High-strength coil spring and method of producing same

Abstract From the Canadian patent

The present invention relates to a highstrength coil spring useful for an engine and other high-strength springs requiring a high fatigueresistance and a method of producing the same. In general a higher tensile strength is, desired for spring materials but it has been known that if a tensile strength exceeds a certain limit a toughness and a fatigue resistance are contrarily reduced. In addition, a coil spring has been used after forming and then being subjected to a quenching treatment followed by being subjected to a shot peening treatment to add a compressive residual stress to a surface thereof but an effective shot peening treatment gives a surface roughness Rmax of 6 to 20 µm, so …