Room temperature indentation creep behaviour of different regions of nitrocarburised AISI 4140 steel is investigated by employing the nanoindentation creep testing method in the present study. A structure consisting of a compound layer, a diffusion layer and a substrate is observed in the nitrocarburised AISI 4140 steel. The stress exponents are calculated from the loading curve produced by nanoindentation during the holding time. The results indicate that with the increase in distance from the material surface, the obtained stress exponent decrease. From the compound layer to the diffusion layer to the substrate, the stress exponent decreases rapidly first, and then decreases gradually revealing a deeper test point that yields a lower creep resistance. The correlations between the room temperature creep behaviour and the corresponding microstructure of nitrocarburising surface are discussed.
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