Investigation of selective oxidation during cooling of hot-rolled iron-manganese-silicon alloys

Highlights: • Oxygen uptake is probably rate determining for the short-term selective oxidation of Fe-Mn-Si alloys at oxygen partial pressure of 2.9 × 10⁻²² bar. • Addition of silicon to Fe-2 Mn was found to significantly accelerate the internal oxidation particularly along the grain boundaries. • Silica is proposed to be formed preferentially which then serves as oxide nuclei for the subsequent formation of Mn-containing oxides. • A solid solution of FeO in the external MnO is of great importance for the kinetics. The kinetics of selective oxidation in iron-manganese-silicon alloys of varying silicon contents was examined at 700°C and oxygen partial pressure of 2.9×10⁻²² bar for up to 2 h. The investigation revealed a linear mass gain over time, suggesting oxygen uptake as the rate-controlling step of reaction. Internal oxidation depth particularly along grain boundaries increased considerably with increasing silicon content. Differences in microstructure and near-surface chemistry of the alloys as a function of the silicon content are discoursed on. The results point to the crucial role of a thin oxide layer, a solid solution between FeO and MnO, in the oxidation process.