Influence of diffusion in the underlying metal during oxidation of iron containing small amounts of copper and nickel

The residual element copper in recycled steels embrittles grain boundaries, causing a surface cracking phenomenon known as hot shortness. Embrittlement is caused by a copper-rich liquid phase that forms at the oxide/metal interface during steel oxidation. Another residual element, nickel, enriches along with copper and reduces hot shortness cracking. The mechanisms by which nickel affects copper enrichment behavior have not yet been adequately studied. This work examines the effects of nickel and copper on the oxidation behavior and oxide/metal interface microstructure of iron. Iron-0.3 wt% copper alloys containing 0.1 wt% nickel and 0.05 wt% nickel were compared. Pure iron was used as a reference material. Alloy samples were oxidized in air at 1150°C. The parabolic oxidation rates for both alloys were found to decrease by a factor of two from that of pure iron. Both alloys had perturbed oxide/metal interfaces consisting of alternating solid/liquid regions. The interface development is due to stabilization of perturbations in the solid/liquid interface. The interface morphology can also explain the observed decrease in oxidation rate.