Carbon Steel Investment Casting Carbon steel is a steel alloy with carbon as the primary alloying element. Cast alloy steels have been developed for use in conditions requiring higher pressure, wear resistance and higher strength, as well as higher toughness and hardenability. The mechanical properties of this alloy are determined by the percentage of carbon; the higher the percentage, the harder and stronger the alloy becomes through heat treatment. Because carbon steel can be machined to obtain a variety of properties, it can be used in a variety of applications. Both medium and low carbon steels are used in investment casting. Medium carbon steel has good ductility, strength and wear resistance. It can also be hardened and tempered by heat treatment. Mild steel is easy to form but cannot be strengthened by heat treatment. As an alternative, carburizing can be used to increase the surface hardness of the alloy.