Martensite is not shown in the equilibrium phase diagram of the iron-carbon system because it is not an equilibrium phase.
42.
Often, after quenching, an iron or steel alloy will be excessively hard and brittle due to an overabundance of Martensite.
43.
The carbon equivalent is a measure of the tendency of the weld to form martensite on cooling and to suffer brittle fracture.
44.
Two common cases of this include cooling a liquid to form an amorphous solid, and cooling eutectoid austenite to form martensite.
45.
Steels that harden by aging are typically referred to as maraging steels, from a combination of the term " martensite aging ."
46.
The transformation is essentially time-independent with the phase fraction depending only the degree of cooling below the critical martensite start temperature.
47.
Further, it occurs without the diffusion of either substitutional or interstitial atoms and so martensite inherits the composition of the parent austenite.
48.
Tempered martensite gives steel good hardness and high toughness; used largely for medical tools ( scalpels, razors and internal clamps ).
49.
Equilibrium phases form by slow cooling rates that allow sufficient time for diffusion, whereas martensite is usually formed by very high cooling rates.
50.
In carbon steels, tempering alters the size and distribution of carbides in the martensite, forming a microstructure called " tempered martensite ".
