Steel plate for structural pipes or tubes, method of producing steel plate for structural pipes or tubes, and structural pipes and tubes

摘要

Disclosed is, as a high-strength steel plate of API X80 grade or higher with a thickness of 38 mm or more, a steel plate for structural pipes or tubes that exhibits excellent resistance to PWHT and excellent toughness at the heat-affected zone, particularly at the butting faces joined by welding, without addition of large amounts of alloying elements. The steel plate for structural pipes or tubes disclosed herein has a specific chemical composition, in which the steel plate has mechanical properties including: (a) a 0.5% yield strength of 555 MPa or more; (b) a tensile strength of 625 MPa or more; and (c) a Charpy absorption energy vE_{−10° C.} at −10° C. at its mid-thickness part of 250 J or more, and maintains the mechanical properties (a) to (c) even after subjection to heat treatment at 650° C. for 2 hours.