| 摘要 |
Provided is a steel plate that has excellent strength and toughness in a mid-thickness part thereof, despite having a plate thickness of 100 mm or greater. The steel plate has a chemical composition that contains specific amounts of C, Si, Mn, P, S, Cr, Ni, Al, N, B, and O, with the balance being Fe and incidental impurities, and that has an equivalent carbon content Ceq IIW of 0.65 or greater. Furthermore, the steel plate has a yield strength of 620 MPa or greater, a plate thickness of 100 mm or greater, and has a microstructure in which prior ³ grain size in a mid-thickness part of the steel plate has a maximum value, expressed as an equivalent circle diameter, of 150 µm or less, and a total area ratio of martensite and bainite in the mid-thickness part is 80% or greater. |
