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

摘要

A high strength steel sheet and a high strength steel pipe having excellent deformation performance and low temperature toughness capable of suppressing a decrease in thickness at the time of deformation, and a method of manufacturing the same, wherein the high strength steel sheet is composed of a composition in a predetermined numerical range, and ferrite and bainite or martensite X-ray random intensity ratio of the {111} plane parallel to the plate surface in the center of thickness having an effective grain size of 20 µm or less at the center of thickness, and having a composite structure of any one or two or more kinds thereof. X-ray random intensity ratio of plane 554} is 1.0 to 3.0, X-ray random intensity ratio of plane {100} is 3.0 or less, and X-ray random intensity ratio of plane {112} and {223} is 0.5 to 4.0, respectively. mm or more and a tensile strength of 565 MPa or more.