Mold flux for continuous casting and continuous casting method

1. A mold flux for continuous casting which has a base material composition containing:

25 to 60 mass % of CaO;

15 to 45 mass % of SiO 2 ;

5 to 25 mass % of F;

0.5 to 1.00 mass % of S; and

0 to 20 mass % of a total of Li 2 O, Na 2 O, and K 2 O,

wherein in the base material composition,

f(1) represented by Formula 1 is 0.90 to 1.90,

f(2) represented by Formula 2 is 0.10 to 0.40,

f(3) represented by Formula 3 is 0 to 0.40, and

a total of CaO, SiO 2 , F, S, Li 2 O, Na 2 O, and K 2 O is 90 to 100 mass %,

f (1)=(CaO) h /(SiO 2 ) h   (Formula 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 }tm (Formula 3)

where (CaO) h , (SiO 2 ) h , (CaF 2 ) h , and (MF) h in Formulae 1 to 3 are calculated as follows,

(CaO) h =W CaO -(CaF 2 ) h ×0.718   (Formula 4)

(SiO 2 ) h =W SiO2   (Formula 5)

(CaF 2 ) h =( W F −W Li2O ×1.27 −W Na2O ×0.613 −W K2O ×0.403)×2.05   (Formula 6)

(MF) h =W Li2O ×1.74+ W Na2O ×1.35+ W K2O ×1.23   (Formula 7)

where W i represents a percentage by mass of each component i.

2. The mold flux for continuous casting according to claim 1 ,

wherein the amount of S is 0.6 to 1.0 mass % in the base material composition.

3. The mold flux for continuous casting according to claim 1 ,

wherein the base material composition further contains 0 to 4.0 mass % of Al 2 O 3 .

4. The mold flux for continuous casting according to claim 1 ,

wherein the base material composition has a solidification point of 1150° C. to 1400° C.

5. The mold flux for continuous casting according to claim 1 ,

wherein the base material composition has a viscosity of 2 poise or less at 1300° C.

6. The mold flux for continuous casting according to claim 1 ,

wherein the base material composition has a basicity of 1.2 to 2.1.

7. The mold flux for continuous casting according to claim 1 ,

wherein a total of CaO, SiO 2 , F, S, Li 2 O, Na 2 O, and K 2 O is 90 to 98 mass % in the base material composition.

8. The mold flux for continuous casting according to claim 1 ,

wherein 0 to 10 parts by mass of C is contained with respect to 100 parts by mass of the base material composition.

9. A continuous casting method comprising:

casting steel having a steel composition containing 0.10 to 3.00 mass % of Al,

using the mold flux for continuous casting according to claim 1 .

10. The continuous casting method according to claim 9 ,

wherein the steel composition further contains 0.06 to 0.20 mass % of C.

11. The continuous casting method according to claim 9 ,

wherein the steel composition contains

0.10 to 3.00 mass % of Al,

0 to 0.20 mass % of C,

0 to 1.0 mass % of Si,

0 to 3.0 mass % of Mn,

0 to 0.030 mass % of P,

0 to 0.010 mass % of S,

0 to 0.30 mass % of each of Cu, Ni, V, Nb, Ti, Cr, Mo, W, and Zr,

0 to 0.030 mass % of each of Ca, Mg, REM, and B, and

the remainder of Fe with impurities.

12. The continuous casting method according to claim 11 ,

wherein the amount of C is 0.06 to 0.20 mass % in the steel composition.