Grain-Size Effects on the High-Temperature Oxidation of Modified 304 Austenitic Stainless Steel

The high-temperature oxidation behavior of modified 304 austenitic stainless steels in a water vapor atmosphere was investigated. Samples were prepared by various thermo mechanical treatments to result in different grain sizes in the range 8–30 μm. Similar Σ3 grain boundary fraction was achieved to eliminate any grain-boundary characteristics effect. Samples were oxidized in an air furnace at 700 °C with 20 % water vapor atmosphere. On the fine-grained sample, a uniform Cr₂O₃ layer was formed, which increased the overall oxidation resistance. Whereas on the coarse-grained sample, an additional Fe₂O₃ layer formed on the Cr-rich oxide layer, which resulted in a relatively high oxidation rate. In the fine-grained sample, grain boundaries act as rapid diffusion paths for Cr and provided enough Cr to form Cr₂O₃ oxide on the entire sample surface.