Effects of Small Additions of Copper and Copper + Nickel on the Oxidation Behavior of Iron

Abstract

This study was undertaken to investigate the effect of small amounts of copper and copper + nickel additions on the oxidation rate and oxide/metal interface microstructure of iron. Three iron-based alloys were compared: 0.3 wt pct copper, 0.3 wt pct copper-0.1 wt pct nickel, and 0.3 wt pct copper-0.05 wt pct nickel. Alloy samples were oxidized in air at 1150°C for 60, 300, and 600 seconds. Pure iron oxidized for 300 seconds was used as a reference material. The parabolic oxidation rate for the iron-copper alloy did not differ from that of pure iron, but the parabolic rate for the nickel-containing alloys decreased by a factor of 2. The microstructure of the iron-copper alloy consisted of a thin, copper-rich layer at the oxide/metal interface. Both nickel-containing alloys had perturbed oxide/metal interfaces consisting of alternating solid/liquid regions. The application of ternary alloy interface stability theories show that the perturbed interfaces arise from unequal diffusivities in the solid c-iron phase. It is suggested that this perturbed interface microstructure causes the observed decrease in oxidation rate, by limiting the iron supply to the oxide.

Effects of 0.1 wt.% Manganese, Aluminum, and Silicon on Oxidation and Copper-rich Liquid Phase Formation in an Iron–0.3 wt.% Copper–0.15 Wt.% Nickel Alloy

“…Enriched regions are then surrounded by oxide and isolated from the bulk of the metal. The simultaneous presence of copper and nickel is sufficient to form a rough interface and internal oxides [15], but the present authors have found that easily oxidizable impurities were necessary additions for achieving significant occlusion [16] in low carbon steels.…”

“…The remaining copper accumulates in the liquid, causing the layer thickness to increase. The enrichment processes that occur once nickel is added to an iron-copper alloy have been described in a previous publication by the current authors [15]. Nickel additions lead to perturbations in the liquid/c interface, resulting in interface regions where there is no liquid copper between the oxide and underlying alloy.…”

A Novel Technology to Develop a Nickel-Enriched Layer on Slab Surface by Utilizing NiO-Containing Synthetic Powder

“…The microscopic observation at the interface between the steel and the scale were in agreement with the previous investigations regarding the role of Ni for the prevention of Cu hot shortness. [16][17][18][19] (3) From the pilot-scale casting results, the Ni enrichment was irregularly developed. Depth of the Ni-enriched layer was longer than what was obtained in the lab-scale experiment.…”

“…In order to prevent the Cu enrichment effectively, the Ni-enriched layer should be remained or react with the enriched Cu near the interface during further oxidation. Webler et al [18] investigated the effect of the presence of Cu and Ni, respectively, on the oxidation rate. They showed that the presence of Cu did not influence the total amount of oxide formed, compared to that of Cu-free iron.…”

“…The other direction is to suppress the Cu enrichment during the reheating process. While making Cu to be left in the steel, it aims to suppress harmfulness of the Cu by treating the steel in various ways: Ni/Si alloying, [16][17][18][19] reheating Cu-containing slab at higher temperature than fayalite melting point, [3,16] and mechanical shot peening. [20] Among these ideas, the Ni alloying has been widely used in several industries.…”