CONTINUOUS CASTING METHOD OF ROUND CAST BILLET FOR MAKING 13CR SEAMLESS STEEL PIPE

PROBLEM TO BE SOLVED: To provide a continuous casting method of a round cast billet for making a 13Cr seamless steel pipe, which can suppress a crack in an axial core part, especially a contraction hole generated in a terminal stage of solidification and a resulting A-type crack, together with a C-type crack at a practical level.SOLUTION: A strand having a round shape in cross section containing unsolidified molten steel inside is forcibly cooled with primary compression stress added by a water quantity density Qby the following expression (1) from a position where a solidification rate fs of the axial core part of the strand is 0.5 to a position where a temperature of the axial core part reaches (Ts-145)°C in a process of continuous casting. It is further preferable that, after completion of the addition of the primary compression stress and forcible cooling, forcible cooling with secondary compression stress added by Qgiven by the following expression (2) is carried out until the temperature of the axial core part of the strand reaches (Ts-255)°C. (1) 10≤Q≤100, (2) 0Q.