| 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 and a conical hole piercing work 40 is applied to the center of the distal end face thereof before performing piercing rolling. The conical hole is formed into a shape in which the depth of the hole is >50 mm and the inlet diameter of the hole is larger than the depth of the hole. 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 in 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 |
