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T0

T0: T0 temperature
Definition:Temperature (or composition) at which the Gibbs energies of two phases are equal.
Explanation:Indentifying the temperature (or composition) where the Gibbs energies of two phases are equal is important because it shows the limit where a diffusionless transformation (martensitic or massive) from one phase to another is possible. Once T0 is known, the modeling of the martensitic transformation temperature (Ms) is a matter of modeling the necessary driving force to initiate (or nucleate) the transformation. This is obviously of importance for a wide range of steels. For high Mn steels, it offers a possibility to predict if plastic deformation can take place by transformation induced plasticity (→TRIP) or twinning induced plasticity (→TWIP).
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Diagram:

(a) Gibbs energies in Fe-Mn. The crossing of two curves marks the T0 for that phase pair. (b) T0, Ms and As (reverse transformation) for the fcc/hcp pair and the Neel temperature (TN) for the fcc phase.
SFB-Link:The T0 for the fcc/hcp phase pair is the starting point for the thermodynamic calculation of stacking fault energy (→SFE) and Ms (for ε-martensite).