I think that the work titled „Welding simulation of steels welded with low transformation temperature (LTT) filler materials” by M.M. Esfahami will be useful for you since it features parts of Fortran code necessary to define phase transformation subroutines in Abaqus.
Also take a look at these two articles:
- „A metallurgical phase transformation framework applied to SLM additive manufacturing processes” by Q. Zhang et al.
- „Phase Transformations in Metals during Additive Manufacturing Processes” by J. Coe et al.
They both refer to Abaqus simulations of somewhat similar (in terms of simulation) group of processes - additive manufacturing.