Influence of annealing on the shot-peened surface of duplex stainless steel at elevated temperatures

In order to investigate the residual stress relaxations of shot-peened surface, isothermal annealing treatments were carried out on duplex stainless steel (DSS) S32205 after shot peening (SP) with temperature ranging from 600 to 700 °C. A new phase with a tetragonal crystal structure (σ-phase) appears apparently at the annealing temperature of 700 °C for 64 min. The rates of residual stress relaxation in austenite (γ-phase) are higher than that in ferrite (α-phase) under the corresponding annealing temperature for 64 min. The residual-stress relaxation process during isothermal annealing could be described by Zener–Wert–Avrami function. The activation enthalpy for residual stress relaxation in γ-phase is lower than that in α-phase. At temperature of 700 °C, the microhardness increases gradually after reduction at the initial stage because the strengthening of the new σ-phase is dominating with the prolongation of annealing time, the content-increased γ-phase may also have a certain contribution.

► The relaxations of residual stresses caused by thermal treatments were studied.
► Dislocation density of γ-phase is higher than that of α-phase in the surface after shot peening.
► A new phase appeared apparently at the annealing temperature of 700 °C.
► Activation enthalpy for stress relaxation of γ-phase is lowered than that of α-phase.
► Microhardness is influenced by dislocation density relief and composition of phases.