Improvements in processes for the manufacture of alloy steels and irons

摘要

Alloy steels and irons with low carbon content and containing a high content of alloying metals such as one or more of the metals chromium, nickel, copper, tungsten, titanium, vanadium, and molybdenum, are made by melting iron or steel in an electric arc furnace having carbon electrodes, removing all but a thin layer of the slag, charging upon the remainder of the slag a mixture of a reducing agent such as ferrosilicon and an excess of a reducible ore of the alloying metal or metals in an amount sufficient to provide a stiff thick slag, and then charging at a point remote from the electrodes scrap metal having a high content of the alloying metal or metals, preferably scrap having approximately the same composition as the steel or iron alloy which is required as the final product. The amount of scrap added may be up to about 50 per cent by weight of the final tapped product. Preferably the scrap and the mixture of ore and reducing agent are divided into batches, a batch of ore and reducing agent being followed by a batch of scrap and all but a thin layer of the resulting slag being removed before the addition of the next batch of ore and reducing agent. When the last batch of scrap has been incorporated in the bath the slag is removed and a finishing slag, e.g. a slag of burnt lime, fluorspar, and ferro-silicon, is added. In order to prevent the absorption of hydrogen produced by the decomposition of moisture the furnace may be vented or a reducing agent may be employed which will dissociate and combine with any hydrogen present. Calcium silicide, i.e. an alloy containing 20-35 per cent of calcium, 50-70 per cent of silicon, and the balance mainly iron, may be used but preferably a mixture of this substance and ferro-silicon is employed. The use of calcium silicide is also stated to prevent contamination of the metal by phosphorus which is present in the slag. Alternatively, to prevent hydrogen absorption, sodium chloride, calcium chloride, potassium chloride, calcium hypochlorite, or metallic calcium or sodium may be added to the bath or the slag. The preferred substance is calcium hypochlorite, this substance being mixed with the ore and reducing agent. A mixture of calcium hypochlorite and the reducible ore is also added to the bath prior to the addition of each batch of the mixture of reducible ore, reducing agent, and calcium hypochlorite. If desired, calcium hypochlorite may also be added during the finishing treatment. The production of an iron-chromium alloy having a carbon content of less than 0,1 per cent and a chromium content of 17-18 per cent is described, the alloy scrap added containing 0,12 per cent of carbon and 18 per cent of chromium. Prior to tapping, manganese, ferromanganese, titanium, &c. may be added to the bath as deoxidants or alloying ingredients. The Provisional Specifications describe the methods of preventing hydrogen absorption set out above applied generally to any process of manufacturing alloy irons or steels by direct reduction.