The Golden Gate at the gates of San Francisco, the Guggenheim museum in Bilbao, the Centre Pompidou in Paris. These are just some of the most famous and impressive infrastructures in the world, made entirely of steel.
Steel is one of the most resistant and versatile materials on the market, which comes from the alloy composed of iron and carbon. Its applications are numerous, from the transport sector to the construction sector.
Thanks to its formidable characteristics, steel is the most widely used material worldwide.
Steel: a unique material with countless faces
What makes it a unique material is the fact that it is a metal capable of offering various performances.
The multiple alloys can generate different characteristics capable of adapting to the most extreme needs.
Using different amounts of carbon and added alloys it is therefore possible to obtain a steel suitable for every need. An example is boron steel, which is steel alloyed with a small amount of boron (usually less than 1 percent).
It is therefore important to understand that each type of steel has a different chemical composition.
The main types of steel for industrial and commercial use
To date, there are more than 3,500 steel grades. This is because there are numerous chemical combinations that can be carried out with iron and carbon.
Boron steel types like 30MnB5 – 1.5531, 28Mn6, and 30Mn5 – 1.1165 have different chemical composition change the characteristics including:
- Tensile strength
- Yield point
- Elongation
- Contraction
- Notch toughness
- Hardness in softened state
- Density
Steel classifications
AISI (American Iron and Steel Institute) establishes the characteristics for a series of types of steel in common use and the initials AISI identify the properties of the specific type of steel.
Steels are generally classified into:
- carbon steels;
- low alloy steels, with less than 5% alloying elements;
- high alloy steels, with more than 5% alloying elements.
Carbon steels
The steels most used for the production of flat rolled products are Carbon Steels which are in turn divided into low carbon or “mild” steels (less than 1% carbon) and steels with a higher or ” hard steels “.
Low alloy steels
Low carbon steels are more ductile and malleable, and have excellent mechanical resistance to traction and compression; they are also very resilient.
High-alloy steels
Steels with a higher carbon content are less resilient, that is, they are more likely to break when subjected to violent impacts and are less workable but are also much harder on the surface; they also take hardening very well, a treatment that does not give good results with mild steels.
The carbon content also determines the division between:
- Cast iron (percentage of carbon and other impurities from 2 to 6%);
- Steel (percentage of carbon between 0.3 and 1.7%).
The alloying elements in steel
In addition to carbon, further alloying elements added in the form of ferroalloys typically present in special steels may be present in the steels.
Among the alloying elements are mentioned: silicon, manganese, nickel, chromium, which give particular mechanical / chemical characteristics. The steels are called high-alloy or low-alloy depending on whether the percentage of the other elements exceeds the 5% threshold or not.
The characteristics conferred by some of these alloying elements are:
- Silicon – gives high strength but reduces weldability;
- Copper – hinders corrosion;
- Manganese – increases hardness but decreases elasticity;
- Chromium – increases hardness and does not reduce elasticity.
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