High strength ERW steel pipe, method for manufacturing steel sheet for high strength ERW steel pipe, and method for manufacturing high strength ERW steel pipe

摘要

In ERW steel pipes, the high strength and toughness required for oil well pipes in recent years are secured. In the case where the component composition is mass% and the reference point is a point defined as a ¼ point of the thickness in the thickness direction from the surface in the base material part of the steel pipe, both in the thickness direction centering on the reference point The metal structure in the region having a width of 0.5 mm is composed of polygonal ferrite: 10 area% or less and the balance: bainetic ferrite, and the thickness is 15 mm or more.