Before the end of the treatment of metal parts in a molten salt bath nitriding/nitrocarburizing station, a chamber, arranged so that the oxygen contained in the chamber can be discharged in order to create an inert atmosphere, is filled with a refrigerant in liquid form and with a strong capacity for volume expansion as it evaporates. All the parts treated are transferred into the chamber. The chamber is closed, and the parts are left in the chamber for a preset length of time to reach a temperature at which the salt congeals and forms a protective barrier. The parts are then removed and subjected to a rinsing operation.