In the Write Interface dialog you can save the position of the solid-liquid interface and the temperature gradients at the interface to a file.
Before you are able to write the interface into a file, you have to compute temperature once with enabled interface tracking. Select Computation > Numerical Parameters. Change to the Forward tab. Be sure the Track Interface button is checked.
Compute the temperature and the gradients.
Select Analysis > Write Interface.
The file *-gradients.dat is now saved.