Developments of ultra-high strength wire rods for valve springs with excellent fatigue life

High stress design has been adopted widely in the design of valve springs to reduce fuel consumption and/or to reduce engine height Such design requires high-strength steel. However, increasing the tensile-strength of a valve spring wire does not necessarily extend fatigue life of the wire unless the size of non-metallic inclusions is reduced to lower the wire's sensitivity to such inclusions. This paper describes the optimum chemical compositions which yield higher fatigue life and sag resistance in valve springs. Also reported are techniques for controlling non-metallic inclusions and the properties of ultra-high strength wire-rods for valve springs with excellent fatigue life.