Steel: an alloy of iron and carbon

Steel is a widely used material because it is strong, durable and easy to produce.

It is an alloy, which means a mixture of several elements, mainly iron and carbon.

Iron, found in large quantities in the Earth’s crust in the form of oxide, must be purified before use.

Carbon, which is also abundant, is added to iron to improve its properties.

This combination makes the metal harder and more resistant, which explains the important role of steel in many industries.

Types of steel according to carbon content

The amount of carbon in iron completely changes its properties:

• 0% carbon → pure iron
• 0.1% to 2% carbon → steel
• more than 2% carbon → cast iron

Thus, the proportion of carbon alters the way the metal can be worked.

Unalloyed steels

Unalloyed steels contain only iron and carbon, without the deliberate addition of other elements.

There is a wide variety of steels, ranging from extra soft steel, which contains very little carbon, easy to work but less hard, to extra hard steel, rich in carbon, more resistant and able to be hardened by quenching (heating followed by rapid cooling).

Alloyed steels

In some cases, other elements are deliberately added to steel to give it special properties:

• chromium makes steel stainless and resistant to rust,
• nickel, cobalt, vanadium and others provide useful qualities in aerospace, automotive, cutlery and more.

Thanks to these additions, there is a very wide variety of steels adapted to specific uses.

Uses and advantages of steel

Steel is everywhere: in construction, tools, cars, aerospace, cooking…

Its advantages are numerous:

• it can be more or less hard depending on its composition,
• it withstands high pressure and returns to its shape,
• it can be worked both hot and cold,
• it is infinitely recyclable, making it a sustainable and environmentally friendly material.