The metallic interior surfaces with cylindrical symmetry have been processed by knocking them with centrifuged balls. The first author has designed the used processing tool and it has been carried out under his instructions. There have been processed cast iron and carbon steel samples, using 80 different combinations for the process parameters: axial advance S, tangential rotation speed of the processed piece V, and the impact force F between the balls and the processed surface. Using the measured values of roughness Ra, Vickers microhardness HV and of the depths of cold-hardening h, we have achieved and used an optimizing computer program for the qualitative parameters of the cold-hardening process, i.e. Ra, HV and h. Also, we found optimal solutions for the processing regime. The study establishes the ability to increase the mechanical characteristics of the turned out metallic surfaces, thus taking out any further mechanical, thermal and/or chemical superficial processing. The results of the current study allow a correct choice of the processing regimes for different materials with similar bulk properties.