HIGH-STRENGTH BOLT EXCELLENT IN DELAYED FRACTURE RESISTANCE CHARACTERISTICS AND ITS STEEL PRODUCT

摘要

The present invention provides a high strength bolt superior in delayed fracture resistant property having a bolt tensile strength of 1200 N/mm2 or more and a steel material for the same. ??A high strength bolt comprised of a head portion and shaft portion formed by a steel material, wherein the relation between a bolt tensile strength TS (N/mm2) and tempering temperature T ( DEG C) satisfies the following expression (1), the relation between the bolt tensile strength TS (N/mm2) and the carbon equivalent Ceq (%) calculated from the chemical composition of the steel material used for the high strength bolt satisfies the following expression (2), and the tensile strength of the bolt is refined to a range of 1200 N/mm2 to 1600 N/mm2 by quenching and tempering: DF NUM="(1)"TS≤.1T+850 /DF DF NUM="(2)"TS≤550Ceq+1000 /DF where, DFCeq=C+(Mn/6)+(Si/24)+(Ni/40) +(Cr/5)+(Mo/4)+(V/14) /DF IMAGE