The mechanism of thermochemical growth of iron borides on iron was studied by analysing the products which form on samples placed in contact with B4C-base powder mixtures with different boronising potential. The analyses were carried out by means of metallographic and X-ray diffraction techniques. Three subsequent stages of growth were observed which explain the occurrence of typical properties of the thermochemically grown boride coatings, such as preferred crystallographic orientations and textures, as well as mechanical compactness and hardness, which play a determining role in the tribological behaviour of borided components. (C) 2004 Kluwer Academic Publishers.