GB881849A - Improvements in or relating to the purification of ferrous alloys - Google Patents

Abstract

Ferrous alloys in the solid state, particularly in the form of sheet, strip, or plate, have their C, N2, O2, S or P contents reduced, and surface scale converted to a less detrimental form, by treating them within the range 700-1300 DEG C. with an alkaline earth metal in a fluid inert to the alloy. The fluid may be inert gas, or may be molten calcium chloride or other inorganic salts, the molten bath being capable of dissolving not less than 0,1% by weight of the alkaline earth metal. The alkaline earth metal may be present in the elemental state, or as not less than 20% by weight of an alloy with aluminium, or as any suitable alloy, and may, depending on the treatment temperature, be in the form of elemental vapour, elemental liquid, liquid alloy, powdered solid alloy, solution of alloy in molten inorganic salt, or elemental solution in such a bath. Where a molten salt bath is used, the alkaline earth metal may be conveniently made available by having one of its halides as a constituent of the bath, to which an alkali metal is added. When a solid alloy is used as the refining agent the powder may be mixed with an alkaline earth metal oxide to reduce sintering. Finally divided TiO2 may be added to a solid or liquid refining agent to eliminate liberation of acetylene on subsequent washing of the treated material, and also aids the attainment of very low carbon contents. The treatment may conveniently be carried out by interleaving the turns of coils of strip, or the individual sheets or plates of a stack, with the refining agent, followed by heating to the desired temperature. If no calcium chloride or other flux is present, the scale is converted to a very adherent form which does not lift during subsequent cold-rolling, although it is readily removable by an acid pickle. Use of a flux renders the scale less adherent. Use of the process for treatment of silicon steel and austenitic steel is referred to, also for surface decarburisation of stainless steel to eliminate weld-decay, and treatment of carbon steel prior to enamelling.