Influence of rare earth La–Ce on inclusions and impact properties of U75V steel

Samples of U75V steel with different contents of lanthanum (La) and cerium (Ce) were melted using a vacuum induction furnace, then were rolled and forged. The morphology, number, aspect ratio, type, and impact properties of the inclusions were tested and analysed. The results indicate that in the absence of rare earth, there are Al 2 O 3 –CaO–SiO 2 –MnO, MnS–Al 2 O 3 –CaO–SiO 2 composite inclusions, and MnS in U75V steel. After adding a mixture of rare earth elements La–Ce to the steel, the inclusions transform into (La–Ce) 2 O 2 S, (La–Ce)S, Ce 2 O 3 , (La–Ce) 2 O 2 S–(La–Ce)S, and (La–Ce) 2 O 2 S–CaO composite inclusions. Adding a mixture of rare earth (La–Ce) significantly reduces the quantity, size, and aspect ratio of the inclusions. The distinction resides in the varying ratio of lanthanum to cerium, resulting in dissimilar circumstances. After adding rare earth lanthanum and cerium, the proportion of small–sized inclusions increases. Sample 2 has the highest proportion of small–sized inclusions. Impact tests and grain size analysed were conducted during the experiment. It was found that sample 2 has the smallest grains and the best impact performance. The “Nailing force” of rare earth inclusions on the microstructure of the steel samples was calculated, and the results show that the addition of rare earth to the steel reduces the microstructural grain size due to the “Nailing force” of the rare earth inclusions. The microstructural grain size of the steel is different due to the differences in the rare earth inclusions generated by different rare earth contents, and this is the fundamental reason for the different microstructural grain sizes of the steel after adding rare earth.