Nitriding in non-toxic salts bath: An approach to implement cleaner production in the metallurgic industry

The need for sustainable development has been reflected in the adoption of cleaner production initiatives in the last years. However, the literature indicates that more research is still necessary to engage industries in adopting alternatives to reduce environmental impact. In that regard, we investigated a way to reduce the environmental impact in the metal-mechanical industry, caused by the conventional salt bath nitriding process. This technique commonly uses cyanides and cyanates salts as a nitrogen source for the formation of nitrides coating to improve the metal surface properties, especially to achieve high hardness. Thereby, this paper sets out an approach, as an alternative to obtain a nitride layer, formed by non-toxic salts: potassium nitrate additivated with a new condition of antioxidative salt, potassium chloride, which improves the nitriding efficiency and surface finish of carbon steel 0.2% C. The results indicated the formation of a white layer of 8 μm thickness and a diffusion zone around 200 μm, after 3 h of nitriding. There was an increase in hardness, from 198 HV on the substrate to 702 HV on the nitrided surface. Consequently, one can conclude that the use of non-toxic salts is an efficient alternative to improve the surface properties in low carbon steel with the advantage of applying green engineering approaches, feasible technologically to the decrease in the amount of pollution.