Abstract
High durability is required for automotive engine valve springs. To ensure the performance of spring, it is necessary to evaluate and measure the residual stress distribution of spring surface and inward direction. Generally, it has been assumed that the residual stress of a material surface treated by the shot peening is uniform. However, the round and spiral shape of a coil spring brings various peening angles corresponding to the surface location, then the uneven peening angles may leads to a non-uniform residual stress on the coil spring surface. In the meanwhile, an analysis method of non-liner sin2 φ diagram, or φ-split analysis, is well known to directionally deformed material. In this study, residual stress distribution of spring material deformed by the shot peening from the different angles was measured and, non-linearity of sin2 φ diagram was studied. In addition, the relationship between microstructure and residual stress was studied by using field emission type scanning electron microscope (FE-SEM). The result reveals that the non-linearity in the sin2 φ diagram for the shot peening samples. The extent of φ-split became larger with the increasing shot peening angle and was dependent not only on the mass fraction of carbide particles but also on the carbide particles size distribution.
