Modification of Al₂O₃ inclusions in SWRH82B steel by La/Y rare-earth element treatment

Abstract

The experimental schemes of lanthanum (La) treatment, yttrium (Y) treatment, and La/Y mixed treatment of inclusions in SWRH82B steel were used. The size distribution, number density, inter-surface distance, the degree of homogeneity, and the area density of inclusions in the test steel were determined. The results show that the rare earths have a certain refinement and homogenization effect on the inclusions, and the mixed rare earths have the best effect on the inclusions in the steel. The average size of inclusions after mixed rare-earth treatment is 1.23 μm, the average size of inclusions after rare-earth La treatment is 1.79 μm, and the average size of inclusions after rare-earth Y treatment is 1.37 μm. Thermodynamic calculations show that the affinity of rare earths to oxygen in steel is higher, and the affinity to sulfur is lower. La and oxygen–sulfur have a higher affinity, and the affinity of Y and oxygen–sulfur is lower. In addition to single inclusions, there are complex inclusions in the steel.