Mold flux for continuous-casting Ti-containing hypo-peritectic steel and method therefor

A method for continuous-casting Ti-containing hypo-peritectic steel, the method comprising:

• continuous-casting hypo-peritectic steel containing 0.1 to 1 mass % of Ti, using a mold flux,
• wherein
• the mold flux contains CaO, SiO2, an alkali metal oxide and a fluorine compound as major components,
• a chemical composition of the mold flux before the mold flux is put into a mold satisfies the formulas (1), (2) and (3),
• a TiO2 content of the mold flux in a melting state during the casting is no more than 20 mass %, and
• a strength ratio of a film of the mold flux in a solidifying state after the casting is no more than 1.0:
• 1.1−0.5×T≤f(1)≤1.9−0.5×T (1)
• 0.05≤f(2)≤0.40 (2)
• 0≤f(3)≤0.40 (3),
• wherein in the formulas (1) to (3),
• f(1)=(CaO)h/(SiO2)h (A)
• f(2)=(CaF2)h/{(CaO)h+(SiO2)h+(CaF2)h} (B)
• f(3)={(alkali metal fluoride)h}/{(CaO)h+(SiO2)h+(alkali metal fluoride)h)} (C),
• wherein in the formulas (A) to (C),
• (CaO)h=WCaO−(CaF2)h×0.718 (D)
• (SiO2)h=WSiO2 (E)
• (CaF2)h=(WF−WLi2O×1.27−WNa2O×0.613−WK2O×0.403)×2.05 (F)
• (alkali metal fluoride)h=WLi2O×1.74+WNa2O×1.35+WK2O×1.23 (G)
• wherein T is a Ti content of molten steel (mass %), WCaO is a CaO content of the mold flux (mass %), WSiO2 is a SiO2 content of the mold flux (mass %), WF is a F content of the mold flux (mass %), and WLi2O, WNa2O and WK2O are contents of Li2O, Na2O and K2O respectively, which are alkali metal oxides, of the mold flux (mass %), and
• wherein the strength ratio of the film means a ratio of a first peak height of perovskite to a first peak height of cuspidine, the ratio being obtained from X-ray diffraction analysis of powder obtained by pulverizing the film of the mold flux.