Manganese sulfide (MnS) inclusion in steel is related to the machinability of steel. Controlling the type and shape of MnS inclusion has been a problem for the steelmaking process for a long time. The effect of tellurium (Te) treatment on the control of MnS inclusion is studied with experiments and discussion of sequential solidification. The result shows that Te addition to the high- and low-sulfur steel dominantly changes the size and shape of MnS inclusions in steel. The aspect ratio of inclusions in cast steel changes with Te/S ranges from 0 to 1.9, which offers an effective way to control the MnS type and thus to improve the machinability and mechanical properties of steel. With an excessive Te addition, no further improvement could be observed by scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS).
Keywords: MnS inclusion; Te treatment; free-cutting steel; inclusion control; sulfide inclusion.