Analysis of Internal Defects Appeared in the Continuous Casting

The paper presents the study of internal defects resulting from the continuous casting of steels. The 50 samples were taken from a total of 20 continuously cast bits of different steel grades. The investigation of the causes of internal defects, shown on the analyzed samples, started from the assumption that the secondary metallurgy was performed correctly. The following internal defects have been evident: internal cracks (axial cracks, section cracks), central porosity and marginal punctuation impurities.

Slag Formation – Thermodynamic Aspects and Experimental Observations

Slags have a central role in pyro-metallurgical processes. They bind impurity compounds and absorb reaction products like oxides and sulfides. Functional slags are made by adding lime, magnesia, fluorspar, bauxite, calcium aluminate or other compounds into the reactor vessel where they form the slag together with the targeted reaction products. Additionally, refractory materials of the vessel tend to dissolve into the slag and thus influence its properties. Converter process for steelmaking is a rapid process and slag formation is extremely essential to ensure slag’s metallurgical functions and to avoid harmful reactions with the refractory materials. In this contribution, the progress of understanding the phenomena controlling slag formation and means to promote it were shortly reviewed. Thermodynamic constraints in slag formation were examined and the influence of fluxing additions was experimentally stated. Prefabricated “self-fluxing” lime was tested in industrial scale and proved to be a potential slag forming agent. Slag formation in secondary metallurgy and reduction of slag with aluminum dross or granules were experienced, and the effect on desulfurization and steel cleanliness was discussed.