The effect of sodium chloride concentration on corrosion resistance of austenitic stainless steel 316L and SMA weldment

Austenitic stainless steel 316L has been widely used in marine environment which containing sodium chloride solution (NaCl). In order to provide matching properties with parent metal, filler metal SMA 316L is commonly produced with slightly over alloyed composition. This work investigated the corrosion behavior of base metal 316L and SMA 316L weld metal by using Electrochemical Impedance Spectroscopy (EIS) to evaluate the mechanism of corrosion behavior based on impedance magnitude measurement at room temperature (27oC ). Various concentrations of sodium chloride solution i.e 1%,2%,3.5%,4%, and 5% NaCl were prepared. Optical Metallography was also conducted to compare microstructure of base and weld metal. By using Nyquist graphs and its related equivalent circuit parameters showed that impedance magnitude of weld metal was higher which compared to base metal at any NaCl concentration. Metallography examination revealed that weld metal 316L had dendritic austenitic with delta ferrite and 316L base metal had austenite with typical twin boundaries structure. Higher chromium and nickel content in weld metal 316L was the key variable that control passive film characteristic rather than its microstructure. The lowest impedance magnitude of both 316L and all-weld metal 316L at various concentration was at 3.5% NaCl. Dissolved oxygen at 3.5% NaCl reach maximum solubility which causes severe pitting corrosion.