Improved Fatigue Strength of Valve Springs and Sheet Springs by Application of a New Fine Shot Peening Technology 2000-01-0791

The peening of fine steel beads with diameters less than 80 micrometers onto the surface of a spring (referred to as SS Treatment in this paper) was found to improve the fatigue limit of the spring effectively since the surface compressive residual stress and surface hardness were improved significantly. As an example, by applying this technology to non–nitrided high–strength valve springs made from the so–called high–strength oil tempered wire, the fatigue limit was increased to the nearly equivalent level as the nitrided and conventionally shot–peened valve springs made from the same high–strength wire. This means that the SS Treatment can be used as a substitute to the nitriding process which has been applied in order to get improved fatigue property of high–strength valve springs.