The Evolution of TiN Inclusions in High-Titanium Wear-Resistant Steel Melt: A Comparative Study of La and Mg Treatments

Large TiN inclusions degrade the performance and castability of high-titanium wear-resistant steel. The evolution of TiN inclusions in molten steel under La and Mg treatments was comparatively investigated by high-temperature simulation experiments and thermodynamic calculations. In all steels, TiN precipitated and coarsened with prolonged holding time. In Al-deoxidized steel, after 60 min holding following Ti addition, the mean sizes of overall inclusions and complex TiN inclusions were 2.3882 and 3.8350 μm, respectively. With 0.0032% La treatment, Al2O3 was modified into finer LaAlO3, reducing these values to 2.1512 and 2.8749 μm. At a higher La content of 0.03%, Al2O3 was transformed into La2O2S, and these values instead increased to 2.4135 and 3.6076 μm due to the co-growth of residual La2O2S and TiN during Ti alloying. Mg treatment refined inclusions more effectively: under 0.0028% and 0.0062% Mg, overall inclusion sizes decreased to 1.9911 and 1.8743 μm, and complex TiN sizes decreased to 2.2963 and 1.9257 μm due to the formation of finer MgAl2O4 and even finer MgO with a low lattice mismatch with TiN. Therefore, Mg treatment, promoting MgO formation, is more promising than La treatment for refining TiN inclusions in high-titanium wear-resistant steel.