Mild steel, it is a type of carbon steel. Carbon is present in all steels and when carbon is the main alloying element in steel it is called carbon steel. On the other hand, the amount of carbon present in the steel determines the type or grade of carbon steel. Mild steel has the lowest carbon content of any steel, but that doesn’t make it less useful. In fact, mild steel is the most commonly used steel grade, accounting for 85% of total U.S. steel production.