GB539461A - Improvements in or relating to the production of low carbon alloys - Google Patents

Abstract

539,461. Low carbon alloys. RENNERFELT, I., and KALLING, B. M. S. March 11, 1940, No. 4540. Convention date, March 11, 1939. [Classes 72 and 82 (i)] Low-carbon alloys of iron and/or another metal similar to iron such as cobalt or nickel, containing up to 30 per cent. of an alloying metal having a greater affinity for oxygen than iron such as chromium or manganese are produced by reducing an ore having a high percentage of alloying metal with carbon and iron ore or iron or similar metal to produce a ferro or like alloy having a high carbon content and an amount of the alloying metal up to 30 per cent. and heating in finely divided state to 1000‹-1200‹C. in a suitable atmosphere, to remove the greater part of the carbon. The alloy may be granulated by crushing, or by cooling in water, to an average size of 1.0-1.5 mm. The decarbonizing may be effected in a tubular rotating furnace not above 1200‹C. to avoid sintering, or in a stationary retort at a higher temperature, or on a conveyer passing through a tunnel furnace, or in an electric furnace. The atmosphere may contain carbon dioxide and monoxide in the proportion of 25 per cent. and 75 per cent., whereby decarbonization of an alloy containing 20 per cent. Cr can be effected without substantial oxidation of the chromium. The de-carbonization may be effected at reduced pressure, or the gas may be diluted with hydrogen or nitrogen to reduce the carbon monoxide concentration. Hydrogen or steam may be added. This gas mixture may be burnt in the cooler zone to pre-heat the charge. An alloy containing 5 per cent. carbon may be de-carbonized down to 0.25 per cent. carbon in an oxidizing atmosphere, and then down to 0.05 per cent. carbon in a hydrogen atmosphere which reduces the metal oxide previously formed. De-carbonization may also be effected by solid and liquid oxidizing substances with the simultaneous supply of some gas such as hydrogen. The chromium alloy which is to be de-carbonized may be produced by direct reduction of chrome and iron ore with carbon in an electric furnace or a blast furnace. The de-carbonization of the granular alloy may be effected first in a gas atmosphere with stirring, and then in retorts at a higher temperature. A metal oxide may be added, and/or a de-carbonizing gas passed through the charge. The partly decarbonized alloy may be compressed into solid bodies, which are heated in a furnace, with solid or gaseous oxidizing matter to oxidize the remaining carbon.