Extended Arc Furnace
A new development in plasma furnace technology in which by relatively simple modifications a more or less conventional arc furnace can be made to produce a long stable plasma flame is described. A very promising application of this technique is in the steel melting as well as in direct reduction of fine iron ore, waste oxides, flotation concentrates, blast furnace dust, fly ash, mill scale, etc.
Hematite reduction by hydrogen plasma: Where are we now?
Currently, iron is extracted from ores such as hematite by carbothermic reduction. The extraction process includes several unit steps/processes that require large-scale equipment and significant financial investments. Additionally, the extraction process produces a substantial amount of harmful carbon dioxide (CO2). Alternative to carbothermic reduction is the reduction by hydrogen plasma (HP). HP is mainly composed of exciting species that facilitate hematite reduction by providing thermodynamic and kinetic advantages, even at low temperatures. In addition to these advantages, hematite reduction by HP produces water, which is environmentally beneficial. This report reviews the theory and practice of hematite reduction by HP. Also, the present state of the art in solid-state and liquid-state hematite reduction by HP has been examined. The in-flight hematite reduction by HP has been identified as a potentially promising alternative to carbothermic reduction. However, the in-flight reduction is still plagued with problems such as excessively high temperatures in thermal HP and considerable vacuum costs in non-thermal HP. These problems can be overcome by using non-thermal atmospheric HP that deviates significantly from local thermodynamic equilibrium.
Evolution of carbide precipitates in Hastelloy N joints during welding and post weld heat treatment
Abstract The effects of welding and post weld heat treatment (PWHT) on the morphology, composition and lattice parameter of the precipitates in the welding joints of Hastelloy N alloy have been investigated. Joint samples were prepared using a gas tungsten arc welding process with ERNiMo-2 fillers, and then solid-solution treated at 1100 °C for 20 min. After welding, eutectic M6C carbides can be observed in the heat affected zones (HAZ) and weld zones (WZ). These eutectic M6C carbides become spheroidized during the following PWHT. The concentration of Si decreases during the transformation from the primary ones to eutectic ones, and then increases during the spheroidizing process. The total concentration of Si + Cr in M6C carbides remains stable during welding and PWHT. At the same time, the heat leads to the outward diffusion of Mo from the M6C carbides, which results in a decrease of the lattice parameter.