A two-stage surface treatment of steel is described. During the first stage, a steel surface is coated with an Fe-14% Ni electrodeposit having an initial hardness of 300-400 HV. Subsequently, the microstructure and hardness of the coatings are modified by thermal and thermochemical treatment. The annealing at temperatures between 500 and 1.000 degrees C leads to the diffusion of carbon from the substrate to the coating and an increase in coating hardness after cooling. In some cases, the en rich ment of coating in carbon is enhanced by applying an external source of carbon and nitrogen. As an example, carburizing and carbonitriding in solid media are presented. Owing to a difference in the temperature of the alpha-gamma phase transformation between the steel substrate and the Fe-Ni coating, the thermal treatment is conducted at a coexistence of alpha-gamma or gamma-gamma diffusion couples. This allows us to obtain the various microstructure and depth-profiles of hardness across the coating thickness and the adjacent region of the substrate. Some benefits of the proposed surface treatment are discussed.