Hot Corrosion of Fe-Cr Alloys with 75 Na2SO4 + 25 NaCl Coating at 1173 K

Abstract Hot corrosion behavior of two Fe-Cr alloys coated with the salt film of 25 NaCl + 75 Na₂SO₄ (mass fraction) in air at 1173 K was studied. Results show that for both alloys of Fe-10Cr and Fe-20Cr, the mass gain of the alloy coated with 40–45 g/m² of 75 Na₂SO₄ + 25 NaCl is greater than that of the alloy coated with 20–25 g/m² of the film with the same composition. The corrosion products of Fe-10Cr alloy can be divided into three layers, of which the outermost scale is Fe₂O₃, the intermediate layer is mixed oxides of Fe₂O₃ and Cr₂O₃, and the innermost layer is mainly chromium sulfide. However, the corrosion products of Fe-20Cr only consist of two layers: the external scale of Fe₂O₃ and Cr₂O₃, and the internal layer of chromium sulfide. Compared to Fe-10Cr, Fe-20Cr has better hot corrosion resistance. The hot corrosion mechanism was proposed and the influence of the different coating mass of 75 Na₂SO₄ + 25 NaCl is also discussed.