Assessing the solute drag of scrap residual elements of Sn and Cu in austenite

Different levels of the scrap residual elements Sn (0.05–0.20 wt %) and Cu (0.15–0.90 wt %) were added individually to a plain C–Mn steel, and their effects on austenite grain growth were investigated in the temperature range of 900 °C–1150 °C. Grain sizes under each condition were measured using optical microscopy (OM). The results show both Sn and Cu suppress grain growth compared with the base alloy; with Sn being more effective. A comparison of the grain size distributions in samples with similar average grain sizes but different Sn and Cu levels indicates that solutes do not significantly alter the statistical characteristics of the grain population during grain growth. Sn segregation along austenite grain boundaries was clearly observed using Scanning Transmission Electron Microscopy (STEM)/energy dispersive X-ray spectroscopy (EDS), while Cu segregation was not evident, after heat treatment at 950 °C for 40 min. The solute drag model was applied to derive the segregation energy of Sn and Cu. The fitted values varied with temperatures, for Sn, from −0.31 eV to −0.52 eV and for Cu from −0.014 eV to −0.060 eV. These segregation energies were applied to predict the potential retardation of grain boundary motion in the presence of solutes.