TRIP steels possess a microstructure consisting of austenite with sufficient thermodynamic instability such that transformation to martensite is achieved during loading or deformation.
Many automotive TRIP steels possess retained austenite within a ferrite matrix, which may also contain hard phases like bainite and martensite.
[2] In the case of these alloys, the high silicon and carbon content of TRIP steels results in significant volume fractions of retained austenite in the final microstructure.
This transformation is dependent on temperature, applied stress, composition, strain rate, and deformation history, among others.
The amount of carbon determines the strain level at which the retained austenite begins to transform to martensite.
At lower carbon levels, the retained austenite begins to transform almost immediately upon deformation, increasing the work hardening rate and formability during the stamping process.
At higher carbon contents, the retained austenite is more stable and begins to transform only at strain levels beyond those produced during forming.
It has been observed that TRIP steels exhibit this exponential strain hardening behavior when deformed at a temperature near to and above Msσ, thereby displaying an optimum in uniform plastic ductility.