Reduction of chromium from chrome-containing fettling materials

Abstract

The relatively high rate of reduction of chromium oxides by carbon dissolved in the metal permits us to conclude that the presence of large carbon concentrations in the metal located in contact with the lining of the furnace prepared from chrome-containing refractories contributes to reduction of the chromium. This must be considered when fettling the working region of the furnace. Parts of the working region coming into contact with the liquid iron during melting (walls, slopes), to avoid reduction of the chromium, should be fettled with magnesite or dolomite. Reduction of the chromium from the material of the hearth leads to an increase not only in the amount of residual chromium in the metal, but also to an increase in the content of Cr2O3 in the slag. The average total rate of reduction of the chromium during the finishing process in the open-hearth furnace varies from 0.018 to 0.042%/h. Calculations show that with a content of chromium in the batch of up to 0.30% and in the finished steel of up to 0.25% (GOST 1050-60) it is possible to fettle with a refractory material containing up to 6.0% Cr2O3. When melting carbon steels with limited contents of residual chromium of up to 0.18%, it is impossible to use chrome materials from fettling. Chrome fettling materials are more suitable in furnaces where alloyed chromium steels are being melted. In calculations requiring the amount of ferrochrome, it is necessary to bear in mind the increase in residual chromium in the metal and the reduction in the chromium waste introduced under these conditions.