These types of steels with greater difficulty in Hardening are treated in core or in vacuum according to their chemical composition and thickness. Carbon steels such as F10 or M7 always require the use of the core as the most energetic cooling medium to achieve the desired characteristics. This medium introduces a higher thermal shock during cooling and consequently a greater dimensional variation after treatment. This core hardening is only efficient up to diameters around 20 mm. Above this measure hardening is recommended with surface enrichment (carbonitriding) to obtain higher values ??of surface hardness. Steels can be hardened in a vacuum or oil, depending on the thickness and mass undergoing treatment.