Fig. 1 a Microstructure of the 304LN austenitic stainless steel used in the experiments; b schematic diagram of the specimen dimensions

Fig. 2 High-temperature and high-pressure SC-CO2 experimental system: a physical photograph and b schematic diagram

Fig. 3 Corrosion kinetics curve of 304LN stainless steel exposed to 650 °C-15 MPa SC-CO2 for 1000 h: relationship between a weight gain (Δω) and time (t), and b weight gain squared ((Δω)2) and time (t)

Fig. 4 Surface and cross-sectional morphologies of the oxide film on 304LN stainless steel corroded for 1000 h in SC-CO2 at 650 °C and 15 MPa: a1 low-magnification images of the oxide film surface morphology, a2 the localized magnification and compositional analysis of the boxed region in a1, b1 low-magnification images of the cross-sectional morphology of the oxide film, and b2 the localized magnification of the boxed region in a

Fig. 5 SIMS analysis results of the uniformly corroded area of 304LN: a SIMS results showing the distribution of elements; b enlarged view of the boxed region in a; c 3D results

Fig. 6 Composition distribution of the uniformly corroded area of 304LN: a STEM and b EDS elemental composition mapping results

Fig. 7 Composition distribution of the locally uniformly corroded area: a BFTEM and b EDS elemental composition mapping results

Fig. 8 TEM characterization of the uniformly corroded area of 304LN stainless steel: a STEM image of the oxide film cross section, b high-magnification STEM image of the region marked box in a, c high-magnification STEM image of the region indicated as c in b, c1, c2 HRTEM and SAED images of the region marked in c, d, d1 HRTEM and SAED patterns of the region marked in b as d, and d2 HRTEM image of the SiO2 layer indicated in d

Fig. 9 TEM characterization of the carbon diffusion region in 304LN: a STEM image of the cross section of the oxide film and matrix; b high-magnification STEM image of the carbon diffusion region marked in the boxed area in a; c HRTEM image of the region marked as c in b; d SAED pattern of the area marked in c

Fig. 10 Schematic diagram of the formation process of the oxide film on 304LN

Fig. 11 Schematic diagram of the carburization process of 304LN

Fig. 12 Comprehensive analysis of SIMS and TEM results: a BFTEM, b element distribution from EDS line scan in a, c SIMS results with the horizontal axis in distance (nm)