Tribological Characterization of Surface-Engineered W350 Grade Tool Steel

Abstract In this study, surface treatments are applied to W350 grade hot work tool steel, including (i) nitrocarburizing and (ii) nitriding, followed by post-oxidation processes, and both tribological performance and wear-related failure of the surfaces against nominal loads (10 and 20 N) at room temperature and 350 °C are evaluated. As a result of nitrocarburizing process, a compound layer (~ 8 µm thick) and a diffusion layer (~ 120 µm depth) are formed on the surface of the steel having a tempered martensitic structure. By nitriding process, a diffusion depth of ~ 20 µm is reached without forming a compound layer and an oxide film (~ 2 µm thick) is coated on this depth with the post-oxidation process. Tribological tests show that (i) material losses due to wear can be reduced due to thermomechanical processes since they provide higher surface hardness compared to the substrate material, (ii) the compound layer can provide higher wear resistance compared to the oxide layer, and (iii) diffusion layer with high load-carrying capacity plays a decisive role in wear performance. Investigations on the worn surfaces indicate that the tendency for abrasive wear can be reduced at room temperature due to the increase in surface hardness by thermochemical processes; however, there is a significant increase in the formation of an adhesive layer on the surface. The resistance of surfaces coated with harder ceramic/oxide components to plastic deformation at higher temperatures has led to a reduction in wear losses.