A mold flux for continuous casting has a base material composition containing 25 to 60 mass % of CaO, 15 to 45 mass % of SiO.sub.2, 5 to 25 mass % of F, 0.2 to 1.0 mass % of S, and 0 to 20 mass % of a total of Li.sub.2O, Na.sub.2O, and K.sub.2O, and in the base material composition, f(1) is 0.90 to 1.90, f(2) is 0.10 to 0.40, f(3) is 0 to 0.40, and a total of CaO, SiO.sub.2, F, S, Li.sub.2O, Na.sub.2O, and K.sub.2O is 90 to 100 mass %.

A mold flux for continuous casting has a base material composition containing 25 to 60 mass % of CaO, 15 to 45 mass % of SiO.sub.2, 5 to 25 mass % of F, 0.2 to 1.0 mass % of S, and 0 to 20 mass % of a total of Li.sub.2O, Na.sub.2O, and K.sub.2O, and in the base material composition, f(1) is 0.90 to 1.90, f(2) is 0.10 to 0.40, f(3) is 0 to 0.40, and a total of CaO, SiO.sub.2, F, S, Li.sub.2O, Na.sub.2O, and K.sub.2O is 90 to 100 mass %.

Provided is mold flux that can prevent longitudinal cracks from forming on a surface of a slab upon continuous-casting hypo-peritectic steel, wherein CaO, SiO.sub.2, an alkali metal oxide and a fluorine compound are contained, 1.1≦(CaO).sub.h/(SiO.sub.2).sub.h≦1.9, 0.10≦(CaF.sub.2).sub.h/((CaO).sub.h+(SiO.sub.2).sub.h+(CaF.sub.2).sub.h)≦0.40 and 0≦(alkali metal fluoride).sub.h/((CaO).sub.h+(SiO.sub.2).sub.h+(alkali metal fluoride).sub.h)≦0.10 are satisfied, a solidification temperature is no less than 1300° C., and viscosity at 1450° C. is no more than 0.1 Pa.Math.s.

A mold powder which prevents surface defects from occurring on a surface of a cast slab of Al-containing hypo-peritectic steel having Al: 0.2% to 2.0%, by mass %, and, in a hypo-peritectic region, C: 0.08% to 0.17%, by mass %. The mold powder includes CaO, SiO.sub.2, Na.sub.2O, Li.sub.2O, F, and C. Li.sub.2O/Na.sub.2O is 0.6 or more, 1.0+0.05×Al≤CaO/SiO.sub.2≤2.0−0.35×Al, 10<Li.sub.2O+0.5×Na.sub.2O+0.8×F<20, and 1.00≤F/(Li.sub.2O+0.5×Na.sub.2O+1.46)≤1.24 are satisfied where Al is content by mass % of molten steel, and respective contents of the remaining elements are by mass %. A viscosity of the mold powder at 1,300° C. is in a range of 0.05 Pa.Math.s to 0.20 Pa.Math.s, and a crystallization temperature of the mold powder is in a range of 1,100° C. to 1,250° C.

A control method for a continuous casting machine, includes: estimating, by on-line real-time system, a flow state of molten steel in a mold by using an operation condition of a continuous casting machine and temperature data on the molten steel in the mold; calculating, by on-line real-time system, a molten steel flow index based on the estimated flow state of the molten steel, the molten steel flow index being a factor of mixing of an impurity into a casting inside the mold; and controlling the operation condition of the continuous casting machine such that the calculated molten steel flow index is within an appropriate range.

Provided is a mold flux used for casing a cast slab, the mold flux including, bases on a total wt % of thereof, 32-38 wt % of aluminum oxide (Al.sub.2O.sub.3), 8-12 wt % of strontium oxide (SrO), 8-12 wt % of potassium oxide (K.sub.2O), 8-12 wt % of fluorine (F), 5-8 wt % of boron oxide (B.sub.2O.sub.3), 3-5 wt % of lithium oxide (Li.sub.2O), and inevitable impurities. Thus, according to the mold flux, a change in components due to silicon oxide (SiO.sub.2) and calcium oxide (CaO) may be suppressed or prevented compared to those in the conventional art.

Provided is a mold flux used for casing a cast slab, the mold flux including, bases on a total wt % of thereof, 32-38 wt % of aluminum oxide (Al.sub.2O.sub.3), 8-12 wt % of strontium oxide (SrO), 8-12 wt % of potassium oxide (K.sub.2O), 8-12 wt % of fluorine (F), 5-8 wt % of boron oxide (B.sub.2O.sub.3), 3-5 wt % of lithium oxide (Li.sub.2O), and inevitable impurities. Thus, according to the mold flux, a change in components due to silicon oxide (SiO.sub.2) and calcium oxide (CaO) may be suppressed or prevented compared to those in the conventional art.

Provided is a mold flux used for casing a cast slab, the mold flux including, bases on a total wt % of thereof, 32-38 wt % of aluminum oxide (Al.sub.2O.sub.3), 8-12 wt % of strontium oxide (SrO), 8-12 wt % of potassium oxide (K.sub.2O), 8-12 wt % of fluorine (F), 5-8 wt % of boron oxide (B.sub.2O.sub.3), 3-5 wt % of lithium oxide (Li.sub.2O), and inevitable impurities. Thus, according to the mold flux, a change in components due to silicon oxide (SiO.sub.2) and calcium oxide (CaO) may be suppressed or prevented compared to those in the conventional art.

In the mold powder, the content of F is 0.5% by mass or less (including 0% by mass), CaO and SiO.sub.2 are included as main components, the mass ratio of CaO to SiO.sub.2 (CaO/SiO.sub.2) is 0.6 to 1.4, the content of B.sub.2O.sub.3 is 0.3 to 2.8% by mass, the content of Na.sub.2O is 5.0 to 20.0% by mass, the total content of Li.sub.2O and K,0 is 0 to 4.0% by mass, the content of MgO is 0 to 3.5% by mass, the content of Al.sub.2O.sub.3 is 1.0 to 8.0% by mass, and the content of MnO is 1.0% by mass or less (including 0% by mass).

A method of producing an exothermic mold powder in a form of sprayed granules of the present invention includes spray-drying into granules, an aqueous slurry containing: a raw material blend; and a metal silicon powder and/or a silicon alloy powder, the method comprising adjusting the pH of the aqueous slurry to 13 or less.