Insights into the role of grain refinement on high-temperature initial oxidation phase transformation and oxides evolution in high aluminium Fe-Mn-Al-C duplex lightweight steel

Influence of grain size on internal oxidation behaviour at 1273 K in dry air of Fe-20Mn-8Al-0.45C (wt.%) has been investigated. The measured weight gains are in parabolic relation to oxidation time and parabolic rate constant degrades with the reduction of grain size. Grain size affects compositions of oxides in the initial oxidation process and diffusion abilities of cations. Fine-grained alloy becomes less permeable to oxygen than coarse-grained alloy. Grain refinement accelerates phase transformation and promotes the rapid formation of pure Al2O3 layer, contributing to the slightly improved oxidation resistance. A brief schematic model is proposed to explain oxides evolution.