METHOD FOR MANUFACTURING SEAMLESS PIPE

摘要

A pusher following a pass line is disposed on the entry side and a plug on the exit side, and a punch, in which a plurality of inclined rolls are disposed in opposition around a plug, is used. When the maximum diameter for an inferior quality area including center segregation and porosity within the billet cross-sectional surface is d [mm], piercing and rolling is carried out under conditions such that the plug tip drawing ratio (TDF) represented by equation (1) satisfies equation (2). TDF = (Bd - D1)/Bd ... (1) TDF = 0.50 x (d/Bd) + 0.06 ... (2) In equation (1) and equation (2), Bd is the billet diameter [mm], and D1 is the space [mm] between the inclined rolls at the position of the plug tip. Thus, during piercing and rolling, occurrences of inside surface defects caused by center segregation and porosity in the billet can be reliably prevented.