Abstract:The effect of 475˝C embrittlement and microstructure process orientation on atmospheric-induced stress corrosion cracking (AISCC) of grade 2205 duplex stainless steel has been investigated. AISCC tests were carried out under salt-laden, chloride-containing deposits, on U-bend samples manufactured in rolling (RD) and transverse directions (TD). The occurrence of selective corrosion and stress corrosion cracking was observed, with samples in TD displaying higher propensity towards AISCC. Strains and tensile stresses were observed in both ferrite and austenite, with similar magnitudes in TD, whereas, larger strains and stresses in austenite in RD. The occurrence of 475˝C embrittlement was related to microstructural changes in the ferrite. Exposure to 475˝C heat treatment for 5 to 10 h resulted in better AISCC resistance, with spinodal decomposition believed to enhance the corrosion properties of the ferrite. The austenite was more susceptible to ageing treatments up to 50 h, with the ferrite becoming more susceptible with ageing in excess of 50 h. Increased susceptibility of the ferrite may be related to the formation of additional precipitates, such as R-phase. The implications of heat treatment at 475˝C and the effect of process orientation are discussed in light of microstructure development and propensity to AISCC.

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ASME qualified welding procedures do not guarantee suitable corrosion and passivation properties for lean duplex stainless steel welds. An evaluation of two ASME qualified welding procedures to optimize the corrosion performance of tungsten inert gas (TIG) welded grade 2101 duplex stainless steel using ER2209 weld consumable was conducted. The evolution of the microstructure was examined by optical and electron microscopy, ferrite-scope measurements, and scanning Kelvin probe force microscopy. An electrochemical mini-cell was then used to characterize the electrochemical behavior of different weld regions using the techniques such as the double loop electrochemical potentiokinetic reactivation test, standard potentiodynamic polarization tests, and cyclic potentiodynamic polarization. The fusion line was the most critical zone for localized corrosion for both welding procedures, due to the formation of Cr- and Mo-depleted zones, resulting in the highest degree of sensitization. The best performance was attributed to the weld face, due to the presence of higher Cr and Mo contents, highlighting the pitting corrosion resistance. A heat input range of 1.6 kJ/mm to 1.9 kJ/mm and low current density (WPS 1) indicated better corrosion performance of all weld regions. The electrochemical corrosion response was in all cases related to microstructural characteristics of the weld regions. The influence of weld parameters on microstructure development and corrosion performance is discussed.