JP2008264791A - Mold powder for continuously casting steel and continuous casting method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide mold powder for continuously casting a steel with which while securing difficulty to enclosure into the steel as high-viscosity powder having ≥0.8 Pa s viscosity at 1300°C, the mold powder has excellent lubrication and a high-grade product having no powder defect can be obtained without obstructing the productivity. <P>SOLUTION: The mold powder for continuously casting the steel is the one, containing at least one of Al and Ti; 0.9-1.2 CaO/SiO<SB>2</SB>mass ratio; ≤38 mass% CaO; 10-35 mass% SiO<SB>2</SB>; 7-25 mass% Al<SB>2</SB>O<SB>3</SB>; 3-10 mass% Na<SB>2</SB>O and substantially containing no MgO; and ≥0.8 Pa s viscosity at 1300°C. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a mold powder for continuous casting of steel used by being added to a mold in continuous casting of steel.

The following properties are required for continuous casting mold powder (hereinafter sometimes referred to as “powder”) used for continuous casting of molten steel.
1) By covering the molten steel surface with molten powder formed by melting powder and an unmelted layer thereon, oxidation of molten steel by air is prevented, and a heat retaining effect is obtained.
2) Since the molten powder enters between the mold and the slab and becomes a lubricant, it must always be supplied in an appropriate amount. For this reason, it has a melting rate that matches the consumption rate and has an appropriate molten powder pool thickness.
3) The molten powder layer absorbs non-metallic inclusions that have floated from the steel, and changes in their physical properties (viscosity, melting temperature) are small.
4) The molten powder flows between the mold and the solidified shell to form a uniform powder film, and has a lubricating action between them.
5) The molten powder has an appropriate viscosity and interfacial tension and should not be caught in molten steel.

  Among these, in particular, the entrainment of powder in steel is often a problem for steels with strict quality requirements such as tinplate materials and steel plates for automobiles even during high-speed casting, medium and low-speed casting.

  For this reason, the highly viscous and high surface tension type hard-to-roll powder shown in Patent Document 1 and the high interfacial tension-type hard-to-roll powder shown in Patent Document 2 have been developed.

When Al or Ti is contained in the steel, SiO _{2 in} the powder reacts with Al or Ti in the molten steel, and the physical properties of the powder change. Therefore, the lubricity of the powder and the entrainment of the powder in the steel are improved. Getting worse. Therefore, even when continuous casting is performed using molten steel containing Al or Ti, molten steel and powder are suppressed by reducing the reactivity of the powder and suppressing the reaction with the powder as shown in Patent Document 3. By reducing the entrainment of the interfacial tension of the powder by reducing the entrainment of the powder into the molten steel, as shown in Patent Document 4, SiO ₂ , Na ₂ O ₃ , Li ₂ O can be reduced, Powders have been developed that can reduce the entrainment of the powder in the molten steel by suppressing the reaction with the molten steel and controlling the powder viscosity.

In addition, in Al-containing steel, lubrication failure may occur due to precipitation of high melting point crystal gehlenite. Therefore, Patent Document 5 proposes a powder that prevents molten steel contamination due to the reaction between molten steel and powder, and prevents precipitation of high melting point gehlenite by the addition of Li ₂ O or F.

Japanese Patent Publication No. 4-40103 JP 2000-71051 A JP 2006-175472 A JP 2006-192440 A JP 2006-110578 A

  However, in recent years, there has been a demand for further high-speed casting and further improvement in quality. As in the technique of Patent Document 1, an appropriate powder can be obtained simply by changing the composition of the powder to make it highly viscous to prevent entrainment. As a result, it becomes impossible to maintain a sufficient lubricity between the mold and the solidified shell, and in the worst case, a breakout is caused and the casting is stopped.

Further, in the technique of Patent Document 2, since CaO / SiO ₂ is very high as 7 or more, the solidification temperature becomes high, an appropriate amount of powder inflow cannot be secured, and sufficient lubricity between the mold and the solidified shell is obtained. It becomes impossible to maintain, and in the worst case, breakout is caused and casting is stopped.

  In the technique of Patent Document 3, it is necessary to increase the viscosity in order to meet the recent demand for higher quality. When the viscosity becomes 0.8 Pa · s or higher, sufficient lubricity between the mold and the solidified shell cannot be maintained, and the heat removal from the mold fluctuates, and the thermoelectric embedded in the mold for breakout detection. The temperature of the pair fluctuates, causing false positives and hindering productivity.

  Also in the technique of Patent Document 4, the inflow property and lubricity are impaired by the generation of a high-melting crystalline phase in the powder flowing between the mold and the slab, and the thermocouple embedded in the mold for breakout detection. Fluctuates in temperature, causing false detections and hindering productivity.

  In the technique of Patent Document 5, the viscosity is about 0.5 Pa · s at the maximum, and entrainment may occur when the casting speed increases due to the recent demand for higher productivity.

  The present invention has been made in view of such circumstances, and as a high-viscosity powder having a viscosity at 1300 ° C. of 0.8 Pa · s or more, it is difficult to entrain in steel and has excellent lubricity. An object of the present invention is to provide a powder for continuous casting of steel, which can obtain a high-quality product free from powder defects and does not hinder productivity.

The gist of the present invention for solving the above problems is as follows.
(1) A mold powder for continuous casting used for continuously casting steel containing at least one of Al or Ti, wherein CaO / SiO ₂ is 0.9 to 1.2 in terms of mass ratio, and CaO is 38 mass. %, SiO ₂ is 10 mass% to 35 mass%, Al ₂ O ₃ is 7 mass% to 25 mass%, Na ₂ O is 3 mass% to 10 mass%, and MgO is substantially contained. A mold powder for continuous casting of steel, characterized in that the viscosity at 1300 ° C. is 0.8 Pa · s or higher.
Here, CaO is a value obtained by converting all Ca contained in the powder into CaO.
(2) The mold powder for continuous casting of steel according to (1), wherein the F content is 2% by mass or more and 10% by mass or less.
(3) The mold powder for continuous casting of steel according to (1) or (2), wherein one or more of ZrO ₂ and SrO of 10% by mass or less are contained.
(4) The mold powder for continuous casting of steel according to any one of (1) to (3), wherein Ca / Si in the mold powder is 0.8 to 2.5 in terms of mass ratio.
(5) In any one of (2) to (4), CaO * / SiO ₂ in the mold powder is 0.6 to 1.2 by mass ratio, and CaO * is 30% by mass or less. Mold powder for continuous casting of steel as described.
Here, CaO * is a value obtained by analyzing Ca and F contained in the powder and converting Ca content obtained by subtracting the amount of Ca into CaO when F is added by CaF ₂ .
(6) The continuous steel according to any one of (1) to (5), wherein the interfacial tension with molten steel containing at least one of Al and Ti is 0.9 N / m or more at 1550 ° C. Mold powder for casting.
(7) The mold powder for continuous casting of steel according to any one of (1) to (6), wherein the activity of SiO ₂ at 1550 ° C. is 0.4 or less.
(8) The mold powder for continuous casting of steel according to any one of (1) to (7), wherein the solidification temperature is 1000 to 1200 ° C.
(9) The mold powder for continuous casting of steel according to any one of (1) to (8), wherein the melting temperature is 1000 to 1250 ° C.
(10) When continuously casting a steel containing at least one of Al and Ti, the continuous casting mold powder according to any one of (1) to (9) is used. .

  According to the present invention, even when continuous casting is performed using molten steel containing Al or Ti, while ensuring the difficulty of entrainment in molten steel as a high-viscosity powder having a viscosity at 1300 ° C. of 0.8 Pa · s or higher. And, it is excellent in lubricity, and furthermore, it can prevent a decrease in interfacial tension between steel and powder, and can stabilize heat removal, and can obtain a high-quality product free from powder defects. A powder for continuous casting of steel can be provided.

  As the casting speed increases due to the demand for higher productivity in recent years, it is desired to use powder with higher viscosity. However, as mentioned above, when the powder with higher viscosity is oriented, the mold and the solidified shell are used. There was a problem that sufficient lubricity could not be maintained. In particular, when continuous casting is performed using molten steel containing Al or Ti, the deterioration of lubricity is remarkable.

  Therefore, as a result of earnest and research, the present inventors have adjusted the powder component to an appropriate range, so that when performing continuous casting using molten steel containing Al or Ti, However, it was newly found that sufficient lubricity between the mold and the solidified shell can be achieved. This will be described in detail below.

In this invention, CaO means the value which converted all Ca contained in powder into CaO. In addition, CaO * means a value obtained by analyzing Ca and F contained in the powder, and assuming that F is added by CaF ₂ , the Ca content obtained by subtracting the amount of Ca is converted to CaO.

The inventors of the present invention are powders having a viscosity at 1300 ° C. of 0.8 Pa · s or higher using molten steel containing 0.1% by mass or less of Al or Ti (hereinafter simply referred to as “%”), and CaO , SiO ₂ , Al ₂ O _3, etc., various powders were examined for the entrainment of the powder into molten steel, the inflow of the powder in continuous casting, and the lubricity. Here, the powder having a viscosity at 1300 ° C. of 0.8 Pa · s or more was used because the powder was used at a temperature of about 1500 ° C., and the melting point of the powder was 1000 to 1250 ° C. This is because it has been experimentally found that if the viscosity is 0.8 Pa · s or higher, the powder can be easily caught in molten steel.

  Moreover, since it is desirable that the powder has a higher viscosity, the upper limit is not particularly specified. However, if the viscosity is too high, the lubricity is deteriorated, so that it can be appropriately selected depending on the casting speed and the like. In measuring the viscosity, a rotating cylinder method can be used.

  The rotor of the E-type viscometer is immersed in molten powder dissolved in an iron crucible using a vertical tubular furnace (Elema furnace) and stabilized at 1300 ° C. for 30 minutes. Torque can be measured to determine viscosity. It is important to calibrate the E-type viscometer with a standard viscosity solution in advance.

For viscosity at 1300 ° C. is to powder 0.8 Pa · s or more high viscosity, but to increase the viscosity of the Al ₂ O ₃ considering the cost and the like are common, the Al ₂ O ₃ for the A high melting point crystal is generated, which inhibits the inflow of the powder and impairs lubricity. As the high melting point crystal containing Al ₂ O ₃ , there is mainly gehlenite (2CaO · Al ₂ O ₃ · SiO ₂ ). Gaelenite has a melting point of 1593 ° C. and is produced at a high temperature, which impairs the inflowability and lubricity of the powder. The gehlenite in the powder after solidification can be measured by X-ray diffraction.

Then, paying attention to the mass ratio of CaO / SiO ₂ in the powder (sometimes referred to as “basicity”), the basicity was 0.9 to 1. In the range of 2, it was newly found out that an effect of preventing powder entrainment can be obtained and lubricity can be secured.

If the basicity in the powder is less than 0.9, the effect of preventing the entrainment of the powder cannot be obtained. As for the activity of SiO ₂ shown later, this value increases, it is difficult to obtain the effect of entanglement preventing. On the other hand, if the basicity exceeds 1.2, the inflow property and lubricity are impaired. This is because the melting point of the powder suddenly rises when the basicity is 0.9 or more, and the effect of preventing the entrainment of the powder is obtained. However, when the basicity exceeds 1.2, the melting point of the powder becomes too high, and a solidified phase of the powder is generated in the powder, and a high melting point crystal of gehlenite is generated in the solidified phase. It is considered that the fluidity of the oil deteriorates remarkably and it becomes difficult to secure the inflow property and lubricity.

  Therefore, the lower the upper limit of the basicity, the less likely the solidified phase is formed in the powder, so 1.15 is preferable, 1.10 is more preferable, and 1.05 is even more preferable. Further, in order to prevent the solidified phase from being generated in the powder more reliably, the upper limit of the basicity is preferably 1.10, and most preferably 0.96.

  Next, the components of the powder will be described.

As the main component of the powder, there are CaO and SiO ₂ . As described above, it is important to maintain the basicity (CaO / SiO ₂ mass ratio) in the powder at 0.9 to 1.2.

  However, if the CaO content exceeds 38% by mass, the solidification temperature becomes high, and the inflow property and lubricity are liable to be impaired.

Further, if the SiO ₂ content is less than 10% by mass, it is difficult to adjust physical properties such as melting temperature and viscosity, and if it exceeds 35% by mass, it is difficult to obtain the effect of suppressing the reaction between powder and molten steel. Mass%.

Al ₂ O ₃ is added to adjust the solidification temperature and viscosity, but if the Al ₂ O ₃ content in the powder is less than 7% by mass, the adjustment effect is small, and if it exceeds 25% by mass, the viscosity increases too much. Inflow and lubricity are impaired, and the heat removal behavior becomes unstable.

Na ₂ O is added in order to adjust the melting point and suppress the formation of a high melting point crystal containing Al ₂ O ₃ by improving the glass property. If the Na ₂ O content in the powder is less than 3% by mass, the effect cannot be obtained. Na ₂ O also has an effect of lowering this value with respect to the activity of SiO ₂ described later. However, since Na ₂ O easily reacts with molten steel, if the Na ₂ O content exceeds 10% by mass, the effect of preventing entrainment due to reaction suppression cannot be obtained.

When MgO is contained, a high melting point crystal containing Al ₂ O ₃ is likely to be formed. Therefore, MgO is not added and MgO is not substantially contained. However, since it may be inevitably mixed, in such a case, it is acceptable if it is less than 1% by mass. However, if it is 1% by mass or more, it is difficult to suppress the formation of a high melting point crystal containing Al ₂ O ₃ .

  Moreover, you may selectively contain the following components in powder.

The F component is added for the purpose of lowering the solidification temperature and viscosity, but if the F concentration in the powder is less than 2% by mass, the effect is small, and if it exceeds 10% by mass, the viscosity will decrease too much and crystals such as CaF ₂ will precipitate. As a result, the heat removal behavior becomes unstable and the powder inflow becomes excessive, and the slab quality tends to deteriorate. Therefore, it is preferable to set it as 2-10 mass%. The supply of F can be exemplified by adjusting Ca content by adding CaF ₂ .

ZrO ₂ is added to ensure the viscosity. However, if the ZrO ₂ concentration in the powder exceeds 10% by mass, the viscosity will increase too much, so 10% by mass or less is desirable.

  SrO is added for the purpose of adjusting the physical properties of the molten powder. When SrO is added, changes in physical property values such as solidification temperature and viscosity with respect to changes in the powder composition can be suppressed. However, if the SrO concentration in the powder exceeds 10% by mass, the cost becomes high, so 10% by mass or less is desirable.

ZrO ₂ and SrO may be contained alone or in combination.

  Furthermore, the present powder can appropriately contain carbonaceous matter such as carbon black, coke powder, and graphite, and organic matter such as fiber and resin. These carbon and organic substances are added for the purpose of adjusting the melting rate, keeping the surface of the molten steel warm, forming a binder, and the like.

  As each component of the powder, a value analyzed by fluorescent X-ray or chemical analysis can be used.

Furthermore, by suppressing the reaction between powder and molten steel, it was clarified that inflow and lubricity can be secured by reducing the entrainment of powder into molten steel. It was also found that by suppressing the reaction with the powder, the concentration of Al ₂ O ₃ and TiO ₂ in the powder can be reduced and the change in viscosity can be prevented.

  Specifically, it has been found that when the interfacial tension of the powder becomes 0.9 N / m or more at 1550 ° C., the entrainment of the powder into the steel is satisfactorily suppressed. When the interfacial tension of the powder is less than 0.9 N / m, the entrainment of the powder into the steel increases.

  Here, since the upper limit of the interfacial tension of the powder is preferably higher, it is not particularly specified, but a value that can be actually adjusted is about 1.7 N / m.

  Further, the reason why the interfacial tension of the powder is set to a value at 1550 ° C. is that the temperature is close to the temperature of the molten steel used for actual continuous casting.

  When using molten steel containing Al or Ti, the interfacial tension between the molten steel and the powder is affected by the reactivity of the components in the powder with Al and Ti in the molten steel. By adjusting the powder to have a low reactivity with Al and Ti in the molten steel so that the interfacial tension of the powder becomes 0.9 N / m or more, the entrainment of the powder in the steel can be reduced.

As a method for adjusting a powder component having low reactivity with Al and Ti in molten steel, SiO ₂ and Na ₂ , which are oxides of elements (Si, Na, Fe, and Mn) that are less oxidized than Al and Ti, are used. An example is to reduce the content of O, FeO, MnO and the like.

  In addition, about the molten steel containing more than 0.1 mass% of Al and Ti, since the reactivity with powder is higher, the effect of this invention is exhibited more.

  Here, the interfacial tension can be measured by a method similar to “Hiroshi Ooi, Tsutomu Nozaki, Hiroshi Yoshii: Iron and Steel, 58 (1972), 890”.

  That is, the steel sample was gently added to the molten powder at 1550 ° C. melted in the crucible to melt the steel, and the shape of the molten steel in the molten powder was photographed from the side by X-ray transmission, from this X-ray transmission photograph. Interfacial tension can be determined by measuring the shape of the steel.

Thus, when using molten steel containing Al or Ti, the activity of SiO _{2 in} the powder (hereinafter sometimes referred to as “aSiO ₂ ”) may be used to suppress the reaction with the powder. By lowering, the reaction between the powder and the molten steel is suppressed, and the entrainment of the powder in the molten steel can be reduced.

  Here, the activity is an index indicating chemical reactivity, and as disclosed in, for example, “Masayasu Otani: Iron Metallurgical Thermodynamics, Nikkan Kogyo Shimbun, Tokyo, (1971), p. 78”. Can be obtained by multiplying by the activity coefficient.

Hereinafter, the preferable range of aSiO ₂ of the powder of the present invention will be described.

  In order to evaluate the entrainment of the powder in the molten steel, the quartz J-shaped tube is immersed in the molten steel floating the molten powder, and the molten steel near the surface of the molten metal is sucked into the steel sucked into the J-shaped tube. The amount of powder to be measured was measured. In addition, the measurement of the amount of powder was calculated | required by observing the cross section of the steel after solidification under a microscope.

Next, using a powder containing CaO, SiO ₂ and Al ₂ O ₃ and variously changing aSiO ₂ , a powder entrainment index was determined from the amount of powder measured by the above method. As a result, a SiO ₂ is less effect of preventing entrainment in greater than 0.4, by the a SiO ₂ and 0.4 or less, was found to be able to suppress the reaction between the molten steel and the powder.

For this reason, it is preferable to set aSiO ₂ to 0.4 or less, since a decrease in the interfacial tension between the molten steel and the powder can be suppressed and the entrainment of the powder in the molten steel can be prevented. Here, the lower limit of aSiO ₂ includes 0.

Moreover, the reason why the aSiO ₂ of the powder was set to a value at 1550 ° C. is that the temperature is close to the temperature of the molten steel used for actual continuous casting.

Here, aSiO ₂ can be obtained by experiment, and can also be obtained by calculation using a thermodynamic model.

The determination of aSiO ₂ in the powder by experiment is usually performed as a method performed when determining the activity of the component in the slag as “Toshiharu Fujisawa, Hiroshi Sakao: Iron and Steel, 63 (1977), p. 1504”. The same method can be used.

That is, by dissolving the powder on the molten steel and holding it until equilibrium is reached, the Si concentration in the molten steel and the SiO ₂ concentration in the powder are analyzed and compared with the equilibrium concentration when pure SiO _2, that is, aSiO ₂ is 1. Is required.

  On the other hand, SOLGASMIX (see “G. Erikson: Chemical Scripta, 8 (1975), p. 100”) and Thermo-Calc (“B. Sundman,” as calculation tools for calculating activity using a thermodynamic model. B. Jansson, JO Andersson: CALHAD, 9 (1985), p. 153 "), etc., and these may be used to calculate from the powder composition.

As described above, in a molten steel containing Al or Ti, when aSiO ₂ in the powder is reduced, the reaction between SiO _{2 in} the powder and Al or Ti in the molten steel is suppressed, and the decrease in interfacial tension is suppressed. The powder entrainment can be reduced.

Furthermore, in the case of molten steel with a high Mn concentration, SiO ₂ in the powder and Mn in the molten steel react to increase the content of MnO in the powder, and as a result, the viscosity of the powder may decrease. . When aSiO ₂ is lowered, the increase in MnO can be suppressed to prevent the viscosity from decreasing.

Next, the reason why Ca / Si in the powder is preferably 0.8 to 2.5 will be described. Here, Ca is the total amount of Ca added with CaO, CaF ₂ or the like.

  When analyzing the composition with a fluorescent X-ray analyzer or the like, it is difficult to analyze CaO itself, so it is practically desirable to adjust the components using the values of Ca and Si obtained by the analysis.

If the Ca / Si content in the powder is less than 0.8, the activity of SiO ₂ is high, and it is difficult to obtain the effect of preventing entrainment. If it exceeds 2.5, the solidification temperature becomes high, and the inflow property and lubricity are impaired. easy.

Furthermore, the reason why CaO * / SiO ₂ in the powder is preferably 0.6 to 1.2 will be described. Here, CaO * is a value obtained by analyzing Ca and F contained in the powder and converting the amount of Ca obtained by subtracting the amount of Ca into CaO, assuming that F is added by CaF ₂ .

When the CaO * / SiO ₂ in the powder is less than 0.6, the SiO ₂ activity is high, and it is difficult to obtain the effect of preventing entrainment. It is easily damaged.

  Further, if CaO * exceeds 30%, the solidification temperature becomes high, and the inflow property and lubricity are liable to be impaired.

  The solidification temperature of the powder is preferably 1000 ° C. or higher and 1200 ° C. or lower. When the solidification temperature of the powder is less than 1000 ° C., the heat removal behavior is unstable, and when it exceeds 1200 ° C., the lubrication characteristics are poor.

  In measuring the solidification temperature, the viscosity is measured at 1300 ° C. by the rotor rotation method, and then the temperature is decreased by 20 ° C., and the viscosity is measured after being held at each temperature to obtain log η and 1 / T (η is viscosity poise, (T represents absolute temperature ° K).

  At the time of this measurement, a crystal was crystallized in the sample due to the temperature drop, and it was no longer a Newtonian fluid.

  Furthermore, the melting temperature of the powder is desirably 1000 ° C. or higher and 1250 ° C. or lower. When the melting temperature of the powder is less than 1000 ° C., the heat removal behavior becomes unstable, and when it exceeds 1250 ° C., the lubrication becomes poor. In measuring the melting temperature, the pulverized powder was formed into a cylinder having a bottom to height ratio of 1: 1 without using a binder, and then heated on a platinum plate. The temperature at which the value becomes can be obtained as the melting temperature.

The powder of the present invention is adjusted by adding Na ₂ O without adding MgO while adjusting the viscosity mainly by Al ₂ O ₃ and adjusting basicity by CaO and SiO ₂ components in addition to this. The powder which can suppress the production | generation of the high melting point crystal | crystallization containing an alumina can be manufactured.

In order to adjust the melting temperature, the solidification temperature, and the viscosity, for example, CaF ₂ , ZrO ₂ , SrO or the like may be added as appropriate.

  Moreover, the powder of this invention can be used conveniently for the continuous casting method of the molten steel containing at least one of Al and Ti.

  The target steel type in which the powder according to the present invention is effectively used is preferably carbon-containing steel. The reason why carbon containing steel is used is that molten steel that does not contain carbon increases the viscosity of the molten steel and the interfacial tension with the powder, making it difficult to exhibit the effect of this powder.

  Moreover, the carbon concentration in the steel is not particularly limited, but in particular, a steel plate manufactured with a steel having a low carbon concentration of 0.0005 mass% to 0.05 mass% is likely to cause defects due to powder entrainment. The effect of the present invention is great.

  Further, in the present invention, the content of Al and Ti in the molten steel is not limited, but when used for molten steel with a relatively low content of at least one of Al and Ti of 0.1% by mass or less However, the effects of the present invention can be sufficiently obtained.

  300ton of molten steel melted in a converter is adjusted to a predetermined component concentration in a vacuum refining furnace (RH), and the molten steel of ultra low carbon steel is tapped with a vertical bending type continuous casting machine via an immersion nozzle. And cast into a slab having a thickness of 250 mm and a width of 1200 mm. The casting speed was 1.8 m / min.

Table 1 shows the composition and physical properties of the powder and the Al and Ti concentrations in the cast molten steel. Powders 1 to 13 show examples of the present invention. A, B, and C show comparative examples using conventional powders. Here, the interfacial tension and aSiO ₂ are values at 1550 ° C., and the viscosity is a value at 1300 ° C.

  The slab obtained by casting is hot rolled, pickled, cold rolled, and annealed by a conventional method to form a thin steel sheet for automobiles. The occurrence was examined.

  As shown in Table 1, in continuous casting using the present invention, the occurrence of operational abnormalities such as breakout warning and breakout due to inflow instability is reduced compared to the comparative example using conventional powder. Further, in the plate using the slab of the example of the present invention, the occurrence rate of surface defects (linear) of the product plate and the occurrence rate of cracks during press working are drastically reduced as compared with the comparative example using the conventional powder.

  This time, vertical bending type continuous casting equipment was used, but the same effect was confirmed in curved type and vertical type continuous casting equipment.

  Further, in this example, the example of manufacturing a slab for a thin steel sheet for automobiles was described, but the essence of the present technology is to prevent defects caused by entrainment of powder, The effect has also been confirmed when producing slabs of other steel types such as steel pipes.

  According to the present invention, it is possible to suppress the entrainment of powder when continuously casting molten steel containing Al and Ti, and to reduce the occurrence of cracks and linear flaws caused by inclusions and inclusions resulting from the entrainment of powder. It is possible to produce a thin steel sheet having excellent surface properties and workability. Of course, a cold-rolled steel sheet can be manufactured using this steel material, and after annealing, as an electrogalvanized steel sheet or an alloyed electrogalvanized steel sheet, an organic coated steel sheet can also be manufactured. Moreover, as long as the continuous annealing conditions are satisfied, it can also be used as a steel material for steel plates for continuous annealing hot dip galvanizing and alloying hot dip galvanizing. Therefore, since it can be applied to a wide range of uses such as household electric appliances, automobiles, and cans, the effect on the industry is extremely large.

Claims (10)

A mold powder for continuous casting used for continuous casting of steel containing at least one of Al or Ti, wherein CaO / SiO ₂ is 0.9 to 1.2 by mass ratio, CaO is 38 mass% or less, SiO ₂ is 10 mass% to 35 mass%, Al ₂ O ₃ is 7 mass% to 25 mass%, Na ₂ O is 3 mass% to 10 mass%, and substantially contains MgO. A mold powder for continuous casting of steel, characterized in that the viscosity at 1300 ° C. is 0.8 Pa · s or more.
Here, CaO is a value obtained by converting all Ca contained in the powder into CaO.   The mold powder for continuous casting of steel according to claim 1, wherein the F content is 2 mass% or more and 10 mass% or less. The mold powder for continuous casting of steel according to claim 1 or 2, wherein one or more of ZrO ₂ and SrO of 10 mass% or less are contained.   The mold powder for continuous casting of steel according to any one of claims 1 to 3, wherein Ca / Si in the mold powder is in a mass ratio of 0.8 to 2.5. 5. The continuous steel according to claim 2, wherein CaO * / SiO ₂ in the mold powder is 0.6 to 1.2 by mass ratio and CaO * is 30% by mass or less. Mold powder for casting.
Here, CaO * is a value obtained by analyzing Ca and F contained in the powder and converting Ca content obtained by subtracting the amount of Ca into CaO when F is added by CaF ₂ .   The mold powder for continuous casting of steel according to any one of claims 1 to 5, wherein an interfacial tension with molten steel containing at least one of Al and Ti is 0.9 N / m or more at 1550 ° C. The mold powder for continuous casting of steel according to any one of claims 1 to 6, wherein the activity of SiO ₂ at 1550 ° C is 0.4 or less.   Solidification temperature is 1000-1200 degreeC, The mold powder for continuous casting of steel in any one of Claims 1-7 characterized by the above-mentioned.   Melting temperature is 1000-1250 degreeC, The mold powder for continuous casting of steel in any one of Claims 1-8 characterized by the above-mentioned.   A continuous casting method for steel, wherein the continuous casting mold powder according to any one of claims 1 to 9 is used when continuously casting a steel containing at least one of Al or Ti and carbon.