Steel can be categorized in four different groups:

• Carbon steels: their main components are iron and carbon (and traces of other components) and they can be subdivided attending to the carbon content (low carbon for carbon concentration below 0.3%, medium carbon for concentration between 0.3% and 0.6%, and, high carbon for concentrations above 0.6%). It is the most common type of steel, accounting for 90% of the total steel production world wide. It is inexpensive and robust enough for most of the applications.
• Alloy steels: they are combinations of steel with additional elements like nickel, copper, chromium or aluminum. They offer improved characteristics over carbon steels such as ductility, corrosion, machinability, strength...
• Stainless steels: they are special alloyed steels which main characteristic is their increased resistance towards adverse weather and almost all types of corrosion. This makes them suitable for outdoors use, medical devices, food processing and piping. To achieve this, the content of chromium in the alloy is taken to values between 10% and 20%. Additionally, they might contain nickel, manganese and silicon.
• Tool steels: the steels under this category perform well in cutting and drilling equipment thanks to their heat resistance, general durability and their capacity to hold their shape under heavy use. These alloys contain tungsten, molybdenum, cobalt and vanadium.