Steel is a metallic alloy composed of approximately 98.5% Fe (iron), 0.5 to 1.7% C (carbon) and traces of Si (silicon), S (sulfur) and P (phosphorus). Therefore, its main component is iron metal, which, as shown in the text “Iron”, is obtained in steel mills through its main mineral, hematite, Fe2O3. THE The word “steel industry”, which comes from the Greek, means “work made on iron” and it is, in general, a specific field of metallurgy that transforms iron into steel.
The iron obtained from steel mills is not pure, but has 2 to 5% carbon in its constitution and is called pig iron. So, before being turned into steel, iron needs to be purified. One way to do this is by injecting oxygen gas into the blast furnace where iron is produced. The carbon then reacts with oxygen and forms carbon dioxide (CO2), which is a gas that gives off, separating from the iron.
The iron used to make steel has the mentioned percentage of carbon, about 0.5 to 1.7%. This metallic alloy has a greyish white color, melting point close to 1300 °C and density equal to 7.7 g/cm3.
Currently, obtaining iron is small in relation to steel production. In 2008, for example, annual steel production exceeded one billion tons worldwide. Steel is more preferred due to its excellent properties, such as can be worked by forging, rolling and extrusion, which is difficult to do with metallic iron; also have bigger tenacity (mechanical resistance) and greater hardness (ability to scratch other materials – property taken into account when using steel in cutting objects). Another point in your favor is yours low cost in relation to other metals and metallic alloys that also have good mechanical resistance.
Iron and steel are used in various materials that we come into daily contact with, such as pans, boilers, straw steel used for cleaning and polishing, tables, gates, bodies, car wheels, bridges, nails, screws, pliers etc. One of its main applications has been in civil construction, such as in reinforced concrete, which is concrete in steel structures. This structure, in addition to reducing construction time and the cost of the work with more materials that would otherwise be used, also allows them to be built several floors, as it is the steel that provides the tensile strength or force perpendicular to the building, such as the strength of the winds.
Furthermore, steel can be applied in the manufacture of other types of metal alloys with different properties that can be used according to need.
As an example, we have the stainless steel, which is composed of 74% common steel, 18% Cr (chromium) and 8% Ni (nickel). As the name implies, stainless steel does not oxidize or corrode easily, as iron does. This is due to the presence of chromium in its constitution, as this metal reacts with oxygen in the air and forms a thin and invisible layer of chromium oxide that makes it difficult for iron to corrode, forming the rust. Stainless steel is widely used in cutlery, kitchen utensils and decoration.
This property of practically not oxidizing is very important, as it is estimated that a portion greater than 30% of the steel produced in the world is used for replacement of parts and parts of equipment and installations that are deteriorated by corrosion, which causes great economic, social and environmental issues.
Another league is the call ofinvar, which has 64% steel and 36% Ni (nickel). There is also the platinitis, formed by 54% steel and 46% Ni. Both have as main property the low coefficient of expansion, with the first alloy being used in pendulums, stopwatches, graduated rulers and tubes. television. Platinum, on the other hand, is used in metal parts soldered to glass in incandescent lamps.
There is also steel that has 94% Fe (iron), 5% W (tungsten) and 1% C (carbon), which is extra hard, being used in cutting tools. Finally, we can mention the alloy formed by 86% Fe (iron), 13% Mn (manganese) and 1% C (carbon). Its main property is hardness, being used in rails.
By Jennifer Fogaça
Graduated in Chemistry
