Fatigue performance improvement in lean duplex stainless steel by peening treatments.

M. C. MARINELLI; S. HEREÑÚ; R. STRUBBIA

Darmstadt

Congreso; Materials Science and Engineering; 2018

DGM · Deutsche Gesellschaft für Materialkunde e. V.

Laser shock peening (LSP) is a surface treatement that enhances the mechanical propierties of metalswith a laser induced shock wave [GUJ 14]. 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 coating on the surface are used to avoid thermal effect. However, in recent yearsit was found that LSP without coating (LSPwC) generates the improvement of the fatigue performance of different metals, including stainless steels [KAR17]. Duplex Stainless Steels (DSS) posses an exceptional combination of properties that stern 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 [ALV09, ALV08]. The development of cost-effect 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. Particularly, no information is founf on the low ciclic fatigue (LCF) life optimizatiocaused by LSPwC in LDSS.Considering that many applications of LDSSs  could involve ciclic loading, this work attempts to rationaleze de influence of LSPwC on the LCF performance of LDX2101(UNS S3210). Spetial interest is placed on relating the fatigue results with the microstructural analysis. The superfitial treatmentswere 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 most intense compressive residual stresses induced in this case. On the other hand, indepemdently 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.