PURPOSE: To greatly improve the life of a piercing plug even with a material having high hot deformation resistance by applying a lubricant on the surface of the plug and biting the plug into a billet without wetting the formed lubricating film with roll cooling water.
CONSTITUTION: The surface temp. of the piercing plug 10 for producing a seamless steel pipe is measured in a position 1 and the temp. is controlled to 80 to 180°C in a cooling tank 14. While the plug 10 is rotated by turning rollers 16 in a position 2, the graphite lubricant is applied to the plug by a spraying device 18 and the film thickness thereof is adjusted to 120 to 180μm. The cooling water from nozzles 26 is stopped at the time of biting the plug to the billet 24 between rolling rolls 22 and 22 or after the water resistant film is applied on the graphite lubricating film, the plug is carried to a position 3 thereby the wetting of the lubricating film with the water is prevented.