Corrosion behavior of UCX, KHR35, and KHR45 alloys in molten nitrates

The corrosion behavior of three high-Ni, high-Cr alloys, that is, UCX, KHR35, and KHR45 alloys, in a mixture of 60% NaNO₃–40% KNO₃ at 600°C has been evaluated by using weight loss tests, potentiodynamic polarization curves, and electrochemical impedance spectroscopy measurements. Cr contents ranged between 23.25 and 43.2 wt.%, whereas Ni ranged between 36.6 and 50.3 wt.%. For comparison, the same studies were performed on 304-type stainless steel (304SS). Tests were complemented with detailed scanning electronic microscope and X-ray diffraction studies. Results showed that that the three high-Ni, high-Cr alloys had lower weight loss than that for 304SS. Polarization tests indicated the formation of a passive layer in all cases. Electrochemical impedance spectroscopy data have shown that the corrosion mechanism for all the alloys was charge transfer from the alloy to the molten salt. Finally, X-ray patterns showed the presence of Cr₂O₃ in all tested alloys, which is responsible for the observed passive behavior and their corrosion resistance.