2005 年 2005 巻 50 号 p. 11-15
The shot peening process is known to produce a hard layer called white-layer on the surface of coil springs. However, little is known about the fatigue properties of this white-layer. In this study, coil springs with white-layer were investigated. The surface of these springs was examined by micro Vickers hardness tester and FE-SEM. to evaluate fatigue strength of the springs. It was found that a microstructure of the white-layer with an average cell size of about 100 nm was observed, with a Vickers hardness rating of 1,000HV. Sample springs were manufactured in two groups utilizing a double-peening process. These springs had the same residual stress distribution and surface roughness. There is only one difference: one group had a nanocrystalline layer on the surface, while the other did not. The results of the fatigue test shows an increase of the fatigue life for the springs with nanocrystalline surface layer by approximately 10%.