Abstract
High temperature corrosion of austenitic TP347H steels with two grain sizes was studied at 600–750 °C in dry air. A relationship between oxidation rate and grain size was found. The surface oxides consisted of iron enriched (Fe,Cr)2O3 nodules and a (Cr,Mn)2O3 scale. Initial oxidation with both grain sizes followed cubic kinetics, a combination of fast oxide formation via oxide grain boundary diffusion at the beginning of oxidation and parabolic kinetics combined with oxygen dissolution to the steel through breakaway oxidation nodules. Above 650 °C, the breakaway oxidation became more severe in coarse grained steel and fine grained steel started to destroy the nodules. Better oxidation resistance was achieved with smaller grain size, especially at higher temperatures. Reducing the TP347H steel grain size lowers the critical chromium concentration needed for the formation and recovering of the protective oxide scale.
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