CONTINUOUS CASTING METHOD OF STEEL

To reduce an overall segregation level of center segregation of a continuously cast slab in a slab width direction and also reduce variation in a segregation degree in the slab width direction.A continuous casting method of steel according to the present invention includes the step of bulging wide side surfaces of a slab having thereinside an unsolidified layer with a total intentional bulging amount of 3 to 10 mm by increasing stepwise toward a downstream side in a casting direction a roller gap of a plurality of pairs of slab support rollers disposed in a continuous casting machine. The method also includes the step of performing rolling reduction on the wide side surfaces of the slab, performed after the bulging of the wide side surfaces of the slab, in a soft reduction zone in which the roller gap of a plurality of pairs of slab support rollers is reduced stepwise toward the downstream side in the casting direction. The wide side surfaces of the slab undergo rolling reduction at a rolling reduction speed of 0.3 to 2.0 mm/min with a total rolling reduction amount smaller than or equal to the total intentional bulging amount in the soft reduction zone. A solid phase fraction at a center of a thickness of the slab is smaller than 0.2, or is greater than or equal to a flow limit solid phase fraction and not greater than 1.0 in a reformation zone in which a shape of the slab in the casting direction is reformed from a circular arc shape into a linear shape.