Thermodynamic Simulation of Niobium-Containing Austenitic Stainless Steels: Microstructure and Corrosion Properties
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In the present work, as cast niobium (Nb) alloyed (0.66 wt%, 1 wt% and 1.75 wt% of Nb) austenitic stainless steels were solution annealed and sensitized at 550 °C, 650 °C and 750 °C for a period of 12 h. Niobium carbide (NbC) precipitation behavior was simulated using ThermoCalc-PRISMA. The microstructural features were studied by SEM. Corrosion properties were analyzed by double-loop electrochemical potentiokinetic reactivation test and electrochemical impedance spectroscopy. Results showed that the nucleation rate and volume fraction of NbC precipitates at grain boundaries (GBs) in 1.75%Nb alloy were higher than other two alloys. The 1.75%Nb alloy was found to have a lower degree of sensitization compared to other two alloys due to formation of NbC at GBs. The corrosion behavior of alloys in the sensitized conditions was in total contrast to that of solution-annealed condition.
KeywordsCorrosion Sensitization Austenitic stainless steels Electrochemical impedance spectroscopy (EIS) ThermoCalc PRISMA