Surface modifications induced in 316L steel by laser peening and shot-peening. Influence on pitting corrosion resistance

The influence of laser peening (LP) on the electrochemical behavior of AISI type 316L stainless steel in a saline environment was evaluated. Surface m odifications were investigated as they might have beneficial effects on the corrosion behaviour. Low residual stress and work hardening levels were fo und, when compared with a conventional shot-peening (SP) treatment, mainly because of the absence of martensite transformation in the case of LP. Surf ace changes were accompanied by small roughening effects and a global prese rvation of the surface chemistry after treatment. Therefore, electrochemica l tests performed on samples after LP and SP treatments showed increases in rest potentials, reductions of passive current densities and anodic shifts of the pitting potentials evidenced by a stochastic approach of pitting. T he better pitting resistance was observed after LP treatment, which seems t o reflect a reduction or an elimination of active sites for pitting at lowe r potentials. Even though the deleterious surface state of shot peened surf aces possibly counterbalances the beneficial influence of residual stresses , a beneficial influence of mechanical surface treatments has been demonstr ated regarding the localized corrosion properties. Published by Elsevier Sc ience S.A.