Entitled mold flux and continuous casting method for a continuous casting
Technical field
[0001]
　The present invention, mold flux, and relates to a continuous casting method for continuous casting. The mold flux and method continuous casting is preferably used in order to prevent cracking that occurs slab surface when producing the cast slab of an Al-containing steel and Al-containing Atsutsumi Akirako by continuous casting.
　The present application, on November 5, 2015, claiming priority based on Japanese Patent Application No. 2015-217238, filed in Japan, the contents of which are incorporated here.
Background technique
[0002]
　When the continuous casting to produce slabs of steel, the molten steel in the mold is solidified by solidified shell is formed. When the thickness of the solidified shell becomes non-uniform, it is likely to occur cracks slab surface.
[0003]
　To prevent cracking of the slab surface to a uniform thickness of the solidified shell in the mold, i.e., to slowly cool the tip of the solidified shell (hereinafter, slow cooling) it is effective. For the purpose of this slow cooling, mold flux has been used.
[0004]
　Mold flux is supplied onto the molten steel in the mold, and melted by heat supplied from the molten steel to form a molten layer on the molten steel. Molten slag forming a molten layer, along the inner wall of the mold flows into the gap between the mold and the solidified shell, to form a film. The molten steel and the solidified shell in contact with the film by the film is slow cooled.
[0005]
　Immediately after the start of casting, the film is solidified by cooling by the mold, to form a glassy film. Then, over time, crystals precipitate from the glass-like film. When promoting the crystallization of the film, roughness of the film surface in the casting mold side is increased. Therefore, interface thermal resistance between the mold and the film is increased, radiant heat transfer in the film is suppressed. As a result, it is possible to appropriately slow cooling molten steel and the solidified shell in contact with the film.
[0006]
　As is prone steel cracked slab surface, Atsutsumi crystal steel are known. As this Atsutsumi Akirako include, for example, steel containing C 0.06 to 0.20 mass%. Atsutsumi Akirako has a higher solidification shrinkage at the time of changing from a liquid phase to a solid phase. Therefore, in particular, in Atsutsumi Akirako, it is important to slow cool the tip of the solidified shell. Preventing cracking of the slab surface in such Atsutsumi Akirako, or, Patent Documents 1 to 7 disclose suppressing means.
[0007]
　For example, as a means of promoting the crystallization of the film as described above, the following method is disclosed in Patent Documents 1-4.
[0008]
　Patent Document 1, a viscosity of 0.6 ~ 2.5poise at 1300 ° C., for continuous casting powder is disclosed solidification temperature is 1150 ~ 1250 ° C.. In Patent Document 1, it is to promote crystallization of the slag (film) by increasing the solidification temperature of the powder.
[0009]
　Patent Document 2, the main component is CaO and SiO 2 are, basicity is 1.2-1.6, for continuous casting powder is disclosed MgO content is 1.5 mass% or less . In Patent Document 2, powder basicity (SiO 2 mass ratio of CaO with respect to) increased, by reducing the MgO content, and promote the crystallization of the slag (film).
[0010]
　Patent Document 3, akermanite (2CaO · MgO · 2SiO 2 ), Gehlenite (2CaO · Al 2 O 3 · SiO 2 ), melilite is these complete solid solution having a composition that precipitates during solidification as the main crystal phase mold powder is disclosed. In Patent Document 3, thereby stabilizing the crystallization of slag by such compositions.
[0011]
　Patent Document 4, CaO-SiO 2 -CaF 2 composition range of mold powder is disclosed in the quaternary system -NaF. This composition range, Ca as shown in Non-Patent Document 1 4 Si 2 O 7 F 2 substantially coincides with the primary phase area of. Therefore, in the disclosed mold powder in Patent Literature 4, Ca 4 Si 2 O 7 F 2 is likely to precipitate. In Patent Document 4, Ca 4 Si 2 O 7 F 2 (Cuspidine: 3CaO · 2SiO 2 · CaF 2 ) In order to accurately utilize into account the affinity between the alkali metal and F. As a result, in Patent Document 4, the crystallization of the film is promoted, slow cooling effect is obtained.
[0012]
　Patent Document 5, CaO-SiO 2 -CaF 2 composition range of mold flux is disclosed in the three-component system. In Patent Document 5, Ca 4 Si 2 O 7 F 2 (Cuspidine: 3CaO · 2SiO 2 · CaF 2 ) In order to accurately utilize into account the affinity between the alkali metal and F. As a result, in Patent Document 5, the crystallization of the film is promoted, slow cooling effect is obtained.
[0013]
　As described above, in Patent Documents 1-5, and the molten steel and the solidified shell in contact with the film based on the characteristics of the solid-phase film was slow cooled. On the other hand, Patent Document 6, thereby suppressing the radiation heat transfer in the film based on the characteristics of the liquid phase film. The patent document 6, the absorption coefficient of the radiation heat at the time of melting is 100 m -1 mold powder is disclosed at least. So as to satisfy the absorption coefficient, this mold powder, oxides of transition metals is contained more than 10 wt%.
[0014]
　Further, as taught in Patent Document 3, S is likely to gather at the interface between the molten slag and the molten steel. Therefore, as taught in Patent Document 7, when the S transitions to the molten steel, with the surface tension of the molten steel is decreased, brittleness of the steel increases. Therefore, in order to prevent surface cracks of the cast slab, it is important that small S concentration in the mold flux. For example, Patent Document 7, a continuous casting method using the powder S concentration is less than the upper limit value according to the casting speed is disclosed. Further, as taught in Patent Document 3, when the small S concentration in the mold flux, since lowering of the interfacial tension between the molten slag and the molten steel by S is small, (the liquid part of the film in) the molten slag There can also be prevented from being caught in the molten steel.
[0015]
　In recent years, the strength of the product, in order to improve the performance such as corrosion resistance, Al-containing steel containing Al 0.10 wt% is required. However, Al in the molten steel is oxidized at the interface between the molten slag resulting from mold flux (films and liquid melt layer) and the molten steel, the film composition changes during continuous casting of Al-containing steel. For example, Ca in the film 4 Si 2 O 7 F 2 : (Cuspidine 3CaO · 2SiO 2 · CaF 2 when) using mold flux occurs, Al occurred 2 O 3 Ca by 4 Si 2 O 7 F 2 is since the dilution, Ca 4 Si 2 O 7 F 2 crystallization is inhibited. As a result, no longer sufficient slow cooling effect is obtained and cracks are generated on the surface of the slab. Also, during casting, when time course of composition of the molten layer on the molten steel in the mold is large, the inflow rate of the molten slag along the inner wall of the mold is uneven. As a result, the temperature variation of the mold copper plate increases, cracks are likely to occur. Further, in order to avoid breakout, operating in a low casting speed, it is necessary to increase the average thickness of the solidified shell. Therefore, continuous casting of Al-containing steel has a lower yield and productivity of the slab than the continuous casting of other grades.
[0016]
　However, in Patent Documents 1-7 described above, Al-containing steel (steel containing 0.10 mass% or more Al) is not disclosed. For example, the amount of Al in the disclosed in Patent Documents 1, 4, 5 and 7 steel, 0.02-0.04 mass% (Patent Document 1), from 0.035 to 0.045 wt% (JP 4), 0.02-0.04 mass% (Patent Document 5), from 0.03 to 0.08 wt% (Patent Document 7). Thus, it has been overlooked that uses a new mold flux in order to increase the continuous casting efficiency of Al-containing steel.
[0017]
　Further, for example, Patent Document 1, increasing the freezing point above 1250 ° C., lubricity is inhibited can not prevent breakout is disclosed. Thus, in the case of obtaining a slab by continuous casting from molten steel Atsutsumi Akirako, there is a limit to the upper limit of the freezing point of the mold flux.
CITATION
Patent Document
[0018]
Patent Document 1: Japanese Patent Laid-Open 8-197214 discloses
Patent Document 2: Japanese Patent Laid-Open 8-141713 discloses
Patent Document 3: Japanese Patent 2005-40835 JP
Patent Document 4: Japanese Patent 2001-179408 JP
Patent Document 5: Japanese Patent 2004-358485 JP
Patent Document 6: Japanese Patent Laid-Open 7-185755 discloses
Patent Document 7: Japanese Sho 61-115653 Patent Publication
Non-Patent Document
[0019]
Non-Patent Document 1: ISIJ International, vol. 42 (2002), No. 5, pp. 489 - 497
Non-Patent Document 2: Tie-Hagane, vol. 70 (1984), No. 9, pp. 1242 ~ 1249
Summary of the Invention
Problems that the Invention is to Solve
[0020]
　The present invention has been made in view of the foregoing problems, the continuous casting method of the mold flux and Al-containing steel to prevent surface cracks of the cast slab of an Al-containing steel containing Al 0.10 wt% an object of the present invention is to provide.
Means for Solving the Problems
[0021]
　The gist of the present invention is as follows.
[0022]
　(1) Continuous casting mold flux according to one aspect of the present invention, CaO: 25 ~ 60 wt%, SiO 2 : 15 ~ 45 wt%, F: 5 ~ 25 wt%, S: 0.2 ~ 1. 0 wt%, Li 2 O and Na 2 O and K 2 sum of O: 0 ~ have a base composition containing 20 mass%, in the base composition, represented by the following (equation 1) f ( 1) is 0.90 to 1.90 the following (a f (2) is 0.10-0.40 of the formula 2), is f (3) represented by the following (equation 3) 0 is ~ 0.40, CaO and SiO 2 and F S and Li 2 O and Na 2 O and K 2 sum of O is 90 to 100 mass%.
f (1) = (CaO) h / (SiO 2 ) h　(Equation 1)
f (2) = (CaF 2 ) h / {(CaO) h + (SiO 2 ) h + (CaF 2 ) h } (formula 2) f (3) = (MF) h / {(CaO) h + (SiO 2 ) h + (MF) h } (equation 3) 　here, the formulas (1) to (3) in the (CaO ) h , (SiO 2 ) h , (CaF 2 ) h , (MF) h is, (CaO) h = W CaO - (CaF 2 ) h × 0.718 (formula 4) (SiO 2 ) h = W SiO2　(equation 5) (CaF 2 ) h = (W F -W Li2O × 1.27-W Na2 O × 0.613-W K2O × 0.403) × 2.05 (equation 6) (MF) h = W Li2O 1.74 + W × Na2 O × 1.35 + W K2O × 1.23 (equation 7) is calculated by, W i is of each component i It shows the mass percentage.

[0023]
　(2) In the base composition of the continuous casting mold flux according to the above (1), S amount may be 0.5 to 1.0 mass%.
[0024]
　(3) In the base composition of the continuous casting mold flux according to (1), in the base composition, S amount may be 0.6 to 1.0 mass%.
[0025]
　(4) above (1) wherein the substrate composition of the continuous casting mold flux according to any one of - (3) further, Al 2 O 3 : also contain 0 to 4.0 mass% good.
[0026]
　(5) above (1) to the base composition of the continuous casting mold flux according to any one of (4) may have a freezing point of 1150 - 1400 ° C..
[0027]
　(6) above (1) to the base composition of the continuous casting mold flux according to any one of (4) may have a viscosity of less 2poise at 1300 ° C..
[0028]
　(7) above (1) wherein the substrate composition of the continuous casting mold flux according to any one of - (6) may have a basicity of from 1.2 to 2.1.
[0029]
　(8) above (1) in the base composition of the continuous casting mold flux according to any one of ~ (7), CaO and SiO 2 and F S and Li 2 O and Na 2 O and K 2 sum of O may be 90 to 98% by weight.
[0030]
　(9) above (1) to a continuous casting mold flux according to any one of (8), with respect to the base composition 100 parts by weight, C: 0 may contain ~ 10 parts by weight.
[0031]
　In the continuous casting method according to one embodiment of the (10) present invention, a continuous casting mold flux according to any one of the above (1) ~ (9), Al: 0.10 ~ 3.00 wt% casting a steel having a steel composition containing.
[0032]
　(11) In the continuous casting method according to (10), wherein the steel composition further, C: may contain from 0.06 to 0.20 wt%.
[0033]
　(12) In the continuous casting method according to (10), said steel composition, Al: 0.10 ~ 3.00 wt%, C: 0 ~ 0.20 wt%, Si: 0 ~ 1.0 mass %, Mn: 0 ~ 3.0 mass%, P: 0 ~ 0.030 wt%, S: 0 ~ 0.010 wt%, Cu, Ni, V, Nb, Ti, Cr, Mo, W, and Zr each 0 to 0.30 wt%, Ca, Mg, REM, each of B: 0 contain to 0.030 mass%, the balance may be made of Fe and impurities.
[0034]
　(13) above the said steel composition of the steel being cast by a continuous casting method according to (12), C content may be from 0.06 to 0.20 mass%.
[0035]
　(14) (10) - (13) In the steel being cast by a continuous casting method according to any one of the steel compositions as a tensile strength after hot rolling and cold rolling is more than 780MPa There may be adjusted.
Effect of the invention
[0036]
　According to the present invention, it is possible to reliably prevent surface cracks when producing a cast slab of an Al-containing steel by continuous casting. Further, according to the present invention, to reduce the variation of the copper plate temperature of the mold, while preventing breakout, the casting speed can be increased. In particular, the present invention is, tensile strength as finished products is the manufacture of high-strength steel sheet is not less than 780 MPa, Al 0.10% by mass or more by continuous casting, containing C 0.06 ~ 0.20 wt% Atsutsumi it is effective to produce a slab of Akirako.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037]
[Figure 1] f (1) and f (2) in the mold flux according to an embodiment of the present invention, f a range (3) (CaO) h - (SiO 2 ) h - (CaF 2 ) h - ( MF) h is a pictorial view showing the state diagram of system. [2] the relationship between the S content and the variation width of the mold copper plate temperatures in the mold flux, and is a diagram showing a relationship between the number of S content and vertical cracks slab in the mold flux.

DESCRIPTION OF THE INVENTION
[0038]
　Hereinafter, a continuous casting method according to an embodiment of the mold flux and the present invention according to an embodiment of the present invention.
[0039]
　In these embodiments, the steel containing Al 0.10 wt% is defined as Al-containing steel. To increase the strength and corrosion resistance of the steel, the steel may contain Al to 3.00 wt%. Thus, Ca even film of include steel 3.00 mass% of Al 4 Si 2 O 7 F 2 crystallizes.
[0040]
　The substrate of mold flux according to the present embodiment, 25 to 60 wt% of CaO, SiO 2 15 to 45 mass%, Na 2 O, Li 2 O, K 2 O (alkali metal oxides three groups) 0-20% by weight in total, the F 5 ~ 25 wt%, contains S 0.20 ~ 1.00 wt%. Mold flux according to the present embodiment includes the substrate, if necessary, in order to adjust the melting rate may include a carbon material such as coke powder and fine carbon powder. The amount of the carbon material is defined by outer percentage of concentration was taken as 100% by mass (total amount of each component in the base material) substrate, 0-10 to the substrate 100 wt% (100 parts by weight) % by mass (10 parts by weight). Mold flux according to the present embodiment is defined by the composition before being added into the mold (initial composition). Further, the composition of mold flux according to the present embodiment is defined by the conventional methods in the art as shown in Example 1 below.
[0041]
　Furthermore, the composition of the substrate in the mold flux according to the present embodiment, the following (Equation 1) f (1) represented by is 0.90 ~ 1.90, f (2 represented by the following (Equation 2) ) is 0.10-0.40, the following (f represented by formula 3) (3) is 0 to 0.40. These f (1) and f (2), the range of f (3) is shown in FIG. 1, (CaO) h - (SiO 2 ) h - (CaF 2 ) h - (MF) h fourth it is a shaded portion in the component phase diagram (two ternary phase diagram). MF refers to the alkali metal fluoride.
[0042]
　f (1) = (CaO) h / (SiO 2 ) h　(式 1)
F (2) = (CAF 2 ) h / {(CaO) h + (SiO 2 ) h + (CAF 2 ) h } (式 　2) f (3) = (MF) h / {(CaO) h + (SiO 2 ) h + (MF) h } (式3)
[0043]
　Here, during the above formulas (1) to (3), (CaO) h is calculated by the following equation (4), (SiO 2 ) h is calculated by the following equation (5), (CaF 2 ) h is calculated by the following equation (6), (MF) h is calculated from the following equation (7).
[0044]
(CaO), h = W CaO - (CaF 2 ) h × 0718 (式 4) (SiO 2 ) h = The SiO2　(式 5) (CaF 2 ) h = (W F -W Li2O × 1.27- The Na2O × 0613-W K 2 × 0403) × 2.05 (式 6) (MF) h = W Li2O × W + 1.74 Na2O × W + 1.35 K2O × 1.23 (式7)

[0045]
　In the above (Formula 4) to (Equation 7), W i indicates the weight percentage of each component i with respect to the total mass of the base material (the total amount of the components in the substrate). That, W CaO is the mass percentage of CaO with respect to the total mass of the base material, W SiO2 is SiO with respect to the total mass of the base material 2 mass percent of, W F is the mass percentage of F with respect to the total mass of the base material , W Li2O is, Li with respect to the total mass of the base material 2 mass percentage of O, W Na2 O is, Na to the total mass of the base material 2 mass percentage of O, W K2O is, K with respect to the total mass of the base material 2 O It shows the mass percentage. Incidentally, f (1), f (2), f (3), (CaO) h , (SiO 2 ) h , (CaF 2 ) h , (MF) h respectively f1, f2, f3, h CaO , h SiO2 , H CaF2 , H MF and may be expressed. Furthermore, (Equation 2) and as understood from (equation 3) and FIG. 1, (CaO) h and (MF) h is a positive value.
[0046]
　f (1) is, SiO 2 is different from the normal basicity defined by the mass ratio of CaO for. CaF 2 because the mass of CaO is reduced with increasing the mass, the f (1), the normal basicity molecules (mass of CaO) (CaO) h is replaced. Thus, f (1) is a corrected basicity, Ca 4 Si 2 O 7 F 2 is important in order to promote the crystallization of. Therefore, it is not necessary to limit the basicity. However, the basicity of the base material of the mold flux according to the present embodiment (CaO / SiO 2 ) may be from 1.2 to 2.1.
[0047]
　Therefore, as shown in the following (Equation 8), the range of f (1) is from 0.90 to 1.90. Scope of this f (1) is, SiO during continuous casting by a redox reaction between Al in the molten steel ([Al] ≧ 0.10 wt%) 2 are determined also consider decreasing. Moreover, the preferable lower limit of f (1) is, 0.95,1.00, or 1.05. preferred upper limit of f (1) is, 1.85,1.80, or 1.75. For example, a desirable range of f (1) is 0.95 to 1.90,1.00 ~ 1.90,1.05 ~ 1.90,0.90 ~ 1.85,0.95 ~ 1.85 , 1.00 to 1.85,1.05 ~ 1.85,0.90 ~ 1.80,0.95 ~ 1.80,1.00 to 1.80 or 1.05 to 1.80 it is.
　0.90 ≦ f (1) ≦ 1.90 ( Formula 8)
[0048]
　f (1) is, or less than 0.90, when or greater than 1.90, Ca 4 Si 2 O 7 F 2 crystal phase is not obtained the required amount, unstable cooling in the mold becomes, variation of the copper plate temperature of the mold increases.
[0049]
　f (2) is, (CaO) h - (SiO 2 ) h (CaF - 2 ) h (CaF to the total amount of components constituting the phase diagram 2 ) h is the mass ratio of. The f (2) also, Ca 4 Si 2 O 7 F 2 it is necessary to adjust the proper range in order to promote the crystallization of. Therefore, as shown in the following (Equation 9), the range of f (2) is 0.10-0.40. f (2) it is, or less than 0.10, when or greater than 0.40, Ca 4 Si 2 O 7 F 2 crystal phase is not obtained sufficient. A preferred lower limit of f (2) is 0.11. preferred upper limit of f (2) is, 0.35,0.30,0.25, or 0.20. For example, a desirable range of f (2) is 0.11 to 0.40,0.11 ~ 0.35,0.11 ~ 0.30,0.11 ~ 0.25,0.11 ~ 0.20 , 0.10 ~ 0.35,0.11 ~ 0.30,0.11 to 0.25, or a 0.11 to 0.20.
　0.10 ≦ f (2) ≦ 0.40 ( Formula 9)
[0050]
　f (3) is, (CaO) h - (SiO 2 ) h - (MF) h Ca to the total amount of components constituting the phase diagram 4 Si 2 O 7 F 2 component that functions in solvent capable of dissolving, That, (MF) h represents the ratio of the. Therefore, the f (3) also, Ca 4 Si 2 O 7 F 2 it is necessary to adjust the proper range in order to promote the crystallization of. Accordingly, as shown in the following (Equation 10), the range of f (3) is 0 to 0.40. Scope of this f (3) is, SiO by a redox reaction between Al in the molten steel ([Al] ≧ 0.10 wt%) 2 is also determined in consideration decreases. f (3) is larger than 0.40, Ca 4 Si 2 O 7 F 2 crystal phase is not obtained sufficient. preferred upper limit of f (3) is, 0.35,0.30,0.25, or 0.20. For example, a desirable range of f (3) is 0 to 0.35,0 ~ 0.30,0 to 0.25, or a 0 to 0.20.
　0 ≦ f (3) ≦ 0.40 ( Equation 10)
[0051]
　The substrate of mold flux according to the present embodiment, as described above, it is necessary to contain S 0.20% by mass to 1.00% by mass. When the S content is 0.20% by mass to 1.00% by mass, even if production of slab from molten steel containing Al steels by continuous casting, a small change with time of the composition of the molten layer. Therefore, the inflow rate of the molten slag along the inner wall of the mold is uniform. Further, even if the film composition has changed and molten slag of Al and the film in the molten steel reacts, Ca in the film 4 Si 2 O 7 F 2 can maintain the rate of crystallization of. As a result, the thickness of the solidified shell tends becomes uniform, variation of the copper plate temperature of the mold is reduced. Moreover, the preferable lower limit of the S amount is 0.30,0.50,0.60, or 0.65 wt%. The preferable upper limit of the S amount is 0.95 mass%.
[0052]
　If the S content is less than 0.20 wt%, the composition of the molten layer is unstable, fluctuation of the copper plate temperature of the mold is large, cracks are generated in the slab surface. If the S content is higher than 1.00 mass%, offset the positive effect that bad influence of S that have migrated in the molten steel has on toughness of interfacial tension and the steel of the molten steel gives the variation of the copper plate temperatures S is mold in molten slag in order to, cracking occurs in the slab surface. Relationship S content (lower axis) and longitudinal crack number of slabs (right axis), and shows the relationship between the amount of S (lower shaft) as a template of the copper plate temperature variation width (left) in FIG. As shown in FIG. 2, when the S amount is 0.20 wt% to 1.00 wt%, it can reliably prevent surface cracking of the slab, seen to be much smaller than the variation width of the copper plate temperature of the mold . Incidentally, when the variation width of the copper plate temperature of the mold is at 20 ° C. or less, it is possible to prevent the deformation solidified shells by uneven cooling of the solidified shell in the mold. Further, as shown in FIG. 2, when the S content exceeds 0.50%, S begins to saturate the effect of reducing the fluctuation band of the copper plate temperature of the mold. Further, the variation width of the copper plate temperature of the mold is at 15 ℃ below, can be almost stable up to the casting speed. Therefore, as shown in FIG. 2, S amount is 0.50% or more 0.60% or 0.60 percent, or, preferably a 0.65% or more.
[0053]
Further, Ca 4 Si 2 O 7 F 2 (Cuspidine: 3CaO · 2SiO 2 · CaF 2 ) In order to sufficient amount generated at a sufficient rate in the film is, Ca in the film, Si, and, F, respectively is a predetermined amount necessary. Therefore, the base material of the mold flux according to the present embodiment, Ca 4 Si 2 O 7 F 2 : (Cuspidine 3CaO · 2SiO 2 · CaF 2 as an essential component for generating a) in the film, as described above, and 25-60 wt% CaO, SiO 15 to 45% by weight 2 and contains a 5 to 25 wt% F. If the amount of these essential components is insufficient, Ca in the film 4 Si 2 O 7 F 2 crystal phase is not obtained sufficient. Moreover, the preferable lower limit of the amount of CaO is 30, or a 35% by mass. The preferred upper limit of the amount of CaO is 55, or 50 wt%. SiO 2 preferable lower limit of the amount of, 20, or 25 wt%. SiO 2 preferred upper limit of the amount of the 40, or a 35% by mass. A preferable lower limit of the F amount is 8 or 10 wt%. The preferable upper limit of the F content is 20, or a 15% by mass.
[0054]
　Alkali metal, a strong affinity with halogen such as F. Mold flux, CaO, SiO 2 and F (i.e., fluorine in the fluoride) was added to, for example, Na 2 O, Li 2 O, K 2 in the case of containing alkali metal oxides such as O, the mold flux below in the molten slag generated from as in (equation 11) to (equation 13), an alkali metal ion of the alkali metal oxide is CaF 2 bind with fluorine ions in the.
　CaF 2 + Li 2 O → CaO + 2LiF (Equation
　11) CaF 2 + Na 2 O → CaO + 2NaF (Equation
　12) CaF 2 + K 2 O → CaO + 2KF (Formula 13)
[0055]
　Therefore, Li in the mold flux 2 O, Na 2 O K and 2 O respectively regarded LiF, NaF, and KF. Further, CaF exchanged these alkali metal oxides and anion 2 is regarded as CaO. As a result, the above-described (Equation 4), have been obtained (Equation 6) and (7). The alkali metal, Li, Na, K, Rb , Cs, is Fr. However, when adding an alkali metal to the mold flux, the alkali metal is Li, Na, When it is 1 or more K preferred. Li 2 O, Na 2 O and K 2 O are other alkali metal oxides (Rb 2 O, Cs 2 O and Fr 2 O) very easily available than. Meanwhile, Rb the mold flux 2 O, Cs 2 O and Fr 2 because industrially large disadvantage to add O, regarded as the other components described below.
[0056]
　The substrate of mold flux according to the present embodiment, as an optional component to adjust the freezing point or the like, Na 2 O, Li 2 O, K 2 may comprise at least one member selected from the group consisting of O. However, when these alkali metal oxides is too much, the amount of the above essential components is insufficient. Therefore, the total amount of the alkali metal oxides exceeds 20 wt%, Ca 4 Si 2 O 7 F 2 crystal phase is not obtained sufficient. Thus, Na 2 O, Li 2 O, K 2 the total amount of O is 0 to 20 mass%. Also, a preferable upper limit of this total amount, 18,15,12,10, or a 8 wt%.
[0057]
　CaO and SiO 2 and F S and Li 2 O and Na 2 O and K 2 and is O, the fundamental component in the base material of the mold flux according to the present embodiment. Ca 4 Si 2 O 7 F 2 crystal phase of the in order to sufficient amounts generated the basic components (CaO, SiO 2 , F, S, Li 2 O, Na 2 O, K 2 O) is the total amount of , it is necessary that 90 to 100 wt%. If the total amount of the basic component is less than% 90, Ca 4 Si 2 O 7 F 2 crystal phase is an amount just obtained not required. It is not necessary to limit the upper limit of the total amount of the basic component. When the substrate of the mold flux comprising other components described later, the total amount of the basic component may be not more than 98 wt%.
[0058]
　The substrate of mold flux according to the present embodiment may contain other components other than the basic component. For example, the base material of the mold flux according to the present embodiment, Al 2 O 3 : 0.1 ~ 10.0 wt%, MgO: 0.1 ~ 10.0 wt%, MnO: 0.1 ~ 4.0 it may contain mass%. However, since the total amount of the basic component is required to be 90 mass% or more, these total amount has to be 10 mass% or less. That is, the total amount of other components is 0 to 10 mass%. Further, Al 2 O 3 amount is 0 to 10.0 mass%, the amount of MgO is 0 to 10.0 mass%. Further, Al 2 O 3 amount is more preferably to be 0 to 4.0 mass%, the amount of MgO is more preferably to be 0 to 4.0 mass%, the amount of MnO is 0-4. more preferably to be 0 wt%
[0059]
　Freezing point of the base material of the mold flux according to the present embodiment is desirable when is 1150 ~ 1400 ° C.. Freezing point Ca to be within this temperature range 4 Si 2 O 7 F 2 can be further promoted crystallization. Freezing point of the flux is determined by rotating and vibrating reed-type viscosity measuring apparatus. A more preferred lower limit of the freezing point, 1200,1240, or a 1250 ° C.. Further, the more preferable upper limit of the freezing point is 1350 or 1300 ° C..
[0060]
　The viscosity of the base material of the mold flux according to the present embodiment is desirable when is 2poise at 1300 ° C. or less (0.2 Pa · s or less). If the viscosity is less 2Poise, it is possible to further increase the crystallization rate, a slow effective cooling. It changes the composition of the molten layer by the reaction in the mold, so higher than the viscosity of the viscosity casting initial molten slag during casting, the low viscosity of the mold flux desired. The viscosity of the flux, as well as the freezing point is measured by a rotary or vibrating reed-type viscosity measuring apparatus. A more preferred upper limit of the viscosity of the flux is 1poise (0.1Pa · s).
[0061]
　In the continuous casting method according to an embodiment of the present invention, steel (molten steel) comprises 0.10 to 3.00 wt% of Al. For greater strength of finished products, the steel may further contain C 0.06 to 0.20 mass%. For example, the tensile strength in the high-strength steel sheet of the finished product is preferably a least 780 MPa. Therefore, the steel composition of the steel may be adjusted so as tensile strength after hot rolling and cold rolling is more than 780 MPa.
[0062]
　As described above, in the continuous casting method according to the present embodiment, the steel, as essential elements, including Al. Further, in the continuous casting method according to the present embodiment, the steel is, as optional elements, C, Si, Mn, P, S, Cu, Ni, V, Nb, Ti, Cr, Mo, W, Zr, Ca, Mg , REM, at least one may include is selected from the group consisting of B. The remainder being Fe and impurities. For example, steel, and 0.10 to 3.00 wt% Al, 0 - 0.20 wt% of C, 0 and Si to 1.0 mass%, and Mn from 0 to 3.0 mass% , 0 to 0.03 mass% of P, 0 and S of 0.01 mass%, and 0 to 0.30 wt% of Cu, and Ni of 0 to 0.30 wt%, 0 to 0.30 mass% and V, and 0 to 0.30 wt% Nb, from 0 to 0.30 wt% of Ti, from 0 to 0.30 wt% of Cr, and 0 to 0.30 wt% Mo, 0 to 0.30 mass% of W, 0 to 0.30 wt% of Zr, and 0 to 0.030 wt% of Ca, and Mg of from 0 to 0.030 wt%, 0 to 0.030 mass % and REM of containing and 0 to 0.030 wt% B, it may be made balance being Fe and impurities.
[0063]
　Further, for example, Si amount of 0.02 to 1.0 mass%, Mn content may be from 0.5 to 3.0 mass%. In order to improve the strength and workability of high strength steel sheet of the finished products, steel, Cu, Ni, V, Nb, Ti, Cr, Mo, W, at least one kind of selected from the group consisting of Zr, respectively 0.30 mass% or less may be contained. Moreover, steel, Ca, Mg, REM, the at least one selected from the group consisting of B and may contain 0.030 wt% or less, respectively. Each of the lower limit of the amount of optional elements need not be limited. For example, the amount of each optional element is 0% or more, or may be 0 percent.
[0064]
　In the continuous casting method according to the present embodiment, using a mold flux according to the above embodiment, the casting of steel having a steel composition described above. In the continuous casting method according to the present embodiment, in the mold the molten slag is formed from the mold flux, even when the composition with the film to an oxidation reaction caused by the Al in the molten steel of Al-containing steel has changed, the film in in, Ca 12 Al 14 F 2 O 32 Ca while allowing the crystallization of 4 Si 2 O 7 F 2 maintains crystallization of, it is possible to slow cool the tip of the overall solidified shell. Further, when the C amount is from 0.06 to 0.20 wt%, there are cases where the steel is Atsutsumi Akirako, in the conventional method, surface cracks tend to occur in the cast piece. In this case as well, by utilizing the slow cooling by crystallization in the film, it is possible to prevent surface cracking.
[0065]
　Moreover, during continuous casting, SiO by Al in the molten steel ([Al] ≧ 0.10 wt%) 2 is reduced is reduced. Therefore, f (1) may select a lower mold flux according to the Al concentration in the molten steel. Further, the composition of the molten layer or film in the continuous casting measured or simulated, the relationship between f (1) which is calculated from the composition of the molten layer or film and f (1) calculated from the composition of mold flux it may be determined. It is also possible to select a more appropriate mold flux on the basis of this relationship. Similarly, SiO by Al in the molten steel 2 If is reduced, f calculated from the composition of the melt layer and the film (3) is increased. increase of f (3) is, Ca 4 Si 2 O 7 F 2 for influencing the crystallization, for example, the composition of the film may be selected appropriate mold flux to be 0.40 or less.
Example 1
[0066]
　With vertical bending type continuous casting machine having two strands, it was cast molten steel 780ton having the composition shown in Table 1. In both strands to give width 1500mm and thickness 250 mm, a slab of length 7000 mm. You set the casting speed to 1.5m / min. In continuous casting, it was selectively used mold flux shown in Tables 2 to 5 for each strand.

The scope of the claims
[Requested item 1]
　CaO: 25 ~ 60 wt%,
SiO 2 : 15 ~ 45 　wt%, F: 5 ~ 25 　wt%, S: 0.20 ~ 1.00 　wt%, Li 2 O and Na 2 O and K 2 with O total: 0 to 20 wt%, a has a substrate composition containing, 　in the base composition, 　f (1) represented by the following (equation 1) and are 0.90 to 1.90, 　the following (formula f represented by 2) (2) of 0.10-0.40, 　an f (3) from 0 to 0.40 represented by the following (equation 　3), CaO and SiO 2 and the F and S li 2 O and Na 2 O and K 2 sum of O is 90 to 100 mass% continuous casting mold flux, characterized in that. f (1) = (CaO) h / (SiO 2 ) h　(Equation 1) f (2) = (CaF 2 ) h / {(CaO) h + (SiO 2 ) h + (CaF 2 ) h } (formula 2) f (3) = (MF) h / {(CaO) h + (SiO 2 ) h + (MF) h } (equation 3) 　here, the formulas (1) to (3) in the (CaO ) h , (SiO 2 ) h , (CaF 2 ) h , (MF) h is, (CaO) h = W CaO - (CaF 2 ) h × 0.718 (formula 4) (SiO 2 ) h = W SiO2　(equation 5) (CaF 2 ) h = (W F -W Li2O × 1.27-W Na2 O × 0.613-W K2O × 0.403) × 2.05 (equation 6) (MF) h = W Li2O 1.74 + W × Na2 O × 1.35 + W K2O × 1.23 (equation 7) is calculated by, W i is of each component i It shows the mass percentage.

[Requested item 2]
　In the base composition, S amount is 0.5 to 1.0 mass%
for continuous casting mold flux according to claim 1, characterized in that.
[Requested item 3]
　In the base composition, S amount is 0.6 to 1.0 mass%
for continuous casting mold flux according to claim 1, characterized in that.
[Requested item 4]
　The substrate composition may further,
　Al 2 O 3 : 0 ~ 4.0 mass%
containing
continuous casting mold flux according to any one of claims 1 to 3, characterized in that.
[Requested item 5]
　The base composition has a freezing point of 1150 ~ 1400 ° C.
for continuous casting mold flux according to any one of claims 1 to 4, characterized in that.
[Requested item 6]
　The base composition has a viscosity of less 2poise at 1300 ° C.
for continuous casting mold flux according to any one of claims 1 to 4, characterized in that.
[Requested item 7]
　The base composition has a basicity of from 1.2 to 2.1
continuous casting mold flux according to any one of claims 1 to 6, characterized in that.
[Requested item 8]
　In the base composition, CaO and SiO 2 and F S and Li 2 O and Na 2 O and K 2 sum of O is 90 to 98% by weight
one of claims 1 to 7, characterized in that continuous casting mold flux according to an item.
[Requested item 9]
　The relative base compositions 100 parts by weight,
　C: 0 ~ 10 parts by weight
containing
continuous casting mold flux according to any one of claims 1 to 8, characterized in that.
[Requested item 10]
　A continuous casting mold flux according to any one of claims ~ 9 1,
　Al: 0.10 ~ 3.00 wt%
casting a steel having a steel composition containing a
continuous casting, characterized in that Method.
[Requested item 11]
　It said steel composition
　further, C: 0.06 ~ 0.20% by weight
containing
continuous casting method according to claim 10, characterized in that.
[Requested item 12]
　The steel
　composition, Al: 0.10 ~ 3.00
　wt%, C: 0 ~ 0.20
　wt%, Si: 0 ~ 1.0
　mass%, Mn: 0 ~ 3.0
　mass%, P: 0 to 0.030
　wt%, S: 0 to 0.010
　mass%, Cu, Ni, V, Nb, Ti, Cr, Mo, W, and Zr each 0 to 0.30
　wt%, Ca, Mg, REM each of B: 0 ~ 0.030 wt%,
it contains, with the balance being Fe and impurities
continuous casting method according to claim 10, characterized in that.
[Requested item 13]
　In the steel composition,
　C amount is 0.06 to 0.20 mass%
is
continuous casting method according to claim 12, characterized in that.
[Requested item 14]
　In the steel, tensile strength after hot rolling and cold rolling the steel composition is adjusted to be above 780MPa
continuous casting method according to any one of claims 10 to 13, wherein the .