Tempering involves a three-step process in which unstable martensite decomposes into ferrite and unstable carbides, and finally into stable cementite, forming various stages of a microstructure called tempered martensite. The martensite typically consists of laths (strips) or plates, sometimes appearing acicular (needle-like) or lenticular (lens-shaped). Depending on the carbon content, it also contains a certain amount of "retained austenite." Retained austenite are crystals which are unable to transform into martensite, even after quenching below the martensite finish (Mf) temperature. An increase in alloying agents or carbon content causes an increase in retained austenite. Austenite has much higher stacking-fault energy than martensite or pearlite, lowering the wear resistance and increasing the chances of galling, although some or most of the retained austenite can be transformed into martensite by cold and cryogenic treatments prior to tempering.