Electrolytic Aluminizing of Low Carbon Steel as Protection Treatment for Current Leads against High Temperature Oxidation

Application of protective aluminum-based coatings is one of the ways to increase the oxidation resistance of low-carbon steel. The electrolytic deposition of aluminum in the NaF33-KF15.2-(AlF3)51.8 wt.% melt at 920°C and the current density of 0.8-1.0 A·cm-2 (0.25 A·h·cm-2) have provided a continuous aluminide coating based on Fe2Al5 with a good adhesion to the steel substrate due to dissolution of oxide film from the surface of the treated products in fluoride melt. The resistance of steel samples to sulfide corrosion was investigated in a lab-scale three-electrode cell at 900°C in contact with a “Soderberg” carbon anode, which was obtained by carbonization of the coal tar pitch containing 2.0-2.5 wt.% of sulphur. The IRC (ohmic voltage drop in contact layer) growth rate was 3.3 times higher for uncoated steel due to formation of the oxide-sulfide layer based on FeS. The electrolytically aluminized steel with preliminarily formed α-Al2O3 layer possessed more stable value of the IRC in comparison with the uncoated steel because of the higher chemical resistance.