Shot peening (SP) and also severe shot peening (SSP) provide high level compressive residual stress on a certain thickness just beneath the surface. By exposing severe plastic deformation (SPD) via SSP, the nanocrystallization is formed without any chemical alteration and the structure is to be hardened by fully mechanized process. The difference among SP, SSP and repeening (RP) is only related with the selection of the input parameters. Most of the input parameters combination constructs the Almen intensity which is the most powerful condition to be made the decision on the final shot peening of real parts. AISI 1045 medium carbon steel is selected for the optimization of input parameters (shot size, peening duration and air pressure at constant coverage-100%) by investigating the output responses (residual stress, hardness) using response surface methodology. Optimum SP parameters are introduced by response optimizer and the model is verified by the confirmation tests. (C) 2019 Elsevier Ltd. All rights reserved.