High-temperature dynamic corrosion mechanisms of austenitic stainless and carbon steels in nitrates for concentrating solar power

Abstract

Abstract: In this paper, to simulate the dynamic corrosion mechanisms of metals exposed to a high-temperature molten salt mixture of NaNO3–KNO3, the experimental samples made of commonly used stainless steel alloys such as 304 (with/without welds) and Q275 were suspended, along with stirring blades, in a specially designed stirred kettle to obtain their corrosion characteristics. For the experimental samples, the Q275 surface exhibited significant quantities of Fe3O4 and Fe2O3, while 304 generated FeCr2O4, Cr2O3, and MgFe2O4 with protective effects. The microstructure of the welding zone in 304 exhibited considerable disparities compared to that of the base material, consequently leading to augmented susceptibility towards localized corrosion. The uneven distribution of chromium in the welding zone resulted in intergranular corrosion and alterations in the crystal structure. Moreover, experimental studies have demonstrated that NO3- in the molten salt undergoes decomposition to generate oxygen ions, which contribute to the corrosion reaction. Notably, under all test conditions, the corrosion rate of samples exhibited the following ranking: 304 (without welds) < 304 (with welds) < Q275.