Phosphating method of steel pieces in order to improve their corrosion and wear resistance

摘要

After a preliminary treatment of their surface, the pieces are placed in contact with a solution containing, principally, protons, phosphate anions and cations taken from Ca2+, Sn2+ and Mn2+. According to the invention this is done so that the preliminary treatment results in the formation, at the surface, of a layer which contains, per 1000 atoms, at least 150 atoms of free iron and 5 to 150 atoms of sulphur, and has a porosity defined by a ratio of actual surface to macroscopic surface of at least 20. According to a first alternative embodiment, these surface characteristics are obtained by nitriding in a bath of molten salts containing sulphurous species. According to a second alternative embodiment, these surface characteristics are obtained by nitriding in a bath of molten salts followed by a conventional sulphurising operation. According to a third alternative embodiment, these surface characteristics are obtained by a deposition of metal followed by a conventional sulphurising operation.