Corrosion Behavior of Fe-12Cr-2Mo Stainless Steel in Na sub(2) SO sub(4)-50%NaCl with Flowing Ar-20%O sub(2) Environments at High Temperature

The behavior of Fe-12Cr-2Mo stainless steel exposed isothermally in tube furnace at 700[degrees]C for 10 h had been studied in different environments; of mixed environment (Ar-20%O sub(2) with coated Na sub(2) SO sub(4)-50%NaCl salts), molten salt (Na sub(2) SO sub(4)-50%NaCl) and dry oxygen (Ar-20%O sub(2)) atmospheres. The exposed samples were characterized by using optical microscopy (OM), scanning electron microscope (SEM), energy dispersive X-ray (EDX) and X-ray diffraction (XRD). The results indicated that, sample exposed in mixed environments undergoes highest corrosion rate compared with other samples. The main phase exists in all samples generally were iron-rich oxides which non-protective and thick. Conversely, EDX analysis on cross-sectional samples revealed the Cr-enrichment developed underneath the iron-rich oxide scales as the chromium concentration increases towards near the substrate. In presence of salt mixture, the oxide scales undergo spallation, however there is no crack observed. The catastrophic corrosion sample was occurred in combined environment due to the oxidation induced by the chloridation and sulfidation phenomena as well.