steel plate

Abstract

The steel plate disclosed herein contains, by mass%, the following: 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 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, the spheroidization rate of ferric carbon particles is more than 85%, and the Cr concentration [Cr]θ (mass%) in the residue, the Mo concentration [Mo]θ (mass%) in the residue, and the C content [C] in the chemical composition of the steel plate, by mass%, satisfy Equation (3). The graphitization rate GR, defined by Equation (4) using [C] and the C concentration [C]CB (mass%) of the carbides in the residue, is less than 5.0%.