The high temperature corrosion behavior of ferritic stainless steel UNS S43940 has been investigated by means of cyclic exposure tests (CETs) at 650°C, in presence of NaCl and CaCl2 containing salt deposits and in test gases with different O2 and H2O concentrations. CETs of steel sheets, coated with a salt layer and steel sheets, covered by a salt-contaminated glass fiber-insulation mat, have been performed. Tested salts were NaCl and CaCl2xH2O in different weight ratios. Steel specimen have been investigated gravimetrically, optically and by means of scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDX). The oxides have been analyzed via X-ray diffraction (XRD), ion chromatography (IC), flame atomic absorption spectroscopy (FAAS) and UV/VIS spectroscopy.
Results show that in presence of NaCl, CaCl2 and oxygen, voluminous Fe2O3- and CaCrO4-containing oxide scales are formed. Highest mass loss was measured on salt-coated steel specimen, exposed to air + 0.05 % H2O. Steel sheets with the salt-contaminated mat showed significantly lower mass loss than those with the salt layer.