Steelmaking has existed for nearly a thousand years, with modern techniques introduced in the 19th century. The process of manufacturing steel involves removal of impurities such as sulfur and silicon, with introduction of chromium and nickel to produce different grades of steel.
The history of steel making is very old, with it being found in ancient China, India, Iran and even Rome. Before the invention of the Bessemer process in 1850s, steel was only produced in small quantities, suitable for demands of small cities and states. The industrial revolution fueled the need of large scale production, with the Bessemer the only method of making steel in such large volumes.
Primary steel making either involves the use of pig iron or converted into steel, or the use of electric arc furnaces to melt steel scrap and recycle the material.
For using pig iron, the basic oxygen steelmaking method is used. This involves blowing oxygen in a carbon heavy melted iron. The oxygen is blown inside the furnace using a hollow pipe called the lance. The lance is liquid cooled to prevent its melting and its mouth is placed a few feet above the surface of the molten iron. The pressurized oxygen reacts with the carbon. The reaction ignites the carbon and an exothermic reaction raises the temperature to around 1,600 Celsius. Burnt lime or dolomite is introduced, which reacts with other impurities such as silicon and forms a layer on the top of the molten liquid, called slag.
After the purification is complete, the vessel is tilted and the molten iron is poured into another ladle furnace, where other metals and chemicals are added (nickel, chromium etc.) and mixed to produce the exact grade of steel required.
Electric Arc Furnace
Electric arc furnaces are usually used for melting scrap iron and steel. The process involves the use of a lined vessel that is fed with scrap and a three graphite rods are lowered, touching the surface. A high voltage electrical current is passed, which creates arcs and produce heat, melting the steel. To assist the process, some pre melted steel may also be added prior to the arcing and sometimes even gas burners are used to bring the temperature up to speed.
As in all steel making, after the melting is complete, the vessel is tilted to remove the liquefied steel, ensuring that the impurities that are floating on top stay behind to be removed later.