THICK STEEL PLATE FOR STRUCTURAL PIPES OR TUBES METHOD OF PRODUCING THICK STEEL PLATE FOR STRUCTURAL PIPES OR TUBES AND STRUCTURAL PIPES AND TUBES

摘要

Provided is a high-strength steel sheet having an API X80 grade or more and a plate thickness of 38 mm or more, and provides a thick steel sheet for structural pipes having excellent strength in the rolling direction and Charpy properties in the center of the sheet thickness without adding a large amount of alloying elements. A ferrite lip having a specific component composition, consisting of a two-phase structure of ferrite and bainite, having an area fraction of ferrite of less than 50%, and having a crystal grain size of 15 µm or less, has an area fraction of 80% or more with respect to the entire ferrite. It is a thick steel sheet for structural pipes, which occupies a microstructure in the center of the sheet thickness, has a tensile strength of 620 MPa or more, and a Charpy absorbed energy vE _-20° C at -20°C in the center of the sheet thickness is 100 J or more.