Research on Precipitation of Inclusions in Calcium- treated Sulfur- containing 20CrMo Gear Steel

In order to meet the rating requirement for inclusions in the steel,the additive amount of calcium to the steel was controlled through thermodynamic calculation,and after calcium treatment,Al₂O₃ was modified to low-melting-point 12CaO·7 Al₂O₃ which could be removed from 20CrMo steel.Thermo-Calc software was used to simulate the precipitation process of calcium aluminates including CA6,CA,and CA2 and MnS inclusions during the solidification of liquid steel.SEM was employed to analyze the spindle-shaped inclusions.It was found that a small amount of inclusions had dark-colored core consisting of Al₂O₃ and CaS etc,and light-colored outer layer consisting of MnS inclusion.It indicates that in the solidification process of liquid steel,composite inclusions precipitated earlier such as Al₂O₃ and CaS can be captured by MnS precipitated later as its core.