Optical and electronic microscopy methods are used to evaluate the contamination of grade D carbon steel with nonmetallic inclusions in steel samples taken at various stages of steelmaking (electric arc furnace (EAF) discharge -> ladle furnace (LF) -> vacuum deoxidation (VD) -> continuous casting) at an electric furnace melting shop. Steel contamination with nonmetallic inclusions and inclusion chemical composition are assessed. It is demonstrated that the aluminum deoxidation of the semiproduct leads to the formation of corundum nonmetallic inclusions (Al2O3) in molten steel. The total amount of corundum reaches 52% for all the stages of steelmaking process. The identification and evaluation of nonmetallic inclusions demonstrates that deoxidation performed at all the stages of secondary steelmaking reduce the amount of inclusions. After vacuum deoxidation and adding Al and SiCa, corundum inclusions become globular in shape with a particle size less than 6 urn. When the continuously cast billet has solidified, the total amount of nonmetallic inclusions does not change, whereas silicate inclusion content decreases and corundum contamination grows, with corundum inclusions being of an irregular shape. A heavy corundum contamination is caused by aluminum secondary deoxidation during steel casting as well as by the fact that the molten residue in the pouring nozzle is carried into the solidifying continuously cast billet.
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.
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