| 摘要 |
Disclosed are a heavy gauge, high tensile strength, hot rolled steel sheet with excellent HIC resistance that is well suited as material for grade X65 or higher high-strength welded steel pipe, and a manufacturing method therefor. Specifically, a heavy gauge, high tensile strength, hot rolled steel sheet with excellent HIC resistance is characterized by having a composition containing, in mass%, C: 0.02-0.08%, Mn: 0.50-1.85%, Nb: 0.03-0.10%, Ti: 0.001-0.05%, B: 0.0005% or less, and containing the same to fulfill (Ti + Nb/2)/C < 4, or further containing one or two types of Ca: 0.010% or less and REM: 0.02% or less, and the remainder Fe and inevitable impurities, and a structure consisting of bainitic ferrite phase or bainite phase, and by the surface layer hardness being a Vickers hardness of 230 HV or less. |
