CONTINUOUS STEEL CASTING METHOD USING SOFT REDUCTION WITH SMALL ROLLING LOAD

An object of the present invention is to provide a continuous steel casting method in which center segregation can be effectively reduced using a relatively small rolling load without the need of a facility with high rolling ability and without the occurrence of internal cracking and the porosity formation inside a strand and in which remaining porosity can be eliminated.In the continuous steel casting method of the present invention, a gap D1 between strand support rolls facing each other with a strand 6 in a rectangular shape interposed therebetween is increased toward a downstream side in a casting direction to thereby bulge the strand having an unsolidified layer 6a thereinside such that the thickness T1 between long-side surfaces of the strand 6 increases within the range of 0.1% or more and 10% or less of the thickness T2 of the strand inside a mold 5. When long-side surfaces S1 of the bulged strand 6 are rolled by a plurality of guide rolls 9, a portion of the strand in which the solid phase fraction in a central portion of the strand 6 is within the range of 0.2 or more and less than 0.9 satisfies a prescribed total rolling reduction and a prescribed reduction gradient, and a portion of the strand in which the solid phase fraction is within the range of 0.9 or more satisfies a prescribed total rolling reduction and a prescribed reduction gradient.