Precipitation Behavior of MnS Inclusion in Unidirectionally-Solidified Fe-18Mn-1Al-0.3C Steels

In order to reasonably control the precipitation of inclusions during solidification in TWIP steels, the precipitation behavior of typical MnS inclusions in high manganese steel was investigated by unidirectional solidification experiments. Through the combined analyses using ASEM-EDS, optical microscope, and thermodynamic calculation, it was found that Mn concentration in the liquid metal region were higher than those in the solid metal region. Furthermore, closer to the inclusion the liquid phase was, higher its Mn content was. In Fe-18mass%Mn-1Al-0.3C, MnS inclusions can precipitate at the positions located in the junction of dendrites at the end of the solidification (solid fraction fs=0.96), Mn content reaching 34.88 mass%. Already existing Al2O3 particles could become the core of MnS to form composite inclusions to promote the MnS precipitation during the solidification process. When fs achieved 0.7 leading the Mn segregation in the liquid phase to 25 mass%, MnS starts to precipitate to attach the Al2O3 surface to form composite inclusion.