ULTRAHIGH STRENGTH STEEL SHEET AND ULTRAHIGH STRENGTH STEEL PIPE HAVING EXCELLENT PIPE LINE DEFORMATION PROPERTY AND LOW TEMPERATURE TOUGHNESS AND METHOD FOR PRODUCING THEM

摘要

PROBLEM TO BE SOLVED: To provide an ultrahigh strength steel pipe having excellent pipe line deformation properties and high speed ductile fracture properties, and having a tensile strength of ≥800 MPa (100 times or more the API Specification), and to provide a method for producing the same.;SOLUTION: The ultrahigh strength steel pipe having excellent pipe line deformation properties and high speed ductile fracture properties contains, by weight, 0.03 to 0.10% C, 0.01 to 0.6% Si, 1.5 to 2.5% Mn, ≤0.015% P, ≤0.003% S, 0.1 to 2.0% Ni, 0.15 to 0.60% Mo, 0.001 to 0.10% Nb, 0.005 to 0.030% Ti and ≤0.06% Al, has structure in which the fraction of bainite or martensite in the structure of the steel sheet is ≥90%, and has a difference in tensile strength between the rolling width direction and the rolling longitudinal direction of ≥30 MPa, or a ratio in tensile strength between the rolling longitudinal direction and the rolling width direction of ≤0.97. The steel sheet is used therefor.;COPYRIGHT: (C)2006,JPO&NCIPI