Method of sequential continuous-casting of different grades of steel

A method of sequential continuous casting wherein continuous casting of a first grade of molten steel is changed over to continuous casting of a second grade of molten steel different in constituent from the first grade of molten steel, comprising the steps of:

• stopping the pouring of the first grade of molten steel into a mold;
• immersing a cooling material formed of a columnar steel stock with its longitudinal axis parallel to one of the transverse axis of the mold and being circular or polygonal in cross section and equipped with guiding jigs transverse to its longitudinal axis into the substantially center portion of the first grade of molten steel in said mold, the length l and the largest transvere dimension d of said cooling material satisfying the following two formulas for said mold having the width of about 1500 mm and the thickness of about 220 mm
• Mold width--200 mm<l<Mold width--100 mm
• Mold thickness--100 mm<d<Mold thickness--20 mm;
• forming around said cooling material a solified layer merging in a solidified shell developed from the wall of said mold;
• and
• pouring the second grade of molten steel into said mold before the surface of the first grade of molten steel above said cooling materials is solidified.