Effect of La Content on Inclusions and Microstructure of C-Mn Steel Treated By Ti-Mg-Ca

Experiments with different lanthanum (La) addition were carried out to investigate the component, size and distribution of inclusions and the change of microstructure in C-Mn steel treated by Ti-Mg-Ca. The samples exacted from the experimental steels were analyzed by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), and optical microscope (OM). The results showed that inclusions in steel changed from MgO-Al2O3, CaO+TixOy, and MnS to La2O2S, LaAlO3, and MnS after adding La. The content of La2O2S gradually increased, while the content of LaAlO3 and MnS in the composite inclusions decreased with the increase of La content. In addition, the amount of inclusions increased first and then decreased with increasing La content. The size of effective inclusions was mainly less than 3 mu m in different samples. The distribution of inclusions was dispersive and more acicular ferrite (AF) were obtained when the content of La was in the range of 0.011-0.025 wt%.