Fatigue resistance improvement of Lean Duplex Stainless Steel by Laser Shock Peening

R. STRUBBIA, ; S. HEREÑÚ; M.C. MARINELLI; C. RUBIO GONZÁLEZ; G. GÓMEZ ROSAS

Darmstadt

Congreso; Congress Materials Science and Engineering 2018 (MSE); 2018

German Materials Society (DGM - Deutsche Gesellschaft für Materialkunde)

Laser shock peening (LSP) is a surface treatment that enhances the mechanical properties of metals with a laser-induced shock wave [1]. These shock waves result from the expansion of plasma induced by the intense pulsed laser irradiation on the material. Thus, LSP technique causes plastic deformation leading to compressive residual stresses in the surface region. In the usual LSP configuration, protective coatings on the surface are used to avoid thermal effects. However, in recent years it was found that LSP without coating (LSPwC) generates the improvement of the fatigue performance of different metals, including stainless steels [2]. Duplex Stainless Steels (DSS) possess an exceptional combination of properties that stem from the mixed of ferrite and austenite phases. DSS are an attractive alternative to austenitic grades founding widespread use in the chemical, gas, oil, paper, offshore, and power industries [3, 4]. The development of cost-efficient DSS, with lower Ni than standard DSS, leads to a newly developed alloy called Lean DSS (LDSS). To date there has been little information available about the effects of LSPwC on cyclic deformation and accompanying substructure in DSS [5, 6]. Particularly, no information is found on the low cycle fatigue (LCF) life optimization caused by LSPwC in LDSSs. Considering that many applications of LDSSs could involve cyclic loading, this work attempts to rationalize the influence of LSPwC on the LCF performance of LDX2101 (UNS S3210). Special interest is placed on relating the fatigue results with the microstructural analysis. The superficial treatments were performed on both sides of specimens, applying two different pulse densities, in order to determine which one is the most efficient for the fatigue life improvement of LDX2101. The material characterization includes; analysis of the dislocation microstructure, determination of phase proportion, grain size, roughness and residual stress. The LSPwC with higher pulse density causes a better improvement in the LCF life of LDX2101 despite its higher roughness. This fact could be rationalized by the more intense compressive residual stresses induced in this case. On the other hand, independently of the pulse density, TEM observations suggest that the austenite is the responsible phase of the fatigue life enhancement as the ferrite phase remains unchanged after LSPwC.