CYCLIC DEFORMATION AND NEAR-SURFACE MICROSTRUCTURES OF NORMALIZED SHOT PEENED STEEL SAE-1045

Cylindrical specimens of the normalized plain carbon steel SAE 1045 we re shot peened and cyclically deformed under stress control. A special cross-sectioning technique was applied to prepare near surface region s for transmission electron microscopy. The resulting properties of th ese regions were characterized by X-ray diffraction and microhardness measurements. The cyclic deformation curves are affected characteristi cally by dislocation arrangements induced by shot peening. The stabili ty of these dislocation arrangements and the depth profile obtained by residual stress and interference line half-width value measurements d epend strongly on the stress amplitude. High stress amplitudes lead to the formation of dislocation cell structures in the shot peened layer s, accompanied by the total disappearance of compressive stresses and the decrease of interference line half-width values down to the initia l level. Thus, a clear correlation between stress relaxation, cyclic d eformation behaviour and microstructural alterations in shot peened re gions is revealed. Experiments carried out on shot peened hollow speci mens indicate that the cyclic deformation behaviour is not merely a fu nction of dislocation arrangement and density but also of the thicknes s of strain hardened near surface material in relation to the diameter of the specimen. (C) 1998 Elsevier Science S.A. All rights reserved.