Characterization Using Point Defect Theory of the Microstructure Effect on Passivity Stability in Austenitic Stainless Steel

The influence of the microstructure on the resistance to pitting potential in austenitic stainless steel UNS S31603 is evaluated to explain the effect of the distribution of features such as carbides. Different microstructures were obtained by processing, via surface laser melting (SLM) and sensitized at 600°C, 700°C, and 800°C. The test solution used for electrochemical testing included a buffer pH 8 brine at room conditions. The characterization of the passive conditions is done by using potentiodynamic, potentiostatic, and Mott Schottky techniques. The results show that the UNS S31603 samples produced by SLM have higher passive layer stability. The correlation with the microstructural features attributes this to a lack of inclusions and carbides characteristic of the SLM process. The analysis of the experimental results using the point defect model description of the passive layer behavior indicates that the stability of the passive layer is a priori inversely proportional to both the metal cation and anion vacancy diffusivities. Experiments reveal the close dependence and explain the properties of the passive layer with respect to a point defect model.