Homogeneous Corrosion Behavior of 310S and 316H Austenitic Stainless Steels in Supercritical Carbon Dioxide Environment

Austenitic stainless steels are now ideal candidates for use in supercritical carbon dioxide (S-CO2) cycle systems due to their good high temperature strength, excellent corrosion resistance, and good processability at relatively low cost. Therefore, it is necessary to study its corrosion behavior under the application conditions. In this study, 310S and 316H austenitic stainless steels were selected as the research objects, and the corrosion test was carried out at 500 ℃ and 25 MPa in S-CO2 environment for up to 3 200 h. The materials were machined into discs of 16 mm diameter and 1 mm thickness and mechanically ground and polished. The materials were ultrasonically cleaned with ethanol before the corrosion experiments and their dimensions and mass were measured. The corrosion tests were carried out in a static high temperature and high pressure gas homogeneous corrosion system. The corrosion materials were analyzed by SEM, TEM, EDS and XRD to characterize the post-corrosion morphology, composition and phase changes and to compare the differences in corrosion behavior between the two materials. The results show that 310S corrosion shows better corrosion resistance, after 3 200 h of corrosion weight gain is only 0.049 02 mg/cm2, its corrosion weight gain over time change curve conforms to the parabolic law, the surface generates a continuous dense Cr2O3 layer, and the lower part of the thin SiO2 is also observed. 310S materials also have a portion of the surface of the iron oxide particles appeared, concentrated in the grains. The corrosion resistance of 316H is poor, after 3 200 h of corrosion weight gain reached 0.341 87 mg/cm2, about 7 times the weight gain of 310S. 316H corrosion rate with the extension of the corrosion time appears to be a sudden change in the corrosion layer shows a two-layer structure, the outer layer of loose Fe3O4, the inner layer of FeCr2O4, both do not have the protective properties. At the interface between the two materials also observed a thin Cr2O3 appeared, indicating that it can generate Cr2O3 in the pre-corrosion period, but due to the Cr content in 316H is not enough to support the continuous growth of the Cr2O3 layer, the main corrosion products are transformed into two kinds of Fe-containing oxides. This paper analyzes the long-term corrosion behavior of two austenitic stainless steels in S-CO2, and explains the differences in the corrosion behavior of the two materials to provide theoretical data support for the system material selection.