High-strength steel sheet excellent in low temperature toughness of brittle crack suppression and stopping characteristics and weld heat-affected zone

摘要

PROBLEM TO BE SOLVED: To provide a high tensile strength steel sheet having excellent low temperature toughness in HAZ and a base metal and further having excellent brittle crack suppression or stopping properties in the base metal (steel member) even if high heat input welding is performed.;SOLUTION: In the steel sheet, a chemical componential composition is suitably controlled, and, when the metallic structure in a face parallel to the rolling direction of the steel sheet with a thickness t (mm) and vertical to the steel sheet surface is observed, the following conditions (a) to (c) are satisfied: (a) where the area ratio of ferrite is ≥75%; (b) the average equivalent circle diameter of the ferrite grains at a t/2 position is ≤20.0 μm; and (c) where the average aspect ratio of the ferrite grains at a t/4 position is ≤2.0.;COPYRIGHT: (C)2009,JPO&INPIT