HIGH-STRENGTH STEEL PLATE AND HIGH-STRENGTH STEEL PIPE HAVING EXCELLENT DEFORMABILITY AND LOW-TEMPERATURE TOUGHNESS, AND MANUFACTURING METHODS THEREFOR

摘要

Provided are a high-strength steel plate and high-strength steel pipe having excellent deformability and low-temperature toughness, by which it is possible to suppress the reduction of thickness during deformation, and manufacturing methods therefor. The high-strength steel plate is characterized in that it comprises a composition within a predetermined numeral value range, it comprises a complex structure with one or more types of ferrite, bainite, and martensite; the effective crystal particle diameter in the central part of the thickness is 20 µm or less; the X-ray random intensity ratio of a {111} plane parallel to the surface of the plate in the central part of the thickness is 0.5-5.0; the X-ray random intensity ratio of a {554} plane is 1.0-3.0; the X-ray random intensity ratio of a {100} plane is 3.0 or less; the X-ray random intensity ratios of a {112} plane and a {223} plane are both 0.5-4.0; the thickness is equal to or greater than 25 mm; and the tensile strength is equal to or greater than 565 MPa.