Two approaches to simulating microstructures typical of additively manufactured (AM) materials are presented. First approach relies on the mathematical description of the microstructure evolution during metal AM process, taking into account complex physical processes involved. The numerical solution is based on a combination of the finite difference method for modeling AM thermal processes and the cellular automata method for describing the grain growth. The other approach provides fast generation of artificial 3D microstructures similar to those produced by AM by geometrical characteristics of grains, using the step-by-step packing method.