Improvement of Fatigue Strength of Nitrided High-Strength Valve Springs by Application of a New Super Fine Shot-Peening Technology

The peening of fine steel beads with diameters less than 80μm (referred to as SS Treatment in this paper) on the surface of nitrided and then conventionally shot-peened (with 0.6mm diameter cut steel wires) high-strength helical springs made from developed high strength valve spring wire, was found to effectively improve spring fatigue strength. This improved fatigue strength is mainly the result of very high compressive residual stress caused by work hardening of the spring surface layer without inducing deleterious surface qualities such as harmful surface micro-fissuring or surface roughness.