Process for nitriding iron and steel in salt baths regenerated with triazine polymers
AssigneeDuetsche Gold- und Silber-Scheideanstalt vormals Roessler
InventorsHermann Beyer, Peter Biberbach, Christian Scondo
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Abstract
Iron and steel are nitrided in a salt bath in a process favorable to the environment. The salt bath consists essentially of potassium cyanate, sodium cyanate, potassium carbonate, and sodium carbonate. Preferably, air flows through the bath. The bath preferably contains 25-57 weight % of cyanate calculated as cyanate ion, 0 to 30% alkali metal chloride and the balance carbonate and alkali metal ions. Preferably cyanide is omitted, but it can be present in an amount up to 5%. Without removing the waste salt, the bath is regenerated by adding melon, melam, or melem.
Claims34
In a process comprising nitriding iron or steel in a salt bath at nitriding temperature, and regenerating the salt bath in which there has been loss of cyanate during the nitriding, the improvement comprising heating the iron or steel in a salt bath consisting essentially of a member of the group consisting of:
- 1. potassium cyanate alone;
- 2. potassium cyanate admixed with at least one compound of the group consisting of sodium cyanate, potassium carbonate, sodium carbonate and an alkali metal chloride;
- and
- 3. sodium cyanate admixed with at least one compound of the group consisting of potassium carbonate, sodium carbonate and an alkali metal chloride,
- said bath containing 25-57 weight % cyanate calculated as cyanate ion, 0-5 weight % cyanide calculated as cyanide ion, 0-30 weight % alkali metal chloride and balance potassium ion, sodium ion and carbonate ion and after the cyanate content of the bath has fallen and the carbonate content increased readjusting the cyanate content and carbonate content by adding triazine polymer of the group consisting of melon, melan and melem to the salt bath without removing waste salts from the bath, the amount of said triazine polymer added being 0.5 to 1.5% for each 1% decrease of cyanate.
In a process for the regeneration of a salt melt bath used for nitriding a metal piece in which there has been loss of cyanate during the nitriding, said salt bath consisting essentially of carbonate and cyanate and in which air is passed through the melt, said bath containing 25-57 weight % cyanate calculated as cyanate ion, 0 to 3% cyanide calculated as cyanide ion and balance potassium ion, sodium ion and carbonate ion, the improvement comprising adding to the bath a triazine polymer selected from the group consisting of melam, melem and melon.
A salt bath suitable for nitriding a metal piece and generated by a composition consisting essentially of:
- a.
- 1. potassium cyanate alone;
- 2. potassium cyanate admixed with at least one compound of the group consisting of sodium cyanate, potassium carbonate, sodium carbonate and an alkali metal chloride;
- and
- 3. sodium cyanate admixed with at least one compound of the group consisting of potassium carbonate, sodium carbonate and an alkali metal chloride, and
- b.
- 1. a triazine polymer selected from the group consisting of melon, melam and melem,
- said bath containing 25-57 weight % cyanate calculated as cyanate ion, 0.14 30 weight % alkali metal chloride, 0 to 5 weight % cyanide calculated as cyanide ion, and balance potassium ion, sodium ion and carbonate ion, there being added to the bath for each decrease of 1 weight % of cyanate 0.5 to 1.5 weight % of said triazine polymer.
Dependencies are inferred from the claim text.