HIGH-STRENGTH ELECTRIC-RESISTANCE-WELDED STEEL PIPE, METHOD FOR PRODUCING STEEL SHEET FOR HIGH-STRENGTH ELECTRIC-RESISTANCE-WELDED STEEL PIPE, AND METHOD FOR PRODUCING HIGH-STRENGTH ELECTRIC-RESISTANCE-WELDED STEEL PIPE

摘要

The purpose of the present invention is to provide an electric-resistance-welded steel pipe that ensures high levels of strength and toughness recently required for oil well pipes. When a point in a base material section of the steel pipe which is positioned apart from the surface by 1/4 of the thickness in the direction of thickness is defined as a reference point, a metal structure in a region extending 0.5 mm in width on both sides of the reference point in the direction of thickness comprises, in mass% of a component composition, not more than 10 % by area of polygonal ferrite with the remainder being bainitic ferrite. The high-strength electric-resistance-welded steel pipe has a thickness of not less than 15 mm.