Research on Inclusion Evolution during Re-Heating Process in Ti-Zr Deoxidized Low Carbon Steel

The effect of the re-heating process on inclusion evolution in Ti-Zr deoxidized low carbon steel was investigated using high-temperature resistance furnace, high-temperature confocal laser scanning microscope, scanning electron microscope with energy-dispersive spectrometer, and electron probe microanalysis with wavelength-dispersive spectrometer. The results indicated that compared with as-cast sample, the entire inclusion characteristics in heated samples were affected by the couple effect of heating temperature and holding time. As temperature and holding time increased, the shape of the Ti-Zr oxide changed from an irregular, curved surface to a smooth, spherical surface owing to the outermost layer being enveloped by liquid inclusion of Si-Mn-Al oxide. Additionally, the Ti-Zr oxide composition distribution changed from homogeneous to heterogeneous during heating in the range of 1100 °C to 1400 °C for 2 hours. Finally, different cooling modes had a significant influence on the inclusion characteristics. Compared with cooling by direct water quenching, the process of initial cooling to 1000 °C with furnace cooling and followed by water quenching could increase the number density of nitrides and sulfides, as well as change the unstable oxide to an effective oxide by precipitation of TiN on the surface.