Process for improving the corrosion resistance of ferrous metal parts
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United States of America Patent
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Aug 26, 1986
Grant Date -
N/A
app pub date -
Mar 19, 1985
filing date -
Mar 20, 1984
priority date (Note) -
Expired
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Abstract
A process for improving the corrosion resistance of ferrous metal parts also subject to heat and chemical treatment following nitriding in association or not with carburizing and/or sulfurizing essentially comprises immersing the parts in a known bath of molten salts to which is added a sufficient quantity of a halogenophosphate having formula: M.sub.2 (PO.sub.3 X).sub.m in which X and is fluorine and M is a metal of subgroup Ia, IIa or IIb of the periodic table of elements, having the valency m. The preferred halogenophosphate is sodium, potassium, calcium or zinc monofluorophosphate. The molten salt bath may be of the oxidizing type, comprising for example, 65% by weight KOH, 25% NaNO.sub.3, 10% Na.sub.2 CO.sub.3, or of the neutral type, for example a eutectic mixture of 50% BaCl.sub.2, 30% CaCl.sub.2, 20% NaCl. The halogenophosphate may be added in proportions of 0.1 to 20 g per kilogram of salt bath.
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