The conversion of pig iron to steel frequently requires the addition of:
$(I)$ oxygen or iron oxide $(II)$ transition elements
$(III)$ inner transition elements  $(IV)$ silica

The conversion of pig iron to steel frequently requires the addition of (I) oxygen or iron oxide and (II) transition elements.
Iron oxide or oxygen oxidizes the impurities such as silicon and manganese which are then removed in the form of slag.
Transition metals such as manganese serve as deoxidizer and reduce FeO (if any). Also Mn makes steel harder and increases its tensile strength.