The machine industry is always looking for new tools, in order to open new markets such as high-rate metal forming in the automotive industry or machining innovative hard materials. To reach such challenges, tools have not only to fulfil high tribological characteristics, but also to resist against the degradations resulting from the medium. For several years the literature relates the efficiency of nanostructured coatings to improve the surface mechanical properties, but often without taking into account the environmental constraints. The objective of this work is to study the corrosion behaviour of coated M2 steel in a saline aggressive solution as well as in high temperature oxidation conditions. Coatings are fabricated by PVD arc evaporation or by magnetron sputtering. Superlattice coatings are composed of TiN and CrN successive layers of several nanometers in thickness (2D-TiN/CrN). In order to determine a "nanostructure effect", multilayered deposits are systematically compared to both TiN and CrN monolayered references. The nature of the external layer, in contact with the aggressive medium, will be a key-parameter of prime importance. Under oxidation conditions in air at 700degreesC during 9 and 24 hours, TiN oxidises into a thick cracked rutile layer, while CrN is covered by a submicrometric dense chromia layer. In the same way, thermogravimetric experiments confirm the better protection afforded by CrN compared to TiN (kinetic reduction of one decade). Concerning nanostructured deposits, their performances are similar to CrN ones : similar low oxidation rate and close values of weight variation. Thus, CrN, acting as a chromia former material, fixes its high intrinsic refractory properties. The chemical nature of the external layer is, in the case of nanostratified TiN/CrN coatings, without any deleterious consequences : indeed, if TiN is deposited as a top layer, it is immediately corroded, and, as soon as the oxidation front reaches CrN, which is transformed into chromia, its progression towards the core of the part is greatly slowed down. When immersed in saline solution, cathodic PVD coatings (like TiN and CrN) often suffer from severe galvanic corrosion of the substrate through the defects of the deposit. However, in the case of a stratified structure, the open porosity is almost eliminated (porosity rate becomes lower than 0.01% !). Nevertheless, this outstanding covering ratio is not the only reason for the good electrochemical properties of multilayered deposits, since it has been shown that CrN spontaneously forms a thin efficient passive film on its top surface. From a wet corrosion point of view, the best characteristics are then obtained for a stratified coating having an external p-type semiconductive CrN layer.