Small-scale structural and mechanical characterization of the nitrided layer in martensitic steel

Pulsed Plasma Nitriding (PPN) of high-strength low-alloy steels used for offshore applications is a promising approach for controlling erosion, corrosion and hydrogen embrittlement under service conditions. In this work, the microstructure, composition and hardness of the nitride layer produced by an optimized PPN process on 2.25Cr-1Mo steel were examined. The nanomechanical properties of the nitride layer were investigated via nanoindentation along the depth of the nitride layer to understand the interconnected effect of the existing microstructure with the one developed after the nitriding process and the nitrogen concentration. The results showed that the nitride layer is composed of a compound layer and diffusion layer with hardness four times higher than the untreated material, which gradually decreases across the diffusion layer.