Process for the deoxidation of ferrous metals with cyclic utilisation and regeneration of slags

摘要

Ferrous metals, i.e. iron, iron alloys, and steels, are deoxidized by treatment with fluid acid slags containing not more than 5 per cent of iron oxide and between 5 and 30 per cent of manganese oxide, the ratio of the manganese oxide content to the iron oxide content being greater than 4. The content of the slag in iron oxide and manganese oxide must be low enough for the slag to retain, under the operating conditions, its power to extract iron and manganese oxides from the metal. After the deoxidation the slag is regenerated to restore the iron oxide to a value below 5 per cent, the manganese oxide to a value between 5 and 30 per cent, and the manganese oxide-iron oxide ratio to above 4. The regeneration preferably comprises a reduction of the iron oxide by means of a reducing agent followed by a replacement of part of the exhausted slag by fresh acid constituents, e.g. silica, this replacement being sufficient to restore the manganese oxide content to the desired value. In treating Thomas steel which contains a small amount of basic slag from the refining operation, the same basic elements, e.g. calcium and magnesium oxides, are added to the deoxidizing slag in such proportions that the replacement of exhausted slag by fresh acid constituents also serves to restore the content of basic elements to their original value. By increasing the manganese oxide content of the slag within the given limits the extraction of manganese from the metal undergoing deoxidation can be avoided or manganese may be introduced into the metal by reaction between the iron of the metal and the manganese oxide of the slag. In the latter case it will be necessary to add manganese oxide during the regeneration. Silicon may also be introduced into the metal during deoxidation by reduction of the silica of the slag. The exhausted slag may if desired be poured back into a mass of the original slag from which it was taken and the whole mass subjected to the regeneration treatment. In the deoxidation the slags may be used in the molten state and intermixed violently with the metal or they may be used in the solid state in a ladle or furnace.