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The study focused on investigating the phenomenon of stress corrosion cracking induced by H 2 S, while also examining the influence of low-temperature oxy-nitriding (LTON) surface modification on the diffusion behavior of hydrogen atoms through electrochemical hydrogen charging experiments. Following the hydrogen charging process, the concentration of diffusible hydrogen in the base material (BM) was measured at 5.41 ppm (ppm), which reduced to 1.10 ppm after implementing LTON treatment. Clearly, the surface-modified layer effectively hindered the diffusion of hydrogen atoms within the steel substrate. In the case of BM specimens exposed to H 2 S stress corrosion, the duration of exposure significantly impacted the formation of corrosion products. Additionally, the externally applied tensile stress played a pivotal role in the cracking behavior, as increasing stress levels led to the emergence of deformation bands outside the C-ring and ultimately initiated cracks at the base of the pits. Notably, H 2 S stress corrosion pits accumulated oxides and sulfides. Excessive hydrogen supersaturation potentially induced localized plastic deformation. Furthermore, due to the presence of sulfide ions, hydrogen atoms could not recombine to form hydrogen molecules, resulting in an accumulation of hydrogen atoms on the steel surface. The diffusion of hydrogen atoms within the steel material strongly influenced the initiation and propagation of stress corrosion cracking. Importantly, the surface modification layer established by LTON treatment exhibited remarkable capability in enhancing the steel material's resistance against H 2 S-induced stress corrosion. This was achieved by effectively preventing acidic medium attack and impeding the penetration of hydrogen atoms. • In comparison to 304 stainless steel, the electrochemical hydrogen charging of the LTON modified layer reduced the hydrogen content in the sample by 80%. • The H 2 S stress corrosion cracking behavior of austenitic stainless steels was investigated to reveal the transformation mechanism of cracks under different corrosion times and stresses. • The composite S-phase layer formed after LTON treatment can significantly improve the stress corrosion performance of stainless steel and prevent the penetration of hydrogen atoms. [ABSTRACT FROM AUTHOR]

Time-dependent experiments were carried out to study the corrosion behavior of AISI 304 austenitic stainless steel before and after low-temperature oxy-nitriding in HCl solution. The weight loss of the untreated sample was higher than that of the nitrided sample after HCl corrosion. When immersed for a short time, the nitrided sample remained relatively intact, while when immersed for a long time, the nitrogen-rich layer was damaged. XPS analysis showed that the passive film of the low-temperature oxy-nitrided sample was complete. The structure of passive film on the LTON sample was characterized by Mott–Schottky test, and the effect of nitrogen on the corrosion resistance of the material was discussed. The wear test results show that the oxy-nitrided samples after HCl immersion corrosion still maintained high wear resistance. [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]

The effects of low-temperature oxy-nitriding (LTON) treatment on the liquid lead-bismuth eutectic (LBE) corrosion behaviors of 316 L ASS were investigated in the stagnant liquid LBE under vacuum at 823 K. Results show that the untreated samples were severely selective leaching in contact with liquid LBE. LTON treatment produced an outer porous Fe-Cr spinel film and inner S phase layer on the sample surface, which transformed into a thicker spinel film containing γ low-N and a region distributed with CrN precipitates after liquid LBE corrosion. This was mainly attributed to the oxidation and decomposition of S phase and inward diffusion of the interstitials, owing to S phase is a metastable phase and is easier to be oxidized than matrix at elevated temperatures. This inspired us that improving the ability to form protective oxide film for materials was maybe a good method to mitigate the liquid LBE corrosion. [Display omitted] [ABSTRACT FROM AUTHOR]