Effects of Small Additions of Tin on High-Temperature Oxidation of Fe-Cu-Sn Alloys for Surface Hot Shortness

Steel produced in an electric arc furnace contains a high amount of copper (Cu) that causes a surface-cracking phenomenon called surface hot shortness. It is known that tin (Sn) can exacerbate the hot shortness problem. A series of iron (Fe)-0.3 wt pct Cu-x wt pct Sn alloys with an Sn content ranging from 0.03 to 0.15 wt pct was oxidized in air at 1423 K (1150 degrees C) for 60 seconds, 300 seconds, and 600 seconds using thermogravimetry. A numerical model developed in a previous article was applied to predict the liquid-gamma Fe interface concentrations and interface morphology in the Fe-Cu-Sn ternary system. Scanning electron microscopy investigations show that (1) The interface between the oxide and the metal is planar as predicted by the numerical model, (2) Sn leads to severe Cu-rich liquid penetration and cracking along the grain boundaries, and (3) open cracks with Fe oxides were found beneath the oxide-metal interface. The focused ion beam serial-sectioning technique was used to reveal a three-dimensional structure of cracks in the grain boundary containing Cu-rich liquid and Fe oxides.