Hot corrosion behavior of Fe-Cr-Ni alloys in thermal energy storage material of molten MgCl2/KCl/NaCl in inert atmosphere

Abstract

Hot corrosion behavior of three commercial Fe-Cr-Ni alloys (SS 310, Incoloy 800 H, Hastelloy C-276) in molten MgCl2/NaCl/KCl (60/20/20 mole%) in inert atmosphere was investigated by long-term immersion tests at 700 °C for 500 hours. SS 310 performed the highest corrosion rate, while Hastelloy C-276 showed the best corrosion resistance performance. Unfortunately, all the studied alloys could not fulfill the requirements of the commercial applications (< 10 µm/year for 30 years lifetime). Microstructural analysis on the exposed alloy samples via SEM, EDX and XRD shows that Cr was dissolved preferentially than Fe and Ni to form a corrosion layer with a porous structure during the corrosion. Moreover, the corrosion products (e.g., MgO, MgCr2O4, etc) precipitated on the surface of the exposed samples, as well as in the Cr-depleted holes in the corrosion layer. For SS 310, which contains 2 wt% Si, Si was also dissolved and corrosion products containing Si were observed in the holes of the corrosion layer. Based on these, an impurity-driven corrosion mechanism was proposed for the hot corrosion behavior of Fe-Cr-Ni alloys in molten MgCl2/NaCl/KCl in inert atmosphere, which could assist the development of corrosion control technologies in future work.