The Effect of La, Ce Rare-Earth Elements on the MnS Inclusion Precipitation and Distribution in U75V Heavy-Rail Steel

The quality of heavy rail steel is significantly influenced by the distribution and morphology of MnS inclusions. With the help of experimental methods and thermodynamic predictions, the evolution of inclusions in heavy rail steels with different rare-earth (RE: La + Ce) additions is investigated, and the relationship between RE inclusions and MnS is better interpreted by the classical two-dimensional mismatch degree theory. The results show that the deoxidizing ability of RE elements added to the steel is greater than the desulfurizing ability. The best data for physical parameters of inclusions in steel are obtained at a RE addition of 122 ppm. The MnS inclusion particles are roughly spherical around the REAlO3 inclusion particles when the aluminum content in the RE inclusion is high. The MnS inclusion particles are better able to fit flatly around the RE2O2S inclusion particles when the sulfur content of the RE inclusion is high. By computing the two-dimensional mismatch between the interfaces of different inclusions, it is discovered that the heterogeneous nucleation efficiency is comparatively low between MnS and REAlO3, relatively high between MnS and RE2O2S, and highest between MnS and RE2O3.