Finite element (FE) process modeling of inertia friction welding between dissimilar high-strength steels, AerMet(A (R)) 100 and SCMV, has been carried out using the DEFORM (TM)-2D (v10.0) software. This model was validated against experimental data collected for a test weld performed between the materials; this included process data such as upset and rotational velocities as well as thermal data collected during the process using embedded thermocouples. The as-welded hoop residual stress from the FE model was also compared with experimental measurements taken on the welded component using synchrotron X-ray and neutron diffraction techniques. The modeling work considered the solid-state phase transformations which occur in the steels, and the trends in the residual stress data were well replicated by the model.