It is a type of processing, which is carried out prior to the heat treatment with the aim of preventing the thermochemical treatment occurring in certain areas. As a matter of fact determined protective products are applied, which prevent the surface enrichment of the protected area. The operation is carried out by specialized personnel by means of automatic plant systems or equipment for dosing and distribution. It is moreover also possible to protect the work pieces intended for the carburizing, gas nitriding, carbonitriding and nitrocarburizing treatments