High‐Temperature Corrosion Behavior of Typical Steels in Novel NaNO ₃ ‐KNO ₃ ‐Ca(NO ₃ ) ₂ Molten Salt

ABSTRACT The corrosion behavior and mechanism of typical steels in the novel proportion NaNO 3 ‐KNO 3 ‐Ca(NO 3 ) 2 (16‐48‐36 wt%, NKC) molten salt have been reported. Static corrosion tests of 347H stainless steel (347H), 321 stainless steel (321SS) and 20# carbon steel (20#CS) were conducted in NKC salt at 480°C for 360 h. Their annual corrosion rates are 10.5, 12.9, and 31.4 µm/year separately, and the corrosion resistance ranks as 347H > 321SS > 20#CS. Corrosion is primarily driven by selective oxidation and elemental dissolution. 347H forms a dense (Fe,Cr) 2 O 3 layer with a flat surface and minor granular products. 321SS undergoes chromium depletion and precipitation, resulting in the formation of Fe 2 O 3 and Fe‐Ni phases, which lead to uneven local corrosion. 20#CS develops a porous Fe 2 O 3 /Fe 3 O 4 mixed layer characterized by distinct pits and general corrosion. These findings provide new insights into steel corrosion and key data for material selection.