Process for Producing a Coil Spring

Author:  Izawa et al.
Source:  US Patent 5,665,179
Doc ID:  1995034
Year of Publication:  1995
Abstract:  
A process for producing a coil spring comprises of: cold drawing a wire comprising: C in an amount of 0.55 to 0.75% by weight; Si in an amount of 1.00 to 2.50% by weight; at least two primary metals selected from the primary metal group consisting of: Mn in an amount of 0.30 to 1.5% by weight; Ni in an amount of 1.00 to 4.00% by weight; Cr in an amount of 0.50 to 2.50% by weight; Mo in an amount of 0.10 to 1.00% by weight; at least one secondary metal selected from the secondary metal group consisting of: V in an amount of 0.05 to 0.60% by weight; Nb in an amount of 0.05 to 0.60% by weight; and the balance of substantially Fe; oil quenching and tempering the wire; hot tempering the wire, thereby preparing the tempered wire whose tensile strength ob falls in the range of from 1370 to 1670 N/mm2; cold coiling; hardengin and tempering; grinding; gas nitriding; high strength two-stage shot peening; and low temperature annealing the tempered wire. Accordingly the present process can product the coil spring whose endurance limit tm is 687+/-560 MPa and which has high strength and high fatigue resistance without breakage.