METHOD FOR MANUFACTURING SEAMLESS STEEL TUBE

A production method of a seamless steel pipe capable of suppressing coarsening of crystal grains in a piercing mill is provided. The production method of a seamless steel pipe according to the present embodiment includes a heating step of heating an Nb-containing steel material to 800 to 1030°C, a pipe-making step of producing a hollow shell by performing piercing-rolling or elongation-rolling on the Nb-containing steel material, by using a piercing mill including a plurality of skewed rolls disposed around a pass line on which the Nb-containing steel material passes, a plug disposed between the plurality of skewed rolls and on the pass line, and a mandrel bar extending rearward of the plug along the pass line from a rear end of the plug, and a cooling step immediately after rolling, of carrying out cooling using a cooling liquid on a hollow shell portion that passes between rear ends of the plurality of skewed rolls, in the hollow shell, so as to reduce an outer surface temperature of the hollow shell portion to 700 to 1000°C within 15.0 seconds after the hollow shell portion passes between the rear ends of the plurality of skewed rolls.