Effect of elevated temperature variations on the corrosion resistance of S31603 and SS2562 austenitic stainless steels in chloride-sulphate environments

Abstract

Effect of environmental temperature variation at 308K, 318K, 333K and 353K on the corrosion resistance of S31603 and SS2562 austenitic stainless steels in 2.5M H2SO4/3.5% NaCl solution was studied by potentiodynamic polarization, potentiostatic measurement and optical microscopy. S31603 exhibited higher general corrosion resistance compared to SS2562 with values of 0.529 mm/y and 8.701 mm/y (308K and 353K) compared to 0.911 mm/y and 17.492 mm/y for SS2562. The corrosion potential of SS2562 shifted to cathodic values compared to S31603 which varies between cathodic and anodic values. At 308K, SS2562 exhibited metastable pitting activity at potential of 0.02 V. Passivation occurs at 0.09 V before breakdown of the protective oxide. Beyond 308K, passivation was absent on SS2562. S31603 exhibited unstable passivation behaviour at 308K and elevated temperatures. The protective oxide of S31603 formed at certain potentials before collapsing at all temperatures studied. Images of both steels showed localized corrosion deterioration at the grain boundaries. Larger micro-pits were visible on SS2562 compared to S31603 which had numerous shallow pits on its surface. At 353K, the extent morphological deterioration has advanced further on SS2562 compared to S31603 with the grain boundaries becoming more visible. The microstructural deterioration on S31603 at 308K and 353K is comparatively minimal. Keywords: Corrosion, Temperature, Steel, Pitting, Chloride, Sulphate