Steel has the properties of being strong, applicable in many areas and inexpensive. Therefore, steel is one of the most widely used materials on earth. Since it can be recycled over and over again, it plays a crucial role in man industries.
The production of the metal is usually carried out by two different ways: the blast furnace, also known as basic oxygen furnace, or electric arc furnace. Combinations and variations of both production processes may occur.
How is steel made?
Steel consists of iron and carbon. However, to influence the properties of the metal, other alloying elements can be added. These include chromium, nickel or aluminum.
As already mentioned, the most common methods are:
- Blast Furnace
- Electric Arc Furnace
The main difference between the two methods is the type of raw material that is used. While the blast furnace process mostly consumes iron ore, coal and recycled steel, the electric arc furnace method, on the other hand, relies primarily on electricity and recycled steel.
The mass production of steel via blast furnace was introduced by the Englishman Henry Bessemer in 1855. Till today, it is the most commonly used method and is accountable for over 70 % of the steel production.
In the process, iron and coke are combined in the furnace. Moreover, a small amount of flux is added. With the help of a lace, 99 % pure oxygen is added to the mixture This leads to a temperature as high as 1700° C. Thus, the scrap melts in the vessel and the impurities oxidize. Further, the carbon content is reduced drastically by 90 %. The result is liquid steel. The molten steel can be drained from the furnace through a tap hole.
Electric arc furnace
Since the electric arc furnace method recycles used steel scarps, basically no new steel is produced during the process. This also means that there is no need for raw materials such as iron ore or coke.
During the production, the furnace is filled with scrap steel till it is full. Next, electrodes are placed in the furnace, which are responsible for the heat in the process. They create an arc of electricity through the scrap steel. This leads to a temperature rise to 1600° C and melts the scrap. To achieve the desired properties of the metal, ferro-alloys are added to the steel. Oxygen, which is blown into the furnace, helps to purify the metal. Added fluorspar and lime fuse with the impurities. These form slag which floats on top of the molten steel.
Typically, electric arc furnaces are used to produce alloy steels such as stainless steel. Approximately, 29 % of steels are produced by this method.
The open hearth furnace method is another option for producing steel. The process is very energy and cost intensive. Further, it is more environmentally damaging than the two other methods. Therefore, it makes up for only about 0,4 % of the global steel production.