The influence of Cu content on high temperature corrosion behavior of heat - resistant molten salt steel

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This work studies the high temperature corrosion behavior of new heat-resistant steel with salt coating method
of 75%Na2SO4+25%NaCl coating on the steel surface at 700℃. The chemical composition of corrosion
products and surface morphology of the corrosion layer were analyzed using X-ray diffractometer (XRD),
scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and investigate the effect of Cu
content on high temperature corrosion behavior of heat resistant steel. The results show that the thermal corrosion
kinetics curve of tested steel follows the parabolic law and the surface is composed of Fe2O3 and
FeCr2O4. The corrosion layer were divided into two layers, the outer layer was loose and porous while the
inner layer was dense and continuous. The structure of the oxide film consists of various protective oxide
films; with increasing of Cu content, the high-temperature corrosion resistance of heat-resistant steel was
improved and the thickness of the corrosion layer was decreased which led to improving the bonding strength
between the inner layer and the matrix. The results of EDS analysis shows that Cu elements can promote the
outward diffusion of Cr elements to oxidation of the steel to form a Cr2O3 protective oxide film for preventing
the diffusion of chlorine elements, oxygen elements into the interior toward the steel with slow down the
process of "activation oxidation", reduce the sensitivity of intergranular corrosion and achieve the function of
protecting materials.
Keywords: Heat-resistant steel. Thermal corrosion. Molten salt. Corrosion layer.