High temperature corrosion of low alloyed steel in air and salt mist atmospheres

The aim of this work has been to show the influence of air oxidation and salt mist corrosion on the behaviour of low alloyed steels 18K (K18), 16M (16Mo3), 15HM (13CrMo4-4) and finally 10CrMo9-10 (10H2M) employed in the Polish energy sector. The exposures have been carried out at 450°C, 500°C, and finally 550°C for 500 hours. The obtained results indicate that in both atmospheres, the exposed steels developed similar phases containing Fe₃O₄ (magnetite) and Fe₂O₃ (hematite). The scale thicknesses developed under both corrosion conditions have indicated similar values. On the other hand, the addition of 1% NaCl - 1% Na₂SO₄ to deionised water generates the development of layered structures on low-alloyed steels with different Fe₂O₃ and Fe₃O₄ ratio, the effect originates most probably from the presence of S and Cl within the oxide scale. The presence of layers with different phase ratio generates the formation of stresses originating from different coefficients of thermal expansion (CTE) between the phases (Fe₂O₃, Fe₃O₄) and between the layers themselves.

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