| 摘要 |
PROBLEM TO BE SOLVED: To provide a piercing rolling method for a billet by which the occurrence of scratches on the inner surface at a distal end part of a seamless steel tube is prevented advantageously. SOLUTION: In the piercing rolling method for a billet performing piercing rolling on the billet 10 after heating it, tapering work 20 is applied to the outer surface of the distal end part of the billet before performing piercing rolling and the tapering work is performed so as to satisfy expression (1): G0. 5Db>D100>D0>Gt, wherein Db denotes the diameter of the billet 10 before the tapering work, D0 and D100 denote the diameters in the distal end position and a position of 100 mm inside from the distal end position after tapering work, respectively, and Gt and G0. 5Db denote gaps between rolls in the distal end position of a plug of a piercer used for the piercing rolling and in a position 0.5×Db upstream from the distal end of the plug, respectively. COPYRIGHT: (C)2010,JPO&INPIT |
