Abstract
The problem to refine high-chromium cast iron melts obtained with the use of a large proportion of scraped metal and scrap is considered herein. Since fluxes containing calcium fluoride are currently considered to be environmentally polluting, it is required to reduce the use of fluorides, or completely replace them. It was shown that a decrease in the melting point of the flux can be achieved with the use of a mixture of calcium and magnesium fluorides or by the introduction of boron oxide into the composition of the fluxes. However, the efficiency of these fluxes, as well as silicocalcium additives and vacuum remelting in the high-chromium cast iron melting when a high proportion of scrap in the charge is used, has not been previously considered. In this regard, the effect of these refining methods on the removal of non-metallic inclusions in high-chromium cast iron of Grade 340Х18HML was experimentally assessed. Thermodynamic calculations were performed for the interaction of magnesium and calcium fluorides with non-metallic oxide inclusions typical of high-chromium cast irons and with oxides used for neutral lining of induction furnaces. It has been shown that fluxes based on boron oxide, magnesium and calcium fluorides and their mixtures effectively remove oxide and sulfide non-metallic inclusions; however, they have a destructive effect on the lining of furnaces, significantly reducing its service life. The addition of silicocalcium reduces the content of sulfides but does not affect the content of non-metallic inclusions in the form of oxides and nitrides. Vacuum remelting effectively reduces the number of nitride inclusions.