The production of steel has become increasingly efficient especially with emerging technologies. Countries with iron ore and steel companies have an edge in technological advancement and sophistication. Therefore, countries such as Russia, USA, China, India, Germany and Ukraine are world giants in steel technology and the products they derive from iron and steel such as military hardware, cars, heavy machinery and construction equipments cab be seen all over the world.
Pig iron, scrap steel and scrap iron are essentially the raw materials needed for making steel. There are basically five major methods of steel production and the remarkable thing here is that all these methods are based on the same principles which are:– to remove all the impurities from molten pig iron via the process of oxidation and to add known quantities of carbon and other elements to molten iron in order to obtain steel of the desired properties and composition.
- Bessemer Process of Steel Making:– A Bessemer converter is a large vessel which can rotate into several positions so as to allow materials to be loaded and unloaded. The inside of the converter is lined with magnesium oxide and calcium oxide containing materials. Molten pig iron from the blast furnace is directed into the Bessemer converter where air is blown into the molten iron from the bottom of the converter to oxidize impurities such as sulphur and carbon to their gaseous oxides.
Other impurities such as manganese, silicon and phosphorus react with calcium and magnesium lining the Bessemer converter to form slag which is easily tapped off and can be used in road construction activities. At this stage, the required amounts of carbon and several other metals are added to give various types of steel for the desired use.
A more common but more efficient Linz-Donawitz(L-D) process also referred to as the Basic Oxygen Process uses a modified Bessemer converter which allows a high speed jet of oxygen to be blown vertically down into the molten pig iron from a water-cooled oxygen lance. The heat generated in the system keeps the iron in a molten form. This process is more efficient because of the reduced time it takes to produce steel and the improved quality of the steel produced because of the absence of nitrogen which would otherwise made the steel brittle unlike in the old Bessemer converter process.
- Electric-Arc Furnace Process of Making Steel:– The electric-arc furnace is designed with a cylindrical shallow hearth with a lid that is removable. Three graphite electrodes protrude from this lid and scrap iron is deposited into the furnace and the lid replaced in firmly in position. Electric current from the electrodes provides the heat needed to melt the scrap iron. A very high temperature of about 1900*C is attained as the electric arcs are struck. Limestone, oxygen and alloying materials are introduced via the openings on the side of the furnace. The molten steel is collected by first tipping the furnace to drain off the slag, and the steel is then poured out into containers to be shaped. This process is quite expensive but produces steel of very high quality. The Ovwian-Aladja steel company in Delta state of Nigeria uses this method in steel production.
- The Direct-Reduction Process of Making Steel:– A direct-reduction process used in steel production reduces the iron ore and produces steel in the same furnace. Hydrogen and carbon(II)oxide are the gasses that reduce the iron ore to iron. There are several advantages of the direct-arc method. They include:–
(i) The low capital cost involved
(ii) The ability to produce all grades of steel
(iii) The cheap source of reducing gases(hydrogen and carbon(II)oxide which are readily produced from petroleum sources and natural gas.
- The Open-Hearth Process of Making Steel:– In this process, the furnace has a broad but shallow hearth flames coming from oil or gas melt the raw materials in the furnace. Iron ore and other materials containing oxygen are added to the furnace to provide the oxygen needed for the oxidation of the impurities. Limestone is also added to remove unwanted products and they come out as slag. When other materials and elements needed for steel making have been added in the required and appropriate proportions, the slag which floats on top of the steel is drawn off and the pure steel is tapped off from the furnace.