A steel wire rod for a high strength spring having excellent drawability into a wire and excellent post bending ability, process for its production, high strength spring and method of making the same

摘要

There is provided a steel wire rod having an excellent drawability into a wire and an excellent post bending ability. The steel wire rod for a high strength spring of the present invention contains C: 0.5 to 0.8%, Si: 1.5 to 2.5%, Mn: 0.5 to 1.5%, Ni: 0.05 to 0 , 5%, Cr: 0.05 to 2.5% and V: 0.05 to 0.5%, with the remainder being iron and unavoidable impurities, with the perlite microstructure area ratio being 95% of the total area or more, the tensile strength (TS) and the necking (RA) satisfy the expression (1) [TS ≦ 1250 MPa, RA ≥ 35%], the standard deviation of tensile strength (TSσ) and the standard deviation of necking (RAσ) of the term (2) [TSσ ≦ 55.0, RAσ ≦ 6.0], and the area ratio of the pearlite microstructure having an interlamellum pitch of 0.9 μm or more is found at the position of d × 1/4 where d is the diameter of the steel wire rod is 20% or less.