Development of a CALPHAD based steel property model library for Martensite and Pearlite

CALPHAD based tools are an important component of Integrated Computational Materials Engineering (ICME) since by combining thermodynamic and mobility data, kinetic reactions during solidification and heat treatment processes can be simulated. The extension of CALPHAD models to predict other properties is now being undertaken. Three such examples are given for steels.

A new Martensite Temperature property model calculates the martensite start temperature (Ms) based on modeling the transformation barrier with fitted analytical equations. The partitionless equilibrium temperature T0 is calculated using a CALPHAD database. The model also gives temperatures corresponding to 50%, 90%, and 99% transformations where Martensite fractions are based on the fraction of athermal martensite calculated using an analytical equation based on Huyan et al. (2016).

A new Pearlite property model also describes the thermodynamics and kinetics of pearlite formation from austenite. Growth rate and lamellar spacing of pearlite are determined by a criteria where either growth rate or Gibbs energy dissipation rate is maximized.