5th International Conference on Advances in Solidification Processes (ICASP-5) 5th International Symposium on Cutting Edge of Computer Simulation of Solidification, Casting and Refining (CSSCR-5)

One of the most powerful tools for studying the development of microstructures is the CALPHAD (Calculated PHAse Diagrams) method because it comprises information derived from thermodynamic principles, presented in a form that makes the data readily accessible. It is much easier and less time consuming to perform these thermodynamic calculations with any of the available software rather than trying to experimentally identify the phase transformations during solidification, but one has to be sure that the temperatures calculated are close to the real system. Even when the thermodynamics tells us what should happen in equilibrium, it does not guarantee that it is what will happen, as the real system may be influenced by kinetics. However, when dealing with complex systems like commercial grades of steel, where many phases may be formed during solidification through various reactions, it is necessary to perform more complex calculations. In this publication two examples will be shown on how the CALPHAD method is used to evaluate the castability of commercial steel grades where complex phases appear during solidification and cooling. The first example will focus on the different phases that can appear in HSLA steels (High Strength Low Alloyed) where the microalloying elements (Nb, V, Ti, Al, etc.) that precipitate as carbo-nitrides at different stages during and just-after solidification are related to the so-called second ductility trough and may cause cracking at the last stages of the casting process. Further, the second case show the possible castability issues for AHSS (Advanced High Strength Steels) that are related to the phase transformation and how the CALPHAD method can help on designing new steels.