| 摘要 |
PROBLEM TO BE SOLVED: To pierce a billet without generating internal lapping marks and biting failure. SOLUTION: In a method for piercing the billet 1 of a base stock for seamless steel tubes with piercing rolls 2 having a barrel-shaped roll body, after heating the billet 1 to 1240-1280 deg.C where the internal lapping marks are not generated with a heating furnace, the range of at least >=50 mm from the end part on the bitten side of the billet 1 is water-cooled and, after making the surface temperature of the water-cooled part 3 to <=1150 deg.C, piercing is started.
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