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What is retained austenite ? This questions troubles us many time.This phase is unfavorable and yes some times favorable also. Let see what exactly retained Austenite is by definition.Cause behind its occurrence and its effect properties.
What is retained austenite ? This questions troubles us many time.This phase is unfavorable and yes some times favorable also. Let see what exactly retained Austenite is by definition.Cause behind its occurrence and its effect properties.
Retained Austenite :
Definition
There is no definition of retained Austenite as such. It is Austenite only which has not been transformed to martensite or cementite or ferrite after cooling to ambient temperature.
What caused retained Austenite?
The extent of martensitic transformation depends on temperature, and it only occurs within a range of temperature defined by a martensite start (Ms) and martensite finish (Mf) temperature. Above the Ms temperature, martensite does not form, even at high cooling rates. The transformation occurs when the steel (cooled at sufficiently high rates) is at temperatures between Ms and Mf. The transformation then ceases when the steel falls below the Mf temperature. Some remaining austenite may still be present when the transformation stops. This remaining austenite is referred to as retained austenite.
Effect Of retained Austenite
When ever there are changes in phases there are volume change associated with it.Each phase have different density , lattice structure.Retained austenite is highly unstable phase over the period retained austeinte if present can decompose in ferrite,cementite oe bainite.This transformation causes change in dimension of product which is not desirable .Its comparatively softer phase it reduces hardness.