steel plate

Abstract

The steel plate disclosed herein contains, by mass%,: C: 0.50~0.80%, Si: more than 0.50~2.10%, Mn: 0.20~1.20%, Al: less than 0.100%, Cr: 0.01~0.60%, N: less than 0.0150%, with the remainder being Fe and impurities. The total surface area ratio of ferrous iron and ferric carbon particles is more than 95%, the average particle size of ferrous iron is less than 20.0 μm, the average particle size of ferric carbon particles is less than 1.50 μm, and the spheroidization rate of ferric carbon particles is more than 75% and less than 85%. The Cr concentration [Cr]θ (mass%) in the residue and the Mo concentration [Mo]θ in the residue are also specified. (mass%), and the C content [C] in the chemical composition of the steel plate in mass%, satisfying equation (3), and the graphitization rate GR defined by equation (4) using [C] and the C concentration [C]CB (mass%) of the carbides in the residue is 5.0% or less.