Abstract: To improve the corrosion resistance of ferrous metal parts containing free r combined sulphur on the surface, the parts are immersed in a bath of molten oxidizing salts at between 350.degree. C. and 450.degree. C., the bath typically having a composition by weight of 60% of potassium hydroxide, 30% of sodium nitrate and 10% of sodium carbonate. Between 0.5% and 15% of oxygen-containing salts, the normal oxidation-reduction potential of which is less than or equal to -1 volt, relative to the hydrogen electrode, such as alkali metal dichromates, permanganates, peroxycarbonates, iodates and periodates, are added to the bath, and an oxygen-containing gas is blown into the bath with an oxygen flow of between 1.5 and 7.5 liters/hour per 100 kg of bath. The molten salts of the bath are filtered continuously through an iron gauze filter cartridge in a furnace, the molten salts being transported into the filter cartridge by entrainment of the salts in a pipe by bubbles of air blown in through the pipe.

Abstract: The surface of a ferrous alloy is treated by electrolytic deposition of a copper-tin alloy surface layer followed by the diffusion heat treatment of the coated surface. Electrolysis is carried out in a bath containing monovalent copper ions, tetravalent tin ions, an alkali metal hydroxide, an alkali metal cyanide, alkali metal carbonates, alkali metal stannites, and an alkali metal citrate; and the diffusion heat treatment is carried out at between 500.degree. and 580.degree.C.