Shot-Peening Time Effect on the Mechanical Properties of AISI 4340 Steel

Although the mechanical properties of shot-peened metallic alloys need to be explored carefully by changing shot-peening parameters, the mechanical properties of shot-peened AISI 4340 steel were not investigated well. In this study, the changes in the mechanical properties of shot-peened AISI 4340 steels with the shot-peening time are investigated. In the early stage, shear strain dissolves the Mo-rich carbides in the matrix, which reduces the mechanical properties of the shot-peened sample. In the later stage, sufficient shear strain induces grain refinement at the surface region, and the strength-ductility enhancement occurs owing to back-stress hardening evolution. The results show the shear straining during shot peening does not always enhance the strength of metallic alloys due to the dissolution of precipitates. Thus, the mechanical properties of shot-peened AISI4340 steel depends on the shot-peening time and an optimal processing time is required for obtaining a high strength–ductility combination.