Centre Stephanois De Recherches Mecaniques Hydromecanique Et Frottement

Gerard Guilhot

Antoine Gaucher

The invention relates to a method of maintaining at very low values the portions of cyanides in molten-salt baths of the kind in which the main active principle is the cyanate anion CNO.sup.-, the method comprising essentially the steps of conjointly providing in the salt bath at least one sulphurized element in a quantity such that the proportion of the sulphur element in the bath is between 0.001 and 0.1 % of the weight of said bath, and introducing periodically or continuously into the bath at least one substance comprising at least one carbonyl group = C = O in its chemical formula, in a quantity such that it corresponds to a weight of between 1 and 25 grams of CO per kg. of bath and per 24 hours maintenance at the bath working temperature of between 480.degree. and 650.degree. C. The substance introducing the carbonyl group may also constitute a regenerating agent for the cyanate anion and can advantageously be obtained by baking carbamide for 3 to 10 hours at a temperature of between 150.degree. and 450.degree. C. The bath may be homogenized by agitation means including insufflation of air. The invention is especially applicable to the nitridation of mechanical parts in heat-treatment salt-baths.

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St-Jean Bonnefonds, France

Gerard Guilhot