Investigating the influence of gas nitriding and gas nitrocarburizing surface hardening processes on AISI 4140, 1.7131 and 1.8550 grade steel's wear, mechanical and microstructure properties

Nitrocarburizing and nitriding surface hardening heat treatment processes that applied on engineering materials to provide better wear and corrosion resistance. After nitrocarburizing process, there will be a white layer on surface, made of ε-Fe2-3(N, C) ve γ-Fe4(N, C) iron nitride and carbide layers, and below this layer there will be diffusion layer consist of alloy nitrides and carbides. The white layer is hard and has high wear resistance while core layer remains it's toughness and impact resistance. Main goal in this heat treatment is providing a surface layer that harder than material's core hardness. As a result of providing a hard surface layer, material losses under wear will be reduced, so material's lifetime will be enhanced. In this study, nitrided and nitrocarburized AISI 4140, 1.7131 and 1.8550 grade steel's mechanical and microstructural features has been examined within this thesis. The white layer has been observed in both Nitriding and Nitrocarburizing methods with increase of hardness, corrosive and fatigue strength. The greatest advantage of nitriding and nitrocarburizing processes over other surface hardening methods is that they are carried out at relatively low temperatures. In this case, the heat penetration into the steels decreases and the thermal distortions that may occur in the part are largely prevented. The advantage of nitriding and nitrocarburizing can be further enhanced by gradually heating the machine elements where the dimensional tolerances are very low. Such nitrided and nitrocarburised parts can be used without any grinding or with very little grinding.