Method of producing seamless metal tube and punch for use therein

摘要

A hole 30 is formed in the center of the rear end face 20 of a round billet 10. The hole 30 has a predetermined depth from the rear end face 20 and a plurality of grooves 31 are provided in the side surface thereof. Each groove 31 extends in the depth direction of the hole 30. Piercing and rolling of the round billet 10 having the hole 30 is performed using a piercing mill having a plug. During piercing and rolling, the bottom surface of the hole 30 is broken through by the plug and a protrusion which is to be the starting point of burrs is formed, and the protrusion is absorbed by the groove 31 as the plug advances. Consequently, formation of burrs at the rear end of a hollow shell after piercing-rolling thereof can be suppressed.