CHANGES IN THE COMPOSITION OF NON-METAL INCLUSIONS AND CONTAMINATION STEEL D DURED BY ALUMINUM

Abstract

Using optical and electron microscopy methods, the pollution of grade D carbon steel by nonmetallic inclusions in samples taken at the stages of metallurgical redistribution (EAF → LF → VOD → Casting). Metal contamination and chemical composition of non-metallic inclusions are determined. It was shown that deoxidation at the stage of production of the intermediate by aluminum leads to the formation of nonmetallic inclusions of corundum (Al2O3) in the metal melt, the proportion of which in total over all redistributions is 52%. Identification and assessment of contamination by non-metallic inclusions showed that subsequent stages of out-of-furnace treatment lead to a decrease in total pollution by inclusions. After evacuation and addition of Al and SiCa, corundum inclusions acquire a globular shape with a maximum size of not more than 6 μm. During solidification, the total contamination by non-metallic inclusions does not change, however. Contamination with silicate inclusions decreases, and the inclusion of corundum increases. The inclusions of corundum are irregular in shape, the high contamination with the inclusions of corundum is caused by secondary oxidation of aluminum during casting, as well as the ingress of products by overgrowing of the casting nozzle into the solidified continuously cast billet.