Hot Corrosion Resistance of Hot-Dip-Aluminized AISI 321 Stainless Steel in a Salt Mixture of 60%V₂O₅ + 40% Na₂SO₄ at 700 °C

Abstract

Hot-dip aluminizing (HDA) is an established surface coating technique to deposit aluminium on ferrous substrates. The aluminium deposit forms a compact layer of alumina when exposed to high temperature, providing high-temperature oxidation and corrosion protection. In the present investigation, HDA of AISI 321 stainless steel was carried out in pure aluminium bath at 700 °C. The steel samples were dipped in molten Al bath for 10 min. The HDA sample was given diffusion treatment at 900 °C for 5 h before subjecting to hot corrosion tests. The microstructural features after hot corrosion tests were analyzed using an X-ray diffractometer and a scanning electron microscope. The aluminized and bare steel samples were subjected to hot corrosion test in a salt mixture of 60%V₂O₅ + 40% Na₂SO₄ at 700 °C. The tests were conducted for 50 cycles, of which each cycle consisted of 1-h heating at 700 °C in furnace followed by 20-min cooling in air. The corrosion kinetics was studied by thermogravimetric analysis. The study revealed that weight gains for aluminized sample were lower than the uncoated sample. The weight gain for the uncoated sample at the end of 50 cycles was 5.87 mg/cm², and that of the aluminized sample was 2.3 mg/cm². Spalling of oxide scales was observed for the uncoated sample, while aluminized sample showed adherent oxide scales resulting in increased hot corrosion resistance.