Effect of rare earth lanthanum on non-metallic inclusions in Fe-Mn-C-Al alloy

The effect of La addition on non-metallic inclusions in Fe-Mn-C-Al alloy was studied by adding different contents of rare earth lanthanum (La). Among the studied samples, the one with La addition of 0.0043 wt.% demonstrates the best inclusion characteristics. In this sample, the average size of inclusions measures at 1.16 μm. Compared with the sample without the addition of rare earth La, the size and area density of inclusions decrease, while the quantity density increases. With the increase of rare earth addition, inclusions in the samples showed a gradually increasing trend in inclusions size and area density, but both were lower than those in the sample without the addition of rare earth La. Through scanning electron microscopy observation, as the amount of rare earth La added increases, MnS inclusions are gradually replaced by rare earth sulfides. Based on classical thermodynamics and Factage thermodynamic software, the modification law of inclusions after La addition was calculated. Combining theoretical calculations and scanning electron microscopy experimental observations, it was found that the main transformation path of non-metallic inclusions in La treated alloy is: Al2O3 → LaAl11O18 → LaAlO3, MnS → MnS + La2S3 → La2S3 + LaS.