The specialty of open-hearth furnaces is the extreme heat that can be obtained from them due to their regenerative process. The charge of pig iron, steel scrap, iron ore, and flux are together kept in a shallow container with a flame burning above it. The process is initiated inside reverbaratory gas-fired regenerative furnaces for greater efficiency.
Regenerators are placed below the furnace and positioned in two pairs. The pairs are heated alternately through the passage of hot gases given out from the furnace in their route to the chimney. This heat is retained by the regenerators and is reversed and given back to the furnace. This heat exchange procedure helps the furnace to maintain high temperatures even with less fuels.
Once the furnace is charged with pig iron, pure oxidizing ores like haematite are added to it from time to time, which helps oxidization and the removal of impurities like silicon, carbon, and manganese in the pig iron. Spiegel is also introduced when the carbon content becomes less than 0.1%, and ferro-manganese after the metal is tapped out into the ladle. Ferro-manganese becomes important for restoring malleability and also for carburizing the iron.
In this process, electric arc or electric high-frequency furnaces are used. In electric arc furnaces which are more common among the two processes, high voltage electric arc struck between carbon electrodes and the charge becomes the source of a very high temperature. The charge is collected directly from an open hearth furnace, the intense arc heat keeps the charge in its molten state, and the impurities are removed in the form of slag.
The high-frequency furnace is based on the principle that when high-frequency alternating current is applied to steel, eddy currents start flowing in them. If this induction is made very strong, it can heat up the steel and melt it.
Electric furnaces are more advantageous compared to the other steel manufacturing processes due to the absence of evolving gases, fumes, etc., which normally become a major problem with fuel operated furnaces.
The duplex process of steel making is a combination of acidic bessemer process and basic open hearth process. This process is in operation at Tata Iron and Steel works, Jamshedpur (Bihar).