Abstract: After preliminary treatment of their surfaces, the parts are brought into contact within a solution containing, essentially, protons, phosphate anions and cations chosen from Ca.sup.2+, Sn.sup.2+ and Mn.sup.2+. The preliminary treatment results in the formation, on the surface, of a layer that comprises, per 1000 atoms, at least 150 atoms of free iron and from 5 to 150 atoms of sulphur, and has a porosity defined by an actual surface area to macroscopic surface area ratio of at least 20. According to an embodiment, these surface characteristics are obtained by nitriding in a bath of molten salts containing sulphur-containing species. According to a second embodiment, these surface characteristics are obtained by nitriding in a bath of molten salts followed by a conventional sulphiding operation. According to a third embodiment, these surface characteristics are obtained by depositing metal, followed by a conventional sulphiding operation.

Abstract: Precision ferrous metal parts subject to severe friction and corrosion in e are nitrided, preferably in a bath of molten salts based on CNO.sup.- cyanate ions, oxidized, preferably in baths of molten oxidizing alkaline salts, and then impregnated with a hydrophobic wax. A layer after the nitriding and oxidation steps is formed of a close-packed deep sub-layer and a porous superficial sub-layer ranging in thickness between 5 and 25 .mu.m, and exhibiting through pores ranging between 0.2 and 3 .mu.m in diameter. The impregnation wax is an organic compound with a high molecular weight between 500 and 10,000, with a surface tension in the liquid state ranging between 10 and 73 mN/m, the contact angle between the solid phase of the superficial layer and the wax in the liquid state ranging between 0 and 75.degree. C.