How steel is made
There are two basic production routes for steel being utilized today by manufacturers, the Blast Furnace Route and the Electric Arc Furnace route (EAF). The former makes use of iron ore that has been processed by a sintering plant whereas the latter uses almost exclusively recycled steel also known in the industry as scrap steel.
Blast Furnace
Blast Furnace plants are larger than EAFs due to the process employed that requires higher volumes at a time to be cost efficient. Typically these plants will produce 1-4 million tonnes per annum.
The first part of the process involves heating the iron ore in the Blast Furnace using Coke (a fuel made from Coal with high Carbon content) to temperatures exceeding 1500°C in a process called reduction. During this process the Carbon from the Coke combines with oxygen found in the oxygen rich iron ore (iron oxide) to produce CO2, leaving the iron ore free from oxygen but still with quite a few impurities (AKA Pig Iron).
The hot metal is then transferred into a basic oxygen burner called a converter where pure oxygen is blown into the material in order to burn unwanted elements and impurities thus transforming the material into steel.
The final stage involves casting the steel into various shapes that can be used in later stages of production like ingots (to be re-melted), Blooms (used for long structural members), Billets (used to roll Rebar) and Plates (used to roll flat products). A Billet for example will be received by a rolling mill, heat-treated and rolled under controlled temperatures to produce Reinforcing Steel Bars. The chemical composition of the Billet will affect the final rolled product. More often than not the rolling mill is directly connected to the casting unit of the plant to produce finished goods in one continuous production line saving energy and time.
Electric Arc Furnace Route
The smaller sized EAFs are typically able to produce 0.5-1.5 million tonnes per annum by using almost exclusively recycled steel (scrap). These are powered by electric energy and hence release fewer pollutants into the surrounding environment.
A designed mix of various scrap steel qualities is added into the Furnace where it is heated to 1800°C by two graphite electrodes that are able to produce an electric arc that reaches 3500°C. The molten material is then transferred into a ladle furnace in order to fine-tune the final chemical composition by introducing various alloying elements.
EAFs are able to produce all kinds of steels and due to their lower capacity and the flexibility they provide makes them increasingly popular in Europe. Further process steps like casting and rolling are comparable to the Blast Furnace route.