Hardenability of Steel

the ability of steel to acquire a high degree of hardness (a martensite structure) as a result of the hardening process. Hardenability is determined mainly by the quantity of carbon in the steel. For example, if the carbon content is increased from 0.3 to 0.7 percent, the Rockwell C hardness of a carbon steel increases from 30 to 65 (a further increase of carbon content does not produce an increase in hardness). At carbon contents of less than 0.4 percent, the hardenability of steel can be increased by alloying with nickel, manganese, chromium, or silicon. Hardenability must be distinguished from hardening depth, which denotes the depth of martensite formation in steel structure upon hardening.