Both are industries that produce metal – the difference is the type of metal produced by them. Metallurgy operates in a broader field, producing various types of metals: aluminum, copper, titanium and iron, for example. A steel plant, on the other hand, is a kind of specialized metallurgical plant: it works exclusively in the production of iron and steel, which is nothing more than “purified” iron, as you can see in the infographic on the side. They are called “base” industries because, in general, their final product is just metal bars or sheets, which are then used as raw material for other industries, which manufacture, there, yes, the infinity of metal products that we use today. – postpone. Both steel and metallurgical plants follow more or less the same manufacturing process. The raw material is always some kind of ore, a rock that mixes the desired metal with oxygen and other impurities. Inside the plants, the ore goes through several processes to eliminate impurities. The main one is the so-called “reduction”, the removal of the oxygen atoms that make up the ore. To do this, it is necessary to melt the raw material at high temperatures – each metal is extracted at a different temperature. One of those that require more heat to melt is iron. For this reason, its large-scale production includes the so-called blast furnaces at steel mills, which exceed 1,300ºC. Metallurgy plants for other metals, on the other hand, can work with smaller furnaces, which do not reach such high temperatures.
In steel mills, steel is created by removing impurities from iron.
1. Steel is a metallic alloy 3 of purified iron. Its main raw material is iron ore – which is not pure iron. In nature, iron is always linked to oxygen atoms, forming oxides such as hematite (Fe2O3), one of the main iron ores
2. As soon as the iron ore arrives at the steel plant, it is mixed with lime (CaCO3, a calcium compound) and coal (C, pure carbon), ingredients that in the following stages will help to purify the iron, transforming it the one in steel
3. The mixture of hematite, lime and coal goes to the blast furnace – a furnace that receives oxygen and burns at 1,200ºC –, where the objective is to purify the iron ore, removing the atoms of oxygen and fine sand that he contains
4. Purification takes place in two steps. First, oxygen atoms (O2) injected into the furnace combine with carbon atoms (C) from coal, forming carbon monoxide (CO) molecules.
5. Then, the carbon monoxide reacts with the hematite (Fe2O3), generating molecules of carbon dioxide (CO2) and iron (Fe) as a product.
6. Lime (CaCO3) also helps with purification: it serves to attract another type of impurity present in iron ore – minerals such as silicon (Si), calcium (Ca) and aluminum (Al). The reaction of lime with these minerals produces the so-called slag, a substance used as a raw material in paving highways.
7. After the purification reactions, the iron that comes out of the blast furnace is called pig iron – iron in a liquid state and without oxygen, but with a high carbon content and impurities such as silicon, manganese and sulfur, elements that make the iron very brittle
8. After passing through the blast furnace, the pig iron reaches the converter, where it receives a spray of magnesium (Mg) and an intense jet of oxygen. This reaction generates sulfur, magnesium, phosphorus and silicon oxides as products (which are removed from the mixture) and steel – iron with a low percentage of carbon (maximum 2%), which goes on
9. Still in a liquid state, the steel is transferred from the converter to a mold, where the incandescent liquid takes the form of bars or plates and is cooled by water jets, changing from a liquid state to a solid state. At the end of this stage, the steel bars or plates are cut by a special torch.
10. Cut into pieces, the steel bars or plates go to the rolling mill, where two things happen: first, the steel is reheated to 1000ºC, making it more moldable. Second, it is molded by cylinders that reduce the thickness of the bar to the desired measurement.
11. After rolling, steel can take two paths. It can be cooled and marketed directly in the form of rebar, metal bars used to erect houses and buildings, for example. Or…
12. …The steel can go down the production line and pass through a machine called a block, which transforms the rolled steel into steel wires and reduces its thickness. The “steel wire”, then, can serve as raw material for the manufacture of other products, such as wires and nails