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What is Hardenability in Heat Treatment ?

 Hardenability is that property of a steel which determines the depth and distribution of hardness obtained by the quenching. It is not an indication of the hardness. Hardenability is usually interpreted as the ability to become uniformly hard or to harden in depth. The depth of hardening is usually taken as distance from the surface to semi-martensitic zone, i.e., 50 per cent martensite plus 50 percent pearlite. 




Full hardening of carbon steels is observed in articles of a diameter or thickness up to 25mm. Alloy steels harden to considerably larger depth due to the high stability of the super cooled austenite and correspondingly lower critical cooling rate. Therefore, alloy steels may be effectively hardened by quenching in oil instead of water.

DETERMINATION OF HARDENABILITY :

Several methods are used to determine the hardenability of steels,

1. By appearance of fracture.

2. By the distribution of the hardness along the cross-section and 

3. By the end quench test.

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