The microstructure of mild carbon steel after laser alloying with SiC is described. The macrostructure of the alloyed layer consisted of three well-defined zones. The first zone consisted of crystals growing epitaxially on the partially remelted matrix grains, the second zone had only columnar crystals, and the third zone consisted of mixed (dendritic/acicular) crystals near the surface. The martensitic structure in the last zone varied in the needle size. The martensitic needles formed at the early stages of the gamma double right arrow alpha' transformation were very large, crossing several primary austenite crystals. The needles that formed during the later stages of the martensitic transformation were much finer. (C) 2003 Elsevier Science B.V. All rights reserved.