THICK STEEL PLATE

摘要

Disclosed is a steel plate. The steel plate has a chemical composition meeting predetermined conditions. A microstructure in the surface layer of the steel plate includes at least one of ferrite and upper bainite in a total fraction of 80 area percent or more, and grains of the at least one of ferrite and upper bainite have an effective grain size of 10.0 µm or less. Of the microstructure of the surface layer, grains of the remainder microstructure excluding the ferrite and the upper bainite have an average equivalent circle diameter of 3.0 pm or less. The steel plate has a dislocation density Á of 2.5×10 15 m -1 or less as determined by X-ray diffractometry. The steel plate having the configuration has excellent fatigue properties.