Influence of Thermocyclic Electrolyte-Plasma Treatment on Mechanical Properties of U9 Tool Steel

The article investigates the influence of thermocyclic electrolytic-plasma treatment (EPT) on the mechanical properties of carbon steel U9 tool steel. U9 steel is often used for manufacturing tools working in conditions that do not cause edge heating: woodworking tools, assembly tools, gauges of simple shape and reduced accuracy classes. In this work, thermocyclic electrolytic-plasma treatment was used as a method of improving mechanical properties. This method combines electrochemical reactions and intensive thermal influence, which allows the formation of surface layers with improved characteristics. As a result of the treatment, U9 steel shows a clear division of the microstructure into three zones: hardened layer, transition layer and base metal. The hardened layer, located up to a depth of 400 μm, is characterized by a finely dispersed structure consisting of martensite and bainite with high hardness (1400–1600 HV₀.₁). This layer provides excellent wear resistance and resistance to mechanical stress. The transition layer (400–700 µm) serves as a buffer zone, distributing stresses evenly. It is characterized by a gradual decrease in hardness (800–1200 HV₀.₁) and a change in structure due to a decrease in martensite content. The base metal, deeper than 700 μm, retains the original structure with hardness 400–600 HV₀.₁, which ensures its ductility and durability. The results show that thermocyclic EPT significantly improves the performance properties of U9 steel by creating a functionally gradient structure. The technology is energy efficient and can be widely used in mechanical engineering and other industries where high mechanical characteristics of materials are required.