| 摘要 |
PROBLEM TO BE SOLVED: To provide a stock for a steel pipe for a line pipe with a thickness of ≥25 mm having a strength in a grate of X70 to 100, and to provide a method for producing the same. SOLUTION: The steel pipe stock with a steel thickness of ≥25 mm having excellent toughness has a composition comprising, by mass%, 0.03 to 0.12% C, 0.01 to 0.50% Si, 1.5 to 3.0% Mn, ≤0.008% P, ≤0.0006% S, ≤0.0060% N, 0.003 to 0.100% Al, 0.0010 to 0.0030% B, 0.1 to 1.0% Ni, 0.01 to 0.5% Cr, 0.01 to 0.08% Nb and 0.005 to 0.020% Ti, and the balance Fe with inevitable impurities, and has a microstructure of the steel essentially composed of bainite, and in which the area ratio of the ferrite structure present in old austenite grain boundaries is ≤5%. COPYRIGHT: (C)2011,JPO&INPIT |
