Oxidation behaviour of silicate–chromate and oxide coated 303 steel in presence of ionic salts over temperature range 400–1000°C

Abstract

The oxidation behaviour of AISI303 steel coated with oxide and silicate–chromate coatings has been investigated in environments containing Na₂SO₄, Na₂CO₃, and NaCl, and mixtures thereof. The tests were carried out over the temperature range 400–1000°C, in air and oxidation behaviour was characterized by measuring the oxidation (weight gain) kinetics. The coated and uncoated steel specimens both follow parabolic rate kinetics over the temperature range 400–800°C, the coated steel having the better oxidation resistance. The silicate–chromate coated steel is much less severely attacked by Na₂SO₄ and Na₂CO₃ than the oxide coated steel. The addition of NaCl to Na₂CO₃ or Na₂SO₄ environments increases the aggressiveness of the melt, resulting in increased corrosion rates, although this effect is less pronounced for the oxide coated steel. These increased corrosion rates in the presence of NaCl are associated with intergranular attack of the alloy matrix by melts containing NaCl.