[Objective

]

This study aims to clarify the long-term corrosion behavior and underlying mechanisms of 304 stainless steel in Hitec molten salt at 400 ℃

with a focus on elucidating the evolution of corrosion damage as a function of immersion time. [Methods

]

Long-term static immersion experiments were conducted in Hitec molten salt(53%KNO_3+7%NaNO_3+40%NaNO

2

) at 400 ℃ for durations of 1

3

and 5 months. A comprehensive range of characterization techniques was employed to systematically investigate the corrosion behavior. Mass change analysis was performed to assess overall corrosion kinetics. X-ray diffraction(XRD) was used to identify the phase composition of corrosion products. Scanning electron microscopy(SEM) was applied to observe surface morphology and cross-sectional m

icrostructural evolution. Energy-dispersive spectroscopy(EDS) enabled elemental mapping and semi-quantitative analysis to track elemental migration. Inductively coupled plasma mass spectrometry(ICP-MS) was utilized to analyze compositional changes in the molten salt medium. Through these complementary methods

the study systematically examined the material's mass variation

surface and crosssectional microstructure evolution

elemental migration behavior

and corresponding changes in the molten salt chemistry. [Results

]

The corrosion process of 304 stainless steel in Hitec molten salt exhibited a typical three-stage characteristic: rapid corrosion

transition

and slow corrosion. In the initial stage

corrosion was dominated by the selective dissolution of chromium(Cr)

leading to severe Cr depletion on the surface. This preferential leaching induced a phase transformation from austenite to ferrite in the near-surface region. With prolonged immersion time

a corrosion product layer mainly composed of Fe and Cr oxides gradually formed on the surface

and the thickness of this layer increased with time. The contents of Ni and Mn exhibited fluctuations

which were presumed to be related to local spallation. Cross-sectional analysis further revealed that Cr element was significantly depleted in the near-surface region

while O element diffused into the substrate

with the corrosion interface gradually becoming clearer and extending inward. [Conclusion

]

This study systematically elucidates the corrosion mechanism of 304 stainless steel in Hitec molten salt by integrating analyses from macroscopic to microscopic scales and from the surface to the interior of the material. The experimental data and mechanistic insights obtained provide a valuable experimental basis and theoretical reference for evaluating the service performance of key metallic components in molten salt energy storage systems

as well as for guiding the design and selection of corrosion-resistant alloys for high-temperature thermal energy storage applic

ations.