Study on the effect of Ba treatment on the cleanliness of low alloy high strength steel containing rare earth

In this study, the influence mechanism of Ba treatment on non-metallic inclusions in low alloy high strength steel with different rare earth La content was systematically discussed. Four heats of Q355B test steel with high rare earth content (90 ppm) and low rare earth content (40 ppm) were prepared by 20 kg vacuum induction furnace. The amount of Ba added was 0, 100 ppm, 200 ppm and 300 ppm, respectively. The morphology, phase composition, size distribution and quantity change of inclusions in each test steel were characterized by SEM-EDS, Aspex analysis and thermodynamic calculation. The results show that within the scope of this experiment, the high rare earth test steel with Ba addition of 300 ppm has the best effect. The total oxygen in the steel is 10 ppm, the sulfur content is 25 ppm, the number of inclusions is 22.67/mm 2 , and the average size is 2.42 μm. Among them, the proportion of inclusions below 2 μm is as high as 38%, and the large size inclusions above 10 μm basically disappear. The deoxidation ability of Ba is weaker than that of La, but stronger than that of Al. In this study, it is mainly responsible for the pre-deep deoxidation before the addition of La. Its deoxidation product BaO is easy to combine with Al 2 O 3 to form large-sized low-melting-point inclusions, and quickly floats to remove them. Finally, the inclusions in steel are modified into rare earth inclusions dominated by La 2 S 3 and La 2 O 2 S, which are less harmful to steel. The research results provide theoretical support for the optimal application of Ba in low alloy high strength steel containing rare earth.