A model for the influence of work hardening and microstructure on the evolution of residual stresses under thermal loading – Application to Inconel 718

This study proposes a model for the influence of work hardening and microstructure on the thermal relaxation of residual stresses. To construct such a model, an experimental campaign is first conducted on shot peened samples of Inconel 718 to generate different levels of residual stress and work hardening. The effect of the grain size and the size of the strengthening precipitates is investigated by producing two modified microstructures. Two shot peening conditions are used to introduce several profiles of residual stress and work hardening. These profiles are evaluated using X-ray diffraction. A thermal loading is then applied at 550°C with varying holding times, leading to a rapid but not complete relaxation of the residual stresses and work hardening. The experimental results exhibit the fact that the work hardening levels have a significant influence on this relaxation while the grain size and the size of the strengthening precipitates have a very moderate influence. Based on these experimental results, a model is proposed that considers the influence of work hardening on the thermal relaxation of residual stresses with some predictive applications. It is therefore possible to estimate the relaxation of residual stresses at any point on a shot peened part.