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

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

Darmstadt

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

Laser shock peening (LSP) is a surface treatment that enhances the mechanical properties of metals with 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 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 [KAR 17]. 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 [ALV 09, ALV 08]. 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 [VAZ 17, RUB 11]. 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.Alvarez-Armas I. Duplex Stainless Steels : Brief History and Some Recent Alloys. Recent Patents Mech Eng 2008;1:51?7.Duplex stainless steels, Edited by I. Alvarez-Armas and S. Degallaix-Moreuil (ISTE Ltd. and John Wiley & Sons Inc., 2009) Gujba AK, Medraj M. Laser peening process and its impact on materials properties in comparison with shot peening and ultrasonic impact peening. vol. 7. 2014. doi:10.3390/ma7127925.Karthik D, Swaroop S. Laser peening without coating - an advanced surface treatment: A review. Rev Mater Manuf Process 2017;32:1565?72. doi:10.1080/10426914.2016.1221095.Rubio-González C, Felix - Martinez C, Gomez-Rosas G, Ocaña JL, Morales M, Porro JS. Effect of laser shock processing on fatigue crack growth of duplex stainless steel. Mater Sci Eng A 2011;528:914?9. doi:10.1016/j.msea.2010.10.020. Vázquez Jiménez CA, Gómez Rosas G, Rubio González C, Granados Alejo V, Hereñú S. Effect of laser shock processing on fatigue life of 2205 duplex stainless steel notched specimens. Opt Laser Technol 2017; 97: 308?15. doi:10.1016/j.optlastec.2017.07.020.