Corrosion Behavior of Fe–25Cr in a N2–0.1% SO2 Atmosphere at 973 K Under Mechanical Loading

Abstract

The corrosion behavior of an Fe-25Cr alloy was investigated in a N2-0.1 vol.% SO2 atmosphere at 973 K with and without stress. Without stress, the surface scale formed at the very initial stage consisting of Cr oxides and sulfides, which later changed to a Cr2O3-rich scale with the initially formed sulfides remaining. Under relatively low constant stress, +15 and +20 MPa, as well as cyclic stress of ±30 or ±40 MPa, the total strain for 36 ks was less than 0.1% and there was little cracking of the external scale, which consisted of Cr2O3 and (Fe, Cr)3O4 with small amounts of sulfide, growing faster. The external scale here was poorly adhesive. Under high stress, +25 and +35 MPa, cracks formed in the external scale and both oxides and Fe sulfide grew rapidly through the cracks to form nodules. The nodules consisted of an FeS-rich core surrounded by Fe3O4. With increasing strain, the preformed Cr2O3-rich scale changed drastically to a multilayered scale with an alternating oxide layer-sulfide layer structure.