Mold steels are characterized by a very great diversity of chemical compositions. They consist of alloys based on iron, carbon, silicon, manganese to which can be added other alloying elements such as chromium or nickel which gives them special properties and they have areas of application extremely varied. Standardization defines three major families :

• Carbon steel (usually 0.15 to 0.5% C)
• Low alloyed steels in which the content of each alloying element is less than 5% (Mn, Ni, Cr, Mo voire V, Cu of Nb)
• High alloyed steels in wich the content of at least one alloying element exceeds 5% (Cr, Ni, Mn)