Desenvolvimento de escórias de refino secundário para o forno panela da V&M do Brasil

Abstract

In order to attend the growing demand for steel with high cleanliness at competitive prices, the V&M do BRASIL company invested in development of knowledge related to the slags used in the secondary refining. At V&M do BRASIL, the secondary refining consists of a ladle furnace, a vacuumdegasser and a gas bubbling station. In these stages a proper slag can improve the quality of the steel ensuring low levels of inclusions. In the present investigation, the slags used in the refining of the VM2011 steel were studied. Based on these studies, including simulations of computational thermodynamics with the Thermocalc software, new slags were proposed and tested in the processes. The main change in the slag composition was an increase in the Al2O3 content up to 25% and a reduction of SiO2 to 10%. The adjustment of SiO2 at the BOF tapping to was also changed. The argon flow rate used in the stirring station was also controlled to prevent reoxidation of steel. The proposed slags and the procedure in this work lead to the reduction of micro inclusions level in the VM2011 steel, reducing the density of inclusion from 0,82inclusions/mm² to 0,27 inclusions/mm² for the thin inclusions serie of size 0,5, according to ASTM E45 method D, without affecting the other quality indexes. These results also reduced the probability of scrapping the steel, based on the NACE test.