Kinetics and mechanisms of high-temperature oxidation of stainless steel 347LSi in synthetic air

The high-temperature oxidation behavior of 347LSi stainless steel coatings is a critical factor for their application in aggressive environments. This study investigates the oxidation kinetics and mechanisms of coatings deposited by GMAW process on 2.25Cr–1Mo steel substrates, using different Ar–CO 2 shielding gas mixtures, in a synthetic air atmosphere at 800, 900, 1000, and 1100 °C. Thermogravimetric analysis revealed predominantly parabolic oxidation behavior for all conditions at times above 10 4 s, allowing the determination of parabolic rate constants (kₚ) and apparent activation energies (Eₐ). At 800 °C, the coatings exhibited low kₚ values and formed a compact and adherent bilayer oxide scale composed of an inner Cr 2 O 3 layer and an outer (Fe, Mn, Cr) 2 O 4 spinel, providing effective protection against oxidation. As the temperature increased to 900–1100 °C, a transition to accelerated oxidation was observed, associated with chromium depletion at the metal/oxide interface and the progressive breakdown of the protective chromia layer. This resulted in the formation of Fe-rich, porous, and poorly adherent oxides, promoting oxide spallation and loss of protective behavior. The shielding gas composition significantly influenced oxidation performance. The mixture containing 4% CO 2 exhibited the best overall behavior, combining lower oxidation rates with improved oxide stability, whereas higher CO 2 contents promoted faster degradation at elevated temperatures. These results demonstrate that oxidation resistance is maintained up to approximately 800 °C, while higher temperatures lead to a transition toward non-protective oxidation mechanisms. The findings highlight the critical role of shielding gas selection in controlling high-temperature oxidation and provide practical guidelines for the design of stainless steel coatings for demanding service conditions.