Iron is a chemical element with atomic number 26 located in group 8, period 4 of the periodic table of elements. Its symbol is Fe (from the Latin fĕrrum) and it has an atomic mass of 55.847 u.
This transition metal is the fourth most abundant element in the Earth's crust, representing 5% and, among metals, only aluminum is more abundant, and it is the first most abundant in planetary mass, because the planet, in its core, concentrates the largest mass of native iron, equivalent to 70%. The Earth's core is made up mainly of iron and nickel in metallic form, generating a magnetic field when it moves. It has been historically very important, and a period in history is called the Iron Age. In cosmology, it is a very special metal, as it is the heaviest metal that can be produced by fusion in the core of massive stars; Elements heavier than iron can only be created in supernovae.
It is the heaviest element that is produced exothermically by fusion, and the lightest that is produced through fission, because its nucleus has the highest binding energy per nucleon (energy necessary to separate a neutron or a nucleus from the nucleus). proton); Therefore, the most stable nucleus is iron-56 (with 30 neutrons).
It presents different structural forms depending on temperature and pressure. At atmospheric pressure:
■ α-Iron: stable up to 911 °C. The crystal system is a body-centered cubic (BCC) lattice.
■ γ-iron: 911-1392 °C; features a face-centered cubic (FCC) lattice.
■ Iron-δ: 1392-1539 °C; again presents a body-centered cubic lattice.
■ Iron-ε: It can be stabilized at high pressures, it has a compact hexagonal structure (HCP).
Steels
Steels are ferrous alloys with a maximum carbon content of 2%, which can be used as an insertion alloy in ferrite and austenite and forming iron carbide. Some alloys are not ferromagnetic. This may have other alloying agents and impurities. Depending on their carbon content, they are classified into the following types:
Low carbon steel: less than 0.25% C by weight. They are soft but ductile. They are used in vehicles, pipes, structural elements, etc. There are also high-strength, low-alloy steels, which contain other alloyed elements up to 10% by weight; They have greater mechanical resistance and can be worked very easily.
Medium carbon steel: between 0.25% and 0.6% C by weight. To improve their properties they are heat treated. They are stronger than low carbon steels, but less ductile; They are used in engineering parts that require high mechanical and wear resistance.
High carbon steel: between 0.60% and 1.4% C by weight. They are even more resistant, but also less ductile. Other elements are added to form carbides, for example, tungsten carbide, WC, is formed with tungsten; These carbides are very hard. These steels are mainly used in tools.>
Alloyed steels: With non-alloyed, or carbon, steels, it is impossible to satisfy the demands of today's industry. To achieve certain characteristics of resilience, wear resistance, hardness and resistance to certain temperatures we must resort to these. Through the action of one or more alloying elements in appropriate percentages, chemical and structural modifications are introduced that affect hardenability, mechanical characteristics, oxidation resistance and other properties.
The most technical and correct classification for carbon (non-alloy) steels according to their carbon content:
■ Hypoeutectoid steels, whose carbon content ranges between 0.02% and 0.8%.
■ Eutectoid steels whose carbon content is 0.8%.
■ Hypereutectoid steels with carbon content of 0.8% to 2%.
Stainless steels: one of the drawbacks of iron is that it rusts easily. Adding 12% chromium is considered stainless steel, because this alloy creates a surface layer of chromium oxide that protects the steel from corrosion or the formation of iron oxides. It may also have other types of alloys such as nickel to prevent the formation of chromium carbides, which provide fragility and enhance intergranular oxidation.