CalPhaD Coffee Lecture – Development of Thermodynamic Database for Clean Manufacturing of Steels and Alloys

Various thermodynamic databases have been developed using the regular solution model to mainly construct phase diagrams. However, the CALPHAD approach without considering strong interactions among the metallic elements and gaseous impurities shows a poor predictability for the practical condition of liquid alloy production including optimum carbothermic reaction for reducing CO2 emission.

The liquid solution properties of the core alloy systems and the effect of impurity elements were described by using the Modified Quasichemical Model (MQM). In this model, the strong attraction force was evaluated as the negative Gibbs free energy of the formation of pairs in the pair approximation. The asymmetry of liquid solution properties can be described by the Short-Range Ordering (SRO) phenomena in the binary systems and geometrical interpolation method in the ternary systems, respectively. The modification of configurational entropy in this model also reduces the weight of temperature dependence in the excess Gibbs energy term of liquid solution. It can also affect the stability of all the solid phases to make Gibbs energy balance for liquidus and solidus.

This database is stored in the current version of FSStel database in FactSage thermochemistry software. The database can be used for the refining of steels and alloys over the entire composition range as well as the recycling and extraction technology of valued metals with environmentally friendly manufacturing processes