Grain morphologies in the weld pool of Ni-Cr alloy are simulated using a multi-scale numerical model based on cellular automaton algorithm. Depending on the CA-FD model with diagonal simulating angle method, the competitive growth process between columnar dendrite grains with different crystallographic orientations and the competitive growth process between columnar grain and equiaxed grain in a finite two-dimension zone of the weld pool are simulated. The simulated results reproduced the grain morphology evolution as well as the solute distribution during the solidification process of the weld pool. It is indicated that the complicated thermal field and solute field can result in complex grain morphologies in the weld pool. The grain boundary segregations in the weld seam are remarkable and they become more severe when there is competitive growth between columnar grains and equiaxed grains. Crown Copyright (C) 2009 Published by Elsevier B.V. All rights reserved.