Improvements in the manufacture of ferrous alloys

摘要

In producing ferrous alloys by the metallothermic reduction of magnetic iron oxide, the materials constituting the charge, including the alloying metals and oxydizing agents, are dried by heating to at least 100 DEG C. before introduction into the crucible in which the reaction is effected, thereby eliminating blisters in the steel produced. The magnetic oxide of iron may be magnetite, roasted iron scales, or a mixture of these. The oxydizing agents may consist of salts of the alkaline earth metals, particularly barium dioxide or barium nitrate, or of mixtures such as potassium nitrate, barium nitrate, and barium oxide. In an example, a mixture is made of magnetite, roasted iron scales, aluminium, potassium nitrate, barium nitrate, and barium dioxide, all ground and dried previous to mixing. A second mixture is formed of dried potassium nitrate, ferro - chromium, and nickel. The mixtures are, if necessary, passed through a grinder-mixer, and both are maintained in a dry atmosphere at at least 100 DEG C. The crucible, also heated to at least 100 DEG C., is charged with a layer of the first mixture, then with a layer formed of an intimate admixture of the first and second mixtures, and finally a layer of the first mixture. Ordinary carbon steel or pig iron scrap is distributed partly on top of the second layer and partly in the top layer. The reaction is started in known manner by an ignition cartridge in the charge, and containing for example aluminium powder, barium dioxide, and magnesium powder. To refine the steel, the ladle into which it is poured may contain a charge of manganese and aluminium; alternatively, above the first layer in the crucible may be placed three superposed layers consisting respectively of manganese, a portion of the first mixture, and another of manganese. In a second example, the charge in the crucible is formed by a layer of a mixture of magnetite, aluminium, potassium nitrate, titanium oxide, barium nitrate, and barium dioxide, a second layer of manganese, a third of a mixture of ferro-molybdenum and silicon, a fourth layer of the first mixture with carbon steel scrap and fragments of pig iron distributed in it, and a top layer of the first mixture alone. Drying is carried out as in the first example.