PURPOSE: To prevent generation of defects such as cracks and spills and to manufacture seamless steel tubes with high productivity by heating a billet at a temp. lower than a boundary temp. of a dual phase region and pierce- rolling the billet by specifying an average deformation speed.
CONSTITUTION: A martensitic stainless steel billet containing, by wt., 0.12W0.30% C and 11W14% Cr is heated at a temp. at least 30°C lower than a boundary temp. between an austenitic single phase region and a ferrite-austenite dual phase region α+β in the equilibrium diagram. Then, an average deformation speed having a condition shown by the equation is set to be ≤1.3sec-1 and the billet is pierce-rolled by a Mannesmann piercer. Thus, stainless steel seamless tubes are obtained with the high yield.
TAKADA ISAO
OKA HIROSHI
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