Patent ID: 7407555

Claim:
A method of producing a steel wire for a cold-formed coil spring comprising the steps of: providing a steel material comprising, in weight percentage, 0.35 to 0.55% C, 1.8 to 3.0% Si, 0.5 to 1.5% Mn, 0.5 to 3.0% Ni, and 0.1 to 1.5% Cr; hot-rolling the steel material to a wire with a predetermined diameter; cold drawing the steel wire with a predetermined reduction of area; heating the steel wire with a first high frequency induction heating, wherein a ferrite fraction of the cold-drawn wire's microscopic structure before the first high frequency induction heating is 40% or less to minimize deleterious effects of a ferrite component when the ferrite fraction is greater than 0% in austenization by the high frequency induction heating; rapid cooling the steel wire; and tempering the steel wire with a second high frequency induction heating.