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The corrosion behavior of austenitic stainless steel after low-temperature liquid oxy-nitriding (LON) was investigated by exposing in H 2 S/CO 2 -saturated liquid and vapor environments up to 720 h at 60 °C. The corrosion rates before and after LON were compared by the weightlessness method, and the microstructure as well as the corrosion scales were characterized using surface analysis methods. The results indicated that the composite S-phase layer with the outer Fe 3 O 4 layer and the inner nitrogen-rich sublayer could improve the corrosion performance in H 2 S/CO 2 -saturated environment. The base material (BM) suffered local corrosion first, which then transformed into uniform corrosion. As a comparison, The LON sample, covered with a thin corrosion product layer, indicated slight local corrosion. The excellent corrosion resistance of the S-phase should be attributed to the blocking effect of the continuous Fe 3 O 4 film as well as the suppression of the atomic mobility by the nitrogen-containing supersaturated solid solution. • The difference in the corrosion behavior of austenitic stainless steel in the vapor and liquid phases is analyzed. • In the H 2 S/CO 2 -saturated liquid/vapor phase, the corrosion rate of the LON sample is 93.1% lower than that of the BM. • The nitrogen atoms in the S-phase can increase the local pH value and accelerate the passivation in acidic environments. • The continuous Fe 3 O 4 layer can effectively block offensive ions. • Supersaturated nitrogen could suppress the atomic mobility thereby reducing the dissolution of metal atoms. [ABSTRACT FROM AUTHOR]

The time-dependent experiment was performed to investigate the corrosion behavior of low-temperature liquid nitrocarburized (LNC) 304 austenitic stainless steel in wet H2S environments. Characteristics of H2S corrosion products, as well as localized corrosion behavior, were investigated using X-ray diffraction (XRD), scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), and optical profilometry. The results revealed that the untreated steels, of which the H2S corrosion product layer on the untreated surface thickened but displayed a layered defect structure as the corrosion proceeded, had a higher weight loss than the LNC. Energy-dispersive spectroscopy (EDS) served to reveal the relationship between corrosion behavior and the content of sulfur, chromium, and other elements, and the valences of these elements were illustrated by XPS. The surface morphology after removing corrosion products showed that the presence of nitrocarburized S phase could prevent general corrosion and inhibit pit propagation. [ABSTRACT FROM AUTHOR]

• Corrosion behaviors of S-phase and austenitic stainless steel in H 2 S/CO 2 /Cl− media were evaluated after long-term immersion. • The types and effects of corrosion products were analyzed at various times. • The Fe 3 O 4 layer can effectively block corrosive ions. • The presence of the S-phase layer reduced the corrosion rate of AISI 304 steel by 89.8 %. S-phase was introduced on stainless steel surface by low-temperature liquid oxy-nitriding and its influence on the corrosion behavior has been explored through surface analysis and weight-loss method. The results indicated that the S-phase layer can significantly improve the corrosion resistance of austenitic stainless steels in H 2 S/CO 2 /Cl− simulated solutions, which was proved by lower corrosion rate, surface, and cross-sectional topography after corrosion. This improvement can be attributed to the fact that the Fe 3 O 4 layer blocking the sulfur-containing medium and the consumption of H+ by the active nitrogen atoms, making it difficult for the corrosive medium to penetrate the steel. [ABSTRACT FROM AUTHOR]