Abstract Boriding thermochemical treatment produces layers with high hardness which improves the tribological performance of ductile cast iron while the austempering treatment improves the mechanical performance of the substrate. In this work, samples of the ductile cast iron alloyed with copper, copper-nickel and copper-nickel-molybdenum were borided in a salt bath (borax + aluminum) at temperatures of 850, 900 and 950°C during 2 and 4 hours. The data for the layers obtained were used to determine the diffusion coefficients and activation energies of this process. The results of the calculated diffusion coefficients were similar to those obtained by the direct measurements of the layer thicknesses. For the sample alloyed with Cu or Cu-Ni the activation energy obtained was 141.27 kJ/mol, and for the sample alloyed with Cu-Ni-Mo the value was 212.98 kJ/mol. The statistical parameters and the correlation coefficients (R) showed satisfactory agreement.