High cycle fatigue life improvement of superferritic stainless steel by laser shock peening without coating

Abstract

The excellent mechanical properties, high thermal conductivity and corrosion resistance combined with moderate cost make superferritic stainless steels (SFSS) commercially attractive. Though these steels are finding increase uses in many applications where fatigue loadings are applied, few studies are devoted to study this theme. Even fewer works aim to investigate the fatigue improvement by surface treatments. Laser shock peening without coating (LSPwC), is a surface modification technology using high-energy laser with no absorbent coating that increases the fatigue life in many alloys. However, though LSPwC in SFSS UNS44600 has reported to produce beneficial compression residual stresses (CRSs) and strain-hardening surface layer, it also causes intergranular corrosion which avoids the improvement of low fatigue life (LCF). Thus, attempting to discern if this result remains in the HCF regimen, the present paper is focused on studying the influence of LSPwC on the high cycle life (HCF) of SFSS UNS S44600. The results showed that LSPwC enhances the HCF of SFSS UNS S44600, being the fatigue life improvement more pronounced with higher pulse density. This can be rationalized considering the main role of the induced CRS in slowing occurrence and growth of crack in corroded grains on HCF regimen. The examination of fracture surface by scanning electron microscopy (SEM) substantiates these fatigue results.