When simulating solidification for aluminium alloys the simple Scheil-Gulliver
model has turned out to be surprisingly accurate. But when simulating
solidification of steels with a significant fraction of interstitial elements
these elements can diffuse fast in the solid phase and the Scheil-Gulliver
model is not good. An alternative model has been implemented in Thermo-Calc to
allow carbon to redistribute between to solid and liquid phases during the
solidification. This gives better agreement with experimental results.
The fast diffusing interstitial elements also affect the equilibria in the
solid state and the para-equilibrium concept has been proposed for calculating
phase equilibria in steels. This has been implemented in Thermo-Calc and makes
it possible to calculate ferrite/austenite transformations requiring only
redistribution of carbon and nitrogen. Comparisons between the stable and the
para-equilibrium phase diagram will be given and also comparisons with DICTRA
simulations and experimental data.