Steel plants observe the decreasing carbon content during the whole steel production process from raw iron with up to 4-5 % carbon to a few ppm in stainless steel. The carbon content influences not only the texture, but also the material properties of iron, such as magnetism, hardness or elasticity. For example, cast iron (2-4 % C) is brittle but castable; tool steel (0.4-1,7 % C) is elastic and ductile, carbon steel (< 0.4 % C) is forgeable and useable for sheets, tubes and steel girders (1). The element carbon can be present in different forms in an iron matrix, bound to other elements as carbide, solved in the iron matrix or as elemental carbon (2). Due to their impact on the material properties, carbon and sulfur concentrations are listed in the cross-reference book Key to Steel.