Assessment of inter-granular corrosion susceptibility of 304L stainless steel using non-destructive electrochemical techniques

Abstract

The effect of heat treatment on the corrosion resistance of AISI 304L stainless steel is studied in the present investigation. As-received samples of 304L stainless steel were solution annealed at 1 050°C for 90 minutes followed by thermal ageing at 750°C for various time durations (upto 24 days). ASTM standard A-262 practice A test was used to detect susceptibility of inter-granular attack. Electron dispersive spectroscopy attached to scanning electron microscopy was performed for identification of carbides. It was observed that no significant amount of attack took place upto 1 day. The extent of sensitization was quantitatively evaluated using double loop electrochemical potentiodynamic reactivation test. The results obtained showed that corrosion resistance decreased with an increase in thermal ageing duration. This behavior was attributed to the precipitation of chromium carbides causing depletion of chromium in the areas adjacent to the grain boundaries (as determined by electron probe micro analyzer). The degree of sensitization of highly aged sample was found to be 24.6%. Further, the degree of sensitization in terms of polarization resistance was computed in the middle of the transpassive potential region (at 1.1 V) using electrochemical impedance spectroscopy.