Improvement of Fatigue Life of Valve Spring Wire by Reducing Non-Metallic Inclusions

After a description of a new evaluation method of inclusions and a manufacturing process of the new clean valve spring steel SAE9254, this paper reports on a quantitative relationship between a non-metallic inclusion size measured at the fatigue fracture initiation site, its depth from the wire surface and the fatigue life which has been obtained through an investigation of both newly developed clean steel and conventional steel for valve springs.

As a result, a remarkable improvement in the fatigue life of newly developed steel has been found. Fatigue crack propagation both from a non-metallic inclusion and from the wire surface is also discussed in this paper.