The effect of surface preparation and stress on oxidation and carburisation of 316 H stainless steel in CO/CO2 conditions

This study demonstrates how surface preparation and mechanical loading affect oxidation and carburisation in 316H stainless steel exposed to CO/CO₂ environments. OPS‑polished surfaces exhibited the greatest susceptibility, forming thick duplex oxides that enabled carbon ingress and substantial hardening, particularly under creep at 350 MPa. The permeability of the duplex oxide allowed carbon to accumulate at the metal–oxide interface, where dislocation activity introduced by pre‑straining and sustained creep facilitated transport; under creep, continued dislocation motion enabled deeper subsurface penetration compared with pre‑strained specimens. In contrast, 600‑grit ground surfaces initially formed a thin chromia film and, when this film was disrupted, developed a discontinuous duplex oxide. The associated near‑surface deformation and high dislocation density are proposed to promote local trapping of carbon close to the interface; once the ~1-2 µm ultrafine‑grained layer (UFGL) is consumed, carbon diffusion into the bulk proceeds more slowly, such that only very limited carburisation is observed even under creep. Overall, the results highlight that dislocation activity and loading history govern both oxidation behaviour and the extent of carbon ingress. • OPS-polished surfaces promote duplex oxide formation and enable carbon ingress via the Boudouard reaction. • Dislocations act as both diffusion pathways and trapping sites, influencing the depth and intensity of carburisation. • Ground surfaces, despite oxide disruption, resist carburisation due to the presence of an ultrafine-grained layer. • Creep promotes deeper carbon transport compared to specimens that were strained then carburised, suggesting continued dislocation motion facilitates solute transport.