PURPOSE: To produce a PC steel bar excellent in strength and delayed breakdown resisting property by supplying a specific raw material to the central part of a molten steel in a casting mold and making compositions of inner and outer layers of a blank material for the steel bar different from each other when blank material for PC steel bar is produced by a continuous casting.
CONSTITUTION: The PC steel bar with about 9mm diameter is produced by sending a steel cylinder 5 in which the casting mold 3 for continuos casting is filled with adding elements consisting essentially of C to the central part of a molten steel 6, hot-rolling an obtained casting piece to form a steel wire bar and subjecting the bar to quenching and tempering. One more kinds from among, in weight, 0.01 to 0.2% C, 0.1 to 2.0% Si, 0.5 to 2.0% Mn, 0.005 to 0.10% Al, 0.0005 to 0.005% B, 0.1 to 2.0% Cr and 0.1 to 2.0% Ni or further 0.01 to 0.1% Ti are incorporated into the outer layer part with 0.2 to 1mm thickness of the steel bar and the part is composed of the mixed organizations of ferrite, bainite and martensite or ferrite and martensite. The inner layer thereof contains 0.15 to 0.5% C, i.e., only C content is higher than the C content of the outer layer, and is composed of martensite or mixed organizations of martensite and bainite.
YAMAMOTO AKIO
KAWACHI YUJI
