Continuous casting method of steel

A continuous casting method of steel, the method comprising:

• step (a)—filling molten steel into a continuous casting mold that is cooled;
• step (b)—solidifying the molten steel with the filling to form a cast slab;
• and
• step (c)—drawing the cast slab from the mold while spraying cooling water toward the cast slab,
• wherein:
• a cooling water spray amount W0 [kg/ton-cast slab] where solidification of molten steel in the cast slab is completed is set as a predetermined target position under a condition where a drawing speed V of the cast slab is set to a speed V0 [m/min],
• a cooling water spray amount W1 [kg/ton-cast slab] is set as the target position under a condition where the drawing speed V of the cast slab is set to a speed V1 [m/min], which differs from the speed V0, and
• the step (c) further comprises:
• drawing the cast slab from the mold at the speed V0 while spraying cooling water to the cast slab such that cooling water spray amount is set to W0, and
• then changing the drawing speed V of the cast slab to V1 while spraying cooling water to the cast slab such that the cooling water spray amount is set to W1,
• wherein:
• a cooling water spray amount Wt [kg/ton-cast slab] is an amount of cooling water that is sprayed to the cast slab during a period of time t [min],
• the period of time t being obtained by dividing a target length Lt of the cast slab from an exit of the mold to the target position along the casting direction by the drawing speed V0, and
• the period of time t beginning from a point of time Tc at which the drawing speed V is changed, and
• a cooling water spray amount Wt [kg/ton-cast slab] during the period of time t satisfying either formula (1) or formula (2):
• Wt<W1 under a condition of V1<V0 (1)
• Wt>W1 under a condition of V1>V0 (2)