Evaluation of the residual stress and microstructure character in SAF 2507 duplex stainless steel after multiple shot peening process

In this study, multiple shot peening treatment was implemented to the SAF 2507 duplex stainless steel. The residual stress, microstructure and strain-induced transformation in the shot-peened specimens were evaluated by X-ray diffraction line profile analysis. Results pointed out that multiple shot peening was helpful to develop deep layer of high compressive residual stress with moderate work hardening. After triple shot peening treatment, a maximum compressive residual stress of −1070.5 MPa (at the surface for austenite) and −910.5 MPa (at 10 μm depth for ferrite) were obtained. The multiple shot peening is more effective in producing the microstructure refinement than single shot peening. The depth of the refinement layer with domain size smaller than 100 nm reached to 150 μm in the austenite and 100 μm in the ferrite phase of the dually shot-peened specimen, the maximum magnitudes of which after single shot peening were 100 μm and 75 μm, correspondingly. The quantitative measurement of stained-induced martensite in the shot-peened samples by X-ray phase analysis revealed that larger amount of α′-martensite formed after multiple shot peening compared to that of single shot peening, nearly 31.6% α′-martensite was formed at the impacted surface of triply peened specimen. The results also demonstrated that multiple shot peening could significantly decrease the surface roughness and help to improve the surface quality.