Some Properties of Ultra Clean Spring Steel

Abstract

There is a recent tendency to develope a motorcar's suspension coil spring that can be used under higher-stressed condition and to develope a valve spring having a higher-level of strength therefore creating better engine performance. Although there is a difference between the level of requirement for suspension coil spring and valve spring steel, improvement of fatigue property is a common destination. In order to achieve this purpose, making the raw material ultra clean may be one of the effective methods.
To get ultra clean steel, the degassing method which satisfies low cost and mass production is applied. And ultra clean steel is examined and tested for the properties needed in suspension coil spring and valve spring steel. The following results are obtained.
(1) Producing Ultra-Low Oxygen steel (ULO steel) which oxygen content is less than 15ppm is one of the effective way to realize a suspension coil spring satisfying 200kgf/mm² high stress level.
(2) ULO+UL·TiN steel produced by ultra low oxygen and ultra low TiN process posseses almost the same endurance limit as the Vacuum Arc-furnace Remelted steel. Therefere, this steel is used for the raw material as a valve spring satisfactorily.