Effect of chloride contents on the corrosion behavior of ferritic and austenitic steels in molten solar salts

摘要

The corrosion behavior of a ferritic-martensitic UNS 42200 (X20Cr-MoV11-1) steel and the stainless steel UNS31600 (316SS) is studied in molten solar salts at 600°C for up to 5000 hours. Focus is based on the effect of chloride impurity level in the molten nitrate salts and the mechanism of corrosion under different chloride contents. Gravimetric and metallographic methods are used to characterize the kinetics of corrosion and the extent of corrosion. Results showed that the ferritic-martensitic steel showed a significant mass gain by forming a thick and non-protective oxide scale in low chloride (up to 0.02 wt%) salt. A significant increase of the corrosion rate was observed when this steel was exposed in high chloride containing salt (up to 0.2wt%). Furthermore, the scale underwent severe deformation in the form of buckling and cracking. Austenitic stainless steel showed superior corrosion resistance in both low chloride and high chloride salts. A passive layer at metal oxide interface formed even for increased chloride level which avoids direct contact between the salt and the austenitic substrate.