The term hardened steel
is often used for a medium or high carbon steel
that has been given the heat treatments of quenching
followed by tempering
. The quenching results in the formation of metastable Martensite
, the fraction of which is reduced to the desired amount during tempering. This is the most common state for finished articles such as tools and machine parts. In contrast, the same steel composition in annealed
state will be softer as required for forming and machining
Case hardened articles starting as low carbon steel can also be labeled hardened steel.