Microsegregation During Solidification

This example shows how Thermo-Calc together with the Add-on Diffusion Module (DICTRA) can be used to investigate and predict microsegregation during solidification, also known as solute redistribution during solidification. The example uses a steel with composition Fe – 0.8% Mn – 0.7%Si – 0.03%P – 0.4%C.

This example is based on a real case where the elemental distribution of a continuously cast steel was measured, revealing concentrations of Si, Mn, and P. As shown in Figure 1, Si and Mn exhibit the expected positive segregation in the interdendritic regions. However, the P content peaks differently, showing unexpected negative segregation in these regions, which is counterintuitive.

Calculated segregation of all elements just after final solidification (600 sec, top) and after cooling to 900 °C (3000 sec, bottom): just after final solidification there is positive P segregation in the final solidification pools between the dendrite arms. On further cooling, P redistribution is controlled by slow Mn and Si diffusion resulting in the unexpected, but experimentally observed, peak shift and negative P segregation.

The calculations are based on ones performed in the frame of a research project funded by the European Union called VESPISM – Virtual Experiments to Solve Problems in Metallurgy – conducted from 2001 to 2004. Read about the research.