Component and tool surfaces are subject to a multitude of conditions that may affect their behaviour and properties. The surface zone must protect the object from corrosion and wear, whilst the base material need only provide the necessary strength. This division of function between the surface zone and the core enables high-performance materials to be made from low-alloy steels using appropriate modification processes. Thermochemical methods offer cost-effective ways to improve the useful properties of steels, such as wear resistance, friction behaviour, fatigue resistance, corrosion resistance and fatigue characteristics.