Method for producing seamless tube/pipe

摘要

By using a piercing mill that includes a pusher on the entrance side, a plug on the exit side along a pass line, and a plurality of angled rolls as being provided around the plug so as face to each other, in the case where the maximum diameter of an unsound region consisting of center segregation and porosity in a cross section of a billet is d [mm], piercing-rolling is performed under the condition that the plug nose rolling reduction ratio (TDF) expressed by Formula (1) satisfies Formula (2).
TDF=(Bd−D1)/Bd  (1)TDF≦−0.50×(d/Bd)+0.06  (2)
In Formulae (1) and (2), Bd is the billet diameter [mm], and D1 is the opening [mm] between the angled rolls at the plug nose position. Thereby, when piercing-rolling is performed, the occurrence of an inner surface flaw attributable to the center segregation and porosity in the billet can be prevented reliably.

主权项

1. A method for producing a seamless tube/pipe by using a piercing mill including a pusher on the entrance side, a plug on the exit side along a pass line, and a plurality of angled rolls as being provided around the plug, the method comprising the steps of:
supplying a billet on the pass line, the billet including an unsound region consisting of center segregation and porosity in a cross section of the billet; pushing the billet to convey the billet toward the angled rolls; and piercing-rolling the billet by the piercing mill so that a plug nose rolling ratio (TDF) expressed by Formula (1) satisfies Formula (2):
TDF=(Bd−D1)/Bd  (1)TDF≦−0.50×(d/Bd)+0.06  (2)where, in Formulae (1) and (2),
Bd: billet diameter [mm], D1: opening [mm] between angled rolls at plug nose position, and d: maximum diameter [mm] of the unsound region in the cross section of the billet.