Thermodynamic Study on the Formation of Lanthanum Inclusions in 20MnSi Steel

The thermodynamic conditions for the formation of lanthanum-containing inclusions in 20MnSi steel are calculated by thermodynamics, and the standard Gibbs free energy of formation of lanthanum-containing oxides, sulfides, and sulfur oxides are obtained. According to the thermodynamic model, the precipitation map of lanthanum-containing inclusions is established. The results show that when the rare earth element lanthanum is added to 20MnSi, when α [O] /α [S] 2 O 2 S is formed, on the contrary, La 2 O 3 is precipitated; when 0.028 [S] 3 S 4 is generated; when α [S] >0.252, La 2 S 3 is formed. Rare earth lanthanum is added to the steel to first deoxidize and then desulfurize. From the perspective of thermodynamics, the Gibbs free energy generated by La 2 O 3 and La 2 O 2 S is much smaller than the Gibbs free energy generated by other lanthanum-containing inclusions. La 2 O 3 can be transformed into La 2 O 2 S. It can be inferred that under the experimental conditions, La 2 O 2 S is mainly precipitated in steel.