Abstract: Low sulfur micro-alloy steel with Al-Si-Mn-Ti complex deoxidation was produced by vacuum induction furnace. Precipitation regularity of MnS was analyzed by thermodynamic calculation. The morphology, size and composition of inclusions and precipitation morphology of MnS on multiple oxide were studied by using FE-SEM with EDS. The results showed that the precipitation of MnS is mainly controlled by Mn and S contents and temperature of the steel. Mn-Si, Mn-Ti, Al-Mn-Ti and Al-Mn-Si complex oxides are all effective to be nucleation site for MnS. MnS takes on mosaiclike precipitation at Si-Mn oxides surface and is encapsulated at TiMn oxides surface. MnS can also be dissolved in Al-Ti-Mn and Al-Si-Mn oxides. The size of complex oxides that can induce formation of IGF is 2－3 μm.

Key words: MnS, inclusions, intragranular ferrite, oxide metallurgy