| 摘要 |
PROBLEM TO BE SOLVED: To manufacture a pipe without causing cost increase even for a hardly workable material or the like and without remaining a flaw on the pipe inner face by obliquely piercing and rolling a round cast metal as casting by using a plug and pressing/piercing a base stock as required, by imparting a back pressure to the base stock through a pusher. SOLUTION: A base stock billet 1 made of a round cast metal as casting, while being bitten with a piercing roll 2, is pierced by pushing a piercing plug 3. In this obliquely piercing and rolling, in the case that the biting of the base stock billet 1 is insufficient due to the reaction force of the plug 3, while imparting a back pressure to the stock 1 with a pusher 4, the piercing is conducted until the billet 1 is stably bitten. In particular, in the case that a round cast metal of the stock is a hardly workable material, this method can produce a seamless tube not having a flaw on the inner face by using conventional equipment. An alloy steel which contains >=0.5% Cr, >=1% Cr+Ni+Mo and further as required, >=0.001% S and in which porosity or the like is apt to cause in the center part of the cast metal, is used as the hardly workable material.
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