Steel is primarily composed of iron and a maximum of 2.06% carbon. Alloys with a higher proportion of carbon are known as cast iron. If the proportion of sulfur and phosphorus accompanying iron is less than 0.025%, it is called stainless steel.

Not every steel can also be welded: only pure steels, i.e. alloys with a carbon content of less than 0.22%, are suitable for this process. As a rule, the more impure the alloy, the harder it is to weld the steel.

MAG welding uses active gases such as pure CO2 or mixed gases (argon, CO2, O2) in various compositions. These are highly reactive. The MAG process is used for unalloyed, low-alloy and high-alloy materials.

MIG welding, on the other hand, uses inert, i.e. unreactive, gases such as pure argon and helium or mixtures of argon and helium. The process is suitable for welding materials such as aluminum, copper, magnesium and titanium.