cannot be sufficiently obtained. The viscosity at 1300 ° C. is more preferably in the range of 8 to 20 poise. The lower limit of viscosity is more preferably 10 poise, and the lower limit of viscosity is more preferably 12 poise.

In the conventional high-viscosity continuous casting powder, the SiO ₂ content in the powder is increased (40 to 60%) to increase the viscosity, and the CaO / SiO ₂ value is also low. In the present invention, the content of SiO ₂ in the powder is set to a low value in order to reduce the SiO ₂ activity of the powder and reduce the reaction between the components in the molten steel and the SiO ₂ in the powder. The SiO ₂ content in the powder is 35% by mass or less, preferably 30% by mass or less.

Even if the SiO ₂ content is reduced, it is necessary to ensure a high viscosity, and it is necessary to supplement other components by the amount that the SiO ₂ content is reduced.

Increasing the Al ₂ O ₃ content in the powder can increase the viscosity. Therefore, in the present invention, in order to reduce the SiO ₂ content without reducing the powder viscosity, first, the Al ₂ O ₃ content is increased. If the Al ₂ O ₃ content is 5.0% by mass or more, the powder viscosity can be secured at 6 poise or more, so the lower limit is made 5.0% by mass. Preferably, the lower limit is 15.0% by mass. On the other hand, if the Al ₂ O ₃ content exceeds 35.0% by mass, a normal molten state cannot be obtained, so the upper limit is made 35.0% by mass. The upper limit of the Al ₂ O ₃ content is preferably 25.0% by mass. The upper limit is more preferably 20.0% by mass. The higher the Al ₂ O ₃ content within the preferred range, the higher the viscosity, and the other components that can be supplemented when reducing the SiO ₂ content is preferred.

As an object to be increased when the content of SiO ₂ in the powder is reduced, T.P. Examples include CaO. Increasing the CaO content decreases the viscosity. In order to set the viscosity at 1300 ° C. to 6 poise or more, T.C. The upper limit of the CaO content is 40.0% by mass. T.A. If the upper limit of the CaO content is 35.0% by mass, the viscosity can be further increased, which is preferable. On the other hand, T.W. When the CaO content is less than 20%, it is difficult to make the SiO ₂ content 35% by mass or less. The lower limit of the CaO content is preferably 20% by mass. T.A. As described above, CaO is the CaO content calculated assuming that all Ca in the powder is CaO.

In order to keep the molten state of the powder suitably, the normal powder often contains Na ₂ O. To reduce the SiO ₂ content in the powder, the Na ₂ O content can be increased, but if the Na ₂ O content exceeds 15.0% by mass, the viscosity at 1300 ° C. should be maintained at 6 poise or more. Therefore, the upper limit of the Na ₂ O content is 15.0% by mass. Preferably, the upper limit of the Na ₂ O content is 10.0% by mass. On the other hand, if the Na ₂ O content is too small, it is difficult to obtain normal powder melting, so the lower limit is made 3.0% by mass. The lower limit is more preferably 5.0% by mass.

In order to keep the molten state of the powder suitably, F is contained in normal powder. The F content can be increased to reduce the SiO ₂ content in the powder. However, if the F content exceeds 10.0% by mass, it becomes difficult to maintain the viscosity at 1300 ° C. at 6 poise or more. Therefore, the upper limit of the F content is 10.0% by mass. Preferably, the upper limit of the F content is 8.0% by mass. On the other hand, if the F content is too small, it is difficult to obtain normal powder melting, so the lower limit is made 2.0 mass%. The lower limit is more preferably 4.0% by mass.

As another component to be included for reducing the SiO ₂ content in the powder, MgO is the most preferred component used. However, in the present invention, when about 3% of MgO is contained in the powder, equiaxed crystals are formed in the powder film when the molten powder is solidified. As a result of analysis, the crystals are slightly acermanite (2CaO · MgO · it has been found 2SiO ₂₎ is gehlenite _{(2CaO · Al 2 O 3 ·} SiO 2) containing. In connection with the formation of gehlenite, when the temperature in the mold during continuous casting is measured with a thermocouple embedded in the mold, the temperature in the mold during continuous casting varies at a position below the meniscus part. It was observed to grow. When the powder component is low SiO ₂ and further high Al ₂ O ₃ , the generation of gehlenite due to the MgO content is particularly remarkable.

When crystals are formed in a powder film in a continuous casting powder that is currently used, most of the crystals that are formed are caspodyne (3CaO · 2SiO ₂ · CaF ₂ ). Caspodyne is formed in a layer form along the mold side of the film as columnar crystals in the powder film. On the other hand, when gehlenite is generated in the powder film, it nucleates and grows locally in the film, so that the radiant heat transfer at the grain boundaries is scattered, resulting in local heat removal from the mold. Presumed to be disturbed. Therefore, in order to stabilize the mold heat transfer through the powder film, it is necessary to prevent the formation of gehlenite on the powder film.

In the present invention, the content of MgO as a powder-containing component is limited to 2.5% by mass or less, thereby making it possible to prevent the formation of gehlenite in the powder film. The MgO content is more preferably 1.5% by mass or less. In the case of reducing the SiO ₂ content in the powder while maintaining the high viscosity of the powder as in the present invention, MgO is the most preferred component to be added instead. Also for the powder described in Patent Document 5, it is clear that the MgO content exceeds 2.5% for the examples in which the viscosity at 1300 ° C. is 8 poise or more and the SiO ₂ content is kept low. . In the present invention, by limiting the upper limit of MgO content to 2.5%, it is possible to prevent the formation of gehlenite and ensure stable heat transfer characteristics when reducing the SiO ₂ content with high viscosity. Made possible.

In the present invention, in order to prevent the formation of gehlenite in the powder film, in addition to defining the upper limit of the MgO content, T.I. CaO / SiO ₂ is limited to 1.05 or less. Within the powder component range of the present invention, T.I. When CaO / SiO ₂ increases, the powder composition approaches that of gehlenite (2CaO · Al ₂ O ₃ · SiO ₂ ), so that gehlenite is easily generated in the powder film. By limiting CaO / SiO ₂ to 1.05 or less, it becomes possible to suppress the generation of gehlenite in the powder film. On the other hand, T.W. When CaO / SiO ₂ is less than 0.15, it is difficult to reduce the SiO ₂ content to 35% or less. The lower limit of CaO / SiO ₂ is 0.15. T.A. More preferably, the lower limit of CaO / SiO ₂ is 0.55.

  The powder for continuous casting of the present invention enables continuous casting with less powder entrainment by setting the viscosity at 1300 ° C. to a high viscosity. On the other hand, if the solidification temperature becomes too high due to the increase in viscosity at 1300 ° C., the powder film that has flowed into the space between the mold and the solidified shell will solidify too early, and the inflow lubrication characteristics of the powder film will deteriorate. Become. In the present invention, when the solidification temperature of the powder is 1260 ° C. or less, the inflow lubrication characteristics of the powder can be maintained well.

Conventional high-viscosity powder achieves high viscosity by increasing the SiO ₂ content, and since the molten steel component reacts with SiO _{2 in the} powder during casting, the powder solidifies due to the change in the powder component resulting from the reaction. A phenomenon in which the temperature decreased was observed. Therefore, even if the solidification temperature as a characteristic of the powder before use is a relatively high temperature, the powder inflow lubrication characteristic tends to be kept good in practice. On the other hand, the powder of the present invention has a small change in the powder component during casting as a result of keeping the SiO ₂ content low, and the solidification temperature during casting is suppressed from decreasing. Therefore, it has been found that a preferable result can be obtained when the solidification temperature as a characteristic of the powder before use is set to a lower temperature as compared with the conventional high SiO ₂ content powder. Specifically, a preferable inflow lubrication characteristic of the powder can be realized by setting the solidification temperature of the powder to 1160 ° C. or less. More preferably, the solidification temperature is 1120 ° C. or lower.

Increasing the ZrO ₂ content in the powder can increase the viscosity. Therefore, in the present invention, it is preferable to contain ZrO ₂ in order to obtain preferable characteristics by setting the viscosity at 1300 ° C. to a higher value. On the other hand, if ZrO ₂ is contained, the solidification temperature of the powder is raised, so the ZrO ₂ content is set to 10% by mass or less. In order to increase the viscosity at 1300 ° C. by containing ZrO ₂ and at the same time maintain the solidification temperature of the powder at 1120 ° C. or less, the ZrO ₂ content is preferably maintained at 3.0% by mass or less. Moreover, the effect of containing ZrO ₂ can be exhibited when the ZrO ₂ content is 1.0% by mass or more.

  MgO is known as a component having a function of lowering the solidification temperature of the powder. However, as described above, when MgO is contained in the powder of the present invention, harmful gelenite is generated at the time of powder solidification, so that the solidification temperature cannot be lowered by containing MgO.

Increasing the Na ₂ O content in the powder can lower the solidification temperature of the powder. In normal powder component design, the Na ₂ O content is often 3-4%. In the present invention, the Na ₂ O content can be increased within an allowable range (upper limit: 15.0%, preferably upper limit: 10.0%) for the purpose of reducing the solidification temperature of the powder.

  As a powder melting rate adjusting agent, C may be contained in the powder. By containing C, the melting rate of the powder can be suppressed. This effect can be exhibited if the C content is 0.4 mass% or more. On the other hand, in the powder used for continuous casting of ultra-low carbon steel, carburization from powder to molten steel becomes a problem, so the upper limit of the C content is 5.0 mass%.

In the present invention, it may be necessary to further contain other components in order to reduce the SiO ₂ content after suppressing the content of components other than SiO ₂ within a predetermined range. Further, it contains other components as inevitable impurities from the raw materials. Examples of other components include SrO, BaO, MnO, TiO ₂ , B ₂ O ₃ , Li ₂ O, and K ₂ O. In the present invention, the targeted powder quality can be maintained by reducing the total content of these other components as much as possible. The total content of other components is preferably 20% by mass or less. The total content of other components is more preferably 15% by mass or less. More preferably, it is 10 mass% or less.

Of the other components, SrO may be added to the powder using SrCO ₃ as a raw material. When carbonate is contained in the powder, it decomposes into oxide and carbon dioxide in the mold, and the generated carbon dioxide stirs the unmelted powder, which promotes the combustion of C in the powder and changes the melting characteristics of the powder. there's a possibility that. By restricting the SrO content to 2.5% by mass or less, occurrence of such a phenomenon can be suppressed.

The continuous casting powder of the present invention has a SiO ₂ content of 35% by mass or less, more preferably 30% by mass or less, and a viscosity at 1300 ° C. of 6 poise or more, preferably 8 poise or more, more preferably 10 poise or more, more preferably Can be 12 poise or more. At the same time, the solidification temperature of the powder can be 1260 ° C. or lower, preferably 1160 ° C. or lower, more preferably 1120 ° C. or lower. In order to make the viscosity at 1300 ° C. of the powder higher, first, the SiO ₂ content is set to a value near the target upper limit. The lower the CaO content, the higher the viscosity can be realized. However, it is indispensable as another component contained in order to reduce the SiO ₂ content. The CaO content is preferably about 30% by mass. In order to maintain the viscosity at a high value while reducing the SiO ₂ content, the Al ₂ O ₃ content is set as high as possible within a preferable range. The Na ₂ O content can be increased as the content decreases within a preferred range. In the case where the increase in viscosity and the decrease in the solidification temperature are realized together, it is preferable that the Na ₂ O content is not reduced too much and is set to about 6%. As for the F content, the higher the viscosity is, the lower the content is within the preferable range. Furthermore, it contains ZrO _2, and the viscosity can be increased as the content is increased within a preferable range. By suppressing the Zr content to 3% or less, it is possible to maintain the solidification temperature at 1120 ° C. or less while increasing the viscosity.

That is, the viscosity at 1300 ° C. can be 6 poise or more within the component range of the present invention, and the viscosity at 1300 ° C. can be further increased by adjusting the content of each component according to the above guidelines. . The SiO ₂ content is about 30%, the Al ₂ O ₃ content is about 20%. By setting the CaO content to less than 30%, the Na ₂ O content to about 6%, the F content to over 4%, and the ZrO ₂ content to about 3%, the low SiO ₂ content is 1300. The viscosity at ° C. can be set to a high value of about 12 poise, and the solidification temperature can be set to a favorable temperature range of about 1100 ° C. Since the SiO ₂ content is low, the reaction between the molten steel and the molten powder can be suppressed, the characteristic change of the powder after powder melting is minimized, and casting with less powder entrainment is possible. Furthermore, since the solidification temperature is low and the formation of gehlenite crystals in the powder film is prevented, the heat removal behavior of the slab through the powder film can be stabilized.

  In the present invention, the rotating cylinder method is preferably used as a method for measuring the viscosity of the powder. The continuous casting powder to be measured is charged into a crucible and completely melted at 1400 ° C., then placed in a vertical annular furnace (Elema furnace), and the rotor of the E-type viscometer is immersed in the molten powder at 1300 ° C. After stabilizing for 30 minutes, the rotor is rotated and the torque due to viscous resistance is measured to determine the viscosity. The E-type viscometer is calibrated with a standard viscometer in advance.

  As a method for measuring the solidification temperature of the powder, in the above-described vertical annular furnace for measuring viscosity, after measuring the viscosity at 1300 ° C., the viscosity is continuously measured while gradually decreasing the temperature of the furnace. At this time, the viscosity gradually increases as the temperature drops. The temperature at which this viscosity rapidly increases is defined as the solidification temperature.

  300ton of molten steel melted in a converter, adjusted to a specified component concentration with RH, is an ultra-low carbon steel molten steel with a vertical bending type continuous casting machine through a tundish and immersion nozzle. Cast into a 1600 mm slab. The molten steel component range is shown in Table 1.

  Powders for continuous casting having the components and characteristics shown in Table 2 were prepared and added into the mold in continuous casting. The casting speed was about 1.8 m / min. The viscosity at 1300 ° C. and the solidification temperature of the powder for continuous casting were measured using the methods described above.

  About the powder entrainment situation to a slab, it evaluated by comparing the coil surface defect incidence after cold-rolling a slab, and comparative example No. The generation index of 6 was standardized as 1.0. The mold heat transfer characteristics were evaluated by measuring the mold temperature using a thermocouple embedded 40 to 400 mm below the meniscus portion in the mold and generating the BO prediction signal.

  Invention Example No. 2 in Table 2 No. 1 satisfied all the conditions of the preferred powder component system of the present invention, and good results could be obtained. Invention Example No. 2 is within the scope of claim 1 and good results could be obtained, but the SrO content deviated from the preferred range, the molten slag was enlarged, and the solidification temperature was higher than the preferred range. Some increase in the frequency of BO prediction occurred. Invention Example No. 3 was within the scope of claim 1 and good results could be obtained, but the coagulation temperature was higher than the preferred range, and a slight increase in the BO prediction occurrence frequency was observed.

Comparative Example No. In No. 4, the MgO content deviated from the scope of the present invention, gehlenite was generated in the powder film, and the increase in the BO prediction occurrence frequency became remarkable. Comparative Example No. In No. 5, CaO / SiO ₂ deviated from the upper limit of the range of the present invention, and gehlenite was generated in the powder film, and the increase in the BO prediction occurrence frequency became remarkable.

Comparative Example No. In No. 6, the SiO ₂ content deviated from the upper limit of the range of the present invention. During casting, the SiO ₂ content dropped to around 40.0%, and the Al ₂ O ₃ and TiO ₂ contents increased. The molten powder was sampled from the mold and the viscosity at 1300 ° C. and the solidification temperature were measured. The viscosity was 8 poise and the solidification temperature was reduced to 1100 ° C. Although the heat transfer characteristics of the casting were good due to the decrease in the solidification temperature, the surface defect occurrence index due to the entrainment of powder was poor at 1.0. Comparative Example No. 7 was the same.

Comparative Example No. No. 8 had a low surface defect index because the viscosity was originally low and the SiO ₂ concentration was outside the upper limit.

Claims (4)

In terms of mass%, SiO ₂ : 5.0 to 35.0%, Al ₂ O ₃ : 5.0 to 35.0%, T.I. CaO: 40.0% or less, Na ₂ O: 3.0 to 15.0%, F: 2.0 to 10.0%, MgO is regulated to 1.5% or less, and other component contents Is 20% or less. A powder for continuous casting, wherein CaO / SiO ₂ is 0.15 to 1.05, the viscosity at 1300 ° C. is 10 to 20 poise, and the solidification temperature is 1260 ° C. or less.
However, T.W. CaO is the CaO content calculated assuming that all Ca in the powder is CaO. Further continuous casting powder according to claim 1, characterized in that it comprises 1.0 to 10 wt% including the ZrO _2. Further continuous casting powder according to claim 1 or 2, characterized in that it has free 0.4 to 5.0% of C. Furthermore, SrO is controlled to 5.0% or less , The powder for continuous casting in any one of the Claims 1 thru | or 3 characterized by the above-mentioned.