High-strength steel sheet with excellent delayed fracture resistance and low-temperature toughness, and high-strength members manufactured using it

摘要

A high strength steel sheet containing chemical components of, in mass%, C: 0.20 to 0.42%, Si: 0.06 to 0.5%, Mn: 0.2 to 2.2%, Cr: 0.1 to 2.5%, B: 0.0005 to 0.01%, O: 0.0020 to 0.020%, Al: 0.001 to 0.03%, Ti: 0.001 to 0.05%, N: 0.1% or less, P: 0.03% or less, S: 0.02% or less, and the balance: Fe and inevitable impurities. In steel, 5 × 10 3 pieces per mm 2 or more to 1 × 10 5 pieces per mm 2 or less of Mn oxides having a maximum length of 1 µm or more to 5 µm or less are present, and 1.7 × 10 2 pieces per mm 2 or more to 5 × 10 3 pieces per mm 2 or less of Mn-Si composite oxides having a short-axial length of 1 µm or more and a longitudinal length of 10 µm or less are present.