We study the steel surface modifications induced by irradiation of several lasers in air. The surface modifications are found to depend on the laser properties (Krf, 248 nm, 26 ns; XeCl, 308 nm, 25 ns, Nd:YAG, 1064 or 532 nm, 5 or 10 ns). The treated surface features (morphology, chemical composition and crystalline structure) are analysed by complementary techniques, such as X-ray photoelectron spectroscopy, nuclear reactions, scanning electron microscopy and grazing incidence X-ray diffraction. First of all, it is shown that the carbon coming from the machining oils is successfully removed under all the studied conditions. The incorporation of oxygen and nitrogen (beyond 1 mum in depth) to the surface is also shown. In addition to the original ferrite phase, new crystalline compounds are detected after treatment such as austenite, oxides (FeO or Fe2O3, Fe3O4) and nitride (epsilon-Fe2-3 N). Depending on the laser characteristics, the main formed crystalline phases are different (oxide or nitride). A discussion of the expected surface modification mechanisms is presented. Under some experimental conditions, the formation of a back-deposition layer composed of oxides and hydroxides is observed. (C) 2003 Elsevier B.V. All rights reserved.