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.