High strength steel sheet excellent in delayed fracture resistance and low temperature toughness, and high strength member manufactured using the same

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, 5×103 pieces per mm2 or more to 1×105 pieces per mm2 or less of Mn oxides having a maximum length of 1 μm or more to 5 μm or less are present, and 1.7×102 pieces per mm2 or more to 5×103 pieces per mm2 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.

主权项

1. A high strength steel sheet comprising 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%, Nb: 0 to 0.1%, Mo: 0 to 1.0%, W: 0 to 0.5%, V: 0 to 0.5%, Ni: 0 to 5.0%, Cu: 0 to 1.0%, N: 0.1% or less, P: 0.03% or less, S: 0.02% or less, and the balance: Fe and inevitable impurities,
wherein, in steel, 5×103 pieces per mm2 or more to 1×105 pieces per mm2 or less of Mn oxides having a maximum length of 1 μm or more to 5 μm or less are present, and1.7×102 pieces per mm2 or more to 5×103 pieces per mm2 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.