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AssigneeCentre Stephanois de Recherches Mecaniques Hydromecanique et Frottement
InventorsBernard Grellet, Jean-Pierre Emmanuel, Bernard Sipp
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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.
A process for improving the corrosion resistance of ferrous metal parts containing free or combined sulphur in their surface layers, in which the parts are immersed in an oxidising bath of molten salts comprising alkali metal hydroxides, alkali metal nitrates and/or nitrites and, if appropriate, alkali metal carbonates, comprising adding to the oxidising bath from 0.5% to 15% by weight of oxygen-containing salts of alkali metals, the normal oxidation-reduction potential of which is less than or equal to -1.0 volt relative to the hydrogen reference electrode;
A process for improving the corrosion resistance of ferrous metal parts containing free or combined sulphur in their surface layers, in which the parts are immersed in an oxidising bath of molten salts comprising alkali metal hydroxides, alkali metal nitrates and/or nitrites and, if appropriate, alkali metal carbonates, comprising adding to the oxidising bath from 0.5% to 15% by weight of oxygen-containing salts of alkali metals selected from the group comprising dichromates, permanganates, peroxycarbonates, iodates and periodates, the alkali metals being sodium and potassium, the normal oxidation-reduction potential of which salts is less than or equal to -1.0 volt relative to the hydrogen reference electrode;
A process for improving the corrosion resistance of ferrous metal parts containing free or combined sulphur in their surface layers, in which the parts are immersed in an oxidising bath of molten salts comprising, by weight, 25% to 35% of alkali metal nitrates and less than 15% of alkali metal carbonates, the remainder being alkali metal hydroxides and the alkali metals being sodium and potassium;
Dependencies are inferred from the claim text.