Manufacturing method of low-temperature annealing after cold forging excellent in steel wire rod and a method for manufacturing the same, and cold forging excellent in steel wire rod

摘要

PROBLEM TO BE SOLVED: To provide a steel wire rod which allows the temperature of annealing for softening before cold forging to be reduced, and achieves excellent cold forgeability after annealing, and to provide a method for producing the same.;SOLUTION: The steel wire rod has a composition comprising, by mass, 0.005 to 0.60% C, 0.01 to 0.40% Si, 0.20 to 1.80% M, ≤0.040% P, ≤0.050% S and 0.0005 to 0.0300% N, and the balance Fe with inevitable impurities, and has a metallic structure composed of a pro-eutectoid ferrite structure, a pearlitic structure and a bainitic structure, wherein the volume ratio of the pearlitic structure is 1.40×C(%)×100% or more, the volume ratio of the pro-eutectoid ferrite is (1-1.25×(C%))×50% or less (including 0%), and the volume ratio of the bainitic structure is ≤20% or less (including 0%), and the steel wire rod has a tensile strength of 340+920×Ceq. MPa or more.;COPYRIGHT: (C)2010,JPO&INPIT