Cyclic deformation and near surface microstructures of normalized shot peened steel SAE 1045

Abstract

Cylindrical specimens of the normalized plain carbon steel SAE 1045 were shot peened and cyclically deformed under stress control. A special cross-sectioning technique was applied to prepare near surface regions for transmission electron microscopy. The resulting properties of these regions were characterized by X-ray diffraction and microhardness measurements. The cyclic deformation curves are affected characteristically by dislocation arrangements induced by shot peening. The stability of these dislocation arrangements and the depth profile obtained by residual stress and interference line half-width value measurements depend strongly on the stress amplitude. High stress amplitudes lead to the formation of dislocation cell structures in the shot peened layers, accompanied by the total disappearance of compressive stresses and the decrease of interference line half-width values down to the initial level. Thus, a clear correlation between stress relaxation, cyclic deformation behaviour and microstructural alterations in shot peened regions is revealed. Experiments carried out on shot peened hollow specimens indicate that the cyclic deformation behaviour is not merely a function of dislocation arrangement and density but also of the thickness of strain hardened near surface material in relation to the diameter of the specimen.