Recycling of valuable scrap through electroslag processing

Recycling of metals and alloys is important for conservation of natural mineral resources, reduction in energy consumption and minimization of environmental pollution. Light scrap of reactive metals and alloys containing reactive elements is diffifult to recyle by conventional methods of melting. At the Defence Metallurgical Research Laboratory (DMRL), Hyderabad, electroslag melting technologies have been developed for recycling light scrap of valuable metals and alloys such as superalloys and oxygen free high conductivity (OFHC) copper. Conventionally, electroslag melting processes use consumable electrodes. Because of the difficulty in compaction of scrap into a consumable electrode of satisfactory quality, non-consumable electrodes such as graphite and water-cooled copper have been designed. Electroslag remelting using water-cooled non-consumable electrode was used to melt scrap of a nickel base superalloy. Sound ingots with smooth surface finish and properties comparable to vacuum melted superalloys could be obtained from scrap using this process. OFHC copper scrap was melted by a modified electroslag crucible melting process using graphite crucible and graphite electrode. Process parameters including slag composition were optimised to produce copper ingots with oxygen less than 10 ppm and electrical conductivity approximate to 100% IACS. The same process was also utilised to produce copper-chromium (Cu-Cr) ingots starting from copper scrap and pure chromium metal. The alloy exhibited superior room temperature tensile properties and high temperature ductility. Alternatively, Cu-Cr could also be produced by in-situ reduction of chromium oxide by aluminium during electroslag crucible melting.