The Effects of Nickel/Tin Ratio on Cu Induced Surface Hot Shortness in Fe

Abstract

Surface hot shortness is of concern in scrap-based electric arc furnace (EAF) steelmaking. The excessive amount of residual copper (Cu) in the steel scrap enriches during the oxidation of the solid steel, and as a result a Cu-rich layer could form which causes inter-granular grain boundary cracking. Other residuals can also influence hot-shortness. Ni is known to improve the resistance to hot shortness whereas Sn is known to worsen it. In this paper, the mechanism through which nickel (Ni) counters the detrimental effects of tin (Sn) on surface hot shortness are investigated in detail. A series of Fe–0.3 wt%Cu-x wt%Ni–0.03 wt%Sn alloys with x content ranging from 0.03 to 0.45 wt% was oxidized in air at 1,423 K (1,150 °C) for 60, 300 and 600 seconds using thermogravimety (TG). The microstructure investigation under scanning electron microscopy (SEM) showed that, significant grain boundary cracking was suppressed by eliminating the highly embrittling Sn containing Cu-rich liquid, through increasing Cu solubility and/or solidifying the liquid phase by the presence of sufficient amount of Ni. Occlusion and decreased oxidation kinetics caused by Ni were shown not to play a significant role. A previous proposed diffusion numerical model was applied to the Fe–Cu–Ni–Sn system to quantitatively support experimental results and provide insight to the enrichment kinetics at the oxide/metal interface.