GB507558A - Improvements in or relating to chromium metallurgy and the manufacture of chromium steel - Google Patents

Abstract

507,558. Alloys ; extracting chromium; purifying iron. UDY, M. J. Nov. 16, 1937, No. 31533. Convention date, Sept. 24. [Classes 72 and 82 (i)] [Also in Group III] Alloys of iron and chromium which may be in scrap or other form are treated at a melting temperature with lime and silica and under oxidizing conditions whereby chromium is selectively oxidixed to form a molten calcium silicochromite, corresponding to the formula (CaO)3Cr2O3nSiO2 where n is less than 3, and a metal containing unoxidized iron, and, if desired, some chromium. The process may be carried out in an electric furnace, a blast furnace or a converter and the lime and silica may be added in the form of lime rook, or other form of calcium carbonate, and quartzite respectively. The oxidizing agent employed may be oxygen, carbon dioxide, iron oxide, or iron-ore. Sufficient coke should be present to maintain a concentration of carbon monoxide so as to prevent oxidation of the iron, and the exothermic nature of the reaction may be increased by adding silicon, ferrosilicon, or an oxidizing agent such as sodium nitrate. The silicochromite may be used in the manufacture of chromates, bichromates, chromic acid, chromic oxide, and chromic sulphate, or in making nickel-chromium and cobalt-chromium alloys, pure chromium (by .reduction with silicon in the presence of additional lime), or alloys of chromium and iron. In the latter case, the silicochromite may contain iron and is granulated, briquetted with a non- carbonaceous reducing agent such as ferrosilicon' or silicon, and added to a bath of low-carbon steel. Alloys of iron with up to 3 per cent and 8 per cent of chromium, an alloy consisting of 42 per cent of chromium, 6 per cent of carbon, 3 per cent of silicon, and 49 per cent of iron, and Specification 437,008 are referred to.