Hot corrosion of Fe-Cr-Ni-Al-Si alloys in molten carbonate

The change in weight of five newly developed steel alloys containing Fe, 10-11.3% Cr, 15-18.27% Ni, 4.98-5.76% Mn, 4.18-5.52% Al and 0. 36-1.5% Si together with Inconel 690 and stainless steel 304 has been investigated in Na2CO3 + K2CO3 eutectic mixture at 800°C under atmospheric pressure and under isothermal and cyclic conditions. The scales formed were examined with optical and scanning electron microscopy and were analysed by energy dispersive X-ray diffraction techniques. It has been shown that the corrosion resistance of the alloys is far better than that of stainless steel 304, but slightly less than that of Inconel 690. The relatively high contents of Si and Al gave alloy 5 its highest corrosion resistance. About 0.2% N were found to refine the grains without the danger of depleting the grain boundaries from Al and Cr. The results have been explained in the light of the alkaline conditions prevailing in the carbonate melt.