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In the ordinary practice of hardening steels, the quenching is not so drastic, and the transformation of austenite back to ferrite and cementite is more or less completely effected, giving rise to certain transitory forms which are known as "martensite," "troostite," "sorbite," and finally, pearlite.

Sorbite is softer and tougher than troostite, and is habitually associated with pearlite.

Troostite is of doubtful composition, but possibly is an unstable mixture of untransformed martensite with sorbite.

Moderate reheating or annealing changes this structure largely into troostite, which is a partly transformed martensite, possessing much of the hardness of martensite, but with a largely increased toughness and shock resistance.