| 摘要 |
PROBLEM TO BE SOLVED: To produce PC steel excellent in delayed fracture characteristics and to provide a method for producing the same. SOLUTION: In this high tensile strength steel rod or steel wire excellent in delayed fracture characteristics, the central part of the steel is provided with tempered martensite in which the fractional ratio of intergranular ferrite or pearlite is <=5%, the difference between the hardness of the surface layer and the hardness of the central part is <=100 Hv, and also, the maximum hardness of the surface layer is lower than the value obtained by adding 50 Hv to the average value of the cross-sectional hardness, and in method for producing the same, a wire rod with a wire diameter of <=9 mm obtained by subjecting a billet containing, by mass, 0.1 to 0.40% C, 0,10 to 0.50% Si, 0.3 to 1.0% Mn, <=0.03% P, <=0.02% S, <=0.005% Al, and the balance iron with inevitable impurities and cast by a billet continuous casting method to hot rolling and thereafter executing cold drawing is quenched in the temperature range of 850 to 1050 deg.C and is tempered in a state of being heated to the temperature range of 350 to 550 deg.C.
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