Oxidation and carburization behaviour of two type 316H stainless steel casts in simulated AGR gas environment at 550 and 600 °C

The time-dependent oxidation and carburization behaviour of two type 316H austenitic stainless steels with varying Mn content differing average austenite grain size 142 µm in ‘Low Mn’ (0.98 wt.% Mn) 81 ‘High (1.52 Mn), were assessed at 550 °C 600 the presence simulated reactor primary gas coolant containing 500 vppm H2O, 100 H2, 300 CH4 1 vol.% CO, balanced CO2. Rupture spallation initial protective chromia layer occurs steel after 2000 h °C, leads to formation a magnetite/spinel oxide that reaches 75% surface coverage only 8000 h. In contrast, ~ 85% 1000 same temperature. development an inner carburized gradually both once duplex is forming. differences are reduced where significantly accelerated. Only 0.02 carbon remains solid solution lattice layer, excess atoms precipitating out form Cr-rich M23C6 particles, present inter- intragranularly. experimental values activation energy for suggest diffusion substitutional solutes as rate-limiting mechanism process. Previously observed depths ≥ 200 ex-service steels, may be achieved by pre-conditioning 6000 °C.